Crystallinity Tuning of Na3 V2 (PO4 )3 : Unlocking Sodium Storage Capacity and Inducing Pseudocapacitance Behavior

Accelerating Electrochemical Responses of Na4VMn(PO4)3 via Bulk-Defects and Architecture Engineering for High-Performance Sodium-Ion Batteries

Manganese-based NASICON-type Na4VMn(PO4)3 (NVMP) has captured widespread attention in sodium-ion batteries (SIBs) due to its abundant reserves and high operating voltages. However, the low intrinsic conductivity and detrimental Jahn-teller (J-T) effect impedes its electron and ion transfer, leading to rapid structural degradation and capacity decay. Herein, a facile multiscale coupling strategy is proposed to synthesize the nanosheet-stacked rods (NVMP-NSRs) with rational defects for improving intrinsic conductivity and structural stability, thus accelerating electrochemical responses. Localized unsaturated coordination states around vanadium atoms in NVMP-NSRs are also regulated, further facilitating rapid Na+ diffusion with relieved volume expansion due to the unique architecture design. Density functional theory (DFT) calculations reveal highly rearranged interfacial charges, yielding benefits for reducing the energy barriers of Na+ migration. The innovative NVMP-NSRs with appropriate bulk defects exhibit considerable discharge capacity (120.1 mAh g-1 at 0.5C), high-rate performance (70.9 mAh g-1 at 30C), and negligible capacity decay (3000 cycles at 20C). Moreover, the assembled NVMP-NSRs//hard carbon full cells demonstrate a high energy density of 391.1 Wh kg-1 with excellent cyclic stability (91.2% after 100 cycles at 1C). The multiscale coupling strategy in this work offers new avenues to design high-performance electrode materials toward fast electrochemical responses and robust structural stability.

High-Voltage Cathode Materials for Sodium-Ion Batteries: Advances and Challenges

Sodium-ion batteries (SIBs) gain attention as a promising, cost-effective, and resource-abundant alternative, especially for large-scale energy storage. Cathode materials play a pivotal role in improving the electrochemical performance of SIBs, with high-voltage cathodes providing enhanced energy density and rate capacity, making SIBs suitable for high-power applications. Common cathode materials, such as layered transition metal oxides, polyanionic compounds, and Prussian blue analogs, each offer unique benefits. However, these materials face challenges under high-voltage conditions, such as phase transitions, metal cation migration, oxygen loss, and electrolyte degradation. This review discusses strategies to address these challenges, including elemental doping, surface coatings, modified synthesis methods, and interfacial adjustments, all aimed at enhancing the stability and electrochemical performance of high-voltage cathode materials. Here also explores how full-cell design optimizations can further improve energy and power density. By analyzing material degradation and failure modes, this review offers insights into the development of stable, high-performance SIBs with better safety and broader application potential in energy storage technologies.

Rapid and reversible sodium-ion cathode materials for NASICON Na3MnTiP3-xBxO12 achieved through Boron-substitution

Na3MnTi(PO4)3 is a promising sodium-ion cathode material due to its relatively high specific capacity, excellent thermodynamic stability and low cost. However, unfavorable electron conductivity and slow kinetics limit its practical application. Here, a strategy of hetero and multivalent anion substitution is proposed to achieve high-rate performance and good capacity retention. Specifically, Na3MnTiP3-xBxO12 (x = 0.1, 0.2, and 0.3) doped with boron (B) at the phosphorus (P) site is prepared through sol-gel method. B-doping enhances the continuity of the electron density distribution and induces structural distortions that expand the diffusion channel for Na+, thereby improving electronic conductivity and ionic conductivity. Moreover, due to the differences in coordination and bond strength between BO and PO bonds, B doping mitigates the irreversible structural distortion during changing and discharging, thus enhancing cycle stability. The modified cathode material Na3MnTiP2.8B0.2O12 exhibits impressive rate performance, achieving 77.39 mAh g-1 at 20C, significantly higher than undoped Na3MnTi(PO4)3 (42.35 mAh g-1). Its specific capacity is 126.48 mAh g-1 with a capacity retention of 82.77 % after 1000 cycles at rate of 5C. Importantly, the assembled Na3MnTiP2.8B0.2O12//hard carbon (HC) full battery provides both high capacity and excellent cycling performance, offering valuable insights for the development of high-performance sodium superionic conductor (NASICON) structural cathode materials.

