A water-based covalently cross-linked binder, its preparation method and use

Abstract

The application belongs to the field of lithium ion battery materials, and provides a water-based covalent cross-linking type binder as well as a preparation method and application thereof. The specific preparation method of the water-based covalent cross-linking type binder is as follows: a monomer A containing a double bond is dissolved in deionized water, then bis[2-(methacryloyloxy)ethyl] phosphate is added as a cross-linking agent, and an initiator is added to carry out a polymerization reaction, so that the water-based covalent cross-linking type binder can be prepared. The method realizes the construction of a three-dimensional network structure in a combination of dynamic and static cross-linking, and introduces a phosphoric acid group as a component of a silicon negative electrode water-based binder, the interaction between the component and silicon is stronger, the binding capacity and mechanical properties of the material are improved, in addition, the method for in-situ preparation of an electrode sheet saves a post-processing step of the polymer, and is simple and convenient.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion battery materials, and relates to a water-based covalent cross-linking type binder as well as a preparation method and application thereof. BACKGROUND

[0002] In order to solve the problem of endurance mileage and further reduce the cost, it is imperative to develop a lithium ion battery with high energy density.

[0003] Silicon has become the preferred choice for developing high-energy-density battery anode materials at present due to its advantages of large theoretical specific capacity and abundant reserves. Silicon stores and releases lithium ions in the form of alloying with lithium ions, and its theoretical specific capacity is as high as 4200 mAh.g -1 , which is about ten times that of the current commercial graphite negative electrode (372 mAh.g -1 ). However, in the actual application process, due to the form of lithium storage of the silicon negative electrode, the silicon will inevitably expand by nearly 400% after forming an alloy with lithium. The repeated deintercalation of lithium ions from the silicon negative electrode in the charging and discharging process of the lithium ion battery causes stress changes in the electrode due to multiple volume expansion and contraction, resulting in cracking of the electrode, and then causing the electrode material to powder and fall off. This phenomenon will cause the capacity of the battery to decrease sharply, affecting the cycle performance of the battery.

[0004] In view of the above problems, considering the complexity and high cost of silicon particle modification, a new type of water-based covalent cross-linking type binder is designed and developed to alleviate the volume expansion of silicon and stabilize the electrode structure, which has become an important topic in the related field. SUMMARY

[0005] In view of the above problems, the application provides a water-based covalent cross-linking type binder as well as a preparation method and application thereof. The phosphoric acid group in the structure of the binder can form dipole-dipole and ion-dipole interactions with the hydroxyl groups on the surface of silicon, thereby improving the adhesion of the material to silicon and stabilizing the electrode structure. The high molecular internal cross-linking achieved by di[2-(methacryloyloxy)ethyl] phosphate can significantly improve the mechanical properties of the material, which is conducive to alleviating the cracking of the electrode caused by the volume expansion of the silicon negative electrode and improving the cycle performance of the battery.

[0006] The application provides a preparation method of a water-based covalent cross-linking type binder, which comprises the following steps:

[0007] A monomer A containing a double bond is dissolved in deionized water, then di[2-(methacryloyloxy)ethyl] phosphate is added as a cross-linking agent, and an initiator is added for polymerization, so that the water-based covalent cross-linking type binder can be prepared.

[0008] Further, the concentration of the monomer A aqueous solution is 0.01-0.10 g / mL, the content of di[2-(methacryloyloxy)ethyl] phosphate is 2-10 mol% of the monomer A, and the content of the initiator is 1-5% of the total mass of the monomer A and di[2-(methacryloyloxy)ethyl] phosphate.

[0009] Further, the monomer A is one of acrylic acid, acrylamide, and acrylate.

[0010] Further, the polymerization reaction is ultraviolet light-induced polymerization.

[0011] Further, the initiator used in the ultraviolet light-induced polymerization reaction is one of 754 photoinitiator, 819 photoinitiator, 1-hydroxycyclohexyl phenyl ketone, and 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone.

[0012] Further, the ultraviolet light-induced polymerization time is 5-30 min, and the temperature is 50-70℃.

