JP6059019B2 - Nonaqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte secondary battery having good charge / discharge cycle characteristics and suppressed swelling.

  Nonaqueous electrolyte secondary batteries such as lithium ion secondary batteries are widely used as power sources for various portable devices because of their high voltage and high capacity. In recent years, the use of medium- and large-sized power tools such as electric tools, electric vehicles, and electric bicycles has been spreading.

In particular, batteries used in mobile phones and game machines that are becoming smaller and more multifunctional are required to have higher capacities, and as a means for this, electrode active materials that exhibit high charge / discharge capacity are required. Research and development are progressing. Among them, as the active material material of the negative electrode, more lithium (ion) such as silicon (Si) and tin (Sn) can be used instead of carbonaceous materials such as graphite, which are used in conventional lithium ion secondary batteries. ) Has been attracting attention. In particular, it has been reported that SiO _x having a structure in which ultrafine particles of Si are dispersed in SiO ₂ has characteristics such as excellent load characteristics (Patent Documents 1 and 2, etc.).

However, since the SiO _x has a large volume expansion / contraction due to the charge / discharge reaction, particles are pulverized every charge / discharge cycle of the battery, and Si deposited on the surface reacts with the non-aqueous electrolyte solvent to have an irreversible capacity. It is also known that problems such as an increase or a gas generated in the battery due to this reaction cause the battery can to swell.

In response to these circumstances, a combination of SiO _x and graphitic carbon material suppresses the change in volume of the negative electrode during charge and discharge reaction (negative electrode mixture layer) technique (Patent Document 3) and, of SiO _x Non-aqueous electrolytic solution in which the volume expansion / shrinkage due to charge / discharge reaction is suppressed by limiting the utilization rate, or a halogen-substituted cyclic carbonate (such as 4-fluoro-1,3-dioxolan-2-one) is added. There have been proposed techniques for improving the charge / discharge cycle characteristics of the battery and suppressing the swelling of the battery can associated with gas generation (Patent Document 4).

Japanese Patent Laid-Open No. 2004-047404 Japanese Patent Laid-Open No. 2005-259697 JP 2011-233369 A JP 2008-210618A

According to the techniques of Patent Document 3 and Patent Document 4, it is possible to satisfactorily achieve improvement in charge / discharge cycle characteristics and suppression of swelling in a nonaqueous electrolyte secondary battery using SiO _x as a negative electrode. However, on the other hand, it is predicted that the charge / discharge cycle characteristics and the level of swelling suppression required for the nonaqueous electrolyte secondary battery will increase further in the future, and the techniques of Patent Document 3 and Patent Document 4 still have room for improvement. There is.

  The present invention has been made in view of the above circumstances, and the object thereof is to ensure good charge / discharge cycle characteristics while using a material containing Si and O as constituent elements for the negative electrode active material, and swelling. An object of the present invention is to provide a non-aqueous electrolyte secondary battery that can suppress the above.

The non-aqueous electrolyte secondary battery of the present invention that has achieved the above object has a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator, and the positive electrode is a positive electrode mixture layer containing a positive electrode active material and a binder. And the positive electrode mixture layer contains a lithium-containing composite oxide containing nickel as a transition metal element as a positive electrode active material, and vinylidene fluoride-chlorotrifluoro The lithium-containing composite oxide containing an ethylene copolymer as a binder and containing nickel as the transition metal element has a nickel ratio a (mol) when the amount of all transition metal elements is 100 (mol%). %) Is 30 ≦ a ≦ 100, and the negative electrode has a negative electrode mixture layer containing a negative electrode active material on one or both sides of the current collector, and the negative electrode mixture The material (provided that the atomic ratio x of O to Si is 0.5 ≦ x ≦ 1.5. Hereinafter, the material referred to as "SiO _x") containing the constituent elements Si and O and And a graphite carbon material as a negative electrode active material.

  According to the present invention, there is provided a nonaqueous electrolyte secondary battery capable of ensuring good charge / discharge cycle characteristics and suppressing swelling while using a material containing Si and O as constituent elements for a negative electrode active material. can do.

It is a schematic diagram showing an example of the nonaqueous electrolyte secondary battery of the present invention, (a) a plan view, (b) a partial longitudinal sectional view. FIG. 2 is a perspective view of FIG. 1.

In a non-aqueous electrolyte secondary battery, for example, SiO _x may be used as the negative electrode active material from the viewpoint of increasing the capacity. However, in such a battery, the amount of expansion and contraction of SiO _x accompanying charge / discharge is large. The negative electrode tends to deteriorate and the charge / discharge cycle characteristics tend to be low.

In the non-aqueous electrolyte secondary battery of the present invention, firstly, although than SiO _x capacity is inferior, expansion and contraction amount due to charging and discharging a small graphitic carbon material than SiO _x, in combination with SiO _x as the anode active material Thus, the volume change of the negative electrode mixture layer associated with charge / discharge is reduced while suppressing the capacity decrease due to the reduction of the proportion of SiO _{x in} the whole negative electrode active material as much as possible. It is possible to suppress deterioration of the negative electrode by repeated charging and discharging.

  However, the deterioration of the charge / discharge cycle characteristics of the nonaqueous electrolyte secondary battery may be caused by other than the deterioration of the negative electrode. For example, when the volume change of the negative electrode mixture layer is large as the battery is charged / discharged, the distance between the negative electrode and the positive electrode (the positive electrode mixture layer) facing the negative electrode There is a risk of non-uniformity when viewed over the entire facing surface, but this may not be a reaction at the time of charging / discharging, especially at locations where the distance between the negative electrode and the positive electrode is larger than other parts. The charge / discharge cycle characteristics of the battery are impaired, and the battery swells.

Therefore, the present inventors have a good balance between the negative electrode mixture layer containing SiO _x and a graphitic carbon material as a negative electrode active material, and the expansion and contraction associated with charge / discharge of the battery, and the interval between the positive electrode and the negative electrode. Investigation was repeated in order to find the structure of the positive electrode mixture layer that can maintain a highly uniform state over the entire facing surface. A positive electrode mixture layer containing a lithium-containing composite oxide containing a specific amount of nickel as a transition metal element as a positive electrode active material and containing vinylidene fluoride-chlorotrifluoroethylene copolymer (VDF-CTFE) as a binder. If it exists, even if charging / discharging of a battery was repeated, it discovered that the space | interval of a positive electrode and a negative electrode could be maintained in a state with high uniformity over these opposing surfaces, and came to complete this invention.

  The negative electrode according to the nonaqueous electrolyte secondary battery of the present invention has a structure having a negative electrode mixture layer containing a negative electrode active material on one side or both sides of a current collector.

As the negative electrode active material, SiO _x and a graphitic carbon material are used in combination. As a result, the capacity of the nonaqueous electrolyte secondary battery can be increased, and excellent charge / discharge cycle characteristics can be ensured by the combination with the specific positive electrode.

The SiO _x may contain Si microcrystal or amorphous phase. In this case, the atomic ratio of Si and O is a ratio including Si microcrystal or amorphous phase Si. That is, SiO _x includes a structure in which Si (for example, microcrystalline Si) is dispersed in an amorphous SiO ₂ matrix, and this amorphous SiO ₂ is dispersed in the SiO ₂ matrix. It is sufficient that the atomic ratio x satisfies 0.5 ≦ x ≦ 1.5 in combination with Si. For example, in the case of a material in which Si is dispersed in an amorphous SiO ₂ matrix and the material has a molar ratio of SiO ₂ to Si of 1: 1, x = 1, so that the structural formula is represented by SiO. The In the case of a material having such a structure, for example, in X-ray diffraction analysis, a peak due to the presence of Si (microcrystalline Si) may not be observed, but when observed with a transmission electron microscope, the presence of fine Si Can be confirmed.

Then, SiO _x is preferably a complex complexed with carbon materials, for example, it is desirable that the surface of the SiO _x is coated with a carbon material. Since SiO _x has poor conductivity, when it is used as a negative electrode active material, from the viewpoint of securing good battery characteristics, a conductive material (conductive aid) is used, and SiO _x and conductive material in the negative electrode are used. Therefore, it is necessary to form a good conductive network by mixing and dispersing with each other. If complexes complexed with carbon material SiO _x, for example, simply than with a material obtained by mixing a conductive material such as SiO _x and the carbon material, good conductive network in the negative electrode Formed.

The complex of the SiO _x and the carbon material, as described above, other although the surface of the SiO _x coated with carbon material, such as granules of SiO _x and the carbon material can be cited.

