It is well known that the microstructure of the Li-ion battery (LIB) electrode can largely impact performance of LIBs. One approach to improve the performance of the LIBs is to gain insight in the correlations between the complex heterogeneous microstructure existing of active material, conductive additive and electrolyte, providing the required electronic and ionic transport. In a recent study we successfully demonstrated a simple and cost effective templating technique utilizing hydrogen carbonate salts to enhance the power density of LiFePO₄electrodes without compromising the electrode density [1]. The applied templating method improves the capacity retention at high rates significantly. More importantly, the template only results in a slight increase in the porosity, leading to a combination of large tap density (high volumetric energy density) and large power density. The electrochemical data analysis indicates the better performance of templated electrodes may due to better interconnectivity and tortuosity within electrolyte induced by the template. However, direct evidence to correlate the microstructure of the templating electrode with LIBs performance is still needed.

In this work, by combining focused ion beam-scanning electron microscopy (FIB-SEM) and neutron depth profiling (NDP), we have obtained three-phase 3D electrode microstructure and Li-ion concentration profiles to better understand the improved rate performance of the templated LiFePO₄ electrodes. Although it is proposed that the hierarchical interconnected porosity in the templated sample can enhance the electrode rate performance, no significant electrolyte tortuosity differences were found between the conventional and carbonate templated LiFePO₄ electrodes. Surprisingly, although the same amount of CB was used in the two electrodes, a better electronic conductive CB network was observed for the templated sample (Figure 1 a, b), enhancing the activity of LiFePO₄ at near the electrolyte-electrode interface as directly observed with NDP. Moreover, the CB structure in the templated electrode possesses a less tortuous pathway for electron transport, and the tortuosity distribution is less heterogeneous than in the conventional electrode, as shown in Figure 1 c-f. This results from 3D microstructure analysis is consistent with the NDP result where the templated electrodes show enhancing charging/discharging activity near the electrolyte-electrode interface than conventional LiFePO₄electrode. The results demonstrate that the templated electrode has better charge transport network, which result in improved performance.  

[1] Singh, D. P.; Mulder, F. M.; Abdelkader, A. M.; Wagemaker, M. Advanced Energy Materials 2013, 3, 572.