JP5226917B2 - Positive electrode active material, method for producing the same, and non-aqueous secondary battery using the same - Google Patents

Description

  The present invention relates to a lithium ion secondary battery, particularly a Mn-based positive electrode active material having a spinel structure, which has a large initial discharge capacity and has a small decrease in discharge capacity even after repeated charge and discharge in an environment of 60 ° C. The present invention relates to a secondary battery, a positive electrode active material thereof, and a method for producing the positive electrode active material.

The positive electrode active material of a non-aqueous electrolyte secondary battery (or abbreviated as “non-aqueous secondary battery”) is a low-cost lithium manganate (or a spinel structure excellent in safety without resource restrictions) (or “Spinel type LiMn ₂ O ₄ ”) is currently under investigation. Spinel-type LiMn ₂ O ₄ (generally having a composition of AB ₂ O ₄ ) has major problems such as a decrease in electric capacity when repeated charging and discharging, and a significant decrease in capacity at high temperatures. ing. In order to solve the above problems, for example, JP-A-2-270268 discloses an improved example using lithium manganate with excessive addition of lithium, and JP-A-2-60056 discloses chromium or the like. Although an improved example using lithium manganate added with the third component is disclosed, the decrease in electric capacity is still severe under an environment of 60 ° C., which is not sufficient as a positive electrode active material of a non-aqueous secondary battery. For example, in a non-aqueous secondary battery using such a material as a positive electrode active material, the discharge capacity when repeated charging and discharging 500 times is only 90 mAh / g at the highest, and further improvement is required. Yes.

For example, in JP-A-7-262984, manganic acid whose surface is coated with a Li ₂ MnO ₃ layer obtained by heat-treating a mixture of a lithium compound and LiMn ₂ O _{4 in} a temperature range of 400 ° C. to 1325 ° C. It is disclosed that lithium is used as a positive electrode active material. In JP-A-10-172571, spinel-structured lithium manganate is immersed in a solution containing Li ions or Mn ions, and this is heat-treated in a temperature range of 300 ° C. to 1200 ° C. to form a two-layer structure manganate. The use of lithium is disclosed.

Problems to be solved by the invention

  The present invention relates to a nonaqueous secondary battery including a negative electrode using lithium as an active material, a nonaqueous electrolyte, and a positive electrode using a spinel composite oxide containing lithium, manganese and oxygen as an active material. A non-aqueous secondary battery having excellent cycle characteristics capable of maintaining a discharge capacity of 95 mAh / g or more when charging / discharging is repeated 500 times, and a positive electrode active material capable of achieving the battery characteristics and a method for producing the same provide.

Means for solving the problem

That is, the present invention
(1) A composite oxide positive electrode active material comprising a spinel structure mainly composed of lithium, manganese and oxygen and β-type MnO ₂ ;
(2) The positive electrode active material of the composite oxide according to item 1 above, wherein the surface layer of the composite oxide is substantially composed of β-type MnO ₂ .
(3) The positive electrode active material of the composite oxide according to item 1 or 2, wherein the β-type MnO ₂ is in the range of 1 to 13 mol% of the compound oxide.
(4) The spinel structure mainly composed of lithium, manganese and oxygen is LiMn ₂ O ₄ composed of lithium, manganese and oxygen, or a part of Li or Mn is chromium, cobalt, aluminum, nickel, iron, magnesium, etc. A composite oxide substituted with different elements of Li _{1 + X} Mn _2−xy M _y O ₄ (where −0.1 ≦ x ≦ 0.2, 0 <y ≦ 0.2) The positive electrode active material of the composite oxide according to any one of the preceding items 1 to 3,

(5) The positive electrode active material of composite oxide according to any one of items 1 to 4, wherein the composite oxide is a granulated product having a particle size of 3 μm to 50 μm.
(6) The positive electrode active material of the composite oxide according to any one of items 1 to 5, which has pores in the range of 30 to 400 mm,
(7) An electrode paste containing the composite oxide positive electrode active material according to any one of items 1 to 6,

(8) A positive electrode comprising the composite oxide positive electrode active material according to any one of claims 1 to 6,
(9) Any one of items 1 to 6 above, wherein the composite oxide containing a spinel structure mainly composed of lithium, manganese, and oxygen is acid-treated and then heat-treated in a temperature range of 200 ° C. or higher and lower than 400 ° C. A method for producing a composite oxide positive electrode active material according to claim 1,
(10) In a non-aqueous secondary battery including a negative electrode using lithium as an active material, a non-aqueous electrolyte, and a positive electrode using a composite oxide containing lithium, manganese, and oxygen as an active material, the composite oxide includes A non-aqueous secondary battery comprising the composite oxide positive electrode active material according to any one of items 1 to 6 is provided.

