CN114628808B

CN114628808B - Method for stripping coating layer on metal substrate and application thereof

Info

Publication number: CN114628808B
Application number: CN202111552934.2A
Authority: CN
Inventors: 孙永明; 陈子和; 陆荣华; 赵建智; 聂瑞超; 冯睿康
Original assignee: Wuhan Weineng Battery Assets Co ltd; Huazhong University of Science and Technology
Current assignee: Wuhan Weineng Battery Assets Co ltd; Huazhong University of Science and Technology
Priority date: 2021-12-17
Filing date: 2021-12-17
Publication date: 2022-12-02
Anticipated expiration: 2041-12-17
Also published as: WO2023109096A1; CN114628808A

Abstract

The invention belongs to the field of coating stripping, and particularly relates to a method for stripping a coating layer on a metal substrate and application thereof. The metal substrate and the coating layer material can be obtained by soaking the metal substrate in an acid solution for acid treatment to ensure that the interface bonding between the metal substrate and the coating layer fails and then stripping, wherein the acid solution comprises a chelating agent. The invention damages the surface of the metal substrate in an acid environment, so that the bonding between the metal and the coating layer fails; meanwhile, at the moment that the interface of the metal substrate and the coating layer is damaged, the chelating agent can chelate dissolved metal ions, and a compact passivation layer is formed on the metal surface, so that the continuous dissolution of the metal substrate can be avoided, and the efficient separation of the metal substrate and the coating layer can be realized.

Description

Method for stripping coating layer on metal substrate and application thereof

Technical Field

The invention belongs to the field of coating stripping, and particularly relates to a method for stripping a coating layer on a metal substrate and application thereof.

Background

Other materials coated on a metal substrate are widely applied to various fields, such as a lithium battery process, and an active substance and a conductive agent are bonded and uniformly coated on an aluminum/copper foil through a bonding agent so as to achieve stable output of battery energy; in the metal corrosion prevention field, the purpose of metal corrosion prevention is achieved by coating polyurethane, fluororesin and organic silicon; in the field of metal high temperature resistance, the aim of metal high temperature resistance is fulfilled through the epoxy resin and the liquid rubber coating; in the field of metal insulation, the purpose of metal insulation is achieved through a water-based insulating paint coating and an insulating ceramic coating.

However, in the using process, the coating layer positioned on the outer surface has limited service life, for example, the performance of the electrode material is degraded along with the increase of the using times of the battery, and the service life of the whole firmware is reduced due to inevitable friction and scratch of the anti-corrosion coating, the high-temperature resistant coating and the insulating coating positioned on the outer surface of the metal, so that the coating layer reaching the service life is stripped and then efficiently recycled, which becomes a key step for secondary utilization on the premise of environmental protection.

CN107464963 discloses a method for breaking a pole piece and then dropping a coating layer from the pole piece by organic solvents such as styrene, acetone, tetrachloroethylene, etc., which utilizes an organic reagent with high solubility to a binder to dissolve the binder, so as to make active substances and conductive carbon black fall off freely.

CN107706481A discloses a method for solid phase recovery of lithium battery positive electrode material based on hollow microsphere, wherein the separation process is: and soaking the lithium ion battery pole piece in alkali liquor for 10-13 hours to dissolve the copper/aluminum current collector so as to obtain filter residue containing the electrode material. The method can effectively separate the electrode material, but like directly dissolving copper/aluminum foil by acid, completely dissolved aluminum ions in the solution can be adsorbed by conductive carbon black in the electrode material, so that the aluminum ions are difficult to remove in the electrode material recovery stage, and the batch consistency of the material is reduced.

CN112442296A discloses a composition and method for removing coatings from surfaces with stripping compositions containing ethers, esters, amines, alcohols and glycosides. However, the method of relaxing or dissolving the coating by a solvent has certain limitations and is highly susceptible to peeling residue due to differences in the bonding strength/corrosion of the coating to the substrate material, as described in the patent, within 10% of the material is difficult to peel even under the preferred conditions. CN113522596A discloses a closed spraying hanger coating physical remover, which realizes the dropping/peeling of a coating layer by continuously colliding metal materials coated with the coating layer, obviously, a physical violent scraping method can avoid pollution to some extent, but has great challenges in avoiding damage to a metal substrate and the coating layer materials and improving peeling efficiency.

