JP2017120746A - Lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-capacity lithium ion secondary battery in which the falling of a negative electrode mixture can be prevented.SOLUTION: A lithium ion secondary battery comprises an electrode body including: a negative electrode having a support body composed of a piece of metal foil having a through-hole extending through the foil from one face to the other, and a negative electrode mixture layer provided on at least one face of the support body and including a negative electrode active material primarily, provided that the negative electrode active material includes a material S which is a Si-containing negative electrode material; and a positive electrode having a support body composed of a piece of metal foil, and a positive electrode mixture layer provided at least one face of the support body and including a metal oxide including, as a positive electrode active material, Li and a metal M other than Li. A method for manufacturing the lithium ion secondary battery comprises the steps of: preparing a third electrode including a Li source; preparing a buffer layer having a Gurley value of 200-800 sec/100 cc; disposing the buffer layer between the outermost negative electrode in the electrode body and the third electrode so that the buffer layer is put in touch with each of them; and short-circuiting the negative electrode and the third electrode to introduce Li ions into the negative electrode.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a lithium ion secondary battery having a high capacity and excellent cycle characteristics.

  Lithium ion secondary batteries, which are one type of electrochemical element, are considered to be applied to portable devices, automobiles, electric tools, electric chairs, household and commercial power storage systems because of their high energy density. Yes. In particular, as a portable device, it is widely used as a power source for a mobile phone, a smartphone, or a tablet PC.

  In addition, lithium ion secondary batteries are required to improve various battery characteristics as well as to increase the capacity in accordance with the spread of applied devices. Since it is a secondary battery especially, the improvement of a charge / discharge cycle characteristic is calculated | required strongly.

Usually, a carbon material such as graphite 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 as a material capable of inserting and desorbing more Li ions, or a material containing these elements has been studied, and especially SiO _x having a structure in which Si fine particles are dispersed in SiO ₂ has attracted attention. Yes. Further, since these materials have low conductivity, a structure in which the surface of particles is covered with a conductor such as carbon has been proposed (Patent Documents 1 and 2).

Further, since SiO _x has a relatively high irreversible capacity, it is desirable to introduce metal Li into the negative electrode side in advance as a Li source, for example (Patent Document 3). However, in the method of sticking the metal Li foil to the negative electrode, there is a variation in the introduction of Li, and lithium dendrite may be deposited on the negative electrode. Therefore, an insulating material and an electron conductive material are formed on the surface of the negative electrode mixture layer. A method of providing a buffer layer containing the above has been proposed (Patent Document 3).

JP 2004-47404 A Japanese Patent Laid-Open No. 2005-259697 International Publication No. WO98 / 033227 JP 2007-242590 A

  In the configuration of Patent Document 3, Li is arranged on the upper or lower portion of the stacked unit of electrodes and separators. According to this configuration, there was a problem that the negative electrode mixture layer disposed closest to Li was dropped and a sufficient battery capacity could not be obtained. Further, according to the configuration of Patent Document 4, although initial charge / discharge efficiency is improved by introducing Li in advance, there is still room for improvement in the reaction uniformity of Li introduction.

  The present invention has been made in view of the above circumstances, and provides a lithium ion secondary battery having a high capacity and excellent cycle characteristics and a method for manufacturing the same.

  The present invention relates to a method for producing a lithium ion secondary battery having an electrode body in which a positive electrode and a negative electrode provided with a mixture layer are provided on at least one surface of a metal foil with a separator interposed therebetween. The negative electrode has a negative electrode mixture layer mainly composed of a negative electrode active material provided on at least one surface of a support made of metal foil, and the negative electrode The active material contains the material S which is a negative electrode material containing Si, and when the total of all the negative electrode active materials contained in the negative electrode is 100% by mass, the content rate of the material S contained as the negative electrode active material is The positive electrode is provided with a positive electrode mixture layer containing a metal oxide composed of a metal M other than Li and Li as a positive electrode active material on at least one surface of a support made of a metal foil. Including Li source A step of preparing three electrodes, a step of preparing a buffer layer having a Gurley value of 200 to 800 sec / 100 cc, and the buffer layer between the outermost negative electrode and the third electrode in the electrode body, respectively. A method of manufacturing a lithium ion secondary battery comprising: a step of arranging the electrodes in contact with each other; and a step of short-circuiting the negative electrode and the third electrode to introduce Li ions into the negative electrode.

In addition, the present invention provides a lithium ion secondary battery in which an electrode body in which a positive electrode and a negative electrode provided with a mixture layer on at least one surface of a metal foil are stacked via a separator is disposed in an exterior body. Has a through hole penetrating from one surface to the other surface, and the negative electrode has a negative electrode mixture layer mainly composed of a negative electrode active material provided on at least one surface of a support made of a metal foil. The negative electrode active material contains a material S that is a negative electrode material containing Si, and the material S included as the negative electrode active material when the total of all negative electrode active materials included in the negative electrode is 100% by mass. The positive electrode has a positive electrode mixture layer containing a metal oxide composed of a metal M other than Li and Li as a positive electrode active material, and at least one of a support made of a metal foil. In front of the The negative electrode mixture layer of the outermost negative electrode in the electrode body is in contact with the buffer layer having a Gurley value of 200 to 800 sec / 100 cc, and is discharged until the voltage reaches 2.0 V at a discharge current rate of 0.1 C. The lithium ion secondary battery is characterized in that the molar ratio (Li / M) of Li and metal M other than Li contained in the positive electrode active material is 0.6 to 1.05.

  According to the present invention, it is possible to provide a lithium ion secondary battery having a high capacity and excellent cycle characteristics.

It is a top view which represents typically an example of the positive electrode which concerns on the lithium ion secondary battery of this invention. It is a top view which represents typically an example of the negative electrode which concerns on the lithium ion secondary battery of this invention. It is sectional drawing which shows the laminated structure of the lithium ion secondary battery of this invention. It is a top view which represents typically an example of the lithium ion secondary battery of this invention. It is the II sectional view taken on the line of FIG.

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

  The negative electrode active material in the present invention contains a material S that is a negative electrode material containing Si. It is known that Si is introduced into Li ions by alloying with Li, but at the same time, it is also known that the volume expansion upon introduction of Li is large.

  The material S containing Si exhibits a capacity of 1000 mAh / g or more, and is characterized by significantly exceeding 372 mAh / g, which is called the theoretical capacity of graphite. On the other hand, compared with the charge / discharge efficiency (90% or more) of general graphite, the material S containing Si often has an initial charge / discharge efficiency of less than 80%, and the irreversible capacity increases, so there is a problem in cycle characteristics. It was. Therefore, it is desired to introduce a Li source into the negative electrode in advance (pre-doping).

  As a method of introducing Li into the negative electrode active material, after forming a negative electrode mixture layer such as attaching a metal lithium foil to the negative electrode mixture layer and forming a Li vapor deposition layer, a Li source is arranged so as to face the mixture layer. In general, Li is introduced by electrochemical contact (short circuit). However, when Li is introduced in a face-to-face relationship with the mixture layer, a Li source must be arranged for each negative electrode mixture layer in the laminated electrode body, resulting in poor production efficiency. Therefore, the metal foil serving as a support for the mixture layer of the positive electrode and the negative electrode has a hole penetrating from one surface to the other surface. Then, by making the Li source face-to-face only on the outermost surface in the stacking direction of the stacked electrode body, Li ions diffuse throughout the stacked electrode body through the through holes of the metal foil, and Li ions are introduced into all the negative electrodes I can do it.