In addition, since the composite in which the surface of SiO _x is coated with a carbon material is further combined with a conductive material (carbon material or the like), a better conductive network can be formed in the negative electrode. Thus, it is possible to realize a non-aqueous electrolyte secondary battery with higher capacity and better battery characteristics (for example, charge / discharge cycle characteristics). The complex of the SiO _x and the carbon material coated with a carbon material, for example, like granules the mixture was further granulated with SiO _x and the carbon material coated with a carbon material.

Further, as SiO _x whose surface is coated with a carbon material, the surface of a composite (for example, a granulated body) of SiO _x and a carbon material having a smaller specific resistance value is further coated with a carbon material. Those can also be preferably used. In a non-aqueous electrolyte secondary battery having a negative electrode containing SiO _x as a negative electrode active material, since a better conductive network can be formed when SiO _x and a carbon material are dispersed inside the granule, Battery characteristics such as heavy load discharge characteristics can be further improved.

Preferred examples of the carbon material that can be used to form a composite with SiO _x include carbon materials such as low crystalline carbon, carbon nanotubes, and vapor grown carbon fibers.

The details of the carbon material include at least one selected from the group consisting of fibrous or coiled carbon materials, carbon black (including acetylene black and ketjen black), artificial graphite, graphitizable carbon, and non-graphitizable carbon. A seed material is preferred. Fibrous or coil-like carbon materials are preferable in that they easily form a conductive network and have a large surface area. Carbon black (including acetylene black and ketjen black), graphitizable carbon, and non-graphitizable carbon have high electrical conductivity and high liquid retention, and even if SiO _x particles expand and contract. This is preferable in that it has a property of easily maintaining contact with the particles.

The negative electrode active material, graphitic carbon material with SiO _x is also used in combination as a negative electrode active material, the graphite carbon material, it may also be used as a carbon material according to the complex of the SiO _x and the carbon material. Graphite carbon material, like carbon black, has high electrical conductivity and high liquid retention, and even when SiO _x particles expand and contract, they easily maintain contact with the particles. Therefore, it can be preferably used for forming a complex with SiO _x .

Among the carbon materials exemplified above, a fibrous carbon material is particularly preferable for use when the composite with SiO _x is a granulated body. Fibrous carbon material can follow the expansion and contraction of SiO _x with the charging and discharging of the battery due to the high shape is thin threadlike flexibility, also because bulk density is large, many and SiO _x particles It is because it can have a junction. Examples of the fibrous carbon include polyacrylonitrile (PAN) -based carbon fiber, pitch-based carbon fiber, vapor-grown carbon fiber, and carbon nanotube, and any of these may be used.

The fibrous carbon material can also be formed on the surface of the SiO _x particles by, for example, a vapor phase method.

The specific resistance value of SiO _x is usually 10 ³ to 10 ⁷ kΩcm, while the specific resistance value of the carbon material exemplified above is usually 10 ^{−5 to} 10 kΩcm.

The composite of SiO _x and the carbon material may further have a material layer (a material layer containing non-graphitizable carbon) that covers the carbon material coating layer on the particle surface.

When a composite of SiO _x and a carbon material is used for the negative electrode, the ratio of SiO _x and the carbon material is based on SiO _x : 100 parts by mass from the viewpoint of satisfactorily exerting the effect of the composite with the carbon material. The carbon material is preferably 5 parts by mass or more, and more preferably 10 parts by mass or more. Further, in the composite, if the ratio of the carbon material to be combined with SiO _x is too large, it may lead to a decrease in the amount of SiO _x in the negative electrode mixture layer, and the effect of increasing the capacity may be reduced. SiO _x: relative to 100 parts by weight, the carbon material, and more preferably preferably not more than 50 parts by weight, more than 40 parts by weight.

The composite of the SiO _x and the carbon material can be obtained, for example, by the following method.

First, a manufacturing method in the case of combining SiO _x will be described. A dispersion liquid in which SiO _x is dispersed in a dispersion medium is prepared, and sprayed and dried to produce composite particles including a plurality of particles. For example, ethanol or the like can be used as the dispersion medium. It is appropriate to spray the dispersion in an atmosphere of 50 to 300 ° C. In addition to the above method, similar composite particles can be produced also by a granulation method by a mechanical method using a vibration type or planetary type ball mill or rod mill.

Incidentally, the SiO _x, in the case of manufacturing a granulated body with small carbon material resistivity than SiO _x is adding the carbon material in the dispersion liquid of SiO _x are dispersed in a dispersion medium, the dispersion by using a liquid, by a similar method to the case of composite of SiO _x may be a composite particle (granule). Further, by granulation process according to the similar mechanical method, it is possible to produce a granular material of the SiO _x and the carbon material.

Next, when the surface of SiO _x particles (SiO _x composite particles or a granulated body of SiO _x and a carbon material) is coated with a carbon material to form a composite, for example, the SiO _x particles and the hydrocarbon-based material The gas is heated in the gas phase, and carbon generated by pyrolysis of the hydrocarbon-based gas is deposited on the surface of the particles. As described above, according to the vapor deposition (CVD) method, the hydrocarbon-based gas spreads to every corner of the composite particle, and the surface of the particle and the pores in the surface are thin and contain a conductive carbon material. Since a uniform film (carbon material coating layer) can be formed, the SiO _x particles can be imparted with good conductivity with a small amount of carbon material.

In the production of SiO _x coated with a carbon material, the processing temperature (atmosphere temperature) of the vapor deposition (CVD) method varies depending on the type of hydrocarbon gas, but usually 600 to 1200 ° C. is appropriate. Among these, the temperature is preferably 700 ° C. or higher, and more preferably 800 ° C. or higher. This is because the higher the treatment temperature, the less the remaining impurities, and the formation of a coating layer containing carbon having high conductivity.

  As the liquid source of the hydrocarbon-based gas, toluene, benzene, xylene, mesitylene and the like can be used, but toluene that is easy to handle is particularly preferable. A hydrocarbon-based gas can be obtained by vaporizing them (for example, bubbling with nitrogen gas). Moreover, methane gas, acetylene gas, etc. can also be used.

In addition, after the surface of SiO _x particles (SiO _x composite particles or a granulated body of SiO _x and a carbon material) is covered with a carbon material by a vapor deposition (CVD) method, a petroleum-based pitch or a coal-based pitch is used. At least one organic compound selected from the group consisting of a thermosetting resin and a condensate of naphthalene sulfonate and aldehydes is attached to a coating layer containing a carbon material, and then the organic compound is attached. The obtained particles may be fired.

Specifically, a dispersion liquid in which a SiO _x particle (SiO _x composite particle or a granulated body of SiO _x and a carbon material) coated with a carbon material and the organic compound are dispersed in a dispersion medium is prepared, The dispersion is sprayed and dried to form particles coated with the organic compound, and the particles coated with the organic compound are fired.

  An isotropic pitch can be used as the pitch, and a phenol resin, a furan resin, a furfural resin, or the like can be used as the thermosetting resin. As the condensate of naphthalene sulfonate and aldehydes, naphthalene sulfonic acid formaldehyde condensate can be used.

As a dispersion medium for dispersing the SiO _x particles coated with the carbon material and the organic compound, for example, water or alcohols (ethanol or the like) can be used. It is appropriate to spray the dispersion in an atmosphere of 50 to 300 ° C. The firing temperature is usually 600 to 1200 ° C., preferably 700 ° C. or higher, and more preferably 800 ° C. or higher. This is because the higher the processing temperature, the less the remaining impurities, and the formation of a coating layer containing a high-quality carbon material with high conductivity. However, the processing temperature needs to be lower than the melting point of SiO _x .

Examples of the graphitic carbon material used as the negative electrode active material together with the SiO _x include natural graphite such as scale-like graphite; graphitizable carbon such as pyrolytic carbons, mesophase carbon microbeads (MCMB), and carbon fibers. And artificial graphite graphitized at 2800 ° C. or higher.

The proportion of SiO _{x in} the total amount of the negative electrode active material is preferably 0.01% by mass or more, and preferably 1% by mass or more from the viewpoint of favorably securing the effect of increasing the capacity by using SiO _x. Is more preferable, and it is more preferable that it is 3 mass% or more. Further, from the viewpoint of better avoiding the problem due to the volume change of SiO _x due to charge / discharge, the proportion of SiO _{x in} the total amount of the negative electrode active material is preferably 20% by mass or less, and 15% by mass or less. It is more preferable.

  The negative electrode mixture layer usually contains a binder. For example, PVDF, polytetrafluoroethylene (PTFE), styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), or the like is suitably used for the binder related to the negative electrode mixture layer.

  Moreover, you may make the negative mix layer contain conductive assistants, such as various carbon blacks, such as acetylene black, and a carbon nanotube, as needed.

