Gel electrolyte for lithium-ion batteries

The electrochemical performance of gel electrolytes based on crosslinked poly[ethyleneoxide-co-2-(2-methoxyethyoxy)ethyl glycidyl ether-co-allyl glycidyl ether] was investigated using graphite/Li_1.1[Ni_1/3Mn_1/3Co_1/3]_0.9O₂ lithium-ion cells. It was found that the conductivity of the crosslinked gel electrolytes was as high as 5.9 mS/cm at room temperature, which is very similar to that of the conventional organic carbonate liquid electrolytes. Moreover, the capacity retention of lithium-ion cells comprising gel electrolytes was also similar to that of cells with conventional electrolytes. Despite of the high conductivity of the gel electrolytes, the rate capability of lithium-ion cells comprising gel electrolytes is inferior to that of the conventional cells. The difference was believed to be caused by the poor wettability of gel electrolytes on the electrode surfaces.     

Additives-containing functional electrolytes for suppressing electrolyte decomposition in lithium-ion batteries

Several olefinic compounds such as vinyl acetate, divinyl adipate and allyl methyl carbonate were studied as additives for propylene carbonate (PC)-based electrolytes in lithium-ion battery, which kind of electrolytes always exfoliate graphitic carbon and decompose drastically to liberate organic gas. Three kinds of graphitic carbons commonly used in lithium-ion batteries, namely, natural graphite, MCMB 6-28 and MCF were chosen to test the decomposition-suppressing ability of additives. The effects of the type of graphitic anodes and the structure of additives on the electrolyte decomposition have been investigated in the terms solid electrolyte interface (SEI) formation, which was characterized by cyclic voltammetry (CV), ac impedance, SEM, XPS analyses, and auger electron spectroscopy (AES). The electrochemical performance of the additives-containing electrolytes in combination with LiCoO₂ cathode and graphitic carbon anode was also tested in coin cells.     

Investigation on the solid electrolyte interface formed on pyrolyzed photoresist carbon anodes for C-MEMS lithium-ion batteries

Carbon-microelectromechanical systems (C-MEMS) obtained from the pyrolysis of patterned photoresists are a powerful solution for the miniaturization of energy storage/conversion devices such as fuel-cells and microbatteries. The 3D shapes and the high aspect ratio of the resulting carbon structures are critical factors in applications where specific surface area plays a key role. Furthermore, lithographic techniques used in the C-MEMS technology may solve the downscaling problems of conventional carbon manufacturing techniques. The application of C-MEMS as a lithium-ion battery anode has already been demonstrated in our previous work. It is well known that a protective film, referred to as the solid electrolyte interface (SEI), forms on carbonaceous materials used as negative electrodes in commercial lithium-ion batteries. The passivating film forms during the first battery charging cycle. Detailed SEI investigations of this film, made up of electrolyte decomposition products, have not been explored yet. In this paper the evolution of the pyrolyzed carbon/electrolyte interface functioning as a lithium-ion battery anode is studied and discussed in detail.     

LiPF6/LiBOB blend salt electrolyte for high-power lithium-ion batteries

LiPF₆/LiBOB blend salt-based electrolytes were investigated as potential candidates for high-power lithium-ion batteries, especially for transportation applications. It was demonstrated that both the power capability and the cycling performance of the lithium-ion cells could be attenuated by controlling the concentration of LiBOB in blend salt electrolytes. The power capability of the lithium-ion cells decreases with the concentration of LiBOB, while the capacity retention of the cells at 55 °C increases with the LiBOB concentration. When electrolytes with no more than 0.1 M LiBOB was used, the MCMB/LiMn_1/3Ni_1/3Co_1/3O₂ cells have excellent capacity retention at 55 °C, while their impedance meets the requirement set by the FreedomCar Partnership. The similar performance improvement on the MCMB/LiMn₂O₄ cells was also observed with the blend salt electrolyte.     

有机电解液在锂离子电池中的充放电机理

讨论了锂离子电池充放电过程中有机电解液的电化学行为,研究发现,有机电解液会在电极活性材料表面发生电化学反应而形成聚合物钝化层(SEI膜),其厚度和疏密性与电解液的组成及充放电制度有关;其组成和电化学性能还将直接影响锂离子电池的充放电容量和循环寿命。通过改变电解液的导电锂盐成分、有机溶剂组成和加入极性添加剂等方法可优化电解液的电化学特性,从而可有效控制该钝化层的成膜过程、膜组成与膜结构,提高锂离子电池的充放电及循环性能。     

Inorganic ceramic fiber separator for electrochemical and safety performance improvement of lithium-ion batteries

