Model-Based Design of Graphite-Compatible Electrolytes in Potassium-Ion Batteries

Abstract

Potassium ion batteries (KIBs) are attractive alternatives to lithium-ion batteries (LIBs) due to their lower cost and global potassium sustainability. However, designing compatible electrolytes with the graphite anode remains challenging. This is because the electrolyte decomposition and/or graphite exfoliation (due to K + -solvent co-insertion) always exist, which is much harder to overcome compared to the case of LIBs due to the higher activities of K + . Herein, we report a general principle to design compatible electrolytes with graphite anode, where the K + can be reversibly (de-)intercalated. We find that the electrolyte composition is critical to determining the graphite performance, which can be tuned by the kind of solvent, anion, additives, and concentration. We present a new interfacial model to understand the variation in performance (i.e., K + (de-)intercalation, or K + -solvent co-insertion or decomposition). Our interfacial model is distinctly different from the solid electrolyte interphase (SEI) interpretation. This work offers new opportunities to design high-performance KIBs and potassium-ion sulfur batteries. Particularly, we present a new guideline to design electrolytes for KIBs and other advanced mobile (ion) batteries.

Phase evolution of electrochemically potassium intercalated graphite

“…Furthermore, when PANa binder is used, an influence of different electrolyte salts of KFSA, KTFSA, and KPF6 appears to be insignificant (Figure S9). We note that a solution of 1.0 mol dm -3 KFSA/EC:DEC still offers higher initial Coulombic efficiency and cycle stability compared to 0.8 mol dm -3 KPF6/EC:DEC. 25 Additionally, an influence of EC-based binary solvents of EC:DEC, EC:DMC, and EC:PC on the reversibility is negligible for the PANa electrode during 100 cycles as confirmed by Figure S10, but 1.0 mol dm -3 KFSA/PC results in continuous electrolyte decomposition at 0.7 V vs. K (equal to 0.8 V vs. Li), which is likely due to co-intercalation of PC-solvated K + ions and/or dissolution of SEI components, leading to graphite exfoliation and electrolyte decomposition 24 similar to Li|LiClO4-PC|graphite cell. [30][31][32] Thus, we selected an electrolyte of 1.0 mol dm -3 KFSA/EC:DEC for the subsequent studies.…”

“…According to Zhang's 24 and our reports, 13,25 selection of potassium electrolyte salts significantly affects reversible capacities, Coulombic efficiency, and cycle stability of the graphite electrode in a K cell. Using PVdF as a binder for the graphite electrodes, we confirmed that the highest Coulombic efficiency and the superior cycle stability are obtained in 1.0 mol dm -3 KFSA/EC:DEC (1:1 v/v) electrolyte compared to those in 0.8 mol dm -3 KPF6/EC:DEC or 1.0 mol dm -3 KTFSA/EC:DEC as shown in Figure S2.…”

State-of-the-art anodes of potassium-ion batteries: synthesis, chemistry, and applications

“… 114 With a specially designed electrolyte, Ming et al improved the areal capacity of graphite anode from 0.2 to 0.5 mA h cm −2 . 181 At this stage, the areal capacity is far from that of conventional LIBs, and unique material engineering and rational electrode design are still required.…”

Effect of Crystallinity of Synthetic Graphite on Electrochemical Potassium Intercalation into Graphite

“…The overall trend of the structural phase transition is consistent with previous reports. 16,[26][27][28][29][30] When comparing details of the two graphite samples, one can see a distinct difference in peak positions during the phase transition between stage-2 and stage-1 (see selected offset-free XRD patterns in Fig. S6 and enlarged patterns in Fig.…”

“…3 to reversibly transforms back into graphite by potassium deintercalation. 16,[26][27][28]30 However, both the graphite electrodes after depotassiation at the 1 st cycle displayed not only a sharp diffraction peak of graphite but also broad peaks of residual K-GIC as shown in Fig. S8.…”