KR20170061620A - Lithium ion secondary battery and manufacturing method thereof - Google Patents

Abstract

[PROBLEMS] To provide a lithium ion secondary battery having a high capacity and excellent charge / discharge cycle characteristics, and a manufacturing method thereof.
[MEANS FOR SOLVING PROBLEMS] A lithium ion secondary battery of the present invention is a lithium ion secondary battery comprising a laminated electrode body composed of a positive electrode, a negative electrode and a separator, a cross section parallel to the stacking direction of the positive electrode, the negative electrode and the separator, (1) when discharged at a discharge current rate of 0.1 C until the voltage reaches 2.0 V, the potential of the metal M other than Li and Li contained in the cathode active material (Li / M) is 0.8 to 1.05, or (2) the third electrode has a Li supply source at a position facing the end face of the laminated electrode body and is electrically connected to the third electrode, And Li ions supplied from the cathode are doped to the cathode.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a lithium ion secondary battery,

The present invention relates to a lithium ion secondary battery having a high capacity and excellent charge / discharge cycle characteristics, and a manufacturing method thereof.

BACKGROUND ART Lithium ion secondary batteries, which are one type of electrochemical devices, are being applied to portable storage devices, automobiles, power tools, power storage systems for electric chairs, households, and businesses because of their high energy density. Particularly, portable devices are widely used as power sources for mobile phones, smart phones, tablet PCs, and the like.

In addition, lithium ion secondary batteries are required to have high capacity and to improve various battery characteristics in accordance with the expansion of the applicable equipment and the like. Particularly, since it is a secondary battery, improvement of the charge-discharge cycle characteristics is strongly demanded.

Generally, a carbon material such as graphite, which is capable of inserting and removing lithium (Li) ions, is widely used as a negative electrode active material of a lithium ion secondary battery. On the other hand, Si or Sn, or a material containing such an element as a material capable of inserting and removing more Li ions has also been studied, and in particular, SiO _{x, which} is a structure in which fine particles of Si are dispersed in SiO ₂ , is attracting attention. Further, since such a material has low conductivity, it has been proposed to have a structure in which a conductive material such as carbon is coated on the surface of the particles (Patent Documents 1 and 2).

In addition, since the negative electrode material containing Si has a relatively high irreversible capacity, it is preferable to introduce Li ions to the cathode side in advance, for example, using Li as a source of metal Li. In the conventional method, Li ions are introduced into the negative electrode by arranging Li opposite to the positive electrode mixture layer side (Patent Documents 3 to 6).

As a means for pre-doping the alkali metal ions to the electrode, a method of arranging the electrodes for positive electrode and negative electrode and the electrode having an alkali metal ion source so as to be immersed in the pre-doping solution in which the alkali metal ions have eluted, A direct current power source is connected between the battery electrode and the supplementary electrode so that the direction of the electric field by the direct current becomes equal to the direction of the electrode surface of the battery electrode (Patent Document 7).

Japanese Patent Application Laid-Open No. 2004-47404 Japanese Patent Application Laid-Open No. 2005-259697 International Publication WO 98/033227 International Publication WO 2007/072713 Japanese Patent Application Laid-Open No. 2007-299698 Japanese Unexamined Patent Application Publication No. 2015-060881 Japanese Unexamined Patent Application Publication No. 2015-088437

However, when Li ion is introduced to face the mixed layer surface of the positive and negative electrodes as described in Patent Documents 3, 4 and 6 by using the material (S) of the anode material containing Si as the anode active material, ) Absorbs Li ions and expands extremely, so that the negative electrode material mixture layer may fall off from the negative electrode current collector.

Further, when the battery electrode is immersed in the pre-doping solution as in Patent Document 7 and pre-doping is performed, and then the battery is assembled, the workability is troublesome. Further, if the electrode is entirely immersed in the pre-doping solution, Li may be precipitated in the tab portion.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a lithium ion secondary battery excellent in charge capacity and charge / discharge cycle characteristics, and a method of manufacturing the same.

The lithium ion secondary battery of the present invention has a laminated electrode body in which a positive electrode and a negative electrode are laminated via a separator and a third electrode used for doping Li ions to the negative electrode, And an end face parallel to the lamination direction of the positive electrode, the negative electrode and the separator. The negative electrode has a negative electrode mixture layer containing a negative electrode active material on at least one surface of the negative electrode collector, Wherein the negative electrode active material contains a material (S) containing Si and the content of the material (S) is 5 mass% or more when the total amount of the negative electrode active materials contained in the negative electrode material mixture layer is 100 mass% , The positive electrode has a positive electrode mixture layer containing a metal oxide as a positive electrode active material composed of a metal M other than Li and Li on at least one surface of the positive electrode collector, Is disposed such that at least a part thereof is opposed to the end face of the laminated electrode body and when discharging is performed until the voltage reaches 2.0 V at a discharge current rate of 0.1 C, And the molar ratio (Li / M) of the metal M is 0.8 to 1.05.

Another aspect of the lithium ion secondary battery of the present invention is a lithium ion secondary battery comprising a laminated electrode body in which a positive electrode and a negative electrode are laminated via a separator and a third electrode used for doping Li ions to the negative electrode, The electrode body has a plane and a cross section parallel to the stacking direction of the positive electrode, the negative electrode and the separator. The negative electrode has a negative electrode mixture layer containing a negative electrode active material on at least one surface of the negative electrode collector And the content of the material (S) is 5% by mass or less and the total content of the negative electrode active materials contained in the negative electrode active material layer is 100% by mass, the content of the material (S) And the positive electrode has a positive electrode mixture layer containing a metal oxide composed of Li and a metal M other than Li as a positive electrode active material on at least one surface of the positive electrode collector, Wherein the third electrode is provided with a Li source and the third electrode is disposed such that the Li supply source faces the end face of the laminated electrode body and the cathode is made conductive to the third electrode, And Li ions supplied from a supply source are doped.

A manufacturing method of a lithium ion secondary battery of the present invention is a manufacturing method of a lithium ion secondary battery comprising a negative electrode having a negative electrode mixture layer containing a material (S) containing Si as a negative electrode active material on at least one surface of an anode current collector, A method of manufacturing a lithium ion secondary battery having a stacked electrode body and a third electrode used for doping Li ions into the negative electrode, wherein the laminate electrode body has a planar surface, Wherein the third electrode has a cross section parallel to the stacking direction of the separator and the third electrode has a Li supply source and the third electrode is disposed such that the Li supply source faces the end face of the laminated electrode body, And a step of conducting Li ions to the cathode from the Li source by conducting to the third electrode.

According to the present invention, it is possible to provide a lithium ion secondary battery having a high capacity and excellent charge / discharge cycle characteristics, and a manufacturing method thereof.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a plan view schematically showing an example of an anode relating to a lithium ion secondary battery of the present invention. FIG.
2 is a plan view schematically showing an example of a cathode relating to the lithium ion secondary battery of the present invention.
3 is a perspective view schematically showing an example of a laminated electrode body related to the lithium ion secondary battery of the present invention.
4 is a perspective view schematically showing an example of a third electrode related to the lithium ion secondary battery of the present invention.
5 is a perspective view showing a state in which the laminated electrode body shown in Fig. 3 and the third electrode shown in Fig. 4 are combined.
6 is a perspective view schematically showing an example of an electrode body related to the lithium ion secondary battery of the present invention.
7 is a plan view schematically showing an example of the lithium ion secondary battery of the present invention.
8 is a sectional view taken along the line I-I in Fig.
Fig. 9 is a plan view schematically showing the third electrode used in Comparative Example 1. Fig.

As the negative electrode relating to the lithium ion secondary battery of the present invention, a negative electrode mixture layer containing a negative electrode active material, a binder, or the like is used, which has a structure having one side or both sides of the current collector.

The negative electrode active material in the present invention contains a material (S) containing Si. It is known that Si is alloyed with Li to introduce Li ions, but it is also known that the volume expansion at the time of introducing Li is large.

The material (S) exhibits a capacity of 1000 mAh / g or more and is characterized in that it greatly exceeds 372 mAh / g, which is the theoretical capacity of graphite. On the other hand, as compared with general charge / discharge efficiency (90% or more) of general graphite, the initial charge / discharge efficiency of the material (S) is less than 80% and irreversible capacity increases. there was. Therefore, it is desired to introduce Li ions into the cathode in advance.