Hereinafter, the present invention will be specifically described.
In the method for producing a positive electrode active material of the present invention, a complex oxide having a spinel structure mainly composed of lithium, manganese, and oxygen is acid-treated, and heat treatment is performed at a specific temperature, that is, a specific temperature of 200 ° C. or more and less than 400 ° C. By doing so, a composite oxide containing a spinel structure mainly composed of lithium, manganese and oxygen and β-type MnO ₂ can be produced. In addition, it is possible to produce a composite oxide in which the surface layer of the composite oxide is substantially composed of β-type MnO ₂ . Here, “a composite oxide having a spinel structure mainly composed of lithium, manganese, and oxygen” means LiMn ₂ O ₄ composed of lithium, manganese, and oxygen, and a part of this Li or Mn as chromium, cobalt, Complex oxides substituted with different elements such as aluminum, nickel, iron, magnesium, etc., Li _{1 + X} Mn _{2- xy My} O ₄ (where -0.1 ≦ x ≦ 0.2, 0 <y ≦ 0 .2). The lattice constant of the composite oxide is preferably 8.240 mm or less.

Furthermore, in the present invention, the term “substantially” means that at least one β-type MnO ₂ lattice is included in the surface layer of the composite oxide having a spinel structure mainly composed of lithium, manganese, and oxygen.
In the present invention, there are no particular limitations on the method for producing a composite oxide having a spinel structure mainly composed of lithium, manganese and oxygen and its starting material. For example, in the production method, a mixture of a manganese compound and a lithium compound, or Further, the mixture to which a compound containing a different element that can substitute for manganese is added may be fired at a temperature of 300 ° C. to 850 ° C. for at least one hour in the air or in an oxygen gas flow atmosphere.

  There is no particular limitation on the crystallinity of the composite oxide having a spinel structure mainly composed of lithium, manganese, and oxygen, and an unreacted lithium compound and manganese oxide may remain. On the other hand, as a starting manganese source, electrolytic manganese dioxide (EMD), chemically synthesized manganese dioxide (CMD), manganese sesquioxide, manganese tetroxide, manganese oxyhydroxide, manganese carbonate, manganese nitrate, and the like can be used. As the source, lithium hydroxide, lithium carbonate, lithium nitrate or the like can be used. As a preferable manganese source, manganese carbonate rich in reactivity with lithium can be mentioned.

  The acid that can be used in the present invention is not particularly limited as long as it can dissolve lithium and manganese on the surface of the composite oxide having a spinel structure mainly composed of lithium, manganese, and oxygen, and Bronsted acid is used. Bronsted acids usually include inorganic acids such as hydrochloric acid, hydrobromic acid, hydroiodic acid, hydrofluoric acid, nitric acid, amidosulfuric acid, sulfuric acid, phosphoric acid, methanesulfonic acid, ethanesulfonic acid, propanesulfonic acid, benzene Examples thereof include organic sulfonic acids such as sulfonic acid, toluenesulfonic acid, naphthalenesulfonic acid and naphthalenedisulfonic acid, and organic carboxylic acids such as trifluoroacetic acid, trichloroacetic acid, formic acid and oxalic acid. Among these, hydrochloric acid, nitric acid, sulfuric acid and organic sulfonic acid are preferable.

When nitric acid is used, for example, by acid treatment, the composite oxide surface layer having a spinel structure mainly composed of lithium, manganese, and oxygen has the following reaction formula (1),
2LiMn ₂ O ₄ + 4HNO ₃ → 2LiNO ₃ + Mn (NO ₃ ) ₂
+ 3λ-MnO ₂ + 2H ₂ O (1)
According to the reaction formula, the surface spinel structure changes to λ-MnO ₂ .
According to the above reaction formula (1), in the method for producing a positive electrode active material of the present invention, the conversion from the spinel structure to λ-MnO ₂ is detected, the completion of the reaction is detected by detecting the pH of the acidic solution, and the acid to be added The conversion rate of the spinel structure can be designed and implemented from the number of moles. And in the manufacturing method of the positive electrode active material of this invention, the surface layer of composite oxide is heat-processed by the specific temperature of 200 degreeC or more and less than 400 degreeC in the composite oxide of the spinel structure partially converted by the acid treatment. A composite oxide substantially consisting of β-type MnO ₂ can be produced.

