Research on Preparation and Electrochemical Performance of the High Compacted Density Ni-Co-Mn Ternary Cathode Materials

The high compacted density LiNi0.5-xCo0.2Mn0.3MgxO2 cathode material for lithium-ion batteries was synthesized by high temperature solid-state method, taking the Mg element as a doping element and the spherical Ni0.5Co0.2Mn0.3 (OH)2, Li2CO3 as raw materials. The effects of calcination temperature on the structure and properties of the products were investigated. The structure and morphology of cathode materials powder were analyzed by X-ray diffraction spectroscopy (XRD) and scanning electronmicroscopy (SEM). The electrochemical properties of the cathode materials were studied by charge-discharge test and cyclic properties test. The results show that LiNi0.4985Co0.2Mn0.3 Mg0.0015O2 cathode material prepared at calcination temperature 930°C has a good layered structure, and the compacted density of the electrode sheet is above 3.68 g/cm3. The discharge capacity retention rate is more than 97.5% after 100 cycles at a charge-discharge rate of 1C, displaying a good cyclic performance.

Modification strategies improving the electrochemical and structural stability of high-Ni cathode materials

With the increasing spotlight in electric vehicles,there is a growing demand for high-energy-density batteries to enhance driving range.Consequently,several studies have been conducted on high-energy-density LiNi_(x)Co_(y)Mn_(z)O_(2)cathodes.However,there is a limit to permanent performance deterioration because of side reactions caused by moisture in the atmosphere and continuous microcracks during cycling as the Ni content to express high energy increases and the content of Mn and Co that maintain structural and electrochemical stabilization decreases.The direct modification of the surface and bulk regions aims to enhance the capacity and long-term performance of high-Ni cathode materials.Therefore,an efficient modification requires a study based on a thorough understanding of the degradation mechanisms in the surface and bulk region.In this review,a comprehensive analysis of various modifications,including doping,coating,concentration gradient,and single crystals,is conducted to solve degradation issues along with an analysis of the overall degradation mechanism occurring in high-Ni cathode materials.It also summarizes recent research developments related to the following modifications,aims to provide notable points and directions for post-studies,and provides valuable references for the commercialization of stable high-energy-density cathode materials.

New carbon-nitrogen-oxygen compounds as high energy density materials

Molecular crystals are complex systems exhibiting various crystal structures,and accurately modeling the crystal structures is essential for understanding their physical behaviors under high pressure.Here,we perform an extensive structure search of ternary carbon-nitrogen-oxygen(CNO)compound under high pressure with the CALYPSO method and first principles calculations,and successfully identify three polymeric CNO compounds with Pbam,C2/m and I4m2symmetries under 100 GPa.More interestingly,these structures are also dynamically stable at ambient pressure,and are potential high energy density materials(HEDMs).The energy densities of Pbam,C2/m and I4m2 phases of CNO are about2.30 kJ/g,1.37 kJ/g and 2.70 kJ/g,respectively,with the decompositions of graphitic carbon and molecular carbon dioxide andα-N(molecular N_(2))at ambient pressure.The present results provide in-depth insights into the structural evolution and physical properties of CNO compounds under high pressures,which offer crucial insights for designs and syntheses of novel HEDMs.

Effects of current density on preparation and performance of Al/conductive coating/α-PbO_2-Ce O_2-TiO_2/β-Pb O_2-MnO_2-WC-ZrO_2 composite electrode materials

Al/conductive coating/α-Pb O2-Ce O2-Ti O2/β-PbO 2-MnO 2-WC-Zr O2 composite electrode material was prepared on Al/conductive coating/α-PbO 2-Ce O2-Ti O2 substrate by electrochemical oxidation co-deposition technique. The effects of current density on the chemical composition, electrocatalytic activity, and stability of the composite anode material were investigated by energy dispersive X-ray spectroscopy（EDXS）, anode polarization curves, quasi-stationary polarization（Tafel） curves, electrochemical impedance spectroscopy（EIS）, scanning electron microscopy（SEM）, and X-ray diffraction（XRD）. Results reveal that the composite electrode obtained at 1 A/dm2 possesses the lowest overpotential（0.610 V at 500 A/m2） for oxygen evolution, the best electrocatalytic activity, the longest service life（360 h at 40 °C in 150 g/L H2SO4 solution under 2 A/cm2）, and the lowest cell voltage（2.75 V at 500 A/m2）. Furthermore, with increasing current density, the coating exhibits grain growth and the decrease of content of Mn O2. Only a slight effect on crystalline structure is observed.

