Anti-swelling silicon-based negative electrode sheet and preparation method thereof

Abstract

The application discloses a kind of anti-expansion silicon-based negative pole and preparation method thereof, from inside to outside including foil, lithium supplement layer attached to both sides of foil, silicon-based active material layer attached to the outside of lithium supplement layer, amorphous carbon layer attached to the outside of silicon-based active material layer and the graphite layer of outermost side;The foil is porous foil, and the hole of porous foil is filled by lithium supplement layer;The thickness of amorphous carbon layer is 20-100 μm, and the area density of amorphous layer is 0.2-5 times of the area density of silicon-based negative pole coating.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical technology, specifically relating to an anti-expansion silicon-based negative electrode sheet and its preparation method, which is mainly used in the preparation of lithium-ion batteries. Background Technology

[0002] The statements herein provide only background information in relation to this invention and do not necessarily constitute prior art.

[0003] Silicon is a high-capacity electrode material that can significantly increase lithium storage capacity. However, the commercialization of silicon-based electrodes for lithium-ion batteries has been severely hampered by the volume changes of silicon particles during the (de)lithiation process. The severe volume deformation of silicon particles during the (de)lithiation process leads to the expansion and contraction of the electrode, resulting in a rapid decay of battery capacity.

[0004] The inventors attempted to coat a porous foil with a lithium-filling coating, and then coat the surface of the lithium-filling coating with a silicon-based anode material coating to prepare an anode sheet. However, during operation, the expansion of the silicon-based anode material deviates from the direction of the porous foil, and its expansion cannot be restricted. Summary of the Invention

[0005] Building upon this, the inventors attempted to coat the surface of the silicon-based anode material coating with a graphite layer. This graphite layer then confines the expansion of the silicon-based anode material, directing it towards the porous foil to utilize the volume of the pores in the foil. This approach can alleviate the expansion problem of silicon-based anode materials to some extent.

[0006] However, the inventors further discovered that under different usage conditions (for example, as the areal density of the silicon-based anode increases, its corresponding expansion volume and expansion stress also increase), the expansion behavior of the silicon-based anode material varies. The graphite layer is relatively brittle; when the volume expansion of the silicon-based anode material exceeds the capacity of the porous foil and lithium-filling coating, it expands outward, exerting outward compressive force on the graphite layer, causing cracks, fractures, or even detachment, thus losing its restraining effect on the silicon-based anode material. In this case, a functional coating that can continue to absorb the expansion volume and stress needs to be added to the entire anode structure. This functional coating can ensure, to a greater extent, that the structure of the anode sheet remains intact when the silicon-based anode expands beyond the porosity of the porous foil.

[0007] To address the shortcomings of existing technologies, the purpose of this invention is to provide an anti-expansion silicon-based anode and its preparation method.

[0008] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0009] In a first aspect, the present invention provides an anti-expansion silicon-based negative electrode, comprising, from the inside out, a foil, a lithium replenishment layer attached to both sides of the foil, a silicon-based active material layer attached to the outside of the lithium replenishment layer, an amorphous carbon layer attached to the outside of the silicon-based active material layer, and an outermost graphite layer.

[0010] The foil is a porous foil, and the lithium replenishment layer fills the pores of the porous foil;

[0011] The thickness of the amorphous carbon layer is 20–150 μm, and the areal density of the amorphous carbon layer is 0.2–5 times that of the areal density of the coated silicon-based anode material. Preferably, it is 0.2–3 times.

