•Zn–Al–In layered double hydroxides (LDHs) are synthesized by hydrothermal method.•Zn–Al–In-LDHs have superior electrochemical cycle stability.•Zn–Al–In-LDHs exhibits high discharge capability and long cycle life.•Zn–Al–In-LDHs possess high rate capability.Zn–Al–In layered double hydroxides (LDHs) are synthesized by hydrothermal method and investigated as negative electrode materials for Ni–Zn batteries. The Fourier transform infrared spectra (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images show the as-prepared samples are well-crystallized and hexagon structure. The electrochemical performances of Zn–Al-LDHs and Zn–Al–In-LDHs with different Zn/Al/In molar ration are investigated by the cyclic voltammograms (CV), Tafel polarization and galvanostatic charge–discharge measurements. Zn–Al-LDHs shows good stability in the first 300-cycles. However, during the subsequent cycles, the discharge capacity decreases with increasing of the cycles. Compared with Zn–Al-LDHs, Zn–Al–In-LDHs with different Zn/Al/In molar rations, especially the sample of Zn/Al/In = 3:0.75:0.25 (molar ration) have higher discharge capacity and more stable cycling performances. This battery can undergo at least 800 charge–discharge cycles at constant current of 1C without dendrite and short circuits. The discharge capacity of Zn–Al–In-LDHs after the 800th cycle remains about 380 mAh g−1. Zn–Al–In-LDHs possess a high rate capability to meet the needs of high-storage applications.

•Calcium zincates were synthesized by alcohol-thermal method for the first time.•The crystallization of as-prepared calcium zincate was well, and the particle size was small.•The samples synthesized in the ethanol exhibited best electrochemical properties.Calcium zincates are synthesized using ZnO and Ca(OH)2 in different alcohol solutions by the alcohol-thermal method. Through the scanning electron microscopy (SEM), transmission electron microscope (TEM) and high resolution transmission electron microscope (HRTEM) analysis, the as-prepared samples with small particles are well-crystallized. Additionally, the morphologies of as-prepared calcium zincates are distinct in different reaction solvents such as ethanol, isopropanol and n-butanol, and the calcium zincates synthesized in the ethanol and isopropanol solutions have more excellent crystallinity. As the negative electrode materials for Ni–Zn batteries, the electrochemistry properties of calcium zincates are examined by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge–discharge testing techniques. The results imply that calcium zincates synthesized in the ethanol solution have lower polarization and better reversibility. The cycle performance analysis shows the as-prepared calcium zincates have a very greatly improvement in cycle life and discharge capacity compared with other methods. All of the test results show that the calcium zincates synthesized in the ethanol solution exhibit the best electrochemical performances.

•Zn–Sn–Al-hydrotalcites with layered structure was prepared and proposed as zinc electrode material for the first time.•The special structure has attributed to the electrochemical performances of zinc electrode with Zn–Sn–Al-hydrotalcites.•Zinc electrode with Zn–Sn–Al-hydrotalcites shows superior electrochemical cycle stability.Zn–Sn–Al-hydrotalcites (LDHs) have been successfully prepared by hydrothermal method and applied as a novel anodic active material in Zn–Ni secondary batteries. The scanning electron microscopy (SEM), X-ray diffractometer (XRD) and FT-IR tests are performed to investigate the morphology and microstructure of Zn–Sn–Al-hydrotalcites. Electrochemical performances of Zn–Sn–Al-hydrotalcites with different Zn/Sn/Al molar ratios are investigated through galvanostatic charge–discharge measurements, cyclic voltammograms (CV) and Tafel polarization curves. Compared with Zn–Al–LDH without Sn addition, Zn–Sn–Al–LDHs still present hexagon layer structure, and present more excellent electrochemical performance. And Zn–Sn–Al–LDH with the molar ratio of 2.8:0.2:1 shows a better cycle stability than the other samples. The results demonstrate that Sn addition can help to perfect the electrochemical performance of zinc electrode with Zn–Sn–Al–LDHs. At the same time, CV tests indicate well reversibility and Tafel curves reveal more positive corrosion potential for Zn–Sn–Al–LDHs.

