JP5565579B2 - Method for producing positive electrode active material for non-aqueous electrolyte secondary battery - Google Patents

Description

The present invention relates to a method for producing a positive electrode active material composed of a lithium-containing composite oxide and applied to a non-aqueous electrolyte secondary battery. More specifically, the present invention relates to a method for producing a positive electrode active material for a non-aqueous secondary battery that has excellent cycle characteristics and can improve the thermal stability of the battery without impairing the initial capacity of the battery.

  In recent years, with the advancement of electronic technology, electronic devices are rapidly becoming smaller and lighter. In particular, as portable electronic devices such as mobile phones and notebook computers have recently become popular and highly functional, it is strongly desired to develop small and lightweight batteries with high energy density for portable power sources used in these devices. ing.

  Lithium ion secondary batteries, which are non-aqueous electrolyte secondary batteries, are small and have high energy, and are therefore used as power sources for portable electronic devices such as mobile phones, video camcorders, and notebook computers. In addition to these small electronic devices, research and development aimed at use as a large-scale power source for hybrid vehicles and electric vehicles is also underway. From such a background, lithium-ion secondary batteries are required to have higher capacity and higher output, but at the same time, it is also required to realize high safety and high cost performance.

A lithium cobalt composite oxide (LiCoO ₂ ), which is relatively easy to synthesize, is used as the positive electrode active material of such a lithium ion secondary battery. This positive electrode active material is a rare and expensive cobalt as a raw material. Since a compound is used, it causes a cost increase. Lowering the cost of active materials and making it possible to manufacture cheaper lithium-ion secondary batteries has significant industrial significance in reducing the cost of portable devices that are currently in widespread use and mounting them in future large batteries. Have.

Lithium nickel composite oxide (LiNiO ₂ ), which is one of the positive electrode materials for lithium ion secondary batteries, has a higher capacity than the current mainstream lithium cobalt composite oxide, and the raw material nickel compared to cobalt. Since it has the advantages of being inexpensive, stable and available, it is expected to be a next-generation cathode material and is actively researched and developed.

  However, when the lithium-nickel composite oxide is left in a fully charged state in a high-temperature environment, the decomposition of the lithium-nickel composite oxide with oxygen release starts at a lower temperature than the lithium-cobalt composite oxide. Has a problem that the battery generates heat due to the reaction between the oxygen and the electrolyte.

In order to solve such problems, improvement of battery characteristics by various additive elements has been studied. For example, Patent Document 1, in order to improve the thermal stability of the lithium ion secondary battery positive electrode _{material, Li a M b Ni c Co} d O e (M is, Al, 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 ≦ b ≦ 0.5, 0.02 ≦ d / c + d ≦ 0.9, 1.8 <e <2.2, and b + c + d = 1) has been proposed. For example, when aluminum is selected as the additive element M, it has been 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 an effective amount of aluminum to ensure sufficient thermal stability substantially reduces the amount of nickel that contributes to the oxidation-reduction reaction with the charge / discharge reaction. There is a problem that the initial capacity, which is important, is greatly reduced.

On the other hand, as an improvement due to the concentration distribution of the additive element, Patent Document 2 describes a LiCoO ₂ core and Al, Mg, Sn, Ca, Ti and the like for the purpose of improving the structural stability and improving the cycle stability. A positive electrode active material for a lithium secondary battery is disclosed, which contains a metal selected from the group consisting of Mn, and the metal is distributed with different concentration gradients from the surface layer to the center of the core. However, this positive electrode active material for lithium secondary batteries is intended to improve the structural stability and improve the cycle stability, and no consideration is given to improving the thermal stability. Moreover, the application to lithium nickel composite oxide is not considered, and the effect is also unclear.

  Furthermore, in Patent Document 3, a seed crystal comprising a lithium manganese composite oxide, a lithium salt, and a manganese compound are wet pulverized and mixed to prepare a slurry. At this time, the number of lithium atoms relative to the number of manganese atoms in the seed crystal The ratio of A is adjusted so that A> B where B is the ratio of the number of lithium atoms derived from the lithium salt to the number of manganese atoms derived from the manganese compound in the slurry, and the resulting slurry is treated with a spray dryer. A lithium manganese composite oxide particle for a non-aqueous lithium secondary battery characterized by having a lithium concentration gradient from the center to the periphery in the particles obtained by firing is disclosed.

