A recovery method of lithium iron phosphate cathode material and lithium iron phosphate cathode material

Abstract

The application discloses a recycling method of lithium iron phosphate positive electrode material and the lithium iron phosphate positive electrode material, and belongs to the technical field of lithium batteries. The lithium iron phosphate positive electrode material comprises a positive electrode active material, a conductive agent and a binder. The binder is obtained by blending a furfuryl alcohol resin and an aldehyde-based crosslinking agent after a free radical graft polymerization reaction of polyvinyl alcohol and an unsaturated carboxylic acid. The binder is crosslinked during the drying process of the lithium iron phosphate positive electrode material. The positive electrode active material, the conductive agent and the binder are ground with water to obtain a positive electrode slurry. The lithium iron phosphate positive electrode material is obtained through coating, vacuum drying, tabletting, slicing and vacuum drying. The binder can improve the performance of the lithium iron phosphate positive electrode material. The binder has better solubility than polyvinylidene fluoride. Alcohol solvents can penetrate into the crosslinked network, destroy the crosslinked part, dissolve the binder, and do not need to use strong acid and strong alkali solvents, thereby being more environmentally friendly. The recycling residue does not contain fluorine elements and aluminum, and is beneficial to the recycling and treatment of waste batteries.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium batteries, and particularly relates to a recycling method of a lithium iron phosphate positive electrode material and the lithium iron phosphate positive electrode material. BACKGROUND

[0002] The lithium iron phosphate battery is a lithium ion battery using lithium iron phosphate (LiFePO4, LFP) as a positive electrode material and carbon as a negative electrode material, has the advantages of long cycle life, good safety performance, small self-discharge rate and no memory effect, and has been widely used. However, during the production process, especially during the process upgrading and improvement, there are inevitably defective products, which also brings a large amount of waste lithium iron phosphate battery materials, especially positive electrode materials, and causes resource waste. Therefore, it is of great significance to realize efficient recycling of waste lithium iron phosphate batteries, to change waste into treasure, and to realize resource utilization, so as to reduce environmental pollution and alleviate resource shortage.

[0003] The lithium iron phosphate positive electrode material includes active material, conductive agent, binder and current collector. Polyvinylidene fluoride (PVDF) is often used as the binder of the lithium iron phosphate positive electrode material. Although PVDF has good chemical stability, heat resistance and bonding performance, the price of PVDF is relatively high, and the price fluctuates greatly with the increase of market demand. The raw materials used in the production process of PVDF can destroy the ozone layer, and its solvent NMP (N-methyl pyrrolidone) is toxic and has certain destructiveness to the environment. PVDF has high hardness and relatively poor flexibility, which may limit its use in some application fields. PVDF is difficult to separate from other components in the lithium iron phosphate positive electrode material, which increases the complexity and cost of recycling. Water-based binder is an environmentally friendly binder using water as the solvent, which has the advantages of low cost and good environmental protection. In the recycling process, it can be separated from the positive electrode material by simple water washing or mild chemical treatment, which reduces the recycling cost and complexity, but the water-based binder also has some disadvantages, such as it may need higher temperature and longer time in the drying process, which increases the energy consumption. In addition, the water-based binder may not provide the same level of mechanical strength and chemical stability as PVDF in some cases. SUMMARY

[0004] The purpose of the present application is to provide a recycling method of a lithium iron phosphate positive electrode material and the lithium iron phosphate positive electrode material, so as to solve the problems of poor separation effect and easy introduction of new impurities in the lithium iron phosphate positive electrode material using PVDF as the binder.

[0005] The purpose of the present application can be achieved by the following technical solutions:

[0006] The first aspect of the application provides a lithium iron phosphate positive electrode material, comprising a positive electrode active material, a conductive agent, and a binder, wherein the binder is obtained by blending a polyvinyl alcohol carboxylic acid copolymer and a furfuryl alcohol resin, and an aldehyde-based crosslinking agent, the polyvinyl alcohol carboxylic acid copolymer is a product of a free radical graft polymerization reaction between polyvinyl alcohol and an unsaturated carboxylic acid, and the binder is crosslinked during the drying process of the lithium iron phosphate positive electrode material at a drying temperature of 65-70℃.

[0007] In a possible implementation, the furfuryl alcohol resin is prepared by the following steps:

[0008] After mixing the furfuryl alcohol and water, the mixture is stirred and dispersed by heating to 60-65℃, an acidic catalyst is added, and the mixture is reacted by heating to 70-75℃ for 3-4h, then ammonia is added for neutralization after the reaction, and the furfuryl alcohol resin is obtained after drying, wherein the ratio of furfuryl alcohol to water is 70g:30mL, and the acidic catalyst is used to adjust the pH value of the system to 2-3.

[0009] In a possible implementation, the acidic catalyst is one of sulfuric acid, oxalic acid, and hydrochloric acid.

[0010] In a possible implementation, the free radical graft polymerization reaction includes the following steps: mixing polyvinyl alcohol and water, then adding sodium persulfate and sodium bisulfite as initiators, heating to 60-65℃, adding unsaturated carboxylic acid, and keeping the temperature unchanged while continuing to stir for 2-3h to obtain the polyvinyl alcohol carboxylic acid copolymer.

