JP2020053275A - Method for selecting substitution element for positive electrode active material for lithium ion secondary battery, method for manufacturing positive electrode active material for lithium ion secondary battery and positive electrode active material for lithium ion secondary battery - Google Patents

Abstract

To provide a selection method for finding a substitution element suitable for a positive electrode active material for a lithium ion secondary battery having a Ni ratio of 80% or more.SOLUTION: A method of selecting a substitution element for a positive electrode active material for a lithium ion secondary battery includes a step 1 of measuring a reaction temperature T between a Li element raw material and a raw element of a substitution element M' other than Li and Ni, measuring a reaction temperature Tbetween the Li element raw material and a Ni element raw material, comparing the reaction temperature T with the reaction temperature T, and selecting the substitution element M' with which the reaction temperature T is higher than the reaction temperature T, and a step 2 for using the element raw material of the substitution element M' selected in step 1 and the element raw materials of Li and Ni to obtain each of burned powder satisfying a composition formula of 80% or more in Ni ratio, and standard burned powder in the case of e=0 (no substitution element M), performing X-ray diffraction analysis on each burned powder, and selecting a substitution element M with which a diffraction peak different from a diffraction result in the case of e=0 does not appear.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for selecting a substitution element of 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.

  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-metal hydride batteries and nickel-cadmium batteries. Therefore, it is widely used as a power supply for portable terminals and small electric devices for consumer use, a stationary power supply for power storage devices and load leveling devices for industrial use, and a power supply for mobile bodies such as ships, railways and automobiles. I have.

  Such lithium ion secondary batteries having a wide range of applications are required to have higher capacities, and the proportion of Ni suitable for higher capacities in the positive electrode active material has been increased, and metal elements other than Li A composition in which the proportion of Ni is greater than 80 atomic% (hereinafter referred to as a composition having 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, and the decrease in battery capacity in the charge / discharge cycle is increased. In order to solve this problem, conventionally, the stability of the crystal has been maintained by increasing the amount of Co, and the capacity retention rate during the charge / discharge cycle has been secured (Patent Documents 1 and 2).

  However, I do not want to increase expensive Co. Patent Literature 3 uses Ti as a substitute element without increasing the amount of Co.

International Publication No. 2011/108598 JP-A-2006-122546 WO 2017/082268 A

According to Patent Literature 3, Ti is added to a lithium transition metal composite oxide to form a concentrated layer of Ti on the outer surface of the secondary particles. Since the Ti-enriched layer takes a form in which the transition metal site of the layered structure belonging to the space group R-3m is substituted with Ti, crystals other than the layered structure are not generated and the capacity does not decrease. Further, it is described that by the function of the Ti-concentrated layer, the generation of a NiO-like heterophase after the charge / discharge cycle can be suppressed, the rate of increase in resistance is suppressed low, and the cycle characteristics (capacity retention rate) are improved. ing.
However, in recent years, it has been desired to convert to an element that has properties equal to or higher than that of Ti, but is more abundant in resources and easily available.

  Thus, the present invention finds an additive element (hereinafter, referred to as a substitution element in the present invention) that has substantially the same composition as that of Ti without substantially forming a heterogeneous phase despite having a composition with a Ni ratio of 80% or more. It is an object to provide a selection method, 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.

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 -0.04 ≦ a ≦ 0.04 and 0.80 ≦ b <1, respectively. 0.0, 0 <e ≦ 0.05, b + e = 1, and −0.2 ≦ α ≦ 0.2. A method for selecting a substitution element of a positive electrode active material for a lithium ion secondary battery, wherein a reaction temperature T between a raw material of Li and a raw material of a replacement element M ′ other than Li and Ni is measured. measuring the reaction temperature T _N and Li-containing material and Ni containing material, the selection and reaction temperature T, and compares the reaction temperature T _N, the reaction temperature T is higher substitution element M'than the reaction temperature T _N Step 1, a raw material of the replacement element M ′ selected in Step 1, and a calcined powder satisfying the composition formula (1) using the raw materials of Li and Ni, and e in the composition formula (1). = 0 (no substitution element M), respectively, and obtain a fired powder, perform X-ray diffraction analysis of each fired powder, and select a substitution element M that does not show a diffraction peak different from the diffraction result of e = 0. Substituting element for positive electrode active material for lithium ion secondary battery having step 2 A selection method.

