Aluminum/titanium bimetallic doping for boosting the high-voltage Li-storage performance of Co-free high nickel cathode

Abstract

Due to the toxicity and high price of Co, Co-free LiNi_xMn_1-xO₂ (x ≥ 0.9) cathode materials have been actively promoted in current production and scientific research. The lack of cobalt leads to unstable structure and high residual lithium content on the surface of such positive electrode materials, causing severe capacity degradation and hindering commercial applications. For this purpose, a dual-doping strategy was adopted in this work, utilizing the coupling hydrolysis and lithiation sintering process of tetrabutyl titanate (C₁₆H₃₆O₄Ti) and aluminum isopropoxide (C₉H₂₁AlO₃) with water to prepare an Al/Ti bimetallic-doped LiNi_0.9Mn_0.1O₂ (NM@AT) cathode material, greatly improving the internal stability and lithium storage property of Co-free cathode materials. DFT calculations show that the strong bonding energy of Al-O and Ti-O covalent bonds in NM@AT enhances the intrinsic structural stability and increases Li/Ni exchange energy in the host material. After 100 cycles, the discharge specific capacity of NM@AT reached 176.08 mAhg⁻¹, and the retention rate increased from 66.19 % to 89.29 %, possessing a stable lithium storage performance at a high operating voltage of 4.5 V. Designing bimetallic doping effects to enhance the structural stability and lithium storage performance of cathode materials may provide new research ideas and feasible methods for improving high nickel cathode materials.