CN111313120A discloses a method for recovering cobalt and lithium metals from waste lithium ion batteries, which comprises the following steps: disassembling the waste lithium ion battery to obtain a positive plate; cutting the positive plate into small pieces, soaking the small pieces into a separation liquid, placing the separation liquid soaked with the positive plate in an ultrasonic environment for a period of time, and taking out an aluminum foil to obtain a mixed liquid; carrying out rotary evaporation on the mixed solution to obtain a solid substance, and drying the solid substance to obtain a lithium ion battery anode material; mixing a positive electrode material with a chelating agent, and then performing mechanical activation treatment to obtain an activated mixture; and performing acid leaching treatment on the obtained activated mixture to obtain enrichment liquid containing cobalt and lithium. Although the technical scheme uses the chelating agent for treatment, different elements are respectively recovered by precipitation after ions are leached, but the separation of the metal substrate and the coating layer is not promoted.

In view of the foregoing, the prior art still lacks a method for efficiently separating a metal substrate and a coating layer.

Disclosure of Invention

Aiming at the defects or the improvement requirements of the prior art, the invention provides a method for stripping a coating layer on a metal substrate, which utilizes a chelating agent to form a passivation layer on the surface of a current collector while the interface of the metal substrate and the coating layer is damaged in an acidic environment, thereby realizing the efficient separation of an electrode material layer and avoiding the continuous dissolution of the metal substrate. The method has the advantages of reasonable design, easy implementation, environmental protection and low cost, can be applied to modern industrial production, and has extremely high economic benefit and social benefit.

In order to achieve the above objects, according to one aspect of the present invention, there is provided a method for peeling off a coating layer on a metal substrate, comprising immersing the metal substrate in an acid solution to perform an acid treatment, thereby causing interfacial adhesion failure between the metal substrate and the coating layer, and then peeling off the metal substrate and the coating layer, wherein the acid solution comprises a chelating agent.

Preferably, the chelating agent contains 2 or more polydentate ligands, and the functional groups of the polydentate ligands include-H ₂ PO ₄ 、-H ₂ PO ₃ 、-Na ₂ PO ₄ 、-K ₂ PO ₄ 、-Na ₂ PO ₃ One or more of, -COONa, -COOH, -SH and-SK.

Preferably, the chelating agent contains 4 or more polydentate ligands, and the functional group of the polydentate ligand is-H ₂ PO ₄ 、-H ₂ PO ₃ -COOH and-SH.

Preferably, the chelating agent includes at least one of phytic acid, hydroxyethylidene-1, 1-diphosphonic acid (HEDP), sodium Ethylene Diamine Tetra Methylene Phosphonate (EDTMPS), ethylene Diamine Tetraacetic Acid (EDTA), aminotrimethylene phosphonic Acid (ATMP), diethylenetriamine pentamethylene phosphonic acid (BNHMTPMP), triethylenetetramine hexamethylene phosphonic acid (tethmmp), bis (1, 6-hexylene) triamine pentamethylene phosphonic acid (BNHMTPMP), polyamino polyether tetramethylene Phosphonic Acid (PAPEMP), dimercaptopropanol, sodium gluconate, and sodium phytate.

Preferably, the mass ratio of the chelating agent in the acid solution is more than 10%; preferably, the chelating agent content is 20-75%.

Preferably, the pH of the acid solution is less than or equal to 5.

Preferably, the solvent in the acid solution comprises at least one of water, methanol, ethanol, ethylene glycol, acetone, dimethyl sulfoxide, ethylenediamine, N-dimethylformamide, dimethylacetamide and triethyl phosphate.

Preferably, the acid solution is an aqueous solution of phytic acid.

According to another aspect of the invention, the application of the method for stripping the coating on the metal substrate is provided, and the application comprises stripping of a current collector and an electrode material in a retired lithium battery pole piece, stripping of a metal polymer coating, stripping of a metal insulating coating or stripping of a metal corrosion-resistant layer.