[0011] In a possible implementation, the mass ratio of polyvinyl alcohol to unsaturated carboxylic acid is 1:1, the amount ratio of polyvinyl alcohol to water is 1g:25mL, the molar ratio of persulfate to sodium bisulfite is 3:5, and the total amount of the initiator added is 0.15%-0.20% of the mass of the unsaturated carboxylic acid.

[0012] In a possible implementation, the unsaturated carboxylic acid is one of acrylic acid, methacrylic acid, and maleic acid.

[0013] In a possible implementation, the aldehyde-based crosslinking agent is at least one of glutaraldehyde, butanedial, and adipaldehyde.

[0014] In a possible implementation, the mass ratio of the polyvinyl alcohol carboxylic acid copolymer, the furfuryl alcohol resin, and the aldehyde-based crosslinking agent is 1:0.8-1:0.14-0.16.

[0015] In a possible implementation, the mass ratio of lithium iron phosphate, the conductive agent, and the binder is 80-90:5-15:5.

[0016] The lithium iron phosphate positive electrode material is prepared by the following steps:

[0017] Step S1, adding positive electrode active material, conductive agent and binder into a mortar, adding water to grind, to obtain a positive electrode slurry;

[0018] Step S2, coating: coating the positive electrode slurry on the aluminum foil with a coater.

[0019] Step S3, drying: drying the coated electrode sheet at 65-70℃ in vacuum for 1.5-2h.

[0020] Step S4, sheet pressing: pressing the dried electrode sheet on a hydraulic press to obtain a smooth surface electrode sheet.

[0021] Step S5, sheet cutting.

[0022] Step S6, vacuum drying: drying the cut electrode sheet at 100℃ in vacuum for 20-24h, and the loading amount of the positive electrode active material of the electrode sheet is 3-4mg / cm 2 .

[0023] The second aspect of the application provides a recycling method of lithium iron phosphate positive electrode material, comprising the following steps:

[0024] The positive electrode sheet is soaked in an alcohol solvent to separate the positive electrode active material from the aluminum foil, to obtain a waste lithium iron phosphate positive electrode material; the waste lithium iron phosphate positive electrode material is calcined under a protective atmosphere; the calcination temperature is 500-700℃;

[0025] After calcination, phosphoric acid is added as a leaching agent, and a reducing acid is used for leaching, to obtain a filtrate of Li + , Fe 2+ and PO4 3- ; ammonia water is added to adjust the pH of the system to 10-12, and then filtered and dried to obtain lithium iron phosphate recycling material.

[0026] In possible embodiments, the reducing acid is at least one of citric acid and ascorbic acid;

[0027] The alcohol solvent is at least one of ethanol, methanol and ethylene glycol.

[0028] The beneficial effects of the application are:

[0029] The application provides a lithium iron phosphate positive electrode material, which comprises a positive electrode active material, a conductive agent and a binder, wherein the binder is obtained by blending polyvinyl alcohol carboxylic acid copolymer, furfuryl alcohol resin and aldehyde-based crosslinking agent, and the polyvinyl alcohol carboxylic acid copolymer is obtained by free radical graft polymerization of polyvinyl alcohol and unsaturated carboxylic acid. The performance of the lithium iron phosphate positive electrode material can be significantly improved by using the binder in the application. Compared with traditional polyvinylidene fluoride (PVDF), the binder has better solubility. The alcohol solvent can effectively penetrate the crosslinked network, destroy the crosslinked structure and promote the dissolution of the binder. Therefore, the binder can be separated from the aluminum foil without the help of strong acid or strong base, no additional impurities are introduced in the recycling process, and the recycling residue does not contain fluorine element and aluminum, which greatly facilitates the recycling of waste batteries.

[0030] The binder has excellent solubility and recyclability, and can significantly enhance the electrochemical performance of the lithium iron phosphate positive electrode material, especially the discharge specific capacity. By accurately controlling the amount of furfuryl alcohol resin and crosslinking agent, the performance of the binder can be further optimized to meet the harsh requirements of high-performance lithium ion batteries. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the application will be clearly and completely described below with reference to the embodiments of the application. Obviously, the described embodiments are only some of the embodiments of the application, rather than all the embodiments. Based on the embodiments of the application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of the application.

[0032] Obviously, the following description is only some examples or embodiments of the application, and for those skilled in the art, the application can be applied to other similar situations without creative labor. In addition, it can be understood that although the efforts made in this development process may be complex and lengthy, for those skilled in the art related to the content disclosed in the application, some design, manufacture or production changes based on the technical content disclosed in the application are only routine technical means, and should not be understood as insufficient disclosure of the content disclosed in the application.

[0033] However, there may be cases of omitting unnecessary detailed description. For example, there are cases of omitting detailed description of well-known matters, repeated description of practically identical structures. This is to avoid the following description from becoming unnecessarily long, facilitating understanding by those skilled in the art. In addition, the following description is provided to enable those skilled in the art to fully understand the application, and is not intended to limit the subject matter recited in the claims.

