Sodium Ion Diffusion Research Articles

Surface structure reconstruction to suppress heterogeneous phase transformation for air-stable single crystalline O3-type sodium oxide

O3-type layered oxide cathode material for sodium-ion batteries (SIBs) has attracted much attention as one of the most viable candidates due to its high specific capacity and mature synthesis process, while the moisture sensitivity and harmful phase transformation lead to poor processing properties and unsatisfactory life-span, hindering its large-scale and commercial application. Herein, single crystallization strategy is adopted to enhance air stability and processing performance, and surface structure reconstruction for single crystalline cathode material O3-NaNi1/3Fe1/3Mn1/3O2 by ammonium tetraborate pretreatment is employed to further remove residual alkali and improve sodium ions diffusion dynamics and suppress heterogeneous phase transformation, achieving superior structure stability. Surface residual alkali is in-situ converted into a protective coating layer of Na2B4O7 and meanwhile partial B atoms enter into the interstitial site of sub-surface or near surface, which accelerates sodium ions transport as well as enhances TM-O bonding and hybridization of surface O (2p)-Fe (3d-t2g) orbital, inhibits TMO6 slabs gliding and strengthens structure on the surface and near surface. Additionally, the formed boron-rich surface exhibits high stability, effectively alleviating structural degradation from surface to bulk and enhancing air stability. Benefiting from the reconstructed surface structure, the modified single crystalline oxides (NFM@B) exhibit distinguished processing performance and electrochemical properties.

Optimizing the crystal structure and electrochemical properties of Na4MnCr(PO4)3 by trace La doping

Na4MnCr(PO4)3, a manganese-based NASICON-type phosphate cathode material, is attracted considerable attention due to its high voltage and energy density. However, its practical application is hindered by poor electronic conductivity and inferior sodium ion diffusion kinetics. In this study, trace La3+ is utilized to optimize the lattice structure of Na4MnCr(PO4)3 due to its unique energy level structure. La3+ doping significantly enhances the local environment of the Mn-O bond and stabilizes the lattice structure by improving covalency, thereby mitigating Mn dissolution during charge–discharge cycles. Additionally, the large ionic radius of La3+ promotes the sodium ion transport kinetics by expanding the cell volume and facilitating rapid sodium storage. As a result, the optimal Na4MnCr0.995La0.005(PO4)3/C sample demonstrates an impressive initial discharge specific capacity of 124.5 mAh g−1 at 0.1C and superior cycling stability with a capacity retention of 70.2 % after 500 cycles at 5C. Furthermore, density functional theory calculations indicate that La3+ doping can enhance conductivity and reduce the energy barrier for sodium ion diffusion. This study presents an effective and cost-efficient doping strategy for modifying high-energy density NASICON-type phosphate cathode materials, showing promising potential in the field of sodium ion batteries.

Mn vacancy engineering design of Fe/Mn based cathodes for breaking the spell between “sodium limiting” in air-stabilization and “sodium promoting” on kinetics

Fe/Mn-based cathode is considered a viable choice for sodium-ion batteries (SIBs) because of its affordability and high theoretical capacity. Nonetheless, bad actually comprehensive performance still impede its commercial application. In this work, based on the systematic study of P2-Na2/3Fe1/2Mn1/2O2 cathode materials with fewer Mn vacancies (NFM-Q), we realized a superior rate, cycling performance, air stability and more importantly unraveled the operation mechanism. Specifically, dual function of fewer Mn vacancies were explicitly clarified, which included the effect of shrinking sodium layers and the sodium-ion diffusion promoting effect, as confirmed by combining XRD, XANES, XAFS, EIS and GITT. So Mn vacancy engineering had the potential to break the contradiction between “sodium limiting” based on air-stabilization mechanism and “sodium promoting” based on kinetics. This has rarely been found before. And a series of characterizations strongly declared rapidly cooling rate could effectively regulated the creation of Mn vacancies. As a result, NFM-Q cathode not only delivered outstanding discharge capacity (192.7 mAh/g), cycling stability (123.8 mAh/g, 65 %, after 50 cycles) and energy density (574.0 Wh Kg−1), but also possessed splendid air stability (185.8 mA h/g, 61.8 % after 50 cycles and immersion). Moreover, ex-situ XRD and XAS further expounded structural evolution and charge compensation mechanism of NFM-Q cathode, confirming its superior performance. This work might offer fresh understanding about the roles of Mn vacancy engineering, which could open up new possibilities on the material design and the property improvement of Fe/Mn-based cathodes.