The action mechanisms and structures designs of F-containing functional materials for high performance oxygen electrocatalysis

Non-renewable fossil fuels have led to serious problems such as global warming,environmental pollution,etc.Oxygen electrocatalysis including oxygen reduction reaction(ORR)and oxygen evolution reaction(OER)plays a central role in clean energy conversion,enabling a number of sustainable processes for future air battery technologies.Fluorine,as the most electronegative element(4.0)not only can induce more efficient regulation for the electronic structure,but also can bring more abundant defects and other novel effects in materials selection and preparation for favorable catalysis with respect to the other nonmetal elements.However,an individual and comprehensive overview of fluorine-containing functional materials for oxygen electrocatalysis field is still blank.Therefore,it is very meaningful to review the recent progresses of fluorine-containing oxygen electrocatalysts.In this review,we first systematically summarize the controllable preparation methods and their possible development directions based on fluorine-containing materials from four preparation methods.Due to the strong electron-withdrawing properties of fluorine,its control of the electronic structure can effectively enhance the oxygen electrocatalytic activity of the materials.In addition,the catalytic enhancement effect of fluorine on carbonbased materials also includes the prevent oxidation and the layer peeling,and realizes the precise atomic control.And the catalytic improvement mechanism of fluorine containing metal-based compounds also includes the hydration of metal site,the crystal transformation,and the oxygen vacancy induction.Then,based on their various dimensions(0D–3D),we also have summarized the advantages of different morphologies on oxygen electrocatalytic performances.Finally,the prospects and possible future researching direction of F-containing oxygen electrocatalysts are presented(e.g.,novel pathways,advanced methods for measurement and simulation,field assistance and multi-functions).The review is considered valuable and helpful in exploring the novel designs and mechanism analyses of advanced fluorine-containing electrocatalysts.

Experimental and theoretical studies on two-dimensional vanadium carbide hybrid nanomaterials derived from V_(4)AlC_(3) as excellent catalyst for MgH_(2)

Hydrogen is considered one of the most ideal future energy carriers.The safe storage and convenient transportation of hydrogen are key factors for the utilization of hydrogen energy.In the current investigation,two-dimensional vanadium carbide(VC) was prepared by an etching method using V_(4)AlC_(3) as a precursor and then employed to enhance the hydrogen storage properties of MgH_(2).The studied results indicate that VC-doped MgH_(2) can absorb hydrogen at room temperature and release hydrogen at 170℃. Moreover,it absorbs 5.0 wt.%of H_(2) within 9.8 min at 100℃ and desorbs 5.0 wt.% of H_(2) within 3.2 min at 300℃.The dehydrogenation apparent activation energy of VC-doped MgH_(2) is 89.3 ± 2.8 kJ/mol,which is far lower than that of additive-free MgH_(2)(138.5 ± 2.4 kJ/mol),respectively.Ab-initio simulations showed that VC can stretch Mg-H bonds and make the Mg-H bonds easier to break,which is responsible for the decrease of dehydrogenation temperature and conducive to accelerating the diffusion rate of hydrogen atoms,thus,the hydrogen storage properties of MgH_(2) are remarkable improved through addition of VC.

Theoretical Study of the N-NO_2 Bond Dissociation Energies for Energetic Materials with Density Functional Theory

The N-NO2 bond dissociation energies （BDEs） for 7 energetic materials were computed by means of accurate density functional theory （B3LYP, B3PW91 and B3P86） with 6-31G＊＊ and 6-311G＊＊ basis sets. By comparing the computed energies and experimental results, we find that the B3P86/6-311G＊＊ method can give good results of BDE, which has the mean absolute deviation of 1.30kcal/mol. In addition, substituent effects were also taken into account. It is noted that the Hammett constants of substituent groups are related to the BDEs of the N-NO2 bond and the bond dissociation energies of the energetic materials studied decrease when increasing the number of NO2 group.

