From Electronic Structure to Ion Transport: Photoelectron Spectroscopy and Molecular Dynamics Simulations Reveal the Role of Anions in Lithium Battery Electrolytes

Journal Article · Tue Jul 08 00:00:00 UTC 2025 · Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment, and General Theory

DOI: https://doi.org/10.1021/acs.jpca.5c03415 · OSTI ID:2574261

Jiang, Yanrong  ^[1]; Cao, Wenjin  ^[2]; Gao, Xiao-Fei  ^[2]; Zeng, Jinzhe  ^[3]; Cao, Haoyu ^[1]; Zhu, Shunwei ^[1]; Wang, Wenhao ^[1]; Cheng, Xue ^[1]; Sun, Dongqin ^[1]; Chen, Feiyu ^[1]; Zhang, Weijia ^[1]; Hu, Zhubin ^[4]; Wang, Xue-Bin  ^[2]

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1. Shaoxing University, Zhejiang (China)
2. Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)
3. Univ. of Science and Technology of China, Hefei (China); Univ. of Science and Technology of China, Suzhou (China); Suzhou Big Data & AI Research and Engineering Center, Suzhou (China)
4. East China Normal Univ. (ECNU), Shanghai (China)

Electrolyte anions are pivotal for lithium battery performance, yet their fundamental electronic structural properties are not well understood. In this work, we employ a combination of negative-ion photoelectron spectroscopy (NIPES), ab initio calculations, and molecular dynamics (MD) simulations to investigate the electronic structures of three representative electrolyte anions. This multiscale approach enables us to elucidate how their intrinsic electronic properties govern anion–solvent interactions in gas-phase clusters, as well as lithium-ion (Li⁺) solvation structures and ion transport behavior in the condensed phase. NIPES reveals that difluoro(oxalato)borate (DFOB^–), bis(fluorosulfonyl)imide (FSI^–), and bis(oxalato)borate (BOB^–) all exhibit high electron binding energies, with vertical/adiabatic detachment energies increasing from DFOB^– (6.09/5.70 eV) to FSI^– (6.80/6.10 eV) to BOB^– (6.82/6.40 eV), correlating with enhanced oxidation stability. Ab initio calculations reveal that DFOB^–/FSI^––solvent complexes bind Li⁺ ∼ 10 kcal/mol stronger than BOB^– series, aligning with the strength of a Li⁺–anion model. DFOB^– exhibits pronounced charge localization on both oxygen and fluorine atoms, enabling their involvement in Li⁺ coordination. In contrast, fluorine atoms in FSI^– are largely electron-depleted and remain excluded from direct Li⁺ binding. MD simulations further demonstrate that LiDFOB and LiFSI systems exhibit Li⁺ diffusion coefficients three and five times higher than those of LiBOB across four common solvents. Notably, LiFSI salt in acetonitrile (AN) exhibits the fastest Li⁺ diffusion among 12 electrolyte systems, highlighting the synergistic effect of FSI^– and AN in promoting ion mobility. In conclusion, these findings provide a molecular-level understanding of the critical roles of anion and its microsolvation in optimizing Li⁺ diffusion dynamics, once again emphasizing the positioning of FSI^– and DFOB^– as prime candidates for next-generation electrolytes.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)
• Sponsoring Organization: National Natural Science Foundation of China; USDOE Office of Science (SC), Basic Energy Sciences (BES). Chemical Sciences, Geosciences & Biosciences Division (CSGB)
• Grant/Contract Number: AC05-76RL01830
• OSTI ID: 2574261
• Report Number(s): PNNL-SA--213371
• Journal Information: Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment, and General Theory, Journal Name: Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment, and General Theory Journal Issue: 28 Vol. 129; ISSN 1089-5639; ISSN 1520-5215
• Publisher: American Chemical SocietyCopyright Statement
• Country of Publication: United States
• Language: English