Anode material for sodium-ion battery with high performance by co-doping of anion and cation

Abstract

The application relates to the technical field of sodium ion battery electrochemical energy storage devices, and particularly discloses a high-performance sodium ion battery positive electrode material co-doped with anions and cations, which has a molecular formula of Na 3.75 V 1.25 Fe 0.75‑1.5x (PO 4‑x F x )3, 0 x ≤0.1.The high-performance sodium ion battery positive electrode material co-doped with anions and cations has vanadium and oxygen in the NASICON structure Na3V2(PO4)3 doped and replaced by iron and fluorine ions, the three-dimensional structure framework is kept stable, the reversible oxidation-reduction reaction of V(IV) / V(V) is activated due to the synergistic effect of iron and fluorine co-doping, the obtained electrode material has the characteristics of high capacity and long cycle stability, and has a good application prospect in sodium ion battery positive electrode materials and large-scale energy storage devices.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of sodium ion battery electrochemical energy storage devices, and particularly relates to a high-performance sodium ion battery positive electrode material co-doped with anions and cations. BACKGROUND

[0002] Lithium ion batteries have been widely used in portable electronic devices and electric vehicles due to their high voltage platform, high energy density and environmental friendliness. However, the low reserves of lithium resources in the earth's crust and high mining costs limit the application of lithium ion batteries in large-scale energy storage devices. Sodium ion batteries have similar working principles as lithium ion batteries, and sodium resources are abundant in the earth's crust, low in price and widely distributed, which has economic and environmental advantages over lithium. Therefore, sodium ion batteries, as the most promising alternative to lithium ion batteries, have attracted widespread attention from global researchers and battery manufacturers.

[0003] Sodium vanadium phosphate (Na3V2(PO4)3, abbreviated as NVP) has a NASICON structure, a stable three-dimensional structural framework and a large sodium ion channel. The strong covalent bond between anion units makes the structure stable, and the volume change during charging and discharging is small, meeting the requirements of long cycle life of the battery. However, NVP also has poor electronic conductivity, which makes the coulombic efficiency of NVP electrode low and the actual reversible capacity not ideal. In the NVP structure, the number of sodium ions participating in the electrochemical reaction is limited, and 1 mol of NVP can only provide 2 mol of sodium ions for reaction, resulting in a low theoretical specific capacity of 117 mAh g -1 . Therefore, how to increase the number of sodium ions participating in the electrochemical reaction in the VNP structure to improve the reversible specific capacity is a research hotspot in the field of NVP-based positive electrode materials, but it also presents a formidable challenge.

[0004] Generally, carbon-coated modification of NVP by traditional organic carbon sources is an effective way to improve the electronic conductivity and actual reversible capacity of such materials. However, vanadium in NVP has certain toxicity and is not very friendly to the environment, and is relatively expensive. In order to reduce the content of vanadium in NVP, researchers use cheap and environmentally friendly transition metals such as Mn, Fe, Ni, Ti, etc. to dope NVP to improve the electrochemical performance. In addition, fluorine has strong electronegativity, and the introduction of fluorine elements in electrode materials can reduce the charge transfer resistance in the electrode electrochemical reaction process, inhibit the irreversible transformation of the material structure, and improve the electrochemical activity. For example, Fe and F are doped into NVP combined with carbon nanotubes to improve the electrochemical performance of NVP, but the number of sodium ions involved in the electrochemical reaction is still limited, resulting in a reversible specific capacity of only 108 mAh / g at 1C, and the electrochemical performance needs to be further improved. SUMMARY

[0005] The purpose of the present application is to provide a cathode material for sodium-ion batteries with high performance by co-doping of anions and cations, and the cathode material is Na 4+ / V 5+ The reversible redox reaction increases the number of sodium ions involved in the electrochemical reaction and improves the reversible capacity of the material.

[0006] To achieve the above purpose, the present application provides a cathode material for sodium-ion batteries with high performance by co-doping of anions and cations, and the cathode material is Na 3.75 V 1.25 Fe 0.75-1.5x (PO 4-x F x )3, 0 < x < 0.1.

[0007] Preferably, in the cathode material for sodium-ion batteries with high performance by co-doping of anions and cations, 0.5 < x < 0.1.

