Less is more: tiny amounts of insoluble multi-functional nanoporous additives play a big role in lithium secondary batteries

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Materials for energy and sustainability, 2022-04, Vol.1 (14), p.847-858
• Main Authors: Qi, Ruoxuan, Yang, Chao, Ma, Liujia, Fan, Xiaoying, Wu, Qiaoyun, Wang, Chao, Cheng, Ya-Jun, Guo, Kunkun, Gao, Yanfeng, Xia, Yonggao
• Format: Article
• Language: English
• Subjects: Additives; Batteries; Binders; Black carbon; Carbon black; Cathodes; Cathodic dissolution; Conductivity; Dissolution; Electrodes; Ion currents; Lithium; Lithium batteries; Lithium ions; Microporosity; Polymers; Rechargeable batteries; Storage batteries
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/d1ta10134j

Binders play an important role in multi-component electrodes for rechargeable batteries based on various elements such as Li, Na, K, Mg, and Zn, which suffer from poor electronic and ionic conductivity. Binder-free electrodes provide another way to resolve problems, where sophisticated structure construction is required. A new concept of electrode processing alternative to binder-containing and binder-free electrodes was established. A multi-functional PIM-1 (a polymer with intrinsic microporosity) additive was used instead of PVDF to form mechanically processable lithium secondary battery cathodes free of dissolution of PIM-1. Due to its unique nanoporous structure built by the spiro-containing rigid aromatic polymer chain, only a tiny amount of PIM-1 is needed to retain good performance (from 1% to 0.05%), far below the typical composition for PVDF. The universal applicability of PIM-1 to cathodes of LiNi 0.8 Co 0.1 Mn 0.1 O 2 , LiNi 0.5 Co 0.2 Mn 0.3 O 2 , LiFePO 4 , and LiCoO 2 is demonstrated. Homogeneous dispersion of carbon black is achieved by PIM-1 via a point-to-plane contact mode, which stabilizes the electrode and increases the electronic conductivity. Mechanical buffering by stiff PIM-1 yields crack-free electrodes after cycles. An inorganic rich cathode-electrolyte interface layer is formed via a desolvation process promoted by PIM-1, because of its strong binding ability with lithium ions, which is beneficial for cyclic stability and rate capability. A new concept of electrode processing with tiny amounts of multi-functional microporous PIM additives was established as an alternative to binder-containing and binder-free electrodes, leading to enhanced electrochemical performance.