[0013] The water-based grafting and cross-linking type binder prepared by the preparation method.

[0014] The water-based grafting and cross-linking type binder in the preparation of a lithium ion battery negative electrode material.

[0015] A method for preparing a lithium ion battery negative electrode material, comprising the following steps:

[0016] A certain amount of silicon powder and a conductive additive are weighed and added into the water-based grafting and cross-linking type binder aqueous solution, and then uniformly stirred and coated on a copper foil for drying to obtain a pole piece for standby use.

[0017] The particle size of the silicon powder is 60-100 nm; the conductive additive is one or more of acetylene black, ketjen black, Super P, and carbon nanotube; and the mass ratio of the silicon powder, the conductive additive, and the water-based grafting and cross-linking type binder is 50-70:30-20:20-10.

[0018] The stirring time is 6-12 h, the drying temperature is 60-120℃, and the drying time is 10-15 h.

[0019] The lithium ion battery silicon negative electrode material prepared by the method for preparing a lithium ion battery negative electrode material.

[0020] The technical solution provided by the application has the following beneficial effects:

[0021] 1. This invention uses di[2-(methacryloyloxy)ethyl]phosphate as a crosslinking agent and achieves polymer internal crosslinking through a combination of dynamic and static crosslinking, thereby constructing a covalent crosslinking network for the binder. This significantly improves the mechanical properties of the material, helps alleviate electrode cracking caused by the volume expansion of the silicon anode, and enhances the cycle performance of the battery. The phosphate groups in its structure can form dipole-dipole and ion-dipole interactions with the hydroxyl groups on the silicon surface, thereby enhancing the adhesion of the aqueous covalent crosslinking binder to silicon, stabilizing the electrode structure, and improving cycle performance.

[0022] 2. The synthesis conditions of the aqueous covalent crosslinking adhesive preparation method provided by the present invention are simple, and the reaction solvent is environmentally friendly and non-toxic.

[0023] 3. The UV-initiated polymerization method used in the preparation method of the aqueous covalent crosslinked adhesive provided by the present invention has the advantages of being simple and efficient.

[0024] 4. The present invention uses an in-situ preparation method for electrode sheets, which eliminates the post-processing steps of polymers, making it simple and convenient. Attached Figure Description

[0025] Figure 1 This is a comparison of the peeling properties of the aqueous covalent crosslinked adhesives obtained in Examples 1 and 2 and Comparative Example 1;

[0026] Figure 2 The cyclic voltammetry curve of the secondary lithium battery prepared using the aqueous covalent crosslinking binder obtained in Example 1 at a scan rate of 0.05 mV is shown.

[0027] Figure 3 The AC impedance spectra of the corresponding secondary lithium batteries prepared by the aqueous covalent crosslinking binders obtained in Example 1 and Comparative Example 1 after cycling are shown.

[0028] Figure 4 The battery cycle performance of lithium batteries prepared with aqueous covalent crosslinked binders obtained in Example 1 and Comparative Examples 1 and 2 at a current density of 0.5C is shown in the figure. Detailed Implementation

[0029] The present invention will be further described in detail below with reference to embodiments, so that those skilled in the art can implement it based on the description.

[0030] It should be noted that, unless otherwise specified, the experimental methods described in the following implementation plan are all conventional methods, and the reagents and materials described are all commercially available unless otherwise specified.

[0031] This invention provides a method for preparing an aqueous covalently crosslinked polymeric adhesive containing phosphonic acid groups, comprising the following steps:

[0032] Monomer A containing double bonds is dissolved in deionized water, then di[2-(methacryloyloxy)ethyl]phosphate is added as a crosslinking agent, and an initiator is added to carry out a polymerization reaction to obtain an aqueous covalent crosslinked adhesive.

[0033] In this invention, the initiator used in the ultraviolet light polymerization reaction is one of 754 photoinitiator, 819 photoinitiator, 1-hydroxycyclohexylphenyl ketone and 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylpropanone, preferably 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylpropanone.

