Sodium-ion battery high-voltage positive electrode composite material Na3Vx (PO4) 3 / C and preparation method thereof

Abstract

The invention discloses a sodium ion battery high-voltage electrode composite material. The composition is Na3Vx (P2O7) 1.5 / C, and x < lt > is greater than or equal to 0.9; and 1.5. A target material is synthesized through a sol method, and the amount of substance of V is adjusted in the synthesis process, so that an electrode material of a V4 + V5 + high-voltage platform can be obtained. When the amount of substance of V changes between 0.9 and 1.1, the amount of substance of PO4 < 3-> is 3.0, and the amount of substance of Na < + > ions is 3.0, the material is mainly composed of Na3V (P2O7) 1.5, and shows a 3.8-3.9 V discharge platform. When the amount of substance of V is increased from 1.2 to 1.5, phase conversion from Na3V (P2O7) 1.5 to Na3V2 (PO4) 3 obviously occurs. The single-phase Na-V-PO4 electrode material with a high-voltage 3.8-3.9 V platform is obtained by regulating and controlling the element proportion, the output power of the material is improved, and the potential application prospect is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium ion battery materials, and in particular relates to a sodium ion battery high-voltage positive electrode composite material having a composition of Na3Vx(PO4)3 / C synthesized by a sol method. Background Art

[0002] In the field of new energy storage technologies, lithium-ion batteries (Li-ion Batteries) have been widely adopted in various applications due to their advantages, including low self-discharge, high power density, and wide voltage window. However, the low reserves and uneven distribution of lithium resources lead to high costs for Li-ion Batteries. Sodium-ion batteries (Na-ion Batteries), with their high abundance, widespread distribution, low cost, and compatibility with Li-ion Batteries, have made them the most promising next-generation energy storage devices. The performance of the cathode material is a key factor influencing the composition of Na-ion batteries. Currently, the main cathode materials include layered oxides, polyanionic composites, and Prussian blue compounds. Among them, the discharge voltage platform of NASICON-type Na₃V₂(PO₄)₃ is stable at 3.3-3.4V, corresponding to the transition between V₃+ and V₄+. When Al, Mn, Bi, Cr, and other materials are partially substituted for V, the discharge process of the composite material sometimes exhibits a discharge platform of 4.0V, corresponding to the transition between V₄+ and V₅+, but the main discharge platform remains stable between 3.3-3.4V. After partially replacing PO43- with anion F, the discharge platform is increased to ~4.1 V and ~3.5 V due to the increase in electrostatic force between the anion and V, thereby improving the output power. Although different doping methods have improved the discharge capacity of Na3V2(PO4)3 to a certain extent, except for the introduction of F- ions, the discharge platform of various composite materials is located between 3.3-3.4V, and there is no clear report on the conversion between V4+ and V5+ corresponding to the high voltage of 4.0V. Therefore, the development of high-voltage cathode materials for sodium-ion batteries corresponding to the conversion of V4+ and V5+ is conducive to improving the overall performance of NASICON-type sodium-ion batteries. Clarifying the relationship between the conversion and composition between V4+ and V3+ and V4+ phases is of great significance for the design and optimization of battery performance. Summary of the Invention

[0003] The object of the present invention is to provide a high-voltage cathode composite material for sodium ion batteries.

[0004] The present invention also aims to provide a method for preparing a high-voltage cathode composite material for a sodium ion battery.

[0005] In order to achieve the purpose of the present invention, the composition of a sodium ion battery high voltage positive electrode composite material provided by the present invention is shown in the following formula: Na3Vx(PO4)3 / C Among them, 0.9≤x≤1.5.

[0006] When 0.9≤x≤1.1, the composite material is mainly composed of Na3V(P2O7)1.5 phase and carbon, and the discharge platform is 3.8V.

[0007] When 1.2≤x<1.5, the composite material transforms from Na3V(P2O7)1.5 phase to Na3V2(PO4)3 phase, showing two discharge platforms of ~3.8V and 3.3V.

[0008] Preferably, the molar ratio of Na+ ions to V in the composite material is 3:0.9 to 3:1.5.

