阅读说明：本技术 一种基于芳香族二硫键的聚硅氧烷及其应用 (Polysiloxane based on aromatic disulfide bond and application thereof ) 是由 李承辉 段磊 左景林 于 2020-03-20 设计创作，主要内容包括：本发明公开了一种基于芳香族二硫键的聚硅氧烷,由氨基端封的聚硅氧烷和取代或非取代的4,4’-二氨基二苯二硫醚与交联剂反应形成酰胺键,缩聚而成。本发明所述的聚硅氧烷不仅具有良好的柔性,并且存在大量可逆的动态键,丰富的氢键和二硫键,在室温或者加热条件下能自发修复损伤,更能够相较于其他自修复材料适应锂电池正极材料的物理环境,具有良好的粘结性能和稳定性,能缓解电池在充放电过程膨胀引起比电容衰减,从而可以修复电池微裂纹、提高电池的循环使用次数,延长了电池使用寿命,可以作为自修复粘结剂用于制备锂电池中正极材料。(The invention discloses polysiloxane based on aromatic disulfide bond, which is prepared by the reaction of amino-end-blocked polysiloxane, substituted or unsubstituted 4,4' -diaminodiphenyl disulfide and a crosslinking agent to form amido bond and condensation polymerization. The polysiloxane provided by the invention has good flexibility, has a large number of reversible dynamic bonds and abundant hydrogen bonds and disulfide bonds, can repair damage spontaneously at room temperature or under a heating condition, can adapt to the physical environment of a lithium battery anode material compared with other self-repairing materials, has good bonding performance and stability, can relieve specific capacitance attenuation caused by expansion of a battery in a charging and discharging process, can repair microcracks of the battery, improves the recycling frequency of the battery, prolongs the service life of the battery, and can be used as a self-repairing binder for preparing the anode material in the lithium battery.)

1. The polysiloxane based on aromatic disulfide bond is characterized in that amino-terminated polysiloxane and substituted or unsubstituted 4,4' -diaminodiphenyl disulfide react with a cross-linking agent to form amido bond, and the polysiloxane is obtained by polycondensation.

2. The aromatic disulfide bond-based polysiloxane according to claim 1, wherein said crosslinking agent is selected from the group consisting of at least twoOne or more of pyridine, benzene or C1-C6 alkyl substituted by the group shown in the specification, wherein a is 0-6, and R is₀Represents halogen, hydroxy orb＝0～6。

3. The aromatic disulfide bond based polysiloxane of claim 2, wherein said pyridine or benzene is further substituted with one or more of H, C1-C8 alkyl, C1-C8 alkoxy, hydroxy, amino, nitro, halogen.

4. The aromatic disulfide bond-based polysiloxane according to claim 2, wherein said crosslinking agent is selected from one or more of 2, 3 pyridine dicarboxylic acid dichloride, 2, 4 pyridine dicarboxylic acid dichloride, 2, 5 pyridine dicarboxylic acid dichloride, 2,6 pyridine dicarboxylic acid dichloride or o-, m-, p-phthaloyl chloride substituted with one or more of H, C1-C8 alkyl, C1-C8 alkoxy, hydroxyl, amino, nitro, halogen.

5. The aromatic disulfide bond based polysiloxane according to any one of claims 1 to 4, wherein said amino-terminated polysiloxane has the following structure:wherein R is₁～R₆Independently selected from H, C1-C8 alkyl or phenyl group, and n is 1-2000.

6. The aromatic disulfide bond-based polysiloxane according to claim 5, characterized by having the following structure:

R₇represents one or more substituents at any position on the pyridine ring, R₈And R₉Represents one or more substituents at any position of the phenyl ring, R₇～R₉Independently selected from H, C1-C8 alkyl, C1-C8 alkoxy, hydroxy, amino, nitro or halogen, and when R is₇～R₉When a plurality of substituents on the ring are independently represented, these substituents may be the same or different.

7. The aromatic disulfide bond-based polysiloxane according to claim 6, wherein p is 1 to 2000; q is 1 to 500.

8. The aromatic disulfide bond-based polysiloxane according to claim 7, characterized in that the p/q value is 1 to 15.

9. Use of the aromatic disulfide bond-based polysiloxane as claimed in any one of claims 1 to 8 as a self-healing binder in the preparation of a lithium battery positive electrode material.

