Preparation method for modified high-nickel ternary positive electrode material

Abstract

A preparation method for a modified high-nickel ternary positive electrode material, comprising the following steps: providing a high-nickel ternary positive electrode material and aluminum diethylphosphinate, wherein lithium carbonate is attached to the surface of the high-nickel ternary positive electrode material; providing a sintering device, wherein the sintering device is filled with a sintering atmosphere; mixing the high-nickel ternary positive electrode material and the aluminum diethylphosphinate; and putting the mixed high-nickel ternary positive electrode material and aluminum diethylphosphinate into the sintering device to perform sintering, wherein the sintering temperature is 500-800℃, the sintering duration is 2-20 h, and the heating rate is 0.5-5℃ / min, so as to prepare a high-nickel ternary positive electrode material having a coating layer, wherein the coating layer is formed by aluminum phosphate and lithium phosphate. A stable interfacial layer, i.e., the coating layer, is constructed on the surface of the high-nickel ternary material, and the coating layer is formed by aluminum phosphate and lithium phosphate, so that the problem of crystal structure degradation of the high-nickel ternary material in the cycle process can be effectively mitigated, thereby effectively prolonging the cycle life.

Description

Preparation method of modified high-nickel ternary positive electrode material TECHNICAL FIELD

[0001] The application belongs to the field of batteries, and particularly relates to a preparation method of a modified high-nickel ternary positive electrode material. BACKGROUND

[0002] Lithium ion batteries have high specific energy, high charging and discharging efficiency and other advantages, and have a huge development prospect. The specific capacity of a positive electrode material of a lithium ion battery directly affects the specific energy of the battery. High-nickel ternary positive electrode material (LiNixCoyMn(1-x-y)O2, x>=0.8) is currently the preferred positive electrode material of a commercial lithium ion battery due to its advantages of large capacity and low cost. However, the performance attenuation of the high-nickel ternary positive electrode material caused by structural degradation during the cycle process, especially under high voltage, limits the further development of the high-nickel ternary positive electrode material to some extent. SUMMARY

[0003] Therefore, the application provides a preparation method of a modified high-nickel ternary positive electrode material to solve the above problems.

[0004] The application provides a preparation method of a modified high-nickel ternary positive electrode material.

[0005] STEP 101: providing high-nickel ternary positive electrode material and aluminum diethylphosphinate, the mass ratio of the high-nickel ternary positive electrode material to the modifying agent aluminum diethylphosphinate being 100:0.01-5, and the surface of the high-nickel ternary positive electrode material being attached with lithium carbonate;

[0006] STEP 102: providing a sintering device, wherein the sintering device is filled with a sintering atmosphere;

[0007] STEP 103: mixing the high-nickel ternary positive electrode material and aluminum diethylphosphinate;

[0008] STEP 104: placing the mixed high-nickel ternary positive electrode material and aluminum diethylphosphinate into the sintering device to perform sintering, the sintering temperature being 500-800 DEG C, the sintering time being 2-20 hours, and the temperature rising speed being 0.5-5 DEG C / min, so as to prepare high-nickel ternary positive electrode material with a coating layer, wherein the coating layer is formed by aluminum phosphate and lithium phosphate.

[0009] Further, the high-nickel ternary positive electrode material is NCM811, and the specification of the NCM811 is 2 microns <D50< 16 microns.

[0010] Further, the sintering atmosphere is one of oxygen, air, nitrogen, argon, hydrogen and hydrogen-argon mixed gas.

[0011] Further, the method for mixing the high-nickel ternary positive electrode material and aluminum diethylphosphinate is one of mechanical mixing and ball milling.

[0012] Further, in the step STEP104, the sintering temperature is 600-700℃.

[0013] Further, in the step STEP104, the sintering time is 10h.

[0014] Further, in the step STEP104, the heating rate is 2℃ / min.

