Lithium-ion battery separators: Recent developments and state of art

Lithium-ion battery separators are receiving increased consideration from the scientific community. Single-layer and multilayer separators are well-established technologies, and the materials used span from polyolefins to blends and composites of fluorinated polymers. The addition of ceramic nanoparticles and separator coatings improves thermal and mechanical properties, as well as electrolyte uptake and ionic conductivity. The state-of-art separators are actively involved in the cell chemistry through specific functional groups on their surface. Among the numerous properties, safety features and long cycle life are high-priority requirements for next-generation lithium-ion batteries.     

锂离子二次电池用隔膜的制备及其性质

本文采用倒相法制备了锂离子二次电池用的PVDF HFP共聚物型多孔聚合物隔膜 ,该聚合物膜具有良好的机械性能 ,其孔隙率可达 75% ,吸附电解液后增重 4 50 % ,电导率为 10 - 3S/cm ,组装成电池后表现出良好的循环性能和较低的极化率     

A roadmap of battery separator development: Past and future

The battery separator is one of the most essential components that highly affect the electrochemical stability and performance in lithium-ion batteries. In order to keep up with a nationwide trend and needs in the battery society, the role of battery separators starts to change from passive to active. Many efforts have been devoted to developing new types of battery separators by tailoring the separator chemistry. In this article, the overall characteristics of battery separators with different structures and compositions are reviewed. In addition, the research directions and prospects of separator engineering are suggested to provide a solid guideline for developing a safe and reliable battery system.     

Recent Development of Polyolefin‐Based Microporous Separators for Li−Ion Batteries: A Review

Secondary Li?ion batteries have been paid attention to wide‐range applications of power source for the portable electronics, electric vehicle, and electric storage reservoir. Generally, lithium‐ion batteries are comprised of four components including anode, cathode, electrolyte and separator. Although separators do not take part in the electrochemical reactions in a lithium‐ion (Li?ion) battery, they conduct the critical functions of physically separating the positive and negative electrodes to prevent electrical short circuit while permitting the free flow of lithium ions through the liquid electrolyte that fill in their open porous structure. Hence, the separator is directly related to the safety and the power performance of the battery. Among a number of separators developed thus far, polyethylene (PE) and polypropylene (PP) porous membrane separators have been the most dominant ones for commercial Li?ion batteries over the decades because of their superior properties such as cost‐efficiency, good mechanical strength and pore structure, electrochemical stability, and thermal shutdown properties. However, there are main issues for vehicular storage, such as nonpolarity, low surface energy and poor thermal stability, although the polyolefin separators have proven dependable in portable applications. Hence, in this review, we decide to provide an overview of the types of polyolefin microporous separators utilized in Li?ion batteries and the methods employed to modify their surface in detail. The remarkable results demonstrate that extraordinary properties can be exhibited by mono‐ and multilayer polyolefin separators if they are modified using suitable methods and materials.     

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.     

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...     

锂电隔膜研究及产业技术进展

隔膜是锂离子电池的关键材料,在极片间起绝缘和提供离子通道的作用.本文以如何构建耐高温的隔膜、如何提高隔膜的离子电导率为重点,介绍了锂电隔膜研究及产业化技术进展,内容主要包括隔膜性能的影响因素、凝胶聚合物电解质膜、拉伸法制备隔膜及其改性、隔膜制造的新方法和新材料.最后展望了隔膜的发展前景.     

