半离子C-F键在钾离子电池碳负极中诱导快速离子储存和电子转移

Semi-ionic C-F bond inducing fast ion storage and electron transfer in carbon anode for potassium-ion batteries

氟(F)杂原子功能化的碳负极可以形成更多的缺陷位点,从而有效提高钾的存储容量.然而,提高电化学性能的机制尚不清楚,尤其是对何种C-F键深入影响钾储存性能仍缺乏基本认识.本文报道了一系列F掺杂的碳,并证明了C-F是半离子键而不是离子键;碳化温度对缺陷程度有显著影响.并且,高比例半离子C-F键诱导的丰富缺陷可以作为活性位点来吸附大量与电容行为相关的钾离子,不仅有利于长循环寿命,而且提升了在高电流密度下的倍率容量.密度泛函理论计算证实半离子C-F键的存在可以提高碳基体对钾离子的吸附能力并同时提高电子电导率,有利于高容量和倍率.此外,通过耦合半离子C-F键和吡啶N键,钾吸附能和电导率被进一步提升,这使得半电池实现了优异的容量(245.2 mA h g^(-1))和倍率,并且组装的全电池具有高能量密度(143.9 W h kg^(-1)).

Fluorine(F)-heteroatom-functionalized carbon anodes can effectively increase the potassium(K)storage capacity by forming more defect sites;however,the mechanism behind the improvement in electrochemical performance remains unclear,and the fundamental understanding of which kind of C-F bond profoundly determines K storage properties is still lacking.Hence,we report a series of F-doped carbon and demonstrate that it is a semi-ionic C-F bond rather than an ionic C-F bond,and carbonization temperature has a substantial impact on the defect level.Moreover,numerous defects induced by the high percentage of semi-ionic C-F bonds can function as active sites to adsorb many K-ions associated with capacitive behavior,which not only lengthens the cycle lifespan,but is also positively correlated with rate capacity at a high current density.Density functional theory calculations confirm that the existence of a semi-ionic C-F bond can improve the K-ion adsorption capability of carbon and simultaneously increase electronic conductivity,leading to a high capacity and rate.Furthermore,both K adsorption energy and conductivity are optimized by coupling semi-ionic C-F and pyridinic N bonds,resulting in superior capacity(245.2 mA h g^(−1))and exceptional rate capacity in a K-half battery and high energy density(143.9 W h kg^(−1))in a K-full battery.