Potassium Fluoride and Carbonate Lead to Cell Failure in Potassium-Ion Batteries
Potassium Fluoride and Carbonate Lead to Cell Failure in Potassium-Ion Batteries
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DOI：
10.1021/acsami.1c15174
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发表时间：
2021-11-17
影响因子：
9.5
通讯作者：
Marbella, Lauren E.
中科院分区：
文献类型：
--
作者：
Ells, Andrew W.;May, Richard;Marbella, Lauren E.
虽然锂离子是主流的商业电池化学，但使用地球上丰富的碱金属(如钠和钾)的电池的开发以潜在的更便宜的技术减轻了对锂的依赖。电解液工程一直是锂离子电池(Lib)研究的主要方向，目前尚不清楚同样的电解液设计原则是否适用于K离子电池(KIB)。碳酸氟乙烯(FEC)是锂离子电解液中常用的添加剂，其牺牲分解产物有助于在阳极表面形成稳定的固体电解质界面(SEI)。在这里，我们表明，在含有硬碳阳极的KIBS中添加FeC会导致容量的急剧下降和电池在两个循环中失效，而对于不含FeC的电解液，容量保持率仍然很高(在C/10下，KPF6和KFSI的容量保持率都达到90%)。结合F-19固体核磁共振(SS核磁共振)谱、X射线光电子能谱(XPS)和电化学阻抗谱(EIS)，我们发现FeC在恒流循环过程中分解，在阳极表面形成不溶的KF和K2CO3，这与电池中界面电阻的增加有关。我们的结果强烈地表明，KiB的性能对无机SEI的积累很敏感，这可能是因为这些化合物中K的运输很差。在使用KPF6或KFSI的两种不同的电解液配方中，证实了FeC分解的这一机理。有趣的是，与它们的锂类似物不同，盐负离子不会自行分解。这些结果表明，KIBS和LIBS的电解液分解途径和有利的SEI组分明显不同，这表明需要全新的方法来设计KIB电解液工程。
While Li-ion is the prevailing commercial battery chemistry, the development of batteries that use earth-abundant alkali metals (e.g., Na and K) alleviates reliance on Li with potentially cheaper technologies. Electrolyte engineering has been a major thrust of Li-ion battery (LIB) research, and it is unclear if the same electrolyte design principles apply to K-ion batteries (KIBs). Fluoroethylene carbonate (FEC) is a well-known additive used in Li-ion electrolytes because the products of its sacrificial decomposition aid in forming a stable solid electrolyte interphase (SEI) on the anode surface. Here, we show that FEC addition to KIBs containing hard carbon anodes results in a dramatic decrease in capacity and cell failure in only two cycles, whereas capacity retention remains high (> 90% over 100 cycles at C/10 for both KPF6 and KFSI) for electrolytes that do not contain FEC. Using a combination of F-19 solid-state nuclear magnetic resonance (SSNMR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and electrochemical impedance spectroscopy (EIS), we show that FEC decomposes during galvanostatic cycling to form insoluble KF and K2CO3 on the anode surface, which correlates with increased interfacial resistance in the cell. Our results strongly suggest that KIB performance is sensitive to the accumulation of an inorganic SEI, likely due to poor K transport in these compounds. This mechanism of FEC decomposition was confirmed in two separate electrolyte formulations using KPF6 or KFSI. Interestingly, the salt anions do not decompose themselves, unlike their Li analogues. Insight from these results indicates that electrolyte decomposition pathways and favorable SEI components are significantly different in KIBs and LIBs, suggesting that entirely new approaches to KIB electrolyte engineering are needed.