A positive electrode current collector pre-treatment coating and method of manufacture

Abstract

The application discloses a positive electrode current collector pretreatment coating, which comprises siloxane surface grafted modified mesoporous phosphate. The positive electrode current collector pretreatment coating of the application is beneficial to the adhesion of the coating and the current collector due to the addition of the siloxane surface grafted modified mesoporous phosphate, and a three-dimensional structure composed of the siloxane surface grafted modified mesoporous phosphate, a binder and a conductive material is formed between the coating and the current collector, which is beneficial to the electron flow from the coating to the current collector, the improvement of the conductivity and specific capacity of the battery; the siloxane surface grafted modified mesoporous phosphate improves the thermal stability and mechanical properties of the coating; the mesoporous structure of the mesoporous phosphate provides continuous or partially continuous nanoscale channels, which is beneficial to the transmission of electrons or ions; the large specific surface area of the mesoporous phosphate provides a large reaction interface, promotes the reaction of active substances, and can effectively improve the contact resistance between the current collector and the positive electrode material.

Description

Technical Field

[0001] This invention relates to the field of positive electrode current collector coating technology, specifically to a positive electrode current collector pretreatment coating and preparation method. Background Technology

[0002] Current collectors are the base metal used to attach active materials in the positive and negative electrodes of lithium-ion batteries. While acting as a carrier for the active materials in both electrodes, their main function is to collect the electrons generated by the active materials and output current, thus converting chemical energy into electrical energy. In the traditional manufacturing process of lithium-ion battery positive electrodes, the active material slurry is directly coated onto the surface of aluminum foil, and after drying, an adhesive is used to fix the active material to the surface of the current collector. However, the metal current collector aluminum foil and the active material particles cannot make sufficient contact, resulting in a high interfacial resistance and high internal resistance, which greatly affects the overall performance of the battery. Furthermore, the bonding strength of the adhesive in the positive electrode active material is limited. During battery use, the positive electrode material is prone to expansion and detachment from the current collector, affecting the battery's long cycle life and safety performance. Therefore, reducing the interfacial resistance between the current collector and the active material and improving the bonding strength between them are important means to improve the performance of lithium-ion batteries.

[0003] Mesoporous phosphates possess high specific surface area, large and uniform pore size, and dimensional order. Researchers have attempted to use mesoporous phosphates in batteries, finding that they facilitate electron transfer within the mesopores, and the thin pore walls promote ion diffusion. However, as the battery temperature increases, the structure of mesoporous phosphates changes, leading to a decrease in their degree of order and thus affecting the battery's electrochemical performance. Summary of the Invention

[0004] This invention addresses the problems in the prior art by disclosing a positive electrode current collector pretreatment coating and its preparation method. The positive electrode current collector pretreatment coating can form a continuous and uniform conductive network on the surface of the current collector, enabling the material to maintain good electrochemical performance and overcoming the shortcomings of low battery conductivity and low specific capacity caused by the limited interfacial resistance between the current collector and active material particles and the limited strength of the binder.

[0005] This invention is achieved through the following technical solution:

[0006] The present invention provides a pretreatment coating for a positive electrode current collector, wherein the coating comprises a siloxane-grafted modified mesoporous phosphate.

[0007] The above-described design of the present invention utilizes the large specific surface area of ​​mesoporous phosphate, which provides a large reaction interface, promotes the reaction of active materials, and can effectively improve the contact resistance between the current collector and the positive electrode material. The mesoporous structure of mesoporous phosphate provides continuous or partially continuous nanoscale channels, which is beneficial for the transport of electrons or ions. However, due to the poor thermal stability of mesoporous phosphate, we graft-modify it. Adding siloxane-surface-grafted modified mesoporous phosphate to the pretreatment coating of the positive electrode current collector helps to improve the adhesion between the coating and the current collector, forming an electron channel for electrons to flow from the coating through the current collector, thereby improving the conductivity and specific capacity of the battery. Furthermore, siloxane-surface-grafted modified mesoporous phosphate has good thermal stability and mechanical properties.

[0008] As a further embodiment, the coating may also include conductive materials, dispersants, thickeners, surfactants, binders, and water.

[0009] As a further embodiment, the ratio of the siloxane surface-grafted modified mesoporous phosphate, conductive material, dispersant, thickener, surfactant, binder and water, by weight, is (0.4-21 parts):(2.1-15 parts):(0.4-15 parts):(0.03-1 part):(0.003-1.5 parts):(3-10 parts):(36.4-121 parts).

[0010] As a further embodiment, the siloxane includes one of alkyltriethoxysilane, alkyltrimethoxysilane, and alkyltriacetoxysilane.

[0011] As a further embodiment, the alkyltriethoxysilane includes methyltriethoxysilane; the alkyltriacetoxysilane includes propyltriacetoxysilane; and the alkyltrimethoxysilane includes methyltrimethoxysilane.

[0012] As a further embodiment, the siloxane is propyltriacetoxysilane. Propyltriacetoxysilane has multiple acetoxy groups, and the acyl group is an acyl group found in carboxyl derivatives, making it more stable and allowing for better adsorption with phosphate groups, thus facilitating the grafting of mesoporous phosphates.

[0013] As a further embodiment, the mesoporous phosphate includes one of the following: mesoporous aluminum phosphate and its mesoporous multi-element doped aluminum phosphate, mesoporous zirconium phosphate, mesoporous titanium phosphate, mesoporous lithium iron phosphate composite material, mesoporous rare earth phosphate, mesoporous sodium zirconium phosphate, and mesoporous magnesium zirconium phosphate; as an even further embodiment, the mesoporous phosphate is mesoporous magnesium zirconium phosphate. It exhibits superior ionic conductivity and thermal stability, and grafting with siloxane further enhances the stability of the grafted mesoporous structure, thus improving electrochemical performance.

[0014] As a further embodiment, the doping element in the mesoporous multi-element doped aluminum phosphate is one of iron, cobalt, titanium, magnesium, manganese, zirconium, and silicon.

