Development of High-Capacity Li-Ion Batteries Using Phosphate-Based Materials and Their Safety Evaluation

The electrochemical properties and safety performance of the phosphate-based cells using a SnO-P2O5 glass (GSPO) anode and glass-ceramic LiFePO4 (GC-LFP) cathode were evaluated. The cell displayed an excellent performance over the wide temperature range of −20°C to 60°C. The laminated-type pouch cell with a capacity of 660 mAh using the GSPO anode and GC-LFP cathode had no thermal runaway during the nail penetration test, in which the internal short-circuit condition occurred only for a moment and then rapidly recovered, accompanied by an increasing nail internal temperature to 49°C and the cell surface temperatures to 29°C. The XRD measurement and Rietveld refinement revealed that the nail penetrated part had a lower tin-lithium alloy content than the other part away from the nail penetrated part, indicating that the GSPO anode must be deeply discharged locally in the internal short-circuit part due to the insulating of the GSPO. Thus, the GSPO anode is the key material to provide the outstanding safety performance. During the overcharge test, no punk and no fire were also observed, though the cell voltage rapidly increased from 10 V to 32 V, accompanied by an increasing cell surface temperature only to 110°C.