A three-dimensional network structure silicon-based negative electrode binder and preparation method thereof, negative electrode sheet and battery

Abstract

In view of the technical problem that silicon expansion in existing silicon-based negative electrodes leads to poor battery cycle performance, the present application provides a three-dimensional network structure silicon-based negative electrode binder and its preparation method, a negative electrode sheet and a battery; the present application provides a three-dimensional network structure silicon-based negative electrode binder, the binder includes an inner core, an intermediate layer and an outermost layer, the inner core is composed of a natural high molecular three-dimensional network polymer with a glass transition temperature of T1, the intermediate layer is composed of a conductive polymer with a glass transition temperature of T2, and the outermost layer is composed of a lithium acrylate copolymer with a glass transition temperature of T3, and T1, T2, and T3 satisfy the following relationship: wherein 40℃≤T1≤100℃, 10℃≤T2≤50℃, and ‑50℃≤T3≤20℃; the three-dimensional network structure silicon-based negative electrode binder provided by the present application has the functions of inhibiting the expansion of silicon-based negative electrodes, improving conductivity, replenishing lithium to participate in film formation, and improving battery cycle performance.

Description

Technical Field

[0001] The invention belongs to the technical field of batteries, and in particular relates to a three-dimensional network structure silicon-based negative electrode binder and a preparation method thereof, a negative electrode sheet and a battery. Background Art

[0002] With the development of new energy electric vehicles, the development of high specific energy, high power and long life negative electrode materials has become one of the research hotspots of lithium-ion batteries. Silicon has attracted extensive attention due to its advantages such as high theoretical specific capacity, low discharge voltage, abundant reserves and low price. However, the volume of silicon expands after charging and discharging, causing the silicon particles to pulverize and even detach from the current collector and lose electrochemical activity, resulting in poor cycle stability, which limits the commercial application of silicon negative electrodes.

[0003] Binder is an important component of the electrode, which plays the role of connecting the electrode active material, conductive agent and current collector. The choice of binder will significantly affect the electrochemical performance of the battery. For the negative electrode binder, the binder usually uses LA133 water-based binder, which has good chemical stability, dispersion properties, etc., and can show good electrochemical properties in traditional carbon material electrodes. However, with the development of silicon-based negative electrodes, the existing water-based binders can no longer meet the current application requirements. During the battery cycle, the silicon in the silicon-based negative electrode expands, resulting in poor battery cycle performance. Summary of the invention

[0004] In order to solve the technical problem that silicon expansion in existing silicon-based negative electrodes leads to poor battery cycle performance, the present application provides a three-dimensional network structure silicon-based negative electrode binder and a preparation method thereof, a negative electrode sheet and a battery.

[0005] In order to solve the above technical problems, the present application provides a three-dimensional network structure silicon-based negative electrode binder, wherein the binder is a capsule unit, including an inner core, an intermediate layer and an outermost layer, wherein the intermediate layer is wrapped around the outer periphery of the inner core, and the outermost layer is wrapped around the outer periphery of the intermediate layer; the inner core is composed of a natural high molecular three-dimensional network polymer with a glass transition temperature of T1, the intermediate layer is composed of a conductive polymer with a glass transition temperature of T2, and the outermost layer is composed of a lithium acrylate copolymer with a glass transition temperature of T3, wherein T1, T2, and T3 satisfy the following relationship:

[0006]

[0007] Among them, 40℃≤T1≤100℃, 10℃≤T2≤50℃, -50℃≤T3≤20℃.

[0008] Preferably, the thickness of the inner core is 5 to 25 nm, the thickness of the middle layer is 10 to 50 nm, and the thickness of the outermost layer is 25 to 70 nm.

[0009] In a second aspect, the present application provides a method for preparing a three-dimensional network structured silicon-based negative electrode binder, comprising the following steps:

[0010] S1: adding a natural polymer material and water into a reaction container, stirring evenly, and then adding a metal salt solution to react to obtain a first mixed solution, and at the same time generating a core of a natural polymer three-dimensional network polymer with a glass transition temperature of T1;

[0011] S2: adding an organic solvent, PAA and PEO to the first mixed solution, performing a first heating reaction, and then adding the first monomer, the second monomer and the initiator, performing a second heating reaction, to obtain a second mixed solution, and simultaneously generating a conductive polymer with a glass transition temperature of T2, and forming the intermediate layer around the inner core;

[0012] S3: adding a third monomer, a fourth monomer and an initiator to the second mixed solution, performing a third heating reaction, and generating a lithiated acrylate copolymer having a glass transition temperature of T3; forming the outermost layer on the periphery of the intermediate layer, and preparing a binder;

[0013] The T1, T2, and T3 satisfy the following relationship:

[0014]

[0015] Among them, 40℃≤T1≤100℃, 10℃≤T2≤50℃, -50℃≤T3≤20℃.

[0016] Preferably, in step S1, 10 to 50 parts of the natural polymer material and 50 to 200 parts of water are added to the reaction container; the stirring time after adding the natural polymer and water is 24 to 48 hours; the reaction time after adding the metal salt solution is 2 to 4 hours;

[0017] The natural polymer material includes one or more of sodium alginate, guar gum, chitosan, carboxymethyl cellulose and gum arabic.

