JP7110876B2 - Method for selecting substitution element for positive electrode active material for lithium ion secondary battery, method for producing positive electrode active material for lithium ion secondary battery - Google Patents

Description

The present invention relates to a method for selecting a replacement element for a positive electrode active material for lithium ion secondary batteries, and a method for producing a positive electrode active material for lithium ion secondary batteries.

As a high energy density secondary battery, the market for lithium ion secondary batteries is expanding. Lithium-ion secondary batteries have higher energy density than conventional secondary batteries such as nickel-hydrogen batteries and nickel-cadmium batteries. For this reason, it is widely used as a power source for portable terminals and small electric devices for consumer use, as a stationary power source for industrial power storage devices and load leveling devices, and as a power source for mobile bodies such as ships, railways, and automobiles. there is

Lithium ion secondary batteries, which have such a wide range of applications, are required to have even higher capacities. A composition with a Ni ratio of more than 80 atomic percent (hereinafter referred to as a composition with a Ni ratio of 80% or more) is being studied. However, when the proportion of Ni in the positive electrode active material is increased in order to increase the capacity of the battery, the crystal structure becomes unstable, resulting in a large decrease in battery capacity during charge-discharge cycles. In order to solve this problem, conventionally, by increasing the amount of Co, the stability of the crystal is maintained and the capacity retention rate during charge-discharge cycles is ensured (Patent Documents 1 and 2).

However, I do not want to increase expensive Co. In Patent Document 3, Ti is used as a substitute element instead of Co without increasing the amount of Co.

International Publication No. 2011/108598 JP 2016-122546 A International Publication No. 2017/082268

According to Patent Document 3, Ti is added to a lithium-transition metal composite oxide to form a Ti-enriched layer on the outer surface of secondary particles. In the Ti-enriched layer, the transition metal sites of the layered structure belonging to the space group R-3m are replaced with Ti, so that crystals other than the layered structure are not generated and the capacity is not lowered. It is also stated that the function of the Ti-enriched layer can suppress the formation of a NiO-like heterogeneous phase after charge-discharge cycles, suppressing the resistance increase rate to a low level and improving the cycle characteristics (capacity retention rate). ing.
However, these days, it is desired to convert to an element that is more abundant in resources and easier to obtain while having properties equal to or better than those of Ti.

Therefore, the present invention finds an additive element (hereinafter referred to as a substitution element in the present invention) that does not substantially generate a heterogeneous phase while having a composition with a Ni ratio of 80% or more and can be expected to have the same characteristics as Ti. An object of the present invention is to provide a selection method and a method for producing a positive electrode active material for a lithium ion secondary battery.

The present invention provides Li _1+a Ni _{b Me} O _2+α (1)
[In the composition formula (1), M represents a substitution element other than Li and Ni, and a, b, e and α are respectively -0.04 ≤ a ≤ 0.04, 0.80 ≤ b < 1 .0, 0<e≦0.05, b+e=1, −0.2≦α≦0.2. ] A method for selecting a substitution element for a positive electrode active material for a lithium ion secondary battery represented by The reaction temperature _TN between the Li element raw material and the Ni element raw material is measured, the reaction temperature T is compared with the reaction temperature _TN , and a substitution element M' having a reaction temperature T higher than the reaction temperature _TN is selected. step 1, and the raw material of the substitution element M' selected in step 1, and the raw material of Li and Ni, the fired powder satisfying the composition formula (1), and the composition formula (1) e = 0 (no substitution element M) is obtained, each calcination powder is subjected to X-ray diffraction analysis, and a substitution element M that does not show a diffraction peak different from the diffraction result of e = 0 is selected. A method for selecting a substitution element for a positive electrode active material for a lithium ion secondary battery, comprising step 2.

