CN115863544A - Positive pole piece and preparation method and application thereof - Google Patents
Positive pole piece and preparation method and application thereof Download PDFInfo
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- CN115863544A CN115863544A CN202310162652.4A CN202310162652A CN115863544A CN 115863544 A CN115863544 A CN 115863544A CN 202310162652 A CN202310162652 A CN 202310162652A CN 115863544 A CN115863544 A CN 115863544A
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Abstract
The invention relates to a positive pole piece and a preparation method and application thereof. The positive pole piece comprises a positive pole current collector and a positive pole active substance layer arranged on at least one surface of the positive pole current collector; a functional protective layer is arranged on at least one surface of the positive electrode active material layer far away from the positive electrode current collector; the functional protective layer contains Tris buffer and acid acceptor. The positive pole piece is prepared by the following method: preparing a positive active material layer on a positive current collector; and preparing a functional protective layer on at least one surface of the positive current collector with the positive active material layer to obtain the positive pole piece. The obtained battery anode piece is applied to a lithium ion battery. The invention adopts Tris buffer and acid acceptor as main functional protective layers, can effectively prevent HF from eroding positive active material and the safety problem caused by battery gas production, and can stably improve the cycle performance and safety of the battery.
Description
Technical Field
The invention belongs to the technical field of lithium batteries, and particularly relates to a positive pole piece and a preparation method and application thereof.
Background
Rapid development of human society relies on the massive consumption of fossil energy. Lithium ion batteries are a good choice for large-scale energy storage due to the advantages of high energy density, high power density, and the like. And has been widely used in portable electronic devices and new energy vehicles in recent years.
The lithium iron phosphate is used as the anode material of the lithium ion battery, has the advantages of long cycle life, good safety performance, stable charging and discharging platform, stable charging and discharging process structure, no environmental pollution and the like compared with other materials, and has wide research and application in the field of the lithium ion battery. With the increasing demand of users for the cycle life of electric vehicles, how to improve the cycle life of batteries is one of the major research directions in the field of lithium ion batteries. In the cycling process of the lithium iron phosphate battery, the positive electrode material is attacked by harmful side reaction hydrofluoric acid (HF) in the electrolyte, so that the positive electrode material is corroded, iron ions in the positive electrode material are forced to dissolve out into the electrolyte and penetrate through the diaphragm to be reduced and deposited on the surface of the negative electrode, and finally the capacity of the battery is attenuated, and on the other hand, the deposition can cause micro short circuit of the battery and puncture the diaphragm to cause safety problems. Secondly, the carbonate-based electrolyte reacts with the positive and negative electrode materials and impurities in the materials of the electrolyte during the circulation process of the battery to generate HF and H 2 、CO、CO 2 、CH 4 The gas production of the battery is dominant (about 60-65% of the gas production). According to the reports of relevant documents, CO in four gases 2 The most amount of production. H 2 CH is close to the amount of CO produced 4 The generation of (2) is the lowest. CO 2 2 Mainly derived from LiPF 6 Decomposition of (2) containing LiPF 6 Electrolyte solution H of 2 And the amount of CO produced is relatively reduced, so CO 2 The gas is the main expansion gas for the expansion of the battery.
Therefore, there is a need to find a relatively simple method for greatly reducing or reducing the corrosion of HF in the electrolyte to the anode and CO in the generated gas 2 Content of gasAnd further achieve the purpose of prolonging the cycle life and improving the safety of the lithium iron phosphate.
Disclosure of Invention
In order to solve the problems that in the prior art, a by-product HF of electrolyte reaches one side of a positive electrode in the battery circulation process, and the HF continuously erodes the positive electrode material when the positive electrode material is not protected by a coating, so that the iron ions in the positive electrode material are dissolved out for a long time, and the battery capacity is attenuated; on the other hand, iron ions dissolved in the electrolyte can shuttle to the negative electrode to be reduced and deposited on the surface of the negative electrode, and the deposits can catalyze the decomposition of the electrolyte to cause excessive consumption of the electrolyte and further cause the downward attenuation of the battery capacity, so that the invention provides the positive pole piece and the preparation method and the application thereof.
Firstly, the invention adopts Tris (hydroxymethyl) aminomethane (Tris) and an acid absorbent (zinc oxide, znO and the like) as the functional protective layer coating of the positive pole piece. When the positive pole piece contains the functional protective layer, the acid absorbent in the protective layer can react with HF coming to the positive side to generate an inorganic ZnF which is favorable for the functional protective layer to be firm and stable 2 、MgF 2 Etc. may continue to maintain protection of the positive electrode material. Secondly, the chemical reaction will have a trace of H 2 In the case of O generation, tris in the functional protective layer coating has excellent water absorption and can absorb water generated by chemical reaction and water generated by reaction of the electrolyte. Eliminating HF, synchronously eliminating trace water produced in the battery, absorbing trace water to become trace Tris buffer solution, wherein the Tris buffer solution can absorb CO in the air 2 A gas. In the battery, CO generated in the battery cycle process can be absorbed 2 The gas can greatly reduce the explosion danger caused by the expansion of the battery and improve the use safety of the battery.
