JP6017364B2 - Positive electrode active material for lithium ion battery, positive electrode for lithium ion battery, and lithium ion battery - Google Patents

Description

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

Lithium-containing transition metal oxides are generally used as positive electrode active materials for lithium ion batteries. Specifically, lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), lithium manganate (LiMn ₂ O ₄ ), etc., improved characteristics (higher capacity, cycle characteristics, storage characteristics, reduced internal resistance) In order to improve the rate characteristics and safety, it is underway to combine them. Lithium ion batteries for large-scale applications such as in-vehicle use and load leveling are required to have different characteristics from those of conventional mobile phones and personal computers.

  The positive electrode active material on the positive electrode side of the lithium ion battery is typified by lithium cobaltate, lithium nickelate, and lithium manganate as described above. However, each has advantages and disadvantages, and lithium cobaltate is a balanced material such as capacity and safety, but cobalt is a rare metal called a rare metal and therefore has a disadvantage of high cost. . Although lithium nickelate has a very high battery capacity, it is poor in safety, and lithium manganate has a very low thermal capacity but has a disadvantage of low capacity. Recently, from the viewpoint of high capacity, safety, and cost, ternary systems represented by NiMnCo and NiCoAl and positive electrode active materials using three kinds have been used. In this ternary system, cracks in the particles after charging / discharging have been reported for materials with a high Ni ratio due to charging / discharging after battery fabrication, and this is said to cause life deterioration.

  As a technique for suppressing cracks in particles during such charge and discharge, for example, Patent Document 1 discloses a positive electrode active material for a lithium secondary battery made of a powdered lithium transition metal composite oxide, When the mode value of the particle diameter is Ra μm and the arithmetic standard deviation is Rb μm, (i) Ra ≧ 0.5, and (ii) the particle size after compression for 1 minute at a pressure of 40 MPa. In the distribution, when the maximum particle diameter closest to Raμm is Rcμm, x defined by x = (Rc−Ra) / Rb is −2.7 <x <−1.2. A positive electrode active material for a lithium secondary battery is disclosed. And according to such a structure, it becomes difficult to generate | occur | produce a crack at the time of use in a high temperature environment, and consists of lithium transition metal complex oxide which can implement | achieve the lithium secondary battery excellent in cycling characteristics, especially high temperature cycling characteristics. It is described that a positive electrode active material can be provided.

JP 2004-342548 A

However, development of a technique that contributes to improvement of battery characteristics such as a charge / discharge cycle other than the means for suppressing cracking of the particles of the positive electrode active material as described above is also desired.
In view of such a problem, an object of the present invention is to provide a positive electrode active material for a lithium ion battery in which variation in how particles are cracked is satisfactorily suppressed, thereby improving battery characteristics.

  As described above, cracking of the positive electrode active material particles occurs during charging and discharging of the battery. If there is a variation in how the secondary particles of the positive electrode active material constituting the electrode are cracked, the battery performance of the electrode cell will vary. If it does so, an electrode cell must be designed on the conditions assumed to be the most deteriorated in variation, and a favorable battery characteristic cannot be expected. Therefore, it has been found that it is effective for improving battery characteristics to control the variation in how the positive electrode active material cracks between secondary particles during the charge / discharge cycle.

In one aspect, the present invention completed based on the above knowledge has a composition formula: Li _x Ni _{1- y My} O _{2 + α}
(In the above formula, M is one or more selected from Mn, Co, Cu, Zn, Mg and Zr , 0.9 ≦ x ≦ 1.2, 0 <y ≦ 0.7, −0.1 ≦ α ≦ 0.1.)
Secondary particles formed by agglomeration of primary particles, or a mixture of primary particles and secondary particles, with an average particle diameter D50 of 7 to 12 μm. when the compressive stress of 3.0 ton / cm ² was added 30 seconds to the particles, Ri Do a particle size distribution with one peak of the peak, and a lithium ion main peak in the compressive stress before and after applying the shift to smaller particle size side It is a positive electrode active material for batteries.

  In one embodiment, the positive electrode active material for a lithium ion battery according to the present invention has an average particle diameter D50 of one peak in the particle size distribution of 1 to 7 μm.

