Well-ordered layered LiNi0.8Co0.1Mn0.1O2 submicron sphere with fast electrochemical kinetics for cathodic lithium storage

Nickel-rich layered oxides have drawn sustainable attentions for lithium ion batteries owing to their higher theoretical capacities and lower cost.However,nickel-rich layered oxides also have exposed several defects for commercial application,such as uncontrollable ordered layered structure,which leads to higher energy barrier for Li+diffusion.In addition,suffering from structural mutability,the bulk nickelrich cathode materials likely trigger overall volumetric variation and intergranular cracks,thus obstructing the lithium ion diffusion path and shortening the service life of the whole device.Herein,we report wellordered layered Li Ni0.8Co0.1Mn0.1O2 submicron spheroidal particles via an optimized co-precipitation and investigated as LIBs cathodes for high-performance lithium storage.The as-fabricated Li Ni0.8Co0.1Mn0.1O2 delivers high initial capacity of 228 mAh g–1,remarkable energy density of 866 Wh kg–1,rapid Li ion diffusion coefficient(10–9cm2s–1)and low voltage decay.The remarkable electrochemical performance should be ascribed to the well-ordered layered structure and uniform submicron spheroidal particles,which enhance the structural stability and ameliorate strain relaxation via reducing the parcel size and shortening Li-ion diffusion distance.This work anticipatorily provides an inspiration to better design particle morphology for structural stability and rate capability in electrochemistry energy storage devices.

Derivative-extremum analysis of current-potential curves showing electrochemical kinetics in the full reversibility range

Derivative-extremum analysis(DEA) of j-E curves is a newly proposed method of half wave potential(E1/2) and activation feature extraction from steady-state voltammetry. Here, the DEA is demonstrated to be valid in the full range of reversibility using numerical simulations with a derived universal electrode equation, providing a novel perspective of electrochemical kinetics in the reversibility domain. The results reveal that E1/2is a better choice of the reference potential instead of equilibrium potential(Eeq) in electrode equations, especially since Eeqis meaningless in an irreversible case. The equations referenced with standard potential, E1/2and Eeq, are summarized in three tables, and their applications in parameter determinations are specified. Finally, reversibility is proved to be a relative measure between kinetic slowness and mass transport of electroactive species, and the reversibility classifications are proposed according to the DEA feature in the reversibility domain. This work, based on the DEA principle, refines the electrode equation forms and generalizes their applicability in the full range of reversibility.

Enhancing low-temperature electrochemical kinetics and high-temperature cycling stability by decreasing ionic packing factor

Present-day Liþstorage materials generally suffer from sluggish low-temperature electrochemical kinetics and poor high-temperature cycling stability.Herein,based on a Ca2þsubstituted Mg_(2)Nb_(34)O_(87) anode material,we demonstrate that decreasing the ionic packing factor is a two-fold strategy to enhance the low-temperature electrochemical kinetics and high-temperature cyclic stability.The resulting Mg_(1.5)Ca_(0.5)Nb_(34)O_(87) shows the smallest ionic packing factor among Wadsley–Roth niobate materials.Compared with Mg_(2)Nb_(34)O_(87),Mg1.5Ca0.5Nb_(34)O_(87) delivers a 1.6 times faster Liþdiffusivity at-20℃,leading to 56%larger reversible capacity and 1.5 times higher rate capability.Furthermore,Mg_(1.5)Ca_(0.5)Nb_(34)O_(87) exhibits an 11%smaller maximum unit-cell volume expansion upon lithiation at 60℃,resulting in better cyclic stability;at 10C after 500 cycles,it has a 7.1%higher capacity retention,and its reversible capacity at 10C is 57%larger.Therefore,Mg_(1.5)Ca_(0.5)Nb_(34)O_(87) is an allclimate anode material capable of working at harsh temperatures,even when its particle sizes are in the order of micrometers.

