JP7214690B2 - Positive electrode active material and lithium ion secondary battery - Google Patents

Description

The present invention relates to positive electrode active materials. The present invention also relates to a lithium ion secondary battery using the positive electrode active material.

In recent years, lithium-ion secondary batteries have been suitably used as portable power sources for personal computers, mobile terminals, etc., and power sources for driving vehicles such as electric vehicles (EV), hybrid vehicles (HV), and plug-in hybrid vehicles (PHV). ing.

Lithium-ion secondary batteries are required to have higher performance as they become more popular. For the purpose of improving the performance of lithium-ion secondary batteries, studies have been made on the crystal structure of the positive electrode active material (see, for example, Patent Document 1). In Patent Document 1, by uniformly dissolving silicon in a lithium-nickel-cobalt-manganese composite oxide, which is a positive electrode active material, by increasing the a-axis and c-axis in the crystal structure, the crystal structure of the positive electrode active material It is stated that the can be stabilized.

JP 2018-60759 A

However, in recent years, the demand for higher performance of lithium ion secondary batteries has been increasing more and more, and above all, higher input/output characteristics are required for lithium ion secondary batteries for vehicles. For this reason, further reduction in the resistance of the secondary battery is required, and as a result of intensive studies by the present inventors, when the conventional positive electrode active material is used, the resistance of the lithium ion secondary battery is insufficiently reduced. It was found that there was a problem that

Accordingly, an object of the present invention is to provide a positive electrode active material that can reduce the resistance of a lithium ion secondary battery.

The positive electrode active material disclosed herein is a positive electrode active material whose crystal structure belongs to space group R-3m. The standard deviation σc of the c-axis length satisfies 0.025 Å≦σc≦0.045 Å. Such a configuration provides a positive electrode active material capable of reducing the resistance of a lithium ion secondary battery.

In a preferred embodiment of the positive electrode active material disclosed herein, the standard deviation σa of the a-axis length satisfies 0.005 Å≦σa≦0.02 Å. With such a configuration, the resistance of the lithium ion secondary battery can be further reduced.

In a preferred embodiment of the positive electrode active material disclosed herein, the positive electrode active material has a layered rock salt structure and a crystallite diameter of 950 Å or more and 1450 Å or less. With such a configuration, the resistance of the lithium ion secondary battery can be further reduced.

From another aspect, the lithium ion secondary battery disclosed herein includes a positive electrode and a negative electrode. The positive electrode includes the positive electrode active material described above. Such a configuration provides a lithium-ion secondary battery with low resistance.

1 is a cross-sectional view schematically showing the configuration of a lithium ion secondary battery constructed using a positive electrode active material according to one embodiment of the present invention; FIG. 1 is a schematic exploded view showing the configuration of a wound electrode body of a lithium ion secondary battery constructed using a positive electrode active material according to one embodiment of the present invention; FIG.

Hereinafter, embodiments according to the present invention will be described with reference to the drawings. Matters not mentioned in this specification but necessary for the implementation of the present invention can be grasped as design matters by those skilled in the art based on the prior art in the relevant field. The present invention can be implemented based on the contents disclosed in this specification and common general technical knowledge in the field. Further, in the following drawings, members and portions having the same function are denoted by the same reference numerals. Also, the dimensional relationships (length, width, thickness, etc.) in each drawing do not reflect the actual dimensional relationships.

In this specification, the term "secondary battery" refers to an electricity storage device that can be repeatedly charged and discharged, and is a term that includes so-called storage batteries and electricity storage elements such as electric double layer capacitors. In this specification, the term “lithium ion secondary battery” refers to a secondary battery that utilizes lithium ions as a charge carrier and is charged/discharged by the transfer of charge associated with the lithium ions between the positive and negative electrodes.

The positive electrode active material according to this embodiment has a crystal structure belonging to the space group R-3m. The standard deviation σc of the c-axis length satisfies 0.025 Å≦σc≦0.045 Å.

Examples of the crystal structure of the positive electrode active material assigned to R-3m include a layered rocksalt crystal structure and a pseudo-spinel crystal structure.

