Reduction of heat generation for lithiated graphite by forming a local galvanic cell with Cu3Sn at elevated temperature

Abstract

A copper-tin intermetallic compound (Cu3Sn) is deposited on copper foil and used as the current collector for graphite electrode. The Cu3Sn phase is inactive for lithiation at ambient temperature, but becomes active to be lithiated at elevated temperatures. Hence, when the Cu3Sn deposit, which makes an intimate contact with the lithiated graphite, is exposed to high-temperature environment, it is lithiated by taking Li+ ions/electrons from the lithiated graphite. As a result, the degree of lithiation in graphite decreases. The formation of local galvanic cell, in which Li+ ions/electrons are transferred from the graphite electrode to the Cu3Sn deposit, is confirmed by electrochemical and X-ray diffraction analysis. The heat generation that is resulted from the exothermic reactions between graphite and electrolyte, which is known to be smaller with a decrease in the degree of lithiation in graphite, is greatly reduced as a result of galvanic cell formation. In short, Cu3Sn can be added into graphite electrodes to enhance thermal safety of lithium-ion batteries.