JP2012204181A - Electrode and method for forming electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode capable of further significantly improving charge/discharge cycles of a lithium secondary battery or the like.SOLUTION: An electrode 100 according to the present invention includes a collector 300 and an active material layer 200. The active material layer 200 includes active material particles 210 and a porous polyimide resin 220. The active material layer 200 is formed on the collector 300. A thickness of the active material layer 200 is more than 0 μm and less than 10 μm. An average particle diameter of the active material particles 210 is more than 0 μm and less than 10 μm. The polyimide resin 220 binds the active material particles 210 with each other.

Description

  The present invention relates to an electrode and an electrode forming method.

  In the past, "utilization of a monomer type polyimide precursor as a binder to be added to a slurry for forming a negative electrode such as a lithium secondary battery" has been proposed (see, for example, Japanese Patent Application Laid-Open No. 2008-033452). This monomer-type polyimide precursor is mainly composed of a tetracarboxylic acid diester compound and a diamine compound. For example, the monomer-type polyimide precursor forms a porous structure while imidizing and increasing the molecular weight by heating, and includes active material particles. A strong mold (MOLD) is formed. Since the active material particles are strongly bound in the pores, the porous structure is maintained without collapsing even if the active material particles repeat severe expansion and contraction, and charge / discharge cycles of lithium secondary batteries and the like are maintained. Dramatically improved.

JP 2008-034352 A

  The subject of this invention is providing the electrode which can improve charge / discharge cycles, such as a lithium secondary battery, further dramatically.

(1)
The electrode according to the present invention includes a current collector and an active material layer. The active material layer includes active material particles and a porous polyimide resin. This active material layer is formed on the current collector. The active material layer has a thickness of more than 0 μm and less than 10 μm. The active material particles have an average particle size of more than 0 μm and less than 10 μm. The polyimide resin binds the active material particles.

  As a result of intensive studies by the inventors of the present application, it is clear that this electrode significantly improves the charge / discharge cycle of a lithium secondary battery and the like, and increases the discharge capacity of a lithium secondary battery, etc. It became.

(2)
The electrode forming method according to the present invention includes a first coating step and a first heating step. In the first application step, the slurry is applied to the current collector. The slurry contains at least active material particles, a tetracarboxylic acid ester compound, a diamine compound, and a first solvent. The average particle diameter of the active material particles is more than 0 μm and less than 10 μm. The first solvent dissolves the tetracarboxylic acid ester compound and the diamine compound. In the first heating step, the slurry applied to the current collector is heated to form an active material layer. The thickness of the active material layer is more than 0 μm and less than 10 μm.

  As a result of intensive studies by the inventors of the present application, the electrode obtained by this electrode forming method further dramatically improves the charge / discharge cycle of a lithium secondary battery and the like and discharges of a lithium secondary battery and the like as compared with the conventional electrode. It became clear that the capacity was increased.

(3)
The electrode forming method (2) further includes an undercoat layer forming step. In the undercoat layer forming step, an undercoat layer is formed on the current collector. In the first application step, the slurry is applied on the undercoat layer. When the undercoat layer is formed on the current collector, after heating the “polyimide resin solution with conductive filler” for forming the undercoat layer at a temperature between 50 ° C. and 100 ° C. for several tens of minutes, It is preferable to apply a mixture slurry. By doing so, the mixture slurry is applied in a state where the undercoat layer is not completely solidified, so that the undercoat layer and the active material layer are well bonded.

  As a result of intensive studies by the inventors of the present application, it has been found that this undercoat layer improves the adhesion of the active material layer to the current collector.

(4)
In the electrode forming method of (3) described above, the undercoat layer forming step includes a second coating step and a second heating step. In the second application step, the coating solution is applied to the current collector. The coating solution contains a conductive filler, a polyimide precursor, and a second solvent. The second solvent dissolves the polyimide precursor. In the second heating step, the coating solution applied to the current collector is heated to form an undercoat layer.

  As a result of intensive studies by the inventors of the present application, it has been found that this undercoat layer improves the adhesion of the active material layer to the current collector.

(5)
In the electrode forming method of (4) described above, the polyimide precursor of the coating solution is preferably a polyamic acid. For example, the polyamic acid is imidized by heating to become a polyimide resin.

  This coating solution containing polyamic acid has better coating properties than a coating solution containing a monomeric polyimide precursor. The monomer-type polyimide precursor is mainly composed of a tetracarboxylic acid diester compound and a diamine compound. For example, the monomer-type polyimide precursor is imidized by heating to have a high molecular weight and become a polyimide resin.

(6)
In the electrode forming method of (4) or (5) above, in the second coating step, the coating solution is applied to the current collector so that the thickness of the undercoat layer becomes a thickness that flattens the unevenness of the current collector surface. It is preferable to apply.

  The undercoat layer improves the adhesion of the active material layer to the current collector by flattening the unevenness of the current collector surface, and improves the manufacturing accuracy of the active material layer provided on the undercoat layer. Let

  The electrode according to the present invention further dramatically improves the charge / discharge cycle of a lithium secondary battery or the like and increases the discharge capacity of a lithium secondary battery or the like as compared with a conventional electrode.

It is sectional drawing of the electrode which concerns on one Embodiment of this invention. It is sectional drawing of the electrode which concerns on the modification (A) of one Embodiment of this invention.

<Negative electrode>
As shown in FIG. 1, a negative electrode 100 that is an electrode according to an embodiment of the present invention includes an active material layer 200 and a current collector 300. This negative electrode 100 is used for a lithium secondary battery or the like. The active material layer 200 is formed on the current collector 300. Hereinafter, each of the active material layer 200 and the current collector 300 will be described in detail.

<Active material layer>
The active material layer 200 includes active material particles 210 and a polyimide resin 220. The thickness of the active material layer 200 is more than 0 μm and less than 10 μm, preferably more than 0 μm and less than 8 μm, more preferably more than 0 μm and less than 6 μm, further preferably more than 0 μm and less than 4 μm, more preferably more than 0 μm Most preferably, it is less than 2 μm.

  The average particle diameter of the active material particles 210 is more than 0 μm and less than 10 μm, preferably more than 0 μm and less than 8 μm, more preferably more than 0 μm and less than 6 μm, more preferably more than 0 μm and less than 4 μm, more preferably 0 μm Most preferably, it is less than 2 μm. In addition, the average particle diameter here is measured by a laser diffraction / scattering method using a particle size distribution measuring apparatus Microtrac MT3100II (manufactured by Nikkiso Co., Ltd.). In a lithium secondary battery or the like, as the average particle size of the active material particles 210 is smaller, better cycle characteristics tend to be obtained. When the active material particles 210 having a small average particle diameter are used, the absolute amount of volume expansion / contraction of the active material particles 210 due to insertion / extraction of lithium in a charge / discharge reaction of a lithium secondary battery or the like is reduced. Therefore, the absolute amount of distortion between the active material particles 210 in the negative electrode 100 during the charge / discharge reaction is also reduced. Therefore, destruction of the mold made of polyimide resin 220 does not occur, a decrease in current collecting property in the negative electrode 100 can be suppressed, and good charge / discharge characteristics can be obtained.

  The particle size distribution of the active material particles 210 is preferably as narrow as possible. If the width of the particle size distribution is wide, there will be a large difference in the absolute amount of volume expansion / contraction associated with insertion / extraction of lithium between the active material particles 210 having greatly different particle sizes. Therefore, there is a high risk that the active material layer 200 is distorted and the mold made of the polyimide resin 220 is destroyed.

  Examples of the active material particles 210 include silicon (Si) particles, silicon oxide (SiO) particles, silicon alloy particles, and tin (Sn) particles. Examples of silicon alloys include solid solutions of silicon and one or more other elements, intermetallic compounds of silicon and one or more other elements, and eutectic alloys of silicon and one or more other elements. . Note that the active material particles 210 may include particles made of a material alloyed with lithium. Examples of such materials include germanium, tin, lead, zinc, magnesium, sodium, aluminum, gallium, indium, and alloys thereof.

