Hybrid Electrolyte with Dual‐Anion‐Aggregated Solvation Sheath for Stabilizing High‐Voltage Lithium‐Metal Batteries

Abstract

Lithium (Li)‐metal batteries (LMBs) with high‐voltage cathodes and limited Li‐metal anodes are crucial to realizing high‐energy storage. However, functional electrolytes that are compatible with both high‐voltage cathodes and Li anodes are required for their developments. In this study, the use of a moderate‐concentration LiPF6 and LiNO3 dual‐salt electrolyte composed of ester and ether co‐solvents (fluoroethylene carbonate/dimethoxyethane, FEC/DME), which forms a unique Li+ solvation with aggregated dual anions, that is, PF6− and NO3−, is proposed to stabilize high‐voltage LMBs. Mechanistic studies reveal that such a solvation sheath improves the Li plating/stripping kinetics and induces the generation of a solid electrolyte interphase (SEI) layer with gradient heterostructure and high Young's modulus on the anode, and a thin and robust cathode electrolyte interface (CEI) film. Therefore, this novel electrolyte enables colossal Li deposits with a high Coulombic efficiency (≈98.9%) for 450 cycles at 0.5 mA cm−2. The as‐assembled LiǁLiNi0.85Co0.10Al0.05O2 full batteries deliver an excellent lifespan and capacity retention at 4.3 V with a rigid negative‐to‐positive capacity ratio. This electrolyte system with a dual‐anion‐aggregated solvation structure provides insights into the interfacial chemistries through solvation regulation for high‐voltage LMBs.

Li2CO3/LiF‐Rich Heterostructured Solid Electrolyte Interphase with Superior Lithiophilic and Li+‐Transferred Characteristics via Adjusting Electrolyte Additives

“…This indicates that the SEI layer formed in TPP-and TFPPcontained electrolytes have high Li + transport, while the SEI layer formed in TPFPP-contained electrolyte is slowest, which is mainly associated with the structure and components of SEI. [15] Simultaneously, the TFPP-contained electrolyte exhibits smallest E a2 (58.17 KJ mol −1 ) with easier Li + desolvation ability relative to other electrolytes (Figure 3e), which is consistent with that of theoretical calculation. The exchange current density (i 0 ) is calculated by fitting with the Tafel plot of various electrolytes to further investigate Li + transfer kinetics at the interface.…”

“…, where T, R 1(2) , and R are the absolute temperature, resistance, and standard gas constant, respectively. [15,41] The SEI formed in TPP-and TFPP-contained electrolytes exhibited smaller E a1 (57.17 and 57.26 KJ mol −1 , respectively) than blank electrolyte (59.67 KJ mol −1 , Figure 3d), but the SEI formed in TPFPP-contained electrolyte showed biggest E a1 (75.87 KJ mol −1 ). This indicates that the SEI layer formed in TPP-and TFPPcontained electrolytes have high Li + transport, while the SEI layer formed in TPFPP-contained electrolyte is slowest, which is mainly associated with the structure and components of SEI.…”

“…In addition, the unstable SEI will also induce uneven ionic diffusion and Li deposition, which would result in uncontrolled dendrite growth and poor electrochemical performance. [9][10][11] Therefore, high-quality SEI is highly desired for superior LMBs.Recently, extensive efforts have been devoted to stabilizing Li anode by engineering a robust SEI mainly through electrolyte formulation [12][13][14][15][16] and artificial SEI. [17][18][19][20] However, the role of the structures and components of SEI has long been debated, and the transport mechanism of Li + ions in the SEI is still not well understood.…”

“…Recently, extensive efforts have been devoted to stabilizing Li anode by engineering a robust SEI mainly through electrolyte formulation [12][13][14][15][16] and artificial SEI. [17][18][19][20] However, the role of the structures and components of SEI has long been debated, and the transport mechanism of Li + ions in the SEI is still not well understood.…”

Regulating Li‐ion Flux through a Dense yet Highly Ionic Conductive Interlayer for Stable Li Deposition

“…Another strategy is to construct a stable artificial solid electrolyte interphase by ex situ or in situ methods to ensure the uniform Li plating/stripping, [17][18][19][20][21][22][23][24][25] but the interfacial layer structure control is complicated to ensure the integrity in long cycling.The Li dendrite growth is mainly due to the uneven distribution of Li + ions on the electrode surface because of the uncontrollable ion diffusion driven by the electric field, which then induces non-uniform Li deposition. [26][27][28][29][30][31][32][33][34] Thus, regulating the Li + ion diffusion in a controlled direction should be a promising way for the uniform Li + ion distribution and then suppress the dendrite Li deposition. Building an artificial ionic conductive layer, such as a solid electrolyte layer, on the separator is an effective strategy to regulate the Li + ion diffusion and enable uniform Li + ion flux on the electrode surface.…”