Silicon-containing negative pole piece as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of lithium ion batteries, and provides a silicon-containing negative pole piece and a preparation method and application thereof, the silicon-containing negative pole piece comprises a current collector, and a first active material layer and a second active material layer stacked on the surface of the current collector; the first active material layer comprises a first silicon-containing material with a median particle size of 6-12 [mu] m, a first negative electrode active material and a pore-forming agent; and the second active material layer comprises a second silicon-containing material with the median particle size of 2-5 microns and a second negative electrode active material. The silicon-containing negative pole piece has the beneficial effects that the silicon-containing negative pole piece contains double active material layers, and the upper layer of the pole piece adopts a small-particle-size silicon-containing material, so that the dynamics is improved; a pore-forming agent is introduced into the lower layer of the pole piece and can be automatically dissolved in electrolyte to form a cavity as an ion migration channel, so that the ion migration rate is increased; therefore, the silicon-containing negative pole piece has excellent fast charging dynamic performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and particularly relates to a silicon-containing negative electrode sheet, a preparation method thereof, and an application thereof. Background Art

[0002] Graphite negative electrodes have been widely used in the field of lithium-ion batteries. The specific capacity per gram of graphite has approached its theoretical value of 372 mAh / g, leaving limited room for improvement. The theoretical specific capacity of silicon-based negative electrode materials is about 4200 mAh / g, and they have relatively high lithium intercalation and deintercalation potentials. However, problems such as swelling and poor conductivity hinder their industrial application.

[0003] To solve the problems existing in silicon-based negative electrode materials at the present stage, existing technologies have taken measures such as coating carbon on the surface of silicon-based negative electrode materials, developing new functional binders, and optimizing electrolytes to slow down side reactions, which have improved the electrochemical performance of silicon-based negative electrodes to a certain extent. However, in the current application process of silicon-based negative electrodes, the defects of silicon-containing electrode sheets in terms of ion transport kinetics are amplified, and their fast charging ability still cannot reach the level of graphite negative electrodes, making it difficult to meet application requirements. Summary of the Invention

[0004] The present application provides a silicon-containing negative electrode sheet, a preparation method thereof, and an application thereof, aiming to solve the problem of insufficient ion transport kinetics in existing silicon-containing negative electrode sheets.

[0005] In a first aspect of the present application, a silicon-containing negative electrode sheet is provided, which includes a current collector, a first active material layer and a second active material layer stacked on the surface of the current collector;

[0006] The first active material layer includes a first silicon-containing material with a median particle size of 6-12 μm, a first negative electrode active material, and a pore-forming agent;

[0007] The second active material layer includes a second silicon-containing material with a median particle size of 2-5 μm and a second negative electrode active material.

[0008] According to some embodiments of the silicon-containing negative electrode sheet of the present application, the current collector includes one or more of copper foil, porous copper foil, carbon-coated porous copper foil, nickel foam, zinc-coated copper foil, nickel-coated copper foil, carbon-coated copper foil, nickel foil, and titanium foil.

[0009] According to some embodiments of the silicon-containing negative electrode sheet of the present application, the first active material layer further includes a first conductive paste, a first conductive agent, a first binder, and deionized water.

[0010] According to some embodiments of the silicon-containing negative electrode sheet of the present application, the second active material layer further includes a second conductive paste, a second conductive agent, a second binder, and deionized water.

[0011] According to some embodiments of the silicon-containing negative electrode sheet of the present application, the mass ratio of the first silicon-containing material, the first negative electrode active material, the pore-forming agent, the first conductive paste, the first conductive agent, the first binder, and deionized water in the first active material layer is (0.01 - 0.14):(0.61 - 0.94):(0.0005 - 0.005):(0.005 - 0.01):(0.01 - 0.05):(0.01 - 0.15):(0.5 - 1.0).

[0012] According to some embodiments of the silicon-containing negative electrode sheet of the present application, the mass ratio of the second silicon-containing material, the second negative electrode active material, the second conductive paste, the second conductive agent, the second binder, and deionized water in the second active material layer is (0.05 - 0.28):(0.66 - 0.94):(0.0005 - 0.005):(0.005 - 0.01):(0.01 - 0.05):(0.5 - 1.0).