  The negative electrode is prepared, for example, by preparing a negative electrode mixture-containing composition in which a negative electrode active material and a binder and, if necessary, a conductive additive are dispersed in a solvent such as N-methyl-2-pyrrolidone (NMP) or water. (However, the binder may be dissolved in a solvent), which is applied to one or both sides of the current collector, dried, and then subjected to a step of performing a pressing process such as a calendar process if necessary. . The negative electrode is not limited to those manufactured by the above-described method, and may be manufactured by other manufacturing methods.

  The thickness of the negative electrode mixture layer is preferably 10 to 100 μm per side of the current collector per side of the current collector. Moreover, as a composition of a negative mix layer, it is preferable that the quantity of a negative electrode active material is 80-95 mass%, for example, it is preferable that the quantity of a binder is 1-20 mass%, and uses a conductive support agent. When it does, it is preferable that the quantity is 1-10 mass%.

  As the current collector for the negative electrode, a foil made of copper or nickel, a punching metal, a net, an expanded metal, or the like can be used, but a copper foil is usually used. In the negative electrode current collector, when the thickness of the entire negative electrode is reduced in order to obtain a battery having a high energy density, the upper limit of the thickness is preferably 30 μm, and the lower limit is preferably 5 μm.

  The positive electrode according to the nonaqueous electrolyte secondary battery of the present invention has a structure having a positive electrode mixture layer containing a positive electrode active material and a binder on one side or both sides of a current collector.

The positive electrode active material is a lithium-containing composite oxide containing nickel (Ni) as a transition metal element. When the amount of all transition metal elements is 100 (mol%), the nickel ratio a (mol%) However, 30 ≦ a ≦ 100 is used. The positive electrode active material has a larger capacity than, for example, LiCoO ₂ which is widely used as a positive electrode active material for nonaqueous electrolyte secondary batteries, and can increase the capacity of nonaqueous electrolyte secondary batteries. Further, the lithium-containing composite oxide containing Ni as the transition metal element has a better balance between the negative electrode mixture layer containing SiO _x and the graphitic carbon material and the expansion and contraction associated with charging / discharging of the battery than LiCoO _2. A positive electrode mixture layer can be formed.

  The lithium-containing composite oxide containing Ni as the transition metal element has a nickel ratio a (mol%) of 30 ≦ a ≦ 100 when the amount of all transition metal elements is 100 (mol%). It does not need to contain transition metal elements other than Ni, and may contain them. However, since it becomes possible to further improve the packing density in the positive electrode mixture layer or to increase the thermal stability of the lithium-containing composite oxide, the lithium-containing composite oxide containing Ni as the transition metal element Is preferably a lithium nickel cobalt manganese composite oxide containing cobalt (Co) and manganese (Mn) in addition to Ni as a transition metal element.

  The lithium nickel cobalt manganese composite oxide is preferably one represented by the following general composition formula (1).

Li _{1 + s} M ¹ O ₂ (1)
In [the general formula (1), a -0.3 ≦ s ≦ 0.3, ^{M 1} is a three or more element group including at least Ni, Co and Mn, each constituting ^{M 1} 30 <a <65, 5 <b <35, and 15 <c <50, where the ratios (mol%) of Ni, Co, and Mn in the element are a, b, and c, respectively. ]

In the lithium nickel cobalt manganese composite oxide represented by the general composition formula (1), Ni is a component that contributes to an increase in capacity of the lithium nickel cobalt manganese composite oxide, and the total number of elements of the element group M ¹ is 100 mol. %, The Ni ratio a is preferably over 30 mol%, more preferably 50 mol% or more. In addition, in the lithium nickel cobalt manganese composite oxide represented by the general composition formula (1), the total number of elements in the element group M ¹ is set to 100 mol from the viewpoint of satisfactorily securing the effect of containing an element other than Ni. %, The Ni ratio a is preferably less than 65 mol% and more preferably 60 mol% or less.

In the lithium nickel cobalt manganese composite oxide represented by the general composition formula (1), Co is a component that contributes to an increase in the capacity of the lithium nickel cobalt manganese composite oxide as well as Ni, and is filled in the positive electrode mixture layer. While it works to improve density, too much may cause an increase in cost and a decrease in safety. In addition to these reasons, all elements of the element group M ¹ in the general composition formula (1) representing the lithium nickel cobalt manganese composite oxide from the viewpoint of satisfactorily securing the action of stabilizing the average valence of Mn described later. When the number is 100 mol%, the Co ratio b is preferably more than 5 mol%, more preferably 20 mol% or more, and preferably less than 35 mol%, and 30 mol% or less. It is more preferable.

Furthermore, in a lithium-nickel-cobalt-manganese composite oxide, when the total number of elements in the element group ^{M 1} in the general formula (1) and 100 mol%, the ratio c of Mn, that is greater than 15 mol% preferably 20 mol% or more, more preferably less than 50 mol%, and even more preferably 30 mol% or less. By including Mn in the amount as described above in the lithium nickel cobalt manganese composite oxide, and making sure that Mn is present in the crystal lattice, the thermal stability of the lithium nickel cobalt manganese composite oxide can be improved. A highly safe battery can be configured.

  Furthermore, in the lithium nickel cobalt manganese composite oxide, Co acts together with Mn to suppress fluctuations in the valence of Mn due to Li doping and dedoping during battery charging / discharging. Therefore, the average valence of Mn can be stabilized at a value in the vicinity of tetravalence, and the reversibility of charge / discharge can be further enhanced. Therefore, by using such a lithium nickel cobalt manganese composite oxide, it becomes possible to constitute a battery having more excellent charge / discharge cycle characteristics.

In the lithium-nickel-cobalt-manganese composite oxide, the element group ^{M 1} is, Ni, may be composed only of Co and Mn, with these elements, Mg, Ti, Zr, Nb , Mo, W, Al, It may contain at least one element selected from the group consisting of Si, Ga, Ge, and Sn. However, when the total number of elements in the element group ^{M 1} was 100mol%, Mg, Ti, Zr , Nb, Mo, W, Al, Si, Ga, total proportion d of Ge and Sn are the following 5 mol% It is preferably 1 mol% or less. Elements other than Ni, Co, and Mn in the element group M ¹ may be uniformly distributed in the lithium nickel cobalt manganese composite oxide, or may be segregated on the particle surface or the like.

The lithium nickel cobalt manganese composite oxide having the above composition has a large true density of 4.55 to 4.95 g / cm ³ and is a material having a high volume energy density. The true density of the lithium nickel cobalt manganese composite oxide containing Mn in a certain range varies greatly depending on its composition. However, the structure is stabilized and the uniformity can be improved in the narrow composition range as described above. For example, it is considered to be a large value close to the true density of LiCoO ₂ . Moreover, the capacity | capacitance per mass of lithium nickel cobalt manganese complex oxide can be enlarged, and it can be set as the material excellent in reversibility.

The lithium nickel cobalt manganese composite oxide has a higher true density particularly when the composition is close to the stoichiometric ratio. Specifically, in the general composition formula (1), −0.3 ≦ s It is preferable that ≦ 0.3, and the true density and reversibility can be improved by adjusting the value of s in this way. s is more preferably −0.05 or more and 0.05 or less. In this case, the true density of the lithium nickel cobalt manganese composite oxide is set to a higher value of 4.6 g / cm ³ or more. Can do.

The lithium nickel cobalt manganese composite oxide represented by the general composition formula (1) includes a Li-containing compound (such as lithium hydroxide), a Ni-containing compound (such as nickel sulfate), a Co-containing compound (such as cobalt sulfate), and a Mn-containing compound. compound (such as manganese sulfate), and the element group M compound containing other element contained in ¹ (oxides, hydroxides, sulfates, etc.) can be produced by, for example, mixing, calcining. Further, in synthesizing the lithium-nickel-cobalt-manganese composite oxide with a higher purity, a composite compound containing a plurality of elements included in the element group M ¹ (hydroxides, such as an oxide) and mixing the Li-containing compound It is preferable to fire.

  Firing conditions can be, for example, 800 to 1050 ° C. for 1 to 24 hours, but once heated to a temperature lower than the firing temperature (for example, 250 to 850 ° C.) and maintained at that temperature, preheating is performed. After that, it is preferable to raise the temperature to the firing temperature to advance the reaction. Although there is no restriction | limiting in particular about the time of preheating, Usually, what is necessary is just to be about 0.5 to 30 hours. The atmosphere during firing can be an atmosphere containing oxygen (that is, in the air), a mixed atmosphere of an inert gas (such as argon, helium, or nitrogen) and oxygen gas, or an oxygen gas atmosphere. The oxygen concentration (volume basis) is preferably 15% or more, and more preferably 18% or more.

