JP6637873B2 - Positive active material for lithium ion secondary battery, positive electrode for lithium ion secondary battery, and lithium ion secondary battery - Google Patents

Description

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

Generally, a lithium-containing transition metal oxide is used as a positive electrode active material of a lithium ion secondary battery. Specifically, it is lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), lithium manganate (LiMn ₂ O ₄ ) or the like, and the characteristics are improved (high capacity, cycle characteristics, storage characteristics, internal resistance reduction). , Rate characteristics) and security in order to improve the security. Lithium-ion secondary batteries for large-scale applications such as vehicles and artificial satellites are required to have different characteristics from those for mobile phones and personal computers. Since power devices such as vehicles require higher current values, that is, higher output, than PCs and mobile devices, the discharge potential does not change much even when the assembled battery is discharged at a high rate. Is required. In this case, generally, if the cycle characteristics at a high rate are good, the discharge potential often does not change much. Therefore, it is desired that the cycle characteristics at a high rate be good in order to suppress the discharge potential change. In addition, such a high-output battery may require high-rate cycle characteristics even in an environment of 40 ° C. or higher or in an environment of 0 ° C. or lower. If a battery capable of exhibiting the above characteristics can be made, further development of a lithium ion secondary battery for high power applications can be expected.

  Conventionally, various researches and developments have been made on the improvement of the battery characteristics required for such a lithium ion secondary battery (Patent Documents 1 and 2).

Japanese Patent No. 3192374 Japanese Patent No. 4872150

  Here, in order to realize a high output, in a positive electrode active material of a lithium ion secondary battery for a vehicle, a so-called Zr or W, which does not actually contribute to charge / discharge but activates a charge / discharge reaction of the entire battery, a so-called, It is known that high output can be achieved by adding an element having a role as an electrode reaction catalyst. However, it has been found that, when a higher output is sought and the added amount of these elements is increased, the output is certainly increased, but the absolute value of the capacity is reduced, which does not lead to stabilization of the discharge potential. For this reason, the upper and lower limits can be set for the amount of the electrode reaction catalyst in relation to the vehicle performance.However, the actual amount of addition is limited to a small amount, and the output gradually decreases when the catalyst is gradually dissolved or reacted. there were.

Here, regarding the electrode reaction catalyst, it is known that Zr operates in a form of Li ₂ ZrO ₃ or the like, and W operates in a form of Li ₂ WO ₄ or the like. These do not dissolve immediately in the electrolytic solution. According to the examination of the above, it was found that W gradually dissolved. As for Zr, as a side reaction of the battery reaction, for example, between Zr and CO ₂ resulting from oxidative decomposition of the electrolyte,
However, since Li ₂ CO ₃ generated here reacts with the electrolyte, Li ₂ CO ₃ and the electrolyte further react once in a state of being separated into ZrO ₂ and Li ₂ CO _3. When the electrolyte is decomposed, the above-described equilibrium reaction proceeds more rapidly from left to right, increasing the chance of the reaction between the electrolyte and Li ₂ CO ₃ , decreasing the amount of Li ₂ ZrO ₃ and increasing the output. It turned out to be impossible to keep.

  In view of such a problem, an object of the present invention is to provide a positive electrode active material for a lithium ion secondary battery that can ensure high output even when repeatedly charged and discharged at high and low temperatures.

  The present inventor has conducted various studies to solve the above-described problems.As a result, the particles of the positive electrode active material have a predetermined composition formula, and Zr and W are attached to the particles at a predetermined molar ratio. It has been found that the above problem can be solved by controlling the amount of Zr and W contained in a filtrate obtained by performing a predetermined mixed acid treatment containing F (fluorine) to a predetermined amount.