Preferably, the stripping of the current collector and the electrode material in the pole piece of the retired lithium battery in the application comprises the following steps:

(1) Disassembling a retired lithium battery into a retired electrode plate, wherein the retired electrode plate comprises a current collector and an electrode material layer coated on the current collector;

(2) Soaking the retired electrode plate in an acid solution for acid treatment, so that the bonding of the electrode material layer and the current collector fails;

(3) Separating the electrode plate after acid treatment to obtain active substances and a current collector;

preferably, the compacted density of the electrode material layer is 1.0-4.0g/cm ³ The composition comprises an active substance, a binder and a conductive agent;

preferably, the active substance comprises one of a ternary nickel cobalt manganese material, a ternary nickel cobalt aluminum material, a lithium iron phosphate material, a lithium cobaltate material, a lithium manganate material, a lithium nickel manganate material, a lithium titanate material, a titanium niobate material, a silicon-based material and graphite;

preferably, the conductive agent includes one of conductive carbon black, conductive graphite, super pli, ketjen black, and carbon nanotubes;

preferably, the binder comprises polyvinylidene fluoride (PVDF), styrene Butadiene Rubber (SBR), carboxymethyl cellulose (CMC), polyacrylic acid (PAA), polyacrylonitrile (PAN), polyvinyl alcohol (PVA), lithiated polyvinyl alcohol (Li-PVA);

preferably, the current collector is an aluminum current collector or a copper current collector.

The Super P Li conductive carbon black is carbon black with high porosity, can form a network structure of the carbon black under a very low addition amount, and endows the product with excellent conductivity.

The invention has the following beneficial effects:

(1) The invention destroys the surface of the metal substrate in acid environment, and the chelating agent can passivate the metal substrate while the hydrogen ions dissolve the metal, and can continuously drive the unexposed metal protected by the coating layer to continuously react with the hydrogen ions to destroy the bonding action between the coating layer and the metal material, so that the bonding between the metal substrate and the coating layer is finally failed, and meanwhile, the chelating agent can protect the dissolved metal ions, thereby avoiding the continuous dissolution of the metal substrate and finally realizing high-efficiency separation and high-quality extraction.

(2) The invention can complete the separation of the electrode material layer in a short time, can realize the high-efficiency separation of the metal substrate and the coating layer, and has more obvious advantages particularly in the stripping process of the retired lithium battery pole piece, namely the good stripping effect is hardly influenced by the compaction density of the pole piece, and the latitude is higher.

(3) According to the method, the interface of the metal substrate and the coating layer is damaged by the acidic solution, and simultaneously, the chelating agent chelates dissolved metal ions to form a compact passivation film on the surface of the metal substrate, so that the continuous dissolution of the metal substrate is avoided, and the result of an inductively coupled plasma generator (ICP) test shows that the content of impurity metal ions in the solution after stripping is at least 0.000%, so that the method effectively avoids the generation of impurity metal elements in the stripping process, greatly improves the purity of the separated product, and effectively omits the subsequent complex purification process.

Drawings

FIG. 1 is a graph showing a compacted density of 3.8g/cm in example 1 ³ LiNi (R) in decommissioning _0.5 Co _0.2 Mn _0.3 O ₂ A separation effect diagram of the positive pole piece;

FIG. 2 is a graph showing a compacted density of 2.2g/cm in example 2 ³ And stripping a real object image of the electrode material layer from the lithium titanate negative plate when the electrode material layer is not dried.

Fig. 3 is a physical diagram of the aluminum foil and the coating layer after direct drying in example 2.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the respective embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

Example 1

From retired single crystal LiNi _0.5 Co _0.2 Mn _0.3 O ₂ Separating a pole piece from the battery: the coating layer was composed of 4% PVDF, 4% conductive carbon black and 92% LiNi _0.5 Co _0.2 Mn _0.3 O ₂ Consisting of and bonded to an aluminum foil by PVDF, characterized by a compacted density of 3.8g/cm ³ . Soaking the product in 25 deg.C aqueous solution containing 75%, 50%, 35%, and 10% phytic acid for 60 s, stirring the solution at 60r/min, separating the coating layer and the current collector, washing with water, and drying at 60 deg.C for 1 hr to obtain the final product, with the separation results shown in Table 1.

