An aqueous positive electrode slurry and a method for preparing the same

Abstract

The application discloses a kind of aqueous positive electrode slurry, the raw material of the positive electrode slurry includes fluorophosphate, maleic anhydride grafting styrene polymer, conductive agent, binder, auxiliary solvent, pH regulator, and the ratio of fluorophosphate: maleic anhydride grafting styrene polymer: conductive agent: binder: auxiliary solvent: pH regulator is (2 parts-10 parts):(1 part-5 parts):(1 part-15 parts):(1 part-10 parts):(2 parts-10 parts):(0.1 part-1 part) by mass.The aqueous battery positive electrode slurry of the application, solvent selects pure water;Low environmental requirements, easy to prepare, low cost and will not produce pollution;Easy to mass production.Through aqueous dispersant maleic anhydride grafting styrene polymer, increase the dispersibility of preparation slurry, solve the problem of uneven coating caused by powder agglomeration, and then improve its cycle performance and rate charge performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of battery cathode, in particular to a kind of water-based cathode slurry and preparation method thereof. BACKGROUND

[0002] In the aspect of lithium battery, it is well known that the cathode of battery guarantees the energy density of battery, and the slurry of battery cathode also directly affects the electrical performance of battery.In the prior art, water-based slurry is used in production because of its green environmental protection and low price, but using water-based slurry often has some technical problems, first, the dispersibility of substances in water-based slurry is poor; second, the adhesion of slurry is weak, and powder falling is prone to occur during slurry coating; third, the wettability between water-based slurry and current collector is poor, thereby causing the wettability of cathode to be poor and the electrical performance of battery to be reduced.

[0003] Fluorinated phosphate is a potential high-energy-density cathode material, and the preparation process is relatively mature at present.However, the water-based slurry of fluorinated phosphate prepared in the prior art is prone to delamination after being placed for a period of time, and in the preparation of cathode slurry of fluorinated phosphate, the fluorinated phosphate nanometer powder is prone to serious agglomeration and difficult to disperse due to its large viscosity, which finally leads to uneven coating. SUMMARY

[0004] In the structure of styrene-maleic anhydride copolymer, a stable transition state is formed by the positive and negative levels of two monomers attracting each other.Styrene-maleic anhydride copolymer is often used as a dispersant, but it is rarely used in battery cathode or anode slurry, first, because its typical alternating copolymerization structure is not conducive to its ion conduction ability, which will affect the electrical performance in cathode / anode to some extent, second, the connection mode of styrene-maleic anhydride copolymer by two monomers attracting each other will affect the stability of its connection structure in cathode or anode to some extent, thereby being not conducive to its dispersion effect.

[0005] The present application discloses a water-based cathode slurry and a preparation method thereof to solve the problems in the prior art.In the water-based slurry of the present application, fluorinated phosphate is used as a cathode active material, and then cooperates with other substances in the slurry, thereby overcoming the technical problems such as delamination and agglomeration of fluorinated phosphate, and obtaining a water-based cathode slurry with good wettability, good adhesion and beneficial to the electrical performance of battery.

[0006] The present application is realized by the following technical solutions:

[0007] The application provides a water-based positive electrode slurry, and raw materials of the positive electrode slurry include fluorophosphate, maleic anhydride grafted styrene polymer, conductive agent, binder, auxiliary solvent and pH regulator, and the mass ratio of the fluorophosphate, the maleic anhydride grafted styrene polymer, the conductive agent, the binder, the auxiliary solvent and the pH regulator is (2-10) :(1-5) :(1-15) :(1-10) :(2-10) :(0.1-1).

[0008] According to the above design of the application, the fluorine substituent in the fluorophosphate can change the energy level of the phosphate monomer and improve the stability of the phosphate on the one hand, and the fluorine substituent is an electron-withdrawing group, which can cooperate with the strong electron-donating group styrene in the maleic anhydride grafted styrene polymer, the maleic anhydride grafted styrene polymer provides a steric hindrance effect, promotes the dispersibility of the fluorophosphate to be improved, and the maleic anhydride grafted styrene polymer adsorbed on the surface of the fluorophosphate particles enhances the polarity of the fluorophosphate, reduces the interfacial energy between the fluorophosphate and water and makes the fluorophosphate disperse in water. The grafting mode of the maleic anhydride grafted styrene polymer improves the stability of the maleic anhydride grafted styrene polymer, thereby facilitating the stable dispersion of the maleic anhydride grafted styrene polymer. In order to further improve the dispersibility of each fluorophosphate in the slurry, the pH regulator is further added, which can adjust the pH of the slurry on the one hand, and promote the electron-donating ability of the electron-donating group of the maleic anhydride grafted styrene polymer on the other hand, break the transition state of the structure of the maleic anhydride grafted styrene polymer, improve the ion-conducting ability of the maleic anhydride grafted styrene polymer, assist the interaction between the maleic anhydride grafted styrene polymer and the fluorophosphate, promote the stable dispersion of the fluorophosphate in the slurry, improve the cooperation between the maleic anhydride grafted styrene polymer and the fluorophosphate, and thereby facilitate the ion transmission in the positive electrode. The cooperation between the auxiliary solvent and the pH regulator can reduce the overall polarity of the slurry, thereby promoting the dissolution and wettability of each substance in the slurry. The conductive agent is beneficial to the electron conduction of the positive electrode, thereby further improving the conductivity of the positive electrode, and the binder is beneficial to the increase of the bonding strength between each substance in the slurry.

[0009] As a further scheme, the fluorophosphate includes Li 1+x Al(PO4)O 1-y F 2y ; wherein 0≤x<1, 0<y<0.1. The doping of Al ions can form Al-O bonds with good orbital bonding ability, thereby facilitating the partial substitution of fluorine atoms for oxygen atoms to form fluorophosphates with more stable structures, and facilitating the cooperation between the fluorophosphate and the fluorine-substituted group and the maleic anhydride grafted styrene polymer.