  In another embodiment of the positive electrode active material for a lithium ion battery according to the present invention, the peak frequency in the particle size distribution is 3 to 12%.

  In one embodiment of the positive electrode active material for a lithium ion battery according to the present invention, the M is one or more selected from Mn and Co.

  In another aspect, the present invention is a positive electrode for a lithium ion battery using the positive electrode active material for a lithium ion battery according to the present invention.

  In still another aspect, the present invention is a lithium ion battery using the positive electrode for a lithium ion battery according to the present invention.

  According to the present invention, it is possible to provide a positive electrode active material for a lithium ion battery in which variation in particle cracking is suppressed satisfactorily, thereby improving battery characteristics.

It is a figure which shows the pattern of the shape of the particle size distribution after compressive stress application. 3 is a graph showing the particle size distribution of Example 1. 3 is a graph showing the particle size distribution of Example 2. 6 is a graph showing the particle size distribution of Example 3. 6 is a graph showing the particle size distribution of Example 4. 10 is a graph showing the particle size distribution of Example 5. 5 is a graph showing the particle size distribution of Comparative Example 1.

(Configuration of positive electrode active material for lithium ion battery)
As a material of the positive electrode active material for lithium ion batteries of the present invention, compounds useful as a positive electrode active material for general positive electrodes for lithium ion batteries can be widely used. In particular, lithium cobaltate (LiCoO ₂ ), It is preferable to use lithium-containing transition metal oxides such as lithium nickelate (LiNiO ₂ ) and lithium manganate (LiMn ₂ O ₄ ). The positive electrode active material for a lithium ion battery of the present invention produced using such a material is
Composition formula: Li _x Ni _{1- y My} O _{2 + α}
(In the above formula, M is a metal, 0.9 ≦ x ≦ 1.2, 0 <y ≦ 0.7, and −0.1 ≦ α ≦ 0.1.)
It is represented by
M is preferably at least one selected from Mn, Co, Cu, Al, Zn, Mg and Zr, more preferably at least one selected from Mn and Co.

  The positive electrode active material for a lithium ion battery of the present invention is composed of secondary particles formed by aggregation of primary particles, or a mixture of primary particles and secondary particles. The average particle diameter D50 of the secondary particles formed by aggregation of these primary particles or the mixture of the primary particles and the secondary particles is 7 to 12 μm. If average particle diameter D50 is 7-12 micrometers, it will become the powder by which the dispersion | variation was suppressed and the dispersion | variation in an electrode composition can be suppressed. For this reason, when used in a lithium ion battery, battery characteristics such as rate characteristics and cycle characteristics are improved. The average particle diameter D50 is preferably 7 to 9 μm.

The pellet compression test of the present invention is performed according to the following procedure. First, a SUS mold is prepared. The mold has an inner space portion with a diameter of 17.5 mm for placing a powder sample therein. Next, 1 ± 0.05 g of a positive electrode active material particle powder is sampled and placed in the inner space of the mold and spread so that the thickness is uniform. Next, the sample in the inner space of the mold is pressed from above with another SUS mold having a pressing surface and compressed for 30 seconds. After returning to normal pressure, the positive electrode active material is removed from the mold. Subsequently, the particle size distribution of the sample is measured. The measurement can be performed with a laser diffraction / scattering particle size distribution measuring apparatus or the like. The positive electrode active material for a lithium ion battery of the present invention has a particle size distribution having a peak when a compressive stress of 3.0 ton / cm ² is applied to the particles of the positive electrode active material for 30 seconds in such a pellet compression test. It becomes.