  However, the lithium manganese composite oxide particles for the non-aqueous lithium secondary battery are also intended to improve the charge / discharge cycle characteristics, and are not intended to improve the thermal stability. In addition, application to lithium-nickel composite oxide is not considered, and the obtained lithium manganese composite oxide particles for non-aqueous lithium secondary batteries have low initial capacity, high capacity and thermal stability. It is difficult to say that it is a positive electrode active material for a non-aqueous electrolyte secondary battery.

  In recent years, the demand for higher capacity for secondary batteries has been increasing, but sacrificing capacity to ensure safety is losing high capacity, which is the greatest merit of lithium nickel composite oxide. Become. In addition, the movement to use lithium ion secondary batteries as power sources for hybrid vehicles and electric vehicles is also active, and solving the problem of lithium nickel composite oxides that have poor thermal stability is a major issue.

  As described above, a lithium metal composite oxide having both high charge / discharge capacity and thermal stability has not been found, and a nonaqueous electrolyte secondary battery that solves these problems is desired.

Japanese Patent Laid-Open No. 5-242891 JP 2001-243948 A JP 2005-122931 A

As described above, the conventional non-aqueous secondary battery using the lithium nickel composite oxide as the positive electrode active material has a problem that it is difficult to provide high-temperature stability while maintaining a high initial capacity.
The present invention has been made paying attention to such problems, and the problem is that the non-aqueous system can improve the thermal stability of the battery without greatly sacrificing the initial capacity of the battery. It is providing the positive electrode active material for electrolyte secondary batteries, and its manufacturing method.

  In order to solve the above-mentioned problems, the present inventors have conducted various studies. As a result, in using a lithium-containing composite oxide in which a part of nickel is substituted with cobalt and titanium as a positive electrode active material, other than lithium at the lithium site. When the site occupancy rate of the metal ions is 5% or less, in addition to obtaining a non-aqueous electrolyte secondary battery excellent in high-temperature stability while maintaining a high initial capacity, the obtained positive electrode active material is washed with water. As a result, the inventors have found that the initial capacity can be further improved while maintaining excellent high temperature stability. The present invention has been completed based on such technical findings.

That is, the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention includes:
Hexagonal lithium-containing composite oxide having a layered structure represented by the general formula: LiNi _1-xy Co _x Ti _y O 2 (where 0 ≦ x ≦ 0.20, 0 ≦ y ≦ 0.10) And each site of 3a, 3b, 6c in the lithium-containing composite oxide is represented by [Li] _3a [Ni _1-xy Co _x Ti _y ] _3b [O ₂ ] _6c , Method for producing positive electrode active material for non-aqueous electrolyte secondary battery, wherein site occupancy rate of metal ions other than lithium at 3a site obtained from Rietveld analysis of X-ray diffraction pattern of lithium-containing composite oxide is 5% or less in the molar ratio of nickel and cobalt (1-x): dissolved in x, metal complex hydroxide shape of the secondary particles are spherical or spheroidal (where, 0 <x ≦ 0.22) , lithium compounds, and The titanium compound is mixed, and wherein the one having a water washing step of washing with water the obtained lithium-containing composite oxide in the mixture was calcined to obtain a lithium-containing composite oxide firing step and firing step.

  The firing is preferably performed at a temperature of 600 ° C. or higher and lower than 850 ° C. for 4 hours or longer.

  Moreover, in the said water-washing process (c), it is preferable to carry out filtration and drying after 30 to 1 hour stirring by throwing 1 to 2 lithium containing complex oxide with respect to the water 1 by mass ratio with respect to the water 1.

  Furthermore, it is preferable to use lithium hydroxide or a hydrate thereof as the lithium compound.

The positive electrode active material obtained by the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention can achieve high high-temperature stability and high capacity at the same time, and uses the positive electrode active material as a positive electrode. The electrolyte secondary battery is suitable not only for use in small batteries such as portable electronic devices, but also for use in hybrid vehicles and electric vehicles. Moreover, the manufacturing method can respond to production on an industrial scale, and the industrial value of the present invention is extremely large.

It is the perspective view and sectional drawing which show the coin battery used for battery evaluation.

Hereinafter, embodiments of the present invention will be described in detail.
As described above, the present invention is high by applying a lithium-containing composite oxide (LiNi _1-xy Co _x Ti _y O ₂ ) in which a part of nickel is substituted with cobalt and titanium to a positive electrode material. The present invention provides a non-aqueous electrolyte secondary battery excellent in high temperature stability while maintaining the initial capacity.

