Enhancing thermodynamic stability of single-crystal Ni-rich cathode material via a synergistic dual-substitution strategy

Nickel(Ni)-rich cathode materials have become promising candidates for the next-generation electrical vehicles due to their high specific capacity.However,the poor thermodynamic stability(including cyclic performance and safety performance or thermal stability)will restrain their wide commercial application.Herein,a single-crystal Ni-rich Li Ni_(0.83)Co_(0.12)Mn_(0.05)O_(2) cathode material is synthesized and modified by a dual-substitution strategy in which the high-valence doping element improves the structural stability by forming strong metal–oxygen binding forces,while the low-valence doping element eliminates high Li^(+)/Ni^(2+)mixing.As a result,this synergistic dual substitution can effectively suppress H2-H3 phase transition and generation of microcracks,thereby ultimately improving the thermodynamic stability of Ni-rich cathode material.Notably,the dual-doped Ni-rich cathode delivers an extremely high capacity retention of 81%after 250 cycles(vs.Li/Li+)in coin-type half cells and 87%after 1000 cycles(vs.graphite/Li^(+))in pouch-type full cells at a high temperature of 55℃.More impressively,the dual-doped sample exhibits excellent thermal stability,which demonstrates a higher thermal runaway temperature and a lower calorific value.The synergetic effects of this dual-substitution strategy pave a new pathway for addressing the critical challenges of Ni-rich cathode at high temperatures,which will significantly advance the high-energy-density and high-safety cathodes to the subsequent commercialization.

A defective iron-based perovskite cathode for high-performance IT-SOFCs:Tailoring the oxygen vacancies using Nb/Ta co-doping

The sluggish kinetics of the electrochemical oxygen reduction reaction(ORR)in intermediatetemperature solid oxide fuel cells(IT-SOFCs)greatly limits the overall cell performance.In this study,an efficient and durable cathode material for IT-SOFCs is designed based on density functional theory(DFT)calculations by co-doping with Nb and Ta the B-site of the SrFeO_(3-δ)perovskite oxide.The DFT calculations suggest that Nb/Ta co-doping can regulate the energy band of the parent SrFeO_(3-δ)and help electron transfer.In symmetrical cells,such cathode with a SrFe_(0.8)Nb_(0.1)Ta_(0.1)O_(3-δ)(SFNT)detailed formula achieves a low cathode polarization resistance of 0.147Ωcm^(2) at 650℃.Electron spin resonance(ESR)and X-ray photoelectron spectroscopy(XPS)analysis confirm that the co-doping of Nb/Ta in SrFeO_(3-δ)B-site increases the balanced concentration of oxygen vacancies,enhancing the electrochemical performance when compared to 20 mol%Nb single-doped perovskite oxide.The cathode button cell with NiSDC|SDC|SFNT configuration achieves an outstanding peak power density of 1.3 W cm^(-2)at 650℃.Moreover,the button cell shows durability for 110 h under 0.65 V at 600℃ using wet H_(2) as fuel.

High‑Entropy Layered Oxide Cathode Enabling High‑Rate for Solid‑State Sodium‑Ion Batteries

Na-ion O3-type layered oxides are prospective cathodes for Na-ion batteries due to high energy density and low-cost.Nevertheless,such cathodes usually suffer from phase transitions,sluggish kinetics and air instability,making it difficult to achieve high performance solid-state sodium-ion batteries.Herein,the high-entropy design and Li doping strategy alleviate lattice stress and enhance ionic conductivity,achieving high-rate performance,air stability and electrochemically thermal stability for Na_(0.95)Li_(0.06)Ni_(0.25)Cu_(0.05)Fe_(0.15)Mn_(0.49)O_(2).This cathode delivers a high reversible capacity(141 mAh g^(−1)at 0.2C),excellent rate capability(111 mAh g^(−1)at 8C,85 mAh g^(−1)even at 20C),and long-term stability(over 85%capacity retention after 1000 cycles),which is attributed to a rapid and reversible O3–P3 phase transition in regions of low voltage and suppresses phase transition.Moreover,the compound remains unchanged over seven days and keeps thermal stability until 279℃.Remarkably,the polymer solid-state sodium battery assembled by this cathode provides a capacity of 92 mAh g^(−1)at 5C and keeps retention of 96%after 400 cycles.This strategy inspires more rational designs and could be applied to a series of O3 cathodes to improve the performance of solid-state Na-ion batteries.

