JP4374491B2 - Negative electrode for lithium secondary battery - Google Patents

Description

  The present invention relates to a negative electrode for a lithium secondary battery, a method for producing a negative electrode for a lithium secondary battery, and a lithium secondary battery.

  In recent years, with the spread of portable electronic devices such as notebook computers and mobile phones, in order to reduce the weight of these devices and enable them to be used for a long time, the size and height of secondary batteries used as a power source are reduced. Energy density is required.

  Conventionally, nickel-cadmium batteries, nickel-hydrogen batteries and the like have been mainstream as secondary batteries. However, the use of lithium secondary batteries tends to increase due to the demand for downsizing and high energy density as described above. It is in.

Currently, the lithium secondary batteries, lithium cobalt oxide, carbon electrode as a negative electrode, a nonaqueous electrolyte prepared by dissolving lithium ion in an organic solvent propylene carbonate as the electrolyte is generally used as a positive electrode.

  In such a lithium ion secondary battery, a carbon electrode used as a negative electrode material has a low usable current density, a theoretical capacity density of only about 372 mAh / g, and a complicated manufacturing process and yield. Has a drawback that the manufacturing cost increases. For this reason, in order to further improve the performance of lithium secondary batteries, new negative electrode materials are being searched for.

  The material having the largest capacity density as the negative electrode material is metallic lithium. Lithium is a material having a theoretical density of 3860 mAh / g and a charge / discharge capacity 10 times or more that of the carbon electrode. However, when metallic lithium is used as the negative electrode of a lithium secondary battery, lithium dendrite grows with repeated charging and discharging, and short-circuiting between electrodes and breakage of the separator are likely to occur. As a result, the charge / discharge cycle of the lithium secondary battery is abruptly lowered, and further, the safety of the battery is also lowered.

  On the other hand, the Sn-based alloy is a material having a theoretical capacity more than twice that of the carbon material, but has a drawback that the cycle life is short because a large volume change is caused by the insertion of Li.

  In recent years, it has been studied to form a Sn or Sn alloy thin film on various current collectors by a surface treatment method and use this as a negative electrode. For example, the tin alloy used as the negative electrode material is selected from the group consisting of an alloy of tin and antimony, bismuth, lead, copper, zinc, etc., a tin bismuth alloy film, and copper, zinc, cobalt, and iron as alloy components. A seed or a tin alloy containing two or more kinds has been reported, and electroplating methods and the like have been disclosed as means for forming a tin or tin alloy thin film (see Patent Documents 1 to 4 below).

  Further, in Patent Document 5 below, an intermediate between the lithium occlusion capacity of the current collector and the lithium occlusion capacity of the tin plating layer or the tin alloy plating layer is provided at the interface between the current collector and the tin plating layer or the tin alloy plating layer. An electrode for a secondary battery in which a layer having lithium storage capacity is formed is disclosed. Furthermore, in Patent Document 6 below, a material in which a tin or tin alloy film having a structure in which fine plating particles are substantially continuous, deposited from an electroplating solution having a specific composition, is formed on one side or both sides of a current collector. An electrode material for a secondary battery is disclosed.

As described above, various attempts have been made to form a tin or tin alloy thin film on the surface of the current collector by a surface treatment method such as electroplating, and use this as a negative electrode material for a lithium secondary battery. However, in spite of these various attempts, the present situation is that a negative electrode material having a sufficient cycle life that can be practically used has not been obtained. This is because even when a tin or tin alloy thin film is formed on the current collector by the above-described method, a large volume is added to the metal thin film as the active material when lithium is occluded / released along with charge / discharge. A major cause is considered to be a change, cracking in the active material layer, and deterioration of the cycle characteristics of the electrode.
Japanese Patent Laid-Open No. 11-242955 JP 2001-68094 A JP 2001-68095 A JP 2002-198091 A JP 2003-157833 A JP 2003-142088 A

  A main object of the present invention is to provide a novel secondary battery electrode that has high charge / discharge capacity and a long cycle life and is highly useful as a negative electrode of a lithium ion secondary battery.

  The present inventor has intensively studied to achieve the above-described object. As a result, when a non-conductive material having a fine structure such as a fiber or a resin foam is used as a substrate and a thin film of tin or tin alloy is formed on this surface by a wet plating method, a dry plating method, etc., as an electrode While maintaining sufficient strength, the volume change associated with the insertion and extraction of lithium is absorbed by the fine movement of the fine structure, suppressing the deformation of the entire electrode and preventing the active material layer from cracking. I found out that it would be possible. Further, when such a non-conductive material having a fine structure is used as a substrate, the substantial film of the film can be formed without reducing the amount of tin or tin alloy as an active material per apparent electrode surface area. Since the thickness can be reduced, the inventors have found that an electrode having a high charge / discharge capacity and excellent cycle characteristics can be obtained. The present invention has been completed based on these findings.

That is, this invention provides the following negative electrode for lithium secondary batteries, the manufacturing method of the negative electrode for lithium secondary batteries, and a lithium secondary battery.
1. A negative electrode for a lithium secondary battery, comprising: a substrate made of a sheet-like non-conductive material having a microstructure; and an active material layer made of tin or a tin alloy formed on the surface portion of the substrate and the surface inside the microstructure.
2. Item 2. The negative electrode for a lithium secondary battery according to Item 1, wherein the sheet-like nonconductive material having a microstructure is a fabric or a resin foam.
3. Item 3. The material according to Item 1 or 2, wherein the sheet-like non-conductive material having a microstructure is a material having an actual surface area of the material including the microstructure portion of 3 times or more with respect to the apparent surface area of the material. Negative electrode for lithium secondary battery.
4). Item 4. The negative electrode for a lithium secondary battery according to any one of Items 1 to 3, wherein the sheet-like nonconductive material having a microstructure is subjected to compression processing.
5. Item 5. The negative electrode for a lithium secondary battery according to any one of Items 1 to 4, wherein the active material layer made of tin or a tin alloy is formed by a wet plating method or a dry plating method.
6). Item 6. The negative electrode for a lithium secondary battery according to any one of Items 1 to 5, wherein a metal layer acting as a current collector is provided between the substrate and the active material layer.
7). Item 7. The negative electrode for a lithium secondary battery according to Item 6, wherein the metal layer acting as a current collector is copper, iron, nickel, or an alloy containing these metals as a main component.
8). Between the metal layer acting as a current collector and the active material layer, the metal layer made of zinc, copper, nickel, silver, indium, antimony, bismuth, lead, or an alloy containing these metals as a main component is further provided. Item 8. The negative electrode for a lithium secondary battery according to Item 6 or 7.
9. Item 9. The negative electrode for a lithium secondary battery according to any one of Items 1 to 8, further comprising a metal layer made of silver, cadmium, indium, antimony, or an alloy containing these metals as a main component on the active material layer.
10. Item 10. The negative electrode for a lithium secondary battery according to any one of Items 1 to 9, obtained by performing heat treatment after forming an active material layer and other metal layers.
11. The negative electrode for a lithium secondary battery according to any one of the above items 6 to 9, wherein by performing heat treatment, an interface between the active material layer and the lower layer is formed between the metal of the metal of the tin and the conductor layer. A negative electrode for a lithium secondary battery, wherein a layer made of a compound is formed.
12 After forming a conductive film on a substrate made of a sheet-like non-conductive material having a fine structure by a dry plating method or an electroless plating method, an active material layer made of tin or a tin alloy is formed by a wet plating method A method for producing a negative electrode for a lithium secondary battery.
13. An active material layer made of tin or a tin alloy is formed by a wet plating method after forming a metal layer acting as a current collector on a substrate made of a sheet-like non-conductive material having a fine structure by a dry plating method or a wet plating method. Forming a negative electrode for a lithium secondary battery.
14 A metal layer acting as a current collector is formed by a dry plating method or a wet plating method on a substrate made of a sheet-like non-conductive material having a fine structure, and then, by a dry plating method or a wet plating method, zinc, copper, It is characterized in that after forming a metal layer made of nickel, silver, indium, antimony, bismuth, lead or an alloy containing these metals as a main component, an active material layer made of tin or a tin alloy is formed by a wet plating method. A method for producing a negative electrode for a lithium secondary battery.
15. Item 15. The method according to any one of Items 12 to 14, wherein an active material layer made of tin or a tin alloy is formed by displacement plating before forming an active material layer made of tin or a tin alloy by a wet plating method. Manufacturing method of negative electrode for lithium secondary battery.
16. After the active material layer is formed by the method described in any one of Items 12 to 15, the active material layer is made of silver, cadmium, indium, antimony or an alloy containing these metals as a main component by a dry plating method or a wet plating method. A method for producing a negative electrode for a lithium secondary battery, comprising forming a metal layer.
17. In the method for producing a negative electrode for a lithium secondary battery according to any one of Items 12 to 16, when at least one of the active material layer and the other metal layer is formed by a wet plating method, the number of carbon atoms is 6 or less. A method for producing a negative electrode for a lithium secondary battery, comprising wet plating using a plating solution containing at least one component selected from the group consisting of lower alcohols, alcohol ethers and ketones.
18. In the method for producing a negative electrode for a lithium secondary battery according to any one of Items 12 to 17, when at least one of the active material layer and the other metal layer is formed by a wet plating method, the number of carbon atoms is 6 or less. A method for producing a negative electrode for a lithium secondary battery, comprising performing pretreatment of wet plating using a pretreatment liquid containing at least one component selected from the group consisting of lower alcohols, alcohol ethers and ketones.
19. 19. A method for producing a negative electrode for a lithium secondary battery, wherein the metal layer is formed by the method according to any one of Items 12 to 18 and then heat treatment is performed.
20. 20. A lithium secondary battery comprising the negative electrode for a lithium secondary battery according to any one of items 1 to 19, an electrolyte, and a positive electrode.

