Conductive Adhesive and Its Preparation Method, Silicon Anode, Lithium Battery and Vehicle

Abstract

The present application discloses a conductive binder, a preparation method thereof, a silicon negative electrode, a lithium battery and a vehicle. The structural formula of the conductive binder is as follows: The imidazole main chain of the binder in the present application is connected with carboxyl groups, PEG segments and polyaniline segments, so that the conductive binder has excellent adhesion performance, ion conduction performance and electrical conductivity. It is beneficial to improve the stability of silicon particles and adapt to the volume change of silicon particles, and at the same time is beneficial to conduct lithium ions; and it is beneficial to keep the silicon negative electrode in electrical connection all the time, thereby improving the cycle service life of the silicon negative electrode.

Description

Technical Field

[0001] The present invention generally relates to the technical field of lithium batteries, and particularly relates to a conductive binder, a preparation method thereof, a silicon negative electrode, a lithium battery and a vehicle. Background Art

[0002] With the application of lithium-ion batteries in hybrid vehicles, pure electric vehicles and energy storage devices, the development of high-energy-density batteries has become the focus of research. The theoretical capacity of the silicon negative electrode is as high as 4200 mAh / g, which is much higher than that of traditional graphite-based negative electrode materials. It is considered to be a good negative electrode material for the development of high-energy-density batteries. However, during the cycling process, the silicon material will undergo significant volume changes, causing the silicon particles to pulverize and separate from the conductive agent or current collector, making some silicon particles lose electrical connection and become "dead" silicon, thus leading to a rapid decay of the battery capacity.

[0003] The existing silicon negative electrode is composed of silicon active material, conductive agent and binder. Among them, high molecular compounds are usually used as the binder to maintain the structural stability of the silicon electrode. However, the existing commonly used binders are only used to bond the silicon active material to the current collector and have no electrical conductivity; moreover, the existing binders cannot conduct lithium ions, which is not conducive to the diffusion and transmission of lithium ions in the electrode material. Summary of the Invention

[0004] In view of the above-mentioned defects or deficiencies in the prior art, it is desirable to provide a conductive binder, a preparation method thereof, a silicon negative electrode, a lithium battery and a vehicle. The conductive binder has high adhesiveness, ionic conductivity and electronic conductivity, ensures the structural stability and charge-discharge cycle stability of the silicon negative electrode, and further improves the cycle life of the battery.

[0005] In a first aspect, the present invention provides a conductive binder, and the structural formula of the conductive binder is as follows:

[0006]

[0007] Wherein, R is selected from one of bis(trifluoromethylsulfonyl)imide radical, bis(fluorosulfonyl)imide radical, perchlorate radical, hexafluorophosphate radical, hexafluoroarsenate radical, tetrafluoroborate radical, bis(oxalato)borate radical, difluoro(oxalato)borate radical or trifluoromethanesulfonate radical;

[0008] m is an integer from 1 to 20; n is an integer from 1 to 100;

[0009] x, y and z are the molar ratios of the corresponding segments in the whole polymer. x, y and z are each independently any decimal between 0 and 1, and x + y + z is equal to 1.0;

[0010] p is the molar ratio of reduced-state polyaniline in the whole polyaniline, and p is any decimal between 0 and 1.

[0011] As an alternative, 0.1 ≤ x ≤ 0.9, 0.05 ≤ y ≤ 0.45, 0.05 ≤ z ≤ 0.45.

[0012] As an alternative, 0.2 ≤ x ≤ 0.6, 0.2 ≤ y ≤ 0.4, 0.2 ≤ z ≤ 0.4.

[0013] As an alternative, 0.4 ≤ p ≤ 0.7.

[0014] As an alternative, the molecular weight of the conductive binder is 1,000 to 1,000,000, preferably 50,000 to 500,000.

