Fluorinated Co-Solvents Enable Excellent Performances of Practical Cells Comprising LixSiO-Graphite Composite Anodes...

Li-ion batteries based on high specific capacity LixSiO-Graphite anodes and LiNi_0.89Co_0.05 Mn_0.05Al_0.01O₂ (NCMA) cathodes may have numerous practical applications owing to high energy density without a necessary compromise on safety. SiO, which is an attractive Li insertion anode material, offers more cycling stability than Si and a higher capacity than graphite. Therefore, a new trend has emerged for developing composite C-Si anodes, possessing the excellent cyclability of graphite coupled with high capacity SiO. The composite structure described herein prevents the volume expansion of SiO and maintains the structural integrity during prolonged cycling. However, graphite electrodes suffer from exfoliation in propylene carbonate (PC) based electrolyte solutions, which avoids well known safety benefits related to a possible use of PC based electrolyte solutions in all kinds of Li batteries. Herein, it is reported that trifluoro propylene carbonate (TFPC) is compatible with graphite anodes. New electrolyte formulations are developed and tested containing fluorinated co-solvents and compared the performance of several electrolyte solutions, including conventional alkyl carbonates-based solutions in full Li-ion cells, which included LixSiO-Graphite anodes and LiNi_0.89Co_0.05Mn_0.05Al_0.01O₂ (NCMA) cathodes. Cells with new electrolyte solutions developed herein demonstrated nearly twice capacity retention in prolonged cycling experiments compared to similar reference cells containing conventional electrolyte solutions.