Carbon-coated lithium-rich graphite negative electrode material and preparation method thereof

Abstract

The application discloses a kind of carbon-coated lithium-rich graphite negative materials and preparation method thereof.The carbon-coated lithium-rich graphite negative material is the core-shell structure of carbon layer coated lithium-rich graphite, wherein lithium-rich graphite is the porous graphite after metal-assisted chemical etching treatment.The preparation method of the carbon-coated lithium-rich graphite negative material includes the following steps: first, lithium-rich graphite is prepared by metal-assisted LiOH alkali etching;Second, lithium-rich graphite is added to the solution of four hydrogen furan with carbon precursor, stirred, and evaporated;Lithium-rich graphite coated with carbon precursor is sintered in a tube furnace in an inert atmosphere to obtain the core-shell structure of carbon-coated lithium-rich graphite negative material.The carbon-coated lithium-rich graphite negative material prepared by the application improves the first coulomb efficiency and cycle performance of the carbon-coated lithium-rich graphite negative material;The preparation method provided by the application is simple in process, low in cost and easy to realize industrial production.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, in particular to a carbon-coated lithium-rich graphite negative electrode material and a preparation method thereof. BACKGROUND

[0002] The information disclosed in the background of the present application is only intended to increase the understanding of the overall background of the present application and should not necessarily be regarded as acknowledging or implicitly suggesting that this information constitutes prior art known to those of ordinary skill in the art.

[0003] With the increasing demand for the energy density of power batteries, the traditional graphite negative electrode has a limited theoretical energy density, which has gradually failed to meet the demand, and therefore it is urgent to modify the traditional graphite material. In the research on the modification of graphite, the technology of etching and pore-making on graphite can increase the specific capacity of graphite material, which has attracted more and more attention and research.

[0004] The lithium-rich graphite material in the prior art can play a pre-lithiation role by introducing lithium elements in etching. However, during the process of alkali etching, a large number of defects will be generated on the surface of the graphite, which increases the specific surface area of the graphite, causes more SEI in the cycle process of the battery, and reduces the first coulomb efficiency. SUMMARY

[0005] In view of the above defects of the prior art, the technical problem to be solved by the present application is to provide a carbon-coated lithium-rich graphite negative electrode material with high first coulomb efficiency (> 95%) and high cycle performance and a preparation method thereof. In the carbon-coated lithium-rich graphite negative electrode material of the present application, a uniform carbon layer is coated on the surface of the lithium-rich graphite, which reduces the defects on the surface of the graphite and improves the first coulomb efficiency of the battery, and at the same time, improves the cycle performance of the battery.

[0006] To achieve the above technical purpose, the present application provides the following technical scheme.

[0007] In a first aspect of the present application, a carbon-coated lithium-rich graphite negative electrode material is provided, which is a core-shell structure of a carbon layer coated lithium-rich graphite, wherein the lithium-rich graphite is a porous graphite after metal-assisted chemical etching treatment, and is rich in lithium elements.

[0008] Preferably, the precursor of carbon is pitch, and the thickness of the carbon layer is 5-20 nm.

[0009] Preferably, the molar ratio of lithium elements in the carbon-coated lithium-rich graphite negative electrode material is 1-50%.

[0010] Preferably, the pore size of the lithium-rich graphite is 0.01-2 μm, and the pore depth is 0.05-5 μm.

[0011] In a second aspect of the present application, a preparation method of the carbon-coated lithium-rich graphite negative electrode material is provided, and the preparation method comprises the following steps:

[0012] Step one: performing hole etching on the graphite by using metal-assisted chemical etching to obtain lithium-rich graphite;

[0013] Step two: dispersing the lithium-rich graphite in a tetrahydrofuran solution in which pitch is dissolved, mechanically stirring, and evaporating the solvent to obtain a lithium-rich graphite / pitch material;

[0014] Step three: sintering the lithium-rich graphite / pitch material obtained in step two to obtain a lithium-rich graphite material coated with pyrolytic carbon.

[0015] Preferably, in step one, the metal-assisted chemical etching method is a Ni-assisted LiOH alkali etching method, and the specific steps are as follows: a salt solution of nickel and graphite powder (molar ratio C:Ni=40:1) are calcined at 600°C under an inert atmosphere, and the obtained powder is mixed with LiOH (molar ratio C:Li=1:1) and then calcined at 800°C under an inert atmosphere again.

[0016] Preferably, the mass ratio of the lithium-rich graphite to the pitch is 1.5:1 to 2.5:1.

[0017] Preferably, in step two, the stirring time is 1 to 1.5 hours, and the temperature for evaporating the solvent is 90 to 100°C.

[0018] Preferably, in step three, the specific process of sintering is as follows: in a tube furnace under an inert atmosphere, the temperature is raised to 100 to 300°C at a first temperature raising rate of 8°C / min, and then the temperature is raised to 900 to 3000°C at a second temperature raising rate of 8°C / min, and the temperature is kept for 1 to 2 hours.

[0019] In a third aspect of the present application, the carbon-coated lithium-rich graphite negative electrode material is applied in a secondary battery.

