JP2014022254A - Current collector, method for manufacturing the same, and power storage device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a current collector which can also be used for an electrode of a lithium ion secondary battery and can effectively prevent an active material layer from being peeled off.SOLUTION: In a current collector, iron base powder is sintered, the porosity is 30 to 55 vol.%, and a conductive metal layer is provided in at least a part of an inner peripheral surface of a hole. An active material can be filled largely since the porosity is high 30 to 55 vol.%, and power supplying to and receiving from the active material is smoothly performed by the conductive metal layer. For that reason, charge/discharge capacity is improved and an active material layer is inhibited from being peeled off since the active material can be retained in the hole.

Description

  The present invention relates to a current collector used for an electrode of a power storage device such as a lithium ion secondary battery, a manufacturing method thereof, and a power storage device using the current collector as an electrode.

  A lithium ion secondary battery is a secondary battery having a high charge / discharge capacity and capable of high output. Currently, it is mainly used as a power source for portable electronic devices, and further expected as a power source for electric vehicles that are expected to be widely used in the future. Lithium ion secondary batteries have active materials capable of inserting and extracting lithium (Li) in the positive electrode and the negative electrode, respectively. And it operates by moving lithium ions in the electrolyte provided between the two electrodes.

  In lithium ion secondary batteries, lithium-containing metal composite oxides such as lithium cobalt composite oxide are mainly used as the active material for the positive electrode, and carbon materials having a multilayer structure are mainly used as the active material for the negative electrode. Yes. This active material is made into a slurry together with an organic binder, applied to the surface of a highly conductive current collector formed of aluminum foil, copper foil, etc., and then pressed and dried to provide an electrode having an active material layer Is formed.

  In order to increase the charge / discharge capacity, it is required to increase the amount of active material in the electrode. However, if the thickness of the active material layer is increased, the thickness of the entire battery is increased, which does not contribute to space saving. Further, the side of the active material layer that is not in contact with the current collector is difficult to conduct with the current collector, and the active material cannot be used efficiently. In addition, the negative electrode of the lithium ion secondary battery has a problem in that separation between the current collector and the active material layer is likely to occur because the volume change during charge / discharge is large and SEI is generated.

  Therefore, it is conceivable to form a current collector from a metal porous body having a large number of pores and fill the pores with an active material.

  For example, in a nickel metal hydride secondary battery, a nickel porous body called nickel cermet is used as a current collector. However, when nickel is used for an electrode of a lithium ion secondary battery, there is a problem that nickel is eluted and deteriorates in the electrolyte solution at the charge / discharge potential. Therefore, if an aluminum porous body manufactured by a manufacturing method described in Japanese Patent Application Laid-Open No. 2011-246779 is used as a current collector for an electrode of a lithium ion secondary battery, the problem of elution can be avoided.

  In this manufacturing method, an aluminum porous body is manufactured by forming a conductive layer made of nickel or the like on a resin porous body made of urethane or melamine, and further plating aluminum in a molten salt bath. However, although the obtained aluminum porous body has a high porosity of 80 to 98%, the volume of the aluminum portion is as small as 2 to 20%, so when used as a current collector, the conductivity of the entire electrode is relatively high. There is a problem that it is low.

  Japanese Patent Application Laid-Open No. 2007-100176 describes a method for producing a porous aluminum body by heating and foaming an unfoamed precursor containing aluminum powder. However, in this method, about 10% by mass of silicon particles must be added as the cell fine particles, and when used as a current collector, there is a problem that the electrical resistance is increased by the silicon.

JP 2011-246779 JP 2007-100176

  The present invention has been made in view of the above circumstances, and solves the problem of providing a current collector that can also be used for an electrode of a lithium ion secondary battery and can effectively prevent peeling of an active material layer. It should be a challenge.

  A feature of the current collector of the present invention that solves the above problems is that the iron-based powder is sintered and the porosity is 30 to 55% by volume, and at least part of the inner peripheral surface of the pores is electrically conductive. A metal layer.

