高性能锂离子电池隔膜的结构设计及其制备与表征

设计并采用高压静电纺丝法制备了单层结构的聚偏氟乙烯(PVDF)/偏氟乙烯与六氟丙烯的共聚物(PVDF-HFP)纳米纤维膜及三层结构、二层结构的PVDF/PVDF-HFP/Al2O3复合纳米纤维膜.复合膜的表面形貌、热物理性质和电化学性能通过扫描电子显微镜(SEM)、示差扫描量热法(DSC)、高温尺寸收缩率、交流阻抗法进行了表征.单层结构的PVDF/PVDF-HFP纳米纤维膜的纤维表面光滑,平均纤维直径2μm,纤维分布较均匀,而PVDF与Al2O3复合后的纤维表面粗糙,平均纤维直径变小,结晶度降低,吸液率增大.二层结构的PVDF/PVDF-HFP/Al2O3复合隔膜在170℃下受热1 h收缩率为3%.将3种结构的复合膜在1 mol/L Li PF6/(EC+DMC+DEC,1∶1∶1,W/W/W)电解质溶液中活化得到聚合物电解质.25℃时,二层结构的PVDF/PVDF-HFP/Al2O3复合隔膜吸液率高达497 wt%,离子电导率可达5.04×10-3S/cm,电化学稳定窗口达到4.62 V(Li/Li+).组装成Li Fe PO4/Li电池测试其电池性能,结果表明,二层结构的PVDF/PVDF-HFP/Al2O3复合膜朝向锂负极时,电池的循环性能更好,且与锂金属负极具有更好的相容性和界面稳定性.     

相转化法制备陶瓷涂层改性锂离子电池隔膜

以聚乙烯（PE）隔膜为基底，涂覆聚偏氟乙烯（PVDF）和纳米氧化铝（nanoAl2O2），通过相转化的方法形成多孔陶瓷涂层，以改善聚乙烯隔膜对电解液的润湿能力、吸液能力及其热稳定性和电化学稳定性。结果表明：当涂层溶液中ω（PVDF）-0．15，72）（nano—Al2O2）-0．3时，改性隔膜的吸液率比纯PE隔膜提高了211．5％，水接触角降低了41．3°，热分解温度和电化学稳定窗口分别提高了73．4℃和0．2V。电池的容量保持率达到96．17％，而纯PE隔膜的只有85．78％。改性后隔膜的润湿能力、稳定性、安全性以及循环性能都有较大程度的提高。     

天然橡胶/丁苯橡胶基隔膜材料的制备与性能

采用相转换法制备出了以天然橡胶(NR)/丁苯橡胶(SBR)为基的多孔状聚合物锂离子电池隔膜材料,系统研究了成膜的工艺参数及机理.利用扫描电镜(SEM)和原子力显微镜(AFM)观察了该聚合物隔膜的微观结构,同时考察了该聚合物膜的吸液保液能力、热稳定性及电化学性能.结果表明,该聚合物膜呈多孔蜂窝状,具有较高的吸液能力,在电解液中浸泡5h后的吸液率达320%,此时该聚合物多孔隔膜的室温电导率也达到了3.93×10-4S/cm;并且保液能力良好,在50℃的空气中保持5h的质量损失仅为31%.同时该聚合物多孔膜具有较宽的电化学稳定窗口和较高的热分解温度,在4.8V和157℃以下能安全使用.与金属锂电极间的界面阻抗在存放10天或经过20次循环伏安扫描内迅速增加,而后趋于稳定,表现出了良好的界面稳定性,有效地抑制了电极与隔膜间的钝化膜(SEI)的进一步生长.     