Recent advances in fabricating high-performance triboelectric nanogenerators via modulating surface charge density

Triboelectric nanogenerators(TENGs),a type of promising micro/nano energy source,have been arousing tremendous research interest since their inception and have been the subject of many striking developments,including defining the fundamental physical mechanisms,expanding applications in mechanical to electric power conversion and self-powered sensors,etc.TENGs with a superior surface charge density at the interfaces of the electrodes and dielectrics are found to be crucial to the enhancement of the performance of the devices.Here,an overview of recent advances,including material optimization,circuit design,and strategy conjunction,in developing TENGs through surface charge enhancement is presented.In these topics,different strategies are retrospected in terms of charge transport and trapping mechanisms,technical merits,and limitations.Additionally,the current challenges in high-performance TENG research and the perspectives in this field are discussed.

Databases of 2D material-substrate interfaces and 2D charged building blocks

Discovery of materials using“bottom-up”or“top-down”approach is of great interest in materials science.Layered materials consisting of two-dimensional(2D)building blocks provide a good platform to explore new materials in this respect.In van der Waals(vdW)layered materials,these building blocks are charge neutral and can be isolated from their bulk phase(top-down),but usually grow on substrate.In ionic layered materials,they are charged and usually cannot exist independently but can serve as motifs to construct new materials(bottom-up).In this paper,we introduce our recently constructed databases for 2D material-substrate interface(2DMSI),and 2D charged building blocks.For 2DMSI database,we systematically build a workflow to predict appropriate substrates and their geometries at substrates,and construct the 2DMSI database.For the 2D charged building block database,1208 entries from bulk material database are identified.Information of crystal structure,valence state,source,dimension and so on is provided for each entry with a json format.We also show its application in designing and searching for new functional layered materials.The 2DMSI database,building block database,and designed layered materials are available in Science Data Bank at https://doi.org/10.57760/sciencedb.j00113.00188.

Particle Size Optimization of Thermochemical Salt Hydrates for High Energy Density Thermal Storage

Thermal energy storage(TES)solutions offer opportunities to reduce energy consumption,greenhouse gas emissions,and cost.Specifically,they can help reduce the peak load and address the intermittency of renewable energy sources by time shifting the load,which are critical toward zero energy buildings.Thermochemical materials(TCMs)as a class of TES undergo a solid-gas reversible chemical reaction with water vapor to store and release energy with high storage capacities(600 kWh m^(-3))and negligible self-discharge that makes them uniquely suited as compact,stand-alone units for daily or seasonal storage.However,TCMs suffer from instabilities at the material(salt particles)and reactor level(packed beds of salt),resulting in poor multi-cycle efficiency and high-levelized cost of storage.In this study,a model is developed to predict the pulverization limit or Rcrit of various salt hydrates during thermal cycling.This is critical as it provides design rules to make mechanically stable TCM composites as well as enables the use of more energy-efficient manufacturing process(solid-state mixing)to make the composites.The model is experimentally validated on multiple TCM salt hydrates with different water content,and effect of Rcrit on hydration and dehydration kinetics is also investigated.

Universal materials model of deep-learning density functional theory Hamiltonian

Realizing large materials models has emerged as a critical endeavor for materials research in the new era of artificial intelligence,but how to achieve this fantastic and challenging objective remains elusive.Here,we propose a feasible pathway to address this paramount pursuit by developing universal materials models of deep-learning density functional theory Hamiltonian(Deep H),enabling computational modeling of the complicated structure-property relationship of materials in general.By constructing a large materials database and substantially improving the Deep H method,we obtain a universal materials model of Deep H capable of handling diverse elemental compositions and material structures,achieving remarkable accuracy in predicting material properties.We further showcase a promising application of fine-tuning universal materials models for enhancing specific materials models.This work not only demonstrates the concept of Deep H's universal materials model but also lays the groundwork for developing large materials models,opening up significant opportunities for advancing artificial intelligencedriven materials discovery.

On the hydro-mechanical behaviour of MX80 bentonite-based materials

Bentonite-based materials have been considered in many countries as engineered barrier/backfilling materials in deep geological disposal of high-level radioactive waste.During the long period of waste storage,these materials will play an essential role in ensuring the integrity of the storage system that consists of the waste canisters,the engineered barrier/backfill,the retaining structures as well as the geological barrier.Thus,it is essential to well understand the hydro-mechanical behaviours of these bentonite-based materials.This review paper presents the recent advances of knowledge on MX80 bentonite-based materials,in terms of water retention properties,hydraulic behaviour and mechanical behaviour.Emphasis is put on the effect of technological voids and the role of the dry density of bentonite.The swelling anisotropy is also discussed based on the results from swelling tests with measurements of both axial and radial swelling pressures on a sand-bentonite mixture compacted at different densities.Microstructure observation was used to help the interpretation of macroscopic hydromechanical behaviour.Also,the evolution of soil microstructure thus the soil density over time is discussed based on the results from mock-up tests.This evolution is essential for understanding the longterm hydro-mechanical behaviour of the engineered barrier/backfill.

