JP2005135779A - Lithium secondary battery and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium secondary battery having an active material layer composed of amorphous silicon and a cathode composed of an electrolytic copper foil, reducing the lowering of initial irreversible capacity and discharge capacity even after repetitive charge and discharge. <P>SOLUTION: The lithium secondary battery having the active material layer composed of amorphous silicon and a cathode composed of the electrolytic copper foil, has a characteristic that discharge capacity after the repetitions of charging and discharging over 2,500 times is not less than 90% of the discharge capacity at the initial 10th time of discharge, and which is manufactured by immersing the electrolytic copper foil in a concentrated acidic aqueous solution, then forming an active material layer composed of the amorphous silicon on the electrolytic copper foil. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a lithium secondary battery having a long discharge life with a small decrease in discharge capacity even after many times of charge and discharge.

  Lithium secondary batteries using silicon as an active material are being studied because they can have higher capacity than lithium secondary batteries using carbon as an active material. Japanese Patent Application Laid-Open No. 2000-83594 discloses a lithium battery electrode including an active material that occludes and releases lithium, and is characterized by using amorphous silicon as the active material. ing. According to the publication, a copper foil having a surface roughness Ra of 0.01 to 1 μm is used as a current collector, and an active material layer made of amorphous silicon is formed on the current collector by a sputtering method. A battery electrode having excellent adhesion between the copper foil as the electrical conductor and the amorphous silicon as the active material is obtained.

In a lithium ion secondary battery in which amorphous silicon is formed on a copper foil by a vacuum deposition method, the present inventors have used a copper foil whose surface has been roughened by a ferric chloride etching method. Is repeated 800 times, a lithium ion secondary battery having a capacity of 2000 mAh / g per gram of active material is obtained.
No. 2000-83594

  The problem to be solved is that the initial irreversible capacity is large, and the capacity drops to about 80% of the initial capacity when charging / discharging is repeated 800 times.

  The present invention provides a lithium secondary battery having a negative electrode made of an active material layer made of amorphous silicon and an electrolytic copper foil, and the discharge capacity after repeating charge and discharge 2500 times is 90% or more of the discharge capacity of the 10th time. There is a lithium secondary battery.

Further, according to the present invention, in a method for manufacturing a lithium secondary battery having an anode made of an active material layer made of amorphous silicon and an electrolytic copper foil, the charge / discharge is performed at a charge / discharge density of 2500 times the initial discharge capacity. 2. The lithium secondary battery according to claim 1, wherein the discharge capacity after repeating the discharge is 90% or more of the discharge capacity of the 10th time.

Furthermore, the present invention provides a method for producing a lithium secondary battery having a negative electrode comprising an active material layer made of amorphous silicon and an electrolytic copper foil, wherein the electrolytic copper foil is immersed in a strongly acidic aqueous solution, and then amorphous silicon is used. 3. The method for producing a lithium secondary battery according to claim 1, wherein an active material layer made of is formed on the electrolytic copper foil.

  The lithium secondary battery having an anode made of an active material layer made of amorphous silicon and an electrolytic copper foil of the present invention has an advantage that the initial irreversible capacity is small, and the decrease in discharge capacity is small even after many times of charge and discharge. is there.

  The electrolytic copper foil used in the present invention is an electrolytic copper foil having fine conical protrusions formed on the surface. In the electrolytic copper foil generally used for printed wiring board production, fine rough particles are formed at the top of the cone for the purpose of improving the adhesion to the base resin. Is not preferable because it becomes difficult. In addition, the copper foil for printed wiring boards is usually formed with a rust-preventing layer with various alloy layers and a silane coupling agent layer that improves adhesion, but the removal process becomes complicated. It is not preferable.

The active material layer made of amorphous silicon can be formed on the electrolytic copper foil by a vacuum deposition method in which massive silicon is heated in vacuum. The heating temperature of silicon is ˜ ° C., and the degree of vacuum is ˜ × 10 ⁻⁴ torr. The electrolytic copper foil is preferably vacuum-deposited immediately after washing with water and drying after removing the oxide layer and chromate treatment layer on the surface in an acidic aqueous solution such as aqueous hydrochloric acid or sulfuric acid. The thickness of the amorphous silicon is controlled by the vacuum deposition time, and is preferably 1000 angstroms or more.

  The following examples illustrate the invention.

As an evaporation source, n-type Si Wafer manufactured by Shin-Etsu Chemical Co., Ltd. (P-doped amount: 10 ^-16 mol / cm ³ ) is polished with a diamond grindstone, and after removing the oxide film on the surface, it is crushed to the size of a rice grain and then tungsten I put it on the boat. A 35 μm thick electrolytic copper foil made by Nippon Electrolytic Co., Ltd. (roughening treatment: none, centerline average roughness Ra: 0.42 μm, surface treatment: chromate layer only) was immersed in 6N hydrochloric acid for 10 seconds and washed with running water. Subsequently, it was immersed in ion exchange water and dried at 80 ° C. for 3 minutes. The above-mentioned electrolytic copper foil was set in a vacuum deposition apparatus with the non-glossy surface facing up, and an active material layer made of amorphous silicon was formed on the electrolytic copper foil by vacuum deposition while monitoring with a quartz vibration film thickness meter. At this time, the internal vacuum was about 4 × 10 ⁻⁵ torr. An electrolytic copper foil on which amorphous silicon is formed is cut into a 1 cm square to form a test electrode, and a constant current charge / discharge test (CCD) is performed in a three-electrode glass cell using metallic lithium as a reference electrode and a counter electrode. evaluated. As the electrolytic solution, propylene carbonate containing 1M LiClO ₄ was used. The measurement was performed at room temperature in a glove box in an argon atmosphere. The initial discharge capacity was 3000 mAh / g, and the result of 2500 charge / discharge cycles at 0.93 mA / cm ² (10C) is shown in FIG.

The electrolytic copper foil was immersed in a 1M FeCl ₃ aqueous solution for 1 minute to etch the surface and roughen the glossy surface. Similarly, vacuum deposition was performed on the roughened glossy surface, and the characteristics were evaluated. The initial discharge capacity was 2600 mAh / g, and the results of charging and discharging 1400 times at 0.93 mA / cm ² (10C) are shown in FIG.

  As is clear from FIG. 1, the lithium secondary battery of the present invention has a small initial irreversible capacity and maintains a capacity of 90% or more even when it is repeatedly charged and discharged 2500 times. Useful as a lifetime power supply.

  Since the initial irreversible capacity is small, the capacity of 90% or more of the initial capacity is maintained even when charging and discharging are repeated 2500 times, and it is useful as a power source with high capacity and long life.

It is the figure which showed the charge / discharge characteristic. (Example 1 and Comparative Example 1)

Claims (3)

  In a lithium secondary battery having an anode made of an active material layer made of amorphous silicon and an electrolytic copper foil, the discharge capacity after repeating charge and discharge 2500 times is 90% or more of the 10th discharge capacity. Lithium secondary battery. Discharge after repeating charge and discharge 2500 times at a charge / discharge density 10 times the initial discharge capacity in a method for manufacturing a lithium secondary battery having an anode made of an active material layer made of amorphous silicon and an electrolytic copper foil The lithium secondary battery according to claim 1, wherein the capacity is 90% or more of the discharge capacity at the 10th time. In a method for producing a lithium secondary battery having an anode made of an active material layer made of amorphous silicon and an electrolytic copper foil, the electrolytic copper foil is immersed in a strongly acidic aqueous solution, and then an active material layer made of amorphous silicon is formed. 3. The method of manufacturing a lithium secondary battery according to claim 1, wherein the method is formed on the electrolytic copper foil.

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