Lithium transition metal silicates Li₂MSiO₄ (M = Fe, Mn, Co, etc.) have been under intense research due to their double theoretical capacity of 330 mAh/g compared to LiFePO₄ (170 mAh/g)^1,2,3_. Their development as cathode materials however has been hampered due in part of their rich polymorphism and phase transitions occurring during cycling not allowing full capacity storage and reversible retention. In this work we focus on the electrochemistry of lithium iron silicate (LFS) ^5-8.  Almost all previous studies have focused solely on the electrochemistry of the high temperature monoclinic phase (m-LFS). According to these studies^4,5,8, the monoclinic phase undergoes electrochemically-induced phase transition during cycling to thermodynamically stable low-temperature orthorhombic phase (o-LFS). This prompted us to take a deep look into the structural and electrochemical behavior of the latter phase as it might hold the key in designing high performance lithium iron orthosilicate cathodes. During this investigation we discovered that upon galvanostatic cycling, the specific capacity of an o-LFS/C nanocomposite cathode exhibited gradual increase from 40 to 165 mAh/g and a shift in Li-storage mechanism from solid solution to biphasic type. This intriguing behavior is currently the subject of further characterizations to elucidate the underlying phenomena that can have significant implications to the development of high energy density LIB cathode materials.

References

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