JP2012054240A - Lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium secondary battery using a silicon and oxygen-containing material as an anode active material and having excellent charge/discharge cycle characteristics.SOLUTION: A lithium secondary battery comprises: a cathode 1; an anode 2; a nonaqueous electrolyte; and a separator 3. The cathode has a cathode mixture layer including a lithium-contained complex oxide as a cathode active material on one or both sides of a collector. The thickness of the collector of the cathode is 10-15 μm. The anode has an anode mixture layer including a material containing silicon and oxygen as constituent elements (an atomic ratio x of oxygen to silicon is 0.5≤x≤1.5.) and a graphitic carbon material as an anode active material on one or both sides of the collector. A ratio P/N of mass P of the cathode active material to mass N of the anode active material is 1.0-3.6. The nonaqueous electrolyte includes a 1-10 mass% fluorine-substituted cyclic carbonate.

Description

  The present invention relates to a lithium secondary battery having good charge / discharge cycle characteristics.

  Non-aqueous electrolyte lithium 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 ( (See Patent Documents 1 and 2).

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 addition, since SiO _x has a fine shape, a certain effect can be recognized in improving the load characteristics of the battery, but there is still room for improvement in that SiO _x itself is a material with low conductivity. It was left.

Under such circumstances, the SiO _x utilization rate is limited to suppress volume expansion and contraction associated with charge / discharge reactions, or the surface of SiO _x is coated with a conductive material such as carbon to improve load characteristics. Or by using a non-aqueous electrolyte to which a halogen-substituted cyclic carbonate (for example, 4-fluoro-1,3-dioxolan-2-one) is added or the like, A technique for suppressing the swelling of the battery can accompanying the generation has also been proposed (see Patent Document 3).

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

According to the technique described in Patent Document 3, a lithium secondary battery having good charge / discharge cycle characteristics, for example, can be obtained while increasing capacity by using SiO _x as a negative electrode active material. In the secondary battery, there is a great demand for longer life, and it is expected that further charge / discharge cycle characteristics need to be improved.

  This invention is made | formed in view of the said situation, The objective is to use the material containing Si and O as a negative electrode active material, and to provide the lithium secondary battery excellent in charging / discharging cycling characteristics.

The lithium 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. The positive electrode contains a lithium-containing composite oxide as a positive electrode active material. The positive electrode current collector has a thickness of 10 to 15 μm, and the negative electrode is a material containing Si and O as constituent elements (however, The atomic ratio x of O to Si is 0.5 ≦ x ≦ 1.5 (hereinafter, the material may be referred to as “SiO _x ”) and a graphitic carbon material is contained as a negative electrode active material. It has a negative electrode mixture layer on one side or both sides of a current collector, and the ratio P / N of the mass P of the positive electrode active material and the mass N of the negative electrode active material is 1.0 to 3.6. As the non-aqueous electrolyte, 1 to 10% by mass of a fluorine-substituted cyclic carbon What used the thing containing an acidate is used.

  ADVANTAGE OF THE INVENTION According to this invention, the material containing Si and O can be used as a negative electrode active material, and the lithium secondary battery excellent in charging / discharging cycling characteristics can be provided.

It is a schematic diagram which shows an example of the lithium secondary battery of this invention, (a) Top view, (b) Cross-sectional view. FIG. 2 is a perspective view of FIG. 1.

As described above, in a battery using SiO _x as a negative electrode active material, highly active Si is exposed by grinding of SiO _x particles caused by volume change accompanying charge / discharge (for details of the structure of SiO _x ) Since this decomposes the non-aqueous electrolyte, there is a problem that the charge / discharge cycle characteristics are likely to deteriorate.

Therefore, in the present invention, while using SiO _x as the negative electrode active material, the balance between the usage amount of the negative electrode active material and the usage amount of the positive electrode active material is adjusted to control the utilization rate of the negative electrode active material, thereby increasing the charge. A non-aqueous electrolytic solution having a component capable of forming a film that satisfactorily coats the SiO _x particles even when the SiO _x particles are crushed and a new surface is generated, while suppressing the pulverization due to the volume change of the SiO _x particles accompanying discharge. By using it, the reaction between the negative electrode active material and the non-aqueous electrolyte is highly suppressed, and a lithium secondary battery excellent in charge / discharge cycle characteristics is obtained.

For the negative electrode according to the lithium secondary battery of the present invention, for example, a negative electrode mixture layer containing a negative electrode active material or a binder is used on one side or both sides of the current collector. Then, the negative active material according to the negative electrode, to complex with SiO _x and the carbon material, and a graphitic carbon material used.

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 a complex complexed with carbon materials, for example, it is desirable that the surface of the SiO _x is coated with a carbon material. As described above, since SiO _x has poor conductivity, when using it as a negative electrode active material, from the viewpoint of securing good battery characteristics, a conductive material (conductive aid) is used, and SiO _x in the negative electrode is used. It is necessary to form an excellent conductive network by mixing and dispersing the material and the conductive material well. 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. Therefore, it is possible to realize a lithium secondary battery with higher capacity and more excellent 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 state where SiO _x and the carbon material are dispersed inside the granulated body, a better conductive network can be formed. Therefore, in a lithium secondary battery having a negative electrode containing SiO _x as a negative electrode active material, a heavy load Battery characteristics such as 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.

A graphite carbon material used in combination with SiO _x as a negative electrode active material can also be used as a carbon material related to a composite of SiO _x and a 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 value 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 composite of SiO _x and the carbon material include natural graphite such as flake graphite; graphitizable carbon such as pyrolytic carbons, MCMB, and carbon fiber. And artificial graphite obtained by graphitizing at 2800 ° C. or higher.

In the negative electrode according to the present invention, from the viewpoint of satisfactorily ensuring the effect of the high capacity by using a SiO _x, the content of the complex of the SiO _x and the carbon material in the anode active material, 0 It is preferably 0.01% by mass or more, and more preferably 3% by mass or more. In addition, the ratio P / N of the mass P of the positive electrode active material and the mass N of the negative electrode active material, which will be described later, can be easily adjusted to the value described later, and the problem caused by the volume change of SiO _x accompanying charge / discharge can be improved. From the viewpoint of avoidance, the content of the composite of SiO _x and the carbon material in the negative electrode active material is preferably 20% by mass or less, and more preferably 10% by mass or less.

  For example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), or the like is preferably used for the binder related to the negative electrode mixture layer. Furthermore, you may add various carbon blacks, such as acetylene black, a carbon nanotube, carbon fiber, etc. as a conductive support agent to a negative mix layer.

  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 calendering process as necessary. However, the manufacturing method of the negative electrode is not limited to the above method, and may be manufactured by other manufacturing methods.

The thickness of the negative electrode mixture layer is preferably 10 to 100 μm per one side of the current collector, and the density of the negative electrode mixture layer (the negative electrode mixture per unit area laminated on the current collector) (Calculated from the mass and thickness of the layer) is preferably 1.0 to 1.9 g / cm ³ . 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 5 μm in order to ensure mechanical strength. Is desirable.

  As the positive electrode according to the lithium secondary battery of the present invention, for example, one having a structure having a positive electrode mixture layer containing a positive electrode active material, a binder, a conductive auxiliary agent and the like on one side or both sides of a current collector can be used.

As a positive electrode active material, what is used for the lithium secondary battery conventionally known, ie, the lithium containing complex oxide which can occlude-release Li (lithium) ion, is used. The positive electrode active material according to the lithium secondary battery of the present invention is represented by the following general composition formula (1) because of its high capacity and excellent thermal stability among lithium-containing composite oxides. It is preferable to use one.
Li _{1 + y} MO ₂ (1)
[However, −0.15 ≦ y ≦ 0.15, and M represents a group of three or more elements including at least Ni, Co, and Mn. In each element constituting M, Ni, Co When the proportions (mol%) of Mn and a are b, c, respectively, 45 ≦ a ≦ 90, 5 ≦ b ≦ 30, 5 ≦ c ≦ 30, and 10 ≦ b + c ≦ 55. ]

  In the lithium-containing composite oxide represented by the general composition formula (1), Ni is a component that contributes to the capacity improvement.

