Electrolyte Engineering Enables High Stability and Capacity Alloying Anodes for Sodium and Potassium Ion Batteries

Abstract

Pursuing rechargeable metal-ion batteries with greater energy density is attracting great attention due to increasing demand for energy storage, where alloying anodes can provide very high capacity. [1][2][3][4][5][6][7] This is particularly true since sodium and potassium ion battery technologies offer limited capacity and stability using classic carbon-based anodes compared to lithium ions. [8][9][10][11] However, alloying anodes are notorious for their severe capacity fading, which has hindered their practical applications. The failure mechanism of alloying anodes has always been ascribed to the large volumetric change (~300%) and/or the fragile solid electrolyte interphase (SEI). [12][13][14][15] This interpretation is popular because the pulverization of the alloy-based electrodes can be observed during the reactions. As a result, many strategies have been developed to overcome this issue. These strategies include nano-structural controlling, carbon modification, and improving electrical conductivity. Thus, many nanostructured alloys including particles, 16 fibers/tubes, 5,17 film/membrane, 18,19 and hierarchical material 20,21 are being explored to stabilize alloying anodes. Characteristic, conductive and/or protective materials such as carbon and artificial solid electrolyte interphase (SEI) have been also used to improve alloying anode capacities stabilities. [22][23][24][25] Herein we show that an unprecedented high capacity (>650 mAh g -1 ) and stability (>500 cycles) can be achieved in alloying anodes by simply tuning the electrolyte composition, without the need for nanostructural control, carbon modification, and/or SEI engineering. We confirm that the cation solvation structure (e.g., Na + , K + ), particularly the type and location of the anions present in the metal salt and solvents, plays a critical role in affecting the alloying anode performance. In addition, we present a new anionic model showing that the anion corrosion plays at least an equally important role in alloying anode stability as the volume variation and fragile SEI models. Moreover, we present a new reaction model for alloying anode to make the ASSOCIATED CONTENT Supporting Information. Experimental and simulation section. Figures S1-S17 and Table S1 are included.

Boosting Coulombic Efficiency of Conversion‐Reaction Anodes for Potassium‐Ion Batteries via Confinement Effect

“…The formation of SEI layers is associated with the electrolyte decomposition and consumes K ions continuously, offering a low coulombic efficiency. [ 7 ] This is the reason for the rapid capacity decay and increasing coulombic efficiency of CuS‐C NFs electrode during the first 30 cycles. From then on, the reconstructed structure of CuS‐C NFs electrode as well as the established SEI layers are kept in stable(Figure 6d–f), which do the electrode a favor to exhibit high coulombic efficiency and negligible capacity decay.…”

“…[ 6 ] Therefore, KIBs are considered to the promising alternatives to LIBs in large energy storage systems and have attracted much attention recently. [ 5,7–9 ]…”

Ionic‐Conducting and Robust Multilayered Solid Electrolyte Interphases for Greatly Improved Rate and Cycling Capabilities of Sodium Ion Full Cells

“…Moreover, the effect of solvation structure and the location of different anions on the sodium ion storage of alloy‐type Sn and Bi was investigated to provide a rational design of electrolyte materials. [ 27 ] In order to deeply understand this phenomenon, the interfacial electrochemical properties and charge transfer kinetics should be systematically interpreted in the two electrolytes. Additionally, although these approaches successfully improved the sodium storage performance of the bismuth‐based anode, the studies on an alloy‐type anode are mostly limited to laboratory scale with low areal mass loadings of 1–1.5 mg cm −2 .…”

Design aspects of electrolytes for fast charge of Li‐ion batteries

“…This subject relates to the structure and stability of Li + ion solvation shell in the electrolytes, as shown in Figure 2, which are intrinsically affected by the type and ratio of solvents and counter anions. [29][30][31][32][33][34] In the electrolyte solutions, the Li + -coordinated solvent molecules are dynamically exchanging with the solvent molecules and counter anions (X − ) in the outer shell. Unlike the solvation and desolvation energies that are equal in value and offset at the anode and cathode, the solvation and desolvation activation energies at the anode and cathode are different in value, and both are required low for fast charge.…”

“…This subject relates to the structure and stability of Li + ion solvation shell in the electrolytes, as shown in Figure 2, which are intrinsically affected by the type and ratio of solvents and counter anions 29‐34 . In the electrolyte solutions, the Li + ‐coordinated solvent molecules are dynamically exchanging with the solvent molecules and counter anions (X − ) in the outer shell.…”