Polyphosphazenes battery electrolytes

A second class of important electrolytes for rechargeable lithium batteries are soHd electrolytes. Of particular importance is the class known as soHd polymer electrolytes (SPEs). SPEs are polymers capable of forming complexes with lithium salts to yield ionic conductivity. The best known of the SPEs are the lithium salt complexes of poly(ethylene oxide) [25322-68-3] (PEO), —(CH2CH20) —, and poly(propylene oxide) [25322-69-4] (PPO) (11—13). Whereas a number of experimental battery systems have been constmcted using PEO and PPO electrolytes, these systems have not exhibited suitable conductivities at or near room temperature. Advances in the 1980s included a new class of SPE based on polyphosphazene complexes suggesting that room temperature SPE batteries may be achievable (14,15). 

Polyphosphazene-based PEMs are potentially attractive materials for both hydrogen/air and direct methanol fuel cells because of their reported chemical and thermal stability and due to the ease of chemically attaching various side chains for ion exchange sites and polymer cross-linking onto the — P=N— polymer backbone. Polyphosphazenes were explored originally for use as elastomers and later as solvent-free solid polymer electrolytes in lithium batteries, and subsequently for proton exchange membranes. 

Some of the most useful polyphosphazenes are fluoroalkoxy derivatives and amorphous copolymers (11.27) that are practicable as flame-retardant, hydrocarbon solvent- and oil-resistant elastomers, which have found aerospace and automotive applications. Polymers such as the amorphous comb polymer poly[bis(methoxyethoxyethoxy)phosphazene] (11.28) weakly coordinate Li " ions and are of substantial interest as components of polymeric electrolytes in battery technology. Polyphosphazenes are also of interest as biomedical materials and bioinert, bioactive, membrane-forming and bioerodable materials and hydrogels have been prepared. 

Applications of polyphosphazenes as flame retardants, electrolytes for special batteries, and biomaterials have been described. Some cyclophosphazene derivatives can serve as hosts for small molecule Clathration. ... 

It should be noted that, in addition to their use as electronic conductors, polymers can also function as ionic conductors. Materials such as poly(ethylene oxide) and certain oligoethyleneoxy-substituted polyphosphazenes and polysiloxanes, which conduct Li" ions, are used in this regard as polymeric electrolytes for battery applications (9]. 

Polyphosphazenes such as (12.240) form amorphous solvent-free complexes with various salts. These are polymer electrolytes which have potential application in batteries, ion sensors, electro-chromic displays, and so on [83-85]. 

Polymer electrolytes are used in lithium ion rechargeable batteries. Pure polymer electrolyte systems include polyethylene oxide (PEO), polymethylene-polyethylene oxide (MPEG), or polyphosphazenes. Chlorinated PVC blended with a terpoly-mer comprising vinylidene chloride/acrylonitrile/methyl methacrylate can make a good polymer electrolyte. Rechargeable lithium ion cells use solid polymer electrolytes. Plasticized polymer electrolytes are safer than liquid electrolytes because of a reduced amount of volatiles and flammables. The polymer membrane can condnct lithinm ions. The polymer membrane acts as both the separator and electrolyte [7],... 

Polyphosphazenes were used as solid polymer electrolytes for batteries, membranes for gas and liquid separations, and proton exchange membranes for fuel cells as well as for energy storage and energy generation applications. ... 

There is no obvious damage to the interface between the lithium metal electrode and polyphosphazene electrolytes during cycling. Electrochemical measurements of the Li/polyphosphazene electrolyte/Li battery show a cycling life of at least 600 times, demonstrating the good chemical stability of the electrolyte with the lithium metal negative electrode. 

Jankowsky, S., Hiller, M.M., Wiemhoefer, H.D. 2014. Preparation and electrochemical performance of polyphosphazene based salt-in-polymer electrolyte membranes for lithium ion batteries. J. Power Sources 253 256-262. 

Polyphosphazenes have emerged as a class of promising solid polymer electrolyte materials for energy applications due to their inherently high stability and a wide range of synthetic variability. Herein, a summary is presented on the synthesis of polyphosphazenes, membrane fabrication and characterization, and applications for lithium batteries, fuel cells, and dye-sensitized solar cells (DSSCs). 

As compared to the numerous literature reports on preparation and characterization of polyphosphazene electrolytes for lithium ion conduction, there have been only a few studies on lithium battery using polyphosphazene electrolyte membranes. 

Abraham, K. M., Alamgir, M., Perrotti, S. J., Rechargeable solid-state Li batteries utilizing polyphosphazene-poly(ethylene oxide) mixed polymer electrolytes. Journal of the Electrochemical Society, 1988, 135, 535-536. 

Several soUd polymer electrolytes (SPEs) based on copolymers have been prepared and complexed with Uthium salts to prepare polymer electrolytes for Uthium batteries. Incorporation of 10 to 20% poly(propylene oxide) (PPO) units in PEO depresses considerably the crystalUnity of the materials. In addition to copolymer containing polyether grafted polyether, polysiloxane and polyphosphazene backbones have been used. Polymer... 

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