[0008] Preferably, in the cathode material for sodium-ion batteries with high performance by co-doping of anions and cations, the cathode material is Na 3.75 V 1.25 Fe 0.6 (PO 3.9 F 0.1 )3.

[0009] The cathode material Na 3.75 V 1.25 Fe 0.75-1.5x (PO 4-x F x)3, substituting and doping with Fe, F, changing the spatial structure of NVP by optimizing the doping amount of Fe, F, the positive electrode material Na 3.75 V 1.25 Fe 0.75-1.5x (PO 4-x F x )3 space group is R32, there are 3 sodium ion sites in the structure, V alone occupies a 6c site, the rest of V and Fe occupy another 6c site, cation V and Fe occupy order, activate V 4+ / V 5+ Reversible redox, thereby improving the electrochemical performance of the positive electrode material.

[0010] Preferably, in the above-mentioned anion and cation co-doped high-performance sodium ion battery positive electrode material, the surface of the positive electrode material particles is coated with an amorphous carbon layer, and the thickness of the carbon layer is between 2-3nm.

[0011] Preferably, in the above-mentioned anion and cation co-doped high-performance sodium ion battery positive electrode material, the synthesis method of the positive electrode material comprises the following steps:

[0012] (1) according to the ratio, sodium source, vanadium source, iron source, phosphorus source, fluorine source and organic carbon source are weighed and dissolved in hot water, magnetic stirring, to obtain a uniform solution; then rotary evaporation of water, vacuum drying, to obtain a solid precursor;

[0013] (2) the precursor obtained in step (1) is ground thoroughly to obtain a powder solid; the powder solid is sintered at 400-500 DEG C under a protective atmosphere for 1.5-3h, and then the temperature is raised to 650-700 DEG C, and sintered for 6-10h, to obtain the positive electrode material.

[0014] Preferably, in the above-mentioned anion and cation co-doped high-performance sodium ion battery positive electrode material, the sodium source is one or more of sodium acetate (NaAc), sodium carbonate (Na2CO3), sodium hydroxide (NaOH), and sodium fluoride (NaF); the vanadium source is vanadium pentoxide (V2O5) or ammonium metavanadate (NH4VO3); the iron source is iron nitrate nonahydrate (Fe(NO3)3·9H2O) or ferrous oxalate dihydrate (Fe(C2O4)·2H2O); the phosphorus source is ammonium dihydrogen phosphate (NH4H2PO4) or phosphoric acid (H3PO4); the fluorine source is sodium fluoride (NaF) or hydrofluoric acid (HF); the organic carbon source is citric acid (C6H8O7, CA) or ascorbic acid (C6H8O6, VC), which acts as a reducing agent to reduce V(V) to V(III) in the solution.

[0015] Preferably, in the above-mentioned anion and cation co-doped high-performance sodium ion battery positive electrode material, in the step (1), the temperature of hot water is 60-70 DEG C; the water is evaporated at 85-95 DEG C by rotary evaporation, and vacuum drying is carried out at 110-120 DEG C.

[0016] Preferably, in the above-mentioned anion and cation co-doped high-performance sodium ion battery positive electrode material, in the step (2), the protective atmosphere is 95% argon and 5% hydrogen mixed gas, the temperature is increased to 450 DEG C at a rate of 2 DEG C per minute, sintering is carried out for 2h, and then the temperature is increased to 650-700 DEG C, and sintering is carried out for 6-10h.

[0017] Preferably, the above-mentioned anion and cation co-doped high-performance sodium ion battery positive electrode material is applied in a sodium ion battery.

[0018] Compared with the prior art, the present application has the following beneficial effects:

[0019] 1. The anion and cation co-doped high-performance sodium ion battery positive electrode material of the present application has good reversible specific capacity and cycle stability, the average reversible specific capacity reaches 136mAh / g at 1C, the super-fast charging and discharging is realized under very high rate 50C (72 seconds), the reversible specific capacity is still as high as 83mAh / g after 10000 cycles, the capacity retention rate is 86%, and the long cycle life requirement of the battery can be met.

