JP4655599B2 - Cathode active material for non-aqueous electrolyte secondary battery, method for producing the same, and non-aqueous electrolyte secondary battery using the same - Google Patents

Description

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

  In recent years, with the widespread use of portable electronic devices such as mobile phones and notebook computers, development of small and lightweight non-aqueous electrolyte secondary batteries having high energy density is strongly desired. As such a secondary battery, there is a lithium ion secondary battery. Lithium metal, lithium alloy, metal oxide, carbon, or the like is used as a negative electrode material for a lithium ion secondary battery. These materials are materials capable of removing and inserting lithium.

Research and development of such lithium ion secondary batteries is being actively conducted. Among these, a lithium ion secondary battery using a lithium metal composite oxide, in particular, a lithium cobalt composite oxide (LiCoO ₂ ), which is relatively easy to synthesize, as a positive electrode material can obtain a high voltage of 4 V, and thus has high energy. It is expected as a battery having a high density and is being put to practical use. In the lithium ion secondary battery using this lithium cobalt composite oxide (LiCoO ₂ ), many developments have been made so far to obtain excellent initial capacity characteristics and cycle characteristics, and various results have already been obtained. ing.
However, since lithium cobalt complex oxide (LiCoO ₂ ) uses a rare and expensive cobalt compound as a raw material, it causes an increase in battery cost. For this reason, it is desired to use materials other than lithium cobalt composite oxide (LiCoO ₂ ) as the positive electrode active material.

In addition, recently, not only small secondary batteries for portable electronic devices but also expectations for applying lithium ion secondary batteries as large-sized secondary batteries for power storage and electric vehicles are increasing. . For this reason, reducing the cost of the active material and making it possible to manufacture a cheaper lithium ion secondary battery is expected to have a large ripple effect in a wide range of fields. The positive electrode active material for lithium ion secondary batteries As newly proposed materials, lithium manganese composite oxide (LiMn ₂ O ₄ ) using manganese, which is cheaper than cobalt, and lithium nickel composite oxide (LiNiO ₂ ) using nickel can be cited. it can.

Lithium-manganese composite oxide (LiMn ₂ O ₄ ) is a powerful alternative to lithium-cobalt composite oxide (LiCoO ₂ ) because it is inexpensive and has excellent thermal stability, in particular, safety with respect to ignition. Although it can be said that the theoretical capacity is only about half that of lithium cobalt composite oxide (LiCoO ₂ ), it has a drawback that it is difficult to meet the demand for higher capacity of lithium ion secondary batteries, which is increasing year by year. Further, at 45 ° C. or higher, there is a drawback that self-discharge is intense and the charge / discharge life is also reduced.

On the other hand, lithium nickel composite oxide (LiNiO ₂ ) has almost the same theoretical capacity as lithium cobalt composite oxide (LiCoO ₂ ), and shows a slightly lower battery voltage than lithium cobalt composite oxide. For this reason, decomposition | disassembly by oxidation of electrolyte solution does not become a problem, and development is performed actively from expecting higher capacity | capacitance. However, when a lithium-ion secondary battery is made using a lithium-nickel composite oxide composed solely of nickel as a positive electrode active material without replacing nickel with other elements, the cycle is higher than that of lithium-cobalt composite oxide. The characteristics are inferior. In addition, there is a disadvantage that battery performance is relatively easily lost when used or stored in a high temperature environment.

In order to solve such drawbacks, for example, in Patent Document 1, Li _w Ni _x Co _y B _z O _{2 is} used as a positive electrode active material capable of maintaining good battery performance during storage and use in a high temperature environment. Lithium nickel composite oxide represented by (0.05 ≦ w ≦ 1.10, 0.5 ≦ x ≦ 0.995, 0.005 ≦ z ≦ 0.20, x + y + z = 1), that is, boron is added. Lithium-containing composite oxides have been proposed.

In Patent Document 2, in order to improve the self-discharge characteristics and cycle characteristics of the lithium ion secondary _{battery, Li x Ni a Co b M} c O 2 (0.8 ≦ x ≦ 1.2,0. 01 ≦ a ≦ 0.99, 0.01 ≦ b ≦ 0.99, 0.01 ≦ c ≦ 0.3, 0.8 ≦ a + b + c ≦ 1.2, M is Al, V, Mn, Fe, Cu and A lithium nickel composite oxide represented by at least one element selected from Zn has been proposed.

  However, in the lithium nickel composite oxide obtained by the above-described conventional manufacturing method, both the charge capacity and discharge capacity are higher and the cycle characteristics are improved as compared with the lithium cobalt composite oxide. If left in the environment, there is a problem that oxygen is released from a temperature lower than that of the cobalt-based composite oxide.

In order to solve such a problem, for example, in Patent Document 3, Li _{a Mb} Ni _c Co _d O _e (M is Al) for the purpose of improving the thermal stability of the positive electrode material of the lithium ion secondary battery. , Mn, Sn, In, Fe, V, Cu, Mg, Ti, Zn, Mo, and at least one metal selected from the group consisting of 0 <a <1.3, 0.02 ≦ d / c + d ≦ 0.9, 1.8 <e <2.2, and b + c + d = 1) has been proposed. In this case, for example, when aluminum is selected as the additive element M, it is confirmed that if the amount of substitution from nickel to aluminum is increased, the decomposition reaction of the positive electrode active material is suppressed and the thermal stability is improved. However, replacing nickel with aluminum, which is effective to ensure sufficient stability, reduces the amount of nickel that contributes to the oxidation-reduction reaction associated with the charge / discharge reaction, so the initial capacity, which is the most important for battery performance, is large. It had the problem of decreasing. Since Al is trivalent and stable, Ni is also matched to charge, and if it is stabilized with trivalent, a portion that does not contribute to the Redox reaction is generated, and it is considered that the capacity decreases.

In Patent Document 4, the general formula _{LiNi 1-x Co y M z} O 2 ( however, 0.1 ≦ x ≦ 0.3,0.05 ≦ y ≦ 0.28,0.02 ≦ z ≦ 0. 25, x = y + z, and M is composed of at least one of Mg, Al, Ca, Ti, V, Cr, Mn, and Fe). A nickel-cobalt-M salt aqueous solution having a salt concentration adjusted, a complexing agent that forms a complex salt with the aqueous solution, and an alkali metal hydroxide, respectively, to form a nickel-cobalt-M complex salt, Next, the complex salt is decomposed with an alkali metal hydroxide to precipitate nickel-cobalt-M hydroxide, and the complex salt is repeatedly generated and decomposed while circulating in the tank. Overflow The nickel-cobalt-M hydroxide having a substantially spherical particle shape obtained by taking it out is used as a raw material, or further calcined to obtain a nickel-cobalt-M oxide, and then a lithium salt is added thereto. It is described that it is obtained by mixing and baking.

  This improves the polarization characteristics of the lithium-containing composite oxide active material by co-precipitation of two or more hydroxides in nickel hydroxide and restricts one of them to cobalt. When the oxide is coprecipitated to stabilize the lattice, the composite element coprecipitated hydroxide obtained by this method is used as a positive electrode active material for a lithium ion secondary battery. It is described that the initial capacity increases as compared with the case where cobalt-nickel hydroxide which is a coprecipitated hydroxide is used, and cycle deterioration due to repeated charge and discharge is suppressed.