  However, since the material S can accept a large amount of Li ions, the expansion due to the acceptance of Li ions is remarkable, so the negative electrode mixture layer of the negative electrode closest to the Li source expands greatly by accepting the most Li ions. In some cases, however, the negative electrode current collector cannot be maintained in an adhesive state and may fall off.

  Therefore, as a result of various studies, when Li ions are introduced into the negative electrode, a buffer layer having a Gurley value of 200 to 800 sec / 100 cc is provided between the negative electrode and Li as the third electrode. It was found that the capacity and cycle characteristics were greatly improved.

The material S is a negative electrode material containing Si. For example, a material in which Si powder and carbon are combined, a material further coated with a carbon material, a material in which Si powder is sandwiched between graphene or scaly graphite, SiO _x containing Si and O as constituent elements (however, for Si The atomic ratio x of O is 0.5 ≦ x ≦ 1.5. Among these, it is preferable to use a material containing SiO _x .

The SiOx 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, the SiOx includes a structure in which Si (for example, microcrystalline Si) is dispersed in an amorphous SiO2 matrix, and the amorphous SiO2 and Si dispersed in the amorphous SiO2 matrix. In addition, it is sufficient that the atomic ratio x satisfies 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 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.

The material S containing SiO _x is preferably a composite that is combined with a carbon material. For example, the surface of the SiO _x is preferably covered with the carbon material. Usually, since SiO _x has poor conductivity, when using it as a negative electrode active material, from the viewpoint of ensuring good battery characteristics, a conductive material (conductive aid) is used, and SiO _x in the negative electrode is electrically conductive. It is necessary to form an excellent conductive network by making good mixing and dispersion with the conductive material. 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.

That is, the specific resistance value of SiO _x is usually 10 ³ to 10 ⁷ kΩcm, whereas the specific resistance value of the carbon material exemplified above is usually 10 ^{−5 to} 10 kΩcm. And the conductivity of SiO _x can be improved.

The complex with the SiO _x and the carbon material, as described above, other although the surface of the SiO _x coated with carbon material, granulated material or the like between the SiO _x and the carbon material can be cited.

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

Details of the carbon material include at least 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. One material is preferred. A fibrous or coiled carbon material is preferable in that it easily forms a conductive network and has 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 the SiO _x particles expand and contract. However, it is preferable in that it has a property of easily maintaining contact with the particles.

Among the carbon materials exemplified above, a fibrous carbon material is particularly preferable as a material used when the composite with SiO _x is a granulated body. The fibrous carbon material has a thin thread shape and high flexibility so that it can follow the expansion and contraction of SiO _x that accompanies charging / discharging of the battery, and because of its large bulk density, it has a large amount of SiO _x particles. It is because it can have the following junction point. 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.

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 SiO _x : 100 parts by weight from the viewpoint of satisfactorily exerting the effect of the composite with the carbon material. On the other hand, the carbon material is preferably 5 parts by weight or more, and more preferably 10 parts by weight or more. In the composite, if the ratio of the carbon material to be composited with SiO _x is too large, the amount of SiO _x in the negative electrode mixture layer may be reduced, and the effect of increasing the capacity may be reduced. The carbon material is preferably 50 parts by weight or less and more preferably 40 parts by weight or less with respect to SiO _x : 100 parts by weight.

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

When the surface of SiO _x is coated with a carbon material to form a composite, for example, the SiO _x particles and the hydrocarbon gas are heated in the gas phase, and are generated by thermal decomposition of the hydrocarbon gas. Carbon is deposited on the surface of the particles. Thus, according to the vapor deposition (CVD) method, a hydrocarbon-based gas spreads to every corner of the SiO _x particle, and a thin and uniform film (carbon material) containing a conductive carbon material on the surface of the particle. Since the 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 the carbon material, the processing temperature (atmosphere temperature) of the CVD method varies depending on the type of hydrocarbon-based gas, but usually 600 to 1200 ° C. is suitable. It is preferable that it is higher than ℃, and more preferable that it is higher than 800 ℃. This is because the higher the treatment temperature, the fewer impurities remain and the formation of a coating layer containing carbon having high conductivity.

  As the liquid source of the hydrocarbon 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.

Further, when a granulated body of SiO _x and a carbon material is prepared, a dispersion liquid in which SiO _x is dispersed in a dispersion medium is prepared, sprayed and dried to obtain a granulated body including a plurality of particles. Make it. 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, a granulated body of SiO _x and a carbon material can be produced also by a granulating method by a mechanical method using a vibration type or planetary type ball mill or rod mill.

In the above-described negative electrode, 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 is 0.01 wt% or more Preferably, it is 1% by weight or more, more preferably 3% by weight or more. Further, from the viewpoint of better avoiding the problem due to the volume change of SiO _x accompanying charge / discharge, the content of the composite of SiO _x and the carbon material in the negative electrode active material is preferably 20% by weight or less. 15% by weight or less is more preferable.

  If the average particle size of the material S is too small, the dispersibility of the material S may be reduced, and the effects of the present invention may not be sufficiently obtained, and the material S has a large volume change associated with charging / discharging of the battery. If the average particle diameter is too large, the material S is likely to collapse due to expansion / contraction (this phenomenon leads to capacity degradation of the material S), and therefore it is preferably 0.1 μm or more and 10 μm or less.

  The content ratio of the material S to the total negative electrode active material in the negative electrode mixture layer is preferably 1% or more, more preferably 10% by mass or more, and most preferably 50% by mass or more. . As described above, the material S is a material that can realize a dramatic increase in capacity compared to graphite. Therefore, if the material S is contained even in a small amount in the negative electrode active material, an effect of improving the capacity of the battery can be obtained. On the other hand, the material S is preferably 10% by mass or more with respect to the front negative electrode active material in order to achieve a dramatic increase in battery capacity. The content of the material S may be adjusted in accordance with various battery uses and required characteristics. In order to exhibit the effect of introducing Li by graphite A and graphite B described later (by electrochemical contact between Li and the negative electrode), the ratio of the material S is 99% by mass or less, preferably 90% by mass or less. More preferably, it is 80 mass% or less.

  In addition to the material S described above, the negative electrode of the present invention may be used in combination with a carbon material capable of electrochemical storage and release of Li, such as graphite. In particular, it is desirable to use in combination with 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 whose graphite particle surface is coated with amorphous carbon.

Examples of the graphite A include natural graphite and artificial graphite which are used as a negative electrode active material of a normal lithium ion secondary battery. As artificial graphite, for example, a coke or organic material fired at 2800 ° C. or higher, or a natural graphite and the coke or organic material mixed and heat-treated at 2800 ° C. or higher, and further coke or organic material at 2800 ° C. or higher. The natural graphite is coated on the surface of the natural graphite. The R value, which is the peak intensity ratio appearing at 1340-1370 cm ⁻¹ with respect to the peak intensity appearing at 1570-1590 cm ⁻¹ in the argon ion laser Raman spectrum, is Graphite that is 0.05 to 0.2 can be used. If the average particle diameter is in the above range, two or more kinds of graphite may be used in combination with the graphite A.