甲基丙烯酸甲酯在聚偏氟乙烯膜上的辐照接枝

采用电子加速器(EB)预辐照接枝的方法,在聚偏氟乙烯(PVDF)膜上接枝甲基丙烯酸甲酯(MMA),制备了PVDF-g-PMMA膜。研究了辐照剂量、单体浓度、反应温度、反应时间以及溶剂等因素对接枝率的影响规律。结果表明,接枝率随辐照剂量的增大而增加;反应初期接枝率随着单体质量分数的增大迅速增加,当单体质量分数达40%时,增加缓慢;单体质量分数达70%时,接枝率最高;从40℃开始接枝率缓慢上升,至60℃时陡增,之后接枝率基本不变;醇类是接枝反应很好的溶剂。用FT-IR、DSC分析了接枝物的组成及热性能。接枝膜成分为PVDF-g-PMMA共聚物,接枝膜在117℃处出现Tg峰,随着接枝率的增加该峰越来越明显,说明发生了接枝反应。随着接枝率的增加,熔融峰左移并最终消失,说明PMMA的接枝破坏了原PVDF膜的结晶性。吸液率随着浸泡时间的增加而增大,PVDF接枝膜达到的最大吸液率为290%,所需要的时间比原PVDF膜长。接枝率为50%的PVDF膜的离子电导率为6.0×10-3S/cm,吸液率达290%,MMA的接枝改善了PVDF电解质膜的电学性能。     

锂硫电池硫正极粘结剂的比较研究

本文将三类粘结剂体系(PVDF、LA133和CMC+SBR)用于构筑锂硫电池硫正极,表征了不同粘结剂材料的官能团结构、结晶性能、热力学性质、电解液吸收性与粘结强度,考察了粘结剂种类对电极电化学性能的影响。结果表明,由1∶1质量比的CMC+SBR制作的硫电极吸液率低,剥离强度低,循环稳定性较差;无定形LA133支持高的粘结强度,维稳电极结构的能力强;PVDF因半结晶状态制约粘结效果,制作的电极吸液量高,但电荷转移阻抗小。基于PVDF制作的硫正极具有相对最优的电化学性能,其0.2C下循环100周后保留的可逆容量达722mAh·g~(-1),容量保持率达82.9%。     

基于静电纺丝和静电喷射技术的P(VDF-HFP)/Al_2O_3/P(VDF-HFP)复合隔膜的制备与电化学性能分析（英文）

通过静电纺丝和静电喷射技术,将三氧化二铝(Al_2O_3)纳米颗粒沉积在两层聚四氟乙烯六氟丙烯[P(VDF-HFP)]静电纺丝隔膜之间,制备出了具有"三明治"结构的P(VDF-HFP)/Al_2O_3/P(VDF-HFP)复合锂离子电池隔膜.分析了隔膜的形态结构、热收缩性能、拉伸性能、电化学性能以及隔膜在电池中的循环性能.测试结果表明,该复合隔膜比纯P(Vd F-HFP)膜拥有更高的吸液率,隔膜更容易吸收电解液从而形成凝胶聚合物电解质(GPEs).该复合隔膜的拉伸强度在4 MPa左右,相对应的断裂伸长率为261.57%.复合隔膜在室温下的离子电导率为1.61×10~(-3)S/cm,且表现出了较高的电化学稳定性(电化学稳定窗口达到5.4 V).在电池的循环测试中,使用钴酸锂(LiCoCO_2)作为正极材料,由该复合隔膜组装的电池的首次放电比容量达到了理想的水平,为145 m A·h·g~(-1).     

原位生成二氧化钛对静电纺聚偏氟乙烯锂离子电池隔膜力学性能及电化学性能的影响

通过钛酸丁酯(TBTi)在聚偏氟乙烯(PVDF)溶液中水解原位生成二氧化钛(TiO2),采用静电纺丝方法制备了PVDF/TiO2复合隔膜,并考察了TiO2含量对隔膜表面形貌、热学性能、力学性能及聚合物电解质电化学性能的影响.结果表明,隔膜的拉伸强度和断裂伸长率由于TiO2的加入得到显著提高,最大增幅分别达到228.6％和244.8％,同时聚合物电解质的电化学性能也得到了增强,室温离子电导率从3.9 mS/cm增加到5.1 mS/cm.     

甲基丙烯酸类聚合物修饰的聚乙烯隔膜在锂离子电池中的应用

将环状碳酸酯基团引入到聚甲基丙烯酸甲酯(PMMA)侧链上, 制备了聚(2,3-环碳酸甘油酯)甲基丙烯酸酯(PDOMMA), 并用其修饰锂离子电池聚乙烯隔膜. 通过热重分析、 差示扫描量热分析及接触角和吸液率测试等研究了PDOMMA的热稳定性及其修饰的聚乙烯隔膜对电解液的浸润性和吸液率的影响, 并通过恒流充放电、 交流阻抗、 倍率性能测试及扫描电子显微镜观测等研究了修饰隔膜对锂离子电池性能的影响. 结果表明, 与未修饰隔膜相比, 修饰隔膜对电解液浸润性更优异(20 s内便完全浸润), 吸液率更高(440%), 电池循环性能更好(放电比容量提高了12.3%).     

