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.

Recent progress in Ni-rich layered oxides and related cathode materials for Li-ion cells

Undoubtedly,the enormous progress observed in recent years in the Ni-rich layered cathode materials has been crucial in terms of pushing boundaries of the Li-ion battery(LIB)technology.The achieved improvements in the energy density,cyclability,charging speed,reduced costs,as well as safety and stability,already contribute to the wider adoption of LIBs,which extends nowadays beyond mobile electronics,power tools,and electric vehicles,to the new range of applications,including grid storage solutions.With numerous published papers and broad reviews already available on the subject of Ni-rich oxides,this review focuses more on the most recent progress and new ideas presented in the literature references.The covered topics include doping and composition optimization,advanced coating,concentration gradient and single crystal materials,as well as innovations concerning new electrolytes and their modification,with the application of Ni-rich cathodes in solid-state batteries also discussed.Related cathode materials are briefly mentioned,with the high-entropy approach and zero-strain concept presented as well.A critical overview of the still unresolved issues is given,with perspectives on the further directions of studies and the expected gains provided.

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.

Optimization Strategies of Na_(3)V_(2)(PO_(4))_(3) Cathode Materials for Sodium‑Ion Batteries

Na_(3)V_(2)(PO_(4))_(3)(NVP)has garnered great attentions as a prospective cathode material for sodium-ion batteries(SIBs)by virtue of its decent theoretical capacity,superior ion conductivity and high structural stability.However,the inherently poor electronic conductivity and sluggish sodium-ion diffusion kinetics of NVP material give rise to inferior rate performance and unsatisfactory energy density,which strictly confine its further application in SIBs.Thus,it is of significance to boost the sodium storage performance of NVP cathode material.Up to now,many methods have been developed to optimize the electrochemical performance of NVP cathode material.In this review,the latest advances in optimization strategies for improving the electrochemical performance of NVP cathode material are well summarized and discussed,including carbon coating or modification,foreign-ion doping or substitution and nanostructure and morphology design.The foreign-ion doping or substitution is highlighted,involving Na,V,and PO_(4)^(3−)sites,which include single-site doping,multiple-site doping,single-ion doping,multiple-ion doping and so on.Furthermore,the challenges and prospects of high-performance NVP cathode material are also put forward.It is believed that this review can provide a useful reference for designing and developing high-performance NVP cathode material toward the large-scale application in SIBs.

Research progresses on cathode materials of aqueous zinc-ion batteries

Electrochemical energy storage and conversion techniques that exhibit the merits such as high energy density,rapid response kinetics,economical maintenance requirements and expedient installation procedures will hold a pivotal role in the forthcoming energy storage technologies revolution.In recent years,aqueous zinc-ion batteries(AZIBs)have garnered substantial attention as a compelling candidate for large-scale energy storage systems,primarily attributable to their advantageous featu res encompassing cost-effectiveness,environmental sustainability,and robust safety profiles.Currently,one of the primary factors hindering the further development of AZIBs originates from the challenge of cathode materials.Specifically,the three mainstream types of mainstream cathode materials,in terms of manganese-based compounds,vanadium-based compounds and Prussian blue analogues,surfer from the dissolution of Mn~(2+),in the low discharge voltage,and the low specific capacity,respectively.Several strategies have been developed to compensation the above intrinsic defects for these cathode materials,including the ionic doping,defect engineering,and materials match.Accordingly,this review first provides a systematic summarization of the zinc storage mechanism in AZIBs,following by the inherent merit and demerit of three kind of cathode materials during zinc storage analyzed from their structure characteristic,and then the recent development of critical strategies towards the intrinsic insufficiency of these cathode materials.In this review,the methodologies aimed at enhancing the efficacy of manganese-based and vanadium-based compounds are emphasis emphasized.Additionally,the article outlines the future prospective directions as well as strategic proposal for cathode materials in AZIBs.

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.

