Entropy configuration phosphate sodium ion battery positive electrode material and preparation method and application thereof

Abstract

The invention discloses an entropy configuration phosphate sodium-ion battery positive electrode material as well as a preparation method and application thereof, and relates to the technical field of sodium-ion batteries. According to the technical scheme, the chemical formula is NaxVyMnzCr alpha Ti beta (PO4) 3, wherein 3.5 < = x < = 4, 0.3 < = y < = 0.8, 0.3 < = z < = 0.8, 0.3 < = alpha < = 0.8, and 0.3 < = beta < = 0.8. The entropy type sodium ion battery positive electrode material is constructed by adopting transition metal elements of V, Mn, Cr and Ti, then coordination binding is performed through a chelating agent, the entropy configuration phosphate positive electrode material with high specific discharge capacity and stable long-period circulation is obtained through a high-temperature calcination mode, no strong acid or strong alkali solvent is used in the whole process, operation is convenient, and the preparation method is simple and easy to implement. The large-scale industrial production is easy.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion batteries, and particularly relates to an entropy-configured phosphate sodium ion battery cathode material, a preparation method thereof, and an application thereof. Background Art

[0002] With the rapid development of renewable energy, the demand for cost-effective large-scale energy storage systems (ESSs) is increasing. Although lithium-ion batteries (LIBs) have made great progress in various fields such as portable electronic devices and electric vehicles, due to the scarcity and uneven distribution of lithium resources, their suitability for ESSs remains somewhat controversial. In this context, sodium ion batteries (SIBs) are considered a promising EESs option because of their low cost, abundant sodium resources, and similar working mechanisms to lithium-ion batteries. SIBs have accumulated rich experience in theoretical research and practical applications. However, developing high-performance cathodes for SIBs remains a huge challenge because multiple interrelated problems need to be solved, including slow reaction kinetics, unstable crystal structures, etc. Through multiple comparisons, polyanion compounds, especially sodium superionic conductor (NASICON) phosphate materials, due to their open 3D framework structure, thus promoting Na + migration, will dominate in EESs.

[0003] However, the practical application of NASICON cathode materials is limited by low electronic conductivity, which stems from the insulating properties of polyanion (PO4 3- ) groups and the local electronic states of transition metal ions. This inherent limitation leads to slow electron transfer, ultimately limiting the release and stability of capacity at high rates. Summary of the Invention

[0004] The technical problem to be solved by the present invention is: to overcome the deficiencies of the prior art, provide an entropy-configured phosphate sodium ion battery cathode material, a preparation method thereof, and an application thereof, construct an entropy-type sodium ion battery cathode material using V, Mn, Cr, Ti transition metal elements, and then perform coordination binding through a chelating agent, and obtain an entropy-configured phosphate cathode material by high-temperature calcination. The whole process does not use strong acid or strong base solvents, is easy to operate, and is easy to scale up for industrial production.

[0005] The technical solution of the present invention is as follows:

[0006] In the first aspect, the present invention provides an entropy-configured phosphate sodium ion battery cathode material with the chemical formula Na x V y Mn z Cr α Ti β(PO4)3, where 3.5 ≤ x ≤ 4, 0.3 ≤ y ≤ 0.8, 0.3 ≤ z ≤ 0.8, 0.3 ≤ α ≤ 0.8, 0.3 ≤ β ≤ 0.8.

[0007] In a second aspect, the present invention provides a method for preparing the positive electrode material of the entropy-configured phosphate sodium ion battery, comprising the following steps:

[0008] S1: Dissolve the metal ion chelating agent in water to obtain solution I;

[0009] S2: Dissolve the sodium source, vanadium source, manganese source, chromium source, and titanium source in solution I to obtain solution II;

[0010] S3: Dissolve the phosphate in water to obtain solution III;

[0011] S4: Dropwise add solution III into solution II and stir well to obtain solution IV;

[0012] S5: Stir solution IV under oil bath conditions, dry it after sufficient reaction, grind it, and then calcine it to obtain the positive electrode material of the entropy-configured phosphate sodium ion battery.

