JP4673287B2 - Spinel type lithium manganese oxide and method for producing the same - Google Patents

Description

  The present invention relates to a method for producing a spinel type lithium manganese oxide, and in particular, a positive electrode active for a secondary battery capable of giving a large discharge capacity even under a large current condition, with a small crystal grain size, little disorder in the crystal structure. The present invention relates to a method for producing lithium manganese oxide as a substance.

  Lithium secondary batteries are excellent in terms of electromotive force and energy density, and are widely used as batteries for portable electronic / communication devices such as small video cameras, mobile phones, and notebook computers. In recent years, attention has been paid not only to portable electronic devices but also to power sources for mobile bodies such as bicycles, electric motorcycles, and automobiles, and development of lithium secondary batteries for these fields has been actively promoted.

Currently, lithium cobaltate (LiCoO ₂ ) is widely used as a positive electrode active material for lithium secondary batteries, but the main raw material cobalt is a rare metal and is expensive and supplied by depleting resources. Anxiety has been pointed out. On the other hand, spinel-type lithium manganese oxide (chemical formula: LiMn ₂ O ₄ , lithium manganate, also called lithium manganese spinel) has abundant resources and is economical in terms of manganese. Therefore, the future is expected.

  For power supplies for portable electronic devices, there is a demand for shortening the time from when the device is turned on until it can be used. For automobiles as well, it is instantaneously large in order to respond to sudden acceleration / deceleration of moving objects. There is a need for a battery that can be energized.

  In general, composite oxides of lithium and transition metals, including spinel-type lithium manganese oxides, generally have low conductivity, and when used as a positive electrode active material for secondary batteries, they are conductive to ensure conductivity within the electrodes. The positive electrode of the lithium secondary battery is prepared by mixing a positive electrode active material such as spinel type lithium manganese oxide with a conductive material such as carbon black or graphite and a binder to prepare a slurry. In general, it is produced by coating the material on an aluminum foil.

  Even in a secondary battery using spinel type lithium manganese oxide as a positive electrode active material, like a normal battery, during a large current discharge, due to the effect of ohmic loss due to internal resistance of the battery or polarization between positive and negative electrodes, There is a problem that the charged electric energy cannot be completely taken out of the battery. In order to solve this problem, attempts have been made to reduce the internal resistance of the battery by reducing the thickness of the electrode or using other techniques.

In order to reduce the thickness of the electrode, it is known that it is advantageous to make the particle size of the positive electrode active material as small as possible. In order to reduce the particle size, it is considered that a method of pulverizing spinel type lithium manganese oxide is effective. For example, Patent Document 1 discloses that the specific surface area of the positive electrode active material is 5.0 m ² / g or more. It is disclosed that a positive electrode active material having a crystallite diameter of 70 nm or less by X-ray diffraction analysis and a 50% cumulative particle diameter of 1 μm or less is used as an electrode for a nonaqueous electrolyte secondary battery. .

  Patent Document 2 discloses a method in which electrolytically deposited manganese dioxide is pulverized and lithium manganese oxide is produced using the obtained electrolytic manganese dioxide having an average particle diameter of 3 to 20 μm. Furthermore, in Patent Document 3, manganese dioxide is pulverized to an average particle size of 0.5 μm, and an aqueous lithium hydroxide solution is added to form a slurry. After drying, firing is performed at 650 to 950 ° C. A method for producing lithium manganate having a narrow distribution with a close shape and an average particle size of about 10 μm is disclosed.

JP 2006-202724 A JP 2000-169151 A JP 10-172567 A

  However, the means for pulverizing the spinel type lithium manganese oxide disclosed in Patent Document 1 has a problem in that the battery characteristics are impaired although the particle size is reduced because the crystal structure of the lithium manganese oxide is damaged in the pulverization step. there were. On the other hand, in the method of preliminarily pulverizing manganese dioxide as a raw material as disclosed in Patent Document 2 or 3, the growth of particles is unavoidable at the time of firing, and eventually a positive electrode capable of giving excellent battery characteristics. An active material cannot be obtained.

  The present invention provides a spinel as a positive electrode active material for a secondary battery that has a small particle size, little disorder in the crystal structure, and can sufficiently take out charged electric energy outside the battery even when a large current discharge is performed. An object of the present invention is to provide a type lithium manganese oxide and a method for producing the same.

  The present inventor has developed a spinel-type lithium manganese oxide that is fine and has no disorder in the crystal structure if heat treatment is performed at a specific temperature condition after sufficiently finely pulverizing the chemically synthesized spinel-type lithium manganese oxide. The present invention was completed by confirming the characteristics of the spinel-type lithium manganese oxide obtained by knowing that it was obtained.