[0015] Compared with the prior art, by constructing a stable interface layer, i.e. the coating layer, on the surface of the high-nickel ternary material, the coating layer being formed by aluminum phosphate and lithium phosphate, the problem of crystal structure degradation of the high-nickel ternary material in the cycle process can be effectively alleviated, and the cycle life can be effectively prolonged. This is mainly because when the phosphate compound is applied to the surface modification of the high-nickel ternary material, on the one hand, it has a stable structure due to the strong covalent bond between P and O, and on the other hand, the phosphate and the residual lithium compound have a certain reactivity at high temperature, and can generate a compound with lithium ion conductivity, i.e. lithium phosphate. The stable interface formed by the two effectively isolates the contact between the electrode material and the electrolyte, inhibits the interface side reaction of the high-nickel ternary material in the electrochemical cycle process, reduces the impedance generated on the electrode surface due to the decomposition of the electrolyte to generate alkyl lithium and other substances, and effectively improves the cycle performance. BRIEF DESCRIPTION OF DRAWINGS

[0016] Fig. 1 is a flow chart of a preparation method of a modified high-nickel ternary positive electrode material provided by the present application.

[0017] Fig. 2 is a cycle performance graph of all samples in Fig. 1 at 1C rate and in the voltage range of 2.75-4.3V.

[0018] Fig. 3 is a charge-discharge curve graph of Comparative Example 1, Examples 1-3 after 80 cycles.

[0019] Fig. 4 is a cycle performance graph of Comparative Example 1, Example 2 and Example 3 at 1C rate and in the voltage range of 2.75-4.5V. DETAILED DESCRIPTION

[0020] The specific embodiments of the present application are further described in detail below. It should be understood that the description of the embodiments of the present application herein is not intended to limit the protection scope of the present application.

[0021] As shown in Fig. 1, it is a flow chart of a preparation method of a modified high-nickel ternary positive electrode material provided by the present application. The preparation method of the modified high-nickel ternary positive electrode material comprises the following steps:

[0022] STEP 101: providing a high-nickel ternary positive electrode material and aluminum diethyl phosphinate, the mass ratio of the high-nickel ternary positive electrode material to aluminum diethyl phosphinate being 100:0.01-5m, and the surface of the high-nickel ternary positive electrode material being attached with lithium carbonate;

[0023] STEP 102: providing a sintering device filled with a sintering atmosphere;

[0024] STEP 103: mixing the high-nickel ternary positive electrode material and aluminum diethyl phosphinate

[0025] STEP 104: placing the mixed high-nickel ternary positive electrode material and aluminum diethyl phosphinate into the sintering device for sintering, the sintering temperature being 500-800°C, the sintering time being 2-20h, and the temperature rising speed being 0.5-5°C / min, to prepare a high-nickel ternary positive electrode material with a coating layer formed mainly by aluminum phosphate and lithium phosphate.

[0026] In STEP 101, the high-nickel ternary positive electrode material is LiNi x Co y Mn (1-x-y) O2, wherein x≥0.8. It can be understood that there are many formula proportions as the values of x and y are different. In the present embodiment, the high-nickel ternary positive electrode material is NCM811. "NCM" represents the elements contained in the high-nickel ternary positive electrode material, i.e., nickel (Ni), cobalt (Co), and manganese (Mn). NCM811 refers to the content ratio of nickel, cobalt, and manganese in the positive electrode material being 8:1:1.

[0027] The mass ratio of the high-nickel ternary positive electrode material to aluminum diethyl phosphinate can be 100:0.01-5. The specification of the NCM811 can be selected as 2μm<D50<16μm, preferably 3μm<D50<5μm, or 9μm<D50<12μm. In the present technical solution, in order to form an effective coating layer after sintering, the mass ratio before mixing the high-nickel ternary material and aluminum diethyl phosphinate is 100:0.01-5. Through the above mass ratio, the capacity of the high-nickel ternary positive electrode material can be effectively improved after modification, and the cycle performance of the high-nickel ternary positive electrode material can also be effectively improved. If the mass ratio is less than 0.01%, the cycle performance of the high-nickel ternary positive electrode material cannot be effectively improved, and if the mass ratio is greater than 5%, the capacity will be greatly reduced.

[0028] In step STEP102, the sintering device can be a box-type atmosphere furnace or other equipment that can provide high temperature and atmosphere conditions at the same time, which is a prior art and is commonly used in the sintering process of ternary materials. The sintering atmosphere can be one of oxygen, air, nitrogen, argon, hydrogen, and hydrogen-argon mixed gas.

