Diethyl phenylphosphonite (DEPP) is used as a novel electrolyte additive to improve the cyclability of spinel LiMn2O4 upon cycling at elevated temperature (55 °C). The charge/discharge cycling stability results indicate that capacity retention of Li/LiMn2O4 cell is significantly improved from 40 to 78% at a rate of 1C (1C = 120 mAh g−1) when 1.0 wt% DEPP is added to the baseline electrolyte (1.0 M LiPF6 in EC/EMC/DEC (3:5:2, vol.%)) after 450 cycles at 55 °C. This improvement can be attributed to the preferential oxidation of DEPP to that of the baseline electrolyte and the subsequent formation of a protective film on the cathode surface. This passivation film suppresses detrimental electrolyte decomposition and in turn protects LiMn2O4 from further decomposition. Molecular energy level calculations, linear sweep voltammetry, and cyclic voltammetry results confirm that DEPP is oxidized on the cathode surface prior to the oxidation of carbonate solvents. Electrochemical impedance spectroscopy illustrates that the the cathode interfacial film generated from DEPP oxidation is more stable and robust than that of the surface film yielded from the baseline electrolyte’s decomposition. Ex situ surface-characterization results further support the claim that DEPP incorporation in the electrolyte suppresses the electrolyte oxidation at elevated temperature and the decomposition of LiMn2O4 cathode material as well.

•EGBE is investigated as an additive for lithium-rich layered cathode (4.8 V).•Cycling performance of Li/Li1.2Mn0.54Ni0.13Co0.13O2 is enhanced with EGBE added.•The surface layer derived from EGBE on the cathode is more stable.•Dissolution of Mn, Co, and Ni can be reduced with added EGBE upon cycling at 4.8 V.Ethylene glycol bis (propionitrile) ether (EGBE) is used as an electrolyte additive to improve the cycling stability and rate capability of Li/Li1.2Mn0.54Ni0.13Co0.13O2 cells at high operating voltage (4.8 V). After 150 cycles, cells with 1.0 wt% of EGBE containing electrolyte have remarkable cycling performance, 89.0% capacity retention; while the cells with baseline electrolyte only remain 67.4% capacity retention. Linear sweep voltammetry (LSV) and computation results demonstrate that EGBE preferably oxidizes on the cathode surface compared to the LiPF6/carbonate electrolyte. In order to further understand the effects of EGBE on Li1.2Mn0.54Ni0.13Co0.13O2 cathode upon cycling at high voltage, electrochemical behaviors and ex-situ surface analysis of Li1.2Mn0.54Ni0.13Co0.13O2 are investigated via electrochemical impedance spectroscopy (EIS), scanning electron spectroscopy (SEM), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and inductive coupled plasma spectroscopy (ICP-MS). The improved cycling performance can be attributed to more stable and robust surface layer yield via incorporation of EGBE, which mitigates the oxidation of electrolyte on the cathode electrode, and also inhibits the dissolution of bulk transition metal ions as well upon cycling at high voltage.

•SDM is investigated as an electrolyte additive for LiNi0.5Mn1.5O4 cathodes.•The cycling performance is enhanced with appropriate amount addition of SDM.•The surface layer derived from SDM on the cathode is more stable and robust.•Dissolution of Mn and Ni of LiNi0.5Mn1.5O4 can be mitigated by adding SDM.A novel electrolyte additive, 1,1′-sulfonyldiimidazole (SDM), is firstly reported to improve the cycling performance of LiNi0.5Mn1.5O4 at high voltage and elevated temperature (55 °C). Linear sweep voltammetry (LSV), initial differential capacity vs. voltage, and computation results indicate that SDM is oxidized at a lower potential than the solvents of the electrolyte. Coulombic efficiency and capacity retention of a Li/LiNi0.5Mn1.5O4 cell can be significantly enhanced in the presence of SDM, and moreover cells with SDM deliver lower impedance after 100 cycles at elevated temperature. To better understand the functional mechanism of the enhanced performance with incorporation of SDM in the electrolyte, ex-situ analytical techniques, including scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and inductively coupled plasma mass spectrometry (ICP-MS) are employed to gain insight into the reaction mechanism of SDM on the LiNi0.5Mn1.5O4 electrode at high voltage and elevated temperature (55 °C). Surface analysis reveals that the improved electrochemical performance of the cells can be ascribed to the highly stable surface layer generated by SDM, which thus mitigates the detrimental decomposition of the electrolyte occurring and stabilizes the interphase of spinel LiNi0.5Mn1.5O4 cathode while cycling at high voltage and elevated temperature.