Method for producing a spinel-type lithium manganese oxide according to the present invention, the chemical composition is represented by the general formula _{Li 1 + x M y Mn 2} -x-y O 4, the maximum particle diameter _{D 100} is 15μm or less, the (400) plane Spinel type lithium having a half width by X-ray diffraction of 0.30 or less and a ratio of I ₄₀₀ / I ₁₁₁ to (111) plane peak intensity I ₁₁₁ of (400) plane peak intensity I ₄₀₀ of 0.33 or more In the method for producing a manganese oxide, the step of synthesizing the spinel type lithium manganese oxide represented by the above general formula, and the spinel type lithium manganese oxide synthesized in the above step, using a jet mill, the largest particle Monodea the diameter _{D 100} is sequentially carried out the steps of crushing 15μm or less, and heat treating the pulverized product obtained by the milling step at 600 to 700 ° C. .
Here, M is one or more metal elements selected from Al, Co, Ni, Mg, Zr and Ti, x is in the range 0 ≦ x ≦ 0.33, and y is 0 ≦ y. The range is ≦ 0.2.

  In the synthesis step of the spinel type lithium manganese oxide, it is preferable that the manganese raw material is electrolytic manganese dioxide.

  According to the present invention, it is possible to provide a spinel type lithium manganese oxide having a small particle size and less disordered crystal structure. By using it as a positive electrode active material, a large current discharge can be achieved in a short time. The secondary battery which can be provided can be provided.

The spinel-type lithium manganese oxide according to the present invention has a chemical composition represented by a general formula: Li _{1 + x} M _y Mn _2−xy O ₄ , a maximum particle diameter D ₁₀₀ of 15 μm or less, and (400) plane X-rays half-width due to diffraction is 0.30 or less, and is (400) the ratio _I 400 _{/ I 111} to the peak intensity _{I 111} of (111) plane peak intensity _{I 400} of the surface 0.33 or more. Here, M is one or more metal elements selected from Al, Co, Ni, Mg, Zr and Ti, x is in the range 0 ≦ x ≦ 0.33, and y is 0 ≦ y. The range is ≦ 0.2.

Spinel-type lithium manganese oxide according to the present invention, the chemical composition _formula: represented by _{Li 1 + x M y Mn 2} -x-y O 4. That is, some of the basic substances spinel-type lithium manganese oxide (chemical formula: LiMn ₂ O ₄ ) in which a part of Mn is replaced with the third metal element M are included, and Li is slightly excessive with respect to Mn. Also included in This metal element M is selected as one that is effective in suppressing elution of manganese components into the battery and improving high temperature characteristics, and is one or two elements selected from Al, Co, Ni, Mg, Zr and Ti. More than seeds can be allocated. The substitution amount of the metal element M is set such that y is in the range of 0 ≦ y ≦ 0.2 in the chemical formula: Li _{1 + x} M _y Mn _2−xy O ₄ . This is because if the amount of substitution is too large, the discharge capacity of secondary batteries using these as a positive electrode active material tends to decrease, and an extreme decrease in discharge capacity is not preferable, so y ≦ 0.2 is limited. . In the spinel type lithium manganese oxide of the present invention, the range of the atomic ratio of Li to Mn (including the substituted metal element M) is set to 1 to 1.33. As the ratio of Li to Mn increases, the discharge capacity of the lithium manganese secondary battery decreases. For example, when Li: 1.33 , the Mn valence is almost 4 and theoretically no charge / discharge occurs in the 4V region. It is.

In the present invention, the maximum particle diameter _{D 100} of the lithium manganese oxide is 15μm or less. Here, the maximum particle size means a particle size with a cumulative value of 100% in the particle size distribution measured by the particle size distribution measuring device of the laser diffraction / scattering method. Microtrack particle size distribution measuring device of Nikkiso Co., Ltd. (Model HRA9320-X100) can be used for measurement. The maximum particle size D ₁₀₀ is desirably as small as possible in consideration of the thinning of the electrode, but the maximum particle size D ₁₀₀ of 15 μm or less is sufficient in consideration of the actual coating thickness. Such pulverization into ultrafine powder can be achieved, for example, by pulverization using a jet mill.

In the present invention, the half-value width of the (400) plane of the crystal by X-ray diffraction is 0.30 or less, and the ratio of the peak intensity I ₄₀₀ of the ( ₄₀₀ ) plane to the peak intensity I ₁₁₁ of the (111) plane is I. ₄₀₀ / I ₁₁₁ is 0.33 or more, and the disorder of the crystal structure is extremely small. As a result, the positive electrode material has an advantage of relatively high crystallinity and excellent battery characteristics. The half width is the peak width at half the height of the diffraction peak, and the peak intensity ratio I ₄₀₀ / I ₁₁₁ is the ratio of the peak height near 44 ° to the peak height near 18 °. is there.

