Positive electrode lithium supplementing slurry and preparation method thereof, positive plate and lithium ion battery

Abstract

The invention provides positive electrode lithium supplementing slurry and a preparation method thereof, a positive plate and a lithium ion battery, and relates to the technical field of lithium ion batteries. According to the positive electrode lithium supplementing slurry, on the basis of existing positive electrode homogenate, acidic additives such as organic weak acids with mild acidity, such as benzenetricarboxylic acid, phthalic acid and benzoic acid are introduced to neutralize alkaline substances in a lithium supplementing material, so that dehydrogenation and fluorine reactions of PVDF are inhibited; furthermore, hydroquinone is added into the positive electrode lithium supplementing slurry as a free radical quenching agent and is used for eliminating free radicals at-CH = CF-fractures, so that recombination reaction is prevented, and cross-linked conjugated polyene is prevented from being formed; by utilizing the synergistic effect of the organic weak acid and the free radical quenching agent, the dispersity and stability of the slurry are improved, the processing quality of the positive pole piece is improved, the electrochemical performance of the lithium ion battery is improved, and meanwhile, the service life of equipment is not influenced.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a positive electrode lithium supplement slurry and a preparation method thereof, a positive electrode sheet and a lithium ion battery. Background Art

[0002] Lithium-ion batteries are widely used in 3C digital products, power batteries and energy storage systems. With the development of science and technology, the market has higher and higher requirements for lithium-ion batteries. For example, new energy vehicles require long driving range and energy storage systems require long cycle life. Lithium replenishment technology improves energy density and cycle life by replenishing the loss of active lithium caused by the formation of solid electrolyte membrane in the first cycle of lithium-ion batteries, and is widely used.

[0003] However, residual alkali (such as lithium hydroxide LiOH) on the surface of the positive electrode lithium supplement material will cause the commonly used positive electrode slurry binder polyvinylidene fluoride (PVDF) to undergo a dehydrogenation fluorination reaction under the catalytic action of lithium hydroxide. The double bonds formed will cause cross-linking reactions between PVDF molecular chains, resulting in slurry gelation. This seriously affects the dispersibility of the binder and the conductive agent, the stability of the slurry, and the uniformity of the coating surface density. In the prior art, the slurry gelation problem can be effectively solved by coating the lithium supplement agent on the surface and coating the positive electrode slurry and the lithium supplement slurry in steps, but the process is relatively cumbersome and increases the production cost. The slurry gelation can be improved by adding oxalic acid with a strong acidity during the homogenization process, but oxalic acid is easy to corrode the homogenization equipment, affecting the service life of the equipment.

[0004] CN114079086A uses a wet coating method to form an aluminum oxide protective layer on the surface of the lithium-rich material, which effectively prevents the internal residual lithium from contacting with the outside air to generate residual alkali, and can prevent the residual alkali from dissolving, thereby reducing the residual alkali value of the positive electrode additive. The positive electrode lithium supplement additive can effectively reduce the viscosity of the positive electrode slurry, make the slurry coating more uniform, improve the processing quality of the positive electrode sheet, and effectively improve the electrochemical performance of the lithium ion battery. However, this method increases the processing steps, and the wet coating method also has the problem of waste liquid treatment.

[0005] CN110137433A provides a method of first coating the positive electrode slurry on the surface of the positive electrode sheet, and then immediately spraying the positive electrode lithium supplement additive on the surface of the positive electrode sheet under the condition of environmental humidity ≤ 1%, drying the positive electrode sheet, and completing the lithium supplement operation. This method can effectively prevent the residual alkali on the surface of the lithium supplement additive from causing the PVDF to undergo a dehydrogenation and fluorination reaction during the homogenization process, causing the slurry to gel. However, the spraying environmental humidity requirement is higher than the normal production environment, and the dehumidification capacity needs to be enhanced, which increases the production cost.

