CN114447307A - Composite positive electrode material, preparation method thereof and electrochemical energy storage device - Google Patents

Abstract

The invention provides a composite anode material, a preparation method thereof and an electrochemical energy storage device. The composite positive electrode material comprises lithium ferrite and a polymer layer coated on the surface of the lithium ferrite; the polymer layer is an olefin-acrylate copolymer. According to the invention, the olefin-acrylate copolymer is coated on the surface of the lithium ferrite to form a hydrophobic polymer layer, so that the structure of the lithium ferrite powder is prevented from being damaged by water molecules, and the olefin-acrylate copolymer can be uniformly dispersed in an N-methyl pyrrolidone solvent and cannot influence the lithium removal process of the lithium ferrite when the composite anode material is in the slurry preparation process of the anode plate.

Description

A composite cathode material, preparation method thereof, and electrochemical energy storage device

technical field

The invention belongs to the technical field of electrode materials, and particularly relates to a composite positive electrode material, a preparation method thereof, and an electrochemical energy storage device.

Background technique

At present, lithium-ion batteries have been widely used in various fields of life. As a commonly used cathode material, lithium ferrite has a specific capacity as high as 650mAh/g. In order to further improve the energy density and cycle life of lithium-ion batteries, research Lithium ferrite has a broad application prospect by adding lithium ferrite to the lithium-ion battery to supplement the active lithium lost due to the formation of the solid electrolyte (SEI) film in the lithium-ion battery. There are still some problems to be solved.

In order to solve the problem that the lithium ferrite powder is easily exposed to the air to have side reactions with water, which leads to a serious loss of the charging capacity of lithium ferrite, at present, a protective layer of amorphous carbon is coated on the surface of lithium ferrite. Avoid direct contact between lithium ferrite and moisture in the environment, thereby reducing the damage of moisture to lithium ferrite powder. At the same time, coating an amorphous carbon protective layer on the surface of lithium ferrite can improve the conductivity of lithium ferrite powder. , which is conducive to the extraction of lithium ions in lithium ferrite. For example, by directly mixing and grinding lithium ferrite and graphite, the graphite is coated on the surface of lithium ferrite, but this method is prone to uneven coating; Alkane and other alkane gases form a uniform carbon layer on the surface of lithium ferrite powder by chemical vapor deposition, but the cost of pure alkane gas is high, which is not conducive to the coating of large-scale cathode materials and application. In addition, the hydrothermal method uses the organic carbon source such as lithium source, carbon source and sugars to be uniformly mixed, and then carbonizes the organic matter on the surface of lithium ferrite by calcination to carry out in-situ carbon coating. However, this method is easy to As a result, the surface carbon layer reduces the ferric iron in the lithium ferrite and causes a capacity loss to the lithium ferrite.

Therefore, in the art, it is expected to develop a cathode material that can not only improve the stability of the lithium ferrite material in air, but also has a simple preparation method, and the prepared lithium ion battery has good electrochemical performance.

SUMMARY OF THE INVENTION

In view of the deficiencies of the prior art, the purpose of the present invention is to provide a composite positive electrode material, a preparation method thereof, and an electrochemical energy storage device. The composite positive electrode material provided by the invention effectively solves the problem that lithium ferrite is unstable in the air and easily absorbs moisture, and improves the electrochemical performance of the composite positive electrode material.

In order to achieve this object of the invention, the present invention adopts the following technical solutions:

In a first aspect, the present invention provides a composite positive electrode material, the composite positive electrode material includes lithium ferrite and a polymer layer coated on the surface of the lithium ferrite;

The polymer layer is an olefin-acrylate copolymer.

The invention uses olefin-acrylate copolymer to coat the surface of lithium ferrite to form a layer of hydrophobic polymer layer, which not only prevents water molecules from destroying the structure of lithium ferrite powder, but also the slurry of composite positive electrode material on the positive electrode sheet. During the preparation process, the olefin-acrylate copolymer can be uniformly dispersed in the N-methylpyrrolidone solvent without affecting the delithiation process of lithium ferrite. This method can effectively improve the practical application of lithium ferrite. performance.

