A high-capacity and high-rate sodium vanadium phosphate cathode material and its preparation method

Abstract

The present invention provides a sodium vanadium phosphate positive electrode material with high capacity and rate, which belongs to the technical field of lithium batteries. 3‑x M x V 2‑y N y (PO4)3, the value range of x in the chemical formula is 0

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and particularly relates to a sodium vanadium phosphate cathode material with high capacity and rate and a preparation method thereof. Background Art

[0002] Lithium-ion batteries have been widely used at present. However, considering the relatively high price of lithium, the demand for developing a new sodium-ion secondary battery system by replacing lithium with sodium, which has similar properties, richer reserves, and lower price, is becoming increasingly strong. Improving the discharge capacity of the cathode, increasing the discharge voltage platform, and increasing the capacity retention rate after cycling can effectively improve the performance of current sodium-ion batteries. The sodium-ion conductor sodium vanadium phosphate cathode material is a potential cathode material for sodium-ion batteries. It has a relatively stable structural framework to provide good capacity retention and material safety. The metal vanadium cations in it provide battery capacity through redox reactions, with good reversibility and can be used for a long time. However, the current sodium vanadium phosphate cathode materials still have the following problems:

[0003] (1) In the charge-discharge range of 2.5 - 4.0V, the redox reaction of vanadium ions only involves the transformation from V3+ to V4+, providing less capacity, and only a voltage platform of about 3.5V can appear during the charge-discharge process, providing a lower energy density.

[0004] (2) At a rate of 20C, with the rapid insertion and extraction of sodium ions, the sodium vanadium phosphate cathode material shows characteristics of large polarization voltage, low specific capacity, and low capacity retention rate, and cannot be well applied to the case of high-rate charge-discharge. Summary of the Invention

[0005] Embodiments of the present application are proposed to make up for the deficiencies of the prior art, and provide a sodium vanadium phosphate cathode material with high capacity and rate and a preparation method thereof to solve the problems existing in the prior art.

[0006] To solve the above technical problems, the present invention provides the following technical solutions:

[0007] A sodium vanadium phosphate cathode material with high capacity and rate, whose chemical formula is Na

[0009] , y ,<0000\\02>,

[0008] ,

[0007] ,

[0006] ,

[0005] ,<00000\\3>, ,<00000\\1>, , , , M x V 2-y N y (PO4)3, where the value range of x in the chemical formula is 0 < x ≤ 0.4, the value range of y is 0 < y ≤ 0.8, M is a combination of K and Li or one of them, and N is one or a combination of more than one of Mn, Fe, Co, and Ni.

[0008] A preparation method of a sodium vanadium phosphate cathode material with high capacity and rate, comprising the following steps:

[0009] S01: dissolving lithium, sodium, potassium, vanadium, manganese, iron, cobalt, nickel compounds, phosphates and reducing chelating acids such as citric acid in deionized water in proportion to obtain a clear solution;

[0010] S02: heating the solution obtained in S01 in a water bath at 80 degrees Celsius to allow the acid and metal ions to undergo hydrolysis and condensation reactions to obtain a gel;

[0011] S03: drying the gel obtained in S02 under vacuum at 120 degrees Celsius to obtain a solid, and grinding it into powder;

[0012] S04: The powder obtained in S03 is pre-calcined at 350 degrees Celsius to obtain a black powder, which is fully ground and placed in an alumina crucible. It is sintered at a high temperature of 800 degrees Celsius in a nitrogen atmosphere, and the co-doped sodium vanadium phosphate positive electrode material is obtained by naturally cooling.

[0013] As a further technical solution of the present invention: the molar ratio of the acid to the metal ion in step S01 is in the range of 0.5:1 to 4:1.

[0014] As a further technical solution of the present invention: stirring in step S02 is 2-4 hours.

[0015] As a further technical solution of the present invention: the pre-baking time in step S03 is 2-8 hours, and the high-temperature sintering time is 4-16 hours.

