Hawari Naufal Hanif, Xie Huiqing, Prayogi Achmad, Sumboja Afriyanti, Ding Ning
Institute of Materials Research and Engineering, A*STAR (Agency for Science, Technology, and Research) 138634 Singapore
Material Science and Engineering Research Group, Faculty of Mechanical and Aerospace, Institut Teknologi Bandung Jl. Ganesha 10 Bandung 40132 Indonesia
RSC Adv. 2023 Aug 29;13(36):25673-25680. doi: 10.1039/d3ra03184e. eCollection 2023 Aug 21.
Anode-free lithium-metal batteries (AFLMBs) have the potential to double the energy density of Li-ion batteries, but face the challenges of mossy dendritic lithium plating and an unstable solid electrolyte interphase (SEI). Previous studies have shown that the AFLMBs with an electrolyte containing lithium difluoro(oxalato)borate (LiDFOB) salt outperform those with lithium hexafluorophosphate (LiPF), but the mechanism behind this improvement is not fully understood. In this study, X-ray photoelectron spectroscopy (XPS) depth profile analysis and electrochemical impedance spectroscopy (EIS) were conducted to investigate the SEI on plated Li from the two conducting salts and their evolution in Cu‖NMC full cells during cycling. XPS results revealed that an inorganic-rich SEI layer is formed in the cell with LiDFOB-based electrolyte, with a low carbon/oxygen ratio of 0.56 compared to 1.42 in the LiPF-based cell. With the inorganic-rich SEI, a dense electroplated Li with a shining surface on the Cu substrate can be retained after ten cycles. The inorganic-rich SEI enhances the reversibility of Li plating and stripping, with a high average CE of ∼98% and a stable charge/discharge voltage profile. The changes in SEI resistance and cathode electrolyte interphase resistance are more prominent compared to the changes in solution and charge transfer resistances, which further validate the role of the passivation films on Li deposits and NMC cathode surfaces in stabilizing AFLMB cycling performance.
无阳极锂金属电池（AFLMBs）有潜力使锂离子电池的能量密度提高一倍，但面临着锂枝晶生长和固体电解质界面（SEI）不稳定的挑战。先前的研究表明，含有二氟草酸硼酸锂（LiDFOB）盐的电解质的AFLMBs性能优于含有六氟磷酸锂（LiPF）的电解质的AFLMBs，但其性能提升背后的机制尚未完全理解。在本研究中，进行了X射线光电子能谱（XPS）深度剖析分析和电化学阻抗谱（EIS），以研究两种导电盐在镀锂上形成的SEI及其在Cu‖NMC全电池循环过程中的演变。XPS结果表明，在基于LiDFOB的电解质的电池中形成了富含无机成分的SEI层，其碳/氧比低至0.56，而基于LiPF的电池中的碳/氧比为1.42。由于存在富含无机成分的SEI，在十次循环后，Cu基底上可以保留表面光亮的致密电镀锂。富含无机成分的SEI提高了锂电镀和剥离的可逆性，平均库仑效率（CE）高达约98%，且充放电电压曲线稳定。与溶液电阻和电荷转移电阻的变化相比，SEI电阻和阴极电解质界面电阻的变化更为显著，这进一步验证了锂沉积物和NMC阴极表面的钝化膜在稳定AFLMB循环性能中的作用。