[0015] As a further embodiment, the chemical formula of the mesoporous lithium iron phosphate composite material is: Li x A a M m B b PO z N n Where x, a, m, b, z, and n represent molar ratios of 0.9 ≤ x ≤ 1.8, 0 ≤ a ≤ 0.1, 0.5 ≤ m ≤ 1, 0 ≤ b ≤ 0.5, 3 ≤ z ≤ 4, and 0 ≤ n ≤ 1; element A includes one or more of Na, Mg, Ti, V, Cr, Cu, Mn, Co, Ni, Zn, Ga, In, Ge, W, Hg, Au, Ag, Nb, and Zr; element M includes one or more of Fe, Co, Mn, Ni, and V; element B includes one or more of Li, Na, K, Ca, Mg, Ti, V, Cr, Cu, Mn, Co, Ni, Zn, Ga, In, Ge, Ag, Nb, Hg, Au, Zr, and W; and elements M and B are not the same element at the same time; Li is lithium, P is phosphorus, O is oxygen, and N is nitrogen; as a further embodiment, the mesoporous lithium iron phosphate composite material is titanium-doped mesoporous lithium iron phosphate. The particle size of titanium is more conducive to directional doping with less impact on the structure. It not only improves electronic conductivity but also does not affect the structural stability of phosphate groups, and has a positive effect on the grafting of siloxanes.

[0016] As a further embodiment, the mesoporous rare earth phosphate includes one of mesoporous cerium phosphate, mesoporous yttrium phosphate, and mesoporous lanthanum phosphate.

[0017] As a further improvement, the mesoporous zirconium phosphate sodium and mesoporous zirconium phosphate magnesium are respectively NaZr2P3O 12 and MgZr4P6O 24 .

[0018] As a further embodiment, the conductive material includes one or more of carbon black, graphite, graphene, and carbon nanotubes.

[0019] As a further embodiment, the dispersant is an anchoring group-grafted polyacrylic acid block copolymer. Acrylic acid block copolymers exhibit good creep resistance and thermal stability.

[0020] As a further embodiment, the anchoring groups include -NR2 and -NR. 3+ One of the following: -COOH, -COO-, -SO3H-, -SO3-, -PO4, -OH, -SH, polyamine, polyol, polyether.

[0021] As a further option, the thickener is one or more of sodium carboxymethyl cellulose, hydroxyethyl cellulose, methyl cellulose, methyl hydroxypropyl cellulose, guar gum, carboxymethyl starch, polyvinyl alcohol, and polyethylene wax.

[0022] As a further embodiment, the surfactant includes a variety of sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, polyethylene glycol, alkylphenol polyoxyethylene ether, waterborne modified polyacrylate, anionic acrylic copolymer, nonionic polyamine-ethylene oxide condensate, and nonionic polyethylene glycol ester.

[0023] As a further option, the adhesive includes one or more of PAA (polyacrylic acid) adhesive, PAN (polyacrylonitrile) adhesive, or resin-based adhesive.

[0024] As a further embodiment, the raw materials for the siloxane-grafted modified mesoporous phosphate include siloxane and mesoporous phosphate, with a mass ratio of siloxane to mesoporous phosphate of (3-8 parts):100 parts; as an even further embodiment, the mass ratio of propyltriacetoxysilane to titanium-doped mesoporous lithium iron phosphate is (4-8 parts):100 parts; as yet another further embodiment, the mass ratio of propyltriacetoxysilane to mesoporous zirconium magnesium phosphate is (7-8 parts):100 parts. Appropriately proportioned siloxane ratios are more conducive to improving the adhesion, thermal stability, and mechanical properties of mesoporous phosphate.

[0025] As a further embodiment, the optimal coating system comprises siloxane-grafted modified mesoporous phosphate, carboxyl-grafted polyacrylic acid block copolymer, sodium carboxymethyl cellulose, sodium dodecylbenzene sulfonate, and polyethylene glycol. This coating system exhibits optimal chemical and mechanical properties. The synergistic interaction among the substances within the system ensures uniform dispersion of the materials within the coating, which is more conducive to the stable functioning of each substance. The adhesion between the coating and the current collector is enhanced, ultimately forming electron and ion transport channels from within the coating to the current collector.

[0026] The present invention also provides a method for preparing the pretreatment coating of the positive electrode current collector, comprising the following steps:

[0027] S1: Add water, conductive material, dispersant and thickener according to the mass ratio, mix evenly, and then disperse to obtain a mixed slurry, which is used as the first slurry;

[0028] S2: Add siloxane-grafted modified mesoporous phosphate, water and surfactant according to the mass ratio and mix evenly to obtain a mixed slurry, which is used as the second slurry;

[0029] S3: Add the first slurry, the second slurry, and the binder according to the mass ratio and mix them evenly to obtain a mixed slurry;

[0030] S4: The mixed slurry is coated onto the surface of the positive electrode current collector foil and dried to obtain a pre-treated coating.

[0031] In the coating preparation process, it is crucial that the substances within the coating do not agglomerate, which is essential for their effective function. Therefore, we divided the coating into a first slurry and a second slurry to ensure thorough and uniform dispersion of the substances. In the pretreatment coating, the silicon-oxygen grafted and modified mesoporous phosphate increases the adhesion between the coating and the current collector, facilitating the transfer of electrons or ions from the coating to the current collector. However, the increased molecular weight of the siloxane-grafted mesoporous phosphate may affect its dispersibility in the coating, thus impacting the overall mechanical properties of the coating. Therefore, we added a surfactant with dispersing properties and the ability to stabilize the order of the mesoporous phosphate to the second slurry. The conductive materials in the coating are prone to agglomeration; therefore, we dispersed the conductive agent and the siloxane-grafted mesoporous phosphate separately, and added a dispersant to the first slurry to improve the dispersion of the conductive materials. The association between the thickener and the binder improves the leveling properties of the coating; however, the thickener itself has a high viscosity, and if it is placed in the same slurry as the high-molecular-weight siloxane-grafted mesoporous phosphate, it may affect the dispersion effect of the siloxane-grafted mesoporous phosphate. Therefore, the thickener was placed in the first slurry. The mixed slurry obtained by the above method exhibits good dispersibility among the substances, and the final coating shows a significant improvement in adhesion.