In addition, the method for selecting a substitution element for the positive electrode active material for a lithium ion secondary battery of the present invention is Li _{1+a Nib Coc Mnd Me} O _2+α (2)
[In composition formula (2), M represents a substitution element other than Li, Ni, Co, and Mn, and a, b, c, d, e, and α are respectively -0.04 ≤ a ≤ 0.04 , 0.80≦b<1.0, 0<c, 0<d, 0<e≦0.05, b+c+d+e=1, −0.2≦α≦0.2. ], wherein the reaction temperature T between the Li raw material and the raw material of the substituted element M' other than Li, Ni, Co, and Mn is Then, the reaction temperature T _N between the Li element raw material and the Ni element raw material, the reaction temperature T _C between the Li element raw material and the Co element raw material, and the reaction temperature T _M between the Li element raw material and the Mn element raw material are measured. Then, the reaction temperature T is compared with the reaction temperatures _TN , _TC , and _TM , respectively, and a substitution element _M ' having a higher reaction temperature T than each of the reaction temperatures _TN , _TC , and TM is selected. step 1, and the raw materials of the substitution element M' and the raw materials of Li, Ni, Co, and Mn selected in step 1 are used to prepare a sintered powder satisfying the composition formula (2) and the composition formula ( In 2), sintered powders in the case of e = 0 (no substitution element M) are obtained, and each of the sintered powders is subjected to X-ray diffraction analysis, and a diffraction peak different from the diffraction result of e = 0 does not appear. and a step 2 of selecting M.

The present invention comprises a selection step of selecting a substitution element M by the method of selecting a substitution element described above, and an element of preparing each raw material of Li, Ni, Co, Mn, and M based on the composition formula (2). A method for producing a positive electrode active material for a lithium ion secondary battery, comprising a raw material preparation step, a pulverizing and mixing step of pulverizing and mixing the raw material powders, and a firing step of firing the mixed powder at the same time.

ADVANTAGE OF THE INVENTION According to this invention, the selection method of the substitution element of the positive electrode active material for lithium ion secondary batteries which can be expected to obtain the characteristic excellent in a high capacity|capacitance and cycling characteristics can be provided. In addition, it is possible to provide a method for producing a positive electrode active material for a lithium ion secondary battery that has substantially no heterogeneous phase by using selected substitution elements.

4 is a graph showing TG analysis using substitution elements according to Examples of the present invention and Comparative Example 1. FIG. FIG. 5 is a graph showing XRD analysis patterns of fired powders using substitution elements according to examples of the present invention. FIG. 7 is a graph showing XRD analysis patterns of fired powder using a substitution element according to Comparative Example 2. FIG.

Hereinafter, a method for selecting a substitution element for a positive electrode active material for a lithium ion secondary battery, a method for producing a positive electrode active material for a lithium ion secondary battery, and a positive electrode active material for a lithium ion secondary battery according to one embodiment of the present invention will be described. do. Hereinafter, "for lithium ion secondary batteries" will be deleted, and simply referred to as a method for selecting a substitution element, a positive electrode active material, a method for producing the same, and the like.

In the method of selecting a substitution element according to the present embodiment, even if the positive electrode active material has a Ni ratio of 80% or more as shown in the following composition formula, if the substitution element does not substantially generate a heterogeneous phase, the layered structure can be maintained. Based on the idea that it is possible to exhibit a capacity retention ratio equivalent to that of the conventional one, candidates for substitution elements are found in the following manner.

<Positive electrode active material>
The method for selecting a substitution element according to this embodiment is the following composition formula (1)
_{Li1 + aNibMeO2 +α} (1)
[In the composition formula (1), M represents a substitution element other than Li and Ni, and a, b, e and α are respectively -0.04 ≤ a ≤ 0.04, 0.80 ≤ b < 1 .0, 0<e≦0.05, b+e=1, −0.2≦α≦0.2. ] can be used for the lithium-transition metal composite oxide represented by

Further, the method for selecting the substitution element according to the present embodiment is the following composition formula (2)
_{Li1 + aNibCocMndMeO2 + α (} 2)
[In composition formula (2), M represents a substitution element other than Li, Ni, Co, and Mn, and a, b, c, d, e, and α are respectively -0.04 ≤ a ≤ 0.04 , 0.80≦b<1.0, 0<c, 0<d, 0<e≦0.05, b+c+d+e=1, −0.2≦α≦0.2. ] is preferably used for the lithium-transition metal composite oxide represented by

The positive electrode active material represented by the composition formulas (1) and (2) has an α-NaFeO ₂ type crystal structure exhibiting a layered structure capable of intercalating and deintercalating lithium ions, and contains Li, Ni, and other than Ni. and a transition metal. This positive electrode active material is mainly composed of, for example, primary particles and secondary particles of a lithium-transition metal composite oxide, and the secondary particles are in a state in which a plurality of primary particles are aggregated and sintered together. In this lithium-transition metal composite oxide, the proportion of Ni per metal excluding Li is 80 atomic % or more, and since the Ni content is high, high charge/discharge capacity can be achieved.