Designing Crystalline/Amorphous NVNPF/NCK Cathode Toward High-Performance Fully-Printed Flexible Aqueous Rechargeable Sodium-Ion Batteries (ARSIBs)

The flexible ARSIBs have great potential in portable and wearable electronics due to their high cost-effectiveness, safety, and amazing flexibility. Nevertheless, achieving both outstanding flexibility and high energy density remains a challenge. Herein, a battery-supercapacitor composite material Na3V1.95Ni0.05(PO4)2F3/10%NC-KOH (NVNPF/NCK) with coexistence of crystalline and amorphous phases is fabricated by loading nitrogenous carbon (NC) onto Na3V1.95Ni0.05(PO4)2F3 (NVNPF) and etching with KOH. It demonstrates high specific capacity (187.26 mAh g-1), ultrahigh energy density (262.16 Wh kg-1), and excellent cycle performance (the capacity retention is 81% at 1 C after 500 cycles). The high performance is achieved by doping Ni2⁺ loading NC and etching with KOH, which generates vacancy defects, enhances structural stability, and accelerates ion-diffusion kinetics. Furthermore, the fully-printed ARSIBs (F-NTP//NVNPF/NCK) with high specific capacity (60.37 mAh g-1), amazing energy density (72.44 Wh kg-1), and excellent cycle performance, are fabricated using screen-printing technique based on the NVNPF/NCK cathode and NaTi1.7Fe0.3(PO4)3 (F-NTP) anode. To the best of the authors' knowledge, F-NTP//NVNPF/NCK is the highest-performing fully-printed flexible ARSIB to date. In particular, these batteries can achieve tunability in shape and size, integration, and high-throughput manufacturing. Thus, this work can offer greater possibilities for the development of high-performance flexible ARSIBs.

Extrinsic Pseudocapacitive CoOOH Achieved by the Suppression of Its Phase Transition Triggered by S2- Doping

The behavior transformation of battery-type materials to extrinsic pseudocapacitive behavior is accomplished by suppressing their phase transition. The resulting extrinsic pseudocapacitive materials are a valuable supplement to intrinsic pseudocapacitive materials, enriching the connotation of pseudocapacitive materials. Nevertheless, the research on this category of materials remains inactive as of now, probably due to the as yet unclear phase transition suppression mechanism and the associated electrochemical mechanism. In this work, the battery-type Co(OH)2 is selected as a research object to create an extrinsic pseudocapacitive material by S2- doping. It is revealed that the K+ intercalation/deintercalation is the essential reason for the phase transition of CoOOH that is irreversibly converted from Co(OH)2, leading to its battery-type behavior. Whereas, the fully protonated CoOOH produced due to the high reaction activity of S2- doped Co(OH)2 only allows the intercalation/deintercalation of H+. During the process of intercalation/deintercalation of H+, CoOOH retains the P3 structure, thereby giving rise to extrinsic pseudocapacitive behavior. The electrochemical measurement results indicate that this extrinsic pseudocapacitive material and the assembled device have electrochemical performance equivalent to that of intrinsic pseudocapacitive materials.