  As a method for producing the silicon alloy, for example, an arc melting method, a liquid quenching method, a mechanical alloying method, a sputtering method, a chemical vapor deposition method, a firing method, or the like is used. In particular, as the liquid quenching method, a single roll quenching method, a twin roll quenching method, and various atomizing methods such as a gas atomizing method, a water atomizing method, and a disk atomizing method are used.

  The active material particles 210 may be core-shell type active material particles in which the above-described silicon (Si) particles, silicon oxide (SiO) particles, silicon alloy particles, tin (Sn) particles, or the like are coated with a metal or the like. Good. The core-shell type active material particles are produced by an electroless plating method, an electrolytic plating method, a chemical reduction method, a vapor deposition method, a sputtering method, a chemical vapor deposition method, or the like. The shell portion is preferably formed of the same metal as that forming the current collector 300. The bondability between the core-shell type active material particles and the current collector 300 is greatly improved, and excellent charge / discharge cycle characteristics can be obtained. The shell portion may be formed of a silane coupling agent instead of the metal. If the surface treatment of the active material particles 210 is performed with a silane coupling agent, the active material particles 210 can be favorably dispersed in a slurry described later, and the binding property of the active material particles 210 to the polyimide resin 220 can be improved. it can.

  The polyimide resin 220 has a porous structure in the active material layer 200, functions as a template material including the active material particles 210, binds the active material particles 210 in the pores, and It plays a role of binding the active material particles 210. At this time, the polyimide resin 220 usually has a porosity of about 20 to 40 parts by volume. This polyimide resin 220 is porous, and is mainly formed from tetracarboxylic acid-derived units and diamine-derived units.

  The polyimide resin 220 preferably has an anionic group. This anionic group is bonded to the diamine-derived unit of the polyimide resin 220.

  The polyimide resin 220 preferably contains a conductive filler. The conductive filler functions as a conductive additive. Examples of the conductive filler include carbon black (oil furnace black, channel black, lamp black, thermal black, ketjen black, acetylene black), carbon nanotube, carbon nanofiber, fullerene, carbon microcoil, graphite (natural graphite, Artificial graphite) carbon black, carbon fiber short fibers (PAN-based carbon short fibers, pitch-based carbon short fibers) and the like are used. These conductive fillers may be used alone or in combination.

  The active material layer 200 is obtained by heating the slurry. The slurry mainly contains a tetracarboxylic acid ester compound, a diamine compound, a first solvent, and active material particles 210. The active material particles 210 in the slurry are present in a dispersed state in a polyimide precursor varnish composed of a tetracarboxylic acid ester compound, a diamine compound and a first solvent.

  The molar ratio of the tetracarboxylic acid ester compound to the diamine compound is usually in the range of 55:45 to 45:55. In addition, the molar ratio of the tetracarboxylic acid ester compound and the diamine compound can be appropriately changed to a ratio other than the above as long as the gist of the present invention is not impaired.

  The tetracarboxylic acid ester compound is preferably an aromatic tetracarboxylic acid ester compound. The tetracarboxylic acid ester compound is preferably a tetracarboxylic acid diester compound. The tetracarboxylic acid ester compound can be obtained very simply by esterifying the corresponding tetracarboxylic dianhydride with an alcohol. The esterification of tetracarboxylic dianhydride is preferably performed at a temperature of 50 ° C. or higher and 150 ° C. or lower.

  Examples of tetracarboxylic dianhydrides for inducing formation of tetracarboxylic acid ester compounds include pyromellitic dianhydride (PMDA), 1,2,5,6-naphthalene tetracarboxylic dianhydride, 1,4,5 , 8-Naphthalenetetracarboxylic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 2,2 ′, 3,3′-biphenyltetracarboxylic dianhydride, 2,3,3 ', 4'-biphenyltetracarboxylic dianhydride, 3,3', 4,4'-biphenyltetracarboxylic dianhydride (BPDA), 2,2 ', 3,3'-benzophenonetetracarboxylic dianhydride 2,3,3 ′, 4′-benzophenone tetracarboxylic dianhydride, 3,3 ′, 4,4′-benzophenone tetracarboxylic dianhydride (BTDA), bis (3,4-dicar Xylphenyl) sulfone dianhydride, bis (2,3-dicarboxyphenyl) methane dianhydride, bis (3,4-dicarboxyphenyl) methane dianhydride, 1,1-bis (2,3-dicarboxyphenyl) ) Ethane dianhydride, 1,1-bis (3,4-dicarboxyphenyl) ethane dianhydride, 2,2-bis [3,4- (dicarboxyphenoxy) phenyl] propane dianhydride (BPADA), 4,4 ′-(hexafluoroisopropylidene) diphthalic anhydride, oxydiphthalic anhydride (ODPA), bis (3,4-dicarboxyphenyl) sulfone dianhydride, bis (3,4-dicarboxyphenyl) sulfoxide Dianhydride, thiodiphthalic dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride, 2,3,6,7-anthracentate Carboxylic dianhydride, 1,2,7,8-phenanthrenetetracarboxylic dianhydride, 9,9-bis (3,4-dicarboxyphenyl) fluorene dianhydride, 9,9-bis [4- ( Aromatic tetracarboxylic dianhydrides such as 3,4′-dicarboxyphenoxy) phenyl] fluorene dianhydride, cyclobutanetetracarboxylic dianhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride 2,3,4,5-tetrahydrofurantetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, 3,4-dicarboxy-1-cyclohexylsuccinic dianhydride, 3 , 4-dicarboxy-1,2,3,4-tetrahydro-1-naphthalene succinic dianhydride and the like are used. These tetracarboxylic dianhydrides may be used alone or in combination.

  As alcohols for induction formation of tetracarboxylic acid ester compounds, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-1-propanol, 2-methyl-2-propanol, 1-pentanol, 2-pentanol, 3-pentanol, 2-methyl-1-butanol, 3-methyl-1-butanol, 2-methyl-2-butanol, 3-methyl-2-butanol, 2,2 -Dimethyl-1-propanol, 1-hexanol, 2-methyl-1-pentanol, 4-methyl-2-pentanol, 2-ethyl-1-butanol, cyclohexanol, 2-methoxyethanol, 2-ethoxyethanol, 2- (methoxymethoxy) ethanol, 2-isopropoxyethanol, 2-butyl Xiethanol, phenol, 1-hydroxy-2-propanone, 4-hydroxy-2-butanone, 3-hydroxy-2-butanone, 1-hydroxy-2-butanone, 2-phenylethanol, 1-phenyl-1-hydroxyethane 2-phenoxyethanol or the like is used. Further, 1,2-ethanediol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol as alcohols for inducing formation of tetracarboxylic acid ester compounds 2,3-butanediol, 1,5-pentanediol, 2-methyl-2,4-pentanediol, glycerol, 2-ethyl-2- (hydroxymethyl) -1,3-propanediol, 1,2, 6-hexanetriol, 2,2′-dihydroxydiethyl ether, 2- (2-methoxyethoxy) ethanol, 2- (2-ethoxyethoxy) ethanol, 3,6-dioxaoctane-1,8-diol, 1- Multivalent alcohols such as methoxy-2-propanol, 1-ethoxy-2-propanol and dipropylene glycol It is used. These alcohols may be used alone or in combination.

  Among the tetracarboxylic acid ester compounds composed of the above tetracarboxylic dianhydride and alcohol, 3,3 ′, 4,4′-benzophenone tetracarboxylic acid diester is particularly preferable. The tetracarboxylic acid ester compound can also be produced by other methods, for example, by directly esterifying tetracarboxylic acid.

  The diamine compound is preferably an aromatic diamine compound. In order to produce the polyimide resin 220 having an anionic group, the diamine compound preferably has an anionic group. As the anionic group, for example, a carboxyl group, a sulfate group, a sulfonic acid group, a phosphoric acid group, a phosphoric acid ester group, or the like is used. Among these anionic groups, a carboxyl group is particularly preferable. Examples of the diamine compound having an anionic group include 3,4-diaminobenzoic acid, 3,5-diaminobenzoic acid, metaphenylenediamine 4-sulfonic acid, and the like.