[0015] In a second aspect, the present invention provides a method for preparing the conductive binder of the first aspect, including the following process:

[0016] Dissolve a compound containing diamino and carboxyl groups, and PEG capped with diamino in a solvent to obtain a mixed solution I. Drop a mixed solution of formaldehyde and acetaldehyde into the mixed solution I, and after adding an acid solution, heat and react to obtain a mixed solution II;

[0017] Add aniline and an initiator to the mixed solution II, heat and react to obtain a mixed solution III. Subject the mixed solution III to a cooling, distillation, and washing process in sequence to obtain a polymer containing an acid root counter anion;

[0018] Add the polymer containing an acid root counter anion to an aqueous solution of an anion exchanger for ion exchange to obtain a precipitate;

[0019] Subject the precipitate to a washing and drying process to obtain the conductive binder.

[0020] As an alternative, the structural formula of the compound containing diamino and carboxyl groups is as follows:

[0021]

[0022] Among them, m is any integer between 1 and 20.

[0023] As an alternative, the solvent is any one of water, N-methylpyrrolidone, N-methylformamide, N-methylacetamide, N,N-dimethylformamide, N,N-dimethylacetamide, sulfolane, or dimethyl sulfoxide.

[0024] As an alternative, the acid solution is any one of acetic acid, hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid.

[0025] As an alternative, the initiator is any one of azobisisobutyronitrile, azobisisoheptonitrile, dimethyl azobisisobutyrate, benzoyl peroxide, tert-butyl benzoyl peroxide, benzophenone, diphenyl ketone, methyl o-benzoylbenzoate, potassium persulfate, ammonium persulfate, potassium dichromate, hydrogen peroxide, and ferric chloride.

[0026] As an alternative, the conditions for the heating reaction are as follows: the heating temperature is 80°C to 100°C, and the reaction time is 0.5 h to 4 h.

[0027] In a third aspect, the present invention provides a silicon negative electrode for a lithium battery, comprising: a current collector and a silicon active material layer formed on the surface of the current collector, and the silicon active material layer includes the conductive binder of the first aspect.

[0028] In a fourth aspect, the present invention provides a lithium battery, comprising the silicon negative electrode for a lithium battery of the third aspect.

[0029] In a fifth aspect, the present invention provides a vehicle, comprising the lithium battery of the fourth aspect.

[0030] The conductive binder provided in this application is an imidazole-based ionic liquid polymer, which contains a carboxyl chain segment, a PEG chain segment, and a polyaniline chain segment, so that the conductive binder has excellent adhesion performance, ionic conduction performance, and electrical conductivity. Among them, the carboxyl group on the imidazole-based main chain can form a strong hydrogen bond with silicon, avoiding the shedding of silicon, which is beneficial to improving the specific capacity and cycle stability of the battery; the flexible PEG chain segment can improve the diffusion and transmission of lithium ions in the electrode material, and at the same time can adapt to the volume change of silicon particles during charge and discharge, which is beneficial to improving the charge and discharge stability of the silicon negative electrode; the polyaniline chain segment has good electrical conductivity, which can improve the electrical conductivity of the polymer, always keep the circuit of the silicon negative electrode connected, prevent it from disconnecting from the silicon active material, inhibit the generation of "dead silicon", and the polyaniline chain segment can improve the tensile strength of the polymer, prevent the polymer from swelling in the electrolyte, and thus improve the cycle performance of the silicon negative electrode. Detailed Embodiments

[0031] The following further elaborates on this application in conjunction with embodiments. It can be understood that the specific embodiments described herein are only used to explain the relevant invention, rather than limiting the invention. Additionally, it should be noted that for ease of description, only parts related to the invention are shown in the embodiments.

[0032] It should be noted that, without conflict, the embodiments in this application and the features in the embodiments can be combined with each other. The following will detail this application with reference to the embodiments.

[0033] An embodiment of the present invention provides a conductive binder, characterized in that the structural formula of the conductive binder is as follows:

[0034]

[0035] Among them, R is selected from one of bis(trifluoromethylsulfonyl)imide anion, bis(fluorosulfonyl)imide anion, perchlorate anion, hexafluorophosphate anion, hexafluoroarsenate anion, tetrafluoroborate anion, bis(oxalato)borate anion, difluoro(oxalato)borate anion or trifluoromethanesulfonate anion;

[0036] m is an integer from 1 to 20; n is an integer from 1 to 100;

[0037] x, y and z are each independently any decimal number between 0 and 1, and x + y + z is equal to 1.0;

[0038] p is the molar ratio of reduced polyaniline in the whole polyaniline, and p is any decimal number between 0 and 1.