Perspectives in Electrochemical in situ Structural Reconstruction of Cathode Materials for Multivalent-ion Storage

Multivalent-ion(such as Zn^(2+),Mg^(2+),Al^(3+))batteries are considered as a prospective alternative for large-scale energy storage.However,the main problem of cathode materials for multivalent-ion batteries is the sluggish diffusion of multivalent ions.Many cathode materials will self-adjust under electrochemical conditions to achieve the optimal state for multivalent-ion storage.In this review,the significant role of electrochemical in situ structural reconstruction of cathode materials is suggested.The types,basic characteristics,and formation mechanisms of reconstructed phases have been systematically discussed and commented.The most important insight we pointed out is that the cathode materials with loose structures after in situ electrochemical activation are conducive to the reversible diffusion of multivalent ions.Moreover,several crucial issues of electrochemical activation and reconstruction were further analyzed and discussed.The challenges and future perspectives are presented in the final section.

Selenium-doped cathode materials with polyaniline skeleton for lithium-organosulfur batteries

Sulfur-containing polymer(SCP)is considered as an outstanding cathode material for lithium-sulfur batteries.However,undesirable soluble polysulfides may shuttle in electrolyte,concluding long-chain Li_(2)S_(n)(n>4)and short-chain Li2Sn(n≤4),as well as the sluggish conversion kinetics are yet to be solved to enhance the performance of lithium-sulfur batteries.Here Se-doped sulfurized polyaniline with adjusted sulfur-chain-S_(x)-(x≤6)contribute to ensure the absence of long-chain polysulfides,and the skeleton with quinoid imine can endow strongly adsorption towards short-chain polysulfides by the reversible transition between deprotonated/protonated imine(-NH^(+)=and-N=),which offer double insurance against suppressing“shuttle effect”.Furthermore,Se atoms are doped into sulfurized polysulfides to accelerate the redox conversion and take a frontier orbital theory-oriented view into catalytic mechanism.Se-doped sulfurized polyaniline as active materials for lithium-organosulfur batteries delivers good electrochemical performance,including high rate,reversible specific capacity(680 mA h g^(-1)at 0.1 A g^(-1)),and lower capacity decay rate only of 0.15%with near 100%coulomb efficiency during long-term cycle.This work provides a valuable guiding ideology and promising solution for the chemistry-oriented structure design and practical application for lithium-organosulfur batteries.

Defective layered Mn-based cathode materials with excellent performance via ion exchange for Li-ion batteries

Defective layered Mn-based materials were synthesized by Li/Na ion exchange to improve their electrochemical activity and Coulombic efficiency.The annealing temperature of the Na precursors was important to control the P3-P2 phase transition,which directly affected the structure and electrochemical characteristics of the final products obtained by ion exchange.The O3-Li_(0.78)[Li_(0.25)Fe_(0.075)Mn_(0.675)]O_(δ) cathode made from a P3-type precursor calcined at 700℃ was analyzed using X-ray photoelectron spectrometry and electron paramagnetic resonance.The results showed that the presence of abundant trivalent manganese and defects resulted in a discharge capacity of 230 mAh/g with an initial Coulombic efficiency of about 109%.Afterward,galvanostatic intermittent titration was performed to examine the Li^(+) ion diffusion coefficients,which affected the reversible capacity.First principles calculations suggested that the charge redistribution induced by oxygen vacancies(OV_(s))greatly affected the local Mn coordination environment and enhanced the structural activity.Moreover,the Li-deficient cathode was a perfect match for the pre-lithiation anode,providing a novel approach to improve the initial Coulombic efficiency and activity of Mn-based materials in the commercial application.

