A high-nickel ternary cathode material, its preparation method and lithium battery

Abstract

This invention discloses a high-nickel ternary cathode material, its preparation method, and a lithium battery, relating to the field of lithium battery technology. A coating layer is formed on a high-nickel ternary cathode material substrate using fluorinated liquid crystal molecules. These fluorinated liquid crystal molecules have a lower melting point, making it easier to form an ideal coating layer compared to traditional coating agents. Furthermore, the liquid crystal molecules exhibit better solvent and electrolyte corrosion resistance, significantly improving the high-temperature cycling performance of the cathode material.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, and more specifically, to a high-nickel ternary cathode material, its preparation method, and a lithium battery thereof. Background Technology

[0002] High-nickel ternary cathode materials are a common type of cathode material for lithium-ion batteries. Their chemical formula is Li(Ni,Co,Mn)O2, in which the nickel content is higher than that of traditional ternary cathode materials, while the cobalt content is relatively lower. High-nickel ternary cathode materials have advantages such as high energy density, good rate performance, and good high-temperature stability, and are therefore widely used in lithium-ion batteries. Their main disadvantages are: relatively short cycle life, high requirements for production equipment, and susceptibility to capacity decay at high temperatures.

[0003] Improving high-nickel ternary cathode materials through coating is a common method. However, common coating agents (alumina, titanium dioxide, zirconium oxide, boric acid, etc.) have poor coating effects after dry coating, making it difficult to form a uniform coating layer. This results in increased interfacial resistance between the material and the electrolyte inside the cell, and exacerbates electrolyte corrosion during cycling, causing the battery to swell and significantly reduce cycle performance.

[0004] Therefore, there is an urgent need to find modification methods that can significantly improve the high-temperature cycling performance of high-nickel ternary cathode materials.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a high-nickel ternary cathode material, its preparation method and lithium battery, which aims to significantly improve the high-temperature cycle performance of the high-nickel ternary cathode material.

[0007] This invention is implemented as follows:

[0008] In a first aspect, the present invention provides a high-nickel ternary cathode material, comprising a high-nickel ternary cathode material substrate and a coating layer coated on the high-nickel ternary cathode material substrate, wherein the coating layer is formed of fluorine-containing liquid crystal molecules;

[0009] The chemical formula of the fluorine-containing liquid crystal molecule is:

[0010] ;

[0011] In the formula, the end-capping group R 1 Selected from alkyl or alkoxy groups;

[0012] End capping group R 2 It contains fluorine groups.

[0013] In an optional embodiment, the capping group R 1It is selected from any one of methyl, methoxy, ethoxy, n-propoxy, n-butoxy, n-pentoxy, n-hexoxy, n-heptoxy, and n-octoxy.

[0014] In an optional embodiment, the capping group R 2 Choose from -F, -CF3, -OCF3, and -CF2H.

[0015] In an optional implementation, the mass percentage of the coating layer is 0.05%-5%.

[0016] In an optional embodiment, the chemical formula of the high-nickel ternary cathode material substrate is LiNi. x Co y Mn z O2, x+y+z=1, 0.8≤x≤1, 0≤y≤0.2, 0≤z≤0.2.

[0017] In a second aspect, the present invention provides a method for preparing a high-nickel ternary cathode material according to any of the foregoing embodiments, comprising: forming a coating layer on a high-nickel ternary cathode material substrate using fluorine-containing liquid crystal molecules.

[0018] In an optional embodiment, fluorine-containing liquid crystal molecules and high-nickel ternary cathode material substrate are mixed and then sintered at a low temperature of 50°C-200°C for 2-24 hours.

[0019] In an optional embodiment, the preparation method of the high-nickel ternary cathode material substrate includes: mixing and sintering a nickel-cobalt-manganese precursor and a lithium salt, controlling the sintering temperature to be 700℃-900℃, using oxygen in the sintering atmosphere, and sintering for 10h-16h.