金属锂电池的热失控与安全性研究进展

锂离子电池在便携式储能器件及电动汽车领域得到了广泛应用,然而频繁发生的电池起火爆炸事故,使热失控和热安全问题备受人们关注,目前已有多篇综述报道了缓解锂离子电池热失控的措施。相比于已经接近理论比能极限的锂离子电池,金属锂负极具有更高的比容量、更低的电势和高反应活性,但是不可控的锂枝晶生长,使得金属锂电池的热失控问题更为复杂和严重。针对金属锂电池的热失控问题,本文首先介绍了热失控的诱因及基本过程和阶段,其次从材料层面综述了提高电池热安全性的多种策略,包括使用阻燃性电解质、离子液体电解质、高浓电解质和局域高浓电解质等不易燃液态电解质体系,开发高热稳定性隔膜、热响应隔膜、阻燃性隔膜和具有枝晶检测预警与枝晶消除功能的新型智能隔膜,以及研究热响应聚合物电解质,最后对金属锂电池热失控在未来的进一步研究进行了展望。     

锂离子电池隔膜的功能化改性及表征技术

随着锂离子电池在动力和规模化储能等新能源领域应用的不断拓展,具有特殊功能且满足特定使用需求隔膜的设计准则、制备/改性方法及表征技术亟需系统深入研究。针对锂离子电池高性能和高安全性的要求,研究人员已通过结构设计和表面化学改性等策略优化了隔膜的本征特性,并通过系列表征技术探讨了隔膜的功能化改性对锂离子电池电化学性能的影响。基于以上背景,本文从离子传输、枝晶形核与生长、及安全性能三个方面详细探讨了隔膜对电池性能影响的关键因素及其改性方法,并系统总结了隔膜结构、物化特性、力学性能、热学性能以及电化学性能的表征技术,以期为功能隔膜的合理设计,从而优化锂离子电池性能提供理论和实践指导。同时,本文对隔膜未来的进一步研究和发展提出了展望。     

纤维素微孔锂电隔膜的制备及性能研究

为了改善锂电隔膜的亲液性和耐高温性,以醋酸纤维素为成膜材料,利用相转化法制备了新型锂电隔膜,通过形貌和孔道结构表征、亲液性能和耐热性能测试对醋酸纤维素隔膜的基本性能进行研究,并将该隔膜装配成锂离子电池进行充放电性能测试. 结果表明,醋酸纤维素隔膜具有均匀的微孔结构,孔隙率达到65%,约为传统聚烯烃隔膜的1.5倍;纤维素材料的良好亲液性和高孔隙率结构改善了隔膜的吸液性能,其吸液率达到285%;该隔膜在150 ^oC、30 min的热处理条件下未发生明显的热收缩. 鉴于上述优点,相对于市售PE隔膜,醋酸纤维素隔膜所装配锂离子电池显示出更优的循环性能和倍率性能.     

锂硫电池多功能涂层隔膜的研究进展与展望

先进储能系统的开发对于满足电动汽车、便携式设备和可再生能源存储不断增长的需求至关重要. 锂硫（Li-S）电池具有比能量高、原材料成本低和环境友好等优点,是新型高性能电池研究领域中的热点. 然而,锂硫电池面向实际应用还存在许多问题,如可溶性多硫化物中间体的穿梭效应、锂枝晶生长以及锂硫电池在使用过程中的热稳定性和安全性等. 设计开发多功能涂层隔膜是改善锂硫电池上述不足的有效策略之一,在本综述中,详细论述了锂硫电池多功能涂层隔膜的研究进展. 包括聚合物材料、碳材料、氧化物材料、催化纳米粒子改性的功能化涂层隔膜及增强电池热稳定性、安全性的特种功能隔膜,对其作用特性进行了系统分析,并对未来研究发展提出展望.     

An enhanced poly(vinylidene fluoride) matrix separator with TEOS for good performance lithium-ion batteries

The low crystallinity poly(vinylidene fluoride)/tetraethyl orthosilicate silane (PVDF/TEOS) composite separator with a finger-like pore structure for lithium-ion battery has been successfully prepared by non-solvent-induced phase separation (NIPS) technique. The PVDF/TEOS composite separator shows the excellent wettability and electrolyte retention properties compared with Celgard 2320 separator. AC impedance spectroscopy results indicate that the novel PVDF/TEOS composite separator has ion conductivity of 1.22 mS cm⁻¹ at 25 °C, higher than that of Celgard 2320 separator (0.88 mS cm⁻¹). The lithium-ion transference number of PVDF composite separator added 0.7% TEOS was 0.481, better than that of Celgard 2400 (0.332). What is more, the lithium-ion batteries assembled with PVDF/TEOS composite separator show good cycling performance and rate capability.

