A double-coated lithium battery cathode material, its preparation method and application

Abstract

This invention discloses a double-coated lithium-ion battery cathode material, its preparation method, and its application, belonging to the field of lithium-ion battery technology. This invention utilizes a low-melting-point Lewis acid salt to treat the cathode material surface, forming fast ion conductor points on the cathode material surface, followed by elastic graphene aerogel coating; thus obtaining a double-coated lithium-ion battery cathode material. The surface treatment of the cathode material with a low-melting-point Lewis acid salt reacts with residual alkali on the surface, reducing the residual alkali content of the cathode material. Simultaneously, the fast ion conductor point coating layer exhibits excellent ionic conductivity, and the graphene aerogel coating layer possesses excellent ionic and electronic conductivity, resulting in excellent rate performance and cycle performance of the cathode material.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a double-coated lithium battery cathode material, its preparation method, and its application. Background Technology

[0002] Nickel-cobalt-manganese ternary layered oxide materials are widely used in electric vehicles due to their high specific capacity, low cost, and environmental friendliness. To fully exploit their high specific capacity, there are currently two main directions for improvement: increasing the nickel content of the cathode material and increasing the charging cut-off voltage. However, this brings new problems—poor cycle performance. The main reasons are: 1) Increasing the nickel content increases the residual lithium on the surface of the ternary material. Residual lithium exposed to air easily forms impurities such as Li₂CO₃ and LiOH, increasing the surface alkali residue and interfacial impedance of the material particles. Furthermore, in deeper delithiation states, the high-valence transition metal ions on the particle surface have strong oxidizing properties and easily react with the electrolyte, worsening the cycle performance. 2) Intergranular cracks and micro-strain: During charging and discharging, the cathode material undergoes volume changes, resulting in newly generated cracks exposed to the electrolyte. Continuous side reactions form additional insulating films, increasing the material's impedance and causing a continuous decrease in capacity. This failure process is even more rapid under high voltage conditions.

[0003] Surface coating is a relatively effective method for reducing residual alkali on the surface of cathode materials and maintaining their cycling performance. Common metal oxides, such as Al2O3, TiO2, and ZrO2, can effectively reduce residual alkali on the cathode material surface, and the inert coating layer can effectively prevent HF corrosion and improve the material's cycle performance. However, these substances themselves have low ionic and electronic conductivity, and large-area coating will reduce the material's rate performance. Therefore, currently, dry mixing is generally used for point coating of Al2O3, TiO2, ZrO2, etc., which results in a small coating area and limited reduction in residual alkali on the material surface. Summary of the Invention

[0004] To address the technical problems existing in the prior art, this invention provides a double-coated lithium battery cathode material, its preparation method, and its application. This invention improves the rate performance and cycle performance of the cathode material through low-melting-point Lewis acid salt melting treatment and elastic graphene aerogel coating.

[0005] This invention first provides a method for preparing a double-coated lithium battery cathode material, comprising the following steps:

[0006] (1) Mix lithium battery cathode material with low melting point Lewis acid salt, and then calcine to obtain dot-coated cathode material;

[0007] The positive electrode material of the lithium battery is LiNi. x Coy Mn 1-x-y O₂, wherein 0.5≤x<1, 0<y≤0.2, and x+y<1;

[0008] (2) mixing graphene oxide, a reducing agent, a cross-linking agent and ethanol to obtain a suspension solution;

[0009] (3) mixing the point-coated cathode material and the suspension solution, then carrying out a hydrothermal reaction, and obtaining a gel after cooling;

[0010] (4) freeze-drying the gel to obtain xerogel;

[0011] (5) calcining the xerogel in an inert atmosphere to obtain the double-coated lithium battery cathode material.

[0012] In the above preparation method of the double-coated lithium battery cathode material, in step (1), the low-melting point Lewis acid salt is at least one selected from anhydrous aluminum chloride, boric acid and anhydrous zirconium chloride;

[0013] the mass ratio of the lithium battery cathode material to the low-melting point Lewis acid salt is 0.15~0.2:1;

[0014] the calcination temperature is 300~450°C, and the calcination time is 2~4h;

[0015] the calcination is performed in an inert atmosphere; specifically, the inert atmosphere is a nitrogen atmosphere.