[0020] The present application has the following advantages:

[0021] In the present application, the carbon coating improves the loss of the first coulomb efficiency of the lithium-rich graphite caused by surface defects, and further improves the first coulomb efficiency of the lithium-rich graphite negative electrode material.

[0022] The carbon-coated lithium-rich graphite negative electrode material prepared in the present application has lithium elements remaining in the interlayer or surface of the lithium-rich graphite, and the lithium-rich graphite is uniformly coated with a carbon layer.

[0023] The preparation method provided in the present application improves the first coulomb efficiency and cycle performance of the lithium-rich graphite negative electrode material. BRIEF DESCRIPTION OF DRAWINGS

[0024] The accompanying drawings, which form a part of this specification, are included to provide a further understanding of the application and are incorporated in and constitute a part of this specification. The embodiments of the application, and their

[0025] Figure 1 The figure of the morphology structure of the carbon-coated lithium-rich graphite negative electrode material in Example 1 of the application.

[0026] Figure 2 The figure of the first charge-discharge capacity of the carbon-coated lithium-rich graphite negative electrode material in Example 1 of the application.

[0027] Figure 3 The figure of the first charge-discharge capacity of the lithium-rich graphite material in the comparative example of the application. DETAILED DESCRIPTION

[0028] It should be noted that the following detailed description is exemplary in nature and is intended to provide further description of the application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0029] Example 1:

[0030] A method for preparing a carbon-coated lithium-rich graphite negative electrode material: at room temperature, 0.3 g of pitch is dissolved in a tetrahydrofuran solution, 0.7 g of lithium-rich graphite is added, stirred for 1 h, heated to 100℃, the tetrahydrofuran solution is evaporated, and the obtained composite material is placed in a tube furnace with argon, heated to 300℃ at a first heating rate of 8℃ / min, kept for 2 h, then heated to 1000℃ at a second heating rate of 8℃ / min, kept for 2 h, to obtain a carbon-coated lithium-rich graphite negative electrode material.

[0031] Comparative Example:

[0032] The comparative example is untreated lithium-rich graphite, and the preparation method refers to the preparation method of a lithium-rich graphite disclosed in a patent (application number: CN202210932639.8).

[0033] Figure 1 The scanning electron microscope image of the carbon-coated lithium-rich graphite negative electrode material in Example 1 of the application. As shown in the figure, the surface of the carbon-coated lithium-rich graphite negative electrode material is uniformly coated with a carbon layer, and there are no obvious defects, which is conducive to improving the first coulombic efficiency.

[0034] Figure 2 The half-cell charge-discharge curve of the carbon-coated lithium-rich graphite negative electrode material in Example 1 of the application. The lithium-rich graphite after carbon coating exhibits higher first coulombic efficiency. The first coulombic efficiency reaches 96% at a current density of 0.1 A g -1 ​

[0035] Figure 3 The first coulombic efficiency of the half-cell charge-discharge curve of the untreated lithium-rich graphite in the comparative example is 90%.

[0036] Example 2:

[0037] A preparation method of the carbon-coated lithium-rich graphite negative electrode material: at room temperature, 0.4 g of pitch is dissolved in a tetrahydrofuran solution, 0.6 g of lithium-rich graphite is added, stirred for 1 h, heated to 100°C, the tetrahydrofuran solution is evaporated, and the obtained composite material is placed in a tube furnace with argon, heated to 300°C at a first heating rate of 8°C / min, kept for 2 h, then heated to 1000°C at a second heating rate of 8°C / min, kept for 2 h, to obtain the carbon-coated lithium-rich graphite negative electrode material.

[0038] Example 3:

[0039] A preparation method of the carbon-coated lithium-rich graphite negative electrode material: at room temperature, 0.5 g of pitch is dissolved in a tetrahydrofuran solution, 0.5 g of lithium-rich graphite is added, stirred for 1 h, heated to 100°C, the tetrahydrofuran solution is evaporated, and the obtained composite material is placed in a tube furnace with argon, heated to 300°C at a first heating rate of 8°C / min, kept for 2 h, then heated to 1000°C at a second heating rate of 8°C / min, kept for 2 h, to obtain the carbon-coated lithium-rich graphite negative electrode material.

[0040] Example 4:

[0041] A preparation method of the carbon-coated lithium-rich graphite negative electrode material: at room temperature, 0.3 g of pitch is dissolved in a tetrahydrofuran solution, 0.7 g of lithium-rich graphite is added, stirred for 0.5 h, heated to 80°C, the tetrahydrofuran solution is evaporated, and the obtained composite material is placed in a tube furnace with argon, heated to 300°C at a first heating rate of 8°C / min, kept for 2 h, then heated to 1000°C at a second heating rate of 8°C / min, kept for 2 h, to obtain the carbon-coated lithium-rich graphite negative electrode material.

