JP2008159560A - Method of manufacturing positive electrode active material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a positive electrode active material excelling in charge/discharge cycle characteristics with high capacity when used for a battery. <P>SOLUTION: A positive electrode 2 has the positive electrode active material. The method of manufacturing the positive electrode active material has processes for forming a layer containing at least a nickel (Ni) compound and/or a manganese (Mn) compound in at least a part of composite oxide particles containing at least lithium (Li) and cobalt (Co), and heat-treating the composite oxide particles formed with the layer, in an atmosphere with more reducing property than air, to form a coating layer provided at least at a part of the composite oxide particles and having an oxide containing lithium (Li) and at least one of elements of nickel (Ni), manganese (Mn) and cobalt (Co). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing a positive electrode active material. More specifically, the present invention relates to a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery.

  In recent years, with the widespread use of portable devices such as video cameras and notebook computers, the demand for small, high-capacity secondary batteries has increased. Most of the secondary batteries currently used are nickel-cadmium batteries using an alkaline electrolyte, but the battery voltage is as low as about 1.2 V, and it is difficult to improve the energy density. Therefore, a lithium secondary battery using lithium metal having a specific gravity of 0.534, which is the lightest of the solid simple substance, the potential is extremely base, and the current capacity per unit weight is the largest among the metal negative electrode materials was examined. .

  However, in a secondary battery using lithium metal as a negative electrode, dendritic lithium (dendrites) is deposited on the surface of the negative electrode during charging and grows by charge / discharge cycles. This dendrite growth not only deteriorates the cycle characteristics of the secondary battery, but in the worst case, it breaks through a diaphragm (separator) arranged so that the positive electrode and the negative electrode do not contact each other, thereby causing an internal short circuit. There was a problem.

  Therefore, for example, as shown in Patent Document 1, a secondary battery that repeats charging and discharging by using a carbonaceous material such as coke as a negative electrode and doping and dedoping alkali metal ions is provided. was suggested. As a result, it has been found that the above-described problem of deterioration of the negative electrode due to repeated charge / discharge can be avoided.

JP 62-90863 A

On the other hand, as a positive electrode active material, a material having a battery voltage of around 4 V has appeared due to the search and development of an active material exhibiting a high potential, and has attracted attention. As such active materials, inorganic compounds such as transition metal oxides containing alkali metals and transition metal chalcogens are known. Of these, Li _X CoO ₂ (0 <x ≦ 1.0), Li _X NiO ₂ (0 <x ≦ 1.0) and the like are most promising in terms of high potential, stability, and long life.

Among these, the positive electrode active material mainly composed of LiCoO ₂ is a positive electrode active material exhibiting a high potential, and is expected to increase the charging voltage and the energy density. For this purpose, it is known to use a mixture of a small amount of LiMn _1/3 Co _1/3 Ni _1/3 O ₂ or the like, or to coat other materials.

  On the other hand, regarding the technique for modifying the positive electrode active material by the surface coating of the positive electrode active material, it is a problem to achieve a coating with high coverage. For this purpose, various methods have been studied, and it has been confirmed that the method of depositing with a metal hydroxide is excellent in covering properties as a result of the study of the present inventors.

In this regard, for example, Patent Document 2 discloses that cobalt (Co) and manganese (Mn) are deposited on the surface of LiNiO ₂ through the hydroxide deposition process. Further, for example, Patent Document 3 discloses that a non-manganese metal is deposited on the surface of a lithium manganese composite oxide through its hydroxide deposition process.

JP-A-9-265985

JP-A-11-71114

However, when the surface modification of the positive electrode active material is performed by a conventional method, there is a problem in that, when charging and discharging are repeated at a high capacity, the capacity is deteriorated and the battery life is shortened. Currently, it is expected to increase the charging voltage and energy density, and as a method to solve the problem of deterioration of charge / discharge cycle characteristics, surface modification of the positive electrode active material mainly composed of lithium cobaltate (LiCoO ₂ ) However, as a part of this, it is a technical problem to uniformly and firmly deposit a desired metal oxide to modify the surface.

  Therefore, the object of the present invention is to perform surface modification of the positive electrode active material so that a desired metal oxide is uniformly and firmly applied, and when used in a battery, it has high capacity and charge / discharge cycle characteristics. It is providing the manufacturing method of the positive electrode active material which was excellent.

In order to solve the above-described problems, the present invention provides:
Forming a layer containing at least a nickel (Ni) compound and / or a manganese (Mn) compound on at least a part of the composite oxide particles containing at least lithium (Li) and cobalt (Co);
The composite oxide particles in which the layer is formed are heat-treated in an atmosphere that is more reducible than air, so that the composite oxide particles are provided on at least a part of the composite oxide particles, and lithium (Li), nickel (Ni), manganese ( Forming a coating layer having an oxide containing at least one of Mn) and cobalt (Co);
It is a manufacturing method of the positive electrode active material characterized by having.

  In the present invention, a layer containing at least a nickel (Ni) compound and / or a manganese (Mn) compound is formed on at least a part of the composite oxide particles containing at least lithium (Li) and cobalt (Co). The composite oxide particles in which the step and the layer are formed are heat-treated in an atmosphere that is more reducible than air, so that the composite oxide particles are provided on at least a part of the composite oxide particles, and lithium (Li) and nickel (Ni) And a step of forming a coating layer having an oxide containing at least one element of manganese (Mn), and a positive electrode active material that uniformly and firmly deposits a desired metal oxide Surface modification can be performed.

  According to the present invention, it is possible to perform surface modification of the positive electrode active material so as to deposit a desired metal oxide uniformly and firmly, and when used in a battery, it has a high capacity and excellent charge / discharge cycle characteristics. A method for producing a positive electrode active material can be provided.

  First, a positive electrode active material that can be produced using a method for producing a positive electrode active material according to an embodiment of the present invention will be described. This positive electrode active material is used for, for example, a non-aqueous electrolyte secondary battery, and at least part of the composite oxide particles includes lithium (Li), nickel (Ni), manganese (Mn), and cobalt (Co). A coating layer having an oxide containing at least one of the above elements is provided. The reason for this configuration is as follows.

The positive electrode active material mainly composed of lithium cobalt oxide (LiCoO ₂ ) can realize high charge voltage and high energy density accompanying it, but if the charge / discharge cycle at high capacity is repeated at high charge voltage, the capacity of There is a lot of decline. Since this cause is caused by the surface of the positive electrode active material particles, the necessity of surface treatment of the positive electrode active material has been pointed out.

  Therefore, various surface treatments have been proposed, but the surface is made of a material that can suppress or contribute to the capacity reduction from the viewpoint of eliminating the capacity reduction per volume or weight or minimizing the capacity reduction. By performing the treatment, it is possible to achieve a high charge voltage property and a high energy density property associated therewith and to obtain a positive electrode active material excellent in charge / discharge cycle characteristics at a high charge voltage.

Accordingly, the inventors of the present application have made a intensive study, and although slightly inferior in the high charge voltage property and the high energy density property associated therewith, the positive electrode active material mainly composed of lithium cobaltate (LiCoO ₂ ) is used as lithium (Li). And a coating layer having an oxide containing at least one of nickel (Ni), manganese (Mn), and cobalt (Co), thereby providing high charging voltage and high energy density associated therewith. In addition, the inventors have found that a positive electrode active material having a high capacity and excellent charge / discharge cycle characteristics can be obtained under high charge voltage conditions.

  The composite oxide contains at least lithium (Li) and cobalt (Co). For example, a compound whose average composition is represented by Chemical Formula 1 is preferable. This is because a high capacity and a high discharge potential can be obtained by using such composite oxide particles.

(Chemical formula 1)
_{Li (1 + x) Co (} 1-y) M y O (2-z)
(In the chemical formula 1, M represents magnesium (Mg), aluminum (Al), boron (B), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), nickel ( Ni), copper (Cu), zinc (Zn), molybdenum (Mo), tin (Sn), or tungsten (W), wherein x, y, and z are −0. (10 ≦ x ≦ 0.10, 0 ≦ y <0.50, −0.10 ≦ z ≦ 0.20)

  Here, in the chemical formula 1, the range of x is, for example, −0.10 ≦ x ≦ 0.10, more preferably −0.08 ≦ x ≦ 0.08, and still more preferably −0.06 ≦ x. ≦ 0.06. When the value decreases outside this range, the discharge capacity decreases, and when the value increases outside this range, it diffuses out of the particles, hindering the control of the basicity of the next processing step, and finally Specifically, this causes a harmful effect of promoting gelation during the kneading of the positive electrode paste.

