JP2004022466A - High-capacity negative electrode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-capacity negative electrode using lithium as a negative electrode active material, utilizing the characteristic of lithium of high capacity, and extremely useful for reducing the weight and size of a battery. <P>SOLUTION: This negative electrode has a structure composed by stacking lithium on both surfaces of a composite collector comprising a resin film, conductive treatment layers formed on both the surfaces of the resin layer, and a metal-plated layer formed on the conductive treatment layers by electrolytic plating. The composite collector has a surface electric resistance of 40 mΩ/cm or below and a tensile strength of 0.8 kg/cm or above, and is characterized by satisfying the condition of the following inequality: Y1+Y2+Y3≤0.8×(X1+X2+X3)×Y3/X3, wherein X1 is the thickness (μm) of the resin film; X2 is the the total thickness (μm) of the conductive treatment layer; X3 is the the total thickness (μm) of the metal-plated layer; Y1 is the weight (mg/cm<SP>2</SP>) of the resin film; Y2 is the weight (mg/cm<SP>2</SP>) of the conductive treatment layer; and Y3 is the weight (mg/cm<SP>2</SP>) of the metal-plated layer. <P>COPYRIGHT: (C)2004,JPO

Description

【００３９】
上記の実施例１〜６及び参考例１の１０ｃｍ^２の負極の両面に以下の電解質を介して、１５ｃｍ^２の正極を組み合せてＬｉ電池とした。
正極：
Ａｌ箔（２０μｍ）の片面に、ＬｉＣｏＯ_２：アセチレンブラック：ＰＶＤＦ＝１００：８：１２（重量比）の組成からなる活物質をいずれの負極活物質に対しても、充分な量である５００ｍｇ／ｃｍ^２積層したもの。
電解質：
プロピレンカーボネートとエチレンカーボネートを等重量比で配合した液にＬｉＢＦ_４を１モル／Ｌ添加した溶液とポリアクリロニトリルを９：１にブレンド後、１６０℃で１分間でゲル化したゲル電解質。
【００４０】
上記のＬｉ電池について、以下の方法により、電池容量及び集電性能指数を算出した。
実施例１〜６及び参考例１の負極を用いて形成されたＬｉ電池を、６０℃の雰囲気中に１ヶ月放置後、充電終了電圧＝４．２Ｖ、放電終了電圧＝２Ｖ、充放電速度＝０．２Ｃの条件下で定電流充放電を行い、放電容量を測定し、下記式により、単位重量の負極の放電容量寄与率（ここでは単位重量負極容量と呼ぶ）を求め、負極性能を評価した。
単位重量負極容量：放電容量（ｍＡｈ）／用いた負極重量（ｇ）
【００４１】
【表２】

【００４２】
【発明の効果】
本発明の負極は、金属リチウムの高容量を活かし、従来の負極に比して軽量化、薄肉化が図れ、ひいては二次電池の高容量化を実現することができる。
【図面の簡単な説明】
【図１】本発明の高容量負極の概略積層構造を示す断面図。
【図２】図１の高容量負極に使用されている複合集電体の層構成を示す断面図。
【図３】図１の高容量負極に使用されている複合集電体の実施態様を示す断面図。
【図４】図１の高容量負極に使用されている複合集電体の他の実施態様を示す断面図。
【符号の説明】
１…高容量負極
１０…複合集電体
１１…樹脂フィルム
１２…導電処理層
１３…金属メッキ層
１５…貫通孔
１７…リード線
２０…金属リチウム箔[0001]
[Field of the Invention]
The present invention relates to a negative electrode mainly used for a lithium-based battery.
[0002]
[Prior art]
In recent years, as electronic devices such as portable wireless telephones, portable personal computers, and portable video cameras have become portable, various electronic devices have been miniaturized, and built-in secondary batteries such as lithium-based and nickel-hydrogen-based batteries have been increased in capacity. There is a strong demand for light and thinning.
