Self-repairing waterborne polyurethane / acrylate emulsion as well as preparation method and application thereof

Abstract

The invention discloses a self-repairing waterborne polyurethane / acrylate emulsion as well as a preparation method and application thereof, and the method comprises the following steps: 1, mixing polyol and a hydrophilic chain extender, and stirring at 40-70 DEG C to obtain a polyol solution; 2, in a nitrogen atmosphere, adding a catalyst into the polyol solution, then adding polyisocyanate, and reacting at 74-80 DEG C to obtain a polyurethane prepolymer; 3, taking 5-(2-ethoxyl)-6-methyl-2-aminouracil, adding the 5-(2-ethoxyl)-6-methyl-2-aminouracil into the polyurethane prepolymer, and reacting at the temperature of 50-70 DEG C to obtain an intermediate product A; 4, adding hydroxyethyl acrylate into the intermediate product A, and reacting at 30-50 DEG C to obtain an intermediate product B; and 5, adding triethylamine into the intermediate product B, and reacting at 30-50 DEG C while dropwise adding deionized water and stirring at a high speed to obtain the white self-repairing waterborne polyurethane / acrylate emulsion which has relatively high toughness and rapid self-repairing performance, and improves the rate capability and cycle performance of the lithium ion battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium battery polymer materials, and relates to a self-healing waterborne polyurethane / acrylic ester emulsion, a preparation method thereof, and an application thereof. Background Art

[0002] As a promising energy storage device, lithium-ion batteries have received extensive attention due to their high energy density and have been widely used in portable electronic devices, automobiles, etc. However, developing a new generation of lithium-ion batteries with high energy density and long cycle life still poses great challenges.

[0003] Silicon-based anode materials can endow lithium batteries with high theoretical specific capacity (4200 mAh·g -1 ), low discharge voltage and safety, making them one of the most promising anode materials. However, during the repeated lithiation / delithiation process of silicon-based anodes, extreme volume expansion and contraction occur, with a maximum volume change rate of up to 300%, which easily causes large-area fragmentation and deteriorates the electrical contact with the current collector, resulting in a rapid decline in the capacity of lithium batteries and poor cycle stability. Currently, various natural rubbers, elastic polymers, and conductive polymers have been used as anode binders for lithium batteries to inhibit the volume change of silicon-based anodes. However, in most cases, due to the lack of an effective repair effect of existing binders on the electrode damage caused by the volume change of silicon-based anodes, the improvement of the electrochemical performance of lithium batteries is limited.

[0004] Therefore, developing a binder that can repair the damage of silicon-based anodes is of great significance for the application of silicon-based anode materials in lithium batteries. Summary of the Invention

[0005] The purpose of the present invention is to provide a self-healing waterborne polyurethane / acrylic ester emulsion, a preparation method thereof, and an application thereof. The prepared self-healing waterborne polyurethane / acrylic ester emulsion has high toughness and rapid self-healing performance, can withstand the volume change of silicon-based anode materials during lithiation / extraction, and improves the initial efficiency, rate performance, and cycle performance of lithium-ion batteries.

[0006] The present invention is achieved through the following technical solutions:

[0007] A preparation method of a self-healing waterborne polyurethane / acrylic ester emulsion includes the following steps:

[0008] Step 1: Mix 10 - 30 g of polyol and 0.7 - 3.1 g of hydrophilic chain extender, and stir at 40 - 70 °C for 20 - 40 min to obtain a polyol solution;

[0009] Step 2: Under a nitrogen atmosphere, first add a catalyst to the polyol solution, and then dropwise add 11.14 - 31.11 g of polyisocyanate. React at 74 - 80 °C for 2.5 - 3.5 h to obtain a polyurethane prepolymer, where: the catalyst accounts for 0.1% - 1% of the mass of the polyisocyanate;

[0010] Step 3: Take 0.22 - 3.21 g of 5-(2-hydroxyethyl)-6-methyl-2-aminouracil and add it to the polyurethane prepolymer. React at 50 - 70 °C for 2 - 4 h to obtain intermediate product A;

[0011] Step 4: Add 3.14 - 7.90 g of hydroxyethyl acrylate to intermediate product A. React at 30 - 50 °C for 2 - 4 h to obtain intermediate product B;

[0012] Step 5: First, take 59.92 - 180.69 g of deionized water for standby. Then, add 0.40 - 2.12 g of triethylamine to intermediate product B. React at 30 - 50 °C for 20 - 40 min. Then, while dropwise adding deionized water, stir at a high speed until a white milky liquid is formed to obtain a white self-healing waterborne polyurethane / acrylic ester emulsion.