Alkali cation intercalation manganese phosphate hydrate boosting electrochemical kinetics for pseudocapacitive energy storage

New insight into the effect on the alkali cations of Liþ,Naþ,and Kþpre-intercalated between adjacent layers of Mn3(PO4)2$3H2O towards the charge storage mechanism and their electrochemical kinetics of intercalation/deintercalation in three alkali electrolytes is demonstrated.The electrochemical perfor-mance of the designed LieMn3(PO4)2$3H2O material outperforms that most of Mn-based pseudocapa-citive electrode materials.The designed unique stratified structure is attractive for quick charge migration,which confirms that the appropriate pre-intercalation of alkali cation between layers is an efficient strategy to improve kinetics for the high-power density pseudocapacitive supercapacitor energy storage application.

Electrochemical Hydrogen Storage Performance of the Nanocrystalline and Amorphous Pr-Mg-Ni-based Alloys Synthesized by Mechanical Milling

The PrMg12-type composite alloy of PrMg_(11)Ni + x wt% Ni (x=100,200) with an amorphous and nanocrystalline microstructure were synthesized through the mechanical milling.Effects of milling duration and Ni content on the microstructures and electrochemical hydrogen storage performances of the ball-milled alloys were methodically studied.The ball-milled alloys obtain the optimum discharge capacities at the first cycle.Increasing Ni content dramatically enhances the electrochemical property of alloys.Milling time varying may obviously impact the electrochemical performance of these alloys.The discharge capacities show a significant upward trend with milling duration prolonging,but milling for a longer time more than 40 h induces a slight decrease in the discharge capacity of the x=200 alloy.As milling duration increases,the cycle stability clearly lowers,while it first declines and then augments under the same condition for the x=200 alloy.The high-rate discharge abilities of the ball-milled alloys show the optimum values with milling time varying.

Influence of ammonium sulfate on the corrosion behavior of AZ31 magnesium alloy in chloride environment

Electrochemical corrosion of AZ31 magnesium alloy in the NH_(4)^(+)-SO_(4)2−-Cl−environment is studied.Effect of NH_(4)^(+)overshadows that of Cl−as the(NH_(4))_(2)SO_(4) concentration is 0.005 M or higher,yielding an evolution from localized corrosion to uniform corrosion.Acceleration effect of NH_(4)^(+)can be attributed to that(i)NH_(4)^(+)dissolves the inner MgO and hinders the precipitation of Mg(OH)_(2) and(ii)the buffering ability of NH_(4)^(+)provides H+,enhances the hydrogen evolution,and expedites the corrosion process.The latter is demonstrated as the dominant factor with the results in unbuffered and buffered environments.The severe corrosion and hydrogen process in NH_(4)^(+)-containing solution results in a high Hads coverage and yields an inductive loop within the low frequency.Meanwhile,SO_(4)^(2−)is helpful in generating cracked but partially protective corrosion products,while Cl−could broaden the corrosion area beneath the corrosion product.

Effect of commercial AB_5 alloy addition on the electrochemical properties of Ml-Mg-Ni-based hydrogen storage alloys

A commercial AB5 hydrogen storage alloy was used as an additive to improve the electrochemical properties of Ml-Mg-Ni-based hydrogen storage alloys. The effect of AB5 alloy addition on the phase structure, charge/discharge characteristics, and electrochemical kinetics of Ml0.90Mg0.10Ni3.08Mn0.13Co0.63Al0.14 alloy was investigated. The maximum discharge capacity of Ml0.90Mg0.10Ni3.08Mn0.13Co0.63Al0.14 ＋ 4 wt.% AB5 electrode reaches 406 mAh/g. The anodic polarization, cyclic voltammetry, and potential step discharge experiments show that the electrochemical kinetics of the electrode with additives was promoted, with the LaNi5 phase of AB5 alloy acting as electro-catalytic sites in the electrode alloy. The high-rate dischargeability of Ml0.90Mg0.10Ni3.08Mn0.13Co0.63Al0.14 ＋ 4 wt.% AB5 alloy electrode at 1100 mA/g reaches 60.9%, which is 9.4% higher than that of Ml0.90Mg0.10Ni3.08Mn0.13Co0.63Al0.14 alloy electrode. The cycling stability of the electrode with 4 wt.% AB5 alloy has also been improved

