Coated lithium-silicon alloy as well as preparation method and application thereof

Abstract

The invention discloses a coated lithium-silicon alloy as well as a preparation method and application thereof. The method comprises the steps that lithium silicon alloy powder is placed in a reaction kettle, hydrofluorocarbon is introduced, heating is carried out for a gas phase reaction, the coated lithium silicon alloy is obtained, and coated components comprise lithium fluoride and lithium carbide. According to the lithium-silicon alloy, the initial coulombic efficiency of a silicon-based negative electrode can be improved; the composite coating layer of lithium fluoride and lithium carbide on the surface of the lithium-silicon alloy matrix solves the problems of high reaction activity and poor air stability of the lithium-silicon alloy, and improves the practicability and feasibility of the lithium-silicon alloy as the negative electrode material of the lithium ion battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium ion batteries, and in particular relates to a coated lithium silicon alloy and a preparation method and application thereof. Background Art

[0002] In recent decades, lithium-ion batteries (LIBs) have been widely used in various industries. With the demand for energy storage and the development of electric vehicles, the capacity of graphite anodes is low and it is difficult to meet the needs of many devices. Silicon, which has a high theoretical specific capacity (4200mAh / g), is one of the most promising negative electrode materials for next-generation lithium-ion batteries. However, silicon-based negative electrodes have large volume expansion (~300%) during charge and discharge and unstable solid electrolyte interface (SEI) films, resulting in low first coulomb efficiency (ICE), electrode failure, and rapid capacity decay, which seriously restricts its commercial application.

[0003] Silicon is highly reactive in the battery system. The electrolyte is reduced to form SEI film on the surface of silicon negative electrode, resulting in irreversible consumption of lithium source. Silicon oxide negative electrode will also form inactive Li2O and a series of lithium silicates in the first lithium insertion process, resulting in its first lithium removal capacity being much smaller than its lithium insertion capacity. Pre-chemical treatment is an effective method to improve the coulombic first efficiency, which improves the first efficiency by compensating in advance for the lithium source consumed by the formation of SEI film and other side reactions, that is, using lithium silicon alloy as the negative electrode material of lithium-ion batteries.

[0004] The formation of lithium-silicon alloy produces a certain amount of pre-expansion, and the amorphous silicon formed after the lithium is removed alleviates the volume change to a certain extent, greatly improving the initial efficiency and cycle stability of the battery. However, the high reactivity of lithium-silicon alloy leads to its poor air stability and incompatibility with conventional solvents. Therefore, this technical problem needs to be overcome to obtain a lithium battery with excellent comprehensive performance. Summary of the invention

[0005] In order to solve the shortcomings and deficiencies of the prior art, the primary purpose of the present invention is to provide a method for preparing a coated lithium silicon alloy. After the lithium silicon alloy is synthesized by ball milling, the surface is coated by a gas phase reaction method, thereby achieving the purpose of improving the coulomb first efficiency, cycle stability and air stability of the lithium silicon alloy. The preparation method of the present invention is simple and easy to operate, has low energy consumption, is environmentally friendly, and is suitable for industrial production.

[0006] Another object of the present invention is to provide a coated lithium silicon alloy obtained by the above preparation method.

[0007] Another object of the present invention is to provide application of the above-mentioned coated lithium-silicon alloy in lithium-ion batteries.

[0008] The purpose of the present invention is achieved through the following technical solutions:

[0009] A method for preparing a coated lithium silicon alloy comprises the following steps:

[0010] The lithium silicon alloy powder is placed in a reaction kettle, hydrofluorocarbon is introduced, and heating is performed for gas phase reaction to obtain a coated lithium silicon alloy, wherein the coated components are lithium fluoride and lithium carbide.

[0011] Preferably, the mass ratio of lithium element to silicon element in the lithium-silicon alloy powder is (0.5-1.1):1.

[0012] Preferably, the lithium silicon alloy powder is Li2Si, Li9Si4, Li 13 Si4、Li 15 Si4、Li 12 Si7, Li7Si3 and Li 22 At least one of Si5.