(1) Positive electrode active material, positive electrode That is, the present invention relates to a positive electrode active material in which a part of nickel is substituted with cobalt for improving cycle characteristics. When the lithium nickel composite oxide (LiNiO ₂ ) is considered as a battery active material, charging / discharging is performed by lithium desorption / insertion. A fully charged state of about 200 mAh / g is a state in which about 70% of lithium is desorbed from LiNiO ₂ . That is, it is Li _0.3 NiO ₂ , but at this time, nickel is partly trivalent and tetravalent. Tetravalent nickel is very unstable and easily releases oxygen at high temperatures to become divalent (NiO). Such decomposition behavior with oxygen release at a high temperature can be evaluated by conducting a thermal analysis of the positive electrode active material in which lithium is extracted by 70 at% and charged. This is because the positive electrode active material in a charged state is sealed together with the electrolytic solution, and the reaction temperature between the decomposition accompanying the oxygen release and the electrolytic solution can be specified by observing the calorific value with respect to the temperature.

As a result of conducting research on the thermal stability of the positive electrode active material by such a method, it was found that titanium is effective in thermal stability. In other words, by further replacing the 3b site of the lithium nickel composite oxide (LiNiO ₂ ) in which a part of nickel is replaced with cobalt with the titanium, the amount of heat generated by the reaction with the electrolytic solution is increased as the amount of titanium increases. A significant effect of reducing the size was observed. However, since the initial capacity tends to decrease as the replacement amount increases, the maximum amount that can be replaced with titanium is about 7 at% from the balance between the improvement in thermal stability and the decrease in the initial capacity. However, the lithium-containing composite oxide in which a part of nickel is substituted with cobalt and titanium can improve the capacity by removing residues such as excess Li compound existing on the particle surface. By doing so, it becomes possible to tolerate a titanium substitution amount of 10 at% or less. In the present invention, it is possible to further increase the initial capacity and the thermal stability by performing a water washing treatment after firing.

The stoichiometry of the lithium-containing composite oxide is examined by Rietveld analysis by X-ray diffraction (for example, R. V. Young, ed., “The Rietveld Method”, Oxford University Press (1992)). The index is the site occupancy of each ion. In the case of a hexagonal compound, there are 3a, 3b, and 6c sites. When LiNiO ₂ has a complete stoichiometric composition, the 3a site is lithium, the 3b site is nickel, and the 6c site is oxygen. % Site occupancy. Therefore, it can be said that the lithium nickel composite oxide having 97% or more is more excellent in stoichiometry as the site occupancy of lithium ions at the 3a site is higher. When considered as a battery active material, since lithium can be desorbed and inserted, crystal integrity can be maintained even if lithium deficiency occurs. Therefore, in practice, it is considered a good method to show the stoichiometry or the crystal perfection with the mixing rate of the metal ions at the 3a site.

  Here, the charge / discharge reaction of the battery proceeds by reversibly entering and leaving the lithium ions at the 3a site. Therefore, when metal ions are mixed into the 3a site, which is the lithium diffusion path in the solid phase, the diffusion path is inhibited, which may cause deterioration of the charge / discharge characteristics of the battery. Therefore, as a result of repeated studies on the positive electrode active materials synthesized by various methods, the occupancy of metal ions other than lithium and the initial characteristics of the battery at the 3a site obtained by Rietveld analysis of the powder X-ray diffraction pattern are deep. It has been found that there is a relationship, and it has been found that the cycle characteristics of the battery can be further improved when this value is 5% or less, preferably 3% or less.

That is, the positive electrode active material for a nonaqueous electrolyte secondary battery obtained by the production method according to the present invention is:
Hexagonal lithium-containing composite oxidation having a layered structure represented by the general formula: LiNi _1-xy Co _x Ti _y O ₂ (where 0 ≦ x ≦ 0.20, 0 ≦ y ≦ 0.10) When the sites 3a, 3b, and 6c in the lithium-containing composite oxide are represented by [Li] _3a [Ni _1-xy Co _x Ti _y ] _3b [O ₂ ] _6c The site occupancy of metal ions other than lithium at the 3a site obtained from the Rietveld analysis of the X-ray diffraction pattern of the lithium-containing composite oxide is 5% or less.