Examples of positive electrode active materials having a layered rock salt crystal structure include lithium composite oxides represented by the general formula LiMO ₂ (M is one or more metal elements other than Li). As the lithium composite oxide, a lithium transition metal oxide containing at least one of Ni, Co, and Mn is preferable as M, and specific examples thereof include lithium-nickel-based composite oxides and lithium-cobalt-based composite oxides. lithium-manganese composite oxides, lithium-nickel-cobalt-manganese-based composite oxides, lithium-nickel-cobalt-aluminum-based composite oxides, lithium-iron-nickel-manganese composite oxides, and the like. Among them, lithium-nickel-cobalt-manganese-based composite oxides are preferable from the viewpoint of lower resistance.

In this specification, the term "lithium-nickel-cobalt-manganese-based composite oxide" refers to an oxide containing Li, Ni, Co, Mn, and O as constituent elements, and one or more of these oxides. It is a term that also includes oxides containing such elements. Examples of such additive elements include transition metal elements such as Mg, Ca, Al, Ti, V, Cr, Y, Zr, Nb, Mo, Hf, Ta, W, Na, Fe, Zn and Sn, and typical A metal element etc. are mentioned. Also, the additive elements may be metalloid elements such as B, C, Si and P, and nonmetal elements such as S, F, Cl, Br and I. The same applies to the above-described lithium-nickel-based composite oxide, lithium-cobalt-based composite oxide, lithium-manganese-based composite oxide, lithium-nickel-cobalt-aluminum-based composite oxide, lithium-iron-nickel-manganese-based composite oxide, and the like. .

In the crystal structure of the positive electrode active material according to this embodiment, the standard deviation σc of the c-axis length satisfies 0.025 Å≦σc≦0.045 Å. The standard deviation σc of the c-axis length is smaller than the standard deviation of the c-axis length of a normal positive electrode active material having a crystal structure belonging to the space group R-3m.

The diffusion of Li ions within the crystal of the positive electrode active material, that is, the diffusion of Li ions within the solid phase, is caused by hopping of Li in the Li layer in the crystal structure of the positive electrode active material. The c-axis length is related to the thickness of the tunnel through which Li ions pass in the crystal, and the passage speed of Li ions decreases in portions where the c-axis length is small. Therefore, by reducing the variation in the c-axis length, that is, by setting the standard deviation σc to 0.045 Å or less, a tunnel through which Li ions can easily pass is formed. On the other hand, however, if the c-axis lengths are too uniform, the positive electrode active material becomes monocrystal-like and the three-dimensional diffusion of Li ions from minute defects disappears, resulting in an increase in resistance. Therefore, by setting the standard deviation σc to 0.025 Å or more, the Li ions can be three-dimensionally diffused. Therefore, when 0.025 Å ≤ σc ≤ 0.045 Å, the diffusibility of Li ions in the crystal of the positive electrode active material is particularly high, and the resistance of the secondary battery using the positive electrode active material is reduced. can be done.

In the crystal structure of the positive electrode active material according to this embodiment, the standard deviation σa of the a-axis length preferably satisfies 0.005 Å≦σa≦0.02 Å. Variation in the a-axis length is also related to the hopping distance of Li. can be enhanced, and the resistance of a secondary battery using the positive electrode active material can be further reduced.

The standard deviation σc of the c-axis length and the standard deviation σa of the a-axis length can be obtained, for example, as follows. The positive electrode active material is observed with an atomic resolution analysis electron microscope. When the positive electrode active material is already contained in the positive electrode, a sample obtained by slicing the positive electrode by FIB processing may be prepared and observed with the electron microscope. An arbitrary primary particle is selected in the field of view of the electron microscope, and 10 or more electron diffraction images are measured within the particle. From the acquired image, the composition of the positive electrode active material with a crystal structure assigned to the space group R-3m (that is, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiNi _0.80 Co _0.15 Al _{0 .05} O ₂ etc.) is measured, and the c-axis length and the a-axis length are obtained. This operation is performed for three or more primary particles. A standard deviation is obtained for each of the c-axis length and the a-axis length at 10 or more points in the primary particles. The standard deviation of the c-axis length and the standard deviation of the a-axis length are determined for each of three or more primary particles whose lattice constants are measured, and the average value of these standard deviations is calculated. Let the average value of the calculated standard deviations of the c-axis lengths be the standard deviation σc of the c-axis lengths, and let the average value of the calculated standard deviations of the a-axis lengths be the standard deviation σa of the a-axis lengths.

The positive electrode active material according to the present embodiment preferably has a layered rock salt structure and a crystallite diameter of 950 Å or more and 1450 Å or less. The crystallite diameter is also related to the diffusivity of Li ions within the crystal. can be increased, and the resistance of the secondary battery using the positive electrode active material can be further reduced.

