JPH1125980A - Positive electrode active material for non-aqueous electrolyte secondary battery and evaluating method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To quickly and accurately determine the appropriateness of a positive electrode active material and to improve the cycle characteristic of a secondary battery by using a relation between a crystal structure obtained by the powder X-ray diffraction of a hexagonal system lithium composite oxide and the cycle characteristic as a reference. SOLUTION: In a hexagonal system lithium composite oxide represented by a formula: [Li]3a[Na1-x-yCox My]3b[O2 ]6c (0.75<1-x-y<=0.90, cobalt addition x:0.05<=z<=0.25, metal M addition y:0<=y<=0.15, added character of [] means site) and having a layer structure, in an atomic position coordinate obtained from the Rietveld analyzing result of X-ray diffraction, 1.065 or lower of the distortion (ODP) of an oxygen octahedron around the metallic atom of 3b site is used as a reference for determining the appropriateness of using a lithium composite oxide active material as a positive electrode active material for a non-aqueous electrolyte secondary battery. Herein, ODP indicates a distance between oxygen atoms within a surface made by an (a) axis and (b) axis or a distance between oxygen atoms outside the surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery using lithium, a lithium alloy or carbon for a negative electrode. (Maintenance of high capacity). The present invention also relates to a method for evaluating the positive electrode active material.

[0002]

2. Description of the Related Art In recent years, with the spread of portable devices such as portable telephones and notebook personal computers, there is a strong demand for the development of small, lightweight, high capacity secondary batteries having a high energy density. As such a device, there is a lithium ion secondary battery using lithium, a lithium alloy or carbon as a negative electrode, and research and development have been actively conducted.
Lithium cobalt complex oxide (LiC
Since a lithium ion secondary battery using oO ₂ ) as a positive electrode active material can obtain a high voltage of 4V class, it is expected as a battery having a high energy density, and its practical use is progressing.

[0003] However, since an expensive cobalt compound is used as a raw material, the unit cost per capacity is about four times that of a nickel-metal hydride battery. Therefore, the applications to which they are applied are quite limited. Reducing the cost of the active material and enabling the production of a cheaper lithium battery is of great industrial significance in reducing the weight and size of portable devices that are currently widespread.

As a new material for the positive electrode active material of a lithium battery, there is a lithium nickel double oxide (LiNiO ₂ ) using nickel, which is cheaper than cobalt. Since this lithium nickel composite oxide shows a lower electrochemical potential than the lithium cobalt composite oxide,
Decomposition due to oxidation of the electrolyte is unlikely to cause a problem, so higher capacity can be expected, and development has been actively conducted. However, it is said that it is difficult to obtain a lithium nickel composite oxide having excellent stoichiometry and it is difficult to synthesize. This is because Ni ³⁺ is unstable at high temperatures and tends to have a non-stoichiometric composition Li _x Ni _1−x O ₂ (0 <x <1) (for example, MGSG Thomas et al, Mat. Res.
Bull., 20, 1137 (1985)). This problem can be avoided by using a highly reactive material such as lithium peroxide or nickel nitrate as a raw material, but it is difficult to handle and is expensive as an industrial raw material. Can not do it.

[0005] Furthermore, the lithium-nickel double oxide having excellent stoichiometry also has a problem in cycle characteristics, which is caused by the joint Jahn-Teller distortion of nickel ions when Li ions are deintercalated. It has been reported that the crystallinity deteriorates and the crystal phase changes to a crystal phase that is difficult to charge and discharge (for example, Ryuji Kanno, Electrochemistry 63, No. 7, 778 (1995)).

The basic characteristics of such an active material are evaluated by actually producing a battery and measuring the capacity. As for the evaluation of the active material, one cycle of the charge / discharge test is insufficient because of the problem of the cycle characteristics, and it is necessary to repeat several tens of cycles and evaluate the capacity retention rate. For this reason, there is a problem that the excellent characteristics of the lithium secondary battery having a large capacity become a negative factor in the evaluation test of the active material, and it takes a long time to evaluate the characteristics.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a lithium nickel double oxide capable of improving the cycle characteristics of a secondary battery (maintaining a discharge capacity). It is another object of the present invention to provide an evaluation method capable of quickly and accurately determining the suitability of an active material.