In Example 5 of Patent Document 4, Ni _0.75 Co _0.20 Ti _0.05 (OH) _2, which is a nickel-cobalt-M hydroxide, is produced using titanium sulfate as the M salt. However, when the inventors tried to make it, titanium sulfate is almost insoluble in water when it is trivalent, and is water-soluble when it is tetravalent. However, since it is easy to cause hydrolysis, a nickel-cobalt-M aqueous solution is used. It was found that the nickel-cobalt-M hydroxide could not be obtained stably, the titanium hydroxide segregated, and the grain growth became difficult, which was unsuitable industrially.

Recently, the demand for higher capacity for small secondary batteries such as portable electronic devices has been increasing year by year, and sacrificing capacity to ensure safety has the advantage of high capacity of lithium nickel composite oxide. You will lose. In addition, a movement to use a lithium ion secondary battery for a large-sized secondary battery is also prominent. In particular, there is a great expectation as a power source for a hybrid vehicle and an electric vehicle. When used as a power source for automobiles, solving the problem of the lithium nickel composite oxide that is inferior in safety is a big problem.
JP-A-8-45509 Japanese Patent Laid-Open No. 8-213015 Japanese Patent Laid-Open No. 5-242891 JP-A-10-27611

  The present invention has been made in view of such problems, and stably coprecipitates nickel, cobalt and titanium hydroxides, titanium hydroxides are not segregated, and grain growth proceeds. Nickel-cobalt-M hydroxide is obtained, and the positive electrode active material produced using the hydroxide as a raw material is used for the positive electrode of a non-aqueous electrolyte secondary battery. An object is to provide a positive electrode active material having a discharge capacity.

Inventors have general formula _{Li 1 + Z Ni 1-x} -y Co x M y O 2 ( where, 0.10 ≦ x ≦ 0.21,0.03 ≦ y ≦ 0.08, -0.05 ≦ z As a result of intensive studies on the lithium-metal composite oxide powder represented by ≦ 0.10), titanium is preferable as the additive element M for improving the thermal stability in the charged state, and in particular, uniform nickel-cobalt. -From the point of preparing titanium hydroxide, we found that it was necessary to use titanyl sulfate as the added titanium salt, and added an alkaline solution to a mixed aqueous solution of nickel salt and cobalt salt and a sulfuric acid aqueous solution of titanyl sulfate to add nickel and A composite hydroxide Ni _1-xy Co _x Ti _y (OH) ₂ obtained by coprecipitation of a hydroxide of cobalt and titanium and a lithium compound are mixed, and the mixture is heated to 650 ° C. or higher and 800 ° C. It has been found that a positive electrode active material for a non-aqueous electrolyte secondary battery obtained by heat treatment at a temperature of ℃ or less becomes a positive electrode active material having good thermal stability and high charge / discharge capacity. It came to be completed.

The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention refers to a lithium metal composite oxide Li _{1 + Z} Ni _1-xy Co _x Ti _y O ₂ (where 0.10 ≦ x ≦ 0. 21, 0.03 ≦ y ≦ 0.08, −0.05 ≦ z ≦ 0.10), a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, comprising a nickel salt and a cobalt salt By adding an alkaline solution to a mixed aqueous solution and a sulfuric acid aqueous solution of titanyl sulfate, and co-precipitating nickel, cobalt and titanium hydroxides under the conditions of 50 ° C. or higher and 80 ° C. or lower and pH 10 or higher and 12.5 or lower. The obtained composite hydroxide Ni _1-xy Co _x Ti _y (OH) ₂ (where 0.10 ≦ x ≦ 0.21, 0.03 ≦ y ≦ 0.08) and a lithium compound And the mixture is 650 ° C. or higher and 800 ° C. or lower. It is characterized in that the heat treatment in degrees.

  Another method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention is characterized in that the sulfuric acid aqueous solution of titanyl sulfate is a titanyl sulfate aqueous solution containing 10 wt% or more of sulfuric acid. In addition, the lithium compound is lithium carbonate, lithium hydroxide, or a hydrate thereof.

Moreover, the positive electrode active material for nonaqueous electrolyte secondary batteries according to the present invention is a lithium metal composite oxide Li _{1 + Z} Ni _1-x obtained by the method for producing a positive electrode active material for nonaqueous electrolyte secondary batteries described above. _-Y Co _x Ti _y O ₂ (where 0.10 ≤ x ≤ 0.21, 0.03 ≤ y ≤ 0.08, -0.05 ≤ z ≤ 0.10) Furthermore, the other positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention is a non-aqueous electrolyte secondary material obtained by the above- described method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery. As a result of measuring the positive electrode active material for the secondary battery by the energy dispersion method, the peak intensity of the _Ti K-line is expressed as I _Ti , and the peak intensity of the Ni L-line is measured regardless of the range of the active material. standard deviation of the intensity ratio _{I Ti} / _{I Ni} when the I _Ni There is a half less of the intensity ratio _{I Ti} / _{I Ni} average always the composition formula _{Li 1 + Z Ni 1-x} -y Co x Ti y O 2 ( where, 0.10 ≦ x ≦ 0.21,0 .03 ≦ y ≦ 0.08, −0.05 ≦ z ≦ 0.10).

  The nonaqueous electrolyte secondary battery according to the present invention is characterized in that the positive electrode active material for a nonaqueous electrolyte secondary battery described above is used for a positive electrode.

The positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention has a general formula Li _{1 + Z} Ni _1-xy Co _x Ti _y O ₂ (where 0.10 ≦ x ≦ 0.21, 0.03 ≦ y ≦ 0.08, −0.05 ≦ z ≦ 0.10), and the powder is a mixed aqueous solution of nickel salt and cobalt salt and an aqueous solution of titanyl sulfate as titanium salt. A composite hydroxide Ni _1-xy Co _x Ti _y (OH) ₂ obtained by coprecipitation of hydroxides of nickel, cobalt and titanium by adding an alkaline solution and a lithium compound are mixed, and the mixture It is a positive electrode active material for a non-aqueous electrolyte secondary battery that can be obtained by heat treatment at a temperature of 650 ° C. or higher and 800 ° C. or lower. By stabilizing the It is possible to prevent a decrease in the initial capacity of the battery due to the replacement of the nickel with another element. Moreover, when it uses as a positive electrode of a lithium ion battery by substituting with titanium with strong oxidizing power, the thermal stability of a battery can be aimed at.

  By using the positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention, a large capacity for a hybrid vehicle and an electric vehicle can be satisfied. A non-aqueous electrolyte secondary battery capable of ensuring the safety required as a power source used for the secondary battery can be obtained and is industrially useful.

  The charge / discharge reaction of the secondary battery according to the present invention proceeds by reversibly entering and exiting lithium ions in the positive electrode active material. The positive electrode active material from which lithium has been extracted by charging is unstable at high temperatures, and when heated, the active material decomposes and releases oxygen, which causes combustion of the electrolyte and an exothermic reaction. To improve the thermal stability of the positive electrode material means to suppress the decomposition reaction of the positive electrode active material from which lithium has been extracted. As a method for suppressing the decomposition reaction of the positive electrode active material disclosed heretofore, it has been generally performed that a part of nickel is substituted with an element having strong covalent bond with oxygen such as aluminum. Certainly, if the amount of substitution from nickel to aluminum is increased, the decomposition reaction of the positive electrode active material is suppressed and the thermal stability is improved, but the amount of nickel contributing to the redox reaction accompanying the charge / discharge reaction is reduced. In order to reduce the charge / discharge capacity, the amount of substitution with aluminum had to be limited to some extent. As a result, a sufficient reversible capacity could not be obtained when sufficient thermal stability was ensured, and thermal stability had to be sacrificed in order to obtain a certain level of capacity.