  When the total number of elements in the element group M in the general composition formula (1) representing the lithium-containing composite oxide is 100 mol%, the Ni ratio a is 45 mol from the viewpoint of improving the capacity of the lithium-containing composite oxide. % Or more, and more preferably 50 mol% or more. However, if the proportion of Ni in the element group M is too large, for example, the amount of Co or Mn is reduced, and the effects of these may be reduced. Therefore, when the total number of elements in the element group M in the general composition formula (1) representing the lithium-containing composite oxide is 100 mol%, the Ni ratio a is preferably 90 mol% or less, and 70 mol% or less. More preferably.

  Further, Co contributes to the capacity of the lithium-containing composite oxide and acts to improve the packing density in the positive electrode mixture layer. On the other hand, if it is too much, it may cause an increase in cost and a decrease in safety. Therefore, when the total number of elements in the element group M in the general composition formula (1) representing the lithium-containing composite oxide is 100 mol%, the Co ratio b is preferably 5 mol% or more and 30 mol% or less.

  In the lithium-containing composite oxide, when the total number of elements in the element group M in the general composition formula (1) is 100 mol%, the Mn ratio c is preferably 5 mol% or more and 30 mol% or less. . By including Mn in the lithium-containing composite oxide in the amount as described above, and by always allowing Mn to be present in the crystal lattice, the thermal stability of the lithium-containing composite oxide can be improved, and the safety is further improved. It is possible to construct a battery with a high value.

  Furthermore, in the lithium-containing composite oxide, by containing Co, fluctuations in the valence of Mn due to Li doping and dedoping during charging and discharging of the battery are suppressed, and the average valence of Mn is set to a value close to tetravalent. The value can be stabilized, and the reversibility of charge / discharge can be further increased. Therefore, by using such a lithium-containing composite oxide, it becomes possible to configure a battery with more excellent charge / discharge cycle characteristics.

  Moreover, in the lithium-containing composite oxide, from the viewpoint of ensuring the above-described effect by using Co and Mn in combination, the total number of elements in the element group M in the general composition formula (1) is set to 100 mol%. In this case, the sum b + c of the Co ratio b and the Mn ratio c is preferably 10 mol% or more and 55 mol% or less (more preferably 50 mol% or less).

  The element group M in the general composition formula (1) representing the lithium-containing composite oxide may contain elements other than Ni, Co, and Mn. For example, Ti, Cr, Fe, Cu, Zn, It may contain elements such as Al, Ge, Sn, Mg, Ag, Ta, Nb, B, P, Zr, Ca, Sr, and Ba. However, in the lithium-containing composite oxide, in order to sufficiently obtain the above-described effect by including Ni, Co and Mn, Ni, Co and when the total number of elements in the element group M is 100 mol% When the total of the ratio (mol%) of elements other than Mn is expressed by f, f is preferably 15 mol% or less, and more preferably 3 mol% or less.

  For example, in the lithium-containing composite oxide, if Al is present in the crystal lattice, the crystal structure of the lithium-containing composite oxide can be stabilized, and the thermal stability thereof can be improved. High lithium secondary battery can be configured. In addition, since Al is present at the grain boundaries and surfaces of the lithium-containing composite oxide particles, the stability over time and side reactions with the electrolytic solution can be suppressed, and a longer-life lithium secondary battery is constructed. It becomes possible.

  However, since Al cannot participate in the charge / discharge capacity, increasing the content in the lithium-containing composite oxide may cause a decrease in capacity. Therefore, in the general composition formula (1) representing the lithium-containing composite oxide, when the total number of elements in the element group M is 100 mol%, the Al ratio is preferably 10 mol% or less. In addition, in order to ensure the above-mentioned effect by containing Al more favorably, when the total number of elements in the element group M is 100 mol% in the general composition formula (1) representing the lithium-containing composite oxide. In addition, the Al ratio is preferably 0.02 mol% or more.

  In the lithium-containing composite oxide, when Mg is present in the crystal lattice, the crystal structure of the lithium-containing composite oxide can be stabilized and the thermal stability thereof can be improved, so that the safety is higher. It becomes possible to constitute a lithium secondary battery. In addition, when a phase transition of the lithium-containing composite oxide occurs due to Li doping and dedoping during charging and discharging of a lithium secondary battery, Mg is rearranged to relax the irreversible reaction, and the lithium-containing composite Since reversibility of the crystal structure of the oxide can be increased, a lithium secondary battery having a longer charge / discharge cycle life can be configured. In particular, in the general composition formula (1) representing the lithium-containing composite oxide, when x <0 and the lithium-containing composite oxide has a Li-deficient crystal structure, Mg instead of Li becomes a Li site. A lithium-containing composite oxide can be formed in a form that enters, and a stable compound can be obtained.

  However, since Mg has little influence on the charge / discharge capacity, if the content in the lithium-containing composite oxide is increased, the capacity may be reduced. Therefore, in the general composition formula (1) representing the lithium-containing composite oxide, when the total number of elements in the element group M is 100 mol%, the ratio of Mg is preferably 10 mol% or less. In addition, in order to ensure the above-mentioned effect by containing Mg more satisfactorily, in the general composition formula (1) representing the lithium-containing composite oxide, when the total number of elements in the element group M is 100 mol% Furthermore, it is preferable that the Mg ratio is 0.02 mol% or more.

In the lithium-containing composite oxide, when Ti is contained in the particles, the lithium-containing composite oxide stabilizes the crystal structure by being disposed in a defect portion of the crystal such as oxygen deficiency in the LiNiO ₂ type crystal structure. The reversibility of the reaction increases, and a lithium secondary battery having more excellent charge / discharge cycle characteristics can be configured. In order to secure the above-described effect satisfactorily, in the general composition formula (1) representing the lithium-containing composite oxide, when the total number of elements in the element group M is 100 mol%, the ratio of Ti is set to 0 It is preferable to set it as 0.01 mol% or more, and it is more preferable to set it as 0.1 mol% or more. However, when the content of Ti increases, Ti does not participate in charging / discharging, so that the capacity may be reduced, or a heterogeneous phase such as Li ₂ TiO ₃ may be easily formed, leading to deterioration in characteristics. Therefore, in the general composition formula (1) representing the lithium-containing composite oxide, when the total number of elements in the element group M is 100 mol%, the proportion of Ti is preferably 10 mol% or less, preferably 5 mol%. More preferably, it is more preferably 2 mol% or less.

  Further, the lithium-containing composite oxide contains at least one element M ′ selected from Ge, Ca, Sr, Ba, B, Zr and Ga as the element group M in the general composition formula (1). Are preferable in that the following effects can be secured.

  When the lithium-containing composite oxide contains Ge, the crystal structure of the composite oxide after Li is destabilized can improve the reversibility of the charge / discharge reaction, It becomes possible to constitute a lithium secondary battery with higher safety and more excellent charge / discharge cycle characteristics. In particular, when Ge is present on the particle surface or grain boundary of the lithium-containing composite oxide, disorder of the crystal structure due to Li desorption / insertion at the interface is suppressed, greatly contributing to improvement of charge / discharge cycle characteristics. be able to.

Moreover, when the lithium-containing composite oxide contains an alkaline earth metal such as Ca, Sr, or Ba, the growth of primary particles is promoted, and the crystallinity of the lithium-containing composite oxide is improved. The non-aqueous electrolysis that the lithium secondary battery has can be achieved by improving the temporal stability of the coating material (positive electrode mixture-containing composition to be described later) that can reduce the active sites and form the positive electrode mixture layer. Irreversible reaction with the liquid can be suppressed. Furthermore, since these elements are present on the particle surfaces and grain boundaries of the lithium-containing composite oxide, the CO ₂ gas in the battery can be trapped. It becomes possible to do. In particular, when the lithium-containing composite oxide contains Mn, the primary particles tend to be difficult to grow. Therefore, the addition of an alkaline earth metal such as Ca, Sr, or Ba is more effective.

