Understanding of the charge storage mechanism of MnO_(2)-based aqueous zinc-ion batteries:Reaction processes and regulation strategies

Though secondary aqueous Zn ion batteries(AZIBs)have been received broad concern in recent years,the development of suitable cathode materials of AZIBs is still a big challenge.The MnO_(2) has been deemed as one of most hopeful cathode materials of AZIBs on account of some extraordinary merits,such as richly natural resources,low toxicity,high discharge potential,and large theoretical capacity.However,the crystal structure diversity of MnO_(2) results in an obvious various of charge storage mechanisms,which can cause great differences in electrochemical performance.Furthermore,several challenges,including intrinsic poor conductivity,dissolution of manganese and sluggish ion transport dynamics should be conquered before real practice.This work focuses on the reaction mechanisms and recent progress of MnO_(2)-based materials of AZIBs.In this review,a detailed review of the reaction mechanisms and optimal ways for enhancing electrochemical performance for MnO_(2)-based materials is proposed.At last,a number of viewpoints on challenges,future development direction,and foreground of MnO_(2)-based materials of aqueous zinc ions batteries are put forward.This review clarifies reaction mechanism of MnO_(2)-based materials of AZIBs,and offers a new perspective for the future invention in MnO_(2)-based cathode materials,thus accelerate the extensive development and commercialization practice of aqueous zinc ions batteries.

Rational construction and decoration of Li_(5)Cr_(7)Ti_(6)O_(25)@Cnanofibers as stable lithium storage materials

Li_(5)Cr_(7)Ti_(6)O_(25) is regarded as a promising anode material for Li-ion batteries(LIBs)because of its low cost and high theoretical capacity.However,the inherently poor conductivity significantly limits the enhancement of its rate capability and cycling stability,especially at high current densities.In this work,we construct one-dimensional Li_(5)Cr_(7)Ti_(6)O_(25)/C nanofibers by electrospinning method to enhance the kinetic,which realizes high cycling stability.Carbon coating enhances the structure stability,insertion/extraction reversibility of Li-ions and electrochemical reaction activity,and facilitates the transfer of Li-ions.Benefited from the unique architecture and component,the Li_(5)Cr_(7)Ti_(6)O_(25)/C(6.6 wt%)nanofiber shows an excellent rate capability with a reversible de-lithiation capacity of 370.8,290.6,269.2,254.3 and 244.9 m Ah g^(-1) at 200,300,500,800 and 1000 m A g^(-1),respectively.Even at a higher current density of 1 A g^(-1),Li_(5)Cr_(7)Ti_(6)O_(25)/C(6.6 wt%)nanofiber shows high cycling stability with an initial de-lithiation capacity of 237.8 m Ah g^(-1) and a capacity retention rate of about 84%after 500 cycles.The density functional theory calculation result confirms that the introduction of carbon on the surface of Li_(5)Cr_(7)Ti_(6)O_(25) changes the total density of states of Li_(5)Cr_(7)Ti_(6)O_(25),and thus improves electronic conductivity of the composite,resulting in a good electrochemical performance of Li_(5)Cr_(7)Ti_(6)O_(25)/C nanofibers.Li_(5)Cr_(7)Ti_(6)O_(25)/C nanofibers indicate a great potential as an anode material for the next generation of high-performance LIBs.

Structure and electrochemical properties of LiLa_xMn_(2-x)O_4 cathode material by the ultrasonic-assisted sol-gel method

