JP2011129258A - Cathode active material for nonaqueous electrolyte secondary battery, method for producing the same, and nonaqueous electrolyte secondary battery using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cathode active material for a nonaqueous electrolyte secondary battery solving a problem of a cathode active material mainly composed of lithium-nickel composite oxide, and capable of absorption/releasing of lithium ions having excellent load characteristics while maintaining long life, and a method for producing the same as well as a nonaqueous electrolyte secondary battery using the same. <P>SOLUTION: Oxide containing Zn and Al is coated on a surface of cathode active material particles mainly composed of lithium-nickel composite oxide. The oxide containing Zn and Al preferably has a ratio "a" of Al to Zn to be 0<a≤16 mol%. Moreover, a mass ratio w of the oxide containing Zn and AL to the mass of the cathode active material preferably has a relation of 0<w≤20 mass%. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery capable of occluding and releasing lithium ions, a method for producing the same, and a non-aqueous electrolyte secondary battery using the same.

  Currently, non-aqueous electrolyte secondary batteries that use a non-aqueous electrolyte and charge and discharge by moving lithium ions between the positive and negative electrodes are used as secondary batteries with high energy density. .

As such a non-aqueous electrolyte secondary battery, LiCoO ₂ is generally used as a positive electrode active material, and a lithium metal, a lithium alloy, or a carbon material capable of occluding and releasing lithium is used as a negative electrode active material. For example, an electrolyte made of lithium salt such as LiBF ₄ or LiPF ₆ dissolved in an organic solvent such as ethylene carbonate or diethyl carbonate is used.

However, cobalt contained in LiCoO ₂ is expensive and has a limited reserve as a resource, and is a scarce resource, resulting in high production costs. For this reason, utilization of lithium nickel composite oxide (LiNiO ₂ etc.), lithium manganese composite oxide (LiMn ₂ O ₄ etc.), etc. is examined as a positive electrode material replacing LiCoO ₂ . In particular, lithium-nickel composite oxides mainly composed of Ni (LiNi _x M _1-x O ₂ , 0 <x <1, M is a transition metal other than Ni and Co, Al, Mn, Fe, Ti, etc.) are LiCoO _2. It is attracting attention because of its high capacity and relatively low cost.

  However, since the positive electrode active material made of a lithium nickel composite oxide has disadvantages such as a low life and structural instability, it is required to improve these characteristics. As one means for that, surface modification of the positive electrode active material as shown in Patent Documents 1 and 2 below has been studied. That is, in Patent Documents 1 and 2 below, an amphoteric compound such as zinc, tin, or lead on the surface of the positive electrode active material (Patent Document 1), The surface modifying material which consists of metal oxides (patent document 2), such as Mg, Si, Ti, and Al, is coated.

JP 2008-277307 A JP2001-028265

  In the positive electrode active material coated with these surface modifiers, it is considered that the battery life characteristics are improved by blocking direct contact between the positive electrode active material and the electrolytic solution, but sufficient effects are obtained. Therefore, it is necessary to coat the surface of the positive electrode active material with a certain amount of the surface modifying material. However, the coating layer made of the surface modifying material described in Patent Documents 1 and 2 cannot be said to be excellent in electronic conductivity, and increases the resistance of the surface of the positive electrode active material. There is a problem in that there is a risk of causing a decrease in load characteristics accompanying the increase.

  The present invention solves the problems of the positive electrode active material comprising such a lithium nickel composite oxide, and has a non-aqueous electrolyte capable of occluding and releasing lithium ions having excellent load characteristics while maintaining a long life. It aims at providing the positive electrode active material for secondary batteries, its manufacturing method, and a nonaqueous electrolyte secondary battery using the same.

  In order to achieve the above object, the positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention is coated with an oxide containing Zn and Al on the surface of positive electrode active material particles mainly composed of a lithium nickel composite oxide. Characterized by wearing.