[0013] Preferably, in step S1, the metal ion chelating agent is tartaric acid, anhydrous citric acid, disodium ethylenediaminetetraacetate, or gluconic acid, and the concentration is 0.1 - 0.2 mmol / mL.

[0014] Preferably, in step S2, the sodium source is sodium acetate or sodium nitrate, and the concentration is 0.1 - 0.3 mmol / L; the vanadium source is ammonium metavanadate or vanadium pentoxide, and the concentration is 0.01 - 0.08 mmol / L; the manganese source is manganese acetate or manganese nitrate, and the concentration is 0.01 - 0.08 mmol / L; the chromium source is chromium acetate or chromium nitrate, and the concentration is 0.01 - 0.08 mmol / L; the titanium source is tetrabutyl titanate or isopropyl titanate, and the concentration is 0.01 - 0.08 mmol / L.

[0015] Preferably, in step S3, the phosphate is ammonium dihydrogen phosphate, and the concentration of phosphate in solution III is 0.05 - 0.2 mol / L.

[0016] Preferably, in step S4, the dropping rate of solution III into solution II is 2 - 6 mL / min; the dropping is carried out by a peristaltic pump.

[0017] Preferably, in step S4, the stirring speed is 200 - 500 r / min, and the stirring time is 20 - 40 min.

[0018] Preferably, in step S5, the oil bath temperature is 60 - 90 °C; the drying temperature is 100 - 120 °C; the drying is carried out in a forced-air drying oven; the calcination is carried out under N2 or an inert gas, the calcination temperature is 600 - 800 °C, and the calcination time is 8 - 14 h.

[0019] Preferably, the molar ratio of the metal ion chelating agent to the total molar amount of the four elements of vanadium, manganese, chromium, and titanium is (1-3):1.

[0020] In the present invention, by selecting V, Mn, Cr, and Ti transition metal elements with empty d orbitals, a path for electron transition is provided; in addition, the transition metals can provide multi-electron transfer to achieve a high discharge capacity; under the action of the entropy configuration, the lattice expansion and contraction during the stable sodium ion insertion and extraction process are achieved. The above advantages provide a new modification method and corresponding modified materials for the field of sodium superionic conductor (NASICON) phosphate cathode materials.

[0021] In the third aspect, the present invention provides the application of the above entropy configuration phosphate sodium ion battery cathode material, using it as a cathode material in a sodium ion battery.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. By regulating the composition and stoichiometric ratio of the transition metal elements, and at the same time controlling the overall process flow design of the preparation method and the key reaction conditions (such as calcination temperature and time), the modified entropy configuration phosphate cathode material is obtained, realizing the improvement of electronic conductivity and the stability of the structure, which is beneficial to the improvement of electrochemical performance. The operation of the present invention is convenient, easy to industrialize, and the prepared entropy configuration phosphate cathode material is easy to regulate, with excellent cycle performance, rate performance, and structural stability.

[0024] 2. The present invention first selects V, Mn, Cr, and Ti transition metal elements to construct an entropy-type sodium ion battery cathode material. Specifically, various metal source materials (i.e., vanadium source, manganese source, chromium source, titanium source, and sodium source) are dissolved in deionized water, coordinated and combined through a chelating agent, and then the entropy configuration phosphate cathode material is obtained by high-temperature calcination. Strong acids and strong base solvents are not used in the whole process, so the method of the present invention is convenient to operate and easy to scale up and industrialize.

[0025] 3. By defining the relationship between the addition amount of the metal ion chelating agent and the transition metal elements, it can be avoided that when the chelating agent is too little, the metal elements cannot be fully chelated, or when the chelating agent is too much, the solution is acidic, which is not conducive to the growth of crystal grains and the formation of sol.