Preferably, the olefin-acrylate copolymers include ethylene-methyl methacrylate copolymer, propylene-methyl methacrylate copolymer, ethylene-ethyl methacrylate, propylene-ethyl methacrylate, ethylene -Any one or a combination of at least two of propyl methacrylate or propylene-butyl methacrylate, such as ethylene-methyl methacrylate copolymer and propylene-methyl methacrylate copolymer, ethylene -Ethyl methacrylate or propylene-ethyl methacrylate, but are not limited to the types listed, and the types not listed within the scope of olefin-acrylate copolymers are equally applicable.

Preferably, the weight average molecular weight of the olefin-acrylate copolymer is 10,000 to 100,000, such as 10,000, 12,000, 15,000, 17,000, 20,000, 22,000, 25,000, 27,000, 30,000, 32,000, 35,000, 37,000, 40,000, 42000, 45000, 47000, 50000, 52000, 55000, 57000, 60000, 62000, 65000, 67000, 70000, 72000, 75000, 77000, 80000, 82000, 85000, 87000, 90000, 0.9

In the present invention, the weight average molecular weight of the olefin-acrylate copolymer is adjusted so that the copolymer can be uniformly coated on the surface of lithium ferrite, and the weight average molecular weight of the olefin-acrylate copolymer is too low The coating of lithium ferrite will be uneven, otherwise, it will be difficult to uniformly disperse the copolymer in the solvent, and the lithium ferrite particles cannot be coated.

Preferably, the mass percentage content of the polymer layer in the composite positive electrode material is 1-10%, for example, it can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%.

In the present invention, by adjusting the mass percentage content of the polymer layer in the composite positive electrode material, the composite positive electrode material has a higher specific charge capacity and promotes lithium ion transport, and the quality of the polymer layer in the composite positive electrode material is If the percentage is too low, the coating layer will be too thin and easily broken, otherwise, the coating layer will be too thick, which will lead to difficulty in lithium ion transmission.

In a second aspect, the present invention provides a method for preparing the composite cathode material described in the first aspect, the method comprising the following steps:

The lithium source and the iron source are mixed, calcined to obtain lithium ferrite powder, and then the lithium ferrite powder and the olefin-acrylate copolymer solution are mixed for a second time, and the solvent is removed to obtain the composite positive electrode material.

Preferably, the lithium source includes any one or a combination of at least two of lithium carbonate, lithium hydroxide, lithium oxide or lithium nitride, such as lithium carbonate and lithium hydroxide, lithium oxide or lithium nitride, However, it is not limited to the types listed, and the types not listed in the lithium source range are also applicable.

Preferably, the iron source comprises any one or a combination of at least two of iron oxide, iron hydroxide, iron nitrate or iron oxalate, such as iron oxide and iron hydroxide, iron nitrate or iron oxalate, but not Limited to the types listed, types not listed in the iron source range are also applicable.

Preferably, the mass ratio of the lithium source and the iron source is (5-10):1, such as 5:1, 6:1, 7:1, 8:1, 9:1, 10:1.

Preferably, the calcination temperature is 700-900°C, for example, 700°C, 720°C, 750°C, 770°C, 800°C, 820°C, 850°C, 870°C, and 900°C.

Preferably, the calcination time is 8-12h, for example, it can be 8h, 9h, 10h, 11h, 12h.

In the present invention, the calcination is carried out in air, nitrogen or argon.

Preferably, the mass concentration of the olefin-acrylate copolymer solution is 1-10%, such as 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% %, 10%.

In the present invention, the olefin-acrylate copolymer solution is prepared by dispersing the olefin-acrylate copolymer into an organic solution, and the organic solvent is selected from N,N-dimethylformamide, dimethylformamide, and dimethylformamide. Any one of sulfoxide, N-methylpyrrolidone, dichloromethane, dichloroethane, ethyl acetate or ethylene glycol dimethyl ether.

In the present invention, by adjusting the mass concentration of the olefin-acrylate copolymer solution, if the mass concentration of the olefin-acrylate copolymer solution is too low, the coating layer will be too thin, otherwise, the dispersion will be uneven .

Preferably, the secondary mixing is carried out with stirring.

Preferably, the stirring time is 30 to 90 minutes, for example, 30 minutes, 35 minutes, 40 minutes, 45 minutes, 50 minutes, 55 minutes, 60 minutes, 65 minutes, 70 minutes, 75 minutes, 80 minutes, 85 minutes, and 90 minutes.

