Enhancing Li+ Transportation at Graphite-Low Concentration Electrolyte Interface Via Interphase Modulation of LiNO3 and Vinylene Carbonate

Abstract

The solvent-rich solvent sheath in low-concentration electrolytes (LCEs) not only results in high desolvation energy of Li⁺, but also forms organic-rich solid electrolyte interface film (SEI) with poor Li⁺ conductivity, which hinders Li⁺ transport at the electrode-electrolyte interface and greatly limits the application of LCEs. Here, the electrochemical performance of the LCEs is enhanced by dual interfacial modification with LiNO₃ and vinylene carbonate (VC) additives. Results show that LiNO₃ is preferentially reduced at about 1.65 V to form an inorganic-rich but incomplete SEI inner layer. The formation of Li₃N and LiN_xO_y inorganic components helps to achieve rapid Li⁺ transport in the SEI film, and the bare electrode surface caused by the incomplete SEI inner layer provides a place for the subsequent decomposition of VC. Then, at a lower potential of about 0.73 V, VC is reduced to generate the poly(VC)-rich SEI outer layer, which provides lithium-philic sites and greatly weakens the interaction between Li⁺ and ethylene carbonate (EC). The interaction modulates the Li⁺ solvation structure at the interface and reduces the desolvation energy of Li⁺. This ingenious design of the bilayer SEI film greatly enhances Li⁺ transport and inhibits the decomposition of traditional carbonate solvents and the swelling of graphite. As a result, the electrochemical performance of the battery using 0.5 M LiPF₆ EC/diethyl carbonate (DEC) + 0.012 M LiNO₃ + 0.5 vt% VC is improved to a higher level than the one using 1.0 M LiPF₆ EC/DEC electrolyte. This research expands the design strategy and promising applications of LCEs by constructing a favorable SEI to enhance Li⁺ transport at the electrode-electrolyte interface.