Powders of spinel LiLaxMn2-xO4 were successfully synthesized by the ultrasonic-assisted sol-gel （UASG） method. The structure and properties of LiLaxMn2-xO4 were examined by X-ray diffraction （XRD）, Fourier transform infrared （FT-IR） spectroscopy, scanning electronic microscopy （SEM）, galvanostatic charge-discharge test, and cyclic voltammetry （CV）. XRD results show that the La^3＋ can partially reptace Mn^3＋ in the spinel and the doped materials with La^3＋ have a larger lattice constant compared with pristine LiMn2O4. FT-IR indicates that the absorption peak of Mn^3＋-O and Mn^4＋- O bonds has a red and blue shift with the increase of doping lanthanum in LiLaxMn2-xO4, respectively. The charge-discharge test exhibits that the initial discharge capacity of LiLaxMn2-xO4 drops off, and the capacity retention increases gradually at C/5 discharge rate with the increase of doping lanthanum, and LiLa0.01Mn1.99O4 has a higher discharge capacity and a better cycling performance at 1C discharge rate. CV reveals that the doping La^3＋ is beneficial to the reversible extraction and intercalation of Li^＋ ions.

Advancement of technology towards high-performance non-aqueous aluminum-ion batteries

Al-ion batteries(AIBs) have been identified as one of the most hopeful energy storage systems after Li-ion batteries on account for the ultrahigh volumetric capacity,high safety and low cost from the rich abundance of Al.Nonetheless,some inevitable shortcomings,such as the formation of passive oxide film,hydrogen side reactions and anode corrosion,finally limit the large-scale application of aqueous AIBs.The nonaqueous AIBs have been considered as one of most hopeful alternatives for high-powered electrochemical energy storage devices.Nonetheless,various technical and scientific obstacles should be resolved because nonaqueous AIBs are still nascent.Some significant efforts have aimed to resolve these issues towards large-scale applications,and some important advancement has been made.In the present review,we mainly intended to offer an overview of non-aqueous AIBs systems,and we comprehensively reviewed the recent research advancement of the cathode materials,anode materials electrolyte and collectors as well as the fundamental understanding of the functional mechanisms.In addition,we have also analyzed several technical challenges and summarized the strategies used for overcoming the challenges in improving the electrochemical properties,including morphology control,surface engineering,doping and construction of composite electrodes as well as the charge storage mechanisms of the materials with different crystal structures.At last,future research orientation and development prospect of the AIBs are proposed.

纳米结构的多孔球形NiO@NiMoO4@PPy作为先进的电化学赝电容器材料

构建了一种PPy缠绕的多孔球形NiO@NiMoO4材料,并应用于高性能的超级电容器.结果表明,NiO改性改变了NiMoO4的形貌,NiO@NiMoO4和NiO@NiMoO4@PPy均呈现一种内部中空和外壳多孔的形貌,并具有较大的比表面积,进而促进了离子和电荷的转移.NiMoO4和PPy壳具有较高的电子电导率,降低了NiO的电荷转移电阻,进而提高了其电化学动力学性能.在电流密度为20A/g时,NiO,NiMoO4,NiO@NiMoO4和NiO@NiMoO4@PPy电极的初始放电比电容分别为456.0,803.2,764.4和941.6F/g.在电流密度增大至30A/g时,NiO@NiMoO4@PPy电极的初始放电比电容为850.2F/g,30000次循环后比电容仍达到655.2F/g,电容保有率为77.1%.第一性原理计算结果表明,更强的Mo–O有利于稳定NiO@NiMoO4复物的结构,进而提高了其循环稳定性.

Enhanced electrochemical property of FePO_4-coated LiNi_(0.5)Mn_(1.5)O_4 as cathode materials for Li-ion battery