[0013] According to some embodiments of the silicon-containing negative electrode sheet of the present application, the molar ratio of silicon elements in the first active material layer and the second active material layer is (0.01 - 0.15):(0.05 - 0.3).

[0014] According to some embodiments of the silicon-containing negative electrode sheet of the present application, the weight of the pore-forming agent in the first active material layer accounts for 1% - 15% of the total weight of the active materials in the first active layer.

[0015] According to some embodiments of the silicon-containing negative electrode sheet of the present application, the particle sizes of the first negative electrode active material and the second negative electrode active material are each independently 9 - 13 μm.

[0016] According to some embodiments of the silicon-containing negative electrode sheet of the present application, the first silicon-containing material and the second silicon-containing material are each independently selected from one or more of silicon oxide, silicon carbide, and silicon alloy.

[0017] According to some embodiments of the silicon-containing negative electrode sheet of the present application, the first negative electrode active material and the second negative electrode active material are each independently selected from one or more of artificial graphite, natural graphite, soft carbon, hard carbon, and mesocarbon microbeads.

[0018] According to some embodiments of the silicon-containing negative electrode sheet of the present application, the pore-forming agent includes one or more of polymethyl methacrylate, polyethylene oxide, and polyethylene glycol.

[0019] According to some embodiments of the silicon-containing negative electrode sheet of the present application, the first conductive paste and the second conductive paste are each independently selected from one or more of single-walled carbon nanotube paste, graphene conductive paste, and multi-walled carbon nanotube paste.

[0020] In some embodiments of the silicon-containing negative electrode sheet according to the present application, the first conductive agent and the second conductive agent are each independently selected from one or more of Super P, Ketjen black, and acetylene black.

[0021] In some embodiments of the silicon-containing negative electrode sheet according to the present application, the first binder and the second binder are each independently selected from one or more of sodium carboxymethyl cellulose, sodium polyacrylate, polyvinylidene fluoride, polytetrafluoroethylene, sodium alginate, styrene-butadiene rubber latex, and guar gum.

[0022] In some embodiments of the silicon-containing negative electrode sheet according to the present application, the thickness of the current collector is 5 - 8 μm.

[0023] In some embodiments of the silicon-containing negative electrode sheet according to the present application, the thickness of the first active material layer is 7 - 60 μm, and the thickness of the second active material layer is 6 - 56 μm.

[0024] In some embodiments of the silicon-containing negative electrode sheet according to the present application, the areal density of the current collector is 10 - 100 g / m 2 。

[0025] In some embodiments of the silicon-containing negative electrode sheet according to the present application, the areal density ratio of the current collector, the first active material layer, and the second active material layer is (40 - 108) : (25 - 90) : (15 - 60).

[0026] In some embodiments of the silicon-containing negative electrode sheet according to the present application, the porosity of the current collector is 0.01 - 20%.

[0027] In some embodiments of the silicon-containing negative electrode sheet according to the present application, the porosity ratio of the current collector, the first active material layer, and the second active material layer is (0.01 - 0.2) : (0.35 - 0.50) : (0.30 - 0.35).

[0028] In some embodiments of the silicon-containing negative electrode sheet according to the present application, the tap density of the first active material layer is 1.5 - 1.6 g / cm 3 ; the tap density of the second active material layer is 1.5 - 1.6 g / cm 3 。

[0029] The second aspect of the present application provides a method for preparing the silicon-containing negative electrode sheet according to the first aspect of the present application, including the following steps:

[0030] (1) Mix the raw materials contained in the first active material layer to obtain a first active slurry; coat the first active slurry on a current collector and dry to obtain a first active material layer;

[0031] (2) Mix the raw materials contained in the second active material layer to obtain a second active slurry; coat the second active slurry onto the first active material layer and dry it to obtain the second active material layer.

