High-performance Cathode For Sodium-ion Batteries Research Articles

Ultrafine Mn-rich P2-type Na0.67Fe0.1Mn0.9O2 particles via combustion synthesis as high-performance sodium-ion battery cathode

Layered transition metal oxide is considered as one of the most promising cathode materials for sodium-ion batteries due to the abundant reserves of Na, Fe, and Mn. Moreover, the trivalent Fe substitution weakens the Jahn–Teller effect and enhance the crystal structure during the de/intercalation of Na+. Herein, a series of Mn-rich P2-type Na0.67Fe0.1Mn0.9O2 (NFMO-600, NFMO-700 and NFMO-800) are prepared using combustion synthesis followed by calcinating at 600, 700 and 800 °C, respectively. As confirmed by XRD and SEM, NFMO-700 owns ultrafine high-purity crystal particles with a larger layer spacing and a smaller crystal size. Owing to these unique structures, NFMO-700 exhibits excellent electrochemical performance, delivering an impressive 179 mA h g−1 at 0.2C, with a capacity retention of 84.43 % after 100 cycles at 0.5C.

Buffer solution induced highly crystalline sodium-rich Prussian blue for sodium storage.

In this work, we have developed an efficient method to synthesize Prussian blue by self-decomposition of sodium ferrocyanide in acetic acid-sodium acetate buffer solution. This buffer solution-based proton pool provides a relatively low and stable concentration of protons for the slow decomposition of sodium ferrocyanide to get highly crystalline and sodium rich Prussian blue, which can be used as the cathode for high-performance sodium-ion batteries.

Copper ferricyanide particles modify Prussian blue and its analogues on the surface as cathode for high-performance sodium-ion batteries

Prussian blue and its analogs are currently attracting widespread attention as cathode materials for sodium-ion batteries due to their accomplished performance and low price. However, the unavoidable disruption of the structure and the dissolution of the surface layer of the material during sodium ion de-embedding affects its stability. In this work, using a simple method, we synthesize a composite material with uniformly grown Copper Ferricyanide particles on the surface of ferric ferricyanide. The material has a high specific capacity of more than 122.57mAhg−1 at 0.2 C (1 C=100mAg−1) and an initial Coulombic efficiency of 99.9 %. It can maintain over 92 % capacity retention after 800 cycles at 1 C. It also has excellent rate performance with a specific capacity of 103.4mAg−1 at 20 C. With its simple method and low cost, this surface modification strategy is of interest in the large-scale production of cathode materials for sodium-ion batteries.

Constructing P2/O3 biphasic structure of Fe/Mn-based layered oxide cathode for high-performance sodium-ion batteries

Fe/Mn-based layered oxide cathode is regarded as a competitive candidate for sodium-ion batteries (SIBs) because of its high theoretical capacity, earth abundance and low cost. However, its poor cycling stability still remains a major bottleneck. Herein, P2/O3 biphasic Na0.67Fe0.425Mn0.425Cu0.15O2 layered oxide is successfully synthesized via a sol–gel method. It is observed that Cu substitution can facilitate the conversion of P2 to O3 phase, and the P2/O3 composite structure can be obtained with an appropriate amount of Cu. Meanwhile, in-situ XRD reveals that constructing P2/O3 composite structure can realize the highly reversible phase transition process of P2/O3–P2/P3–OP4/OP2 and decrease the lattice mismatch during Na+ insertion/extraction. Consequently, the biphasic P2/O3-Na0.67Fe0.425Mn0.425Cu0.15O2 electrode exhibits 87.1 % capacity retention after 100 cycles at 1C, while the single phase P2-Na0.67Fe0.5Mn0.5O2 electrode has only 36.4 %. Therefore, the constructing biphasic structure is proved to be an effective strategy for designing high-performance Fe/Mn-based layered oxide cathodes.

