Synergistic Coupling Effect of Electronic Conductivity and Interphase Compatibility on High-Voltage Na₃V₂(PO₄)₂F₃ Cathodes

Abstract

Na3V2(PO4)2F3 (NVPF) has been considered an up-and-coming cathode material candidate for sodium (Na) ion batteries in light of its high specific capacity and working voltage. However, an erratic cathode/electrolyte interface layer is inevitably formed, accompanied by continuous electrolyte decomposition on the NVPF surface, when the voltage exceeds 4.2 V vs Na+/Na. Herein, the interphase features of NVPF are obviously enhanced owing to the ameliorated electronic conductivity obtained by combining it with carbon nanotubes (CNT). The NVPF with 3 wt % CNT (NVPF@3% CNT) reduces the Na+ diffusion kinetic energy barrier and electron transport resistance. Furthermore, the conducting network formed by CNT with sturdy structure strength can promptly accommodate the volumetric changes during sequential Na+ extraction/insertion and thus effectively improve the long-term cyclic performance of NVPF/hard carbon full cells. The initial discharge capacity approaches 105 mA h g–1 at 0.5C, and it retains 94% capacity retention after 200 cycles at the temperature of −10 °C. The cathode/electrolyte interphase characterization results further demonstrate that the interphase layer on the NVPF@3% CNT cathode is thinner and more compact compared with pristine samples. This research provides a competitive strategy to facilitate the interfacial compatibility between the NVPF and electrolytes and accelerate the commercialization of high-performance Na-ion batteries.

Green Large-Scale Preparation of Na3V2(PO4)3 with Good Rate Capability and Long Cycling Lifespan for Sodium-Ion Batteries

“…In recent years, considerable focus has been directed toward the development of sustainable devices for energy storage to meet the substantial energy requirements of modern civilization. While fossil fuels are convenient for energy storage, they unfortunately lead to environmental pollution. − To achieve sustainable development and foster a “green” environment, it is necessary to establish an efficient and low-energy loss energy storage system. , Presently, the utilization of lithium-ion batteries (LIBs) has become prevalent in various mobile devices and portable electronics due to their environmentally friendly nature, high energy density, commendable safety performance, as well as being a novel form of energy storage device. − However, lithium resources are severely limited with uneven distribution, which hinders their additional utilization in large-scale energy storage fields. − Sodium-ion batteries (SIBs), which possess similar properties and storage mechanisms as LIBs but offer desirable characteristics such as superior safety performance, cost-efficiency, and abundant sodium resources, have attracted more attention recently. − The performance of SIBs is significantly affected by the cathode material; therefore, to focus research endeavors on the advancement of cathode materials with exceptional performance for SIBs is particularly important. − …”