As a method of introducing Li ions into the negative electrode active material, there is a method in which a negative electrode material mixture layer is formed by sticking a metal lithium foil to the negative electrode material mixture layer or by forming an Li deposition layer on the negative electrode material mixture layer, A method of disposing a Li source so as to oppose and introducing Li ions by electrochemical contact (short circuit) was common. However, when Li ions are introduced in a face-to-face relationship with the compounded layer, it is necessary to dispose an Li source in each of the negative electrode mixture layers in the laminated electrode body, and the production efficiency deteriorates. Therefore, a metal foil (current collector) serving as a support for the mixed layer of the positive electrode and the negative electrode has a hole penetrating from one surface to the other surface. By doing so, Li ions are introduced into all the cathodes by passing the Li source across the outermost surface in the stacking direction of the laminated electrode body, through the through holes of the metal foil, and diffusing Li ions into the entire laminated electrode body.

However, since the material S can receive a large amount of Li ions, the expansion due to the Li ions is remarkable. Therefore, the negative electrode material mixture layer of the negative electrode closest to the Li source receives the largest amount of Li ions and greatly expands , The state of adhesion with the negative electrode current collector can not be maintained, and the battery may fall off.

Therefore, in the present invention, a laminated electrode body formed by laminating an anode and a cathode with a separator interposed therebetween is used, and the cross section (that is, the anode, the cathode, and the separator are stacked in parallel) The Li supply source for Li ion doping into the cathode is disposed on the surface of the battery. This makes it possible to reduce the number of places in which the Li supply source is disposed in the battery as much as possible, , And that the negative electrode mixture layer related to some of the negative electrodes is excessively expanded to deteriorate the adhesion state with the current collector. Further, in the present invention, since the formation of the through holes is not required in the current collector for the positive electrode and the negative electrode, particularly, the current collector of the negative electrode is required to be expanded and contracted by the charge / discharge of the negative electrode active material, So that it is possible to apply a structure which can withstand the expansion and contraction sufficiently.

The reason why the negative electrode is doped with Li ions is that when the battery is discharged at a discharge current rate of 0.1 C until the voltage reaches 2.0 V, the molar ratio (Li / Li) of Li contained in the positive electrode active material to the metal M other than Li, M). In one embodiment of the lithium ion secondary battery of the present invention, the molar ratio (Li / M) is 0.8 or more and 1.05 or less. The molar ratio (Li / M) becomes smaller than the lower limit value in the case where the material (S) is used as the negative electrode active material and the negative electrode is not doped with Li ions.

The analysis of the composition of the cathode active material when discharged at a discharge current rate of 0.1 C until the voltage reached 2.0 V can be performed as follows using the ICP (Inductive Coupled Plasma) method. First, 0.2 g of the cathode active material to be measured is sampled and placed in a 100-mL vessel. Thereafter, 5 mL of pure water, 2 mL of aqua regia and 10 mL of pure water were added in this order, and the mixture was dissolved by heating. After cooling, the mixture was further diluted 25 times with pure water and analyzed by a calibration curve method using an ICP analyzer "ICP-757" manufactured by JARRELASH The composition is analyzed. The composition amount can be derived from the obtained results. The molar ratio (Li / M) described in the following Examples is a value obtained by this method.

The material (S) is a negative electrode material containing Si. Specific examples of the material (S) include a material obtained by compounding Si powder and carbon, a material coated with carbon material, a material obtained by sandwiching Si powder with graphene or flake graphite, Si and O A material represented by a composition formula SiO _x (where the atomic ratio x of O to Si is 0.5? X? 1.5) contained in the constituent elements. Of these, it is preferable to use SiO _x .

The SiO _x may contain a microcrystalline or amorphous phase of Si. In this case, the atomic ratio of Si and O is a ratio of Si to the microcrystalline or amorphous phase containing Si. That is, SiO _x includes a structure in which Si (for example, microcrystalline Si) is dispersed in an amorphous SiO ₂ matrix, and the amorphous SiO ₂ and Si dispersed therein are combined so that the atomic ratio x 0.5? X? 1.5. For example, in the case of a material in which Si is dispersed in an amorphous SiO ₂ matrix and a molar ratio of SiO ₂ to Si is 1: 1, x = 1, and hence the structural formula is expressed by SiO 2. In the case of the 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 in some cases, but when observed with a transmission electron microscope, .

The SiO _x is preferably a complex compounded with a carbon material. For example, it is preferable that the surface of SiO _x is coated with a carbon material. In general, when SiO _x is used as an anode active material, it is necessary to use a conductive material (conductive auxiliary agent) and to mix and disperse SiO _x and a conductive material in the cathode, It is necessary to form a good conductive network. A composite in which SiO _x is complexed with a carbon material can form a conductive network in the negative electrode better than, for example, a material obtained by mixing only a conductive material such as SiO _x with a carbon material.

That is, the specific resistance value of the SiO _x is usually 10 ^{3-10 7} kΩ㎝ compared to the specific resistance value of the carbon material of the foregoing is by the composite is usually from 10 ^-5 ~10kΩ㎝, SiO _x and the carbon material, SiO _x The conductivity can be improved.

As the complex of the SiO _x and the carbon material, an SiO _x and an assembly of a carbon material (granulated body) and the like can be mentioned as well as the surface of the SiO _x is coated with a carbon material as described above.

The carbon material that can be used for forming the composite with SiO _{x is preferably} a carbon material such as low crystalline carbon, carbon nanotube, vapor grown carbon fiber, or the like.

Examples of the carbon material include a carbon material in the form of a fiber or a coil, carbon black (including acetylene black and Ketjen black), artificial graphite, graphitized carbon and hard graphite And carbon) is preferable. The fibrous or coil-shaped carbon material is preferable in that it is easy to form a conductive network and has a large surface area. Carbon black (including acetylene black and Ketjen black), graphitized carbon and non-graphitized carbon have high electrical conductivity and high liquid retentivity, and SiO _x particles expand and shrink Is also preferable in that it has a property of easily maintaining contact with the particles.

Among the above-mentioned carbon materials, a fibrous carbon material is particularly preferable for use when the composite with SiO _x is an assembly. Since the fibrous carbon material has a thin shape and a high flexibility, it can follow the expansion and contraction of SiO _{x as} the battery is charged and discharged. Further, since the bulk density is large, the SiO _x particles and many junction points . ≪ / RTI > Examples of the fibrous carbon include polyacrylonitrile (PAN) carbon fibers, pitch carbon fibers, vapor-grown carbon fibers, and carbon nanotubes, and any of them may be used.

When using the SiO _x and the composite of the carbon material in the negative electrode, the ratio of the SiO _x and the carbon material, from the viewpoint of satisfactorily exert the effect of the composite with the carbon material, SiO _x: based on 100 parts by mass of a carbon material More preferably 5 parts by mass or more, and more preferably 10 parts by mass or more. In the above composite, is connected to the SiO _x and the proportion of the carbon material composite is too large, the cathode reduction in SiO _x content in the material mixture layer, and in that the concerned be small, the effect of high capacity, SiO _x: 100 by weight The carbon material is preferably 50 parts by mass or less, more preferably 40 parts by mass or less.

The complex of the above-mentioned SiO _x and the carbon material can be obtained, for example, by the following method.

In the case where the surface of SiO _x is coated with a carbon material to form a composite, for example, the SiO _x particles and the hydrocarbon-based gas are heated in a gas phase to cause carbon generated by pyrolysis of the hydrocarbon gas to be deposited on the surface of the particles . As described above, according to the vapor phase growth (CVD) method, the hydrocarbon-based gas widely spreads to every corner of the SiO _x particles to form a thin uniform coating film (carbon material coating layer) containing a carbon material having conductivity on the surface of the particles It is possible to impart conductivity to SiO _x particles with good uniformity by a small amount of carbon material.