[0013] Preferably, the preparation method of the lithium silicon alloy powder is: ball milling lithium sheets and silicon-based materials in a lubricant and inert gas atmosphere to obtain the lithium silicon alloy powder.

[0014] More preferably, in the method for preparing the lithium-silicon alloy powder, the mass ratio of the lithium sheet to the silicon-based material is (0.5-1.2):1, more preferably 1.1:1.

[0015] More preferably, in the method for preparing the lithium silicon alloy powder, the lubricant is a non-polar solvent, more preferably at least one of cyclohexane, hexane and toluene; and the ratio of the lithium sheet to the lubricant is 1g: (15-50)ml.

[0016] More preferably, in the method for preparing the lithium-silicon alloy powder, the silicon-based material is at least one of silicon and silicon monoxide.

[0017] More preferably, in the method for preparing the lithium-silicon alloy powder, the inert gas is at least one of argon and helium.

[0018] More preferably, in the method for preparing the lithium silicon alloy powder, the ball milling speed is 400-600 rpm and the time is 10-24 h.

[0019] Preferably, the hydrofluorocarbon is at least one of HFC-32, HFC-125 and HFC-134a.

[0020] Preferably, the hydrofluorocarbon is at least one of HFC-125 and HFC-134a.

[0021] Preferably, the conditions for the gas phase reaction are: hydrofluorocarbon pressure 1-5 bar, temperature 150-200° C., and time 5-24 h.

[0022] More preferably, the conditions of the gas phase reaction are: hydrofluorocarbon pressure 1-1.5 bar, temperature 160-180° C., and time 5-24 h.

[0023] Preferably, the mass ratio of lithium fluoride to lithium carbide is 1:4-2:1.

[0024] A coated lithium-silicon alloy is prepared by the above preparation method.

[0025] The above-mentioned coated lithium-silicon alloy is used in lithium-ion batteries.

[0026] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0027] (1) The present invention prepares lithium silicon alloy by ball milling to improve the Coulomb first effect and cycle stability of silicon-based negative electrodes, and reacts the lithium silicon alloy with hydrofluorocarbons under normal conditions to form a composite coating layer of lithium fluoride and lithium carbide on the surface of the lithium silicon alloy. Lithium fluoride can improve the air stability of lithium silicon alloy and improve its compatibility with electrolytes. At the same time, lithium fluoride has a high elastic modulus with high surface energy, which can better adapt to the volume expansion of silicon-based negative electrodes and prevent particle crushing. Lithium carbide is a thermodynamically stable lithium-rich carbide, and can also be used as an electrode material for lithium-ion batteries to provide lithium storage capacity.

[0028] (2) The reaction raw material hydrofluorocarbon used in the present invention is a widely used refrigerant, which is cheap and easy to obtain. As people's environmental awareness increases, this type of refrigerant will gradually be replaced. The present invention can provide a high-value recycling method for waste refrigerants.

[0029] (3) The preparation process of the coated lithium silicon alloy of the present invention is simple, and the preparation conditions are also very easy to achieve. It can be combined with fluidized bed technology for scaled-up production, which helps to improve the practicality of the lithium silicon alloy negative electrode and promote the commercialization of the lithium silicon alloy negative electrode. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is the first charge and discharge curve in Example 1 of the present invention;

[0031] Figure 2 is the XRD pattern in Example 4 of the present invention;

[0032] Figure 3 This is the XPS spectrum in Example 4 of the present invention;

[0033] Figure 4 This is the SEM image in Example 4 of the present invention;

[0034] Figure 5 This is the first charge and discharge curve in Example 4 of the present invention;

[0035] Figure 6 This is the first charge and discharge curve in Example 5 of the present invention;

[0036] Figure 7 This is the first charge and discharge curve in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0037] The present invention is further described in detail below in conjunction with embodiments and drawings, but the embodiments of the present invention are not limited thereto.

[0038] If no specific conditions are specified in the examples of the present invention, the experiments were carried out under conventional conditions or conditions recommended by the manufacturer. All raw materials, reagents, etc., whose manufacturers are not specified, are conventional products that can be purchased commercially.

