CN105489859A - Surface-modified high-voltage lithium nickel manganese oxide material and preparation method thereof - Google Patents

Abstract

The invention discloses a surface-modified high-voltage lithium nickel manganese oxide material and a preparation method thereof. The surface-modified high-voltage lithium nickel-manganese oxide material is formed by coating the surface of the high-voltage lithium nickel-manganese oxide material with a Li-La-Zr-O solid electrolyte to modify the surface of the high-voltage lithium nickel-manganese oxide material. . The present invention coats a Li-La-Zr-O layer on the surface of the high-voltage lithium nickel manganese oxide material through an ex-situ surface modification process. Direct contact prevents the electrolyte from being oxidized to form a solid-liquid interface layer, which greatly improves the cycle performance of lithium nickel manganese oxide batteries.

Description

Surface-modified high-voltage lithium nickel manganese oxide material and preparation method thereof

technical field

The invention belongs to the technical field of lithium-ion battery cathode materials, and relates to a surface-modified high-voltage spinel lithium nickel-manganese oxide cathode material, more specifically, to a surface-modified high-voltage lithium nickel-manganese oxide material and a preparation method thereof .

Background technique

In recent years, the research and development of 5V high-voltage cathode materials has attracted more and more attention from many researchers. LiNi _0.5 Mn _1.5 O ₄ with a spinel-like structure has both high voltage and good cycle performance, and its application prospects are broad. LiNi _0.5 Mn _1.5 O ₄ is developed from the spinel LiMn ₂ O ₄ material. Because Ni ²⁺ replaces Mn ³⁺ , this change in element adjustment fundamentally changes the material’s internal electronic orbital overlap and The surface properties effectively control the dissolution of Mn, so the cycle stability of the material at high temperature is qualitatively improved compared with the original lithium manganese oxide. At the same time, the Mn ⁴⁺ octahedral structure is more stable than the Mn ³⁺ octahedron. When LiNi _0.5 Mn _1.5 O ₄ is formed, the ferromagnetic Mn ⁴⁺ -O2--Mn ⁴⁺ in the system transforms into the diamagnetic Ni ²⁺ - O2--Mn ⁴⁺ further increases the stability of the material. Therefore, the spinel LiNi _0.5 Mn _1.5 O ₄ has a more stable crystal structure than LiMn ₂ O ₄ . The theoretical capacity of LiNi _0.5 Mn _1.5 O ₄ is almost the same as that of LiMn ₂ O ₄ , which is 146.7mAh/g. At present, the actual specific capacity has reached the level of 130-140mAh/g. From the point of view of raw material sources, LiNi _0.5 Mn _1.5 O ₄ uses Mn and Ni, which are more abundant than Co and less expensive. Therefore, the LiNi _0.5 Mn _1.5 O ₄ material has become a hotspot in the research of high-voltage spinel cathode materials.

At present, lithium nickel manganese oxide materials are still not used in a large scale. The reason is that the cycle performance of lithium nickel manganese oxide materials, especially the high temperature performance, needs to be further improved. Since LiNi _0.5 Mn _1.5 O ₄ has a discharge voltage as high as 4.7 V, on the one hand, there will be a reaction between this cathode material and the electrolyte to oxidize the electrolyte to form a solid-liquid interface layer; on the other hand, as mentioned above, the electrolytic The HF in the liquid will dissolve some Ni ions or Mn ions, which will reduce the charge and discharge capacity of the positive electrode material and deteriorate the cycle performance. Surface modification or surface coating of electrode materials is beneficial to improve the interfacial properties of electrode materials, thereby improving their performance. Surface modification can form oxides, fluorides, or metal phosphates on the surface of active material particles, which can effectively resolve the negative effects of materials caused by high voltage. On the one hand, the coating layer provides a barrier film to avoid direct contact between the electrolyte and the active particles, so that the degree of oxidation of the electrolyte to form a solid-liquid interface layer will not be further deepened; on the other hand, the substances in the coating, such as Al ₂ O ₃ can react with HF in the electrolyte to consume HF, thereby reducing the dissolution of Ni ions and Mn ions, and inhibiting the formation of a solid-liquid interface layer, improving the performance of the battery.