[0012] Amorphous carbon layers, characterized by their soft texture, loose structure, and numerous micropores, serve two main purposes when placed between the silicon-based active material layer and the graphite layer. Firstly, they act as a buffer. When the silicon-based active material layer expands significantly, and the porous foil cannot absorb the excess expansion volume and stress of the silicon-based negative electrode, the amorphous carbon layer absorbs the excess stress and expansion, preventing excessive force from the silicon-based active material layer on the graphite layer. This is particularly effective in mitigating excessive localized forces on the graphite layer, preventing cracks and fractures in the graphite layer (which could lead to the failure of the entire negative electrode). Secondly, the soft texture of the amorphous carbon layer allows the graphite layer to evenly transfer forces to the silicon-based active material layer. The amorphous carbon layer, in turn, can better confine the silicon-based active material layer, causing it to expand towards the porous foil (when the lithium battery is charging, the expansion of the silicon-based negative electrode diffuses in both directions towards the porous foil voids and the amorphous carbon layer, while the outermost graphite coating also exerts expansion pressure on the amorphous carbon coating. The expansion stress of the silicon-based negative electrode in the amorphous carbon meets the pressure exerted by the graphite coating on the amorphous carbon, and the pressure of the graphite coating compresses the expansion pressure of the silicon-based negative electrode, causing the expansion pressure of the silicon-based negative electrode to fill the voids of the amorphous carbon coating and the porous foil); thirdly, the amorphous carbon layer has good conductivity and does not affect the normal operation of the battery. The amorphous carbon coating is also a negative electrode active material coating, which also provides negative electrode capacity).

[0013] In some embodiments, the amorphous carbon in the amorphous carbon layer is selected from soft carbon, hard carbon, or mesophase carbon microspheres.

[0014] Preferably, the amorphous carbon layer includes amorphous carbon, a conductive agent, and a binder, and the mass ratio of amorphous carbon, conductive agent, and binder is 85-98:1-6:1-10.

[0015] Amorphous carbon itself is also a negative electrode active material and provides negative electrode capacity, so its composition is similar to that of other coatings.

[0016] In some embodiments, the mass ratio of graphite, conductive agent, and binder in the graphite layer is 85–98:1–6:0.8–5.

[0017] More preferably, the conductive agent is selected from one or a combination of Super P, SFG, Ketjen Black, VGCF, CNTs, and graphene. Amorphous carbon itself is also a negative electrode active material and provides negative electrode capacity, thus its composition is similar to other coatings.

[0018] More preferably, the adhesive is selected from one or a combination of styrene-butadiene rubber, polyacrylic acid, polyacrylonitrile, polymethacrylic acid, polyacrylate, sodium carboxymethyl cellulose, or polyvinylidene fluoride.

[0019] In some embodiments, the foil thickness is 8–20 μm; the silicon-based active material layer thickness is 30–120 μm; and the graphite layer thickness is 40–150 μm.

[0020] In some embodiments, the mass ratio of lithium metal powder, conductive agent, and binder in the lithium replenishment layer is 94–98:1–3:1–4; the conductive agent is a soft particle conductive agent (with good flexibility, which does not affect the subsequent entry of the silicon-based negative electrode).

[0021] Preferably, the soft particle conductive agent is conductive agent KS-6 or KS-15.

[0022] Secondly, the present invention provides a method for preparing an expansion-resistant silicon-based anode, comprising the following steps:

[0023] A silicon-based active material electrode sheet is taken, which includes, from the inside out, a porous foil, a lithium replenishment layer attached to both sides of the foil, and a silicon-based active material layer attached to the outside of the lithium replenishment layer.

[0024] A slurry, which is a mixture of amorphous carbon, conductive agent and binder in a mass ratio of 85-98:1-6:1-10, is uniformly coated on both sides of a silicon-based active material electrode to obtain an amorphous carbon layer.

[0025] Graphite, conductive agent and binder are mixed in a mass ratio of 85-98:1-6:0.8-5 and then uniformly coated onto an amorphous carbon layer to obtain a graphite layer.

[0026] The obtained negative electrode sheet is dried and then rolled to obtain the final product.

[0027] Rolling is an essential process in lithium battery manufacturing. Rolling is unrelated to the coating extrusion expansion in this patent. Rolling is a physical extrusion, while the expansion of the coating in this patent is an electrochemical expansion.

[0028] In some embodiments, the active material of the silicon-based active material layer is silicon suboxide or Si / C.