[0013] Further, the polyol in Step 1 is polycaprolactone diol, polytetrahydrofuran ether diol, polypropylene glycol, polyethylene glycol, polyoxypropylene glycol, polyhexanediol neopentyl glycol ester, or poly(1,4-butylene adipate);

[0014] The molecular weight of the polyol is 1000 - 2000.

[0015] Further, the hydrophilic chain extender in Step 1 is 2,2-dimethylolbutyric acid, 2,2-dimethylolpropionic acid, or sodium 2-(2-aminoethylamino)ethanesulfonate.

[0016] Further, the polyisocyanate in Step 2 is isophorone diisocyanate, 2,4-toluene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, or 4,4′-dicyclohexylmethane diisocyanate.

[0017] Further, the catalyst in Step 2 is dibutyltin dilaurate or stannous octoate.

[0018] Further, the stirring in Step 5 is carried out at a speed of 800 - 1000 rpm for 20 - 60 min.

[0019] A self-healing waterborne polyurethane / acrylic ester emulsion.

[0020] Application of a self-healing waterborne polyurethane / acrylic ester emulsion as a negative electrode binder of a lithium battery in a negative electrode sheet of a lithium battery.

[0021] Furthermore, the negative electrode sheet of the lithium battery is prepared by the following method:

[0022] S1. According to the mass ratio of (86-92):(2-6):(1-3):(2-5), mix the negative electrode active material, the conductive agent, sodium carboxymethyl cellulose and the negative electrode binder of the lithium battery, and stir evenly to obtain a negative electrode slurry;

[0023] S2. Coating the negative electrode slurry on the copper foil, drying at 120 °C, and rolling to obtain the negative electrode sheet of the lithium battery.

[0024] Compared with the prior art, the present invention has the following beneficial technical effects:

[0025] The present invention copolymerizes 5-(2-hydroxyethyl)-6-methyl-2-semicarbazidepyrimidine groups with waterborne polyurethane / acrylic ester to prepare a self-healing waterborne polyurethane / acrylic ester emulsion. Due to the existence of multiple hydrogen bonds between 5-(2-hydroxyethyl)-6-methyl-2-semicarbazidepyrimidine molecules, after polymerizing it onto the binder chain, the binder of the self-healing waterborne polyurethane / acrylic ester generates cross-linking, thus having excellent self-healing characteristics, effectively repairing the damage caused by the expansion of the electrode sheet, maintaining the integrity of the electrode sheet, promoting complete electrical contact between the active material and the current collector, and improving the cycle performance of the battery; in addition, the nitrogen atom in the molecular structure of 5-(2-hydroxyethyl)-6-methyl-2-semicarbazidepyrimidine contains lone pair electrons, which can effectively complex lithium ions and accelerate the migration of lithium ions, thereby improving the initial efficiency and rate performance of the battery. Description of the Drawings

[0026] Figure 1 It is a bar chart of the initial Coulombic efficiency of the button battery assembled with the negative electrode sheets of the lithium battery prepared in Examples 1-6 and Comparative Example 1 of the present invention;

[0027] Figure 2 It is a bar chart of the discharge rate of the button battery assembled with the negative electrode sheets of the lithium battery prepared in Example 1 and Comparative Example 1 of the present invention at different current densities;

[0028] Figure 3 It is a bar chart of the charge rate of the button battery assembled with the negative electrode sheets of the lithium battery prepared in Example 1 and Comparative Example 1 of the present invention at different current densities;

[0029] Figure 4 It is a cyclic performance characterization of the button battery assembled with the negative electrode sheets of the lithium battery prepared in Example 1 and Comparative Example 1 of the present invention. Detailed Embodiments

[0030] The following further detailed description of the present invention is made in conjunction with specific embodiments, which is an explanation rather than a limitation of the present invention.

[0031] In addition to the polycaprolactone diol, polytetrahydrofuran ether diol, polypropylene glycol, polyethylene glycol, polypropylene oxide diol, and neopentyl glycol polyhexanediate used in Examples 1 to 6, the polyol of the present invention may also be 1,4-butanediol adipate.

[0032] In addition to the silicon-carbon material selected in Examples 1 to 6, the negative electrode active material of the present invention may also be silicon nanoparticles or silicon-oxygen materials.