[0039] Among them, adjusting the values of m and n is beneficial to controlling the length of the main chain of the imidazolium-based ionic liquid polymer, and thus beneficial to controlling the adhesiveness and ionic conductivity of the polymer.

[0040] The values of x, y and z respectively represent the molar ratios of the carboxyl-containing segment, PEG segment and polyaniline segment in the total molar amount of the polymer; adjusting the values of x, y and z is beneficial to regulating the adhesiveness, ionic conductivity and electrical conductivity of the polymer, so that the polymer has good adhesiveness, ionic conductivity and electrical conductivity.

[0041] The polyaniline segment is composed of a reduced polyaniline segment and an oxidized polyaniline segment. p represents the molar ratio of reduced polyaniline in the whole polyaniline, and 1 - p represents the molar ratio of oxidized polyaniline in the whole polyaniline. In the coexistence of reduced polyaniline and oxidized polyaniline, the polymer has good electrical conductivity.

[0042] Compared with traditional binders, the conductive binder of this example has excellent adhesiveness, ionic conductivity and electrical conductivity, which is beneficial to ensuring the stability of silicon particles, the diffusion and transmission of lithium ions, and the integrity of the connection of the whole electrode, and thus improving the specific capacity and cycle stability of the battery.

[0043] The conductive binder of this embodiment includes carboxyl groups, flexible PEG segments, and polyaniline segments. Among them, the carboxylic acid groups on the polymer backbone can form strong hydrogen bond interactions with silicon, thereby improving the charge-discharge cycle stability of the silicon negative electrode; the PEG segments can improve the diffusion and transport of lithium ions in the electrode material and reduce polarization; at the same time, the PEG segments provide flexibility to the polymer, enabling it to adapt to the volume change of silicon particles during charge and discharge, thus improving the charge-discharge cycle stability of the silicon negative electrode; the polyaniline segments can endow the polymer with good electronic conductivity, enabling the silicon material to always maintain electrical connection, preventing it from disconnecting from the active material, reducing the possibility of the active material forming "dead silicon", and enhancing the performance of the battery; moreover, polyaniline, as a rigid segment, can increase the tensile strength of the polymer, which is beneficial to preventing the polymer from swelling in the electrolyte.

[0044] Due to the lack of groups such as carboxyl and hydroxyl groups, polyaniline has poor binding performance, and polyaniline is rigid and cannot adapt to the volume expansion of silicon; polyaniline cannot conduct lithium ions, which will increase the impedance of the electrode; the processability of polyaniline is also very poor, and it cannot be well formulated into a slurry when used as a binder. In the polymer of this embodiment, imidazole cations, carboxyl groups, PEG segments, and polyaniline segments are introduced simultaneously. The combination of polyaniline segments and other segments is beneficial to improving the processability of polyaniline; at the same time, combining adhesiveness and conductivity on one polymer can more reliably prevent the conductive agent from disconnecting from the active material, which is then beneficial to maintaining the electrical connection of silicon particles; the carboxyl groups and the amino groups on polyaniline can form hydrogen bonds and electrostatic interactions, enabling it to construct a cross-linked three-dimensional network structure around the silicon particles, effectively preventing irreversible slippage of the silicon particles and buffering volume changes, thereby maintaining the electrical connection and integrity of the electrode and further extending the service life of the battery; moreover, the hydrogen bonds and electrostatic interactions formed by carboxyl groups and amino groups can be reversibly opened and rebuilt, enabling the polymer to repair mechanical damage, thus improving the cycling performance of the silicon negative electrode.