Organic cathode materials for rechargeable magnesium-ion batteries:Fundamentals, recent advances, and approaches to optimization

Rechargeable magnesium-ion batteries(MIBs) are favorable substitutes for conventional lithium-ion batteries(LIBs) because of abundant magnesium reserves, a high theoretical energy density, and great inherent safety. Organic electrode materials with excellent structural tunability,unique coordination reaction mechanisms, and environmental friendliness offer great potential to promote the electrochemical performance of MIBs. However, research on organic magnesium battery cathode materials is still preliminary with many significant challenges to be resolved including low electrical conductivity and unwanted but severe dissolution in useful electrolytes. Herein, we provide a detailed overview of reported organic cathode materials for MIBs. We begin with basic properties such as charge storage mechanisms(e.g., n-, p-, and bipolartype), moving to recent advances in various types of organic cathodes including carbonyl-, nitrogen-, and sulfur-based materials. To shed light on the diverse strategies targeting high-performance Mg-organic batteries, elaborate summaries of various approaches are presented.Generally, these strategies include molecular design, polymerization, mixing with carbon, nanosizing and electrolyte/separator optimization.This review provides insights on exploring high-performance organic cathodes in rechargeable MIBs.

Enhanced Electrochemical Performances of Ni Doped Cr_(8)O_(21)Cathode Materials for Lithium-ion Batteries

Cathode materials,nickel doped Cr_(8)O_(21),were synthesized by a solid-state method.The effects of Ni doping on the electrochemical performances of Cr_(8)O_(21) were investigated.The experimental results show that the discharge capacities of the samples depend on the nickel contents,which increases firstly and then decreases with increasing Ni contents.Optimized Ni_(0.5)Cr_(7.5)O_(21)delivers a first capacity up to 392.6 m Ah·g^(-1)at 0.1C.In addition,Ni doped sample also demonstrates enhanced cycling stability and rate capability compared with that of the bare Cr_(8)O_(21).At 1 C,an initial discharge capacity of 348.7 m Ah·g^(-1)was achieved for Ni_(0.5)Cr_(7.5)O_(21),much higher than 271.4 m Ah·g^(-1)of the un-doped sample,with an increase of more than 28%.Electrochemical impedance spectroscopy results confirm that Ni doping reduces the growth of interface resistance and charge transfer resistance,which is conducive to the electrochemical kinetic behaviors during charge-discharge.

CoSnO_(3)/C nanocubes with oxygen vacancy as high-capacity cathode materials for rechargeable aluminum batteries

Rechargeable aluminum batteries(RABs)are attractive cadidates for next-generation energy storage and conversion,due to the low cost and high safety of Al resources,and high capacity of metal Al based on the three-electrons reaction mechanism.However,the development of RABs is greatly limited,because of the lack of advanced cathode materials,and their complicated and unclear reaction mechanisms.Exploring the novel nanostructured transition metal and carbon composites is an effective route for obtaining ideal cathode materials.In this work,we synthesize porous CoSnO_(3)/C nanocubes with oxygen vacancies for utilizing as cathodes in RABs for the first time.The intrinsic structure stability of the mixed metal cations and carbon coating can improve the cycling performance of cathodes by regulating the internal strains of the electrodes during volume expansion.The nanocubes with porous structures contribute to fast mass transportation which improves the rate capability.In addition to this,abundant oxygen vacancies promote the adsorption affinity of cathodes,which improves storage capacity.As a result,the CoSnO_(3)/C cathodes display an excellent reversible capacity of 292.1 mAh g^(-1) at 0.1 A g^(-1),a good rate performance with 109 mAh g^(-1) that is maintained even at 1 A g^(-1) and the provided stable cycling behavior for 500 cycles.Besides,a mechanism of intercalation of Al^(3+)within CoSnO_(3)/C cathode is proposed for the electrochemical process.Overall,this work provides a step toward the development of advanced cathode materials for RABs by engineering novel nanostructured mixed transition-metal oxides with carbon composite and proposes novel insights into chemistry for RABs.