[0020] 2. The anion and cation co-doped high-performance sodium ion battery positive electrode material of the present application is doped and modified with iron and fluorine ions on the NASICON structure Na3V2(PO4)3, Fe is doped on V sites and F is doped on O sites, the three-dimensional framework structure is maintained, the space group of NVP is changed by optimizing the doping amount of Fe and F, the positive electrode material Na 3.75 V 1.25 Fe 0.75-1.5x (PO 4-x F x )3 of the present application has a space group R32, there are three sodium ion sites in the structure, V alone occupies a 6c site, the remaining V and Fe occupy another 6c site, the cations V and Fe are ordered, due to the synergistic effect of iron and fluorine co-doping, V 4+ / V 5+ is activated for reversible oxidation and reduction, thereby improving the comprehensive electrochemical performance of the positive electrode material.

[0021] 3. The anion and cation co-doped high-performance sodium ion battery positive electrode material of the present application has simple preparation process, raw materials are easy to obtain, has certain universality, and is conducive to further popularization of the material. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 It is the XRD pattern of the positive electrode material of Example 3 of the present application.

[0023] Figure 2 Structure diagram of the positive electrode material of Example 3 of the present application.

[0024] Figure 3 Scanning electron microscope element distribution diagram of the positive electrode material of Example 3 of the present application.

[0025] Figure 4 Transmission electron microscope diagram of the positive electrode material of Example 3 of the present application.

[0026] Figure 5 XRD pattern of the positive electrode material of Comparative Example 1 of the present application.

[0027] Figure 6 XRD pattern of the positive electrode material of Comparative Example 2 of the present application.

[0028] Figure 7 Cyclic voltammogram of the battery prepared from the positive electrode material of Example 3 of the present application.

[0029] Figure 8 Cyclic voltammogram of the battery prepared from the positive electrode material of Comparative Example 1.

[0030] Figure 9 Voltage-capacity diagram of the battery prepared from the positive electrode material of Example 3 of the present application at 0.2C charge-discharge.

[0031] Figure 10 Voltage-capacity diagram of the battery prepared from the positive electrode material of Comparative Example 1 at 0.2C charge-discharge.

[0032] Figure 11 Different rate performance diagram of the battery prepared from the positive electrode material of Example 3 of the present application.

[0033] Figure 12 Cycle performance diagram of the battery prepared from the positive electrode material of Example 3 of the present application at 50C. DETAILED DESCRIPTION

[0034] The specific embodiments of the present application are described in detail below, but it should be understood that the scope of protection of the present application is not limited by the specific embodiments.

[0035] Example 1

[0036] A high-performance sodium-ion battery positive electrode material co-doped with anions and cations, having a composition of Na 3.75 V 1.25 Fe 0.675 (PO 3.95 F 0.05 )3.

[0037] The high-performance sodium-ion battery positive electrode material co-doped with anions and cations of the present embodiment is Na3.75 V 1.25 Fe 0.675 (PO 3.95 F 0.05 The synthesis method of 3 includes the following steps:

[0038] (1) Weigh out sodium acetate (NaAc), vanadium pentoxide (V2O5), ferric nitrate nonahydrate (Fe(NO3)3·9H2O), ammonium dihydrogen phosphate (NH4H2PO4), sodium fluoride (NaF), and citric acid (CA) and dissolve them in hot water at 60℃. The molar ratio of NaAc to NaF is 24:1, the molar ratio of NaAc to V2O5 is 5.76:1, the molar ratio of NaAc to Fe(NO3)3·9H2O is 16:3, the molar ratio of NaAc to NH4H2PO4 is 1.2:1, and the molar ratio of NaAc to citric acid is 1:1.56.

[0039] A homogeneous solution was obtained by magnetic stirring and heating for 60 minutes, then transferred to a rotary evaporator, where water was evaporated at 90°C, and then dried under vacuum at 120°C to obtain a solid precursor.

[0040] (2) Grind the precursor obtained in step (1) thoroughly for 1 hour to obtain a powder solid. Transfer the powder solid to a tube furnace, and use a protective atmosphere of 95% argon and 5% hydrogen mixed gas. Increase the temperature to 450°C at a heating rate of 2°C / min, and sinter for 2 hours to allow the organic matter to decompose completely. Finally, raise the temperature to 650°C and hold for 6 hours to obtain the target product Na with carbon coating. 3.75 V 1.25 Fe 0.675 (PO 3.95 F 0.05 3.