In an oxide containing Zn and Al, Zn ions are substituted with Al ions in the ZnO crystal structure, and one electron is emitted, so that Zn alone, Al alone, Sn, Pb, Mg, Si, Ti Electron conductivity is superior to each oxide such as. Therefore, according to the positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention, the surface of the positive electrode active material particle mainly composed of lithium nickel composite oxide is coated with an oxide containing Zn and Al having excellent electron conductivity. The positive electrode active material for a non-aqueous electrolyte secondary battery having excellent load characteristics while maintaining a long life as compared with the positive electrode active material mainly composed of the lithium nickel composite oxide of the conventional example. Can be obtained. The lithium nickel composite oxide that can be used as the positive electrode active material for the non-aqueous electrolyte secondary battery of the present invention includes Li _{1 + x} Ni _y M _1-y O ₂ , 0 ≦ x <0.5, 0.3 ≦ y ≦ 1, M is a transition metal other than Ni, and preferably contains at least one selected from Co, Al, Mn, Fe, Ti, Mg, Cr, Ga, Cu, and Zn.

  In the positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention, the oxide containing Zn and Al has a ratio a of Al to Zn (Al / Zn: mol%) of 0 <a ≦ 16 mol. % Is preferred.

  In the oxide containing Zn and Al, the electron conductivity is improved by increasing the ratio of Al to Zn. Conversely, when the ratio of Al to Zn is higher than 16 mol%, the electron conductivity is decreased. To do. Therefore, the Al ratio a to Zn is preferably 0 <a ≦ 16 mol%.

  In the positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention, the mass ratio w of the oxide containing Zn and Al with respect to the mass of the positive electrode active material is preferably 0 <w ≦ 20% by mass. .

  According to the positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention, by increasing the mass ratio w of the oxide containing Zn and Al with respect to the mass of the positive electrode active material, the oxide containing Zn and Al The surface modification reduces the resistance of the positive electrode active material and, as a result, improves the discharge load characteristics of the battery. Conversely, if the surface modification is too large, the discharge capacity per mass of the positive electrode active material decreases. Therefore, in the positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention, it is preferable that 0 <w ≦ 20% by mass.

  Furthermore, in order to achieve the above object, the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention includes an excessive amount of Li source relative to the stoichiometric composition of the lithium nickel composite oxide during firing of the positive electrode active material. The positive electrode active material mainly composed of a lithium nickel composite oxide in which the Li salt remains on the surface of the positive electrode active material (hereinafter referred to as a Li-excess composition) is charged into a solution in which a metal salt containing Zn and Al is dissolved. Stirring, depositing an oxide containing Zn and Al on the surface using Li salt remaining on the surface of the positive electrode active material as a catalyst, and drying and heat-treating the obtained positive electrode active material powder To do.

  A metal salt containing Zn and Al is dissolved in a solvent, and a positive electrode active material mainly composed of a lithium-nickel composite oxide having an excess of Li is added thereto, whereby the residual Li salt on the surface of the positive electrode active material acts as a catalyst. Then, a metal salt containing Zn and Al is hydrolyzed to obtain a positive electrode active material powder in which an oxide containing Zn and Al and a hydroxide containing Zn and Al are attached to the surface of the positive electrode active material. When the obtained positive electrode active material powder is dried and heat-treated, the hydroxide containing Zn and Al is easily dehydrated and changed to an oxide containing Zn and Al.

  As conditions for heat-treating the obtained positive electrode active material powder, it is desirable that the temperature be lower than the firing temperature (about 700 ° C.) of the positive electrode active material. If it is higher than this, substitution of Li and Ni in the crystal structure of the positive electrode active material (cation mixing) may occur, and the discharge capacity may be reduced. Therefore, the heat treatment condition is desirably 700 ° C. or lower. Also, when the heat treatment temperature is low, it is more desirable because in the oxide containing Zn and Al, Zn ions and Al ions are not sufficiently substituted and dissolved in the crystal, and good electron conductivity may not be obtained. Is 300-500 ° C.

  Further, in the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention, as the lithium nickel composite oxide having an excessive Li composition, the lithium nickel composite oxide having an excessive Li composition includes a nickel salt, Co, After obtaining nickel composite hydroxide by coprecipitation from an aqueous solution containing at least one salt selected from Al, Mn, Fe, Ti, Mg, Cr, Ga, Cu, Zn, lithium hydroxide Can be used by adding and then baking.

  According to the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention, it is possible to easily obtain a lithium-nickel composite oxide having a Li-excess composition having a large Li salt catalytic activity.

