JP2006054107A - Cathode active substance for nonaqueous electrolyte secondary battery and secondary battery using the same, and manufacturing method and inspection method of cathode activating substance for nonaqueous electrolyte secondary batter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cathode activating substance with excellent output characteristics in the case of use as a cathode for a nonaqueous electrolyte secondary battery. <P>SOLUTION: The cathode activating substance is composed of powder of lithium metal complex oxide expressed in a general formula: LiNi<SB>1-x</SB>M<SB>x</SB>O<SB>2</SB>(where, a range of value of x is 0<x≤0.25, and M denotes at least one element selected from a group consisting of Co, Al, Mg, Mn, Ti, Fr, Cu, Zn, and Ga), and an amount of heat generated when dipping the powder in electrolyte solution used for the nonaqueous electrolyte secondary battery is made to be 0.5J/g or more. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

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

  In recent years, with the widespread use of portable devices such as mobile phones and notebook computers, development of small and lightweight 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 lithium-ion secondary batteries are currently being actively conducted.

Among these, a lithium ion secondary battery using a lithium metal composite oxide, particularly a lithium cobalt composite oxide that is relatively easy to synthesize as a positive electrode material, has a high energy density because a high voltage of 4V can be obtained. Is expected to be 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.

  Recently, there is an increasing expectation that lithium ion secondary batteries will be applied not only to small secondary batteries for portable devices, but also to large secondary batteries for power storage and electric vehicles. For this reason, reducing the cost of the active material and making it possible to manufacture a cheaper lithium ion secondary battery has a large ripple effect on a wide range of fields.

Newly proposed materials as positive electrode active materials for lithium ion secondary batteries include lithium manganese composite oxide (LiMn ₂ O ₄ ) using manganese, which is cheaper than cobalt, and lithium nickel composite oxide using nickel. (LiNiO ₂ ).

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 (safety with respect to ignition, etc.) However, since 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 lithium ion secondary batteries that are 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 substantially 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. Inferior properties. In addition, the battery performance is relatively low when used or stored in a high temperature environment.

In order to solve such drawbacks, for example, in Patent Document 1 (Japanese Patent Laid-Open No. Hei 8-213015), Li _x Ni _a Co is used for the purpose of improving the self-discharge characteristics and cycle characteristics of a lithium ion secondary battery. _{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 ≦ There has been proposed a lithium nickel composite oxide represented by a + b + c ≦ 1.2, where M is at least one element selected from Al, V, Mn, Fe, Cu, and Zn.

In Patent Document 2 (Japanese Patent Laid-Open No. 8-45509), 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. A 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) has been proposed. .

  Even if the lithium nickel composite oxide is obtained by a conventional manufacturing method, both the charge capacity and the discharge capacity are higher than those of the lithium cobalt composite oxide, and the cycle characteristics are also improved. However, even with the lithium-nickel composite oxide described in Patent Documents 1 and 2, the output characteristics were not sufficient. This is mainly due to the low conductivity of the positive electrode active material and the insufficient diffusibility of lithium. Therefore, when forming a battery, it is necessary to increase the amount of the conductive material mixed with the positive electrode active material in order to ensure sufficient conductivity. As a result, the capacity per unit mass and the volume per unit volume There was a problem of becoming smaller.

  As described above, recently, a movement to use a lithium ion secondary battery for a large-sized battery is also active, and 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, the output characteristic is particularly important. Therefore, it is a big problem to solve the problem of the lithium nickel composite oxide that the output characteristic is not sufficient.

  Next, techniques related to battery charge / discharge reactions will be described.

  The charge / discharge reaction of the battery proceeds as lithium ions in the positive electrode active material reversibly enter and exit. Since lithium ions enter and exit from the surface of the positive electrode active material through the electrolyte, the current density per unit area of the active material decreases as the surface area of the positive electrode active material increases for the same current amount. Works in an advantageous manner.

  Therefore, the positive electrode active material having a particle size as small as possible and a specific surface area as large as possible has better lithium diffusibility and can be expected to improve output characteristics.

  For this reason, among the conventionally disclosed methods, there are many methods in which the specific surface area of the positive electrode active material is controlled from the above viewpoint and the specific surface area and pore volume are regulated within a certain range (for example, Patent Documents). 3-5).

  However, the specific surface area measured by the BET method measured using a gas such as an inert gas represents the area where the positive electrode active material and the electrolytic solution are substantially in contact (when the positive electrode active material is in the electrolytic solution). There are few things. For this reason, the specific surface area measured by the BET method does not necessarily correspond to battery characteristics, particularly output characteristics.

