3D printing of fast kinetics reconciled ultra-thick cathodes for high areal energy density aqueous Li–Zn hybrid battery

The limitation of areal energy density of rechargeable aqueous hybrid batteries (RAHBs) has been a significant longstanding problem that impedes the application of RAHBs in miniaturized energy storage. Constructing thick electrodes with optimized geometrical properties is a promising strategy for achieving high areal energy density, but the sluggish ion/electron transfer and poor mechanical stability, as well as the increased electrode thickness, itself present well-known problems. In this work, a 3D printing technique is introduced to construct an ultra-thick lithium iron phosphate (LFP)/carboxylated carbon nanotube (CNT)/carboxyl terminated cellulose nanofiber (CNF) composite electrode with uncompromised reaction kinetics for high areal energy density Li-Zn RAHBs. The uniformly dispersed CNTs and CNFs form continuous interconnected 3D networks that encapsulate LFP nanoparticles, guaranteeing fast electron transfer and efficient stress relief as the electrode thickness increases. Additionally, multistage ion diffusion channels generated from the hierarchical porous structure assure accelerated ion diffusion. As a result, LFP/Zn hybrid pouch cells assembled with 3D printed electrodes deliver a well-retained reversible gravimetric capacity of about 143.5 mAh g-1 at 0.5 C as the electrode thickness increases from 0.52 to 1.56 mm, and establish a record-high areal energy density of 5.25 mWh cm-2 with an impressive utilization of active material up to 30 mg cm-2 for an ultra-thick (2.08 mm) electrode, which outperforms almost all reported zinc-based hybrid-ion and single-ion batteries. This work opens up exciting prospects for developing high areal energy density energy storage devices using 3D printing.