A separator based on ceramic fibers with excellent properties, utilized for powerful laminated lithium ion batteries, was prepared by low-cost production process. Physical and chemical characteristics of the separator and the electrochemical as well as the safety performance of lithium ion batteries were extensively investigated, and compared to commercialized polyethylene (PE) and ceramic-coating PE (C-PE) separators. The results demonstrated that inorganic ceramic fiber (CF) membrane exhibited higher porosity (85%), higher electrolyte uptake (381%) and higher ionic conductivity (1.48 mS/cm). Moreover, CF separator did not display thermal shrinkage at 160 °C for 1 h, manifesting that the separator possession of high thermal stability. The lithium nickel cobalt manganese oxide LiNi_0.5Co_0.2Mn_0.3O₂/ graphite battery employing the CF membrane displayed superior rate capability, which delivered the discharge capacities of 13.206 A h (0.2 C), 12.729 A h (0.5 C), and 12.074 A h (1 C), respectively. In addition, this battery improved cycle stability, with the capacity retention of 101.4% following 100 cycles at 1 C rate. Results of safety tests presented that batteries with CF separator passed both nail penetration and extrusion tests, implying that the safety performance was remarkably improved. Additionally, CF membrane had only 20 cents in cost for 1 Ah cells, which was ten times lower than commercial PE and C-PE separators. The perfect combination of good properties and low cost made it possible for the CF separator to be a promising separator for laminated lithium-ion batteries, which are especially used in electric vehicles.     

Current oscillations in anodic electrodissolution of copper in lithium-ion battery electrolyte

Current oscillations were observed during electrodissolution of copper in nonaqueous lithium-ion battery electrolyte under potentiostatic conditions using copper foil electrodes. Mixed-mode oscillations were observed over certain ranges of stir rate and applied potential. A nonlinear dynamics technique (return map) was applied to characterize the oscillations. The dynamic stir conditions of the electrolyte influenced the frequency and pattern of the oscillations. The amplitude of the oscillations increased with increasing potential. Also, cyclic voltammetry (CV) showed that the oscillatory current was correlated to the oxidation of the copper electrode.     

Preparation of poly(acrylonitrile-butyl acrylate) gel electrolyte for lithium-ion batteries

Poly(acrylonitrile-butyl acrylate) gel polymer electrolyte was prepared for lithium ion batteries. The preparation started with synthesis of poly(acrylonitrile-butyl acrylate) by radical emulsion polymerization, followed by phase inversion to produce microporous membrane. Then, the microporous gel polymer electrolytes (MGPEs) was prepared with the microporous membrane and LiPF₆ in ethylene carbonate/diethyl carbonate. The dry microporous membrane showed a fracture strength as high as 18.98 MPa. As-prepared gel polymer electrolytes presented ionic conductivity in excess of 3.0 × 10⁻³ S cm⁻¹ at ambient temperature and a decomposition voltage over 6.6 V. The results showed that the as-prepared gel polymer electrolytes were promising materials for Li-ion batteries.     

锂离子电池硅基负极电解液成膜添加剂的研究进展

锂离子电池是能源储存和利用的一项关键技术,能量密度已成为现代电池发展中的一个关键指标。硅基负极由于其较高的理论比容量,得到广泛关注,但硅基材料存在严重的体积膨胀问题。功能性添加剂对电池性能有明显的改善效果,是电解液体系不可缺少的部分,具有“用量小,见效快”的特点,通过成膜添加剂形成稳定的固态电解质界面（SEI）膜进而稳定电极电解液界面,改善硅基负极电池性能。本文总结了近年来硅基负极电解液成膜添加剂的研究进展,对成膜添加剂按照官能团或元素进行分类论述,并对多组分成膜添加剂的协同作用进行了简要阐述。最后,针对目前硅基负极电解液添加剂的研究现状进行了总结,并展望了未来的研究方向。     

A novel intrinsically porous separator for self-standing lithium-ion batteries

γ-LiAlO₂, Al₂O₃ and MgO were used as fillers in a PVdF-HFP polymer matrix to form self-standing, intrinsically porous separators for lithium-ion batteries. These separators can be hot-laminated onto the electrodes without losing their ability to adsorb liquid electrolyte. The electrochemical stability of the separators was tested by constructing half-cells with the configuration: Li/fibre-glass/filler-based separator/electrode. MgO-based separators were found to work well with both positive and negative electrodes. An ionic conductivity of about 4×10⁻⁴ S cm⁻¹ was calculated for the MgO-based separator containing 40% 1 M solution of LiPF₆ in an EC/DMC 1:1 solvent. Self-standing, lithium-ion cells were constructed using the MgO-based separator and the resulting battery performance evaluated in terms of cyclability, power and energy density.     

