JP2018116856A - Positive electrode active material for lithium ion secondary battery - Google Patents

Abstract

A positive electrode active material for a lithium-ion secondary battery having a core-shell structure in which the surface of a spinel-type LiNiMn-based composite oxide is covered with an olivine-type lithium metal phosphorous oxide, and the capacity deterioration of the lithium-ion secondary battery is prevented. Provided is a positive electrode active material capable of suppressing and reducing battery resistance. A positive electrode active material for a lithium ion secondary battery disclosed herein has a core part and a shell part. The core portion is a composite oxide having a composition represented by Li1+xNi0.5Mn1.5O4 (wherein 0.05≦x≦0.3, which may be doped with a specific element or anion) and a spinel type crystal structure. It is composed of The shell portion is Li1+yMPO4 (wherein 0.05≦y≦0.3, M is at least one selected from the group consisting of Fe, Mn, Ni, and Co, and is doped with a specific element or anion. May be present) and a phosphorus oxide having an olivine type crystal structure. [Selection diagram] Figure 1

Description

  The present invention relates to a positive electrode active material for a lithium ion secondary battery.

  Lithium ion secondary batteries are lighter and have a higher energy density than existing batteries, and have recently been used as so-called portable power sources for vehicles and personal computers and power sources for driving vehicles. Lithium-ion secondary batteries are expected to become increasingly popular as high-output power sources for driving vehicles such as electric vehicles (EV), hybrid vehicles (HV), and plug-in hybrid vehicles (PHV). Yes.

  Lithium ion secondary batteries used for high output power sources for driving vehicles are required to have higher performance, and higher energy density is being achieved as part of higher performance. One way to increase the energy density of a lithium ion secondary battery is to use a positive electrode active material having a high operating potential (high potential positive electrode active material).

  As a typical positive electrode active material having a high operating potential, a lithium nickel manganese composite oxide having a spinel crystal structure having Li, Ni, and Mn as main constituent metal elements is known. In a lithium ion secondary battery, it is known that the nonaqueous electrolytic solution is decomposed and the battery capacity is deteriorated due to the decomposition. This decomposition of the non-aqueous electrolyte tends to occur more easily as the operating potential of the positive electrode active material is higher. Therefore, in Patent Document 1, the surface of a lithium nickel manganese composite oxide having a spinel type crystal structure is coated with a lithium metal phosphate having an olivine type crystal structure, in order to suppress the capacity deterioration of the lithium ion secondary battery. A positive electrode active material having a (coated) core-shell structure has been proposed.

JP 2013-191540 A

  However, as a result of intensive studies by the present inventor, according to the positive electrode active material having a core-shell structure in which the surface of the spinel type lithium nickel manganese composite oxide described in Patent Document 1 is coated with olivine type lithium metal phosphate. The present inventors have found that although it is possible to suppress the capacity deterioration of the lithium ion secondary battery, there is a problem that the battery resistance increases.

  Therefore, the present invention provides a positive electrode active material for a lithium ion secondary battery having a core-shell structure in which the surface of a lithium nickel manganese composite oxide having a spinel crystal structure is coated with a lithium metal phosphate having an olivine crystal structure Then, it aims at providing the positive electrode active material for lithium ion secondary batteries which makes it possible to control the capacity | capacitance degradation of a lithium ion secondary battery, and to reduce battery resistance.