[0034] If there is no special description, all the embodiments and optional embodiments of the present application can be combined to form new technical solutions, and all the technical features and optional technical features of the present application can be combined to form new technical solutions.

[0035] Generally, the positive material of lithium iron phosphate battery mainly includes: lithium iron phosphate, conductive carbon black and polyvinylidene fluoride (as a binder). The main thing that needs to be recovered is the lithium iron phosphate therein.

[0036] The following is a detailed description of the recovery method of the lithium iron phosphate positive material and the lithium iron phosphate positive material of the embodiment of the present application.

[0037] The first aspect of the embodiment of the present application provides a lithium iron phosphate positive material, which comprises a positive active material, a conductive agent and a binder. The binder is obtained by blending a radical grafting polymerization reaction product of polyvinyl alcohol and an unsaturated carboxylic acid with furfuryl alcohol resin and aldehyde-based crosslinking agent. The crosslinking temperature of the binder is the same as the drying temperature, and the binder is crosslinked during the drying process of the lithium iron phosphate positive material, thereby having good bonding performance. The binder of the present application can improve the performance of the lithium iron phosphate positive material. The self-made binder is obtained by blending a radical grafting polymerization reaction product of polyvinyl alcohol and an unsaturated carboxylic acid with furfuryl alcohol resin and aldehyde-based crosslinking agent. The binder has better solubility than polyvinylidene fluoride. Alcohol solvents can penetrate into the crosslinked network to destroy the crosslinked part, so that the binder can be dissolved. Therefore, the binder can be peeled off from the aluminum foil without adding strong acid or strong base solvents, and new impurities are not introduced during the recovery process. In addition, the recovery residue does not contain fluorine element and aluminum, which is beneficial to the recovery and treatment of waste batteries.

[0038] In some specific embodiments, the furfuryl alcohol resin is prepared by the following steps:

[0039] After mixing furfuryl alcohol and water, the mixture is stirred and dispersed by heating to 60-65℃. An acidic catalyst is added, and the mixture is reacted by heating to 70-75℃ for 3-4h. After the reaction is completed, the mixture is neutralized by adding ammonia water, and then dried to obtain the furfuryl alcohol resin. In this process, the ratio of furfuryl alcohol to water is 70g:30mL, and the pH value of the system is adjusted to 2-3 by the acidic catalyst.

[0040] The furfuryl alcohol resin is formed by condensation of furfuryl alcohol, has an alternating carbon-carbon double bond structure, forms a conjugated electron cloud to provide a path for electron transfer, can form a more effective electron transport network, reduces the transmission resistance of electrons in the electrode, maintains the structural integrity of the electrode, prevents the active material from falling off or gathering due to volume change during high-rate discharge, and further improves the discharge specific capacity of the battery.

[0041] In some specific embodiments, the acidic catalyst is one of sulfuric acid, oxalic acid and hydrochloric acid.

[0042] In some specific embodiments, the free radical graft polymerization reaction comprises the following steps:

[0043] The polyvinyl alcohol and water are mixed, then sodium persulfate and sodium bisulfite are added as initiators, the temperature is raised to 60-65℃, the unsaturated carboxylic acid is added, the temperature is kept constant and the reaction is continued for 2-3h, to obtain a polyvinyl alcohol carboxylic acid copolymer. The mass ratio of polyvinyl alcohol and unsaturated carboxylic acid is 1:1; the amount ratio of polyvinyl alcohol and water is 1g:25mL. The molar ratio of persulfate to sodium bisulfite is 3:5; the total amount of initiator added is 0.15%-0.20% of the mass of the unsaturated carboxylic acid.

[0044] In some specific embodiments, the unsaturated carboxylic acid is one of acrylic acid, methacrylic acid and maleic acid. Among them, acrylic acid has relatively low price, wide source, high economy and operability.

[0045] In some specific embodiments, the aldehyde-based crosslinking agent is at least one of glutaraldehyde, butanedial and adipaldehyde;

[0046] The conductive agent is at least one of conductive carbon black (such as SuperP, acetylene black), carbon nanotube and graphene.

[0047] In some specific embodiments, the mass ratio of lithium iron phosphate, conductive agent and binder is 80-90:5-15:5.

[0048] In some specific embodiments, the mass ratio of polyvinyl alcohol carboxylic acid copolymer, furfuryl alcohol resin and aldehyde-based crosslinking agent is 1:0.8-1:0.14-0.16. The amount of aldehyde-based crosslinking agent added is 8% of the total mass of polyvinyl alcohol carboxylic acid copolymer and furfuryl alcohol resin.

[0049] The lithium iron phosphate positive electrode material is prepared by the following steps:

[0050] Step S1, adding the positive electrode active material, conductive agent and binder into a mortar, adding an appropriate amount of water for grinding, to obtain a positive electrode slurry;

[0051] Step S2, coating: using a coater to coat the positive electrode slurry on an aluminum foil;

[0052] Step S3, drying: drying the coated electrode piece at 65-70℃ in a vacuum for 1.5-2h;

[0053] Step S4, tabletting: tabletting the dried electrode piece on a hydraulic press to obtain a smooth-surfaced electrode piece;

[0054] Step S5, slicing;

[0055] Step S6, vacuum drying: the cut polar piece is vacuum dried in a vacuum drying oven at 100℃ for 20-24h, and the loading of the positive active material of the polar piece is 3-4mg / cm 2 .

