Swollen Polymethacrylonitrile Urethane Networks for Lithium Batteries

Abstract

Copolymers of methacrylonitrile are reported. Surprisingly, their curing through urethane cross-links acts as an internal plasticization. This cross-linking prevents any dissolution or leakage, up to 90°C, when the networks are swollen by liquid organic electrolytes. These provide high conductivities, and the increase in resistivity with respect to pure liquid electrolytes remains р2. The specifications of lithium batteries intended for electronic application imposes an operation at low temperature which can be obtained only with liquid organic electrolytes. In parallel these batteries must be able to tolerate a temperature of 80°C over a period of several days. Within the framework of cellular phone application, the tendency is to decrease volume and weight, but operational requirements, i.e., accessibility of the keys, reading of the screen, make it impossible to envisage a reduction in the surface of the telephone.1 Consequently, it is desirable to substitute prismatic batteries by flexible and thin batteries. The majority of the commercial batteries, in particular, prismatic, use a microporous polyolefin separator, which confers a particular safety, shut-down effect, to the battery with respect to a great increase in temperature. However, this type of separator exhibits poor affinities for the polar organic electrolytes and makes difficult their use for the manufacture of flexible and thin batteries. An alternative to these microporous separators consists in using a polymer swollen by the liquid organic electrolytes. Thirty years ago, 2 these polymers swollen by the electrolyte were intended to manufacture ''thin-layer'' electrochemical elements. The polymers proposed were polyacrylonitrile ͑PAN͒, 3,4 copolymer poly͑methyl methacrylate͒ P͑AN-co-PMMA͒, 5-6 polyvinyl chloride ͑PVC͒, 7 polyacetals as polyvinylbutyral ͑PVB͒, fluoropolymers as polyvinylidene fluoride-co-polyhexafluoropropene ͑VDF/HFP͒, [8][9][10] or PMMA copolymers. [11][12][13] The solvent retention ability of polymer gels decreases in the order of PMMA у PAN ϭ poly͑vinylidene difluoride͒ P͑VdF-HFP͒ у PVdF.14 The lowaffinity polymers are advantageous with respect to the mechanical strength of polymer gels but are a disadvantage with respect to ionic conductivity. It was also proposed to use poly͑oxyethylene͒ ͑POE͒ networks. 15 These adapted well to dry lithium-polymer applications but are much less interesting compared to organic solvents.We chose to use a polynitrile because of the strong dipole moment of the nitrile group and the affinity of PAN for the usual lithium salts and the polar solvents which constitute the liquid electrolyte. However, the electrochemical instability of PAN with a lithium negative electrode has been known for a long time and has been highlighted from measurements of PAN electrolyte/lithium interface resistances and their evolution with time. 16 We attributed much of the PAN instability to the existence of the rather ''acidic'' hydrogen in the alpha position of the nitrile group. To solve this we chose polymethacryloni...

NMR and Electrochemical Study on Lithium Oligoether Sulfate in Polymeric and Liquid Electrolytes

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Development of sodium-conducting polymer electrolytes: comparison between film-casting and films obtained via green processes

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NMR Study of Cation, Anion, and Solvent Mobilities in Macroporous Poly(vinylidene fluoride)

“…To obtain thin and flexible batteries adapted to the evolution of portable electronics, the old concept of gelled polymer electrolyte has recently been studied using several thermoplastic or cross-linked polymer matrixes such as polyacrylonitrile (PAN), − poly(methyl methacrylate) (PMMA), , polymethacrylonitrile (PMAN) networks, or poly(vinylidene fluoride)−hexafluoropropene (PVdF−HFP). , Generally, prior to the battery formation, the gelled polymer electrolyte is prepared by swelling the polymer matrix with the liquid electrolyte. Lithium-ion battery manufacturers, however, prefer a “dry” approach consisting of assembling a PVdF membrane free of electrolyte with the electrodes.…”