  The production method of the present invention that can produce the current collector of the present invention is characterized in that a powder molded body having a porosity of 30 to 55% by volume filled with a raw material powder containing an iron-based powder and pressed. A powder forming body is heated and sintered in a non-oxidizing atmosphere to form a sintered body having a porosity of 30 to 55% by volume, and a current collector shape. The conductive step of forming a conductive metal layer on at least a part of the inner peripheral surface of the pores of the sintered body is performed in this order.

  According to the current collector of the present invention, since the porosity is as high as 30 to 55% by volume, a large amount of active material can be filled. And since it has a conductive metal layer on the inner peripheral surface of the hole, the exchange of electricity with the active material is performed smoothly. These effects act synergistically to improve the charge / discharge capacity. Further, since the active material can be held in the pores, separation of the active material layer is suppressed, and cycle characteristics in the power storage device are improved. Furthermore, since iron-based powder is used as a raw material, it is cheaper than conventional current collectors.

It is a typical principal part expanded sectional view of the electrical power collector which concerns on one Example of this invention. It is a graph which shows the relationship between a cycle number and a discharge capacity maintenance factor.

  The current collector of the present invention has a porosity of 30 to 55% by volume obtained by sintering an iron-based powder, and has a conductive metal layer on at least a part of the inner peripheral surface of the pores.

  The current collector of the present invention has a porosity of 30 to 55% by volume. In other words, the occupied volume ratio of the iron-based powder is 45 to 70% by volume. When the porosity is lower than 30% by volume or when the occupied volume ratio is higher than 70% by volume, the action of suppressing the peeling of the active material layer is reduced. When the porosity is higher than 55% by volume, or the occupied volume ratio is 45% by volume. When it is lower, the strength is lowered, and the exchange of electricity is lowered due to the reduction of the contact area with the active material. The porosity is more preferably 40 to 55% by volume, and further preferably 45 to 55% by volume.

  By the way, when a current collector made of iron-based powder is used as an electrode of a lithium-based power storage device, iron may be eluted into the electrolytic solution by a high potential. Therefore, the current collector of the present invention has a conductive metal layer different from the sintered base material on at least a part of the inner peripheral surface of the pores. Examples of the material of the conductive metal layer include copper, nickel, aluminum, silver, and gold. When used for an electrode of a lithium-based power storage device, elution of iron from the current collector can be prevented by forming a conductive metal layer from a conductive metal other than nickel eluted in the electrolyte solution.

  The conductive metal layer only needs to be formed on at least a part of the inner peripheral surface of the hole, but the entire inner peripheral surface of the hole and the entire skeleton surface of the sintered body so that the sintered body is not exposed. It is desirable that it is formed.

  Since the current collector of the present invention is obtained by sintering an iron-based powder, the area of the inner peripheral surface of the pores is larger than that of a conventional cermet or the like. For this reason, the area of the conductive metal layer in the pores, and consequently the volume of the conductive metal layer, is increased, so that the amount of electricity exchanged with the active material is large and high conductivity is exhibited.

  In order to produce the current collector of the present invention, first, a raw material powder containing iron-based powder is filled in a powder molding die and pressed to form a powder compact with a porosity of 30 to 55% by volume. A process is performed. The iron-based powder is a powder containing iron as a main component, and examples thereof include pure iron powder, atomized powder, iron alloy powder, or metal powder that becomes an iron alloy in the sintering process, but in some cases, iron oxide powder is used. You can also. Examples of alloy elements other than iron in iron alloys include C, B, Cr, Mo, and V.

  The iron-based powder preferably has an average particle size of 50 μm to 150 μm, and more preferably an average particle size of 75 μm to 100 μm. When the average particle diameter is less than 50 μm, the pore diameter and the porosity become too small, and the effect of the present invention is hardly exhibited, and when it exceeds 150 μm, the strength as a current collector becomes insufficient.

  In the molding step, it is desirable that an organic binder that melts at a low temperature lower than the sintering temperature in the sintering step described later is mixed with an iron-based powder and filled in a powder molding die. Since the molten organic binder is interposed between the surfaces of the iron-based powder particles, the fluidity of the iron-based powder during pressurization increases and stable molding becomes possible, and the iron-based powder particles are fixed after molding. As a result, the strength of the powder compact is improved.