[0018] Preferably, the preparation steps of the metal salt solution are as follows:

[0019] Dissolve 10 to 30 parts of a metal salt in 100 to 200 parts of deionized water, mix well, and obtain a metal salt solution;

[0020] The metal salt includes one or more of nickel sulfate, cupric chloride, zinc sulfate, copper sulfate, zinc chloride, nickel chloride, ferric chloride, and ferric sulfate.

[0021] Preferably, in step S2, the organic solvent added is 50-100 parts, the PAA is 20-50 parts, the PEO is 10-30 parts, the first monomer is 2-10 parts, the second monomer is 10-20 parts, and the initiator is 0.5-2 parts;

[0022] The molecular weight of the PAA is 10 3 ~10 5 ; The molecular weight of the PEO is 10 3 ~10 6 ;

[0023] The organic solvent includes one or more of toluene, tetrahydrofuran, dimethyl sulfoxide, and chloroform;

[0024] The first monomer includes one or both of aniline or polystyrene sulfonate;

[0025] The second monomer includes one or more of styrene, methyl methacrylate, and butyl acrylate.

[0026] Preferably, the first heating reaction temperature is 50-80°C, and the reaction time is 12-24 hours; the second heating reaction temperature is 80-90°C, and the reaction time is 6-12 hours.

[0027] Preferably, in step S3, the third monomer added is 5 to 10 parts, the fourth monomer is 20 to 50 parts, and the initiator is 0.5 to 2 parts; the third heating reaction temperature is 80 to 85° C., and the reaction time is 6 to 24 hours;

[0028] The third monomer includes one or more of acrylic acid, methacrylic acid, butyl acrylate, and tert-butyl acrylate; the fourth monomer includes one or more of lithium acrylate, lithium methacrylate, lithium carbonate, and lithium hydroxide.

[0029] Preferably, the initiator includes one or more of sodium persulfate and ammonium persulfate.

[0030] In a third aspect, the present application provides a negative electrode sheet, comprising a negative electrode material layer, wherein the negative electrode material layer comprises a silicon-based negative electrode material, a conductive agent and a binder, wherein the binder is prepared by the preparation method of the three-dimensional network structure silicon-based negative electrode binder or the three-dimensional network structure silicon-based negative electrode binder described above.

[0031] In a fourth aspect, the present application provides a battery, comprising a positive electrode sheet, a negative electrode sheet and an electrolyte, wherein the negative electrode is the negative electrode sheet described above.

[0032] Beneficial effects:

[0033] Compared with the prior art, the three-dimensional network structure silicon-based negative electrode binder provided in the present application includes a natural polymer three-dimensional network polymer with a glass transition temperature of T1, a conductive polymer with a glass transition temperature of T2, and a lithium acrylate copolymer with a glass transition temperature of T3, wherein 40°C≤T1≤100°C, 10°C≤T2≤50°C, and -50°C≤T3≤20°C; and T1, T2, and T3 satisfy the following relationship: Natural macromolecular three-dimensional network polymers have strong adhesion. Conductive polymers not only have adhesion and self-healing ability, but also have high conductivity. They have the ability to self-heal when the binder is mechanically damaged, and can also improve the conductivity of the binder, thereby improving the conductivity of the negative electrode material layer and improving the cycle performance of the battery. Lithiated acrylate copolymers not only have adhesion, but also have the function of replenishing lithium. During the battery charging and discharging process, the lithium in the binder will be deintercalated and participate in the formation of the negative electrode SEI film, playing a role in replenishing lithium. The three-dimensional network structure silicon-based negative electrode binder provided in this application has the function of inhibiting the expansion of the silicon-based negative electrode, improving conductivity, replenishing lithium to participate in film formation, and improving the battery cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a schematic diagram of the structure of a three-dimensional network structure silicon-based negative electrode binder;

[0035] 1. Natural polymer three-dimensional network polymer; 2. Conductive polymer; 3. Lithium acrylate copolymer. DETAILED DESCRIPTION

[0036] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0037] like Figure 1 As shown, the present application provides a three-dimensional network structure silicon-based negative electrode binder, the binder is a capsule unit, including an inner core, an intermediate layer and an outermost layer, the intermediate layer is wrapped around the outer core, and the outermost layer is wrapped around the outer core; the inner core is composed of a natural polymer three-dimensional network polymer 1 with a glass transition temperature of T1, the intermediate layer is composed of a conductive polymer 2 with a glass transition temperature of T2, and the outermost layer is composed of a lithium acrylate copolymer 3 with a glass transition temperature of T3, and T1, T2, and T3 satisfy the following relationship:

[0038]

[0039] Among them, 40℃≤T1≤100℃, 10℃≤T2≤50℃, -50℃≤T3≤20℃.

