Boosted Storage Kinetics in Thick Hierarchical Micro-Nano Carbon Architectures for High Areal Capacity Li-Ion Batteries

A practical and effective approach to increase the energy storage capacity of lithium ion batteries(LIBs)is to boost their areal capacity.Developing thick electrodes is one of the most crucial ways to achieve high areal capacity but limited by sluggish ion/electron transport,poor mechanical stability,and high-cost manufacturing strategies.Here we address these constraints by engineering a unique hierarchical-networked 10 mm thick all-carbon electrode,providing a scalable strategy to produce high areal capacity LIB electrodes.The hierarchical-networked structure utilizes micrometer-sized carbon fibers(MCFs)as building blocks,nano-sized carbon nanotubes(CNTs)as good continuous network with excellent electrical conductivity,and pyrolytic carbon as the binder and active material with excellent storage capacity.The combination of the above features endows our HNT-MCF/CNT/PC electrode with excellent performance including high reversible capacity of 15.44 mAh cm^(-2) at 2.0 mA cm^(-2) and exhibits excellent rate capability of 2.50 mAh cm^(-2) under 10.0 mA cm^(-2) current density.The Li-ion storage mechanism in HNT-MCF/CNT/PC involves dual-storage mechanism including intercalation and surface adsorption(pseudocapacitance)confirmed by the cyclic voltammetry and symmetric cell analysis.This work provides insights into the construction of high mechanical stability thick electrode for the next generation high areal capacity LIBs and beyond.

Combined forecast method of HMM and LS-SVM about electronic equipment state based on MAGA

For the deficiency that the traditional single forecast methods could not forecast electronic equipment states, a combined forecast method based on the hidden Markov model（HMM） and least square support vector machine（LS-SVM） is presented. The multi-agent genetic algorithm（MAGA） is used to estimate parameters of HMM to overcome the problem that the Baum-Welch algorithm is easy to fall into local optimal solution. The state condition probability is introduced into the HMM modeling process to reduce the effect of uncertain factors. MAGA is used to estimate parameters of LS-SVM. Moreover, pruning algorithms are used to estimate parameters to get the sparse approximation of LS-SVM so as to increase the ranging performance. On the basis of these, the combined forecast model of electronic equipment states is established. The example results show the superiority of the combined forecast model in terms of forecast precision,calculation speed and stability.

Effect of Er_(30)Cu_(70) on microstructure and properties of sintered Nd-Fe-B by grain boundary reconstruction

Usually it is generally believed that the Er element forms the Er_(2)Fe_(14)B phase,which will seriously deteriorate the magnetic properties.Distinctly,here we report the balance of corrosion resistance and coercivity in Nd-Fe-B sintered magnets through using simple Er_(30)Cu_(70) additive whose price is much lower than Dy and Tb.By reasonably controlling Er_(30)Cu_(70) addition,the corrosion resistance is improved at the minimum limit of reducing the magnetic properties.Through studying the influence mechanism of Er element,it is found that the main effect of Er elements is to replace the Nd elements at the edge of the main phase grains to form a(Er,Nd)_(2)Fe_(14)B shell with low H_(A),resulting in the reduction of magnetic properties.The improvement of corrosion resistance mainly comes from the more stable Cu element introduced at the grain boundary.At the same time,the target magnets also show different advantages under different heat treatment methods.Above findings may spur progress towards developing the lowcost permanent magnets that rival the commercial Nd-Fe-B counterpart.

Effects of Sm-doping on microstructure,magnetic and microwave absorption properties of BiFeO_(3)

In this paper,polycrystalline samples of Bi_(1-x)Sm_(x)FeO_(3)(x=0,0.05,0.1,0.15) were successfully synthesized by sol-gel method.The effects of Sm concentration on the crystal structure,morphology,chemical states,magnetic properties and microwave absorption performance were studied by X-ray diffraction(XRD),scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray photoelectron spectroscopy(XPS),a vibrating sample magnetometer(VSM) and a Vector network analyzer(VNA),respectively.The results show that the rare earth Sm doping causes the crystal structure to change.When x≤0.1,Bi_(1-x)Sm_(x)FeO_(3) is the distorted rhombohedral structure with space group R3c.With the increase of Sm doping amount to x=0.15,the phase structure of Bi_(1-x)Sm_(x)FeO_(3) changes from rhombohedral structure to cubic structure with the space group Pm3 m.The particle size decreases with the increase of the Sm doping amount.The analysis results show that Sm doping can effectively reduce the oxygen vacancies and significantly improve its magnetic properties.The results exhibit that moderately doped rare earth Sm element can effectively improve microwave absorption properties of Bi_(1-x)Sm_(x)FeO_(3) powders.When Sm doping amount of x is 0.1,the Bi_(0.9)Sm_(0.1)FeO_(3) compound has good microwave absorption performance,and the minimum reflection loss value of Bi_(0.9)Sm_(0.1)FeO_(3) powder reaches about-32.9 dB at11.7 GHz,and its effective absorption bandwidth(RL <-10 dB) is 2.6 GHz with the optimal matching thickness of 2.0 mm.

