The popularly reported energy storage mechanisms of potassium-ion batteries (PIBs) are based on alloy-, de-intercalation-, and conversion-type processes, which inevitably lead to structural damage of the electrodes caused by intercalation/de-intercalation of K+ with a relatively large radius, which is accompanied by poor cycle stabilities. Here, we report the exploration of robust high-temperature PIBs enabled by a carboxyl functional group energy storage mechanism, which is based on an example of p-phthalic acid (PTA) with two carboxyl functional groups as the redox centers. In such a case, the intercalation/de-intercalation of K+ can be performed via surface reactions with relieved volume change, thus favoring excellent cycle stability for PIBs against high temperatures. As proof of concept, at the fixed working temperature of 62.5 °C, the initial discharge and charge specific capacities of the PTA electrode are ∼660 and 165 mA⋅h⋅g−1, respectively, at a current density of 100 mA⋅g−1, with 86% specific capacity retention after 160 cycles. Meanwhile, it delivers 81.5% specific capacity retention after 390 cycles under a high current density of 500 mA⋅g−1. The cycle stabilities achieved under both low and high current densities are the best among those of high-temperature PIBs reported previously.

Currently, a big challenge for the practical use of potassium-ion batteries (PIBs) is their intrinsically poor cycling stability, due to the relatively large radius of K+ and sluggish kinetics for intercalation/deintercalation. Here we report the scalable fabrication of N/S-codoped hollow carbon nanocubes (NSHCCs), which have the potential as an electrode for advanced PIBs with robust stability. Their discharge and charge specific capacities are ∼560 mA h g–1 and 310 mA h g–1 at a current density of 50 mA g–1, respectively. Meanwhile, they exhibit 100% specific capacity retention after 620 cycles over 9 months at a low current density of 50 mA g–1, which is state-of-the-art among carbon materials. Moreover, they demonstrate nearly no sacrifice in specific capacities with 99.9% retention after 3000 cycles over 4 months under a high current density of 1000 mA g–1, superior to most carbon analogues for potassium storage previously reported. The improved electrochemical performance of NSHCC can be mainly attributed to the unique hollow carbon nanocubes with incorporated N and S dopants, which can expand the carbon layer spacing, facilitate K+ adsorption, and relieve the volume change during the intercalation/deintercalation of K+ ions.

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