Mg2+-doped Na3V2(PO4)3/C decorated with graphene sheets: An ultrafast Na-storage cathode for advanced energy storage

NASICON-type Na₃V₂(PO₄)₃ is one of the most promising cathode materials for sodium-ion batteries, delivering about two Na⁺-ions extraction/insertion from/into the unit structure. However, the low electronic conductivity which leads to bad rate capability and poor cycle performance, limits its practical application for sodium-ion batteries. To overcome the kinetic problem, we attempt to prepare the carbon-coated Na₃V₂(PO₄)₃ nanocrystals further decorated by graphene sheets and doped with Mg²⁺ ion via the two steps of sol-gel process and solid-state treatment for the first time. Such architecture synergistically combines the advantages of two-dimensional graphene sheets and 0-dimensional Mg²⁺-doped Na₃V₂(PO₄)₃/C nanoparticles. It greatly increases the electron/Na⁺-ion transport kinetics and assures the electrode structure integrity, leading to attractive electrochemical performance. When used as sodium-ion batteries cathode, the hybrid composite delivers an initial discharge capacity of 115.2 mAh g⁻¹ at 0.2 C rate, and retains stable discharge capacities of 113.1, 109.0, 102.4, 94.0 and 85.2 mAh g⁻¹ at high current rates of 1, 2, 5, 10 and 20 C rate, respectively. Thus, this nanostructure design provides a promising pathway for developing high-performance Na₃V₂(PO₄)₃ material for sodium-ion batteries.     

Synthesis of nanosheet-structured Na3V2(PO4)3/C as high-performance cathode material for sodium ion batteries using anthracite as carbon source

Recently, Na₃V₂(PO₄)₃ has shown great promise as cathode material for sodium-ion batteries. In this study, a series of carbon-modified Na₃V₂(PO₄)₃ (NVP/C) composites have been synthesized using anthracite as the carbon source. The NVP/C composite shows a nanosheet shape with a 3D continuously conductive network composed of carbon layer and carbon bump. The effect of anthracite dosage on the electrochemical performance of NVP/C has also been investigated. The results show that the NVP/C composite prepared with 10 wt% anthracite (NVP/C-10) exhibits the highest rate capability and a great cycle stability. Especially the NVP/C-10 electrode behaves an average capacity as high as 97 mAh g⁻¹ at a high current rate of 10 C. Moreover, NVP/C-10 still delivers a high specific capacity of 97.5 mAh g⁻¹ even after 800 cycles at 5 C, showing a very low capacity fading ratio of 0.012% per cycle. The excellent rate capability and cycle stability of NVP/C-10 can be ascribed to the synergistic effects of the nanosheet structure and the 3D continuously conductive network. Our results demonstrate that anthracite can be a promising carbon source for the preparation of NVP/C and other polyanion cathode materials as well.     

Effect of Fe-doping followed by C+SiO2 hybrid layer coating on Li3V2(PO4)3 cathode material for lithium-ion batteries

A novel Li₃V₂(PO₄)₃ composite modified with Fe-doping followed by C+SiO₂ hybrid layer coating (LVFP/C-Si) is successfully synthesized via an ultrasonic-assisted solid-state method, and characterized by XRD, XPS, TEM, galvanostatic charge/discharge measurements, CV and EIS. This LVFP/C-Si electrode shows a significantly improved electrochemical performance. It presents an initial discharge capacity as high as 170.8 mA h g⁻¹ at 1 C, and even delivers an excellent initial capacity of 153.6 mA h g⁻¹ with capacity retention of 82.3% after 100 cycles at 5 C. The results demonstrate that this novel modification with doping followed by hybrid layer coating is an ideal design to obtain both high capacity and long cycle performance for Li₃V₂(PO₄)₃ and other polyanion cathode materials in lithium ion batteries.     

Evaluation of the electrochemical behavior and structural reversibility of Li3−xNaxV2(PO4)3/C (0≤x≤3) as anode materials for Na-ion batteries

