•LiNi0.5Mn1.5O4 electrodes with water soluble binder, carbon-coated Al current collector.•Carbon-coated layer enhances adhesion strength and flexibility.•Carbon-coated layer inhibits corrosion and reduces charge transfer resistance.•Excellent cycle stability and rate capability for 5 V LiNi0.5Mn1.5O4.5 V LiNi0.5Mn1.5O4 (LNMO) cathodes are prepared using carboxymethyl chitosan (CCTS) as a water soluble binder and carbon coated aluminum foils (CAl) as current collector in Li-ion batteries (LIBs). CCTS exhibits an electrochemical oxidation potential as high as 5.0 V. The electrochemical performance of LNMO cathode with CCTS binder is investigated and compared with the commercial non-aqueous polyvinylidene difluoride (PVDF). CCTS-CAl-LNMO electrode shows higher capacity retention (95.8%) than that of PVDF-CAl-LNMO (92.9%) and PVDF-Al-LNMO (88.52%) after 100 cycles. And, CCTS-CAl-LNMO electrode exhibits better rate capability than PVDF-CAl-LNMO, and PVDF-Al-LNMO, retaining specific capacity of 95.8 mAhg−1 at 10C rate, only 87.6 mAhg−1 and 1 mAhg−1 for PVDF-CAl-LNMO, and PVDF-Al-LNMO, respectively. This approach can also be extended its use to other cathode materials such as LiNi1/3Co1/3Mn1/3O2 (NCM).Download high-res image (124KB)Download full-size image

•Carboxymethyl chitosan/poly(ethylene oxide) (CCTS/PEO) is used as water soluble binder.•CCTS/PEO shows a high electrochemical oxidation potential of above 5.0 V.•Optimized composition of CCTS/ PEO (85/15) exhibits enhanced adhesive strength.•CCTS/PEO shows good cycling stability for 5 V LiNi0.5Mn1.5O4.Carboxymethyl chitosan/poly (ethylene oxide) (CCTS/PEO) composite is firstly reported as a water soluble binder for the application of 5 V LiNi0.5Mn1.5O4 cathode in Li-ion batteries. Both CCTS and PEO show a high electrochemical oxidation potential of above 5.0 V (vs. Li/Li+). The electrochemical performances of LiNi0.5Mn1.5O4 (LNMO) cathodes with CCTS/PEO composite binders of different mass rates are investigated, it is found that LiNi0.5Mn1.5O4 cathode with an optimized CCTS/PEO (85/15, w/w) composite exhibits a slightly better cycling performance than that of polyvinylidene fluoride (PVDF), retaining 81.4% capacity as compared with 79.8% for PVDF at 0.5C rate after 200 cycles. LNMO with PEO/CCTS (85/15, w/w) exhibited the better rate capability than that of PVDF. These results demonstrate that CCTS/PEO composite can be potentially used as a water-soluble binder for 5 V LNMO cathode.Download high-res image (174KB)Download full-size image

•Xanthan gum (XG) is employed as water soluble binder for LiFePO4 (LFP) cathode in LIBs.•XG binder exhibits good thermal stability and adhesion strength.•XG binder shows better dispersion capability with LFP, thus better processing property than PVDF.•LFP with XG binder shows better cycle stability and rate capability than PVDF.Xanthan Gum (XG) is systematically investigated and employed as water soluble binder for LiFePO4 (LFP) cathode in Li-ion batteries. XG binder exhibits good thermal stability and processes abundant functional groups such as carboxyl and hydroxyl, displaying a better adhesion strength of 0.085 N cm−1 than sodium carboxymethyl cellulose (CMC, 0.050 N cm−1), but inferior to polyvinylidene difluoride (PVDF, 0.170 N cm−1). The Rheology test reveals that the viscosity of LFP slurry prepared with XG binder is higher than that of PVDF, resulting in a better dispersion of LFP and carbon black particles. The electrochemical performances of LFP-XG electrode are investigated and compared with those of aqueous CMC and conventional PVDF binder. LFP-XG displays better cycle stability and rate performance than PVDF, comparable to CMC, which retains 55.3% capacity of C/5 at 5 C as compared to PVDF (34.8%) and CMC (57.8%). Cyclic voltammetry (CV) shows that LFP-XG has smaller redox polarization and faster lithium diffusion rate than PVDF while electrochemical impedance spectroscopy (EIS) measurement at specified intervals reveals its more favorable electrochemical kinetics than that with PVDF, similar to CMC, thus better rate capability. Scanning electron microscopy (SEM) displays that LFP-XG has a more homogenous distribution of LFP and conductive carbon black particles with XG before cycling and better maintains its structure integrity after 100 cycles than that of PVDF. Furthermore, LFP-XG is observed to process a high ionic conductivity supported by dQ/dV profiles.Download high-res image (294KB)Download full-size image

