Lithium with gelled electrolytes

Most lithium cells available in the market utilize nonaqueous electrolyte solutions, where lithium salts are dissolved in organic solvents. The gelled electrolytes used in lithium-ion polymer batteries are also regarded as an organic electrolyte immobilized with a high molecular weight polymer. 

Therefore, we have to use non-aqueous electrolytes. Two families of electrolyte are presents on the market today liquid electrolytes in combination with inert porous separators and gelled polymer electrolytes in combination with liquid electrolytes. In addition, research is being conducted to define a new, ionic type of electrolyte which is more thermostable. Thus, on a commercial level, today s lithium-ion technology can be subdivided into two subsets ... 

Lithium-Ion Secondary Batteries with Gelled Polymer Electrolytes... 

To overcome the poor mechanical properties of polymer and gel polymer type electrolytes, microporous membranes impregnated with gel polymer electrolytes, such as PVdF. PVdF—HFP. and other gelling agents, have been developed as an electrolyte material for lithium batteries.Gel coated and/ or gel-filled separators have some characteristics that may be harder to achieve in the separator-free gel electrolytes. For example, they can offer much better protection against internal shorts when compared to gel electrolytes and can therefore help in reducing the overall thickness of the electrolyte layer. In addition the ability of some separators to shutdown... 

In modem commercial lithium-ion batteries, a variety of graphite powder and fibers, as well as carbon black, can be found as conductive additive in the positive electrode. Due to the variety of different battery formulations and chemistries which are applied, so far no standardization of materials has occurred. Every individual active electrode material and electrode formulation imposes special requirements on the conductive additive for an optimum battery performance. In addition, varying battery manufacturing processes implement differences in the electrode formulations. In this context, it is noteworthy that electrodes of lithium-ion batteries with a gelled or polymer electrolyte require the use of carbon black to attach the electrolyte to the active electrode materials.49-54 In the following, the characteristic material and battery-related properties of graphite, carbon black, and other specific carbon conductive additives are described. 

In this case, we have an electrolyte identical to that which is present in lithium-polymer batteries, made of poly(ethylene oxide) (or PEO) in the presence of a lithium salt, solid at ambient temperature, and which needs to be heated above ambient temperature in order for the battery to work (T > 65°C for PEO). Thus, the electrolyte, in its molten state, exhibits sufficient ionic conductivity for the lithium ions to pass. This type of electrolyte can be used on its own (without a membrane) because it ensures physical separation of the positive and negative electrodes. This type of polymer electrolyte needs to be differentiated from gelled or plasticized electrolytes, wherein a polymer is mixed with a lithium salt but also with a solvent or a blend of organic solvents, and which function at ambient temperature. In the case of a Li-S battery, dry polymer membranes are often preferred because they present a genuine all solid state at ambient temperature, which helps limit the dissolution of the active material and therefore self-discharge. Similarly, in the molten state (viscous polymer), the diffusion of the species is slowed, and there is the hope of being able to contain the lithium polysulfides near to the positive electrode. In addition, this technology limits the formation of dendrites on the metal lithium... 

Positive and negative intercalation electrodes (lithium-ion) with a gelled polymer electrolyte (PEO-based). 

Bohrike O, Frand G, Rezrazi M, Rousselot C, Ttuche C (1993) Fast ion transport in new lithium electrolytes gelled with PMMA. 1. Influence of polymer concentration. Solid State Ion 66(l-2) 97-104, http //dx.doi.org/10.1016/0167-2738(93)90032-X... 

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