In-situ lithium-supplementing positive electrode material and preparation method thereof

Abstract

The invention discloses an in-situ lithium-supplementing positive electrode material and a preparation method thereof. The in-situ lithium-supplementing positive electrode 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 formed by compounding polyvinylidene fluoride and polyethyleneimine modified by aldehyde group polyethylene glycol aldehyde group. According to the in-situ lithium-supplementing positive electrode material, the cycling stability of a positive electrode can be improved, and the electrochemical performance of a battery is effectively improved.

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 wide attention.

[0003] Among many lithium-supplementing technologies, the cathode lithium-supplementing technology has attracted the attention of many enterprises due to 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: 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 Li 5 FeO 4 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; Among them, the binder is a compound of polyvinylidene fluoride and polyethyleneimine modified with aldehyde group polyethylene glycol aldehyde group.

[0006] 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).

[0007] 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: 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.

[0008] 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.

[0009] In one or more embodiments of the present invention, the additive is at least one of silicon oxide, zirconium oxide, and titanium dioxide.

[0010] 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.

[0011] In one or more embodiments of the present invention, the lithium iron phosphate surface-coated with carbon and Li 5 FeO 4 is prepared by the following method: Dissolve the lithium salt and the iron salt in a dopamine solution to make a coating solution; Place the lithium iron phosphate in the coating solution, take it out, and after centrifugation, drying, and sintering, obtain the lithium iron phosphate surface-coated with carbon and Li 5 FeO 4 .

[0012] In one or more embodiments of the present invention, based on the lithium atoms and iron atoms, the molar ratio of the lithium salt to the iron salt is (5-6):1.

[0013] 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 ferric nitrate and ferric sulfate.

[0014] The technical solution provided by another specific embodiment of the present invention is as follows: A method for preparing an in-situ lithium-supplemented cathode material, according to the ratio, mix the lithium iron phosphate surface-coated with carbon and Li 5 FeO 4 , a conductive agent, a binder, an additive, and a solvent to obtain an in-situ lithium-supplemented cathode material.

[0015] Compared with the prior art, the present invention first coats carbon and Li on the surface of lithium iron phosphate 5 FeO 4 , improving the cycle performance of the battery. Secondly, by compounding polyvinylidene fluoride and polyethyleneimine modified with aldehyde group polyethylene glycol aldehyde group, the stability of the cathode material is improved, thereby improving the electrochemical performance of the battery. Specific Embodiments

[0016] 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 of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

[0017] A specific embodiment of the present invention provides an in-situ lithium-supplemented cathode component, comprising the following components in parts by weight: lithium iron phosphate coated with carbon and Li 5 FeO 4 80 - 90 parts, conductive agent 5 - 8 parts, binder 5 - 8 parts, additive 3 - 5 parts, and solvent 40 - 50 parts; wherein, the binder is a compound of polyvinylidene fluoride and polyethyleneimine modified with aldehyde group polyethylene glycol aldehyde group.

[0018] Further, the mass ratio of polyvinylidene fluoride to polyethyleneimine modified with aldehyde group polyethylene glycol aldehyde group is 1:(2 - 3).

[0019] 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 Li 5 FeO 4 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 cycle 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 Li 5 FeO 4 used in the present invention can better improve the initial charge-discharge capacity and cycle stability of the cathode material.

[0020] 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 active material from falling off. Polyethyleneimine modified with aldehyde group polyethylene glycol aldehyde group has a network structure, which can effectively adhere to each raw material component. The polyethylene glycol chain in the aldehyde group polyethylene glycol aldehyde group 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.

[0021] Further, the preparation of polyethyleneimine modified with aldehyde group polyethylene glycol aldehyde group is as follows: 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 the reaction at room temperature. After the reaction, polyethyleneimine modified with aldehyde group polyethylene glycol aldehyde group is obtained.

[0022] Further, the mass ratio of aldehyde group polyethylene glycol aldehyde group to polyethyleneimine is (1 - 3):1.

[0023] Specifically, by controlling the dosage of aldehyde group polyethylene glycol aldehyde group, the prepared polyethyleneimine modified by aldehyde group polyethylene glycol aldehyde group can better improve the charge and discharge performance of the positive electrode.

