Preparation of Tough, Binder-Free, and Self-Supporting LiFePO₄ Cathode by Using Mono-Dispersed Ultra-Long Single-Walled Carbon Nanotubes for High-Rate Performance Li-Ion Battery

Low-contents/absence of non-electrochemical activity binders, conductive additives, and current collectors are a concern for improving lithium-ion batteries' fast charging/discharging performance and developing free-standing electrodes in the aspects of flexible/wearable electronic devices. Herein, a simple yet powerful fabricating method for the massive production of mono-dispersed ultra-long single-walled carbon nanotubes (SWCNTs) in N-methyl-2-pyrrolidone solution, benefiting from the electrostatic dipole interaction and steric hindrance of dispersant molecules, is reported. These SWCNTs form a highly efficient conductive network to firmly fix LiFePO₄ (LFP) particles in the electrode at low contents of 0.5 wt% as conductive additives. The binder-free LFP/SWCNT cathode delivers a superior rate capacity of 161.5 mAh g⁻¹ at 0.5 C and 130.2 mAh g⁻¹ at 5 C, with a high-rate capacity retention of 87.4% after 200 cycles at 2 C. The self-supporting LFP/SWCNT cathode shows excellent mechanical properties, which can withstand at least 7.2 MPa stress and 5% strain, allowing the fabrication of high mass loading electrodes with thicknesses up to 39.1 mg cm⁻². Such self-supporting electrodes display conductivities up to 1197 S m⁻¹ and low charge-transfer resistance of 40.53 Ω, allowing fast charge delivery and enabling near-theoretical specific capacities.