[0045] Furthermore, 0.1 ≤ x ≤ 0.9, 0.05 ≤ y ≤ 0.45, 0.05 ≤ z ≤ 0.45. For example, x can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, and 0.9, etc.; y can be 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, and 0.45, etc.; z can be 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, and 0.45, etc. The value ranges of x, y, and z disclosed in the embodiments of this application are beneficial to adjusting the contents of carboxyl groups, PEG segments, and polyaniline segments, enabling the carboxyl groups, PEG segments, and polyaniline segments to have appropriate proportions, and improving the adhesiveness, ion conductivity, and conductivity of the binder.

[0046] As a preferred embodiment, 0.2 ≤ x ≤ 0.6, 0.2 ≤ y ≤ 0.4, 0.2 ≤ z ≤ 0.4. For example, x can be 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, etc.; y can be 0.2, 0.25, 0.3, 0.35, 0.4, etc.; z can be 0.2, 0.25, 0.3, 0.35, 0.4, etc. The value ranges of x, y, and z disclosed in this embodiment optimize the adhesiveness, ionic conductivity, and electrical conductivity of the conductive binder.

[0047] Further, 0.4 ≤ p ≤ 0.7. For example, p can be 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7. The value range of p disclosed in the embodiments of this application enables a suitable ratio of reduced polyaniline and oxidized polyaniline, thereby improving the electrical conductivity of the polymer.

[0048] Further, the molecular weight of the conductive binder is 1000 - 1000000. For example, the molecular weight of the conductive binder can be 1000, 3000, 5000, 8000, 10000, 30000, 50000, 60000, 80000, 100000, 2000000, 500000, 700000, 800000, 1000000, etc. The preferred molecular weight of the conductive binder is 50000 - 500000. The embodiments of the present invention do not limit the specific molecular weight.

[0049] In summary, compared with traditional binders, the conductive binder of the embodiments of this application has good adhesiveness, ionic conductivity, and electrical conductivity, can be tightly combined with silicon, improve the stability of silicon particles, and at the same time can adapt to the volume change of silicon particles, improving the stability of the silicon negative electrode during charge and discharge; and is conducive to conducting lithium ions and reducing polarization; in addition, good adhesiveness and electrical conductivity enable the silicon negative electrode to always maintain electrical connection, avoid the formation of "dead silicon", and thus improve the cycle service life of the silicon negative electrode.

[0050] Moreover, by controlling the content of each functional group, the binder has optimal adhesiveness, ionic conductivity, and electrical conductivity.

[0051] In the second aspect, the embodiments of the present invention provide a preparation method of the conductive binder of the first aspect, including the following process:

[0052] Dissolve a compound containing diamino and carboxyl groups, and PEG capped with diamino in a solvent to obtain a mixed solution I, drop a mixed solution of formaldehyde and acetaldehyde into the mixed solution I, and after adding an acid solution, heat and react to obtain a mixed solution II;

[0053] Aniline and an initiator are added to the mixed solution II, and after heating and reacting, a mixed solution III is obtained. The mixed solution III is successively subjected to cooling, distillation, and washing processes to obtain a polymer containing an acid radical counter anion.

[0054] The polymer containing an acid radical counter anion is added to an aqueous solution of an anion exchanger for ion exchange to obtain a precipitate.

[0055] The precipitate is subjected to washing and drying processes to obtain a conductive binder.

[0056] It should be noted that a compound containing a diamino group and a carboxyl group and a PEG capped with a diamino group are first reacted with formaldehyde and acetaldehyde, and polymerized to form an imidazole main chain connected with a carboxyl group and PEG. Then, the imidazole main chain of the carboxyl group and PEG is combined with a polyaniline chain segment to obtain a conductive binder. The method of this embodiment not only enables the polymer to have good adhesiveness, ionic conductivity, and electrical conductivity simultaneously, but also improves the processability of polyaniline.

[0057] Among them, the compound containing a diamino group and a carboxyl group and the compound capped with a diamino group can be in any ratio, and any compound containing a diamino group and a carboxyl group and the compound capped with a diamino group can be any compound. The embodiments of the present application do not make specific limitations on the above ratios and compounds.