  Even when B is contained in the lithium-containing composite oxide, the growth of primary particles is promoted and the crystallinity of the lithium-containing composite oxide is improved. Therefore, active sites can be reduced, Irreversible reactions with moisture, the binder used for forming the positive electrode mixture layer, and the non-aqueous electrolyte of the battery can be suppressed. For this reason, stability over time when it is used as a coating material for forming the positive electrode mixture layer is improved, gas generation in the battery can be suppressed, and a lithium secondary battery having better storage and a longer life can be obtained. It can be configured. In particular, when the lithium-containing composite oxide contains Mn, the addition of B is more effective because primary particles tend to be difficult to grow.

  When Zr is contained in the lithium-containing composite oxide, the electrochemical properties of the lithium-containing composite oxide are impaired due to the presence of Zr at the grain boundaries and surfaces of the particles of the lithium-containing composite oxide. In addition, since the surface activity is suppressed, it is possible to construct a lithium secondary battery having a better shelf life and a longer life.

  When Ga is contained in the lithium-containing composite oxide, the growth of primary particles is promoted and the crystallinity of the lithium-containing composite oxide is improved, so that the active sites can be reduced, and the positive electrode mixture Stability over time when a coating for forming a layer is improved, and an irreversible reaction with a non-aqueous electrolyte can be suppressed. Moreover, by dissolving Ga in the crystal structure of the lithium-containing composite oxide, the layer spacing of the crystal lattice can be expanded, and the rate of expansion and contraction of the lattice due to insertion and desorption of Li can be reduced. For this reason, the reversibility of a crystal structure can be improved and it becomes possible to comprise a lithium secondary battery with a longer charge-discharge cycle life. In particular, when the lithium-containing composite oxide contains Mn, the addition of Ga is more effective because primary particles tend to be difficult to grow.

  In order to easily obtain the effect of the element M ′ selected from Ge, Ca, Sr, Ba, B, Zr, and Ga, the ratio is 0.1 mol% or more in all elements of the element group M. It is preferable. Further, the ratio of these elements M ′ in all elements of the element group M is preferably 10 mol% or less.

  Elements other than Ni, Co and Mn in the element group M may be uniformly distributed in the lithium-containing composite oxide, or may be segregated on the particle surface or the like.

  In the general composition formula (1) representing the lithium-containing composite oxide, when the relation between the Co ratio b and the Mn ratio c in the element group M is b> c, the lithium-containing composite oxide is used. By promoting the growth of the oxide particles, the lithium-containing composite oxide having a high packing density at the positive electrode (the positive electrode mixture layer) and a higher reversibility can be obtained. Further improvement can be expected.

  On the other hand, in the general composition formula (1) representing the lithium-containing composite oxide, when the relationship between the Co ratio b and the Mn ratio c in the element group M is b ≦ c, more thermal stability is obtained. The lithium-containing composite oxide can be made high, and further improvement in the safety of the battery using this can be expected.

The lithium-containing 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. Note that the true density of the lithium-containing composite oxide containing Mn in a certain range varies greatly depending on the composition, but the structure is stabilized and the uniformity can be improved in the narrow composition range as described above. It is considered to be a large value close to the true density of LiCoO ₂ . Moreover, the capacity | capacitance per mass of lithium containing complex oxide can be enlarged, and it can be set as the material excellent in reversibility.

The lithium-containing composite oxide has a higher true density especially when the composition is close to the stoichiometric ratio. Specifically, in the general composition formula (1), −0.15 ≦ y ≦ 0. .15 is preferable, and the true density and reversibility can be improved by adjusting the value of y in this way. y is more preferably −0.05 or more and 0.05 or less. In this case, the true density of the lithium-containing composite oxide can be set to a higher value of 4.6 g / cm ³ or more. .

  The lithium-containing composite oxide represented by the general composition formula (1) includes Li-containing compounds (such as lithium hydroxide monohydrate), Ni-containing compounds (such as nickel sulfate), and Co-containing compounds (such as cobalt sulfate). Mn-containing compounds (such as manganese sulfate) and compounds containing other elements contained in element group M (such as aluminum sulfate and magnesium sulfate) can be mixed and fired. Further, in order to synthesize the lithium-containing composite oxide with higher purity, a composite compound (hydroxide, oxide, etc.) containing a plurality of elements contained in the element group M and a Li-containing compound are mixed and fired. It is preferable to do.

  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.

Further, as the positive electrode active material, a lithium-containing composite oxide other than the lithium-containing composite oxide represented by the general composition formula (1) may be used. Examples of such lithium-containing composite oxides include lithium cobalt oxides such as LiCoO ₂ ; lithium manganese oxides such as LiMnO ₂ and Li ₂ MnO ₃ ; lithium nickel oxides such as LiNiO ₂ ; LiCo _1-x NiO Lithium-containing composite oxide having a layered structure such as ₂ ; Lithium-containing composite oxide having a spinel structure such as LiMn ₂ O ₄ and Li _4/3 Ti _5/3 O ₄ ; Lithium-containing composite oxide having an olivine structure such as LiFePO ₄ And oxides having the above-described oxide as a basic composition and substituted with various elements.

As the positive electrode active material, those exemplified above including the lithium-containing composite oxide represented by the general composition formula (1) may be used alone or in combination of two or more. However, as described above, it is preferable to use at least the lithium-containing composite oxide represented by the general composition formula (1), and use only the lithium-containing composite oxide represented by the general composition formula (1). or, or, it is more preferred to use a lithium-containing composite oxide and LiCoO ₂ represented by the general formula (1).

  When the lithium-containing composite oxide represented by the general composition formula (1) is used in combination with another lithium-containing composite oxide, the lithium-containing composite oxide represented by the general composition formula (1) From the viewpoint of ensuring a better effect by use, the proportion of the other lithium-containing composite oxide is desirably 80% by mass or less of the entire active material.

  As the binder for the positive electrode mixture layer, the same binders as those exemplified above as the binder for the negative electrode mixture layer can be used. In addition, as the conductive auxiliary agent related to the positive electrode mixture layer, for example, graphite (graphite carbon material) such as natural graphite (flaky graphite), artificial graphite; acetylene black, ketjen black, channel black, furnace black, Carbon materials such as carbon black such as lamp black and thermal black; carbon fiber;

  For the positive electrode, for example, a paste-like or slurry-like positive electrode mixture-containing composition in which a positive electrode active material, a binder, and a conductive additive are dispersed in a solvent such as N-methyl-2-pyrrolidone (NMP) is prepared. The binder may be dissolved in a solvent), and this is applied to one or both sides of the current collector, dried, and then subjected to a calendering process as necessary. However, the manufacturing method of the positive electrode is not limited to the above method, and may be manufactured by other manufacturing methods.

The thickness of the positive electrode mixture layer is preferably, for example, 10 to 100 μm per side of the current collector, and the density of the positive electrode mixture layer (the mass of the positive electrode mixture layer per unit area laminated on the current collector, (Calculated from the thickness) is preferably 3.0 to 4.5 g / cm ³ . 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 can be the same as that used for the positive electrode of a conventionally known lithium secondary battery. For example, an aluminum foil having a thickness of 10 to 30 μm is preferable.

In the lithium secondary battery of the present invention, the ratio P / N between the mass P of the positive electrode active material and the mass N of the negative electrode active material is 3.6 or less. As a result, the utilization rate of the negative electrode active material is lowered to limit the charge electric capacity, thereby suppressing the volume change of SiO _x accompanying charge / discharge and suppressing the deterioration of charge / discharge cycle characteristics of the battery due to pulverization of the active material particles. it can. However, if the P / N is too small, the effect of increasing the battery capacity may be reduced.

