CN115000407B - Silicon-based negative electrode plate and preparation method and application thereof - Google Patents

Silicon-based negative electrode plate and preparation method and application thereof Download PDF

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CN115000407B
CN115000407B CN202210665966.1A CN202210665966A CN115000407B CN 115000407 B CN115000407 B CN 115000407B CN 202210665966 A CN202210665966 A CN 202210665966A CN 115000407 B CN115000407 B CN 115000407B
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silicon
negative electrode
coating layer
conductive agent
binder system
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张小祝
苏敏
陈云
李凡群
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Wanxiang A123 Systems Asia Co Ltd
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Abstract

The invention relates to the field of lithium batteries, and provides a silicon-based negative electrode plate and a preparation method and application thereof, aiming at the problems that the negative electrode plate has high capacity and high initial efficiency and cycle performance of a full battery are not compatible, wherein the silicon-based negative electrode plate comprises a current collector, a first coating layer and a second coating layer, the first coating layer comprises a silicon-containing active substance A1, a conductive agent and a binder system A2, the second coating layer comprises a silicon-containing active substance B1, a conductive agent and a binder system B2, the silicon-containing active substance A1 consists of a high initial efficiency silicon-oxygen negative electrode material and artificial graphite, the binder system A2 comprises CMC and PAA, the silicon-containing active substance B1 consists of one or more of a conventional silicon-oxygen negative electrode material, a nano silicon material and artificial graphite, and the binder system B2 comprises CMC and SBR. The silicon-based negative electrode plate is applied to a lithium ion battery, and the battery has higher first efficiency and good cycling stability.

Description

Silicon-based negative electrode plate and preparation method and application thereof
Technical Field
The invention relates to the field of lithium batteries, in particular to a silicon-based negative electrode plate, and a preparation method and application thereof.
Background
The current commercial lithium ion battery cathode material is mainly graphite, and through years of development, the specific capacity of the current commercial lithium ion battery cathode material is close to a theoretical value (372 mAh/g), and the current market demand for high-energy density lithium ion batteries cannot be met. Silicon-based materials as novel lithium storage materials because the lithium intercalation process forms Li 15 Si 4 And Li (lithium) 22 Si 5 The theoretical capacity of the alloy is far higher than that of a graphite material (4200 mAh/g), the silicon material is rich in content, the lithium intercalation potential is low, and the alloy is the next-generation negative electrode material which is hopeful to replace a graphite negative electrode. SiO (SiO) x The material (0 < x < 2) has relatively small volume expansion while exhibiting high specific capacity because of a special nano silicon and silicon oxide mixed phase structure, so that the material has more industrialization prospect, but also has the problems of low first efficiency, poor conductivity and the like. The high-first-effect silica material is prepared into MgSiO in advance by doping Mg metal or Li metal into the common silica material 3 、Mg 2 SiO 4 、Li 2 SiO 3 、Li 2 Si 2 O 5 And the components are the same, and lithium of a positive electrode is not consumed, so that the first efficiency and reversible capacity of the whole battery cell are improved, and at present, conventional silica and high-first-effect silica materials are applied to the fields of portable electronic equipment, electric automobiles and the like in a certain scale.
