A silicon-carbon anode material and its preparation method, anode sheet and lithium-ion battery

Abstract

This invention discloses a silicon-carbon anode material and its preparation method, anode sheet, and lithium-ion battery. The silicon-carbon anode material has a core-shell structure, wherein the core contains silicon-carbon material, and the shell layer includes ethylene carbonate and lithium salt; and the ethylene carbonate in the shell layer can dissolve and vaporize at a predetermined temperature to form a porous structure on the surface of the silicon-carbon material that can be filled with lithium salt. The preparation method of the silicon-carbon anode material includes: (1) heating and dissolving ethylene carbonate, adding lithium salt to make it uniformly dispersed in ethylene carbonate, then adding silicon-carbon material, stirring thoroughly, and draining the solvent to obtain a silicon-carbon mixture; (2) cooling the silicon-carbon mixture obtained in step (1), the ethylene carbonate gradually solidifies, and the ethylene carbonate and lithium salt form a coating shell on the surface of the silicon-carbon material, thereby obtaining the silicon-carbon anode material. The silicon-carbon anode material provided by this invention has the advantages of high initial efficiency, low expansion rate, and long life when applied in lithium-ion batteries.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery manufacturing technology, and in particular to a silicon-carbon anode material and its preparation method, anode sheet and lithium-ion battery. Background Technology

[0002] In recent years, the widespread application of lithium-ion batteries in mobile phones, laptops, new energy vehicles, and energy storage has led to a growing demand from consumers for higher energy density. The main components of a lithium-ion battery are the negative electrode, electrolyte, positive electrode, separator, and encapsulation components. The negative electrode provides the space for lithium-ion intercalation; currently, graphite is the most commonly used negative electrode, with a theoretical specific energy of 372 mAh / g, but practical applications have already developed to approach the theoretical level. Novel silicon-based negative electrodes have a lithium intercalation capacity approximately ten times that of graphite and are one of the most widely researched materials.

[0003] However, silicon-based anodes suffer from problems such as low initial efficiency, volume expansion, material peeling, pulverization, and electrolyte consumption due to repeated SEI film growth during use, which limit their practical application. To address these issues, several optimization approaches exist: (1) using novel binders, such as polyacrylic acid (PAA) and sodium alginate; (2) developing novel electrolyte additives to improve the SEI film of silicon-based anodes; (3) lithium replenishment to improve initial efficiency; and (4) modification of silicon materials, such as carbon coating and silicon-carbon composites. These approaches can only improve certain aspects of the electrode's performance to a certain extent, but they do not enhance the overall performance of silicon-based anodes. Furthermore, the lithium replenishment process is demanding and costly. Existing inventions involving lithium replenishment on the surface of silicon-carbon anode sheets not only have demanding process conditions but may also lead to lithium dendrite formation, posing a short-circuit risk. Moreover, adding a lithium replenishment layer between the silicon-carbon material and the current collector can easily cause active material peeling and pulverization, reducing battery life.

[0004] Therefore, there is an urgent need to provide a simple and easy-to-operate method that can enhance the adhesion between the silicon-carbon anode and the current collector, improve battery life, and achieve safe lithium replenishment. Summary of the Invention

[0005] The purpose of this invention is to provide a simple and easy-to-operate method that can enhance the adhesion between silicon-carbon anode materials and current collectors, improve battery life, and achieve safe lithium replenishment.

[0006] To achieve the above objectives, the first aspect of the present invention provides a silicon-carbon anode material having a core-shell structure, including a core and a shell, wherein the shell covers at least a portion of the surface of the core, the core comprises silicon-carbon material, and the shell comprises ethylene carbonate and lithium salt; and the ethylene carbonate of the shell can dissolve and vaporize at a predetermined temperature to form a porous structure on the surface of the silicon-carbon material that can be filled with lithium salt.

[0007] Preferably, the lithium salt is at least one of lithium hydroxide, lithium carbonate, lithium fluoride, lithium oxalate, (CH2OCO2Li)2, CH3OCH2Li, and LiCH2CH2OCO2Li.

