Anion-Induced Interfacial Liquid Layers on LiCoO2 in Salt-in-Water Lithium-Ion Batteries

Hyunjeong Oh; Seung-Jae Shin; Eunjin Choi; Hirona Yamagishi; Toshiaki Ohta; Naoaki Yabuuchi; Hun-Gi Jung; Hyungjun Kim; Hye Ryung Byon

doi:10.1021/jacsau.3c00061

Anion-Induced Interfacial Liquid Layers on LiCoO₂ in Salt-in-Water Lithium-Ion Batteries

JACS Au. 2023 Apr 28;3(5):1392-1402. doi: 10.1021/jacsau.3c00061. eCollection 2023 May 22.

Authors

Hyunjeong Oh^{1

2}, Seung-Jae Shin¹, Eunjin Choi^{1

2}, Hirona Yamagishi³, Toshiaki Ohta³, Naoaki Yabuuchi⁴, Hun-Gi Jung⁵, Hyungjun Kim¹, Hye Ryung Byon^{1

2}

Affiliations

¹ Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea.
² Advanced Battery Center, KAIST Institute for NanoCentury, Daejeon 34141, Republic of Korea.
³ Sychrotron Radiation (SR) Center, Ritsumeikan University, Kusatsu, Shiga 525-8577, Japan.
⁴ Department of Chemistry and Life Science, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama, Kanagawa 240-8501, Japan.
⁵ Energy Storage Research Center, Clean Energy Research Division, Korea Institute of Science and Technology (KIST), Seoul 02792, Republic of Korea.

Abstract

The incompatibility of lithium intercalation electrodes with water has impeded the development of aqueous Li-ion batteries. The key challenge is protons which are generated by water dissociation and deform the electrode structures through intercalation. Distinct from previous approaches utilizing large amounts of electrolyte salts or artificial solid-protective films, we developed liquid-phase protective layers on LiCoO₂ (LCO) using a moderate concentration of 0.5∼3 mol kg^-1 lithium sulfate. Sulfate ion strengthened the hydrogen-bond network and easily formed ion pairs with Li⁺, showing strong kosmotropic and hard base characteristics. Our quantum mechanics/molecular mechanics (QM/MM) simulations revealed that sulfate ion paired with Li⁺ helped stabilize the LCO surface and reduced the density of free water in the interface region below the point of zero charge (PZC) potential. In addition, in situ electrochemical surface-enhanced infrared absorption spectroscopy (SEIRAS) proved the appearance of inner-sphere sulfate complexes above the PZC potential, serving as the protective layers of LCO. The role of anions in stabilizing LCO was correlated with kosmotropic strength (sulfate > nitrate > perchlorate > bistriflimide (TFSI^-)) and explained better galvanostatic cyclability in LCO cells.