[0009] Preferably, the molar ratio of V to PO43- ions in the composite material is 0.9:3 to 1.5:3.

[0010] Preferably, the molar ratio of carbon source to V in the Na3Vx(PO4)3 / C composite material is 1:1.

[0011] When the amount of V in the present invention varies between 0.9 and 1.1, it is almost a single-phase Na3V(P2O7)1.5, mainly corresponding to a high-voltage discharge platform at 3.8V, corresponding to the conversion of V4+ to V5+; as x increases from 1.2 to 1.5, the composition of the composite material changes from Na3V(P2O7)1.5 to Na3V2(PO4)3 phase, and at this time the discharge platform is composed of 3.8 V and 3.3V, indicating that the change of the discharge platform is closely related to the change of composition.

[0012] The method for preparing the composite material of the present invention comprises the following steps: (1) Weighing sodium salt, vanadium source, phosphate and carbon source according to the stoichiometric ratio, mixing them, adding deionized water to the mixture, and incubating in an oil bath at 80°C to 100°C for 1 to 3 hours. After the reaction is completed, heating to 100°C to 120°C and drying for 8 to 12 hours to obtain a gel precursor; (2) A certain amount of gel precursor was calcined twice in a tubular furnace with Ar gas, the first calcination being at 450°C for 6 h and the second calcination being at 750°C-850°C for 6-10 h to obtain a composite material; The sodium salt is one of sodium dihydrogen phosphate, sodium citrate, sodium carbonate, and sodium bicarbonate; the vanadium source is NH4VO3 or V2O5; and the carbon source is one of sodium citrate, citric acid, EDTA, and oxalic acid.

[0013] In the above preparation method, as preferred conditions, in step (1), the oil bath temperature is 80°C and the time is 2h.

[0014] In the above preparation method, as preferred conditions, in step (1), the drying temperature is 120°C and the drying time is 10 hours.

[0015] In the above preparation method, as a preferred condition, in step (2), the second calcination temperature is 750°C and the time is 7h.

[0016] The obtained product composite material contains a new sodium ion battery high-voltage positive electrode composite material, and its structural composition is shown by the following formula: Na3V(P2O7)1.5 / C.

[0017] In the present invention, the sodium salts are NaH2PO4, Na3C6H5O7, Na2CO3, and NaH2CO3. This avoids the introduction of other ions, resulting in a single elemental product and avoiding the influence of other anions. The carbon source is sodium citrate, citric acid, EDTA, or oxalic acid, which can provide sufficient electrons, increasing the electron density around V. NaH2PO4 and NH4H2PO4 are used to provide PO43- ions.

[0018] In the composition of the Na3Vx(PO4)3 / C sodium ion battery positive electrode composite material provided by the present invention, the amount of substance ratio of Na to V is 3:0.9~3:1.5, the ratio of V to PO43- is 0.9:3~1.5:3 or the ratio of V to P2O74- is 0.9:1.5~1.5:1.5, and the ratio of carbon source to V is 1:1. In the solution, V forms a complex with the carbon source, so that the electron cloud density around V changes. When PO43- ions are added, their strong attraction causes the electrons around V to further shift, and at this time the electron cloud density around V is larger, thereby presenting a trivalent or tetravalent form. In the subsequent heat treatment process, due to the presence of strong chemical bonds, the vanadium in the product exists in a trivalent form, resulting in a discharge voltage platform of 3.8~3.9 V.

[0019] Experiments have confirmed that the discharge capacity of the Na₃Vx(PO₄)₃ / C (0.9≤x≤1.1) composite material is ≥ 40 mAh g⁻¹ at a discharge cutoff voltage of 2.5 V and a discharge current of 117 mA g⁻¹. After 500 charge-discharge cycles, the discharge plateau remains stable at 3.8-3.9 V, with no significant change in discharge capacity. When the x content is further increased to 1.5, the discharge plateau of the corresponding product decreases to around 3.3 V, while the discharge capacity increases.