  The negative electrode for a lithium secondary battery according to the present invention includes a substrate made of a sheet-like non-conductive material having a microstructure, and an active material layer made of tin or a tin alloy formed on the surface portion of the substrate and the surface inside the microstructure. It has. Hereafter, each component of this invention is demonstrated concretely.

Non-conductive material In the present invention, a sheet-like non-conductive material having a fine structure is used as a base of a negative electrode for a lithium secondary battery. By using such a substrate and forming an active material layer made of a thin film of tin or a tin alloy on the surface portion of the substrate and the surface inside the microstructure, the volume change accompanying the insertion / release of lithium is microstructured. It can be absorbed by minute movements of the body, suppressing deformation of the entire electrode and preventing cracking of the active material layer.

  As for this nonelectroconductive material, it is desirable that the real surface area including the fine structure inside is not less than 3 times the apparent surface area of the sheet-like front and back. By using a material having such a fine structure, it is possible to reduce the substantial film thickness of the coating without reducing the amount of tin or tin alloy deposited per apparent electrode surface area.

  In the present specification, the ratio of the actual surface area to the apparent surface area of the non-conductive material is the same size (vertical x horizontal) for the non-conductive material and the smooth copper plate. When formed, it can be determined from the ratio of the weight of copper deposited on the non-conductive material to the weight of copper deposited on the copper plate. Specific examples of the measurement method will be shown in the examples described later.

  As the sheet-like non-conductive material having a fine structure, for example, a cloth, a resin foam, or the like can be used.

  As the fabric, a woven fabric, a knitted fabric, a nonwoven fabric, a cocoon, or the like can be used. As the material of the fabric, either natural fiber or synthetic fiber can be used. As the synthetic fiber, for example, polyester, polyamide, polypropylene and the like are preferably used. Moreover, you may use the fiber which mixed the synthetic fiber from which a kind differs. These fabrics may be subjected to compression processing as long as the actual surface area is three or more times the apparent surface area.

  Furthermore, in order to improve the adhesion between the base made of a non-conductive material and the active material layer, when using synthetic fibers as the base, the fibers are preferably subjected to false twisting. For example, a cloth made of centrifugal false twisted yarn (DTY) can be used.

  Moreover, since the base body made of the non-conductive material is incorporated in the battery as it is as a constituent element of the electrode, it is desirable that the base body is flame retardant. The flame retardant fiber may be flame retardant per se, or may be made flame retardant by adding a flame retardant to a material that is not flame retardant. Moreover, the fiber which gave the flame-retardant process may be sufficient. Examples of such flame retardant fibers include polyamide imide, flame retardant polyester, flame retardant polyamide, meta- or para-aromatic polyamide, norbonex and the like.

  Further, when the electrode based on the non-conductive material is used for a lithium battery, since the presence of moisture is not desirable, the fiber used as the base material preferably has a low moisture absorption, and has a moisture absorption at RH 65%. It is preferably 7% or less.

  The type of the resin foam used as the sheet-like non-conductive material having a fine structure is not particularly limited, and known ones can be used. In particular, polyurethane resin foam, silicon resin foam and the like are preferable. In particular, an open-cell foam is preferable.

  The resin foam preferably has a cell density of 20 cells / inch or more before being subjected to compression processing described below. According to such a foam having a high cell density, the actual surface area is increased, and the substantial film thickness of the active material layer can be reduced.

  The sheet-like non-conductive material having a fine structure is preferably subjected to compression processing in order to increase the density of the active material in the electrode and to obtain a higher capacity electrode. The compression processing may be performed at any stage before, during or after the process of forming the active material layer and other metal layers made of tin or tin alloy. For example, taking the case of wet plating most commonly applied as an example, when the sheet-like non-conductive material is a fabric, it is preferable to perform compression processing before the plating step. In some cases, it is preferable to perform compression processing during or after the plating step.

  Although the compression processing method is not particularly limited, for example, a roll press method can be applied. The degree of the compression process is not particularly limited, but usually the compression process may be performed so that the thickness is about 10 to 90% of the thickness before the compression process. The degree of compression is determined by the slit width (clearance) of the roll, but since the restoration rate varies depending on many factors such as the material, thickness, and type of active material layer of the non-conductive material, the slit width should be unified. It cannot be specified. Generally, the slit width may be set to about 0.2 to 30% of the thickness of the nonconductive material on which the metal layer is formed.

  The substrate made of a sheet-like nonconductive material having a fine structure preferably has a thickness of about 3 mm or less, more preferably about 0.03 to 2 mm. In addition, when performing a compression process, it is desirable for the thickness of the base | substrate after a compression process to enter into the said range. By setting it to such a thickness, the penetration of the electrolytic solution becomes sufficient, and charging / discharging with a high current becomes possible.

Active material layer In the electrode for a lithium secondary battery of the present invention, as the active material layer, a thin film made of tin or a tin alloy is formed on a substrate made of a sheet-like non-conductive material having the above-described microstructure. . In this case, since the substrate has a fine structure, the active material layer is formed not only on the surface portion of the substrate but also inside the fine structure. Note that the active material layer may be formed on both sides of the substrate or only on one side.

