O2 Cathode Research Articles

Oxygenated carbon nitride‐based high‐energy‐density lithium‐metal batteries

AbstractLithium (Li)‐metal batteries with polymer electrolytes are promising for high‐energy‐density and safe energy storage applications. However, current polymer electrolytes suffer either low ionic conductivity or inadequate ability to suppress Li dendrite growth at high current densities. This study addresses both issues by incorporating two‐dimensional oxygenated carbon nitride (2D OCN) into a polyvinylidene fluoride (PVDF)‐based composite polymer electrolyte and modifying the Li anode with OCN. The OCN nanosheets incorporated PVDF electrolyte exhibits a high ionic conductivity (1.6 × 10−4 S cm−1 at 25°C) and Li+ transference number (0.62), wide electrochemical window (5.3), and excellent fire resistance. Furthermore, the OCN‐modified Li anode in situ generates a protective layer of Li3N during cycling, preventing undesirable reactions with PVDF electrolyte and effectively suppressing Li dendrite growth. Symmetric cells using the upgraded PVDF polymer electrolyte and modified Li anode demonstrate long cycling stability over 2500 h at 0.1 mA cm−2. Full cells with a high‐voltage LiNi0.8Co0.1Mn0.1O2 cathode exhibit high energy density and long‐term cycling stability, even at a high loading of 8.2 mg cm−2. Incorporating 2D OCN nanosheets into the PVDF‐based electrolyte and Li‐metal anode provides an effective strategy for achieving safe and high‐energy‐density Li‐metal batteries.

Advancing Lithium-Ion Batteries' Electrochemical Performance: Ultrathin Alumina Coating on Li(Ni0.8Co0.1Mn0.1)O2 Cathode Materials.

Ni-rich Li(NixCoyMnz)O2 (x ≥ 0.8)-layered oxide materials are highly promising as cathode materials for high-energy-density lithium-ion batteries in electric and hybrid vehicles. However, their tendency to undergo side reactions with electrolytes and their structural instability during cyclic lithiation/delithiation impairs their electrochemical cycling performance, posing challenges for large-scale applications. This paper explores the application of an Al2O3 coating using an atomic layer deposition (ALD) system on Ni-enriched Li(Ni0.8Co0.1Mn0.1)O2 (NCM811) cathode material. Characterization techniques, including X-ray diffraction, scanning electron microscopy, and transmission electron microscopy, were used to assess the impact of alumina coating on the morphology and crystal structure of NCM811. The results confirmed that an ultrathin Al2O3 coating was achieved without altering the microstructure and lattice structure of NCM811. The alumina-coated NCM811 exhibited improved cycling stability and capacity retention in the voltage range of 2.8-4.5 V at a 1 C rate. Specifically, the capacity retention of the modified NCM811 was 5%, 9.11%, and 11.28% higher than the pristine material at operating voltages of 4.3, 4.4, and 4.5 V, respectively. This enhanced performance is attributed to reduced electrode-electrolyte interaction, leading to fewer side reactions and improved structural stability. Thus, NCM811@Al2O3 with this coating process emerges as a highly attractive candidate for high-capacity lithium-ion battery cathode materials.

Bonded Interface Enabled Durable Solid‐state Lithium Metal Batteries with Ultra‐low Interfacial Resistance of 0.25 Ω cm2