In connection with this reaction, Journal of Solid State Chemistry 39, 142-147 (1981) reports that spinel-type LiMn ₂ O ₄ can be converted to λ-MnO ₂ by treating it with an aqueous acid solution. There is no description or suggestion that only the surface layer of the composite having a spinel structure is converted to λ-MnO ₂ . Further, there is no description of a composite oxide having a two-layer structure in which the surface layer of spinel-type LiMn ₂ O ₄ is λ-MnO ₂ , and further, a spinel structure having such a two-layer structure is used as a positive electrode of a non-aqueous secondary battery. There is no description or suggestion of using it as an active material. Further, Journal of Solid State Chemistry 39, 142-147 (1981) describes that λ-MnO ₂ is a metastable phase and is returned to β-MnO ₂ as a stable phase by sufficient heat treatment. There is no description or suggestion of using the spinel structure having the two-layer structure as described above or an active material for a positive electrode of a non-aqueous secondary battery.

The positive electrode active material produced by the production method of the present invention is a composite oxide containing a spinel structure mainly composed of lithium, manganese and oxygen and β-type MnO ₂ , and preferably a surface layer of the spinel-type composite oxide There composite oxide consisting essentially of β-type MnO ₂ can be effectively used as a cathode material of a nonaqueous secondary battery.
The surface treatment of the composite oxide having a spinel structure mainly composed of lithium, manganese, and oxygen by the acid treatment is performed according to the concentration of the acid to be added and the acid concentration according to the amount (molar amount) of the target region of λ-MnO ₂ . Molar amount and reaction time can be determined. The conversion mol% from the spinel structure to λ-MnO ₂ is preferably 1 to 13 mol%, more preferably 2 to 7 mol%, and further desirably 3 to 5 mol% with respect to the spinel structure composite oxide. It is. If the conversion rate to λ-MnO ₂ (mol%) is less than 1 mol%, the expected effect associated with the surface treatment does not appear, and if it exceeds 13 mol%, the initial discharge capacity of the non-aqueous secondary battery when the battery is constructed. The amount of decrease is too large, which is not preferable.

If the surface of the composite oxide remains λ-MnO ₂ , lithium ions are taken in during discharge and return to the single phase of the spinel structure composite oxide, and the surface layer is stabilized by repeated charge and discharge of the battery. Can not be converted. Therefore, in the positive electrode active material of the present invention, a composite oxide in which the β-type MnO ₂ is formed in a range of 1 to 13 mol% of the spinel composite oxide is used as a positive electrode material for a non-aqueous secondary battery. The

In the nonaqueous secondary battery of the present invention, the composite oxide used as the positive electrode active material is preferably a composite oxide having a β-type MnO ₂ phase on the surface layer, and further has a primary particle size of 0.1 μm to 1. The composite oxide having a thickness of 0 μm, preferably 0.2 μm to 0.5 μm is used. In the present invention, a composite oxide having a β-type MnO ₂ phase on the surface layer of particles obtained by granulating the primary particles to 3 μm to 50 μm, preferably 5 μm to 30 μm is also preferably used.

The composite oxide having a spinel structure mainly composed of lithium, manganese, and oxygen used in the present invention is obtained by crushing the fired product and then obtaining pulverized particles (this is a primary particle or a collection of primary particles). Secondary particles, preferably having an average particle diameter of 2 μm or less), and using dense granulated particles that are granulated and fired by adding and mixing a sintering acceleration aid (granulation accelerator). Good. Here, the dense granulated particles mean that there are no or few voids between the primary particles of the oxide, and can be produced by the following method using a sintering accelerator.
The mixing method of the pulverized and pulverized composite oxide particles mainly composed of lithium, manganese and oxygen and the sintering accelerating aid is not particularly limited. For example, a medium agitating pulverizer, a ball mill, a paint shaker, A mixing mixer can be used. The mixing method may be either dry or wet. When the composite oxide is pulverized and pulverized, a sintering accelerator aid may be added and mixed at the same time.