[0008] Preferably, the silicon-carbon material is a mixture of amorphous silicon and graphite.

[0009] Preferably, the mass ratio of ethylene carbonate, silicon carbide material and lithium salt is (8-14):(4-6):(1-2).

[0010] Preferably, the mass ratio of ethylene carbonate, silicon carbide material, and lithium salt is 10:5:1. In this case, the resulting silicon carbide anode material exhibits the strongest adhesion to the current collector.

[0011] Preferably, the specific capacity of the silicon-carbon material is 420-600 mAh / g.

[0012] Preferably, the thickness of the shell layer is 0.1-2 μm.

[0013] Preferably, the predetermined temperature is >35°C.

[0014] A second aspect of this invention provides a method for preparing a silicon-carbon anode material, comprising the following steps:

[0015] (1) Heating and dissolving ethylene carbonate, adding lithium salt to disperse it evenly in ethylene carbonate, then adding silicon carbon material, stirring thoroughly, draining the solvent, and obtaining a silicon carbon mixture;

[0016] (2) Cool the silicon-carbon mixture obtained in step (1) to gradually solidify the ethylene carbonate. The ethylene carbonate and lithium salt form a coating layer on the surface of the silicon-carbon material to obtain the silicon-carbon anode material.

[0017] Preferably, the heating temperature for dissolving ethylene carbonate is >35°C, and the cooling and solidification temperature is 5-8°C. Ethylene carbonate has a melting point of 35-38°C. During heating, an excess of ethylene carbonate is added as a solvent to ensure complete dissolution. During cooling and solidification, the stirring temperature needs to be controlled at 5-8°C to prevent the ethylene carbonate from dissolving during this process.

[0018] A third aspect of the present invention provides a silicon-carbon anode material prepared by the above-described preparation method.

[0019] A fourth aspect of the present invention provides a negative electrode sheet made of the aforementioned silicon-carbon negative electrode material.

[0020] The fifth aspect of the present invention provides a lithium-ion battery made from the above-described negative electrode sheet.

[0021] During the coating process, the coating temperature is 80-120℃. At this temperature, EC will dissolve and vaporize, forming a porous structure. Under the slurry colloid, lithium salt and silicon-carbon material are bonded together. The silicon-carbon material forms pores on its surface and fills with lithium salt. The lithium salt can penetrate into the interior of the negative electrode active material layer. After baking, a metastable SEI film is formed. This metastable SEI film will reach a stable state after the battery is activated by charging and discharging.

[0022] The beneficial effects of this invention are as follows: This invention discloses a silicon-carbon anode material, comprising ethylene carbonate, silicon-carbon material, and lithium salt. The silicon-carbon material is pore-forming and filled with lithium salt by dissolving and vaporizing ethylene carbonate. The lithium salt can penetrate into the interior of the anode active material layer, forming a metastable SEI film after baking. This metastable SEI film reaches a stable state after battery charge-discharge activation, thereby helping to reduce irreversible capacity loss and improve the battery's initial efficiency. This invention also discloses a silicon-carbon anode sheet with high initial efficiency and long lifespan, and a lithium-ion battery containing this anode sheet. This anode sheet has strong adhesion to the current collector, good electrolyte wettability, high initial efficiency, and long cycle life. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the silicon-carbon anode material of the present invention.

[0024] Figure 2 This is a flowchart illustrating the preparation process of the silicon-carbon anode material of the present invention.

[0025] In the diagram: 1-core; 2-shell; 21-lithium salt; 22-ethylene carbonate. Detailed Implementation

[0026] To make the technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] The first aspect of the present invention provides a silicon-carbon anode material having a core-shell structure, including a core and a shell, wherein the shell covers at least a portion of the surface of the core, the core comprises silicon-carbon material, and the shell comprises ethylene carbonate and lithium salt; and the ethylene carbonate of the shell can dissolve and vaporize at a predetermined temperature to form a porous structure on the surface of the silicon-carbon material that can be filled with lithium salt.

