A modified ternary positive electrode material and its preparation method and application

Abstract

The present invention provides a modified ternary positive electrode material and a preparation method and application thereof. The preparation method comprises the following steps: (1) preparing manganese sulfate into a manganese sulfate solution, spraying the manganese sulfate solution by a spraying method to obtain a ternary positive electrode material surface; (2) mixing the material with a solvent to obtain a suspension, dripping the suspension, a manganese source solution, an iron source solution and a complexing agent solution into the solvent at the same time for reaction, adjusting the pH value, and obtaining a precursor; (3) mixing the precursor, a lithium source and a phosphorus source, adding a carbon source, grinding and sintering, and obtaining the modified ternary positive electrode material; wherein, in the coating layer of the precursor material obtained in step (2), the content of manganese element decreases from the interface to the outside along the core, and the content of iron element increases from zero along the interface to the outside along the core. The present invention overcomes the safety problem of high-nickel ternary materials on the one hand, and avoids the reaction between lithium manganese iron phosphate and the ternary material when the carbon coating layer is formed on the other hand.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium ion batteries and relates to a modified ternary positive electrode material and a preparation method and application thereof. Background Art

[0002] In recent decades, lithium-ion batteries have attracted more and more attention due to their high energy density, light weight, long cycle life and good environmental performance, and have been widely used in electric vehicles and electronic equipment. At the same time, influenced by market policies and the increasing requirements for long driving range of electric vehicles, the demand for high energy density lithium-ion batteries is also increasing; and the specific capacity of the positive electrode material is a key factor in determining the energy density of the battery. Among them, high-nickel ternary materials have attracted much attention due to their advantages such as high specific capacity, low cost, environmental protection and no need for high-voltage electrolytes.

[0003] The thermal stability of the material will decrease as the nickel content increases; in addition, the safety of the battery will decrease as the nickel content increases.

[0004] CN110233249A discloses a lithium iron phosphate nano powder coated high nickel ternary positive electrode material and a preparation method thereof, comprising the following steps: 1) mixing a nickel cobalt manganese precursor and a lithium source in a mixing device according to a certain lithiation ratio to obtain a ternary precursor mixture; 2) calcining and grinding the ternary precursor mixture obtained in step 1); 3) preparing a polyethylene glycol solution, adding the lithium iron phosphate nano powder thereto, and continuing to stir until a gel is formed; immersing the high nickel ternary material not coated with lithium iron phosphate in the obtained gel, and continuing to stir to obtain a mixture; 4) drying, wherein the lithium iron phosphate is coated on the surface of the high nickel ternary material; sintering the obtained dry material, and grinding to obtain the high nickel ternary positive electrode material coated with lithium iron phosphate.

[0005] CN111668464A discloses a lithium iron phosphate coated nickel cobalt aluminum ternary positive electrode material and its preparation method and application. The preparation method of the lithium iron phosphate coated nickel cobalt aluminum ternary positive electrode material is as follows: water, carbon source and iron phosphate are evenly dispersed and ground to a particle size of 200-400nm; water and nickel cobalt aluminum hydroxide are evenly dispersed and ground to a particle size of 5-10μm; the two slurries are evenly mixed, lithium salt is added, ball milling is performed to obtain a mixed slurry, and powder is obtained by drying; the powder is sintered in an oxygen atmosphere to obtain a lithium iron phosphate coated nickel cobalt aluminum ternary positive electrode material.

[0006] The above scheme improves the safety of the material by in-situ growing lithium iron phosphate positive electrode material or grinding and coating it on the surface of high-nickel ternary positive electrode material; however, high-temperature calcination is required in the process of synthesizing lithium iron phosphate. At high temperature, the trivalent nickel ions and trivalent cobalt ions in the ternary material will react with the divalent iron in the lithium iron phosphate, thereby affecting the overall performance of the material. Summary of the invention

[0007] The purpose of the present invention is to provide a modified ternary positive electrode material and a preparation method and application thereof. On the one hand, the present invention overcomes the safety problem of high-nickel ternary materials, and on the other hand, avoids the reaction between lithium manganese iron phosphate and the ternary material when forming a carbon coating layer.

[0008] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0009] In a first aspect, the present invention provides a method for preparing a modified ternary cathode material, the preparation method comprising the following steps:

[0010] (1) mixing manganese sulfate and a first solvent to prepare a manganese sulfate solution, and spraying the manganese sulfate solution on the surface of the ternary positive electrode material by a spraying method;

[0011] (2) mixing the material obtained in step (1) with a second solvent to obtain a suspension, and simultaneously dropping the suspension, a manganese source solution, an iron source solution, and a complexing agent solution into a third solvent for reaction, adjusting the pH during the reaction, to obtain a precursor material;

[0012] (3) mixing the precursor material, lithium source and phosphorus source, adding a carbon source, grinding and sintering to obtain the modified ternary positive electrode material;

[0013] In the coating layer of the precursor material obtained in step (2), the content of manganese element decreases gradually from the interface along the core to the outside, and the content of iron element increases gradually from zero along the interface along the core to the outside.

