O3-type NaNi0 Research Articles

Understanding of a Ni-Rich O3-Layered Cathode for Sodium-Ion Batteries: Synthesis Mechanism and Al-Gradient Doping.

O3-type NaNi0.8Mn0.1Co0.1O2 (NaNMC811) cathode active materials for sodium-ion batteries (SIBs), with a theoretical high specific capacity (∼187mAhg-1), are in the preliminary exploration stage. This study comprehensively investigates NaNMC811 from multiple perspectives. For the first time, the phase evolution ( - - ) during the solid-state synthesis is systemically investigated, which elucidates in-depth the mechanisms of the thermal sodiation process. Furthermore, an Al-gradient doping of NaNMC811 wassuccessfully implemented through Al2O3 coating on the cathode active material (CAM) precursor. The modified Al-NaNi0.8Mn0.1Co0.1O2 (Al-NaNMC811) exhibits excellent electrochemical dynamics and performance, maintaining a specific capacity above 100mAhg-1 after 100 cycles at 0.1 C (1.5-4.1 V) while providing a promising capacity retention of 63%. Additionally, the material demonstrates excellent rate capabilities, retaining a specific capacity of 107 mAh g-1 at 5 C. Compared to pristine NaNMC811, the modified Al-NaNMC811 is proven to have improved electrochemical kinetics with a higher Na+ diffusion coefficient due to dilated (003) interplanar spacing, and a more stable structure during the electrochemical charge-discharge processes, which is attributed to stronger Al-O bond energy. Understanding phase formations during the synthesis and comprehensive insight in the gradient doping for O3-type NaNMC811 CAMs guides further development of next-generation SIBsmaterials.

Ti-Substituted O3-NaNi0.5Mn0.3Ti0.2O2 Material with a Disordered Transition Metal Layer and a Stable Structure.

O3-type NaNi0.5Mn0.5O2 (NNM) is very competitive for sodium-ion batteries (SIBs) due to its high capacity and easy production. Nevertheless, the intricate phase transitions during the charging-discharging significantly impede its practical application. This paper proposes a strategy for successfully synthesizing NaNi0.5Mn0.3Ti0.2O2 (NNMT) by combining coprecipitation and a high-temperature solid-state method. This method introduces Ti elements while retaining the electrochemically active Ni2+ content, thus, the NNMT has a high initial specific capacity of 151.4 mAh g-1 at 1 C. It is demonstrated that introducing Ti4+ leads to the transition metal layers becoming disordered by ex situ XRD, thus mitigating the irreversible phase transition of the material. In addition, Ti4+ does not have an outer electron, which can reduce electron delocalization in the transition metal layer and improve the material's cyclic stability. The NNMT possesses a capacity retention rate of 60.66% after 150 cycles, much higher than the initial NNM's 18.96%. It also exhibits an excellent discharge capacity of 86.8 mAh g-1 at 5 C. In conclusion, the cycling and rate performance of the Ti-substituted NNMT are greatly improved without capacity loss, which offers innovative concepts for the modification means of the SIBs layered oxide cathode materials.

Preparation and Property Optimization of High Capacity O3-type NaNi0.4Fe0.2Mn0.4O2

O3-type NaNi0.4Fe0.2Mn0.4O2 cathode materials are structurally stable and have a high nickel content, allowing for stable high-capacity output. However, their performance needs further improvement. First, we investigated the effects of different sodium contents on the structure, morphology, and electrochemical performance of NaxNi0.4Fe0.2Mn0.4O2(x = 0.85, 0.9, 0.95, 1, 1.05) materials. The Na0.9Ni0.4Fe0.2Mn0.4O2 material exhibited initial discharge specific capacities of 148.11 and 181.80 mAh·g−1 at voltage ranges of 2–4.1 V and 2–4.2 V, respectively. To further optimize the cycling performance of the material, we doped NaNi0.4Fe0.2Mn0.4O2 with different calcium contents. Ca2+ doping significantly enhanced the electrochemical performance of the material. Subsequently, we synthesized Na0.96Ca0.02(NMF)0.95Zn0.05O2, and the dual-doped NMF-Ca0.02Zn0.05 maintains approximately 80% capacity retention at 1–4.05 V, and around 70% as the cut-off voltage increases to 4.15 V in full cells.

