JP2018098021A - Negative electrode for nonaqueous electrolyte solution-based electrochemical element, method for manufacturing the same, lithium ion secondary battery and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a lithium ion secondary battery superior in charge and discharge cycle characteristics; a method for manufacturing the lithium ion secondary battery; a negative electrode for a nonaqueous electrolyte solution-based electrochemical element, which enables the formation of the lithium ion secondary battery; and a method for manufacturing the negative electrode.SOLUTION: A negative electrode for a nonaqueous electrolyte solution-based electrochemical element according to the present invention is arranged by doping a negative electrode mixture layer including a Li-free negative electrode active material with Li ions. The negative electrode comprises: a current collector composed of a piece of metal foil of which the tensile strength is 300 N/mmor more; and the negative electrode mixture layer laminated on the current collector. A lithium ion secondary battery of the invention comprises, as a negative electrode, the negative electrode for a nonaqueous electrolyte solution-based electrochemical element.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a lithium ion secondary battery having excellent charge / discharge cycle characteristics and a method for producing the same, and a negative electrode for a non-aqueous electrolyte based electrochemical device that can constitute the lithium ion secondary battery and a method for producing the same. .

  Lithium-ion secondary batteries have high voltage and high capacity, so there are great expectations for their development. Under these circumstances, various materials used in batteries, such as positive electrode active materials and negative electrode active materials involved in battery reactions, non-aqueous electrolytes, binders used in positive electrodes and negative electrodes, have been improved.

  Recently, in particular, there has been a demand for further capacity enhancement of miniaturized and multifunctional lithium ion secondary batteries for portable devices. In response to this demand, the negative electrode active material is made from graphite, which has been widely used. Considering changing to materials that can accommodate more Li (lithium), such as low crystalline carbon, Si (silicon), Sn (tin), etc. (hereinafter also referred to as “high capacity negative electrode material”) Has been.

  However, in a lithium ion secondary battery using a high-capacity negative electrode material, a problem that is difficult to occur when graphite is used may occur due to a larger amount of Li accepted than graphite. There are also proposals for techniques to avoid such problems.

For example, in Patent Document 1, in using a high-capacity negative electrode material, a negative electrode active material-containing layer (negative electrode mixture layer) is formed using at least one binder selected from the group consisting of polyimide, polyamideimide, and polyamide. By using a negative electrode current collector that is formed and has a 0.2% proof stress of 250 N / mm ² or more or a tensile strength of 300 N / mm ² or more, it accompanies charging and discharging of a lithium ion secondary battery. Techniques for suppressing the volume change and deformation of the negative electrode have been proposed.

  In addition, in a battery configured using a high-capacity negative electrode material, in general, among Li released from the positive electrode by charging, a large proportion of the lithium that is taken into the high-capacity negative electrode material and remains without being discharged at the next discharge, There is a tendency that the capacity that the battery originally has cannot be drawn out sufficiently.

  In order to reduce the irreversible capacity of such a battery, the negative electrode (negative electrode mixture layer) is doped with Li ions (pre-doping) to increase the proportion of Li that can travel between the positive electrode and the negative electrode during charge / discharge of the battery. Technology is also being considered. Such a pre-doping technique of Li ions into the negative electrode is described in Patent Documents 2 and 3 in addition to means for pre-doping Li ions into the negative electrode in the battery (hereinafter sometimes referred to as “in-system pre-doping”). Thus, means for assembling a battery using a negative electrode pre-doped with Li ions in advance (hereinafter, pre-doping of Li ions into the negative electrode by such means may be referred to as “outside pre-doping”) has also been proposed.

JP 2011-192563 A JP-A-11-283670 JP 2008-91191 A

  However, when the negative electrode mixture layer is doped with Li ions by pre-doping outside the system, the negative electrode mixture layer expands and the hardness increases, which tends to deteriorate the charge / discharge cycle characteristics of the lithium ion secondary battery. There is room for improvement.

  The present invention has been made in view of the above circumstances, and the object thereof is a lithium ion secondary battery excellent in charge / discharge cycle characteristics, a method for producing the same, and non-aqueous electrolysis that can constitute the lithium ion secondary battery. The object is to provide a negative electrode for a liquid electrochemical device and a method for producing the same.

The negative electrode for a non-aqueous electrolyte-based electrochemical device of the present invention that has achieved the above object is formed by laminating a negative electrode mixture layer containing a negative electrode active material and a binder on a current collector, and Li The negative electrode mixture layer containing a negative electrode active material not included is doped with Li ions, and the current collector is a metal foil having a tensile strength of 300 N / mm ² or more.

  The negative electrode for a non-aqueous electrolyte-based electrochemical device of the present invention is drawn out of a negative electrode wound around a roll and introduced into an electrolyte bath provided with a non-aqueous electrolyte and a lithium metal electrode. The non-aqueous electrolyte after doping Li ions into the negative electrode mixture layer by conducting a current between the negative electrode and the lithium metal electrode to form a negative electrode for a non-aqueous electrolyte based electrochemical device. It can manufacture by the manufacturing method of this invention which has the process of winding up the negative electrode for system electrochemical elements in roll shape.

  Further, the lithium ion secondary battery of the present invention comprises a negative electrode, a positive electrode having a positive electrode mixture layer containing a positive electrode active material and a binder, a separator, and a non-aqueous electrolyte contained in an exterior body. It has the negative electrode for non-aqueous-electrolyte type | system | group electrochemical elements of invention.

  The lithium ion secondary battery of the present invention can be manufactured by the manufacturing method of the present invention including a step of assembling a lithium ion secondary battery using the negative electrode for a non-aqueous electrolyte based electrochemical device obtained by the above manufacturing method. it can.

  ADVANTAGE OF THE INVENTION According to this invention, the lithium ion secondary battery excellent in charging / discharging cycling characteristics, its manufacturing method, the negative electrode for non-aqueous-electrolyte type | system | group electrochemical elements which can comprise the said lithium ion secondary battery, and its manufacturing method are provided. can do.

It is explanatory drawing of the process of doping Li ion to the negative mix layer of a negative electrode by the roll-to-roll method. It is a longitudinal cross-sectional view which represents typically an example of the lithium ion secondary battery of this invention.

  The negative electrode for non-aqueous electrolyte based electrochemical devices of the present invention (hereinafter simply referred to as “negative electrode”) has a non-aqueous electrolyte, such as a lithium ion secondary battery or a super capacitor, and is repeatedly charged and discharged. It is used for the negative electrode of an element. And the negative electrode of the present invention has a negative electrode mixture layer containing a negative electrode active material and a binder that do not contain Li. For example, the negative electrode mixture layer has a structure formed on one side or both sides of a current collector. Furthermore, the negative electrode mixture layer is doped with Li ions by pre-doping outside the system.

  The negative electrode in which the negative electrode mixture layer is doped with Li ions by pre-doping outside the system has increased hardness, and the negative electrode active material layer expands greatly, so that the negative electrode mixture layer also expands. . And in the lithium ion secondary battery comprised using the negative electrode which such a deformation | transformation produced, the capacity | capacitance fall by repeating charging / discharging tends to arise.

Therefore, in the present invention, when a lithium ion secondary battery is configured using a negative electrode in which a negative electrode mixture layer is doped with Li ions through external pre-doping, a negative electrode current collector has a tensile strength of 300 N / mm ² or more, Preferably, a metal foil of 350 N / mm ² or more was used. If it is the negative electrode of this invention which uses the metal foil which has the said tensile strength as an electrical power collector, even if it doped Li ion to a negative mix layer by an out-of-system pre dope, it will be hard to produce deformation | transformation, such as a curve. Therefore, in the lithium ion secondary battery of the present invention using the negative electrode of the present invention, good charge / discharge cycle characteristics can be secured.

  In addition, when pre-doping outside the system, considering the productivity, the negative electrode before doping with Li ions is wound into a roll shape, and Li ions are doped in the middle of transporting the negative electrode drawn from the roll, and then again It is preferable to dope Li ions continuously by a so-called roll-to-roll method of winding in a roll shape. However, when pre-doping outside the system by the roll-to-roll method, tension is applied to the negative electrode, and therefore, when the large deformation occurs, the negative electrode is likely to be cut.

  However, in the case of the negative electrode of the present invention, the deformation at the time of pre-doping outside the system can be suppressed by the action of the current collector having the above-described tensile strength. The occurrence of defects can be suppressed. Therefore, the negative electrode of the present invention has good productivity. The effect of the present invention is naturally useful when a negative electrode active material having a large proportion of irreversible capacity is used, but the greater the amount of pre-doping in the negative electrode mixture layer outside the system, the more remarkable the effect regardless of the proportion of irreversible capacity. Indicates. For example, the present invention is useful when doping a negative electrode in a lithium ion capacitor (LIC) or a negative electrode combined with a positive electrode having no Li source in a lithium ion secondary battery.

  The tensile strength of the metal foil used as the negative electrode current collector in this specification was obtained by cutting the metal foil used as the negative electrode current collector into a size of 160 mm × 25 mm using “Small Desktop Testing Machine EZ-L” manufactured by Shimadzu Corporation. This is a value obtained by measuring a sample as a measurement sample under the conditions of a tensile speed of 2 mm / min and a temperature of 20 ° C.

Further, the metal foil serving as the negative electrode current collector preferably has a 0.2% proof stress of 250 N / mm ² or more, and more preferably 300 N / mm ² or more. In this case, deformation of the negative electrode due to pre-doping of Li ions can be suppressed more favorably, so that productivity of the negative electrode can be further improved, and charge / discharge cycle characteristics of the lithium ion secondary battery can be further improved. it can.

  The 0.2% proof stress of the metal foil used as the negative electrode current collector in this specification is determined by performing a tensile test under the same measurement method and conditions as the tensile strength to obtain a stress-strain curve. It means “Fε”, which is obtained by setting the permanent elongation to 0.2% by the “offset method” defined in “8. (d)” of Industrial Standard (JIS) Z 2241.

  As materials for the negative electrode current collector, Cu, Ni, Ti, and alloys thereof can be used. To increase the tensile strength and 0.2% proof stress as described above, the negative electrode current collector is made of Zr. It is preferable to use a foil made of a Cu alloy containing at least one element selected from the group consisting of Cr, Sn, Zn, Ni, Si and P. If it is the foil of Cu alloy containing the above elements, a collector with a large tensile strength and 0.2% proof stress can be constituted as described above.

  More preferable examples of the composition of the Cu alloy include Cu—Cr, Cu—Ni, Cu—Cr—Zn, and Cu—Ni—Si. The amount of alloy components other than Cu in the Cu alloy is preferably 0.01 to 5% by mass (in this case, the balance is, for example, Cu and inevitable impurities).

  In the case of a Cu—Cr—Zn alloy, the content of each alloy component is preferably, for example, Cr: 0.05 to 0.5 mass%, Zr: 0.01 to 0.3 mass%. In the Cu—Cr—Zn alloy, for example, Mg, Zn, Sn, P, and the like may be contained within the range of the preferable content of the alloy components as necessary.

