TWI598293B - A cathode active material for a lithium secondary battery , a method for preparing the same , and a lithium secondary battery including the same - Google Patents

Description

Cathode active material for lithium secondary battery, preparation method thereof and lithium secondary battery using the cathode active material

The present invention relates to a cathode active material for use in a lithium secondary battery, a method for producing the cathode active material, and a lithium secondary battery including the cathode active material.

The battery generates electricity by using an electrochemically active material for the cathode and the anode. In the present invention, unless otherwise indicated, the cathode means "positive electrode" and the anode means "negative electrode". A representative example of such a battery is a lithium secondary battery which is used to generate electric energy by a change in chemical potential during the process of intercalating/embedding lithium ions into the cathode and the anode.

The lithium secondary battery uses a material capable of reversely intercalating/embedding lithium ions as a cathode active material and an anode active material, and between the cathode and the anode, the organic electrolyte or the polymer electrolyte is filled. Lithium secondary battery.

Various carbonaceous materials which can embed/embed lithium ions, such as artificial graphite, natural graphite, hard carbon, etc., can also be used as the anode active material of the lithium secondary battery.

Regarding the cathode active material used in the lithium secondary battery, a lithium composite metal compound is used. Composite metal oxides such as LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiNi _1-x Co _x O ₂ (0<x<1), LiMnO ₂ , and LiFePO ₄ are all under investigation.

The main object of the present invention is to provide cathode activity for a lithium secondary battery Materials with high output characteristics, high capacitance characteristics, high thermal stability, and high service life characteristics.

Another object of the present invention is to provide a method of preparing a cathode active material for use in the lithium secondary battery.

Still another object of the present invention is to provide a lithium secondary battery including the cathode active material used in the lithium secondary battery.

An aspect of the present invention provides a cathode active material for use in a lithium secondary battery, comprising: a core comprising a compound represented by Chemical Formula 1; and a shell layer comprising a compound represented by Chemical Formula 2 Wherein the core and the shell system have different material combinations.

[Chemical Formula 1] Li _x1 M1 _y1 M2 _z1 PO _4-w1 E _w1

[Chemical Formula 2] Li _x2 M3 _y2 M4 _z2 PO _4-w2 E _w2

In the chemical formulas 1 and 2, M1, M2, M3 and M4 are the same or different, and each of them is independently selected from the group consisting of Ni, Co, Mn, Fe, Na, Mg, Ca, Ti, V, Cr, a group consisting of Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga, B and combinations of the foregoing; E is selected from the group consisting of F, S and combinations of the foregoing Group; 0<x1 1,0 Y1 1,0 Z1 1, and 0<x1+y1+z1 2,0 W1 0.5,0<x2 1,0 Y2 1,0 Z2 1, and 0<x2+y2+z2 2 and, 0 W2 0.5.

M1 and M3 may be the same material, and M2 and M4 may be the same material, In x1=x2, y1<y2, and z1>z2. Herein, M1 and M3 may be selected from the group consisting of Fe, Co, Ni, Mn and a combination of the foregoing; M2 and M4 may be selected from the group consisting of Mn, Ni, Co, Fe and the foregoing substances. A group of combinations.

Among the cathode active materials used in the lithium secondary battery, M1 and M3 may be different materials. Moreover, M2 and M4 can also be different materials.

The M1 system can be different from M2. The core may have a structure in which the concentration of M1 gradually increases in a direction away from the center of the core, and the concentration of M2 gradually decreases. Here, M1 is selected from the group consisting of Co, Ni and a combination of the foregoing, and M2 is selected from the group consisting of Ni, Co and a combination of the foregoing.

The core can have a diameter of about 5 to 20 μm.

M3 and M4 systems can be different. The shell layer has a structure in which the concentration of M3 gradually increases in a direction away from the center of the core, and the concentration of M4 gradually decreases. Here, M3 is selected from the group consisting of Co, Ni and a combination of the foregoing, and M4 is selected from the group consisting of Ni, Co and a combination of the foregoing.

The shell layer can have a thickness of between about 100 nm and 5 μm.

The cathode active material used in the lithium secondary battery may further include a carbon coating layer on a surface of one of the shell layers.

The carbon coating layer can have a thickness of from about 10 nm to 200 nm.

The cathode active material used in the lithium secondary battery may further include an intermediate layer between the core and the shell layer, and the intermediate layer may include a compound represented by Chemical Formula 3; The composition of the material may differ from the material of the core and the shell.

[Chemical Formula 3] Li _x3 M5 _y3 M6 _z3 PO _4-w3 E _w3

In the chemical formula 3, M5 and M6 are the same or different, and each of them is independently selected from Ni, Co, Mn, Fe, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, a group consisting of Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga, B and combinations of the foregoing; E is selected from the group consisting of F, S and combinations of the foregoing; 0 < x3 1,0 Y3 1,0 Z3 1, and 0<x3+y3+z3 2, and 0 W3 0.5.

M1, M3 and M5 may be the same material, and M2, M4 and M6 may also be the same material: wherein x1=x2=x3, y1<y3<y2, and z1>z3>z2. Here, M1, M3 and M5 are selected from the group consisting of Co, Ni and a combination of the above substances, and M2, M4 and M6 are selected from the group consisting of Ni, Co and a combination of the foregoing.

Among the cathode active materials used in the lithium secondary battery, M1, M3 and M5 may be different materials, and M2, M4 and M6 may be different materials. M5 can be different from M6. The intermediate layer may have a structure in which the concentration of M5 gradually increases in a direction away from the center of the core, and the concentration of M6 gradually decreases. Here, M5 may be selected from the group consisting of Co, Ni and a combination of the foregoing, and M6 may be selected from the group consisting of Ni, Co and a combination of the foregoing.

The intermediate system has a thickness of about 100 nm to 24 μm.

The cathode active material used in the lithium secondary battery may have a diameter of about 5 μm to 25 μm, and may have a knock tightness of about 1 g/cm ³ to 2 g/cm ³ .

Further, another aspect of the present invention provides a method for preparing a cathode active material for use in a lithium secondary battery, the method comprising the steps of: forming a core precursor by mixing an M1 source, an M2 source, and a phosphoric acid source Forming a core-shell precursor by mixing the core precursor with an M3 source, an M4 source, and a source of phosphoric acid, the core-shell precursor comprising a shell precursor formed in The surface of the core precursor; by means of the core-shell The precursor is heat treated to form a core-shell composite; and the core-shell composite is mixed with a lithium source and then calcined.

Another aspect of the present invention further provides a method for preparing a cathode active material for use in a lithium secondary battery, the method comprising the steps of: forming a core precursor by mixing an M1 source and an M2 source; The core precursor is mixed with an M3 source and an M4 source to form a core-shell precursor, the core-shell precursor comprising a shell precursor formed on the surface of the core precursor; The core-shell precursor is mixed with a lithium source and a source of phosphoric acid and then calcined.

The descriptions of M1, M2, M3, and M4 are the same as described above.

The M1 source, the M2 source, the M3 source, and the M4 source may each comprise a sulfur oxide, an oxynitride, an oxychloride, a phosphorus oxide, a chloride, an oxalate, a fluorine of M1, M2, M3, and M4. a compound, a carbonate or a combination of the foregoing.

The phosphoric acid source may comprise phosphoric acid (H ₃ PO ₄ ), diammonium phosphate ((NH ₄ ) ₂ HPO ₄ ), ammonium phosphate trihydrate ((NH ₄ ) ₃ PO ₄ .3H ₂ O), metaphosphoric acid, Orthophosphoric acid, monoammonium phosphate (NH ₄ H ₂ PO ₄ ) or a combination of the foregoing.

The lithium source may include lithium phosphate (Li ₃ PO ₄ ), lithium nitrate (LiNO ₃ ), lithium acetate (LiCH ₃ COOH), lithium carbonate (Li ₂ CO ₃ ), lithium hydroxide (LiOH), lithium dihydrogen phosphate ( LiH ₂ PO ₄ ) or a combination of the foregoing.