The sintering accelerating aid that can be used is only required to be able to sinter the pulverized / pulverized particles of the composite oxide particles mainly composed of lithium, manganese, and oxygen for granulation, and more preferably, 900 ° C. A compound that melts at the following temperature, for example, an oxide that can be melted at a temperature of 550 ° C. to 900 ° C. or a precursor that can be converted to the oxide, or an oxide that is melted by solid solution or reaction with lithium or manganese, or an oxidation thereof Any compound that can become a product may be used. For example, the sintering acceleration aid includes compounds containing elements such as Bi, B, W, Mo, and Pb, and these compounds may be used in any combination, and B ₂ O ₃ and A compound combining LiF or a compound combining MnF ₂ and LiF is also used. Among these, compounds containing Bi, B, and W elements are particularly preferable because they have a large sintering shrinkage effect.

For example, Bi compounds include bismuth trioxide, bismuth nitrate, bismuth benzoate, bismuth oxyacetate, bismuth oxycarbonate, bismuth citrate, bismuth hydroxide, and the like. Examples of the B compound include boron trioxide, boron carbide, boron nitride, and boric acid. Examples of the W compound include tungsten dioxide and tungsten trioxide.
The addition amount of the sintering accelerating aid is preferably in the range of 0.0001 to 0.05 mol with respect to 1 mol of Mn in the composite oxide in terms of added metal element. This is because there is no sintering shrinkage effect if the amount added in terms of added metal element is less than 0.0001 mol, and the initial capacity of the active material becomes too small if it exceeds 0.05 mol. Preference is given to 0.005 to 0.03 mol.

  The sintering promoting aid may be used in a powder state or in a liquid state dissolved in a solvent. When added in a powder state, the average particle diameter of the sintering accelerator aid is preferably 50 μm or less, more preferably 10 μm or less, and further preferably 3 μm or less. Although it is preferable to add the sintering promoting aid before granulation / sintering, the granulated product may be impregnated and sintered at a temperature at which the sintering promoting aid can be melted after granulation.

Next, the granulation method will be described.
Examples of the granulation method include spray granulation method, fluidized granulation method, compression granulation method, stirring granulation method and the like using the above-mentioned sintering acceleration aid, and also include medium fluidized drying and medium vibration drying. You may use together. Agitation granulation and compression granulation are particularly preferred because the density of secondary particles is increased, and spray granulation is particularly preferred because the granulated particle shape is a perfect sphere. Examples of the agitating granulator include a vertical granulator manufactured by Paulek Co., Ltd. and a Spartan Luther manufactured by Fuji Paudal Co., Ltd. Examples of the compression granulator include Kurimoto Tekko Co., Ltd. Examples thereof include a roller compactor MRCP-200 type. As an example of a spray granulator, Ashizawairo atomizer Co., Ltd. Mobile minor type spray dryer etc. are mentioned.

In the present invention, the size of the granulated particles used for the positive electrode is not particularly limited. When the average particle size of the granulated particles is too large, it may be crushed and pulverized lightly immediately after granulation or after sintering, and classified and sized to obtain the desired particle size. In order to increase the granulation efficiency, an organic granulation aid may be added. Examples of the granulation aid include acrylic resins, copolymers of isobutylene and maleic anhydride, polyvinyl alcohol, polyethylene glycol, polyvinyl pyrrolidone, hydroxypropyl cellulose, methyl cellulose, corn starch, gelatin, and lignin.
The addition amount of the granulating aid is preferably 5 parts by weight or less, more preferably 2 parts by weight with respect to 100 parts by weight of the composite oxide having a spinel structure mainly composed of lithium, manganese and oxygen and the sintering promoting aid. Or less.

Next, a method for firing the granulated particles will be described.
The granulated particles are degreased by holding them in the air or in a gas atmosphere containing oxygen at a temperature range of 300 ° C. to 550 ° C. for 10 minutes or more. The carbon residue in the defatted granulated product is preferably 0.1% or less. The granulated particles after degreasing are sintered by being held for 1 minute or more in a temperature range of 550 ° C. to 900 ° C. in an atmosphere containing air or oxygen.
In addition, the firing of the granulated particles without using the above-mentioned organic-based granulation aids is similarly performed in the air or in a gas atmosphere containing oxygen to sinter and shrink, thereby densifying the secondary particles. Can do.

