A multifunctional high-conductivity microcapsule and self-repairing silicon anode

Abstract

The present invention belongs to the technical field of lithium-ion batteries, and specifically provides a multifunctional high-conductivity microcapsule and a self-repairing silicon negative electrode, which are used to solve the problem that the existing silicon negative electrode generates huge stress due to volume expansion during the cycle and cracks are generated after expansion, resulting in electrode detachment; in the present invention, the multifunctional high-conductivity microcapsule is introduced into the silicon negative electrode as a self-repairing additive to form a multifunctional high-conductivity microcapsule / silicon self-repairing silicon negative electrode, and the volume change occurring during the lithium insertion and extraction process of silicon particles induces the rupture of the microcapsule additive, releasing liquid metal with high conductivity and fluidity, and as it flows inside the electrode, it fills the cracks in the electrode and forms a highly conductive network, ultimately realizing the repair of the conductive network and structural integrity of the electrode; and based on the rich carboxyl and hydroxyl functional groups on the surface of the microcapsule shell, the microcapsule is given better adhesion strength, which reduces the amount of binder while increasing the silicon particle loading amount, thereby constructing a high-energy density silicon negative electrode.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and specifically relates to a multifunctional highly conductive microcapsule and its application as a self-repairing additive in a silicon negative electrode. Background Art

[0002] Lithium-ion batteries (LIBs) are widely used as reliable power sources for portable electronic devices and electric vehicles, as well as storage devices for renewable energy, and have attracted increasing research attention. Silicon (Si) has a high specific capacity (4200 mA g -1 , Li 4.4 Si), low discharge potential and environmental friendliness show great potential as anode materials for LIBs. However, Si materials face large volume changes and low electrical conductivity during the lithium insertion / delithiation process. In particular, the alloying / de-alloying reaction between Si and Li can lead to a volume change of about 300%, thereby generating large stress that may destroy the Si-Si bond and cause electrical contact failure. Therefore, the capacity of silicon anode decays rapidly during cycling.

[0003] In response to the above problems, many studies on advanced silicon anodes have been made public, with the main directions being structural modification of silicon or silicon-carbon composites. In particular, Si / C composites not only buffer the huge stress generated by the continuous volume expansion of internal silicon, but also effectively improve the electrical conductivity of silicon. For example, in the literature "Wang, K.; Pei, S.; He, Z.; Huang, L.; Zhu, S.; Guo, J.; Shao, H.; Wang, J. Synthesis of a novel porous silicon microsphere@carbon core-shell composite via in situ MOF coating for lithium ion battery anodes. Chem. Eng. J. 2019, 356, 272-281.", a porous Si / C core-shell composite material synthesized by self-corrosion reaction, annealing and etching treatment was obtained. The composite material has a good conductivity of 1Ag -1 After 500 cycles, the reversible capacity is 1027.8 mAg -1 However, in the reported Si / C composite materials, once cracks and spalling occur, the electron transmission channel may be broken, resulting in poor cycle stability of the silicon negative electrode, which is difficult to meet the requirements of commercial applications. Summary of the Invention