[0014] The present invention pre-sprays a layer of manganese salt on the surface of the ternary positive electrode material to use it as the starting point for the in-situ growth of lithium manganese iron phosphate. By respectively controlling the flow rate and / or concentration of the manganese source solution and the iron source solution, the content of manganese element decreases gradually from the ternary interface to the outside along the core, and the content of iron element increases gradually from zero along the core from the ternary interface to the outside, that is, the iron content at the junction of the ternary and the lithium manganese iron phosphate is 0, and the farther from the interface, the higher the iron content. The lithium manganese iron phosphate positive electrode material with gradient changes in Mn and Fe contents is in-situ grown on the surface of the ternary material, thereby improving the safety of the high-nickel ternary material, the thermal stability of the material and the cycle performance.

[0015] Preferably, in step (1), the first solvent comprises deionized water.

[0016] Preferably, the molar concentration of the manganese sulfate solution is 0.05-0.12 mol / L, for example, 0.05 mol / L, 0.08 mol / L, 0.1 mol / L, 0.11 mol / L or 0.12 mol / L.

[0017] Preferably, the mass ratio of the manganese sulfate solution to the ternary positive electrode material is 1:(1.5-2.5), for example: 1:1.5, 1:1.8, 1:2, 1:2.2 or 1:2.5, etc.

[0018] Preferably, in step (2), the concentration and / or dripping speed of the manganese source solution and the iron source solution are controlled so that the manganese content in the precursor coating layer decreases gradually from the interface to the outside along the core, and the iron content increases gradually from zero along the interface to the outside along the core.

[0019] Preferably, the second solvent comprises anhydrous ethanol.

[0020] Preferably, the molar ratio of manganese element in the manganese source solution to iron element in the iron source solution is 3:(1.5-2.5), for example: 3:1.5, 3:1.8, 3:2, 3:2.2 or 3:2.5, etc.

[0021] Preferably, the iron source solution contains citric acid.

[0022] Preferably, the solute of the complexing agent solution comprises ammonium oxalate.

[0023] Preferably, the molar concentration of the complexing agent solution is 0.8-1.2 mol / L, for example, 0.8 mol / L, 0.9 mol / L, 1 mol / L, 1.1 mol / L or 1.2 mol / L.

[0024] Preferably, the third solvent in step (2) comprises deionized water.

[0025] Preferably, the reaction temperature is 40-60°C, for example, 40°C, 45°C, 50°C, 55°C or 60°C.

[0026] Preferably, the reaction time is 3 to 5 h, for example, 3 h, 3.5 h, 4 h, 4.5 h or 5 h.

[0027] Preferably, after the reaction, the obtained precursor material is filtered, washed and dried.

[0028] Preferably, the detergent for the suction filtration washing comprises deionized water and / or ethanol.

[0029] Preferably, the suction filtration and washing are performed 2 to 4 times, for example, 2 times, 3 times or 4 times.

[0030] Preferably, the pH in step (2) is 4.5 to 5.5, for example, 4.5, 4.8, 5, 5.2 or 5.5.

[0031] Preferably, the method for adjusting pH comprises adding sulfuric acid or ammonia water.

[0032] Preferably, the lithium source in step (3) comprises lithium carbonate.

[0033] Preferably, the phosphorus source comprises diammonium phosphate.

[0034] Preferably, the molar ratio of the precursor material, the lithium element in the lithium source and the phosphorus source is 1:(1.01-1.2):(0.8-1.2), for example: 1:1.01:0.8, 1:1.01:1, 1:1.05:1, 1:1.08:1.1 or 1:1.2:1.2, etc.

[0035] Preferably, the carbon source comprises glucose.

[0036] Preferably, the grinding process comprises wet ball milling.

[0037] Preferably, the solvent for the wet ball milling comprises ethanol.

[0038] Preferably, the sintering temperature in step (3) is 500-700°C, for example, 500°C, 550°C, 600°C, 650°C or 700°C.

[0039] Preferably, the sintering time is 6 to 10 hours, for example, 6 hours, 7 hours, 8 hours, 9 hours or 10 hours.

