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In lithium-ion batteries (LIBs), separators play a vital role in lithium-ion (Li+) transport, and thus affect rate performance, battery life, and safety. Here, a new kind of multifunctional copolymer poly(acrylonitrile-co-lithium acrylate-co-butyl acrylate) (PAAB-Li) is synthesized through soap-free emulsion polymerization, and is used to form homogeneous-covered separator based on PP matrix by a simple dip-annealing process. Compared to the bare PP separator, the modified separators with PAAB-Li enable higher ionic conductivity, higher lithium ion transference number (increased from 0.360 to 0.525), and lower interface impedance (reduced from 155 Ω to 34 Ω). It has been indicated that PAAB-Li functional layer significantly promotes the fast transport of Li+ and improves the compatibility of the separator/electrolyte-electrode interface. The LiCoO2/graphite cells with the PAAB-Li-assisted separator demonstrate excellent cycle stability and rate performance. In addition, the Li symmetric cells with the modified separator stably cycle over 800 h, indicating the functional layer effectively suppresses the lithium dendrite growth. This facile strategy can be easily applied to LIBs requiring high safety and even be scalable to Li metal batteries. Moreover, the possible mechanism of the PAAB-Li functional layer promoting fast and uniform Li+ transport is discussed in this paper. [ABSTRACT FROM AUTHOR]

ABSTRACT To effectively improve the affinity of polyethylene (PE) separators with liquid electrolyte without causing a serious pore blockage and to develop a more suitable technology for the industrial production process, porous polyvinylidene fluoride (PVDF) layer-coated PE separators are prepared by the dip-coating method followed by a dry-cast process. Different from previous investigations, a less volatile solvent and a relatively volatile nonsolvent are used to yield a preferable pore structure. A brief introduction on the pore formation mechanism during the dry-cast process is provided. The pore structure of coating layer is found to be successfully controlled by changing evaporation temperature, nonsolvent content, and PVDF concentration. The porous PVDF coating layer-modified separators show better affinity with liquid electrolyte and thermal stability. Especially, the ionic conductivity of the modified separator/liquid electrolyte system with a suitable porous coating layer on the separator could reach two times as that of PE separator/liquid electrolyte system, and the cell assembled with modified PE separator shows better cycle performances. This modification process is proved to be a facile, controllable, and effective method for PE separator modification. Meanwhile, this work could provide some theoretical and technical guidance for the production process. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41036. [ABSTRACT FROM AUTHOR]

Abstract: In this work, polyether chains such as polyethylene glycol (PEG) chains were grafted onto polypropylene (PP) separators based on mussel-inspired dopamine coating. This method was proved to be also effective to modify other separators, such as polyethylene (PE) and polyvinylidene fluoride (PVDF) separators. Meanwhile, considering the extensive utilization of polyether chains in other fields, e.g., water treatment, biomedical, and so on, this work provided a facile and effective way for introducing polyether chains onto the surfaces of the other kinds of materials. Compared to the virgin PP separators, the introduction of polyether chains onto PP separators enhanced the affinity between the separator and liquid electrolyte. The PEG modified PP separators show higher ambient ionic conductivity, up to 0.99×10−3 Scm−1. Also, the PEG chains effectively decreased the interface resistance and enhanced the interfacial stability, which was beneficial for high performances of separators for lithium ion batteries (LIBs). [Copyright &y& Elsevier]

Abstract: In this work, PMMA layer was immobilized onto PE separator skeleton via surface-initiated ATRP based on dopamine pretreatment. The incorporated “active” layer made separator matrix could be swollen by electrolyte solution to some extent and show some properties of gel polymer electrolyte. Resulted separators were characterized by ATR-FTIR, SEM, contact angle and electrochemical methods. The prepared separators showed improved thermal stability. The electrolyte uptake and ionic conductivity were also elevated due to the improved affinity between separator and liquid electrolyte. The room temperature ion conductivity reached up to 1.19×10−3 Scm−1. The stability of liquid electrolyte trapped in the separator was enhanced obviously. Cells assembled with such “active separators” showed better cycle performances. These results primarily showed that it was a promising way to prepare high performance PE based separators for lithium ion batteries. [Copyright &y& Elsevier]

Abstract: Porous high density polyethylene (HDPE) membrane is an important type of separator for lithium ion batteries (LIBs). To improve the electrochemical performances of HDPE-based separators, a copolymer of poly(ethylene-block-ethylene glycol) (PE-b-PEG) was blended into porous HDPE separators via TIPS process. By measuring the composition, morphology and crystallinity, etc., the phase behavior and surface enrichment behavior of the HDPE/PE-b-PEG/LP system were studied. Compared with pure HDPE separators, surface enrichment of PE-b-PEG chains enhanced the compatibility between separators and liquid electrolyte and electrodes. The ionic conductivity of liquid electrolyte soaked blend separator was up to 1.24×10−3 Scm−1 at 25°C. Furthermore, the interface resistance between separator and electrode was effectively reduced by the surface enriched polyether chains. All the results indicated that PE-b-PEG could be a promising blend substance to improve the electrochemical performances of HDPE separators prepared via TIPS process. [Copyright &y& Elsevier]

To improve the performances of HDPE-based separators, polyether chains were incorporated into HDPE membranes by blending with poly(ethylene- block-ethylene glycol) (PE- b-PEG) via thermally induced phase separation (TIPS) process. By measuring the composition, morphology, crystallinity, ion conductivity, etc, the influence of PE- b-PEG on structures and properties of the blend separator were investigated. It was found that the incorporated PEG chains yielded higher surface energy for HDPE separator and improved affinity to liquid electrolyte. Thus, the stability of liquid electrolyte trapped in separator was increased while the interfacial resistance between separator and electrode was reduced effectively. The ionic conductivity of liquid electrolyte soaked separator could reach 1.28 × 10 S·cm at 25°C, and the electrochemical stability window was up to 4.5 V (versus Li/Li). These results revealed that blending PE- b-PEG into porous HDPE membranes could efficiently improve the performances of PE separators for lithium batteries. [ABSTRACT FROM AUTHOR]

Lithium metal is a promising anode candidate for the next-generation higher energy density batteries. In this work, a detailed study is carried out to clearly explore the influence of separator wettability on ionic conduction and interface properties for lithium-metal anode batteries. Firstly, polyphenol and polyamine are facilely assembled on the surface of polyethylene (PE) separator with the assistant of periodate. Wettability and electrolyte uptake of the polyphenol-polyamine treated PE separator improves significantly, which resulted in the increase of ionic conductivity and lithium-ion transference number (from 0.37 to 0.49). Subsequently, galvanostatic measurements and electrochemical impedance spectra (EIS) are performed on Li symmetric cells to investigate the effect of separator wettability on interface properties. It is found that the modified PE separator favors the electrochemical process by providing lower interfacial resistance, better interface compatibility, and more uniform deposition of Li + , which correspondingly mitigate the formation of Li dendrites. Finally, lithium-metal anode cells (LiCoO 2 (LCO)/Li) assembled with different separators are tested, and superior battery performance is displayed in case of the polyphenol-polyamine treated substrate. These results are expected to be instructive for the design of more durable Li electrodes. [ABSTRACT FROM AUTHOR]