  Further, examples of the Cu—Ni—Si alloy include a Corson alloy. In this case, the content of each alloy component is, for example, Ni: 1.0 to 4.0 mass%, Si: 0.1 to 1 It is preferably 0.0% by mass. If necessary, the Cu—Ni—Si alloy may contain, for example, Mg, Zn, Sn, P, or the like within the range of the preferred content of the alloy components.

  The thickness of the negative electrode current collector is preferably 6 μm or more, and more preferably 8 μm or more, from the viewpoint of increasing the elastic range of the negative electrode current collector and increasing the strength. However, if the negative electrode current collector is too thick, the volume ratio of the negative electrode current collector that does not directly participate in the power generation reaction in the battery increases, the amount of the active material of the positive and negative electrodes decreases, and Li ion pre-doping is required. There is a concern that the effect of increasing the capacity by using a negative electrode active material having a large capacity may be reduced. Therefore, the thickness of the negative electrode current collector is preferably 16 μm or less, and more preferably 14 μm or less.

Regarding the tensile strength and 0.2% proof stress of the metal foil to be the negative electrode current collector, it is difficult to make the thickness of, for example, 16 μm or less with a Cu alloy foil having a very large tensile strength and 0.2% proof stress, As described above, when a current collector having such a thickness is used, the effect of increasing the capacity may be reduced. Therefore, the tensile strength of the negative electrode current collector is preferably 800 N / mm ² or less, more preferably 750 N / mm ² or less. The 0.2% yield strength of the negative electrode current collector is preferably 750 N / mm ² or less, more preferably 700 N / mm ² or less.

  The negative electrode current collector has, for example, a Cu alloy foil having the above composition and the above thickness, and having the above tensile strength, more preferably having the above 0.2% proof stress. Can be selected and used. A rolled foil obtained by a rolling method can be preferably used as a negative electrode current collector because a foil having a high tensile strength is easily obtained.

  The negative electrode active material used for the negative electrode mixture layer does not contain Li, and specific examples thereof include graphite, pyrolytic carbons, cokes, glassy carbons, fired bodies of organic polymer compounds, meso Examples thereof include carbon materials such as carbon microbeads, carbon fibers and activated carbon; Si or Sn alone; alloys containing Si or Sn; oxides containing Si or Sn. As the negative electrode active material, only one of these may be used, or two or more may be used in combination.

  Among such negative electrode active materials, since the effect of the present invention becomes more remarkable, for example, a material containing Si and O as constituent elements (provided that the atomic ratio x of O to Si is 0.5 ≦ x ≦ 1.5, hereinafter, it is preferable to use this material).

Examples of the material S include materials containing Si and O as constituent elements and not containing Li as a constituent element, such as those represented by the composition formula SiO _x (0.5 ≦ x ≦ 1.5). Can be mentioned.

The SiO _x may contain Si microcrystal or amorphous phase. In this case, the atomic ratio of Si and O is a ratio including Si microcrystal or amorphous phase Si. That is, the SiO _x includes a structure in which Si (for example, microcrystalline Si) is dispersed in an amorphous SiO ₂ matrix, and is dispersed in the amorphous SiO ₂ . In combination with Si, the atomic ratio x may satisfy 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, since x = 1, the structural formula is represented by SiO. . 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 preferably constitutes a composite that is combined with a carbon material. For example, the surface of the material S is preferably covered with the carbon material. In general, since the material S has poor conductivity, when using it as a negative electrode active material, a conductive material (conductive aid) is used from the viewpoint of securing good battery characteristics, and the material S and the conductive material in the negative electrode are electrically conductive. It is necessary to form an excellent conductive network by making good mixing and dispersion with the conductive material. In the case of a composite in which the material S is combined with a carbon material, for example, the conductive network in the negative electrode is better than when a material obtained by simply mixing the material S and a conductive material such as a carbon material is used. Formed.

  Examples of the composite of the material S and the carbon material include a granulated body of the material S and the carbon material as well as the material S whose surface is covered with the carbon material as described above.

  As a carbon material that can be used for forming a complex with the material S, for example, low crystalline carbon, carbon nanotube, vapor grown carbon fiber, and the like are preferable.

  The details of the carbon material include at least one selected from the group consisting of fibrous or coiled carbon materials, carbon black (including acetylene black and ketjen black), artificial graphite, graphitizable carbon, and non-graphitizable carbon. A seed material is preferred. 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. Even if the particles expand and contract, 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 the material S 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 the material S that accompanies charging / discharging of the battery, and since the bulk density is large, This is because it can have many junctions. 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.

  In the composite of the material S and the carbon material, the ratio of the material S and the carbon material is 5 parts by mass or more and 7 parts by mass or more of the carbon material with respect to 100 parts by mass of the material S. More preferably, it is 20 parts by mass or less, and preferably 17 parts by mass or less. The reason is not clear, but when Li ions are doped, the charge / discharge cycle characteristics of the battery can be further improved by adjusting the ratio of the material S and the carbon material in the composite as described above. It becomes.

  A composite of the material S and the carbon material can be obtained, for example, by the following method.

  When the surface of the material S is coated with a carbon material to form a composite, for example, the particles of the material S 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, the hydrocarbon-based gas spreads to every corner of the particle of the material S, and a thin and uniform film (carbon) containing a conductive carbon material on the particle surface. Since the material covering layer) can be formed, the conductivity of the particles of the material S can be imparted with good uniformity with a small amount of carbon material.

  In the production of the material S coated with the carbon material, the processing temperature (atmosphere temperature) of the CVD method varies depending on the type of hydrocarbon gas, but is usually 600 to 1200 ° C., and particularly 700 ° C. It is preferable that it is above, and it is still more preferable that it is 800 degreeC or more. This is because the higher the treatment temperature, the less the remaining impurities, and the formation of a coating layer containing carbon having high conductivity.

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

  In addition, when producing a granulated body of the material S and the carbon material, a dispersion liquid in which the material S 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 the material S and the 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.

  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 of the composite in the total amount of the negative electrode active material contained in the negative electrode mixture layer is, for example, 5% by mass or more from the viewpoint of better ensuring the effect of increasing the battery capacity by using the composite. It is preferably 10% by mass or more, more preferably 20% by mass or more, and further preferably 50% by mass or more. In addition, since only the said composite may be used for a negative electrode active material, the suitable upper limit of content of the said composite in the negative electrode active material whole quantity which a negative mix layer contains is 100 mass%.

  The negative electrode active material content (total content of all negative electrode active materials) in the negative electrode mixture layer is preferably 80 to 99.5% by mass.

  As the binder for the negative electrode mixture layer, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), polyimide, polyamide, polyamideimide, or the like can be used. However, it is preferable to use a copolymer having a unit represented by the following formula (1) and a unit represented by the following formula (2) [hereinafter referred to as “copolymer (A)”].

  In the formula (2), R is hydrogen or a methyl group, and M ′ is an alkali metal element.

  When the negative electrode mixture layer of the negative electrode is doped with Li ions by pre-doping outside the system, the hardness of the negative electrode mixture layer usually increases and becomes brittle, so that defects in the negative electrode mixture layer easily occur during pre-doping outside the system. However, the negative electrode mixture layer using the copolymer (A) as a binder is highly flexible and improves the peel strength from the negative electrode current collector. However, defects in the negative electrode mixture layer hardly occur, and the handleability is improved. Therefore, when the copolymer (A) is used for the binder of the negative electrode mixture layer, the productivity of the negative electrode is further improved, and when the pre-doping is performed by the roll-to-roll method in producing the negative electrode However, since a defective part is hard to generate | occur | produce, when doping a Li ion to a negative mix layer by this, productivity of a negative electrode can be improved further.

  In the case where the copolymer (A) is used for the binder of the negative electrode mixture layer, in an electrochemical element such as a lithium ion secondary battery (lithium ion secondary battery of the present invention) configured using the negative electrode. However, since the deterioration of the negative electrode mixture layer due to repeated charge / discharge can be suppressed, the charge / discharge cycle characteristics are further improved.

  Furthermore, the load characteristic of electrochemical elements, such as a lithium ion secondary battery, improves by using a copolymer (A) for the binder of a negative mix layer. This is thought to be because the negative electrode mixture layer using the copolymer (A) as a binder has a structure in which the nonaqueous electrolytic solution penetrates well inside. In addition, by using the copolymer (A) as a binder, it is possible to suppress the precipitation of Li on the negative electrode surface, which may occur with the use of an electrochemical element, to a higher degree.

  The copolymer (A) having the unit represented by the formula (1) and the unit represented by the formula (2) has a vinyl ester and at least one of an acrylate ester and a methacrylate ester as monomers. A copolymer obtained by polymerization can be obtained by saponification.

  Examples of the vinyl ester for obtaining the copolymer (A) include vinyl acetate, vinyl propionate, and vinyl pivalate, and one or more of them can be used. Among these vinyl esters, vinyl acetate is more preferable.

  The copolymer of vinyl ester and at least one of acrylic acid ester and methacrylic acid ester for obtaining copolymer (A) is a unit derived from monomers other than vinyl ester, acrylic acid ester and methacrylic acid ester. You may have.

  The copolymer of vinyl ester and at least one of acrylic acid ester and methacrylic acid ester is a suspension in which polymerization is performed in a state where these monomers are suspended in an aqueous solution containing a polymerization catalyst and a dispersant, for example. Polymerization can be performed by a turbid polymerization method. As the polymerization catalyst at this time, organic peroxides such as benzoyl peroxide and lauryl peroxide; azo compounds such as azobisisobutyronitrile and azobisdimethylvaleronitrile; and the like can be used. In addition, the dispersant used in the suspension polymerization includes water-soluble polymers (polyvinyl alcohol, poly (meth) acrylic acid or a salt thereof, polyvinyl pyrrolidone, methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, etc.), inorganic compounds (Calcium phosphate, magnesium silicate, etc.) can be used.

  The temperature at which the suspension polymerization is performed may be about -20 to + 20 ° C with respect to the 10-hour half-life temperature of the polymerization catalyst, and the polymerization time may be several hours to several tens of hours.

  Saponification of a copolymer of vinyl ester with at least one of acrylic acid ester and methacrylic acid ester uses an alkali (sodium hydroxide, potassium hydroxide, lithium hydroxide, etc.) containing an alkali metal, and is aqueous. It can be performed in a mixed solvent of an organic solvent and water. By this saponification, the unit derived from the vinyl ester becomes a unit in which a hydroxyl group is directly bonded to the main chain of the copolymer [that is, a unit represented by the above formula (1)]. The unit derived from at least one monomer is a unit in which an alkali metal salt (group) of a carboxyl group is directly bonded to the main chain of the copolymer [that is, a unit represented by the formula (2)]. Therefore, examples of M ′ in the formula (2) include sodium, potassium, and lithium.

  Examples of the aqueous organic solvent used for saponification include lower alcohols (such as methanol and ethanol) and ketones (such as acetone and methyl ethyl ketone). The use ratio of the aqueous organic solvent and water is preferably 3/7 to 8/2 in terms of mass ratio.

  The temperature at the time of saponification should just be 20-60 degreeC, and the time in that case should just be about several hours.

  The saponified copolymer may be taken out from the reaction solution, washed, and then dried.

