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Monday, May 14, 2007 - 2:50 PM

Investigation of Spray Conditions and Performances of Cold-Sprayed Pure Silicon Anodes for Lithium Secondary Batteries

K. Sakaki, S. Shinkai, Y. Shmizu, Shinshu University, Nagano City, Japan

The higher capacity of a battery with the lithium alloy anode requires the development of a larger theoretical electrochemical capacity than graphite. Silicon is a promising anode material, having a theoretical capacity more than 10 times that of the graphite used in these lithium alloy batteries. There are two common methods of fabricating silicon anodes: direct deposition techniques such as electron beam deposition and sputtering; and slurry coating of silicon particles with a binder. Alternative methods are being investigated. One of such methods is cold spray. In this study, numerical simulation of, and experiments investigating, cold spray conditions and the performances of cold-sprayed silicon anodes are presented. Silicon was cold-sprayed on copper foil substrates using three different starting materials (with particle sizes of 4.65 µm, 6.74 µm and 9.63 µm). (1)The average thickness of the as-deposited silicon anodes is between 0.4 and 0.7 µm. Cross-section SEM images show that the thickness of the anode is not uniform across the film, with thicknesses ranging from 0.2 to 1.5 µm. Since the thickness is much less than the size of the starting particle, the film is most likely formed from fragments of the original particles. The anodes made from 6.74 µm silicon particles had the largest thickness. (2)Silicon anodes (20 mm by 20 mm) have a capacity of about 1.5 to 2.5 mAh. The overall capacity depends on the size of the starting material, with the largest capacity from the anodes made with a starting size of 6.74 µm. This is consistent with the thickness measurement. (3)First cycle efficiency was about 90 %. Charge capacity initially improves with cycling (up to 10th cycle). This is probably due to better electrolyte soaking during the first several cycles. A decrease in charge capacity is observed upon further cycling.

Summary: There are two common methods to make silicon anodes - by direct deposition techniques such as electron beam deposition and sputtering, or by slurry coating silicon particles with a binder. Alternative methods are being investigated. Cold spray is one of such methods. In this study, numerical simulation and experiments investigated cold spray conditions and the performances of cold-sprayed silicon anodes are presented. Silicon was cold-sprayed on copper foil substrates using 3 different starting materials (particle size of 4.65ìm, 6.74ìm and 9.63ìm). First cycle efficiency was about 90%. Charge capacity initially improves with cycling (up to 10th cycle). This is probably due to better electrolyte soaking during the first several cycles. A decrease in charge capacity is observed upon further cycling.