Self-Template Construction of Hierarchical Bi@C Microspheres as Competitive Wide Temperature-Operating Anodes for Superior Sodium-Ion Batteries

Huge volume changes of bismuth (Bi) anode leading to rapid capacity hindered its practical application in sodium-ion batteries (SIBs). Herein, porous Bi@C (P-Bi@C) microspheres consisting of self-assembled Bi nanosheets and carbon shells were constructed via a hydrothermal method combined with a carbothermic reduction. The optimized P-Bi@C-700 (annealed at 700 °C) demonstrates 359.8 mAh g-1 after 1500 cycles at 1 A g-1. In situ/ex situ characterization and density functional theory calculations verified that this P-Bi@C-700 relieves the volume expansion, facilitates Na+/electron transport, and possesses an alloying-type storage mechanism. Notably, P-Bi@C-700 also achieved 360.8 and 370.3 mAh g-1 at 0.05 A g-1 under 0 and 60 °C conditions, respectively. Na3V2(PO4)3//P-Bi@C-700 exhibits a capacity of 359.7 mAh g-1 after 260 cycles at 1 A g-1. These hierarchical microspheres effectively moderate the volume fluctuation, preserving structural reversibility, thereby achieving superior Na+ storage performance. This self-template strategy provides insight into designing high-volumetric capacity alloy-based anodes for SIBs.

Manipulating amorphous and crystalline hybridization of Na3V2(PO4)3/C for enhancing sodium-ion diffusion kinetics

Na3V2(PO4)3 (NVP) has attracted considerable attention as a promising cathode material for sodium-ion batteries (SIBs). But its insufficient electronic conductivity, limited capacities, and fragile structure hinder its extended application, particularly in scenarios involving rapid charging and prolonged cycling. A hybrid cathode material has been developed to integrate both amorphous and crystalline phases, with the objective of improving the rate performance and Na storage capacity by leveraging bi-phase coordination. Consequently, the combination of amorphous and crystalline phases enhanced the kinetics of Na-ion diffusion, resulting in a 1-2 orders of magnitude enhancement in diffusion dynamics. Furthermore, the existence of amorphous states has been demonstrated to elevate the active Na2 site content, resulting in an increased reversible capacity. This assertion is substantiated by evidence derived from solid-state nuclear magnetic resonance (ss-NMR) and electrochemical characteristics. The innovative bi-phase collaborative material provides a specific capacity of 114 mAh/g at 0.2 C, exceptional rate performance of 82 mAh/g at 10 C, and remarkable long-term cycle stability, retaining 95 mAh/g at 5 C even after 300 cycles. In conclusion, the homogeneous hybridization of amorphous and crystalline phases presents itself as a promising and effective strategy for improving Na-ion storage capacity of cathodes in SIBs.

Carbon coated Na3+xV2-xCux(PO4)3@C cathode for high-performance sodium ion batteries

Na3V2(PO4)3 is considered as one of the most promising cathodes for sodium ion batteries owing to its fast Na+ diffusion, good structural stability and high working potential. However, its practical application is limited by its low intrinsic electronic conductivity. Herein, a carbon coated Cu2+-doped Na3V2(PO4)3 cathode was prepared. The carbon coating not only improve its apparent conductivity, but also inhibit crystal growth and prevent agglomeration of particles. Moreover, Cu2+ doping contributes to an enhanced intrinsic conductivity and decreased Na+ diffusion energy barrier, remarkably boosting its charge transfer kinetics. Based on the structure characterizations, electrochemical performances tests, charge transfer kinetics analyses and theoretical calculations, it's proved that such an elaborate design ensures the excellent rate performances (116.9 mA h g-1 at 0.1C; 92.6 mA h g-1 at 10C) and distinguished cycling lifespan (95.8 % retention after 300 cycles at 1C; 84.8 % retention after 3300 cycles at 10C). Besides, a two-phase reaction mechanism is also confirmed via in-situ XRD. This research is expected to promote the development of Na3V2(PO4)3-based sodium ion batteries with high energy/power density and excellent cycling lifespan.