Insights into unrevealing the effects of the monovalent cation substituted tunnel-type cathode for high-performance sodium-ion batteries

Tunnel-type Na0.44MnO2 (NMO) has attracted extensive concern as a prospective cathode for sodium-ion batteries due to the advantages of facile synthesis and cost-effectiveness. Nonetheless, the low capacity, unsatisfactory rate performance, and sluggish kinetics of NMO impede its further development for commercial application. Herein, a series of Li-substituted Na0.44Mn1-xLixO2 samples are synthesized to address the abovementioned issues. Results demonstrate that Li substitution can not only stabilize the crystal structure but also facilitate the Na+ diffusion behavior during the charging/discharging process. Density functional theory (DFT) calculations reveal that Li introduction can effectively strengthen the metallicity of NMO, which is conducive to electron transferability. Accordingly, the optimized Na0.44Mn0.94Li0.06O2 (NMOL0.06) can exhibit an improved reversible capacity of 106.1mAh g−1 at 5C, accompanying extraordinary cycling durability with 80.6 % capacity retention after 700 cycles at 10C. More importantly, the full cell combined with the NMOL0.06 cathode and the commercial hard carbon anode displays a high energy density of 257.2Wh kg−1, and superior capacity retention of 83.6 % after 300 cycles at 1C, demonstrating its great potential for practical applications. This work not only provides some insights into the influence of Li substitution on tunnel-type materials but also elucidates the construction of ultra-stable and high-performance cathodes for sodium-ion batteries.

A Mn-based ternary NASICON-type Na3.5MnTi0.5Cr0.5(PO4)3/C cathode for high-performance sodium-ion batteries

The Mn-based Natrium superionic conductor (NASICON)-type materials are promising cathode materials for sodium-ion batteries (SIBs) due to their environmental friendliness and cost-effectiveness. However, the practical application of Mn-based materials is hindered by their poor cycle performance, arising from intrinsic kinetic limitation and negative structural degradation caused byMn. Herein, a Mn-based ternary NASICON-type Na3.5MnTi0.5Cr0.5(PO4)3/C (NMTCP-50) is designed featuring multi-metal synergy with enhanced effect from each component, which contributes to breaking through the bottleneck of inferior cycle performance for Mn-based NASICON-type materials. The results of ex-situ X-ray diffraction corroborate that both solid-solution and bi-phase electrochemical reactions are involved in the sodiation/desodiation processes, and the volume variation is only 2.55 %. Galvanostatic intermittent titration technique tests and density functional theory calculations further demonstrate the fast reaction kinetics of the NMTCP-50 electrode. NMTCP-50 can deliver an excellent cycling durability of 75 % after 5000 cycles at 2 A g−1 and a high reversible capacity of 137.6 mAh g−1. The availability of NMTCP-50 has been evaluated by a full cell assembled with hard carbon. This work offers theoretical support for understanding the multi-metal synergistic effect in NASICON materials and provides a blueprint for designing low-cost NASICON cathodes.

α/β–Type NaMn0.89Ni0.11O2: as high-performance sodium-ion battery cathode

α/β–Type NaMn0.89Ni0.11O2: as high-performance sodium-ion battery cathode

Sodium Stoichiometry Tuning of the Biphasic-Nax MnO2 Cathode for High-Performance Sodium-Ion Batteries.

Sodium-ion batteries (SIBs) are promising alternatives for large-scale energy storage owing to the rich resource and cost effectiveness. However, there are limitations of suitable low-cost, high-rate cathode materials for fast charging and high-power delivery in grid systems. Herein, a biphasic tunnel/layered 0.80Na0.44 MnO2 /0.20Na0.70 MnO2 (80T/20L) cathode delivering exceptional rate performance through subtly regulating the sodium and manganese stoichiometry is reported. It delivers a reversible capacity of 87mAhg-1 at 4Ag-1 (33C), much higher than that of tunnel Na0.44 MnO2 (72mAhg-1 ) and layered Na0.70 MnO2 (36mAhg-1 ). It proves that the one-pot synthesized 80T/20L is able to suppress the deactivation of L-Na0.70 MnO2 under air-exposure, which improves the specific capacity and cycling stability. Based on electrochemical kinetics analysis, the electrochemical storage of 80T/20L is mainly based on pseudocapacitive surface-controlled process. The thick film of 80T/20L cathode (a single-side mass loading over 10mgcm-2 ) also has superior properties of pseudocapacitive response (over 83.5% at a low sweep rate of 1mVs-1 ) and excellent rate performance. In this sense, the 80T/20L cathode with outstanding comprehensive performance could meet the requirements of high-performance SIBs.