In the case where a granulated product thus produced (including secondary particles) or a composite oxide having a β-type MnO ₂ phase is used as the positive electrode active material on the surface layer of the primary particles, the non-aqueous secondary battery The initial discharge capacity is large, and even when charging / discharging is repeated in an environment of 60 ° C., the discharge capacity is hardly reduced. The surface layer thickness of the β-type MnO ₂ phase is, for example, 20 μm of granulated secondary particles. In this case, a film formed in the range of 0.02 μm to 0.22 μm, preferably 0.05 μm to 0.08 μm is preferable.

In the method for producing a positive electrode active material of the present invention, β-MnO ₂ on the surface of the composite oxide having the spinel structure is heat-treated at a temperature of 200 ° C. or more and less than 400 ° C. -MnO ₂ is characterized in that when the heat treatment temperature is less than 200 ° C., the change from λ-MnO ₂ to β-MnO ₂ hardly occurs, and at 400 ° C. or more, the lithium of the spinel structure composite oxide is on the surface. And the spinel structure composite oxide surface cannot be stabilized. Whether or not Li has diffused on the surface can be determined by the fact that the lattice constant becomes larger than the lattice constant when heat-treated at 200 ° C. or higher and lower than 400 ° C. The heat treatment time may be at least 5 minutes.

In the present invention, the composite oxide having a spinel structure mainly composed of lithium, manganese, and oxygen can be modified to particles having pores in the range of 30 to 400% by acid treatment. By using the composite oxide having such a pore state as the positive electrode active material, it is considered that the local current density on the surface of the positive electrode active material during charging and discharging can be reduced, and the cycle characteristics are greatly improved. It is done.
In general, in order to obtain excellent battery characteristics, it is said that a positive electrode active material having a small specific surface area (1 m ² / g or less) is desirable because it is necessary to suppress side reactions of the positive electrode active material. However, surprisingly, although the specific surface area of the positive electrode active material of the present invention is as large as 1.5 m ² / g or more, superior battery characteristics can be obtained compared to the conventional one.

Next, a method for using the positive electrode active material of the present invention as a positive electrode material for a non-aqueous secondary battery will be described.
The positive electrode material is a mixture of the positive electrode active material, a conductivity imparting agent such as carbon black or graphite, and a binder (binding material) such as polyvinylidene fluoride dissolved in a predetermined ratio (for example, N-methylpyrrolidone). The electrode paste is applied to the current collector, and then dried and pressed by a roll press or the like. As the current collector, a known metal current collector such as aluminum, stainless steel or titanium is used.

As an electrolyte salt in the electrolytic solution used in the nonaqueous secondary battery of the present invention, a known lithium salt containing fluorine can be used. For example, LiPF ₆ , LiBF ₄ , LiN (CF ₃ SO ₂ ) ₂ , LiAsF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ can be used. The electrolyte solution of the non-aqueous secondary battery is used by dissolving at least one electrolyte of a known lithium salt containing fluorine in a non-aqueous electrolyte solution. The non-aqueous solvent of the non-aqueous electrolyte solution can be used without limitation as long as it is chemically and electrochemically stable and aprotic. For example, dimethyl carbonate, propylene carbonate, ethylene carbonate, methyl ethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, methyl butyl carbonate, diethyl carbonate, ethyl propyl carbonate, diisopropyl carbonate, dibutyl carbonate, 1,2-butylene carbonate, ethyl isopropyl carbonate, Examples thereof include carbonates such as ethylbutyl carbonate. Also, oligoethers such as triethylene glycol methyl ether and tetraethylene glycol dimethyl ether, aliphatic esters such as methyl propionate and methyl formate, aromatic nitriles such as benzonitrile and tolunitrile, amides such as dimethylformamide, dimethyl Examples include sulfoxides such as sulfoxide, lactones such as γ-butyrolactone, sulfur compounds such as sulfolane, N-vinylpyrrolidone, N-methylpyrrolidone, and phosphate esters. Of these, in the present invention, carbonates, aliphatic esters and ethers are preferred.