Pristine LiNi_(0.5)Mn_(1.5)O_4and FePO_4-coated one with Fd-3m space groups were prepared by a sol-gel method.The structure and performance were studied by X-ray diffraction(XRD)rietveld refinement,scanning electron microscopy(SEM),high resolution transmission electron microscopy(HRTEM),energy dispersive spectrometer(EDS)mapping,electrochemical impedance spectroscopy(EIS)and chargedischarge tests,respectively.The lattice parameters of all samples almost remain the same from the Rietveld refinement,revealing that the crystallographic structure has no obvious difference between pristine LiNi_(0.5)Mn_(1.5)O_4and FePO_4-coated one.All materials show similar morphologies with uniform particle distribution with small particle size,and FePO_4coating does not affect the morphology of LiNi_(0.5)Mn_(1.5)O_4material.EDS mapping and HRTEM show that FePO_4may be successfully wrapped around the surfaces of LiNi_(0.5)Mn_(1.5)O_4particles,and provides an effective coating layer between the electrolyte and the surface of LiNi_(0.5)Mn_(1.5)O_4particles.FePO_4(1 wt%)-coated LiNi_(0.5)Mn_(1.5)O_4cathode shows the highest discharge capacity at high rate(2C)among all samples.After 80 cycles,the reversible discharge capacity of FePO_4(1 wt%)coated Li Ni-0.5Mn1.5O4is 117 m Ah g1,but the pristine one only has 50 m Ah g^(-1).FePO_4coating is an effective and controllable way to stabilize the LiNi_(0.5)Mn_(1.5)O_4/electrolyte interface,and avoids the direct contact between LiNi_(0.5)Mn_(1.5)O_4powders and electrolyte,then suppresses the side reactions and enhances the electrochemical performance of the LiNi_(0.5)Mn_(1.5)O_4.

Interconnected Bi_(5)Nb_(3)O_(15)@CNTs network as high-performance anode materials of Li-ion battery

In this work,the facile carbon nanotubes(CNTs) modulation strategy was successfully used to fabricate Bi_(5) Nb_(3) O_(15)@CNTs composites as anode materials for lithium-ion battery by a simple solid-state route.The introduction of CNTs does not change the structure of the Bi_(5) Nb_(3) O_(15) materials,the Bi_(5) Nb_(3) O_(15) particles are decorated on a three-dimensional CNTs network,and the high conductive network promotes transfer of electron/ion and relieve the volume change of Bi_(5) Nb_(3) O_(15).The Bi_(5) Nb_(3) O_(15)@CNTs(8 wt%) electrode shows a superior rate capability with charge(discharge) capacities of 490(898.7),379.1(401.6),311.3(326.9),276.5(285.5) and 243.4(252)mAh·g^(-1) at 50,100,200,300 and 500 mA·g^(-1),respectively.However,the Bi_(5) Nb_(3) O_(15) only shows charge(discharge) capacities of 431(772.6),278.6(309.9),193.1(213.7),160.8(171.1),129.9(139.1) mAh·g^(-1) at the corresponding rates,respectively.The excellent rate capability of Bi_(5) Nb_(3) O_(15)@CNTs can be ascribed to the homogeneous distribution of Bi_(5) Nb_(3) O_(15) particles in the CNTs conductive network and the enhancement of conductivity.Hence,the CNTs modulation can be considered as an effective strategy to enhance electrochemical performances of Bi_(5) Nb_(3) O_(15) materials.

Approaching high-performance electrode materials of ZnCo2S4 nanoparticle wrapped carbon nanotubes for supercapacitors

In this work,CNTs-wrapped ZnCo2S4 nanoparticle composites were constructed by a simple hydrothermal process.This process allows to wrap ZnCo2S4 nanoparticle in an interconnected CNT matrix that combines excellent electronic conductivity with good mechanical stability.The CNTs wrapping suppresses the aggregation of ZnCo2S4 nanoparticle,and assures an effective contact between electrolyte and ZnCo2S4 particles,then promotes rapid ion transportation.Specifically,ZnCo2S4@CNTs(5 wt%)composite shows the highest specific surface area,lowest polarization and the highest reversibility during cycling among all samples.ZnCo2S4@CNTs(0,2.5,5 and 10 wt%)electrodes deliver specific capacitances of 360.4,1012.8,1190.4 and 1015.6 F g^(-1) with capacitance retentions of 32.9%,81.3%,84.2%and 79.3%at 10 Ag^(-1) after 10,000 cycles.Even at higher current density of 30 A g^(-1),ZnCo2S4@CNTs(5 wt%)composite also delivers a specific capacitance of about 880 F g^(-1) with a capacitance retention of 93%after 30,000 cycles,revealing outstanding cycling stability.The above results exhibit that ZnCo2S4@CNTs composites can be promising candidates as electrode materials for pseudocapacitors with excellent electrochemical property in future applications.

