Cathode Material For Sodium-ion Batteries Research Articles

Achieving structurally stable O3-type layered oxide cathodes through site-specific cation-anion co-substitution for sodium-ion batteries

O3-type layered oxides have garnered great attention as cathode materials for sodium-ion batteries because of their abundant reserves and high theoretical capacity. However, challenges persist in the form of uncontrollable phase transitions and intricate Na+ diffusion pathways during cycling, resulting in compromised structural stability and reduced capacity over cycles. This study introduces a special approach employing site-specific Ca/F co-substitution within the layered structure of O3-NaNi0.5Mn0.5O2 to effectively address these issues. Herein, the strategically site-specific doping of Ca into Na sites and F into O sites not only expands the Na+ diffusion pathways but also orchestrates a mild phase transition by suppressing the Na+/vacancy ordering and providing strong metal–oxygen bonding strength, respectively. The as-synthesized Na0.95Ca0.05Ni0.5Mn0.5O1.95F0.05 (NNMO-CaF) exhibits a mild O3 → O3 + O'3 → P3 phase transition with minimized interlayer distance variation, leading to enhanced structural integrity and stability over extended cycles. As a result, NNMO-CaF delivers a high specific capacity of 119.5 mA h g−1 at a current density of 120 mA g−1 with a capacity retention of 87.1% after 100 cycles. This study presents a promising strategy to mitigate the challenges posed by multiple phase transitions and augment Na+ diffusion kinetics, thus paving the way for high-performance layered cathode materials in sodium-ion batteries.

Exploring the Effect of V2O5 and Nb2O5 Content on the Structural, Thermal, and Electrical Characteristics of Sodium Phosphate Glasses and Glass-Ceramics.

Na-V-P-Nb-based materials have gained substantial recognition as cathode materials in high-rate sodium-ion batteries due to their unique properties and compositions, comprising both alkali and transition metal ions, which allow them to exhibit a mixed ionic-polaronic conduction mechanism. In this study, the impact of introducing two transition metal oxides, V2O5 and Nb2O5, on the thermal, (micro)structural, and electrical properties of the 35Na2O-25V2O5-(40 - x)P2O5 - xNb2O5 system is examined. The starting glass shows the highest values of DC conductivity, σDC, reaching 1.45 × 10-8 Ω-1 cm-1 at 303 K, along with a glass transition temperature, Tg, of 371 °C. The incorporation of Nb2O5 influences both σDC and Tg, resulting in non-linear trends, with the lowest values observed for the glass with x = 20 mol%. Electron paramagnetic resonance measurements and vibrational spectroscopy results suggest that the observed non-monotonic trend in σDC arises from a diminishing contribution of polaronic conductivity due to the decrease in the relative number of V4+ ions and the introduction of Nb2O5, which disrupts the predominantly mixed vanadate-phosphate network within the starting glasses, consequently impeding polaronic transport. The mechanism of electrical transport is investigated using the model-free Summerfield scaling procedure, revealing the presence of mixed ionic-polaronic conductivity in glasses where x < 10 mol%, whereas for x ≥ 10 mol%, the ionic conductivity mechanism becomes prominent. To assess the impact of the V2O5 content on the electrical transport mechanism, a comparative analysis of two analogue series with varying V2O5 content (10 and 25 mol%) is conducted to evaluate the extent of its polaronic contribution.

Electrochemical Performance of Na2Mn3O7 as a Cathode Material in Sodium-Ion Batteries Using the Precipitation Method with Ethylene Glycol Chelating Agent