  In the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention, it is preferable to use an alcohol solution in which zinc acetate and aluminum acetate are dissolved as the solution in which the metal salt containing Zn and Al is dissolved. .

  Metal salts such as zinc acetate and aluminum acetate used in the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention are relatively inexpensive and the alcohol solution is stable. Therefore, according to the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention, an oxide containing Zn and Al can be easily formed on the surface of a lithium nickel composite oxide having a Li-rich composition. .

  Furthermore, in order to achieve the above object, the nonaqueous electrolyte secondary battery of the present invention comprises a positive electrode containing any one of the positive electrode active materials described above, a negative electrode, and a nonaqueous electrolyte. To do.

  The positive electrode used in the nonaqueous electrolyte secondary battery of the present invention can be produced in the same manner as the conventional positive electrode for nonaqueous electrolytic secondary batteries. For example, any positive electrode active material powder, conductive agent powder, and binder are mixed in an organic solvent to prepare a positive electrode mixture slurry, and the positive electrode mixture slurry is adjusted to have a constant thickness. A positive electrode used in the non-aqueous electrolyte secondary battery of the present invention can be produced by applying it to the surface of an aluminum foil as an electric body and then compressing it after drying so as to have a predetermined packing density and thickness.

  The conductive agent added to the positive electrode mixture may be any material having conductivity, and at least one of oxides, carbides, nitrides, and carbon materials that are particularly excellent in conductivity can be used. Examples of the oxide include tin oxide and indium oxide. Examples of the carbide include tungsten carbide and zirconium carbide. Examples of the nitride include titanium nitride and tantalum nitride.

  When the conductive agent is added in this way, if the amount added is small, the conductivity in the positive electrode cannot be sufficiently improved. On the other hand, if the amount added is too large, the proportion of the active material in the positive electrode is small. Thus, a high energy density cannot be obtained. For this reason, the amount of the conductive agent is in the range of 0% by mass to 30% by mass, preferably 0% by mass to 20% by mass, more preferably 0% by mass to 10% by mass of the whole positive electrode mixture. To be.

  The binder to be added to the positive electrode mixture is selected from polytetrafluoroethylene, polyvinylidene fluoride, polyethylene oxide, polyvinyl acetate, polymethacrylate, polyacrylate, polyacrylonitrile, polyvinyl alcohol, styrene-butadiene rubber, and ruboxymethyl cellulose. Can be used.

  When the amount of the binder added to the positive electrode mixture is large, the ratio of the positive electrode active material contained in the positive electrode mixture becomes small, so that a high energy density cannot be obtained. Therefore, the amount of the binder is 0% by mass or more and 30% by mass or less, preferably 0% by mass or more and 20% by mass or less, more preferably 0% by mass or more and 10% by mass or less.

  Nonaqueous solvents that can be used in the nonaqueous electrolyte of the nonaqueous electrolyte secondary battery of the present invention include cyclic carbonates, chain carbonates, esters, cyclic ethers, chain ethers, nitriles, amides. And the like.

  Examples of the cyclic carbonate include ethylene carbonate, propylene carbonate, butylene carbonate and the like, and those in which some or all of these hydrogen groups are fluorinated can also be used. Ethyl carbonate or the like can be used. As the chain carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl isopropyl carbonate, etc. can be used, and some or all of these hydrogens are fluorinated. It is also possible to use what is.

  Examples of the esters include methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and γ-butyrolactone. As cyclic ethers, 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, propylene oxide, 1,2-butylene oxide, 1,4-dioxane, 1,3,5 -Trioxane, furan, 2-methylfuran, 1,8-cineol, crown ether and the like.

  As chain ethers, 1,2-dimethoxyethane, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, dihexyl ether, ethyl vinyl ether, butyl vinyl ether, methyl phenyl ether, ethyl phenyl ether, butyl phenyl ether, pentyl phenyl Ether, methoxytoluene, benzyl ethyl ether, diphenyl ether, dibenzyl ether, o-dimethoxybenzene, 1,2-diethoxyethane, 1,2-dibutoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, 1,1 -Dimethoxymethane, 1,1-diethoxyethane, triethylene glycol dimethyl ether, tetraethy Such as glycol dimethyl ether, and the like.