  Before the compressive stress is applied, the particle size distribution has a peak of one peak, but after the compressive stress is applied, it has a peak of one or two peaks. When the compressive stress is applied, the average particle size of the particle size distribution is reduced. However, when there is a variation in the hardness of the particles, there are two peaks, and when there is no variation, there is a peak. There are four patterns (1) to (4) shown in FIG. 1 as the shape of the particle size distribution after the compression stress is applied. (1) and (2) are peaks of peaks, and the particles are uniformly separated into primary particles after compressive stress is applied. On the other hand, (3) and (4) are peaks of two peaks, and a portion separated into primary particles after applying compressive stress and a portion that remains as secondary particles but not separated into primary particles are mixed. The peak “mountain” can also be referred to as the maximum portion in the peak curve. In (2), most of the original average particle diameter D50 (for example, 7 to 12 μm) is cracked, the main peak is shifted to the small particle diameter side, and only some of the particles remain in the shoulder shape. . On the other hand, in (3), cracking proceeds only partially with respect to the original average particle diameter D50 (for example, 7 to 12 μm), and the main peak is not shifted to the small particle diameter side. Both (2) and (3) are not perfect two peaks, but are distinguished by whether or not the main peak shifts to the small particle size side before and after applying compressive stress. Regarding the battery characteristics, the main peak is shifted to the small particle size side (2) is superior to the main peak not shifted to the small particle size side (3).

The mixture of primary particles and secondary particles after the application of compressive stress is manifested in the form of variations between the particles, and hence variations in the electrode cells. When the hardness between the secondary particles is uniform, each secondary particle is separated into a shape corresponding to the primary particle by the press during the manufacturing process, etc. When there is variation, an abnormal portion that has not been destroyed in the manufacturing process is destroyed by the expansion and contraction of the lattice due to charge and discharge, which causes deterioration of battery characteristics. Here, the positive electrode active material for a lithium ion battery of the present invention has a particle size distribution having a peak when a compressive stress of 3.0 ton / cm ^{2 is} applied to the positive electrode active material particles for 30 seconds in a pellet compression test. It becomes. For this reason, the variation in how the particles of the positive electrode active material used as the electrode material after charging and discharging of the battery are cracked is suppressed, and the battery characteristics are improved.

  It is preferable that the average particle diameter D50 of one peak in the particle size distribution is 1 to 7 μm. According to such a configuration, variation in how the positive electrode active material particles are cracked is further suppressed, and battery characteristics are further improved. Moreover, it is more preferable that the average particle diameter D50 of the peak of the peak in the particle size distribution is 2 to 5 μm.

  It is preferable that the frequency of a peak in the particle size distribution is 3 to 12%. According to such a configuration, variation in how the positive electrode active material particles are cracked is further suppressed, and battery characteristics are further improved. Moreover, it is more preferable that the peak frequency in the particle size distribution is 4 to 9%.

(Configuration of positive electrode for lithium ion battery and lithium ion battery using the same)
The positive electrode for a lithium ion battery according to an embodiment of the present invention includes, for example, a positive electrode mixture prepared by mixing a positive electrode active material for a lithium ion battery having the above-described configuration, a conductive additive, and a binder from an aluminum foil or the like. The current collector has a structure provided on one side or both sides. Moreover, the lithium ion battery which concerns on embodiment of this invention is equipped with the positive electrode for lithium ion batteries of such a structure.

(Method for producing positive electrode active material for lithium ion battery)
Next, the manufacturing method of the positive electrode active material for lithium ion batteries which concerns on embodiment of this invention is demonstrated in detail.
First, a metal salt solution is prepared. The metals are Ni and metal M. The metal M is preferably at least one selected from Mn, Co, Cu, Al, Zn, Mg and Zr, more preferably at least one selected from Mn and Co. The metal salt is sulfate, chloride, nitrate, acetate, etc., and nitrate is particularly preferable. This is because even if it is mixed as an impurity in the firing raw material, it can be fired as it is, so that the washing step can be omitted, and nitrate functions as an oxidant, and promotes the oxidation of the metal in the firing raw material. Each metal contained in the metal salt is adjusted so as to have a desired molar ratio. Thereby, the molar ratio of each metal in the positive electrode active material is determined.

Next, lithium carbonate is suspended in pure water, and then the metal salt solution of the metal is added to prepare a metal carbonate slurry. At this time, fine particles of lithium-containing carbonate precipitate in the slurry. If the lithium compound does not react during heat treatment such as sulfate or chloride as a metal salt, it is washed with a saturated lithium carbonate solution and then filtered off. When the lithium compound reacts as a lithium raw material during the heat treatment, such as nitrate or acetate, it can be used as a calcined precursor by washing and drying as it is without washing.
Next, the lithium-containing carbonate separated by filtration is dried to obtain a lithium salt composite (precursor for lithium ion battery positive electrode material) powder.