[0040] The theoretical specific capacity of graphite negative electrode is only 372mAh / g, which can no longer meet the requirements of today's lithium-ion batteries for high specific energy. The theoretical specific capacity of silicon negative electrode material can reach 4200mAh / g, which is one of the promising negative electrode materials. However, the volume expansion of Si negative electrode in the charged state can reach 300%, and the large expansion reduces the cycle performance of the battery. In response to this problem, the inventors have conducted extensive research and started from the binder direction to prepare a three-dimensional network structure silicon-based negative electrode binder to inhibit the expansion of the silicon-based negative electrode. The binder is conductive and can improve the conductivity of the silicon-based negative electrode, which has the effect of improving the cycle performance of the silicon-based negative electrode.

[0041] Specifically, in the preparation process of the three-dimensional network structure silicon-based negative electrode binder, a natural high molecular three-dimensional network polymer 1 with a glass transition temperature of T1 is generated, and the temperature range of T1 is 40-100°C, such as T1 can be 40°C, 43°C, 48°C, 50°C, 55°C, 57°C, 60°C, 63°C, 65°C, 68°C, 70°C, 72°C, 75°C, 77°C, 80°C, 85°C, 88°C, 90°C, 95°C, 100°C, etc. The natural high molecular three-dimensional network polymer 1 has strong adhesion, and can bond the negative electrode active material, the conductive agent, and the current collector together, thereby improving the adhesion between the negative electrode material layer and the current collector. The glass transition temperature T2 of the conductive polymer 2 is 10°C to 50°C, such as 10°C, 15°C, 18°C, 22°C, 27°C, 30°C, 34°C, 38°C, 40°C, 42°C, 47°C, 50°C, etc. The conductive polymer 2 not only has adhesiveness and self-healing ability, but also has high conductivity, has the ability to self-heal when the binder is mechanically damaged, and can also improve the conductivity of the binder, thereby improving the conductivity of the negative electrode material layer, thereby improving the cycle performance of the battery. The glass transition temperature T3 of the lithiated acrylate copolymer 3 is -50°C to 20°C, such as -50°C, -43°C, -48°C, -35°C, -30°C, -27°C, -24°C, -22°C, -19°C, -15°C, -10°C, -5°C, -8°C, -7°C, -2°C, 0°C, 4°C, 9°C, 12°C, 15°C, 18°C, 20°C, etc. The lithiated acrylate copolymer 3 not only has adhesive properties, but also has the function of replenishing lithium. During the battery charging and discharging process, the lithium in the binder will be deintercalated and participate in the formation of the negative electrode SEI film, playing a role in replenishing lithium. It should be noted that T1, T2, and T3 must satisfy the following relationship: The prepared binder has the function of inhibiting the expansion of silicon-based negative electrode, improving conductivity, replenishing lithium to participate in film formation, and improving battery cyclability. If the relationship between T1, T2, and T3 is The conductivity, adhesion and ability of the binder to inhibit the expansion of the silicon-based negative electrode are reduced, and it cannot effectively play a role in improving the battery cycle performance.

[0042] In some embodiments, the thickness of the inner core is 5 to 25 nm, the thickness of the middle layer is 10 to 50 nm, and the thickness of the outermost layer is 25 to 70 nm.

[0043] In a second aspect, the present application provides a method for preparing a three-dimensional network structured silicon-based negative electrode binder, comprising the following steps:

[0044] S1: adding a natural polymer material and water into a reaction container, stirring evenly, and then adding a metal salt solution to obtain a first mixed solution, and at the same time generating a core of a natural polymer three-dimensional network polymer 1 having a glass transition temperature of T1;

[0045] S2: adding an organic solvent, PAA and PEO to the first mixed solution, performing a first heating reaction, and then adding the first monomer, the second monomer and the initiator, performing a second heating reaction, to obtain a second mixed solution, and simultaneously generating a conductive polymer 2 having a glass transition temperature of T2, and forming the intermediate layer around the inner core;

[0046] S3: adding the third monomer, the fourth monomer and the initiator to the second mixed solution, performing a third heating reaction, and generating a lithium acrylate copolymer 3 having a glass transition temperature of T3; forming the outermost layer on the periphery of the intermediate layer to prepare a negative electrode binder

[0047] The T1, T2, and T3 satisfy the following relationship:

[0048]

[0049] Among them, 40℃≤T1≤100℃, 10℃≤T2≤50℃, -50℃≤T3≤20℃.

[0050] In step S1, natural polymer materials, water, and metal salt solutions are added, and the metal ions interact with the natural polymers to achieve cross-linking, thereby improving the adhesion of the binder and providing a strong adhesive force on the negative electrode material. In step S2, organic solvents, PAA, and PEO are added, and PEO and PAA undergo polymerization reactions, giving the binder the ability to enhance spontaneous healing of the binder after mechanical damage. The first monomer, the second monomer, and the initiator react with the polymer generated by PAA and PEO to form a conductive polymer 2 with conductivity and adhesion. In step S3, the third monomer, the fourth monomer, and the initiator are added to react to form a lithium acrylate copolymer 3 with adhesion and lithium supplementation.

[0051] In some embodiments, in step S1, the natural polymer material is added to the reaction container in an amount of 10 to 50 parts, and the water is added in an amount of 50 to 200 parts; the stirring time after adding the natural polymer and water is 24 to 48 hours; the reaction time after adding the metal salt solution is 2 to 4 hours;

[0052] The natural polymer material includes one or more of sodium alginate, guar gum, chitosan, carboxymethyl cellulose and gum arabic.