[0032] (3) Perform a rolling process on the current collector coated with the first active material layer and the second active material layer to obtain the silicon-containing negative electrode sheet.

[0033] According to some embodiments of the method for preparing the silicon-containing negative electrode sheet of the present application, the drying temperature in steps (1) and (2) is independently 84 - 88 °C, and the drying time is independently 8 - 12 min.

[0034] The third aspect of the present application provides a lithium-ion battery, including the silicon-containing negative electrode sheet described in the first aspect of the present application or the silicon-containing negative electrode sheet obtained by the preparation method described in the second aspect of the present application.

[0035] The beneficial effects of the present application include: the silicon-containing negative electrode sheet of the present application contains a double-layer active material layer. The upper layer of the sheet uses a small-particle-size silicon-containing material to improve kinetics; a pore-forming agent is introduced into the lower layer of the sheet, which can self-dissolve in the electrolyte to form cavities as ion migration channels, improving the ion migration rate; enabling the silicon-containing negative electrode sheet to have excellent fast-charging kinetic performance. Description of the Drawings

[0036] Figure 1 It is a schematic structural diagram of the silicon-containing negative electrode sheet described in Example 1 of the present application.

[0037] In the figure: 1 is the current collector; 2 is the first active material layer; 3 is the second active material layer. Detailed Embodiments

[0038] The embodiments of the present invention will be described in detail below. The examples are exemplary and are intended to explain the present invention, but should not be construed as limiting the present invention.

[0039] In the present invention, terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0040] An embodiment of the present application provides a silicon-containing negative electrode sheet, which includes a current collector, a first active material layer and a second active material layer stacked on the surface of the current collector;

[0041] The first active material layer includes a first silicon-containing material with a median particle size of 6-12 μm, a first negative electrode active material and a pore-forming agent; the median particle size of the first silicon-containing material can be 6 μm, 7 μm, 8 μm, 9 μm, 11 μm, 12 μm, etc., preferably 8-9 μm.

[0042] The second active material layer includes a second silicon-containing material with a median particle size of 2-5 μm and a second negative electrode active material; the median particle size of the second silicon-containing material can be 2 μm, 2.5 μm, 3 μm, 3.8 μm, 4 μm, 5 μm, etc.

[0043] The silicon-containing negative electrode sheet of the present application designs a double-layer negative electrode active layer, and uses silicon materials with different particle sizes to improve the kinetics of the negative electrode system; an electrolyte self-ablation substance is introduced into the first negative electrode active layer to construct a cavity, which can not only serve as a lithium ion migration channel to improve the ion migration rate; but also serve as a buffer space for the expansion of the silicon negative electrode to improve the negative electrode expansion.

[0044] In some embodiments of the present application, the current collector includes one or more of copper foil, porous copper foil, carbon-coated porous copper foil, nickel foam, zinc-coated copper foil, nickel-coated copper foil, carbon-coated copper foil, nickel foil and titanium foil.

[0045] In some embodiments of the present application, the first active material layer further includes a first conductive paste, a first conductive agent, a first binder and deionized water.

[0046] In some embodiments of the present application, the second active material layer further includes a second conductive paste, a second conductive agent, a second binder and deionized water.

[0047] In some embodiments of the present application, the mass ratio of the first silicon-containing material, the first negative electrode active material, the pore-forming agent, the first conductive paste, the first conductive agent, the first binder and deionized water in the first active material layer is (0.01-0.14):(0.61-0.94):(0.0005-0.005):(0.005-0.01):(0.01-0.05):(0.01-0.15):(0.5-1.0).

[0048] In some embodiments of the present application, the mass ratio of the second silicon-containing material, the second negative electrode active material, the second conductive paste, the second conductive agent, the second binder and deionized water in the second active material layer is (0.05-0.28):(0.66-0.94):(0.0005-0.005):(0.005-0.01):(0.01-0.05):(0.5-1.0).

[0049] In one embodiment of the present application, the molar ratio of silicon element in the first active material layer to that in the second active material layer is (0.01 - 0.15):(0.05 - 0.3).