The invention is realized by the following technical scheme:
the invention provides a positive pole piece, which comprises a positive pole current collector and a positive pole active substance layer arranged on at least one surface of the positive pole current collector, wherein the positive pole active substance layer contains lithium iron phosphate and/or lithium manganese iron phosphate; a functional protection layer is arranged on at least one surface of the positive electrode active material layer far away from the positive electrode current collector; the functional protective layer contains a Tris buffer and an acid absorbent.
In one embodiment of the invention, the positive current collector is selected from a substrate consisting of an oxidation-resistant metal foil or alloy; further, aluminum foil is preferable.
In one embodiment of the invention, the acid scavenger is selected from ZnO, mgO, al (OH) 3 、C 36 H 70 CaO 4 And a polyamide.
In one embodiment of the invention, the thickness of the functional protective layer is 5 μm to 8 μm. The protection of the anode material with the thickness less than 5 mu m does not achieve the purpose of the invention; the energy density is correspondingly reduced when the thickness is more than 8 mu m, or the thickness of the battery cell is influenced, which is not beneficial to the case entering of the battery cell in the later period.
In one embodiment of the present invention, the functional protective layer further comprises an iron ion chelating agent.
In one embodiment of the invention, the iron ion chelating agent is selected from one or more of ethylenediaminetetraacetic acid, disodium ethylenediaminetetraacetate, disodium magnesium ethylenediaminetetraacetate, nitrilotriacetic acid, diethylenetriaminepentaacetic acid, N-carboxyethylethylenediaminetriacetic acid, dipotassium ethylenediaminetetraacetate. The chelating agent such as ethylenediamine tetraacetic acid and the like has the capability of complexing iron ions, can be used for preventing the iron ions from shuttling to a negative electrode for reduction and deposition, and is also a functional additive in a Tris-picric acid buffer.
The second purpose of the invention is to provide a preparation method of the positive pole piece, which comprises the following steps:
(1) Preparing a positive active material layer on the positive current collector;
(2) Preparing a functional protective layer on at least one surface of the positive current collector with the positive active material layer to obtain the positive pole piece; the functional protective layer contains a Tris buffer and an acid acceptor.
In one embodiment of the present invention, in the step (1), the method for preparing the positive active material layer on the positive current collector is not limited and is a conventional method in the art, including but not limited to one or more of a spray coating method, a space coating method, a sputtering method, a roll coating method, a pulse laser deposition method, a chemical vapor deposition method, an atomic layer deposition method, an electrochemical deposition method, and a 3D printing method. The roll coating method is preferable.
In one embodiment of the present invention, in the step (2), the method for preparing the functional protective layer is not limited and is a conventional method in the art, including but not limited to one or more of a spray coating method, a space coating method, a sputtering method, a roll coating method, a pulsed laser deposition method, a chemical vapor deposition method, an atomic layer deposition method, an electrochemical deposition method, and a 3D printing method. The roll coating method is preferable.
In one embodiment of the present invention, the slurry of the functional protective layer is prepared by the following method:
s1, mixing and dissolving Tris powder and acid in water, and stirring for reaction to obtain a Tris buffer solution;
s2, adding an acid acceptor into the Tris buffer solution obtained in the step S1, and dissolving to obtain a mixed solution;
s3, drying the mixed solution obtained in the step S2, and grinding a solid mixture obtained by drying to obtain solid powder;
and S4, adding a binder and a solvent into the solid powder obtained in the step S3, and mixing and dissolving to obtain the slurry of the functional protective layer.
In one embodiment of the present invention, step S1 further comprises adding an iron ion chelating agent.
In one embodiment of the present invention, the concentration of the iron ion chelating agent is 0.5M, and the mass-to-volume ratio of the acid scavenger to the iron ion chelating agent is 10 to 20.
In one embodiment of the present invention, in step S1, at least one of the following conditions is satisfied:
a) The acid is selected from one or more of picric acid, glycine, tri (hydroxymethyl) methylglycine, hydrochloric acid and boric acid;
b) The Tris buffer solution is selected from one or more of Tris-picric acid buffer solution, tris-glycine buffer solution, tris-tricine buffer solution, tris-hydrochloric acid buffer solution and Tris-boric acid buffer solution;
c) And the pH value of the Tris buffer solution is 5-7.