A series of Li_3−xNa_xV₂(PO₄)₃/C (0≤x≤3) materials are successfully prepared by a simple solid-state reaction method and used for the first time as anode materials for Na-ion batteries. Powder X-ray diffraction (XRD) results show that the phase structures of Li_3−xNa_xV₂(PO₄)₃/C evolve along with the change of Li/Na atomic ratio (0≤x≤3). With increasing x in Li_3−xNa_xV₂(PO₄)₃/C from 0.0 to 3.0, the main phase in as-prepared sample transforms from monoclinic Li₃V₂(PO₄)₃ to rhombohedral Li₃V₂(PO₄)₃, and finally to rhombohedral Na₃V₂(PO₄)₃, which results in different sodium storage behavior and performance between Li_3−xNa_xV₂(PO₄)₃/C (0≤x≤3) materials. Electrochemical results show that Li_3−xNa_xV₂(PO₄)₃/C (x=0.0, 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0) can deliver the initial charge capacities of 21.1, 35.9, 33.8, 41.7, 43.3, 43.9 and 47.7 mAh g⁻¹ at a current density of 10 mA g⁻¹, respectively. After 45 cycles, the reversible capacities can be kept at 16.9, 45.1, 32.6, 44.6, 43.7, 37.8 and 27.3 mAh g⁻¹ for Li₃V₂(PO₄)₃/C, Li_2.5Na_0.5V₂(PO₄)₃/C, Li₂NaV₂(PO₄)₃/C, Li_1.5Na_1.5V₂(PO₄)₃/C, LiNa₂V₂(PO₄)₃/C, Li_0.5Na_2.5V₂(PO₄)₃/C and Na₃V₂(PO₄)₃/C, respectively. Furthermore, the structural reversibility of Li_3−xNa_xV₂(PO₄)₃/C (x=1.0, 2.0, and 3.0) is also observed by in-situ XRD observation during sodiation/de-sodiation process. All these observed evidences indicate that only some of Li_3−xNa_xV₂(PO₄)₃/C (0≤x≤3) can be used as possible sodium storage materials.     

Synthesis and electrochemical properties of a composite LiMn0.63Fe0.37PO4 with Li3V2(PO4)3 for lithium-ion battery cathode materials

A composite materials LiMn_0.63Fe_0.37PO₄ with Li₃V₂(PO₄)₃ can be synthesized by a sol-gel method using N,N-dimethylformamide (DMF) as a dispersing agent. The structures, characteristics of the appearance, and electrochemical properties of the composites have been studied by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), charge/discharge tests, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The composites contained LiMnPO₄/C (LMP/C), LiFePO₄/C (LFP/C), and Li₃V₂(PO₄)₃/C (LVP/C) phases with a nano-sized dispersion. The TEM images showed that the composites are crystalline with a grain size of 10–50 nm. The Mn2p, V2p, and Fe2p valence states were analyzed by X-ray photoelectron spectroscopy (XPS). The incorporation of LVP and LFP with LMP effectively enhanced the electrochemical kinetics of the LMP phase by a structural modification and shortened the lithium diffusion length in LMP. The capacity of the composite 0.79LiMn_0.63Fe_0.37PO₄·0.21Li₃V₂(PO₄)₃/C remained at 152.3 mAh g⁻¹ (94.7%) after 50 cycles at a 0.05 C rate. The composite exhibited excellent reversible capacities 159.4, 150, 140.1, 133.7 and 123.6 mAh g⁻¹ at charge-discharge rates of 0.05, 0.1, 0.2, 0.5 and 1 C, respectively.     

One-pot pyro-synthesis of a high energy density LiFePO4-Li3V2(PO4)3 nanocomposite cathode for lithium-ion battery applications

A highly crystalline carbon-coated 0.66LiFePO₄•0.33Li₃V₂(PO₄)₃ (LFP-LVP) nanocomposite was synthesized by a one-pot pyro-synthetic strategy using a polyol medium at low temperature. Prior to any additional heat treatment, electron microscopy confirmed the as-synthesized composite to consist of spherical particles with average diameters in the range of 30–60 nm. A crystal growth phenomenon and particle aggregation was observed upon heat treatment at 800 °C, thus resulting in an increase in the average particle size to 200–300 nm. When tested for a lithium-ion cell, the nanocomposite electrode demonstrated impressive electrochemical properties with higher operating potentials hence enhanced energy densities. Specifically, the composite cathode delivered a high reversible capacity of 156 mAh g⁻¹ at 0.1 C and exhibited a remarkable reversible capacity of 119 mAh g⁻¹, corresponding to an energy density of 46.88 Wh Kg⁻¹ at 6.4 C. When cycling was performed at 6.4 C, the electrode could recover up to 85% of the capacity observed at low current density of 0.1 C, which indicates the excellent rate capability of the nanocomposite electrode. The enhanced performance was attributed to the inclusion of the high potential LVP phase constituent in the present cathode by a simple one-pot polyol-assisted pyro strategy.     