Further, the method of selecting a substitution element of the positive electrode active material for a lithium ion secondary battery of the present _{invention, Li 1 + a Ni b Co} c Mn d M e O 2 + α ··· (2)
[In the composition formula (2), M represents a substitution element other than Li, Ni, Co, and Mn, and a, b, c, d, e, and α are -0.04 ≦ a ≦ 0.04, respectively. , 0.80 ≦ b <1.0, 0 <c, 0 <d, 0 <e ≦ 0.05, b + c + d + e = 1, and −0.2 ≦ α ≦ 0.2. The method of selecting a substitution element for a positive electrode active material for a lithium ion secondary battery represented by the formula: wherein the reaction temperature T between the Li element and the element of the substitution element M ′ other than Li, Ni, Co, and Mn is determined. measured, measuring the reaction temperature T _N of the Li-containing material and Ni containing _material, the reaction temperature T _M of the reaction temperature T _C and the Li-containing material and Mn raw material of the Li-containing material and Co-containing raw material, respectively and, selection and said reaction temperature T, the reaction temperature _{T N,} T C, compared to _{T M} respectively, the reaction temperature _{T N,} T C, the reaction temperature T is higher substitution element M'than each of _{T M} Step 1, using the raw material of the replacement element M ′ selected in Step 1 and the raw materials of Li, Ni, Co, and Mn, and a calcined powder satisfying the composition formula (2); In 2), the fired powder in the case of e = 0 (no substitution element M) is used. It is obtained, each of said fired powder X-ray diffraction analysis, and step 2 for selecting the substituting element M that diffraction peaks different from the diffraction results of e = 0 does not appear, and has a.

  The present invention provides a selection step of selecting a replacement element M by the above-described method for selecting a replacement element, and a method 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 preparing step, a pulverizing and mixing step of pulverizing and mixing the raw material powders, and a firing step of simultaneously firing the mixed powders.

The present invention is a positive electrode active material for a lithium ion secondary battery including the substitution element M selected by the method for selecting a substitution element described above,
Li _{1 + a} Ni _b Co _c M n _{d Me} O _{2 + α} (2)
[In the composition formula (2), M represents a substitution element other than Li, Ni, Co, and Mn, and a, b, c, d, e, and α are -0.04 ≦ a ≦ 0.04, respectively. , 0.80 ≦ b <1.0, 0 <c, 0 <d, 0 <e ≦ 0.05, b + c + d + e = 1, and −0.2 ≦ α ≦ 0.2. And wherein the substitution element M is at least one element selected from the group consisting of Al, Ga, Mg, Zr, and Zn, and is a positive electrode active material for a lithium ion secondary battery.

  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 high capacity and the characteristic excellent in the cycle characteristic 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 and a positive electrode active material for a lithium ion secondary battery, which have substantially no foreign phase using the selected substitution element.

4 is a graph showing TG analysis using a substitution element according to an example of the present invention and Comparative Example 1. It is a graph which shows the pattern of XRD analysis of the baked powder using the substitution element concerning the example of the present invention. 9 is a graph showing an XRD analysis pattern of a fired powder using a substitution element according to Comparative Example 2.

  Hereinafter, a method for selecting a substitution element of 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 an embodiment of the present invention will be described. I do. Hereinafter, “for lithium ion secondary batteries” will be deleted, and simply described as a method for selecting a replacement element, a positive electrode active material, a method for producing the same, and the like.

  The method for selecting a replacement element according to the present embodiment is such that a layered structure is maintained even in a cathode active material having a Ni ratio of 80% or more as long as the replacement element does not substantially generate a heterogeneous phase as in the following composition formula. Thus, based on the idea that a capacity retention ratio equivalent to that of a conventional one can be exhibited, a candidate for a substitution element is found as follows.

