•Self-supported PVdF/P(VC-VAc) blended polymer membranes are prepared.•Membranes with rich porous structure can be acquired via the phase inversion method.•The blended polymer electrolytes exhibit superior compatibility with electrodes.•This electrolyte has promising applications in high-voltage lithium ion batteries.New self-supported poly(vinylidene fluoride)/poly (vinyl chloride-co-vinyl acetate) (PVdF/P(VC-VAc)) blended polymer membranes are prepared via a phase inversion method, and then their electrochemical performances, immersed in the liquid electrolyte as the polymer electrolyte for lithium-ion batteries (LIBs), are evaluated. The Fourier transform infrared spectroscopy analysis, the differential scanning calorimeter test and the X-ray diffraction measurement demonstrate that homogeneous PVdF/P(VC-VAc) polymer composites can form at all blend compositions and the crystallinity degree of the blended polymers decreases as the P(VC-VAc) content increases. Specifically, when the proportion of PVdF/P(VC-VAc) is 70:30 (wt%), membranes with a rich surface and internal porous structure can be acquired. The ionic conductivity of the polymer electrolyte achieves a maximum value of 3.57 mS cm−1 at room temperature, and favourable electrochemical performances of LIBs can be obtained. LiNi0.5Mn1.5O4/Li cells with the as-prepared polymer electrolyte exhibit a higher initial discharge capacity of 131.0 mAh g−1 and superior cycle stability with a capacity retention of 96.1% at 0.2 C after 200 cycles compared to cells based on pure PVdF and P(VC-VAc) membranes. This can be attributed to the superior compatibility of the electrolyte with the electrodes. The results also indicate this electrolyte has promising applications in high-voltage LIBs.Download high-res image (288KB)Download full-size image

•Li1.2Mn0.54Ni0.13Co0.13O2/graphite battery with DPDS as additive is evaluated.•DPDS was oxidized and reduced prior to the solvent to form SEI films.•DPDS help improve the high-temperature performance of lithium ion batteries.The effect of diphenyl disulfide (DPDS) as a bifunctional additive on the performance of Li1.2Mn0.54Ni0.13Co0.13O2/graphite batteries cycled at elevated temperature was evaluated. The batteries with 1.0 wt.% DPDS exhibited a capacity retention of 68.4% after 100 cycles under 55 °C, which was higher than that without DPDS (44.4%). In addition, the self-discharge of the Li1.2Mn0.54Ni0.13Co0.13O2/graphite battery was also suppressed in a storage test at 85 °C for 8 h by adding 1.0 wt.% DPDS in the electrolyte. Linear sweep voltammetry and cyclic voltammetry combined with density functional theory calculations indicated that DPDS was oxidized and reduced prior to the solvent to participate in the formation of solid electrolyte interface (SEI) films on the cathode and anode simultaneously. The alternating current impedance and X-ray diffraction suggest that the SEI films derived from DPDS are helpful for enhancing the interface performance of the electrodes and protecting the Li1.2Mn0.54Ni0.13Co0.13O2 and graphite structures from deterioration during high-temperature cycling, which is responsible for the improvement in the performance of the Li1.2Mn0.54Ni0.13Co0.13O2/graphite batteries at elevated temperature.

•1H,1H,5H-Perfluoropentyl-1,1,2,2-tetrafluoroethylether is evaluated as a co-solvent.•F-EAE improves the oxidation stability of the electrolyte at high voltage.•F-EAE facilitates the formation of a passivation interphase on the graphite anode.•Use Three-electrode pouch cells in tracking the impedance changes of each electrodes.1H,1H,5H-Perfluoropentyl-1,1,2,2-tetrafluoroethylether (F-EAE) mixed with ethylene carbonate (EC), diethyl carbonate (DEC), and lithium hexafluorophosphate (LiPF6) is evaluated as a co-solvent high-potential electrolyte of LiNi1/3Co1/3Mn1/3O2/graphite batteries. Linear sweep voltammetry (LSV) and cyclic voltammetry (CV) indicate that the EC/DEC-based electrolyte with F-EAE possesses a high oxidation potential (>5.2 V vs. Li/Li+) and excellent film-forming characteristics. With 40 wt% F-EAE in the electrolyte, the capacity retention of the LiNi1/3Co1/3Mn1/3O2/graphite pouch cells that are cycled between 3.0 and 4.5 V is significantly improved from 28.8% to 86.8% after 100 cycles. In addition, electrochemical impedance spectroscopy (EIS) of three-electrode pouch cells, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) are used to characterize the effects of F-EAE on the enhanced capacity retention. It is demonstrated that F-EAE facilitates the formation of a stable surface electrolyte interface (SEI) layer with low impedance on the anode and effectively suppresses an increase in the charge-transfer resistance on the cathode. These results suggest that F-EAE can serve as an alternative electrolyte solvent for 4.5 V high voltage rechargeable lithium-ion batteries.

•Diphenyl disulfide is evaluated as a new bifunctional electrolyte additive.•DPDS can improve the high-voltage performance of LiCoO2/graphite batteries.•The films induced by DPDS can be formed on the two electrodes at higher potentials.•These films can provide effective protection for the LiCoO2 and graphite materials.Diphenyl disulfide (DPDS) is evaluated as a new bifunctional electrolyte additive to improve the high-voltage performance of LiCoO2/graphite batteries. With the addition of DPDS in the electrolyte, the cell with 2.0 wt% DPDS exhibits enhanced performance in the normal voltage range of 3.0 V–4.2 V. In particular, when the cut-off potential is increased from 4.2 V to 4.4 V, the cell with 1.0 wt% DPDS also exhibits improved discharge capacity and cycle performance. Linear sweep voltammetry and cyclic voltammetry indicate that the DPDS can be reduced prior to the solvent and that the oxidative decomposition of the electrolyte can also be suppressed. In addition, X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy analyses demonstrate that the solid electrolyte interface (SEI) film is produced primarily on the graphite anode via the decomposition of DPDS at normal voltage and that the SEI films induced by DPDS can be formed simultaneously on the two electrodes at higher potentials. It is hypothesized that these compact SEI films covering the electrode surface provide protection for the LiCoO2 and graphite materials and accordingly improve the cyclic performance of battery in the voltage range of 3.0 V–4.4 V.