The range of y is, for example, 0 ≦ y <0.50, preferably 0 ≦ y <0.40, and more preferably 0 ≦ y <0.30. When it becomes larger outside this range, the high charge voltage property of lithium cobaltate (LiCoO ₂ ) and the high energy density property associated therewith are impaired.

  The range of z is, for example, −0.10 ≦ z ≦ 0.20, more preferably −0.08 ≦ z ≦ 0.18, and still more preferably −0.06 ≦ z ≦ 0.16. When the value decreases outside this range, and when the value increases outside this range, the discharge capacity tends to decrease.

  The composite oxide particles can be used as starting materials that are usually available as positive electrode active materials, but in some cases, the composite oxide particles may be used after pulverizing the secondary particles using a ball mill or a grinder. it can.

  The coating layer is provided on at least a part of the composite oxide particles, and includes an oxide containing lithium (Li) and at least one of nickel (Ni), manganese (Mn), and cobalt (Co). It is what you have. By providing this coating layer, it is possible to realize a high charge voltage property and a high energy density property associated therewith, and to improve charge / discharge cycle characteristics of a high capacity under a high charge voltage condition.

  The constituent ratio of nickel (Ni) and manganese (Mn) in the coating layer is preferably in the range of 100: 0 to 30:70, and in the range of 100: 0 to 40:60 in terms of molar ratio. Is more preferable. If the amount of manganese (Mn) increases beyond this range, the occlusion of lithium (Li) will decrease, eventually reducing the capacity of the positive electrode active material and increasing the electrical resistance when used in a battery. It is a factor.

  In addition, nickel (Ni) and manganese (Mn) in the oxide of the coating layer are replaced with magnesium (Mg), aluminum (Al), boron (B), titanium (Ti), vanadium (V), chromium (Cr), iron Replacing at least one metal element selected from the group consisting of (Fe), cobalt (Co), copper (Cu), zinc (Zn), molybdenum (Mo), tin (Sn), and tungsten (W). it can.

  Thereby, the stability of the positive electrode active material and the diffusibility of lithium ions can be improved. The substitution amount of the selected metal element is, for example, 40 mol% or less of the total amount of nickel (Ni) and manganese (Mn) of the oxide of the coating layer, preferably 30 mol% or less, and more Preferably it is 20 mol% or less. This is because if the substitution amount of the selected metal element is increased beyond this range, the occlusion of lithium (Li) is lowered and the capacity of the positive electrode active material is lowered.

  The amount of the coating layer is, for example, 0.5% to 50% by weight of the composite oxide particles, preferably 1.0% to 40% by weight, and more preferably 2.0% by weight. % To 35% by weight. This is because when the weight of the coating layer increases beyond this range, the capacity of the positive electrode active material decreases. This is because if the weight of the coating layer decreases from this range, the stability of the positive electrode active material decreases.

  The average particle diameter of the positive electrode active material is preferably 2.0 μm to 50 μm. If the average particle size is less than 2.0 μm, it peels off when pressed during positive electrode fabrication, and the surface area of the active material increases, so it is necessary to increase the amount of conductive agent and binder added, and the unit weight This is because the per-energy density tends to decrease. On the other hand, if the average particle size exceeds 50 μm, the particles tend to penetrate the separator and cause a short circuit.

  Next, the manufacturing method of the positive electrode active material by one Embodiment of this invention is demonstrated. The method for producing a positive electrode active material according to an embodiment of the present invention can be broadly divided into at least part of composite oxide particles containing at least lithium (Li) and cobalt (Co), and at least a compound of nickel (Ni). And / or a first step of forming a layer containing a compound of manganese (Mn), and the composite oxide particles having the layer formed thereon are heat-treated in an atmosphere having a reducing property than air, thereby producing composite oxide particles. And forming a coating layer having an oxide containing lithium (Li) and at least one of nickel (Ni), manganese (Mn), and cobalt (Co). It has these processes.

  In the first step, a layer containing at least a nickel (Ni) compound and / or a manganese (Mn) compound is formed on at least a part of the surface of the composite oxide particles.

  Specifically, as an example of the first step, as a nickel (Ni) compound and / or a manganese (Mn) compound, a nickel (Ni) hydroxide and / or a manganese (Mn) hydroxide are used. In use, this is applied to at least a part of the surface of the composite oxide particles.

  Further, as another example of the first step, in addition to the nickel (Ni) compound and / or the manganese (Mn) compound, at least part of the surface of the composite oxide particle, lithium (Li) A layer containing a compound is formed, and an easily decomposable metal compound is used as the nickel (Ni) compound, the manganese (Mn) compound, and the lithium (Li) compound.

  First, an example of the first step will be described in detail. In an example of the first step, nickel (Ni) hydroxide and / or manganese (Mn) hydroxide is used as the nickel (Ni) compound and / or manganese (Mn) compound. It is made to adhere to at least one part of the surface of complex oxide particle.

  In this case, the deposition of nickel (Ni) hydroxide and / or manganese (Mn) hydroxide is preferably performed in a solvent system mainly composed of water having a pH of 12 or more, and mainly composed of water having a pH of 13 or more. It is more preferable to carry out in a solvent system, and it is more preferred to carry out in a solvent system mainly composed of water having a pH of 14 or higher. The higher the pH value of the water-based solvent system, the better the uniformity of hydroxide deposition and the higher the reaction rate, and the advantages of improved productivity and improved quality by shortening the processing time. is there.

  As a conventional method for providing a coating layer on composite oxide particles, lithium (Li) compound, nickel (Ni) compound and / or manganese (Mn) compound, composite oxide particles and finely pulverized particles Dry-mixed, deposited, and fired, and a coating layer made of an oxide containing lithium (Li) and at least one of nickel (Ni) and manganese (Mn) is provided on the surface of the composite oxide particle. Method, lithium (Li) compound, nickel (Ni) compound and / or manganese (Mn) compound dissolved or mixed in solvent, wet-coated and fired, lithium (Li) and nickel A method of providing a coating layer made of an oxide containing at least one coating element of (Ni) and manganese (Mn) on the surface of the composite oxide particle can be proposed. However, these methods yielded results in which a highly uniform coating could not be achieved.

  Therefore, the inventors of the present application have further studied diligently. As a result, nickel (Ni) and / or manganese (Mn) was deposited as a hydroxide and heated and dehydrated to form a coating layer. It was found that highly uniform coating can be realized. In this deposition treatment, a nickel (Ni) compound and / or a manganese (Mn) compound is dissolved in a water-based solvent system, and then the composite oxide particles are dispersed in the solvent system. The basicity of the dispersion is increased by adding a base to the system, and nickel (Ni) hydroxide and / or manganese (Mn) hydroxide is precipitated on the surface of the composite oxide particles.

  Furthermore, the inventors of the present application have found that the uniformity of coating on the composite oxide particles can be further improved by performing this deposition treatment in a solvent system mainly composed of water having a pH of 12 or higher. That is, the metal composite oxide particles are dispersed in advance in a solvent system mainly composed of water having a pH of 12 or more, and a nickel (Ni) compound and / or a manganese (Mn) compound is added to the metal composite oxide. Nickel (Ni) hydroxide and / or manganese (Mn) hydroxide is deposited on the surface of the product particles.

  Then, the composite oxide particles coated with nickel (Ni) hydroxide and / or manganese (Mn) hydroxide are heated and dehydrated by the deposition treatment, and the coating layer is formed on the surface of the composite oxide particles. To form. Thereby, the uniformity of the coating on the surface of the composite oxide particles can be improved.

  Here, in an example of the first step, as a raw material for the deposition treatment of nickel (Ni) hydroxide, examples of the nickel compound include nickel hydroxide, nickel carbonate, nickel nitrate, nickel fluoride, nickel chloride. , Nickel bromide, nickel iodide, nickel perchlorate, nickel bromate, nickel iodate, nickel oxide, nickel peroxide, nickel sulfide, nickel sulfate, nickel hydrogen sulfate, nickel nitride, nickel nitrite, nickel phosphate, Inorganic compounds such as nickel thiocyanate, and organic compounds such as nickel oxalate and nickel acetate can be used, and one or more of these may be used.

  Similarly, as a raw material for the deposition treatment of manganese (Mn) hydroxide, manganese compounds include, for example, manganese hydroxide, manganese carbonate, manganese nitrate, manganese fluoride, manganese chloride, manganese bromide, manganese iodide. , Manganese chlorate, manganese perchlorate, manganese bromate, manganese iodate, manganese oxide, manganese phosphinate, manganese sulfide, manganese hydrogen sulfide, manganese sulfate, manganese hydrogen sulfate, manganese thiocyanate, manganese nitrite, manganese phosphate Inorganic compounds such as manganese dihydrogen phosphate and manganese hydrogen carbonate, and organic compounds such as manganese oxalate and manganese acetate can be used, and one or more of these may be used.