<Positive electrode active material>
The method for selecting a substitution element according to the present embodiment is based on the following composition formula (1):
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 -0.04 ≦ a ≦ 0.04 and 0.80 ≦ b <1, respectively. 0.0, 0 <e ≦ 0.05, b + e = 1, and −0.2 ≦ α ≦ 0.2. ] The lithium transition metal composite oxide represented by the formula:

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

The positive electrode active material represented by the composition formulas (1) and (2) has an α-NaFeO ₂ type crystal structure having a layered structure capable of inserting and removing lithium ions, and includes Li, Ni, and other than Ni. And a transition metal. The 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. The lithium transition metal composite oxide has a Ni content of 80 atomic% or more per metal excluding Li, and has a high Ni content, so that a high charge / discharge capacity can be realized.

On the other hand, the high nickel content tends to make the crystal structure unstable during charge and discharge. Nickel forms a NiO ₂ layer in the crystal, and lithium ions are inserted between the layers during discharging, and the lithium ions are desorbed during charging. It is considered that lattice distortion and a change in crystal structure occur due to insertion and desorption of lithium ions during charge / discharge, which leads to a reduction in capacity retention rate in charge / discharge cycles. On the other hand, if a layer in which the substitution element M capable of suppressing the formation of a NiO-like hetero phase such as Ti is concentrated is formed on the outer surfaces of the primary particles and the secondary particles, the crystal structure can be stabilized. Can be expected. Such a substitution element M is selected by the selection method of the present invention. This selection method can be applied to either the composition formulas (1) or (2), but it is considered to be preferable to use the composition formula (2), which can expect a synergistic effect in addition to stabilization by Co and Mn. Hereinafter, the case according to the composition formula (2) will be mainly described.

<Selection of substitution element>
The method for selecting a replacement element according to the present embodiment is performed by performing the following steps 1 and 2.

First, step 1 is to react a mixed powder of a Li raw material powder (Li source) and a raw material powder of a substitution element M ′ (M ₁ , M ₂ , M ₃ ...) Which is a candidate other than Li and Ni. Measure the temperature. Here, the reaction temperature is preferably measured by thermogravimetric analysis (TG analysis). The change in weight loss due to temperature rise was measured by TG analysis, and the temperature at which the weight loss ratio due to the reaction was １ ／ of the value at 900 ° C. was 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 ratio due to each reaction was reduced to half the value at a temperature of 900 ° C. The corresponding reaction temperature was determined, 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 set to "the temperature at which the weight loss ratio due to the reaction is 1/2 of the value at a temperature of 900 ° C" will be described below. First, since the Ni ratio is as high as 80% or more in the present invention, if the firing temperature exceeds 900 ° C., cation mixing in which Ni is mixed in the Li layer and collapse of the layered structure are likely to occur. Since the capacity of such a positive electrode active material decreases, 900 ° C. is set as the upper limit. Next, an index that ranks and evaluates the “reactivity between the Li source and each of the substitution elements M ′” up to 900 ° C. is important, and the Li source and each of the substitution elements M ′ are composed of a Li—M′—O oxide Is gradually formed, and the CO ₂ gas is released to reduce the weight. Since this reaction process is different and complicated for each substitution element, the intermediate process in which the reaction proceeds, "reaction temperature at which the weight loss ratio due to the reaction corresponds to 1/2 of the value at a temperature of 900 ° C" is experimentally measured. Then, the order of each substitution element is evaluated at the high and low temperatures. In addition to the TG analysis, for example, differential scanning calorimetry (DSC) or generated gas analysis (EGA) can be used.

The reaction temperature of each of the substituting element _{M'T 1, T 2, T} 3 ... and, Ni, Co, reaction temperature _T N of _Mn, T C, and _{T M} respectively compared, the reaction temperature _{T N} , T _C , and T _M are selected. For _example, T 1, _{T 2} are _{T N,} T C, but satisfies the greater than _{T M, T 3} if do not satisfy even one element _{T 1} and _{T 2} are the candidates for substitution elements M made, but the element of T ₃ will be excluded here. In the composition formula (1), the reaction temperature T _{N of} Ni measured in the same manner is compared with the reaction temperature T, and a substitution element having a higher reaction temperature T than the reaction temperature T _N is selected.