For example, a lithium secondary battery collects a negative electrode formed by holding a carbon-based negative electrode active material on the surface of a current collector and a positive electrode active material that reversibly electrochemically reacts with lithium ions such as lithium cobalt composite oxide. It has a positive electrode held on the body surface and an electrolytic solution, and a separator for preventing a short circuit between both electrodes is disposed between the negative electrode and the positive electrode.
In such a lithium secondary battery, since the proportion of the negative electrode (particularly the current collector) occupying the total weight of the battery is large, it is necessary to reduce the weight of the negative electrode particularly in reducing the weight.
[0003]
[Problems to be solved by the invention]
As an attempt to reduce the weight of the current collector, for example, JP-A-5-31494 proposes a method of laminating an extremely thin conductive layer on a resin film by metal vapor deposition or sputtering. However, in this method, the upper limit of the thickness of the metal conductor layer laminated on the resin film is about 2000 mm from the viewpoint of economy and heat resistance of the resin. In other words, the conductive layer has to be extremely thin, and the current collection capability is not only inferior, but also due to corrosion in the battery over time, the ultrathin conductive layer dissolves and disappears, further increasing the current collection capability. It was not very useful for practical use.
[0004]
Further, metallic lithium has attracted attention as a negative electrode active material. Metallic lithium is a high-capacity active material, and a battery using the lithium has a large battery capacity per unit weight and unit volume, and is highly expected in terms of weight reduction of the battery.
However, metal Li is a high-capacity active material, but has a drawback of low mechanical strength. For this reason, when it is used alone for the negative electrode, it is necessary to make it thicker than necessary (for example, 150 μm or more) in order to ensure mechanical strength, and the characteristic of metal Li that it has a high capacity is sufficient. The battery capacity per unit weight and volume has not been increased.
Moreover, although Cu foil was used as a current collector and metal lithium was laminated on this Cu foil to make a negative electrode recently, since Cu foil has a high specific gravity, even in such a method, The characteristic of metallic lithium that the capacity per unit weight is large was impaired.
[0005]
Accordingly, an object of the present invention is to provide a high-capacity negative electrode that uses metallic lithium as a negative electrode active material and fully utilizes the high-capacity characteristic of metallic lithium, and is extremely useful for reducing the weight and size of batteries. There is.
[0006]
[Means for Solving the Problems]
According to the present invention, on both surfaces of a composite current collector comprising a resin film, a conductive treatment layer formed on both surfaces of the resin film, and a metal plating layer formed on the conductive treatment layer by electrolytic plating treatment. The composite current collector has a structure in which metallic lithium is laminated, has a surface electrical resistance of 40 mΩ / cm or less and a tensile strength of 0.8 kg / cm or more, and satisfies the following formula: High capacity negative electrode characterized by satisfaction;
Y1 + Y2 + Y3 ≦ 0.8 × (X1 + X2 + X3) × Y3 / X3
In the formula, X1: thickness of resin film (μm)
X2: Total thickness of the conductive treatment layer (μm)
X3: Total thickness of metal plating layer (μm)
Y1: Weight of resin film (mg / cm ² )
Y2: Weight of conductive treatment layer (mg / cm ² )
Y3: Weight of metal plating layer (mg / cm ² )
Is provided.
[0007]
That is, in the present invention, instead of a high specific gravity Cu foil, a resin film having a low specific gravity but a strong mechanical strength is used as a core, and a metal film is provided on both sides of the resin film via a conductive treatment layer. By using a composite current collector with a laminated plating layer, the weight of the current collector is reduced while securing the mechanical strength, and capacitive metal lithium is laminated on both sides of the composite current collector. By doing so, it is possible to effectively realize the high capacity of metallic lithium.
In the present invention,
1. The metallic lithium has a thickness of 2 to 50 μm per side,
2. The current carrying resistance of the composite current collector is 100 mΩ / cm or less,
3. The metal plating layer is mainly composed of Cu;
4). The total thickness (X1 + X2 + X3) of the resin film, the conductive treatment layer, and the metal plating layer is 9 μm or less,
Is preferred.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the high capacity | capacitance negative electrode of this invention is demonstrated in detail based on the specific example shown to an accompanying drawing.