Bilayer or even multilayer coating is very common in the preparation process of pole pieces made of silicon-based materials, but has disadvantages. For example, patent CN110148708A adopts a double-layer coating technology to prepare a graphite layer close to a current collector and a negative electrode plate of a silicon-containing coating far away from the current collector, which has the performances of high compaction and high capacity, but because of the obvious capacity difference of the two coating layers, the design of the excessive ratio (AC ratio) of the negative electrode plate to the positive electrode plate may be problematic, the AC ratio is low in design, the graphite layer close to the current collector may have the risk of lithium precipitation, and the first efficiency of the full battery may be reduced if the AC ratio is too high; the silicon content of the active material layer on the negative electrode plate is distributed in a gradient manner, the active material with high silicon content is adopted in the middle layer, the active material with low silicon content is adopted in the outer layer, and a sandwich structure is formed, so that the volume expansion in the cell circulation process can be relieved, and the cell performance is improved; the patent CN112909262A prepares a pole piece of a double-layer silicon-containing negative electrode, ensures the cohesiveness between an electrode and a current collector through the difference of upper and lower layers of binders, simultaneously better inhibits the expansion of the silicon negative electrode, and improves the cycle performance of a battery, but the patent does not consider the matching problem of different binders and silicon materials, so that the performance of the electrode is not exerted to the greatest extent. Therefore, in the prior art, different binder systems are not adopted for different silicon-based materials, so that more matching researches are carried out, and the performance of the materials is better exerted; the characteristics of the conventional silicon-based material and the high first-efficiency silicon-based material are not combined, and reasonable design is carried out at the pole piece end, so that the first efficiency and the cycle performance of the full battery are improved while the high capacity of the negative pole piece is reserved, and an ideal solution is needed.
Disclosure of Invention
In order to solve the problems of high capacity of the negative electrode plate, high initial efficiency of the full battery and unavailable cycle performance, the invention provides the silicon-based negative electrode plate, wherein the binder system in the first coating layer is a CMC+PAA system which takes flexibility and stripping force into account, and the binder system in the second coating layer is a CMC+SBR system which takes flexibility and inter-particle cohesion into account, so that active particles have better binding force and have good inhibition effect on expansion of silicon-based materials.
In order to achieve the above purpose, the present invention adopts the following technical scheme:
the silicon-based negative electrode plate comprises a current collector, a first coating layer coated on the surface of the current collector and a second coating layer coated on the surface of the first coating layer, wherein the first coating layer comprises a silicon-containing active substance A1, a conductive agent and a binder system A2, the second coating layer comprises a silicon-containing active substance B1, a conductive agent and a binder system B2, the silicon-containing active substance A1 comprises a high-first-effect silicon-oxygen negative electrode material and artificial graphite, the binder system A2 comprises CMC and PAA, the silicon-containing active substance B1 comprises one or more of a conventional silicon-oxygen negative electrode material, a nano silicon material and artificial graphite, and the binder system B2 comprises CMC and SBR.
The adhesive system A2 is a CMC+PAA system, wherein the mass ratio of CMC to PAA is 1 (2-10), the bonding force is enhanced through the bonding effect formed by the PAA and an oxide layer on the surface of the foil, and the bonding of CMC and PAA can generate strong bonding effect on graphite and silicon-based materials and has good inhibition effect on the expansion of the silicon-based materials; the binder system B2 is a CMC+SBR system, wherein the mass ratio of CMC to SBR is 1 (2-8), and the binder system has flexibility and inter-particle cohesion.
Preferably, the high-first-effect silicon oxide anode material is an SiO/C anode material subjected to doping treatment of an Mg source or an Li source, and the doping amount of the Mg source or the Li source is 5-15wt%; the conventional silicon-oxygen anode material is a carbon-coated SiO anode material, the carbon content is 3-8wt%, and the nano silicon material is a composite material in which nano silicon grows on the surface of graphite or is embedded in the internal structure of graphite.
Preferably, the conductive agent is a mixture of a dot-shaped or net-shaped conductive agent and a single-arm carbon tube.
Preferably, the raw materials of the first coating layer comprise the following components in parts by weight: 93-97 parts of silicon-containing active substance A1, 0.3-1 part of conductive agent and 2.3-4 parts of binder system A2; the second coating layer comprises the following components in parts by weight: 94-96 parts of silicon-containing active substance B1, 0.3-1 part of conductive agent and 2.5-4 parts of binder system B2.