[0041] Example 2

[0042] A high-performance sodium-ion battery cathode material co-doped with cations and anions, with the composition Na 3.75 V 1.25 Fe 0.675 (PO 3.95 F 0.05 3.

[0043] This embodiment presents a high-performance sodium-ion battery cathode material with co-doped anion and cations, Na. 3.75 V 1.25 Fe 0.675 (PO 3.95 F 0.05 The synthesis method of 3 includes the following steps:

[0044] (1) Sodium carbonate (Na2CO3), ammonium metavanadate (NH4VO3), ferrous oxalate dihydrate (Fe(C2O4)·2H2O), phosphoric acid (H3PO4), hydrofluoric acid (HF) and ascorbic acid (C6H8O6, VC) are dissolved in hot water at 60℃, wherein the molar ratio of Na2CO3 to hydrofluoric acid is 25:2, the molar ratio of Na2CO3 to NH4VO3 is 3:2, the molar ratio of Na2CO3 to Fe(C2O4)·2H2O is 25:9, the molar ratio of Na2CO3 to H3PO4 is 1.25:2, and the molar ratio of Na2CO3 to ascorbic acid is 1:2;

[0045] The magnetic stirring is heated for 60 minutes to obtain a uniform solution, which is then transferred to a rotary evaporator to evaporate water at 90℃, and then dried in vacuum at 120℃ overnight to obtain a solid precursor;

[0046] (2) The precursor obtained in step (1) is ground for 1 hour to obtain a powder solid, which is transferred to a tube furnace, and the protective atmosphere is 95% argon and 5% hydrogen mixed gas, and the temperature is raised to 450℃ at a rate of 2℃ / min, and sintered for 2 hours to fully decompose the organic matter, and finally the temperature is raised to 700℃, and sintered for 8 hours to obtain the target product Na 3.75 V 1.25 Fe 0.675 (PO 3.95 F 0.05 )3.

[0047] Example 3

[0048] A cation-anion co-doped high-performance sodium-ion battery anode material, which is composed of Na 3.75 V 1.25 Fe 0.6 (PO 3.9 F 0.1 )3.

[0049] The synthesis method of the cation-anion co-doped high-performance sodium-ion battery anode material Na 3.75 V 1.25 Fe 0.6 (PO 3.9 F 0.1 )3 of the embodiment comprises the following steps:

[0050] (1) Sodium acetate (NaAc), vanadium pentoxide (V2O5), iron nitrate nonahydrate (Fe(NO3)3·9H2O), ammonium dihydrogen phosphate (NH4H2PO4), sodium fluoride (NaF) and citric acid (CA) are dissolved in hot water at 60℃, wherein the molar ratio of NaAc to NaF is 11.5:1, the molar ratio of NaAc to V2O5 is 5.52:1, the molar ratio of NaAc to Fe(NO3)3·9H2O is 5.75:1, the molar ratio of NaAc to NH4H2PO4 is 1.15:1, and the molar ratio of NaAc to citric acid is 1:1.5;

[0051] The magnetic stirring is heated for 60 minutes to obtain a uniform solution, which is then transferred to a rotary evaporator to evaporate water at 90℃, and then dried in vacuum at 120℃ overnight to obtain a solid precursor;

[0052] (2) The precursor obtained in step (1) is ground for 1 hour to obtain a powder solid, which is transferred to a tube furnace, and the protective atmosphere is 95% argon and 5% hydrogen mixed gas, and the temperature is raised to 450℃ at a rate of 2℃ / min, and sintered for 2 hours to fully decompose the organic matter, and finally the temperature is raised to 650℃, and sintered for 6 hours to obtain the target product Na 3.75 V 1.25 Fe 0.6 (PO 3.9 F 0.1 )3 with carbon coating.

[0053] Example 4

[0054] A kind of anion-cation co-doped high-performance sodium ion battery positive material, the composition is Na 3.75 V 1.25 Fe 0.6 (PO 3.9 F 0.1 )3.