[0050] In some embodiments of the present application, the weight of the pore former in the first active material layer accounts for 1% - 15% of the total weight of the active materials in the first active material layer; for example, 1%, 5%, 8%, 10%, 12%, 15%, etc.

[0051] In some embodiments of the present application, the particle sizes of the first negative electrode active material and the second negative electrode active material are each independently 9 - 13 μm, for example, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, etc.

[0052] In some embodiments of the present application, the first silicon-containing material and the second silicon-containing material are each independently selected from one or more of silicon oxide, silicon carbide, and silicon alloy.

[0053] In some embodiments of the present application, the first negative electrode active material and the second negative electrode active material are each independently selected from one or more of artificial graphite, natural graphite, soft carbon, hard carbon, and mesophase carbon microspheres.

[0054] In some embodiments of the present application, the pore former includes one or more of polymethyl methacrylate, polyethylene oxide, and polyethylene glycol. The polymethyl methacrylate used in the embodiments of the present application is purchased from Aladdin, the polyethylene oxide is purchased from Aladdin, and the polyethylene glycol is purchased from Aladdin.

[0055] In some embodiments of the present application, the first conductive paste and the second conductive paste are each independently selected from one or more of single-walled carbon nanotube paste, graphene conductive paste, and multi-walled carbon nanotube paste.

[0056] In some embodiments of the present application, the first conductive agent and the second conductive agent are each independently selected from one or more of Super P, Ketjen black, and acetylene black.

[0057] In some embodiments of the present application, the first binder and the second binder are each independently selected from one or more of sodium carboxymethyl cellulose, sodium polyacrylate, polyvinylidene fluoride, polytetrafluoroethylene, sodium alginate, styrene-butadiene rubber latex, and guar gum.

[0058] In some embodiments of the present application, the thickness of the current collector is 5-8 μm, such as 5 μm, 6 μm, 7 μm, 8 μm, etc., the thickness of the first active material layer is 7-60 μm, such as 7 μm, 10 μm, 15 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, etc., and the thickness of the second active material layer is 6-56 μm; such as 6 μm, 12 μm, 26 μm, 38 μm, 43 μm, 50 μm, 56 μm, etc.

[0059] In some embodiments of the present application, the areal density of the current collector is 10-100 g / m 2 ; such as 10 g / m 2 、20 g / m 2 、30 g / m 2 、53 g / m 2 、67 g / m 2 、75 g / m 2 、82 g / m 2 、93 g / m 2 、100 g / m 2 etc.

[0060] In some embodiments of the present application, the areal density ratio of the current collector, the first active material layer, and the second active material layer is (40-108):(25-90):(15-60).

[0061] In some embodiments of the present application, the porosity of the current collector is 0.01-20%, such as 0.01%, 0.05%, 1.5%, 5%, 8%, 10%, 16%, 20%, etc.

[0062] In some embodiments of the present application, the porosity ratio of the current collector, the first active material layer, and the second active material layer is (0.01-0.2):(0.35-0.50):(0.30-0.35).

[0063] In some embodiments of the present application, the tap density of the first active material layer is 1.5-1.6 g / cm 3 ; such as 1.5 g / cm 3 、1.53 g / cm 3 、1.56 g / cm 3 、1.58 g / cm 3 、1.60 g / cm 3 etc., and the tap density of the second active material layer is 1.5-1.6 g / cm 3 ,such as 1.5 g / cm 3 、1.53 g / cm 3 、1.56 g / cm 3, 1.58 g / cm 3 , 1.60 g / cm 3 etc.

[0064] The embodiment of the present application also provides a preparation method of the silicon-containing negative electrode sheet described in the first aspect of the present application, including the following steps:

[0065] (1) Mix the raw materials contained in the first active material layer to obtain a first active slurry; coat the first active slurry on a current collector and dry it to obtain a first active material layer;

[0066] (2) Mix the raw materials contained in the second active material layer to obtain a second active slurry; coat the second active slurry on the first active material layer and dry it to obtain a second active material layer;

[0067] (3) Perform a rolling process on the current collector coated with the first active material layer and the second active material layer to obtain the silicon-containing negative electrode sheet.