Therefore, in order to solve the above problems, the general formula _{Li 1 + Z Ni 1-x} -y Co x M y O 2 ( where, 0.10 ≦ x ≦ 0.21,0.03 ≦ y ≦ 0.08, -0.05 ≦ z ≦ 0.10), and by substituting with tetravalent and stable titanium as the additive element M, a part of Ni is made trivalent. Since it is possible to prevent a decrease in the initial capacity of the battery by substituting nickel for another element by being stabilized at divalent, titanium as an additive element M is preferable for improving thermal stability in a charged state. In particular, it is necessary to use titanyl sulfate from the viewpoint of producing a uniform nickel-cobalt-titanium hydroxide.

In the present invention, the general formula Li _{1 + Z} Ni _1-xy Co _x Ti _y O ₂ (where 0.10 ≦ x ≦ 0.21, 0.03 ≦ y ≦ 0.08, −0.05 ≦ z ≦ The lithium nickel cobalt titanium composite oxide having a layered structure represented by 0.10) is first of nickel salt and cobalt salt so that the atomic ratio of cobalt, nickel and titanium is the atomic ratio of the above general formula. Add alkaline solution to mixed aqueous solution and aqueous solution of titanyl sulfate, stir them at a constant speed, and co-precipitate in reaction tank so that atomic ratio of cobalt, nickel and titanium is the atomic ratio of the above general formula . Then, after reaching a steady state, a precipitate is collected, filtered and washed with water to obtain a nickel cobalt titanium composite hydroxide. Thereafter, this is mixed with a lithium compound and subjected to heat treatment to obtain a lithium nickel cobalt titanium composite oxide useful as a positive electrode active material for a lithium ion secondary battery in a desired ratio.

  Next, embodiments of the lithium ion secondary battery according to the present invention will be described in detail for each component. The lithium ion secondary battery according to the present invention is composed of the same components as those of a general lithium ion secondary battery, such as a positive electrode, a negative electrode, and a non-aqueous electrolyte. The embodiments described below are merely examples, and the non-aqueous electrolyte secondary battery of the present invention is implemented in various modified and improved embodiments based on the knowledge of those skilled in the art, including the following embodiments. can do. Moreover, the use of the nonaqueous electrolyte secondary battery of the present invention is not particularly limited.

(1) Positive electrode active material, positive electrode The positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention has a general formula Li _{1 + Z} Ni _1-xy Co _x Ti _y O ₂ (where 0.10 ≦ x ≦ 0 .21, 0.03 ≦ y ≦ 0.08, −0.05 ≦ z ≦ 0.10).
The present invention is characterized in that a composite hydroxide in which three elements are uniformly dispersed is obtained by preparing a composite aqueous solution of nickel salt and cobalt salt and an aqueous solution of titanyl sulfate and simultaneously adding them together with an alkaline aqueous solution. This is because when preparing a mixed aqueous solution of nickel salt, cobalt salt and titanium salt, titanium chloride or titanium sulfate, which is representative of titanium salt, is hydrolyzed or oxidized at that time, and titanium hydroxide or titanium oxide is generated. This is because segregation occurs. Therefore, it is industrially necessary to use titanyl sulfate having high solubility in water as the titanium salt to be used.

Next, the manufacturing method of the positive electrode active material for nonaqueous electrolyte secondary batteries which concerns on this invention is demonstrated.
The positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention is obtained by adding an alkaline solution to a mixed aqueous solution of nickel salt and cobalt salt and an aqueous titanyl sulfate solution, stirring them at a constant speed, Coprecipitation is performed so that the atomic ratio of nickel, titanium, and titanium is the atomic ratio of the above general formula. Then, after reaching a steady state, a precipitate is collected, filtered and washed with water to obtain a nickel cobalt titanium composite hydroxide. Thereafter, nickel cobalt titanium composite hydroxide obtained by coprecipitation of nickel, cobalt and titanium hydroxide and a lithium compound are mixed, and the mixture is heat-treated at a temperature of 650 ° C. to 800 ° C. is required.

  As the lithium compound, lithium carbonate, lithium hydroxide, and hydrates thereof are preferable. Nickel oxide, nickel carbonate, nickel nitrate, nickel hydroxide, nickel oxyhydroxide, etc. can be used as the nickel compound, and oxides, carbonates, etc. can be used as the compound related to the additive element. It is more preferable to use an oxide or a complex oxide. Moreover, it is preferable to use a titanyl sulfate aqueous solution containing 10 wt% or more of sulfuric acid as the titanyl sulfate. This is because in general titanium chloride and titanium sulfate, hydrolysis or oxidation proceeds at that time, and titanium hydroxide or titanium oxide is generated, causing segregation of titanium. Therefore, as the titanium salt to be used, it is industrially necessary to use titanyl sulfate having high solubility in water and to be a sulfuric acid aqueous solution. When titanyl sulfate containing less than 10 wt% sulfuric acid is hydrolyzed during storage and titanium hydroxide is precipitated to produce a composite hydroxide, segregation of titanium occurs, which is not industrially preferable.

The reaction conditions vary depending on whether or not a complexing agent is used, but coprecipitation is performed by adding an alkaline solution so that the mixed aqueous solution has a pH of 10 to 12.5 in a temperature range of 50 ° C. to 80 ° C. Let After stirring at a constant speed under a predetermined condition and the inside of the reaction tank is in a steady state, the overflowed precipitate can be collected, filtered and washed with water to obtain nickel cobalt titanium composite hydroxide particles.
By this method, particles in which the atomic ratio of nickel, cobalt, and titanium is uniformly mixed can be obtained. Furthermore, the obtained particles are nearly spherical, and have good filterability and excellent handling properties.

  Unlike the conventional method, the titanium solution is added separately from the nickel or cobalt salt mixed aqueous solution. When the sulfuric acid aqueous solution of titanyl sulfate and the other sulfuric acid mixed aqueous solution are mixed first, the hydrolysis of titanium occurs due to the decrease in sulfuric acid concentration. Since segregation may occur and titanium hydroxide is amphoteric and redissolved with acid and alkali, sulfuric acid and caustic soda in the reaction solution are consumed for re-dissolution of titanium hydroxide and nickel and cobalt are dissolved. This is because the growth of the particles is not promoted because the precipitation is inhibited, and the powder tends to be fine.