[0010] As a further solution, the fluorophosphate includes Li 1+x Al(PO4)O 1-y F 2y ; wherein 0≤x<1, 0.06≤y<0.1. Better electrical performance is obtained while maintaining the structural stability of the fluorophosphate.

[0011] As a further solution, the conductive agent includes one or more of carbon black, acetylene black, carbon nanotube, carbon fiber.

[0012] As a further solution, the particle size of the conductive agent is 20-50 nm. It is conducive to the construction of ion transmission channels in the slurry, thereby facilitating the balance of electron transmission and ion transmission.

[0013] As a further solution, the particle size of the conductive agent is 25-35 nm. A more suitable ion transmission channel structure is formed.

[0014] As a further solution, the binder includes one or more of cellulose-based binder, rubber-based binder. The cellulose-based binder has more hydroxyl oxygen and carboxyl, on the one hand, it is conducive to more cooperation between the maleic anhydride grafted styrene polymer, on the other hand, the hydroxyl oxygen and carboxyl have electron-withdrawing ability, and the cellulose-based binder is more easily bonded to the conductive agent in the slurry.

[0015] As a further solution, the cellulose-based binder includes one or more of sodium carboxymethyl cellulose, carboxyethyl cellulose, ethyl cellulose, carboxymethyl ethyl cellulose, hydroxymethyl cellulose, hydroxypropyl cellulose.

[0016] As a further solution, the rubber-based binder includes styrene-butadiene rubber.

[0017] As a further solution, the auxiliary solvent includes one or more of alcohol, amine, acid ester. The alcohol substance can be dissolved in the aqueous solution on the one hand, and more easily cooperate with the pH adjustment to reduce the polarity of the aqueous slurry.

[0018] As a further solution, the alcohol includes one or more of ethanol, isopropyl alcohol.

[0019] As a further solution, the amine includes N,N-dimethylformamide.

[0020] As a further solution, the acid ester includes one or more of ethyl acetate, dibutyl phthalate.

[0021] As a further solution, the pH regulator includes one or more of organic acid and biological fermentation acid. The organic acid has fewer hydroxyl groups, which can reduce the ability of the pH regulator to weaken the pH regulator, and reduce the amount of the pH regulator in the slurry.

[0022] As a further embodiment, the organic acid includes one or more of acetic acid, citric acid, and tartaric acid.

[0023] As a further embodiment, the bio-fermentation acid includes gluconic acid.

[0024] As a further embodiment, the raw materials for the positive electrode slurry also include a solvent, which includes deionized water or pure water. The amount of solvent added can be adjusted by those skilled in the art according to actual conditions, as long as the viscosity of the obtained positive electrode slurry is within the range of 5000 mPa·s to 10000 mPa·s.

[0025] As a further embodiment, the raw materials of the positive electrode slurry include fluorophosphate, maleic anhydride-grafted styrene polymer, a 25nm-35nm conductive agent, a cellulose binder, alcohols, and organic acids. By mass, the ratio of fluorophosphate:maleic anhydride-grafted styrene polymer:25nm-35nm conductive agent:cellulose binder:alcohol:organic acid is (2-10 parts):(1-5 parts):(1-15 parts):(1-10 parts):(2-10 parts):(0.1-1 part). The fluorophosphate includes Li... 1+x Al(PO4)O 1-y F 2y Where 0 ≤ x < 1, 0.06 ≤ y < 0.1. Based on the above explanation, we further found that cellulose binders, alcohols, and organic acids have similar structures, making them easier to coordinate. The electron-withdrawing groups of carboxyl and hydroxyl groups in organic acids are beneficial for improving the electron-donating ability of the styrene electron-donating groups in maleic anhydride-grafted styrene polymers. Both organic acids and alcohols have hydroxyl groups, which can better coordinate and reduce the polarity of aqueous slurries. The phosphate group in fluorophosphates has a lone pair of electrons, which can be further adsorbed by maleic anhydride-grafted styrene polymers, thus facilitating the dispersion of fluorophosphates.

[0026] As a further embodiment, the raw materials of the positive electrode slurry include fluorophosphate, maleic anhydride-grafted styrene polymer, 25nm-35nm acetylene black, carboxyethyl cellulose, isopropanol, and tartaric acid. By mass, the ratio of fluorophosphate: maleic anhydride-grafted styrene polymer: 25nm-35nm acetylene black: carboxyethyl cellulose: isopropanol: tartaric acid acetic acid is (2-10 parts): (1-5 parts): (1-15 parts): (1-10 parts): (2-10 parts): (0.1-1 part). The fluorophosphate includes Li... 1+x Al(PO4)O 1-y F 2y; where 0 ≤ x < 1 and y = 0.08. On the above basis, we further found that the acetylene black crystallization and secondary structure are more developed, its conductivity and liquid absorption are better, and its wettability in the aqueous slurry is stronger. With the combination of isopropanol and tartaric acid, the polarity of the aqueous slurry is significantly reduced.

[0027] As a further scheme, the fluorophosphate Li 1+x Al(PO4)O 1-y F 2y ; where 0 ≤ x < 1 and 0 < y < 0.1. In the X-ray powder diffraction pattern expressed by the diffraction angle 2θ, there are characteristic diffraction peaks at 21.7°, 28.2°, 31.1°, 35.7°, 35.8°, 42.2°, 46.5°, 48.1°, and 53.4°.

[0028] The present invention also provides a preparation method of the positive electrode slurry. The preparation method includes: respectively weighing a fluorophosphate, a maleic anhydride grafted styrene polymer, a conductive agent, a binder, an auxiliary solvent, and a pH regulator according to a metering ratio, adding them into a solvent, and stirring evenly to obtain the positive electrode slurry.