[0008]

Means for Solving the Problems In order to solve the above problems, the present inventors have conducted various studies and found that there is a deep relationship between the crystal structure obtained by powder X-ray diffraction and the cycle characteristics. I found it. FIG. 1A schematically shows the crystal structure of the present active material.

In particular, NiO ₂ layers formed from NiO ₆ octahedra sharing a ridge are called slabs (A. Rougier, C. Del.
mas and AV Chadwick, Solid State Commun., 94 [2]
(1995) 123-127.) L sandwiched with this slab
When the i-ions enter and exit reversibly, the charge / discharge reaction of the battery progresses and acts as an active material. Therefore, the NiO ₂ slab structure was considered to be a great guide to know the stability of the active material during the battery reaction. Therefore, as a result of conducting various studies to achieve the above object, there is a deep relationship between the structure of the oxygen octahedron shown in FIG. 1 (b) centered on nickel Ni atoms in the slab and the cycle characteristics. Was found. In the figure, it is written in octahedron, but actually oxygen 1 and oxygen 2
(In the plane formed by the a-axis and b-axis) and oxygen 1 and oxygen 3
This octahedron is distorted before Li desorbs because the length is different at the (interplane) distance. When this distortion takes a certain value, the change in crystal structure between charging and discharging is small,
It was speculated that lithium ions could easily enter and exit.

As a result, without conducting a battery test on a lithium-nickel double oxide having excellent stoichiometry, the results of X-ray diffraction Rietveld analysis showed that nickel Ni atoms (3
It was found that the active material can be evaluated by determining the strain of the oxygen octahedra centering on the metal atom at the b site).

That is, the present invention relates to the following formula: [Li] 3a [Ni ₁ -x-y Cox My] 3b [O ₂ ] 6c where 0.75 <1-xy ≦ 0.90 0.05 ≦ x ≦ 0.25 Addition amount of metal M y: 0 ≦ y ≦ 0.15 The suffix [] indicates a site.

In the hexagonal system lithium complex oxide represented by the following formula and having a layered structure, the oxygen octane centered on the metal atom at the 3b site is determined from the atomic position coordinates obtained from the Rietveld analysis result of X-ray diffraction. Face Distortion (ODP = Octahedr
al Distoration Parameter) ODP = dO-O, intra / dO-O, inter where dO-O and intra are distances between oxygen atoms in the plane formed by the a-axis and b-axis, and dO-O and inter are out-of-plane When the distance between oxygen atoms is determined, the ODP value is 1.065 or less, which is a positive electrode active material for a non-aqueous electrolyte secondary battery.

Further, the positive electrode active material for a non-aqueous electrolyte secondary battery is characterized in that the a-axis lattice constant obtained by Rietveld analysis is 2.863 to 2.865 angstroms. This concept can be applied to the case where Co and Mn (M = Mn) are added for improving the cycle characteristics, and serves as a guideline for obtaining a higher addition effect.

That is, the present invention relates to the following formula: [Li] 3a [Ni ₁ -x-y Cox Mny] 3b [O ₂ ] 6c where 0.75 <1-xy ≦ 0.90, 0.05 ≦ x ≦ 0.25, 0 <y ≦ 0.
In the hexagonal lithium double oxide having a layered structure and represented by the following formula, the oxygen octahedron centered on the metal atom at the 3b site from the atomic position coordinates obtained from the Rietveld analysis result of X-ray diffraction. Is a positive electrode active material for a non-aqueous electrolyte secondary battery, characterized in that the strain (ODP value) is 1.060 or less. Further, this idea can be applied to the case where M = Al in order to improve cycle characteristics.
It serves as a guideline for obtaining a higher addition effect.

That is, the present invention relates to the following formula: [Li] 3a [Ni ₁ -x-y Cox Aly] 3b [O ₂ ] 6c where 0.75 <1-xy ≦ 0.90, 0.05 ≦ x ≦ 0.25, 0 <y ≦ 0.
In the hexagonal lithium double oxide having a layered structure and represented by the following formula, the oxygen octahedron centered on the metal atom at the 3b site from the atomic position coordinates obtained from the Rietveld analysis result of X-ray diffraction. Is a positive electrode active material for a non-aqueous electrolyte secondary battery, characterized by having a distortion (ODP value) of 1.058 or less.