[0053] The binder needs to have adhesiveness. In this application, 10 to 50 parts of natural polymer materials are added, and a metal salt solution is used as a cross-linking agent to perform a cross-linking reaction to generate a natural polymer three-dimensional network polymer 1 with strong adhesive force. The amount of natural polymer materials added can be 10 parts, 15 parts, 20 parts, 25 parts, 30 parts, 35 parts, 40 parts, 45 parts, 50 parts, etc. Water plays a role in dissolving the natural polymer materials.

[0054] In some embodiments, the metal salt solution is prepared as follows:

[0055] Dissolve 10 to 30 parts of a metal salt in 100 to 200 parts of deionized water, mix well, and obtain a metal salt solution;

[0056] The metal salt includes one or more of nickel sulfate, cupric chloride, zinc sulfate, copper sulfate, zinc chloride, nickel chloride, ferric chloride, and ferric sulfate.

[0057] The metal salt mainly plays a cross-linking role, and the metal ions and the natural polymer materials undergo a complex cross-linking reaction to generate a strong adhesive natural polymer three-dimensional network polymer 1. The amount of the metal salt can be 10 parts, 13 parts, 15 parts, 18 parts, 20 parts, 22 parts, 25 parts, 27 parts, 29 parts, 30 parts, etc.

[0058] In some embodiments, in step S2, the organic solvent added is 50-100 parts, the PAA is 20-50 parts, and the PEO is 10-30 parts;

[0059] The molecular weight of the PAA is 10 3 ~10 5 ; The molecular weight of the PEO is 10 3 ~10 6 ; The organic solvent includes one or more of toluene, tetrahydrofuran, dimethyl sulfoxide, and chloroform.

[0060] PAA and PEO are dissolved in an organic solvent, and PAA and PEO undergo polymerization in the solvent to form polymers with adhesiveness and self-healing ability. PAA and PEO can also interact with metal ions in metal salt solutions to enhance the self-healing properties of the adhesive and form polymers with strong self-healing ability. The content of PAA is 20 to 50 parts, such as 20, 24, 28, 30, 34, 36, 42, 48, 50, etc., and different amounts of PAA are added as needed. The amount of PEO is 10 to 30 parts, such as 10, 14, 15, 18, 20, 22, 26, 28, 30, etc. The organic solvent plays a role in dissolving PAA and PEO, facilitating the cross-linking reaction of PAA and PEO, and the content is 50 to 100 parts, such as 50, 60, 70, 80, 90, 100, etc.

[0061] In some embodiments, the first monomer is 2 to 10 parts, the second monomer is 10 to 20 parts, and the initiator is 0.5 to 2 parts; the first monomer includes one or both of aniline or polystyrene sulfonate; the second monomer includes one or more of styrene, methyl methacrylate, and butyl acrylate.

[0062] The first monomer, the second monomer and the initiator react with the polymer generated by the polymerization of PAA and PEO to undergo a cross-linking reaction to generate a conductive polymer 2 with strong adhesion, strong self-healing ability and strong conductivity, thereby improving the conductivity of the binder and the cycle stability of the battery. The first monomer is 2 to 10 parts, preferably 3 to 8 parts, and more preferably 4 to 7 parts, such as the first monomer can be 2 parts, 3 parts, 4 parts, 5 parts, 6 parts, 7 parts, 8 parts, 9 parts, 10 parts, etc. The second monomer is 10 to 20 parts, preferably 12 to 18 parts, and more preferably 14 to 17 parts; for example, the content of the second monomer can be 10, 12, 14, 15, 16, 17, 18, 19, 20, etc.

[0063] In some embodiments, the first heating reaction temperature is 50-80°C, and the reaction time is 12-24 hours; the second heating reaction temperature is 80-90°C, and the reaction time is 6-12 hours.

[0064] The first heating reaction temperature can be 50°C, 53°C, 56°C, 59°C, 60°C, 62°C, 65°C, 67°C, 69°C, 70°C, 72°C, 75°C, 76°C, 79°C, 80°C, etc. Different heating temperatures can be selected according to the amount of PAA and PEO added, and different heating times can be selected in the same way. Different heating times can also be selected for the second heating reaction temperature and reaction time, such as the second heating reaction temperature can be 80°C, 81°C, 82°C, 83°C, 84°C, 85°C, 86°C, 87°C, 88°C, 89°C, 90°C, etc.

[0065] In some embodiments, in step S3, the third monomer added is 5 to 10 parts, the fourth monomer is 20 to 50 parts, and the initiator is 0.5 to 2 parts; the third heating reaction temperature is 80 to 85° C., and the reaction time is 6 to 24 hours;

[0066] The third monomer includes one or more of acrylic acid, methacrylic acid, butyl acrylate, and tert-butyl acrylate; the fourth monomer includes one or more of lithium acrylate, lithium methacrylate, lithium carbonate, and lithium hydroxide.

