JP2011040326A - Negative electrode for non-aqueous secondary battery, and the non-aqueous secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a negative electrode for non-aqueous secondary batteries having excellent mobility of electrons as compared with a conventional electrode using polyimide as a binder. <P>SOLUTION: The negative electrode for non-aqueous secondary batteries includes a negative electrode active material including silicon (Si) and the binder for binding the negative electrode active material. The binder includes a polyimide and an acryl-silica hybrid resin. Also, a non-aqueous secondary battery having the negative electrode for non-aqueous secondary batteries uses a non-aqueous electrolytic solution, where an electrolyte material is dissolved into an organic solvent including propylene carbonate (PC), thus effectively suppressing an increase in resistance following an increase in the number of cycles. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a negative electrode for a non-aqueous secondary battery and a non-aqueous secondary battery.

  Secondary batteries such as lithium ion secondary batteries are small and have a large capacity, and are therefore used in a wide range of fields such as mobile phones and notebook computers. A lithium ion secondary battery has an active material capable of inserting and removing lithium (Li) in each of a positive electrode and a negative electrode. And it operate | moves because Li ion moves in the electrolyte solution provided between both electrodes. The performance of such a secondary battery depends on the materials contained in the positive electrode, the negative electrode, and the electrolyte constituting the secondary battery. Also, the combination of the material contained in the electrode and the material contained in the electrolyte is important for battery performance.

For example, an electrode using an active material containing silicon such as Li _x Si has attracted attention. The use of such an electrode is expected to increase the capacity of the battery, but it is known that the active material expands and contracts due to the charge / discharge cycle. If the electrode expands greatly or contracts greatly, the electrode expands greatly in the thickness direction, resulting in a decrease in the current collecting performance of the current collector, bending of the electrode, or even expansion of the battery itself. This will reduce the durability of the battery. In addition, due to expansion / contraction, there is a problem that the conductive path in the electrode is broken and the battery capacity is remarkably lowered or the internal resistance is increased. Therefore, in Patent Document 1, the durability of the battery is improved by using polyimide (PI) having excellent binding properties instead of general polyvinylidene fluoride (PVdF) as a binder.

  Patent Document 2 discloses a negative electrode manufactured using Ti—Si alloy powder as an active material and polyimide and polyacrylic acid as a binder. When polyimide is used as described in Patent Document 1, the low temperature characteristics are lowered, that is, the resistance value is increased when used at low temperatures. However, the combined use of polyimide and polyacrylic acid suppresses the decrease in low-temperature characteristics due to the use of polyimide. Further, in Patent Document 2, such a negative electrode is prepared by using an electrolyte solution (propylene carbonate (PC), ethylene carbonate (EC), and 1,2-dimethoxyethane (DME)) as a solvent (PC: EC: DME = volume ratio). 1: 1: 1). It is known that the addition of PC improves the low-temperature characteristics of the battery. However, depending on the amount added, it is said that the resistance increases when used near room temperature.

JP 2004-288520 A JP 2007-95670 A

  However, it is difficult to say that the electrode as disclosed in Patent Document 1 using polyimide as a binder exhibits a sufficiently low resistance when used not only at a low temperature but also at a normal temperature. Further, the inventors of the present invention repeatedly charge and discharge at room temperature for a battery in which a negative electrode containing Ti-Si alloy powder, polyimide and polyacrylic acid and an electrolytic solution containing PC are combined as in Patent Document 2. It was newly found that the increase in resistance with the increase in the number of cycles is remarkable.

  In view of the above problems, the present inventors have an object to provide a negative electrode for a non-aqueous secondary battery that is superior in electron mobility to a conventional electrode using polyimide as a binder. It is another object of the present invention to provide a non-aqueous secondary battery that can suppress an increase in resistance due to an increase in the number of cycles even when it is repeatedly charged and discharged at room temperature.

  The negative electrode for a non-aqueous secondary battery according to the present invention is a negative electrode for a non-aqueous secondary battery including a negative electrode active material containing silicon (Si) and a binder for binding the negative electrode active material. The agent is characterized by containing polyimide and acrylic-silica hybrid resin.

  Moreover, the non-aqueous secondary battery of this invention is equipped with the negative electrode for non-aqueous secondary batteries of the said invention. That is, a non-aqueous system comprising: a positive electrode; a negative electrode including a negative electrode active material containing silicon (Si); a binder that binds the negative electrode active material; and a non-aqueous electrolyte obtained by dissolving an electrolyte material in an organic solvent. In the secondary battery, the binder includes polyimide and an acrylic-silica hybrid resin, and the organic solvent includes propylene carbonate (PC).

  Furthermore, the method for producing a negative electrode for a non-aqueous secondary battery according to the present invention is for forming a negative electrode mixture layer comprising a negative electrode active material containing silicon (Si) and a binder raw material solution containing a polyamic acid and a silane-modified acrylic resin. A composition preparation step for forming a negative electrode mixture layer for preparing a composition, a negative electrode mixture layer formation step for forming the negative electrode mixture layer by applying the composition to a current collector, and heating the negative electrode mixture layer And a heating step of imidizing the polyamic acid and hydrolyzing and condensing the silane-modified acrylic resin to obtain a negative electrode containing polyimide and an acrylic-silica hybrid resin as a binder.

