JP2016192314A - Positive electrode material, nonaqueous electrolyte secondary battery positive electrode and nonaqueous electrolyte secondary battery - Google Patents

Abstract

Disclosed is a positive electrode material, a positive electrode for a non-aqueous electrolyte secondary battery, and a non-aqueous electrolyte secondary battery, which are suppressed in collapse of the crystal structure during charge and discharge and are excellent in safety.
The positive electrode material of the present invention comprises Li ₂ Ni _α M ¹ _β M ² _γ Mn _η O _4-ε (0.50 <α ≦ 1.33, 0.33 ≦ γ ≦ 1.1, 0 ≦ η ≦ 1.00, 0 ≦ β <0.67, 0 ≦ ε ≦ 1.00, M ¹ : at least one selected from Co, Ga, M ² : at least one selected from Ge, Sn, Sb) And a layered structure including a Li layer and a Ni layer, wherein the bond length between Ni and oxygen is smaller than the bond length calculated from Shannon's ion radius table. The positive electrode 14 for a nonaqueous electrolyte secondary battery and the nonaqueous electrolyte secondary battery 1 of the present invention are characterized by using this positive electrode material.
[Selection figure] None

Description

  The present invention relates to a positive electrode material, a positive electrode for a non-aqueous electrolyte secondary battery, and a non-aqueous electrolyte secondary battery using the same.

  With the widespread use of electronic devices such as notebook computers, mobile phones, and digital cameras, the demand for secondary batteries for driving these electronic devices is increasing. In recent years, these electronic devices have been demanded to improve the performance of secondary batteries because power consumption has increased with the progress of higher functionality and miniaturization is expected. Among secondary batteries, non-aqueous electrolyte secondary batteries (particularly lithium ion secondary batteries) can be increased in capacity, and thus are being used in various electronic devices.

  A nonaqueous electrolyte secondary battery generally includes a positive electrode in which a positive electrode active material layer having a positive electrode material typified by a positive electrode active material is formed on the surface of a positive electrode current collector, and a negative electrode active material layer having a negative electrode active material. The negative electrode formed on the surface of the electric body is connected via a non-aqueous electrolyte (non-aqueous electrolyte solution) and is stored in the battery case.

  In a lithium ion secondary battery that is a typical example of a nonaqueous electrolyte secondary battery, a lithium composite oxide is used as a positive electrode material (positive electrode active material). As this complex oxide, it describes in patent documents 1-6, for example.

Patent Document 1 describes that a positive electrode active material in which Li _x CoMO ₂ and LiNiMnMO ₂ are mixed is used (M: all selected from predetermined elements). This positive electrode active material includes an active material having a high average voltage during discharge and an active material having high thermal stability.

Patent Document 2 describes a positive electrode active material including a crystal layer having a layered rock salt structure of LiNiMnTiO ₂ . When this positive electrode active material contains Ti, a high charge / discharge capacity can be obtained as compared with the case where it does not contain Ti.

Patent Document 3 describes that a positive electrode active material in which Li _x MnMO ₄ and LiNiMO ₂ are mixed is used (M: all selected from predetermined elements). This positive electrode active material is excellent in battery performance after high-temperature storage.

Patent Document 4 describes a positive electrode active material in which a part of Li in a LiMnMO ₂ layer having a polycrystalline structure is deficient (M: all selected from predetermined elements). This positive electrode active material is stabilized in strain and chemical bond in the crystal, and effects such as cycle stability and durability stability during charging and discharging are obtained.

Patent Document 5 describes a positive electrode active material in which Li and Co are partially substituted with a predetermined element M in LiCoO ₂ (M: both are selected from predetermined elements). In this positive electrode active material, each of Li and Co is replaced by the element M, whereby the bonding force between the lithium layer and the cobalt layer is strengthened, and the strain between the layers and the expansion of the crystal lattice are suppressed. Effects such as cycle stability and durability stability can be obtained.

Patent Document 6 describes that a positive electrode active material in which LiNiMnCoO ₂ and Li ₂ MO ₃ are mixed is selected (M: selected from predetermined elements). This positive electrode active material has an active material that exhibits an effect excellent in battery capacity and safety, and an active material that exhibits an effect on cycle characteristics and storage characteristics.

However, all of these positive electrode active materials (positive electrode materials) have a problem in that the collapse of the crystal structure during charge / discharge cannot be sufficiently suppressed, leading to a decrease in the capacity of the nonaqueous electrolyte secondary battery.
Regarding safety, Non-Patent Document 1 describes a technique of using a positive electrode containing Ti, that is, LiNiMnTiO ₂ .
However, as described in Non-Patent Document 1, it is described that there is no overwhelming improvement in safety when about 30% of Ti is added.

