Robust high-temperature potassium-ion batteries enabled by carboxyl functional group energy storage

Abstract

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.

Multiple Accessible Redox-Active Sites in a Robust Covalent Organic Framework for High-Performance Potassium Storage

“…The rate performance of the carbon additive (Super P) is also evaluated and proved to be limited in capacity (Figure S13), suggesting that the capacity for the electrode mainly comes from the active COF. Compared to the representative reported organic anodes, ,,− the rate performance of this COF anode for KIBs shows a slow decrease in capacity with the increase in the current density (Figure c). This rate performance was also much better than that of the widely reported carbonaceous anode for KIBs (Figure S14).…”

“…It is much lower than that of the alloy-type, conversion-type, and deintercalation-type anode for K + storage. 25 The small volumetric expansion for the COF anode could be explained by the surface-dominated K + -storage behavior as identified by the CV analysis for this COF anode, 15 which would alleviate the structural damage for outstanding cycling endurance. The small volumetric expansion for highcapacity K + storage agrees well with the theoretical simulation (Figure 1c).…”

“…Organic anode materials are now drawing increasing research interest in the field of rechargeable batteries due to their abundance, high theoretical capacity, and huge room for function designability. − The built-in groups in the organic molecules like CN, CO, and NN could act as redox-active sites for metal-ion storage. Considering the issue of easy dissolution for small organic molecule electrodes in organic electrolytes, immobilizing the redox-active groups into the porous two- or three-dimensional (2D or 3D) frameworks has been widely explored and demonstrated an effective strategy to get a more reliable electrode. − Particularly, constructing redox-active groups into a covalent organic framework (COF), which was assembled from light components (C, N, O, etc.)…”

A Fast‐Charging and High‐Temperature All‐Organic Rechargeable Potassium Battery

“…The sharp peak at ≈18° is ascribed to the polytetrafluoroethylene (PTFE) binder, which is overlapped with one of the XRD peaks for TBPS. [ 41 ] Compared with the TBPS/NG powder, XRD peaks in the range from 30° to 40° are weakened in the pristine TBPS/NG anode but become stronger after cycling at different temperatures. The peak at 37.5° disappears after cycling at high temperatures, but the peaks at 24.7°, 27.9°, 31.8°, 34.2° and 36.6° remain after cycling at 70–100 °C, indicating that the crystalline structure changes after cycling and the newly formed crystalline structure shows high stability at high temperatures.…”

“…Considerable efforts have been devoted to developing advanced RPBs at ambient temperature and high temperature. Though there are some reports of RPBs operating at 50–60 °C, [ 39 , 40 , 41 ] the demonstrations of RPBs at temperatures above 65 °C are very few due to the low melting point of metallic K (63.65 °C) and unstable electrolytes/SEI at high temperatures. In contrast, all‐organic RPBs are ideal candidates for high‐temperature RPBs due to their advantages as follows: 1 ) The all‐organic RPBs based on p‐type organic cathodes and n‐type organic anodes do not require metallic K, so the working temperature is not limited by the melting point of metallic K; 2) Most OEMs are thermally stable at the temperatures below 200 °C; [ 42 ] 3) The high flexibility of OEMs retains the structural integrity during fast ion/electron transfer at high temperatures.…”