  Examples of the organic binder include aliphatic hydrocarbons, higher fatty acids, higher fatty acid salts, higher alcohols, higher fatty acid esters, amide waxes, thermoplastic resins, and the like, but stearic acid, stearate having a lubricating action, It is preferable to use one selected from stearic acid esters.

  The addition amount of the organic binder is preferably 2.5 parts by mass to 3.5 parts by mass with respect to 100 parts by mass of the iron-based powder. If it is less than 2.5 parts by mass, it is difficult to obtain the added effect, and if it exceeds 3.5 parts by mass, stable molding during powder molding may be difficult, and the strength of the current collector may be reduced. The range of 3.0 parts by mass to 3.2 parts by mass is particularly preferable.

  In addition to the iron-based powder and the organic binder, it is also preferable to add carbon such as graphite, carbon black, and acetylene black to the raw material powder in the molding step. Addition of carbon improves the electrical conductivity of the current collector, and also improves the sinterability and strength, thereby improving the retention of the active material, increasing the electrode strength, and improving the cycle life. . Further, if burnt out or eluted in the sintering process, a lubricant or an additive may be included.

  The amount of carbon added is preferably in the range of 0.7 to 0.9 parts by mass with respect to 100 parts by mass of the iron-based powder. If it is less than 0.7 parts by mass, it is difficult to obtain the added effect, and if it exceeds 0.9 parts by mass, a compound of iron and carbon may be formed and become brittle.

  In the molding step, the raw material powder is filled in a powder molding die and pressed to form a powder compact with a porosity of 30 to 55% by volume. The applied pressure varies depending on the average particle diameter of the iron-based powder, the amount of organic binder added, etc., but is determined so that the porosity is 30 to 55% by volume. By setting the porosity to 30 to 55% by volume, the strength of the powder molded body is ensured, and a sintered body having the same shape as the powder molded body can be produced in the sintering step. When an organic binder is included, it is desirable to pressurize in a state where the organic binder is heated above the melting point or softening temperature of the organic binder.

  In the sintering step, the powder compact is heated and sintered in a non-oxidizing atmosphere to form a sintered compact having a porosity of 30 to 55% by volume. When an organic binder is included in the powder compact, the organic binder decomposes and burns away in this sintering process, but there is almost no effect on the porosity, and the porosity and shape of the sintered compact are the same as those of the powder compact. It will reflect the porosity and shape. By setting the porosity of the sintered body to 30 to 55% by volume, the amount of active material that can be filled is increased and the adhesion to the active material layer is improved, so that the impregnation property such as plating solution in the conductive process is improved. To do.

  The non-oxidizing atmosphere may be a vacuum atmosphere, an inert gas atmosphere, a nitrogen gas atmosphere, or the like, and the sintering temperature may be 1080 ° C. to 1100 ° C.

  In the conductive step, a conductive metal layer is formed on at least a part of the inner peripheral surface of the pores of the sintered body having a current collector shape. When the shape of the sintered body does not match the shape of the target current collector, the sintered body is formed into a current collector shape by machining or the like, and then a conductive metal layer is formed. By using a sintered body having a porosity of 30 to 55% by volume, it is possible to form a conductive metal layer also in the internal pores.

  The conductive metal layer can be formed from copper, nickel, aluminum, silver, gold, or the like using an electroless plating method, an electroplating method, a CVD method, a PVD method, or the like. The layer thickness of the conductive metal layer is not particularly limited. The conductive metal layer is desirably formed on the entire inner peripheral surface of the pores of the sintered body having a current collector shape and on the entire skeleton surface of the sintered body. In addition, when a void | hole does not connect with the exterior and it is an independent hole of sealed space, it is not necessary to form a conductive metal layer in the inner peripheral surface. When there are few vacancies exposed on the surface of the sintered body, the vacancies may be exposed by machining the surface layer of the sintered body or etching with a chemical.

