To investigate the influence of cell formats during a cell development programme, lithium-ion cells have been prepared in three different formats. Coin cells, single layer pouch cells, and stacked pouch cells gave a range of scales of almost three orders of magnitude. The cells used the same electrode coatings, electrolyte and separator. The performance of the different formats was compared in long term cycling tests and in measurements of resistance and discharge capacities at different rates. Some test results were common to all three formats. However, the stacked pouch cells had higher discharge capacities at higher rates. During cycling tests, there were indications of differences in the predominant degradation mechanism between the stacked cells and the other two cell formats. The stacked cells showed faster resistance increases, whereas the coin cells showed faster capacity loss. The difference in degradation mechanism can be linked to the different thermal and mechanical environments in the three cell formats. The correlation in the electrochemical performance between coin cells, single layer pouch cells, and stacked pouch cells shows that developments within a single cell format are likely to lead to improvements across all cell formats.

The electrode formulation has a significant effect on the performance of lithium ion cells. The active material, binder, and conductive carbon all have different roles, and finding the optimum composition can be difficult using an iterative approach. In this study, a design of experiment (DoE) methodology is applied to the optimisation of a cathode based on lithium iron phosphate (LFP). The minimum LFP content in the electrodes is 94 wt%. Seventeen mixes are used to evaluate adhesion, resistivity, and electrochemical performance. The coating adhesion increases with binder content, and the coating conductivity increases with carbon nano-tube content. The best coatings achieve 5C:0.2C capacity ratios above 50%, despite the relatively high coat weight. Models based on just the component mixture do not replicate the discharge capacities at high rates. However, a combined mixture + process model can fit the data, and is used to predict an optimum formulation.

The impacts on battery cell ageing from high current operation are investigated using commercial cells. This study utilised two tests–(i) to establish the maximum current limits before cell failure and (ii) applying this maximum current until cell failure. Testing was performed to determine how far cycling parameters could progress beyond the manufacturer’s recommendations. Current fluxes were increased up to 100 C cycling conditions without the cell undergoing catastrophic failure. Charge and discharge current capabilities were possible at magnitudes of 1.38 and 4.4 times, respectively, more than that specified by the manufacturer’s claims. The increased current was used for longer term cycling tests to 500 cycles and the resulting capacity loss and resistance increase was dominated by thermal fatigue of the electrodes. This work shows that there is a discrepancy between manufacturer-stated current limits and actual current limits of the cell, before the cell undergoes catastrophic failure. This presumably is based on manufacturer-defined performance and lifetime criteria, as well as prioritised safety factors. For certain applications, e.g., where high performance is needed, this gap may not be suitable; this paper shows how this gap could be narrowed for these applications using the testing described herein.

The size of a lithium iron phosphate (LFP) cathode mix was increased by a factor of thirty, and the capacity of the cells produced with it by a factor of three-hundred. As well as rate and cycling tests, the coatings were also characterised for adhesion and resistivity. The adhesion and total through-plane resistance were both dependent on the drying conditions during coating. The discharge capacities at high rates and the pulse resistances showed much less influence from the drying temperature. The mix formulation contained 97 wt% LFP, and was based on an earlier design of experiments (DoE) study, using relatively high active material contents. Overall, the mix exceeded the performance predicted by the modelling study.

Solid state lithium-metal batteries show substantial promise for overcoming theoretical limitations of state-of-the-art Li-ion batteries to enable gravimetric and volumetric energy densities upwards of 500 Wh kg−1 and1000WhL−1, respectively. Whilezerolithiumexcessconfigurationsareparticularlyattractivefrom both an energy density and a manufacturing standpoint, inhomogeneous lithium plating on charge results in active lithium loss and a subsequent coulombic efficiency penalty accrued from Li anode irreversibility, which severely limits cycle life. Excess lithium in the form of a lithium foil is therefore currently needed to extend cycle life to practical values. On the other hand, excess lithium negatively impacts energy density and thus limiting its thickness is essential to derive any practical benefit from adoption of a lithium metal-based battery architecture. Currently, costs associated with the production of these foils at such thicknesses and scale are a major impediment to adoption by industry. Here we discuss the viability of various technologies in the realisation of thin lithium films that can be scaled up to surface areas required for gigafactory production. We identify thermal evaporation as a potentially cost-effective route to address these challenges and provide a technoeconomic assessment of the projected costs associated with the fabrication of thin, dense lithium metal foils using this process. Finally we estimate solid state pack costs made using thermally evaporated Li foils.