JP3084050B2 - Negative electrode for secondary battery - Google Patents

Description

The present invention relates to a negative electrode for a secondary battery.

[Related Art] In recent years, lithium secondary batteries have attracted attention as chargeable / dischargeable high energy density batteries. When metallic lithium is used as the negative electrode active material of this lithium secondary battery, there are problems such as dendrite being generated or moss-like lithium having lost activity being deposited on the battery negative electrode due to charge and discharge,
Alloying of the electrolyte composition or the negative electrode lithium is being studied. The latter is attracting attention as a method for surely solving the problem of the negative electrode lithium. The elements that form the lithium alloy include aluminum, silicon, tin, magnesium,
Zinc, lead, manganese and the like can be mentioned, but the alloying of lithium and aluminum easily proceeds with the reaction, and is excellent in the amount of absorbed lithium and the lightness of the electrode. However, an alloy mainly composed of lithium / aluminum has various properties depending on the alloying ratio of lithium and aluminum. Alloys made by metallurgical methods have a lithium ratio of 10 atom
Below ic%, it is used as a stable structural material with high strength. When the lithium ratio is 80 atomic% or more, a lithium / aluminum alloy dispersed state is obtained in Li. In this range, the extensibility of lithium is maintained, but all are suitable as electrodes for storing lithium ions. Absent.

However, in the 10-80% region between these two regions, a lithium / aluminum alloy having α, β, and γ layers can be obtained in the form of a bulk powder. Become.

As described above, since an alloy having self-holding properties cannot be obtained by the metallurgical method, an alloy manufactured by the following method is used as an electrode.

(1) an electrochemical manufacturing method in which lithium is electrodeposited and alloyed with a metal to be alloyed in a non-aqueous electrolyte containing a lithium salt; (2) lithium is bonded to an aluminum substrate having a sufficient thickness. (3) a method in which the bonding of (2) is performed by electrochemical treatment in an electrolytic solution, and (4) a method in which lithium and aluminum are interposed in the electrolytic solution. However, when the conventional lithium / aluminum alloy thus obtained is used as a negative electrode for a secondary battery, it is necessary to sufficiently extract the energy of the positive electrode in a wide discharge current range. Unless the thickness of the alloy layer is increased, the charge / discharge cycle characteristics are still insufficient.

In addition, the above-mentioned laminate of lithium / aluminum alloy and aluminum is liable to fall off the surface of the aluminum substrate due to the brittleness of the alloy layer, or the aluminum substrate is susceptible to corrosion during repeated charge / discharge cycles. There is also a problem such as having a sufficient diffusion layer of lithium,
A sheet having sufficient performance as a sheet has not yet been obtained.

[Problems to be Solved by the Invention] In view of such circumstances, an object of the present invention is to provide a negative electrode for a secondary battery having a high energy density and excellent charge / discharge characteristics.

Means for Solving the Problems The present inventors have made intensive studies to solve the above-mentioned problems, and as a result, have improved the polarization characteristics of the negative electrode by using an aluminum substrate having a large surface area, and have reduced the reaction resistance of the negative electrode. Can be reduced, and a composite metal with lithium is laminated on an aluminum substrate, and Mg, Mn, Zn,
It has been found that by containing a metal selected from Pb, even if the surface area of aluminum is increased, the alloy layer does not easily fall off or collapse, and a negative electrode having excellent self-holding properties and battery charge / discharge cycle performance can be obtained. Invented the invention. That is,
The present invention relates to an aluminum substrate having a high surface area and lithium-
A secondary battery negative electrode having a laminated structure of an aluminum alloy, characterized in that the negative electrode for a secondary battery contains a metal selected from Mg, Mn, Zn, and Pb in the alloy layer.

The surface area of the aluminum substrate used for the negative electrode of the present invention is increased by an abrasive or a polishing machine, or by chemical or electrolytic etching, preferably by electrolytic etching. The material of the aluminum substrate used at this time is preferably aluminum having mainly (100).
Aluminum, which mainly has a (100) plane, can have a high surface area without reducing the strength of the base material because etching pits can be regularly provided perpendicular to the plane when the surface area is increased by electrolytic etching or the like. ,preferable.

The negative electrode of the present invention forms a lithium / aluminum alloy layer while leaving the aluminum substrate by performing an alloying process after laminating a metal mainly composed of lithium on the aluminum substrate having a high surface area. And a metal selected from Mg, Mn, Zn, and Pb in the aluminum or alloy layer.

