O3-type Cathode Research Articles

Inhomogeneous Coordination in High-Entropy O3-Type Cathodes Enables Suppressed Slab Gliding and Durable Sodium Storage.

O3-type layered oxides are highly promising cathodes for sodium-ion batteries (SIBs), however they undergo complex phase transitions and exhibit high sensibility to air, leading to subpar cycling performance and commercial viability. In this work, we report a layered cathode material (NaNi0.29Cu0.1Mg0.05Li0.05Mn0.2Ti0.2Sn0.11O2) with a sate-of-the-art high-entropy compositional design. We unveil that such a configuration featuring inhomogeneous coordination environment of transition metal (TM) elements, can enable enhanced gliding energy (-0.38 vs -0.58 eV) of TMO2 slabs upon desodiation both theoretically and experimentally, which underlies the fundamental origin of the outstanding structural stability of HEO materials. As a consequence, the complex phase transitions (O3-O'3-P3-P'3-P3'-O3') of conventional O3-type cathode have been eliminated, and the as-obtained material demonstrates exceptional structural robustness and integrity with an ultra-long cycle life in a quasi-solid-state cell (maintaining 73.2 % capacity after 1000 cycles at 2 C). Moreover, the material presents satisfactory air stability, with minimal structural and electrochemical degradation when directly exposed to the air. An Ah-scale pouch cell based on the cathode material is constructed, demonstrating a capacity retention of 83.6 % after 500 cycles, signaling substantial promise for commercial applications.

Enhanced cyclability of O3-NaNi0.33Fe0.31Mn0.36O2 by Mg and Cu synergistic doping with strengthened Mn[sbnd]O bonds

Among some practical O3-type layered oxide cathodes, NaNi1/3Fe1/3Mn1/3O2 (NFM) features a high specific capacity and moderate cyclability. However, sluggish Na+ transfer kinetics, low structural stability, and rapid capacity loss during long-term cycling, are still posing a challenge to commercial applications of this material. In this work, we propose a Mg and Cu co-doped O3-type NaMg0.02Cu0.02Ni0.33Fe0.27Mn0.36O2 (MC-NFM) with a stable structure and good cycling stability. It was found that the MnO bonds in MC-NFM are obviously reinforced by synergistic doping with small amounts of Mg and Cu, leading to enhanced structural robustness, decreased Na+ migration barrier, and delayed O3-P3 phase transition. As a result, longer cycle life and enhanced rate performance are achieved. MC-NFM can yield a specific capacity of 142.1 mAh g−1 at 0.1C and 116.0 mAh g−1 at 5C, and maintain 83.6 % of its initial capacity after 400 cycles at 1C. This work provides a promising design of O3-type cathode for sodium-ion batteries.

Robust interface for O3-type layered cathode towards stable ether-based sodium-ion full batteries

Developing a robust cathode-electrolyte interface (CEI) is crucial for stable layered cathode in sodium-ion batteries (SIBs). A CEI based on ester electrolytes often exhibit poor stability and robustness, which cannot address the issues of structural collapse and material dissolution in layered cathodes. However, there are few reports on constructing a stable CEI for layered cathode based on ether electrolytes. Here we develop a robust CEI for O3-type cathode via DME solvent, which enables a long-term stability of full SIBs. The results indicate that unique decomposition process of DME yields favorable organic component (e.g. RCH2ONa) and high content of inorganic components (e.g. NaF and Na2CO3) in the CEI, which is quite different from ester electrolyte, improving Na+ diffusion kinetic and interfacial stability. Notably, the O3-NaNi0.5Mn0.5O2||Na cell with the designed electrolyte demonstrates outstanding stability up to 500 cycles. Furthermore, the full cell exhibits remarkable cycling performance with a capacity retention of 85% over 200 cycles. This work provides an opportunity for stable operation of layered cathode materials via inexpensive ether electrolytes.