  As for the pH region, when there is no complexing agent, pH = 10 to 11 is selected, and the temperature of the mixed aqueous solution is set to a range of more than 60 ° C. and 80 ° C. or less. In the absence of a complexing agent, crystallization occurs at a pH higher than pH 11, particularly around pH 13, resulting in fine particles, poor filterability and no spherical particles. On the other hand, if the pH is less than 10, the rate of hydroxide formation is remarkably slow, Ni remains in the filtrate, and the amount of precipitation of Ni deviates from the target composition, making it impossible to obtain a mixed hydroxide of the target ratio. End up. As described above, by adjusting the pH to 10 to 11 and maintaining the temperature of the mixed aqueous solution above 50 ° C., that is, by increasing the reaction temperature and increasing the solubility of Ni, the amount of precipitation of Ni can be reduced by the desired composition. It avoids the phenomenon that it does not co-precipitate due to deviation. At this time, if the temperature of the mixed aqueous solution exceeds 80 ° C., the slurry concentration becomes high due to a large amount of water evaporation, the solubility of Ni decreases, and crystals such as sodium sulfate are generated in the filtrate, and the impurity concentration Since a state that causes a decrease in charge / discharge capacity of the positive electrode material occurs, such as an increase in the positive electrode material, it is not preferable. On the other hand, in the case of using a complexing agent such as ammonia, the solubility of Ni increases, so that the pH range can be expanded to pH 10 to 12.5 and the temperature range can be expanded to 50 ° C. to 80 ° C. The metal composite hydroxide is preferably composed of spherical secondary particles in which a plurality of primary particles of 1 μm or less are aggregated.

The positive electrode active material of the present invention is prepared by mixing a predetermined amount of a lithium compound and the composite hydroxide Ni _1-xy Co _x Ti _y (OH) ₂ obtained by the above method, and in an oxygen stream at 650 ° C. It can synthesize | combine by baking for about 10 to 20 hours at the temperature of about -800 degreeC. When the temperature is lower than 650 ° C., the reaction with the lithium compound does not proceed sufficiently, and it becomes difficult to synthesize a lithium nickel composite oxide having a desired layered structure. When the temperature exceeds 800 ° C., Ni is mixed into the Li layer and Li is mixed into the Ni layer, so that the layered structure is disturbed, and the site occupancy rate of metal ions other than lithium at the 3a site becomes larger than 2%. The metal ion mixing rate at the 3a site is increased, the lithium ion diffusion path is hindered, and a battery using the positive electrode is not preferable because the initial capacity and output are reduced.

  Moreover, d50 of the particle size distribution of the obtained positive electrode active material is preferably 4.5 to 8.1 μm, and the tap density is preferably 1.2 to 1.76 g / ml. If it is out of the above range, it becomes unsuitable as a positive electrode material, for example, the positive electrode active material cannot be sufficiently filled when producing the positive electrode.

Next, the positive electrode mixture forming the positive electrode and each material constituting the positive electrode mixture will be described.
General formula Li _{1 + Z} Ni _1-xy Co _x Ti _y O ₂ (where 0.10 ≦ x ≦ 0.21, 0.03 ≦ y ≦ 0.08, −0.05 ≦ z ≦ 0.10) For example, the positive electrode using the lithium metal composite oxide represented by (2) is produced as follows.

  A powdered positive electrode active material, a conductive material, and a binder are mixed, and activated carbon and a target solvent such as viscosity adjustment are added as necessary, and these are kneaded to prepare a positive electrode mixture paste. The respective mixing ratios in the positive electrode mixture are also important factors that determine the performance of the lithium secondary battery. When the total mass of the solid content of the positive electrode mixture excluding the solvent is 100% by mass, the content of the positive electrode active material is 60 to 95% by mass as in the case of the positive electrode of a general lithium secondary battery. It is desirable that the content is 1 to 20% by mass and the content of the binder is 1 to 20% by mass. The obtained positive electrode mixture paste is applied to the surface of a current collector made of, for example, aluminum foil, and dried to disperse the solvent. If necessary, pressurization may be performed by a roll press or the like to increase the electrode density. In this way, a sheet-like positive electrode can be produced. The sheet-like positive electrode can be cut into an appropriate size according to the intended battery and used for battery production. However, the manufacturing method of the positive electrode is not limited to the above-described examples, and may depend on other methods.

In producing the positive electrode, as the conductive agent, for example, graphite (natural graphite, artificial graphite, expanded graphite, etc.), carbon black materials such as acetylene black, ketjen black, and the like can be used.
As the binder, for example, polyvinylidene fluoride, polytetrafluoroethylene, ethylene propylene diene rubber, fluororubber, styrene butadiene, cellulose resin, polyacrylic acid, and the like can be used.
The binder plays a role of holding the active material particles, and for example, fluorine-containing resins such as polytetrafluoroethylene, polyvinylidene fluoride, and fluororubber, and thermoplastic resins such as polypropylene and polyethylene can be used. If necessary, a positive electrode active material, a conductive material, and activated carbon are dispersed, and a solvent that dissolves the binder is added to the positive electrode mixture. Specifically, an organic solvent such as N-methyl-2-pyrrolidone can be used as the solvent. Activated carbon can be added to the positive electrode mixture in order to increase the electric double layer capacity.

(2) Negative electrode For the negative electrode, metallic lithium, lithium alloy, or the like, and a negative electrode mixture made by mixing a binder with a negative electrode active material capable of occluding and desorbing lithium ions and adding an appropriate solvent to form a paste. In addition, it is applied to the surface of a metal foil current collector such as copper, dried, and compressed to increase the electrode density as necessary.
As the negative electrode active material, for example, natural graphite, artificial graphite, a fired organic compound such as phenol resin, or a powdery carbon material such as coke can be used. In this case, as the negative electrode binder, a fluorine-containing resin such as polyvinylidene fluoride can be used as in the case of the positive electrode, and the active material and the solvent for dispersing the binder include N-methyl-2-pyrrolidone. Organic solvents can be used.

(3) Separator A separator is interposed between the positive electrode and the negative electrode. The separator separates the positive electrode and the negative electrode and retains the electrolyte, and a thin film such as polyethylene or polypropylene and a film having many fine holes can be used.

(4) Non-aqueous electrolyte The non-aqueous electrolyte is obtained by dissolving a lithium salt as a supporting salt in an organic solvent.
Examples of the organic solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and trifluoropropylene carbonate; chain carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, and dipropyl carbonate; and tetrahydrofuran, 2- One kind selected from ether compounds such as methyltetrahydrofuran and dimethoxyethane, sulfur compounds such as ethylmethylsulfone and butanesultone, phosphorus compounds such as triethyl phosphate and trioctyl phosphate, etc. are used alone or in admixture of two or more. be able to.
As the supporting salt, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , or a composite salt thereof can be used.
Furthermore, the non-aqueous electrolyte solution may contain a radical scavenger, a surfactant, a flame retardant, and the like.

(5) Shape and configuration of battery The shape of the lithium secondary battery according to the present invention composed of the positive electrode, the negative electrode, the separator, and the non-aqueous electrolyte described above is various, such as a cylindrical type and a laminated type. be able to.
In any case, the positive electrode and the negative electrode are laminated via a separator to form an electrode body, and this electrode body is impregnated with the non-aqueous electrolyte. The positive electrode current collector and the positive electrode terminal that communicates with the outside, and the negative electrode current collector and the negative electrode terminal that communicates with the outside are connected using a current collecting lead or the like. The battery having the above structure can be sealed in a battery case to complete the battery.
[Example]

Hereinafter, an embodiment of the present invention will be described in detail with reference to the preferred drawings. Table 1 summarizes the composition of Li _{1 + Z} Ni _1-xy Co _x Ti _y O ₂ synthesized in each example and comparative example and the evaluation results thereof.

