Preparation method of composite aqueous binder for high-voltage and high-load positive electrode

Abstract

The invention relates to a preparation method of a composite aqueous binder for a high-voltage and high-load positive electrode, which comprises the following steps: adding sericin into deionized water to prepare a sericin aqueous solution; adding sodium carboxymethyl cellulose into deionized water to prepare a sodium carboxymethyl cellulose aqueous solution; the sericin aqueous solution is taken and added into the carboxymethyl cellulose aqueous solution, the mass ratio of sodium carboxymethyl cellulose to sericin is 2: 1, water bath heating and stirring are carried out for 2 h, the heating temperature is 50 DEG C, after heating and stirring are finished, stirring continues to be carried out overnight at the room temperature, polymerization is carried out, and the uniform and transparent composite water-based binder is obtained. The binder has the advantages that the raw materials are easy to obtain, the cost is low, the binder is environment-friendly, the binder is suitable for increasing the thickness of a high-load and high-voltage lithium-rich positive electrode, the binder has excellent mechanical performance to inhibit active particles from being broken and layered, and the binder also has high lithium ion mobility and electronic conductivity.

Description

Technical Field

[0001] The present invention is applied to the field of new energy secondary batteries, that is, a binder for high-load and high-voltage cathode materials of lithium-ion batteries, and specifically relates to a preparation method of a high-voltage stable composite aqueous binder for high-load cathodes. Background Art

[0002] With the rapid development of the new energy vehicle industry, the requirements for battery energy density are getting higher and higher. The cathode material of the battery is the main body for storing lithium ions in the lithium-ion battery, and its performance directly affects the energy density of the battery. At present, most new energy vehicles use lithium-ion batteries as power sources. The cathode material of the lithium-ion battery completes the charge and discharge process of the battery by absorbing and releasing lithium ions. In order to achieve higher energy density lithium-ion batteries, there are mainly two aspects for the lithium-ion battery cathode material: 1) developing new cathode materials with higher specific capacity; 2) obtaining an advanced battery structure with higher electrochemical activity by improving the battery structure.

[0003] The new cathode materials of high-nickel and lithium-rich lithium-ion batteries have the characteristics of high energy density. Among them, the lithium-rich manganese (LRMO) cathode material has a discharge specific capacity of more than 250 mAh / g, and can even reach 300 mAh / g due to its high-voltage charge and discharge mechanism above 4.8 V, far exceeding the discharge specific capacity of the currently commercially applied lithium iron phosphate and ternary cathode materials, almost twice the actual capacity of the currently commercially applied cathode materials. However, the battery energy density still cannot meet the requirements of high-energy density lithium-ion batteries. If the energy density of the lithium-ion battery is to be increased to 500 Wh·kg -1 and above, it is also necessary to improve the battery structure and increase the proportion of active substances to improve the battery energy density. Among many battery structure improvement methods, increasing the cathode thickness is the most direct and effective method; theoretically, increasing the cathode thickness can greatly increase the load of active substances per unit area. Such a high-load cathode can effectively improve the energy density of the battery without changing the existing battery system.

[0004] However, with the increase in the electrode thickness of the lithium-rich manganese (LRMO) cathode material, the loading amount of the active material also increases significantly. Such high-loading cathode materials pose higher requirements for the performance of the binder. The polyvinylidene fluoride (PVDF) binder commonly used in the preparation of traditional lithium battery electrodes shows obvious deficiencies in the application of thick electrodes. As an electron / ion insulator, polyvinylidene fluoride (PVDF) reduces the conductivity of thick electrodes, thereby increasing the electrochemical impedance, which has an adverse effect on the performance of the battery. In addition, the binding effect of polyvinylidene fluoride (PVDF) mainly relies on the relatively weak van der Waals forces between molecules, which is difficult to effectively maintain the mechanical integrity of the electrode network under the high-loading conditions of thick electrodes, easily leading to the rupture and delamination of active particles, and thus affecting the cycle stability and rate performance of the battery. More importantly, the PVDF binder is expensive, and the solvent N-methylpyrrolidone (NMP) used in its preparation is toxic, which not only increases the material cost but also raises the difficulty and cost of material recycling and reuse. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a preparation method of a composite aqueous binder for high-voltage and high-loading cathodes, with easily available raw materials, low cost, and environmental friendliness. This binder is suitable for high-loading and high-voltage lithium-rich cathodes with increased thickness, having excellent mechanical properties to inhibit the rupture and delamination of active particles, and high lithium ion mobility and electronic conductivity.

