Fe doping mechanism of Na0.44MnO2 tunnel phase cathode electrode in sodium-ion batteries.

Due to its stability and low cost, the tunnel-style sodium-manganese oxide (Na0.44MnO2) material is deemed a popular cathode choice for sodium-ion rechargeable batteries. However, the Jahn-Teller effect caused by Mn3+ in the material results in poor capacity and cycling stability. The purpose of this experimental study is to partially replace Mn3+ with Fe3+, in order to reduce the Jahn-Teller effect of the material during charging and discharging process. The results of Raman spectroscopy and X-ray photoelectron spectroscopy confirmed that the content of Mn3+ decreased after Fe3+ doping. Electrochemical studies show that the Na0.44Mn0.994Fe0.006O2 cathode has better rate performance (exhibits a reversible capacity of 87.9 mAh/g at 2 C) and cycle stability in sodium-ion batteries. The diffusion coefficient of sodium ions increases by Fe3+ doping. The excellent rate performance and capacity improvement are verified by density functional theory (DFT) calculation. After doping, the band gap decreases significantly, and the results show that the state density of O 2p increases near the Fermi level, which promotes the oxidation-reduction of oxygen. This work provides a straightforward approach to enhance the performance of Na0.44MnO2 nanorods, and this performance improvement has guiding significance for the design of other materials in the energy storage domain.

3D Fast Sodium Transport Network of MoS2 Endowed by Coupling of Sulfur Vacancies and Sn Doping for Outstanding Sodium Storage.

A sulfur vacancy-rich, Sn-doped as well as carbon-coated MoS2 composite (Vs-SMS@C) is rationally synthesized via a simple hydrothermal method combined with ball-milling reduction, which enhances the sodium storage performance. Benefiting from the 3D fast Na+ transport network composed of the defective carbon coating, Mo─S─C bonds, enlarged interlayer spacing, S-vacancies, and lattice distortion in the composite, the Na+ storage kinetics is significantly accelerated. As expected, Vs-SMS@C releases an ultrahigh reversible capacity of 1089 mAh g-1 at 0.1 A g-1, higher than the theoretical capacity. It delivers a satisfactory capacity of 463 mAh g-1 at a high current density of 10 A g-1, which is the state-of-the-art rate capability compared to other MoS2 based sodium ion battery anodes to the knowledge. Moreover, a super long-term cycle stability is achieved by Vs-SMS@C, which keeps 91.6% of the initial capacity after 3000 cycles under the current density of 5 A g-1 in the voltage of 0.3-3.0 V. The sodium storage mechanism of Vs-SMS@C is investigated by employing electrochemical methods and ex situ techniques. The synergistic effect between S-vacancies and doped-Sn is evidenced by DFT calculations. This work opens new ideas for seeking excellent metal sulfide anodes.

Multistep optimization for the electrodeposited mixed perovskite FA1-yCsyPbBrxI3-xsolar cells.

The electrodeposition method has recently been developed for the fabrication of perovskite solar cells due to its potential advantages in commercial preparation. However, there is few studies on the preparation of perovskite solar cells by the electrodeposition method, especially on the perovskite FAPbI3-based solar cells. Herein, we fabricated the mixed perovskite FA1-yCsyPbBrxI3-xsolar cells by an optimized electrodeposition method, in which the electrodeposited PbO2reacts directly with FAI and an appropriate amount of CsBr dopants. The corresponding solar cells display the best PCE of 4.97%. By regulating the growth temperature in the reaction between PbO2and FAI/CsBr, the efficiency of the mixed perovskite solar cells can be promoted to 10.18%. These results illustrate that the element doping and growth environment regulation can optimize the quality of the perovskite films, thus promoting the efficiency of the perovskite solar cells. With further optimizing the growth process in the electrodeposition method, it is expected to open up a new commercial preparation route for the perovskite solar cells in the near future.

Preparation of Li3V2(PO4)3 as cathode material for aqueous zinc ion batteries by a hydrothermal assisted sol-gel method and its properties.

To alleviate the depletion of lithium resources and improve battery capacity and rate capacity, the development of aqueous zinc-ion batteries (AZIBs) is crucial. The open channels monoclinic structure Li3V2(PO4)3 is conducive to the transfer and diffusion of guest ions, making it a promising cathode material for AZIBs. Therefore, in this study, nanoneedles and particles Li3V2(PO4)3 cathode materials for AZIBs were prepared by a hydrothermal assisted sol-gel method, and the effect of synthesized pH values was studied. XRD results show that all samples had the monoclinic structure, and the Li3V2(PO4)3 sample prepared at pH = 7 exhibits (LVP-pH7) the highest peak tips and narrowest peak widths. SEM images demonstrate that all samples have the morphology character of randomly oriented needles and irregular particles, with the LVP-pH7 sample having more needle-like particles that contribute to ion diffusion. EDS results show uniform distribution of P, V, and O elements in the LVP-pH7 sample, and no obvious aggregation phenomenon is observed. Electrochemical tests have shown that the LVP-pH7 sample exhibits excellent cycling performance (97.37% after 50 cycles at 200 mA g-1) and rate ability compared to other samples. The CV test results showed that compared with other samples, the LVP-pH7 sample had the most excellent ionic diffusion coefficient (2.44 × 10-12 cm2 s-1). Additionally, the Rct of LVP-pH7 is the lowest (319.83 Ω) according to the findings of EIS and Nyquist plot fitting, showing a decreased charge transfer resistance and raising the kinetics of the reaction.

Initiating a high-temperature zinc ion battery through a triazolium-based ionic liquid.