[0006] CN118017048A adds lithium ferrite and oxalic acid during the synthesis of lithium iron phosphate slurry, so that the lithium ferrite positive electrode lithium supplement meets the existing positive electrode slurry process standards and has a good coating effect; assembled into a lithium-ion half-cell, the lithium supplemented battery pack has a 2.6% increase in gram capacity in the first week of charging, and has good cycle stability. However, oxalic acid is a medium-strong acid that easily corrodes the slurry equipment, affecting the service life of the equipment. Summary of the invention

[0007] The purpose of the present invention is to provide a positive electrode lithium supplement slurry and a preparation method thereof, a positive electrode sheet and a lithium ion battery. Based on the original positive electrode homogenate, the present invention does not add other processes, and introduces mildly acidic organic weak acids such as trimesic acid, phthalic acid, benzoic acid and other acidic additives without affecting the service life of the equipment, and at the same time neutralizes the alkaline substances in the lithium supplement material, thereby inhibiting the dehydrofluorination reaction of PVDF and inhibiting the formation of -CH=CF- double bonds; and hydroquinone is added as a free radical quencher to eliminate free radicals at the -CH=CF- fracture, prevent the occurrence of recombination reactions, and prevent the formation of cross-linked conjugated polyolefins.

[0008] On the other hand, by utilizing the synergistic effect of organic weak acid and free radical quencher, the dispersion and stability of the slurry are improved, the processing quality of the positive electrode sheet is improved, and the electrochemical performance of the lithium-ion battery is improved. At the same time, this method has the characteristics of simple operation, safety, low cost, and good compatibility with existing manufacturing processes.

[0009] In a first aspect, the present application provides a positive electrode lithium supplement slurry:

[0010] A positive electrode lithium replenishing slurry, comprising a positive electrode active main material, a binder, a conductive agent, a positive electrode lithium replenishing agent, an acidic additive and a free radical quencher in a mass ratio of (93.65-99): (0.5-3.0): (0.5-3.0): (0.01-8.0): (0.1-1.0): 0.05;

[0011] The acidic additive includes one or a combination of at least two of trimesic acid, trimesic acid, trimellitic acid, phthalic acid, isophthalic acid, terephthalic acid, and benzoic acid;

[0012] The free radical quencher includes one of phenol, catechol, hydroquinone, resorcinol, and phloroglucinol, or a combination of at least two of them.

[0013] Furthermore, the mass ratio of the positive electrode active main material, the binder, the conductive agent, the positive electrode lithium supplement agent, the acidic additive and the free radical quencher is (93.65-97):1.2:1.8:3.0:(0.15-0.3):0.05.

[0014] Further, the positive electrode lithium supplement slurry includes an organic solvent, and the organic solvent includes one or a combination of at least two of N-methylpyrrolidone, ethylene carbonate, fluoroethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, methyl formate, ethyl formate, methyl acetate, ethyl acetate, ethyl propionate, propyl propionate, ethyl butyrate, propyl butyrate, ethylene glycol dimethyl ether, 1,3-dioxolane, 1,3-dioxane, dimethyl sulfoxide and polyethylene glycol;

[0015] The positive electrode lithium supplement slurry has a solid content of 58-78wt% and a viscosity of 2000-9000 mPa·s.

[0016] Furthermore, the positive electrode lithium supplement slurry has a solid content of 65-75wt% and a viscosity of 3500-7000 mPa·s.

[0017] Further, the positive electrode lithium supplement includes one or a combination of at least two of Li2O, Li2O2, Li3N, LiF, Li2SiO3, Li2SiO4, Li2S, Li2CuO2, Li2S2O3, Li2S2O4, Li2C2O4, Li5FeO4, Li2NiO2, and Li5±xMyO4;

[0018] Wherein 0≤x≤5, y>0, and M represents one or at least two of Ni, Co, Mn, Fe, Zn, Al, Pt, Te, V, Ti, Mo, Sb, Si, Sn, and Ge.