[0024] 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 positive electrode material and contribute to improving the cycle stability of the battery.

[0025] Further, the conductive agent is at least one of conductive carbon black, carbon nanotubes, graphene, and carbon fibers.

[0026] Further, the solvent is NMP (N-methylpyrrolidone).

[0027] Further, the lithium iron phosphate coated with carbon and Li 5 FeO 4 is prepared by the following method: Dissolve the lithium salt and the iron salt in the dopamine solution to make a coating solution; Place the lithium iron phosphate in the coating solution, take it out, and after centrifugation, drying, and sintering, obtain the lithium iron phosphate coated with carbon and Li 5 FeO 4

[0028] 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 15-20 h.

[0029] Another specific embodiment of the present invention provides a method for preparing an in-situ lithium-supplemented positive electrode material. According to the ratio, mix the lithium iron phosphate coated with carbon and Li 5 FeO 4 with the conductive agent, binder, additive, and solvent to obtain the in-situ lithium-supplemented positive electrode material.

[0030] The following further elaborates on the present invention with specific examples.

[0031] 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; polyvinylidene fluoride has the brand Arkema and the grade FR902.

[0032] Preparation Example 1 ​Take lithium squarate and iron nitrate. Based on the molar ratio of lithium atoms to iron atoms being 6:1, add lithium squarate and antimony nitrate to a weakly alkaline aqueous dopamine solution with a concentration of 5M (pH 8.5) to prepare a coating solution. Immerse lithium iron phosphate in the coating solution, take it out and centrifuge and dry it. Repeat this step 10 times to obtain a preliminary product. Sinter the preliminary product at 850 °C for 15 h to obtain lithium iron phosphate with carbon and Li5FeO4 coated on its surface.

[0033] Preparation Example 2 Mix aldehyde group polyethylene glycol aldehyde group and methanol in a mass ratio of 1:5, and 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 the mass ratio of aldehyde group polyethylene glycol aldehyde group to polyethyleneimine being 1:1, and 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.

[0034] Preparation Example 3 Mix aldehyde group polyethylene glycol aldehyde group and methanol in a mass ratio of 1:5, and 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 the mass ratio of aldehyde group polyethylene glycol aldehyde group to polyethyleneimine being 2:1, and 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.

[0035] Preparation Example 4 Mix aldehyde group polyethylene glycol aldehyde group and methanol in a mass ratio of 1:5, and 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 the mass ratio of aldehyde group polyethylene glycol aldehyde group to polyethyleneimine being 3:1, and 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.

[0036] Preparation Example 5 Mix aldehyde group polyethylene glycol aldehyde group and methanol in a mass ratio of 1:5, and 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 the mass ratio of aldehyde group polyethylene glycol aldehyde group to polyethyleneimine being 0.6:1, and 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.

[0037] Example 1 By weight, take the one with carbon and Li 5 FeO 480 parts of lithium iron phosphate, 6 parts of conductive carbon black, 5 parts of binder, 3 parts of titanium dioxide, 40 parts of NMP. The binder includes polyvinylidene fluoride and aldehyde group polyethylene glycol aldehyde group modified polyethyleneimine in Preparation Example 2 with a mass ratio of 1:2. Mix the above raw materials and stir evenly to obtain the in-situ lithium-supplemented cathode material.

[0038] Example 2 By weight, take lithium iron phosphate coated with carbon and Li 5 FeO 4 86 parts, 5 parts of conductive carbon black, 8 parts of binder, 5 parts of titanium dioxide, 50 parts of NMP. The binder includes polyvinylidene fluoride and aldehyde group polyethylene glycol aldehyde group modified polyethyleneimine in Preparation Example 2 with a mass ratio of 1:2. Mix the above raw materials and stir evenly to obtain the in-situ lithium-supplemented cathode material.