As another attempt to achieve both safety and high stabilization of the crystal, a technique for forming a positive electrode containing Si having a strong binding force with oxygen in the same amount as the transition metal, that is, Li ₂ MnSiO ₄ is described in Non-Patent Document 2. It is described in.
However, in this positive electrode, the transition metal has a four-coordinate coordination structure, the structure becomes unstable during charging, and it is not a positive electrode with sufficient durability.

In Patent Document 7, Li [Li _x Me _y M ′ _z ] O _{2 + d} (x + y + z = 1, 0 <x <0.33, 0.05 ≦ y ≦ 0.15, 0 <d ≦ 0.1, Me : At least one selected from Mn, V, Cr, Fe, Co, Ni, Al, and B, and M ′: at least one selected from Ge, Ru, Sn, Ti, Nb, and Pt). A positive electrode active material is described.

  However, in the battery using this positive electrode active material, the improvement in safety was insufficient. Specifically, the addition ratio of the element represented by Me in the transition metal is about 14 atm%, and oxygen atoms that do not bind to the element represented by Me existed. The bond between the element represented by Me and the oxygen atom is strong, and bond breakage (desorption of oxygen) hardly occurs. That is, oxygen atoms that do not bind to the element represented by Me contained in the positive electrode active material of Cited Document 7 become oxygen gas when the battery is formed, and the safety of the battery is lowered.

JP 2007-188703 A JP 2008-127233 A JP 2001-345101 A JP 2001-250551 A Japanese Patent No. 3782058 JP 2006-202702 A U.S. Pat. No. 8,734,994

Seung-Taek Myung and 5 others, "Synthesis of LiNi0.5Mn0.5-xTixO2 by an Emulsion Drying Method and Effect of Ti on Structure and Electrochem." R. Dominko Li2MSiO4 (M = Fe and / or Mn) cathode materials, Journal of Power Sources, 2008, 184, P462-P468

  The present invention has been made in view of the above circumstances, and has a positive electrode material, a positive electrode for a non-aqueous electrolyte secondary battery, and a non-aqueous electrolyte secondary battery that are suppressed in crystal structure during charge and discharge and are excellent in safety. It is an issue to provide.

In order to solve the above problems, the inventors focused on the structure of the positive electrode material, which is a positive electrode material containing a large amount of M ² element that strongly bonds to oxygen in addition to Ni element, and the Ni—O bond length is Shannon. It was found that the above problem can be solved by making the structure smaller than the bond length calculated from the ion radius table.

That is, the positive electrode material of the present invention is Li ₂ Ni _α M ¹ _β M ² _γ Mn _η O _4-ε (0.50 <α ≦ 1.33, 0.33 ≦ γ ≦ 1.1, 0 ≦ η ≦ 1.00, 0 ≦ β <0.67, 0 ≦ ε ≦ 1.00 M ¹ : at least one selected from Co, Ga, M ² : at least one selected from Ge, Sn, Sb), Li It has a layered structure including a layer and a Ni layer, and a bond length between Ni and oxygen is smaller than a bond length calculated from Shannon's ion radius table.
The positive electrode for a nonaqueous electrolyte secondary battery of the present invention is characterized by using the positive electrode material according to claim 1 or 2.

  The nonaqueous electrolyte secondary battery of the present invention is a positive electrode for a nonaqueous electrolyte secondary battery using the positive electrode material according to claim 1 or 2, and at least a positive electrode for a nonaqueous electrolyte secondary battery according to claim 3. It is characterized by using one.

  The positive electrode material of the present invention contains Ni in its composition. This Ni forms a local structure in which oxygen (O) is 6-coordinated (6-coordinated local structure). As a result, stable charging / discharging is performed. Further, high capacity can be achieved by containing a large amount of Ni, which is a redox species, in the range of 0.50 <α ≦ 1.33.

Further, by containing a large amount of M ¹ element and M ² element, crystal structure is more stable, the crystal structure during charge and discharge is suppressed, decrease in battery capacity can be suppressed as a result. The M ² element strongly fixes oxygen. As a result, the desorption of oxygen, which is a concern during abnormal heat generation, is suppressed, thereby further improving battery safety. Furthermore, the amount of M ² element, when became 0.33 or more, on average, all of the oxygen in the Ni layer is adjoin the M ² element, and to have a bond with M ² element Therefore, the oxygen desorption effect is remarkably increased.

