High power NVPF/HC-based sodium-ion batteries

Abstract

The Na-ion battery consisting of Na3V2(PO4)2F3 (NVPF) cathode and hard carbon (HC) anode has been developed and commercialized by Tiamat. This study focuses on the assessments of NVPF/HC-based prototype cells in a cylindrical cell format. The specific cell for this investigation has a capacity of 0.61 Ah, a specific energy of 68 Wh/kg, and an energy density of 135 Wh/L at 1C. The cycle life of this specific cell generation (2020) shows 1600 cycles at 5C charge and 5C discharge, but more recent cell generations show improved cycle stability: a trend of enhancement in cell cycle life is presented in the development timeline, and the latest version cell achieves a cycle life of 3200 cycles at 2C charge and 5C discharge. The cell shows excellent power rate capabilities up to 20C discharge and 10C charge. It is highlighted that >90 % of capacity and >80 % of energy (compared to 1C) can still be accessed at 20C discharge. Safety tests with different abuse conditions (overcharge, external heating, short circuit, and nail penetration) were performed. For all these abuse conditions, the specific cell version showed no thermal runaway. Thus, the NVPF/HC-based Na-ion technology seems to develop towards a well-suited candidate for high-power energy storage applications.