  As the tin alloy, an alloy of tin and at least one metal selected from the elements of Groups 13 to 15 of Periods 3 to 6 and Groups 8 to 12 of Periods 4 to 6 of the Periodic Table is used. It can be illustrated. Specific examples of elements forming alloys with these tin include Al, Si, P, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Ag, Cd, In, Sb, Au, Hg, Tl , Pb, Bi and the like. In particular, an alloy of tin and at least one metal selected from the group consisting of zinc, copper, antimony, bismuth, cobalt and iron is preferred, and an alloy of tin and at least one metal selected from the group consisting of copper and zinc Is more preferable.

  The tin content in the tin alloy is preferably about 30% by weight or more, and more preferably about 50% by weight or more.

  In the present invention, a tin-copper alloy having a copper content of about 30 to 70% by weight, preferably about 30 to 50% by weight, is particularly preferable.

The amount of the active material layer made of tin or tin alloy is preferably about 20 g / m ² or more per apparent unit area of the base made of a non-conductive material in order to ensure sufficient charge / discharge capacity, More preferably, it is about 40 g / m ² or more. In addition, the charge / discharge capacity increases as the amount of active material deposited increases, but the cycle characteristics tend to decrease. Therefore, the active material layer preferably has an average thickness of less than about 20 μm as observed by a cross-sectional microscope. More preferably, it is less than about 5 μm.

Other metal layers In the negative electrode for a lithium secondary battery according to the present invention, in addition to the above-described active material layer made of tin or a tin alloy, the following metal layers (1) to (3) are optionally formed. Can be formed in one layer or two or more layers.

(1) Current collector layer In the negative electrode for a lithium secondary battery of the present invention, a current collector is provided between a substrate made of a sheet-like non-conductive material having a fine structure and an active material layer made of tin or a tin alloy. A metal layer (hereinafter also referred to as a “current collector layer”) that functions as a metal layer may be formed. By forming the current collector layer, the conductivity of the entire electrode is improved as compared with the case where the active material layer itself has a function as a current collector, which is advantageous particularly in charging and discharging at a high current. .

  There is no limitation in particular as a metal which comprises a collector layer, The metal currently used as the collector for conventional negative electrodes can be used suitably. For example, copper, iron, nickel, an alloy containing these as main components, or the like can be used. In this case, the alloy preferably contains at least about 90% by weight of at least one metal selected from copper, iron and nickel. Among these, copper, nickel, and alloys containing these as main components are preferable, and copper or copper alloys are particularly preferable.

The adhesion amount of the current collector layer is not particularly limited, but in order to give sufficient conductivity, the basis weight per unit area of the substrate is preferably about 20 g / m ² or more, and 50 g / M ² or more is more preferable. The upper limit of the thickness of the current collector layer is not particularly limited, but is usually about 10 μm or less.

(2) Diffusion control layer In the negative electrode for a lithium secondary battery of the present invention, zinc, copper, nickel, silver, indium, antimony, bismuth, lead, or any of these may be provided between the current collector layer and the active material layer. You may form the metal layer which consists of an alloy which has a metal as a main component. In this case, the alloy preferably contains about 90% by weight or more of at least one metal selected from zinc, copper, nickel, silver, indium, antimony, bismuth and lead. By forming this metal layer, when the intermetallic compound of the metal of the current collector layer and tin of the active material layer is formed in the heat treatment described later, the metal of the current collector layer is excessively diffused. It can suppress and it can prevent that the original function of an electrical power collector called electrical conductivity improvement is impaired. Hereinafter, this metal layer is sometimes referred to as a diffusion control layer.

The diffusion control layer is particularly preferably formed of zinc or a zinc alloy.
The thickness of the diffusion control layer is preferably about 0.01 μm or more, and more preferably about 0.2 to 1 μm.

(3) Stress relaxation layer An active material layer made of tin or tin alloy is made of silver, cadmium, indium, antimony or an alloy containing these metals as a main component in order to relieve stress during charge / discharge. A layer (hereinafter also referred to as “stress relaxation layer”) may be formed. In this case, the alloy preferably contains at least about 90% by weight of at least one metal selected from silver, cadmium, indium and antimony. Of these, silver is particularly preferable. By forming the stress relaxation layer on the active material layer, it is possible to suppress deterioration of cycle characteristics due to expansion / contraction due to insertion / extraction of lithium.

  The thickness of the stress suppression layer is not particularly limited, but is preferably about 0.01 to 0.5 μm.

Method for producing negative electrode A negative electrode for a lithium secondary battery according to the present invention comprises an active material layer made of tin or a tin alloy on a substrate made of a sheet-like non-conductive material having a microstructure, and if necessary, 1 or 2 or more layers selected from the above (1) to (3) are formed.

  Each of these layers can be formed by a wet plating method or a dry plating method. As the wet plating method, an electroplating method or an electroless plating method can be employed. Among these, as the dry plating method, for example, a vacuum deposition method, a sputtering method, a CVD method, a PVD method, or the like can be employed. As electroless plating, reduction plating, displacement plating, or the like can be employed. The specific conditions of each of these methods are not particularly limited, and the conditions may be appropriately determined according to ordinary methods so that the target metal layer is formed with a predetermined film thickness.

  In the case where the lowermost active material layer or current collector layer is formed by electroplating, it is necessary to form a conductive film in order to impart conductivity to a substrate made of a non-conductive material. .

  As a method for forming the conductive film, a dry plating method such as a vacuum deposition method, a sputtering method, a CVD method, a PVD method, or an electroless plating method can be employed. The thickness of the conductive film is usually about 0.01 to 0.5 μm.

  In the electroless plating method for forming the conductive film, an electroless nickel plating solution, an electroless nickel alloy plating solution, an electroless copper plating solution, or the like can be used as the plating solution. As the electroless nickel plating solution, a bath containing a known reducing agent such as hypophosphite and dimethylamine borane can be used, and thereby a nickel alloy film such as a nickel-phosphorus film and a nickel-boron film can be used. It may be formed. Further, by using an electroless nickel plating bath containing hydrazine, trivalent titanium or the like as a reducing agent, an electroless nickel film substantially free of nickel or boron can be formed to further improve the adhesion. it can.

  As the electroless copper plating bath, a bath using a known reducing agent such as formalin and formic acid can be used.

  In order to improve the adhesion between the non-conductive material and the lowermost layer before forming the lowermost layer made of the active material layer or the conductor layer on the base made of the non-conductive material, it is acidic with respect to the non-conductive material. Alternatively, pretreatment with an alkaline solution is preferably performed. The specific treatment liquid may be appropriately selected depending on the type of fiber. For example, in the case of polyester fiber, pretreatment with an alkaline solution is desirable. For example, in a sodium hydroxide aqueous solution of about 80 to 200 g / l, 50 What is necessary is just to perform immersion treatment for about 1 to 10 minutes at about ~ 100 ° C. In the case of polyamide fiber, pretreatment with an acidic solution is desirable. For example, immersion treatment may be performed at room temperature for about 1 to 10 minutes in an aqueous hydrochloric acid solution of about 80 to 120 g / l.

  Furthermore, in order to improve the adhesion between the nonconductive material and the lowermost layer, the nonconductive material may be subjected to corona discharge treatment. Although the corona discharge treatment alone has an effect of improving the adhesion, the adhesion can be further improved by performing in combination with the pretreatment with the acidic or alkaline solution.

  When the lowermost layer is formed by a wet plating method, it is preferable to subject the non-conductive material to a hydrophilic treatment with a solution containing a surfactant prior to wet plating. The surfactant is not particularly limited, and various surfactants such as known nonionic, cationic, anionic and amphoteric surfactants can be used. In particular, a cationic surfactant is preferable. Usually, pretreatment of electroless plating on non-conductive materials is performed by appropriately combining degreasing, alkali treatment, acid treatment, neutralization treatment, catalyzing treatment, etc., but adding a surfactant to these treatment solutions Alternatively, it may be treated with a solution containing a surfactant separately from these treatments. The surfactant concentration in the treatment liquid is preferably about 0.001 to 10 g / l, and more preferably about 0.01 to 5 g / l.

