Key Factor Determining the Cyclic Stability of the Graphite Anode in Potassium-Ion Batteries

Abstract

Graphite is the most commonly used anode material for not only commercialized lithium-ion batteries (LIBs) but also the emerging potassium-ion batteries (PIBs). However, the graphite anode in PIBs using traditional dilute ester-based electrolyte systems shows obvious capacity fading, which is in contrast with the extraordinary cyclic stability in LIBs. More interestingly, the graphite in concentrated electrolytes for PIBs exhibits outstanding cyclic stability. Unfortunately, this significant difference in cycling performance has not raised concern up to now. In this work, by comparing the cyclic stability and graphitization degree of the graphite anode upon cycling, we reveal that the underlying mechanism of the capacity fading of the graphite anode in PIBs is not the larger volume expansion of graphite caused by the intercalation of potassium ions but the continual accumulation of the solid electrolyte interphase (SEI) on the surface of graphite. By X-ray photoelectron and nuclear magnetic resonance spectroscopies combined with chemical synthesis, it is concluded that the accumulation of the SEI may mainly come from the continual deposition of a kind of oligomer component, which blocks intercalation and deintercalation of potassium ions in graphite anodes. The designed SEI-cleaning experiment further verifies the above conclusion. This finding clarifies the crucial factor determining the cyclic stability of graphite and provides scientific guidance for application of the graphite anode for PIBs.

Study of the influence of the formation protocol on the SEI layer formed at the graphite electrode surface of a non-aqueous potassium-ion hybrid supercapacitor (KIC) through STEM and XPS analyses

“…In the case of K-ion batteries (KIBs), it has been shown that the stability of the SEI formed at the surface of the negative electrode is a key factor for cycling stability. 27 The difference in stability of the SEI according to the formation protocol applied could therefore help to explain the very different cycling performances. Moreover, in lithium-ion batteries, lithium fluoride (LiF) is known for its protective function for the electrode within the SEI 12 and it has been shown that the KF content has a strong impact on the performance of KIBs, 23 as detailed previously.…”

Engineering Electrode/Electrolyte Interphase Chemistry toward High-Rate and Long-Life Potassium Ion Full-Cell

“…On the cathode side, the Prussian Blue analogues (PBAs) are the most promising candidates that show a preference for K + and Na + insertion. , The 3D open framework enables reversible filling and better fit of large K ions in the cavities of PBAs, which stabilizes the electrode’s structure and therefore leads to higher redox voltage, more stable cycling performance, and excellent rate capability. , On the anode side, the commercial graphite exhibits reversible potassiation–depotassiation with an impressive cycle life over 2000 cycles as reported in the literature and delivers a high theoretical capacity of 279 mAh g –1 (KC 8 ) with a suitable average potential of ∼0.2 V vs K/K + , thus is considered as the most suitable anode material for PIBs. , Currently, most relevant studies focused on the utilization of half-cells (with alkali metals as counter and reference electrodes) to investigate the electrode material’s electrochemical performance . However, the serious K dendritic growth and parasitic reactions within the electrolytes typically led to safety issues and rapid capacity degradation, and more importantly concealed the real cycling performance of the working electrodes. − Therefore, the full-cell evaluation of PBAs paired with graphite is crucial, especially for determining their commercial feasibility. Generally speaking, the electrochemical performance of PIBs is largely dictated by the reversible number of K + shuttled between the cathode and anode within per cell mass and cell voltage. , Whereas almost infinite K + could be provided by the K metal in a half-cell, the number of K + in full-cells is limited by those preexisting in PBA’s structure.…”

2023 roadmap for potassium-ion batteries

“…In 2019, Naylor et al, found that thick and unstable SEI is generated on graphite anode during cycling in the classical EC-based electrolyte (0.8 M KPF 6 EC:DEC), which should be the reason for the rapid capacity fading of graphite anode [231]. Recently, our group revealed that the thick and unstable SEI should be accumulated oligomers [232]. Apparently, the classical EC-based electrolytes are not able to form stable SEI and exploit the full capability of graphite anode.…”