  For example, when polyimide is used alone as a binder, the durability of the battery is improved by the excellent heat resistance and binding property of the polyimide, but the low temperature characteristics of the battery are lowered. This is because the formation of a conductive path is hindered by the active material particles containing Si being firmly coated with polyimide having excellent adhesion, and the electron mobility (also referred to as “mobility”) of the negative electrode is lowered. Because. Therefore, the negative electrode for a non-aqueous secondary battery of the present invention uses a binder containing an acrylic-silica hybrid resin in addition to polyimide with respect to a negative electrode active material containing Si.

  When a binder raw material solution containing a polyamic acid (polyamic acid) which is a polyimide precursor and a silane-modified acrylic resin which is a precursor of an acrylic-silica hybrid resin is used as a raw material for the binder, a negative electrode active material containing Si The silane-modified acrylic resin is preferentially bonded to the surface of the film to form a stable film, and the negative electrode active material is difficult to be directly coated with polyamic acid. This is because the alkoxyl group possessed by the silane moiety contained in the silane-modified acrylic resin easily reacts with the surface hydroxyl group (—OH group) of the negative electrode active material. As a result of the preferential bonding of the silane-modified acrylic resin to the negative electrode active material, the negative electrode active material is less likely to be directly coated with polyimide, improving the electron conductivity of the negative electrode, and using polyimide alone as a binder The deterioration of the low-temperature characteristics of the battery that occurs when the battery is damaged can be suppressed. In addition, since both polyimide and acrylic-silica hybrid resin are used as the binder, the excellent binding properties of polyimide can provide the same durability as when polyimide is used alone as the binder. it is conceivable that.

  Moreover, in the non-aqueous secondary battery of this invention, the non-aqueous secondary battery negative electrode of the said invention and the non-aqueous electrolyte containing propylene carbonate (PC) are used together. Use of a non-aqueous electrolyte containing PC at room temperature is considered to cause an increase in resistance value. However, by using together with the negative electrode for a non-aqueous secondary battery of the present invention using a binder containing an acrylic-silica hybrid resin, an increase in resistance associated with an increase in the number of cycles is suppressed. Moreover, when using PC for electrolyte solution, if the stable film is not formed in the surface of a negative electrode active material, PC will be reduced and decomposed with charging / discharging of a battery. The negative electrode for a non-aqueous secondary battery of the present invention using a binder containing an acrylic-silica hybrid resin forms a stable film on the surface of the negative electrode active material containing Si as already described. This coating is formed on the surface of the negative electrode active material to an extent sufficient to suppress the reductive decomposition of PC. As a result, even if the battery is repeatedly charged and discharged at room temperature, an increase in resistance due to an increase in the number of cycles is suppressed.

It is a graph which shows the result of the charging / discharging test using the battery provided with the negative electrode for non-aqueous secondary batteries of this invention, and the battery provided with the conventional negative electrode, Comprising: Of the fall amount (IR drop) of direct-current resistance with respect to the increase in cycle number Showing change. It is a graph which shows the result of the charging / discharging test using the non-aqueous secondary battery of this invention, and the conventional non-aqueous secondary battery, Comprising: The change of IR drop with respect to the increase in cycle number is shown. It is the graph which expanded and showed the range of the cycle numbers 35-60 of the graph shown in FIG. It is a graph which shows the discharge current capacity | capacitance obtained from the charging / discharging test using the non-aqueous secondary battery of this invention, and the conventional non-aqueous secondary battery. It is explanatory drawing which shows the structure of the electrode group of a laminate cell.

  Below, the best form for implementing the negative electrode for non-aqueous secondary batteries of this invention and a non-aqueous secondary battery is demonstrated. Unless otherwise specified, the numerical range “x to y” described in this specification includes the lower limit x and the upper limit y.

<Negative electrode for non-aqueous secondary battery>
The negative electrode for a non-aqueous secondary battery includes a negative electrode active material and a binder, and may include a conductive additive as necessary. The binder binds the negative electrode active material or the negative electrode active material and the conductive additive. Note that the negative electrode active material and the binder are applied to the current collector as a negative electrode mixture layer to constitute an electrode.

  The negative electrode active material contains silicon (Si). That is, the negative electrode active material is made of silicon and / or a silicon compound, and is preferably used in a powder form. And a negative electrode active material has the surface hydroxyl group produced | generated by the oxidation of Si on the surface. Specifically, powders such as a simple substance of Si, an oxide containing Si, a nitride containing Si, and an alloy containing Si can be given. If the negative electrode active material is an alloy, it may contain a transition metal together with Si. Since the transition metal easily forms a surface hydroxyl group on the surface of the negative electrode active material as well as Si, the surface of the negative electrode active material and the silane-modified acrylic resin are easily bonded. The transition metal is preferably at least one selected from the group consisting of Ti, Fe, Ni, Mo, Mn, and Cu. Note that the negative electrode active material may be crystalline or amorphous. These negative electrode active materials can be produced using methods known in the art. The average particle diameter of the negative electrode active material is preferably 0.01 to 10 μm, more preferably 0.01 to 5 μm.