The heat treatment is carried out at a temperature in the range of about 300 ° C to 700 ° C.

The calcining execution temperature ranges from about 600 ° C to 900 ° C.

The method for preparing a cathode active material for use in a lithium secondary battery, after the step of forming the core-shell composite or the step of forming the core-shell precursor, may further comprise the step of: forming the core-shell Forming a carbon coating on the surface of the layer composite or the core-shell precursor Floor.

The method for preparing a cathode active material for a lithium secondary battery may further comprise the step of: mixing the core precursor with the M5 source, the M6 source, and the phosphoric acid after the step of forming the core precursor The source, or by mixing the core precursor with the M5 source and the M6 source, forms an intermediate layer precursor on the surface of the core precursor.

The descriptions of M5 and M6 are the same as described above.

The M5 source and the M6 source may respectively contain M5, M6 sulfur oxides, nitrogen oxides, oxyethylene oxides, phosphorus oxides, chlorides, oxalates, fluorides, carbonates, and combinations thereof.

Another aspect of the present invention provides a lithium secondary battery comprising: a cathode comprising the cathode active material; an anode comprising an anode active material; and an electrolyte.

Other details relating to the present invention will be described in detail later.

According to the present invention, the cathode active material used in the lithium secondary battery has a core-shell structure and thus has high output characteristics, high capacitance characteristics, high heat stability, and high service life characteristics.

100‧‧‧Lithium secondary battery

112‧‧‧Anode

114‧‧‧ cathode

113‧‧‧Baffle

120‧‧‧Battery

140‧‧‧Sealing components

Fig. 1 is a view showing the structure of a lithium secondary battery of an embodiment of the present invention.

Figure 2 is a scanning electron microscope (SEM) cross-sectional view of the core-shell precursor of Example 1 of the present invention.

Fig. 3a shows the analysis data of energy scattered X-ray (EDX) at point A in Fig. 2, and Fig. 3b shows the analysis data of energy scattered X-ray (EDX) at point B in Fig. 2.

Fig. 4 is a cross-sectional view showing a scanning electron microscope (SEM) of the active material precursor of Comparative Example 1 of the present invention.

Fig. 5a shows the analysis data of energy scatter X-ray (EDX) at point C in Fig. 4, and Fig. 5b shows the analysis data of energy scatter X-ray (EDX) at point D in Fig. 4.

Fig. 6 is a charge-discharge diagram of the coin-type half-cell of Example 2 of the present invention.

Fig. 7 is a primary charge-discharge diagram of the coin-type half-cell of Comparative Example 3 of the present invention.

In the following, the embodiments of the present invention will be described with reference to the drawings of the present invention, so that those skilled in the art can easily understand the contents of the present invention. However, the above description and drawings are merely illustrative of the embodiments of the present invention and are not intended to limit the invention. The invention is defined only by the scope of the patent application.

In the accompanying drawings, the thickness of the In the description, like components will be designated by the same reference numerals.

In the description of the present invention, when a component (e.g., a layer, a film, an area, or a sheet) is referred to as being "above" another component, the component can be directly above the other component. ", or another component is somewhere in between. Conversely, when a component is "directly above" another component, there may be no intervening components between the two.

According to an embodiment of the present invention, a cathode active material for a lithium secondary battery includes: a core comprising a compound represented by Chemical Formula 1; and a shell layer comprising a compound comprising the compound Is represented by Chemical Formula 2; wherein the core and The shell layer has a different constituent material. In other words, in the chemical formulas 1 and 2, the following will not occur: x1 = x2, M1 = M3, y1 = y2, M2 = M4, z1 = z2, and w1 = w2, and x1 = x2, M2 = M3 , z1=y2, M1=M4, y1=z2, and w1=w2.

[Chemical Formula 1] Li _x1 M1 _y1 M2 _z1 PO _4-w1 E _w1

[Chemical Formula 2] Li _x2 M3 _y2 M4 _z2 PO _4-w2 E _w2

In the chemical formulas 1 and 2, M1, M2, M3 and M4 are the same or different, and each of them is independently selected from the group consisting of Ni, Co, Mn, Fe, Na, Mg, Ca, Ti, V, Cr, a group consisting of Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga, B and combinations of the foregoing, in particular selected from the group consisting of Ni, Co and combinations of the foregoing Group E; selected from the group consisting of F, S and combinations of the foregoing, particularly selected from F; it may be 0 < x1 1,0 Y1 1,0 Z1 1,0<x1+y1+z1 2, especially possibly 0.9<x1 1.1,0 Y1 1,0 Z1 1,0.9<x1+y1+z1 2, and it may also be 0 W1 0.5, especially 0 W1 0.3, and it may be 0<x2 1,0 Y2 1,0 Z2 1, and 0<x2+y2+z2 2, especially possibly 0.9<x2 1.1,0 Y2 1,0 Z2 1, and 0.9<x2+y2+z2 2, and it may also be 0 W2 0.5, especially 0 W2 0.3.

The cathode active material used in the lithium secondary battery may include the core and the shell layer, thereby effectively improving various physical properties of the lithium secondary battery. For example, when a material having high voltage characteristics and high energy density is used as a core, and a material having high heat stability characteristics and high service life characteristics is used as a shell layer, it can not only improve the output power and electricity of the lithium secondary battery. The capacity characteristics can also improve the thermal stability and service life of a lithium secondary battery including a cathode active material used in a lithium secondary battery. However, the invention is not limited thereto. Constitute the core and The materials of the shell layers may be the same or different, and they may each have materials that selectively include various electrochemical and physical properties. Therefore, the cathode active material used in the lithium secondary battery has an advantage in that various properties required can be effectively achieved.

The core and the cathode active material used in the lithium secondary battery may each have a spherical shape, an elliptical shape, and a combination of the foregoing shapes. However, the invention is not limited thereto.

For example, M1 and M3 may be the same material, and M2 and M4 may also be the same material, where x1=x2, y1<y2, and z1>z2. Here, even if the core and the shell layer comprise the same material, the materials contained in the core and the shell layer each have different densities, that is, different material combinations. Therefore, it can overcome the disadvantages of only one material combination (such as low oxidation/reduction potential, low discharge capacity, low service life, low thermal stability, etc.). In other words, the cathode active material used in the lithium secondary battery prepared therefrom can effectively exhibit the advantages of the composition of each material.

Here, M1 and M3 may be selected from the group consisting of Co, Ni and a combination of the foregoing; M2 and M4 may be selected from the group consisting of Ni, Co and a combination of the foregoing. However, the invention is not limited thereto. According to the order of Ni>Co, the high voltage characteristics can be made superior; according to the order of Co>Ni, the thermal stability and the service life can be further improved. Therefore, in consideration of the characteristics described above, high voltage characteristics, thermal stability, and service life can be effectively improved by appropriately selecting the core and the material of the shell layer. For example, the combination of M1 and M2 may be (Co, Ni), (Ni, Co), etc., and the combination of M3 and M4 may be (Co, Ni), (Ni, Co), etc., but the present invention Not limited to this.

Specifically, M1 and M3 may be Co (y1 = 0), and M2 and M4 may be Ni (z2 = 0). In this case, the core may be a lithium-nickel-phosphoric acid complex which enhances high voltage characteristics and increases energy density; and the shell layer may be a lithium-cobalt-phosphoric acid composite which exhibits high thermal stability. And high service life characteristics.

Therefore, the cathode active material used for the lithium secondary battery including the core and the shell layer can have not only high output and high capacitance characteristics, but also high heat stability and high service life characteristics.