[0032] As a further embodiment, the method for preparing the siloxane-modified mesoporous phosphate includes weighing siloxane and mesoporous phosphate according to a mass ratio and mixing them uniformly with water as a medium.

[0033] As a further embodiment, the mixing speed is 100rpm-2000rpm, and the mixing time is 30min-180min.

[0034] As a further embodiment, in S1, the mixing speed is 2000 r / min-5000 r / min, and the mixing time is 5 min-60 min; the dispersion speed is 8000 r / min-15000 r / min, and the dispersion time is 10 min-90 min; in S2, the mixing speed is 1000 r / min-3000 r / min, and the mixing time is 30 min-120 min; in S3, the mixing speed is 200 r / min-1500 r / min, and the mixing time is 10 min-30 min. By mass, the ratio of first slurry: second slurry: binder is (50-90 parts): (5-40 parts): (3-10 parts); in S4, the coating method is one of roller coating, spin coating, spray coating, brush coating, or electrospinning, the coating thickness is 2 μm-20 μm, and the drying is carried out in a vacuum environment at a temperature of 50℃-150℃.

[0035] The features and beneficial effects of this invention are as follows:

[0036] (1) The present invention provides a positive electrode current collector pretreatment coating. Due to the addition of siloxane surface graft modified mesoporous phosphate, the coating and current collector are better bonded. A three-dimensional structure composed of siloxane surface graft modified mesoporous phosphate, binder and conductive material is formed between the coating and the current collector, which is beneficial to improve the flow of electrons from the coating to the current collector and improve the conductivity and specific capacity of the battery.

[0037] (2) Grafting and modifying mesoporous phosphates on the surface of siloxanes improves the thermal stability and mechanical properties of the coating.

[0038] (3) The mesoporous structure of mesoporous phosphate provides continuous or partially continuous nanoscale channels, which is beneficial for the transport of electrons or ions.

[0039] (4) The large specific surface area of ​​mesoporous phosphate provides a large reaction interface, which promotes the reaction of active materials and can effectively improve the contact resistance between the current collector and the positive electrode material. Detailed Implementation

[0040] To facilitate understanding of the positive electrode current collector pretreatment coating of the present invention, the preparation method of the positive electrode current collector pretreatment coating of the present invention will be described more comprehensively below, and embodiments of the present invention will be given, but this does not limit the scope of the present invention.

[0041] Example 1

[0042] This example provides a pretreatment coating for a positive electrode current collector containing mesoporous phosphate. The preparation method includes the following steps: The preparation method of siloxane surface graft modified mesoporous phosphate is as follows: Methyltrimethoxysilane and titanium-doped mesoporous lithium iron phosphate are mixed in a high-speed mixer with water as the medium at a ratio of 4:100, the mixing speed is 700 rpm and the mixing time is 90 min.

[0043] S1: 79.9 parts water, 10 parts carbon black, 10 parts carboxyl-grafted polyacrylic acid block copolymer, and 0.1 parts sodium carboxymethyl cellulose were mixed evenly using a high-speed disperser at 3000 rpm for 10 min. The evenly mixed slurry was then placed in a high-shear emulsifier and further dispersed at 9000 rpm for 30 min, and then milled using 0.3 mm zirconium beads to obtain the first slurry.

[0044] S2: 15 parts of siloxane-surface-grafted modified titanium-doped mesoporous lithium iron phosphate, 84 parts of water, and 1 part of surfactant were mixed evenly using a high-speed disperser at 2000 r / min for 90 min to obtain the second slurry.

[0045] S3: Mix 60 parts of the first slurry, 20 parts of the second slurry, and 10 parts of the PAN adhesive evenly to obtain the final slurry;

[0046] S4: The final slurry is coated onto the surface of the positive electrode current collector foil and dried at 70°C for 15 minutes to obtain the pretreated coating.

[0047] The surfactant is a 1:1 mixture of sodium dodecylbenzenesulfonate and water-modified polyacrylate.

[0048] The coating method is blade coating, and the thickness is 10μm.

[0049] Example 2

[0050] This example provides a pretreatment coating for a positive electrode current collector containing mesoporous phosphate, which is basically the same as that in Example 1, except that the mesoporous phosphate is mesoporous yttrium phosphate.

[0051] This example provides a pretreatment coating for a positive electrode current collector containing mesoporous phosphate. The preparation method includes the following steps: The preparation method of siloxane surface graft modified mesoporous phosphate is as follows: Methyltrimethoxysilane and mesoporous yttrium phosphate are mixed in a high-speed mixer with water as the medium at a ratio of 4:100, the mixing speed is 700 rpm and the mixing time is 90 min.

[0052] S1: 79.9 parts water, 10 parts carbon black, 10 parts carboxyl-grafted polyacrylic acid block copolymer, and 0.1 parts sodium carboxymethyl cellulose were mixed evenly using a high-speed disperser at 3000 rpm for 10 min. The evenly mixed slurry was then placed in a high-shear emulsifier and further dispersed at 9000 rpm for 30 min, and then milled using 0.3 mm zirconium beads to obtain the first slurry.

[0053] S2: 15 parts of siloxane-grafted modified mesoporous yttrium phosphate, 84 parts of water, and 1 part of surfactant were dispersed at 2000 r / min for 90 min using a high-speed disperser to obtain a second slurry.

[0054] S3: Mix 60 parts of the first slurry, 20 parts of the second slurry, and 10 parts of the PAN adhesive evenly to obtain the final slurry.

[0055] S4: The final slurry is coated onto the surface of the positive electrode current collector foil and dried at 70°C for 15 minutes to obtain the pretreated coating.

[0056] The surfactant is a 1:1 mixture of sodium dodecylbenzenesulfonate and water-modified polyacrylate.

[0057] The coating method is blade coating, and the thickness is 10μm.

[0058] Example 3

[0059] This example provides a pretreatment coating for a positive electrode current collector containing mesoporous phosphate. The preparation method includes the following steps: The preparation method of siloxane surface graft modified mesoporous phosphate is as follows: Triacetyloxysilane and titanium-doped mesoporous lithium iron phosphate are mixed in a high-speed mixer with water as the medium at a ratio of 4:100, the mixing speed is 700 rpm and the mixing time is 90 min.