Influences of transition metal on structural and electrochemical properties of Li[Ni_xCo_yMn_z]O_2(0.6≤x≤0.8) cathode materials for lithium-ion batteries

Li[NixCoyMn2]O2（0.6≤x≤0.8） cathode materials with a typical hexagonal α-NaFeO2 structure were prepared utilizing a co-precipitation method.It is found that the ratio of peak intensities of（003） to（104） observed from X-ray diffraction（XRD）increases with decreasing the Ni content or increasing the Co content.The scanning electron microscopy（SEM） images reveal that the small primary particles are agglomerated to form the secondary ones.As the Mn content increases,the primary and secondary particles become larger and the resulted particle size for the Li[Ni（0.6）Co（0.2）Mn（0.2）]O2 is uniformly distributed in the range of100-300 nm.Although the initial discharge capacity of the Li/Li[NixCoyMn2]O2 cells reduces with decreasing the Ni content,the cyclic performance and rate capability are improved with higher Mn or Co content.The Li[Ni（0.6）Co（0.2）Mn（0.2）]O2 can deliver excellent cyclability with a capacity retention of 97.1%after 50 cycles.

Grinding sol gel synthesis and electrochemical performance of mesoporous Li_3V_2(PO_4)_3 cathode materials

Li3V2（PO4）3 precursor was obtained with V2Os.nH2O , LiOH＇H2O, NH4H2PO4 and sucrose as starting materials by grinding-sol-gel method, and then the monoclinic-typed Li3Vz（PO4）3 cathode material was prepared by sintering the amorphous Li3V2（PO4）3. The as-sintered samples were investigated by X-ray diffraction （XRD）, transmission electron microscopy （TEM）, N2 adsorption-desorption and electrochemical measurement. It is found that Li3Vz（PO4）3 sintered at 700 ℃ possesses good wormhole-like mesoporous structure with the largest specific surface area of 188 cmZ/g, and the smallest pore size of 9.3 nm. Electrochemical test reveals that the initial discharge capacity of the 700 ℃ sintered sample is 155.9 mA.h/g at the rate of 0.2C, and the capacity retains 154 mA.h/g after 50 cycles, exhibiting a stable discharge capacity at room temperature.

Overcharge-to-thermal-runaway behavior and safety assessment of commercial lithium-ion cells with different cathode materials:A comparison study

In this paper,overcharge behaviors and thermal runaway(TR)features of large format lithium-ion(Liion)cells with different cathode materials(LiFePO4(LFP),Li[Ni_(1/3)Co_(1/3)Mn_(1/3)]O_(2)(NCM111),Li[Ni_(0.6)Co_(0.2)Mn_(0.2)]O_(2)(NCM622)and Li[Ni_(0.8)Co_(0.1)Mn_(0.1)]O_(2)(NCM811))were investigated.The results showed that,under the same overcharge condition,the TR of LFP Li-ion cell occurred earlier compared with the NCM Li-ion cells,indicating its poor overcharge tolerance and high TR risk.However,when TR occurred,LFP Li-ion cell exhibited lower maximum temperature and mild TR response.All NCM Liion cells caught fire or exploded during TR,while the LFP Li-ion cell only released a large amount of smoke without fire.According to the overcharge behaviors and TR features,a safety assessment score system was proposed to evaluate the safety of the cells.In short,NCM Li-ion cells have better performance in energy density and overcharge tolerance(or low TR risk),while LFP Li-ion cell showed less severe response to overcharging(or less TR hazards).For NCM Li-ion cells,as the ratio of nickel in cathode material increases,the thermal stability of the cathode materials becomes poorer,and the TR hazards increase.Such a comparison study on large format Li-ion cells with different cathode materials can provide deeper insights into the overcharge behaviors and TR features,and provide guidance for engineers to reasonably choose battery materials in automotive applications.