For an ideal coating material, it should first have a certain stability, that is, it cannot be dissolved in the electrolyte system and cannot be destroyed at a higher potential; it should also have good electronic and lithium ion conductivity, In order to facilitate the conduction of electrons in the electrode and the diffusion of lithium ions. At present, most of the substances used as surface modification belong to metal fluorides, metal oxides, metal phosphates, and metal simple substances. The solid electrolyte material is a solid ion conductor, and some have high ion conductivity and low conductance activation energy close to or even exceeding that of molten salt. Since the non-conductive ions in the crystal can form a rigid skeleton, there are more occupiable positions than the number of conductive ions inside the crystal lattice, and these positions are connected to each other to form a one-dimensional tunnel type, two-dimensional planar type or three-dimensional conductive ion diffusion channel, The conductive ions can move freely in the channel. In particular, solid electrolytes have a wide electrochemical window, which can achieve high voltage output; stable structure, long service life, and high safety. As a high-voltage lithium nickel manganese oxide cathode material, its charging cut-off voltage reaches 5V and above. Therefore, the use of solid electrolyte as a surface modifier has positive significance for optimizing the lithium nickel manganese oxide electrode interface.

Contents of the invention

The purpose of the present invention is to improve the electrochemical performance of spinel lithium nickel manganese oxide, especially the high-temperature cycle performance, thereby providing a surface-modified high-voltage lithium nickel manganese oxide material and a preparation method thereof.

In order to achieve the above object, the present invention provides a surface-modified high-voltage lithium nickel manganese oxide material, which is coated on the surface of the high-voltage lithium nickel manganese oxide material by using Li-La-Zr-O solid electrolyte to High voltage lithium nickel manganese oxide material is formed by surface modification.

The atomic ratio of metal elements Li:La:Zr in the Li-La-Zr-O solid electrolyte is 7:3:2.

The coating amount of the Li-La-Zr-O solid electrolyte is 1%-10% relative to the high-voltage lithium nickel manganese oxide material, in mass percentage.

The present invention also provides a method for preparing the above-mentioned surface-modified high-voltage lithium nickel manganese oxide material, the method comprising the following steps:

Step 1, dissolving lithium-containing compounds, lanthanum-containing compounds, and zirconium-containing compounds in ethanol to obtain a lithium-lanthanum-zirconium ethanol solution;

Step 2, dissolving citric acid and ethylene glycol sequentially in the ethanol solution containing lithium, lanthanum, and zirconium ions in step 1 to form a mixed solution;

Step 3, stirring the mixed solution in the above step 2 at 30-80°C until the solution forms a milky white transparent colloidal solution;

Step 4, adding the high-voltage lithium nickel manganese oxide material into the above-mentioned transparent colloidal solution, and continuously stirring at 30-80°C until the ethanol solution is completely volatilized to form a dry mixture;

Step 5, bake the above dry mixture at 120~150°C for 1~5h, and then bake at 300~800°C for 4~10h, so that the Li-La-Zr-O solid electrolyte is coated on the high-voltage nickel-manganese Lithium oxide material surface, so as to obtain the high-voltage lithium nickel manganese oxide material modified by the surface of Li-La-Zr-O solid electrolyte.

In step 1, the atomic ratio of metal elements Li:La:Zr in the lithium-containing compound, lanthanum-containing compound, and zirconium-containing compound is 7:3:2; The total concentration of ions is 0.1-0.25mol/L.

In step 1, the lithium-containing compound is selected from any one or more of lithium nitrate, lithium acetate, lithium hydroxide, and lithium alkoxide; the lanthanum-containing compound is selected from lanthanum nitrate, lanthanum acetate, and lanthanum hydroxide. Any one or several; the zirconium-containing compound is selected from any one of zirconyl nitrate and zirconium n-propoxide or a mixture of both.

In step 2, the stoichiometric ratio of citric acid to ethylene glycol is 1:5 (in moles), and the moles of citric acid are equal to the total moles of lanthanum ions and zirconium ions in the mixed solution. Citric acid is complexed with lanthanum ions and zirconium ions to form a colloidal solution in step 3.

In step 5, the mass ratio of the Li-La-Zr-O solid electrolyte to the high-voltage lithium nickel manganese oxide material is 1% to 10%.

In step 5, the baking refers to baking in an oven; the roasting refers to baking in a muffle furnace.

In step 5, the baking condition in the muffle furnace is 400° C. for 5 hours.

The beneficial effects that the present invention has are:

In the present invention, a layer of Li-La-Zr-O solid electrolyte is coated on the surface of the high-voltage lithium nickel-manganese oxide material through an ex-situ surface modification process to form the surface-modified high-voltage lithium nickel-manganese oxide material of the present invention. The surface-modified high-voltage lithium nickel manganese oxide material is used in lithium nickel manganese oxide batteries, which can avoid direct contact between the electrolyte and the active particles, so that the degree of oxidation of the electrolyte to form a solid-liquid interface layer will not be further deepened, thereby greatly improving Cycle performance of lithium nickel manganese oxide battery.