[0020] The chemical formula of the nickel-cobalt-manganese precursor is Ni x Co y Mn z OH, x+y+z=1, 0.8≤x≤1, 0≤y≤0.2, 0≤z≤0.2.

[0021] In an optional implementation, the amount of lithium salt is controlled so that the molar ratio of lithium to the total amount of nickel, cobalt, and manganese is (1.01-1.1):1.

[0022] Thirdly, the present invention provides a lithium battery comprising any of the high-nickel ternary cathode materials described in the foregoing embodiments or high-nickel ternary cathode materials prepared by any of the preparation methods described in the foregoing embodiments.

[0023] The present invention has the following beneficial effects: a coating layer is formed on a high-nickel ternary cathode material substrate by using fluorine-containing liquid crystal molecules. The fluorine-containing liquid crystal molecules have a lower melting point and are easier to form an ideal coating layer than traditional coating agents. Moreover, the liquid crystal molecules have better resistance to solvents and electrolyte corrosion, which can significantly improve the high-temperature cycling performance of the cathode material. Attached Figure Description

[0024] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 The figures show the high-temperature cycling performance test results of the high-nickel ternary cathode materials prepared in the examples and comparative examples. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0027] This embodiment provides a method for preparing a high-nickel ternary cathode material. By using fluorine-containing liquid crystal molecules to form a coating layer on the high-nickel ternary cathode material substrate, the high-temperature cycling performance of the cathode material can be significantly improved. The specific steps are as follows:

[0028] S1. Preparation of high-nickel ternary cathode material substrate

[0029] The high-nickel ternary cathode material substrate can be commercially available or prepared in-house; its chemical formula can be LiNi. x Co y Mn z O2, x+y+z=1, 0.8≤x≤1, 0≤y≤0.2, 0≤z≤0.2. Specifically, the values ​​of x can be 0.80, 0.85, 0.90, 0.95, 0.98, etc.; the values ​​of y can be 0.05, 0.10, 0.15, 0.18, etc.; and the values ​​of z can be 0.05, 0.10, 0.15, 0.18, etc.

[0030] If a high-nickel ternary cathode material substrate is to be prepared independently, the preparation method includes: mixing and sintering a nickel-cobalt-manganese precursor and a lithium salt, controlling the sintering temperature at 700℃-900℃, using an oxygen atmosphere, and sintering for 10h-16h to ensure sufficient reaction. Specifically, the sintering temperature of the nickel-cobalt-manganese precursor and lithium salt can be 700℃, 750℃, 800℃, 850℃, 900℃, etc.; the sintering time can be 10h, 12h, 14h, 16h, etc.

[0031] To ensure that the chemical formula of the high-nickel ternary cathode material substrate meets the above requirements, the chemical formula of the nickel-cobalt-manganese precursor is Ni. x Co y Mn z OH, x+y+z=1, 0.8≤x≤1, 0≤y≤0.2, 0≤z≤0.2.

[0032] Furthermore, in the process of preparing high-nickel ternary cathode material substrate, the amount of lithium salt is controlled so that the molar ratio of lithium element to total nickel, cobalt and manganese is (1.01-1.1):1, such as 1.01:1, 1.05:1, 1.07:1, 1.09:1, or 1.10:1.

[0033] Specifically, the type of lithium salt is not limited and can include commonly used lithium salts such as lithium carbonate and lithium hydroxide.

[0034] S2, Formation of the coating layer

[0035] This invention utilizes fluorinated liquid crystal molecules to form a coating layer. Because fluorinated liquid crystal molecules are nano-sized powders with a low melting point, they are easier to form an ideal coating layer compared to traditional coating agents. Furthermore, liquid crystal molecules exhibit better resistance to solvents and electrolyte corrosion, thus improving the stability of the cathode material.

[0036] The chemical formula of the fluorine-containing liquid crystal molecule used in this embodiment of the invention is:

[0037] ;

[0038] In the formula, the end-capping group R 1 Selected from alkyl or alkoxy groups; end-capping group R 2 It contains fluorine groups.

