Hitherto Unknown Solvent and Anion Pairs in Solvation Structures Reveal New Insights into High‐Performance Lithium‐Ion Batteries

Abstract

Solvent-solvent and solvent-anion pairings in battery electrolytes have been identified for the first time by nuclear magnetic resonance spectroscopy. These hitherto unknown interactions are enabled by the hydrogen bonding induced by the strong Lewis acid Li + , and exist between the electron-deficient hydrogen (𝜹 + H) present in the solvent molecules and either other solvent molecules or negatively-charged anions. Complementary with the well-established strong but short-ranged Coulombic interactions between cation and solvent molecules, such weaker but longer-ranged hydrogen-bonding casts the formation of an extended liquid structure in electrolytes that is influenced by their components (solvents, additives, salts, and concentration), which in turn dictates the ion transport within bulk electrolytes and across the electrolyte-electrode interfaces. The discovery of this new inter-component force completes the picture of how electrolyte components interact and arrange themselves, sets the foundation to design better electrolytes on the fundamental level, and probes battery performances.

Dipole–Dipole Interaction Induced Electrolyte Interfacial Model To Stabilize Antimony Anode for High-Safety Lithium-Ion Batteries

“…Note that such interaction between TEP and HFE is a dipole−dipole interaction, which differs from the detected hydrogen bonding between the neighboring solvent molecules (e.g., DME/DOL) in our recent work. 61 In contrast, the negligible interaction between HFE and Li + can be further proved by the Raman spectra, where there is no peak variation of C�O in either HFE solvent or TEP/HFE electrolyte when the LiFSI or LiTFSI salt was used as the solute (Figure 3h). Moreover, the decreased frequency of Li + −O TEP in the electrolyte of 1.2 M LiFSI in TEP/HFE (vs 4.4 M LiFSI in TEP) further demonstrates that HFE can compress the Li + solvation structure and weaken the Li + −O TEP interaction, eventually increasing the FSI − /Li + interaction (Figure 3i).…”

“…Moreover, the type of the interaction between TEP and HFE can be further confirmed by 1 H– 19 F heteronuclear Overhauser effect spectroscopy (HOESY) experiments, in which the dipolar contacts between H and F can be obtained, indicating the solvent–solvent dipole–dipole interaction formed by the electronegative fluorine (δ – F) and electropositive hydrogen (δ + H) between TEP and HFE (Figure S4c,d). Note that such interaction between TEP and HFE is a dipole–dipole interaction, which differs from the detected hydrogen bonding between the neighboring solvent molecules (e.g., DME/DOL) in our recent work . In contrast, the negligible interaction between HFE and Li + can be further proved by the Raman spectra, where there is no peak variation of CO in either HFE solvent or TEP/HFE electrolyte when the LiFSI or LiTFSI salt was used as the solute (Figure h).…”

Weak Solvent–Solvent Interaction Enables High Stability of Battery Electrolyte

“…were changed in different battery systems. Thus, our discovery may provide a new challenging direction which is to quantify the solvent–solvent interaction. − We believe more advanced techniques and simulations need to be developed to realize it, by which a certain critical value that the interaction intensity should surpass to stabilize the electrolytes could be estimated.…”

Interfacial and Interphasial Chemistry of Electrolyte Components to Invoke High‐Performance Antimony Anodes and Non‐Flammable Lithium‐Ion Batteries

“…The dipole‐dipole interaction between the two solvents also presents in the electrolytes and strengthens the shielding effect on DME (Figure 2i), otherwise, the 1 H peaks of DME should be more de‐shielded in the lower salt concentration. [ 16 ] The dipole‐dipole interaction could be the reason for the weakened interactions between Li + and DME due to the existence of HFE (Figure 2f). In addition, such DME‐HFE interactions ensure the stability of DME solvent in the electrolyte, leading to a much lower saturated vapor pressure that in turn enhances the nonflammability of the electrolyte.…”