In the production of SiO _x coated with a carbon material, the treatment temperature (atmospheric temperature) of the CVD method varies depending on the kind of the hydrocarbon-based gas, but is usually in the range of 600 to 1200 캜, More preferably 800 DEG C or higher. This is because a coating layer containing carbon having a small amount of impurities and having high conductivity can be formed at a higher treatment temperature.

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

In the case of manufacturing an assembly of SiO _x and a carbon material, a dispersion in which SiO _x is dispersed in a dispersion medium is prepared, sprayed, and dried to produce an assembly containing a plurality of particles. As the dispersion medium, for example, ethanol and the like can be used. The spraying of the dispersion liquid is suitably carried out usually in an atmosphere of 50 to 300 캜. In addition to the above method, an assembly of SiO _x and a carbon material can also be produced in a method of granulation by a mechanical method using a vibrating or planetary ball mill or rod mill.

Not less than the sum of the negative electrode active material contained in the negative electrode material mixture layer when the 100% by weight, the material (S) content (for example, SiO _x and a complex of a carbon material) is at least 5% by weight, 10% by weight And more preferably 50 mass% or more. As described above, the material S is a material capable of achieving a significantly high capacity as compared with graphite, so that even when a small amount of the material S is included in the negative electrode active material, the capacity improving effect of the battery can be obtained. On the other hand, in order to further realize the high capacity of the battery, it is preferable that the total amount of the negative electrode active material contains 10 mass% or more of the material (S). The content of the material (S) may be adjusted in accordance with the application of the various batteries and the required characteristics. The ratio of the material (S) is preferably 99% by mass or less, more preferably 90% by mass or less, in order to exhibit the effect of introducing Li by electrochemical contact between Li and the cathode by graphite A and graphite B More preferably 80% by mass or less.

When the average particle diameter of the material (S) is too small, the dispersibility of the material (S) deteriorates and the effect of the present invention may not be sufficiently obtained. The material (S) An excessively large average particle diameter makes it easy for the material S to collapse due to expansion and contraction (this phenomenon is linked to the deterioration of the capacity of the material S.) Or less.

In addition to the above-described material (S), a carbon material capable of electrochemically intercalating and deintercalating Li, such as graphite, may be used for the cathode. Particularly, graphite A having an average particle diameter of more than 15 μm and not more than 25 μm and graphite B having an average particle diameter of 8 μm or more and 15 μm or less and the surface of graphite particles coated with amorphous carbon are preferably used in combination.

Examples of the graphite A include natural graphite and artificial graphite which are used as a negative electrode active material of a conventional lithium ion secondary battery. Examples of the artificial graphite include those obtained by baking coke or an organic material at 2800 DEG C or higher or a mixture of natural graphite and the coke or an organic material and performing heat treatment at 2800 DEG C or higher, in and the like having been coated on the surface of the natural graphite that the firing, the argon ion laser Raman represented by 1340~1370㎝ ^-1 to the peak intensity expressed by 1570~1590㎝ ^-1 in the spectrum peak Graphite having an R value of 0.05 to 0.2 which is an intensity ratio can be used. When the average particle diameter is within the above-mentioned range, two or more types of graphite may be used in combination with the graphite A.

Graphite B is composed of graphite particles that become the parent particles and amorphous carbon that covers the surface. Specifically, it is a graphite having an R value of 0.1 to 0.7 which is a peak intensity ratio expressed by 1340 to 1370 cm ^-1 with respect to a peak intensity expressed by 1570 to 1590 cm ^-1 in an argon ion laser Raman spectrum. The R value is more preferably 0.3 or more so as to secure a sufficient covering amount of the amorphous carbon. The R value is preferably 0.6 or less because the irreversible capacity increases when the amount of coating of amorphous carbon is excessively large. Such graphite B is, for example, natural graphite having a d ₀₀₂ of 0.338 nm or less or graphite obtained by shaping artificial graphite into a spherical shape as a base material (parent particle), and its surface is coated with an organic compound to obtain 800 Firing at ~ 1500 ° C, followed by shredding, and sieving through a sieve. Examples of the organic compound coating the base material include aromatic hydrocarbons; Tar or pitch obtained by polycondensing aromatic hydrocarbons under heating and pressure; Tar, pitch or asphalt mainly containing a mixture of aromatic hydrocarbons; And the like. In order to coat the base material with the organic compound, a method of impregnating and kneading the base material with the organic compound may be employed. Graphite B can also be produced by a vapor phase method in which a hydrocarbon gas such as propane or acetylene is carbonized by thermal decomposition and deposited on the surface of graphite having d ₀₀₂ of 0.338 nm or less.

The graphite B has a high water solubility (for example, it can be quantified in terms of the ratio of the constant current charging capacity to the total charging capacity) of the Li ion. Therefore, the lithium ion secondary battery in which graphite B is used in combination is excellent in water solubility of Li ions and has better charge / discharge cycle characteristics. As described above, when Li is introduced into the negative electrode containing the material (S) by electrochemical contact (short circuit), unevenness of introduction of Li can be suppressed when the graphite B is used in combination, I thought that it was planned.

However, it has been found that sufficient improvement of battery characteristics can not be obtained by simply using graphite B as a single material. Since graphite B is made of graphite activated as spherical in the above-described manner as described above, there is a place in graphite B that can not sufficiently secure the contact points between particles, and this causes the unevenness in the introduction of Li So that the water solubility of the Li ion in the whole of the negative electrode did not improve and it was presumed that the improvement of the battery characteristics did not reach a great improvement. Here, the inventors of the present invention have found that by using graphite A having an average particle diameter larger than graphite B, specifically, greater than 15 탆 and 25 탆 or less, with graphite B, battery characteristics are significantly improved. Specifically, the total content of graphite A and graphite B in the entire negative electrode active material contained in the negative electrode is 20 mass% or more and 99 mass% or less, and the graphite A to the graphite B in the total negative electrode active material contained in the negative electrode (A / B) of not less than 0.5 and not more than 4.5. By using the graphite A and the graphite B in combination in this manner, the points where the contact points of the graphite B can not be secured are reduced, that is, the nonuniformity of introduction of Li ions into the negative electrode is reduced, Is the reason for the increase.

Further, it is preferable that the particle size of the graphite A is not too small as the specific surface area becomes excessively large (the irreversible capacity increases) if the particle diameter is too small. Therefore, it is preferable to use graphite A having an average particle diameter of more than 15 mu m. In addition, graphite B has too small a particle diameter, and the coating amount of amorphous carbon covering the surface is irregular, and it is impossible to sufficiently exhibit the feature of graphite B, . Therefore, it is preferable to use graphite B having an average particle diameter of 8 mu m or more.

The average particle diameter of graphite (graphite A, graphite B and other graphite) and the material S can be measured by a laser scattering particle size distribution meter (for example, a microtrack particle size distribution measuring apparatus " HRA9320 " manufactured by Hitachi Kasei Kogyo Co., Ltd.), a value of a 50% diameter in the integrated fraction based on the volume when the integral volume is obtained from the particles having a small particle size distribution measured by dispersing these particles in a medium which does not dissolve or swell them (D _50% ) is the median diameter.

The specific surface area of graphite A and graphite B (according to the BET method) is preferably 1.0 m 2 / g or more, more preferably 5.0 m 2 / g or less, in the case of a device such as "Bellows Mini"

The crystallite size in the c-axis direction in the crystal structure of graphite A and graphite B: Lc is preferably 3 nm or more, more preferably 8 nm or more, and still more preferably 25 nm or more. This range is preferable because the storage and removal of lithium ions are easier. The upper limit value of Lc of graphite is not particularly limited, but is usually about 200 nm.

The negative electrode active material is not limited to the above-described material (S), the negative electrode active material other than graphite A and graphite B (for example, graphite A which is the same kind as graphite A and has an average particle diameter of less than 15 mu m, , Graphite which does not correspond to graphite A and graphite B), an alloy of Si or Sn, an alloy containing Si or Sn, or an oxide containing Si or Sn to such an extent as not to impair the effect of the present invention It is possible.