In another example, M1 and M3 can be different materials, and M2 and M4 can be different materials. Specifically, M1, M2, M3, and M4 may be different materials. Here, each of M1 to M4 may be independently selected from the group consisting of Fe, Co, Ni, Mn and a combination of the foregoing, but the present invention is not limited thereto. Specifically, the combination of M1 and M2 included in the core may be (Ni, Co), (Co, Ni), etc., and the combination of M3 and M4 included in the shell layer may be (Co, Ni). ), (Ni, Co), etc., but the invention is not limited thereto. In this case, the core can enhance high voltage characteristics and increase energy density, while the shell can improve high thermal stability and high service life characteristics. Therefore, the cathode active material used for the lithium secondary battery including the core and the shell layer can have high output characteristics, high capacitance characteristics, high thermal stability, and high service life characteristics.

Meanwhile, in the cathode active material used in the lithium secondary battery, M1 may be different from M2. The core may have a structure in which the concentration of M1 gradually increases in a direction away from the center of the core, and the concentration of M2 gradually decreases along the direction. The change in concentration can be continuous, but the invention is not limited thereto. The change in concentration can be discontinuous, wherein the core can be a multilayer structure. Of course, the structures can be applied not only to the case where the materials constituting the core and the shell layer are the same, but also to the case where the materials constituting the core and the shell layer are different. In this core, when the concentrations of M1 and M2 described above are changed as described above, a stable crystal structure can be formed by avoiding a sudden change in the composition of the core material. In addition, it can also compensate for the respective electrochemical properties of the different materials constituting the core. The shortcomings of quality. Similarly, in a portion adjacent to the shell layer, the generation of an impurity phase can be avoided or reduced by avoiding abrupt changes in the material composition between the core and the shell layer.

The core may have a diameter of from about 5 [mu]m to 20 [mu]m. When the diameter is within the range described above, it can easily form a core-shell composite and can effectively enhance electrochemical properties. In particular, the core may have a diameter of from about 7 [mu]m to 15 [mu]m.

In the cathode active material used in the lithium secondary battery, M3 may be different from M4. The shell layer has a structure in which the concentration of M3 gradually increases in a direction away from the intermediate layer between the core and the shell layer, and the concentration of M4 gradually decreases along the direction. The change in concentration can be continuous, but the invention is not limited thereto. The change in concentration may also be discontinuous, wherein the shell layer may be a multilayer structure. Of course, the structures can be applied not only to the case where the materials constituting the core and the shell layer are the same, but also to the case where the materials constituting the core and the shell layer are different. Here, M3 may be selected from the group consisting of Co, Ni and a combination of the foregoing, and M4 may be selected from the group consisting of Ni, Co and a combination of the foregoing, but the invention is not limited herein. In the shell layer, when the concentrations of the above M3 and M4 are changed as described above, a stable crystal structure can be formed by avoiding a sudden change in the composition of the shell material. In addition, it can also compensate for the disadvantages of the respective electrochemical properties of the different materials that make up the shell. Similarly, in a portion adjacent to the core, the generation of an impurity phase can be avoided or reduced by avoiding abrupt changes in the material composition between the core and the shell.

The shell layer has a thickness of about 100 nm to 5 μm. When the thickness is within the range described above, it is not only easy to form a core-shell composite, but also maintains the morphology of the core-shell composite. In addition, it can also effectively compensate the electrochemical properties of the core, and thereby effectively improve the electrochemical properties of the cathode active material used in the lithium secondary battery including the core.

In particular, the core may have a thickness of between about 200 nm and 3 μm.

The cathode active material used in the lithium secondary battery may further include a carbon coating layer on one surface of the shell layer. Since the carbon coating layer is further included to enhance conductivity, the cathode active material used in the lithium secondary battery may have high electrochemical properties.

The carbon coating layer has a thickness of about 10 nm to 200 nm. When the thickness of the carbon coating layer is within the range described above, the electrical conductivity can be effectively increased. Therefore, the cathode active material used for the lithium secondary battery including the carbon coating layer can have high electrochemical properties. Specifically, the carbon coating layer has a thickness of about 15 nm to 100 nm.

In the cathode active material used in the lithium secondary battery, the core and the shell layer are separately described separately, but the present invention is not limited thereto. When the core is the same as the material included in the shell layer and distributed in the same continuous concentration gradient, the cathode active material used in the lithium secondary battery may also form a single particle shape without a boundary between the core and the shell layer.

The cathode active material used in the lithium secondary battery may further include an intermediate layer between the core and the shell layer, and the material composition of the intermediate layer may be different from the material of the core and the shell layer. Here, the intermediate layer may include a compound represented by Chemical Formula 3.

[Chemical Formula 3] Li _x3 M5 _y3 M6 _z3 PO _4-w3 E _w3 In the chemical formula 3, M5 and M6 are the same or different, and each of them is independently selected from Ni, Co, Mn, Fe, Na, a group consisting of Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga, B and combinations of the foregoing, and may especially be selected from a group consisting of Ni, Co and a combination of the foregoing; E is selected from the group consisting of F, S and combinations of the foregoing, and especially F, which may be 0 < x3 1,0 Y3 1,0 Z3 1, and 0<x3+y3+z3 2, and especially can be 0.9<x3 1.1, 0.1 Y3 0.9, 0.1 Z3 0.9, and 1.1<x3+y3+z3 2.9. It can be 0 W3 0.5, and especially 0 W3 0.3.

In one example, M1, M3, and M5 can be the same material, and M2, M4, and M6 can be the same material, where x1 = x2 = x3, y1 < y3 < y2, and z1 > z3 > z2. Here, even if the core, the intermediate layer, and the shell layer comprise the same material, the materials located in the core, the intermediate layer, and the shell layer are individually of different densities, that is, composed of different materials. Therefore, when the intermediate layer is present and has a material composition as described above, it is possible to avoid a sudden difference in material composition between the core and the shell layer, and to avoid or reduce the generation of an impurity phase. In addition, since a phase boundary is not suddenly formed, the crystal structure can be stabilized.

Here, M1, M3 and M5 may be selected from the group consisting of Co, Ni and a combination of the foregoing, and M2, M4 and M6 may be selected from Ni, Co and a combination of the foregoing. Groups, but the invention is not limited thereto. In one example, the combination of M1 and M2 may be (Ni, Co), (Co, Ni), etc., and the combination of M3 and M4 may be (Ni, Co), (Co, Ni), etc., a combination of M5 and M6. Then it may be (Ni, Co), (Co, Ni) or the like.

Specifically, M1, M3, and M5 may be Fe (y1 = 0), and M2, M4, and M6 may be Mn (z2 = 0). In this case, the core may be a lithium-manganese-phosphate composite which enhances high voltage characteristics and increases energy density; the intermediate layer may be a lithium-iron-manganese-phosphate composite, which can reduce the core and The composition between the shells changes abruptly; and the shell layer can be a lithium-iron-phosphate composite that exhibits high thermal stability and high lifetime characteristics.

Specifically, M1, M3, and M5 may be Co (y1 = 0), and M2, M4, and M6 may be Ni (z2 = 0).

In this case, the core may be a lithium-nickel-phosphate composite which enhances the high voltage characteristic and increases the energy density, and the intermediate layer may be a lithium-cobalt-nickel-phosphate composite. The sudden change in composition between the core and the shell layer is reduced, and the shell layer can be a lithium-cobalt-phosphoric acid composite that exhibits high thermal stability and high service life characteristics.

Therefore, the cathode active material used for the lithium secondary battery including the core and the shell layer can have a stable crystal structure and can have high output characteristics, high capacitance characteristics, high thermal stability, and high service life characteristics.