For example, in the case of a positive electrode active material having a very small specific surface area such that the specific surface area measured by the BET method is about 0.2 m ² / g or less, the contact area between the positive electrode active material and the electrolytic solution is also Certainly, it is small and the output characteristics tend to deteriorate. On the other hand, even in the case of a positive electrode active material having a specific surface area measured by the BET method of about 0.4 m ² / g or more, the output characteristics are not always excellent, and only the specific surface area measured by the BET method is focused. However, there is a problem that a desired positive electrode active material satisfying output characteristics is not always obtained.

Japanese Patent Laid-Open No. 8-213015 JP-A-8-45509 JP-A-6-60887 JP-A-6-2443897 JP-A-8-138673

  This invention is made | formed in view of this problem, Comprising: It aims at providing the positive electrode active material with favorable output characteristics, when it uses for the positive electrode of a non-aqueous electrolyte secondary battery.

The positive electrode active material for a non-aqueous electrolyte secondary battery according to the first invention of the present application has a general formula LiNi _1-x M _x O ₂ (where the value of x in the formula is 0 <x ≦ 0.25) M in the formula represents at least one element selected from the group consisting of Co, Al, Mg, Mn, Ti, Fe, Cu, Zn, and Ga.) It is made of powder, and the amount of heat generated when the powder is immersed in an electrolytic solution used in a non-aqueous electrolyte secondary battery is 0.5 J / g or more. In addition, although it is preferable to use diethyl carbonate as said electrolyte solution, it is not restricted to this.

  The lithium metal composite oxide powder is preferably secondary particles formed by aggregating a plurality of primary particles, and the shape of the secondary particles is preferably spherical or elliptical.

  A nonaqueous electrolyte secondary battery can be obtained by using the positive electrode active material for a nonaqueous electrolyte secondary battery as a positive electrode.

  The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to the second invention of the present application is selected from the group consisting of a lithium compound, a nickel compound, and Co, Al, Mg, Mn, Ti, Fe, Cu, Zn, and Ga. A step of mixing a predetermined amount of each compound composed of at least one element to obtain a mixture, a step of firing the mixture in an oxygen stream to obtain a positive electrode active material for a non-aqueous electrolyte secondary battery, and a non-aqueous type The amount of heat generated when the positive electrode active material for a nonaqueous electrolyte secondary battery is immersed in an electrolytic solution used for an electrolyte secondary battery, for example, diethyl carbonate, is measured per 1 g of the positive electrode active material for the nonaqueous electrolyte secondary battery. And a step of judging the quality of the positive electrode active material for a non-aqueous electrolyte secondary battery based on the measured amount of heat.

A method for inspecting a positive electrode active material for a non-aqueous electrolyte secondary battery according to the third invention of the present application is applied to an electrolytic solution used in a non-aqueous electrolyte secondary battery, such as diethyl carbonate, for example, a general formula LiNi _1-x M _x O ₂ (However, the range of the value of x in the formula is 0 <x ≦ 0.25, and M in the formula is a group consisting of Co, Al, Mg, Mn, Ti, Fe, Cu, Zn, and Ga. The amount of heat generated when the positive electrode active material for a non-aqueous electrolyte secondary battery composed of a powder of a lithium metal composite oxide represented by the formula (2) is immersed in the non-aqueous electrolyte secondary. It is measured per 1 g of the positive electrode active material for a battery, and the quality of the positive electrode active material for a non-aqueous electrolyte secondary battery is determined based on the measured amount of heat.

  Since the positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention generates 0.5 J / g or more of heat when immersed in an electrolyte used in a non-aqueous electrolyte secondary battery, The substantial contact area is large. For this reason, when used as a positive electrode of a lithium ion battery, the speed at which lithium ions diffuse in the battery is increased, the output is increased, the internal resistance of the battery is reduced, and the coulomb efficiency is improved.

  As a result of repeated investigations on the positive electrode active material synthesized by various methods, the present inventors have found that the amount of heat generated when the active material powder is actually immersed in an electrolytic solution used in a non-aqueous electrolyte secondary battery ( If the heat of wetting) is measured, the value of this amount of heat substantially represents the contact area between the electrolytic solution and the positive electrode active material, that is, the amount of heat generated when the active material powder is immersed in the electrolytic solution, and lithium It was found that there is a correlation between the output characteristics of the ion secondary battery. Furthermore, it has been found that by using a positive electrode active material having a heat of wetting of 0.5 J / g or more as the positive electrode active material of the lithium ion secondary battery, the ratio of materials having excellent output characteristics is dramatically improved. It came to.