•MoS2/C nanocomposite was synthesized by hydrothermal method and subsequent carbonization of glucose.•Pluronic is an essential dispersing agent to obtain monodispersed MoS2/C.•MoS2/C exhibits improved cycling stability and rate capability than MoS2.A novel molybdenum disulfide/carbon (MoS2/C) nanocomposite is synthesized by a simple hydrothermal method using glucose as a carbon source and Pluronic F127 as promoting agent in presence of MoS2 nanoparticles and followed by carbonization. Pluronic F127 is used as an essential agent which inhibits the spontaneous formation of carbon microspheres during the hydrothermal reaction. The composite electrode exhibits excellent cycling stability and rate capability, delivering a reversible capacity of 882.6 mA h g−1 at a current density of 50 mA g−1 and a capacity retention of 82.8% after 100 cycles at a current density of 100 mA g−1. At a higher current density of 300/500 mA g−1, it still retains a capacity of 603.6/461.6 mA h g−1 respectively, as compared to 295.6/228.4 mA h g−1 for the pristine MoS2 electrode. The composite shows favorable electrochemical kinetics compared with pristine MoS2 due to the incorporation of homogenous conductive carbon layer and its nanostructured morphology.

•Novel choline-based ionic liquids synthesized as safe electrolytes for Li-ion batteries.•Delivered a stable capacity of 152 mAh g−1 over 90 cycles at a cut-off voltage of 4.4 V.•Displayed a lower propagation rate than the commercial carbonate electrolyte.Three choline-based ionic liquids functionalized with trimethylsilyl, allyl, and cynoethyl groups are synthesized in an inexpensive route as safe electrolytes for high-voltage lithium-ion batteries. The thermal stabilities, viscosities, conductivities, and electrochemical windows of these ILs are reported. Hybrid electrolytes were formulated by doping with 0.6 M LiPF6/0.4 M lithium oxalydifluoroborate (LiODFB) as salts and dimethyl carbonate (DMC) as co-solvent. By using 0.6 M LiPF6/0.4 M LiODFB trimethylsilylated choline-based IL (SN1IL-TFSI)/DMC as electrolyte, LiCoO2/graphite full cell showed excellent cycling performance with a capacity of 152 mAh g-1 and 99% capacity retention over 90 cycles at a cut-off voltage of 4.4 V. The propagation rate of SN1IL-TFSI)/DMC electrolyte is only one quarter of the commercial electrolyte (1 M LiPF6 EC/DEC/DMC, v/v/v = 1/1/1), suggesting a better safety feature.Choline based ionic liquid containing trimethylsilyl and TFSI substituents showed excellent cycling performance in LiCoO2/graphite full cell at 4.4 V.

•Ce-doped Li4Ti5O12 samples were prepared by a sol-gel method.•Li4Ti4.85 Ce0.15O12 exhibits the best rate capability.•The Doping Effects of Cerium on Li4Ti5O12 Anode material was investigated by a combined experimental and theoretical study.Aliovalently Ce3+-doped Li4Ti5O12 (LTO) is firstly synthesized by a sol-gel method using Ce(CH3COOH)3 as the dopant and CH3COOLi/(C4H9O)4Ti as starting materials. The structure and morphology of Ce3+-doped LTO with various doping level (Li4Ti5-xCexO12; x = 0, 0.05, 0.10, 0.15 and 0.20) are characterized by XRD, EDX, Raman, XPS, SEM and TEM. Pure phase Ce3+-doped Li4Ti5O12 is obtained when x ≤ 0.10, while CeO2 impurity is observed when x > 0.10. The Ce3+-doped LTO with appropriate content of CeO2 impurity shows much improved rate capability and specific capacity compared with the pristine and Ce3+-doped LTO without CeO2 impurity. Particularly, the Li4Ti5-xCexO12 (x = 0.15) electrode exhibits the best rate capability and long-term cycling stability among all samples, delivering a capacity of 120.0 mAh g−1 at 5C even after 1000 cycles. This work demonstrates that aliovalently Ce3+-doping is an effective approach for enhancing LTO’s rate-performance.

