Improvement for tolerance of lithium metal counter electrodes towards sodium contamination in hybrid Li/Na-ion electrolytes
Since the concept of hybrid Li/Na-ion batteries (HLNIBs) was proposed, many cathode materials with excellent performance and low cost have been studied. However, in HLNIBs, mixed cationic electrolyte is formed as Na + is extracted from the cathode, resulting in relatively complicated and unstable electrochemical performance, especially for the half-cell test with lithium metal as the anode. It is necessary to consider the tolerance of lithium metal counter electrode to sodium contamination in half-cell test with hybrid-ion electrolyte containing different cations. In this work, we have found that lithium metal electrodes in hybrid-ion electrolyte are unstable and Na + causes significant polarization. The polarization influences over potential and complex interface properties and thus reduces the accuracy of half-cell tests. To solve the problem, lithium difluoro(oxalato)borate (LiDFOB) with excellent film-forming properties was utilized as an additive of symmetrical batteries to form solid electrolyte interface (SEI) film. The adverse effect of Na + on the kinetics of hybrid-ion electrolyte was confirmed by regulating the SEI film on lithium metal electrode. The SEI film exhibits a selective effect on Li + and Na + and inhibits the interfacial transport of Na + , which significantly reduces the overpotential of the batteries and the interface migration impedance and also improves the stability of lithium counter electrode. Lithium metal with stable interfacial properties in the presence of LiDFOB is a reliable counter electrode that resists sodium contamination in half-cell test. Graphical abstract
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