Electrochemical Hydrogen Storage Performances of the Si Added La-Mg-Ni-based A_2B_7-type Electrode Alloys for Ni/MH Battery Application

The casting and annealing technologies were applied to fabricate the La0.8Mg0.2Ni3.3Co0.2Six （x = 0-0.2） electrode alloys. The effects of Si content and annealing temperature on the structure and electrochemical performances of the alloys were investigated systematically. The analyses of XRD and SEM show that all the alloys possess a multiphase structure, involving two main phases （La, Mg）2Ni7 and LaNi5 as well as a residual phase LaNi3. The addition of Si brings on an evident increase in the LaNi5 phase and a decrease in the （La, Mg）2Ni7 phase, without altering the main phase component of the alloy, which also makes the lattice constants and cell volumes of the alloy enlarged. Likewise, the annealing treatment engenders the same action on the lattice constants and cell volumes as adding Si. Simultaneously, it gives rise to the variation of the phase abundance and the coarsening of the alloy grains. The electrochemical measurements indicate that the addition of Si ameliorates the cycle stability of the as-cast and annealed alloys significantly, but impairs their discharge capacities clearly. Similarly, the annealing treatment makes a positive contribution to the cycle stability of the alloy evidently, and the discharge capacity of the alloy shows a maximum value with annealing temperature rising. Furthermore, the high rate discharge ability （HR） first augments and then declines with the rising of Si content and annealing temperature.

Magnetic properties and resistivity of a 2:17-type SmCo magnet doped with ZrO_(2)

In order to counteract the demagnetization caused by eddy current loss,widespread attention has been devoted to increasing the resistivity of permanent magnets.We prepared 2:17-type Sm Co magnets doped with different ZrO_(2)contents and investigated the influence of the ZrO_(2)content on the magnetic properties and resistive anisotropism.The results showed that not only was the resistivity of the magnet improved,but,in addition,the coercivity of the magnet was significantly increased.The microstructure was studied with TEM,which showed that ZrO_(2)doping was able to cause a decrease in the lamellar phase density and the growth of cellular structures.The increased grain boundaries and Sm_(2)O_(3)phases were favorable to the improvement of resistivity.The decrease of the lamellar phases caused a narrowing of the resistive anisotropism.The additional Cu in the center of the cellular boundaries was the main reason for the enhancement of Hcj.However,an excessive amount caused an increase of the Zr_6(Fe Co)_(23)phase and a deterioration of the cellular structure,thereby leading to a decrease in coercivity.

Difficulties, strategies, and recent research and development of layered sodium transition metal oxide cathode materials for high-energy sodium-ion batteries

Energy-storage systems and their production have attracted significant interest for practical applications.Batteries are the foundation of sustainable energy sources for electric vehicles(EVs),portable electronic devices(PEDs),etc.In recent decades,Lithium-ion batteries(LIBs) have been extensively utilized in largescale energy storage devices owing to their long cycle life and high energy density.However,the high cost and limited availability of Li are the two main obstacles for LIBs.In this regard,sodium-ion batteries(SIBs) are attractive alternatives to LIBs for large-scale energy storage systems because of the abundance and low cost of sodium materials.Cathode is one of the most important components in the battery,which limits cost and performance of a battery.Among the classified cathode structures,layered structure materials have attracted attention because of their high ionic conductivity,fast diffusion rate,and high specific capacity.Here,we present a comprehensive review of the classification of layered structures and the preparation of layered materials.Furthermore,the review article discusses extensively about the issues of the layered materials,namely(1) electrochemical degradation,(2) irreversible structural changes,and(3) structural instability,and also it provides strategies to overcome the issues such as elemental phase composition,a small amount of elemental doping,structural design,and surface alteration for emerging SIBs.In addition,the article discusses about the recent research development on layered unary,binary,ternary,quaternary,quinary,and senary-based O3-and P2-type cathode materials for high-energy SIBs.This review article provides useful information for the development of high-energy layered sodium transition metal oxide P2 and O3-cathode materials for practical SIBs.