[0004] The purpose of the present invention is to provide a multifunctional high-conductivity microcapsule and a self-repairing silicon negative electrode, so as to solve the problem that the existing silicon negative electrode generates huge stress due to volume expansion during the cycle and cracks after expansion, resulting in electrode detachment; the multifunctional high-conductivity microcapsule of the present invention is emulsified in a high-viscosity polyvinyl alcohol (PVA) or alginic acid (Alg) solution, which is conducive to the stable and uniform emulsification of liquid metal, and further forms a urea-formaldehyde resin / PVA or urea-formaldehyde resin / Alg composite shell layer through an in-situ polycondensation reaction of phenol-urea-formaldehyde on the surface of the liquid metal emulsion, thereby obtaining a multifunctional high-conductivity microcapsule with high sphericity and high monodispersity; further In the first step, the multifunctional high-conductivity microcapsules in the present invention are introduced into the silicon negative electrode as a self-repairing additive to form a multifunctional high-conductivity microcapsule / silicon self-repairing silicon negative electrode. The volume change occurring during the lithium deintercalation process of the silicon particles induces the rupture of the microcapsule additive, releasing liquid metal with high conductivity and fluidity. As it flows inside the electrode, it fills the cracks in the electrode and forms a highly conductive network, ultimately achieving the repair of the conductive network and structural integrity of the electrode. Moreover, based on the rich carboxyl and hydroxyl functional groups on the surface of the microcapsule shell, the microcapsules are given better adhesion strength, which reduces the amount of binder and increases the silicon particle loading capacity, thereby constructing a high-energy density silicon negative electrode.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] A multifunctional highly conductive microcapsule comprises a shell material and a core material, wherein the core material is encapsulated in the shell material; the microcapsule is spherical, the shell material is a urea-formaldehyde resin / polyvinyl alcohol (PVA) composite layer or a urea-formaldehyde resin / alginic acid (Alg) composite layer, and the core material is one of the following low-melting-point liquid metals: unitary liquid metal: Ga, binary liquid metals: Ga / In, Ga / Sn, Ga / Al, Ga / Zn, Ga / Ag, and multi-component liquid metals: Ga / In / Sn, In / Sn / Bi, Bi / Pb / Sn, Bi / Pb / Sn / Cd, Bi / Pb / Sn / Cd / In; the multifunctional highly conductive microcapsule is used as a self-healing additive in silicon negative electrodes.

[0007] Furthermore, the particle size of the microcapsules is distributed between 500 nm and 50 um.

[0008] Furthermore, the thickness of the shell material is distributed between 200nm and 5um.

[0009] Furthermore, the content of the core material is 30 to 85 wt%.

[0010] Furthermore, the outer surface of the microcapsule is rich in hydroxyl (-OH) and carboxyl (-COOH) groups, so that the microcapsules can also act as a binder when used in the silicon negative electrode; the hydroxyl (-OH) and carboxyl (-COOH) groups introduced on the surface of the microcapsule can form strong hydrogen bonds with the silicon oxide layer on the Si surface to help buffer the huge volume changes of the silicon particles during the cycle. At the same time, the hydrogen bonds can also tightly combine the silicon particles and the current collector, ensuring the stability of the electrochemical performance of the battery.

[0011] Furthermore, the preparation method of the multifunctional highly conductive microcapsules comprises the following steps:

[0012] Step A, adding the ethylene-methyl acrylate copolymer (EMA) solution to the polyvinyl alcohol (PVA) solution or the alginic acid (Alg) solution, and mechanically stirring until the solution is uniform, at a stirring rate of 500 to 800 rpm;

[0013] Step B: Add urea, resorcinol, and ammonium chloride to the solution obtained in step A in the mass ratio of EMA: urea: resorcinol: ammonium chloride of 3:10:1:1, and continue stirring until completely dissolved;

[0014] Step C: placing the solution obtained in step B in a constant temperature water bath, setting the water bath temperature to 35°C, adjusting the solution pH to 3.5 with NaOH, adding 5 to 28 g of the core material to the solution for dispersion, and continuing mechanical stirring and ultrasonic dispersion for 50 to 120 minutes; the ultrasonic power is 150 W to 300 W, and the mechanical stirring rate is 1000 rpm to 2000 rpm;

[0015] Step D: Add the formaldehyde solution to the solution obtained in step C at a mass ratio of urea to formaldehyde of 1:3, adjust the water bath temperature to 60°C to 80°C and continue stirring for 2h to 3h, then reduce the speed to 1000 rpm and continue stirring for 2.5h to 4h to obtain microcapsules;

[0016] Step E: Cool the microcapsules to 25° C. at room temperature, wash them repeatedly with deionized water, and then wash them with excess alcohol. After washing, dry them to obtain multifunctional highly conductive microcapsules.

[0017] Furthermore, in step A, the concentration of the polyvinyl alcohol solution is 2wt% to 15wt%, the concentration of the alginate solution is 1wt% to 4wt%, the concentration of the olefin-methyl acrylate copolymer solution is 2wt% to 5wt%, and the volume ratio of the olefin-methyl acrylate copolymer solution: the polyvinyl alcohol solution or the alginate solution is 1:(3 to 5).

[0018] Furthermore, based on the above-mentioned multifunctional highly conductive microcapsules, the present invention also provides a self-repairing silicon anode, comprising:

[0019] 60wt% to 95wt% silicon particles,

[0020] 2wt%~20wt% conductive agent,

[0021] 3wt%~20wt% binder,

[0022] and 5wt% to 40wt% of the self-repairing additive relative to the mass of silicon.