10. A positive electrode material for a lithium battery, characterized by comprising a binder, a positive electrode active material and a conductive material, wherein the binder is the aromatic disulfide bond-based polysiloxane according to any one of claims 1 to 8.

Technical Field

The invention relates to the technical field of organic silicon and the field of lithium batteries, in particular to polysiloxane based on aromatic disulfide bonds and application of the polysiloxane as a self-repairing binder in preparation of a lithium battery cathode material.

Background

With the rapid development of social economy, the traditional fossil energy is gradually exhausted, and the development of renewable energy has become a hot spot of human research. Lithium ion batteries are the energy storage materials which are developed more mature at present. The novel solar cell module has the advantages of being environment-friendly, high in capacity density, good in cycle stability and the like, and is widely applied to numerous fields such as wearable equipment, smart phones and new energy automobiles, and is closely related to daily life. As an efficient and convenient energy storage technology, the lithium battery not only meets the requirements of consumer electronics products, but also has more important cycle life and safety when being used as a power battery. The binder plays an important role as a component of the battery, although the proportion of the binder is relatively small. Good adhesion greatly improves the cycle stability and safety of the battery.

The electrode of the lithium battery is prepared by uniformly stirring an active substance, a conductive agent and a binder in a solvent, coating the mixture on a current collector and drying the mixture. The binder well adheres the active substance and the conductive agent together, ensures that the battery has good conductivity in the charging and discharging process, and ensures that lithium ions cannot fall off from the current collector in the embedding and releasing process between the anode and the cathode. Thus, the binder plays an important role in the stability of the lithium battery.

The high molecular binder occupies a small proportion in the battery, but influences the mechanical properties of the whole electrode. The binder is required to have good binding performance so as to ensure that the active substance and the conductive agent are adhered to the current collector; the binder also needs some toughness and stretchability to cope with volume expansion caused during charge and discharge of the battery; in addition, the binder material needs to be non-reactive with the electrolyte and resistant to swelling and corrosion by the electrolyte.

The most widely used lithium battery binder at present is polyvinylidene fluoride (PVDF), and the PVDF needs an organic solvent N-methyl pyrrolidone in the use process, so that certain pollution is caused to the environment. During the use process of the lithium battery, the volume is obviously changed due to lithium intercalation/lithium deintercalation, and the PVDF binder has high tensile strength but low elongation at break, which can cause the active substance and the binder to be further crushed and shed. Finally leading to pulverization of the electrode slice, capacity reduction and shortened service life. Although a water-soluble binder such as sodium carboxymethyl cellulose is an environment-friendly material, the material is brittle and easy to separate in the using process due to a large amount of hydrogen bonds, and the stability is poor. Therefore, the development of a binder having good cycle stability and being environmentally friendly is urgently needed.

Disclosure of Invention

The invention aims to provide a novel self-repairing silicon rubber-based binder which can repair damage caused by expansion of a lithium battery, improve the flexibility of a pole piece and the cycle stability of the lithium battery, resist the corrosion of a battery electrolyte and have good corrosion resistance and stability.

The invention is realized by adopting the following technology:

the polysiloxane based on aromatic disulfide bond is prepared by the reaction of amino end-blocked polysiloxane and substituted or unsubstituted 4,4' -diaminodiphenyl disulfide with a cross-linking agent to form amido bond and condensation polymerization.

Preferably, the cross-linking agent is selected from the group consisting of at least twoOne or more of pyridine, benzene or C1-C6 alkyl substituted by the shown group, a is 0-6, R₀Represents halogen, hydroxy orb＝0～6。

Further, the pyridine or benzene can be substituted by one or more of H, C1-C8 alkyl, C1-C8 alkoxy, hydroxyl, amino, nitro and halogen.

Preferably, the cross-linking agent is selected from one or more of 2, 3 pyridine diformyl chloride, 2, 4 pyridine diformyl chloride, 2, 5 pyridine diformyl chloride, 2,6 pyridine diformyl chloride or o-, m-or p-phthaloyl chloride substituted by one or more of H, C1-C8 alkyl, C1-C8 alkoxy, hydroxyl, amino, nitro and halogen.

In a specific technical scheme of the invention, the cross-linking agent is 2,6 pyridine diformyl chloride or paraphthaloyl chloride.