Description of drawings

Fig. 1 is the charge-discharge curve of the surface-modified lithium nickel manganese oxide material prepared in Example 1 of the present invention.

Fig. 2 is the cycle performance of the surface-modified lithium nickel manganese oxide material prepared in Example 1 of the present invention.

detailed description

The specific implementation manner of the present invention will be described in detail below in conjunction with the accompanying drawings and examples.

Example 1

Weigh 0.7 mol of lithium nitrate, 0.3 mol of lanthanum nitrate and 0.2 mol of zirconyl nitrate at a molar ratio of 7:3:2, dissolve them in dehydrated ethanol and prepare a mixed solution of 0.1 mol/L. Weigh citric acid according to the stoichiometric ratio, weigh ethylene glycol according to the ratio of 1:5 (citric acid: ethylene glycol), and dissolve them in the mixed solution respectively. The mixed solution was stirred at 60° C. until a milky white transparent colloidal solution was formed. Then, calculate according to the Li-La-Zr-O solid electrolyte coating amount of 2%, and weigh the corresponding mass of lithium nickel manganese oxide material. Slowly add it into the high-speed stirring transparent colloidal solution, keep stirring at 60°C, and finally form a dry mixture. The dry mixture was baked at 140°C for 2h, cooled and kept at 500°C in a muffle furnace for 5h to obtain a Li-La-Zr-O-coated lithium nickel manganese oxide material. The coated Li-La- Zr-O is Li-La-Zr-O solid electrolyte.

The charge-discharge curves of the surface-modified LiNi _0.5 Mn _1.5 O ₄ material are shown in Figure 1, and the charge-discharge curves appear a voltage plateau near 4.7V, which corresponds to Ni ²⁺ /Ni ³⁺ and Ni ³⁺ /Ni ^{4 +} redox reaction. Its specific discharge capacity reaches 135mAh/g.

The cycle performance curve of the LiNi _0.5 Mn _1.5 O ₄ material is shown in Figure 2. The charge and discharge are carried out at a current of 1C, the discharge specific capacity is 135mAh/g, the cycle is 200 times, and the capacity retention rate is close to 98%.

Example 2

Weigh 0.7 mol of lithium nitrate, 0.3 mol of lanthanum nitrate and 0.2 mol of zirconyl nitrate at a molar ratio of 7:3:2, dissolve them in dehydrated ethanol and prepare a mixed solution of 0.1 mol/L. Weigh citric acid according to the stoichiometric ratio, weigh ethylene glycol according to the ratio of 1:5 (citric acid: ethylene glycol), and dissolve them in the mixed solution respectively. The mixed solution was stirred at 50° C. until a milky white transparent colloidal solution was formed. Then, calculate according to the Li-La-Zr-O solid electrolyte coating amount of 4%, and weigh the corresponding mass of lithium nickel manganese oxide material. Slowly add it into the high-speed stirring transparent colloidal solution, keep stirring at 50°C, and finally form a dry mixture. The dry mixture was baked at 120°C for 2h, cooled and kept at 400°C for 5h in a muffle furnace to obtain a Li-La-Zr-O-coated lithium nickel manganate material. The material was made into a button battery for electrical performance testing, and its first discharge specific capacity reached 132mAh/g. Charge and discharge at a current of 1C, cycle 200 times, and the capacity retention rate is close to 97%.

Example 3

Weigh 0.35mol of lithium nitrate, 0.15mol of lanthanum nitrate and 0.1mol of zirconium oxynitrate at a molar ratio of 7:3:2, and dissolve them in dehydrated ethanol to prepare a 0.1mol/L mixed solution. Weigh citric acid according to the stoichiometric ratio, weigh ethylene glycol according to the ratio of 1:5 (citric acid: ethylene glycol), and dissolve them in the mixed solution respectively. The mixed solution was stirred at 60° C. until a milky white transparent colloidal solution was formed. Then, calculate according to the Li-La-Zr-O solid electrolyte coating amount of 6%, and weigh the corresponding mass of lithium nickel manganese oxide material. Slowly add it into the high-speed stirring transparent colloidal solution, keep stirring at 60°C, and finally form a dry mixture. The dry mixture was baked at 120°C for 2h, cooled and kept at 600°C for 1h in a muffle furnace to obtain a Li-La-Zr-O-coated lithium nickel manganese oxide material. The material was made into a button battery for electrical performance testing, and its first discharge specific capacity reached 130mAh/g. Charge and discharge at a current of 1C, cycle 200 times, and the capacity retention rate is close to 97.4%.