[0056] The second aspect of the embodiment of the present application provides a recycling method of a lithium iron phosphate positive electrode material, comprising the following steps:

[0057] The positive electrode piece is soaked in an alcohol solvent to separate the positive active material from the aluminum foil, thereby obtaining a waste lithium iron phosphate positive electrode material; the waste lithium iron phosphate positive electrode material is calcined under a protective atmosphere; the calcination temperature is 500-700℃;

[0058] After calcination, phosphoric acid is added as a leaching agent, and a reducing acid is used for leaching, thereby obtaining a filtrate of Li + , Fe 2+ and PO4 3- ; ammonia water is added to adjust the pH of the system to 10-12, and then filtration and drying are performed to obtain a lithium iron phosphate recycled material.

[0059] In some specific embodiments, the reducing acid is at least one of citric acid and ascorbic acid.

[0060] In some specific embodiments, the alcohol solvent is at least one of ethanol, methanol and ethylene glycol.

[0061] The following will be specifically described with examples.

[0062] Example 1

[0063] The embodiment provides a lithium iron phosphate positive electrode material, which is prepared by the following steps:

[0064] Raw material preparation: polyvinyl alcohol (Mw=88000g / mol) and water are mixed, then sodium persulfate and sodium bisulfite are added as initiators, the temperature is raised to 60℃, unsaturated carboxylic acid is added, the temperature is kept unchanged, and the stirring reaction is continued for 2h to obtain a polyvinyl alcohol carboxylic acid copolymer. The mass ratio of polyvinyl alcohol to unsaturated carboxylic acid is 1:1; the amount ratio of polyvinyl alcohol to water is 1g:25mL. The molar ratio of persulfate to sodium bisulfite is 3:5; the total addition amount of the initiator is 0.15% of the mass of the unsaturated carboxylic acid. The unsaturated carboxylic acid is acrylic acid.

[0065] After the furfuryl alcohol and water are mixed, the temperature is raised to 60℃ for stirring and dispersion, an acidic catalyst is added, the temperature is raised to 70℃ for reaction for 3h, ammonia water is added for neutralization after the reaction is completed, and then drying is performed to obtain a furfuryl alcohol resin. The ratio of furfuryl alcohol to water is 70g:30mL, and the pH value of the system is adjusted to 3 by the acidic catalyst; the acidic catalyst is oxalic acid.

[0066] The polyvinyl alcohol carboxylic acid copolymer, furfuryl alcohol resin and aldehyde crosslinking agent are mixed to obtain the adhesive; the aldehyde crosslinking agent is glutaraldehyde. The mass ratio of the polyvinyl alcohol carboxylic acid copolymer, furfuryl alcohol resin and aldehyde crosslinking agent is 1:0.8:0.014.

[0067] Step S1, the positive electrode active material lithium iron phosphate, the conductive agent (carbon black (SuperP)) and the binder are added into a mortar, water is added for grinding to obtain a positive electrode slurry; the mass ratio of lithium iron phosphate, the conductive agent and the binder is 80:15:5.

[0068] Step S2, coating: the positive electrode slurry is coated on the aluminum foil by using a coater.

[0069] Step S3, drying: the coated electrode piece is dried in an oven at 65-70°C for 2h under vacuum.

[0070] Step S4, tabletting: the dried electrode piece is pressed on a hydraulic press to obtain a smooth-surfaced electrode piece.

[0071] Step S5, tabletting: the positive and negative electrode pieces are cut into circular electrode pieces with a diameter of 16mm by using a tabletting machine.

[0072] Step S6, vacuum drying: the cut electrode piece is vacuum dried in a vacuum drying box at 100°C for 24h, and the loading amount of the positive electrode active material of the electrode piece after drying is 3-4mg / cm 2 .

[0073] Example 2

[0074] The embodiment provides a lithium iron phosphate positive electrode material, which is prepared by the following steps:

[0075] Raw material preparation: polyvinyl alcohol (Mw=88000g / mol) and water are mixed, then sodium persulfate and sodium bisulfite are added as initiators, the temperature is raised to 60°C, unsaturated carboxylic acid is added, the temperature is kept unchanged, and the reaction is continuously stirred for 2h to obtain a polyvinyl alcohol carboxylic acid copolymer. The mass ratio of polyvinyl alcohol and unsaturated carboxylic acid is 1:1; the dosage ratio of polyvinyl alcohol and water is 1g:25mL. The molar ratio of persulfate to sodium bisulfite is 3:5; the total addition amount of the initiator is 0.15% of the mass of the unsaturated carboxylic acid. The unsaturated carboxylic acid is methacrylic acid.