[0006] The technical solution of the present invention is as follows:

[0007] A preparation method of a composite aqueous binder for high-voltage and high-loading cathodes is as follows:

[0008] (1) Prepare a sericin solution

[0009] Add sericin to deionized water to prepare an aqueous sericin solution.

[0010] (2) Prepare a sodium carboxymethyl cellulose solution

[0011] Add sodium carboxymethyl cellulose to deionized water to prepare an aqueous sodium carboxymethyl cellulose solution.

[0012] (3) Prepare a highly conductive and lithium-conductive composite binder

[0013] Take the aqueous sericin solution and add it to the aqueous carboxymethyl cellulose solution, where the mass ratio of sodium carboxymethyl cellulose to sericin is 2:1. Carry out water bath heating and stirring for 2 h at a heating temperature of 50 °C. After the heating and stirring are completed, continue stirring overnight at room temperature for polymerization to obtain a uniform and transparent composite aqueous binder.

[0014] Further, the mass concentration of the sericin protein aqueous solution is 2%.

[0015] Further, the concentration of the sodium carboxymethyl cellulose aqueous solution is 2%.

[0016] Further, when stirring while heating in a water bath, the stirring speed is 400 rpm.

[0017] Further, when stirring overnight at room temperature, the stirring speed is 300 rpm and the stirring time is 12 h.

[0018] An application of the above composite aqueous binder as a binder in a positive electrode sheet of a lithium-ion battery.

[0019] Further, the positive electrode sheet of the lithium-ion battery is a lithium-rich manganese-based positive electrode sheet.

[0020] Further, the preparation of the positive electrode sheet of the lithium-ion battery is as follows:

[0021] The active material, conductive agent, and binder are uniformly mixed to make a slurry, coated on an aluminum foil, and dried in a vacuum oven at 80 °C for 12 h to obtain a lithium-rich manganese-based positive electrode sheet.

[0022] Further, the mass ratio of the active material, conductive agent, and binder is 85:10:5.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] (1) The preparation method of the present invention is relatively simple. By a physical method of heating in a water bath, water-soluble polymers are crosslinked to form covalent bonds such as ionic bonds and hydrogen bonds, thereby obtaining a binder with excellent performance. Without complex post-treatment steps, the production cost is reduced and the production efficiency is improved.

[0025] (2) By using an aqueous binder, the problem of pollution caused by traditional organic solvents is avoided, and green production is realized.

[0026] (3) The introduction of sericin protein contains a polypeptide structure, which contains abundant polar hydrophilic groups such as carboxyl, hydroxyl, and amino groups, making it have excellent mechanical properties and high stability when polymerized with sodium carboxymethyl cellulose. At the same time, by the water bath heating method, the interaction between functional groups is promoted, and ionic bonds, hydrogen bonds, covalent bonds, etc. formed by crosslinking can strengthen the adhesion between the active material and the conductive agent, inhibit particle breakage during the cycle, and further improve the cycle performance of the thick electrode.

[0027] (4) The present invention is used for a high-loading positive electrode material, so that the prepared lithium-rich manganese-based thick electrode has 16.6 g / cm 2The high-active material loading is such that the thickness of the electrode sheet is as high as 200 μm. At the same time, no cracking or other phenomena occur after the electrode sheet is dried, which can effectively improve the mechanical properties of the thick electrode.