  The power storage device of the present invention has an electrode formed by holding an active material on the current collector of the present invention. Examples of the power storage device include a secondary battery, an electric double layer capacitor, and a lithium ion capacitor. The electrode formed by holding the active material on the current collector of the present invention may be either a positive electrode or a negative electrode. In the case where the power storage device is a lithium ion secondary battery, it is preferably used as a current collector for a negative electrode that has a large volume change due to the entry and exit of lithium ions during charging and discharging.

  Hereinafter, the configuration of the power storage device in the case of a non-aqueous secondary battery will be specifically described.

  The electrode is configured by holding an active material layer on a current collector. To form the active material layer, a slurry in which a negative electrode active material or a positive electrode active material is mixed with a conductive additive, a binder, an organic solvent, and the like is used. Can be formed.

Negative electrode active materials include graphite, highly oriented graphite, carbon such as mesocarbon microbeads, hard carbon, soft carbon, alkali metals such as lithium and sodium, metal compounds, boron-added carbon, silicon, carbon fiber, tin (Sn ), Known materials such as silicon oxide can be used. Among these, a silicon oxide represented by SiO _x (0.3 ≦ x ≦ 1.6) is particularly preferable. Each particle of the silicon oxide powder is composed of SiO _x decomposed into fine Si and SiO ₂ covering Si by a disproportionation reaction. When x is less than the lower limit, the Si ratio increases, so that the volume change during charge / discharge becomes too large, and the cycle characteristics deteriorate. When x exceeds the upper limit value, the Si ratio is lowered and the energy density is lowered. A range of 0.5 ≦ x ≦ 1.5 is preferable, and a range of 0.7 ≦ x ≦ 1.2 is more desirable.

In general, when oxygen is turned off, it is said that almost all SiO disproportionates and separates into two phases at 800 ° C. or higher. Specifically, the raw material silicon oxide powder containing amorphous SiO powder is subjected to heat treatment at 800 to 1200 ° C. for 1 to 5 hours in an inert atmosphere such as in a vacuum or an inert gas. A silicon oxide powder containing two phases of an amorphous SiO ₂ phase and a crystalline Si phase is obtained.

  The silicon oxide powder desirably has an average particle size in the range of 1 μm to 10 μm. When the average particle size is larger than 10 μm, the charge / discharge characteristics of the non-aqueous secondary battery are degraded.When the average particle size is less than 1 μm, the particles are aggregated and become coarse particles. May decrease.

As silicon oxides, with respect to SiO _x may be used as complexed with from 1 to 50% by weight of carbon material. By combining carbon materials, cycle characteristics are improved. If the composite amount of the carbon material is less than 1% by mass, the effect of improving the conductivity cannot be obtained, and if it exceeds 50% by mass, the proportion of SiO _x is relatively decreased and the negative electrode capacity is decreased. The composite amount of the carbon material is preferably in the range of 5 to 30% by mass, more preferably in the range of 5 to 20% by mass with respect to SiO _x . In order to combine the carbon material with SiO _x , a CVD method or the like can be used.

Examples of the carbon material include natural graphite, artificial graphite, coke, mesophase carbon, vapor-grown carbon fiber, pitch-based carbon fiber, and PAN-based carbon fiber, and carbon fiber having excellent buffer performance is preferable. Note D ₅₀ average particle size of the carbon material is desirably 1 to 10 [mu] m.

  A conductive additive can be used in combination with the negative electrode active material. The conductive assistant is added to increase the conductivity of the electrode. Carbon black, graphite, acetylene black (AB), ketjen black (KB), vapor grown carbon fiber (VGCF), etc., which are carbonaceous fine particles, are used alone or in combination of two or more as conductive aids. Can be added. The amount of the conductive aid used is not particularly limited, but can be, for example, about 20 to 100 parts by mass with respect to 100 parts by mass of the active material. If the amount of the conductive auxiliary is less than 20 parts by mass, an efficient conductive path cannot be formed, and if it exceeds 100 parts by mass, the moldability of the electrode deteriorates and the energy density decreases. Note that when the silicon oxide combined with the carbon material is used as the active material, the amount of the conductive auxiliary agent added can be reduced or eliminated.