The lithium-nickel double oxide of M = Mn or Al, which has a hexagonal crystal structure and whose Rietveld analysis by X-ray diffraction shows that the non-lithium ion occupancy of the 3a site is 2% or less. A positive electrode active material for a non-aqueous electrolyte secondary battery, wherein the ratio of the c-axis lattice constant to the a-axis lattice constant (c / a) is 4.94 or more and 4.96 or less. Further, the positive electrode active material for a non-aqueous electrolyte secondary battery is characterized in that the lattice constant of the a-axis obtained by Rietveld analysis is 2.855 to 2.870 angstroms.

Further, the present invention has the _{formula: [Li] 3a [Ni 1} -x-yCox My] 3b [O 2] 6c However, 0.75 <1-xy ≦ 0.90 , the addition amount of Co x: 0.05 ≦ x
≦ 0.25, addition amount of metal M y: 0 ≦ y ≦ 0.15, and in a hexagonal lithium complex oxide having a layered structure, from atomic coordinates obtained from Rietveld analysis results by X-ray diffraction. The distance between oxygen atoms in the plane (d
oo, intra) and the out-of-plane oxygen atom distance (do-o, inter) sandwiching the layer of metal atoms at the 3b site (do-o, inter) are determined. = do-o, intra / do-o, inter, to judge the suitability of the lithium double oxide-based active material. Further, when the ODP value is 1.
The method for evaluating a positive electrode active material for a non-aqueous electrolyte secondary battery is characterized in that it is determined that the positive electrode active material is suitable as an active material if the value is 065 or less.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION The crystal structure and stoichiometry
Rietveld analysis by X-ray diffraction (for example, RA Youn
g, ed., The Rietveld Method, Oxford University Press
(1992).), And this analysis can determine the site occupancy of each ion as an index of crystal integrity (stoichiometry) in addition to the lattice constant.

In the case of a hexagonal compound, 3a, 3
There are sites b and 6c, and in the case of perfect stoichiometry, Li is the site 3a, Ni is the site 3b, and O is the site occupancy of 100%, respectively. It can be said that a lithium-nickel double oxide having a Li ion site occupancy of the 3a site of 98% or more has excellent stoichiometry. In other words, it can be said that a lithium nickel double oxide in which the mixing ratio of metal ions other than Li ions into the 3a site is 2% or less is excellent in stoichiometry.

The seat occupancy of Li ions at the 3a site is 98
% Or more, if the NiO ₂ slab structure is stable, it is possible to suppress the transformation / decomposition of the active material due to the change in the crystal structure during charging. That is, as long as the strain of the oxygen octahedra centering on the nickel Ni atoms forming the slab is small, the active material is a good active material with little capacity deterioration even after repeated charge / discharge cycles.

When considered as a battery active material, since Li can be desorbed and inserted, the integrity of the crystal can be maintained even if Li deficiency occurs. Therefore, in practice, it is considered that it is a good method to indicate the stoichiometry or the crystal perfection based on the mixing ratio of non-lithium ions at the 3a site.

In the active material of the present invention, the lithium-nickel compound oxide has a strain (ODP) of oxygen octahedron in the NiO 2 slab structure of 1.065 or less and a lattice constant of a-axis of 2.863 to 2.865 angstroms. It is a positive electrode active material for an aqueous electrolyte secondary battery.

The active material of the present invention is a lithium-nickel composite oxide in which a part of nickel of the above-mentioned lithium-nickel composite oxide is replaced with Co and Mn or Co and Al, and has an NiO ₂ slab structure. Of the oxygen octahedron of
DP) is 1.058 or less, the a-axis lattice constant is 2.855 to 2.870 °, and the ratio (c / a) of the c-axis lattice constant to the a-axis lattice constant is 4.94 or more and 4.96 or less. Is a positive electrode active material for a non-aqueous electrolyte secondary battery.

[0024]

【Example】

Example 1 Synthesis of Active Material Sample Lithium Hydroxide (LiOH.H ₂ O: Purity)
99%) and the formula: (Ni ₁ -x-yCox My) (OH) _n is a nickel-cobalt coprecipitated hydroxide prepared such that x and y have the following values, respectively:
2. Lithium / (nickel + cobalt) The weight ratio is weighed so that the respective atomic ratios have the following predetermined values, and the total weight thereof is 3.
4 kg was mixed for 5 minutes using a mixing granulator (manufactured by Fukae Kogyo Co., Ltd .; High Speed Mixer), and 430 cc of a 2% PVA aqueous solution was added, followed by granulation for 10 minutes. Next, after collecting the granulated material, after drying at 100 ° C. for 2 hours, this was heated to a predetermined temperature at a heating rate of 300 ° C./h using a magnesia setter in an atmosphere with an oxygen flow rate of 3.0 L / min. Fifteen
It was synthesized by holding for a time.