[0028] (5) The present invention has high-voltage stability at a high voltage of 4.8 V. During the electrode cycling process, electrons can be effectively transmitted, reducing the resistance of electron transmission. At a voltage of 4.8 V, the initial specific capacity of the battery can reach as high as 280.47 mAh / g, and the initial charge-discharge efficiency is up to 83.71%. The capacity retention rate after 100 cycles reaches 84.81%, greatly improving the initial Coulomb efficiency, cycling performance, and voltage and capacity decay problems of the high-loading positive electrode sheet in lithium batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is the first charge-discharge curve diagram of the battery assembled with the modified binder-rich lithium manganese-based positive electrode material in Example 1 of the present invention at 30 °C and a rate of 0.1C;

[0030] Figure 2 is the discharge specific capacity decay diagram of the battery assembled with the modified binder-rich lithium manganese-based positive electrode material in Example 1 of the present invention at 30 °C and 1C for 100 cycles;

[0031] Figure 3 is the XRD comparison diagram of the modified binder-rich lithium manganese-based positive electrode material of the present invention (corresponding to Example 1 and Comparative Example 1);

[0032] Figure 4 is the SEM diagram with a magnification of 5000 times of the modified binder-rich lithium manganese-based positive electrode material of the present invention (corresponding to Example 1);

[0033] Figure 5 is the SEM diagram with a magnification of 50000 times of the modified binder-rich lithium manganese-based positive electrode material of the present invention (corresponding to Example 1);

[0034] Figure 6 is the first charge-discharge curve diagram of the battery assembled with the modified binder-rich lithium manganese-based positive electrode material in Comparative Example 1 of the present invention at 30 °C and a rate of 0.1C;

[0035] Figure 7 is the discharge specific capacity decay diagram of the battery assembled with the modified binder-rich lithium manganese-based positive electrode material in Comparative Example 1 of the present invention at 30 °C and 1C for 100 cycles;

[0036] Figure 8 is the SEM diagram with a magnification of 5000 times of the modified binder-rich lithium manganese-based positive electrode material in Comparative Example 1 of the present invention;

[0037] Figure 9SEM image of the lithium-rich manganese-based cathode material with modified binder (corresponding to Comparative Example 1) of the present invention at a magnification of 50,000 times;

[0038] Figure 10 First charge-discharge curve of the battery assembled with the lithium-rich manganese-based cathode material with modified binder (corresponding to Comparative Example 2) of the present invention at 30 °C and a rate of 0.1C;

[0039] Figure 11 Discharge specific capacity decay diagram of the battery assembled with the lithium-rich manganese-based cathode material with modified binder (corresponding to Comparative Example 2) of the present invention after 100 cycles at 30 °C and 1C;

[0040] Figure 12 First charge-discharge curve of the battery assembled with the lithium-rich manganese-based cathode material with modified binder (corresponding to Comparative Example 3) of the present invention at 30 °C and a rate of 0.1C;

[0041] Figure 13 Discharge specific capacity decay diagram of the battery assembled with the lithium-rich manganese-based cathode material with modified binder (corresponding to Comparative Example 3) of the present invention after 100 cycles at 30 °C and 1C;

[0042] Figure 14 First charge-discharge curve of the battery assembled with the lithium-rich manganese-based cathode material with modified binder (corresponding to Comparative Example 4) of the present invention at 30 °C and a rate of 0.1C;

[0043] Figure 15 Discharge specific capacity decay diagram of the battery assembled with the lithium-rich manganese-based cathode material with modified binder (corresponding to Comparative Example 4) of the present invention after 100 cycles at 30 °C and 1C;

[0044] Figure 16 First charge-discharge curve of the battery assembled with the lithium-rich manganese-based cathode material with modified binder (corresponding to Comparative Example 5) of the present invention at 30 °C and a rate of 0.1C;

[0045] Figure 17 Discharge specific capacity decay diagram of the battery assembled with the lithium-rich manganese-based cathode material with modified binder (corresponding to Comparative Example 5) of the present invention after 100 cycles at 30 °C and 1C.