[0076] After the furfuryl alcohol and water are mixed, the temperature is raised to 60°C for stirring and dispersion, an acidic catalyst is added, the temperature is raised to 70°C for reaction for 3h, ammonia is added for neutralization after the reaction is completed, and furfuryl alcohol resin is obtained after drying, wherein the ratio of furfuryl alcohol and water is 70g:30mL, and the pH value of the system is adjusted to 3 by using the acidic catalyst; the acidic catalyst is oxalic acid.

[0077] The polyvinyl alcohol carboxylic acid copolymer, furfuryl alcohol resin and aldehyde crosslinking agent are mixed to obtain the adhesive; the aldehyde crosslinking agent is glutaraldehyde. The mass ratio of the polyvinyl alcohol carboxylic acid copolymer, furfuryl alcohol resin and aldehyde crosslinking agent is 1:0.8:0.014.

[0078] The remaining raw materials and preparation process are the same as those in Example 1.

[0079] Example 3

[0080] The present example provides a lithium iron phosphate positive electrode material, which is prepared by the following steps:

[0081] Raw material preparation: polyvinyl alcohol (Mw=88000 g / mol) and water are mixed, then sodium persulfate and sodium bisulfite are added as initiators, the temperature is raised to 60°C, unsaturated carboxylic acid is added, the temperature is kept constant and the reaction is continued for 2h, to obtain a polyvinyl alcohol carboxylic acid copolymer. The mass ratio of polyvinyl alcohol and unsaturated carboxylic acid is 1:1; the amount ratio of polyvinyl alcohol and water is 1g:25mL. The molar ratio of persulfate to sodium bisulfite is 3:5; the total amount of initiator added is 0.15% of the mass of unsaturated carboxylic acid. The unsaturated carboxylic acid is maleic acid.

[0082] After mixing furfuryl alcohol and water, the temperature is raised to 60°C and stirred and dispersed, an acidic catalyst is added, the temperature is raised to 70°C and reacted for 3h, after the reaction is completed, ammonia is added for neutralization, and after drying, a furfuryl alcohol resin is obtained, wherein the ratio of furfuryl alcohol and water is 70g:30mL, and the acidic catalyst adjusts the pH value of the system to 3; the acidic catalyst is oxalic acid.

[0083] The polyvinyl alcohol carboxylic acid copolymer, furfuryl alcohol resin and aldehyde crosslinking agent are mixed to obtain the adhesive; the aldehyde crosslinking agent is glutaraldehyde. The mass ratio of the polyvinyl alcohol carboxylic acid copolymer, furfuryl alcohol resin and aldehyde crosslinking agent is 1:0.8:0.014.

[0084] The remaining raw materials and preparation process are the same as those in Example 1.

[0085] Example 4

[0086] The present example provides a lithium iron phosphate positive electrode material, which is prepared by the following steps:

[0087] Raw material preparation: polyvinyl alcohol (Mw=88000 g / mol) and water are mixed, then sodium persulfate and sodium bisulfite are added as initiators, the temperature is raised to 60°C, unsaturated carboxylic acid is added, the temperature is kept constant and the reaction is continued for 2h, to obtain a polyvinyl alcohol carboxylic acid copolymer. The mass ratio of polyvinyl alcohol and unsaturated carboxylic acid is 1:1; the amount ratio of polyvinyl alcohol and water is 1g:25mL. The molar ratio of persulfate to sodium bisulfite is 3:5; the total amount of initiator added is 0.15% of the mass of unsaturated carboxylic acid. The unsaturated carboxylic acid is maleic acid.

[0088] The furofuranol and water are mixed, heated to 60°C and stirred to disperse, an acidic catalyst is added, heated to 70°C and reacted for 3h, ammonia is added after the reaction to neutralize, and dried to obtain the furofuranol resin, wherein the ratio of the furofuranol and water is 70g:30mL, and the pH value of the system is adjusted to 2 by the acidic catalyst; the acidic catalyst is oxalic acid.

[0089] The polyvinyl alcohol carboxylic acid copolymer, the furofuranol resin and the aldehyde crosslinking agent are mixed to obtain the adhesive; the aldehyde crosslinking agent is glutaraldehyde. The mass ratio of the polyvinyl alcohol carboxylic acid copolymer, the furofuranol resin and the aldehyde crosslinking agent is 1:0.8:0.014.

[0090] The remaining raw materials and preparation process are the same as those in Example 1.

[0091] Example 5

[0092] The present embodiment provides a lithium iron phosphate positive electrode material, which is prepared by the following steps:

[0093] Raw material preparation: polyvinyl alcohol (Mw=88000g / mol) and water are mixed, then sodium persulfate and sodium bisulfite are added as initiators, heated to 60°C, and unsaturated carboxylic acid is added, the temperature is kept unchanged, and the stirring reaction is continued for 2h to obtain a polyvinyl alcohol carboxylic acid copolymer. The mass ratio of the polyvinyl alcohol and the unsaturated carboxylic acid is 1:1; the amount ratio of the polyvinyl alcohol and water is 1g:25mL. The molar ratio of the sodium persulfate to the sodium bisulfite is 3:5; the total amount of the initiator added is 0.15% of the mass of the unsaturated carboxylic acid. The unsaturated carboxylic acid is acrylic acid.

