Successful Strategies to Enable High Voltage NMC/Graphite Li-ion Cells

Single-crystal mid nickel NMC positive electrode materials, like LiNi 0.65 Mn 0.30 Co 0.05 O 2 , are gaining interest for a variety of applications, including electric vehicles. Such materials can be produced at lower cost than high Ni materials, like LiNi 0.91 Mn 0.045 Co 0.045 O 2 , and can yield Li-ion cells with competitive energy density provided they can be charged to 4.4 V repeatedly. We show how electrolyte additives and simple surface coatings can enable the operation of mid-nickel NMC cells to 4.4 V for thousands of charge-discharge cycles at 40 o C. Emphasis is placed in the lecture on illustrating the mysteries behind the function of the additives and coatings. Figure 1, taken from reference 1, shows the impact of various electrolyte additives on the lifetime of NMC640 cells tested at C/3 and at 40 o C. Coatings show a comparatively enhanced effect. Figure 1. Number of cycles to 80% original capacity for cells charged to 4.4V plotted versus number of cycles to 80% original capacity for cells charged to 4.3 V. The cathode was single crystal NMC640. The data point labelled “Control” is for cells with no additives. Electrolyte additives are listed by “code” which is available in reference 1. Reference 1 – Saad Azam et al. J. Electrochem. Soc., 2024 171 110510 Figure 1