  In one example of the first step, the temperature of the treatment dispersion is 40 ° C. or higher, preferably 60 ° C. or higher, more preferably 80 ° C. or higher. The higher the temperature value of the treatment dispersion, the better the uniformity of the deposition of nickel (Ni) hydroxide and / or manganese (Mn) hydroxide, the higher the reaction rate, and the longer the treatment time. There are advantages of improving productivity and quality by shortening. Although it is determined in consideration of the cost and productivity of the apparatus, it can be performed at 100 ° C. or higher by using an autoclave, because the uniformity of deposition is improved and the processing time is shortened by improving the reaction rate. Recommended from a production standpoint.

  Furthermore, when depositing nickel (Ni) hydroxide and / or manganese (Mn) hydroxide on the composite oxide particles, the composite oxide particles are mainly composed of water having a pH of 12 or more. Dispersed in the solvent system, nickel (Ni) compound and / or manganese (Mn) compound is added thereto, and nickel (Ni) hydroxide / manganese (Mn) is added to the surface of the composite oxide particles. ) Hydroxide may be applied.

  In one example of the first step, the pH of the solvent system mainly composed of water can be reached by dissolving the alkali in the solvent system mainly composed of water. Examples of the alkali include lithium hydroxide, sodium hydroxide and potassium hydroxide, and mixtures thereof.

  Although it is possible to carry out using these alkalis as appropriate, it is preferable to use lithium hydroxide because the purity and performance of the positive electrode active material finally obtained are excellent. The advantage of using lithium hydroxide is that nickel (Ni) hydroxide and / or manganese (Mn) is present on at least a part of the surface of the composite oxide particles dispersed in a solvent system mainly composed of water having a pH of 12 or higher. By controlling the amount of dispersion medium composed of a solvent mainly composed of water when the composite oxide particles formed with a layer containing hydroxide are taken out of the solvent system mainly composed of water, This is because the amount of lithium in the obtained positive electrode active material can be controlled.

  Another example of the first step will be described in detail. In another example of the first step, in addition to the nickel (Ni) compound and / or the manganese (Mn) compound, at least a part of the surface of the composite oxide particle, a lithium (Li) compound is further added. An easily decomposable metal compound is used as the nickel (Ni) compound, the manganese (Mn) compound, and the lithium (Li) compound. Specifically, for example, as an easily decomposable metal compound, an easily decomposable nickel compound, an easily decomposable manganese compound, and an easily decomposable lithium compound are pulverized and mixed with the composite oxide particles.・ Be sure to wear it.

  In the example of the first step described above, the uniformity is excellent in the thin deposition, but there is a problem that the deviation from the charged metal compound is likely to occur. Further, in the final dehydration heating firing, the amount of lithium (Li) to be added to the metal oxide is small in the amount of metal oxide mainly composed of oxides of nickel (Ni) and manganese (Mn). For this reason, it is difficult to accurately control the amount of addition.

  In another example of the first step, non-uniformity is surprisingly small and good characteristics can be obtained unless extremely thin deposition is performed. This is because, in the deposition state of easily decomposable metal compounds of lithium (Li), nickel (Ni) and manganese (Mn), the particle property of the compound is remarkable, and the uniformity of the micro composition is not necessarily good. In addition, the adhesion to the metal composite oxide particles is not necessarily excellent, but by heating and heating this, decomposition and diffusion of easily decomposable compounds and sintering on the surface of the metal composite oxide particles are performed. Diffusion accompanied by condensation achieves coating uniformity on the surface of the metal composite oxide particles as well as composition uniformity. By using the positive electrode active material prepared in this way, the stability at a high charge voltage is high, and accordingly, the high energy density can be improved, and a high capacity charge / discharge cycle under a high charge voltage condition. Thus, a positive electrode active material with good repeatability can be obtained.

  As a readily decomposable metal compound, a compound that generates a strongly acidic chemical species by decomposition and a compound that generates a large amount of carbon accompanying decomposition can be used, and preferred metal compounds are as follows. For example, metal hydroxide, metal hydrated oxide, metal carbonate, metal hydrogen carbonate, and good results can be obtained by using these.

  More specifically, as the easily decomposable lithium compound, for example, lithium hydroxide anhydride, lithium hydroxide monohydrate, lithium carbonate, lithium hydrogen carbonate, and the like can be used. Moreover, as an easily decomposable nickel compound, nickel hydroxide, nickel carbonate, nickel oxyhydroxide etc. can be used, for example. Furthermore, as the easily decomposable manganese compound, for example, manganese oxide hydroxide, manganese carbonate, or the like can be used.

  In another example of the first step, the composite oxide particles and the easily decomposable metal compound that coats the composite oxide particles are pulverized and mixed, so that the entire composite oxide particles are coated in a smaller amount. be able to. As this means, a ball mill, a jet mill, a grinder, a fine grinder, or the like can be used. In this case, it is also effective to add some liquid, which can be exemplified by water.

  In another example of the first step, as a method of depositing the easily decomposable metal compound on the composite oxide particles, for example, a method of performing dry firing or mixing and firing after the particles are wet can be used.

  Furthermore, it is preferable that the easily decomposable metal compound particles used for coating are coated on the composite oxide particles that are the core material by applying compression and shearing force. By applying compression and shearing force to the composite oxide particles before the firing, the coating layer is prevented from falling off the core material during firing, so This is because phase generation can be easily performed. As this means, for example, mechano-fusion can be used.

  In the second step, the heat treatment of the composite oxide particles on which the layer is formed is performed in an atmosphere that is more reducible than air. An atmosphere that is more reducible than air is, for example, an atmosphere in which oxygen is present at 21% by volume or less, preferably a pure nitrogen atmosphere, and other inert gases such as argon and helium, and in some cases, hydrogen and organic gases. May be contained in a small amount. In the heat treatment, for example, a composite oxide particle in which a layer is formed in an electric furnace is put, a temperature rising process for raising the temperature, a holding process for holding the raised temperature, a cooling process for cooling the temperature, To do.

  Here, the inventors of the present invention examined the surface composition and the heat treatment conditions for obtaining high efficiency in high-current charge / discharge at a high charge voltage, and discharge capacity. As a result, lithium (Li), nickel (Ni), and manganese were investigated. The composition ratio (Ni: Mn) of nickel (Ni) and manganese (Mn) in the coating layer made of an oxide containing at least one element of (Mn) is 100: 0 to 30 in terms of molar ratio. : It has been found that when it is within the range of 70, high efficiency and discharge capacity in high current charge / discharge at a high charge voltage can be obtained due to a synergistic effect with heat treatment conditions.

  Furthermore, preferably, the structural ratio (Ni: Mn) of nickel (Ni) and manganese (Mn) is in the range of 100: 0 to 40:60 in terms of molar ratio. Then, a calcining heat treatment is applied to the precursor in which a compound of nickel (Ni) and / or a compound of manganese (Mn) is deposited on the surface of the composite oxide particle so as to achieve this composition ratio.

  Thereby, the compound of nickel (Ni), the compound of manganese (Mn), etc. are decomposed to become a metal oxide, and a mixed metal compound in which plural kinds of compounds such as nickel (Ni) and manganese (Mn) are mixed In the method, a metal oxide in a state where a plurality of metal oxides are mixed or dissolved is formed. Through the heat treatment that accompanies this formation and the subsequent heat treatment, the metal ions of the metal oxide diffuse into the composite oxide particles, and the metal ions of the composite oxide particles diffuse into the metal oxide to form a metal. Ions diffuse to each other.

  When the precursor having at least a nickel (Ni) compound and / or a manganese (Mn) compound deposited on the surface of the composite oxide particles so as to have the above-described composition ratio is subjected to a firing heat treatment, The maximum temperature is 300 ° C to 1100 ° C, preferably 400 ° C to 1000 ° C. When the maximum temperature is lower than the lower limit of this temperature range, it becomes difficult to decompose the metal compound and form a metal oxide. When the maximum temperature is higher than the upper limit of this temperature range, the metal composite oxide particles of metal ions of the metal oxide As a result, diffusion to the inside proceeds excessively, and as a result, the presence of the surface metal oxide formed on the surface becomes unclear and it becomes difficult to achieve the desired effect.

