Method for removing residual alkali on surface of high-nickel positive electrode material in ternary lithium battery and application of method

Abstract

The invention discloses a method for removing residual alkali on the surface of a high-nickel positive electrode material in a ternary lithium battery and application of the method, and belongs to the technical field of lithium ion battery positive electrode materials. After the lithium ion ternary positive electrode material is subjected to coating treatment, residual alkali compounds on the surface of the lithium ion ternary positive electrode material are remarkably reduced, and a coating material protection layer can be constructed on the surface of the lithium ion ternary positive electrode material in situ; therefore, an electrode / electrolyte interface structure is strengthened, side reaction and interface impedance are inhibited, and the specific discharge capacity and rate capability of the battery are remarkably improved. The method is simple and convenient in process and mild in condition, and has a good industrial application prospect.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion battery cathode materials, and particularly relates to a method for removing surface residual alkali of a ternary medium-high nickel cathode material and application thereof. BACKGROUND

[0002] Medium-high nickel layered oxide LiNi x Co y Mn 1-x-y O2 (NCM for short) is widely used in power and energy storage batteries due to high energy density and controllable cost. Representative medium nickel 6 series materials and high nickel 8 series materials have high specific capacity, but as the nickel content increases, the chemical stability of the material surface significantly decreases: during high-temperature sintering, storage and transportation, the particle surface is easy to absorb moisture and react with air to generate alkali by-products (i.e., "residual alkali") such as LiOH and Li2CO3. The residual alkali reacts with the electrolyte during battery assembly and charging and discharging, causing gas evolution, unstable interface film, polarization and impedance increase, thereby affecting the initial efficiency and cycle life.

[0003] Existing treatment routes include water washing, acid washing, and metal oxide coating. Water washing reduces residual alkali while also causing lithium loss; acid washing can reduce residual alkali but may erode the main lattice and induce structural defects; metal oxide coating is easy to form an electronically insulating layer, thicken the interface and increase polarization, and the process is relatively complex. Overall, how to efficiently remove surface residual alkali under mild and controllable conditions and obtain a long-term stable electrode / electrolyte interface is still a key technical problem in the industrial application of high-nickel NCM. SUMMARY

[0004] The application provides a method for removing surface residual alkali of a ternary medium-high nickel cathode material and application thereof, which can efficiently reduce the content of particle surface residual alkali (LiOH and Li2CO3) under mild and controllable conditions. The application lies in that the LiF-coated medium-high nickel ternary cathode material obtained by the preparation method has improved electrochemical performance and structural stability when in use. At the same time, the scheme takes into account the simplicity of the process and the implementability of industrialization.

[0005] To solve the above technical problems, the application provides the following technical scheme: a method for coating and treating a medium-high nickel NCM cathode material to remove surface residual alkali and repair performance, comprising the following steps:

[0006] Step (1), selecting commercial medium-high nickel NCM cathode material powder as raw material, and exposing it to air to lose effectiveness;

[0007] Step (2), adding a coating agent to anhydrous ethanol, stirring to form a mixed solution;

[0008] Step (3), the powder obtained in step (1) is added to the mixed solution obtained in step (2) and stirred uniformly, and then dried in a vacuum drying box;

[0009] Step (4), the dried mixed powder is placed in an oxygen atmosphere for high-temperature sintering treatment to obtain a coated medium-high nickel NCM positive electrode material.

[0010] Further, in the aforementioned step (1), the temperature of the inactivation treatment is 25-35 DEG C, and the humidity is 35-70%.

[0011] Further, in the aforementioned step (2), the coating agent is selected from any one or any combination of ammonium fluoride, ammonium chloride, ammonium bromide, ammonium iodide, ammonium nitrate, ammonium sulfate, ammonium bicarbonate, and ammonium acetate.

[0012] Further, in the aforementioned step (2), the amount of the coating material is 1-3 mol% of the total molar amount of the medium-high nickel NCM material.

[0013] Further, in the aforementioned step (3), the stirring speed is 400-600 rpm / min, and the stirring time is 1-2 h.