As the binder related to the negative electrode material mixture layer, for example, a material which is electrochemically inactive to Li and does not affect other materials as much as possible in the range of the potential of the negative electrode is selected. Concretely, there can be mentioned, for example, styrene butadiene rubber (SBR), polyvinylidene fluoride (PVDF), carboxymethylcellulose (CMC), polyvinyl alcohol (PVA), methylcellulose, polyimide, polyamideimide, And derivatives and copolymers thereof, and the like. These binders may be used alone or in combination of two or more.

A conductive material may be further added to the negative electrode mixture layer as a conductive auxiliary agent. Examples of such a conductive material include carbon black (thermal black, furnace black, channel black, ketjen black, acetylene black and the like), carbon fiber, metal powder (Such as copper, nickel, aluminum, and silver powder), metal fibers, and polyphenylene derivatives (described in Japanese Patent Application Laid-Open No. 59-20971). Of these, carbon black is preferably used, and ketjen black and acetylene black are more preferable.

The negative electrode is prepared by preparing a composition containing a negative electrode mixture in which a negative active material and a binder and, if necessary, a conductive auxiliary agent are dispersed in a solvent such as N-methyl-2-pyrrolidone (NMP) , And the binder may be dissolved in a solvent), and this is coated on one side or both sides of the current collector, dried, and then subjected to calendering if necessary. However, the method for producing the negative electrode is not limited to the above method, and may be produced by another manufacturing method.

The thickness of the negative electrode mixture layer is preferably 10 to 100 占 퐉 per one side of the current collector. The density of the negative electrode material mixture layer (calculated from the mass and thickness of the negative electrode material mixture layer per unit area stacked on the current collector) is preferably 1.0 g / cm 3 or more, more preferably 1.2 g / Cm < 3 > or more. If the density of the negative electrode material mixture layer is too high, adverse effects such as lowering of the permeability of the nonaqueous electrolyte solution occur, and therefore, it is preferably 1.6 g / cm 3 or less. The composition of the negative electrode material mixture layer is preferably, for example, 80 to 99 mass% of the negative electrode active material, and preferably 0.5 to 10 mass% of the binder, The amount is preferably 1 to 10% by mass.

As the negative electrode collector for supporting the negative electrode collector and the negative electrode mixture layer, for example, a copper foil or a nickel foil can be used. It is also possible to use a copper or nickel foil having a through hole penetrating from one surface of the negative electrode current collector to the other surface, a punching metal, a mesh, or an expanded metal. The upper limit of the thickness of the negative electrode current collector is preferably 30 占 퐉, and the lower limit is preferably 4 占 퐉 to secure the mechanical strength.

When a foil having no through hole in the collector is used, since the contact area between the negative electrode mixture layer and the negative electrode collector becomes larger, the negative electrode material mixture layer expands and shrinks to prevent dropout more preferably, Therefore, it is desirable.

Further, a lead body for electrically connecting to another member in the lithium ion secondary battery may be formed on the cathode in accordance with a usual method, if necessary.

As the positive electrode relating to the lithium ion secondary battery of the present invention, for example, a positive electrode mixture layer containing a positive electrode active material, a conductive auxiliary agent and a binder may be used in one side or both sides of the positive electrode current collector.

The positive electrode active material used for the positive electrode is a metal oxide (lithium-containing transition metal oxide) composed of Li and a metal M (Mg, Mn, Fe, Co, Ni, Cu, Zn, Al, Ti, Ge, Cr, Is used. Specific examples of such lithium-containing transition metal oxides include Li _x CoO ₂ , Li _x NiO ₂ , Li _x MnO ₂ , Li _x Co _y Ni _{1 - y} O ₂ , Li _x Co _y M _{1 - y} O ₂ , Li _x Ni _{1 - y} M _y O ₂ , Li _x Mn _y Ni _z Co _{1 -yz} O ₂ , Li _x Mn ₂ O ₄ , and Li _x Mn _{2 - y} M _y O ₄ . In the above structural formulas, M is at least one metal element selected from the group consisting of Mg, Mn, Fe, Co, Ni, Cu, Zn, Al, Ti, Ge and Cr, 1.1, 0 < y < 1.0 and 1.0 < z < 2.0.

The conductive auxiliary used for the positive electrode may be any one that is chemically stable in the battery. For example, graphite such as natural graphite and artificial graphite; Carbon black such as acetylene black, Ketjen black (trade name), channel black, furnace black, lamp black, and thermal black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as aluminum powder; Carbon fluoride; Zinc oxide; Conductive whiskers composed of potassium titanate and the like; Conductive metal oxides such as titanium oxide; Organic conductive materials such as polyphenylene derivatives; These may be used singly or in combination of two or more kinds. Among these, graphite having high conductivity and carbon black having excellent liquid-absorbing property are preferable. As the form of the conductive auxiliary agent, not only primary particles but also secondary aggregates and aggregates such as chain structures can be used. Such assemblies are easy to handle, and productivity is improved.

PVDF, vinylidene fluoride-chlorotrifluoroethylene [P (VDF-CTFE)], polytetrafluoroethylene (PTFE), SBR and the like can be used as the binder relating to the positive electrode material mixture layer.

The positive electrode is prepared by preparing a composition containing a positive electrode active material mixture in the form of a paste or slurry in which the above-mentioned positive electrode active material, conductive auxiliary agent and binder are dispersed in a solvent such as NMP (provided that the binder is dissolved in a solvent ), Which is then coated on one side or both sides of the current collector, dried, and subjected to calendering if necessary. The production method of the anode is not limited to the above method, but may be produced by another production method.

It is preferable that the thickness of the positive electrode material mixture layer is, for example, 10 to 100 占 퐉 per one side of the current collector. The amount of the positive electrode active material is preferably 65 to 95 mass%, the amount of the binder is preferably 1 to 15 mass%, and the amount of the conductive auxiliary is 3 to 20 % By mass.

Examples of the positive electrode current collector include a foil made of aluminum and the like. It is also possible to use a foil made of aluminum, a punching metal, a mesh, or an expanded metal having a through hole penetrating from one surface to the other surface of the positive electrode collector. The upper limit of the thickness of the positive electrode collector is preferably 30 占 퐉, and the lower limit is preferably 4 占 퐉 to secure the mechanical strength.

Further, a lead body for electrically connecting to another member in the lithium ion secondary battery may be formed on the anode by a conventional method, if necessary.

Examples of the separator include polyolefins such as polyethylene, polypropylene and ethylene-propylene copolymer; Polyesters such as polyethylene terephthalate and copolymerized polyesters; And the like. It is preferable that the separator has a property of closing the hole at 100 to 140 占 폚 (that is, a shutdown function). Therefore, it is more preferable that the separator comprises a thermoplastic resin having a melting point, that is, a melting temperature measured using a differential scanning calorimeter (DSC) of 100 to 140 占 폚, in accordance with JIS K 7121, Or a laminated porous film having as a constituent a porous film such as a laminated porous film in which two to five layers of polyethylene and polypropylene are laminated. In the case of mixing or laminating a resin having a melting point higher than that of polyethylene such as polyethylene and polypropylene, it is preferable that the resin constituting the porous film is polyethylene in an amount of 30 mass% or more, more preferably 50 mass% or more.

Examples of such a resin porous film include a porous film composed of the above-mentioned thermoplastic resin used in a conventionally known lithium ion secondary battery or the like, that is, an ion permeable porous film produced by a solvent extraction method, a dry or wet drawing method, Film can be used.

The average pore diameter of the separator is preferably 0.01 占 퐉 or more, more preferably 0.05 占 퐉 or more, preferably 1 占 퐉 or less, and more preferably 0.5 占 퐉 or less.

The characteristics of the separator are preferably in accordance with JIS P 8117, and it is preferable that the gel value represented by the number of seconds that 100 ml of air permeates through the membrane under a pressure of 0.879 g / mm 2 is 10 to 500 seconds. If the air permeability is too large, the ion permeability becomes small. On the other hand, if the air permeability is too small, the strength of the separator may be reduced. The strength of the separator is preferably 50 g or more as the stamper strength using a needle having a diameter of 1 mm. If the penetration strength is too small, a short circuit may occur due to tearing of the separator when lithium dendrite crystals are generated.