Construction of Na_(2)Li_(2)Ti_(6)O_(14)@LiAlO_(2)Composites as Anode Materials of Lithium-Ion Battery with High Performance

In this work,we construct Na_(2)Li_(2)Ti_(6)O_(14)@LiAlO_(2)(NLTO-L)composites by a simple ball milled process and post-calcination in air atmosphere to improve the electrochemical performance.The thickness of the LiAlO_(2)coating layer is approximate2 nm.The morphology and particle size of Na_(2)Li_(2)Ti_(6)O_(14)are not dramatically altered after LiAlO_(2)coating.All samples display similar particles with a size range from 150 to 500 nm.The LiAlO_(2)coating can supply fast charge transmission paths with good insertion/extraction dynamics of lithium ions and provide an excellent rate performance and cycle performance of as-prepared Na_(2)Li_(2)Ti_(6)O_(14)@LiAlO_(2)anodes.Therefore,LiAlO_(2)coating efficiently enhances the rate performance and cycle performance of Na_(2)Li_(2)Ti_(6)O_(14)anode,even at large current densities.As a result,Na_(2)Li_(2)Ti_(6)O_(14)@LiAlO_(2)(5 wt%)reveals remarkable rate properties with reversible charge capacity of 238.7,214.7,185.8,168.5 and 139.8 mAh g^(-1)at 50,100,200,300 and 500 mA g^(-1),respectively.Na_(2)Li_(2)Ti_(6)O_(14)@LiAlO_(2)(5 wt%)also possesses a good cycle performance with a de-lithiation capacity of 166.5 mAh g-1 at 500 mA g^(-1)after 200 cycles.Nonetheless,the corresponding de-lithiation capacity of pure Na_(2)Li_(2)Ti_(6)O_(14)is only 140.1 mAh g^(-1).Consequently,LiAlO_(2)coating is efficeient approach to enhance the electrochemical performances of Na_(2)Li_(2)Ti_(6)O_(14).

PPy-Encapsulated Na_(2)Li_(2)Ti_(6)O_(14) Composites as High-Performance Anodes for Li-Ion Battery

Na_(2)Li_(2)Ti_(6)O_(14) as a reliable anode material is becoming a hopeful candidate for Li-ion battery.Nevertheless,the pristine Na_(2)Li_(2)Ti_(6)O_(14) usually suffer from bad rate performance and poor cycling stability under high current due to limited diffusion kinetics and poor electrical conductivity.Here,the PPy-coated Na_(2)Li_(2)Ti_(6)O_(14) composites are successfully obtained via the solid-state method and followed by chemical oxidation process in the first time.The results of tests prove that the Na_(2)Li_(2)Ti_(6)O_(14)@PPy composites have better electrochemical performance than the bare Na_(2)Li_(2)Ti_(6)O_(14) because of the excellent electrical conductivity and the special macromolecular architecture of PPy.In particular,the Na_(2) Li_(2) Ti_(6) O_(14) @PPy(4 wt%)exhibits excellent charge capacities of about 223.2,218.0,200.8,184.3 and 172.6 mAh g^(-1) at 50,100,200,300 and500 mA g^(-1),respectively,revealing the best rate capability of all electrode materials.The Na_(2)Li_(2)Ti_(6)O_(14)@PPy(4 wt%)not only has the highest charge capacity under 0.5 mA g^(-1),but also has the highest capacity retention of 85.12%among all samples after 100 loops.Hence,the PPy coating is known as a promising way to improve the electrochemical property of Na_(2)Li_(2)Ti_(6)O_(14).The PPy-coated Na_(2)Li_(2)Ti_(6)O_(14) demonstrates the great prospect as promising negative materials for Li-ion batteries.