The positive electrode active material for a lithium ion secondary battery disclosed herein has a core part and a shell part that covers the core part. The core portion is Li _{1 + x} Ni _0.5 Mn _1.5 O ₄ (wherein x is a value satisfying 0.05 ≦ x ≦ 0.3, and some of Ni and Mn are Mg, Zn, It may be substituted with at least one metal element selected from the group consisting of Co, Fe, Cr, Al, Ti, Zr, Nb, Ta, Ru, and W, and F ⁻ , Cl ⁻ , and N ³⁻ At least one anion selected from the group consisting of: a compound oxide having a spinel crystal structure. The shell is Li _{1 + y} MPO ₄ (wherein y is a value satisfying 0.05 ≦ y ≦ 0.3, and M is at least one selected from the group consisting of Fe, Mn, Ni, and Co) Even if a part of M is substituted with at least one metal element selected from the group consisting of Mg, Zn, Cr, Al, Ti, Zr, Nb, Ta, Ru, and W. Phosphorus oxide having a composition represented by the formula (which may be doped with at least one anion selected from the group consisting of F ⁻ , Cl ⁻ , and N ³⁻ ) and having an olivine type crystal structure It is made up of.

  According to such a configuration, since the core part and the shell part have a Li-excess composition, lithium ions can easily move at the interface between the core part and the shell part when the lithium ion secondary battery is charged and discharged. Thus, battery resistance can be reduced. Moreover, the suppression effect of the capacity deterioration of the lithium ion secondary battery by the core-shell structure is also maintained. That is, according to such a configuration, a positive electrode active material for a lithium ion secondary battery that can suppress the capacity deterioration of the lithium ion secondary battery and reduce the battery resistance is provided.

It is sectional drawing which shows typically the structure of the positive electrode active material for lithium ion secondary batteries which concerns on one Embodiment of this invention. It is sectional drawing which shows typically the structure of the lithium ion secondary battery constructed | assembled using the positive electrode active material for lithium ion secondary batteries which concerns on one Embodiment of this invention. It is a schematic diagram which shows the structure of the winding electrode body of the lithium ion secondary battery constructed | assembled using the positive electrode active material for lithium ion secondary batteries which concerns on one Embodiment of this invention.

  Embodiments according to the present invention will be described below with reference to the drawings. Note that matters other than the matters specifically mentioned in the present specification and necessary for carrying out the present invention (for example, a general configuration of a positive electrode active material for a lithium ion secondary battery that does not characterize the present invention) Can be understood as a design matter of those skilled in the art based on the prior art in the field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field. Moreover, in the following drawings, the same code | symbol is attached | subjected and demonstrated to the member and site | part which show | plays the same effect | action. In addition, the dimensional relationships (length, width, thickness, etc.) in each drawing do not reflect actual dimensional relationships.

  As shown in FIG. 1, the positive electrode active material 10 for a lithium ion secondary battery according to this embodiment includes a core portion 12 and a shell portion 14 that covers the core portion 12. That is, it has a core-shell structure. In addition, although the positive electrode active material 10 is spherical in FIG. 1, the shape of the positive electrode active material 10 is not limited to this, and may be non-spherical such as indefinite.

The core portion 12 is Li _{1 + x} Ni _0.5 Mn _1.5 O ₄ (wherein x is a value satisfying 0.05 ≦ x ≦ 0.3, and some of Ni and Mn are Mg, Zn, It may be substituted with at least one metal element selected from the group consisting of Co, Fe, Cr, Al, Ti, Zr, Nb, Ta, Ru, and W, and F ⁻ , Cl ⁻ , and N ³⁻ And at least one kind of anion selected from the group consisting of: a complex oxide having a spinel crystal structure. By using the lithium nickel manganese composite oxide having the spinel structure having such a composition for the core portion 12 of the positive electrode active material 10, the operating potential of the positive electrode active material 10 is increased, and 4.5 V (vs. Li / Li ⁺ ) It may show a working potential higher than that.
The amount of the metal element substituting a part of Ni and Mn is preferably 0.2 mol or less, more preferably 0.15 mol or less with respect to 1 mol of the composite oxide having a spinel crystal structure. .
The anion doping amount is, for example, 0.1 mol or less with respect to 1 mol of the composite oxide having a spinel crystal structure.