[0034] In this invention, monomer A includes one of acrylic acid, acrylamide, and acrylates, preferably any one of acrylic acid and acrylamide; the concentration of monomer A is 0.01 to 0.10 g / mL, preferably 0.01 to 0.05 g / mL, and more preferably 0.02 g / mL.

[0035] In this invention, di[2-(methacryloyloxy)ethyl]phosphate accounts for 1 to 10 mol% of monomer A, preferably 1 to 5 mol%, more preferably 3 mol%; the initiator accounts for 1 to 5% of the total mass of monomer A and di[2-(methacryloyloxy)ethyl]phosphate, preferably 2 to 4%, more preferably 2%.

[0036] In this invention, the ultraviolet light-initiated polymerization time is 5 to 30 minutes, preferably 10 to 20 minutes, and more preferably 15 minutes; the polymerization temperature is 50 to 70°C, preferably 60°C.

[0037] This invention provides a method for preparing a silicon anode corresponding to the above-mentioned aqueous grafted crosslinking binder, comprising the following steps:

[0038] A certain amount of silicon powder and conductive additives are weighed into an aqueous solution of a water-based grafted crosslinking binder, stirred evenly, coated onto copper foil, and dried to obtain an electrode sheet for later use.

[0039] In this invention, the silicon powder has a particle size of 60-100 nm, more preferably 80 nm; the mass ratio of silicon powder, conductive additive and water-based grafted crosslinking binder is 50-70:30-20:20-10, preferably 60-70:20:20-10, more preferably 60:20:20.

[0040] In this invention, the stirring time is 6-12 hours, preferably 7-10 hours, and more preferably 8-9 hours; the drying temperature is 60-120°C, preferably 70-110°C, and more preferably 80-100°C; and the drying time is 10-15 hours, preferably 12 hours.

[0041] Example 1

[0042] Dissolve 0.1600 g of acrylic acid in 8 mL of deionized water. After complete dissolution, add 0.0215 g of di[2-(methacryloyloxy)ethyl]phosphate, where the molar ratio of acrylic acid monomer to di[2-(methacryloyloxy)ethyl]phosphate is 100:3. Then add 2% (by mass) of 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone, which is the total mass of acrylic acid monomer and di[2-(methacryloyloxy)ethyl]phosphate. Next, place the reaction system under a UV lamp to initiate polymerization for 15 min at a polymerization temperature of 60 °C. Finally, obtain an aqueous covalent crosslinked adhesive solution for later use.

[0043] The lithium-ion battery manufacturing method corresponding to this case is as follows:

[0044] Take 0.1200g of silicon powder and 0.0400g of Super P in an aqueous solution containing 0.0400g of aqueous covalent crosslinking binder, stir thoroughly for 8 hours to obtain a uniformly dispersed slurry, then coat the slurry uniformly onto the surface of a 9μm copper foil using a coating machine, dry at 100℃ for 12 hours, and finally cut into circular electrode sheets with a radius of 7.5mm for later use.

[0045] Example 2

[0046] Dissolve 0.1600 g of acrylamide in 8 mL of deionized water. After complete dissolution, add 0.0219 g of di[2-(methacryloyloxy)ethyl]phosphate, where the molar ratio of acrylamide monomer to di[2-(methacryloyloxy)ethyl]phosphate is 100:3. Then add 2% (by mass) of 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone, which is the total mass of acrylamide monomer and di[2-(methacryloyloxy)ethyl]phosphate. Next, place the reaction system under a UV lamp to initiate polymerization for 15 min at a polymerization temperature of 60 °C. Finally, obtain an aqueous covalent crosslinking adhesive solution for later use.

[0047] The lithium-ion battery manufacturing method corresponding to this case is as follows:

[0048] Take 0.1200g of silicon powder and 0.0400g of Super P in an aqueous solution containing 0.0400g of the above-mentioned aqueous covalent crosslinking binder, stir thoroughly for 8 hours to obtain a uniformly dispersed slurry, then coat the slurry uniformly onto the surface of a 9μm copper foil using a coating machine, dry at 100℃ for 12 hours, and finally cut into circular electrode sheets with a radius of 7.5mm for later use.