Interface engineering-induced enhancements in sodium-ion batteries: A nexus of ZnS nanoparticles and reduced graphene oxide for augmented storage and conductivity

Due to the inherent sluggish kinetics and the pronounced volumetric expansion of zinc sulfide (ZnS), it has become a prevalent modification strategy to regulate its morphology and composite with graphene for using ZnS as anodes in sodium-ion batteries (SIBs). Nevertheless, the elucidation of mechanisms underpinning the electrochemical performance facilitated by graphene incorporation remains scant. To further describe the synergistic mechanism, the ultrafine ZnS nanoparticles anchored on reduced graphene oxide (rGO) were synthesized through a simple solvothermal method. Research shows that the ZSG (ZnS nanoparticles-reduced graphene oxide composite) electrode suggests superior rate capability, maintaining a reversible specific capacity of 228.6 mAh·g−1 upon returning from a high current density of 5 A·g−1. Furthermore, the nanoscale integration of ZnS particles with rGO synergistically mitigates the structural expansion of the ZSG electrode encountered during cycling, thereby decelerating the degradation of cyclic performance. Insights gleaned from first-principles calculations and comprehensive electrochemical evaluations reveal that the built-in electric field, engendered within the composite architecture, substantially augments charge transfer ability and mitigates the energy barriers impeding sodium ion (Na+) diffusion accordingly. Consequently, the methodology adopted for synthesis and the synergistic modification mechanism can proffer a reference for the design of advanced anode materials in SIBs.

Enhancing Na+ diffusion dynamics and structural stability of O3-NaMn0.5Ni0.5O2 cathode by Sc and Zn dual-substitution

Sc and Zn were introduced into O3-NaMn0.5Ni0.5O2 (NaMN) using the combination of solution combustion and solid-state method. The effect of Sc and Zn dual-substitution on Na+ diffusion dynamics and structural stability of NaMN was investigated. The physicochemical characterizations suggest that the introduction of Sc and Zn broaden Na+ diffusion channels and weaken the Na—O bonds, thereby facilitating the diffusion of sodium ions. Simulations indicate that the Sc and Zn dual-substitution decreases the diffusion barrier of Na-ions and improves the conductivity of the material. The dual-substituted NaMn0.5Ni0.4Sc0.04Zn0.04O2 (NaMNSZ44) cathode delivers impressive cycle stability with capacity retention of 71.2 % after 200 cycles at 1C and 54.8% after 400 cycles at 5C. Additionally, the full cell paired with hard carbon anode exhibits a remarkable long-term cycling stability, showing capacity retention of 64.1% after 250 cycles at 1C. These results demonstrate that Sc and Zn dual-substitution is an effective strategy to improve the Na+ diffusion dynamics and structural stability of NaMN.

Binder-free Cu-Sb-Sn-Zn-P alloys as high-efficiency anodes for sodium-ion batteries via double-pulse electrodeposition

Alloy anodes are widely recognized for their high theoretical specific capacity and have garnered significant attention among the anode materials studied for sodium-ion batteries. In this study, we synthesize Cu68.6Sb23.0Sn3.2Zn0.3P4.9 anodes using a double-pulse electrodeposition method. This binder-free alloy anode, comprising five high-capacity elements, significantly enhances specific capacity and improves cycling stability, while also demonstrating excellent sodium storage capability. Specifically, the Cu68.6Sb23.0Sn3.2Zn0.3P4.9 anode achieves an initial charge capacity of 368.8 mAh∙g−1 and remains highly stable over 100 cycles, with a capacity decay of only 0.1 %. In addition, the anode delivers 290.3 mAh∙g−1 even at a current density of 3200 mA∙g−1. The outstanding electrochemical performance can be attributed to improved electronic transfer efficiency due to the introduction of Cu into Cu68.6Sb23.0Sn3.2Zn0.3P4.9 alloy via reverse potential, as well as the porous structure that facilitates electrolyte penetration and sodium ion transport. The galvanostatic intermittent titration technique reveals a high sodium ion diffusion coefficient, further highlighting the potential of this alloy anode in advancing sodium-ion batteries.