[0058] The purpose of adding the acid solution is to provide an acidic condition. At the same time, the acid radical ions serve as the counter anions of the synthesized polymer cations, and the acid radical ions are beneficial for ion exchange with other ions.

[0059] The mixture of formaldehyde and acetaldehyde is used to react with the compound capped with a diamino group under acidic conditions to generate a polymer main chain containing an imidazole group.

[0060] Exemplarily,

[0061] A compound containing a diamino group and a carboxyl group , m = 1, and a compound capped with a diamino group , n = 2, are dissolved in water in a ratio of 4:3 to obtain a mixed solution I. The mixed solution of formaldehyde and acetaldehyde is added dropwise to the mixed solution I under an ice-water bath condition. After stirring evenly, acetic acid is added, and the mixture is heated to 100 °C and reacted for 2 h to obtain a mixed solution II.

[0062] Aniline and potassium persulfate are added to the mixed solution II, heated to 100 °C, and reacted for 2 h to obtain a mixed solution III. After the mixed solution III is successively subjected to cooling, vacuum distillation, and washing processes, a polymer containing acetate counter anions is obtained. Among them, the ratio of aniline to potassium persulfate is 1:0.1, and the ratio among aniline, and is 3:4:3.

[0063] After dissolving the polymer containing acetate as the counter anion in water, it is dropped into an aqueous solution of lithium bis(trifluoromethanesulfonyl)imide for ion exchange to obtain a precipitate;

[0064] The precipitate is washed and dried to obtain a conductive binder, and its structural formula is as follows:

[0065]

[0066] Furthermore, the structural formula of the compound containing diamino and carboxyl groups is as follows:

[0067]

[0068] Among them, m is any integer between 1 and 20.

[0069] Furthermore, the solvent is any one of water, N-methylpyrrolidone, N-methylformamide, N-methylacetamide, N,N-dimethylformamide, sulfolane or dimethyl sulfoxide.

[0070] Furthermore, the acid solution is any one of acetic acid, hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid.

[0071] Furthermore, the initiator is any one of azobisisobutyronitrile, azobisisoheptonitrile, dimethyl azobisisobutyrate, benzoyl peroxide, tert-butyl benzoyl peroxide, benzophenone, dibenzoyl peroxide, methyl o-benzoylbenzoate, potassium persulfate, ammonium persulfate, potassium dichromate, hydrogen peroxide, ferric chloride.

[0072] Furthermore, the conditions for the heating reaction are: the heating temperature is 80°C to 100°C, and the reaction time is 0.5 h to 4 h. For example, the temperature is 80°C, 85°C, 90°C or 100°C, etc.; the time is 0.5 h, 1 h, 2 h, 3 h or 4 h, etc. The specific reaction temperature and time are not limited in the embodiments of the present application. Among them, under heating conditions, it is beneficial to promote the reaction and improve the yield of the reactants.

[0073] Furthermore, the anion exchanger is any one of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium perchlorate, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate or lithium trifluoromethanesulfonate.

[0074] In a third aspect, the present invention provides a silicon negative electrode for a lithium battery, including: a current collector and a silicon active material layer formed on the surface of the current collector, and the silicon active material layer includes the conductive binder of the first aspect. Those skilled in the art can understand that the silicon negative electrode of this lithium battery has all the characteristics and advantages of the aforementioned conductive binder, and will not be elaborated herein.

[0075] In a specific embodiment, the silicon anode of the lithium battery is prepared through the following process:

[0076] Mix the silicon-based active material, binder, and conductive agent (which can be omitted), add a dispersant and stir well. Coat the mixed slurry on a copper foil, then dry it and cut it into electrode sheets.