FIG. 1 is a cross-sectional view showing a schematic laminated structure of a high capacity negative electrode of the present invention.
FIG. 2 is a cross-sectional view showing the layer structure of the composite current collector used in the high capacity negative electrode of FIG.
FIG. 3 is a cross-sectional view showing an embodiment of the composite current collector used in the high capacity negative electrode of FIG.
4 is a cross-sectional view showing another embodiment of the composite current collector used in the high-capacity negative electrode of FIG.
[0009]
In FIG. 1, a high-capacity negative electrode 1 of the present invention indicated by 1 as a whole is composed of a composite current collector 10 and metal lithium foils 20 laminated on both surfaces thereof.
[0010]
In the high-capacity negative electrode 1, the composite current collector 10 includes a core resin film 11, conductive treatment layers 12 formed on both surfaces of the film, and the conductive treatment layer 12, as shown in FIG. It consists of the formed metal plating layer 13. That is, the metal lithium foil 20 is laminated on the metal plating layer 13.
[0011]
The resin film 11 can be made of various materials depending on the type of battery and required performance, and is not particularly limited. Generally, polyethylene terephthalate (PET), polyethylene naphthalate is used. (PEN), polypropylene (PP), polyethylene (PE), an acid-modified olefin resin modified with an unsaturated carboxylic acid such as acrylic acid or maleic acid, or the like is used.
In the present invention, the thickness of the resin film 11 is set to a thickness that satisfies a conditional expression described later. Generally, as long as the conditional expression is satisfied, characteristics required for the negative electrode, for example, mechanical Depending on the mechanical strength, lightness, thin film properties, etc., it is preferable to set the range of 2 μm to 20 μm.
Furthermore, the resin film 11 is stretched or unstretched, or the crystallinity of the resin film 11 is not particularly limited. However, when mechanical strength is particularly required, the resin film 11 is stretched. It is preferable to use a film. When adhesion to the conductive treatment layer 12 described below is required, it is preferable to use an unstretched and low crystallinity film.
[0012]
The conductive treatment layer 12 is provided to form a metal plating layer 13 to be described later on the resin film 11, and is generally a metal mainly composed of Cu, Ni, Ag, or the like, or a conductive agent. It is formed from carbon powder or the like.
For example, the conductive treatment layer 12 can be provided by forming the ultrathin metal film on the resin film 11 by means such as vapor deposition or sputtering. Also, a conductive agent containing at least one of the above metal powder and carbon powder is mixed with a vehicle (for example, epoxy phenol resin) to prepare a coating solution, and the coating solution is thinly coated on the surface of the resin film 11. Then, the conductive coating film formed by drying can be used as the conductive treatment layer 12.
Furthermore, a conductive coating film can be formed on the above-mentioned ultra-thin metal film, and such a composite layer can be used as the conductive treatment layer 12. When such a composite layer is used as the conductive treatment layer 12, since the upper conductive coating serves as a barrier, it is possible to form an ultrathin film using a metal such as Al which is easily affected by the plating solution. is there.
[0013]
The conductive treatment layer 12 should have a thickness such that the electrical resistance of the layer is 1.3 Ω / cm or less. This is because if the electric resistance is higher than 1.3 Ω / cm, it is difficult to form a metal plating layer 13 described below on the electric resistance.
[0014]
A metal plating layer 13 is formed on the conductive treatment layer 12 by electrolytic plating.
Examples of the metal constituting the metal plating layer include Cu and Ni, but Cu is usually preferable.
[0015]
The thickness of the metal plating layer is set so that the surface electrical resistance of the composite current collector 10 after plating is 40 mΩ or less.
In addition, this surface electrical resistance means that the composite current collector 10 on which the plating layer 13 is formed is cut into a size of 1 cm width, and has an area of 4 mm ^{2 at} intervals of 1 cm on the measurement surface of this sample. It is a value obtained by measuring the electrical resistance by sufficiently bringing the + terminal and the-terminal into contact with each other. When measuring the surface electrical resistance value, it is necessary to remove the conductive treatment layer and the metal plating layer on the non-measurement surface to eliminate the influence of the non-measurement surface.
