A detailed understanding on how electrode composition and microstructure design influence capacity and kinetics is key to balancing the energy and power density of Li-ion batteries and ensuring a long battery life. 

 In our study, we compare different commercial 21700 high-energy cells. Despite very similar technical specifications (Capacity: 5 Ah / energy densities: 264 Wh/kg, 735 Wh/l), cells showed significant differences in performance tests with respect to rate capability and cyclic ageing. 

 To reveal the microstructure-property relations and the most critical microstructural parameters, complementary analytical methods such as optical and scanning electron microscopy, µCT- and FIB/SEM tomography, EDS and XRD were used to characterise the architecture of fresh and cycled electrodes at different length scales. We combined these results with results from detailed electrochemical studies such as OCV and half-cell tests with rebuilt half cells as well as electrochemical impedance spectroscopy. 

 Moreover, the 3D data from FIB/SEM tomography was used as the input for microstructure-resolved simulations, which allows for further investigation of the electrode microstructure and its effect on the electrochemical performance. 

By combining experimental and simulation results, we gained a comprehensive data set that allowed us to understand the differences in the electrochemical behaviour of both cells and their different behaviour during cyclic ageing. In this way, our study contributes to the development of guidelines for the design of optimised microstructural electrodes that combine energy with power and long battery life. 

Some main findings are: (i) The electrodes are highly densified with typical densities <3.6 g/cm³ for the cathode and <1.6 g/cm³ for the anode. (ii) Cathodes comprise of Ni-rich active materials, whereas anodes comprise of graphite and Si-rich phases with different morphologies. (iii) Electrode loadings differ by about 25% and have different carbon-binder (CBD) content. (iv) Microstructure-resolved simulations indicate that a low CBD content critically affects the electronic conductivity of the electrodes. (v) Thicker electrodes with low CBD content show inferior rate capability and cyclic stability. 

Acknowledgements: 
The authors gratefully acknowledge the funding of the project MiCha (03XP0317) by the German Federal Ministry of Education and Research (BMBF) within the AQua-Cluster.