[0023] Based on the above technical solution, the beneficial effects of the present invention are:

[0024] The present invention provides a multifunctional high-conductivity microcapsule, which adopts an in-situ polymerization method to prepare a urea-formaldehyde resin layer (shell material) on the surface of liquid metal (core material) to form a multifunctional high-conductivity microcapsule, wherein the liquid metal is wrapped in the shell material and is evenly dispersed and can avoid oxidation, thereby ensuring the fluidity and high conductivity of the liquid metal; further, the multifunctional high-conductivity microcapsule is added to the silicon negative electrode as a self-repairing additive to form a multifunctional high-conductivity microcapsule / silicon self-repairing negative electrode. During the electrode cycle, the huge stress generated by the volume expansion of the silicon particles can induce the microcapsule to rupture, thereby releasing liquid metal with high conductivity and fluidity. The liquid metal can act as a buffer for the volume charge of the silicon particles and can spontaneously fill the cracks in the electrode piece and form a highly conductive network, ultimately realizing the repair of the electrode piece conductive network and self-repair of the structural integrity. Furthermore, the surface of the multifunctional high-conductivity microcapsule in the present invention is rich in hydroxyl (-OH) and carboxyl (-COOH), so that the microcapsule can be used in the silicon negative electrode and also act as a binder.

[0025] In addition, the preparation process of the multifunctional highly conductive microcapsules of the present invention is simple. By emulsifying in a high-viscosity polyvinyl alcohol (PVA) or alginic acid (Alg) solution, an emulsification system with a density close to that of the liquid metal is constructed, which is conducive to the stable and uniform emulsification of the liquid metal. Furthermore, a urea-formaldehyde resin / PVA or urea-formaldehyde resin / Alg composite shell layer is formed by an in-situ polycondensation reaction of phenol-urea-formaldehyde on the surface of the liquid metal emulsion, thereby obtaining multifunctional highly conductive microcapsules with high sphericity and high monodispersity.

[0026] In summary, the present invention provides a multifunctional highly conductive microcapsule as a self-repairing additive added to the silicon negative electrode, which can effectively solve the problem of the existing silicon negative electrode generating huge stress due to volume expansion during the cycle and cracks after expansion leading to electrode detachment, and significantly improve the negative electrode performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is an SEM image of the multifunctional and highly conductive microcapsules prepared in accordance with the present invention.

[0028] Figure 2The constant current charge-discharge cycle curve of the multifunctional high-conductivity microcapsule / silicon self-repairing negative electrode prepared in the embodiment of the present invention (2.1Ag -1 ).

[0029] Figure 3 This is the rate cycling curve of the multifunctional high-conductive microcapsule / silicon self-repairing negative electrode prepared in an embodiment of the present invention.

[0030] Figure 4 Comparison of the morphology SEM images of the multifunctional high-conductive microcapsule / silicon self-repairing negative electrode and the Pure Si silicon negative electrode before and after charge and discharge cycles prepared in an embodiment of the present invention; wherein, (a) is the morphology SEM image of the Pure Si silicon negative electrode before charge and discharge cycles, (b) is the morphology SEM image of the Pure Si silicon negative electrode after charge and discharge cycles, (c) is the morphology SEM image of the multifunctional high-conductive microcapsule / silicon self-repairing negative electrode before charge and discharge cycles, and (d) is the morphology SEM image of the multifunctional high-conductive microcapsule / silicon self-repairing negative electrode after charge and discharge cycles. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solutions and beneficial effects of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0032] Example 1