Correction to “Air Stable O3-Type Cathode Material with Nanometer Size for Durable Low-Temperature Sodium-Ion Batteries”

Correction to “Air Stable O3-Type Cathode Material with Nanometer Size for Durable Low-Temperature Sodium-Ion Batteries”

Optimizing O3-type cathode materials with modified collector for sodium-ion batteries: Insights of interfacial reaction between collector and electrolyte

In order to obtain a sodium-ion battery with high energy density and good kinetic properties, high specific capacity of O3-type NaNi1/3Fe1/3Mn1/3O2 (NFM111) cathode material and high ion migration rate of NaClO4 electrolyte are selected. The cycling performance of NaNi1/3Fe1/3Mn1/3O2 is tested at 0.5 C after pre-activation at 0.1 C. During the electrochemical testing, a kind of side reaction products are found on the surface of the electrode piece. Through Scanning emission microscopy (SEM), X-ray photoelectron spectroscopy analysis (XPS) and Raman tests, side reaction products are found on the current collector with NaClO4 and Fluoroethylene carbonate (FEC). The protective layers are constructed on the surface of Al foil to effectively avoid the occurrence of side reactions. The prepared half cells have excellent stability and rate performance by the modified current collector. After 100 cycles at 0.5 C, the specific discharge capacity is 106 mA h g−1. The specific discharge capacity at 5 C is 107.2 mA h g−1. This measure provides a new idea to the NFM111 cathode materials electrochemical test and offers research basis for the design of sodium ion battery with excellent dynamic performance. Meanwhile, it also eliminates industry doubts about the performance of sodium-ion batteries.

Topography control and component design strategies to enhance electrochemical performance of O3-Type cathode materials for Sodium-ion batteries

Layered transition metal oxides (NaxTMO2, 0 < x ≤ 1) are considered one of the most promising cathodes for Sodium-ion batteries (SIBs) due to their high theoretical capacity and operability. However, NaxTMO2 still faces significant challenges, including poor kinetic performance and low energy efficiency. Herein, in order to enhance the kinetics of NaNi1/3Fe1/3Mn1/3O2 (NaNFMO), topography control and component design were proposed: First, Cu doping (Cu-NaNFMO) was used to expand lattice channels and improve “flat sheet” of layered oxide, which synergistically enhanced transport kinetics of Na+. Second, Co coating (NaNFMO@Co) reacted with surface residue to form a fast-ionic conductor NaxCoO2 (0 < x ≤ 1), which inhibited interfacial side reactions and enhanced transport kinetics of Na+. Furthermore, the presence of strong Cu-O bonds in Cu-NaNFMO and fast-ionic conductor NaxCoO2 in NaNFMO@Co led to better electrochemical redox performance, the initial charge specific capacity of NaNFMO was increased from 141.5 mAh g⁻1 to 145.8 mAh g⁻1 and 144 mAh g⁻1, with capacity retention improving by nearly 10 % after 100 cycles. Furthermore, NaNFMO@Co improves ICE from 90.56 % to 93.57 %. With the improved kinetics, the DCR of pouch cells decreased, and the energy efficiency increased from 93.3 % to 94 % and 95.7 %.

Full Exploitation of Charge Compensation of O3-type Cathode Toward High Energy Sodium-Ion Batteries by High Entropy Strategy.

O3-type cathodes with sufficient Na content are considered as promising candidates for sodium-ion batteries (SIBs). However, these cathodes suffer from insufficient utilization of the active elements, restraining the delivered capacity. In this work, a high entropy strategy is applied to a typical O3 cathode NaLi0.1Ni0.35Mn0.55O2 (NLNM), forming a high entropy oxide NaLi0.1Ni0.15Cu0.1Mg0.1Ti0.2Mn0.35O2 (Na-HE). Results show that the active elements are fully exploited in Na-HE, with a two-electron reaction by Ni2+/4+ (further extended to Cu redox and even oxygen redox), vastly different from a one-electron reaction of Ni2+/3+ in NLNM. The full utilization of the active elements dramatically improves the output capacity of the cathode (122.6 mAh g-1 of Na-HE versus 81 mAh g-1 of NLNM). Moreover, the detrimental phase transition is well suppressed in Na-HE. The cathode exhibits high capacity retention of 88.7% after 100 cycles at 130mA g-1, compared to only 36.4% for NLNM. These findings provide new insight for the design of new cathode materials for SIBs with high energy density and robust stability.