Triazolium-based ionic liquids (T1, T2 and T3) with or without terminal hydroxyl groups were prepared via Cu(i) catalysed azide-alkyne click chemistry and their properties were investigated using various technologies. The hydroxyl groups obviously affected their physicochemical properties, where with a decrease in the number of hydroxyl groups, their stability and conductivity were enhanced. T1, T2 and T3 showed relatively high thermal stability, and their electrochemical stability windows (ESWs) were 4.76, 4.11 and 3.52 V, respectively. T1S-20 was obtained via the addition of zinc trifluoromethanesulfonic acid (Zn(CF3SO3)2) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) to T1, displaying conductivity and ESW values of 1.55 × 10-3 S cm-1 and 6.36 V at 30 °C, respectively. Subsequently, a Zn/Li3V2(PO4)3 battery was assembled using T1S-20 as the electrolyte and its performances at 30 °C and 80 °C were investigated. The battery showed a capacity of 81 mA h g-1 at 30 °C, and its capacity retention rate was 89% after 50 cycles. After increasing the temperature to 80 °C, its initial capacity increased to 111 mA h g-1 with a capacity retention rate of 93.6% after 100 cycles, which was much higher than that of the aqueous electrolyte (WS-20)-based zinc ion battery (71.8%). Simultaneously, the T1S-20 electrolyte-based battery exhibited a good charge/discharge efficiency, and its Coulomb efficiency was 99%. Consequently, the T1S-20 electrolyte displayed a better performance in the Zn/Li3V2(PO4)3 battery than that with the aqueous electrolyte, especially at high temperature.

Layered manganese dioxide nanoflowers with Cu2+and Bi3+ intercalation as high-performance cathode for aqueous zinc-ion battery.

For aqueous zinc ion batteries (AZIBs), birnessite MnO2 (δ-MnO2) has been intensively used as one of the most potential cathode materials due to its layered structure, which is conducive to reversible insertion/extraction of zinc ions. However, δ-MnO2 has not been attained for zinc ion storage performance because of its inferior conductivity as well as the undesirable structural degradation upon charge/discharge cycling. Herein, we have designed two kinds of cathode materials of Cu0.06MnO2·1.7H2O (CuMO) and Bi0.09MnO2·1.5H2O (BiMO) with nanoflower structure for the first time by a facile one-step hydrothermal method, which will be applied for high-performance AZIBs.The pre-intercalated metal ions and water molecules serve as pillars to sustain the layered structures, improving the stability of these materials. Particularly, the CuMO may experience a replacement reaction except the zinc ion insertion/extraction to form metallic Cu during the cycling process, which can enhance the diffusion rate of Zn2+, thus resulting in an excellent electronic conductivity and exhibiting remarkable specific capacities. Furthermore, a pseudo-capacitance that is derived from the surface-adsorbed Cu2+and Bi3+ also contributes to the improved electrochemical performances. The reversible capacity of CuMO is estimated as 350 mAh g-1 at 0.5 A g-1, which is much higher than that of pure δ-MnO2 (190 mAh g-1 at 0.5 A g-1). However, BiMO demonstrates long-term cycling stability, maintaining a capacity of 114.5 mAh g-1 even after 1100 charged-discharged cycles at 1 A g-1. The capacity retention is found to be as high as 98.6%, which is much higher than that of pure δ-MnO2 (53.8%). This can contribute to the development of high-performance AZIBs and the application of metal ion pre-intercalation methods in other areas.

Improved Electrochemical Performance of 0.5Li2MnO3·0.5LiNi0.5Mn0.5O2 Cathode Materials for Lithium Ion Batteries Synthesized by Ionic-Liquid-Assisted Hydrothermal Method.

Well-dispersed Li-rich Mn-based 0.5Li2MnO3·0.5LiNi0.5Mn0.5O2 nanoparticles with diameter ranging from 50 to 100 nm are synthesized by a hydrothermal method in the presence of N-hexyl pyridinium tetrafluoroborate ionic liquid ([HPy][BF4]). The microstructures and electrochemical performance of the prepared cathode materials are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electrochemical measurements. The XRD results show that the sample prepared by ionic-liquid-assisted hydrothermal method exhibits a typical Li-rich Mn-based pure phase and lower cation mixing. SEM and TEM images indicate that the extent of particle agglomeration of the ionic-liquid-assisted sample is lower compared to the traditional hydrothermal sample. Electrochemical test results indicate that the materials synthesized by ionic-liquid-assisted hydrothermal method exhibit better rate capability and cyclability. Besides, electrochemical impedance spectroscopy (EIS) results suggest that the charge transfer resistance of 0.5Li2MnO3· 0.5LiNi0.5Mn0.5O2 synthesized by ionic-liquid-assisted hydrothermal method is much lower, which enhances the reaction kinetics.

Cryptomelane-Type KMn8O16 as Potential Cathode Material - for Aqueous Zinc Ion Battery.

Aqueous battery has been gained much more interest for large-scale energy storage fields due to its excellent safety, high power density and low cost. Cryptomelane-type KMn8O16 confirmed by X-ray diffraction (XRD) was successfully synthesized by a modified hydrothermal method, followed by annealed at 400°C for 3 h. The morphology and microstructure of as-prepared KMn8O16 investigated by field-emission scanning electron microscopy (FE-SEM) with the energy spectrum analysis (EDS) and transmission electron microscopy (TEM) demonstrate that one-dimensional nano rods with the length of about 500 nm constitute the microspheres with the diameter about 0.5~2 µm. The cyclic voltammetry measurement displays that the abundant intercalation of zinc ions on the cathode takes place during the initial discharge process, indicating that cryptomelane-type KMn8O16 can be used as the potential cathode material for aqueous zinc ion batteries. The electrode shows a good cycling performance with a reversible capacity of up to 77.0 mAh/g even after 100 cycles and a small self-discharge phenomenon.