[0016]
In the present invention, it is important that the resin film 11, the conductive treatment layer 12, and the metal plating layer 13 described above are combined so as to satisfy the following formula to form the composite current collector 10.
Y1 + Y2 + Y3 ≦ 0.8 × (X1 + X2 + X3) × Y3 / X3
In the formula, X1: thickness of resin film (μm)
X2: Total thickness of the conductive treatment layer (μm)
X3: Total thickness of metal plating layer (μm)
Y1: weight of the resin film (mg / ^cm 2)
Y2: Weight of conductive treatment layer (mg / cm ² )
Y3: Weight of metal plating layer (mg / cm ² )
The above conditional expression means that the weight of the composite current collector 10 is reduced to 80% or less compared to the weight of the same thickness of a simple metal current collector made of only the metal component of the plating layer. Thereby, the weight reduction of the high capacity | capacitance negative electrode 1 provided with the metal lithium foil 20 can be achieved.
[0017]
When the high-capacity negative electrode 1 is required to be thin as well as light, the total thickness (X1 + X2 + X3) of the resin film 11, the conductive treatment layer 12, and the metal plating layer 13 is preferably 9 μm or less. .
[0018]
In the present invention, the tensile strength of the composite current collector formed as described above needs to be 0.8 kg / cm or more. When the tensile strength is less than 0.8 kg / cm, in combination with the low strength of the metal lithium foil 20, the high capacity negative electrode 1 or the composite current collector 10 cannot withstand the tension when assembling the battery, and breakage occurs. Or deformation.
This tensile strength means the yield point strength when the composite current collector 10 is cut to a length of 1 cm and a length of 10 cm and pulled at a speed of 20 mm / min.
[0019]
In general, it is difficult for a single metal to stably produce a foil having a thickness of 9 μm or less, and it is also difficult to obtain a sufficient tensile strength. In the present invention, by combining the resin film 11, the conductive treatment layer 12, and the metal plating layer 13 so as to satisfy the conditional expressions described above, not only weight reduction but also thinning is possible, and the utility is extremely great.
[0020]
In the present invention, it is preferable that the front and back energization resistance of the composite current collector 10 is 100 mΩ or less. If the energization resistance exceeds 100 mΩ, when only one side of the lead wire is bonded, the current collecting property of the non-bonded surface is remarkably inferior, which causes a decrease in battery performance.
The energizing resistance is a positive terminal having an area of 4 mm ² is sufficiently brought into contact with one surface of the above-described sample for measuring the surface electrical resistance of the composite current collector 10 and is disposed on the back surface thereof (the part located on the opposite side of the positive terminal) ), And the electric resistance was measured by sufficiently contacting a negative terminal having an area of 4 mm ² .
[0021]
In the present invention, the metal lithium foil 20 formed on both surfaces of the above-described composite current collector 10, that is, the metal plating layer 13, is formed by pressure molding using, for example, a metal lithium foil. 10 is laminated.
In general, the thickness of the metal lithium foil 20 is preferably 2 to 50 μm in order to obtain a necessary battery capacity. When the thickness is less than 2 μm, it is difficult to find the features of the high capacity negative electrode, and when it exceeds 50 μm, the superiority to the metallic lithium alone is reduced. In the present invention, metallic lithium used as the negative electrode active material has a high capacity, so even if the thickness is thin and light, it is advantageous to obtain a high capacity battery. Further, the drawback of metallic lithium having low strength is sufficiently compensated by using the composite current collector 10 described above, and the high capacity performance of metallic lithium can be sufficiently exhibited.
[0022]
In the present invention, the composite current collector 10 shown in FIG. 1 or 2 has a flat shape, but is not limited to such a shape. For example, as shown in FIG. Alternatively, the shape may have a wave-like undulation. Moreover, it can also be set as the shape by which the unevenness | corrugation was formed in the surface.
By adopting such a shape, it is possible to contribute to the improvement of battery performance by increasing the negative electrode area or the like.
In addition, the throwing effect of metallic lithium in contact with the current collector surface can be achieved, the adhesion with metallic lithium can be improved, and the chemical reaction in the battery can be promoted.