[0033] Example 1

[0034] Step 1: Mix 20 g of polycaprolactone diol with a molecular weight of 1000 and 2.2 g of 2,2-dimethylolbutanoic acid, and stir at 60 °C for 30 min to obtain a polyol solution.

[0035] Step 2: Under a nitrogen atmosphere, first add 0.04 g of dibutyltin dilaurate to the polyol solution, and then dropwise add 22.2 g of isophorone diisocyanate. React at 80 °C for 3 h to obtain a polyurethane prepolymer.

[0036] Step 3: Add 2.29 g of 5-(2-hydroxyethyl)-6-methyl-2-aminouracil to the polyurethane prepolymer, and react at 60 °C for 3 h to obtain intermediate product A.

[0037] Step 4: Add 5.83 g of 2-hydroxyethyl acrylate to intermediate product A, and react at 40 °C for 2 h to obtain intermediate product B.

[0038] Step 5: First, set aside 126 g of deionized water. Then add 1.5 g of triethylamine to intermediate product B, react at 40 °C for 30 min, while dropwise adding deionized water and stirring at a speed of 1000 rpm for 60 min to obtain a white self-healing waterborne polyurethane / acrylic ester emulsion.

[0039] Step 6: Weigh silicon-carbon material powder, conductive agent, sodium carboxymethylcellulose, and self-healing waterborne polyurethane / acrylic ester emulsion according to a mass ratio of 90:5:2:3, mix them, and stir for 50 min to obtain a negative electrode paste. Coat the negative electrode paste on a copper foil, dry at 120 °C, and roll it to obtain a negative electrode sheet for a lithium battery.

[0040] Example 2

[0041] Step 1: Mix 10 g of neopentyl glycol polyhexanediate with a molecular weight of 1000 and 0.7 g of 2,2-dimethylolbutanoic acid, and stir at 50 °C for 25 min to obtain a polyol solution.

[0042] Step 2: Under a nitrogen atmosphere, first add 0.012 g of dibutyltin dilaurate to the polyol solution, and then dropwise add 11.14 g of isophorone diisocyanate. React at 78 °C for 3 h to obtain a polyurethane prepolymer;

[0043] Step 3: Take 0.22 g of 5-(2-hydroxyethyl)-6-methyl-2-aminouracil and add it to the polyurethane prepolymer. React at 70 °C for 2 h to obtain intermediate A;

[0044] Step 4: Add 3.14 g of hydroxyethyl acrylate to intermediate A. React at 30 °C for 2 h to obtain intermediate B;

[0045] Step 5: First, set aside 59.92 g of deionized water. Then add 0.4 g of triethylamine to intermediate B. React at 30 °C for 30 min. While dropwise adding deionized water, stir at a speed of 900 rpm for 60 min to obtain a white self-healing waterborne polyurethane / acrylic ester emulsion;

[0046] Step 6: Weigh silicon carbide material powder, conductive agent, sodium carboxymethyl cellulose, and self-healing waterborne polyurethane / acrylic ester emulsion according to a mass ratio of 84:6:3:2, mix them, and stir for 50 min to obtain a negative electrode slurry. Coating the negative electrode slurry on a copper foil, drying at 120 °C, and rolling to obtain a lithium battery negative electrode sheet.

[0047] Example 3

[0048] Step 1: Mix 25 g of polyoxypropylene glycol with a molecular weight of 1000 and 2.6 g of 2,2-dimethylolpropionic acid, and stir at 40 °C for 35 min to obtain a polyol solution;

[0049] Step 2: Under a nitrogen atmosphere, first add 0.13 g of dibutyltin dilaurate to the polyol solution, and then dropwise add 26.67 g of diphenylmethane diisocyanate. React at 74 °C for 3.5 h to obtain a polyurethane prepolymer;

[0050] Step 3: Take 2.71 g of 5-(2-hydroxyethyl)-6-methyl-2-aminouracil and add it to the polyurethane prepolymer. React at 65 °C for 3 h to obtain intermediate A;

[0051] Step 4: Add 7.90 g of hydroxyethyl acrylate to intermediate A. React at 50 °C for 3 h to obtain intermediate B;

[0052] Step 5: First, reserve 153 g of deionized water. Then, add 1.78 g of triethylamine to intermediate product B. React at 50 °C for 40 min. While dropping deionized water, stir at a speed of 1000 rpm for 20 min to obtain a white self-healing waterborne polyurethane / acrylic ester emulsion.