As the separator, a laminate type separator having a porous layer (I) mainly composed of a thermoplastic resin and a porous layer (II) containing a filler having a heat-resistant temperature of 150 ° C or higher as a main component may be used. The separator has shutdown characteristics, heat resistance (heat shrinkability) and high mechanical strength. It is expected that the high mechanical strength exhibited by this separator exhibits high resistance to the expansion and contraction of the negative electrode in charge and discharge cycles and that the twisting of the separator is suppressed to maintain the adhesion between the negative electrode and the separator and the positive electrode.

In the present specification, "heat-resistant temperature of 150 ° C or higher" means that no deformation such as softening is observed at 150 ° C or more.

The porous layer (I) related to the separator is mainly for securing a shutdown function. When the battery reaches the melting point or higher of the thermoplastic resin which is a main component of the porous layer (I), the porous layer The thermoplastic resin is melted to block the pores of the separator, thereby causing shutdown which suppresses the progress of the electrochemical reaction.

The thermoplastic resin to be the main component of the porous layer (I) is preferably a resin having a melting point of not higher than 140 DEG C measured by a differential scanning calorimeter (DSC) in accordance with the melting point, that is, according to JIS K 7121, , For example, polyethylene. Examples of the form of the porous layer (I) include those obtained by applying a dispersion containing polyethylene particles to a base material such as a microporous membrane, a nonwoven fabric or the like which is generally used as a separator for a battery, and drying Of a sheet shape. Here, the total volume of the constituent components of the porous layer (I) (total volume excluding the void portion; The same shall apply hereinafter with respect to the volume content of the constituent components of the porous layer (I) and the porous layer (II) related to the separator), the volume content of the thermoplastic resin as a main body is 50% by volume or more and 70% desirable. Further, for example, when the porous layer (I) is formed of the microporous membrane of polyethylene, the volume ratio of the thermoplastic resin is 100 volume%.

The porous layer (II) related to the 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 battery rises. The function of the filler having a heat resistance temperature of 150 deg. . That is, when the battery is heated to a high temperature, a short circuit due to direct contact of the positive and negative electrodes, which may occur when the separator is thermally shrunk by the porous layer (II) which is difficult to shrink even if the porous layer (I) . Further, since the heat-resistant porous layer (II) acts as a skeleton of the separator, the heat shrinkage of the porous layer (I), that is, the heat shrinkage of the entire separator itself can be suppressed.

The filler relating to the porous layer (II) has a heat-resistant temperature of 150 DEG C or higher and is stable to an electrolyte solution contained in the battery. If the electrolyte is electrochemically stable, which is difficult to be oxidized and reduced in the operating voltage range of the battery, It may be organic particles, but it is preferably fine particles in terms of dispersion and the like, and inorganic oxide particles, more specifically, alumina, silica and boehmite are preferable. Since alumina, silica and boehmite have high oxidation resistance and can adjust the particle size and shape to a desired value, it is easy to control the porosity of the porous layer (II) with good precision. As the filler having a heat-resistant temperature of 150 ° C or higher, for example, the above-mentioned fillers may be used singly or two or more thereof may be used in combination.

The content of the filler in the porous layer (II) is preferably 70 vol% or more, preferably 80 vol% or more, more preferably 90 vol% or more, Or more. The content of the filler in the porous layer (II) is preferably 99% by volume or less of the total volume of the constituent components of the porous layer (II), because the porous layer (II) usually contains a binder.

The binder of the porous layer (II) may contain at least one selected from the group consisting of fluororesins (such as PVDF), fluorinated rubbers, SBR, CMC, hydroxyethyl cellulose (HEC), polyvinyl alcohol (PVA), polyvinyl butyral (PVP), poly N-vinylacetamide, crosslinked acrylic resin, polyurethane, epoxy resin and the like.

The thickness of the separator (the laminated separator and the other separator) is preferably 6 占 퐉 or more, more preferably 10 占 퐉 or more from the viewpoint of separating the positive electrode and the negative electrode more reliably. On the other hand, if the separator is too thick, the energy density of the battery may be lowered. Therefore, the thickness is preferably 50 탆 or less, more preferably 30 탆 or less.

It is preferable that the thickness of the porous membrane (I) (the total thickness when a plurality of porous membranes (I) exist) is 5 to 30 占 퐉. The thickness of the porous layer (II) (the total thickness when a plurality of porous layers (II) exist) is preferably at least 1 mu m, more preferably at least 2 mu m, even more preferably at least 4 mu m, , And preferably 20 m or less, more preferably 10 m or less, and even more preferably 6 m or less.

As the non-aqueous electrolyte relating to the lithium ion secondary battery, a nonaqueous electrolyte solution in which a lithium salt is dissolved in an organic solvent can be used.

The organic solvent used in the nonaqueous electrolyte solution is not particularly limited as long as it dissolves the lithium salt described above and does not cause side reactions such as decomposition in a voltage range used as a battery. For example, cyclic carbonates such as ethylene carbonate, propylene carbonate, and butylene carbonate; Chain carbonates such as dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate; Chain esters such as methyl propionate; cyclic esters such as? -butyrolactone; Chain ethers such as dimethoxyethane, 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; Sulfurous acid esters such as ethylene glycol sulfite; These may be used in combination of two or more. In order to obtain a cell having better characteristics, it is preferable to use a combination such that a high conductivity can be obtained, such as a mixed solvent of ethylene carbonate and chain carbonate.

The lithium salt used for the non-aqueous electrolyte is not particularly limited as long as it dissociates in a solvent to form lithium ions and it is difficult to cause side reactions such as decomposition in a voltage range used as a battery. For example, inorganic lithium salts such as LiClO ₄ , LiPF ₆ , LiBF ₄ , LiAsF ₆ and LiSbF ₆ ; _{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 (2 _{≤n≤7), LiN (RfOSO 2)} 2 [wherein, Rf is a fluoroalkyl group] the organic lithium salts such as; .

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

The nonaqueous electrolytic solution may contain at least one selected from the group consisting of vinylene carbonate, vinylethylene carbonate, anhydrous acid, sulfonic acid ester, dinitrile, 1,3-diol, 1,3-propanediol, (Including derivatives thereof) such as benzene, toluene, xylene, propane, propane, diphenyl disulfide, cyclohexylbenzene, biphenyl, fluorobenzene, t-butylbenzene, phosphonoacetate compounds and 1,3- It can also be added.

A non-aqueous electrolyte solution may also be prepared by adding a known gelling agent such as a polymer to gelation (gel electrolyte).

In a conventional lithium ion secondary battery, the negative electrode and the positive electrode are laminated by a separator (laminated electrode body), a wound body (wound electrode body) obtained by further winding the laminate in a spiral shape, Is used. In the case of the laminated electrode body, even when the volume of the negative electrode is changed by charging / discharging of the battery, the distance between the electrode and the positive electrode is easier to maintain, so that battery characteristics are better maintained. For this reason, in the lithium ion secondary battery of the present invention, a laminated electrode body is used.

The lithium ion secondary battery of the present invention has a third electrode for doping Li ions into a negative electrode (negative electrode mixture layer). The third electrode is disposed so that at least a part of the third electrode faces the end face of the laminated electrode body, and is electrically connected to the cathode. The third electrode in the step of assembling the battery has a Li source for Li ion doping at a position where it is intended to face the end face of the laminated electrode body.

Here, the laminated electrode body will be described with reference to the drawings. Fig. 1 is a plan view schematically showing an example of an anode related to the lithium ion secondary battery of the present invention, and Fig. 2 is a plan view schematically showing an example of a cathode relating to the lithium ion secondary battery of the present invention Respectively. The positive electrode 10 shown in Fig. 1 has a positive electrode mixture layer 11 on both surfaces of a positive electrode collector 12 (a metal foil made of aluminum or the like), and has a positive electrode tab portion 13. The negative electrode 20 shown in Fig. 2 has a negative electrode mixture layer 21 on both surfaces of a negative electrode collector 22 (a metal foil made of copper, etc.) and has a negative electrode tab portion 23.