[0094] The furofuranol and water are mixed, heated to 60°C and stirred to disperse, an acidic catalyst is added, heated to 70°C and reacted for 3h, ammonia is added after the reaction to neutralize, and dried to obtain the furofuranol resin, wherein the ratio of the furofuranol and water is 70g:30mL, and the pH value of the system is adjusted to 3 by the acidic catalyst; the acidic catalyst is oxalic acid.

[0095] The polyvinyl alcohol carboxylic acid copolymer, the furofuranol resin and the aldehyde crosslinking agent are mixed to obtain the adhesive; the aldehyde crosslinking agent is glutaraldehyde. The mass ratio of the polyvinyl alcohol carboxylic acid copolymer, the furofuranol resin and the aldehyde crosslinking agent is 1:0.8:0.014.

[0096] The remaining raw materials and preparation process are the same as those in Example 1.

[0097] Example 6

[0098] The present embodiment provides a lithium iron phosphate positive electrode material, which is prepared by the following steps:

[0099] Raw material preparation: polyvinyl alcohol (Mw=88000 g / mol) and water were mixed, then sodium persulfate and sodium bisulfite were added as initiators, the temperature was raised to 60°C, unsaturated carboxylic acid was added, the temperature was kept constant and the reaction was continued to stir for 2h to obtain polyvinyl alcohol carboxylic acid copolymer. The mass ratio of polyvinyl alcohol and unsaturated carboxylic acid is 1:1; the amount ratio of polyvinyl alcohol and water is 1g:25mL. The molar ratio of persulfate to sodium bisulfite is 3:5; the total amount of initiator is 0.15% of the mass of unsaturated carboxylic acid. The unsaturated carboxylic acid is acrylic acid.

[0100] After mixing furfuryl alcohol and water, the temperature was raised to 60°C and stirred and dispersed, an acidic catalyst was added, the temperature was raised to 70°C and reacted for 3h, then ammonia was added to neutralize after the reaction was completed, and furfuryl alcohol resin was obtained after drying, wherein the ratio of furfuryl alcohol and water is 70g:30mL, the acidic catalyst adjusts the pH value of the system to 3; the acidic catalyst is oxalic acid.

[0101] The polyvinyl alcohol carboxylic acid copolymer, furfuryl alcohol resin and aldehyde crosslinking agent were mixed to obtain a binder; the aldehyde crosslinking agent was hexanedial. The mass ratio of polyvinyl alcohol carboxylic acid copolymer, furfuryl alcohol resin and aldehyde crosslinking agent is 1:0.8:0.014.

[0102] The remaining raw materials and preparation process are the same as in Example 1.

[0103] Example 7

[0104] This example provides a lithium iron phosphate positive electrode material, which is prepared by the following steps:

[0105] Raw material preparation: polyvinyl alcohol (Mw=88000 g / mol) and water were mixed, then sodium persulfate and sodium bisulfite were added as initiators, the temperature was raised to 60°C, unsaturated carboxylic acid was added, the temperature was kept constant and the reaction was continued to stir for 2h to obtain polyvinyl alcohol carboxylic acid copolymer. The mass ratio of polyvinyl alcohol and unsaturated carboxylic acid is 1:1; the amount ratio of polyvinyl alcohol and water is 1g:25mL. The molar ratio of persulfate to sodium bisulfite is 3:5; the total amount of initiator is 0.15% of the mass of unsaturated carboxylic acid. The unsaturated carboxylic acid is acrylic acid.

[0106] After mixing furfuryl alcohol and water, the temperature was raised to 60°C and stirred and dispersed, an acidic catalyst was added, the temperature was raised to 70°C and reacted for 3h, then ammonia was added to neutralize after the reaction was completed, and furfuryl alcohol resin was obtained after drying, wherein the ratio of furfuryl alcohol and water is 70g:30mL, the acidic catalyst adjusts the pH value of the system to 3; the acidic catalyst is oxalic acid.

[0107] The polyvinyl alcohol carboxylic acid copolymer, furfuryl alcohol resin and aldehyde crosslinking agent were mixed to obtain a binder; the aldehyde crosslinking agent was hexanedial. The mass ratio of polyvinyl alcohol carboxylic acid copolymer, furfuryl alcohol resin and aldehyde crosslinking agent is 1:0.8:0.014.

[0108] Step S1, the positive active lithium iron phosphate, conductive agent and binder are added into a mortar, water is added for grinding, and a positive electrode slurry is obtained; the mass ratio of lithium iron phosphate, conductive agent and binder is 80:5:5.

[0109] The remaining raw materials and preparation process are the same as those in Example 1.

[0110] Example 8

[0111] The present example provides a lithium iron phosphate positive electrode material, which is prepared by the following steps:

[0112] Raw material preparation: polyvinyl alcohol (Mw=88000 g / mol) and water are mixed, then sodium persulfate and sodium bisulfite are added as initiators, the temperature is raised to 60°C, unsaturated carboxylic acid is added, the temperature is kept constant and the reaction is continued for 2h with stirring, to obtain a polyvinyl alcohol carboxylic acid copolymer. The mass ratio of polyvinyl alcohol and unsaturated carboxylic acid is 1:1; the amount ratio of polyvinyl alcohol and water is 1g:25mL. The molar ratio of persulfate to sodium bisulfite is 3:5; the total amount of initiator added is 0.15% of the mass of unsaturated carboxylic acid. The unsaturated carboxylic acid is acrylic acid.