Electrochemical performances of as-cast and annealed La_(0.8-x)Nd_xMg_(0.2)Ni_(3.35)Al_(0.1)Si_0.05(x=0-0.4) alloys applied to Ni/metal hydride (MH) battery

The La-Mg-Ni-based A2B7-type Lao.8_xNdx Mgo.2Ni3.35Alo.lSio.o5 （x = 0, 0.1, 0.2, 0.3, and 0.4） electrode alloys were prepared by casting and annealing. The influence of the partial substitution of Nd for La on the structure and electrochemical performances of the alloys was investigated. The structural analysis of X-ray diffraction and scanning electron microscopy reveals that the experimental alloys consist of two major phases： （La,Mg）2Ni7 with the hexagonal Ce2Ni7-type structure and LaNi5 with the hexagonal CaCus-type structure as well as some residual phases of LaNi3 and NdNis. The electrochemical measurements indicate that an evident change of the electrochemical performance of the alloys is associated with the substitution of Nd for La. The discharge capacity of the alloy first increases then decreases with the growing Nd content, whereas their cycle stability clearly grows all the time. Furthermore, the measurements of the high rate discharge ability, the limiting current density, and hydrogen diffusion coefficient all demonstrate that the electrochemical kinetic properties of the alloy electrodes first augment then decline with the rising amount of Nd substitution.

In sight of K-deficient layered K_(x)MnO_(2) cathode for potassium-ions batteries

Potassium-ions batteries(PIBs)are attracting increasing attention as up-and-coming youngster in largescale grid-level energy storage benefiting from its low-cost and high energy density.Nevertheless,enough researches regarding indispensable cathode materials for PIBs are badly absent.Herein,we synthesize K-deficient layered manganese-based oxides(P2-K_(0.21)MnO_(2) and P3-K_(0.23)MnO_(2))and investigate them as cathode of PIBs for the first time.As the newcomer of potassium-containing layered manganese-based oxides(K_(x)MnO_(2))group,P2-K_(0.21)MnO_(2) delivers high discharge capacity of 99.3 mAh g^(-1) and P3-K_(0.23)MnO_(2) exhibits remarkable capacity retention rate of 75.5%.Besides,in-situ XRD and ex-situ XRD measurements reveal the reversible phase transition of P2-K_(0.21)MnO_(2) and P3-K_(0.23)MnO_(2) with the potassium-ions extraction and reinsertion,respectively.This work contributes to a better understanding for the potassium storage in K-deficient layered K_(x)MnO_(2)(x≤0.23),possessing an important basic scientific significance for the exploitation and application of layered K_(x)MnO_(2) in PIBs.

Superconductivity in LaPd2Bi2 with CaBe2Ge2-type structure

Since the discovery of superconductivity in LaFeAsO1-xFx, the high-Tc iron-based superconductors have been extensively studied from both experimental and theoretical viewpoints [1-8].However,the mechanism of the unconventional superconductivity is still to be resolved.To address such issues,numerous 3d,4d,5d transition metal pnietide,silicide,germanide,chalcogenide materials crystalizing in the similar crystal structure with iron pnictide/ selenide suoerconductors were studied [9-24].

Phase forming law and electrochemical properties of A2B7-type La-Y-Ni-based hydrogen storage alloys with different La/Y ratios

The effects of different proportions of La and Y elements in the A-side on the structure and properties of A_(2)B_(7)-type La-Y-Ni hydrogen storage alloys were investigated.The(La,Y)_(2)Ni_(7)hydrogen storage alloys with different La/Y ratios were prepared by sintering the Y_(2)Ni_(4)precursor and different AB_(5)-type precursors at 1298 K for 5 h and subsequently annealed for 20 h at 1248 K.All the alloys only contain Ce_(2)Ni_(7)(2H-type)and Gd_(2)Co_(7)(3R-type)phases with different mass ratios.As the La/Y ratio decreases,the cell volume of the two phases declines and the corresponding plateau pressure gradually increases.As the proportion of Y in the alloy increases,the hydrogen storage capacity increases gradually from 1.309 wt%(La/Y=1/1)to 1.713 wt%(La/Y=1/5)and the high-rate discharge(HRD1500)ability of the alloy electrodes increases gradually from 62.7%(La/Y=1/1)to 88.6%(La/Y=1/5).The hydrogen diffusion rate in the bulk of the alloy is the controlling step of hydriding/dehydriding kinetics.The Y ele ment can effectively inhibit the hydrogen-induced amorphous(HIA)of La-Y-Ni alloys,but the poor stability of the Y element in alkaline KOH aqueous solution leads to a decrease in the electrochemical cyclic stability with increasing Y content.