Electrochemical Kinetic Modulators in Lithium–Sulfur Batteries:From Defect-Rich Catalysts to Single Atomic Catalysts

Lithium–sulfur batteries exhibit unparalleled merits in theoretical energy density(2600 W h kg^(-1))among next-generation storage systems.However,the sluggish electrochemical kinetics of sulfur reduction reactions,sulfide oxidation reactions in the sulfur cathode,and the lithium dendrite growth resulted from uncontrollable lithium behaviors in lithium anode have inhibited high-rate conversions and uniform deposition to achieve high performances.Thanks to the“adsorption-catalysis”synergetic effects,the reaction kinetics of sulfur reduction reactions/sulfide oxidation reactions composed of the delithiation of Li_(2)S and the interconversions of sulfur species are propelled by lowering the delithiation/diffusion energy barriers,inhibiting polysulfide shuttling.Meanwhile,the anodic plating kinetic behaviors modulated by the catalysts tend to uniformize without dendrite growth.In this review,the various active catalysts in modulating lithium behaviors are summarized,especially for the defect-rich catalysts and single atomic catalysts.The working mechanisms of these highly active catalysts revealed from theoretical simulation to in situ/operando characterizations are also highlighted.Furthermore,the opportunities of future higher performance enhancement to realize practical applications of lithium–sulfur batteries are prospected,shedding light on the future practical development.

Selective sulfur conversion with surface engineering of electrocatalysts in a lithium-sulfur battery

The sluggish kinetics of multiphase sulfur conversion with homogeneous and heterogeneous electrochemical processes,causing the“shuttle effect”of soluble polysulfide species(PSs),is the challenges in terms of lithium-sulfur batteries(LSBs).In this paper,a Mn_(3)O_(4-x) catalyst,which has much higher activity for heterogeneous reactions than for homogeneous reactions(namely,preferentialactivity catalysts),is designed by surface engineering with rational oxygen vacancies.Due to the rational design of the electronic structure,the Mn_(3)O_(4-x) catalyst prefers to accelerate the conversion of Li2S4 into Li_(2)S_(2)/Li_(2)S and optimize Li_(2)S deposition,reducing the accumulation of PSs and thus suppressing the“shuttle effect.”Both density functional theory calculations and in situ X-ray diffraction measurements are used to probe the catalytic mechanism and identify the reaction intermediates of MnS and Li_(y)Mn_(z)O_(4-x) for fundamental understanding.The cell with Mn_(3)O_(4-x) delivers an ultralow attenuation rate of 0.028% per cycle over 2000 cycles at 2.5 C.Even with sulfur loadings of 4.93 and 7.10mg cm^(-2) in a lean electrolyte(8.4μL mg s^(-1)),the cell still shows an initial areal capacity of 7.3mAh cm^(-2).This study may provide a new way to develop preferential-activity heterogeneous-reaction catalysts to suppress the“shuttle effect”of the soluble PSs generated during the redox process of LSBs.

CHRONOABSORPTOMETRY FOR THE DETERMINATION OF KINETIC PARAMETERS OF ELECTRON TRANSFER REACTIONS USING LONG-OPTICAL-PATH ELECTROCHEMICAL CELL

A single potential step chronoabsorptometric method for the determination of ki- netic parameters of simple quasi-reversible reactions is described.It is verified by determining the kinetic parameters for the electroreduction of ferricyanide.A long-optical-path electro- chemical cell with a plug-in electrode is used.The thickness of solution layer is 0.55 mm

Insights into the kinetics–morphology relationship of 1-, 2-, and 3D TiNb_(2)O_(7) anodes for Li-ion storage