  The unit represented by the formula (1) of the copolymer (A) obtained through the saponification has a structure in which an unsaturated bond of vinyl alcohol is opened and polymerized, The unit represented by (2) is an acrylate or methacrylate (hereinafter referred to as “(meth) acrylate” collectively, and acrylic acid and methacrylic acid are collectively referred to as “(meth) A structure in which an unsaturated bond of “acrylic acid” is polymerized by opening. Therefore, the copolymer (A) uses vinyl alcohol or (meth) acrylate as a monomer and is not obtained by copolymerizing these, but for convenience, “vinyl alcohol and (meth) It may also be referred to as an acrylate salt [a copolymer of (meth) acrylic acid alkali metal neutralized product].

  In the copolymer (A), the composition ratio of the unit represented by the formula (1) and the unit represented by the formula (2) is the formula (1) when the total of these units is 100 mol%. Is preferably 5 mol% or more, more preferably 50 mol% or more, still more preferably 60 mol% or more, and preferably 95 mol% or less, and 90 mol%. The following is more preferable. That is, when the total of the unit represented by the formula (1) and the unit represented by the formula (2) is 100 mol%, the ratio of the unit represented by the formula (2) is 5 mol% or more. Is preferably 10 mol% or more, more preferably 95 mol% or less, more preferably 50 mol% or less, and still more preferably 40 mol% or less.

  The content of the copolymer (A) in the negative electrode mixture layer is determined by the effects of its use (the effect of enhancing the charge / discharge cycle characteristics and load characteristics of the battery, the removal of the negative electrode active material, the negative electrode mixture layer and the current collector, From the viewpoint of favorably ensuring the effect of suppressing the peeling of the resin, it is preferably 2% by mass or more, and more preferably 5% by mass or more. However, if the amount of the copolymer (A) in the negative electrode mixture layer is too large, the capacity and load characteristics of the battery may be deteriorated. Therefore, the content of the copolymer (A) in the negative electrode mixture layer is preferably 15% by mass or less, and more preferably 10% by mass or less.

  In the negative electrode mixture layer, together with the copolymer (A), binders used in the negative electrode mixture layer related to the negative electrode of ordinary lithium ion secondary batteries, for example, SBR, CMC, polyvinylidene fluoride (PVDF), etc. Can also be used. However, the content of the binder other than the copolymer (A) in the total amount of binder contained in the negative electrode mixture layer is preferably 50% by mass or less.

  The negative electrode mixture layer may contain a conductive additive as necessary. Examples of conductive assistants to be included in the negative electrode mixture layer include graphites such as natural graphite (scaly graphite, etc.), artificial graphite and the like; acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black and the like. -It is preferable to use carbon materials such as bon blacks; carbon fibers; and conductive fibers such as metal fibers; carbon fluorides; metal powders such as aluminum; zinc oxide; conductivity such as potassium titanate. Whiskers; conductive metal oxides such as titanium oxide; organic conductive materials such as polyphenylene derivatives; and the like can also be used. As the conductive assistant, those exemplified above may be used singly or in combination of two or more.

  When the conductive additive is contained in the negative electrode mixture layer, the content of the conductive additive in the negative electrode mixture layer is preferably 10% by mass or less.

  The negative electrode to be used for extra-dope, for example, a negative electrode active material, a binder, and a negative electrode mixture containing a conductive auxiliary agent as necessary in a solvent such as N-methyl-2-pyrrolidone (NMP) or water. Disperse to prepare a paste-like or slurry-like negative electrode mixture-containing composition (however, the binder may be dissolved in a solvent), and this is applied to one or both sides of the current collector and dried. If necessary, it can be manufactured through a step of performing a pressing process such as a calendar process. However, the negative electrode to be used for pre-doping outside the system is not limited to those manufactured by the above method, but may be manufactured by other methods.

  The thickness of the negative electrode mixture layer (in the case where the negative electrode mixture layer is provided on both sides of the current collector) is preferably 10 to 100 μm.

  The negative pre-doping of the negative electrode includes, for example, immersing a negative electrode (working electrode) and a lithium metal electrode (counter electrode; lithium metal foil or lithium alloy foil is used) in a non-aqueous electrolyte and energizing between them. It can be performed by the method to do. As the non-aqueous electrolyte solution, the same non-aqueous electrolyte solution (described later in detail) for an electrochemical element such as a lithium ion secondary battery can be used. The doping amount of Li ions at this time can be controlled by adjusting the current density per area of the negative electrode (negative electrode mixture layer) and the amount of electricity to be energized.

  As described above, the negative pre-dope of the negative electrode draws out the negative electrode wound around a roll and introduces it into an electrolyte bath provided with a non-aqueous electrolyte and a lithium metal electrode, and the negative electrode and the It is preferable to carry out by a roll-to-roll method in which the negative electrode mixture layer is doped with Li ions by energizing between the lithium metal electrode and the subsequent negative electrode is wound into a roll shape. If the negative electrode of the present invention is used, it is difficult for defects to occur in the negative electrode mixture layer even if it is wound into a roll after doping with Li ions. Therefore, productivity can be further improved by applying the roll-to-roll method.

  FIG. 1 shows an explanatory diagram of a step of doping Li ions into the negative electrode mixture layer of the negative electrode by a roll-to-roll method. First, the negative electrode 2a is pulled out from the roll 20a around which the negative electrode 2a for use in doping Li ions is wound, and introduced into the electrolytic solution tank 101 for doping Li ions. The electrolyte bath 101 has a non-aqueous electrolyte (not shown) and a lithium metal electrode 102, and can be energized by a power source 103 between the negative electrode 2 a passing through the electrolyte bath 101 and the lithium metal electrode 102. It is configured as follows. When the negative electrode 2a passes through the electrolytic solution tank 101 while facing the lithium metal layer 202, the negative electrode mixture layer of the negative electrode 2a is energized between the negative electrode 2a and the lithium metal electrode 102 by the power source 103. Is doped with Li ions.

  The negative electrode 2 after the negative electrode mixture layer is doped with Li ions and passed through the electrolytic solution tank 101 is preferably washed and then wound on a roll 20. The negative electrode 2 can be cleaned, for example, by allowing the negative electrode 2 to pass through a cleaning tank 104 filled with a cleaning organic solvent, as shown in FIG. Moreover, it is preferable that the negative electrode 2 after passing through the cleaning tank 104 is wound around the roll 20 after passing through the drying means 105 and being dried. The drying method in the drying means 105 is not particularly limited as long as the organic solvent adhering to the negative electrode 2 can be removed in the cleaning tank 104. For example, drying with warm air or an infrared heater, or in a dry inert gas Various methods such as drying through can be applied.

  In addition, the electrolytic solution tank 101 shown in FIG. 1 is lithium metal so that the negative electrode mixture layer formed on both surfaces of the negative electrode current collector can be doped with Li ions simultaneously on the negative electrode mixture layers on both surfaces. In the case of an electrolyte bath that has two electrodes 102, but is used only for doping Li ions to the negative electrode mixture layer of the negative electrode having a negative electrode mixture layer only on one side of the negative electrode current collector, the negative electrode It suffices to provide one lithium metal electrode only at a location facing the mixture layer.

  In this way, the negative electrode after the Li-ion is doped in the negative electrode mixture layer is cut into a necessary size and used for the production of an electrochemical element such as a lithium ion secondary battery. Moreover, you may form the lead body for electrically connecting with the other member in electrochemical elements, such as a lithium ion secondary battery, according to a conventional method to a negative electrode as needed.

  As described above, the negative electrode of the present invention is used as a negative electrode of an electrochemical element having a non-aqueous electrolyte and repeatedly charged and discharged, such as a lithium ion secondary battery and a super capacitor. The application is a lithium ion secondary battery.

  The lithium ion secondary battery using the negative electrode of the present invention (lithium ion secondary battery of the present invention) is one in which the negative electrode, the positive electrode, the separator, and the non-aqueous electrolyte are accommodated in an outer package. is there.

  A positive electrode according to a lithium ion secondary battery has a positive electrode mixture layer containing a positive electrode active material and a binder. For example, the positive electrode mixture layer has a structure formed on one side or both sides of a current collector. And those composed of a positive electrode mixture layer (positive electrode mixture molded body).

As the positive electrode active material, a metal oxide (lithium-containing composite oxide) composed of Li and a metal M other than Li (Co, Ni, Mn, Fe, Mg, Al, etc.) is used. Examples of such lithium-containing composite oxides include lithium cobalt oxides such as LiCoO ₂ ; lithium manganese oxides such as LiMnO ₂ and Li ₂ MnO ₃ ; lithium nickel oxides such as LiNiO ₂ ; LiCo _1-x NiO Lithium-containing composite oxide having a layered structure such as ₂ ; Lithium-containing composite oxide having a spinel structure such as LiMn ₂ O ₄ and Li _4/3 Ti _5/3 O ₄ ; Lithium-containing composite oxide having an olivine structure such as LiFePO ₄ And oxides having the above-described oxide as a basic composition and substituted with various elements.

Among such positive electrode active materials, lithium cobalt oxide (lithium cobaltate) containing at least Co and at least one element M ¹ selected from the group consisting of Mg, Zr, Ni, Mn, Ti, and Al. ) Is preferred. The positive electrode material mixture layer more preferably contains a positive electrode material in which the surfaces of such lithium cobalt oxide particles are coated with an Al-containing oxide. When the positive electrode material is used, since the resistance at the positive electrode during battery charging can be increased, it is difficult for Li to precipitate at the negative electrode, so the composite in the negative electrode mixture layer Even if the proportion of the body is increased, the charge / discharge cycle characteristics of the lithium ion secondary battery can be further improved.

The lithium cobalt oxide is an element that includes Co, at least one element M ¹ selected from the group consisting of Mg, Zr, Ni, Mn, Ti, and Al, and other elements that may further be contained. when the group ^{M a,} is represented by the composition formula ^LiM a _{O 2.}

In the lithium cobalt oxide, the element M ¹ has an effect of increasing the stability of the lithium cobalt oxide in a high voltage region and suppressing the elution of Co ions, and the thermal stability of the lithium cobalt oxide. It also has the effect of increasing

In the lithium cobalt oxide, the amount of the element M ¹ is preferably such that the atomic ratio M ¹ / Co with Co is 0.003 or more from the viewpoint of more effectively exerting the above action, and 0.008 or more. It is more preferable that

However, when the amount of the element M ¹ in the lithium cobalt oxide is too large, too small amounts of Co, there is a possibility can not be sufficient action by these. Therefore, in the lithium cobaltate, the amount of the element M ¹ is preferably such that the atomic ratio M ¹ / Co with Co is 0.06 or less, and more preferably 0.03 or less.

In the lithium cobaltate, Zr adsorbs hydrogen fluoride that may be generated due to a fluorine-containing lithium salt (such as LiPF ₆ ) contained in the non-aqueous electrolyte, and suppresses deterioration of the lithium cobaltate. have.

  Fluorine-containing lithium contained in the non-aqueous electrolyte if some moisture is inevitably mixed in the non-aqueous electrolyte used in the lithium ion secondary battery or if moisture is adsorbed by other battery materials Reacts with salt to produce hydrogen fluoride. When hydrogen fluoride is generated in the battery, the action causes deterioration of the positive electrode active material.