Redox shuttles for safer lithium-ion batteries

Overcharge protection is not only critical for preventing the thermal runaway of lithium-ion batteries during operation, but also important for automatic capacity balancing during battery manufacturing and repair. A redox shuttle is an electrolyte additive that can be used as intrinsic overcharge protection mechanism to enhance the safety characteristics of lithium-ion batteries. The advances on stable redox shuttles are briefly reviewed. Fundamental studies for designing stable redox shuttles are also discussed.     

Experimental and theoretical investigations on 4,5-dimethyl-[1,3]dioxol-2-one as solid electrolyte interface forming additive for lithium-ion batteries

4,5-Dimethyl-[1,3]dioxol-2-one (DMDO) was used as a novel electrolyte additive for lithium-ion batteries. The effect of DMDO on the formation of the solid electrolyte interface (SEI) on anode and cathode of MCMB/LiNi_0.8Co_0.2O₂ cells was investigated via a combination of electrochemical methods, X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations. It is found that cells with electrolyte containing 2% DMDO have better capacity retention than cells without DMDO and this improved performance is ascribed to the assistance of DMDO in forming better SEIs on anode and cathode. DMDO-decomposition products are identified experimentally on the surface of the anode and cathode and supported by theoretical calculations.     

Electrochemical behavior of carbon-coated SnS2 for use as the anode in lithium-ion batteries

Carbon-coated SnS₂ nanoparticles were prepared by a simple solvothermal route at low temperature. A carbon coating with a thickness of about 5 nm was deposited on nano-sized SnS₂ particles to serve as the anode in lithium-ion batteries. Both the nanostructure and the morphology of the SnS₂ powders were characterized by X-ray diffraction (XRD), Raman spectroscopy, and transmission electron microscopy (TEM). The coated samples were used as active anode materials for lithium-ion batteries, and their electrochemical properties were examined by constant current charge-discharge cycling, cyclic voltammetry and electrochemical impedance spectroscopy. The reversible capacity of the carbon-coated SnS₂ after 50 cycles was 668 mAh/g, which was much higher than that of the uncoated SnS₂ (293 mAh/g). The carbon-coated SnS₂ also had a better rate capability than the uncoated SnS₂ in the range of 0.008-1 C. The capacity retention of the carbon-coated SnS₂ was improved due to its good conductivity and the effective buffer matrix that alleviated volume expansion during the charge-discharge process.     

Hollow microspheres of NiO as anode materials for lithium-ion batteries

NiO hollow spheres are prepared by heating the NiCl₂/resorcinol-formaldehyde (RF) gel in argon at 700 °C for 2 h, and subsequently in oxygen at 700 °C for 2 h. X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) are employed to characterize the structure and morphology of the as-prepared NiO hollow spheres. These hollow spheres have a diameter of about 2 μm, which are composed of NiO particles of about 200 nm. The electrochemical properties of these NiO hollow spheres are investigated to determine the reversible capacity and cycling performance as anode materials for lithium-ion batteries, and the advantages of their hollow spherical morphology to the electrochemical performance are discussed.     

CuO/graphene composite as anode materials for lithium-ion batteries

CuO/graphene composite is synthesized from CuO and graphene oxide sheets following reduced by hydrazine vapor. As the electrode material for lithium-ion batteries, CuO nanoparticles with sizes of about 30 nm homogeneously locate on graphene sheets, and act as spacers to effectively prevent the agglomeration of graphene sheets, keeping their high active surface. In turn, the graphene sheets with good electrical conductivity server as a conducting network for fast electron transfer between the active materials and charge collector, as well as buffered spaces to accommodate the volume expansion/contraction during discharge/charge process. The synergetic effect is beneficial for the electrochemical performances of CuO/graphene composite, such as improved initial coulombic efficiency (68.7%) and reversible capacity of 583.5 mAh g⁻¹ with 75.5% retention of the reversible capacity after 50 cycles.     

Three-dimensional porous Sn-Cu alloy anode for lithium-ion batteries

A binder-free three-dimensional (3D) porous Cu₆Sn₅ anode was prepared for lithium-ion batteries. In this novel approach, tin was deposited by electroless-plating on copper foam which was served as anode current collector as well as the source of copper for Cu₆Sn₅ alloy formation. With optimized post-treatment condition, Cu₆Sn₅ alloy with thickness of 1.2 μm was formed on the surface of copper foam network. 3D porous Sn-Cu₆Sn₅ and Cu₃Sn-Cu₁₀Sn₃-Cu₆Sn₅ composite anodes were also prepared for comparison. Electrochemical tests showed that 3D porous Cu₆Sn₅ anode exhibits the best electrochemical performance in terms of specific capacitance and cycleability, which delivers a rechargeable capacity of 404 mAh g⁻¹ over 100 cycles.     