New insights into the pre-lithiation kinetics of single-crystalline Ni-rich cathodes for long-life Li-ion batteries

Developing single-crystalline Ni-rich cathodes is an effective strategy to improve the safety and cycle life of Li-ion batteries(LIBs).However,the easy-to-loss of Li and O in high-temperature lithiation results in unsatisfactory ordered layered structure and stoichiometry.Herein,we demonstrate the synthesis of highly-ordered and fully-stoichiometric single-crystalline LiNi_(0.83)Co_(0.12)Mn_(0.05)O_(2)(SC-NCM83)cathodes by the regulation of pre-lithiation kinetics.The well-balanced pre-lithiation kinetics have been proved to greatly improve the proportion of layered phase in the intermediate by inhibiting the formation of metastable spinel phase,which promoted the rapid transformation of the intermediate into highly-ordered layered SC-NCM83 in the subsequent lithiation process.After coating a layer of Li_(2)O–B_(2)O_(3),the resultant cathodes deliver superior cycling stability with 90.9%capacity retention at 1C after 300 cycles in pouch-type full batteries.The enhancement mechanism has also been clarified.These findings exhibit fundamental insights into the pre-lithiation kinetics process for guiding the synthesis of high-quality singlecrystalline Ni-rich cathodes.

Manipulating Na occupation and constructing protective film of P2-Na_(0.67)Ni_(0.33)Mn_(0.67)O_(2) as long-term cycle stability cathode for sodium-ion batteries

P2-Na_(0.67)Ni_(0.33)Mn_(0.67)O_(2)(NNMO)is promising cathode material for sodium-ion batteries(SIBs)due to its high specific capacity and fast Na+diffusion rate.Nonetheless,the irreversible P2-O_(2)phase transformation,Na+/vacancy ordering,and transition metal(TM)dissolution seriously damage its cycling stability and restrict its commercialization process.Herein,Na occupation manipulation and interface stabilization are proposed to strengthen the phase structure of NNMO by synergistic Zn/Ti co-doping and introducing lithium difluorophosp(LiPO_(2)F_(2))film-forming electrolyte additive.The Zn/Ti co-doping regulates the occupancy ratio of Nae/Nafat Na sites and disorganizes the Na+/vacancy ordering,resulting in a faster Na+diffusion kinetics and reversible P2-Z phase transition for P2-Na_(0.67)Ni_(0.28)Zn_(0.05)Mn_(0.62)Ti_(0.05)O_(2)(NNZMTO).Meanwhile,the LiPO_(2)F_(2)additive can form homogeneous and ultrathin cathode-electrolyte interphase(CEI)on NNZMTO surface,which can stabilize the NNZMTO-electrolyte interface to prevent TM dissolution,surface structure transformation,and micro-crack generation.Combination studies of in situ and ex situ characterizations and theoretical calculations were used to elucidate the storage mechanism of NNZMTO with Li PO_(2)F_(2)additive.As a result,the NNZMTO displays outstanding capacity retention of 94.44%after 500 cycles at 1C with 0.3 wt%Li PO_(2)F_(2),excellent rate performance of 92.5 mA h g^(-1)at 8C with 0.1 wt%Li PO_(2)F_(2),and remarkable full cell capability.This work highlights the important role of manipulating Na occupation and constructing protective film in the design of layered materials,which provides a promising direction for developing high-performance cathodes for SIBs.