A nest-like hierarchical porous V2O5 as a high-performance cathode material for Li-ion batteries

In this article, V₂O₅ with a novel nest-like hierarchical porous structure has been synthesized by a facile solvothermal method and investigated as cathode material for lithium-ion batteries. The nest-like V₂O₅ with a diameter of about 1.5 µm, was composed of interconnected nanosheets with a highly porous structure. Without other modification, the as-prepared V₂O₅ electrode exhibited superior capacity. An initial discharge capacity of 330 mAh g⁻¹ (at a current density of 100 mA g⁻¹) could be delivered and a stable discharge capacity of 240 mAh g⁻¹ after 50 cycles is maintained. The excellent performance was attributed to the hierarchical porous structure that could buffer against the local volume change and shorten the lithium-ions diffusion distance.     

Cathode materials based on carbon nanotubes for high-energy-density lithium–sulfur batteries

The rational integration of conductive nanocarbon scaffolds and insulative sulfur is an efficient method to build composite cathodes for high-energy-density lithium–sulfur batteries. The full demonstration of the high-energy-density electrodes is a key issue towards full utilization of sulfur in a lithium–sulfur cell. Herein, carbon nanotubes (CNTs) that possess robust mechanical properties, excellent electrical conductivities, and hierarchical porous structures were employed to fabricate carbon/sulfur composite cathode. A family of electrodes with areal sulfur loading densities ranging from 0.32 to 4.77 mg cm⁻² were fabricated to reveal the relationship between sulfur loading density and their electrochemical behavior. At a low sulfur loading amount of 0.32 mg cm⁻², a high sulfur utilization of 77% can be achieved for the initial discharge capacity of 1288 mAh g_S⁻¹, while the specific capacity based on the whole electrode was quite low as 84 mAh g_{C/S+binder+Al}⁻¹ at 0.2 C. Moderate increase in the areal sulfur loading to 2.02 mg cm⁻² greatly improved the initial discharge capacity based on the whole electrode (280 mAh g_{C/S+binder+Al}⁻¹) without the sacrifice of sulfur utilization. When sulfur loading amount further increased to 3.77 mg cm⁻², a high initial areal discharge capacity of 3.21 mAh cm⁻² (864 mAh g_S⁻¹) was achieved on the composite cathode.     

Facile synthesis of micro-spherical LiMn0.7Fe0.3PO4/C cathodes with advanced cycle life and rate performance for lithium-ion battery

A series of micro-spherical LiMn_0.7Fe_0.3PO₄/C (LMFP) cathode materials are synthesized via co-precipitation method combining spray drying and solid-state reaction. All as-prepared materials are well-characterized to determine their crystal structure, morphology and electrochemical performance. All as-obtained LMFP materials correspond to orthorhombic olivine structure with Pbnm space group and show uniform porous spherical structure with an average particle size of 3 µm and a carbon coating layer of about 3 nm. In particular, the resulting LMFP material prepared at 600 °C exhibits a high discharge capacity of 160 mAh g⁻¹ at 0.1 C. Even at a high rate of 10 C, it can still deliver 133 mAh g⁻¹ and maintain capacity retention of 84.9% after 200 cycles. The excellent electrochemical performance is ascribed to the synergetic effect of porous micro-spherical structure and uniform carbon coating layer.     

Electrochemical characterization of P2-type layered Na2/3Ni1/4Mn3/4O2 cathode in aqueous hybrid sodium/lithium ion electrolyte

P2-type layered Na_2/3Ni_1/4Mn_3/4O₂ has been synthesized by a solid-state method and its electrochemical behavior has been investigated as a potential cathode material in aqueous hybrid sodium/lithium ion electrolyte by adopting activated carbon as the counter electrode. The results indicate that the Na⁺/Li⁺ ratio in aqueous electrolyte has a strong influence on the capacity and cyclic stability of the Na_2/3Ni_1/4Mn_3/4O₂ electrode. Increase on the Li⁺ content leads to a shift of the redox potential towards a high value, which is favorable for the improvement of the working voltage of the layered material as cathode. It is found that the coexistence of Na⁺ and Li⁺ in aqueous electrolyte can improve the cyclic stability for the Na_2/3Ni_1/4Mn_3/4O₂ electrode. A reversible capacity of 54 mAh g⁻¹ was obtained with a high cyclability as the Na⁺/Li⁺ ratio was 2:2. Furthermore, an aqueous hybrid ion cell was assembled with the as-proposed Na_2/3Ni_1/4Mn_3/4O₂ as cathode and NaTi₂(PO₄)₃/graphite synthesized in this work as anode in 1 M Na₂SO₄/Li₂SO₄ (mole ratio as 2:2) mixed electrolyte. The cell shows an average discharge voltage at 1.2 V, delivering an energy density of 36 Wh kg⁻¹ at a power density of 16 W kg⁻¹ based on the total mass of the active materials.     