[0028] In one embodiment of the present invention, the lithium salt is at least one of lithium hydroxide, lithium carbonate, lithium fluoride, lithium oxalate, (CH2OCO2Li)2, CH3OCH2Li, and LiCH2CH2OCO2Li.

[0029] In one embodiment of the present invention, the silicon-carbon material is a mixture of amorphous silicon and graphite. This silicon-carbon material is commercially available or can be prepared using existing methods.

[0030] In one embodiment of the present invention, the mass ratio of ethylene carbonate, silicon carbide material and lithium salt is (8-14):(4-6):(1-2).

[0031] In one embodiment of the present invention, the mass ratio of ethylene carbonate, silicon carbide material, and lithium salt is 10:5:1. At this ratio, the resulting silicon carbide anode material exhibits the strongest adhesion to the current collector.

[0032] In one embodiment of the present invention, the specific capacity of the silicon-carbon material is 420-600 mAh / g. For example, it can be 420 mAh / g, 450 mAh / g, 480 mAh / g, 500 mAh / g, 550 mAh / g, 580 mAh / g, or 600 mAh / g, etc.

[0033] In one embodiment of the present invention, the thickness of the shell layer is 0.1-2 μm. For example, it can be 0.1 μm, 0.5 μm, 1 μm, 1.5 μm, or 2 μm, preferably 0.5-1.5 μm. Too small a thickness will affect the number of pores formed by ethylene carbonate on the surface during the coating process, thus affecting the amount of lithium salt penetrating into the interior of the negative electrode active material layer; too large a thickness will result in resource waste.

[0034] In one embodiment of the present invention, the predetermined temperature is >35°C. For example, it can be 38°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, or 120°C, preferably 80-120°C. Since the melting point of ethylene carbonate is approximately 35°C, the dissolution and vaporization of ethylene carbonate to form a void structure can only be achieved within this predetermined temperature range.

[0035] A second aspect of this invention provides a method for preparing a silicon-carbon anode material, comprising the following steps:

[0036] (1) Heating and dissolving ethylene carbonate, adding lithium salt to disperse it evenly in ethylene carbonate, then adding silicon carbon material, stirring thoroughly, draining the solvent, and obtaining a silicon carbon mixture;

[0037] (2) Cool the silicon-carbon mixture obtained in step (1) to gradually solidify the ethylene carbonate. The ethylene carbonate and lithium salt form a coating layer on the surface of the silicon-carbon material to obtain the silicon-carbon anode material.

[0038] Preferably, the heating temperature for dissolving ethylene carbonate is >35°C, and the cooling and solidification temperature is 5-8°C. Ethylene carbonate has a melting point of 35-38°C. During heating, an excess of ethylene carbonate is added as a solvent to ensure complete dissolution. During cooling and solidification, the stirring temperature needs to be controlled at 5-8°C to prevent the ethylene carbonate from dissolving during this process.

[0039] A third aspect of the present invention provides a silicon-carbon anode material prepared by the above-described preparation method. The structural and compositional characteristics of the silicon-carbon anode material are as described above and will not be repeated here.

[0040] A fourth aspect of the present invention provides a negative electrode sheet made of the aforementioned silicon-carbon negative electrode material.

[0041] A fifth aspect of the present invention provides a lithium-ion battery made from the aforementioned negative electrode sheet. The lithium-ion battery includes the silicon-carbon negative electrode material provided by the present invention, a positive electrode material containing lithium, a separator, and an electrolyte.

[0042] The structure of the lithium-ion battery provided by the present invention is well known to those skilled in the art. Generally, a separator is located between the positive electrode and the negative electrode. The positive electrode contains the aforementioned positive electrode material, and the negative electrode contains the aforementioned silicon-carbon negative electrode material. The present invention does not particularly limit the specific composition of the lithium-containing positive electrode material, and it can be any lithium-containing positive electrode material conventionally used in the art.