Chemical Substitution Strategies for Tailoring P2- and O3-Type Layered Oxide Cathodes in Sodium-Ion Batteries

Among cathodes for sodium-ion batteries (SIBs), layered transition metal oxides Na x MO2 (M = transition metal) are very promising due to their easy synthesis and high theoretical capacity.1,2 In this class, Ni/Mn/Fe-based layered oxides are attractive due to the high redox potential of Ni2+/ Ni4+ and Jahn Teller inactive centers (Ni2+, Fe3+,and Mn4+).3 However, complex phase transitions, Na+/vacancy ordering and transition-metal (TM) migration degrade their electrochemical performances.4 To address the issues, a widely studied cathode- P2-type Na0.67[Ni0.33Mn0.67]O2 is chosen and Li+ is substituted in the TM-layer to tailor a series of high Na-content cathodes. Among them, Na0.85[Li0.14Ni0.29Mn0.57]O2 cathode with optimal Li-substitution exhibits a reversible capacity of 168 mAh g-1 at 0.1 C rate and good cycling stability (82% retention after 100 cycles).5 In-situ XRD measurement reveals a complete solid-solution formation and X-ray absorption spectroscopy studies confirm the participation of Ni4+/Ni2+ and Mn4+/Mn3+ redox couples during Na+-extraction/insertion. Lastly, a full Na-ion cell with hard carbon is demonstrated with an energy density of 420 Wh kg-1. In subsequent work, a Li and Ti co-substitution strategy is applied to design a high-entropy O3-type NaLixNiyFezMn0.5Ti0.5-aO2 cathode.6 It retains 77% of its initial capacity after 400 cycles at a 2 C rate with a facile O3-P3-OP2-P3-O3 phase transition. The co-substitution strategy uplifts the average voltage of the system, improves the reversibility of the high-voltage OP2 phase, and enhances the Na-ion diffusion rate. A mere 1.32% unit cell volume change and diminishing electrochemical cell resistance over cycling ensure its superior long-term cycling performance. A full cell is fabricated, which holds 62% of its initial capacity even after 1000 cycles at a 0.5 C rate. Therefore, mono- and di-ion substitution strategies hold enormous potential for designing high-performing P2- and O3-type cathode materials for practical SIBs. References T. Hosaka, K. Kubota, A. S. Hameed, and S. Komaba, Chem. Rev., 120, 6358–6466 (2020).J. Y. Hwang, S. T. Myung, and Y. K. Sun, Chem. Soc. Rev., 46, 3529–3614 (2017).F. Zhang, J. Liao, L. Xu, W. Wu, and X. Wu, ACS Appl. Mater. Interfaces, 13, 40695–40704 (2021).Z. Lu and J. R. Dahn, J. Electrochem. Soc., 148, A1225 (2001).A. Ghosh, B. Senthilkumar, S. Ghosh, P. Amonpattaratkit, and P. Senguttuvan, J. Electrochem. Soc., 170, 030538 (2023).A. Ghosh, R. Hegde, and P. Senguttuvan, J. Mater. Chem. A., submitted(2023).

La-doped O3-type layered oxide cathode with enhanced cycle stability for sodium-ion batteries

Despite the considerable potential of O3-type layered oxide cathodes in sodium-ion batteries due to their high theoretical capacities, the rapid capacity degradation caused by high Na+ diffusion barriers and irreversible phase transitions seriously hampers their practical application. Herein, we propose the La-doping strategy in O3-type layered oxide to decrease diffusion barriers and strengthen transition metal–oxygen (TM-O) bonds, thereby significantly improving the electrochemical performance. The strong La-O bonding facilitates highly reversible O3-P3 phase transitions during (de)sodiation and enhances the stability of lattice oxygen at high voltages. Specifically, the La-doped O3-type oxide exhibits impressive cycling stability, with the capacity retention increasing from 63 % to 80 % after 500 cycles at 1C. The full cell assembly with La-doped oxide as cathode and hard carbon as anode demonstrates a high energy density of 323.7 Wh kg−1 at 0.1C, with a capacity retention of 74.6 % after 300 cycles at 1C. This work provides new insights in La-doping to promote the commercial application of O3-type cathodes for sodium ion batteries.

