KR102352203B1 - Lithium secondary battery - Google Patents

Abstract

The present invention relates to a lithium secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, and more particularly, the positive electrode includes a lithium-metal oxide in which at least one of the metals has a continuous concentration gradient from the center to the surface. It includes a positive electrode active material, wherein the negative electrode includes a negative electrode active material including graphite having d002 of 3.356 to 3.365 Å, and thus relates to a lithium secondary battery having improved high temperature storage characteristics and lifespan characteristics.

Description

Lithium secondary battery {LITHIUM SECONDARY BATTERY}

The present invention relates to a lithium secondary battery, and more particularly, to a lithium secondary battery having excellent high-temperature storage characteristics and lifespan characteristics.

BACKGROUND With the rapid development of electronics, communication, and computer industries, portable electronic communication devices, such as camcorders, mobile phones, and notebook PCs, are admirably developing. Accordingly, the demand for lithium secondary batteries as a power source capable of driving them is increasing day by day. In particular, as an eco-friendly power source, R&D is being actively carried out in Japan, Europe, and the United States as well as in Korea in relation to the application of electric vehicles, uninterruptible power supplies, power tools, and satellites.

Among the currently applied secondary batteries, the lithium secondary battery developed in the early 1990s contains an anode made of a carbon material capable of occluding and releasing lithium ions, a cathode made of lithium-containing oxide, etc., and lithium salt dissolved in an appropriate amount in a mixed organic solvent. It is composed of a non-aqueous electrolyte.

However, as the application range of lithium secondary batteries has been expanded, the need to use lithium secondary batteries in harsher environments such as high temperature or low temperature environments is increasing.

However, lithium transition metal oxide or composite oxide used as a positive electrode active material of a lithium secondary battery has a problem in that the metal component is separated from the positive electrode when stored at a high temperature in a fully charged state, and thus is placed in a thermally unstable state.

In order to solve this problem, Korean Patent Application Laid-Open No. 2006-0134631 discloses a cathode active material having a core-shell structure in which a core part and a shell part are made of different lithium transition metal oxides, but the improvement in lifespan characteristics is still insufficient. do.

Patent Document 1: Korean Patent Publication No. 2006-0134631

An object of the present invention is to provide a lithium secondary battery having excellent high-temperature storage characteristics and lifespan characteristics.

1. A positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode includes a positive active material including lithium-metal oxide, wherein at least one of the metals has a continuous concentration gradient from the center to the surface, and the negative electrode has an interplanar spacing d002 is 3.356 to 3.365 Å, including a negative active material comprising graphite, a lithium secondary battery.

2. The lithium secondary battery according to item 1, wherein the other one of the metals forming the lithium-metal oxide has a constant concentration from the center to the surface.

3. The method according to item 1, wherein the lithium-metal oxide comprises a first metal having a concentration gradient range in which the concentration increases from the center to the surface portion, and a second metal having a concentration gradient range in which the concentration decreases from the center to the surface portion. which is a lithium secondary battery.

4. The method of item 1, wherein the lithium-metal oxide is represented by the following formula (1), M1 in the following formula (1), At least one of M2 and M3 has a continuous concentration gradient from the central portion to the surface portion, a lithium secondary battery:

[Formula 1]

Li _x M1 _a M2 _b M3 _c O _y

(wherein, M1, M2 and M3 are selected from the group consisting of Ni, Co, Mn, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga and B becomes,

0<x≤1.1, 2≤y≤2.02, 0≤a≤1, 0≤b≤1, 0≤c≤1, 0<a+b+c≤1).

5. The method according to item 4, wherein M1, At least one of M2 and M3 has a concentration gradient section in which the concentration increases from the center portion to the surface portion, and the remainder has a concentration gradient section in which the concentration decreases from the center portion to the surface portion.

6. The method according to item 4, wherein M1, One of M2 and M3 has a concentration gradient section in which the concentration increases from the center to the surface portion, the other has a concentration gradient section in which the concentration decreases from the center portion to the surface portion, and the other one has a constant concentration from the center to the surface portion. having, a lithium secondary battery.

7. Item 4, wherein said M1, M2 and M3 are Ni, Co and Mn, respectively, a lithium secondary battery.

8. The lithium secondary battery according to any one of items 4 to 7, wherein M1 is Ni, and 0.6≤a≤0.95 and 0.05≤b+c≤0.4.