Improving cycling performance of the NaNiO2 cathode in sodium-ion batteries by titanium substitution

O3-type layered oxide cathodes, such as NaNi0.5Mn0.5O2, have garnered significant attention due to their high theoretical specific capacity while using abundant and low-cost sodium as intercalation species. Unlike the lithium analog (LiNiO2), NaNiO2 (NNO) exhibits poor electrochemical performance resulting from structural instability and inferior Coulomb efficiency. To enhance its cyclability for practical application, NNO was modified by titanium substitution to yield the O3-type NaNi0.9Ti0.1O2 (NNTO), which was successfully synthesized for the first time via a solid-state reaction. The mechanism behind its superior performance in comparison to that of similar materials is examined in detail using a variety of characterization techniques. NNTO delivers a specific discharge capacity of ∼190 mAh g−1 and exhibits good reversibility, even in the presence of multiple phase transitions during cycling in a potential window of 2.0‒4.2 V vs. Na+/Na. This behavior can be attributed to the substituent, which helps maintain a larger interslab distance in the Na-deficient phases and to mitigate Jahn–Teller activity by reducing the average oxidation state of nickel. However, volume collapse at high potentials and irreversible lattice oxygen loss are still detrimental to the NNTO. Nevertheless, the performance can be further enhanced through coating and doping strategies. This not only positions NNTO as a promising next-generation cathode material, but also serves as inspiration for future research directions in the field of high-energy-density Na-ion batteries.

First-principles study of the titanium-doping effects on the properties of O3-type NaNi0.25Fe0.25Mn0.5O2 cathode material for sodium-ion batteries

We carried out first-principles calculations on titanium-doped O3-type NaNi0.25Fe0.25Mn0.5O2 oxide material for titanium substitution at 0.02, 0.04, 0.06, 0.08, and 0.1. The results obtained show that materials doped with titanium have higher structural stability than undoped material. Also after doping, the conductivity of the materials increases greatly but Na(Ni0.25Fe0.25Mn0.5)0.98Ti0.02O2 is slightly more conductive (ΔEg = 0.017 eV). Na(Ni0.25Fe0.25Mn0.5)1-xTixO2 (NNFM-Tix) (x = 0.02, 0.04, 0.06, 0.08, and 0.1) indicates a larger sodium layer, which allows easy migration of sodium ions during charge/discharge processes than NNFM. Sodium ions diffuse faster in NNFM-Ti0.06 and NNFM-Ti0.08 compared to other doped-NNFMs. In addition, the Pugh index value of NNFM (1.8222) is lower than that of NNFM-Ti0.02, NNFM-Ti0.04, NNFM-Ti0.06, NNFM-Ti0.08, and NNFM-Ti0.1 (2.1376), demonstrating enhancement of elastic ductility after doping. Titanium-doped materials exhibited improved stability under temperature effects between −20 and 60 °C, which represent the operating temperature range of sodium-ion batteries, although this effect did not vary much with the doping rate. The improved thermodynamic stability indicates that the doped materials can better resist degradation, have high efficiency, and a long cycle life. These Na(Ni0.25Fe0.25Mn0.5)1-xTixO2 materials, particularly those with the titanium rate at 0.06 and 0.08 are therefore powerful materials for the accomplishment of efficient sodium-ion batteries cathodes.

A Two-Step Surface Modification Optimization for Performance Recovery of NaNi0.33Fe0.33Mn0.33O2

Due to its excellent electrochemical performance, O3-type NaNi0.33Fe0.33Mn0.33O2 (NFM) is one of the most promising cathode materials for sodium ion. However, its poor air stability has limited the industrialization process. In this work, a low-temperature two-step method which included carbon doping and acid treatment was used to improve the electrochemical property of the air-aged NaNi0.33Fe0.33Mn0.33O2. X-ray diffraction results indicated that the structure of modified NFM (NFM-M) has good crystal structure stability. NFM-M, NFM-48H (NFM after air ageing of 48 h) and fresh NFM possessed a discharge capacity of 95.25, 74.92, and 100.79 mAh·g−1 in the first cycle, respectively. The modified sample exhibits outstanding cycling stability, with a capacity retention of 90.15% after 100 cycles at 0.1 C rate. Moreover, the NFM-M sample delivers excellent rate capability with improved capacity retention of 66.9% at 2.0 C rate.