Structural modulation of Na4Fe3(PO4)2P2O7 via cation engineering towards high-rate and long-cycling sodium-ion batteries

Mixed iron-based phosphate Na4Fe3(PO4)2P2O7/C (NFPP) has gradually emerged as a promising cathode material for sodium-ion batteries (SIBs) owing to its affordability and convenient preparation. However, poor electrical conductivity and inadequate sodium-ion diffusion limit the exertion of its electrochemical properties. Herein, a structural modulation strategy based on Cd doping is applied to NFPP to address the above limitations. In situ X-ray diffraction analysis reveals that Cd-doped NFPP (NFCPP) undergoes an incomplete solid-solution reaction driven by Fe2+/Fe3+ redox. Cd doping effectively stabilises the crystal structure, resulting in a minimal 1 % change in unit cell volume during cycling. Density of state calculations indicate that Cd doping reduces the band gap, increases the local electron density and significantly improves electron conductivity. Benefitting from the enhanced electrochemical kinetics and intercalation pseudocapacitance, the optimised Na4Fe2.91Cd0.09(PO4)2P2O7/C (NFCPP@3%) exhibits exceptional rate performance (capacity of 62 mAh/g at 20 C) and ultra-long cycling life (82.7 % after 6000 cycles at 20 C). A full SIB prepared using NFCPP@3% and hard carbon, display a 91 % capacity retention rate at a current density of 130 mA g−1 over 200 cycles. This work demonstrates that doping can effectively enhance electrochemical performance and offers insights into future development of SIBs.

A general methodology for the in situ construction of MxSy@N,S-C composites from L-cysteine for sodium-ion battery applications

High-capacity metal sulfides have been extensively investigated as cathode materials for secondary batteries. Despite their high capacity, the redox potential of metal sulfides is limited to 2.7 V. Therefore, researchers explored its application as a negative electrode material and discovered its exceptional electrochemical performance. However, the conventional methods for synthesizing transition metal sulfides (TMS) inevitably require an external source of sulfur for secondary sulfidation, resulting in energy dissipation. In this study, L-cystine was adopted as a polydentate ligand for the synthesis of MxSy@N, SC metal-organic frameworks, which can confine the desired carbon, nitrogen, and sulfur sources within the framework. This approach facilitates one-step sintering to obtain nitrogen-doped transition metal sulfides. The structure composition and electrochemical reaction mechanism of FeS@N,S-C as the negative electrode in Na-ion batteries were studied through scanning electron microscopy (SEM)/transmission electron microscopy (TEM) and X-ray diffraction (XRD)/X-ray photoelectron spectroscopy (XPS) analysis. The electrochemical properties of FeS@N,S-C materials were test as an example. The FeS@N, SC composite exhibited a reversible Na+ storage capacity of 724.4 mAh g−1 at a current density of 200 mA g−1, and still maintained a reversible capacity of 600.7 mAh g−1 at a current density of 2000 mA g−1, demonstrating excellent rate performance. After 200 cycles, the material was still able to retain 97.3 % of the discharge specific capacity, demonstrating fine cycle performance. It shows that the FeS@N, SC composite has rapid electron conduction ability and high sodium ion diffusion coefficient. At the same time, a rapidly charge-discharge process can be achieved with a large capacitive contribution, indicating the great potential of this material as a sodium-ion battery.

Prussian White/Reduced Graphene Oxide Composite as Cathode Material to Enhance the Electrochemical Performance of Sodium-Ion Battery.