[0023]
For example, after forming the conductive treatment layer 12 on the surface of the resin film 11, the embossing process is performed by pressing the hot roll formed with the embossed pattern up and down, and then conducting the conductive process. This can be easily performed by forming the metal plating layer 13 on the treatment layer 12.
In conventional metal current collectors, hot embossing is difficult, so mechanical plastic deformation is used, but the metal is cracked, non-uniform in shape, or embossed. However, mechanical plastic deformation processing is not easy, for example, the embossing disappears in the active material forming step. Also from this point, the industrial utility of the present invention using the composite current collector 10 having the resin film 11 as a core is great.
[0024]
Furthermore, in this invention, as shown in FIG. 4, many through-holes 15 can also be formed in the resin film 11. FIG. By forming such a through hole 15, not only can the front and back energization be ensured, but the effect depends on the hole diameter, but a further reduction in weight can be achieved.
[0025]
Formation of the through hole 15 in the resin film 11 can be performed by, for example, pressing a mold provided with a large number of heated needles. Further, the through hole 15 can be easily formed by electric discharge machining, punching using a small diameter punch, or the like, and the means is not particularly limited.
[0026]
Moreover, by forming the through holes 15 as described above, the conductivity between the metal plating layers 13 formed on the front and back of the composite current collector 10 is enhanced, for example, as shown in FIG. The effect that the lead wire 17 is bonded only to one surface of the composite current collector 10 and electrically connected to a predetermined terminal (not shown) is exhibited.
That is, when a metal foil such as Cu foil is used as a current collector, both surfaces thereof become current collecting surfaces, and a lead wire only needs to be provided on one surface, but a composite using a resin film as a core. In the current collector, there is a problem that it is necessary to join lead wires on both sides, and the manufacturing process becomes complicated. However, by providing the through-holes 15 in the resin film 11 as described above, the conductivity between the metal plating layers 13 formed on both surfaces of the composite current collector 10 can be improved, so that this problem is effectively prevented. It can be avoided.
[0027]
The reason why the conductivity between the metal plating layers 13 is enhanced by forming the through holes 15 is considered as follows.
That is, when the conductive treatment layer 12 and the metal plating layer 13 are formed on the resin film 11 in which the through holes 15 are formed by the above-described method, the metal plating layer 13 wraps around the through holes 15, and as a result, both surfaces It is considered that the electrical conductivity between the metal plating layers 13 is improved. Actually, when the inside of the through hole 15 is observed with a microscope, it is possible to confirm the wraparound of the metal plating layer 13.
Of course, in the present invention, the conductive property between the metal plating layers 13 can be further enhanced by forming the conductive treatment layer 12 on the inner surface of the through hole 15.
[0028]
The negative electrode of the present invention comprising the composite current collector 10 described above and the metal lithium foil 20 provided on both surfaces thereof is not particularly distinguished between a primary battery and a secondary battery, but is particularly suitable for use as a secondary battery. By using this negative electrode, the characteristics of metallic lithium can be utilized to reduce the weight and capacity of the battery.
For example, in a lithium secondary battery, the positive electrode is not limited to this, but a current collector such as an Al foil is made of a lithium cobalt-based composite oxide such as LiCoO ₂ or a conductive polymer such as polyaniline. What provided the layer of the positive electrode active material is used, and what melt | dissolved electrolyte salt in the nonaqueous solvent is used as an electrolyte between a positive electrode and a negative electrode. Non-aqueous solvents include carbonates such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate and dipropyl carbonate, cyclic esters such as γ-butyrolactone and propiolactone, chain ethers such as diethoxyethane and dimethoxyethane, dimethyl There are amides such as acetamide, nitriles such as acetonitrile and propionitrile, and mixed solvents thereof. As the electrolyte _{salt, LiPF 6, LiClO 4, CF} 3 SO 3 Li, C 4 F 6 SO 3 Li, (CF 3 SO 2) 2 NLi, (CF 3 SO 2) 3 CLi, LiBF 4, LiAsF 6 There are lithium salts. Furthermore, as the separator, a polyolefin-based porous film such as polyethylene or polypropylene is used. When the electrolyte is solid, the separator is not always necessary.