[0029] The beneficial effects achieved by one or more embodiments of the present invention described above are as follows:

[0030] When a lithium battery is charged for the first time, the lithium replenishment coating inside the foil replenishes lithium for the silicon anode material, improving the battery's initial efficiency and increasing its energy density.

[0031] After the lithium powder in the lithium replenishment coating is consumed, the pores in the foil that were originally filled by the lithium replenishment material will have a lot more space. The silicon anode material in the silicon-based active material layer will expand in volume during charging, expanding in both directions towards the foil and the amorphous carbon layer. This is because many pores have appeared inside the foil due to the consumption of the lithium replenishment material. As a result, the stress and volume change caused by the expansion of the silicon-based active material layer will be preferentially released into the pores of the foil. Thus, the pores of the foil effectively solve the stress and volume change caused by the expansion of the silicon-based active material layer during charging and discharging.

[0032] Meanwhile, after the amorphous carbon material coating is coated and rolled on the negative electrode sheet, it is softer and more porous than the silicon-based active material layer and graphite layer. It contains a large number of micropores and can also absorb the stress and expansion brought by the silicon-based active material layer. Together with the foil, it can improve the use of silicon-based negative electrodes. Especially in ultra-high capacity silicon negative electrode materials, the silicon-based active material layer can also greatly improve the expansion problem of silicon negative electrodes together with the foil. Attached Figure Description

[0033] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0034] Figure 1 This is a cross-sectional view of the anti-expansion silicon negative electrode sheet according to an embodiment of the present invention.

[0035] The components are: 1. Foil; 2. Lithium replenishment layer; 3. Silicon-based active material layer; 4. Amorphous carbon layer; 5. Graphite layer. Detailed Implementation

[0036] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0037] The present invention will be further described below with reference to the embodiments.

[0038] Example 1

[0039] like Figure 1As shown, an anti-expansion silicon-based negative electrode includes, from the inside out, a foil 1, a lithium replenishment layer 2 attached to both sides of the foil 1, a silicon-based active material layer 3 attached to the outside of the lithium replenishment layer 2, an amorphous carbon layer 4 attached to the outside of the silicon-based active material layer 3, and an outermost graphite layer 5.

[0040] The foil 1 is a porous foil with holes that are circular, square, triangular or hexagonal in cross-sectional shape, 3-4 mm in diameter, and 40% porosity. The holes are through holes, and the lithium replenishment layer 2 fills the holes of the porous foil.

[0041] Lithium replenishment layer fabrication:

[0042] The required amount of lithium metal powder is M. 锂 M 锂 =((P3*S*C3*(1-L3)*80%*Y)+

[0043] (P4*S*C4*(1-L4)*80%*Y)+(P5*S*C5*(1-L5)*80%*Y)) / C 锂 ;

[0044] Where P3 is the layer density of silicon-based active material; S is the electrode area; C3 is the specific capacity of silicon-based active material layer; L3 is the initial coulombic efficiency of silicon-based active material layer; and Y is the negative electrode margin.

[0045] P4 is the density of the amorphous carbon layer; C4 is the specific capacity of the amorphous carbon layer; L4 is the first coulombic efficiency of the amorphous carbon layer.

[0046] P5 is the graphite layer density; C5 is the graphite layer specific capacity; L5 is the initial coulombic efficiency of the graphite layer; C 锂 The specific capacity of the lithium metal powder is 3600mAh / g.

[0047] Table 1

[0048]

[0049] The electrode area is S = 120 cm² 2 The pre-lithiation design capacity C0 is 80% of the irreversible capacity of the negative electrode, and the specific capacity of the lithium metal powder is C. 锂 =3600mAh / g, the positive and negative electrode NP ratio is 1.12, that is, the negative electrode margin is Y = 12%.

[0050] The calculated mass of lithium powder required is 3.024 mg.

[0051] A lithium-ion slurry containing 97% lithium metal powder, 1.5% KS-6 conductive agent, and 1.5% polyacrylic acid binder was uniformly mixed in a tetrahydrofuran solution and then sprayed onto a porous copper foil. The porous copper foil was 8 μm thick and had a porosity of 30%.