Improvement in magnetic properties,corrosion resistance and microstructure of Nd-Fe-B sintered magnets through intergranular addition of Tb_(68)Ni_(32)

New energy vehicles and offshore wind power industries have a high demand for sintered Nd-Fe-B magnets with high intrinsic coercivity and high corrosion resistance.In this study,the magnetic properties,anticorrosion properties,and micro structure of Nd-Fe-B sintered magnets with the intergranular addition of low-melting-point eutectic Tb_(68)Ni_(32) alloy powders were investigated.The aim is to determine if the addition of Tb_(68)Ni_(32) can improve these properties.A low melting-point eutectic alloy Tb_(68)Ni_(32) powders was prepared as a grain boundary additive and blended with the master alloy powders prior to sintering.The coercivity of the resultant magnets gradually increases from 1468 to 2151 kA/m by adding increasing amounts of Tb_(68)Ni_(32).At the same time,the remanence first increases and then slightly decreases.After studying the microstructure and elemental composition of the Tb_(68)Ni_(32) added magnets,it is found that the significant increase in coercivity and the negligible reduction in remanence is due to densificatio n,improved grain orientation,a unifo rm and continuous boundary phase distribution,as well as the generation of a(Nd,Pr,Tb)_(2) Fe_(14)B "core-shell" structure surrounding the main-phase grain.Moreover,the corrosion resistance of the magnet is greatly improved owing to the enhancement of electrochemical stability,as well as the optimization of the distribution and morphology of the intergranular phase.

Double core-shell nanostructured Sn-Cu alloy as enhanced anode materials for lithium and sodium storage

Sn-based alloy materials are considered as a promising anode candidate for lithium-ion batteries(LIBs)and sodium-ion batteries(SIBs),whereas they suffer from severe volume change during the discharge/charge process.To address the issue,double core-shell structured Sn-Cu@SnO2@C nanocomposites have been prepared by a simple co-precipitation method combined with carbon coating approach.The double core-shell structure consists of Sn-Cu multiphase alloy nanoparticles as the inner core,intermediate SnO2 layer anchored on the surface of Sn-Cu nanoparticle and outer carbon layer.The Sn-Cu@SnO2@C electrode exhibits outstanding electrochemical perfor-mances,delivering a reversible capacity of 396 mA·h·g^-1 at 100 mA·g^-1 after 100 cycles for LIBs and a high initial reversible capacity of 463 mA·h·g^-1 at 50 mA·g^-1 and a capacity retention of 86% after 100 cycles,along with a remarkable rate capability(193 mA·h·g^-1 at 5000 mA·g^-1)for SIBs.This work provides a viable strategy to fabricate double core-shell structured Sn-based alloy anodes for high energy density LIBs and SIBs.

FeSb@N-doped carbon quantum dots anchored in 3D porous N-doped carbon with pseudocapacitance effect enabling fast and ultrastable potassium storage

Potassium-ion batteries(PIBs)are promising ne15t-generation energy storage candidates due to abundant resources and low cost.Sb-based materials with high theoretical capacity(660 mAh·g^(-1))and low working potential are considered as promising anode for PIBs.The remaining challenge is poor stability and slow kinetics.In this work,FeSb@N-doped carbon quantum dots anchored in three-dimensional(3D)porous N-doped carbon(FeSb@C/Nc3DC/N),a Sb-based material with a particular structure,is designed and constructed by a green salt-template method.As an anode for PIBs,it exhibits extraordinarily high-rate and long-cycle stability(a capacity of 245 mAh·g^(-1) at 3,080 mAh·g^(-1) after 1,000 cycles).The pseudocapacitance contribution(83%)is demonstrated as the origin of high-rate performance of the FeSb@C/NС3DC/N electrode.Furthermore,the potassium storage mechanism in the electrode is systematically investigated through ex-situ characterization techniques including ex-situ transmission electron microscopy(TEM)and X-ray photoelectron spectroscopy(XPS).Overall,this study could provide a useful guidance for future design of high-performance electrode materials for PIBs.