WO2018048174A1 - Cathode active material for lithium secondary battery and lithium secondary battery comprising same - Google Patents

Abstract

Provided are a cathode active material for a lithium secondary battery and a lithium secondary battery comprising the same, the cathode active material including a lithium iron phosphate and an active carbon, wherein the lithium iron phosphate is in the form of secondary particles into which the primary particles are agglomerated, each of the primary particles having a short side to a long side length ratio of 0.3 to less than 1, with the short side ranging in length from 40 nm to 300 nm.

Description

 【Specification】

 [Name of invention]

 Cathode active material for lithium secondary battery and lithium secondary battery comprising same [Technical Field]

 It relates to a cathode active material for a lithium secondary battery and a lithium secondary battery comprising the same. (

 Background Art

 12V lead acid batteries are mainly used for starting systems of vehicles, including two-wheeled vehicles, and a capacity of 3 Ah or 6 Ah is generally used. In accordance with the traditional starting system of such lead acid batteries, the whole starting circuit system of the vehicle is also formed accordingly.

 Carbon-based materials and lithium metal oxides were used as cathode and anode, respectively. In the case of a general lithium secondary battery, the voltage normally used is 2.5V to 4.3V. However, considering the starting system of a typical 12V lead acid battery, the charge pressure is not sufficient when a lithium secondary battery having a general composition is composed of a series of three batteries. In the case of charging up to 4V, the positive electrode active material will have a layer voltage of less than 4V in consideration of the lithium occlusion voltage of the negative electrode, and thus the state of charge (SOC) is very low. The structure is characterized by not easy operation. [Detailed Description of the Invention]

 [Technical problem]

 One embodiment is to provide a cathode active material for a lithium secondary battery with improved high current pulse discharge characteristics and fast charge and discharge characteristics.

Another embodiment is to provide a lithium secondary battery including the positive electrode active material. ^"[Technical Solution]

 One embodiment includes lithium iron phosphate and activated carbon, wherein the lithium iron phosphate is a secondary particle assembled with primary particles, the primary particle is a form in which the length ratio of the short side to the long side '0.3 or more less than 1 It provides a positive electrode active material for a lithium secondary battery having a short side length of the primary particles of 40 nm to 300 nm.

 The primary particles may have a form in which the length ratio of the short side to the long side is 0.33 to 0.9.

 The primary particles may have a cylindrical shape.

 The secondary particles may comprise spherical particles, granule particles, or combinations thereof.

The specific surface area of the activated carbon may be 500 m ² / g to 3000 m ² / g.

 The average particle diameter (D50) of the activated carbon is 10% to the size of the secondary particles

 Can be 3000%.

 Another embodiment includes a cathode including the cathode active material; A negative electrode including a negative electrode active material; And it provides a lithium secondary battery comprising an electrolyte solution.

 The anode active material may include amorphous carbon.

 The operating average voltage (SOC 50%) of the lithium secondary battery may be less than 3.55V. Specific details of other embodiments are included in the following detailed description. 【Effects of the Invention】

 A lithium secondary battery having improved high current fill discharge characteristics and high speed layer discharge characteristics may be implemented.

 [Brief Description of Drawings]

 1 is a schematic view showing a rechargeable lithium battery according to one embodiment.

FIG. 2 is a scanning electron micrograph of secondary particles of lithium iron phosphate according to one embodiment. FIG. ^• '<description of the sign>

 100: lithium secondary battery

 10: electrode assembly

 20: battery container

 13: electrode tab

 [Best form for implementation of the invention]

 Hereinafter, embodiments of the present invention will be described in detail. However, this is presented as an example, by which the present invention is not limited and the present invention is defined only by the scope of the claims to be described later.

 Hereinafter, a cathode active material for a rechargeable lithium battery according to one embodiment is described. The cathode active material for a rechargeable lithium battery according to one embodiment may include lithium iron phosphate and activated carbon.

 The lithium iron phosphate may include LiFeP t.

 The lithium iron phosphate may have a form of secondary particles formed by assembling primary particles as fine particles. The final structure of the lithium iron phosphate has a form of secondary particles, but the particles directly participating in the electrochemical reaction in contact with the electrolyte may be primary particles.

