Importance of synergistic role of cobalt and aluminum on a greatly improved electrochemical performance of Li-rich oxyfluoride spinel at elevated-temperature

Abstract

Spinel LiMn2O4 cathode material has been successfully commercialized for various lithium ion batteries (LIBs) and is a very promising candidate for emerging large-scale applications in pure electric vehicles (EVs). Despite its advantages, LiMn2O4 suffers from fast capacity fading at elevated temperature stemming from Mn dissolution and structural distortion. Herein, an investigation on the structure and electrochemical performance of single/double/triple-ion substituted Li1.05Mn1.95O4, which was synthesized by a Sol-gel method combined with heat treatment at 750 °C, was firstly carried out. Enhancements of the tap density, rate capability, and cycling performance at high temperature were achieved without sacrificing its specific capacity via unique morphology control and triple-substitution (Al3+, Co3+, and F− ions) strategy. The as-prepared Li1.05Al0.05Mn1.85Co0.05O3.9F0.1 (LAMCOF) sample exhibits a high specific capacity, a superior rate capability, and an excellent long-term cyclability at the high temperature (55 °C), with the specific discharge capacities of 115 and 110 mAh g−1 and the corresponding capacity retention of 72.3% and 73.0% for up to 800 cycles at 2 and 5 C rates, respectively. The high specific capacity, an excellent cyclability, and a superior rate performance are believed to be caused by the three main reasons: (1) improvement of the specific capacity by the substitution of O2− by F−, (2) stabilization of the crystal structure derived from the synergistic roles of triple substitution by Al3+, Co3+, and F− ions, which decreases the Jahn-Teller distortions and Mn dissolution; and (3) formation of a stable interface of the active material/electrolyte resulting from the high content of Mn4+ at the surface and its unique morphology, which reduces the charge transfer resistances and favors fast Li+ intercalation/deintercalation kinetics. The as-prepared LAMCOF sample may offer a promising cathode material for the high-power LIBs with extended cycle life and superior rate capability at elevated temperature.