In another example, M1, M3, and M5 can be different materials, and M2, M4, and M6 can be different materials. Here, each of M1 to M6 may be independently selected from the group consisting of Co, Ni, and a combination of the foregoing, but the present invention is not limited thereto. Specifically, the combination of M1 and M2 included in the core may be (Ni, Co), (Co, Ni), etc., and the combination of M5 and M6 included in the intermediate layer may be (Co, Ni). (Ni, Co), etc., and the combination of M3 and M4 included in the shell layer may be (Ni, Co), (Co, Ni) or the like, but the invention is not limited thereto. In this case, the core can enhance high voltage characteristics and increase energy density, while the shell can improve high thermal stability and high service life characteristics. Additionally, the intermediate layer can compensate for the electrochemical properties of the core and the shell. Therefore, the cathode active material used for the lithium secondary battery including the core, the intermediate layer and the shell layer can have high output characteristics, high capacitance characteristics, high heat stability, and high service life characteristics.

Meanwhile, in the cathode active material used in the lithium secondary battery, M5 may be different from M6, and the intermediate layer may have a structure in which the concentration of M5 gradually increases in a direction away from the core. The concentration of M6 gradually decreases along this direction. The change in concentration can be continuous, but the invention is not limited thereto. The change in concentration can be discontinuous, wherein the intermediate layer can be a multilayer structure. Of course, the structures may be applied not only to the materials constituting the core, but also to the shell layer and the intermediate layer, and the materials may be respectively applied to the core, the shell layer and the intermediate layer. The situation of different people. Here, M5 It may be selected from the group consisting of Co, Ni and a combination of the foregoing, and M6 may be selected from the group consisting of Ni, Co and a combination of the foregoing, but the invention is not limited thereto . In the intermediate layer, when the concentrations of the above M5 and M6 are changed as described above, a stable crystal structure can be formed by avoiding a sudden change in the material composition of the intermediate layer. In addition, it can also compensate for the disadvantages of the respective electrochemical properties of the different materials constituting the intermediate layer, as well as the advantages of the respective electrochemical properties of the different materials of the intermediate layer after combination. Similarly, in a portion adjacent to the core or shell layer, by avoiding abrupt changes in the material composition between the core and the intermediate layer or by avoiding sudden changes in the material composition between the shell layer and the intermediate layer, The generation of impurity phases can be avoided or reduced.

The intermediate layer can have a thickness of from about 100 nm to 24 μm. When the thickness is within the range described above, the generation of the impurity phase can be effectively avoided or reduced by avoiding abrupt changes in the material composition between the core and the shell. In addition, since a phase boundary is not suddenly formed, the crystal structure can be stabilized. Specifically, the intermediate layer may have a thickness of about 1 μm to 20 μm.

In the cathode active material used in the lithium secondary battery, although the core, the intermediate layer, and the shell layer are individually described, the present invention is not limited thereto. When the core, the intermediate layer and the shell layer comprise the same material and are distributed in a continuous concentration gradient, the cathode active material used in the lithium secondary battery can form a single particle shape without a core, an intermediate layer and a shell layer. Demarcation.

Although the cathode active material used in the lithium secondary battery according to an embodiment of the present invention has been described with many examples, the present invention is not limited thereto.

The cathode active material used in the lithium secondary battery may have a diameter of about 5 μm to 25 μm. When the diameter of the cathode active material used in the lithium secondary battery is within the range described above, the energy density can be effectively increased due to the high knocking degree.

Specifically, the cathode active material used in the lithium secondary battery may have a diameter of about 5 μm to 15 μm.

The cathode active material used in the lithium secondary battery may have a knocking degree of about 1 g/cm ³ to 2 g/cm ³ . When the knocking property of the cathode active material used in the lithium secondary battery is within the range described above, the energy density can be effectively increased. Specifically, the cathode active material used in the lithium secondary battery may have a knocking degree of about 1.2 g/cm ³ to 1.7 g/cm ³ . More specifically, the knocking degree is from 1.5 g/cm ³ to 1.7 g/cm ³ .

According to another embodiment of the present invention, a method for preparing a cathode active material for use in the lithium secondary battery includes the steps of: forming a core precursor by mixing an M1 source, an M2 source, and a phosphoric acid source; The core precursor is mixed with an M3 source, an M4 source, and a monophosphate source to form a core-shell precursor, the core-shell precursor comprising a shell precursor formed in the core precursor The surface of the object; forming a core-shell composite by heat treating the core-shell precursor; and mixing the core-shell composite with a lithium source and then calcining. Hereinafter, when not further explained, M1, M2, M3, and M4 are as described above.

According to still another embodiment of the present invention, a method for preparing a cathode active material for a lithium secondary battery includes the steps of: forming a core precursor by mixing an M1 source and an M2 source; The precursor is mixed with an M3 source and an M4 source to form a core-shell precursor, the core-shell precursor comprising a shell precursor formed on the surface of the core precursor; and the core - The shell precursor is mixed with a lithium source and a source of phosphoric acid and then calcined. Hereinafter, when not further explained, M1, M2, M3, and M4 are as described above.

The M1 source, the M2 source, the M3 source, and the M4 source may each comprise a sulfur oxide, an oxynitride, an oxyhydroxide, a hydroxide, a chloride, an oxalate, a fluorine of M1, M2, M3, and M4. a compound, a carbonate or a combination of the foregoing. The phosphoric acid source may comprise phosphoric acid (H ₃ PO ₄ ), diammonium phosphate ((NH ₄ ) ₂ HPO ₄ ), ammonium phosphate trihydrate ((NH ₄ ) ₃ PO ₄ .3H ₂ O), metaphosphoric acid, positive Phosphoric acid, monoammonium phosphate (NH ₄ H ₂ PO ₄ ) or a combination of the foregoing.

In the method for preparing a cathode active material for use in a lithium secondary battery, each of the core precursor and the shell precursor may include phosphorus oxides, oxalates, carbonates, hydroxides, and the like. The combination.

In the step of heat-treating the core-shell precursor to form a core-shell composite, the heat treatment may be carried out at a temperature ranging from about 300 ° C to 700 ° C for about 1 to 20 hours. When the heat treatment is performed under the above conditions, it can enhance the crystallinity of the formed core-shell composite, thereby effectively improving the cathode used in the lithium secondary battery formed by the core-shell composite. The electrochemical properties of the active material. Specifically, the heat treatment can be carried out at a temperature ranging from about 400 ° C to 700 ° C for 5 to 15 hours.

The rate of rise of the temperature during heat treatment may range from about 1 ° C/min to 10 ° C/min. When the rate of rise of temperature is within the range described above, the core-shell composite formed may have a uniform degree of crystallinity. Therefore, it can effectively form a cathode active material for an olivine-shaped lithium secondary battery without generating an impurity phase. Specifically, the temperature rise rate may range from 2 ° C/min to 5 ° C/min during the heat treatment.

In the step of mixing the lithium source and the core-shell composite or mixing the lithium source, the phosphoric acid source and the core-shell composite, the lithium source may comprise lithium phosphate (Li ₃ PO ₄ ). Lithium nitrate (LiNO ₃ ), lithium acetate (LiCH ₃ COOH), lithium carbonate (Li ₂ CO ₃ ), lithium hydroxide (LiOH), lithium dihydrogen phosphate (LiH ₂ PO ₄ ) or a combination thereof, but the present invention Not limited to this. The source of phosphoric acid is as described above.

The core-shell composite is mixed with the lithium source in a molar ratio of about 1:0.8 to 1:1.2. When the molar ratio of the core-shell composite to the lithium source is within the above range, it can effectively form a cathode active material for a structurally stable olivine-based lithium secondary battery. In addition, since no impurity phase is formed, the cathode active material used in the lithium secondary battery may have a high electrochemical property. Specifically, the core-shell composite and the lithium source may be mixed in a molar ratio of about 1:0.9 to 1:1.1.

After calcining the lithium source and the core-shell composite or mixing the lithium source, the phosphoric acid source and the core-shell composite, the calcination may be performed at a temperature of about 600 ° C to 900 ° C. The range is about 5 to 20 hours. When calcination is carried out under the above-described conditions, it can increase the crystallinity of the cathode active material used in the formed lithium secondary battery. In addition, since no impurity phase is formed, the cathode active material used in the lithium secondary battery can be made to have high electrochemical properties. Specifically, calcination can be carried out for about 10 to 15 hours at a temperature ranging from about 650 ° C to 800 ° C.