 Since lithium iron phosphate has a relatively larger reaction area than other lithium metal oxides, the lithium iron phosphate has high output characteristics when applied to a lithium secondary battery. In addition, since the charge and discharge voltage is between 3.4V and 3.5V for lithium metal, when the cell voltage is low and charges up to 12V through a series 4-cell configuration, it is possible to realize more than 80% of SOC (state of charge) so that 12V lead-acid Battery replacement is possible.

The size of the primary particles of the lithium iron phosphate may be 5 nm to 1, for example, 5 nm to 800 nm. When the size of the primary particles is within the above range, it may be advantageous for high output power of the lithium secondary battery. ^• The primary particles can have a long cylindrical shape. Specifically, the primary particles may have a long side in the longitudinal direction and a short side in the width direction based on the shape shown on the scanning electron microscope (SEM). The short side of the width direction may include both a long diameter and a short diameter when the diameter of the width and the length is different in the cross section.

 In this case, the length ratio of the short side to the long side may have a shape of 0.3 or more and less than 1, specifically, the length ratio may be 0.33 to 0.9, more specifically 0.35 to 0.9,0.4 to 0.9, or 0.5 to 0.9, for example 5 to 0.8. When the primary particles have a form having a length ratio within the above range, the transfer distance of lithium ions decreases, and the area where the lithium ions contact the electrolyte increases, which is advantageous for lithium emission, which is advantageous for high output.

The length of the short side of the primary particles may be 40 nm to 300 nm, specifically 40 nm to 290 nm, more specifically 40 nm to 280 nm, 40 nm to 270 nm, 40 nm to 260 nm, or 40 nm to 250 nm. Also, 50 nm to 280 nm, 50 nm to 270 nm, 50 nm to 260 nm, or 50 nm to 250 nm, specifically 60 nm to 280 nm, 60 nm to 270 nm, 60 nm to 260 nm, or 60 nm to 250 nm And, more specifically, 70 nm to 280 nm, 70 nm to 270 nm, 70 nm to 260 nm, or 70 nm to 250 nm ¾. In one specific embodiment, 80 nm to 280 nm, 80 nm to 270 nm, 80 nm to 260 nm, or 80 nm to 250 nm, more specifically 90 nm to 280 nm, 90 nm to 270 nm, 90 nm to 260 nm, or 90 nm To 250 nm, for example, 100 nm to 280 nm, 100 nm to 270 nm, 100 nm to 260 nm, or 100 nm to 250 nm. The most specific embodiment may be 100 nm to 250 nm, for example 150 nm to 250 nm. When the length of the short side of the primary particles is within the above range, it is possible to form a thick electrode and to ^• Large diffusion speed ensures excellent high-speed layer discharge characteristics.

 The secondary particles are formed by granulating the primary particles, and may include spherical particles, granule-type particles, or a combination thereof.

In addition, the size of the secondary particles may be 1 to 50 / 皿, specifically, 3 _. μα to 40, for example 5 to 30 jm. More

 Specifically, it may be 5 to 25, and in one specific embodiment, 5 urn to 20. When the size of the secondary particles is less than 1 // m, the surface area is too large to increase the consumption of the electrolyte solution, and thus a large amount of gas may be emitted. Particle cracking may occur during furnace rolling and may cause gas generation.

The lithium iron phosphate may be included in 50 parts by weight _^0/0 to 98 parts by weight _^0/0 with respect to the total of the activated carbon and the lithium iron phosphate, for example, it may be included up to 70% by weight to 96% by weight. More specifically, may be included to 80 weight _^0/0 to 95% by weight, it may be included in a specific embodiment to 85 weight _^0/0 to 90% by weight. When the content of the lithium iron phosphate is less than 50% by weight, the capacity of the battery may be reduced. When the content of the lithium iron phosphate is more than 98% by weight, the high-speed layer discharge function by the activated carbon is deteriorated, thereby making the battery unsuitable for a high output battery.

 The activated carbon has a function of adsorption and desorption of ions. When the activated carbon is used together with the lithium iron phosphate, a large current pulse discharge of 100 C—rate or more, that is, a current discharge of 100 times the 1C capacity of the cell for 1.2 minutes is possible.

The specific surface area of the activated carbon may be 500 m ² / g to 3000 m ² / g, for example, 600 m ² / g to 2800 m ² / g. More specifically, it may be 700 m ² / g to 2600 m ² / g, for example 800 m ² / g to 2400 m ² / g,

In embodiments it may be 1000 m ² / g to 2000 m ² / g. When the specific surface area of the activated carbon is within the above range, lithium having excellent high current pulse discharge characteristics and fast charge / discharge characteristics ^' Secondary battery can be implemented.