The positive electrode material of the present invention has a layered structure including a Li layer and a Ni layer, and thus has excellent Li ion conductivity. The Li layer is a layer formed mainly of Li and is substantially made of Li. The Ni layer is a layer formed with Ni (Ni compound) as a main component and is substantially a layer containing Ni, M ¹ element, and M ² element as main components.

In the positive electrode material of the present invention, the bond length between Ni and oxygen is smaller than the bond length calculated from Shannon's ion radius table. Thereby, it is possible to adopt a structure in which all oxygen and M ² elements are adjacent to each other.
As described above, the positive electrode material of the present invention can provide a non-aqueous electrolyte secondary battery in which a decrease in battery performance is suppressed and is excellent in safety.
Moreover, the positive electrode for nonaqueous electrolyte secondary batteries and the nonaqueous electrolyte secondary battery of the present invention use the positive electrode material of the present invention, and can exhibit the effects obtained by the positive electrode material of the present invention.

It is a schematic sectional drawing which shows the structure of the coin-type lithium ion secondary battery of embodiment. 4 is a graph showing measurement results of powder XRD of the positive electrode material of Example 1. 2 is a graph showing charging characteristics and discharging characteristics of Example 1. FIG.

Hereinafter, the present invention will be specifically described with reference to embodiments.
[Embodiment]
The present embodiment is a coin-type lithium ion secondary battery 1 whose structure is shown in a schematic sectional view in FIG. The lithium ion secondary battery 1 of the present embodiment is a secondary battery (nonaqueous electrolyte secondary battery) using a positive electrode (a positive electrode for a nonaqueous electrolyte secondary battery) having the positive electrode material of the present invention as a positive electrode active material. .

  The lithium ion secondary battery 1 of this embodiment includes a positive electrode case 11, a sealing material 12 (gasket), a nonaqueous electrolyte 13, a positive electrode 14, a positive electrode current collector 140, a positive electrode mixture layer 141, a separator 15, a negative electrode case 16, and a negative electrode. 17, a negative electrode current collector 170, a negative electrode mixture layer 171, a holding member 18, and the like.

  The positive electrode 14 of the lithium ion secondary battery 1 of this embodiment has a positive electrode mixture layer 141 containing a positive electrode active material made of the positive electrode material of the present invention. The positive electrode mixture layer 141 includes members such as a binder and a conductive material as necessary in addition to the positive electrode active material.

(Positive electrode material)
The positive electrode material is Li ₂ Ni _α M ¹ _β M ² _γ Mn _η O _4-ε (0.50 <α ≦ 1.33, 0.33 ≦ γ ≦ 1.1, 0 ≦ η ≦ 1.00, 0 ≦ β <0.67, 0 ≦ ε ≦ 1.00, M ¹ : at least one selected from Co, Ga, M ² : at least one selected from Ge, Sn, Sb).

  The positive electrode material contains Ni in its composition. This Ni forms a local structure in which oxygen (O) is 6-coordinated (6-coordinated local structure). As a result, stable charging / discharging is performed. Further, high capacity can be achieved by containing a large amount of Ni, which is a redox species, in the range of 0.50 <α ≦ 1.33.

Further, by containing a large amount of M ¹ element and M ² element, the crystal structure becomes more stable, the crystal structure at the time of charge / discharge is kept stable, and as a result, the decrease in battery capacity is suppressed. The M ¹ element is an element having a trivalent formal valence, and the addition of the M ¹ element is expected to suppress the penetration of Li having a significantly different valence into the Ni layer. The M ² element strongly fixes oxygen, and as a result, the desorption of oxygen, which is a concern during abnormal heat generation, is suppressed, and the safety of the battery is improved. Furthermore, the amount of M ² element, when became 0.33 or more, on average, all of the oxygen in the Ni layer is adjoin the M ² element, and to have a bond with M ² element Therefore, the oxygen desorption effect is remarkably increased.

Furthermore, it is preferable that the M ¹ element and the M ² element are also in a six-coordinate state, and by this configuration, a structural gap with an adjacent transition metal element (Ni or Mn coordination structure) is reduced. And durability can be further improved.

  The positive electrode material of this embodiment may further contain Mn (a ratio of 0 or more and 1.00 or less) which is a transition metal in the composition. Like Mn, this Mn forms a local structure in which oxygen (O) is 6-coordinated (6-coordinated local structure). By being contained at this ratio, the effect of stabilizing the Ni layer is exhibited.

