Enhanced charging capability of lithium metal batteries based on lithium bis(trifluoromethanesulfonyl)imide-lithium bis(oxalato)borate dual-salt electrolytes

• Fast chargeability of Li metal batteries with carbonate electrolytes was studied.
• LiTFSI-LiBOB electrolyte greatly enhances fast chargeability of Li metal battery.
• LiTFSI-LiBOB electrolyte gives much longer cycle life than LiPF6 electrolyte.
• LiTFSI-LiBOB electrolyte builds up a thinner interphase layer on Li metal anode.
• LiTFSI-LiBOB electrolyte leads to more conductive sulfur-rich interphase layer.

Rechargeable lithium (Li) metal batteries with conventional LiPF6-carbonate electrolytes have been reported to fail quickly at charging current densities of about 1.0 mA cm−2 and above. In this work, we demonstrate the rapid charging capability of Li||LiNi0.8Co0.15Al0.05O2 (NCA) cells can be enabled by a dual-salt electrolyte of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium bis(oxalato)borate (LiBOB) in a carbonate solvent mixture. The cells using the LiTFSI-LiBOB dual-salt electrolyte significantly outperform those using the LiPF6 electrolyte at high charging current densities. At the charging current density of 1.50 mA cm−2, the Li||NCA cells with the dual-salt electrolyte can still deliver a discharge capacity of 131 mAh g−1 and a capacity retention of 80% after 100 cycles. The Li||NCA cells with the LiPF6 electrolyte start to show fast capacity fading after the 30th cycle and only exhibit a low capacity of 25 mAh g−1 and a low retention of 15% after 100 cycles. The reasons for the good chargeability and cycling stability of the cells using the LiTFSI-LiBOB dual-salt electrolyte can be attributed to the good film-formation ability of the electrolyte on the Li metal anode and the highly conductive nature of the sulfur-rich interphase layer.

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