JP2007200683A - Manufacturing method of cathode active substance for lithium secondary battery, cathode for lithium secondary battery and lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a manganese oxide having a spinel structure as shown in a general formula Li<SB>1+a</SB>Mn<SB>2-x-a</SB>M<SB>x</SB>O<SB>4+y</SB>(0≤x≤0.5, -0.2≤y<0.5, 0≤a≤0.2, M for at least a kind of a transition metal selected from a group of Ni, Fe, and Ti), in which formation of impurities is controlled. <P>SOLUTION: The manufacturing method of a cathode active substance for a lithium secondary battery includes a process in which a Li raw material, an M raw material and a Mn raw material are mixed and crushed, and a process in which the mixed and crushed raw materials are calcined, and in the above mixing and crushing process, after the Li raw material and the Mn raw material are mixed and crushed, the Mn raw material is added and mixed to raise a reactivity of the Li raw material and the Mn raw material. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention belongs to the field of lithium secondary batteries, and in particular, relates to a positive electrode active material for lithium secondary batteries containing a manganese oxide having a spinel structure, a positive electrode for lithium secondary batteries, and a method for manufacturing a lithium secondary battery.

In recent years, non-aqueous electrolyte secondary batteries used as a main power source for mobile communication devices and portable electronic devices are characterized by high electromotive force and high energy density. As a positive electrode active material for a non-aqueous electrolyte secondary battery, a lithium-containing composite oxide having a layered structure is mainly used. Among these, lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), and the like have a potential of 4 V or more with respect to metallic lithium.

Studies are also actively conducted on the use of manganese oxide having a spinel structure as a positive electrode active material of a non-aqueous electrolyte secondary battery. For example, utilization of LiMn ₂ O ₄ , Li ₄ Mn ₅ O ₁₂ , Li ₂ Mn ₄ O _{9 and the} like has been proposed.

Since LiMn ₂ O ₄ is inexpensive, it has attracted attention from the viewpoint of reducing the manufacturing cost of the nonaqueous electrolyte secondary battery. However, when charging / discharging of the battery containing LiMn ₂ O ₄ is repeated at around 3 V, the discharge capacity is significantly reduced. This is considered to be caused by a change in crystal structure derived from the Jahn-Teller strain.

Li ₄ Mn ₅ O ₁₂ or Li ₂ Mn ₄ O ₉ is less susceptible to Yanterer distortion. In particular, Li ₂ Mn ₄ O ₉ has a high capacity density because it has a defect at the cation site. However, the reduction in the discharge capacity when charging / discharging is repeated at around 3 V is still large.

Patent Document 1 discloses LiD _{x / b} Mn _2−x O ₄₊ δ (element D is a monovalent or polyvalent metal element, 0 <x ≦ 0.33, 0 ≦ δ <0.5, b Proposes the use of the oxidation number of element D). As the element D, Li, Mg, or Co has been proposed.

Patent Document 2 proposes a method for producing a manganese oxide having a spinel structure. According to this proposal, lithium salt and manganese salt are mixed and pulverized and fired at 200-600 ° C. in the atmosphere.
US Pat. No. 5,316,877 US Pat. No. 4,980,251

  According to Patent Document 1, a decrease in discharge capacity when charging / discharging is repeated in the vicinity of 4V is suppressed, but it is not sufficient for a decrease in discharge capacity in the vicinity of 3V.

Patent Document 2 proposes a method for producing a manganese oxide having a spinel structure. When Mn ₃ O ₄ , Mn ₂ O ₃ , and MnO ₂ are used as the Mn raw material, the Mn raw material has an average particle diameter. Thus, a single phase cannot be obtained unless pulverization is performed until it becomes 1 μm or less. Further, when the manganese salt is pulverized to 1 μm or less, the manganese oxide obtained after firing also becomes fine particles of 1 μm or less, and the packing density of the positive electrode is lowered.

  The present invention is a method for producing a manganese oxide having a spinel structure, and an object thereof is to produce a manganese oxide having a high-purity spinel structure having high charge / discharge cycle characteristics.