[0113] After mixing furfuryl alcohol and water, the temperature is raised to 60°C and stirred and dispersed, an acidic catalyst is added, the temperature is raised to 70°C and reacted for 3h, then ammonia is added for neutralization after the reaction is completed, and dried to obtain furfuryl alcohol resin. The ratio of furfuryl alcohol to water is 70g:30mL, and the pH value of the system is adjusted to 3 by an acidic catalyst; the acidic catalyst is oxalic acid.

[0114] The polyvinyl alcohol carboxylic acid copolymer, furfuryl alcohol resin and aldehyde-based crosslinking agent are mixed to obtain a binder; the aldehyde-based crosslinking agent is glutaraldehyde. The mass ratio of polyvinyl alcohol carboxylic acid copolymer, furfuryl alcohol resin and aldehyde-based crosslinking agent is 1:1:0.16.

[0115] Step S1, the positive active lithium iron phosphate, conductive agent and binder are added into a mortar, water is added for grinding, and a positive electrode slurry is obtained; the mass ratio of lithium iron phosphate, conductive agent and binder is 80:5:5.

[0116] The remaining raw materials and preparation process are the same as those in Example 1.

[0117] Comparative Example 1

[0118] The present example is compared with Example 1, the difference is that the mass ratio of polyvinyl alcohol carboxylic acid copolymer, furfuryl alcohol resin and aldehyde-based crosslinking agent is 1:0.2:0.1. The remaining raw materials and preparation process are the same as those in Example 1.

[0119] Comparative Example 2

[0120] The comparative example is compared with example 1, the difference is that no aldehyde crosslinking agent is added, and the rest of the raw materials and the preparation process are the same as example 1.

[0121] Comparative example 3

[0122] The comparative example is compared with example 1, the difference is that the mass ratio of polyvinyl alcohol carboxylic acid copolymer, furfuryl alcohol resin and aldehyde crosslinking agent is 1:2:0.24. The rest of the raw materials and the preparation process are the same as example 1.

[0123] Comparative example 4

[0124] The comparative example is compared with example 1, the difference is that the binder uses polytetrafluoroethylene, and the rest of the raw materials and the preparation process are the same as example 1.

[0125] The samples prepared in example 1 to example 8 and comparative example 1 to comparative example 4 are tested for performance;

[0126] Peeling test: 180° peeling test is carried out according to ASTM-D903 test standard, and the results are shown in table 1 as follows:

[0127] Table 1

[0128]

[0129] According to table 1, the lithium iron phosphate positive electrode material prepared in the application has high bonding strength and can be bonded on the surface of aluminum foil (current collector). The crosslinking temperature of the binder in the application is the same as the drying temperature, and crosslinking occurs during the drying process of lithium iron phosphate positive electrode material. Compared with the polytetrafluoroethylene used in comparative example 4, the binder in the application has good bonding performance. The addition amount of furfuryl alcohol resin in comparative example 1 is small, and no aldehyde crosslinking agent is added in comparative example 2, which will reduce the crosslinking degree and affect the bonding performance. In comparative example 3, the addition amount of furfuryl alcohol resin is too much, which makes the dispersibility of the binder poor, and is not conducive to the bonding performance.

[0130] Electrochemical performance test: metal lithium (99.9%) is used as negative electrode, celgard2400 diaphragm is used with TC-E201 electrolyte to assemble CR2025 type button cell. The specific capacity of the battery material is obtained by constant current charge and discharge test. The results are shown in table 2:

[0131] Table 2

[0132]

[0133] According to the test results, the system capacity of Comparative Examples 1 to 4 is lower than that of Example 1. In Comparative Example 1, the amount of furfuryl alcohol resin added is insufficient, and it fails to fully play its role; in Comparative Example 3, the amount of furfuryl alcohol resin added is excessive, resulting in poor dispersibility of the binder, both of which are not conducive to the improvement of the specific discharge capacity. In Comparative Example 2, no crosslinking agent is added, resulting in a low degree of crosslinking of the binder, enhanced water absorption, and difficulty in completely removing water during drying, and the residual water will lead to a decrease in the specific capacity. In Comparative Example 4, the used polytetrafluoroethylene has poor conductivity. In Example 1, an appropriate amount of furfuryl alcohol resin is added, which has good conductivity and forms a crosslinked structure, can effectively improve the electron transport efficiency and reduce the electron transport resistance, thereby significantly improving the specific discharge capacity of the battery.

[0134] Example 9

[0135] The embodiment provides a recycling method of a lithium iron phosphate positive electrode material, and comprises the following steps:

[0136] The positive electrode sheet obtained by the method in Example 1 is soaked in ethanol to separate the positive electrode active material from the aluminum foil, thereby obtaining a waste lithium iron phosphate positive electrode material; the waste lithium iron phosphate positive electrode material is calcined under a protective atmosphere; the calcination temperature is 500-700 DEG C.