  Examples of the diamine compound having no anionic group include paraphenylenediamine (PPD), metaphenylenediamine (MPDA), 2,5-diaminotoluene, 2,6-diaminotoluene, 4,4′-diaminobiphenyl, 3, 3′-dimethyl-4,4′-diaminobiphenyl, 3,3′-dimethoxy-4,4′-diaminobiphenyl, 2,2-bis (trifluoromethyl) -4,4′-diaminobiphenyl, 3,3 '-Diaminodiphenylmethane, 4,4'-diaminodiphenylmethane (MDA), 2,2-bis- (4-aminophenyl) propane, 3,3'-diaminodiphenylsulfone (33DDS), 4,4'-diaminodiphenylsulfone (44DDS), 3,3′-diaminodiphenyl sulfide, 4,4′-diaminodiph Nyl sulfide, 3,3′-diaminodiphenyl ether, 3,4′-diaminodiphenyl ether (34 ODA), 4,4′-diaminodiphenyl ether (ODA), 1,5-diaminonaphthalene, 4,4′-diaminodiphenyldiethylsilane, 4,4′-diaminodiphenylsilane, 4,4′-diaminodiphenylethylphosphine oxide, 1,3-bis (3-aminophenoxy) benzene (133APB), 1,3-bis (4-aminophenoxy) benzene (134APB) ), 1,4-bis (4-aminophenoxy) benzene, bis [4- (3-aminophenoxy) phenyl] sulfone (BAPSM), bis [4- (4-aminophenoxy) phenyl] sulfone (BAPS), 2 , 2-Bis [4- (4-aminophenoxy) f Nyl] propane (BAPP), 2,2-bis (3-aminophenyl) 1,1,1,3,3,3-hexafluoropropane, 2,2-bis (4-aminophenyl) 1,1,1 , 3,3,3-hexafluoropropane, 9,9-bis (4-aminophenyl) fluorene and the like are used. These diamine compounds may be used alone or in combination.

  In addition, you may mix and use the diamine compound which has an anionic group, and the diamine compound which does not have an anionic group. In this case, the diamine compound having an anionic group preferably accounts for 30 mol% or more of the total diamine compound, more preferably accounts for 40 mol% or more of the total diamine compound, and further accounts for 60 mol% or more. Preferably, it occupies 80 mol% or more, more preferably 90 mol% or more, and more preferably 95 mol% or more.

  The first solvent dissolves the tetracarboxylic acid ester compound and the diamine compound. As the first solvent, for example, alcohols for inducing formation of the above-described tetracarboxylic acid ester are preferably used. Specifically, lower alcohols such as methanol, ethanol, 1-propanol, and 2-propanol are preferably used as alcohols. In addition to the alcohols, N-methyl-2-pyrrolidone, dimethylacetamide, aromatic hydrocarbons and the like may be added to the first solvent.

  The slurry preferably contains the conductive filler described above. Moreover, it is preferable that a dispersing agent etc. contain in a slurry. The dispersant added to the slurry uniformly disperses the active material particles 210 in the slurry. As the dispersant, for example, sorbitan monooleate, N, N-dimethyllaurylamine, N, N-dimethylstearylamine, N-cocoalkyl-1,3-diaminopropane and the like are used. These dispersants may be used alone or in combination.

  The content of the polyimide resin 220 in the active material layer 200 is preferably 5% by weight or more and 50% by weight or less of the total weight of the active material layer 200, and more preferably 10% by weight or more and 30% by weight or less. More preferably, the content is 12% by weight or more and 20% by weight or less. If the polyimide resin 220 in the active material layer 200 is less than 5% by weight, the adhesion between the active material particles 210 and the adhesion between the active material particles 210 and the current collector 300 may be insufficient. When the polyimide resin 220 in the active material layer 200 is more than 50% by weight, the resistance in the negative electrode 100 increases and initial charging may be difficult.

<Current collector>
The current collector 300 is preferably a conductive metal foil. This conductive metal foil is formed of, for example, a metal such as copper, nickel, iron, titanium, or cobalt, or an alloy such as stainless steel obtained by combining these metals.

  The surface of the current collector 300 is preferably roughened in order to improve the binding property with the active material layer 200. The current collector 300 is roughened by providing electrolytic copper or an electrolytic copper alloy on the surface of the current collector 300.

  Note that the current collector 300 may be roughened by subjecting the surface of the current collector 300 to a roughening treatment. Examples of the roughening treatment include a vapor phase growth method, an etching method, and a polishing method. Examples of the vapor phase growth method include a sputtering method, a CVD method, and a vapor deposition method. Examples of the etching method include a physical etching method and a chemical etching method. Examples of the polishing method include polishing by sandpaper or polishing by a blast method.

<Electrode formation method>
The slurry is produced through the first mixing step and the second mixing step in order. In the first mixing step, carbon black is mixed with the monomer-type polyimide precursor solution without substantially applying shear stress to prepare a carbon black-added polyimide precursor solution. Here, “substantially without applying shear stress” means that shear stress to such an extent that the structure of carbon black is not destroyed is allowed. The monomer-type polyimide precursor solution contains a tetracarboxylic acid ester compound, a diamine compound having an anionic group, and a first solvent. Note that a tetracarboxylic acid ester compound and a diamine compound are dissolved in the first solvent.

  In the second mixing step, active material particles are mixed with the carbon black-added polyimide precursor solution to prepare a slurry. When the active material particle 210 is 100 parts by weight, the solid content of the monomer-type polyimide precursor solution is preferably in the range of 5 to 11 parts by weight. For this reason, if this slurry manufacturing method is utilized, carbon black will be disperse | distributed to a monomer type polyimide precursor solution, without destroying the structure | tissue of carbon black. Therefore, if this slurry manufacturing method is utilized, the electroconductivity of the active material layer 200 obtained from the slurry can be improved.

  Next, the negative electrode 100 is formed through a first coating process and a first heating process in this order. In the first application step, the slurry is applied to the current collector 300.

  In the first heating step, the slurry applied to the current collector 300 is heated to form the active material layer 200 having a thickness of more than 0 μm and less than 10 μm. The slurry is preferably heated, for example, in a non-oxidizing atmosphere such as a vacuum, a nitrogen atmosphere, or an argon atmosphere, or in a reducing atmosphere such as a hydrogen atmosphere.

  As a heating method, for example, a method using an ordinary constant temperature furnace, a discharge plasma sintering method, a hot press method, or the like is used. By forming the active material layer 200 on the current collector 300, not only the active material particles 210 but also the active material particles 210 and the current collector 300 are formed in the active material layer 200 by the porous polyimide resin 220. Firmly bound.

  Before heating the slurry, a slurry (hereinafter referred to as “coating film”) applied to the current collector 300 may be rolled together with the current collector 300 or may not be rolled. From the viewpoint of preventing breakage, it is preferable not to roll. When the coating film is rolled together with the current collector 300, “packing density of the active material particles 210 in the coating film”, “adhesion between the active material particles 210”, and “adhesion between the active material particles 210 and the current collector 300”. ”Is too high and the cycle life is reduced. By not rolling, destruction of the mold made of the current collector 300 and the polyimide resin 220 can be prevented, and good charge / discharge cycle characteristics can be obtained as a result.

  The heating temperature is preferably not less than the temperature at which the monomer-type polyimide precursor in the slurry is imidized and becomes sufficiently high molecular weight, and not more than the melting points of the current collector 300 and the active material particles 210. The monomer-type polyimide precursor is mainly composed of a tetracarboxylic acid diester compound and a diamine compound. For example, the monomer-type polyimide precursor is imidized by heating to become a high molecular weight to be a polyimide resin. The recommended heating temperature for the slurry is between 100 ° C and 400 ° C. The firing temperature of the slurry is more preferably a temperature between 150 ° C. and 400 ° C., and further preferably a temperature between 200 ° C. and 400 ° C. This is to prevent the current collector 300 from being deteriorated by heat and to maintain the crosslinked structure of the polyimide resin 220.

  In particular, when a copper foil is used as the current collector 300, when the copper foil is heated at a temperature higher than 300 ° C., its strength (tensile strength) decreases. However, if this electrode formation method is used, even if the current collector 300 is a copper foil, it is possible to suppress a decrease in strength (tensile strength) of the copper foil. In addition, when an alloy foil such as stainless steel or a copper alloy foil is used as the current collector 300, the strength can be maintained even when heated at a temperature exceeding 300 ° C., so that it is used within the recommended heating temperature range of the slurry. It is possible.

