Synergetic Effect of LiNO3 and Fluorine-Containing Additives on Stabilizing Electrode-Electrolyte Interfaces in Lithium Metal Batteries

Abstract

Listen

Translate article

Lithium metal batteries (LMBs) are regarded as an ideal candidate for next-generation batteries to meet the increasing demand for high energy density batteries. Due to the high theoretical capacity (3860 mAh g-1) and the low electrochemical redox potential (- 3.04 V vs Standard Hydrogen Electrode (SHE)) of lithium metal anodes, lithium metal batteries can achieve a high energy density. However, the poor compatibility of conventional carbonate electrolytes with lithium metal anodes has limited the commercialization of LMBs. The unstable solid-electrolyte interphase (SEI) generated from the charging and discharging process leads to the dendritic growth of lithium and the continuous depletion of the electrolyte, limiting the cycle life of LMBs. Furthermore, the unstable cathode-electrolyte interphase (CEI) limits the charge transfer kinetics of Li+ and decomposes at high voltage operation of LMBs. Therefore, the formation of stable electrode-electrolyte interfaces is crucial for the adoption of LMBs. Numerous studies have been attempted to regulate the electrode-electrolyte interfaces by introducing additives to the electrolyte. Lithium nitrate (LiNO3) is an effective additive for regulating the SEI layers through the formation of a highly lithium ion-conductive SEI components derived from the reduction of NO3 - ions such as Li3N (2~4 x 10-4 S cm-1). However, it is vulnerable to volume expansion, leading to continuous consumption of the additive itself. Fluorine-containing additives such as fluoroethylene carbonate (FEC) and lithium difluoro(oxalate)borate (LiDFOB) can promote the formation of a robust, high mechanical strength (64.7 GPa) LiF-rich SEI layer to enhance the mechanical strength of the SEI layer to mitigate the lithium dendrite growth. Nevertheless, LiF can hinder the lithium ion transport, due to its low ionic conductivity (10-9 ~ 10-14 cm-2). The synergetic effect of LiF and Li3N as SEI components may be able to enable highly reversible LMBs. In addition, the LiDFOB additive have been reported to form a thin and stable CEI via B-O bonds with anchoring transition metal ions in the cathode, preventing the degradation of the cathode. The electrolyte system with FEC and LiDFOB is able to increase the cycle life of LMBs by the formation of robust SEI and CEI layer. Herein, the synergetic effects of LiNO3, FEC, and LiDFOB additive is discussed to further enhance the stability of the electrode-electrolyte interfaces for high energy density LMBs. The LiNO3 additive is sustainably released through the use of a porous film which consists of LiNO3 embedded polyacrylonitrile (PAN) nanofibers (LiNO3/PAN) to overcome the low solubility of LiNO3 in the carbonate electrolyte. Moreover, fluorine containing additives, LiDFOB and FEC are introduced with LiNO3 in order to form a LiF/Li3N-rich SEI to lengthen the life cycle of LMBs. LiDFOB-derived CEI also contributed to the enhanced stability of the cathode. Consequently, through the synergetic effects of LiNO3 and fluorine-containing additives, the capacity retention of ultra-thin Li (20 μm)||nickel-rich NCM811 cells is improved.