The shell portion 14 is Li _{1 + y} MPO ₄ (wherein y is a value satisfying 0.05 ≦ y ≦ 0.3, and M is at least one selected from the group consisting of Fe, Mn, Ni, and Co) Even if a part of M is substituted with at least one metal element selected from the group consisting of Mg, Zn, Cr, Al, Ti, Zr, Nb, Ta, Ru, and W. Phosphorus oxide having a composition represented by the formula (which may be doped with at least one anion selected from the group consisting of F ⁻ , Cl ⁻ , and N ³⁻ ) and having an olivine type crystal structure It is made up of. By using a lithium metal phosphor oxide having an olivine crystal structure having such a composition, it is possible to suppress deterioration of the battery capacity of the lithium ion secondary battery.
The amount of the metal element substituting for a part of M is preferably 0.2 mol or less, more preferably 0.15 mol or less with respect to 1 mol of phosphorus oxide having an olivine type crystal structure.
The amount of anion doped is, for example, 0.1 mol or less with respect to 1 mol of phosphoric oxide having an olivine type crystal structure.

In the positive electrode active material 10 according to the present embodiment, x satisfies 0.05 ≦ x ≦ 0.3 in the core portion 12, and y satisfies 0.05 ≦ y ≦ 0. 3 is satisfied. That is, both the core part 12 and the shell part 14 have a composition that causes Li excess.
In the conventional core-shell type positive electrode active material, neither the core portion nor the shell portion has a composition with excess Li.
However, like the positive electrode active material 10 according to the present embodiment, by having a composition in which both the core portion 12 and the shell portion 14 are excessive in Li, the battery resistance of the lithium ion secondary battery can be reduced. Can do. This is because when both the core part 12 and the shell part 14 have a composition in which Li is excessive, lithium ions at the interface between the core part 12 and the shell part 14 when the lithium ion secondary battery is charged and discharged. This is thought to be due to the ease of movement.

  From the viewpoint of further suppressing capacity deterioration and further reducing battery resistance, x and y satisfy 0.07 ≦ x ≦ 0.23 and 0.07 ≦ y ≦ 0.23 in the above composition formula. It is preferable that 0.10 ≦ x ≦ 0.20 and 0.10 ≦ y ≦ 0.20 are satisfied.

The average particle diameter of the positive electrode active material 10 according to this embodiment is preferably 2 μm or more and 20 μm or less, and more preferably 5 μm or more and 15 μm or less. In the present specification, the “average particle diameter” means a particle diameter (D ₅₀ ) corresponding to a cumulative 50% in a volume-based particle size distribution based on a general laser diffraction / light scattering method. Therefore, the positive electrode active material 10 may exist in the form of primary particles or may form secondary particles.

  In the positive electrode active material 10 according to the present embodiment, the shell portion 14 has a covering layer that covers the core portion 12 entirely (particularly uniformly) as shown in FIG. 1 rather than partially covering the core portion 12. It is preferable to form. As thickness of the shell part 14 of the positive electrode active material 10 which concerns on this embodiment, 100 micrometers or less (especially 10 micrometers or more and 100 micrometers or less) are preferable.

  In the positive electrode active material 10 according to this embodiment, the coverage of the shell portion 14 is preferably 70 atm% or more as a percentage (atm%) of the atomic ratio represented by P / (Ni + Mn + P). The percentage (atm%) of the ratio can be obtained by quantifying each element by XPS analysis.

  The positive electrode active material 10 according to the present embodiment can be produced, for example, by the method described below. In addition, the positive electrode active material 10 which concerns on this embodiment is not restricted to what is produced by the method demonstrated below.