  In this electrode forming method, the slurry is heated at a relatively low temperature. For this reason, if this electrode formation method is utilized, the polyimide resin 220 can be made relatively soft. Therefore, if this electrode forming method is used, the polyimide resin 220 can easily follow the expansion of the active material particles 210, and the active material particles 210 can be prevented from dropping from the polyimide resin 220.

<Positive electrode>
As the positive electrode, a known positive electrode for a lithium secondary battery or the like is used, but an electrode having the same configuration as that of the negative electrode 100 may be used except that the material of the active material particles and the current collecting layer is appropriately changed. In that case, for example, lithium-containing transition metal oxides such as lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), and lithium manganate (LiMn ₂ O ₄ ) are used as the active material particles for the positive electrode. it can. As the current collecting layer for the positive electrode, for example, aluminum, aluminum alloy, nickel, titanium, or the like can be used.

<Effect in this embodiment>
As a result of intensive studies by the inventors of the present application, the negative electrode 100 can dramatically improve the charge / discharge cycle of a lithium secondary battery and the like and increase the discharge capacity of a lithium secondary battery and the like as compared with the conventional negative electrode. It became clear.

  As a result of intensive studies by the inventors of the present application, the negative electrode 100 obtained by this electrode formation method further dramatically improves the charge / discharge cycle of a lithium secondary battery or the like as compared with the conventional negative electrode, and also the lithium secondary battery or the like. It has been found that the discharge capacity is increased.

<Modification>
(A)
As shown in FIG. 2, in the negative electrode 100 a, an undercoat layer 400 may be formed between the active material layer 200 and the current collector 300. The undercoat layer 400 is obtained by heating the coating solution, and improves the binding property between the active material layer 200 and the current collector 300. The undercoat layer 400 is formed of a resin that can be satisfactorily bonded to the polyimide resin 220 and a conductive filler that imparts conductivity to the undercoat layer 400.

  The coating solution contains a conductive filler, a polyimide precursor, and a second solvent. What can be used as a conductive filler of said slurry can be used as a conductive filler of a coating solution. The conductive filler of the coating solution may be the same as the conductive filler of the slurry, or may be different from the conductive filler of the slurry. The second solvent dissolves the polyimide precursor. As the material for the second solvent, those that can be used as the material for the first solvent can be used. The material of the second solvent may be the same as the material of the first solvent, or may be different from the material of the first solvent.

  As the polyimide precursor, polyamic acid is preferably used. For example, the polyamic acid is imidized by heating to become a polyimide resin.

  This coating solution containing polyamic acid has better coating properties than a coating solution containing a monomeric polyimide precursor.

  The negative electrode 100a is obtained by forming the undercoat layer 400 on the current collector 300, applying the slurry on the undercoat layer 400, and heating the slurry. Specifically, the negative electrode 100a is formed through an undercoat layer forming step, a first coating step, and a first heating step in this order. The undercoat layer forming step includes a second coating step and a second heating step. In the second application process, the coating solution is applied to the current collector 300. In the second heating step, the coating solution applied to the current collector 300 is heated to form the undercoat layer 400. In the first application step, the slurry is applied on the undercoat layer 400.

  In the second coating step, it is preferable to apply the coating solution to the current collector 300 so that the thickness of the undercoat layer 400 is a thickness that flattens the unevenness on the surface of the current collector 300. The thickness of the undercoat layer 400 is preferably as small as possible. For example, the undercoat layer 400 is formed with a thickness of 0.5 μm to 2 μm.

  As a result of intensive studies by the inventors of the present application, it has been clarified that the undercoat layer 400 improves the adhesion of the active material layer 200 to the current collector 300.

  The undercoat layer 400 improves the adhesion of the active material layer 200 to the current collector 300 by flattening the unevenness of the surface of the current collector 300, and the active material layer provided on the undercoat layer 400 200 manufacturing accuracy is improved.

  Next, examples and comparative examples according to the negative electrode 100 of the present invention will be described. In addition, this invention is not limited at all by the Example.

Example 1
<Production of lithium secondary battery>
1. Preparation of Monomer Type Polyimide Precursor Solution A 200 mL three-necked flask was equipped with a stirring bar equipped with a stirring blade made of polytetrafluoroethylene to prepare a synthesis container. In this synthesis container, 10.19 g (0.032 mol) of 3,3 ′, 4,4′-benzophenone tetracarboxylic dianhydride (BTDA) (BTDA) (so that the solid content of the polyimide precursor solution is 28% by weight) Daicel Chemical Industries, Ltd.) and 2.91 g (0.063 mol) of ethanol (Ueno Chemical Industries, Ltd.) were added, and the contents in the synthesis vessel were stirred for 1 hour while heating at 90 ° C. A BTDA diester solution was prepared.

  After the BTDA diester solution is cooled to 45 ° C. or lower, 4.81 g (0.032 mol) of 3,5-diaminobenzoic acid (3,5-DABA) (manufactured by Tokyo Chemical Industry Co., Ltd.) is added to the BTDA diester solution. The mixture was stirred for 1 hour while being heated to 50 ° C. again to prepare a monomer type polyimide precursor solution. Moreover, the glass transition point (Tg) of the film produced from this monomer type polyimide precursor solution was 339 degreeC.

2. Production of Negative Electrode 37.3 g of silicon powder (purity 99.9%) having an average particle diameter of 2.1 μm (manufactured by Fukuda Metal Foil Powder Co., Ltd.) and primary particle diameter of 7.3 g of the monomer type polyimide precursor solution described above After adding 2.4 g of 39.5 nm ketjen black (Fukuda Metal Foil Powder Co., Ltd.) and mixing well with a planetary (automatic revolving) mixer (Sinky Co., Ltd.), the negative electrode mixture slurry Prepared.

  The negative electrode mixture slurry was applied to one surface (rough surface) of an electrolytic copper foil (thickness 35 μm) having a rough surface roughness (arithmetic mean roughness) Rz of 4.0 μm as a current collector, and the thickness after drying was 19 μm. After being applied, the negative electrode intermediate was prepared by drying. The negative electrode intermediate was cut into a circular shape of φ11, heat-treated (fired) at 300 ° C. for 1 hour in a nitrogen atmosphere, and sintered to produce a negative electrode.

3. Counter electrode The counter electrode was produced by cutting out a lithium metal foil having a thickness of 0.5 mm into a circular shape having a diameter of 13 mm.

4). Volume ratio and preparation of ethylene carbonate and diethyl carbonate in the nonaqueous electrolytic solution 1: For solvent were formulated in 1, LiPF ₆ was used a non-aqueous electrolyte prepared by dissolving LiPF ₆ to be 1 mol / L.

5. Production of Lithium Secondary Battery A negative electrode, a counter electrode and a non-aqueous electrolyte produced as described above were assembled inside a CR2032 type SUS coin cell to produce a lithium secondary battery. In addition, the positive electrode and the counter electrode were disposed so as to face each other with a polypropylene separator (Celgard 2400: manufactured by Celgard) reinforced with a glass fiber fabric.

<Charge / discharge cycle test of lithium secondary battery>
The charge / discharge cycle test of the lithium secondary battery obtained as described above was performed. In the charge / discharge cycle test, the environmental temperature is set to 30 ° C., the charge / discharge rate is set to 0.1C, the cut-off voltage is set to 0.0V for charge, 1.0V for discharge, and the charge / discharge cycle is set to 50 times. The discharge capacity (mAh / g) was measured every time. Further, as a maintenance factor, “a ratio of the discharge capacity of the 30th cycle to the discharge capacity of the second cycle” and “a ratio of the discharge capacity of the 50th cycle to the discharge capacity of the second cycle” were obtained. In addition, the capacity density per electrode area of this lithium secondary battery was 2.32 mAh / cm ² (see Table 1).