In one embodiment of the invention, in the step S2, the dissolution is carried out by heating and stirring, wherein the heating temperature is 40-70 ℃, and the stirring time is 1-3 h.
In one embodiment of the present invention, in step S2, the acid scavenger is selected from ZnO, mgO, al (OH) 3 、C 36 H 70 CaO 4 And a polyamide.
In one embodiment of the invention, the mass ratio of the acid acceptor to the Tris powder is 10-20:10:20.
in one embodiment of the present invention, in step S3, at least one of the following conditions is met:
1) Drying under vacuum condition;
2) Drying and heating rate: raising the temperature to 60-70 ℃ at the speed of 2-5 ℃/min;
3) The drying time is 10-12 h.
In one embodiment of the present invention, in step S4, the binder is selected from one or more of polyvinylidene fluoride (PVDF), polyvinylidene fluoride, styrene rubber, nitrile rubber, styrene Butadiene Rubber (SBR), polyacrylamide (PAA), polytetrafluoroethylene (PTFE), polyacrylonitrile (PAN), polyimide (PI), butadiene rubber, modified butadiene rubber, carboxyl modified styrene butadiene rubber, and modified polyorganosiloxane-based polymer.
In one embodiment of the present invention, in step S4, the solvent is NMP.
The third purpose of the invention is to provide a lithium ion battery, which comprises the positive pole piece.
Compared with the prior art, the technical scheme of the invention has the following advantages:
the invention adopts Tris-picric acid buffer solution and zinc oxide as main anode coating materials, and utilizes the chemical reaction of acid-absorbing agent (zinc oxide and the like) in the coating and HF coming to the anode side, and the specific functions are as follows: (1) GeneratingInorganic ZnF favorable for coating firmness and stability 2 The protection of the anode material can be continuously kept; (2) The Tris-picric acid powder can absorb the water generated by the chemical reaction and the water generated by the electrolyte reaction; (3) Trace moisture generated in the battery is synchronously eliminated while HF is eliminated; (4) The Tris-picric acid buffer can absorb CO generated in the battery circulation process 2 A gas; (5) The Tris-picric acid buffer can also dissociate metal cations, and can activate dead lithium formed in the battery circulation process and return to the battery circulation system again, so that the utilization rate of the insulated dead lithium is improved. The adsorption of HF to inhibit the dissolution of iron ions in the positive electrode material can prevent the collapse of the positive electrode material, improve the cycle performance of the battery, reduce the safety problem caused by explosion of an explosion-proof valve due to excessive gas generation of the battery, and stably improve the cycle performance and safety of the battery.
2, the preparation process is simple and easy to realize industrial production.
Drawings
In order that the present disclosure may be more readily and clearly understood, reference is now made to the following detailed description of the present disclosure taken in conjunction with the accompanying drawings, in which:
fig. 1 is a graph of the gas composition of a pouch cell prepared from the material obtained in the example of the present invention over a three cycle 1C/1C cycle; wherein B is comparative example 1 and D is example 1.
FIG. 2 is a graph comparing the 1C/1C cycle three cycle gassing volume of pouch cells prepared from the materials obtained in the examples of the present invention; wherein B is comparative example 1 and D is example 1.
Detailed Description
The present invention is further described below in conjunction with the following figures and specific examples so that those skilled in the art may better understand the present invention and practice it, but the examples are not intended to limit the present invention.
The invention relates to a material preparation method and a detection method, which comprises the following steps:
1. preparing a positive plate:
(1) Lithium iron phosphate, a conductive agent and a binder PVDF are mixed according to the mass ratio of 8:1:1, adding NMP solvent, uniformly mixing to prepare anode slurry, uniformly coating the anode slurry on an aluminum foil coated with a conductive carbon layer according to a certain proportion, and performing vacuum drying at 80-120 ℃ to obtain the anode material coated with an active substance layer. The conductive agent is one or more of SP, CNT and graphite.
(2) And (3) carrying out cold pressing, die cutting and slitting on the positive pole piece obtained in the step (1) to obtain the positive pole piece.
2. Preparing a negative plate:
mixing a negative electrode active material graphite, conductive carbon black and a negative electrode binder according to a ratio of 8:1:1 and deionized water are mixed evenly to prepare cathode slurry. And uniformly coating the negative electrode slurry on a copper foil according to a certain proportion, carrying out vacuum drying at 70-90 ℃, and carrying out die cutting to obtain the negative electrode piece. The negative electrode binder is prepared from carboxymethyl cellulose (CMC) and Styrene Butadiene Rubber (SBR) according to a mass ratio of 4:6, mixing and forming.
