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

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 Cu ₃Sn 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.