In a nonaqueous electrolyte secondary battery (lithium ion battery), when overcharge or the like proceeds, there may be a problem of ignition and smoke generation. The ignition smoke in this battery is greatly influenced by oxygen released from the positive electrode active material (positive electrode material) in the process leading to the smoke. Specifically, with charge, electrons are deprived of oxygen of the positive electrode active material, leading to oxygen release. In the positive electrode material of the present invention, the M ² element is added, and the added M ² element is more strongly bonded to oxygen than Ni or Mn (transition metal). That is, by adding the M ² element, oxygen release during charging / discharging can be minimized.

The positive electrode material of this embodiment has a layered structure including a Li layer and a Ni layer. With this configuration, the positive electrode material is excellent in Li ion conductivity. The Li layer refers to a layer formed with Li as a main component, and is a layer substantially made of Li. The Ni layer is a layer formed with Ni (Ni compound) as a main component, and is substantially a layer formed with Ni and elements M ¹ and M ² as main components.

  The bond length between Ni and oxygen in the positive electrode material of the present invention can be known by using a conventionally known crystal structure analysis method (apparatus). In particular, it is more preferable to determine the local structure of the positive electrode material by analyzing the X-ray absorption fine structure (hereinafter referred to as XAFS). Hereinafter, general XAFS will be briefly described.

  When the absorbance of a substance is measured while changing the energy of incident X-rays, when the incident X-ray energy is equal to the core level of the atoms constituting the measurement substance, a rapid increase in absorbance (absorption edge) is observed. Thereafter, as the incident X-ray energy increases, a moderate attenuation of the absorbance is observed. When this spectrum is examined in detail, there is a spectrum structure having a large change near the absorption edge. In addition, there is a spectrum structure having a small but gentle vibration structure even in a higher energy region than the absorption edge.

  The former is called the X-ray absorption edge structure (XANES), the latter is called the wide-area X-ray absorption fine structure (EXAFS), and both are collectively called the X-ray absorption fine structure (XAFS).

The spectral structure of XANES reflects the density of the vacant state of the measurement element in order to correspond to the transition from the core level of the atoms constituting the measurement substance to various vacant levels.
On the other hand, the spectral structure of EXAFS is caused by the interference effect between electrons emitted out of the atom by incident X-rays and electrons scattered by surrounding atoms, so the number of atoms around the measurement atom (the arrangement of the measurement atoms It reflects information such as order), type, and distance (coupling length).
The present inventors have identified the bond length between Ni and oxygen atoms by analyzing the spectral structure of EXAFS.

The EXAFS vibration (χ (k)) obtained by the EXAFS analysis is expressed by the following equation according to the plane wave single scattering theory.

Here, the subscript i is the coordination zone number, S ₀ ² is the attenuation factor, N _i is the number of atoms in the i-th coordination zone, F _i (ki) is the backscattering intensity, k _i is the wave number, r _i is a coupling distance, σ _i is a Debye-Waller (DW) factor, and φ _i (ki) is a phase shift.

In general, as the number of atoms (N _i ) in each coordination sphere decreases, the amplitude of EXAFS oscillation (χ (k)) decreases. It can also be seen from the above formula that the information of the atom having a shorter bond distance (r _i ) with the measurement atom is reflected in the EXAFS vibration (χ (k)) more greatly.

  Further, the EXAFS vibration (χ (k)) is weighted by k3 to obtain an EXAFS function (k3χ (k)) in which the vibration on the high wavenumber side is enhanced. Then, the obtained EXAFS function (k3χ (k)) is Fourier transformed in a range of 3 <k ≦ 12 to obtain a radial distribution function which is one-dimensional distance information from the Ni element center. The present inventors determined the bond length from the Ni element center to the oxygen atom from this radial distribution function.

  The positive electrode active material should just have said positive electrode material as a positive electrode active material, and may have another positive electrode active material (positive electrode material) further. The other positive electrode active material may be another material included in the above chemical formula, or may be another compound.

(Configuration other than positive electrode active material)
The configuration of the lithium ion secondary battery 1 of the present embodiment can be the same as that of a conventional lithium ion secondary battery except that the above positive electrode material is used as the positive electrode active material.
In the positive electrode 14, a positive electrode mixture layer 141 is formed by applying a positive electrode mixture obtained by mixing a positive electrode active material, a conductive material, and a binder to the positive electrode current collector 140.

  The conductive material ensures the electrical conductivity of the positive electrode 14. As the conductive material, graphite fine particles, acetylene black, ketjen black, carbon black such as carbon nanofiber, amorphous carbon fine particles such as needle coke, and the like can be used, but are not limited thereto.

  The binder binds the positive electrode active material particles and the conductive material. Examples of the binder include, but are not limited to, polyvinylidene fluoride (PVDF), ethylene-propylene-diene rubber (EPDM), styrene-butadiene rubber (SBR), nitrile rubber (NBR), and fluorine rubber. .