  Further, the negative electrode active material may contain another known active material. Specifically, graphite, Sn, Al, Ag or the like. Among these, one kind or a mixture of two or more kinds can be used.

  As a conductive support material, a material generally used for an electrode of a non-aqueous secondary battery may be used. For example, it is preferable to use a conductive carbon material such as carbon black, acetylene black, or carbon fiber. In addition to these carbon materials, a known conductive aid such as a conductive organic compound may be used. One of these may be used alone or in combination of two or more. The blending ratio of the conductive additive is, by mass ratio, negative electrode active material: conductive additive = 1: 0.01 to 1: 0.5, 1: 0.02 to 1: 0.2, or 1: 0.05. It is preferably ˜1: 0.08. Or when the sum total of a negative electrode active material, a binder, and a conductive support material is 100 mass%, it is preferable to contain 1-20 mass%, 2-10 mass%, and also 4-6 mass% of conductive support materials. This is because if the amount of the conductive additive is too small, a good conductive network cannot be formed, and if the amount of the conductive additive is too large, the moldability of the electrode deteriorates and the energy density of the electrode decreases.

  The binder includes polyimide and acrylic-silica hybrid resin. The chemical formula of polyamic acid (polyamic acid) which is a precursor of polyimide is shown below.

The polyamic acid can be used as long as it is conventionally used as a binder. The main constituent materials of polyamic acid are tetracarboxylic acids and diamines. For example, in the above chemical formula, R ¹ is pyromellitic acid anhydride, 1,2,3,4-benzenetetracarboxylic acid anhydride, 1,4,5,8-naphthalenetetracarboxylic acid anhydride, 2,3, 6,7-naphthalenetetracarboxylic anhydride, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, 2,2 ′, 3,3′-biphenyltetracarboxylic dianhydride, 2,3 , 3 ′, 4′-biphenyltetracarboxylic dianhydride, 3,3 ′, 4,4′-benzophenone tetracarboxylic dianhydride, 2,3,3 ′, 4′-benzophenone tetracarboxylic dianhydride 3,3 ′, 4,4′-diphenyl ether tetracarboxylic dianhydride, 2,3,3 ′, 4′-diphenyl ether tetracarboxylic dianhydride, 3,3 ′, 4,4′-diphenylsulfone tetra Carboxylic dianhydride 2,3,3 ′, 4′-diphenylsulfonetetracarboxylic dianhydride, 2,2-bis (3,3 ′, 4,4′-tetracarboxyphenyl) tetrafluoropropane dianhydride, 2,2 ′ -Bis (3,4-dicarboxyphenoxyphenyl) sulfone dianhydride, 2,2-bis (2,3-dicarboxyphenyl) propane dianhydride, 2,2-bis (3,4-dicarboxyphenyl) Aromatic tetracarboxylic acids exemplified by propane dianhydride, cyclopentanetetracarboxylic anhydride, butane-1,2,3,4-tetracarboxylic acid, 2,3,5-tricarboxycyclopentylacetic anhydride, etc. These are sites derived from these, and these may be used alone or in combination of two or more. R ² is p-phenylenediamine, m-phenylenediamine, 3,3′-diaminodiphenyl ether, 3,4′-diaminodiphenyl ether, 4,4′-diaminodiphenyl ether, 3,3′-diaminodiphenyl sulfide, 3,4 '-Diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminobenzophenone, 4,4′-diaminobenzophenone, 3,4′-diaminobenzophenone, 3,3′-diaminodiphenylmethane, 4,4′-diaminodiphenylmethane, 3,4′-diaminodiphenylmethane, 2,2-di (3-aminophenyl) ) Propane, 2,2-di (4-aminophenyl) ) Propane, 2- (3-aminophenyl) -2- (4-aminophenyl) propane, 2,2-di (3-aminophenyl) -1,1,1,3,3,3-hexafluoropropane, 2,2-di (4-aminophenyl) -1,1,1,3,3,3-hexafluoropropane, 2- (3-aminophenyl) -2- (4-aminophenyl) -1,1, 1,3,3,3-hexafluoropropane, 1,1-di (3-aminophenyl) -1-phenylethane, 1,1-di (4-aminophenyl) -1-phenylethane, 1- (3 -Aminophenyl) -1- (4-aminophenyl) -1-phenylethane, 1,3-bis (3-aminophenoxy) benzene, 1,3-bis (4-aminophenoxy) benzene, 1,4-bis (3-aminophenoxy) benzene, , 4-bis (4-aminophenoxy) benzene, 1,3-bis (3-aminobenzoyl) benzene, 1,3-bis (4-aminobenzoyl) benzene, 1,4-bis (3-aminobenzoyl) benzene 1,4-bis (4-aminobenzoyl) benzene, 1,3-bis (3-amino-α, α-dimethylbenzyl) benzene, 1,3-bis (4-amino-α, α-dimethylbenzyl) Benzene, 1,4-bis (3-amino-α, α-dimethylbenzyl) benzene, 1,4-bis (4-amino-α, α-dimethylbenzyl) benzene, 1,3-bis (3-amino- α, α-ditrifluoromethylbenzyl) benzene, 1,3-bis (4-amino-α, α-ditrifluoromethylbenzyl) benzene, 1,4-bis (3-amino-α, α-ditrifluoromethyl) Rubenzyl) benzene, 1,4-bis (4-amino-α, α-ditrifluoromethylbenzyl) benzene, 2,6-bis (3-aminophenoxy) benzonitrile, 2,6-bis (3-aminophenoxy) Pyridine, 4,4′-bis (3-aminophenoxy) biphenyl, 4,4′-bis (4-aminophenoxy) biphenyl, bis [4- (3-aminophenoxy) phenyl] ketone, bis [4- (4 -Aminophenoxy) phenyl] ketone, bis [4- (3-aminophenoxy) phenyl] sulfide, bis [4- (4-aminophenoxy) phenyl] sulfide, bis [4- (3-aminophenoxy) phenyl] sulfone, Bis [4- (4-aminophenoxy) phenyl] sulfone, bis [4- (3-aminophenoxy) phenyl] ether Bis [4- (4-aminophenoxy) phenyl] ether, 2,2-bis [4- (3-aminophenoxy) phenyl] propane, 2,2-bis [4- (4-aminophenoxy) phenyl] propane 2,2-bis [3- (3-aminophenoxy) phenyl] -1,1,1,3,3,3-hexafluoropropane, 2,2-bis [4- (4-aminophenoxy) phenyl] -1,1,1,3,3,3-hexafluoropropane, 1,3-bis [4- (3-aminophenoxy) benzoyl] benzene, 1,3-bis [4- (4-aminophenoxy) benzoyl Benzene, 1,4-bis [4- (3-aminophenoxy) benzoyl] benzene, 1,4-bis [4- (4-aminophenoxy) benzoyl] benzene, 1,3-bis [4- (3- A Minophenoxy) -α, α-dimethylbenzyl] benzene, 1,3-bis [4- (4-aminophenoxy) -α, α-dimethylbenzyl] benzene, 1,4-bis [4- (3-aminophenoxy) ) -Α, α-dimethylbenzyl] benzene, 1,4-bis [4- (4-aminophenoxy) -α, α-dimethylbenzyl] benzene, 4,4′-bis [4- (4-aminophenoxy) Benzoyl] diphenyl ether, 4,4′-bis [4- (4-amino-α, α-dimethylbenzyl) phenoxy] benzophenone, 4,4′-bis [4- (4-amino-α, α-dimethylbenzyl) Phenoxy] diphenylsulfone, 4,4′-bis [4- (4-aminophenoxy) phenoxy] diphenylsulfone, 3,3′-diamino-4,4′-diphenoxybenzophenone Aromatic diamines exemplified by 3,3′-diamino-4,4′-dibiphenoxybenzophenone, 3,3′-diamino-4-phenoxybenzophenone, 3,3′-diamino-4-biphenoxybenzophenone, and the like These are sites derived from these, and these may be used alone or in combination of two or more. Moreover, n is good in it being 1-5000.