  Next, the precursor for a lithium ion battery positive electrode material is fired. In the present invention, the particle size distribution after applying compressive stress is controlled according to the firing conditions. The mechanism in which the shape of the particle size distribution of the positive electrode active material particles peaks and peaks in the pellet compression test is that when the firing raw material is filled in the firing mortar, the firing raw material is hardened and uneven during filling. One cause of this is that the firing raw material is agglomerated before the filling and becomes non-uniform, and these non-uniform portions locally cause abnormal firing when the temperature of firing is increased. In order to prevent the firing raw material from agglomerating, it is important to make the packing density in the mortar (firing container) uniform. When filling the baking raw material into the baking mortar, the filling density is suppressed by vibrating the mortar for a certain period of time. Further, if the firing rate is partially high, abnormal firing is likely to occur. Some of the fired parts other than those at the time of temperature rise return to normal parts, but there are particles that remain abnormally fired. Since such particles remain even after the crushing step performed after firing, the abnormally fired particles remain unbroken in the pellet compression test, resulting in two peaks.

As the firing step, first, a firing container having a predetermined capacity is prepared, and this firing container is filled with a precursor powder for a lithium ion battery positive electrode material. When filling the firing raw material into the firing container, the raw material is prevented from agglomerating. Next, the firing container filled with the precursor powder for the lithium ion battery positive electrode material is transferred to a firing furnace and fired. Firing is heated to 900 to 1000 ° C. at a temperature raising rate of 100 to 300 ° C./h in the temperature raising step, and subsequently held at the temperature for 1 to 4 hours. Thereafter, the temperature is lowered at a temperature lowering rate of 100 to 200 ° C./h. Due to such firing conditions, heat is uniformly input in the temperature raising step, and the heat conductivity between the particles is improved. In the temperature lowering process, structural changes such as rearrangement of atoms in the transition metal layer, generation of stacking faults, oxygen defects and the like in the transition metal layer are promoted by rapid cooling and appropriate control of the temperature lowering atmosphere. By controlling the firing conditions in this way, abnormal firing is suppressed, and when a compressive stress of 3.0 ton / cm ^{2 is} applied to the positive electrode active material particles for 30 seconds in the pellet compression test, it has a peak. The particle size distribution can be controlled.
Further, it is preferable to perform baking under pressure of 101 to 202 KPa because the amount of oxygen in the composition further increases.
In the manufacturing method of the positive electrode active material for lithium ion batteries of this invention, crystallization is accelerated | stimulated by making a calcination temperature high and the average particle diameter D50 is controlled to 7-12 micrometers.

  Examples for better understanding of the present invention and its advantages are provided below, but the present invention is not limited to these examples.

(Example)
First, a predetermined amount of lithium carbonate was suspended in pure water, and then a metal salt solution was added. By this treatment, fine particles of lithium-containing carbonate were precipitated in the solution, and this precipitate was filtered off using a filter press.
Subsequently, the precipitate was dried to obtain a lithium-containing carbonate (a precursor for a lithium ion battery positive electrode material).
Next, a firing container was prepared, and this firing container was filled with a lithium-containing carbonate. Next, firing was performed under the firing conditions shown in Table 1. Subsequently, after cooling to room temperature, it was crushed to obtain a powder of a positive electrode material for a lithium ion secondary battery.

(Comparative example)
A lithium ion secondary battery positive electrode powder was prepared in the same manner as in the example except that the firing conditions were different when the firing container was filled with the raw materials.

(Evaluation)
-Evaluation of composition of positive electrode material-
The metal content in each positive electrode material was measured with an inductively coupled plasma optical emission spectrometer (ICP-OES), and the composition ratio (molar ratio) of each metal was calculated. It was confirmed that the composition ratio of each metal was as shown in Table 2. The oxygen content was measured by the LECO method and α was calculated.

-Evaluation of average particle diameter D50-
A particle cross section was cut out by FIB, and a SIM image was obtained as it was using an FIB apparatus (SMI3050SE) manufactured by SSI Nanotechnology. The average particle diameter D50 was calculated by measuring the constant direction diameter of only the particles existing on an arbitrary straight line on the SIM image.