[0026] 4. The content of Na in the metal source material of the present invention is slightly higher, which can effectively fill the vacancy defects in NASICON and provide sufficient Na + for insertion and extraction.

[0027] 5. The cathode material of the entropy-configured sodium-ion phosphate battery prepared by the present invention has unfilled d empty orbitals in V, Mn, Cr, and Ti, which can provide a transfer path for electron transition, realize the electron delocalization effect, and thus improve the electronic conductivity to enhance the electrochemical performance at high rates. Moreover, due to the disordered entropy configuration, the crystal stability can be improved to optimize the lattice distortion during long-cycle cycling. Starting from the electron configuration level, the present invention strengthens the overall material configuration in all aspects, making it more adaptable to the actual use conditions of high current and long cycle (40C, 1000 cycles). In summary, the present invention has the characteristics of convenient operation and easy large-scale production. The prepared entropy-configured phosphate cathode material is easy to regulate, has good structural stability, excellent rate performance, and cycle performance. Description of the Drawings

[0028] Figure 1 It is the XRD pattern of the NVMCTP-1 cathode material prepared in Example 1 of the present invention.

[0029] Figure 2 It is the SEM image of the NVMCTP-2 cathode material prepared in Example 2 of the present invention.

[0030] Figure 3 It is the cycle performance test chart of the battery assembled with the NVMCTP-3 cathode material prepared in Example 3 of the present invention.

[0031] Figure 4 It is the charge-discharge test chart of the battery assembled with the NVMCTP-3 cathode material prepared in Example 3 of the present invention.

[0032] Figure 5 It is the charge-discharge test chart of the battery assembled with the NVMCTP-S cathode material prepared in Comparative Example 1 of the present invention.

[0033] Figure 6 It is the charge-discharge test chart of the battery assembled with the NVMCTP-V cathode material prepared in Comparative Example 2 of the present invention.

[0034] Figure 7 It is the charge-discharge test chart of the battery assembled with the NVMCTP-Mn cathode material prepared in Comparative Example 3 of the present invention.

[0035] Figure 8 It is the charge-discharge test chart of the battery assembled with the NVMCTP-Cr cathode material prepared in Comparative Example 4 of the present invention.

[0036] Figure 9 It is the charge-discharge test chart of the battery assembled with the NVMCTP-Ti cathode material prepared in Comparative Example 5 of the present invention.

[0037] Figure 10It is the charge-discharge test chart of the battery assembled with the NVMCTP-Na cathode material prepared in Comparative Example 6 of the present invention.

[0038] Figure 11 It is the charge-discharge test chart of the battery assembled with the NVMCTP-900 cathode material prepared in Comparative Example 7 of the present invention.

[0039] Figure 12 It is the charge-discharge test chart of the battery assembled with the NVMCTP-16 cathode material prepared in Comparative Example 8 of the present invention. Detailed implementation manners

[0040] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention.

[0041] Example 1

[0042] The preparation method of the entropy-configured phosphate sodium-ion battery cathode material in this example includes the following steps:

[0043] S1: Weigh 8 mmol of the metal ion chelator anhydrous citric acid and dissolve it in 80 mL of deionized water to obtain Solution I;

[0044] S2: Weigh 14 mmol of sodium acetate, 2 mmol of ammonium metavanadate, 2 mmol of manganese acetate, 2 mmol of chromium acetate, and 2 mmol of isopropyl titanate, and dissolve them in Solution I to obtain Solution II;

[0045] S3: Weigh 3 mmol of ammonium dihydrogen phosphate and dissolve it in 20 mL of deionized water to obtain Solution III;

[0046] S4: Use a peristaltic pump to drop Solution III into Solution II at a rate of 2 mL / min, and then stir well at a rotation speed of 300 r / min for 30 min to obtain Solution IV;

[0047] S5: Place Solution IV in a constant temperature oil bath at 70 °C and stir. After sufficient reaction, dry it in a forced air drying oven at 110 °C; then grind the dried material into powder, place it in a tube furnace, and calcine it at 700 °C for 10 h in an Ar atmosphere to obtain the entropy-configured phosphate sodium-ion battery cathode material (it can be naturally cooled to room temperature and then transferred to a glove box for storage), denoted as NVMCTP-1, and its chemical formula is Na 3.5 V 0.5 Mn 0.5 Cr 0.5 Ti 0.5 (PO4)3.