[0068] In some embodiments of the present application, the drying temperature in step (1) and step (2) is independently 84 - 88 °C, such as 84 °C, 85 °C, 87 °C, 88 °C, etc., and the drying time is independently 8 - 12 min, such as 8 min, 9 min, 10 min, 12 min, etc.

[0069] The embodiment of the present application also provides a lithium-ion battery, including the silicon-containing negative electrode sheet described in the first aspect of the present application or the silicon-containing negative electrode sheet obtained by the preparation method described in the second aspect of the present application.

[0070] The technical solution of the present application will be further described below in conjunction with specific embodiments.

[0071] Example 1

[0072] A preparation method of a silicon-containing negative electrode sheet, including the following steps:

[0073] S1. Mix 25.0 g of silicon-carbon with a median particle size of 8 um, 475.0 g of artificial graphite with a median particle size of 13 um, 5.0 g of conductive carbon black, 132.2 g of single-walled carbon nanotube slurry, 158.6 g of sodium polyacrylate, 18.5 g of styrene-butadiene rubber latex, 25.0 g of polymethyl methacrylate, and 243.3 g of deionized water evenly to obtain a first active slurry;

[0074] S2. Coat the first active slurry prepared in step S1 on a copper foil current collector with a thickness of 6 um, the areal density of the first active material layer is 50 g / m 2 , the porosity is 23%, and then transfer it to an oven and dry it at 84 °C for 10 min to obtain a thickness of 33 um and a tap density of 1.5 g / cm3 The first active material layer;

[0075] S3. Mix 50.0 g of silicon carbide with a median particle size of 3 um, 450.0 g of artificial graphite with a median particle size of 13 um, 5.0 g of conductive carbon black, 132.2 g of single-walled carbon nanotube slurry, 158.6 g of sodium polyacrylate, 18.5 g of styrene-butadiene rubber latex, and 243.3 g of deionized water evenly to obtain a second active slurry;

[0076] S4. Coat the second active slurry on the surface of the first active material layer. The areal density of the second active layer is 50 g / m 2 , the porosity is 26%, and then transfer it to an oven and dry it at 88 °C for 10 min to obtain a second active material layer with a thickness of 31 um and a tap density of 1.6 g / cm 3 ;

[0077] S5. Perform a rolling process on the current collector coated with the first active material layer and the second active material layer to obtain a silicon-containing negative electrode sheet with a tap density of 1.6 g / cm 3 and having the ability of rapid ion transport.

[0078] Example 2

[0079] The preparation method of the silicon-containing negative electrode sheet described in Example 2 is only different from that of Example 1 in that the median particle size of the first silicon-containing material in the first active material layer during the preparation of the silicon-containing negative electrode sheet described in Example 2 is 6 um, and the remaining operations are the same as those in Example 1.

[0080] Example 3

[0081] The preparation method of the silicon-containing negative electrode sheet described in Example 3 is only different from that of Example 1 in that the median particle size of the first silicon-containing material in the first active material layer during the preparation of the silicon-containing negative electrode sheet described in Example 3 is 10 um, and the remaining operations are the same as those in Example 1.

[0082] Example 4

[0083] The preparation method of the silicon-containing negative electrode sheet described in Example 4 is only different from that of Example 1 in that the median particle size of the first silicon-containing material in the first active material layer during the preparation of the silicon-containing negative electrode sheet described in Example 4 is 12 um, and the remaining operations are the same as those in Example 1.

[0084] Example 5

[0085] The preparation method of the silicon-containing negative electrode sheet described in Example 5 is only different from that of Example 1 in that the median particle size of the second silicon-containing material in the second active material layer during the preparation of the silicon-containing negative electrode sheet described in Example 5 is 2 um, and the remaining operations are the same as those in Example 1.