[0042] Example 5:

[0043] A preparation method of the carbon-coated lithium-rich graphite negative electrode material: at room temperature, 0.3 g of pitch is dissolved in a tetrahydrofuran solution, 0.7 g of lithium-rich graphite is added, stirred for 1 h, heated to 100°C, the tetrahydrofuran solution is evaporated, and the obtained composite material is placed in a tube furnace with argon, heated to 300°C at a first heating rate of 10°C / min, kept for 1 h, then heated to 1000°C at a second heating rate of 10°C / min, kept for 1 h, to obtain the carbon-coated lithium-rich graphite negative electrode material.

[0044] Example 6:

[0045] A preparation method of a carbon-coated lithium-rich graphite negative electrode material: at room temperature, 0.3g of pitch is dissolved in a tetrahydrofuran solution, 0.7g of lithium-rich graphite is added, stirred for 1h, heated to 100℃, the tetrahydrofuran solution is evaporated, and the obtained composite material is placed in a tube furnace with argon, heated to 300℃ at a first heating rate of 8℃ / min, kept for 2h, then heated to 900℃ at a second heating rate of 8℃ / min, kept for 2h, to obtain the carbon-coated lithium-rich graphite negative electrode material.

[0046] Example 7:

[0047] A preparation method of a carbon-coated lithium-rich graphite negative electrode material: at room temperature, 0.3g of pitch is dissolved in a tetrahydrofuran solution, 0.7g of lithium-rich graphite is added, stirred for 1h, heated to 100℃, the tetrahydrofuran solution is evaporated, and the obtained composite material is placed in a tube furnace with argon, heated to 300℃ at a first heating rate of 8℃ / min, kept for 2h, then heated to 3000℃ at a second heating rate of 8℃ / min, kept for 2h, to obtain the carbon-coated lithium-rich graphite negative electrode material.

[0048] Preparation and testing of electrodes: the silicon-carbon negative electrode material prepared in the application is mixed with conductive carbon (acetylene black) and a binder (CMC and SBR in a mass ratio of 3:2) at a weight ratio of 8.5:0.5:1 to prepare electrode slurry, CMC is carboxymethyl cellulose, SBR is styrene-butadiene latex, the electrode slurry is uniformly coated on a copper foil using a 250μm high doctor blade, then pressed, cut, and a negative electrode sheet is prepared.

[0049] Performance testing is carried out in a button lithium ion battery. The battery is assembled as follows: lithium sheet is used as the counter electrode, Celgard2300 is used as the separator, and the electrolyte is an EC-DEC (1:1) solution containing 1M LiPF6, LiPF6 is lithium hexafluorophosphate, EC is ethylene carbonate, and DEC is diethyl carbonate. During testing, the temperature is room temperature, constant current charging and discharging is used, the current density is 100mA / g, and the voltage control range is 0.05-2V. The performance test results of some batteries of the examples and the comparative examples are shown in the following table:

[0050] Table 1 comparison of first coulombic efficiency

[0051] Case First coulombic efficiency / % Example 1 96 Example 2 92 Example 3 94 Example 4 92 Example 5 93 Example 6 95 Example 7 96 Comparative Example 90

[0052] The above only describes the preferred embodiments of the application and is not intended to limit the application. Various modifications and changes can be made to the application by those skilled in the art. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the application shall be included in the protection scope of the application.

Claims

1. A method for preparing a carbon-coated lithium-rich graphite negative electrode material, characterized in that, The preparation method comprises the following steps: Step one: using metal-assisted chemical etching method to etch holes on the graphite to obtain lithium-rich graphite; Step two: dispersing the lithium-rich graphite in the tetrahydrofuran solution in which the asphalt is dissolved, mechanically stirring, evaporating the solvent to obtain a lithium-rich graphite / asphalt material; Step three: sintering the lithium-rich graphite / asphalt material obtained in step two to obtain a pyrolytic carbon-coated lithium-rich graphite material; In step three, the specific process of sintering is as follows: in a tube furnace with inert atmosphere, heating to 100-300℃ at a first heating rate of 8℃ / min, keeping for 1-2h, then heating to 900-3000℃ at a second heating rate of 8℃ / min, keeping for 1-2h.

2. The method of claim 1, wherein, In step one, the metal-assisted chemical etching method is Ni-assisted LiOH alkali etching.

3. The preparation method according to claim 1, characterized in that, The specific steps of the metal-assisted chemical etching method are as follows: calcining the nickel salt solution and graphite powder at 600℃ under inert atmosphere, mixing the obtained powder with LiOH and calcining again at 800℃ under inert atmosphere; wherein the amount of the nickel salt solution and graphite powder is in a molar ratio of C:Ni=40:1; when mixing the obtained powder with LiOH, the amount ratio is in a molar ratio of C:Li=1:

1.

4. The preparation method according to claim 1, characterized in that, The mass ratio of the lithium-rich graphite to asphalt is 1.5:1-2.5:

1.

5. The method of claim 1, wherein the step of forming the first and second layers is performed by a process selected from the group consisting of: sputtering, evaporation, and chemical vapor deposition. In step two, the stirring time is 1-1.5h, and the temperature for evaporating the solvent is 90-100℃.

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