Quasi-Solid-State Lithium Metal Batteries Using the LiNi_0.8Co_0.1Mn_0.1O₂–Li_1+<i>x</i>Al_<i>x</i>Ti_2–<i>x</i>(PO₄)₃ Composite Positive Electrode

NASICON-type Li_1+<i>x</i>Al_<i>x</i>Ti_2–<i>x</i>(PO₄)₃ (LATP) is a promising solid electrolyte (SE) candidate for next-generation solid-state batteries. However, its use in solid-state composite electrodes is inhibited by its stiffness, which results in poor interparticle contact unless high-temperature treatments are applied. The poor LATP–LATP and LATP-active material in the positive electrode (cathode) composite produced at ambient temperature yield poor ionic conductivity, impeding the electrode’s performance. Herein, we focus on the optimization of the electrochemical performance of LiNi_0.8Co_0.1Mn_0.1O₂ (NCM₈₁₁)–LATP composite electrodes made by tape casting, taking advantage of a small fraction of an ionic liquid electrolyte (ILE) filling the composite cathode porosity. The incorporated LATP particles are found to closely surround the large NCM₈₁₁ secondary particles, partially filling the composite electrode pores and resulting in a porosity reduction from 37 vol % (NCM₈₁₁ only) to 32 vol % (NCM₈₁₁–LATP). After filling up the majority of the electrode porosity with ILE, the NCM₈₁₁–LATP composite electrodes offer improved capacity retention upon both long-term cycling tests (>99.3% after 200 cycles) and high-rate tests (>70% at 2 C-rate), due to the more stable LATP|NCM₈₁₁ interface, and facilitated Li⁺ diffusion in the composite electrode bulk. Results obtained from proof-of-concepts monopolar (3.0–4.3 V) and bipolar-stacked (6.0–8.6 V) cells are reported.