Dynamic Lithium Intercalation/Deintercalation in 18650 Lithium Ion Battery by Time-Resolved High Energy Synchrotron X-Ray Diffraction

Abstract

A time-resolved in situ high energy synchrotron X-ray diffraction (HESXRD) technique is employed to study the lithiation/delithiation of cathode/anode in a commercial 18650 battery under real working condition (current rate is 4 C). The phases and their changes in both the cathode and anode are identified simultaneously. For the anode component, during the charge process, as well as the LixC6 phase, a lithium-rich phase close to LiC6 phase and a series of intermediate phases between the Li0.5C6 and LiC6 phases are observed. A distinct lithium intercalation/deintercalation mechanism is proposed for the cathode. The transforms of LiFePO4 into the FePO4 consists three periods with different components of phases, i.e., LiFePO4 + lithium-deficient solid solution phases (period I), FePO4 + LiFePO4 phases (period II), and FePO4 + lithium-rich solid solution phases (period III). The changes in both the andode and cathode during the discharge process are just inversed to those occurrs during the charge process. The present work indicates that dynamic lithiation/delithaition process under real working condition is different from those at the thermodynamic state, and the in situ HESXRD is one of the most promising technique to monitor such kind of dynamic lithium behavior.