Semiconductor-to-metal transition renders intrinsic pseudocapacitance and high volumetric capacity for iron chalcogenide anode

Abstract

There is a burgeoning need for high-power-density sodium-ion batteries (SIBs) with compressed size, whereas it is very challenging to integrate fast kinetics and high volumetric capacity into one material. Herein, we demonstrate an effective strategy to jointly promote the power and volumetric energy densities from the perspective of materials’ electronic conductivity. Via semiconductor-to-metal transition, we successfully develop the first intrinsic pseudocapacitive chalcogenide material, metallic FeS1-xSex(x ≥ 0.5), which shows inherent capacitor-like faradic charge storage, even when crystallizes in micrometer bulk material and operates in the absence of conducting additives. Therefore, it enables conducting-additive-free (CA-free) electrodes with high volumetric capacities of 965 mA h cm−3, which also delivers exceptional rate capability with a capacity above 392 mA h cm−3 at 50C-rate, among the best state-of-the-art SIB anodes. These superior performances can be attributed to a rare intrinsic intercalation pseudocapacitive mechanism, which is related to the nature of metallic behavior and unique layered structure. This discovery not only provides a valuable complement to our understanding of pseudocapacitive processes, but also facilitates the design of high-rate electrode materials with compressed sizes in the future.