According to one aspect of the present invention, which has been completed based on the above findings, the composition formula is LiMO ₂ (where M is at least one of Ni, Co, and Mn, and when Ni is contained, the composition ratio is Ni / M). 0.5 or more, and when Co is contained, the composition ratio: Co / M is 0.2 or less, and when Mn is contained, the composition ratio: Mn / M is 0.3 or less.) there are sparse portions and dense portions particle, a positive electrode active material in the sparse portion of the particles Zr and W are attached, and M of the composition formula, adheres to sparse portion of the particles In a molar ratio with Zr and W, Zr / M = 0.005 to 0.007, and satisfying W / M = 0.001 to 0.002, and 10 mL of a mixed acid containing F at a concentration of 1 mol / L is added, After stirring for 10 seconds, the mixture is filtered through a 0.1 μm filter to obtain a filtrate and a residue. Then, after performing the first F-containing mixed acid treatment A on 0.1 g of the positive electrode active material to obtain a filtrate 1 and a residue 1, the residue 1 is further subjected to the second F-containing mixed acid treatment A. When the residue (X-1) is subjected to the X-th mixed acid treatment A containing F to obtain the filtrate X and the residue X, the operation of obtaining the filtrate 2 and the residue X is repeated. The filtrate 10 obtained by performing the tenth F-containing mixed acid treatment A has a higher molar ratio of Zr in the filtrate: Zr / (Ni + Co + Mn) than the filtrate 1 obtained by performing the mixed acid treatment A. The molar ratio of W: W / (Ni + Co + Mn) is small, and the filtrate obtained by performing the mixed acid treatment A with F after any one of the 30th to 50th times has a Zr molar ratio of Zr / (Ni + Co + Mn) and W molar ratio: W / (Ni + Co + Mn) This is a positive electrode active material for a lithium ion secondary battery, which is also less than 0.001. The term “mixed acid containing F at a concentration of 1 mol / L” referred to in the present invention refers to HF at a concentration of 1 mol / L, HNO _{3 at} a concentration of 1 mol / L, and H ₂ SO _{4 at} a concentration of 1 mol / L. Are mixed at a volume ratio of 0.4: 24.9: 74.7.

  In another aspect, the present invention is a positive electrode for a lithium ion secondary battery, including the positive electrode active material for a lithium ion secondary battery of the present invention.

  In still another aspect, the present invention is a lithium ion secondary battery including the positive electrode for a lithium ion secondary battery of the present invention, a negative electrode, and an electrolyte.

  ADVANTAGE OF THE INVENTION According to this invention, the positive electrode active material for lithium ion secondary batteries which can ensure high output even if charge / discharge is repeatedly performed at high temperature and low temperature can be provided.

(Composition of positive electrode active material for lithium ion secondary battery)
The positive electrode active material for a lithium ion secondary battery of the present invention has a composition formula of LiMO ₂ (where M is at least one of Ni, Co, and Mn, and when Ni is contained, the composition ratio: Ni / M is 0) 0.5 or more, and when Co is contained, the composition ratio: Co / M is 0.2 or less, and when Mn is contained, the composition ratio: Mn / M is 0.3 or less.) Zr and W are attached to the sparse portion of the active material. Zr and W are elements constituting an electrode reaction catalyst. Further, in the positive electrode active material for a lithium ion secondary battery of the present invention, the molar ratio of M in the particle composition formula to Zr and W attached to the sparse portion of the positive electrode active material is Zr / M = 0.005. ０．００0.007 and W / M = 0.001 to 0.002. According to such a configuration, it is possible to suppress the dissolution of the catalyst that rapidly absorbs the carbon dioxide generated by the decomposition of the electrolyte, suppress the deterioration of the output when repeatedly used at high and low temperatures, and reduce the output at high and low temperatures. It is possible to provide a positive electrode active material for a lithium ion secondary battery capable of ensuring a high output even when repeatedly charged and discharged.