  As the positive electrode active material, only a lithium-containing composite oxide containing Ni as the transition metal element [preferably a lithium nickel cobalt manganese composite oxide, more preferably represented by the general composition formula (1)] is used. However, these lithium-containing composite oxides may be used in combination with other lithium-containing composite oxides.

  For example, lithium nickel cobalt manganese composite oxide and lithium cobalt composite oxide containing different metal elements other than lithium, nickel, cobalt and manganese are preferably used as the positive electrode active material.

  In this case, the lithium cobalt composite oxide includes a lithium cobalt composite oxide (A) having an average particle diameter A (μm) of more than 10 μm and 30 μm or less, and an average particle diameter B (μm) of 1 μm or more and 10 μm or less. The difference between the average particle size A of the lithium cobalt composite oxide (A) and the average particle size B of the lithium cobalt composite oxide (B) "A-B" Is preferably 5 (μm) or more. Further, in the lithium nickel cobalt manganese composite oxide, when the average particle diameter is C (μm), the relationship with the average particle diameter B of the lithium cobalt composite oxide (B) is C> B. Is preferably used.

  By using the lithium cobalt composite oxide (A) and the lithium cobalt composite oxide (B) as described above in combination with the lithium nickel cobalt manganese composite oxide, the lithium cobalt composite oxide ( A) and the lithium nickel cobalt manganese composite oxide particles can be filled with the lithium cobalt composite oxide (B) having a small particle diameter, so that the density of the positive electrode mixture layer is increased and the positive electrode in the positive electrode mixture layer. The amount of active material can be increased.

Moreover, the lithium nickel cobalt manganese composite oxide used as the positive electrode active material has higher stability under a high voltage than, for example, LiCoO _2. Further, the lithium cobalt composite oxide (A) and the lithium cobalt composite oxide (B ) Is improved in stability under a higher voltage than, for example, LiCoO ₂ by the action of the different metal element. Therefore, in addition to lithium nickel cobalt manganese composite oxide, when lithium cobalt composite oxide (A) and lithium cobalt composite oxide (B) are used as the positive electrode active material, the voltage is set at a final voltage of 4.3 V or more. Even if it is used in a method of performing current-constant voltage charging, the positive electrode active material is unlikely to deteriorate, so that the charge / discharge cycle characteristics of the nonaqueous electrolyte secondary battery can be further enhanced.

  The lithium nickel cobalt manganese composite oxide tends to cause gas generation in the battery, particularly when the particle size is small. However, the lithium-cobalt composite oxide (B), which is less likely to cause gas generation in the battery than the lithium-nickel-cobalt-manganese composite oxide, in the positive-electrode active material having a small particle diameter that enters the gap between the positive-electrode active material particles having a large particle size. By using, for example, the occurrence of swelling during storage can be suppressed. Therefore, when lithium cobalt composite oxide (A) and lithium cobalt composite oxide (B) are used as the positive electrode active material in addition to lithium nickel cobalt manganese composite oxide, the storage characteristics of the nonaqueous electrolyte secondary battery Will also be good.

  The average particle diameter A of the lithium cobalt composite oxide (A) is more preferably 17 μm or more, and more preferably 24 μm or less. Furthermore, the average particle diameter B of the lithium cobalt composite oxide (B) is more preferably 5 μm or more, and more preferably 10 μm or less.

  The average particle size of the lithium nickel cobalt manganese composite oxide is preferably 10 μm or more, more preferably 11 μm or more, and preferably 17 μm or less, more preferably 16 μm or less. .

  The average particle diameter A of the lithium cobalt composite oxide (A), the average particle diameter B of the lithium cobalt composite oxide (B), and the average particle diameter C (μm) of the lithium nickel cobalt manganese composite oxide are A ≧ It is preferable that the relationship C> B is satisfied, and it is more preferable that the relationship A> C> B is satisfied. In this case, the effect of increasing the filling amount of the positive electrode active material by improving the density of the positive electrode mixture layer, the effect of improving the charge / discharge cycle characteristics accompanying the improvement of the stability of the positive electrode active material, the particle size of the lithium nickel cobalt manganese composite oxide The effect of improving the storage characteristics by increasing the amount to some extent can be secured more favorably.

The average particle size of the lithium cobalt composite oxide (A), lithium cobalt composite oxide (B), and lithium nickel cobalt manganese composite oxide referred to in this specification is the Nikkiso Co., Ltd. Microtrac particle size distribution measuring device “HRA9320”. It is a 50% diameter value (d ₅₀ ) median diameter in the volume-based integrated fraction when the integrated volume is obtained from particles having a small particle size distribution measured by use.

  In the lithium cobalt composite oxide (A) having the average particle size A and the lithium cobalt composite oxide (B) having the average particle size B, the total amount of cobalt and the different metal element is The proportion of the different metal element is preferably greater in the lithium cobalt composite oxide (B) than in the lithium cobalt composite oxide (A).

  As the particle size of the lithium cobalt composite oxide is smaller, the stability under high voltage and the stability against heat are inferior. Therefore, the lithium cobalt composite oxide (B) having a smaller average particle size contains a large amount of the different metal element having an effect of enhancing the stability, thereby charging / discharging the battery and heat stability. It is possible to improve the charge / discharge cycle characteristics and storage characteristics of the nonaqueous electrolyte secondary battery.

  However, since the dissimilar metal element is a component that cannot contribute to the capacity of the lithium cobalt composite oxide, when the amount in the lithium cobalt composite oxide increases, the capacity of the lithium cobalt composite oxide decreases. Therefore, in the lithium cobalt composite oxide (A) having a larger average particle size and higher stability, the capacity reduction due to the inclusion of the different metal element is made possible by reducing the content of the different metal element. It is possible to further improve the balance between stability and capacity.

  The lithium cobalt composite oxide (A) and the lithium cobalt composite oxide (B) are preferably those represented by the following general composition formula (2).

Li _{1 + y} Co _z M ² _1-z O ₂ (2)
[In the general composition formula (2), −0.3 ≦ y ≦ 0.3, 0.95 ≦ z <1.0, and M ² is selected from the group consisting of Mg, Zr, Al, and Ti. At least one element. ]

In the general composition formula (2), M ² corresponds to the different metal element. The different metal element M ² contained in the lithium cobalt composite oxide (A) and the lithium cobalt composite oxide (B) may be any of Mg, Zr, Al, and Ti as described above, and one of these or Two or more types may be used, but since the lithium cobalt composite oxide (A) and the lithium cobalt composite oxide (B) are more effective in increasing the stability and thermal stability under high voltage, Mg And / or Zr is more preferred.

Incidentally, the lithium-cobalt composite oxide (A) and lithium cobalt composite oxide in (B), Co While a component contributing to the capacity increase, different metal elements M ² can not contribute to the capacity increase. Therefore, in the general composition formula (2) representing the lithium cobalt composite oxide (A) and the lithium cobalt composite oxide (B), the amount z of Co is set to 0.95 from the viewpoint of keeping these capacities high. The above is preferable. Further, in the general composition formula (2), the amount of Co z is less than 1.0, but from the viewpoint of better ensuring the above-mentioned effect by containing the different metal element M ² , the different metal element The amount “1-z” of M ² is more preferably 0.005 or more, and therefore the amount z of Co is more preferably 0.995 or less.

When the lithium cobalt composite oxide (A) and the lithium cobalt composite oxide (B) are those represented by the general composition formula (2), the lithium cobalt composite oxide (A) and the lithium cobalt composite oxide ( B) and, as the different metal elements M ^2, also contain the same elements may contain different elements, lithium cobalt composite oxides the amount of different metal elements M ² containing the (a) and "1-z1", lithium-cobalt composite oxide the amount of different metal elements ^{M 2} containing the (B) is taken as "1-z2", the relationship of (1-z1) <(1 -z2) It only has to satisfy. More specifically, “1-z1” is more preferably 0.01 or more, and further preferably 0.02 or less. “1-z2” is more preferably 0.02 or more, and further preferably 0.03 or less.

  The lithium cobalt composite oxide (A) and the lithium cobalt composite oxide (B) have a higher true density and a higher energy volume density, particularly when the composition is close to the stoichiometric ratio. Specifically, in the composition formula, it is preferable to satisfy −0.3 ≦ y ≦ 0.3, and by adjusting the value of y in this way, the true density and reversibility at the time of charge / discharge are improved. Can do.