[0046] Figure 18 First charge-discharge curve of the battery assembled with the lithium-rich manganese-based cathode material with modified binder (corresponding to Comparative Example 6) of the present invention at 30 °C and a rate of 0.1C;

[0047] Figure 19 Discharge specific capacity decay diagram of the battery assembled with the lithium-rich manganese-based cathode material with modified binder (corresponding to Comparative Example 6) of the present invention after 100 cycles at 30 °C and 1C.

[0048] Figure 20 This is the first charge-discharge curve of the battery assembled with the modified binder-rich lithium manganese-based cathode material of the present invention (corresponding to Comparative Example 7) at 30 °C and 0.1C rate;

[0049] Figure 21 This is the discharge specific capacity decay diagram of 100 cycles of the battery assembled with the modified binder-rich lithium manganese-based cathode material of the present invention (corresponding to Comparative Example 7) at 30 °C and 1C condition. Detailed implementation manners

[0050] The following further illustrates the specific implementation methods of the present invention in combination with examples. It should be noted here that the specific implementation methods described herein are only for explaining and interpreting the present invention and are not used to limit the protection scope of the present invention.

[0051] Example 1

[0052] Step 1: Add 0.1 g of sericin to 4.9 g of deionized water, stir evenly at room temperature for 12 hours, and prepare a transparent and uniform sericin aqueous solution; at the same time, add 0.2 g of sodium carboxymethylcellulose to 9.8 g of deionized water, stir evenly at room temperature for 12 hours, and prepare a transparent and uniform sodium carboxymethylcellulose aqueous solution;

[0053] Step 2: Take 5 g of the sericin aqueous solution and add it to 10 g of the sodium carboxymethylcellulose solution, heat it in a water bath at 50 °C on a magnetic stirrer, stir at 400 rpm for 2 hours, and then continue to stir at a low speed of 300 rpm overnight (12 h) at room temperature for polymerization to obtain a transparent and uniform composite binder;

[0054] Step 3: Uniformly mix the lithium-rich manganese cathode material 0.5Li2MnO3·0.5LiNi 0.33 Co 0.33 Mn 0.33 O2, conductive agent SuperP, and composite binder in a mass ratio of 85:10:5 to make a slurry, coat the slurry on an aluminum foil current collector with an 800-μm doctor blade, dry it in a vacuum oven at 80 °C for 12 h, and then cut it into pieces to obtain a lithium-rich manganese-based cathode electrode sheet, and the product is denoted as CP21@50.

[0055] Comparative Example 1

[0056] Step 1: Add 0.2 g of sodium carboxymethylcellulose to 9.8 g of deionized water, stir evenly at room temperature for 12 hours, and prepare a transparent and uniform sodium carboxymethylcellulose aqueous solution;

[0057] Step 2: Use the prepared sodium carboxymethylcellulose solution as a binder and the lithium-rich manganese cathode material 0.5Li2MnO3·0.5LiNi0.33 Co 0.33 Mn 0.33 O2, the conductive agent Super P, and the like are mixed into a slurry at a mass ratio of 5:85:10. The slurry is coated on an aluminum foil current collector with an 800-μm doctor blade. After drying in a vacuum oven at 80 °C for 12 h, the resulting product is cut into pieces to obtain a lithium-rich manganese-based positive electrode sheet, which is denoted as CMC.

[0058] As Figure 3 shown in the XRD patterns of the products prepared in Example 1 and Comparative Example 1 of the present invention, Figure 3 it can be seen that after introducing the composite aqueous binder of Example 1, the structure and components of the lithium-rich manganese electrode sheet have not changed.

[0059] As Figure 5 and Figure 9 shown in the SEM images of the products prepared in Example 1 and Comparative Example 1 of the present invention, Figure 5 and Figure 9 it can be seen that after introducing the composite aqueous binder of Example 1, the surface of the lithium-rich manganese is uniform and flat. In contrast, the surface of the electrode sheet prepared using sodium carboxymethyl cellulose has obvious cracks.