Example 1-1 x = 0.08, y = 0, Li / (Ni
+ Co) = 1.1, synthesis temperature = 700 ° C. Example 1-2 x = 0.16, y = 0, Li / (Ni + Co) = 1.05,
Synthesis temperature = 680 ° C. Example 1-3 x = 0.16, y = 0, Li / (Ni + Co) = 1.05,
Synthesis temperature = 700 ° C. Example 1-4 x = 0.16, y = 0, Li / (Ni + Co) = 1.05,
Synthesis temperature = 720 ° C. Comparative Example 1-1 x = 0.17, y = 0, Li / (Ni + Co) = 1.05,
Synthesis temperature = 750 ° C. Comparative Example 1-2 x = 0.17, y = 0, Li / (Ni + Co) = 1.10,
Synthesis temperature = 750 ° C. Comparative Example 1-3 x = 0.15, y = 0, Li / (Ni + Co) = 1.05,
Synthesis temperature = 650 ° C

[X-ray Diffraction] The X-ray diffraction pattern of each sample was measured using an X-ray diffractometer (RADrVB) manufactured by Rigaku Corporation. The measurement conditions were CuKα radiation (tube voltage 40 kV, tube current 1
50mA), sampling width 0.02 °, scanning speed 4.00
At ／ ° / min, the slits diverge 1.00 ° and scattering 1.00, respectively.
° Light reception was set to 0.3 mm.

The X-ray diffraction pattern was analyzed based on the R3m crystal model using a Rietveld analysis program XReitan. As an example, Table 1 shows the obtained atomic coordinate positions in the case of Example 1-1.

[0028]

[Table 1]

The octahedral distortion ODP was determined based on the following equation.

(Equation 1) Here, Z indicates the X coordinate position of the oxygen atom determined by Rietveld analysis, and its value is shown in the Z column of Table 1. In Table 1, the X and Y columns also show the positions of the X and Y coordinates. a and c are lattice constants of the a-axis and the c-axis, respectively.

Table 2 summarizes the 3a-site non-Li ion mixing ratio, lattice constant, and ODP. Example 1-2,
3. In Comparative Examples 1 to 3, the oxygen coordinate atom positions were similarly determined.
The a-site non-Li ion mixing ratio, lattice constant, and ODP were determined. Table 2 summarizes the results.

[Battery Test] A battery was prepared using the obtained active material as follows, and the charge / discharge capacity was measured. 85% by weight of active material powder and 6% by weight of acetylene black and PVDF
9 wt% (polyvinylidene fluoride) was mixed, and NMP (n-methylpyrrolidone) was added to form a paste. This is applied to an expanded metal mesh made of aluminum so that the weight of the active material after drying becomes 0.07 g / cm ² , and dried.
Further, vacuum drying was performed at 120 ° C. to obtain a positive electrode. Li metal was used as a negative electrode, and an electrolytic solution was a mixed solution of an equal amount of ethylene carbonate (EC) and diethyl carbonate (DEC) using 1M LiPF ₆ as a supporting salt. The beaker battery shown in FIG. 2 is assembled in a glove box in an Ar atmosphere. The prepared battery was left for about 10 hours, and after the open circuit voltage (OCV) was stabilized, the current density with respect to the positive electrode was 1.
The charge / discharge test was performed at a cutoff of 4.3 to 3.0 V at 0 mA / cm ² . Table 2 shows the results. However, the capacity retention ratio (%) is 100 × (100th discharge capacity) / (first discharge capacity).

[0032]

[Table 2] As shown in Table 2, when the non-Li ion mixing ratio of the 3a site of the active material is 2% or less and the ODP value is in a range of 1.065 or less, the discharge capacity is high and the capacity retention ratio is high. It can be seen that a battery having

Although the battery in this example was a battery using Li metal as a negative electrode, the use of the active material of the present invention is not limited to this. Li is reversibly applied to the negative electrode by a battery reaction. Carbon such as carbon fiber and graphite that can be intercalated can also be used.