•TMSP is used as an electrolyte additive for LiNi0.5Mn1.5O4 cathode battery at high voltage (4.9 V).•The cyclability of the Li-ion battery at RT and ET can be improved by the use of TMSP.•The rate capability of the Li-ion battery can be improved by the use of TMSP.•Incorporation of TMSP can form a more stable and more conductive surface film on the cathode.In this work, tris (trimethylsilyl) phosphate (TMSP) is used as an electrolyte additive to improve the cycling performance of Li/LiNi0.5Mn1.5O4 cell upon cycling at high voltage, 4.9 V vs. Li/Li+ at room temperature and elevated temperature (55 °C). The effects of TMSP on the cathode interface and the cycling performance of Li/LiNi0.5Mn1.5O4 cell were investigated via the combination of electrochemical methods, including cycling test, cyclic voltammetry (CV), chronoamperometry, and electrochemical impedance spectroscopy (EIS). It is found that cells with electrolyte containing TMSP have better capacity retention than that of the cells without TMSP upon cycling at high voltage at room temperature and elevated temperature. The functional mechanism of incorporation of TMSP to the electrolyte to improve the cycling performance is conducted with ex-situ analysis approaches, including X-ray diffraction (XRD), scanning electron microscope (SEM), thermal gravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), transmission electron microscope (TEM) and ICP-MS. The surface analysis results reveal that more stable and more conductive surface layer is formed on the LiNi0.5Mn1.5O4 electrode with TMSP containing electrolyte, which is a leading factor for the enhanced the cycling performance of Li/LiNi0.5Mn1.5O4 cells upon cycling at high voltage at room temperature and elevated temperature.

•TPFPP decreases the flammability and inhibits the oxidation of the electrolyte.•TPFPP is oxidized on LiMn2O4 electrode prior to the electrolyte.•TPFPP is reduced on graphite prior to the electrolyte.•TPFPP improves the thermal stability of the electrolyte.Tris (pentafluorophenyl) phosphine (TPFPP) additive possesses a dual functionality. The first of which is aimed at decreasing the flammability of the electrolyte, while the second is directed at the inhibition of the oxidative decomposition of electrolyte on cathode materials in lithium-ion batteries. The properties of the electrolyte containing TPFPP and the enhancements of cycling performance of Li/LiMn2O4 cells are investigated via a combination of electrochemical methods, self-extinguishing time (SET), differential scanning calorimeter (DSC), as well as density functional theory (DFT) computations. It is found that the incorporation of TPFPP to 1.0 M LiPF6 in 1:1:1 (v/v/v) ethylene carbonate/dimethyl carbonate/diethyl carbonate improves the thermal stability and decrease the flammability of the electrolyte. In addition, the initial discharge capacity and cycling stability of Li/LiMn2O4 is improved as well. The improved cycling performance with TPFPP added can be ascribed to the participation in surface layer formation process with incorporation of TPFPP. DFT theoretical computations are in good agreement with the modified cyclic voltammetry behavior of electrolyte with and without TPFPP additive on LiMn2O4 and graphite electrodes.

•DDS can dramatically improve the safety of Li-ion batteries during overcharge process.•No sacrifice on capacity and cycling stability with DDS incorporation.•Electro-polymerized layer can postpone the voltage rising up during overcharge state.The electrochemical properties and working mechanisms of dimethoxydiphenylsilane (DDS) as an electrolyte additive for overcharge protection of lithium ion batteries have been investigated by microelectrode cyclic voltammetry, galvanostatic charge-discharge cycling, and SEM observation on both the cathode and separator of the overcharged cells. DDS can be electrochemically polymerized when the cell was overcharged to 4.9 V (vs. Li/Li+), resulting in a polymer layer on the electrode and the separator, which increases the internal resistance of the cell and postpones the voltage rising up during the overcharge process. Therefore, the safety issue of lithium-ion batteries during overcharge state can be significantly improved by utilization of DDS. Furthermore, incorporation of DDS does not significantly degrade the performance of the cell as there is only a small capacity loss during the normal charge–discharge process.

Dimethylacetamide (DMAc) is used as an electrolyte stabilizing additive for lithium ion battery. The effects of DMAc on the enhancements of electrolyte thermal stability and the solid electrolyte interphases (SEIs) on graphite anode and LiFePO4 cathode were investigated via a combination of electrochemical methods, nuclear magnetic resonance (NMR), Fourier transform infrared-attenuated total reflectance (FTIR-ATR), as well as X-ray photoelectron spectroscopy (XPS). It was found that 1.0 M LiPF6 EC/DMC/DEC (1/1/1,weight ratio) electrolyte with 1% DMAc incorporation can be stable at 85 °C for over 6 months without precipitation and color change. In addition, the addition of 1% dimethylacetamide (DMAc) can significantly improve the cyclic performance of a LiFePO4/graphite cell at elevated temperature. These improved performances are ascribed to the enhancement of the thermal stability of the electrolyte and the modification of SEI components on graphite anode and LiFePO4 cathode. The explicit working mechanism of DMAc stabilizing LiPF6-based electrolyte is also discussed by the density functional theory (DFT) calculations.