Main properties of polymer electrolytes

From a practical point of view, the polymer electrolyte for rechargeable lithium ion batteries should satisfy the following requirements (Koksbang et al, 1996). 

To achieve the performance level of liquid electrolyte-based systems which can be discharged at current densities of up to several mA/cm, the polymer electrolyte should possess ion conductivities approaching or beyond 10 S/ cm at ambient temperature. As the polymer electrolyte can be processed into a self-standing membrane, the ion conductivity is usually measured via AC impedance analysis with an electrochemical cell consisting of the polymer electrolyte film sandwiched between two blocks of stainless steel. 

Since a polymer electrolyte membrane is interposed between the cathode and the anode, its chemical stability must be such that no undesired chemical reactions occur when the electrodes come into direct contact. In addition, in order to operate in an appropriate temperature range, polymer 

4 Linear sweep voltammetry curve of a polymer electrolyte. 

In general the electrochemical stability can be characterized by an electrochemical window which is measured via a cychc voltammogram measurement (Fig. 14.3) or linear sweep voltammetry (Fig. 14.4). The flat areas occurring in both figures represent the electrochemical window. 

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