Preparation and Electrochemical Evaluation of LiCoO2 Film Prepared with Cold Spraying for Development of Lithium-Ion Battery
Authors: Okuyama Kohei , Yoshida Naoki , Sato Kazuhisa , Hashida Toshiyuki 
Published: February 2020

Since the 1980s, lithium-ion batteries (LIBs) have emerged as one of the most important power sources for portable electronics due to their high specific energy and good cyclability. In LIBs, LiCoO2 has been widely used as the cathode material due to the advantages of high specific capacity, high operating voltage, and long life cycle . Technology of electrode deposition is one of the considerable methods for LIBs. Thermal spraying has advantage in width of materials that can be used. In this study we focused on cold spraying. Cold spray is a coating technology in which a high pressure gas is accelerated through a de Laval nozzle. Powder materials are injected into the nozzle by a carrier gas and accelerated by a carrier gas. Technique can minimize the adverse effect caused by a molten or semi-molten state. Previous reports show that TiO2 film is deposited using cold spraying. It shows cold spraying may have ability to make electrode film for LIBs. In this study, LiCoO2 film for LIBs cathode is deposited by cold spraying. And then from observation and electrochemical evaluation of LiCoO2 film, we show the ability to apply cold spraying to make electrodes. And we suggest cold spraying as a way to making electrodes for LIBs.

LiCoO2 was prepared by the solid-state reaction of a stoichiometric amount of Li2CO3 (Wako Pure Chemical Industries, Ltd.) and Co3O4 (Kojundo Chemical Laboratory Co., Ltd) at 900 ºC in air. X-ray diffraction (XRD, Shimadzu Co., XRD-7000X) was used to identify the crystalline phase of the material. Sintered LiCoO2 was ground with a mortar and average size was about 9 mm.

LiCoO2 film was deposited using the low pressure cold spray system DYMET 403J (Obninsk Center for Powder Spraying). In cold spray method, air was used as a driving gas with a spraying pressure of 0.5MPa and temperature of 475 °C. Air was also used as the powder carrier gas. The stand-off distance of the sample from the nozzle exit was at 10 mm. Spraying pitch was 2 mm and powder feeding rate was 0.3 mg/sec. In this study, synthesized LiCoO2 powder was used as spraying material, and Al plate with thickness of 0.8 mm was employed as a substrate.

For electrochemical evaluation, half-cell was prepared by using LiCoO2 film deposited by cold spraying. We used stainless steel as vessel of cell. The cathode was LiCoO2 film prepared with cold spraying and the anode consisted of lithium ribbon of 0.5 mm thickness. LiCoO2 film was cut into squares about 0.8 cm × 0.8 cm and used as working electrode. The electrodes were assembled into cell with separator. 1M LiPF6 in dimethyl carbonate / ethylene carbonate (1:1 v/v) (Kishida Chemical Co., Ltd) was used as the electrolyte. Handling cell was performed in an argon-filled glove box.

Cyclic voltammetry test was performed in half-cell with VMP-300 by Bio-Logic. Data were taken at a scan rate of 0.5 mV/cm with the voltage limit between 3.0 and 4.2 V. Cycle number of CV test was 120 cycles.

By using cold spraying, LiCoO2 film was successfully deposited. The film prepared with cold spray was approximately uniform. From SEM observation the thickness of synthesized LiCoO2 film was about 20 mm. There are no cracks in cross section of film. From XRD results, LiCoO2 film was similar to the result of crystalline LiCoO2 and suggested that LiCoO2 film prepared with cold spray was well-crystalline.

From cyclic voltammetry test, we found that LiCoO2 film deposited by cold spraying is electrochemically active. The anodic and cathodic peak potentials were roughly correspond with previous reports. In terms of cyclability, at first LiCoO2 film lost electric capacity gradually. But over 80th cycle its electric capacity stabilized. From this result LiCoO2 film deposited by cold spraying may have advantage in cyclability. In this study, mass of LiCoO2 for working electrode was unknown. At LiCoO2 deposition stage, mass of LiCoO2 must be known in order to compare electrochemical characteristics with previous reports.

By cold spraying, electrochemically active LiCoO2 film was successfully deposited. The thickness of deposited LiCoO2 film was about 20 mm. And the surface of it was approximately uniform. By charge/discharge test, we show that the LiCoO2 film prepared with cold spray had good cyclability. Although future developments are needed, LiCoO2 film prepared with cold spraying may have the potential application for LIB.