The negative electrode used in the nonaqueous secondary battery of the present invention is not particularly limited as long as it is a material capable of reversibly occluding and releasing lithium ions. For example, lithium metal, lithium alloy, carbon material (including graphite) Metal chalcogen etc. can be used.
Next, a method for evaluating electrode characteristics will be described.
A positive electrode active material, a Cabot Vulcan XC-72 as a conductive material, and a tetrafluoroethylene resin as a binder are mixed at a weight ratio of 50:34:16, and the mixture is swollen with toluene for 12 hours. The swollen mixture is applied onto a current collector made of aluminum expanded metal, and pressure-molded at ² t / cm ² , and toluene is dried to form a positive electrode. On the other hand, lithium foil is used as the negative electrode. As the electrolytic solution, a solution obtained by dissolving LiPF ₆ at a concentration of 1 mol / liter in a mixed solution in which propylene carbonate and dimethyl carbonate are mixed at a volume ratio of 1: 2 is used. A separator made of polypropylene is used, and silica fiber filter paper QR-100 manufactured by Advantech Toyo Co., Ltd. is also used as a reinforcing material for the purpose of preventing micro shorts caused by dendrite formation of the negative electrode. Using these positive electrode, negative electrode, electrolytic solution, separator and reinforcing material, a 2016 coin battery is prepared and subjected to 500 charge / discharge cycle tests in a thermostat set at 60 ° C. The measurement conditions are constant current constant voltage charge-constant current discharge, charge and discharge rate 1C (charge suspend in 2.5 hours from the start of charge), and scanning voltage 3.1V to 4.3V.

In the following examples and comparative examples, the positive electrode active material of the present invention and the non-aqueous secondary battery using the same will be specifically described, but the present invention is not limited to these.
Regarding the pore distribution measurement of the positive electrode active material of the present invention, the following method was adopted for the measurement of pores of 400 mm or less. In other words, CarloWS made by Carlo Elba (Porosimeter) was used as the measuring device, and the positive electrode active material and mercury were held in vacuum for 1 hour as a pretreatment for measurement, and then pressed into 2000 bar for 40 minutes to measure the pores of the positive electrode active material. did.
The structure confirmation of the positive electrode active material was determined by measuring under the following conditions by the X-ray diffraction method. X-ray source: CuKα, output: 50 kV, 180 mA, slit: 1 / 2-1 / 2-0.15 mm, measurement method: 2θ / θ method, measurement range: 20 to 90 °, scan speed 5 ° / min.

Example 1
Manganese carbonate, lithium carbonate, and aluminum hydroxide were mixed with a ball mill so that the molar ratio of Li / Mn / Al was 1.02: 1.967: 0.013, and the reaction was performed at 650 ° C. for 4 hours in an air atmosphere. Spinel structure mainly composed of lithium, manganese and oxygen having an average primary particle size of 0.5 μm and a specific surface area of 4.2 m ² / g, mixed again by a ball mill and fired at 750 ° C. for 20 hours in an air atmosphere. Composite oxide particles were obtained. The obtained spinel structure composite oxide particles were put into an aqueous solution containing 5 mol% nitric acid with respect to the composite oxide, and it was confirmed that the pH of the aqueous solution became constant (pH = 5) near neutrality. Then, it filtered and wash | cleaned and vacuum-dried at 100 degreeC. And it heat-processed at 300 degreeC for 4 hours, and obtained the positive electrode active material of this invention. When the positive electrode active material obtained here was measured by an X-ray diffraction method, an X-ray peak derived from β-MnO ₂ not found in an untreated material was detected in the vicinity of 2θ = 30 °.

Next, this positive electrode active material, Cabot Vulcan XC-72 as a conductive material, and tetrafluoroethylene resin as a binder are mixed at a weight ratio of 50:34:16, and positive electrode current collection is performed by a conventional method. The positive electrode was produced by applying on the body. Then, a positive electrode, a lithium negative electrode, an electrolytic solution in which LiPF ₆ is dissolved at a concentration of 1 mol / liter in a mixed solution in which propylene carbonate and dimethyl carbonate are mixed at a volume ratio of 1 to 2, a polypropylene separator and a silica fiber system A 2016-type coin-type non-aqueous secondary battery was manufactured by stacking reinforcing materials including the.
Next, 500 charge / discharge cycle tests were performed in a thermostat set to 60 ° C. The measurement conditions were constant current constant voltage charge-constant current discharge, charge and discharge rate 1C (charge suspend in 2.5 hours from the start of charge), and scan voltage 3.1V to 4.3V.
Details of the results are shown in Table 1.