[0067] Specifically, the fourth monomer includes a lithium salt, and the third monomer, the fourth monomer, and the initiator react to obtain a lithiated acrylate copolymer 3 having adhesiveness and lithium replenishing effects. In the prepared binder, part of the lithium can be released from the binder structure during the battery charging and discharging process, and participate in the SEI formation reaction, thereby reducing the loss of active lithium in the positive electrode and playing a certain lithium replenishing role.

[0068] The third monomer is 5 to 10 parts, and the specific third monomer can be 5 parts, 6 parts, 7 parts, 8 parts, 9 parts, 10 parts, etc. The fourth monomer is 20 to 50 parts, such as the fourth monomer can be an integer such as 20 parts, 22 parts, 25 parts, 28 parts, 29 parts, 30 parts, 31 parts, 35 parts, 38 parts, 40 parts, 42 parts, 45 parts, 46 parts, 48 ​​parts, 50 parts, etc., and can also be a decimal. In some embodiments, the initiator includes one or more of sodium persulfate and ammonium persulfate.

[0069] The initiator plays the role of initiating the monomer reaction. For example, the initiator initiates the first monomer and the second monomer to participate in the chemical reaction; the initiator initiates the third monomer and the fourth monomer to react.

[0070] It should be noted that the added amounts of the natural polymer material, metal salt, first monomer, second monomer, third monomer, fourth monomer, PAA, PEO, initiator, water, organic solvent, etc. described above may be parts by weight or molar amounts, etc., preferably parts by weight.

[0071] The three-dimensional network structure silicon-based negative electrode binder provided in the present application, the natural polymer three-dimensional network polymer 1 is conducive to the adhesion with the negative electrode active material, the conductive agent, and the current collector, and enhances the adhesion between the negative electrode material layer and the current collector; the conductive polymer 2 has strong self-healing ability, adhesion and conductivity, and has the function of inhibiting the expansion of the silicon-based negative electrode and improving the conductivity of the binder; the lithiated acrylate copolymer 3 contains lithium and has a lithium replenishing effect. During the battery charging and discharging process, part of the lithium can be released from the binder and participate in the formation of the SEI film at the negative electrode interface, reducing the consumption of the positive electrode active material and playing a certain lithium replenishing role.

[0072] The three-dimensional network structure silicon-based negative electrode binder provided in the present application has strong adhesion, conductivity, strong self-healing ability, chemical stability, thermal stability, strong mechanical properties, processing properties and dispersion properties, and also has a lithium supplement effect.

[0073] In a third aspect, the present application provides a negative electrode sheet, comprising a negative electrode material layer, wherein the negative electrode material layer comprises a silicon-based negative electrode material, a conductive agent and a binder, wherein the binder comprises a binder prepared by the above-mentioned method for preparing the three-dimensional network structure silicon-based negative electrode binder.

[0074] Specifically, the negative electrode active material is a silicon-based negative electrode material, such as silicon carbide, silicon oxide, silicon oxide compounds, silicon lithium compounds, etc. The negative electrode sheet provided in the present application includes a three-dimensional network structure silicon-based negative electrode binder, which can inhibit the expansion of the silicon-based negative electrode material, enhance the bonding force of the negative electrode material layer, improve the conductivity of the negative electrode sheet, and improve the cycle performance of the battery.

[0075] In a fourth aspect, the present application provides a battery, comprising a positive electrode sheet, a negative electrode sheet and an electrolyte, wherein the negative electrode is the negative electrode sheet described above.

[0076] The three-dimensional network structure silicon-based negative electrode binder provided in the present application is applied to a battery and can improve the cycle performance of the battery during the battery charge and discharge process.

[0077] The specific embodiments of the present invention will be further explained below through examples, but it does not mean that the protection scope of the present invention is limited to the scope described in the examples.

[0078] Example 1

[0079] Preparation of three-dimensional network structure silicon-based negative electrode binder:

[0080] S1: adding 10 parts of sodium alginate and 100 parts of water into a reaction container, stirring evenly, and then adding a metal salt solution to react to obtain a first mixed solution, and at the same time generating a natural high molecular three-dimensional network polymer 1 having a glass transition temperature T1 of 45°C;

[0081] The preparation method of the metal salt solution is as follows: take 10 parts of copper chloride, dissolve it in 100 parts of deionized water, and obtain the metal salt solution after the dissolution is completed.

[0082] S2: 60 parts of toluene solution, 20 parts of PAA with a molecular weight of 1000, and 10 parts of PEO with a molecular weight of 1000 are added to the first mixed solution, and then the temperature is raised to 60°C and the reaction time is 15 hours; then 3 parts of the first monomer aniline, 12 parts of the second monomer styrene, and 1 part of the initiator sodium persulfate are added, and a second heating reaction is carried out at a temperature of 80°C and a reaction time of 8 hours to obtain a second mixed solution, and at the same time, a conductive polymer 2 with a glass transition temperature T2 of 10°C is generated.

[0083] S3: Add 5 parts of the third monomer acrylic acid, 20 parts of the fourth monomer lithium acrylate and 1 part of the initiator sodium persulfate to the second mixed solution, and carry out a third heating reaction at a heating temperature of 80°C for 10 hours, and simultaneously generate a lithiated acrylate copolymer 3 having a glass transition temperature T3 of -50°C.