[0086] Example 6

[0087] The preparation method of the silicon-containing negative electrode sheet described in Example 6 is different from that of Example 1 only in that the median particle size of the second silicon-containing material in the second active material layer during the preparation process of the silicon-containing negative electrode sheet described in Example 6 is 4 μm, and the remaining operations are the same as those in Example 1.

[0088] Example 7

[0089] The preparation method of the silicon-containing negative electrode sheet described in Example 7 is different from that of Example 1 only in that the median particle size of the second silicon-containing material in the second active material layer during the preparation process of the silicon-containing negative electrode sheet described in Example 7 is 5 μm, and the remaining operations are the same as those in Example 1.

[0090] Example 8

[0091] The preparation method of the silicon-containing negative electrode sheet described in Example 8 is different from that of Example 1 only in that the weight of the pore-forming agent in the first active material layer accounts for 1% of the total weight of the active materials in the first active material layer during the preparation process of the silicon-containing negative electrode sheet described in Example 8, and the remaining operations are the same as those in Example 1.

[0092] Example 9

[0093] The preparation method of the silicon-containing negative electrode sheet described in Example 9 is different from that of Example 1 only in that the weight of the pore-forming agent in the first active material layer accounts for 10% of the total weight of the active materials in the first active material layer during the preparation process of the silicon-containing negative electrode sheet described in Example 9, and the remaining operations are the same as those in Example 1.

[0094] Example 10

[0095] The preparation method of the silicon-containing negative electrode sheet described in Example 10 is different from that of Example 1 only in that the weight of the pore-forming agent in the first active material layer accounts for 15% of the total weight of the active materials in the first active material layer during the preparation process of the silicon-containing negative electrode sheet described in Example 10, and the remaining operations are the same as those in Example 1.

[0096] Example 11

[0097] The preparation method of the silicon-containing negative electrode sheet described in Example 11 is different from that of Example 1 only in that the pore-forming agent used during the preparation process of the silicon-containing negative electrode sheet described in Example 11 is polyethylene oxide, and the remaining operations are the same as those in Example 1.

[0098] Example 12

[0099] The preparation method of the silicon-containing negative electrode sheet described in Example 12 is different from that of Example 1 only in that the pore-forming agent used during the preparation process of the silicon-containing negative electrode sheet described in Example 12 is polyethylene glycol, and the remaining operations are the same as those in Example 1.

[0100] Comparative Example 1

[0101] The preparation method of the silicon-containing negative electrode sheet described in Comparative Example 1 is different from that of Example 1 only in that the first active material layer in the preparation process of the silicon-containing negative electrode sheet described in Comparative Example 1 does not contain a raw material pore former, and the remaining operations are the same as those in Example 1.

[0102] Comparative Example 2

[0103] The preparation method of the silicon-containing negative electrode sheet described in Comparative Example 2 is different from that of Example 1 only in that the median particle size of the first silicon-containing material in the first active material layer in the preparation process of the silicon-containing negative electrode sheet described in Comparative Example 2 is 3 μm, and the median particle size of the second silicon-containing material in the second active material layer is 8 μm, and the remaining operations are the same as those in Example 1.

[0104] Electrochemical performance study of the silicon-containing negative electrode sheets described in Examples 1-12 and Comparative Examples 1-2 of the present application

[0105] Half-cell test method: The silicon-containing negative electrode sheets described in Examples 1-12 and Comparative Examples 1-2 were respectively assembled into 2032-type button cells in a glove box. The counter electrode used a lithium metal sheet with a thickness of 0.25 mm. The electrolyte was LiPF6 / EC+DMC+DEC (volume ratio 1:1:1), and the concentration of LiPF6 was 1.0 mol / L; the separator was a 12-μm polypropylene separator; the working voltage was 0.005V-2V, and constant current charge and discharge tests were carried out at 0.1C / 0.1C at 25°C. The porosity of the fresh electrode sheet, the porosity of the electrode sheet after the first de-lithiation, the first lithium insertion expansion, and the fast charge lithium precipitation conditions were tested. The test results are shown in Table 1.