9. The lithium secondary battery according to any one of items 4 to 7, wherein M1 is Ni, and 0.7≤a≤0.9 and 0.1≤b+c≤0.3.

10. The lithium secondary battery according to item 1, wherein the primary particles of the lithium-metal oxide have a rod-type shape.

11. The lithium secondary battery according to item 1, wherein the graphite has an interplanar spacing d002 of 3.361 to 3.365 Å.

12. The lithium secondary battery according to item 1, wherein the graphite is a mixture of first graphite having d002 of 3.356 to 3.360 Å and second graphite having d002 of 3.361 to 3.365 Å.

13. The lithium secondary battery according to item 12, wherein a mixing weight ratio of the first graphite and the second graphite is 0:100 to 90:10.

14. The lithium secondary battery according to item 12, wherein a mixing weight ratio of the first graphite and the second graphite is 0:100 to 50:50.

In the lithium secondary battery of the present invention, both high-temperature storage characteristics and lifespan characteristics can be significantly improved by combining a positive electrode active material containing a metal having a continuous concentration gradient and a negative electrode active material containing graphite having a specific structure.

1 is a diagram schematically illustrating a position for measuring a concentration of a lithium-metal oxide according to an embodiment.
2 is a TEM photograph of the lithium-metal oxide of Example 1.
3 is a TEM photograph of the lithium-metal oxide of Comparative Example 1.

The present invention relates to a lithium secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode includes a positive active material comprising a lithium-metal oxide in which at least one of the metals has a continuous concentration gradient from the center to the surface portion, The negative electrode relates to a lithium secondary battery having improved high temperature storage characteristics and lifespan characteristics by including a negative active material including graphite having d002 of 3.356 to 3.365 Å.

Hereinafter, the present invention will be described in more detail.

cathode active material

The positive active material according to the present invention includes a lithium-metal oxide in which at least one of the metals has a continuous concentration gradient from the central portion to the surface portion. Such a positive active material has excellent lifespan characteristics compared to a positive active material having no change in concentration.

In the present invention, that the metal among lithium-metal oxides has a continuous concentration gradient from the center to the surface means that metals other than lithium have a concentration distribution that changes with a constant tendency from the center to the surface of the lithium-metal oxide particles. it means. A constant trend means that the overall concentration change trend decreases or increases, and does not exclude having a value opposite to the trend at some points.

In the present invention, the central portion of the particle means within a radius of 0.2 μm from the center of the active material particle, and the surface portion of the particle means within 0.2 μm from the outermost part of the particle.

The positive electrode active material according to the present invention includes at least one metal having a concentration gradient. Accordingly, as an embodiment, the first metal having a concentration gradient section in which the concentration increases from the center to the surface portion and the second metal having a concentration gradient section in which the concentration decreases from the center portion to the surface portion may be included. The first metal or the second metal may be independently of one another.

As another embodiment of the present invention, the positive electrode active material according to the present invention may include a metal having a constant concentration from the center to the surface portion.

Specific examples of the positive electrode active material according to the present invention include a lithium-metal oxide represented by the following formula (1), M1 in the following formula (1), At least one of M2 and M3 has a continuous concentration gradient from the center to the surface:

[Formula 1]

Li _x M1 _a M2 _b M3 _c O _y

(wherein, M1, M2 and M3 are selected from the group consisting of Ni, Co, Mn, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga and B becomes,

0<x≤1.1, 2≤y≤2.02, 0≤a≤1, 0≤b≤1, 0≤c≤1, 0<a+b+c≤1).

In one embodiment of the present invention, M1, At least one of M2 and M3 may have a concentration gradient section in which the concentration increases from the central portion to the surface portion, and the rest may have a concentration gradient section in which the concentration decreases from the center portion to the surface portion.

In another embodiment of the present invention, M1, One of M2 and M3 has a concentration gradient section in which the concentration increases from the center to the surface portion, the other has a concentration gradient section in which the concentration decreases from the center portion to the surface portion, and the other one has a constant concentration from the center to the surface portion. can have

As a specific example of the present invention, M1, M2 and M3 may be Ni, Co and Mn, respectively.

The lithium-metal oxide according to the present invention may have a relatively high content of nickel (Ni). When nickel is used, it helps to improve battery capacity. In the conventional positive electrode active material structure, when the content of nickel is large, there is a problem in that the life is charged. does not Accordingly, the positive active material of the present invention may exhibit excellent lifespan characteristics while maintaining high capacity.