[0060] S1: 75.9 parts water, 12 parts carbon black, 12 parts carboxyl-grafted polyacrylic acid block copolymer, and 0.1 parts sodium carboxymethyl cellulose were mixed evenly using a high-speed disperser at 3000 rpm for 10 min. The evenly mixed slurry was then placed in a high-shear emulsifier and further dispersed at 9000 rpm for 30 min, and then milled using 0.3 mm zirconium beads to obtain the first slurry.

[0061] S2: 20 parts of siloxane-surface-grafted modified titanium-doped mesoporous lithium iron phosphate, 79 parts of water, and 1 part of surfactant were mixed evenly using a high-speed disperser at 2000 r / min for 90 min to obtain the second slurry.

[0062] S3: Mix 65 parts of the first slurry, 15 parts of the second slurry, and 10 parts of the PAN adhesive evenly to obtain the final slurry.

[0063] S4: The final slurry is coated onto the surface of the positive electrode current collector foil and dried at 70°C for 15 minutes to obtain the pretreated coating.

[0064] The surfactant is a 1:1 mixture of sodium dodecylbenzenesulfonate and polyethylene glycol.

[0065] The coating method is blade coating, and the thickness is 10μm.

[0066] Example 4

[0067] This example provides a pretreatment coating for a positive electrode current collector containing mesoporous phosphate. The preparation method includes the following steps: The preparation method of siloxane surface graft modified mesoporous phosphate is as follows: Triacetoxysilane and titanium-doped mesoporous lithium iron phosphate are mixed in a high-speed mixer with water as the medium at a ratio of 8:100, the mixing speed is 700 rpm and the mixing time is 90 min.

[0068] S1: 75.9 parts water, 12 parts carbon black, 12 parts carboxyl-grafted polyacrylic acid block copolymer, and 0.1 parts sodium carboxymethyl cellulose were mixed evenly using a high-speed disperser at 3000 rpm for 10 min. The evenly mixed slurry was then placed in a high-shear emulsifier and further dispersed at 9000 rpm for 30 min, and then milled using 0.3 mm zirconium beads to obtain the first slurry.

[0069] S2: 20 parts of siloxane-surface-grafted modified titanium-doped mesoporous lithium iron phosphate, 79 parts of water, and 1 part of surfactant were mixed evenly using a high-speed disperser at 2000 r / min for 90 min to obtain the second slurry.

[0070] S3: Mix 65 parts of the first slurry, 15 parts of the second slurry, and 10 parts of the PAN adhesive evenly to obtain the final slurry.

[0071] S4: The final slurry is coated onto the surface of the positive electrode current collector foil and dried at 70°C for 15 minutes to obtain the pretreated coating.

[0072] The surfactant is a 1:1 mixture of sodium dodecylbenzenesulfonate and polyethylene glycol.

[0073] The coating method is blade coating, and the thickness is 10μm.

[0074] Example 5

[0075] This example provides a pretreatment coating for a positive electrode current collector containing mesoporous phosphate. The preparation method includes the following steps: The preparation method of siloxane surface graft modified mesoporous phosphate is as follows: Propyltriacetoxysilane and mesoporous zirconium magnesium phosphate are mixed in a high-speed mixer with water as the medium at a ratio of 8:100, the mixing speed is 700 rpm and the mixing time is 90 min.

[0076] S1: 75.9 parts water, 12 parts carbon black, 12 parts carboxyl-grafted polyacrylic acid block copolymer, and 0.1 parts sodium carboxymethyl cellulose were mixed evenly using a high-speed disperser at 3000 rpm for 10 min. The evenly mixed slurry was then placed in a high-shear emulsifier and further dispersed at 9000 rpm for 30 min, and then milled using 0.3 mm zirconium beads to obtain the first slurry.

[0077] S2: 20 parts of siloxane-grafted modified mesoporous zirconium magnesium phosphate, 79 parts of water, and 1 part of surfactant were dispersed at 2000 r / min for 90 min using a high-speed disperser to obtain a second slurry.

[0078] S3: Mix 65 parts of the first slurry, 15 parts of the second slurry, and 10 parts of the PAN adhesive evenly to obtain the final slurry.

[0079] S4: The final slurry is coated onto the surface of the positive electrode current collector foil and dried at 70°C for 15 minutes to obtain the pretreated coating.

[0080] The surfactant is a 1:1 mixture of sodium dodecylbenzenesulfonate and polyethylene glycol.

[0081] The coating method is blade coating, and the thickness is 10μm.

[0082] Example 6

[0083] This example provides a pretreatment coating for a positive electrode current collector containing mesoporous phosphate. The preparation method includes the following steps: The preparation method of siloxane surface graft modified mesoporous phosphate is as follows: Propyltriacetoxysilane and mesoporous zirconium magnesium phosphate are mixed in a high-speed mixer with water as the medium at a ratio of 7:100, the mixing speed is 1000 rpm and the mixing time is 100 min.

[0084] S1: 84.9 parts water, 10 parts carbon black, 5 parts carboxyl-grafted polyacrylic acid block copolymer, and 0.1 parts sodium carboxymethyl cellulose were mixed evenly using a high-speed disperser at 3000 rpm for 10 min. The evenly mixed slurry was then placed in a high-shear emulsifier and further dispersed at 9000 rpm for 30 min, and then milled using 0.3 mm zirconium beads to obtain the first slurry.

[0085] S2: 15 parts of siloxane-grafted modified mesoporous zirconium magnesium phosphate, 84.8 parts of water, and 0.2 parts of surfactant were dispersed at 3000 r / min for 70 min using a high-speed disperser to obtain a second slurry.

[0086] S3: Mix 70 parts of the first slurry, 12 parts of the second slurry, and 8 parts of the PAN adhesive evenly to obtain the final slurry.

[0087] S4: The final slurry is coated onto the surface of the positive electrode current collector foil and dried at 70°C for 15 minutes to obtain the pretreated coating.

[0088] The surfactant is a 1:1 mixture of sodium dodecylbenzenesulfonate and polyethylene glycol.

[0089] The coating method is blade coating, and the thickness is 10μm.