The rate of temperature rise during calcination may range from about 1 ° C/min to 10 ° C/min. When the temperature rise rate is within the range described above, it can increase the crystallinity of the cathode active material used in the formed lithium secondary battery. Further, since the impurity phase is not formed, the cathode active material used in the lithium secondary battery can be made to have high electrochemical properties. Specifically, the rate of rise of the temperature may range from 2 ° C/min to 5 ° C/min.

The preparation method of the cathode active material used in the lithium secondary battery may further comprise the following steps after forming the core-shell composite or forming the core-shell precursor: in the core-shell composite or The surface of the core-shell precursor forms a carbon coating layer. The carbon coating layer can be formed by mixing the core-shell precursor with a carbon source such as asphalt, sucrose, glucose, polyvinyl alcohol, polypyrrole, polycellulose, acetylene black, and superconducting. Carbon black (super p).

In addition, in forming the core precursor, forming the core-shell precursor or a combination of the above steps, the carbon source described above may be further mixed to introduce carbon into the core precursor, the core-shell layer Precursor or a combination of the above. Thereby, it can improve the electrical conductivity of the cathode active material used in the formed lithium secondary battery.

The method for preparing a cathode active material for use in the lithium secondary battery may further comprise the steps of: mixing the core precursor with the M5 source, the M6 source, and the phosphoric acid source after the step of forming the core precursor The surface of the core precursor forms an intermediate layer precursor. Subsequently, the intermediate layer precursor will form an intermediate layer by heat treatment and calcination. In the following, unless otherwise stated, M5 and M6 are as described above.

The intermediate layer precursor can be formed by mixing and reacting the M5 source and the M6 source with the core precursor, and the M5 source and the M6 source respectively comprise M5, M6 sulfur oxides, nitrogen oxides, ruthenium oxide, Phosphorus oxides, chlorides, oxalates, fluorides, carbonates, and combinations of the foregoing, but the invention is not limited thereto. Meanwhile, in the step of forming the intermediate layer precursor, a source of monophosphate may be further mixed. The source of the phosphate is as described above.

In the preparation method of the cathode active material used in the lithium secondary battery, regarding the description of the complexing agent (for example, ammonia water), the pH adjuster (for example, the hydroxyl group provided by the alkaline solution), and the heat treatment environment, since it is in the field Ignore the person, so it is omitted.

According to an embodiment of the present invention, a cathode active material for obtaining the lithium secondary battery can be prepared via the method.

The cathode active material used in the lithium secondary battery can be generally used as a cathode of an electrochemical cell such as a lithium secondary battery. The lithium secondary battery includes an anode (including an anode active material), and an electrolyte and the cathode.

The cathode includes a current collector, and a cathode active material is formed on the current collector Material layer.

Further, the cathode active material layer includes a binder and a conductive material.

The function of the binder is to sufficiently adhere the respective cathode active material particles to each other and to sufficiently adhere the cathode active material to the current collector. Representative examples of the binder may include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer, and the polymer includes Ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, ring Oxygen resin, nylon, etc., but the invention is not limited thereto.

The electrically conductive material is used to provide electrical conduction to an electrode. In terms of materials, there is no limitation as long as it is a conductive material and does not cause chemical changes in the constructed battery.

Examples of the conductive material may include natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, metal powder, and metal fibers (such as copper, nickel, aluminum, silver, etc.), polyphenylene derivatives or the foregoing. a mixture of one or more of the substances.

Aluminum can be used as the current collector, but the present invention is not limited thereto.

The anode includes a current collector, and an anode active material layer is formed on the current collector, and the anode active material layer includes an anode active material.

The anode active material includes a material capable of reversibly intercalating/embedding lithium ions, a lithium metal, a lithium metal alloy, and a material capable of doping or dedoping lithium or a transition metal oxide.

A material capable of reversibly intercalating/embedding lithium ions may include a carbon material. The carbon-based anode active material is not particularly limited as long as it can be used in a lithium secondary battery. Representative examples of the carbon material may include crystalline carbon, amorphous carbon, or a combination of the foregoing. Crystalline carbon Examples thereof may include amorphous/plated, flaked, spherical or fibrous natural/non-natural graphite, and examples of the amorphous carbon may include soft carbon (low temperature coal-fired carbon) or hard carbon, mesophase pitch carbon, Dry coke, etc.

The alloy of lithium metal includes an alloy of lithium and a metal selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, A group consisting of Ge, Al, and Sn.

The material capable of doping or dedoping lithium may include Si, SiO _x (0<x<2), and Si-M alloy (M (non-Si) is selected from the group consisting of alkali metals, alkaline earth metals, and groups 13 to 16 a group consisting of an element, a transition metal, a rare earth element, and a combination of the foregoing), Sn, SnO ₂ , and Sn-M (M (non-Sn) are selected from the group consisting of alkali metals, alkaline earth metals, and elements 13 to 16 , a group of transition metals, rare earth elements, and combinations of the foregoing, and the like). Further, at least one of the materials listed above is mixed with SiO ₂ . The element M may be selected from the group consisting of Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, A group consisting of Bi, S, Se, Te, Po, and combinations of the foregoing.

The transition metal oxide may include vanadium oxide, lithium vanadium oxide, or the like.

Further, the anode active material layer may include a binder, and may further selectively include a conductive material.

The role of the binder is to sufficiently adhere the anode active material particles to each other and to sufficiently adhere the anode active material to the current collector. Representative examples of the binder may include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide, polyvinyl pyrrolidone, polyurethane, Polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butyl An olefin rubber, an epoxy resin, a nylon, or the like, but the invention is not limited thereto.

The electrically conductive material is used to provide electrical conduction to an electrode. As long as the conductive material is a conductive material and does not cause chemical changes in the constructed battery, there is no limitation.

Examples of the conductive material may include: a carbon-based material such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber; a metal-based material including metal powder, metal fiber (such as copper, nickel, aluminum, silver) ); a conductive polymer material, including a polyphenylene derivative or a mixture thereof.

The current collector may include copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, or a combination thereof.

The manufacturing steps of each of the cathode and the anode are as follows: an active material composition is prepared by mixing an active material, a conductive material, and a binder in a solvent, and the composition is applied to a current collector. Electrode manufacturing methods such as these are well known in the art, and thus detailed description thereof will be omitted in the present specification. N-methylpyrrolidone or the like can also be used as the solvent, but the present invention is not limited thereto.

As the electrolyte to be filled in the lithium secondary battery, a nonaqueous electrolyte or a generally known solid electrolyte can be used, and an electrolyte including a dissolved lithium salt can also be used.

The solvent of the nonaqueous electrolyte may include: a cyclic carbonate such as ethylene carbonate, diethyl carbonate, propylene carbonate, butylene carbonate, vinylene carbonate; a chain carbonate such as dimethyl carbonate or carbonic acid Ethyl ester, diethyl carbonate; esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone; ethers such as 1,2-dimethyl Oxyethane, 1,2-diethoxyethane, tetrahydrofuran, 1,2-dioxane, 2-methyltetrahydrofuran; nitriles such as acetonitrile; amides such as dimethylformamide; or the like But the invention is not in the game Limited to this. The foregoing substances may be used singly or in combination of two or more kinds. In particular, a mixed solvent of a cyclic carbonate and a chain carbonate can be used.

Further, a gel polymer obtained by impregnating an electrolyte solution into a polymer electrolyte such as polyethylene oxide, polyacrylonitrile or an inorganic solid electrolyte such as LiI or Li3N may be used as the electrolyte. However, the invention is not limited to this.

