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 (Rion) and charge‐transfer resistance (Rct) 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 LiNi0.80Co0.15Al0.05O2 (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 Rion and Rct due to short diffusion lengths, which improves electrochemical performances in LIBs with a high volumetric energy density of ≈710 Wh L−1.

High-Area-Capacity Cathode by Ultralong Carbon Nanotubes for Secondary Binder-Assisted Dry Coating Technology

“…As shown in the cross-sectional SEM images (Figure S7), MWCNT entangles and wraps the active material, demonstrating a nano “hook-and-loop” fastening effect within the electrode, which is similar to the roles of carbon nanotubes in the previously reported slurry-casted electrodes. , Some other research reports that MCNT will form a nano “hook-and-loop” with the binder to fasten the internal component of the electrode. , It is worth emphasizing that robust mechanical properties play a pivotal role in the fabrication of dry electrodes . Considering that PTFE will form PTFE film with the temperature over 110 °C, we carry out tensile tests on the M-LCO which was stored at 150 °C for 12 h . The M-LCO still showed 5.4% on the percentage of strain and 0.133 MPa on the tensile strength (Figure S8), indicating good tensile strength compared to the previous film.…”

“…17,41 It is worth emphasizing that robust mechanical properties play a pivotal role in the fabrication of dry electrodes. 42 Considering that PTFE will form PTFE film with the temperature over 110 °C, we carry out tensile tests on the M-LCO which was stored at 150 °C for 12 h. 43 The M-LCO still showed 5.4% on the percentage of strain and 0.133 MPa on the tensile strength (Figure S8), indicating good tensile strength compared to the previous film. Furthermore, the electrical resistivity of the dry electrode exhibited an immediate reduction upon the transition from using Super P to MWCNT as conductive additives.…”

Dry Electrode Processing Technology and Binders

“…It is obviously different from the air spraying process mentioned above in that the electrostatic spraying method is firstly used instead of the air spraying method to complete the deposition and film-forming operation of the powder mixture on the surface of the metal collector, and then the roller pressing is used instead of the hot pressing to complete the pressing and molding operation of the electrode. The advantage of electrostatic spraying is that it can deposit the powder mixture into the active layer [29] more quickly and conveniently, and roller pressing can better control the thickness and density of the film [40]. As shown in Figure 2, the main process is as follows: firstly, LiCO 2 (LCO), C65 (Super C65 carbon), and PVDF are mixed with a mass ratio of 90:5:5 to make a powder mixture, followed by using a high-pressure electrostatic spray gun to uniformly deposit the powder on a metal collector (Al foil) ground at one end; the deposited semi-finished electrode was then heat-treated at 250 • C for 1 h (for activated PVDF [41,42]), and then the deposited active layer was tightly pressed with the Al foil using a roll-pressing device to obtain electrodes.…”