For example, in the lithium-metal oxide according to the present invention, the molar ratio of nickel may be 0.6 to 0.95, preferably 0.7 to 0.9. That is, when M1 in Formula 1 is Ni, 0.6≤a≤0.95 and 0.05≤b+c≤0.4, preferably, 0.7≤a≤0.9 and 0.1≤b+c≤0.3.

The lithium-metal oxide according to the present invention does not specifically limit the particle shape, but preferably, the primary particle may have a rod-type shape.

The particle size of the lithium-metal oxide according to the present invention is not particularly limited, and may be, for example, 3 to 20 μm.

The positive electrode active material according to the present invention may further include a coating layer on the above-described lithium-metal oxide. The coating layer may include a metal or a metal oxide. For example, it may include Al, Ti, Ba, Zr, Si, B, Mg, P and alloys thereof, or an oxide of the metal.

If necessary, the cathode active material according to the present invention may be doped with the above-described lithium-metal oxide with a metal or a metal oxide. The dopable metal or metal oxide may be Al, Ti, Ba, Zr, Si, B, Mg, P and alloys thereof, or an oxide of the metal.

The lithium-metal oxide according to the present invention can be prepared using a co-precipitation method.

Hereinafter, an embodiment of a method for manufacturing a cathode active material according to the present invention will be described.

First, metal precursor solutions having different concentrations are prepared. The metal precursor solution is a solution including a precursor of at least one metal to be included in the positive electrode active material. Metal precursors are typically halides, hydroxides, acid salts of metals, and the like.

The metal precursor solution to be prepared obtains two types of precursor solutions, a precursor solution having a concentration of the composition of the central portion of the positive electrode active material to be prepared, and a precursor solution having a concentration corresponding to the composition of the surface portion, respectively. For example, in the case of manufacturing a metal oxide positive active material containing nickel, manganese, and cobalt in addition to lithium, a precursor solution having concentrations of nickel, manganese, and cobalt corresponding to the central composition of the positive active material and the surface portion composition of the positive electrode active material Prepare a precursor solution having concentrations of nickel, manganese and cobalt corresponding to .

Next, a precipitate is formed while mixing the two kinds of metal precursor solutions. Upon mixing, the mixing ratio of the two metal precursor solutions is continuously changed to correspond to the concentration gradient in the desired active material. Thus, the precipitate has a concentration gradient in the concentration of the metal in the active material. Precipitation may be performed by adding a chelating reagent and a base upon mixing.

After the prepared precipitate is heat-treated, mixed with lithium salt and heat-treated again, the positive electrode active material according to the present invention can be obtained.

negative active material

The negative active material according to the present invention includes graphite having an interplanar spacing d002 of 3.356 to 3.365 Å. In the lithium secondary battery of the present invention, when graphite having the specific d002 value is used as an anode active material and used together with the cathode active material of the present invention, lifespan characteristics may be significantly increased. In this respect, it is more preferable that the interplanar spacing d002 is 3.361 to 3.365 Å. When the interplanar spacing d002 is less than 3.356 Å, the lifetime characteristic is deteriorated, and when it exceeds 3.365 Å, the capacity is decreased.

If necessary, the graphite according to the present invention may be used as a mixture of first graphite having d002 of 3.356 to 3.360 Å and second graphite having d002 of 3.361 to 3.365 Å. When used as such a mixture, it is more preferable in terms of improvement of life characteristics. In this case, the mixing weight ratio of the first graphite and the second graphite may be 0:100 to 90:10. In the case of mixing the first graphite and the second graphite, it is more preferable that the mixing weight ratio of the first graphite and the second graphite is 0:100 to 50:50 from the viewpoint of improving the lifespan characteristics. As the content of the second graphite is greater than that of the first graphite, the degree of improvement in the lifespan characteristics is further increased.

The size of the graphite used in the present invention is not particularly limited, but may have an average particle diameter of 5 to 30 μm.

secondary battery

The present invention provides a lithium secondary battery manufactured using the positive electrode active material and the negative electrode active material according to the present invention described above.

The lithium secondary battery according to the present invention may be manufactured including a positive electrode, a negative electrode, and a non-aqueous electrolyte.