Tests were conducted on Na2Mn3O7 as a cathode material in sodium-ion batteries, aiming to synthesize Na2Mn3O7 precursor using commercial and synthetic MnCO3 variants. Sample A utilized commercial MnCO3, while sample B utilized MnCO3 synthesized from MnSO4.1H2O and Na2CO3. Both variants were mixed with Na2CO3 to form Na2Mn3O7 precursor, which was then sintered at 700°C for 4 hours, ground, and sieved. A slurry was prepared by mixing the active materials PVDF: Super P in an 8:1:1 ratio with 3.5 mL of NMP. Sample A exhibited a conductivity of 3.4706×10-7 S/cm, and sample B had a conductivity of 2.7304×10-7 S/cm in the EIS results. In the CV test, sample A showed oxidation and reduction peaks at 2.77 V and 1.62 V, respectively, while sample B had peaks at 2.842 V and1.716 V. In the CD test, sample A reached maximum and minimum peaks of 4.3 V and 1.4 V, while sample B reached peaks of 4.2 V and 1.3 V. Sample A exhibited a capacity of 117.02 mAh/g on charge and 93.47 mAh/g on discharge, whereas sample B showed capacities of 79.17 mAh/g on charge and 65.79 mAh/g on discharge. These results indicate the superior performance of sample A over sample B.

Synergetic enhancement of structural stability and kinetics of P’2-type layered cathode for sodium-ion batteries via cation–anion co-doping

The P’2-type layered oxides attract much attention as viable cathode materials for sodium-ion batteries (SIBs), due to their high specific capacity and environmental friendliness. Nevertheless, the sluggish Na+ diffusion kinetics and drastic capacity decay triggered by irreversible phase transition limit their large-scale application. In this study, we employ a synergistic optimization strategy involving cation and anion dopants to successfully restrain intergranular strain and tune local electronic structure, strengthening structural stability and electrochemical performance of the cathode material. Specifically, the Mg2+ dopant suppresses Na+/vacancy rearrangement and Mn-O anisotropic changes, while the F− dopant facilitates Na+ transport and alleviates phase evolution in high-voltage regions. Through this co-doping design, the modified electrodes display more alleviated voltage decay and exceptional capacity retention enhancements ranging from 6.57 % to 81.23 % after 750 cycles at 1000 mA g–1. This work provides novel perspectives on precise design of cathode materials, making layered oxides promising contenders for the next generation energy storage systems.

Selective recovery of metals in spent batteries by electrochemical precipitation to cathode material for sodium-ion batteries

The recycling of key components in waste lithium-ion batteries (LIBs) is an important route to make up for the shortage of battery materials. Metal separation and purification is an important step. It is of great significance to propose an efficient and green separation technology. In this paper, an electrochemical precipitation method was applied to metal separation from spent LiNi0.5Mn1.5O4 cathode material. The Li and metal elements were effective separated and the precipitates were then used as precursor to synthesize high-performance R–O3-NaNFM cathode material for sodium-ion batteries. The R–O3-NaNFM exhibits excellent electrochemical cycling stability. The capacity retains 71.3 mAh g−1 after a long-term cycling of 200 times at 1 C. This method offers a referable strategy of the recycling for the waste cathode material in spent LIBs.

Unveiling charge compensation mechanisms in Na2/3MgxNi1/3-xMn2/3O2 cathode materials: insights into cationic and anionic redox

P2-type Na2/3Ni1/3Mn2/3O2 cathode material for sodium-ion batteries exhibits negligible voltage hysteresis during charge and discharge cycles, with oxygen redox mechanisms playing a pivotal, non-negligible role. Conversely, for the Na2/3Mg1/3Mn2/3O2 material featuring Mg substitution for Ni, O redox largely governs the entire charge and discharge process, accompanied by a pronounced voltage hysteresis. Upon combining these two materials – Na2/3MgxNi1/3-xMn2/3O2 – the transition metal and O redox processes, constituting the charge compensation mechanism, become paramount. These phenomena underscore the transition metal's influence on anionic redox, a topic with limited in-depth exploration in the existing literature. Within this study, we synthesized two materials, Na2/3Mg1/9Ni2/9Mn2/3O2 and Na2/3Mg2/9Ni1/9Mn2/3O2 (Mg-0.11, Mg-0.22), subsequently probing their transition metal and oxygen redox contributions to electrochemical capacity during the initial and 10th cycle charge and discharge processes by synchrotron-based mapping of resonant inelastic X-ray scattering and soft X-ray Absorption Spectroscopy. Our findings corroborate the presence of similar O redox contributions in the Mg-substituted materials. Intriguingly, the Mg-0.11 material exhibits a substantial enhancement in O redox following ten cycles, warranting further investigation due to its exceptional multiplicity, cycling performance, minimal voltage hysteresis, and potential impact on advancing sodium-ion battery commercialization.