The form of deposition of Zr and W to the positive electrode active material, for example, the center of the positive electrode active material particles is dense, when the particle surface is sparse, but a gap on the particle surface, Li ₂ the gap Examples include a form in which an electrode reaction catalyst of a Zr compound such as ZrO ₃ and a W compound such as Li ₂ WO ₄ is present. In such a form, the function of the electrode reaction catalyst can be exhibited, and the elution of the catalyst can be prevented. This makes it possible to form a battery having good cycle characteristics when repeatedly charged at a high rate under both high and low temperatures. In addition, it is preferable that a large amount of additional elements be present in a portion where the active material is sparse (that is, a portion where acid is easily eluted) because of the unevenness of density not only within the particles but also between the particles. This is because, for example, sparse precursor particles are not only pores that simply go from the surface to the center, but also fine particles that once enter the center from the surface and then move in a direction parallel to the particle surface or toward the particle surface again. There may be pores, and the precursor particles having such pores are greatly shrunk during firing to become rugged active material particles, so that the current is excessively concentrated on the projections during charging and discharging. This is because cycle characteristics deteriorate. The compounds of Zr and W not only function as an additive element as a catalyst, but also retain the particle skeleton of these sparse precursor particles and suppress the generation of rugged active material particles during firing. It has contributed to improvement. In addition, the sparse part of the active material is likely to come into contact with the electrolyte when a lithium secondary battery is manufactured using the active material. Since the portion where CO ₂ accumulates as a result of the oxidative decomposition of the electrolytic solution is a sparse portion of the active material, by disposing an electrode reaction catalyst in this portion, the generated CO ₂ can be efficiently absorbed. Can be.

The positive electrode active material for a lithium ion secondary battery of the present invention is prepared by adding 10 mL of an F-containing mixed acid having a concentration of 1 mol / L, stirring the mixture for 10 seconds, and then filtering through a 0.1 μm filter to obtain a filtrate and a residue. The mixed acid treatment A was performed, and the first F-containing mixed acid treatment A was performed on 0.1 g of the positive electrode active material to obtain a filtrate 1 and a residue 1. Then, the residue 1 was further subjected to a second F-containing mixed acid treatment A. When the residue (X-1) is subjected to the Xth mixed acid treatment A with F to obtain the filtrate X and the residue X, the first mixed acid treatment A with F is performed. The filtrate 10 obtained by performing the mixed acid treatment A with F ten times has a higher molar ratio of Zr in the filtrate: the molar ratio of Zr / (Ni + Co + Mn) and W than the filtrate 1 obtained by performing : W / (Ni + Co + Mn) is small, 30 times or more The filtrate obtained by performing the mixed acid treatment A containing F in the 0th or subsequent times has a molar ratio of Zr: Zr / (Ni + Co + Mn) and a molar ratio of W: W / (Ni + Co + Mn) of less than 0.001. .
As described above, the filtrate 10 obtained by performing the tenth F-containing mixed acid treatment A has a higher molar ratio of Zr in the filtrate than the filtrate 1 obtained by performing the first F-containing mixed acid treatment A. The ratio: Zr / (Ni + Co + Mn) and the molar ratio of W: W / (Ni + Co + Mn) both become small, so that the Zr compound and the W compound remain in the sparse portion of the active material and absorb carbon dioxide as described above. This has the effect of acting as a catalyst. Further, the filtrate obtained by performing the mixed acid treatment A containing F in any of the 30th to 50th times has a molar ratio of Zr: Zr / (Ni + Co + Mn) and a molar ratio of W: W / (Ni + Co + Mn) of 0. 0.001 or less, so that the sparse portion of the active material contains more Zr compounds and W compounds, while the dense portion of the active material contains almost no Zr compound and W compound. Will be. For this reason, it is possible to arrange the Zr compound and the W compound preferentially in a portion that comes into contact with the electrolytic solution, and to absorb carbon dioxide for a long time even if it is decomposed to generate carbon dioxide. Just coating the surface of the active material with a Zr compound and a W compound as in Comparative Example 4 described below immediately loses the ability to absorb carbon dioxide, and deteriorates the cycle characteristics at high temperature and high rate and low temperature and high rate. Has been invited. Also, when Zr and W are present throughout the active material as in Comparative Example 3, the contact between the Zr compound and the W compound and the electrolytic solution is poor in the first place, and the high-temperature high-rate and low-temperature high-rate This leads to deterioration of cycle characteristics. Note that, for a 0.1 μm filter, for example, if a 0.1 μm PTFE membrane filter is used, the mixed acid treatment A containing F can be easily performed. Further, a filter or a beaker which comes into contact with the mixed acid containing F is preferably made of a fluororesin such as Teflon (registered trademark) or coated with a fluororesin such as Teflon (registered trademark) from the viewpoint of preventing contamination of impurities. At this time, if the SPC filter holder coated with Teflon (registered trademark) is used, the mixed acid treatment A containing F can be easily performed. When a support screen is used, a screen made of a fluororesin such as Teflon (registered trademark) is preferable.