[0016] As a further technical solution of the present invention: the soluble substances of lithium, sodium and potassium in step S01 are a mixture of one or more of hydroxide, carbonate, bicarbonate, acetate, nitrate and phosphate.

[0017] As a further technical solution of the present invention: the salts of manganese, iron, cobalt and nickel in step S01 are carbonates, sulfates, acetates, oxalates, nitrates, acetylacetonates, phosphates or one or more mixtures of oxides, peroxides, hydroxides and oxyhydroxyl groups.

[0018] As a further technical solution of the present invention: the vanadium source in step S01 is ammonium metavanadate, vanadium pentoxide, sodium metavanadate, sodium pyrovanadate or vanadium hydroxide.

[0019] As a further technical solution of the present invention: in step S01, the phosphorus source is ammonium dihydrogen phosphate, sodium dihydrogen phosphate, sodium hydrogen phosphate or ammonium hydrogen phosphate.

[0020] As a further technical solution of the present invention: in step S01, the reducing chelating acid is oxalic acid, citric acid or hydrated citric acid.

[0021] One or more technical solutions provided in the embodiments of this application have at least the following technical effects or advantages:

[0022] 1. A high-capacity sodium vanadium phosphate cathode material method using dual-site co-doping was achieved, achieving higher discharge specific capacity and energy density in the voltage range of 2.5-4.0V. This can be attributed to the valence mixing of vanadium ions caused by low-valent doping of metal ions, which stimulates the transformation of vanadium ions from V4+ to V5+ at a new reversible charge and discharge platform at 3.8V within this range. At the same time, the redox reaction of nickel and manganese ions themselves also participates in the charge and discharge process, allowing more sodium ions to migrate.

[0023] 2. The dual-site co-doping prepared by the present invention achieves high-capacity sodium vanadium phosphate positive electrode material with better structural stability. The incorporation of larger radius ions into the crystal increases the unit cell volume and acts as supporting ions, reducing the irreversible structural damage caused by phase change, thereby improving the specific capacity at high rate and achieving better capacity retention. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a powder X-ray diffraction comparison diagram of the co-doped sodium vanadium phosphate positive electrode material and the sodium vanadium phosphate positive electrode material in Example 1.

[0025] Figure 2 This is a first cycle charge and discharge curve diagram of the co-doped sodium vanadium phosphate positive electrode material and the sodium vanadium phosphate positive electrode material in Example 1 at 0.1C in the voltage range of 2.5-4.0V.

[0026] Figure 3 This is a cycle curve diagram of the co-doped sodium vanadium phosphate positive electrode material and the sodium vanadium phosphate positive electrode material in Example 1 at 20C in the voltage range of 2.5-4.0V.

[0027] Figure 4 This is a variable charge rate cycle curve diagram of the co-doped sodium vanadium phosphate positive electrode material and the sodium vanadium phosphate positive electrode material in Example 1 within the voltage range of 2.5-4.0V.

[0028] In the figure, the charge and discharge rates are 0.1C, 0.5C, 1C, 2C, 5C, 10C, 20C, and 0.1C, respectively, and each charge and discharge cycle is 10 cycles.

[0029] Wherein NVP is sodium vanadium phosphate positive electrode material, and NVMP is the co-doped sodium vanadium phosphate positive electrode material in Example 1. DETAILED DESCRIPTION

[0030] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0031] Reference Figure 1-4 A high-capacity and high-rate sodium vanadium phosphate cathode material and its preparation method, with the chemical formula Na3-xMxV2-yNy(PO4)3, characterized in that the value range of x in the chemical formula is 0 < x ≤ 0.4, the value range of y is 0 < y ≤ 0.8, M is a combination of K and Li or one of them, and N is a combination of one or more of Mn, Fe, Co, and Ni.

