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

Abstract

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_0.8Co_0.1Mn_0.1O₂, LiNi_0.5Co_0.2Mn_0.3O₂, LiFePO₄, and LiCoO₂ 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.