  As a result, the discharge capacity of the first cycle is 4176.3 mAh / g, the discharge capacity of the second cycle is 3592.3 mAh / g, the discharge capacity of the 30th cycle is 3247.0 mAh / g, The cycle discharge capacity was 2815.4 mAh / g. Further, the ratio (maintenance rate) of the discharge capacity of the 30th cycle to the discharge capacity of the 2nd cycle is 90.39% (= 3247.0 / 3592.3 × 100), and the 50th to the discharge capacity of the second cycle. The ratio (maintenance rate) of the discharge capacity of the cycle was 78.37% (= 2815.4 / 3592.3 × 100) (see Table 1).

(Example 2)
A lithium secondary battery was obtained in the same manner as Example 1 except for the following. The negative electrode mixture slurry was applied to one side of the current collector 300 so that the thickness after drying was 1 μm and then dried to prepare a negative electrode intermediate. In addition, the capacity density per electrode area of this lithium secondary battery was 2.07 mAh / cm ² (see Table 1).

  In the same manner as in Example 1, the charge / discharge cycle characteristics of the lithium secondary battery were measured. As a result, the discharge capacity of the first cycle is 4448.6 mAh / g, the discharge capacity of the second cycle is 3820.2 mAh / g, the discharge capacity of the 30th cycle is 3448.6 mAh / g, The cycle discharge capacity was 2975.5 mAh / g. Further, the ratio (maintenance rate) of the discharge capacity of the 30th cycle to the discharge capacity of the 2nd cycle is 90.27% (= 3448.6 / 3820.2 × 100), and the 50th to the discharge capacity of the second cycle. The ratio (maintenance rate) of the discharge capacity of the cycle was 77.89% (= 2975.5 / 3820.2 × 100) (see Table 1).

(Example 3)
A lithium secondary battery was obtained in the same manner as Example 1 except for the following. The negative electrode mixture slurry was applied to one surface of the current collector 300 so that the thickness after drying was 2 μm and then dried to prepare a negative electrode intermediate. In addition, the capacity density per electrode area of this lithium secondary battery was 2.25 mAh / cm ² (see Table 1).

  In the same manner as in Example 1, the charge / discharge cycle characteristics of the lithium secondary battery were measured. As a result, the discharge capacity of the first cycle is 4323.9 mAh / g, the discharge capacity of the second cycle is 3692.1 mAh / g, the discharge capacity of the 30th cycle is 3321.9 mAh / g, The cycle discharge capacity was 2867.4 mAh / g. Further, the ratio (maintenance rate) of the discharge capacity of the 30th cycle to the discharge capacity of the 2nd cycle is 89.97% (= 3321.9 / 3692.1 × 100), and the 50th to the discharge capacity of the second cycle. The ratio (maintenance rate) of the discharge capacity of the cycle was 77.66% (= 2867.4 / 3692.1 × 100) (see Table 1).

Example 4
A lithium secondary battery was obtained in the same manner as Example 1 except for the following. The negative electrode mixture slurry was applied to one side of the current collector 300 so that the thickness after drying was 4 μm and then dried to prepare a negative electrode intermediate. Further, the negative electrode intermediate was cut into a circular shape of φ11 and heated at 350 ° C. for 4 hours in a nitrogen atmosphere to prepare the negative electrode 100. In addition, the capacity density per electrode area of this lithium secondary battery was 2.02 mAh / cm ² (see Table 1).

  In the same manner as in Example 1, the charge / discharge cycle characteristics of the lithium secondary battery were measured. As a result, the discharge capacity of the first cycle is 4689.5 mAh / g, the discharge capacity of the second cycle is 4074.1 mAh / g, the discharge capacity of the 30th cycle is 3720.4 mAh / g, The cycle discharge capacity was 3173.9 mAh / g. Further, the ratio (maintenance rate) of the discharge capacity of the 30th cycle to the discharge capacity of the 2nd cycle is 91.32% (= 3720.4 / 4074.1 × 100), and the 50th of the discharge capacity of the second cycle. The ratio (maintenance rate) of the discharge capacity of the cycle was 77.90% (= 3173.9 / 4074.1 × 100) (see Table 1).

(Example 5)
A lithium secondary battery was obtained in the same manner as Example 1 except for the following. The negative electrode mixture slurry was applied to one surface of the current collector 300 so that the thickness after drying was 3 μm and then dried to prepare a negative electrode intermediate. Further, the negative electrode intermediate was cut into a circular shape of φ11 and heated at 350 ° C. for 4 hours in a nitrogen atmosphere to prepare the negative electrode 100. The capacity density per electrode area of the lithium secondary battery was 1.87 mAh / cm ² (see Table 1).

  In the same manner as in Example 1, the charge / discharge cycle characteristics of the lithium secondary battery were measured. As a result, the discharge capacity of the first cycle is 5258.3 mAh / g, the discharge capacity of the second cycle is 4539.7 mAh / g, the discharge capacity of the 30th cycle is 4153.2 mAh / g, The cycle discharge capacity was 3552.8 mAh / g. Further, the ratio (maintenance rate) of the discharge capacity of the 30th cycle to the discharge capacity of the 2nd cycle is 91.49% (= 4153.2 / 4539.7 × 100), and the 50th to the discharge capacity of the second cycle. The ratio (maintenance rate) of the discharge capacity of the cycle was 78.26% (= 3552.8 / 4539.7 × 100) (see Table 1).

(Example 6)
A lithium secondary battery was obtained in the same manner as Example 1 except for the following. The negative electrode mixture slurry was applied to one side of the current collector 300 so that the thickness after drying was 1 μm and then dried to prepare a negative electrode intermediate. Further, the negative electrode intermediate was cut into a circular shape of φ11 and heated at 350 ° C. for 4 hours in a nitrogen atmosphere to prepare the negative electrode 100. In addition, the capacity density per electrode area of the lithium secondary battery was 2.00 mAh / cm ² (see Table 1).

  In the same manner as in Example 1, the charge / discharge cycle characteristics of the lithium secondary battery were measured. As a result, the discharge capacity of the first cycle is 4850.2 mAh / g, the discharge capacity of the second cycle is 4186.4 mAh / g, the discharge capacity of the 30th cycle is 3777.2 mAh / g, The cycle discharge capacity was 3307.7 mAh / g. The ratio (maintenance rate) of the discharge capacity of the 30th cycle to the discharge capacity of the 2nd cycle is 90.22% (= 3777.2 / 4186.4 × 100), and the 50th to the discharge capacity of the second cycle. The ratio (maintenance rate) of the discharge capacity of the cycle was 79.01% (= 3307.7 / 4186.4 × 100) (see Table 1).

(Example 7)
A lithium secondary battery was obtained in the same manner as Example 1 except for the following. For the negative electrode mixture slurry, silicon powder (purity 99.9%) having an average particle diameter of 0.9 μm (manufactured by Fukuda Metal Foil Powder Co., Ltd.) was used. The negative electrode mixture slurry was applied to one side of the current collector 300 so that the thickness after drying was 1 μm and then dried to prepare a negative electrode intermediate. Further, the negative electrode intermediate was cut into a circular shape of φ11, and heated at 200 ° C. for 10 hours in a nitrogen atmosphere to prepare the negative electrode 100. In addition, the capacity density per electrode area of this lithium secondary battery was 1.82 mAh / cm ² (see Table 2).

  In the same manner as in Example 1, the charge / discharge cycle characteristics of the lithium secondary battery were measured. As a result, the discharge capacity of the first cycle is 4425.8 mAh / g, the discharge capacity of the second cycle is 3843.5 mAh / g, the discharge capacity of the 30th cycle is 3364.5 mAh / g, The cycle discharge capacity was 3021.8 mAh / g. The ratio (maintenance rate) of the discharge capacity of the 30th cycle to the discharge capacity of the 2nd cycle is 87.54% (= 3364.5 / 3843.5 × 100), and the 50th to the discharge capacity of the second cycle. The cycle discharge capacity ratio (retention rate) was 78.62% (= 3021.8 / 3843.5 × 100) (see Table 2).

(Example 8)
A lithium secondary battery was obtained in the same manner as Example 1 except for the following. For the negative electrode mixture slurry, silicon powder (purity 99.9%) having an average particle diameter of 0.9 μm (manufactured by Fukuda Metal Foil Powder Co., Ltd.) was used. The negative electrode mixture slurry was applied to one surface of the current collector 300 so that the thickness after drying was 3 μm and then dried to prepare a negative electrode intermediate. Further, the negative electrode intermediate was cut into a circular shape of φ11, and heated at 200 ° C. for 10 hours in a nitrogen atmosphere to prepare the negative electrode 100. In addition, the capacity density per electrode area of this lithium secondary battery was 2.12 mAh / cm ² (see Table 2).