The present invention has the general formula Li _{1 + a} Mn _2−xa M _x O _{4 + y} (0 ≦ x ≦ 0.5, −0.2 ≦ y <0.5, 0 ≦ a ≦ 0.2, M is A method for producing a positive electrode active material for a lithium secondary battery having a spinel structure represented by at least one transition metal selected from the group consisting of Ni, Fe, and Ti, wherein a Li raw material, an M raw material, and a Mn raw material are mixed A step of pulverizing and a step of firing the mixed and pulverized raw material. In the step of mixing and pulverizing the raw material, after mixing and pulverizing the Li raw material and the M raw material, adding and mixing and pulverizing the Mn raw material Features.

  According to the present invention, it is possible to produce a manganese oxide having a high-purity spinel structure having high charge / discharge cycle characteristics, and at least one selected from the group consisting of Mn, Ni, Fe, and Ti is substituted. By doing so, the cycle life characteristics are improved.

  In addition, by using the positive electrode of the present invention for a lithium secondary battery, a lithium secondary battery having a high capacity and excellent charge / discharge cycle characteristics can be provided.

The present invention has the general formula Li _{1 + a} Mn _2−xa M _x O _{4 + y} (0 ≦ x ≦ 0.5, −0.2 ≦ y <0.5, 0 ≦ a ≦ 0.2, M is A method for producing a positive electrode active material for a lithium secondary battery having a spinel structure represented by at least one transition metal selected from the group consisting of Ni, Fe, and Ti, wherein a Li raw material, an M raw material, and a Mn raw material are mixed A step of pulverizing and a step of firing the mixed and pulverized raw material. In the step of mixing and pulverizing the raw material, after mixing and pulverizing the Li raw material and the M raw material, adding and mixing and pulverizing the Mn raw material Features.

The manganese oxide in the present invention has a general formula: Li _{1 + a} Mn _2−xa M _x O _{4 + y} (M is at least one transition metal selected from the group consisting of Ni, Fe and Ti, 0 ≦ x ≦ 0.5, −0.2 ≦ y ≦ 0.5, 0 ≦ a ≦ 0.2). That is, the manganese oxide according to the present invention has a crystal structure in which Mn is substituted with at least one selected from the group consisting of Ni, Fe and Ti. Such a crystal structure is considered to be very stable and hardly cause Yanterer distortion. Therefore, good cycle life characteristics can be obtained.

  In the above general formula, the a value indicating the amount of lithium substituted with Mn may be in the range of 0 to 0.2. When the a value exceeds 0.2, the discharge capacity decreases. When a <0, Mn or element M is coordinated to the 8a site that is usually occupied by Li. Since Li at the 8a site contributes to the charge / discharge reaction, the discharge capacity decreases when a different element is substituted. Therefore, it is desirable that 0 ≦ a. A preferable range of the a value is 0 ≦ a ≦ 0.15.

  Moreover, y value which shows excess oxygen amount should just be the range of -0.2-0.5. In order for the y value to be greater than 0.5, the valence of Mn or the additive element needs to be 4 or more, which makes synthesis difficult. In addition, it is desirable that 0 ≦ y from the viewpoint of imparting a cation deficiency to the manganese oxide and suppressing Yanterer distortion. A preferable range of the y value is 0 ≦ y ≦ 0.5.

The method for producing a manganese oxide having the spinel structure according to the present invention includes a step of mixing and pulverizing a Li raw material, an M raw material, and a Mn raw material, and a step of firing the mixed and pulverized raw material, and mixing and pulverizing the raw material. In the process, the Li raw material and the M raw material are mixed and pulverized until the average particle diameter becomes 1 μm or less, and then the Mn raw material is added and mixed and pulverized so that the average particle diameter of the Mn raw material becomes 3 μm or more and 30 μm or less. Features. According to the present invention, when the Li raw material and the M raw material are made into fine particles, the reactivity with the Mn raw material becomes high, and it becomes easy to obtain a manganese oxide having a high-purity spinel structure. In addition, since the Mn raw material is not finely pulverized, the manganese oxide having a spinel structure after firing does not become fine particles, and a high packing density is possible during electrode production.

  Furthermore, the invention is characterized in that, in the step of firing the mixed raw materials, the firing temperature is 300 ° C. or higher and 600 ° C. or lower.

  When the temperature is lower than 300 ° C., the raw material is not decomposed and remains as an impurity. On the other hand, when the temperature is 600 ° C. or lower, the manganese oxide having a spinel structure is in a cation deficient state. This increases the discharge capacity. Moreover, when charging / discharging at 3V, the fall of the valence of Mn can be suppressed and the fall of the discharge capacity at the time of charging / discharging can be suppressed.