  Examples of nitriles include acetonitrile, and examples of amides include dimethylformamide. And the nonaqueous solvent which can be used with the nonaqueous electrolyte of the nonaqueous electrolyte secondary battery of this invention can use at least 1 sort (s) selected from these.

In addition, as an electrolyte salt that can be used in the nonaqueous electrolyte of the nonaqueous electrolyte secondary battery of the present invention, those generally used as an electrolyte in conventional nonaqueous electrolyte secondary batteries can be used, for example, Selected from LiBF ₄ , LiPF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiAsF ₆ , lithium difluoro (oxalato) borate At least one of the above can be used.

  Examples of the negative electrode used in the present invention include materials capable of inserting and extracting lithium, such as carbon materials such as lithium metal, lithium alloy, and graphite, silicon materials, and lithium composite oxides.

It is a figure which shows the structure of the monopolar test cell used by each Example and the comparative example. It is a graph which shows the relationship between the discharge load characteristic of Examples 1-4 and Comparative Examples 1-3, and the ratio a of Al with respect to Zn in the oxide containing Zn and Al. It is a graph which shows the relationship between the discharge load characteristic of Example 1, 5, 6 and the comparative example 3, and the mass ratio of the oxide containing Zn and Al with respect to the mass of a positive electrode active material.

  Hereinafter, the form for implementing this invention is demonstrated in detail using an Example and a comparative example. However, the following examples show one example of a nonaqueous electrolyte secondary battery for embodying the technical idea of the present invention, and are not intended to limit the present invention to this example. The present invention can be equally applied to various modifications without departing from the technical idea shown in the claims.

[Example 1]
First, a specific method for producing a monopolar test cell as a nonaqueous electrolyte secondary battery used in Example 1 will be described.
[Synthesis of positive electrode active material]
An aqueous solution was prepared using sulfates of nickel, cobalt, and aluminum, and nickel cobalt aluminum hydroxide was obtained by coprecipitation by dropping a lithium hydroxide aqueous solution into the aqueous solution. Lithium hydroxide was added thereto, so that the amount of Li charged was Li / (Ni + Co + Al) = 1.12 to obtain a nickel-cobalt aluminum hydroxide powder having an excessive lithium composition. Next, the nickel-cobalt aluminum hydroxide powder having an excessive lithium composition was fired at 700 ° C. for 20 hours in an oxygen atmosphere to synthesize an Li-rich lithium nickel composite oxide powder containing cobalt and aluminum. .

The amount of each element of the Li-rich lithium nickel composite oxide was analyzed by ICP-AES (inductively coupled plasma emission analysis) method. As a result, Li _1.12 Ni _0.80 Co _0.15 Al _0.05 O ₂ I confirmed that there was. Next, in 200 ml of ethanol, zinc acetate and aluminum acetate are added at a ratio of Al to Zn of a = 8 mol% and stirred at 75 ° C. for 2 hours to prepare a metal salt solution having a concentration of 0.1M. did. Then, 0.33 mol of Li _1.12 Ni _0.80 Co _0.15 Al _0.05 O ₂ synthesized therein was added and stirred for 30 minutes, whereby residual Li salt (LiOH) was used as a catalyst on the surface of the positive electrode active material. An oxide containing Zn and Al was surface-modified. The deposition amount of the oxide containing Zn and Al was set to 5% by mass with respect to the mass of the positive electrode active material. Next, the obtained positive electrode active material was dried and heat-treated at 300 ° C. for 2 hours to obtain a powder of the positive electrode active material of the present invention.

[Production of monopolar test cell]
The positive electrode active material was 95% by mass, and acetylene black as a conductive agent was 2.5% by mass of the total positive electrode mixture, and mixed. Thereafter, polyvinylidene fluoride (PVdF) as a binder is added to this so as to be 2.5% by mass of the entire positive electrode mixture, and an appropriate amount of N-methylpyrrolidone (NMP) is added and mixed, and the positive electrode mixture slurry Was prepared. This positive electrode mixture slurry was applied to one side of a 15 μm thick Al foil using a doctor blade and dried at 110 ° C. using a hot plate. This was cut into a size of 2 cm × 2 cm and rolled using a roller. This was vacuum dried at 110 ° C. and used as a positive electrode plate. Moreover, the lithium metal cut to the predetermined magnitude | size was used for the negative electrode. Moreover, lithium metal was cut into a predetermined size to prepare a reference electrode.