  Moreover, as a polyimide, the polyimide-silica hybrid resin which uses a silane modified polyamic acid as a precursor can also be used.

  The silane-modified acrylic resin that is a precursor of the acrylic-silica hybrid resin is obtained, for example, by reacting a carboxyl group-containing acrylic polymer and an epoxy group-containing alkoxysilane partial condensate. The chemical formula of the epoxy group-containing alkoxysilane partial condensate is shown below.

In this chemical formula, R ³ is preferably an alkyl group having 1 to 8 carbon atoms, and R ⁴ is preferably an alkoxy group having 1 to 8 carbon atoms or an alkyl group. m is preferably 1 to 100.

  Next, the chemical formula of the silane-modified acrylic resin is shown below.

The silane-modified acrylic resin is formed by bonding the aforementioned epoxy group-containing alkoxysilane partial condensate to CO—O— of the addition-polymerized acrylic group. Here, R is preferably H and an alkyl group having 1 or 2 carbon atoms. p is preferably 20 to 200. Z bonded to the acrylic group is not essential, but examples thereof include methyl methacrylate, butyl methacrylate, butyl acrylate, 2-hydroxyethyl methacrylate, acryloylmorpholine, styrene, vinyl acetate, dimethylacrylamide, acrylonitrile, glycidyl methacrylate, and the like. Good. o is preferably 0 to 1000. In the acrylic-silica hybrid resin used in the examples described later, R is a methyl group, p is 70 to 120, R ³ is a methyl group, R ⁴ is a methoxy group, m is 1 to 5, Z is methyl methacrylate, o Is 500-900.

  As described above, the silane-modified acrylic resin is obtained by reacting a carboxyl group-containing acrylic polymer and an epoxy group-containing alkoxysilane partial condensate. The ratio between the carboxyl group-containing acrylic polymer and the epoxy group-containing alkoxysilane partial condensate is not particularly limited. [Equivalent of epoxy group of epoxy group-containing alkoxysilane partial condensate] / [Carboxylic acid of carboxyl group-containing acrylic polymer] Equivalent] is preferably 0.5-10. If it is 0.5 or more, the electron mobility and the cycle characteristics are satisfactorily exhibited.