The above crystallite size can be determined, for example, by measuring the positive electrode active material powder using a known X-ray diffraction (XRD) apparatus. Specifically, for example, the crystallite diameter can be determined using the half-value width (half-value width) of the (003) plane, the 2θ value, and the Scherrer formula. In addition, when the positive electrode active material is already contained in the positive electrode, only the positive electrode active material may be isolated according to a known method and used as a measurement sample.

The positive electrode active material may be composed of primary particles, or may be composed of secondary particles in which primary particles are agglomerated. The average particle size (D50) of the positive electrode active material is not particularly limited, but is, for example, 0.05 μm or more, preferably 1.0 μm or more. On the other hand, the average particle size (D50) of the positive electrode active material is, for example, 20 μm or less, preferably 15 μm or less. Note that the average particle size (D50) of the positive electrode active material can be obtained by, for example, a laser diffraction scattering method. When the positive electrode active material is in the form of secondary particles, this average particle size is the average particle size of the secondary particles.

A positive electrode active material, especially a lithium composite oxide, is usually produced by preparing hydroxide particles containing a metal element other than lithium as a precursor by a crystallization method, mixing this with a lithium compound, and sintering it. be. This precursor is usually heated for drying. Here, the variation in the c-axis length (that is, the standard deviation σc) can be adjusted by changing the conditions for drying the precursor and the conditions for lowering the temperature after firing. Specifically, when the precursor is heat-treated for drying, the dehydration causes strain in the metal layer (particularly the transition metal layer), increasing the c-axis length variation (ie, the standard deviation σc). Therefore, by drying the precursor by vacuum drying or the like without heating, the variation in the c-axis length (that is, the standard deviation σc) can be reduced. Furthermore, when the heating rate after firing is high, internal defects tend to occur and the variation in the c-axis length (that is, the standard deviation σc) tends to increase. Therefore, the variation in the c-axis length (ie, the standard deviation σc) can be reduced by increasing the temperature drop after firing for a long time (ie, by decreasing the rate of temperature drop).

Also, the variation in the a-axis length (that is, the standard deviation σa) can be adjusted by performing two stages of firing and changing the temperature of the second stage of firing. Specifically, by lowering the temperature of the second-stage firing, it is possible to selectively eliminate defects by stopping the growth of nuclei, thereby reducing the variation in the a-axis length (that is, the standard deviation σa). be able to. For example, the first-stage firing is performed at 800 to 950° C., and the second-stage firing is performed at a temperature about 100° C. lower than that to sufficiently reduce the variation in the a-axis length (that is, the standard deviation σa). be able to.

Also, the crystallite size can be adjusted by changing the firing temperature. At this time, the higher the firing temperature, the larger the crystallite size tends to be.

When a lithium-ion secondary battery is constructed using the positive electrode active material according to the present embodiment, the lithium-ion secondary battery has a low resistance and, therefore, excellent output characteristics. Therefore, the positive electrode active material according to this embodiment is preferably a positive electrode active material for a lithium ion secondary battery.

Accordingly, from another aspect, the lithium ion secondary battery disclosed herein includes a positive electrode and a negative electrode. The positive electrode includes the positive electrode active material according to the present embodiment described above. A specific configuration example of the lithium ion secondary battery will be described below with reference to the drawings.

The lithium ion secondary battery 100 shown in FIG. 1 is constructed by housing a flat wound electrode body 20 and a non-aqueous electrolyte (not shown) in a flat rectangular battery case (that is, an outer container) 30. It is a sealed battery that is The battery case 30 is provided with a positive terminal 42 and a negative terminal 44 for external connection, and a thin safety valve 36 that is set to release the internal pressure of the battery case 30 when it rises above a predetermined level. It is The positive and negative terminals 42 and 44 are electrically connected to the positive and negative current collecting plates 42a and 44a, respectively. As the material of the battery case 30, for example, a metal material such as aluminum that is lightweight and has good thermal conductivity is used.

