Concentrated ternary ether electrolyte allows for stable cycling of a lithium metal battery with commercial mass loading high‐nickel NMC and thin anodes. Issue 3 (25th October 2022) - Yang, Jun
Abstract: A new concentrated ternary salt ether‐based electrolyte enables stable cycling of lithium metal battery (LMB) cells with high‐mass‐loading (13.8 mg cm −2, 2.5 mAh cm −2 ) NMC622 (LiNi0.6 Co0.2 Mn0.2 O2 ) cathodes and 50 μm Li anodes. Termed "CETHER‐3, " this electrolyte is based on LiTFSI, LiDFOB, and LiBF4 with 5 vol% fluorinated ethylene carbonate in 1, 2‐dimethoxyethane. Commercial carbonate and state‐of‐the‐art binary salt ether electrolytes were also tested as baselines. With CETHER‐3, the electrochemical performance of the full‐cell battery is among the most favorably reported in terms of high‐voltage cycling stability. For example, LiNi x Mn y Co1– x – y O2 (NMC)‐Li metal cells retain 80% capacity at 430 cycles with a 4.4 V cut‐off and 83% capacity at 100 cycles with a 4.5 V cut‐off (charge at C/5, discharge at C/2). According to simulation by density functional theory and molecular dynamics, this favorable performance is an outcome of enhanced coordination between Li + and the solvent/salt molecules. Combining advanced microscopy (high‐resolution transmission electron microscopy, scanning electron microscopy) and surface science (X‐ray photoelectron spectroscopy, time‐of‐fight secondary ion mass spectroscopy, Fourier‐transform infrared spectroscopy, Raman spectroscopy), it is demonstrated that a thinner and more stable cathode electrolyte interphase (CEI) and solid electrolyte interphase (SEI) are formed. The CEI is rich in lithium sulfide (Li2 SO3 ), while the SEI is rich in Li3 N and LiF. During cycling, the CEI/SEI suppresses both the deleterious transformation of the cathode R‐3m layered near‐surface structure into disordered rock salt and the growth of lithium metal dendrites. Abstract : A new concentrated ternary salt ether‐based electrolyte enables stable cycling of lithium metal battery cells with high mass loading NMC622 cathodes and thin Li anodes under a high cut‐off voltage of 4.4/4.5 V through the formation of a thinner and more stable cathode electrolyte interphase/solid electrolyte interphase and suppression of deleterious phase transformation and lithium dendrite growth.