  At this time, due to the combination with other technologies, the positive electrode active material for a lithium ion secondary battery utilizing the technology of the present invention is already combined with another conductive auxiliary, a polymer, etc. to form a composite. In this case, it is originally desirable to remove them and perform the mixed acid treatment A with F using only the positive electrode active material. However, if it is difficult, for example, the amount of the collected positive electrode active material is adjusted to 0.1 g as a net positive electrode active material. By determining, it may be possible to determine whether the positive electrode active material conforms to the technical scope of the present invention. For example, a composite in which the positive electrode active material, the conductive additive, and the polymer of the present invention are constituted at a ratio of 80.0 (% by mass): 10.0 (% by mass): 10.0 (% by mass). In this case, 0.125 g of the composite is collected, and the mixed acid treatment A containing F is performed on the composite to determine whether or not the positive electrode active material conforms to the technical scope of the present invention. there is a possibility.

(Positive electrode for lithium ion secondary battery and configuration of lithium ion secondary battery using the same)
The positive electrode for a lithium ion secondary battery of the present invention is, for example, a positive electrode mixture prepared by mixing a positive electrode active material for a lithium ion secondary battery with the above-described configuration, a conductive auxiliary, and a binder from an aluminum foil or the like. It has a structure provided on one side or both sides of a current collector. Di (bis (6-t-butyl-4-methylphenoxy)) titanium and the like can be further added to the positive electrode. Further, the lithium ion secondary battery of the present invention includes the positive electrode for a lithium ion secondary battery having such a configuration, a negative electrode, and an electrolytic solution.

(Method for producing positive electrode active material for lithium ion secondary battery)
Next, a method for producing the positive electrode active material for a lithium ion secondary battery according to the present invention will be described.
First, an acidic aqueous solution of M represented by the composition formula of the positive electrode active material particles, an aqueous solution of L-arginine as a complexing agent, and an aqueous solution of sodium hydroxide are prepared. Is added to one reaction vessel in nitrogen so that the value is 11.5 ± 0.2. The reaction can be carried out at a temperature usually within the range normally assumed by those skilled in the art, but is generally preferably 40 to 80 ° C. At this time, since seed crystals are generated by coprecipitation, a mixture of the three forms a slurry. If possible, it is desirable that the acidic aqueous solution of M and the aqueous solution of L-arginine be separately and simultaneously added to the reaction vessel so as to be well complexed. The molar ratio between M and L-arginine can be determined, for example, in the range of 0.1 to 10. However, if it is about 1, rapid fluctuation of the pH of the liquid in the reaction tank can be suppressed in many cases. Becomes easier. The seed crystal is removed from the slurry by filtration and washing with water. Subsequently, the seed crystal is dispersed again in water to form a seed crystal slurry, and the aqueous solution of M, the aqueous solution of sodium hydroxide, and aqueous ammonia are added in nitrogen to promote nucleus growth of the precursor particles. In this case as well, the reaction can be carried out at a temperature usually assumed by those skilled in the art. In this case, it is considered that the same effect is exerted even if the complexing agent used is not L-arginine but a part or all of the complexing agent is replaced with any of the bases softer than ammonia according to the HSAB rule. At this time, the concentration of the aqueous solution, the molar ratio to M, the pH of the liquid in the reaction tank, the reaction temperature, and the like are appropriately set according to the type of the base to be used.
Here, the aqueous ammonia is added while gradually decreasing the addition rate according to the following equation from the initial stage of the addition.
Addition rate (L / min) = Initial addition rate (L / min)-0.014 x addition time (h)
The initial addition rate in the formula can be set within a range normally assumed by those skilled in the art. For example, the initial molar ratio of NH ₃ to M is set to any value between 0.1 and 10, and M The initial addition rate may be determined in a manner corresponding to the addition rate of the aqueous solution.
Also, the aqueous sodium hydroxide solution is added so that the pH of the liquid in the reaction tank is maintained at, for example, 11.5 ± 0.2 during the nucleus growth.