With the specific surface area measured by the BET method that has been conventionally performed, if the specific surface area is about 0.4 m ² / g or more, the quality of the output characteristics of the lithium ion secondary battery cannot be distinguished. Specifically, a positive electrode material of about 0.5 to 0.7 m ² / g was conventionally considered optimal from the viewpoint of powder characteristics and handling, and also from the viewpoint of output characteristics. Even when a positive electrode active material obtained by synthesizing a material having such a specific surface area is used for a positive electrode of a lithium ion secondary battery, a lithium ion secondary battery having excellent output characteristics is not necessarily obtained.

  Since the amount of heat generated when the positive electrode active material according to the present invention is immersed in the electrolytic solution is 0.5 J / g or more, the area per unit mass of the positive electrode active material in contact with the electrolytic solution is surely increased. For this reason, in the non-aqueous electrolyte secondary battery using the positive electrode active material according to the present invention, the reversible entry and exit of lithium ions into the positive electrode active material is good, and the output characteristics and coulombic efficiency are improved. It is possible to reduce the internal resistance of the battery.

  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 embodiment described below is merely an example, and the nonaqueous electrolyte secondary battery of the present invention is implemented in various modifications and improvements based on the knowledge of those skilled in the art, including the following embodiment. 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 is LiNi _1-x M _x O ₂ (where M is Co, Al, Mg, Mn, Ti, Fe, Cu And at least one metal element selected from the group consisting of Zn, Ga, wherein x is a powder of lithium nickel composite oxide represented by 0 <x ≦ 0.25. The amount of heat generated when the powder is immersed in an electrolytic solution used in a non-aqueous electrolyte secondary battery is 0.5 J / g or more.

  The reason why the range of the value x in the formula is 0 <x ≦ 0.25 is that when x> 0.25, the proportion of metal elements other than Li mixed in the Li layer increases, and the cycle is good. This is because a battery having the characteristics cannot be formed.

The additive element M is at least one metal element selected from the group consisting of Co, Al, Mg, Mn, Ti, Fe, Cu, Zn, and Ga. Co and Mn mainly serve to stabilize the crystal structure of the lithium nickel composite oxide. By stabilizing the crystal structure, the cycle characteristics of the non-aqueous electrolyte secondary battery are kept good, and in particular, deterioration of the battery capacity due to charge / discharge and storage at a high temperature such as 60 ° C. or higher is suppressed. In particular, Co has the effect of suppressing capacity reduction due to element substitution, and the resulting composite oxide Li (Co, Ni) O ₂ is in a completely solid solution type, so that even if it is added, the decrease in crystallinity is minimized. There is an advantage that it can be limited to.

  In addition, Al, Mg, Mn, Ti, Fe, Cu, Zn, and Ga mainly play a role of suppressing the decomposition reaction of the active material accompanying oxygen release and improving the thermal stability. Among these elements, it is more desirable to use Al. This is because Al has the advantage of minimizing capacity reduction while improving thermal stability.

  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 a mixture of a lithium compound, a nickel compound, and a compound related to an additive element, each in a predetermined amount, and in an oxygen stream at a temperature of about 650 to 850 ° C. for 20 hours. It can be manufactured by firing to a certain extent.

  As the lithium compound, lithium hydroxide, lithium carbonate and the like are preferable. As the nickel compound, nickel oxide, nickel carbonate, nickel nitrate, nickel hydroxide, nickel oxyhydroxide and the like can be used. An oxide, a carbonate, etc. can be used as a compound concerning an additional element.

  Next, a preferable particle configuration of the positive electrode active material will be described.

  In the case where the primary particles are well dispersed and do not aggregate, the specific surface area measured by the BET method and the heat of wetting have a relatively good correlation. For this reason, it is considered that the smaller the primary particle size, the larger the specific surface area, the larger the contact area with the electrolytic solution, and the higher the output. However, the finer the particles, the more inconveniences in production, such as the generation of dust, and the lowering of the packing density when used as an electrode results in a decrease in the capacity of the battery as a whole.

  On the other hand, when the primary particles are small to some extent and the primary particles are aggregated to form secondary particles, there is no inconvenience in handling and the packing density does not decrease. On the other hand, particles having such a structure have micropores that allow gas to enter but not liquid, and the specific surface area measured by the BET method and the heat of wetting are not necessarily proportional. However, when the sintering of each primary particle is not progressing so much, a certain amount of gaps remain between the primary particles, and the electrolyte soaks into the gaps, and lithium ions pass through the electrolyte to the inside of the secondary particles. Can be supplied. As a result, the speed at which lithium ions diffuse throughout the secondary particles is increased, and the output characteristics are improved. Further, it is preferable that the shape of the secondary particles is spherical or elliptical because the packing density is improved.

  Therefore, the lithium metal composite oxide according to the present invention has a particle configuration in which a plurality of primary particles of the composite oxide are aggregated to form secondary particles, and the secondary particles are some amount between the primary particles. It is preferable that the secondary particles have a lot of gaps and the shape thereof is spherical or elliptical.