Graphite B is composed of graphite particles serving as mother particles and amorphous carbon covering the surface. Specifically, it is graphite in which the R value, which is a peak intensity ratio appearing at 1340 to 1370 cm ⁻¹ with respect to the peak intensity appearing at 1570 to 1590 cm ⁻¹ in the argon ion laser Raman spectrum, is 0.1 to 0.7. The R value is more preferably 0.3 or more in order to ensure a sufficient coating amount of amorphous carbon. Moreover, since an irreversible capacity | capacitance will increase if there is too much coating amount of amorphous carbon, R value is 0.6 or less. Such graphite B uses, for example, natural graphite having d ₀₀₂ of 0.338 nm or less or graphite obtained by spherically shaping artificial graphite as a base material (base particle), and the surface thereof is coated with an organic compound. It can be obtained by calcining at 0 ° C., pulverizing, and sizing through a sieve. The organic compound covering the base material includes aromatic hydrocarbons; tars or pitches obtained by polycondensation of aromatic hydrocarbons under heat and pressure; tars mainly composed of a mixture of aromatic hydrocarbons. , Pitch or asphalt; In order to coat the base material with the organic compound, a method of impregnating and kneading the base material into the organic compound can be employed. Alternatively, graphite B can be produced by a vapor phase method in which a hydrocarbon gas such as propane or acetylene is carbonized by pyrolysis and deposited on the surface of graphite having d ₀₀₂ of 0.338 nm or less.

Furthermore, the graphite B has high Li ion acceptability (for example, it can be quantified by the ratio of the constant current charge capacity to the total charge capacity). Therefore, the lithium ion secondary battery when graphite B is used in combination has good acceptability of Li ions and good charge / discharge cycle characteristics. As described above, when the Li source is introduced into the negative electrode containing the material S by electrochemical contact (short circuit), if the graphite B is used in combination, the uneven introduction of Li can be suppressed. We thought that the characteristics could be improved.

  However, it has been found that sufficient improvement in battery characteristics cannot be obtained only by using graphite B alone. Because graphite B is based on graphite activated in a spherical shape as described above, graphite B alone cannot provide sufficient contact between the particles, which causes unevenness in the introduction of Li, and the negative electrode. It is presumed that the overall Li ion acceptability was not improved and the battery characteristics were not greatly improved. Accordingly, it has been found that the battery characteristics are significantly improved by using graphite A having an average particle size higher than that of graphite B, specifically, more than 15 μm and not more than 25 μm in combination with graphite B. Specifically, the total content of graphite A and graphite B in the total negative electrode active material contained in the negative electrode is 20% by mass or more and 99% by mass or less, and the graphite with respect to graphite B in the total negative electrode active material contained in the negative electrode The content ratio (A / B) of A is 0.5 or more and 4.5 or less. By using graphite A and graphite B together in this way, the number of places where the contact of graphite B cannot be secured is reduced, that is, the introduction of Li ions into the negative electrode is reduced, so that Li ions are used rather than graphite B alone. This is presumed to be due to the increased acceptability of.

  In addition, when the particle diameter of graphite A is too small, the specific surface area is excessively increased (the irreversible capacity is increased), so that the particle diameter is preferably not too small. Therefore, it is preferable to use graphite A having an average particle diameter of more than 15 μm. In addition, if the particle size of graphite B is too small, the coating amount of amorphous carbon covering the surface varies, and there are reasons that the features of graphite B cannot be fully exhibited. It is preferable not to be too small. Therefore, it is preferable to use graphite B having an average particle diameter of 8 μm or more.

The average particle size of graphite (graphite A, graphite B, and other graphites) can be obtained by, for example, dissolving the graphite using a laser scattering particle size distribution meter (for example, Microtrack particle size distribution measuring device “HRA9320” manufactured by Nikkiso Co., Ltd.). It is a 50% diameter median diameter (D _50% ) median diameter in the volume-based integrated fraction when the integrated volume is determined from particles having a small particle size distribution measured by dispersing graphite in a medium that does not swell or swell.

The specific surface area of the graphite A and graphite B (according to the BET method. Device example like manufactured by Nippon Bell "Bell soap mini".) Is preferably 1.0 m ² / g or more,, 5.0 m ² / g or less is preferable.

  The crystallite size in the c-axis direction: Lc in the crystal structures of graphite A and graphite B is preferably 3 nm or more, more preferably 8 nm or more, and further preferably 25 nm or more. This is because, within this range, insertion / extraction of lithium ions becomes easier. The upper limit value of Lc of graphite is not particularly limited, but is usually about 200 nm.

  Further, the negative electrode active material includes negative electrode active materials other than the material S, graphite A, and graphite B described above (for example, the same kind as graphite A and having an average particle diameter of less than 15 μm or more than 25 μm). As described above, graphite that does not correspond to graphite A and graphite B), a simple substance of Si or Sn, an alloy containing Si or Sn, or an oxide containing Si or Sn is used to the extent that the effect of the present invention is not hindered. You can also.

  As the binder related to the negative electrode mixture layer, for example, a material that is electrochemically inactive with respect to Li in the working potential range of the negative electrode and does not affect other substances as much as possible is selected. Specifically, for example, styrene butadiene rubber (SBR), polyvinylidene fluoride (PVDF), carboxymethylcellulose (CMC), polyvinyl alcohol (PVA), methylcellulose, polyimide, polyamideimide, polyacrylic acid, and derivatives and co-polymers thereof. A polymer etc. are mentioned as a suitable thing. These binders may use only 1 type and may use 2 or more types together.

  A conductive material may be further added to the negative electrode mixture layer as a conductive aid. Such a conductive material is not particularly limited as long as it does not cause a chemical change in the battery. For example, carbon black (thermal black, furnace black, channel black, ketjen black, acetylene black, etc.), carbon It is possible to use one or more materials such as fiber, metal powder (powder of copper, nickel, aluminum, silver, etc.), metal fiber, polyphenylene derivative (described in JP-A-59-20971). it can. Among these, carbon black is preferably used, and ketjen black and acetylene black are more preferable.

  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 side of the current collector, and the density of the negative electrode mixture layer (from the mass and thickness of the negative electrode mixture layer per unit area laminated on the current collector) (Calculated) is preferably 1.0 g / cm ³ or more, more preferably 1.2 g / cm ³ or more in order to increase the capacity of the battery. In addition, if the density of the negative electrode mixture layer is too high, adverse effects such as a decrease in the permeability of the non-aqueous electrolyte solution occur, so 1.6 g / cm ³ or less is desirable. Moreover, as a composition of a negative mix layer, it is preferable that the quantity of a negative electrode active material is 80-99 mass%, for example, it is preferable that the quantity of a binder is 0.5-10 mass%, and a conductive support agent. When using, it is preferable that the quantity is 1-10 mass%.

  The support (current collector) for supporting the current collector of the negative electrode and the negative electrode mixture layer has a through hole penetrating from one surface of the current collector to the other surface, for example, made of copper or nickel A foil, a punching metal, a net, an expanded metal, or the like can be used.