As a method for producing the negative electrode of the present invention, a metal selected from Mg, Mn, Zn, and Pb is deposited or electrochemically laminated on an aluminum substrate, and then lithium is laminated, and the above-described (1) to (4) are used.
This is performed by the method (4). When a lithium layer is laminated by vapor deposition, alloying is performed according to the method (2) or (3). In the case of the bonding of (2) or (4), after the lithium is bonded to the aluminum / metal, an electrochemical method of alloying by applying DC or AC in a non-aqueous electrolyte, or lithium The heating method of alloying by heating at a temperature equal to or lower than the melting point is effective. In the case of a sheet-shaped negative electrode, when bonding, the alloy layer becomes thicker and loses flexibility, so the surface area is increased, and lithium is deposited on an aluminum sheet base material laminated with a metal selected from Mg, Mn, Zn, Pb Then, it is obtained by a method of alloying by heating or applying a direct current or an alternating current in an electrolytic solution, or a method of (4) obtained by contacting lithium and the above aluminum through the electrolytic solution.

The thickness of the alloy thus obtained is desirably 80% or less based on the aluminum of the base material. If it is 80% or more, the role of the substrate itself is lost. Therefore, even if both surfaces of the aluminum substrate are alloyed, it is necessary that the aluminum substrate remain at least 20% of the total thickness. In this case, if the aluminum base or alloy layer does not contain a metal selected from Mg, Mn, Zn, and Pb, there is almost no self-holding property, and it is mounted as a large-area sheet-type battery or a spiral-mounted cylindrical battery. It is impossible to do.

The lithium secondary battery can be made by using the negative electrode of the present invention, and the basic structure of the lithium secondary battery is composed of the negative electrode, the positive electrode, and the electrolytic solution, and if necessary, the separator and the solid electrolyte may be used. it can.

As the non-aqueous electrolyte, a solution obtained by dissolving an electrolyte salt in a non-aqueous solvent is used.The electrolyte salt is not particularly limited as long as it is used for a normal non-aqueous electrolyte battery.
_{O 4, LiBF 4, LiAsF 6} , LiPF 6, LiSbF 6, LiCF 3 SO 3, CF 3 COO
Li, NaClO ₄ , NaBF ₄ , NaSCN, KBF ₄ , (Bu) ₄ NBF ₄ , (E
One or more salts such as t) ₄ NBF ₄ , (Bu) ₄ NClO ₄ and (Bu) ₄ NClO ₄ can be used.

In the combination with the present negative electrode, LiClO ₄ and CF ₃ SO ₃ Li are particularly preferable, and it is possible to dramatically increase the charge / discharge efficiency.

Examples of the non-aqueous solvent include propylene carbonate, γ-butyl lactone, ethylene carbonate, sulfolane, dioxolan, tetrahydrofuran, 2methyltetrahydrofuran, dimethyl sulfoxide, and 1,2-dimethoxyethane, 1,2-ethoxymethoxyethane, methyldiglyme, Methyltriglyme, methyltetraglyme,
Ethyl glyme, ethyl diglyme, butyl glyme can be exemplified, but propylene carbonate, γ
A combination of -butyl lactone and or glymes is most preferable in terms of electric conductivity and solubility of the inorganic salt, and in combination with the present negative electrode, a solvent composition mainly composed of γ-butyl lactone enhances the charge / discharge efficiency. Particularly preferred. The concentration of the electrolyte salt is 0.5M to 7M, preferably 1M to 5M.

Further, a solid electrolyte can be used as a separator or an electrolytic solution.For example, in an inorganic system, AgCl, AgBr,
Metal halides such as AgI and LiI, RbAg ₄ I ₃ , RbAg ₄ I ₄ CN
And the like. Further, in the organic system, polyethylene oxide, polypropylene oxide, polyvinylidene fluoride, polyacrylamide, etc. as a polymer matrix, the above-mentioned electrolyte salt is dissolved in the polymer matrix, or a composite thereof, or a crosslinked body thereof, a low molecular weight polyethylene oxide, A polymer electrolyte in which an ion dissociating group such as a crown ether is grafted to a polymer main chain or a viscoelastic solid electrolyte in which an electrolytic solution is contained in a polymer is exemplified. A combination with a solid electrolyte is preferable, and is preferable in preventing collapse of the negative electrode, falling off of the alloy layer, and the like, or reducing contact resistance between the negative electrode and the solid electrolyte.

As the positive electrode active material for a battery according to the present invention, TiS ₂ , Nb
_{3 S 4, MoS 2, Mo} 3 S 4, CoS 2, FeS 2, V 2 O 5, Cr 2 O 5, MnO 2, C
Examples include chalcogenite compounds such as oO ₂ and conductive polymers such as polyaniline, polypyrrole, poly-3-methylthiophene, and polydiphenylbenzine.

In a polymer active material, it is necessary to dissolve the electrolyte in the electrolytic solution so as to correspond to the doping amount, and it is desired that the electrolyte has a high concentration and a high liquid content.

Each element of the positive electrode and the electrolytic solution is not particularly limited, but the conductive polymer material and the electrolyte salt are CF ₃ S
In the case of a battery system using O ₃ Li, LiClO ₄ and γ-butyl lactone as a solvent, the cycle characteristics of the present negative electrode are dramatically improved.

