CN115395115A - Multifunctional high-conductivity microcapsule and self-repairing silicon cathode - Google Patents

Abstract

The invention belongs to the technical field of lithium-ion batteries, and specifically provides a multi-functional high-conductivity microcapsule and a self-repairing silicon negative electrode, which are used to solve the problems caused by the huge stress caused by the volume expansion of the existing silicon negative electrode during the cycle and the cracks generated after the expansion. The problem of falling off; in the present invention, multifunctional high-conductivity microcapsules 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, and the volume change that occurs during the deintercalation of silicon particles into lithium then induces microparticles The capsule additive ruptures, releasing liquid metal with high conductivity and fluidity, along with its flow inside the pole piece, fills the cracks in the pole piece and forms a highly conductive network, and finally realizes the repair of the pole piece’s conductive network and structural integrity ; Moreover, based on the rich carboxyl and hydroxyl functional groups on the surface of the microcapsule shell, the microcapsules are endowed with better adhesion strength, and the loading of silicon particles is increased while reducing the amount of binder, to construct a high-energy-density silicon negative electrode.

Description

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

technical field

The invention belongs to the technical field of lithium-ion batteries, in particular to a multifunctional high-conductivity microcapsule and its application as a self-repairing additive in a silicon negative electrode.

Background technique

Lithium-ion batteries (LIBs) are widely used as reliable power sources for portable electronic devices, electric vehicles, and storage devices for renewable energy, attracting increasing research attention. Silicon (Si) has shown great potential as an anode material for LIBs due to its high specific capacity (4200mA g ^-1 , Li _4.4 Si), low discharge potential, and environmental friendliness; Facing a large volume change and low electrical conductivity, in particular, the alloying/dealloying reaction of Si with Li can cause a volume change of about 300%, thereby generating large stresses that can break Si-Si bonds and lead to failure of electrical contacts. ; Therefore, the capacity of the silicon anode decays rapidly during cycling.

In response to the above problems, many studies on advanced silicon anodes have been published, the main direction is the structural modification of silicon or silicon-carbon composites, etc.; especially Si/C composite materials, not only buffer the huge stress generated by the continuous volume expansion of internal silicon, but also Effectively enhance the conductivity of silicon; for example 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@carboncore-shell composite via in situ MOF coating for lithium ion batteries.Chem.Eng.J.2019,356,272-281."Porous Si synthesized by self-corrosion reaction, annealing and etching /C core-shell composite with a reversible capacity of 1027.8 mAg ^-1 after 500 cycles at 1Ag ^-1 ; however, in reported Si/C composites, once cracks and exfoliation occur, electron transport channels may Fracture, resulting in poor cycle stability of the silicon negative electrode, it is difficult to meet the requirements of commercial applications.

Contents of the invention

The purpose of the present invention is to provide a multi-functional high-conductivity microcapsule and a self-repairing silicon negative electrode to solve the problem that the existing silicon negative electrode generates huge stress due to volume expansion during the cycle and cracks after expansion, causing the electrode to fall off; the present invention In the invention, the multifunctional high-conductivity microcapsules are emulsified in high-viscosity polyvinyl alcohol (PVA) or alginic acid (Alg) solution, which is conducive to the stable and uniform emulsification of liquid metal, and further through phenol-urea-formaldehyde in liquid metal The in-situ polycondensation reaction on the surface of the emulsion forms a composite shell of urea-formaldehyde resin/PVA or urea-formaldehyde resin/Alg, and obtains multifunctional and highly conductive microcapsules with high sphericity and high monodispersity; further, the multifunctional and highly conductive microcapsules in the present invention are used as The self-healing additive is introduced into the silicon negative electrode to form a multifunctional high-conductivity microcapsule/silicon self-healing silicon negative electrode. The volume change that occurs during the lithium-deintercalation process of silicon particles induces the rupture of the microcapsule additive and releases a liquid with high conductivity and fluidity. Metal, along with its flow inside the pole piece, fills the cracks in the pole piece and forms a highly conductive network, and finally realizes the restoration of the conductive network and structural integrity of the pole piece; and, based on the abundant carboxyl and hydroxyl groups on the surface of the microcapsule shell The functional group endows microcapsules with better adhesion strength, increases the loading of silicon particles while reducing the amount of binder, and builds a high-energy-density silicon negative electrode.

