High Rate Capability and Cycling Stability in Multi-Domain Nanocomposite LiNi_1- _xTi₃ _x _/4O₂ Positive Electrodes.

Abstract

LiNiO₂ positive electrode materials for lithium-ion batteries have experienced a revival of interest due to increasing technological energy demands. Herein a specific Ti⁴⁺ substitution is targeted into LiNiO₂ to access new compositions by synthesizing the LiNi_1- _xTi₃ _x _/4O₂ solid solution with the aim of retaining Ni³⁺. Compositions in the range 0.025 ≤ x ≤ 0.2 form nanocomposites of compositionally homogeneous ordered R <math xmlns="http://www.w3.org/1998/Math/MathML"> <semantics><mover><mn>3</mn> <mo>¯</mo></mover> <annotation>$\bar 3$</annotation></semantics> </math> m and disordered Fm <math xmlns="http://www.w3.org/1998/Math/MathML"> <semantics><mover><mn>3</mn> <mo>¯</mo></mover> <annotation>$\bar 3$</annotation></semantics> </math> m rock salt domains as observed via X-ray and neutron diffraction, and STEM. The disordered rock salt domains stabilize the ordered structure to provide excellent structural reversibility via the formation of coherent interfaces during cycling and enable deep delithiation using a constant voltage charging step without structural degradation. The detrimental structural phase transitions associated with the poor cyclability of LiNiO₂ are suppressed to yield a low strain positive electrode material with high capacity retention that offers high-rate capability even under increased cell electrode mass loadings. The composition x = 0.075 (LiNi_0.925Ti_0.05625O₂) affords a 93% capacity retention after 100 cycles (100 mA g^-1) and demonstrates high reversible capacities of 125 mAh g^-1 even under rates of 3200 mA g^-1. LiNi_0.925Ti_0.05625O₂ exhibits exceptional performance at electrode mass loadings (13.6 mg cm^-2) comparable to those required for commercial cell applications.