Publication date: 10th April 2024
One of the strategies to improve the performance of the positive electrode in Li-ion batteries consists of mixing multiple active materials, typically two of them. If properly selected, this results in synergistic effects that could potentially enhance the performance beyond what the rule of mixtures predicts. Unfortunately, the internal dynamics of these electrodes remain poorly understood. One synergistic effect involves lithium redistribution within electrode components, especially after periods of high discharge current that force one of the materials to accommodate excess lithium. This interaction has been termed as “buffer effect” and could potentially be exploited to enhance the cell´s performance in high intermittent loads, often imposed to EV batteries.
Blended electrodes containing binary mixtures of four of the most used active materials, namely LiNi0.5Mn0.3Co0.2O2 (NMC), LiMn2O4 (LMO), LiFePO4 (LFP) and LiFe0.35Mn0.65PO4 (LFMP) have been investigated with the aim to understand the contribution of each material as a function of state of charge during both continuous1 and pulsed discharges (3C) . A special experimental decoupled blend electrode setup2 and operando synchrotron XRD and XANES measurements on real blended electrodes are used.
Results derived from both experiment types are in good agreement and shed light to internal processes and their dependence on material’s voltage profile and state of charge (SoC). It is found that individual materials are subjected to rates significantly higher than the cell’s nominal. Furthermore, the magnitude and directionality of the buffer effect strongly vary depending on the binary combination of materials and the battery SoC.
Authors are grateful for access to ALBA synchrotron for beamtime. ICMAB-CSIC members thank the Spanish Agencia Estatal de Investigación Severo Ochoa Programme for Centres of Excellence in R&D (CEX2019-000917-S) and funding through grant PID2020-113805GB-I00. D.C. wants to acknowledge DESTINY MSCA PhD Programme. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under Grant Agreement No 945357. People that contributed to this work are also Marcus Fehse , Maria Angeles Cabañero, Natalia Romano and Damien Saurel of CIC energiGUNE, Ashley Black of ICMAB-CSIC, Violetta Arszelewska and Pierre-Etienne Cabelguen of UMICORE and François Fauth of ALBA-CELLS.
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