AbstractThe solid‐state batteries (SSBs) with Li anode present one of the most promising energy storage systems due to their enhanced energy density and safety. However, interfacial problems between Li anode and solid‐state electrolyte hinder the advancement of SSBs. Among them, insufficient solid‐solid interfacial contact is the main issue, which causes large resistance and hinders Li+ diffusion, leading to current distribution unevenness and lithium dendrites growth. To meet these challenges, a silver/carbon interlayer composed of ultrafine Ag nanoparticles (≈5 nm) grown on COOH‐CNTs (nano‐Ag@COOH‐CNTs) is constructed. In which, nano‐Ag is designed to guide homogeneous Li deposition, while CNTs substrate bonds with Li6.5La3Zr1.5Ta0.5O12 (LLZTO) electrolyte by reactions between ─COOH groups and LLZTO alkaline surface, thus transforming loose physical solid‐solid contact to chemical bonding contact. In addition, nano‐Ag is immobilized by CNTs, avoiding the migration of Li+ implanted nano‐Ag during cycling. Therefore, nano‐Ag@COOH‐CNTs interlayer can boost Li+ transport at LLZTO/Li interface and inhibit Li dendrites, achieving an ultra‐low interfacial resistance of 0.25 Ω cm2, a high critical current density of 1.7 mA cm−2 and a long cycling over 2155 h at 0.5 mA cm−2. The modified SSBs with LiNi0.83Co0.12Mn0.05O2 cathode cycles stably over 500 cycles. Moreover, high‐loading SSBs operate stably for 85 cycles.

Air‐stable Li3.12P0.94Bi0.06S3.91I0.18 solid‐state electrolyte with high ionic conductivity and lithium anode compatibility toward high‐performance all‐solid‐state lithium metal batteries

AbstractSulfide solid‐state electrolytes (SSEs) with superior ionic conductivity and processability are highly promising candidates for constructing all‐solid‐state lithium metal batteries (ASSLMBs). However, their practical applications are limited by their intrinsic air instability and serious interfacial incompatibility. Herein, a novel glass‐ceramic electrolyte Li3.12P0.94Bi0.06S3.91I0.18 was synthesized by co‐doping Li3PS4 with Bi and I for high‐performance ASSLMBs. Owing to the strong Bi‒S bonds that are thermodynamically stable to water, increased unit cell volume and Li+ concentration caused by P5+ substitution with Bi3+, and the in situ formed robust solid electrolyte interphase layer LiI at lithium surface, the as‐prepared Li3.12P0.94Bi0.06S3.91I0.18 SSE achieved excellent air stability with a H2S concentration of only 0.205 cm3 g−1 (after 300 min of air exposure), outperforming Li3PS4 (0.632 cm3 g−1) and the most reported sulfide SSEs, together with high ionic conductivity of 4.05 mS cm−1. Furthermore, the Li3.12P0.94Bi0.06S3.91I0.18 effectively improved lithium metal stability. With this SSE, an ultralong cyclability of 700 h at 0.1 mA cm−2 was realized in a lithium symmetrical cell. Moreover, the Li3.12P0.94Bi0.06S3.91I0.18‐based ASSLMBs with LiNi0.8Mn0.1Co0.1O2 cathode achieved ultrastable capacity retention rate of 95.8% after 300 cycles at 0.1 C. This work provides reliable strategy for designing advanced sulfide SSEs for commercial applications in ASSLMBs.

Morphology-controlled metal–organic frameworks as molecular traps for enhanced ion dynamics in practical semi-solid lithium metal batteries

Controlling electrostatic interactions between charged molecules is crucial to enabling advanced batteries with reliable lithium (Li)-ion conductors. To address this issue, herein, we present a class of morphology-controlled metal–organic frameworks (MOFs) that serve as Li+ boosting molecular traps for fast Li+ conduction. A rod-like MOF is incorporated into semi-interpenetrating polymer networks to construct Li+ boosting fluidic nanochannels, which enable fast Li+ transport (σ = 1.5 mS cm−1, tLi+ = 0.76) through the ionic pathway. Molecular dynamics simulations further elucidate the Li+ transport mechanism in these MOF-based molecular traps. This unusual Li+ conduction behavior of MOF-based semi-solid electrolytes suppresses the anion-triggered ion concentration gradient and facilitates the electrochemical reaction kinetics at the electrodes, ultimately improving the rate performance and cycling retention of Li-metal cells (consisting of LiNi0.7Co0.2Mn0.1O2 cathodes and Li-metal anodes). Notably, a scalable pouch-type semi-solid Li-metal cell provides stable cycling performance for realistic batteries, exceeding those of previously reported Li batteries including porous crystalline frameworks.