3. Preparing a battery: and assembling the positive plate, the diaphragm and the negative plate together to form the battery, wherein the diaphragm is required to be capable of completely wrapping the positive plate and the negative plate. The electrolyte (1M LiPF) was injected into the cell 6 Solution, wherein the solvent of the electrolyte was EC: DMC = 1%, 5% fec). And finally, preparing the soft-package lithium iron phosphate battery through standing, formation, volume grading and other processes.
4. The slurry of the functional protective layer is prepared by the following method:
a. weighing 10-20mg of Tris powder, 0.2-0.7 mg of acid, 0.4-1.0 mL of 0.5M iron ion chelating agent, dissolving in 20-100 mL of water, and stirring for 1-3 h until all the iron ion chelating agent is dissolved to prepare a Tris-buffer solution with the pH range of 5.0-7.0;
b. adding 10mg-20mg of acid acceptor in the step a, heating and stirring to be uniform at the temperature of 40-70 ℃, and stirring for 1h-3h until the acid acceptor is completely dissolved;
c. and (c) transferring the solution in the step (b) to an oven for drying, vacuumizing, raising the temperature of 5 ℃ per minute to 60-70 ℃, drying for 10-12 h, grinding and screening to obtain solid powder (the pH value of the solid powder ranges from 6.0 to 8.0), and finally adding a binder and a solvent into the obtained solid powder to mix and dissolve to obtain the slurry of the functional protective layer.
5. And (3) cycle testing:
charging the battery to 3.65V at a constant current and a constant voltage of 1C at 25 +/-2 ℃, and cutting off the current of 0.05C; standing for 60min, then discharging to 2.5V at 1C, and continuing the process until the capacity decays to 80% of the initial capacity, and recording the number of cycles.
6. And (3) testing the iron dissolution of the anode material after 1000 cycles:
charging the battery to 3.65V at a constant current and a constant voltage of 1C at the temperature of 45 +/-2 ℃, and stopping the current at 0.05C; standing for 30min, and then discharging to 2.5V at 1C; the capacity retention rate of the battery after 1000-circle cycle test is recorded, the negative plate of the battery is disassembled, the negative electrode is dissolved by 0.1mol/L HCl aqueous solution, and the amount of iron ions in the HCl solution is tested by ICP-OES, so that the cycle iron dissolution condition of the battery in each embodiment/comparative example is compared.
7. Testing the gas production volume and content of the soft package battery:
the measuring instrument selects GC/GC-MS, the gas production volume of the soft package battery is obtained after three-cycle charge and discharge cycles under the current density of 1C, and the actual gas production volume is obtained by subtracting the amount before gas production from the amount after gas production; the composition of the gas is then analyzed.
Examples of the invention
Example 1
The embodiment provides a positive electrode material and a positive electrode plate for a lithium iron phosphate battery and a preparation method thereof, and the preparation method specifically comprises the following steps:
(1) Preparing a positive electrode material: lithium iron phosphate, a conductive agent SP and a binder PVDF are mixed according to the mass ratio of 8:1:1, then adding NMP solvent, uniformly mixing to prepare anode slurry, coating the anode slurry on aluminum foil with a conductive carbon layer according to the thickness of 150 +/-5 mu m, and carrying out vacuum drying at 80 ℃ to obtain the anode sheet coated with an active material layer.
(2) Preparing anode coating slurry: 30mg of PVDF is weighed in weighing paper, a small beaker is taken, magnetons are placed in the small beaker, an appropriate amount of NMP is added, the small beaker is placed in a stirrer, and the PVDF is added and fully stirred until the mixture is transparent. Weighing 10mg of Tris powder, 0.3mg of picric acid and 0.5M of ethylenediamine tetraacetic acid, taking 0.5mL of the EDTA, dissolving the Tris powder, the picric acid and the EDTA in 40mL of deionized water, stirring the mixture at room temperature until the Tris powder, the picric acid and the EDTA are completely dissolved to prepare a Tris-picric acid buffer solution, wherein the pH value is 6.0; and then adding 10mg of ZnO powder, heating and stirring until the ZnO powder is uniform, controlling the temperature at 45 ℃, stirring for 3 hours until the ZnO powder is completely dissolved, transferring the solution to an oven for drying, vacuumizing, raising the temperature to 70 ℃ per minute, drying for 10 hours to obtain solid powder, placing the solid powder into a mortar for grinding, and finally adding PVDF slurry to mix and dissolve to obtain the anode coating slurry.