  Next, an example of a method for producing a manganese oxide having a spinel structure will be described.

  For example, a lithium salt and a salt of the element M are previously pulverized and mixed at a predetermined molar ratio, and an Mn raw material is added and pulverized and mixed. If the mixture is baked in air at 300 to 600 ° C. for 5 to 24 hours, the desired manganese oxide is obtained. As manganese dioxide, for example, electrolytic manganese dioxide is suitable.

  Suitable lithium salts include lithium hydroxide and lithium carbonate. As the salt of the element M, for example, hydroxide, nitrate, carbonate, sulfate, acetate, oxide and the like can be used.

  In addition, when the element M is Ni, nickel hydroxide, nickel carbonate, etc. are suitable. When the element M is Fe, ferric hydroxide, ferric oxyhydroxide, and the like are preferable. When the element M is Ti, meta titanium hydroxide (β-type), ortho titanium hydroxide (α-type), tetramethoxy titanium, and the like are preferable.

  Next, a positive electrode including the positive electrode active material, a negative electrode including a negative electrode active material, and a nonaqueous electrolyte secondary battery including a lithium ion conductive nonaqueous electrolyte will be described. The shape of the nonaqueous electrolyte secondary battery is not particularly limited. The present invention is applicable to, for example, coin-type, cylindrical-type, square-type, and sheet-type batteries.

  In the case of a coin-type battery, the positive electrode is obtained by forming a positive electrode mixture into, for example, a pellet shape. In addition to the positive electrode active material, the positive electrode mixture contains a conductive agent, a binder, a liquid component (dispersion medium) and the like as optional components. The positive electrode of the cylindrical battery or the square battery is produced by, for example, applying a positive electrode mixture paste on both surfaces of a positive electrode current collector, drying, and rolling to form a positive electrode mixture layer. The positive electrode mixture paste is prepared by mixing the positive electrode mixture with a liquid dispersion medium.

  In the case of a coin-type battery, the negative electrode can use metallic lithium or a lithium alloy punched into a pellet. However, in order to obtain good cycle characteristics, it is preferable to form the negative electrode mixture in a pellet form. In addition to the negative electrode active material, the negative electrode mixture contains a binder, a conductive agent, a thickener and the like as optional components. In the case of a cylindrical battery or a prismatic battery, the negative electrode is, for example, coated with a negative electrode mixture paste on both sides of the negative electrode current collector, dried and rolled to form a negative electrode mixture layer in the same manner as the positive electrode. It is produced by this.

The negative electrode active material is not particularly limited, but preferably contains silicon element in consideration of compatibility with the positive electrode active material. For example, the negative electrode active material is preferably at least one selected from the group consisting of simple silicon, silicon oxide, silicon carbide, silicon nitride, and silicon alloy. Among these, it is particularly preferable to use a silicon alloy. However, carbon materials (for example, graphite, graphitizable carbon material, non-graphitizable carbon material, etc.) can also be preferably used.

  The silicon alloy preferably includes an A phase mainly composed of silicon and a B phase made of an intermetallic compound of a transition metal element and a silicon element. In the silicon alloy containing the A phase and the B phase, the influence due to expansion is easily mitigated, and the electronic conductivity is hardly lowered. Therefore, very excellent cycle life characteristics can be realized by combining with the positive electrode active material of the present invention.

  The A phase is a phase responsible for insertion and extraction of Li. The A phase is a phase that can electrochemically react with Li. The A phase may be a phase mainly composed of Si, but is preferably Si alone from the viewpoint of realizing a high capacity. However, Si alone is a semiconductor and has poor electron conductivity. Therefore, it is effective to include a trace amount of impurities in the A phase up to about 5% by weight. Examples of impurities include phosphorus, boron, hydrogen, and transition metal elements.

  The B phase is composed of an intermetallic compound of a transition metal element and silicon. The intermetallic compound containing silicon has high affinity with the A phase. Therefore, even when the alloy expands during charging, cracks are unlikely to occur at the interface between the A phase and the B phase. In addition, the B phase has higher electron conductivity and higher hardness than the Si single phase. Therefore, the B phase supplements the low electronic conductivity of the A phase and contributes to maintaining the shape of the alloy particles. A plurality of B phases may be present. Two or more intermetallic compounds having different compositions may exist as the B phase.