To achieve the above object, the technical solution adopted in the present invention is:

A kind of multifunctional high conductivity microcapsule, comprises shell material and core material, and core material is coated in shell material; It is characterized in that, described microcapsule is spherical, and described shell material is urea-formaldehyde resin/polyvinyl alcohol (PVA ) composite layer or urea-formaldehyde resin/alginic acid (Alg) composite layer, the core material is one of the following low-melting liquid metals: unit liquid metal: Ga, binary liquid metal: Ga/In, Ga/Sn , Ga/Al, Ga/Zn, Ga/Ag, multiple liquid metals: Ga/In/Sn, In/Sn/Bi, Bi/Pb/Sn, Bi/Pb/Sn/Cd, Bi/Pb/Sn/Cd /In; the multifunctional highly conductive microcapsules are used in silicon negative electrodes as self-healing additives.

Further, the particle size distribution of the microcapsules is between 500nm and 50um.

Further, the thickness distribution of the shell material is between 200nm and 5um.

Further, the content of the core material is 30-85wt%.

Further, the outer surface of the microcapsules is rich in hydroxyl (-OH) and carboxyl (-COOH), so that the microcapsules are used in the silicon negative electrode and simultaneously act as a binder; the hydroxyl (-COOH) introduced on the surface of the microcapsules OH) and carboxyl (-COOH) can form strong hydrogen bonds with the silicon oxide layer on the Si surface to help buffer the huge volume change of silicon particles during cycling, and hydrogen bonds can also make silicon particles and current collectors tightly combined, The electrochemical performance stability of the battery is guaranteed.

Further, the preparation method of the multifunctional high-conductivity microcapsules comprises 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 until the solution is in a uniform state, with a stirring rate of 500 to 800 rpm;

Step B, according to EMA: urea: resorcinol: ammonium chloride mass ratio is 3:10:1:1, sequentially add urea, resorcinol, ammonium chloride to the solution obtained in step A, continue stirring until completely dissolved;

Step C, put the solution obtained in step B in a constant temperature water bath, set the temperature of the water bath to 35°C, use NaOH to adjust the pH of the solution to 3.5, add 5-28g of core material into the solution for dispersion, mechanical stirring and ultrasonic dispersion continue 50min～120min; ultrasonic power is 150W～300W, mechanical stirring rate is 1000rpm～2000rpm;

Step D. According to the mass ratio of urea: formaldehyde is 1:3, add the formaldehyde solution to the solution obtained in step C, adjust the temperature of the water bath to 60°C-80°C and continue stirring for 2h-3h, then reduce the speed to 1000rpm and continue stirring for 2.5h ~4h to obtain microcapsules;

Step E, cooling the microcapsules at room temperature to 25° C., washing them repeatedly with deionized water, then washing them with excess alcohol, and drying them after washing to obtain multifunctional high-conductivity microcapsules.

Further, in step A, the concentration of the polyvinyl alcohol solution is 2wt% to 15wt%, the concentration of the alginic acid solution is 1wt% to 4wt%, and the concentration of the alkene-methyl acrylate copolymer solution is 2wt% to 5wt%, The volume ratio of alkene-methyl acrylate copolymer solution: polyvinyl alcohol solution or alginic acid solution is 1: (3-5).

Further, based on the above-mentioned multifunctional high-conductivity microcapsules, the present invention also provides a self-healing silicon negative electrode, including:

60wt% ~ 95wt% silicon particles,

2wt%～20wt% conductive agent,

3wt%～20wt% binder,

And 5wt%-40wt% self-healing additive relative to silicon mass.

Based on the above-mentioned technical scheme, the beneficial effects of the present invention are:

The invention provides a multifunctional high-conductivity microcapsule, which uses an in-situ polymerization method to prepare a urea-formaldehyde resin layer (shell material) on the surface of a liquid metal (core material) to form a multifunctional high-conductivity microcapsule, wherein the liquid metal is wrapped in the shell material The dispersion is uniform in the middle and can avoid oxidation, which ensures the fluidity and high conductivity of the liquid metal; further, the multi-functional high-conductivity microcapsules are added to the silicon negative electrode as a self-repair additive to form a multi-functional high-conductivity microcapsule/silicon self-repair Negative electrode, during the electrode cycle, the huge stress generated by the volume expansion of silicon particles can induce the rupture of microcapsules, thereby releasing liquid metal with high conductivity and fluidity. Liquid metal can be used as a buffer for the volume charge of silicon particles, It can also spontaneously fill the cracks in the pole piece and form a highly conductive network, and finally realize the self-repair of the pole piece conductive network and structural integrity. Furthermore, the surface of the multifunctional high-conductivity microcapsules in the present invention is rich in hydroxyl (-OH) and carboxyl (-COOH), so that the microcapsules can be used in the silicon negative electrode and also play the role of a binder.