Preferably, the binder system A2 is a copolymer, and the preparation method thereof is as follows: the preparation method comprises the steps of firstly copolymerizing methyl methacrylate and n-butyl acrylate in a molar ratio of 45-50:55 to obtain a preliminary block polymer X, copolymerizing the preliminary block polymer X and acrylic acid AA to form a block polymer, and grafting CMC chain segments on the block polymer to obtain a final copolymer, wherein the mass ratio of each chain segment in the copolymer is CMC:X:AA= (20-30): 10-20:50. The copolymer of methyl methacrylate and n-butyl acrylate has self-healing property at room temperature, acrylic acid is a flexible chain segment, and carboxymethyl cellulose is a rigid chain segment, and the self-healing capability and the excellent tensile property of the adhesive are formed after the copolymer of methyl methacrylate and n-butyl acrylate, so that the strain caused by the volume change of micron silicon particles can be effectively buffered, the pulverization of the silicon particles in the circulation process is inhibited, and the electrochemical property of the micron silicon particle electrode is obviously improved. Of course, the ratio of the three components is an important influencing factor.
Preferably, the thickness of the first coating layer is 20-150 μm, and the thickness of the second coating layer is 20-150 μm.
Preferably, the current collector is a copper foil having a thickness of 6-8 μm.
The invention also provides a preparation method of the silicon-based negative electrode plate, which comprises the following steps:
1) Uniformly mixing a silicon-containing active material, a conductive agent and a binder system to prepare a first coating layer and a second coating layer cathode slurry respectively;
2) Placing the first coating layer slurry on a lower die head in a slot extrusion type double-layer coating mode, placing the second coating layer slurry on an upper die head, and simultaneously coating the second coating layer slurry on a current collector;
3) After one surface of the current collector is coated, the other surface is repeatedly coated in the same way;
4) And drying, rolling and slitting the coated pole piece to obtain the silicon-based negative pole piece.
The invention also provides application of the silicon-based negative electrode plate in a lithium ion battery. The lithium ion battery comprises a positive plate, a negative plate, a diaphragm, electrolyte and a shell, wherein the positive plate comprises an aluminum foil and positive active substances distributed on the aluminum foil, and the negative plate is the silicon-based negative plate. The silicon-based negative electrode plate is applied to a lithium ion battery to obtain the lithium ion battery with high energy density, and the battery has higher first efficiency and good cycling stability.
Therefore, the invention has the beneficial effects that: (1) The silicon-containing active substance A1 in the first coating layer is a mixture of a high-first-effect silicon-oxygen negative electrode material and artificial graphite, and the binder system A2 is a CMC+PAA system with both flexibility and stripping force, so that a strong stripping force exists between the active substance and a current collector; the silicon-containing active substance B1 in the second coating layer is a mixture of a conventional silicon-oxygen negative electrode material and/or a nano silicon material and artificial graphite, and the binder system B2 is a CMC+SBR system which takes the flexibility and the inter-particle cohesion into account, so that the active particles have better binding power and have good inhibition effect on the expansion of the silicon-based material; (2) The silicon-based negative electrode plate is applied to a lithium ion battery to obtain the lithium ion battery with high energy density, and the battery has higher first efficiency and good cycling stability.
Drawings
FIG. 1 is a schematic view of a silicon negative electrode sheet structure of the present invention;
FIG. 2 is a graph showing the cycle performance of the silicon negative electrodes prepared in example 1 and comparative examples 1 to 3.
In the figure, 1, a current collector, 2, a first coating layer, 3 and a second coating layer.
Detailed Description
The technical scheme of the invention is further described through specific embodiments.
In the present invention, unless otherwise specified, the materials and equipment used are commercially available or are commonly used in the art, and the methods in the examples are conventional in the art unless otherwise specified.