Effect of Particle Size and Polytypes on Redox Reversibility of Layered Na0.76Ni0.38Mn0.62O2 Electrode

Interest in sodium ion batteries (SIBs) has considerably increased in recent years for low-cost and sustainable energy storage systems. Among positive electrode materials in SIBs, layered sodium nickel manganese oxides such as O3-type NaNi0.5Mn0.5O2 and P2-type Na0.67Ni0.33Mn0.67O2 and their derivatives have been extensively investigated. Despite their high capacity delivered by Ni2+/4+ redox processes, significant surface-electrolyte reactivity with Ni and inferior structural integrity due to phase transformations eventually lead to capacity fade over cycling. To suppress the problems, substitution for Ni and/or Mn, surface coating, and morphology modification have been applied. In lithium ion batteries, tunning morphology without altering chemical compositions has shown improved electrochemical properties for layered lithium cathode materials, LiNixMnyCoyO2 (NMC, x + y + z = 1). For example, single-crystal NMC of micron-scale particles limit the surface reactivity and particle cracking, which is beneficial for cycle life. Another way is spherical secondary particles in micron-size where primary nanoparticles are composed of. Due to the hierarchical morphology, detrimental surface reactions are suppressed while ionic and electronic conductivity are preserved. Those strategies are expected to be advantageous for the counterparts of SIBs, however less studies have been carried out.In this study, we focus on the strategy of secondary spherical particles for layered sodium nickel manganese oxides. To understand the effect of secondary particle size, two different diameters of 4 µm and 10 µm were synthetized using (Ni0.38Mn0.62)OH2 and Na2CO3. In addition, different heating temperatures were used as polytypes are an interesting character for layered sodium oxides. Heating at 700 °C and 900 °C produces different polytypes of P3- and P2-type Na0.76Ni0.38Mn0.62O2, respectively. Increased temperature tends to enlarge primary particle size and yields NiO impurity, while no influence on the spherical morphology is found.To examine the redox stability depending on voltage ranges as well as polytypes, 10 µm of P3- and P2-type Na0.76Ni0.38Mn0.62O2 were galvanostatically cycled at four diverse voltage ranges (1.6-4.4 V, 1.6-3.8 V, 2.5-4.4 V, and 2.5-3.8 V) in non-aqueous sodium cells. When the lower cut-off voltage is 2.5 V, charge/discharge profiles on the first cycle are almost identical regardless of polytypes. The difference occurs below 2.0 V where a sloping plateau is observed in P2-type Na0.76Ni0.38Mn0.62O2 while a flat plateau is found in P3-type Na0.76Ni0.38Mn0.62O2. Those dissimilarity originates from the phase transition of P2-P’2 and P3-O3 as confirmed by ex-situ XRD. The widest voltage range of 1.6-4.4 V results in capacity fade, which is more significant for P2-type Na0.76Ni0.38Mn0.62O2. The narrowest voltage range of 2.5-3.8 V permits the best cyclability where no apparent phase changes occur. Decreased lower cut-off voltage to 1.6 V, keeping the upper cut-off voltage at 3.8 V, deteriorates slightly the cycle life, which is again more pronounced for P2-type Na0.76Ni0.38Mn0.62O2. In the voltage range of 2.5-4.4 V, however, capacity notably decays, retaining only 57% and 51% of their initial capacity after 60 cycles for P3- and P2-type Na0.76Ni0.38Mn0.62O2, respectively. These results indicate that reactions beyond 3.8 V are detrimental to capacity retention for both polytypes, and P3-type Na0.76Ni0.38Mn0.62O2 shows enhanced cyclability.4 µm of P3- and P2-type Na0.76Ni0.38Mn0.62O2, galvanostatically cycled at two voltage ranges (1.6-4.4 V and 1.6-3.8 V), show same trends as those of 10 µm: significant capacity fade in the voltage range of 1.6-4.4 V, and worse capacity retention for P2-type Na0.76Ni0.38Mn0.62O2. It is worth noting the capacity fade is more pronounced than that for 10 µm.Given that no influence of secondary particle size on the phase changes, confirmed by ex-situ XRD, degradation of Na0.76Ni0.38Mn0.62O2 driven by surface reactions is suspected to play an important role for the capacity fade. To understand further, cross-sectional morphology for 4 µm and 10 µm of P3-type Na0.76Ni0.38Mn0.62O2 was examined. Pristine electrode of 4 µm sample exhibits some pores within the secondary particles, which is barely modified during the first cycle between 1.6 and 4.4 V. After 100 cycles, pulverized secondary particles are observed, accelerating electrolyte penetration into the particle interior. In the case of 10 µm, tightly packed primary particles are shown at pristine electrode and no significant microcracks appear on the secondary particles after charge to 3.8 V. Further charge to 4.4 V develops the microcracks and the prevalent microcracks are also observed after discharge to 1.6 V. After 100 cycles, the microcracks are more developed, however exposed internal surface is lower compared to that of 4 µm. This reduces the exposure of internal surface to the infiltrated electrolyte, retarding the degradation of active materials. Figure 1