Lithium cobalt composite oxide (A) and lithium cobalt composite oxide (B) is, Li-containing compound (lithium hydroxide, etc.), Co-containing compound (such as cobalt sulfate), and compounds containing different metallic element M ¹ (oxidation Compound, hydroxide, sulfate, etc.) and the raw material mixture can be fired. In order to synthesize lithium cobalt composite oxide (A) and lithium cobalt composite oxide (B) with higher purity, a composite compound (hydroxide, oxide, etc.) containing Co and a different metal element M ¹ is used. It is preferable to mix a Li-containing compound and the like and to fire this raw material mixture.

  The firing conditions of the raw material mixture for synthesizing the lithium cobalt composite oxide (A) and the lithium cobalt composite oxide (B) can be, for example, 800 to 1050 ° C. for 1 to 24 hours. It is preferable to preheat by heating to lower temperature (for example, 250-850 degreeC), and hold | maintaining at that temperature, and to raise temperature to a calcination temperature after that, and to advance reaction. Although there is no restriction | limiting in particular about the time of preheating, Usually, what is necessary is just to be about 0.5 to 30 hours. The atmosphere during firing can be an atmosphere containing oxygen (that is, in the air), a mixed atmosphere of an inert gas (such as argon, helium, or nitrogen) and oxygen gas, or an oxygen gas atmosphere. The oxygen concentration (volume basis) is preferably 15% or more, and more preferably 18% or more.

  In a non-aqueous electrolyte secondary battery, when lithium cobalt composite oxide (A) and lithium cobalt composite oxide (B) are used as the positive electrode active material, lithium cobalt composite oxide (A) and lithium cobalt composite oxide are used. When the total with the product (B) is 100% by mass, the content of the lithium cobalt composite oxide (A) is preferably 50% by mass or more, more preferably 70% by mass or more. , Preferably less than 100% by mass, more preferably 90% by mass or less.

  In the case of using lithium nickel cobalt manganese composite oxide, lithium cobalt composite oxide (A) and lithium cobalt composite oxide (B) in the nonaqueous electrolyte secondary battery, lithium nickel cobalt manganese composite oxide When the total of lithium cobalt complex oxide (A) and lithium cobalt complex oxide (B) is 100% by mass, the content of lithium nickel cobalt manganese complex oxide is preferably 15% by mass or more. 20 mass% or more, more preferably 45 mass% or less, and even more preferably 30 mass% or less.

  As the positive electrode active material, an active material other than the lithium cobalt composite oxide (A) and the lithium cobalt composite oxide (B), a lithium-containing composite oxide containing Ni as the transition metal element [preferably lithium Nickel cobalt manganese composite oxide, more preferably those represented by the general composition formula (1)]. In this case, for example, a lithium-containing composite oxide containing Ni as the transition metal element [preferably a lithium nickel cobalt manganese composite oxide, more preferably represented by the general composition formula (1)] and other active materials May be used, and lithium nickel cobalt manganese composite oxide, lithium cobalt composite oxide (A), lithium cobalt composite oxide (B), and other active materials may be used.

Examples of such other active materials include LiCoO ₂ ; lithium manganese oxides such as LiMnO ₂ and Li ₂ MnO ₃ ; lithium having a spinel structure such as LiMn ₂ O ₄ and Li _4/3 Ti _5/3 O _4. Olivine-structured lithium-containing composite oxides such as LiFePO ₄ ; oxides obtained by substituting the above-mentioned oxides with basic elements and various elements; and one or more of these can be exemplified. Can be used.

  However, from the viewpoint of ensuring the effect of the present invention satisfactorily, the content of the other active material in the total amount of the positive electrode active material is preferably 10% by mass or less, and more preferably 5% by mass or less. preferable.

VDF-CTFE is used for the binder related to the positive electrode mixture layer. The positive electrode mixture layer containing a lithium-containing composite oxide containing Ni as the transition metal element, which is a positive electrode active material, includes a negative electrode mixture layer containing SiO _x and a graphitic carbon material as a negative electrode active material, and a battery charge. The balance of expansion and contraction associated with discharge is better than, for example, a positive electrode mixture layer containing LiCoO ₂ as a positive electrode active material. However, in addition to the use of such a positive electrode active material, when VDF-CTFE is used for the binder of the positive electrode mixture layer, for example, a polyfluoride widely used as a binder of the positive electrode mixture layer of a nonaqueous electrolyte secondary battery. Compared with the case where vinylidene (PVDF) is used, the distance between the positive electrode and the negative electrode can be maintained in a more uniform state over the entire facing surfaces. This is because VDF-CTFE has a higher action to relieve this volume change when the positive electrode mixture layer receives expansion and contraction of the negative electrode mixture layer that occurs as a result of charging / discharging of the battery, compared with PVDF, for example. It is estimated that.

  When the density of the positive electrode mixture layer is increased by using the lithium cobalt composite oxide (A) and the lithium cobalt composite oxide (B) and the lithium nickel cobalt manganese composite oxide as described above, Since the hardness of the positive electrode mixture layer is increased, for example, when the positive electrode and the negative electrode are overlapped with a separator and wound in a spiral shape, a wound electrode body (especially a wound electrode body having a flat cross section) is produced. , Cracks are likely to occur in the positive electrode mixture layer. However, since VDF-CTFE used as a binder for the positive electrode mixture layer in the present invention has an action to relieve the applied stress superior to, for example, PVDF, the structure of the positive electrode active material is the positive electrode as described above. Even if the density of the mixture layer is increased, the occurrence of cracking of the positive electrode mixture layer in the wound electrode body (particularly, the wound electrode body having a flat cross section) can be suppressed.

  Further, when PVDF is used as a binder, defluorination occurs after the battery is formed, and this reacts with moisture inevitably mixed in the battery to generate hydrogen fluoride, which is caused by corrosion of the positive electrode active material by hydrogen fluoride. Elution of metal ions such as Co and Mn may occur. In the configuration of the present invention, generation of such hydrogen fluoride can also be suppressed, and thereby an effect of improving battery characteristics such as charge / discharge cycle characteristics can be expected.

  The composition of VDF-CTFE used for the positive electrode mixture layer is such that the unit derived from vinylidene fluoride is used in order to better ensure the effect of improving the charge / discharge cycle characteristics of the nonaqueous electrolyte secondary battery by using VDF-CTFE. When the total with the unit derived from chlorotrifluoroethylene is 100 mol%, the ratio of the unit derived from chlorotrifluoroethylene is preferably 0.5 mol% or more, and more preferably 1 mol% or more. However, if the proportion of units derived from chlorotrifluoroethylene in VDF-CTFE becomes too high, the nonaqueous electrolyte (nonaqueous electrolyte) is easily absorbed and swelled, and the characteristics of the positive electrode may be deteriorated. Therefore, in VDF-CTFE used for the positive electrode mixture layer, when the total of the units derived from vinylidene fluoride and the units derived from chlorotrifluoroethylene is 100 mol%, the ratio of the units derived from chlorotrifluoroethylene is 15 mol% or less is preferable.

  As a binder related to the positive electrode mixture layer, only VDF-CTFE may be used, and a non-aqueous electrolyte secondary such as VDF-CTFE and another binder (for example, a fluorine resin other than VDF-CTFE such as PVDF). You may use together the binder used widely by the positive mix layer of a battery. However, from the viewpoint of better ensuring the above-described effects by using VDF-CTFE, the amount of binder other than VDF-CTFE in the total amount of binder in the positive electrode mixture layer is preferably 50% by mass or less. .

  The positive electrode mixture layer usually contains a conductive additive. Examples of the conductive auxiliary agent related to the positive electrode mixture layer include graphites such as natural graphite (flaky graphite, etc.) and artificial graphite; acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, etc. It is preferable to use carbon materials such as carbon blacks; carbon fibers; and conductive fibers such as metal fibers; carbon fluorides; metal powders such as aluminum; zinc oxide; Conductive whiskers; conductive metal oxides such as titanium oxide; organic conductive materials such as polyphenylene derivatives; and the like can also be used.

  The thickness of the positive electrode mixture layer is preferably, for example, 10 to 100 μm per one side of the current collector. Moreover, as a composition of a positive mix layer, it is preferable that the quantity of a positive electrode active material is 60-95 mass%, for example, it is preferable that the quantity of a binder is 1-15 mass%, and the quantity of a conductive support agent. Is preferably 3 to 20% by mass.

  The current collector of the positive electrode is the same as that used for the positive electrode of a conventionally known non-aqueous electrolyte secondary battery, for example, aluminum (including an aluminum alloy. The same applies hereinafter unless otherwise specified) .) Made of punching metal, net, expanded metal, etc. can be used, but an aluminum foil having a thickness of 10 to 30 μm is preferred.