First, core particles composed of a lithium nickel manganese composite oxide having a spinel structure that becomes the core portion 12 are prepared. The core particle can be produced according to a conventional method.
Specifically, for example, a composite water containing nickel and manganese in a molar ratio of 0.5: 1.5 using an aqueous solution of a nickel salt, a manganese salt, and an alkali compound (eg, sodium hydroxide) by crystallization. Oxide particles are prepared as precursor particles.
Next, the precursor particles and the lithium salt are mixed. At this time, it adds so that Li contained in lithium salt may be 1.05 mol or more and 1.3 mol or less with respect to 1 mol of precursor particles. And the obtained mixture can be baked and the core particle comprised from the lithium nickel manganese type complex oxide which has a spinel structure can be made.
The shell portion 14 can be formed by coating the surface of the core particle with lithium metal phosphate.
Specifically, for example, it can be formed by sputtering while rotating the core particles using the lithium metal phosphorous oxide having the above-described Li-excess composition which is a material constituting the shell portion for the target.
Note that metal elements other than Li, Ni, and Mn, and anions (F ⁻ , Cl ⁻ , and N ³⁻ ) can be added according to a known doping method.
In this way, the positive electrode active material 10 according to this embodiment can be obtained.

The positive electrode active material 10 according to the present embodiment is for a lithium ion secondary battery, and the lithium ion secondary battery including the positive electrode active material 10 has both reduced capacity deterioration and reduced battery resistance. It becomes. Hereinafter, a configuration example of the lithium ion secondary battery 100 using the positive electrode active material 10 according to the present embodiment will be described with reference to the drawings.
In the present specification, the “secondary battery” refers to a general power storage device that can be repeatedly charged and discharged, and is a term including a power storage element such as a so-called storage battery and an electric double layer capacitor.
In the present specification, the “lithium ion secondary battery” refers to a secondary battery that uses lithium ions as a charge carrier and is charged and discharged by movement of charges accompanying the lithium ions between the positive and negative electrodes.

  A lithium ion secondary battery 100 shown in FIG. 2 is constructed by accommodating a flat wound electrode body 20 and a nonaqueous electrolyte (not shown) in a flat rectangular battery case (that is, an exterior container) 30. This is a sealed lithium ion secondary battery 100. 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 set to release the internal pressure when the internal pressure of the battery case 30 rises to a predetermined level or more. It has been. The positive and negative terminals 42 and 44 are electrically connected to the positive and negative current collectors 42a and 44a, respectively. As the material of the battery case 30, for example, a light metal material having good thermal conductivity such as aluminum is used.

  As shown in FIGS. 2 and 3, the wound electrode body 20 has a positive electrode active material layer 54 formed along the longitudinal direction on one side or both sides (here, both sides) of an elongated positive electrode current collector 52. The positive electrode sheet 50 and the negative electrode sheet 60 in which the negative electrode active material layer 64 is formed along the longitudinal direction on one side or both sides (here, both sides) of the long negative electrode current collector 62 are two long shapes. The separator sheet 70 is overlapped and wound in the longitudinal direction. The positive electrode active material layer non-forming portion 52a (that is, the positive electrode) formed so as to protrude outward from both ends in the winding axis direction of the wound electrode body 20 (referred to as the sheet width direction orthogonal to the longitudinal direction). The portion where the active material layer 54 is not formed and the positive electrode current collector 52 is exposed) and the negative electrode active material layer non-formed portion 62a (that is, the portion where the negative electrode active material layer 64 is not formed and the negative electrode current collector 62 is exposed). ) Are joined with a positive current collector 42a and a negative current collector 44a, respectively.

  Examples of the positive electrode current collector 52 constituting the positive electrode sheet 50 include aluminum foil. The positive electrode active material layer 54 includes the positive electrode active material 10 for a lithium ion secondary battery according to the above-described embodiment. The positive electrode active material layer 54 can 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 (such as graphite) carbon materials can be suitably used. As the binder, for example, polyvinylidene fluoride (PVDF) can be used.

  Examples of the negative electrode current collector 62 constituting the negative electrode sheet 60 include copper foil. The negative electrode active material layer 64 includes a negative electrode active material. As the negative electrode active material, for example, a carbon material such as graphite, hard carbon, or soft carbon can be used. The negative electrode active material layer 64 can further include a binder, a thickener, and the like. As the binder, for example, styrene butadiene rubber (SBR), polyvinylidene fluoride (PVDF), or the like can be used. As the thickener, for example, carboxymethyl cellulose (CMC) can be used.