[0029] As a further scheme, the viscosity of the positive electrode slurry is 5000 mPa·s - 10000 mPa·s. When the measured viscosity range of the positive electrode slurry is within 5000 mPa·s - 10000 mPa·s, those skilled in the art can stop adding the solvent according to the actual situation.

[0030] As a further scheme, the stirring time is 1 h - 3 h, and the stirring speed is 1500 rpm - 2500 rpm.

[0031] The present invention also provides a preparation method of the fluorophosphate Li 1+x Al(PO4)O 1-y F 2y ; where 0 ≤ x < 1 and 0 < y < 0.1. The method includes respectively weighing aluminum phosphate, a fluorine-containing material, and a lithium-containing material, and mixing them to obtain a mixed material; performing crystallization treatment on the mixed material.

[0032] As a further scheme, the temperature of the crystallization treatment is 550 °C - 650 °C, the crystallization time is 5 h - 40 h, and the heating rate is 2 °C / min - 15 °C / min. The gradual increase of the crystallization temperature not only helps to overcome the agglomeration phenomenon caused by the mixed material, but also helps to stabilize the crystal structure.

[0033] As a further scheme, the mixing method includes a dry mixing method or a wet mixing method.

[0034] As a further option, the dry mixing method is selected from one of the two options i-ii:

[0035] Option i: Perform high-speed mixing, with a mixing time of 2-10 minutes and a rotation speed of 1500 rpm-3500 rpm;

[0036] Option ii: Ball milling is performed at a speed of 500 rpm to 650 rpm for 1 to 10 hours.

[0037] As a further option, the wet mixing method is selected from one of the two options i-ii:

[0038] Solution i: Add solvent to the mixed materials, stir to obtain a slurry with a solid content of 30%, and then mix it by sand milling. The average output particle size of the sand mill is less than 0.3μm, and the rotation speed is 1500rpm-2000rpm.

[0039] Option ii: Ball milling is performed at a mass ratio of 6:1:1 for balls, mixed materials, and solvent, at a speed of 500-650 rpm, for a time of 1-10 hours. This method promotes uniform particle dispersion in the mixed materials and facilitates the alignment of particles into a triclinic crystal structure.

[0040] As a further option, the solvent includes either deionized water or alcohol.

[0041] As a further step, the mixed materials need to be dried after the wet mixing method.

[0042] As a further option, the drying method includes one of the following: oven drying, vacuum rake drying, and spray drying.

[0043] As a further improvement, the temperature of the blower oven drying and the vacuum rake drying is 140℃-210℃, and the drying time is 18-26h; the spray dryer drying has an outlet temperature of not higher than 300℃, an inlet temperature of not lower than 110℃, and a pressure of 0.4Mpa-0.5Mpa.

[0044] As a further embodiment, the fluorine-containing material includes one or more of lithium fluoride, ammonium fluoride, hydrogen fluoride, and aluminum fluoride, and the lithium-containing material includes lithium fluoride.

[0045] As a further option, the aluminum phosphate can be used to provide Al and P elements, the fluorine-containing material can be used to provide F element, and the lithium-containing material can be used to provide Li element. In some cases, a single raw material can also provide multiple required elements simultaneously. For example, when the fluorine-containing material also contains lithium, it can simultaneously provide F and Li elements. In this case, the fluorine-containing material can also be regarded as a lithium-containing material and used as such.

[0046] As a further step, the elements Al(PO4), Li, and F are measured, with a molar ratio of 1:(1-1.5):(1-2.5). The added mass of aluminum phosphate, lithium-containing materials, and fluorine-containing materials can be calculated and measured according to the above molar ratio of Al(PO4), Li, and F.

[0047] The present invention also provides the application of the positive electrode slurry in a positive electrode.

[0048] The features and beneficial effects of this invention are as follows:

[0049] (1) The aqueous battery positive electrode slurry of the present invention uses pure water as the solvent; it has low environmental requirements, is easy to prepare, has low cost and does not cause pollution; and is easy to mass-produce.

[0050] (2) By grafting styrene polymer with maleic anhydride as an aqueous dispersant, the dispersibility of the prepared slurry is increased, which solves the problem of uneven coating caused by powder agglomeration, thereby improving its cycle performance and rate charging performance.

[0051] (3) The positive electrode of the battery provided by the present invention has excellent wettability, uniform thickness and high peel strength. Attached Figure Description

[0052] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0053] Figure 1 These are layered diagrams of the fluorophosphates of Example 1 and Comparative Example 1 of the present invention, wherein... Figure 1 In example 'a', the example 'Example 1' is used. Figure 1 In the middle, b represents comparative example 1.

[0054] Figure 2 This is a layered diagram of the fluorophosphates of Example 1 and Comparative Example 1 of the present invention.

[0055] Figure 3 This is a picture taken during the coating process in Embodiment 1 of the present invention.

[0056] Figure 4 This is a picture during the coating of Comparative Example 1 of the present invention.

[0057] Figure 5 This is the X-ray diffraction (XRD) pattern of the fluorophosphate in Examples 1-4 of the present invention. Detailed implementation manners

[0058] To facilitate the understanding of an aqueous cathode slurry of the present invention, the cathode slurry of the present invention will be described more comprehensively below. Examples of the present invention are given, but the scope of the present invention is not limited thereby.

[0059] Example 1

[0060] This example provides an aqueous cathode slurry, including 2-10 parts of cathode active material, 1-15 parts of conductive agent, 1-10 parts of binder, 35-90 parts of main solvent, 2-10 parts of auxiliary solvent, 1-5 parts of aqueous dispersant, and 0.1-1 part of pH regulator; the cathode active material is a fluorophosphate cathode material with the chemical formula Li 1+x Al(PO4)O 1-y F 2y ; where 0≤x<1, 0<y<0.1; in this example, x takes the value of 0, y takes the value of 0.02, and the chemical formula of the cathode material is LiAl(PO4)O 0.98 F 0.04 , the binder is an aqueous binder, and the main solvent is deionized water; the aqueous dispersant is a maleic anhydride grafted styrene polymer dispersant.