Prussian white (PW) is considered a promising cathode material for sodium-ion batteries. However, challenges, such as lattice defects and poor conductivity limit its application. Herein, the composite materials of manganese-iron based Prussian white and reduced graphene oxide (PW/rGO) were synthesized via a one-step in situ synthesis method with sodium citrate, which was employed both as a chelating agent to control the reaction rate during the coprecipitation process of PW synthesis and as a reducing agent for GO. The low precipitation speed helps minimize lattice defects, while rGO enhances electrical conductivity. Furthermore, the one-step in situ synthesis method is simpler and more efficient than the traditional synthesis method. Compared with pure PW, the PW/rGO composites exhibit significantly improved electrochemical properties. Cycling performance tests indicated that the PW/rGO-10 sample exhibited the highest initial discharge capacity and the best cyclic stability. The PW/rGO-10 has an initial discharge capacity of 128 mAh g-1 at 0.1 C (1 C = 170 mA g-1), and retains 49.53% capacity retention after 100 cycles, while the PW only delivers 112 mAh g-1 with a capacity retention of 17.79% after 100 cycles. Moreover, PW/rGO-10 also shows better rate performance and higher sodium ion diffusion coefficient (DNa+) than the PW sample. Therefore, the incorporation of rGO not only enhances the electrical conductivity but also promotes the rapid diffusion of sodium ions, effectively improving the electrochemical performance of the composite as a cathode material for sodium-ion batteries.

Facilitating superior electrochemical efficacy and ultra rapid kinetic in Co/Ni-free layered oxides for sodium-ion batteries with phosphate-growing layer fast ion conductors

Co/Ni-free layered oxides have garnered significant interest due to their environmental friendliness and facile synthesis methodologies, while facing major challenges of inferior cycling stability and rate capability. Addressing these drawbacks necessitates the enhancement of the surface properties of Co/Ni-free layered oxides. This work introduces a Co/Ni-free layered oxide, Na0.67Mn0.65Fe0.3Al0.05O2 (NMFA), which has been subjected to phosphate-based surface engineering. This targeted surface modification aims to augment the specific surface area and establish a protective layer on NMFA. Such improvements are critical for expanding the effective electrochemical reaction zone, broadening sodium ion diffusion pathways, curtailing the P2-OP4 phase transition, and reducing the activation energy for interfacial charge transfer. This multifaceted surface treatment epitomizes the ingenious design and realization of advanced Co/Ni-free layered oxide cathode materials through straightforward processing techniques. Notably, the NMFA subjected to 3%-AlPO4 surface modification demonstrated an initial discharge capacity of 189.1 mAh/g at 0.1C, maintaining its capacity after 500 cycles at 10C. Additionally, DFT calculations corroborate that such surface growth can bolster electrical conductivity, restrain oxygen liberation and foster sodium ion migration. This elucidates that the phosphate growth layer serves as the oxygen reservoir. Accordingly, this investigation propounds a promising avenue to circumvent the challenges confronting Co/Ni-free layered oxides, thus paving the way for the development of high-performance cathode materials.

Effects of multi-element composition regulation on the structure and electrochemistry of P2-type layered cathode materials

P2-type Mn-based oxides are promising cathode materials for sodium-ion batteries due to their low cost and high capacity virtue. However, the irreversible phase transition and unstable anion redox at high operating voltages (∼4.2 V) will cause structural distortions, leading to slow sodium-ion diffusion kinetics and severe capacity degradation. Herein, a multi-elemental composition regulation strategy is proposed to enhance the structural stability of P2-type cathode by optimizing the structure and modulating the irreversible oxygen redox during high-voltage cycling. A series of multi-element cathodes Na0.67(Fe1/4Co1/4Ni1/4Ti1/4)1-xMnxO2 (x = 0.4,0.5,0.6,0.7,0.8,0.9) are designed and the effects of component modulation on their structure and electrochemical behavior are systematically investigated. Especially, the optimized Na0.67Fe0.05Co0.05Ni0.05Ti0.05Mn0.8O2 cathode maintains P2 phase during the initial charging/discharging between 1.5 V and 4.5 V, inhibits irreversible oxygen redox, and exhibits small lattice expansion. Impressively, the above optimized cathode exhibits superior cycling stability with capacity retention of nearly 90 % and reversible capacity of 130.1 mAhg−1 after 100 cycles at 1C rate. Furthermore, the optimized cathode also displays an excellent rate capability (capacity of 108.2 mAh g−1 at 5 C rate) due to the enhanced Na+ diffusion kinetics. This work provides new insight into developing high-stable Mn-based oxide cathodes operating at high voltage for sodium-ion batteries.