[0033] This embodiment provides a multifunctional high-conductivity microcapsule used as a self-repairing additive in a silicon anode, a corresponding multifunctional high-conductivity microcapsule / silicon self-repairing anode (GaInSn-MS / Si), and a further assembled CR2032 lithium-ion half-cell; the content of the multifunctional high-conductivity microcapsule in the self-repairing anode is 20wt% relative to the mass of Si. This embodiment is based on the ternary liquid metal Ga 68.5 In 21.5 Sn 10(abbreviated as GaInSn) has the self-repairing, high conductivity and liquid conformability properties. The liquid metal is wrapped in a multifunctional high-conductivity microcapsule by using an in-situ synthesized urea-formaldehyde resin / polyvinyl alcohol shell. By adding multifunctional high-conductivity microcapsules to the silicon negative electrode, the liquid conformability of GaInSn is used to buffer the expansion stress in the negative electrode, thereby alleviating the cracking and shedding of the silicon negative electrode. When the multifunctional high-conductivity microcapsules are ruptured by the expansion stress of the silicon negative electrode, GaInSn penetrates into the damaged silicon negative electrode and diffuses during the charge and discharge cycle, filling microcracks, cracks and other pores, thereby realizing self-repair of the silicon negative electrode conductive network. At the same time, since the surface of the multifunctional high-conductivity microcapsules is rich in hydroxyl (-OH) and carboxyl (-COOH), the microcapsules can also act as a binder when used in the silicon negative electrode. The preparation process of the multifunctional highly conductive microcapsules in this embodiment is simple. By emulsifying the microcapsules in a high-viscosity polyvinyl alcohol (PVA) solution, an emulsification system with a density close to that of the liquid metal is constructed, which is conducive to the stable and uniform emulsification of the liquid metal. Furthermore, a urea-formaldehyde resin / PVA composite shell layer is formed through an in-situ polycondensation reaction of phenol-urea-formaldehyde on the surface of the liquid metal emulsion, resulting in multifunctional highly conductive microcapsules with high sphericity and high monodispersity.

[0034] Furthermore, in this embodiment, the multifunctional high-conductivity microcapsules, the multifunctional high-conductivity microcapsules / silicon self-repairing negative electrode and the CR2032 type lithium-ion half-cell are prepared by the following steps:

[0035] Step 1: Encapsulate GaInSn with an in-situ synthesized urea-formaldehyde resin / polyvinyl alcohol shell to form a multifunctional highly conductive microcapsule; specifically:

[0036] Step 1-1: Add 5 ml of EMA solution (2.5 wt%) and 20 mL of PVA solution (5 wt%) to a 100 mL beaker and mechanically stir until the solution is homogeneous. The specific stirring time is 5 min and the stirring rate is set to 500 rpm.

[0037] Step 1-2, add 0.503g urea, 0.05g resorcinol, and 0.065g ammonium chloride to the solution obtained in step 1-1 and continue stirring until completely dissolved. The specific stirring time is 10 minutes;

[0038] Step 1-3: Place the beaker in a constant temperature water bath at 35°C. Use NaOH (10 wt%) to adjust the pH of the solution to 3.5. Place the ultrasonic probe in the solution without contacting the beaker wall. Set the ultrasonic power to 250 W and the mechanical stirring rate to 1600 rpm. Slowly add 28 g of GaInSn (core material) to the solution for dispersion. Continue mechanical stirring and ultrasonic dispersion for 50 min.

[0039] After the core material is dispersed in step 1-4, 1.456 g of formaldehyde solution is added to the solution obtained in step 1-3. The water bath temperature is adjusted to 60°C and stirring is continued for 2 hours. The stirring rate is then reduced to 1000 rpm and stirring is continued for 2.5 hours until the reaction is complete to obtain urea-formaldehyde resin / polyvinyl alcohol shell liquid metal microcapsules;

[0040] Steps 1-5: After the reaction is completed, the reaction product is cooled to 25° C. at room temperature, washed repeatedly with deionized water 6 times, and then the obtained microcapsules are washed with excess alcohol. After washing, the microcapsules are dried to obtain multifunctional highly conductive microcapsules.

[0041] Step 2: Using the multifunctional highly conductive microcapsules obtained in step 1 as additives to prepare a negative electrode of a battery; specifically:

[0042] Step 2-1: adding nano-silicon powder, a binder, and a conductive agent in a mass ratio of 7:2:1 in batches and continuously ball-milling for 3 hours to fully mix the slurry to obtain an original conductive slurry; wherein the binder comprises polystyrene butadiene copolymer and carboxymethyl cellulose, and the conductive agent comprises conductive carbon;

[0043] Step 2-2: adding multifunctional highly conductive microcapsules to the original conductive slurry, wherein the content of the multifunctional highly conductive microcapsules is 20 wt% of the mass of silicon; to maintain the integrity of the liquid metal microcapsules, the slurry is stirred using magnetic stirring after the addition of the microcapsules, with a specific stirring time of 1 hour and a stirring rate of 500 rpm;

