Fabrication of computationally designed cathode and separator materials for a high performance Na-ion battery

Abstract

The stipulations of high-performance batteries with sustainable and green benevolent energy storage systems have swiftly been increasing their demands attributable to the proliferation and modifications of renewable energy sources which has occupied an apex with markets with high-end of grid-scale battery applications. Regarding those facts, sodium (Na)-ion batteries (SIBs) has introduced as promising and talented candidates [1] due to the abundance and profusion of sodium in earth crust [2] as well as sea water- making low-cost resources- analogous characteristics with the established lithium-ion batteries. Last three decades, some researches had finished to develop the sodium ion batteries, unfortunately numerous problems, such as its material stability, cyclability, performances, the lack of great combination with electrodes, separators and the electrolytes have faced as new research design as well as energy/power density and long cyclic stability for commercialization, environmental issues have raised to throw the uncontrolled challenges in the area of electrochemistry and optoelectronics materials. As a result, this study has designed to convey the maximum requirements for newly designed materials of cathodes and separator of a Na-ion battery.

In this century, the computational tool from computational chemistry deals a towering significance to design new materials without waste the chemical, cost, time consumption, and employment investigation with environmental sustainability [3]. Consequently, the CASTEP code from Material Studio version 8.0 was used to investigation the electronic structure, band gap, total density of state (DOS), partial density of state (PDOS), optical properties, elastic constant, mechanical properties and redox potential for selecting cathodes materials {Na₃V₂(PO₄)₂F₃ [4] and changing the fluorine (F) atom by Cl^-, Br^-, I^- anions and NO₃^-} using the Density functional theory (DFT). Besides, for the separator material, another crucial part of a battery, electrospun hybrid PVDF – HFP/SiO₂ fiber-based separator (EHS) [5], modified cellulose acetate separator (MCA) [6], cross-linked carboxymethyl cellulose (CMC) and hydroxyethyl cellulose (HEC) [7], cross-linked carboxymethyl cellulose (CMC) and modified cellulose acetate separator (MCA), cross-linked hydroxyethyl cellulose (HEC) and modified cellulose acetate separator (MCA) was studied as similar to cathode with same functional. To say more, the analysis of the separator the properties such as heat capacity, surface properties, elastic properties and other mechanical properties was investigated by DFT method. From the computational study, the superior cathode and separator were selected for wet based study focusing the fabrication process.

The cathode and separators were reported to be prepared by different methods like two-step method [8], facile sol-gel method [9], and non-solvent induced phase separation (NIPS) [7]. Typical preparation process for Na₃V₂(PO₄)₂F₃ was followed the procedure as below: the stoichiometric amount of NH₄VO₃, NaF and NH₄H₂PO₄ with the molar ratio of 2:3:2 was dissolved in deionized water. Then saturated citric acid [HOC(COOH)(CH₂COOH)₂] solution was dropped into the above solution until the ratio of vanadium: citric acid equals to 5:4. The obtained solution was evaporated at 80 ^oC, dried at 120 ^oC for 12 hours and ground to form precursor. Finally, the precursor was pre-heated at 300 ^oC for 4 hours and sintered at 650 ^oC for 8 hours under nitrogen atmosphere with inter-mediate grinding to obtain the NVPF@C nanocomposite [9]. The XRD method to characterize the crystal structure and size of the prepared sample, scanning electron microscopy (SEM) for investigating surface morphology, transmission electron microscopy (TEM) for microstructure, Fourier transform infrared spectroscopy (FT-IR) for chemical composition, and Differential scanning calorimetry (DSC) for thermal properties was used.