Since at least a part of —OR ³ and —OR ⁴ of polysiloxane is likely to react with the surface hydroxyl group (—OH) of the negative electrode active material, the silane-modified acrylic resin is preferentially bonded to the negative electrode active material. It is considered that the negative electrode active material is difficult to be directly coated with the polyamic acid. That is, in the negative electrode, Si contained in the negative electrode active material and the acrylic-silica hybrid resin are firmly bonded via oxygen atoms. In addition, since it is thought that reaction of the surface hydroxyl group of a negative electrode active material and a silane modified acrylic resin advances only by mixing both, it is thought that it is not necessary to provide energy for the purpose of performing this reaction. However, heating for the purpose of promoting this reaction may be performed.

  The ratio of polyimide (PI) and acrylic-silica hybrid resin (AC) in the binder (that is, the ratio of the solid content of polyamic acid and silane-modified acrylic resin in the binder raw material solution described later) is PI: AC = The ratio may be 1: 0.01 to 1: 2, 1: 0.05 to 1: 1.5, or 1: 0.1 to 1: 1. Alternatively, when the total of the negative electrode active material, the binder, and the conductive additive (that is, the negative electrode mixture layer) is 100% by mass, the acrylic-silica hybrid resin is 0.1 to 10% by mass and 0.5 to 10% by mass. %, And preferably 2 to 7.5% by mass. If the content of the acrylic-silica hybrid resin contained in the negative electrode mixture layer is too small, the negative electrode active material is likely to be firmly covered with polyimide, and thus it is difficult to reduce the resistance. However, when the proportion of polyimide is small, the durability is not preferable.

  The binder may further contain a binder other than PI and AC as long as it is 50% by mass or less and further 10% by mass or less when the total amount of the binder is 100% by mass. For example, a polyimide-silica hybrid resin having a silane-modified polyamic acid as a precursor is suitable. The chemical formula of the silane-modified polyamic acid is shown below.

In the above chemical formula, q is preferably 1 to 5000, and r is preferably 1 to 1000. R ^{1 to} R ⁴ and m are as described above. The above R and R ¹ to R ⁴ described are each independently in any of the formula shows a structure in which the above recited independently.

  The silane-modified polyamic acid is obtained by reacting a polyamic acid with an epoxy group-containing alkoxysilane partial condensate. The use ratio of the polyamic acid and the epoxy group-containing alkoxysilane partial condensate is not particularly limited. [Equivalent of epoxy group of epoxy group-containing alkoxysilane partial condensate] / [Carboxylic acid group of tetracarboxylic acids used for polyamic acid] Is equivalent to about 0.01 to 0.4. It is preferable that the above numerical value is 0.01 or more and 0.4 or less because the transparency of the coating film after film formation becomes good. In addition, when a polyamic acid having a sum of q and r of 50 or more is used, care must be taken because the above value is 0.3 or more, and gelation may occur due to a reaction between an epoxy group and a carboxylic acid group. .

<Method for producing negative electrode for non-aqueous secondary battery>
The negative electrode for a non-aqueous secondary battery can be produced through a negative electrode mixture layer forming composition preparation step, a negative electrode mixture layer formation step, and a heating step described below.

  The negative electrode mixture layer forming composition preparation step is a step of preparing a negative electrode mixture layer forming composition containing a negative electrode active material containing Si and a binder raw material solution containing a polyamic acid and a silane-modified acrylic resin. . In this step, a conductive additive may be further mixed. The negative electrode active material, polyamic acid, and silane-modified acrylic resin are as described above. Prior to mixing with the binder, at least the negative electrode active material may be classified (sieved) to 10 μm or less, further 5 μm or less.

  The polyamic acid and the silane-modified acrylic resin are mixed with a negative electrode active material or the like in a powder form or a solution (or dispersion) dissolved (or dispersed) in an organic solvent. In addition, even if it is a powder-form binder, the paste-form composition for negative mix layer formation which is easy to provide to a collector is obtained by adding an organic solvent to powder. Usable organic solvents include N-methyl-2-pyrrolidone (NMP), methanol, methyl isobutyl ketone (MIBK) and the like.

  In addition, the compounding ratio of the organic solvent is a viscosity suitable for the composition for forming the obtained negative electrode mixture layer to be applied to the current collector in the subsequent negative electrode mixture layer forming step, specifically, room temperature ( It is desirable that the value is determined to be 3000 to 5000 mPa · s as measured by a rotary (B-type) viscometer at 25 ° C.

  When mixing the negative electrode active material and the binder raw material solution, a general mixing device such as a planetary mixer, a defoaming kneader, a ball mill, a paint shaker, a vibration mill, a reiki machine, an agitator mill may be used. .