  The A phase and the B phase are preferably composed of microcrystalline or amorphous regions. In the microcrystalline or amorphous region, the size of crystallites (crystal grains) is preferably 100 nm or less, more preferably 5 nm or more and 100 nm or less.

  The crystallite size can be determined by X-ray diffraction measurement. Specifically, the half-value width of the peak attributed to each phase is obtained from the diffraction spectrum of the alloy obtained by X-ray diffraction measurement. The crystallite size can be calculated from the half width and Scherrer's equation. When there are a plurality of peaks attributed to each phase, the half width of the peak with the highest intensity is obtained, and the Scherrer formula is applied thereto. Usually, if the half width is 0.09 ° or more, the crystallite size can be determined to be 100 nm or less.

  The transition metal element constituting the intermetallic compound is preferably at least one selected from the group consisting of Ti, Zr, Ni, Cu and Fe, and particularly preferably Ti. Titanium silicides have higher electronic conductivity and higher hardness than other elemental silicides.

  The lithium ion conductive non-aqueous electrolyte may be a gel electrolyte or a solid electrolyte, but a non-aqueous solvent in which a lithium salt is dissolved is most common. Nonaqueous solvents include, for example, cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl Chain carbonates such as methyl carbonate (EMC) and dipropyl carbonate (DPC), aliphatic carboxylic acid esters such as methyl formate, methyl acetate, methyl propionate and ethyl propionate, and γ-lactones such as γ-butyrolactone , 1,2-dimethoxyethane (DME), 1,2-diethoxyethane (DEE), chain ethers such as ethoxymethoxyethane (EME), cyclic ethers such as tetrahydrofuran, 2-methyltetrahydrofuran, etc. Can do. These are preferably used in combination.

Examples of the lithium salt dissolved in the non-aqueous solvent include LiClO ₄ , LiBF ₄ , LiPF ₆ ,
LiAlCl ₄ , LiSbF ₆ , LiSCN, LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , Li (CF ₃ SO ₂ ) ₂ , LiAsF ₆ , LiB ₁₀ Cl ₁₀ , lower aliphatic lithium carboxylate, LiCl, LiBr, LiI, chloroborane Lithium, lithium tetraphenylborate, imides (lithium bispentafluoroethylsulfonic acid imide (LiN (C ₂ F ₅ SO ₂ ) _2, etc.)) and the like can be given. These may be used alone or in combination. The amount of lithium salt dissolved in the non-aqueous solvent is not particularly limited, but is preferably 0.2 to 2.0 mol / L, and more preferably 0.5 to 1.5 mol / L.

  EXAMPLES Next, although this invention is demonstrated to a specific example based on an Example, this invention is not limited to a following example. In Examples and Comparative Examples, positive electrodes and coin-type batteries were produced and evaluated in the following manner.

Example 1
Lithium hydroxide monohydrate (Kanto Chemical Co., Ltd., Deer Special Grade) was pulverized in isopropanol with a zirconia ball having a diameter of 5 mm for 15 hours in an isopropanol to an average particle size of 0.3 μm. Next, electrolytic manganese dioxide (Mitsui Metals, average particle size: 30 μm) was added and further mixed and pulverized for 1 hour, so that the average particle size of manganese dioxide was 7 μm. The slurry-like mixture thus obtained was separated from the balls, and then the solvent was evaporated and dried at 40 ° C. under reduced pressure by a rotary evaporator to obtain a powder-like mixture. The mixing ratio of the raw materials was 1: 2 in terms of the Li: Mn molar ratio. This powdery mixture was baked in air at 400 ° C. for 12 hours to obtain a manganese oxide having a cation-deficient spinel structure represented by LiMn ₂ O _4.2 . This was designated as Sample A. The composition of the active material was calculated by performing quantitative analysis of cations by ICP emission spectroscopic analysis and quantitative analysis of oxygen by infrared absorption method.