3 is a perspective view schematically showing an example of a laminated electrode body related to the lithium ion secondary battery of the present invention. The laminated electrode assembly 50 includes a negative electrode 20, a separator 40, a positive electrode 10, a separator 40, a negative electrode 20, , And an anode 10 and a cathode 20 are laminated via a separator 40. As shown in Fig. Here, the cross section of the laminated electrode body 50 is a plane parallel to the lamination direction of the positive electrode 10, the negative electrode 20 and the separator 40 (for example, in FIG. 3, Respectively. The plane perpendicular to the lamination direction of the laminated electrode bodies is referred to as a plane (the plane 211 in Fig. 3) of the laminated electrode body. In the laminated electrode assembly 50 shown in Fig. 3, the separators 40 are disposed one by one between the positive electrode 10 and the negative electrode 20, but the elongated separator is bent in a Z- , And the anode and the cathode may be disposed therebetween. The number of electrodes in the laminated electrode body is not limited to three cathodes and two anodes as shown in Fig. The plurality of positive electrode tab portions 13 and the negative electrode tab portions 23 may be connected to the positive electrode outer terminal and the negative electrode outer terminal, respectively, but they are omitted in FIG. 3 (and later FIG. 5).

3, the cross section 210 of the laminated electrode body 50 and the plane 211 are shown only on one side, but the present invention is not limited thereto. For example, the cross section 210 of the laminated electrode body 50 3, and the plane 211 of the laminated electrode body 50 is also the same. The cross section of the laminated electrode body may be a plane in Fig. 3, or a curved surface depending on the shape of the electrode. The plane of the laminated electrode body corresponds to one of the positive electrode, the negative electrode and the separator.

In Fig. 3, the two electrodes on the outermost layer of the laminated electrode body 50 are all made of the cathode 20, but either one of them may be used as a positive electrode, or both electrodes may be used as a positive electrode.

Fig. 4 is a perspective view schematically showing an example of the third electrode. The third electrode 30 has a third electrode current collector 32 and two Li sources 33 and 33. The third electrode current collector 32 is bent in an alphabet C shape so that the two Li supply sources 33 and 33 are inwardly inward. The Li supply source 33 on the left side in the drawing is indicated by a dotted line, which means that the Li supply source 33 is disposed on the back surface of the third electrode collector 32 shown in the figure. The third electrode collector 32 shown in Fig. 4 has a third electrode tab portion 31. Fig.

Fig. 5 is a perspective view showing a state in which the third electrode 30 shown in Fig. 4 is combined with the laminated electrode body 50 shown in Fig. The third electrode 30 is disposed outside the laminated electrode body 50 such that the two Li supply sources 33 and 33 are opposed to each of the two end faces of the laminated electrode body 50.

4 and 5, the Li supply sources 33 and 33 are disposed on both end faces of the third electrode current collector 32, but they may be disposed only on the face of the bundle, (The upper side in the figure) or the lower side (the lower side in the figure) of the body 50. [

When the material (S) is used as the negative electrode active material as in the present invention, the material (S) has a relatively high irreversible capacity, and therefore it is preferable to previously introduce Li ions into the negative electrode. In an electrochemical device having a laminated electrode body, a mixture layer of positive cathodes is usually provided on a current collector made of a metal foil having through holes, and the mixture layer surface is arranged so as to face Li (in the present invention, The Li ion was passed through the metal foil having the mixture layer and the through hole to introduce Li ions into all the negative electrode mixture layers of the laminated electrode body. In this case, Li ions must diffuse to other cathodes in the battery through the cathode closest to the Li source. Since the material S can receive a large amount of Li ions, the expansion due to the Li ions is remarkable. Therefore, the mixed layer of the negative electrode (most of which is the anode closest to the Li source) There is a problem in that Li ion is introduced into the mixture layer and the mixture layer is greatly expanded to be damaged and sometimes can not maintain the state of adhesion with the negative electrode collector and fall off from the negative electrode collector.

Thus, in the present invention, a means for introducing Li ions into the negative electrode mixture layer is found by arranging the Li supply source on the end face of the laminated electrode body. When such a means is employed, there is no case where a large amount of Li ions is locally introduced into one negative electrode even when a material having a significant expansion and shrinkage due to charging and discharging is used for the negative electrode active material. Therefore, And the distance between the Li source and each of the cathodes is the same, and there is no negative electrode which is extremely damaged by the expansion. Therefore, deterioration of the charge-discharge cycle characteristics of the battery can be suppressed.

In the case of using a metal foil in which the through holes are not provided in the collectors of the positive and negative electrodes, the strength is improved as compared with the case where the through holes are provided, And contributes to suppression of dropout of the compound layer.

The third electrode may be made of a metal foil such as copper or nickel (including one having a through hole penetrating from one surface to the other surface), a punching metal, a mesh, an expanded metal, A predetermined amount of Li foil (including Li foil, metal Li foil and Li alloy foil, which are sources of Li, is included in the three-electrode current collector, the same applies hereinafter). Of course, after the Li foil is pressed on the third electrode current collector, the third electrode collector may be cut out so that Li is a predetermined amount.

The third electrode formed by pressing the Li foil on the third electrode collector can be formed by welding a tab portion of a third electrode current collector and a tab portion of a negative electrode of the laminate electrode body to a . As long as the third electrode is electrically connected to the cathode of the laminated electrode body, there is no limitation to the method and the form, and electrical conduction may be ensured by a method other than welding.

In the lithium ion secondary battery in which the Li ion doping to the cathode is completed, the third electrode remains, but a part of the Li supply source provided on the third electrode remains or is completely destroyed.

It is preferable to use a metal laminate film sheath for an external body related to the lithium ion secondary battery of the present invention. The metal laminate film sheath is easier to deform than, for example, a metal can sheer, and therefore, even if the negative electrode is expanded due to charging of the battery, breakage of the negative electrode mixture layer and the negative electrode collector is unlikely to occur .

As the metal laminate film constituting the metal laminate film sheath, for example, a metal laminate film having a three-layer structure composed of an outer resin layer / a metal layer / a built-in resin layer is used.

As the metal layer in the metal laminate film, an aluminum film, a stainless steel film, or the like can be used. As the internal resin layer, a thermally fusible resin (for example, a modified polyolefin ionomer that exhibits thermal fusion at a temperature of about 110 to 165 DEG C) And a constituted film. Examples of the exterior resin layer of the metal laminate film include nylon film (nylon 66 film and the like) and polyester film (polyethylene terephthalate film and the like).

In the metal laminate film, the thickness of the metal layer is preferably 10 to 150 mu m, the thickness of the built-in resin layer is preferably 20 to 100 mu m, and the thickness of the external resin layer is preferably 20 to 100 mu m.

The shape of the outer body is not particularly limited, and examples thereof include polygons such as triangular, tetragonal, pentagonal, hexagonal, hexagonal, and octagonal in plan view. Squares (rectangles or squares) are common. The size of the outer body is not particularly limited, and various sizes such as a so-called thin shape and a large size can be used.

The metal laminate film sheath may be formed by folding one metal laminate film in two, or by stacking two metal laminate films.

When the planar shape of the casing is polygonal, the sides for drawing out the positive and negative external terminals may be the same or different.

The width of the heat-sealed portion in the outer body is preferably 5 to 20 mm.

In the lithium ion secondary battery of the present invention, the upper limit voltage of charging may be set to about 4.2 V as in the conventional lithium ion secondary battery, but it is also possible to set the upper limit voltage of charging to 4.4 V or higher Thus, it is possible to stably exhibit excellent characteristics even when repeatedly used for a long period of time while aiming at high capacity. The upper limit of the charging of the lithium ion secondary battery is preferably 4.7 V or less.

The lithium ion secondary battery of the present invention can be applied to the same application as a conventionally known lithium ion secondary battery.

[Example]

Hereinafter, the present invention will be described in detail based on examples. However, the following examples do not limit the present invention. Table 1 shows various physical properties of the negative electrode active material (composite material obtained by coating the surfaces of SiO and SiO with a carbon material and graphite) used in Examples.