Vacancies-regulated Prussian Blue Analogues through Precipitation Conversion for Cathodes in Sodium-ion Batteries with Energy Densities over 500 Wh/kg.

Prussian blue analogues (PBAs) have been widely applied in many fields, especially as cathode materials of sodium-ion batteries on account of their low cost and open framework for fast ions transport. However, the capacity of reported PBAs has a great distance from its theoretical value. Herein, we proposed that [Fe(CN)6] vacancies are crucial point for the high specific capacity for the first time. The [Fe(CN)6] vacancies may create net electrons and reduce obstacles to ionic transport, which is conducive to rate performance of PBAs by increasing electronic and ionic conductivity to some extent. As a proof of concept, a series of PBAs have been prepared by co-precipitation method. And then, a novel precipitation conversion method has been designed, by which unique PBAs with a specific quantity of [Fe(CN)6] vacancies was successfully synthesized. Remarkably, the as-prepared PBAs possessing hierarchical hollow morphology have reached a unprecedent level of high capacity (168 mAh g-1 at 25 mA g-1, close to PBAs' theoretical capacity 170 mAh g-1), high rate performance (90 mAh g-1 at 5 A g-1), and high energy density (over 500 Wh kg-1).

P2/O3 Biphasic Cathode Material through Magnesium Substitution for Sodium-Ion Batteries.

P2-type Fe-Mn-based oxides offer excellent discharge specific capacity and are as affordable as typical layered oxide cathode materials for sodium-ion batteries (SIBs). After Cu modification, though they can improve the cycling performance and air stability, the discharge specific capacity will be reduced. Considering the complementary nature of biphasic phases in electrochemistry, hybridizing P2/O3 hybrid phases can enhance both the storage performance of the battery and specific capacity. Herein, a hybrid phase composite with high capacity and good cycle performance is deliberately designed and successfully prepared by controlling the amount of Mg doping in the layered oxide. It has been found that the introduction of Mg can activate anion redox in the oxide layer, resulting in a significant increase in the specific discharge capacity of the material. Meanwhile, the dual-phase structure can produce an interlocking effect, thus effectively alleviating structure strain. The degradation of cycling performance caused by structural damage during the high-voltage charging and discharging process is clearly mitigated. The results show that the specific discharge capacity of Na0.67Cu0.2Mg0.1Fe0.2Mn0.5O2 is as high as 212.0 mAh g-1 at 0.1C rate and 186.2 mAh g-1 at 0.2C rate. After 80 cycles, the capacity can still maintain 88.1%. Moreover, the capacity and cycle performance as well as the stability can still remain stable even in the high-voltage window. Therefore, this work offers an insightful exploration for the development of composite cathode materials for SIBs.

Fluoride Doping Na3Al2/3V4/3(PO4)3 Microspheres As Cathode Materials for Sodium-Ion Batteries with Multielectron Redox.

Sodium-ion batteries (SIBs) are potential candidates for large energy storage usage because of the natural abundance and cheap sodium. Nevertheless, improving the energy density and cycling steadiness of SIB cathodes remains a challenge. In this work, F-doping Na3Al2/3V4/3(PO4)3(NAVP) microspheres (Na3Al2/3V4/3(PO4)2.9F0.3(NAVPF)) are synthesized via spray drying and investigated as SIB cathodes. XRD and Rietveld refinement reveal expanded lattice parameters for NAVPF compared to the undoped sample, and the successful cation doping into the Na superionic conductor (NASICON) framework improves Na+ diffusion channels. The NAVPF delivers an ultrahigh capacity of 148 mAh g-1 at 100mA g-1 with 90.8% retention after 200 cycles, enabled by the activation of V2+/V5+ multielectron reaction. Notably, NAVPF delivers an ultrahigh rate performance, with a discharge capacity of 83.6 mAh g-1 at 5000mA g-1. In situ XRD demonstrates solid-solution reactions occurred during charge-discharge of NAVPF without two-phase reactions, indicating enhanced structural stability after F-doped. The full cell with NAVPF cathode and Na+ preintercalated hard carbon anode shows a large discharge capacity of 100 mAh g-1 at 100mA g-1 with 80.2% retention after 100 cycles. This anion doping strategy creates a promising SIB cathode candidate for future high-energy-density energy storage applications.