  The positive electrode mixture is dispersed in a solvent and applied to the positive electrode current collector 140. As the solvent, an organic solvent that normally dissolves the binder is used. Examples include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, NN-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, and the like. Although it can, it is not limited to these. In some cases, a positive electrode active material is slurried with polytetrafluoroethylene (PTFE) by adding a dispersant, a thickener, or the like to water.

  As the positive electrode current collector 140, for example, a processed metal such as aluminum or stainless steel, for example, a foil processed into a plate shape, a net, a punched metal, a foam metal, or the like can be used, but is not limited thereto.

(Non-aqueous electrolyte)
The non-aqueous electrolyte 13 is formed by dissolving a supporting salt in an organic solvent.
The type of the supporting salt of the nonaqueous electrolyte 13 is not particularly limited, but an inorganic salt selected from LiPF ₆ , LiBF ₄ , LiClO ₄ and LiAsF ₆ , derivatives of these inorganic salts, LiSO ₃ CF ₃ , An organic salt selected from LiC (SO ₃ CF ₃ ) ₃ and LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiN (SO ₂ CF ₃ ) (SO ₂ C ₄ F ₉ ), In addition, it is desirable to be at least one of these organic salt derivatives. These supporting salts can further improve the battery performance, and can maintain the battery performance higher even in a temperature range other than room temperature. The concentration of the supporting salt is not particularly limited, and it is preferable to appropriately select the supporting salt and the organic solvent in consideration of the use.

The organic solvent (non-aqueous solvent) in which the supporting salt dissolves is not particularly limited as long as it is an organic solvent used for a normal non-aqueous electrolyte. For example, carbonates, halogenated hydrocarbons, ethers, ketones, Nitriles, lactones, oxolane compounds and the like can be used. In particular, propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, vinylene carbonate and the like, and mixed solvents thereof are suitable. Among these organic solvents mentioned in the examples, in particular, by using one or more non-aqueous solvents selected from the group consisting of carbonates and ethers, the solubility of the supporting salt, the dielectric constant and the viscosity are excellent, and the battery The charge / discharge efficiency is preferable.
In the lithium ion secondary battery 1 of the present embodiment, the most preferable nonaqueous electrolyte 13 is one in which the supporting salt is dissolved in an organic solvent.

(Negative electrode)
In the negative electrode 17, a negative electrode mixture obtained by mixing a negative electrode active material and a binder is applied to the surface of the negative electrode current collector 170 to form a negative electrode mixture layer 171.
As the negative electrode active material, a conventional negative electrode active material can be used. A negative electrode active material containing at least one element of Sn, Si, Sb, Ge, and C can be given. Among these negative electrode active materials, C is preferably a carbon material capable of occluding and desorbing electrolyte ions of the lithium ion secondary battery 1 (having Li storage ability), and is preferably amorphous coated natural graphite. More preferred.

  Of these negative electrode active materials, Sn, Sb, and Ge are alloy materials that have a large volume change. These negative electrode active materials may form an alloy with another metal such as Ti—Si, Ag—Sn, Sn—Sb, Ag—Ge, Cu—Sn, and Ni—Sn.

  As the conductive material, a carbon material, metal powder, conductive polymer, or the like can be used. From the viewpoint of conductivity and stability, it is preferable to use a carbon material such as acetylene black, ketjen black, or carbon black.

As the binder, PTFE, PVDF, fluororesin copolymer (for example, tetrafluoroethylene / hexafluoropropylene copolymer (FEP)), SBR, acrylic rubber, fluororubber, polyvinyl alcohol (PVA), Examples thereof include styrene / maleic acid resin, polyacrylate, and carboxymethyl cellulose (CMC).
Examples of the solvent include organic solvents such as N-methyl-2-pyrrolidone (NMP) or water.

  As the negative electrode current collector 170, a conventional current collector can be used, which is obtained by processing a metal such as copper, stainless steel, titanium or nickel, for example, a foil processed into a plate shape, a net, a punched metal, a foam metal. However, it is not limited to these.

(Other configurations)
The positive electrode case 11 and the negative electrode case 16 seal the built-in material via an insulating sealing material 12. The built-in materials are a non-aqueous electrolyte 13, a positive electrode 14, a separator 15, a negative electrode 17, a holding member 18, and the like.
The positive electrode mixture layer 141 is in surface contact with the positive electrode case 11 through the positive electrode current collector 140 to conduct electricity. The negative electrode mixture layer 171 is brought into contact with the negative electrode case 16 through the negative electrode current collector 170 to be conductive.

