Engineering the diphasic Li-rich Mn-based composite with alleviated Jahn–Teller effect for high-energy Li-ion batteries

Abstract

The unique oxygen stacking sequence of O2-type structures restricts the irreversible transition metal movement into Li vacancies for the delithiated Li-rich layered oxides (LLOs) and maintains outstanding voltage stability. However, the ion-exchange synthesis promotes the Mn-ion valence reduction and aggravates the Jahn–Teller (J–T) distortion alongside disproportionation. Since the main oxidation state of the Mn ions is +4 in the traditional O3-type LLOs, synergistic effects of the O2-type and O3-type structures are expected in the O2/O3 diphasic Li-rich material. Herein, O2/O3 biphasic intergrowth LLOs were rationally designed, and the synergic optimization of the biphasic structure was planned to retard the J–T effect. The O2/O3 intergrowth nature was confirmed, and the percentages of the O2 and O3 phases were 56% and 44%, respectively. Density functional theory calculations demonstrated that the Mn²⁺(EC) sheath had a remarkably lower energy barrier than the Li⁺(EC) sheath. This finding suggests that Mn²⁺ ions that are dissolved into the electrolyte accelerate the electrolyte oxidization, so the deposition of the cathode electrolyte interface for pristine O2-LLOs causes a high electrochemical impedance. The designed O2/O3 biphasic LLOs boost the capacity stability and suppress the voltage drop upon repeated Li⁺ de-intercalation. The phase regulation strategy offers great potential for developing low-cost LLOs with enhanced structural stability for advanced Li-ion batteries.

Graphical abstract