Structure and electrochemical hydrogen storage characteristics of the as-cast and annealed La_(0.8-x)SmxMg_(0.2)Ni_(3.15)Co_(0.2)Al_(0.1)Si_(0.05) (x=0-0.4) alloys

In order to ameliorate the electrochemical cycle stability of the RE-Mg-Ni based A2B7-type electrode alloys, the Mg content in the alloy was reduced and La in the alloy was partially substituted by Sm. The La0.8-xSmxMg0.2Ni3.15Co0.2Al0.1Si0.05 （x=0, 0.1, 0.2, 0.3, 0.4） elec-trode alloys were fabricated by casting and annealing. The microstructures of the as-cast and annealed alloys were characterized by XRD and SEM. The electrochemical hydrogen storage characteristics of the as-cast and annealed alloys were measured. The results revealed that all of the experimental alloys mainly consisted of two phases： （La,Mg）2Ni7 phase with the hexagonal Ce2Ni7-type structure and LaNi5 phase with the hexagonal CaCu5-type structure. As Sm content grew from 0 to 0.4, the discharge capacity and the high rate discharge ability （HRD） first in-creased and then decreased for the as-cast and annealed alloys, whereas the capacity retaining rate （S100） after 100 cycles increased continuously.

Study on structure and electrochemical properties of the (LaGdMg)Ni_(3.35-x)Co_xAl_(0.15)(x=0-2.0) hydrogen storage alloys

Hydrogen storage alloys(LaGdMg)Ni3.35-xCoxAl0.15(x=0,0.1,0.3,0.5,1.0,1.5,2.0) were prepared by induction melting followed by annealing treatment in argon atmosphere.The effects of partly replacing Ni by Co element in(LaGdMg)Ni3.35Al0.15 on the phase structure and electrochemical properties of(LaGdMg)Ni3.35-xCoxAl0.15 alloys were investigated.Structure analysis showed that the alloys consisted of Ce2Ni7-type(Gd2Co7-type),CaCu5-type,Pr5Co19-type,PuNi3-type phase structure.The addition of Co element obviously reduced the contents of CaCu5-type phase and increased the contents of Ce2Ni7-type phase.However,Pr5Co19-type and CaCu5-type phase obviously increased with the high content of Co.Rietveld analysis showed that the c-axis lattice parameters and cell volumes of the component phases increased with increasing Co content.The electrochemical measurements showed that as the Co content increased,the maximum discharge capacity and the cyclic stability of the annealed alloys both first increased then decreased.The(LaGdMg)Ni3.05Co0.3Al0.15 alloy electrode exhibited the maximum discharge capacity(392.92 mAh/g),and the(LaGdMg)Ni1.85Co1.0Al0.15 alloy electrode showed the best cyclic stability(S100=96.1%).

Electrochemical mechanism of high Na-content P2-type layered oxides for sodium-ion batteries

The development on capacity and structure issues of P2-type cathode has so far focused on ion-doping/substitution strategy.In a recent report published in Journal of the American Chemical Society,Hu and colleagues demonstrated that high Na-content P2-type layered oxides exhibit higher capacities as well as great structural stability.

Insights into the Ti^(4+) doping in P2-type Na_(0.67)Ni_(0.33)Mn_(0.52)Ti_(0.15)O_(2) for enhanced performance of sodium-ion batteries