基于静电纺丝和静电喷射技术的P(VDF-HFP)/Al2O3/P(VDF-HFP)复合隔膜的制备与电化学性能分析

通过静电纺丝和静电喷射技术, 将三氧化二铝(Al₂O₃)纳米颗粒沉积在两层聚四氟乙烯六氟丙烯[P(VDF-HFP)]静电纺丝隔膜之间, 制备出了具有“三明治”结构的P(VDF-HFP)/Al₂O₃/P(VDF-HFP)复合锂离子电池隔膜. 分析了隔膜的形态结构、 热收缩性能、 拉伸性能、 电化学性能以及隔膜在电池中的循环性能. 测试结果表明, 该复合隔膜比纯P(VdF-HFP)膜拥有更高的吸液率, 隔膜更容易吸收电解液从而形成凝胶聚合物电解质(GPEs). 该复合隔膜的拉伸强度在4 MPa左右, 相对应的断裂伸长率为261.57%. 复合隔膜在室温下的离子电导率为1.61×10^-3 S/cm, 且表现出了较高的电化学稳定性(电化学稳定窗口达到5.4 V). 在电池的循环测试中, 使用钴酸锂(LiCoCO₂)作为正极材料, 由该复合隔膜组装的电池的首次放电比容量达到了理想的水平, 为145 mA·h·g^-1.     

隔膜对BMImBF_4离子液体电解液中镁沉积-溶出性能的影响

研究了实验扣式电池中Celgard2400,Celgard2500,ENTEK ET20-60,TEKLON UH2054以及一种玻璃纤维隔膜对含有0.5mol·L-1Mg(CF3SO3)2的BMImBF4离子液体电解液中镁的电化学沉积-溶出性能的影响.通过扫描电镜对五种隔膜的表面形貌进行了分析,吸液实验比较了不同隔膜对Mg(CF3SO3)2/BMImBF4离子液体电解液的吸液性能,交流阻抗技术测定了隔膜的电导率,恒电流充放电测试研究了扣式电池中镁的沉积-溶出性能.在这五种隔膜中,虽然玻璃纤维隔膜的机械强度较差,但该材料对Mg(CF3SO3)2/BMImBF4离子液体电解液有较好的吸液性和液体保持性,特别是具有高的离子电导率,有利于大电流下镁的沉积-溶出.     

Fabrication and characterization of SiO2/PVDF composite nanofiber‐coated PP nonwoven separators for lithium‐ion batteries

SiO₂/polyvinylidene fluoride (PVDF) composite nanofiber‐coated polypropylene (PP) nonwoven membranes were prepared by electrospinning of SiO₂/PVDF dispersions onto both sides of PP nonwovens. The goal of this study was to combine the good mechanical strength of PP nonwoven with the excellent electrochemical properties of SiO₂/PVDF composite nanofibers to obtain a new high‐performance separator. It was found that the addition of SiO₂ nanoparticles played an important role in improving the overall performance of these nanofiber‐coated nonwoven membranes. Among the membranes with various SiO₂ contents, 15% SiO₂/PVDF composite nanofiber‐coated PP nonwoven membranes provided the highest ionic conductivity of 2.6 × 10^?3 S cm^?1 after being immersed in a liquid electrolyte, 1 mol L^?1 lithium hexafluorophosphate in ethylene carbonate, dimethyl carbonate and diethyl carbonate. Compared with pure PVDF nanofiber‐coated PP nonwoven membranes, SiO₂/PVDF composite fiber‐coated PP nonwoven membranes had greater liquid electrolyte uptake, higher electrochemical oxidation limit, and lower interfacial resistance with lithium. SiO₂/PVDF composite fiber‐coated PP nonwoven membrane separators were assembled into lithium/lithium iron phosphate cells and demonstrated high cell capacities and good cycling performance at room temperature. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 1719–1726     

Talcum-doped composite separator with superior wettability and heatproof properties for high-rate lithium metal batteries

Separator is supposed to own outstanding thermal stability, superior wettability and electrolyte uptake,which is essential for developing high-rate and safe lithium metal batteries(LMBs). However, commercial polyolefin separators possess poor wettability and limited electrolyte uptake. For addressing this issue, we put forward a composite separator to implement above functions by doping layered-silicate(talcum) into polyvinylidene fluoride(PVDF). With significant improvement of electrolyte absor...     