(3) Preparing a positive plate containing the positive coating slurry: transferring the anode coating slurry prepared in the step (2) to the surface of the anode plate prepared in the step (1), carrying out blade coating, placing in dry air for 2 hours to prepare a functional coating with the thickness of 8 mu m, transferring the prepared anode plate containing the coating into a vacuum oven, and drying at 80 ℃ for 10 hours to obtain the anode plate containing the coating material.
Example 2
The embodiment provides a positive electrode material and a positive electrode plate for a lithium iron phosphate battery and a preparation method thereof, and the preparation method specifically comprises the following steps:
(1) Preparing a positive electrode material: lithium iron phosphate, a conductive agent SP and a binder PVDF are mixed according to the mass ratio of 8:1:1, then adding NMP solvent, uniformly mixing to prepare anode slurry, coating the anode slurry with the thickness of 150 +/-5 mu m on an aluminum foil coated with a conductive carbon layer, and carrying out vacuum drying at 80 ℃ to obtain the anode sheet coated with an active material layer.
(2) Preparing anode coating slurry: a small beaker is taken and put into a magneton, a proper amount of NMP is added into the magneton, and the small beaker is put into a stirrer, 30mg of PVDF is added into the stirrer, and the mixture is fully stirred until the mixture is transparent. Weighing Tris powder 5mg, picric acid 0.3mg and ethylenediamine tetraacetic acid 0.5M, taking 0.5mL, dissolving in deionized water 40mL, stirring at room temperature until all the solution is dissolved, and preparing into Tris-picric acid buffer solution with pH value of 6.0; adding 10mg of ZnO powder, heating and stirring until the ZnO powder is uniform, controlling the temperature at 45 ℃, stirring for 3 hours until the ZnO powder is completely dissolved, transferring the solution to an oven for drying, vacuumizing, raising the temperature to 70 ℃ per minute, drying for 10 hours to obtain solid powder, placing the solid powder into a mortar for grinding, and finally adding PVDF slurry to mix and dissolve to obtain the anode coating slurry.
(3) Preparing a positive plate containing the positive coating slurry: transferring the prepared anode coating slurry to the surface of the prepared anode plate, carrying out blade coating, placing in dry air for 2h to prepare a functional coating with the thickness of 8 mu m, transferring the prepared anode plate containing the coating into a vacuum oven, and drying at 80 ℃ for 10h to obtain the anode plate containing the coating material.
Example 3
The embodiment provides a positive electrode material and a positive electrode plate for a lithium iron phosphate battery and a preparation method thereof, and the preparation method specifically comprises the following steps:
(1) Preparing a positive electrode material: lithium iron phosphate, a conductive agent SP and a binder PVDF are mixed according to the mass ratio of 8:1:1, then adding NMP solvent, uniformly mixing to prepare anode slurry, uniformly coating the anode slurry with the thickness of 150 +/-5 mu m on an aluminum foil coated with a conductive carbon layer, and carrying out vacuum drying at 80 ℃ to obtain the anode sheet coated with an active material layer.
(2) Preparing anode coating slurry: a small beaker is taken and put into a magneton, a proper amount of NMP is added into the magneton, and the small beaker is put into a stirrer, 30mg of PVDF is added into the stirrer, and the mixture is fully stirred until the mixture is transparent. Weighing 10mg of Tris powder, 0.3mg of picric acid and 0.5mL of 0.5M ethylenediaminetetraacetic acid, dissolving in 40mL of deionized water, stirring at room temperature to completely dissolve, and preparing into Tris-picric acid buffer solution with the pH value of 6.0; adding 5mg of ZnO powder, heating and stirring to be uniform, controlling the temperature at 45 ℃, stirring for 3 hours until the ZnO powder is completely dissolved, transferring the solution to an oven for drying, vacuumizing, raising the temperature to 70 ℃ per minute, drying for 10 hours to obtain solid powder, placing the solid powder into a mortar for grinding, and finally adding PVDF slurry to mix and dissolve the solid powder to obtain the anode coating slurry.
(3) Preparing a positive plate containing the positive coating slurry: transferring the prepared anode coating slurry to the surface of the prepared anode plate, carrying out blade coating, placing in dry air for 2h to prepare a functional coating with the thickness of 8 mu m, transferring the prepared anode plate containing the coating into a vacuum oven, and drying at 80 ℃ for 10h to obtain the anode plate containing the coating material.
Comparative example 1
The comparative example provides a positive electrode material and a positive electrode plate for a lithium iron phosphate battery and a preparation method thereof, and the preparation method specifically comprises the following steps:
(1) Preparing a positive electrode material: lithium iron phosphate, a conductive agent SP and a binder PVDF are mixed according to the mass ratio of 8:1:1, then adding NMP solvent, uniformly mixing to prepare anode slurry, coating the anode slurry on an aluminum foil coated with a conductive carbon layer according to the thickness of 150 +/-5 mu m, and carrying out vacuum drying at 80 ℃ to obtain the anode sheet coated with an active material layer.