[0055] The synthesis method of the anion-cation co-doped high-performance sodium ion battery positive material Na 3.75 V 1.25 Fe 0.6 (PO 3.9 F 0.1 )3 of the embodiment includes the following steps:

[0056] (1) Weigh sodium hydroxide (NaOH), vanadium pentoxide (V2O5), iron nitrate nonahydrate (Fe(NO3)3·9H2O), phosphoric acid (H3PO4), sodium fluoride (NaF) and citric acid (CA) into hot water at 60℃, wherein the molar ratio of NaOH to NaF is 11.5:1, the molar ratio of NaOH to V2O5 is 5.52:1, the molar ratio of NaOH to Fe(NO3)3·9H2O is 5.75:1, the molar ratio of NaOH to H3PO4 is 1.15:1, and the molar ratio of NaOH to citric acid is 1:1.5;

[0057] The magnetic stirring is heated for 60 minutes to obtain a uniform solution, which is then transferred to a rotary evaporator to evaporate water at 90℃, and then dried in vacuum at 120℃ overnight to obtain a solid precursor;

[0058] (2) The precursor obtained in step (1) is ground for 1 hour to obtain a powder solid, which is transferred to a tube furnace, and the protective atmosphere is 95% argon and 5% hydrogen mixed gas. The temperature is raised to 450℃ at a rate of 2℃ / min, and sintered for 2 hours to fully decompose the organic matter. Finally, the temperature is raised to 700℃, and sintered for 10 hours to obtain the target product Na 3.75 V 1.25 Fe 0.6 (PO 3.9 F 0.1 )3.

[0059] Example 5

[0060] A cation-anion co-doped high-performance sodium-ion battery anode material, which is composed of Na 3.75 V 1.25 Fe 0.6 (PO 3.9 F 0.1 )3.

[0061] The synthesis method of the cation-anion co-doped high-performance sodium-ion battery anode material Na 3.75 V 1.25 Fe 0.6 (PO 3.9 F 0.1 )3 of the embodiment includes the following steps:

[0062] (1) Weigh out sodium hydroxide (NaOH), ammonium metavanadate (NH4VO3), ferrous oxalate dihydrate (Fe(C2O4)·2H2O), phosphoric acid (H3PO4), hydrofluoric acid (HF), and citric acid (CA) and dissolve them in hot water at 60℃. The molar ratio of NaOH to HF is 12.5:1, the molar ratio of NaOH to NH4VO3 is 3:1, the molar ratio of NaOH to Fe(C2O4)·2H2O is 6.25:1, the molar ratio of NaOH to H3PO4 is 1.25:1, and the molar ratio of NaOH to citric acid is 1:1.5.

[0063] A homogeneous solution was obtained by magnetic stirring and heating for 60 minutes, then transferred to a rotary evaporator, where water was evaporated at 90°C, and then vacuum dried at 120°C overnight to obtain a solid precursor.

[0064] (2) Grind the precursor obtained in step (1) thoroughly for 1 hour to obtain a powder solid. Transfer the powder solid to a tube furnace, and use a protective atmosphere of 95% argon and 5% hydrogen mixed gas. Increase the temperature to 450°C at a heating rate of 2°C / min, and sinter for 2 hours to allow the organic matter to decompose completely. Finally, raise the temperature to 650°C and hold for 6 hours to obtain the target product Na with carbon coating. 3.75 V 1.25 Fe 0.6 (PO 3.9 F 0.1 3.

[0065] Comparative Example 1

[0066] The cathode material in this comparative example has the composition Na. 3.75 V 1.25 Fe 0.75 (PO4)3. The synthesis method is the same as in Example 3, except that sodium fluoride is not added, the molar ratio of NaAc to V2O5 is 6:1, the molar ratio of NaAc to Fe(NO3)3·9H2O is 5:1, the molar ratio of NaAc to NH4H2PO4 is 1.25:1, and the molar ratio of NaAc to citric acid is 1:1.5.

[0067] Comparative Example 2

[0068] The cathode material in this comparative example has the composition Na. 3.75 V 1.25 Fe 0.525 (PO 3.85 F 0.15 3. The synthesis method is the same as in Example 1, except that the raw material ratios are different. The XRD pattern of the cathode material obtained in this comparative example is shown below. Figure 6 As shown in the figure, the impurity peak of NaFePO4 appears at 33.5°, proving that a pure phase was not obtained.