Preferably, the pressure for removing the solvent is -500kpa～-50kpa, such as -50kpa, -80kpa, -100kpa, -120kpa, -140kpa, -160kpa, -180kpa, -200kpa, -220kpa, -240kpa, - 260kpa, -300kpa, -320kpa, -340kpa, -360kpa, -400kpa, -420kpa, -440kpa, -460kpa, -480kpa, -500kpa.

Preferably, the temperature for removing the solvent is 80-200°C, such as 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C, 120°C, 125°C, 130°C , 135℃, 140℃, 145℃, 150℃, 155℃, 160℃, 165℃, 170℃, 175℃, 180℃, 185℃, 190℃, 195℃, 200℃.

Preferably, after removing the solvent, cooling treatment is also included.

In a third aspect, the present invention provides an electrochemical energy storage device, the electrochemical energy storage device includes a positive electrode, a negative electrode and an electrolyte, and the positive electrode is the composite positive electrode material described in the first aspect.

Compared with the prior art, the present invention has the following beneficial effects:

The invention provides a hydrophobic polymer layer formed on the surface of lithium ferrite by using olefin-acrylate copolymer, which not only prevents water molecules from destroying the structure of lithium ferrite powder, but also prevents the composite positive electrode material from destroying the structure of the lithium ferrite powder. During the preparation of the slurry of the sheet, the olefin-acrylate copolymer can be uniformly dispersed in the N-methylpyrrolidone solvent, and at the same time, it will not affect the delithiation process of lithium ferrite. This method can effectively improve the ferric acid. Practical application properties of lithium.

Description of drawings

FIG. 1 is a SEM characterization diagram of the composite cathode material provided in Example 1, and its scale is 1 μm;

FIG. 2 is a charging curve diagram of the composite cathode material provided in Example 1. FIG.

Detailed ways

The technical solutions of the present invention will be further described below with reference to the accompanying drawings and specific embodiments. It should be understood by those skilled in the art that the embodiments are only for helping the understanding of the present invention, and should not be regarded as a specific limitation of the present invention.

Example 1

This embodiment provides a composite positive electrode material, the composite positive electrode material includes lithium ferrite and a polymer layer of ethylene-methyl methacrylate copolymer coated on the surface of lithium ferrite, wherein the composite positive electrode material is The mass percentage of the polymer layer is 5%.

The preparation method comprises the following steps:

Lithium carbonate and iron oxide with a mass ratio of 7:1 were mixed, and calcined at 800 °C for 10 h in an argon atmosphere to obtain lithium ferrite powder, and an ethylene-methyl methacrylate copolymer with a weight average molecular weight of 50,000 was obtained. Disperse in the dimethyl sulfoxide solvent to form an ethylene-methyl methacrylate copolymer solution with a mass concentration of 5%, and then stir the lithium ferrite powder and the ethylene-methyl methacrylate copolymer solution. The time is 60 min, and the solvent is removed at a pressure of -250 kpa and 140° C. and then cooled to finally obtain the composite cathode material.

FIG. 1 is a SEM characterization diagram of the composite positive electrode material provided in Example 1, and it can be seen that the composite positive electrode material is irregular bulk particles.

Example 2

This embodiment provides a composite positive electrode material, the composite positive electrode material includes lithium ferrite and a polymer layer of a propylene-methyl methacrylate copolymer coated on the surface of the lithium ferrite, wherein the composite positive electrode material is The mass percentage of the polymer layer is 3%.

The preparation method comprises the following steps:

Lithium hydroxide and ferric nitrate with a mass ratio of 6:1 were mixed, calcined at 750 °C for 11 h in an argon atmosphere to obtain lithium ferrite powder, and propylene-methyl methacrylate with a weight average molecular weight of 30,000 was copolymerized The material was dispersed in N,N-dimethylformamide solvent to form a propylene-methyl methacrylate copolymer solution with a mass concentration of 3%, and then the lithium ferrite powder and propylene-methyl methacrylate copolymer were mixed. Stir, the stirring time is 45 min, and the solvent is removed at a pressure of -150 kpa and 110° C. and then cooled to finally obtain the composite positive electrode material.

Example 3

This embodiment provides a composite positive electrode material, the composite positive electrode material includes lithium ferrite and a polymer layer of propylene-ethyl methacrylate copolymer coated on the surface of the lithium ferrite, wherein the composite positive electrode material is The mass percentage of the polymer layer is 7%.