[0016] the lithium battery cathode material is LiNi 0.85 Co 0.1 Mn 0.05 O₂.

[0017] In the above preparation method of the double-coated lithium battery cathode material, in step (2), the graphene oxide is added in the form of an aqueous graphene oxide dispersion;

[0018] specifically, the concentration of the aqueous graphene oxide dispersion is 8~10mg / L;

[0019] the reducing agent is at least one selected from diisopropylamine, ethylenediamine and triethanolamine;

[0020] the cross-linking agent is at least one selected from sodium borate, polyethylene glycol dimethacrylate and polyethylene glycol diacrylate;

[0021] in the suspension solution, the concentration of the graphene oxide is 2~4g / L; the mass ratio of the reducing agent to the graphene oxide to the cross-linking agent is 1.5~2:1:0.005~0.01;

[0022] the ethanol is absolute ethanol.

[0023] In the above-mentioned method for preparing double-coated lithium battery cathode material, in step (3), the solid content of the dot-coated cathode material in the mixed solution of the dot-coated cathode material and the suspension solution is 1300-1800 g / L.

[0024] The hydrothermal reaction temperature is 120–150°C; the hydrothermal reaction time is 6–10 hours.

[0025] The hydrothermal reaction is carried out in a microwave heating device; specifically, the microwave heating power is 1600-2000W.

[0026] In the above-mentioned method for preparing double-coated lithium battery cathode material, in step (4), the freeze-drying temperature is -20 to -10°C; and the freeze-drying time is 10 to 12 hours.

[0027] In the above-mentioned method for preparing double-coated lithium battery cathode material, in step (5), the calcination temperature is 200-350℃; and the calcination time is 6-8h.

[0028] The calcination is carried out in an inert atmosphere; specifically, it can be a nitrogen atmosphere.

[0029] In the above-mentioned method for preparing double-coated lithium battery cathode material, step (1) further includes the steps of washing and drying the dot-coated cathode material;

[0030] Step (4) also includes washing and drying the dry gel.

[0031] Specifically, the washing is performed using anhydrous ethanol;

[0032] In step (1), the washing is performed 3 to 5 times; the solid-liquid volume ratio is 1:2.

[0033] The drying process is vacuum drying, with a temperature of 80–100°C and a drying time of 4–6 hours.

[0034] In step (4), the washing is performed 2 to 3 times; the solid-liquid volume ratio is 1:3.

[0035] The drying process is vacuum drying, with a temperature of 100–120°C and a time of 4–6 hours.

[0036] The present invention also provides a double-coated lithium battery cathode material prepared by the above preparation method.

[0037] Finally, the application of the double-coated lithium battery cathode material in the preparation of lithium battery cathodes also falls within the scope of protection of this invention.

[0038] The present invention has the following beneficial effects:

[0039] (1) The present invention utilizes low-melting-point Lewis acid salts to treat the surface of the cathode material, which reacts with the residual alkali on the surface to reduce the residual alkali content on the surface of the cathode material. At the same time, fast ion conductors (lithium aluminate, lithium borate or lithium zirconate) can be formed on the surface of the cathode material.

[0040] (2) The fast ion conductor coating layer in the cathode material of the present invention has excellent ionic conductivity, and the graphene aerogel coating layer has excellent ionic and electronic conductivity, which makes the cathode material have excellent rate performance; at the same time, the elastic graphene aerogel coating layer overcomes the problem that the coating layer breaks due to the volume change of the cathode material and thus loses the coating effect, which significantly improves the cycle life of the cathode material. Attached Figure Description

[0041] Figure 1 Photograph F of the dry gel prepared in step (5) of Example 5. Detailed Implementation

[0042] The present invention will be further described in detail below with reference to specific embodiments. The embodiments given are only for illustrating the present invention and are not intended to limit the scope of the present invention.