General examples
The silicon-based negative electrode plate comprises a current collector, a first coating layer coated on the surface of the current collector and a second coating layer coated on the surface of the first coating layer, wherein the raw materials of the first coating layer comprise the following components in parts by weight: 93-97 parts of silicon-containing active substance A1, 0.3-1 part of conductive agent and 2.3-4 parts of binder system A2; the second coating layer comprises the following components in parts by weight: 94-96 parts of silicon-containing active substance B1, 0.3-1 part of conductive agent and 2.5-4 parts of binder system B2. The silicon-containing active material A1 consists of a high-first-effect silicon-oxygen negative electrode material and artificial graphite, wherein the high-first-effect silicon-oxygen negative electrode material is an SiO/C negative electrode material doped with an Mg source or an Li source, and the doping amount of the Mg source or the Li source is 5-15wt%; the binder system A2 comprises CMC and PAA with the mass ratio of 1 (2-10). The silicon-containing active substance B1 consists of one or more of a conventional silicon-oxygen negative electrode material and a nano silicon material and artificial graphite, wherein the conventional silicon-oxygen negative electrode material is a carbon-coated SiO negative electrode material, the carbon content is 3-8wt%, and the nano silicon material is a composite material with nano silicon growing on the surface of graphite or embedded in the internal structure of graphite; the binder system B2 comprises CMC and SBR with the mass ratio of 1 (2-8). The conductive agent is a mixture of a punctiform or netlike conductive agent and a single-arm carbon tube.
The thickness of the first coating layer is 20-150 mu m, and the thickness of the second coating layer is 20-150 mu m. The current collector is a copper foil, and the thickness of the copper foil is 6-8 mu m.
The invention also provides a preparation method of the silicon-based negative electrode plate, which comprises the following steps:
1) Uniformly mixing a silicon-containing active material, a conductive agent and a binder system to prepare a first coating layer and a second coating layer cathode slurry respectively;
2) Placing the first coating layer slurry on a lower die head in a slot extrusion type double-layer coating mode, placing the second coating layer slurry on an upper die head, and simultaneously coating the second coating layer slurry on a current collector;
3) After one surface of the current collector is coated, the other surface is repeatedly coated in the same way;
4) And drying, rolling and slitting the coated pole piece to obtain the silicon-based negative pole piece.
The invention also provides application of the silicon-based negative electrode plate in a lithium ion battery. The lithium ion battery comprises a positive plate, a negative plate, a diaphragm, electrolyte and a shell, wherein the positive plate comprises an aluminum foil and positive active substances distributed on the aluminum foil, and the negative plate is the silicon-based negative plate.
Example 1
A silicon-based negative electrode plate is shown in fig. 1, and comprises a current collector 1, a first coating layer 2 coated on the surface of the current collector 1, and a second coating layer 3 coated on the surface 2 of the first coating layer.
The preparation method of the silicon-based negative electrode plate comprises the following steps:
1) Preparing a first coating layer slurry: the mass ratio of the components of the first coating slurry of the negative plate is that the high-first-effect silicon-oxygen negative electrode material comprises artificial graphite, a conductive agent and CMC, wherein the CMC is PAA=12:84:0.6:1:2.4, the high-first-effect silicon-oxygen negative electrode material is an SiO/C negative electrode material subjected to 10wt% Mg source doping treatment, and the conductive agent is a mixture of a point conductive agent and a single-arm carbon tube;
firstly, CMC is dissolved in water to prepare 1.3 percent of glue solution, a conductive agent, a high first effect silicon-oxygen negative electrode material, graphite and PAA glue solution are sequentially added, each step is uniformly dispersed, the viscosity of the final slurry is controlled to be 2000-4000 mPa.s, and the fineness is controlled to be less than or equal to 30 mu m;
2) Preparing a second coating layer slurry: the second coating layer of the negative plate comprises the following components in mass ratio of conventional silicon-oxygen negative electrode material, artificial graphite and conductive agent, wherein CMC is prepared from SBR=8.5:87.5:0.6:0.6:2.8, the conventional silicon-oxygen negative electrode material is a SiO negative electrode material coated with 5wt% carbon, and the conductive agent is a mixture of a punctiform conductive agent and a single-arm carbon tube;
firstly, CMC is dissolved in water to prepare 1.3 percent of glue solution, a conductive agent, a conventional silicon-oxygen cathode material, graphite and SBR glue solution are sequentially added, each step is uniformly dispersed, the viscosity of the final slurry is controlled to be 2000-4000 mPa.s, and the fineness is controlled to be less than or equal to 30 mu m;
3) Preparing a negative electrode plate: the slit extrusion type double-layer coating mode is adopted, the first coating layer slurry is placed in a lower die head, the second coating layer slurry is placed in an upper die head, and is coated on copper foil with the thickness of 6 mu m, and the density of the coated double surfaces is 200g/m 2 The thickness of the first coating layer is 100 mu m, the thickness of the second coating layer is 100 mu m, and the silicon-based negative electrode plate is obtained by drying, rolling and cutting the electrode plate.