The positive electrode active material includes a metal composite hydroxide (where 0 <x ≦ 0.22), a lithium compound, and a titanium compound, in which the molar ratio of nickel and cobalt is (1-x): x the combined mixed, obtained by the production method having a water washing step of washing with water the obtained lithium-containing composite oxide in the calcination step of obtaining a lithium-containing composite oxide by firing the mixture firing step.

When forming a positive electrode plate of a battery using the positive electrode active material powder, a high tap density is required for the powder itself in order to realize a high packing density. For this purpose, the powder particles are spherical or elliptical and the secondary particles in the metal composite hydroxide used in the firing step are spherical or elliptical. Spherical positive electrode active material powder can be obtained

    Such a metal composite hydroxide having a secondary or spherical spherical shape is obtained by a known neutralization eutectoid method, and the solution concentration, composition, and neutralization conditions are set so as to obtain a desired particle size and shape. Should be selected.

  Examples of the lithium compound include lithium hydroxide, lithium hydroxide monohydrate, lithium carbonate, lithium nitrate, and lithium peroxide, and lithium hydroxide or a hydrate thereof is particularly preferable. The lithium compound is preferably mixed so that lithium is in a ratio of 0.95 to 1.15 with respect to a metal element other than lithium.

  As said mixing method, the method used normally may be sufficient and the method of mixing nickel-cobalt composite hydroxide or composite oxide and a lithium compound with various powder mixers with a solid state is used. Any method may be used, but it may be mixed sufficiently using a shaker or the like so that the composite hydroxide particles or composite oxide particles are not destroyed.

  Examples of the nickel compound include nickel oxide, nickel hydroxide, nickel carbonate, nickel nitrate, and nickel sulfate. Examples of the cobalt compound include cobalt oxide, cobalt hydroxide, cobalt carbonate, cobalt nitrate, cobalt sulfate, and cobalt chloride. Examples of the titanium compound include titanium oxide, titanium chloride, titanyl sulfate and the like in addition to titanium metal.

In firing the above mixture, the temperature is 600 ° C. or higher and lower than 850 ° C., preferably 650 ° C. or higher and 750 ° C. or lower, and 4 hours or longer, so that titanium is completely dissolved without causing a heterogeneous phase such as LiTiO _2. It is possible to make the crystal structure highly complete, that is, the site occupancy of metal ions other than lithium at the 3a site can be 5% or less.

  As the furnace used for firing, various furnaces whose atmosphere can be controlled can be used, but it is preferable to use an electric furnace that does not generate exhaust gas. In industrial production, a pusher furnace, a roller hearth furnace, etc. Thus, it is preferable to use a furnace capable of continuous firing.

  Further, when heat treatment is performed in the firing step, for example, in the range of 600 to 900 ° C. in the air atmosphere, when using metal composite hydroxide, oxidation roasting is performed so that the shape is maintained. Good. It is preferable to perform the heat treatment because the generation of water vapor during firing can be suppressed and the crystallinity of the lithium-containing composite oxide can be further increased. Moreover, the apparatus used may also be a normally used apparatus, and an electric furnace, kiln, tubular furnace, pusher furnace, etc. are used.

  In the water washing step, it is preferable that the fired lithium-containing composite oxide is added to the water 1 in a mass ratio of 1 to 2 to make a slurry, stirred for 30 minutes to 1 hour, filtered and dried. When the lithium-containing composite oxide is more than the above range with respect to water, the removal effect of surface residues such as excess Li compound may not be sufficient, and conversely, when less than the above range, the surface is washed with water. Since the damage is large, battery characteristics such as capacity may deteriorate, which is not preferable.

  In this way, in the hexagonal lithium-containing composite oxide having a layered structure in which a part of nickel is substituted with cobalt and titanium, the site occupancy of metal ions other than lithium at the 3a site is 5% or less. By applying as a positive electrode active material, it is possible to provide a non-aqueous electrolyte secondary battery excellent in high-temperature stability while maintaining a high initial capacity and cycle characteristics.

  Next, the positive electrode mixture forming the positive electrode and each material constituting the positive electrode mixture will be described. The positive electrode is formed from a positive electrode mixture containing a positive electrode active material, a conductive material, and a binder. Since the positive electrode active material is as described above, the description thereof is omitted.

