Journal of Power Sources 125 (2004) 10–16 Composite polymer electrolytes reinforced by non-woven fabrics Min-Kyu Song a , Young-Taek Kim a , Jin-Yeon Cho b , Byung Won Cho c , Branko N. Popov d , Hee-Woo Rhee a,∗ a Hyperstructured Organic Materials Research Center, Department of Chemical Engineering, Sogang University, Seoul 121-742, South Korea b Battery Research Institute/Battery Tech Center, LG Chem, Ltd., Daejeon 305-380, South Korea c Battery and Fuel Cell Research Center, Korea Institute of Science and Technology, Seoul 130-650, South Korea d Center for Electrochemical Engineering, Department of Chemical Engineering, University of South Carolina, Columbia, SC 29208, USA Received 16 May 2003; accepted 14 July 2003 Abstract Composite electrolytes composed of a blend of polyethylene glycol diacrylate (PEGDA), poly(vinylidene fluoride) (PVDF) and poly(methyl methacrylate) (PMMA) together with a non-woven fabric have been prepared by means of ultra-violet cross-linking. As the non-woven fabric serves as a mechanical support medium, the composite electrolyte has good integrity up to an initial liquid electrolyte uptake of 1000% (ethylene carbonate (EC)–dimethyl carbonate (DMC)–ethylmethyl carbonate (EMC)–LiPF 6 ). The ionic conductivity of the composite electrolytes reaches 4.5 mS cm -1 at an ambient temperature of around 18 ◦ C and are electrochemically stable up to about 4.8 V versus Li/Li + . The conductivity and interfacial resistance remain almost constant even at 80 ◦ C. Scanning electron micrographs show that the high-temperature behavior is associated with structural stability that is induced by chain entanglement between PVdF, PMMA and PEGDA network. A MCMB|LiCoO 2 cell using the composite electrolytes retains >97% of its initial discharge capacity after 100 cycles at the C/2 rate (150 mA), and delivers more than 80% of full capacity with an average load voltage of 3.6 V at the 2C rate. The cell also shows much better cycle-life than one with a PVdF-coated composite electrolyte at high temperatures because of the better liquid electrolyte retention capability. © 2003 Elsevier B.V. All rights reserved. Keywords: Lithium-ion polymer battery; Polyethylene glycol diacrylate; Non-woven fabric; Composite electrolyte; Ultra-violet curing 1. Introduction Rechargeable lithium batteries have become a key com- ponent of modern portable electronic devices since the remarkable commercial success of Li-ion cells distributed first by SONY in 1991 [1]. Li-ion batteries operate on the same principle as Li-metal batteries, but do not have critical problems associated with the unstable Li–metal interface because they utilize Li + -intercalated carbonaceous anodes instead of reactive metallic lithium [2]. In the next genera- tion of lithium batteries, usually named Li-ion polymer bat- teries (LiPB), gel polymer electrolyte (GPE) technologies will play a major role to improve scale-up, safety, and design flexibility [3]. Even though various gel polymer electrolytes plasticized by organic liquid solvents eliminate the room-temperature conductivity limit of dry polymer systems based on poly- ∗ Corresponding author. Tel.: +82-2-705-8483; fax: +82-2-711-0439. E-mail address: hwrhee@ccs.sogang.ac.kr (H.-W. Rhee). ethylene oxide (PEO) [4], their mechanical strength is still not sufficient to allow high-speed battery manufacturing that would employ the lamination and packing processes commonly used in plastic industry [5]. Therefore, there have been several recent reports [6–10] on LiPBs with gel polymer electrolytes which include thin microporous polyolefin separator films [6–10]. The gelled polymers are accompanied with an inert separator film, the support film endows the final polymer electrolyte matrix with sufficient mechanical properties for practical battery assembly pro- cedures. This concept is technically analogous to the out- standing Gore-Select TM membrane, a composite ionomer reinforced by microporous Teflon ® film, that is used in hydrogen fuel-cell applications [11]. In any cases, these ap- proaches may yield the best compromise between apparent areal resistance and mechanical integrity. In gel-coated electrolyte systems poly(vinylidene fluo- ride) (PVdF) and its copolymers with hexafluoropropylene (PVdF–HFP) are commonly chosen as an ionic conductive gel layer because of their high electrochemical properties and better adhesion with electrode laminates that contain a 0378-7753/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0378-7753(03)00826-7