Here, the lithium salt may be selected from the group consisting of LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , Li(CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiSbF ₆ A group consisting of LiAlO ₄ , LiAlO ₂ , LiAlCl ₄ , LiCl and LiI, but the invention is not limited thereto.

According to the kind of the lithium secondary battery, a separator may be present between the cathode and the anode. The separator may use, for example, polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer (two or more layers) structure thereof. Of course, the separator may also use a mixed multilayer structure to form a two-layer separator such as polyethylene/polypropylene, a three-layer separator of polyethylene/polypropylene/polyethylene, or a polypropylene/polyethylene/poly. A three-layer separator of propylene.

The lithium secondary battery can be classified into a lithium ion battery, a lithium ion polymer battery, and a lithium polymer battery according to the type of the separator and the electrolyte. Further, the lithium secondary battery can be classified into a cylindrical battery, a prismatic battery, a coin type battery, and a pouch type battery according to the shape; according to the size, it can be classified into a large volume battery and a thin film type battery. The configuration and manufacturing method of these batteries are well known in the art, and thus detailed description thereof will be omitted.

Fig. 1 is a view showing the structure of a lithium secondary battery according to an embodiment of the present invention. As shown in FIG. 1 , the lithium secondary battery 100 mainly includes an anode 112 , a cathode 114 , a separator 113 between the anode 112 and the cathode 114 , a permeation into the anode 112 , the cathode 114 and the An electrolyte (not shown) of the separator 113, a battery cell 120, and a sealing member 140 for sealing the battery cell 120. According to the present invention, the lithium secondary battery has no special shape limit. According to an embodiment of the present invention, as long as the lithium secondary battery includes an electrolyte of a lithium secondary battery and can function as a battery, the lithium secondary battery may of course be of any shape such as a cylindrical type, a coin type, and a pouch type.

Example

Hereinafter, the present invention will be described in more detail with reference to the examples and comparative examples. However, the examples and comparative examples described below are merely illustrative, but are not intended to limit the invention.

Example 1: Preparation of a cathode active material for use in a lithium secondary battery . NiSO _{4 was} introduced at a molar ratio of 3:2:6 in a 4 L continuous stirred tank reactor (CSTR) (capacity: 4 L, rotary motor output: 90 W or more). 6H ₂ O, H ₃ PO ₄ and NH ₄ OH were reacted at pH 7. Here, NiSO ₄ is used. The molar concentration of 6H ₂ O was 2.2M. The internal temperature of the reactor was maintained at 55 ° C while stirring at 1000 rpm. After 12 hours of stirring, a micro-spherical active material precursor, Ni ₃ (PO ₄ ) ₂ , can be synthesized. xH ₂ O.

Then, the introduction of NiSO _{4 is} stopped. 6H ₂ O, followed by introduction of 2.2 M molar concentration of CoSO ₄ . 7H ₂ O, followed by stirring. Therefore, on the surface of the core precursor, it is possible to form Co ₃ (PO ₄ ) ₂ . A shell precursor of xH ₂ O, thereby synthesizing a core-shell precursor.

Then, the active material precursor was filtered through a vacuum pump and dried at 70 ° C for 24 hours under a vacuum.

Then, the dried precursor was heat-treated at 550 ° C for 10 hours in a reducing atmosphere to provide a nickel phosphate-cobalt phosphate salt.

Then, the nickel phosphate-cobalt phosphate is mixed with 5 parts by weight of pitch carbon relative to 100 parts by weight of the nickel phosphate-cobalt phosphate, and then stirred to form a carbon coating on the surface of the nickel phosphate-cobalt phosphate. Cloth layer.

Then, the nickel phosphate-cobalt phosphate and the formed carbon coating layer are mixed with lithium phosphate (Li ₃ PO ₄ ) at a molar ratio of 1:1, and heated to 750 ° C at a heating rate of 5 ° C / min. Then calcined for 10 hours. As a result, a cathode active material for an olivine-type lithium secondary battery having a structure of LiNiPO ₄ (core)-LiCoPO ₄ (shell layer) can be obtained.

Example 2: Manufacturing of a lithium secondary battery . The cathode active material used in the lithium secondary battery prepared in Example 1, the conductive carbon black as a conductive material, and polyvinylidene fluoride (PVdF) as a binder were mixed at a weight ratio of 85:7.5:7.5. A slurry is provided. The slurry was uniformly coated on an aluminum foil having a thickness of 20 μm , and vacuum dried at 120 ° C to provide a cathode.

Then, a coin-type half-cell was prepared according to a conventionally known manufacturing method, and a porous polyethylene film (Celgard 2300, thickness: 25 μm , Celgard LLC) was used by using the obtained cathode and lithium foil as counter electrodes. As a separator, and an electrolyte solution, the electrolyte solution was formed by dissolving in 1.2 M LiPF ₆ in a solvent including ethylene carbonate and ethyl methyl carbonate in a volume ratio of 3:7.

Comparative Example 1: Preparation of a cathode active material for use in a lithium secondary battery . NiSO4.6H2O, H3PO4, and NH4OH were introduced at a molar ratio of 3:2:6 in a 4 L continuous stirred tank reactor (CSTR) (capacity: 4 L, rotary motor output: 90 W or more), and the reaction was carried out at pH 7. Here, NiSO ₄ is used. The molar concentration of 6H ₂ O was 2.2M. The internal temperature of the reactor was maintained at 55 ° C while stirring at 1000 rpm. After 12 hours of stirring, a micro-spherical active material precursor, Ni ₃ (PO ₄ ) ₂ , was synthesized. xH ₂ O.

Then, the active material precursor was filtered through a vacuum pump and dried at 70 ° C for 24 hours under a vacuum.

Then, the dried precursor is subjected to a reducing environment at 550 ° C for 15 hours. Heat treatment to provide nickel phosphate.

Then, nickel phosphate was mixed with 2 parts by weight of pitch carbon and nickel phosphate with respect to 100 parts by weight, and further stirred to form a carbon coating layer on the surface of the nickel phosphate.

Then, the nickel phosphate formed with the carbon coating layer was mixed with lithium phosphate (Li ₃ PO ₄ ) at a molar ratio of 1:1, and heated to 750 ° C at a temperature elevation rate of 5 ° C/min, followed by calcination for 10 hours. . As a result, a LiNiPO ₄ cathode active material for an olivine-type lithium secondary battery can be obtained.

Comparative Example 2: Preparation of a cathode active material precursor for use in a lithium secondary battery . In a 4 L continuous stirred tank reactor (CSTR) (capacity: 4 L, rotary motor output: 90 W or more), CoSO4.7H2O, H3PO4, and NH4OH were introduced at a molar ratio of 3:2:6, and the reaction was carried out at pH 7. Here, CoSO ₄ having a molar concentration of 2.2 M was used. 7H ₂ O. The internal temperature of the reactor was maintained at 55 ° C while stirring at 1000 rpm. After 12 hours of stirring, a micro-spherical active material precursor, Co ₃ (PO ₄ ) ₂ , can be synthesized. xH ₂ O.

Then, the active material precursor was filtered through a vacuum pump and dried at 70 ° C for 24 hours under a vacuum.

Then, the dried precursor was heat-treated at 550 ° C for 15 hours in a reducing atmosphere to provide cobalt phosphate.

Then, cobalt phosphate was mixed with 2 parts by weight of pitch carbon with respect to 100 parts by weight of manganese phosphate, followed by stirring, whereby a carbon coating layer was formed on the surface of the cobalt phosphate.

Then, cobalt phosphoric acid having a carbon coating layer formed thereon is mixed with lithium phosphate (Li ₃ PO ₄ ) at a molar ratio of 1:1, and heated to 750 ° C at a temperature elevation rate of 5 ° C/min, followed by calcination for 15 hours. . As a result, a LiNiPO ₄ cathode active material for an olivine-type lithium secondary battery can be obtained.