Due to the sodium abundance and availability,sodium-ion batteries(SIBs)have the potential to meet the worldwide growing demand of electrical energy storage.P2-type sodium transition-metal layer oxides with a high energy density are considered as the most promising cathode materials for SIBs.We present here a detailed study of the enhanced rate capability and cyclic stability of the Ti-doped Na_(0.67)Ni_(0.33)Mn_(0.67)O_(2)cathode material.The combined analysis of ex-situ X-ray absorption fine structure(XAFS)spectroscopy,aberration-corrected high resolution transmission electron microscopy(AB-HRTEM)and X-ray diffraction(XRD)show that the strong Ti–O bond in the transition metal layers stabilizes the local structure,destroy the Na+-vacancy ordering and arrest the irreversible multiphase transformation that occurs during the intercalation/deintercalation process.Actually,Na_(0.67)Ni_(0.33)Mn_(0.52)Ti_(0.15)O_(2)exhibits a reversible capacity of 89.6 mA h g^(-1)even at 5 C,an excellent cyclability with 88.78%capacity retention after 200 cycles at 0.5 C.This study provides a better understanding in optimization of the design of high-energy cathode materials based on titanium doped layered oxides for SIBs.

Electrochemical performance of La_(2–x)Sm_xMg_(16)Ni+200 wt.% Ni(x=0, 0.1, 0.2, 0.3, 0.4) alloys

Nanocrystalline and amorphous La_（2–x）Sm_xMg_（16）Ni＋200wt.% Ni（x=0, 0.1, 0.2, 0.3, 0.4） alloys were prepared by mechanical milling technology. The structures of as-cast and milled alloys were investigated by X-ray diffraction（XRD）, scanning electron microscopy（SEM） and transmission electron microscopy（TEM）. Electrochemical performance of the alloy was studied by using an automatic galvanostatic system. The electrochemical impedance spectra（EIS） and Tafel polarization curves were measured by electrochemical workstation. The results indicated that the structures of the as-cast and milled alloys presented a multiphase structure with nanocrystalline and amorphous phase, moreover, transforming from nanocrystalline to amorphous phase with Sm doping. With the increase of Sm content, the maximum discharge capacity of the alloy was decreased from 922.6 to 649.1 m Ah/g, the high-rate discharge ability（HRD） was decreased, the cycle stability was strengthened, and the alloy exhibited excellent electrochemical kinetics. In addition, the charge-transfer resistance（R_（ct）） of alloy was lessened from 0.05874 to 0.02953 ？ and the limiting current density（I_L） was descended from 2.08366 to 1.04592 A/g with increasing Sm content.

Self-templating construction of hollow microspheres assembled by nanosheets with exposed active planes for sodium ion storage

P2-type layered metal oxides have been considered as one of the promising cathode candidates for high-performance Na-ion batteries(SIBs).However,it is still challenging to balance the contradiction of high energy density and long cycle life due to the structural degradation and sluggish ion diffusion dynamics.Here,the hierarchical P2-Na2/3Ni1/3Mn2/3O2 hollow microspheres assembled by nanosheets are constructed via a self-template approach.The obtained nanosheets with more exposed electrochemical active planes serving as desodiation/sodiation reactors can provide substantial Na+channels,shorten the diffusion pathways,and accommodate the volume changes during charge/discharge process.Benefiting from the facile Na+diffusion paths and optimal architecture modulation,the cathode delivers a high initial Coulombic efficiency of 96.0%with a high energy density of 299.7 Wh·kg^(−1).The highly reversible structural evolutions processes are verified by galvanostatic intermittent titration technique(GITT)and operando electrochemical impedance spectroscopy(EIS)measurement,which would significantly improve the cycle stability(83.3%capacity retention at 1.0 C over 500 loops).Furthermore,the full cell assembled by hard carbon presents a high reversible capacity of 71 mAh·g^(−1)at 0.2 C and promising capacity retention(91.5%after 50 cycles).The designing concept of morphological configuration in this work paves an accessible route for building high-performance electrode materials.

New DySrAlO_4 Compound Synthesis and Formation Process Correlations for LnSrAlO_4(Ln=Nd,Gd,Dy) Series

For the first time, DySrA104 of K2NiF4-type structure was synthesized. The parameters of DySrA104 ele- mentary unit cell are determined as follows： a = 0.368 （4） nm, c = 1.229 （2） nm, V = 0.166 （4） nm3. The research of the complex aluminates ZnSrA104 （Ln = Nd, Gd, Dy） solid-state process demonstrated the change of the formation mecha- nism among LnSrA104 （Ln = Nd, Gd, Dy） series from DySrA104 oxide. The performed analysis provided a possibility to realize why chemists couldn＇t get DySrA104 for a long period of time.