Furthermore, as the non-aqueous electrolyte, 1.0 mol / l of lithium hexafluorophosphate (LiPF ₆ ) was added to a non-aqueous solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 3: 7 (25 ° C.). What was added so that it might become the density | concentration of was used. Then, as shown in FIG. 1, in the argon inert atmosphere, the positive electrode plate is used as the working electrode 2, lithium metal is used for the negative electrode 3 and the reference electrode 4 as the counter electrode, and the working electrode 2 and By laminating a separator 5 made of a polyethylene microporous membrane between the negative electrode 3 and between the working electrode 2 and the reference electrode 4, and injecting the nonaqueous electrolyte 7 into the laminate container 6. A monopolar test cell 1 of Example 1 was produced. Reference numeral 8 is a lead wire.

The theoretical capacity of the obtained monopolar test cell 1 is 1 It = 3.5 mA / cm ² , and the area of the positive electrode plate is 2 cm × 2 cm = 4 cm ² , so that 1 It = 14 mA. And the discharge load characteristic and the cycle characteristic were calculated | required on the conditions shown below using the monopolar test cell 1 of the above-mentioned Example 1, respectively.

[Measurement of discharge load characteristics]
Using the monopolar test cell 1 manufactured as described above, charging is performed at 25 ° C. with a constant current of 0.2 It = 2.8 mA until the battery voltage becomes 4.3 V on the basis of lithium. After the voltage of the test cell 1 reached 4.3 V, the battery was charged at a constant voltage of 4.3 V until the charging current reached (1/50) It = 0.28 mA, and the battery was fully charged. Then, the initial discharge capacity | capacitance was calculated | required by discharging the monopolar test cell 1 of a full charge state by 0.2 It = 2.8 mA until it became 2.75V on the basis of lithium. Similarly, 0.8 It = 1.12 mA, 1.2 It = 16.8 mA, and 1 until the voltage reaches 2.75 V on the basis of the lithium for the fully charged single-pole test cell 1. The battery was discharged at a constant current of .6 It = 22.4 mA, and the discharge capacity in each case was determined. The results are summarized in Table 1.

[Measurement of cycle characteristics]
The cycle characteristics were measured at a constant current of 0.2 It = 2.8 mA and a battery voltage of 4.3 V on a lithium basis at 25 ° C. with respect to the monopolar test cell 1 whose initial discharge capacity was measured as described above. Until the voltage of the unipolar test cell 1 reaches 4.3V, the battery is charged at a constant voltage of 4.3V until the charging current reaches (1/50) It = 0.28 mA. Charged. Thereafter, the charge / discharge operation of discharging the fully charged unipolar test cell 1 at 0.2 It = 2.8 mA until the voltage reaches 2.75 V with respect to lithium is performed for 30 cycles, and the discharge capacity at the 30th cycle is set as the initial discharge capacity. As a percentage of The results are summarized in Table 1.

[Examples 2 to 6]
In Example 2, a monopolar test cell was prepared in the same manner as in Example 1 except that in the preparation of the metal salt solution, the ratio a of Al to Zn in zinc acetate and aluminum acetate was set to a = 4 mol%. Discharge load characteristics and cycle characteristics were measured. In Example 3, a monopolar test cell was prepared in the same manner as in Example 1 except that in the preparation of the metal salt solution, the ratio a of Al to Zn was set to a = 12 mol%. The discharge load characteristics and the cycle characteristics were measured. Further, in Example 4, a monopolar test cell was prepared in the same manner as in Example 1 except that in the preparation of the metal salt solution, the ratio a of Al to Zn in zinc acetate and aluminum acetate was set to a = 16 mol%. The discharge load characteristics and the cycle characteristics were measured.