  As the separator 70, various microporous sheets similar to those conventionally used in lithium ion secondary batteries can be used. For example, a microporous resin made of a resin such as polyethylene (PE) or polypropylene (PP). Sheet. Such a microporous resin sheet may have a single-layer structure or a multilayer 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 include a heat resistant layer (HRL).

The non-aqueous electrolyte can be the same as that of a conventional lithium ion secondary battery, and typically, an organic solvent (non-aqueous solvent) containing a supporting salt can be used. As the non-aqueous solvent, aprotic solvents such as carbonates, esters and ethers can be used. Of these, carbonates such as ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) can be preferably used. Alternatively, a fluorine-based solvent such as fluorinated carbonate such as monofluoroethylene carbonate (MFEC), difluoroethylene carbonate (DFEC), monofluoromethyl difluoromethyl carbonate (F-DMC), or trifluorodimethyl carbonate (TFDMC) is preferably used. be able to. Such a non-aqueous solvent can be used individually by 1 type or in combination of 2 or more types as appropriate. As the supporting salt, for example, a lithium salt such as LiPF ₆ , LiBF ₄ , or LiClO ₄ can be suitably used. The concentration of the supporting salt is preferably 0.7 mol / L or more and 1.3 mol / L or less.
The non-aqueous electrolyte is a component other than the above-described non-aqueous solvent and supporting salt, such as a gas generating agent, a film forming agent, a dispersing agent, and a thickening agent, as long as the effects of the present invention are not significantly impaired. Additives can be included.

  The lithium ion secondary battery 100 can be used for various applications. Suitable applications include drive power sources mounted on vehicles such as plug-in hybrid vehicles (PHV), hybrid vehicles (HV), and electric vehicles (EV). The lithium ion secondary battery 100 can also be used in the form of an assembled battery in which a plurality of lithium ion secondary batteries are electrically connected.

  As described above, a rectangular lithium ion secondary battery including a flat wound electrode body has been described as an example. However, the positive electrode active material according to the present embodiment can be used for other types of lithium ion secondary batteries according to a known method. For example, a lithium ion secondary battery including a stacked electrode body can be constructed using the positive electrode active material according to the present embodiment. Moreover, a cylindrical lithium ion secondary battery, a laminate type lithium ion secondary battery, etc. can also be constructed using the positive electrode active material according to this embodiment.

  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.

<No. Preparation of 1 to 15 positive electrode active materials>
In the reaction vessel, an aqueous nickel sulfate solution and an aqueous manganese sulfate solution were mixed so as to have a molar ratio of Ni / Mn = 0.5 / 1.5. At this time, it adjusted by adding sodium hydroxide aqueous solution so that pH of a liquid mixture might become 11-12.
The produced precipitate was filtered and dried to obtain composite hydroxide precursor particles.
The obtained precursor particles and lithium hydroxide were mixed. At this time, it mixed so that Li, Ni, and Mn might become the molar ratio of the composition shown in Table 1 and Table 2.
The obtained mixture was fired at 900 ° C. for 12 hours, and further fired at 600 ° C. for 36 hours, thereby producing core particles composed of a lithium nickel manganese composite oxide having a spinel structure serving as a core part. In addition, No. For the positive electrode active material, the particles obtained here were directly used as the positive electrode active material.
Subsequently, _Li 1 + y FePO ₄ to the target (in the formula, y is a value shown in Table 1), using a _Li 1.1 FePO ₄ and _Li 1.1 MnPO ₄ in consideration of Table 2, rotates the core particles By sputtering, a uniform coating layer (that is, shell) was formed on the surface of the core particle. The sputtering was performed using a direct current at a film forming speed of 1 nm / h. In the examination of Table 1, the sputtering time was adjusted so that the coating thickness of the coating layer was 10 nm, and in the examination of Table 2, the coating layer was adjusted to the coating thickness shown in Table 2.
In this way, no. 2-No. A positive electrode active material having a core-shell structure having a core portion composed of a lithium nickel manganese composite oxide having 15 spinel structures and a shell portion composed of lithium metal phosphate having an olivine type crystal structure was obtained.
Moreover, in the examination of Table 2, the percentage of the atomic ratio represented by P / (Ni + Mn + P) as the coverage (atm%) was determined by elemental quantification by XPS analysis.