  When a metal foil having a through hole penetrating from one surface of the foil to the other surface is used as the support (current collector), the negative electrode mixture layer provided on both surfaces is electrically connected through the through hole. Since it is connected, if a Li source is arranged on one of the surfaces, Li ions move from one negative electrode mixture layer to the other negative electrode mixture layer through the through holes, and the negative electrodes on both surfaces Li will be introduced into the mixture layer, and the work of arranging the Li source can be simplified.

  When a metal foil having a plurality of through holes penetrating from one surface to the other surface is used as a support (current collector) for the negative electrode mixture layer, the upper limit of the thickness is preferably 30 μm, In order to ensure strength, the lower limit is preferably 4 μm. Further, the size of the through hole is preferably 0.05 mm or more for the purpose of making the introduction of Li uniform. However, if the size of the through-hole is too large, 0.3 mm or less is desirable because the mechanical strength cannot be maintained.

When using a metal foil having a plurality of through holes penetrating from the one surface to the other surface, the porosity is preferably 30 to 55%. When the porosity is less than 30%, there is a problem that the effect of improving the loss of the negative electrode mixture layer is lowered. Further, when the porosity exceeds 55%, the mechanical strength of the metal foil is too low, and there is a problem that the foil is cut. The porosity here is calculated by the following equation.
Porosity = {1− (Current collector weight / Current collector true specific gravity) / Current collector apparent volume} × 100 (%)

  In the lithium ion secondary battery of the present invention, when a material having a high capacity and a large irreversible capacity such as the material S is used for the negative electrode active material, Li released from the positive electrode (positive electrode active material) by the initial charge of the battery. Since a relatively large number of ions cannot return to the positive electrode in the next discharge, there is a possibility that the capacity that the positive electrode originally has cannot be sufficiently extracted. Therefore, in the lithium ion secondary battery of the present invention, when a negative electrode active material having a large irreversible capacity such as the material S is used, a Li supply source (Li supply for pre-doping) is used to fill the irreversible capacity during manufacture. A third electrode including a source is provided separately from the positive electrode.

  Examples of the Li supply source include a Li metal foil and a Li alloy foil (hereinafter collectively referred to as “Li foil”), and are adjacent to the outermost negative electrode in the electrode body through a buffer layer described later. Thus, this Li supply source may be arranged. Specifically, for example, a third electrode formed by attaching a Li foil as a Li supply source to a metal foil such as a copper foil as a current collector is used. The Li electrode of the third electrode functions as a Li supply source by electrically connecting the Li electrode to the negative electrode and causing a short circuit.

  In the battery provided with the third electrode for pre-doping the negative electrode active material, the amount of the Li supply source to be introduced (the amount of Li contained in the Li supply source) is set to 0. When discharging is performed until the voltage reaches 2.0 V at a 1 C discharge current rate, the molar ratio Li / M of Li and metal M contained in the positive electrode active material is, for example, the following value: It is preferable to adjust. When the ratio of the material S in the total amount of the negative electrode active material contained in the negative electrode mixture layer is 5 to 10% by mass, the molar ratio Li / M is preferably 0.9 to 1.05, When the ratio of the material S is 10 to 60% by mass, the molar ratio Li / M is preferably 0.8 to 0.9, and the ratio of the material S is 60 to 100. In the case of mass%, the molar ratio Li / M is preferably 0.6 to 0.8.

  As described above, the Li supply source (the Li foil) is incorporated into the negative electrode active material in order to fill the irreversible capacity of the negative electrode active material. However, when the molar ratio Li / M satisfies the above value, it can be determined that the battery is a battery in which a negative electrode active material is pre-doped by introducing a Li supply source.

  In addition, even when charging / discharging is repeated for several tens of cycles (100 cycles or less) in a battery in which a Li supply source is introduced, the molar ratio Li / M does not greatly change after the discharge in the first charge / discharge. Therefore, in a battery that has passed the number of charge / discharge cycles of about 100 cycles or less, when the molar ratio Li / M satisfies the above value, a Li supply source is introduced at the time of battery assembly and the negative electrode active material is pre-doped. Can be considered.

  In addition, in a battery that introduces a Li supply source for pre-doping of the negative electrode, from the viewpoint of promoting pre-doping more efficiently, a positive electrode having a current collector containing a plurality of through holes is used. In addition, one having a current collector containing a plurality of through holes penetrating from one side to the other side is used.

  Li / M can be determined using the ICP (Inductive Coupled Plasma) method as follows. First, 0.2 g of the positive electrode active material to be measured is collected and placed in a 100 mL container. Thereafter, 5 mL of pure water, 2 mL of aqua regia, and 10 mL of pure water were added in order and dissolved by heating. After cooling, the mixture was further diluted 25 times with pure water and an ICP analyzer “ICP-757” manufactured by JARRELASH was used. The composition is analyzed by a calibration curve method. Li / M can be derived from the obtained results.

  For the positive electrode according 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 additive and a binder is used on one or both sides of the positive electrode current collector. be able to.

The positive electrode active material used for the positive electrode is not particularly limited except that it contains a metal oxide composed of a metal M other than Li and Li, and a generally usable active material such as a lithium-containing transition metal oxide is used. That's fine. For example, examples of the metal M include Co, Ni, Mn, Al, Zn, Ti, and the like. Specific examples of the lithium-containing transition metal oxide include, for example, Li _x CoO ₂ , Li _x NiO ₂ , Li _x MnO ₂ , Li _x Co _y Ni _1-y O ₂ , and Li _x Co _y M ¹ _1-y O. ^{_{2, Li x Ni 1-y}} M 1 y O 2, Li x Mn y Ni z Co 1-y-z O 2, Li x Mn 2 O 4, Li x Mn 2-y M 1 y O 4 and the like exemplified Is done. However, in each structural formula above, M ¹ is at least one metal element selected from the group consisting of Mg, Mn, Fe, Co, Ni, Cu, Zn, Al, Ti, Ge, and Cr, 0 ≦ x ≦ 1.1, 0 <y <1.0, 2.0 <z <1.0.

As a conductive support agent used for the said positive electrode, what is chemically stable should just be in a 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 fiber such as carbon fiber and metal fiber; aluminum Metal powders such as powders; Fluorinated carbon; Zinc oxide; Conductive whiskers made of potassium titanate; Conductive metal oxides such as titanium oxide; Organic conductive materials such as polyphenylene derivatives, etc. You may use independently and may use 2 or more types together. Among these, highly conductive graphite and carbon black excellent in liquid absorption are preferable. Further, the form of the conductive auxiliary agent is not limited to primary particles, and secondary aggregates and aggregated forms such as chain structures can also be used. Such an assembly is easier to handle and has better productivity.

  Moreover, PVDF, P (VDF-CTFE), polytetrafluoroethylene (PTFE), SBR, etc. can be used for the binder which concerns on a positive mix layer.

The positive electrode is prepared, for example, as a paste-like or slurry-like positive electrode mixture-containing composition in which the above-described positive electrode active material, conductive additive and binder are dispersed in a solvent such as N-methyl-2-pyrrolidone (NMP). (However, the binder may be dissolved in a solvent.) After applying this to one or both sides of the current collector and drying, it can be produced through a process of calendering if necessary. . The manufacturing method of a positive electrode is not necessarily restricted to said method, It can also manufacture with another manufacturing method.