Example 2 [Synthesis of Active Material Sample] Instead of the nickel cobalt coprecipitated hydroxide used in Example 1 as a raw material powder, the following formula: (Ni ₁ -x-yCox Mny) (OH) _n Synthesis was performed in the same manner as in Example 1 except that nickel cobalt manganese coprecipitated hydroxide prepared such that x and y had the following values was used.

Example 2-1 x = 0.16, y = 0.04, Li /
(Ni + Co + Mn) = 1.0, synthesis temperature = 700 ° C. Example 2-2 x = 0.10, y = 0.10, Li / (Ni + Co + Mn) =
1.0, synthesis temperature = 700 ° C. Example 2-3 x = 0.15, y = 0.10, Li / (Ni + Co + Mn) =
1.0, synthesis temperature = 700 ° C. Example 2-4 x = 0.20, y = 0.05, Li / (Ni + Co + Mn) =
1.0, synthesis temperature = 700 ° C. Comparative Example 2-1 x = 0, y = 0.20, Li / (Ni + Co + Mn) =
1.0, synthesis temperature = 700 ° C. Comparative Example 2-2 x = 0.16, y = 0.04, Li / (Ni + Co + Mn) =
1.0, synthesis temperature = 780 ° C. Comparative Example 2-3 x = 0.10, y = 0.10, Li / (Ni + Co + Mn) =
1.0, synthesis temperature = 650 ° C

[X-ray Diffraction] An X-ray diffraction pattern of the active material sample was measured and analyzed in the same manner as in Example 1. Example 2-1
Are shown in Table 3. In this analysis, the mixed metal ions at the 3a site were only nickel ions. However, even when three ions of cobalt, manganese, and nickel were mixed, similar analysis results can be obtained. No error occurs.

[0037]

[Table 3]

The octahedral strain ODP was determined in the same manner as in Example 1. Table 4 summarizes the 3a site non-Li ion mixing ratio, lattice constant, and ODP. Although the result of Rietveld analysis was used for the lattice constant, evaluation can be performed using a value obtained by ordinary measurement of lattice constant in order to obtain c / a.

[Battery test] Using the obtained active material, a battery was fabricated in the same manner as in Example 1, and the charge / discharge capacity was measured.
Table 4 shows the results.

[0040]

[Table 4]

As described above, the lithium-nickel double oxide of the present invention, in which a part of nickel is replaced by Co and Mn and the ODP is controlled to 1.060 or less, when used as an active material of a lithium secondary battery, It can be seen that a battery having a high capacity and a high capacity retention ratio can be obtained. On the other hand, as shown in the comparative example, the mere addition of Co or Mn lowers the crystallinity, so that the cycle characteristics cannot be improved.

Example 3 [Synthesis of Active Material Sample] In place of the nickel cobalt coprecipitated hydroxide used in Example 1 as a raw material powder, the following formula: (Ni ₁ -x-yCox Aly) (OH) _n The synthesis was carried out in the same manner as in Example 1 except that nickel cobalt aluminum coprecipitated hydroxide prepared such that x and y had the following values respectively was used.
All the synthesis temperatures were 700 ° C.

Example 3-1 x = 0.16, y = 0.03, Li /
(Ni + Co + Al) = 1.0 Example 3-2 x = 0.11, y = 0.03, Li / (Ni + Co + Al) =
1.0 Example 3-3 x = 0.15, y = 0.10, Li / (Ni + Co + Al) =
1.0 Example 3-4 x = 0.10, y = 0.10, Li / (Ni + Co + Al) =
1.0 Comparative Example 3-1 x = 0.10, y = 0.16, Li / (Ni + Co + Al) =
1.0 Comparative Example 2-2 x = 0.04, y = 0.28, Li / (Ni + Co + Al) =
1.0 Comparative Example 3-3 x = 0, y = 0.16, Li / (Ni + Co + Al) =
1.0

[X-ray Diffraction] The X-ray diffraction pattern of the active material sample was measured and analyzed in the same manner as in Example 1. Table 5 shows the obtained atomic coordinate positions in Example 3-1 as an example. In this analysis, the mixed metal ions at the 3a site were only nickel ions, but the same analysis results can be obtained even when three ions of aluminum, cobalt and nickel are mixed. No error occurs.