[0040] In a second aspect, the present invention provides a modified ternary positive electrode material, which is prepared by the method described in the first aspect.

[0041] In a third aspect, the present invention provides a positive electrode plate, wherein the positive electrode plate comprises the modified ternary positive electrode material as described in the second aspect.

[0042] In a fourth aspect, the present invention provides a lithium-ion battery, wherein the lithium-ion battery comprises the positive electrode sheet as described in the third aspect.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] (1) The modified ternary positive electrode material of the present invention has an extremely high manganese content and almost zero iron content at the interface between the ternary core and the lithium iron manganese phosphate, thereby avoiding the reaction between the divalent iron in the lithium iron manganese phosphate and the trivalent cobalt and trivalent nickel in the ternary material when forming the carbon coating layer, thereby improving the stability and cycle performance of the ternary material.

[0045] (2) The battery made of the modified ternary positive electrode material of the present invention has an initial discharge capacity of more than 211 mAh / g at 0.1C, a charge and discharge efficiency of more than 92%, a discharge capacity of more than 192 mAh / g at the 100th cycle at 0.1C, and a capacity retention rate of more than 91.3% after 100 cycles at 0.1C. DETAILED DESCRIPTION

[0046] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0047] Example 1

[0048] This embodiment provides a modified ternary positive electrode material, and the preparation method of the modified ternary positive electrode material is as follows:

[0049] (1) Manganese sulfate was added to 50 ml of deionized water to prepare a 0.1 mol / L manganese sulfate solution, and then the solution was sprayed onto the surface of 100 g of NCM811 material by a spray method and dried at 100 °C;

[0050] (2) Take the NCM in step (1) 811 was added to 100g of anhydrous ethanol, and the mixture was stirred to obtain a suspension A. Manganese sulfate and ferrous sulfate were weighed according to the stoichiometric ratio of n(Mn):n(Fe)=0.6:0.4 to prepare 1mol / L manganese sulfate solution B and 1mol / L ferrous sulfate solution C. 0.2g of citric acid was added to solution C to prevent oxidation. Ammonium oxalate was dissolved in deionized water to prepare 1mol / L ammonium oxalate solution D. The suspension A, solution B, solution C and solution D were simultaneously dripped into a 50°C reactor containing 100ml of deionized water for reaction. The dripping speed of the manganese sulfate solution was decreased from 4mL / min to 0.1mL / min, and the dripping speed of the ferrous sulfate solution was increased from 0.1mL / min to 4mL / min. During the reaction, 1mol / L sulfuric acid and ammonia water were dripped to stabilize the reaction pH at about 5. After reacting for 4h, a precipitate was obtained, which was repeatedly filtered and washed with deionized water and ethanol for 3 times, and then dried at 60°C for 7h to obtain a precursor material.

[0051] (3) Precursors, lithium carbonate and diammonium phosphate (Mn(Mn 0.6 Fe 0.4 ):n(Li):n(PO4)=1:1:1) after being evenly mixed, 5% glucose was added as a carbon source, and an appropriate amount of ethanol was added for ball milling for 5 hours; then, it was placed in a nitrogen atmosphere and calcined at 600°C for 8 hours to obtain the modified ternary positive electrode material.

[0052] Example 2

[0053] This embodiment provides a modified ternary positive electrode material, and the preparation method of the modified ternary positive electrode material is as follows:

[0054] (1) Manganese sulfate was added to 50 ml of deionized water to prepare a 0.12 mol / L manganese sulfate solution, and then the solution was sprayed onto the surface of 100 g of NCM811 material by a spray method and dried at 100 °C;

[0055] (2) NCM 811 in step (1) was added to 100 g of anhydrous ethanol and stirred to obtain suspension A. Manganese sulfate and ferrous sulfate were weighed according to the stoichiometric ratio of n(Mn):n(Fe)=0.58:0.42 to prepare 1 mol / L manganese sulfate solution B and 1 mol / L ferrous sulfate solution C. 0.2 g of citric acid was added to solution C to prevent oxidation. Ammonium oxalate was dissolved in deionized water to prepare 1 mol / L ammonium oxalate solution D. The suspension A, solution B, solution C and solution D were simultaneously dripped into the containing The reaction was carried out in a 50°C reactor containing 100 ml of deionized water, the dropping speed of the manganese sulfate solution was decreased from 4 mL / min to 0.1 mL / min, and the dropping speed of the ferrous sulfate solution was increased from 0.1 mL / min to 4 mL / min. During the reaction, 1 mol / L of sulfuric acid and ammonia water were added dropwise to stabilize the reaction pH at about 5.2. After reacting for 4 hours, a precipitate was obtained, which was repeatedly filtered and washed with deionized water and ethanol for 3 times, and then dried at 60°C for 7 hours to obtain a precursor material.

