Martin Manuel Hiller

Salt-in-Polymer Electrolytes for Lithium Ion Batteries Based on Organo-Functionalized Polyphosphazenes and Polysiloxanes

Abstract An overview is given on polymer electrolytes based on organo-functionalized polyphosphazenes and polysiloxanes. Chemical and electrochemical properties are discussed with respect to the synthesis, the choice of side groups and the goal of obtaining membranes and thin films that combine high ionic conductivity and mechanical stability. Electrochemical stability, concentration polarization and the role of transference numbers are discussed with respect to possible applications in lithium batteries. It is shown that the ionic conductivities of salt-in-polymer membranes without additives and plasticizers are limited to maximum conductivities around 10-4S/cm. Nevertheless, a straightforward strategy based on additives can increase the conductivities to at least 10-3S/cm and maybe further. In this context, the future role of polymers for safe, alternative electrolytes in lithium batteries will benefit from concepts based on polymeric gels, composites and hybrid materials. Presently developed polymer electrolytes with oligoether sidechains are electrochemically stable in the potential range 0–4.5V (vs. Li/Li+ reference).

Salt-in-Polymer Electrolytes Based on Polysiloxanes for Lithium-Ion Cells: Ionic Transport and Electrochemical Stability

In this work, the ion transport and the electrochemical stability has been investigated for cross linked salt-in-polysiloxane membranes containing the two lithium salts with boron based anions, i.e. LiDFOB (lithium difluoro(oxalato)borate) and LiBOB (lithium bis(oxalato)borate) have been investigated. The stability was characterized by cyclic voltammetry at 70 °C in a three electrode cell with Li as counter and reference electrodes and a nickel or platinum working electrode. The electrochemical stability window of polysiloxane based electrolytes ranged between 0 V and 4.7 V vs. Li/Li + . The high ionic conductivity of 6.61 x 10 -2 mS/cm at 30 °C has been examined with impedance spectroscopy on blocking electrodes. The investigated polymer electrolytes showed an outstanding thermal resistance as confirmed by thermal analysis with DSC. Furthermore, analysis of the lithium transference number has been carried out using the potentiostatic polarization method introduced by BRUCE and VINCENT.