Activating Ga0.8Ti0.4Nb0.8O4 cathode for direct electrolysis of CO2via electrochemical switching and infiltration of co-catalyst

Solid oxide electrolysis cell (SOEC) can efficiently convert CO2 into CO using renewable energy sources. SOECs that operate at around 800 °C and negative bias for CO2 reduction pose demanding requirements on the stability of the cathode. Here, a non-perovskite niobate, Ga0.8Ti0.4Nb0.8O4 (GTN), is developed as a robust cathode that can be activated under a −1.4 V bias at 800 °C for CO2 splitting. A gradual increase in the current density of the electrolysis cell with GTN cathode is accompanied by the partial reduction of Nb5+ to Nb4+ to produce NbO2 and a pseudorutile phase. The coupling of NbO2 nanoparticles and the defective pseudorutile surface layer serves as a good combination for the electrochemical reduction of CO2 at elevated temperatures: the electrolysis performance is slightly enhanced by ionic infiltration of Ni because the in situ grown metallic NbO2 can serve as the electron reservoir, similar to the metal Ni. The presence of CeO2 can increase the activation of CO2 and provide the ionic transport between the interface of the electrolyte and cathode. This work demonstrates a robust niobate that can be reduced by electrochemical switching to reduce the stubborn Nb5+ to produce a composite functional layer for efficient CO2 splitting.

K-Doping Suppresses Oxygen Redox in P2-Na0.67Ni0.11Cu0.22Mn0.67O2 Cathode Materials for Sodium-Ion Batteries.

In P2-type layered oxide cathodes, Na site-regulation strategies are proposed to modulate the Na+ distribution and structural stability. However, their impact on the oxygen redox reactions remains poorly understood. Herein, the incorporation of K+ in the Na layer of Na0.67Ni0.11Cu0.22Mn0.67O2 is successfully applied. The effects of partial substitution of Na+ with K+ on electrochemical properties, structural stability, and oxygen redox reactions have been extensively studied. Improved Na+ diffusion kinetics of the cathode is observed from galvanostatic intermittent titration technique (GITT) and rate performance. The valence states and local structural environment of the transition metals (TMs) are elucidated via operando synchrotron X-ray absorption spectroscopy (XAS). It is revealed that the TMO2 slabs tend to be strengthened by K-doping, which efficiently facilitates reversible local structural change. Operando X-ray diffraction (XRD) further confirms more reversible phase changes during the charge/discharge for the cathode after K-doping. Density functional theory (DFT) calculations suggest that oxygen redox reaction in Na0.62K0.03Ni0.11Cu0.22Mn0.67O2 cathode has been remarkably suppressed as the nonbonding O 2p states shift down in the energy. This is further corroborated experimentally by resonant inelastic X-ray scattering (RIXS) spectroscopy, ultimately proving the role of K+ incorporated in the Na layer.

Enhanced electrochemical performance of a cost-effective Sm2O3-coated spinel LiNi0.5Mn1.5O4 cathode for high-voltage lithium-ion batteries

Spinel LiNi0.5Mn1.5O4 (LNMO) has gained significant attention as a promising cathode material for lithium-ion batteries due to its high working voltage (>4.7 V) and energy density. However, challenges such as electrolyte decomposition-induced material interface erosion and transition metal dissolution under high operating voltage hinder its commercial use. In this study, a thin and uniform Sm2O3 layer has been successfully deposited on the surface of LNMO using a wet chemical method. A comprehensive investigation of surface morphology, crystal structure, and electrochemical performance of the modified LNMO is conducted. The results demonstrate that the Sm2O3 surface modification acts as a robust multifunctional protective layer, effectively shielding against hydrofluoric acid-induced chemical attack and enhancing the migration efficiency of lithium ions. Notably, the capacity retention rate of LNMO@Sm2O3 (3 wt%) remains up to 88 % after 280 cycles, significantly surpassing the uncoated counterpart. The coated material exhibits a capacity of 114 mAh g−1 even under 10 C rate conditions. Moreover, the AC impedance values and manganese dissolution of the modified material in the organic electrolyte are considerably lower than those of the uncoated counterpart. Theoretical calculations strongly support the experimental findings, revealing higher Mn vacancy formation energy and density of states at the Fermi energy level for the Sm2O3-modified electrodes. This research contributes to the field of surface modification and paves the way for further enhancements in the electrochemical performance of other high-voltage manganese-based lithium-ion batteries (LIBs).