[0060] Comparative Example 2

[0061] Step 1: Add 0.1 g of sericin to 4.9 g of deionized water, and stir evenly at room temperature for 12 hours to prepare a transparent and uniform sericin aqueous solution; at the same time, add 0.1 g of sodium carboxymethyl cellulose to 4.9 g of deionized water, and stir evenly at room temperature for 12 hours to prepare a transparent and uniform sodium carboxymethyl cellulose aqueous solution.

[0062] Step 2: Take 5 g of the sericin aqueous solution and add it to 5 g of the sodium carboxymethyl cellulose solution. Heat it in a water bath at 50 °C on a magnetic stirrer, stir at 400 rpm for 2 hours, and then continue to stir at a low speed of 300 rpm overnight (12 h) at room temperature for polymerization to obtain a transparent and uniform composite binder.

[0063] Step 3: Use the prepared sodium carboxymethyl cellulose solution as a binder and mix it with the lithium-rich manganese positive electrode material 0.5Li2MnO3·0.5LiNi 0.33 Co 0.33 Mn 0.33 O2, the conductive agent Super P, and the like are mixed into a slurry at a mass ratio of 5:85:10. The slurry is coated on an aluminum foil current collector with an 800-μm doctor blade. After drying in a vacuum oven at 80 °C for 12 h, the resulting product is cut into pieces to obtain a lithium-rich manganese-based positive electrode sheet, which is denoted as CP11@50.

[0064] Comparative Example 3

[0065] Step 1: Add 0.1 g of sericin into 4.9 g of deionized water, stir evenly at room temperature for 12 hours, and prepare a transparent and uniform sericin aqueous solution; at the same time, add 0.3 g of sodium carboxymethylcellulose into 14.7 g of deionized water, stir evenly at room temperature for 12 hours, and prepare a transparent and uniform sodium carboxymethylcellulose aqueous solution;

[0066] Step 2: Take 5 g of the sericin aqueous solution and add it to 15 g of the sodium carboxymethylcellulose solution, heat it in a water bath at 50 °C on a magnetic stirrer, stir at 400 rpm for 2 hours, and then continue to stir at a low speed of 300 rpm overnight (12 h) at room temperature for polymerization to obtain a transparent and uniform composite binder;

[0067] Step 3: Use the prepared sodium carboxymethylcellulose solution as a binder and mix it with the lithium-rich manganese cathode material 0.5Li2MnO3·0.5LiNi 0.33 Co 0.33 Mn 0.33 O2 and the conductive agent Super P in a mass ratio of 5:85:10 to form a slurry. Coat the slurry on an aluminum foil current collector with an 800-μm scraper, dry it in a vacuum oven at 80 °C for 12 h, and then cut it into pieces to obtain a lithium-rich manganese-based cathode electrode sheet, and the product is denoted as CP31@50.

[0068] Control Example 4 Adjust the polymerization temperature of the composite binder

[0069] Step 1: Add 0.1 g of sericin into 4.9 g of deionized water, stir evenly at room temperature for 12 hours, and prepare a transparent and uniform sericin aqueous solution; at the same time, add 0.2 g of sodium carboxymethylcellulose into 9.8 g of deionized water, stir evenly at room temperature for 12 hours, and prepare a transparent and uniform sodium carboxymethylcellulose aqueous solution;

[0070] Step 2: Take 5 g of the sericin aqueous solution and add it to 10 g of the sodium carboxymethylcellulose solution, heat it in a water bath at 30 °C on a magnetic stirrer, stir at 400 rpm for 2 hours, and then continue to stir at a low speed of 300 rpm overnight (12 h) at room temperature for polymerization to obtain a transparent and uniform composite binder;

[0071] Step 3: Use the prepared sodium carboxymethylcellulose solution as a binder and mix it with the lithium-rich manganese cathode material 0.5Li2MnO3·0.5LiNi 0.33 Co 0.33 Mn 0.33 O2 and the conductive agent Super P in a mass ratio of 5:85:10 to form a slurry. Coat the slurry on an aluminum foil current collector with an 800-μm scraper, dry it in a vacuum oven at 80 °C for 12 h, and then cut it into pieces to obtain a lithium-rich manganese-based cathode electrode sheet, and the product is denoted as CP21@30.