Nitrogen-Doped Carbon Coated Na3V2(PO4)2F3 Derived from Polyvinylpyrrolidone as a High-Performance Cathode for Sodium-Ion Batteries

Na super ionic conductor (NASICON)-type Na3V2(PO4)2F3 (NVPF) has been regarded as a prospective candidate of cathode materials for sodium-ion batteries due to its excellent structural stability, relatively high capacity and working voltage. However, the poor cyclability and rate capability, resulting from its low intrinsic electronic conductivity, have become a serious obstacle to their practical large-scale application. In this work, N-doped carbon coated NVPF composites (NVPF@NC) were successfully synthesized via a simple sol–gel method, in which low-cost polyvinylpyrrolidone was introduced as a nitrogen source. After high-temperature pyrolysis, a highly conductive N-doped carbon layer was in-situ constructed on the particle surface to enhance the sodium storage performance of NVPF. The optimized NVPF@NC cathode delivered high reversible capacity, excellent rate capability and long-term cycle life compared to pristine NVPF@C. The remarkable electrochemical performance of NVPF@NC cathode benefits from the modification strategy of introducing a heteroatom-doped carbon layer, triggering the formation of extrinsic defects and active sites in the N-doped amorphous carbon layer, which greatly enhances the electrical conductivity and the diffusion rate of sodium ions. This work provides a facile and effective approach for the preparation of N-doped carbon coated NVPF with remarkable sodium storage properties, which could be extended to other electrode materials electrochemical for energy storage.

Boosting cycling stability through Al(PO3)3 loading in a Na4MnV(PO4)3/C cathode for high-performance sodium-ion batteries

Mn-based NASICON-type Na4MnV(PO4)3 (NMVP) has been widely investigated as one of the most promising alternatives to Na3V2(PO4)3 cathodes for sodium-ion batteries (SIBs) due to its higher energy density, higher abundance, and lower cost and toxicity compared to V. However, electrochemical performance for large-scale applications is limited by NMVP’s inferior conductivity and structural degradation during cycling. Herein, a facile strategy to modify the surface/interphase properties of NMVP/C was reported using the thermally stable Al(PO3)3 precursor with a wet process followed by heat treatment to enhance the interface stability of electrodes. The nanomodified layer has the benefits of an ionic conductor (slight NaPO3) and robust composite (Al(PO3)3), which can facilitate the stability of Mn-based cathode materials and ionic conductivity. These merits endow 1 wt% Al(PO3)3-loaded NMVP/C cathodes with a high rate performance (102/61 mAh g−1 at 0.2/50 C) and impressive cyclability (88.5%/89.7% at 5 C/10 C after 3000/4000 cycles) in Na-ion batteries at 2.5–3.8 V. Moreover, when the cutoff voltage is raised to 4 V, improved electrochemical properties (111.6/50.8 mAh g−1 at 0.2/10 C and 71.4% after 1000 cycles at 5 C) are also realized. Such an enhancement indicates that facial surface modification engineering limits organic electrolyte erosion, inhibits transition metal dissolution and suppresses surface lattice degradation, which is confirmed by ex situ X-ray diffractometry and transmission electron microscopy. Therefore, the Al(PO3)3 surface modification strategy combined with mechanism analysis can provide a possible reference for advanced electrochemical properties in energy storage devices.