[0061] In this example, the raw materials are weighed by mass parts, including: first taking 2 g of maleic anhydride grafted styrene polymer dispersant as the aqueous dispersant, and dissolving 4 g of auxiliary solvent ethanol in 76.5 g of deionized water. Then add 2 g of sodium carboxymethylcellulose (CMC) and 10 g of nano-conductive carbon black to the above mixture, where the average particle size of the carbon black is 20 nm; then add 5 g of cathode material with an average particle size of 100 nm, and disperse and stir for 2 h at a stirring speed of 2000 rpm; then add 0.5 g of pH regulator acetic acid and stir and disperse for another 1 h; obtain a cathode slurry with a pH value of about 7 (LiAl(PO4)O 0.98 F 0.04 :dispersant:ethanol:conductive carbon black:CMC:acetic acid:water = 5:2:4:10:2:0.5:76.5). The cathode material is an aqueous slurry prepared by sanding, and the solid content is 30%; the addition thereof requires adding the introduced deionized water to 76.5 g of deionized water.

[0062] The viscosity of the above-prepared positive electrode paste was tested by a viscometer to be 5000 mPa·s. The above-prepared mixed paste was coated on one side surface of the positive electrode current collector aluminum foil by means of doctor blade coating; the thickness of the coated paste was 5 μm, and it was placed in a vacuum drying oven for vacuum thermal curing. The curing temperature of the vacuum thermal curing was 80 °C and the time was 20 min.

[0063] Among them, the preparation process of the fluorophosphate:

[0064] Step 1: Weigh aluminum phosphate and lithium fluoride, and the molar ratio of aluminum phosphate to lithium fluoride is 1:1; weigh 4.2 Kg of aluminum phosphate and 896 g of lithium fluoride.

[0065] Step 2: Mix the weighed aluminum phosphate and lithium fluoride, and the mixing method is dry mixing; use a high-speed mixer for mixing treatment, and the rotational speed of the mixing blade is 2000 rmp - 3000 rmp; the mixing time is 2 min.

[0066] Step 3: Crystallize the mixture obtained in Step 2, the crystallization temperature is 550 °C, the crystallization time is 40 h; the heating rate is 2 °C / min.

[0067] The novel positive electrode material LiAl(PO4)OF is obtained through the above steps 0.98 F 0.04 , and the XRD diffraction pattern of this material is as Figure 4 shown, and the crystal structure conforms to the standard card PDF#80 - 1011; it can be seen from Figure 4 that the crystal structure obtained by this method is compared with the pure one.

[0068] Example 2

[0069] This example provides an aqueous positive electrode paste, including 2 - 10 parts of positive electrode active material, 1 - 15 parts of conductive agent, 1 - 10 parts of binder, 35 - 90 parts of main solvent, 2 - 10 parts of auxiliary solvent, 1 - 5 parts of aqueous dispersant, and 0.1 - 1 part of pH regulator; the positive electrode active material is a fluorophosphate-based positive electrode material with the chemical formula Li 1+x Al(PO4)OF 1-y F 2y ; where 0 ≤ x < 1 and 0 < y < 0.1; in this example, x takes the value of 0 and y takes the value of 0.04, and the chemical formula of the positive electrode material is LiAl(PO4)OF 0.96 F 0.08 , the binder is an aqueous binder, and the main solvent is deionized water; the aqueous dispersant is a maleic anhydride grafted styrene polymer dispersant.

[0070] In this embodiment, the raw materials are weighed by mass parts, including: first, 2 g of the aqueous dispersant maleic anhydride grafted styrene polymer dispersant and 4 g of the auxiliary solvent ethanol are dissolved in 76.5 g of deionized water. Then, 2 g of sodium carboxymethyl cellulose (CMC), 10 g of nano-conductive carbon black with an average particle size of 20 nm are added to the above mixture; then, 5 g of the positive electrode material with an average particle size of 100 nm is added, and it is dispersed and stirred for 2 h at a stirring speed of 2000 rpm; then, 0.5 g of the pH regulator acetic acid is added, and it is stirred and dispersed for 1 h; a positive electrode paste (LiAl(PO4)O 0.96 F 0.08 : dispersant: ethanol: conductive carbon black: CMC: acetic acid: water = 5:2:4:10:2:0.5:76.5) is obtained. The positive electrode material is an aqueous paste prepared by sanding, and the solid content is 30%; when adding it, the introduced deionized water needs to be added to 76.5 g of deionized water.

[0071] The viscosity of the above-prepared positive electrode paste is tested by a viscometer to be 5000 mPa·s. The above-prepared mixed paste is coated on one side surface of the positive electrode current collector aluminum foil by the way of blade coating; the thickness of the coated paste is 5 μm, and it is placed in a vacuum drying oven for vacuum thermal curing. The curing temperature of the vacuum thermal curing is 80 °C and the time is 20 min.

[0072] Example 3

[0073] This embodiment provides an aqueous positive electrode paste, which includes 2-10 parts of positive electrode active material, 1-15 parts of conductive agent, 1-10 parts of binder, 35-90 parts of main solvent, 2-10 parts of auxiliary solvent, 1-5 parts of aqueous dispersant, and 0.1-1 part of pH regulator; the positive electrode active material is a fluorophosphate-based positive electrode material with the chemical formula Li 1+x Al(PO4)O 1-y F 2y ; where 0 ≤ x < 1, 0 < y < 0.1; in this embodiment, x takes the value of 0 and y takes the value of 0.06, and the chemical formula of the positive electrode material is LiAl(PO4)O 0.94 F 0.12 , the binder is an aqueous binder, and the main solvent is deionized water; the aqueous dispersant is maleic anhydride grafted styrene polymer dispersant.