[0020] The present invention achieves the following beneficial effects: Testing of the composite material prepared by the present invention shows that, while maintaining the amounts of sodium and phosphate, when the amount of vanadium is between 0.9 and 1.1, a single-phase Na3V(P2O7)1.5 material with a high voltage of 3.8V is obtained. The high-voltage discharge platform exhibited by the material corresponds to the conversion between V4+ and V5+, filling a gap in the research of V4+ and V5+ high-voltage single-phases in NASICON-type Na3V2(PO4)3 structures. The preparation method of the present invention is simple and low-cost, providing a new option for the development of high-voltage and high-power NASICON-type electrode composite materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the XRD pattern of Example 1.

[0022] Figure 2 This is the charge and discharge curve diagram of Example 1.

[0023] Figure 3 This is the cyclic stability diagram of Example 1.

[0024] Figure 4 This is the CV curve diagram of Example 1. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0026] The following examples illustrate the present invention. Example 1

[0027] Preparation of composite material Na3Vx (PO4)3 / C (x=1) Preparation process: (1) NaH2PO4, NH4VO3 and citric acid were weighed according to the stoichiometric ratio, wherein the molar ratio of Na+ to V was 3:1, the molar ratio of V to PO43- was 1:3, and the molar ratio of citric acid to vanadium was 1:1. After mixing them, 50 mL of deionized water was added to the mixture, and the mixture was in an 80°C oil bath for 2 h. After the reaction was completed, the temperature was raised to 100°C~120°C and dried for 10 h to obtain a gel precursor; (2) The obtained gel precursor was calcined at 450°C for 6 h in an Ar atmosphere and then calcined at 750°C for 7 h to obtain a Na3V(PO4)3 / C composite material composed of Na3V(P2O7)1.5 phase and carbon.

[0028] Material experiment: The Na3V(PO4)3 / C composite material composed of the Na3V(P2O7)1.5 / C phase prepared above is used as a positive electrode material for sodium ion batteries.

[0029] Experiments have confirmed that the Na3Vx (PO4)3 / C (x=1) composite material is almost composed of a single phase of Na3V(P2O7)1.5 and carbon (see Figure 1 ), which is significantly different from the composition and morphology of the reported Na3V2(PO4)3, and its corresponding discharge platform is located at 3.8~3.9V (see Figure 2 ), at a discharge current of 117 mA g-1, the discharge capacity remains at 40 mAh g-1 (see Figure 3 The cyclic voltammetry curve shows that there is a strong oxidation peak at 4.0V and a reduction peak at 3.8V (see Figure 4 ), which corresponds to the charge-discharge platform and the conversion between V4+ and V5+ reported in the literature. This indicates that the charge-discharge process of this composite material is similar to the discharge between V4+ and V5+ in NASICON-type Na3V2(PO4)3, providing a useful reference for the development of high-voltage electrode materials. Example 2

[0030] Preparation of composite material Na3Vx (PO4)3 / C (x=1) Preparation process: (1) NaH2PO4, V2O5 and citric acid were weighed according to the stoichiometric ratio, wherein the molar ratio of Na+ to V was 3:1, the molar ratio of V to PO43- was 1:3, and the molar ratio of citric acid to vanadium was 1:1. After mixing them, 50 mL of deionized water was added to the mixture, and the mixture was incubated in an oil bath at 80°C for 2 h and dried at 120°C for 10 h to obtain a gel precursor. (2) The obtained gel precursor was calcined at 450°C for 6 h in an Ar atmosphere and then calcined at 750°C for 7 h to obtain a Na3V(PO4)3 / C composite material composed of Na3V(P2O7)1.5 phase and carbon.

[0031] Material experiment: The Na3V(PO4)3 / C composite material composed of the Na3V(P2O7)1.5 / C phase prepared above was used as a positive electrode material for a sodium ion battery in the same manner as in Example 1. Example 3

[0032] Preparation of composite material Na3Vx (PO4)3 / C (x=1) Preparation process: (1) Sodium citrate, NH4VO3, and NH4H2PO4 were weighed in a stoichiometric ratio, wherein the molar ratio of Na+ to V was 3:1, the molar ratio of V to PO43- was 1:3, and the molar ratio of citrate to vanadium was 1:1. After mixing them, 50 mL of deionized water was added to the mixture, and the mixture was incubated in an 80°C oil bath for 2 h and dried at 120°C for 10 h to obtain a gel precursor. (2) The obtained gel precursor was calcined at 450°C for 6 h in an Ar atmosphere and then calcined at 750°C for 7 h to obtain a Na3V(PO4)3 / C composite material composed of Na3V(P2O7)1.5 phase and carbon.