Understanding the influence of electrode material’s morphology on electrochemical behavior is of great significance for the development of rechargeable batteries,however,such studies are often limited by the inability to precisely control the morphology of electrode materials.Herein,nanostructured titanium niobium oxides(TiNb_(2)O_(7))with three different morphologies(one-dimensional(1D),two-dimensional(2D),and three-dimensional(3D))were synthesized via a facile microwave-assisted solvothermal method.The influence of the morphological dimension of TiNb_(2)O_(7) as electrode material on the electrochemical performance in Li-ion batteries(LIBs)and the underlying correlation with the electrochemical kinetics were studied in detail.2D TiNb_(2)O_(7)(TNO-2D)shows a superior rate capability and cycling stability,associated with improved kinetics for charge transfer and Li-ion diffusion,compared to the 1D and 3D materials.Operando X-ray diffraction measurements reveal the structural stability and crystallographic evolution of TNO-2D upon lithiation and delithiation and correlate the Li-ion diffusion kinetics with the lattice evolution during battery charge and discharge.Moreover,carbon-coated TNO-2D achieves enhanced rate capability(205 mAh·g^(-1) at 50 C)and long-term cycling stability(87%after 1000 cycles at 5 C).This work provides insights into the rational morphology design of electrode materials for accelerated charge transfer and enhanced fast-charging capability,pushing forward the development of electrode materials for high-power rechargeable batteries in future energy storage.

MOF-derived molybdenum selenide on Ti_(3)C_(2)T_(x) with superior capacitive performance for lithium-ion capacitors

Two-dimensional Ti_(3)C_(2)T_(x) exhibits outstanding rate property and cycle performance in lithium-ion capacitors(LICs)due to its unique layered structure,excellent electronic conductivity,and high specific surface area.However,like graphene,Ti_(3)C_(2)T_(x) restacks during electrochemical cycling due to hydrogen bonding or van der Waals forces,leading to a decrease in the specific surface area and an increase in the diffusion distance of electrolyte ions between the interlayer of the material.Here,a transition metal selenide MoSe_(2) with a special three-stacked atomic layered structure,derived from metal-organic framework(MOF),is introduced into the Ti_(3)C_(2)T_(x) structure through a solvo-thermal method.The synergic effects of rapid Li+diffusion and pillaring effect from the MoSe_(2) and excellent conductivity from the Ti_(3)C_(2)T_(x) sheets endow the material with excellent electrochemical reaction kinetics and capacity.The composite Ti_(3)C_(2)T_(x)@MoSe_(2) material exhibits a high capacity over 300 mAh·g^(-1) at 150 mA·g^(-1) and excellent rate property with a specific capacity of 150 mAh·g^(-1) at 1500 mA·g^(-1).Addition-ally,the material shows a superior capacitive contribution of 86.0%at 2.0 mV·s^(-1) due to the fast electrochemical reactions.A Ti_(3)C_(2)T_(x)@MoSe_(2)//AC LIC device is also fabricated and exhibits stable cycle performance.

Nanostructured N-doped carbon materials derived from expandable biomass with superior electrocatalytic performance towards V^(2+)/V^(3+) redox reaction for vanadium redox flow battery