[0019] Further, the positive electrode binder includes polyvinylidene fluoride; the acidic additive includes one or a combination of at least two of trimesic acid, trimesic acid, trimellitic acid, phthalic acid, isophthalic acid, terephthalic acid, and benzoic acid;

[0020] The conductive agent comprises one or a combination of at least two of conductive carbon black, carbon nanotubes, acetylene black and Ketjen black;

[0021] The positive electrode active material includes one or a combination of at least two of ternary lithium nickel cobalt manganese oxide, ternary lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium manganese iron phosphate, and lithium cobalt oxide.

[0022] In a second aspect, the present application provides a method for preparing a positive electrode lithium supplement slurry:

[0023] A method for preparing a positive electrode lithium supplement slurry comprises the following preparation steps:

[0024] S1, mixing the positive electrode binder, the acidic additive and the solvent evenly to obtain a positive electrode glue solution;

[0025] S2, uniformly dispersing the conductive agent and the free radical quencher in the positive electrode glue to obtain a conductive glue;

[0026] S3, adding the positive electrode active material to the conductive glue, stirring evenly, to obtain a positive electrode slurry;

[0027] S4, adding the lithium supplement additive to the positive electrode slurry, stirring evenly, and adjusting to a suitable viscosity and solid content to obtain a positive electrode lithium supplement slurry;

[0028] The mass ratio of the positive electrode active main material, the binder, the conductive agent, the positive electrode lithium supplement, the acidic additive and the free radical quencher is (93.65-99): (0.5-3.0): (0.5-3.0): (0.01-8.0): (0.1-1.0): 0.05;

[0029] The acidic additive includes one or a combination of at least two of trimesic acid, trimesic acid, trimellitic acid, phthalic acid, isophthalic acid, terephthalic acid, and benzoic acid;

[0030] The free radical quencher includes one of phenol, catechol, hydroquinone, resorcinol, and phloroglucinol, or a combination of at least two of them.

[0031] The solid content of the positive electrode glue is 5.0-10.0wt%.

[0032] In a third aspect, the present application provides a positive electrode sheet:

[0033] A positive electrode sheet comprises a positive electrode current collector and a positive electrode active layer; the raw material for preparing the positive electrode active layer comprises the positive electrode lithium supplement slurry of the present application.

[0034] In a fourth aspect, the present application provides a lithium-ion battery:

[0035] A lithium-ion battery adopts the positive electrode sheet of the present application.

[0036] Beneficial effects:

[0037] 1. The positive electrode lithium supplement slurry of the present invention introduces mildly acidic organic weak acids such as trimesic acid, phthalic acid, benzoic acid and other acidic additives on the basis of the existing positive electrode homogenate to neutralize the alkaline substances in the lithium supplement material, thereby inhibiting the dehydrofluorination reaction of PVDF and the formation of -CH=CF- double bonds, improving the fluidity and dispersibility of the slurry, reducing the viscosity of the slurry, and increasing the first cycle charging gram capacity of the lithium ion battery without affecting the service life of the equipment.

[0038] 2. Furthermore, hydroquinone is added to the positive electrode lithium replenishment slurry as a free radical quencher to eliminate free radicals at the -CH=CF- fracture, prevent the occurrence of recombination reactions, and prevent the formation of cross-linked conjugated polyenes; by utilizing the synergistic effect of organic weak acids and free radical quenchers, the dispersibility and stability of the slurry are improved, the processing quality of the positive electrode sheet is improved, and the electrochemical performance of lithium-ion batteries is enhanced.

[0039] 3. The preparation of the positive electrode lithium supplement slurry, positive electrode sheet and lithium-ion battery of the present application is simple, safe, low-cost and has good compatibility with existing manufacturing processes. DETAILED DESCRIPTION

[0040] In order to make the technical solution of the present invention clearer, the present invention is further described in detail below in conjunction with specific embodiments.