  When each of the above layers is formed by wet plating, at least one component selected from the group consisting of lower alcohols having 6 or less carbon atoms, alcohol ethers, and ketones is used in the plating solution used to form these layers. Can be added. By adding these components, the plating solution can penetrate into the fine structure of the substrate to form a uniform metal film. Furthermore, the plating particles can be made finer and the stability of the plating bath can be improved.

  Specific examples of lower alcohols, alcohol ethers and ketones include methanol, ethanol, (n- and i-) propanol, (n-, i- and t-) butanol, 1,2,6-hexanetriol, thiodiglycol , Pentanediol, hexanediol, 1,3-propanediol, 1,4-butanediol, ethylene glycol, propylene glycol, acetone, methyl ethyl ketone, and the like. Of these, i-propanol and acetone windows are preferred, and i-propanol is particularly preferred.

  The amount of addition of at least one component selected from the group consisting of lower alcohols having 6 or less carbon atoms, alcohol ethers and ketones to the plating solution also affects the concentration of other additives, so that it is generally specified However, if the concentration becomes too high, it will inhibit the stabilization of the bath. In particular, for alcohol, this adverse effect increases when the concentration exceeds 300 g / l. Further, if the concentration is too high, the odor becomes intense, which is not preferable from the viewpoint of the working environment. For this reason, the concentration of these components is preferably about 0.5 g / l to 200 g / l, and more preferably about 1 g / l to 200 g / l.

  Moreover, you may add at least 1 sort (s) of components chosen from the group which consists of above-mentioned C6 or less lower alcohol, alcohol ether, and a ketone to the pre-processing liquid for a plating process. Examples of such pretreatment liquid include each treatment liquid used for degreasing, alkali treatment, acid treatment, neutralization treatment, catalyzing treatment, and the like. The above components may be added to only one kind of these pretreatment liquids, or may be added to two or more kinds. The composition of the pretreatment liquid is not particularly limited, and a known treatment liquid can be used. By adding these components to the pretreatment liquid, the pretreatment liquid can penetrate into the fine structure of the substrate, and the uniformity of the formed metal film can be improved.

  The concentration in the pretreatment liquid of at least one component selected from the group consisting of lower alcohols having 6 or less carbon atoms, alcohol ethers and ketones is not particularly limited, but a high concentration is not preferable in the working environment. Usually, it may be about 1 to 200 g / l.

  The cycle characteristics can be improved by performing heat treatment after forming the active material layer and other metal layers formed as necessary. In particular, when a conductor layer is formed between the substrate and the active material layer, the metal of the conductor layer diffuses into the active material layer by heat treatment, and tin is formed at the interface between the active material layer and the lower layer. And a layer made of an intermetallic compound of the conductor layer metal. This intermetallic compound usually has an intermediate lithium occlusion ability between the current collector layer and the active material layer, and the presence of the intermetallic compound makes it possible to change the volume of the active material layer accompanying the occlusion of lithium. Relaxing can greatly extend the cycle life of the negative electrode. However, if the metal in the current collector layer is excessively diffused, the conductivity is lowered. Therefore, it is preferable that the current collector layer is present at about 1 μm or more even after the heat treatment. For this purpose, it is effective to appropriately set the heat treatment temperature, the heating time, etc., and to form a diffusion control layer.

Examples of the type of intermetallic compound include Cu ₃ Sn, Cu ₆ Sn _{5 and the} like when the current collector layer is made of copper or a copper alloy. When it is made of an iron alloy, Fe ₃ Sn, Fe ₂ Sn, Fe ₃ Sn ₂ , FeSn _{2 and the} like can be mentioned. When the current collector is made of nickel or a nickel alloy, Ni ₄ Sn, Ni ₃ Sn, Ni ₃ Sn ₂ , Ni ₃ Sn _{4 and the} like can be mentioned.

  In particular, when a current collector layer made of copper or a copper alloy is formed, an intermetallic compound of copper and tin is formed by heat treatment, and the cycle characteristics can be greatly improved.

  In addition, when the current collector layer is formed of copper or a copper alloy and a diffusion control layer made of zinc or a zinc alloy is further formed between the current collector layer and the active material layer, cycle characteristics by heat treatment The effect of improvement appears significantly.

  The heat treatment conditions are not particularly limited. Usually, heat treatment is performed in a vacuum or in a non-oxidizing atmosphere such as argon, nitrogen, hydrogen, etc., at a temperature lower than the melting point of the tin or tin alloy layer as the active material layer. Is preferred. Usually, the heat treatment may be performed at a temperature in the range of about 160 to 230 ° C. The heat treatment time may be appropriately selected from the relationship between the production rate of the intermetallic compound between the metal of the current collector layer and tin of the active material layer, the metal reduction rate of the current collector layer, etc. About hours are preferred.

  When the active material layer made of tin or a tin alloy is formed by a wet plating method, specifically, an electroless plating method such as a reduction plating method or a displacement plating method, an electroplating method, or the like can be employed. An advantage common to these methods is that a tin or tin alloy film can be easily formed on a substrate having a large area, and a negative electrode can be produced at low cost. Furthermore, according to the electroless plating method, a very uniform thin film having a small film thickness distribution can be formed over the entire electrode. The electroplating method is a method suitable for mass production because a thick film can be formed in a shorter time. Therefore, it is desirable to select these methods as appropriate according to the application, and it is also effective to combine them in some cases. For example, in the case of a method in which a tin or tin alloy film is first thinly formed by a displacement plating method and then a tin or tin alloy film is further grown by an electroplating method, the adhesion between the active material layer and the underlying layer is improved. Can be improved. In this case, the thickness of the tin or tin alloy film formed by the displacement plating method is not particularly limited, but may be usually about 0.01 to 1 μm. The plating bath and plating conditions used for the electroless plating or electroplating are not particularly limited, and known plating baths and plating conditions may be appropriately applied.

  Here, a method for forming an active material layer made of tin or a tin alloy by a wet plating method will be described in more detail.

  As a plating solution for forming tin or a tin alloy film, a known plating bath may be used. Specific examples are shown below.

  As the tin salt, it is preferable to use a soluble salt containing a divalent tin ion for both the electroplating bath and the electroless plating bath. The tin salt may be added to the bath in the form of methanesulfonate, phenolsulfonate, pyrophosphate, sulfate, chloride or the like. The divalent tin ion concentration may usually be in the range of about 5 g / l to 200 g / l.

  What is necessary is just to add a well-known soluble salt to a plating bath also about the other metal alloyed with tin. The concentration of these metal salts varies depending on conditions such as the deposition potential, and therefore the concentration range cannot be strictly limited. However, the concentration may normally be in the range of about 5 g / l to 200 g / l.

  The tin or tin alloy plating bath is an organic sulfonate ion, sulfate ion, chloride ion, borofluoride ion, sulfamate ion, phosphate ion, pyrophosphate ion and any of electroplating bath and electroless plating bath. It is preferable to contain one or more selected from nitrate ions. These ions play a role as counter ions or free acids of the metal ions so that tin and elements forming an alloy with tin are stably present in the plating bath. The concentration depends on the divalent tin ion concentration, but is usually in the range of about 3 g / l to 300 g / l.