[0033] Material experiment: The Na3V(PO4)3 / C composite material composed of the Na3V(P2O7)1.5 / C phase prepared above was used as a positive electrode material for a sodium ion battery in the same manner as in Example 1. Example 4

[0034] Preparation of composite material Na3Vx (PO4)3 / C (x=1) Preparation process: (1) Sodium citrate, V2O5, and NH4H2PO4 were weighed in a stoichiometric ratio, wherein the molar ratio of Na+ to V was 3:1, the molar ratio of V to PO43- was 1:3, and the molar ratio of citrate to vanadium was 1:1. They were mixed, 50 mL of deionized water was added to the mixture, and the mixture was incubated in an oil bath at 80°C for 2 h and dried at 120°C for 10 h to obtain a gel precursor. (2) The obtained gel precursor was calcined at 450°C for 6 h in an Ar atmosphere and then calcined at 750°C for 7 h to obtain a Na3V(PO4)3 / C composite material composed of Na3V(P2O7)1.5 phase and carbon.

[0035] Material experiment: The Na3V(PO4)3 / C composite material composed of the Na3V(P2O7)1.5 / C phase prepared above is used as a positive electrode material for a sodium ion battery, using the same method as in Example 1. Example 5

[0036] Preparation of composite material Na3Vx (PO4)3 / C (x=1) Preparation process: (1) NaH2PO4, NH4VO3 and EDTA were weighed according to the stoichiometric ratio, wherein the molar ratio of Na+ to V was 3:1, the molar ratio of V to PO43- was 1:3, and the molar ratio of EDTA to vanadium was 1:1. They were mixed, 50 mL of deionized water was added to the mixture, and the mixture was incubated in an 80°C oil bath for 2 h and dried at 120°C for 10 h to obtain a gel precursor. (2) The obtained gel precursor was calcined at 450°C for 6 h in an Ar atmosphere and then calcined at 750°C for 7 h to obtain a Na3V(PO4)3 / C composite material composed of Na3V(P2O7)1.5 phase and carbon.

[0037] Material experiment: The Na3V(PO4)3 / C composite material composed of the Na3V(P2O7)1.5 / C phase prepared above is used as a positive electrode material for a sodium ion battery, using the same method as in Example 1. Example 6

[0038] Preparation of composite material Na3Vx (PO4)3 / C (x=0.9) Preparation process: (1) NaH2PO4, NH4VO3 and oxalic acid were weighed according to the stoichiometric ratio, wherein the molar ratio of Na+ to V was 3:0.9, the molar ratio of V to PO43- was 0.9:3, and the molar ratio of citric acid to vanadium was 1:1. They were mixed, 50 mL of deionized water was added to the mixture, and the mixture was incubated in an oil bath at 80°C for 2 h and dried at 120°C for 10 h to obtain a gel precursor. (2) The obtained gel precursor was calcined at 450°C for 6 h in an Ar atmosphere and then calcined at 750°C for 7 h to obtain a Na3V(PO4)3 / C composite material composed of Na3V(P2O7)1.5 phase and carbon.

[0039] Material experiment: The Na3V0.9(PO4)3 / C composite material composed of the Na3V(P2O7)1.5 / C phase prepared above was used as a positive electrode material for a sodium ion battery in the same manner as in Example 1. Example 7

[0040] Preparation of composite material Na3Vx (PO4)3 / C (x=1.1) Preparation process: (1) NaH2PO4, NH4VO3 and citric acid were weighed according to the stoichiometric ratio, wherein the molar ratio of Na+ to V was 3:1.1, the molar ratio of V to PO43- was 1.1:3, and the molar ratio of citric acid to vanadium was 1:1. They were mixed, 50 mL of deionized water was added to the mixture, and the mixture was incubated in an oil bath at 80°C for 2 h and dried at 120°C for 10 h to obtain a gel precursor. (2) The obtained gel precursor was calcined at 450°C for 6 h in an Ar atmosphere and then calcined at 750°C for 7 h to obtain a Na3V(PO4)3 / C composite material composed of Na3V(P2O7)1.5 phase and carbon.