[0090] Comparative Example 1

[0091] This example provides a pretreatment coating for a positive electrode current collector, and the preparation method includes the following steps:

[0092] S1: 75.9 parts water, 12 parts carbon black, 12 parts carboxyl-grafted polyacrylic acid block copolymer, and 0.1 parts sodium carboxymethyl cellulose were mixed evenly using a high-speed disperser at 3000 rpm for 10 min. The evenly mixed slurry was then placed in a high-shear emulsifier and further dispersed at 9000 rpm for 30 min, and then milled using 0.3 mm zirconium beads to obtain the final slurry.

[0093] S2: Mix 90 parts of slurry with 10 parts of PAN binder to obtain the final slurry.

[0094] S3: The final slurry is coated onto the surface of the positive electrode current collector foil and dried at 70°C for 15 minutes to obtain the pretreated coating.

[0095] The coating method is blade coating, and the thickness is 10μm.

[0096] Comparative Example 2

[0097] Blank positive current collector aluminum foil.

[0098] Comparative Example 3

[0099] This example provides a pretreatment coating for a positive electrode current collector. The preparation method of siloxane surface graft modified mesoporous phosphate is as follows: Methyltrimethoxysilane and ordinary nano-sized titanium-doped lithium iron phosphate are mixed in a high-speed mixer with water as the medium at a ratio of 4:100, the mixing speed is 700 rpm and the mixing time is 90 min.

[0100] S1: 79.9 parts water, 10 parts carbon black, 10 parts carboxyl-grafted polyacrylic acid block copolymer, and 0.1 parts sodium carboxymethyl cellulose were mixed evenly using a high-speed disperser at 3000 rpm for 10 min. The evenly mixed slurry was then placed in a high-shear emulsifier and further dispersed at 9000 rpm for 30 min, and then milled using 0.3 mm zirconium beads to obtain the first slurry.

[0101] S2: 15 parts of siloxane-surface-grafted modified ordinary nano-scale titanium-doped mesoporous lithium iron phosphate, 84 parts of water, and 1 part of surfactant were dispersed at 2000 r / min for 90 min using a high-speed disperser to obtain a second slurry.

[0102] S3: Mix 60 parts of the first slurry, 20 parts of the second slurry, and 10 parts of the PAN adhesive evenly to obtain the final slurry.

[0103] S4: The final slurry is coated onto the surface of the positive electrode current collector foil and dried at 70°C for 15 minutes to obtain the pretreated coating.

[0104] The surfactant is a 1:1 mixture of sodium dodecylbenzenesulfonate and water-modified polyacrylate.

[0105] The coating method is blade coating, and the thickness is 10μm.

[0106] Comparative Example 4

[0107] This example provides a pretreatment coating for a positive electrode current collector containing mesoporous phosphate, and the preparation method includes the following steps:

[0108] S1: 75.9 parts water, 12 parts carbon black, 12 parts carboxyl-grafted polyacrylic acid block copolymer, and 0.1 parts sodium carboxymethyl cellulose were mixed evenly using a high-speed disperser at 3000 rpm for 10 min. The evenly mixed slurry was then placed in a high-shear emulsifier and further dispersed at 9000 rpm for 30 min, and then milled using 0.3 mm zirconium beads to obtain the first slurry.

[0109] S2: 20 parts of titanium-doped mesoporous lithium iron phosphate, 79 parts of water, and 1 part of surfactant are dispersed at 2000 r / min for 90 min using a high-speed disperser to obtain a second slurry.

[0110] S3: Mix 65 parts of the first slurry, 15 parts of the second slurry, and 10 parts of acrylic PAN adhesive evenly to obtain the final slurry.

[0111] S4: The final slurry is coated onto the surface of the positive electrode current collector foil and dried at 70°C for 15 minutes to obtain the pretreated coating.

[0112] The surfactant is a 1:1 mixture of sodium dodecylbenzenesulfonate and polyethylene glycol.

[0113] The coating method is blade coating, and the thickness is 10μm.

[0114] Comparative Example 5

[0115] This example provides a pretreatment coating for a positive electrode current collector containing mesoporous phosphate. The preparation method includes the following steps: The preparation method of siloxane surface graft modified mesoporous phosphate is as follows: Propyltriacetoxysilane and mesoporous zirconium magnesium phosphate are mixed in a high-speed mixer with water as the medium at a ratio of 1:100, the mixing speed is 1000 rpm and the mixing time is 100 min.

[0116] S1: 75.9 parts water, 12 parts carbon black, 12 parts carboxyl-grafted polyacrylic acid block copolymer, and 0.1 parts sodium carboxymethyl cellulose were mixed evenly using a high-speed disperser at 3000 rpm for 10 min. The evenly mixed slurry was then placed in a high-shear emulsifier and further dispersed at 9000 rpm for 30 min, and then milled using 0.3 mm zirconium beads to obtain the first slurry.

[0117] S2: 20 parts of siloxane-grafted modified mesoporous zirconium magnesium phosphate, 79 parts of water, and 1 part of surfactant were dispersed at 2000 r / min for 90 min using a high-speed disperser to obtain a second slurry.

[0118] S3: Mix 65 parts of the first slurry, 15 parts of the second slurry, and 10 parts of the PAN adhesive evenly to obtain the final slurry.

[0119] S4: The final slurry is coated onto the surface of the positive electrode current collector foil and dried at 70°C for 15 minutes to obtain the pretreated coating.

[0120] The surfactant is a 1:1 mixture of sodium dodecylbenzenesulfonate and polyethylene glycol.

[0121] Comparative Example 6

[0122] This example provides a pretreatment coating for a positive electrode current collector containing mesoporous phosphate. The preparation method includes the following steps: The preparation method of siloxane surface graft modified mesoporous phosphate is as follows: Propyltriacetoxysilane and mesoporous zirconium magnesium phosphate are mixed in a high-speed mixer with water as the medium at a ratio of 20:100, the mixing speed is 1000 rpm and the mixing time is 100 min.

[0123] S1: 75.9 parts water, 12 parts carbon black, 12 parts carboxyl-grafted polyacrylic acid block copolymer, and 0.1 parts sodium carboxymethyl cellulose were mixed evenly using a high-speed disperser at 3000 rpm for 10 min. The evenly mixed slurry was then placed in a high-shear emulsifier and further dispersed at 9000 rpm for 30 min, and then milled using 0.3 mm zirconium beads to obtain the first slurry.

