Abstract

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.

Highlights

  • When developing a lithium-ion cell chemistry, it is necessary to produce prototypes in a fully sized cell format, to provide information on electrochemical performance, energy density, and safety

  • After cell formation is complete, the most common test applied to lithium-ion cells is long term cycling

  • The galvanostatic intermittent titration technique (GITT) current density and step durations should be optimised for different cell chemistries [32]

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Summary

Introduction

When developing a lithium-ion cell chemistry, it is necessary to produce prototypes in a fully sized cell format, to provide information on electrochemical performance, energy density, and safety. The cell technology is scaled up to a fully engineered stacked or wound prototype [1]. This approach is adopted by every lithium-ion cell manufacturer. Electrolytes or electrode formulations are evaluated on a small scale, and progressively scaled up to full sized cells. This can be in a cylindrical, prismatic or soft pouch enclosure [1], depending on the target application and previous capital investment in specific cell making equipment

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