Toward Highly Reliable Potassium‐Ion Half and Full Coin Cells

Abstract To develop high energy and high‐power potassium‐ion batteries (KIBs), performance need to be evaluated in full‐cells instead of half‐cells based on the highly reactive K metal that leads to misinterpretation of the results. However, assembling KIBs full‐cells is not trivial as many parameters are critical to the obtained performance. This work demonstrates approaches to assemble reliable K‐ion full‐cells using graphite and KVPO₄F_0.5O_0.5 based electrodes. First, the optimal separators choice/number and electrolyte choice/volume are determined in half‐cells then the optimal electrolyte volume is determined in full‐cells. Importantly, the electrolyte volume should be fixed to about 4 times the porosity volume for both half‐ and full‐cells. Then, using 3‐electrodes cells, the optimal negative/positive (N/P) diameter ratio then the optimal N/P capacity ratio are determined to be 1.16±0.2. Finally, these approaches allow assembling KVPFO//graphite coin‐cells with an energy density of about 47 Wh kg_device⁻¹ using a high N/P loading ratio of 4/10 (in mg_{active‐material} cm⁻²). Overall, this work can be used as a guide to assemble any KIBs full‐cell system and thus paves the way to the determine the best negative/positive materials combination in order to develop efficient KIBs.