[0014] Further, in the aforementioned step (4), the temperature increasing rate is 5 DEG C / min, the holding temperature is 400-500 DEG C, and the holding time is 4-6 h.

[0015] Further, in the aforementioned step (3), the drying temperature is 60-80 DEG C, and the drying time is 12-15 h.

[0016] Another aspect of the present application provides a coated medium-high nickel NCM positive electrode material prepared by the method of the present application, which contains a layer of coating compound on the surface and the main body is an NCM positive electrode material.

[0017] The present application also provides a lithium ion battery, the positive electrode material of which is the coated medium-high nickel NCM material obtained by the method of the present application.

[0018] Compared with the prior art, the present application has the following beneficial technical effects by adopting the above technical solutions:

[0019] 1. The present application introduces mild treatment conditions and simple process, and the coating reaction is easy to carry out, while avoiding the collapse of the main body layer structure and maintaining the integrity of the crystal phase, which is suitable for industrial application.

[0020] 2. The residual alkali removal method introduced in the present application utilizes the characteristics of being able to react with surface LiOH and Li2CO3, which can significantly reduce the residual alkali content.

[0021] ​3. The LiF-based protective layer prepared by the present application has the characteristic of lithium ion permeability, reduces interface impedance and polarization;

[0022] 4. The residual base removal method introduced in the present application can improve the initial efficiency of the material by about 1% to 10% after treatment, and the rate performance is restored at each current density.

[0023] 5. The present application provides a method for mild removal of residual base on the surface of middle-high nickel ternary material, which takes advantage of the characteristics of the reaction of with the surface LiOH, to significantly reduce the residual base content. The stable LiF-based protective layer formed has the effect of reducing the interface impedance, so that the material that has been disabled is restored with a large increase in discharge capacity and a significant improvement in rate performance. The method of the present application is not only suitable for removing residual base on the surface of ternary middle-high nickel single crystal material, but also suitable for removing residual base on the surface of ternary middle-high nickel agglomerate material. For other types of lithium ion materials, such as the removal of residual base on the surface of lithium-rich layered oxides, the method of the present application is also applicable. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 The scanning electron microscope images of the high-nickel ternary positive electrode material (LiNi 0.88 Co 0.06 Mn 0.06 O2) before and after repair in Example 1 of the present application, wherein (a) is the scanning electron microscope image of the material after exposure to failure, (b) is the scanning electron microscope image of the material after coating, and (c) is the spectrum analysis image.

[0025] Figure 2 The X-ray diffraction patterns of the high-nickel ternary positive electrode material (LiNi 0.88 Co 0.06 Mn 0.06 O2) before and after repair in Example 1 of the present application.

[0026] Figure 3 The X-ray photoelectron spectroscopy images of the high-nickel ternary positive electrode material (LiNi 0.88 Co 0.06 Mn 0.06 O2) before and after repair in Example 1 of the present application.

[0027] Figure 4 The residual base content diagram of the high-nickel ternary positive electrode material (LiNi 0.88 Co 0.06 Mn 0.06 O2) before and after repair in Example 1 of the present application.

[0028] Figure 5 The residual base content diagram of the high-nickel ternary positive electrode material (LiNi0.88 Co 0.06 Mn 0.06 O2) on the first cycle charge-discharge diagram of the lithium battery.

[0029] Figure 6 The high-nickel ternary positive electrode material (LiNi 0.88 Co 0.06 Mn 0.06 O2) on the cycle performance diagram of the lithium battery.

[0030] Figure 7 The high-nickel ternary positive electrode material (LiNi 0.88 Co 0.06 Mn 0.06 O2) on the rate performance diagram of the lithium battery. DETAILED DESCRIPTION

[0031] In order to better understand the technical content of the present application, specific embodiments are described below with reference to the accompanying drawings.

