Demonstration of Li-Ion Capacity of MAX Phases

Herein we report on the reversible electrochemical intercalation of Li ions into Ti₂SC and Ti₃SiC₂, layered ternary transition-metal carbides, known as MAX phases. It is demonstrated that the particle size plays an important role in the electrochemical performance of MAX phases. Ti₂SC particles with a size of hundreds of nanometers showed an initial reversible capacity of ∼80 mAh g^-1 at 4 C, which increased to ∼180 mAh g^-1 after 1000 cycles. This capacity was two times higher than that of Ti₂SC with micrometer-sized particles. The increasing capacity with cycling was considered evidence for the reversible intercalation of Li ions into Ti₂SC, as confirmed by transmission electron microscopy and Raman spectroscopy. In addition to Ti₂SC, other MAX phases, such as Ti₃SiC₂, also exhibit promising Li-ion storage capability. This work suggests that the MAX phases, a large family of more than 70 stoichiometric phases and numerous solid solutions, are promising anode materials for Li-ion batteries and capacitors.