  The conductive material is for ensuring the electrical conductivity of the positive electrode, and for example, a material obtained by mixing one or two or more carbon material powders such as carbon black, acetylene black, and graphite 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.
Moreover, activated carbon can be added to the positive electrode mixture in order to increase the electric double layer capacity.

  The positive electrode is produced as follows. A powdery positive electrode active material, a conductive material, and a binder are mixed, and if necessary, a target solvent such as activated carbon and viscosity adjustment is added and 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, respectively, 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 scatter the solvent. If necessary, pressure may be applied by a roll press or the like to increase the electrode density.

  A sheet-like positive electrode can be manufactured as described above. The sheet-like positive electrode can be cut into an appropriate size according to the intended battery and used for battery production.

(2) Negative electrode For the negative electrode, metallic lithium, lithium alloy, etc., and a negative electrode active material capable of inserting and extracting lithium ions are mixed with a binder, and an appropriate solvent is added to form a paste. The negative electrode mixture 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) Nonaqueous electrolytic solution The nonaqueous electrolytic solution 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 the group consisting of ether compounds such as methyltetrahydrofuran and dimethoxyethane, sulfur compounds such as ethylmethylsulfone and butanesultone, phosphorus compounds such as triethyl phosphate and trioctyl phosphate, or a mixture of two or more. Can be used.
LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , or a composite salt thereof can be used as the lithium salt as the supporting salt.
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 above-described positive electrode, negative electrode, separator, and non-aqueous electrolyte solution are used. The non-aqueous electrolyte secondary battery according to the present invention has a cylindrical shape and a laminated type. Etc., and can be various.
In any case, the positive electrode and the negative electrode are laminated via a separator to form an electrode body, and the electrode body is impregnated with the non-aqueous electrolyte solution. The positive electrode current collector and the positive electrode terminal communicating with the outside, and the negative electrode current collector and the negative electrode terminal communicating 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.

Examples of the present invention will be specifically described below.
Example 1
In order to synthesize the positive electrode active material, a commercially available lithium hydroxide monohydrate, a metal composite hydroxide composed of spherical secondary particles and having a molar ratio of nickel and cobalt of 83:17, and a commercially available product After the titanium oxide was weighed so that the molar ratio of lithium to a metal other than lithium was 1: 1 and the molar ratio of nickel, cobalt, and titanium was 82: 17: 1, spherical secondary particles were obtained. Thoroughly mixed with sufficient strength to maintain the shape of This mixed powder was calcined at 350 ° C. for 2 hours in an oxygen stream, then baked at 750 ° C. for 20 hours, and cooled to the room temperature. The obtained fired product was added to water 1 in a mass ratio of 1.5 to form a slurry, stirred for 30 minutes, filtered, and vacuum dried at 150 ° C. to obtain a positive electrode active material. When the composition of the obtained positive electrode active material was chemically analyzed and analyzed by X-ray diffraction, it was confirmed that it was a desired positive electrode active material having a hexagonal layered structure. Moreover, the occupation rate of metal ions other than lithium at the 3a site was determined from the Rietveld analysis of the powder X-ray diffraction pattern using Cu Kα rays. These results are shown in Table 1 below.

Next, a 2032 coin-type secondary battery as shown in FIG. 1 was produced using the obtained positive electrode active material.
First, 90% by mass of the positive electrode active material powder was mixed with 5% by mass of acetylene black and 5% by mass of PVDF (polyvinylidene fluoride), and NMP (N-methyl-2-pyrrolidone) was added to form a paste. This was applied to a 20 μm thick aluminum foil so that the weight of the positive electrode active material after drying was 0.05 g / cm ² , vacuum-dried at 120 ° C., and then punched into a disk shape having a diameter of 1 cm. did.
Further, lithium metal was applied as the negative electrode, and an equivalent mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC) using 1 mol / liter LiClO ₄ as a supporting salt was used as the electrolyte.
Then, a battery was fabricated in a glove box in an argon atmosphere in which a separator made of polyethylene was impregnated with an electrolytic solution and the dew point was controlled at −80 ° C.

The fabricated secondary battery is left for about 24 hours, and after the open circuit voltage (OCV) is stabilized, the current density with respect to the positive electrode is 0.5 mA / cm ² and the charge / discharge test is performed at a cutoff voltage of 4.3 to 3.0 V. Went. The obtained first discharge capacity is shown in Table 1 as the initial discharge capacity.