Comparative Example 3: Preparation of a lithium secondary battery . The cathode active material used in the lithium secondary battery prepared in Comparative Example 1, the superconducting carbon black as a conductive material, and the polyvinylidene fluoride (PVdF) as a binder were mixed at a weight ratio of 85:7.5:7.5. To provide a slurry. The slurry was uniformly coated on an aluminum foil having a thickness of 20 μm , and vacuum dried at 120 ° C to provide a cathode.

Then, a coin-type half-cell was prepared according to a conventionally known manufacturing method, and a porous polyethylene film (Celgard 2300, thickness: 25 μm , Celgard LLC) was used by using the obtained cathode and lithium foil as counter electrodes. As a separator, and an electrolyte solution, the electrolyte solution includes 1.2 M LiPF ₆ dissolved in a solvent including ethylene carbonate and ethyl methyl carbonate in a volume ratio of 3:7.

Comparative Example 4: Preparation of a lithium secondary battery . The cathode active material used in the lithium secondary battery prepared in Comparative Example 2, the superconducting carbon black as a conductive material, and polyvinylidene fluoride (PVdF) as a binder were mixed at a weight ratio of 85:7.5:7.5. In order to provide a slurry. The slurry was uniformly coated on an aluminum foil having a thickness of 20 μm , and vacuum dried at 120 ° C to provide a cathode.

Then, a coin-type half-cell was prepared according to a conventionally known manufacturing method, and a porous polyethylene film (Celgard 2300, thickness: 25 μm , Celgard LLC) was used by using the obtained cathode and lithium foil as counter electrodes. As a separator, and an electrolyte solution, the electrolyte solution includes 1.2 M LiPF ₆ dissolved in a solvent including ethylene carbonate and ethyl methyl carbonate in a volume ratio of 3:7.

Experimental Example 1: Measurement of knock tightness . 10 ml of the cathode active material used for each of the lithium secondary batteries prepared in Example 1, Comparative Examples 1 and 2 was subjected to 500 strokes using a graduated cylinder to measure the knocking degree.

The cathode active material used in the lithium secondary battery prepared in Example 1 had a knocking degree of 1.5 g/cm ³ ; the cathode active material used in the lithium secondary battery prepared in Comparative Example 1 had 1.4 g/cm ³ The knocking degree of the cathode active material used in the lithium secondary battery prepared in Comparative Example 2 had a knocking degree of 1.2 g/cm ³ .

From these results, it was judged that the knocking-off property of the cathode active material used in the lithium secondary battery prepared in Example 1 was higher than that of the cathode active material used in the lithium secondary battery prepared in Comparative Examples 1 and 2. Tightness.

Experimental Example 2: Scanning electron microscope (SEM) and energy dispersive X-ray (EDX) analysis . The core-shell precursor of Example 1 and the active material precursors of Comparative Examples 1 and 2 were sampled on each carbon magnetic tape, coated with platinum (Pt) plasma to obtain SEM photographs, and energy-scattering X-rays were performed. analysis.

At this time, a scanning electron microscope (SEM) JSM 6400 was used.

Fig. 2 is a cross-sectional view showing a core-shell precursor in a scanning electron microscope (SEM) according to Example 1 of the present invention.

Further, the 3a and 3b graphs respectively show energy-scattering X-ray (EDX) analysis data for points A and B of Fig. 2, respectively.

As shown in Figures 2, 3a, and 3b, the core-shell precursor determination according to Example 1 is formed by a core-shell structure having a core comprising Ni and a shell comprising Co.

Therefore, referring to Figures 2, 3a, and 3b, it is foreseen that the cathode active material used for forming the lithium secondary battery according to the core-shell precursor of Example 1 by heating and firing has LiNiPO ₄ (core) -LiCoPO ₄ (shell) structure.

Meanwhile, Fig. 4 is a cross-sectional view showing a scanning electron microscope (SEM) of an active material precursor of Comparative Example 1 according to the present invention.

Further, the 5th and 5th graphs respectively show analysis data of energy dispersive X-rays (EDX) at points C and D of Fig. 4.

As shown in the figures 4, 5a, and 5b, it was confirmed that the active material precursor according to Comparative Example 1 was formed of a single particle structure containing Ni.

Therefore, referring to Figures 4, 5a, and 5b, it is foreseen that the active material according to Comparative Example 1 has a LiNiPO ₄ particle structure.

Experimental Example 3: Measurement of initial charge capacity, initial discharge capacity, and coulombic efficiency . The coin-type half-cells according to Example 2 and Comparative Examples 3 and 4 were respectively subjected to one charge-discharge at 30 ° C, 3.0 V to 5.3 V, and 0.05 C-rate (7.5 mA/g), and the initial charge was measured. Capacity, initial discharge capacity, and coulombic efficiency.

Fig. 6 is a view showing a charge-discharge diagram of the coin-type half-cell according to Example 2. The coin-type half-cell according to Example 2 had an initial charge capacity of 109.6 mAh/g, an initial discharge capacity of 63.2 mAh/g, and a coulombic efficiency of about 58%.

Fig. 7 is a view showing a charge-discharge diagram of the coin-type half-cell according to Comparative Example 3. The coin-type half-cell according to Comparative Example 3 had an initial charge capacity of 99.5 mAh/g, an initial discharge capacity of 14.4 mAh/g, and a coulombic efficiency of about 14%.

Therefore, it was confirmed that the coin-type half-cell according to Example 2 has a more remarkable initial charge capacity, initial discharge capacity, and coulombic efficiency than the coin-type half-cell according to Comparative Example 3.

While the present invention has been described in its preferred embodiments, the invention is not limited thereto, but may be varied within the scope of the appended claims. Moreover, it is to be understood that variations made are also within the scope of the invention.

100‧‧‧Lithium secondary battery

112‧‧‧Anode

114‧‧‧ cathode

113‧‧‧Baffle

120‧‧‧Battery

140‧‧‧Sealing components

Claims (32)