(Example 2)
Lithium hydroxide monohydrate (Kanto Chemical Co., Ltd., Shika Special Grade) and nickel hydroxide (High Purity Chemical Laboratory, 99.9% up) were ground in isopropanol with a ball mill made of zirconia having a diameter of 5 mm for 15 hours. The average particle size was 0.3 μm. Next, electrolytic manganese dioxide (Mitsui Metals, average particle size: 30 μm) was added and further mixed and pulverized for 1 hour, so that the average particle size of manganese dioxide was 7 μm. The slurry-like mixture thus obtained was separated from the balls, and then the solvent was evaporated and dried at 40 ° C. under reduced pressure by a rotary evaporator to obtain a powder-like mixture. The mixing ratio of the raw materials was 1: 1.6: 0.4 in terms of a molar ratio of Li: Mn: Ni. This powdery mixture was calcined in air at 400 ° C. for 12 hours to obtain a manganese oxide having a cation-deficient spinel structure represented by LiMn _1.6 Ni _0.4 O _4.2 . This was designated as Sample B.

(Example 3)
A cation deficient type represented by LiMn _1.6 Fe _0.4 O _4.2 was synthesized in the same manner as in Example 2 except that ferric hydroxide (99% up) was used instead of nickel hydroxide. A manganese oxide having a spinel structure was obtained. This was designated as Sample C.

Example 4
Synthesis was carried out in the same manner as in Example 2 except that titanium meta-hydroxide (β-type), (H ₂ TiO ₃ ) (Kishida Chemical Co., Ltd.) was used instead of nickel hydroxide, and LiMn _1.6 Ti _0.4 O _4.2 A manganese oxide having a cation-deficient spinel structure represented was obtained. This was designated as Sample D.

(Example 5)
Sample E obtained by synthesis in the same manner as in Example 1 except that the firing temperature was 500 ° C. was used.
At this time, a deoxygenation reaction occurred because the firing temperature was high.

(Example 6)
A sample F obtained by synthesis in the same manner as in Example 1 except that the firing temperature was 600 ° C. was used. At this time, a deoxygenation reaction occurred because the firing temperature was high.

(Comparative Example 1)
Lithium hydroxide monohydrate (Kanto Chemical Co., Ltd., deer special grade) and electrolytic manganese dioxide (Mitsui Metals, average particle size: 30 μm) are mixed and ground in isopropanol for 1 hour in a ball mill with a zirconia ball having a diameter of 5 mm, The thickness was 10 μm and 7 μm, respectively. The slurry-like mixture thus obtained was separated from the balls, and then the solvent was evaporated and dried at 40 ° C. under reduced pressure by a rotary evaporator to obtain a powder-like mixture. The mixing ratio of the raw materials was 1: 2 in terms of the Li: Mn molar ratio. This powdery mixture was baked in air at 400 ° C. for 12 hours to obtain a sample G obtained.

(Comparative Example 2)
Lithium hydroxide monohydrate (Kanto Chemical Co., Inc., Shika Special Grade) and nickel hydroxide (High Purity Chemical Laboratory, 99.9% up) and electrolytic manganese dioxide (Mitsui Metals, average particle size: 30 μm) 5 mm in diameter Were mixed and ground for 1 hour in isopropanol by a ball mill together with zirconia balls of 10 μm, 3 μm and 7 μm, respectively. The slurry-like mixture thus obtained was separated from the balls, and then the solvent was evaporated and dried at 40 ° C. under reduced pressure by a rotary evaporator to obtain a powder-like mixture. The mixing ratio of the raw materials was 1: 1.6: 0.4 in terms of a molar ratio of Li: Mn: Ni. This powdery mixture was baked in air at 400 ° C. for 12 hours to obtain Sample H thus obtained.

(Comparative Example 3)
Synthesis was carried out in the same manner as in Comparative Example 2 except that ferric hydroxide (High Purity Chemical Laboratory, 99% up) was used instead of nickel hydroxide, and Sample I was obtained.

(Comparative Example 4)
Synthesis was performed in the same manner as in Comparative Example 2 except that titanium meta-hydroxide (β-type), (H ₂ TiO ₃ ) (Kishida Chemical Co., Ltd.) was used instead of nickel hydroxide, and the obtained sample J was obtained. .

(Comparative Example 5)
Lithium hydroxide (Kanto Chemical Co., Ltd., Shika Special Grade) and electrolytic manganese dioxide (Mitsui Metals, average particle size: 30 μm) were mixed and ground in isopropanol for 16 hours in a ball mill with zirconia balls having a diameter of 5 mm, each 0.7 μm 0.5 μm. The slurry-like mixture thus obtained was separated from the balls, and then the solvent was evaporated and dried at 40 ° C. under reduced pressure by a rotary evaporator to obtain a powder-like mixture. This powdery mixture was baked in air at 400 ° C. for 12 hours to obtain a manganese oxide having a cation-deficient spinel structure represented by LiMn ₂ O _4.2 . This was designated as Sample K.

