A highly conductive and stable hybrid solid electrolyte for high voltage lithium metal batteries

Abstract

Understanding Li⁺ migration behavior in hybrid solid-state electrolytes (HSEs) is essential for realizing the conductivity of HSE and high energy density Li metal batteries. Here, a highly conductive HSE with a continuous lithium-ion (Li⁺) transport pathway consisting of an anionic-type single Li⁺ conductor polymer (lithium taurine-grafted poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)-Li_x, x represents the amount of lithium taurine)) and Li_1.4Al_0.4Ti_1.6(PO₄)₃ (LATP) particles are prepared for solid-state lithium metal batteries. The prepared ionomer P(VDF-HFP)-Li_x can enhance the transmission efficiency of Li⁺ in the polymer substrate, forming a “Li⁺ transport bridge” between inorganic particles to provide rapid and continuous Li⁺ transmission channels in HSE, and eliminating interface charge accumulation caused by an excessive impedance difference of the polymer/ceramic. The P(VDF-HFP)-Li₁₀-50LATP HSE possesses high ionic conductivity (7.88 × 10⁻⁴ S cm⁻¹ at 25 °C), Li⁺ transference number (t_Li⁺ = 0.61) and electrochemical stability (>5.16 V vs. Li⁺/Li). Furthermore, the Li‖HSE‖Li symmetrical battery achieves a stability over more than 1000 h at 0.1 mA cm⁻², while the HSE-based LiNi_0.6Mn_0.2Co_0.2O₂ (NCM622)‖Li and LiNi_0.5Mn_1.5O₄ (LNMO)‖Li batteries show high specific capacity (160 mA h g⁻¹ and 126.8 mA h g⁻¹ at 0.5C) and good cycling stability (capacity retention of 93% and 80% after 200 cycles, respectively). This work provides a an effective to achieve high ionic conductivity and stability for HSEs, simultaneously.