According to step 1, the selectable substitution element M ′ (eg, M ₁ , M ₂ ) has a higher reaction temperature with the Li source than Ni, Co, and Mn, and thus the reaction between the Li source and Ni, Co, and Mn. And a ternary layered structure is easily formed. Thereby, the possibility that crystals other than the layered structure required for the positive electrode active material are generated is reduced. And since these substitution elements M 'react slowly with the Li source, it can be expected that the substitution elements M' are effectively concentrated on the outer surfaces of the active material particles.

Next, in Step 2, a crystal structure suitable for a lithium transition metal composite oxide is obtained when each of the substitution elements M ′ (for example, M ₁ and M ₂ ) selected in Step 1 is co-fired with another raw material. It is determined whether it can be performed. Using the raw material powder of each of the substitution elements M ′ (for example, M ₁ and M ₂ ) selected in Step 1 and the raw material powders of Li, Ni, Co, and Mn, the positive electrode active material satisfying the above composition formula (2). Obtain a calcined powder of the substance. On the other hand, in the composition formula (2), e = 0, that is, a calcined powder containing no substitution element M ′ is obtained in the same manner. Then, these calcined powders are subjected to X-ray diffraction analysis (XRD analysis). At this time, the diffraction result of e = 0 is set as a standard, and the diffraction result of e = 0 is compared with the diffraction result of each fired powder. As a result, an element in which a diffraction peak different from the diffraction result of e = 0 is not generated, that is, an element in which a heterophase peak does not appear is selected as the substitution element M. Here, the expression that no different diffraction peaks (heterophase peaks) appear in the present invention means that the intensity of the XRD analysis is lower than the background, which is substantially equivalent to noise and negligible. In such a case, it is assumed that substantially no foreign phase is generated.

  According to step 2, the replacement element selected from the viewpoint that it can be added without breaking the layered structure of the lithium transition metal composite oxide in step 1 is fired together with other raw materials, and the crystallinity of the fired body is determined by XRD. After confirming, the appropriateness of the substitution element that does not cause a different phase is determined. If crystals (heterophase) other than the layered structure are generated during firing of the lithium transition metal composite oxide, the heterophase does not act as a positive electrode material of the battery, so that the capacity at the time of charge / discharge decreases and, depending on the form of the heterophase, The resistance increases, leading to a decrease in battery performance. By providing this step, it is possible to obtain a positive electrode active material having good performance without generation of a different phase.

As a procedure of the XRD analysis, an XRD pattern of a composition of e = 0 only of Li, Ni, Co, and Mn containing no substitution element was used as a standard, and a composition obtained by adding a substitution element M ′ thereto (0 <e). The diffraction peaks not detected by the standard are judged to be different phases by comparing the XRD patterns in the above (2). This is to judge whether there is a possibility that the capacity of the positive electrode may decrease or the resistance may increase when the substitution element selected in step 1 is added.
As described above, if it is possible to select the replacement element M that satisfies Steps 1 and 2, the following manufacturing method of the present invention may be performed using the selected replacement element M.

<Production method of positive electrode active material>
The method for producing a positive electrode active material according to the present embodiment is performed in the following steps 1 to 3 after the selection step of selecting the replacement element M.

Step 1 is a step of preparing a raw material powder of Li and 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, for example, based on the composition formula (2). Examples of the form of the compound used as the raw material include lithium carbonate such as lithium carbonate, lithium acetate, lithium nitrate, lithium sulfate, lithium chloride, and lithium hydroxide. As compounds of metals other than lithium, such as Ni, Co, and Mn, carbonates, hydroxides, oxyhydroxides, acetates, citrates, oxides, and the like are used. The required amount of the compound is determined from the purity of the element of the raw material contained in the compound. If the composition of the raw materials is deviated, in the subsequent stage of firing the raw material powder, the firing state changes even at the same temperature, and a fired powder having a predetermined crystal structure cannot be obtained. Therefore, the purity of the raw material in the compound and the composition of the whole raw material mixed powder before firing are analyzed for deviation.

