Analysis of the Synergic Effects in LiFePO4/Li2CuO2 Cathode Blends for Li Ion Batteries Via Electrochemical and EPR Experiments

Much of the focus in improving the specific energy in Li-ion batteries is centered on the cathode, specifically designing new active materials; moreover, a promising alternative is the use of ‘blended’ electrodes, which are comprised of at least two different active materials working synergically. Although the principle behind these collaborative properties is not yet fully understood, the reasoning behind this proposal is based on the correlation of property-function of each component. Blending two or more cathode materials can result in a cathode with fewer of the drawbacks than the parent materials, allowing for an optimized performance compared to what would be possible with the individual materials. LiFePO 4 and LiCoO 2 are two of the most commercial cathode materials because of their high stability and adequate specific capacities, but are unable to meet the higher capacity demands of newer technologies. Li 2 CuO 2 is a promising cathode material with a specific capacity of 490 mAh/g, notwithstanding it undergoes irreversible phase changes during cycling, resulting in poor cyclability and a specific capacity far lower than its theoretical capacity 1 . The objective of this study is to take advantage of the stability of commercial active materials, such as LiFePO 4 and LiCoO 2 to stabilize the high capacity Li 2 CuO 2 phase for practical use. Preliminary results of the Li 2 CuO 2 /LiFePO 4 blends have shown an improved capacity, albeit still below the theoretical capacity of Li2CuO2, and a slight improvement with respect to the cyclability. The method used to blend these materials as well as the inclusion of the conductive and binding additives and the order of addition during the blending have all shown to affect the battery’s performance. Electron Paramagnetic Resonance (EPR) experiments have shown that electrodes blended with a ball mill presumably lead to the formation of stable oxygen vacancies which have an effect on the synergy which is not observable in pure Li 2 CuO 2 blended cathodes or physical mixtures. Additionally, the presence of the conductive and binding additives during the blending process appear to result in a more homogenous mixture, preventing the reversion of Li 2 CuO 2 into its precursors during the blending process, thus promoting higher specific capacities. The authors thank CONACyT-SENER- 416 Sustentabilidad No. 245754 for the financial support. 1. G. Ramos-Sanchez et al., Solid State Ionics , 303 , 89–96 (2017).