The application of the silicon-based negative electrode plate in the lithium ion battery comprises the following steps: and (3) the positive plate, the silicon-based negative plate, the diaphragm and the electrolyte are subjected to lamination, tab welding, aluminum-plastic film packaging, liquid injection and other procedures according to a conventional method to complete battery manufacturing. The manufacturing method of the positive plate comprises the following steps: the mass ratio of each component of the positive plate slurry is nickel-cobalt-manganese ternary 811:conductive agent:binder=97:1.3:1.7, firstly, polyvinylidene fluoride as binder is dissolved in NMP to prepare 7% glue solution, conductive agent and ternary main material are sequentially added, each step is uniformly dispersed, the viscosity of the final slurry is controlled at 1000-6000 mPa.s, the fineness is controlled at less than or equal to 20 mu m, the mixed slurry is uniformly coated on aluminum foil with the thickness of 12 mu m, and the double-sided density of the coating is 430g/m 2 Drying, rolling and cutting the pole piece to obtain a positive pole piece。
Example 2
The preparation method of the silicon-based negative electrode plate comprises the following steps:
1) Preparing a first coating layer slurry: the mass ratio of the components of the first coating slurry of the negative plate is that the high-first-effect silicon-oxygen negative electrode material comprises artificial graphite, a conductive agent and CMC, wherein the CMC is PAA=12:84:0.6:1:2.4, the high-first-effect silicon-oxygen negative electrode material is an SiO/C negative electrode material subjected to 10wt% Mg source doping treatment, and the conductive agent is a mixture of a point conductive agent and a single-arm carbon tube;
firstly, CMC is dissolved in water to prepare 1.3 percent of glue solution, a conductive agent, a high first effect silicon-oxygen negative electrode material, graphite and PAA glue solution are sequentially added, each step is uniformly dispersed, the viscosity of the final slurry is controlled to be 2000-4000 mPa.s, and the fineness is controlled to be less than or equal to 30 mu m;
2) Preparing a second coating layer slurry: the mass ratio of the components of the second coating layer of the negative electrode plate is nanometer silicon negative electrode material, artificial graphite, conductive agent and CMC, wherein the nanometer silicon negative electrode material is a composite material formed by growing nanometer silicon on the surface of graphite, and the conductive agent is a mixture of punctiform conductive agent and single-arm carbon tubes;
firstly, CMC is dissolved in water to prepare 1.3 percent of glue solution, a conductive agent, a nano silicon negative electrode material, graphite and SBR glue solution are sequentially added, each step is uniformly dispersed, the viscosity of the final slurry is controlled to be 2000-4000 mPa.s, and the fineness is controlled to be less than or equal to 30 mu m;
3) Preparing a negative electrode plate: the slit extrusion type double-layer coating mode is adopted, the first coating layer slurry is placed in a lower die head, the second coating layer slurry is placed in an upper die head, and is coated on copper foil with the thickness of 8 mu m, and the density of the coated double surfaces is 210g/m 2 The thickness of the first coating layer is 100 mu m, the thickness of the second coating layer is 100 mu m, and the silicon-based negative electrode plate is obtained by drying, rolling and cutting the electrode plate.