  The thickness of the positive electrode mixture layer is preferably, for example, 10 to 100 μm per one side of the current collector. Moreover, as a composition of a positive mix layer, it is preferable that the quantity of a positive electrode active material is 65-95 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.

  Examples of the current collector include a plurality of through holes penetrating from one surface to the other surface, such as an aluminum foil, a punching metal, a net, and an expanded metal.

  When adopting the above-described method of introducing Li into the negative electrode mixture layer in advance, a metal foil having a plurality of through holes penetrating the negative electrode current collector from one surface to the other surface is used, and the positive electrode current collector In addition, by using a metal foil having a plurality of through holes penetrating from one surface to the other surface, Li moves to the entire inside of the battery through the through holes of the negative electrode current collector and the positive electrode current collector. It is not necessary to bring the Li source into contact with all the negative electrodes, and the working efficiency can be improved.

  When a metal foil having a plurality of through holes penetrating from one surface to the other surface is used as the positive electrode current collector, the upper limit of the thickness is preferably 30 μm, and the lower limit is in order to ensure mechanical strength. It is desirable to be 4 μm. Further, the size of the through hole is preferably 0.05 mm or more for the purpose of making the movement of Li uniform. However, if the size of the through-hole is too large, 0.4 mm or less is desirable because the mechanical strength cannot be maintained.

  Moreover, you may form the lead body for electrically connecting with the other member in a lithium ion secondary battery according to a conventional method to a positive electrode as needed.

  The separator is preferably a porous film composed of polyolefin such as polyethylene, polypropylene, and ethylene-propylene copolymer; polyester such as polyethylene terephthalate and copolymer polyester; In addition, it is preferable that a separator has the property (namely, shutdown function) which the hole obstruct | occludes in 100-140 degreeC. Therefore, the separator has a melting point, that is, a thermoplastic resin having a melting temperature measured using a differential scanning calorimeter (DSC) of 100 to 140 ° C. in accordance with JIS K 7121 as a component. Preferably, it is a single layer porous film mainly composed of polyethylene or a laminated porous film comprising a porous film such as a laminated porous film in which 2 to 5 layers of polyethylene and polypropylene are laminated. Is preferred. When a resin having a melting point higher than that of polyethylene such as polyethylene and polypropylene is used by mixing or laminating, it is desirable that polyethylene is 30% by mass or more, and 50% by mass or more as a resin constituting the porous membrane. More desirable.

  As such a resin porous membrane, for example, a porous membrane composed of the above-mentioned exemplified thermoplastic resin used in a conventionally known lithium ion secondary battery or the like, that is, a solvent extraction method, a dry type Alternatively, an ion-permeable porous film manufactured by a wet stretching method or the like can be used.

  The average pore size of the separator is preferably 0.01 μm or more, more preferably 0.05 μm or more, preferably 1 μm or less, more preferably 0.5 μm or less.

Moreover, as a characteristic of the separator, a Gurley value represented by the number of seconds in which 100 ml of air permeates the membrane under a pressure of 0.879 g / mm ² is 10 to 500 sec. It is desirable to be. If the air permeability is too high, the ion permeability is reduced, whereas if it is too low, the strength of the separator may be reduced. Further, the strength of the separator is desirably 50 g or more in terms of piercing strength using a needle having a diameter of 1 mm. If the piercing strength is too small, a short circuit may occur due to the piercing of the separator when lithium dendrite crystals are generated.

  As the separator, a laminated separator having a porous layer (I) mainly composed of a thermoplastic resin and a porous layer (II) mainly composed of a filler having a heat resistant temperature of 150 ° C. or higher may be used. . The separator has both shutdown characteristics, heat resistance (heat shrinkage resistance), and high mechanical strength. It has also been found that cycle characteristics can be further improved by using a laminated separator. The reason is not clear, but the high mechanical strength of this separator shows high resistance to negative electrode expansion / contraction associated with the charge / discharge cycle. The reason is that it can be maintained.

  In this specification, “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 separator is mainly for ensuring a shutdown function, and when the battery has reached the melting point of the thermoplastic resin that is the main component of the porous layer (I), The thermoplastic resin related to the porous layer (I) melts and closes the pores of the separator, thereby causing a shutdown that suppresses the progress of the electrochemical reaction.

  The thermoplastic resin that is the main component of the porous layer (I) is a resin having a melting point, that is, a melting temperature of 140 ° C. or less measured using a differential scanning calorimeter (DSC) in accordance with JIS K 7121. Specific examples include polyethylene. As the form of the porous layer (I), a microporous membrane usually used as a battery separator or a dispersion containing polyethylene particles is applied to a base material such as a nonwoven fabric and dried. Examples thereof include sheet-like materials such as those obtained. Here, in the total volume of the constituent components of the porous layer (I) [total volume excluding pores. The same applies to the volume content of the constituent components of the porous layer (I) and the porous layer (II) relating to the separator. ], The volume content of the thermoplastic resin as a main component 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 polyethylene microporous film, the volume content of the thermoplastic resin is 100% by volume.

  The porous layer (II) according 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, and has a heat resistance temperature of 150 ° C. or higher. The function is secured by. That is, when the battery becomes high temperature, even if the porous layer (I) shrinks, the porous layer (II) which is difficult to shrink can directly generate positive and negative electrodes that can be generated 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.

  The filler related to the porous layer (II) has a heat-resistant temperature of 150 ° C. or higher, is stable with respect to the electrolyte solution of the battery, and is electrochemically stable that is not easily oxidized or reduced in the battery operating voltage range. If present, inorganic particles or organic particles may be used, but fine particles are preferable from the viewpoint of dispersion and the like, and inorganic oxide particles, more specifically, 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, the filler whose heat-resistant temperature is 150 degreeC or more may use the thing of the said illustration individually by 1 type, and may use 2 or more types together, for example.

As the nonaqueous electrolytic solution according to the lithium ion secondary battery of the present invention, a nonaqueous electrolytic solution in which a lithium salt is dissolved in an organic solvent can be used.

The organic solvent used for the non-aqueous electrolyte is not particularly limited as long as it dissolves the lithium salt and does not cause a side reaction such as decomposition in a voltage range used as a battery. For example, cyclic carbonates such as ethylene carbonate, propylene carbonate, and butylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate; chain esters such as methyl propionate; cyclic esters such as γ-butyrolactone; dimethoxyethane, Chain ethers such as diethyl ether, 1,3-dioxolane, diglyme, triglyme and tetraglyme; cyclic ethers such as dioxane, tetrahydrofuran and 2-methyltetrahydrofuran; nitriles such as acetonitrile, propionitrile and methoxypropionitrile; ethylene Examples thereof include sulfites such as glycol sulfite, and these may be used as a mixture 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.

The lithium salt used in the non-aqueous electrolyte is not particularly limited as long as it dissociates in a solvent to form lithium ions and does not easily cause 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 (2 ≦ n ≦ 7), LiN (RfOSO ₂ ) ₂ [where Rf is a fluoroalkyl group] or the like is used. be able to.

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.