  In order to easily obtain this particle shape, it is preferable to use nickel hydroxide among the nickel compounds described above. When nickel hydroxide is produced by a precipitation method, there is a method (coprecipitation method) in which an additive element is simultaneously added and a hydroxide of the additive element is also produced as a precipitate. When the coprecipitation method is used, the additive elements are preferably mixed uniformly. Further, in the obtained hydroxide, a plurality of primary particles are aggregated to form spherical or elliptical secondary particles. If the nickel metal composite hydroxide and the lithium compound are mixed with such a strength that the shape of the secondary particles is maintained to produce a lithium nickel composite oxide, the powder particles of the lithium nickel composite oxide are: Spherical or elliptical secondary particles in which a plurality of primary particles of the composite oxide are aggregated are formed.

  The structure of the secondary particles of the positive electrode active material is such that the powder characteristics of the raw material compounds such as nickel, cobalt, and aluminum used in the raw material, the conditions of calcination, the firing temperature and firing time, the atmosphere during firing, up to that temperature Since it is strongly influenced by the heating rate and cooling rate, the structure of secondary particles can be controlled by controlling these conditions.

  However, not all such firing conditions are uniquely determined by the setting conditions of the firing apparatus. For example, only the weight of the fired product differs from the size of the firing container, the amount of heat received by the actual fired product is different, the rate of temperature rise is different even under the same firing conditions, or the time that is maintained at the desired firing temperature Are different. The same thing happens depending on the size of the firing electric furnace. The firing atmosphere is the same. Even if firing is performed in an air flow of the same flow rate, the local atmosphere around the fired product varies depending on the size of the electric furnace and the weight of the fired product, and the gas generated from the fired product during firing is different. The volatilization rate is different. Therefore, it is a common practice to change the firing conditions for obtaining a positive electrode active material having desired characteristics depending on the firing apparatus used for firing.

  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 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, 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, 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.

  In addition, as a constituent requirement of the present invention, there is a requirement that heat of wetting when the powder is immersed in an electrolytic solution is 0.5 J / g or more. Since the heat of wetting is proportional to the area where the electrolytic solution is in contact with the powder, it also represents the area of the particles that are in contact with the electrolytic solution. On the other hand, Li ions enter and exit through the surface of the particles in contact with the electrolyte. Therefore, the positive electrode active material that satisfies the requirement that the heat of wetting is 0.5 J / g or more has good Li ion entry / exit between the electrolyte solution, and such a positive electrode active material is used as a lithium ion secondary battery. When used for the positive electrode, the output characteristics of the battery are good. The heat of wetting can be measured relatively easily using a microcalorimeter.

  On the other hand, the specific surface area and pore distribution measured by the BET method, which is often used in the past, use intrusion of inert gas or mercury, etc., and the specific surface area and pore distribution of particles measured using them as a medium Does not necessarily represent the area of particles in contact with the electrolyte when the battery is actually constructed.

(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 the electrode body is impregnated with the non-aqueous electrolyte. 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.

(Example 1)
In order to synthesize LiNi _0.82 Co _0.15 Al _0.03 O _{2 in} which 15 at% of the total number of Ni atoms were replaced with Co and 3 at% was replaced with Al in LiNiO ₂ , the molar ratio of nickel, cobalt, and aluminum was 82:15: A metal composite hydroxide dissolved in 3 was prepared. This metal composite hydroxide was obtained by neutralizing a mixed aqueous solution of nickel sulfate, cobalt sulfate and sodium aluminate by adding sodium hydroxide and drying the resulting precipitate. This metal composite hydroxide is composed of spherical secondary particles (average particle diameter 11.6 μm, specific surface area 9.7 m ² / g) in which a plurality of primary particles 1 μm or less are aggregated.

  A molar ratio of lithium to metal (total of Ni, Co and Al) of the metal composite hydroxide and commercially available lithium hydroxide monohydrate (manufactured by Kemetal Corp.) pulverized by a jet mill is 1: 1. Then, the mixture was thoroughly mixed at such a strength that the shape of spherical secondary particles was maintained.

  2.4 kg of this mixture was inserted into a 30 cm square SUS-made baking vessel, and the temperature was set at 450 ° C. for 5 hours in an oxygen stream with a flow rate of 35 L / min. After calcination, the temperature was raised to 730 ° C. at a rate of temperature rise of 5 ° C./min, baked for 32 hours, and then cooled to room temperature.