The preparation method comprises the following steps:

Lithium carbonate and iron oxide with a mass ratio of 8:1 were mixed, calcined at 850 °C for 9 hours in a nitrogen atmosphere to obtain lithium ferrite powder, and the propylene-ethyl methacrylate copolymer with a weight average molecular weight of 70,000 was dispersed A propylene-ethyl methacrylate copolymer solution with a mass concentration of 7% was formed in an ethyl acetate solvent, and then the lithium ferrite powder and the propylene-ethyl methacrylate copolymer solution were stirred for 75 minutes. , remove the solvent at a pressure of -380kpa and 170°C, and then cool down to finally obtain the composite cathode material.

Example 4

This embodiment provides a composite positive electrode material, the composite positive electrode material includes lithium ferrite and a polymer layer of ethylene-methyl methacrylate copolymer coated on the surface of lithium ferrite, wherein the composite positive electrode material is The mass percentage of the polymer layer is 1%.

The preparation method comprises the following steps:

Lithium carbonate and iron oxide with a mass ratio of 5:1 were mixed, calcined at 700 °C for 12 hours in an argon atmosphere to obtain lithium ferrite powder, and ethylene-methyl methacrylate copolymer with a weight average molecular weight of 10,000 was obtained. Disperse in the dimethyl sulfoxide solvent to form an ethylene-methyl methacrylate copolymer solution with a mass concentration of 1%, and then stir the lithium ferrite powder and the ethylene-methyl methacrylate copolymer solution. The time is 30 min, and the solvent is removed at a pressure of -50 kpa and 80° C. and then cooled to finally obtain the composite positive electrode material.

Example 5

This embodiment provides a composite positive electrode material, the composite positive electrode material includes lithium ferrite and a polymer layer of ethylene-methyl methacrylate copolymer coated on the surface of lithium ferrite, wherein the composite positive electrode material is The mass percentage of the polymer layer is 10%.

The preparation method comprises the following steps:

Lithium carbonate and iron oxide with a mass ratio of 10:1 were mixed, calcined at 900 °C for 8 hours in an argon atmosphere to obtain lithium ferrite powder, and ethylene-methyl methacrylate copolymer with a weight average molecular weight of 100,000 was obtained. Disperse in the dimethyl sulfoxide solvent to form an ethylene-methyl methacrylate copolymer solution with a mass concentration of 10%, and then stir the lithium ferrite powder and the ethylene-methyl methacrylate copolymer solution. The time is 90 min, and the solvent is removed at a pressure of -500 kpa and 200° C. and then cooled to finally obtain the composite positive electrode material.

Comparative Example 1

The difference between this comparative example and Example 1 is that in the preparation process, the weight-average molecular weight of the ethylene-methyl methacrylate copolymer is 5000, and the others are the same as those in Example 1.

Comparative Example 2

The difference between this comparative example and Example 1 is that in the preparation process, the weight-average molecular weight of the ethylene-methyl methacrylate copolymer is 150,000, and the others are the same as in Example 1.

Comparative Example 3

The difference between this comparative example and Example 1 is that in the preparation process, the mass concentration of the ethylene-methyl methacrylate copolymer solution is 15%, and the others are the same as Example 1.

Comparative Example 4

The difference between this comparative example and Example 1 is that in the preparation process, the mass percentage content of the polymer layer of the ethylene-methyl methacrylate copolymer in the composite positive electrode material is 15%, and the rest are the same as the implementation. Example 1 is the same.

Comparative Example 5

The difference between this comparative example and Example 1 is that in the preparation process, the mass percentage content of the polymer layer of the ethylene-methyl methacrylate copolymer in the composite positive electrode material is 0.5%, and the rest are the same as those in the implementation. Example 1 is the same.

Application example 1-5 and comparative application example 1-5

The composite positive electrode materials provided in Examples 1-5 and Comparative Examples 1-5 were prepared to obtain lithium ion batteries, and the preparation method was as follows:

Preparation of positive electrode sheet: The composite positive electrode material, conductive agent carbon black and binder polyvinylidene fluoride are added to the solvent according to the mass ratio of 8:1:1, fully stirred to obtain a mixed slurry, and then the mixed slurry is mixed. It is evenly coated on aluminum foil, and the desired positive electrode sheet is obtained after drying, rolling and cutting;

Preparation of electrolyte: Lithium hexafluorophosphate is used as lithium salt, and the solvent is a mixed solvent of EC and DEC with a mass ratio of 1:1, wherein the concentration of lithium hexafluorophosphate is 1 mol/L;

Preparation of lithium ion battery: Assemble the prepared positive electrode sheet, separator, counter electrode lithium sheet and electrolyte into a button-type half-cell, and then test the electrochemical performance.