[0041] Embodiment 1, a lithium ion battery:

[0042] The mass ratio of positive electrode active main material: binder: conductive agent: positive electrode lithium supplement agent: acidic additive: free radical quencher = 93.8:1.2:1.8:3.0:0.15:0.05.

[0043] The specific steps include:

[0044] Step 1: Preparation of positive electrode lithium supplement slurry

[0045] 60g of binder, 7.5g of trimesic acid acid additive and 940g of nitrogen methyl pyrrolidone (NMP) were mixed, the speed was set to 1500 rpm / min, and the mixture was stirred and dispersed for 6 hours to obtain a glue solution; 90g of conductive agent carbon black and 2.5g of hydroquinone free radical quencher were added to the glue solution, the speed was set to 3000 rpm / min, and the mixture was stirred and dispersed for 1 hour to obtain a conductive glue; 2390g of nickel-cobalt-manganese ternary 9 series positive electrode material was added to the conductive glue, the speed was 3000rpm / min, and the mixture was stirred for 1 hour; the remaining 2300g of nickel-cobalt-manganese ternary 9 series positive electrode material, 150g of positive electrode lithium supplement additive Li5FeO4 and 909.3g of NMP were added, the speed was set to 3000rpm / min, and the mixture was stirred and dispersed in a vacuum for 3 hours to obtain a positive electrode lithium supplement slurry.

[0046] Step 2: Preparation of positive electrode

[0047] The positive electrode lithium supplement slurry is coated on the surface of 12µm aluminum foil with a surface density of 218g / m 2 , then dried and cold pressed to obtain the positive electrode sheet.

[0048] Step 3: Preparation of electrolyte

[0049] In an argon atmosphere glove box, fluoroethylene carbonate, ethylene carbonate, diethyl carbonate and ethyl methyl carbonate were uniformly mixed in a mass ratio of 10:20:30:40, and then lithium hexafluorophosphate was added to the mixed organic solvent at a concentration of 1 mol / L. Finally, 1% of vinylene carbonate additive based on the total mass of the electrolyte was added, and the electrolyte was obtained after stirring evenly.

[0050] Step 4: Preparation of the diaphragm

[0051] A wet process was used to use a polyethylene porous membrane coated with alumina ceramic on both sides as the diaphragm.

[0052] Step 5: Preparation of the battery

[0053] The lithium-supplemented positive electrode sheet was punched into a disc with a diameter of 12 mm; the lithium-supplemented positive electrode sheet, separator (thickness 16µm) and metal lithium sheet (thickness 0.8mm) were placed in order, the electrolyte injection volume was 150 μL, and a button battery was assembled.

[0054] Embodiment 2, a lithium ion battery:

[0055] The preparation process is the same as that of Example 1, except that the mass ratio of the positive electrode active main material: binder: conductive agent: positive electrode lithium replenisher: acidic additive: free radical quencher is 93.65:1.2:1.8:3.0:0.3:0.05.

[0056] Embodiment 3, a lithium ion battery:

[0057] The preparation process is the same as that of Example 1, except that the acidic additive in step 1 is phthalic acid.

[0058] Embodiment 4, a lithium ion battery:

[0059] The preparation process is the same as that of Example 1, except that: the mass ratio of the positive electrode active main material: binder: conductive agent: positive electrode lithium replenisher: acidic additive: free radical quencher is 93.65:1.2:1.8:3.0:0.3:0.05; the acidic additive in step 1 is phthalic acid.

[0060] Embodiment 5, a lithium ion battery:

[0061] The preparation process is the same as that of Example 1, except that the acidic additive in step 1 is benzoic acid.

[0062] Embodiment 6, a lithium ion battery:

[0063] The preparation process is the same as that of Example 1, except that: the mass ratio of the positive electrode active main material: binder: conductive agent: positive electrode lithium replenisher: acidic additive: free radical quencher is 93.65:1.2:1.8:3.0:0.3:0.05; the acidic additive in step 1 is benzoic acid.