When the obtained fired product was analyzed by X-ray diffraction, it was a positive electrode active material (LiNi _0.82 Co _0.15 Al _0.03 O ₂ ) having a hexagonal layered structure. The average particle diameter measured by a microtrack particle size distribution measuring device (manufactured by Nikkiso) (hereinafter referred to as “Microtrack”) was 10.8 μm, and the specific surface area measured by the BET method was 0.66 m ² / g. Further, it was confirmed by measurement with a microtrack that fine powders of 1 μm or less were present in a mass ratio of 4.6%.

  The obtained positive electrode active material was vacuum-dried at 150 ° C. for 3 hours for deaeration treatment, and then 4 g of the positive electrode active material was immersed in 24 cc of diethyl carbonate (manufactured by Kishida Chemical) in a heat insulating container. The amount of heat generated was measured using a multi-micro calorimeter (Tokyo Riko MMC-5111). A measurement chart of the obtained heat of wetting is shown in FIG. The horizontal axis indicates the measurement time, and the vertical axis indicates the output voltage of the amplifier. The output voltage of the amplifier is proportional to the amount of heat generated. Table 1 shows the calorific value (heat of wetting per gram of the sample) calculated from the integrated value of the exothermic peak in this chart.

The output evaluation of the active material was performed as follows. 90% by mass of the active material powder was mixed with 5% by mass of acetylene black and 5% by mass of PVDF (polyvinylidene fluoride), and NMP (n-methylpyrrolidone) was added to form a paste. This was applied to a 20 μm-thick aluminum foil so that the weight of the active material after drying was 0.05 g / cm ² , vacuum-dried at 120 ° C., and punched into a 1 cm ² disk shape to obtain a positive electrode.

Lithium metal was used as the negative electrode, and an equivalent mixed solution of ethylene carbonate (EC) (manufactured by Toyama Pharmaceutical Co., Ltd.) and diethyl carbonate (DEC) (manufactured by Toyama Pharmaceutical Co., Ltd.) with 1M LiClO ₄ as the 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 was left for about 24 hours, and after the OCV was stabilized, the battery was charged to a charge depth of 60% with a current density of 0.5 mA / cm ² with respect to the positive electrode. At the state of charge of 60%, the current density ^{J 1.0mA / cm 2, 2.0mA /} cm 2, subjected to varied 10 seconds charging and discharging and 4.0 mA / cm ^2, current density from the potential dV dropped across the discharge The slope dV / J with respect to J was determined. The current density J1 when the potential dropped to 3V using the obtained slope dV / J was calculated by the following formula 1. Here, the open circuit voltage at a charging depth of 60% is V1. The output value per 1 cm ² of the positive electrode at a discharge voltage of 3 V was obtained by the following equation 2 using the current density J1 obtained by the following equation 1. The output evaluation results obtained are shown in Table 1.

(Example 2)
In order to synthesize LiNi _0.82 Co _0.15 Al _0.03 O _{2 in} which 15 at% of the total number of Ni atoms were replaced with Co and 3 at% was replaced with Al in LiNiO ₂ , the molar ratio of nickel, cobalt, and aluminum was 82:15: The metal composite hydroxide dissolved in 3 was prepared in the same manner as in Example 1. This metal composite hydroxide is composed of spherical secondary particles (average particle diameter 10.6 μm, specific surface area 8.5 m ² / g) in which a plurality of primary particles of 1 μm or less are aggregated.

  This metal composite hydroxide was mixed with lithium hydroxide monohydrate (manufactured by Kemetal) in the same manner as in Example 1. 100 g of this mixture was inserted into a 12 cm × 4 cm magnesia firing container, calcined in a small atmosphere furnace at a flow rate of 1 L / min in an oxygen stream at a temperature of 350 ° C. and a time of 2 hours, and then heated. The temperature was raised to 730 ° C. at a rate of 5 ° C./min, baked for 20 hours, and furnace-cooled to room temperature.

When the obtained fired product was analyzed by X-ray diffraction, it was a desired positive electrode active material (LiNi _0.82 Co _0.15 Al _0.03 O ₂ ) having a hexagonal layered structure. The average particle diameter measured by Microtrac was 9.4 μm, and the specific surface area measured by BET method was 0.69 m ² / g. Further, it was confirmed by measuring with Microtrac that the fine powder of 1 μm or less was present in a mass ratio of 2.7%.

  A measurement chart of wet heat measured by the same method as in Example 1 is shown in FIG.

(Example 3)
In order to synthesize LiNi _0.82 Co _0.15 Al _0.03 O _{2 in} which 15 at% of the total number of Ni atoms were replaced with Co and 3 at% was replaced with Al in LiNiO ₂ , the molar ratio of nickel, cobalt, and aluminum was 82:15: The metal composite hydroxide dissolved in 3 was prepared in the same manner as in Example 1. This metal composite hydroxide is composed of spherical secondary particles (average particle diameter 10.9 μm, specific surface area 9.5 m ² / g) in which a plurality of primary particles of 1 μm or less are aggregated.