  The lithium manganese oxide having the above characteristics can be produced by the following method.

First, a spinel-type lithium manganese oxide having a chemical composition represented by the general formula Li _{1 + x} M _y Mn _2−xy O ₄ is chemically synthesized. This step may be a step of producing an existing spinel type lithium manganese oxide, and is not particularly limited. For example, as described in JP-A-10-255798, a water-soluble lithium salt and manganese nitrate are reacted as a cation carrier in the presence of a nonionic water-soluble polymer substance to obtain a lithium manganese oxide. A method of drying and baking this may be used. However, when a method of firing after mixing pulverized electrolytic manganese dioxide and lithium raw material such as lithium hydroxide is advantageous, it is advantageous because it can economically synthesize spinel-type lithium manganese oxide with less internal voids. .

Then, the spinel-type lithium-manganese oxide obtained in the step is the maximum particle diameter D ₁₀₀ is ground to be 15μm or less. As a means for crushing, a maximum particle diameter D ₁₀₀ By using a jet mill known as micronizer can be easily ground to 15μm or less.

  The pulverized spinel type lithium manganese oxide obtained as described above is then performed to recover the disorder of the crystal structure generated in the pulverization process, and its temperature range is determined based on the following experiment etc. .

Lithium carbonate, electrolytic manganese dioxide, tricobalt tetroxide and aluminum hydroxide so that the atomic ratio is Li: Mn: Al: Co = 1.1: 1.82: 0.04: 0.04, Spinel-type lithium manganese oxide having a composition formula of Li _1.1 Mn _1.82 Al _0.04 Co _0.04 O ₄ by dry mixing using a precision mixer and firing in the air at 800 ° C. for 20 hours. Was synthesized. The resulting spinel-type lithium manganese oxide, using a jet mill, a maximum particle diameter D ₁₀₀ is ground to be 11 [mu] m. A sample was cut out from this pulverized product, heat-treated at 350 to 800 ° C. in the air atmosphere for 20 hours, and the maximum particle diameter D _{100 of} the obtained spinel type lithium manganese oxide was obtained by X-ray diffraction of (400) plane. the half width and (400) plane of the ratio _I 400 _{/ I 111} for (111) plane peak intensity _{I 111} of the peak intensity _{I 400} was carried out an experiment to measure. FIG. 1 shows the results of the above experiment arranged as a relationship diagram between the heat treatment temperature and the characteristic value.

As is apparent from FIG. 1, when the heat treatment temperature is less than 600 ° C., the reduction of the half width due to the X-ray diffraction of the (400) plane is not sufficient, and the (111) of the (400) plane peak intensity I ₄₀₀ The increase of the ratio I ₄₀₀ / I _{111 to} the surface peak intensity I ₁₁₁ is also not sufficient. On the other hand, when the heat treatment temperature exceeds 700 ° C., although elevated decreased and the ratio _I 400 _{/ I 111} of the half width is sufficiently large, the maximum particle diameter _{D 100} is now greater than 15 [mu] m, an object of the present invention particles It becomes impossible to provide a spinel type lithium manganese oxide having a small diameter and a thin coating thickness. Therefore, the heat treatment temperature is limited to a range of 600 to 700 ° C.

  Note that the heat treatment time only needs to achieve recovery of the disorder of the crystal structure, and the heat treatment atmosphere may be an air atmosphere.

  The lithium manganese oxide heat-treated as described above is sieved into a product and provided as a positive electrode material for a secondary battery. The sieving may be performed so as to obtain the above particle diameter, and the means is not particularly limited.

Even when the lithium manganese based composite oxide according to the present invention is used as a positive electrode active material, the negative electrode active material is a material capable of inserting and extracting lithium, such as a carbon material and a lithium storage alloy, as in the case of a normal lithium manganese oxide. As the electrolytic solution, a non-aqueous electrolytic solution obtained by dissolving a lithium salt in a non-aqueous electrolytic solution or a resin is used. That is, lithium hexafluorophosphate (LIPF6) was used as the lithium salt, and a mixed solution of ethylene carbonate and dimethyl carbonate was used as the non-aqueous electrolyte. In addition, LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiSO ₃ CF ₃ , LiN (SO ₃ CF ₃ ), and the like and mixtures thereof are used as lithium salts. Further, as the non-aqueous electrolyte, diethyl carbonate, propylene carbonate or the like or a mixture thereof, and a polymer solid electrolyte (resin) having high ion conductivity having ethylene oxide, ethylene sulfide, ethyleneimine or the like as the main chain are used. It is possible.