Study of Carbamate‐Modified Disiloxane in Porous PVDF‐HFP Membranes: New Electrolytes/Separators for Lithium‐Ion Batteries

A gel electrolyte membrane is obtained through the absorption of a carbamate‐modified liquid disiloxane‐containing lithium bis(trifluoromethane)sulfonimide (LiTFSI) by using macroporous poly(vinylidene fluoride–hexafluoropropylene) (PVDF‐HFP) membranes. The porous membranes are prepared by means of a phase inversion technique. The resulting gel electrolyte membrane is studied by using differential scanning calorimetry, Fourier‐transform infrared (FTIR) spectroscopy, and microscope mapping through coherent anti‐Stokes Raman scattering (CARS) confocal microscopy and impedance spectroscopy. The ionic conductivity of the gel electrolyte is 10^?4 S cm^?1 at 20 °C. FTIR spectroscopy reveals interactions between LiTFSI and the carbonyl moiety of the disiloxane. No interactions between LiTFSI and PVDF‐HFP or between disiloxane and PVDF‐HFP are detected by FTIR spectroscopy. Furthermore, the distribution of the α and β/γ phases of PVDF‐HFP and the homogeneous distribution of disiloxane/LiTFSI in the gel electrolyte membranes are examined by FTIR mapping. CARS confocal microscopy is used to image the three‐dimensional interconnectivity, which reveals a reticulated structure of macrovoids in the porous PVDF‐HFP framework. Owing to properties such as electrochemical and thermal stability of the disiloxane‐based liquid electrolyte and the mechanical stability of the porous PVDF‐HFP membrane, the gel electrolyte membranes presented herein are promising candidates for applications as electrolytes/separators in lithium‐ion batteries.     

Poly(vinylidene fluoride) separators with dual-asymmetric structure for high-performance lithium ion batteries

Dual-asymmetric poly(vinylidene fluoride)(PVDF) separators have been fabricated by thermally induced phase separation with dimethyl sulfone(DMSO2) and glycerol as mixed diluents. The separators have a porous bulk with large interconnected pores(~1.0 μm) and two surfaces with small pores(~30 nm). This dual-asymmetric porous structure endows the separators with higher electrolyte uptake amount and rapider uptake rate, as well as better electrolyte retention ability than the commercialized Celgard 2400. The separators even maintain their dimensional stability up to 160 °C, at which temperature the surface pores close up, leading to a dramatic decrease of air permeability. The electrolyte filled separators also show high ion conductivity(1.72 m S?cm―1) at room temperature. Lithium iron phosphate(Li Fe PO4)/lithium(Li) cells using these separators display superior discharge capacity and better rate performance as compared with those from the commercialized ones. The results provide new insight into the design and development of separators for high-performance lithium ion batteries with enhanced safety.     

Separator technologies for lithium-ion batteries

Although separators do not participate in the electrochemical reactions in a lithium-ion (Li-ion) battery, they perform the critical functions of physically separating the positive and negative electrodes while permitting the free flow of lithium ions through the liquid electrolyte that fill in their open porous structure. Separators for liquid electrolyte Li-ion batteries can be classified into porous polymeric membranes, nonwoven mats, and composite separators. Porous membranes are most commonly used due to their relatively low processing cost and good mechanical properties. Although not widely used in Li-ion batteries, nonwoven mats have the potential for low cost and thermally stable separators. Recent composite separators have attracted much attention, however, as they offer excellent thermal stability and wettability by the nonaqueous electrolyte. The present paper (1) presents an overview of separator characterization techniques, (2) reviews existing technologies for producing different types of separators, and (3) discusses directions for future investigation. Research into separator fabrication techniques and chemical modifications, coupled with the numerical modeling, should lead to further improvements in the performance and abuse tolerance as well as cost reduction of Li-ion batteries.     