[0049] Example 3

[0050] Dissolve 0.1600 g of acrylic acid in 8 mL of deionized water. After complete dissolution, add 0.0215 g of di[2-(methacryloyloxy)ethyl]phosphate, where the molar ratio of acrylic acid monomer to di[2-(methacryloyloxy)ethyl]phosphate is 100:3. Then add 3% (by mass) of 1-hydroxycyclohexylphenyl ketone (based on the total mass of acrylic acid monomer and di[2-(methacryloyloxy)ethyl]phosphate). Next, place the reaction system under a UV lamp to initiate polymerization for 15 min at a polymerization temperature of 60 °C. Finally, obtain an aqueous covalent crosslinking adhesive solution for later use.

[0051] The lithium-ion battery manufacturing method corresponding to this case is as follows:

[0052] Take 0.1200g of silicon powder and 0.0400g of Super P in an aqueous solution containing 0.0400g of the above-mentioned water-based grafted crosslinking binder, stir thoroughly for 8 hours to obtain a uniformly dispersed slurry, then coat the slurry uniformly onto the surface of a 9μm copper foil using a coating machine, dry at 100℃ for 12 hours, and finally cut into circular electrode sheets with a radius of 7.5mm for later use.

[0053] Compare with Example 1

[0054] Dissolve 0.4000g of acrylic acid in 20mL of deionized water. After thorough mixing, add 2% (by weight of total acrylic acid) of 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone initiator and stir to dissolve. Then, place the reaction system under a UV lamp for initiation polymerization for 15 minutes at a polymerization temperature of 60℃ to obtain an aqueous solution of polyacrylic acid binder for later use.

[0055] The lithium-ion battery manufacturing method corresponding to this case is as follows:

[0056] Take 0.1200g of silicon powder and 0.0400g of Super P in an aqueous solution containing 0.0400g of the above polymer, stir thoroughly for 8 hours to obtain a uniformly dispersed slurry, then coat the slurry uniformly onto the surface of a 9μm copper foil using a coating machine, dry at 100℃ for 12 hours, and finally cut into circular electrode sheets with a radius of 7.5mm for later use.

[0057] Compare with Example 2

[0058] Dissolve 0.4000g of sodium carboxymethyl cellulose in 20mL of deionized water for later use.

[0059] The lithium-ion battery manufacturing method corresponding to this case is as follows:

[0060] Take 0.1200g of silicon powder and 0.0400g of Super P in an aqueous solution containing 0.0400g of the above polymer, stir thoroughly for 8 hours to obtain a uniformly dispersed slurry, then coat the slurry uniformly onto the surface of a 9μm copper foil using a coating machine, dry at 100℃ for 12 hours, and finally cut into circular electrode sheets with a radius of 7.5mm for later use.

[0061] Compare with Example 3

[0062] Dissolve 0.1600 g of acrylic acid in 8 mL of deionized water. After complete dissolution, add 0.0072 g of di[2-(methacryloyloxy)ethyl]phosphate, where the molar ratio of acrylic acid monomer to di[2-(methacryloyloxy)ethyl]phosphate is 100:1. Then add 2% (by mass) of 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone, which is the total mass of acrylic acid monomer and di[2-(methacryloyloxy)ethyl]phosphate. Next, place the reaction system under a UV lamp to initiate polymerization for 15 min at a polymerization temperature of 60 °C. Finally, obtain an aqueous covalent crosslinked adhesive solution for later use.

[0063] The lithium-ion battery manufacturing method corresponding to this case is as follows:

[0064] Take 0.1200g of silicon powder and 0.0400g of Super P in an aqueous solution containing 0.0400g of the above-mentioned aqueous covalent crosslinking binder, stir thoroughly for 8 hours to obtain a uniformly dispersed slurry, then coat the slurry uniformly onto the surface of a 9μm copper foil using a coating machine, dry at 100℃ for 12 hours, and finally cut into circular electrode sheets with a radius of 7.5mm for later use.