NASICON-Type NaTi2(PO4)3 Surface Modified O3-Type NaNi0.3Fe0.2Mn0.5O2 for High-Performance Cathode Material for Sodium-Ion Batteries.

Sodium-ion batteries (SIBs) have shown great potential as energy storage devices due to their low price and abundant sodium content. Among them, O3-type layered oxides are a promising cathode material for sodium-ion batteries; however, most of them suffer from slow kinetics and unfavorable structural stability, which seriously hinder their practical application. O3-NaNi0.3Fe0.2Mn0.5O2 surface modification is performed by a simple wet chemical method of coating NaTi2(PO4)3 on the surface. The NASICON-type NaTi2(PO4)3 coating layer has a special three-dimensional channel, which facilitates the rapid migration of Na+, and the NaTi2(PO4)3 coating layer also prevents direct contact between the electrode and the electrolyte, ensuring the stability of the interface. In addition, the NaTi2(PO4)3 coating layer induces part of the Ti4+ doping into the transition metal layer of NaNi0.3Fe0.2Mn0.5O2, which increases the stability of the transition metal layer and reduces the resistance of Na+ diffusion. More importantly, the NaTi2(PO4)3 coating layer can suppress the O3-P3 phase transition and reduce the volume change of the materials throughout the charge/discharge process. Thus, the NaTi2(PO4)3 coating layer can effectively improve the electrochemical performance of the cathode materials. The NFM@NTP3 has a capacity retention of 86% (2.0-4.0 V vs Na+/Na, 300 cycles) and 85% (2.0-4.2 V vs Na+/Na, 100 cycles) at 1C and a discharge capacity of 107 mAh g-1 (2.0-4.0 V vs Na+/Na) and 125 mAh g-1 (2.0-4.2 V vs Na+/Na) at 10C, respectively. Therefore, this surface modification strategy provides a simple and effective way to design and develop high-performance layered oxide cathode materials for sodium-ion batteries.

Stabilized O3-Type Layered Sodium Oxides with Enhanced Rate Performance and Cycling Stability by Dual-Site Ti4+ /K+ Substitution.

High-capacity O3-type layered sodium oxides are considered one of the most promising cathode materials for the next generation of Na-ion batteries (NIBs). However, these cathodes usually suffer from low high-rate capacity and poor cycling stability due to structure deformation, native air sensitivity, and interfacial side reactions. Herein, a multi-site substituted strategy is employed to enhance the stability of O3-type NaNi0.5 Mn0.5 O2 . Simulations indicate that the Ti substitution decreases the charge density of Ni ions and improves the antioxidative capability of the material. In addition, the synergistic effect of K+ and Ti4+ significantly reduces the formation energy of Na+ vacancy and delivers an ultra-low lattice strain during the repeated Na+ extraction/insertion. In situ characterizations verify that the complicated phase transformation is mitigated during the charge/discharge process, resulting in greatly improved structure stability. The co-substituted cathode delivers a high-rate capacity of 97mAhg-1 at 5C and excellent capacity retention of 81% after 400 cycles at 0.5C. The full cell paired with commercial hard carbon anode also exhibits high capacity and long cycling life. This dual-ion substitution strategy will provide a universal approach for the new rational design of high-capacity cathode materials for NIBs.