[0124] S2: 20 parts of siloxane-grafted modified mesoporous zirconium magnesium phosphate, 79 parts of water, and 1 part of surfactant were dispersed at 2000 r / min for 90 min using a high-speed disperser to obtain a second slurry.

[0125] S3: Mix 65 parts of the first slurry, 15 parts of the second slurry, and 10 parts of the PAN adhesive evenly to obtain the final slurry.

[0126] S4: The final slurry is coated onto the surface of the positive electrode current collector foil and dried at 70°C for 15 minutes to obtain the pretreated coating.

[0127] The surfactant is a 1:1 mixture of sodium dodecylbenzenesulfonate and polyethylene glycol.

[0128] (1) The prepared mixed slurry is coated on the current collector, and then the traditional positive electrode slurry is coated and rolled. The adhesion of the coating (mixed slurry + positive electrode slurry) on the carbon foil is tested: the peel strength is obtained by performing a 90° peel test using a universal testing machine.

[0129] (2) The above embodiments were used to make CR2032 button cells, and the electrical performance was tested using Blue Electric Button Cell Testing Equipment.

[0130] (3) The thermal stability of the mesoporous phosphates after different treatments in the above examples and comparative examples was tested. The weight loss rate was tested when the phosphates were heated to 1000°C in air.

[0131] (4) Tensile properties were tested on the mesoporous phosphates after different treatments in the above comparative examples.

[0132] Validation Result Analysis

[0133] Table 1 Test results of the examples and comparative examples

[0134]

[0135]

[0136] We prepared six different cathode current collector pretreatment coatings using the method of this invention. We tested the cathode current collector pretreatment coatings prepared in the examples and comparative examples, and the test results are shown in Table 1. We found that the cathode current collector pretreatment coating prepared by this invention is superior to the comparative example in both electrochemical and physical performance.

[0137] We found that coating the current collector is beneficial to improving the electrochemical performance of the battery. For example, comparing Examples 1-6, Comparative Example 1 (coating prepared by conventional method), and Comparative Example 2 (blank aluminum foil), we found that after using the pre-treated coating, the adhesion between the coating and the current collector increased, and the electrochemical performance of the battery was improved. We further compared Examples 1-6 and Comparative Example 1. After the pre-treated coating in Examples 1-6, the physical properties of the coating and the electrochemical performance of the battery were better than those in Comparative Example 1. We believe that the coating of the present invention is enhanced by the siloxane surface grafted modified mesoporous phosphate, which strengthens the mechanical properties of the coating itself and the adhesion between the coating and the current collector, and establishes an electron transport channel from the coating to the current collector, thereby improving the electrochemical performance of the battery.

[0138] We first investigated the physical properties of the positive electrode current collector pretreatment coatings prepared in this embodiment and comparative examples. The coatings prepared in this invention exhibit excellent physical properties. Grafting siloxane onto mesoporous phosphates is beneficial for improving the coating's adhesion, thermal stability, and mechanical strength. Comparisons were made with Examples 1-6, Comparative Examples 5-6 (both Comparative Examples 5 and 6 underwent grafting), and Comparative Example 4 (without grafting modification). The adhesion, weight loss, and tensile strength of the grafted mesoporous phosphate coatings were all superior to those of the ungrafted mesoporous phosphate coatings. (Comparative Example 4) We further found that a suitable amount of siloxane grafting is more conducive to mesoporous phosphates obtaining better physical properties. As seen in Examples 1-6 and Comparative Examples 5-6, we believe that if the grafting amount is too small, the mesoporous phosphate cannot be sufficiently modified, resulting in less improvement in the coating's adhesion, mechanical properties, and thermal stability. If the grafting amount is too large, it may affect the interaction between the grafts, or even allow excess siloxane to be grafted again onto the grafts, thus causing a gradual decrease in the structural stability of the mesoporous phosphate grafted onto the entire siloxane surface. In summary, we selected a mass ratio of siloxane to mesoporous phosphate of (3-8 parts): 100 parts.

[0139] We further compared the differences in electrochemical performance between the batteries with positive electrode current collector pretreatment coatings prepared in this embodiment and the comparative example. Mesoporous phosphates have a large specific surface area, which is beneficial for promoting the reaction of active materials on their surface. The mesoporous structure of mesoporous phosphates provides continuous or partially continuous nanoscale channels, which is conducive to the formation of ion and electron transport channels. It can be seen that mesoporous phosphates are beneficial for improving the contact resistance between the current collector and the positive electrode material, and thus improving the electrochemical performance of the battery. If the phosphate used does not have a mesoporous structure, it may not be able to form transport channels, ultimately affecting the electrochemical performance of the battery, as shown in the comparison between Examples 1-6 and Comparative Example 3 (ordinary nanoscale phosphate).

[0140] We also compared the effects of different mesoporous phosphates on the electrochemical performance of the batteries. For example, compared to Example 2, the capacity retention and first-cycle discharge specific capacity of the two different coatings in Example 1 were not significantly different. However, the adhesion of Example 1 was better than that of Example 2. We believe this may be because the directional doping of titanium has less impact on the structure of mesoporous lithium iron phosphate, thus obtaining a stable phosphate structure, making it easier for siloxanes to be adsorbed. This is beneficial for the grafting of siloxanes and titanium-doped mesoporous lithium iron phosphate. Furthermore, titanium-doped mesoporous lithium iron phosphate has better thermal stability and lower structural expansion, which is more conducive to electron transport from the coating to the current collector. Therefore, the conductivity of Example 1 is better than that of Example 2, and we chose titanium-doped mesoporous lithium iron phosphate. Compared to Example 5, the overall capacity of the batteries with the two different coatings in Example 4 was not significantly different. However, the mesoporous magnesium zirconium phosphate in Example 5 had better ionic conductivity and lower thermal expansion. Therefore, although the adhesion was lower than that in Example 4, the conductivity and thermal stability of Example 5 were better, and we further chose mesoporous magnesium zirconium phosphate.