A cathode active material for a lithium secondary battery, comprising: a core comprising a compound represented by Chemical Formula 1; and a shell comprising a compound represented by Chemical Formula 2 Wherein the core and the shell have different material compositions; wherein, [Chemical Formula 1] Li _x1 M1 _y1 M2 _z1 PO _4-w1 E _w1 [Chemical Formula 2] Li _x2 M3 _y2 M4 _z2 PO _4-w2 E _w2 In the chemical formulas 1 and 2, M1, M2, M3 and M4 are the same or different, and each of them is independently selected from the group consisting of Ni, Co, Mn, Fe, Na, Mg, Ca, Ti, V, Cr, Cu. a group consisting of Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga, B and combinations of the foregoing; E is selected from the group consisting of F, S and combinations of the foregoing ;0<x1 1,0 Y1 1,0 Z1 1, and 0<x1+y1+z1 2,0 W1 0.5,0<x2 1,0 Y2 1,0 Z2 1, and 0<x2+y2+z2 2, and 0 W2 0.5; and, the cathode active material has a knock-tightness of about 1 g/cm ³ to 2 g/cm ³ . The cathode active material used in the lithium secondary battery according to claim 1, wherein M1 and M3 are the same material, and M2 and M4 are the same material, wherein x1=x2, y1<y2, and z1> Z2. A cathode active material for use in a lithium secondary battery according to claim 2, wherein M1 and M3 are selected from the group consisting of Fe, Co, Ni, Mn and a combination of the foregoing; M2 and M4 are selected A group consisting of free Mn, Ni, Co, Fe, and combinations of the foregoing. A cathode active material for use in a lithium secondary battery according to claim 1, wherein M1 and M3 are different materials. A cathode active material for use in a lithium secondary battery according to claim 1, wherein the M2 and the M4 are different materials. The cathode active material used in the lithium secondary battery of claim 1, wherein the M1 is different from the M2 system, and the core has a structure in which the concentration of M1 is along the center away from the core. The direction is gradually increased, and the concentration of M2 is gradually decreased along the direction; M1 is selected from the group consisting of Fe, Co, Ni, Mn and a combination of the foregoing, and the M2 is selected from Mn, Ni, Co. , a group of Fe and a combination of the foregoing. The cathode active material for use in a lithium secondary battery according to claim 1, wherein the core has a diameter of about 5 to 20 μm. The cathode active material used in the lithium secondary battery of claim 1, wherein the M3 is different from the M4 system, and the shell layer has a structure in which the concentration of M3 is away from the core. The direction of the center gradually increases, and the concentration of M4 gradually decreases along the direction; M3 is selected from the group consisting of Fe, Co, Ni, Mn and a combination of the foregoing, and the M4 is selected from Mn, Ni, A group consisting of Co, Fe, and combinations of the foregoing. The cathode active material for use in a lithium secondary battery according to claim 1, wherein the shell layer has a thickness of about 100 nm to 5 μm. The cathode active material for use in a lithium secondary battery according to claim 1, further comprising a carbon coating layer on a surface of the shell layer. The cathode active material for use in a lithium secondary battery according to claim 10, wherein the carbon coating layer has a thickness of about 10 nm to 200 nm. The cathode active material for use in a lithium secondary battery according to claim 1, further comprising an intermediate layer between the core and the shell layer; wherein the intermediate layer comprises a compound The compound is represented by Chemical Formula 3, and the material composition of the intermediate layer is different from the material composition of the core and the shell layer; wherein, [Chemical Formula 3] Li _x3 M5 _y3 M6 _z3 PO _4-w3 E _w3 In Chemical Formula 3, M5 and M6 are the same or different, and each of them is independently selected from the group consisting of Ni, Co, Mn, Fe, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, a group consisting of Ag, Ba, Zr, Nb, Mo, Al, Ga, B and a combination of the foregoing; E is selected from the group consisting of F, S and a combination of the foregoing; 0 < x3 1,0 Y3 1,0 Z3 1, and 0<x3+y3+z3 2, and 0 W3 0.5. The cathode active material used in the lithium secondary battery according to claim 12, wherein M1, M3 and M5 are the same material, and M2, M4 and M6 are the same material, wherein x1=x2=x3, Y1<y3<y2, and z1>z3>z2. The cathode active material for use in a lithium secondary battery according to claim 13, wherein M1, M3 and M5 are selected from the group consisting of Fe, Co, Ni, Mn and a combination of the foregoing, and M2, M4 and M6 are selected from the group consisting of Mn, Ni, Co, Fe and combinations of the foregoing. A cathode active material for use in a lithium secondary battery according to claim 12, wherein M1, M3 and M5 are different materials. A cathode active material for use in a lithium secondary battery according to claim 12, wherein M2, M4 and M6 are different materials. The cathode active material used in the lithium secondary battery of claim 12, wherein the M5 is different from the M6 system; the intermediate layer has a structure in which the concentration of the M5 is further away from the The direction of the core center is gradually increased, and the concentration of M6 is gradually decreased along the direction; M5 is selected from the group consisting of Fe, Co, Ni, Mn and a combination of the foregoing, and the M6 is selected from Mn, Ni, A group consisting of Co, Fe, and combinations of the foregoing. The cathode active material for use in a lithium secondary battery according to claim 12, wherein the intermediate layer has a thickness of about 100 nm to 24 μm. A cathode active material for use in a lithium secondary battery according to claim 1, which has a diameter of about 5 μm to 25 μm. A method for preparing a cathode active material for use in a lithium secondary battery, the method comprising the steps of: forming a core precursor by mixing an M1 source, an M2 source, and a phosphoric acid source; by using the core precursor Mixing with an M3 source, an M4 source, and a phosphoric acid source to form a core-shell precursor comprising a shell precursor formed on the surface of the core precursor; Heat treating the core-shell precursor to form a core-shell composite; The core-shell composite is mixed with a lithium source and then calcined, wherein M1, M2, M3 and M4 are the same or different, and each of them is independently selected from Ni, Co, Mn, Fe, A group consisting of Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga, B and combinations of the foregoing. The method of claim 20, wherein the M1 source, the M2 source, the M3 source, and the M4 source each comprise M1, M2, M3, M4 sulfur oxides, nitrogen oxides, and oxidation Anthracene, hydroxide, chloride, oxalate, fluoride, carbonate or a combination thereof. The method of claim 20, wherein the phosphoric acid source comprises phosphoric acid (H ₃ PO ₄ ), diammonium phosphate ((NH ₄ ) ₂ HPO ₄ ), ammonium phosphate trihydrate ((NH ₄ ) ₃ PO ₄ .3H ₂ O)), metaphosphoric acid, orthophosphoric acid, monoammonium phosphate (NH ₄ H ₂ PO ₄ ) or a combination of the foregoing. The method of claim 20, wherein the lithium source comprises lithium phosphate (Li ₃ PO ₄ ), lithium nitrate (LiNO ₃ ), lithium acetate (LiCH ₃ COOH), lithium carbonate (Li ₂ CO ₃ ) Lithium hydroxide (LiOH), lithium dihydrogen phosphate (LiH ₂ PO ₄ ) or a combination of the foregoing. The method of claim 20, wherein the heat treatment has an execution temperature range of between about 300 ° C and 700 ° C. The method of claim 20, wherein the calcining execution temperature range is between about 600 ° C and 900 ° C. The method of claim 20, after the step of forming the core-shell composite, further comprising the step of forming a carbon coating layer on the surface of the core-shell composite. The method of claim 20, after the step of forming the core precursor, further comprising the steps of: mixing the core precursor with an M5 source, an M6 source, and a phosphoric acid source; The surface of the core precursor forms an intermediate layer precursor; wherein M5 and M6 are the same or different, and each of them is independently selected from Ni, Co, Mn, A group consisting of Fe, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga, B and combinations of the foregoing. The method of claim 27, wherein the M5 source and the M6 source respectively comprise M5, M6 sulfur oxides, nitrogen oxides, cerium oxide, phosphorus oxides, chlorides, oxalates, fluorine a compound, a carbonate or a combination thereof; and the phosphoric acid source comprises phosphoric acid (H ₃ PO ₄ ), diammonium phosphate ((NH ₄ ) ₂ HPO ₄ ), ammonium phosphate trihydrate ((NH ₄ ) ₃ PO ₄ . 3H ₂ O)), metaphosphoric acid, orthophosphoric acid, monoammonium phosphate (NH ₄ H ₂ PO ₄ ) or a combination thereof. A method for preparing a cathode active material for use in a lithium secondary battery, the method comprising the steps of: forming a core precursor by mixing an M1 source and an M2 source; by using the core precursor and an M3 source An M4 source is mixed to form a core-shell precursor, the core-shell precursor comprising a shell precursor, the shell precursor system being formed on a surface of the core precursor; and the core-shell layer The precursor is mixed with a lithium source and a source of monophosphate and then calcined; wherein, M1, M2, M3 and M4 are the same or different, and each of them is independently selected from Ni, Co, Mn, Fe, Na, A group consisting of Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga, B and combinations of the foregoing. The method of claim 29, after the step of forming the core-shell precursor, further comprising the step of forming a carbon coating layer on the surface of the core-shell precursor. The method of claim 29, after the step of forming the core precursor, further comprising the step of: mixing the core precursor with an M5 source and an M6 source, and the core precursor Forming an intermediate layer precursor on the surface; Wherein, M5 and M6 are the same or different, and each of them is independently selected from the group consisting of Ni, Co, Mn, Fe, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, A group consisting of Ba, Zr, Nb, Mo, Al, Ga, B and combinations of the foregoing. A lithium secondary battery comprising: a cathode comprising a cathode active material; an anode comprising an anode active material; and an electrolyte; wherein the cathode active material is as claimed in claim 1 A cathode active material for use in a lithium secondary battery according to any one of items 18.