Polyvinylidene Fluoride-Derived Carbon-Confined Microcrystalline Graphite with Improved Cycling Life and Rate Performance for Potassium Ion Batteries

The practical application of the state-of-art graphite anode materials for potassium ion batteries (KIBs) is currently frustrated by their poor cycling life and unsatisfactory rate performance. Herein, a bifunctional carbon coating derived from polyvinylidene fluoride is developed not only to create a confinement effect for suppressing the enormous c-axis volume expansion of graphite host during the potassiation/depotassiation process but also to tune the electrode surface condition through an increased specific surface, enriched mesopores, and F-doping. After the coverage with the featured carbon coating, the charge transfer/K ion diffusion kinetics is enhanced prominently, which is verified through systematic kinetics analyses, including determining the capacitive contribution, the calculation of the K ion diffusion coefficient, and investigating the impedance spectroscopy. The hybridized electrode exhibits substantially improved cycling stability (especially long-term ability) and rate capability. Typically, a high charge capacity of 191 mAh g–1 is well-retained after 120 cycles at 0.1 A g–1, and a favorable rate capacity retention of 42.2% is still maintained under the large current density of 1.0 A g–1. This study demonstrates that the confinement strategy with a well-designed robust carbon coating is feasible to solve the deficiency of graphite materials when used in KIBs and sheds light on the further exploration of high-performance graphite electrodes for practical KIBs.