On the other hand, the high nickel content tends to make the crystal structure unstable during charging and discharging. In the crystal, nickel forms layers of NiO ₂ , and lithium ions are inserted between the layers during discharge, and desorption of lithium ions occurs during charge. Intercalation and deintercalation of lithium ions during charge/discharge causes changes in lattice strain and crystal structure, which is thought to lead to a decrease in capacity retention rate during charge/discharge cycles. On the other hand, the crystal structure can be stabilized by forming a layer enriched with a substitution element M such as Ti that can suppress the formation of a NiO-like heterogeneous phase on the outer surfaces of the primary particles and secondary particles. can be expected. Such a substitution element M is selected by the selection method of the present invention. Although this selection method can be applied to both composition formulas (1) and (2), it is preferable to use composition formula (2) where a synergistic effect in addition to the stabilization by Co and Mn can be expected. In the following, the case based on the compositional formula (2) will be mainly described.

<Selection of substitution element>
In the method of selecting a substitution element according to this embodiment, the following steps 1 and 2 are performed for selection.

First, in step 1, a mixed powder of a Li raw material powder (Li source) and a raw raw material powder of a candidate substitution element M′ (M ₁ , M ₂ , M ₃ . . . ) other than Li and Ni is reacted. Measure the temperature. Here, the reaction temperature is preferably measured by thermogravimetric analysis (TG analysis). By TG analysis, the change in weight loss due to temperature rise was measured, and the temperatures at which the rate of weight loss due to reaction was 1/2 of the value at 900° C. were determined as reaction temperatures T ₁ , T ₂ , T ₃ . On the other hand, the same TG analysis was performed on the mixed powder of the Li raw material powder and the Ni, Co, and Mn raw material powders, and the weight reduction rate due to each reaction was 1/2 of the value at a temperature of 900 ° C. Corresponding reaction temperatures were obtained, and the reaction temperature of Ni was T _N , the reaction temperature of Co was T _C , and the reaction temperature of Mn was T _M .

The reason why the reaction temperature in the present invention is defined as "the temperature at which the rate of weight loss due to the reaction corresponds to 1/2 of the value at a temperature of 900° C." will be described below. First, in the present invention, since the Ni ratio is as high as 80% or more, if the firing temperature exceeds 900° C., cation mixing in which Ni is mixed into the Li layer increases and the layered structure tends to collapse. Since such a positive electrode active material causes a decrease in capacity, 900° C. is set as the upper limit. Next, an index for ranking the "reactivity between the Li source and each substitution element M'" up to 900 ° C. is important. is gradually formed, CO ₂ gas is released, and the weight decreases. Since this reaction process differs for each substituting element and is complicated, the intermediate process in which the reaction progresses, "the reaction temperature at which the rate of weight loss due to the reaction is equivalent to 1/2 of the value at a temperature of 900°C" is experimentally measured. Then, the ranking of each substituting element is evaluated depending on the temperature. Besides the TG analysis, for example, differential scanning calorimetry (DSC) or evolved gas analysis (EGA) can be used.

_Next , the reaction temperatures _{T 1} , _{T 2} , _{T 3} , . , T _C , and T _M are selected. For example, if T ₁ and T ₂ are larger than T _N , T _C , and T _M , but even one of T ₃ is not satisfied, the elements T ₁ and T ₂ are candidates for the replacement element M. However _, the elements of T3 will be excluded here. In composition formula (1), the reaction temperature _TN of Ni measured in the same manner is compared with the reaction temperature T, and a substitution element having a reaction temperature T higher than the reaction temperature _TN is selected.

According to step 1, the substitution element M′ (e.g., M ₁ , M ₂ ) that can be selected has a higher reaction temperature with the Li source than Ni, Co, and Mn, so the reaction between the Li source and Ni, Co, and Mn is progressing, facilitating the formation of a ternary layered structure. This reduces the possibility of forming crystals other than the layered structure required for the positive electrode active material. Since these substitution elements M' progress slowly in the reaction with the Li source, it can be expected that the substitution elements M' are effectively concentrated on the outer surface of the active material particles.