[0044] Step 2-3: The slurry obtained in step 2-2 is evenly coated on a smooth and clean copper foil with a scraper to a wet film thickness of 250 μm. After the coating is completed, it is placed in a vacuum oven at 100°C and dried for 12 hours to obtain a self-repairing silicon negative electrode. The self-repairing silicon negative electrode is cut into circular electrode pieces with a diameter of 10 mm for standby use;

[0045] Step 3: Assemble a CR2032 lithium-ion half-cell using the self-repairing silicon negative electrode obtained in step 2; specifically:

[0046] The self-healing silicon anode in step 2 was used to assemble a CR2032 lithium-ion battery in a glove box. The electrolyte of the CR2032 lithium-ion battery was LB-011, and the separator was Celgard 2500. After the lithium battery was prepared, it was allowed to stand at room temperature for 12 hours before subsequent electrochemical performance tests.

[0047] like Figure 2 、 Figure 3 The constant current charge-discharge cycle curve of the multifunctional high conductive microcapsule / silicon self-repairing negative electrode prepared in Example (2.1Ag -1 ), as can be seen from the figure, at 2.1Ag -1After 100 cycles at the current density, the discharge capacity of the embodiment electrode reached 798.5 mAh g -1 The capacity retention rate is 34.79%, which is significantly better than the electrode without multifunctional high-conductivity microcapsules. And the rate test curve shows that the self-repairing lithium-ion battery (embodiment) exhibits better rate cycling performance than the pure silicon battery (Pure Si) in the control group.

[0048] like Figure 4 The following is a comparison of the morphology of the multifunctional high-conductive microcapsule / silicon self-repairing anode prepared in Example 1 and the Pure Si silicon anode before and after charge and discharge cycles. Scanning electron microscopy (SEM) tests show that:

[0049] Before cycling, the morphology of the Pure Si negative electrode is basically the same as that of the embodiment. The addition of liquid metal microcapsules does not cause significant changes in the surface morphology of the silicon negative electrode. Figure 4 In (a) and (c), the density of liquid metal microcapsules is much greater than that of silicon anode materials, so after the silicon anode is formed, most of the liquid metal microcapsules are located at the bottom layer of the anode material and are not easily observed on the surface;

[0050] After cycling, the surface of the Pure Si negative electrode cracked and fell off severely, such as Figure 4 (b); However, the surface cracks of the negative electrode of the embodiment are relatively few, and most of them are microcracks, such as Figure 4 (d); It can be seen that after the liquid metal microcapsules are mixed into the silicon negative electrode material, the expansion stress generated by the silicon during the charge and discharge process is effectively buffered, and the cracking and falling off of the silicon negative electrode are alleviated. This is also one of the reasons why the embodiment battery exhibits better electrochemical performance during the charge and discharge cycle.

[0051] The above description is only a specific embodiment of the present invention. Any feature disclosed in this specification, unless otherwise stated, can be replaced by other equivalent or alternative features with similar purposes; all disclosed features, or all steps in the methods or processes, except for mutually exclusive features and / or steps, can be combined in any way.

