标题：A Novel Graphene Oxide Wrapped Na2Fe2(SO4)3/C Cathode Composite for Long Life and High Energy Density Sodium-Ion Batteries
Abstract: The cathode materials in the Na-ion battery system are always the key issue obstructing wider application because of their relatively low specifc capacity and low energy density. A graphene oxide (GO) wrapped composite, Na2Fe2(SO4)3@C@GO, is fabricated via a simple freeze-drying method. The as-prepared material can deliver a 3.8 V platform with discharge capacity of 107.9 mAh g-1 at 0.1 C (1 C = 120 mA g-1) as well as offering capacity retention above 90% at a discharge rate of 0.2 C after 300 cycles. The well-constructed carbon network provides fast electron transfer rates, and thus, higher power density also can be achieved (75.1 mAh g-1 at 10 C). The interface contribution of GO and Na2Fe2(SO4)3 is recognized and studied via density function theory calculation. The Na storage mechanism is also investigated through in situ synchrotron X-ray diffraction, and pseudocapacitance contributions are also demonstrated. The diffusion coeffcient of Na+ ions is around 10-12–10-10.8 cm2 s-1 during cycling. The higher working voltage of this composite is mainly ascribed to the larger electronegativity of the element S. The research indicates that this well-constructed composite would be a competitive candidate as a cathode material for Na-ion batteries.
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