[Example] Negative electrode production example 1 A negative electrode was obtained by blasting aluminum having a purity of 98% and a thickness of 300 µm with # 150 emery particles under a pressure of 1 kg.
Platinum was used as the positive electrode, and a 1 mol / magnesium perchlorate / propylene carbonate solution was electrolyzed at a constant current of 1 mA / cm ² at a current of 0.5 C / cm ² and a 100 μm lithium foil was pressed against a hot plate using a hot plate. It was heated at 150 ° C. for 15 seconds from the aluminum surface. As a result, a laminate of aluminum and a lithium aluminum alloy was obtained. The thickness of the alloy layer was about 120 μm, and the total thickness of the electrodes was 405 μm (negative electrode A
-1).

Negative electrode production example 2 Aluminum with a purity of 99.9% and a thickness of 70 μm was sufficiently polished with # 200 emery paper as the negative electrode and platinum as the positive electrode.
In a 1 mol / magnesium perchlorate / propylene carbonate solution, electrolysis was performed at 1 mA / cm ² and a current of 0.3 C / cm ² , but 1 mol of LiBF ₄ was dissolved on the surface of propylene carbonate / dimethoxyethane 7: 3. The solution was uniformly dropped and brought into contact with a 50 μm lithium foil for about 15 minutes to alloy both surfaces of the aluminum surface.

The thickness of the alloy layer was 15 μm on one side, and the total thickness of the electrode was 85 μm (negative electrode A-2).

Negative electrode production example 3 An aluminum foil having a thickness of 75 μm was electrochemically etched to form numerous pits in a direction perpendicular to the surface. Using this aluminum foil as a negative electrode and platinum as a positive electrode, electrolysis was carried out in a magnesium perchlorate / propylene carbonate solution at 1 mA / cm ² and a current of 0.2 C / cm ² . Lithium was vapor-deposited on both sides so that the thickness was 20 μm on one side.

Then, it was heated at 140 ° C. in a heating furnace to alloy even in the pit. The thickness of the alloy layer is 25 μm on one side. The total thickness of the electrode is
It was 102 μm (negative electrode A-3).

Negative electrode production examples for comparison Negative electrodes produced in the same manner as negative electrode production examples 1 to 3 were used as B-1, B-2, and B-3, respectively, except that an aluminum sheet having a purity of 98% was used as it was.

Example 1 A positive electrode mixture pellet having a thickness of 0.6 mm and a diameter of 1.6 cmφ was prepared from a paste obtained by adding 25% of acetylene black and 5% of PTFE to a sintered electrolytic manganese dioxide (0.1 g) and forming a paste. A 2016 type coin-type battery was manufactured using the separator (Duraguard 2500), PC / EME (7/3) in which 1MLiPF ₆ was dissolved as an electrolyte, and A-1 as a negative electrode.

Example 2 A polyaniline sheet electrode obtained by depositing 0.12 g of polyaniline on a 40 × 60 mm stainless sheet (20 μm thick) by electrolytic polymerization was used as a positive electrode and a separator (Duragard) was used.
2500) A sheet type battery using A-2 was mounted on the negative electrode. A positive electrode, a negative electrode, and a high-pressure mercury lamp after impregnating a solution obtained by dissolving 19.2 parts by weight of ethoxydiethylene glycol and 0.8 parts by weight of methylbenzoylformate in 80 parts by weight of a γ-butyl lactone solution in which 3M LiBF ₄ is dissolved as an electrolyte, and Irradiated with active light was used.

Example 3 AA batteries were manufactured in the same manner as in Example 2 except that A-3 was used for the negative electrode and CF ₃ SO ₃ Li was used as the electrolyte.

Comparative Examples 1 to 3 The negative electrodes of Examples 1 to 3 were sequentially taken as B-1 and B-, respectively.
2 and Comparative Examples 1, 2, and 3 using B-3.

[Effects of the Invention] As described above, by using the negative electrode of the present invention, a lithium secondary battery having a large energy density and a large capacity and excellent in charge / discharge characteristics can be obtained.

Continuation of the front page (56) References JP-A-64-63268 (JP, A) JP-A-63-116417 (JP, A) JP-A-64-77870 (JP, A) JP-A-63-16551 (JP) JP-A-63-285865 (JP, A) JP-A-63-314762 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4/36-4/62 H01M 4/02-4/04

Claims (2)

(57) [Claims] 1. A negative electrode for a secondary battery having a laminated structure of an aluminum substrate having a high surface area and a lithium-aluminum alloy, wherein the alloy layer contains a metal selected from Mg, Mn, Zn, and Pb. Negative electrode for a secondary battery. 2. The negative electrode for a secondary battery according to claim 1, wherein the aluminum substrate mainly has a (100) plane.