  There is no restriction | limiting in particular in an organic solvent, The mixture of a some solvent may be sufficient. N-methyl-2-pyrrolidone and N-methyl-2-pyrrolidone and ester solvents (ethyl acetate, n-butyl acetate, butyl cellosolve acetate, butyl carbitol acetate, etc.) or glyme solvents (diglyme, triglyme, tetraglyme, etc.) The mixed solvent is particularly preferred.

  When the power storage device of the present invention is a lithium ion secondary battery, the silicon oxide constituting the negative electrode can be predoped with lithium. In order to dope lithium into the negative electrode, for example, an electrode formation method in which a half battery is assembled using metallic lithium as the counter electrode and electrochemically doped with lithium can be used. The amount of lithium doped is not particularly limited.

  When the power storage device of the present invention is a lithium ion secondary battery, the positive electrode may be any battery that can be used in a non-aqueous secondary battery. The positive electrode has a current collector and a positive electrode active material layer bound on the current collector. The positive electrode active material layer includes a positive electrode active material and a binder, and may further include a conductive additive. 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.

Positive electrode active materials include metallic lithium, LiNiO ₂ , LiCoO ₂ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiNi _0.8 Co _0.15 Al _0.05 O ₂ , Li ₂ MnO ₂ , LiMn ₂ O ₄ , LiNi Examples include _0.5 Mn _0.5 O ₂ , LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , and sulfur. The current collector is not particularly limited as long as it is generally used for the positive electrode of a lithium ion secondary battery, such as aluminum, nickel, and stainless steel. As the conductive auxiliary agent, the same ones as described in the above negative electrode can be used.

The power storage device may further include an electrolytic solution, a current collecting terminal, and the like. As the electrolytic solution, an organic solvent-based electrolytic solution in which an electrolyte is dissolved in an organic solvent or a non-aqueous electrolytic solution such as a polymer electrolyte in which the electrolytic solution is held in a polymer can be suitably used. The organic solvent contained in the electrolytic solution or the polymer electrolyte more preferably contains a chain ester from the viewpoint of load characteristics. As the chain ester, for example, one or more selected from propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC) and the like can be used. As the electrolyte to be dissolved, a lithium metal salt soluble in an organic solvent such as LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiI, LiClO ₄ , LiCF ₃ SO ₃ can be used.

For example, an organic solvent such as ethylene carbonate, dimethyl carbonate, propylene carbonate, or dimethyl carbonate is mixed with a lithium metal salt such as LiClO ₄ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO _{3 at} a concentration of about 0.5 mol / L to 1.7 mol / L. A dissolved solution can be used.

  A separator will not be specifically limited if it can be used for a non-aqueous secondary battery. The separator separates the positive electrode and the negative electrode and holds the electrolytic solution, and a thin microporous film such as polyethylene or polypropylene can be used. Alternatively, a woven fabric or a nonwoven fabric made of polypropylene, polyethylene terephthalate, methyl cellulose, or the like can be used.

  When the power storage device of the present invention is a non-aqueous secondary battery, the shape 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 connection using a lead or the like, this electrode body is sealed in a battery case together with an electrolyte to form a battery.

  Hereinafter, the present invention will be described more specifically with reference to examples.

  FIG. 1 shows a schematic enlarged cross-sectional view of the main part of the current collector according to this example. The current collector (1) includes a powder sintered body made of iron-based particles (10) and a copper plating layer (11) formed on the surface thereof, and has pores (12). Hereinafter, a method for producing the current collector (1) will be described, and a detailed description of the configuration will be given.

<Mixing process>
As raw material powder, reduced iron powder (pure iron: JFE Steel `` JIP240M '', average particle size 75 μm) is 96.3 parts by mass, graphite is 0.7 parts by mass, Dainichi Chemical Co., Ltd. 3 parts by mass of “W-02” (stearic acid, melting point 60 ° C.) was mixed for 1 hour using a milling apparatus.

