An in-situ lithium-supplemented cathode material and its preparation method

Abstract

The present invention discloses an in-situ lithium-supplemented cathode material and a preparation method thereof. The in-situ lithium-supplemented cathode material comprises the following raw materials in parts by weight: 80-90 parts of lithium iron phosphate coated with carbon and Li5FeO4 on the surface, 5-8 parts of a conductive agent, 5-8 parts of a binder, 3-5 parts of an additive, and 40-50 parts of a solvent; wherein, the binder is a compound of polyvinylidene fluoride and polyethyleneimine modified with aldehyde groups of polyglycol aldehyde. The in-situ lithium-supplemented cathode material in the present invention can improve the cycle stability of the cathode and effectively improve the electrochemical performance of the battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium batteries, and particularly relates to an in-situ lithium-supplemented cathode material and a preparation method thereof. Background Art

[0002] Compared with other types of secondary batteries, lithium-ion batteries have the advantages of high discharge voltage, long cycle life, high specific energy, etc. During the charge and discharge process of lithium-ion batteries, the lithium source is provided by the cathode material. In addition, a part of the active lithium is lost during the initial delithiation process to form a stable SEI film on the surface of the anode, which will reduce the energy density and cycle life of the battery to a certain extent. Therefore, the problem of active lithium compensation has received extensive attention.

[0003] Among many lithium-supplementing technologies, the cathode lithium-supplementing technology has attracted the attention of many enterprises because of its high safety and the need not to change the battery manufacturing equipment and process. Based on this, the present invention aims to provide an in-situ lithium-supplemented cathode material. Summary of the Invention

[0004] The purpose of the present invention is to provide an in-situ lithium-supplemented cathode material and a preparation method thereof, and the in-situ lithium-supplemented cathode material can improve the electrochemical performance of the battery.

[0005] In order to achieve the above purpose, the technical solution provided by a specific embodiment of the present invention is as follows:

[0006] An in-situ lithium-supplemented cathode material, comprising the following components in parts by weight: 80-90 parts of lithium iron phosphate coated with carbon and Li5FeO4, 5-8 parts of conductive agent, 5-8 parts of binder, 3-5 parts of additive, and 40-50 parts of solvent;

[0007] Among them, the binder is a compound of polyvinylidene fluoride and polyethyleneimine modified with aldehyde group polyethylene glycol aldehyde group.

[0008] In one or more embodiments of the present invention, the mass ratio of the polyvinylidene fluoride to the polyethyleneimine modified with aldehyde group polyethylene glycol aldehyde group is 1:(2-3).

[0009] In one or more embodiments of the present invention, the preparation of the polyethyleneimine modified with aldehyde group polyethylene glycol aldehyde group is as follows:

[0010] Dissolve aldehyde group polyethylene glycol aldehyde group and polyethyleneimine in solvents respectively to form a first solution and a second solution, mix the first solution and the second solution, and carry out a reaction at room temperature. After the reaction, the polyethyleneimine modified with aldehyde group polyethylene glycol aldehyde group is obtained.

[0011] In one or more embodiments of the present invention, the mass ratio of the aldehyde group polyethylene glycol aldehyde group to the polyethyleneimine is (1-3):1.

[0012] In one or more embodiments of the present invention, the additive is at least one of silicon oxide, zirconium oxide, and titanium dioxide.

[0013] In one or more embodiments of the present invention, the conductive agent is at least one of conductive carbon black, carbon nanotubes, graphene, and carbon fiber.

[0014] In one or more embodiments of the present invention, the lithium iron phosphate coated with carbon and Li5FeO4 on the surface is prepared by the following method:

[0015] Dissolve the lithium salt and the iron salt in the dopamine solution to make a coating solution;

[0016] Place the lithium iron phosphate in the coating solution, take it out, and then obtain the lithium iron phosphate coated with carbon and Li5FeO4 on the surface after centrifugation, drying, and sintering.

[0017] In one or more embodiments of the present invention, the molar ratio of the lithium salt and the iron salt in terms of lithium atoms and iron atoms is (5-6):1.

[0018] In one or more embodiments of the present invention, the lithium salt is selected from squaric acid lithium, lithium nitrate, and lithium sulfate, and the iron salt is selected from iron nitrate and iron sulfate.

