High-rate capability of Na2FePO4F nanoparticles by enhancing surface carbon functionality for Na-ion batteries
- High-rate capability of Na2FePO4F nanoparticles by enhancing surface carbon functionality for Na-ion batteries
- 김형석; Jesse S. Ko; Vicky V.T. Doan-Nguyen; Xavier Petrissans; Ryan H. DeBlock; Christopher S. Choi; Jeffrey W. Long; Bruce S. Dunn
- Issue Date
- Journal of materials chemistry. A, Materials for energy and sustainability
- VOL 5, NO 35-18715
- Metal phosphate compounds are considered promising candidates as positive electrode materials for Na-ion batteries because they offer higher cation-insertion potentials than analogous metal oxides. One such example is sodium iron fluorophosphate (Na2FePO4F), a compound that is typically synthesized by high-temperature solid-state routes. In this study, we prepare phase-pure Na2FePO4F using the polyol route, a low-temperature process that allows for the synthesis of nanoparticles (15-25 nm), a form that enhances Na-ion insertion kinetics and cycling stability. We then apply two methods to enhance the electronic conductivity of Na2FePO4F: (i) converting residual organic byproducts of the polyol synthesis to conductive carbon coatings; and (ii) preparing a nanocomposite with reduced graphene oxide. The resulting electrode materials are characterized in nonaqueous Na-ion electrolytes, assessing such metrics as specific capacity, rate capability, and cycling stability. A thorough electrochemical kinetics analysis is performed to deconvolve surface-vs.-bulk Na-ion insertion as a function of composite structure. Specific capacities between 60-110 mA h g(-1) were achieved in galvanostatic charge-discharge tests when cycling in the range from 10C to C/10, respectively.
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