[0048] The XRD pattern of the NVMCTP-1 cathode material prepared in this example is as Figure 1 shown, and it is composed ofFigure 1 It can be seen that the NVMCTP-1 cathode material prepared in this example has no impurity peaks and exhibits a typical sodium superionic structure.

[0049] Example 2

[0050] The preparation method of the entropy configuration phosphate sodium-ion battery cathode material in this example includes the following steps:

[0051] S1: Weigh 8 mmol of the metal ion chelating agent tartaric acid and dissolve it in 80 mL of deionized water to obtain Solution I;

[0052] S2: Weigh 15.2 mmol of sodium nitrate, 1.6 mmol of vanadium pentoxide, 2.4 mmol of manganese nitrate, 1.6 mmol of chromium nitrate, and 2.4 mmol of tetrabutyl titanate, and dissolve them in Solution I to obtain Solution II;

[0053] S3: Weigh 1.2 mmol of ammonium dihydrogen phosphate and dissolve it in 20 mL of deionized water to obtain Solution III;

[0054] S4: Use a peristaltic pump to drop Solution III into Solution II at a rate of 6 mL / min, then stir well at a rotation speed of 500 r / min for 20 min to obtain Solution IV;

[0055] S5: Place Solution IV in a constant temperature oil bath at 90 °C and stir. After sufficient reaction, dry it in a forced air drying oven at 120 °C; then grind the dried material into powder, place it in a tubular furnace, and calcine it at 800 °C for 8 h in an Ar atmosphere to obtain the entropy configuration phosphate sodium-ion battery cathode material (it can be naturally cooled to room temperature and then transferred to a glove box for storage), denoted as NVMCTP-2, and its chemical formula is Na 3.8 V 0.4 Mn 0.6 Cr 0.4 Ti 0.6 (PO4)3.

[0056] The SEM image of the NVMCTP-2 cathode material prepared in this example is as Figure 2 shown. It can be seen from Figure 2 this that the NVMCTP-2 cathode material prepared in this example presents a granular shape.

[0057] Example 3

[0058] The preparation method of the entropy configuration phosphate sodium-ion battery cathode material in this example includes the following steps:

[0059] S1: Weigh 8 mmol of the metal ion chelating agent gluconic acid and dissolve it in 80 mL of deionized water to obtain Solution I;

[0060] S2: Weigh 12 mmol of sodium acetate, 2 mmol of ammonium metavanadate, 2 mmol of manganese acetate, 2 mmol of chromium acetate, and 2 mmol of isopropyl titanate, and dissolve them in Solution I to obtain Solution II.

[0061] S3: Weigh 3 mmol of ammonium dihydrogen phosphate and dissolve it in 20 mL of deionized water to obtain Solution III.

[0062] S4: Use a peristaltic pump to dropwise add Solution III into Solution II at a rate of 5 mL / min, and then stir well at a rotation speed of 200 r / min for 40 min to obtain Solution IV.

[0063] S5: Place Solution IV in a constant-temperature oil bath at 60 °C and stir. After sufficient reaction, dry it in a forced-air drying oven at 100 °C. Subsequently, grind the dried material into powder, place it in a tubular furnace, and calcine it at 600 °C for 14 h under an Ar atmosphere to obtain the positive electrode material for the entropy configuration sodium-ion battery (it can be transferred to a glove box for storage after naturally cooling to room temperature), denoted as NVMCTP-3, with the chemical formula Na 3.5 V 0.5 Mn 0.5 Cr 0.5 Ti 0.5 (PO4)3.

