Electrodeposited polymer electrolytes for 3D Li-ion microbatteries

Abstract

The electropolymerisation of vinyl monomers has been investigated as a route to the conformal deposition of thin polymer electrolyte films on porous electrode surfaces, for application in 3D Li-ion microbatteries. The deposition of poly(acrylonitrile) and poly(poly(ethylene glycol) diacrylate) has been monitored using cyclic voltammetry and an electrochemical quartz crystal microbalance (EQCM). It was determined that the polymerisation reaction may be initiated either by direct reduction of the monomer or via a separate reactive intermediate such as the superoxide anion. Furthermore, it was established that film thickness was easily controlled under cyclic voltammetry conditions, for example by varying the number of cycles. However, the choice of solvent and electrode surface was found to be of critical importance.

This electropolymerisation technique was adapted to achieve the single step electrodeposition of a gel polymer electrolyte based on poly(ethylene glycol) diacrylate (PEGDA). Modification of the polymer to improve the mechanical properties and ionic conductivity was achieved by the incorporation of silica nanoparticles and plasticising monoacrylates into the polymer matrix. Through these modification procedures a PEGDA-based electrolyte was prepared with an ionic conductivity of the order of 10?4 S cm?1 and demonstrated, for the first time, sufficient mechanical strength to be used as the separator in spring-pressured planar half- and full cell configurations.

The conformal nature of the deposit was assessed by scanning electron microscopy (SEM) and it was found that a uniform film of thickness as low as 2 ?m was easily achievable. An initial attempt at a full 3D Li-ion microbattery cell based on a carbon foam substrate using composite electrode materials was made. The electrodeposited polymer electrolyte showed good electronic isolation and the cell showed limited cycling ability. The internal structure of the 3D cell was investigated by SEM and x-ray computed tomography.

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Identifiers

ORCID for John R. Owen: orcid.org/0000-0002-4938-3693

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