Understanding the influence of crystal packing density on electrochemical energy storage materials

Crystal structure determines electrochemical energy storage characteristics;this is the underlying logic of material design.To date,hundreds of electrode materials have been developed to pursue superior performance.However,it remains a great challenge to understand the fundamental structure–performance relationship and achieve quantitative crystal structure design for efficient energy storage.In this review,we introduce the concept of crystal packing factor(PF),which can quantify crystal packing density.We then present and classify the typical crystal structures of attractive cathode/anode materials.Comparative PF analyses of different materials,including polymorphs,isomorphs,and others,are performed to clarify the influence of crystal packing density on energy storage performance through electronic and ionic conductivities.Notably,the practical electronic/ionic conductivities of energy storage materials are based on their intrinsic characteristics related to the PF yet are also affected by extrinsic factors.The PF provides a novel avenue for understanding the electrochemical performance of pristine materials and may offer guidance on designing better materials.Additional approaches involve size regulation,doping,carbon additives,and other methods.We also propose extended PF concepts to understand charge storage and transport behavior at different scales.Finally,we provide our insights on the major challenges and prospective solutions in this highly exciting field.

Particle breakage of granular materials during sample preparation

Particle breakage is commonly observed in granular materials when subjected to external loads. It was found that particle breakage would occur during both sample preparation and loading stages. However,main attention was usually paid to the particle breakage behaviour of samples during loading stage. This study attempts to explore the breakage behaviour of granular materials during sample preparation.Triaxial samples of rockfill aggregates are prepared by layered compaction method to achieve different relative densities. Extents of particle breakage based on the gradings before and after test are presented and analysed. It is found that particle breakage during sample preparation cannot be ignored. Gradings after test are observed to shift away from the initial grading. Aggregates with larger size that appear to break are more than the smaller-sized ones. Irrespective of the initial gradings, an increase in the extent of particle breakage with the increasing relative density is observed during sample preparation.

First-principles study of high performance lithium/sodium storage of Ti3C2T2 nanosheets as electrode materials

Ti3C2Tx nanosheet,the first synthesized MXene with high capacity performance and charge/discharge rate,has attracted increasingly attention in renewable energy storage applications.By performing systematic density functional theory calculations,the theoretical capacity of the intrinsic structure of single-and multi-layered Ti3C2T2(T=F or O)corresponding to M(M=Li and Na)atoms are investigated.Theoretical volumetric capacity and gravimetric capacity are obtained,which are related to the stacking degree.The optimal ratios of capacity to structure are determined under different stacking degrees for understanding the influence of surface functional groups on energy storage performance.Its performance can be tuned by performing surface modification and increasing the interlayer distance.In addition,the reason for theoretical capacity differences of M atoms is analyzed,which is attributed to difference in interaction between the M-ions and substrate and the difference in electrostatic exclusion between adsorbed M-ions.These results provide an insight into the understanding of the method of efficiently increasing the energy storage performance,which will be useful for designing and using high performance electrode materials.

Nitrogen-doped carbon stabilized Li Fe0.5Mn0.5PO4/rGO cathode materials for high-power Li-ion batteries

Exploring high ion/electron conductive olivine-type transition metal phosphates is of vital significance to broaden their applicability in rapid-charging devices.Herein,we report an interface engineered Li Fe0.5Mn0.5PO4/rGO@C cathode material by the synergistic effects of r GO and polydopamine-derived N-doped carbon.The well-distributed Li Fe0.5Mn0.5PO4nanoparticles are tightly anchored on r GO nanosheet benefited by the coating of N-doped carbon layer.The design of such an architecture can effectively suppress the agglomeration of nanoparticles with a shortened Li+transfer path.Meantime,the high-speed conducting network has been constructed by r GO and N-doped carbon,which exhibits the face-to-face contact with Li Fe0.5Mn0.5PO4nanoparticles,guaranteeing the rapid electron transfer.These profits endow the Li Fe0.5Mn0.5PO4/rGO@C hybrids with a fast charge-discharge ability,e.g.a high reversible capacity of 105 m Ah·g^-1at 10 C,much higher than that of the Li Fe0.5Mn0.5PO4@C nanoparticles(46 mA·h·g^-1).Furthermore,a 90.8%capacity retention can be obtained even after cycling 500 times at 2 C.This work gives a new avenue to fabricate transition metal phosphate with superior electrochemical performance for high-power Li-ion batteries.