The application of the silicon-based negative electrode plate in the lithium ion battery comprises the following steps: as in example 1.
Example 3
The difference from example 1 is step 1): the mass ratio of the components of the first coating slurry of the negative plate is that the high-first-effect silicon-oxygen negative electrode material comprises artificial graphite and conductive agent, wherein the copolymer=12:84:0.6:3.4, the high-first-effect silicon-oxygen negative electrode material is an SiO/C negative electrode material subjected to 10wt% Mg source doping treatment, and the conductive agent is a mixture of a dot conductive agent and a single-arm carbon tube; firstly, dissolving the copolymer in water to prepare a 1.3% glue solution, sequentially adding a conductive agent, a high-first-effect silicon-oxygen negative electrode material and graphite, uniformly dispersing in each step, and controlling the viscosity of the final slurry to be 2000-4000 mPa.s and the fineness to be less than or equal to 30 mu m.
The preparation method of the copolymer comprises the following steps: firstly, copolymerizing methyl methacrylate and n-butyl acrylate to obtain a preliminary block polymer X in a molar ratio of 45:55, copolymerizing the preliminary block polymer X and acrylic acid AA to form a block polymer, and grafting CMC chain segments on the block polymer to obtain a final copolymer, wherein the mass ratio of each chain segment in the copolymer is CMC:X:AA=25:15:50. The preparation method of the copolymer is carried out by adopting a conventional method and comprises the following steps of: dissolving methyl methacrylate and n-butyl acrylate copolymer chain segment in ethanol solvent, dropwise adding a mixture of acrylic acid monomer and peroxy radical initiator for 3 hours, and continuing to perform heat preservation reaction for 4 hours after the dropwise adding is completed to obtain a reaction solution. Ultrasonic treating carboxymethyl cellulose water solution to break chain of carboxymethyl cellulose, adding into reaction liquid under nitrogen protection, adding initiator ferrous ammonium sulfate/H 2 O 2 The system was reacted at 45℃and pH=8 for 3 hours, and the block copolymer was obtained by condensing with steam. Wherein the carboxymethyl cellulose has a molecular weight of 2.18 x 10 5 The carboxymethyl substitution degree is 1.02, the mass concentration of the carboxymethyl cellulose aqueous solution is 4%, the ultrasonic frequency is 20kHz, the output power is 600W, and the ultrasonic treatment is carried out for 15min.
Example 4
The difference from example 3 is that the copolymer does not contain polypropylene.
Example 5
The difference from example 3 is that the copolymer does not contain CMC.
Example 6
The difference from example 3 is that the mass ratio of the segments in the copolymer is CMC: X: aa=25:5:50.
Example 7
The difference from example 3 is that the mass ratio of the segments in the copolymer is CMC: X: aa=40:15:50.
Comparative example 1
The difference from example 1 is that the silicon-based negative electrode tab is coated with the first coating slurry only on the surface of the current collector copper foil.
Comparative example 2
The difference from example 1 is that the silicon-based negative electrode tab is coated with the second coating slurry only on the surface of the current collector copper foil.