  Further, in Example 5, Li was increased in the same manner as in Example 1 except that the amount of Li charged during synthesis of the positive electrode active material was set to Li / (Ni + Co + Al) = 1.24 in order to increase the residual Li salt serving as a catalyst. An over-composition lithium nickel composite oxide powder was synthesized. In preparation of the metal salt solution, the concentration of the metal salt solution is 0.2 mol / l, the ratio a of zinc acetate and aluminum acetate is a = 8 mol% with respect to Zn, and the oxidation includes Zn and Al. A monopolar test cell was prepared in the same manner as in Example 1 except that the amount of the deposited material was 10% by mass with respect to the mass of the positive electrode active material, and the discharge load characteristics and the cycle characteristics were measured. . Furthermore, in Example 6, a lithium nickel composite oxide powder having a Li-excess composition was prepared in the same manner as in Example 1 except that the amount of Li charged during synthesis of the positive electrode active material was Li / (Ni + Co + Al) = 1.48. Synthesized. In preparation of the metal salt solution, the concentration of the metal salt solution is 0.4 mol / l, the ratio a of zinc acetate and aluminum acetate is Al = 8 mol% with respect to Zn, and the oxide containing Zn and Al is used. A monopolar test cell was prepared in the same manner as in Example 1 except that the amount of the deposited material was 20% by mass with respect to the mass of the positive electrode active material, and the discharge load characteristics and the cycle characteristics were measured. . The results are summarized in Table 1.

[Comparative Examples 1-3]
In Comparative Example 1, a monopolar test cell was prepared in the same manner as in Example 1 except that only zinc acetate was used in preparing the metal salt solution, and the discharge load characteristics and the cycle characteristics were measured. In Comparative Example 2, a monopolar test cell was prepared in the same manner as in Example 1 except that only aluminum acetate was used in the preparation of the metal salt solution, and the discharge load characteristics and the cycle characteristics were measured. In Comparative Example 3, a monopolar test cell was prepared in the same manner as in Example 1 except that an oxide containing Zn and Al was not deposited, and the discharge load characteristics and the cycle characteristics were measured. The results are summarized in Table 1.

  FIG. 2 shows the relationship between the discharge load ratio (vs. 0.2 It) at 1.6 lt of Examples 1 to 4 and Comparative Examples 1 to 3 and the ratio a of Al to Zn in the oxide containing Zn and Al. Indicated. Furthermore, the relationship between the discharge load characteristics of Examples 1, 5, 6 and Comparative Example 3 and the mass ratio of the oxide containing Zn and Al to the mass of the positive electrode active material is shown in FIG.

  From the results shown in Table 1 and FIG. That is, when the ratio of Al to Zn in the oxide containing Zn and Al corresponding to Examples 1 to 4 is 0 <a ≦ 16 mol%, the discharge load factor (vs. 0.2 It) at 1.6 lt is the surface. Compared with Comparative Example 3 without modification, the cycle characteristics are also improved as compared with Comparative Example 3 without surface modification. This is because as the amount of Al in the oxide containing Zn and Al increases, the electron conductivity of the oxide containing surface-modified Zn and Al is improved, and the oxide containing the Zn and Al is also improved. This is probably because the reaction between the positive electrode active material and the non-aqueous electrolyte was suppressed by the surface modification.

In Comparative Example 1 in which a is 0 mol% and composed only of ZnO and Comparative Example 2 composed of only Al ₂ O ₃ , both cycle characteristics are improved as compared with Comparative Example 3 without surface modification. The 6 It discharge load factor is greatly reduced. This is considered to be due to an increase in resistance of the positive electrode active material because ZnO and Al ₂ O ₃ are electrically insulating. From the above results, it is considered that the ratio a of Al to Zn in the oxide containing Zn and Al is preferably 0 <a ≦ 16 mol%.

From the relationship between the discharge load characteristics of Examples 1, 5, 6 and Comparative Example 3 shown in Table 1 and FIG. 3 and the deposition amount w of the oxide containing Zn and Al with respect to the mass of the positive electrode active material, I understand that. That is, it can be confirmed that the initial discharge capacity decreases as the deposition amount w of the oxide containing Zn and Al with respect to the mass of the positive electrode active material increases. This is because the proportion of the lithium nickel composite oxide involved in the charge / discharge reaction in the positive electrode active material decreases. From the above results, in order to fully utilize the merit (high discharge capacity of LiCoO ₂ of about 165 mAh / g) of the lithium nickel composite oxide, the deposition amount of the oxide containing Zn and Al is sufficient. Is preferably 0 <w ≦ 20 mass%.