(Comparative Example 6)
A sample L obtained by synthesis in the same manner as in Example 1 except that the firing temperature was 700 ° C. was used.

(Evaluation 1)
Samples A to L were subjected to average particle diameter and X-ray diffraction measurement (CuKα ray). The results are shown in Table 1.

試料Ａ〜Ｄはスピネルの単一相が得られたのに対し、試料Ｇ〜Ｊはスピネル以外の不純物が確認された。このことから、水酸化リチウム一水和物とＭｎ置換元素の原料を予め粉砕することにより、スピネル構造を有するマンガン酸化物の単一相が得られやすい傾向が見られる。

Samples A to D obtained a single phase of spinel, while samples G to J showed impurities other than spinel. From this fact, there is a tendency that a single phase of manganese oxide having a spinel structure can be easily obtained by previously pulverizing the raw materials of lithium hydroxide monohydrate and the Mn substitution element.

  In Sample K, a single phase of manganese oxide having a spinel structure is obtained, but since the Mn raw material is also pulverized, the average particle size of manganese oxide is as small as 0.5 μm. Thus, when the particle diameter of an active material is small, the packing density at the time of electrode preparation will become small.

  As the firing temperature is lower than those of Samples A, E, F, and L, a tendency to form a cation-deficient spinel structure is observed.

(Example 7)
(1) Production of positive electrode Sample A obtained in Example 1, carbon black as a conductive agent, and fluororesin (polytetrafluoroethylene) as a binder in a weight ratio of 90: 6: 4 To obtain a positive electrode mixture. The binder was used in the form of an aqueous dispersion. This positive electrode mixture was molded into a pellet shape having a diameter of 4.3 mm and a thickness of 1.1 mm at a pressure of 1 ton / cm ² . Thereafter, the pellet-shaped positive electrode was dried in the air at 250 ° C. for 10 hours.

(2) Production of negative electrode active material (silicon alloy) Metal Ti was used as a raw material of the transition metal element to be alloyed with silicon. The metal Ti was a powder having a purity of 99.9% and a particle diameter of 100 μm. As a raw material of silicon, Si simple powder (purity 99.9%, average particle size 3 μm) was used.

  Ti: Si = 36.8: 63.2 (weight ratio) so that the proportion of the A phase in the total of the A phase composed of simple silicon and the B phase composed of the intermetallic compound is about 20% by weight. ) The raw materials were mixed.

1.7 kg of each mixed powder was weighed and put into a vibration mill device (manufactured by Chuo Kako Co., Ltd., model number FV-20). Further, 300 kg of stainless steel balls (diameter 2 cm) were put into the vibration mill apparatus. After evacuating the inside of the container, argon gas (purity 99.999%, Japanese oxygen (
Co., Ltd.) was introduced to 1 atm. The operating conditions of the mill apparatus were an amplitude of 8 mm and a rotational speed of 1200 rpm, and mechanical alloying operation was performed for 80 hours under these conditions. The Ti—Si alloy obtained by the above operation was recovered and classified to a particle size of 45 μm or less.

  When each alloy was analyzed by X-ray diffraction measurement using CuKα rays, a spectrum showing microcrystals was obtained. Further, in the diffraction spectrum obtained by the X-ray diffraction measurement, each calculated based on the half-value width of the strongest diffraction peak observed in the diffraction angle range of 2θ = 10 ° to 80 ° and the Scherrer equation. The grain size of the alloy crystal grains (crystallites) was about 10 nm.

As a result of X-ray diffraction measurement, it was found that each alloy has an A phase composed of Si alone, and each Ti—Si alloy has a B phase composed of TiSi ₂ .

(3) Production of negative electrode A negative electrode was prepared by punching a metal lithium foil having a thickness of 0.5 mm to a diameter of 4.3 mm.

(4) Preparation of non-aqueous electrolyte LiN (CF ₃ SO ₂ ) ₂ was added to a mixed solvent of propylene carbonate (PC), ethylene carbonate (EC), and dimethoxyethane (DME) in a volume ratio of 3: 1: 3. Those dissolved at a concentration of 1 mol / L were used.