The mass P of the positive electrode active material is obtained by subtracting the mass of the current collector (aluminum foil or the like) corresponding to the size from the mass of the positive electrode cut into an arbitrary size, It can be calculated by multiplying the composition ratio of the positive electrode active material contained in the positive electrode mixture layer. Further, the mass N of the negative electrode active material can be calculated in the same manner. In calculating the mass N of the negative electrode active material, the amount of carbon material contained in the composite of SiO _x and carbon material is also included.

  As the nonaqueous electrolytic solution according to the lithium secondary battery of the present invention, a solution obtained by dissolving a lithium salt in an organic solvent and containing a halogen-substituted cyclic carbonate and vinylene carbonate (VC) is used.

In the lithium secondary battery of the present invention, the ratio P / N between the mass P of the positive electrode active material and the mass N of the negative electrode active material is controlled as described above, and SiO due to volume expansion / contraction of SiO _x accompanying charge / discharge is reduced. The crushing of _x particles is highly suppressed. However, even when such pulverization of SiO _x particles cannot be completely prevented, a film derived from the cyclic carbonate is formed on the new surface generated by pulverization of SiO _x by using a non-aqueous electrolyte containing a halogen-substituted cyclic carbonate. The reaction with the non-aqueous electrolyte is suppressed. In addition, when the non-aqueous electrolytic solution contains VC together with the halogen-substituted cyclic carbonate, a film having good properties is formed by the newly formed surface of SiO _x , and the reaction between the negative electrode active material and the non-aqueous electrolytic solution is good. Since it can suppress, it can be set as the lithium secondary battery excellent in charging / discharging cycling characteristics, ensuring a high capacity | capacitance.

  As the halogen-substituted cyclic carbonate, a compound represented by the following general formula can be used.

In the general formula, R ¹ , R ² , R ^3, and R ⁴ represent hydrogen, a halogen element, or an alkyl group having 1 to 10 carbon atoms, and part or all of the hydrogen in the alkyl group is substituted with a halogen element. may ^be, at least one of R ^1, R 2, ^{R 3} and ^{R 4} are ^halogen, R ^1, R 2, ^{R 3} and ^{R 4} may be different, respectively, Two or more may be the same. When R ¹ , R ² , R ³ and R ⁴ are alkyl groups, the smaller the number of carbon atoms, the better. As the halogen element, fluorine is particularly preferable.

  Among the cyclic carbonates substituted with such a halogen element, 4-fluoro-1,3-dioxolan-2-one (FEC) is particularly preferable.

The halogen-substituted cyclic carbonate and VC content in the non-aqueous electrolyte used for the battery (non-aqueous electrolyte used for assembling the battery; the same applies hereinafter) are the halogen-substituted cyclic carbonate and VC. From the viewpoint of securing the above-mentioned effect satisfactorily, the content of the halogen-substituted cyclic carbonate is 1% by mass or more, preferably 1.5% by mass or more, and the content of VC is It is 1 mass% or more, and it is preferable that it is 1.5 mass% or more. However, if the amount of halogen-substituted cyclic carbonate or VC in the non-aqueous electrolyte is too large, the activity of the SiO _x that is the negative electrode active material is reduced or excessive gas is generated during film formation. There is a risk of causing the outer body to swell. Therefore, in the nonaqueous electrolytic solution used for the battery, the content of the halogen-substituted cyclic carbonate is 10% by mass or less, preferably 5% by mass or less, and the VC content is 10% by mass. % Or less, and preferably 5% by mass or less.

The lithium salt used in the non-aqueous electrolyte is not particularly limited as long as it is dissociated in a solvent to form Li ⁺ ions and hardly causes a side reaction 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 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.

  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, 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, non-aqueous electrolytes used in batteries include acid anhydrides, sulfonic acid esters, dinitriles, 1% for the purpose of further improving charge / discharge cycle characteristics and improving safety such as high-temperature storage and prevention of overcharge. , 3-propane sultone, diphenyl disulfide, cyclohexyl benzene, biphenyl, fluorobenzene, t-butylbenzene and other additives (including these derivatives) can also be added as appropriate.

  The separator according to the lithium secondary battery of the present invention has a property that the pores are closed at 80 ° C. or higher (more preferably 100 ° C. or higher) and 170 ° C. or lower (more preferably 150 ° C. or lower) (that is, shutdown function). It is preferable that a separator used in a normal lithium secondary battery, for example, a microporous film 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.

  The separator according to the battery of the present invention includes a porous layer (I) mainly composed of a resin having a melting point of 140 ° C. or less, a resin that does not melt at a temperature of 150 ° C. or less, or an inorganic filler having a heat resistant temperature of 150 ° C. or more. It is preferable to use a laminated separator having a porous layer (II) containing as a main component. Here, the “melting point” means a melting temperature measured using a differential scanning calorimeter (DSC) in accordance with JIS K 7121. In addition, “does not melt at a temperature of 150 ° C. or lower” means that the melting temperature measured using DSC exceeds 150 ° C. according to the provisions of JIS K 7121. This means that the melting behavior is not exhibited at the temperature. Furthermore, “the heat resistant temperature is 150 ° C. or higher” means that deformation such as softening is not observed at least at 150 ° C.

  The porous layer (I) according to the multilayer separator is mainly for ensuring a shutdown function, and the melting point of the resin, which is a component in which the lithium secondary battery is the main component of the porous layer (I) When the temperature reaches the value, the resin related to the porous layer (I) melts to close the pores of the separator, thereby causing a shutdown that suppresses the progress of the electrochemical reaction.

  Examples of the resin having a melting point of 140 ° C. or lower, which is the main component of the porous layer (I), include PE, and the form thereof is a substrate such as a microporous film used in the above-described lithium secondary battery or a nonwoven fabric. And a dispersion obtained by applying a dispersion containing PE particles and drying. Here, in all the constituent components of the porous layer (I), the volume of the resin having a main melting point of 140 ° C. or less is 50% by volume or more, and more preferably 70% by volume or more. For example, when the porous layer (I) is formed of the microporous film of PE, the volume of the resin having a melting point of 140 ° C. or lower is 100% by volume.

  The porous layer (II) according to the multilayer separator has a function of preventing a short circuit due to direct contact between the positive electrode and the negative electrode even when the internal temperature of the lithium secondary battery is increased. The function is secured by a resin that does not melt at a temperature of ℃ or less or an inorganic filler with a heat resistant temperature of 150 ℃ or more. That is, when the battery becomes hot, even if the porous layer (I) shrinks, the porous layer (II) that does not easily shrink can cause the positive and negative electrodes directly when the separator is thermally contracted. It is possible to prevent a short circuit due to the contact of. Moreover, since this heat-resistant porous layer (II) acts as a skeleton of the separator, the thermal contraction of the porous layer (I), that is, the thermal contraction of the entire separator itself can be suppressed.

  When the porous layer (II) is mainly composed of a resin having a melting point of 150 ° C. or higher, for example, a microporous film formed of a resin that does not melt at a temperature of 150 ° C. or lower (for example, the above-mentioned PP microporous for battery The film is laminated on the porous layer (I), and a dispersion containing resin particles that do not melt at a temperature of 150 ° C. or less is applied to the porous layer (I) and dried to form the porous layer (I). An application lamination type form in which the porous layer (II) is formed on the surface of the substrate is mentioned.

  Examples of resins that do not melt at a temperature of 150 ° C. or less include PP; crosslinked polymethyl methacrylate, crosslinked polystyrene, crosslinked polydivinylbenzene, styrene-divinylbenzene copolymer crosslinked product, polyimide, melamine resin, phenol resin, benzoguanamine-formaldehyde condensation And various crosslinked polymer fine particles; polysulfone; polyether sulfone; polyphenylene sulfide; polytetrafluoroethylene; polyacrylonitrile; aramid; polyacetal and the like.

  When using resin particles that do not melt at a temperature of 150 ° C. or lower, the average particle size is, for example, preferably 0.01 μm or more, more preferably 0.1 μm or more, It is preferably 10 μm or less, and more preferably 2 μm or less. In addition, the average particle diameter of the various particles referred to in the present specification is determined by, for example, using a laser scattering particle size distribution meter (for example, “LA-920” manufactured by HORIBA, Ltd.) and dispersing these fine particles in a medium that does not dissolve the resin. The measured average particle diameter D is 50%.