As shown in FIGS. 1 and 2, the wound electrode body 20 is formed by stacking a positive electrode sheet 50 and a negative electrode sheet 60 with two long separator sheets 70 interposed therebetween and winding them in the longitudinal direction. morphology. The positive electrode sheet 50 has a configuration in which a positive electrode active material layer 54 is formed along the longitudinal direction on one side or both sides (here, both sides) of a long positive electrode current collector 52 . The negative electrode sheet 60 has a configuration in which a negative electrode active material layer 64 is formed along the longitudinal direction on one side or both sides (here, both sides) of a long negative electrode current collector 62 . The positive electrode active material layer non-formed portion 52a (that is, the portion where the positive electrode current collector 52 is exposed without the positive electrode active material layer 54 being formed) and the negative electrode active material layer non-formed portion 62a (that is, the negative electrode active material layer 64 is formed). The portion where the negative electrode current collector 62 is exposed without being wound) is formed so as to protrude outward from both ends of the wound electrode body 20 in the winding axial direction (that is, the sheet width direction orthogonal to the longitudinal direction). there is A positive collector plate 42a and a negative collector plate 44a are joined to the positive electrode active material layer non-formed portion 52a and the negative electrode active material layer non-formed portion 62a, respectively.

Examples of the positive electrode current collector 52 forming the positive electrode sheet 50 include aluminum foil. The positive electrode active material layer 54 contains at least the positive electrode active material according to the present embodiment described above. Also, the positive electrode active material layer 54 may further include a conductive material, a binder, and the like. As the conductive material, for example, carbon black such as acetylene black (AB) and other carbon materials (such as graphite) can be suitably used. As the binder, for example, polyvinylidene fluoride (PVDF) or the like can be used.

Examples of the negative electrode current collector 62 forming the negative electrode sheet 60 include copper foil. The negative electrode active material layer 64 contains a negative electrode active material. Carbon materials such as graphite, hard carbon, and soft carbon can be used as the negative electrode active material. The negative electrode active material layer 64 may further contain binders, thickeners, and the like. As the binder, for example, styrene-butadiene rubber (SBR) or the like can be used. As a thickening agent, for example, carboxymethyl cellulose (CMC) or the like can be used.

As the separator 70, various porous sheets similar to those conventionally used in lithium ion secondary batteries can be used. A resin sheet is mentioned. Such a porous resin sheet may have a single-layer structure or a multi-layer structure of two or more layers (for example, a three-layer structure in which PP layers are laminated on both sides of a PE layer). The separator 70 may comprise a heat resistant layer (HRL).

The same non-aqueous electrolyte as used in conventional lithium ion secondary batteries can be used, and typically an organic solvent (non-aqueous solvent) containing a supporting electrolyte can be used. Aprotic solvents such as carbonates, esters and ethers can be used as the non-aqueous solvent. Among them, carbonates are preferable because the effect of reducing the low-temperature resistance by the positive electrode material is particularly high. Examples of carbonates include ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), monofluoroethylene carbonate (MFEC), difluoroethylene carbonate (DFEC), monofluoromethyl difluoromethyl carbonate (F-DMC), trifluorodimethyl carbonate (TFDMC) and the like. Such non-aqueous solvents can be used singly or in combination of two or more. Lithium salts such as LiPF ₆ , LiBF ₄ and lithium bis(fluorosulfonyl)imide (LiFSI) can be suitably used as supporting salts. The concentration of the supporting salt is preferably 0.7 mol/L or more and 1.3 mol/L or less.

In addition, the non-aqueous electrolyte includes various components other than the non-aqueous solvent and the supporting salt, such as gas generating agents, film-forming agents, dispersing agents, and thickening agents, as long as the effects of the present invention are not significantly impaired. It may contain additives.

The lithium ion secondary battery 100 has advantages of low initial resistance and excellent output characteristics.

The lithium ion secondary battery 100 can be used for various purposes. Suitable applications include drive power supplies mounted in vehicles such as electric vehicles (EV), hybrid vehicles (HV), and plug-in hybrid vehicles (PHV). Moreover, the lithium ion secondary battery 100 can be used as a storage battery such as a small power storage device. The lithium ion secondary battery 100 can also be used typically in the form of an assembled battery in which a plurality of batteries are connected in series and/or in parallel.

The prismatic lithium ion secondary battery including the flattened wound electrode assembly has been described above as an example. However, the positive electrode active material according to this embodiment can also be used for other types of lithium ion secondary batteries according to known methods. For example, using the positive electrode active material according to the present embodiment, constructing a lithium ion secondary battery including a laminated electrode body (that is, an electrode body in which a plurality of positive electrodes and a plurality of negative electrodes are alternately laminated) can also Moreover, a cylindrical lithium ion secondary battery, a coin type lithium ion secondary battery, a laminate type lithium ion secondary battery, or the like can be constructed using the positive electrode active material according to the present embodiment. Furthermore, it is also possible to construct an all-solid secondary battery in which the electrolyte is a solid electrolyte.

