A novel low-cost and environment-friendly cathode with large channels and high structure stability for potassium-ion storage

一种新型廉价、环境友好、结构稳定且具有大离子通道的钾离子电池正极材料

Potassium-ion batteries (KIBs) are promising candidates for large-scale energy storage due to the abundance of potassium and its chemical similarity to lithium.Nevertheless,the performances of KIBs are still unsatisfactory for practical applications,mainly hindered by the lack of suitable cathode materials.Herein,combining the strong inductive effect of sulphate and the feasible preparation of Fe^(2+)-containing compounds in oxalate system,a compound with novel architecture,K_(4)Fe_(3)(C_(2)O_(4))_(3)(SO_(4))_(2),has been identified as a lowcost and environmentally friendly cathode for stable potassium-ion storage.Its unique crystal structure possesses an unprecedented two-dimensional framework of triple layers,with 3.379Åinterlayer distance and large intralayer rings in the size of 4.576×6.846Å.According to first-principles simulations,such a configuration is favorable for reversible K-ion migration with a very low volume change of 6.4%.Synchrotron X-ray absorption spectra and X-ray diffraction characterizations at different charging/discharging states and electrochemical performances based on its half and full cells further verify its excellent reversibility and structural stability.Although its performance needs to be improved via further composition tuning with multi-valent transition metals,doping,structural optimization,etc.,this study clearly presents a stable structural model for K-ion cathodes with merits of low cost and environmental friendliness.

得益于钾的地壳丰度及其与锂的化学相似性,钾离子电池有望应用于大规模储能领域.目前,钾离子电池的性能尚不能满足实用需求,主要原因在于缺乏合适的正极材料.基于硫酸根的强诱导效应和草酸体系制备亚铁化合物的优势,本文制备了一种新型廉价、环境友好且稳定的储钾正极材料K_(4)Fe_(3)(C_(2)O_(4))_(3)(SO_(4))_(2).其独特的二维层状晶体结构具有3.379Å的层间距,且层内具有4.576×6.846Å的大环.根据第一性原理计算,该结构有利于钾离子的可逆迁移,且体积变化仅为6.4%.不同充放电态样品的同步辐射X射线吸收光谱和XRD、半电池以及全电池的电化学表征证实了其优异的电化学可逆性和结构稳定性.通过成分调控、掺杂、结构优化等策略,K_(4)Fe_(3)(C_(2)O_(4))_(3)(SO_(4))_(2)正极材料的电化学性能有望进一步提升.因此,本工作为廉价、环保的储钾正极材料提供了一种新的稳定晶体模型.