  In addition, in the non-aqueous electrolyte, vinylene carbonate, vinyl ethylene carbonate, acid anhydride, sulfonic acid ester, for the purpose of improving the safety such as further improvement of charge / discharge cycle characteristics and high temperature storage property and prevention of overcharge, Additives (including these derivatives) such as dinitrile, 1,3-propane sultone, diphenyl disulfide, cyclohexylbenzene, biphenyl, fluorobenzene, t-butylbenzene, phosphonoacetate compounds, 1,3-dioxane as appropriate It can also be added.

  Further, as the non-aqueous electrolyte, a gel (gel electrolyte) obtained by adding a known gelling agent such as a polymer can be used.

  In the lithium ion secondary battery of the present invention, the negative electrode and the positive electrode are a laminated body (laminated electrode body) superposed via a separator, or a wound body (winding electrode) obtained by further winding the laminated body in a spiral shape. Body). In the case of a laminated electrode body, even if the volume of the negative electrode changes due to charging / discharging of the battery, the battery characteristics are more favorably maintained because it is easier to maintain the distance from the positive electrode. . For these reasons, it is more preferable to use a laminated electrode body in the lithium ion secondary battery of the present invention.

In the manufacturing process of the lithium ion secondary battery of the present invention, the third electrode described above is used. Further, a buffer layer having a Gurley value of 200 to 800 sec / 100 cc is provided between the outermost negative electrode in the electrode body and the third electrode. The Gurley value referred to here is a numerical value obtained by a method based on JIS P 8117 for obtaining the Gurley value of the separator described above.

By providing a buffer layer having a Gurley value of 200 to 800 sec / 100 cc between the outermost negative electrode and the third electrode in the electrode body, the negative electrode mixture layer is dropped when Li ions are introduced into the negative electrode mixture layer Can be prevented. This limits to some extent the buffer layer from moving Li ions from the Li source to the outermost negative electrode. Accordingly, it is possible to prevent Li ions from being introduced to the outermost negative electrode all at once, and to prevent the negative electrode mixture layer from rapidly expanding, thereby preventing the negative electrode mixture layer from falling off.
When the Gurley value of the buffer layer is less than 200 sec / 100 cc, the effect of preventing the negative electrode mixture layer from falling off is lowered. Further, if it exceeds 800 sec / 100 cc, there is a problem that it takes a long time to introduce Li into the negative electrode.

The buffer layer having a Gurley value of 200 to 800 sec / 100 cc may be composed of a plurality of layers having different materials and thicknesses. However, if all of the single layer or the plurality of layers constituting the buffer layer are conductors, the negative electrode and Li are short-circuited, and the negative electrode mixture layer will drop off, so that it is composed of a plurality of layers. In some cases, at least one layer is preferably an insulator. For example, a separator having a thickness of 20 μm or more, a laminate of a plurality of separators having a thickness of 20 μm or more, a porous body such as a nonwoven fabric loaded with an insulator such as alumina or resin, and a metal foil having a plurality of through holes And a laminate of a conductor having a negative electrode or a positive electrode mixture layer provided on at least one surface thereof and a separator.

  It is preferable to use a metal laminate film outer package for the outer package according to the lithium ion secondary battery of the present invention. Since the metal laminate film outer package is easier to deform than, for example, a metal outer can, the negative electrode mixture layer and the negative electrode current collector are hardly broken even if the negative electrode expands due to battery charging. It is.

  As the metal laminate film constituting the metal laminate film exterior body, for example, a metal laminate film having a three-layer structure composed of exterior resin layer / metal layer / interior resin layer is used.

  The metal layer in the metal laminate film is an aluminum film, a stainless steel film or the like, and the interior resin layer is a heat-sealing resin (for example, a modified polyolefin ionomer that develops heat-fusibility at a temperature of about 110 to 165 ° C.). A structured film may be mentioned. Examples of the exterior resin layer of the metal laminate film include a nylon film (such as nylon 66 film) and a polyester film (such as polyethylene terephthalate film).

In the metal laminate film, the thickness of the metal layer is preferably 10 to 150 μm, the thickness of the interior resin layer is preferably 20 to 100 μm, and the thickness of the exterior resin layer is preferably 20 to 100 μm.

  The shape of the exterior body is not particularly limited. For example, the shape of the exterior body may be a polygon such as a triangle, a quadrangle, a pentagon, a hexagon, a heptagon, and an octagon in plan view. A square (rectangular or square) is common. The size of the exterior body is not particularly limited, and can be various sizes such as a so-called thin shape and large size.

  The metal laminate film exterior body may be configured by folding a single metal laminate film in two, or may be configured by stacking two metal laminate films.

  When the planar shape of the exterior body is a polygon, the side from which the positive external terminal is drawn out and the side from which the negative external terminal is drawn out may be the same side or different sides.

  The width of the heat fusion part in the outer package is preferably 5 to 20 mm.

  The lithium ion secondary battery of the present invention can be used with a charging upper limit voltage of about 4.2 V as in the case of the conventional lithium ion secondary battery. However, the charging upper limit voltage is higher than 4.4 V. It is possible to set and use as described above. With this, it is possible to stably exhibit excellent characteristics even when repeatedly used over a long period of time while increasing the capacity. In addition, it is preferable that the upper limit voltage of charge of a lithium ion secondary battery is 4.5V or less.

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

  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 the physical properties of the composites obtained by coating the graphite and SiO surfaces used in the examples with carbon materials.

Example 1
<Preparation of positive electrode>
LiCoO _{2 as} positive electrode active material: 96.5 parts by mass, NMP solution containing P (VDF-CTFE) as a binder at a concentration of 10% by mass: 20 parts by mass, and acetylene black as a conductive auxiliary agent: 1. 5 parts by mass was kneaded using a biaxial kneader, and NMP was further added to adjust the viscosity to prepare a positive electrode mixture-containing paste. This paste was applied to both sides of an aluminum foil having a through hole penetrating from one surface to the other surface (thickness 15 μm, through hole diameter 0.3 mm, porosity 16%), and at 120 ° C. Vacuum drying was performed for 12 hours, a positive electrode mixture layer was formed on both surfaces of the aluminum foil, a press treatment was performed, and the film was cut into a predetermined size to obtain a strip-shaped positive electrode. In addition, when applying the positive electrode mixture-containing paste to the aluminum foil, a part of the aluminum foil is exposed, and the positive electrode mixture-containing paste is applied to both sides of the aluminum foil. The applied part was also made into the application part. The thickness of the positive electrode mixture layer of the obtained positive electrode (the thickness per one side when the positive electrode mixture layer was formed on both surfaces of the aluminum foil) was 55 μm.

  Forming the positive electrode mixture layer so that a part of the exposed portion of the aluminum foil (positive electrode current collector) protrudes so that the strip-like positive electrode having the positive electrode mixture layer formed on both surfaces of the aluminum foil becomes a tab portion. The part was punched out with a Thomson blade so as to have a substantially quadrangular shape with four corners being curved, and a positive electrode for a battery having a positive electrode mixture layer on both surfaces of the positive electrode current collector was obtained. FIG. 1 is a plan view schematically showing the battery positive electrode (however, in order to facilitate understanding of the structure of the positive electrode, the size of the positive electrode shown in FIG. 1 does not necessarily match the actual one). Not) The positive electrode 10 has a shape having a tab portion 13 punched out so that a part of the exposed portion of the positive electrode current collector 12 protrudes, and the shape of the formation portion of the positive electrode mixture layer 11 is a substantially rectangular shape with four corners curved. In the figure, the lengths a, b and c were 8 mm, 37 mm and 2 mm, respectively.