Next, in step 2, for each of the substituting elements M′ (e.g., M ₁ and M ₂ ) selected in step 1, a crystal structure suitable for the lithium-transition metal composite oxide is obtained when co-fired with other raw materials. determine whether or not A positive electrode active material satisfying the above composition formula (2) is obtained by using raw material powder of each substitution element M′ (for example, M ₁ and M ₂ ) selected in step 1 and raw material powder of Li, Ni, Co, and Mn. A calcined powder of the substance is obtained. On the other hand, e=0 in the composition formula (2), that is, a sintered powder containing no substitution element M′ is similarly obtained. Then, each of these fired powders is subjected to X-ray diffraction analysis (XRD analysis). At this time, the diffraction result of e=0 is used as a standard, and the diffraction result of e=0 and the diffraction result of each fired powder are compared. As a result, an element is selected as the substitution element M that does not produce a diffraction peak different from the diffraction result of e=0, that is, does not show a heterophasic peak. Here, in the present invention, the fact that different diffraction peaks (heterogeneous peaks) do not appear means that the intensity of the XRD analysis is below the background, which substantially corresponds to noise and can be ignored. It is assumed that there is substantially no formation of foreign phases in such cases.

According to step 2, the substitution element selected in step 1 from the viewpoint that it can be added without breaking the layered structure of the lithium transition metal composite oxide is fired together with other raw materials, and the crystallinity of the fired body is measured by XRD. It is selected by confirming the suitability of the substitution element that does not cause heterogeneous phases. If a crystal (heterogeneous phase) other than a layered structure is formed during firing of the lithium-transition metal composite oxide, the heterogeneous phase does not act as a positive electrode material for the battery. Resistance rises, leading to deterioration of battery performance. By providing this step, it is possible to obtain a positive electrode active material with good performance without generation of heterogeneous phases.

As a procedure for XRD analysis, the XRD pattern of a composition of e = 0 of Li, Ni, Co, and Mn that does not contain a substitution element is used as a standard, and a composition (0 < e ), and diffraction peaks not detected in the standard are determined to be heterophases. This is to determine whether or not there is a possibility that the addition of the substitution element selected in step 1 may cause a decrease in capacity or an increase in resistance of the positive electrode.
If the replacement element M that satisfies step 1 and step 2 can be selected as described above, then the selected replacement element M can be used to carry out the following manufacturing method of the present invention.

<Method for producing positive electrode active material>
In the method for producing a positive electrode active material according to this embodiment, after the selection step of selecting the substitution element M, the following steps 1 to 3 are performed.

Step 1 is a step of preparing a raw material powder of Li, a raw material powder of Ni, Co, Mn and a substitution element M based on the composition formulas (1) and (2) (raw material preparation step ).
In step 1, a raw material powder containing Li, Ni, Co, Mn and a substitution element M is weighed based on, for example, the compositional formula (2). Examples of forms of compounds used as raw materials include lithium carbonate, lithium acetate, lithium nitrate, lithium sulfate, lithium chloride, and lithium hydroxide. Carbonates, hydroxides, oxyhydroxides, acetates, citrates, oxides, and the like are used as compounds of metals other than lithium such as Ni, Co, and Mn. The necessary amount of the compound is determined from the purity of the elements of the raw materials contained in the compound. If the composition of the raw material is deviated, the sintering state will change even if the temperature is the same in the subsequent sintering of the raw material powder, making it impossible to obtain a sintered powder having a predetermined crystal structure. Therefore, the purity of the raw materials in the compound and the composition of the mixed powder of all raw materials before firing are analyzed for deviations.