High-energy bimetallic substituted Na3V2(PO4)3 cathode for advanced sodium-ion batteries

NASICON-type cathodes have attracted great attention due to their open three-dimensional (3D) frame structure and excellent ion transport properties. Accordingly, how to improve the stability and energy density of materials is a hot topic of research. In this study, the significant effects of aluminum-zirconium bimetallic substitution on electrode kinetics and structural stability are reported. The designed Na2.9V1.8Al0.1Zr0.1(PO4)3 cathode exhibits a highly reversible capacity of 107 mAh g-1 at 1C and decent cyclic stability (75 mAh g-1 capacity after 2000 cycles at 20C). These excellent electrochemical properties can be attributed to expanding the lattice structure and activating part of V4+, which facilitates the migration of Na+ and increases the reversible capacity. The cyclic voltammetry, electrochemical impedance spectra and galvanostatic intermittent titration technique tests analyze the diffusion kinetics of sodium ions and confirm the desired sodium ion diffusion coefficients (DNa+). In situ X-ray diffraction reveals reversible structural changes during the electrochemical reaction, which confirms that the bimetallic doping strategy slows down material volume change. This work provides a new perspective for the construction of high-performance NASICON cathode materials.

Structural basis of inhibition of human NaV1.8 by the tarantula venom peptide Protoxin-I.

Voltage-gated sodium channels (NaVs) selectively permit diffusion of sodium ions across the cell membrane and, in excitable cells, are responsible for propagating action potentials. One of the nine human NaV isoforms, NaV1.8, is a promising target for analgesics, and selective inhibitors are of interest as therapeutics. One such inhibitor, the gating-modifier peptide Protoxin-I derived from tarantula venom, blocks channel opening by shifting the activation voltage threshold to more depolarised potentials, but the structural basis for this inhibition has not previously been determined. Using monolayer graphene grids, we report the cryogenic electron microscopy structures of full-length human apo-NaV1.8 and the Protoxin-I-bound complex at 3.1 Å and 2.8 Å resolution, respectively. The apo structure shows an unexpected movement of the Domain I S4-S5 helix, and VSDI was unresolvable. We find that Protoxin-I binds to and displaces the VSDII S3-S4 linker, hindering translocation of the S4II helix during activation.

Regulating the Pore Structure of Biomass-Derived Hard Carbon for an Advanced Sodium-Ion Battery.

Biomass-derived hard carbon materials are attractive for sodium-ion batteries due to their abundance, sustainability, and cost-effectiveness. However, their widespread use is hindered by their limited specific capacity. Herein, a type of bamboo-derived hard carbon with adjustable pore structures is developed by employing a ball milling technique to modify the carbon chain length in the precursor. It is observed that the length of the carbon chain in the precursor can effectively control the rearrangement behavior of the carbon layers during the high-temperature carbonization process, resulting in diverse pore structures ranging from closed pores to open pores, which significantly impact the electrochemical properties. The optimized hard carbon with abundant closed pores exhibits a high specific capacity of 356 mAh g-1 at 20 mA g-1, surpassing that of bare hard carbon (243 mAh g-1) and hard carbon with abundant open pores (129 mAh g-1 at 20 mA g-1). However, the kinetic analysis reveals that hard carbon with open pores shows better sodium-ion diffusion kinetics, indicating that a balance between the closed and open pores should be considered. This research offers valuable insights into pore design and presents a promising approach for enhancing the performance of hard carbon anode materials derived from biomass precursors.