  However, when the lithium cobaltate is synthesized so as to also contain Zr, Zr oxide is deposited on the surface of the particles, and this Zr oxide adsorbs hydrogen fluoride. Therefore, deterioration of the lithium cobalt oxide due to hydrogen fluoride can be suppressed.

  In addition, when Zr is included in the positive electrode active material, the load characteristics of the battery are improved. When the lithium cobalt oxide contained in the positive electrode material is two materials having different average particle diameters, the larger average particle diameter is lithium cobalt oxide (A), and the smaller average particle diameter is lithium cobalt oxide (B). And In general, when a positive electrode active material having a large particle size is used, the load characteristics of the battery tend to deteriorate. Therefore, among the positive electrode active materials constituting the positive electrode material, it is preferable that lithium cobaltate (A) having a larger average particle diameter contains Zr. On the other hand, lithium cobaltate (B) may contain Zr or may not contain it.

  In the lithium cobaltate, the amount of Zr is such that the atomic ratio Zr / Co with Co is preferably 0.0002 or more, more preferably 0.0003 or more, from the viewpoint of better exerting the above action. Is more preferable. However, if the amount of Zr in the lithium cobalt oxide is too large, the amount of other elements decreases, and there is a possibility that the effects of these elements cannot be sufficiently ensured. Therefore, the amount of Zr in the lithium cobaltate is preferably such that the atomic ratio Zr / Co with Co is 0.005 or less, and more preferably 0.001 or less.

The lithium cobaltate includes Li-containing compounds (such as lithium hydroxide and lithium carbonate), Co-containing compounds (such as cobalt oxide and cobalt sulfate), Mg-containing compounds (such as magnesium sulfate), Zr-containing compounds (such as zirconium oxide) and elements It can be synthesized by mixing a compound containing M ¹ (oxide, hydroxide, sulfate, etc.) and firing this raw material mixture. Incidentally, in synthesizing the lithium cobaltate with a higher purity, composite compound containing Co and the element M ¹ (hydroxides, oxides, etc.) and the like and Li-containing compound are mixed and firing the raw material mixture It is preferable.

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

In the positive electrode material, the surface of the lithium cobalt oxide particles is coated with an Al-containing oxide (for example, 90 to 100% or more of the total area of the surface of the lithium cobalt oxide particles includes Al-containing oxides). Things are present). Examples of the Al-containing oxide covering the surface of the lithium cobalt oxide particles include Al ₂ O ₃ , AlOOH, LiAlO ₂ , and LiCo _1-w Al _w O ₂ (where 0.5 <w <1). Of these, only one of them may be used, or two or more of them may be used in combination. For example, when the surface of the lithium cobalt oxide is coated with Al ₂ O ₃ by a method described later, an Al-containing oxide containing elements such as Co, Li, and Al transferred from the lithium cobalt oxide in the Al ₂ O ₃ Although a film in which a part is mixed is formed, the film formed of an Al-containing oxide that covers the surface of the lithium cobaltate constituting the positive electrode material may be a film containing such a component. .

  The average coating thickness of the Al-containing oxide according to the positive electrode material increases the resistance due to the inhibition of the Al-containing oxide in the positive and negative electrode active materials during charging and discharging of the battery according to the positive electrode material, From the viewpoint of further improving the charge / discharge cycle characteristics of the battery by suppressing Li deposition at the negative electrode, and from the viewpoint of satisfactorily suppressing the reaction between the positive electrode active material according to the positive electrode material and the non-aqueous electrolyte, the thickness is 5 nm or more. It is preferable that the thickness is 15 nm or more. In addition, from the viewpoint of suppressing deterioration of the load characteristics of the battery due to the Al-containing oxide inhibiting the lithium ion in and out of the positive electrode active material during charging and discharging of the battery, the average coating of the Al-containing oxide according to the positive electrode material The thickness is preferably 50 nm or less, and more preferably 35 nm or less.

The “average coating thickness of the Al-containing oxide” as used herein refers to a cross section of the positive electrode material obtained by processing by the focused ion beam method, observed at a magnification of 400,000 times using a transmission electron microscope, Of the positive electrode material particles existing in the field of view of 500 × 500 nm, particles having a cross-sectional size within the average particle diameter (d ₅₀ ) ± 5 μm of the positive electrode material are arbitrarily selected for 10 fields, and for each field, Al It means the average value (number average value) calculated for all thicknesses (thicknesses at 100 locations) obtained by measuring the thickness of the coating film of the contained oxide at 10 arbitrary locations.

The specific surface area of the positive electrode material is preferably 0.1 m ² / g or more, more preferably 0.2 m ² / g or more, and preferably 0.4 m ² / g or less, More preferably, it is 0.3 m ² / g or less. When the specific surface area of the positive electrode material is in the above value, the resistance during charging / discharging of the battery is further increased, so that the charge / discharge cycle characteristics of the battery are further improved.

  When the surface of the lithium cobalt oxide constituting the positive electrode material is coated with an Al-containing oxide or when Zr oxide is deposited on the surface of the lithium cobalt oxide particles, the positive electrode material is usually used. The surface becomes rough and the specific surface area increases. For this reason, the positive electrode material has a small specific surface area as described above if the properties of the Al-containing oxide film covering the surface of the lithium cobalt oxide particles are good in addition to a relatively large particle size. It is preferable because it is easy.

  About the said lithium cobaltate which the said positive electrode material contains, one type may be sufficient, as above-mentioned, two materials from which an average particle diameter differs may be sufficient, and three or more from which an average particle diameter differs It may be a material.

  In order to adjust the specific surface area of the positive electrode material to the above value, when one type of the lithium cobaltate is used, the average particle diameter of the positive electrode material is preferably 10 to 35 μm.

  When two materials having different average particle diameters are used for the lithium cobalt oxide contained in the positive electrode material, the surface of lithium cobalt oxide (A) particles is coated with an Al-containing oxide, and the average particle diameter is 1 The surface of the positive electrode material (a) having a particle size of ˜40 μm and the lithium cobalt oxide (B) particles are coated with an Al-containing oxide, the average particle diameter is 1 to 40 μm, and more than the positive electrode material (a). It is preferable that at least the positive electrode material (b) having a small average particle diameter is included. More preferably, it is an embodiment composed of large particles [positive electrode material (a)] having an average particle diameter of 24 to 30 μm and small particles [positive electrode material (b)] having an average particle diameter of 4 to 8 μm. And when a positive electrode material contains positive electrode material (a) and positive electrode material (b), it is preferable that the ratio of positive electrode material (a) in positive electrode material whole quantity is 75-90 mass%. As a result, not only can the specific surface area be adjusted, but also when the positive electrode mixture layer is pressed, the positive electrode material having a small particle size enters the gap between the positive electrode materials having a large particle size, so that the stress applied to the positive electrode mixture layer is entirely reduced. It is possible to disperse and to suppress the cracking of the positive electrode material particles satisfactorily, so that the action by the coating with the Al-containing oxide can be exhibited better.

The particle size distribution of the positive electrode material in the present specification means a particle size distribution obtained by a method for obtaining an integrated volume from particles having a small particle size distribution using a microtrack particle size distribution measuring apparatus “HRA9320” manufactured by Nikkiso Co., Ltd. . In addition, the average particle diameter of the positive electrode material and other particles (such as the material S) in the present specification is the volume-based integrated fraction when the integrated volume is obtained from particles having a small particle size distribution using the above-described apparatus. Means the value of 50% diameter (d ₅₀ ).

In order to coat the surface of the lithium cobalt oxide particles with an Al-containing oxide to form the positive electrode material, for example, the following method can be employed. In a lithium hydroxide aqueous solution having a pH of 9 to 11 and a temperature of 60 to 80 ° C., the lithium cobalt oxide particles are charged and dispersed by stirring, and Al (NO ₃ ) ₃ · 9H ₂ O and Aqueous ammonia for suppressing fluctuations in pH is added dropwise to produce an Al (OH) ₃ coprecipitate and adhere to the surface of the lithium cobalt oxide particles. Thereafter, the lithium cobalt oxide particles to which the Al (OH) ₃ coprecipitate is adhered are taken out from the reaction solution, washed, dried, and then heat-treated to form an Al-containing oxide on the surface of the lithium cobalt oxide particles. A film is formed to form the positive electrode material. The heat treatment of the lithium cobaltate particles to which the Al (OH) ₃ coprecipitate is adhered is preferably performed in the air atmosphere, and the heat treatment temperature is 200 to 800 ° C. and the heat treatment time is 5 to 15 hours. preferable. When the surface of the lithium cobalt oxide particles is coated with an Al-containing oxide by this method, the Al-containing oxide as a main component constituting the coating is changed to Al ₂ O ₃ or AlOOH by adjusting the heat treatment temperature. Or LiAlO ₂ or LiCo _1-w Al _w O ₂ (where 0.5 <w <1).

When the positive electrode material and another positive electrode active material are used, the continuous charge characteristics of the battery are further improved, and the charge / discharge cycle characteristics and storage characteristics of the lithium ion secondary battery using the positive electrode material at a high temperature Therefore, nickel acid containing Ni and Co and element M ² selected from the group consisting of Mg, Mn, Ba, W, Ti, Zr, Mo, and Al as the other positive electrode active material It is preferable to use lithium.

The lithium nickelate is represented by the chemical formula LiM ^b O ₂ when Ni, Co, and the element M ² , and other elements that may further be contained, are combined into an element group M ^b . when Ni of the total number of atoms in 100 mol% of the element group ^{M 2,} the amount of Co and the element ^{M 2,} respectively, expressed in s (mol%), t ( mol%) and u (mol%), 30 ≦ s ≦ 97, 0.5 ≦ t ≦ 40, 0.5 ≦ u ≦ 40 are preferable, and 70 ≦ s ≦ 97, 0.5 ≦ t ≦ 30, and 0.5 ≦ u ≦ 5 are more preferable. preferable.

The lithium nickelate, Li-containing compound (lithium hydroxide, etc. lithium carbonate), Ni-containing compound (such as nickel sulfate), Co-containing compound (cobalt sulfate, cobalt oxide, etc.), and containing the element M ^b as necessary The compound (oxide, hydroxide, sulfate, etc.) to be mixed can be mixed, and this raw material mixture can be fired. Incidentally, in synthesizing the lithium nickel oxide at a higher purity, Ni, complex compound containing a plurality of elements among the elements M ^b be contained if Co and the required (hydroxides, oxides, etc.), It is preferable to mix other raw material compounds (such as Li-containing compounds) and to fire this raw material mixture.

  The firing conditions of the raw material mixture for synthesizing the lithium nickelate can also be set to, for example, 800 to 1050 ° C. for 1 to 24 hours, as in the case of the lithium cobaltate, but once lower than the firing temperature. It is preferable to perform heating by heating to a temperature (for example, 250 to 850 ° C.) and maintaining at that temperature, and then proceeding to the reaction by raising the temperature to the firing temperature. Although there is no restriction | limiting in particular about the time of preheating, Usually, what is necessary is just about 0.5 to 30 hours. The atmosphere during firing can be an atmosphere containing oxygen (that is, in the air), a mixed atmosphere of an inert gas (such as argon, helium, or nitrogen) and oxygen gas, or an oxygen gas atmosphere. The oxygen concentration (volume basis) is preferably 15% or more, and more preferably 18% or more.

