Anion-Containing Solvation Structure Reconfiguration Enables Wide-Temperature Electrolyte for High-Energy-Density Lithium-Metal Batteries

Abstract

The demand for high-energy-density lithium batteries (LBs) that work under a wide temperature range (−40 to 60 °C) has been increasing recently. However, the conventional lithium hexafluorophosphate (LiPF6)-based ester electrolyte with a solvent-based solvation structure has limited the practical application of LBs under extreme temperature conditions. In this work, a novel localized high-concentration electrolyte (LHCE) system is designed to achieve the anion-containing solvation structure with less free solvent molecules using lithium difluorophosphate (LiPO2F2) as a lithium salt, which enables wide-temperature electrolyte for LBs. The optimized solvation structure contributes to the cathode–electrolyte interface (CEI) with abundant LiF and P–O components on the surface of the LiNi0.5Co0.2Mn0.3O2 (NCM523) cathode, effectively inhibiting the decomposition of electrolyte and the dissolution of transition-metal ions (TMIs). Moreover, the weakened Li+–dipole interaction is also beneficial to the desolvation process. Therefore, the 4.3 V Li||NCM523 cell using the modified electrolyte maintains a high capacity retention of 81.0% after 200 cycles under 60 °C. Meanwhile, a considerable capacity of 70.9 mAh g–1 (42.0% of that at room temperature) can be released at an extremely low temperature of −60 °C. This modified electrolyte dramatically enhances the electrochemical stability of NCM523 cells by regulating the solvation structure, providing guidelines for designing a multifunctional electrolyte that works under a wide temperature range.

Solvation Structure-Tunable Phase Change Electrolyte for Stable Lithium Metal Batteries

“…Therefore, tremendous efforts have been made to modulate the LSS, including changing the components of solvents, introducing additives, and adjusting the concentration and species of Li salts. − For instance, based on diethyl ether solvent, a unique electrolyte LSS of a contact ion pair (CIP) was reported by Holoubek et al, which favored uniform Li metal growth at extremely low temperatures . The unique “solvent-in-salt” electrolyte with a high concentration of Li salt in the solvent was widely reported. − The LSS regulates the solid–electrolyte interphase (SEI) component and protects lithium anodes against the undesired growth of lithium dendrites, and provides high Coulombic efficiency.…”

Synergistic Effect of Dual-Anion Additives Promotes the Fast Dynamics and High-Voltage Performance of Ni-Rich Lithium-Ion Batteries by Regulating the Electrode/Electrolyte Interface

“…The DFT (density functional theory) calculation of the lowest unoccupied molecular orbital (LUMO) in this study was conducted on the Gaussian 09 software package. The B3LYP42 method at the 6-311+G (d, p) basis set was used to optimize the geometry structure …”

Lithium Difluorophosphate as a Widely Applicable Additive to Boost Lithium‐Ion Batteries: a Perspective

“…While for the battery working at a high temperature (>40 °C), the battery utilizes the stability of the LiDFP‐derived SEI/CEI which is rich in inorganics, more robust, and thus can effectively suppress electron tunneling and TM dissolution [ 16 ] of the TM‐based cathodes. [ 23,37 ]…”

“…The NMC532||Li cell using this LHCE maintained a capacity retention of 81.0% after 200 cycles at 60 °C. [ 23 ]…”

“…According to the morphology comparison observed with scanning electron microscopy (SEM), LiDFP helps to form a thin and dense SEI/ CEI. [10,23] The element analysis of X-ray photoelectron spectroscopy (XPS) and time of flight secondary ion mass spectrometry (TOF-SIMS) results show that the SEI/CEI formed in the LiDFP-containing electrolytes is rich in P and F containing inorganics, such as Li 3 PO 4 and LiF. [12,14,23,[31][32][33] Moreover, the PO rich inorganic interphase is generally an excellent Li + ion conductor, endowing the battery with low interfacial impedance.…”