  In this case, the oxidizability and reducibility of the atmosphere of this heat treatment are greatly related to the valence of metal ions on the surface of the metal oxide. The valence of the metal ion is greatly involved in the thermal diffusion of the metal ion in the heat treatment, is greatly involved in the electrochemical reaction at the positive electrode interface in the battery system, the durability of the positive electrode at a high charging voltage, and the lithium in the positive electrode. It is important for high efficiency and high discharge capacity in high current charge / discharge by improving ion diffusivity.

  Furthermore, the inventors of the present application have made extensive studies and found that the larger the valence of manganese ions on the positive electrode surface, the more effective the cycle life is. On the other hand, it can be seen that the larger the valence of nickel ions, the greater the diffusion of nickel (Ni). This is because the ionic diameter of nickel ions decreases as the valence of nickel ions increases. It is interpreted as

  Therefore, in order to improve the cycle life by controlling the oxidizing property or reducing property of the atmosphere in the heat treatment, preferably at least in the cooling process which is a stage from the high temperature state before the final removal of the heat treatment of the positive electrode to the cooling, It is effective to increase the oxidation of the atmosphere and increase the oxidation state of manganese (Mn). That is, in the second step, at least the cooling process is performed in an oxidizing atmosphere equal to or more than an atmosphere that is more reducible than air, or more than manganese (Mn). The effect of suppressing the reduction in the oxidation state can be enhanced, and it is effective for improving the cycle life. Here, the oxidizing atmosphere above the reducing atmosphere than the air means, for example, an atmosphere in which the oxygen partial pressure of the reducing atmosphere than the air is higher than the reducing atmosphere than the air, for example, An atmosphere that is more oxidizing than air, and ultimately an atmosphere in which only oxygen (O) or the like exists, for example.

  Furthermore, when the metal compound is decomposed into a metal oxide, a plurality of mixed metal compounds form a metal oxide in a mixed or solid solution state of a plurality of metal oxides, and the metal oxide nickel In the stage where ions diffuse into the composite oxide particles, heat treatment is performed under an atmospheric condition with low oxidizability and high reducibility, for example, an inert atmosphere condition such as a pure nitrogen atmosphere. By preventing the nickel ion from decreasing, the diffusion of nickel ions into the composite oxide particles is suppressed, and the nickel ion concentration on the surface of the composite oxide particles is increased. Finally, an effective surface can be formed on the obtained positive electrode active material. Further, in the above stage, when heat treatment is performed under an inert atmosphere condition such as a pure nitrogen atmosphere, a surface effective for the finally obtained positive electrode active material can be formed by a lower temperature heat treatment.

  That is, in the second step, for example, the temperature raising process may be performed in an atmosphere that is more reducible than air, thereby preventing the valence of nickel ions from increasing. By preventing the diffusion of nickel ions into the composite oxide particles and increasing the nickel ion concentration on the surface of the composite oxide particles. A smooth surface.

  Next, a nonaqueous electrolyte secondary battery using the above-described positive electrode active material will be described. As described above, the positive electrode active material is preferably used as an electrode active material, and among them, it is preferably used for a nonaqueous electrolyte secondary battery electrode and a nonaqueous electrolyte secondary battery.

  FIG. 1 shows a cross-sectional structure of a first example of a nonaqueous electrolyte secondary battery using the positive electrode active material described above.

  In this secondary battery, the open circuit voltage in a fully charged state per pair of positive electrode and negative electrode is, for example, 4.25V or more and 4.65V or less.

  This secondary battery is a so-called cylindrical type, and is a wound electrode in which a strip-shaped positive electrode 2 and a strip-shaped negative electrode 3 are wound via a separator 4 inside a substantially hollow cylindrical battery can 1. It has a body 20.

  The battery can 1 is made of, for example, iron (Fe) plated with nickel (Ni), and has one end closed and the other end open. Inside the battery can 1, a pair of insulating plates 5 and 6 are arranged perpendicular to the winding peripheral surface so as to sandwich the winding electrode body 20.

  At the open end of the battery can 1, a battery lid 7, a safety valve mechanism 8 and a thermal resistance element (PTC element) 9 provided inside the battery lid 7 are interposed via a gasket 10. It is attached by caulking, and the inside of the battery can 1 is sealed. The battery lid 7 is made of, for example, the same material as the battery can 1. The safety valve mechanism 8 is electrically connected to the battery lid 7 via a heat sensitive resistance element 9, and the disk plate 11 is reversed when the internal pressure of the battery becomes a certain level or more due to internal short circuit or external heating. Thus, the electrical connection between the battery lid 7 and the wound electrode body 20 is cut off. When the temperature rises, the heat sensitive resistance element 9 limits the current by increasing the resistance value and prevents abnormal heat generation due to a large current. The gasket 10 is made of, for example, an insulating material, and asphalt is applied to the surface.

  The wound electrode body 20 is wound around, for example, the center pin 12. A positive electrode lead 13 made of, for example, aluminum (Al) or the like is connected to the positive electrode 2 of the spirally wound electrode body 20, and a negative electrode lead 14 made of, for example, nickel (Ni) or the like is connected to the negative electrode 3. The positive electrode lead 13 is electrically connected to the battery cover 7 by being welded to the safety valve mechanism 8, and the negative electrode lead 14 is welded and electrically connected to the battery can 1.

[Positive electrode]
FIG. 2 shows an enlarged part of the spirally wound electrode body 20 shown in FIG. As shown in FIG. 2, the positive electrode 2 includes, for example, a positive electrode current collector 2A having a pair of opposed surfaces, and a positive electrode mixture layer 2B provided on both surfaces of the positive electrode current collector 2A. In addition, you may make it have the area | region where the positive mix layer 2B was provided only in the single side | surface of 2 A of positive electrode collectors. The positive electrode current collector 2A is made of, for example, a metal foil such as an aluminum (Al) foil. The positive electrode mixture layer 2B includes, for example, a positive electrode active material, and may include a conductive agent such as graphite and a binder such as polyvinylidene fluoride as necessary. The positive electrode active material described above can be used as the positive electrode active material.

[Negative electrode]
As shown in FIG. 2, the negative electrode 3 includes, for example, a negative electrode current collector 3A having a pair of opposed surfaces, and a negative electrode mixture layer 3B provided on both surfaces of the negative electrode current collector 3A. In addition, you may make it have the area | region in which the negative mix layer 3B was provided only in the single side | surface of 3 A of negative electrode collectors. The negative electrode current collector 3A is made of a metal foil such as a copper (Cu) foil. The negative electrode mixture layer 3B includes, for example, a negative electrode active material, and may include a binder such as polyvinylidene fluoride as necessary.

The negative electrode active material includes a negative electrode material capable of inserting and extracting lithium (Li) (hereinafter referred to as a negative electrode material capable of inserting and extracting lithium (Li) as appropriate). Examples of negative electrode materials capable of inserting and extracting lithium (Li) include carbon materials, metal compounds, oxides, sulfides, lithium nitrides such as LiN ₃ , lithium metals, metals that form alloys with lithium, and high Examples include molecular materials. Among these, a carbonaceous material is preferably used as the negative electrode active material. If the carbonaceous material has insufficient electronic conductivity for the purpose of current collection, it is also preferable to add a conductive agent.

  Examples of the carbon material include non-graphitizable carbon, graphitizable carbon, graphite, pyrolytic carbons, cokes, glassy carbons, organic polymer compound fired bodies, carbon fibers, and activated carbon. Among these, examples of coke include pitch coke, needle coke, and petroleum coke. An organic polymer compound fired body is a carbonized material obtained by firing a polymer material such as a phenol resin or a furan resin at an appropriate temperature, and part of it is non-graphitizable carbon or graphitizable carbon. Some are classified as: Examples of the polymer material include polyacetylene and polypyrrole.

  Among such negative electrode materials capable of inserting and extracting lithium (Li), those having a charge / discharge potential relatively close to lithium metal are preferable. This is because the lower the charge / discharge potential of the negative electrode 3, the easier it is to increase the energy density of the battery. Among these, a carbon material is preferable because a change in crystal structure that occurs during charge / discharge is very small, a high charge / discharge capacity can be obtained, and good cycle characteristics can be obtained. In particular, graphite is preferable because it has a high electrochemical equivalent and can provide a high energy density. Moreover, non-graphitizable carbon is preferable because excellent cycle characteristics can be obtained.

