Cathode For Sodium-ion Batteries Research Articles

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.

Boosting sodium-ion battery performance by anion doping in NASICON Na4MnCr(PO4)3 cathode

Na superionic conductor (NASICON)-structured Na4MnCr(PO4)3 (NMCP) possessing unique three-electron transfer process renders admirable energy density for sodium ion batteries (SIBs). However, the current issues like its sluggish Na+ diffusion kinetics, deficient intrinsic conductivity, and unsatisfactory structural stability, hinder its practical application. Herein, a selective replacement of O elements in PO4 group by Cl anions in the NMCP system was developed to significantly enhance its electrochemical performance. The results affirm that the enhanced performance of Cl doped samples can be attributed to the enlargement of cell size, the creation of Na vacancies and the weakness of Na2O bond after Cl doping. The as-prepared Na3.85□0.15MnCr(PO3.95Cl0.05)3/C (NMCPC − 15/C) cathode delivers a high capacity (128.0 mAh/g at 50 mA g−1) and excellent rate performance (73.0 mAh/g at 1000 mA g−1) in contrast to NMCP/C that merely provides 105.2 mAh/g at 50 mA g−1 and reduces to 47.4 mAh/g at 1000 mA g−1. Meanwhile, NMCPC − 15/C shows a capacity retention of 60.7 % at 1000 mA g−1 after 500 cycles, while only 37.1 % for NMCP/C in the same test conditions. Moreover, the satisfactory performance and energy density of NMCPC − 15/C||hard carbon (HC) full cell confirm the potential practicality of NMCPC − 15. Therefore, chloride ions doping into NMCP has practical application prospects in the preparation of high-performance cathode materials and our work also offers new inspiration to apply anion doping strategies in promoting the performance of the other NASICON-structured cathodes for SIBs.

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).

Low‐Temperature Sodium‐Ion Batteries: Challenges and Progress

AbstractAs an ideal candidate for the next generation of large‐scale energy storage devices, sodium‐ion batteries (SIBs) have received great attention due to their low cost. However, the practical utility of SIBs faces constraints imposed by geographical and environmental factors, particularly in high‐altitude and cold regions. In these areas, the low‐temperature (LT) performance of SIBs presents a pressing technological challenge that requires significant breakthroughs. In LT environments, the electrochemical reaction kinetics of SIBs are sluggish, the electrode/electrolyte interface is unstable, and the diffusion of sodium ions in electrode materials is slow, leading to a decrease in battery performance. Therefore, the reasonable design of electrolyte and electrode materials is of great significance for optimizing the LT performance of SIBs. In this review, the research progress of LT SIBs electrolytes, cathode, and anode materials, as well as sodium metal batteries and solid‐state electrolytes is systematically summarized in recent years, aiming to understand the design principles of LT SIBs, clarify the basic research and development of high‐performance SIBs in practical applications, and promote the development of SIBs technology in the full temperature range.

Fast-charge high-voltage layered cathodes for sodium-ion batteries

Fast-charge high-voltage layered cathodes for sodium-ion batteries

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.

Modulating the oxygen redox activity of an ultra-high capacity P3 type cathode for sodium-ion batteries via beryllium introduced

Sodium-ion batteries (SIBs) show great potential for energy storage due to their good electrochemical properties and intrinsic cost performance, and sodium-ion cathode materials with high capacity and stable structure are the inevitable future development trend. While conventional anionic redox-active layered oxide cathode materials offer the advantage of extra capacity, challenges such as irreversible oxygen release still need to be addressed. Herein, beryllium is successfully introduced into P3-NaxLiyMn1-yO2 series of layered oxide materials for the first time, and the developed P3-Na0.6Li0.2Be0.25Mn0.675O2 (NLBMO) with the modulation of lattice oxygen activity can reach an ultra-high reversible capacity of 212.6 mAh g−1, significantly surpassing the P3-Na0.6Li0.2Mn0.8O2 (NLMO, 165.7 mAh g−1). Based on a comprehensive comparison with the P3-NLMO, the effect of beryllium on the Mn/O charge complementary mechanism is revealed. Since the strong covalency of beryllium can inhibit the oxidation of excess O through the formation of stable Be-O bonds, while irreversible peroxidation of partially unstable (O2)n− occurs to stimulate more Mn4+/Mn3+ to replace O for charge compensation. As a result, pollution and structural damage caused by O peroxidation are effectively suppressed while achieving ultra-high capacity. In-situ XRD reveals that P3-NLBMO exhibits high structural reversibility during charging and discharging processes, indicating that the formation of Be-O bonds can also further stabilize the crystal structure during cycling. Therefore, beryllium modification strategy proposed in this work provides a novel route to synthesize novel SIBs cathode materials with higher performance.