In summary, the present invention adopts Li-La-Zr-O solid electrolyte as the surface modification layer, and uses an ex-situ method to modify the surface of the high-voltage lithium nickel manganese oxide material. The present invention coats a layer of Li-La-Zr-O layer (that is, Li-La-Zr-O solid electrolyte) on the surface of the high-voltage lithium nickel manganese oxide material through an ex-situ surface modification process to form the surface of the present invention. Modified high voltage lithium nickel manganese oxide material. The surface-modified high-voltage lithium nickel manganese oxide material is used in lithium nickel manganese oxide batteries, which can avoid direct contact between the electrolyte and the active particles, so that the degree of oxidation of the electrolyte to form a solid-liquid interface layer will not be further deepened, thereby greatly improving Cycle performance of lithium nickel manganese oxide battery.

Although the content of the present invention has been described in detail through the above preferred embodiments, it should be understood that the above description should not be considered as limiting the present invention. Various modifications and alterations to the present invention will become apparent to those skilled in the art upon reading the above disclosure. Therefore, the protection scope of the present invention should be defined by the appended claims.

Claims (10)

1. A surface-modified high voltage lithium nickel manganese oxide material, characterized in that the material is coated on the surface of the high voltage lithium nickel manganese oxide material by using a Li-La-Zr-O solid electrolyte, and the high voltage nickel manganese oxide It is formed by surface modification of lithium acid materials. 2. the high voltage lithium nickel manganese oxide material of surface modification as claimed in claim 1, is characterized in that, in described Li-La-Zr-O solid electrolyte, metal element Li: La: the atomic ratio of Zr is 7 :3:2. 3. the surface-modified high-voltage nickel-manganese acid lithium material as claimed in claim 1 or 2, is characterized in that, the coating amount of described Li-La-Zr-O solid electrolyte is relative to high-voltage nickel-manganese acid Lithium material is 1%~10%, calculated by mass percentage. 4. a preparation method of the high voltage lithium nickel manganese oxide material of surface modification according to claim 1, is characterized in that, the method comprises the following steps: Step 1, dissolving lithium-containing compounds, lanthanum-containing compounds, and zirconium-containing compounds in ethanol to obtain a lithium-lanthanum-zirconium ethanol solution; Step 2, dissolving citric acid and ethylene glycol sequentially in the ethanol solution containing lithium, lanthanum, and zirconium ions in step 1 to form a mixed solution; Step 3, stirring the mixed solution in the above step 2 at 30-80°C until the solution forms a milky white transparent colloidal solution; Step 4, adding the high-voltage lithium nickel manganese oxide material into the above-mentioned transparent colloidal solution, and continuously stirring at 30-80°C until the ethanol solution is completely volatilized to form a dry mixture; Step 5, bake the above dry mixture at 120-150°C for 1-5h, and then bake at 300-800°C for 4-10h to obtain a high-voltage battery surface-modified by Li-La-Zr-O solid electrolyte Lithium nickel manganese oxide material. 5. preparation method as claimed in claim 4 is characterized in that, in step 1, the atomic ratio of metal element Li:La:Zr in described lithium-containing compound, lanthanum-containing compound, zirconium-containing compound is 7:3: 2. In the lithium lanthanum zirconium ethanol solution, the total concentration of lithium lanthanum zirconium metal ions is 0.1-0.25mol/L. 6. The preparation method according to claim 4, wherein in step 1, the lithium-containing compound is selected from any one or more of lithium nitrate, lithium acetate, lithium hydroxide, and lithium alkoxide; The lanthanum-containing compound is selected from any one or several of lanthanum nitrate, lanthanum acetate, and lanthanum hydroxide; the zirconium-containing compound is selected from any one or a mixture of zirconium oxynitrate and zirconium n-propoxide. 7. the preparation method as claimed in claim 4 is characterized in that, in step 2, the stoichiometric ratio of described citric acid and ethylene glycol is 1:5, and the molar number of citric acid is equal to the lanthanum in mixed solution The total number of moles of ions and zirconium ions. 8. The preparation method according to claim 4, wherein in step 5, the mass ratio of the Li-La-Zr-O solid electrolyte to the high-voltage lithium nickel manganese oxide material is 1% to 10%. 9. The preparation method according to claim 4, characterized in that, in step 5, said baking refers to baking in an oven; said roasting refers to roasting in a muffle furnace. 10. The preparation method according to claim 9, characterized in that in step 5, the calcination condition in the muffle furnace is 400° C. for 5 h.