[0019] The technical solution provided by another specific embodiment of the present invention is as follows:

[0020] A preparation method of an in-situ lithium-complemented cathode material, according to the ratio, mix the lithium iron phosphate coated with carbon and Li5FeO4 on the surface, the conductive agent, the binder, the additive, and the solvent to obtain the in-situ lithium-complemented cathode material.

[0021] Compared with the prior art, the present invention first coats carbon and Li5FeO4 on the surface of lithium iron phosphate to improve the cycle performance of the battery. Secondly, polyvinylidene fluoride and polyethyleneimine modified with aldehyde groups of polyethylene glycol aldehyde are compounded to improve the stability of the cathode material, thereby improving the electrochemical performance of the battery. Specific Embodiments

[0022] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0023] A specific embodiment of the present invention provides an in-situ lithium-supplemented cathode component, comprising the following components in parts by weight: 80-90 parts of lithium iron phosphate coated with carbon and Li5FeO4 on the surface, 5-8 parts of a conductive agent, 5-8 parts of a binder, 3-5 parts of an additive, and 40-50 parts of a solvent; wherein, the binder is a compound of polyvinylidene fluoride and polyethyleneimine modified with aldehyde-terminated polyethylene glycol aldehyde.

[0024] Further, the mass ratio of polyvinylidene fluoride to polyethyleneimine modified with aldehyde-terminated polyethylene glycol aldehyde is 1:(2-3).

[0025] Specifically, lithium iron phosphate has excellent thermal stability and chemical stability, and can maintain a high capacity retention rate during long-term cycling. Coating carbon and Li5FeO4 on the surface of lithium iron phosphate helps to improve the lithium ion diffusion rate, and carbon coating is beneficial to reducing the adverse effects of the electrolyte on lithium iron phosphate, which can improve the cycling performance of the battery. Compared with the problem of uneven mixing caused by physically mixing the cathode material and the lithium supplement agent in the traditional method, the lithium iron phosphate coated with carbon and Li5FeO4 used in the present invention can better improve the initial charge-discharge capacity and cycling stability of the cathode material.

[0026] In addition, polyvinylidene fluoride can effectively bond each raw material component, and has high chemical stability and electrochemical stability. Good mechanical strength and flexibility also help to improve the volume change of the electrode during charge and discharge, and prevent the shedding of active substances. Polyethyleneimine modified with aldehyde-terminated polyethylene glycol aldehyde has a network structure, which can effectively adhere to each raw material component. The polyethylene glycol chain in aldehyde-terminated polyethylene glycol aldehyde has good flexibility, which helps to improve the mechanical properties of the cathode material and maintain the cathode structure. Moreover, the linear structure of polyethylene glycol enables it to crosslink with polyethyleneimine through the aldehyde groups at both ends during the stretching process, thereby effectively forming a network structure to achieve the purpose of bonding each raw material component and improving the electrochemical performance of the battery.

[0027] Further, the preparation of polyethyleneimine modified with aldehyde-terminated polyethylene glycol aldehyde is as follows:

[0028] Dissolve aldehyde-terminated polyethylene glycol aldehyde and polyethyleneimine in solvents respectively to form a first solution and a second solution. Mix the first solution and the second solution, and carry out the reaction at room temperature. After the reaction, polyethyleneimine modified with aldehyde-terminated polyethylene glycol aldehyde is obtained.

[0029] Further, the mass ratio of aldehyde-terminated polyethylene glycol aldehyde to polyethyleneimine is (1-3):1.

[0030] Specifically, by controlling the dosage of aldehyde-terminated polyethylene glycol aldehyde, the prepared polyethyleneimine modified with aldehyde-terminated polyethylene glycol aldehyde can better improve the charge-discharge performance of the cathode.

[0031] Further, the additive is at least one of silicon oxide, zirconium oxide, and titanium dioxide. Additives of the above types can enhance the stability of the cathode material and contribute to improving the cycle stability of the battery.

[0032] Further, the conductive agent is at least one of conductive carbon black, carbon nanotubes, graphene, and carbon fiber.

[0033] Further, the solvent is NMP (N-methylpyrrolidone).

[0034] Further, the lithium iron phosphate coated with carbon and Li5FeO4 on the surface is prepared by the following method:

[0035] Dissolve the lithium salt and the iron salt in the dopamine solution to make a coating solution;

[0036] Place the lithium iron phosphate in the coating solution, take it out, and then perform centrifugation, drying, and sintering to obtain the lithium iron phosphate coated with carbon and Li5FeO4 on the surface.