[0029]
【Example】
The invention is illustrated by the following examples.
[0030]
Example 1
As the resin film, a PET film having a thickness of 4 μm (X1 = 4) was used, and a Ni-based paint in which Ni powder was blended by 1 μm in dry thickness as a conductive agent was applied to both surfaces and dried (X2 = 2).
Further, Cu having a thickness of 2 μm was plated on both surfaces (X3 = 4) to prepare a composite current collector.
In this composite current collector, the weight of the PET film is 0.564 mg / cm ² (Y1 = 0.564), and the weight of the conductive treatment layer coated with the Ni-based paint is 0.644 mg / cm ² (Y2 = 0.644). ), The weight of the Cu plating was 3.572 mg / cm ² (Y3 = 3.572).
On both surfaces of the composite current collector prepared above, metallic lithium (thickness 50 μm) each having the same thickness was laminated as an active material to form a negative electrode.
[0031]
(Example 2)
A PET film having a thickness of 4 μm (X1 = 4) was used as the resin film, and a Ni-based paint similar to that of Example 1 was applied to each side by a dry thickness of 1 μm and dried (X2 = 2).
Furthermore, Cu of thickness: 0.3 micrometer was plated on both surfaces (X3 = 0.6), and the composite electrical power collector was created.
In this composite current collector, the weight of the PET film is 0.564 mg / cm ² (Y1 = 0.564), and the weight of the conductive treatment layer coated with the Ni-based paint is 0.644 mg / cm ² (Y2 = 0.644). ), the weight of Cu plating was ^{0.536mg / cm 2 (Y3 = 0.536} ).
Except for using the above composite current collector, a metal lithium foil was laminated in the same manner as in Example 1 to obtain a negative electrode.
[0032]
(Example 3)
As a resin film, a PET film having a thickness of 14 μm (X1 = 14) was used, and a Ni-based paint similar to that in Example 1 was applied to each of the both surfaces by a dry thickness of 1 μm and dried (X2 = 2).
Furthermore, Cu of thickness: 4 μm was plated on both surfaces (X3 = 8) to prepare a composite current collector.
In this composite current collector, the weight of the PET film was 1.974 mg / cm ² (Y1 = 1.974), and the weight of the conductive treatment layer coated with the Ni-based paint was 0.644 mg / cm ² (Y2 = 0.644). ), The weight of the Cu plating was 7.144 mg / cm ² (Y3 = 7.144).
Except for using the above composite current collector, a metal lithium foil was laminated in the same manner as in Example 1 to obtain a negative electrode.
[0033]
(Example 4)
A 4 μm thick (X1 = 4) PET film was used as the resin film, and Cu vapor-deposited layers were formed on both sides of the PET film (X2 = 0.1).
Further, Cu having a thickness of 2 μm was plated on both surfaces (X3 = 4) to prepare a composite current collector.
In this composite current collector, the weight of the PET film is 0.564 mg / cm ² (Y1 = 0.564), the weight of the conductive treatment layer deposited with Cu is 0.047 mg / cm ² (Y2 = 0.047), The weight of Cu plating was 3.572 mg / cm ² (Y3 = 3.572).
Except for using the above composite current collector, a metal lithium foil was laminated in the same manner as in Example 1 to obtain a negative electrode.
[0034]
(Example 5)
A negative electrode was prepared in the same manner as in Example 4 except that the thickness of the laminated metal lithium was 2 μm.
[0035]
(Example 6)
A negative electrode was prepared in the same manner as in Example 4 except that a maleic acid-modified olefin film having a thickness of 14 μm (X1 = 14) was used as the resin film.
[0036]
(Reference Example 1)
A negative electrode was obtained in exactly the same manner as in Example 1, except that an active material (20 mg / cm ² ) having a composition of graphite: PVDF = 100: 11 (weight ratio) was laminated on a 15 μm Cu foil.