[0052] The density of lithium metal is 534 mg / cm³. 3 The theoretical thickness D of the lithium replenishment layer 理论 :

[0053] D 理论 =M 锂 / Lithium density / S*100000 / 97%;

[0054] The lithium replenishment layer is coated on the foil surface with a thickness D. 表面 :

[0055] D 表面 =(D 理论 - (copper foil thickness * porosity) / 2;

[0056] Calculations show that D 表面 It is 1.16 μm.

[0057] Preparation of silicon-based active material layer: The negative electrode active material silicon oxide material, conductive agent Super-P, and binder polyvinylidene fluoride are mixed evenly in a weight ratio of 97:1.5:1.5 to form a slurry. The slurry is then coated on both sides of the lithium replenishment layer.

[0058] Fabrication of amorphous carbon layer: Hard carbon, conductive agent Super-P, and binder polyvinylidene fluoride are mixed evenly in a weight ratio of 96.5:1.5:2.0 to form a slurry. The slurry is then coated on both sides of the silicon-based active material layer.

[0059] Graphite layer preparation: The negative electrode active material artificial graphite, conductive agent Super-P, and binder polyvinylidene fluoride are mixed evenly in a weight ratio of 96.5:1.5:2.0 to form a slurry. The slurry is then coated on both sides of the amorphous carbon layer.

[0060] like Figure 1 The image shows the fabricated negative electrode sheet, which is dried and then rolled. The resulting sheet is then slit to obtain the desired negative electrode sheet.

[0061] Positive electrode sheet fabrication: The ternary positive electrode material, conductive agent, and binder are mixed evenly at a mass ratio of 96.5:2.0:1.5, and then coated onto the positive electrode current collector. The mixture is then rolled and slit to obtain the desired positive electrode sheet.

[0062] Battery manufacturing: The positive and negative electrode sheets are stacked, baked, packaged, and filled with electrolyte to obtain the desired battery.

[0063] Comparative Example 1-1:

[0064] The positive electrode is the same as that in Example 1;

[0065] The specific capacity of the negative electrode material - silicon oxide material is 425 mAh / g, and the total capacity of the negative electrode coating is the same as the total capacity of the negative electrode in Example 1;

[0066] The negative electrode material was mixed evenly with the conductive agent Super-P and the binder polyvinylidene fluoride at a ratio of 97.0:1.5:1.5, and then the mixture was prepared with an areal density of 14 mg / cm³. 2 It is coated onto a lithium replenishing foil (the same as in Example 1, foil + lithium replenishing layer).

[0067] Battery manufacturing: The positive and negative electrode sheets are stacked, baked, packaged, and filled with electrolyte to obtain the desired battery.

[0068] The performance of the batteries prepared in Example 1 and Comparative Example 1-1 is shown in Table 2.

[0069] Table 2

[0070]

[0071]

[0072] As can be seen from the data in Table 2, Example 1 effectively reduced the full-charge rebound rate of the negative electrode sheet. It can be seen that Example 1 can make better use of the gaps in the foil compared with Comparative Example 1-1, thereby improving the charging expansion of the silicon-based negative electrode and further improving the cycle performance.

[0073] Comparative Examples 1-2:

[0074] The positive electrode is the same as that in Example 1;

[0075] The specific capacity of the negative electrode material - silicon oxide material is 425 mAh / g, and the total capacity of the negative electrode coating is the same as the total capacity of the negative electrode in Example 1;

[0076] The negative electrode material, conductive agent Super-P, and binder polyvinylidene fluoride were mixed evenly at a ratio of 97.0%:1.5%:1.5%, and the mixture was then prepared with an areal density of 14 mg / cm³. 2 It is coated onto a foil, which is a standard carbon-coated foil used in the industry.

[0077] Battery manufacturing: The positive and negative electrode sheets are stacked, baked, packaged, and filled with electrolyte to obtain the desired battery.

[0078] The performance of the batteries prepared in Example 1 and Comparative Examples 1-2 is shown in Table 3.