High-entropy O3-type cathode enabling low-temperature performance for sodium-ion batteries

High-entropy layered oxide (HEO) cathodes have become a focal point of research in sodium-ion batteries. Herein, we identify two guidelines that are vital for the design and fabrication of HEO O3-type cathodes: enhanced energy storage capacity and robust cathode architecture. To achieve these benchmarks, precise methods are required to adjust the energy levels of the transition metals and maintain ionic radius discrepancies within 15%. We have synthesized and examined various HEO O3-type cathode composites. Specifically, the O3-Na[FeCoNiTi]1/6Mn1/4Zn1/12O2 (O3-FCNTMZ1/12) has demonstrated an impressive reversible capacity of 127.3 mAh g−1, with exceptional long-cycle stability and superb rate capabilities. Notably, the O3-FCNTMZ1/12 cathode exhibits superior Na storage performance at low temperatures. At −20 °C, it maintains 109.6 and 91.1 mAh g−1 at 0.1 and 1 C, respectively, with an impressive 88% capacity retention after 1000 cycles at 1 C. In situ X-ray diffraction analysis reveals a subtle phase transition from O3 to P3, with only a 3% volume expansion. Moreover, ex situ X-ray absorption spectroscopy confirms minimal fluctuation in the TM-O and TM-TM distances, remaining under 9.9%. These well-defined criteria offer a clear strategy for designing and developing the O3-FCNTMZ1/12 cathode, facilitating high-performance sodium-ion batteries, especially for demanding low-temperature applications.

Facilitating an Ultrastable O3-Type Cathode for 4.5 V Sodium-Ion Batteries via a Dual-Reductive Coupling Mechanism.

O3-type layered oxides for sodium-ion batteries (SIBs) have attracted extensive attention due to their inherently sufficient Na content, which have been considered as one of the most promising candidates for practical applications. However, influenced by the irreversible oxygen loss and the phase transition of O3-P3, the O3-type cathodes are always limited by low cutoff voltages (typically <4.2 V), restraining the full release of the capacity. In this study, we originally propose a dual-reductive coupling mechanism in a novel O3-type Na0.8Li0.2Fe0.2Ru0.6O2 cathode with the suppressed O3-P3 phase transition, aiming at improving the reversibility of oxygen redox at high voltage regions. Consequently, thanks to the formation of the strong covalent Fe/Ru-(O-O) bonding and inhibited slab gliding from the O to P phase, the cathode delivers the preeminent cyclic stability among the numerous O3-type cathodes within a high voltage of 4.5 V (a capacity retention of 95.4% after 100 cycles within 1.5-4.5 V). More importantly, HAADF-STEM and 7Li solid-state NMR results reveal the absence of transition metal migration and the presence of reversible Li migration during cycling, which further contributes to the improved structural robustness of the cathode. This study proposes an innovative strategy to boost the reversibility of anionic redox and to achieve stable high-voltage O3-type layered oxides, promoting the further development of SIBs.