Unlocking high-efficiency lithium-ion batteries: Sucrose-derived carbon coating on nickel-rich single crystal Li[Ni₀.₈Co₀.₁Mn₀.₁]O₂ cathodes

This study introduces a novel approach to enhancing the electrochemical properties of nickel-rich single crystal NCM811 (Li[Ni0.8Co0.1Mn0.1]O2) cathodes through carbon surface coating. Utilizing low-cost sucrose as a precursor, we applied a carbon-doped shell-like structure to the sNCM811 surface via convective flow treatment, optimized for temperature and coating density. This carbon surface layer significantly improved the delithiation kinetics, enabling rapid and stable electrochemical reactions. Notably, it mitigated electrical isolation, suppressed irreversible phase transitions, and reduced electrolyte-related side reactions within the sNCM811 during repeated charge-discharge cycles. Cathodes with a 7 wt.% sucrose coating demonstrated a high discharge capacity of 218 mAh g−1 at 0.1C/0.1C charge/discharge rates, with impressive capacity retention of 89 % after 100 cycles at 1C/1C charging/discharging. This represents a performance enhancement of 16 % and an improvement in cycle stability of 5.6 % over bare sNCM811. Furthermore, even at high charging/discharging rates of 5C/5C, the coated cathodes maintained a notable capacity of 125 mAh g−1, effectively mitigating structural degradation under high-output conditions. These findings suggest that carbon-coated sNCM811 is a promising solution for addressing degradation issues in high-capacity, high-output nickel-rich cathodes, potentially revolutionizing lithium-ion battery systems in demanding applications.

One-Step Realization of Layered/Spinel Heterostructures and Na Doping by Sodium Dodecyl Sulfate-Assisted Sol-Gel Method for Li-Ion Batteries.

Li-rich layered oxide cathodes have attracted extensive attention due to their high energy density. However, due to the low initial Coulombic efficiency and the capacity fading and voltage fading during cycling, its practical application is still a great challenge. Here, we report the one-step realization of layered/spinel heterostructures and Na doping by the sodium dodecyl sulfate (SDS)-assisted sol-gel method. The spinel phase provides 3D diffusion channels for Li-ions, and sodium doping changes the layered lattice constant and expands the layer spacing. Therefore, the designed Li1.15Mn0.54Ni0.13Co0.13Na0.05O2 (SDS-2) cathode possesses excellent electrochemical performance such as higher initial Coulombic efficiency and rate capacity and also alleviates voltage decay. The initial discharge-specific capacity of SDS-2 is 298.8 mAh g-1 at 0.1 C, and the discharge-specific capacity can reach 111.7 mAh g-1 at 10 C. This strategy can provide new insights into the design and synthesis of high-performance Li-rich layered oxide cathode materials.

Si anode with high initial Coulombic efficiency, long cycle life, and superior rate capability by integrated utilization of graphene and pitch-based carbon

A variety of strategies have been developed to enhance the cycling stability of Si-based anodes in lithium-ion batteries. Although significant progress has been made in enhancing the cycling stability of Si-based anodes, the low initial Coulombic efficiency (ICE) remains a significant challenge to their commercial application. Herein, pitch-based carbon (C) coated Si nanoparticles (NPs) were wrapped by graphene (G) to obtain Si@C/G composite with a small specific surface area of 11.3 m2 g−1, resulting in a high ICE of 91.2% at 500 mA g−1. Moreover, the integrated utilization of graphene and soft carbon derived from the low-cost petroleum pitch strongly promotes the electrical conductivity, structure stability, and reaction kinetics of Si NPs. Consequently, the synthesized Si@C/G with a Si loading of 54.7% delivers large reversible capacity (1191 mAh g−1 at 500 mA g−1), long cycle life over 200 cycles (a capacity retention of 87.1%), and superior rate capability (952 mAh g−1 at 1500 mA g−1). When coupled with a homemade LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode in a full cell, it exhibits a promising cycling stability for 200 cycles. This work presents an innovative approach for the manufacture of Si-based anode materials with commercial application.