In addition, the preparation process of the multifunctional high-conductivity microcapsules of the present invention is simple. By emulsifying in high-viscosity polyvinyl alcohol (PVA) or alginic acid (Alg) solution, an emulsification system with a density close to that of liquid metal is constructed, which is beneficial to The liquid metal is stable and uniformly emulsified, and further forms a urea-formaldehyde resin/PVA or urea-formaldehyde resin/Alg composite shell through the in-situ polycondensation reaction of phenol-urea-formaldehyde on the surface of the liquid metal emulsion to obtain a high sphericity and high monodispersity. Functional highly conductive microcapsules.

In summary, the present invention provides a multifunctional high-conductivity microcapsule as a self-healing additive added to the silicon negative electrode, which can effectively solve the problems caused by the huge stress caused by the volume expansion of the existing silicon negative electrode during the cycle and the cracks after expansion. The problem of electrode falling off, and significantly improve the performance of the negative electrode.

Description of drawings

Fig. 1 is the SEM image of the multi-functional high-conductivity microcapsule prepared by the embodiment of the present invention.

Fig. 2 is a constant current charge-discharge cycle curve (2.1Ag ^-1 ) of the multi-functional high-conductivity microcapsule/silicon self-healing negative electrode prepared in the embodiment of the present invention.

Fig. 3 is the rate cycle curve of the multi-functional high-conductivity microcapsule/silicon self-healing negative electrode prepared in the embodiment of the present invention.

Figure 4 is a comparison of the SEM images of the multi-functional high-conductivity microcapsule/silicon self-healing negative electrode and the Pure Si silicon negative electrode before and after the charge-discharge cycle prepared by the embodiment of the present invention; where (a) is before the charge-discharge cycle The morphology SEM image of Pure Si silicon negative electrode, (b) is the morphology SEM image of Pure Si silicon negative electrode after charge-discharge cycle, (c) is the morphology of multifunctional high-conductivity microcapsule/silicon self-healing negative electrode before charge-discharge cycle SEM image, (d) is the SEM image of the multifunctional high-conductivity microcapsule/silicon self-healing anode after charge-discharge cycles.

Detailed ways

In order to make the purpose, technical solutions and beneficial effects of the present invention more clear, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments.

Example 1

The present embodiment provides a multifunctional high-conductivity microcapsule used as a self-healing additive in a silicon negative electrode, a corresponding multifunctional high-conductivity microcapsule/silicon self-healing negative electrode (GaInSn-MS/Si), and a further assembled CR2032 type Lithium-ion half-battery; the content of multifunctional and highly conductive microcapsules in the self-repairing negative electrode is 20wt% relative to the mass of Si. This embodiment is based on the self-healing, high conductivity, and liquid conformal characteristics of the ternary liquid metal Ga _68.5 In _21.5 Sn ₁₀ (abbreviated as GaInSn), and uses in-situ synthesis of urea-formaldehyde resin/polyvinyl alcohol shell to wrap the liquid metal In the multi-functional high-conductivity microcapsules, and by adding multi-functional high-conductivity microcapsules to the silicon negative electrode, the liquid conformality of GaInSn is used to buffer the expansion stress in the negative electrode and relieve the cracking and falling off of the silicon negative electrode; when the multi-functional high-conductivity microcapsules When the capsule is broken by the expansion stress of the silicon negative electrode, GaInSn penetrates into the damaged silicon negative electrode, and diffuses during the charge-discharge cycle, filling pores such as microcracks and cracks, and realizing the self-repair of the conductive network of the silicon negative electrode; at the same time, due to the multifunctional The surface of the highly conductive microcapsules is rich in hydroxyl (-OH) and carboxyl (-COOH), so that the microcapsules can be used in the silicon negative electrode and also act as a binder. The preparation process of the multifunctional high-conductivity microcapsules in this embodiment is simple. By emulsifying in a high-viscosity polyvinyl alcohol (PVA) solution, an emulsification system with a density similar to that of liquid metal is constructed, which is conducive to stable and uniform emulsification of liquid metal. And further, the urea-formaldehyde resin/PVA composite shell is formed through the in-situ polycondensation reaction of phenol-urea-formaldehyde on the surface of the liquid metal emulsion, and multifunctional and high-conductivity microcapsules with high sphericity and high monodispersity are obtained.