[0032] Meanwhile, the present invention also provides a preparation method for a high-capacity and high-rate sodium vanadium phosphate cathode material, and the preparation method includes the following steps:

[0033] S01: Dissolve soluble substances of lithium, sodium, and potassium, iron compounds, vanadium sources, and reducing chelating acids in deionized water in proportion to obtain a clear solution;

[0034] S02: Heat the solution obtained in S01 in a water bath at 80 °C and stir for 2 - 4 h to allow the acid and metal ions to fully undergo hydrolysis and condensation reactions to obtain a gel;

[0035] S03: Vacuum-dry the gel obtained in S02 at 120 °C to obtain a solid, and grind it into powder;

[0036] S04: Pre-calcine the powder obtained in S03 at 350 °C for 2 - 8 h to obtain a black powder. After fully grinding, place it in an alumina crucible, and sinter it at 800 °C for 4 - 16 h under a nitrogen atmosphere, and naturally cool to obtain the co-doped sodium vanadium phosphate cathode material.

[0037] Further, in S01, the molar ratio of the acid to the metal ions ranges from 0.5:1 to 4:1.

[0038] Still further, in S01, the soluble substances of lithium, sodium, and potassium are one or more mixtures of hydroxides, carbonates, bicarbonates, acetates, nitrates, and phosphates.

[0039] Still further, in S01, the iron compounds are one or more mixtures of carbonates, sulfates, acetates, oxalates, nitrates, acetylacetonates, phosphates, or oxides, peroxides, hydroxides, and hydroxyoxides.

[0040] Still further, in S01, the vanadium source is ammonium metavanadate, vanadium pentoxide, sodium metavanadate, sodium pyrophosphate, vanadium hydroxide, and other vanadates.

[0041] Still further, in S01, the reducing chelating acid is citric acid or hydrated citric acid, oxalic acid, etc. [[ID=​

[0043] Example 1:

[0044] Preparation of co-doped sodium vanadium phosphate cathode material Na by sol-gel method 2.9 K 0.1 V 1.8 Mn 0.1 Fe 0.1 The (PO4)3 process includes the following steps:

[0045] S01: Oxalic acid (0.002 mol), sodium metavanadate (0.0036 mol), ammonium dihydrogen phosphate (0.0060 mol), sodium hydroxide (0.0004 mol), potassium hydroxide (0.0002 mol), ferrous oxalate dihydrate (0.0002 mol), and manganese oxalate (0.0002 mol) were dissolved in 60 mL of deionized water in sequence to obtain a clear solution.

[0046] S02: The solution obtained in S01 is heated in a water bath at 80 degrees Celsius and stirred for 2-4 hours to allow the citric acid and metal ions to undergo sufficient hydrolysis and condensation reactions to obtain a gel;

[0047] S03: drying the gel obtained in S02 under vacuum at 120 degrees Celsius to obtain a solid, and grinding it into powder;

[0048] S04: The powder obtained in S03 was pre-baked at 350 degrees Celsius for 2 hours to obtain a black powder. After being fully ground, it was placed in an alumina crucible and sintered at 800 degrees Celsius for 10 hours under a nitrogen atmosphere. The co-doped sodium vanadium phosphate positive electrode material Na was obtained by naturally cooling. 2.9 K 0.1 V 1.8 Mn 0.1 Fe 0.1 (PO4)3.

[0049] The co-doped sodium vanadium phosphate cathode material prepared in this example was mixed with the conductive agent acetylene black and the binder PVDF in a mass ratio of 8:1:1 to form a slurry, which was then coated to form a positive electrode sheet. Constant-rate charge-discharge testing at a rate of 0.1C over a voltage range of 2.5-4.0V revealed an initial discharge capacity of 114 mAh / g. At 20C, the discharge capacity reached 86 mAh / g, maintaining 75% of the 0.1C capacity. After 1000 cycles at 20C, the capacity retention rate was 94%.