[0041] Material experiment: The Na3V1.1(PO4)3 / C composite material composed of the Na3V(P2O7)1.5 / C phase prepared above is used as a positive electrode material for a sodium ion battery in the same manner as in Example 1. Example 8

[0042] Preparation of composite material Na3Vx (PO4)3 / C (x=1.2) Preparation process: (1) NaH2PO4, NH4VO3 and citric acid were weighed according to the stoichiometric ratio, wherein the molar ratio of Na+ to V was 3:1.2, the molar ratio of V to PO43- was 1.2:3, and the molar ratio of citric acid to vanadium was 1:1. They were mixed, 50 mL of deionized water was added to the mixture, and the mixture was incubated in an oil bath at 80°C for 2 h and dried at 120°C for 10 h to obtain a gel precursor. (2) The obtained gel precursor was calcined at 450°C for 6 h in an Ar atmosphere and then calcined at 750°C for 7 h to obtain a Na3V1.2(P2O7)1.5 / C composite material, which is mainly composed of Na3V(P2O7)1.5 phase, Na3V2(PO4)3 phase and carbon.

[0043] Material experiment: The Na3V1.2(PO4)3 / C composite material composed of the Na3V(P2O7)1.5 / C and Na3V2(PO4)3 / C prepared above was used as a positive electrode material for a sodium ion battery in the same manner as in Example 1. Example 9

[0044] Preparation of composite material Na3Vx (PO4)3 / C (x=1.4) Preparation process: (1) NaH2PO4, NH4VO3 and citric acid were weighed according to the stoichiometric ratio, wherein the molar ratio of Na+ to V was 3:1.4, the molar ratio of V to PO43- was 1.4:3, and the molar ratio of citric acid to vanadium was 1:1. They were mixed, 50 mL of deionized water was added to the mixture, and the mixture was incubated in an oil bath at 80°C for 2 h and dried at 120°C for 10 h to obtain a gel precursor. (2) The obtained gel precursor was calcined at 450°C for 6 h in an Ar atmosphere and then calcined at 750°C for 7 h to obtain a Na3V1.4(PO4)3 / C composite material, which is mainly composed of Na3V2(PO4)3 phase, Na3V(P2O7)1.5 phase and carbon.

[0045] Material experiment: The Na3V1.4(PO4)3 / C composite material composed of the Na3V2(PO4)3 / C and Na3V(P2O7)1.5 / C prepared above was used as a positive electrode material for a sodium ion battery in the same manner as in Example 1. Example 10

[0046] Preparation of composite material Na3Vx (PO4)3 / C (x=1.5) Preparation process: (1) NaH2PO4, NH4VO3 and citric acid were weighed according to the stoichiometric ratio, wherein the molar ratio of Na+ to V was 3:1.5, the molar ratio of V to PO43- was 1.5:3, and the molar ratio of citric acid to vanadium was 1:1. They were mixed, 50 mL of deionized water was added to the mixture, and the mixture was incubated in an oil bath at 80°C for 2 h and dried at 120°C for 10 h to obtain a gel precursor. (2) The obtained gel precursor was calcined at 450°C for 6 h in an Ar atmosphere and then at 750°C for 7 h to obtain a Na3V1.5(PO4)3 composite material. It is mainly composed of Na3V2(PO4)3 phase, Na3V(P2O7)1.5 phase and carbon.

[0047] Material experiment: The Na3V1.5(PO4)3 / C composite material composed of the Na3V2(PO4)3 / C and Na3V(P2O7)1.5 / C prepared above was used as a positive electrode material for a sodium ion battery in the same manner as in Example 1. Example 11

[0048] Preparation of composite material Na3Vx (PO4)3 / C (x=1.5).