  In the same manner as in Example 1, the charge / discharge cycle characteristics of the lithium secondary battery were measured. As a result, the discharge capacity of the first cycle is 3541.5 mAh / g, the discharge capacity of the second cycle is 3076.5 mAh / g, the discharge capacity of the tenth cycle is 3026.4 mAh / g, The discharge capacity of the cycle was 2803.4 mAh / g, and the discharge capacity of the 50th cycle was 2424.6 mAh / g. Further, the ratio (maintenance ratio) of the discharge capacity of the 10th cycle to the discharge capacity of the 2nd cycle is 98.37% (= 3026.4 / 3076.5 × 100), and the 30th to the discharge capacity of the second cycle. The ratio (maintenance rate) of the discharge capacity of the cycle is 91.12% (= 2803.4 / 3076.5 × 100), and the ratio (maintenance rate) of the discharge capacity of the 50th cycle to the discharge capacity of the second cycle is It was 78.81% (= 2424.6 / 3076.5 × 100) (see Table 2).

Example 9
A lithium secondary battery was obtained in the same manner as Example 1 except for the following. For the negative electrode mixture slurry, silicon powder (purity 99.9%) having an average particle diameter of 0.9 μm (manufactured by Fukuda Metal Foil Powder Co., Ltd.) was used. The negative electrode mixture slurry was applied to one side of the current collector 300 so that the thickness after drying was 1 μm and then dried to prepare a negative electrode intermediate. In addition, the capacity density per electrode area of this lithium secondary battery was 1.69 mAh / cm ² (see Table 2).

  In the same manner as in Example 1, the charge / discharge cycle characteristics of the lithium secondary battery were measured. As a result, the discharge capacity of the first cycle is 4700.7 mAh / g, the discharge capacity of the second cycle is 414.8 mAh / g, the discharge capacity of the 30th cycle is 3401.5 mAh / g, The cycle discharge capacity was 2955.6 mAh / g. Further, the ratio (maintenance ratio) of the discharge capacity of the 30th cycle to the discharge capacity of the 2nd cycle is 82.46% (= 3401.5 / 414.8 × 100), and the 50th to the discharge capacity of the second cycle. The cycle discharge capacity ratio (retention rate) was 71.65% (= 2955.6 / 414.8 × 100) (see Table 2).

(Example 10)
A lithium secondary battery was obtained in the same manner as Example 1 except for the following. Silicon powder (purity 99.9%) having an average particle diameter of 0.9 μm (manufactured by Fukuda Metal Foil Powder Co., Ltd.) was used for the negative electrode mixture slurry. The negative electrode mixture slurry was applied to one side of the current collector 300 so that the thickness after drying was 1 μm and then dried to prepare a negative electrode intermediate. In addition, the capacity density per electrode area of this lithium secondary battery was 2.00 mAh / cm ² (see Table 2).

  In the same manner as in Example 1, the charge / discharge cycle characteristics of the lithium secondary battery were measured. As a result, the discharge capacity in the first cycle was 3898.5 mAh / g, the discharge capacity in the second cycle was 3384.8 mAh / g, the discharge capacity in the 30th cycle was 2997.9 mAh / g, The cycle discharge capacity was 2559.5 mAh / g. Further, the ratio (maintenance ratio) of the discharge capacity of the 30th cycle to the discharge capacity of the 2nd cycle is 88.57% (= 2997.9 / 3384.8 × 100), and the 50th to the discharge capacity of the second cycle. The cycle discharge capacity ratio (retention rate) was 75.62% (= 2559.5 / 3384.8 × 100) (see Table 2).

(Example 11)
A lithium secondary battery was obtained in the same manner as Example 1 except for the following. For the negative electrode mixture slurry, silicon powder (purity 99.9%) having an average particle diameter of 0.9 μm (manufactured by Fukuda Metal Foil Powder Co., Ltd.) was used. The negative electrode mixture slurry was applied to one side of the current collector 300 so that the thickness after drying was 1 μm and then dried to prepare a negative electrode intermediate. Further, the negative electrode intermediate was cut into a circular shape of φ11 and heated at 350 ° C. for 4 hours in a nitrogen atmosphere to prepare the negative electrode 100. In addition, the capacity density per electrode area of this lithium secondary battery was 1.77 mAh / cm ² (see Table 2).

  In the same manner as in Example 1, the charge / discharge cycle characteristics of the lithium secondary battery were measured. As a result, the discharge capacity of the first cycle is 4282.7 mAh / g, the discharge capacity of the second cycle is 3748.8 mAh / g, the discharge capacity of the 30th cycle is 3113.2 mAh / g, The cycle discharge capacity was 2704.6 mAh / g. Further, the ratio (maintenance ratio) of the discharge capacity of the 30th cycle to the discharge capacity of the 2nd cycle is 83.05% (= 3113.2 / 3748.8 × 100), and the 50th to the discharge capacity of the second cycle. The cycle discharge capacity ratio (maintenance rate) was 72.15% (= 2704.6 / 3748.8 × 100) (see Table 2).

(Example 12)
A lithium secondary battery was obtained in the same manner as Example 1 except for the following. For the negative electrode mixture slurry, silicon powder (purity 99.9%) having an average particle diameter of 0.9 μm (manufactured by Fukuda Metal Foil Powder Co., Ltd.) was used. The negative electrode mixture slurry was applied to one side of the current collector 300 so that the thickness after drying was 1 μm and then dried to prepare a negative electrode intermediate. Further, the negative electrode intermediate was cut into a circular shape of φ11 and heated at 350 ° C. for 4 hours in a nitrogen atmosphere to prepare the negative electrode 100. In addition, the capacity density per electrode area of this lithium secondary battery was 1.95 mAh / cm ² (see Table 2).

  In the same manner as in Example 1, the charge / discharge cycle characteristics of the lithium secondary battery were measured. As a result, the discharge capacity of the first cycle is 3714.4 mAh / g, the discharge capacity of the second cycle is 3231.6 mAh / g, the discharge capacity of the 30th cycle is 2835.7 mAh / g, The cycle discharge capacity was 2405.2 mAh / g. The ratio (maintenance rate) of the discharge capacity of the 30th cycle to the discharge capacity of the 2nd cycle is 87.75% (= 2835.7 / 3231.6 × 100), and the 50th to the discharge capacity of the second cycle. The cycle discharge capacity ratio (maintenance rate) was 74.43% (= 2405.2 / 3231.6 × 100) (see Table 2).

(Example 13)
A lithium secondary battery was obtained in the same manner as Example 1 except for the following. For the negative electrode mixture slurry, silicon powder (purity 99.9%) having an average particle diameter of 0.9 μm (manufactured by Fukuda Metal Foil Powder Co., Ltd.) was used. The negative electrode mixture slurry was applied to one side of the current collector 300 so that the thickness after drying was 1 μm and then dried to prepare a negative electrode intermediate. Further, the negative electrode intermediate was cut into a circular shape of φ11, and heated at 400 ° C. for 1 hour in a nitrogen atmosphere to prepare the negative electrode 100. In addition, the capacity density per electrode area of this lithium secondary battery was 1.69 mAh / cm ² (see Table 2).

  In the same manner as in Example 1, the charge / discharge cycle characteristics of the lithium secondary battery were measured. As a result, the discharge capacity of the first cycle is 4424.0 mAh / g, the discharge capacity of the second cycle is 3873.1 mAh / g, the discharge capacity of the 30th cycle is 3226.9 mAh / g, The cycle discharge capacity was 2686.3 mAh / g. Further, the ratio (maintenance ratio) of the discharge capacity of the 30th cycle to the discharge capacity of the 2nd cycle is 83.32% (= 3226.9 / 3873.1 × 100), and the 50th to the discharge capacity of the second cycle. The cycle discharge capacity ratio (maintenance ratio) was 69.36% (= 2686.3 / 3873.1 × 100) (see Table 2).