Step 2 is a step of pulverizing and mixing the powder of all the raw material compounds prepared in step 1 (pulverizing and mixing step).
In step 2, pulverization and mixing are performed to bring the powder of all the raw material compounds into a mixed state suitable for the calcination performed in step 3 below. The particle size of the raw material is not uniform and varies depending on the type of raw material / compound, the place of purchase, and the like. Since the particle size of the raw material compound affects the mixing state, it is preferable that the particle size falls within a predetermined range. Therefore, all the raw materials are pulverized to adjust the particle size. In addition, when 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 intended layered structure, or crystals other than the layered structure are generated. Because of the possibility, it is preferable to grind and mix the mixture to obtain a uniform state. As a means for pulverizing the raw material, a ball mill, a bead mill, a jet mill or the like can be used. The raw material powder is pulverized to a predetermined particle size by collision or friction with a pulverizing medium or liner.

  After the pulverizing and mixing step, a granulation step is preferably performed. The mixture obtained in the pulverizing and mixing step is granulated to obtain secondary particles (granules) in which the particles are aggregated. Granulation of the mixture may be performed using either dry granulation or wet granulation. As the granulation method for granulating the mixture, spray granulation is particularly preferred. As the spray granulator, various systems such as a two-fluid nozzle system, a four-fluid nozzle system, and a disk system can be used. In the case of the spray granulation method, the slurry of the mixture that has been precisely mixed and pulverized by wet pulverization can be granulated while drying. In addition, it is possible to precisely control the particle diameter of the secondary particles within a predetermined range by adjusting the concentration of the slurry, the spray pressure, the number of rotations of the disk, etc. Can be obtained efficiently.

Step 3 is a step of simultaneously firing all raw material mixed powders ground and mixed in step 2 (firing step).
In step 3, a powder having a layered structure composed of Ni, Co, Mn, and the substituting element M is generated by simultaneously firing powders in which all the raw materials are mixed. At this time, since the substitution element M having the highest reaction initiation temperature causes a reaction at the end with respect to the secondary particles already having the layered structure, a layer in which the substitution element M is concentrated is formed on the outer surface of the particles. It will be easier. The feature of the present invention is a means for selecting the substitution element M that facilitates disposing the concentrated layer on the outer surface of the particle. It is also a feature of the production method of the present invention that all the raw material powders containing the selected substitution element M are heat-treated at the same time and fired by a solid-phase reaction. As a means for firing the raw material powder, a firing furnace such as a rotary kiln or a roller hearth kiln can be used.

  Here, in order to obtain a crystal having a layered structure in the firing of the mixed powder of all the raw materials, it is preferable to raise the firing temperature in one step or stepwise according to the composition and fire in multiple steps.

For example, when the compound form of the raw material is Li, Co, Mn as carbonate, Ni as hydroxide, and substitution element M as oxide by multi-stage sintering by the solid-phase method, low temperature (about 500 ° C. to 700 ° C.) (° C. or lower), CO ₂ is gradually released from the carbonate, and the hydroxide and the hydroxide are also gradually thermally decomposed and the reaction to the oxide proceeds, and the solid phase on the particle surface between the raw materials is also increased. Diffusion proceeds. In baking at a medium temperature (about 700 ° C. or more and 800 ° C. or less), Li melts and liquid phase diffusion advances, and the reaction between another elementary material (oxide) and Li advances.

  In the subsequent firing at a high temperature (about 800 ° C. or more and 900 ° C. or less), the diffusion reaction between Li and other raw materials and the other raw materials further proceeds, and a layered lithium-transition metal composite oxide is produced. As described above, simultaneous firing of all the raw materials is preferably performed by performing multi-stage firing because a positive electrode active material having a layered structure containing all of Li, Ni, Co, Mn, and the substitution element M is easily obtained.

