Beyond slurry cast: battery electrodes by design
File(s)
Author(s)
Hair, Samuel
Type
Thesis
Abstract
All commercial battery electrodes today are manufactured by slurry-casting active material powder on to a metal current collector foil. This manufacturing process has been proven over decades and is embedded, but the resulting electrodes limit cell performance. This thesis documents a quantitative, first-principles re-design of the battery electrode for improved gravimetric energy density at commercial cell level.
First, an existing commercial lithium-ion battery is quantitatively analysed to establish a baseline and identify the key sources of loss. The LGM50 cell only achieves 52% of its theoretical gravimetric energy density at a discharge rate of 0.1C, and less than 20% at a discharge rate of 4C. Next, pyrolytic graphite sheet is identified as a promising material for low inactive mass, low overpotential electrodes. Laser drilling is used to manufacture pyrolytic graphite sheet electrodes with arrays of electrolyte channels. Following the introduction of electrolyte channels, the gravimetric active material capacity of pyrolytic graphite sheet is measured to increase from 10 to 450 mA h g⁻¹.
A model is developed to estimate the gravimetric energy density of a commercial cell from electrode characterisation data. This model reveals that the manufactured pyrolytic graphite sheet electrodes would severely restrict the gravimetric energy density of a commercial cell, despite having high gravimetric active material capacity. The manufactured electrodes perform poorly due to low areal capacity and high electrode porosity. To optimise their design for use in a commercial cell, a second model is developed to estimate the gravimetric active material capacity for a given electrode design. A pyrolytic graphite sheet electrode with a hexagonal array of 5 µm diameter, 20 µm pitch channels could increase the gravimetric energy density of a LGM50 cell by 15% to 302 W h kg⁻¹.
First, an existing commercial lithium-ion battery is quantitatively analysed to establish a baseline and identify the key sources of loss. The LGM50 cell only achieves 52% of its theoretical gravimetric energy density at a discharge rate of 0.1C, and less than 20% at a discharge rate of 4C. Next, pyrolytic graphite sheet is identified as a promising material for low inactive mass, low overpotential electrodes. Laser drilling is used to manufacture pyrolytic graphite sheet electrodes with arrays of electrolyte channels. Following the introduction of electrolyte channels, the gravimetric active material capacity of pyrolytic graphite sheet is measured to increase from 10 to 450 mA h g⁻¹.
A model is developed to estimate the gravimetric energy density of a commercial cell from electrode characterisation data. This model reveals that the manufactured pyrolytic graphite sheet electrodes would severely restrict the gravimetric energy density of a commercial cell, despite having high gravimetric active material capacity. The manufactured electrodes perform poorly due to low areal capacity and high electrode porosity. To optimise their design for use in a commercial cell, a second model is developed to estimate the gravimetric active material capacity for a given electrode design. A pyrolytic graphite sheet electrode with a hexagonal array of 5 µm diameter, 20 µm pitch channels could increase the gravimetric energy density of a LGM50 cell by 15% to 302 W h kg⁻¹.
Version
Open Access
Date Issued
2023-09-02
Date Awarded
2024-02-01
Copyright Statement
Creative Commons Attribution NonCommercial NoDerivatives Licence
Advisor
Cooper, Samuel
Shaffer, Milo
Publisher Department
Materials
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)