[0029] In step STEP103, the method of mixing the high-nickel ternary positive electrode material and aluminum diethyl phosphinate is one of mechanical mixing and ball milling. The mechanical mixing and ball milling are prior arts, which are used to uniformly mix the high-nickel ternary positive electrode material and aluminum diethyl phosphinate. The specific mixing method is not described here.

[0030] In step STEP104, the mixed high-nickel ternary positive electrode material and aluminum diethyl phosphinate are placed in the sintering device. The method of placing can be to place the uniformly mixed high-nickel ternary material and aluminum diethyl phosphinate in a high-temperature-resistant and non-hermetic container, generally a refractory crucible. Then the crucible is placed in the sintering device.

[0031] The sintering temperature during sintering is 500-800°C, and the sintering temperature is preferably 600-700°C. Since the pyrolysis temperature of aluminum diethyl phosphinate is 450°C, if the sintering temperature is too low, aluminum diethyl phosphinate will not undergo thermal degradation reaction, which will make it difficult to form the coating layer of the technical solution. If the temperature is too high, the morphology and structure of the high-nickel ternary material will be damaged during sintering, which will cause a significant decrease in capacity and reduce the cycle performance of the formed high-nickel ternary material.

[0032] The sintering time during sintering is 2-20h, and the sintering time is 10h. If the sintering time is too short during sintering, the degree of reaction during sintering is low, and the cycle performance improvement is not obvious. The reaction that occurs during sintering will be described in detail below. If the sintering time is too long, the performance improvement is not obvious, and it will cause a certain waste of resources.

[0033] During sintering, the heating rate is 0.5-5°C / min, and the preferred heating rate is 2°C / min. Because the heating rate will affect the degree of thermal decomposition reaction, if the heating rate is too low, on the one hand, it is extremely high for the equipment to control the temperature, which is not conducive to reducing production costs. If the heating rate is too high, it will cause aluminum diethyl phosphinate to be more inclined to volatilize rather than to pyrolyze, which will affect the formation of the surface coating layer, i.e., no pyrolysis occurs to perform the following reaction.

[0034] During the above sintering process, the main decomposition products of aluminum diethyl phosphinate are diethyl phosphinic acid and aluminum phosphate, and the specific equation is as follows:

[0035]

[0036] It is known that the surface of the high-nickel ternary positive electrode material will have residual lithium, which will react with water to generate lithium hydroxide, and further react with carbon dioxide to generate lithium carbonate. Therefore, it is generally assumed that the surface of the high-nickel ternary positive electrode has lithium hydroxide and lithium carbonate, and there is no need to attach lithium carbonate to the surface of the high-nickel ternary positive electrode material through a special process. The aluminum phosphate can dope aluminum into the high-nickel ternary under high temperature conditions and react with the lithium carbonate on the surface of the high-nickel ternary to generate a lithium phosphate compound. The specific reaction equation is as follows:

[0037]

[0038] The high-nickel ternary positive electrode material with a coating layer prepared through the above steps is modified, and the coating layer is formed by aluminum phosphate and lithium phosphate.

[0039] Example 1

[0040] Take 15 g of the high-nickel ternary positive electrode material described in Comparative Example 1, and take 0.015 g of aluminum diethyl phosphinate. Mix them uniformly through a mixer, and perform sintering under an oxygen atmosphere. The sintering procedure is: sintering at 700°C for 10 h, with a temperature rising rate of 2°C / min.

[0041] Example 2

[0042] Take 15 g of the high-nickel ternary positive electrode material described in Comparative Example 1, and take 0.030 g of aluminum diethyl phosphinate. Mix them uniformly through a high-speed mixer, and perform sintering under an oxygen atmosphere. The sintering procedure is: sintering at 700°C for 10 h, with a temperature rising rate of 2°C / min.

[0043] Example 3

[0044] Take 15 g of the high-nickel ternary positive electrode material described in Comparative Example 1, and take 0.075 g of aluminum diethyl phosphinate. Mix them uniformly through a high-speed mixer, and perform sintering under an oxygen atmosphere. The sintering procedure is: sintering at 700°C for 10 h, with a temperature rising rate of 2°C / min.

