Graphite Anode Functionalized with a Gel Biopolymer Binder for Li-Ion Batteries Operating in a Broad Temperature Range

A graphite anode with a polymer gel binder (PGB), consisting of chitosan, the ionic liquid PYR14 DCA, and the lithium salt LiTFSI, was developed for high-power Li-ion batteries. The electrochemical properties of graphite with a PGB and polyvinylidene difluoride (PVDF) as a reference were investigated at 10 °C, 25 °C, and 60 °C and compared with each other. During cycling, a PGB has an effect on the composition of the solid-electrolyte-interface (SEI) layer by forming a LiF-enriched component. The charge/discharge behavior of graphite is determined to some extent by the stability and resistance of the SEI, especially at elevated and low temperatures. A stable SEI was formed on graphite/PGB electrodes leading to an excellent cycling and rate performance. Graphite/PGB delivered a discharge capacity of 230 mAh·g–1 after 1000 cycles at 1.86 A·g–1 current density (5C) at room temperature. At 60 °C, the replacement of PVDF by a PGB resulted in an enhancement of the electrochemical performance with a high capacity of 345 mAh·g–1 after 200 cycles at 5C, while the conventional graphite/PVDF electrode only displayed 57 mAh·g–1. The high Li+ diffusion provided by a PGB and the LiF-rich SEI on the graphite/PGB surface also contributed to a better electrochemical performance at a low temperature.