 The average particle diameter (D50) of the activated carbon may be 10% to 3000% of the size of the secondary particles of the lithium iron phosphate, for example, 10% to 500%. Specifically, the average particle diameter (D50) of the activated carbon may be 30 or less, for example, 5 皿 to 28, and more specifically 10 / to 20 / m. When the average particle diameter of the activated carbon is within the above range, a lithium secondary battery having excellent high current pulse discharge characteristics and high speed charge / discharge characteristics may be implemented.

 Hereinafter, FIG. 1 is described with reference to a rechargeable lithium battery according to another embodiment.

 This is explained with reference.

 1 is a schematic view showing a rechargeable lithium battery according to one embodiment.

 Referring to FIG. 1, a lithium secondary battery 100 according to an embodiment is an electrode

 Assembly 10, a battery container 20 containing the electrode assembly 10, and an electrode tab 13, which serves as an electrical passage for guiding the current formed in the electrode assembly 10 to the outside. have. Two surfaces of the battery container 20 are sealed by overlapping surfaces facing each other. In addition, the electrolyte is injected into the battery container 20 containing the electrode assembly (10).

 The electrode assembly 10 is composed of a positive electrode, a negative electrode facing the positive electrode, and a separator disposed between the positive electrode and the negative electrode.

 The positive electrode includes a current collector and a positive electrode active material layer formed on the current collector. The positive electrode active material layer includes a positive electrode active material, a binder, and optionally a conductive material.

 A1 may be used as the current collector, but is not limited thereto. The cathode active material is as described above.

The binder adheres positively to the positive electrode active material particles, and also serves to adhere the positive electrode active material to the current collector, and specific examples thereof include polyvinyl alcohol, Carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymer, polyvinylpyridone, polyurethane ,

 Polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrenebutadiene rubber, epoxy resin, nylon, and the like, but are not limited thereto.

 The conductive material is used to impart conductivity to the electrode, and any battery can be used as long as it is an electronic conductive material without causing chemical change in the battery. For example, natural graphite, artificial graphite, carbon black, acetylene black, and ketjen. Metal powder, metal fiber, etc., such as a contact | attach, carbon fiber, copper, nickel, aluminum, silver, etc. can be used, and electroconductive materials, such as a polyphenylene derivative, can be used 1 type or in mixture of 1 or more types.

 The negative electrode includes a current collector and a negative electrode active material layer formed on the current collector.

 The current collector may use Cu, but is not limited thereto.

 The negative electrode active material layer includes a negative electrode active material, a binder, and optionally a conductive material.

 As the negative electrode active material, lithium ions are reversibly

 Intercalation / deintercalable materials, lithium metals, alloys of lithium metals, materials capable of doping and undoping lithium, or transition metal oxides.

The material capable of reversibly intercalating / deintercalating the lithium ions is a carbon material, and any carbon-based negative electrode active material generally used in a lithium secondary battery may be used. , Amorphous carbon or these can be used together. Examples of the crystalline carbon include amorphous, plate-like, flake, spherical or fibrous natural or artificial graphite or artificial graphite. The same graphite may be mentioned, and examples of the amorphous carbon include soft carbon:

Low temperature calcined carbon) or hard carbon, mesophase pitch carbide, calcined coke, and the like.

 Examples of the alloy of the lithium metal include lithium and Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn. Alloys of the metals selected may be used.

Examples of a material capable of doping and undoping lithium include Si, SiO _x (0 <X <2), Si-C composites, Si-Q alloys (Q is an alkali metal, an alkaline earth metal, and a group 13 to 16). Element, transition metal, rare earth element or combination thereof, not Si), Sn, Sn0 ₂ , Sn-C composite, Sn-R (wherein R is alkali metal, alkaline earth metal, group 13 to 16 element, transition metal Or a rare earth element or a combination thereof, not Sn), and at least one of these and Si0 ₂ may be mixed and used. Specific elements of Q and R include 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, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, or a combination thereof is mentioned.

 Examples of the transition metal oxide include vanadium oxide, lithium vanadium oxide, and the like.