Next, a precursor is produced by filtering, washing and drying the product obtained by adding an acidic aqueous solution of M, an aqueous sodium hydroxide solution and aqueous ammonia.
Next, the precursor particles are impregnated with a zirconium compound and a tungsten compound in nitrogen. As the impregnation means, first, the precursor is charged into a concentrated aqueous solution of ammonium tungstate to form a precursor slurry.

Next, this is impregnated in a vacuum and calcined in nitrogen to obtain a tungsten-impregnated precursor. Next, the tungsten-impregnated precursor is charged into a zirconia slurry, impregnated in vacuum to impregnate the tungsten-impregnated precursor with zirconia, and then filtered, washed with water and dried to obtain an impregnated precursor.
Next, after the impregnated precursor and lithium hydroxide are mixed, firing is performed. At this time, the amount of the Li source is such that the molar ratio of Li / M is 1.01 to 1.10. And the amount of Li / (Zr + W) is 2.00 to 2.03. Is preferably blended. Here, the reason why Li is charged more than the stoichiometric composition is that Li is volatilized a little at the time of sintering, so that Li is added in consideration of the amount. The firing conditions also depend on the composition and the like. For example, those having a Ni: Co: Mn of 8: 1: 1 have a firing temperature of 750 to 800 ° C. in an atmosphere having an oxygen partial pressure of 0.08 MPa or more. Can be time.

  Next, the fired powder (fired powder) is crushed using a roll mill, a pulverizer or the like, if necessary, to obtain a positive electrode active material having a predetermined average particle diameter.

  Hereinafter, examples for better understanding of the present invention and its advantages will be provided, but the present invention is not limited to these examples.

In the following Examples 1 to 6 and Comparative Examples 1 to 4, all the steps up to impregnation with additives were performed in nitrogen.
-Example 1
<Preparation of seed crystal>
First, an aqueous solution A in which nickel sulfate, cobalt sulfate, and manganese sulfate were dissolved in a molar ratio of Ni: Co: Mn of 8: 1: 1 was prepared. The concentration of the transition metal in this is 1 mol / L in total. Separately from this, 1820 g of L-arginine was prepared, slowly added to 10 L of water at 80 ° C., sufficiently stirred and dissolved, and then gradually cooled to prepare an aqueous L-arginine solution B. Also, a 0.2 mol / L sodium hydroxide aqueous solution C was prepared. These were charged into one reaction vessel at 50 ° C. at 0.6 L / min by a tube pump. However, C was added so that the pH was maintained at 11.5 ± 0.2 during the reaction. When the L-arginine aqueous solution B disappeared, the supply of the above A, B, and C was stopped. This was filtered and washed with water to give a seed crystal.

<Preparation of precursor>
0.1 mol / L aqueous ammonia D was prepared. The seed crystal and water were placed in a reaction vessel at a weight ratio of 1:10 and mixed to obtain a seed crystal slurry. While adding A at a rate of 0.6 L / min at 50 ° C. to the slurry, D was added to the seed crystal slurry at the following addition rate. Further, C was added so as to maintain the pH at 11.5 ± 0.2 during the reaction.
Addition rate (L / min) = Initial addition rate (L / min)-0.014 x addition time (h)
When the addition rate became 0, all the liquid feeding was stopped, filtration and washing were performed, and then the precursor was dried to obtain a precursor.