Vanadium redox flow battery(VRFB)is one of the most promising large-scale energy storage systems,which ranges from kilowatt to megawatt.Nevertheless,poor electrochemical activity of electrode for two redox couples still restricts the extensive applications of VRFB.Compared with V^(2+)/V^(3+)redox reaction,V^(2+)/V^(3+)reaction plays a more significant role in voltage loss of VRFB owing to slow heterogeneous electron transfer rate.Herein,N-doped carbon materials derived from scaphium scaphigerum have been developed as negative electrocatalyst by hydrothermal carbonization and high-temperature nitridation treatments.The undoped carbon material hardly has electrocatalytic ability for V^(2+)/V^(3+)reaction.Based on this,N-doped carbon materials with urea as nitrogen source exhibit excellent electrocatalytic properties.And the material nitrided at 850°C(SSC/N-850)exhibits the best performance among those from700 to 1000℃.SSC/N-850 can accelerate the electrode process including V^(2+)/V^(3+)reaction and mass transfer of active ions due to the large reaction place,more active sites,and good hydrophilicity.The effect of catalyst on comprehensive performance of cell was evaluated.SSC/N-850 can improve the charge-discharge performance greatly.Utilization of SSC/N-850 can lessen the electrochemical polarization of cell,further resulting in increased discharge capacity and energy efficiency.Discharge capacity and energy efficiency increase by 81.5%and 9.8%by using SSC/N-850 as negative catalyst at 150 m A cm^(-2),respectively.Our study reveals that the developed biomass-derived carbon materials are the low-cost and efficient negative electrocatalyst for VRFB system.

Mechanistic insights into homogeneous electrocatalytic reaction for energy storage using finite element simulation

The application of homogeneous electrocatalytic reactions in energy storage and conversion has driven surging interests of researchers in exploring the reaction mechanisms of molecular catalysts.In this paper,homogeneous electrocatalytic reaction between hydroxymethylferrocene(HMF)and L-cysteine is intensively investigated by cyclic voltammetry and square wave voltammetry for which,the secondorder rate constant(k_(ec))of the chemical reaction between HMF^(+)and L-cysteine is determined via a 1D homogeneous electrocatalytic reaction model based on finite element simulation.The corresponding k_(ec)(1.1(mol·m^(-3))^(-1)·s^(-1))is further verified by linear sweep voltammograms under the same model.Square wave voltammetry parameters including potential frequency(f),increment(Estep)and amplitude(ESW)have been comprehensively investigated in terms of the voltammetric waveform transition of homogeneous electrocatalytic reaction.Specifically,the effect of potential frequency and increment is in accordance with the potential scan rate in cyclic voltammetry and the increase of pulsed potential amplitude results in a conspicuous split oxidative peaks phenomenon.Moreover,the proposed methodology of k_(ec)prediction is examined by hydroxyethylferrocene(HEF)and L-cysteine.The present work facilitates the understanding of homogeneous electrocatalytic reaction for energy storage purpose,especially in terms of electrochemical kinetics extraction and flow battery design.

Effect of ultramicropores and inner space of carbon materials on the capacitive sodium storage performance

1.Introduction Carbon materials have been widely investigated as the anode materials for Na+storage due to their moderate capacity,good stability,and low cost.The Na+storage mechanisms of carbon are generally classified into diffusion-controlled interlayer insertion/desertion and capacitive-controlled surface adsorption/desorption[1].

Improved electrochemical kinetic performances of La-Mg-Ni-based hydrogen storage alloys with lanthanum partially substituted by yttrium

Yttrium （Y） has been used as the partial substitution element for lanthanum （La） to improve the electrochemical kinetic performances of La-Mg-Ni-based hydrogen storage alloys. Lao.80-xYxMg0.20Ni2.85Mn0.10Coo.55Al0.10 （x=0.00, 0.05 and 0.10） alloys were prepared by the inductive melting technique. The alloys were composed of LaNi5 and （La,Mg）2Ni7 phases, the introduction of Y promoted the formation of （La,Mg）2Ni7 phase, and thus the Y-substituted alloy electrodes exhibited higher discharge capacities. Y substitution was also found to be effective to improve the discharge kinetics of the alloy electrodes. When the Y content x increased from 0.00 to 0.10, the high-rate dischargeability of the alloy electrodes at a discharge current density of 1800 mA/g （HRDl800） in- creased from 23.6% to 39.7% at room temperature. In addition, the measured HRD1800 showed a linear dependence on both the ex- change current density and the hydrogen diffusion coefficient at different temperatures, respectively.