  Lithium carbonate, electrolytic manganese dioxide and, if necessary, a substance containing a third metal element are dry-mixed with a precision mixer to a predetermined ratio, and calcined in air at 800 ° C. for 20 hours to oxidize spinel lithium manganese The product was synthesized. The obtained spinel-type lithium manganese oxide was pulverized using a jet mill so that the maximum particle size was 15 μm or less, and heat-treated under the conditions shown in Table 1 to obtain a product.

As the characteristic values of the obtained product, the maximum particle diameter D ₁₀₀ , the half width by X-ray diffraction of the (400) plane, the ratio I _{400 of the} (400) plane peak intensity I _{400 to} the (111) plane peak intensity I ₁₁₁ / I ₁₁₁ was measured, and these were used as positive electrode active materials to assemble a three-electrode open-type test cell to measure battery characteristics. The measurement was performed by charging and discharging in a potential range of 3.0 V to 4.3 V using metal Li as a counter electrode and a reference electrode, and assuming that the current density at which the entire cell was discharged in 1 hour was 1 C, 0.2 C and 3.0 C The discharge capacity was measured under the conditions. Further, the discharge capacity under the condition of 3.0 C relative to the discharge capacity measured under the condition of 0.2 C was calculated as the rate characteristic.

  As is clear from Table 1, when the heat treatment was performed at 600 ° C., 650 ° C., or 700 ° C. for 20 hours after pulverization with a jet mill, the heat treatment was not performed, or 450 at a lower temperature side than the range of the present invention. The peak width of the (400) plane is narrower than that subjected to heat treatment at ℃, and the peak intensity of the (400) plane is stronger than the relative intensity with respect to the (111) plane, and the crystallinity is high. Was confirmed. From this, it was confirmed that the crystallinity of the spinel type lithium manganese oxide was improved by the heat treatment after pulverization.

  In addition, as can be seen from the battery characteristics, those manufactured by the present invention are excellent in the 0.2C discharge capacity and the 3C discharge capacity with respect to the comparative example in the same component composition. The ratio of the 3C discharge capacity to the 0.2C discharge capacity was also large, and it was confirmed that discharge with a large current was possible in a short time even under severe conditions.

  FIG. 2 shows the results of measurement of the discharge capacity at 0.2 C and the discharge capacity at 3 C and rate characteristics when spinel type lithium manganese oxide was used as the positive electrode active material, including the above examples. It is the graph shown as layered under the conditions shown.

From FIG. 2, the half width by X-ray diffraction of the (400) plane is extremely narrow as 0.25 or less, and the ratio I ₄₀₀ of the peak intensity I ₄₀₀ of the ( ₄₀₀ ) plane to the peak intensity I ₁₁₁ of the (111) plane. (A) with / I ₁₁₁ of 0.33 or more has excellent 0.2C discharge capacity and 3.0C discharge capacity, and the rate characteristics exceed 90%, enabling discharge with large current in a short time. is there. On the other hand, the half width is within the range of the present invention, but the strength ratio is small (B) and the half width and the strength ratio are outside the range of the present invention (C) are 3.0 C discharge capacity. The rate characteristics are inferior and the discharge rate is not suitable for discharging with a large current in a short time.

It is a graph which shows the relationship between the heat processing temperature after the grinding | pulverization of the synthesized spinel type lithium manganese oxide, and a characteristic value. The result of measuring the discharge capacity and rate characteristics when spinel type lithium manganese oxide was used as the positive electrode active material was calculated as (111) of the (400) plane X-ray diffraction half width and (400) plane peak intensity I ₄₀₀ (111). ) is a graph showing stratified by the ratio value of the _I 400 _{/ I 111} to the peak intensity _{I 111} of the surface.

Claims (2)

The chemical composition is represented by the general formula Li _{1 + x} M _y Mn _2−xy O ₄ , the maximum particle diameter D ₁₀₀ is 15 μm or less, and the half width by X-ray diffraction of (400) plane is 0.30 or less, and a process for the preparation of (400) plane of spinel-type lithium manganese oxide (111) the ratio _I 400 _{/ I 111} to the peak intensity _{I 111} of the surface is 0.33 or more peak intensity _{I 400,}
The step of synthesizing the spinel type lithium manganese oxide represented by the general formula and the spinel type lithium manganese oxide synthesized in the above step are pulverized to a maximum particle size D ₁₀₀ of 15 μm or less using a jet mill. A method for producing a spinel type lithium manganese oxide, comprising sequentially performing a step and a step of heat-treating the pulverized material obtained in the pulverization step at 600 to 700 ° C. Here, M is one or more metal elements selected from Al, Co, Ni, Mg, Zr and Ti, x is in the range 0 ≦ x ≦ 0.33, and y is 0 ≦ y. The range is ≦ 0.2. The process according to claim 1 spinel-type lithium-manganese oxide according to the manganese raw material in the synthesis stage of the spinel-type lithium manganese oxide, characterized in that an electrolytic manganese dioxide.

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