  In particular, sulfate ion, organic sulfonate ion and the like are preferable. Examples of the organic sulfonic acid include methanesulfonic acid, methanedisulfonic acid, methanetrisulfonic acid, trifluoromethanesulfonic acid, ethanesulfonic acid, propanesulfonic acid, 2-propanesulfonic acid, butanesulfonic acid, 2-butanesulfonic acid, Pentanesulfonic acid, hexanesulfonic acid, decanesulfonic acid, dodecanesulfonic acid, 2-hydroxyethane-1-sulfonic acid, 1-hydroxypropane-2-sulfonic acid, 3-hydroxypropane-1-sulfonic acid, 2-hydroxypropane -1-sulfonic acid, 2-hydroxybutanesulfonic acid, 2-hydroxypentanesulfonic acid, 2-hydroxyhexane-1-sulfonic acid, 2-hydroxydecanesulfonic acid, 2-hydroxydodecanesulfonic acid, 1-carboxyethanesulfonic acid 2 Carboxyethanesulfonic acid, 1,3-propanedisulfonic acid, allylsulfonic acid, 2-sulfoacetic acid, 2- or 3-sulfopropionic acid, sulfosuccinic acid, sulfomaleic acid, sulfofumaric acid, monochloromethanesulfonic acid, perchloroethanesulfonic acid , Trichlorodifluoropropanesulfonic acid, perfluoroethanesulfonic acid, monochlorodifluoromethanesulfonic acid, trifluoromethanesulfonic acid, trifluoroethanesulfonic acid, tetrachloropropanesulfonic acid, trichlorodifluoroethanesulfonic acid, monochloroethanolsulfonic acid, dichloropropanolsulfonic acid, Monochlorodifluorohydroxypropane sulfonic acid, benzene sulfonic acid, toluene sulfonic acid, xylene sulfonic acid, nitrobenzene sulfone , Sulfobenzoic acid, sulfosalicylic acid, benzaldehyde sulfonic acid, p-phenolsulfonic acid, phenol-2,4-disulfonic acid, 2-sulfoacetic acid, 2-sulfopropionic acid, 3-sulfopropionic acid, sulfosuccinic acid, sulfomethylsuccinic acid Acid, sulfofumaric acid, sulfomaleic acid, 2-sulfobenzoic acid, 3-sulfobenzoic acid, 4-sulfobenzoic acid, 5-sulfosalicylic acid, 4-sulfophthalic acid, 5-sulfoisophthalic acid, 2-sulfoterephthalic acid Etc. can be illustrated. In particular, methanesulfonic acid, 2-hydroxyethane-1-sulfonic acid, 2-hydroxypropane-1-sulfonic acid, phenolsulfonic acid, cresolsulfonic acid, trifluoromethanesulfonic acid, and the like are preferable.

  The plating bath may further contain a complexing agent for both the electroplating bath and the electroless plating bath. In particular, at least one compound selected from the group consisting of carboxylic acid, amine carboxylic acid, hydroxycarboxylic acid and aliphatic polyamine is preferably used as the complexing agent. Specific examples include oxalic acid, malonic acid, succinic acid, glycolic acid, lactic acid, tartaric acid, citric acid, tartronic acid, malic acid, gluconic acid, ascorbic acid, glycine, alanine, valine, leucine, isoleucine, lysine, serine, Threonine, phenylalanine, aspartic acid, glutamic acid, methionine, mercaptosuccinic acid, cystine, sulfosuccinic acid, ethylenediaminetetraacetic acid, iminodiacetic acid, nitrilotriacetic acid, diethylenetriaminepentaacetic acid, triethylenetetraminehexaacetic acid, ethylenedioxybis (ethylamine) -N, N, N ′, N′-tetraacetic acid, glycol ethylenediaminetetraacetic acid, N-hydroxyethylethylenediaminetetraacetic acid and the like can be mentioned. Of these, sulfosuccinic acid, glycolic acid, lactic acid, tartaric acid, citric acid, gluconic acid, ethylenediaminetetraacetic acid, nitrilotriacetic acid and the like are preferable.

  A surfactant can be further added to the plating bath as an additive for both the electroplating bath and the electroless plating bath.

  A known surfactant can be used as the surfactant. Any of nonionic, anionic, amphoteric, and cationic surfactants can be used, and they can be used alone or in an appropriate mixture. In particular, nonionic, anionic and amphoteric surfactants are preferred. The concentration of the surfactant varies depending on the type and combination of the compounds, but in general, it is preferably in the range of about 0.1 g / l to 50 g / l.

  Specific examples of nonionic surfactants include polyoxyalkylene alkyl ether (or ester), polyoxyalkylene phenyl (or alkylphenyl) ether, polyoxyalkylene naphthyl (or alkyl naphthyl) ether, polyoxyalkylene styrenated phenyl Ether (or a polyoxyalkylene chain added to the phenyl group), polyoxyalkylene bisphenol ether, polyoxyethylene polyoxypropylene block polymer, polyoxyalkylene sorbitan fatty acid ester, polyoxyalkylene sorbite fatty acid ester, polyethylene glycol fatty acid Polyoxyalkylene ester, polyoxyalkylene glycerin fatty acid ester, polyoxyalkylene alkylamine, ethylenediamine Alkylene condensate adduct, polyoxyalkylene fatty acid amide, polyoxyalkylene castor (or / and hydrogenated castor oil) oil, polyoxyalkylene alkylphenyl formalin condensate, glycerin (or polyglycerin) fatty acid ester surfactant, pentaerythritol Examples thereof include fatty acid esters, sorbitan mono (sesqui, tri) fatty acid ester surfactants, higher fatty acid mono (di) ethanolamides, alkyl / alkylroadamides, and oxyethylene alkylamines.

  Specific examples of the anionic surfactant include alkyl (or formalin condensate) -β-naphthalene sulfonic acid (or salt thereof), fatty acid soap, alkyl sulfonate, α-olefin sulfonate, alkyl benzene sulfonate. , Alkyl (or alkoxy) naphthalene sulfonate, alkyl diphenyl ether disulfonate, alkyl ether sulfonate, alkyl sulfate, polyoxyethylene alkyl ether sulfate, polyoxyethylene alkylphenol ether sulfate, higher alcohol phosphorus Acid monoester salt, polyoxyalkylene alkyl ether phosphoric acid (salt), polyoxyalkylene alkyl phenyl ether phosphate, polyoxyalkylene phenyl ether phosphate, polyoxyethylene Len alkyl ether acetate, alkyl ylsarcosine, alkyl yl sarcosineate, alkyl ylmethyl alanine salt, N acyl sulfocarboxylate, alkyl sulfoacetate, sodium acylmethyl taurate, alkyl fatty acid glycerine sulfate, hardened coconut Examples include oil fatty acid sodium glyceryl sulfate, alkylsulfocarboxylic acid ester salt system, alkylsulfosuccinate, dialkylsulfosuccinate, alkylpolyoxyethylenesulfosuccinate, sulfosuccinate monooleylamide sodium salt (or ammonium, TEA salt) and the like. it can.

  Specific examples of amphoteric surfactants include 2-alkyl-N-carboxymethyl (or ethyl) -N-hydroxyethyl (or methyl) imidazolinium betaine, 2-alkyl-N-carboxymethyl (or ethyl)- N-carboxymethyloxyethyl imidazolinium betaine, dimethylalkyl betaine, N-alkyl-β-aminopropionic acid (or its sodium salt), alkyl (poly) aminoethylglycine, N-alkyl-N-methyl-β-alanine (Or its sodium salt), fatty acid amidopropyldimethylaminoacetic acid betaine, and the like.