  The separator 15 interposed between the positive electrode mixture layer 141 and the negative electrode mixture layer 171 electrically insulates the positive electrode mixture layer 141 and the negative electrode mixture layer 171 and holds the nonaqueous electrolyte 13. As the separator 15, for example, a porous synthetic resin film, particularly a porous film of a polyolefin polymer (polyethylene or polypropylene) is used. The separator 15 is formed with a size larger than that of the mixture layers 141 and 171 in order to ensure electrical insulation between the two mixture layers 141 and 171.

  The holding member 18 plays a role of holding the positive electrode current collector 140, the positive electrode mixture layer 141, the separator 15, the negative electrode mixture layer 171 and the negative electrode current collector 170 in place. When an elastic member such as an elastic piece or a spring is used, it can be easily held in place.

(Other forms)
The lithium ion secondary battery 1 of the present embodiment has a coin shape as described above. However, the shape is not particularly limited, and can be applied to batteries of various shapes such as a cylindrical shape and a rectangular shape, and a laminate outer package. It can be set as the battery of the irregular shape enclosed.

(Production method)
If the positive electrode material of this form has said structure, the manufacturing method will not be limited. Examples of production methods include solid-phase synthesis, coprecipitation synthesis, hydrothermal synthesis, complex polymerization synthesis, methods via ion exchange, synthesis by high-temperature and high-pressure treatment, sol-gel method, spray-drying method, supercritical synthesis The method etc. are mentioned, The method of combining these methods individually or in multiple numbers etc. can be mentioned.

Hereinafter, the present invention will be described using examples.
As an example for specifically explaining the present invention, a positive electrode material (positive electrode active material), a positive electrode using the positive electrode material, and a lithium ion secondary battery were manufactured. In the example, the lithium ion secondary battery shown in FIG. 1 was manufactured.

Example 1
First, Na ₂ NiSnO ₄ as a starting material was manufactured. Specifically, a compound containing one or more elements of Na, Ni, and Sn was weighed and mixed so that these elements had a predetermined atomic ratio. And it baked (atmosphere atmosphere) and obtained the starting material which has the crystal structure of a substantially single phase.
Subsequently, the obtained Na ₂ NiSnO ₄ was heated in a molten salt composed of Li nitrate and Li chloride to perform an ion exchange treatment.
Thus, the positive electrode material (Li ₂ NiSnO ₄ powder) of this example was manufactured.

When the produced Li ₂ NiSnO ₄ powder was observed with powder XRD, the diffraction result shown in FIG. 2 was obtained.
According to FIG. 2, it can be confirmed that the compound is almost a single phase.

(Example 2)
An aqueous solution containing each metal complex of Li, Ni, Mn, and Ge was prepared. The obtained complex solution was mixed so as to have the composition ratio of the target positive electrode material, that is, the atomic ratio of Li: Ni: Mn: Ge was 2.1: 1: 0.67: 0.33. .
The obtained mixed solution was dried in a drying furnace to remove organic components by heat treatment, and then heated and baked.
Thus, the positive electrode material (Li _2.1 NiMn _0.67 Ge _0.33 O ₄ powder) of this example was manufactured.

When the produced Li _2.1 NiMn _0.67 Ge _0.33 O ₄ powder was observed with a powder XRD, it was confirmed to be a substantially single-phase compound.

Example 3
In the same manner as the starting material of Example 1, almost single-phase Na ₂ NiMn _0.67 Ge _0.33 O ₄ was produced.
Subsequently, the obtained Na ₂ NiMn _0.67 Ge _0.33 O ₄ was subjected to an ion exchange treatment in the same manner as in Example 1.
Thus, the positive electrode material (Li ₂ NiMn _0.67 Ge _0.33 O ₄ powder) of this example was manufactured.

When the produced Li ₂ NiMn _0.67 Ge _0.33 O ₄ powder was observed with a powder XRD, it was confirmed to be a substantially single-phase compound.

Example 4
In the same manner as in Example 2, a positive electrode material (Li _2.1 NiMn _0.67 Sn _0.33 O ₄ powder) of this example was produced from an aqueous solution containing a metal complex.

When the manufactured Li _2.1 NiMn _0.67 Sn _0.33 O ₄ powder was observed with a powder XRD, it was confirmed to be a substantially single-phase compound.

(Example 5)
In the same manner as the starting material of Example 1, almost single phase Na ₂ NiMn _0.67 Sn _0.33 O ₄ was produced.
Subsequently, the obtained Na ₂ NiMn _0.67 Sn _0.33 O ₄ was subjected to an ion exchange treatment in the same manner as in Example 1.
Thus, the positive electrode material (Li ₂ NiMn _0.67 Sn _0.33 O ₄ powder) of this example was manufactured.