[0137] After calcination, phosphoric acid is added as a leaching agent, and ascorbic acid is added for leaching, and the filtrate of Li + (98.20% of leaching rate), Fe 2+ (98.13% of leaching rate) and PO4 3- is obtained, ammonia water is added to adjust the pH of the system to 10-12, filtration and drying are performed to obtain lithium iron phosphate recycling material. The whole recycling process has mild conditions, no new impurities are introduced in the recycling process, and the recycling residue does not contain fluorine element and aluminum, which is beneficial to the recycling treatment of waste batteries.

[0138] It should be noted that, in this text, relational terms such as first and second are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "contain" or any other variants thereof are intended to cover non-exclusive inclusion, so that the process, method, article or equipment including a series of elements not only includes those elements, but also includes other elements not explicitly listed or inherent to such process, method, article or equipment.

[0139] While embodiments of the application have been shown and described, it is to be understood that the embodiments described are merely exemplary of the principles and application of the present application. Numerous modifications and adaptions can be effected without departing from the spirit and scope of the present application, which is not limited to the exact construction and arrangement described. It is intended, therefore, to cover all modifications and adaptions that fall within the scope of the claims and their equivalents.

Claims

1. A lithium iron phosphate cathode material, characterized in that, The positive electrode active material, the conductive agent, the binder, the binder being obtained by blending polyvinyl alcohol carboxylic copolymer and furfuryl alcohol resin, aldehyde crosslinking agent, the polyvinyl alcohol carboxylic copolymer being the product after radical graft polymerization of polyvinyl alcohol and unsaturated carboxylic acid, the binder being crosslinked during the drying process of the lithium iron phosphate positive electrode material, the drying temperature being 65-70 DEG C.

2. The lithium iron phosphate cathode material of claim 1, wherein, The furfuryl alcohol resin is prepared by the following steps: After mixing furfuryl alcohol and water, stirring and dispersing under heating to 60-65 DEG C, adding an acidic catalyst, heating to 70-75 DEG C and reacting for 3-4 h, adding ammonia to neutralize after the reaction, and drying to obtain the furfuryl alcohol resin, wherein the ratio of furfuryl alcohol to water is 70 g:30 mL, the acidic catalyst adjusts the pH value of the system to 2-3; the acidic catalyst is one of sulfuric acid, oxalic acid and hydrochloric acid.

3. The lithium iron phosphate cathode material of claim 1, wherein, The radical graft polymerization reaction includes the following steps: mixing polyvinyl alcohol and water, then adding sodium persulfate and sodium bisulfite as initiators, heating to 60-65 DEG C, adding unsaturated carboxylic acid, keeping the temperature unchanged and continuing to stir and react for 2-3 h to obtain the polyvinyl alcohol carboxylic copolymer.

4. The lithium iron phosphate cathode material of claim 3, wherein, The mass ratio of polyvinyl alcohol to unsaturated carboxylic acid is 1:1; the ratio of the amount of polyvinyl alcohol to water is 1 g:25 mL; the molar ratio of persulfate to sodium bisulfite is 3:5; the total addition amount of the initiator is 0.15%-0.20% of the mass of the unsaturated carboxylic acid.

5. The lithium iron phosphate cathode material of claim 1, wherein, The unsaturated carboxylic acid is one of acrylic acid, methacrylic acid and maleic acid.

6. The lithium iron phosphate cathode material of claim 1, wherein, The aldehyde crosslinking agent is at least one of glutaraldehyde, butanedial and adipaldehyde.

7. The lithium iron phosphate cathode material of claim 1, wherein the lithium iron phosphate cathode material has a tap density of at least 2.0 g / cm3. The mass ratio of polyvinyl alcohol carboxylic copolymer, furfuryl alcohol resin and aldehyde crosslinking agent is 1:0.8-1:0.14-0.

16.

8. The lithium iron phosphate cathode material of claim 1, wherein, The mass ratio of lithium iron phosphate, conductive agent and binder is 80-90:5-15:

5.

9. A method for recycling lithium iron phosphate cathode material, characterized in that, The lithium iron phosphate positive electrode material is recovered by the following steps: The positive electrode sheet is soaked in an alcohol solvent to separate the positive electrode active material from the aluminum foil to obtain the waste lithium iron phosphate positive electrode material; the waste lithium iron phosphate positive electrode material is calcined under a protective atmosphere; the calcination temperature is 500-700 DEG C; After calcination, phosphoric acid is added as leaching agent, and the leaching is carried out with a reducing acid, and the filtrate of Li + , Fe 2+ and PO4 3- is obtained, the pH of the system is adjusted to 10-12, filtration and drying are carried out to obtain lithium iron phosphate recovery material.

10. The recovery method of the lithium iron phosphate cathode material according to claim 9, characterized in that, The reducing acid is at least one of citric acid and ascorbic acid; the alcohol solvent is at least one of ethanol, methanol and ethylene glycol.

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