  Prepare a mixed solution of nickel sulfate and cobalt sulfate and an aqueous solution of titanyl sulfate so that the molar ratio of nickel: cobalt: titanium is 81: 15: 4, and simultaneously add 12.5% sodium hydroxide solution to the reaction vessel. The nickel cobalt titanium composite hydroxide particles were formed by a coprecipitation method while keeping the pH in the range of 10 to 11 and the reaction temperature in the range of 50 to 80 ° C. Thereafter, the entire amount of hydroxide slurry in the reaction vessel was recovered, filtered, washed with water and dried to obtain a dry powder of nickel cobalt titanium composite hydroxide.

  After weighing this nickel cobalt titanium composite hydroxide and commercially available lithium carbonate (manufactured by FMC) so that the atomic ratio of nickel cobalt titanium and lithium is 1: 1.05, the shape of spherical secondary particles is The mixture was sufficiently mixed using a shaker mixer (TURBULA Type T2C manufactured by WAB Co., Ltd.) at such a strength as to be maintained. 20 g of this mixture was inserted into a 5 cm × 12 cm × 3 cm magnesia firing vessel, and heated to 730 ° C. at a heating rate of 5 ° C./min in an oxygen stream with a flow rate of 3 L / min using a closed electric furnace. The mixture was baked for 10 hours and then cooled to room temperature.

The obtained fired product was analyzed by X-ray diffraction. As shown in FIG. 1, the fired product had a hexagonal layered structure containing no heterogeneous phase, and chemical analysis methods (ICP emission analyzer for Ni, Co, and Ti). (OPTIMA 3300DV manufactured by PERKINELMER), Li was analyzed by atomic absorption analysis (analyzed by VARIAN, Spectr AA-40 atomic absorption method), and the composition formula (Li _1.05 Ni _0.81 Co _0.15 Ti _0.04 It was found to be a positive electrode active material that becomes O ₂ ). D50 of the particle size distribution measured by Microtrac was 6.6 μm, and the tap density was 1.46 g / ml.
Moreover, about the positive electrode active material which consists of this metal complex oxide, the dispersion | variation in a composition was judged by the energy dispersion method using the energy dispersion measuring apparatus (EDX apparatus FALCON by EDAX). The measurement was carried out by placing the composite oxide on a conductive double-sided tape on a sample stage with a thickness of several particles, applying a vacuum, checking the image with an SEM, setting a measurement target, and measuring.
The measurement conditions were a voltage of 15 kV, a current of 10 ⁻⁹ to 10 ⁻¹⁰ A, an electron beam diameter of 3 to 5 nm, and an extraction angle of 20 °. In this measurement, information on a thickness of several μm is picked up by a part of the composite oxide particles. In the above measurement, it is judged by the average value and standard deviation of the intensity ratio I _Ti / I _Ni where n = 10 when the peak intensity of Ti K-line is I _Ti and the peak intensity of Ni L-line is I _Ni. did.
As a result of measurement at n = 10, the peak intensity of the _Ti K-line is I _Ti , and the peak intensity of the Ni L-line is I I regardless of the range of the positive electrode active material made of this metal composite oxide. The average value when _Ni is 0.045 and the standard deviation is 0.005, which always satisfies the composition formula Li _1.05 Ni _0.81 Co _0.15 Ti _0.04 O ₂ .
The above measurement method was also used in other examples and comparative examples.

The initial capacity evaluation of the obtained positive electrode active material was performed as follows. 70% by mass of the active material powder was mixed with 20% by mass of acetylene black and 10% by mass of PTFE, and 150 mg was taken out from this to produce a pellet to obtain a positive electrode. Lithium metal was used as the negative electrode, and an equivalent mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC) (made by Toyama Pharmaceutical Co., Ltd.) using 1M LiClO ₄ as a supporting salt was used as the electrolyte. A 2032 type coin battery as shown in FIG. 1 was produced in an Ar atmosphere glove box whose dew point was controlled at −80 ° C.

The produced battery is left for about 24 hours, and after the open circuit voltage OCV (Open Circuit Voltage) is stabilized, the current density with respect to the positive electrode is set to 0.5 mA / cm ² and charged to a cutoff voltage of 4.3 V to obtain an initial charge capacity. The capacity when the battery was discharged to a cutoff voltage of 3.0 V after a one hour rest was defined as the initial discharge capacity.

The safety evaluation of the positive electrode is performed by CCCV charging (constant current-constant voltage charging. First, charging is operated at a constant current) to a cutoff voltage of 4.5V using a 2032 type coin battery manufactured by the same method as described above. Then, the charging method using a charging process of two phases of ending charging at a constant voltage.), And then disassembling with care not to short-circuit, and taking out the positive electrode. 3.0 mg of this electrode was measured, 1.3 mg of the electrolyte was added, sealed in an aluminum measurement container, and a temperature increase rate of 10 ° C./degree using a differential scanning calorimeter (DSC) (PTC-10A manufactured by Rigaku). The heat generation behavior was measured from room temperature to 400 ° C. in min.
Table 1 shows the elemental analysis value of the obtained lithium nickel cobalt titanium composite oxide, the initial discharge capacity obtained by battery evaluation, and the heat generation rate obtained by DSC measurement.

A metal composite hydroxide having a nickel: cobalt: titanium molar ratio of 78: 15: 7 was prepared in the same manner as in Example 1, and this was performed in the same manner as in Example 1 with lithium and metal. Were mixed at a molar ratio of 1.05: 1, calcined in an oxygen stream at a flow rate of 3 L / min for 2 hours at 500 ° C. for 2 hours, and then heated at a rate of 5 ° C./min. After heating up to 730 ° C. and baking for 10 hours, the furnace was cooled to room temperature. The obtained fired product was analyzed by X-ray diffraction and chemical analysis. As a result, a positive electrode active material (Li _1.05 Ni _0.78 Co _0.15 Ti _0.07 having a hexagonal layer structure not containing a heterogeneous phase) was obtained. O ₂ ). D50 of the particle size distribution measured by Microtrac was 6.1 μm, and the tap density was 1.56 g / ml.
The positive electrode active material composed of this metal composite oxide was measured by the energy dispersion method in the same manner as in Example 1. As a result, the peak intensity of the _Ti K-line was measured as I _Ti , Ni. The average value of the intensity ratio I _Ti / I _Ni when the peak intensity of the L line is I _Ni is 0.078, the standard deviation is 0.015, and the composition formula is always Li _1.05 Ni _0.78 Co _{0 .15} Ti _0.07 O ₂ was satisfied.
The initial capacity evaluation of this positive electrode active material was performed in the same manner as in Example 1. Table 1 shows the obtained initial discharge capacity and the heat generation rate of the positive electrode obtained from the DSC measurement.

A metal composite hydroxide having a nickel: cobalt: titanium molar ratio of 81: 15: 4 was prepared in the same manner as in Example 1, and this was performed in the same manner as in Example 1 with lithium and metal. Were mixed at a molar ratio of 1.05: 1, calcined in an oxygen stream at a flow rate of 3 L / min for 2 hours at 500 ° C. for 2 hours, and then heated at a rate of 5 ° C./min. After heating up to 800 ° C. and baking for 10 hours, the furnace was cooled to room temperature. The obtained fired product was analyzed by X-ray diffraction and chemical analysis. As a result, the positive electrode active material (Li _1.05 Ni _0.81 Co _0.15 Ti _{0. 04} O ₂ ). D50 of the particle size distribution measured by Microtrac was 8.04 μm, and the tap density was 1.76 g / ml.
The positive electrode active material composed of this metal composite oxide was measured by the energy dispersion method in the same manner as in Example 1. As a result, the peak intensity of the _Ti K-line was measured as I _Ti , Ni. next average value of the intensity ratio _{I Ti} / _{I Ni} when the peak intensity of the L line was _{I Ni} is 0.052, the standard deviation is 0.012, and the always composition formula _Li 1.05 _{Ni 0.81} Co _{0 .15} Ti _0.04 O ₂ was satisfied.
The initial capacity evaluation of this positive electrode active material was performed in the same manner as in Example 1. Table 1 shows the obtained initial discharge capacity and the heat generation rate of the positive electrode obtained from the DSC measurement.