<Molding process>
Prepare a powder molding die with a rectangular cylinder cavity of 60mm length, 60mm width, 30mm depth, fill the cavity with the above mixed powder, and pressurize with a punch at 50MPa while heating to 160 ° C Molding was performed.

  The obtained powder compact had an occupied volume ratio of about 50% by volume and a porosity of about 50% by volume as measured by image processing of the pores by cross-sectional metallographic observation. However, despite the high porosity, each particle was bound by stearic acid and had a strength that could be handled with bare hands.

<Sintering process>
The obtained powder compact was put in an electric furnace and sintered by heating at 1080 ° C. for 30 hours in a vacuum atmosphere. The obtained sintered body had an occupied volume ratio of about 50% by volume and a porosity of about 50% by volume as measured by image processing of the pores by cross-sectional metallographic observation.

<Conductivity process>
The obtained sintered body was cut into a size of 31 mm × 26 mm × 30 μm to obtain a current collector precursor. Subsequently, the current collector precursor was subjected to copper plating by an electroless copper plating method using a formaldehyde bath, and the surface of the iron-based particles (10) and the pores (12) constituting the current collector precursor were subjected to copper plating. A copper plating layer (11) having a thickness of about 5 μm was formed on the peripheral surface to obtain a current collector for negative electrode (1).

<Formation of negative electrode>
SiO powder (manufactured by Sigma-Aldrich Japan, average particle size 5 μm) was heat-treated at 900 ° C. for 2 hours to prepare SiO _x powder having an average particle size of 5 μm. With this heat treatment, if silicon monoxide SiO is a homogeneous solid having a ratio of Si to O of approximately 1: 1, it is separated into two phases of Si phase and SiO ₂ phase by solid internal reaction. The Si phase obtained by separation is very fine.

Mix 50 parts by mass of the obtained SiO _x powder, 37 parts by mass of natural graphite powder, 3 parts by mass of ketjen black, and 100 parts by mass of polyvinylidene fluoride (PolyVinylidene DiFluoride: PVDF) solution (10 parts by mass as PVDF) To prepare a slurry. This slurry was applied to the surface of the negative electrode current collector (1) using a doctor blade to form a negative electrode active material layer on the surface of the current collector (1). Thereafter, the pressure was applied by a roll press, and the current collector (1) and the negative electrode active material layer were firmly bonded. At this time, the negative electrode active material was also filled in the pores (12). This was vacuum-dried at 100 ° C. for 3 hours to form a negative electrode having a negative electrode active material layer thickness of 16 μm.

<Preparation of positive electrode>
Li [Mn _0.3 Ni _0.5 Co _0.2 ] O ₂ as a positive electrode active material, acetylene black (AB) as a conductive additive, and polyvinylidene fluoride (PVdF) as a binder resin are mixed together to form a slurry-like positive electrode composite. A material was prepared. The composition ratio of each component (solid content) in the slurry was Li [Mn _0.3 Ni _0.5 Co _0.2 ] O ₂ : AB: PVdF = 93: 4: 3 (mass ratio). This slurry was applied to a current collector, and a positive electrode mixture layer was laminated on the current collector. Specifically, this slurry was applied to the surface of an aluminum foil (current collector) of 30 mm × 25 mm × 20 μm using a doctor blade.

  Thereafter, drying was performed at 80 ° C. for 20 minutes, and the organic solvent was volatilized and removed from the positive electrode mixture. After drying, the electrode density was adjusted with a roll press. This was heat-cured at 120 ° C. for 6 hours in a vacuum drying furnace to obtain a positive electrode in which a positive electrode mixture layer having a thickness of about 50 μm was laminated on the upper layer of the current collector.