[0045] Example 4

[0046] Take 15 g of the high-nickel ternary positive electrode material described in Comparative Example 2, and take 0.015 g of aluminum diethyl phosphinate. Mix them uniformly through a high-speed mixer, and perform sintering under an oxygen atmosphere. The sintering procedure is: sintering at 700°C for 10 h, with a temperature rising rate of 2°C / min.

[0047] Example 5

[0048] Take 15 g of high nickel ternary positive electrode material described in Comparative Example 2, and take 0.015 g of aluminum diethylphosphinate, mix uniformly by high-speed mixer, and sinter in an oxygen atmosphere. The sintering procedure is: sintering at 700°C for 10 h, with a heating rate of 2°C / min.

[0049] Comparative Example 1

[0050] Take NCM811 precursor (3 μm < D50 < 5 μm) and lithium hydroxide monohydrate, mix uniformly according to a molar ratio of 1:1.05, and sinter in an oxygen atmosphere. The sintering procedure is: sintering at 400°C for 4 h and sintering at 800°C for 12 h, with a heating rate of 2°C / min.

[0051] Comparative Example 2

[0052] Take NCM811 precursor (9 μm < D50 < 12 μm) and lithium hydroxide monohydrate, mix uniformly according to a molar ratio of 1:1.05, and sinter in an oxygen atmosphere. The sintering procedure is: sintering at 400°C for 4 h and sintering at 800°C for 12 h, with a heating rate of 2°C / min.

[0053] High-pressure cycle performance tests were performed on some of the samples: the sieved samples, conductive carbon black, and binder were dispersed in an NMP (N-methyl pyrrolidone) solution at a mass ratio of 92:4:4, and mixed uniformly using a high-speed mixer. The slurry was coated, dried, and rolled on aluminum. In a glove box, a circular electrode sheet was cut into a straight circular electrode sheet as a positive electrode sheet, lithium was used as a negative electrode sheet, a mixed solution of 1 mol / L LiPF6 ethylene carbonate and dimethyl carbonate (volume ratio 1:1) was used as an electrolyte, and a polyethylene microporous membrane was used as a separator. CR2035 type button half-batteries were assembled in the glove box, and the cycle performance of the batteries was tested using a blue electric test system. The window voltage was 2.75V-4.5V.

[0054] Table 1 is the capacity retention rate of all samples after 80 cycles. As is known, the capacity retention rate refers to the ratio of the discharge specific capacity of the battery after a certain number of cycles at 1C rate to the discharge specific capacity of the first cycle. The higher the capacity retention rate, the better the electrochemical cycle performance of the material. As can be seen from Table 1, the capacity retention rates of Comparative Examples 1 and 2 after 80 cycles at 1C are 71.92% and 63.56%, respectively, and the cycle performance is poor. However, the capacity retention rates of the samples of Examples 1 to 5 after 80 cycles at 1C are greatly improved, and some samples can exceed 85%. The great improvement in capacity retention rate is mainly due to the addition of the modifier aluminum diethylphosphinate and the corresponding heat treatment process.

[0055] Table 1 is the capacity retention rate of all samples after 80 cycles

[0056] Capacity retention rate (80 cycles) / % Comparative example 1 71.92 Example 1 88.85 Example 2 84.77 Example 3 88.66 Comparative example 2 63.56 Example 4 83.84 Example 5 79.02

[0057] Figure 2 is a cycle performance diagram of all samples, the capacity of samples corresponding to examples 1-5 is obviously higher than that of samples of comparative examples 1-2 at the later stage of cycle, so the cycle performance of modified high-nickel ternary positive electrode materials of examples 1-5 is good. In order to further study the electrochemical performance of high-nickel ternary, comparative example 1 and examples 1-3 are selected to compare the charge-discharge curves.