(Example 1)

<Fabrication of positive electrode>

A LiCoO ₂ positive electrode active material: 96.5 parts by weight, NMP solution containing a binder, P (VDF-CTFE) at a concentration of 10% by mass: 20 parts by mass, and a conductive auxiliary agent of acetylene black, 1.5 parts by mass, an twin screw kneading , And further NMP was added to adjust the viscosity to prepare a paste containing the positive electrode mixture. This paste was applied to both sides of an aluminum foil having a thickness of 15 탆 and vacuum dried at 120 캜 for 12 hours to form a positive electrode material mixture layer on both sides of the aluminum foil, Thus, a strip-shaped positive electrode was obtained. When the paste containing the positive electrode material mixture was applied to the aluminum foil, a portion of the aluminum foil was exposed, and a part of the aluminum foil was applied as a coating portion on the surface. The thickness of the positive electrode mixture layer of the obtained positive electrode (the thickness per side of the positive electrode mixture layer formed on both sides of the aluminum foil) was 55 μm.

Shaped anode in which a positive electrode material mixture layer is formed on both surfaces of an aluminum foil is formed so that a part of the exposed portion of the aluminum foil (positive electrode collector) protrudes in order to form a tab portion and the four corners of the formed portion of the positive electrode material mixture layer are curved The battery positive electrode having the shape shown in Fig. 1 was obtained (with the proviso that in order to facilitate understanding of the structure of the positive electrode, Fig. 1 The size of the anode to be represented does not necessarily match the actual one). The positive electrode 10 is formed into a shape having a tab portion 13 so as to protrude so that a part of the exposed portion of the positive electrode collector 12 protrudes and the shape of the portion where the positive electrode mixture layer 11 is formed has a curved shape at four corners And the lengths of a, b, and c in the figure are 8 mm, 37 mm, and 2 mm, respectively.

<Fabrication of negative electrode>

10% by mass of graphite A-1 (graphite whose surface is not coated with amorphous carbon) and 10% by mass of graphite B-1 (graphite coated with amorphous carbon whose surface is coated with mother particles made of graphite) Si-1 (average particle diameter of 8 mu m, specific surface area of 7.9 m &lt; 2 &gt; / g and amount of carbon material in the composite of 20 mass%): 80 mass% Were mixed with a V-type blender for 12 hours to obtain a negative electrode active material.

100 parts by mass of polyacrylic acid were added to 500 parts by mass of ion-exchanged water and dissolved by stirring. Then, 70 parts by mass of NaOH was added thereto to dissolve with stirring until the pH became 7 or less. Further, ion-exchanged water was added to adjust a 5 mass% aqueous solution of a sodium salt of polyacrylic acid. To the aqueous solution, the negative electrode active material, a 1 mass% aqueous solution of CMC, and carbon black were added and stirred to obtain a negative electrode material mixture-containing paste. The composition ratio (mass ratio) of the negative electrode active material: carbon black: sodium salt of polyacrylic acid: CMC in this paste was 94: 1.5: 3: 1.5.

The negative electrode material mixture containing paste was applied to one side or both sides of a copper foil having a thickness of 8 占 퐉 and dried to form a negative electrode material mixture layer on the surface of the copper foil and subjected to a press treatment to adjust the density of the negative electrode material mixture layer to 1.4 g / Cm &lt; 3 &gt; and cut to a predetermined size to obtain a strip-shaped negative electrode having a negative electrode mixture layer on one side of the negative electrode collector and a strip-shaped negative electrode having a negative electrode mixture layer on both surfaces of the negative electrode collector. In the case of applying the paste containing the negative electrode material mixture to the copper foil, a portion of the copper foil is exposed and the negative electrode material mixture layer is formed on both surfaces of the negative electrode collector. In this case, Respectively. The thickness of the negative electrode mixture layer of the obtained negative electrode (the thickness per one surface of the copper foil serving as the negative electrode collector) was 65 占 퐉.

In order to make the strip-like negative electrode into a tab portion, a part of the exposed portion of the copper foil (negative electrode collector) is projected and the formed portion of the negative electrode material mixture layer is formed into a substantially rectangular shape with four corners curved To obtain a negative electrode for a battery having a negative electrode mixture layer on both surfaces and one surface of the negative electrode collector in the shape shown in Fig. 2 (however, in order to facilitate understanding of the structure of the negative electrode, the size of the negative electrode shown in Fig. And not coinciding with). The negative electrode 20 is formed into a shape having a tab portion 23 so as to protrude so that a part of the exposed portion of the negative electrode current collector 22 protrudes and the shape of the portion of the negative electrode material mixture layer 21 in which the four corners are curved And the lengths of d, e, and f in the figure are 9 mm, 38 mm, and 2 mm, respectively.

<Fabrication of Third Electrode>

The third electrode 30 having the shape shown in Fig. 4 was fabricated as follows. (Thickness: 10 mu m, diameter of through-hole: 0.1 mm, porosity: 47%) having through-holes penetrating from one surface to the other surface was cut into a size of 45 x 25 mm, A third electrode current collector 32 having a third electrode tab portion 31 of 2 mm was produced. A Li foil 33 having a thickness of 200 mu m and a mass of 18 mg is compressed in the vicinity of both ends of the third electrode current collector 32 so that the Li foil 33, So that the third electrode 30 was obtained.

&Lt; Assembly of Battery >

Two negative electrodes for a battery in which a negative electrode mixture layer was formed on one surface of the negative electrode collector, 16 sheets of negative electrodes for a battery in which a negative electrode mixture layer was formed on both surfaces of the negative electrode collector, and 17 sheets of positive electrodes for a battery in which a positive electrode mixture layer was formed on both surfaces of the positive electrode collector. , And a polyethylene separator (thickness: 12 mu m) were used to form a laminate. In this laminate, a negative electrode for a battery in which a negative electrode mixture layer was formed on one side of an anode current collector at the outermost side was disposed, and a positive electrode mixture layer was formed on both sides of the positive electrode current collector. And a negative electrode for a battery having a layer formed thereon were alternately arranged. Then, one separator was interposed between the positive electrode for each battery and the negative electrode for each battery. When the positive electrode for a battery and the negative electrode for a battery were laminated, the tab portions of all the positive electrodes for the battery were made to be on the same side, and all the negative electrode tab portions for the battery were on the same side and different from the tab portion on the positive electrode for a battery.

Next, the third electrode was superposed on the laminate. The positional relationship between the stacked body and the third electrode is the same as the positional relationship between the stacked electrode body 50 and the third electrode 30 shown in Fig. 5 when the third electrode is packed in the stacked body. Further, the tab portions of the positive electrode for each battery in the laminate were welded together and integrated, and this integral piece was welded to the positive electrode external terminal for the battery. Further, the tab portions of the negative electrode for each battery and the tab portion of the third electrode in the laminate were welded together and integrated, and this integral piece was welded to a negative electrode external terminal for a battery to obtain an electrode body. Fig. 6 shows a perspective view schematically showing the obtained electrode body. 6, a laminate composed of an anode, a cathode, and a separator is not shown. In the electrode assembly 102, a third electrode is formed on the laminate so that the end face of the laminate and the Li foils 33, A positive electrode external terminal 103 which is connected to an integral piece formed by collecting the positive electrode tab portions of all the positive electrodes of the laminate and welded to the negative electrode tab portion of the negative electrode tab portion and the third electrode tab of all the cathodes in the laminate, And a cathode external terminal 104 connected to the integrally welded portion is welded to the body of the electrode body 102.

Then, the electrode body was inserted into the concave portion of the aluminum laminate film having a thickness of 0.15 mm, a width of 34 mm and a height of 50 mm, in which the concave portion was formed so as to accommodate the electrode body, A laminate film was put thereon, and three sides of both aluminum laminate films were heat-welded.

Subsequently, LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate at a volume ratio of 3: 7 from the remaining one side of both aluminum laminate films at a concentration of 1 mol / l, and further 3 mass parts of vinylene carbonate %) Was injected into the solution. Thereafter, the remaining one side of each of the two aluminum laminated films was subjected to vacuum heat sealing, and a lithium ion secondary battery having the sectional structure shown in Fig. 8 was produced by the appearance shown in Fig.