<Production of negative electrode>
Graphite A-1 shown in Table 1 (graphite whose surface is not coated with amorphous carbon): 10% by mass and graphite B-1 (the surface of the mother particles made of graphite, with pitch as the carbon source) Graphite coated with amorphous carbon: 10% by mass and a composite Si-1 whose SiO surface is coated with a carbon material (average particle diameter is 8 μm, specific surface area is 7.9 m ² / g, carbon in the composite) The material amount was 20% by mass): 80% by mass was mixed with a V-type blender for 12 hours to obtain a negative electrode active material.
After adding 100 parts by mass of polyacrylic acid to 500 parts by mass of ion-exchanged water and stirring and dissolving, NaOH: 70 parts by mass was added and stirred and dissolved until the pH became 7 or less. Further, ion exchange water was added to prepare a 5% by mass aqueous solution of sodium salt of polyacrylic acid. The negative electrode active material, a 1% by weight aqueous solution of CMC, and carbon black were added to this aqueous solution and mixed by stirring to obtain a negative electrode mixture paste. The composition ratio (mass ratio) of 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 mixture paste is applied to both sides of a copper foil (thickness is 10 μm, diameter of the through hole is 0.1 mm, porosity is 47%) having a through hole penetrating from one surface to the other surface. Drying is performed, negative electrode mixture layers are formed on both sides of the copper foil, press treatment is performed, and the density of the negative electrode mixture layer is adjusted to 1.4 g / cm ³ , and then cut into a predetermined size to form a strip shape. The negative electrode was obtained. In addition, when apply | coating the negative mix containing paste to copper foil, a part of copper foil was exposed and the back surface also made the application part the part made into the application part on the surface. The thickness of the negative electrode mixture layer of the obtained negative electrode (thickness per one side of the copper foil as the negative electrode current collector) was 65 μm.

The negative electrode mixture paste is applied to one side of a copper foil (thickness is 10 μm, diameter of the through hole is 0.1 mm, porosity is 47%) having a through hole penetrating from one side to the other side. Drying is performed, a negative electrode mixture layer is formed on one side of the copper foil, press treatment is performed to adjust the density of the negative electrode mixture layer to 1.4 g / cm ³ , and then a predetermined size is cut. The negative electrode was obtained. In addition, when apply | coating the negative mix containing paste to copper foil, a part of copper foil was exposed and the back surface also made the application part the part made into the application part on the surface. The thickness of the negative electrode mixture layer of the obtained negative electrode (thickness per one side of the copper foil as the negative electrode current collector) was 65 μm.

  In order to make the strip-shaped negative electrode into a tab portion, a part of the exposed portion of the copper foil (negative electrode current collector) protrudes, and the negative electrode mixture layer forming portion has a substantially square shape with four corners curved. Thus, a negative electrode for a battery having a negative electrode mixture layer on both surfaces and one surface of the negative electrode current collector was obtained. FIG. 2 is a plan view schematically showing the battery negative electrode (however, in order to facilitate understanding of the structure of the negative electrode, the size of the negative electrode shown in FIG. 2 does not necessarily match the actual size). Not) The negative electrode 20 has a shape having a tab portion 23 punched out so that a part of the exposed portion of the negative electrode current collector 22 protrudes, and the shape of the formation portion of the negative electrode mixture layer 21 is a substantially rectangular shape with four corners curved. In the figure, the lengths of d, e, and f were 9 mm, 38 mm, and 2 mm, respectively.

A copper foil having a through-hole penetrating 18 mg of Li foil having a thickness of 200 μm from one surface to the other surface, similar to that used in the negative electrode (thickness is 10 μm, and the diameter of the through-hole is 0.1 mm). 1 mm and the porosity is 47%), and punched out with a Thomson blade so as to have the same size as the negative electrode shown in FIG.

<Battery assembly>
Two third electrodes with Li foil bonded to one side of the negative electrode current collector, two negative electrodes for a battery with a negative electrode mixture layer formed on one side of the negative electrode current collector, and a negative electrode mixture layer on both sides of the negative electrode current collector A laminated electrode body was formed using 16 formed negative electrodes for a battery and 17 positive electrodes for a battery in which a positive electrode mixture layer was formed on both surfaces of a positive electrode current collector. In the laminated electrode body, as shown in FIG. 3, the upper and lower ends are arranged as third electrodes 31 so that the respective current collectors face outward, and a PE separator (thickness 12 μm, Gurley value 150 sec / sec) is placed between them. 100 cc) are arranged to provide a buffer layer 32. The Gurley value of the buffer layer composed of 4 separators was 600 sec / 100 cc. Furthermore, the negative electrode 33 for a battery in which a negative electrode mixture layer was formed on one side of the negative electrode current collector, the positive electrode 10 for a battery in which a positive electrode mixture layer was formed on both sides of the positive electrode current collector, and the negative electrode mixture layer were formed on both sides. The battery negative electrodes 20 are alternately arranged, and one PE separator 34 (thickness 12 μm) is interposed between each positive electrode and each negative electrode. The tab portion between the positive electrodes, the tab portion between the negative electrodes, and the third electrode Each of the tab portions was welded to produce a laminated electrode body. And the said laminated electrode body is inserted in the said hollow of the aluminum laminate film of thickness: 0.15mm, width: 34mm, and height: 50mm which formed the hollow so that the said laminated electrode body might be accommodated, and said and above An aluminum laminate film of the same size was placed and three sides of both aluminum laminate films were heat-welded. Then, from the remaining one side of both aluminum laminate films, LiPF ₆ was dissolved at a concentration of 1 mol / l in a non-aqueous electrolyte (a mixed solvent of ethylene carbonate and diethyl carbonate in a volume ratio of 3: 7), and vinylene carbonate was further added. The solution added in an amount of 3% by mass) was injected. Thereafter, the remaining one side of both aluminum laminate films was vacuum heat sealed to produce a lithium ion secondary battery having the appearance shown in FIG. 4 and the cross-sectional structure shown in FIG.

Here, FIG. 4 and FIG. 5 will be described. FIG. 4 is a plan view schematically showing a lithium ion secondary battery, and FIG. 5 is a cross-sectional view taken along the line II in FIG. The nonaqueous secondary battery 100 includes a laminated electrode body 102 constituted by laminating a positive electrode and a negative electrode with a separator in an aluminum laminated film outer package 101 constituted by two aluminum laminated films, and a nonaqueous electrolytic solution. (Not shown) is housed, and the aluminum laminate film outer package 101 is sealed by heat-sealing the upper and lower aluminum laminate films at the outer peripheral portion thereof. In addition, in FIG. 5, in order to avoid that drawing becomes complicated, each layer which comprises the aluminum laminate film exterior body 101, and the positive electrode, negative electrode, and separator which are comprising the laminated electrode body are not distinguished and shown. .

