10 mAh cm⁻² Cathode by Roll‐to‐Roll Process for Low Cost and High Energy Density Li‐Ion Batteries

Abstract

Roll‐to‐roll dry processing enables the manufacture of high energy density and low cost Li‐ion batteries (LIBs). However, as the thickness of the electrode fabricated by dry processing becomes greater (≥10 mAh cm⁻²), Li‐ion migration resistance (R_ion) and charge‐transfer resistance (R_ct) in the electrode dramatically increase due to long diffusion lengths for Li‐ion and electron. Therefore, it is important to reduce diffusion lengths in the electrode to achieve high energy density LIBs. The dry electrode with a high areal capacity of 10 mAh cm⁻² and low resistance can be achieved by following three characteristics. First, the fibrillization behavior of polytetrafluoroethylene (PTFE) binder is controlled by adjusting the processing temperature during the fibrillization process, which enables uniform distribution of PTFE binder and carbon black (CB). Second, pore size/distribution and conducting network are engineered by multi‐dimensional conducting agents, enhancing Li‐ions and electrons transport in the electrode. Finally, the structural integrity of LiNi_0.80Co_0.15Al_0.05O₂ (NCA) particles is improved without fractures, which enables uniform pore distribution in the electrode by controlling the calendering step. The prepared 10 mAh cm⁻² dry electrode with homogeneous microstructure shows reduced R_ion and R_ct due to short diffusion lengths, which improves electrochemical performances in LIBs with a high volumetric energy density of ≈710 Wh L⁻¹.