[0039] Example 1

[0040] S1: 1.100 g lithium flakes and 1.000 g silicon powder obtained by grinding were added into an alumina ball mill, 15 ml cyclohexane was added as a lubricant, and ground on a planetary ball mill for 15 h at a speed of 500 rpm under an argon protective atmosphere.

[0041] S2: 500 mg of the alloy powder prepared in step S1 was placed in a reaction kettle, HFC-134a was introduced, the pressure was 1 bar, and the reaction was carried out at 160° C. for 10 h to obtain coated lithium silicon alloy powder.

[0042] Figure 1 The first charge and discharge curve at 0.1C of the half-cell assembled from the dry electrode prepared by using polytetrafluoroethylene as a binder and Super P as a conductive agent for the coated lithium silicon alloy powder in Example 1. The first discharge capacity is 1685.98 mAh / g, and the first charge capacity is 909.03 mAh / g.

[0043] Example 2

[0044] S1: 1.100 g lithium flakes and 1.000 g silicon powder obtained by grinding were added into an alumina ball mill, 15 ml cyclohexane was added as a lubricant, and ground on a planetary ball mill for 15 h at a speed of 500 rpm under an argon protective atmosphere.

[0045] S2: 500 mg of the alloy powder prepared in step S1 was placed in a reaction kettle, HFC-125 was introduced, the pressure was 1 bar, and the reaction was carried out at 160° C. for 10 h to obtain coated lithium silicon alloy powder.

[0046] Example 3

[0047] S1: 1.100 g lithium flakes and 1.000 g silicon powder obtained by grinding were added into an alumina ball mill, 15 ml cyclohexane was added as a lubricant, and ground on a planetary ball mill for 15 h at a speed of 500 rpm under an argon protective atmosphere.

[0048] S2: 500 mg of the alloy powder from step S1 was placed in a reaction kettle, HFC-134a was introduced, the pressure was 1.5 bar, and the reaction was carried out at 160° C. for 10 h to obtain coated lithium silicon alloy powder.

[0049] Example 4

[0050] S1: 1.100 g lithium flakes and 1.000 g silicon powder obtained by grinding were added into an alumina ball mill, 15 ml cyclohexane was added as a lubricant, and ground on a planetary ball mill for 15 h at a speed of 500 rpm under an argon protective atmosphere.

[0051] S2: 500 mg of the alloy powder prepared in step S1 was placed in a reaction kettle, HFC-134a was introduced, the pressure was 1 bar, and the reaction was carried out at 170° C. for 10 h to obtain coated lithium silicon alloy powder.

[0052] Figure 2 The XRD diagram of the coated lithium-silicon alloy in Example 4 shows that Li 21 Characteristic peaks of Si5, Li2O, LiC, and LiF.

[0053] Figure 3 This is the XPS spectrum of the coated lithium silicon alloy in Example 4, which further proves the formation of lithium fluoride and lithium carbide.

[0054] Figure 4 This is the SEM picture of the coated lithium silicon alloy in Example 4. It can be seen from the picture that the particle size of the primary particles of the lithium silicon alloy is 200-600nm, the surface is smooth, and it is approximately spherical. The particle size of the secondary particles is 2-6μm.

[0055] Figure 5 The first charge and discharge curve of the dry electrode prepared by using polytetrafluoroethylene as a binder and Super P as a conductive agent for the coated lithium silicon alloy powder in Example 4 and assembled into a half-cell at 0.1C. The first discharge capacity is 2020.35 mAh / g, and the first charge capacity is 1436.05 mAh / g.

[0056] Example 5

[0057] S1: 1.100 g lithium flakes and 1.000 g silicon powder obtained by grinding were added into an alumina ball mill, 15 ml cyclohexane was added as a lubricant, and ground on a planetary ball mill for 15 h at a speed of 500 rpm under an argon protective atmosphere.

[0058] S2: 500 mg of the alloy powder prepared in step S1 was placed in a reaction kettle, HFC-134a was introduced, the pressure was 1 bar, and the reaction was carried out at 180° C. for 10 h to obtain coated lithium silicon alloy powder.