<Impregnation of additives>
An aqueous solution of 3.6% by weight of ammonium tungstate is prepared, and the aqueous solution of ammonium tungstate and the precursor are mixed so that the ratio of tungsten to the total amount of transition metals in the precursor is 0.001 mol. A tungsten-added slurry was prepared. This was placed in a container that can be evacuated and evacuated. Foam was generated from the slurry, but when the foam was no longer generated, the slurry was taken out of the vacuum vessel, filtered, and calcined at 400 ° C. for 1 hour to obtain a tungsten-impregnated precursor. A water-dispersed slurry having a pH of 11 containing 1% by weight of zirconia and an appropriate amount of ammonia is prepared, and a tungsten-impregnated precursor is added into the slurry so as to have a ratio of 0.005 mol with respect to the total amount of (Ni + Co + Mn + W). This was added to produce a zirconia-added slurry. This was placed in a container that can be evacuated and evacuated. Foam was generated from the zirconia-added slurry, but when the foam ceased to be generated, the zirconia-added slurry was taken out of the vacuum vessel and filtered and washed with water. At this time, the water used for the water washing had a pH of 7.0 ± 0.5, and the filtrate after the water washing did not become cloudy. When the pH was settled at 7.0 ± 0.5, the end point of the water washing was reached. And The cake obtained by this water washing was dried at 120 ° C. for 12 hours to obtain an impregnated precursor.

<Manufacture of positive electrode active material>
The above-impregnated precursor and LiOH.H ₂ O were mixed and calcined at 780 ° C. for 10 hours in oxygen to obtain a positive electrode active material. At this time, the amount of LiOH.H ₂ O was determined as follows. First, the amounts of Ni, Co, Mn, W, and Zr in the impregnated precursor were calculated by ICP. Calculate the amount of LiOH.H ₂ O to be 2.02 mol. For W and Zr, the amount of LiOH.H ₂ O to be 2.01 mol. Was calculated. The amounts of these two LiOH.H ₂ O were added together to obtain a LiOH.H ₂ O mixing amount with respect to the impregnated precursor. If there is no addition of W and Zr in the production method of this item, there is no difference from the calculation of Li / Me in consideration of the volatile matter of Li at the time of calcination usually performed by those skilled in the art. The mass after firing was crushed using a roll crusher and a pulverizer to obtain a positive electrode active material of the present invention.

-Example 2
After mixing a positive electrode active material, acetylene black, and an NMP solution of PVdF to prepare a slurry, 0.1% by mass of di (bis (6-t-t- An experiment was performed in the same manner as in Example 1 except that butyl-4-methylphenoxy)) titanium was added, mixed, and the viscosity was adjusted with NMP.

-Example 3
For the first aqueous solution A, an experiment was performed in the same manner as in Example 1 except that the molar ratio of Ni: Co: Mn was 5: 2: 3 and the firing temperature was 950 ° C.

-Example 4
<Impregnation of additive> Same as Example 1 except that a tungsten-impregnated precursor was added so as to have a ratio of 0.007 mol to the total amount of (Ni + Co + Mn + W) to prepare a zirconia-added slurry. Was tested.

-Example 5
In <Impregnation of Additives>, a 3.6 wt% aqueous solution of ammonium tungstate was prepared, and the aqueous solution of ammonium tungstate was prepared such that the ratio of tungsten to the total amount of transition metal in the precursor was 0.002 mol. The test was conducted in the same manner as in Example 1 except that the precursor and the precursor were mixed.

-Example 6
In <Impregnation of Additives>, a 3.6 wt% aqueous solution of ammonium tungstate was prepared, and the aqueous solution of ammonium tungstate was prepared such that the ratio of tungsten to the total amount of transition metal in the precursor was 0.002 mol. And a precursor are mixed to produce a tungsten-added slurry, and a tungsten-impregnated precursor is added so as to have a ratio of 0.007 mol to the total amount of (Ni + Co + Mn + W) to produce a zirconia-added slurry. A test was performed in the same manner as in Example 1 except that the test was performed.

-Comparative example 1
The experiment was performed in the same manner as in Example 1 except that Zr and W were not added.

-Comparative example 2
For the first aqueous solution A, an experiment was conducted in the same manner as in Example 1 except that the molar ratio of Ni: Co: Mn was 1: 1: 1 and the firing temperature was 980 ° C.

-Comparative example 3
At the time of preparing a seed crystal and at the time of preparing a precursor, zirconium sulfate is added to A so that the molar ratio becomes Zr / (Ni + Co + Mn) = 0.001, and 0.002 mol / L ammonium tungstate is added to C. An experiment was carried out in the same manner as in Example 1 except that no subsequent impregnation of the additive was performed and the precursor was used in <Production of positive electrode active material> instead of the impregnated precursor.