[0043] According to the lithium-ion battery provided by the present invention, the separator can be selected from various separators used in lithium-ion batteries that are known to those skilled in the art, such as polypropylene microporous membrane, polyethylene felt, glass fiber felt or ultrafine glass fiber paper.

[0044] According to the lithium-ion battery provided by the present invention, the electrolyte can be various conventional electrolytes, such as non-aqueous electrolytes. The non-aqueous electrolyte is a solution of an electrolyte lithium salt in a non-aqueous solvent, and conventional non-aqueous electrolytes known to those skilled in the art can be used. For example, the electrolyte can be selected from at least one of lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), and lithium hexafluorosilicate (LiSiF6). The non-aqueous solvent can be selected from a mixed solution of chain esters and cyclic esters, wherein the chain ester can be at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), methyl propyl carbonate (MPC), and dipropyl carbonate (DPC). The cyclic ester can be at least one of ethylene carbonate (EC), propylene carbonate (PC), and vinylene carbonate (VC).

[0045] The present invention will be further described below through specific embodiments.

[0046] Example 1

[0047] like Figure 1 As shown, this embodiment provides a silicon-carbon anode material with a core-shell structure, including a core 1 and a shell 2. The shell 2 covers at least a portion of the surface of the core 1. The core 1 contains silicon-carbon material, and the shell 2 includes ethylene carbonate 22 and lithium salt 21. The ethylene carbonate 22 is uniformly distributed in the lithium salt 21, and the ethylene carbonate 22 in the shell 2 can dissolve and vaporize at a predetermined temperature to form a porous structure on the surface of the silicon-carbon material that can be filled with lithium salt.

[0048] like Figure 2 As shown, the preparation method of this silicon-carbon anode material is as follows:

[0049] (1) Dissolve 10g of ethylene carbonate by heating at 39°C, add 1g of lithium salt to disperse it evenly in ethylene carbonate, add 5g of silicon carbon material, stir thoroughly, drain the solvent, and obtain a silicon carbon mixture.

[0050] (2) Cool the silicon-carbon mixture obtained in step (1) to gradually solidify the ethylene carbonate. The ethylene carbonate and lithium salt form a coating layer on the surface of the silicon-carbon material to obtain the silicon-carbon anode material.

[0051] In this embodiment, the silicon-carbon material has a specific capacity of 420 mAh / g. The silicon-carbon anode material obtained by the above method forms a 0.5 μm thick coating layer of ethylene carbonate and lithium salt on the surface of the silicon-carbon material. This silicon-carbon anode material is used to fabricate an anode sheet, which is then applied to a lithium-ion battery. Testing showed that the lithium-ion battery has an initial efficiency of 89%, an expansion rate of 29%, and a cycle life of 3000 cycles.

[0052] Example 2

[0053] Unlike Example 1, in this example, the silicon-carbon anode material prepared by the method of the present invention forms a 1.0 μm thick coating layer of ethylene carbonate and lithium salt on the surface of the silicon-carbon material. This silicon-carbon anode material is used to fabricate an anode sheet, which is then applied to a lithium-ion battery. Testing showed that the lithium-ion battery had an initial efficiency of 90%, an expansion rate of 27%, and a cycle life of 3500 cycles.

[0054] Example 3

[0055] Unlike Example 1, the silicon-carbon material used has a specific capacity of 600 mAh / g. In this example, the silicon-carbon anode material prepared by the method of this invention is used to fabricate an anode sheet, which is then applied to a lithium-ion battery. Testing showed that the lithium-ion battery had an initial efficiency of 87%, an expansion rate of 35%, and a cycle life of 2500 cycles.

[0056] Example 4

[0057] Unlike Example 1, the silicon-carbon material used in this example has a specific capacity of 600 mAh / g. In this example, the silicon-carbon anode material prepared by the method of the present invention forms a 1.0 μm thick coating layer of ethylene carbonate and lithium salt on the surface of the silicon-carbon material. Anode sheets were fabricated using this silicon-carbon anode material and applied to lithium-ion batteries. Testing showed that the initial efficiency of this lithium-ion battery was 89%, the expansion rate was 33%, and the cycle life was 3000 cycles.