A novel organosilicon-based ionic plastic crystal, N,N,N,-diethylmethyl-N-[(trimethylsilyl)methyl]ammonium bistrifluoromethane sulfonimide ([DTMA][TFSI]) was designed and synthesized as solid-state electrolyte for lithium-ion batteries. The chemical structure and the physical and electrochemical properties were characterized in detail. The ionic conductivity of [DTMA][TFSI] was improved significantly by doping with lithium oxalyldifluoroborate (LiODFB) and propylene carbonate (PC). An optimized plastic crystal composite ([DTMA][TFSI]:LiODFB:PC=8:1:1 in molar ratio) as a solid-state electrolyte exhibited a decent cycling stability in LiFePO4/Li half-cell, with a specific discharge capacity of 144 mA·h/g and capacity retention of 94% after 50 cycles at C/20.合成新型的有机硅基离子塑晶材料 [DTMA][TFSI], 测试材料的物理和电化学性 能, 研究其掺杂改性并作为固态电解质用于锂 离子电池。1. 合成新型的有机硅基离子型塑晶材料; 2. 将 三元复合塑晶材料作为固态电解质在室温下用 于锂离子电池。1. 通过热性能分析, 得到材料的塑晶温度区间 和融化熵值(图1 和表1); 2. 通过电导率测 试, 确定塑晶掺杂对导电性能的影响(图2); 3. 通过对扣式电池的充放电性能、倍率性能、 循环性能以及阻抗的测试(图4~7), 得到塑晶 复合物作为固态电解质的电化学性能以及电池 循环的稳定性和可逆性。1. 合成新型有机硅基离子塑晶材料 [DTMA][TFSI], 塑晶温度区间为–26 °C 到 54 °C; 2. 在纯塑晶IPC 中添加10% LiODFB 和 10% PC, 得到复合物的电导率为1×10−4 S/cm, 提高塑晶作为固态电解质在室温下应用的可行 性; 3. 将复合物用于LiFePO4/Li 半电池测试, 在C/20 倍率下, 电池的放电比容量为 144 mA·h/g, 库伦效率为99%。在50 次循环 后, 容量保持率为94%; 4. 测试结果表明, 新 型有机硅基离子塑晶的复合物可作为固态电解 质材料应用于锂离子电池, 以及更高能量密度 的锂-硫和锂-空电池。

The polyacrylic latex (LA132) was firstly reported as a water-soluble binder for LiNi1/3Co1/3Mn1/3O2 (NCM) cathode in Li-ion battery. The electrochemical performances of NCM cathode with LA132 binder were investigated and compared with the conventional water-soluble sodium carboxymethyl cellulose (CMC) and commercial non-aqueous polyvinylidene difluoride (PVDF). NCM cathode with LA132 binder exhibited a much higher specific capacity of 146 mAh g−1 and capacity retention of 96.4 % after 100 cycles as compared with 122 mAh g−1/88 % and 121 mAh g−1/75% for the NCM electrode with CMC and PVDF, respectively. In addition, NCM cathode with LA132 binder exhibited better rate capability than that of CMC and PVDF, e.g., retaining 34.3 % capacity of C/5 at 5 C rate as compared with 28.5 and 10.9 % for CMC and PVDF, respectively.

We report a novel Li4Ti5−xWxO12−xBrx (x = 0.025, 0.050 and 0.100) anode material simultaneously doped with W6+ and Br− ions prepared by a simple solid-state reaction in air, aiming to significantly improve electrical conductivity of Li4Ti5O12. Our theoretical calculation predicts that codoping with W6+ on the Ti4+ site and Br− on the O2− site can remarkably narrow down the band gap, and thus facilitate the electron transport in the lattice of LTO. The comparative experiments prove that W & Br-codoped LTO exhibits higher electrical conductivity compared with undoped LTO as expected, thus leading to improved rate capability and specific capacity. Particularly, Li4Ti5−xWxO12−xBrx (x = 0.05) exhibits the best rate capability and cycling stability with an outstanding capacity retention of 88.7% even at 10 C rate after 1000 cycles. This codoping strategy with high valence transition metal and halide ions holds promise to be applied to other insulating cathode materials suffering from inferior electrical conductivity.

