Mechanism studies and electrochemical performance optimization on xLiFePO4·(1 − x)Li3V2(PO4)3 hybrid materials

Abstract

Hybrid materials xLiFePO 4 ·(1−x)Li 3 V 2 (PO 4 ) 3 were synthesized by sol-gel method, with phenolic resin as carbon source and chelating agent, methylglycol as surfactant. The crystal structure, morphology and electrochemical performance of the prepared samples were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), cyclic voltammetry (CV), galvanostatic charge-discharge test and particle size analysis. The results show that LiFePO 4 and Li 3 V 2 (PO 4 ) 3 co-exist in hybrid materials, but react in single phase. Compared with individual LiFePO 4 and Li 3 V 2 (PO 4 ) 3 samples, hybrid materials have smaller particle size and more uniform grain distribution. This structure can facilitate Li ions extraction and insertion, which greatly improves the electrochemical properties. The sample 0.7LiFePO 4 ·0.3Li 3 V 2 (PO 4 ) 3 retains the advantages of LiFePO 4 and Li 3 V 2 (PO 4 ) 3 , obtaining an initial discharge capacity of 166 mA h/g at 0.1 C rate and 109 mA h/g at 20 C rate, with a capacity retention rate of 73.3% and an excellent cycle stability.

Structure and Performances of xLiFePO4/C·(1 − x)Li3V2(PO4)3/C Cathode for Lithium‐Ion Batteries by Using Poly(vinyl alcohol) as Carbon Source

“…The electronic conductivities of pyrolysis carbon from PVA, phenolic resin, and epoxy resin are 8.88 × 10 −1 , 1.73 × 10 −2 , and 1.82 × 10 −3 S/cm, respectively. Phenolic resin has been used in the synthesis of 0.7LiFePO 4 ·0.3Li 3 V 2 (PO 4 ) 3 with excellent electrochemical performances . The conductivity of PVA pyrolysis carbon is much larger than that of phenolic resin.…”

“…Phenolic resin has been used in the synthesis of 0.7LiFe-PO 4 Á0.3Li 3 V 2 (PO 4 ) 3 with excellent electrochemical performances. 19 The conductivity of PVA pyrolysis carbon is much larger than that of phenolic resin. Therefore, it is inferred that PVA can also be used as carbon source to synthesize xLi-…”

“…Carbon sources play a significant role especially when high valence raw materials are used because carbon can reduce it to low valence. Several kinds of carbon sources, such as polyethylene glycol, oxalic acid, citric acid, C 12 H 22 O 11 , sucrose, glucose, phenolic resin, and petroleum coke, have been researched to improve the performances of LiFePO 4 /C·Li 3 V 2 (PO 4 ) 3 /C cathode.…”

Effect of ion doping on the electrochemical performances of LiFePO4–Li3V2(PO4)3composite cathode materials

“…8b1 and b2. 81 Compared with single dopants, large numbers of defects can also be produced by dual dopants (especially by Fe and V); this would greatly improve the electrochemical properties of the materials. Li 3 V 2 (PO 4 ) 3 has an inherently high ionic conductivity, with the large polyanions helping to stabilize the structure as an open 3D framework and allowing fast ion migration.…”

“…Fig.8Charge-discharge and cycling performances of xLiFePO 4 -$yLi 3 V 2 (PO 4 ) 3 composites (the first charge-discharge curves of the xLiFePO 4 $yLi 3 V 2 (PO 4 ) 3 /C composites (a1) and cycling performances of 9LiFePO 4 $Li 3 V 2 (PO 4 ) 3 /C at different discharge rates (a2) and at different working temperatures (a3); charge-discharge curves of sample D (b1) and cycling performances of the samples at different discharge rates (b2)) 46,81. …”