ZnAl–CO3 layered double hydroxides (LDHs) are prepared by the constant pH co-precipitation method in this study and proposed as a novel anodic material for Nickel–Zinc secondary cells. The as-prepared samples are well-crystallized and have the plate-like morphology. It is shown that the reversibility of the electrode reaction of the ZnAl-hydrotalcites is much better than that of ZnO electrode in alkaline system probably due to the lamellar structure of ZnAl-hydrotalcites and the presence of aluminum ions. In spite of a little lower specific capacity, Zn–Al-hydrotalcite electrode has more stable cycling performance, higher charge efficiency and utilization ratio in comparison with ZnO electrode. The effect of Zn/Al molar ratio on the electrochemical performance is investigated and ZnAl-hydrotalcites with Zn/Al molar ratio of 4:1 exhibit the best performance. It delivers an initial discharge capacity of 400 mAh g−1 and the capacity retention ratio of 92.7% over 50 cycles. This proves that ZnAl-hydrotalcites electrode is more stable than ZnO electrode in alkaline electrolyte, thus resulting in much better cycling stability.Highlights► ZnAl-hydrotalcites were proposed as zinc electrode materials for the first time. ► The electrochemical performances of ZnAl-hydrotalcites were firstly investigated. ► ZnAl-hydrotalcites have superior electrochemical cycle stability. ► The sample of Zn/Al = 4/1 (molar ratio) exhibits best electrochemical properties.

•Zn–Al–La-LDHs were proposed as zinc electrode materials for the first time.•The electrochemical performances of Zn–Al–La-LDHs were firstly investigated.•Zn–Al–La-LDHs have superior electrochemical cycle stability.•The sample of Al/La = 0.8/0.2 (molar ratio) exhibits best electrochemical properties.Zn–Al–La–CO3 layered double hydroxides (LDHs) are prepared by the constant pH co-precipitation method and proposed as a novel anodic material in Zinc–Nickel secondary cells. The X-ray diffraction (XRD) patterns and scanning electron microscopy (SEM) images reveal that the as-prepared samples are well-crystallized and hexagon layer structure. Electrochemical performances of Zn–Al–La-hydrotalcites with different Zn/Al/La molar ratios are investigated by galvanostatic charge–discharge measurements, cyclic voltammograms (CV) and Tafel polarization curves. In comparison with the Zn–Al-hydrotalcite, Zn–Al–La-hydrotalcites with different Zn/Al/La molar ratios have more stable cycling performance. After 400 cell cycles, Zn–Al–La-LDH with Zn/Al/La = 3:0.8:0.2 retains specific discharge capacity of 297 mAh g−1 with a retention rate of 79.0%, which is much superior to that of 205 mAh g−1 with a retention rate of 53.5% for the Zn–Al–La-LDH with Zn/Al/La = 3:0.9:0.1 and 241 mAh g−1 with a retention rate of 69.0% for the Zn–Al–La-LDH with Zn/Al/La = 3:0.6:0.4. The results demonstrate that the Zn–Al–La-LDH with Zn/Al/La = 3:0.8:0.2 has the best reversible cycling behavior. The CV exhibits well reversibility and the Tafel polarization curves reveal more positive corrosion potential for Zn–Al–La-hydrotalcite.

The ZnO samples coated with carbon are successfully synthesized by using a high energy ball milling method. The scanning electron microscopy (SEM) images and energy dispersive spectrometer (EDS) spectra of the carbon-coated ZnO and pure ZnO show that the carbon-coated ZnO (carbon source: glucose, citric acid) samples and the untreated ZnO sample have similar particle size and crystal form. The particles have prismatic microstructure whose sizes are about 100–200 nm. However, the carbon-coated ZnO (carbon source: sucrose) sample has become agglomeration after calcination whose size has been increased to 2–6 μm. The uncoated ZnO powders have more complete crystal shape and they are glazed quadrangular materials, while the carbon coated ZnO particles has a rough surface, which resulted from the growth of carbon coating on ZnO particles. X-ray diffraction (XRD) patterns of the carbon-coated ZnO and the pure ZnO show carbon formed on the surface of ZnO is amorphous. Tafel plot, cyclic voltammetry (CV), AC impedance spectroscopy and galvanostatic charge–discharge measurement are utilized to examine the electrochemical performances of the carbon-coated ZnO. The carbon-coated ZnO (carbon source: glucose) have the most positive steady-state potential and lowest corrosion current density in the zinc electrodes which indicates that it has a good anticorrosion ability. A lower charge platform and a higher discharge platform of carbon-coated ZnO indicate that it have a better charge/discharge performance as anodic material for Ni/Zn cells. A smaller ohmic resistance and charge-transfer resistance imply that the carbon film upon ZnO could greatly decrease the impedance of the reaction process. Meanwhile, the carbon-coated ZnO also showed more excellent cycling performance than pure ZnO. The reason of improvement about electrochemical performance can be ascribed as the unique structure of amorphous carbon layer.

