Performance enhanced high-nickel lithium metal batteries through stable cathode and anode electrolyte interfaces†
The interface stability between the cathode and anode with the electrolyte is the key to the performances of lithium metal batteries (LMBs). An FEC optimized LiTFSI-LiBOB dual salt (Dual-salt + FEC) electrolyte is employed to systematically investigate its effects on LMBs. The high nickel Li‖NCM full LMBs using the Dual-salt + FEC electrolyte present significantly enhanced long-term cycling stability with 83.8% capacity retention after 500 cycles, which is much higher than 65.4% for the LiPF6-based electrolyte. The improvement mechanism has been studied using aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) imaging combined with X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). The HAADF-STEM results firstly provide direct evidence at the atomic scale that the corrosion and transition metal dissolution for the high nickel NCM cathode cycled in the Dual-salt + FEC electrolyte could be effectively suppressed. Moreover, the HRTEM and XPS results further disclose that a stable CEI on the cathode and a thinner, smoother and strong adhesion of the SEI on the Li metal anode in the high nickel Li‖NCM cell could be achieved using the Dual-salt + FEC electrolyte. This holistic analysis of the cathode and anode electrolyte interfaces will significantly advance the LMB design principles through manipulation of the electrolyte chemistry.