Transport electrification has resulted in an expansion of the Li-ion battery application from Wh to kWh storage. This has brought up additional requirements to improve performance (e.g. power, cycle life) enhance of sustainability and decrease of cost. Blending different active materials at the same cell electrode, an empirical approach commonly used for primary cells, has been readily applied to commercial EV Li-ion batteries mostly on the positive side. The global aim is to promote positive synergetic effects between the different electrode components, which have unfortunately received limited attention at the fundamental research level.

Materials with fast reaction kinetics, such as LiMn₂O₄ (LMO) can sustain significantly higher effective rates than the nominal rate applied to the electrode. This has motivated the widespread commercial use of NMC:LMO blends as LiNi_xMn_yCo_zO₂ (x+y+z=1, NMC) despite having slow kinetics, exhibits high capacity (especially for large amounts of Ni) and the addition of LMO lowers overall costs while enhancing power performance. Olivine LiMPO₄ (M=Fe, Mn) based blends have a lower presence in commercial cells to date but they have also deserved attention at the laboratory scale as they can as well exhibit fast kinetics and are based on low cost abundant transition metals.

Results will be presented related to different blends, consisting of combinations of LMO, NMC, LiFePO₄ (LFP) and LiFe_0.35Mn_0.65PO₄ (LFMP). Electrochemical experiments coupled to time-resolved synchrotron operando X-ray diffraction experiments enable to capture charge transfer events between blend components which are dependent on both voltage profile and kinetics of individual blend components. The results demonstrate the significant impact of the voltage profiles of individual materials on the current distribution, with the effective C-rate of each component varying throughout the state of charge (SoC).

Finally, systematic operando synchrotron X-ray diffraction and absorption experiments will be presented for NMC and LFP with diverse experimental conditions (cell type, radiation energy etc.) to illustrate the existence of beam-induced effects which may bias interpretation of results. These range from total reaction inhibition to partial hindrance and negligible deviations from the expected mechanism, and have been consistently observed across various experimental conditions, photon energies, photon fluxes and exposure times. The total radiation dose per cycle seems to be a useful predictor of the magnitude of beam-induced electrochemical delay and could serve as a guideline to define reliable measurement protocols.