[0043] Unless otherwise specified, the experimental methods described in the following examples are conventional methods.

[0044] In the quantitative experiments in the following examples, three replicate experiments were set up, and the average value of the results was taken.

[0045] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0046] The following examples LiNi 0.85 Co 0.1 Mn 0.05 The O2 cathode material was purchased from Rongbai Technology.

[0047] Example 1

[0048] (1) LiNi 0.85 Co 0.1 Mn 0.05 The O2 cathode material was mixed evenly with boric acid, and then transferred to a calcination furnace and calcined at 300°C for 2 hours under a nitrogen atmosphere. After natural cooling, mixture A was obtained, in which the mass ratio of cathode material to boric acid was 0.15:1.

[0049] (2) Mixture A was added to anhydrous ethanol at a solid-liquid volume ratio of 1:2 and stirred and washed. The mixture was then filtered to remove unreacted salts. The washing and filtration were repeated 3 times. After vacuum drying at 80°C for 4 hours, the dot-coated positive electrode material B was obtained.

[0050] (3) A 10 mg / L aqueous solution of graphene oxide, diisopropylamine, and sodium borate were added to anhydrous ethanol and sonicated to obtain suspension C. In suspension C, the concentration of graphene oxide was 2 g / L, and the mass ratio of diisopropylamine, graphene oxide, and sodium borate was 1.5:1:0.005.

[0051] (4) The above-mentioned coated positive electrode material B and the suspension solution C were mixed according to the solid content of positive electrode material 1300g / L. After stirring evenly, a mixed slurry D was obtained. The mixed slurry D was transferred to a microwave reactor and hydrothermally reacted at 120℃ for 6h. After cooling, gel E was obtained. The microwave heating power was 1600W.

[0052] (5) Gel E was freeze-dried at -10℃ for 10h to obtain dry gel F;

[0053] (6) Add the dry gel F to anhydrous ethanol at a solid-liquid volume ratio of 1:3, wash and filter to remove residual reactants, and wash and filter twice; then dry at 100℃ under vacuum for 4 hours to obtain dry gel G.

[0054] (7) The dry gel G is calcined at 200°C for 6 hours under nitrogen atmosphere, crushed by roller pressing, and air-classified to remove particles and fine powders that do not contain positive electrode material, thus obtaining the double-coated positive electrode material.

[0055] Example 2

[0056] (1) LiNi 0.85 Co 0.1 Mn 0.05 The O2 cathode material was mixed evenly with anhydrous aluminum chloride, and then transferred to a calcination furnace and calcined at 350°C for 4 hours under a nitrogen atmosphere. After natural cooling, mixture A was obtained, in which the mass ratio of cathode material to anhydrous aluminum chloride was 0.2:1.

[0057] (2) Mixture A was added to anhydrous ethanol at a solid-liquid volume ratio of 1:2 and stirred and washed. The mixture was then filtered to remove unreacted salts. The washing and filtration were repeated 5 times. After vacuum drying at 100℃ for 6 hours, the dot-coated positive electrode material B was obtained.

[0058] (3) A 10 mg / L aqueous solution of graphene oxide, ethylenediamine, and polyethylene glycol dimethacrylate were added to anhydrous ethanol and sonicated to obtain suspension C. In suspension C, the concentration of graphene oxide was 4 g / L, and the mass ratio of ethylenediamine, graphene oxide, and polyethylene glycol dimethacrylate was 2:1:0.01.

[0059] (4) The above-mentioned coated positive electrode material B and the suspension solution C were mixed according to the solid content of positive electrode material 1800g / L. After stirring evenly, a mixed slurry D was obtained. The mixed slurry D was transferred to a microwave reactor and hydrothermally reacted at 150℃ for 10h. After cooling, gel E was obtained. The microwave heating power was 2000W.