[0058] Example 5

[0059] (1) Dissolve 8g of ethylene carbonate by heating at 38°C, add 1g of lithium salt to disperse it evenly in the ethylene carbonate, add 4g of silicon carbon material, stir thoroughly, drain the solvent, and obtain a silicon carbon mixture.

[0060] (2) Cool the silicon-carbon mixture obtained in step (1) to gradually solidify the ethylene carbonate. The ethylene carbonate and lithium salt form a coating layer on the surface of the silicon-carbon material to obtain the silicon-carbon anode material.

[0061] The silicon-carbon material used has a specific capacity of 420 mAh / g. In the silicon-carbon anode material prepared by the above method, ethylene carbonate and lithium salt form a 1.5 μm thick coating layer on the surface of the silicon-carbon material. This silicon-carbon anode material is used to fabricate an anode sheet, which is then applied to a lithium-ion battery. Testing showed that the lithium-ion battery has an initial efficiency of 88%, an expansion rate of 28%, and a cycle life of 3300 cycles.

[0062] Example 6

[0063] Unlike Example 5, the silicon-carbon material used has a specific capacity of 600 mAh / g. In this example, the silicon-carbon anode material prepared by the method of this invention is used to fabricate an anode sheet, which is then applied to a lithium-ion battery. Testing showed that the lithium-ion battery had an initial efficiency of 89%, an expansion rate of 35%, and a cycle life of 2600 cycles.

[0064] Example 7

[0065] (1) 14g of ethylene carbonate was heated to dissolve at 38°C, 2g of lithium salt was added to disperse it evenly in the ethylene carbonate, and then 6g of silicon carbon material was added. The mixture was stirred thoroughly and the solvent was drained to obtain a silicon carbon mixture.

[0066] (2) Cool the silicon-carbon mixture obtained in step (1) to gradually solidify the ethylene carbonate. The ethylene carbonate and lithium salt form a coating layer on the surface of the silicon-carbon material to obtain the silicon-carbon anode material.

[0067] The silicon-carbon material used has a specific capacity of 420 mAh / g. In the silicon-carbon anode material prepared by the above method, ethylene carbonate and lithium salt form a 2.0 μm thick coating layer on the surface of the silicon-carbon material. This silicon-carbon anode material is used to fabricate an anode sheet, which is then applied to a lithium-ion battery. Testing showed that the lithium-ion battery has an initial efficiency of 87%, an expansion rate of 27%, and a cycle life of 3200 cycles.

[0068] Example 8

[0069] Unlike Example 7, the silicon-carbon material used has a specific capacity of 600 mAh / g. In this example, the silicon-carbon anode material prepared by the method of the present invention is used to fabricate an anode sheet, which is then applied to a lithium-ion battery. Testing showed that the lithium-ion battery had an initial efficiency of 88%, an expansion rate of 36%, and a cycle life of 2800 cycles.

[0070] Comparative Example 1

[0071] The silicon-carbon material used in this comparative example has a specific capacity of 420 mAh / g. This silicon-carbon material was directly used as the silicon-carbon anode material, and a negative electrode sheet was fabricated and applied to a lithium-ion battery. Testing showed that the lithium-ion battery had an initial efficiency of 85%, an expansion rate of 35%, and a cycle life of 3000 cycles.

[0072] Comparative Example 2

[0073] The silicon-carbon material used in this comparative example has a specific capacity of 600 mAh / g. This silicon-carbon material was directly used as the silicon-carbon anode material, and a negative electrode sheet was fabricated and applied to a lithium-ion battery. Testing showed that the lithium-ion battery had an initial efficiency of 83%, an expansion rate of 45%, and a cycle life of 1000 cycles.