Peculiarities of charge-discharge processes in Prussian white electrodes with different level of dehydration

Prussian White (PW) is a promising cathode material for sodium-ion batteries. PW exhibits advantages such as high specific capacity, ease of synthesis, and low cost. However, the presence of interstitial and coordinated water in PW materials significantly influences their electrochemical properties. In this work, a dehydration of the commercial PW powder and an impact of the preheating of the PW electrodes on their structural and electrochemical behavior have been examined using in situ/operando neutron and X-ray diffraction, along with complex TG-IR and FTIR techniques. The dehydration of the PW powder under the vacuum annealing conditions occurs mainly between 100 and 150 °C. At temperatures above 180 °C, a decomposition of the PW powder is detected. Preheating the electrode at 180 °C promotes the formation of a larger fraction of dehydrated rhombohedral phase, resulting in higher capacity compared to electrodes without preheating and preheated at 140 °C. Carbon content has been shown to be an important factor for stable electrode cycling. Capacity values of ∼100 mAh g–1 and 83 mAh g–1 at 5 C and 10 C cycling rates, respectively, are achieved when using 15 wt% content of carbon additive for the electrode preparation. Structural aspects of the degradation of PW electrodes during cycling are discussed.

Tailoring Cu-rich surface spinel phase for high-performance O3-type layered cathode materials for sodium-ion batteries

O3-type layered oxide cathodes are primarily limited by complex phase transitions and sluggish kinetics resulting in rapid capacity drop and poor rate capability. Even worse, its inherent air sensitivity leads to spontaneous extraction of lattice Na-ions and the deactivation of the cathode. Simultaneous modification of both the bulk phase and the surface structure is promising to offset the above deficiencies. A spinel@O3 type layered composite structure Na0.9Mn0.5Ni0.5Cu0.1O2+x (NMNCO-SL) was constructed for the design of cathodes with higher cycling, rate and air stability. The atomic-level Cu-rich spinel structure on the surface was identified by scanning transmission electron microscopy, elemental linear scanning analysis and Raman spectra. In situ charge-discharge X-ray diffraction results show that the phase transition of NMNCO-SL is significantly suppressed. Finally, the material maintains good electrochemical properties after exposure to stringent humidity environments. The results indicate that the spinel structure at the surface plays a significant role in improving ion-diffusion dynamics, enhancing structural integrity, and increasing air stability. 1 Ah pouch cell based on NMNCO-SL showed 92% capacity retention after 500 cycles of charge/discharge cycling at 1 C, demonstrating the potential prospects of customizing the surface phase structure for materials engineering applications.

Experimental and theoretical investigation of cobalt and manganese substitution in Na4Fe3(PO4)2P2O7 as a high energy density cathode material for sodium-ion batteries

As an inexpensive and environmentally-friendly cathode for sodium-ion batteries, Na4Fe3(PO4)2P2O7 (NFPP) is considered to be a promising candidate for practical applications. However, the theoretical capacity of NFPP is limited to 129 mAh g−1, due to the fact that only three electrons can be participated in the reaction during the charge/discharge process. Herein, the critical role of cobalt and manganese in elevating the energy density of the pristine NFPP structure was investigated, and Na4Co0.5Mn0.5Fe2(PO4)2P2O7 (NCMFPP) is prepared in order to trigger a redox reaction with 3.5 electrons during the charge/discharge process. It is found that the NCMFPP can provide a high initial discharge capacity of 139 mAh g−1 at 0.1C (1C = 129 mA g−1), with an excellent rate capacity (75 mAh g−1 at 10C) and a remarkable long cycling stability with a capacity retention of 65.2 % after 2000 cycles at 10C. The reaction of the Mn3+/Mn4+ redox couple was characterized by X-ray photoelectron spectroscopy analysis during the charge/discharge process. These results verified the effectiveness of cobalt and manganese in elevating the energy density of NFPP as a cathode as a cathode material for low-cost sodium-ion batteries.