[0141] Within a certain range (based on a mass ratio of siloxane to mesoporous phosphate of (3-8 parts): 100 parts), although increasing the amount of siloxane added is beneficial for grafting and improving the physical properties of siloxane-grafted mesoporous phosphate, the differences between mesoporous phosphates result in varying degrees of improvement in the physical properties of siloxane-grafted mesoporous phosphate due to the grafting of different types of siloxane and phosphate, thus affecting the battery conductivity. For example, compared to titanium-doped mesoporous lithium iron phosphate, in Example 4, the amount of propyltriacetoxysilane added is twice that in Example 3, but the coating adhesion of Example 4 differs from that of Example 3 by 0.4 N·mm. -1 The conductivity of Example 4 increased by 0.1 x 10⁻⁶ compared to Example 3. -4 S / cm indicates that titanium-doped mesoporous lithium iron phosphate exhibits low grafting sensitivity to propyltriacetoxysilane, allowing for a wider range of propyltriacetoxysilane grafting amounts. Therefore, a further optimized mass ratio of propyltriacetoxysilane to titanium-doped mesoporous lithium iron phosphate is (4-8 parts): 100 parts. Due to the inherent conductivity of mesoporous phosphates and the differences in surface ions, for mesoporous phosphates with superior conductivity (mesoporous zirconium magnesium phosphate), even a small change in the ratio of siloxane to mesoporous phosphate can achieve the same level of improvement in battery conductivity, as seen in Examples 5 and 6. The amount of propyltriacetoxysilane added in Example 6 is not significantly different from that in Example 5, and the adhesion between Examples 5 and 6 differs by only 0.1 N·mm. -1 The battery conductivity also increased by 0.1 x 10⁻⁶. -4S / cm. It can be seen that mesoporous zirconium phosphate has a high sensitivity to propyltriacetoxysilane grafting. We further optimized the mass ratio of propyltriacetoxysilane to mesoporous zirconium phosphate to be (7-8 parts): 100 parts.

[0142] Mesoporous phosphates grafted into different siloxane grafting systems result in varying physical properties of the grafted products. However, the mixing and reaction within different systems have a greater impact on the electrochemical performance of the coating. For example, comparing Examples 1 and 3 reveals little difference in coating adhesion and tensile strength, but significant differences in battery electrochemical performance. We believe that the compatibility of substances in the mixed slurry influences the resulting coating. Firstly, we believe that because the grafted mesoporous phosphate has a high molecular weight, in order to improve the uniform dispersion of the siloxane-grafted mesoporous phosphate in the coating and thus better utilize its electrochemical and mechanical properties, we would choose a substance that is more conducive to its dispersion. Sodium dodecylbenzenesulfonate, an ionic substance, was added to disperse the grafted mesoporous phosphate. Sodium dodecylbenzenesulfonate not only improves the dispersion between particles but also benefits the mesoporous order of the mesoporous phosphate. However, in Example 1, water-modified polyacrylate was also added. Because of its high water absorption and lower flowability compared to polyethylene glycol, it may lead to a decrease in the dispersion of the siloxane-grafted mesoporous phosphate in the slurry and affect the first and second slurries. While the mixing and bonding effect of the materials is good, polyethylene glycol has good compatibility, which not only facilitates the dispersion of siloxane-grafted mesoporous phosphates but also promotes the fusion between substances. To ensure uniform mixing of the first and second slurries, we further selected sodium carboxymethyl cellulose, an ionic thickener of the same type as sodium dodecylbenzene sulfonate. Furthermore, since the second slurry contains conductive materials and the surfactant polyethylene glycol in the first slurry has a relatively large molecular weight, to further improve the dispersibility after mixing the first and second slurries, we selected a carboxyl-grafted polyacrylic acid block copolymer with carboxyl anchoring groups. The carboxyl groups are more conducive to enhancing the anchoring effect, thereby improving the dispersion effect of the dispersant and preventing agglomeration after mixing the first and second slurries. The coating obtained under this system has stronger adhesion between the coating and the current collector, which is beneficial for electron transport and thus improves the electrochemical performance of the battery. In summary, we selected the coating system of Example 3 as the optimal coating system.

[0143] In summary, adding siloxane-grafted modified mesoporous phosphate to the coating of the current collector surface is beneficial to improving the resistance between the active material and the current collector, increasing the bonding strength between the coating and the current collector, and improving the electrochemical performance of the battery.

[0144] 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. A positive electrode current collector pre-treatment coating, characterized in that, The coating comprises siloxane surface grafting modified mesoporous phosphate; The siloxane comprises one of alkyl triethoxysilane, alkyl trimethoxysilane and alkyl triacetoxy silane; The mesoporous phosphate comprises one of mesoporous aluminum phosphate and mesoporous multi-element doped aluminum phosphate, mesoporous zirconium phosphate, mesoporous titanium phosphate, mesoporous lithium iron phosphate composite material, mesoporous rare earth phosphate, mesoporous zirconium sodium phosphate and mesoporous zirconium magnesium phosphate; The coating further comprises conductive material, dispersant, thickening agent, surfactant, binder and water; The ratio of the siloxane surface grafting modified mesoporous phosphate, conductive material, dispersant, thickening agent, surfactant, binder and water is (0.4-21 parts):(2.1-15 parts):(0.4-15 parts):(0.03-1 part):(0.003-1.5 parts):(3-10 parts):(36.4-121 parts) by mass.

2. A positive electrode current collector pre-treatment coating according to claim 1, wherein, The conductive material comprises one or more of carbon black, graphite, graphene and carbon nanotube.

3. The positive electrode current collector pre-treatment coating of claim 1, wherein, The dispersant is an anchor group grafted polyacrylic acid block copolymer.

4. The positive electrode current collector pre-treatment coating of claim 1, wherein, The thickening agent is one or more of sodium carboxymethyl cellulose, hydroxyethyl cellulose, methyl cellulose, methyl hydroxypropyl cellulose, guar gum, carboxymethyl starch, polyvinyl alcohol and polyethylene wax.