[0074] In this embodiment, the raw materials are weighed by mass fraction, including: first, 2 g of the aqueous dispersant maleic anhydride grafted styrene polymer dispersant, and 4 g of the auxiliary solvent ethanol are dissolved in 76.5 g of deionized water. Then, 2 g of sodium carboxymethyl cellulose (CMC) and 10 g of nano-conductive carbon black with an average particle size of 20 nm are added to the above mixture. Then, 5 g of the cathode material with an average particle size of 100 nm is added, and the mixture is dispersed and stirred for 2 h at a stirring speed of 2000 rpm. Then, 0.5 g of the pH regulator acetic acid is added, and the mixture is stirred and dispersed for another 1 h. A cathode slurry (LiAl(PO4)O 0.94 F 0.12 : dispersant: ethanol: conductive carbon black: CMC: acetic acid: water = 5:2:4:10:2:0.5:76.5) is obtained. The cathode material is an aqueous slurry prepared by sanding, and the solid content is 30%. When adding it, the introduced deionized water needs to be added to 76.5 g of deionized water.

[0075] The viscosity of the above-prepared cathode slurry is measured by a viscometer to be 5000 mPa·s. The above-prepared mixed slurry is coated on one side surface of the cathode current collector aluminum foil by means of doctor blade coating. The thickness of the coated slurry is 5 μm, and it is placed in a vacuum drying oven for vacuum thermal curing. The curing temperature of the vacuum thermal curing is 80 °C, and the time is 20 min.

[0076] Example 4

[0077] This embodiment provides an aqueous cathode slurry, which includes 2 - 10 parts of cathode active material, 1 - 15 parts of conductive agent, 1 - 10 parts of binder, 35 - 90 parts of main solvent, 2 - 10 parts of auxiliary solvent, 1 - 5 parts of aqueous dispersant, and 0.1 - 1 part of pH regulator; the cathode active material is a fluorophosphate-based cathode material with the chemical formula Li 1+x Al(PO4)O 1-y F 2y ; where 0 ≤ x < 1, 0 < y < 0.1; in this embodiment, x takes the value of 0 and y takes the value of 0.08, and the chemical formula of the cathode material is LiAl(PO4)O 0.92 F 0.16 , the binder is an aqueous binder, and the main solvent is deionized water; the aqueous dispersant is maleic anhydride grafted styrene polymer dispersant.

[0078] In this embodiment, the raw materials are weighed according to the following proportions by weight: 2g of aqueous dispersant maleic anhydride-grafted styrene polymer dispersant and 4g of auxiliary solvent ethanol are dissolved in 76.5g of deionized water. Then, 2g of sodium carboxymethyl cellulose (CMC) and 10g of nano-conductive carbon black with an average particle size of 20nm are added to the above mixture; 5g of positive electrode material with an average particle size of 100nm is added, and the mixture is dispersed and stirred for 2 hours at a stirring speed of 2000rpm; then 0.5g of pH adjuster acetic acid is added, and the mixture is stirred and dispersed for another 1 hour; a positive electrode slurry (LiAl(PO4)O) with a pH value of approximately 7 is obtained. 0.92 F 0.16 The ratio of dispersant, ethanol, conductive carbon black, CMC, acetic acid, and water is 5:2:4:10:2:0.5:76.5. The positive electrode material is an aqueous slurry prepared by sand milling, with a solid content of 30%. Its addition requires adding the introduced deionized water to 76.5g of deionized water.

[0079] The viscosity of the prepared positive electrode slurry was measured to be 5000 mPa·s using a viscometer. The prepared mixed slurry was then coated onto one side of the positive electrode current collector aluminum foil using a blade coating method. The coating thickness was 5 μm. The slurry was then placed in a vacuum drying oven for vacuum thermosetting at a temperature of 80°C for 20 min.

[0080] Example 5

[0081] Unlike Example 1, in this example, x is 0.2, y is 0.08, and the chemical formula of the cathode material is Li. 1.2 Al(PO4)O 0.92 F 0.16 In this embodiment, the raw materials are weighed according to the following proportions by weight: 3g of aqueous dispersant maleic anhydride-grafted styrene polymer dispersant and 3g of auxiliary solvent isopropanol are dissolved in 80.8g of deionized water. Then, 3g of carboxyethyl cellulose and 4g of nano-acetylene black are added to the above mixture, wherein the average particle size of the acetylene black is 30nm; then, 6g of positive electrode material with an average particle size of 200nm is added, and the mixture is dispersed and stirred for 3 hours at a stirring speed of 2000rpm; then, 0.2g of tartaric acid pH adjuster is added, and the mixture is stirred and dispersed for another 1 hour; a positive electrode slurry (Li) with a pH value of approximately 7 is obtained. 1.2 Al(PO4)O 0.92 F 0.16 The composition of the mixture is: dispersant: isopropanol: acetylene black: carboxyethyl cellulose: tartaric acid: water = 6:3:3:4:3:0.2:80.8. The positive electrode material is an aqueous slurry prepared by sand milling, with a solid content of 35%; its addition requires adding the introduced deionized water to 80.8g of deionized water.

[0082] The viscosity of the prepared positive electrode slurry was measured to be 8000 mPa·s using a viscometer. The prepared mixed slurry was then coated onto one side of the positive electrode current collector aluminum foil using a blade coating method. The coating thickness was 5 μm. The slurry was then placed in a vacuum drying oven for vacuum thermosetting at a temperature of 100°C for 15 min.