A ZIF-8 modified Prussian blue cathode material for sodium-ion batteries with long cycling life and excellent storage stability

Prussian blue analogues have been intensely investigated as promising cathode materials for sodium-ion batteries owing to their high capacities, easy synthesis and low cost. However, the poor cycling performance due to the presence of lattice defects and the structural deterioration when exposed to humid air hinder their practical application. Herein we report an effective surface modification method to tackle these issues. A Zinc-zeolitic imidazolate framework (ZIF-8) modified PB sample is prepared by in-situ growth via simple wet chemical reaction. The obtained PB@ZIF-8 composite with a ZIF-8 coating layer of ∼70 nm thickness on the 2–5 μm PB particle surface shows excellent cycling stability with reversible capacity of 106.5 mAh g−1 at 1C charge-discharge rate and a remarkable capacity retention of 96.7 % after 500 cycles. Furthermore, the PB@ZIF-8 composite shows excellent storage stability owing to its moisture-proof property. After exposure to high humidity air (RH=70 %) for 24 h or storage for 180 days in a bottle filled with air of relative humidity RH=40 %, the PB@ZIF-8 sample still maintains excellent cycling performance. ZIF-8 coating layer not only acts as a shield for PB particles against the electrolyte corrosion, but also resists the H2O attacking in humid environment.

Entropy-Driven Enhancement of the Conductivity and Phase Purity of Na4Fe3(PO4)2P2O7 as the Superior Cathode in Sodium-Ion Batteries.

Na4Fe3(PO4)2(P2O7) (NFPP) is regarded as a promising cathode material for sodium-ion batteries (SIBs) owing to its low cost, easy manufacture, environmental purity, high structural stability, unique three-dimensional Na-ion diffusion channels, and appropriate working voltage. However, for NFPP, the low conductivity of electrons and ions limits their capacity and power density. The generation of NaFeP2O7 and NaFePO4 inhibits the diffusion of sodium ions and reduces reversible capacity and rate performance during the manufacturing process in synthesis methods. Herein, we report an entropy-driven approach to enhance the electronic conductivity and, concurrently, phase purity of NFPP as the superior cathode in sodium-ion batteries. This approach was realized via Ti ions substituting different ratios of Fe-occupied sites in the NFPP lattice (denoted as NTFPP-X, T is the Ti in the lattice, X is the ratio of Ti-substitution) with the configurational entropic increment of the lattice structures from 0.68 R to 0.79 R. Specifically, 5% Ti-substituted lattice (NTFPP-0.05) inducing entropic augmentation not only improves the electronic conductivity from 7.1 × 10-2 S/m to 8.6 × 10-2 S/m but also generates the pure-phase of NFPP (suppressing the impure phases of the NaFeP2O7 and NaFePO4) of the lattice structure, which is validated by a series of characterizations, including powder X-ray diffraction (XRD), Fourier transform infrared spectra (FT-IR), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT). Benefiting from the Ti replacement in the lattice, the optimal NTFPP-0.05 composite shows a high first discharge capacity (118.5 mAh g-1 at 0.1 C), superior rate performance (70.5 mAh g-1 at 10 C), and excellent long cycling life (1200 cycles at 10 C with capacity retention of 86.9%). This research proposes a new entropy-driven approach to improve the electrochemical performance of NFPP and reports a low-cost, ultrastable, and high-rate cathode material of NTFPP-0.05 for SIBs.

N-doped dual carbon-layer-modified Na3V2(PO4)3 as a high-performance cathode material for sodium-ion batteries