[0058] As shown in Figure 3, the charge-discharge curves of examples 1-3 samples are obviously better than that of comparative example 1, the impedance increase of examples 1-3 samples is better than that of comparative example 1 sample after 80 cycles, which is mainly because the coating layer formed on the surface of high-nickel ternary after heat treatment of aluminum diethylphosphinate can effectively inhibit the side reaction of high-nickel ternary with electrolyte, delay the structural degradation of high-nickel ternary in the cycle process, and improve the overall cycle performance of high-nickel ternary. Among them, examples 2 and 3 samples still have a higher discharge platform voltage after 80 cycles at 4.3V, which can further verify the cycle performance at high voltage of 4.5V.

[0059] Figure 4 is a cycle performance diagram of comparative example 1, example 2 and example 3 samples at working voltage of 2.75-4.5V, the specific capacity after 60 cycles at 1C rate is 122.5, 178.1 and 173.9mAh / g respectively, and the corresponding capacity retention rate is 56.71%, 84.49% and 82.97% respectively, the cycle performance of example samples is much better than that of comparative example samples, which shows that the high-nickel ternary lithium positive electrode material modified by aluminum diethylphosphinate can effectively improve the cycle performance at high voltage.

[0060] Compared with the prior art, by constructing a stable interface layer, i.e. the coating layer, on the surface of the high-nickel ternary material, the coating layer is formed by aluminum phosphate and lithium phosphate, so that the crystal structure degradation problem of high-nickel ternary material in the cycle process can be effectively alleviated, and the cycle life can be effectively prolonged. This is mainly because when phosphate compounds are applied to the surface modification of high-nickel ternary material, on the one hand, it can rely on the strong covalent bond between P and O to have a stable structure, on the other hand, phosphate and residual lithium compounds have a certain reactivity at high temperature, and can generate lithium phosphate which has lithium conductivity, the stable interface formed by the two can effectively isolate the contact between the electrode material and the electrolyte, inhibit the interface side reaction of high-nickel ternary in the electrochemical cycle process, reduce the impedance generated on the electrode surface by the decomposition of alkyl lithium and other substances generated by the electrolyte, and effectively improve the cycle performance.

[0061] The above merely describes the preferred embodiments of the present application and is not used to limit the protection scope of the present application, and any modification, equivalent replacement or improvement within the spirit of the present application is covered within the protection scope of the present application.

Claims

1. A method for preparing a modified high-nickel ternary cathode material, comprising the following steps: STEP 101: providing a high-nickel ternary cathode material and aluminum diethylphosphinate, wherein the mass ratio of the high-nickel ternary cathode material to the aluminum diethylphosphinate is 100:0.01-5, and lithium carbonate is attached to the surface of the high-nickel ternary cathode material; STEP 102: providing a sintering device filled with a sintering atmosphere; STEP 103: mixing the high-nickel ternary cathode material and the aluminum diethylphosphinate; STEP 104: placing the mixed high-nickel ternary cathode material and aluminum diethylphosphinate into the sintering device to perform sintering, wherein the sintering temperature is 500-800°C, the sintering time is 2-20h, and the temperature rising speed is 0.5-5°C / min, so as to prepare a high-nickel ternary cathode material with a coating layer formed by aluminum phosphate and lithium phosphate. 2.The method for preparing modified high-nickel ternary cathode material according to claim 1, characterized in that: The high-nickel ternary cathode material is NCM811, and the specification of the NCM811 is 2μm 3. The method for preparing the modified high-nickel ternary cathode material as described in claim 1, characterized in that: The sintering atmosphere is one of oxygen, air, nitrogen, argon, hydrogen, and hydrogen-argon mixed gas. 4.The method for preparing modified high-nickel ternary cathode material according to claim 1, characterized in that: The method for mixing the high-nickel ternary cathode material and the aluminum diethylphosphinate is one of mechanical mixing and ball milling.

5. The method for preparing modified high-nickel ternary cathode material according to claim 1, characterized in that: In STEP 104, the sintering temperature is 600-700°C.

6. The method for preparing a modified high-nickel ternary cathode material according to claim 1, characterized in that: In STEP 104, the sintering time is 10h.

7. The method for preparing the modified high-nickel ternary cathode material as described in claim 1, characterized in that: In STEP 104, the temperature rising speed is 2°C / min.

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