[0083] Example 6

[0084] Unlike Example 1, in this example, x is 0.5, y is 0.06, and the chemical formula of the cathode material is Li. 1.5 Al(PO4)O 0.94 F 0.12 In this embodiment, the raw materials are weighed according to the following proportions by weight: 4g of aqueous dispersant maleic anhydride-grafted styrene polymer dispersant and 2g of auxiliary solvent ethyl acetate are dissolved in 73g of deionized water. Then, 4g of carboxymethyl ethyl cellulose and 8 parts of carbon nanotubes with an average particle size of 50nm are added to the above mixture; then, 8g of positive electrode material with an average particle size of 300nm is added, and the mixture is dispersed and stirred for 4 hours at a stirring speed of 2000rpm; then, 1 part of pH adjuster citric acid is added, and the mixture is stirred and dispersed for another 1 hour; a positive electrode slurry (Li) with a pH value of approximately 7 is obtained. 1.5 Al(PO4)O 0.94 F 0.12 The composition of the dispersion is: ethyl acetate: carbon nanotubes: carboxymethyl ethyl cellulose: citric acid: water = 8:4:2:8:4:1:73. The positive electrode material is an aqueous slurry prepared by sand milling, with a solid content of 40%. Its addition requires adding the introduced deionized water to 73g of deionized water.

[0085] The viscosity of the prepared positive electrode slurry was measured to be 10000 mPa·s using a viscometer. The prepared mixed slurry was then coated onto one side of the positive electrode current collector aluminum foil using a blade coating method. The coating thickness was 5 μm. The slurry was then placed in a vacuum drying oven for vacuum thermosetting at a temperature of 120°C for 10 min.

[0086] Comparative Example 1

[0087] The preparation method is the same as in Example 1, except that the dispersant in Example 1 is replaced with an acrylic dispersant (dispersant Acusol 845), and all other steps are the same.

[0088] Comparative Example 2

[0089] The preparation method is the same as in Example 1, except that no pH adjuster is added in Comparative Example 2, and all other steps are the same.

[0090] Comparative Example 3

[0091] The preparation method is the same as that of Example 1. In Comparative Example 3, the value of x for the fluorophosphate is 0.5, the value of y is 0.12, and the chemical formula of the cathode material is Li 1.5 Al(PO4)O 0.88 F 0.24 , and other steps are the same.

[0092] We also obtained the cathode electrode sheets for testing, and used the obtained cathode electrode sheets in the battery, and tested the electrical properties.

[0093] Preparation method of the battery: A coin cell is made with the cathode electrode sheet as the cathode and a lithium sheet as the anode. Among them, the cathode active material is Li 1+x Al(PO4)O 1-y F 2y ; where 0 ≤ x < 1, 0 < y < 0.1, the anode is a metallic lithium sheet, the separator is a polypropylene film (PP film), 1 mole of electrolyte is injected, and the electrolyte is a mixed solution of LiPF6 and ethylene carbonate EC / dimethyl carbonate DMC (volume ratio 1:1).

[0094] Contact angle test: The same electrolyte is dropped onto the cathode electrode sheets prepared in Examples 1 - 6 and the cathode electrode sheets prepared in Comparative Examples 1 - 3 respectively; a contact angle measuring instrument is used to measure the contact angle θ between the electrolyte and the cathode to compare the influence on the wettability of the battery material. The smaller the contact angle, the more electrolyte is immersed, and the better the wettability.

[0095] Peel strength test: According to the 180° peel strength test method for pressure - sensitive adhesive tapes in GB2792 - 1998, the peel strength value of the separator is tested. Instrument: Universal testing machine.

[0096] Test of cycle performance: The coin cells prepared above are charged and discharged at a 1C rate for 1000 cycles to test their capacity retention rate.

[0097] Fluorophosphate stratification test: The prepared cathode slurry is allowed to stand for a period of time, and the precipitation of the slurry at the bottom is observed with the naked eye by tilting the loading container to understand whether there is stratification inside the slurry.

[0098] Analysis of verification results

[0099] Table 1 Test results of the examples and comparative examples of the present invention

[0100]

[0101]

[0102] We successfully obtained an aqueous cathode slurry containing fluorophosphate using the method of this invention. The cathode slurry exhibits excellent dispersibility. We prepared a cathode using this slurry and tested it. The test results are shown in Table 1. Table 1 shows that Examples 1-6 are superior to Comparative Example 1. This demonstrates that the cathode slurry prepared by this invention has excellent dispersibility, and the wettability and adhesion of the obtained cathode are significantly enhanced, thus contributing to improved battery electrical performance. We believe that the fluorine substituents in the fluorophosphate can interact with the strong electron-donating styrene groups in the maleic anhydride-grafted styrene polymer. On one hand, the maleic anhydride-grafted styrene polymer provides steric hindrance to the fluorophosphate, promoting its dispersion. On the other hand, the maleic anhydride-grafted styrene polymer adsorbed on the surface of the fluorophosphate enhances its polarity, reduces the interfacial energy between the fluorophosphate and water, and disperses it in water, thereby improving the wettability of the fluorophosphate. To further improve the dispersion effect of maleic anhydride-grafted styrene polymer on fluorophosphate, we added a pH adjuster. The pH adjuster assists the interaction between the maleic anhydride-grafted styrene polymer and fluorophosphate, promoting stable dispersion of fluorophosphate in the slurry, and also neutralizes the pH of the slurry. To further improve the wettability of other substances in the slurry, we added an auxiliary solvent. The synergistic effect of the auxiliary solvent and pH adjuster reduces the overall polarity of the aqueous slurry, thereby improving the wettability of each substance. The conductive agent not only facilitates electron conduction in the positive electrode but also constructs ion transport channels, which is beneficial for improving battery cycle performance. The binder helps bind the various substances in the slurry, reducing powder shedding and thus improving the adhesion between the positive electrode slurry and the current collector. Therefore, the positive electrode slurry of this invention overcomes the technical difficulties of fluorophosphate layering and agglomeration, and obtains an aqueous positive electrode slurry with good wettability, excellent adhesion, and beneficial to battery electrical performance. As shown in Table 1, in Examples 1-6 of the present invention, no obvious stratification was observed in the positive electrode slurry after one week of standing, while in Comparative Examples 1-3, obvious precipitation and stratification occurred within one week. We can further illustrate this by... Figures 1-2 Verification, this invention Figure 1 and Figure 2 Images show the results of the positive electrode slurries of Example 1 and Comparative Example 1 after standing for one week. Furthermore, when Example 1 of the present invention was coated onto the current collector, no agglomeration was observed, while Comparative Example 1 showed obvious agglomeration. This can be seen through… Figure 3 and Figure 4 Verification was conducted, among which Figure 3 As in Example 1, and Figure 4 As shown in Comparative Example 1, it can be seen that in Figure 4Agglomeration occurred. Moreover, in the present invention, through the cooperation of a pH regulator, the transition state of the maleic anhydride grafted styrene polymer structure was also broken, improving the ion-conducting ability of the maleic anhydride grafted styrene polymer, thereby facilitating the cooperation with fluorophosphate to improve the ion transport ability of the positive electrode. We can verify this through the comparison between Examples 1 - 6 and Comparative Example 2. The cycle performance of the batteries in Examples 1 - 6 is significantly better than that of Comparative Example 2.

