4.4 V lithium-ion polymer batteries with a chemical stable gel electrolyte

Abstract: We tested 4.2V Li-ion polymer batteries (LIPB) with physical gel electrolyte, poly(vinylidene fluoride) (PVDF), 4.4V LIPB and 4.4V Li-ion batteries (LIB) with a liquid electrolyte. The discharge capacity of the 4.4V LIPB reached 520Whl−1 which was 9% higher than that of the 4.2V LIPB. The 4.4V LIPB had a high capacity retention ratio of 91.4% at 3C because of the excellent ion conductivity of the PVDF gel. The capacity retention ratio of the 4.4V LIPB was 82% after 500 cycles, which is comparable to those of some commercial LIBs. The 4.4V LIPB retained its original thickness even after many cycles and after being stored at 90°C, whereas the 4.4V LIB swelled by over 20%. Peaks in the FT-IR spectrum of the discolored separator in the 4.4V LIB after storage were assigned to Cbonds, suggesting that the separator in direct contact with the 4.4V cathode had been oxidized. The PVDF gel electrolyte not only had a high ionic conductivity but also completely suppressed oxidation. The 4.4V LIPB with PVDF gel electrolyte has properties suitable for practical cells, namely, high energy density, high permanence and it is safe to use. [Copyright &y& Elsevier]