Next, in order to investigate the thermal stability of the obtained positive electrode active material in a fully charged state, its thermal behavior was measured.
As a method for bringing the positive electrode active material into a fully charged state, in addition to the electrochemical method, as described above, about 70% of lithium was desorbed from the lithium-containing composite oxide in the fully charged state of about 200 mAh / g. Since it is in a state, a method of dispersing an active material in an acid aqueous solution and stirring it is known (Arai et al., Abstracts of the 38th Battery Discussion Meeting p83, 1997). Unlike the electrochemical method, this method can extract lithium under the condition that there is no influence of a conductive agent or a binder. By applying this to thermal analysis, the thermal behavior of the active material alone can be obtained. Can be evaluated.
Therefore, according to this method, 6.0 g of the obtained positive electrode active material was put into 100 ml (ml) of an aqueous hydrochloric acid solution adjusted to a concentration of 1 N, and stirred for 5 hours to obtain the chemical formula Li _1-x Ni _0.83. In Co _0.17 Ti _0.01 O ₂ , lithium was extracted so that x = 0.7.
It was then filtered and the remaining slurry, 24 hours at 40 ° C., dried in air for 3 days at 0.99 ° C., and water is evaporated by heating and drying in vacuum, Li _{0 .3} Ni _0.82 Co _0.17 Ti _0.01 O ₂ powder was obtained.
The powder was impregnated with the same electrolytic solution as that used to produce the coin battery, sealed in a sealed sample holder, and subjected to differential scanning calorimetry (DSC) to investigate thermal behavior. In differential scanning calorimetry, the heating rate was set to 10 ° C./min. Table 1 shows the exothermic peak temperature and exothermic peak height obtained by DSC measurement.

(Example 2)
In order to synthesize the positive electrode active material, a positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that the molar ratio of nickel, cobalt, and titanium was 81: 16: 3. The evaluation results are shown in Table 1.

(Example 3)
In order to synthesize the positive electrode active material, a positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that the molar ratio of nickel, cobalt, and titanium was 79: 16: 5. The evaluation results are shown in Table 1.

(Example 4)
In order to synthesize the positive electrode active material, a positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that the molar ratio of nickel, cobalt, and titanium was 76: 16: 8. The evaluation results are shown in Table 1.

(Comparative Example 1)
In order to synthesize the positive electrode active material, commercially available lithium hydroxide monohydrate and nickel hydroxide composed of spherical secondary particles were weighed so that the molar ratio of lithium to nickel was 1: 1. A positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that the water washing treatment was not performed after firing. The evaluation results are shown in Table 1.

(Comparative Example 2)
A positive electrode active material was obtained and evaluated in the same manner as in Example 4 except that the water washing treatment was not performed after firing. The evaluation results are shown in Table 1.

（評価）
（１）作製された各実施例ならびに比較例に係る二次電池を評価したところ、これら実施例の電池のサイクル特性は比較例に比較して概ね良好であった。
（２）二次電池の初期容量（第１回目の放電容量）については、作製された各実施例ならびに比較例１のいずれも１５０ｍＡｈ／ｇ以上の高い放電容量を示した。
（３）二次電池の熱安定性（ＤＳＣ測定）については、作製された各実施例の発熱ピーク温度が比較例１に比較して高温側へシフトしていると同時に、チタンの置換量の増大とともに発熱ピーク高さが減少しており、熱安定性が改善されていることが確認される。
（４）チタン置換量の増大とともに放電容量は減少する傾向があるが、水洗処理を行うことで、１５０ｍＡｈ／ｇ以上の高い放電容量を維持可能なチタン置換量は、ＬｉＮｉ_{１−ｘ−ｙ}Ｃｏ_ｘＴｉ_ｙＯ_２で表されるｙが、０≦ｙ≦０．１０の範囲まで拡大されることがわかる。
（５）水洗処理を行っていない比較例２では、１４２ｍＡｈ／ｇと十分な放電容量が得られていない。なお、各実施例に係るリチウム含有複合酸化物の合成条件はすべて７５０℃で２０時間としているが、６００℃以上８５０℃未満かつ４時間以上であれば、上記リチウム含有複合酸化物の３ａサイトにおけるリチウム以外の金属イオンのサイト占有率を５％以下にすることができることを実験で確認している。
また、各実施例に係るリチウム含有複合酸化物の３ａサイトにおけるリチウム以外の金属イオンのサイト占有率はすべて２．２％以下となっているが、金属イオンのサイト占有率が２．２％以上のリチウム含有複合酸化物についても同様の実験を行っており、これら二次電池についても、金属イオンのサイト占有率が５％以下であれば、実施例と略同一の特性を示す傾向があることを確認している。