[0069] The XRD pattern of the positive electrode material obtained in Example 3 is shown in Figure 1 The Rietveld refinement fitting was performed by X-ray diffraction data, and the refinement residual factor R wp was 1.62%, R P was 1.12%, and R Bragg was 0.24%, indicating the rationality of the refinement result, and the space group was R32. The structure is shown in Figure 2 There were three sodium ion sites in the structure, and V occupied a 6c site alone, and the rest of V and Fe occupied another 6c site, which indicated that the cations V and Fe were ordered in the occupation. The scanning electron microscope element distribution map (see Figure 3 ) showed that Na, V, Fe, P, O, F and C elements were uniformly distributed in the sample. Figure 4 The transmission electron microscope picture of Example 3 is shown in the figure, from which it can be observed that the surface of the sample particles is coated with an amorphous carbon layer of about 3 nm, which will improve the electronic conductivity of the sample, and the lattice fringe spacing in the figure is about 0.43 nm, which corresponds to the interplanar spacing of the (104) crystal plane of the R32 space group, further proving that the synthesized sample has high crystallinity.

[0070] Figure 5 The XRD pattern of the positive electrode material obtained in Comparative Example 1 is shown in the figure, and the refinement residual factor R wp was 2.50%, R p was 1.87%, and R Bragg was 0.23%, indicating the rationality of the refinement result, and the space group was which was different from the space group of the positive electrode material of the example.

[0071] Application Example 1

[0072] The positive electrode materials synthesized in Example 3 and Comparative Example 1 were mixed with conductive carbon black and binder PVDF in a mass ratio of 80%:10%:10% in N-methyl pyrrolidone to obtain electrode slurry, which was coated on an aluminum foil and dried to obtain electrodes. A metal sodium was used as a reference electrode and a counter electrode, and 1 mol / L NaClO4 90% propylene carbonate (PC) and 10% fluoroethylene carbonate (FEC) were used as electrolyte, and a coin cell was assembled for cyclic voltammetry and cyclic charge-discharge tests. The voltage range of all electrochemical tests was 2-4.2V, and the scan rate of the cyclic voltammetry test was 0.2mV / s.

[0073] The cyclic voltammetry curve of the battery obtained from the positive electrode material of Example 3 is shown in Figure 7 From the figure, it can be seen that there are three pairs of redox peaks at 2.43-2.53V, 3.34-3.49V and 4.01-4.06V, respectively, corresponding to Fe 2+ / Fe 3+ V 3+ / V 4+ and V 4+ / V 5+ The redox couple indicates a synergistic effect between Fe and F doping, activating V. 4+ / V 5+ Redox couple. The cyclic voltammetry curve of the battery obtained for the cathode material of Comparative Example 1 is shown below. Figure 8 As shown in the figure, Fe can be observed during the charging process. 2+ / Fe 3+ V 3+ / V 4+ and V 4+ / V 5+ Oxidation couple, but only V remains during discharge. 4+ / V 3+ and Fe 3+ / Fe 2+ The reduced redox couple.

[0074] The voltage-capacity of the battery obtained from the positive electrode material of Example 3 of the present invention during charge-discharge at 0.2C is as follows: Figure 9 As shown, oxidation plateaus exist at approximately 2.5V, 3.45V, and 4V during the charging process, corresponding to Fe... 2+ / Fe 3+ V 3+ / V 4+ and V 4+ / V 5+ Oxidation couple, and V exists during discharge. 4+ / V 5+ V 3+ / V 4+ and Fe 2+ / Fe 3+ The reduction pairs are consistent with the results of the cyclic voltammetry test; as shown in the figure, the initial discharge specific capacity of the battery is as high as 158 mAh / g, and the gravimetric energy density of the battery reaches 540 Wh / kg. The voltage-capacity of the battery obtained from the cathode material of Comparative Example 1 at 0.2C charge-discharge is as follows: Figure 10 As shown in the figure, V does not exist during the first discharge process. 5+ / V 4+ The reduction voltage platform has an initial discharge capacity of 149 mAh / g and a battery mass energy density of 498 Wh / kg.