  The negative electrode mixture layer forming step is a step of forming a negative electrode mixture layer by applying the composition prepared in the negative electrode mixture layer forming composition preparation step to a current collector. In general, a negative electrode for a non-aqueous secondary battery has an active material layer formed by binding at least a negative electrode active material with a binder attached to a current collector. Therefore, the obtained negative electrode mixture is preferably applied to the surface of the current collector. A metal mesh or metal foil can be used for the current collector. Examples of the current collector include a porous or non-porous conductive substrate made of a metal material such as stainless steel, titanium, nickel, aluminum, or copper, or a conductive resin. Examples of the porous conductive substrate include a mesh body, a net body, a punching sheet, a lath body, a porous body, a foamed body, a fiber group molded body such as a nonwoven fabric, and the like. Examples of the non-porous conductive substrate include a foil, a sheet, and a film. As a coating method, a conventionally known method such as a doctor blade or a bar coater may be used.

  The heating step is a step of heating the negative electrode mixture layer to imidize the polyamic acid and hydrolyze / condense the silane-modified acrylic resin. By heating, the polyamic acid is cured to polyimide, and the silane-modified acrylic resin is cured to an acrylic-silica hybrid resin. The heating temperature and time may be appropriately selected according to the type of polyamic acid and silane-modified acrylic resin to be used, but heating at 130 to 250 ° C. for 1 to 5 hours is ideal.

  Furthermore, you may shape | mold a negative electrode so that it may become desired thickness and density by well-known methods, such as a roll press and a press. The obtained negative electrode is in the form of a sheet, and is used after being cut into dimensions according to the specifications of the non-aqueous secondary battery to be produced.

<Non-aqueous secondary battery>
A non-aqueous secondary battery is composed of the positive electrode, the negative electrode for a non-aqueous secondary battery, and a non-aqueous electrolyte solution in which an electrolyte material is dissolved in an organic solvent. This non-aqueous secondary battery includes a separator and a non-aqueous electrolyte sandwiched between a positive electrode and a negative electrode in addition to a positive electrode and a negative electrode, as in a general secondary battery.

  The separator separates the positive electrode and the negative electrode and holds the non-aqueous electrolyte, and a thin microporous film such as polyethylene or polypropylene can be used.

The nonaqueous electrolytic solution is obtained by dissolving an alkali metal salt as an electrolyte in an organic solvent. There is no limitation in particular in the kind of nonaqueous electrolyte solution used with a nonaqueous secondary battery provided with said negative electrode for nonaqueous secondary batteries. However, by using an organic solvent containing propylene carbonate (PC), an increase in resistance accompanying an increase in the number of cycles is effectively suppressed. The organic solvent is preferably a mixed solvent obtained by adding another organic solvent to PC, rather than using PC alone. As the organic solvent to be added to PC, an aprotic organic solvent such as ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC) or the like is used. it can. When using a mixed solvent as an organic solvent, it is good to contain 10-50 volume%, 15-30 volume%, and also 19-21 volume% of PC when the whole organic solvent is 100 volume%. If the content of PC is too small, even if the negative electrode for a non-aqueous secondary battery of the present invention is used, the effect of suppressing an increase in resistance due to an increase in the number of cycles is not satisfactorily exhibited, which is not preferable. As the electrolyte to be dissolved, an alkali metal salt soluble in an organic solvent such as LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiI, LiClO ₄ , NaPF ₆ , NaBF ₄ , NaAsF ₆ , LiBOB can be used.

The negative electrode is as described above. The positive electrode includes a positive electrode active material into which alkali metal ions can be inserted and removed, and a binder that binds the positive electrode active material. Further, a conductive aid may be included. The positive electrode active material, the conductive additive, and the binder are not particularly limited as long as they can be used in the nonaqueous secondary battery. Specifically, examples of the positive electrode active material include LiCoO ₂ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , Li ₂ MnO ₂ , and S. The current collector may be any material that is generally used for the positive electrode of a non-aqueous secondary battery, such as aluminum, nickel, and stainless steel.

  The shape of the non-aqueous secondary battery is not particularly limited, and various shapes such as a cylindrical shape, a stacked shape, and a coin shape can be employed. Regardless of the shape, a separator is sandwiched between the positive electrode and the negative electrode to form an electrode body, and the space between the positive electrode current collector and the negative electrode current collector to the positive electrode terminal and the negative electrode terminal is used for current collection. After connecting using a lead or the like, the electrode body is sealed in a battery case together with a non-aqueous electrolyte to form a battery.

  As mentioned above, although embodiment of the negative electrode for non-aqueous secondary batteries and non-aqueous secondary battery of this invention was described, this invention is not limited to the said embodiment. The present invention can be implemented in various forms without departing from the gist of the present invention, with modifications and improvements that can be made by those skilled in the art.

  Based on the said embodiment, the negative electrode for lithium ion secondary batteries and the lithium ion secondary battery using the same were produced. A charge / discharge test was performed on the fabricated battery at room temperature. Hereinafter, these contents will be described.