Comparative example 3
The difference from example 1 is the preparation method of the silicon-based negative electrode sheet:
1) Preparing a first coating layer slurry: the mass ratio of the components of the first coating slurry of the negative plate is conventional silicon-oxygen material to artificial graphite to conductive agent to CMC to SBR=8 to 88 to 1 to 0.6 to 2.4, wherein the conventional silicon-oxygen negative electrode material is a SiO negative electrode material coated with 5wt% of carbon, and the conductive agent is a mixture of a punctiform conductive agent and a single-arm carbon tube;
firstly, CMC is dissolved in water to prepare 1.3 percent of glue solution, a conductive agent, a conventional silicon-oxygen cathode material, graphite and SBR glue solution are sequentially added, each step is uniformly dispersed, the viscosity of the final slurry is controlled to be 2000-4000 mPa.s, and the fineness is controlled to be less than or equal to 30 mu m;
2) Preparing a second coating layer slurry: the mass ratio of the components of the second coating layer of the negative plate is high-first-effect silicon-oxygen negative electrode material to artificial graphite to conductive agent to CMC to PAA=12:84:0.6:1:2.4, wherein the high-first-effect silicon-oxygen negative electrode material is an SiO/C negative electrode material subjected to doping treatment of 10wt% of Mg source, and the conductive agent is a mixture of a punctiform conductive agent and a single-arm carbon tube;
firstly, CMC is dissolved in water to prepare 1.3 percent of glue solution, a conductive agent, a conventional silicon-oxygen anode material, graphite and PAA glue solution are sequentially added, each step is uniformly dispersed, the viscosity of the final slurry is controlled to be 2000-4000 mPa.s, and the fineness is controlled to be less than or equal to 30 mu m;
3) Preparing a negative electrode plate: the slit extrusion type double-layer coating mode is adopted, the slurry of the first coating layer is arranged at a lower die head, the slurry of the second coating layer is arranged at an upper die head, and the slurry is coated at the thickness of 8 mu mThe density of the coated double-sided copper foil is 210g/m 2 The thickness of the first coating layer is 100 mu m, the thickness of the second coating layer is 100 mu m, and the silicon-based negative electrode plate is obtained by drying, rolling and cutting the electrode plate.
Characterization of Performance
1. The negative electrode sheets prepared in examples and comparative examples were subjected to peel strength and full-charge disassembly expansion rate test after formation (thickness after full charge versus thickness increase rate after rolling), and the results are shown in the following table.
Pole piece Peel strength (mN/mm) Full electrical expansion ratio (%)
Example 1 28.84 29.87
Example 2 28.31 30.98
Example 3 28.89 27.01
Example 4 23.34 31.47
Example 5 27.12 32.51
Example 6 28.80 28.76
Example 7 27.91 27.97
Comparative example 1 26.70 29.85
Comparative example 2 15.09 32.55
Comparative example 3 14.32 31.23
As can be seen from comparing example 1 with comparative examples 1-3, cmc+paa is more strongly bonded to the copper foil as a binder, and is suitable for the first coating layer, and the full electrical expansion is slightly higher than the high first effect silicone coating layer. The second coating layer of example 2 has a nano-silicon material so that the full electrical expansion rate is slightly greater than that of example 1, but it can be seen that the nano-silicon material is helpful for the cycle stability in combination with the cycle performance. Example 3 the adhesive having self-healing ability and excellent tensile properties formed by copolymerizing carboxymethyl cellulose, methyl methacrylate, n-butyl acrylate copolymer, and acrylic acid can effectively reduce the rate of full electrical expansion, compared to comparative example 1. It can be seen from examples 4 and 5 that there are no three, and from examples 6 and 7 that the ratio of the three has an important effect on the adhesive properties, and only in the preferred range can the best effect be achieved.
2. The lithium ion batteries prepared in the embodiment 1 and the comparative examples 1-3 are subjected to cycle performance test under the conditions of 45 ℃ and voltage ranges of 2.8-4.2V and 1C/1C, a cycle effect diagram is shown in fig. 2, the cycle stability of the battery can be obviously improved by double-layer coating, and the cycle performance of the battery can be furthest exerted by the high-first-effect silica material matched with a CMC+PAA binder system as a first coating layer close to a current collector.
The present invention is not limited to the above-mentioned embodiments, but is intended to be limited to the following embodiments, and any modifications, equivalent changes and variations in the above-mentioned embodiments can be made by those skilled in the art without departing from the scope of the present invention.

