Ecofriendly K-Ion Batteries Relying on Abundant Chemical Elements and Water-Based Processes

Current Li-ion batteries are mainly composed of a graphite anode and a cathode based on either NMC (LiNi x Mn y Co z O 2 ) or LFP (LiFePO 4 ) materials. However, the rapid growth of the electric car market will generate significant stress on key chemical elements (nickel, cobalt, copper, lithium). Moreover, the production of NMC and LFP materials turns out to be very energy intensive (multiple calcinations) and uses toxic solvents (NMP, ammonia). Because of that, Li-ion batteries are quite expensive and their ecological footprint is relatively high. The scope of our work is to develop a potassium-ion battery which does not require any critical element and whose production significantly reduces the ecological footprint of the system. Such a battery technology could find its place either in low-cost electric cars or in large-scale-energy-storage devices. We focused our efforts on the development of a Prussian White cathode material based on potassium, manganese and iron (K 2 Mn[Fe(CN) 6 ) showing a theoretical capacity of 155 mAh/g with a potential close to 4 V vs K + /K. The synthesis of this material takes place in water at ambient temperature and it does not involve any calcination. First we optimized the synthesis via a chelating route: tuning the morphology of the Prussian White particles allowed us to come closer to the theoretical capacity of the material. Then we developed water-based coating slurries for our material. We were able to obtain electrodes containing 90 wt% of active material by optimizing both carbon additive and binder. These electrodes showed similar performances compared to electrodes obtained with literature-standard conditions (70 wt% active material, NMP-based slurries). Finally, we tested our Prussian White in full cells versus graphite in coin cells and pouch cells.