Abstract
Performance properties of lithium-ion battery electrodes; capacity, rate and lifetime, are determined by the design of the coating composite microstructure. The internal pore structure and electronic networks for high coat weight graphite electrodes are manipulated through changes in the ink rheological properties, and through an syringe dispensing printing process. The rheological properties of a water-based, high viscosity graphite ink were optimised using a secondary solvent for the rheological requirements of a syringe dispensing method. The microstructure of high coat-weight battery electrodes produced from printing and tape cast methods were compared and the electrochemical performance evaluated. Cross sectional analysis of the slurry cast coatings showed improved component homogeneity, lower graphite alignment with 0.1% to 10% weight increase of the secondary solvent, with a corresponding change in tortuosity of the electrodes of 5.3–2.8. Improved cycle life is observed with a printed electrode containing an embedded electrolyte channel. Performance properties were elucidated through charge discharge, GITT and PEIS measurements. Improved electronic conductivities, exchange currents and diffusion coefficients were observed for the syringe deposited electrode. This digital deposition process for manufacturing electrodes shows promise for further optimisation of electrodes for long-life, high energy density batteries.
Highlights
Lithium ion batteries (LIB) must overcome two key technical challenges to meet the demand for high throughput production of EVs; further reduction of the production costs and an increase in energy density of the battery pack [1]
The increase of octanol content up to 1.0 wt% enhances the Carbon black (CB) distribution between the graphite particles, this could be due to the increased viscosity of the inks, and the higher shear forces induced in the mixing process upon the carbon black agglomerates
CMC is used as a thickening agent in these water-based systems, it stabilises the slurry from sedimentation and coats the graphite and carbon black in a surface layer which aids the dispersion of the components in the water solvent
Summary
Lithium ion batteries (LIB) must overcome two key technical challenges to meet the demand for high throughput production of EVs; further reduction of the production costs and an increase in energy density of the battery pack [1]. The composite based slurry is typically coated by tape casting methods onto the current collectors (copper for anodes and aluminium for cathodes), and subsequently dried to form the battery electrodes For both intercalation and conversion materials, design of electrode structures is key for optimisation of performance properties. An effective method of achieving high energy batteries, is to increase the areal capacity of the battery electrodes, and create higher loading and thick electrodes (currently electrodes are manufactured with thicknesses of 50 – 100 mm), in order to minimise the relative weight and volume of inactive components, i.e. separators and current collectors [1,20] This introduces challenges related to lithium-ion transport pathways and uniform electronic conductivity, both of which are critical to energy and power output. The effect upon the electrode microstructures from the rheological changes, and the deposition method were analysed, and their electrochemical parameters elucidated
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