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

In the following, an example according to the selection of the substitution element M will be described.
First, the reaction temperature of the substitution element M ′ was measured by TG analysis in order to ascertain the reactivity with the Li raw material powder based on Step 1. As candidates for the substitution element M ′, Al, Ga, Mg, Zr, and Zn were mentioned, and Ti was mentioned as a reference element. Ni, Co, Mn and the substitution element M ′ are oxides, and Li is a carbonate. The Li raw material and the raw material of the substitution element M ', the Li raw material and the Ni raw material, the Li raw material and the Co raw material, and the Li raw material and the Mn raw material were weighed at a molar ratio of 1: 1. FIG. 1 shows the results of the TG analysis. The horizontal axis of the figure is the temperature, and the vertical axis is the reduction ratio of the sample weight to the initial sample weight. The test conditions were as follows: the temperature was raised from room temperature to 900 ° C. at a heating rate of 10 ° C./min.

The reaction temperature was determined from the TG analysis results. Here, the reaction temperature is a temperature at which the weight loss ratio due to the reaction is half the value at 900 ° C. This is because the weight reduction ratio with respect to the temperature rise ratio differs depending on the element as described above.
Than 1, the reaction temperature _{T N} of Ni is about 610 ° C., the reaction temperature _{T C} of Co is about 590 ° C., the reaction temperature _{T M} of Mn was about 410 ° C.. Therefore, the reaction temperature T for determining whether or not 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 as follows: Al is about 760 ° C., Ga is about 610 ° C., Mg is about 850 ° C., Zr is about 680 ° C., 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 higher than the pass / fail judgment temperature. Moreover, it was equal to or more than that of Ti.

  By the above Step 1, the above five substitution elements have a higher reaction temperature with Li than Ni, Co, and Mn constituting the positive electrode active material, and when used as a substitution element (addition element), the layered structure is broken. It was confirmed that no heterophase could be formed.

(Comparative Example 1)
B (boron) and La were used as comparative examples. Both B and La used an oxide, and TG analysis was performed in the same manner as in the above-described example. The result is 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 had a higher reaction temperature than Ni, Mn, and Co, and completed Step 1. On the other hand, B has a low reaction temperature and is a semimetal, so it is judged to be unsuitable as the substitution element M.

Subsequently, based on Step 2, a calcined powder having a composition of Li _1.02 Ni _0.90 Mn _0.05 Co _0.03 M _0.02 was prepared and subjected to XRD analysis. A sample is prepared by filling a ball mill with elemental powders of Li ₂ CO ₃ , Ni (OH) ₂ , MnCO ₃ , CoCO ₃ and a substitution element oxide together with pure water, pulverizing for a predetermined time, drying the pulverized slurry under vacuum, and mixing Powder. The average particle size of the mixed powder is 0.5 to 0.6 μm. The firing of the mixed powder was performed in three stages: temporary firing at a low temperature (650 ° C. × 10 hr), intermediate firing at a medium temperature (755 ° C. × 10 hr), and main firing at a high temperature (840 ° C. × 4 hr).
XRD analysis was performed on the fired powders of the respective compositions to which Al, Ga, Mg, Zr, Zn, and Ti, which are candidate replacement elements selected in Step 1, were added. The result is shown in FIG. The XRD analysis was performed under the following conditions.

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

FIG. 2 also shows the case of the standard composition (e = 0) to which the substitution element is not added.
2, the diffraction pattern when Al, Ga, Mg, Zr, Zn, and Ti were added was the same as the diffraction pattern of the standard composition, and no heterophase peak larger than the background was detected. It was confirmed that no heterophase was generated in the main firing for each element.

(Comparative Example 2)
As a comparative example, FIG. 3 shows the result of the same firing using the substitution element La having a higher reaction temperature than Ni, Mn, and Co in step 1 at the same composition ratio, and similarly subjected to XRD analysis. Heterophase peaks were confirmed at the positions indicated by the circles in the figure with respect to the standard composition. In La, it can be determined that a crystal (heterophase) different from the standard composition is generated. Therefore, La cannot clear Step 2, and is determined to be unsuitable as the replacement element M.