  When the positive electrode material and another positive electrode active material (for example, the lithium nickelate) are used as the positive electrode active material, the amount of the positive electrode material in a total of 100 mass% of the positive electrode material and the other positive electrode active material Is preferably 50% by mass or more, more preferably 80% by mass or more (that is, the amount of the other positive electrode active material used together with the positive electrode material is the same as that of the positive electrode material and the other positive electrode active material). The total content is preferably 50% by mass or less, and more preferably 20% by mass or less. Since only the positive electrode material may be used as the positive electrode active material, the preferred upper limit of the amount of the positive electrode material in the total of 100% by mass of the positive electrode material and the other positive electrode active material is 100% by mass. is there. However, in order to better ensure the continuous charge characteristics improvement effect of the battery by using the lithium nickelate, the amount of the lithium nickelate in a total of 100% by mass of the positive electrode material and the lithium nickelate, It is preferably 5% by mass or more, and more preferably 10% by mass or more.

  Conductive aids for the positive electrode mixture layer include natural graphite (such as flake graphite), graphite such as artificial graphite (graphitic carbon material); acetylene black, ketjen black, channel black, furnace black, lamp black, thermal Carbon material such as carbon black such as black; carbon fiber; Moreover, PVDF, polytetrafluoroethylene (PTFE), vinylidene fluoride-chlorotrifluoroethylene copolymer [P (VDF-CTFE)], SBR, CMC, etc. are suitably used for the binder relating to the positive electrode mixture layer. It is done.

  The positive electrode is prepared, for example, by preparing a paste-like or slurry-like positive electrode mixture-containing composition in which a positive electrode active material (such as the above-mentioned positive electrode material), a conductive additive and a binder are dispersed in a solvent such as NMP. May be dissolved in a solvent), and this is applied to one or both sides of the current collector, dried, and then subjected to a press treatment such as a calender treatment as necessary.

  However, the positive electrode is not limited to those manufactured by the above manufacturing method, and may be manufactured by other methods. For example, when the positive electrode is formed into a pellet-like positive electrode mixture molded body, the positive electrode is produced by a method of pressing a positive electrode mixture containing a positive electrode active material, a conductive additive, a binder, and the like into a pellet shape. can do.

  The current collector can be the same as that used for the positive electrode of a conventionally known lithium ion secondary battery, for example, aluminum foil, punching metal, net, expanded metal, etc. The thickness is preferably 5 to 30 μm.

  As the composition of the positive electrode mixture layer and the positive electrode mixture molded body, the amount of the positive electrode active material (including the positive electrode material) is preferably 60 to 95% by mass, and the amount of the binder is 1 to 15% by mass. It is preferable that the amount of the conductive auxiliary is 3 to 20% by mass. Moreover, in the case of the positive electrode of the form which has a positive mix layer and a collector, it is preferable that the thickness (thickness per one side of a collector) of a positive mix layer is 30-150 micrometers. On the other hand, in the case of a positive electrode composed of a positive electrode mixture molded body, the thickness is preferably 0.15 to 1 mm.

  In the lithium ion secondary battery, the negative electrode (negative electrode after pre-doping outside the system) and the positive electrode are laminated with a separator (stacked electrode body) or the laminate is further wound in a spiral shape. It is used in the form of a wound body (wound electrode body).

  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 preferable that polyethylene is 30% by mass or more, and 50% by mass or more as a resin constituting the porous membrane. More preferred.

  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, more preferably 1 μm or less, and even more preferably 0.5 μm or less.

  As the separator, a laminated separator having a porous film (I) mainly composed of a thermoplastic resin and a porous layer (II) mainly including 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. Moreover, the charge / discharge cycle characteristics of the battery are further improved by using the laminated separator. The reason for this is not clear, but the high mechanical strength of the laminated separator shows high resistance to the expansion and contraction of the negative electrode accompanying the charge / discharge cycle of the battery. It is presumed that this is because the adhesion between the positive electrodes 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 membrane (I) according to the separator is mainly for ensuring a shutdown function, and when the battery reaches or exceeds the melting point of the thermoplastic resin, which is the main component of the porous membrane (I), The thermoplastic resin related to the porous membrane (I) melts and closes the pores of the separator, and a shutdown that suppresses the progress of the electrochemical reaction occurs.

  The thermoplastic resin that is the main component of the porous membrane (I) is preferably a resin having a melting point of 140 ° C. or lower, and specifically includes polyethylene. In addition, as the form of the porous membrane (I), a microporous membrane usually used as a battery separator or a dispersion containing polyethylene particles is applied to a substrate such as a nonwoven fabric and dried. Examples thereof include sheet-like materials such as those obtained. Here, among the total volume of the constituent components of the porous membrane (I) [the total volume excluding the void portion. The same applies to the volume content of the constituent components of the porous membrane (I) and the porous layer (II) according to the separator. ], The volume content of the resin whose main melting point is 140 ° C. or lower is 50% by volume or more, and more preferably 70% by volume or more. For example, when the porous membrane (I) is formed of the polyethylene microporous membrane, the volume content of the resin having a melting point of 140 ° C. or lower 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 membrane (I) shrinks, the porous layer (II) which does not easily shrink can cause the positive and negative electrodes directly when the separator is thermally shrunk. It is possible to prevent a short circuit due to the contact. In addition, since the heat-resistant porous layer (II) acts as a skeleton of the separator, thermal contraction of the porous membrane (I), that is, 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 non-aqueous electrolyte of the battery, and is electrochemically stable that is difficult to be oxidized and reduced within the battery operating voltage range. Any inorganic particles or organic particles may be used as long as they are fine, 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 control the porosity of the porous layer (II) with high accuracy. 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.

  The phrase “containing a filler having a heat resistant temperature of 150 ° C. or higher as a main component” of the porous layer (II) means that 70% by volume or more of the filler is included in the total volume of the constituent components of the porous layer (II). doing. The amount of the filler in the porous layer (II) is preferably 80% by volume or more and more preferably 90% by volume or more in the total volume of the constituent components of the porous layer (II). By making the said filler in porous layer (II) high content as mentioned above, the thermal contraction of the whole separator can be suppressed favorably and high heat resistance can be provided.

  The porous layer (II) preferably contains an organic binder to bind the fillers or bind the porous layer (II) and the porous membrane (I). From such a viewpoint, the suitable upper limit of the amount of filler (B) in the porous layer (II) is, for example, 99% by volume in the total volume of the constituent components of the porous layer (II). When the amount of the filler (B) in the porous layer (II) is less than 70% by volume, for example, it is necessary to increase the amount of the organic binder in the porous layer (II). There is a possibility that the pores of the layer (II) are filled with the organic binder, and the function as a separator is lost, for example.

  As an organic binder used for the porous layer (II), the fillers or the porous layer (II) and the porous film (I) can be bonded well, are electrochemically stable, and are used for an electrochemical element. There is no particular limitation as long as it is stable with respect to the non-aqueous electrolyte. Specifically, fluororesin (such as PVDF), fluororubber, SBR, CMC, hydroxyethyl cellulose (HEC), polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polyvinyl pyrrolidone (PVP), poly N-vinylacetamide, Cross-linked acrylic resin, polyurethane, epoxy resin and the like can be mentioned. These organic binders may be used alone or in combination of two or more.

  The laminated separator is, for example, a composition for forming a porous layer (II) containing, in the porous membrane (I), the filler, an organic binder, and the like, and a solvent (an organic solvent such as water and ketones) ( It can be manufactured by applying a slurry, paste, etc.) and then drying at a predetermined temperature to form the porous layer (II).

  The laminated separator may have one or more porous membranes (I) and porous layers (II), respectively. Specifically, the porous layer (II) is disposed only on one side of the porous membrane (I) to form the laminated separator. For example, the porous layer (II) is formed on both sides of the porous membrane (I). May be used as the laminated separator. However, if the number of layers of the multilayer separator is too large, it is not preferable because the thickness of the separator is increased, which may increase the internal resistance of the battery or decrease the energy density. Is preferably 5 layers or less.

  The thickness of the separator (the laminated separator and other separators) is preferably 6 μm or more and more preferably 10 μm or more from the viewpoint of more reliably separating the positive electrode and the negative electrode. 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 μm or less, and more preferably 30 μm or less.

  In addition, the thickness of the porous membrane (I) [the total thickness when a plurality of porous membranes (I) are present] is preferably 5 to 30 μm. Further, the thickness of the porous layer (II) [when there are a plurality of porous layers (II), the total thickness] is preferably 1 μm or more, more preferably 2 μm or more, and 4 μm or more. Further, it is preferably 20 μm or less, more preferably 10 μm or less, and further preferably 6 μm or less.

  The porosity of the separator (the laminated separator and other separators) is preferably 30 to 70%.

  Moreover, it is preferable that the separator (the laminated separator and other separators) has an adhesive layer on one side or both sides thereof. When the separator and the electrode are integrated by the adhesive layer of the separator when forming the laminated electrode body or the wound electrode body, even if charging / discharging is repeated in a battery using such an electrode body, Since the shape change can be suppressed, the charge / discharge cycle characteristics of the battery are further improved. In the case of a battery using a flat wound electrode body having a flat cross section, the effect of improving the charge / discharge cycle characteristics by the adhesive layer is particularly remarkable.

  It is preferable that the adhesive layer of the separator contains an adhesive resin that exhibits adhesiveness when heated. In the case of an adhesive layer containing an adhesive resin, the separator and the electrode can be integrated by undergoing a step of pressing while heating the electrode body (heating press). The minimum temperature at which the adhesiveness of the adhesive resin is expressed needs to be lower than the temperature at which shutdown occurs in the layers other than the adhesive layer in the separator. Specifically, the temperature is from 60 ° C to 120 ° C. Preferably there is. Further, when the separator is the laminated separator, the minimum temperature at which the adhesive resin exhibits adhesiveness needs to be lower than the melting point of the thermoplastic resin that is the main component of the porous membrane (I). .

  By using such an adhesive resin, deterioration of the separator can be satisfactorily suppressed when the separator and the positive electrode and / or the negative electrode are integrated by hot pressing.

  Due to the presence of the adhesive resin, the peel strength obtained when a peel test at 180 ° between the electrode (for example, the negative electrode) constituting the electrode body and the separator is carried out is preferable in the state before the hot press. Is 0.05 N / 20 mm or less, particularly preferably 0 N / 20 mm (a state having no adhesive force), and a delayed tack property of 0.2 N / 20 mm or more after being heated and pressed at a temperature of 60 to 120 ° C. It is preferable to have.

  However, if the peel strength is too strong, the electrode mixture layer (the positive electrode mixture layer and the negative electrode mixture layer) may peel from the current collector of the electrode, and the conductivity may be lowered. The peel strength by the peel test at ° is preferably 10 N / 20 mm or less after being hot-pressed at a temperature of 60 to 120 ° C.