Claims (9)

1. The silicon-based negative electrode plate is characterized by comprising a current collector, a first coating layer coated on the surface of the current collector and a second coating layer coated on the surface of the first coating layer, wherein the first coating layer comprises a silicon-containing active substance A1, a conductive agent and a binder system A2, the second coating layer comprises a silicon-containing active substance B1, a conductive agent and a binder system B2, the silicon-containing active substance A1 consists of a high-first-effect silicon-oxygen negative electrode material and artificial graphite, the binder system A2 comprises CMC and PAA, the silicon-containing active substance B1 consists of one or more of a conventional silicon-oxygen negative electrode material, a nano silicon material and artificial graphite, and the binder system B2 comprises CMC and SBR;
the high-first-effect silicon oxide anode material is an SiO/C anode material doped with an Mg source or an Li source;
the adhesive system A2 is a copolymer, and the preparation method thereof comprises the following steps: the preparation method comprises the steps of firstly copolymerizing methyl methacrylate and n-butyl acrylate in a molar ratio of 45-50:55 to obtain a preliminary block polymer X, copolymerizing the preliminary block polymer X and acrylic acid AA to form a block polymer, and grafting CMC chain segments on the block polymer to obtain a final copolymer, wherein the mass ratio of each chain segment in the copolymer is CMC:X:AA= (20-30): 10-20:50.
2. The silicon-based negative electrode plate according to claim 1, wherein the mass ratio of CMC to PAA in the binder system A2 is 1 (2-10); the mass ratio of CMC to SBR in the binder system B2 is 1 (2-8).
3. The silicon-based negative electrode plate according to claim 1 or 2, wherein the high-first-effect silicon-oxygen negative electrode material is an SiO/C negative electrode material doped with an Mg source or an Li source, and the doping amount of the Mg source or the Li source is 5-15wt%; the conventional silicon-oxygen anode material is a carbon-coated SiO anode material, the carbon content is 3-8wt%, and the nano silicon material is a composite material in which nano silicon grows on the surface of graphite or is embedded in the internal structure of graphite.
4. The silicon-based negative electrode sheet according to claim 1, wherein the conductive agent is a mixture of a dot-like or net-like conductive agent and a single-arm carbon tube.
5. The silicon-based negative electrode plate according to claim 1, wherein the raw materials of the first coating layer comprise the following components in parts by weight: 93-97 parts of silicon-containing active substance A1, 0.3-1 part of conductive agent and 2.3-4 parts of binder system A2; the second coating layer comprises the following components in parts by weight: 94-96 parts of silicon-containing active substance B1, 0.3-1 part of conductive agent and 2.5-4 parts of binder system B2.
6. The silicon-based negative electrode tab of claim 1, wherein the first coating layer has a thickness of 20-150 μm and the second coating layer has a thickness of 20-150 μm.
7. A silicon-based negative electrode sheet according to claim 1 or 6, wherein the current collector is a copper foil having a thickness of 6-8 μm.
8. The method for preparing the silicon-based negative electrode plate as claimed in any one of claims 1 to 7, comprising the steps of:
1) Uniformly mixing a silicon-containing active material, a conductive agent and a binder system to prepare a first coating layer and a second coating layer cathode slurry respectively;
2) Placing the first coating layer slurry on a lower die head in a slot extrusion type double-layer coating mode, placing the second coating layer slurry on an upper die head, and simultaneously coating the second coating layer slurry on a current collector;
3) After one surface of the current collector is coated, the other surface is repeatedly coated in the same way;
4) And drying, rolling and slitting the coated pole piece to obtain the silicon-based negative pole piece.
9. The use of any one of claims 1-7 in a lithium ion battery, wherein the lithium ion battery comprises a positive electrode sheet, a negative electrode sheet, a diaphragm, an electrolyte and a housing, the positive electrode sheet comprises an aluminum foil and positive electrode active materials distributed on the aluminum foil, and the negative electrode sheet is the silicon-based negative electrode sheet.
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