[0032] Aspects of the present application are described in this disclosure with reference to the accompanying drawings, in which a number of illustrative embodiments are shown. The embodiments of the present application are not limited to the illustrated embodiments but can be practiced by any of the inventive concepts and embodiments introduced above, as well as the concepts and embodiments described in detail below, since the inventive concepts and embodiments disclosed are not limited to any of the embodiments. In addition, some aspects disclosed herein can be used alone or in any suitable combination with other aspects disclosed herein.

[0033] Example 1:

[0034] A method for removing surface residual alkali and repairing performance based on ammonium fluoride coated medium-high nickel NCM positive electrode material, the steps are as follows:

[0035] Step (1), 0.0077 g of NH4F powder was weighed into 10 mL of anhydrous ethanol, mixed and stirred for 30 min to form a mixed solution;

[0036] Step (2), 1.0 g of air-deactivated high-nickel ternary positive electrode material (LiNi 0.88 Co 0.06 Mn 0.06 O2) was added to the above mixed solution, mixed and stirred for 1 h at a stirring speed of 500 r / min, and then dried in a 60°C vacuum drying oven for 12 h;

[0037] Step (3): Place the powder obtained after drying in step (2) into an oxygen atmosphere for high-temperature calcination treatment. The calcination temperature is 450°C, the heating rate is 5°C / min, the holding time is 5h, and after cooling, the powder is sieved to obtain the required material.

[0038] Step (4): Assemble the obtained positive electrode material into a lithium battery.

[0039] like Figure 1 The image shown is a scanning electron microscope (SEM) image of the high-nickel ternary cathode material after repair in Example 1. In the image, (a) is a scanning electron microscope image of the material after exposure failure, (b) is a scanning electron microscope image of the material after coating, and (c) is a spectral analysis diagram. It can be seen from the image that after coating, the original layer of residual alkali compound generated on the surface of the material becomes sparse, and the F element can be seen to be uniformly distributed on the surface of the material.

[0040] like Figure 2 The figure shows the X-ray diffraction patterns of the high-nickel ternary cathode material before and after repair in Example 1. As can be seen from the figure, the structure of the repaired sample is still well maintained compared with the original sample.

[0041] like Figure 3 The figure shows the X-ray photoelectron spectrum of the high-nickel ternary cathode material after repair in Example 1. As can be seen from the figure, the repaired material has a LiF peak, which further indicates that a LiF coating is formed on the surface of the material.

[0042] like Figure 4 The figure shows the surface residual alkali content of the high-nickel ternary cathode material before and after repair in Example 1. The total alkali content of the original sample was 18337 ppm, as measured by potentiometric titration; the total alkali content of the repaired sample was 11269 ppm. This indicates a significant reduction in the surface residual alkali content of the original sample.

[0043] like Figure 5 The figure shows the first charge-discharge curves of the lithium anode battery assembled with the positive electrode material before and after repair in Example 1. The positive electrode material was within the voltage range of 2.8~4.3V at 0.2C (1C=200 mAh g). -1 The original sample underwent charge-discharge testing. Its discharge capacity was 136.91 mAh / g, and its coulombic efficiency was 79.83%. The repaired sample had a discharge capacity of 183.18 mAh / g and a coulombic efficiency of 81.75%. This indicates that the cathode material obtained in this invention has recovered some capacity, and the first-cycle coulombic efficiency has also improved.

[0044] like Figure 6The figure shows the 100-cycle performance of the positive electrode material before and after repair in Example 1, after assembling the lithium negative electrode into a battery. The positive electrode material was tested at 1C (1C = 200 mAh g) within a voltage range of 2.8~4.3V. -1 Charging and discharging are performed under these conditions.

[0045] like Figure 7 The figure shows the rate performance of the lithium anode battery assembled with the positive electrode material before and after repair in Example 1. The current density of the test battery was increased from 0.1C to 10C (1C = 200 mAh g⁻¹). -1 The original sample discharge capacities were 150.34 mAh / g, 128.16 mAh / g, 115.29 mAh / g, 104.44 mAh / g, 93.38 mAh / g, 77.04 mAh / g, and 62.51 mAh / g, respectively; the repaired sample discharge capacities were 210.98 mAh / g, 184.32 mAh / g, 166.78 mAh / g, 155.11 mAh / g, 140.94 mAh / g, 121.07 mAh / g, and 100.79 mAh / g. This indicates that the repaired cathode material consistently exhibits excellent rate performance at various current densities.