The positive electrode and the negative electrode are prepared by mixing and stirring the positive electrode active material and the negative electrode active material according to the present invention with a solvent and, if necessary, a binder, a conductive material, a dispersing material, etc. Then, it can be compressed and dried to manufacture a positive electrode and a negative electrode.

As a binder, those used in the art may be used without particular limitation, for example, vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (polyvinylidenefluoride, PVDF), An organic binder such as polyacrylonitrile and polymethylmethacrylate, or an aqueous binder such as styrene-butadiene rubber (SBR) may be used together with a thickener such as carboxymethyl cellulose (CMC).

As the conductive material, a conventional conductive carbon material may be used without particular limitation.

The current collector made of a metal material has high conductivity and is a metal to which the positive or negative electrode active material mixture can easily adhere, and any metal that has no reactivity in the voltage range of the battery may be used. Non-limiting examples of the positive electrode current collector include a foil made of aluminum, nickel, or a combination thereof, and non-limiting examples of the negative electrode current collector include copper, gold, nickel, or a copper alloy or a combination thereof. foil, etc.

A separator is interposed between the positive electrode and the negative electrode. As the separator, a conventional porous polymer film conventionally used as a separator, such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/ A porous polymer film made of a polyolefin-based polymer such as a methacrylate copolymer may be used alone or by laminating them, or a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting glass fiber, polyethylene terephthalate fiber, etc. can be used, but is not limited thereto. As a method of applying the separator to a battery, in addition to winding, which is a general method, lamination, stacking, and folding of a separator and an electrode are possible.

The non-aqueous electrolyte includes a lithium salt as an electrolyte and an organic solvent, and the lithium salt can be used without limitation those commonly used in electrolytes for lithium secondary batteries. Examples of the organic solvent include propylene carbonate (PC), ethylene carbonate (ethylene carbonate, EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), methylpropyl carbonate, dipropyl carbonate, dimethylsulfuroxide, acetonitrile, dimethoxy Any one selected from the group consisting of ethane, diethoxyethane, vinylene carbonate, sulfolane, gamma-butyrolactone, propylene sulfite, and tetrahydrofuran, or a mixture of two or more thereof may be used.

The non-aqueous electrolyte is injected into an electrode structure comprising a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode to prepare a lithium secondary battery. The external shape of the lithium secondary battery of the present invention is not particularly limited, but may be a cylindrical shape using a can, a prismatic shape, a pouch type, or a coin type.

Hereinafter, preferred embodiments are presented to help the understanding of the present invention, but these examples are merely illustrative of the present invention and do not limit the appended claims, and are within the scope and spirit of the present invention. It is obvious to those skilled in the art that various changes and modifications are possible, and it is natural that such variations and modifications fall within the scope of the appended claims.

Example One

<Anode>

As a cathode active material, the total composition is LiNi _{0 . 8} Co _{0 . 1} Mn _{0 . 1} O ₂ , and the surface composition LiNi _{0 from the central composition LiNi 0.84} Co _0.11 Mn _0.05 O _{2 . 78} Co _{0 . 10} Mn _{0 . A} positive electrode mixture was prepared using lithium-metal oxide (hereinafter CAM-10) having a concentration gradient up to 12 O ₂ , Denka Black as a conductive material, PVDF as a binder, and each mass ratio composition of 92: 5: 3 Then, it was coated, dried, and pressed on an aluminum substrate to prepare a positive electrode.

For reference, the concentration gradient of the prepared lithium-metal oxide is shown in Table 1 below, and the concentration measurement position is as shown in FIG. 1 . Measurement positions were measured at intervals of 5/7 μm from the surface for lithium-metal oxide particles having a distance of 5 μm from the center of the particle to the surface.

location Ni Mn Co One 77.97 11.96 10.07 2 80.98 9.29 9.73 3 82.68 7 10.32 4 82.6 7.4 10 5 82.55 7.07 10.37 6 83.24 5.9 10.86 7 84.33 4.84 10.83

<Cathode>

A negative electrode mixture comprising 93 wt% of natural graphite (d002 3.358Å) as an anode active material, 5 wt% of KS6, a flake type conductive material, as a conductive material, 1 wt% of SBR and 1 wt% of a thickener CMC as a binder is coated on a copper substrate and dried and press to prepare a negative electrode.