[0079] Table 3

[0080]

[0081]

[0082] As can be seen from the data in Table 3, compared with conventional batteries, Example 1 can effectively reduce the full-charge rebound rate of the negative electrode, improve the charging expansion and cycle performance of silicon-based negative electrodes, and at the same time improve the first-time efficiency of lithium batteries and increase the specific capacity of the positive electrode.

[0083] Example 2

[0084] Preparation of the lithium replenishment layer:

[0085] Table 4

[0086]

[0087] The electrode area is S = 120 cm² 2 The pre-lithiation design capacity C0 is 80% of the irreversible capacity of the negative electrode, and other parameters are the same as in Example 1. The calculated mass of lithium powder is 3.483 mg.

[0088] The lithium metal powder (97% by mass), conductive agent KS-15 (1.5% by mass), and binder polyvinylidene fluoride (1.5% by mass) are mixed evenly in a tetrahydrofuran solution, and the lithium replenishing slurry is coated onto a porous copper foil by spraying.

[0089] The porous copper foil is 8μm thick and has a porosity of 30%.

[0090] According to the formula in Example 1, the thickness of the lithium replenishment layer coated on the foil surface was calculated to be 1.518 μm.

[0091] Fabrication of silicon-based active material layer: Compared with Example 1, the conductive agent Super-P is replaced with KS-6, and everything else is the same as in Example 1.

[0092] Fabrication of amorphous carbon layer: The intermediate phase carbon microspheres of negative electrode active material, conductive agent KS-15, and binder polyvinylidene fluoride are mixed evenly in a weight ratio of 96.5:1.5:2.0 to form a slurry. The slurry is then coated on both sides of the silicon-based active material layer.

[0093] Graphite layer preparation: The negative electrode active material artificial graphite, conductive agent super-P, and binder polyvinylidene fluoride are mixed evenly in a weight ratio of 96.5:1.5:2.0 to form a slurry. The slurry is then coated on both sides of the amorphous carbon layer.

[0094] After drying, the negative electrode sheet is rolled and cut to obtain the desired negative electrode sheet.

[0095] The preparation of the positive electrode and the battery is the same as in Example 1.

[0096] Comparative Example 2-1:

[0097] The positive electrode is the same as that in Example 2;

[0098] The specific capacity of the negative electrode material - silicon oxide material is 444 mAh / g, and the total capacity of the negative electrode coating is the same as the total capacity of the negative electrode in Example 2;

[0099] The negative electrode material, conductive agent Super-P, and binder polyvinylidene fluoride were mixed evenly at a ratio of 96.8:1.5:1.7, and then the mixture was prepared with an areal density of 15 mg / cm³. 2 It is coated onto a lithium replenishing foil (same as in Example 2, foil + lithium replenishing layer).

[0100] Battery manufacturing: The positive and negative electrode sheets are stacked, baked, packaged, and filled with electrolyte to obtain the desired battery.

[0101] The performance of the batteries prepared in Example 2 and Comparative Example 2-1 is shown in Table 5.

[0102] Table 5

[0103]

[0104] As can be seen from the data in Table 5, Example 2 effectively reduced the full-charge rebound rate of the negative electrode sheet. It can be seen that Example 2 made better use of the gaps in the foil compared with Comparative Example 2-1, thereby improving the charging expansion of the silicon-based negative electrode and further improving the cycle performance.

[0105] Comparative Example 2-2:

[0106] The positive electrode is the same as that in Example 2;

[0107] The specific capacity of the negative electrode material - silicon oxide material is 444 mAh / g, and the total capacity of the negative electrode coating is the same as the total capacity of the negative electrode in Example 2;

[0108] The negative electrode material, conductive agent Super-P, and binder polyvinylidene fluoride were mixed evenly at a ratio of 96.8:1.5:1.7, and then the mixture was prepared with an areal density of 15 mg / cm³. 2 The coating is applied to a carbon-coated foil. The substrate of the carbon-coated foil is the same as in Example 2, and the carbon coating layer does not contain lithium powder (i.e., carbon-coated foil is used normally in the industry).