Step 2 is a step of pulverizing and mixing the powder of the all-element compound prepared in step 1 (pulverizing and mixing step).
In step 2, pulverization and mixing are performed in order to make the powder of the all-element raw material compound into a mixed state suitable for firing in the next step 3. The particle size of the raw material is not uniform, and varies depending on the type of raw material/compound, purchaser, and the like. Since the particle size of the raw material compound affects the mixing state, it is preferable that the particle size is within a predetermined range. Therefore, the all-element raw material is pulverized to adjust the particle size. In addition, if the raw material powder is not sufficiently mixed and the distribution of the raw material is uneven, the crystal structure of the fired powder after firing does not grow to the desired layered structure, or crystals other than the layered structure are generated. Because of this possibility, it is preferable to grind and mix for uniformity. A ball mill, a bead mill, a jet mill, or the like can be used as means for pulverizing the raw material. The raw material powder is pulverized to a predetermined particle size by collision and friction with media and liners for pulverization.

A granulation step is preferably performed after the pulverization and mixing step. The mixture obtained in the pulverization and mixing step is granulated to obtain secondary particles (granules) in which particles are aggregated. Granulation of the mixture may be performed using either dry granulation or wet granulation. A spray granulation method is particularly preferable as the granulation method for granulating the mixture. Various systems such as a two-fluid nozzle system, a four-fluid nozzle system, and a disk system can be used as the spray granulator. In the case of the spray granulation method, slurry of a mixture obtained by precision mixing and pulverization by wet pulverization can be granulated while being dried. In addition, by adjusting the slurry concentration, spray pressure, disk rotation speed, etc., it is possible to precisely control the particle size of the secondary particles within a predetermined range. can be efficiently obtained.

Step 3 is a step of simultaneously firing the all-element mixed powder pulverized and mixed in step 2 (firing step).
In step 3, a layered structure crystal composed of Ni, Co, Mn and the substitution element M is produced by simultaneously firing the mixed powder of all elemental raw materials. At this time, the substituting element M, which has the highest reaction initiation temperature, reacts last with the secondary particles that have already formed a layered structure, so that a layer in which the substituting element M is concentrated is formed on the outer surface of the particle. becomes easier. A feature of the present invention is the means for selecting the substitution element M that facilitates the formation of the concentrated layer on the outer surface of the particle. Further, it is also a feature of the manufacturing method of the present invention that the all-element raw material powder containing the selected substitution element M is heat-treated at the same time and sintered by a solid-phase reaction. As a means for sintering the raw material powder, a sintering furnace such as a rotary kiln or a roller hearth kiln can be used.

Here, in order to obtain a layered structure crystal in the firing of the mixed powder of all elemental raw materials, it is preferable to increase the firing temperature by one step or step by step and perform multi-step firing according to the composition.

For example, when the compound form of the raw materials is Li, Co, and Mn in the form of carbonates, Ni in hydroxides, and the substitution element M in oxides in multistage sintering by a solid-phase method, low temperatures (approximately 500° C. to 700° C. ℃ or less), _CO2 is gradually released from the carbonate to form an oxide, and the hydroxide is also gradually thermally decomposed to proceed with the reaction to form an oxide. Diffusion progresses. In firing at medium temperature (approximately 700° C. or higher and 800° C. or lower), Li is melted and liquid phase diffusion progresses, and reaction between other raw materials (oxides) and Li progresses.

In the subsequent high-temperature firing (approximately 800° C. or higher and 900° C. or lower), the diffusion reaction between Li and other raw materials and between other raw materials proceeds further to produce a lithium-transition metal composite oxide having a layered structure. As described above, simultaneous sintering of all elemental raw materials by multi-stage sintering facilitates obtaining a positive electrode active material having a layered structure containing all of Li, Ni, Co, Mn and the substituting element M, which is preferable.

In addition, the lithium-transition metal composite oxide according to the present embodiment includes, in addition to the lithium-transition metal composite oxide as the main component, impurities derived from raw materials and manufacturing processes, and other components that coat the particles of the lithium-transition metal composite oxide. (boron, phosphorus, sulfur, fluorine, organic matter, etc.), which are mixed with the particles of the lithium-transition metal composite oxide.
By subjecting the substituting element M obtained in step 2 to the above-described single-stage or multi-stage heat treatment together with the raw materials of Li, Ni, Co, and Mn, the above problems can be solved, and the capacity and performance of the battery do not decrease. It becomes possible to obtain a positive electrode active material.