Further, in this embodiment, the multifunctional high-conductivity microcapsules, the multifunctional high-conductivity microcapsules/silicon self-repairing negative electrode and the CR2032 lithium-ion half-battery were prepared by the following steps:

Step 1. In-situ synthetic urea-formaldehyde resin/polyvinyl alcohol shell is used to wrap GaInSn to form multifunctional high-conductivity microcapsules; specifically:

Step 1-1. Add 5ml of EMA solution (2.5wt%) and 20mL of PVA solution (5wt%) into a 100mL beaker, and mechanically stir until the solution is in a uniform state. The specific stirring time is 5min, and the stirring rate is set to 500rpm;

Step 1-2, add 0.503g urea, 0.05g resorcinol, and 0.065g ammonium chloride into the solution obtained in step 1-1 and continue stirring until completely dissolved, the specific stirring time is 10min;

Step 1-3, put the beaker into a constant temperature water bath, set the water bath temperature to 35°C, use NaOH (10wt%) to adjust the pH of the solution to 3.5, put the ultrasonic probe into the solution without contacting the beaker wall, set the ultrasonic power to 250W, adjust the mechanical stirring rate to 1600rpm, slowly add 28g GaInSn (core material) into the solution for dispersion, mechanical stirring and ultrasonic dispersion continue for 50min;

Step 1-4. After the core material is dispersed, add 1.456g of formaldehyde solution to the solution obtained in Step 1-3, adjust the temperature of the water bath to 60°C and continue stirring for 2h, then reduce the stirring speed to 1000rpm and continue stirring for 2.5h until the reaction is completed , to obtain urea-formaldehyde resin/polyvinyl alcohol shell liquid metal microcapsules;

Steps 1-5. After the reaction is over, cool the reaction product at room temperature to 25°C, wash it repeatedly with deionized water for 6 times, then wash the obtained microcapsules with excess alcohol, and dry them after washing to obtain a multifunctional high-conductivity Microcapsules;

Step 2, using the multifunctional and highly conductive microcapsules obtained in step 1 as an additive to make the negative electrode of the battery; specifically:

Step 2-1, adding nano-silica powder, binder, and conductive agent in batches according to the mass ratio of 7:2:1 for continuous 3h ball milling, so that the slurry is fully mixed to obtain the original conductive slurry; Among them, the binder includes: polystyrene butadiene copolymer and carboxymethyl cellulose, and the conductive agent is conductive carbon;

Step 2-2, adding multifunctional high conductive microcapsules to the original conductive paste, the content of multifunctional high conductive microcapsules is 20wt% of the silicon mass; in order to maintain the integrity of the liquid metal microcapsules, magnetic stirring is used after adding the microcapsules Stir the above slurry, the specific stirring time is 1h, and the stirring rate is 500rpm;

Step 2-3, uniformly coat the slurry obtained in step 2-2 on a flat and clean copper foil with a scraper, the wet film thickness is 250 μm, after the coating is completed, place it in a vacuum oven at 100°C for 12 hours to obtain Self-repairing silicon negative electrode, and cutting the self-repairing silicon negative electrode into a circular pole piece with a diameter of 10mm for use;

Step 3. Use the self-repairing silicon negative electrode obtained in step 2 to assemble a CR2032 lithium-ion half battery; specifically:

Use the self-healing silicon negative electrode in step 2 to complete the assembly of the CR2032 lithium-ion battery in the glove box. The electrolyte of the CR2032 lithium-ion battery is LB-011, and the separator is Celgard 2500; after the lithium battery is prepared, it is allowed to stand at room temperature for 12 hours Afterwards, subsequent electrochemical performance tests were carried out.

As shown in Fig. 2 and Fig. 3, it is the constant current charge-discharge cycle curve (2.1Ag ^-1 ) of the multi-functional high-conductivity microcapsule/silicon self-repairing negative electrode prepared by the embodiment, as can be seen from the figure, at a current density of 2.1Ag ^-1 After 100 cycles, the discharge specific capacity of the electrode in this example reaches 798.5mAhg ^-1 , and the capacity retention rate is 34.79%, which is significantly better than that of the electrode without multifunctional high-conductivity microcapsules; and the self-repairing lithium-ion battery can be seen from the rate test curve (Example) Compared with the pure silicon battery (Pure Si) of the control group, it shows better rate cycle performance.