Na3V2(PO4)3 (NVP) is one of the most potential cathode materials for sodium-ion batteries (SIBs), but its actual electrochemical performance is limited by large electron and ion transfer resistance, resulting in lower rate performance and cycle stability. Herein, N-doped dual-carbon decoration strategy is proposed to solve the above problems of NVP. The N-doped double carbon-wrapped NVP (NVP/NC@CNTs) is successfully synthesized via introducing highly conductive CNTs and carbonization of N-rich urea. The results indicate that the NVP/NC@10 %CNTs composites exhibit a high initial reversible capacity of 106.5 mAh g−1 at 0.1C, with have high rate capability (94.8 mAh g−1 at 5C) and excellent capacity retention at high rates (98.9 % capacity retention at 20C after 2000 cycles). Additionally, the tests of multiple methods (CV, EIS and GITT) exhibit significant improvement in the kinetic properties. More importantly, density functional theory (DFT) calculations confirm that N-doped carbon layers combined with CNTs can significantly reduce the energy bandwidths of the carbon layers and enhance the adsorption energy for Na+, thus increasing the electrical conductivity of the carbon layers and lowering the diffusion energy barrier for Na+. The symmetric full cells are assembled and measured its electrochemical performance. The cells exhibit good compatibility and excellent cycling stability. The excellent performance of NVP/NC@10 %CNTs composites can be attributed to the defects and active site generation of N-doped double carbon co-modified NVP composites, resulting in increased electronic conductivity and diffusion rate of sodium ions.

Perylenetetracarboxylic Diimide Composite Electrodes as Organic Cathode Materials for Rechargeable Sodium-Ion Batteries: A Joint Experimental and Theoretical Study.

The organic semiconductor 3,4,9,10-perylenetetracarboxylic diimide (PTCDI), a widely used industrial pigment, has been identified as a diffusion-less Na-ion storage material, allowing for exceptionally fast charging/discharging rates. The elimination of diffusion effects in electrochemical measurements enables the assessment of interaction energies from simple cyclic voltammetry experiments through the theoretical work of Laviron and Tokuda. In this work, the two N-substituted perylenes, N,N'-dimethyl-3,4,9,10-perylenetetracarboxylic diimide (Me2PTCDI) and N,N'-diphenyl-3,4,9,10-perylenetetracarboxylic diimide (Ph2PTCDI), as well as the parent molecule 3,4,9,10-perylenetetracarboxylic diimide (H2PTCDI) are investigated as thin-film composite electrodes on carbon fibers for sodium-ion batteries. The composite electrodes are analyzed with Raman spectroscopy. Interaction parameters are extracted from cyclic voltammetry measurements. The stability and rate capability of the three PTCDI derivatives are examined through galvanostatic measurements in sodium-ion half-cell batteries and the influence of the interactions on those parameters is evaluated. In addition, self-consistent charge density function tight binding calculations of the different PTCDI systems interacting with graphite have been carried out. The results show that the binding motif displays notable deviations from an ideal ABA stacking, especially for the neutral state. In addition, data obtained for the electron-transfer integrals show that the difference in performance between different PTCDI thin-film batteries cannot be solely explained by the electron-transfer properties and other factors such as H-bonding have to be considered.

NASICON-Type Na3V1.5Cr0.4Fe0.1(PO4)3: High-Voltage and High-Rate Cathode Materials for Sodium-Ion Batteries.

Cationic alteration related to a sodium super ion conductor (NASICON)-structured Na3V2(PO4)3 (NVP) is an effective strategy for formulating high-energy and stable cathodes for sodium-ion batteries (SIBs). In this study, we altered the structure of NVP with dual cations, namely, Cr and Fe, to develop Na3V1.5Cr0.4Fe0.1(PO4)3 cathodes for SIBs with high-rate capability (∼71 mAh g-1 at 100 C) and an extreme cycle life output (∼75 mAh g-1 with 95% capacity retention for 10,000 cycles). These excellent electrochemical properties can be ascribed to the synergistic effects of Cr and Fe in the NVP structure, as verified experimentally and theoretically. Therefore, the proposed cosubstitution method can enhance the performance of SIBs by improving their structural stability, electronic conductivity, and phase-change behavior.

Accelerating the electrochemical kinetics of Na3V2(PO4)3 cathode for high-performance sodium ion batteries with superior cycling stability by Cl− substitution

