Reversible K-ion intercalation in CrSe2 cathodes for potassium-ion batteries: combined operando PXRD and DFT studies

In the pursuit of more affordable battery technologies, potassium-ion batteries (KIBs) have emerged as a promising alternative to lithium-ion systems, owing to the abundance and wide distribution of potassium resources. While chalcogenides are uncommon as intercalation cathodes in KIBs, this study's electrochemical tests on CrSe2 revealed a reversible K+ intercalation/deintercalation process. The CrSe2 cathode achieved a KIB battery capacity of 125 mA h g−1 at a 0.1C rate within a practical 1–3.5 V vs. K+/K operation range, nearly matching the theoretical capacity of 127.7 mA h g−1. Notably, the battery retained 85% of its initial capacity at a high 1C rate, suggesting that CrSe2 is competitive for high-power applications with many current state-of-the-art cathodes. In-operando PXRD studies uncovered the nature of the intercalation behavior, revealing an initial biphasic region followed by a solid-solution formation during the potassium intercalation process. DFT calculations helped with the possible assignment of intermediate phase structures across the entire CrSe2–K1.0CrSe2 composition range, providing insights into the experimentally observed phase transformations. The results of this work underscore CrSe2's potential as a high-performance cathode material for KIBs, offering valuable insights into the intercalation mechanisms of layered transition metal chalcogenides and paving the way for future advancements in optimizing KIB cathodes.