As described above, when the substitution element is added to the positive electrode active material using the lithium transition metal composite oxide, by performing the above steps 1 and 2 to select the substitution element M, the calcined lithium transition metal composite The oxide does not contain a different phase other than the layered structure, so that it is possible to obtain a positive electrode which is expected to suppress a rise in resistance and to suppress a decrease in capacity retention ratio and a decrease in charge / discharge capacity.

Claims (4)

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 -0.04 ≦ a ≦ 0.04 and 0.80 ≦ b <1, respectively. 0.0, 0 <e ≦ 0.05, b + e = 1, and −0.2 ≦ α ≦ 0.2. ] The method for selecting a substitution element of the positive electrode active material for a lithium ion secondary battery represented by
The reaction temperature T between the Li raw material and the raw material of the substitution element M ′ other than Li and Ni was measured,
Measuring the reaction temperature _TN between the Li base material and the Ni base material,
Wherein the reaction temperature T, and step 1 for comparing the reaction temperature T _N, selects a replacement element M'high reaction temperature T than the reaction temperature T _N,
Using the raw material of the replacement element M ′ selected in step 1 and the raw materials of Li and Ni, a calcined powder satisfying the composition formula (1), and a case where e = 0 in the composition formula (1) Obtain each baked powder,
X-ray diffraction analysis of each of the calcined 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 of a positive electrode active material for a lithium ion secondary battery, comprising: Li _{1 + a} Ni _b Co _c M n _{d Me} O _{2 + α} (2)
[In the composition formula (2), M represents a substitution element other than Li, Ni, Co, and Mn, and a, b, c, d, e, and α are -0.04 ≦ a ≦ 0.04, respectively. , 0.80 ≦ b <1.0, 0 <c, 0 <d, 0 <e ≦ 0.05, b + c + d + e = 1, and −0.2 ≦ α ≦ 0.2. ] The method for selecting a substitution element of the positive electrode active material for a lithium ion secondary battery represented by
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 was measured,
The Li-containing starting material and the reaction temperature of the Ni-containing material T _N, the reaction temperature T _M of the reaction temperature T _C and the Li-containing material and Mn raw material of the Li-containing material and Co-containing raw material were measured,
Selecting the said reaction temperature T, the reaction temperature _{T N,} T C, compared to _{T M} respectively, the reaction temperature _{T N,} T C, the reaction temperature T is higher substitution element M'than each of _{T M} 1 and
Using the raw material of the replacement element M ′ selected in Step 1 and the raw materials of Li, Ni, Co, and Mn, a calcined powder satisfying the composition formula (2), and e = Obtain the baked powder in the case of 0, respectively,
X-ray diffraction analysis of each of the calcined 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 of a positive electrode active material for a lithium ion secondary battery, comprising: A selection step of selecting a replacement element M by the method for selecting a replacement element according to claim 2;
A raw material preparation step of preparing each raw material of Li, Ni, Co, Mn, and M based on the composition formula (2);
Grinding and mixing step of grinding and mixing each of the raw material powders,
A firing step of simultaneously firing the mixed powder,
A method for producing a positive electrode active material for a lithium ion secondary battery, comprising: A positive electrode active material for a lithium ion secondary battery, comprising the substitution element M selected by the method for selecting a substitution element according to claim 2,
Li _{1 + a} Ni _b Co _c M n _{d Me} O _{2 + α} (3)
[In the composition formula (3), M represents a substitution element other than Li, Ni, Co, and Mn, and a, b, c, d, e, and α are -0.04 ≦ a ≦ 0.04, respectively. , 0.80 ≦ b <1.0, 0 <c, 0 <d, 0 <e ≦ 0.05, b + c + d + e = 1, and −0.2 ≦ α ≦ 0.2. ],
The positive electrode active material for a lithium ion secondary battery, wherein the substitution element M is one or more elements selected from the group consisting of Al, Ga, Mg, Zr, and Zn.