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Lithium difluoroborate (LiDFOB), lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiDFBOP) and lithium difluorophosphate (LiPF2O2) are investigated as electrolyte additives to alleviate the severe cycle capacity fading of spinel LiMn2O4 cathode of lithium-ion batteries, especially at elevated temperatures. Compared with that of the routine electrolyte, the capacity retention is significantly improved at both room temperature and 55 °C by adding LiBOB and LiDFOB as electrolyte additives. Moreover, surface layer formation processes on the LiMn2O4 electrode in the presence of the LiBOB, LiDFOB, LiDFBOP and LiPF2O2 are investigated by photoelectron spectroscopy (XPS) and X-ray diffraction. According to the analysis results, BOB− anions from LiBOB or LiDFOB bond with the dissolved Mn2+ to form an insoluble and stable surface layer on the LiMn2O4 surface, which is beneficial to the suppression of the LiMn2O4 dissolution and electrolyte decomposition, and eventually to the improvement of the cycling performance at elevated temperatures.Graphical abstract: [ABSTRACT FROM AUTHOR]

Abstract: In this paper, graphene-modified Li3V2(PO4)3 composites have been developed as Li-ion battery cathode materials with high specific capacity and excellent cycling stability. The composites are prepared by spray–drying process using graphene oxide nanosheet and citric acid as carbon source. X-ray diffraction patterns demonstrate that the as-prepared samples are well crystallized with orderly monoclinic structures. SEM and TEM images reveal that the 3D network graphene and Li3V2(PO4)3 primary nanoparticles interlace with each other. The citric acid-derived amorphous carbon species interrupt the stacking of graphene sheets and minimize in-plane anisotropy of electronic migration within graphene layers, which would facilitate fast electron migration and Li+ diffusion throughout the micro-sized spherical secondary particles. The discharge capacity of the composite could respectively achieve 131.4 and 181.5mAhg−1 in the voltage range 3.0–4.3V and 3.0–4.8V at 0.1C discharge rate, which almost reach the theoretical capacity of the cathode material. Both of them nearly showed no capacity decay at 0.1C charging and discharging rate after long cycles. [Copyright &y& Elsevier]