Cu-Doped Spherical P2-Type Na0.7Fe0.23-xCuxMn0.77O2 Cathode for High-Performance Sodium-Ion Batteries.

Sodium-ion batteries (SIBs), owing to their abundant resources and cost-effectiveness, have garnered considerable interest in the realm of large-scale energy storage. The properties of cathode materials profoundly affect the cycle stability and specific capacity of batteries. Herein, a series of Cu-doped spherical P2-type Na0.7Fe0.23-xCuxMn0.77O2 (x = 0, 0.05, 0.09, and 0.14, x-NFCMO) was fabricated using a convenient hydrothermal method. The successful doping of Cu efficaciously mitigated the Jahn-Teller effect, augmented the electrical conductivity of the material, and diminished the resistance to charge transfer. The distinctive spherical structure remained stable and withstood considerable volumetric strain, thereby improving the cyclic stability of the material. The optimized 0.09-NFCMO cathode exhibited a high specific capacity of 168.6 mAh g-1 at 100 mA g-1, a superior rate capability (90.9 mAh g-1 at 2000 mA g-1), and a good cycling stability. This unique structure design and doping approach provides new insights into the design of advanced electrode materials for sodium-ion batteries.

Long-Cycle Lithium Batteries with LiNi0.8Co0.1Mn0.1O2 Cathodes above 4.5V Enabled by Uniform Coating of Nanosized Garnet Electrolytes

Abstract The pursuit of high-energy cathode materials has been focused on raising the charging cutoff voltage of nickel (Ni)-rich layered oxide cathode such as LiNi0.8Co0.1Mn0.1O2 (NCM811). However, the NCM811 suffers from rapid capacity fading upon cycling at cutoff voltage higher than 4.5 V, owing to their structural degradation and labile surface reactivity. Surface-coating with solid electrolytes has been recognized as an effective method to mitigate the performance failure of NCM811 at high voltage. Herein, the nano-sized Li6.4La3Ta0.6Zr1.4O12 (LLZTO) is uniformly coated on the surface of single-crystal NCM811 particles, accompanied with the long-range Ta5+ diffusion into the transition metal layer of NCM811 lattice. It is revealed that the LLZTO coating can not only inhibit the surface reactions of NCM811 with liquid electrolytes but also play an important role in suppressing the bulk microcracking within the NCM811 particles. The incorporation of Ta5+ ion expands the lattice spacing and thereby improves the homogeneity of the Li+ diffusion in the single-crystal NCM811, which alleviates the mechanical strain and intragranular cracks caused by nonuniform phases-transformation at high charging voltage. The synergy of surface protection and structural stabilization realized by LLZTO coating enables the NCM811-based lithium batteries to achieve a remarkable electrochemical performance. Typically, LLZTO coated NCM811 delivers a high reversible specific capacity of 202.1 mAh⋅g−1 with an excellent capacity retention as high as 70% over 1000 cycles upon charging to 4.5 V at 1 C.