[0037] Specifically, based on the lithium atoms and iron atoms, the molar ratio of the lithium salt to the iron salt is (5-6):1. The lithium salt is selected from lithium squarate, lithium nitrate, and lithium sulfate, and the iron salt is selected from iron nitrate and iron sulfate. During sintering, the temperature is 850-950°C and the time is 15-20h.

[0038] Another specific embodiment of the present invention provides a method for preparing an in-situ lithium-supplemented cathode material. According to the ratio, mix the lithium iron phosphate coated with carbon and Li5FeO4 on the surface, the conductive agent, the binder, the additive, and the solvent to obtain the in-situ lithium-supplemented cathode material.

[0039] The following further elaborates on the present invention with specific examples.

[0040] In the present invention, the brand of aldehyde group-polyethylene glycol-aldehyde group is Tansh, and the product number is 80020109; polyethyleneimine is purchased from Shanghai Aladdin; the brand of polyvinylidene fluoride is Arkema, and the grade is FR902.

[0041] Preparation Example 1

[0042] Take lithium squarate and iron nitrate, with a molar ratio of lithium atoms to iron atoms of 6:1. Add lithium squarate and antimony nitrate to a 5M dopamine weak alkaline aqueous solution (pH 8.5) to make a coating solution. Immerse the lithium iron phosphate in the coating solution, take it out, centrifuge and dry it. This step is repeated 10 times to obtain a preliminary product. Sinter the preliminary product at 850°C for 15h to obtain the lithium iron phosphate coated with carbon and Li5FeO4 on the surface.

[0043] Preparation Example 2

[0044] Mix aldehyde group - polyethylene glycol - aldehyde group and methanol in a mass ratio of 1:5, mix polyethyleneimine and methanol in a mass ratio of 1:5, then mix the aldehyde group - polyethylene glycol - aldehyde group solution and the polyethyleneimine solution according to a mass ratio of aldehyde group - polyethylene glycol - aldehyde group to polyethyleneimine of 1:1, react at room temperature for 30 min, after the reaction, dry the reaction solution at 50 °C for 10 h to obtain polyethyleneimine modified with aldehyde group - polyethylene glycol - aldehyde group.

[0045] Preparation Example 3

[0046] Mix aldehyde group - polyethylene glycol - aldehyde group and methanol in a mass ratio of 1:5, mix polyethyleneimine and methanol in a mass ratio of 1:5, then mix the aldehyde group - polyethylene glycol - aldehyde group solution and the polyethyleneimine solution according to a mass ratio of aldehyde group - polyethylene glycol - aldehyde group to polyethyleneimine of 2:1, react at room temperature for 30 min, after the reaction, dry the reaction solution at 50 °C for 10 h to obtain polyethyleneimine modified with aldehyde group - polyethylene glycol - aldehyde group.

[0047] Preparation Example 4

[0048] Mix aldehyde group - polyethylene glycol - aldehyde group and methanol in a mass ratio of 1:5, mix polyethyleneimine and methanol in a mass ratio of 1:5, then mix the aldehyde group - polyethylene glycol - aldehyde group solution and the polyethyleneimine solution according to a mass ratio of aldehyde group - polyethylene glycol - aldehyde group to polyethyleneimine of 3:1, react at room temperature for 30 min, after the reaction, dry the reaction solution at 50 °C for 10 h to obtain polyethyleneimine modified with aldehyde group - polyethylene glycol - aldehyde group.

[0049] Preparation Example 5

[0050] Mix aldehyde group - polyethylene glycol - aldehyde group and methanol in a mass ratio of 1:5, mix polyethyleneimine and methanol in a mass ratio of 1:5, then mix the aldehyde group - polyethylene glycol - aldehyde group solution and the polyethyleneimine solution according to a mass ratio of aldehyde group - polyethylene glycol - aldehyde group to polyethyleneimine of 0.6:1, react at room temperature for 30 min, after the reaction, dry the reaction solution at 50 °C for 10 h to obtain polyethyleneimine modified with aldehyde group - polyethylene glycol - aldehyde group.