  Examples of the negative electrode material capable of inserting and extracting lithium (Li) include lithium metal alone, a metal element or metalloid element simple substance, alloy or compound capable of forming an alloy with lithium (Li). These are preferable because a high energy density can be obtained, and in particular, when used together with a carbon material, a high energy density can be obtained and excellent cycle characteristics can be obtained, and therefore, it is more preferable. Note that in this specification, alloys include those composed of one or more metal elements and one or more metalloid elements in addition to those composed of two or more metal elements. The structures include solid solutions, eutectics (eutectic mixtures), intermetallic compounds, or those in which two or more of them coexist.

Examples of such metal elements or metalloid elements include tin (Sn), lead (Pb), aluminum (Al), indium (In), silicon (Si), zinc (Zn), antimony (Sb), and bismuth. (Bi), cadmium (Cd), magnesium (Mg), boron (B), gallium (Ga), germanium (Ge), arsenic (As), silver (Ag), zirconium (Zr), yttrium (Y) or hafnium (Hf). These alloys or compounds, for example, those represented by the chemical formula Ma _s Mb _t Li _u or a chemical formula Ma _p Mc _q Md _r,. In these chemical formulas, Ma represents at least one of a metal element and a metalloid element capable of forming an alloy with lithium, Mb represents at least one of a metal element and a metalloid element other than lithium and Ma, Mc represents at least one of nonmetallic elements, and Md represents at least one of metallic elements and metalloid elements other than Ma. The values of s, t, u, p, q, and r are s> 0, t ≧ 0, u ≧ 0, p> 0, q> 0, and r ≧ 0, respectively.

  Among these, a simple substance, alloy or compound of Group 4B metal element or semimetal element in the short-period type periodic table is preferable, and silicon (Si) or tin (Sn), or an alloy or compound thereof is particularly preferable. These may be crystalline or amorphous.

In addition, inorganic compounds that do not contain lithium (Li), such as MnO ₂ , V ₂ O ₅ , V ₆ O ₁₃ , NiS, and MoS, can also be used.

[Electrolyte]
As the electrolytic solution, a nonaqueous electrolytic solution in which an electrolyte salt is dissolved in a nonaqueous solvent can be used. As the non-aqueous solvent, for example, it is preferable to contain at least one of ethylene carbonate and propylene carbonate. This is because the cycle characteristics can be improved. In particular, it is preferable to mix and contain ethylene carbonate and propylene carbonate because cycle characteristics can be further improved. The nonaqueous solvent preferably contains at least one of chain carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, or methyl propyl carbonate. This is because the cycle characteristics can be further improved.

  The non-aqueous solvent preferably further contains at least one of 2,4-difluoroanisole and vinylene carbonate. This is because 2,4-difluoroanisole can improve discharge capacity, and vinylene carbonate can further improve cycle characteristics. In particular, it is more preferable that they are mixed and contained because both the discharge capacity and the cycle characteristics can be improved.

  Non-aqueous solvents further include butylene carbonate, γ-butyrolactone, γ-valerolactone, those in which part or all of the hydrogen groups of these compounds are substituted with fluorine groups, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyl Tetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, methyl acetate, methyl propionate, acetonitrile, glutaronitrile, adiponitrile, methoxyacetonitrile, 3-methoxypropironitrile, N, N-dimethylformamide N-methylpyrrolidinone, N-methyloxazolidinone, N, N-dimethylimidazolidinone, nitromethane, nitroethane, sulfolane, dimethyl sulfoxide, or trimethyl phosphate may be included. Yes.

  Depending on the electrode to be combined, the reversibility of the electrode reaction may be improved by using a material in which part or all of the hydrogen atoms of the substance contained in the non-aqueous solvent group are substituted with fluorine atoms. Therefore, these substances can be used as appropriate.

Examples of the lithium salt that is an electrolyte salt include LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiClO ₄ , LiB (C ₆ H ₅ ) ₄ , LiCH ₃ SO ₃ , LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) _2. , LiC (SO ₂ CF ₃ ) ₃ , LiAlCl ₄ , LiSiF ₆ , LiCl, LiBF ₂ (ox), LiBOB, or LiBr are suitable, and one or more of these are used in combination. be able to. Among them, LiPF ₆ is preferable because it can obtain high ion conductivity and can improve cycle characteristics.

[Separator]
Below, the separator material which can be utilized for one Embodiment is demonstrated. As a separator material used for the separator 4, it is possible to use those used in conventional batteries. Among these, it is particularly preferable to use a polyolefin microporous film that is excellent in short-circuit prevention effect and can improve battery safety by a shutdown effect. For example, a microporous film made of polyethylene or polypropylene resin is preferable.

  Further, as the separator material, it is more preferable to use a laminate or mixture of polyethylene having a lower shutdown temperature and polypropylene having excellent oxidation resistance from the viewpoint of achieving both shutdown performance and float characteristics.

  Next, the manufacturing method of a nonaqueous electrolyte secondary battery is demonstrated. Hereinafter, a method for manufacturing a nonaqueous electrolyte secondary battery will be described by taking a cylindrical nonaqueous electrolyte secondary battery as an example.

  The positive electrode 2 is produced as described below. First, for example, a positive electrode active material, a conductive agent, and a binder are mixed to prepare a positive electrode mixture, and this positive electrode mixture is dispersed in a solvent such as N-methyl-2-pyrrolidone to form a positive electrode mixture. Use slurry. Since the method for manufacturing the positive electrode active material has been described above, a detailed description thereof will be omitted.

  Next, after applying this positive electrode mixture slurry to the positive electrode current collector 2A and drying the solvent, the positive electrode mixture layer 2B is formed by compression molding with a roll press or the like, and the positive electrode 2 is produced.

  The negative electrode 3 is produced as described below. First, for example, a negative electrode active material and a binder are mixed to prepare a negative electrode mixture, and the negative electrode mixture is dispersed in a solvent such as N-methyl-2-pyrrolidone to obtain a negative electrode mixture slurry.

  Next, after applying this negative electrode mixture slurry to the negative electrode current collector 3A and drying the solvent, the negative electrode mixture layer 3B is formed by compression molding using a roll press or the like, and the negative electrode 3 is produced.

  Moreover, the negative electrode mixture layer 3B may be formed by, for example, a gas phase method, a liquid phase method, or a firing method, or a combination of two or more thereof. As the vapor phase method, for example, a physical deposition method or a chemical deposition method can be used. Specifically, a vacuum deposition method, a sputtering method, an ion plating method, a laser ablation method, a thermal CVD (Chemical Vapor Deposition), or the like. A chemical vapor deposition method) or a plasma CVD method can be used. As the liquid phase method, a known method such as electrolytic plating or electroless plating can be used. A known method can also be used for the firing method, and for example, an atmosphere firing method, a reaction firing method, or a hot press firing method can be used.

  Next, the positive electrode lead 13 is attached to the positive electrode current collector 2A by welding or the like, and the negative electrode lead 14 is attached to the negative electrode current collector 3A by welding or the like. Next, the positive electrode 2 and the negative electrode 3 are wound through the separator 4, and the tip of the positive electrode lead 13 is welded to the safety valve mechanism 8, and the tip of the negative electrode lead 14 is welded to the battery can 1. The rotated positive electrode 2 and negative electrode 3 are sandwiched between a pair of insulating plates 5 and 6 and stored in the battery can 1.

  Next, an electrolytic solution is injected into the battery can 1 and the separator 4 is impregnated with the electrolytic solution. Next, the battery lid 7, the safety valve mechanism 8, and the heat sensitive resistance element 9 are fixed to the opening end of the battery can 1 by caulking through the gasket 10. Thus, a nonaqueous electrolyte secondary battery is produced.

  A second example of the non-aqueous electrolyte secondary battery using the positive electrode active material described above will be described. FIG. 3 shows a structure of a second example of the nonaqueous electrolyte secondary battery using the positive electrode active material described above. As shown in FIG. 3, this non-aqueous electrolyte secondary battery is sealed by housing the battery element 30 in an exterior material 37 made of a moisture-proof laminate film and welding the periphery of the battery element 30. The battery element 30 is provided with a positive electrode lead 32 and a negative electrode lead 33, and these leads are sandwiched between outer packaging materials 37 and pulled out to the outside. A resin piece 34 and a resin piece 35 are coated on both surfaces of the positive electrode lead 32 and the negative electrode lead 33 in order to improve the adhesion to the exterior material 37.