Accurate machine learning models based on small dataset of energetic materials through spatial matrix featurization methods

A large database is desired for machine learning(ML) technology to make accurate predictions of materials physicochemical properties based on their molecular structure.When a large database is not available,the development of proper featurization method based on physicochemical nature of target proprieties can improve the predictive power of ML models with a smaller database.In this work,we show that two new featurization methods,volume occupation spatial matrix and heat contribution spatial matrix,can improve the accuracy in predicting energetic materials' crystal density(ρ_(crystal)) and solid phase enthalpy of formation(H_(f,solid)) using a database containing 451 energetic molecules.Their mean absolute errors are reduced from 0.048 g/cm~3 and 24.67 kcal/mol to 0.035 g/cm~3 and 9.66 kcal/mol,respectively.By leave-one-out-cross-validation,the newly developed ML models can be used to determine the performance of most kinds of energetic materials except cubanes.Our ML models are applied to predict ρ_(crystal) and H_(f,solid) of CHON-based molecules of the 150 million sized PubChem database,and screened out 56 candidates with competitive detonation performance and reasonable chemical structures.With further improvement in future,spatial matrices have the potential of becoming multifunctional ML simulation tools that could provide even better predictions in wider fields of materials science.

Anode materials for potassium-ion batteries: Current status and prospects

Potassium-ion batteries(KIBs)as one of the most promising alternatives to lithium-ion batteries have been highly valued in recent years.However,progress in KIBs is largely restricted by the sluggish development in anode materials.Therefore,it is imperative to systematically outline and evaluate the recent research advances in the field of anode materials for KIBs toward promoting the development of high-performance anode materials for KIBs.In this review,the recent achievements in anode materials for KIBs are summarized.The electrochemical properties(ie.charge storage mechanism,capacity,rate performance,and cycling stability)of these reported anode materials,as well as their advantages/disadvantages,are discerned and analyzed,enabling high-performance KIBs to meet the requirements for practical applications.Finally,technological developments,scientific challenges,and future research opportunities of anode materials for KIBs are briefly reviewed.

Computational screening of doping schemes for LiTi2(PO4)3 as cathode coating materials

In all-solid-state lithium batteries,the impedance at the cathode/electrolyte interface shows close relationship with the cycle performance.Cathode coatings are helpful to reduce the impedance and increase the stability at the interface effectively.LiTi2(PO4)3(LTP),a fast ion conductor with high ionic conductivity approaching 10^(-3)S·cm^(-1),is adopted as the coating materials in this study.The crystal and electronic structures,as well as the Li^+ion migration properties are evaluated for LTP and its doped derivatives based on density functional theory(DFT)and bond valence(BV)method.Substituting part of Ti sites with element Mn,Fe,or Mg in LTP can improve the electronic conductivity of LTP while does not decrease its high ionic conductivity.In this way,the coating materials with both high ionic conductivities and electronic conductivities can be prepared for all-solid-state lithium batteries to improve the ion and electron transport properties at the interface.

High-throughput theoretical design of lithium battery materials

The rapid evolution of high-throughput theoretical design schemes to discover new lithium battery materials is re- viewed, including fiigh-capacity cathodes, low-strain cathodes, anodes, solid state eleclrolytes, and electrolyte additives. With tfie development of efficient theoretical methods and inexpensive computers, high-throughput theoretical calculations have played an increasingly important role in the discovery of new malerials. With the help of automatic simnlation flow, many types of materials can be screened, optimized and designed from a structural database according to specific search criteria. In advanced cell technology, new materials for next generation lithium batteries are of great significance to achieve perlbmmnce, and some representative criteria are： higher energy density, better safety, and faster charge/discharge speed.