[0060] (5) Gel E was freeze-dried at -20℃ for 12h to obtain dry gel F;

[0061] (6) The dry gel F was added to anhydrous ethanol at a solid-liquid volume ratio of 1:3 for washing and filtration to remove residual reactants. The washing and filtration were performed 3 times. The dry gel G was obtained by vacuum drying at 120℃ for 6 hours.

[0062] (7) The dry gel G is calcined at 350°C for 8 hours under nitrogen atmosphere, crushed by roller pressing, and air-classified to remove particles and fine powders that do not contain positive electrode material, thus obtaining the double-coated positive electrode material.

[0063] Example 3

[0064] (1) Quantitative LiNi 0.85 Co 0.1 Mn 0.05 The O2 cathode material was mixed evenly with anhydrous zirconium chloride, and then transferred to a calcination furnace and calcined at 450°C for 4 hours under a nitrogen atmosphere. After natural cooling, mixture A was obtained, in which the mass ratio of cathode material to anhydrous zirconium chloride was 0.2:1.

[0065] (2) Mixture A was added to anhydrous ethanol at a solid-liquid volume ratio of 1:2 and stirred and washed. The mixture was then filtered to remove unreacted salts. The washing and filtration were repeated 4 times. After vacuum drying at 100℃ for 6 hours, the dot-coated positive electrode material B was obtained.

[0066] (3) A 10 mg / L aqueous solution of graphene oxide, triethanolamine, and polyethylene glycol diacrylate were added to anhydrous ethanol and sonicated to obtain suspension C. In suspension C, the concentration of graphene oxide was 3 g / L, and the mass ratio of triethanolamine, graphene oxide, and polyethylene glycol diacrylate was 2:1:0.01.

[0067] (4) The above-mentioned coated positive electrode material B and the suspension solution C were mixed according to the solid content of positive electrode material 1600g / L. After stirring evenly, a mixed slurry D was obtained. The mixed slurry D was transferred to a microwave reactor and hydrothermally reacted at 150℃ for 10h. After cooling, gel E was obtained. The microwave heating power was 1600W.

[0068] (5) Gel E was freeze-dried at -20℃ for 12h to obtain dry gel F;

[0069] (6) The dry gel F was added to anhydrous ethanol at a solid-liquid volume ratio of 1:3 for washing and filtration to remove residual reactants. The washing and filtration were performed 3 times. The dry gel G was obtained by vacuum drying at 120℃ for 6 hours.

[0070] (7) The dry gel G is calcined at 300°C for 6 hours under nitrogen atmosphere, crushed by roller pressing, and air-classified to remove particles and fine powder that do not contain positive electrode material, thus obtaining the double-coated positive electrode material.

[0071] Example 4

[0072] (1) Quantitative LiNi 0.85 Co 0.1 Mn 0.05 The O2 cathode material was mixed evenly with boric acid, and then transferred to a calcination furnace and calcined at 400°C for 4 hours under a nitrogen atmosphere. After natural cooling, mixture A was obtained, in which the mass ratio of cathode material to boric acid was 0.2:1.

[0073] (2) Mixture A was added to anhydrous ethanol at a solid-liquid volume ratio of 1:2 and stirred and washed. The mixture was then filtered to remove unreacted salts. The washing and filtration were repeated 4 times. After vacuum drying at 100℃ for 6 hours, the dot-coated positive electrode material B was obtained.

[0074] (3) Add a 10 mg / L aqueous solution of graphene oxide, ethylenediamine, and sodium borate to anhydrous ethanol and sonicate to obtain a suspension C; in the suspension C, the concentration of graphene oxide is 3 g / L, and the mass ratio of ethylenediamine, graphene oxide and sodium borate is 2:1:0.01.

[0075] (4) The above-mentioned coated positive electrode material B and the suspension solution C were mixed according to the solid content of the positive electrode material of 1600g / L. After stirring evenly, the mixed slurry D was obtained. The mixed slurry D was transferred to a microwave reactor and hydrothermally reacted at 140℃ for 10h. After cooling, gel E was obtained. The microwave heating power was 1600W.