[0050] Example 2:

[0051] Preparation of co-doped sodium vanadium phosphate cathode material Na by sol-gel method 2.8 K 0.15 Li 0.05 The V2(PO4)3 process includes the following steps:

[0052] S01: Dissolve citric acid monohydrate (0.004 mol), ammonium metavanadate (0.004 mol), ammonium dihydrogen phosphate (0.006 mol), anhydrous sodium carbonate (0.0028 mol), anhydrous potassium carbonate (0.00015 mol), and lithium carbonate (0.00005 mol) in 60 mL of deionized water in sequence to obtain a clear solution;

[0053] S02: The solution obtained in S01 is heated in a water bath at 80 degrees Celsius and stirred for 2-4 hours to allow the citric acid and metal ions to undergo sufficient hydrolysis and condensation reactions to obtain a gel;

[0054] S03: drying the gel obtained in S02 under vacuum at 120 degrees Celsius to obtain a solid, and grinding it into powder;

[0055] S04: The powder obtained in S03 was pre-baked at 350 degrees Celsius for 3 hours to obtain a black powder. After being fully ground, it was placed in an alumina crucible and sintered at 800 degrees Celsius for 8 hours under a nitrogen atmosphere. The co-doped sodium vanadium phosphate positive electrode material Na 2.8 K 0.15 Li 0.05 V2(PO4)3.

[0056] The co-doped sodium vanadium phosphate cathode material prepared in this example was mixed with the conductive agent acetylene black and the binder PVDF in a mass ratio of 8:1:1 to form a slurry, which was then coated to form a positive electrode sheet. Constant-rate charge-discharge tests at a rate of 0.1C within a voltage range of 2.5-4.0V demonstrated a first-cycle discharge capacity of 102 mAh / g. At 20C, the first-cycle discharge capacity was 20 mAh / g.

[0057] Example 3:

[0058] Preparation of co-doped sodium vanadium phosphate cathode material Na by sol-gel method 2.8 K 0.2 V 1.8 Mn 0.15 Fe 0.05 The (PO4)3 process includes the following steps:

[0059] S01: Oxalic acid (0.008 mol), sodium metavanadate (0.0036 mol), ammonium dihydrogen phosphate (0.0060 mol), sodium acetate (0.0002 mol), potassium acetate (0.0004 mol), ferric oxalate pentahydrate (0.0001 mol), and manganese acetate tetrahydrate (0.0003 mol) were dissolved in 60 mL of deionized water in sequence to obtain a clear solution.

[0060] S02: The solution obtained in S01 is heated in a water bath at 80 degrees Celsius and stirred for 2-4 hours to allow the citric acid and metal ions to undergo sufficient hydrolysis and condensation reactions to obtain a gel;

[0061] S03: drying the gel obtained in S02 under vacuum at 120 degrees Celsius to obtain a solid, and grinding it into powder;

[0062] S04: The powder obtained in S03 was pre-baked at 350 degrees Celsius for 6 hours to obtain a black powder. After being fully ground, it was placed in an alumina crucible and sintered at 800 degrees Celsius for 10 hours under a nitrogen atmosphere. The co-doped sodium vanadium phosphate positive electrode material Na 2.8 K 0.2 V 1.8 Mn 0.15 Fe 0.05( PO4)3.

[0063] The co-doped sodium vanadium phosphate cathode material prepared in this example was mixed with the conductive agent acetylene black and the binder PVDF in a mass ratio of 8:1:1 to form a slurry, which was then coated to form a positive electrode sheet. Constant-rate charge-discharge tests at a rate of 0.1C within a voltage range of 2.5-4.0V revealed a discharge capacity of 107 mAh / g. At 20C, the discharge capacity was 85 mAh / g, with a capacity retention of 94% after 1000 cycles.