A multilayer composite separator consisting of non-woven mats and ceramic particles for use in lithium ion batteries

Battery separator is a porous membrane that is placed between the positive and negative electrodes to avoid their electric contact, while maintaining a good ionic flow through the liquid electrolyte filled in its pores. Non-woven mats have been evaluated as battery separators due to their highly porous structures. In this study, composite non-woven mats were fabricated through electrospinning and lamination with a ceramic layer, and evaluated as lithium ion battery separators. The lamination with the ceramic layer provides not only improved separator dimensional stability at elevated temperatures but also the potential to increase the production rate of electrospun separators. The electrospun mats keep ceramic particles from dropping avoiding the non-uniform current density distribution caused by the loss of the ceramic particles. The composite separators enabled good ionic conductivity when saturated with a liquid electrolyte. Coin cells with this type of separators showed not only stable cycling performance but also good rate capabilities at room temperature.     

PVDF/PAN/SiO<Subscript>2</Subscript> polymer electrolyte membrane prepared by combination of phase inversion and chemical reaction method for lithium ion batteries

PVDF/PAN/SiO₂ polymer electrolyte membranes based on non-woven fabrics were prepared via introducing a chemical reaction into Loeb-Sourirajan (L-S) phase inversion process. It was found that physical properties (porosity, electrolyte uptake and ionic conductivity) and electrochemical properties were obviously improved. A favorable membrane structure with fully connective porous and uniform pore size distribution was obtained. The effects of PVDF/PAN weight ratio on the morphology, crystallinity, porosity, and electrochemical performances of membranes were studied. The optimized PVDF/PAN (70/30 w/w) (designated as M_pc30) polymer electrolyte membrane delivered excellent electrolyte uptake of 246.8 % and the highest ionic conductivity of 3.32 × 10^?3 S/cm with electrochemical stability up to 5.0 V (vs. Li/Li⁺). In terms of cell performance, the Li/M_pc30 polymer electrolyte/LiFePO₄ battery exhibited satisfactory electrochemical properties including high discharge capacity of 149 mAh/g at 0.2 C rate and good discharge performance at different current densities. The promising results reported here clearly indicated that PVDF/PAN/SiO₂ polymer electrolyte membranes prepared by the combination of phase inversion and chemical reaction method were promising enough to be applied in power lithium ion batteries.     

Rational Design of Cellulose Nanofibrils Separator for Sodium-Ion Batteries

Cellulose nanofibrils (CNF) with high thermal stability and excellent electrolyte wettability attracted tremendous attention as a promising separator for the emerging sodium-ion batteries. The pore structure of the separator plays a vital role in electrochemical performance. CNF separators are assembled using the bottom-up approach in this study, and the pore structure is carefully controlled through film-forming techniques. The acid-treated separators prepared from the solvent exchange and freeze-drying demonstrated an optimal pore structure with a high electrolyte uptake rate (978.8%) and Na⁺ transference number (0.88). Consequently, the obtained separator showed a reversible specific capacity of 320 mAh/g and enhanced cycling performance at high rates compared to the commercial glass fiber separator (290 mAh/g). The results highlight that CNF separators with an optimized pore structure are advisable for sodium-ion batteries.     

Recent Progress in High-Performance Lithium Sulfur Batteries: The Emerging Strategies for Advanced Separators/Electrolytes Based on Nanomaterials and Corresponding Interfaces

Lithium-sulfur (Li−S) batteries, possessing excellent theoretical capacities, low cost and nontoxicity, are one of the most promising energy storage battery systems. However, poor conductivity of elemental S and the “shuttle effect” of lithium polysulfides hinder the commercialization of Li−S batteries. These problems are closely related to the interface problems between the cathodes, separators/electrolytes and anodes. The review focuses on interface issues for advanced separators/electrolytes based on nanomaterials in Li−S batteries. In the liquid electrolyte systems, electrolytes/separators and electrodes system can be decorated by nano materials coating for separators and electrospinning nanofiber separators. And, interface of anodes and electrolytes/separators can be modified by nano surface coating, nano composite metal lithium and lithium nano alloy, while the interface between cathodes and electrolytes/separators is designed by nano metal sulfide, nanocarbon-based and other nano materials. In all solid-state electrolyte systems, the focus is to increase the ionic conductivity of the solid electrolytes and reduce the resistance in the cathode/polymer electrolyte and Li/electrolyte interfaces through using nanomaterials. The basic mechanism of these interface problems and the corresponding electrochemical performance are discussed. Based on the most critical factors of the interfaces, we provide some insights on nanomaterials in high-performance liquid or state Li−S batteries in the future.