[0084] Example 2

[0085] The difference between Example 2 and Example 1 is that step S1 is different, and the rest is the same, as follows:

[0086] S1: adding 30 parts of chitosan and 100 parts of water into a reaction container, stirring evenly, and then adding a metal salt solution to react to obtain a first mixed solution, and at the same time generating a natural high molecular three-dimensional network polymer 1 with a glass transition temperature T1 of 75°C;

[0087] The preparation method of the metal salt solution is as follows: take 22 parts of copper sulfate, dissolve it in 100 parts of deionized water, and obtain the metal salt solution after the dissolution is completed.

[0088] Example 3

[0089] The difference between Example 3 and Example 1 is that step S1 is different, and the rest is the same, as follows:

[0090] S1: Add 50 parts of gum arabic and 100 parts of guar gum to a reaction container, stir evenly, then add a metal salt solution, react to obtain a first mixed solution, and simultaneously generate a natural high molecular three-dimensional network polymer 1 having a glass transition temperature T1 of 100° C.;

[0091] The preparation method of the metal salt solution is as follows: 30 parts of zinc chloride are dissolved in 100 parts of deionized water, and the metal salt solution is obtained after the dissolution is completed.

[0092] Example 4

[0093] The difference between Example 4 and Example 1 is that step S2 is different, and the rest is the same, as follows:

[0094] S2: 100 parts of dimethyl sulfoxide solution, 35 parts of PAA with a molecular weight of 20,000, and 20 parts of PEO with a molecular weight of 1,000 are added to the first mixed solution, and then the temperature is raised to 80°C and the reaction time is 20 hours; then 6 parts of the first monomer aniline, 15 parts of the second monomer styrene, and 1.2 parts of the initiator sodium persulfate are added, and a second heating reaction is carried out at a temperature of 80°C and a reaction time of 8 hours to obtain a second mixed solution, and at the same time, a conductive polymer 2 with a glass transition temperature T2 of 35°C is generated.

[0095] Example 5

[0096] The difference between Example 5 and Example 1 is that step S2 is different, and the rest is the same, as follows:

[0097] S2: 100 parts of dimethyl sulfoxide solution, 50 parts of PAA with a molecular weight of 20,000, and 30 parts of PEO with a molecular weight of 1,000 are added to the first mixed solution, and then the temperature is raised to 80°C and the reaction time is 20 hours; then 10 parts of the first monomer polystyrene sulfonate, 20 parts of the second monomer styrene, and 2 parts of the initiator sodium persulfate are added, and a second heating reaction is carried out at 90°C and the reaction time is 8 hours to obtain a second mixed solution, and at the same time, a conductive polymer 2 with a glass transition temperature T2 of 50°C is generated.

[0098] Example 6

[0099] The difference between Example 6 and Example 1 is that step S3 is different, and the rest is the same, as follows:

[0100] S3: Add 7 parts of the third monomer methacrylic acid, 32 parts of the fourth monomer lithium methacrylate and 1 part of the initiator ammonium persulfate to the second mixed solution, and carry out a third heating reaction at a heating temperature of 82° C. for 20 hours, and simultaneously generate a lithiated acrylate copolymer 3 having a glass transition temperature T3 of -10° C.

[0101] Example 7

[0102] The difference between Example 7 and Example 1 is that step S3 is different, and the rest is the same, as follows:

[0103] S3: Add 10 parts of the third monomer butyl acrylate, 48 parts of the fourth monomer lithium carbonate and 2 parts of the initiator ammonium persulfate to the second mixed solution, and carry out a third heating reaction at a heating temperature of 85°C for 24 hours, and simultaneously generate a lithiated acrylate copolymer 3 having a glass transition temperature T3 of 20°C.

[0104] Comparative Example 1

[0105] The difference between Comparative Example 1 and Example 1 is that 9 parts of the third monomer acrylic acid and 35 parts of the fourth monomer lithium acrylate are added, and the rest is the same as Example 1.

[0106] Comparative Example 2

[0107] The difference between Comparative Example 2 and Example 1 is that step S1 is different: 8 parts of sodium alginate are added, and the rest is the same as Example 1; a natural high molecular three-dimensional network polymer 1 with a glass transition temperature T1 of 35° C. is obtained.

[0108] Comparative Example 3

[0109] The difference between Comparative Example 3 and Example 1 is that step S1 is different: 60 parts of sodium alginate are added; during the preparation of the metal salt solution, 40 parts of copper chloride and 300 parts of deionized water are added, and the rest is the same as Example 1; a natural polymer three-dimensional network polymer 1 with a glass transition temperature T1 of 105°C is obtained.

[0110] Comparative Example 4

[0111] The difference between Comparative Example 4 and Example 1 is that step S2 is different: 1 part of the first monomer aniline and 8 parts of the second monomer styrene are added, and the rest is the same as Example 1; a conductive polymer 2 with a glass transition temperature T2 of 5° C. is obtained.

[0112] Comparative Example 5

[0113] The difference between Comparative Example 5 and Example 1 is that step S2 is different: 15 parts of the first monomer aniline and 23 parts of the second monomer styrene are added, and the rest is the same as Example 1; a conductive polymer 2 with a glass transition temperature T2 of 52° C. is obtained.