Test Conditions

The lithium ion batteries provided by Application Examples 1-5 and Comparative Application Examples 1-5 were tested for electrochemical performance, and the test method was as follows:

Charge to 4.3V at a current density of 0.05C at a constant current and constant voltage at 45°C, and observe the charge-discharge curve to determine the delithiation platform of lithium ferrite. As shown in Figure 2, the specific capacity of lithium ferrite for the first charge is 600mAh/ g or more.

The test results are shown in Table 1:

Table 1

It can be seen from the data in Table 1 that the composite positive electrode materials provided by Application Examples 1 to 5 in the present invention can effectively improve the specific charge capacity of lithium ferrite positive electrode materials through the coating of olefin-acrylate copolymers, reduce Moisture damages the structure of lithium ferrite cathode materials. Comparative application example 1 and comparative application example 2 show that the molecular weight of the olefin-acrylate copolymer affects the coating uniformity of the polymer layer. Uneven coverage. Comparative Application Example 4 and Comparative Application Example 5 show that the surface of the lithium ferrite cathode material is coated with too much olefin-acrylate copolymer, which will also affect the capacity of the lithium ferrite cathode material, and the olefin-acrylate copolymer coating Too thick will lead to difficulty in lithium ion transport, and too little olefin-acrylate coating will lead to insufficient protection of the lithium ferrite cathode material.

The applicant declares that the present invention illustrates the process method of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned process steps, that is, it does not mean that the present invention must rely on the above-mentioned process steps to be implemented. Those skilled in the art should understand that any improvement to the present invention, the equivalent replacement of the selected raw materials of the present invention, the addition of auxiliary components, the selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims (10)

1. a composite positive electrode material, is characterized in that, described composite positive electrode material comprises lithium ferrite and the polymer layer that is coated on lithium ferrite surface; The polymer layer is an olefin-acrylate copolymer. 2. The composite positive electrode material according to claim 1, wherein the olefin-acrylate copolymer comprises ethylene-methyl methacrylate copolymer, propylene-methyl methacrylate copolymer, ethylene-methyl methacrylate copolymer Any one or a combination of at least two of ethyl acrylate, propylene-ethyl methacrylate, ethylene-propyl methacrylate or propylene-butyl methacrylate; Preferably, the weight average molecular weight of the olefin-acrylate copolymer is 10,000-100,000. 3. The composite positive electrode material according to claim 1 or 2, wherein the mass percentage content of the polymer layer in the composite positive electrode material is 1-10%. 4. A method for preparing the composite positive electrode material according to any one of claims 1-3, wherein the method comprises the following steps: The lithium source and the iron source are mixed, calcined to obtain lithium ferrite powder, and then the lithium ferrite powder and the olefin-acrylate copolymer solution are mixed for a second time, and the solvent is removed to obtain the composite positive electrode material. 5. The method according to claim 4, wherein the lithium source comprises any one or a combination of at least two of lithium carbonate, lithium hydroxide, lithium oxide or lithium nitride; Preferably, the iron source includes any one or a combination of at least two of iron oxide, iron hydroxide, iron nitrate or iron oxalate. The method according to claim 4 or 5, wherein the mass ratio of the lithium source and the iron source is (5-10):1. 7. The method according to any one of claims 4-6, wherein the calcining temperature is 700-900°C; Preferably, the calcination time is 8-12 hours. 8. The method according to any one of claims 4-7, wherein the mass concentration of the olefin-acrylate copolymer solution is 1-10%; Preferably, the secondary mixing is performed under stirring; Preferably, the stirring time is 30-90 min. 9. The method according to any one of claims 4-8, wherein the pressure for removing the solvent is -500kpa～-50kpa; Preferably, the temperature for removing the solvent is 80-200°C; Preferably, after removing the solvent, cooling treatment is also included. 10. An electrochemical energy storage device, characterized in that the electrochemical energy storage device comprises a positive electrode, a negative electrode and an electrolyte, and the positive electrode is the composite positive electrode material according to any one of claims 1-3.

Images