Characterising the Ionic Transport and Thermodynamic Properties of Potassium-Ion Electrolytes

Abstract

The lithium price has increased more than sevenfold since the start of 2021 (as of May 2022), reaching unprecedented price levels and demonstrating significant challenges for the security of supply of lithium for lithium-ion batteries (LIBs)1. With forecasts showing a potential significant lithium supply deficit by 20301, the case for alternative chemistries based on abundant minerals which can fulfil some LIB functions has never been stronger. Sodium-ion batteries (NIBs) and potassium-ion batteries (KIBs) are emerging as promising complementary technologies to lithium-ion batteries (LIBs) due to the availability and low cost of sodium and potassium, and the minerals comprising their leading electrodes2 , 3. KIBs have a significant advantage over NIBs as K+ can reversibly intercalate into the graphite electrodes used in LIBs, thus one of the primary components of KIBs is already available at commercial scale, unlike for NIBs2. The lower charge density of K+ compared to Li+ has also been suggested to result in superior ion transport in the electrolyte with KIBs potentially able to deliver superior rate capability and low-temperature performance. However, a comprehensive characterisation of the ionic transport and thermodynamic properties of nonaqueous K-ion electrolytes, critical to the development of KIBs, has not yet been reported. Here, for the first time, we fully characterise the ionic transport and thermodynamic properties of a nonaqueous K-ion electrolyte4, potassium bis(fluorosulfonyl)imide (KFSI) in 1,2-dimethoxyethane (DME) and compare it with its Li-ion equivalent (LiFSI in DME) over the concentration range 0.25–2 m. This was realised by developing a K metal preparation protocol enabling sufficient K metal stability for electrolyte characterisation. Our results demonstrate that the K-ion electrolyte indeed displays significantly higher salt diffusion coefficients and transference numbers than the Li-ion electrolyte, evidencing the potential for high-power applications of KIBs. IEA. Global EV Outlook 2022. (IEA, 2022).Dhir, S., Wheeler, S., Capone, I. & Pasta, M. Outlook on K-Ion Batteries. Chem vol. 6 2442–2460 (2020). doi: 10.1016/j.chempr.2020.08.012Hosaka, T., Kubota, K., Hameed, A. S. & Komaba, S. Research Development on K-Ion Batteries. Chem. Rev. acs.chemrev.9b00463 (2020) doi:10.1021/acs.chemrev.9b00463.Dhir, S., Jagger, B., Maguire, A. & Pasta, M. Characterising the Ionic Transport and Thermodynamic Properties of Potassium-ion Electrolytes. Res. Sq. (2022) doi:10.21203/RS.3.RS-2310020/V1. Figure 1