[0103] We first studied the optimal ratio of oxygen and fluorine elements in fluorophosphate. When the value of y in fluorophosphate is selected within the range of 0 < y < 0.1, as the addition amount of the fluorine-containing material increases, both the capacity retention rate of the battery prepared from the obtained positive electrode material and the wettability of the battery increase, as shown in Examples 1 - 4. The positive electrode material LiAl(PO4)O 0.92 F 0.16 prepared in Example 4, where y is 0.08, and its capacity retention rate reaches a maximum of 90%. We believe that, firstly, due to the high electronegativity and strong electron-withdrawing ability of fluorine ions, it is beneficial for electrons to move towards the positive electrode, which is conducive to enhancing the discharge capacity of the battery. Therefore, partial substitution of oxygen elements by fluorine elements can improve the electrochemical performance of the battery. Secondly, fluorine substituents are beneficial for enhancing the wettability between the positive electrode and the electrolyte, thereby facilitating the performance of the battery's electrical properties.

[0104] When the value of y in fluorophosphate is selected such that y > 0.1, we found that although more fluorine substituents are beneficial for the electrical properties of the battery, it will also reduce the occupancy of oxygen ions. We believe that too many fluorine ions substituting oxygen ions will affect the structure of the positive electrode material. Due to the relatively large atomic radius of fluorine atoms themselves, when fluorine atoms substitute oxygen atoms, it may cause distortion of the crystal structure, resulting in the detachment of oxygen atoms from the unit cell, affecting the stability of the Al - O bond, and thus also affecting the stability of fluorine substituents in fluorophosphate, ultimately affecting its electrical properties, as shown in Comparative Example 3. In addition, more fluorine occupancy will further increase the polarity of phosphate, causing agglomeration between fluorophosphate particles and exacerbating the stratification of the aqueous slurry containing fluorophosphate. To sum up, we further selected fluorophosphate Li 1+x Al(PO4)O 1-y F 2y with the range of 0.06 ≤ y < 0.1.

[0105] On this basis, we further studied the optimal combination between various substances in the positive electrode slurry of the present invention. We found that the fluorophosphate in the present invention is Li 1+x Al(PO4)O 1-y F 2y; where \(0\leq x\lt1\) and \(0\lt y\lt0.1\). The doping of Al ions can form Al-O bonds with good orbital bonding ability, which is conducive to the partial substitution of oxygen atoms by fluorine atoms, forming a more stable fluorophosphate, and thus facilitating the cooperation between the electron-withdrawing group fluorine substitution group in the fluorine substitution group and the strong electron-donating group styrene in the maleic anhydride grafted styrene polymer. On this basis, in order to further promote the dispersion of the maleic anhydride grafted styrene polymer on the fluorophosphate, we further selected an organic acid. The organic acid has carboxyl groups and fewer hydroxyl groups. On the one hand, it can cooperate with the styrene groups in the maleic anhydride grafted styrene polymer to promote the dispersion of the fluorophosphate in the slurry. On the other hand, fewer hydroxyl groups can reduce the ability of more hydroxyl groups to weaken the ability of the pH regulator to adjust the slurry, which is conducive to reducing the dosage of the pH regulator in the slurry and can be conducive to increasing the addition amount of the fluorophosphate. In order to further promote the wettability of various substances in the slurry in an aqueous solution, we also selected the alcohol substance in Example 5. The hydroxyl groups in the alcohol substance can promote the dispersion and dissolution of the auxiliary solvent in the aqueous solution, and can also cooperate with the hydroxyl groups in the organic acid to reduce the polarity of the aqueous slurry, thus being conducive to improving the wettability of the substances in the slurry. Compared with the acid ester auxiliary solvent in Example 6, the alcohol substance in Example 5 has stronger stability, and the alcohol substance in Example 5 does not affect the adjustment of the slurry by the organic acid. In order to promote the balance between the electron-conducting ability and the ion-conducting ability in the positive electrode, we further designed the particle size of the conductive agent in Example 5 to be 25 nm - 35 nm. The conductive agent at this particle size can balance the conduction balance of electrons and ions in the positive electrode, and ions can be transported through the ion channels constructed by the conductive agent. Compared with Example 4 and Example 6, the selection of the conductive agent particles in Example 5 can form a lithium ion migration channel with richer pores and more appropriate pore sizes. On this basis, we further selected a cellulose binder. The cellulose binder has more hydroxyl oxygen and carboxyl groups. On the one hand, it is conducive to the cooperation with the maleic anhydride grafted styrene polymer. On the other hand, hydroxyl oxygen and carboxyl groups have electron-withdrawing ability, and the cellulose-based binder is easier to bind the conductive agent in the slurry. In addition, the cellulose binder, alcohol, and organic acid have similar structures and are easier to achieve cooperation. We can find through comparison and verification of Examples 4 - Example 6 that although the sheet resistivity of the battery in Example 5 of the present invention is increased compared with Example 4 and Example 6, the battery electrical performance of Example 5 is significantly better than that of Comparative Examples 1 - Comparative Example 2, and the wettability of the positive electrode in Example 5 is better than that of Example 4 and Example 6, and the adhesive force and cycling performance of the sheet are better.We further optimize the raw materials of the positive electrode slurry, which include fluorophosphate, maleic anhydride-grafted styrene polymer, 25nm-35nm conductive agent, cellulose binder, alcohol, and organic acid. The ratio of fluorophosphate: maleic anhydride-grafted styrene polymer: 25nm-35nm conductive agent: cellulose binder: alcohol: organic acid by mass is (2 parts-10 parts): (1 part-5 parts): (1 part-15 parts): (1 part-10 parts): (2 parts-10 parts): (0.1 part-1 part).

