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

摘要

Spinel LiMn 2 O 4 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, LiMn 2 O 4 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 Li 1.05 Mn 1.95 O 4 , 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 (Al 3+ , Co 3+ and F − ions) strategy. The as-prepared Li 1.05 Al 0.05 Mn 1.85 Co 0.05 O 3.9 F 0.1 (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 O 2− by F − , (2) stabilization of the crystal structure derived from the synergistic roles of triple substitution by Al 3+ , Co 3+ 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 Mn 4+ 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.