Second-Generation Polymer Electrolytes

The main advantage of PEO as a host is that it is chemically and electrochemically stable since it contains only strong unstrained C-0, C-C, and C-H bonds. The disadvantage is the inherent crystallinity, and considerable effort has gone into synthesizing all-amorphous polymer hosts. Unfortunately, with the bulk conductivity as the prime motivator, many amorphous polymer hosts incorporate organic functional groups which limit their practical application. Detailed accounts of many of the hosts synthesized have been reviewed [8, 32-36]. 

Random copolymers are similar to PEO but when the regular helical structure of the chains is demolished, the crystallinity is also destroyed. One of the simplest and most successful amorphous host polymers is an oxyethylene- oxymethylene structure in which medium length but statistically variable EO units are interspersed with methylene oxide groups. First described in 1990 [37], flPEO has the general structure 

Both radiation and chemical crosslinking can produce amorphous, mechanically stable networks. Radiation crosslinking has a practical advantage in that polymer elec- 

One of the major drawbacks to many pronaising copolymers is their unsatisfactory electrochemical stability. Carbonyl groups which feature in many of the back-bone/chain linking groups are likely to cause stability concerns. Likewise, urethane, alcohol, and siloxane functions are. sensitive to lithium metal. With this in mind, a recent trend has been to find synthetic routes to amorphous structures with 

The first of such materials was reported in 1990 [52] and was based on the general structure 4. 

Comb-branched copolymer and block copolymer architectures are similar in that they are generally based on short polyether chains supported in some manner to give the material its mechanical stability. Success has been variable in attempts to 

Both radiation and chemical crosslinking can produce amorphous, mechanically stable networks. Radiation crosslinking has a practical advantage in that polymer electrolyte films can be fashioned to the desired thickness or shape, and even incorporated into a device before crosslinking. Chemical crosslinking often introduces undesirable functional groups which may offer few advantages from a practical viewpoint, but this route can be very useful in the simple preparation of networks for fundamental studies [33, 49-51). 

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If studies on the electrode interface in first generation polymer electrolyte cells are scarce, they are practically non-existent in second and third generation polymer electrolyte cells, i.e. in those systems which are currently proposed as the most promising for the development of multi-purpose LPBs. However, lithium passivation in these multi-phase, multi-component cell systems is expected to be even more severe than that experienced with the cells based on the relatively simple membranes formed by binary mixtures of PEO and lithium salts. In fact, the second and third generation membranes are commonly based on liquid additives and plasticizers (e.g. propylene carbonate, see Chapter 3) which are very reactive with the lithium metal electrode... 

In the scope of the thesis, a steady-state model of polymer electrolyte membrane fuel cell was made by Matlab. The model was based on simplified chemical and electrical equations. The most important performance related parameters, namely operation temperature and pressure, were parametrically investigated. Output voltage, electrical output power, heat generation, material inputs and outputs, and efficiencies according to first and second law of thermodynamics were plotted by the change of temperature and pressure against current density. 

The heart of the process was the fabrication of the polymer laminate for the cathode. The cathode formulation, including polymer precursor, vanadium oxide, and carbon, was mixed and coated onto the carbon current collector. A second layer, the electrolyte, was coated on the cathode to provide the ionic conductivity and separate the eathode from the lithium anode. The coated laminate was then passed through an electron beam generator to crosslink the polymer precursors and produce the solid polymer material. 

In the second step, the three-dimensional relief-like structure of the resist polymer generated by deep lithography is transferred into a complementary metallic structure by means of electroforming, starting from the electrically conductive substrate. Usually a nickel sulfamate electrolyte is applied, but there are also proven electrolytes available for deposition of other metals and metal alloys. 

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