Synthesis of TiO2(B)/SnO2 composite materials as an anode for lithium-ion batteries

A TiO₂(B) nanosheets/SnO₂ nanoparticles composite was prepared by the hydrothermal and chemical bath deposition (CBD) methods, and its electrochemical properties were investigated for use as the anode material of a lithium-ion battery. The as-prepared composites consisted of monoclinic-phase TiO₂(B) nanosheets and cassiterite structure SnO₂ nanoparticles, in which SnO₂ nanoparticles were uniformly decorated on the TiO₂(B) nanosheets. The TiO₂(B)/SnO₂ composites showed a higher reversible capacity and better durability than that of the pure TiO₂(B) for use as a battery anode. The composite electrodes exhibiting a high initial discharge capacity of 2239.1 mAh g⁻¹ and a discharge capacity of more than 868.7 mAh g⁻¹ could be maintained after 50 cycles at 0.1 C in a voltage range of 1.0–3.0 V at room temperature. The results suggest that TiO₂(B) nanosheets coated with SnO₂ could be suitable for use as a stable anode material for lithium-ion batteries. In addition, the coulombic efficiency of the nanosheets remains at an average of 93.1% for the 3rd–50th cycles.     

离子液体作为电解液添加剂用于高压锂离子电池

合成了功能化离子液体1-丁基-3-甲基咪唑双（三氟甲磺酰）亚胺盐（BMIMTFSI）作为高压锂离子电池电解液添加剂,用于抑制有机溶剂的氧化,以提高碳酸酯类电解液的耐高压性。分别采用充放电测试、电化学交流阻抗（EIS）、循环伏安法（CV）和扫描电子显微镜（SEM）等研究了LiNi_0.5Mn_1.5O₄/Li电池的电化学行为和LiNi_0.5Mn_1.5O₄材料表面形貌。结果表明,当在电解液中添加20% （体积分数）BMIMTFSI时,LiNi_0.5Mn_1.5O₄/Li电池在室温、0.2C下的最高放电比容量是126.81 mA·h·g^-1,5C下的放电比容量为109.36 mA·h·g^-1,比在1 mol·L^-1 LiPF₆-EC/DMC电解液中的放电比容量提高了91.7%;且该电池在0.2C下循环50圈后的放电比容量保持率在95%左右,比用碳酸酯类电解液提高了近10%。SEM结果表明,在碳酸酯类电解液中加入BMIMTFSI后,LiNi_0.5Mn_1.5O₄电极表面附着了一层均匀且致密的固态电解质界面（SEI）膜。     

The effects of LiBOB additive for stable SEI formation of PP13TFSI-organic mixed electrolyte in lithium ion batteries

A safe electrolyte system is prepared from N-methyl-N-propylpiperidinium bis (trifluoromethanesulfonyl) imide (PP13TFSI), organic electrolyte (1 mol L⁻¹ LiPF₆/EC-DEC) and lithium bis (oxalato) borate (LiBOB). The additive of LiBOB enhances the stability of interface between electrolyte and anode. The LiBOB-containing mixed electrolytes show non-flammability and good compatibility with active materials. The performance of anode for lithium ion battery is successfully improved by LiBOB-containing mixed electrolytes, which shows 200 mA h g⁻¹ reversible capacities at 0.3 C rate. The ionic conductivity and the lithium ion transference number in LiBOB-containing mixed electrolytes system also suits to application for lithium ion battery.     

丁二酸酐在锂离子电池电解液中的应用

在锂离子电池电解液1 mol/L六氟磷酸锂/碳酸乙烯酯+碳酸二甲酯+碳酸甲乙酯（体积比为1∶1∶1）溶液中添加丁二酸酐作为提高电池充放电效率的添加剂。 采用恒流充放电测试、循环伏安曲线、线性伏安曲线和电化学阻抗谱等手段,研究了添加剂丁二酸酐对电解液电化学稳定窗口的影响,以及丁二酸酐与锰酸锂材料的相容性。结果表明：在电解液中添加2%（质量分数）的丁二酸酐,提高了LiMn2O4/Li电池常温和高温容量保持率。丁二酸酐可以优先于基础电解液发生少量氧化分解,从而降低了LiMn2O4/Li电池的极化。同时,丁二酸酐也可降低电池循环过程的阻抗。