Toward Long-Life, Ultrahigh-Nickel Layered Oxide Cathodes for Lithium-Ion Batteries: Optimizing the Interphase Chemistry with a Dual-Functional Polymer

摘要

Boosting the Ni content in LiMO2 (M = Ni, Co, Mn, etc.) layered oxides is a promising way to establish high-energy-density, low-cost cathodes, but the poor cathode surface stability is a daunting challenge for their practical viability. Herein, by constructing a dual-functional binder framework with a conductive polymer-polyaniline (PANI), the ultrahigh-Ni layered oxide cathode (LiNi0.94Co0.06O2) exhibits significantly improved cyclability, with a capacity retention greatly increased from 47% to 81% over 1000 cycles in full cells. It is demonstrated that the acidic species (e.g., HF) in the electrolyte can be efficiently scavenged through a protonation process of PANI, hence the cathode surface reactivity is greatly suppressed, and the rock-salt phase propagation into bulk structure is considerably alleviated. Furthermore, the PANT binder system effectively prevents both the cathode-electrolyte interphase (CEI) and the anode-electrolyte interphase (AEI) from degrading to a thick "triple-layer" architecture upon extensive cycling, resulting in more robust, thinner CEI and AEI with regulated interphasial chemistry. Moreover, the delocalized pi-conjugated electrons along the backbone of PANI facilitate fast electron transfer and promote rate capability even at low temperatures (-20 degrees C). This work sheds light on rational binder engineering for developing high-energy-density lithium-ion batteries with acceptable cycle life.