[0065] Figure 1 This is a comparison of the peeling properties of the water-based grafted crosslinking adhesives used in Example 1 and Comparative Examples 1 and 3. Figure 1 It can be seen that, compared with Comparative Example 3 and Comparative Example 1, the peel strength of Example 1 is significantly improved. This is due to the introduction of an appropriate amount of crosslinking agent, which promotes the interaction between adhesive chain segments. The network structure constructed by the combination of dynamic and static crosslinking enhances the bonding ability of the aqueous covalent crosslinking adhesive.

[0066] Figure 2 The image shows the cyclic voltammogram of the secondary lithium battery prepared in Example 1 at a scan rate of 0.05 mV. Figure 2 It can be seen that during multiple scans, lithium ion insertion / extraction peaks in silicon material appeared at 0.01V, 0.19V and 0.37V, 0.53V respectively, indicating that the aqueous covalent crosslinked binder material of Example 1 did not affect the lithium ion insertion / extraction process in the battery and could exist stably in the electrochemical window of 0.01-1.5V.

[0067] Figure 3 The images show the AC impedance spectra of the secondary lithium batteries after cycling for Example 1 and Comparative Example 1. Figure 3 It can be seen that the battery corresponding to Example 1 has a smaller SEI impedance value after cycling, indicating that a thin and stable solid electrolyte layer is formed inside the battery, which helps to improve the lithium-ion transport capability. The corresponding aqueous covalent crosslinking binder helps to maintain the stability of the battery's internal structure.

[0068] Figure 4 This is a comparison graph showing the cycling results of the lithium batteries prepared in Example 1 and Comparative Examples 1 and 2 at a current density of 2.1 A / g. Figure 4 It can be seen that the battery corresponding to Example 1 still has a discharge specific capacity of 1909 mAh / g after 100 cycles, which shows excellent cycle performance compared with the two control examples.

[0069] Where there is no conflict, the above embodiments and features described herein can be combined with each other.

[0070] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing an aqueous covalently crosslinked adhesive, characterized in that, Includes the following steps: Monomer A containing double bonds is dissolved in deionized water, then di[2-(methacryloyloxy)ethyl] phosphate is added as a crosslinking agent, and an initiator is added to carry out a polymerization reaction to obtain an aqueous covalent crosslinked adhesive. The concentration of the aqueous solution of monomer A is 0.01~0.10 g / mL, and the di[2-(methacryloyloxy)ethyl]phosphate accounts for 2~10 mol% of monomer A, while the initiator accounts for 1~5% of the total mass of monomer A and di[2-(methacryloyloxy)ethyl]phosphate. The monomer A is one of acrylic acid and acrylamide; The polymerization reaction is a UV-initiated polymerization reaction; The initiator used in the ultraviolet light-initiated polymerization reaction is one of 754 photoinitiator, 819 photoinitiator, 1-hydroxycyclohexylphenyl ketone and 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone; The time for UV-initiated polymerization is 5-30 min, and the temperature is 50-70℃.

2. An aqueous covalently crosslinked adhesive prepared by the preparation method as described in claim 1.

3. The application of the aqueous covalent crosslinking binder as described in claim 2 in the preparation of lithium-ion battery anode materials.

4. A method for preparing a negative electrode material for lithium-ion batteries, characterized in that, Includes the following steps: Weigh a certain amount of silicon powder and conductive additives and add them to the aqueous covalent crosslinking binder aqueous solution as described in claim 2. After stirring evenly, coat the mixture onto copper foil and dry it to obtain an electrode sheet for later use. The silicon powder has a particle size of 60-100 nm; the conductive additive is one or more of acetylene black, Ketjen black, Super P, and carbon nanotubes; the mass ratio of silicon powder, conductive additive and aqueous covalent crosslinking binder is 50-70:30-20:20-10. The stirring time is 6~12 h, the drying temperature is 60~120℃, and the drying time is 10~15 h.

5. A silicon anode material for lithium-ion batteries prepared by the method for preparing lithium-ion battery anode materials according to claim 4.

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