5. The positive electrode current collector pre-treatment coating of claim 1, wherein, The surfactant comprises one or more of sodium dodecyl benzene sulfonate, sodium dodecyl sulfate, polyethylene glycol, alkyl phenol polyoxyethylene ether, water-based modified polyacrylate, anionic acrylic copolymer, non-ionic polyamine-ethylene oxide condensate and non-ionic polyethylene glycol ester.

6. The positive electrode current collector pre-treatment coating of claim 1, wherein, The binder comprises one or more of PAA binder, PAN binder and resin binder.

7. The positive electrode current collector pre-treatment coating of claim 1, wherein, The alkyl triethoxysilane comprises methyl triethoxysilane; the alkyl triacetoxy silane comprises propyl triacetoxy silane; and the alkyl trimethoxysilane comprises methyl trimethoxysilane.

8. The positive electrode current collector pre-treatment coating of claim 1, wherein, The doping element in the mesoporous multi-element doped aluminum phosphate is one of iron, cobalt, titanium, magnesium, manganese, zirconium and silicon; the chemical general formula of the mesoporous lithium iron phosphate composite material is Li x A a M m B b PO z N n , wherein x, a, m, b, z, n represent molar ratios respectively, 0.9≤x≤1.8, 0≤a≤0.1, 0.5≤m≤1, 0≤b≤0.5, 3≤z≤4, 0≤n≤1; element A includes one or more of Na, Mg, Ti, V, Cr, Cu, Mn, Co, Ni, Zn, Ga, In, Ge, W, Hg, Au, Ag, Nb, Zr; element M includes one or more of Fe, Co, Mn, Ni, V; element B includes one or more of Li, Na, K, Ca, Mg, Ti, V, Cr, Cu, Mn, Co, Ni, Zn, Ga, In, Ge, Ag, Nb, Hg, Au, Zr, W; and element M and element B are not the same element at the same time; Li is a lithium element, P is a phosphorus element, O is an oxygen element, and N is a nitrogen element; the mesoporous rare earth phosphate includes one of mesoporous cerium phosphate, mesoporous yttrium phosphate and mesoporous lanthanum phosphate.

9. A positive electrode current collector pre-treatment coating according to claim 3, wherein, The anchoring group comprises one of -NR2, -NR 3+ -COOH, -COO-, -SO3H-, -SO3-, -PO4, -OH, -SH, a polyamine, a polyol, a polyether.

10. The positive electrode current collector pre-treatment coating of claim 1, wherein, The siloxane is propyl triacetoxy silane.

11. The positive electrode current collector pre-treatment coating of claim 1, wherein, The mesoporous phosphate is mesoporous zirconium magnesium phosphate.

12. The positive electrode current collector pre-treatment coating of claim 1, wherein, The mesoporous lithium iron phosphate composite material is titanium doped mesoporous lithium iron phosphate.

13. The positive electrode current collector pre-treatment coating of claim 1, wherein, The mesoporous zirconium sodium phosphate and mesoporous zirconium magnesium phosphate are NaZr2P3O 12 and MgZr4P6O 24 respectively.

14. The positive electrode current collector pre-treatment coating of claim 1, wherein, The raw materials of the siloxane surface grafting modified mesoporous phosphate comprise siloxane and mesoporous phosphate, and the ratio of the siloxane and the mesoporous phosphate is (3-8 parts):100 parts by mass.

15. The positive electrode current collector pre-treatment coating of claim 1, wherein, The siloxane is propyl triacetoxy silane, and the mesoporous phosphate is titanium doped mesoporous lithium iron phosphate, and the ratio of the propyl triacetoxy silane and the titanium doped mesoporous lithium iron phosphate is (4-8 parts):100 parts by mass.

16. The positive electrode current collector pre-treatment coating of claim 1, wherein, The siloxane is propyl triacetoxy silane, and the mesoporous phosphate is mesoporous zirconium magnesium phosphate, and the ratio of the propyl triacetoxy silane and the mesoporous zirconium magnesium phosphate is (7-8 parts):100 parts by mass.

17. The positive electrode current collector pre-treatment coating of claim 1, wherein, The dispersant is a carboxyl grafted polyacrylic acid block copolymer; the thickening agent is sodium carboxymethyl cellulose; and the surfactant comprises sodium dodecyl benzene sulfonate and polyethylene glycol.

18. A method of making a positive current collector pre-treatment coating according to any one of claims 1 to 17, The method comprises the following steps: S1: adding water, conductive material, dispersant and thickening agent in a mass ratio, mixing uniformly, then dispersing to obtain a mixed slurry as a first slurry; S2: adding the first slurry, binder and surfactant in a mass ratio, mixing uniformly, then dispersing to obtain a second slurry; S2: adding siloxane surface grafting modified mesoporous phosphate, water and surfactant according to mass ratio, mixing uniformly to obtain mixed slurry, as second slurry; S3: adding first slurry, second slurry and binder according to mass ratio, mixing uniformly to obtain mixed slurry; S4: coating the mixed slurry on the surface of the positive electrode current collector foil and drying to obtain a pretreatment coating.

19. The method of claim 18, wherein, The preparation method of the siloxane surface grafting modified mesoporous phosphate comprises taking siloxane and mesoporous phosphate according to mass ratio, and mixing uniformly in water as medium.

20. The method of claim 18, wherein, The rotation speed for mixing uniformly is 100 rpm-2000 rpm, and the mixing uniformly time is 30 min-180 min.

21. The method of claim 18, wherein, The rotation speed for mixing uniformly in S1 is 2000 r / min-5000 r / min, and the mixing uniformly time is 5 min-60 min; the rotation speed for dispersing is 8000 r / min-15000 r / min, and the dispersing time is 10 min-90 min; the rotation speed for mixing uniformly in S2 is 1000 r / min-3000 r / min, and the mixing uniformly time is 30 min-120 min; the rotation speed for mixing uniformly in S3 is 200 r / min-1500 r / min, and the mixing uniformly time is 10 min-30 min; by mass, the first slurry:second slurry:binder is (50-90 parts):(5-40 parts):(3-10 parts); the coating mode in S4 is one of roll coating, spin coating, spraying, brushing and electrospinning, the coating thickness is 2 μm-20 μm, the drying is in vacuum environment, and the drying temperature is 50℃-150℃.

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