Tailoring electrolyte solvation to push the capacity limit of layered oxide cathodes via polarized ferroelectric polymers

The critical challenges for full lithium utilization in nickel-rich lithium transition metal oxide cathodes are the capacity loss and power fading, which stem from irreversibly structural transition and unstable cathode-electrolyte interface upon excessive delithiation at high charge voltages. Here we discover a novel electrochemical phenomenon that the local solvation structure of the electrolyte can be regulated by well-polarized ferroelectric polymer and demonstrate its potential in pushing the capacity limit of Ni-rich lithium layered oxide cathodes without sacrificing their structural integrity. This polarized configuration in the ferroelectric polyvinylidene fluoride (PVDF) coating tailors the local solvation structure by repelling the electrolyte anions and promoting the aggregation of lithium-ions at the cathode-electrolyte interface, which significantly boost the (de)lithiation kinetics, redox reversibility and structural integrity of the cathodes. The LiNi0.8Co0.1Mn0.1O2 cathode with polarized PVDF displays an exceptionally high capacity of 232 mAh g−1 with a high initial Coulombic efficiency of 92.5%, and the NCM811/graphite pouch cell with polarized-PVDF/PP separator shows a higher capacity retention rate of 88.6% after 200 cycles at 55 °C.