Phase-engineering modulation of Mn-based oxide cathode for constructing super-stable sodium storage

The Mn-based oxide cathode with enriched crystal phase structure and component diversity can provide the excellent chemistry structure for Na-ion batteries.Nevertheless,the broad application prospect is obstructed by the sluggish Na^(+)kinetics and the phase transitions upon cycling.Herein,we establish the thermodynamically stable phase diagram of various Mn-based oxide composites precisely controlled by sodium content tailoring strategy coupling with co-doping and solid-state reaction.The chemical environment of the P2/P'3 and P2/P3 biphasic composites indicate that the charge compensation mechanism stems from the cooperative contribution of anions and cations.Benefiting from the no phase transition to scavenge the structure strain,P2/P'3 electrode can deliver long cycling stability(capacity retention of 73.8%after 1000 cycles at 10 C)and outstanding rate properties(the discharge capacity of 84.08 mA h g^(-1)at 20 C)than P2/P3 electrode.Furthermore,the DFT calculation demonstrates that the introducing novel P'3 phase can significantly regulate the Na^(+)reaction dynamics and modify the local electron configuration of Mn.The effective phase engineering can provide a reference for designing other high-performance electrode materials for Na-ion batteries.

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.

Suppressed Internal Intrinsic Stress Engineering in High-Performance Ni-Rich Cathode Via Multi layered In Situ Coating Structure

LiNi_(x)Co_(y)Al_(z)O_(2)(NCA)cathode materials are drawing widespread attention,but the huge gap between the ideal and present cyclic stability still hinders their further commercial application,especially for the Ni-rich LiNi_(x)Co_(y)Al_(z)O_(2)(x>0.8,x+y+z=1)cathode material,which is owing to the structural degradation and particles'intrinsic fracture.To tackle the problems,Li_(0.5)La_(2)Al_(0.5)O_(4)in situ coated and Mn compensating doped multilayer LiNi_(0.82)Co_(0.14)Al_(0.04)O_(2)was prepared.XRD refinement indicates that La-Mn co-modifying could realize appropriate Li/Ni disorder degree.Calculated results and in situ XRD patterns reveal that the LLAO coating layer could effectively restrain crack in secondary particles benefited from the suppressed internal strain.AFM further improves as NCA-LM2 has superior mechanical property.The SEM,TEM,XPS tests indicate that the cycled cathode with LLAO-Mn modification displays a more complete morphology and less side reaction with electrolyte.DEMS was used to further investigate cathode-electrolyte interface which was reflected by gas evolution.NCA-LM2 releases less CO_(2)than NCA-P indexing on a more stable surface.The modified material presents outstanding capacity retention of 96.2%after 100 cycles in the voltage range of 3.0-4.4 V at 1C,13%higher than that of the pristine and 80.8%at 1 C after 300 cycles.This excellent electrochemical performance could be attributed to the fact that the high chemically stable coating layer of Li_(0.5)La_(2)Al_(0.5)O_(4)(LLAO)could enhance the interface and the Mn doping layer could suppress the influence of the lattice mismatch and distortion.We believe that it can be a useful strategy for the modification of Ni-rich cathode material and other advanced functional material.

Boosting oxygen reduction activity and CO_(2) resistance on bismuth ferrite-based perovskite cathode for low-temperature solid oxide fuel cells below 600℃

Developing efficient and stable cathodes for low-temperature solid oxide fuel cells(LT-SOFCs) is of great importance for the practical commercialization.Herein,we propose a series of Sm-modified Bi_(0.7-x)Sm_xSr_(0.3)FeO_(3-δ) perovskites as highly-active catalysts for LT-SOFCs.Sm doping can significantly enhance the electrocata lytic activity and chemical stability of cathode.At 600℃,Bi_(0.675)Sm_(0.025)Sr_(0.3)FeO_(3-δ)(BSSF25) cathode has been found to be the optimum composition with a polarization resistance of 0.098 Ω cm^2,which is only around 22.8% of Bi_(0.7)Sr_(0.3)FeO_(3-δ)(BSF).A full cell utilizing BSSF25 displays an exceptional output density of 790 mW cm^(-2),which can operate continuously over100 h without obvious degradation.The remarkable electrochemical performance observed can be attributed to the improved O_(2) transport kinetics,superior surface oxygen adsorption capacity,as well as O_(2)p band centers in close proximity to the Fermi level.Moreover,larger average bonding energy(ABE) and the presence of highly acidic Bi,Sm,and Fe ions restrict the adsorption of CO_(2) on the cathode surface,resulting in excellent CO_(2) resistivity.This work provides valuable guidance for systematic design of efficient and durable catalysts for LT-SOFCs.

