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

Abstract

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–K_1.0CrSe₂ 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.