Examples of the cationic surfactants, tetra lower alkyl Rua Nmo halide, alkyl trimethyl ammonium halides, hydroxide Sierra chill alkyl imidazolines, polyoxyethylene alkyl methyl ammonium Niu Mucha chloride, alkyl benzalkonium halides, dialkyldimethylammonium Ann monitor um halides, alkyl dimethyl benzyl ammonium halides, alkylamino emissions salt salt, alkylamine acetates, alkylamine oleates, alkylamino Noe Chirugurishin, alkyl pyridinium halide, and the like are preferable.

  In the tin or tin alloy plating bath, a smoothing agent, a brightening agent, and the like can be added singly or in combination of two or more, and is particularly effective in the case of electroplating. As these components, known substances used in tin or tin alloy plating baths can be used. Specific examples of these compounds include polymer compounds; sulfanilic acid, derivatives thereof and salts thereof; quinolines: triazole and derivatives thereof; benzothiazole and derivatives thereof; imines; triazines; guanamines; Esters; Compounds having a double bond at the position of conjugation with C = O; Aldehydes; Diketones; Aniline and derivatives thereof; Nitro compounds or sodium, potassium, ammonium salts thereof; Mercaptocarboxylic acids; Heterocyclic compounds Acetophenones; amine alcohols; aliphatic primary or secondary amines and aldehyde condensates.

  These compounds can be used alone or in combination. The amount used is suitably about 0.5 to 50 g / l, preferably about 1 to 20 g / l when a polymer substance is used. About other additives, about 0.001-50 g / l is suitable, and about 0.02-20 g / l is preferable.

  An antioxidant can be further added to the tin or tin alloy plating bath for both the electroplating bath and the electroless plating bath. Although there is no particularly strict upper limit for the concentration, it is usually sufficient to set the concentration to about 50 g / l or less. Specific examples of the antioxidant include hydroquinone, catechol, resorcin, pyrogallol, oxyhydroquinone, phloroglysin, gallic acid, catechol sulfonic acid, guaiacol, hydroquinone sulfonic acid, 3,4-dihydroxybenzoic acid, 3,4,5- Phenols such as trihydroxybenzoic acid, p-phenol sulfonic acid, cresol sulfonic acid, hydroquinone sulfonic acid, β-naphthol; aliphatic polyhydroxy compounds such as sorbic acid, sorbitol, budo sugar, ascorbic acid, isoascorbic acid, etc. Can be mentioned. These antioxidants can be used singly or in combination of two or more. In particular, a compound in which a hydroxyl group is bonded to a benzene ring or a naphthalene ring is preferable.

In order to form an active material layer made of tin or a tin alloy using the plating bath described above, a known wet plating method may be applied as appropriate. In the case of electroplating, for example, to form a tin or tin alloy using the above ^{bath, 0.1A / dm 2 ~100A / dm} 2 about the cathode current density is preferable. Although the temperature of a plating bath should just be changed suitably according to the kind of plating bath, about 10 to 95 degreeC is preferable normally. As the anode, either an insoluble anode or a soluble anode may be used. As the insoluble anode, titanium, platinum, iridium oxide, a carbon electrode, or the like can be used. As the soluble anode, tin, a tin alloy, or the like can be used.

  By performing appropriate stirring during plating, the current efficiency is increased, and an efficient plating film can be produced. In addition, by performing stirring, it is possible to form an excellent plating film having a uniform film thickness and free of plating defects such as pinholes. As a stirring method, a method of stirring a plating bath by a mechanical method, a method of forcibly controlling a liquid flow by a pump, a bubbling method using a gas such as oxygen or nitrogen, and the like can be applied. May be combined as appropriate.

  In the case of electroless plating, in addition to the components described above, a substitution accelerator such as thiourea is further added to substitution plating, and a reducing agent such as trivalent titanium is further added to reduction-type electroless plating. And plating.

  Moreover, before performing these wet plating, well-known pretreatments, such as degreasing, pickling, and an activation process, can be performed as needed.

Lithium secondary battery A lithium secondary battery using the negative electrode described above has a positive electrode, a negative electrode, and an electrolyte as main components, and the specific configuration may be the same as that of a known lithium secondary battery. . Such a lithium secondary battery has a higher charge / discharge capacity than a lithium secondary battery using a carbon electrode that is currently in practical use, and also has good cycle characteristics.

  In the lithium secondary battery of the present invention, as the positive electrode, lithium cobaltate, lithium nickelate, lithium manganate or the like can be usually used.

  Since the electrolyte needs to contain lithium ions, the electrolyte salt is preferably a lithium salt. Specifically, lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, etc. can be used as this lithium salt, and these can be used alone or in combination of two or more. Can be used. Since these lithium salts have high electronegativity and are easily ionized, they are excellent in charge / discharge cycle characteristics and can improve charge / discharge capacity.

  As the electrolyte solvent, for example, propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, and the like can be used, and these can be used alone or in combination of two or more. In particular, propylene carbonate alone, a mixture of ethylene carbonate and diethyl carbonate, γ-butyrolactone alone, and the like are suitable. In addition, the mixture of ethylene carbonate and diethyl carbonate can be arbitrarily adjusted in the range of 10 to 90% or less of mixing ratio.

The negative electrode for a secondary battery according to the present invention is obtained by using a sheet-like nonconductive material having a fine structure as a base, and forming an active material layer made of tin or a tin alloy on the surface portion and inside the fine structure. The negative electrode having such a structure retains sufficient strength as an electrode, absorbs the volume change accompanying the insertion and extraction of lithium by the fine movement of the fine structure, and deforms as a whole electrode. It can suppress and the crack of an active material layer can be prevented.

  Further, when such a non-conductive material having a fine structure is used as a substrate, the substantial film of the film can be formed without reducing the amount of tin or tin alloy as an active material per apparent electrode surface area. Since the thickness can be reduced, an electrode having a high charge / discharge capacity and excellent cycle characteristics can be obtained.

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

Example 1
An electrode was produced by the following method using a polyester fabric (size 100 mm × 100 mm × 0.10 mm: actual surface area / apparent surface area = 5.6) as a substrate. In each example, the ratio of the apparent surface area to the actual surface area is a value calculated by the following method.

* Calculation method of actual surface area / apparent surface area:
Both a nonconductive material having an apparent area (vertical x horizontal) of 1 dm ² and a tough pitch copper plate (JIS C1100P) were immersed in a 10% aqueous hydrochloric acid solution at 25 ° C. for 5 minutes, and then a palladium catalyst solution (trade name: It was immersed in Dyne Actor PB840 (manufactured by Daiwa Kasei Co., Ltd.) at 30 ° C. for 2 minutes to perform a catalyst treatment.

Next, after washing with water, activation treatment was performed in a 5% sulfuric acid aqueous solution at 25 ° C. for 3 minutes, and immersion was carried out for 5 minutes in the following electroless copper plating bath to perform electroless copper plating.
(Electroless copper plating solution composition)
Copper sulfate pentahydrate 10g / l
EDTA 25g / l
Rochelle salt 5g / l
Formaldehyde (37%) 10g / l
Bipyridyl 3mg / l
Polyethylene glycol 1g / l
pH 12.3
Bath temperature 45 ° C
After the electroless copper plating, the weight of copper deposited on the non-conductive material and the weight of copper deposited on the tough pitch copper plate were measured, and the ratio of the actual surface area to the apparent surface area of the non-conductive material was determined from the following formula.
(Ratio of actual surface area to apparent surface area of nonconductive material) = (weight of copper plated on nonconductive material) / (weight of copper plated on tough pitch copper plate)

  First, the above woven fabric made of polyester was immersed in a 90 g / l aqueous solution of caustic soda at 80 ° C. for 5 minutes, and then washed with water. Next, the polyester fabric is immersed in a 10% aqueous hydrochloric acid solution for neutralization treatment, and then immersed in a palladium catalyst solution (trade name: Dyne Actor PB840, manufactured by Daiwa Kasei Co., Ltd.) for catalysis. Processed.