Entropy-Enhanced Multi-Doping Strategy to Promote the Electrochemical Performance of Na4Fe3(PO4)2P2O7.

Sodium-ion batteries (SIBs) have been regarded as promising candidates for large-scale energy storage system, and their electrochemical performance is determined by the cathode materials. Recently, the polyanion-type cathode Na4Fe3(PO4)2P2O7 (NFPP) demonstrates decent performance, while there exists promotion space with respect to its cycle stability and rate capability. Herein, an entropy-enhanced Na4Fe2.95(NiCoMnMgZn)0.01(PO4)2P2O7 (HE-NFPP) cathode is proposed with improved rate performance (67.1mAhg-1 at 50C) and cycle performance (retention of 92.0% after 1000 cycles at 1C). The enhancement of configuration entropy improves the structural stability of NFPP thermodynamically. In-situ XRD illustrates the sodium storage mechanism of HE-NFPP as an imperfect solid solution reaction driven by Fe2+/Fe3+ redox with a low volume change of 4.0% (90.9% of NFPP). Through doping, the structure distortion and abrupt rearrangement are inhibited. Additionally, HE-NFPP and hard carbon (HC) are utilized to fabricate pouch cell that demonstrates an average working voltage of 3.0V and a maximum energy density of 165Whkg-1 (based on the total mass of active materials). These results highlight the potential for enhancing the high-rate and long-cycle performance of NFPP as a promising cathode for SIBs through an entropy-enhanced multi-doping strategy.

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.

Aromatic Ketones as Mild Presodiating Reagents toward Cathodes for High-Performance Sodium-Ion Batteries.

Chemical presodiation (CP) is an effective strategy to enhance energy density of sodium ion batteries. However, the sodiation reagents reported so far are basically polycyclic aromatic hydrocarbons (PAHs) wth low reductive potential (~0.1 V vs. Na+ /Na), which could easily cause over-sodiation and structural deterioration of the presodiated cathodes. In this work, Aromatic ketones (AKs) are rationally designed as mild presodiating reagents by introducing a carbonyl group (C=O) into PAHs to balance the conjugated and inductive effect. As the representatives, two compounds 9-Fluorenoneb (9-FN) and Benzophenone (BP) manifest favorable equilibrium potential of 1.55 V and 1.07 V (vs. Na+ /Na), respectively. Note that 9-FN demonstrates versatile presodiating capability toward multiple Na uptake hosts (tunneled Na0.44 MnO2 , layered Na0.67 Ni0.33 Mn0.67 O2 , polyanionic Na4 Fe2.91 (PO4 )2 P2 O7 , Na3 V2 (PO4 )3 and Na3 V2 (PO4 )2 F3 ), enabling greatly improved initial charging capacity of the cathode to balance the irrevisible capacity of the anode. Our results indicate that the Aromatic ketones are competitive presodiating cathodic reagents for high-performance sodium-ion batteries, and will inspire more studies and application attempts in the future.

Slow-Released Cationic Redox Activity Promoted Stable Anionic Redox and Suppressed Jahn-Teller Distortion in Layered Sodium Manganese Oxides.