[Exterior material]
The packaging material 37 has, for example, a stacked structure in which an adhesive layer, a metal layer, and a surface protective layer are sequentially stacked. The adhesive layer is made of a polymer film. Examples of the material constituting the polymer film include polypropylene (PP), polyethylene (PE), unstretched polypropylene (CPP), linear low density polyethylene (LLDPE), and low density. A polyethylene (LDPE) is mentioned. The metal layer is made of a metal foil, and an example of a material constituting the metal foil is aluminum (Al). Moreover, as a material which comprises metal foil, it is also possible to use metals other than aluminum (Al), for example. Examples of the material constituting the surface protective layer include nylon (Ny) and polyethylene terephthalate (PET). The surface on the adhesive layer side is a storage surface on the side where the battery element 30 is stored.

[Battery element]
For example, as shown in FIG. 4, the battery element 30 includes a strip-shaped negative electrode 43 provided with a gel electrolyte layer 45 on both sides, a separator 44, and a strip-shaped positive electrode 42 provided with a gel electrolyte layer 45 on both sides. The battery element 30 is a wound type battery element 30 that is formed by laminating the separator 44 and wound in the longitudinal direction.

  The positive electrode 42 includes a strip-shaped positive electrode current collector 42A and a positive electrode mixture layer 42B formed on both surfaces of the positive electrode current collector 42A.

  One end of the positive electrode 42 in the longitudinal direction is provided with a positive electrode lead 32 connected by, for example, spot welding or ultrasonic welding. As a material of the positive electrode lead 32, for example, a metal such as aluminum can be used.

  The negative electrode 43 includes a strip-shaped negative electrode current collector 43A and a negative electrode mixture layer 43B formed on both surfaces of the negative electrode current collector 43A.

  Similarly to the positive electrode 42, the negative electrode lead 33 connected by, for example, spot welding or ultrasonic welding is also provided at one end portion of the negative electrode 43 in the longitudinal direction. As a material of the negative electrode lead 33, for example, copper (Cu), nickel (Ni) or the like can be used.

  The positive electrode current collector 42A, the positive electrode mixture layer 42B, the negative electrode current collector 43A, and the negative electrode mixture layer 43B are the same as in the first example.

  The gel electrolyte layer 45 includes an electrolytic solution and a polymer compound serving as a holding body that holds the electrolytic solution, and has a so-called gel shape. The gel electrolyte layer 45 is preferable because it can obtain high ionic conductivity and prevent battery leakage. The configuration of the electrolytic solution (that is, the liquid solvent and the electrolyte salt) is the same as that in the first example.

  Examples of the polymer compound include polyacrylonitrile, polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polytetrafluoroethylene, polyhexafluoropropylene, polyethylene oxide, polypropylene oxide, polyphosphazene, and polysiloxane. , Polyvinyl acetate, polyvinyl alcohol, polymethyl methacrylate, polyacrylic acid, polymethacrylic acid, styrene-butadiene rubber, nitrile-butadiene rubber, polystyrene or polycarbonate. In particular, from the viewpoint of electrochemical stability, polyacrylonitrile, polyvinylidene fluoride, polyhexafluoropropylene, or polyethylene oxide is preferable.

  Next, the manufacturing method of the 2nd example of the nonaqueous electrolyte secondary battery using the positive electrode active material mentioned above is demonstrated. First, a precursor solution containing a solvent, an electrolyte salt, a polymer compound, and a mixed solvent is applied to each of the positive electrode 42 and the negative electrode 43, and the mixed solvent is volatilized to form the gel electrolyte layer 45. The positive lead 32 is attached to the end of the positive current collector in advance by welding, and the negative lead 33 is attached to the end of the negative current collector 43A by welding.

  Next, the positive electrode 42 and the negative electrode 43 on which the gel electrolyte layer 45 is formed are laminated through a separator 44 to form a laminated body, and then the laminated body is wound in the longitudinal direction to form a wound battery element. 30 is formed.

  Next, a recess 36 is formed by deep-drawing an exterior material 37 made of a laminate film, the battery element 30 is inserted into the recess 36, and an unprocessed portion of the exterior material 37 is folded back to the upper portion of the recess 36. The outer peripheral part of is thermally welded and sealed. Thus, a nonaqueous electrolyte secondary battery is produced.

  Specific embodiments of the present invention will be described below with reference to examples, but the present invention is not limited thereto.

<Example 1>
First, 20 parts by weight of lithium cobalt oxide having an average chemical composition analysis value of Li _1.03 Co _0.98 Al _0.01 Mg _0.01 O _2.02 and an average particle diameter of 13 μm measured by a laser scattering method is added to 300 parts by weight of pure water at 80 ° C. for 1 hour. The mixture was dispersed with stirring.

Then, nitric acid was added nickel _{(Ni (NO 3) 2 ·} 6H 2 O) 1.54 parts by weight, of manganese nitrate _{(Mn (NO 3) 2 ·} 6H 2 O) 1.65 parts by weight of commercially available reagents. Further, a 2N LiOH aqueous solution was added to pH 13 over 30 minutes, and stirring and dispersion were further continued at 80 ° C. for 3 hours, followed by cooling.

Next, the dispersion was filtered and washed, and dried at 120 ° C. to obtain a precursor sample having a hydroxide formed on the surface. In addition, the analysis result of the metal molar content ratio of the precursor sample was Li _1.00 Co _0.94 Ni _0.02 Mn _0.02 Al _0.01 Mg _0.01 .

  Next, in order to adjust the amount of lithium, 10 parts by weight of the precursor sample was impregnated with 2 parts by weight of 2N LiOH aqueous solution, and uniformly mixed and dried to obtain a calcined precursor. The calcined precursor was heated to 900 ° C. at a rate of 5 ° C./min in an electric furnace in an electric furnace and held for 5 hours, and then cooled to room temperature in a pure oxygen atmosphere as in Example 1. The positive electrode active material was obtained.

<Example 2>
20 parts by weight of the same lithium cobalt oxide as in Example 1 was stirred and dispersed in 300 parts by weight of a 2N LiOH aqueous solution at 80 ° C. for 2 hours.

Next, nickel nitrate (Ni (NO ₃ ) ₂ .6H ₂ O) 1.54 parts by weight, manganese nitrate (Mn (NO ₃ ) ₂ .6H ₂ O) 1.65 wt. An aqueous solution was prepared by adding pure water to 10 parts by weight, and the total amount of 10 parts by weight of this aqueous solution was added over 30 minutes, followed by stirring and dispersing at 80 ° C. for 3 hours and allowing to cool. Next, this dispersion was filtered and dried at 120 ° C. to obtain a precursor sample in which hydroxide was formed on the surface. The analysis result of the metal content ratio of the precursor sample was Li _1.04 Co _0.94 Ni _0.02 Mn _0.02 Al _0.01 Mg _0.01 .

  Next, this precursor sample was heated to 900 ° C. at a rate of 5 ° C./min in a nitrogen atmosphere in an electric furnace, and the furnace atmosphere was changed to air and held for 5 hours. It cooled in atmosphere and the positive electrode active material of Example 2 was obtained.

<Example 3>
An aqueous solution was prepared by adding pure water to 3.08 parts by weight of nickel nitrate and 3.30 parts by weight of manganese nitrate obtained by doubling the weights of nickel nitrate and manganese nitrate of Example 2, respectively. A total of 20 parts by weight of aqueous solution was added over 1 hour. Other than this, a precursor sample was obtained in the same manner as in Example 2. The analysis result of the metal content ratio of the precursor sample was Li _1.03 Co _0.88 Ni _0.05 Mn _0.05 Al _0.01 Mg _0.01 .

  Next, the precursor sample was heated to 900 ° C. in a pure nitrogen atmosphere at a rate of 5 ° C. per minute in the electric furnace, and the furnace atmosphere was subjected to a volume ratio of pure nitrogen to air (pure nitrogen: air). Was changed to a 3: 1 mixed gas and held for 5 hours, and then cooled to room temperature in a pure oxygen atmosphere as it was to obtain a positive electrode active material of Example 3.

<Example 4>
Li ₂ CO ₃ : Ni (OH) ₂ : MnCO ₃ = 1.08: 1: 1 (Li _1.08 Ni _0.5 Mn _0.5 O ₂ equivalent) Weighed so that the average particle diameter is 1 μm or less by a ball mill device And then dried under reduced pressure at 70 ° C. 10 parts by weight of the obtained powder and 100 parts by weight of lithium cobaltate used in Example 1 were treated for 1 h by a mechanofusion apparatus, and Li ₂ CO ₃ , Ni (OH) ₂ , MnCO ₃ was applied to the lithium cobaltate surface. Was deposited to prepare a precursor sample.