  When the porous layer (II) is formed mainly of an inorganic filler having a heat resistant temperature of 150 ° C. or higher, for example, a dispersion containing an inorganic filler having a heat resistant temperature of 150 ° C. or higher is applied to the porous layer (I). Examples of the coating laminated type in which the porous layer (II) is formed by drying.

  The inorganic filler related to the porous layer (II) has a heat-resistant temperature of 150 ° C. or higher, is stable to the non-aqueous electrolyte of the battery, and is electrochemically stable to be hardly oxidized or reduced in the battery operating voltage range. However, fine particles are preferable from the viewpoint of dispersion, and alumina, silica, and boehmite are preferable. Alumina, silica, and boehmite have high oxidation resistance, and the particle size and shape can be adjusted to the desired numerical values, making it easy to accurately control the porosity of the porous layer (II). It becomes. In addition, as for the inorganic filler whose heat-resistant temperature is 150 degreeC or more, the thing of the said illustration may be used individually by 1 type, and may use 2 or more types together, for example. In addition, an inorganic filler having a heat resistant temperature of 150 ° C. may be used in combination with a resin that does not melt at a temperature of 150 ° C. or lower.

  The shape of the inorganic filler having a heat resistant temperature of 150 ° C. or higher related to the porous layer (II) is not particularly limited, and is substantially spherical (including true spherical), substantially elliptical (including elliptical), plate-like, etc. Various shapes can be used.

  Further, the average particle diameter of the inorganic filler having a heat resistant temperature of 150 ° C. or higher related to the porous layer (II) is preferably 0.3 μm or more because the ion permeability is lowered if it is too small. More preferably, it is 5 μm or more. In addition, if the inorganic filler having a heat resistant temperature of 150 ° C. or higher is too large, the electrical characteristics are likely to be deteriorated. Therefore, the average particle diameter is preferably 5 μm or less, and more preferably 2 μm or less.

  In the porous layer (II), the resin that does not melt at a temperature of 150 ° C. or lower and the inorganic filler having a heat resistant temperature of 150 ° C. or higher are mainly contained in the porous layer (II). The amount in (II) [when the porous layer (II) contains only one of a resin that does not melt at a temperature of 150 ° C. or less and an inorganic filler that has a heat resistant temperature of 150 ° C. or more, is the amount, If both are included, the total amount. The same applies to the amount of the resin that does not melt at a temperature of 150 ° C. or less and the amount of the inorganic filler having a heat resistant temperature of 150 ° C. or more in the porous layer (II). ] Is 50% by volume or more in the total volume of the constituent components of the porous layer (II), preferably 70% by volume or more, more preferably 80% by volume or more, and 90% by volume or more. More preferably it is. By making the inorganic filler in the porous layer (II) high as described above, even when the lithium secondary battery becomes high temperature, the thermal contraction of the entire separator can be satisfactorily suppressed, Generation | occurrence | production of the short circuit by the direct contact of a positive electrode and a negative electrode can be suppressed more favorably.

  As will be described later, since it is preferable that the porous layer (II) also contains an organic binder, a porous layer (II) of a resin that does not melt at a temperature of 150 ° C. or lower and an inorganic filler having a heat resistant temperature of 150 ° C. or higher. ) In the total volume of the constituent components of the porous layer (II) is preferably 99.5% by volume or less.

  In the porous layer (II), a resin that does not melt at a temperature of 150 ° C. or less, or an inorganic filler having a heat resistant temperature of 150 ° C. or more is bound, or the porous layer (II) and the porous layer (I) For integration or the like, it is preferable to contain an organic binder. Examples of organic binders include ethylene-vinyl acetate copolymers (EVA, those having a structural unit derived from vinyl acetate of 20 to 35 mol%), ethylene-acrylic acid copolymers such as ethylene-ethyl acrylate copolymers, and fluorine-based binders. Examples include rubber, SBR, CMC, hydroxyethyl cellulose (HEC), polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polyvinyl pyrrolidone (PVP), cross-linked acrylic resin, polyurethane, and epoxy resin. A heat-resistant binder having a heat-resistant temperature is preferably used. As the organic binder, those exemplified above may be used singly or in combination of two or more.

  Among the organic binders exemplified above, highly flexible binders such as EVA, ethylene-acrylic acid copolymer, fluorine-based rubber, and SBR are preferable. Specific examples of such highly flexible organic binders include Mitsui DuPont Polychemical's “Evaflex Series (EVA)”, Nihon Unicar's EVA, Mitsui DuPont Polychemical's “Evaflex-EAA Series (Ethylene). -Acrylic acid copolymer) ", Nippon Unicar EEA, Daikin Industries" DAI-EL Latex Series (Fluororubber) ", JSR" TRD-2001 (SBR) ", Nippon Zeon" BM-400B " (SBR) ".

  When the organic binder is used for the porous layer (II), it can be used in the form of an emulsion dissolved or dispersed in the solvent for the composition for forming the porous layer (II) described later. Good.

  The coating laminate type separator is, for example, a composition for forming a porous layer (II) containing a resin particle that does not melt at a temperature of 150 ° C. or lower, an inorganic filler having a heat resistant temperature of 150 ° C. or higher (liquid such as slurry). The composition etc.) can be applied to the surface of the microporous membrane for constituting the porous layer (I) and dried at a predetermined temperature to form the porous layer (II).

  The composition for forming the porous layer (II) contains resin particles that do not melt at a temperature of 150 ° C. or lower and / or an inorganic filler having a heat resistant temperature of 150 ° C. or higher, and an organic binder as necessary. Is dispersed in a solvent (including a dispersion medium; the same shall apply hereinafter). The organic binder can be dissolved in a solvent. The solvent used in the composition for forming the porous layer (II) can uniformly disperse resin particles and inorganic filler that do not melt at a temperature of 150 ° C. or lower, and can dissolve or disperse the organic binder uniformly. For example, general organic solvents such as aromatic hydrocarbons such as toluene, furans such as tetrahydrofuran, ketones such as methyl ethyl ketone and methyl isobutyl ketone are preferably used. In addition, for the purpose of controlling the interfacial tension, alcohols (ethylene glycol, propylene glycol, etc.) or various propylene oxide glycol ethers such as monomethyl acetate may be appropriately added to these solvents. In addition, when the organic binder is water-soluble or used as an emulsion, water may be used as a solvent. In this case, alcohols (methyl alcohol, ethyl alcohol, isopropyl alcohol, ethylene glycol, etc.) are appropriately added. It is also possible to control the interfacial tension.

  The composition for forming the porous layer (II) has a solid content containing, for example, a resin particle that does not melt at a temperature of 150 ° C. or lower and / or an inorganic filler having a heat resistant temperature of 150 ° C. or higher, and an organic binder. It is preferable to set it as -80 mass%.

  In the laminated separator, the porous layer (I) and the porous layer (II) do not have to be one each, and a plurality of layers may be present in the separator. For example, a configuration in which the porous layer (I) is disposed on both sides of the porous layer (II) or a configuration in which the porous layer (II) is disposed on both sides of the porous layer (I) may be employed. However, increasing the number of layers may increase the thickness of the separator and increase the internal resistance of the battery or decrease the energy density. Therefore, it is not preferable to increase the number of layers. The total number of the porous layers (I) and (II) is preferably 5 or less.

  The thickness of the separator according to the battery of the present invention (a separator made of a microporous membrane made of polyolefin or the laminated separator) is preferably 10 to 30 μm, for example.

  In the laminated separator, the thickness of the porous layer (II) [when the separator has a plurality of porous layers (II), the total thickness] is determined by each of the functions of the porous layer (II). From the viewpoint of exhibiting more effectively, it is preferably 3 μm or more. However, if the porous layer (II) is too thick, the energy density of the battery may be lowered. Therefore, the thickness of the porous layer (II) is preferably 8 μm or less.