(Example 14)
A lithium secondary battery was obtained in the same manner as Example 1 except for the following. For the negative electrode mixture slurry, silicon powder (purity 99.9%) having an average particle diameter of 0.9 μm (manufactured by Fukuda Metal Foil Powder Co., Ltd.) was used. The negative electrode mixture slurry was applied to one side of the current collector 300 so that the thickness after drying was 1 μm and then dried to prepare a negative electrode intermediate. Further, the negative electrode intermediate was cut into a circular shape of φ11, and heated at 400 ° C. for 1 hour in a nitrogen atmosphere to prepare the negative electrode 100. In addition, the capacity density per electrode area of this lithium secondary battery was 1.87 mAh / cm ² (see Table 2).

  In the same manner as in Example 1, the charge / discharge cycle characteristics of the lithium secondary battery were measured. As a result, the discharge capacity of the first cycle is 3870.7 mAh / g, the discharge capacity of the second cycle is 3391.8 mAh / g, the discharge capacity of the 30th cycle is 2977.3 mAh / g, The cycle discharge capacity was 2524.6 mAh / g. Further, the ratio (maintenance ratio) of the discharge capacity of the 30th cycle to the discharge capacity of the 2nd cycle is 87.78% (= 2977.3 / 3391.8 × 100), and the 50th to the discharge capacity of the second cycle. The cycle discharge capacity ratio (maintenance rate) was 74.43% (= 2524.6 / 3391.8 × 100) (see Table 2).

(Example 15)
A lithium secondary battery was obtained in the same manner as Example 1 except for the following. For the negative electrode mixture slurry, silicon powder (purity 99.9%) having an average particle diameter of 0.9 μm (manufactured by Fukuda Metal Foil Powder Co., Ltd.) was used. The negative electrode mixture slurry was applied to one side of the current collector 300 so that the thickness after drying was 4 μm and then dried to prepare a negative electrode intermediate. Further, the negative electrode intermediate was cut into a circular shape of φ11, and heated at 200 ° C. for 10 hours in a nitrogen atmosphere to prepare the negative electrode 100. In addition, the capacity density per electrode area of this lithium secondary battery was 1.67 mAh / cm ² (see Table 2).

  In the same manner as in Example 1, the charge / discharge cycle characteristics of the lithium secondary battery were measured. As a result, the discharge capacity of the first cycle was 3736.7 mAh / g, the discharge capacity of the second cycle was 3195.2 mAh / g, and the discharge capacity of the 10th cycle was 3083.1 mAh / g. Further, the ratio (maintenance rate) of the discharge capacity of the 10th cycle to the discharge capacity of the 2nd cycle was 96.49% (= 3083.1 / 3195.2 × 100) (see Table 2).

(Example 16)
A lithium secondary battery was obtained in the same manner as Example 1 except for the following. Silicon powder (purity 99.9%) having an average particle diameter of 0.9 μm (manufactured by Fukuda Metal Foil Powder Co., Ltd.) was used for the negative electrode mixture slurry. The negative electrode mixture slurry was applied to one side of the current collector 300 so that the thickness after drying was 4 μm and then dried to prepare a negative electrode intermediate. Further, the negative electrode intermediate was cut into a circular shape of φ11, and heated at 200 ° C. for 10 hours in a nitrogen atmosphere to prepare the negative electrode 100. In addition, the capacity density per electrode area of this lithium secondary battery was 1.49 mAh / cm ² (see Table 2).

  In the same manner as in Example 1, the charge / discharge cycle characteristics of the lithium secondary battery were measured. As a result, the discharge capacity of the first cycle was 4022.2 mAh / g, the discharge capacity of the second cycle was 3490.8 mAh / g, and the discharge capacity of the 10th cycle was 3441.9 mAh / g. Further, the ratio (maintenance rate) of the discharge capacity of the 10th cycle to the discharge capacity of the 2nd cycle was 98.60% (= 3441.9 / 3490.8 × 100) (see Table 2).

(Comparative Example 1)
A lithium secondary battery was obtained in the same manner as Example 1 except for the following. The negative electrode mixture slurry was applied to one surface of the current collector 300 so that the thickness after drying was 19 μm and then dried to prepare a negative electrode intermediate. In addition, the capacity density per electrode area of this lithium secondary battery was 4.62 mAh / cm ² (see Table 3).

  In the same manner as in Example 1, the charge / discharge cycle characteristics of the lithium secondary battery were measured. As a result, the discharge capacity of the first cycle is 4309.6 mAh / g, the discharge capacity of the second cycle is 3584.8 mAh / g, the discharge capacity of the 30th cycle is 3115.0 mAh / g, The cycle discharge capacity was 2689.8 mAh / g. Further, the ratio (maintenance rate) of the discharge capacity of the 30th cycle to the discharge capacity of the 2nd cycle is 86.89% (= 3115.0 / 3584.8 × 100), and the 50th of the discharge capacity of the second cycle. The ratio (maintenance rate) of the discharge capacity of the cycle was 75.03% (= 2689.8 / 3584.8 × 100) (see Table 3).

(Comparative Example 2)
A lithium secondary battery was obtained in the same manner as Example 1 except for the following. The negative electrode mixture slurry was applied to one side of the current collector 300 so that the thickness after drying was 14 μm and then dried to prepare a negative electrode intermediate. In addition, the capacity density per electrode area of this lithium secondary battery was 4.70 mAh / cm ² (see Table 3).

  In the same manner as in Example 1, the charge / discharge cycle characteristics of the lithium secondary battery were measured. As a result, the discharge capacity of the first cycle is 4194.7 mAh / g, the discharge capacity of the second cycle is 3470.1 mAh / g, the discharge capacity of the 30th cycle is 3026.7 mAh / g, The cycle discharge capacity was 2614.1 mAh / g. Further, the ratio (maintenance rate) of the discharge capacity of the 30th cycle to the discharge capacity of the 2nd cycle is 87.22% (= 3026.7 / 3470.1 × 100), and the 50th to the discharge capacity of the second cycle. The ratio (maintenance rate) of the discharge capacity of the cycle was 75.33% (= 2614.1 / 3470.1 × 100) (see Table 3).

(Comparative Example 3)
A lithium secondary battery was obtained in the same manner as Example 1 except for the following. The negative electrode mixture slurry was applied to one side of the current collector 300 so that the thickness after drying was 23 μm and then dried to prepare a negative electrode intermediate. Further, the negative electrode intermediate was cut into a circular shape of φ11 and heated at 350 ° C. for 4 hours in a nitrogen atmosphere to prepare the negative electrode 100. In addition, the capacity density per electrode area of this lithium secondary battery was 4.75 mAh / cm ² (see Table 3).

  In the same manner as in Example 1, the charge / discharge cycle characteristics of the lithium secondary battery were measured. As a result, the discharge capacity of the first cycle is 4238.8 mAh / g, the discharge capacity of the second cycle is 3500.8 mAh / g, the discharge capacity of the 30th cycle is 3014.6 mAh / g, The cycle discharge capacity was 2601.3 mAh / g. The ratio (maintenance rate) of the discharge capacity of the 30th cycle to the discharge capacity of the 2nd cycle is 86.11% (= 3014.6 / 3500.8 × 100), and the 50th to the discharge capacity of the second cycle. The ratio (maintenance rate) of the discharge capacity of the cycle was 74.31% (= 2601.3 / 3500.8 × 100) (see Table 3).

(Comparative Example 4)
A lithium secondary battery was obtained in the same manner as Example 1 except for the following. The negative electrode mixture slurry was applied to one surface of the current collector 300 so that the thickness after drying was 16 μm and then dried to prepare a negative electrode intermediate. Further, the negative electrode intermediate was cut into a circular shape of φ11 and heated at 350 ° C. for 4 hours in a nitrogen atmosphere to prepare the negative electrode 100. In addition, the capacity density per electrode area of this lithium secondary battery was 4.80 mAh / cm ² (see Table 3).

