In this study, ester co-solvents and fluoroethylene carbonate (FEC) were used as low-temperature electrolyte additives to improve the formation of the solid electrolyte interface (SEI) on graphite anodes in lithium-ion batteries (LIBs). Four ester co-solvents, namely methyl acetate (MA), ethyl acetate, methyl propionate, and ethyl propionate, were mixed with 1.0 M LiPF6 ethylene carbonate:diethyl carbonate:dimethyl carbonate (1:1:1 by vol%) as the base electrolyte (BE). Different concentrations were used to compare the electrochemical performance of the LiCoO2/ graphite full cells. Among various ester co-solvents, the cell employing BE mixed with 30 vol% MA (BE/MA30) achieved the highest discharge capacity at − 20 °C. In contrast, mixing esters with low-molecular-weight degraded the cell performance owing to the unstable SEI formation on the graphite anodes. Therefore, FEC was added to BE/MA30 (BE/MA30-FEC5) to form a stable SEI layer on the graphite anode surface. The LiCoO2/ graphite cell using BE/MA30-FEC5 exhibited an excellent capacity of 127.3 mAh g− 1 at − 20 °C with a capacity retention of 80.6% after 100 cycles owing to the synergistic effect of MA and formation of a stable and uniform inorganic SEI layer by FEC decomposition reaction. The low-temperature electrolyte designed in this study may provide new guidelines for resolving low-temperature issues related to LIBs, graphite anodes, and SEI layers.

Ester-based electrolytes for graphite solid electrolyte interface layer stabilization and low-temperature performance in lithium-ion batteries
    Abstract
        Graphical abstract
    1 Introduction
    2 Experiments
        2.1 Materials
        2.2 Preparation of electrolytes and electrodes
        2.3 Characterization
        2.4 Electrochemical analysis
    3 Results and discussion
        3.1 Characteristics of various low-molecular-weight esters
        3.2 Optimal concentration of esters for the LT condition
        3.3 Electrochemical performance of cells utilizing ester-added BEs at LT
        3.4 Addition of electrolyte additive and SEI characteristics at LT
    4 Conclusions
    Acknowledgements 
    References

• Chan‑Gyo Kim(Department of Chemical and Biological Engineering, Hanbat National University, 125 Dongseo‑daero, Yuseong‑gu, Daejeon 34158, Korea)
• Suk Jekal(Department of Chemical and Biological Engineering, Hanbat National University, 125 Dongseo‑daero, Yuseong‑gu, Daejeon 34158, Korea)
• Jiwon Kim(Department of Chemical and Biological Engineering, Hanbat National University, 125 Dongseo‑daero, Yuseong‑gu, Daejeon 34158, Korea)
• Ha‑Yeong Kim(Department of Chemical and Biological Engineering, Hanbat National University, 125 Dongseo‑daero, Yuseong‑gu, Daejeon 34158, Korea)
• Gyu‑Sik Park( Department of Intelligent Nano Semiconductor, Hanbat National University, 125 Dongseo‑daero, Yuseong‑gu, Daejeon 34158, Korea)
• Yoon‑Ho Ra(Department of Chemical and Biological Engineering, Hanbat National University, 125 Dongseo‑daero, Yuseong‑gu, Daejeon 34158, Korea)
• Jungchul Noh(McKetta Department of Chemical Engineering and Texas Material Institute, The University of Texas at Austin, Austin, TX 78712, USA)
• Chang‑Min Yoon(Department of Chemical and Biological Engineering, Hanbat National University, 125 Dongseo‑daero, Yuseong‑gu, Daejeon 34158, Korea) Corresponding author