[0053] Step 6: Weigh silicon carbon material powder, conductive agent, sodium carboxymethyl cellulose, and self-healing waterborne polyurethane / acrylic ester emulsion according to the mass ratio of 88:5:3:4, mix them, and stir for 50 min to obtain a negative electrode paste. Coat the negative electrode paste on a copper foil, dry at 120 °C, and roll press to obtain a lithium battery negative electrode sheet.

[0054] Example 4

[0055] Step 1: Mix 30 g of polyethylene glycol with a molecular weight of 1000 and 3.1 g of 2,2-dimethylolpropionic acid, and stir at 70 °C for 20 min to obtain a polyol solution.

[0056] Step 2: Under a nitrogen atmosphere, first add 0.04 g of stannous octoate to the polyol solution, and then dropwise add 21.1 g of hexamethylene diisocyanate. React at 80 °C for 3 h to obtain a polyurethane prepolymer.

[0057] Step 3: Add 3.21 g of 5-(2-hydroxyethyl)-6-methyl-2-aminouracil to the polyurethane prepolymer, and react at 60 °C for 3 h to obtain intermediate product A.

[0058] Step 4: Add 4.33 g of hydroxyethyl acrylate to intermediate product A, and react at 40 °C for 2 h to obtain intermediate product B.

[0059] Step 5: First, reserve 180.69 g of deionized water. Then, add 2.12 g of triethylamine to intermediate product B. React at 40 °C for 30 min. While dropping deionized water, stir at a speed of 1000 rpm for 40 min to obtain a white self-healing waterborne polyurethane / acrylic ester emulsion.

[0060] Step 6: Weigh silicon carbon material powder, conductive agent, sodium carboxymethyl cellulose, and self-healing waterborne polyurethane / acrylic ester emulsion according to the mass ratio of 92:4:2:2, mix them, and stir for 50 min to obtain a negative electrode paste. Coat the negative electrode paste on a copper foil, dry at 120 °C, and roll press to obtain a lithium battery negative electrode sheet.

[0061] Example 5

[0062] Step 1: Mix 20 g of polytetrahydrofuran ether glycol with a molecular weight of 1000 and 1.9 g of ethylenediaminoethanesulfonic acid, and stir at 60 °C for 40 min to obtain a polyol solution.

[0063] Step 2: Under a nitrogen atmosphere, first add 0.312 g of stannous octoate to the polyol solution, and then dropwise add 31.11 g of 4,4′-dicyclohexylmethane diisocyanate. React at 80 °C for 3 h to obtain a polyurethane prepolymer;

[0064] Step 3: Take 1.72 g of 5-(2-hydroxyethyl)-6-methyl-2-semicarbazide pyrimidine and add it to the polyurethane prepolymer. React at 60 °C for 3 h to obtain intermediate product A;

[0065] Step 4: Add 5.52 g of hydroxyethyl acrylate to intermediate product A. React at 40 °C for 2 h to obtain intermediate product B;

[0066] Step 5: First, take 120.3 g of deionized water for standby. Then add 1.26 g of triethylamine to intermediate product B. React at 40 °C for 20 min. While dropwise adding deionized water, stir at a speed of 1000 rpm for 50 min to obtain a white self-healing waterborne polyurethane / acrylic ester emulsion;

[0067] Step 6: Weigh silicon carbon material powder, conductive agent, sodium carboxymethyl cellulose, and self-healing waterborne polyurethane / acrylic ester emulsion according to the mass ratio of 86:6:3:5, mix them, and stir for 50 min to obtain a negative electrode paste. Coating the negative electrode paste on a copper foil and drying at 120 °C, after rolling, a lithium battery negative electrode sheet is obtained.