(2) Preparing anode coating slurry: a small beaker is taken and put into a magneton, a proper amount of NMP is added into the beaker, the beaker is put into a stirrer, and 30mg of PVDF is added into the beaker and fully stirred until the beaker becomes transparent. Adding 10mg of ZnO powder, stirring uniformly, and mixing to obtain the anode coating slurry.
(3) Preparing a positive plate containing the positive coating slurry: transferring the prepared anode coating slurry to the surface of the prepared anode plate, carrying out blade coating, placing in dry air for 2h to prepare a functional coating with the thickness of 8 mu m, transferring the prepared anode plate containing the coating into a vacuum oven, and drying at 80 ℃ for 10h to obtain the anode plate containing the coating material.
Comparative example 2
The comparative example provides a positive electrode material and a positive electrode plate for a lithium iron phosphate battery and a preparation method thereof, and the preparation method specifically comprises the following steps:
(1) Preparing a positive electrode material: lithium iron phosphate, a conductive agent SP and a binder PVDF are mixed according to the mass ratio of 8:1:1, then adding NMP solvent, uniformly mixing to prepare anode slurry, coating the anode slurry on an aluminum foil coated with a conductive carbon layer according to the thickness of 150 +/-5 mu m, and carrying out vacuum drying at 80 ℃ to obtain the anode sheet coated with an active material layer.
(2) Preparing anode coating slurry: a small beaker is taken and put into a magneton, a proper amount of NMP is added into the magneton, and the small beaker is put into a stirrer, 30mg of PVDF is added into the stirrer, and the mixture is fully stirred until the mixture is transparent. 10mg of Tris powder was added thereto, and the mixture was stirred to be uniform and mixed to obtain a positive electrode coating slurry.
(3) Preparing a positive plate containing the positive coating slurry: transferring the prepared anode coating slurry to the surface of the prepared anode plate, carrying out blade coating, placing in dry air for 2h to prepare a functional coating with the thickness of 8 mu m, transferring the prepared anode plate coating-containing layer into a vacuum oven, and drying at 80 ℃ for 10h to obtain the anode plate containing the coating material.
Comparative example 3
The comparative example provides a positive electrode material and a positive electrode plate for a lithium iron phosphate battery and a preparation method thereof, and the preparation method specifically comprises the following steps:
preparing a positive electrode material; lithium iron phosphate, a conductive agent SP and a binder PVDF are mixed according to the mass ratio of 8:1:1, then adding NMP solvent, uniformly mixing to prepare anode slurry, coating the anode slurry on an aluminum foil coated with a conductive carbon layer according to the thickness of 150 +/-5 mu m, and carrying out vacuum drying at 80 ℃ to obtain the anode material coated with an active material layer.
Comparative example 4
The comparative example provides a positive electrode material and a positive electrode plate for a lithium iron phosphate battery and a preparation method thereof, and the preparation method specifically comprises the following steps:
(1) Preparing a positive electrode material: lithium iron phosphate, a conductive agent SP and a binder PVDF are mixed according to the mass ratio of 8:1:1, then adding NMP solvent, uniformly mixing to prepare anode slurry, uniformly coating the anode slurry with the thickness of 150 +/-5 mu m on an aluminum foil coated with a conductive carbon layer, and carrying out vacuum drying at 80 ℃ to obtain the anode sheet coated with an active material layer.
(2) Preparing anode coating slurry: a small beaker is taken and put into a magneton, a proper amount of NMP is added into the magneton, and the small beaker is put into a stirrer, 30mg of PVDF is added into the stirrer, and the mixture is fully stirred until the mixture is transparent. Weighing 10mg of Tris powder, 0.3mg of picric acid and 0.5mL of 0.5M ethylenediamine tetraacetic acid, dissolving in 40mL of deionized water, stirring at room temperature to completely dissolve to prepare a Tris-picric acid buffer solution with the pH value of 6.0; adding 10mg of ZnO powder, heating and stirring to be uniform, controlling the temperature to be 45 ℃, stirring for 3 hours until the ZnO powder is completely dissolved, transferring the solution to an oven for drying, vacuumizing, raising the temperature to 70 ℃ per minute, drying for 10 hours to obtain solid powder, placing the solid powder into a mortar for grinding, and finally adding PVDF slurry to mix and dissolve the solid powder to obtain the anode coating slurry.
(3) Preparing a positive plate containing the positive coating slurry: transferring the prepared anode coating slurry to the surface of the prepared anode plate, carrying out blade coating, placing in dry air for 2h to prepare a functional coating with the thickness of 4 mu m, transferring the prepared anode plate containing the coating into a vacuum oven, and drying at 80 ℃ for 10h to obtain the anode plate containing the coating material.