[0106] Building upon the above, we further discovered that the acetylene black selected as the conductive agent in Example 5 exhibits more developed crystalline and secondary structures, resulting in superior conductivity and liquid absorption. It also demonstrates stronger wettability in the aqueous slurry and is easier to disperse compared to Example 4. In Example 5, isopropanol, compared to ethanol in Example 4, significantly reduces the polarity of the aqueous slurry in conjunction with tartaric acid. Furthermore, isopropanol enhances the wettability of acetylene black by adsorbing onto its surface, and its branched structure provides spatial positions, thus facilitating its dispersion in the slurry. The centrosymmetric structure of tartaric acid in Example 5, compared to citric acid in Example 6, promotes ion transport in the positive electrode during battery cycling under external voltage intervention. The carboxyethyl cellulose in Example 5 exhibits a more stable structure within a pH range of 2-12, and its viscosity is consistently higher within this range, which is beneficial for binding particles in the slurry and provides stable binding capacity even when the slurry pH is adjusted with tartaric acid. Through comparative verification using Examples 4-6, we found that the positive electrode in Example 5 exhibited the best wettability, as well as the best adhesion and electronic conductivity. We further selected the following raw materials for the positive electrode slurry: fluorophosphate, maleic anhydride-grafted styrene polymer, 25nm-35nm acetylene black, carboxyethyl cellulose, isopropanol, and tartaric acid. By mass, the ratio of fluorophosphate: maleic anhydride-grafted styrene polymer: 25nm-35nm acetylene black: carboxyethyl cellulose: isopropanol: tartaric acid acetic acid was (2-10 parts): (1-5 parts): (1-15 parts): (1-10 parts): (2-10 parts): (0.1-1 part). The fluorophosphate included Li... 1+x Al(PO4)O 1-y F 2y Where 0≤x<1, y=0.08.

[0107] In summary, the positive electrode obtained after coating with the positive electrode slurry obtained by the present invention has excellent wettability and adhesion, and the fluorophosphate in the slurry does not show stratification, resulting in excellent electrical performance of the positive electrode.

[0108] It should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An aqueous positive electrode slurry, characterized in that, The raw materials for the positive electrode slurry include fluorophosphate, maleic anhydride-grafted styrene polymer, conductive agent with a particle size of 25nm-35nm, cellulose binder, alcohol, and organic acid. By mass, the ratio of fluorophosphate:maleic anhydride-grafted styrene polymer:conductive agent with a particle size of 25nm-35nm:cellulose binder:alcohol:organic acid is (2-10 parts):(1-5 parts):(1-15 parts):(1-10 parts):(2-10 parts):(0.1-1 part). The fluorophosphate includes Li... 1+x Al(PO4)O 1-y F 2y Where 0≤x<1, 0.06≤y<0.

1.

2. The aqueous positive electrode slurry according to claim 1, characterized in that, The raw materials for the positive electrode slurry also include solvents, including deionized water or pure water.

3. The aqueous positive electrode slurry according to claim 1, characterized in that, The conductive agent includes one or more of carbon black, acetylene black, carbon nanotubes, and carbon fibers.

4. The aqueous positive electrode slurry according to claim 1, characterized in that, The cellulose-based binder includes one or more of sodium carboxymethyl cellulose, carboxyethyl cellulose, ethyl cellulose, carboxymethyl ethyl cellulose, hydroxymethyl cellulose, and hydroxypropyl cellulose.

5. The aqueous positive electrode slurry according to claim 1, characterized in that, The alcohols include one or more of ethanol and isopropanol.

6. The aqueous positive electrode slurry according to claim 1, characterized in that, The organic acid includes one or more of acetic acid, citric acid, and tartaric acid.

7. The aqueous positive electrode slurry according to claim 1, characterized in that, The raw materials for the positive electrode slurry include fluorophosphate, maleic anhydride-grafted styrene polymer, 25nm-35nm acetylene black, carboxyethyl cellulose, isopropanol, and tartaric acid. By mass, the ratio of fluorophosphate: maleic anhydride-grafted styrene polymer: 25nm-35nm acetylene black: carboxyethyl cellulose: isopropanol: tartaric acid acetic acid is (2-10 parts): (1-5 parts): (1-15 parts): (1-10 parts): (2-10 parts): (0.1-1 part). The fluorophosphate includes Li... 1+x Al(PO4)O 1-y F 2y Where 0≤x<1, y=0.

08.

8. A method for preparing the positive electrode slurry according to any one of claims 1-7, the preparation method comprising: According to the stoichiometric ratio, weigh out fluorophosphate, maleic anhydride-grafted styrene polymer, conductive agent, binder, alcohol, and pH adjuster, add them to the solvent, stir evenly, and obtain positive electrode slurry.

9. The preparation method according to claim 8, characterized in that, The viscosity of the positive electrode slurry is 5000 mPa·s-10000 mPa·s.

10. The preparation method according to claim 8, characterized in that, The stirring time is 1-3 hours, and the stirring speed is 1500-2500 rpm.

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