When the produced Li ₂ NiMn _0.67 Sn _0.33 O ₄ powder was observed with a powder XRD, it was confirmed to be a substantially single-phase compound.

(Example 6)
The positive electrode material of this example is Li ₂ NiGeO ₄ powder. This composition was confirmed by ICP analysis.
When Li ₂ NiGeO ₄ powder, which is the positive electrode material of this example, was observed with powder XRD, it was confirmed that it was a substantially single-phase compound and had a layered rock salt type crystal structure.

(Comparative Example 1)
In the same manner as in Example 2, a positive electrode material (Li _2.1 NiTiO ₄ powder) of this example was produced from an aqueous solution containing a metal complex.

When the produced Li _2.1 NiTiO ₄ powder was observed with a powder XRD, it was confirmed to be a substantially single-phase compound.

(Comparative Example 2)
In the same manner as in Comparative Example 1, a positive electrode material (Li _2.1 NiMn _0.33 Ti _0.67 O ₄ powder) of this example was produced from an aqueous solution containing a metal complex.

When the manufactured Li _2.1 NiMn _0.33 Ti _0.67 O ₄ powder was observed with a powder XRD, it was confirmed to be a substantially single-phase compound.

(Comparative Example 3)
In the same manner as in Comparative Example 1, a positive electrode material (Li _1.05 NiO ₂ powder) of this example was produced from an aqueous solution containing a metal complex.

When the produced Li _1.05 NiO ₂ powder was observed with a powder XRD, it was confirmed to be a substantially single-phase compound.

[Evaluation]
As evaluation of the positive electrode material in each of the above examples, a lithium ion secondary battery was assembled, and charge / discharge characteristics were evaluated. After measuring the charge / discharge characteristics, the coin-type battery was disassembled and the positive electrode was taken out, and safety was evaluated.

(Lithium ion secondary battery)
A test cell (2032 type coin type half cell) made of a lithium ion secondary battery was assembled and evaluated using the positive electrode active material of each of the above examples.

(Coin type half cell)
The test cell (coin-type half cell) has the same configuration as the coin-type lithium ion secondary battery 1 whose configuration is shown in FIG.
The positive electrode is obtained by applying a positive electrode mixture obtained by mixing 91 parts by mass of a positive electrode active material (positive electrode active material of each example), 2 parts by mass of acetylene black, and 7 parts by mass of PVDF to a positive electrode current collector 140 made of an aluminum foil. Then, the one in which the positive electrode mixture layer 141 was formed was used.

Metal lithium was used for the negative electrode (counter electrode). Metallic lithium corresponds to the negative electrode mixture layer 171 in FIG.
The nonaqueous electrolyte 13 was prepared by dissolving LiPF ₆ in a mixed solvent of 30% by volume of ethylene carbonate (EC) and 70% by volume of diethyl carbonate (DEC) so as to be 1 mol / liter. .
After the test cell was assembled, an activation process was performed by charge / discharge of 1 / 3C × 2 cycles.
The test cell (half cell) of each example was manufactured by the above.

[Charge / discharge characteristics]
The lithium ion secondary battery was charged and discharged at a 1/50 C rate. Charging was performed by CC charging with 4.5V cut, and discharging was performed by CC discharging with 2.6V cut.

  Table 1 shows the measurement results of the charge capacity and discharge capacity of the lithium ion secondary batteries of Examples 1 to 6 and Comparative Examples 1 to 3. In addition, the charge / discharge characteristics of the lithium ion secondary battery of Example 1 are shown in FIG.

As shown in Table 1, the secondary batteries of each example are superior in charge capacity and discharge capacity compared to Comparative Examples 1 and 2.
Moreover, as shown in FIG. 3, it was confirmed that the secondary battery of Example 1 has good charge / discharge characteristics.

[Safety test]
The lithium ion secondary battery was charged by CC charging up to 4.8 V at a 1/50 C rate.
After charging, the battery was disassembled and the positive electrode was taken out.

The positive electrode taken out was washed with DMC and then heated at a temperature increase rate of 20 ° C./min from room temperature to 1000 ° C. in a helium atmosphere. At that time, the amount of oxygen generated from the positive electrode was measured by TPD-MS measurement.
The measurement results are shown in Table 1.

  As shown in Table 1, the secondary battery of each example has a smaller amount of oxygen generation than Comparative Example 2 and Comparative Example 3, that is, both are excellent in safety.