An advanced medium-entropy substituted tunnel-type Na0.44MnO2cathode for high-performance sodium-ion batteries

NMO-1 exhibits good electrochemical performance, with a capacity retention of more than 80% after 2000 cycles at a rate of 10C between 2 and 4 V. The suggested approach of medium-entropy substitution offers insight into the design of high-energy Na-ion cathode materials.

Ca-doped NaV6O15 film electrodes as high-performance cathodes for sodium-ion batteries

The Ca-doped NaV6O15 films have been prepared on indium-doped tin oxide (ITO) conductive glasses using a low-temperature liquid-phase deposition method. The crystal structure, morphology, and structural information of the Ca-doped NaV6O15 films were systematically studied by X-ray diffraction, scanning electron microscopy and infrared spectroscopy. X-ray photoelectron spectroscopy revealed that the Ca-doped NaV6O15 had a lower ratio of V5+/V4+, which was the compensation for doped Ca2+. Electrochemical properties of films were measured by cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge/discharge tests. The results proved the doped Ca2+ obviously improved electrochemical performance, which exhibited quicker diffusion process, higher specific capacity, and longer lifespan. The Ca-doped NaV6O15 films showed a high discharge capacity of 237.476 mA h m−2 at 1C rate, which was larger than 96.719 mA h m−2 of the pure NaV6O15 films. The capacity retention reached to 84.72 % at 0.5C rate after 100 cycles, the excellent cyclic ability was attributed to the doped Ca2+ with strong electronegativity stabilizing the structure. This work presents a great potential approach that explores high-performance cathodes for sodium-ion batteries.

Molecular design and post-synthetic vulcanization on two-dimensional covalent organic framework@rGO hybrids towards high-performance sodium-ion battery cathode

Covalent organic frameworks (COFs) with stable porous structure are considered as promising electrode materials for next-generation sustainable sodium-ion batteries (SIBs). However, how to enhance their surface activity and utilize more superficial active sites remains great challenge to satisfy the potential applications. Herein, a “three-in-one” structure regulation strategy including morphology control, molecular design and post-synthetic vulcanization is proposed to design an enhanced polyimide COFs cathode. Through morphology control, two-dimensional COFs nanosheets can be easily controlled due to the directing effect of the π-π interactions between rGO and the structure units of COFs, which leads to short channels to make more active sites available for sodium storage; Through molecular design, COFs with more active atoms can be acquired by simply replacing N atom with triazine ring in monomer, resulting in more active sites in the COFs skeleton; Through post-synthetic modification, the transformation of CO bonds to CS bonds can be facilely realized via Lawesson reagent, leading to the activity enhancement of the COF surface due to the higher activity of CS to sodium. With these triplex structural enhancements, the resulting S@TAPT-COFs (sulfuretted 2,4,6-Tris(4-aminophenyl)-1,3,5-triazine) nanosheets cathode exhibits excellent SIBs performances with a high specific capacity of 109.3 mAh g−1 at 0.1 A g−1 and a long-term stability with 68.6 mAh/g specific capacity remaining after 2000 cycles of charge/discharge process at 2.0 A g−1. This three-in-one strategy integrating morphology control, molecular design and post-synthetic modification provides an effective route to inspire the development of novel organic electrodes especially COFs for sustainable and durable rechargeable batteries.

Boosting anionic redox through lithium doping in P2-layered cathode for high-performance sodium-ion batteries

Anionic chemistry has become a new paradigm for increasing the energy density of rechargeable batteries. Herein to boost the activity of cationic redox in P2-Na0.8Cu0.1Mn0.9O2, a new Li-doped P2-Na0.8Li0.15Cu0.1Mn0.75O2 cathode is designed, and the electrochemical performances of both materials are systematically investigated. Compared with the undoped sample, P2-Na0.8Li0.15Cu0.1Mn0.75O2 cathode material displays higher reversible capacity, better rate capability and stronger cycling stability. These improvements are supposed to be originated from the positive effect of Li on triggering the anionic redox under high operating voltage, stabilizing the crystal structure as well as facilitating the diffusion of Na+ and electron during the sodiation/desodiation process. This work pursues superior electrochemical performance in P2-layered cathodes through boosting the anionic redox, which probably offers some insights for designing high-performance sodium-ion batteries.