EXAMPLES Examples relating to the present invention will be described below, but the present invention is not intended to be limited to those shown in the examples.

<Preparation of positive electrode active material>
[Examples 1 to 9 and Comparative Examples 1 and 2]
Using nickel sulfate, cobalt sulfate, and manganese sulfate as raw materials, a composite hydroxide containing nickel, cobalt, and manganese in a molar ratio of 1:1:1 is obtained as a precursor by crystallization according to a conventional method. rice field. This composite hydroxide and lithium carbonate were mixed in a mortar so that the molar ratio of lithium to the sum of nickel, cobalt and manganese was 1:1. The mixture was transferred to an alumina crucible and fired in a muffle furnace. In this way, lithium composite oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) particles with a layered rock salt type crystal structure, which are positive electrode active material particles, were obtained. Here, the standard deviation of the c-axis length was changed by changing the drying temperature of the precursor in the range of room temperature to 400° C. and changing the time for cooling after firing in the range of 2 hours to 12 hours. rice field. Moreover, the standard deviation of the a-axis length was changed by performing firing in two steps and changing the firing temperature in the second step. Furthermore, the crystallite size was changed by changing the firing temperature in the first stage within the range of 800°C to 950°C.

[Example 10 and Comparative Example 3]
Using nickel sulfate, cobalt sulfate, and aluminum sulfate as raw materials, a composite hydroxide containing nickel, cobalt, and aluminum in a molar ratio of 80:15:5 is obtained as a precursor by crystallization according to a conventional method. rice field. This composite hydroxide and lithium hydroxide were mixed in a mortar so that the molar ratio of lithium to the sum of nickel, cobalt and aluminum was 1:1. The mixture was transferred to an alumina crucible and fired in a muffle furnace. In this manner, layered structure lithium composite oxide (LiNi _0.80 Co _0.15 Al _0.05 O ₂ ) particles, which are positive electrode active material particles, were obtained. Here, in Example 10, the composite hydroxide was dried at room temperature, and in Comparative Example 3, the composite hydroxide was heated and dried. The standard deviation of the c-axis length was varied.

<Measurement of standard deviation of c-axis length and standard deviation of a-axis length of positive electrode active material>
The positive electrode active material of each example and each comparative example prepared above was observed using an atomic resolution analysis electron microscope "JEM-ARM300F" (manufactured by JEOL). An arbitrary primary particle was selected in the field of view of the electron microscope, and electron diffraction images at 10 or more points within the particle were measured. From the acquired images, in Examples 1 to 9 and Comparative Examples 1 and 2, the lattice constant when assigned to LiNi _1/3 Co _1/3 Mn _1/3 O ₂ was measured, and the c-axis length and a-axis length were measured. asked for In Example 10 and Comparative Example 3, the lattice constant when assigned to LiNi _0.80 Co _0.15 Al _0.05 O ₂ was measured to obtain the c-axis length and the a-axis length. This operation was performed for 3 or more primary particles, and the standard deviation was determined for each of the c-axis length and the a-axis length at 10 or more points within the primary particles. The standard deviation of the c-axis length and the standard deviation of the a-axis length are obtained for each of three or more primary particles whose lattice constants are measured, the average value of these standard deviations is calculated, and the average value is The standard deviation σc of the length and the standard deviation σa of the a-axis length were used. In addition, for analysis. Analysis software "INDEX" (manufactured by Nanomegas) was used. Table 1 shows the results.

<Measurement of crystallite size>
The positive electrode active material of each example and each comparative example prepared above was analyzed using an XRD device "smart Lab" (manufactured by Rigaku) and analysis software "PDXL2" (manufactured by Rigaku). The crystallite size was determined using the value width, 2θ value, and Scherrer's formula. Table 1 shows the results.

<Production of lithium-ion secondary battery for evaluation>
The positive electrode active material of each example and each comparative example prepared above, acetylene black (AB) as a conductive material, and polyvinylidene fluoride (PVDF) as a binder were combined into a positive electrode active material: AB:PVDF=85:10. : 5 in N-methylpyrrolidone (NMP) to prepare a paste for forming a positive electrode active material layer. A positive electrode sheet was produced by applying this paste onto an aluminum foil having a thickness of 15 μm and drying it.