Niobium oxide anode materials with suppressed activity toward hydrogen evolution reaction for aqueous batteries

The hydrogen evolution reaction is the most prominent parasitic reaction for aqueous battery chemistries. Although water-in-salt electrolytes show greatly enhanced electrochemical stability, increasing the voltage of aqueous batteries further by lowering the potential of the negative electrode remains a major challenges due to reductive water splitting. Here, we systematically investigate twelve niobium-based anode materials that show much lower activity towards hydrogen evolution reaction than classic titanium-based anode materials such as lithium titanate (Li4Ti5O12) or titanium dioxide and are therefore a much better choice for aqueous batteries. We confirm Zn2Nb34O87 to be the most suitable anode material for aqueous batteries among these niobates and present full-cell cycling data with LiMn2O4 and LiNi0.8Mn0.1Co0.1O2 cathodes in a water-in-salt/ionic liquid hybrid electrolyte. Furthermore, we compare the catalytic activities of Zn2Nb34O87 and Cu2Nb34O87, with the latter being incompatible with aqueous batteries, and discuss the origin of the large difference in activity toward hydrogen evolution reaction.

Li1.5Al0.5Zr1.5(PO4)3-coated Li1.2Mn0.54Ni0.13Co0.13O2 cathode materials with high lithium-ion diffusion rate and long cycling stability for lithium-ion batteries

Li1.5Al0.5Zr1.5(PO4)3-coated Li1.2Mn0.54Ni0.13Co0.13O2 cathode materials with high lithium-ion diffusion rate and long cycling stability for lithium-ion batteries

Constructing layered/tunnel interlocking oxide cathodes for sodium-ion batteries based on breaking Mn3+/Mn4+ equilibrium in Na0.44MnO2 via trace Mo doping

Sodium-ion batteries (SIBs) with Mn-based oxide cathodes have attracted much interest because of their cost effectiveness, minimal toxicity, and remarkable electrochemical activity. The typical tunnel Na0.44MnO2 cathode for SIBs exhibits stable cycling performance, but its low sodium content hinders the practical application. And the other NaxMnO2 cathodes with layered structures provide higher capacity but less satisfactory cycling. Therefore, it is of great significance to construct Mn-based oxide cathodes to integrate high specific capacity layered structure and high stability tunnel structure. Herein, the strategy of breaking the Mn3+/Mn4+ equilibrium in Na0.44MnO2 via doping trace amounts of Mo was proposed to promote the transformation from the original tunnel to the layered structure and to in-situ construct a layered/tunnel biphasic interlocking structure. The optimized interlocking layered/tunnel Na0.44Mn0.97Mo0.03O2 (NMO-3M) cathode integrates the advantages of layered and tunnel structures, and achieves highly reversible phase transition and excellent electrochemical performance, which delivers a high specific capacity of 178.9 mAh g−1 at 0.1 C and capacity retention of 77.8 % after 100 cycles at 1 C. The well-maintained P2 phase was revealed by the in-situ X-ray diffraction (XRD), demonstrating the highly reversible charge compensation and structural evolution. In addition, NMO-3M cathode shows a good storage performance in air over 270 days. This research designed a layered/tunnel interlocking structure induced by trace Mo doping to construct a stable and high capacity oxide cathode, providing a guideline for the preparation of excellent oxide cathodes for SIBs in the future.

Electrochemical and microstructural analysis of LiNi1/3Mn1/3Co1/3O2 cathode composites prepared using the SEED method.

Cathode composites were fabricated using the nuclear growth (SEED) method. Compared to mortar mixing, the SEED method demonstrated higher cycle stability, with a 90LiNi1/3Mn1/3Co1/3O2-10Li7P2S8I composite retaining 99.7% discharge capacity after six cycles compared to 66.1%. Cross-sectional SEM-EDX images suggest that the solid electrolyte was more uniformly distributed in the cathode composite prepared using the SEED method. This study opens up the potential for higher cathode-active material loading ratios.

Earth-Abundant Kaolinite Nanoplatelet Gel Electrolytes for Solid-State Lithium Metal Batteries.