Next, after rinsing with water, activation treatment was performed in a 5% aqueous sulfuric acid solution and immersed in the following electroless copper plating bath for 5 minutes to deposit a 20 g / m ² copper film on the polyester fabric. .

Electroless copper plating solution Copper sulfate pentahydrate 10g / l
EDTA 25g / l
Rochelle salt 5g / l
Formaldehyde (37%) 10g / l
Bipyridyl 3mg / l
Polyethylene glycol 1g / l
pH 12.3
Bath temperature 45 ° C
Subsequently, electroplating was performed for 7 minutes in a tin plating bath having the following composition, and an electrode was obtained by depositing a tin plating film of 60 g / m ² .

Tin plating bath Tin methanesulfonate 200g / l
Methanesulfonic acid 100g / l
Benzalacetone 0.5g / l
Catechol 2g / l
Current density 3A / dm ²
Bath temperature 25 ° C

Comparative Example 1
A rolled copper foil (size 100 mm × 100 mm × 0.02 mm) was electrolytically degreased at a current density of 1 A / dm ² for 1 minute in an alkaline electrolytic degreasing solution at room temperature, and then washed with water. Next, the copper foil was pickled with a 10% aqueous sulfuric acid solution, then washed with water, and electroplated for 7 minutes using the tin plating bath used in Example 1 to deposit a 60 g / m ² tin film. Thus, an electrode was obtained.

Example 2
After depositing an electroless copper plating film on the same polyester fabric as that used in Example 1 under the same conditions as in Example 1, electroplating is performed in the following tin-copper alloy plating bath for 5 minutes, A tin-copper alloy film having a copper content of 40% by weight was deposited at 60 g / m ² to obtain an electrode.

Tin-copper plating solution Tin sulfate 60g / l
Copper sulfate pentahydrate 60g / l
Sulfuric acid 100g / l
Cresol sulfonic acid 10g / l
Hydroquinone 1g / l
Ethylene glycol 50g / l
Polyoxyethylene lauryl ether 2g / l
Bath temperature 25 ° C
Current density 5A / dm ²
Bath temperature 25 ° C

Example 3
A polyurethane catalyst (size 100 mm × 100 mm × 2.00 mm: actual surface area / apparent surface area = 6.2) made of polyurethane is immersed in a 10% hydrochloric acid aqueous solution and acid-treated, and then a palladium catalyst. It was immersed in a liquid (trade name: Dyne Actor PB840, manufactured by Daiwa Kasei Co., Ltd.) to perform a catalyst treatment. Next, after washing with water, activation treatment was performed in a 5% sulfuric acid aqueous solution, and electroplating was performed for 5 minutes in the following electroless nickel-phosphorus plating bath to deposit a 20-g / m ² nickel-phosphorus film.

Electroless nickel-phosphorus plating bath Nickel sulfate hexahydrate 20g / l
Sodium hypophosphite 21g / l
Sodium acetate 5g / l
Trisodium citrate 36g / l
Lactic acid 3ml / l
pH 4.8
Bath temperature 60 ° C
Next, electroplating was performed in the tin plating bath used in Example 1 for 7 minutes to deposit a 60 g / m ² tin film. Furthermore, it was compressed by passing a press roll whose slit width was adjusted to 0.3 mm to obtain an electrode having a thickness of 0.4 mm.

Example 4
After depositing an electroless copper plating film under the same conditions as in Example 1 on a woven fabric (size 100 mm × 100 mm × 0.11 mm: actual surface area / apparent surface area = 5.1) made of flame retardant polyester, Plating was performed in a tin-silver alloy plating bath for 20 minutes to deposit 60 g / m ² of a tin-silver film having a silver content of 8% by weight in the film to obtain an electrode.

Tin-silver plating solution Tin methanesulfonate 60g / l
Silver methanesulfonate 30g / l
Gluconic acid 100g / l
Gallic acid 1g / l
Isopropanol 5g / l
Polyoxyethylene lauryl ether 2g / l
pH 6.3
Bath temperature 25 ° C
Current density 1A / dm ²
Bath temperature 25 ° C

Example 5
A copper film was deposited on a knitted fabric made of polypropylene (size: 100 mm × 100 mm × 0.15 mm: actual surface area / apparent surface area = 4.1) under the same conditions as in Example 1, and then a tin-zinc plating bath having the following composition. In particular, electroplating was performed for 10 minutes to deposit 60 g / m ² of a tin-zinc alloy film having a zinc content of 10% by weight. This was heat-treated at 220 ° C. for 5 hours under vacuum to obtain an electrode.

Tin-zinc plating bath Tin methanesulfonate 280g / l
Zinc sulfate heptahydrate 15g / l
Trisodium citrate dihydrate 200g / l
Ammonium sulfate 130g / l
Sodium L-ascorbate 1g / l
pH 5
Current density 2A / dm ²
Bath temperature 25 ° C

Comparative Example 2
An electrolytic copper foil having a thickness of 20 μm was electrolytically degreased at a current density of 1 A / dm ² for 1 minute in an alkaline electrolytic degreasing solution at room temperature, and then washed with water. Next, after pickling with a 10% sulfuric acid aqueous solution, washing with water and electroplating for 10 minutes in the tin-zinc plating bath used in Example 5, the zinc content in the coating was 10% by weight. A zinc alloy film 60 g / m ² was deposited. This was heat-treated at 220 ° C. for 5 hours under vacuum to obtain an electrode.

Example 6
After depositing an electroless copper plating film on a fabric made of the same polyester as that used in Example 1 under the same conditions as in Example 1, plating was performed in the following substituted tin plating bath for 25 minutes to form a tin film. 60 g / m ^{2 was} deposited. This was heat-treated at 220 ° C. for 5 hours under vacuum to obtain an electrode.

Substitution tin plating bath Tin (added as tin methanesulfonate solution) 60g / l
Methanesulfonic acid 60g / l
Thiourea 80g / l
Iminodiacetic acid 2g / l
Hydroquinone 0.5g / l
Polyoxyethylene nonylphenyl ether 1g / l
Bath temperature 75 ° C

Example 7
A fabric made of polyamide (size 100 mm × 100 mm × 0.10 mm: actual surface area / apparent surface area = 4.3) is dipped in a 10% hydrochloric acid aqueous solution and subjected to acid treatment, and then a palladium catalyst solution (Dyneactor PB840, Yamato). (Chemical Conversion Co., Ltd.) and catalyzed. Next, after thoroughly washing with water, activation treatment was performed in a 5% sulfuric acid aqueous solution, and plating was carried out for 5 minutes in the electroless copper plating bath used in Example 1 to deposit 20 g / m ² of copper on the fabric. To be deposited.

Next, electroplating was performed for 6 minutes in a zinc plating bath having the following composition to deposit a 7 g / m ² zinc film.

Zinc plating bath Zinc sulfate heptahydrate 40g / l
Ammonium sulfate 40 g / l
pH 5
Current density 2A / dm ²
Bath temperature 30 ° C
Further, plating was carried out for 10 minutes in the tin-zinc plating bath used in Example 5 to deposit 60 g / m ² of a tin-zinc alloy film having a zinc content of 10% by weight in the film. This was heat-treated at 200 ° C. for 5 hours under vacuum to obtain an electrode.