[0068] Example 6

[0069] Step 1: Mix 15 g of polypropylene glycol with a molecular weight of 2000 and 1.3 g of ethylenediaminoethanesulfonic acid sodium, and stir at 60 °C for 30 min to obtain a polyol solution;

[0070] Step 2: Under a nitrogen atmosphere, first add 0.04 g of stannous octoate to the polyol solution, and then dropwise add 17.42 g of 2,4-toluene diisocyanate. React at 80 °C for 2.5 h to obtain a polyurethane prepolymer;

[0071] Step 3: Take 0.97 g of 5-(2-hydroxyethyl)-6-methyl-2-semicarbazide pyrimidine and add it to the polyurethane prepolymer. React at 50 °C for 4 h to obtain intermediate product A;

[0072] Step 4: Add 6.18 g of hydroxyethyl acrylate to intermediate product A. React at 40 °C for 4 h to obtain intermediate product B;

[0073] Step 5: First, reserve 90 g of deionized water. Then, add 0.83 g of triethylamine to Intermediate Product B. React at 40 °C for 30 min. While dropping deionized water, stir at a speed of 800 rpm for 60 min to obtain a white self-healing waterborne polyurethane / acrylic ester emulsion.

[0074] Step 6: Weigh silicon-carbon material powder, conductive agent, sodium carboxymethyl cellulose, and self-healing waterborne polyurethane / acrylic ester emulsion according to the mass ratio of 91:3:1:5, mix them, and stir for 50 min to obtain a negative electrode slurry. Coat the negative electrode slurry on a copper foil, dry it at 120 °C, and roll it to obtain a lithium battery negative electrode sheet.

[0075] Comparative Example 1

[0076] Step 1: Mix 20 g of polycaprolactone diol with a molecular weight of 1000 and 2.2 g of 2,2-dimethylolbutanoic acid, and stir at 60 °C for 30 min to obtain a polyol solution.

[0077] Step 2: Under a nitrogen atmosphere, first add 0.04 g of dibutyltin dilaurate to the polyol solution, then dropwise add 22.2 g of isophorone diisocyanate, and react at 80 °C for 3 h to obtain a polyurethane prepolymer.

[0078] Step 3: Add 5.83 g of hydroxyethyl acrylate to the polyurethane prepolymer, and react at 40 °C for 2 h to obtain an intermediate product.

[0079] Step 4: First, reserve 126 g of deionized water. Then, add 1.5 g of triethylamine to the intermediate product, react at 40 °C for 30 min. While dropping deionized water, stir at a speed of 1000 rpm for 60 min to obtain a white emulsion.

[0080] Step 5: Weigh silicon-carbon material powder, conductive agent, sodium carboxymethyl cellulose, and the white emulsion according to the mass ratio of 90:5:2:3, mix them, and stir for 50 min to obtain a negative electrode slurry. Coat the negative electrode slurry on a copper foil, dry it at 120 °C, and roll it to obtain a lithium battery negative electrode sheet.

[0081] Comparative Example 2

[0082] Take a commercially available SBR emulsion on the market. Weigh silicon-carbon material powder, conductive agent, sodium carboxymethyl cellulose, and the SBR emulsion according to the mass ratio of 90:5:2:3, mix them, and stir for 50 min to obtain a negative electrode slurry. Coat the negative electrode slurry on a copper foil, dry it at 120 °C, and roll it to obtain a lithium battery negative electrode sheet.

[0083] The binder emulsions prepared in Example 1, Comparative Example 1 and Comparative Example 2 were dried into films. Scratches were made on the glue films with a scalpel. After heat treatment under the same conditions for 30 min, the repair effect of the glue films was observed and the repair efficiency was calculated. The specific data are shown in Table 1 below. It can be seen from Table 1 that the self-repair efficiency of the sample prepared in Example 1 was 72.2%, significantly higher than the self-repair efficiency of 26.4% of the sample prepared in Comparative Example 1 and the self-repair efficiency of 22.1% of the sample prepared in Comparative Example 2, indicating that the modified binder material of the present invention has remarkable self-repair performance, so it can greatly repair the cracks generated in the expanded electrode sheet and maintain the electrode stability.

[0084] Table 1 Repair effect of the binder films prepared in Example 1, Comparative Example 1 and Comparative Example 2

[0085] Sample Initial scratch width (μm) Scratch width after repair (μm) Repair efficiency % Example 1 20.2 5.6 72.2 Comparative Example 1 20.1 14.8 26.4 Comparative Example 2 19.5 15.2 22.1

[0086] The lithium battery negative electrode sheets prepared in Example 1 to Example 6, Comparative Example 1 and Comparative Example 2 were respectively assembled with the existing electrolyte, separator and positive electrode sheet into 8 groups of secondary button cells in a glove box, and the cycle performance and rate performance of the cells were tested. The results are as follows:

[0087] From Figure 1 It can be seen that the initial Coulombic efficiencies of the button cells assembled with the lithium battery negative electrode sheets prepared in Example 1 to Example 6 were 87.43%, 83.94%, 84.30%, 86.87%, 85.83% and 86.02% in turn. The initial Coulombic efficiency of the button cell assembled with the lithium battery negative electrode sheet prepared in Comparative Example 1 was 82.00%, and the initial Coulombic efficiency of the button cell assembled with the lithium battery negative electrode sheet prepared in Comparative Example 2 was 83.00%, which were significantly lower than the initial Coulombic efficiencies of the button cells assembled with the lithium battery negative electrode sheets prepared in Example 1 to Example 6. This is attributed to the fact that the 5-(2-hydroxyethyl)-6-methyl-2-semicarbazide (HMA) groups introduced in Example 1 to Example 6 copolymerized with waterborne polyurethane / acrylic ester, making the binder in the claims have an excellent network structure, thereby forming a SEI film on the surface of the silicon-carbon material, which can prevent the direct contact between the electrolyte and the silicon-carbon material, reduce the occurrence of side reactions, reduce lithium loss, and improve the Coulombic efficiency of the battery;

[0088] From Figure 2It can be seen that after activation, the button cells assembled with the lithium battery negative electrode sheets prepared in Example 1 have discharge specific capacities of 515.17 mAh / g, 484.16 mAh / g, 424.12 mAh / g, 339.07 mAh / g, and 199.05 mAh / g at current densities of 0.1C, 0.2C, 0.5C, 1C, and 2C, respectively. After discharge at a rate of 0.1 - 2C and then again at a current density of 0.1C, the discharge specific capacity is 494.07 mAh / g. On the contrary, for the button cells assembled with the lithium battery negative electrode sheets prepared in Comparative Example 1, the discharge specific capacities are 492.74 mAh / g, 446.7 mAh / g, 366.75 mAh / g, 223.66 mAh / g, and 73.51 mAh / g at current densities of 0.1C, 0.2C, 0.5C, 1C, and 2C, respectively. After discharge at a rate of 0.1 - 2C and then again at a current density of 0.1C, the discharge specific capacity is 471.15 mAh / g. By comparison, it can be found that the discharge specific capacity of the button cells assembled with the lithium battery negative electrode sheets prepared in Example 1 is always higher than that of the button cells assembled with the lithium battery negative electrode sheets prepared in Comparative Example 1;

[0089] From Figure 3 It can be seen that after activation, the button cells assembled with the lithium battery negative electrode sheets prepared in Example 1 have charge specific capacities of 512.46 mAh / g, 486.53 mAh / g, 423.89 mAh / g, 338.56 mAh / g, and 230.73 mAh / g at current densities of 0.1C, 0.2C, 0.5C, 1C, and 2C, respectively. After discharge at a rate of 0.1 - 2C and then again at a current density of 0.1C, the discharge specific capacity is 499.96 mAh / g. On the contrary, for the button cells assembled with the lithium battery negative electrode sheets prepared in Comparative Example 1, the charge specific capacities are 488.5 mAh / g, 443.92 mAh / g, 364.66 mAh / g, 222.68 mAh / g, and 73.22 mAh / g at current densities of 0.1C, 0.2C, 0.5C, 1C, and 2C, respectively. After charge at a rate of 0.1 - 2C and then again at a current density of 0.1C, the charge specific capacity is 471.19 mAh / g. By comparison, it can be found that the charge specific capacity of the button cells assembled with the lithium battery negative electrode sheets prepared in Example 1 is always higher than that of the button cells assembled with the lithium battery negative electrode sheets prepared in Comparative Example 1;

[0090] From Figure 4It can be seen that for the coin cells assembled with the lithium battery negative electrode sheets prepared in Example 1, the capacity retention rate was still 74.36% after 25 cycles, while for the coin cells assembled with the lithium battery negative electrode sheets prepared in Comparative Example 1, the capacity retention rate was only 55.50% after 25 cycles, indicating that the cycling performance of the coin cells assembled with the lithium battery negative electrode sheets prepared in Example 1 was significantly better than that of the coin cells assembled with the lithium battery negative electrode sheets prepared in Comparative Example 1;