[0045]

[Table 5]

Further, the octahedral distortion OD was obtained in the same manner as in Example 1.
P was determined. Table 6 summarizes the 3a-site non-Li ion mixing ratio, lattice constant, and ODP. Although the result of Rietveld analysis was used for the lattice constant, evaluation can be performed using a value obtained by ordinary measurement of lattice constant in order to obtain c / a.

[Battery Test] Using the obtained active material, the charge / discharge capacity was measured in the same manner as in Example 1. Table 6 shows the results.

[0048]

[Table 6]

As described above, a part of nickel is changed to Co and A.
The lithium nickel double oxide of the present invention, in which ODP is controlled to 1.058 or less, has a high discharge capacity and a high capacity retention rate when used as an active material of a lithium secondary battery. Is obtained. On the other hand, as shown in the comparative example, simply adding Co and Al improves the cycle characteristics of the battery but decreases the capacity.

[0050]

The use of the lithium-cobalt double oxide according to the present invention as a positive electrode active material for a non-aqueous secondary battery has the effect of producing a secondary battery having an excellent capacity retention ratio. According to the method, it is possible to easily and reliably measure the characteristics of the positive electrode active material for a non-aqueous secondary battery. Therefore, it is possible to easily obtain a high-performance lithium secondary battery by evaluating the active material using the active material and the evaluation method of the present invention and assembling the battery based on the evaluation.

[Brief description of the drawings]

FIG. 1 schematically shows the crystal structure of a lithium-nickel double oxide, wherein (a) is an overall view thereof, and (b) is its N-structure.
FIG. 4 is an enlarged view of an oxygen octahedron in an iO ₂ slab.

FIG. 2 is a longitudinal sectional view of a beaker type battery used for a charge / discharge capacity test.

[Explanation of symbols]

 1. Beaker 2. Electrolyte 3. Teflon stopper 4. Positive electrode 5. Counter electrode (Li metal) 6. Reference electrode (Li metal)

Claims (8)

[Claims] 1. The formula: [Li] 3a [Ni ₁ -x-yCox M
y] 3b [O ₂ ] 6c where 0.75 < _1- xy ≦ 0.90 Cobalt addition x: 0.05 ≦ x ≦ 0.25, metal M addition y: 0 ≦ y ≦ 0 .15 The subscript in [] indicates a site. In the hexagonal lithium compound oxide having a layered structure and represented by the following formula, the distortion of the oxygen octahedron centered on the metal atom at the 3b site from the atomic position coordinates obtained from the Rietveld analysis result of X-ray diffraction (ODP = Octahedral Distorati
on Parameter) ODP = do-o, intra / do-o, inter where do-o and intra are the distances between oxygen atoms in the plane formed by the a-axis and b-axis, and do-o and inter are out-of-plane oxygen The cathode active material for a non-aqueous electrolyte secondary battery, wherein the ODP value is 1.065 or less when the interatomic distance is determined. 2. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein when y = 0, the lattice constant of the a-axis obtained by Rietveld analysis is 2.863 to 2.865 angstroms. 3. The metal M is Mn and the ODP value is 1.0.
The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the positive electrode active material is 60 or less. 4. The metal M is Al and has an ODP value of 1.0.
The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the positive electrode active material is 58 or less. 5. A lithium-nickel double oxide having a hexagonal structure and having a non-lithium ion site occupancy of 3a site of 2% or less in a result of Rietveld analysis by X-ray diffraction, the c-axis lattice constant and a-axis lattice constant ratio (c / a)
5. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 3, wherein the positive electrode active material is 4.94 or more and 4.96 or less. 6. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 3, wherein the lattice constant of the a-axis obtained by Rietveld analysis is 2.855 to 2.870 angstroms. 7. The in-plane formed by the a-axis and the b-axis from the atomic position coordinates obtained from the Rietveld analysis result of X-ray diffraction, in the hexagonal system lithium double oxide having a layered structure according to claim 1. Between oxygen atoms (do-o, intra) and the distance between out-of-plane oxygen atoms (do-o, inter) sandwiching the layer of metal atoms at the 3b site are determined. A method for evaluating a positive electrode active material for a non-aqueous electrolyte secondary battery, comprising determining whether or not the lithium double oxide-based active material is appropriate based on octahedral distortion (ODP). 8. The evaluation method according to claim 7, wherein the OD
A method for evaluating a positive electrode active material for a non-aqueous electrolyte secondary battery, wherein a P value of 1.065 or less is determined to be suitable as an active material.