Abstract
Iron fluoride, an intercalation-conversion cathode for lithium ion batteries, promises a high theoretical energy density of 1922 Wh kg–1. However, poor electrochemical reversibility due to repeated breaking/reformation of metal fluoride bonds poses a grand challenge for its practical application. Here we report that both a high reversibility over 1000 cycles and a high capacity of 420 mAh g−1 can be realized by concerted doping of cobalt and oxygen into iron fluoride. In the doped nanorods, an energy density of ~1000 Wh kg−1 with a decay rate of 0.03% per cycle is achieved. The anion’s and cation’s co-substitutions thermodynamically reduce conversion reaction potential and shift the reaction from less-reversible intercalation-conversion reaction in iron fluoride to a highly reversible intercalation-extrusion reaction in doped material. The co-substitution strategy to tune the thermodynamic features of the reactions could be extended to other high energy conversion materials for improved performance.
Highlights
Iron fluoride, an intercalation-conversion cathode for lithium ion batteries, promises a high theoretical energy density of 1922 Wh kg–1
It will be plausible to suppress the conversion reaction by extending the capacity of highly reversible intercalation-extrusion reaction, achieving both high capacity and long cycle life. We report that such a high-performance Fe0.9Co0.1OF cathode with high energy density of ~1000 Wh kg−1 and long cycle life of 1000 cycles can be realized by a costeffective and simple strategy of concerted At a charge/discharge current of 500 mA can deliver a capacity of 350 mAh g−1 for dg−op1,intgheCFo/eO0.9Cino0F.1eOF3F. 1000 cycles
Considering the pair distribution function (PDF) analysis of FeOF by Wiaderek et al.[38], we propose the lithiation of Fe0.9Co0.1OF will go through a similar process, involving intercalation and two steps of extrusion reactions (Eq 4)
Summary
An intercalation-conversion cathode for lithium ion batteries, promises a high theoretical energy density of 1922 Wh kg–1. The anion’s and cation’s co-substitutions thermodynamically reduce conversion reaction potential and shift the reaction from less-reversible intercalationconversion reaction in iron fluoride to a highly reversible intercalation-extrusion reaction in doped material. Current LIB cathodes such as LiCoO2, LiFePO4, or LiNixMnyCo1 – x – yO2 are exclusively based on intercalation mechanism, which involves topotactic intercalation/deintercalation of Li+ in a host lattice These cathodes have specific capacities ranged only from 140 to 200 mAh g−1, which limit their energy densities[1,2]. Certain metallic oxide, sulfide, or halide compounds can experience conversion reactions with Li+ by accepting multiple electrons per formula, delivering much higher capacities. In the intercalation reaction at ~3.0 LiFeF3 providing a capacity of
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