Table 1 example 1 separation results table

Mass ratio of phytic acid	10％	35％	50％	75％
					Length of peeling	30 minutes and 17 seconds	15 minutes and 22 seconds	7 minutes and 20 seconds	5 minutes and 18 seconds
Aluminum content in solution	0.000％	0.000％	0.006％	0.012％
					Peeling rate of coating layer	98.65％	99.73％	99.98％	99.98％
Current collector peeling rate	100％	100％	99.99％	99.97％

As can be seen from Table 1, the retired single crystal LiNi _0.5 Co _0.2 Mn _0.3 O ₂ The stripping time of the pole piece coating and the aluminum metal is shortened along with the increase of the acidity (phytic acid content) of the solution, when the phytic acid content is 75wt%, the stripping of 99.98% of the coating is realized only in 5 minutes and 18 seconds, but the aluminum metal is slightly dissolved out due to the low acidity, and the industrial application requirements are met. In general, 35% of phytic acid has ideal separation effect.

FIG. 1 is a diagram of a retired LiNi in example 1 _0.5 Co _0.2 Mn _0.3 O ₂ And (5) a separation effect diagram of the positive pole piece.

As can be seen from FIG. 1, a retired single crystal LiNi _0.5 Co _0.2 Mn _0.3 O ₂ The positive pole piece is soaked in the aqueous solution with the phytic acid content of 75 percent for 5 minutes and 18 seconds to finish 99.97 percent of aluminum foil and 99.98 percent of coatingThe coating peels off, and both maintain a good integrity after drying.

The surface of the aluminum foil is smooth and clean, the electrode material layer is successfully stripped in a large sheet shape, and the stripping rate is 99.98%. The Al content in the electrode material layer is only 0.012 percent through the test of an inductively coupled plasma spectrum generator.

Example 2

Disassembling the retired lithium iron phosphate battery, and separating out the lithium iron phosphate battery with the compaction density of 2.2g/cm ³ The lithium titanate negative electrode sheet of (1) was immersed in a water/ethanol mixed solution (v/v = 1) of hydroxyethylidene-1, 1-diphosphonic acid (HEDP), polyaminopolyether tetramethylene phosphonic acid (papamp), bis (1, 6-hexylene) triamine pentamethylene phosphonic acid (BNHMTPMP) having a content of 50% at 25 ℃, ph was adjusted to 1.0 using sulfuric acid, and then the solution was stirred at room temperature for 2 minutes at 100r/min, and the peeled current collector and electrode material layer were respectively washed with water and dried at 80 ℃ for 1 hour to obtain a product, and the results are shown in table 2 below.

Table 2 example 2 separation results table

The HEDP, PAPEMP, BNHMTPMP and phytic acid molecules have 2, 4, 5 and 6 chelating ligands respectively, and as can be seen from table 2, when the retired lithium iron phosphate pole piece is immersed in different chelating acid solutions with a pH of 1.0, the number of chelating ligands is small, the chelating ability is poor, more metal ions are dissolved in the solution, but the stripping rate is faster. Of course, even the less effective HEDP still has a certain peeling effect.

FIG. 2 is a graph showing a compacted density of 2.2g/cm in example 2 ³ And stripping a real object image of the electrode material layer from the lithium titanate negative plate when the electrode material layer is not dried. The undried electrode material layer is peeled off after stirring, the electrode material layer has better integrity, and the mechanical strength of the electrode material layer is not broken when the electrode material layer is taken by tweezers. The electrode material layer which is not dried after being stripped from the retired pole piece has better integrity and mechanical strength.

FIG. 3 is a schematic representation of the aluminum foil and coating layer after drying without stirring in example 2. Due to bonding failure and volume shrinkage in the drying process, the dried electrode material layer can be naturally separated.

Example 3

The steel material using the polyurethane coating as the corrosion prevention coating was immersed in an aqueous solution of a mixture of hydrochloric acid and acetic acid at 10 ℃,20% ethylenediaminetetraacetic acid (EDTA), 20% sodium phytate, and 5% phytic acid, having pH values of 1.0, 1.5, and 2.0, respectively, and after the coating layer surface had significant wrinkles, the coating layer was rinsed with water and dried, and the peeling results after drying are shown in table 3 below.

Table 3 example 3 separation results table

As can be seen from tables 2 and 3, since the anticorrosive coating is dense, stripping of the anticorrosive coating requires a longer time than stripping of the coating layer in the electrode sheet, and a higher pH helps to shorten the separation time.