A metal composite hydroxide having a nickel: cobalt: titanium molar ratio of 81: 15: 4 was prepared in the same manner as in Example 1, and this was performed in the same manner as in Example 1 with lithium and metal. Were mixed at a molar ratio of 1.05: 1, calcined in an oxygen stream at a flow rate of 3 L / min for 2 hours at 500 ° C. for 2 hours, and then heated at a rate of 5 ° C./min. The temperature was raised to 650 ° C., baked for 10 hours, and then cooled to room temperature. The obtained fired product was analyzed by X-ray diffraction and chemical analysis. As a result, the positive electrode active material (Li _1.05 Ni _0.81 Co _0.15 Ti _{0. 04} O ₂ ). D50 of the particle size distribution measured by Microtrac was 4.6 μm, and the tap density was 1.24 g / ml.
This metal composite hydroxide was measured by the energy dispersion method in the same manner as in Example 1. As a result, the peak intensity of the _Ti K-line was measured as I _Ti and the peak of the Ni L-line regardless of the range. When the strength is I _Ni , the average value of the strength ratio I _Ti / I _Ni is 0.063 and the standard deviation is 0.025, and the composition formula Li _1.05 Ni _0.81 Co _0.15 Ti _{0 is} always obtained. _.04 O ₂ was satisfied.
The initial capacity evaluation of this positive electrode active material was performed in the same manner as in Example 1. Table 1 shows the obtained initial discharge capacity and the heat generation rate of the positive electrode obtained from the DSC measurement.

A metal composite hydroxide having a nickel: cobalt: titanium molar ratio of 75: 21: 4 was prepared in the same manner as in Example 1, and this was performed in the same manner as in Example 1 with lithium and metal. Were mixed at a molar ratio of 1.05: 1, calcined at 500 ° C. for 2 hours in an oxygen stream at a flow rate of 3 L / min using a sealed electric furnace, and then the temperature rising rate was 5 ° C./min. Was heated to 730 ° C., baked for 10 hours, and then cooled to room temperature. The obtained fired product was analyzed by X-ray diffraction and chemical analysis. As a result, a positive electrode active material (Li _1.05 Ni _0.75 Co _0.21 Ti _0.04 having a hexagonal layer structure not containing a heterogeneous phase) was obtained. O ₂ ). D50 of the particle size distribution measured by Microtrac was 4.7 μm, and the tap density was 1.26 g / ml.
The positive electrode active material composed of this metal composite oxide was measured by the energy dispersion method in the same manner as in Example 1. As a result, the peak intensity of the _Ti K-line was measured as I _Ti , Ni. next average value of the intensity ratio _{I Ti} / _{I Ni} when the peak intensity of the L line was _{I Ni} is 0.053, the standard deviation is 0.007, and the always composition formula _Li 1.05 _{Ni 0.75} Co _{0 .21} Ti _0.04 O ₂ was satisfied.
The initial capacity evaluation of this positive electrode active material was performed in the same manner as in Example 1. Table 1 shows the obtained initial discharge capacity and the heat generation rate of the positive electrode obtained from the DSC measurement.

A metal composite hydroxide in which the molar ratio of nickel: cobalt: titanium is 86: 10: 4 is prepared in the same manner as in Example 1, and this is performed in the same manner as in Example 1 with lithium and metal. Were mixed at a molar ratio of 1.05: 1, calcined in an oxygen stream at a flow rate of 3 L / min for 2 hours at 500 ° C. for 2 hours, and then heated at a rate of 5 ° C./min. After heating up to 730 ° C. and baking for 10 hours, the furnace was cooled to room temperature. When the obtained fired product was analyzed by X-ray diffraction and chemical analysis, a positive electrode active material (Li _1.05 Ni _0.86 Co _0.10 Ti _0.04 having a hexagonal layer structure not containing a heterogeneous phase) was obtained. O ₂ ). D50 of the particle size distribution measured by Microtrac was 6.6 μm, and the tap density was 1.46 g / ml.
This metal composite hydroxide was measured by the energy dispersion method in the same manner as in Example 1. As a result, the peak intensity of the _Ti K-line was measured as I _Ti and the peak of the Ni L-line regardless of the range. When the strength is I _Ni , the average value of the strength ratio I _Ti / I _Ni is 0.043, the standard deviation is 0.015, and the composition formula is always Li _1.05 Ni _0.86 Co _0.10 Ti _{0. .04} O ₂ was satisfied.
The initial capacity evaluation of this positive electrode active material was performed in the same manner as in Example 1. Table 1 shows the obtained initial discharge capacity and the heat generation rate of the positive electrode obtained from the DSC measurement.
(Comparative Example 1)

A mixed solution of nickel sulfate, cobalt sulfate, and titanium sulfate and a 12.5% sodium hydroxide solution were simultaneously added to the reaction vessel so that the molar ratio of nickel: cobalt: titanium was 81: 15: 4, and the pH was adjusted to 10 to 10. 11, the reaction temperature is kept constant in the range of 60 ° C. to 80 ° C., nickel cobalt titanium composite hydroxide particles are formed by coprecipitation method, and a metal composite hydroxide is produced in the same manner as in Example 1. This was mixed in the same manner as in Example 1 so that the molar ratio of lithium to metal was 1.05: 1. Using a closed electric furnace, this was mixed at 500 ° C. in an oxygen stream with a flow rate of 3 L / min. After calcining for a time, the temperature was raised to 730 ° C. at a rate of temperature rise of 5 ° C./min, baked for 10 hours, and then cooled to room temperature. When the fired product obtained was analyzed by X-ray diffraction and chemical analysis, a positive electrode active material having a hexagonal layered structure (Li _1.05 Ni _0.82 Co _0.16 Ti _0.04 O ₂ ) and It was a mixture of titanium dioxide TiO _2. D50 of the particle size distribution measured by Microtrac was 7.2 μm, and the tap density was 1.54 g / ml.
The positive electrode active material composed of this metal composite oxide was measured by the energy dispersion method in the same manner as in Example 1. As a result, when measured at n = 10, the peak intensity of the _Ti K line was that of the I _Ti and Ni L lines. It can be seen that the average value of the intensity ratio I _Ti / I _Ni when the peak intensity is I _Ni is 0.088, the standard deviation is 0.061, and the composition variation is large. The composition formula Li _1.05 Ni _0.85 Co _0.15 Ti _0.04 O ₂ was not satisfied.
The initial capacity evaluation of this positive electrode active material was performed in the same manner as in Example 1. Table 1 shows the initial discharge capacity obtained thereby and the heat generation rate of the positive electrode obtained from the DSC measurement.
(Comparative Example 2)