[Evaluation of bond length between Ni and oxygen atoms derived from EXAFS analysis]
The bond length between the Ni atom contained in the positive electrode materials obtained in Examples 1 to 6 and the oxygen atom which is the first adjacent atom was identified as follows. The results are shown in Table 1. If there is a jump value or missing data in the data, and if an inappropriate background process is performed for EXAFS analysis, parameters corresponding to this purpose are set. Even in this case, it can be within the scope of the present invention.
(1) A proper amount of the positive electrode material of Example 1 and boron nitride were mixed and compression molded to produce pellets.
(2) X-ray absorption measurement was performed by the transmission method in the range of 8032 to 9432 eV.
(3) The measurement result data is opened with analysis software (Athena (Ver. 0.9.013)) using a plug-in for directly reading energy and X-ray absorption. Then, the background is removed and E0 is determined by a default algorithm. For the pre-edge, the range of −150 to −30 eV from E0 was applied, and the normalization range was 150 to 980 eV from E0.
(4) In the range of 3 <k ≦ 12, Fourier transform using the Hanning window as a window function is performed to obtain a radial distribution function that is one-dimensional distance information from the Ni atom center of each example. At this point, no phase adjustment was performed.
(5) The data that has undergone Fourier transform is read by analysis software (Artemis (Ver. 0.8.012)).
(6) As a fitting condition, a peak corresponding to the first coordination zone is set as a fitting target, and 3 is set as k-weight.
(7) In deriving the theoretical EXAFS function in consideration of the phase shift and the backscattering factor, the software (Atoms) added to the analysis software (Artemis) is used, and the layered rock salt type crystal structure Li ₂ NiMnO ₄ (CifNo00000001805552) is used. The calculation was performed using a model with a cluster size of 6 mm, where Ni at the Ni / Mn (3b) site was Core.
(8) Among the obtained paths, a Ni-O path that is an element corresponding to the first coordination sphere is selected. For the selected path, amp: 0.1 (guess), coordination number N = 6, enot: 0.01 (guess), delr: 0.01 (guess), ss (DW factor): 0. The initial setting was 01 (guess), and fitting of the first adjacent element was performed.
(9) The R factor obtained was 0.00009. That is, it can be determined that the analysis was performed with high accuracy. Furthermore, ss was 0.0081 2, enot was 4.41 eV, and amp was 0.88. The bond length between Ni—O output at this time, that is, the distance from the Ni center to the oxygen atom was 1.97 cm (Table 1). Since the bond length between Ni—O calculated from the Shannon ion radius table is 2.04 mm, it was found to be smaller than the bond length calculated from the Shannon ion radius table.

  In the same manner as described above, the bond length between Ni—O in each positive electrode material of Examples 2 to 6 was identified and shown in Table 1. From Table 1, it was found that the bond length between Ni—O in each positive electrode material of Examples 2 to 6 was also smaller than the bond length calculated from Shannon's ion radius table.

1: Lithium ion secondary battery 11: Positive electrode case 12: Sealing material (gasket)
13: Nonaqueous electrolyte 14: Positive electrode 140: Positive electrode current collector 141: Positive electrode mixture layer 15: Separator 16: Negative electrode case 17: Negative electrode 170: Negative electrode current collector 171: Negative electrode mixture layer 18: Holding member

Claims (4)

Li ₂ Ni _α M ¹ _β M ² _γ Mn _η O _4-ε (0.50 <α ≦ 1.33, 0.33 ≦ γ ≦ 1.1, 0 ≦ η ≦ 1.00, 0 ≦ β <0 .67, 0 ≦ ε ≦ 1.00, M ¹ : at least one selected from Co, Ga, M ² : at least one selected from Ge, Sn, Sb)
Having a layered structure comprising a Li layer and a Ni layer;
A positive electrode material, wherein a bond length between Ni and oxygen is smaller than a bond length calculated from Shannon's ion radius table.   Compared to the X-ray absorption measurement result of K-edge of Ni, the first proximity in the radial distribution function result obtained by Fourier transform in the region of 3 <k ≦ 12 corresponding to the wide X-ray absorption fine structure (EXAFS) region The positive electrode material according to claim 1, wherein the distance from the Ni center to the peak position corresponding to is less than 2.04 mm.   A positive electrode (14) for a non-aqueous electrolyte secondary battery using the positive electrode material according to claim 1 or 2.   A non-aqueous electrolyte using at least one of the positive electrode for a non-aqueous electrolyte secondary battery using the positive electrode material according to claim 1 and the positive electrode for the non-aqueous electrolyte secondary battery according to claim 3. Secondary battery (1).

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