[0056] (3) Precursors, lithium carbonate and diammonium phosphate (Mn(Mn 0.6 Fe 0.4 ):n(Li):n(PO4)=1:1.02:1) after being evenly mixed, 5% glucose was added as a carbon source, and an appropriate amount of ethanol was added for ball milling for 5 hours; then, it was placed in a nitrogen atmosphere and calcined at 600°C for 8 hours to obtain the modified ternary positive electrode material.

[0057] Example 3

[0058] The only difference between this embodiment and embodiment 1 is that the volume ratio of the manganese source solution to the iron source solution is 3:1, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0059] Example 4

[0060] The only difference between this embodiment and embodiment 1 is that the volume ratio of the manganese source solution to the iron source solution is 1:1.2, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0061] Comparative Example 1

[0062] This comparative example directly uses NCM811 ternary positive electrode material.

[0063] Comparative Example 2

[0064] The only difference between this comparative example and Example 1 is that manganese sulfate is not sprayed on the surface of the ternary positive electrode material in advance, and other conditions and parameters are exactly the same as those in Example 1.

[0065] Comparative Example 3

[0066] The only difference between this comparative example and Example 1 is that the dripping speed of the manganese source solution and the iron source solution remains unchanged, and the other conditions and parameters are exactly the same as those in Example 1.

[0067] Performance Test:

[0068] The positive electrode material prepared in the above examples and comparative examples is used as the active material, super P is used as the conductive agent, and polyvinylidene fluoride (PVDF) is used as the binder, and the mass ratio of the three is 8:1:1. PVDF powder is dissolved in a small amount of NMP, and then 0.56g of active material, 0.07g of super P and an appropriate amount of PVDF are placed in a vial and magnetically stirred overnight. The stirred slurry is applied to the surface of the current collector and vacuum dried to obtain a positive electrode sheet;

[0069] Use 2025 button cells, Celgard2400 as the diaphragm, polypropylene as the microdiaphragm, and the electrolyte is 1.0 mol / L LiPF6 dissolved in a mixture of DMC, DEC and EC. In an inert gas glove box, place the positive electrode in the positive electrode shell, add 2 drops of electrolyte to fully wet the positive electrode, then slowly put on the diaphragm, add 3 drops of electrolyte, then put in the metal lithium sheet as the counter electrode, then put in the gasket and shrapnel, and finally buckle the negative electrode shell, and seal the battery with a sealing machine. The charge and discharge test was carried out at a voltage range of 2 to 4V and 0.1C. The discharge specific capacity and capacity retention rate after 100 cycles are shown in Table 1:

[0070] Table 1

[0071]

[0072] As can be seen from Table 1, from Examples 1-2, the battery prepared by the modified ternary positive electrode material of the present invention has an initial discharge capacity of more than 211 mAh / g at 0.1C, a charge and discharge efficiency of more than 92%, a discharge capacity of more than 192 mAh / g at the 100th week at 0.1C, and a capacity retention rate of more than 91.3% after 100 cycles at 0.1C.

[0073] By comparing Example 1 and Examples 3-4, it can be seen that in the preparation process of the modified ternary positive electrode material described in the present invention, the amount of manganese and iron added will affect the performance of the modified ternary positive electrode material. The amount of manganese and iron added is controlled at 3: (1.5~2.5), and the performance of the modified ternary positive electrode material is better. If the proportion of manganese is too large, the conductivity of lithium manganese iron phosphate will be reduced. If the proportion of iron is too large, the voltage platform of the coating layer will be reduced, making the difference with the voltage platform of the inner layer too large, thereby affecting the cycle stability of the entire positive electrode material.

[0074] By comparing Example 1 and Comparative Example 1, it can be seen that although the initial discharge specific capacity of the ternary material after lithium manganese iron phosphate coating is slightly lower than that of the uncoated ternary positive electrode material, the charge and discharge efficiency and the discharge specific capacity and retention rate at 100 cycles are better than those of the uncoated ternary material; this is because the coating layer can effectively isolate the corrosion and damage of the electrolyte to the structure of the ternary material, thereby improving the cycle stability of the ternary material after coating.

[0075] By comparing Example 1 and Comparative Example 2, it can be seen that the present invention pre-sprays a layer of manganese sulfate on the surface of the positive electrode material to use it as the starting point for the in-situ growth of lithium iron manganese phosphate. Since the manganese content at the junction of the ternary and lithium iron manganese phosphate is extremely high, and the iron content is almost zero, the reaction between the divalent iron in the lithium iron manganese phosphate and the trivalent cobalt and trivalent nickel in the ternary material is avoided when the carbon coating layer is formed, thereby improving the stability and cycle performance of the ternary material.