A metal composite hydroxide in which the molar ratio of nickel: cobalt: titanium is 70:15:15 was prepared in the same manner as in Example 1, and this was performed in the same manner as in Example 1 with lithium and metal. Were mixed at a molar ratio of 1.05: 1, calcined in an oxygen stream at a flow rate of 3 L / min for 2 hours at 500 ° C. for 2 hours, and then heated at a rate of 5 ° C./min. After heating up to 730 ° C. and baking for 10 hours, the furnace was cooled to room temperature. The obtained fired product was analyzed by X-ray diffraction and chemical analysis. As a result, the positive electrode active material having a hexagonal layered structure (Li _1.05 Ni _0.70 Co _0.15 Ti _0.15 O ₂ ) was used. there were. The d50 of the particle size distribution measured by Microtrac was 8.7 μm, and the tap density was 1.00 g / ml.
The positive electrode active material composed of this metal composite oxide was measured by the energy dispersion method in the same manner as in Example 1. As a result, the peak intensity of the _Ti K-line was measured as I _Ti , Ni. The average value of the intensity ratios I _Ti / I _Ni when the peak intensity of the L line was I _Ni was 0.182, and the standard deviation was 0.063.
The initial capacity evaluation of this positive electrode active material was performed in the same manner as in Example 1. The obtained initial discharge capacity and the heat generation rate of the positive electrode obtained from the DSC measurement are shown in Table 1.
(Comparative Example 3)

A mixed solution of nickel sulfate and cobalt sulfate and a 12.5% sodium hydroxide solution were simultaneously added to the reaction vessel so that the molar ratio of nickel: cobalt was 82:18, and the pH was in the range of 10-11 and the reaction temperature was A metal composite hydroxide in which nickel cobalt titanium composite hydroxide particles were formed by coprecipitation method while being kept constant in the range of 60 ° C. to 80 ° C. was produced in the same manner as in Example 1, and this was the same as in Example 1. In the same manner as above, the molar ratio of lithium and metal was mixed to 1.05: 1, and calcined at 500 ° C. for 2 hours in an oxygen stream at a flow rate of 3 L / min using a sealed electric furnace. After heating up to 730 degreeC with the temperature increase rate of 5 degree-C / min and baking for 10 hours, the furnace was cooled to room temperature. When the obtained fired product was analyzed by X-ray diffraction and chemical analysis, it was a positive electrode active material (Li _1.05 Ni _0.82 Co _0.18 O ₂ ) having a hexagonal layered structure. The particle size distribution d50 measured with Microtrac was 9.0 μm, and the tap density was 1.54 g / ml.
Since the positive electrode active material made of this metal composite oxide did not contain titanium, measurement by the energy dispersion method was not performed.
The initial capacity evaluation of the obtained positive electrode active material was performed in the same manner as in Example 1, and the initial discharge capacity obtained and the heat generation rate of the positive electrode obtained from the DSC measurement are shown in Table 1.
(Comparative Example 4)

A metal composite hydroxide having a nickel: cobalt: titanium molar ratio of 81: 15: 4 was prepared in the same manner as in Example 1, and this was performed in the same manner as in Example 1 with lithium and metal. Were mixed at a molar ratio of 1.05: 1, calcined in an oxygen stream at a flow rate of 3 L / min for 2 hours at 500 ° C. for 2 hours, and then heated at a rate of 5 ° C./min. After heating up to 900 ° C. and baking for 10 hours, the furnace was cooled to room temperature. The obtained fired product was analyzed by X-ray diffraction and chemical analysis. As a result, the positive electrode active material having a hexagonal layer structure (Li _1.05 Ni _0.81 Co _0.15 Ti _0.04 O ₂ ) was used. there were. The d50 of the particle size distribution measured by Microtrac was 2.55 μm, and the tap density was 2.63 g / ml.
The positive electrode active material made of this metal composite oxide was measured by the energy dispersion method in the same manner as in Example 1. As a result, when the Ti K-line peak intensity was I _Ti and the Ni L-line peak intensity was I _Ni. The average value of the intensity ratios I _Ti / I _Ni is 0.052 and the standard deviation is 0.032, which indicates that the composition variation is large.
The initial capacity evaluation of this positive electrode active material was performed in the same manner as in Example 1. Table 1 shows the obtained initial discharge capacity and the heat generation rate of the positive electrode obtained from the DSC measurement.
(Comparative Example 5)

A metal composite hydroxide having a nickel: cobalt: titanium molar ratio of 81: 15: 4 was prepared in the same manner as in Example 1, and this was performed in the same manner as in Example 1 with lithium and metal. Were mixed at a molar ratio of 1.05: 1, calcined in an oxygen stream at a flow rate of 3 L / min for 2 hours at 500 ° C. for 2 hours, and then heated at a rate of 5 ° C./min. After heating up to 600 ° C. and baking for 10 hours, the furnace was cooled to room temperature. When the obtained fired product was analyzed by X-ray diffraction and chemical analysis, a positive electrode active material having a hexagonal layered structure (Li _1.05 Ni _0.83 Co _0.12 Ti _0.04 O ₂ ) and It was a mixture of nickel oxide NiO. D50 of the particle size distribution measured by Microtrac was 3.21 μm, and the tap density was 1.81 g / ml.
The positive electrode active material made of this metal composite oxide was measured by the energy dispersion method in the same manner as in Example 1. As a result, when the Ti K-line peak intensity was I _Ti and the Ni L-line peak intensity was I _Ni. The average value of the intensity ratios I _Ti / I _Ni is 0.093, the standard deviation is 0.062, and it can be seen that the composition variation is large.
The initial capacity evaluation of the obtained positive electrode active material was performed in the same manner as in Example 1, and the obtained initial discharge capacity is shown in Table 1. Note that the DSC measurement was not performed because the initial discharge capacity was too low.
(Comparative Example 6)

A metal composite hydroxide in which the molar ratio of nickel: cobalt: titanium is 74: 22: 4 is prepared in the same manner as in Example 1, and this is performed in the same manner as in Example 1 with lithium and metal. Were mixed at a molar ratio of 1.05: 1, calcined in an oxygen stream at a flow rate of 3 L / min for 2 hours at 500 ° C. for 2 hours, and then heated at a rate of 5 ° C./min. After heating up to 730 ° C. and baking for 10 hours, the furnace was cooled to room temperature. The obtained fired product was analyzed by X-ray diffraction and chemical analysis. As a result, the positive electrode active material (Li _1.05 Ni _0.74 Co _0.22 Ti _0.04 O ₂ ) having a hexagonal layered structure was used. there were. D50 of the particle size distribution measured by Microtrac was 4.4 μm, and the tap density was 1.11 g / ml.
The positive electrode active material made of this metal composite oxide was measured by the energy dispersion method in the same manner as in Example 1. As a result, when the Ti K-line peak intensity was I _Ti and the Ni L-line peak intensity was I _Ni. The average value of the intensity ratio I _Ti / I _Ni was 0.052, the standard deviation was 0.009, and the composition variation was small.
The initial capacity evaluation of this positive electrode active material was performed in the same manner as in Example 1. The obtained initial discharge capacity and the heat generation rate of the positive electrode obtained from the DSC measurement are shown in Table 1.
(Comparative Example 7)

