Polymer Electrolytes and Electrodes for Energy Storage Obtained from Sustainable Materials and Methods
This PhD thesis deals with the preparation of polymer materials for energy storage applications. The study can be divided into two main lines. On one side, the preparation of thermoplastic polymer electrolytes (ETP) processed by melt-compounding, and on the other side, the development of polythiophene-derivatives composite materials for polymer electrodes.
ETP were prepared by melt-compounding, mixing polyethylene oxide, lithium bis(trifluoromethane sulfonimide) (LiTFSI), modified sepiolite with D-α-tocoferol-polyethyleneglycol 1000 succinate (TPGS-S), and a set of room temperature ionic liquids (RTILS). The most interesting electrolytes were tested on lithium-metal electrochemical cells and were characterized in terms of discharge capacity, cycle number, and lithium-anode stability.
In parallel with polymer electrolytes development, two types of in-situ polythiophene derivates composite materials were explored to prepare flexible supercapacitors electrodes: (1) polymer/cellulose composite materials using poly(3,4-ethylenedioxithiophene) (PEDOT) prepared by in-situ polymerization as polymer matrix, and (2) a similar in-situ polymerization but in presence of carbon particles such as reduced graphene oxide, multi-walled carbon nanotubes, and activated carbon. Prepared materials were used in combination with some ETP prepared previously to develop flexible electrode-electrolyte systems.
ETP were successfully obtained with values of ionic conductivity in the range from 10-3 to 10-4 S∙cm-1 at 25 ºC, with a pseudosolid behaviour and dimensionally stability of years. Best materials tested in electrochemical cells presented up to 400 charge-discharge cycles maintaining more than 80% of its initial capacity. On the other hand, PEDOT-cellulose flexible composite materials obtained presented electrical conductivities of approximately 1 S∙cm-1. Electrical conductivities of PEDOT composite materials depends both on the nature of conductive filler used and its content. Results obtained are very promising towards the development of energy flexible and safer storage devices with higher capacity than current devices.