The La2O3-doped ZnO was synthesized successfully via a simple calcination method subsequent to a co-precipitation process. The X-ray diffraction (XRD) patterns and scanning electron microscope (SEM) images show that the as-prepared sample has a main wurtzite structure and a pie-like morphology. The electrochemical performances were investigated through galvanostatic charge–discharge, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements. As the anode material, La2O3-doped ZnO has an initial discharge capacity of 455.7 mAh g−1 and a capacity retention ratio of 83.5% at 90th cycle, showing an obviously superior stability of cycle life compared with pure ZnO. Furthermore, La2O3-doped ZnO has a lower resistance and a better reversibility. All these results prove that the La2O3-doped ZnO can deliver a better electrochemical performance than pure ZnO in alkaline electrolyte.

In(OH)3-coated Zn-Al-hydrotalcite is prepared by homogeneous precipitation method. The X-ray diffraction (XRD) patterns and scanning electron microscopy (SEM) images reveal that the In(OH)3 is successfully coated on the surface of the Zn-Al-hydrotalcite particles. And about 2.5 wt% of coating is determined through the energy dispersive X-ray spectrum (EDS). The electrochemical performance of In(OH)3-coated Zn-Al-hydrotalcite is investigated by cyclic voltammetry (CV), electrochemical impedance spectroscope (EIS), Tafel polarization curves and galvanostatic charge–discharge measurements. The EIS exhibits a higher charge-transfer resistance and the Tafel polarization curves reveal a more positive corrosion potential for the In(OH)3-coated Zn-Al-hydrotalcite, in comparison with the pristine Zn-Al-hydrotalcite and the mixture of Zn-Al-hydrotalcite and In(OH)3. After 50 cell cycles, the In(OH)3-coated Zn-Al-hydrotalcite retains a specific discharge capacity of 364.0 mAh g−1 with a retention rate of 96.9%, which is much superior to that of 262.2 mAh g−1 with a retention rate of 67.6% for the pristine Zn-Al-LDHs and 299.2 mAh g−1 with a retention rate of 81.2% for the mixture of Zn-Al-LDHs with In(OH)3.

Nanostructured Zn–Al layered double hydroxide (LDH) and carbon nanotubes (CNTs) have been successfully assembled to form LDH/CNT composite by electrostatic force. The morphology and microstructure of LDH/CNT composites were investigated by transmission electron microscopy and X-ray diffractometer. The assembly mechanism of LDH with CNTs was also discussed. Furthermore, the unique three-dimensional composite thus prepared was used as a new anode material for Ni–Zn secondary batteries to enhance the cell performance for the first time. The electrochemical performances of LDH/CNT composite as anode active material for Ni–Zn cells were investigated by galvanostatic charge/discharge cycling and cyclic voltammogram. The obtained results clearly demonstrated that the LDH/CNT composite had superior cycle stability compared with the conventional ZnO and Zn–Al–LDH, and the discharge capacity could maintain 390 mAh g−1 after 200 cycling tests. At the same time, the LDH/CNT composite also exhibited lower charge plateau voltage and higher discharge plateau voltage, and the average utilization ratio of the anode could reach 95.6%. These results indicated that this kind of composite is a promising anode material for Ni/Zn cells. It exhibits a high capacity (∼400 mAh g−1) and high cycling stability.

The hollow fusiform ZnO and the hexagonal taper-like ZnO have been prepared by hydrothermal method. The synthetic materials have been characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). As anodic materials for Ni/Zn cells, electrochemical performances of the hollow fusiform ZnO and the hexagonal taper-like ZnO have been investigated by cyclic voltammetry (CV) and galvanostatic charge–discharge measurement. Compared to the conventional ZnO, the hollow fusiform ZnO and the hexagonal taper-like ZnO have shown better cycle stability than the conventional ZnO. Furthermore, the initial discharge capacity of hollow fusiform ZnO is 476 mAh g−1, and the discharge capacity is almost unchangeable with the capacity retention ratio of 99.5% over 50 cycles. Comparatively, the hexagonal taper-like ZnO delivers an initial discharge capacity of 470 mAh g−1 and with the capacity retention ratio of 94.7% over 50 cycles. They are much higher than that of the conventional ZnO. The better electrochemical performance is attributed to higher electrochemical activity, which is ascribed to the novel initial morphology and size of as-prepared ZnO active material. And the formation of zinc dendrite is suppressed much essentially, the reason could be attributable to initial morphology of the active materials. And the zinc dendrite is suppressed effectively, which results in improvement of cycle stability of Ni/Zn secondary cells.