[0049] Preparation process: (1) Sodium citrate, NH4VO3, NH4H2PO4 and citric acid were weighed according to the stoichiometric ratio, where the molar ratio of Na+ to V was 3:1.5, the molar ratio of V to PO43- was 1.5:3, and the molar ratio of citric acid to vanadium was 1:1. 50 mL of deionized water was added, and the mixture was in an oil bath at 80°C for 2 h and dried at 120°C for 10 h. (2) The obtained precursor was calcined at 450°C for 6 h in an Ar atmosphere and then at 750°C for 7 h to obtain a Na3V1.5(PO4)3 composite material. It is mainly composed of Na3V2(PO4)3 phase, Na3V(P2O7)1.5 phase and carbon.

[0050] Material experiment: The Na3V1.5(PO4)3 / C composite material composed of the Na3V2(PO4)3 / C and Na3V(P2O7)1.5 / C prepared above was used as a positive electrode material for a sodium ion battery in the same manner as in Example 1. Example 12

[0051] Preparation of single-phase Na3Vx (PO4)3 / C (x=1.3) composite materials.

[0052] The preparation process includes: (1) Sodium citrate, V2O5, NH4H2PO4, and EDTA were weighed according to the stoichiometric ratio, where the molar ratio of Na+ to V was 3:1.3, the molar ratio of V to PO43- was 1.3:3, and the molar ratio of citric acid to vanadium was 1:1. 50 mL of deionized water was added, and the mixture was incubated in an oil bath at 80°C for 2 h, and then dried at 120°C for 10 h. (2) The obtained precursor was calcined at 450°C for 6 h in an Ar atmosphere and then at 750°C for 7 h to obtain a Na3V1.3(PO4)3 composite material. It is mainly composed of Na3V(P2O7)1.5 phase, Na3V2(PO4)3 and carbon.

[0053] Material experiment: The Na3V1.3 (PO4)3 / C composite material composed of the Na3V(P2O7)1.5 / C and Na3V2(PO4)3 / C prepared above was used as a positive electrode material for a sodium ion battery in the same manner as in Example 1.

[0054] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A sodium ion battery high voltage cathode composite material, characterized in that: Its composition is represented by the following formula: Na3V x (PO4)3 / C, where 0.9≤ x ≤1.

5.

2. The composite material according to claim 1, characterized in that 0.9≤ x ≤1.1。 3. The composite material according to claim 1, characterized in that The composition of the composite material + The molar ratio of ions to V is 3:0.9~3:1.

5.

4. The composite material according to claim 1, characterized in that The molar ratio of carbon source to V in the composite material is 1:

1.

5. The composite material according to claim 1, characterized in that V and PO4 in the composite material 3- The molar ratio of ions is 0.9:3~1.5:

3.

6. A method for preparing the composite material according to claim 1, characterized in that: The following steps are involved: (1) Weighing sodium salt, vanadium source, phosphate and carbon source according to the stoichiometric ratio, mixing them, adding deionized water to the mixture, and incubating in an oil bath at 80°C to 100°C for 1 to 3 hours. After the reaction is completed, heating to 100°C to 120°C and drying for 8 to 12 hours to obtain a gel precursor; (2) a certain amount of gel precursor was calcined in a tubular furnace with Ar gas at 450°C for 6 h, and then calcined at 750°C-850°C for 6-10 h to obtain a composite material; The sodium salt is one of sodium dihydrogen phosphate, sodium citrate, sodium carbonate or sodium bicarbonate; the vanadium source is NH4VO3 or V2O5; and the carbon source is one of sodium citrate, citric acid, EDTA and oxalic acid.

7. The preparation method according to claim 6, characterized in that In step (1), the oil bath temperature is 80°C and the time is 2h.

8. The preparation method according to claim 6, characterized in that In step (1), the drying temperature is 120°C and the drying time is 10 hours.

9. The preparation method according to claim 6, characterized in that In step (2), the second calcination temperature is 750°C and the time is 7h.

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