Experimental challenges for electrochemical evaluation of cathodes in lithium-ion battery half-cells

The rising demand for lithium-ion batteries and the constant requirements for better performance have stimulated the development and improvement of materials. Reliable procedures and careful evaluations are needed in order to guarantee quality of the improvements proposed. Thus, in the current work several steps from material characterization to electrochemical analysis were investigated for NMC811 cathode. It is demonstrated that slurry rheology is affected by materials characteristics, preparation, and mixing, parameters that must be controlled to obtain adequate electrode. Calendering and uncaledering electrodes were studied with porosity values of 28, 38, and 61 %. As confirmed by rate capability and impedance measurements, calendering improves performance; however, optimization is required to ensure morphology integrity of the NMC particles, as evidenced by scanning electron microscopy analysis. The effects of separator were also evaluated, where an interesting approach using glass fibers is demonstrated to be appropriated for electrochemical evaluation in half-cells. Two distinct cathode mass loadings (4 and 17 mg·cm−2) were investigated to demonstrate how it can lead to different results, especially at high C-rates and over stability measurements. The influence of all the mentioned factors is reported and discussed in detail. The experimental results show the importance of careful analysis of several aspects of half-cell preparation and measurements.