(5) Production of coin-type battery A coin-type battery having an outer diameter of 6.8 mm and a thickness of 2.1 mm as shown in FIG. 1 was produced.

  For the positive electrode can 1 also serving as the positive electrode terminal, stainless steel having excellent corrosion resistance was used. The same stainless steel as the positive electrode can 1 was also used for the negative electrode can 2 that also served as the negative electrode terminal. Polypropylene was used for the gasket 3 that insulates the positive electrode can 1 and the negative electrode can 2. Pitch was applied to the contact surface between the positive electrode can 1 and the gasket 3 and the contact surface between the negative electrode can 2 and the gasket 3. The pellet-shaped positive electrode 4 was placed on the bottom surface of the positive electrode can 1. Li metal 7 punched into a columnar shape was pressed onto the negative electrode can 2, and the pellet-shaped negative electrode 5 was placed on the Li metal 7. On the positive electrode 4, a separator 6 made of a non-woven fabric made of polyethylene was disposed. After pouring a non-aqueous electrolyte into the positive electrode can 1, the positive electrode can 1 and the negative electrode can 2 were fitted to complete the battery A.

(Example 8)
A battery B was produced in the same manner as in Example 7 except that the sample B was used as the positive electrode active material.

Example 9
A battery C was produced in the same manner as in Example 7, except that the sample C was used as the positive electrode active material.

(Example 10)
A battery D was produced in the same manner as in Example 7 except that the sample D was used as the positive electrode active material.

(Example 11)
A battery E was produced in the same manner as in Example 7 except that the sample E was used as the positive electrode active material.

(Example 12)
A battery F was produced in the same manner as in Example 7 except that the sample F was used as the positive electrode active material.

(Comparative Example 7)
A battery G was produced in the same manner as in Example 7 except that the sample G was used as the positive electrode active material.

(Comparative Example 8)
A battery H was produced in the same manner as in Example 7 except that the sample H was used as the positive electrode active material.

(Comparative Example 9)
A battery I was produced in the same manner as in Example 7 except that the sample I was used as the positive electrode active material.

(Comparative Example 10)
A battery J was produced in the same manner as in Example 7 except that the sample J was used as the positive electrode active material.

(Comparative Example 11)
A battery K was produced in the same manner as in Example 7 except that the sample K was used as the positive electrode active material.

(Comparative Example 12)
A battery L was produced in the same manner as in Example 7 except that the sample L was used as the positive electrode active material.

(Evaluation 2)
(Initial discharge capacity)
In a thermostat set at 20 ° C., the batteries A to L were charged and discharged at a current density of 0.1 mA / cm ² at a battery voltage of 2.5 to 3.5 V. Table 2 shows the discharge capacity and battery capacity per active material in the second cycle.

表２より、電池Ａ〜Ｄの活物質当たりの放電容量が電池Ｇ〜Ｊに比べて大きい。これは電池Ａ〜Ｄ正極活物質の方が高純度であるためである。また、電池Ａに比べ電池Ｋの電池容量が小さいがこれは活物質の平均粒子径が小さく電極の充填密度が低いためである。

From Table 2, the discharge capacity per active material of batteries A to D is larger than batteries G to J. This is because the batteries A to D positive electrode active material have higher purity. Further, the battery capacity of the battery K is smaller than that of the battery A because the average particle diameter of the active material is small and the packing density of the electrode is low.

  From the results of the batteries A, E, F, and L, it can be seen that the lower the firing temperature, the larger the discharge capacity per active material. This is because the cation deficient spinel structure has a larger discharge capacity.

(Cycle life)
The constant current charging / discharging of the batteries A to H was repeated 50 times in a thermostat set to 20 ° C.

Charging was performed at a current density of 0.4 mA / cm ² and a charge end voltage of 3.5 V, and discharging was performed at a current density of 0.4 mA / cm ² and a discharge end voltage of 2.5 V.

  The amount of decrease in the discharge capacity at the 50th cycle relative to the discharge capacity at the 2nd cycle was determined as a percentage (%), and was defined as the cycle deterioration rate. The closer the cycle deterioration rate is to 0 (%), the better the cycle life. The results are shown in Table 2.

  From Table 2, the cycle deterioration rate per active material of batteries A to D is smaller than batteries G to J. This is because the battery A to D positive electrode active material has high purity.

