Dual modification of Ni-rich LiNi_0.8Co_0.1Mn_0.1O₂ cathode via Ti doping and Li₄Ti₅O₁₂ coating for mitigating interfacial degradation and improving cycle stability in all-solid-state batteries

All-solid-state batteries (ASSBs) face critical challenges, including the structural collapse of cathode active materials (CAMs) during cycling and interfacial instability between the sulfide-based solid electrolyte (SE) and the cathode, which leads to deteriorated electrochemical performance. Here, we report high-performance ASSBs enabled by localized titanium (Ti) doping and the formation of a Li₄Ti₅O₁₂ (LTO) coating layer on CAMs, utilizing residual lithium (Li) components present on their surface as the Li source. The LTO offers a cost-effective, earth-abundant, and electrochemically stable alternative to LiNbO₃. Ti incorporation into the LiNi_xCo_yMn_1-x-yO₂ (NCM) lattice enhances the mechanical robustness of secondary particles by reinforcing their structural integrity. Moreover, the conformal LTO layer serves as a chemically stable interphase that effectively suppresses undesirable side reactions with sulfide-based SEs. The combination of Ti doping and LTO surface modification synergistically improves the mechanical integrity and interfacial stability of the electrode. As a result, ASSBs employing Ti-NCM@LTO with a high areal capacity of 8 mAh/cm² exhibit enhanced electrochemical properties, including an initial capacity of 165.9 mAh/g, outstanding cycle stability of 83.4 % at 0.1C over 100 cycles, and a rate capability (reversible capacity) of 166.4, 148.4, 135.5, 130.4 and 119.4 mAh/g at 0.05, 0.1, 0.2, 0.5, and 1.0C, respectively.