Polarity-Switchable Symmetric Graphite Batteries with High Energy and High Power Densities.

Multifunctional batteries with enhanced safety performance have received considerable attention for their applications at extreme conditions. However, few batteries can endure a mix-up of battery polarity during charging, a common wrong operation of rechargeable batteries. Herein, a polarity-switchable battery based on the switchable intercalation feature of graphite is demonstrated. The unique redox-amphoteric intercalation behavior of graphite allows a reversible switching of graphite between anode and cathode, thus enabling polarity-switchable symmetric graphite batteries. The large potential gap between anion and cation intercalation delivers a high midpoint device voltage (≈average voltage) of ≈4.5 V. Further, both the graphite anode and cathode are kinetically activated during the polarity switching. Consequently, polarity-switchable symmetric graphite batteries exhibit a remarkable cycling stability (96% capacity retention after 500 cycles), a high power density of 8.66 kW kg-1 , and a high energy density of 227 Wh kg-1 (calculated based on the total weight of active materials in both anode and cathode), which are superior to other symmetric batteries and recently reported dual-graphite or dual-carbon batteries. This work will inspire the development of new multifunctional energy-storage devices based on novel materials and electrolyte systems.