(Evaluation)
(1) When the fabricated secondary batteries according to the examples and comparative examples were evaluated, the cycle characteristics of the batteries of these examples were generally better than those of the comparative examples.
(2) Regarding the initial capacity (first discharge capacity) of the secondary battery, each of the produced Examples and Comparative Example 1 showed a high discharge capacity of 150 mAh / g or more.
(3) Regarding the thermal stability (DSC measurement) of the secondary battery, the exothermic peak temperature of each of the produced examples is shifted to the high temperature side as compared with Comparative Example 1, and at the same time, the amount of substitution of titanium The exothermic peak height decreases with the increase, confirming that the thermal stability is improved.
(4) Although the discharge capacity tends to decrease as the titanium substitution amount increases, the titanium substitution amount capable of maintaining a high discharge capacity of 150 mAh / g or more by performing the water washing treatment is LiNi _1-xy Co. y represented by _x Ti _y O ₂ is seen to be expanded to a range of 0 ≦ y ≦ 0.10.
(5) In Comparative Example 2 where no water washing treatment is performed, a sufficient discharge capacity of 142 mAh / g is not obtained. In addition, although all the synthesis conditions of the lithium containing complex oxide which concern on each Example are 750 degreeC and 20 hours, if it is 600 degreeC or more and less than 850 degreeC and 4 hours or more, in the 3a site of the said lithium containing complex oxide Experiments have confirmed that the site occupancy of metal ions other than lithium can be 5% or less.
In addition, the site occupancy of metal ions other than lithium at the 3a site of the lithium-containing composite oxide according to each example is 2.2% or less, but the site occupancy of metal ions is 2.2% or more. The same experiment was conducted with respect to lithium-containing composite oxides, and these secondary batteries also had a tendency to exhibit substantially the same characteristics as the examples if the site occupancy of metal ions was 5% or less. Have confirmed.

In order to take advantage of the non-aqueous electrolyte secondary battery obtained by the manufacturing method of the present invention that has a high initial discharge capacity while being excellent in safety, a small portable electronic device that always requires a high capacity is used. Use as a power source is suitable.

  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, but the non-aqueous electrolyte of the present invention 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 preferred. Note that the power source for electric vehicles includes not only the use of electric vehicles that are driven purely by electric energy but also the use of so-called hybrid vehicles that are used in combination with combustion engines such as gasoline engines and diesel engines.

DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 3 Separator 4 Gasket 5 Positive electrode can 6 Negative electrode can B Coin battery

Claims (4)

Hexagonal lithium content having a layered structure represented by the general formula: LiNi _1-xy Co _x Ti _y O ₂ (where 0 <x ≦ 0.20, 0.01 ≦ y ≦ 0.10 ) It is made of a composite oxide powder, and the sites 3a, 3b, and 6c in the lithium-containing composite oxide are represented by [Li] _3a [Ni _1-xy Co _x Ti _y ] _3b [O ₂ ] _6c In this case, the positive electrode active material for a non-aqueous electrolyte secondary battery in which the site occupancy of metal ions other than lithium at the 3a site obtained from Rietveld analysis of the X-ray diffraction pattern of the lithium-containing composite oxide is 5% or less In the metal composite hydroxide in which the molar ratio of nickel to cobalt is (1-x): x and the secondary particles have a spherical or elliptical shape (where 0 <x ≦ 0. 22), lithium compound And, mixing the titanium compound, characterized by having a water washing step of washing with water the obtained lithium-containing composite oxide in the mixture was calcined to obtain a lithium-containing double focus oxide firing step and firing step A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 , wherein the firing is performed at a temperature of 600 ° C or higher and lower than 850 ° C for 4 hours or longer. In the washing step, to water 1 in a mass ratio of the lithium-containing composite oxide, 1-2 charged to the slurry, after stirring for 30 minutes to 1 hour, filtered, claim, characterized in that drying 1 or the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to 2. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein lithium hydroxide or a hydrate thereof is used as the lithium compound.

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