Low porosity NMC622 and NMC811 electrodes made by severe calendering

The porosity of electrodes is one of the key parameters in designing high-performance and durable lithium-ion batteries. Although the volumetric energy density of batteries increases with decreasing porosity, high porosity is generally considered necessary for adequate ionic transport, especially for thick (i.e., high energy) electrodes. Since a high pressure or compression ratio during the calendering process can cause cracking of the electrode, which is believed to be detrimental, exceedingly low porosity electrodes have rarely been explored. Encouraged by our recent work on low porosity NMC622 electrodes, we report in this paper the effects of porosity on the structure, mechanical property, and electrochemical performance of high-loading electrodes (e.g., 4 mAh cm⁻²) made with either meatball-shaped polycrystalline LiNi_0.8Mn_0.1Co_0.1O₂ (NMC811) or single-crystalline LiNi_0.6Mn_0.2Co_0.2O₂ (NMC622) particles. Although severe calendaring caused cracking of NMC particles of both types, our half-cell tests demonstrated that the low-porosity electrodes can have better C-rate performance than high-porosity electrodes, contrary to the common belief that high porosity is necessary for high C-rate performance. Full-cell cycling tests showed that the low-porosity electrodes have better stability and capacity retention than that of the high-porosity electrodes. This work suggests new possibilities for high-density electrodes, especially for applications where high volumetric energy density is required.