Manganese-based layered oxides are considered promising cathodes for sodium ion batteries due to their high capacity and low-cost manganese and sodium resources. Triggering the anionic redox reaction (ARR) can exceed the capacity limitation determined by conventional cationic redox. However, the unstable ARR charge compensation and Jahn-Teller distortion of Mn3+ ions readily result in structural degradation and rapid capacity fade. Here, we report a P2-type Na0.8Li0.2Mn0.7Cu0.1O2 cathode that shows a capacity retention of 84.5% at 200 mA/g after 200 cycles. Combining in situ X-ray diffraction and multi other ex situ characterizations, we reveal that the enhanced cycling stability is ascribed to a slow release of cationic redox activity which can well suppress the Jahn-Teller distortion and favor the ARR reversibility. Furthermore, density-functional theory calculations demonstrate that the inhibited interlayer migration and reduced band gap facilitate the stability and kinetic behavior of ARR. These findings provide a perspective for designing high-energy-density cathode materials with ARR activity.

Realizing high initial Coulombic efficiency in manganese-based layered oxide cathodes for sodium-ion batteries via P2/O′3 biphasic structure optimization

Realizing high initial Coulombic efficiency in manganese-based layered oxide cathodes for sodium-ion batteries via P2/O′3 biphasic structure optimization

Enhanced conductivity and stability of Prussian blue cathodes in sodium-ion batteries by surface vapor-phase molecular self-assembly

Enhanced conductivity and stability of Prussian blue cathodes in sodium-ion batteries by surface vapor-phase molecular self-assembly

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.

Hybrid Binder Chemistry with Hydrogen-Bond Helix for High-Voltage Cathode of Sodium-Ion Batteries.

Since sodium-ion batteries (SIBs) have become increasingly commercialized in recent years, Na3V2(PO4)2O2F (NVPOF) offers promising economic potential as a cathode for SIBs because of its high operating voltage and energy density. According to reports, NVPOF performs poorly in normal commercial poly(vinylidene fluoride) (PVDF) binder systems and performs best in combination with aqueous binder. Although in line with the concept of green and sustainable development for future electrode preparation, aqueous binders are challenging to achieve high active material loadings at the electrode level, and their relatively high surface tension tends to cause the active material on the electrode sheet to crack or even peel off from the collector. Herein, a cross-linkable and easily commercial hybrid binder constructed by intermolecular hydrogen bonding (named HPP) has been developed and utilized in an NVPOF system, which enables the generation of a stable cathode electrolyte interphase on the surface of active materials. According to theoretical simulations, the HPP binder enhances electronic/ionic conductivity, which greatly lowers the energy barrier for Na+ migration. Additionally, the strong hydrogen-bond interactions between the HPP binder and NVPOF effectively prevent electrolyte corrosion and transition-metal dissolution, lessen the lattice volume effect, and ensure structural stability during cycling. The HPP-based NVPOF offers considerably improved rate capability and cycling performance, benefiting from these benefits. This comprehensive binder can be extended to the development of next-generation energy storage technologies with superior performance.

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.

Aluminum ion chemistry of Na4Fe3(PO4)2(P2O7) for all-climate full Na-ion battery

Na4Fe3(PO4)2(P2O7) (NFPP) is currently drawing increased attention as a sodium-ion batteries (SIBs) cathode due to the cost-effective and NASICON-type structure features. Owing to the sluggish electron and Na+ conductivities, however, its real implementation is impeded by the grievous capacity decay and inferior rate capability. Herein, multivalent cation substituted microporous Na3.9Fe2.9Al0.1(PO4)2(P2O7) (NFAPP) with wide operation-temperature is elaborately designed through regulating structure/interface coupled electron/ion transport. Greatly, the derived Na vacancy and charge rearrangement induced by trivalent Al3+ substitution lower the ions diffusion barriers, thereby endowing faster electron transport and Na+ mobility. More importantly, the existing Al—O—P bonds strengthen the local environment and alleviate the volume vibration during (de)sodiation, enabling highly reversible valence variation and structural evolution. As a result, remarkable cyclability (over 10,000 loops), ultrafast rate capability (200 C), and exceptional all-climate stability (−40–60 °C) in half/full cells are demonstrated. Given this, the rational work might provide an actionable strategy to promote the electrochemical property of NFPP, thus unveiling the great application prospect of sodium iron mixed phosphate materials.

