Superior initiator reactivity and electrochemical properties of In(OTf)3 over Sn(OTf)2 for 1,3-dioxolane based solid polymer electrolyte
The in-situ polymerization of 1,3-dioxolane (PDOL) in battery cells has attracted extensive attention, however, the differences of Lewis acid initiators on the DOL monomer conversion (C%) and electrochemical properties has been ignored. Here, it is demonstrated that compare with Sn(OTf) 2 Lewis acid initiator, the gelation of DOL is achieved at the lower addition of In(OTf) 3 . By optimizing their content in the gelation process, their C% are comparable which are 95.7 % and 93.5 % for In(OTf) 3 and Sn(OTf) 2 , respectively. However, the higher ionic conductivity (7.1 × 10 −4 S cm −1 at room temperature), electrochemical window (~4.5 V) and Li + transference number (0.42) are obtained for DOL initiated with In(OTf) 3 , due to its lower molecular weight which is helpful to the intermolecular Li + transport along PDOL main chain; In addition, the Li/Li symmetrical cell of In(OTf) 3 can be stably cycled for >500 h at 3 mA cm −2 , with an over-potential of 178mv. The storage and cycling impedances of half cells further proves the stable interface of In(OTf) 3 initiated DOL toward to lithium metal in comparison with those of Sn(OTf) 2 . Scanning electron microscopy results show a denser and thinner interface in the DOL catalyzed by In(OTf) 3 . Finally, the assembled Li/LiFePO 4 battery delivers specific discharge capacity and capacity retention rates of 115.5mAh g −1 and 85 %, respectively after 300 cycles at 1C. Through the initiator selection, the DOL synthesis and electrochemical properties can be tuned, which further broadens the design idea of PDOL based solid polymer electrolyte.
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