  This metal composite hydroxide was mixed with lithium hydroxide monohydrate (manufactured by Kemetal) in the same manner as in Example 1. 2.0 kg of this mixture is weighed and inserted into a 25 cm square SUS baking container, and four such baking containers are arranged side by side using a roller feed type large continuous furnace, and the flow rate is 10 L / min from five gas inlets. After calcining at a temperature of 450 ° C. and for a time of 5 hours in an oxygen stream blown in each step, the temperature was raised to 730 ° C. at a heating rate of 10 ° C./min, baked for 32 hours, and cooled to room temperature.

When the obtained fired product was analyzed by X-ray diffraction, it was a desired positive electrode active material (LiNi _0.82 Co _0.15 Al _0.03 O ₂ ) having a hexagonal layered structure. The average particle size measured by Microtrac was 9.4 μm, and the specific surface area measured by BET method was 0.63 m ² / g. Further, it was confirmed by measurement with a microtrack that fine powders of 1 μm or less were present in a mass ratio of 4.1%.

  A measurement chart of wet heat measured by the same method as in Example 1 is shown in FIG.

(Comparative Example 1)
In order to synthesize LiNi _0.82 Co _0.15 Al _0.03 O _{2 in} which 15 at% of the total number of Ni atoms were replaced with Co and 3 at% was replaced with Al in LiNiO ₂ , the molar ratio of nickel, cobalt, and aluminum was 82:15: The metal composite hydroxide dissolved in 3 was prepared in the same manner as in Example 1. This metal composite hydroxide is composed of spherical secondary particles (average particle diameter 10.8 μm, specific surface area 9.4 m ² / g) in which a plurality of primary particles of 1 μm or less are aggregated.

  This metal composite hydroxide was mixed with lithium hydroxide monohydrate (manufactured by Kemetal) in the same manner as in Example 1. 2.4 kg of this mixture was inserted into a 30 cm square alumina firing vessel, and temporarily moved at a temperature of 450 ° C. and a time of 5 hours in a 45 L / min oxygen stream using an elevating closed large electric furnace. After baking, the temperature was raised to 700 ° C. at a temperature rising rate of 10 ° C./min, baked for 32 hours, and cooled to room temperature.

When the obtained fired product was analyzed by X-ray diffraction, it was a desired positive electrode active material (LiNi _0.82 Co _0.15 Al _0.03 O ₂ ) having a hexagonal layered structure. The average particle size measured by Microtrac was 10.1 μm, and the specific surface area measured by the BET method was 0.63 m ² / g. Further, it was confirmed by measuring with a microtrack that 3.5% of fine powder of 1 μm or less was present by mass ratio.

  A measurement chart of wet heat measured by the same method as in Example 1 is shown in FIG.

(Comparative Example 2)
In order to synthesize LiNi _0.82 Co _0.15 Al _0.03 O _{2 in} which 15 at% of the total number of Ni atoms were replaced with Co and 3 at% was replaced with Al in LiNiO ₂ , the molar ratio of nickel, cobalt, and aluminum was 82:15: The metal composite hydroxide dissolved in 3 was prepared in the same manner as in Example 1. This metal composite hydroxide is composed of spherical secondary particles (average particle size 11.2 μm, specific surface area 8.4 m ² / g) in which a plurality of primary particles of 1 μm or less are aggregated.

  This metal composite hydroxide was mixed with lithium hydroxide monohydrate (manufactured by Kemetal) in the same manner as in Example 1. 300 g of this mixture was inserted into a 10 cm square magnesia baking vessel, and calcined in a stream of oxygen at a flow rate of 3 L / min using a small atmosphere furnace at a temperature of 350 ° C. and a time of 2 hours, and then the rate of temperature increase The temperature was raised to 800 ° C. at 10 ° C./min, baked for 20 hours, and furnace-cooled to room temperature.

When the obtained fired product was analyzed by X-ray diffraction, it was a desired positive electrode active material (LiNi _0.82 Co _0.15 Al _0.03 O ₂ ) having a hexagonal layered structure. The average particle size measured by Microtrac was 10.2 μm, and the specific surface area measured by the BET method was 0.65 m ² / g. Further, it was confirmed by measuring with Microtrac that the fine powder of 1 μm or less was present in a mass ratio of 3.7%.

  A measurement chart of wet heat measured by the same method as in Example 1 is shown in FIG.