<Preparation of negative electrode for lithium ion secondary battery>
Commercially available Si powder (manufactured by Fukuda Metals, particle size of 10 μm or less) having a purity of 99.9% or more was prepared as a negative electrode active material, and ketjen black (average particle size: 30 to 50 nm) was prepared as a conductive additive. In addition, as a raw material for a binder for binding these negative electrode active material and conductive additive, polyamic acid (manufactured by Arakawa Chemical Industries), silane-modified acrylic resin (composeran AC601 manufactured by Arakawa Chemical Industries, Ltd.) and polyacrylic acid ( Nippon Catalyst's Aquaric AS58) was prepared. 1 to 4, the Si powder is “Si”, the polyamic acid (that is, polyimide) is “PI”, the silane-modified acrylic resin (that is, acrylic-silica hybrid resin) is “AC601”, and the polyacrylic acid is “ “PAA” and ketjen black are abbreviated as “KB”.

  Mix the Si powder, polyamic acid, silane-modified acrylic resin, polyacrylic acid, and ketjen black so that the solid content is in the ratio shown in Table 1, and further, the viscosity is easy to apply to the current collector. NMP was added so that a paste-like composition for forming a negative electrode mixture layer was obtained.

  Next, this negative electrode mixture was applied to the surface of a copper foil having a thickness of 18 μm so as to have a thickness of about 10 μm, dried, volatilized with an organic solvent, pressed, and punched into a predetermined shape. Then, it heated at predetermined temperature and time with the vacuum furnace, and obtained 4 types of negative electrodes shown in Table 1. In addition, in Table 1, although the negative electrode composition as solid content contained in the composition for negative electrode composite material layer formation is described, the active material contained in the negative electrode composite material layer after forming in a collector and heating Also, the content of the binder (acrylic-silica hybrid resin and polyimide) itself is substantially equal to the values in Table 1.

  The structure of the obtained negative electrode is demonstrated using FIG. FIG. 5 is an explanatory view showing the configuration of the electrode plate group of the laminate cell, which will be described in detail later, and the negative electrode produced by the above procedure corresponds to the electrode 11 of FIG. The electrode 11 includes a sheet-shaped current collector foil 12 made of a copper foil, and a negative electrode active material layer 13 formed on the surface of the current collector foil 12. The current collector foil 12 includes a rectangular (26 mm × 31 mm) composite material coating portion 12a and a tab weld portion 12b extending from a corner of the composite material coating portion 12a. A negative electrode active material layer 13 is formed on one surface of the composite material coating portion 12a. As described above, the negative electrode active material layer 13 is made of Si powder, a conductive additive, and a binder that binds both.

  A nickel tab 14 was resistance welded to the tab weld 12 b of the current collector foil 12. Furthermore, the resin film 15 was adhered to the tab weld portion 12b.

<Production of lithium ion secondary battery>
A laminate cell was prepared using a positive electrode containing LiCoO ₂ as a positive electrode active material as a counter electrode of the negative electrode obtained by the above procedure. The laminate cell has the above-mentioned No. 1 to 4, an electrode plate group 10 in which the electrode 11, the counter electrode 16 and the separator 19 are laminated, a laminate film (not shown) that encloses and seals the electrode plate group 10, and the laminate film A non-aqueous electrolyte to be injected. The production procedure of the laminate cell will be described with reference to FIG.

The configuration of the electrode 11 was as described above. As the counter electrode 16, a positive electrode containing LiCoO ₂ (manufactured by Piotrek Co., Ltd.) as a positive electrode active material was used. In this positive electrode, an aluminum foil having a thickness of 15 μm was used as a current collector, a capacity was 2.2 mAh / cm ² , and an electrode density was 2.8 g / cm ² . Like the electrode 11, the counter electrode 16 includes a rectangular (25 mm × 30 mm) composite material coating portion 16a and a tab weld portion 16b extending from a corner of the main body portion 16a, both of which are made of aluminum foil. It became the composition which becomes. A positive electrode active material layer containing LiCoO ₂ was formed on one surface of the composite material coating portion 16a. An aluminum tab 17 was resistance welded to the tab weld 16b. Further, a resin film 18 was attached to the tab weld 16b.

  As the separator 19, a rectangular sheet (27 mm × 32 mm, thickness 25 μm) made of polypropylene resin was used. In this order, the negative electrode active material layer and the positive electrode active material layer are stacked so that the negative electrode active material layer and the positive electrode active material layer face each other through the separator 19 in this order. A plate group 10 was constructed.

  Next, the electrode plate group 10 was covered with a set of two laminated films, the three sides were sealed, and then a predetermined nonaqueous electrolyte was poured into the bag-like laminated film. Thereafter, the remaining one side was sealed to obtain a laminate cell in which the four sides were hermetically sealed, and the electrode plate group 10 and the non-aqueous electrolyte were sealed. Note that some of the tabs 15 and 17 on both poles extend outward for electrical connection with the outside.

The non-aqueous electrolyte was obtained by dissolving LiPF ₆ at a concentration of 1 mol in the following organic solvent (1) EC / DEC or (2) EC / PC / DEC. “PC” is propylene carbonate, “EC” is ethylene carbonate, “DEC” is diethyl carbonate, and the following numerical values are volume ratios. And No. Two types of laminate cells each using the non-aqueous electrolyte solution of (1) or (2) were prepared for each of the negative electrodes 1 to 4.
(1) A mixed solvent in which EC and DEC are mixed at EC: DEC = 1: 1.
(2) A mixed solvent in which EC, PC and DEC are mixed at EC: PC: DEC = 2: 2: 6.