  Further, in the laminated separator, the thickness of the porous layer (I) [when the separator has a plurality of porous layers (I), the total thickness thereof. same as below. ] Is preferably 6 μm or more, and more preferably 10 μm or more, from the viewpoint of more effectively exerting the above-described action (particularly shutdown action) by using the porous layer (I). However, if the porous layer (I) is too thick, there is a possibility that the energy density of the battery may be lowered. In addition, the force that the porous layer (I) tends to shrink is increased, and the heat of the entire separator is increased. There is a possibility that the action of suppressing the shrinkage becomes small. Therefore, the thickness of the porous layer (I) is preferably 25 μm or less, more preferably 20 μm or less, and further preferably 14 μm or less.

The porosity of the separator as a whole is preferably 30% or more in a dried state in order to secure the amount of electrolyte solution retained and to improve ion permeability. On the other hand, from the viewpoint of securing separator strength and preventing internal short circuit, the separator porosity is preferably 70% or less in a dry state. Note that the porosity of the separator: P (%) can be calculated by calculating the sum of each component i from the thickness of the separator, the mass per area, and the density of the constituent components using the following equation (2).
P = 100− (Σa _i / ρ _i ) × (m / t) (2)
Here, in the above formula, a _i : ratio of component i expressed by mass%, ρ _i : density of component i (g / cm ³ ), m: mass per unit area of separator (g / cm ² ), t: The thickness (cm) of the separator.

In the case of the multilayer separator, in the formula (2), m is the mass (g / cm ² ) per unit area of the porous layer (I), and t is the thickness of the porous layer (I) ( cm), the porosity: P (%) of the porous layer (I) can also be obtained using the formula (2). The porosity of the porous layer (I) determined by this method is preferably 30 to 70%.

Further, in the case of the laminated separator, in the formula (2), m is the mass per unit area (g / cm ² ) of the porous layer (II), and t is the thickness of the porous layer (II) ( cm), the porosity: P (%) of the porous layer (II) can also be obtained using the formula (2). The porosity of the porous layer (II) obtained by this method is preferably 20 to 60%.

The separator preferably has high mechanical strength. For example, the puncture strength is preferably 3N or more. For example, when SiO _x having a large volume change due to charge / discharge is used as the negative electrode active material, mechanical damage is also applied to the facing separator due to expansion / contraction of the entire negative electrode by repeating charge / discharge. If the piercing strength of the separator is 3N or more, good mechanical strength is ensured, and mechanical damage to the separator can be reduced.

  Examples of the separator having a puncture strength of 3N or more include the above-described laminated separator, and in particular, an inorganic filler having a heat resistant temperature of 150 ° C. or higher in the porous layer (I) mainly composed of a resin having a melting point of 140 ° C. or lower. A separator in which a porous layer (II) containing as a main component is laminated is preferable. This is probably because the mechanical strength of the inorganic filler is high, so that the mechanical strength of the entire separator can be increased by supplementing the mechanical strength of the porous layer (I).

  The puncture strength can be measured by the following method. A separator is fixed on a plate having a hole with a diameter of 2 inches so as not to be wrinkled or bent, and a semispherical metal pin having a tip diameter of 1.0 mm is lowered onto a measurement sample at a speed of 120 mm / min. Measure the force when making a hole in the separator 5 times. And an average value is calculated | required about the measurement of 3 times except the maximum value and the minimum value among the said measurement values of 5 times, and this is made into the piercing strength of a separator.

  The positive electrode, the negative electrode, and the separator are formed in the form of a laminated electrode body in which a separator is interposed between the positive electrode and the negative electrode, or a wound electrode body in which the separator is wound in a spiral shape. It can be used for the battery of the invention.

  In the laminated electrode body and the wound electrode body, the laminated separator, particularly the porous layer (I) mainly composed of a resin having a melting point of 140 ° C. or less, mainly comprises an inorganic filler having a heat resistant temperature of 150 ° C. or more. In the case of using a separator in which the porous layer (II) contained as a laminate is used, it is preferable that the porous layer (II) is disposed so as to face at least the positive electrode. In this case, the porous layer (II), which mainly contains an inorganic filler having a heat-resistant temperature of 150 ° C. or more, and more excellent in oxidation resistance, faces the positive electrode, so that the oxidation of the separator by the positive electrode can be suppressed more favorably. Therefore, the storage characteristics and charge / discharge cycle characteristics of the battery at a high temperature can be improved. Further, when an additive such as VC or cyclohexylbenzene is added to the non-aqueous electrolyte, a film is formed on the positive electrode side to clog the pores of the separator, which may cause deterioration of battery characteristics. Therefore, an effect of suppressing pore clogging can be expected by making the relatively porous porous layer (II) face the positive electrode.

  On the other hand, when one surface of the multilayer separator is the porous layer (I), it is preferable that the porous layer (I) faces the negative electrode. The thermoplastic resin melted from the layer (I) is suppressed from being absorbed by the electrode mixture layer, and can be efficiently used to close the pores of the separator.

  Examples of the form of the lithium secondary battery of the present invention include a cylindrical shape (such as a rectangular tube 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.

  The lithium secondary battery of the present invention can be used for the same applications as various applications to which conventionally known lithium 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 positive electrode active material>
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 2.4 mol / dm ^3. , 0.8 mol ^/ dm 3, a mixed aqueous solution containing a concentration of 0.8 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 6: 2: 2. 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. 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 850 ° 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.

For the lithium-containing composite oxide was measured for a composition by an atomic absorption _{spectrometer,} and found to be a composition represented by _{Li 1.02 Ni 0.6 Co 0.2 Mn 0.2} O 2.

<Preparation of positive electrode>
100 parts by mass of the lithium-containing composite oxide, 20 parts by mass of an NMP solution containing PVDF as a binder at a concentration of 10% by mass, 1 part by mass of artificial graphite and 1 part by mass of ketjen black, which are conductive assistants, The mixture was kneaded using a biaxial kneader, and the viscosity was adjusted by adding NMP to prepare a positive electrode mixture-containing paste.

  The positive electrode mixture-containing paste is intermittently applied to both surfaces of an aluminum foil (positive electrode current collector) having a thickness of 15 μm while adjusting the thickness, dried, and then subjected to a calendar process so that the total pressure becomes 130 μm. The thickness of the positive electrode mixture layer was adjusted, and the positive electrode was produced by cutting so as to have a width of 54.5 mm. In this positive electrode, the mass P of the positive electrode active material measured by the method described above was 12 g. Further, a tab was welded to the exposed portion of the aluminum foil of the positive electrode to form a lead portion.

<Production of negative electrode>
A composite in which the surface of SiO _x having an average particle diameter D50% of 8 μm is coated with a carbon material (the amount of the carbon material in the composite is 10% by mass) and graphite having an average particle diameter D50% of 16 μm are combined with SiO _x. Mixture in which the amount of the composite whose surface was coated with a carbon material was 0.01% by mass: a mixture of 98% by mass and a 1% by mass CMC aqueous solution whose viscosity was adjusted to the range of 1500 to 5000 mPa · s: 1.0 part by mass and SBR: 1.0 part by mass were mixed with ion-exchanged water having a specific conductivity of 2.0 × 10 ⁵ Ω / cm or more as a solvent to prepare an aqueous negative electrode mixture-containing paste. .

  The negative electrode mixture-containing paste is intermittently applied on both sides of a copper foil (negative electrode current collector) having a thickness of 8 μm while adjusting the thickness, dried, and then subjected to a calendar treatment so that the total thickness becomes 110 μm. The thickness of the negative electrode mixture layer was adjusted, and the negative electrode was produced by cutting so as to have a width of 55.5 mm. In this negative electrode, the mass N of the negative electrode active material measured by the method described above was 5.2 g. Further, a tab was welded to the exposed portion of the copper foil of the negative electrode to form a lead portion.