[0106] Among them,

[0107] The calculation method of the first lithium insertion expansion C is as follows:

[0108] C = (h1 - h0) / (h0 - d) * 100%, where C is the first lithium insertion expansion ratio, h1 is the thickness of the electrode sheet after the first lithium insertion, h0 is the initial thickness of the electrode sheet, and d is the thickness of the copper foil;

[0109] Table 1

[0110] Porosity of fresh electrode Porosity of electrode after first de-lithiation Swelling during first lithiation Lithium precipitation during fast charging Example 1 31.20％ 32.64％ 35.34％ No lithium precipitation at 3.5C Example 2 31.20％ 34.49％ 36.89％ No lithium precipitation at 4.0C Example 3 31.20％ 35.72％ 38.95％ No lithium precipitation at 2.8C Example 4 31.20％ 37.13％ 42.17％ No lithium precipitation at 1.2C Example 5 30.37％ 31.74％ 35.12％ No lithium precipitation at 3.5C Example 6 30.89％ 31.59％ 35.66％ No lithium precipitation at 2.8C Example 7 31.02％ 32.85％ 36.24％ No lithium precipitation at 2.8C Example 8 27.20％ 33.35％ 38.24％ No lithium precipitation at 2.8C Example 9 36.20％ 37.02％ 36.75％ No lithium precipitation at 2.8C Example 10 41.20％ 41.46％ 35.99％ No lithium precipitation at 3.5C Example 11 31.20％ 34.64％ 36.64％ No lithium precipitation at 1.0C Example 12 31.20％ 37.31％ 36.21％ No lithium precipitation at 1.0C Comparative Example 1 26.20％ 34.90％ 39.09％ No lithium precipitation at 1.0C Comparative Example 2 31.92％ 33.23％ 40.18％ No lithium precipitation at 1.0C

[0111] Note: The porosity of the present application was tested by the mercury intrusion method;

[0112] The fast charge lithium precipitation test method was to design a high-rate charge and discharge test. After 10 cycles of testing, the negative electrode sheet was disassembled after being fully lithiated to check the lithium precipitation situation at the negative electrode interface.

[0113] It can be seen from Table 1 that: Examples 1-4 of the present application show that as the median particle size of the first silicon-containing material in the first active material layer increases, the charging capacity shows a downward trend; Examples 1, 5-7 show that as the median particle size of the second silicon-containing material in the second active material layer increases, the charging capacity shows a downward trend; Examples 1, 8-10 show that the appropriate addition amount of the pore-forming agent in the first active material layer <15%, and the charging capacity is optimal near 10%; Examples 1, 11, 12 show that the optimal type of the pore-forming agent in the first active material layer is polymethyl methacrylate; Examples 1 and Comparative Example 1 show that introducing a pore-forming agent to construct a buffer space and an ion transport channel is beneficial to improving the fast charging capacity; Examples 1 and Comparative Example 2 show that using large-particle-size silicon carbide for the first silicon-containing material in the first active material layer and small-particle-size silicon carbide for the second silicon-containing material in the second active material layer is beneficial to improving the fast charging capacity.

[0114] Although the above embodiments have been shown and described, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Any changes, modifications, substitutions, and variations made by those of ordinary skill in the art to the above embodiments are within the protection scope of the present invention.

Claims

1. A silicon-containing negative electrode sheet, characterized in that, It includes a current collector, a first active material layer and a second active material layer stacked on the surface of the current collector; The first active material layer includes a first silicon-containing material with a median particle size of 6-12 μm, a first negative electrode active material and a pore-forming agent; The second active material layer includes a second silicon-containing material with a median particle size of 2-5 μm and a second negative electrode active material.

2. The silicon-containing negative electrode sheet according to claim 1, wherein The current collector includes one or more of copper foil, porous copper foil, carbon-coated porous copper foil, nickel foam, zinc-plated copper foil, nickel-plated copper foil, carbon-coated copper foil, nickel foil and titanium foil; And / or, the first active material layer further includes a first conductive paste, a first conductive agent, a first binder and deionized water; And / or, the second active material layer further includes a second conductive paste, a second conductive agent, a second binder and deionized water.