<Charge / discharge test>
The laminate cell produced by the above procedure was subjected to a charge / discharge test at room temperature (30 ° C.). In the charge / discharge test, CCCV charge (constant current / constant voltage charge) was performed at 0.2C to 4.25V for 10 hours, and then CC discharge (constant current discharge) was performed to 2.6V at 0.2C. As a cycle, 60 cycles were repeated. The current was a constant current of 3.4 mA. The voltage change from the start of discharge in each cycle to 10 seconds later is ΔV (unit is V), and I = 3.4 × 10 ⁻³ (unit is A), and ΔV / I (unit is Ω) From this, the amount of decrease in DC resistance (IR drop) was calculated. The results are shown in FIGS. 3 is an enlarged graph of a part of the graph of FIG. FIG. 4 shows the current capacity during discharge when the same charge / discharge test was repeated 100 cycles.

  FIG. 1 is a graph showing the results of a charge / discharge test performed on a battery including an electrolytic solution containing an organic solvent (1) composed of EC and DEC. No. using a binder composed of polyimide and acrylic-silica hybrid resin. 1 or No. No. 4 using a binder composed only of polyimide was used for all of the batteries having the negative electrode 4. The IR drop value was lower than that of the battery having 3 negative electrodes. In particular, No. 1 containing a large amount of acrylic-silica hybrid resin. A battery having one negative electrode showed low resistance.

  FIG. 2 and FIG. 3 are graphs showing the results of a charge / discharge test performed on a battery including an electrolytic solution containing an organic solvent (2) composed of EC, PC, and DEC. No. using a binder consisting only of polyimide. No. 3 using a binder containing an acrylic-silica hybrid resin or acrylic acid. The increase in IR drop was significant compared to batteries with 1, 2 or 4 negative electrodes. No. All of the batteries having 1, 2 or 4 negative electrodes showed no significant difference until about 30 cycles. However, as shown in FIG. 3, as the number of cycles increased, the difference in IR drop between these batteries increased. That is, when the number of cycles is increased, No. 1 using a binder composed of polyimide and acrylic-silica hybrid resin. 1 or No. No. 4 using a binder made of polyimide and acrylic acid. The value of IR drop was lower than that of a battery having 2 negative electrodes. This is presumably because the use of acrylic-silica hybrid resin rather than polyacrylic acid facilitates the formation of a stable coating on the Si powder and suppresses reductive decomposition of PC. In particular, No. 1 containing a large amount of acrylic-silica hybrid resin. The battery having the negative electrode 1 had a small slope in the graph of FIG. 3, and the effect of suppressing an increase in resistance accompanying an increase in the number of cycles was remarkable.

  Note that FIG. 1 or No. It is a graph which shows the charging / discharging test result done about the battery provided with the electrolyte solution containing the organic solvent (2) which consists of 2 negative electrodes and EC, PC, and DEC. In any of the batteries, the capacity decreased as the number of cycles increased, but No. 1 containing an acrylic-silica hybrid resin in the binder. No. 1 containing a polyacrylic acid in the binder is used to reduce the capacity of the battery including the negative electrode 1. It was restrained smaller than a battery provided with 2 negative electrodes. This is considered due to an increase in resistance of the negative electrode accompanying an increase in the number of cycles.

Claims (6)

A negative electrode for a non-aqueous secondary battery comprising a negative electrode active material containing silicon (Si) and a binder for binding the negative electrode active material,
The negative electrode for a non-aqueous secondary battery, wherein the binder includes polyimide and an acrylic-silica hybrid resin.   Furthermore, the negative electrode for non-aqueous secondary batteries of Claim 1 containing a conductive support material.   The non-aqueous secondary according to claim 2, comprising 0.1% by mass or more and 10% by mass or less of acrylic-silica hybrid resin when the total of the negative electrode active material, the binder, and the conductive additive is 100% by mass. Battery negative electrode. A non-aqueous secondary comprising: a positive electrode; a negative electrode including a negative electrode active material containing silicon (Si); a binder that binds the negative electrode active material; and a non-aqueous electrolyte obtained by dissolving an electrolyte material in an organic solvent. A battery,
The binder includes polyimide and acrylic-silica hybrid resin,
The non-aqueous secondary battery, wherein the organic solvent contains propylene carbonate (PC).   5. The non-aqueous secondary battery according to claim 4, comprising 10% by volume to 50% by volume of propylene carbonate (PC) when the organic solvent is 100% by volume. A negative electrode mixture layer forming composition preparation step for preparing a negative electrode mixture layer forming composition comprising a negative electrode active material containing silicon (Si) and a binder raw material solution containing a polyamic acid and a silane-modified acrylic resin;
A negative electrode mixture layer forming step of forming the negative electrode mixture layer by applying the composition to a current collector;
A heating step of heating the negative electrode mixture layer to imidize the polyamic acid and hydrolyze and condense the silane-modified acrylic resin;
To obtain a negative electrode containing polyimide and an acrylic-silica hybrid resin as a binder, and a method for producing a negative electrode for a non-aqueous secondary battery.

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