The mechanism of side reaction induced capacity fading of Ni-rich cathode materials for lithium ion batteries

Ni-rich cathode materials show great potential of applying in high-energy lithium ion batteries,but their inferior cycling stability hinders this process.Study on the electrode/electrolyte interfacial reaction is indispensable to understand the capacity failure mechanism of Ni-rich cathode materials and further address this issue.This work demonstrates the domain size effects on interfacial side reactions firstly,and further analyzes the inherent mechanism of side reaction induced capacity decay through comparing the interfacial behaviors before and after MgO coating.It has been determined that LiF deposition caused thicker SEI films may not increase the surface film resistance,while HF erosion induced surface phase transition will increase the charge transfer resistance,and the later plays the dominant factor to declined capacity of Ni-rich cathode materials.This work suggests strategies to suppress the capacity decay of layered cathode materials and provides a guidance for the domain size control to match the various applications under different current rates.

Electrochemical performance of sulfur composite cathode materials for rechargeable lithium batteries

The structure and characteristic of carbon materials have a direct influence on the electrochemical performance of sulfur-carbon composite electrode materials for lithium-sulfur battery. In this paper, sulfur composite has been synthesized by heating a mixture of elemental sulfur and activated carbon, which is characterized as high specific surface area and microporous structure. The composite, contained 70% sulfur, as cathode in a lithium cell based on organic liquid electrolyte was tested at room temperature. It showed two reduction peaks at 2.05 V and 2.35 V, one oxidation peak at 2.4 V during cyclic voltammogram test. The initial discharge specific capacity was 1180.8 mAh g-1 and the utilization of electrochemically active sulfur was about 70.6% assuming a complete reaction to the product of Li2S. The specific capacity still kept as high as 720.4 mAh g^-1 after 60 cycles retaining 61% of the initial discharge capacity.

Synthesis and characterization of phosphate-modified LiMn_2O_4 cathode materials for Li-ion battery

LiMn2O4 spinel cathode materials were modified with 2 wt.%Li-M-PO4（M=Co,Ni,Mn） by polyol synthesis method.The phosphate surface-modified LiMn2O4 cathode materials were physically characterized by X-ray diffraction（XRD）,scanning electron microscopy（SEM） and energy dispersive X-ray spectroscopy（EDS）.The charge-discharge test showed that the cycling and rate capacities of LiMn2O4 cathode materials were significantly enhanced by stabilizing the electrode surface with phosphate.

Influence of Doping Rare Earth on Performance of Lithium Manganese Oxide Spinels as Cathode Materials for Lithium-Ion Batteries

Some rare earth doping spinel LiMn_(2-x)RE_xO_4 (RE=La, Ce, Nd) cathode materials for lithium ion batteries were synthesized by the solid-state reaction method. The structure characteristics of these produced samples were investigated by XRD, SEM, and particle size distribution analysis. According to the microstructure and charge-discharge testing, the effect of doping rare earth on stabilizing the spinel structure was analyzed. Through a series of doping experiments, it is shown that when the doping content x within the range of 0.01～0.02 the cycle performance of the materials is greatly improved. The discharge capacity of the sample LiMn_(1.98)La_(0.02)O_4, LiMn_(1.98)Ce_(0.02)O_4 and LiMn_(1.98)Nd_(0.02)O_4 remain 119.1, 114.2 and 117.5 mAh·g^(-1) after 50 cycles.

Mixed polyanion cathode materials:Toward stable and high-energy sodium-ion batteries

Sodium-ion batteries(SIBs)are considered as one of the most fascinating alternatives to lithium-ion batteries for grid-scale energy storage applications because of the low cost and wide abundance of sodium resources.Among various cathode materials,mixed polyanion compounds come into the spotlight as promising electrode materials due to their superior electrochemical properties,such as high working voltage,long cycling stability,and facile reaction kinetics.In this review,we summarize the recent development in the exploration of different mixed polyanion cathode materials for SIBs.We provide a comprehensive understanding of the structure-composition-performance relationship of mixed polyanion cathode materials together with the discussion of their sodium storage mechanisms.It is anticipated that further innovative works on the material design of advanced cathode materials for batteries can be inspired.