•Si/(S-doped-C nanowire-network) prepared by carbonizing Si/(PEDOT nanowire-network).•Deliver capacity of 820 mAh g−1 after 400 cycles with capacity fade of 0.09%/cycle.•S-doped-C nanowire-network constructs robust conducting network in the composite.•S-doped-C nanowire-network improves structural stability of the composite.Novel nanostructured silicon composites, Si/Poly(3,4-ethylenedioxythiophene) nanowire network (Si/PNW) and Si/(S-doped-carbon nanowire network) (Si/S-CNW), are prepared by a soft-template polymerization of 3,4-ethylenedioxythiophene (EDOT) using sodium dodecyl sulfate (SDS) as surfactant with the presence of Si nanoparticles and a subsequent carbonization of Si/PNW, respectively. The presence of Si nanoparticles in the soft-template polymerization of EDOT plays a critical role in the formation of PEDOT nanowire network instead of 1D nanowire. After the carbonization of PEDOT, the S-doped-carbon nanowire network matrix shows higher electrical conductivity than PNW counterpart, which facilitates to construct robust conductive bridges between Si nanoparticles and provide large electrode/electrolyte interfaces for rapid charge transfer reactions. Thus, Si/S-CNW composite exhibits excellent cycling stability and rate capability as anode material, retaining a specific capacity of 820 mAh g−1 after 400 cycles with a very small capacity fade of 0.09% per cycle.

Two triethoxyl-/trimethoxyl-silyl functionalized glycerol carbonates and one disiloxanyl functionalized glycerol carbonate were synthesized through a cycloaddition reaction of carbon dioxide with allyl glycidyl ether followed by a hydrosilylation with the corresponding hydrosilanes. Their chemical structures were fully characterized by 1H and 13C nuclear magnetic resonance (NMR) spectroscopy and their basic physicochemical properties including dielectric constant, viscosity, ionic conductivity, apparent lithium transference number and electrochemical window, were systematically measured. Trimethoxysilyl functionalized glycerol carbonate as electrolyte solvent with LiPF6 (0.6 M) and lithium oxalyldifluoroborate (0.4 M) binary salts exhibited good cycling stability over 2.7–4.4 V in high-voltage-LiCoO2/graphite full cells. Disiloxane functionalized glycerol carbonate acted as an efficient electrolyte additive to improve the wetting property on the separator in Li/LiCoO2 cells.

The formation mechanism of LiTi2O4, prepared by a carbon thermal reduction reaction using Li2CO3 and TiO2 (anatase) as starting materials and acetylene black as a reducing agent, was investigated by in situ variable temperature X-ray diffraction and thermal gravimetric analysis/differential scanning calorimetry system. It was found that the cooling rate significantly impacts on obtaining pure phase LiTi2O4 sample after forming LiTi2O4 product during the carbon thermal reduction reaction. LiTi2O4 has excellent cycling stability, remaining a specific capacity of 126.6/111.9 mA h g−1 with a capacity fade of 5.1%/3.1% at 0.5C/1C rate after 200 cycles.

A dinitrile compound containing ethylene oxide moiety (4,7-dioxa-1,10-decanedinitrile, NEON) is synthesized as an electrolyte solvent for high-voltage lithium-ion batteries. The introduction of ethylene oxide moiety into the conventional aprotic aliphatic dinitrile compounds improves the solubility of lithium hexafluorophosphate (LiPF6) used commercially in the lithium-ion battery industry. The electrochemical performances of the NEON-based electrolyte (0.8 M LiPF6 + 0.2 M lithium oxalyldifluoroborate in NEON:EC:DEC, v:v:v = 1:1:1) are evaluated in graphite/Li, LiCoO2/Li, and LiCoO2/graphite cells. Half-cell tests show that the electrolyte exhibits significantly improved compatibility with graphite by the addition of vinylene carbonate and lithium oxalyldifluoroborate and excellent cycling stability with a capacity retention of 97 % after 50 cycles at a cutoff voltage of 4.4 V in LiCoO2/Li cell. A comparative experiment in LiCoO2/graphite full cells shows that the electrolyte (NEON:EC:DEC, v:v:v = 1:1:1) exhibits improved cycling stability at 4.4 V compared with the electrolyte without NEON (EC:DEC, v:v = 1:1), demonstrating that NEON has a great potential as an electrolyte solvent for the high-voltage application in lithium-ion batteries.