<Production of lithium ion secondary battery>
Both the positive electrode and the negative electrode were accommodated in a laminate film. That is, a separator made of a polypropylene microporous membrane (“Celgard 2400” manufactured by Celgard) was sandwiched between the positive electrode and the negative electrode. This was covered with a laminate film, three sides were sealed, and the following electrolyte was injected into the bag-like laminate 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 and the electrolyte were sealed. The electrolyte solution is FEC (fluoroethylene carbonate), EC (ethylene carbonate), MEC (methyl ethyl carbonate), DMC (dimethyl carbonate) in a mixed solution of 0.4: 2.6: 3: 4 (volume ratio) with 1 mol / liter of LiPF _6. It was used at a concentration which becomes dm ^3. The positive electrode and the negative electrode were provided with a tab that could be electrically connected to the outside, and a part of this tab extended to the outside of the laminate cell. Through the above steps, a lithium ion secondary battery of a single-layer laminate cell was obtained.

[Comparative example]
As the negative electrode current collector, a negative electrode was formed in the same manner as in the example except that a 31 mm × 26 mm × 20 μm copper foil was used instead of the current collector (1). A lithium ion secondary battery of a single layer laminate cell was obtained in the same manner as in the example.

<Evaluation test>
About the lithium ion secondary battery of an Example and a comparative example, the charge / discharge test in 25 degreeC was performed 1000 cycles. In the charge / discharge test, the battery was charged at 4.2 V under the condition of 1 C CCCV charge (constant current constant voltage charge), and discharged at 3.0 V under the condition of 1/3 C CC discharge. The discharge capacity retention rate at each cycle number was calculated, and the results are shown in FIG. The discharge capacity retention rate is obtained as a percentage of a value obtained by dividing the discharge capacity at the Nth cycle by the initial discharge capacity. The number of samples in the example is n = 4, and the number of samples in the comparative example is n = 6.

  From FIG. 2, the lithium ion secondary battery of the example has a higher discharge capacity retention rate than the comparative example, and is excellent in cycle characteristics. This means that the deterioration of the negative electrode active material layer was prevented, and it is clear that this is the effect of suppressing the peeling of the negative electrode active material layer by using the current collector of the present invention.

  The power storage device of the present invention can be used for secondary batteries, electric double layer capacitors, lithium ion capacitors, and the like. It is also useful as a non-aqueous secondary battery for motor drive of electric vehicles and hybrid vehicles, personal computers, portable communication devices, home appliances, office equipment, industrial equipment, etc. It can be optimally used for driving motors of electric vehicles and hybrid vehicles.

Claims (11)

  A current collector obtained by sintering iron-based powder and having a porosity of 30 to 55% by volume, and having a conductive metal layer on at least a part of the inner peripheral surface of the pores.   2. The current collector according to claim 1, wherein the porosity is 40 to 55% by volume.   3. The current collector according to claim 1, wherein the conductive metal layer is a copper plating layer.   4. The current collector according to claim 1, wherein the conductive metal layer is formed on the entire inner peripheral surface of the hole. A molding step of filling a raw material powder containing iron-based powder into a powder molding die and pressurizing it to form a powder molded body having a porosity of 30 to 55% by volume;
A sintering step in which the powder compact is heated and sintered in a non-oxidizing atmosphere to form a sintered compact having a porosity of 30 to 55% by volume;
A conductive step of forming a conductive metal layer on at least a part of the inner peripheral surface of at least the pores of the sintered body in the shape of a current collector, in this order; Production method.   6. The method for producing a current collector according to claim 5, wherein the iron-based powder has an average particle size of 50 μm to 150 μm.   7. The collection according to claim 5, wherein the molding step mixes the organic binder that melts at a temperature lower than the sintering temperature in the sintering step with the iron-based powder and fills the powder molding die. A method of manufacturing an electric body.   8. The method for producing a current collector according to claim 5, wherein the organic binder is stearic acid or stearate, and 2.5 to 3.5 parts by mass are added to 100 parts by mass of the iron-based powder.   9. The method for producing a current collector according to claim 5, wherein the conducting step is performed by an electroless plating method.   5. A power storage device comprising an electrode in which an active material is held on the current collector according to claim 1.   11. The power storage device according to claim 10, wherein the power storage device is a lithium ion secondary battery and the electrode is a negative electrode.

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