[0064] Comparative Example 1

[0065] The difference from Example 1 is that in step S1, the addition amount of the metal ion chelating agent anhydrous citric acid is 20 mmol. The obtained positive electrode material for the sodium-ion battery is denoted as NVMCTP-S.

[0066] Comparative Example 2

[0067] The difference from Example 1 is that in step S2, the addition amount of ammonium metavanadate is 8 mmol. The obtained positive electrode material for the sodium-ion battery is denoted as NVMCT-V.

[0068] Comparative Example 3

[0069] The difference from Example 1 is that in step S2, the addition amount of manganese acetate is 8 mmol. The obtained positive electrode material for the sodium-ion battery is denoted as NVMCT-Mn.

[0070] Comparative Example 4

[0071] The difference from Example 1 is that in step S2, the addition amount of chromium acetate is 8 mmol. The obtained positive electrode material for the sodium-ion battery is denoted as NVMCT-Cr.

[0072] Comparative Example 5

[0073] The difference from Example 1 is that in step S2, the addition amount of isopropyl titanate is 8 mmol. The obtained cathode material of the sodium-ion battery is denoted as NVMCT-Ti.

[0074] Comparative Example 6

[0075] The difference from Example 1 is that in step S2, the addition amount of sodium acetate is 32 mmol. The obtained cathode material of the sodium-ion battery is denoted as NVMCT-Na.

[0076] Comparative Example 7

[0077] The difference from Example 1 is that in step S5, the calcination temperature is 900 °C. The obtained cathode material of the sodium-ion battery is denoted as NVMCT-900.

[0078] Comparative Example 8

[0079] The difference from Example 1 is that in step S5, the calcination time is 16 h. The obtained cathode material of the sodium-ion battery is denoted as NVMCT-16.

[0080] Assemble the cathode materials prepared in Examples 1-3 and Comparative Examples 1-8 into batteries: Mix the cathode active material, conductive agent, and binder (PVDF) in a ratio of 8:1:1, add the solvent NMP to make a uniform slurry; coat the slurry on the cathode current collector aluminum foil, dry it and roll it into a thin sheet, and cut it into a circular cathode sheet matching the inner diameter of the battery case. Place the following in the cathode case in sequence: cathode sheet (active material side up) → separator (covering the cathode sheet, with edges aligned) → dropwise add electrolyte (soaking the separator, about 50-100 μL of liquid electrolyte). Cover the negative electrode material (sodium sheet) on the separator, ensure alignment with the center of the cathode sheet, and avoid edge short circuit. Place an insulating gasket (to prevent short circuit between the negative electrode and the cathode case) and a sealing ring (to ensure the battery tightness). Cover the negative electrode case (stainless steel case, with grooves), place it in a press, and apply a certain pressure (5-10 MPa) to crimp and seal the outer shell to form a complete battery.

[0081] The battery assembled in Example 3 was cycled 1000 times at a high rate of 40 °C, and its capacity retention rate was measured as Figure 3 shown. It can be seen from the figure that after cycling 1000 times at a high rate of 40 °C, it still maintains a capacity retention rate of 91%.

[0082] The batteries assembled in Example 3 and Comparative Examples 1-8 were tested for charge-discharge performance at a current density of 0.1 C and a voltage range of 1.5-4.5 V, and the test results are as Figures 4 - 12 shown. It can be known from Figure 4 that the discharge capacity of Example 3 is 171.3 mAh g -1 . And it can be known from Figure 5It can be seen that in Comparative Example 1, an excessive amount of metal ion chelating agent was added, resulting in an imbalance in the pH of the solution environment. The transition metal elements could not be well glued, leading to a decline in the electrochemical performance of the cathode material and a significant decrease in the discharge capacity of the battery. From Figures 6 - 10 It can be seen that when too much Na element or transition metal element is added, the electrochemical performance of the cathode material will decline, and the discharge capacity of the battery will decrease significantly. From Figures 11 - 12 It can be seen that due to the too high calcination temperature and too long calcination time in Comparative Example 7 and Comparative Example 8, the crystal structure was damaged, resulting in a decline in the electrochemical performance of the cathode material and a significant decrease in the discharge capacity of the battery.