Enhanced electrochemical performance of Li3V2(PO4)3 structurally converted from LiVOPO4 by graphite nanofiber addition

In this work, the structural conversion of LiVOPO₄ to Li₃V₂(PO₄)₃ due to the addition of graphene nanofiber (GNF) was investigated, and the resulting materials were found to exhibit enhanced capacity and cyclability. First, LiVOPO₄ was synthesized using a solid-state method followed by annealing at 900 °C for 12 h under nitrogen atmosphere. Then, the conversion from the triclinic LiVOPO₄ structure to the monoclinic Li₃V₂(PO₄)₃ structure due to the GNF addition was observed. No impurity peak was observed in the X-ray diffraction patterns of LiVOPO₄ or Li₃V₂(PO₄)₃, and the structural conversion caused no defects to form in the resulting Li₃V₂(PO₄)₃ crystallite. Field emission-scanning electron microscope studies clearly demonstrate that larger corroded-structure-like particles formed which were mixed with GNF. This provided both a large active area and fast transport of lithium ions, which afforded enough active sites for simultaneous intercalation of many lithium ions, leading to improved electrochemical properties of the material. Compared with LiVOPO₄, the Li₃V₂(PO₄)₃–GNF showed better properties, such as an improved lithium ion diffusion coefficient, improved cyclability, and smaller impedance. Furthermore, the optimized Li₃V₂(PO₄)₃–GNF (7%) battery showed the best discharge capacity of 181 mA h g⁻¹ at 0.1 C and lithium ion diffusion coefficient of 6.01×10⁻⁹ cm² s⁻¹.     

Ag enhanced electrochemical performance for Na2Li2Ti6O14 anode in rechargeable lithium-ion batteries

Due to the characteristics of an electronic insulator, Na₂Li₂Ti₆O₁₄ always suffers from low electronic conductivity as anode material for lithium storage. Via Ag coating, Na₂Li₂Ti₆O₁₄@Ag is fabricated, which has higher electronic conductivity than bare Na₂Li₂Ti₆O₁₄. Enhancing the Ag coating content from 0.0 to 10.0 wt%, the surface of Na₂Li₂Ti₆O₁₄ is gradually deposited by Ag nanoparticles. At 6.0 wt%, a continuous Ag conductive layer is formed on Na₂Li₂Ti₆O₁₄. While, particle growth and aggregation take place when the Ag coating content reaches 10.0 wt%. As a result, Na₂Li₂Ti₆O₁₄@6.0 wt% Ag displays better cycle and rate properties than other samples. It can deliver a lithium storage capacity of 131.4 mAh g⁻¹ at 100 mA g⁻¹, 124.9 mAh g⁻¹ at 150 mA g⁻¹, 119.1 mAh g⁻¹ at 200 mA g⁻¹, 115.8 mAh g⁻¹ at 250 mA g⁻¹, 111.9 mAh g⁻¹ at 300 mA g⁻¹ and 109.4 mAh g⁻¹ at 350 mA g⁻¹, respectively.     

Synthesis and electrochemical properties of LiFe0.95VxNi0.05−xPO4/C cathode material for lithium-ion battery

In this study, crystalline LiFe_0.95V_xNi_0.05−xPO₄/C powders are successfully synthesized using the hydrothermal method. Materials characterization and the electrochemical performance of LiFe_0.95V_xNi_0.05−xPO₄/C are investigated. The structure, morphology, and electrochemical performances of the prepared samples are investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), cyclic voltammetry, and AC impedance. The XRD pattern indicates that the LiFe_0.95V_xNi_0.05−xPO₄/C powders are single-phased with an orthorhombic olivine structure. The LiFe_0.95V_0.05PO₄ sample has the highest capacity of 141 mAh g⁻¹, which is 6% higher than that of pure LiFePO₄ at 0.1 C. As the discharge rate increases to 10 C, the LiFe_0.95V_0.04Ni_0.01PO₄ sample has the highest capacity of 100 mAh g⁻¹, which is 18% higher than that of pure LiFePO₄. The CV results prove that the LiFe_0.95V_0.04Ni_0.01PO₄ cathode has high capacity and good cyclic performance caused by the high lithium-ion diffusion transport, which is improved by Ni and V doping.     

