Green synthesis of polyimide by using an ethanol solvothermal method for aqueous zinc batteries.

Polyimides (PIs) are welcomed by battery researchers because of their exceptional heat resistance, structural design versatility, and ion-bearing capabilities. However, most of the reported PIs are synthesized by using toxic and hazardous reagents, such as ethylenediamine, p-phenylenediamine, 1-methyl-2-pyrrolidone (NMP), N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), etc., which are not conducive to environmentally friendly development. In this paper, we aim at employing green solvents and raw materials to prepare PIs using a facile solvothermal method. The reactants are urea and 1,4,5,8-naphthalene tetracarboxylic acid dianhydride (NTCDA). The solvents include pure water, pure ethanol, or water-ethanol mixed solvent. The volume ratio of ethanol in the mixed solvent is regulated to obtain the optimum synthesis condition. Depending on the proportion of ethanol, the polyimide products are labeled as U-PI-0, U-PI-50, U-PI-100, etc. The polymerization degree and structure of synthesized PIs are characterized by gel permeation chromatography (GPC), X-ray diffraction (XRD), scanning electron microscopy (SEM), etc. The results indicate that U-PIs exhibit diverse morphological features, including small fragmented, strip-like, and sheet-like structures, and have relative molecular weights ranging from 7500 to 83 000. Notably, the sheet-like U-PI-100 possesses the largest specific surface area, reaching up to 4.20 m2 g-1. When employed as an electrode material in aqueous zinc batteries, U-PI-100 demonstrates superior electrochemical performance compared to others. At a charge-discharge rate of 0.05C, the initial charge/discharge capacity of U-PI-100 is measured to be 314.2/443.7 mA h g-1.

High specific capacity FeFe(CN)6 as the cathode material in aqueous rechargeable zinc-sodium hybrid batteries.

Aqueous zinc-sodium hybrid batteries with a Prussian blue cathode have been extensively studied in recent years. However, less research has been conducted on low-cost ferric ferricyanide (FeFe(CN)6) cathode materials. Considering that both Zn2+ and Na+ can be reversibly embedded in FeFe(CN)6 crystals, here we focus on mixed electrolytes with different concentrations of ZnSO4 and Na2SO4 in deionized water to explore the preference of FeFe(CN)6 towards Zn2+ and Na+. As a result, by using 0.1 M ZnSO4 + 1 M Na2SO4 electrolyte, a superior battery performance is obtained, which reveals that the co-function of Zn2+ and Na+ in this electrolyte promotes Zn//FeFe(CN)6 cells to exert a superior specific capacity. In this work, FeFe(CN)6 is synthesized by a co-precipitation method and is analyzed by XRD, SEM, etc., and then used as the cathode material in Zn-Na hybrid batteries. Cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) tests show that FeFe(CN)6 in 0.1 M ZnSO4 + 1 M Na2SO4 electrolyte delivers the highest discharge/charge capacities of 165.2/165.9 mA h g-1 (theoretical specific capacity: 212.2 mA h g-1) at a 0.1 C current density, with good capacity retention of 84% after 200 cycles at 15 C, outperforming many of the reported Zn-Na hybrid cells.

An overview of the preparation and application of counter electrodes for DSSCs.

Dye-sensitized solar cells (DSSCs) are potential products for the next generation of photovoltaic technology, which is one of the research hotspots in photovoltaics. The counter electrode in DSSCs collects electron in the external circuit and catalyzes the reduction of the redox electrolyte and hole transport in the solid electrolyte. Thus, it undoubtedly has an important impact on the photovoltaic performance, long-term stability, and cost of DSSCs. In this work, the materials of counter electrodes are classified into metals, carbon materials, conductive polymers, and inorganic compounds. The preparation, mechanism, conversion efficiency, and properties of counter electrodes are reviewed.

Multiwalled carbon nanotube network connected Mg0.5Ti2(PO4)3 composites to improve sodium storage performance.

The research on sodium-ion batteries (SIDs) has aroused intensive attention. In this work, the Mg0.5Ti2(PO4)3 (MTP) composite material with NASICON structure has been studied as an anode material in SIDs. The sol-gel method is used to synthesize the Mg0.5Ti2(PO4)3 with a conductive network that can be constructed by using carbon nanotubes (CNTs) and phenolic resin as the amorphous source of carbon coating. The CNT network is used not only to improve the outcome of electrolyte penetration and reduce the internal resistance to diffusion but also to create a fast path for electron transport, thereby elevating the level of electronic conductivity. The phenolic resin is generated on the surface of MTP which extends its cycle life. The carbon-coated Mg0.5Ti2(PO4)3 with 0.10 g CNTs (MTP-CNT10) displays optimal performance as an anode material in SIDs, and shows a discharge capacity of 298.8 mA h g-1, 258.3 mA h g-1 and 254.8 mA h g-1 at 0.1C, 0.5C and 1C, respectively. Besides, the capacity retention rate reaches 92% after 300 cycles at 10C. This study contributes an effective solution to improving the electrochemical performance of electrode materials through the introduction of carbon coating and highly conductive materials.