Strengthened High-Concentration Quasi-Solid Electrolytes for Lithium Metal with Ultralong Stable Cyclability

The lithium metal batteries coupled with nickel-rich LiNiCoMn_1-O₂ (x > 0.7) cathodes hold promise for surpassing the current energy density limit of lithium-ion batteries. However, conventional electrolytes containing free active solvents are highly susceptible to decomposition, particularly at the interfaces of lithium anode and high-voltage cathode. Herein, we have developed a composite quasi-solid electrolyte (CQSE) utilizing sulfated Al₂O₃ (S-Al₂O₃)-bridged cellulose triacetate (CTA) to stabilize the interfaces between the electrolyte and electrodes. S-Al₂O₃ competitively dissociates Li⁺ through coordination interactions with anions, facilitating the formation of a distinctive solvation structure characterized by prevalent ion pairs and aggregates. In addition, coordination of S-Al₂O₃ with CTA forms S-Al₂O₃-bridged CTA molecular chain networks, enhancing the mechanical strength of the CQSE and immobilizing free liquid molecules. Consequently, the CQSE demonstrates an enhanced tensile strength of up to 7.4 MPa and a high ionic conductivity of 1.8 × 10^-3 S cm^-1 at room temperature. Furthermore, the CQSE not only suppresses electrode-electrolyte side reactions but also enables the formation of an inorganic-rich solid/cathode electrolyte interphase. As a result, the Li|CQSE|LiNi_0.83Co_0.11Mn_0.06O₂ (NCM83) batteries retain 84% capacity after 1000 cycles at 1 C, with the pouch cells demonstrating 80% capacity retention after 250 cycles at 0.5 C.