According to one embodiment, the amorphous carbon may be used as the anode active material. The amorphous carbon may be suitable for high output pulses because of low interfacial resistance of the cathode, and may be suitable for large current discharges of less than 0 ^° C. or more than 50 C-rate.

 The binder adheres the negative electrode active material particles to each other well, and also adheres the negative electrode active material to the current collector well.

Polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose,

Polyvinylchloride, carboxylated polyvinylchloride, polyvinylfluoride, ethylene oxide containing polymers, polyvinylpyridone, polyurethane, Polytetrafluoroethylene, rivinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon and the like may be used, but is not limited thereto.

As being used to impart conductivity to the conductive material electrodes, in the constituted battery, it is possible to use anything without causing a chemical change is electronically conductive material ^■,. Examples of natural hokyeon, artificial hokyeon, carbon black, acetylene black, Carbon-based materials such as ketjen black and carbon fiber; Metal materials such as metal powder or metal fibers such as copper, nickel, aluminum and silver; Conductive polymers such as polyphenylene derivatives, or a mixture thereof.

 The negative electrode and the positive electrode are prepared by mixing an active material, a conductive material, and a binder in a solvent to prepare a slurry, and then applying the slurry to each current collector. As the solvent, an organic solvent such as N-methylpyrrolidone may be used, or an aqueous solvent such as water may be used depending on the type of binder, but is not limited thereto. Since such an electrode manufacturing method is well known in the art, detailed description thereof will be omitted.

 The electrolyte solution contains an organic solvent and a lithium salt.

 The organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move. The organic solvent may be selected from carbonate, ester, ether, ketone, alcohol and aprotic solvents.

 Examples of the carbonate solvent include dimethyl carbonate,

DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methoxyl carbonate (MPC), ethylpropyl carbonate (EPC), ethylmethyl carbonate, EMC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) and the like can be used. In particular, in the case where a chain carbonate compound and a cyclic carbonate compound are used in combination, the dielectric constant may be increased and a solvent having a low viscosity may be prepared. In this case, the cyclic carbonate compound and the chain carbonate compound may be mixed and used in a volume ratio of about 1: 1 to 1: 9.

In addition, the ester solvent, for example, methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, decanolide, valerolactone, Melononolactone _: caprolactone and the like can be used. As the ether solvent, for example, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, and the like may be used. As the ketone solvent, cyclonucleanone may be used. Can be. In addition, ethyl alcohol, isopropyl alcohol, etc. may be used as the alcohol solvent.

 The organic solvent may be used alone or in combination of one or more, and the mixing ratio when using one or more in combination according to the desired battery performance

It can be adjusted appropriately.

 The sea solution may further include an additive such as an overcharge inhibitor such as ethylene carbonate and pyrocarbonate.

 The lithium salt is dissolved in an organic solvent, the lithium ion in the battery

It is a material that acts as a source to enable the operation of the basic lithium secondary battery, and promotes the movement of lithium ions between the positive electrode and the negative electrode.

Specific examples of the lithium salt are LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiN (S0 ₃ C ₂ F ₅ ) ₂ , LiC ₄ F ₉ S0 ₃ , L1CIO ₄ , LiA10 ₂ , L1AICI ₄ , LiN (C _x F _{2x + 1} S0 ₂ ) (C _y F _{2y +} iS0 ₂ ) (where x and y are natural numbers), LiCl, Lil, LiB (C ₂ 0 ₄ ) ₂ (lithium bis (oxalato) borate LiBOB), or a combination thereof.

The concentration of the lithium salt is used within the range of about 0.1M to about 2.0M -good. ^{When the} concentration of the lithium salt is included in the above range, since the electrolyte has an appropriate conductivity and viscosity, it can exhibit excellent electrolyte performance, and lithium ions can move effectively.

 The separator separates the negative electrode from the positive electrode and provides a passage for moving lithium ions, and any separator can be used as long as it is commonly used in lithium batteries. In other words, those having low resistance to ion migration of the electrolyte and excellent electrolyte-wetting ability can be used. For example, it is selected from glass fiber, polyester, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), or a combination thereof, and may be in a nonwoven or woven form. For example, polyolefin-based polymer separators such as polyethylene and polypropylene are mainly used for lithium ion batteries, and coated separators containing ceramic components or polymer materials may be used to secure heat resistance or mechanical strength. Can be used as a structure.