•Carboxymethyl chitosan firstly reported as a water soluble binder for Si anode.•Strong hydrogen bonding formed between the Si surface and carboxymethyl chitosan.•Exhibited a high first discharge capacity of 4270 mAh g−1.•Maintained a capacity of 950 mAh g−1 at 500 mA g−1 over 50 cycles.Carboxymethyl chitosan (C-chitosan) is investigated as a new water soluble binder for Si anode of Li-ion batteries. The Fourier transformation infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) measurements reveal that the strong hydrogen bonding is formed between the hydroxylated Si surface and the polar groups (–OH, –COOH and –NH2) of C-chitosan. The Si/C-chitosan anode (Si:carbon black:C-chitosan = 62:30:8 in weight ratio) exhibits a high first discharge capacity (4270 mAh g−1) with a first coulombic efficiency of 89%, and maintains a capacity of 950 mAh g−1 at the current density of 500 mA g−1 over 50 cycles.

Carboxymethyl chitosan (C-CTS) was firstly reported as a water soluble binder for LiFePO4 cathode in Li-ion batteries. The electrochemical performances of LiFePO4 cathode with C-CTS binder was investigated and compared with the conventional water-soluble sodium carboxymethyl cellulose (CMC) and the commercial non-aqueous polyvinylidene difluoride (PVDF). LiFePO4 cathode with C-CTS exhibited a comparable cycling performance, but better rate capability than that of CMC and PVDF, retaining 65% capacity of C/5 at 5 C rate as compared with 55.9% and 39.4% for CMC and PVDF, respectively. In addition, LiFePO4 cathode with C-CTS exhibited excellent cycling performance at 60 °C, retaining 91.8%/62.1% capacity after 80 cycles at 1 C/10 C, respectively.

A novel Si/porous-C composite with buffering voids was prepared by the co-assembly of phenol-formaldehyde resin, SiO2 and Si nanoparticles, followed by a carbonizing process and subsequent removal of SiO2 template. Si nanoparticle was coated with a layer of porous carbon shell with rationally designed void in between which provides the accommodating space for the volume change of Si over cycling. The as-prepared composite electrode exhibited good electrochemical performances as an anode material in lithium-ion cells, showing a stable reversible capacity of 980 mAh g−1 over 80 cycles with small capacity fade of 0.17%/cycle and high rate capability (721 mAh g−1 at 2000 mA g−1).

Organosilicon-functionalized quaternary ammonium ionic liquids (ILs) with oligo(ethylene oxide) substituent are designed and synthesized. Such properties as viscosity, conductivity, and thermal/electrochemical stability of these ILs are characterized. These ILs are miscible with the commercial carbonate electrolyte (EC: DEC = 1:1(w/w), 1 M LiPF6) and are used as cosolvents to form hybrid electrolytes in proportions up to 30 vol%. By using such hybrid electrolytes, the LiFePO4/Li half cells exhibit no deterioration in specific capacity and cyclability, and the graphite/Li half cells show improved compatibility in the presence of lithium oxalyldifluoroborate. These hybrid electrolytes exhibit less flammability compared with the commercial baseline electrolyte, and thus improved safety for use in lithium-ion batteries.

Micro/nano-structured SnS2 was prepared by a hydrothermal method using biomolecular l-cysteine and SnCl4·5H2O as sulfur source and tin source, respectively. The electrochemical performances of SnS2 electrodes were investigated using water-soluble binders of carboxymethyl chitosan (C-chitosan) and chitosan lactate, and compared with the conventional water-soluble sodium carboxymethyl cellulose (CMC) and non-aqueous polyvinylidene difluoride (PVDF). SnS2 electrode using the water-soluble binders (C-chitosan, chitosan lactate, and CMC) showed higher initial coulombic efficiency, larger reversible capacity, and better rate capabilities than that of PVDF. In addition, SnS2 electrode using C-chitosan binder exhibited somewhat worse cycling stability, but better rate capability at a high rate of 5C than CMC.