-Comparative example 4
The following treatment was performed on the positive electrode active material of Comparative Example 1 to obtain a positive electrode active material of this example. That is, 100 g of the positive electrode active material of Comparative Example 1 was dispersed in 300 mL of a 0.4 g / L aqueous solution of ammonium tungstate ((NH ₄ ) ₂ WO ₄ ) adjusted to pH = 11 with an aqueous sodium hydroxide solution to form a slurry. The surface was coated with tungsten by dropping sulfuric acid of pH = 4 one by one (about 0.03 mL). This was dried, and the tungsten content was determined by ICP. Li ₂ CO ₃ was mixed so that the molar ratio of Li / W became 2, followed by firing at 780 ° C. for 1 hour in an oxygen atmosphere. This was crushed by a roll crusher, and 85 g thereof was dispersed in 300 mL of a 0.4 g / L zirconium sulfate aqueous solution. To this, zirconium was coated on the surface by dropping an aqueous solution of sodium hydroxide having a pH of 11 drop by drop (about 0.03 mL). This was dried, and the zirconium content was determined by ICP. Li ₂ CO ₃ was mixed so that the molar ratio of Li / Zr became 2, followed by firing at 780 ° C. for 1 hour in an oxygen atmosphere. This was crushed with a roll crusher to obtain a positive electrode active material.

<Analysis of positive electrode active material>
The composition of the obtained positive electrode active material was analyzed by ICP-OES (SPS3100 manufactured by Hitachi High-Tech Science) and ion chromatograph (ICS-1600 manufactured by Thermo Fisher). Separately, Zr and W amounts were measured by acid elution according to the following method. First, 249 mL of 1 mol / L HNO ₃ was prepared in a 2 L Teflon (registered trademark) beaker, and 747 mL of 1 mol / L H ₂ SO ₄ was gradually added thereto while stirring without heating. . After completion of the addition, 4 mL of 1 mol / L HF was added while maintaining the stirring to obtain a mixed acid containing F at a concentration of 1 mol / L. Next, 0.1 g of the positive electrode active material was placed in a 50 cc Teflon (registered trademark) beaker, and 10 mL of the F-containing mixed acid having a concentration of 1 mol / L was added thereto. After stirring for about 10 seconds, a 0.1 μm PTFE membrane filter was used. And suction filtered. This filtrate was used as the first filtrate (filtrate 1), and the residue on the PTFE membrane filter (residue 1) was taken out of the PTFE membrane filter, transferred to a 50 cc Teflon (registered trademark) beaker, and again mixed with the F-containing mixed acid described above. In addition, the same treatment was performed, and the filtrate was used as a second filtrate (filtrate 2). This was repeated thereafter, and the molar ratio of Zr and W to (Ni + Co + Mn) for the first to 100th filtrates (filtrate 1 to filtrate 100) was determined using the above ICP-OES.

<Production of lithium ion secondary battery>
The obtained positive electrode active material, acetylene black, and an NMP solution of PVdF (PVdF content of 10% by mass) are mixed so that the weight ratio of the positive electrode active material: acetylene black: PVdF is 85: 10: 5, In addition, pure NMP was gradually added so that the viscosity became 20 to 25 Pa · s at 20 to 25 ° C. This was applied on an aluminum foil so as to have a thickness of 100 μm on a wet base using a 100 μm applicator, dried at 120 ° C. for 10 hours, and pressed with a linear load of 10 kN / cm to obtain a positive electrode plate. Separately, artificial graphite and the NMP solution of PVdF were mixed so that the weight ratio of artificial graphite: PVdF was 9: 1, and NMP was gradually added, and the viscosity was increased to 20 to 25 ° C. At 20 to 25 Pa · s. This was applied on a copper foil so as to have a thickness of 100 μm on a wet base using a 100 μm applicator, dried at 120 ° C. for 10 hours, and pressed at a linear load of 10 kN / cm to obtain a negative electrode plate. Separately, a separator (A089 (trade name) manufactured by Celgard Co., Ltd.) was prepared, and the separator, the positive electrode plate, and the negative electrode plate were cut into a size of 15 cm × 15 cm. The positive electrode plate and the separator negative electrode plate were overlapped so that the upper negative electrode coating film faced. This was used as one electrode group, and eight electrode groups were prepared, and all the electrode groups were overlapped so that the aluminum foil and the copper foil were in contact with each other. One end of a negative terminal with a length of 10 cm on the outermost copper foil (there is an insulating coating except for the portion 2 cm from both ends), and a positive terminal with a length of 10 cm on the aluminum foil (the insulating coating except for the portion 2 cm from both ends). One end was spot-welded. Two laminated films were prepared so that the glue after sealing was 18 cm long and 18 cm wide, and three sides were sealed. The electrode group with the terminal was put in the film bag, and the terminal was made to go out of the bag. 1M LiPF ₆ / (EC + EMC) was placed in the bag as an electrolyte. Here, the mixing ratio of EC (ethylene carbonate) and EMC (ethyl methyl carbonate) was EC: EMC = 3: 7 in volume ratio. At this time, all the electrodes were soaked. The other one was sealed with a ceiling-hanging sealing machine to obtain a lithium ion secondary battery.