(Example 2)
Implemented in the same manner as in Example 1 except that manganese carbonate, lithium carbonate, and aluminum hydroxide were mixed by a ball mill so that the molar ratio of Li / Mn / Al was 0.968: 1.935: 0.097. The results of battery evaluation are shown in Table 1.
(Example 3)
The results of battery evaluation are shown in Table 1 in the same manner as in Example 2 except that acid treatment was performed with an aqueous solution containing 10 mol% nitric acid.

Example 4
Manganese carbonate and lithium carbonate were mixed with a ball mill so that the Li / Mn molar ratio was 0.51, and the reaction was carried out in an air atmosphere at 650 ° C. for 4 hours. The obtained reaction product was dispersed in an ethanol solvent and pulverized with a wet ball mill to make the average particle size 0.5 μm. To this pulverized powder, bismuth oxide having an average particle diameter of 2 μm was added and mixed so that the Bi / Mn molar ratio was 0.0026, and the mixture was mixed with Fuji Powder Co., Ltd. Spartan Luzer RMO-6H. Granulated. As a granulation aid, 1.5 parts by weight of polyvinyl alcohol was dissolved in an aqueous solution and added to 100 parts by weight of the mixed powder of pulverized reactant and bismuth oxide, and granulated for 16 minutes. The obtained granulated material was lightly crushed and pulverized with a mixer, and sized with an air classifier to an average particle size of 20 μm. The sized granulated product is kept in the atmosphere at 500 ° C. for 2 hours, degreased (polyvinyl alcohol is decomposed), and then baked in the atmosphere at 750 ° C. for 20 hours to obtain a composite oxidation with a specific surface area of 1.6 m ² / g. I got a thing. The following operation was performed in the same manner as in Example 1 except that the obtained spinel structure composite oxide was acid-treated by adding it to an aqueous solution containing 2 mol% nitric acid with respect to the composite oxide. The results are shown in Table 1.

(Example 5)
The results of battery evaluation are shown in Table 1 in the same manner as in Example 4 except that acid treatment was performed with an aqueous solution containing 5 mol% nitric acid.

(Example 6)
Lithium carbonate, manganese carbonate and vapor phase alumina were mixed with a ball mill so that the molar ratio of Li / Mn / Al was 1.02: 1.967: 0.013, and the reaction was carried out at 650 ° C. for 4 hours in the atmosphere. I let you. Boron oxide (0.8% by mass) was added to the resulting reaction powder, and wet pulverized with a ball mill using water as a dispersion medium to an average particle size of 0.3 μm. After drying the slurry, the slurry was granulated with a Spartan Luser RMO-6H manufactured by Fuji Powder Corporation. The pulverized powder was granulated by adding 1.5% by weight of polyvinyl alcohol as an aqueous solution as a granulating binder. The obtained granulated powder was lightly pulverized and pulverized with a mixer and sized to 20 μm by air classification. The sized granulated powder was kept in the atmosphere at 500 ° C. for 2 hours, degreased, and then baked at 750 ° C. for 30 minutes to obtain a composite oxide of 1.4 m ² / g.

Pure water was added to the obtained composite oxide to form a slurry with a solid content concentration of 20%, ultrasonic treatment was performed for 5 minutes, and the process up to removing the supernatant was repeated 10 times for washing and drying. After drying at 100 ° C., acid treatment and heat treatment were performed in the same manner as in Example 1 to obtain the positive electrode active material of the present invention. When the pores of the obtained positive electrode active material were measured, it was found that 50 to 320 mm pores not present in the untreated product were generated. Further, when the obtained positive electrode active material was measured by the X-ray diffraction method under the following conditions, an X-ray peak derived from β-MnO ₂ not found in the untreated material was detected in the vicinity of 2θ = 30 °.
The obtained positive electrode active material was subjected to battery evaluation in the same manner as described in Example 1, and the results are shown in Table 1.