Ce-doping promotes the electrochemical performance of NaNi0.5Mn0.5O2

Layered sodium ion cathode material is increasingly popular due to the superiority of low-cost and excellent rate performance. However, it usually suffers from poor capacity retention arising from microcracks during multiple-phase transitions. Herein, a Ce-doped O3-type cathode material NaNi0.5Mn0.5O2(NNM) was synthesized by high shear mixer-assisted precipitation of oxalate precursors. Using the characterizations of XRD, XPS, HRTEM, GITT, etc., the results indicate that Ce dopants can adjust the initial phase structure as well as postpone the phase transition in such O3-type material. The optimal NNM-0.06Ce shows a superior initial discharge capacity of 128.3 mAh g−1 and a retention of 85.96% after 100 cycles (1.5–4.0 V, 1 C, 25 °C), as well as superior rate performance of 107 mAh g−1 at 5 C. HAADF-STEM images disclose that the doped Ce atoms are probably located in the sodium layer of the cathode material, moreover, DFT calculations reveal that the Ce dopant is prone to occupy the Na site and cause charge rising of Ni and Mn. In-situ XRD tests indicate that the earlier formed O1 phase induced by Ce dopants can postpone the phase transition and increase the reversibility of the cathode, therefore improving the electrochemical performance of cathode materials.

Air Stable O3-Type Cathode Material with Nanometer Size for Durable Low-Temperature Sodium-Ion Batteries

Air Stable O3-Type Cathode Material with Nanometer Size for Durable Low-Temperature Sodium-Ion Batteries

Optimizing O3-type cathode materials for sodium-ion batteries: Insights from precursor-based structural control and particle sizing strategies

Utilization of secondary spherical structures derived from metal hydroxides as precursor materials is one of the most promising approaches in terms of energy density and industrial viability for sodium-ion batteries. However, the understanding of how the particle size and arrangement of these secondary spherical structures influence electrochemical performance remains limited. Herein, a series of O3-type layered oxide cathode materials with various sizes (6, 8, 10, and 12 μm) and internal structures (hollow and radial arrangements) were tailored based on precursor-based structural control and particle sizing strategies. The relation in precursor size/structure, cathode characteristics, crystal microstress, structural stability, and electrochemical performance was established through a combination of structure, morphology, and electrochemical characterization. Notably, the size of secondary spherical particles exerted influence on microstress, leading to consequential changes in the c-axis. Elevated microstress levels induced compression of the unit cell along the c-axis, hampering sodium ion migration and undermining the stability of secondary spherical particles during cyclic charge-discharge processes. The optimized NaNi1/3Fe1/3Mn1/3O2-10 material exhibits the least micro stress and significant layer distance, delivers a capacity of 110 mAh g−1, and maintains an impressive capacity retention rate of 91.8% after 100 cycles at 10 C. This work offers valuable insights in energy-density cathode materials in sodium ion batteries.

High-entropy configuration of O3-type layered transition-metal oxide cathode with high-voltage stability for sodium-ion batteries

The O3-type cathode of NaNi0.4Fe0.2Mn0.4O2 stands out for its remarkable theoretical capacity, straightforward production process, affordability, and ecological compatibility for sodium-ion batteries.

Suppression of multistep phase transitions of O3-type cathode for sodium-ion batteries

O3-type layered oxide cathodes have been widely investigated due to their high reversible capacities and sufficient Na+ reservoirs. However, such materials usually suffer from complex multistep phase transitions along with drastic volume changes, leading to the unsatisfied cycle performance. Herein, we report a Mg/Ti co-doped O3-type NaNi0.5Mn0.5O2, which can effectively suppress the complex multistep phase transition and realize a solid-solution reaction within a wide voltage range. It is confirmed that, the Mg/Ti co-doping is beneficial to enhance the structural stability and integrity by absorbing micro-strain and distortions. Thus, the as obtained sample delivers an outstanding cyclic performance (82.3% after 200 cycles at 1 C) in the voltage range of 2.0–4.0 V, and a high discharge capacity of 86.6 mAh/g after 100 cycles within the wide voltage range (2.0–4.5 V), which outperform the existing literatures. This co-doping strategy offers new insights into high performance O3-type cathode for sodium ion batteries.

Triggering reversible anion redox chemistry in O3-type cathodes by tuning Na/Mn anti-site defects

We propose the triggering of reversible anion redox chemistry in the O3-NaMn1/3Fe1/3Ni1/3O2 cathode by tuning Na/Mn anti-site defects with Ho doping.