Two Birds with One Stone: V4 C3 MXene Synergistically Promoted VS2 Cathode and Zinc Anode for High-Performance Aqueous Zinc-Ion Batteries

Aqueous zinc-ion batteries (AZIBs) are considered to be a rising star in the large-scale energy storage area because of their low cost and environmental friendliness properties. However, the limited electrochemical performance of the cathode and severe zinc dendrite of the anode severely hinder the practical application of AZIBs. Herein, a novel 3D interconnected VS2 ⊥V4 C3 Tx heterostructure material is prepared via one-step solvothermal method. Morphological and structural characterizations show that VS2 nanosheets are uniformly and dispersedly distributed on the surface of the V4 C3 MXene substrate, which can effectively suppress volume change of the VS2 . Owing to the open heterostructure along with the high conductivity of V4 C3 MXene, the VS2 ⊥V4 C3 Tx cathode shows a high specific capacity of 273.9 mAh g-1 at 1 A g-1 and an excellent rate capability of 143.2 mAh g-1 at 20 A g-1 . The V4 C3 MXene can also effectively suppress zinc dendrite growth when used as protective layer for the Zn anode, making the V4 C3 Tx @Zn symmetric cell with a stable voltage profile for ≈1700 h. Benefitting from the synergistic modification effect of V4 C3 MXene on both the cathode and anode, the VS2 ⊥V4 C3 Tx ||V4 C3 Tx @Zn battery exhibits a long cycling lifespan of 5000 cycles with a capacity of 157.1 mAh g-1 at 5A g-1 .

In Situ Constructing Ultrafast Ion Channel for Promoting High-Rate Cycle Stability of Nano-Na3V2(PO4)3 Cathode

Encapsulating nanomaterials in carbon is one of the main ways to increase the cathode stability, but it is difficult to simultaneously optimize the rate capacity and enhance durability derived from the insufficient ion transport channels and deficient ion adsorption sites that constipate the ion transport and pseudocapacitive reaction. Herein, we develop the ligand-confined growth strategy to encapsulate the nano-Na3V2(PO4)3 cathode material in various carbon channels (microporous, mesoporous, and macroporous) to discriminate the optimal carbon channels for synchronously improving rate capacity and holding the high-rate cycle stability. Benefiting from the unobstructed ion/charge transport channels and flexible maskant created by the interconnected mesoporous carbon channels, the prepared Na3V2(PO4)3 nanoparticles confined in mesoporous carbon channel (Mes-NVP/C) achieve a discharge-specific capacity of 70 mAh g-1 even at the ultrahigh rate of 100 C, higher than those of the Na3V2(PO4)3 nanoparticles confined in microporous and macroporous carbon channel (Micr-NVP/C and Macr-NVP/C), respectively. Significantly, the capacity retention rate of Mes-NVP/C after 5000 cycles at 20 C is as high as 90.48%, exceeding most of the reported work. These findings hold great promise for traditional cathode materials to synergistically realize fast charging ability and long cycle life.

Conductive Ti3C2Tx networks to optimize Na3V2O2(PO4)2F cathodes for improved rate capability and low-temperature operation

Na₃V₂O₂(PO₄)₂F (NVOPF) is gaining attention as a high-energy cathode candidate for sodium-ion batteries owing to its wide operating voltage, high energy density and excellent thermal stability. However, its intrinsic poor electrical conductivity results in its current sodium-storage performance being far below expectations. Herein, two-dimensional Ti₃C₂T_x MXene nanosheets with excellent electrical conductivity are introduced to construct an interconnected conductive framework to tightly encapsulate NVOPF nanoparticles. The Ti₃C₂T_x nanosheets ensure superior electronic contacts, along with inhibiting the agglomeration of NVOPF nanoparticles, thus accelerating electron and ion transfer during sodium-ion de/intercalation and maximizing the storage capacity. As a result, the optimized NVOPF/Ti₃C₂T_x cathode exhibits high rate capabilities (111 mA h g^-1 at 0.2 C and 78 mA h g^-1 at 20 C), with an impressively high capacity retention of 74.8% over a wide temperature range (from -20 to 20 °C). Additionally, the assembled sodium-ion full cell provides a highly reversible capacity of 116 mA h g^-1 at 1 C, with a capacity retention of 67.2% after 100 cycles. These inspiring results provide new insights for improving the charge-transfer kinetics of the NVOPF cathode and this methodology may be extended to other cathode materials.