[0051] Example 1

[0052] By weight, take 80 parts of lithium iron phosphate coated with carbon and Li5FeO4 on the surface, 6 parts of conductive carbon black, 5 parts of binder, 3 parts of titanium dioxide, and 40 parts of NMP. The binder includes polyvinylidene fluoride and polyethyleneimine modified with aldehyde group - polyethylene glycol - aldehyde group in Preparation Example 2 in a mass ratio of 1:2. Mix the above - mentioned raw materials and stir evenly to obtain an in - situ lithium - supplemented cathode material.

[0053] Example 2

[0054] Taking 86 parts of lithium iron phosphate coated with carbon and Li5FeO4, 5 parts of conductive carbon black, 8 parts of binder, 5 parts of titanium dioxide, and 50 parts of NMP by weight, wherein the binder includes polyvinylidene fluoride and the aldehyde group polyethylene glycol aldehyde group modified polyethyleneimine in Preparation Example 2 with a mass ratio of 1:2, mixing the above raw materials and stirring evenly to obtain an in-situ lithium-supplemented cathode material.

[0055] Example 3

[0056] Taking 90 parts of lithium iron phosphate coated with carbon and Li5FeO4, 8 parts of conductive carbon black, 7 parts of binder, 4 parts of titanium dioxide, and 46 parts of NMP by weight, wherein the binder includes polyvinylidene fluoride and the aldehyde group polyethylene glycol aldehyde group modified polyethyleneimine in Preparation Example 2 with a mass ratio of 1:2, mixing the above raw materials and stirring evenly to obtain an in-situ lithium-supplemented cathode material.

[0057] Example 4

[0058] Taking 80 parts of lithium iron phosphate coated with carbon and Li5FeO4, 6 parts of conductive carbon black, 5 parts of binder, 3 parts of titanium dioxide, and 40 parts of NMP by weight, wherein the binder includes polyvinylidene fluoride and the aldehyde group polyethylene glycol aldehyde group modified polyethyleneimine in Preparation Example 2 with a mass ratio of 1:3, mixing the above raw materials and stirring evenly to obtain an in-situ lithium-supplemented cathode material.

[0059] Example 5

[0060] Taking 80 parts of lithium iron phosphate coated with carbon and Li5FeO4, 6 parts of conductive carbon black, 5 parts of binder, 3 parts of titanium dioxide, and 40 parts of NMP by weight, wherein the binder includes polyvinylidene fluoride and the aldehyde group polyethylene glycol aldehyde group modified polyethyleneimine in Preparation Example 3 with a mass ratio of 1:2, mixing the above raw materials and stirring evenly to obtain an in-situ lithium-supplemented cathode material.

[0061] Example 6

[0062] Taking 80 parts of lithium iron phosphate coated with carbon and Li5FeO4, 6 parts of conductive carbon black, 5 parts of binder, 3 parts of titanium dioxide, and 40 parts of NMP by weight, wherein the binder includes polyvinylidene fluoride and the aldehyde group polyethylene glycol aldehyde group modified polyethyleneimine in Preparation Example 4 with a mass ratio of 1:2, mixing the above raw materials and stirring evenly to obtain an in-situ lithium-supplemented cathode material.

[0063] Example 7

[0064] Taking 80 parts of lithium iron phosphate coated with carbon and Li5FeO4 on the surface, 6 parts of conductive carbon black, 5 parts of binder, 3 parts of titanium dioxide, and 40 parts of NMP by weight, wherein the binder comprises polyvinylidene fluoride and aldehyde group polyethylene glycol aldehyde group modified polyethyleneimine in a mass ratio of 1:2. Mix the above raw materials and stir evenly to obtain the in-situ lithium-complemented cathode material.

[0065] Comparative Example 1

[0066] Taking 80 parts of lithium iron phosphate coated with carbon and Li5FeO4 on the surface, 6 parts of conductive carbon black, 5 parts of polyvinylidene fluoride, 3 parts of titanium dioxide, and 40 parts of NMP by weight. Mix the above raw materials and stir evenly to obtain the in-situ lithium-complemented cathode material.

[0067] Comparative Example 2

[0068] Taking 80 parts of lithium iron phosphate coated with carbon and Li5FeO4 on the surface, 6 parts of conductive carbon black, 5 parts of binder, 3 parts of titanium dioxide, and 40 parts of NMP by weight, wherein the binder comprises polyvinylidene fluoride and polyethyleneimine in a mass ratio of 1:2. Mix the above raw materials and stir evenly to obtain the in-situ lithium-complemented cathode material.

