A solid state energy storage device with supercapacitor-battery hybrid design

High power and high energy density are important requirements for advanced energy storage systems in mobile electronic devices, electric vehicles, and military-grade high-rate energy storage systems. However, achieving both high power and high energy in a single device is very challenging because high power density usually leads to a tradeoff with low energy density in devices that rely on a single ion storage mechanism. In this work, we designed a hybrid energy storage device consisting of an intercalative battery cathode and a capacitive supercapacitor anode. As a proof-of-concept, we used LiFePO4 (LFP) nanoparticles on an aluminum (Al) leaf current collector as the battery electrode and a free-standing reduced graphene oxide/carbon nanotube (RGO/CNT) nanocarbon membrane as the supercapacitor electrode. The hybrid device possesses outstanding features including (1) an asymmetric electrode configuration; (2) an ultra-lightweight current collector for the cathode; (3) a current collector free anode; (4) a quasi-solid-state gel polymer electrolyte. Compared with conventional supercapacitors and lithium-ion batteries, our hybrid device exhibits superior performance with both high energy density (180 W h kg(-1)) and high power density (218 W kg(-1)), and enhanced safety imparted by the quasi-solid-state gel electrolyte, representing one new direction for developing high-energy/high-power energy storage devices.