     

A novel sandwiched membrane as polymer electrolyte for lithium ion battery

A novel kind of sandwiched polymer membrane was prepared by coating three layers of poly(vinyl difluoride) (PVDF), poly(methyl methacrylate) (PMMA) and PVDF, separately. Its characteristics were investigated by scanning electron microscopy, FT-IR, X-ray diffraction, and differential thermal analysis. It consists of two phases. The outer PVDF layers are porous, and the inner PMMA layer is solid. Since the PMMA has a good compatibility with the carbonate-based liquid electrolyte, the membrane can easily absorb the electrolyte to form a gelled polymer electrolyte (GPE). As a result, the evaporation peak of the liquid electrolyte is increased to 160 °C. Due to very low evaporation of the liquid electrolyte, LiCoO₂ shows good cycling behavior in the range of 4.4–3.0 V when this GPE is used as the separator and polymer electrolyte, and lithium as the counter and reference electrode. This unique sandwiched membrane is promising for application in scale-up lithium ion batteries with high safety and high energy density.     

A Review on Lithium-Ion Battery Separators towards Enhanced Safety Performances and Modelling Approaches

In recent years, the applications of lithium-ion batteries have emerged promptly owing to its widespread use in portable electronics and electric vehicles. Nevertheless, the safety of the battery systems has always been a global concern for the end-users. The separator is an indispensable part of lithium-ion batteries since it functions as a physical barrier for the electrode as well as an electrolyte reservoir for ionic transport. The properties of separators have direct influences on the performance of lithium-ion batteries, therefore the separators play an important role in the battery safety issue. With the rapid developments of applied materials, there have been extensive efforts to utilize these new materials as battery separators with enhanced electrical, fire, and explosion prevention performances. In this review, we aim to deliver an overview of recent advancements in numerical models on battery separators. Moreover, we summarize the physical properties of separators and benchmark selective key performance indicators. A broad picture of recent simulation studies on separators is given and a brief outlook for the future directions is also proposed.     

An enhanced poly(vinylidene fluoride) matrix separator with high density polyethylene for good performance lithium ion batteries

A sponge-like poly(vinylidene fluoride)/high density polyethylene (PVDF/HDPE) separator exhibiting high ionic conductivity and transference number of Li⁺ ion for lithium ion battery has been prepared by non-solvent induced phase separation (NIPS) method. HDPE fillers with size smaller than 250 nm are prepared with moderated reverse phase emulsion. The ion conductivity of PVDF/HDPE separator saturated with 1.0 M LiPF₆–ethylene carbonate (EC)/dimethyl carbonate (DMC)/ethyl methyl carbonate (EMC) (1:1:1, v/v/v) can be up to 2.54 mS cm^?1 at 25 °C, which is higher than that of pristine PVDF separator (1.85 mS cm^?1). The transference number of lithium ion with PVDF/HDPE separator is 0.495, better than that with commercial PP separator (0.33) and pristine PVDF separator (0.27). What is more, LiCoO₂/Li cells assembled with PVDF/HDPE separator show good C-rate and cycling performance which indicates great potential in serving as a good candidate of polymer separator for lithium ion batteries application.     

Polyolefin‐Based Janus Separator for Rechargeable Sodium Batteries

Rechargeable sodium batteries are a promising technology for low‐cost energy storage. However, the undesirable drawbacks originating from the use of glass fiber membrane separators have long been overlooked. A versatile grafting–filtering strategy was developed to controllably tune commercial polyolefin separators for sodium batteries. The as‐developed Janus separators contain a single–ion‐conducting polymer‐grafted side and a functional low‐dimensional material coated side. When employed in room‐temperature sodium–sulfur batteries, the poly(1‐[3‐(methacryloyloxy)propylsulfonyl]‐1‐(trifluoromethanesulfonyl)imide sodium)‐grafted side effectively enhances the electrolyte wettability, and inhibits polysulfide diffusion and sodium dendrite growth. Moreover, a titanium‐deficient nitrogen‐containing MXene‐coated side electrocatalytically improved the polysulfide conversion kinetics. The as‐developed batteries demonstrate high capacity and extended cycling life with lean electrolyte loading.     