[0109] Battery manufacturing: The positive and negative electrode sheets are stacked, baked, packaged, and filled with electrolyte to obtain the desired battery.

[0110] The performance of the batteries prepared in Example 2 and Comparative Example 2-2 is shown in Table 6.

[0111] Table 6

[0112]

[0113] Comparing the data from Example 2 and Comparative Example 2-2, it can be seen that the battery produced by this invention significantly improves the negative electrode rebound caused by negative electrode expansion. Furthermore, the battery produced in Example 2 outperforms ordinary batteries in terms of initial efficiency, specific capacity, and cycle life.

[0114] Example 3

[0115] Preparation of the lithium replenishment layer:

[0116] Table 7

[0117]

[0118] The electrode area is S = 120 cm² 2 The pre-lithiation design capacity C0 is 80% of the irreversible capacity of the negative electrode, and other parameters are the same as in Example 1. The calculated mass of lithium powder is 4.256 mg.

[0119] The lithium metal powder (97% by mass), conductive agent KS-15 (1.5% by mass), and binder polyvinylidene fluoride (1.5% by mass) were mixed evenly in a tetrahydrofuran solution, and the lithium replenishment slurry was coated onto a porous copper foil by magnetron sputtering deposition.

[0120] The porous copper foil is 8μm thick and has a porosity of 30%.

[0121] According to the formula in Example 1, the thickness of the lithium replenishment layer coated on the foil surface was calculated to be 2.121 μm.

[0122] Fabrication of silicon-based active material layer: The negative electrode active material silicon oxide material, conductive agent super-P, and binder polyvinylidene fluoride are mixed evenly in a weight ratio of 97:1.5:1.5 to form a slurry. The slurry is then coated on both sides of the lithium replenishment layer.

[0123] Fabrication of amorphous carbon layer: Hard carbon, KS-6 conductive agent, and polyvinylidene fluoride binder are mixed evenly in a weight ratio of 96.5:1.5:2.0 to form a slurry. The slurry is then coated on both sides of the silicon-based active material layer.

[0124] Graphite layer preparation: The negative electrode active material artificial graphite, conductive agent KS-6, and binder polyvinylidene fluoride are mixed evenly in NMP at a weight ratio of 96.5:1.5:2.0 to form a slurry. The slurry is then coated on both sides of the amorphous carbon layer.

[0125] The negative electrode sheet is dried and then rolled. It is then slit to obtain the desired negative electrode sheet.

[0126] The preparation of the positive electrode and the battery is the same as in Example 1.

[0127] Comparative Example 3-1:

[0128] The positive electrode is the same as that in Example 3;

[0129] The specific capacity of the negative electrode material - silicon oxide material is 467 mAh / g, and the total capacity of the negative electrode coating is the same as the total capacity of the negative electrode in Example 3;

[0130] The negative electrode material, conductive agent Super-P, and binder polyvinylidene fluoride were mixed evenly at a ratio of 96.8:1.5:1.7, and then the mixture was prepared with an areal density of 15 mg / cm³. 2 It is coated onto a lithium replenishing foil (same as in Example 2, foil + lithium replenishing layer).

[0131] The battery manufacturing process is the same as in Example 1.

[0132] The performance of the batteries prepared in Example 3 and Comparative Example 3-1 is shown in Table 8.

[0133] Table 8

[0134]

[0135] As can be seen from the data in Table 8, Example 3 effectively reduced the full-charge rebound rate of the negative electrode, thereby greatly improving the charging expansion of the silicon-based negative electrode and further improving the cycle performance.

[0136] Comparative Example 3-2:

[0137] The positive electrode is the same as that in Example 3;

[0138] The specific capacity of the negative electrode material - silicon oxide material is 467 mAh / g, and the total capacity of the negative electrode coating is the same as the total capacity of the negative electrode in Example 3;

[0139] The negative electrode material, conductive agent Super-P, and binder polyvinylidene fluoride were mixed evenly at a ratio of 96.8:1.5:1.8, and then the mixture was prepared with an areal density of 15 mg / cm³. 2 The coating is applied to a carbon-coated foil, which uses the same foil material as in Example 3, but the carbon coating layer does not contain lithium powder (i.e., carbon-coated foil is normally used in the industry).