An example of selection of the substitution element M will be described below.
Regarding the substituting element M', first, based on Step 1, the reaction temperature was measured by TG analysis in order to grasp the reactivity with the Li element raw material powder. Al, Ga, Mg, Zr, and Zn were listed as candidates for the replacement element M', and Ti was listed as a reference element. Ni, Co, Mn and the substitution element M' are oxides, and Li is a carbonate. The Li element raw material and the raw material of the substituting element M', the Li element raw material and the Ni element raw material, the Li element raw material and the Co element raw material, and the Li element raw material and the Mn element raw material were weighed at a molar ratio of 1:1. The results of TG analysis are shown in FIG. In the figure, the horizontal axis is the temperature, and the vertical axis is the reduction rate of the sample weight relative to the initial sample weight. The test conditions were a heating rate of 10°C/min and heating from room temperature to 900°C.

The reaction temperature was determined from the TG analysis results. Here, the reaction temperature is defined as the temperature at which the rate of weight loss due to the reaction corresponds to 1/2 of the value at a temperature of 900°C. This is because the weight reduction rate with respect to the temperature rise rate differs depending on the element, as described above.
From FIG. 1, the reaction temperature _TN of Ni was approximately 610°C, the reaction temperature TC of Co was approximately 590° _C , and the reaction temperature TM of _Mn was approximately 410°C. Therefore, the reaction temperature T for judging whether the substitution element is acceptable is 610° C. in this embodiment.

On the other hand, the reaction temperature of each oxide of Al, Ga, Mg, Zr, Zn and Ti is about 760° C. for Al, about 610° C. for Ga, about 850° C. for Mg, about 680° C. for Zr, and about 680° C. for Zn. was about 900°C and Ti was about 620°C. Therefore, the reaction temperature of each of Al, Ga, Mg, Zr and Zn was higher than that of Ni, Mn and Co and was equal to or higher than the pass/fail judgment temperature. Moreover, it was equal to or higher than that of Ti.

As a result of the above step 1, the above-described five substitution elements have higher reaction temperatures with Li than Ni, Co, and Mn constituting the positive electrode active material, and when used as substitution elements (additional elements), the layered structure is broken. It was confirmed that no heterogeneous phase could be generated.

(Comparative example 1)
B (boron) and La were used as comparative examples. Both B and La are oxides, and TG analysis was performed in the same manner as in the above-described example. The results are shown in FIG.
From FIG. 1, the reaction temperature of B was about 190°C, and the reaction temperature of La was about 730°C. La has a higher reaction temperature than Ni, Mn, and Co, and step 1 is cleared. On the other hand, since B has a low reaction temperature and is a semimetal, it is judged to be unsuitable as the substitution element M.

Subsequently, based on Step 2, a sintered powder having a composition of Li _1.02 Ni _0.90 Mn _0.05 Co _0.03 M _0.02 was produced and subjected to XRD analysis. The samples were obtained by filling Li ₂ CO ₃ , Ni(OH) ₂ , MnCO ₃ , CoCO ₃ and substituting element oxide raw material powders together with pure water in a ball mill, pulverizing them for a predetermined time, and then vacuum-drying and mixing the pulverized slurry. Powdered. The mixed powder has an average particle size of 0.5 to 0.6 μm. Firing of the mixed powder was carried out in three stages: low-temperature (650° C.×10 hr) temporary calcination, medium-temperature (755° C.×10 hr) intermediate calcination, and high-temperature main calcination (840° C.×4 hr).
XRD analysis was performed on the sintered powder of each composition to which Al, Ga, Mg, Zr, Zn and Ti, which are candidates for substitution elements selected in step 1, were added. The results are shown in FIG. XRD analysis was performed under the following conditions.

<Powder X-ray diffraction measurement>
An XRD (X-ray diffraction) measurement method will be described below as a method for confirming the crystal structure. A powder X-ray diffractometer "RINT (manufactured by Rigaku)" was used.
The fired powder was filled in an aluminum sample holder. After that, measurement was performed under the following conditions: radiation source: CuKα, tube voltage: 40 kV, tube current: 100 mA, scanning angle: 15 to 80°, scanning speed: 1.0°/min, sampling interval: 0.02°/step.

FIG. 2 also shows the case of the standard composition (e=0) in which no substitution element is added.
From FIG. 2, the diffraction pattern when Al, Ga, Mg, Zr, Zn and Ti are added is the same as the diffraction pattern of the standard composition, and no heterogeneous peak larger than the background was detected. It was confirmed that no heterogeneous phase was generated in the main firing for each element.