[0064] Comparative Example 1, a lithium ion battery:

[0065] The preparation process is the same as that of Example 1, except that the mass ratio of the positive electrode active main material: binder: conductive agent: positive electrode lithium replenisher: acidic additive: free radical quencher is 97:1.2:1.8:0:0:0, that is, no positive electrode lithium replenisher, acidic additive and free radical extractant are added.

[0066] Comparative Example 2, a lithium ion battery:

[0067] The preparation process is the same as that of Example 1, except that the mass ratio of the positive electrode active main material: binder: conductive agent: positive electrode lithium replenisher: acidic additive: free radical quencher is 93.95:1.2:1.8:3:0:0.05, that is, no acidic additive is added to the lithium replenishing slurry.

[0068] Comparative Example 3, a lithium ion battery:

[0069] The preparation process is the same as that of Example 1, except that the mass ratio of the positive electrode active main material: binder: conductive agent: positive electrode lithium replenisher: acidic additive: free radical quencher is 93.85:1.2:1.8:3.0:0.15:0, that is, no free radical quencher is added to the lithium replenishing slurry.

[0070] The following describes the test process:

[0071] 1. Slurry viscosity test: The slurry viscosity was tested using an American Brookfield fully automatic rotational viscometer. The test results are shown in Table 1.

[0072] 2. The first cycle of gram capacity test of lithium-ion battery: At 25℃, the battery was cross-current charged to 4.4V at a rate of 0.1C, and then charged at a constant voltage of 4.4V with a cut-off current of 0.05C. The test results are shown in Table 1.

[0073] Table 1. Slurry viscosity and lithium-ion battery gram capacity test

[0074] serial number Discharge viscosity (mPa.s) 24h viscosity growth rate (%) First circle gram capacity (mAh / g) Example 1 5437 122.55 252.59 Example 2 5082 89.72 254.63 Example 3 5589 129.65 251.25 Example 4 5263 103.54 253.11 Example 5 5724 137.37 250.12 Example 6 5460 114.33 251.78 Comparative Example 1 5288 98.79 241.21 Comparative Example 2 6514 218.23 246.96 Comparative Example 3 5982 179.38 248.82

[0075] From the comparison of Examples 1 to 6 with Comparative Example 2 in Table 1, it can be concluded that the slurries of Examples 1 to 6 have better dispersibility, no obvious agglomeration, relatively stable viscosity changes, and lower viscosity growth rates; the viscosity rebound of Comparative Example 2 is larger, the slurry fluidity is lower after 24 hours, agglomeration occurs, and there is a tendency to gel. At the same time, the first charge gram capacity of Examples 1 to 6 is greater than 250 mAh / g, which is higher than the first cycle gram capacity of the Comparative Example. Comparison of Example 1 with Comparative Example 3 shows that the viscosity and dispersibility of the slurry are effectively improved by adding a free radical quencher. Compared with Comparative Examples 2 and 3, the positive electrode lithium supplement slurry of the embodiment has better dispersibility, indicating that the synergistic effect of the acidic additive and the free radical quencher can effectively inhibit the slurry gel, and the lithium-ion battery of the embodiment has a higher first cycle charge gram capacity.

[0076] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A positive electrode lithium supplement slurry, characterized in that: Including positive electrode active main material, binder, conductive agent, positive electrode lithium supplement agent, acid additive and free radical quencher in a mass ratio of (93.65~99):(0.5~3.0):(0.5~3.0):(0.01~8.0):(0.1~1.0):0.05; The acidic additive includes one or a combination of at least two of trimesic acid, trimesic acid, trimellitic acid, phthalic acid, isophthalic acid, terephthalic acid, and benzoic acid; The free radical quencher includes one of phenol, catechol, hydroquinone, resorcinol, and phloroglucinol, or a combination of at least two of them.

2. The positive electrode lithium supplement slurry according to claim 1, characterized in that: The mass ratio of the positive electrode active main material, the binder, the conductive agent, the positive electrode lithium supplement agent, the acidic additive and the free radical quencher is (93.65-97):1.2:1.8:3.0:(0.15-0.3):0.