Synthesis,characterization and electrochemical performance of Sn3F3PO4 anode material for lithium-ion batteries

Tin fluorophosphate (Sn₃F₃PO₄) powder was synthesized via a microemulsion route. Physical properties of the synthesized material were investigated by means of X-ray powder diffractometry (XRD) and field emission scanning electron microscopy (FE-SEM). The investigation showed that the synthesized powder was crystalline Sn₃F₃PO₄ with needle-like morphology with a thickness of 300–500 nm and length of 5–10 μm. The electrochemical performance of the synthesized powder as a negative electrode for Li-ion batteries was studied. The results showed that the synthesized Sm₃F₃PO₄ possessed an initial discharge capacity of 1370 mAh g^?1 and charge capacity of 968 mAh g^?1 in a potential range of 0.005–3 V. In addition, the material showed capacity retention of 70.8% after 30 cycles at a constant current density of 100 mA g^?1.     

Porous Fe2O3 nanorods anchored on nitrogen-doped graphenes and ultrathin Al2O3 coating by atomic layer deposition for long-lived lithium ion battery anode

Porous iron oxide (Fe₂O₃) nanorods anchored on nitrogen-doped graphene sheets (NGr) were synthesized by a one-step hydrothermal route. After a simple microwave treatment, the iron oxide and graphene composite (NGr-I-M) exhibits excellent electrochemical performances as an anode for lithium ion battery (LIB). A high reversible capacity of 1016 mAh g⁻¹ can be reached at 0.1 A g⁻¹. When NGr-I-M electrode was further coated by 2 ALD cycles of ultrathin Al₂O₃ film, the first cycle Coulombic efficiency (CE), rate performance and cycling stability of the coated electrode can be greatly improved. A stable capacity of 508 mAh g⁻¹ can be achieved at 2 A g⁻¹ for 200 cycles, and an impressive capacity of 249 mAh g⁻¹ at 20 A g⁻¹ can be maintained without capacity fading for 2000 cycles. The excellent electrochemical performance can be attributed to the synergy of porous iron oxide structures, nitrogen-doped graphene framework, and ultrathin Al₂O₃ film coating. These results highlight the importance of a rational design of electrode materials improving ionic and electron transports, and potential of using ALD ultrathin coatings to mitigate capacity fading for ultrafast and long-life battery electrodes.     

LiSixMn2−xO4 (x≤0.10) cathode materials with improved electrochemical properties prepared via a simple solid-state method for high-performance lithium-ion batteries

LiSi_xMn_2−xO₄ (x≤0.10) cathode materials were prepared via a simple solid-state process with tetraethylorthosilicate (TEOS) as the silicon source. The effects of Si-doping on the structure, morphology and electrochemical performance were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), galvanostatic charge-discharge tests and electrochemical impedance spectroscopy (EIS), respectively. All the Si-doped LiMn₂O₄ samples showed the intrinsic spinel structure. With the increasing of Si-doping concentration, the crystal lattice constant of LiSi_xMn_2−xO₄ samples increased and the particle size distribution becomes more uniform to some extent. Among these samples, the optimal Si-doped LiMn₂O₄ exhibited an initial discharge capacity of 134.6 mAh g⁻¹ at 0.5 C, which was higher than that of the undoped spinel. After 100 cycles, the discharge capacity could still reach up to 114.5 mAh g⁻¹ with capacity retention of 85.1%. Especially, at the high rate of 5.0 C, a high discharge capacity of 87.5 mAh g⁻¹ was obtained while the undoped spinel only exhibited 33.7 mAh g⁻¹. Such high performance indicated that doping the manganese sites with appropriate amount of silicon ions could effectively improve the specific capacity and cycling stability.     

Improved cyclability of lithium–sulfur battery cathode using encapsulated sulfur in hollow carbon nanofiber@nitrogen-doped porous carbon core–shell composite

Hollow carbon nanofiber@nitrogen-doped porous carbon (HCNF@NPC) core–shell composite, which was carbonized from HCNF@polyaniline, was prepared as an improved high conductive carbon matrix for encapsulating sulfur as a cathode composite material for lithium–sulfur batteries. The prepared HCNF@NPC-S composite with high sulfur content of 77.5 wt.% showed an obvious core–shell structure with an NPC layer coating on the surface of the HCNFs and sulfur homogeneously distributed in the coating layer. This material exhibited much better electrochemical performance than the HCNF-S composite, delivered initial discharge capacity of 1170 mAh g⁻¹, and maintains 590 mAh g⁻¹ after 200 cycles at the current density of 837.5 mA g⁻¹ (0.5 C). The significantly improved electrochemical performance of the HCNF@NPC-S composite was attributed to the synergetic effect between HCNF cores, which provided electronic conduction pathways and worked as mechanical support, and the NPC shells with relatively high surface area and pore volume, which could trap sulfur/polysulfides and provide Li⁺ conductive pathways.     