  The nonaqueous electrolyte secondary battery of the present invention has a positive electrode, a negative electrode, a nonaqueous electrolyte, and a separator, the negative electrode is the negative electrode, and the positive electrode is the positive electrode. Other configurations and structures There is no particular limitation on the above, and various configurations and structures employed in conventionally known nonaqueous electrolyte secondary batteries can be applied.

  The separator according to the nonaqueous electrolyte secondary battery of the present invention is a separator used in a normal nonaqueous electrolyte secondary battery, for example, a microporous membrane made of polyolefin such as polyethylene (PE) or polypropylene (PP). Can be used. The microporous film constituting the separator may be, for example, one using only PE or one using PP, or a laminate of a PE microporous film and a PP microporous film. There may be.

  Moreover, you may use the laminated separator which formed the heat resistant porous layer containing a heat resistant inorganic filler on the surface of the said microporous film. When such a stacked separator is used, the shrinkage of the separator is suppressed even when the temperature in the battery rises, and a short circuit due to contact between the positive electrode and the negative electrode can be suppressed. A high nonaqueous electrolyte secondary battery can be obtained.

  As the inorganic filler to be contained in the heat-resistant porous layer, boehmite, alumina, silica and the like are preferable, and one or more of them can be used.

  The heat-resistant porous layer preferably contains a binder for binding the inorganic fillers or bonding the heat-resistant porous layer and the microporous film. The binder includes an ethylene-vinyl acetate copolymer (EVA, having a structural unit derived from vinyl acetate of 20 to 35 mol%), an ethylene-acrylic acid copolymer such as an ethylene-ethyl acrylate copolymer, and a fluorine-based rubber. Styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polyvinyl pyrrolidone (PVP), cross-linked acrylic resin, polyurethane, epoxy resin, etc. Are preferred, and one or more of these can be used.

  The thickness of the separator (a separator made of a microporous membrane made of polyolefin, or the laminated separator) is preferably 10 to 30 μm, for example. In the case of the laminated separator, the heat-resistant porous layer preferably has a thickness of 3 to 8 μm, for example.

For the nonaqueous electrolyte according to the nonaqueous electrolyte secondary battery of the present invention, for example, a solution (nonaqueous electrolyte) in which a lithium salt is dissolved in an organic solvent can be used. The lithium salt is not particularly limited as long as it dissociates in a solvent to form Li ⁺ ions and hardly causes side reactions such as decomposition in a voltage range used as a battery. For example, LiClO ₄ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiSbF ₆ and other inorganic lithium salts, LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , Li ₂ C ₂ F ₄ (SO ₃ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiC _n F _{2n + 1} SO ₃ (n ≧ 2), LiN (RfOSO ₂ ) ₂ [where Rf is a fluoroalkyl group] and the like can be used. .

  The organic solvent used for the non-aqueous electrolyte is not particularly limited as long as it dissolves the lithium salt and does not cause a side reaction such as decomposition in a voltage range used as a battery. For example, cyclic carbonates such as ethylene carbonate, propylene carbonate, and butylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate; chain esters such as methyl propionate; cyclic esters such as γ-butyrolactone; dimethoxyethane; Chain ethers such as diethyl ether, 1,3-dioxolane, diglyme, triglyme and tetraglyme; cyclic ethers such as dioxane, tetrahydrofuran and 2-methyltetrahydrofuran; nitriles such as acetonitrile, propionitrile and methoxypropionitrile; ethylene Sulfites such as glycol sulfite; and the like. These may be used in combination of two or more. In order to obtain a battery with better characteristics, it is desirable to use a combination that can obtain high conductivity, such as a mixed solvent of ethylene carbonate and chain carbonate. In addition, for the purpose of improving safety such as improvement of charge / discharge cycle characteristics, high-temperature storage properties and prevention of overcharge, these non-aqueous electrolytes may be used in acid anhydrides, sulfonic acid esters, dinitriles, vinylene carbonates, 1,3- Additives (including these derivatives) such as propane sultone, diphenyl disulfide, cyclohexylbenzene, biphenyl, fluorobenzene, and t-butylbenzene may be added as appropriate.

  The concentration of the lithium salt in the non-aqueous electrolyte is preferably 0.5 to 1.5 mol / l, and more preferably 0.9 to 1.25 mol / l.

  Moreover, you may use for the nonaqueous electrolyte secondary battery of this invention what added gelling agents, such as a well-known polymer, to the said nonaqueous electrolyte solution, and was made into the gel form (gel electrolyte).

  Examples of the form of the non-aqueous electrolyte secondary battery of the present invention include a tubular shape (such as a square tubular shape or a cylindrical shape) using a steel can or an aluminum can as an outer can. Moreover, it can also be set as the soft package battery which used the laminated film which vapor-deposited the metal as an exterior body.

  Since the nonaqueous electrolyte secondary battery of the present invention has a high capacity and excellent charge / discharge cycle characteristics, it can be preferably used for applications requiring such characteristics, and conventionally known nonaqueous electrolytes It can also be used for various applications to which secondary batteries are applied.

  Hereinafter, the present invention will be described in detail based on examples. However, the following examples do not limit the present invention.

Example 1
<Synthesis of lithium composite oxide>
Nickel sulfate, cobalt sulfate, manganese sulfate and magnesium sulfate, ^{respectively, 3.78mol / dm 3, 0.25mol /} dm 3, 0.08mol / dm 3, a mixed aqueous solution containing a concentration of 0.08 mol / dm ³ Prepared. Next, ammonia water whose pH was adjusted to about 12 by addition of sodium hydroxide was put into a reaction vessel, and while stirring it vigorously, the mixed aqueous solution and 25% by mass concentration of ammonia water were respectively added thereto. , 23 cm ³ / min, and 6.6 cm ³ / min at a rate of dropwise addition using a metering pump to synthesize a coprecipitation compound of Ni, Co, Mn, and Mg (spherical coprecipitation compound). At this time, the temperature of the reaction solution is maintained at 50 ° C., and a 3 mol / dm ³ concentration sodium hydroxide aqueous solution is simultaneously dropped so that the pH of the reaction solution is maintained at around 12, and further nitrogen is added. Gas was bubbled at a flow rate of 1 dm ³ / min.

The coprecipitated compound was washed with water, filtered and dried to obtain a hydroxide. This hydroxide, LiOH.H ₂ O, BaSO ₄ and Al (OH) ₃ are mixed in ethanol so that the molar ratio is 1: 1: 0.01: 0.01. After being dispersed to form a slurry, the mixture was mixed for 40 minutes with a planetary ball mill and dried at room temperature to obtain a mixture. Next, the mixture is put in an alumina crucible, heated to 600 ° C. in a dry air flow of 2 dm ³ / min, kept at that temperature for 2 hours for preheating, further heated to 900 ° C. and heated to 12 ° C. The lithium-containing composite oxide was synthesized by firing for a period of time.

  The obtained lithium-containing composite oxide was washed with water, heat-treated at 700 ° C. for 12 hours in the air (oxygen concentration of about 20 vol%), and then pulverized in a mortar to obtain a powder. The lithium-containing composite oxide after pulverization was stored in a desiccator.

About the said lithium containing complex oxide, the composition analysis was performed as follows using ICP (Inductively Coupled Plasma) method. First, 0.2 g of the lithium-containing composite oxide was collected and placed in a 100 mL container. Thereafter, 5 mL of pure water, 2 mL of aqua regia, and 10 mL of pure water were added in order and dissolved by heating. After cooling, the mixture was further diluted 25 times and analyzed by ICP (“ICP-757” manufactured by JARRELASH) (calibration). Line method). From the obtained results, the composition of the lithium-containing composite oxide was derived. As a result, Li _1.0 Ni _0.89 Co _0.05 Mn _0.02 Mg _0.02 Ba _0.01 Al _0.01 O ₂ It was found to be the represented composition. Moreover, the average particle diameter of the said lithium nickel cobalt manganese complex oxide was 15 micrometers.

<Synthesis of lithium cobalt composite oxide (A)>
Co (OH) ₂ , Mg (OH) ₂ , Al (OH) ₃ and Li ₂ CO ₃ were mixed at a molar ratio of 1.97: 0.02: 0.01: 1.02. The mixture was heat-treated at 950 ° C. for 12 hours in the atmosphere (oxygen concentration of about 20 vol%) to synthesize lithium cobalt composite oxide (A), and then pulverized in a mortar to obtain a powder. The lithium cobalt composite oxide (A) after pulverization was stored in a desiccator.

