He Jiarong, Tao Tao, Yang Fan, Sun Zhipeng
School of Materials and Energy, Guangdong University of Technology, Guangzhou 510006, China.
ACS Appl Mater Interfaces. 2021 Dec 22;13(50):60099-60114. doi: 10.1021/acsami.1c21271. Epub 2021 Dec 10.
Sodium-ion batteries (SIBs) have aroused intense research and academic interest due to the natural abundance and cost-effectiveness of sodium resources. Presently, cathode materials based on the Na(VOPO)F (0 ≤ ≤ 1, NVPF) polyanionic framework show intriguing electrochemical performances toward practical and advanced SIBs due to its high operating voltage (>3.9 V) and high energy density (>500 Wh kg). Different from conventional approaches focusing on delicate morphology design, metal ion substitution, and the conductive matrix's incorporation to overcome the low intrinsic electrical conductivity, here we adopt a one-step microwave-assisted hydrothermal approach to optimize the electrochemical performances of NVPF via manipulating its phase compositions with different vanadium sources and distinguishing the tetragonal (4/) symmetry of the Na(VOPO)F phase from the orthorhombic symmetry () of the NaV(PO)F phase. The introduction of the conductive reduced graphene oxide (rGO) framework and its impacts on the phase compositions were systematically investigated. The rGO framework with different calcination temperature can alter the phase composition and the electrical conductivity of NVPF cathodes significantly, thus having a great impact on their electrochemical performances. Galvanostatic charge/discharge, cyclic voltammetry, electrochemical impedance spectroscopy, and the galvanostatic intermittent titration technique are adopted to compare their electrode polarization and kinetics difference and show that NVPF@rGO-600 °C possesses a high rate, small polarization, and fast kinetics electrochemical properties. This work provides new insights into manipulating phase compositions of the NVPF cathode by modulating the synthesis conditions and revealing their synergistic effect with a rGO conductive framework toward a superior rate capability and more realistic practical applications for SIBs.
由于钠资源的天然丰富性和成本效益，钠离子电池（SIBs）引起了广泛的研究和学术关注。目前，基于Na(VOPO)F（0≤≤1，NVPF）聚阴离子框架的阴极材料因其高工作电压（>3.9V）和高能量密度（>500Wh kg）而在实际和先进的SIBs方面表现出引人注目的电化学性能。与传统方法不同，传统方法侧重于精细的形态设计、金属离子取代和引入导电基质以克服低固有电导率，在这里我们采用一步微波辅助水热法，通过使用不同的钒源控制其相组成，并区分Na(VOPO)F相的四方（4/）对称性和NaV(PO)F相的正交对称性（）来优化NVPF的电化学性能。系统地研究了导电还原氧化石墨烯（rGO）框架的引入及其对相组成的影响。具有不同煅烧温度的rGO框架可以显著改变NVPF阴极的相组成和电导率，从而对其电化学性能产生重大影响。采用恒电流充/放电、循环伏安法、电化学阻抗谱和恒电流间歇滴定技术来比较它们的电极极化和动力学差异，结果表明NVPF@rGO-600°C具有高倍率、小极化和快速动力学的电化学性能。这项工作通过调节合成条件来控制NVPF阴极的相组成，并揭示其与rGO导电框架对SIBs优异倍率性能和更实际应用的协同效应，提供了新的见解。