A nanostructured silicon/porous carbon spherical composite was prepared by a simple hydrothermal method using glucose as a carbon source and Pluronic F127 as a soft template/pore forming agent in the presence of silicon nanoparticles, and a subsequent carbonization process. In this composite, silicon nanoparticles were individually and separately coated with a porous carbon shell with a thickness of 15–20 nm and a pore size of 3–5 nm. The composite electrode exhibited excellent cycling stability and rate capability, delivering a stable capacity of 1607 mA h g−1 at a current density of 0.4 A g−1 after 100 cycles, and a reversible capacity of 1050 mA h g−1 even at a high current density of 10 A g−1. Detailed analysis of cyclic voltammetry and electrochemical impedance spectroscopy revealed that the composite showed favorable electrochemical kinetics due to the nano-sized porous carbon shell, which facilitated the formation of a solid electrolyte interface film and the transportation of Li ions and electrons, and decreased the charge transfer resistance, thus significantly improving the electrochemical performance compared with the bare nano-Si electrode.

A new aminoalkylsilane compound, ((2-(2-(N,N-dimethylamino)ethoxy)ethoxy) methyl)trimethylsilane (TMSC1N2) based on the oligo(ethylene oxide) chain end-capped with organosilicon functional group and alkylamine group on each end, was introduced as an electrolyte additive for lithium-ion batteries. Electrochemical performances of different volume ratios of TMSC1N2 in the baseline electrolyte were conducted through cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge/discharge tests of lithium-ion batteries. With adding 5 vol.% TMSC1N2 to the baseline electrolyte (1 mol/L LiPF6 in ethylene carbonate and diethyl carbonate (EC:DEC = 1:1, in volume)), the capacity retention of LiFePO4/Li cells could be significantly improved from 74.7% to 90.8% after 130 cycles. Furthermore, TMSC1N2 showed good compatibility with graphite electrode and would not deteriorate the electrochemical performance of graphite/Li anode cells. These data suggested that TMSC1N2 could be utilized as an effective additive for lithium-ion batteries.

Poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) counter electrodes, doped with polyethylene glycol (PEG) and acetylene black as binding and conductivity promoting agent, were prepared by a simple mixing method for dye-sensitized solar cell. The electrochemical properties of the electrodes were characterized by cyclic voltammetry, electrochemical impedance spectroscopy (EIS), and Tafel polarization curves. Using PEG dopant, the electrocatalytic activity of PEDOT:PSS electrode was much improved, and further improved by adding a small amount of conducting acetylene black (0.2 wt%). The DSSC cells, using the PEDOT:PSS electrode with PEG (5 wt%) dopant and the composite electrode with PEG (5 wt%)/acetylene black, exhibited an energy conversion efficiency of 3.57 and 4.39 %, comparable with 4.50 % of the commonly used Pt electrode under the same experimental conditions. These results demonstrate that PEG-modified PEDOT:PSS counter electrode is promising to replace the expensive Pt for low cost DSSC, especially to meet the large-scale fabrication demands.

Aminoalkylsilanes with oligo(ethylene oxide) units were designed and synthesized as multifunctional electrolyte additives for lithium-ion batteries. The chemical structures were fully characterized by nuclear magnetic resonance (NMR) spectroscopy and their thermal properties, viscosities, electrochemical windows, and ionic conductivities were systematically measured. With adding one of these compounds (1 vol. %, DSC3N1) in the baseline electrolyte 1.0 M LiPF6 in EC: DEC (1:1, in volume), Li/LiCoO2 half cell tests showed an improved cyclability after 100 cycles and improved rate capability at 5C rate condition. Electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS), and energy dispersive spectroscopic (EDS) analysis confirmed the acid scavenging function and film forming capability of DSC3N1. These results demonstrated that the multifunctional organosilicon compounds have considerable potential as additives for use in lithium-ion batteries.