  Next, this precursor sample was heated to 800 ° C. in a nitrogen atmosphere at a rate of 5 ° C. per minute in an electric furnace, and the furnace atmosphere was changed to pure oxygen and maintained for 3 hours. The mixture was cooled in an oxygen atmosphere to obtain a positive electrode active material of Example 4.

<Example 5>
After the temperature increase, the furnace atmosphere was changed to a mixed gas atmosphere having a volume ratio of pure nitrogen to air (pure nitrogen: air) of 2: 1, held for 3 hours, and then cooled to room temperature as it was under the same atmosphere. A positive electrode active material of Example 5 was obtained in the same manner as Example 4 except for the above.

<Example 6>
Example 1 except that the heat treatment was performed at a rate of 5 ° C. per minute in a pure nitrogen atmosphere, maintained at 850 ° C. for 4 hours, and then cooled to room temperature as it was in a pure nitrogen atmosphere. Similarly, the positive electrode active material of Example 6 was obtained.

<Example 7>
20 parts by weight of lithium cobalt oxide similar to that in Example 1 was stirred and dispersed in 300 weights of 2N LiOH aqueous solution at 80 ° C. for 2 hours.

Next, an aqueous solution in which pure water was added to 3.10 parts by weight of nickel nitrate (Ni (NO ₃ ) ₂ .6H ₂ O), a commercially available reagent similar to Example 1, to 10 parts by weight was prepared. The whole amount by weight was added over 30 minutes, and the mixture was further stirred and dispersed at 80 ° C. for 3 hours and allowed to cool. Next, this dispersion was filtered and dried at 120 ° C. to obtain a precursor sample in which hydroxide was formed on the surface. The analysis result of the metal content ratio of the precursor sample was Li _1.04 Co _0.94 Ni _0.04 Al _0.01 Mg _0.01 .

  Next, this precursor sample was heated to 850 ° C. at a rate of 5 ° C. per minute in an electric furnace in a pure nitrogen atmosphere, held for 5 hours, and then cooled to room temperature as it was in a pure oxygen atmosphere. The positive electrode active material of Example 7 was obtained.

<Example 8>
Li ₂ CO ₃ : Ni (OH) ₂ : MnCO ₃ = 1.08: 1.5: 0.5 (Li _1.08 Ni _0.75 Mn _0.25 O ₂ equivalent) After pulverizing to 1 μm or less, it was dried at 70 ° C. under reduced pressure. 10 parts by weight of the obtained powder and 100 parts by weight of lithium cobaltate used in Example 1 were treated for 1 h by a mechanofusion apparatus, and Li ₂ CO ₃ , Ni (OH) ₂ , MnCO ₃ was applied to the lithium cobaltate surface. Was deposited to prepare a precursor sample.

  Next, this precursor sample was heated to 800 ° C. at a rate of 5 ° C. per minute in a pure nitrogen atmosphere in an electric furnace, held for 3 hours, and then cooled to room temperature as it was in a pure nitrogen atmosphere. The positive electrode active material of Example 8 was obtained.

<Comparative Example 1>
In the same manner as in Example 1, except that the heat treatment was performed at a rate of 5 ° C. per minute in an air atmosphere, held at 900 ° C. for 5 hours, and then cooled in the air atmosphere as it was. The positive electrode active material of Comparative Example 1 was obtained.

<Comparative example 2>
In the same manner as in Example 2, except that the heat treatment was performed at a rate of 5 ° C. per minute in an air atmosphere, held at 900 ° C. for 5 hours, and then directly cooled in the air atmosphere. A positive electrode active material of Comparative Example 2 was obtained.

<Comparative Example 3>
In the same manner as in Example 3, except that the heat treatment was performed at a rate of 5 ° C. per minute in an air atmosphere, held at 900 ° C. for 5 hours, and then cooled in the air atmosphere as it was. A positive electrode active material of Comparative Example 3 was obtained.

<Comparative Example 4>
Except that the firing was performed at a rate of 5 ° C. per minute in an air atmosphere, held at 800 ° C. for 3 hours, and then cooled in the air atmosphere as in Example 4, A positive electrode active material of Comparative Example 4 was obtained.

<Comparative Example 5>
The heat treatment was performed in the same manner as in Example 6 except that the temperature was raised at a rate of 5 ° C. per minute in an air atmosphere, held at 850 ° C. for 5 hours, and then cooled in the air atmosphere as it was. The positive electrode active material of Comparative Example 5 was obtained.

<Comparative Example 6>
The heat treatment was performed in the same manner as in Example 7 except that the heat treatment was performed at a rate of 5 ° C. per minute in an air atmosphere, held at 850 ° C. for 5 hours, and then cooled in the air atmosphere as it was. The positive electrode active material of Comparative Example 6 was obtained.

<Comparative Example 7>
The heat treatment was performed in the same manner as in Example 8 except that the heat treatment was performed at a rate of 5 ° C. per minute in an air atmosphere, maintained at 800 ° C. for 3 hours, and then cooled in the air atmosphere as it was. Thus, a positive electrode active material of Comparative Example 7 was obtained.

(Evaluation)
The cylindrical batteries shown in FIGS. 1 and 2 were produced using the produced positive electrode active materials of Examples 1 to 8 and Comparative Examples 1 to 7, and the cycle characteristics at high temperatures were evaluated.

  First, 86% by weight of the positive electrode active material, 10% by weight of graphite as a conductive agent, and 4% by weight of polyvinylidene fluoride (PVdF) as a binder are mixed and dispersed in N-methyl-2-pyrrolidone (NMP). Thus, a positive electrode mixture slurry was obtained.

  Next, the positive electrode mixture slurry was uniformly applied to both surfaces of a strip-shaped aluminum foil having a thickness of 20 microns and dried, and then compressed with a roller press to obtain a strip-shaped positive electrode 2. At this time, the voids in the electrode were adjusted so that the volume ratio was 26%. An aluminum positive electrode lead 13 was attached to the positive electrode current collector 2A.

  Further, 90% by weight of powdered artificial graphite as a negative electrode active material and 10% by weight of polyvinylidene fluoride (PVdF) as a binder are mixed and dispersed in N-methyl-2-pyrrolidone (NMP) to form a negative electrode composite. An agent slurry was obtained.

  Next, the negative electrode mixture slurry was uniformly applied to both surfaces of a copper foil having a thickness of 10 microns, and dried and then compressed with a roller press to obtain a strip-shaped negative electrode. A negative electrode lead 14 made of nickel was attached to the negative electrode current collector 3A.

  The strip-like positive electrode 2 and the strip-like negative electrode 3 produced as described above were wound many times through a porous polyolefin film as the separator 4 to produce a spiral wound electrode body 20. Next, the spirally wound electrode body 20 was housed in a nickel-plated iron battery can 1, and a pair of insulating plates 5 and 6 were disposed on the upper and lower surfaces of the spirally wound electrode body 20.

  Next, the aluminum positive electrode lead 13 is led out from the positive electrode current collector 2A and welded to the protrusion of the safety valve mechanism 8 in which electrical continuity with the battery lid 7 is secured, and the nickel negative electrode lead 14 is connected to the negative electrode current collector. Derived from the body 3A and welded to the bottom of the battery can 1.

  Finally, after injecting the electrolytic solution into the battery can 1 in which the above-described wound electrode body 20 is incorporated, the battery can 1 is caulked through the insulating sealing gasket 10, whereby the safety valve mechanism 8, the heat sensitive resistance element 9 and the battery lid 7 were fixed, and a cylindrical battery having an outer diameter of 18 mm and a height of 65 mm was produced.

The electrolyte used was prepared by dissolving LiPF ₆ to a concentration of 1.0 mol / dm ³ in a mixed solution having a volume mixing ratio of ethylene carbonate and diethyl carbonate of 1: 1. .

  About the non-aqueous electrolyte secondary battery produced as described above, after charging under conditions of an environmental temperature of 45 ° C., a charging voltage of 4.40 V, a charging current of 1000 mA, and a charging time of 2.5 hours, a discharging current of 800 mA, The initial capacity was measured by discharging at a final voltage of 2.75V.

  Moreover, charging / discharging was repeated on the same conditions as the case where the initial capacity | capacitance was calculated | required, the discharge capacity of 200th cycle was measured, and the capacity | capacitance maintenance factor with respect to the initial capacity | capacitance was calculated | required. The measurement results are shown in Table 1.

