Investigations of rate limitation in nanostructured composite electrodes and experiments towards a 3D Li-ion microbattery

Abstract

The factors effecting discharge rate limitation within LiFePO4 composite electrode structures have been investigated. It was found that for composite electrodes containing ‘small particles’ of active material solid state processes are not necessarily rate limiting. A simple model has been developed to describe the rate limitation that occurs in the composite electrode structure due to electrolyte concentration, electrode thickness and lithium ion transference number. The conformal electrodeposition of cathode materials onto 3D current collectors has been achieved with good control of film thickness. The advantage of the 3D current collector configuration over a conventional thin film arrangement has been realised by a 250 times capacity increase for a given footprint area. It was suggested the observed rate performance of half-cell 3D microbatteries, based on a manganese dioxide cathode and a lithium foil anode, was limited by the lithium ion transport distance through the porous 3D structure. The electrodeposition of conformal polymers layers onto 3D substrates was investigated. The use of electrodeposited, electrolyte swollen, poly(acrylonitrile) and poly(aniline) films as polymer electrolytes was demonstrated. A novel method for the determination and differentiation of electronic and ionic resistance in electrodeposited polymer layers has been developed. A ‘working’ cell based on consecutively electrodeposited cathode and polymer electrolyte layers and a ‘soft contact’ liquid anode was presented

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

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