[0072] Comparative Example 5

[0073] Step 1: 0.1 g of sericin was added to 4.9 g of deionized water, and the mixture was stirred at room temperature for 12 hours to prepare a transparent and uniform sericin aqueous solution; meanwhile, 0.2 g of sodium carboxymethyl cellulose was added to 9.8 g of deionized water, and the mixture was stirred at room temperature for 12 hours to prepare a transparent and uniform sodium carboxymethyl cellulose aqueous solution;

[0074] Step 2: 5 g of sericin aqueous solution was added to 10 g of sodium carboxymethyl cellulose solution, heated in a water bath at 70° C. on a magnetic stirrer, stirred at 400 rpm for 2 hours, and then stirred at 300 rpm overnight (12 hours) at room temperature for polymerization to obtain a transparent and uniform composite adhesive;

[0075] Step 3: Use the prepared sodium carboxymethyl cellulose solution as a binder and the lithium-rich manganese positive electrode material 0.5Li2MnO3·0.5LiNi 0.33 Co 0.33 Mn 0.33 O2 and conductive agent Super P were mixed into a slurry in a mass ratio of 5:85:10, and the slurry was coated on the aluminum foil current collector with an 800μm scraper. After drying in a vacuum oven at 80℃ for 12h, the lithium-rich manganese-based positive electrode sheet was cut and the product was recorded as CP21@70.

[0076] The positive electrode sheet of Example 1 or Comparative Examples 1-5 is used, a metal Li sheet is used as a reference electrode and a counter electrode, a Celgard-2400 is used as a diaphragm, and the electrolyte is Xinzhoubang 3045I. The assembly is carried out in a glove box filled with argon gas with oxygen and water content less than 0.01ppm. Its electrochemical performance is tested for charge and discharge using a 2025 button battery on a Xinwei test system, and the test voltage window is 2.0-4.8V. The test temperature is 27±1℃, and the first three cycles are activated at a rate of 0.1C (1C=200mAh / g), and the 1C rate cycle is used from the 4th cycle. The performance test results are listed in Table 1.

[0077] Comparative Example 6

[0078] Step 1: 0.05 g of sericin was added to 4.95 g of deionized water, and the mixture was stirred at room temperature for 12 hours to prepare a transparent and uniform sericin aqueous solution; meanwhile, 0.2 g of sodium carboxymethyl cellulose was added to 9.8 g of deionized water, and the mixture was stirred at room temperature for 12 hours to prepare a transparent and uniform sodium carboxymethyl cellulose aqueous solution;

[0079] Step 2: Add 5 g of sericin protein aqueous solution to 10 g of sodium carboxymethyl cellulose solution, heat it in a water bath at 50 °C on a magnetic stirrer, stir at 400 rpm for 2 hours, and then continue to stir at a low speed of 300 rpm overnight (12 h) at room temperature for polymerization to obtain a transparent and uniform composite binder;

[0080] Step 3: Uniformly mix 0.5Li2MnO3·0.5LiNi 0.33 Co 0.33 Mn 0.33 O2, conductive agent SuperP, and the composite binder in a mass ratio of 85:10:5 to make a slurry. Coat the slurry on an aluminum foil current collector with an 800-μm doctor blade, dry it in a vacuum oven at 80 °C for 12 h, and then cut it into pieces to obtain a lithium-rich manganese-based positive electrode sheet. The product is denoted as 1% SP@50.