[0064] Example 4:

[0065] Preparation of co-doped sodium vanadium phosphate cathode material Na by sol-gel method 2.6 K 0.4 V 1.8 Mn 0.1 Ni 0.1 The (PO4)3 process includes the following steps:

[0066] S01: Dissolve citric acid monohydrate (0.020 mol), ammonium metavanadate (0.0036 mol), ammonium monohydrogen phosphate (0.0060 mol), sodium hydroxide (0.0052 mol), potassium hydroxide (0.0008 mol), nickel hydroxide (0.0002 mol), and manganese acetate tetrahydrate (0.0002 mol) in 60 mL of deionized water in sequence to obtain a clear solution.

[0067] S02: The solution obtained in S01 is heated in a water bath at 80 degrees Celsius and stirred for 2-4 hours to allow the citric acid and metal ions to undergo sufficient hydrolysis and condensation reactions to obtain a gel;

[0068] S03: drying the gel obtained in S02 under vacuum at 120 degrees Celsius to obtain a solid, and grinding it into powder;

[0069] S04: The powder obtained in S03 was pre-baked at 350 degrees Celsius for 8 hours to obtain a black powder. After being fully ground, it was placed in an alumina crucible and sintered at 800 degrees Celsius for 16 hours under a nitrogen atmosphere. The co-doped sodium vanadium phosphate positive electrode material Na was obtained by naturally cooling. 2.6 K 0.4 V 1.8 Mn 0.1 Ni 0.1 (PO4)3.

[0070] The co-doped sodium vanadium phosphate cathode material prepared in this example was mixed with the conductive agent acetylene black and the binder PVDF in a mass ratio of 8:1:1 to form a slurry, which was then coated to form a positive electrode sheet. Constant-rate charge-discharge tests were conducted at a rate of 0.1C over a voltage range of 2.5-4.0V. The initial discharge capacity was 110mAh / g. At 20C, the discharge capacity was 70mAh / g. After 1000 cycles at 20C, the capacity retention rate was 90%.

[0071] Example 5:

[0072] Preparation of co-doped sodium vanadium phosphate cathode material Na by sol-gel method 2.7 K 0.3 V 1.8 Mn 0.1 Co 0.1 The (PO4)3 process includes the following steps:

[0073] S01: Oxalic acid (0.024 mol), ammonium metavanadate (0.0036 mol), ammonium dihydrogen phosphate (0.0060 mol), anhydrous sodium carbonate (0.0027 mol), anhydrous potassium carbonate (0.0003 mol), cobalt hydroxide (0.0002 mol), and manganese oxalate (0.0002 mol) were dissolved in 60 mL of deionized water in sequence to obtain a clear solution.

[0074] S02: The solution obtained in S01 is heated in a water bath at 80 degrees Celsius and stirred for 2-4 hours to allow the citric acid and metal ions to undergo sufficient hydrolysis and condensation reactions to obtain a gel;

[0075] S03: drying the gel obtained in S02 under vacuum at 120 degrees Celsius to obtain a solid, and grinding it into powder;

[0076] S04: The powder obtained in S03 was pre-baked at 350 degrees Celsius for 8 hours to obtain a black powder. After being fully ground, it was placed in an alumina crucible and sintered at 800 degrees Celsius for 16 hours under a nitrogen atmosphere. The co-doped sodium vanadium phosphate positive electrode material Na was obtained by naturally cooling. 2.7 K 0.3 V 1.8 Mn 0.1Co 0.1 (PO4)3.

[0077] The co-doped sodium vanadium phosphate cathode material prepared in this example was mixed with the conductive agent acetylene black and the binder PVDF in a mass ratio of 8:1:1 to form a slurry, which was then coated to form a positive electrode sheet. Constant-rate charge-discharge tests were conducted at a rate of 0.1C over a voltage range of 2.5-4.0V. The initial discharge capacity was 108mAh / g. At 20C, the discharge capacity was 75mAh / g. After 1000 cycles at 20C, the capacity retention rate was 92%.