[0039] In some embodiments, the capping group R 1 Selected from any one of methyl, methoxy, ethoxy, n-propoxy, n-butoxy, n-pentoxy, n-hexoxy, n-heptoxy, and n-octoxy, and can be any one of the above groups. End-capping group R 2 It can be selected from any one of -F, -CF3, -OCF3 and -CF2H, and can be any of the above fluorine-containing groups.

[0040] It should be noted that the fluorine-containing liquid crystal molecules provided in the embodiments of the present invention are commercially available and can be synthesized independently. The synthesis method is as follows: [The following text appears to be a separate, unrelated section:] ...containing the corresponding para-R... 1 Hydroxybiphenyl compounds and triethylamine were dissolved in tetrahydrofuran under ice bath conditions, followed by the addition of 10%-20% by mass of the corresponding para-R... 2 A tetrahydrofuran solution of benzoyl chloride was gradually added dropwise to the above solution. The ice bath was removed, and the reaction was carried out at room temperature for 48 h. After the reaction was complete, the solvent was removed by rotary evaporation, and ethanol was added to precipitate the product. After filtration and washing, the product was obtained by recrystallization and drying of a mixture of acetone and ethanol.

[0041] In some embodiments, the process of forming the coating layer includes: mixing fluorinated liquid crystal molecules and a high-nickel ternary cathode material substrate, followed by low-temperature sintering at a temperature of 50℃-200℃ (e.g., 50℃, 100℃, 150℃, 200℃, etc.), using an oxygen atmosphere, and for a sintering time of 2h-24h (e.g., 2h, 5h, 10h, 15h, 20h, 24h, etc.). The fluorinated liquid crystal molecules are nano-sized powders, which are sintered at a relatively low temperature, causing the liquid crystal molecules to melt and obtain an ideal liquid crystal small molecule coating layer. Using a dry coating method achieves the desired coating effect, avoids the use of organic solvents, and is easy to commercialize.

[0042] The chemical formula of the fluorine-containing liquid crystal molecule is:

[0043] ;

[0044] In the formula, the end-capping group R1 is selected from alkyl or alkoxy groups; the end-capping group R2 is a fluorine-containing group.

[0045] It should be noted that fluorinated biphenyl liquid crystal molecules possess biphenyl liquid crystal units and highly polar groups such as fluorine-containing groups, resulting in a molecular structure with good structural stability and corrosion resistance. Furthermore, in the liquid crystal state, the liquid crystal molecules have low viscosity and good fluidity. By coating fluorinated liquid crystal molecules onto ternary cathode materials, a uniform coating layer can be formed to resist the erosion of the cathode material by the electrolyte, thereby improving the material's cycle performance.

[0046] In an optional embodiment, the capping group R 1 It is selected from any one of methyl, methoxy, ethoxy, n-propoxy, n-butoxy, n-pentoxy, n-hexoxy, n-heptoxy, and n-octoxy.

[0047] In an optional embodiment, the capping group R 2 Choose from -F, -CF3, -OCF3, and -CF2H.

[0048] By controlling the mass ratio of fluorinated liquid crystal molecules to high-nickel ternary cathode material substrate, the mass percentage of the coating layer in the prepared cathode material is made to be 0.05%-5%. That is, during the preparation process, the mass ratio of fluorinated liquid crystal molecules to high-nickel ternary cathode material substrate is controlled to be 0.05:100, 0.10:100, 0.15:100, 0.20:100, 0.25:100, 0.30:100, 0.35:100, 0.40:100, 0.45:100, 0.50:100, etc.

[0049] This invention provides a high-nickel ternary cathode material, comprising a high-nickel ternary cathode material substrate and a coating layer coated on the high-nickel ternary cathode material substrate. The coating layer is formed of fluorine-containing liquid crystal molecules and can be prepared by the above-described preparation method. The chemical formula and structure of the end-capping groups of the fluorine-containing liquid crystal molecules are not repeated here.