[0081] Comparative Example 7

[0082] Step 1: Add 0.15 g of sericin protein to 4.85 g of deionized water, stir and mix evenly at room temperature for 12 hours to prepare a transparent and uniform sericin protein aqueous solution; at the same time, add 0.2 g of sodium carboxymethyl cellulose to 9.8 g of deionized water, stir and mix evenly at room temperature for 12 hours to prepare a transparent and uniform sodium carboxymethyl cellulose aqueous solution;

[0083] Step 2: Add 5 g of sericin protein aqueous solution to 10 g of sodium carboxymethyl cellulose solution, heat it in a water bath at 50 °C on a magnetic stirrer, stir at 400 rpm for 2 hours, and then continue to stir at a low speed of 300 rpm overnight (12 h) at room temperature for polymerization to obtain a transparent and uniform composite binder;

[0084] Step 3: Uniformly mix 0.5Li2MnO3·0.5LiNi 0.33 Co 0.33 Mn 0.33 O2, conductive agent SuperP, and the composite binder in a mass ratio of 85:10:5 to make a slurry. Coat the slurry on an aluminum foil current collector with an 800-μm doctor blade, dry it in a vacuum oven at 80 °C for 12 h, and then cut it into pieces to obtain a lithium-rich manganese-based positive electrode sheet. The product is denoted as 3% SP@50.

[0085] The active material loadings and electrochemical performances of Example 1 and Comparative Examples 1-7 of the present invention are shown in Table 1:

[0086] Table 1

[0087]

[0088] According to Table 1, under the same doctor blade and coating process, different binders have a great influence on the loading of active materials on the electrode. In Example 1, a suitable binder can make the loading amount of active materials as high as 16.6 mg / cm 2 , and at the same time, the thickness of the electrode is measured to be as high as 200 μm, realizing the electrochemical reaction under high loading.

[0089] Comparing Example 1 and Comparative Example 1: From Figure 1 and Figure 6 , it can be seen that the introduction of sericin can improve the first-cycle Coulombic efficiency. The first-cycle discharge capacity of the cathode material in Example 1 reaches 280.47 mAh / g. From Figure 2 and Figure 7 , it can be seen that the introduction of sericin improves the cycle stability. The capacity retention rate of the cathode material in Example 1 after 100 cycles at 1C is 84.81%.

[0090] Comparing Example 1, Comparative Example 2 and Comparative Example 3, it can be seen that the introduced sericin contains rich functional groups and can polymerize with the hydroxymethyl on carboxymethyl cellulose. When the concentration is 2 wt%, the appropriate ratio of sericin and carboxymethyl cellulose can reach the optimal concentration of the binder, improving the loading amount of active materials and the electrochemical performance of the electrode at the same time. Comparing Figure 1 , Figure 10 , Figure 12 , it can be seen that the first-cycle discharge specific capacity is the highest and the first-cycle Coulombic efficiency is the highest when the ratio is 2:1. Comparing Figure 2 , Figure 11 , Figure 13 , it can be seen that the capacity retention rate after 100 cycles at 1C is the highest; comparing Comparative Example 2 and Comparative Example 3, although the introduction of sericin can improve the electrochemical performance, when the amount of carboxymethyl cellulose is too small, it will affect the viscosity, and the viscosity is low, resulting in poor binding performance of the binder for the thick electrode, which has a certain impact on the binding performance and toughness of the binder for the thick electrode; when the amount of carboxymethyl cellulose is large, the viscosity of the slurry is high, which will affect the uniformity and smoothness of the slurry during coating.

[0091] Comparing Example 1, Comparative Example 4 and Comparative Example 5, it can be seen that the temperature of water bath heating has a great influence on the polymerization of the binder. Comparing Example 1 and Comparative Example 5, from Figure 17 , it can be seen that too high temperature will cause the change of the polypeptide structure in sericin, which will have a great impact on the capacity as the cycle progresses. Comparing Example 1 and Comparative Example 4, from Figure 15It can be seen that although sericin can improve the first-cycle Coulombic efficiency and the first-cycle discharge specific capacity, when the temperature is relatively low, it is not conducive to the polymerization of various functional groups in sericin and carboxymethyl cellulose, and the unstable structure of the binder leads to relatively poor cycle stability. In Example 1, the heating temperature of 50 °C is conducive to the formation of hydrogen bonds, ionic bonds, and covalent bonds between the two polymers, which can better improve the discharge specific capacity and cycle stability of the battery, and the effect is remarkable.

