Journal
JOURNAL OF POWER SOURCES
Volume 408, Issue -, Pages 120-127Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.jpowsour.2018.09.088
Keywords
Na3-xLixV2(PO4)(2)F-3 solid solutions; Mechanical activation; Chemical Na/Li ion exchange; Cycling in Na and Li cells; Cyclic voltammetry; Conductivity
Funding
- State Assignment to ISSCM SB RAS [0301-2018-0001]
- Russian Foundation for Basic Research
- government of the Novosibirsk region of the Russian Federation [18-43-540022]
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The Na+/Li+ substitution in Na3V2(PO4)(2)F-3 is studied using different synthesis approaches: equilibrium and non-equilibrium. In the equilibrium solid-state process, the reagent mixtures with various Na/Li ratios are preliminary mechanically activated using a high-energy AGO-2 planetary mill and then annealed in an Ar flow. Non-equilibrium chemical Na/Li ion exchange is performed in the organic solution of LiBr as a Li source. Phase composition, crystal structure, morphology and electrochemical properties of the as-prepared materials are analysed by XRD, SEM, TEM, EIS, galvanostatic cycling, and cyclic voltammetry. It is shown that the solid-state synthesis leads to the lower substitution degree and is accompanied by the formation of the V2O3 impurity. These samples are characterized by enhanced electrical conductivity (by about 4 orders of magnitude) compared to that of the pristine Na3V2(PO4)(2)F-3, and improved high-rate performance both in Na and Li-cells. The origin of the excellent high-rate capability of the as-prepared Na3-xLixV2(PO4)(2)F-3 is partially attributed to the pseudo capacitive effect initiated from the rational design of the materials, including submicron particles, mixed in-situ coating with electron-conductive carbon and V2O3.
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