[0074] The battery performance test results of Examples 1-8 and Comparative Examples 1-2 are shown in the table below:

[0075]

[0076]

[0077] The test results in the table show that the silicon-carbon anode material prepared by this invention has a higher initial efficiency in batteries than conventional batteries using silicon-carbon materials directly as anode materials. The battery expansion rate is also lower than conventional batteries, and the cycle life is half as long. This demonstrates that coating the surface of the silicon-carbon material with ethylene carbonate and lithium salt significantly improves the initial efficiency and cycle life of the battery while reducing its expansion rate.

[0078] The results of Examples 1 and 2 show that the silicon-carbon anode material prepared by this invention, containing ethylene carbonate and lithium salt coatings, exhibits little change in initial efficiency and expansion rate when the specific capacity is the same but the thickness of the ethylene carbonate and lithium salt coatings differs, but significantly affects its cycle life. Furthermore, the results of Examples 2, 5, and 7 indicate that when the thickness of the ethylene carbonate and lithium salt coatings reaches a certain level, the impact on cycle life becomes less significant.

[0079] The results of Examples 1 and 3 show that for lithium-ion batteries made with silicon-carbon materials of different specific capacities, the larger the specific capacity, the greater the impact on the initial efficiency, expansion rate, and cycle life.

[0080] In summary, in Example 2, when the thickness of the silicon-carbon material coating ethylene carbonate and lithium salt is 1.0 μm and the specific capacity of the silicon-carbon material is 420 mAh / g, the prepared battery exhibits the best initial efficiency, expansion rate, and cycle life.

[0081] In summary, the silicon-carbon anode material provided by this invention, when applied to lithium-ion batteries, has the advantages of high initial efficiency, low expansion rate, and long lifespan.

[0082] Based on the disclosure and teachings of the foregoing specification, those skilled in the art can make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the specific embodiments described above, and any obvious improvements, substitutions, or modifications made by those skilled in the art based on the present invention are within the scope of protection of the present invention. Furthermore, although some specific terms are used in this specification, these terms are only for convenience of explanation and do not constitute any limitation on the present invention.

Claims

1. A silicon-carbon anode material, characterized in that, The silicon-carbon anode material has a core-shell structure, including a core and a shell. The shell covers at least a portion of the surface of the core. The core contains silicon-carbon material, and the shell contains ethylene carbonate and lithium salt. The ethylene carbonate in the shell can dissolve and vaporize at a predetermined temperature to form a porous structure on the surface of the silicon-carbon material that can be filled with lithium salt. The predetermined temperature is >35°C.

2. The silicon-carbon anode material according to claim 1, characterized in that, The lithium salt is at least one of lithium hydroxide, lithium carbonate, lithium fluoride, lithium oxalate, (CH2OCO2Li)2, CH3OCH2Li, and LiCH2CH2OCO2Li.

3. The silicon-carbon anode material according to claim 1, characterized in that, The specific capacity of the silicon-carbon material is 420-600 mAh / g.

4. The silicon-carbon anode material according to claim 1, characterized in that, The thickness of the shell is 0.1-2 μm.

5. A method for preparing a silicon-carbon anode material according to any one of claims 1-4, characterized in that, Includes the following steps: (1) Heating and dissolving ethylene carbonate, adding lithium salt to disperse it evenly in ethylene carbonate, then adding silicon carbon material, stirring thoroughly, draining the solvent to obtain a silicon carbon mixture; wherein, the mass ratio of ethylene carbonate, silicon carbon material and lithium salt is (8-14):(4-6):(1-2). (2) Cool the silicon-carbon mixture obtained in step (1) to gradually solidify the ethylene carbonate. The ethylene carbonate and lithium salt form a coating layer on the surface of the silicon-carbon material to obtain the silicon-carbon anode material.

6. The method for preparing a silicon-carbon anode material according to claim 5, characterized in that, The heating temperature for dissolving ethylene carbonate is >35℃, and the cooling and solidification temperature is 5-8℃.

7. A negative electrode sheet, characterized in that: Includes the silicon-carbon anode material as described in any one of claims 1-4.

8. A lithium-ion battery, characterized in that, Includes the negative electrode sheet as described in claim 7.

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