3. The silicon-containing negative electrode sheet according to claim 2, wherein The mass ratio of the first silicon-containing material, the first negative electrode active material, the pore-forming agent, the first conductive paste, the first conductive agent, the first binder and deionized water in the first active material layer is (0.01-0.14):(0.61-0.94):(0.0005-0.005):(0.005-0.01):(0.01-0.05):(0.01-0.15):(0.5-1.0); And / or, the mass ratio of the second silicon-containing material, the second negative electrode active material, the second conductive paste, the second conductive agent, the second binder and deionized water in the second active material layer is (0.05-0.28):(0.66-0.94):(0.0005-0.005):(0.005-0.01):(0.01-0.05):(0.5-1.0).

4. The silicon-containing negative electrode sheet according to claim 1, wherein The molar ratio of silicon elements in the first active material layer and the second active material layer is (0.01-0.15):(0.05-0.3); And / or, the weight of the pore-forming agent in the first active material layer accounts for 1%-15% of the total weight of the active materials in the first active material layer; And / or, the particle sizes of the first negative electrode active material and the second negative electrode active material are independently 9-13 μm.

5. The silicon-containing negative electrode sheet according to claim 2, wherein, The first silicon-containing material and the second silicon-containing material are independently selected from one or more of silicon oxide, silicon carbon and silicon alloy; And / or, the first negative electrode active material and the second negative electrode active material are independently selected from one or more of artificial graphite, natural graphite, soft carbon, hard carbon and mesophase carbon microspheres; And / or, the pore-forming agent includes one or more of polymethyl methacrylate, polyethylene oxide and polyethylene glycol; And / or, the first conductive paste and the second conductive paste are independently selected from one or more of single-walled carbon nanotube paste, graphene conductive paste and multi-walled carbon nanotube paste; And / or, the first conductive agent and the second conductive agent are independently selected from one or more of Super P, Ketjen black and acetylene black; And / or, the first binder and the second binder are independently selected from one or more of sodium carboxymethyl cellulose, sodium polyacrylate, polyvinylidene fluoride, polytetrafluoroethylene, sodium alginate, styrene-butadiene rubber latex and guar gum.

6. The silicon-containing negative electrode sheet according to claim 1, wherein The thickness of the current collector is 5 - 8 μm, the thickness of the first active material layer is 7 - 60 μm, and the thickness of the second active material layer is 6 - 56 μm; and / or, the areal density of the current collector is 10 - 100 g / m 2 ; and / or, the areal density ratio of the current collector, the first active material layer, and the second active material layer is (40 - 108):(25 - 90):(15 - 60).

7. The silicon-containing negative electrode sheet according to claim 1, characterized in that, The porosity of the current collector is 0.01 - 20%; and / or, the porosity ratio of the current collector, the first active material layer, and the second active material layer is (0.01 - 0.2):(0.35 - 0.50):(0.30 - 0.35); and / or, the tap density of the first active material layer is 1.5-1.6 g / cm 3 ; the tap density of the second active material layer is 1.5-1.6 g / cm 3 .

8. The preparation method of the silicon-containing anode sheet according to any one of claims 1-7, characterized in that, comprising the following steps: (1) Mix the raw materials contained in the first active material layer to obtain a first active slurry; coat the first active slurry onto the current collector and dry to obtain the first active material layer; (2) Mix the raw materials contained in the second active material layer to obtain a second active slurry; coat the second active slurry onto the first active material layer and dry to obtain the second active material layer; (3) Perform a rolling process on the current collector coated with the first active material layer and the second active material layer to obtain the silicon-containing negative electrode sheet.

9. The preparation method of the silicon-containing negative electrode sheet according to claim 8, wherein, In steps (1) and (2), the drying temperature is independently 84 - 88 °C, and the drying time is independently 8 - 12 min.

10. A lithium-ion battery, characterized in that, comprising the silicon-containing negative electrode sheet according to any one of claims 1 - 7 or the silicon-containing negative electrode sheet obtained by the preparation method according to any one of claims 8 - 9.

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