▎ 摘　　要

NOVELTY - A thin film comprises a silicon oxide layer (L1) containing silicon oxide, a silicon layer provided on one surface of the silicon oxide layer (L1) and containing silicon, and a silicon oxide layer (L2) provided on the other surface of the silicon layer, which is opposite to the surface on which the silicon oxide layer (L1) is provided, and including silicon oxide. The silicon oxide layer (L1), the silicon layer, and the silicon oxide layer (L2) are doped with phosphorus. USE - Thin film used for electrode for lithium secondary battery (all claimed) for mobile device. ADVANTAGE - The thin film prevents deformation and breakage due to volume expansion during charging and discharging processes, and improves initial charge and discharge efficiency and charge/discharge life. DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following: production of negative electrode; and a lithium secondary battery.