Preferentially selective extraction of lithium from spent LiCoO_(2)cathodes by medium-temperature carbon reduction roasting

Lithium recovery from spent lithium-ion batteries(LIBs)have attracted extensive attention due to the skyrocketing price of lithium.The medium-temperature carbon reduction roasting was proposed to preferential selective extraction of lithium from spent Li-CoO_(2)(LCO)cathodes to overcome the incomplete recovery and loss of lithium during the recycling process.The LCO layered structure was destroyed and lithium was completely converted into water-soluble Li2CO_(3)under a suitable temperature to control the reduced state of the cobalt oxide.The Co metal agglomerates generated during medium-temperature carbon reduction roasting were broken by wet grinding and ultrasonic crushing to release the entrained lithium.The results showed that 99.10%of the whole lithium could be recovered as Li2CO_(3)with a purity of 99.55%.This work provided a new perspective on the preferentially selective extraction of lithium from spent lithium batteries.

Tuning Li/Ni mixing by reactive coating to boost the stability of cobalt-free Ni-rich cathode

Cobalt-free cathode materials are attractive for their high capacity and low cost,yet they still encounter issues with structural and surface instability.AlPO_(4),in particular,has garnered attention as an effective stabilizer for bulk and surface.However,the impact of interfacial reactions and elemental interdiffusion between AlPO_(4) and LiNi_(0.95)Mn_(0.05)O_(2) upon sintering on the bulk and surface remains elusive.In this study,we demonstrate that during the heat treatment process,AlPO_(4) decomposes,resulting in Al doping into the bulk of the cathode through elemental interdiffusion.Simultaneously,PO_(4)^(3-)reacts with the surface Li of material to form a Li_3PO_(4) coating,inducing lithium deficiency,thereby increasing Li/Ni mixing.The suitable Li/Ni mixing,previously overlooked in AlPO_(4) modification,plays a pivotal role in stabilizing the bulk and surface,exceeding the synergy of Al doping and Li_3PO_(4) coating.The presence of Ni^(2+)ions in the lithium layers contributes to the stabilization of the delithiated structure via a structural pillar effect.Moreover,suitable Li/Ni mixing can stabilize the lattice oxygen and electrode-electrolyte interface by increasing oxygen removal energy and reducing the overlap between the Ni^(3+/4+)e_g and O^(2-)2p orbitals.These findings offer new perspectives for the design of stable cobalt-free cathode materials.

Impact of Transition Metal Layer Vacancy on the Structure and Performance of P2 Type Layered Sodium Cathode Material

This study explores the impact of introducing vacancy in the transition metal layer of rationally designed Na_(0.6)[Ni_(0.3)Ru_(0.3)Mn_(0.4)]O_(2)(NRM)cathode material.The incorporation of Ru,Ni,and vacancy enhances the structural stability during extensive cycling,increases the operation voltage,and induces a capacity increase while also activating oxygen redox,respectively,in Na_(0.7)[Ni_(0.2)V_(Ni0.1)Ru_(0.3)Mn_(0.4)]O_(2)(V-NRM)compound.Various analytical techniques including transmission electron microscopy,X-ray absorption near edge spectroscopy,operando X-ray diffraction,and operando differential electrochemical mass spectrometry are employed to assess changes in the average oxidation states and structural distortions.The results demonstrate that V-NRM exhibits higher capacity than NRM and maintains a moderate capacity retention of 81%after 100 cycles.Furthermore,the formation of additional lone-pair electrons in the O 2p orbital enables V-NRM to utilize more capacity from the oxygen redox validated by density functional calculation,leading to a widened dominance of the OP4 phase without releasing O_(2) gas.These findings offer valuable insights for the design of advanced high-capacity cathode materials with improved performance and sustainability in sodium-ion batteries.