[0076] (5) Gel E was freeze-dried at -20℃ for 12h to obtain dry gel F;

[0077] (6) The dry gel F was added to anhydrous ethanol at a solid-liquid volume ratio of 1:3 for washing and filtration to remove residual reactants. The washing and filtration were performed 3 times. The dry gel G was obtained by vacuum drying at 120℃ for 6 hours.

[0078] (7) The dry gel G is calcined at 300°C for 6 hours under a nitrogen atmosphere, crushed by roller pressing, and air-classified to remove particles and fine powders that do not contain cathode material, thus obtaining the double-coated cathode material.

[0079] Example 5

[0080] The preparation method of the double-coated positive electrode material in this embodiment is the same as that in Example 4, except that the boric acid in step (1) of Example 4 is replaced with anhydrous aluminum chloride. The dry gel obtained in step (5) of this embodiment is shown in the image below. Figure 1 .

[0081] Comparative Example 1

[0082] Using uncoated modified LiNi 0.85 Co 0.1 Mn 0.05 O2 was directly used for electrical performance testing and pH value testing.

[0083] Comparative Example 2

[0084] The difference compared to Example 5 is as follows:

[0085] Without steps (1) and (2) of the low-melting-point Lewis acid salt treatment of the cathode material, uncoated LiNi is directly used in step (4). 0.85 Co 0.1 Mn 0.05 O2 is used to replace the coating cathode material B and is mixed with suspension solution C to synthesize the coating cathode material;

[0086] Comparative Example 3

[0087] The difference compared to Example 5 is as follows:

[0088] No crosslinking agent is added in step (3) (i.e., no sodium borate is added);

[0089] Step (5) The drying process is changed to drying gel E at 80℃ for 12 hours to obtain dry gel F. Conventional drying replaces freeze drying.

[0090] Comparative Example 4

[0091] The difference compared to Example 5 is as follows:

[0092] Without steps (3)(4)(5)(6), the elastic graphene coating process was carried out directly using the dot-coated positive electrode material B in the experiment;

[0093] The specific steps are as follows:

[0094] (1) Quantitative LiNi 0.85 Co 0.1 Mn 0.05 The O2 cathode material was mixed evenly with aluminum chloride water, and then transferred to a calcination furnace and calcined at 400°C for 4 hours under a nitrogen atmosphere. After natural cooling, mixture A was obtained, in which the mass ratio of cathode material to boric acid was 0.2:1.

[0095] (2) Mixture A was added to anhydrous ethanol at a solid-liquid volume ratio of 1:2 and stirred and washed. The mixture was then filtered to remove unreacted salts. The washing and filtration were repeated 4 times. After vacuum drying at 100℃ for 6 hours, the dot-coated positive electrode material B was obtained.

[0096] Example 6: Electrochemical Performance Characterization

[0097] The positive electrode materials prepared in Examples 1-5 and Comparative Examples 1-4 were used to fabricate button batteries. The positive electrode material, conductive carbon black, and polyvinylidene fluoride were ground and mixed evenly at a mass ratio of 90:5:5. An appropriate amount of N-methylpyrrolidone was added and stirred to adjust the viscosity. The slurry was then evenly coated onto aluminum foil and dried at 80°C for 12 hours. After the electrode sheets were rolled and pressed, they were assembled into 2016-type button batteries in a glove box. The electrolyte was a 1M LiPF6 solution, in which the solvent was a mixture of EC, DEC, and DMC (volume ratio 1:1:1). The negative electrode was a lithium sheet, and the separator was a polypropylene microporous membrane.

[0098] The test voltage range was 2.8–4.35V. The voltage was obtained under 1C charge and 1C discharge conditions. The results are shown in Table 1.

[0099] Table 1. Electrical performance data and pH values ​​of each sample

[0100]

[0101] The pH values ​​of the materials in Table 1 were obtained by testing the pH of the filtrate in section 5.5.2 of GB / T41704-2022.

