Nanoparticle-coated separators for lithium-ion batteries with advanced electrochemical performance

We report a simple, scalable approach to improve the interfacial characteristics and, thereby, the performance of commonly used polyolefin based battery separators. The nanoparticle-coated separators are synthesized by first plasma treating the membrane in oxygen to create surface anchoring groups followed by immersion into a dispersion of positively charged SiO(2) nanoparticles. The process leads to nanoparticles electrostatically adsorbed not only onto the exterior of the surface but also inside the pores of the membrane. The thickness and depth of the coatings can be fine-tuned by controlling the ζ-potential of the nanoparticles. The membranes show improved wetting to common battery electrolytes such as propylene carbonate. Cells based on the nanoparticle-coated membranes are operable even in a simple mixture of EC/PC. In contrast, an identical cell based on the pristine, untreated membrane fails to be charged even after addition of a surfactant to improve electrolyte wetting. When evaluated in a Li-ion cell using an EC/PC/DEC/VC electrolyte mixture, the nanoparticle-coated separator retains 92% of its charge capacity after 100 cycles compared to 80 and 77% for the plasma only treated and pristine membrane, respectively.     

Rational design on separators and liquid electrolytes for safer lithium-ion batteries

As the energy density of lithium-ion batteries (LIBs) continues to increase,their safety has become a great concern for further practical large-scale applications.One of the ultimate solution of the safety issue is to develop intrinsically safe battery components,where the battery separators and liquid electrolytes are critical for the battery thermal runaway process.In this review,we summarize recent progress in the rational materials design on battery separators and liquid electrolyte towards the goal of improving the safety of LIBs.Also,some strategies for further improving safety of LIBs are also briefly outlooked.     

Preparation and characterization of electrospun nanofiber-coated membrane separators for lithium-ion batteries

Nanofiber-coated membrane separators were prepared by electrospinning polyvinylidene fluoride-co-chlorotrifluoroethylene (PVDF-co-CTFE) nanofibers onto three different microporous membrane substrates. The nanofibers on the membrane substrates showed uniform morphology with average fiber diameters ranging from 129 to 134 nm. Electrolyte uptakes, ionic conductivities, and interfacial resistances were studied by soaking the nanofiber-coated membrane separators with a liquid electrolyte solution of 1 M lithium hexafluorophosphate in ethylene carbonate/dimethylcarbonate/ethylmethyl carbonate (1:1:1 by volume). Compared with uncoated membranes, nanofiber-coated membranes had greater electrolyte uptakes and lower interfacial resistances to the lithium electrode. It was also found that after soaking in the liquid electrolyte solution, nanofiber-coated membranes exhibited higher ionic conductivities than uncoated membranes. In addition, lithium-ion half cells containing nanofiber-coated membranes were evaluated with a LiFePO₄ cathode for charge–discharge capacities and cycle performance. The cells containing a nanofiber-coated separator membrane showed high discharge specific capacities and good cycling stability at room temperature. Results demonstrated that coating PVDF-co-CTFE nanofibers onto microporous membrane substrates is a promising approach to obtain new and high-performance separators for rechargeable lithium-ion batteries.     

Physical, thermal, and electrochemical characterization of stretched polyethylene separators for application in lithium-ion batteries

The single-layered microporous polyethylene separator is prepared by dry process and has been stretched in uni-axial direction to two different ratios namely 180 and 300 % in order to create high-performance and cost-effective separator for practical application in lithium-ion batteries. In this study, the structures of the microporous polyethylene separator prepared by dry process and uni-axially stretched to two different ratios of 180 and 300 % were characterized. The physical structure of the stretched separator is characterized by key factors such as thickness, mean pore size, porosity, Gurley value, ionic resistivity, MacMullin number and tortuosity. The thermal behavior of the stretched separator is explained by using differential scanning calorimeter (DSC). DSC explains the melting and shutdown behavior of the separator. Electrochemical property is studied by linear sweep voltammetry, electrochemical impedance spectroscopy (EIS) and cyclic performance. EIS is performed to explain, in elaborate, the resistance of separator and the specific discharge capacity is observed using the cyclic performance. Three hundred percent stretched separator is observed to have comparatively less resistance and higher discharge capacity than the 180 % stretched separator.     

Influence of the pore structure parameters of mesoporous anatase microspheres on their performance in lithium-ion batteries

Monodisperse mesoporous anatase microspheres were prepared by a combination of sol–gel and liquid–crystal template methods. With the change in annealing temperature, the pore structure parameters of samples were regulated. The influence of pore structure parameters on lithium-ion battery performance was systematically investigated. Results of electrochemical test and analysis demonstrated that the pore structure parameters significantly influenced the specific capacity, charging and discharging curves, rate capability, and cycle performance of the batteries. The first irreversible capacity increased with increased specific surface area. Materials with larger specific surface area showed better rate capability. When the average pore size was too small, the transport of Li⁺ in the electrolyte was impeded, which affected the rate capability of the materials. Based on the charging and discharging curves, the capacity of the plateau section corresponding to lithium insertion/extraction ions in the interstitial octahedral sites of anatase became smaller with increased specific surface area. By contrast, the capacity of the oblique line section corresponding to the Li⁺ insertion/extraction into/from the surface layer of anatase became larger. The pore volume influenced the cycling stability.     

Polyimide separators for rechargeable batteries

Separators are indispensable components of modern electrochemical energy storage devices such as lithium-ion batteries (LIBs).They perform the critical function...     

A broad pore size distribution mesoporous SnO2 as anode for lithium-ion batteries

Journal of Solid State Electrochemistry - We demonstrate here that mesoporous tin dioxide (abbreviated M-SnO2) with a broad pore size distribution can be a prospective anode in lithium-ion...     