Phase engineering of Ni-Mn binary layered oxide cathodes for sodium-ion batteries

Nickel-manganese binary layered oxides with high working potential and low cost are potential candidates for sodium-ion batteries, but their electrochemical properties are highly related to compositional diversity. Diverse composite materials with various phase structures of P3, P2/P3, P2, P2/O3, and P2/P3/O3 were synthesized by manipulating the sodium content and calcination conditions, leading to the construction of a synthetic phase diagram for NaxNi0.25Mn0.75O2 (0.45 ≤ x ≤ 1.1). Then, we compared the electrochemical characteristics and structural evolution during the desodiation/sodiation process of P2, P2/P3, P2/O3, and P2/P3/O3-NaxNi0.25Mn0.75O2. Among them, P2/P3-Na0.75Ni0.25Mn0.75O2 exhibits the best rate capability of 90.9 mA h g−1 at 5 C, with an initial discharge capacity of 142.62 mA h g−1 at 0.1 C and a capacity retention rate of 78.25% after 100 cycles at 1 C in the voltage range of 2–4.3 V. The observed superior sodium storage performance of P2/P3 hybrids compared to other composite phases can be attributed to the enhanced Na+ transfer dynamic, reduction of the Jahn-teller effect, and improved reaction reversibility induced by the synergistic effect of P2 and P3 phases. The systematic research and exploration of phases in NaxNi0.25Mn0.75O2 provide new sights into high-performance nickel-manganese binary layered oxide for sodium-ion batteries.

Vanadium substituted Fe, Cr co-doped high performance C/Na3V2(PO4)2F3 cathode for sodium-ion batteries

In recent years, Na3V2(PO4)2F3 (NVPF) has been considered as one of the most promising candidates for cathodes in sodium ion batteries (SIBs). However, presence of vanadium makes the material costly. Besides, its electrochemical properties are hampered due to its low electronic conductivity. Herein, carbon coated Fe, Cr co-doped Na3V2(PO4)2F3 has been synthesized using rota-tumbler assisted sol–gel method. The effects of co-doping on structure, morphology and electrochemical performances are systematically studied. It is confirmed that co-doping of Fe and Cr can enhance the electrochemical performances of NVPF. Among all, Na3V1.9Fe0.095Cr0.005(PO4)2F3 shows a high initial capacity of 119.85 mAhg−1 at 0.1C and maintains a capacity retention of 88.58 % after 500 cycles at 1C. Increase in the size of the saddle point, planes of monocapped trigonal prisms and the hexagonal cavities help in decreasing the ion diffusion activation energy, thus improving the diffusivity of the doped material. The improved electrochemical performances can be attributed to the increase in the electronic conductivity of the material. Besides, vanadium reduction in the cathode aids in manufacturing cost reduction. Our work demonstrates that carbon coated Na3V1.9Fe0.095Cr0.005(PO4)2F3 can be considered as a potential cathode candidate for practical applications in SIBs.

Bimetal‐Substituted Polyanion Cathode for Sodium‐Ion Batteries: Less Vanadium and Boosted Low‐Temperature Kinetics

Sodium‐ion batteries (SIBs) have emerged as an attractive alternative for large‐scale energy storage due to their low cost and high safety. The selection of cathode materials, which determine SIB performance, becomes a crucial aspect. Vanadium‐based phosphates are known for their multielectron transfer properties and stable structure, but their intrinsic electronic conductivity is limited. In this regard, bimetallic substitution is an excellent modification method for improving the conductivity property. Herein, a novel Na4VMn0.7Ni0.3(PO4)3@C (NVMNP@C) cathode with less vanadium is designed for SIBs, which exhibits outstanding electrochemical performance at 25 °C, delivering rate capacity of 67 mA h g−1 at 3 A g−1, and long‐term cyclability of remaining 74.6% after 4800 cycles at 2 A g−1. Furthermore, excellent low‐temperature adaptability (82 mA h g−1 at 20 mA g−1, 60 mA h g−1 at 400 mA g−1, and 90.4% capacity retention after 230 cycles at 100 mA g−1) at −40 °C is also achieved. This unique work has broken a feasible pathway for high‐performance SIB cathode at low temperature.