Gelified Co-continuous Polymer Blend System as Polymer Electrolyte for Li Batteries

Abstract

In this work, the co-continuous polymer blend was synthesized for use as the electrolyte in lithium batteries. Such electrolytes were characterized by a co-continuous morphology consisting of two three-dimensionally interpenetrated polymer networks simply formed by hot-mixing two nonmiscible polymers. A preliminary electrochemical characterization of the gelified cocontinuous polymer blend as electrolyte for lithium batteries is also reported.The fast development of portable electronic devices requires the continuous improvement of the energy sources ͑batteries͒ both in terms of power and energy. The introduction of rechargeable lithium-ion batteries in the late 1980s ͑Sony͒ substantially relieved this problem by providing better performance for portable electronics. However, these batteries make use of liquid electrolytes supported on porous plastic separators. The presence of these volatile and flammable liquids in high-energy content devices raises concern regarding safety. Most of the work on the development of lithiumion batteries is now devoted to the substitution of the separator supporting liquid electrolyte by a gel-polymer electrolyte film in which the electrolytic solution is immobilized.The current gel-polymer electrolytes have two major problems related to the nature of the polymer-solvent interaction. Weakly interacting polymers ͓e.g., poly͑vinylidene fluoride͔͒ lead to the formation of sponge-like or unstable gels that show extensive loss of solvent by evaporation or syneresis. 1,2 However, they are characterized by very good mechanical properties. On the other hand, strongly interacting polymers ͓e.g., poly͑ethylene oxide, PEO͔͒ tend to form very stable gels but are characterized by very poor mechanical properties. Gel-polymer electrolytes based on high molecular weight PEO (Ͼ10 6 a.u.͒ are sticky, highly viscous fluids when their ionic conductivity is above 10 Ϫ4 S cm Ϫ1 . 3 Most of the current research intent on improving mechanical properties is based on gel-polymer electrolytes consisting of copolymers and/or cross-linked polymers. 4 However, these systems have several problems relating to the process ability of the final material.Polymer blends have been already considered as base materials for the synthesis of gel electrolytes, 5,6 but no particular investigations were devoted to the optimization of their microscopic morphology. Mixing immiscible polymers in the molten state, results in the formation of materials characterized by heterogeneous microstructures, which strongly affect the properties of the polymer blend itself. 7 An example of microstructures that can be formed are droplet/matrix, fibrous, lamellar, and, of most interest, cocontinuous microstructures. This latter morphology of polymer blends is of particular interest for electrochemical applications as supporting matrixes for true gel-polymer electrolytes. In previous work 8,9 it was demonstrated that the feasibility of preparing cocontinuous polymer blend-based gel-polymer electrolytes by simply hot-mixing polystyrene and poly...

Electrolytes and Interphases in Li-Ion Batteries and Beyond

“…A polymer blend consisting of PEO and PS was prepared by Passerini et al, who apparently planned to combine the ion conduction property of the former and the mechanical strength of the latter via hotblending. 423 A co-continuous morphology resulted, in which two independent networks existed for these immiscible polymer chains. The blend was gelled by nonaqueous electrolytes successfully, and the resultant GPE was tested in LiFePO 4 half cells with modest cycling performance.…”

“…Preliminary tests in a full LIB based on graphitic anode and LiCoO 2 yielded satisfactory electrochemical performance. A polymer blend consisting of PEO and PS was prepared by Passerini et al, who apparently planned to combine the ion conduction property of the former and the mechanical strength of the latter via hot-blending . A co-continuous morphology resulted, in which two independent networks existed for these immiscible polymer chains.…”

Creation of highly functional thin films using electrochemical nanotechnology

“…Therefore, a gel electrolyte made from low‐cost materials and by a simple process is in strong demand. To meet this demand, we suggested the use of a “polymer blend gel electrolyte.”122–124 This electrolyte was prepared by blending poly(ethylene oxide) (PEO), which has a high ionic conductivity, and polystyrene (PS), which has a high mechanical strength. The new electrolyte has a structure with microphase separation with alternate continuity, exhibiting the characteristics of both PEO and PS.…”

Electrochemical Properties of Gel Polymer Electrolytes Based on Poly-(Ethylene Glycol Methyl Ether Methacrylate-Co-Benzyl Methacrylate)

“…The copolymer was prepared via photo-induced radical polymerization of two methacrylate monomers with different side chains, an ethylene oxide (EO) and a benzyl (Bn) side chain. While the EO side chain is interacting with the liquid electrolyte thus, keeping the liquid in the polymer matrix, the Bnside chain provides mechanical stability enabling the use of this GPEs as separators [3]. Mechanically stable GPEs with a liquid electrolyte content of up to 80wt% could be obtained (see Fig.…”