Each positive electrode of the laminated electrode body 102 is integrated by welding the tab portions together, and the integrated product of the welded tab portions is connected to the positive electrode external terminal 103 in the battery 100, although not shown. The negative electrodes of the laminated electrode body 102 are also integrated by welding the tab portions together, and the integrated product of the welded tab portions 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 are drawn out to the outside of the aluminum laminate film exterior body 101 so that they can be connected to an external device or the like.
The lithium ion secondary battery produced as described above was stored in a constant temperature bath at 45 ° C. for 1 week.

(Examples 2-9)
Example 1 except that a negative electrode active material obtained by mixing the material S and graphite shown in Table 1 at a mass ratio shown in Table 2 and using a buffer layer whose Gurley value was adjusted by the number of separators shown in Table 3 was used. In the same manner, a lithium ion secondary battery was produced.

(Example 10)
Copper foil having a through-hole penetrating the negative electrode mixture paste prepared in Example 5 from one surface to the other surface (thickness is 8 μm, diameter of the through-hole is 0.3 mm, porosity is 17%) Is applied to one side or both sides of the copper foil and dried to form a negative electrode mixture layer on one side or both sides of the copper foil, and press treatment is performed to adjust the density of the negative electrode mixture layer to 1.4 g / cm ^3. A strip-shaped negative electrode was obtained. Thereafter, a lithium ion secondary battery was produced in the same manner as in Example 5.

(Example 11)
Copper foil having a through hole penetrating the negative electrode mixture paste prepared in Example 5 from one surface to the other surface (thickness is 13 μm, diameter of the through hole is 0.1 mm, porosity is 60%) Is applied to one side or both sides of the copper foil and dried to form a negative electrode mixture layer on one side or both sides of the copper foil, and press treatment is performed to adjust the density of the negative electrode mixture layer to 1.4 g / cm ^3. A strip-shaped negative electrode was obtained. Thereafter, a lithium ion secondary battery was produced in the same manner as in Example 5.

(Comparative Example 1)
Copper foil having a through-hole penetrating the negative electrode mixture paste prepared in Example 1 from one surface to the other surface (thickness is 8 μm, diameter of the through-hole is 0.3 mm, porosity is 17%) Is applied to one side or both sides of the copper foil and dried to form a negative electrode mixture layer on one side or both sides of the copper foil, and press treatment is performed to adjust the density of the negative electrode mixture layer to 1.4 g / cm ^3. A strip-shaped negative electrode was obtained. A lithium ion secondary battery was fabricated in the same manner as in Example 1 except that the number of separators used as the buffer layer and the Gurley value of the buffer layer were adjusted as shown in Table 3.

(Comparative Examples 2 and 3)
A lithium ion secondary battery was fabricated in the same manner as in Example 1 except that the number of separators used as the buffer layer and the Gurley value of the buffer layer were adjusted as shown in Table 3.

<Extraction of outermost negative electrode mixture layer and presence / absence of residual Li>
About each lithium ion secondary battery of an Example and a comparative example, after storing for one week in a 45 degreeC thermostat, it disassembled in an argon glove box, loss | disappearance of Li of a 3rd electrode, and removal of a negative mix layer The presence or absence was observed. Table 4 shows the evaluation results of each battery.

<Measurement of Li content in positive electrode active material>
About each lithium ion secondary battery of Example and Comparative Example (battery different from those observed for the presence or absence of dropping), a lithium ion secondary battery stored for 24 hours in a constant temperature bath at 60 ° C. was discharged at 0.1 C. The battery was discharged until the voltage reached 2.0 V at the current rate. Thereafter, the aluminum laminate was disassembled in the glove box, and only the positive electrode was taken out. The positive electrode taken out was washed with diethyl carbonate, the positive electrode mixture layer was scraped out, and the composition ratio (Li / M) of metals other than Li and Li was calculated by the ICP method described above. The results are shown in Table 4.

DESCRIPTION OF SYMBOLS 10 Positive electrode 11 Positive electrode mixture layer 12 Positive electrode collector 13 Tab part 20 Negative electrode 21 Negative electrode mixture layer 22 Negative electrode collector 23 Tab part 31 3rd electrode 32 Buffer layer 33 Negative electrode (mixture layer only on one side)
34 Separator 100 Lithium ion secondary battery 101 Metal laminate film exterior body 102 Laminated electrode body 103 Positive electrode external terminal 104 Negative electrode external terminal

Claims (6)

In a method for producing a lithium ion secondary battery having an electrode body in which a positive electrode and a negative electrode provided with a mixture layer on at least one surface of a metal foil are laminated via a separator,
The metal foil has a through-hole penetrating from one surface to the other surface,
The negative electrode is provided with a negative electrode mixture layer mainly composed of a negative electrode active material on at least one surface of a support made of a metal foil,
The negative electrode active material contains a material S that is a negative electrode material containing Si,
When the total of all the negative electrode active materials contained in the negative electrode is 100% by mass, the content of the material S contained as the negative electrode active material is at least 5% by mass,
The positive electrode is provided with a positive electrode mixture layer containing a metal oxide composed of a metal M other than Li and Li as a positive electrode active material on at least one surface of a support made of a metal foil,
Preparing a third electrode containing a Li source;
Preparing a buffer layer having a Gurley value of 200 to 800 sec / 100 cc;
Between the outermost negative electrode in the electrode body and the third electrode, the step of arranging the buffer layer in contact with each other;
A method of manufacturing a lithium ion secondary battery, comprising: short-circuiting the negative electrode and the third electrode to introduce Li ions into the negative electrode. 2. The method for manufacturing a lithium ion secondary battery according to claim 1, wherein the material S includes SiO _x (wherein the atomic ratio x of O to Si is 0.5 ≦ x ≦ 1.5).   The method for producing a lithium ion secondary battery according to claim 1 or 2, wherein the metal foil used for the negative electrode has a porosity of 30 to 55%. In a lithium ion secondary battery in which an electrode body in which a positive electrode and a negative electrode provided with a mixture layer on at least one surface of a metal foil are stacked via a separator is disposed in an exterior body,
The metal foil has a through-hole penetrating from one surface to the other surface,
The negative electrode is provided with a negative electrode mixture layer mainly composed of a negative electrode active material on at least one surface of a support made of a metal foil,
The negative electrode active material contains a material S that is a negative electrode material containing Si,
When the total of all the negative electrode active materials contained in the negative electrode is 100% by mass, the content of the material S contained as the negative electrode active material is at least 5% by mass,
The positive electrode is provided with a positive electrode mixture layer containing a metal oxide composed of a metal M other than Li and Li as a positive electrode active material on at least one surface of a support made of a metal foil,
The negative electrode mixture layer of the outermost negative electrode in the electrode body is in contact with a buffer layer having a Gurley value of 200 to 800 sec / 100 cc,
When discharged at a discharge current rate of 0.1 C until the voltage reaches 2.0 V, the molar ratio (Li / M) between Li and metal M other than Li contained in the positive electrode active material is 0.6 to 1. .05, a lithium ion secondary battery. The lithium ion secondary battery according to claim 4, wherein the material S includes SiO _x (wherein the atomic ratio x of O to Si is 0.5 ≦ x ≦ 1.5).   The lithium ion secondary battery according to claim 4 or 5, wherein the metal foil used for the negative electrode has a porosity of 30 to 55%.

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