[0140] The battery manufacturing process is the same as in Example 1.

[0141] The performance of the batteries prepared in Example 3 and Comparative Example 3-2 is shown in Table 9.

[0142] Table 9

[0143]

[0144] When the silicon content continues to increase to the most advanced level in the industry, the battery made by this method can still ensure a significant improvement in negative electrode expansion compared to ordinary batteries.

[0145] Example 4

[0146] Preparation of the lithium replenishment layer:

[0147] Table 10

[0148]

[0149] The electrode area is S = 120 cm² 2 The pre-lithiation design capacity C0 is 80% of the irreversible capacity of the negative electrode, and other parameters are the same as in Example 1. The calculated mass of lithium powder is 4.368 mg.

[0150] The lithium metal powder (97% by mass), conductive agent KS-6 (1.5% by mass), and binder polyvinylidene fluoride (1.5% by mass) were mixed evenly in a tetrahydrofuran solution, and the lithium replenishment slurry was coated onto a porous copper foil by magnetron sputtering deposition.

[0151] The porous copper foil is 8μm thick and has a porosity of 30%.

[0152] According to the formula in Example 1, the thickness of the lithium replenishment layer coated on the foil surface was calculated to be 2.208 μm.

[0153] Fabrication of silicon-based active material layer: The negative electrode active material silicon oxide material, conductive agent super-P, and binder polyvinylidene fluoride are mixed evenly in a weight ratio of 97:1.5:1.5 to form a slurry. The slurry is then coated on both sides of the lithium replenishment layer.

[0154] Fabrication of amorphous carbon layer: Hard carbon, conductive agent super-P, and binder polyvinylidene fluoride are mixed evenly in a weight ratio of 96.5:1.5:2.0 to form a slurry. The slurry is then coated on both sides of the silicon-based active material layer.

[0155] Graphite layer preparation: The negative electrode active material artificial graphite, conductive agent super-P, and binder polyvinylidene fluoride are mixed evenly in a weight ratio of 96.5:1.5:2.0 to form a slurry. The slurry is then coated on both sides of the amorphous carbon layer.

[0156] The negative electrode sheet is dried and then rolled. It is then slit to obtain the desired negative electrode sheet.

[0157] The preparation of the positive electrode and the battery is the same as in Example 1.

[0158] Comparative Example 4-1:

[0159] The positive electrode is the same as that in Example 4;

[0160] The specific capacity of the negative electrode material - silicon oxide material is 476 mAh / g, and the total capacity of the negative electrode coating is the same as the total capacity of the negative electrode in Example 3;

[0161] The negative electrode material, conductive agent Super-P, and binder polyvinylidene fluoride were mixed evenly at a ratio of 96.8:1.5:1.7, and then the mixture was prepared with an areal density of 15 mg / cm³. 2 It is coated onto a lithium replenishing foil (same as in Example 2, foil + lithium replenishing layer).

[0162] The battery manufacturing process is the same as in Example 1.

[0163] The performance of the batteries prepared in Example 4 and Comparative Example 4-1 is shown in Table 11.

[0164] Table 11

[0165]

[0166] As can be seen from the data in Table 11, compared with Example 3, the porosity of the foil in Example 4 has been basically utilized. However, the amorphous carbon coating can still effectively alleviate the expansion of the silicon-based negative electrode material and absorb the stress changes it brings, thereby effectively reducing the full-charge rebound rate of the negative electrode sheet, improving the charging expansion of the silicon-based negative electrode, and improving the cycle performance.

