Monitoring of particle fracture by acoustic emission during charge and discharge of Li/MnO2 cells

Charge and discharge of Li/MnO2 cells were examined with monitoring of particle fracture of manganese dioxide by acoustic emission. Manganese dioxide used was electrolytic manganese dioxide heat-treated at 400 degrees C for 24 h in air [HEMD(400)]. The acoustic-emission technique worked well to monitor events that occurred inside a cell. During the first discharge to prepare a deep-discharge product, a closely packed series of acoustic events was observed, especially in the latter half of the discharge process, which contained most of the acoustic events. During cycling, acoustic events were concentrated at the end of discharge while no event was observed during charge, indicating that particle fracture took place during lithium-ion insertion into a solid matrix. Rate-capability tests showed that the rate of acoustic events was a function of current drain, i.e., a higher discharging current accelerated particle fracture. From these results we discuss the important role of mechanical properties of materials upon the lithium-insertion scheme. We also discuss the ideal considerations regarding insertion materials for advanced batteries.