Example 8
After a DTY-treated polyester fabric (size 100 mm x 100 mm x 0.11 mm: actual surface area / apparent surface area = 5.3) is passed through a press roll with a slit width of 85 μm at room temperature and compressed to an average thickness of 93 μm Then, after depositing a copper film and a tin-zinc alloy film under the same conditions as in Example 6, plating was performed for 1 minute in the following silver plating bath (Dyne Silver AG-PL 30, Yamato Kasei Co., Ltd.). A silver film of / m ² was deposited. Furthermore, it was heat-treated at 220 ° C. for 3 hours under a nitrogen atmosphere to obtain an electrode.

Silver plating bath (Dyne Silver AG-PL 30, Daiwa Kasei Co., Ltd.)
pH 7
Current density 1A / dm ²
Bath temperature 30 ° C

Example 9
After depositing a copper film under the same conditions as in Example 1 on a foam made of silicon (size 100 mm × 100 mm × 2.00 mm: actual surface area / apparent surface area = 7.1), tin-bismuth plating of the following composition Electroplating was performed in a bath for 20 minutes to deposit 60 g / m ² of a tin-bismuth alloy film having a bismuth content of 9% by weight. A press roll whose slit width was adjusted to 0.3 mm was passed through and subjected to compression processing to obtain an electrode having a thickness of 0.5 mm. Furthermore, it was heat-treated at 220 ° C. for 3 hours under a nitrogen atmosphere to obtain an electrode.

Tin-bismuth plating bath Tin methanesulfonate 280g / l
Bismuth methanesulfonate 40g / l
Methanesulfonic acid 200g / l
Ammonium sulfate 75g / l
Sodium L-ascorbate 1g / l
Polyoxyethylene lauryl ether 2g / l
Current density 1A / dm ²
Bath temperature 25 ° C

Battery evaluation Using the electrodes obtained in the above Examples and Comparative Examples as negative electrodes, the performance was evaluated by the following method.
First, using a lithium foil as a counter electrode, a coin-type cell was manufactured using a 1: 1 mixed solution of ethylene carbonate and dimethyl carbonate in which 1 mol / l LiPF ₆ was dissolved as an electrolyte. Using this coin cell, cycle characteristics were evaluated in a voltage range of 0-1 V at a current density of 1 mA / cm ² .

  Table 1 below shows the capacity at the first cycle (in the Li insertion reaction) and the capacity retention rate at the 50th cycle. The capacity maintenance rate at 50 cycles is shown as the ratio of the capacity at the 50th cycle to the capacity at the 1st cycle.

以上の結果から明らかなように、実施例１〜４で得た負極を用いた場合には、比較例と比べて、初回容量が大きくサイクル特性も良好であった。特に、めっき後、熱処理を行って得た実施例５〜９の負極を用いた場合には、さらにサイクル特性が向上することがわかった。

As is clear from the above results, when the negative electrodes obtained in Examples 1 to 4 were used, the initial capacity was large and the cycle characteristics were good as compared with the comparative example. In particular, when the negative electrodes of Examples 5 to 9 obtained by heat treatment after plating were used, it was found that the cycle characteristics were further improved.

Claims (18)

It is seen containing a substrate made of a non-conductive material sheet and an active material layer made of tin or tin alloy formed on the surface portion and microstructure internal surface of the substrate having a microstructure substrate and the active material layer And a negative electrode for a lithium secondary battery having a metal layer acting as a current collector ,
Between the metal layer acting as a current collector and the active material layer, it further has a metal layer made of zinc or an alloy containing zinc as a main component,
A negative electrode for a lithium secondary battery obtained by performing heat treatment after forming an active material layer and other metal layers .   The negative electrode for a lithium secondary battery according to claim 1, wherein the sheet-like non-conductive material having a fine structure is a cloth or a resin foam.   The sheet-like non-conductive material having a microstructure is a material in which the actual surface area of the material including the microstructure portion is not less than three times the apparent surface area of the material. Negative electrode for lithium secondary battery.   The negative electrode for a lithium secondary battery according to any one of claims 1 to 3, wherein the sheet-like non-conductive material having a fine structure is subjected to compression processing.   The negative electrode for a lithium secondary battery according to any one of claims 1 to 4, wherein the active material layer made of tin or a tin alloy is formed by a wet plating method or a dry plating method.   The elements that form alloys with tin in the tin alloys are Al, Si, P, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Ag, Cd, In, Sb, Au, Hg, Tl, Pb, The negative electrode for a lithium secondary battery according to any one of claims 1 to 5, which is an alloy of tin and at least one metal selected from the group consisting of Bi and Bi.   The negative electrode for a lithium secondary battery according to any one of claims 1 to 6, wherein the tin alloy is an alloy of tin and at least one metal selected from the group consisting of zinc, copper, antimony, bismuth, cobalt, and iron. . The negative electrode for a lithium secondary battery according to any one of claims 1 to 7, wherein the metal layer acting as a current collector is copper, iron, nickel, or an alloy containing these metals as a main component.   The negative electrode for a lithium secondary battery according to any one of claims 1 to 8, further comprising a metal layer made of silver, cadmium, indium, antimony or an alloy containing these metals as a main component on the active material layer. The negative electrode for a lithium secondary battery according to any one of claims 1 to 9, wherein by performing a heat treatment, an interface between tin and the metal of the conductor layer is formed at an interface between the active material layer and the lower layer thereof. A negative electrode for a lithium secondary battery, wherein a layer made of a compound is formed. A base made of a non-conductive material sheet having a microstructure, forming a metal layer which acts as a current collector by a dry plating method or a wet plating method, followed by dry plating method or a wet plating method, nitrous Namarimata is After forming a metal layer made of an alloy containing zinc as a main component, an active material layer made of tin or a tin alloy is formed by a wet plating method ,
A method for producing a negative electrode for a lithium secondary battery, wherein a heat treatment is performed after forming the metal layer . 12. The lithium secondary battery according to claim 11 , wherein the active material layer made of tin or tin alloy is formed by displacement plating before forming the active material layer made of tin or tin alloy by electroplating. Manufacturing method for negative electrode. After the active material layer is formed by the method according to claim 11 or 12 , a metal layer made of silver, cadmium, indium, antimony or an alloy containing these metals as a main component is formed by a dry plating method or a wet plating method. A method for producing a negative electrode for a lithium secondary battery, comprising forming the negative electrode. The method for producing a negative electrode for a lithium secondary battery according to any one of claims 11 to 13 , wherein at least one of the active material layer and the other metal layer is formed by a wet plating method, the carbon number is 6 or less. A method for producing a negative electrode for a lithium secondary battery, comprising wet plating using a plating solution containing at least one component selected from the group consisting of lower alcohols, alcohol ethers and ketones. The method for producing a negative electrode for a lithium secondary battery according to any one of claims 11 to 14 , wherein at least one of the active material layer and the other metal layer is formed by a wet plating method, the carbon number is 6 or less. A method for producing a negative electrode for a lithium secondary battery, comprising performing pretreatment of wet plating using a pretreatment liquid containing at least one component selected from the group consisting of lower alcohols, alcohol ethers and ketones.   The elements that form alloys with tin in the tin alloys are Al, Si, P, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Ag, Cd, In, Sb, Au, Hg, Tl, Pb, The method for producing a negative electrode for a lithium secondary battery according to any one of claims 10 to 15, which is an alloy of tin and at least one metal selected from the group consisting of Bi and Bi.   The negative electrode for a lithium secondary battery according to any one of claims 10 to 16, wherein the tin alloy is an alloy of at least one metal selected from the group consisting of zinc, copper, antimony, bismuth, cobalt and iron. Manufacturing method. A negative electrode for a lithium secondary battery according to any one of claims 1 to 10, and an electrolyte, a lithium secondary battery comprising a positive electrode.