[0091] In summary, from Figures 1 to 4 the analysis, it can be known that compared with the white emulsion prepared in Comparative Example 1, the self-healing waterborne polyurethane / acrylic ester emulsions prepared in Examples 1 to 6, when used as the lithium battery negative electrode binder, have excellent self-healing characteristics and can endow the lithium battery with higher initial Coulomb efficiency, cycling performance and rate performance. This is because the multiple hydrogen bonds between 5-(2-hydroxyethyl)-6-methyl-2-semicarbazide molecules can effectively control the crosslinking strength and segmental movement ability of the waterborne polyurethane acrylate polymer, thereby endowing the waterborne polyurethane / acrylic ester with high toughness and rapid self-healing performance. When used as the lithium battery negative electrode binder, it has strong adhesion to the silicon negative electrode active material, can withstand the huge volume changes caused during the lithium intercalation / deintercalation process, and can release the internal stress of the silicon particles, thereby improving the cycle life of the lithium ion battery.

Claims

1. A preparation method of a self-healing waterborne polyurethane / acrylic ester emulsion, characterized in that It includes the following steps: Step 1: Mix 10 - 30 g of polyol and 0.7 - 3.1 g of hydrophilic chain extender, and stir at 40 - 70 °C for 20 - 40 min to obtain a polyol solution; Step 2: Under a nitrogen atmosphere, first add a catalyst to the polyol solution, then dropwise add 11.14 - 31.11 g of polyisocyanate, and react at 74 - 80 °C for 2.5 - 3.5 h to obtain a polyurethane prepolymer, where: the catalyst accounts for 0.1% - 1% of the mass of the polyisocyanate; Step 3: Add 0.22 - 3.21 g of 5-(2-hydroxyethyl)-6-methyl-2-aminouracil to the polyurethane prepolymer, and react at 50 - 70 °C for 2 - 4 h to obtain intermediate product A; Step 4: Add 3.14 - 7.90 g of hydroxyethyl acrylate to intermediate product A, and react at 30 - 50 °C for 2 - 4 h to obtain intermediate product B; Step 5: First, prepare 59.92 - 180.69 g of deionized water for standby. Then, add 0.40 - 2.12 g of triethylamine to intermediate product B, react at 30 - 50 °C for 20 - 40 min, and then, while dropping the deionized water, stir at a high speed until a white milky liquid is formed to obtain a white self-healing waterborne polyurethane / acrylic ester emulsion.

2. The preparation method of the self-healing aqueous polyurethane / acrylic ester emulsion according to claim 1, characterized in that, The polyol in Step 1 is polycaprolactone diol, polytetrahydrofuran ether diol, polypropylene glycol, polyethylene glycol, polypropylene oxide glycol, polyhexanediol neopentyl ester, or poly(1,4-butylene adipate); The molecular weight of the polyol is 1000 - 2000.

3. The preparation method of the self-repairing aqueous polyurethane / acrylic ester emulsion according to claim 1, characterized in that, The hydrophilic chain extender in Step 1 is 2,2-dimethylolbutyric acid, 2,2-dimethylolpropionic acid, or sodium 2-(ethylamino)ethanesulfonate.

4. The preparation method of the self-healing aqueous polyurethane / acrylic ester emulsion according to claim 1, wherein, The polyisocyanate in Step 2 is isophorone diisocyanate, 2,4-toluene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, or 4,4'-dicyclohexylmethane diisocyanate.

5. The preparation method of the self-healing aqueous polyurethane / acrylic ester emulsion according to claim 1, wherein, The catalyst in Step 2 is dibutyltin dilaurate or stannous octoate.

6. The preparation method of the self-healing aqueous polyurethane / acrylic ester emulsion according to claim 1, characterized in that, The stirring in Step 5 is carried out at a rotation speed of 800 - 1000 rpm for 20 - 60 min.

7. A self-healing waterborne polyurethane / acrylic ester emulsion prepared by the method according to any one of claims 1 - 6.

8. Application of the self-healing waterborne polyurethane / acrylic ester emulsion according to claim 7 as a negative electrode binder for lithium batteries in a lithium battery negative electrode sheet.

9. The application of the lithium battery anode binder according to claim 8 in a lithium battery anode sheet, characterized in that, The lithium battery negative electrode sheet is prepared by the following method: S1: Mix the negative electrode active material, conductive agent, sodium carboxymethyl cellulose, and the lithium battery negative electrode binder according to the mass ratio of (86 - 92):(2 - 6):(1 - 3):(2 - 5), and stir evenly to obtain a negative electrode slurry; S2: Coat the negative electrode slurry on a copper foil, dry at 120 °C, and roll to obtain a lithium battery negative electrode sheet.

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