For the lithium cobalt composite oxide (A), that the composition analysis is a composition represented by _{Li 1.0 Co 0.985 Mg 0.01 Al 0.005} O 2 was performed using the ICP method There was found. The average particle size of the lithium cobalt composite oxide (A) was 20 μm.

<Synthesis of lithium cobalt composite oxide (B)>
Co _{(OH) 2} and Mg _{(OH) 2} and Al _{(OH) 3} and a molar ratio of the ZrO ₂ and _{Li 2 CO 3 1.946: 0.03:} 0.02: 0.004: 1.02 The mixture was heat-treated at 950 ° C. for 12 hours to synthesize lithium cobalt composite oxide (B) in the atmosphere (oxygen concentration of about 20 vol%), and then pulverized in a mortar to obtain a powder. . The lithium cobalt composite oxide (B) after pulverization was stored in a desiccator.

The lithium-cobalt composite oxide for (B), the composition analysis, is represented by _{Li 1.0 Co 0.973 Mg 0.015 Al 0.01} Zr 0.002 O 2 was performed using the ICP method It turned out to be a composition. Moreover, the average particle diameter of the said lithium cobalt complex oxide (B) was 8 micrometers.

<Preparation of positive electrode>
74 parts by mass of a mixture obtained by mixing the lithium cobalt composite oxide (A) and the lithium cobalt composite oxide (B) at a mass ratio of 80:20; 18 parts by mass of the lithium nickel cobalt manganese composite oxide; NMP solution containing VDF-CTFE as a binder at a concentration of 3% by mass: 20 parts by mass, artificial graphite as a conductive auxiliary agent: 1.5 parts by mass and Ketjen black: 1.5 parts by mass A positive electrode mixture-containing paste was prepared by kneading using a shaft kneader and further adjusting the viscosity by adding NMP.

After coating the positive electrode mixture-containing paste on both surfaces of an aluminum foil (positive electrode current collector) having a thickness of 15 μm, vacuum drying is performed at 120 ° C. for 12 hours to form a positive electrode mixture layer on both surfaces of the aluminum foil. did. Thereafter, press treatment was performed to adjust the thickness and density of the positive electrode mixture layer, and a lead body made of nickel was welded to the exposed portion of the aluminum foil to produce a 54 mm strip-shaped positive electrode. The total thickness of the positive electrode mixture layer in the obtained positive electrode was 145 μm, and the density of the positive electrode mixture layer was 3.85 g / cm ³ .

<Production of negative electrode>
Complex the SiO surface is coated with a carbon material average particle size d ₅₀ is a negative electrode active material is 8μm and (amount of 10% by weight of the carbon material in the composite), graphite average particle diameter D50% is 16μm A mixture in which the amount of the composite whose SiO surface is coated with a carbon material is 3.75% by mass: 97.5 parts by mass, SBR as a binder: 1.5 parts by mass, and a thickener Certain carboxymethyl cellulose: 1 part by mass of water was added and mixed to prepare a negative electrode mixture-containing paste.

  After applying the negative electrode mixture-containing paste to both sides of a copper foil (negative electrode current collector) having a thickness of 8 μm, vacuum drying is performed at 120 ° C. for 12 hours to form a negative electrode mixture layer on both sides of the copper foil. did. Thereafter, press treatment was performed to adjust the thickness and density of the negative electrode mixture layer, and a nickel lead body was welded to the exposed portion of the copper foil to produce a strip-shaped negative electrode having a width of 55 mm. The total thickness of the negative electrode mixture layer in the obtained negative electrode was 136 μm.

<Battery assembly>
Next, the negative electrode and the positive electrode are overlapped via a microporous polyethylene film separator (thickness 18 μm, porosity 50%) and wound into a roll, and then terminals are connected to the positive and negative electrodes. It welded and inserted in the aluminum alloy exterior can of thickness 49mm, width 42mm, and height 61mm (494261 type | mold), and the lid was welded and attached. Thereafter, non-aqueous electrolysis prepared by further dissolving LiPF ₆ to 1 mol% in a solution in which 3% by mass of vinylene carbonate was dissolved in EC: DEC = 3: 7 (volume ratio) from the liquid inlet of the lid. The liquid was poured into the container and sealed to obtain a rectangular non-aqueous secondary battery having the structure shown in FIG. 1 and the appearance shown in FIG.

  Here, the battery shown in FIGS. 1 and 2 will be described. FIG. 1A is a plan view, and FIG. 1B is a partial cross-sectional view thereof. As shown in FIG. 2 is spirally wound through the separator 3 and then pressed to form a flat shape to form a flat wound electrode body 6 in a rectangular (square tube) battery case 4 together with a non-aqueous electrolyte. Contained. However, in FIG. 1, in order to avoid complication, a metal foil, a non-aqueous electrolyte, or the like as a current collector used for manufacturing the positive electrode 1 and the negative electrode 2 is not illustrated.

  The battery case 4 is made of an aluminum alloy and constitutes an outer package of the battery. The battery case 4 also serves as a positive electrode terminal. And the insulator 5 which consists of PE sheets is arrange | positioned at the bottom part of the battery case 4, and it connects to each one end of the positive electrode 1 and the negative electrode 2 from the flat wound electrode body 6 which consists of the positive electrode 1, the negative electrode 2, and the separator 3. The positive electrode lead body 7 and the negative electrode lead body 8 thus drawn are drawn out. A stainless steel terminal 11 is attached to a sealing lid plate 9 made of aluminum alloy for sealing the opening of the battery case 4 via a polypropylene insulating packing 10, and an insulator 12 is attached to the terminal 11. A stainless steel lead plate 13 is attached.

  And this cover plate 9 is inserted in the opening part of the battery case 4, and the opening part of the battery case 4 is sealed by welding the joint part of both, and the inside of the battery is sealed. Further, in the battery of FIG. 1, a non-aqueous electrolyte inlet 14 is provided in the cover plate 9, and a sealing member is inserted into the non-aqueous electrolyte inlet 14, for example, laser welding or the like. As a result, the battery is sealed by welding. Further, the lid plate 9 is provided with a cleavage vent 15 as a mechanism for discharging the internal gas to the outside when the temperature of the battery rises.

  In the battery of this Example 1, the outer can 5 and the cover plate 9 function as a positive electrode terminal by directly welding the positive electrode lead body 7 to the lid plate 9, and the negative electrode lead body 8 is welded to the lead plate 13, The terminal 11 functions as a negative electrode terminal by conducting the negative electrode lead body 8 and the terminal 11 through the lead plate 13, but depending on the material of the battery case 4, the sign may be reversed. There is also.

  FIG. 2 is a perspective view schematically showing the external appearance of the battery shown in FIG. 1. FIG. 2 is shown for the purpose of showing that the battery is a square battery. FIG. 1 schematically shows a battery, and only specific members of the battery are shown. Also in FIG. 1, the inner peripheral portion of the electrode body is not cross-sectional.

Example 2
<Synthesis of lithium nickel cobalt manganese composite oxide>
Aqueous ammonia whose pH was adjusted to about 12 by adding sodium hydroxide was placed in a reaction vessel, and while vigorously stirring, nickel sulfate, cobalt sulfate and manganese sulfate were each added to 2.0 mol / dm ^3. , 0.8 mol ^/ dm 3, a mixed aqueous solution containing a concentration of 1.2 mol / dm ^3, and aqueous ammonia 25% strength by weight, respectively, 23cm ³ / min at a rate of 6.6 cm ³ / min, The solution was added dropwise using a metering pump to synthesize a coprecipitation compound of Ni, Co, and Mn (spherical coprecipitation compound). At this time, the temperature of the reaction solution is kept at 50 ° C., and a sodium hydroxide aqueous solution having a concentration of 6.4 mol / dm ³ is dropped at the same time so that the pH of the reaction solution is maintained around 12. Further, nitrogen gas was bubbled at a flow rate of 1 dm ³ / min.

The coprecipitated compound was washed with water, filtered and dried to obtain a hydroxide containing Ni, Co and Mn in a molar ratio of 5: 2: 3. 0.196 mol of this hydroxide and 0.204 mol of LiOH.H ₂ O were dispersed in ethanol to form a slurry, and then mixed with a planetary ball mill for 40 minutes and dried at room temperature to obtain a mixture. . Next, the mixture is put in an alumina crucible, heated to 600 ° C. in a dry air flow of 2 dm ³ / min, kept at that temperature for 2 hours for preheating, further heated to 900 ° C. and heated to 12 ° C. Lithium nickel cobalt manganese composite oxide was synthesized by firing for a period of time.