Electrochemical behavior of potassium ferrate(VI) (K2FeO4) coated with different content of 2,3-Naphthalocyanine (H2Nc) is investigated as a function of exposure time in electrolyte. Galvanostatic discharge curves indicate that the stability of K2FeO4 cathode is improved by coating a layer of H2Nc. In short exposing time of 3 h, the capacity of coated K2FeO4 shows slight decrease with increase of H2Nc content. But in longer exposing time of more than 6 h, the K2FeO4 cathode coated with more than 2% H2Nc shows better capacity. Open-circuit potential curves indicate that the stability of K2FeO4 increases with increasing H2Nc content. Electrochemical impedance spectroscopy (EIS) results reveal that H2Nc partially hinders the contact between K2FeO4 and the aqueous media, and enhances the ability of electron transfer in the electrode, which are responsible for the enhancement of K2FeO4 stability.Highlights► The discharge capacity is increased 26–50% by H2Nc (1%, 2%, 3%) as coatings. ► The open-circuit potential increased with the content of H2Nc coatings increasing. ► EIS indicates that H2Nc can enhance the ability of electron transfer in the electrode.

In-doped ZnO (IZO) samples were synthesized by a simple co-precipitation method. X-ray diffraction (XRD) patterns, Raman spectra and scanning electron microscopy (SEM) images show that IZO with 2.5 wt% In2O3 has a pure wurtzite structure and a plate-like morphology. IZO with 16.3 wt% In2O3 (theoretical value) mainly shows a wurtzite structure. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge–discharge measurement were utilized to examine the electrochemical performances of IZO with 2.5 wt% In2O3 as anode material for Ni–Zn simulated cells. Compared with the physical mixture of ZnO with In2O3, IZO increases the charge-transfer resistance of zinc electrode. Furthermore, the initial discharge capacity of IZO is 569 mAh g−1, and the discharge capacity decays slightly with the capacity retention ratio of 95.2% over 73 cycles, which is much higher than that of the physical mixture of ZnO with In2O3.Highlights► In-doped ZnO (IZO) is synthesized via a simple co-precipitation method. ► IZO is utilized as anode material in Ni-Zn secondary cell. ► The electrochemical performances of IZO are studied. ► IZO delivers a high discharge capacity with good capacity retention.

Electrochemical intercalation of potassium into graphite in molten potassium fluoride at 1163 K was investigated by means of cyclic voltammetry, galvanostatic electrolysis and open-circuit potential measurements. It was found that potassium intercalated into graphite solely between graphite layers. In addition, the intercalation compound formed in graphite bulk in molten KF was quite unstable and decomposed very fast. X-ray diffraction measurements indicate that a very dilute potassium–graphite intercalation compound was formed in graphite matrix in the fluoride melt. Analysis with scanning electron microscope and transmission electron microscope shows that graphite was exfoliated to sheets and tubes due to lattice expansion caused by intercalation of potassium in molten KF.

An ultrasound-assisted convenient method was developed for the synthesis of battery grade potassium ferrate (K2FeO4) with high yield (53–59%). The purity of the synthesized salt was determined by chromite method to be 95–96.8%. It was found that sample of the solid potassium ferrate has a tetrahedral structure with a space group of D2h (Pnma) from X-ray diffraction (XRD) spectrum. From the scanning electronic microscopy (SEM), the K2FeO4 powders were crystallized polyhedron-shaped stick, and the particles had dimensions on the order of 25–200 μm in length and 1–10 μm in width. The electrochemical performance of the K2FeO4 electrodes was studied by using cyclic voltammetry and galvanostatic discharge methods in 10 mol/L KOH aqueous electrolyte. The synthesized product possesses a capacity of 302.4 mAh/g and coulombic efficiency of 74.5%.

The stability of potassium ferrate(VI) (K2FeO4) electrodes was dramatically improved by using 2,3-Naphthalocyanine (C48H26N8) as coating. The electrode material with the coating was characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). K2FeO4 electrodes coated with 2,3-Naphthalocyanine provided a superior capacity and stability to uncoated K2FeO4 electrodes. Cathodic charge capacity of K2FeO4 coated with 2,3-Naphthalocyanine is 42% higher than that of K2FeO4 uncoated when discharged at rate of 0.25 C to a cutoff of 0.8 V after storing in the 10 mol/L KOH solution for 3 h.