Claims

1. Entropy-configured sodium-ion battery cathode material, characterized in that The chemical formula is Na x V y Mn z Cr α Ti β (PO4)3, where 3.5 ≤ x ≤ 4, 0.3 ≤ y ≤ 0.8, 0.3 ≤ z ≤ 0.8, 0.3 ≤ α ≤ 0.8, 0.3 ≤ β ≤ 0.

8.

2. The preparation method of the cathode material of the entropy configuration sodium-ion phosphate battery according to claim 1, characterized in that It includes the following steps: S1: Dissolve a metal ion chelating agent in water to obtain Solution I; S2: Dissolve a sodium source, a vanadium source, a manganese source, a chromium source, and a titanium source in Solution I to obtain Solution II; S3: Dissolve phosphate in water to obtain Solution III; S4: Slowly add dropwise Solution III into Solution II and stir well to obtain Solution IV; S5: Stir Solution IV under an oil bath condition, fully react, dry, grind, and then calcine to obtain the entropy configuration phosphate sodium ion battery cathode material.

3. The preparation method of the cathode material of the entropy-configured sodium-ion phosphate battery according to claim 2, characterized in that, In step S1, the metal ion chelating agent is tartaric acid, anhydrous citric acid, disodium ethylenediaminetetraacetate, or gluconic acid, and the concentration is 0.1 - 0.2 mmol / mL.

4. The preparation method of the cathode material of the entropy-configured sodium-ion phosphate battery according to claim 1, characterized in that, In step S2, the sodium source is sodium acetate or sodium nitrate, and the concentration is 0.1 - 0.3 mmol / L; the vanadium source is ammonium metavanadate or vanadium pentoxide, and the concentration is 0.01 - 0.08 mmol / L; the manganese source is manganese acetate or manganese nitrate, and the concentration is 0.01 - 0.08 mmol / L; the chromium source is chromium acetate or chromium nitrate, and the concentration is 0.01 - 0.08 mmol / L; the titanium source is tetrabutyl titanate or isopropyl titanate, and the concentration is 0.01 - 0.08 mmol / L.

5. The preparation method of the positive electrode material of the entropy configuration sodium-ion phosphate battery according to claim 1, characterized in that, In step S3, the phosphate is ammonium dihydrogen phosphate, and the concentration of phosphate in Solution III is 0.05 - 0.2 mol / L.

6. The preparation method of the positive electrode material of the entropy configuration sodium-ion phosphate battery according to claim 1, characterized in that, In step S4, the dropping rate of Solution III into Solution II is 2 - 6 mL / min; the dropping is carried out by a peristaltic pump.

7. The preparation method of the positive electrode material of the entropy configuration sodium-ion phosphate battery according to claim 1, characterized in that, In step S4, the stirring speed is 200 - 500 r / min, and the stirring time is 20 - 40 min.

8. The preparation method of the positive electrode material of the entropy configuration sodium ion phosphate battery according to claim 1, characterized in that In step S5, the oil bath temperature is 60 - 90 °C; the drying temperature is 100 - 120 °C; the drying is carried out in a forced air drying oven; the calcination is carried out under N2 or an inert gas, the calcination temperature is 600 - 800 °C, and the calcination time is 8 - 14 h.

9. The preparation method of the positive electrode material of the entropy configuration sodium-ion phosphate battery according to claim 1, characterized in that The molar ratio of the metal ion chelating agent to the total molar amount of the four elements of vanadium, manganese, chromium, and titanium is (1 - 3):

1.

10. The application of the entropy-configured sodium-ion battery cathode material as claimed in claim 1, wherein, Use it as the cathode material in a sodium ion battery.

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