Zirconia fiber membranes based on PVDF as high-safety separators for lithium-ion batteries using a papermaking method

Journal of Solid State Electrochemistry - Lithium-ion batteries have been receiving more and more attention because of the energy crisis. As an important subassembly of lithium-ion batteries, the...     

High safety separators for rechargeable lithium batteries

Lithium-ion batteries(LIBs) are presently dominant mobile power sources due to their high energy density, long lifespan, and low self-discharging rates. The safety of LIBs has been concerned all the time and become the main problem restricting the development of high energy density LIBs. As a significant part of LIBs, the properties of separators have a significant effect on the capacity and performances of batteries and play an important role in the safety of LIBs. In recent years, researchers devoted themselves to the development of various multi-functional safe separators from different views of methods, materials, and practical requirements. In this review, we mainly focus on the recent progress in the development of high-safety separators with high thermal stability, good lithium dendritic resistance, high mechanical strength and novel multifunction for high-safety LIBs and have in-depth discussions regarding the separator's significant contribution to enhance the safety and performances of the batteries. Furthermore, the future directions and challenges of separators for the next-generation high-safety and high energy density rechargeable lithium batteries are also provided.     

Membranes and separators for redox flow batteries

Ion-exchange membranes are performance- and cost-relevant components of redox flow batteries. Currently used materials are largely ‘borrowed’ from other applications that have different functional requirements. The trend toward higher current densities and the complex transport phenomena of the different species in flow batteries need to be taken into consideration for the design of next-generation membrane/separator materials. In this article, the key requirements and current development trends for membranes and separators for the vanadium redox flow battery are highlighted and discussed.     

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.     

Recent developments of cellulose materials for lithium-ion battery separators

This paper reviews the recent developments of cellulose materials for lithium-ion battery separators. The contents are organized according to the preparation methods such as coating, casting, electrospinning, phase inversion and papermaking. The focus is on the properties of cellulose materials, research approaches, and the outlook of the applications of cellulose materials for 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.     

Characterization of anodes for lithium-ion batteries

Journal of Solid State Electrochemistry - The lithium-ion batteries are energy storage systems of high performance and low cost. They are employed in multiple portable devices, and these require...     

Silicon nanotube anode for lithium-ion batteries

This work describes a promising strategy for large-scale fabrication of silicon (Si) nanotubes. The process began with preparation of silica nanotubes using rod-like NiN₂H₄ as a template and the resulting silica nanotubes were then converted to Si nanotubes by a thermal reduction process assisted with magnesium powder. The electrochemical properties of Si nanotubes were investigated as anode of lithium-ion batteries. It was demonstrated that the as-developed Si nanotubes showed significantly improved rate capability and long-term cycling performance compared with commercial silicon meshes.     

Bifunctional electrolyte additive for lithium-ion batteries

2-(Pentafluorophenyl)-tetrafluoro-1,3,2-benzodioxaborole was reported as a bifunctional electrolyte additive for lithium-ion batteries. It was found that the reported additive had a redox potential of 4.43 V vs. Li⁺/Li with a reversible oxidation/reduction reaction. Therefore, it is a promising redox shuttle for overcharge protection of most positive electrode materials for current lithium-ion-battery technology. At the same time, the boron center of this additive is a strong Lewis acid and can act as an anion receptor to dissolve LiF generated during the operation of lithium-ion batteries. The possibility of using the novel additive as both the redox shuttle and the anion receptor was discussed.     

LiFePO4 as a dual-functional coating for separators in lithium-ion batteries:A new strategy for improving capacity and safety

Lithium-ion batteries(LIBs) require separators with high performance and safety to meet the increasing demands for energy storage applications. Coating electrochemically inert ceramic materials on conventional polyolefin separators can enhance stability but comes at the cost of increased weight and decreased capacity of the battery. Herein, a novel separator coated with lithium iron phosphate(LFP),an active cathode material, is developed via a simple and scalable process. The LFP-coated separato...     

原子尺度锂离子电池电极材料的近平衡结构

锂离子电池充放电过程中电极材料的结构变化与材料的电化学反应机理和性能密切相关.通过在原子尺度上直接观察脱/嵌锂前后电极材料的近平衡微观结构,有助于从更深层次认识电极反应机理和性能演化规律,对于全面理解材料的电化学行为以及改善锂离子电池性能具有重要的指导意义.本文详述了球差校正扫描透射成像技术在研究电极材料表界面结构及反应机理方面的进展,探讨了未来建立电极材料原子尺度结构与性能相关联可能的研究方向.     

Electrolytic iron sulfides for thin-layer lithium-ion batteries

Thin-layer electrolytic iron sulfides synthesized on stainless steel substrates were studied in prototype lithium and lithium-ion batteries with an electrolyte composed of ethylene carbonate, dimethyl carbonate, and 1 M LiClO₄. A two-volt lithium-ion system with electrolytic iron sulfide and LiCoO₂ as negative and positive electrodes, respectively, was suggested. The discharge capacity of the prototype system is 350–400 mA h g⁻¹ Fe sulfide.     

The development in aqueous lithium-ion batteries

To meet the growing energy demands, it is urgent for us to construct grid-scale energy storage system than can connect sustainable energy resources. Aqueous Li-ion batteries(ALIBs) have been widely investigated to become the most promising stationary power sources for sustainable energy such as wind and solar power. It is believed that advantages of ALIBs will overcome the limitations of the traditional organic lithium battery in virtue of the safety and environmentally friendly aqueous electrolyte. In the past decades, plentiful works have been devoted to enhance the performance of different types of ALIBs.In this review, we discuss the development of cathode, anode and electrolyte for acquiring the desired electrochemical performance of ALIBs. Also, the main challenges and outlook in this field are briefly discussed.