 The operating average voltage (SOC 50%) of the lithium secondary battery may be less than 3.55V, for example, may be 3.3V to 3.5V. When layering up to 12V through the series 4-cell configuration within the voltage range, a state of charge (SOC) of 80% or more can be realized, and thus a 12V lead acid battery can be replaced.

 [Form for implementation of invention]

 The following presents specific embodiments of the present invention. However, the embodiments described below are merely for illustrating or explaining the present invention in detail, and thus the present invention is not limited thereto. In addition, the contents not described herein are those that can be inferred technically by those skilled in the art will not be described.

 (Anode manufacturing)

Example 1 The mixture of FeC ₂ 0 ₄ , Li ₂ CO ₃ and (NH ₄ ) ₂ HP0 ₄ in a molar ratio of 1: 1: 1.2 was mixed with ethyl alcohol for 10 hours and ball milled for 10 hours at 80 ^° C. After spray drying, after primary heat treatment at 350 ^° C. for 2 hours in nitrogen gas, 5 parts by weight of carbon black was added to 100 parts by weight of the first heat-treated compound, followed by mixing in 5% of H _{2 in} mixed nitrogen gas. By secondary heat treatment at a temperature of 700 ^° C and maintained for 10 hours,

LiFePO ₄ was prepared.

Manufactured LiFeP0 ₄ 86 parts by weight _^0/0, and a specific surface area of 1500 m ² / g and 4% by weight of the average particle diameter (D50) of 15-carbon, 4 wt% of carbon black, and

Polyvinylidene fluoride were dispersed in (PVdF) 6 combined wave the weight _^0/0, and then, the Ν- methyl-pyrrolidone to prepare a slurry. Next, after applying the slurry on an aluminum foil, and dried and rolled to prepare a positive electrode.

 Example 2

The positive electrode was prepared in the same manner as in Example 1, except that the raw material mixture was heat-treated at 300 ^° C. for 2 hours, and then heat-treated at 800 ^° C. for 2 hours, and then maintained for 6 hours to produce LiFePO ₄ . Prepared.

 Example 3

After the first heat treatment of the raw material mixture at 400 ^° C for 2 hours, the second heat treatment at a temperature of 900 ^° C and maintained for 4 hours to produce LiFeP0 ₄ , the positive electrode in the same manner as in Example 1 Was prepared.

 Comparative Example 1

The raw material mixture of Example 1 was ground by a ball mill treatment for 10 hours, dried at a temperature of 80 ^° C for 10 hours, and then subjected to a first heat treatment at 300 ^° C for 5 hours, followed by a second heat treatment ^at a temperature of 900 ^° C. A positive electrode was manufactured in the same manner as in Example 1, except that LiFePO ₄ was prepared by keeping for a time.

Comparative Example 2 Except that the second heat treatment at 1000 ^° C., a positive electrode was prepared in the same manner as in Example 1.

 Comparative Example 3

 Except not using the activated carbon, a positive electrode was prepared in the same manner as in Example 1.

 (Lithium secondary battery production)

d002 is a soft carbon 3.5A 92.5 weight _^0/0, the carbon black increased 5 _^0/0, styrene-butadiene rubber (SBR) agarose (CMC) as a 1 wt. _^0/0, and 1.5 parts by weight of carboxymethyl selreul _^0/0 water A slurry was prepared by mixing with. Next, after applying the slurry on the copper foil, it was dried and rolled to prepare a negative electrode.

Using the positive electrode and the negative electrode and a separator made of polyethylene, as described in Korean Patent No. 1156377, a jelly having a tab shape was manufactured, and a lithium secondary battery was prepared by putting the jelly in a pouch. At this time, an electrolyte solution in which 1.2 M LiPF ₆ was dissolved in a solvent in which ethylene carbonate (EC), diethyl carbonate (DEC) and dimethyl carbonate (DMC) were mixed in a volume ratio of 1: 1 is used. Evaluation l: Structural Analysis of LiFeP0 ₄

Sizes of the primary particles and the secondary particles for LiFePO ₄ prepared in Examples 1 to 3 and Comparative Examples 1 to 3 were analyzed, and the results are shown in Table 1 below.

 Primary particles and secondary particles were observed magnified more than 10,000 times through a high magnification scanning electron microscope.