05.

3. The positive electrode lithium supplement slurry according to claim 1, characterized in that: The positive electrode lithium supplement slurry includes an organic solvent, and the organic solvent includes one or a combination of at least two of N-methylpyrrolidone, ethylene carbonate, fluoroethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, methyl formate, ethyl formate, methyl acetate, ethyl acetate, ethyl propionate, propyl propionate, ethyl butyrate, propyl butyrate, ethylene glycol dimethyl ether, 1,3-dioxolane, 1,3-dioxane, dimethyl sulfoxide and polyethylene glycol; The positive electrode lithium supplement slurry has a solid content of 58-78 wt % and a viscosity of 2000-9000 mPa·s.

4. The positive electrode lithium supplement slurry according to claim 1, characterized in that: The positive electrode lithium supplement slurry has a solid content of 65-75wt% and a viscosity of 3500-7000 mPa·s.

5. The positive electrode lithium supplement slurry according to claim 1, characterized in that: The positive electrode lithium supplement includes one or a combination of at least two of Li2O, Li2O2, Li3N, LiF, Li2SiO3, Li2SiO4, Li2S, Li2CuO2, Li2S2O3, Li2S2O4, Li2C2O4, Li5FeO4, Li2NiO2, and Li5±xMyO4; Wherein 0≤x≤5, y>0, and M represents one or at least two of Ni, Co, Mn, Fe, Zn, Al, Pt, Te, V, Ti, Mo, Sb, Si, Sn, and Ge.

6. The positive electrode lithium supplement slurry according to claim 1, characterized in that: The positive electrode binder includes polyvinylidene fluoride; the acidic additive includes one or a combination of at least two of trimesic acid, trimesic acid, trimellitic acid, phthalic acid, isophthalic acid, terephthalic acid, and benzoic acid; The conductive agent comprises one or a combination of at least two of conductive carbon black, carbon nanotubes, acetylene black and Ketjen black; The positive electrode active material includes one or a combination of at least two of ternary lithium nickel cobalt manganese oxide, ternary lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium manganese iron phosphate, and lithium cobalt oxide.

7. A method for preparing a positive electrode lithium supplement slurry according to any one of claims 1 to 6, characterized in that: The method comprises the following preparation steps: S1, mixing the positive electrode binder, the acidic additive and the solvent evenly to obtain a positive electrode glue solution; S2, uniformly dispersing the conductive agent and the free radical quencher in the positive electrode glue to obtain a conductive glue; S3, adding the positive electrode active material to the conductive glue, stirring evenly, to obtain a positive electrode slurry; S4, adding the lithium supplement additive to the positive electrode slurry, stirring evenly, and adjusting the viscosity and solid content to obtain a positive electrode lithium supplement slurry; The mass ratio of the positive electrode active main material, the binder, the conductive agent, the positive electrode lithium supplement, the acidic additive and the free radical quencher is (93.65-99): (0.5-3.0): (0.5-3.0): (0.01-8.0): (0.1-1.0): 0.05; The acidic additive includes one or a combination of at least two of trimesic acid, trimesic acid, trimellitic acid, phthalic acid, isophthalic acid, terephthalic acid, and benzoic acid; The free radical quencher includes one of phenol, catechol, hydroquinone, resorcinol, and phloroglucinol, or a combination of at least two of them.

8. The method for preparing a positive electrode lithium supplement slurry according to claim 7, characterized in that: The solid content of the positive electrode glue is 5.0-10.0wt%.

9. A positive electrode sheet, characterized in that: It comprises a positive electrode current collector and a positive electrode active layer; the raw material for preparing the positive electrode active layer comprises a positive electrode lithium replenishing slurry as described in any one of claims 1 to 6.

10. A lithium ion battery, characterized in that: The positive electrode sheet as claimed in claim 9 is used.