<Battery>

The positive and negative electrode plates are notched to the appropriate size and laminated, and a separator (polyethylene, thickness 25㎛) is interposed between the positive and negative electrode plates to form a cell, and the tab of the positive electrode and the tab portion of the negative electrode are welded, respectively. did The welded anode/separator/cathode combination was placed in a pouch and sealed on three sides except for the electrolyte injection side. In this case, the part with the tab is included in the sealing part. After injecting electrolyte into the remaining part, the remaining side was sealed and impregnated for more than 12 hours. _{The electrolyte solution was prepared by preparing a 1M LiPF 6} solution with a mixed solvent of EC/EMC/DEC (25/45/30; volume ratio), then vinylene carbonate (VC) 1wt%, 1,3-propensultone (PRS) 0.5wt % and lithium bis(oxalato)borate (LiBOB) of 0.5 wt% was used.

Thereafter, pre-charging was performed for 36 minutes at a current (2.5A) corresponding to 0.25C. After 1 hour of degasing and aging for 24 hours or more, chemical charge and discharge were performed (charge condition CC-CV 0.2C 4.2V 0.05C CUT-OFF, discharge condition CC 0.2C 2.5V CUT-OFF). After that, standard charge/discharge was performed (charge condition CC-CV 0.5C 4.2V 0.05C CUT-OFF, discharge condition CC 0.5C 2.5V CUT-OFF).

Example 2-7

A battery was prepared in the same manner as in Example 1, except that a mixture of natural graphite (d002 3.358 Å) and artificial graphite (d002 3.363 Å) was used as the negative electrode active material. The mixing ratio of graphite is shown in Table 2 below.

comparative example One

LiNi _{0 .8} in the positive electrode active material having a uniform composition in the entire particles _{Co 0 .1 Mn 0 .1 O 2} ( hereinafter CAM-20) was prepared and is the battery in the same manner as in Example 1 except for using.

comparative example 2-7

A battery was prepared in the same manner as in Comparative Example 1, except that a mixture of natural graphite (d002 3.358 Å) and artificial graphite (d002 3.363 Å) was used as the negative electrode active material. The mixing ratio of graphite is shown in Table 2 below.

comparative example 8-11

A battery was prepared in the same manner as in Comparative Example 1, except that those shown in Table 3 were used as the positive electrode active material and the negative electrode active material.

Experimental example One

1. Room temperature life characteristics

After repeating charging (CC-CV 2.0 C 4.2V 0.05C CUT-OFF) and discharging (CC 2.0C 2.75V CUT-OFF) 500 times with the cells prepared in Examples and Comparative Examples, the discharge capacity at 500 times The room temperature life characteristics were measured by calculating as a percentage of the discharge capacity at one time.

The results are shown in Table 2 below.

2. Capacity recovery rate

After the cells of Examples and Comparative Examples charged under CC-CV 0.5 C 4.2V 0.05C CUT-OFF condition were stored in an oven at 60° C. for 4 weeks, discharged under CC 0.5C 2.75V CUT-OFF condition and CC-CV 0.5 After charging under the C 4.2V 0.05C CUT-OFF condition, it was discharged again under the CC 0.5C 2.75V CUT-OFF condition.

The results are shown in Table 2 below.

anode
active material anode active material life span(%)
(500cycle) high temperature storage
After 4 weeks left
Capacity recovery rate (%) Kinds mixing ratio Example 1 CAM-10 Natural graphite/artificial graphite 100/0 80 78 Example 2 CAM-10 Natural graphite/artificial graphite 90/10 82 81 Example 3 CAM-10 Natural graphite/artificial graphite 70/30 86 83 Example 4 CAM-10 Natural graphite/artificial graphite 50/50 88 85 Example 5 CAM-10 Natural graphite/artificial graphite 30/70 90 87 Example 6 CAM-10 Natural graphite/artificial graphite 10/90 92 89 Example 7 CAM-10 Natural graphite/artificial graphite 0/100 95 90 Comparative Example 1 CAM-20 Natural graphite/artificial graphite 100/0 70 80 Comparative Example 2 CAM-20 Natural graphite/artificial graphite 90/10 71 81 Comparative Example 3 CAM-20 Natural graphite/artificial graphite 70/30 73 83 Comparative Example 4 CAM-20 Natural graphite/artificial graphite 50/50 75 85 Comparative Example 5 CAM-20 Natural graphite/artificial graphite 30/70 77 87 Comparative Example 6 CAM-20 Natural graphite/artificial graphite 10/90 79 89 Comparative Example 7 CAM-20 Natural graphite/artificial graphite 0/100 80 90 Comparative Example 8 CAM-10 Natural graphite (d002 0.350Å) single use 76 78 Comparative Example 9 CAM-10 Artificial graphite (d002 3.370Å) single use 97 90 Comparative Example 10 CAM-20 Natural graphite (d002 3.350Å) single use 65 80 Comparative Example 11 CAM-20 Artificial graphite (d002 3.370Å) single use 83 90

Referring to Table 2, it can be seen that the batteries of Examples exhibit superior lifespan characteristics and high temperature storage characteristics (capacity recovery rate after high temperature storage) compared to Comparative Examples.