(Comparative Example 3)
In order to synthesize LiNi _0.82 Co _0.15 Al _0.03 O _{2 in} which 15 at% of the total number of Ni atoms were replaced with Co and 3 at% was replaced with Al in LiNiO ₂ , the molar ratio of nickel, cobalt, and aluminum was 82:15: The metal composite hydroxide dissolved in 3 was prepared in the same manner as in Example 1. This metal composite hydroxide is composed of spherical secondary particles (average particle diameter of 10.5 μm, specific surface area of 9.2 m ² / g) in which a plurality of primary particles of 1 μm or less are aggregated.

  This metal composite hydroxide was mixed with lithium hydroxide monohydrate (manufactured by Kemetal) in the same manner as in Example 1. 2.4 kg of this mixture is weighed and inserted into a 30 cm square alumina baking vessel, and four of the baking vessels are arranged side by side using a roller feed type large continuous furnace, and the flow rate is 10 L / min from eight gas inlets. After calcining at a temperature of 450 ° C. and for a time of 5 hours in an oxygen stream blown in each step, the temperature was raised to 730 ° C. at a heating rate of 5 ° C./min, baked for 32 hours, and cooled to room temperature.

When the obtained fired product was analyzed by X-ray diffraction, it was a desired positive electrode active material (LiNi _0.82 Co _0.15 Al _0.03 O ₂ ) having a hexagonal layered structure. The average particle diameter measured by Microtrac was 9.8 μm, and the specific surface area measured by the BET method was 0.59 m ² / g. Further, it was confirmed by measuring with Microtrac that the fine powder of 1 μm or less was present in a mass ratio of 2.7%.

  FIG. 2 shows a measurement chart of wet heat measured by the same method as in Example 1, and Table 1 shows wet heat and battery output.

As can be seen from Table 1 above, the positive electrode active materials synthesized by the methods of Comparative Examples 1 to 3 are similar to Examples 1 to 3 in terms of average particle diameter and specific surface area, but reflect the penetration of the electrolyte. The heat of wetting is small. For this reason, the coin battery comprised using the active material of Comparative Examples 1-3 as a result has a low output compared with the positive electrode active material of an Example.

  The present inventors have confirmed that there is no practical problem if the output of the coin battery is 80 mW or more. As can be seen from Table 1, if the heat of wetting is 0.5 J / g or more. An output of 80 mW or more can be obtained by output evaluation with a coin battery. In each of Examples 1 to 3, the heat of wetting is 0.5 J / g or more, and the output of the coin battery is 80 mW or more. On the other hand, all of Comparative Examples 1 to 3 have a wetting heat of less than 0.5 J / g, and the output of the coin battery is less than 80 mW.

In Examples 1 to 3 and Comparative Examples 1 to 3, the specific surface area is about 0.6 (m ² / g), about 50% larger than 0.4 (m ² / g), and only the specific surface area From the above, it is determined that all of Examples 1 to 3 and Comparative Examples 1 to 3 are good positive electrode active materials, but the actual output characteristics are 80 (mW) or more in Examples 1 to 3, and Comparative Example 1 to 3 is less than 80 (mW), and there is a clear difference. In the specific surface area which is an index for determining the quality of the conventional positive electrode active material, in the region where the specific surface area is large, specifically, in the region where the specific surface area is larger than 0.4 (m ² / g), the output of the positive electrode active material It can be seen that it is impossible to judge the quality of the characteristics. However, if wetting heat, which is an index used in the present invention, is used as an index, the quality of the output characteristics of the positive electrode active material can be clearly judged even in a region where the specific surface area is larger than 0.4 (m ² / g). It can be done.

  In addition, about the positive electrode active material of Examples 1-3 and Comparative Examples 1-3, the ratio of the fine powder of 1 micrometer or less was calculated | required by mass ratio, respectively, but the reason is that as the particle becomes finer, the dust becomes smaller as described above. This is because inconveniences in production such as the occurrence of oxidization occur, and the packing density when used as an electrode is reduced, resulting in a decrease in the capacity of the battery as a whole.

  The ratio of fine powder of 1 μm or less for the positive electrode active materials of Examples 1 to 3 is 2.7% to 4.6%, and the ratio of fine powder of 1 μm or less for the positive electrode active materials of Comparative Examples 1 to 3 is 2. It is 7% to 3.7%, and it is considered that there is no significant difference between Examples and Comparative Examples.

  Finally, the reason why the heat of wetting of the active materials synthesized by the methods of Comparative Examples 1 to 3 is reduced will be described. This is thought to be a result of intricately intertwining the temperature and firing time.

  For example, in Example 1 and Comparative Example 1, the same firing furnace (lifting and closing type large electric furnace) is used. In Example 1, a SUS firing container is used, whereas Comparative Example 1 is used. Uses a firing container made of alumina. Also, the oxygen flow rate is lower in Example 1 than in Comparative Example 1. For this reason, in Example 1, the heat conductivity to the fired product is excellent, and since the oxygen flow rate is small compared to Comparative Example 1, the amount of heat lost to the airflow is small, and the temperature near the fired product is used for controlling the furnace. It seems that it is easier to follow. For this reason, it is presumed that the calcination and firing times are different from each other, and this difference is presumed to have influenced the internal structure of the particles.

