Redox-active Ti3+/Ti4+ substitution providing high ionic conductivity and extra electrochemical capacity for chloride electrolyte

The advancement of all-solid-state lithium batteries (ASSLBs) is significantly hindered by the trade-off between ionic conductivity and interfacial stability of solid-state electrolytes (SSEs). Chloride SSEs, particularly Li 2 ZrCl 6 , offer high oxidation stability but suffer from moderate ionic conductivity and intrinsic instability against lithium metal. This work, by introducing redox-active aliovalent substituents, attempts to address these interconnected challenges and endow extra electrochemical capacity for chloride electrolytes. Specifically, Li 2+4 x Zr 1−4 x Ti 3 x Al x Cl 6 (4 x = 0.15) exhibits enhanced ionic conductivity (0.87 mS cm −1 ) and low activation energy (0.218 eV). Interestingly, cyclic voltammetry and X-ray photoelectron spectroscopy tests confirm that the incorporated Ti 3+ ions serve as reversible redox centers (Ti 3+ /Ti 4+ ), providing the chloride electrolyte an extra specific capacity of 9.68 mAh g −1 . This transforms the SSE from an ion conductor into a capacity contributor. Furthermore, by designing a Li 5.4 PS 4.4 Cl 1.6 (LPSC)-Li 2+4 x Zr 1−4 x Ti 3 x Al x Cl 6 bilayer electrolyte, the chloride acts as an “anchor” layer to effectively suppress the dendrite propagation, enabling the symmetric lithium cell to cycle stably at 0.6 mA cm −2 . When assembled into ASSLBs with LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC811) cathode and Li anode, the battery delivers a high specific capacity of 185.30 mAh g −1 at 0.05 C, demonstrating superior rate capability and cycling stability (84.12% capacity retention after 120 cycles at 0.2 C) compared with the unsubstituted chloride. This work presents a paradigm-shifting approach to designing redox-active, high-performance chloride SSEs, paving a new avenue for developing high-energy-density ASSLBs.