<Production of evaluation lithium-ion secondary battery>
No. produced above. 1-No. 15 positive electrode active materials, acetylene black (AB) as a conductive material, and polyvinylidene fluoride (PVDF) as a binder, N-methyl at a mass ratio of positive electrode active material: AB: PVDF = 90: 5: 5 A slurry for forming a positive electrode active material layer having a solid content concentration of 55% was prepared by mixing with pyrrolidone. This positive electrode active material layer forming slurry was applied to an aluminum foil at a basis weight of 10 mg / cm ² and dried at 120 ° C. to prepare a positive electrode sheet.
Further, natural graphite as a negative electrode active material and polyvinylidene fluoride (PVDF) as a binder are mixed with N-methylpyrrolidone at a mass ratio of natural graphite: PVDF = 95: 5 to obtain a solid content concentration of 55%. A slurry for forming a negative electrode active material layer was prepared. This negative electrode active material layer forming slurry was applied to a copper foil at a basis weight of 5 mg / cm ² and dried at 120 ° C. to prepare a negative electrode sheet.
A porous polyolefin sheet having a three-layer structure of PP / PE / PP was prepared as a separator.
The produced positive electrode sheet and the negative electrode sheet were opposed to each other through a separator to produce an electrode body.
A current collector was attached to the produced electrode body, and it was housed in a laminate case together with a non-aqueous electrolyte, and sealed to obtain a lithium ion secondary battery for evaluation. As the non-aqueous electrolyte, a solution obtained by dissolving LiPF ₆ at a concentration of 1 mol / L in a mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 50:50 was used.

<Conditioning>
Each evaluation lithium ion secondary battery was placed in an environment of 25 ° C., and charged and discharged three times at a constant current of 1 C to 4.9 V and then a constant current of 1 C to 3.5 V. At this time, the discharge capacity at the time of discharge at the third cycle was measured.

<IV resistance measurement>
After the conditioning (in a discharged state), each evaluation lithium ion secondary battery was charged to 55% of the discharge capacity in the third cycle (that is, adjusted to 55% SOC), and at 25 ° C for 5 seconds at 5C. A constant current (CC) discharge was performed. At this time, IV resistance was calculated according to the following formula.
IV resistance (Ω) = ΔV / I
No. No. 1 when the IV resistance of the lithium ion secondary battery for evaluation using the positive electrode active material of No. 1 is 1. 2-No. The ratio of IV resistance of the lithium ion secondary battery for evaluation using 15 positive electrode active materials was determined. The results are shown in Tables 1 and 2.

<Charge / discharge cycle test>
Each evaluation lithium ion secondary battery was placed in an environment of 50 ° C. and charged and discharged 100 times at a constant current up to 4.9 V at 1 C and then discharged at a constant current to 3.5 V at 1 C. At this time, the discharge capacity at the first charge / discharge cycle and the discharge capacity at the 100th charge / discharge cycle were measured. The capacity deterioration rate was calculated according to the following formula.
Capacity degradation rate (%) = (discharge capacity at the first charge / discharge cycle−discharge capacity at the 100th charge / discharge cycle) / discharge capacity at the first charge / discharge cycle × 100
No. No. 1 when the capacity deterioration rate of the evaluation lithium ion secondary battery using the positive electrode active material No. 1 is 1. 2-No. The ratio of the capacity deterioration rate of the lithium ion secondary battery for evaluation using 15 positive electrode active materials was determined. The results are shown in Tables 1 and 2.