Here, referring to FIGS. 7 and 8, FIG. 7 is a plan view schematically showing a lithium ion secondary battery, and FIG. 8 is a sectional view taken along a line I-I in FIG. The lithium ion secondary battery 100 accommodates an electrode assembly 102 and a nonaqueous electrolyte solution (not shown) in an aluminum laminate film enclosure 101 formed of two aluminum laminate films, and the aluminum laminate film enclosure 101 (101) is sealed by thermally welding the upper and lower aluminum laminate films on the outer peripheral portion thereof. 8, the layers constituting the aluminum laminate film enclosure 101 and the anodes, the cathodes, the separators and the third electrodes constituting the electrode body are separately shown in order to avoid the complication of the drawing not.

The respective positive electrodes of the electrode assembly 102 are welded to each other to form an integral body and the integral body of the welded tab portion is connected to the positive electrode external terminal 103 in the battery 100, Each of the negative electrode and the third electrode of the electrode assembly 102 is also welded to each other to weld them together and the integral body of the welded tab is connected to the negative electrode external terminal 104 in the battery 100. The positive electrode external terminal 103 and the negative electrode external terminal 104 draw the one end side outward of the aluminum laminated film sheath 101 so as to be connectable with an external device or the like.

The lithium ion secondary battery thus fabricated was stored in a thermostatic chamber at 45 캜 for one week.

(Examples 2 to 9)

The same procedure was followed as in Example 1 except that the negative electrode active material shown in Table 1 was used in a mass ratio shown in Table 2 and the Li foil pressed on the third electrode was changed to the mass (Li amount) Thereby preparing a lithium ion secondary battery.

(Example 10)

<Fabrication of Separator>

3 parts by weight of a resin binder of modified polybutyl acrylate, 97 parts by weight of a boehmite powder (average particle size of 1 mu m) and 100 parts by weight of water were mixed to prepare a slurry for forming the porous layer (II). This slurry was applied to one side of a 12 μm-thick polyethylene-made microporous membrane (porous layer (I)) for lithium ion batteries and dried to obtain a porous layer (II) containing boehmite as a main body on one surface of the porous layer (I) A separator was formed. The thickness of the porous layer (II) was 3 m.

A lithium ion secondary battery was fabricated in the same manner as in Example 5 except that this separator was used.

(Example 11)

A lithium ion secondary battery was fabricated in the same manner as in Example 1 except that the same separator as that produced in Example 10 was used.

(Example 12)

A lithium ion secondary battery was fabricated in the same manner as in Example 2 except that the same separator as that produced in Example 10 was used.

(Example 13)

A lithium ion secondary battery was fabricated in the same manner as in Example 4 except that the same separator as that produced in Example 10 was used.

(Examples 14 and 15)

A lithium ion secondary battery was fabricated in the same manner as in Example 1 except that the Li foil pressed on the third electrode was changed to that of the mass shown in Table 2. [

(Comparative Example 1)

<Fabrication of Third Electrode>

Fig. 9 is a plan view schematically showing the third electrode used in the battery of Comparative Example 1. Fig. A copper foil (thickness: 10 mu m, through-hole diameter: 0.1 mm, porosity: 47%) having through-holes penetrating from one surface to the other surface was cut into a size of 45 x 25 mm, A third electrode current collector 32 having a third electrode tab portion 31 of x 2 mm was fabricated. A Li foil 33 having a thickness of 200 mu m and a mass of 36 mg was pressed on the center face of the third electrode current collector 32 to obtain a third electrode 30B.

A lithium ion secondary battery was fabricated in the same manner as in Example 1 except that the third electrode was used.

(Comparative Example 2)

A lithium ion secondary battery was fabricated in the same manner as in Example 1 except that the third electrode was not used.

Each of the lithium ion secondary batteries of Examples and Comparative Examples was evaluated in the following manner.

&Lt; Evaluation of Charge /

The lithium ion secondary batteries of the examples and comparative examples after being stored in a thermostatic chamber at 45 캜 for one week were allowed to stand in a constant temperature bath at 25 캜 for 5 hours and then each battery was charged with a current value of 0.5 C to 4.4 V Then, the battery was charged at a constant voltage of 4.4 V (the total charging time of the constant current charging and the constant voltage charging was 2.5 hours), and thereafter discharged at a constant current of 0.2 C to 2.0 V to obtain the initial discharging capacity. Next, each battery was charged with a current of 1 C at a constant current up to 4.4 V, then charged at a constant voltage of 4.4 V until the current value reached 0.05 C, and then discharged at a current value of 1 C to 2.0 V Was used as one cycle, and this was cycled 300 times. Then, for each cell, a constant current-constant voltage charge and a constant current discharge were carried out under the same conditions as those for the measurement of the initial discharge capacity to determine the discharge capacity. The value obtained by dividing the discharge capacity by the initial discharge capacity was expressed as a percentage, and the cycle capacity retention rate was calculated.

The composition of the negative electrode active material of each of the lithium ion secondary batteries in Examples and Comparative Examples and the amount of Li (mass per one Li foil) placed on the third electrode are shown in Table 2 and the evaluation results are shown in Table 3.

10: anode
11: anode mixture layer
12: anode current collector
13:
20: cathode
21: anode mixture layer
22: cathode collector
23:
30: Third electrode
31: Third electrode tab
32: Third electrode current collector
33: Li source (Li foil)
40: Separator
50: laminated electrode body
100: Lithium ion secondary battery
101: metal laminate film outer body
102: Electrode body
103: Positive external terminal
104: cathode external terminal

Claims (5)

A lithium ion secondary battery having a laminated electrode body in which a positive electrode and a negative electrode are laminated via a separator and a third electrode used for doping Li ions into the negative electrode,
Wherein the laminated electrode body has a plane and a cross section parallel to the lamination direction of the positive electrode, the negative electrode and the separator,
The negative electrode has a negative electrode mixture layer containing a negative electrode active material on at least one surface of the negative electrode collector,
Wherein the negative electrode active material contains a material (S) containing Si,
When the total amount of the negative electrode active materials contained in the negative electrode material mixture layer is 100 mass%, the content of the material (S) is 5 mass%
The positive electrode has a positive electrode mixture layer containing a metal oxide composed of Li and a metal M other than Li as a positive electrode active material on at least one surface of the positive electrode collector,
And the third electrode is arranged such that at least a part of the third electrode is opposed to the end face of the laminated electrode body,
(Li / M) of Li and a metal M other than Li contained in the cathode active material is 0.8 to 1.05 when discharged at a discharge current rate of 0.1 C until the voltage reaches 2.0 V. Ion secondary battery. A lithium ion secondary battery having a laminated electrode body in which a positive electrode and a negative electrode are laminated via a separator and a third electrode used for doping Li ions into the negative electrode,
Wherein the laminated electrode body has a plane and a cross section parallel to the lamination direction of the positive electrode, the negative electrode and the separator,
The negative electrode has a negative electrode mixture layer containing a negative electrode active material on at least one surface of the negative electrode collector,
Wherein the negative electrode active material contains a material (S) containing Si,
When the total amount of the negative electrode active materials contained in the negative electrode material mixture layer is 100 mass%, the content of the material (S) is 5 mass%
The positive electrode has a positive electrode mixture layer containing a metal oxide composed of Li and a metal M other than Li as a positive electrode active material on at least one surface of the positive electrode collector,
The third electrode is provided with a Li source, and the third electrode is arranged so that the Li source is opposed to the end face of the laminated electrode body,
And lithium ions supplied from the Li supply source are doped into the cathode through conduction with the third electrode. 3. The method according to claim 1 or 2,
Wherein SiO _x (where 0.5? _X? 1.5) is contained as the material (S). 4. The method according to any one of claims 1 to 3,
Wherein the separator has a porous film (I) mainly composed of a thermoplastic resin and a porous layer (II) comprising a filler having a heat-resistant temperature of 150 ° C or higher as a main component. A laminated electrode body in which a negative electrode having a negative electrode mixture layer containing a material S containing Si as a negative electrode active material on at least one surface of the negative electrode collector and an anode are stacked with a separator interposed therebetween; A method for producing a lithium ion secondary battery having a third electrode used for doping Li ions,
Wherein the laminated electrode body has a plane and a cross section parallel to the lamination direction of the positive electrode, the negative electrode and the separator,
The third electrode is provided with a Li source, and the third electrode is arranged so that the Li source is opposed to the end face of the laminated electrode body,
And a step of conducting lithium ions from the Li source to the cathode by conducting to the third electrode.

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