[0046] Example 2:

[0047] A method for removing surface residual alkali and repairing performance based on ammonium fluoride coating of medium-high nickel NCM cathode material, comprising the following steps:

[0048] Step (1): Add 0.0038 g of NH4F powder to 10 mL of anhydrous ethanol and mix and stir for 30 min to form a mixed solution;

[0049] Step (2): Add 1.0g of air-depleted medium-nickel ternary cathode material (LiNi) 0.6 C0 0.1 Mn 0.3 O2) was added to the above mixed solution, and the mixture was stirred for 1 hour at a stirring speed of 500 r / min. Then it was dried in a vacuum drying oven at 60°C for 12 hours.

[0050] Step (3): Place the powder obtained after drying in step (2) into an oxygen atmosphere for high-temperature calcination treatment. The calcination temperature is 450°C, the heating rate is 5°C / min, the holding time is 5h, and after cooling, the powder is sieved to obtain the required material.

[0051] Step (4): Assemble the obtained positive electrode material into a lithium battery.

[0052] Example 3:

[0053] A method for removing surface residual alkali and repairing performance based on ammonium fluoride coating of medium-high nickel NCM positive electrode material, the steps are as follows:

[0054] Step (1), 0.0115 g of NH4F powder was added to 10 mL of anhydrous ethanol, mixed and stirred for 30 min to form a mixed solution;

[0055] Step (2), 1.0 g of air-failed medium nickel ternary positive electrode material (LiNi 0.88 Co 0.06 Mn 0.06 O2) was added to the above mixed solution, mixed and stirred for 1 h at a stirring speed of 500 r / min, and then dried in a 60°C vacuum drying oven for 12 h;

[0056] Step (3), the powder obtained after drying in step (2) was placed in an oxygen atmosphere for high-temperature calcination treatment, the calcination temperature was 450°C, the heating rate was 5°C / min, the holding time was 5 h, and after cooling, the material was obtained by sieving;

[0057] Step (4), the obtained positive electrode material was assembled into a lithium battery.

[0058] Example 4:

[0059] A method for removing surface residual alkali and repairing performance based on ammonium fluoride coating of medium-high nickel NCM positive electrode material, the steps are as follows:

[0060] Step (1), 0.0039 g of NH4F powder was added to 10 mL of anhydrous ethanol, mixed and stirred for 30 min to form a mixed solution;

[0061] Step (2), 1.0 g of air-failed high nickel ternary positive electrode material (LiNi 0.6 Co 0.1 Mn 0.3 O2) was added to the above mixed solution, mixed and stirred for 1 h at a stirring speed of 500 r / min, and then dried in a 60°C vacuum drying oven for 12 h;

[0062] Step (3), the powder obtained after drying in step (2) was placed in an oxygen atmosphere for high-temperature calcination treatment, the calcination temperature was 450°C, the heating rate was 5°C / min, the holding time was 5 h, and after cooling, the material was obtained by sieving;

[0063] Step (4), the obtained positive electrode material was assembled into a lithium battery.

[0064] Example 5:

[0065] A method for removing surface residual alkali and repairing performance based on ammonium fluoride coating middle-high nickel NCM positive electrode material, the steps are as follows:

[0066] Step (1), 0.0077 g of NH4F powder was added to 10 mL of anhydrous ethanol, mixed and stirred for 30 min to form a mixed solution.

[0067] Step (2), 1.0 g of air-failed high-nickel ternary positive electrode material (LiNi 0.6 Co 0.1 Mn 0.3 O2) was added to the above mixed solution, mixed and stirred for 1 h at a stirring speed of 500 r / min, and then dried in a 60°C vacuum drying oven for 12 h;

[0068] Step (3), the powder obtained after drying in step (2) was placed in an oxygen atmosphere for high-temperature calcination treatment, the calcination temperature was 450°C, the heating rate was 5°C / min, the holding time was 5 h, and after cooling, the material was obtained by sieving.