Simple fabrication of a Fe2O3/carbon composite for use in a high-performance lithium ion battery

A simple approach was developed for the fabrication of a Fe₂O₃/carbon composite by impregnating activated carbon with a ferric nitrate solution and calcinating it. The composite contains graphitic layers and 10 wt.% Fe₂O₃ particles of 20–50 nm in diameter. The composite has a high specific surface area of ∼828 m² g⁻¹ and when used as the anode in a lithium ion battery (LIB), it showed a reversible capacity of 623 mAh g⁻¹ for the first 100 cycles at 50 mA g⁻¹. A discharge capacity higher than 450 mAh g⁻¹ at 1000 mA g⁻¹ was recorded in rate performance testing. This highly improved reversible capacity and rate performance is attributed to the combination of (i) the formation of graphitic layers in the composite, which possibly improves the matrix electrical conductivity, (ii) the interconnected porous channels whose diameters ranges from the macro- to meso- pore, which increases lithium-ion mobility, and (iii) the Fe₂O₃ nanoparticles that facilitate the transport of electrons and shorten the distance for Li⁺ diffusion. This study provides a cost-effective, highly efficient means to fabricate materials which combine conducting carbon with nanoparticles of metal or metal oxide for the development of a high-performance LIB.     

Unique cyclic performance of post-treated carbide-derived carbon as an anode electrode

Carbide-derived carbon (CDC) is an attractive anode material for Li-ion battery applications because diverse pore textures and structures from amorphous to highly ordered graphite can be controlled by changing the synthesis conditions and precursor, respectively. To elucidate the unique cycling behavior of the post air-treated CDC anode, electrochemical performance was studied under variation of C-rates with structural changes before and after cycling. By tailoring the pore texture of CDCs as removal of amorphous phase by post air-activation, the anode electrode showed a high increase of capacity under prolonged cycling and under high C-rate conditions such as 0.3–1.0 C-rates. The discharge capacities of the treated CDC increased from 400 mAh g⁻¹ to 913 mAh g⁻¹ with increasing cycle number and were close to high initial irreversible value, 1250 mAh g⁻¹, at the 220th cycle under a 0.1C-rate condition, which are unique and unusual cyclic properties in carbon anode applications. Under high C-rate conditions, the discharge capacities started to increase from around 160 mAh g⁻¹ and values of 415 mAh g⁻¹, 372 mAh g⁻¹, and 336 mAh g⁻¹, were observed at 0.3, 0.5, and 1.0 C-rates, respectively, at 600 cycles, demonstrating stable capacity performance.     

The influences of sodium sources on the structure evolution and electrochemical performances of layered-tunnel hybrid Na0.6MnO2 cathode

Manganese (Mn) based oxide materials are regarded as promising cathodes for sodium ion batteries (SIBs) due to their high energy density, low-cost and environmental benignity. Here, we focus on the influences of various sodium sources on the structure diversity and electrochemical performances changes of layered-tunnel hybrid Na_0.6MnO₂ cathode. The Na_0.6MnO₂ cathodes were prepared by precipitation method followed by grinding with different sodium sources and annealing in air. The XRD results evidenced that the mass ratio of layered and tunnel components would be markedly influenced by sodium source. Electrochemical test results also demonstrate distinctive performances of Na_0.6MnO₂ cathodes with various sodium sources. Na_0.6MnO₂ cathode with Na₂C₂O₄ exhibited the best performances with 90 mAh g⁻¹ retained after 100 cycles at 1.0C. Superior rate performance with average discharge capacities of 180, 159, 143, 126, 112 and 93 mAh g⁻¹ at 0.1, 0.5, 1.0, 2.0, 4.0 and 8.0C was also observed. Furthermore, the EIS demonstrate that Na_0.6MnO₂ cathode with Na₂C₂O₄ displayed smaller charge transfer and fast Na⁺ diffusion rate, which indicated enhanced electrochemical reaction kinetics. The excellent electrochemical performance of Na_0.6MnO₂ with Na₂C₂O₄ is mainly due to the appropriate proportion of layered-tunnel component and their synergistic effects, which are influenced by sodium sources.