Natural graphite (C) as a negative electrode active material, styrene-butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener were mixed at a mass ratio of C: SBR: CMC = 98: 1: 1. were mixed in ion-exchanged water to prepare a paste for forming a negative electrode active material layer. This paste was applied onto a copper foil having a thickness of 10 μm and dried to prepare a negative electrode sheet.

As a separator sheet, a 20 μm thick porous polyolefin sheet having a three-layer structure of PP/PE/PP was prepared.

The positive electrode sheet, the negative electrode sheet, and the separator sheet were superimposed, electrode terminals were attached, and the stack was housed in a laminate case. Subsequently, a non-aqueous electrolyte was injected into the laminate case, and the laminate case was hermetically sealed. The non-aqueous electrolyte contains a mixed solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 3:4:3, and LiPF ₆ as a supporting electrolyte. A solution dissolved at a concentration of 1.0 mol/L was used. As described above, lithium ion secondary batteries for evaluation of each example and each comparative example having a capacity of 10 mAh were obtained.

<Initial resistance measurement>
Each lithium-ion secondary battery for evaluation was adjusted to an SOC (State of charge) of 50%, and then placed in an environment of 25°C. The battery was discharged at a current value of 100 mA for 10 seconds, the voltage value was measured 10 seconds after the start of discharge, and the initial battery resistance was calculated. For Examples 1 to 9 and Comparative Examples 1 and 2, the ratio of the resistance of the other lithium ion secondary batteries for evaluation was determined when the resistance of the lithium ion secondary battery for evaluation of Comparative Example 1 was set to 100. . For Example 10 and Comparative Example 3, the ratio of the resistance of the lithium ion secondary battery for evaluation of Example 10 to the resistance of the lithium ion secondary battery for evaluation of Comparative Example 3 as 100 was obtained. Table 1 shows the results.

LiNi _1/3 Co _1/3 Mn _1/3 O ₂ and LiNi _0.80 Co _0.15 Al _0.05 O ₂ are cathode active materials whose crystal structures belong to space group R-3m. From the results of Table 1, in the positive electrode active material whose crystal structure belongs to the space group R-3m, when the standard deviation σc of the c-axis length satisfies 0.025 Å ≤ σc ≤ 0.045 Å, lithium ion secondary It can be seen that the resistance of the battery is significantly reduced. Therefore, according to the positive electrode active material disclosed here, it turns out that the resistance of a lithium ion secondary battery can be made small.

Further, from a comparison of Example 1 and Examples 3 to 5, the resistance of the lithium ion secondary battery is particularly small when the standard deviation σa of the a-axis length satisfies 0.005 Å≦σa≦0.02 Å. I understand. Furthermore, from a comparison of Examples 5 to 9, it can be seen that the resistance of the lithium ion secondary battery is particularly small when the crystallite diameter is 950 Å or more and 1450 Å or less.

Although specific examples of the present invention have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

20 Wound electrode assembly 30 Battery case 36 Safety valve 42 Positive electrode terminal 42a Positive electrode current collector 44 Negative electrode terminal 44a Negative electrode current collector 50 Positive electrode sheet (positive electrode)
52 positive electrode current collector 52a positive electrode active material layer non-formed portion 54 positive electrode active material layer 60 negative electrode sheet (negative electrode)
62 Negative electrode current collector 62a Negative electrode active material layer non-formation portion 64 Negative electrode active material layer 70 Separator sheet (separator)
100 Lithium ion secondary battery

Claims (3)

A positive electrode active material whose crystal structure belongs to the space group R-3m,
The standard deviation σc of the c-axis length satisfies 0.025 Å ≤ σc ≤ 0.045 Å,
The standard deviation σa of the a-axis length satisfies 0.005 Å ≤ σa ≤ 0.02 Å,
It has a layered rock salt structure,
The crystallite diameter obtained by using the Scherrer formula from the half-value width of the (003) plane obtained by X-ray diffraction measurement is 950 Å or more and 1450 Å or less.
Positive electrode active material. The positive electrode active material according to claim 1, wherein the positive electrode active material is _a lithium composite oxide having a composition represented by LiNi1 / _3Co1/ 3Mn1 _{/ 3O2} . including a positive electrode and a negative electrode,
The positive electrode comprises the positive electrode active material according to claim 1 or 2 ,
Lithium-ion secondary battery.

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