[0167] Comparative Example 4-2:

[0168] The positive electrode is the same as that in Example 4;

[0169] The specific capacity of the negative electrode material - silicon oxide material is 467 mAh / g, and the total capacity of the negative electrode coating is the same as the total capacity of the negative electrode in Example 4;

[0170] The negative electrode material, conductive agent Super-P, and binder polyvinylidene fluoride were mixed evenly at a ratio of 96.8:1.5:1.7, and then the mixture was prepared with an areal density of 15 mg / cm³. 2 The coating is applied to a carbon-coated foil, which uses the same foil material as in Example 4, but the carbon coating layer does not contain lithium powder (i.e., carbon-coated foil is normally used in the industry).

[0171] The battery manufacturing process is the same as in Example 1.

[0172] The performance of the batteries prepared in Example 4 and Comparative Example 4-2 is shown in Table 12.

[0173] Table 12

[0174]

[0175] This invention utilizes both foil and multi-layer coating methods. Compared to ordinary batteries, batteries made using this method have significant advantages in terms of negative electrode rebound when fully charged, initial efficiency, specific capacity utilization, and cycle life.

[0176] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An anti-swelling silicon-based anode, characterized in that: From the inside out, it includes a foil, lithium replenishment layers attached to both sides of the foil, a silicon-based active material layer attached to the outside of the lithium replenishment layer, an amorphous carbon layer attached to the outside of the silicon-based active material layer, and the outermost graphite layer. The foil is a porous foil, and the lithium replenishment layer fills the pores of the porous foil; The thickness of the amorphous carbon layer is 20~100μm; The amorphous carbon in the amorphous carbon layer is selected from soft carbon, hard carbon, or mesophase carbon microspheres; The areal density of the amorphous carbon layer is 0.2 to 5 times that of the areal density of the silicon-based anode coating; The amorphous carbon layer absorbs excess stress and expansion, preventing the silicon-based active material layer from exerting excessive force on the graphite layer; The foil thickness is 8~20μm; The thickness of the silicon-based active material layer is 30~120μm; the thickness of the graphite layer is 40~150μm.

2. The anti-swelling silicon-based anode of claim 1, wherein: The amorphous carbon layer includes amorphous carbon, a conductive agent, and a binder, with a mass ratio of amorphous carbon, conductive agent, and binder of 85~98:1~6:1~10.

3. The anti-swelling silicon-based anode of claim 1, wherein: In the graphite layer, the mass ratio of graphite, conductive agent and binder is 85~98:1~6:0.8~5.

4. The anti-swelling silicon-based anode of claim 2, wherein: The conductive agent is selected from one or a combination of Super P, SFG, Ketjen Black, VGCF, CNTs, and graphene.

5. The anti-swelling silicon-based anode of claim 2 or 3, wherein: The adhesive is selected from one or a combination of styrene-butadiene rubber, polyacrylic acid, polyacrylonitrile, polymethacrylic acid, polyacrylate, sodium carboxymethyl cellulose, or polyvinylidene fluoride.

6. The anti-swelling silicon-based anode of claim 1, wherein: The mass ratio of lithium metal powder, conductive agent, and binder in the lithium replenishment layer is 94~98:1~3:1~4; the conductive agent is a soft particle conductive agent.

7. The anti-swelling silicon-based anode of claim 6, wherein: The soft particle conductive agent is conductive agent KS-6 or KS-15.

8. A method of making the swell resistant silicon-based anode of claim 1, wherein: Includes the following steps: A silicon-based active material electrode sheet is taken, which includes, from the inside out, a porous foil, a lithium replenishment layer attached to both sides of the foil, and a silicon-based active material layer attached to the outside of the lithium replenishment layer. A slurry, which is a mixture of amorphous carbon, conductive agent and binder in a mass ratio of 85~98:1~6:1~10, is uniformly coated on both sides of a silicon-based active material electrode to obtain an amorphous carbon layer. Graphite, conductive agent and binder are mixed in a mass ratio of 85~98:1~6:0.8~5 and then uniformly coated onto an amorphous carbon layer to obtain a graphite layer; The obtained negative electrode sheet is dried and then rolled to obtain the final product.

9. The method of claim 8, wherein: The active material in the silicon-based active material layer is silicon suboxide or Si / C.

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