As shown in Figure 4, it is a comparison of the morphology SEM images of the multi-functional high-conductivity microcapsule/silicon self-repairing negative electrode and the Pure Si silicon negative electrode before and after the charge-discharge cycle prepared by the embodiment. It can be found by scanning electron microscopy (SEM) :

Before cycling, the appearance of Pure Si was basically the same as that of the negative electrode of the example, and the addition of liquid metal microcapsules did not cause a major change to the surface morphology of the silicon negative electrode, as shown in (a) and (c) in Figure 4, the density of liquid metal microcapsules Much larger than the silicon negative electrode material, so the liquid metal microcapsules are mostly located at the bottom of the negative electrode material after the silicon negative electrode is formed, and the surface is not easy to observe;

After cycling, severe cracking and falling off occurred on the surface of Pure Si negative electrode, as shown in (b) in Figure 4; After the microcapsules are mixed into the silicon negative electrode material, the expansion stress generated by silicon in the charging and discharging process is effectively buffered, and the cracking and falling off of the silicon negative electrode are alleviated, which is why the battery of the example shows better electrochemical performance during the charging and discharging cycle one of the reasons.

The above is only a specific embodiment of the present invention. Any feature disclosed in this specification, unless specifically stated, can be replaced by other equivalent or alternative features with similar purposes; all the disclosed features, or All method or process steps may be combined in any way, except for mutually exclusive features and/or steps.

Claims (8)

1. a multifunctional high-conductivity microcapsule, comprises shell material and core material, and core material is coated in shell material; It is characterized in that, described microcapsule is spherical, and described shell material is urea-formaldehyde resin/polyvinyl alcohol Composite layer or urea-formaldehyde resin/alginic acid composite layer, the core material is one of the following low-melting liquid metals: unit liquid metal: Ga, binary liquid metal: Ga/In, Ga/Sn, Ga/Al , Ga/Zn, Ga/Ag, multiple liquid metals: Ga/In/Sn, In/Sn/Bi, Bi/Pb/Sn, Bi/Pb/Sn/Cd, Bi/Pb/Sn/Cd/In; The multifunctional and highly conductive microcapsules described above are used in silicon anodes as self-healing additives. 2. The multifunctional high-conductivity microcapsule according to claim 1, wherein the particle size distribution of the microcapsule is between 500nm and 50um. 3. The multifunctional high-conductivity microcapsule according to claim 1, wherein the thickness of the shell material is distributed between 200nm and 5um. 4. The multifunctional high-conductivity microcapsule according to claim 1, wherein the content of the core material is 30-85 wt%. 5. by the described multifunctional high-conductivity microcapsule of claim 1, it is characterized in that, the outer surface of described microcapsule is rich in hydroxyl (-OH), carboxyl (-COOH), makes microcapsule be used in silicon negative electrode simultaneously Act as a binder. 6. by the preparation method of the described multifunctional high-conductivity microcapsule of claim 1, it is characterized in that, comprises the following steps: Step A, adding ethylene-methyl acrylate copolymer (EMA) solution into polyvinyl alcohol (PVA) solution or alginic acid (Alg) solution, and mechanically stirring until the solution is in a uniform state, the stirring rate is 500-800rpm; Step B, according to EMA: urea: resorcinol: ammonium chloride mass ratio is 3:10:1:1, sequentially add urea, resorcinol, ammonium chloride to the solution obtained in step A, continue stirring until completely dissolved; Step C, put the solution obtained in step B in a constant temperature water bath, set the temperature of the water bath to 35°C, use NaOH to adjust the pH of the solution to 3.5, add 5-28g of core material into the solution for dispersion, mechanical stirring and ultrasonic dispersion continue 50min～120min; ultrasonic power is 150W～300W, mechanical stirring rate is 1000rpm～2000rpm; Step D. According to the mass ratio of urea: formaldehyde is 1:3, add the formaldehyde solution to the solution obtained in step C, adjust the temperature of the water bath to 60°C-80°C and continue stirring for 2h-3h, then reduce the speed to 1000rpm and continue stirring for 2.5h ~4h to obtain microcapsules; Step E, cooling the microcapsules at room temperature to 25° C., washing them repeatedly with deionized water, then washing them with excess alcohol, and drying them after washing to obtain multifunctional high-conductivity microcapsules. 7. by the preparation method of the described multifunctional high-conductivity microcapsule of claim 6, it is characterized in that, in step A, the concentration of polyvinyl alcohol solution is 2wt%～15wt%, the concentration of alginic acid solution is 1wt%～4wt% , the concentration of ene-methyl acrylate copolymer solution is 2wt%-5wt%, and the volume ratio of ene-methyl acrylate copolymer solution: polyvinyl alcohol solution or alginic acid solution is 1:(3-5). 8. A self-repairing silicon negative electrode, comprising: 60wt% ~ 95wt% silicon particles, 2wt%～20wt% conductive agent, 3wt%～20wt% binder, And 5wt%-40wt% self-healing additive relative to silicon mass.

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