The preparation of polyethylene-supported poly(vinylidene fluoride)/cellulose acetate butyrate/nano-SiO2 particle (PVDF-CAB-SiO2/PE) blended gel polymer electrolytes (GPEs) is reported here. The electrolyte uptake, mechanical properties, thermal stability, and electrochemical performance of these electrolytes are characterized to evaluate their potential application in lithium-ion batteries (LIBs). The results indicate that the particle size of SiO2 can be adjusted by the tetraethyl orthosilicate (TEOS) concentration and affects the physicochemical properties of the membrane. By doping 5 wt.% SiO2 (500 nm) into the PVdF-CAB blended polymer, the porosity of the membrane increases from 40 to 42.3 %, the mechanical strength from 117.3 to 138.7 MPa, the electrolyte uptake from 149 to 195 %, the oxidation decomposition potential from 4.7 to 5.2 V, and the ionic conductivity of the corresponding GPE is improved from 1.16 to 2.98 mS cm−1 at ambient temperature. The PVDF-CAB-SiO2/PE-based GPE and the two electrodes are suitably compatible, and the thermal stability is higher than that of the polyethylene (PE) membrane. The LIBs with the as-prepared GPE also exhibit enhanced discharge capacity and cycle stability, indicating the promising application of these GPEs in LIBs.

Vinyl ethylene carbonate (VEC) is investigated as an electrolyte additive to improve the electrochemical performance of LiNi0.4Mn0.4Co0.2O2/graphite lithium-ion battery at higher voltage operation (3.0–4.5 V) than the conventional voltage (3.0–4.25 V). In the voltage range of 3.0–4.5 V, it is shown that the performances of the cells with VEC-containing electrolyte are greatly improved than the cells without additive. With 2.0 wt.% VEC addition in the electrolyte, the capacity retention of the cell is increased from 62.5 to 74.5 % after 300 cycles. The effects of VEC on the cell performance are investigated by cyclic voltammetry(CV), electrochemical impedance spectroscopy(EIS), x-ray powder diffraction (XRD), energy dispersive x-ray spectrometry (EDS), scanning electron microscopy (SEM), and attenuated total reflectance-Fourier transform infrared (ATR-FTIR). The results show that the films electrochemically formed on both anode and cathode, derived from the in situ decomposition of VEC at the initial charge–discharge cycles, are the main reasons for the improved cell performance.

This study demonstrates that tris(trimethylsilyl)borate (TMSB) additive in the electrolyte can dramatically improve the cycling performance of LiNi0.5Co0.2Mn0.3O2/graphite cell at higher voltage operation. And the effects of this additive are characterized by linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). In the voltage range of 3.0–4.4 V, LiNi0.5Co0.2Mn0.3O2/graphite cell with TMSB in the electrolyte retains about 92.3% of its initial capacity compared to the cell without additive in the electrolyte that retains only 28.5% of its initial capacity after 150 cycles, showing the promising prospect of TMSB at higher voltage. The enhanced cycling performance is attributed to the thinner film originated from TMSB on the LiNi0.5Co0.2Mn0.3O2 and the combination of TMSB with PF6− and F− in the electrolyte, which not only protects the undesirable decomposition of EC solvents but also results in lower interfacial impedance.Highlights► TMSB is evaluated as an electrolyte additive in LiNi0.5Co0.2Mn0.3O2 based cell at high voltage. ► A thinner cathode electrolyte interface can be formed using TMSB in the electrolyte. ► The combination of TMSB with anion can lower the interfacial impedance. ► The cycle performance of LIBs (3.0–4.4 V) can be improved using this additive.

In order to overcome the capacity fading of LiCoO2/graphite Lithium-ion batteries (LIBs) cycled in the voltage range of 3.0–4.5 V (vs. Li/Li+), methylene methanedisulfonate (MMDS) is newly evaluated as an electrolyte additive. The linear sweep voltammetry (LSV) and cyclic voltammetry (CV) indicate that MMDS has a lower oxidation potential in the mixed solvents of ethylene carbonate (EC) and ethyl methyl carbonate (EMC), and participates in the formation process of the cathode electrolyte interface (CEI) film. With the addition of 0.5 wt.% MMDS into the electrolyte, the capacity retention of the LiCoO2/graphite cells cycled in 3.0–4.5 V is significantly increased from 32.0% to 69.6% after 150 cycles, and the rate capacity is also improved compared with the cells without MMDS additive in the electrolyte, showing the promising prospect in the electrolyte. In addition, the results of electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) demonstrate that the enhanced electrochemical performances of the cells can be ascribed to the modification of components of cathodes surface layer in the presence of MMDS, which resulting the suppression of the electrolyte oxidized decomposition and the improvement of CEI conductivity.Highlights► MMDS is newly evaluated as an electrolyte additive. ► This additive tends to be decomposed on LiCoO2 cathode prior to the solvents. ► A highly ionic conductivity film can be formed using MMDS in the electrolyte. ► The cycle performance of LIB (3.0–4.5 V) can be improved using this additive.