  In addition, the peel strength at 180 ° between the electrode and the separator in the present specification is a value measured by the following method. The separator and the electrode are each cut into a size of 5 cm in length and 2 cm in width, and the cut-out separator and the electrode are overlapped. When obtaining the peel strength in the state after being hot-pressed, a test piece is prepared by hot-pressing a 2 cm × 2 cm region from one end. The end of the test piece on the side where the separator and electrode are not heated and pressed is opened, and the separator and the negative electrode are bent so that these angles are 180 °. Thereafter, using a tensile tester, both the one end side of the separator opened at 180 ° of the test piece and the one end side of the electrode are gripped and pulled at a pulling speed of 10 mm / min. Measure the strength when peeled off. In addition, the peel strength of the separator and the electrode before heating press was determined by preparing a test piece in the same manner as above except that the separator and electrode cut out as described above were stacked and pressed without heating. The peel test is performed in the same manner as described above.

  Therefore, the adhesive resin has almost no adhesiveness (stickiness) at room temperature (for example, 25 ° C), and the minimum temperature at which the adhesiveness is developed is less than the temperature at which the separator shuts down, preferably 60 ° C to 120 ° C. Those having tackiness are desirable. The temperature of the heating press when integrating the separator and the electrode is more preferably 80 ° C. or more and 100 ° C. or less at which the thermal contraction of the separator does not occur significantly, and the adhesiveness of the adhesive resin is exhibited. The minimum temperature is more preferably 80 ° C. or higher and 100 ° C. or lower.

  As the adhesive resin having a delayed tack property, a resin that has almost no fluidity at room temperature, exhibits fluidity when heated, and has a property of being adhered by pressing is preferable. A resin of a type that is solid at room temperature, melts by heating, and exhibits adhesiveness by a chemical reaction can also be used as the adhesive resin.

  The adhesive resin preferably has a softening point in the range of 60 ° C. or higher and 120 ° C. or lower with the melting point, glass transition point and the like as indices. The melting point and glass transition point of the adhesive resin can be measured, for example, by a method prescribed in JIS K 7121, and the softening point of the adhesive resin can be measured, for example, by a method prescribed in JIS K 7206.

  Specific examples of such adhesive resins include, for example, low density polyethylene (LDPE), poly-α-olefin [polypropylene (PP), polybutene-1, etc.], polyacrylate ester, ethylene-vinyl acetate copolymer. (EVA), ethylene-methyl acrylate copolymer (EMA), ethylene-ethyl acrylate copolymer (EEA), ethylene-butyl acrylate copolymer (EBA), ethylene-methyl methacrylate copolymer (EMMA), ionomer resin Etc.

  Each resin, or a resin having adhesiveness at room temperature such as SBR, nitrile rubber (NBR), fluorine rubber, or ethylene-propylene rubber is used as a core, and the melting point and softening point are within a range of 60 ° C to 120 ° C. It is also possible to use a resin having a core-shell structure with a resin as a shell as an adhesive resin. In this case, various acrylic resins and polyurethane can be used for the shell. Further, as the adhesive resin, one-pack type polyurethane, epoxy resin, or the like that exhibits adhesiveness in a range of 60 ° C. or higher and 120 ° C. or lower can be used.

  As the adhesive resin, the above-exemplified resins may be used alone or in combination of two or more.

  When an adhesive layer made of an adhesive resin and containing substantially no pores is formed, there is a risk that the non-aqueous electrolyte of the battery will be difficult to contact the surface of the electrode integrated with the separator. For this reason, it is preferable that a portion where the adhesive resin exists and a portion where the adhesive resin does not exist are formed on the surface where the adhesive resin exists in the positive electrode, the negative electrode, and the separator. Specifically, for example, the location where the adhesive resin is present and the location where the adhesive resin is not present may be alternately formed in a groove shape, and the location where the adhesive resin such as a circle is not present in a plan view is not present. A plurality may be formed continuously. In these cases, the locations where the adhesive resin is present may be regularly arranged or randomly arranged.

  In addition, in the presence surface of the adhesive resin in the positive electrode, the negative electrode, and the separator, when forming the location where the adhesive resin is present and the location where the adhesive resin is not present, The area (total area) may be such that, for example, the peel strength at 180 ° after thermocompression bonding of the separator and the electrode is the above value, and depending on the type of adhesive resin used Specifically, the adhesive resin is preferably present in 10 to 60% of the surface area of the adhesive resin in plan view.

Further, in the presence of the adhesive resin, the basis weight of the adhesive resin improves the adhesion with the electrode. For example, the peel strength at 180 ° after the pressure bonding between the separator and the electrode is performed as described above. to adjust the value is preferably to 0.05 g / ^{m 2} or more, and more preferably set to 0.1 g / ^{m 2} or more. However, if the basis weight of the adhesive resin is too large in the presence of the adhesive resin, the electrode body becomes too thick, or the adhesive resin blocks the pores of the separator, and the movement of ions inside the battery is hindered. There is a risk of doing. Therefore, the existing surface of the adhesive resin, the basis weight of the adhesive resin is preferably 1 g / m ² or less, more preferably 0.5 g / m ² or less.

  The adhesive layer is composed of a porous film or a porous film (I) and a porous layer (II) using a composition for forming an adhesive layer (adhesive resin solution or emulsion) containing an adhesive resin and a solvent as a separator. ) And a step of applying to one side or both sides of the laminate.

  As the nonaqueous electrolytic solution according to the lithium ion secondary battery, for example, a solution prepared by dissolving a lithium salt in the following nonaqueous solvent can be used.

  Non-aqueous solvents include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), γ-butyrolactone (γ-BL ), 1,2-dimethoxyethane (DME), tetrahydrofuran (THF), 2-methyltetrahydrofuran, dimethyl sulfoxide (DMSO), 1,3-dioxolane, formamide, dimethylformamide (DMF), dioxolane, acetonitrile, nitromethane, Methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivative, sulfolane, 3-methyl-2-oxazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, Aprotic organic solvents such as diethyl ether and 1,3-propane sultone can be used singly or as a mixed solvent in which two or more are mixed.

The lithium salt according to the non-aqueous electrolyte solution, for _{example, LiClO 4, LiPF 6, LiBF} 4, LiAsF 6, 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 (n ≧ 2), LiN (RfOSO ₂ ) ₂ [where Rf is a fluoroalkyl group] At least one selected from the above. The concentration of these lithium salts in the non-aqueous electrolyte is preferably 0.6 to 1.8 mol / l, and more preferably 0.9 to 1.6 mol / l.

  Non-aqueous electrolytes include vinylene carbonate, vinyl ethylene carbonate, acid anhydride, sulfonic acid for the purpose of further improving the charge / discharge cycle characteristics of the battery and improving safety such as high temperature storage and overcharge prevention. Additives (including these derivatives) such as esters, dinitriles, 1,3-propane sultone, diphenyl disulfide, cyclohexylbenzene, biphenyl, fluorobenzene, and t-butylbenzene may be added as appropriate.

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

  There is no restriction | limiting in particular about the form of a lithium ion secondary battery. For example, any of a small cylindrical shape, a coin shape, a button shape, a flat shape, a square shape, a large size used for an electric vehicle, and the like may be used.

  Some lithium-ion secondary batteries having a negative electrode in which the negative electrode mixture layer is doped with Li ions include those in which the negative electrode mixture layer is doped with Li ions by in-system pre-doping. Separately, a battery is assembled using an electrode having a Li supply source (third electrode), and the third electrode is energized to dope Li ions from the Li supply source to the negative electrode mixture layer in the battery. There is. Therefore, in this type of battery, even when the doping of Li ions is completed, the third electrode in which a part of the Li supply source remains or all of it disappears remains in the battery. Since the lithium ion secondary battery is assembled using a negative electrode in which the negative electrode mixture layer is previously doped with Li ions by pre-doping outside the system, a third electrode used (or used) for doping Li ions is provided inside. do not do.

  In-system pre-doping is performed by facing the mixture layer after forming the negative electrode mixture layer by attaching a metal lithium foil to the negative electrode mixture layer or forming a Li vapor deposition layer on the negative electrode mixture layer. In general, a method of introducing Li ions by arranging a Li source so as to perform electrochemical contact (short circuit) is generally used. However, when Li ions are introduced while facing the surface of the mixture layer, the negative electrode mixture layer of the negative electrode closest to the Li source may not maintain the adhesive state with the negative electrode current collector and may fall off. . This is because the short-circuit current is high due to electrochemical contact, so that the Li ion doping reaction preferentially proceeds to the negative electrode mixture layer of the negative electrode closest to the Li source, and the negative electrode combination of the negative electrode closest to the Li source is increased. It is presumed that the agent layer accepts the most Li ions and expands greatly. It is considered that the damage to the negative electrode mixture layer adversely affects various characteristics such as a charge / discharge cycle when the battery is used.

  In the lithium ion secondary battery, the negative electrode mixture layer of the negative electrode is doped with Li ions when the battery is discharged at a discharge current rate of 0.1 C until the voltage reaches 2.0 V. It can be grasped by the molar ratio (Li / M) of Li and metal M other than Li contained in the positive electrode active material. In the lithium ion secondary battery, it is preferable to use a negative electrode in which the Li ion doping amount of the negative electrode mixture layer is adjusted so that the molar ratio Li / M is 0.8 or more and 1.05 or less. Incidentally, in a battery having a negative electrode mixture layer containing a negative electrode active material not containing Li and having a negative electrode in which Li ions are not pre-doped (and pre-doped in the system), the molar ratio Li / M is usually the lower limit. Smaller than.

  The composition analysis of the positive electrode active material when discharged at a discharge current rate of 0.1 C until the voltage reaches 2.0 V can be performed as follows using an ICP (Inductively Coupled Plasma) method. First, 0.2 g of a 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 sample was further diluted 25 times with pure water, and calibrated using an ICP analyzer “ICP-757” manufactured by JARRELASH. The composition is analyzed by the line method. The composition amount can be derived from the obtained results. The molar ratio Li / M described in the examples described later is a value determined by this method.

  Note that the positive electrode active material for obtaining the molar ratio Li / M in this specification includes a positive electrode material in which the surface of the positive electrode active material particles is coated with a specific material (such as an Al-containing oxide). The amount of the metal contained in the specific material existing on the surface of the positive electrode material is also included in the amount of the metal M for obtaining the molar ratio Li / M.

Incidentally, the molar ratio Li / M will be described by taking Example 1 described later as an example. In Example 1, LiCo _0.9795 Mg _0.011 Zr _0.0005 Al _0.009 O ₂ of lithium cobalt oxide (A1) The cathode material (a1) having an Al-containing oxide film formed on the surface and the LiCo _0.97 Mg _0.012 Al _0.009 O ₂ lithium cobalt oxide (B1) surface formed with an Al-containing oxide film The positive electrode material (b1) is used, and the metal M other than Li at this time refers to Co, Mg, Zr, and Al. That is, after producing the lithium ion secondary battery, the battery after predetermined charge / discharge is disassembled, and the positive electrode material (mixture in this Example 1) is collected and analyzed from the positive electrode mixture layer to derive the molar ratio Li / M.

  The negative electrode mixture layer was negatively doped with Li ions by pre-doping outside the system, and the degree of doping of the Li ions was adjusted so that the molar ratio Li / M in the positive electrode active material was within the above range. In the case of a battery assembled using a negative electrode, since an appropriate amount of Li ions is doped to reduce the irreversible capacity of the negative electrode active material, for example, generation of Li dendrite can be suppressed, and this generation causes a slight short circuit of the battery. It can suppress well occurring.