  In Example 2 and Comparative Example 2, the firing furnace (small atmosphere furnace) and the material of the firing container (made of magnesia) are the same, but Example 1 has a lower firing temperature and a lower oxygen flow rate. It is presumed that the amount of heat applied per unit mass of the fired product was substantially different, and it was assumed that this difference affected the internal structure of the particles.

  Furthermore, in Example 3 and Comparative Example 3, the firing furnace and the firing temperature are the same, but the material of the firing container of Example 3 is SUS, whereas the material of the firing container of Comparative Example 3 is alumina. is there. For this reason, since Example 3 is superior in heat transfer to the fired product as compared with Comparative Example 3, it is presumed that the firing conditions differed and the internal structure of the particles was affected.

  As can be seen from the above description, in order to obtain a positive electrode active material having a target heat of wetting, it is necessary to appropriately combine these firing conditions. Although this inventor has confirmed appropriate conditions for every furnace used for baking, it has not yet been able to prescribe | regulate the conditions which do not depend on the furnace to be used.

  In order to take advantage of the non-aqueous electrolyte secondary battery of the present invention, which has excellent output characteristics, it can be used as a power source for devices that instantly input large energy and output large energy instantaneously. Is preferred. In other words, it is preferably used as a power source for applications that are charged with a large current immediately after the start of charging, and discharged with a large current immediately after the start of discharging.

  In a power source for an electric vehicle, it is necessary to be able to regenerate large energy by regenerative braking instantaneously at the time of deceleration or the like. Also, it is necessary to output a large amount of power at the time of start-up, sudden start, sudden acceleration, and the like. Therefore, the lithium ion secondary battery of the present invention is suitable as a power source for electric vehicles.

  The electric vehicle power source means not only an electric vehicle driven purely by electric energy but also a so-called hybrid vehicle power source used in combination with a combustion engine such as a gasoline engine or a diesel engine. .

Cross-sectional view of a coin battery for battery evaluation Wet heat measurement chart

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)

General formula LiNi _1-x M _x O ₂ (where the range of x in the formula is 0 <x ≦ 0.25, where M is Co, Al, Mg, Mn, Ti, Fe And an electrolyte used for a non-aqueous electrolyte secondary battery, and comprising at least one element selected from the group consisting of Cu, Zn, and Ga. A positive electrode active material for a non-aqueous electrolyte secondary battery, wherein the amount of heat generated when the powder is immersed is 0.5 J / g or more. The lithium metal composite oxide powder is secondary particles formed by aggregating a plurality of primary particles, and the shape of the secondary particles is spherical or elliptical. The positive electrode active material for nonaqueous electrolyte secondary batteries as described. A non-aqueous electrolyte secondary battery using the positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 for a positive electrode. A step of obtaining a mixture by mixing a predetermined amount of each of a lithium compound, a nickel compound, and a compound comprising at least one element selected from the group consisting of Co, Al, Mg, Mn, Ti, Fe, Cu, Zn, and Ga. And baking the mixture in an oxygen stream to obtain a positive electrode active material for a non-aqueous electrolyte secondary battery; and a positive electrode active material for the non-aqueous electrolyte secondary battery in an electrolyte used for the non-aqueous electrolyte secondary battery. And determining whether the positive electrode active material for the nonaqueous electrolyte secondary battery is good or not based on the step of measuring the amount of heat generated when the cathode is immersed per 1 g of the positive electrode active material for the nonaqueous electrolyte secondary battery. A process for producing a positive electrode active material for a non-aqueous electrolyte secondary battery. The amount of heat generated when the positive electrode active material for a non-aqueous electrolyte secondary battery is immersed in the electrolyte solution used for the non-aqueous electrolyte secondary battery is measured per 1 g of the positive electrode active material for the non-aqueous electrolyte secondary battery, and the measured amount of heat. A method for inspecting a positive electrode active material for a nonaqueous electrolyte secondary battery, wherein the quality of the positive electrode active material for a nonaqueous electrolyte secondary battery is determined based on the above. The positive electrode active material for a non-aqueous electrolyte secondary battery has a general formula LiNi _1-x M _x O ₂ (where the value of x in the formula is 0 <x ≦ 0.25, and M in the formula Represents at least one element selected from the group consisting of Co, Al, Mg, Mn, Ti, Fe, Cu, Zn, and Ga.). The inspection method for a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 5, characterized in that:

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