[0050] This invention provides a lithium battery comprising the aforementioned high-nickel ternary cathode material. The improvement of the cathode material significantly enhances the electrochemical performance of the lithium battery, such as improving the battery's high-temperature cycle performance.

[0051] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0052] Example 1

[0053] This embodiment provides a method for preparing a high-nickel ternary cathode material, including the following steps:

[0054] (1) Provide fluorine-containing liquid crystal molecules

[0055] The structural formula of fluorine-containing liquid crystal molecules is:

[0056] ;

[0057] In the formula, the end-capping group R 1 It is a hexyloxy group; the end-capping group R 2 for - F.

[0058] The preparation method is as follows: 25.3 g of 4-hexyloxy-4'-hydroxybiphenyl and 12.14 g of triethylamine were dissolved in 500 mL of tetrahydrofuran under ice bath conditions. Then, 19.02 g of p-fluorobenzoyl chloride, prepared as a 15% (w / w) tetrahydrofuran solution, was gradually added dropwise to the above solution. The ice bath was removed, and the reaction was carried out at room temperature for 48 h. After the reaction was completed, the solvent was removed by rotary evaporation, and ethanol was added to precipitate the product. After filtration and washing, the product was obtained by recrystallization and drying of a mixture of acetone and ethanol.

[0059] (2) Preparation of high-nickel ternary cathode material substrate

[0060] The nickel-cobalt-manganese precursor and lithium hydroxide were mixed and sintered at a controlled sintering temperature of 830℃ for 12 hours. The chemical formula of the nickel-cobalt-manganese precursor is Ni. 0.9 Co 0.05 Mn 0.05 OH, control the amount of lithium salt used to make the molar ratio of lithium element to total nickel, cobalt and manganese 1.08:1.

[0061] (3) Formation of a coating layer

[0062] The high-nickel ternary cathode material substrate prepared in step (2) is mixed with the fluorine-containing liquid crystal molecules in step (1) at a mass ratio of 1:0.02, and then sintered at low temperature. The sintering temperature is controlled at 180°C, the sintering atmosphere is oxygen, and the sintering time is 8h.

[0063] Example 2

[0064] The only difference from Example 1 is that in step (3), the high-nickel ternary cathode material substrate and fluorine-containing liquid crystal molecules are mixed at a mass ratio of 1:0.04.

[0065] Example 3

[0066] The only difference from Example 1 is that in step (3), the high-nickel ternary cathode material substrate and fluorine-containing liquid crystal molecules are mixed at a mass ratio of 1:0.01.

[0067] Example 4

[0068] The only difference from Example 1 is that in the structure of the fluorine-containing liquid crystal molecule in step (1), the end-capping group R 1 It is a hexyloxy group; the end-capping group R 2 It is CF3.

[0069] Example 5

[0070] The only difference from Example 1 is that in the structure of the fluorine-containing liquid crystal molecule in step (1), the end-capping group R 1 It is a hexyloxy group; the end-capping group R 2 It is -OCF3.

[0071] Example 6

[0072] The only difference from Example 1 is that in the structure of the fluorine-containing liquid crystal molecule in step (1), the end-capping group R 1 It is a hexyloxy group; the end-capping group R 2 It is -CF2H.

[0073] Comparative Example 1

[0074] The only difference from Example 1 is that the high-nickel ternary cathode material was prepared in step (2) without coating, serving as a blank control.

[0075] Comparative Example 2

[0076] The only difference from Example 1 is that in the structure of the fluorine-containing liquid crystal molecule in step (1), the end-capping group R 1 It is a hexyloxy group; the end-capping group R 2 It is a methyl group.

[0077] Comparative Example 3

[0078] The only difference from Example 1 is that in the structure of the fluorine-containing liquid crystal molecule in step (1), the end-capping group R 1 It is a hexyloxy group; the end-capping group R 2 It is -Cl.