Optimizing O bonding environment to improve structural stability and performance of O3-type NaNi0.5Mn0.5O2 cathode material

O3-type sodium layered oxides are regarded as a highly suitable cathode for sodium-ion batteries (SIBs) owing to their high capacities and high compositional diversity. Nevertheless, rapid capacity decline and slow kinetics caused by complex phase transition and high tetrahedral site energy of Na+ diffusion transition state limit their practical use. Herein, we propose an effective strategy of optimizing O bonding environment to enhance the stability of the M-O bond and layered structure of the O3-type NaMn0.5Ni0.5O2 (NaMN) by Zn/Ti codoping, which has been confirmed by electrochemical tests, ex situ X-ray powder diffraction (XRD), and Rietveld refinement. As a consequence, Zn/Ti codoped O3-NaMn0.4Ni0.4Zn0.1Ti0.1O2 (NaMNZT) electrode delivers a high discharge capacity of 165.1 mAh g−1 at 0.1C, superior rate performance of 80.8 mAh g−1 at 5C, and 76.4% capacity retention after 100 cycles at 0.2C. This concept of optimizing O bonding environment affords a promising strategy for designing and constructing stable sodium ion host.

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.

Dual metal (Fe and Mg) substituted layered titanium-based P2 and O3-type negative electrodes for rechargeable sodium batteries

A first attempt was made to enhance the electrochemical performances, using the binary metal (Fe and Mg) substitution on the layered Titanium-based P2-type Na0.5Ni0.2Ti0.6O2 (P2-NNTFMO) and O3-type NaNi0.2Ti0.6O2 (O3-NNTFMO) anode materials, via traditional solid state reaction for sodium ion batteries (SIBs). The XPS analysis of the O3-NNTFMO negative material exhibit the presence of Ti, Ni, Fe and Mg ions happens in +4, +2, +3 and +1 valance states respectively. The discharge and charge curves reveal the P2-NNTFMO and O3-NNTFMO anode materials have the charge capacities of 117.60 and 128.48 mAh/g respectively. The limited amount of co-substitution (Fe and Mg) in transition metal oxide layers would enlarge the sodium ion diffusion layers during cycling for O3 and P2-type anodes, due to the shrinkage of TMO6 octahedrons and decrease of TM-O bond lengths.

Ti, F Codoped Sodium Manganate of Layered P2-Na 0.7 MnO 2.05 Cathode for High Capacity and Long-Life Sodium-Ion Battery

Ti, F Codoped Sodium Manganate of Layered P2-Na _0.7 MnO _2.05 Cathode for High Capacity and Long-Life Sodium-Ion Battery

A distinctive strategy of Sb doped quaternary oxide cathodes materials toward energy storage of electric equipment for sodium-ion batteries

The poor cycle stability and rate capability for sodium-ion batteries is largely due to electrochemical irreversibility and sluggish mobility of Na+ in the cathode materials. Herein, a new strategy of introducing Sb ions into the ternary oxide NiMnTi-based layer-structured cathode material is designed. Reversible phase transition in this cathode NMTSb0.03 restraint the rapid capacity decay issued from intense volume variation, exhibiting a reversible capacity of 147.8 mAh g−1 and retaining 103.5 mAh g−1 over 200 cycles at 1C. The enough space after Sb substitution allows the effective accommodation of Na+ intercalation and deintercalation, affording a specific capacity of 90 mAh g−1 at 8C. The improvement is attributed to the enhanced Na+ diffusion kinetics with the meliorative equilibrium conductance and the higher cohesive energy after Sb doping. Considering its simple preparation and scale-up capability, the O3-type NaNi0.5Mn0.3Ti0.2O2 with Sb5+may find extensive applications in designing electrode for sodium-ion batteries.

Facile Synthesis of O3-Type NaNi0.5Mn0.5O2 Single Crystals with Improved Performance in Sodium-Ion Batteries.