[0102] As can be seen from the data in Table 1, double coating has almost no effect on the initial discharge capacity of the cathode material, but the rate performance of the material is significantly improved after double coating. This indicates that the coating significantly improves the electronic and lithium-ion transport performance of the material. This is mainly because the melting treatment of low-melting-point Lewis acid salts consumes the residual alkali on the material surface and also generates fast ion conductors such as lithium aluminate, lithium borate, or lithium zirconate on the material surface. At the same time, the coated graphene aerogel has excellent ionic and electronic conductivity. These factors lead to a significant improvement in the rate performance of the cathode material. Correspondingly, due to the consumption of residual alkali on the surface, the pH value of the material also decreases significantly.

[0103] Based on the data from Comparative Examples 2-4 and Example 5, it can be seen that the elastic graphene aerogel coating is the main reason for the significant improvement in the material's cycle performance. The cathode material undergoes volume changes during cycling, and the elastic aerogel coating avoids the problem of coating failure caused by the coating layer breaking and falling off during the charging and discharging process.

Claims

1. A method for preparing a double-coated lithium battery cathode material, comprising the following steps: (1) Mix lithium battery cathode material with low melting point Lewis acid salt and then calcine to obtain dot-coated cathode material; The lithium battery cathode material is LiNi x Co y Mn 1-x-y O2, wherein 0.5≤x<1, 0<y≤0.2, and x+y<1; The low-melting-point Lewis acid salt is at least one of anhydrous aluminum chloride, boric acid, and anhydrous zirconium chloride. The mass ratio of the lithium battery cathode material to the low-melting-point Lewis acid salt is 0.15~0.2:1; The roasting temperature is 300~450℃, and the time is 2~4h; The calcination is carried out in an inert atmosphere; (2) Mix graphene oxide, reducing agent, crosslinking agent and ethanol to obtain a suspension solution; The reducing agent is at least one of diisopropylamine, ethylenediamine, and triethanolamine; The crosslinking agent is at least one of sodium borate, polyethylene glycol dimethacrylate, and polyethylene glycol diacrylate; (3) The positive electrode material and the suspension solution are mixed, and then a hydrothermal reaction is carried out. After cooling, a gel is obtained. The temperature of the hydrothermal reaction is 120~150℃; (4) Freeze-dry the gel to obtain a dry gel; (5) The dry gel is calcined under an inert atmosphere to obtain the double-coated lithium battery cathode material; The roasting temperature is 200~350℃.

2. The method for preparing the double-coated lithium battery cathode material according to claim 1, characterized in that: In step (2), the graphene oxide is added in the form of an aqueous dispersion of graphene oxide; In the suspension, the concentration of graphene oxide is 2-4 g / L; the mass ratio of the reducing agent, graphene oxide and crosslinking agent is 1.5-2:1:0.005-0.

01.

3. The method for preparing the double-coated lithium battery cathode material according to claim 1, characterized in that: In step (3), the solid content of the dot-coated positive electrode material in the mixed solution of the dot-coated positive electrode material and the suspension solution is 1300~1800g / L; The hydrothermal reaction takes 6 to 10 hours.

4. The method for preparing the double-coated lithium battery cathode material according to claim 3, characterized in that: The hydrothermal reaction is carried out in a microwave heating device; the microwave heating power is 1600~2000W.

5. The method for preparing the double-coated lithium battery cathode material according to claim 1, characterized in that: In step (4), the freeze-drying temperature is -20 to -10°C; the freeze-drying time is 10 to 12 hours.

6. The method for preparing the double-coated lithium battery cathode material according to claim 1, characterized in that: In step (5), the roasting time is 6-8 hours.

7. The method for preparing the double-coated lithium battery cathode material according to claim 1, characterized in that: Step (1) also includes washing and drying the dot-coated cathode material; Step (4) also includes washing and drying the dry gel.

8. The double-coated lithium battery cathode material prepared by the preparation method according to any one of claims 1-7.

9. The application of the double-coated lithium battery cathode material according to claim 8 in the preparation of lithium battery cathodes.

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