Suppressed P2–P2′ phase transition of Fe/Mn-based layered oxide cathode for high-performance sodium-ion batteries

P2-type Fe/Mn-based layered oxide cathode has attracted enormous interest as a prospective candidate for sodium-ion batteries (SIBs) used in large-scale energy storage owing to its low cost, low toxicity, earth abundance and high theoretical specific capacity. However, the P2–P2′ phase transition associated with the Jahn–Teller effect of Mn 3+ at the end of the discharge process often appears, leading to severe capacity fading during charge-discharge process. Herein, we propose an effective strategy of using Al-doping to completely inhibit the harmful P2–P2′ phase transition by suppressing the Jahn–Teller effect of Mn 3+ , which has been verified by ex-situ and in-situ X-ray powder diffraction (XRD), high-resolution transmission electron microscope (HR-TEM) and ex-situ X-ray photoelectron spectroscopy (XPS). Consequently, Al-doped P2-Na 0.67 Fe 0.5 Mn 0.45 Al 0.05 O 2 electrode exhibits excellent cycling stability (92.8% capacity retention after 200 cycles at 1 C within 2.0–4.0 V). Meanwhile, Al-doping could widen interspacing of Na + layer to accelerate the migration of Na + , further improve rate capability (from 32 to 48% under the ratio of 5 to 0.1 C). This work provides a new sight to effectively suppress P2–P2′ phase transition for Fe/Mn-based layered oxide cathode.

Hydrothermally prepared composite of Na3V2(PO4)2F3 with gelatin and graphene used as a high-performance sodium ion battery cathode

To improve the inherently low electrical conductivity of Na3V2(PO4)2F3, we design a three-dimensional conductive network and prepare it by hydrothermal strategy. Gelatin can reduce impurities and make the material shape more regular while graphene acts as conductive network that can improve the electrochemical properties. The prepared NVPF-gel/rGO shows a superior sodium storage performance. The reversible capacity is 125.1 mAh g-1 at 0.2 C, 108 mAh g-1 after 200 cycles, and 90.6 mAh g-1 at 5 C. Furthermore, the full cell is successfully fabricated using the hard carbon anode (average working voltage of 3.3 V). NVPF-gel/rGO composite is a potential sodium storage cathode with a good practical application prospect.

Phase-manipulated hierarchically core-shell Na3(VO1-xPO4)2F1+2x (0≤x≤1)@Na3V2(PO4)3 and its synergistic effect with conformally wrapped reduced graphene oxide framework towards high-performance cathode for sodium-ion batteries

Sodium-ion batteries (SIBs) are regarded as promising candidates for large-scale stationary energy storage systems because of the high abundance of Na resources. Na superionic conductor polyanionic cathode (NASICON), such as Na3(VO1-xPO4)2F1+2x (0 ≤ x ≤ 1, NVPF1+2x) and Na3V2(PO4)3 (NVP), shows intriguing electrochemical performances due to their robust open structure and superior cycle stability. Inspired by phase manipulation and conductive reduced graphene oxide (rGO) incorporation, a hierarchical NVPF1+2x@NVP core-shell structure is elaborately synthesized and conformally wrapped by rGO via a facial microwave-assisted hydrothermal approach. F-free surface of NVPF1+2x@NVP particle possesses intimate contact with rGO framework without strong mutual repulsive force while conductive rGO endows NVPF1+2x@NVP with high electronic conductivity to ensure fast electron transport. Combining the synergistic effect between delicate design of core-shell structure and conductive rGO framework, the NVPF1+2x@NVP/rGO-600 °C electrode achieves a high discharge capacity of 105.9 mAh g−1 at 0.5 C with an impressive capacity retention of 99.1% after 200 cycles, delivering an excellent rate capability of 90.6 mAh g−1 at 10 C. Moreover, the NVPF1+2x@NVP/rGO-600 °C electrode possesses an alleviated polarization, small impedance and fast electron/Na + diffusion properties due to this synergistic effect. The full cell using NVPF1+2x@NVP/rGO-600 °C cathode and hard carbon (HC) anode shows an initial discharge capacity of 80.0 mAh g−1 at 0.2 C and rate capability of 45.2 mAh g−1 at 10 C, which could light an LED lamp and manifest its prospective application. Our findings provide new insights into a broadly applicable material design combining morphological phase manipulation with conductive rGO framework incorporation, which synergistically boosts the electrochemical performance of NASICON cathode towards advanced SIBs with a higher energy density, faster charging rate and more practical applications.