  As described above, by using the positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention, a non-aqueous electrolyte secondary battery having excellent load characteristics can be obtained while maintaining a long life.

  In Examples 1 to 6 and Comparative Examples 1 to 3, an example in which a monopolar test cell was formed in order to confirm the operation and effect of each battery was shown. This is a positive electrode active material. In order to obtain the non-aqueous electrolyte secondary battery, it may be produced in the same manner as in the conventional example. For example, the NMP solution is 94% by mass of the positive electrode active material of the example obtained as described above, 3% by mass of carbon powder as a conductive agent, and 3% by mass of PVdF powder as a binder. To prepare a slurry. This slurry was applied to both sides of an aluminum current collector having a thickness of 20 μm by a doctor blade method to form an active material layer on both sides of the positive electrode current collector, and then dried by passing through a dryer. A positive electrode plate having a short side length of 30 mm and a long side length of 450 mm is prepared by compressing to a thickness of 130 μm using a roller and cutting.

  As the negative electrode plate, 95% by mass of a negative electrode active material made of graphite powder, 3% by mass of a thickener made of carboxymethylcellulose (CMC), and 2% by mass of a binder made of styrene butadiene rubber (SBR), Mix with appropriate amount of water to make slurry. This slurry is applied on both sides of a copper current collector having a thickness of 20 μm by a doctor blade method to form an active material layer, then dried by passing through a drier, and then made 150 μm in thickness using a compression roller. By compressing and cutting, a negative electrode plate having a short side length of 32 mm and a long side length of 460 mm is produced.

  The positive electrode plate and the negative electrode plate produced as described above are arranged so as to face each other with a separator made of a polyethylene microporous film having a width of 34 mm and a thickness of 25 μm, and then around the cylindrical winding core. Winding to produce a cylindrical electrode body, and then pressing the cylindrical electrode body to obtain a flat spiral electrode body. The flat spiral electrode body produced as described above is inserted into an outer can (5.5 × 35 × 40 mm) and vacuum dried at 110 ° C. Thereafter, 2.5 g of the above-described non-aqueous electrolyte is injected, an aluminum plate is placed in the injection hole, and the non-aqueous electrolyte secondary battery is obtained by sealing with laser welding.

DESCRIPTION OF SYMBOLS 1 ... Single electrode type test cell 2 ... Working electrode 3 ... Negative electrode 4 ... Reference electrode 5 ... Separator 6 ... Laminate container 7 ... Nonaqueous electrolyte 8 ... Lead wire

Claims (7)

  A positive electrode active material for a non-aqueous electrolyte secondary battery, wherein an oxide containing Zn and Al is deposited on the surface of positive electrode active material particles mainly composed of a lithium nickel composite oxide.   2. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the oxide containing Zn and Al has a ratio of Al to Zn of 0 <a ≦ 16 mol%.   2. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein a mass ratio w of an oxide containing Zn and Al to a mass of the positive electrode active material is 0 <w ≦ 20 mass%. .   A positive electrode active material mainly composed of a lithium nickel composite oxide having a Li-excess composition is charged into a solution in which a metal salt containing Zn and Al is dissolved, and the Li salt remaining on the surface of the positive electrode active material is stirred. A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, comprising depositing an oxide containing Zn and Al as a catalyst on a surface, and drying and heat-treating the obtained positive electrode active material powder.   The Li-rich lithium-nickel composite oxide is an aqueous solution containing a nickel salt and at least one salt selected from Co, Al, Mn, Fe, Ti, Mg, Cr, Ga, Cu, and Zn. 5. The non-aqueous electrolyte secondary battery according to claim 4, wherein the nickel composite hydroxide is obtained by coprecipitation, lithium hydroxide is added, and then calcined. A method for producing a positive electrode active material.   The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 4, wherein the solution in which the metal salt containing Zn and Al is dissolved is an alcohol solution in which zinc acetate and aluminum acetate are dissolved. .   A nonaqueous electrolyte secondary battery comprising a positive electrode containing the positive electrode active material according to claim 1, a negative electrode, and a nonaqueous electrolyte.

Images