(Comparative Example 1)
Except that the acid treatment and the heat treatment were not performed, the same procedure as in Example 1 was performed, and the results of battery evaluation are shown in Table 1.
(Comparative Example 2)
Table 1 shows the results of battery evaluation performed in the same manner as in Example 1 except that heat treatment was performed at 150 ° C. for 4 hours after the acid treatment.
(Comparative Example 3)
Table 1 shows the results of battery evaluation performed in the same manner as in Example 1 except that heat treatment was performed at 400 ° C. for 4 hours after the acid treatment. The lattice constant of the compound produced in Example 1, which was heat treated at 300 ° C. for 4 hours, was 8.231 、, whereas the lattice constant of the compound obtained here was as large as 8.235 Å. .

(Comparative Example 4)
Table 1 shows the results of battery evaluation performed in the same manner as in Example 4 except that acid treatment was performed with an aqueous solution containing 15 mol% nitric acid.
(Comparative Example 5)
Washing and acid treatment The same steps as in Example 6 were performed except that the following steps were not performed. When the obtained positive electrode active material was examined, pores of 400 mm or less did not exist, and no X-ray peak derived from β-MnO ₂ was detected. The obtained positive electrode active material was subjected to battery evaluation in the same manner as described in Example 1, and the results are shown in Table 1.

Effect of the invention

The positive electrode active material of the present invention is a nonaqueous secondary battery including a negative electrode using lithium as an active material, a nonaqueous electrolyte, and a positive electrode using a composite oxide containing lithium, manganese, and oxygen as an active material. By using it as a positive electrode active material, it provides extremely excellent battery characteristics that can be maintained at a discharge capacity of 95 mAh / g or more when charging and discharging are repeated 500 times in an environment of 60 ° C., which was impossible with conventional products. can do.
The positive electrode active material of the present invention is obtained by acid-treating the surface of a spinel structure composite oxide mainly composed of lithium, manganese, and oxygen, and heat-treating the surface of the spinel structure composite oxide within a specific temperature range. By converting it to MnO ₂ and using it, it shows an exceptional improvement effect that is excellent with respect to charge and discharge in a 60 ° C. environment.

  Further, in the present invention, the positive electrode active material (particles) having pores in the range of 30 to 400 mm is obtained by acid treatment of the positive electrode active material of spinel composite oxide mainly composed of lithium, manganese and oxygen. Can be quality. By using the composite oxide having such a pore state as a positive electrode active material of a non-aqueous secondary battery, the local current density on the surface of the positive electrode active material during charge / discharge can be reduced, and cycle characteristics can be reduced. This is considered to be extremely improved.

Claims (10)

A positive electrode active material comprising a part having a spinel structure mainly comprising lithium, manganese and oxygen , and a composite oxide particulate material having a surface layer substantially comprising β-type MnO ₂ ,
The composite oxide granular material has a primary particle diameter of 0.1 μm to 1.0 μm.
Positive electrode active material.
The positive electrode active material according to claim 1, wherein the amount of β-type MnO ₂ in the composite oxide is 1 to 13 mol%.
A portion having a spinel structure mainly containing lithium, manganese, and oxygen,
LiMn ₂ O ₄ or _{Li 1 + x Mn 2-xy} M y O 4,
(However, M represents Cr, Co, Al, Ni, Fe or Mg. Further, −0.1 <x ≦
0.2 and 0 <y ≦ 0.2. )
The positive electrode active material of Claim 1 or 2 containing the compound represented by these .
4. The positive electrode active material according to claim 1, wherein the composite oxide granular material has a primary particle diameter of 0.2 μm to 0.5 μm .
The positive electrode active material according to claim 4, wherein the composite oxide granular material is obtained by granulating primary particles to a particle diameter of 3 μm to 50 μm.
6. The positive electrode active material according to claim 1, wherein the composite oxide granular material has pores in a range of 30 to 400 μm.
The paste for electrodes which contains the positive electrode active material of any one of Claims 1-6.
A positive electrode comprising the positive electrode active material according to claim 1.
Acid treatment of a composite oxide having a spinel structure mainly containing lithium, manganese, and oxygen;
Then, the manufacturing method of the positive electrode active material of any one of Claims 1-6 including heat-processing in the temperature range of 200 to 400 degreeC.
A nonaqueous secondary battery comprising a negative electrode made of a material capable of reversibly occluding and releasing lithium ions, a nonaqueous electrolyte, and the positive electrode according to claim 8.