-Evaluation of particle size distribution-
A SUS mold was prepared. The mold has an inner space portion with a diameter of 17.5 mm for placing a powder sample therein. Next, 1 ± 0.05 g of a positive electrode active material particle powder was sampled and placed in an inner space of a mold, which was spread so that the thickness was uniform. Next, the sample in the inner space of the mold was pressed with another SUS mold having a pressing surface from above with a compressive stress of 3.0 ton / cm ² and compressed for 30 seconds. After returning to normal pressure, the positive electrode active material was taken out of the mold. Subsequently, the particle size distribution of the sample was measured with a Microtrac MT3300EX II laser diffraction / scattering particle size distribution measuring device manufactured by Nikkiso Co., Ltd.

-Evaluation of discharge capacity and charge / discharge efficiency-
Each positive electrode active material, a conductive material, and a binder are weighed in a ratio of 90: 5: 5, and the positive electrode active material and the conductive material are mixed in a material in which the binder is dissolved in an organic solvent (N-methylpyrrolidone). Thus, a positive electrode mixture was prepared by slurrying, applied onto an Al foil, dried and pressed to obtain a positive electrode. Subsequently, a 2032 type coin cell for evaluation with Li as the counter electrode was prepared, and a discharge at a current density of 0.2 C was performed using 1M-LiPF6 dissolved in EC-DMC (1: 1) as an electrolyte. The capacity was measured. The charge / discharge efficiency was calculated from the initial discharge capacity and the initial charge capacity obtained by battery measurement.
These results are shown in Tables 1-3.

As shown in Table 3, Examples 1 to 9 all have an average particle diameter D50 of 7 to 12 μm, and when a compressive stress of 3.0 ton / cm ^{2 is} applied to the positive electrode active material particles for 30 seconds in the pellet compression test, The particle size distribution had peak peaks, and the discharge capacity and charge / discharge efficiency of the produced battery were good.
In Comparative Examples 1 to 4, in the pellet compression test, when a 3.0 ton / cm ² compressive stress was applied to the positive electrode active material particles for 30 seconds, the particle size distribution had two peaks, and charge and discharge of the produced battery Efficiency was poor.
The graph which shows the particle size distribution of Examples 1-5 and Comparative Example 1 is shown in FIGS. 2 to 7, the particle size distribution of the positive electrode active material, which was compressed by 30 ton / cm ² of the above-described compression for 30 seconds, as measured by the Nikkiso Microtrac MT3300EX II laser diffraction / scattering particle size distribution analyzer, 3.0T ". Further, for Examples 1 to 5 and Comparative Example 1, the sample before compression was also measured for particle size distribution using a Microtrac MT3300EX II laser diffraction / scattering particle size distribution measuring device manufactured by Nikkiso Co., Ltd., which is a positive electrode active material. 0T ".

Claims (6)

Composition formula: Li _x Ni _{1- y My} O _{2 + α}
(In the above formula, M is one or more selected from Mn, Co, Cu, Zn, Mg and Zr , 0.9 ≦ x ≦ 1.2, 0 <y ≦ 0.7, −0.1 ≦ α ≦ 0.1.)
Represented by
Secondary particles formed by aggregation of primary particles, or a mixture of primary particles and secondary particles,
The average particle diameter D50 is 7-12 μm,
In pellet compression test, when applying a compressive stress particles of 3.0 ton / cm ² of the cathode active material 30 seconds, Ri Do a particle size distribution with one peak of the peak, and the main peak in the compressive stress before and after applying a small A positive electrode active material for lithium ion batteries that shifts to the particle size side .   2. The positive electrode active material for a lithium ion battery according to claim 1, wherein an average particle diameter D50 of a mountain peak in the particle size distribution is 1 to 7 μm.   3. The positive electrode active material for a lithium ion battery according to claim 1, wherein the peak frequency in the particle size distribution is 3 to 12%. Wherein M is a positive active material for a lithium ion battery according to claim 1 is at least one selected from Mn and Co. The positive electrode for lithium ion batteries using the positive electrode active material for lithium ion batteries in any one of Claims 1-4 . The lithium ion battery using the positive electrode for lithium ion batteries of Claim 5 .