[0075] Figure 11The battery assembled with the positive electrode material obtained in the inventive example 3 was tested for rate performance at different rates (1C, 5C, 10C, 20C, 40C, 50C) and in the voltage range of 2-4.2V. The average reversible specific capacity at 1C, 5C, 10C, 20C, 40C, 50C was 136, 124, 117, 109, 94, 87mAh / g, respectively. The average reversible specific capacity of the battery corresponding to the comparative example 1 at 1C, 5C, 10C, 20C (cycled for 10 times) was 127, 107, 90, 64mAh / g, respectively. It can be seen from the above that the reversible specific capacity of the battery of the inventive example 3 is obviously improved compared with the battery of the comparative example 1. Even in the case of high rate 10C (6 minutes) fast charging, the reversible specific capacity (117mAh / g) reaches the theoretical capacity (117mAh / g) of Na3V2(PO4)3.

[0076] The cycle performance graph of the battery obtained from the positive electrode material of the inventive example 3 at 50C is shown in Figure 12 It can be seen from the graph that even in the case of very high rate 50C (72 seconds) fast charging and discharging, the capacity retention rate after 2000 cycles is 102%, and the reversible specific capacity is still as high as 83mAh / g after 10000 cycles, and the capacity retention rate is 86%. The results of the cycle charging and discharging show that the synergistic effect of Fe and F co-doping triggers the redox pair of V 4+ / V 5+ , significantly improving the reversible specific capacity and cycle stability of the material.

[0077] The foregoing description of specific exemplary embodiments of the application is intended to be illustrative only and is not intended to limit the application to the precise forms described. Many modifications and variations are possible in light of the above teachings without departing from the spirit or essential characteristics of the application. The exemplary embodiments were chosen and described in order to explain the principles of the application and its practical application to thereby enable others skilled in the art to best utilize the application and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the scope of the application be defined by the claims and their equivalents.

Claims

1. A sodium-ion battery cathode material co-doped with cations and anions, characterized in that, The positive electrode material is Na. 3.75 V 1.25 Fe 0.6 (PO 3.9 F 0.1 )3, the positive electrode material is a NASICON-type polyanionic compound with ordered V and Fe cations occupying the site, and the space group is R32.

2. The sodium-ion battery cathode material co-doped with anions and cations according to claim 1, characterized in that, The surface of the cathode material particles is coated with an amorphous carbon layer.

3. The sodium-ion battery cathode material co-doped with anions and cations according to claim 1, characterized in that, The method for synthesizing the cathode material includes the following steps: (1) Weigh out sodium source, vanadium source, iron source, phosphorus source, fluorine source and organic carbon source according to the ratio, dissolve them in hot water, stir magnetically to obtain a homogeneous solution; then evaporate the water by rotary evaporation, dry under vacuum to obtain a solid precursor; (2) Grind the solid precursor obtained in step (1) thoroughly to obtain a powder solid; sinter the powder solid at 400~500℃ for 1.5~3h under a protective atmosphere, and then raise the temperature to 650~700℃ and hold for sintering for 6~10h to obtain the cathode material.

4. The sodium-ion battery cathode material co-doped with anions and cations according to claim 3, characterized in that, The sodium source is one or more of sodium acetate, sodium fluoride, sodium carbonate, and sodium hydroxide; the vanadium source is vanadium pentoxide or ammonium metavanadate; the iron source is ferric nitrate nonahydrate or ferrous oxalate dihydrate; the phosphorus source is ammonium dihydrogen phosphate or phosphoric acid; the fluorine source is sodium fluoride or hydrofluoric acid; and the organic carbon source is citric acid or ascorbic acid.

5. The anion and cation co-doped sodium-ion battery cathode material according to claim 3, characterized in that, In step (1), the hot water temperature is 60~70℃; the water is evaporated by rotary evaporation at 85~95℃ and vacuum dried at 110~120℃.

6. The anion and cation co-doped sodium-ion battery cathode material according to claim 3, characterized in that, In step (2), the protective atmosphere is a mixture of 95% argon and 5% hydrogen. The temperature is raised to 450°C at a rate of 2°C per minute, and sintered for 2 hours. Then the temperature is raised to 650~700°C and held for sintering for 6-10 hours.

7. The application of the anion and cation co-doped sodium-ion battery cathode material according to any one of claims 1 to 2 in sodium-ion batteries.

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