[0079] Experimental Example 1

[0080] The electrochemical performance of the high-nickel ternary cathode materials prepared in the test examples and comparative examples is shown in Table 1 and the results are presented in Table 1. Figure 1 As shown.

[0081] Test method:

[0082] (1) Battery assembly: The positive electrode material, conductive agent Super P, and binder PVDF were mixed at a mass ratio of 90:5:5, and an appropriate amount of NMP was added to prepare the positive electrode material slurry. After coating, vacuum drying, rolling, and slicing, coin cells 2025 were assembled for testing. The electrolyte was 1.2 mol / L LiPF6, and the solvent was EC:EMC=3:7 (volume ratio); the separator was Celgard PP membrane.

[0083] (2) Capacity test: The button cell test was carried out under a constant temperature environment of 25℃. At 2.8 to 4.3V, the CC / CV system was used to perform 0.1C charge and discharge, and the 0.1C discharge capacity was recorded.

[0084] (3) Cyclic test: In a constant temperature environment of 45℃, at 2.8 to 4.3V, 50 cycles of 1C charge and discharge were performed using the CC / CV system, and the capacity retention rate at the end of the 50th cycle was recorded.

[0085] Table 1. Performance test results of materials prepared in the examples and comparative examples.

[0086]

[0087] As can be seen from Table 1, the positive electrode material prepared in the examples has significantly better electrochemical performance and a significantly higher capacity retention rate than the comparative example.

[0088] from Figure 1 It can be seen that coating liquid crystal molecules greatly improves high-temperature cycling performance, and liquid crystal molecules with fluorine-containing end caps are even more effective in comparison.

[0089] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A high-nickel ternary cathode material, characterized in that, The invention includes a high-nickel ternary cathode material substrate and a coating layer coated on the high-nickel ternary cathode material substrate, wherein the coating layer is formed of fluorine-containing liquid crystal molecules; The chemical formula of the fluorine-containing liquid crystal molecule is: ； wherein the end-capping group R 1 is selected from any one of methyl, methoxy, ethoxy, n-propoxy, n-butoxy, n-pentoxy, n-hexoxy, n-heptoxy, and n-octoxy; End capping group R 2 Choose from -F, -CF3, -OCF3, and -CF2H.

2. The high-nickel ternary cathode material according to claim 1, characterized in that, The mass percentage of the coating layer is 0.05%-5%.

3. The high-nickel ternary cathode material according to claim 1, characterized in that, The high-nickel ternary positive electrode material substrate has a chemical formula of LiNi x Co y Mn z O2, x+y+z=1, 0.8≤x<1, 0 0.

2.

4. A method for preparing the high-nickel ternary cathode material according to any one of claims 1-3, characterized in that, include: The fluorine-containing liquid crystal molecules are used to form a coating layer on the high-nickel ternary cathode material substrate; Specifically, the fluorine-containing liquid crystal molecules and the high-nickel ternary cathode material substrate are mixed and then sintered at a low temperature of 50℃-200℃ for 2h-24h.

5. The preparation method according to claim 4, characterized in that, The preparation method of the high-nickel ternary cathode material substrate includes: mixing and sintering a nickel-cobalt-manganese precursor and a lithium salt, controlling the sintering temperature at 700℃-900℃, using oxygen in the sintering atmosphere, and sintering for 10h-16h. The chemical formula of the nickel-cobalt-manganese precursor is Ni x Co y Mn z OH, x+y+z=1, 0.8≤x<1, 0<y≤0.2, 0<z≤0.

2.

6. The preparation method according to claim 5, characterized in that, By controlling the amount of lithium salt used, the molar ratio of lithium to total nickel, cobalt, and manganese is made to be (1.01-1.1):

1.

7. A lithium battery, characterized in that, This includes the high-nickel ternary cathode material according to any one of claims 1-3 or the high-nickel ternary cathode material prepared by the preparation method according to any one of claims 4-6.

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