Improving High-Voltage Cycling Stability and High-Rate Capability of Sodium-Ion Layered Cathode Oxides through Trace Amounts of Low-Valence Metals.

With the increasing demand for clean energy sources, the need for large-scale energy storage systems to ensure the stable output of renewable energy sources, such as wind and solar, has also increased. Sodium-ion batteries have emerged as a potential solution for these storage systems owing to their high energy density, abundance in the Earth's crust, and low cost. However, the larger atomic radius of sodium ions results in higher energy barriers for ion migration in cathode materials, which can affect the cycle life and rate performance of the battery. Therefore, developing a suitable structure that facilitates rapid sodiation and desodiation and maintains good cycling stability remains a significant challenge. This study aimed to reduce the content of trivalent manganese ions and minimize the impact of the Jahn-Teller effect to enhance the capacity retention of manganese-based layered oxides. Additionally, a series of P2-type Na0.78Li0.1ZnxNi0.15-xMn0.75O2 compounds were successfully synthesized through doping with divalent zinc ions. Structural analyses of the doped material indicated that Zn doping did not alter the crystal structure but increased the interlayer distance of the transition metals. Electrochemical performance tests revealed that appropriate Zn2+ doping promoted sodium-ion diffusion and improved the reversible capacity of the battery. This study provides a promising approach for developing sodium-ion batteries with rapid charging and discharging capabilities.

Co doping in NASICON-structured Na3.5MnTi(PO4)3 enables superior structural stabilization and rate performance

NASICON-type Na3MnTi(PO4)3 has been regarded as one of the most ideal cathodes due to its high earth content elements and considerable cycling stability. However, poor electrical conductivity, low redox potential of Ti3+/4+ and undesirable rate performance remain restrict its practical application. Herein, a series of Co-doping Na3.5MnTi1-xCox(PO4)3 (x = 0, 0.05, 0.07 and 0.10) cathode materials are designed via the sol-gel method. By partial substitution with Co, the capacity contribution of the Mn2+/3+and Mn3+/4+ is increased and the rate performance is significantly enhanced. The Na3.5MnTi0.93Co0.07(PO4)3 (NMTP-0.07) delivers a high capacity (150.5 mA h g−1 at 0.1 C), superior rate performance (112.0 mA h g−1 at 10 C) and excellent cycling performance (94.7 % capacity retention after 100 cycles at 1 C). Benefiting from Co doping, the EIS and GITT affirm the superior sodium ion diffusion ability of NMTP-0.07 and the enhancement of its own conductivity. Moreover, in situ XRD measurement validates the highly reversible structural evolution and both solid-solution reaction and two-phase reaction are involved in the sodiation/desodiation process. This contribution provides a new perspective on the doping studies of NASICON materials.

High-entropy doping NASICON[sbnd]Cathode breaks the kinetic barriers and suppresses voltage hysteresis for sodium ion batteries

The NASICON-type Na3MnTi(PO4)3 material has garnered widespread attention for its stable three-dimensional structure, rapid sodium-ion transport channels and excellent thermal stability. However, its poor electronic conductivity, cyclic stability and structural decay during cycling have posed significant obstacles to its commercialization. Herein, a high-entropy doping Na3.12MnTi0.9(VFeMgCrZr)0.02(PO4)3 cathode was successfully synthesized, exhibiting a high reversible capacity of 169.6 mAh g-1 and a high energy density of over 500 Wh kg-1. The DFT and machine learning MD results show that benefiting from the high-entropy effect of multi-element synergy in HE-NMTP, the electronic conductivity and sodium ion diffusion kinetics are significantly improved. Simultaneously, the voltage hysteresis and energy loss are mitigated, while crystal structural stability is improved. Furthermore, the full-cell achieves an impressive energy density of 440 Wh kg-1 (for cathode) at 0.2C. These results demonstrate the advantages of the high-entropy doping cathode as a potential cathode material for sodium-ion batteries and provide a valuable strategy for other NASICON system cathodes as well as polyanion cathodes.