<Preparation of separator>
Add 5 kg of ion-exchanged water and 0.5 kg of a dispersant (aqueous polycarboxylic acid ammonium salt, solid content concentration 40 mass%) to 5 kg of boehmite with an average particle diameter D50% of 1 μm, and have an internal volume of 20 L and 40 turns. A dispersion was prepared by pulverizing with a ball mill for 10 hours per minute. The treated dispersion was vacuum-dried at 120 ° C. and observed with a scanning electron microscope (SEM).

  To 500 g of the above dispersion, 0.5 g of xanthan gum as a thickener and 17 g of a resin binder dispersion (modified polybutyl acrylate, solid content 45% by mass) as a binder are added and stirred with a three-one motor for 3 hours to form a uniform slurry. [Slurry for forming porous layer (II), solid content ratio 50 mass%] was prepared.

PE microporous separator for lithium secondary batteries [porous layer (I): thickness 12 μm, porosity 40%, average pore diameter 0.08 μm, PE melting point 135 ° C.] on one side corona discharge treatment (discharge amount 40 W)・ Min / m ² ), a porous layer (II) forming slurry is applied to the treated surface by a micro gravure coater, and dried to form a porous layer (II) having a thickness of 4 μm. A separator was obtained. The mass per unit area of the porous layer (II) in this separator was 5.5 g / m ² , the boehmite volume content was 95% by volume, and the porosity was 45%.

<Battery assembly>
The positive electrode and the negative electrode obtained as described above were stacked with the separator porous layer (II) facing the positive electrode and wound in a spiral shape to produce a wound electrode body. The obtained wound electrode body is crushed into a flat shape, put into an aluminum alloy outer can having a thickness of 5 mm, a width of 42 mm, and a height of 61 mm, and a non-aqueous electrolyte solution (volume ratio of ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate). LiPF ₆ was dissolved at a concentration of 1.1 mol / l in a solvent mixed at 1: 1: 1, and a solution in which FEC and VC were further added in an amount of 0.1% by mass was injected.

  After injecting the non-aqueous electrolyte, the outer can was sealed to produce a lithium secondary battery having the structure shown in FIG. 1 and the appearance shown in FIG. This battery includes a cleavage vent for lowering the pressure when the internal pressure rises at the top of the can.

  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 as described above, and then pressed so as to be flattened and accommodated in a rectangular tube-shaped outer can 4 together with the electrolyte as a flat wound electrode body 6 Has been. However, in FIG. 1, in order to avoid complication, a metal foil, an electrolytic solution, and the like as a current collector used for manufacturing the positive electrode 1 and the negative electrode 2 are not illustrated. Also, the separator layers are not shown separately.

  The outer can 6 is made of an aluminum alloy and constitutes an outer casing of the battery. The outer can 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 armored can 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 outer can 4 through a PP 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 armored can 4, and the opening part of the armored can 4 is sealed by welding the junction part of both, and the inside of a 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. (See FIG. 1 and FIG. 2, in practice, the non-aqueous electrolyte inlet 14 is actually sealed with the non-aqueous electrolyte inlet.) Although it is a member, for ease of explanation, it is shown as a non-aqueous electrolyte inlet 14). 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 outer can 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 among the members constituting the battery are shown. Also in FIG. 1, the inner peripheral portion of the electrode group is not cross-sectional.

Examples 2-7
Except that the content of the composite in which the surface of SiO _x in the negative electrode active material was coated with the carbon material and the content of FEC and VC in the non-aqueous electrolyte used in the battery were as shown in Table 1, Examples In the same manner as in Example 1, a lithium secondary battery was produced.

Example 8
The content of the composite in which the surface of SiO _x in the negative electrode active material is coated with a carbon material, and the content of FEC and VC in the non-aqueous electrolyte used in the battery are as shown in Table 1, and further include a positive electrode mixture In the same manner as in Example 1, except that the paste application mass was changed so that the mass P of the positive electrode active material in the positive electrode mixture layer was 5.2 g and P / N was as shown in Table 1. A secondary battery was produced.

Example 9
The content of the composite in which the surface of SiO _x in the negative electrode active material is coated with a carbon material, and the content of FEC and VC in the non-aqueous electrolyte used in the battery are as shown in Table 1, and further include a positive electrode mixture In the same manner as in Example 1, except that the paste application mass was changed so that the mass P of the positive electrode active material in the positive electrode mixture layer was 18.7 g and P / N was as shown in Table 1. A secondary battery was produced.

Examples 10 and 11
The PE microporous separator for a lithium secondary battery used in the production of the separator in Example 1 was used as a separator without forming the porous layer (II), and the SiO _x surface in the negative electrode active material was used. Lithium secondary battery in the same manner as in Example 1 except that the content of the composite coated with the carbon material and the contents of FEC and VC in the non-aqueous electrolyte used in the battery were as shown in Table 1. Was made.

Example 12
By adjusting the concentration of the raw material compound in the mixed aqueous solution used for the synthesis of the coprecipitation compound, a hydroxide containing 6: 3: 1 molar ratio of Ni, Co, and Mn was synthesized and used. A lithium-containing composite oxide having the composition shown in Table 3 was synthesized in the same manner as in Example 1, and a positive electrode was produced in the same manner as in Example 1 except that this lithium-containing composite oxide was used. And the lithium secondary battery was produced like Example 3 except having used this positive electrode.

Example 13
By adjusting the concentration of the raw material compound in the mixed aqueous solution used for the synthesis of the coprecipitation compound, a hydroxide containing 6: 1: 3 molar ratio of Ni, Co, and Mn was synthesized and used. A lithium-containing composite oxide having the composition shown in Table 3 was synthesized in the same manner as in Example 1, and a positive electrode was produced in the same manner as in Example 1 except that this lithium-containing composite oxide was used. And the lithium secondary battery was produced like Example 3 except having used this positive electrode.

Example 14
By adjusting the concentration of the raw material compound in the mixed aqueous solution used for the synthesis of the coprecipitation compound, a hydroxide containing Ni, Co, and Mn in a molar ratio of 5.5: 1.5: 3 is synthesized, A lithium-containing composite oxide having the composition shown in Table 4 was synthesized in the same manner as in Example 1 except that this was used, and a positive electrode was formed in the same manner as in Example 1 except that this lithium-containing composite oxide was used. Produced. And the lithium secondary battery was produced like Example 3 except having used this positive electrode.

Example 15
By adjusting the concentration of the raw material compound in the mixed aqueous solution used for the synthesis of the coprecipitated compound, a hydroxide containing Ni, Co, and Mn in a molar ratio of 5.5: 2: 2.5 is synthesized, A lithium-containing composite oxide having the composition shown in Table 4 was synthesized in the same manner as in Example 1 except that this was used, and a positive electrode was formed in the same manner as in Example 1 except that this lithium-containing composite oxide was used. Produced. And the lithium secondary battery was produced like Example 3 except having used this positive electrode.

Example 16
By adjusting the concentration of the raw material compound in the mixed aqueous solution used for the synthesis of the coprecipitation compound, a hydroxide containing Ni, Co, and Mn in a molar ratio of 5: 2: 3 was synthesized and used. A lithium-containing composite oxide having the composition shown in Table 4 was synthesized in the same manner as in Example 1, and a positive electrode was produced in the same manner as in Example 1 except that this lithium-containing composite oxide was used. And the lithium secondary battery was produced like Example 3 except having used this positive electrode.

Example 17
By adjusting the concentration of the raw material compound in the mixed aqueous solution used for the synthesis of the coprecipitation compound, a hydroxide containing Ni, Co, and Mn in a molar ratio of 5: 3: 2 was synthesized and used. A lithium-containing composite oxide having the composition shown in Table 4 was synthesized in the same manner as in Example 1, and a positive electrode was produced in the same manner as in Example 1 except that this lithium-containing composite oxide was used. And the lithium secondary battery was produced like Example 3 except having used this positive electrode.

