The development of low-cost, resource-friendly, high-energy-density cathode materials is becoming more and more imminent, so as to meet the rapidly increasing demand for electrical energy storage. In current lithium-ion batteries, due to the low cost and high metal reserves, manganese-based high-capacity cathode materials will have particularly promising potential and can replace nickel and cobalt, which are resource scarce and have outstanding safety issues, and/or Mn4+ oxidation. The stability of the state is good, so it has attracted the attention of researchers. The development of high-capacity cathode materials based on other redox metals can achieve high capacity requirements by exchanging two electron transition metals, such as Ni2+/Ni4+ pairs similar to NMC cathodes. The low cost and low toxicity of Mn2+/Mn4+ couplings is particularly desirable for high-performance lithium-ion batteries that are environmentally friendly.

[Introduction]

Recently, the research group Jinhyuk Lee and Gerbrand Ceder of the University of California, Berkeley (the co-corresponding author) published an article titled "Reversible Mn2+/Mn4+ double redox in lithium-excess cathode materials" at Nature. The team provided a strategy for combining high cations and partially fluorine-substituted oxygen in the disorder-rock salt structure to couple the reversible Mn2+/Mn4+ double redox couple into the lithium excess cathode material. The lithium-rich cathode produced has high capacity (>300 mAh g-1) and high energy density (about 1,000 Wh kg-1). Due to the high capacity of manganese, only a small amount of redox is needed to provide a total capacity of more than 300 mAh g-1, thereby reducing redox-related problems. The use of Mn2+/Mn4+ redox reduces the redox activity and stabilizes the material state, opening up new opportunities for the design of high-performance manganese-rich anodes for advanced lithium-ion batteries.

[Introduction]

Fig. 1 Design and structure characterization of Li2Mn2/3Nb1/3O2F.

Fig. 2 Electrochemical properties of Li2Mn2/3Nb1/3O2F

Fig. 3 Reaction mechanism of Li2Mn2/3Nb1/3O2F

Fig. 4 Correlation calculation of redox mechanism of Li2Mn2/3Nb1/3O2F.

Fig. 5 Structural characterization and electrochemical performance of Li2Mn1/2Ti1/2O2F.