Claims

1. A multifunctional highly conductive microcapsule comprising a shell material and a core material, wherein the core material is encapsulated in the shell material; characterized in that: The microcapsules are spherical, the shell material is a urea-formaldehyde resin / polyvinyl alcohol composite layer or a urea-formaldehyde resin / alginate composite layer, and the core material is one of the following low-melting-point liquid metals: unit liquid metal: Ga, binary liquid metals: Ga / In, Ga / Sn, Ga / Al, Ga / Zn, Ga / Ag, and multi-component liquid metals: Ga / In / Sn, In / Sn / Bi, Bi / Pb / Sn, Bi / Pb / Sn / Cd, and Bi / Pb / Sn / Cd / In; the multifunctional and highly conductive microcapsules are used as self-repairing additives in silicon negative electrodes; The multifunctional highly conductive microcapsules are prepared by the following steps: Step A: adding the ethylene-methyl acrylate copolymer (EMA) solution to the polyvinyl alcohol (PVA) solution or the alginic acid (Alg) solution, and mechanically stirring the solution until the solution is homogeneous at a stirring rate of 500 to 800 rpm; Step B: Add urea, resorcinol, and ammonium chloride to the solution obtained in step A in the mass ratio of EMA: urea: resorcinol: ammonium chloride of 3:10:1:1, and continue stirring until completely dissolved; Step C: placing the solution obtained in step B in a constant temperature water bath, setting the water bath temperature to 35°C, adjusting the solution pH to 3.5 with NaOH, adding 5-28 g of the core material to the solution for dispersion, and continuing mechanical stirring and ultrasonic dispersion for 50 min to 120 min; the ultrasonic power is 150 W to 300 W, and the mechanical stirring rate is 1000 rpm to 2000 rpm; Step D: Add formaldehyde solution to the solution obtained in step C at a urea:formaldehyde mass ratio of 1:3, adjust the water bath temperature to 60°C to 80°C and continue stirring for 2 h to 3 h, then reduce the speed to 1000 rpm and continue stirring for 2.5 h to 4 h to obtain microcapsules; Step E: Cool the microcapsules to 25° C. at room temperature, wash them repeatedly with deionized water, and then wash them with excess alcohol. After washing, dry them to obtain multifunctional highly conductive microcapsules.

2. The multifunctional highly conductive microcapsule according to claim 1, characterized in that: The particle size distribution of the microcapsules is between 500nm and 50um.

3. The multifunctional highly conductive microcapsule according to claim 1, characterized in that: The thickness of the shell material is distributed between 200nm and 5um.

4. The multifunctional highly conductive microcapsule according to claim 1, characterized in that: The content of the core material is 30-85 wt %.

5. The multifunctional highly conductive microcapsule according to claim 1, characterized in that: The outer surface of the microcapsule is rich in hydroxyl groups (-OH) and carboxyl groups (-COOH), so that the microcapsule can be used in the silicon negative electrode and also serve as a binder.

6. The method for preparing the multifunctional high-conductive microcapsules according to claim 1, characterized in that: The following steps are involved: Step A: adding the ethylene-methyl acrylate copolymer (EMA) solution to the polyvinyl alcohol (PVA) solution or the alginic acid (Alg) solution, and mechanically stirring the solution until the solution is homogeneous at a stirring rate of 500 to 800 rpm; Step B: Add urea, resorcinol, and ammonium chloride to the solution obtained in step A in the mass ratio of EMA: urea: resorcinol: ammonium chloride of 3:10:1:1, and continue stirring until completely dissolved; Step C: placing the solution obtained in step B in a constant temperature water bath, setting the water bath temperature to 35°C, adjusting the solution pH to 3.5 with NaOH, adding 5-28 g of the core material to the solution for dispersion, and continuing mechanical stirring and ultrasonic dispersion for 50 min to 120 min; the ultrasonic power is 150 W to 300 W, and the mechanical stirring rate is 1000 rpm to 2000 rpm; Step D: Add formaldehyde solution to the solution obtained in step C at a urea:formaldehyde mass ratio of 1:3, adjust the water bath temperature to 60°C to 80°C and continue stirring for 2 h to 3 h, then reduce the speed to 1000 rpm and continue stirring for 2.5 h to 4 h to obtain microcapsules; Step E: Cool the microcapsules to 25° C. at room temperature, wash them repeatedly with deionized water, and then wash them with excess alcohol. After washing, dry them to obtain multifunctional highly conductive microcapsules.

7. The method for preparing the multifunctional high-conductive microcapsules according to claim 6, characterized in that: In step A, the concentration of the polyvinyl alcohol solution is 2wt%~15wt%, the concentration of the alginic acid solution is 1wt%~4wt%, the concentration of the ene-methyl acrylate copolymer solution is 2wt%~5wt%, and the volume ratio of the ene-methyl acrylate copolymer solution: the polyvinyl alcohol solution or the alginic acid solution is 1:(3~5).

8. A self-repairing silicon anode, comprising: 60wt%~95wt% silicon particles, 2wt%~20wt% conductive agent, 3wt%~20wt% binder, and 5wt% to 40wt% of a self-healing additive relative to the mass of silicon; The self-repairing additive is the multifunctional highly conductive microcapsule according to claim 1.

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