Sodium-ion batteries can be a practical alternative to lithium-ion batteries due to the relatively high abundance of sodium and the projected scarcity of lithium. Both of these factors are critical considerations for grid-scale energy storage, but the central challenge to implementing sodium layered oxides in sodium-ion batteries is their relatively poor cycle life. Single-crystal particles with micrometer size can mitigate several failure mechanisms related to sodium layered oxides and can improve performance when compared to the commonly used polycrystalline particles. This work demonstrates a novel two-step molten-salt synthesis method using sodium chloride and metal oxides to form "single crystals" of a mixed-phase, spinel/rock-salt intermediate that crystallizes as micron-sized truncated octahedra. The mixed-phase spinel/rock-salt material is effectively used as a precursor to form O3-type NaNi0.5Mn0.5O2 with large primary particles and substantially improved cycle life. This synthesis route offers the added benefit of using simple metal oxides instead of hydroxide precursors, eliminating the need for coprecipitation. Particle morphology is found to be a critical factor in mitigating the structural damages incurred during phase transformations and maintaining the electrochemical performance.

Enhanced Na-storage properties of O3-type NaNi0.5Mn0.5O2 cathodes by doping and coating dual-modification strategy

Due to their high theoretical specific capacities and good structural compatibility, O3-layered oxides are considered as high-performance cathode candidates for sodium-ion batteries. However, serious side reactions and structural degradation during long-term cycling have greatly hindered their practical applications. Herein, O3-type NaNi0.5Mn0.5O2 (NNMO) was prepared by partially substituting Ni2+ with Cu2+ and inducing CuO surface coating to enhance the structural stability without sacrificing the high capacity. In Particular, Cu2+ incorporated at a molar ratio of 0.10 greatly improved the electrochemical performance of pristine NNMO. The NaMn0.5Ni0.4Cu0.1O2 electrode exhibited a capacity retention of 64.5% after 300 cycles at 0.5 C. Microscopic and spectral studies revealed that the CuO coating layer suppressed detrimental side reactions upon cycling. Moreover, the bulk doping of Cu2+ ultimately enhanced the structural stability by mitigating irreversible phase transitions. Hence, the integration of bulk Cu2+ doping and CuO surface coating contributed to the increased structural stability and electrochemical performance of NNMO. The doping and coating dual-modification strategy established in this work effectively suppressed the side reactions and structural degradation of NNMO, and this work provides new insight into the effective design of electrode microstructures for use in high-performance batteries.

Enhanced electrochemical performance of O3-type NaNi0.5Mn0.3Co0.2O2 cathodes for sodium-ion batteries via Al-doping

O3-type NaNi0.5Mn0.3Co0.2O2 based positive electrode materials are very promising for sodium-ion batteries. However, the irreversible phase transition due to structural deformation leads to sluggish kinetics, rapid capacity fade, and low C-rate performance, limiting its wide practical applications. The partial substitution of Co3+ (0.545 Å) by Al3+ (0.535 Å) ions in the transition-metal layer in NaNi0.5Mn0.3Co0.2-xAlxO2 (0.01 ≤ x ≤ 0.02) is an effective strategy to address the issue of structural deformation and thus to improve the electrochemical performance of NaNi0.5Mn0.3Co0.2O2 cathode. Solution combustion synthesis of NaNi0.5Mn0.3Co0.2-xAlxO2 (x = 0.01, 0.02) shows O3-type structure of NaNi0.5Mn0.3Co0.2−xAlxO2 material with the space group of R3¯m. The composition with an overall x = 0.02 Al doping delivers an initial 120 mAh g−1 capacity at a 0.1 C rate. It retains 90 % capacity even after 200 cycles than the other stoichiometric aluminum substitution, x = 0.01 (77 %). Moreover, the NaNi0.5Mn0.3Co0.18Al0.02O2 shows a good capacity of ~ 83 mAh g−1 even at a high C-rate of 5 C, almost 70 % of the initial capacity at the 0.1 C rate. The Al-substitute NaNi0.5Mn0.3Co0.2−xAlxO2 cathode's electrochemical performance is attributed to the enhancement in the structural stability of the sodium layered transition metal oxide after the partial substitution of Co3+ by Al3+ ion. Finally, the practical sodium-ion full cells are realized using a hard carbon-based anode and NaNi0.5Mn0.3Co0.18Al0.02O2 cathode, showing 91 % capacity retention at the end of 100th cycles with an OCV of 3.5 V.