[0078] In summary, the sodium vanadium phosphate positive electrode material Na3V2(PO4)3 synthesized by a similar method in the present invention has a discharge capacity of only 103mAh / g at 0.1C in the voltage range of 2.0-4.5V; the discharge capacity at 20C is 40mAh / g, which only retains 39% of the discharge capacity at 0.1C. After 1000 cycles at 20C, the capacity retention rate is only 62%.

[0079] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations that come within the meaning and range of equivalents of the claims be embraced therein.

[0080] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment have also been appropriately combined to form other implementation methods that are easy for those skilled in the art to understand.

Claims

1. A sodium vanadium phosphate cathode material with high capacity and rate, characterized by: Its chemical formula is Na 3-x M x V 2-y N y (PO4)3, where the value range of x in the chemical formula is 0 < x ≤ 0.4, the value range of y is 0 < y ≤ 0.8, M is a combination of K and Li or one of them, and N is a combination of one or more of Mn, Fe, Co, and Ni.

2. A method for preparing the high-capacity and high-rate sodium vanadium phosphate positive electrode material according to claim 1, characterized in that: The following steps are involved: S01: dissolving lithium, sodium, potassium, vanadium, manganese, iron, cobalt, nickel compounds, phosphate and citric acid reducing chelating acid in deionized water in proportion to obtain a clear solution; S02: The solution obtained in S01 is heated in a water bath at 80 degrees Celsius with stirring to allow the acid and metal ions to undergo sufficient hydrolysis and condensation reactions to obtain a gel; S03: drying the gel obtained in S02 under vacuum at 120 degrees Celsius to obtain a solid, and grinding it into powder; S04: The powder obtained in S03 is pre-calcined at 350 degrees Celsius to obtain a black powder, which is fully ground and placed in an alumina crucible. It is sintered at a high temperature of 800 degrees Celsius in a nitrogen atmosphere, and the co-doped sodium vanadium phosphate positive electrode material is obtained by naturally cooling.

3. The method for preparing a high-capacity and high-rate sodium vanadium phosphate cathode material according to claim 2, characterized in that: The molar ratio of the acid to the metal ion in step S02 is in the range of 0.5:1 to 6:

1.

4. The method for preparing a high-capacity and high-rate sodium vanadium phosphate cathode material according to claim 2, characterized in that: The stirring time in step S02 is 2-4 h.

5. The method for preparing a sodium vanadium phosphate cathode material with high capacity and rate according to claim 2, characterized in that: The pre-baking time in step S04 is 2-8 h, and the high-temperature sintering time is 4-16 h.

6. The method for preparing a sodium vanadium phosphate cathode material with high capacity and rate according to claim 2, characterized in that: The lithium, sodium, and potassium compounds in step S01 are a mixture of one or more of hydroxides, carbonates, bicarbonates, acetates, nitrates, and phosphates.

7. The method for preparing a sodium vanadium phosphate cathode material with high capacity and rate according to claim 2, characterized in that: The manganese, iron, cobalt and nickel compounds in step S01 are carbonates, sulfates, acetates, oxalates, nitrates, acetylacetonates, phosphates or mixtures of one or more of oxides, peroxides, hydroxides and oxyhydroxides.

8. The method for preparing a sodium vanadium phosphate cathode material with high capacity and rate according to claim 2, characterized in that: The vanadium compound in step S01 is ammonium metavanadate, vanadium pentoxide, sodium metavanadate, sodium pyrovanadate or vanadium hydroxide.

9. The method for preparing a sodium vanadium phosphate cathode material with high capacity and rate according to claim 2, characterized in that: In step S01, the phosphate is ammonium dihydrogen phosphate, sodium dihydrogen phosphate, sodium hydrogen phosphate or ammonium hydrogen phosphate.

10. The method for preparing a sodium vanadium phosphate cathode material with high capacity and rate according to claim 2, characterized in that: In step S01, the reducing chelating acid is oxalic acid.

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