Phase structure and electrochemical performances of Co-free La–Mg–Ni-based alloys with Nd/Sm partial substitution for La

In this paper, the Co-free hydrogen storage alloys with the nominal compositions of La0.75R0.05Mg0.20Ni3.40Al0.10（R = La, Nd and Sm） were prepared by induction melting, and then the phase structure and electrochemical properties of these alloys were comparatively investigated. It is found that the alloys mainly consist of（La, Mg）2Ni7phase, La Ni5 phase and（La, Mg）5Ni19phase.Refinement results further show that Nd substitution for La remarkably promotes the formation of La Ni5 phase, while Sm is beneficial for the formation of（La, Mg）5Ni19phase.At discharge current density of 1,875 m A g-1, the highrate dischargeability（HRD） of alloy electrodes increases by 13.9 % and 6.5 % with La substituted by Nd and Sm,respectively. The electrochemical kinetic measurements reveal that the exchange current density（I0）, charge transfer resistance（R） and hydrogen diffusion coefficient（D） for the alloy electrode are all facilitated with Nd and Sm partial substitution for La. Subsequently, a linear correlation between the HRD1875 and the corresponding I0/D is found.

Structures and electrochemical performances of as-cast and spun RE-Mg-Ni-Mn-based alloys applied to Ni-MH battery

The RE-Mg-Ni-Mn-based AB2-type La（1-x）CexMgNi（3.5）Mn（0.5）（ x = 0- 0. 4） alloys were prepared by spinning treatment. For obtaining the optimum performance,the effects of Ce content and spinning rate on the hydrogen storage performance of the alloys were studied systematically. The results show that the variations of the spinning rate and Ce content result in noteworthy changes of the phase content without altering phase composition of the alloys. Specifically,the LaMgNi4 phase increases and LaNi5 phase decreases when increasing the spinning rate and Ce content. Furthermore,the crystalline grains of Cecontaining alloys prepared by spinning treatment are remarkably refined. The alloys own superior electrochemical performance. All alloys reach the optimal discharge capacity at the initial cycle. Increasing Ce content and spinning rate lead the discharge capacity and electrochemical kinetics rise to an optimal value and then start to reduce. Meanwhile,the electrochemical cycle stability is also improved,which is ascribed to the great enhancement of anti-pulverization and anti-corrosion abilities resulting from the spinning treatment and the substitution of Ce for La.

Initial Electrode Kinetics of Anion Intercalation and De-intercalation in Nonaqueous Al-Graphite Batteries

Graphitic materials with intercalated sites are considered as the mostly used positive electrode materials in nonaqueous Al batteries.Unlike the small-size cations,the intercalation/de-intercalation of large-size anions into/out of graphite would induce large volume expansion and micro-structure reconfiguration,leading to unexpected coulombic efficiency in the full cells(<95%within initial several cycles).

Freestanding MoSe_(2)nanoflowers for superior Li/Na storage properties

MoSe_(2),with high theoretical specific capacity,has attracted a lot of attention.There remains an open challenge to effectively suppress the irreversible selenium dissolution and rapid capacity decrease induced by severe volume change during cycling.Herein,we synthesize MoSe_(2)nanoflowers dispersed on one-dimensional(1D)N-doped carbon nanofibers(MoSe_(2)@NCNFs)for use as a freestanding electrode.In this unique structure,the 1D N-doped carbon nanofibers are found to not only enhance the conductivity but also ensure the structural integrity during the Li^(+)/Na^(+)insertion/destraction processes.As expected,at 2 A·g^(-1),the specific capacity of the MoSe_(2)@NCNFs is maintained at 180 mAh·g^(-1)after 500 cycles when used in lithium storage applications.Furthermore,in the case of sodium storage,at 1 A·g^(-1),the MoSe_(2)@NCNFs shows a capacity of 122mAh·g^(-1)after 500 cycles.These findings suggest that the MoSe_(2)@NCNF electrodes may be a promising candidate for use in reversible Li/Na storage applications.