Unlocking the potential of internal Li-ion transfer in Ni-rich cathodes blended with LiFePO4 to address first cycle irreversible capacity loss and degradation

Abstract

Ni-rich cathodes are widely used in lithium-ion batteries (LIBs) due to their high capacity and cost-effectiveness. However, they suffer from significant irreversible capacity loss during the first cycle (initial capacity loss, ICL), which limits their practical potential. The ICL stems from the intrinsic properties of the material, specifically a decrease in the number of Li vacancies-i.e., available sites for Li-ion intercalation-toward the end of discharge, severely hindering further lithiation. While various strategies, such as doping and coating, have been explored, a definitive solution remains elusive. Here, we propose a novel approach to mitigate ICL in Ni-rich cathodes by blending them with LiFePO4. Our findings reveal unique internal Li-ion transfer between the two materials at the end of discharge. Initially, Li-ions intercalate into FePO4 and are then rapidly transferred to Li1-xNiO2, driven by electrochemical potential differences. This process introduces a fast, spontaneous Li insertion mechanism at the end of discharge, replenishing vacancies in Li1-xNiO2 and mitigating ICL. Additionally, we found that this internal Li-ion transfer becomes more enhanced with cycling, thereby slowing down the rate of capacity degradation. Thus, this study highlights the potential of leveraging internal Li-ion transfer in blended electrodes to overcome the inherent challenges of battery materials. By simply blending Ni-rich cathodes with conventional materials like LiFePO4, we can significantly enhance both performance and longevity.