Structural properties of P2 and O2-type layered lithium manganese oxides as potential coating materials

Surface coatings have been reported to improve the performance of cathode materials by altering the surface chemistry or providing a physical protective layer. There is currently a challenge of obtaining the most suitable coating materials between the O2 and P2 type structure for coating the O3-type cathode material to mitigate the structural degradation that occurs during cycling. The density functional theory was used to investigate the structural and electronic properties of these materials in a quest to monitor their stability upon their usage as coating materials for O3-Li2MnO3. The partial density of states of the O2 and P2 bulk materials and O2 and P2 materials with vacancies indicated that the electron contribution at the fermi level was due to the p state of oxygen and the d state of manganese. Furthermore, the electronic band structures showed that the materials are metallic, with a band gap of zero. The P2 and O2-type cathode materials have been known to offer high energy density and excellent cycling stability while the P2 has been found to not only enhance the reversibility and air/thermal stability of other cathodes but also improve their electrochemical kinetics and reduce the charge transfer resistance.

Clarification of underneath capacity loss for O3-type Ni, co free layered cathodes at high voltage for sodium ion batteries

Earth abundant O3-type NaFe0.5Mn0.5O2 layered oxide is regarded as one of the most promising cathodes for sodium ion batteries due to its low cost and high energy density. However, its poor structural stability and cycle life strongly impede the practical application. Herein, the dynamic phase evolution as well as charge compensation mechanism of O3-type NaFe0.5Mn0.5O2 cathode during sodiation/desodiation are revealed by a systemic study with operando X-ray diffraction and X-ray absorption spectroscopy, high resolution neutron powder diffraction and neutron pair distribution functions. The layered structure experiences a phase transition of O3 → P3 → OP2 → ramsdellite during the desodiation, and a new O3′ phase is observed at the end of the discharge state (1.5 V). The density functional theory (DFT) calculations and nPDF results suggest that depletion of Na+ ions induces the movement of Fe into Na layer resulting the formation of an inert ramsdellite phase thus causing the loss of capacity and structural integrity. Meanwhile, the operando XAS clarified the voltage regions for active Mn3+/Mn4+ and Fe3+/Fe4+ redox couples. This work points out the universal underneath problem for Fe-based layered oxide cathodes when cycled at high voltage and highlights the importance to suppress Fe migration regarding the design of high energy O3-type cathodes for sodium ion batteries.

Study on the effect of co-substitution of transition metals on O3-type Na-Mn-Ni-O cathode materials for promising sodium-ion batteries

BackgroundThe substitution of small quantity of electrochemically inactive and active elements described a propitious strategy for sodium-ion batteries (SIBs) to enrich the structural stability and electrochemical performance of O3-type cathodes. MethodsWe prepared the co-substitution of (Cu and Ti) O3-Na0.9Mn0.60Ni0.30Cu0.05Ti0.05O2 (MNCT), (Ti and Mg) O3-Na0.9Mn0.60Ni0.30Ti0.05Mg0.05O2 (MNTM), (Mg and Cu) O3-Na0.9Mn0.60Ni0.30Mg0.05Cu0.05O2 (MNMC), and bare O3-Na0.9Mn0.60Ni0.40O2 (MN) cathode materials by typical solid state reaction for SIBs. Significant findingsFrom Rietveld refinement, the MNCT, MNTM and MNMC cathode materials revealed a rhombohedral structure with the space group (R-3m), in which sodium ions occupied octahedral site. The MNCT, MNTM, MNMC and MN electrodes have discharge capacities of 184, 179, 174, and 218 mAh g−1 in a voltage range of 2–4 V at 0.1C rate, respectively. The bare MN system suffered the structural stability, it was rectified upon co-substituting with two different combinations using the partial amount of copper (Cu), titanium (Ti) and magnesium (Mg). The substitution in transition metal oxide (TMO2) layers enriched structural immovability of the O3-type cathode materials during electrochemical reaction for rechargeable SIBs.