Abstract
Li3V2(PO4)3−xBrx/carbon (x = 0.08, 0.14, 0.20, and 0.26) composites as cathode materials for lithium-ion batteries were prepared through partially substituting PO43− with Br−, via a rheological phase reaction method. The crystal structure and morphology of the as-prepared composites were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), and electrochemical properties were evaluated by charge/discharge cycling and electrochemical impedance spectroscopy (EIS). XRD results reveal that the Li3V2(PO4)3−xBrx/carbon composites with solid solution phase are well crystallized and have the same monoclinic structure as the pristine Li3V2(PO4)3/carbon composite. It is indicated by SEM images that the Li3V2(PO4)3−xBrx/carbon composites possess large and irregular particles, with an increasing Br− content. Among the Li3V2(PO4)3−xBrx/carbon composites, the Li3V2(PO4)2.86Br0.14/carbon composite shows the highest initial discharge capacity of 178.33 mAh·g−1 at the current rate of 30 mA·g−1 in the voltage range of 4.8–3.0 V, and the discharge capacity of 139.66 mAh·g−1 remains after 100 charge/discharge cycles. Even if operated at the current rate of 90 mA·g−1, Li3V2(PO4)2.86Br0.14/carbon composite still releases the initial discharge capacity of 156.57 mAh·g−1, and the discharge capacity of 123.3 mAh·g−1 can be maintained after the same number of cycles, which is beyond the discharge capacity and cycleability of the pristine Li3V2(PO4)3/carbon composite. EIS results imply that the Li3V2(PO4)2.86Br0.14/carbon composite demonstrates a decreased charge transfer resistance and preserves a good interfacial compatibility between solid electrode and electrolyte solution, compared with the pristine Li3V2(PO4)3/carbon composite upon cycling.
Highlights
Lithium-ion batteries (LIBs) as advanced electrochemical power sources are considered to be the ideal choice for numerous portable consumer electronics, such as smartphones, tablets, notebook PCs, and camcorders, due to their high energy density, low self-discharge rate, wide operating temperature range, lack of a memory effect, and environmental friendliness.Especially in recent years, LIBs have been regarded as the most promising power sources for hybrid electric vehicles (HEVs) and electric vehicles (EVs), which require very high energy and power densities for LIBs [1,2,3,4,5,6,7]
Strenuous efforts have been devoted to improving the electronic conductivity of Li3 V2 (PO4 )3 (LVP), including lattice doping with metal ions [10,14,15,16,17], surface coating with carbon sources [18,19,20] or high electrical conductivity metal oxides [21,22,23], reducing particle size [24,25], and controlling particle morphologies [26,27,28]
The LVPBC composite cathode materials were prepared by the rheological phase reaction method, in a similar manner to those reported in previous references [38,39,40]
Summary
Lithium-ion batteries (LIBs) as advanced electrochemical power sources are considered to be the ideal choice for numerous portable consumer electronics, such as smartphones, tablets, notebook PCs, and camcorders, due to their high energy density (both volumetric and gravimetric), low self-discharge rate, wide operating temperature range, lack of a memory effect, and environmental friendliness. The main drawback of pure LVP is its very low intrinsic electronic conductivity, which causes high electrode polarization and restricts its application in the field of dynamic batteries [11,12,13] To overcome this problem, strenuous efforts have been devoted to improving the electronic conductivity of LVP, including lattice doping with metal ions [10,14,15,16,17], surface coating with carbon sources [18,19,20] or high electrical conductivity metal oxides [21,22,23], reducing particle size [24,25], and controlling particle morphologies [26,27,28]. A comparison of the LVPBC composites with the pristine LVPC composite, and the effects of Br− -doping on the crystal structure, morphology, and electrochemical properties of LVPC, have been studied in detail
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