[0092] Comparing Example 1, Comparative Example 6, and Comparative Example 7, it can be seen that the concentration of the sericin aqueous solution has an impact on both the electrode loading and the electrochemical performance. From Figure 1 , Figure 18 , Figure 20 it can be seen that when the concentration of the sericin aqueous solution is 2%, the first-cycle discharge capacity of the electrode is the highest. From Table 1, it can be seen that when the concentration of the sericin aqueous solution is relatively low, the polymerization of sericin and carboxymethyl cellulose is incomplete, which has a greater impact on the viscosity of the binder, thereby affecting the loading of the active material on the electrode.

[0093] From Table 1 and Example 1, it can be known that when the total concentration of the binder is 2 wt%, when the mass ratio of sericin to carboxymethyl cellulose is 1:2, the electrode has a better loading amount. The electrode prepared through the polymerization process of heating in a water bath at 50 °C for 2 hours has better electrochemical performance. The first-cycle Coulombic efficiency of the battery reaches 83.71%. The battery made of this composite binder has the optimal discharge specific capacity and cycle stability. The first-cycle discharge capacity at 0.1C reaches 280.47 mAh / g, the first-cycle discharge capacity at 1C reaches 204.52 mAh / g, and the capacity retention rate after 100 cycles is as high as 84.81%.

[0094] The above are only specific embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a composite aqueous binder for a high-voltage, high-load positive electrode, characterized in that: The specific steps are as follows: (1) Preparation of sericin solution Adding sericin to deionized water to prepare a sericin aqueous solution; (2) Preparation of sodium carboxymethyl cellulose solution Adding sodium carboxymethyl cellulose into deionized water to prepare a sodium carboxymethyl cellulose aqueous solution; (3) Preparation of high-conductivity lithium-conducting composite binders Take the sericin aqueous solution and add it to the carboxymethyl cellulose aqueous solution, wherein the mass ratio of sodium carboxymethyl cellulose to sericin is 2:1, and heat and stir in a water bath for 2 hours at a heating temperature of 50°C. After the heating and stirring, continue stirring at room temperature overnight for polymerization to obtain a uniform and transparent composite water-based adhesive.

2. The method for preparing a composite aqueous binder for a high-voltage, high-load positive electrode according to claim 1, characterized in that: The mass concentration of the sericin aqueous solution is 2%.

3. The method for preparing a composite aqueous binder for a high-voltage, high-load positive electrode according to claim 1, characterized in that: The concentration of the sodium carboxymethylcellulose aqueous solution is 2%.

4. The method for preparing a composite aqueous binder for a high-voltage, high-load positive electrode according to claim 1, characterized in that: When heated and stirred in a water bath, the stirring speed was 400 rpm.

5. The method for preparing a composite aqueous binder for a high-voltage, high-load positive electrode according to claim 1, characterized in that: When stirring overnight at room temperature, the stirring speed was 300 rpm and the stirring time was 12 h.

6. Use of the composite aqueous binder as claimed in claim 1 as a binder in a positive electrode sheet of a lithium ion battery.

7. The use according to claim 6, characterized in that: The lithium-ion battery positive electrode plate is a lithium-manganese-rich positive electrode plate.

8. The use according to claim 7, characterized in that: The preparation of the positive electrode plate of the lithium ion battery is as follows: The active material, conductive agent and binder are uniformly mixed to form a slurry, which is then coated on an aluminum foil and dried in a vacuum oven at 80° C. for 12 hours to obtain a lithium-rich manganese-based positive electrode sheet.

9. The use according to claim 8, characterized in that: The mass ratio of the active material, the conductive agent and the binder is 85:10:5.

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