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

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

Example 1
<Production of negative electrode>
A unit represented by the above formula (1) and a unit represented by the above formula (2), wherein R is hydrogen and M 'is potassium in the above formula (2). A copolymer (A) having a molar ratio of 6/4 to the unit represented by the formula (2) is dissolved in ion-exchanged water, and an aqueous solution having a copolymer (A) concentration of 8% by mass is obtained. Prepared. In this aqueous solution, a composite Si-1 in which the surface of SiO serving as the negative electrode active material was coated with a carbon material (average particle diameter was 5 μm, specific surface area was 8.8 m ² / g, and the amount of carbon material in the composite was SiO 2 : 10 parts by mass with respect to 100 parts by mass) and carbon black were added and mixed by stirring to obtain a negative electrode mixture-containing paste. The composition ratio (mass ratio) of negative electrode active material: carbon black: copolymer (A) in this paste was 90: 2: 8.

On one side of the copper foil unwound from a copper foil roll wound with a copper foil having a thickness of 10 μm (manufactured by Furukawa Electric, tensile strength is 350 N / mm ² , 0.2% proof stress is 270 N / mm ² ), The mixture-containing paste is continuously applied and dried, a negative electrode mixture layer is formed on one side of the copper foil, and after pressing, the density of the negative electrode mixture layer is adjusted to 1.2 g / cm ³ to form a roll. To obtain a negative electrode roll.

For the negative electrode drawn from the negative electrode roll, the negative electrode mixture layer was doped with Li ions by the method shown in FIG. 1 (roll-to-roll method). The negative electrode 2a was pulled out from the negative electrode roll 20a, and 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 30:70), and vinylene carbonate: 4 mass. %, 4-fluoro-1,3-dioxolan-2-one: a solution added in an amount of 5% by mass) and a lithium metal electrode. In the electrolyte bath 101, an electric current corresponding to 500 mAh / g per mass of the negative electrode active material is obtained between the negative electrode 2a and the lithium metal electrode 102 at a current density of 0.2 mA / cm ² per area of the negative electrode. The amount was energized to dope the negative electrode mixture layer with Li ions.

  The negative electrode 2 after Li ion doping is washed in a washing tank 104 equipped with diethyl carbonate after passing through the electrolytic solution tank 101, further dried in a drying tank 105 filled with argon gas, and then wound around a roll 20. It was.

<Preparation of positive electrode>
Li ₂ CO ₃ that is a Li-containing compound, Co ₃ O ₄ that is a Co-containing compound, Mg (OH) ₂ that is a Mg-containing compound, ZrO ₂ that is a Zr compound, and Al (OH that is an Al-containing compound ₃ ) was mixed in a mortar at an appropriate mixing ratio, then solidified into a pellet, and baked in an air atmosphere (under atmospheric pressure) at 950 ° C. for 24 hours using an muffle furnace, and ICP (Inductive Coupled) Lithium cobaltate (A1) having a composition formula determined by the Plasma) method of LiCo _0.9795 Mg _0.011 Zr _0.0005 Al _0.009 O ₂ was synthesized.

Next, 10 g of the lithium cobaltate (A1) is added to 200 g of a lithium hydroxide aqueous solution having a pH of 10 and a temperature of 70 ° C., and the mixture is stirred and dispersed. Then, Al (NO ₃ ) is added thereto. ) ₃ · _9H 2 O: and 0.0154G, and ammonia water to suppress variation in pH, was added dropwise over 5 hours, to produce a Al _{(OH) 3} coprecipitate, the lithium cobalt oxide (A1 ). Thereafter, the lithium cobalt oxide (A1) to which the Al (OH) ₃ coprecipitate is adhered is taken out from the reaction solution, washed, dried, and then heat-treated at 400 ° C. for 10 hours in an air atmosphere. Thus, an Al-containing oxide film was formed on the surface of the lithium cobalt oxide (A1) to obtain a positive electrode material (a1).

  With respect to the positive electrode material (a1) obtained, its average particle diameter was measured by means of the method as described before, thereby finding that it was 27 μm.

Li ₂ CO ₃ that is a Li-containing compound, Co ₃ O ₄ that is a Co-containing compound, Mg (OH) ₂ that is an Mg-containing compound, and Al (OH) ₃ that is an Al-containing compound are appropriately mixed. After mixing in a mortar, the mixture was hardened into pellets, baked at 950 ° C. for 4 hours in an atmospheric atmosphere (under atmospheric pressure) using a muffle furnace, and the composition formula obtained by ICP method was LiCo _0.97. Mg _0.012 Al _0.009 O ₂ lithium cobaltate (B1) was synthesized.

Next, 10 g of the lithium cobalt oxide (B1) is added to 200 g of lithium hydroxide aqueous solution: 200 having a pH of 10 and a temperature of 70 ° C., and dispersed by stirring. _{3) 3} · _9H 2 O: and 0.077 g, and ammonia water to suppress variation in pH, was added dropwise over 5 hours, to produce a Al _{(OH) 3} coprecipitate, the lithium cobaltate ( It was made to adhere to the surface of B1). Thereafter, the lithium cobaltate (B1) to which the Al (OH) ₃ coprecipitate is adhered is taken out from the reaction solution, washed, dried, and then heat-treated at 400 ° C. for 10 hours in an air atmosphere. Then, an Al-containing oxide film was formed on the surface of the lithium cobalt oxide (B1) to obtain a positive electrode material (b1).

  With respect to the positive electrode material (b1) obtained, its average particle diameter was measured by means of the method as described before, thereby finding that it was 7 μm.

Then, the positive electrode material (a1) and the positive electrode material (b1) were mixed at a mass ratio of 85:15 to obtain a positive electrode material (1) for battery preparation. When the average coating thickness of the Al-containing oxide on the surface of the obtained positive electrode material (1) was measured by the above method, it was 30 nm. Moreover, when the composition of the film was confirmed by element mapping when measuring the average coating thickness, the main component was Al ₂ O ₃ . Furthermore, when the volume-based particle size distribution of the positive electrode material (1) was confirmed by the above method, the average particle diameter was 25 μm, and peak tops were observed at the respective average particle diameters of the positive electrode material (a1) and the positive electrode material (b1). Two peaks were observed with Moreover, it was 0.25 m < ² > / g when the BET specific surface area of positive electrode material (1) was measured using the specific surface area measuring apparatus by a nitrogen adsorption method.

  Positive electrode material (1): 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 Part was kneaded using a biaxial kneader, and NMP was added to adjust the viscosity to prepare a positive electrode mixture-containing paste. This paste is applied to one side of an aluminum foil having a thickness of 15 μm, vacuum-dried at 120 ° C. for 12 hours to form a positive electrode mixture layer on one side of the aluminum foil, and press treatment is performed to obtain a positive electrode. It was.

<Preparation of separator>
Modified polybutyl acrylate resin binder: 3 parts by mass, boehmite powder (average particle size 1 μm): 97 parts by mass, and water: 100 parts by mass were mixed to prepare a slurry for forming a porous layer (II). This slurry was applied to one side of a polyethylene microporous membrane [porous layer (I)] having a thickness of 12 μm and dried. A separator in which a porous layer (II) mainly composed of boehmite was formed on one surface of the porous layer (I) was obtained. The thickness of the porous layer (II) was 3 μm.

<Assembly of coin-type lithium ion secondary battery>
The negative electrode after Li doping, the positive electrode, and the separator were punched out so that their diameters were 17 mm, 16 mm, and 18 mm, respectively. Punched negative electrode, a positive electrode and the separator, the nonaqueous electrolytic solution (mixed at a volumetric ratio of 30:70 of ethylene carbonate and diethyl carbonate, LiPF ₆ was dissolved at a concentration of 1 mol / l, vinylene carbonate: 4 mass%, 4-fluoro-1,3-dioxolan-2-one: 5% by mass, adiponitrile: 0.5% by mass, and 1,3-dioxane: 0.5% by mass of added solution) and battery container A coin-type lithium ion secondary battery having a diameter of 20 mm and a thickness of 1.6 mm and having a structure shown in FIG. 2 was produced.

  Here, FIG. 2 will be described. FIG. 2 is a longitudinal sectional view schematically showing the coin-type lithium ion secondary battery of Example 1. FIG. In the lithium ion secondary battery 10, the positive electrode 1 is accommodated inside a metal outer can 4, and the negative electrode 2 is disposed thereon via a separator 3. The negative electrode 2 is in contact with the inner surface of the metal sealing plate 5. In FIG. 2, the layers of the positive electrode 1, the negative electrode 2, and the separator 3 are not shown separately, but the positive electrode 1 and the negative electrode 2 are opposed to each other with the positive electrode mixture layer and the negative electrode mixture layer through the separator 3. Thus, the separator 3 is arranged so that the porous layer (II) is on the positive electrode 1 side. Further, a non-aqueous electrolyte (not shown) is injected into the lithium ion secondary battery 10.

  In the lithium ion secondary battery 10, the outer can 4 also serves as a positive electrode terminal, and the sealing plate 5 also serves as a negative electrode terminal. And the opening part of the armored can 4 presses the resin-made annular packing 6 arrange | positioned in the peripheral part of the sealing board 5 by the inward fastening of the opening edge part of the armored can 4, and the sealing plate 5 The peripheral edge and the inner peripheral surface of the opening end of the outer can 4 are pressed against each other and sealed. That is, in the coin-type lithium ion battery 10, a resin packing 6 is interposed between the positive electrode terminal (exterior can 4) and the negative electrode terminal (sealing plate 5), and is sealed by this packing 6.

(Example 2)
Artificial graphite having an average particle size of 22 μm: 50 mass% and composite Si-1: 50 mass% were mixed in a V-type blender for 12 hours to obtain a negative electrode active material. A negative electrode mixture-containing paste was prepared in the same manner as in Example 1 except that this negative electrode active material was used, and a negative electrode roll was obtained in the same manner as in Example 1 except that this negative electrode mixture-containing paste was used. The negative electrode mixture layer of the negative electrode related to the negative electrode roll was doped with Li ions in the same manner as in Example 1 except that the amount of electricity supplied was 250 mAh / g per mass of the negative electrode active material. And the coin-type lithium ion secondary battery was produced like Example 1 except having used this negative electrode.

(Example 3)
A negative electrode active material was obtained in the same manner as in Example 2 except that the ratio of artificial graphite and composite Si-1 in the negative electrode active material was 95% by mass of artificial graphite and 5% by mass of composite Si-1. A negative electrode mixture-containing paste was prepared in the same manner as in Example 1 except that this negative electrode active material was used, and a negative electrode roll was obtained in the same manner as in Example 1 except that this negative electrode mixture-containing paste was used. The negative electrode mixture layer of the negative electrode related to this negative electrode roll was doped with Li ions in the same manner as in Example 1 except that the amount of electricity supplied was 50 mAh / g per mass of the negative electrode active material. And the coin-type lithium ion secondary battery was produced like Example 1 except having used this negative electrode.

