High-volumetric-energy-density redox-active polymer batteries

Abstract

Lithium ion batteries (LIBs) have conquered the energy storage device market due to its high energy densities. Even higher densities are being pursued as LIBs’ applications are extended from small devices to larger ones including electric vehicles and energy storage devices. Energy densities (EDs) can be considered from two different bases: mass and volume. Volumetric EDs should be emphasized in space-limited situations even if gravimetric EDs are more considered in literatures. Here we demonstrate lithium metal | redox-active polymer batteries showing high volumetric EDs. Polyvinylcarbazole (PVK) was used as an organic redox-active material while polyvinylidene fluoride (PVdF) and carbon black were used as a binder and a conducting agent respectively. The high volumetric EDs were achieved by spray deposition that we emphasize as a novel electrode-fabrication process in this work. The mixtures of the electrode components in solvents were spray-deposited on current collectors. Tiny droplets (size = 50um) containing the components were generated from nozzles. Solvent of the droplets were rapidly evaporated during the time of flight as well as when they met heated current collectors. The components originally included in the droplets were densely packed on the current collectors. The electrode densities achieved by the spray deposition were several times higher those of conventional blading methods. Accordingly, several times higher EDs were obtained from our lithium metal | redox-active polymer cells when compared with the cells prepared by blading methods. The volumetric ED gains overwhelmed the loss of porosity leading to mass transfer problems so that the volumetric EDs of spray-deposited electrodes were higher even at high rates than those of bladed electrodes. We expect that the spray deposition method is appropriate for preparing all-polymer-flexible batteries while conventional inorganic materials can be deposited by the method.