Comparative example 5
The comparative example provides a positive electrode material and a positive electrode plate for a lithium iron phosphate battery and a preparation method thereof, and the preparation method specifically comprises the following steps:
(1) Preparing a positive electrode material: lithium iron phosphate, a conductive agent SP and a binder PVDF are mixed according to the mass ratio of 8:1:1, then adding NMP solvent, uniformly mixing to prepare anode slurry, uniformly coating the anode slurry with the thickness of 150 +/-5 mu m on an aluminum foil coated with a conductive carbon layer, and carrying out vacuum drying at 80 ℃ to obtain the anode plate coated with an active material layer.
(2) Preparing anode coating slurry: a small beaker is taken and put into a magneton, a proper amount of NMP is added into the magneton, and the small beaker is put into a stirrer, 30mg of PVDF is added into the stirrer, and the mixture is fully stirred until the mixture is transparent. Weighing 10mg of Tris powder, 0.3mg of picric acid and 0.5mL of 0.5M ethylenediamine tetraacetic acid, dissolving in 40mL of deionized water, stirring at room temperature to completely dissolve to prepare a Tris-picric acid buffer solution with the pH value of 6.0; adding 10mg of ZnO powder, heating and stirring to be uniform, controlling the temperature to be 45 ℃, stirring for 3 hours until the ZnO powder is completely dissolved, transferring the solution to an oven for drying, vacuumizing, raising the temperature to 70 ℃ per minute, drying for 10 hours to obtain solid powder, placing the solid powder into a mortar for grinding, and finally adding PVDF slurry to mix and dissolve the solid powder to obtain the anode coating slurry.
(3) Preparing a positive plate containing the positive coating slurry: transferring the prepared anode coating slurry to the surface of the prepared anode plate, carrying out blade coating, placing in dry air for 2h to prepare a functional coating with the thickness of 12 mu m, transferring the prepared anode plate containing the coating into a vacuum oven, and drying at 80 ℃ for 10h to obtain the anode plate containing the coating material.
Test example
1, assembling the positive plates containing the coating materials obtained in the examples 1-3 and the comparative examples 1-5 into a lithium iron phosphate battery for performance test, wherein the content of the performance test comprises that the positive electrode is subjected to 45 ℃ circulation for 1000 weeksIron dissolution of the material, CO after three weeks 2 Gas content, cycle life.
2, the positive plates containing the coating materials obtained in the example 1 and the comparative example 1 are assembled into a lithium iron phosphate battery to be subjected to a 1C/1C cycle three-cycle gas performance test.
The results are shown in Table 1 and FIGS. 1-2.
TABLE 1 parameters and results of examples and comparative examples
As can be seen from table 1, in example 1, when ZnO or Tris-picric acid was used alone to prepare a coating material, a great difference occurred in the performance of the corresponding prepared battery, as compared to comparative examples 1 and 2. Such as: (1) In the case of the iron elution of the positive electrode material after 1000 cycles at 45 ℃, the iron elution amount in example 1 is reduced by 33.8% and 60.3% compared with those in comparative examples 1 and 2, and it can be seen that the iron elution amount in the embodiment of the present invention is greatly reduced; (2) Three weeks later CO 2 In the results of gas contents, the gas amounts of comparative examples 1 and 2 were 10.3 times and 1.8 times as much as those of example 1, and it is apparent from fig. 1 that the cell of comparative example 1 produces CO, as compared with fig. 1, in conjunction with the results of fig. 1 and 2 2 The content is much higher than in example 1, it can be seen that Tris-picric acid in the coating material has good CO absorption 2 Under the action of gas, the expansion phenomenon of the battery can be greatly reduced by adding Tris-picric acid; (3) In the results of the cycle life of the battery, the cycle performance of the battery is remarkably improved by 12.5% and 19.5% in example 1 compared with comparative examples 1 and 2.
Example 1 when the functional coating is not within the thickness range specified in the present invention, the battery performance is greatly affected, and when the thickness is 4 μm, iron elution of the positive electrode material after 1000 weeks of 45 c cycle increases by 98.2%, CO, compared to comparative examples 4 and 5 2 The gas content increased by 418%, and the cycle life was much shorter than that of example 1; when the thickness is larger than 8 μm (12 μm), the energy density of the battery is correspondingly reduced, or the thickness of the battery cell is influenced, so that the later-stage battery cell casing is not facilitated, and the cycle life is not prolonged. Selection of the thickness of the functional coatingIt is very important.