Cation-doped LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2) cathode with high rate performance

The nickel-rich layered cathode material LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2)(NCM811)has high energy density,lower cost and is a promising cathode material currently under development.However,its electrochemical and structural stability is poor during cycling.Among the many modification methods,cation doping has been consistently proven to be an effective strategy for enhancing electrochemical performance.Herein,the NCM811 cathode material was modified by solid-phase reactions with Mg and Al doped.In addition,the corresponding mechanism of NCM811 cathode material-doped modification is explored by density functional theory(DFT)calculations,and we have extended this approach to other ternary cathode materials with different ratios and obtained universal laws.Combined with DFT calculations,the results show that Mg2+occupies the Li+site and reduces the degree of Li^(+)/Ni^(2+) mixture;Al^(3+) acts as a structural support during charging and discharging to prevent structural collapse.The electrochemical properties were tested by an electrochemical workstation and the LAND system,and the results showed that the capacity retention rate increased to varying degrees from 63.66%to 69.87%and 89.05%for NCM811-Mg and NCM811-Al at room temperature after 300 cycles,respectively.This study provides a theoretical basis and design strategy for commercializing cationic-doped modification of nickel-rich cathode materials.

Corrigendum to“Anthraquinone derivatives supported by Ti_(3)C_(2)(MXene)as cathode materials for aluminum-organic batteries”[J.Energy Chem.74(2022)174–183]

The authors regret that the printed version of the above article contained an error reference.We hope to correct it here.[14]B.J.M.Christophe Legein,Franck Fayon,Angew.Chem.Int.Ed.,132(2020)19409–19415.

Advances in cathode materials for Li-O_(2)batteries

Lithium-oxygen(Li-O_(2))batteries have attracted significant attention due to their ultra-high theoretical energy density.However,serious challenges,such as potential lag,low-rate capability,round-trip efficiency,and poor cycle stability,greatly limit their practical application.This review provides a comprehensive account of the development of Li-O_(2)batteries,elucidates the current discharge/charge mechanism,and highlights both the advantages and bottlenecks of this technology.In particular,recent research progress on various cathode materials,such as carbon-based materials,noble metals,and non-noble metals,for Li-O_(2)batteries is deeply reviewed,emphasizing the impact of design strategies,material structures,chemical compositions,and microphysical parameters on oxygen reduction reaction(ORR)and oxygen evolution reaction(OER)kinetics,as well as discharge products and overall battery performance.This review will also shed light on future research directions for oxygen electrode catalysts and material construction to facilitate the development of Li-O_(2)batteries with maximized electrochemical performance.

Constructing a stable interface on Ni-rich LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2) cathode via lactic acid-assisted engineering strategy

Ni-rich layered oxides are potential cathode materials for next-generation high energy density Li-ion batteries due to their high capacity and low cost.However,the inherently unstable surface properties,including high levels of residual Li compounds,dissolution of transition metal cations,and parasitic side reactions,have not been effectively addressed,leading to significant degradation in their electrochemical performance.In this study,we propose a simple and effective lactic acid-assisted interface engineering strategy to regulate the surface chemistry and properties of Ni-rich LiNi_(0.8)Co_(0.1)Mr_(0.1)O_(2) cathode.This novel surface treatment method successfully eliminates surface residual Li compounds,inhibits structural collapse,and mitigates cathode-electrolyte interface film growth.As a result,the lactic acidtreated LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2) achieved a remarkable capacity retention of 91.7% after 100 cycles at 0.5 C(25℃) and outstanding rate capability of 149.5 mA h g^(-1) at 10 C,significantly outperforming the pristine material.Furthermore,a pouch-type full cell incorporating the modified LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2) cathode demonstrates impressive long-term cycle life,retaining 81.5% of its capacity after 500 cycles at 1 C.More importantly,the thermal stability of the modified cathode is also dramatically improved.This study offers a valuable surface modification strategy for enhancing the overall performance of Ni-rich cathode materials.

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.