Specifically, when Examples 1 to 7 and Comparative Examples 1 to 7 are compared, when the positive electrode active material according to the present invention is used, high-temperature storage characteristics show superiority equal to or greater than that of Comparative Examples, and life characteristics are positive electrodes without a concentration gradient It can be confirmed that it is superior to the active material .

In addition, it can be seen that as the content of artificial graphite with d002 of 3.363 Å increases, the increase in lifespan characteristics increases. In particular, it can be seen that the difference in increase becomes clear when artificial graphite is greater than or equal to natural graphite.

On the other hand, in Comparative Examples 9 and 11, where d002 is outside the scope of the present invention, the lifespan characteristics and high temperature storage characteristics showed the Example level, but the capacity of the negative active material was 300 mAh/g or less, so the capacity of the battery was not actually used. decreased to the extent that

In addition, TEM photographs of the positive active material particles of Example 1 and Comparative Example 1 are shown in FIGS. 2 and 3, respectively. Referring to FIGS. 2 (Example 1) and 3 (Comparative Example 1), the primary particles of the positive active material of the Example have a rod-like shape, whereas the positive active material of the Comparative Example has a shape close to a spherical shape, it can be seen that there is

Claims (15)

anode, cathode and non-aqueous electrolyte;
The positive electrode includes a positive active material comprising a lithium-metal oxide particle represented by the following Chemical Formula 1;
In the following formula (1), M1 has a continuous concentration gradient section between the particle center and the surface portion, a is 0.7797 or more in all regions of the particle, c is 0.12 or less in all regions of the particle,
The negative electrode has an interplanar spacing d002 of 3.356 to 3.365 Å, and graphite including natural graphite and artificial graphite in a weight ratio of 0:100 to 90:10; A lithium secondary battery comprising a negative active material comprising a.
[Formula 1]
Li _x M1 _a M2 _b M3 _c O _y
(wherein, M1, M2 and M3 are Ni, Co and Mn, respectively, 0<x≤1.1, 2≤y≤2.02, 0<a<1, 0<b<1, 0<c<1, 0<a+b+c ≤1).
The lithium secondary battery according to claim 1, wherein at least one of M2 and M3 has a constant concentration from a particle center to a surface portion.
The method according to claim 1, wherein M1 has a concentration gradient section in which the concentration decreases from the particle center to the surface portion, and at least one of M2 and M3 has a concentration gradient section in which the concentration increases from the particle center to the surface portion direction, lithium secondary battery.
delete The lithium secondary battery according to claim 1, wherein M1 has a concentration gradient section in which the concentration decreases from the particle center to the surface portion, and M2 and M3 have a concentration gradient section in which the concentration increases from the particle center to the surface portion direction. .
The method according to claim 1, wherein M1 has a concentration gradient section in which the concentration decreases in the direction from the particle center to the surface portion, M3 has a concentration gradient section in which the concentration increases in the direction from the particle center to the surface portion, and M2 is the particle center A lithium secondary battery having a constant concentration from to the surface portion.
delete The lithium secondary battery according to claim 1, wherein 0.6<a≤0.95 and 0.05≤b+c<0.4.
The lithium secondary battery according to claim 1, wherein 0.7<a≤0.9 and 0.1≤b+c<0.3.
The lithium secondary battery of claim 1 , wherein the lithium-metal oxide particles include rod-type primary particles.
delete The lithium secondary battery of claim 1, wherein d002 of the natural graphite is 3.356 to 3.360 Å, and d002 of the artificial graphite is 3.361 to 3.365 Å.
delete The lithium secondary battery according to claim 1, wherein a weight ratio of the natural graphite and the artificial graphite is 0:100 to 50:50.
The lithium secondary battery according to claim 1, wherein the concentration gradient section is formed entirely from the particle center to the surface portion.

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