[0069] Performance Test

[0070] Coat the in-situ lithium-complemented cathode materials in each example and each comparative example evenly on the aluminum foil, and place them in an 80°C oven for drying to obtain the positive electrode sheets. Assemble the positive electrode sheets into button cells, the electrolyte is 1 mol / L LiPF6 (EC:DMC = 1:1), and the negative electrode uses lithium sheets.

[0071] Perform constant current charge and discharge tests on the button cells, the charge and discharge voltage range is 2.0 - 3.8V, the charge and discharge rate is 1C, record the capacity retention rate of the battery after 500 cycles, and record the initial Coulomb efficiency at the same time.

[0072] Table 1 Performance Test Results

[0073]

[0074] As can be seen from Table 1, compared with Comparative Example 1, the present invention uses a compound of polyvinylidene fluoride and aldehyde group polyethylene glycol aldehyde group modified polyethyleneimine, which can better improve the initial loss of the battery in the first cycle, and can also maintain the stability of the battery in subsequent cycles.

[0075] Compared with Comparative Example 2, the present invention uses aldehyde group polyethylene glycol aldehyde group to modify polyethyleneimine, which can promote the formation of the network structure, improve the adhesion of the binder to each raw material component, thereby ensuring the stability of the structure and performance of the cathode material and improving the electrochemical performance of the battery.

[0076] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above-described exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, in any regard, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be embraced within the present invention. In addition, it should be understood that although this specification is described in terms of embodiments, not every embodiment only contains an independent technical solution. This narrative manner of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. An in-situ lithium supplementation positive electrode material, characterized in that: The invention comprises the following components by weight: 80-90 parts of lithium iron phosphate coated with carbon and Li5FeO4, 5-8 parts of a conductive agent, 5-8 parts of a binder, 3-5 parts of an additive and 40-50 parts of a solvent; The binder is a compound of polyvinylidene fluoride and aldehyde-modified polyethyleneimine of aldehyde-polyethylene glycol.

2. The in-situ lithium supplementation positive electrode material according to claim 1, characterized in that: The mass ratio of the polyvinylidene fluoride to the aldehyde-polyethylene glycol aldehyde-modified polyethyleneimine is 1:(2-3).

3. The in-situ lithium supplementation positive electrode material according to claim 1, characterized in that: The preparation of the aldehyde-polyethylene glycol aldehyde-modified polyethyleneimine is as follows: The aldehyde group polyethylene glycol aldehyde group and polyethylene imine are dissolved in solvents to prepare a first solution and a second solution respectively, the first solution and the second solution are mixed, and reacted at room temperature to obtain the aldehyde group polyethylene glycol aldehyde group-modified polyethylene imine.

4. The in-situ lithium supplementation positive electrode material according to claim 3, characterized in that: The mass ratio of the aldehyde polyethylene glycol aldehyde group to the polyethylene imine is (1-3):

1.

5. The in-situ lithium supplementation positive electrode material according to claim 1, characterized in that: The additive is at least one of silicon oxide, zirconium oxide and titanium dioxide.

6. The in-situ lithium supplementation positive electrode material according to claim 1, characterized in that: The conductive agent is at least one of conductive carbon black, carbon nanotubes, graphene, and carbon fiber.

7. The in-situ lithium supplementation positive electrode material according to claim 1, characterized in that: The lithium iron phosphate coated with carbon and Li5FeO4 is prepared by the following method: dissolving lithium salt and iron salt in dopamine solution to prepare an encapsulation solution; The lithium iron phosphate is placed in a coating liquid, taken out, centrifuged, dried, and sintered to obtain lithium iron phosphate with carbon and Li5FeO4 coated on the surface.

8. The in-situ lithium supplementation positive electrode material according to claim 7, characterized in that: The molar ratio of the lithium salt and the iron salt is (5-6):1, calculated based on lithium atoms and iron atoms.

9. The in-situ lithium supplementation positive electrode material according to claim 7, characterized in that: The lithium salt is selected from lithium squarate, lithium nitrate and lithium sulfate, and the iron salt is selected from iron nitrate and iron sulfate.

10. A method for preparing an in-situ lithium supplementation positive electrode material according to any one of claims 1 to 9, characterized in that: According to the proportion, lithium iron phosphate with carbon and Li5FeO4 coated on the surface, a conductive agent, a binder, an additive and a solvent are mixed evenly to obtain an in-situ lithium replenishment positive electrode material.

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