Mg/Fe site-specific dual-doping to boost the performance of cobalt-free nickle-rich layered oxide cathode for high-energy lithium-ion batteries

Layer-type LiNi0.9Mn0.1O2is promising to be the primary cathode material for lithium-ion batteries(LIBs)due to its excellent electrochemical performance.Unfortunately,the cathode with high nickel content suffers from severely detrimental structural transformation that causes rapid capacity attenuation.Herein,site-specific dual-doping with Fe and Mg ions is proposed to enhance the structural stability of LiNi0.9Mn0.1O2.The Fe3+dopants are inserted into transition metal sites(3b)and can favorably provide additional redox potential to compensate for charge and enhance the reversibility of anionic redox.The Mg ions are doped into the Li sites(3a)and serve as O_(2)^(-)-Mg^(2+)-O_(2)^(-)pillar to reinforce the electrostatic cohesion between the two adjacent transition-metal layers,which further suppress the cracking and the generation of harmful phase transitions,ultimately improving the cyclability.The theoretical calculations,including Bader charge and crystal orbital Hamilton populations(COHP)analyses,confirm that the doped Fe and Mg can form stable bonds with oxygen and the electrostatic repulsion of O_(2)^(-)-O_(2)^(-)can be effectively suppressed,which effectively mitigates oxygen anion loss at the high delithiation state.This dual-site doping strategy offers new avenues for understanding and regulating the crystalline oxygen redox and demonstrates significant potential for designing high-performance cobalt-free nickel-rich cathodes.

Direct Regeneration of Spent Lithium-Ion Battery Cathodes:From Theoretical Study to Production Practice

Direct regeneration method has been widely concerned by researchers in the field of battery recycling because of its advantages of in situ regeneration,short process and less pollutant emission.In this review,we firstly analyze the primary causes for the failure of three representative battery cathodes(lithium iron phosphate,layered lithium transition metal oxide and lithium cobalt oxide),targeting at illustrating their underlying regeneration mecha-nism and applicability.Efficient stripping of material from the collector to obtain pure cathode material has become a first challenge in recycling,for which we report several pretreatment methods currently available for subsequent regeneration processes.We review and discuss emphatically the research progress of five direct regeneration methods,including solid-state sintering,hydrothermal,eutectic molten salt,electrochemical and chemical lithiation methods.Finally,the application of direct regeneration technology in production practice is introduced,the problems exposed at the early stage of the industrialization of direct regeneration technol-ogy are revealed,and the prospect of future large-scale commercial production is proposed.It is hoped that this review will give readers a comprehensive and basic understanding of direct regeneration methods for used lithium-ion batteries and promote the industrial application of direct regeneration technology.

Phase engineering of Ni-Mn binary layered oxide cathodes for sodiumion batteries

Nickel-manganese binary layered oxides with high working potential and low cost are potential candidates for sodium-ion batteries,but their electrochemical properties are highly related to compositional diversity.Diverse composite materials with various phase structures of P3,P2/P3,P2,P2/O3,and P2/P3/O3 were synthesized by manipulating the sodium content and calcination conditions,leading to the construction of a synthetic phase diagram for Na_(x)Ni_(0.25)Mn_(0.75)O_(2)(0.45≤x≤1.1).Then,we compared the electrochemical characteristics and structural evolution during the desodiation/sodiation process of P2,P2/P3,P2/03,and P2/P3/O3-Na_(x)Ni_(0.25)Mn_(0.75)O_(2).Among them,P2/P3-Na0.75Ni0.25Mn0.75O2exhibits the best rate capability of 90.9 mA h g^(-1)at 5 C,with an initial discharge capacity of 142.62 mA h g^(-1)at 0.1 C and a capacity retention rate of 78.25%after 100 cycles at 1 C in the voltage range of 2-4.3 V.The observed superior sodium storage performance of P2/P3 hybrids compared to other composite phases can be attributed to the enhanced Na^(+)transfer dynamic,reduction of the Jahn-teller effect,and improved reaction reversibility induced by the synergistic effect of P2 and P3 phases.The systematic research and exploration of phases in Na_(x)Ni_(0.25)Mn_(0.75)O_(2)provide new sights into high-performance nickel-manganese binary layered oxide for sodium-ion batteries.