A metal composite hydroxide having a nickel: cobalt: titanium molar ratio of 87: 9: 4 was prepared in the same manner as in Example 1, and this was performed in the same manner as in Example 1 with lithium and metal. Were mixed at a molar ratio of 1.05: 1, calcined in an oxygen stream at a flow rate of 3 L / min for 2 hours at 500 ° C. for 2 hours, and then heated at a rate of 5 ° C./min. After heating up to 730 ° C. and baking for 10 hours, the furnace was cooled to room temperature. The obtained fired product was analyzed by X-ray diffraction and chemical analysis. As a result, the positive electrode active material having a hexagonal layered structure (Li _1.05 Ni _0.87 Co _0.09 Ti _0.04 O ₂ ) was used. there were. The d50 of the particle size distribution measured by Microtrac was 7.5 μm, and the tap density was 1.43 g / ml.
The positive electrode active material made of this metal composite oxide was measured by the energy dispersion method in the same manner as in Example 1. As a result, when the Ti K-line peak intensity was I _Ti and the Ni L-line peak intensity was I _Ni. The average value of the strength ratio I _Ti / I _Ni was 0.035, the standard deviation was 0.008, and the composition variation was relatively small.
The initial capacity evaluation of the obtained positive electrode active material was performed in the same manner as in Example 1. Table 1 shows the obtained initial discharge capacity and the heat generation rate of the positive electrode obtained from the DSC measurement.

［評価］

[Evaluation]

As shown in Table 1, since the lithium nickel cobalt titanium composite oxides obtained in Examples 1 to 6 were uniformly dissolved in titanium, the initial discharge capacity exceeded 180 (mAh / g), and lithium cobalt It can be seen that this is a material that can be used as a new battery material to replace the composite oxide (LiCoO ₂ ).
The present inventors have confirmed that there is no practical problem with safety as an actual battery if the calorific value is suppressed to 11.00 mJ / sec / g or less in the safety evaluation using DSC.
The positive electrode active materials shown in Examples 1 to 6 have a small calorific value of 11.00 mJ / sec / g or less, indicating that the material is highly safe.

  On the other hand, since the lithium nickel cobalt titanium composite oxide obtained in Comparative Example 1 used titanium sulfate as a titanium raw material, it was analyzed by X-ray diffraction. As a result, the positive electrode active material having a hexagonal layered structure and titanium dioxide were analyzed. It can be seen that it is a mixture, and since titanium is segregated, the initial discharge capacity is 180 (mAh / g) or less, indicating that the battery material is not desirable. In addition, the calorific value exceeds 11.00 mJ / sec / g, indicating that the material is not desirable for safety.

Comparative Example 2 is an example in which the molar ratio of nickel: cobalt: titanium is 70:15:15. The lithium nickel cobalt titanium composite oxide thus obtained has a large amount of titanium, and there is no safety problem, but the initial discharge capacity is low, and the voltage is lower than that of the lithium cobalt composite oxide (LiCoO ₂ ), so the energy density is low. There is a practical problem as a low positive electrode active material. Moreover, although the comparative example 3 is an example which did not substitute with titanium, there is a problem on safety because the heat generation rate is large. Comparative Examples 6 and 7 are cases in which the amount of cobalt is out of the range of the present invention, the initial discharge capacity is low, and in Comparative Example 7 where the amount of cobalt is small, the heat generation rate is large and there is also a safety problem. I know that there is.

  Comparative Example 4 is a case where the firing temperature is too high at 900 ° C., and the initial discharge amount is low, the layered structure of the positive electrode active material is disturbed, and it is estimated that the diffusion path of lithium ions is inhibited. . On the other hand, in Comparative Example 5, since the firing temperature was as low as 600 ° C., the reaction with the lithium compound did not proceed sufficiently, and nickel oxide was present in addition to the lithium nickel composite oxide having the desired layered structure. I understood from the analysis. For this reason, the initial discharge amount of the obtained positive electrode active material is low.

  In order to take advantage of the non-aqueous electrolyte secondary battery of the present invention that has high initial capacity while being excellent in safety, it is suitable for use as a power source for small portable electronic devices that always require high capacity It is. In addition, in the power source for electric vehicles, it is indispensable to ensure safety by increasing the size of the battery and to install an expensive protection circuit for ensuring higher safety. The secondary battery has excellent safety, so that not only is it easy to ensure safety, but it can also be used as a power source for electric vehicles in that it can simplify expensive protection circuits and reduce costs. Is also suitable. The electric vehicle power source can be used not only for an electric vehicle driven purely by electric energy but also for a so-called hybrid vehicle used in combination with a combustion engine such as a gasoline engine or a diesel engine.

X-ray diffraction diagram of Example 1 Cross section of coin battery used for battery evaluation

Explanation of symbols

1 Lithium metal negative electrode 2 Separator (electrolyte impregnation)
3 Positive electrode (Evaluation electrode)
4 Gasket 5 Negative electrode can 6 Positive electrode can 7 Current collector

Claims (6)

Lithium metal composite oxide Li _{1 + Z} Ni _1-xy Co _x Ti _y O ₂ (however, 0.10 ≦ x ≦ 0.21, 0.03 ≦ y ≦ 0.08, −0.05 ≦ z ≦ 0 .10) a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, wherein an alkaline solution is added to a mixed aqueous solution of nickel salt and cobalt salt and a sulfuric acid aqueous solution of titanyl sulfate, and the temperature is 50 ° C. to 80 ° C. Composite hydroxide Ni _1-xy Co _x Ti _y (OH) obtained by coprecipitation of hydroxides of nickel, cobalt and titanium under the conditions of pH 10 to 12.5 below ₂ (where 0.10 ≦ x ≦ 0.21, 0.03 ≦ y ≦ 0.08) and a lithium compound are mixed, and the mixture is heat-treated at a temperature of 650 ° C. to 800 ° C. Cathode active for non-aqueous electrolyte secondary batteries Method of manufacturing quality.   The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the sulfuric acid aqueous solution of titanyl sulfate is a titanyl sulfate aqueous solution containing 10 wt% or more of sulfuric acid.   The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the lithium compound is lithium carbonate, lithium hydroxide, or a hydrate thereof. A lithium metal composite oxide Li _{1 + Z} Ni _1-xy Co _x Ti _y O ₂ (obtained by the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1. However, the positive electrode for a non-aqueous electrolyte secondary battery, characterized by comprising a powder of 0.10 ≦ x ≦ 0.21, 0.03 ≦ y ≦ 0.08, −0.05 ≦ z ≦ 0.10) Active material As a result of measuring the positive electrode active material for a nonaqueous electrolyte secondary battery obtained by the method for producing a positive electrode active material for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 3, by an energy dispersion method, Regardless of which range of the active material is measured, the standard deviation of the intensity ratio I _Ti / I _Ni when the peak intensity of the _Ti K line is I _Ti and the peak intensity of the Ni L line is I _Ni Is within 1/2 of the average value of the intensity ratio I _Ti / I _Ni , and is always represented by the composition formula Li _{1 + Z} Ni _1-xy Co _x Ti _y O ₂ (where 0.10 ≦ x ≦ 0.21, 0.03 ≦ y ≦ 0.08 and −0.05 ≦ z ≦ 0.10). A positive electrode active material for a non-aqueous electrolyte secondary battery.   A non-aqueous electrolyte secondary battery using the positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 4 for a positive electrode.

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