  As shown in Table 1, in Examples 1 to 8 in which heat treatment was performed in an atmosphere having a reducing property than air, in Example 1, in Comparative Example 1 and Example 2 in which heat treatment was performed in an air atmosphere, air was used. Comparative Example 2 and Example 6 in which heat treatment was performed in an atmosphere In Comparative Example 3 and Example 3 in which heat treatment was performed in an air atmosphere Comparative Examples 4 and 6 in which heat treatment was performed in an air atmosphere in Examples 4 and 5 In Comparative Example 5 in which heat treatment was performed in an air atmosphere, in Example 7, in Comparative Example 6 in which heat treatment was performed in an air atmosphere, and in Example 8, in Comparative Example 7 in which heat treatment was performed in an air atmosphere, the initial capacity and capacity Maintenance rate improved. That is, it was found that the initial capacity and capacity retention rate can be improved by performing heat treatment in an atmosphere that is more reducible than air. It has also been found that it is effective to perform at least the cooling process in an atmosphere that is more reducible than air or in an oxidizing atmosphere that is greater than the atmosphere that is more reducible than air.

  The present invention is not limited to the above-described embodiments of the present invention, and various modifications and applications are possible without departing from the spirit of the present invention. For example, the nonaqueous electrolyte secondary battery using the positive electrode active material produced by the method for producing a positive electrode active material according to one embodiment of the present invention is not particularly limited in its shape. For example, in addition to the cylindrical shape, a square shape, a coin shape, a button shape, or the like may be provided.

  Further, in the first example of the non-aqueous electrolyte secondary battery, the non-aqueous electrolyte secondary battery having an electrolytic solution as the electrolyte, and in the second example of the non-aqueous electrolyte secondary battery, the non-aqueous electrolyte secondary battery having a gel electrolyte as the electrolyte. Although the water electrolyte secondary battery has been described, it is not limited thereto.

  For example, as the electrolyte, in addition to the above-described ones, a polymer solid electrolyte using an ion conductive polymer or an inorganic solid electrolyte using an ion conductive inorganic material can be used. It may be used in combination with the electrolyte. Examples of the polymer compound that can be used for the polymer solid electrolyte include polyether, polyester, polyphosphazene, and polysiloxane. Examples of the inorganic solid electrolyte include ion conductive ceramics, ion conductive crystals, and ion conductive glass.

  Furthermore, for example, a conventional nonaqueous solvent-based electrolytic solution is used as the electrolytic solution of the nonaqueous electrolyte secondary battery without any particular limitation. Among these, the electrolyte solution of a secondary battery comprising a non-aqueous electrolyte solution containing an alkali metal salt includes propylene carbonate, ethylene carbonate, γ-butyrolactone, N-methylpyrrolidone, acetonitrile, N, N-dimethylformamide, dimethylsulfate. For example, foxoxide, tetrahydrofuran, 1,3-dioxolane, methyl formate, sulfolane, oxazolidone, thionyl chloride, 1,2-dimethoxyethane, diethylene carbonate, and derivatives and mixtures thereof are preferably used. The electrolyte contained in the electrolyte includes alkali metal, especially calcium halide, perchlorate, thiocyanate, borofluoride, phosphofluoride, arsenic fluoride, yttrium fluoride, trifluoromethylsulfate, etc. Is preferably used.

It is a schematic sectional drawing of the 1st example of the nonaqueous electrolyte secondary battery using the positive electrode active material produced with the manufacturing method of the positive electrode active material by one Embodiment of this invention. FIG. 2 is an enlarged sectional view of a part of a wound electrode body shown in FIG. 1. It is the schematic of the 2nd example of the nonaqueous electrolyte secondary battery using the positive electrode active material produced with the manufacturing method of the positive electrode active material by one Embodiment of this invention. FIG. 4 is an enlarged cross-sectional view of a part of the battery element shown in FIG. 3.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Battery can 2 ... Positive electrode 2A ... Positive electrode collector 2B ... Positive electrode mixture layer 3A ... Negative electrode collector 3B ... Negative electrode mixture layer 3 ... Negative electrode 4 .... Separator 5, 6 .... Insulating plate 7 .... Battery cover 8 .... Safety valve mechanism 9 .... Heat-sensitive element 10 ... Gasket 11 .... Disc plate 12. ..Center pin 13 ... Positive lead 14 ... Negative lead 20 ... Wound electrode body 30 ... Battery element 32 ... Positive lead 33 ... Negative lead 34, 35 ... Resin piece 36 ... Recess 37 ... Exterior material 42 ... Positive electrode 42A ... Positive electrode current collector 42B ... Positive electrode mixture layer 43 ... Negative electrode 43A ... Negative electrode current collector 43B ... Negative electrode mixture layer 44 ... Separator 45 ... Gel electrolyte layer

Claims (16)

Forming a layer containing at least a nickel (Ni) compound and / or a manganese (Mn) compound on at least a part of the composite oxide particles containing at least lithium (Li) and cobalt (Co);
The composite oxide particles having the layer formed thereon are heat-treated in an atmosphere that is more reducible than air, so that the composite oxide particles are provided on at least a part of the lithium oxide (Li), nickel (Ni), Forming a coating layer having an oxide containing at least one of manganese (Mn) and cobalt (Co);
The manufacturing method of the positive electrode active material characterized by having. 2. The method for producing a positive electrode active material according to claim 1, wherein in the heat treatment, at least a cooling process is performed in an atmosphere that is more reducible than the air or an atmosphere that is more oxidizing than the atmosphere. The method for producing a positive electrode active material according to claim 1, wherein in the heat treatment, the temperature raising process is performed in an atmosphere that is more reducible than air. 2. The method for producing a positive electrode active material according to claim 1, wherein the atmosphere that is more reducible than air is an inert atmosphere. The nickel (Ni) compound is a nickel (Ni) hydroxide,
2. The method for producing a positive electrode active material according to claim 1, wherein the compound of manganese (Mn) is a hydroxide of manganese (Mn). The formation of the layer containing the nickel (Ni) hydroxide and / or the manganese (Mn) hydroxide is carried out in a solvent system mainly composed of water having a pH of 12 or more. A method for producing a positive electrode active material. The composite oxide particles are dispersed in a solvent system mainly composed of water having a pH of 12 or more, and a nickel (Ni) compound and / or a manganese (Mn) compound is added thereto, and the nickel (Ni) hydroxide is added. The method for producing a positive electrode active material according to claim 6, wherein a layer containing an oxide and / or a hydroxide of manganese (Mn) is formed. The method for producing a positive electrode active material according to claim 6, wherein the solvent system mainly composed of water having a pH of 12 or more contains lithium hydroxide. The layer further includes a lithium compound,
2. The method for producing a positive electrode active material according to claim 1, wherein an easily decomposable metal compound is used as the lithium (Li) compound, the nickel (Ni) compound, and / or the manganese (Mn) compound. . The method for producing a positive electrode active material according to claim 9, wherein the layer containing the easily decomposable metal compound is formed by applying compression and shearing force to the composite oxide particles. The method for producing a positive electrode active material according to claim 1, wherein the composite oxide particles have an average composition represented by chemical formula (1).
(Chemical formula 1)
_{Li (1 + x) Co (} 1-y) M y O (2-z)
(In the chemical formula 1, M is magnesium (Mg), aluminum (Al), boron (B), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), nickel (Ni ), Copper (Cu), zinc (Zn), molybdenum (Mo), tin (Sn), and tungsten (W), wherein x, y, and z are −0.10. ≦ x ≦ 0.10, 0 ≦ y <0.50, −0.10 ≦ z ≦ 0.20.) 2. The positive electrode active material according to claim 1, wherein the composition ratio (Ni: Mn) of nickel (Ni) and manganese (Mn) in the coating layer is within a range of 100: 0 to 30:70 in terms of molar ratio. A method for producing a substance. The oxide of the coating layer contains 40 mol% or less of the total amount of nickel (Ni) and manganese (Mn), magnesium (Mg), aluminum (Al), boron (B), titanium (Ti), vanadium ( V), chromium (Cr), iron (Fe), cobalt (Co), copper (Cu), zinc (Zn), molybdenum (Mo), tin (Sn), at least selected from the group consisting of tungsten (W) 2. The method for producing a positive electrode active material according to claim 1, wherein the positive electrode active material is replaced with one kind of metal element. 2. The positive electrode active material according to claim 1, wherein the composition ratio of the nickel (Ni) and the manganese (Mn) in the coating layer is in a range of 100: 0 to 30:70 in terms of molar ratio. Method. The method for producing a positive electrode active material according to claim 1, wherein the amount of the coating layer is in the range of 0.5 wt% to 50 wt% with respect to the composite oxide particles. The method for producing a positive electrode active material according to claim 1, wherein the positive electrode active material has an average particle size in the range of 2.0 μm to 50 μm.

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