Chromium doped NASICON-structured Na3MnTi(PO4)3/C cathode for high-performance sodium-ion batteries

Na3Mn1−xCrxTi(PO4)3/C composites with different chromium doping contents (x = 0.01, 0.03, 0.05, 0.07, 0.10, 0.12, 0.15), a potential cathode material in sodium-ion batteries with its classical 3D NASCION structure, has been synthesized via a feasible sol-gel route. The doping effects on the crystal structure were verified by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman and Fourier-infrared spectra (FT-IR). The results show that chromium doping does not alter the structure of the material, and chromium is successfully doped for manganese site. Proper chromium doped Na3Mn1−xCrxTi(PO4)3/C composites exhibit a high reversible capacity and structural stability. Among them, Na3Mn0.93Cr0.07Ti(PO4)3/C and Na3Mn0.90Cr0.10Ti(PO4)3/C achieve the highest capacity retention (90.19% after 100 cycles at 0.2 C) and initial discharge specific capacity (119.65 mA h g-1 at 0.2 C), yielding the coulombic efficiency of ~100%. Interestingly, even after cycling at 10 C over 500 cycles, the Na+-storage capacity of 94.37 and 101.51 mA h g-1 with a capacity retention of 79.70% and 73.74% were respectively still obtained with x = 0.07 and 0.10, highlighting their excellent long cycling life and remarkable rate performances. Results from the cyclic voltammetry and impedance spectroscopy studies were combined to verify the enhanced sodium-ion diffusion coefficients.

Unraveling the Synergistic Effect of Mg and Ti Codoping to Realize an Ordered Structure and Excellent Performance for Sodium-Ion Batteries.

Layered cathodes have been recognized as potential advanced candidates for sodium-ion batteries (SIBs), but the poor electrochemical performance has seriously hindered their further development. Herein, an ordered Na2/3[Ni2/9Mg1/9Mn5/9Ti1/9]O2 (NMMT) is designed and investigated as a high-performance cathode for SIBs through the synergistic effect of Mg and Ti codoping. Compared to the single Mg- or Ti-doped materials, NMMT clearly exhibits superstructure ordering diffraction peaks, and neutron diffraction further confirms that the diffraction peaks can be well indexed by a larger supercell P63, rather than the common unit cell P63/mmc by X-ray diffraction (XRD). High-resolution transmission electron microscopy also approves the ordering arrangement. This material shows an obvious capacity activation process during the first cycles, thus delivering 113 mA h g-1 specific capacity at 0.1 C (close to the theoretical value). Excellent rate capability even at 15 C and cycling stability after 500 cycles between 2.0 and 4.3 V can also be achieved, indicating that an ordered cathode is still promising. Besides, a single-phase reaction mechanism is revealed by ex situ/in situ XRD experiments. This study offers some insights into the material design and characterization of layered oxide cathodes for high-performance SIBs in the future.

A nitrogen- and carbonyl-rich conjugated small-molecule organic cathode for high-performance sodium-ion batteries

A highly functionalized extended π-conjugated molecule HATAQ with a unique hydrogen-bonding enabled supramolecular graphite-like structure is found to have superior performance as a cathode material for sodium-ion batteries.