高性能锂离子电池正极黏合剂研究进展

正极黏合剂是维持锂离子电池正极结构稳定性的关键材料,对于锂离子电池的能量密度及安全性具有重要作用.本文综述了锂离子电池正极黏合剂材料的研究及应用进展,重点介绍了锂离子电池正极黏合剂对于正极材料及锂离子电池电化学性能的影响,详细总结了以聚偏氟乙烯(PVDF)、聚酰亚胺(PI)、功能性聚合物黏合剂为代表的油溶性黏合剂和以聚丙烯酸(PAA)、羧甲基纤维素(CMC)为代表的水溶性黏合剂的特点:PVDF具备良好的化学稳定性,黏合效果较好,但耐高温性能差且在电解液中易溶胀;PI的耐高温性能优异,机械性能较好,但成本相对较高;功能性聚合物黏合剂具备良好的导电性,可有效抑制Li-S锂电池中多硫化物的穿梭效应,但制备工艺复杂;PAA的柔性较好,抗高压能力较强,但是力学性能较差;CMC具有良好的分散性,机械强度较大,因脆性较大需与丁苯橡胶(SBR)配合使用.结合已有的研究报道,探讨了高性能锂离子电池先进正极黏合剂材料的未来发展方向及前景.     

锂离子电池凝胶聚合物隔膜的研究进展

作为锂离子电池重要组分,隔膜由多孔聚烯烃高分子材料组成;电解质体系由有机碳酸酯和六氟磷酸锂混合组成,虽具有高离子电导率,但因液态碳酸酯的易燃特性给锂离子电池带来了安全隐患。利用能够将液态电解质体系凝胶化的聚合物制备得到的凝胶聚合物隔膜,结合了液态电解质体系高电导率和固态电解质高安全性的优点。凝胶聚合物隔膜的研究从简单微孔凝胶聚合物隔膜开始,经历了引入少量纳米无机颗粒的掺杂凝胶聚合物隔膜,到引入大量纳米颗粒的凝胶陶瓷隔膜的发展历程。本文详细介绍这三种类型凝胶聚合物隔膜的物理化学特性,最后展望凝胶聚合物隔膜的发展趋势。     

Experimental and molecular simulating study on promoting electrolyte-immersed mechanical properties of cellulose/lignin separator for lithium-ion battery

Lithium-ion batteries have been developing intensively and earn an unprecedented reputation, yet advanced performance and safety issue still require considerable investigation. Separator is vital to comprehensive properties of batteries, where the mechanical properties are key to breaking through of new-type separator. Unfortunately, electrolyte submersion has caused damage to strength of cellulose separator. Whereupon, in this work, cellulose separator is optimized by introducing lignin particles to promote electrolyte-immersed mechanical strength. Experiments are conducted concerning surface morphology, contact angle, porosity, electrolyte uptake, mechanical properties and electrochemical performance. Molecular simulation is implemented to explore the mechanism of tensile behavior of cellulose and lignin subjected to electrolyte solvents. Experimental results confirm positive effect of lignin addition in improving mechanical properties and simultaneously maintaining impressive electrochemical performance of the cellulose/lignin composites separators. Besides, lignin addition amount of 2.5% and 5% is recommended to achieve promising overall properties. Molecular simulation has successfully unveiled that weakening of cellulose separator submerged in electrolyte is resulted by the deformed cellulose amorphous region and the promoting effect of adding lignin is contributed from the new hydrogen bonds generated between cellulose and lignin molecules. Hopefully, this work provides novel insight on preparing remarkable separator and mechanism of materials behavior.     

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.