[0059] The coated lithium silicon alloy powder obtained in Example 5 was filled into the foamed copper and placed into a mold for tableting at a pressure of 10 MPa. The obtained electrodes were assembled into a half-cell for testing. Figure 6 This is the first charge and discharge curve of the coated lithium silicon alloy powder at 0.1C in Example 4. The first discharge capacity is 532.45 mAh / g, and the first charge capacity is 603.77 mAh / g.

[0060] Comparative Example 1

[0061] This comparative example only uses silicon powder obtained by grinding as the negative electrode material, which is the same material as the silicon powder in Example 1.

[0062] Figure 7 The first charge and discharge curve of the dry electrode prepared by using polytetrafluoroethylene as a binder and Super P as a conductive agent for the lithium silicon alloy powder in Comparative Example 1 and assembled into a half-cell at 0.1C. The first discharge capacity is 991.26 mAh / g, and the first charge capacity is 122.14 mAh / g.

[0063] Comparative Example 2

[0064] The lithium silicon alloy obtained in step S1 of Example 1 was placed in air with a humidity of 20% and a temperature of 30° C. for 24 hours.

[0065] Comparative Example 3

[0066] The coated lithium silicon alloy obtained in Example 4 was placed in air at a humidity of 20% and a temperature of 30° C. for 24 hours.

[0067] The negative electrode materials obtained in Comparative Examples 2-3 were assembled into button-type batteries and subjected to charge and discharge tests.

[0068] Table 1 Battery charge and discharge test results

[0069]

[0070]

[0071] It can be seen from Table 1 that the air stability of the coated lithium-silicon alloy is better than that of the uncoated lithium-silicon alloy.

[0072] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for preparing a coated lithium silicon alloy, characterized in that: The following steps are involved: The lithium silicon alloy powder is placed in a reaction kettle, hydrofluorocarbon is introduced, and heating is performed for gas phase reaction to obtain a coated lithium silicon alloy, wherein the coated components are lithium fluoride and lithium carbide.

2. The method for preparing a coated lithium silicon alloy according to claim 1, characterized in that: The conditions of the gas phase reaction are: hydrofluorocarbon pressure 1-5 bar, temperature 150-200° C., time 5-24 h.

3. The method for preparing a coated lithium silicon alloy according to claim 1, characterized in that: The hydrofluorocarbon is at least one of HFC-32, HFC-125 and HFC-134a; The mass ratio of lithium fluoride to lithium carbide is 1:4-2:

1.

4. The method for preparing a coated lithium silicon alloy according to claim 1, characterized in that: The gas phase reaction conditions are: hydrofluorocarbon pressure 1-1.5 bar, temperature 160-180° C., time 5-24 h; The hydrofluorocarbon is at least one of HFC-125 and HFC-134a.

5. The method for preparing a coated lithium silicon alloy according to claim 1, characterized in that: The mass ratio of lithium element to silicon element in the lithium-silicon alloy powder is (0.5-1.1):

1.

6. The method for preparing a coated lithium silicon alloy according to claim 1, characterized in that: The lithium silicon alloy powder is Li2Si, Li9Si4, Li 13 Si4、Li 15 Si4、Li 12 Si7, Li7Si3 and Li 22 At least one of Si5.

7. The method for preparing a coated lithium silicon alloy according to claim 1, characterized in that: The preparation method of the lithium silicon alloy powder is as follows: ball milling lithium sheets and silicon-based materials in a lubricant and inert gas atmosphere to obtain lithium silicon alloy powder; The mass ratio of the lithium sheet to the silicon-based material is (0.5-1.2):1; The lubricant is a non-polar solvent, specifically at least one of cyclohexane, hexane and toluene; the ratio of the lithium sheet to the lubricant is 1g: (15-50)ml; The silicon-based material is at least one of silicon and silicon monoxide.

8. The method for preparing a coated lithium silicon alloy according to claim 7, characterized in that: The inert gas is at least one of argon and helium; The ball milling speed is 400-600 rpm, and the time is 10-24 hours.

9. A coated lithium silicon alloy obtained by the preparation method according to any one of claims 1 to 8.

10. Use of the coated lithium-silicon alloy according to claim 9 in lithium-ion batteries.

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