[0069] Step (4), the obtained positive electrode material was assembled into a lithium battery.

[0070] Example 6:

[0071] A method for removing surface residual alkali and repairing performance based on ammonium fluoride coating middle-high nickel NCM positive electrode material, the steps are as follows:

[0072] Step (1), 0.0117 g of NH4F powder was added to 10 mL of anhydrous ethanol, mixed and stirred for 30 min to form a mixed solution.

[0073] Step (2), 1.0 g of air-failed high-nickel ternary positive electrode material (LiNi 0.6 Co 0.1 Mn 0.3 O2) was added to the above mixed solution, mixed and stirred for 1 h at a stirring speed of 500 r / min, and then dried in a 60°C vacuum drying oven for 12 h;

[0074] Step (3), the powder obtained after drying in step (2) was placed in an oxygen atmosphere for high-temperature calcination treatment, the calcination temperature was 450°C, the heating rate was 5°C / min, the holding time was 5 h, and after cooling, the material was obtained by sieving.

[0075] Step (4), the obtained positive electrode material was assembled into a lithium battery.

[0076] While the application has been described by way of example with reference to certain embodiments thereof, it is to be understood that the application is not limited to the embodiments described above, but intrinsically extends to various modifications and changes in form and details. Therefore, the scope of the application should be determined not by the embodiments described above, but by the scope of the appended claims and their equivalents.

Claims

1. A method for coating high nickel NCM cathode material in order to remove surface residual alkali and repair performance, characterized in that, The steps are as follows: Step (1), selecting a medium-high nickel NCM positive electrode powder as a raw material, exposing it to air to cause failure; Step (2), adding a coating agent to anhydrous ethanol and stirring to form a mixed solution; Step (3), adding the powder obtained in step (1) to the mixed solution obtained in step (2) and stirring until uniform, then drying in a vacuum drying box; Step (4), placing the dried mixed powder in an oxygen atmosphere and performing high-temperature sintering treatment to obtain a coated medium-high nickel NCM positive electrode material.

2. The method for removing surface residual alkali and repairing performance of a coated high-nickel NCM positive electrode material in a coating process according to claim 1, characterized in that, In step (1), the failure treatment temperature is 25-35℃, and the humidity is 35-70%.

3. The method for removing surface residual alkali and repairing performance of a coated high-nickel NCM positive electrode material according to claim 1, characterized in that, In step (2), the coating agent is selected from any one or any combination of ammonium fluoride, ammonium chloride, ammonium bromide, ammonium iodide, ammonium nitrate, ammonium sulfate, ammonium bicarbonate, and ammonium acetate.

4. The method for removing surface residual alkali and repairing performance of a coated high-nickel NCM positive electrode material according to claim 1, characterized in that, In step (2), the amount of coating material is 1-3 mol% of the total molar amount of the medium-high nickel NCM material.

5. The method for removing surface residual alkali and repairing performance of a coated high nickel NCM positive electrode material according to claim 1, characterized in that, In step (3), the stirring speed is 400-600 rpm / min, and the stirring time is 1-2h.

6. The method for removing residual alkali on the surface of a middle-high nickel positive electrode material according to claim 1, characterized in that, In step (4), the heating rate is 5℃ / min, the holding temperature is 400-500℃, and the holding time is 4-6h.

7. The method for removing surface residual alkali and repairing performance of a coated high nickel NCM cathode material according to claim 1, characterized in that, In step (3), the drying temperature is 60-80℃, and the drying time is 12-15h.

8. The coated medium-high nickel NCM cathode material prepared by the method of any one of claims 1-7, characterized in that, It has a layer of coating compound on its surface, and the main body is NCM positive electrode material.

9. A lithium-ion battery, characterized by The positive electrode material is the coated medium-high nickel NCM material obtained by the method of claims 1-7.

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