Example 4
Scale A graphite powder: 97 parts by mass and silicon powder: 3 parts by mass were mixed by a mixing method involving compressive force and shear force to obtain a mixture A. Mixture B was prepared by mixing 100 parts by mass of this mixture A and 3 parts by mass of non-graphitic carbon material by a mixing method involving compression force and shearing force. The mixture B was heated at 1000 ° C. for 1 hour in an inert atmosphere, and then crushed, and composite particles in which silicon sandwiched between the flaky graphite particles was fixed by amorphous carbon were obtained. Obtained. A negative electrode mixture-containing paste was prepared in the same manner as in Example 1 except that this was used as the negative electrode active material, and a negative electrode roll was obtained in the same manner as in Example 1 except that this negative electrode mixture-containing paste was used. The negative electrode mixture layer of the negative electrode according to this negative electrode roll was doped with Li ions in the same manner as in Example 1 except that the amount of electricity supplied was 100 mAh / g per mass of the negative electrode active material. And the coin-type lithium ion secondary battery was produced like Example 1 except having used this negative electrode.

(Example 5)
A negative electrode mixture-containing paste in the same manner as in Example 1, except that only the same artificial graphite as that used in Example 2 was used as the negative electrode active material, and SBR was used instead of the copolymer (A) as the binder. A negative electrode roll was prepared in the same manner as in Example 1 except that this negative electrode mixture-containing paste was used. The negative electrode was doped with Li ions in the same manner as in Example 1, except that the amount of electricity supplied was 30 mAh / g per mass of the negative electrode active material. And the coin-type lithium ion secondary battery was produced like Example 1 except having used this negative electrode.

(Example 6)
The same artificial graphite as used in Example 2: 50% by mass, and material Si-2 whose SiO surface is not coated with a carbon material (average particle diameter is 5 μm, specific surface area is 6.8 m ² / g): 50 Mass% was mixed for 12 hours with a V-type blender to obtain a negative electrode active material. A negative electrode mixture-containing paste was prepared in the same manner as in Example 1 except that this negative electrode active material was used, and a negative electrode roll was obtained in the same manner as in Example 1 except that this negative electrode mixture-containing paste was used. The negative electrode mixture layer of the negative electrode related to the negative electrode roll was doped with Li ions in the same manner as in Example 1 except that the amount of electricity supplied was 250 mAh / g per mass of the negative electrode active material. And the coin-type lithium ion secondary battery was produced like Example 1 except having used this negative electrode.

(Example 7)
In the negative electrode mixture layer of the negative electrode related to the same negative electrode roll (negative electrode before doping Li ions to the negative electrode mixture layer) as prepared in Example 1, the amount of electricity supplied was 430 mAh / g per negative electrode active material mass. Except for this, Li ions were doped in the same manner as in Example 1. And the coin-type lithium ion secondary battery was produced like Example 1 except having used this negative electrode.

(Example 8)
In the negative electrode mixture layer of the negative electrode related to the same negative electrode roll (negative electrode before doping Li ions into the negative electrode mixture layer) as prepared in Example 1, the amount of electricity supplied was 565 mAh / g per negative electrode active material mass. Except for this, Li ions were doped in the same manner as in Example 1. And the coin-type lithium ion secondary battery was produced like Example 1 except having used this negative electrode.

Example 9
In the negative electrode mixture layer of the negative electrode related to the same negative electrode roll (negative electrode before doping Li ions to the negative electrode mixture layer) as prepared in Example 1, the amount of electricity supplied was 403 mAh / g per negative electrode active material mass. Except for this, Li ions were doped in the same manner as in Example 1. And the coin-type lithium ion secondary battery was produced like Example 1 except having used this negative electrode.

(Example 10)
In the negative electrode mixture layer of the negative electrode related to the same negative electrode roll (negative electrode before doping Li ions to the negative electrode mixture layer) as prepared in Example 1, the amount of electricity supplied was 645 mAh / g per mass of the negative electrode active material. Except for this, Li ions were doped in the same manner as in Example 1. And the coin-type lithium ion secondary battery was produced like Example 1 except having used this negative electrode.

(Comparative Example 1)
A coin-type lithium ion secondary battery was prepared in the same manner as in Example 1 except that the same negative electrode as that prepared in Example 1 (negative electrode before doping Li ions into the negative electrode mixture layer) was used as it was. Produced.

(Comparative Example 2)
A negative electrode was prepared in the same manner as in Example 1 except that a copper foil having a thickness of 10 μm (a tensile strength of 250 N / mm ² and a 0.2% proof stress of 210 N / mm ² ) was used. During the winding, the negative electrode broke and could not be wound well. And the coin-type lithium ion secondary battery was produced like Example 1 except having used the said negative electrode which doped Li ion to the negative mix layer.

(Comparative Example 3)
The same negative electrode as prepared in Example 1 (negative electrode before doping Li ions into the negative electrode mixture layer) was punched out so as to have a diameter of 17 mm. A metal Li foil (thickness: 50 μm) corresponding to an amount of electricity of 500 mAh / g per mass of the negative electrode active material was attached to the center of the negative electrode. A coin-type lithium ion secondary battery was produced in the same manner as in Example 1 except that this negative electrode was used.

  The following charge / discharge cycle characteristic evaluation was performed about the Example and the lithium ion secondary battery.

<Charge / discharge cycle characteristics evaluation>
Five lithium ion secondary batteries of Examples and Comparative Examples were each charged with a constant current of up to 4.4 V at a current value of 0.5 C, and subsequently reached a current value of 0.02 C at a constant voltage of 4.4 V. Charged until Then, it discharged to 2.0V with the constant current of 0.2C, and calculated | required the initial discharge capacity.

  After the initial discharge capacity measurement, the lithium ion secondary batteries (5 each) were charged at a constant current of up to 4.4V at a current value of 0.5C, and subsequently the current value was set at 0.02C at a constant voltage of 4.4V. Charged until it reached. Then, it discharged to 2.0V with the constant current of 0.2C, and calculated | required the initial discharge capacity. Next, each battery was charged with a constant current up to 4.4 V at a current value of 1 C, subsequently charged with a constant voltage of 4.4 V until the current value reached 0.05 C, and then 2. with a current value of 1 C. A series of operations for discharging to 0 V was taken as one cycle, and this was repeated 500 times. And about each battery, the constant current-constant voltage charge and the constant current discharge were performed on the same conditions as the time of first time discharge capacity measurement, and the discharge capacity was calculated | required. Then, a value obtained by dividing these discharge capacities by the initial discharge capacities was expressed as a percentage to obtain a capacity maintenance ratio, and an average value of 5 pieces was calculated for each.

  Each evaluation result is shown in Table 1 together with the configuration of the negative electrode current collector according to each lithium ion secondary battery, the state of the negative electrode during pre-doping outside the system, and the molar ratio Li / M.

  As shown in Table 1, the lithium ion secondary batteries of Examples 1 to 10 using a negative electrode having a copper foil having an appropriate tensile strength and a suitable 0.2% proof stress as a current collector are charged. The capacity retention rate at the time of discharge cycle characteristic evaluation was high, and the battery had excellent charge / discharge cycle characteristics. Moreover, when the negative electrode used for the lithium ion secondary battery of Examples 1-6 doped Li ion to the negative mix layer by the roll-to-roll system, deformation | transformation, such as a cutting | disconnection and a curvature, did not arise. Therefore, it can be said that these negative electrodes are excellent in productivity.

  On the other hand, the battery of the comparative example 1 using the negative electrode which did not dope Li ion to the negative mix layer, the battery of the comparative example 2 using the negative electrode which used the copper foil with small tensile strength as a collector. The battery of Comparative Example 3 in which the negative electrode mixture layer was doped with Li ions in the battery had a lower capacity retention rate at the time of charge / discharge cycle characteristic evaluation than the battery of the example, and had a charge / discharge cycle characteristic. It was inferior. Moreover, when the negative electrode used for the battery of Comparative Example 2 was doped with Li ions into the negative electrode mixture layer by the roll-to-roll method, cutting and bending occurred, and the productivity was poor.

DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 2a Negative electrode before Li dope 3 Separator 4 Exterior can 5 Sealing plate 6 Resin packing 10 Lithium ion secondary battery 20 Roll which wound negative electrode 2 20a Roll which wound negative electrode 2a 101 Electrolyte tank 102 Lithium metal electrode 103 Power supply 104 Cleaning tank 105 Drying means

Claims (10)

A negative electrode for a non-aqueous electrolyte based electrochemical device, in which a negative electrode mixture layer containing a negative electrode active material and a binder is laminated on a current collector,
The negative electrode mixture layer containing a negative electrode active material not containing Li is doped with Li ions,
The current collector is a metal foil having a tensile strength of 300 N / mm ² or more, and a negative electrode for a non-aqueous electrolyte based electrochemical device. ^{2. The} negative electrode for a non-aqueous electrolyte based electrochemical device according to claim 1, wherein the current collector has a 0.2% yield strength of 250 N / mm ² or more.   The negative electrode for a non-aqueous electrolyte based electrochemical device according to claim 1, wherein the negative electrode active material contains a material S containing Si. The negative electrode for a non-aqueous electrolyte based electrochemical device according to claim 3, wherein the material S contains SiO _x (where 0.5 ≦ x ≦ 1.5). The negative electrode for a non-aqueous electrolyte based electrochemical device according to claim 4, wherein the SiO _x constitutes a composite with a carbon material.   The negative electrode for a non-aqueous electrolyte based electrochemical device according to claim 5, wherein the content of the composite in the total amount of the negative electrode active material contained in the negative electrode mixture layer is 5% by mass or more. The negative electrode mixture layer contains a copolymer having a unit represented by the following formula (1) and a unit represented by the following formula (2) as the binder. The negative electrode for non-aqueous-electrolyte type electrochemical elements as described in 2.

[In the formula (2), R is hydrogen or a methyl group, and M ′ is an alkali metal element. ] A method for producing a negative electrode for a non-aqueous electrolyte based electrochemical device according to any one of claims 1 to 7,
By pulling out the negative electrode wound around a roll and introducing it into an electrolyte bath equipped with a non-aqueous electrolyte and a lithium metal electrode, and energizing between the negative electrode and the lithium metal electrode in the electrolyte bath The negative electrode mixture layer is doped with Li ions to form a negative electrode for a non-aqueous electrolyte-based electrochemical device, and the negative electrode for non-aqueous electrolyte-based electrochemical device after doping with Li ions is wound into a roll. The manufacturing method of the negative electrode for non-aqueous-electrolyte type electrochemical elements characterized by the above-mentioned. A lithium ion secondary battery in which a negative electrode, a positive electrode having a positive electrode mixture layer containing a positive electrode active material and a binder, a separator, and a non-aqueous electrolyte are housed in an outer package,
A lithium ion secondary battery comprising the negative electrode for a non-aqueous electrolyte based electrochemical device according to any one of claims 1 to 7 as the negative electrode. A method for manufacturing the lithium ion secondary battery according to claim 9, comprising:
A method for producing a lithium ion secondary battery, comprising the step of assembling a lithium ion secondary battery using the negative electrode for a non-aqueous electrolyte based electrochemical device obtained by the production method according to claim 8.

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