A novel porous Si/S-doped carbon composite was prepared by a magnesiothermic reaction of mesoporous SiO2, subsequently coating with a sulfur-containing polymer-poly(3,4-ethylene dioxythiophene), and a post-carbonization process. The as-prepared Si composite was homogeneously coated with disordered S-doped carbon with 2.6 wt.% S in the composite and retained a high surface area of 58.8 m2 g−1. The Si/S-doped carbon composite exhibited superior electrochemical performance and long cycle life as an anode material in lithium ion cells, showing a stable reversible capacity of 450 mAh g−1 even at a high current rate of 6,000 mA g−1.

{3-[2-(2-methoxyethoxy) ethoxy]-propyl} triethoxysilane (TESM2) was synthesized and used as an electrolyte additive to improve the performances of lithium-ion batteries (LIBs). The electrochemical properties of the electrolyte (1 mol/L lithium hexafluorophosphate (LiPF6)/ethylene carbonate (EC):diethylene carbonate (DEC):dimethyl carbonate (DMC), 1:1:1) with different contents of TESM2 were characterized by ionic conductivity measurement, galvanostatic charge/discharge test of graphite/Li half cells, and electrochemical impedance spectroscopy. Both the cycling performances and C-rate capabilities of graphite/Li half cells were significantly improved with an optimized content of 15% TESM2 in the electrolyte. The graphite/Li half cell delivered a very high specific capacity of 370 mAh/g at 0.2C rate without any capacity loss for 60 cycles, and retained a capacity of 292 mAh/g at 2C rate. The solid electrolyte interphase (SEI) film on the surface of the graphite anode was investigated by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS), indicating that TESM2 was effectively involved in the formation of SEI film on the surface of graphite.

Oligo(ethylene oxide)-functionalized trialkoxysilanes were synthesized through hydrosilylation reaction by reacting trialkoxysilane with oligo(ethylene oxide) allyl methyl ether using PtO2 as a catalyst. The physical properties of these compounds, such as viscosity, dielectric constant, and ionic conductivity, were characterized. Among them, [3-(2-(2-methoxyethoxy)ethoxy)-propyl]triethoxysilane (TESM2) exhibited a commercial viable ionic conductivity of 1.14 mS cm−1 and a wide electrochemical window of 5.2 V. A preliminary investigation was conducted by using TESM2 as an electrolyte solvent for high-voltage applications in lithium-ion batteries. Using 1 M LiPF6 in TESM2 with 1 vol% vinyl carbonate as an electrolyte, LiCoO2/Li half-cell delivered a specific capacity of 153.9 mAh g−1 and 90 % capacity retention after 80 cycles (3.0–4.35 V, 28 mA g−1); Li1.2Ni0.2Mn0.6O2/Li4Ti5O12 full cell exhibited the initial capacity of 161.3 mAh g−1 and 86 % capacity retention after 30 cycles (0.5–3.1 V, 18 mA g−1).

Allyl cyanide (AC) was investigated as a film-forming additive in propylene carbonate (PC)-based electrolytes for graphite anode in lithium-ion batteries. The film-forming behavior of AC was characterized with cyclic voltammetry, electrochemical impedance spectroscopy, scanning electron microscopy, and Fourier transform infrared spectroscopy. By adding 2 wt% AC in the electrolyte of 1 M LiPF6-PC/DMC (1:1, in vol), the exfoliation of graphite anode was effectively suppressed over cycling. Graphite/Li half-cell showed an initial coulombic efficiency of 75 % and a specific capacity of 300 mAh/g after 48 cycles. A possible reductive polymerization mechanism of AC on the surface of graphite was proposed.

Nano-silicon composites, Si/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and Si/C, were prepared by an in situ chemical polymerization of 3,4-ethylenedioxythiophene (EDOT) with nano-Si particles in a PSS aqueous solution and subsequent carbonization of Si/PEDOT:PSS, respectively. The nano-Si particles were embedded in a shapeless PEDOT:PSS matrix and amorphous carbon in the corresponding composite. Energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) measurements revealed that 2.66 wt% of the element sulfur was doped in the carbon matrix for Si/C composite. Both the Si/PEDOT:PSS and Si/C composite electrodes exhibited higher initial coulombic efficiency and better cycling performance than the bare nano-Si anode. The Si/C composite showed the best electrochemical performance, retaining a specific capacity of 768 mA h g−1 and a Coloumbic efficiency of 99.2% after 80 cycles, with a very small initial capacity loss of 2.80% and a capacity fade of 0.48% per cycle.