Na3V2(PO4)3 (NVP) has been recognized as one of most prospective cathode materials of sodium-ion batteries (SIBs) due to its excellent thermal stability and high voltage plateau. Nevertheless, its inherent poor electronic conductivity limits its further large-scale applications. Herein, we propose an efficient strategy to improve electrochemical kinetics of Na3V2(PO4)3 cathode by Cl− doping. The incorporation of Cl effectively enhances the electronic transport pathways within the NVP material. Additionally, it introduces supplementary charge carriers, thereby modulating the internal charge balance of the crystal lattice and mitigating electron confinement. Although the as-prepared Na3V2(PO4)2.8Cl0.6 and pristine NVP material show similar discharge capacity at low rate (0.1C), the former delivers higher capacity at high rates (0.2, 0.5, 1, 2, 5, 10, and 20C), indicating excellent rate performance. Notably, even after 2000 cycles at 10C, Na3V2(PO4)2.8Cl0.6 maintains a capacity retention of approximately 70 %. Remarkably, it retains 63 % of its initial capacity (48.1 mAh/g) after 5000 cycles at the demanding 20C, with a Coulombic efficiency approaching 100 %. These findings underscore the efficacy of Cl doping as a means to enhance the electrochemical properties of NVP, providing valuable insights into the designing of high-performance SIBs cathode materials.

Greener, Safer and Better Performing Aqueous Binder for Positive Electrode Manufacturing of Sodium Ion Batteries.

P2-type cobalt-free MnNi-based layered oxides are promising cathode materials for sodium-ion batteries (SIBs) due to their high reversible capacity and well chemical stability. However, the phase transformations during repeated (dis)charge steps lead to rapid capacity decay and deteriorated Na+ diffusion kinetics. Moreover, the electrode manufacturing based on polyvinylidene difluoride (PVDF) binder system has been reported with severely defluorination issue as well as the energy intensive and expensive process due to the use of toxic and volatile N-methyl-2-pyrrolidone (NMP) solvent. It calls for designing a sustainable, better performing, and cost-effective binder for positive electrode manufacturing. In this work, we investigated inorganic sodium metasilicate (SMS) as a viable binder in conjunction with P2-Na0.67Mn0.55Ni0.25Fe0.1Ti0.1O2 (NMNFT) cathode material for SIBs. The NMNFT-SMS electrode delivered a superior electrochemical performance compared to carboxy methylcellulose (CMC) and PVDF based electrodes with a reversible capacity of ~161 mAh/g and retaining ~83 % after 200 cycles. Lower cell impedance and faster Na+ diffusion was also observed in this binder system. Meanwhile, with the assistance of TEM technique, SMS is suggested to form a uniform and stable nanoscale layer over the cathode particle surface, protecting the particle from exfoliation/cracking due to electrolyte attack. It effectively maintained the electrode connectivity and suppressed early phase transitions during cycling as confirmed by operando XRD study. With these findings, SMS binder can be proposed as a powerful multifunctional binder to enable positive electrode manufacturing of SIBs and to overall reduce battery manufacturing costs.

Achieving Fast and Stable Sodium Storage in Na4Fe3(PO4)2(P2O7) via Entropy Engineering.

Na4Fe3(PO4)2(P2O7) (NFPP) has been considered a promising cathode material for sodium-ion batteries (SIBs) owing to its environmental friendliness and economic viability. However, its electrochemical performance is constrained by connatural low electronic conductivity and inadequate sodium ion diffusion. Herein, a high-entropy substitution strategy is employed in NFPP to address these limitations. Ex situ X-ray diffraction analysis reveals a single-phase electrochemical reaction during the sodiation/desodiation processes and the increased configurational entropy in HE-NFPP endows an enhanced structure, which results in a minimal volume variation of only 1.83%. Kinetic analysis and density functional theory calculation further confirm that the orbital hybrid synergy of high-entropy transition metals offers a favorable electronic structure, which efficaciously boosts the charge transfer kinetics and optimizes the sodium ion diffusion channel. Based on this versatile strategy, the as-prepared high-entropy Na4Fe2.5Mn0.1Mg0.1Co0.1Ni0.1Cu0.1(PO4)2(P2O7) (HE-NFPP) cathode can deliver a prominent rate performance of 55mAhg-1 at 10Ag-1 and an ultra-long cycling lifespan of over 18000cycles at 5Ag-1. When paired with a hard carbon (HC) anode, HE-NFPP//HC full cell exhibits a favorable cycling durability of 1000cycles. This high-entropy engineering offers a feasible route to improve the electrochemical performance of NFPP and provides a blueprint for exploring high-performance SIBs.