Comparative example 1

Decommissioned single crystal LiNi _0.5 Co _0.2 Mn _0.3 O ₂ Disassembling the battery, and separating out the battery with the compacted density of 3.8g/cm ³ The positive electrode sheet of (1) was immersed in a solution of N-methylpyrrolidone (NMP) at 25 ℃ for 1 hour, and then the solution was stirred at 60r/min, and no significant falling of the electrode material was observed.

Comparative example 2

Decommissioned single crystal LiNi _0.5 Co _0.2 Mn _0.3 O ₂ Disassembling the battery, and separating out the battery with the compacted density of 3.8g/cm ³ The positive electrode sheet of (1) was immersed in water at 25 ℃ for 1 hour, and then the solution was stirred at 60r/min, and no significant peeling of the electrode material was observed.

It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims

1. A method for stripping a coating layer on a metal substrate is characterized in that the metal substrate is soaked in an acid solution for acid treatment, so that the interface bonding between the metal substrate and the coating layer is failed, and then stripping is carried out, so that a material of the metal substrate and the coating layer can be obtained, wherein the acid solution comprises a chelating agent;

at least one of the chelating agents contains more than 4 polydentate ligands, and the functional groups of the polydentate ligands comprise-H ₂ PO ₄ 、-H ₂ PO ₃ 、-Na ₂ PO ₄ 、-K ₂ PO ₄ 、-Na ₂ PO ₃ One or more of, -COONa, -COOH, -SH and-SK.

2. The method of claim 1, wherein the chelating agent comprises at least one of phytic acid, hydroxyethylidene-1, 1-diphosphonic acid, sodium ethylene diamine tetra methylene phosphonate, ethylene diamine tetraacetic acid, aminotrimethylene phosphonic acid, diethylenetriamine pentamethylene phosphonic acid, triethylene tetramine hexamethylene phosphonic acid, bis (1, 6-hexamethylene) triamine pentamethylene phosphonic acid, polyaminopolyether tetramethylene phosphonic acid, dimercaptopropanol, sodium gluconate, and sodium phytate.

3. The method according to claim 1, wherein the chelating agent is present in the acid solution in an amount of 10% by mass or more.

4. The method of claim 3, wherein the chelating agent is present in an amount of 20 to 75%.

5. The method of claim 1, wherein the acid solution has a pH of 5 or less.

6. The method of claim 1, wherein the solvent in the acid solution comprises at least one of water, methanol, ethanol, ethylene glycol, acetone, dimethyl sulfoxide, ethylenediamine, N-dimethylformamide, dimethylacetamide, and triethyl phosphate.

7. The method according to claim 1, wherein the acid solution is an aqueous solution of phytic acid.

8. The application of the method for stripping the coating layer on the metal substrate according to any one of claims 1 to 7, wherein the application comprises stripping of a current collector and an electrode material in a retired lithium battery pole piece, stripping of a metal polymer coating, stripping of a metal insulating coating or stripping of a metal corrosion-resistant layer.

9. The application of claim 8, wherein the stripping of the current collector and the electrode material in the pole piece of the in-application retired lithium battery comprises the following steps:

(1) Disassembling a retired electrode pole piece from a retired lithium battery, wherein the retired electrode pole piece comprises a current collector and an electrode material layer coated on the current collector;

(3) And separating the electrode plate after acid treatment to obtain active substances and a current collector.

10. Use according to claim 9, wherein the compacted density of the electrode material layer is 1.0-4.0g/cm ³ The conductive paste comprises an active substance, a binder and a conductive agent.

11. The use of claim 10, wherein the active material comprises one of a ternary nickel cobalt manganese material, a ternary nickel cobalt aluminum material, a lithium iron phosphate material, a lithium cobaltate material, a lithium manganate material, a lithium nickel manganate material, a lithium titanate material, a titanium niobate material, a silicon-based material, and graphite.

12. The use according to claim 10, wherein the conductive agent comprises one of conductive carbon black, conductive graphite, super pli, ketjen black, and carbon nanotubes.

13. Use according to claim 10, wherein the binder comprises polyvinylidene fluoride, styrene butadiene rubber, carboxymethyl cellulose, polyacrylic acid, polyacrylonitrile, polyvinyl alcohol, lithiated polyvinyl alcohol.

14. The use according to claim 9, wherein the current collector is an aluminum current collector or a copper current collector.