  The lithium nickel cobalt manganese composite oxide was washed with water, then heat-treated in the atmosphere (oxygen concentration of about 20 vol%) at 850 ° C. for 12 hours, and then pulverized in a mortar to obtain a powder. The lithium nickel cobalt manganese composite oxide after pulverization was stored in a desiccator.

About the said lithium nickel cobalt manganese complex oxide, the composition analysis was performed as follows using ICP method. First, 0.2 g of the lithium nickel cobalt manganese composite oxide was sampled and placed in a 100 mL container. Thereafter, 5 mL of pure water, 2 mL of aqua regia, and 10 mL of pure water were added in order and dissolved by heating. After cooling, the mixture was further diluted 25 times and analyzed by ICP (“ICP-757” manufactured by JARRELASH) (calibration). Line method). From the obtained results, the composition of the lithium nickel cobalt manganese composite oxide was derived and found to be a composition represented by Li _1.02 Ni _0.5 Co _0.2 Mn _0.3 O ₂ . . Moreover, the average particle diameter of the said lithium nickel cobalt manganese complex oxide was 15 micrometers.

  A positive electrode was produced in the same manner as in Example 1 except that the nickel-cobalt-manganese composite oxide was changed to that described above, and a nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that this positive electrode was used.

Comparative Example 1
A positive electrode was produced in the same manner as in Example 1 except that the binder was changed to PVDF, and a nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that this positive electrode was used.

Comparative Example 2
A positive electrode was produced in the same manner as in Example 2 except that the binder was changed to PVDF, and a nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that this positive electrode was used.

  The following evaluations were performed on the nonaqueous electrolyte secondary batteries of Examples and Comparative Examples.

<Battery capacity>
About each battery of an Example and a comparative example, it charges until it reaches 4.35V with a constant current of 1C at the normal temperature (25 ° C.) after the first charge / discharge, and then charges with a constant voltage of 4.35V-constant current-constant Voltage charge (total charge time: 2.5 hours) was performed, and then 0.2 C constant current discharge (discharge end voltage: 3.0 V) was performed, and the obtained discharge capacity (mAh) was defined as the battery capacity.

<Charge / discharge cycle characteristics>
About each battery of an Example and a comparative example, after first charge / discharge, charging / discharging is repeated 1000 cycles by making a series of operation of charge and discharge of the same conditions as measurement of battery capacity into 1 cycle, 200th cycle, 400th cycle, 600th cycle The capacity maintenance rate was calculated | required by measuring the discharge capacity in the cycle, the 800th cycle, and the 1000th cycle, and expressing each discharge capacity by the discharge capacity obtained in the first cycle in percentage. It means that the larger the value of the capacity retention rate, the better the charge / discharge cycle characteristics of the battery.

<60 ° C storage test (battery expansion)>
About each battery of an Example and a comparative example, it charged on the same conditions as the measurement of battery capacity after initial charge / discharge. After charging, measured in advance thickness T ₁ of the battery outer can, then left, after a predetermined time stored in a thermostatic chamber set at 60 ° C. the cells, taken out from the constant temperature bath, 1 minute at room temperature later, to measure the thickness T ₂ of the battery outer can again. In addition, the battery outer can thickness said in this test means the thickness between the wide surfaces of the side part of an outer can. The thickness of the battery outer can was measured in units of 1/100 mm using a vernier caliper (“CD-15CX” manufactured by Mitutoyo Corporation) with the central portion of the wide surface as the measurement target. In addition, the storage days in a thermostat shall be 1, 10, 20, 40, 60, and 80 days, and for each different battery, the thickness T of the battery outer can after each storage period has elapsed. ₂ was measured.

The battery swelling was evaluated from the rate of change to the outer can thickness T ₁ and T ₂ before and after storage relative to the outer can thickness T ₁ before storage at 60 ° C. That is, the battery swelling (%) was obtained by the following formula.
Battery swelling (%) = 100 × (T ₂ −T ₁ ) / (T ₁ )

  The evaluation results are shown in Tables 1 and 2.

As shown in Table 1 and Table 2, SiO _x and graphitic carbon material are used for the negative electrode active material, lithium-containing composite oxide containing Ni as a transition metal is used for the positive electrode active material, and the positive electrode mixture layer The batteries of Examples 1 and 2 using VDF-CTFE as the binder were compared with the batteries of Comparative Examples 1 and 2 using PVDF as the binder relating to the positive electrode mixture layer in each cycle number at the time of charge / discharge cycle evaluation. The capacity retention rate is high, the charge / discharge cycle characteristics are good, and the amount of swelling is small and the storage characteristics are also good when the storage characteristics are evaluated, particularly when the storage days are long.

1 Positive electrode 2 Negative electrode 3 Separator

Claims (7)

A non-aqueous electrolyte secondary battery having a positive electrode, a negative electrode, a non-aqueous electrolyte and a separator,
The positive electrode has a positive electrode mixture layer containing a positive electrode active material and a binder on one side or both sides of a current collector,
The positive electrode mixture layer contains a lithium nickel cobalt manganese composite oxide and a lithium cobalt composite oxide containing a different metal element other than lithium, nickel, cobalt, and manganese as a positive electrode active material, and vinylidene fluoride- Contains chlorotrifluoroethylene copolymer as binder,
The lithium nickel cobalt manganese composite oxide has a nickel ratio a (mol%) of 30 ≦ a ≦ 100, assuming that the amount of all transition metal elements is 100 mol%.
The lithium cobalt composite oxide includes a lithium cobalt composite oxide (A) having an average particle size A (μm) of more than 10 μm and 30 μm or less, and a lithium cobalt composite oxide having an average particle size B (μm) of 1 μm or more and 10 μm or less. The object (B) is used so as to satisfy the relationship of AB ≧ 5,
The ratio of the different metal element in the total amount of cobalt and the different metal element in the lithium cobalt composite oxide (B) is different in the total amount of cobalt and the different metal element in the lithium cobalt composite oxide (A). Greater than the proportion of metallic elements,
When the average particle diameter of the lithium nickel cobalt manganese composite oxide used as the positive electrode active material is C (μm), C> B,
The negative electrode has a negative electrode mixture layer containing a negative electrode active material on one side or both sides of a current collector,
The negative electrode mixture layer is SiO _x (where the atomic ratio x of O to Si having the structure microcrystal Si to SiO ₂ matrix of amorphous dispersed is a 0.5 ≦ x ≦ 1.5 ) And a graphitic carbon material as a negative electrode active material ,
The proportion of SiO _x in the anode active material total amount, the non-aqueous electrolyte secondary battery, characterized der Rukoto least 0.01 wt% 20 wt% or less. The lithium nickel cobalt manganese composite oxide has the following general composition formula (1)
Li _{1 + s} M ¹ O ₂ (1)
In [the general formula (1), a -0.3 ≦ s ≦ 0.3, ^{M 1} is a three or more element group including at least Ni, Co and Mn, each constituting ^{M 1} 30 <a <65, 5 <b <35, and 15 <c <50 when the ratio (mol%) of Ni, Co, and Mn in the element is a, b, and c, respectively. The non-aqueous electrolyte secondary battery according to claim 1 . The average particle diameter A (μm) of the lithium cobalt composite oxide (A), the average particle diameter B (μm) of the lithium cobalt composite oxide (B), and the average particle diameter C (μm of the lithium nickel cobalt manganese composite oxide) ), but, a ≧ C> the nonaqueous electrolyte secondary battery according to claim 1 or 2 satisfies the relationship of B. The lithium cobalt composite oxide (A) and the lithium cobalt composite oxide (B) have the following general composition formula (2)
Li _{1 + y} Co _z M ² _1-z O ₂ (2)
[In the general composition formula (2), −0.3 ≦ y ≦ 0.3, 0.95 ≦ z <1.0, and M ² is selected from the group consisting of Mg, Zr, Al, and Ti. The nonaqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the nonaqueous electrolyte secondary battery is at least one element. The nonaqueous electrolyte secondary battery according to claim 4 , wherein M ² in the general composition formula (2) is Mg and / or Zr. When the total of the lithium cobalt composite oxide (A) and the lithium cobalt composite oxide (B) used in the positive electrode mixture layer is 100% by mass, the content of the lithium cobalt composite oxide (A) is 50% by mass. the non-aqueous electrolyte secondary battery according to any one of claims 1 to 5 or more percent. When the total of the lithium cobalt composite oxide (A), lithium cobalt composite oxide (B) and lithium nickel cobalt manganese composite oxide used in the positive electrode mixture layer is 100% by mass, the lithium nickel cobalt manganese composite oxide The nonaqueous electrolyte secondary battery according to any one of claims 1 to 6 , wherein the content of is 15 mass% or more and 45 mass% or less.

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