[0076] By comparing Example 1 and Comparative Example 3, it can be seen that the safety of the high-nickel ternary material, the thermal stability of the material and the cycle performance are improved by in-situ growing a lithium manganese iron phosphate positive electrode material with a gradient change in Mn and Fe content on the surface of the ternary material.

[0077] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a modified ternary positive electrode material, characterized in that: The preparation method comprises the following steps: (1) mixing manganese sulfate and a first solvent to prepare a manganese sulfate solution, and spraying the manganese sulfate solution onto the surface of the ternary positive electrode material by a spraying method; (2) mixing the material obtained in step (1) with a second solvent to obtain a suspension, and simultaneously dropping the suspension, a manganese source solution, an iron source solution, and a complexing agent solution into a third solvent for reaction, adjusting the pH during the reaction, to obtain a precursor material; (3) mixing the precursor material, lithium source and phosphorus source, adding a carbon source, grinding and sintering to obtain the modified ternary positive electrode material; Wherein, in the coating layer of the precursor material obtained in step (2), the content of manganese element decreases gradually from the interface along the core to the outside, and the content of iron element increases gradually from zero along the interface along the core to the outside; Step (2) controlling the concentration and / or drop rate of the manganese source solution and the iron source solution so that the content of manganese in the precursor coating layer decreases gradually from the interface to the outside along the core, and the content of iron increases gradually from zero along the interface to the outside along the core; The sintering temperature in step (3) is 500-700°C.

2. The preparation method according to claim 1, characterized in that In step (1), the first solvent comprises deionized water.

3. The preparation method according to claim 1, characterized in that: The molar concentration of the manganese sulfate solution is 0.05-0.12 mol / L.

4. The preparation method according to claim 1, characterized in that: The mass ratio of the manganese sulfate solution to the ternary positive electrode material is 1:(1.5-2.5).

5. The preparation method according to claim 1, characterized in that: The second solvent includes anhydrous ethanol.

6. The preparation method according to claim 1, characterized in that: The molar ratio of manganese element in the manganese source solution to iron element in the iron source solution is 3:(1.5-2.5).

7. The preparation method according to claim 1, characterized in that: The iron source solution contains citric acid.

8. The preparation method according to claim 1, characterized in that: The solute of the complexing agent solution includes ammonium oxalate.

9. The preparation method according to claim 1, characterized in that: The molar concentration of the complexing agent solution is 0.8-1.2 mol / L.

10. The preparation method according to claim 1, characterized in that: The third solvent in step (2) includes deionized water.

11. The preparation method according to claim 1, characterized in that: The reaction temperature is 40-60°C.

12. The preparation method according to claim 1, characterized in that: The reaction time is 3 to 5 hours.

13. The preparation method according to claim 1, characterized in that: After the reaction, the obtained precursor material is filtered, washed and dried.

14. The preparation method according to claim 13, characterized in that: The detergent for the suction filtration and washing includes deionized water and / or ethanol.

15. The preparation method according to claim 13, characterized in that: The suction filtration and washing are performed 2 to 4 times.

16. The preparation method according to claim 1, characterized in that: The pH of step (2) is 4.5 to 5.

5.

17. The preparation method according to claim 1, characterized in that: The method for adjusting pH includes adding sulfuric acid or ammonia water.

18. The preparation method according to claim 1, characterized in that: The lithium source in step (3) includes lithium carbonate.

19. The preparation method according to claim 1, characterized in that: The phosphorus source includes diammonium phosphate.

20. The preparation method according to claim 1, characterized in that: The molar ratio of the precursor material, the lithium element in the lithium source and the phosphorus source is 1:(1.01-1.2):(0.8-1.2).

21. The preparation method according to claim 1, characterized in that: The carbon source includes glucose.

22. The preparation method according to claim 1, characterized in that: The grinding process includes wet ball milling.

23. The preparation method according to claim 22, characterized in that: The solvent for the wet ball milling includes ethanol.

24. The preparation method according to claim 1, characterized in that: The sintering time is 6 to 10 hours.

25. A modified ternary positive electrode material, characterized in that: The modified ternary positive electrode material is prepared by the preparation method as described in any one of claims 1-24.

26. A positive electrode plate, characterized in that: The positive electrode sheet comprises the modified ternary positive electrode material as described in claim 25.

27. A lithium ion battery, characterized in that: The lithium-ion battery comprises the positive electrode sheet as claimed in claim 26.

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