Facile design and synthesis of Co-free layered O3-type NaNi0.2Mn0.2Fe0.6O2 as promising cathode material for sodium-ion batteries

• Design the structure of the cathode material by capturing the cation potential. • The O3-type NaNi 0.2 Mn 0.2 Fe 0.6 O 2 were synthesized with co-precipitation method. • Valence Changes of Iron Elements by 57 Fe-M o ¨ ssbauer spectroscopy. O3-type layered oxides have received extensive attention as a class of battery layered materials. However, problems such as rate capability, stable period difference, and voltage deviation of these oxides hinder their practical application. The method of orthogonal experiment was adopted, and the reaction temperature, raw material concentration, reaction time and ammonia concentration were regarded as single factors. Finally, the optimal conditions for synthesizing cathode materials were obtained as follows: the reaction temperature was 50 °C, the raw material concentration was 0.2 mol·L -1 , the reaction time was 16 h, and the ammonia concentration was 1 mol·L -1 . A layered oxide cathode material Co-free NaNi 0.2 Mn 0.2 Fe 0.6 O 2 with high iron content was synthesized by co-precipitation method. When the charging voltage is greater than 4 V, the higher the utilization rate of sodium ions, the higher the energy density. But the higher the cut-off voltage, the worse the cycle stability. Due to the low manganese content and the high iron content, the average oxidation state of manganese is low. 57 Fe-M o ¨ ssbauer spectroscopy showed that the synthesized samples had high spin Fe 3+ . Under the control of the optimal synthesis conditions, the specific discharge capacity of the reaction increased from 105 mAhּ·g −1 to 112.5 mAhּ·g −1 at 0.1C.

Mitigating the voltage fading and air sensitivity of O3-type NaNi0.4Mn0.4Cu0.1Ti0.1O2 cathode material via La doping

The practical application of O3-type layered oxides cathode materials for sodium ion batteries (SIBs) is hindered by two major difficulties, including capacity decay rooted in multiphase transitions and storage issue originated from sensitivity to moisture. Herein, we report a series of O3-type layered oxides Na(Ni0.4Cu0.1Mn0.4Ti0.1)1-xLaxO2 (x = 0, 0.001, 0.003, 0.005, termed as NMCT, NMCT-Lax, respectively) cathode materials synthesized via spray pyrolysis followed by high-temperature sintering method, which manifest enhanced electrochemical performance and air stability as compared to the NaNi0.5Mn0.5O2 (termed as NM) material. Optimum performance is achieved in the NMCT-La0.001 material that delivers a high initial discharge capacity of 170.1 mAh g−1 in the voltage range of 2.0–4.4 V at 0.1C (1C = 150 mA g−1). NMCT-La0.001 exhibits a highly reversible structural transformation during charging/discharging as demonstrated by in-situ XRD, and it keeps the original crystal structure after being exposed to the air for 30 days. The capacity decay of NMCT is effectively decelerated at high voltage (>4.2 V) after La doping, as which can stabilize the structure of the material by reducing the Mn3+ content through suppressing the Jahn-Teller effect. The research with respect to La doping provides a facile and instructive way for the design of high-performance cathode materials for SIBs.

O3-NaNi0.47Zn0.03Mn0.5O2 cathode material for durable Na-ion batteries

O3-type transition metal oxides as the cathodes for Na-ion batteries have attracted extensive attention owing to their high theoretical specific capacity and ease of synthesis. This work indicates enhanced electrochemical reversibility and improved air stability via a rational Zn2+ doping for O3-NaNi0.5Mn0.5O2. It exhibits a discharge capacity of 113 mAh g−1 at 0.5 C, excellent capacity retention of 80% after 150 cycles, and the capability to release a capacity of 82 mAh g−1 at 5 C in the voltage range of 2–4 V. The doped cathode undergoes a phase transition of O3-O3/O′3-P3-P′3-O''3 with a small volume change of approximately 2.00% in the voltage range of 2–4 V, and a subsequent slight structural change in the high voltage range of 4–4.2 V, which well demonstrates the enhanced cyclic stability. The assembled full cell confirms the feasibility of applying O3-type NaNi0.47Zn0.03Mn0.5O2 cathode for Na-ion batteries. Thus, the work suggests an efficient strategy to better release the potential of high-energy cathode for Na-ion batteries.