[0037]
Regarding the composite current collectors used in Examples 1 to 6 and Reference Example 1, the surface electrical resistance is 40 mΩ / cm or less, and the tensile strength is 0.8 kg / cm or more. there were. Further, Table 1 shows values of parameters of X1 to X3 and Y1 to Y3 in these composite current collectors.
[0038]
[Table 1]

[0039]
Lithium batteries were obtained by combining 15 cm ² positive electrodes on both sides of the 10 cm ² negative electrodes of Examples 1 to 6 and Reference Example 1 via the following electrolyte.
Positive electrode:
An active material having a composition of LiCoO ₂ : acetylene black: PVDF = 100: 8: 12 (weight ratio) is provided on one side of an Al foil (20 μm) in a sufficient amount for any negative electrode active material, 500 mg / cm ² laminated.
Electrolytes:
A gel electrolyte prepared by blending a solution prepared by adding 1 mol / L of LiBF ₄ and polyacrylonitrile in a mixture of propylene carbonate and ethylene carbonate at an equal weight ratio to 9: 1, and then gelling at 160 ° C. for 1 minute.
[0040]
About said Li battery, the battery capacity and the current collection performance index were computed with the following method.
Li batteries formed using the negative electrodes of Examples 1 to 6 and Reference Example 1 were left in an atmosphere of 60 ° C. for one month, and then charge termination voltage = 4.2V, discharge termination voltage = 2V, charge / discharge rate = Charge and discharge at a constant current under the condition of 0.2 C, measure the discharge capacity, obtain the discharge capacity contribution ratio (referred to as unit weight negative electrode capacity here) of the negative electrode of unit weight by the following formula, and evaluate the negative electrode performance did.
Unit weight Negative electrode capacity: discharge capacity (mAh) / negative electrode weight used (g)
[0041]
[Table 2]

[0042]
【The invention's effect】
The negative electrode of the present invention can be made lighter and thinner than conventional negative electrodes by taking advantage of the high capacity of metallic lithium, thereby realizing a higher capacity of the secondary battery.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a schematic laminated structure of a high capacity negative electrode of the present invention.
2 is a cross-sectional view showing a layer structure of a composite current collector used in the high capacity negative electrode of FIG.
3 is a cross-sectional view showing an embodiment of a composite current collector used in the high capacity negative electrode of FIG.
4 is a cross-sectional view showing another embodiment of the composite current collector used in the high capacity negative electrode of FIG. 1. FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... High capacity | capacitance negative electrode 10 ... Composite collector 11 ... Resin film 12 ... Conductive treatment layer 13 ... Metal plating layer 15 ... Through-hole 17 ... Lead wire 20 ... Metal lithium foil

Claims (5)

Metallic lithium was laminated on both sides of a composite current collector comprising a resin film, a conductive treatment layer formed on both surfaces of the resin film, and a metal plating layer formed on the conductive treatment layer by electrolytic plating. The composite current collector has a surface electrical resistance of 40 mΩ / cm or less and a tensile strength of 0.8 kg / cm or more, and satisfies the condition of the following formula: Features high capacity negative electrode;
Y1 + Y2 + Y3 ≦ 0.8 × (X1 + X2 + X3) × Y3 / X3
In the formula, X1: thickness of resin film (μm)
X2: Total thickness of the conductive treatment layer (μm)
X3: Total thickness of metal plating layer (μm)
Y1: Weight of resin film (mg / cm ² )
Y2: Weight of conductive treatment layer (mg / cm ² )
Y3: Weight of metal plating layer (mg / cm ² ). The high capacity negative electrode according to claim 1, wherein the metallic lithium has a thickness of 2 to 50 μm per side. The high-capacity negative electrode according to claim 1 or 2, wherein the composite current collector has a front and back energization resistance of 100 mΩ / cm or less. The high capacity negative electrode according to claim 1, wherein the metal plating layer is mainly composed of Cu. 5. The high-capacity negative electrode according to claim 1, wherein a total thickness (X1 + X2 + X3) of the resin film, the conductive treatment layer, and the metal plating layer is 9 μm or less.

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