Lithium-ion batteries are the leading energy storage technology for portable electronics and vehicle electrification. However, demands for enhanced energy density, safety, and scalability necessitate solid-state alternatives to traditional liquid electrolytes. Moreover, the rapidly increasing utilization of lithium-ion batteries further requires that next-generation electrolytes are derived from earth-abundant raw materials in order to minimize supply chain and environmental concerns. Toward these ends, clay-based nanocomposite electrolytes hold significant promise since they utilize earth-abundant materials that possess superlative mechanical, thermal, and electrochemical stability, which suggests their compatibility with energy-dense lithium metal anodes. Despite these advantages, nanocomposite electrolytes rarely employ kaolinite, the most abundant variety of clay, due to strong interlayer interactions that have historically precluded efficient exfoliation of kaolinite. Overcoming this limitation, here we demonstrate a scalable liquid-phase exfoliation process that produces kaolinite nanoplatelets (KNPs) with high gravimetric surface area, thus enabling the formation of mechanically robust nanocomposites. In particular, KNPs are combined with a succinonitrile (SN) liquid electrolyte to form a nanocomposite gel electrolyte with high room-temperature ionic conductivity (1 mS cm-1), stiff storage modulus (>10 MPa), wide electrochemical stability window (4.5 V vs Li/Li+), and excellent thermal stability (>100 °C). The resulting KNP-SN nanocomposite gel electrolyte is shown to be suitable for high-rate rechargeable lithium metal batteries that employ high-voltage LiNi0.8Co0.15Al0.05O2 (NCA) cathodes. While the primary focus here is on solid-state batteries, our strategy for kaolinite liquid-phase exfoliation can serve as a scalable manufacturing platform for a wide variety of other kaolinite-based nanocomposite applications.

High-Energy Earth-Abundant Cathodes with Enhanced Cationic/Anionic Redox for Sustainable and Long-Lasting Na-Ion Batteries.

Layered iron/manganese-based oxides are a class of promising cathode materials for sustainable batteries due to their high energy densities and earth abundance. However, the stabilization of cationic and anionic redox reactions in these cathodes during cycling at high voltage remain elusive. Here, an electrochemically/thermally stable P2-Na0.67Fe0.3Mn0.5Mg0.1Ti0.1O2 cathode material with zero critical elements is designed for sodium-ion batteries (NIBs) to realize a highly reversible capacity of ≈210mAhg-1 at 20mAg-1 and good cycling stability with a capacity retention of 74% after 300 cycles at 200mAg-1, even when operated with a high charge cut-off voltage of 4.5V versus sodium metal. Combining a suite of cutting-edge characterizations and computational modeling, it is shown that Mg/Ti co-doping leads to stabilized surface/bulk structure at high voltage and high temperature, and more importantly, enhances cationic/anionic redox reaction reversibility over extended cycles with the suppression of other undesired oxygen activities. This work fundamentally deepens the failure mechanism of Fe/Mn-based layered cathodes and highlights the importance of dopant engineering to achieve high-energy and earth-abundant cathode material for sustainable and long-lasting NIBs.

Heteroatom anchoring to enhance electrochemical reversibility for high-voltage P2-type oxide cathodes of sodium-ion batteries

P2-type cathode has received extensive attention due to its faster Na+ diffusion and a high theoretical capacity in sodium-ion batteries (SIBs). However, undesirable phase transformations have induced dramatic capacity decay of SIBs during the cycling process. In this study, heteroatom anchoring through Cu/Mg dual doping is introduced into P2-type Na0.67Ni0.33Mn0.67O2 cathode to enhance high-voltage electrochemical reversibility and modulate interfacial Na+ kinetics. The as-prepared Na0.67Ni0.23Mg0.05Cu0.05Mn0.67O2 exhibits an outstanding capacity retention (83.4 % after 2000 cycles at 10 C) and rate performance (73 mAh g−1 at 10 C, accounting for 58.7 % of that at 0.1 C) over the voltage range of 2.5–4.4 V. Intensive explorations further manifest that the modified mechanism of dual-ion doping strategy is attributed to the synergistic coupling effect of a substantial change in Na occupancy distribution and an increase in oxygen vacancy buffer. Thus, the optimized cathode expedites Na+ diffusion and reduces detrimental phase transformation, which favors high-rate performance and long-term cycling stability. This study develops a route to rationally design high-voltage cathode materials for SIBs.