[0114] Comparative Example 6

[0115] The difference between Comparative Example 6 and Example 1 is that step S3 is different: 2 parts of the third monomer acrylic acid and 18 parts of the fourth monomer lithium acrylate are added, and the rest is the same as Example 1; a lithiated acrylate copolymer 3 with a glass transition temperature T3 of -52°C is obtained.

[0116] Comparative Example 7

[0117] The difference between Comparative Example 6 and Example 1 is that step S3 is different: 14 parts of the third monomer acrylic acid and 60 parts of the fourth monomer lithium acrylate are added, and the rest is the same as Example 1; a lithiated acrylate copolymer 3 with a glass transition temperature T3 of 23° C. is obtained.

[0118] Comparative Example 8

[0119] The difference between Comparative Example 8 and Example 1 is that there is no S3 step; the prepared binder only contains the natural high molecular three-dimensional network polymer 1 and the conductive polymer 2.

[0120] Comparative Example 9

[0121] The difference between Comparative Example 8 and Example 1 is that there is no S2 step; the prepared binder only contains the natural high molecular three-dimensional network polymer 1 and the lithiated acrylate copolymer 3.

[0122] Examples 1-7 and Comparative Examples 1-9

[0123] Preparation of negative electrode

[0124] Silicon carbide is selected as the negative electrode active material, carbon nanotubes are selected as the conductive agent, and the binder is the binder prepared by Example 1-7 and Comparative Example 1-9, which are mixed in a mass ratio of 97.7:1.1:1.2, and then deionized water is added and stirred to disperse to obtain a negative electrode slurry, and the negative electrode slurry is coated on the surface of the copper current collector and dried to obtain a negative electrode sheet.

[0125] The positive electrode sheet is prepared according to the prior art and will not be described in detail here.

[0126] Lithium battery preparation:

[0127] The positive electrode sheet, negative electrode sheet, separator and aluminum-plastic film prepared as above are made into a battery, and then the processes of liquid injection and formation are carried out, and finally the electrical performance of the battery is tested.

[0128] Battery performance test:

[0129] 25℃ normal temperature cycle test:

[0130] The battery prepared above was placed at a room temperature of 25°C, charged at a constant current of 1C to 4.2V, then charged at a constant voltage of 4.2V, with a cut-off current of 0.05C, and then discharged at a constant current of 1C to 3.0V, and this cycle was repeated for 500 cycles;

[0131] Calculate the 500-cycle capacity retention rate = the 500th-cycle discharge capacity / the average value of the 1st-3rd-cycle discharge capacity × 100%. See Table 1 for specific test results.

[0132] Table 1 Glass transition temperature parameters and electrical properties of Examples 1-7 and Comparative Examples 1-9

[0133]

[0134] From Table 1, it can be seen that when comparing Examples 1-7 with Comparative Example 1, the relationship between T1, T2, and T3 is The battery cycle capacity retention rate is reduced; it is speculated that the conductivity and adhesion of the binder are reduced, and the ability to inhibit the expansion of the silicon-based negative electrode is reduced, thereby affecting the battery cycle performance. Comparing Examples 1-7 with Comparative Examples 2-7, the relationship between T1, T2, and T3 is However, the glass transition temperature T1 of the natural polymer three-dimensional network polymer 1 does not meet the range of 40 to 100°C, the glass transition temperature T2 of the conductive polymer 2 is not within the range of 10 to 50°C, and the glass transition temperature T3 of the lithium acrylate copolymer 3 does not meet the range of -50 to 20°C. The prepared battery cycle capacity retention rate is basically less than 78%; this indicates that the prepared three-dimensional network structure silicon-based negative electrode binder, even if the glass transition temperatures of T1, T2, and T3 in the obtained binder satisfy the relationship If the glass transition temperature of one layer is not within the range specified in this application, the conductivity or adhesion of the conductive agent is reduced. During the battery charging and discharging process, the self-healing ability and conductivity of the binder are reduced, and the silicon-based negative electrode expansion cannot be better suppressed, thereby reducing the cycle performance of the battery.

[0135] Comparing Examples 1-7 with Comparative Examples 8 and 9, the binder in Comparative Example 8 has a two-layer structure of a natural polymer three-dimensional network polymer 1 and a conductive polymer 2, and the binder in Comparative Example 9 has a two-layer structure of a natural polymer three-dimensional network polymer 1 and a lithium acrylate copolymer 3. The prepared battery has a cycle performance of less than 77%, indicating that the three-layer structure of the binder in Examples 1-7 is synergistic with each other, can improve the conductivity and adhesion of the binder, has good self-healing ability when the binder is mechanically damaged, and also has a lithium replenishing effect. The three-layer structure cooperates with each other to jointly improve the battery's cycle capacity retention rate and enhance the battery's cycle performance.