(Comparative example 2)
As a comparative example, the replacement element La, whose reaction temperature was higher than that of Ni, Mn, and Co in step 1, was sintered at the same composition ratio, and the results of the XRD analysis are shown in FIG. A different-phase peak was confirmed at the position indicated by the circle in the figure with respect to the standard composition. In La, it can be determined that a crystal (heterogeneous phase) different from the standard composition is generated. Therefore, La cannot clear Step 2 and is judged to be unsuitable as the replacement element M.

As described above, when adding the replacement element to the positive electrode active material using the lithium-transition metal composite oxide, by performing the above-described steps 1 and 2 to select the replacement element M, the fired lithium-transition metal composite The oxide does not contain a heterogeneous phase other than a layered structure, and it is possible to obtain a positive electrode that is expected to suppress an increase in resistance, thereby suppressing a decrease in capacity retention rate and a decrease in charge/discharge capacity.

Claims (3)

_{Li1 + aNibMeO2 +α} (1)
[In the composition formula (1), M represents a substitution element other than Li and Ni, and a, b, e and α are respectively -0.04 ≤ a ≤ 0.04, 0.80 ≤ b < 1 .0, 0<e≦0.05, b+e=1, −0.2≦α≦0.2. ] A method for selecting a substitution element for a positive electrode active material for a lithium ion secondary battery represented by
measuring the reaction temperature T between the Li raw material and the raw material of the substitution element M' other than Li and Ni,
Measuring the reaction temperature _TN between the Li element raw material and the Ni element raw material,
a step 1 of comparing the reaction temperature T and the reaction temperature _TN and selecting a substitution element M' having a higher reaction temperature T than the reaction temperature _TN ;
Using the raw materials of the substitution element M' selected in step 1 and the raw materials of Li and Ni, the fired powder satisfying the composition formula (1) and the composition formula (1) in the case of e = 0 Obtain each baked powder,
Step 2 of performing X-ray diffraction analysis of each of the fired powders and selecting a substitution element M that does not show a diffraction peak different from the diffraction result of e = 0;
A method for selecting a substitution element for a positive electrode active material for a lithium ion secondary battery, comprising: _{Li1 + aNibCocMndMeO2 + α (} 2)
[In composition formula (2), M represents a substitution element other than Li, Ni, Co, and Mn, and a, b, c, d, e, and α are respectively -0.04 ≤ a ≤ 0.04 , 0.80≦b<1.0, 0<c, 0<d, 0<e≦0.05, b+c+d+e=1, −0.2≦α≦0.2. ] A method for selecting a substitution element for a positive electrode active material for a lithium ion secondary battery represented by
measuring the reaction temperature T between the Li raw material and the raw material of the substitution element M' other than Li, Ni, Co, and Mn,
Measuring the reaction temperature T _N between the Li element raw material and the Ni element raw material, the reaction temperature T _C between the Li element raw material and the Co element raw material, and the reaction temperature T _M between the Li element raw material and the Mn element raw material,
A step of comparing the reaction temperature T with the reaction temperatures _TN , _TC , and _TM , respectively, and selecting a substitution element _M ' having a higher reaction temperature T than each of the reaction temperatures _TN , _TC , and TM. 1 and
Using the raw material of the substitution element M' selected in step 1 and the raw material of Li, Ni, Co, and Mn, the sintered powder satisfying the composition formula (2) and e = in the composition formula (2) Obtaining each fired powder in the case of 0,
Step 2 of performing X-ray diffraction analysis of each of the fired powders and selecting a substitution element M that does not show a diffraction peak different from the diffraction result of e = 0;
A method for selecting a substitution element for a positive electrode active material for a lithium ion secondary battery, comprising: A selection step of selecting a substitution element M by the substitution element selection method according to claim 2;
a raw material preparation step of preparing raw materials of Li, Ni, Co, Mn, and M based on the composition formula (2);
A pulverizing and mixing step of pulverizing and mixing the raw material powders;
A sintering step of simultaneously sintering the mixed powder;
A method for producing a positive electrode active material for a lithium ion secondary battery, comprising:

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