  In the same manner as in Example 1, the charge / discharge cycle characteristics of the lithium secondary battery were measured. As a result, the discharge capacity of the first cycle is 4121.4 mAh / g, the discharge capacity of the second cycle is 3414.3 mAh / g, the discharge capacity of the 30th cycle is 2945.5 mAh / g, The cycle discharge capacity was 2544.7 mAh / g. Further, the ratio (maintenance rate) of the discharge capacity of the 30th cycle to the discharge capacity of the 2nd cycle is 86.27% (= 2945.5 / 3414.3 × 100), and the 50th to the discharge capacity of the second cycle. The ratio (maintenance rate) of the discharge capacity of the cycle was 74.53% (= 2544.7 / 3414.3 × 100) (see Table 3).

(Comparative Example 5)
A lithium secondary battery was obtained in the same manner as Example 1 except for the following. The negative electrode mixture slurry was applied to one surface of the current collector 300 so that the thickness after drying was 15 μm and then dried to prepare a negative electrode intermediate. Further, the negative electrode intermediate was cut into a circular shape of φ11 and heated at 350 ° C. for 4 hours in a nitrogen atmosphere to prepare the negative electrode 100. In addition, the capacity density per electrode area of this lithium secondary battery was 4.90 mAh / cm ² (see Table 3).

  In the same manner as in Example 1, the charge / discharge cycle characteristics of the lithium secondary battery were measured. As a result, the discharge capacity of the first cycle was 4144.9 mAh / g, the discharge capacity of the second cycle was 3412.6 mAh / g, the discharge capacity of the 30th cycle was 2959.5 mAh / g, The cycle discharge capacity was 2531.3 mAh / g. The ratio (maintenance rate) of the discharge capacity of the 30th cycle to the discharge capacity of the 2nd cycle is 86.72% (= 2959.5 / 3412.6 × 100), and the 50th of the discharge capacity of the second cycle. The ratio (maintenance rate) of the discharge capacity of the cycle was 74.18% (= 2531.3 / 3412.6 × 100) (see Table 3).

(Example 17)
A lithium secondary battery was obtained in the same manner as Example 1 except for the following. A monomer type polyimide precursor solution was prepared by replacing 2.3732 g (0.0156 mol) of 3,5-diaminobenzoic acid (3,5-DABA) with m-phenylenediamine (m-PDA). The negative electrode mixture slurry was applied to one surface of the current collector 300 so that the thickness after drying was 6 μm and then dried to prepare a negative electrode intermediate. In addition, the capacity density per electrode area of the lithium secondary battery was 2.02 mAh / cm ² (see Table 4).

  Except for the following, the charge / discharge cycle characteristics of the lithium secondary battery were measured in the same manner as in Example 1. In the charge / discharge cycle test, an environmental temperature was set to 25 ° C., a charge / discharge rate was set to 0.1 C, and a charge / discharge cycle was performed 100 times with a cut-off voltage of 0.0 V during charge and 1.0 V during discharge. As a result, the discharge capacity of the first cycle is 3994.1 mAh / g, the discharge capacity of the second cycle is 3408.6 mAh / g, the discharge capacity of the 30th cycle is 2573.4 mAh / g, The discharge capacity of the cycle was 2133.0 mAh / g, and the discharge capacity of the 100th cycle was 1565.5 mAh / g. The ratio (maintenance rate) of the discharge capacity of the 30th cycle to the discharge capacity of the 2nd cycle is 75.50% (= 2573.4 / 3408.6 × 100), and the 50th to the discharge capacity of the second cycle. The ratio (maintenance rate) of the discharge capacity of the cycle was 62.58% (= 2133.0 / 3408.6 × 100) (see Table 4).

(Example 18)
A lithium secondary battery was obtained in the same manner as Example 17 except for the following. To 2.3 g of the monomer type polyimide precursor solution described above, 12.4 g of silicon powder having an average particle size of 0.9 μm (purity 99.9%) (manufactured by Fukuda Metal Foil Powder Industry Co., Ltd.) and a primary particle size of 39.5 nm After adding 0.8 g of ketjen black (made by Fukuda Metal Foil Powder Co., Ltd.), the mixture was mixed well with a planetary (auto revolving) mixer (made by Shinky Co., Ltd.) to prepare a negative electrode mixture slurry. The negative electrode mixture slurry was applied to one surface of the current collector 300 so that the thickness after drying was 3 μm and then dried to prepare a negative electrode intermediate. In addition, the capacity density per electrode area of this lithium secondary battery was 1.62 mAh / cm ² (see Table 4).

  In the same manner as in Example 1, the charge / discharge cycle characteristics of the lithium secondary battery were measured. As a result, the discharge capacity of the first cycle is 4225.8 mAh / g, the discharge capacity of the second cycle is 3670.2 mAh / g, the discharge capacity of the 30th cycle is 3082.8 mAh / g, The discharge capacity of the cycle was 2645.7 mAh / g, and the discharge capacity of the 100th cycle was 2011. 2 mAh / g. Further, the ratio (maintenance rate) of the discharge capacity of the 30th cycle to the discharge capacity of the 2nd cycle is 84.00% (= 3082.8 / 3670.2 × 100), and the 50th to the discharge capacity of the second cycle. The ratio (maintenance rate) of the discharge capacity of the cycle was 72.08% (= 2645.7 / 3670.2 × 100) (see Table 4).

(Comparative Example 6)
A lithium secondary battery was obtained in the same manner as Example 17 except for the following. The negative electrode mixture slurry was applied to one side of the current collector 300 so that the thickness after drying was 21 μm and then dried to prepare a negative electrode intermediate. In addition, the capacity density per electrode area of this lithium secondary battery was 5.46 mAh / cm ² (see Table 4).

  In the same manner as in Example 1, the charge / discharge cycle characteristics of the lithium secondary battery were measured. As a result, the discharge capacity of the first cycle is 3925.4 mAh / g, the discharge capacity of the second cycle is 3208.3 mAh / g, the discharge capacity of the 30th cycle is 2333.4 mAh / g, and the 50th cycle The discharge capacity was 1957.9 mAh / g, and the discharge capacity of the 100th cycle was 1234.5 mAh / g. Further, the ratio (maintenance rate) of the discharge capacity of the 30th cycle to the discharge capacity of the 2nd cycle is 72.73% (= 2333.4 / 3208.3 × 100), and the 50th to the discharge capacity of the second cycle. The ratio (maintenance rate) of the discharge capacity of the cycle was 61.03% (= 1957.9 / 3208.3 × 100) (see Table 4).

  From the above-mentioned results, it is clear that the negative electrode 100 according to the present invention further dramatically improves the charge / discharge cycle of the lithium secondary battery and increases the discharge capacity of the lithium secondary battery than the conventional negative electrode. It was.

100, 100a electrode (negative electrode)
200 Active Material Layer 210 Active Material Particles 220 Polyimide Resin 300 Current Collector 400 Undercoat Layer

Claims (6)

A current collector,
An active material layer having an average particle diameter of more than 0 μm and less than 10 μm, and a porous polyimide resin that binds the active material particles to each other, and is formed on the current collector ,
The active material layer is an electrode having a thickness of more than 0 μm and less than 10 μm. A slurry containing at least active material particles having an average particle diameter of more than 0 μm and less than 10 μm, a tetracarboxylic acid ester compound, a diamine compound, and a first solvent that dissolves the tetracarboxylic acid ester compound and the diamine compound is collected. A first application step of applying to the electric body;
A first heating step of heating the slurry applied to the current collector to form an active material layer having a thickness of more than 0 μm and less than 10 μm. Further comprising an undercoat layer forming step of forming an undercoat layer on the current collector,
The electrode forming method according to claim 2, wherein in the first application step, the slurry is applied onto the undercoat layer. The undercoat layer forming step includes applying a coating solution containing a conductive filler, a polyimide precursor, and a second solvent for dissolving the polyimide precursor to the current collector;
The electrode forming method according to claim 3, further comprising a second heating step of heating the coating solution applied to the current collector to form the undercoat layer.   The electrode forming method according to claim 4, wherein the polyimide precursor of the coating solution is a polyamic acid.   The said coating solution is apply | coated to the said electrical power collector so that the thickness of the said undercoat layer may become the thickness which makes the unevenness | corrugation of the said electrical power collector surface flat in a said 2nd application | coating process. Electrode forming method.

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