[0136] 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 and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A three-dimensional network structure silicon-based negative electrode binder, characterized in that: The binder is a capsule unit, including an inner core, an intermediate layer and an outermost layer, wherein the intermediate layer is wrapped around the outer core, and the outermost layer is wrapped around the outer core; the inner core is composed of a natural high molecular three-dimensional network polymer with a glass transition temperature of T1, the intermediate layer is composed of a conductive polymer with a glass transition temperature of T2, and the outermost layer is composed of a lithium acrylate copolymer with a glass transition temperature of T3, wherein T1, T2, and T3 satisfy the following relationship: Among them, 40℃≤T1≤100℃, 10℃≤T2≤50℃, -50℃≤T3≤20℃; The natural macromolecular three-dimensional network polymer is obtained by cross-linking reaction between metal salt and natural macromolecular material; the natural macromolecular material includes one or more of sodium alginate, guar gum, chitosan, carboxymethyl cellulose and gum arabic.

2. The three-dimensional network structure silicon-based negative electrode binder according to claim 1, characterized in that: The thickness of the inner core is 5-25 nm, the thickness of the middle layer is 10-50 nm, and the thickness of the outermost layer is 25-70 nm.

3. A method for preparing the three-dimensional network structure silicon-based negative electrode binder according to any one of claims 1 to 2, characterized in that: The following steps are involved: S1: adding a natural polymer material and water into a reaction container, stirring evenly, and then adding a metal salt solution to react to obtain a first mixed solution, and at the same time generating a core of a natural polymer three-dimensional network polymer with a glass transition temperature of T1; S2: adding an organic solvent, PAA and PEO to the first mixed solution, performing a first heating reaction, and then adding the first monomer, the second monomer and the initiator, performing a second heating reaction, to obtain a second mixed solution, and simultaneously generating a conductive polymer with a glass transition temperature of T2, and forming the intermediate layer around the inner core; S3: adding a third monomer, a fourth monomer and an initiator to the second mixed solution, performing a third heating reaction, and generating a lithiated acrylate copolymer having a glass transition temperature of T3, and forming the outermost layer at the periphery of the intermediate layer; preparing a binder; The T1, T2, and T3 satisfy the following relationship: Among them, 40℃≤T1≤100℃, 10℃≤T2≤50℃, -50℃≤T3≤20℃.

4. The method for preparing a three-dimensional network structure silicon-based negative electrode binder according to claim 3, characterized in that: In step S1, 10 to 50 parts of the natural polymer material and 50 to 200 parts of water are added to the reaction container; the stirring time after adding the natural polymer and water is 24 to 48 hours; the reaction time after adding the metal salt solution is 2 to 4 hours; The natural polymer material includes one or more of sodium alginate, guar gum, chitosan, carboxymethyl cellulose and gum arabic.

5. The method for preparing the three-dimensional network structure silicon-based negative electrode binder according to claim 3, characterized in that: The preparation steps of the metal salt solution are as follows: Dissolve 10-30 parts of metal salt in 100-200 parts of deionized water, mix well, and obtain a metal salt solution; The metal salt includes one or more of nickel sulfate, cupric chloride, zinc sulfate, copper sulfate, zinc chloride, nickel chloride, ferric chloride, and ferric sulfate.

6. The method for preparing the three-dimensional network structure silicon-based negative electrode binder according to claim 3, characterized in that: In step S2, the organic solvent added is 50-100 parts, the PAA is 20-50 parts, the PEO is 10-30 parts, the first monomer is 2-10 parts, the second monomer is 10-20 parts, and the initiator is 0.5-2 parts; The molecular weight of the PAA is 10 3 ~10 5 ; The molecular weight of the PEO is 10 3 ~10 6 ; The organic solvent includes one or more of toluene, tetrahydrofuran, dimethyl sulfoxide, and chloroform; The first monomer includes one or both of aniline or polystyrene sulfonate; The second monomer includes one or more of styrene, methyl methacrylate, and butyl acrylate; The first heating reaction temperature is 50~80℃, and the reaction time is 12~24h; the second heating reaction temperature is 80~90℃, and the reaction time is 6~12h.

7. The method for preparing the three-dimensional network structure silicon-based negative electrode binder according to claim 3, characterized in that: In step S3, 5 to 10 parts of the third monomer, 20 to 50 parts of the fourth monomer, and 0.5 to 2 parts of the initiator are added; the third heating reaction temperature is 80 to 85° C., and the reaction time is 6 to 24 hours; The third monomer includes one or more of acrylic acid, methacrylic acid, butyl acrylate, and tert-butyl acrylate; the fourth monomer includes one or more of lithium acrylate, lithium methacrylate, lithium carbonate, and lithium hydroxide.

8. The method for preparing the three-dimensional network structure silicon-based negative electrode binder according to claim 3, characterized in that: The initiator includes one or more of sodium persulfate and ammonium persulfate.

9. A negative electrode sheet, characterized in that: The negative electrode sheet includes a negative electrode material layer, and the negative electrode material layer includes a silicon-based negative electrode material, a conductive agent and a binder. The binder is prepared by the preparation method of the three-dimensional network structure silicon-based negative electrode binder according to any one of claims 3-8 or the three-dimensional network structure silicon-based negative electrode binder according to any one of claims 1-2.

10. A battery, characterized in that: The invention comprises a positive electrode sheet, a negative electrode sheet and an electrolyte, wherein the negative electrode sheet is the negative electrode sheet according to claim 9.

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