Nano-Si/(multi-wall carbon nanotube) (Si/MWCNT) composite paper was prepared as flexible electrode for lithium ion batteries by a simple filtration method using sodium carboxymethyl cellulose (CMC) as a dispersing/binding agent, followed by a thermal sintering process. Scanning electron microscopy (SEM) showed that nanosized Si particles were dispersed homogeneously and intertwined by the MWCNT throughout the whole paper electrode. After thermal sintering, Si/MWCNT paper electrode exhibited a significantly improved flexibility with a high Si content of 35.6 wt% as compared with before sintering, and retained a specific capacity of 942 mAh g−1 after 30 cycles with a capacity fade of 0.46%/cycle.Nano-Si/multi-wall carbon nanotube composite paper was prepared as free-standing electrode for lithium-ion batteries by a simple filtration method using sodium carboxymethyl cellulose as a dispersing/binding agent, followed by a thermal sintering process. The prepared paper electrode exhibited a significantly improved electrochemical performance, maintaining a specific capacity of 942 mAh g−1 after 30 cycles with a capacity fade of 0.46%/cycle.

A nanostructured silicon/porous carbon spherical composite was prepared by a simple hydrothermal method using glucose as a carbon source and Pluronic F127 as a soft template/pore forming agent in the presence of silicon nanoparticles, and a subsequent carbonization process. In this composite, silicon nanoparticles were individually and separately coated with a porous carbon shell with a thickness of 15–20 nm and a pore size of 3–5 nm. The composite electrode exhibited excellent cycling stability and rate capability, delivering a stable capacity of 1607 mA h g−1 at a current density of 0.4 A g−1 after 100 cycles, and a reversible capacity of 1050 mA h g−1 even at a high current density of 10 A g−1. Detailed analysis of cyclic voltammetry and electrochemical impedance spectroscopy revealed that the composite showed favorable electrochemical kinetics due to the nano-sized porous carbon shell, which facilitated the formation of a solid electrolyte interface film and the transportation of Li ions and electrons, and decreased the charge transfer resistance, thus significantly improving the electrochemical performance compared with the bare nano-Si electrode.

We report a novel Li4Ti5−xWxO12−xBrx (x = 0.025, 0.050 and 0.100) anode material simultaneously doped with W6+ and Br− ions prepared by a simple solid-state reaction in air, aiming to significantly improve electrical conductivity of Li4Ti5O12. Our theoretical calculation predicts that codoping with W6+ on the Ti4+ site and Br− on the O2− site can remarkably narrow down the band gap, and thus facilitate the electron transport in the lattice of LTO. The comparative experiments prove that W & Br-codoped LTO exhibits higher electrical conductivity compared with undoped LTO as expected, thus leading to improved rate capability and specific capacity. Particularly, Li4Ti5−xWxO12−xBrx (x = 0.05) exhibits the best rate capability and cycling stability with an outstanding capacity retention of 88.7% even at 10 C rate after 1000 cycles. This codoping strategy with high valence transition metal and halide ions holds promise to be applied to other insulating cathode materials suffering from inferior electrical conductivity.

Nano-silicon composites, Si/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and Si/C, were prepared by an in situ chemical polymerization of 3,4-ethylenedioxythiophene (EDOT) with nano-Si particles in a PSS aqueous solution and subsequent carbonization of Si/PEDOT:PSS, respectively. The nano-Si particles were embedded in a shapeless PEDOT:PSS matrix and amorphous carbon in the corresponding composite. Energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) measurements revealed that 2.66 wt% of the element sulfur was doped in the carbon matrix for Si/C composite. Both the Si/PEDOT:PSS and Si/C composite electrodes exhibited higher initial coulombic efficiency and better cycling performance than the bare nano-Si anode. The Si/C composite showed the best electrochemical performance, retaining a specific capacity of 768 mA h g−1 and a Coloumbic efficiency of 99.2% after 80 cycles, with a very small initial capacity loss of 2.80% and a capacity fade of 0.48% per cycle.