 TABLE 1

^■실시예 1 150 300 0.5 12 실시예 2 250 350 0.71 8 실시예 3 200 400 0.5 20 비교예 1 320 500 0.64 24 비교예 2 350 600 0.58 27 비교예 3 35 300 0.12 12

^■ Example 1 150 300 0.5 12 Example 2 250 350 0.71 8 Example 3 200 400 0.5 20 Comparative Example 1 320 500 0.64 24 Comparative Example 2 350 600 0.58 27 Comparative Example 3 35 300 0.12 12

 Referring to Table 1, the LiFeP t prepared in Examples 1 to 3 is a primary particle is assembled in the form of the length of the short side is in the range of 40 nm to 300 nm and the length ratio of the short side to the long side of 0.3 or less than 1 It can be seen that.

 In addition, the structure of the secondary particles formed by assembling the primary particles can be seen in FIG.

 FIG. 2 is a scanning electron micrograph of secondary particles of lithium iron phosphate according to one embodiment. FIG.

 Referring to Figure 2, it can be seen that the particle surface formed of secondary particles are assembled into a lump or spherical shape or assembled into a dumbbell-shaped sintered body in which spherical particles are connected.

 The determination of the short side and the long side is based on particles that can be identified as one particle by the primary particles themselves. Evaluation 2: High-speed layer discharge characteristics of a lithium secondary battery

The lithium secondary batteries prepared according to Examples 1 to 3 and Comparative Examples 1 to 3 were layered with CCCV up to 3.6V at room temperature, and then left at -10 ^° C for 10 hours, and then discharged at 100A for 1 second at the same temperature. When the voltage was measured, the results are shown in Table 2 below.

In addition, lithium secondary prepared according to Examples 1 to 3 and Comparative Examples 1 to 3 After completion of the chemical conversion process, after the complete discharge at 0.2C to 2V at 30 C-rate constant current layer charge, to calculate the percentage of the charge capacity of ΑΑ 30 Α to the layer charge capacity is shown in Table 2 below.

 TABLE 2

 Referring to Table 2, in the case of Examples 1 to 3 of the activated carbon

 It can be seen that both the fast charge and discharge behavior by the adsorption and desorption process and the fast ion transfer ability of the particulate LFP are shown. It can be seen that the LFP primary particles have a spherical or prismatic shape in the anode where the same activated carbon is mixed, so that the pulses are easily discharged when the length of the short side is short.

 In the case of Comparative Example 1, the activated carbon is mixed during layer transfer to achieve a filling rate of 80% or more up to 12 V. However, since the ion transfer distance due to the size of the primary particles of the LFP is longer than that of the examples, the performance of the combined performance with the activated carbon decreases. As a result, it can be seen that the pulse and layer properties are reduced compared to the embodiments.

 Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concepts of the present invention defined in the following claims are also provided. It belongs to the scope of the invention.

Claims

[Range of request]  [Claim 1]  Including lithium iron phosphate and activated carbon,  The lithium iron phosphate is a secondary particle assembled primary particles,  The primary particles have a form in which the length ratio of the short side to the long side is 0.3 or more and less than 1,  The positive electrode active material for lithium secondary batteries whose length of the short side of the said primary particle is 40 nm-300 nm.  [Claim 2]  In crab 1,  The primary particle has a positive electrode active material for a lithium secondary battery having a shape having a length ratio of the short side to the long side of 0.33 to 0.9.  [Claim 3]  From crab 1  The primary particles are a cathode active material for a lithium secondary battery having a cylindrical shape [Claim 4]  In claim 1,  The secondary particles are spherical particles, granules (granule) particles, or a combination thereof, a cathode active material for a lithium secondary battery.  [Claim 5]  In paragraph 1, The specific surface area of the activated carbon is 500 m ² / g to 3000 m ² / g positive electrode active material for a lithium secondary battery. ^' [Claim 6] Out of 11 The average particle diameter (D50) of the activated carbon is 10% to 3000% compared to the size of the secondary particles positive electrode active material for a lithium secondary battery.  [Claim 7]  A positive electrode comprising the positive electrode active material of any one of claims 11 to 6; A negative electrode including a negative electrode active material; And  Electrolyte  Lithium secondary battery comprising a.  [Claim 8]  In claim 7,  The negative active material is a lithium secondary battery containing amorphous carbon.  [Claim 9]  In crab 7,  Lithium secondary battery having an operating average voltage (SOC 50%) of less than 3.55V of the lithium secondary battery