The amino-terminated polysiloxane of the present invention preferably has the following structure:

wherein R is₁～R₆Independently selected from H, C1-C8 alkyl or phenyl group, n is 1-2000, preferably n is 5-300.

One specific structure of the invention is as follows:

R₇represents one or more substituents at any position on the pyridine ring, R₈And R₉Represents one or more substituents at any position of the phenyl ring, R₇～R₉Independently selected from H, C1-C8 alkyl, C1-C8 alkoxy, hydroxy, amino, nitro or halogen, and when R is₇～R₉When a plurality of substituents on the ring are independently represented, these substituents may be the same or different. p is 1-2000; q is 1 to 500. Preferably, n is 5-300; p is 5-300; q is 1 to 50.

Preferably, the p/q value is 1-15.

The polysiloxane based on the aromatic disulfide bond can be prepared by the following method:

uniformly mixing amino-terminated polysiloxane and 4,4' -diaminodiphenyl disulfide; and then adding a cross-linking agent aromatic diformyl, an acid-binding agent and a solvent, reacting, and removing the solvent to obtain the polysiloxane based on the aromatic disulfide bond with the self-repairing property.

The acid-binding agent is one or more of triethylamine, pyridine, ethylenediamine and 4-dimethylamino pyridine.

The solvent is one or more of tetrahydrofuran, acetone, toluene, ethyl acetate, petroleum ether, N-dimethylformamide, dimethyl sulfoxide and chlorine-containing solvent.

The reaction temperature is-10 to 50 ℃, and the reaction time is 1 to 48 hours.

Preferably, the weight ratio of the raw materials is as follows:

40-90 parts of amino end-sealed polysiloxane;

10-60 parts of 4,4' -diamino diphenyl disulfide;

100 parts of aromatic diformyl;

1 to 15 portions of acid-binding agent.

The invention also aims to provide application of the polysiloxane based on the aromatic disulfide bond as a self-repairing binder in preparation of a lithium battery cathode material.

The lithium battery positive electrode material comprises a binder, a positive electrode active substance and a conductive substance, wherein the binder is the polysiloxane based on the aromatic disulfide bond.

The invention also provides a method for preparing the lithium battery electrode plate by using the binder, which comprises the following steps:

dissolving the binder in a solvent, adding an active substance and a conductive substance, uniformly mixing, and performing ultrasonic dispersion to obtain the electrode slurry. Coating the slurry on a current collector and drying.

Preferably, the weight ratio of the raw materials is as follows:

5-20 parts of a binder;

70-100 parts of active substances;

5-40 parts of conductive substances.

The active substance is a positive electrode material and is respectively selected from LiFePO₄、TiO₂、LiMn₂O₄、LiCo₂O₄S, Si, Sn, graphite, FeS₂And one or more of Li plate and the like.

The conductive material is one or more of carbon nano tube or graphene, acetylene black, superconducting carbon black and the like.

The current collector is selected from one or more of copper foil, aluminum foil, carbon cloth, carbon-coated copper foil, carbon-coated aluminum carbon and the like.

The solvent is one or more of ethanol, tetrahydrofuran, acetone, toluene, N-methyl pyrrolidone and chlorine-containing solvents.

The drying temperature of the pole piece is 50-120 ℃, and the drying time is 5-48 h.

The invention has the advantages that:

(1) the invention relates to polysiloxane and 4,4' -diaminodiphenyl di-terminated by amino endThe thioether reacts with a cross-linking agent to form an amide bond, and the amide bond is condensed to form a polysiloxane compound with an aromatic disulfide bond. Because the long-chain polysiloxane has good flexibility and abundant hydrogen bonds, compared with the commercialized PVDF and sodium carboxymethyl cellulose, the aromatic disulfide-bonded polysiloxane has good stretchability and repairability. The active substance and the conductive agent are ensured to be adhered to the current collector in the using process, and the active substance and the conductive agent are prevented from cracking and falling off. The self-repairing binder contains a large number of reversible dynamic bonds, such as abundant hydrogen bonds, disulfide bonds and the like, and can spontaneously repair damage at room temperature or under a heating condition, so that the mechanical property is recovered, the service life of the battery is effectively prolonged, and the cycling stability of the battery is effectively improved. The cyclic performance of the battery at 0.5C using aromatic disulfide-bonded polysiloxane and PVDF polymer as a binder for lithium-sulfur batteries is shown in fig. 3. The initial specific capacitance of the battery prepared by the self-repairing adhesive reaches 1006.3mAh g^-1After circulating 100 circles, specific capacitance maintains 763.6mAh g^-1The capacity of the battery prepared by the PVDF binder is only 497.5mAh g^-1. FIG. 4 shows the cycling stability of the lithium-sulfur battery under 2C, even under high multiplying power, the cycling stability of the self-repairing binder is much better than that of the traditional PVDF binder, and when 400 cycles are performed, the specific capacitance of the battery prepared by the self-repairing binder reaches 545.7mAh g^-1Which is 2 times of that of the battery prepared by the traditional binder. The capacity fading of each cycle is only 0.068%, the coulombic efficiency is close to 100%, and the aromatic disulfide bond polysiloxane serving as the lithium-sulfur battery binder has good self-healing capacity and flexibility and can remarkably improve the cycle performance.

(2) The disulfide bond in the polysiloxane structure based on the aromatic disulfide bond can be reversibly broken and formed in the charge-discharge cycle process to generate short-chain organic lithium sulfide, so that the conversion of polysulfide is accelerated, and the specific capacitance of a lithium battery is effectively improved. FIG. 5a shows that for the original lithium sulfur cell positive electrode, the C-S peak binding energy corresponds to 164.2eV, and two S-S peaks corresponding to 163.5eV and 164.9eV are seen from the S2 p spectrum. In the XPS spectrum of the discharge (FIG. 5b), the final discharge product Li₂S is at 16Two peaks at 0.0eV and 160.8eV, and short-chain organic lithium sulfide (C-S-Li)⁺) There is a peak at 161.6 eV. This indicates a relatively complete conversion of sulfur to Li₂S or C-S-Li⁺. In the charged XPS spectra (FIG. 5C), peaks of S-S and C-S appear again, indicating that reversible electrochemical conversion of sulfur and short-chain organic sulfides occurs at the positive electrode. Analysis through XPS test proves that disulfide bonds in polysiloxane molecules based on aromatic disulfide bonds are reversibly broken and formed in the process of charge and discharge cycles to generate short-chain organic lithium sulfide, so that the conversion of polysulfide is accelerated.

(3) The amido bond in the polysiloxane structure based on the aromatic disulfide bond is more stable in the battery electrolyte environment. The topography of the electrode after 5 cycles at C/10 observed by a scanning electron microscope is shown in FIG. 6, and cracks and holes appear on the electrode surface of the PVDF binder (FIG. 6a), which leads to reduced conductivity and low sulfur utilization rate. In contrast, the aromatic disulfide-bonded polysiloxane binder with self-healing ability and excellent mechanical properties can be combined with the sulfur positive electrode without cracking and damage (fig. 6b), showing a uniform, flat morphology. The advantage of good circulation stability of the amido bond in the battery electrolyte is demonstrated.

Drawings

FIG. 1 is a NMR chart of aromatic disulfide bond-based polysiloxane prepared in example 1 of the present invention.

FIG. 2 is an infrared spectrum of a polysiloxane based on aromatic disulfide bonds prepared in example 1 of the present invention.

Fig. 3 is a graph of specific capacity and coulombic efficiency during cycling at 0.5C for half cells of example 1 of the invention using an aromatic disulfide based polysiloxane binder and comparative example PVDF.

Fig. 4 is a graph of specific capacity and coulombic efficiency during cycling at 2C for half cells of example 1 of the invention using the aromatic disulfide based polysiloxane binder and comparative example PVDF.

Fig. 5 is XPS graphs of a half-cell before charging and discharging (a), in a fully charged state (b), and in a fully discharged state (c) in example 1 of the present invention, which was assembled using a polysiloxane binder based on aromatic disulfide bonds.

FIG. 6 is a scanning electron micrograph of a positive electrode after 5 cycles at a rate of C/10 using comparative example PVDF (a) and an aromatic disulfide bond-based polysiloxane binder (b) in example 1 of the present invention.

Detailed Description

In order to further illustrate the present invention, the following examples are provided to describe the preparation method and application of the aromatic disulfide polysiloxane binder of the present invention in detail, but should not be construed as limiting the scope of the present invention.