  From the results of batteries A, E, F, and L, it can be seen that the lower the firing temperature, the greater the discharge capacity per active material. This is because the cation-deficient spinel structure has a crystal structure distortion of the positive electrode active material during cycling. This is because of the small size.

  The present invention is a method for producing a manganese oxide having a spinel structure, and is useful for producing a manganese oxide having a high-purity spinel structure.

  The present invention can be applied to various non-aqueous electrolyte secondary batteries. For example, non-aqueous electrolyte secondary batteries serving as driving power sources for consumer electronic devices, portable information terminals, portable electronic devices, portable devices, cordless devices, and the like. Applicable to batteries. The present invention is also applicable to a power source for a small household electric power storage device, a motorcycle, an electric vehicle, a hybrid electric vehicle, and the like.

  The shape of the battery is not particularly limited, and the present invention can be applied to any shape such as a coin shape, a button shape, a sheet shape, a cylindrical shape, a flat shape, and a square shape. The form of the electrode plate group is not limited, and the present invention can be applied to any form such as a wound type and a laminated type. The size of the battery is not limited, and the present invention can be used for any size such as small size, medium size, and large size.

1 is a longitudinal sectional view of a coin-type battery according to an embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Positive electrode can 2 Negative electrode can 3 Gasket 4 Positive electrode 5 Negative electrode 6 Separator 7 Lithium foil

Claims (5)

Formula _{Li 1 + a Mn 2-xa} M x O 4 + y (0 ≦ x ≦ 0.5, -0.2 ≦ y <0.5,0 ≦ a ≦ 0.2, M is Ni, Fe, A method for producing a positive electrode active material for a lithium secondary battery having a spinel structure represented by (at least one kind of transition metal selected from the group consisting of Ti), wherein a Li raw material, an M raw material, and a Mn raw material are mixed and pulverized; And a step of firing the mixed and pulverized raw material. In the step of mixing and pulverizing the raw material, the Li raw material and the M raw material are mixed and pulverized, and then the Mn raw material is added and mixed and pulverized. A method for producing a positive electrode active material for a secondary battery.   In the step of mixing and pulverizing the raw materials, the Li raw material and the M raw material are mixed and pulverized until the average particle diameter is 1 μm or less, and then the Mn raw material is added so that the average particle diameter of the Mn raw material becomes 3 μm or more and 30 μm or less. The method for producing a positive electrode active material for a lithium secondary battery according to claim 1, wherein the mixture is pulverized and ground.   2. The method for producing a positive electrode active material for a lithium secondary battery according to claim 1, wherein in the step of firing the mixed and pulverized raw material, a firing temperature is 300 ° C. or more and 600 ° C. or less. Formula _{Li 1 + a Mn 2-xa} M x O 4 + y (0 ≦ x ≦ 0.5, -0.2 ≦ y <0.5,0 ≦ a ≦ 0.2, M is Ni, Fe, A method for producing a positive electrode for a lithium secondary battery, comprising: a positive electrode active material represented by (at least one transition metal selected from the group consisting of Ti), a conductive agent, and a binder; After mixing and grinding, adding Mn raw material and mixing and grinding;
Manufacturing a positive electrode for a lithium secondary battery, comprising: a step of firing a mixed and pulverized raw material to obtain a positive electrode active material; and a step of kneading the positive electrode active material, a conductive agent and a binder. Method. Formula _{Li 1 + a Mn 2-xa} M x O 4 + y (0 ≦ x ≦ 0.5, -0.2 ≦ y <0.5,0 ≦ a ≦ 0.2, M is Ni, Fe, Lithium having a positive electrode composed of a positive electrode active material represented by (at least one transition metal selected from the group consisting of Ti), a conductive agent, and a binder, and a negative electrode composed of a negative electrode active material capable of occluding and releasing lithium. A method for producing a secondary battery, comprising mixing and pulverizing Li raw material and M raw material, then adding and pulverizing Mn raw material, firing the mixed and pulverized raw material to obtain a positive electrode active material, A step of kneading and mixing the positive electrode active material, a conductive agent and a binder, obtaining a positive electrode, a step of kneading and mixing the negative electrode active material, a conductive agent and a binder, and obtaining the negative electrode; and the positive electrode and the negative electrode And a step of sealing the organic electrolyte and the separator with a positive electrode case, a negative electrode case, and a gasket. A method for manufacturing a lithium secondary battery.

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