As can be seen from the above, the combination of the experimental results of example 1 and comparative examples 1 to 3 shows that the positive electrode coating material has the effects of inhibiting the elution of iron ions and absorbing CO in the battery 2 The performance of the battery can be better improved only when ZnO and Tris-picric acid exist in the coating material at the same time, and a certain synergistic effect exists between the ZnO and the Tris-picric acid, so that the safety and the cycle performance of the battery can be improved.
It should be understood that the above examples are only for clarity of illustration and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. And obvious variations or modifications of the invention may be made without departing from the spirit or scope of the invention.
Claims (11)
1. A positive pole piece comprises a positive pole current collector and a positive pole active substance layer arranged on at least one surface of the positive pole current collector, and is characterized in that the positive pole active substance layer contains lithium iron phosphate and/or lithium manganese iron phosphate; a functional protection layer is arranged on at least one surface of the positive electrode active material layer far away from the positive electrode current collector; the functional protective layer contains a Tris buffer and an acid absorbent.
2. The positive electrode sheet according to claim 1, wherein the acid acceptor is selected from ZnO, mgO, al (OH) 3 、C 36 H 70 CaO 4 And a polyamide.
3. The positive electrode sheet according to claim 1, wherein the thickness of the functional protective layer is 5 μm to 8 μm.
4. The positive electrode sheet according to any one of claims 1 to 3, wherein the functional protective layer further contains an iron ion chelating agent.
5. The positive electrode sheet according to claim 4, wherein the iron ion chelating agent is one or more selected from the group consisting of ethylenediaminetetraacetic acid, disodium ethylenediaminetetraacetate, disodium magnesium ethylenediaminetetraacetate, nitrilotriacetic acid, diethylenetriaminepentaacetic acid, N-carboxyethylethylenediaminetriacetic acid, and dipotassium ethylenediaminetetraacetate.
6. A preparation method of a positive pole piece is characterized by comprising the following steps:
(1) Preparing a positive active material layer on the positive current collector;
(2) Preparing a functional protective layer on at least one surface of the positive current collector with the positive active material layer to obtain the positive pole piece; the functional protective layer contains a Tris buffer and an acid acceptor.
7. The production method according to claim 6, wherein in the step (2), the slurry of the functional protective layer is produced by:
s1, mixing and dissolving Tris powder and acid in water, and stirring for reaction to obtain a Tris buffer solution;
s2, adding an acid acceptor into the Tris buffer solution obtained in the step S1, and dissolving to obtain a mixed solution;
s3, drying the mixed solution obtained in the step S2, and grinding a solid mixture obtained by drying to obtain solid powder;
and S4, adding a binder and a solvent into the solid powder obtained in the step S3, and mixing and dissolving to obtain the slurry of the functional protective layer.
8. The method of claim 7, wherein step S1 further comprises adding an iron ion chelating agent.
9. The method according to claim 7, wherein at least one of the following conditions is satisfied in step S1:
a) The acid is selected from one or more of picric acid, glycine, tris (hydroxymethyl) methylglycine, hydrochloric acid and boric acid;
b) The Tris buffer solution is selected from one or more of Tris-picric acid buffer solution, tris-glycine buffer solution, tris-tricine buffer solution, tris-hydrochloric acid buffer solution and Tris-boric acid buffer solution;
c) And the pH value of the Tris buffer solution is 5-7.
10. The method according to claim 7, wherein the mass ratio of the acid scavenger to Tris powder is 10-20:10:20.
11. a lithium ion battery, characterized by comprising the positive electrode plate of any one of claims 1 to 5 or the positive electrode plate obtained by the preparation method of any one of claims 6 to 10.
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| CN114725319A (en) * | 2022-04-29 | 2022-07-08 | 深圳市德方纳米科技股份有限公司 | Positive electrode, positive electrode slurry, preparation method and lithium ion battery |
| CN114824259A (en) * | 2021-01-27 | 2022-07-29 | 郑州宇通集团有限公司 | Lithium ion battery composite positive plate, preparation method thereof and lithium ion battery |
| US20220255068A1 (en) * | 2019-09-03 | 2022-08-11 | Georgia Tech Research Corporation | Deeply Rechargeable Battery Systems and Methods |
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| CN106711431A (en) * | 2016-12-31 | 2017-05-24 | 武汉理工大学 | Silicon-base cathode material for lithium ion battery and preparation method of silicon-base cathode material |
| CN107572497A (en) * | 2017-09-26 | 2018-01-12 | 南京理工大学 | The preparation method of N doping grade hole carbon material |
| US20220255068A1 (en) * | 2019-09-03 | 2022-08-11 | Georgia Tech Research Corporation | Deeply Rechargeable Battery Systems and Methods |
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