No. 1 is a positive electrode active material having no shell (a lithium nickel manganese composite oxide having a spinel structure). 2 has a core-shell structure corresponding to the prior art, but the core part (lithium nickel manganese-based composite oxide having a spinel structure) and the shell part (lithium metal phosphate having an olivine type crystal structure) are both in excess of Li. It is a positive electrode active material not having a composition (that is, x = 0, y = 0). No. 1 and No. 2, according to the positive electrode active material having the core-shell structure of the conventional structure in which the core part and the shell part do not have a Li-excess composition, while the capacity deterioration of the lithium ion secondary battery can be suppressed, the battery resistance It turns out that will become high. Furthermore, no. 3 and no. From the result of 4, it can be seen that even if only one of the core part and the shell part has a Li-excess composition, although the capacity deterioration of the lithium ion secondary battery can be suppressed, the battery resistance becomes high.
In contrast, no. 5-No. From the result of 11, the positive electrode active in which both the core part and the shell part have a Li-excess composition (a composition in which at least x and y satisfy 0.05 ≦ x ≦ 0.3 and 0.05 ≦ y ≦ 0.3). According to the substance, not only the capacity deterioration of the lithium ion secondary battery can be suppressed as in the prior art, but also the battery resistance of the lithium ion secondary battery can be reduced to 1/2 or less compared to the prior art. I understand that.

  No. 5 and no. 12-No. From the result of No. 14, when the coat thickness (thickness of the shell portion) is increased, the capacity deterioration can be further suppressed, but the battery resistance tends to increase. No. From the result of 15, it can be seen that even if the type of the metal element of the lithium metal phosphorous oxide having an olivine type crystal structure is changed, it is possible to suppress the capacity deterioration of the lithium ion secondary battery and reduce the battery resistance.

  As mentioned above, although the specific example of this invention was demonstrated in detail, these are only illustrations and do not limit a claim. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

DESCRIPTION OF SYMBOLS 10 Positive electrode active material 12 Core part 14 Shell part 20 Winding electrode body 30 Battery case 36 Safety valve 42 Positive electrode terminal 42a Positive electrode current collecting plate 44 Negative electrode terminal 44a Negative electrode current collecting plate 50 Positive electrode sheet (positive electrode)
52 Positive Current Collector 52a Positive Electrode Active Material Layer Non-Forming 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-formed portion 64 Negative electrode active material layer 70 Separator sheet (separator)
100 Lithium ion secondary battery

Claims (1)

A positive electrode active material for a lithium ion secondary battery, having a core part and a shell part covering the core part,
The core portion is Li _{1 + x} Ni _0.5 Mn _1.5 O ₄ (wherein x is a value satisfying 0.05 ≦ x ≦ 0.3, and some of Ni and Mn are Mg, Zn, It may be substituted with at least one metal element selected from the group consisting of Co, Fe, Cr, Al, Ti, Zr, Nb, Ta, Ru, and W, and F ⁻ , Cl ⁻ , and N ³⁻ The composition may be doped with at least one kind of anion selected from the group consisting of: and a composite oxide having a spinel crystal structure,
The shell is Li _{1 + y} MPO ₄ (wherein y is a value satisfying 0.05 ≦ y ≦ 0.3, and M is at least one selected from the group consisting of Fe, Mn, Ni, and Co) Even if a part of M is substituted with at least one metal element selected from the group consisting of Mg, Zn, Cr, Al, Ti, Zr, Nb, Ta, Ru, and W. Phosphorus oxide having a composition represented by the formula (which may be doped with at least one anion selected from the group consisting of F ⁻ , Cl ⁻ , and N ³⁻ ) and having an olivine type crystal structure Composed of,
The positive electrode active material for lithium ion secondary batteries characterized by the above-mentioned.

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