<Measurement of lithium ion secondary battery>
Two identical batteries were prepared, one was charged and discharged at 50 ° C. and 2.5 C, and the percentage of the ratio of the 100th discharge capacity to the first discharge capacity was determined as a high-temperature high-rate cycle characteristic (%). The other was charged and discharged at −10 ° C. and 2.5 C, and the percentage of the ratio of the 100th discharge capacity to the first discharge capacity was determined as a low-temperature high-rate cycle characteristic (%).
Table 1 shows the results.

Examples 1 to 6 all had good high-temperature high-rate cycle characteristics and low-temperature high-rate cycle characteristics.
Comparative Examples 1 to 4 all had poor high-temperature high-rate cycle characteristics and low-temperature high-rate cycle characteristics.

Claims (3)

The composition formula is LiMO ₂
(Wherein, M is at least one of Ni, Co, and Mn. When Ni is contained, the composition ratio: Ni / M is 0.5 or more. When Co is contained, the composition ratio: Co / M is 0. .2 or less, and when Mn is contained, the composition ratio: Mn / M is 0.3 or less.)
Is a positive electrode active material in which sparse parts and dense parts are present in the particles, and Zr and W are attached to the sparse parts of the particles ,
And M of the composition formula, the molar ratio of Zr and W adhering to sparse portion of the particles, Zr / M = 0.005-0.007, and, W / M = 0.001 to 0.002 The filling,
HF at a concentration of 1 mol / L, HNO _{3 at} a concentration of 1 mol / L, and H ₂ SO _{4 at} a concentration of 1 mol / L were mixed at a volume ratio of 0.4: 24.9: 74.7. 10 mol / L of a mixed acid containing F was added, and the mixture was stirred for 10 seconds and filtered through a 0.1 μm filter to obtain a filtrate and a residue.
After performing the first F-containing mixed acid treatment A on 0.1 g of the positive electrode active material to obtain a filtrate 1 and a residue 1, the residue 1 is further subjected to the second F-containing mixed acid treatment A. When the operation of obtaining the liquid 2 and the residue 2 is repeated and the residue (X-1) is subjected to the Xth mixed acid treatment A with F to obtain a filtrate X and a residue X,
The filtrate 10 obtained by performing the tenth F-containing mixed acid treatment A is more likely to have a molar ratio of Zr in the filtrate than the filtrate 1 obtained by performing the first F-containing mixed acid treatment A: The molar ratio of Zr / (Ni + Co + Mn) and W: W / (Ni + Co + Mn) is small;
The filtrate obtained by performing the mixed acid treatment A with F after any one of the 30th to 50th times has a molar ratio of Zr: Zr / (Ni + Co + Mn) and a molar ratio of W: W / (Ni + Co + Mn) of 0. A positive electrode active material for a lithium ion secondary battery, which is less than 001.   A positive electrode for a lithium ion secondary battery, comprising the positive electrode active material for a lithium ion secondary battery according to claim 1.   A lithium ion secondary battery comprising the positive electrode for a lithium ion secondary battery according to claim 2, a negative electrode, and an electrolyte.