Example 18
Nickel sulfate, cobalt sulfate, manganese sulfate and magnesium sulfate, ^{respectively, 2.69mol / dm 3, 0.84mol /} dm 3, 0.63mol / dm 3, a mixed aqueous solution containing a concentration of 0.04 mol / dm ³ A coprecipitated compound was synthesized in the same manner as in Example 1 except that it was used. Then, a hydroxide containing Ni, Co, Mn, and Mg in a molar ratio of 64: 20: 15: 1 was synthesized in the same manner as in Example 1 except that this coprecipitation compound was used. A lithium-containing composite oxide having the composition shown in Table 4 was synthesized in the same manner as in Example 1 except that 0.2 mol of the oxide and 0.2 mol of LiOH.H ₂ O were used. A positive electrode was produced in the same manner as in Example 3 except that this lithium-containing composite oxide was used, and a lithium secondary battery was produced in the same manner as in Example 3 except that this positive electrode was used.

Example 19
0.2 mol of a hydroxide containing Ni, Co, Mn, and Mg synthesized in the same manner as in Example 18 in a molar ratio of 64: 20: 15: 1, 0.2 mol of LiOH.H ₂ O, A lithium-containing composite oxide having the composition shown in Table 4 was synthesized in the same manner as in Example 1 except that 0.0004 mol of GeO ₂ was used. A positive electrode was produced in the same manner as in Example 3 except that this lithium-containing composite oxide was used, and a lithium secondary battery was produced in the same manner as in Example 3 except that this positive electrode was used.

Example 20
0.2 mol of a hydroxide containing Ni, Co, Mn, and Mg synthesized in the same manner as in Example 18 in a molar ratio of 64: 20: 15: 1, 0.2 mol of LiOH.H ₂ O, A lithium-containing composite oxide having the composition shown in Table 4 was synthesized in the same manner as in Example 1 except that 0.0002 mol of B ₂ O ₃ was used. A positive electrode was produced in the same manner as in Example 3 except that this lithium-containing composite oxide was used, and a lithium secondary battery was produced in the same manner as in Example 3 except that this positive electrode was used.

Example 21
0.2 mol of a hydroxide containing Ni, Co, Mn, and Mg synthesized in the same manner as in Example 18 in a molar ratio of 64: 20: 15: 1, 0.2 mol of LiOH.H ₂ O, A lithium-containing composite oxide having the composition shown in Table 4 was synthesized in the same manner as in Example 1 except that 0.0002 mol of Ga ₂ O ₃ was used. A positive electrode was produced in the same manner as in Example 3 except that this lithium-containing composite oxide was used, and a lithium secondary battery was produced in the same manner as in Example 3 except that this positive electrode was used.

Example 22
0.2 mol of a hydroxide containing Ni, Co, Mn, and Mg synthesized in the same manner as in Example 18 in a molar ratio of 64: 20: 15: 1, 0.2 mol of LiOH.H ₂ O, A lithium-containing composite oxide having the composition shown in Table 4 was synthesized in the same manner as in Example 1 except that 0.0004 mol of SrCO ₃ was used. A positive electrode was produced in the same manner as in Example 3 except that this lithium-containing composite oxide was used, and a lithium secondary battery was produced in the same manner as in Example 3 except that this positive electrode was used.

Example 23
0.2 mol of a hydroxide containing Ni, Co, Mn, and Mg synthesized in the same manner as in Example 18 in a molar ratio of 64: 20: 15: 1, 0.2 mol of LiOH.H ₂ O, A lithium-containing composite oxide having the composition shown in Table 4 was synthesized in the same manner as in Example 1 except that 0.0004 mol of Ba (OH) ₂ was used. A positive electrode was produced in the same manner as in Example 3 except that this lithium-containing composite oxide was used, and a lithium secondary battery was produced in the same manner as in Example 3 except that this positive electrode was used.

Comparative Example 1
The PE microporous separator for a lithium secondary battery used in the production of the separator in Example 1 was used as a separator without forming the porous layer (II), and the SiO _x surface in the negative electrode active material was used. The content of the composite coated with the carbon material, and the contents of FEC and VC in the non-aqueous electrolyte used in the battery are as shown in Table 2, and the thickness of the positive electrode mixture layer was changed and P / N A lithium secondary battery was produced in the same manner as in Example 1 except that the values were as shown in Table 2.

Comparative Examples 2 and 3
The PE microporous separator for a lithium secondary battery used in the production of the separator in Example 1 was used as a separator without forming the porous layer (II), and the SiO _x surface in the negative electrode active material was used. Lithium secondary battery in the same manner as in Example 1 except that the content of the composite coated with the carbon material and the contents of FEC and VC in the non-aqueous electrolyte used in the battery were as shown in Table 2. Was made.

The content of the composite in which the SiO _x surface of the negative electrode used in the lithium secondary batteries of Examples 1 to 23 and Comparative Examples 1 to 3 was coated with a carbon material in the negative electrode active material (in the table, “SiO _x complex content ”), the FEC content and VC content in the non-aqueous electrolyte, and the ratio P / N of the mass P of the positive electrode active material and the mass N of the negative electrode active material (in the table“ Table 1 and Table 2 show the composition of the positive electrode active material (lithium-containing composite oxide).

  For the lithium secondary batteries of Examples 1 to 23 and Comparative Examples 1 to 3, constant current-constant voltage charging with a constant current of 1 C (equivalent to 1630 mA) and a constant voltage of 4.2 V at room temperature (25 ° C.) After performing the total charge time: 3 hours, 1C constant current discharge (discharge end voltage: 3.0 V) was performed, and the discharge capacity (mAh) was measured. In addition, charging / discharging was repeated with this series of charging and discharging operations as one cycle, and the number of cycles N at which a capacity retention rate of 80% could be maintained was examined. The capacity retention rate is calculated by “Nth cycle discharge capacity / first cycle discharge capacity × 100%”. These results are shown in Tables 5 and 6.

  As shown in Table 5 and Table 6, the value of the ratio P / N between the mass P of the positive electrode active material and the negative electrode active material N is appropriate, and the amounts of FEC and VC in the used non-aqueous electrolyte are also appropriate. The lithium secondary batteries of Examples 1 to 23 have a large number of cycles N capable of maintaining a capacity retention rate of 80%, and have good charge / discharge cycle characteristics.

  On the other hand, the battery of Comparative Example 1 in which the value of P / N is too large, and the batteries of Comparative Examples 2 and 3 using a non-aqueous electrolyte not containing any one of FEC and VC are 80% capacity retention. The number of cycles N that can hold the charge is small, and the charge / discharge cycle characteristics are poor.

1 Positive electrode 2 Negative electrode 3 Separator

Claims (5)

A lithium 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 lithium-containing composite oxide as a positive electrode active material on one side or both sides of a current collector,
The positive electrode current collector has a thickness of 10 to 15 μm,
The negative electrode contains a material containing Si and O as constituent elements (however, the atomic ratio x of O to Si is 0.5 ≦ x ≦ 1.5) and a graphitic carbon material as a negative electrode active material. It has a negative electrode mixture layer on one side or both sides of a current collector,
The ratio P / N of the mass P of the positive electrode active material and the mass N of the negative electrode active material is 1.0 to 3.6,
A lithium secondary battery using 1 to 10% by mass of a fluorine-substituted cyclic carbonate as the non-aqueous electrolyte.   The lithium secondary battery according to claim 1, wherein the negative electrode active material contains a composite of a material containing Si and O as constituent elements and a carbon material.   3. The lithium secondary battery according to claim 2, wherein the content of the composite of the material containing Si and O as constituent elements and the carbon material in the negative electrode active material is 0.01 to 20 mass%.   The lithium secondary battery according to any one of claims 1 to 3, wherein the fluorine-substituted cyclic carbonate contained in the nonaqueous electrolytic solution is 4-fluoro-1,3-dioxolan-2-one.   The lithium secondary battery according to any one of claims 1 to 4, further comprising a non-aqueous electrolyte containing 1 to 10% by mass of vinylene carbonate.

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