Deep insights into the sodium transport mechanism and phase evolution in Na4VP2O9 cathode/anode material

For the entire intercalation/deintercalation range of Na4VP2O9, quantum mechanics is applied to investigate sodium transport mechanism and a machine learning force field is used instead of ab initio method to offers an applicable method for the full understanding of the complicated Na + movements dynamically. It shows chain of '8′ shaped units horizontally and repeated alternating round aggregate and '8′ shaped long chain vertically. For primitive Na4VP2O9, facile Na+ transportation along a-axis is observed with an energy barrier of 0.16 V. As a cathode material, Na3VP2O9 also shows fast Na + diffusion with a minimal diffusion energy barrier 0.27 eV along a-axis. However, for the fully sodiated state of Na4VP2O9, Na+ diffusion in the lattice is significantly restricted with an energy barrier of 0.92 eV along b-axis. Accordingly, the sodium ion diffusion coefficients at room temperature for Na3VP2O9, Na4VP2O9 and Na5VP2O9 are 1.2 × 10−9 cm2 s−1, 5.9 × 10−9 cm2 s−1 and 8.2 × 10−11 cm2 s−1, respectively. The formation energy convex hull originated from the removal of Na1 sites and the occupation of E8cO8 cavities reveals an intermediate phase, Na3.5VP2O9, for the NaxVP2O9 (3 ≤ x ≤ 4) and three intermediate phases, Na4.5VP2O9, Na4.625VP2O9 and Na4.75VP2O9, for the NaxVP2O9 (4 ≤ x ≤ 5).

Lithium substitution modulation of P2-type manganese-rich oxide toward high-stable and high-voltage cathode for sodium-ion batteries

P2-type manganese-rich layered oxide have attracted much attention as cathodes of sodium-ion batteries owing to the low cost, high capacity and fast sodium ion diffusion kinetics. However, the Jahn-Teller effect of Mn3+, P2-O2 phase transition and anionic redox on charging to the high-voltage, resulted in a severe capacity delay. Herein, an effective Li substitution strategy is proposed to suppress the Jahn-Teller effect of Mn3+, the harmful phase transition of P2-O2 and the anionic redox. As a result, the as-prepared sample Na0.67(Ni0.25Mn0.75)0.9Li0.1O2 (67L10) displays a discharge specific capacity of 168.6 mA h g−1 at 0.1 C, enhanced average working voltage, and improved cycling stability at 1 C after 200 cycles within 1.5–4.5 V voltage window (capacity retention of 83.3 %, specific capacity of 106.8 mA h g−1) compared with that of pristine Na0.67Ni0.25Mn0.75O2(capacity retention of 34.2 %, specific capacity of 51.3 mA h g−1). This work demonstrates the favorable effect of Li doping in P2-type layered materials to suppress the phase transition and inhibit the redox activity of Mn and O ions, and it provides an effective approach for the development of cathodes for sodium-ion batteries with high specific energy and long life.

Coal-derived flaky hard carbon with fast Na+ transport kinetic as advanced anode material for sodium-ion batteries

Hard carbon (HC) has demonstrated a significant potential in anode for sodium-ion batteries (SIBs) due to its superior electrochemical properties. Coal is considered a promising hard carbon precursor due to its high carbon yield. However, the widespread adoption of coal-derived HC faces challenges such as limited storage capacity and decreased rate performance, primarily attributed to the dense structure of coal. In this study, a molten salt-assisted approach was developed to adjust the microstructure of coal-derived HC. The dense coal is etched into a flaky structure by molten salt, which is conducive to the diffusion and transport of sodium ions. The optimized HC materials possess large interlayer spacing and abundant pseudo-graphitic domains, exhibiting a remarkable reversible capacity of 303.6 mA h g−1 at 30 mA g−1 and 82.1 mA h g−1 at 500 mA g−1. Besides, a full cell with the configuration of as-prepared coal derived HC versus Na3V2(PO4)2O2F (NVPOF) is presented with a high initial coulombic efficiency of 76.15 % and capacity of 100.7 mA h g−1. The results indicate that our synthesis strategy is feasible for the application of coal derived carbon materials in SIBs.