[0039] Example 3 By weight, take lithium iron phosphate coated with carbon and Li 5 FeO 4 90 parts, 8 parts of conductive carbon black, 7 parts of binder, 4 parts of titanium dioxide, 46 parts of NMP. The binder includes polyvinylidene fluoride and aldehyde group polyethylene glycol aldehyde group modified polyethyleneimine in Preparation Example 2 with a mass ratio of 1:2. Mix the above raw materials and stir evenly to obtain the in-situ lithium-supplemented cathode material.

[0040] Example 4 By weight, take lithium iron phosphate coated with carbon and Li 5 FeO 4 80 parts, 6 parts of conductive carbon black, 5 parts of binder, 3 parts of titanium dioxide, 40 parts of NMP. The binder includes polyvinylidene fluoride and aldehyde group polyethylene glycol aldehyde group modified polyethyleneimine in Preparation Example 2 with a mass ratio of 1:3. Mix the above raw materials and stir evenly to obtain the in-situ lithium-supplemented cathode material.

[0041] Example 5 By weight, take lithium iron phosphate coated with carbon and Li 5 FeO 4 80 parts, 6 parts of conductive carbon black, 5 parts of binder, 3 parts of titanium dioxide, 40 parts of NMP. The binder includes polyvinylidene fluoride and aldehyde group polyethylene glycol aldehyde group modified polyethyleneimine in Preparation Example 3 with a mass ratio of 1:2. Mix the above raw materials and stir evenly to obtain the in-situ lithium-supplemented cathode material.

[0042] Example 6 By weight, take lithium iron phosphate coated with carbon and Li 5 FeO 480 parts of lithium iron phosphate, 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 aldehyde group polyethylene glycol aldehyde group modified polyethyleneimine in Preparation Example 4 with a mass ratio of 1:2. Mix the above raw materials and stir evenly to obtain the in-situ lithium-supplemented cathode material.

[0043] Example 7 By weight, take lithium iron phosphate coated with carbon and Li 5 FeO 4 80 parts of lithium iron phosphate, 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 aldehyde group polyethylene glycol aldehyde group modified polyethyleneimine in Preparation Example 5 with a mass ratio of 1:2. Mix the above raw materials and stir evenly to obtain the in-situ lithium-supplemented cathode material.

[0044] Comparative Example 1 By weight, take lithium iron phosphate coated with carbon and Li 5 FeO 4 80 parts of lithium iron phosphate, 6 parts of conductive carbon black, 5 parts of polyvinylidene fluoride, 3 parts of titanium dioxide, and 40 parts of NMP. Mix the above raw materials and stir evenly to obtain the in-situ lithium-supplemented cathode material.

[0045] Comparative Example 2 By weight, take lithium iron phosphate coated with carbon and Li 5 FeO 4 80 parts of lithium iron phosphate, 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 with a mass ratio of 1:2. Mix the above raw materials and stir evenly to obtain the in-situ lithium-supplemented cathode material.

[0046] Performance Test Uniformly coat the in-situ lithium-supplemented cathode materials in each example and each comparative example on the aluminum foil, and place them in an oven at 80 °C for drying to obtain the positive electrode sheets. Assemble the positive electrode sheets into button cells, and the electrolyte is 1 mol / L LiPF 6 (EC:DMC = 1:1), and the negative electrode uses a lithium sheet.

[0047] Conduct a constant current charge-discharge test on the button cells. The charge-discharge voltage range is 2.0 - 3.8 V, and the charge-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.

[0048] Table 1 Performance Test Results As can be seen from Table 1, compared with Comparative Example 1, the present invention uses a combination of polyvinylidene fluoride and polyethyleneimine modified with aldehyde group polyethylene glycol aldehyde group, which can better improve the initial loss of the battery in the first cycle and maintain the stability of the battery in subsequent cycles.

[0049] Compared with Comparative Example 2, the present invention uses aldehyde group polyethylene glycol aldehyde group to modify polyethyleneimine, which can promote the formation of a network structure, improve the adhesion of the binder to each raw material component, thereby ensuring the stability of the structure and performance of the positive electrode material and improving the electrochemical performance of the battery.

[0050] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above 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, from any point of view, 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 included in the present invention. In addition, it should be understood that although this specification is described according to embodiments, not every embodiment only contains an independent technical solution. This narrative way 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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