[0077] Among them, the mass percentage of the binder in the total mass of the silicon-based active material, binder, and conductive agent is 2% - 30%; the mass percentage of the silicon-based active material is 60% - 97.5%; the mass percentage of the conductive additive is 0.5% - 10%;

[0078] The stirring method can be mortar grinding, blender grinding, ball milling, etc. Preferably, it is mortar grinding, and the grinding time is 5 min - 30 min;

[0079] The drying method can be air drying, vacuum drying, freeze drying, etc. Preferably, it is vacuum drying, the drying temperature is 80°C - 150°C, and the time is 4 h - 24 h;

[0080] The silicon-based active material includes nano-silicon, micro-silicon, porous silicon, amorphous silicon, silicon monoxide, silicon-carbon composite, and silicon alloy;

[0081] The conductive agent is one or more of graphite, acetylene black, Super P, Super S, graphene, carbon fiber, carbon nanotube, and Ketjen black;

[0082] The dispersant is one or more of water, N-methylpyrrolidone, N-methylformamide, N-methylacetamide, N,N-dimethylformamide, N,N-dimethylacetamide, sulfolane, and dimethyl sulfoxide.

[0083] Fourthly, the present invention provides a lithium battery, including the silicon anode of the lithium battery in the third aspect. Those skilled in the art can understand that this lithium battery has all the characteristics and advantages of the aforementioned conductive binder, and will not be elaborated here too much. Generally speaking, the lithium battery of the embodiment of the present invention has a good cycle life.

[0084] In a specific embodiment,

[0085] The lithium battery further includes: a positive electrode, a separator, and an electrolyte. Among them, the positive electrode includes a positive electrode current collector and an active material layer located on the positive electrode current collector. The active material layer includes a positive electrode active material, a binder, and a conductive agent. The positive electrode active material can be selected from lithium cobalt oxide (LiCoO 2 ), lithium nickel oxide (LiNiO 2 ), lithium iron phosphate (LiFePO 4 ), lithium cobalt phosphate (LiCoPO 4 ), lithium manganese phosphate (LiMnPO4 ), lithium nickel phosphate (LiNiPO 4 ), lithium manganate (LiMnO 2 ), binary material LiNi x A (1-x) O 2 (where A is selected from one of Co and Mn, 0 < x < 1), ternary material LiNimBnC (1-m-n) O 2 (where B and C are independently selected from at least one of Co, Al, and Mn, and B and C are different, 0 < m < 1, 0 < n < 1).

[0086] The separator can be any separator material used in existing lithium batteries. Specifically, it can be polyethylene, polypropylene, polyvinylidene fluoride, and their multi-layer composite films.

[0087] The electrolyte includes an organic solvent, a lithium salt, and an additive. Among them, the organic solvent can be selected from at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl formate, ethyl formate, ethyl propionate, propyl propionate, methyl butyrate, ethyl acetate, acid anhydride, N-methylpyrrolidone, N-methylformamide, N-methylacetamide, acetonitrile, sulfolane, dimethyl sulfoxide, ethylene sulfite, propylene sulfite, methyl sulfide, diethyl sulfite, dimethyl sulfite, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol methyl ethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, 1,4-dioxane, tetrahydrofuran, fluorinated cyclic organic esters, sulfur-containing cyclic organic esters; the lithium salt is selected from at least one of organic lithium salts and inorganic lithium salts, such as LiPF 6 , LiBF, LiClO 4 , LiAsF 6 , LiBOB, LiDFOB, LiTFOP; the additive can be selected from at least one of vinylene carbonate, fluorinated carbonate, difluorinated ethylene carbonate, fluorinated ethylene carbonate, ethylene vinylene carbonate, ethylene sulfite, methylene methanedisulfonate, 1,3-propane sultone, 1,3-propene sultone, ethylene sulfate, lithium difluorophosphate, lithium difluoro(oxalato)phosphate, lithium tetrafluoro(oxalato)phosphate.

[0088] In a fifth aspect, the present invention provides a vehicle including the lithium battery of the fourth aspect. For example, it may include a plurality of battery packs composed of the aforementioned lithium batteries. Thus, the vehicle has all the features and advantages of the aforementioned lithium battery, which will not be elaborated here.

[0089] The present invention will be described below through specific embodiments. It should be noted that the following specific embodiments are only for illustrative purposes and do not limit the scope of the present invention in any way.

[0090] Example 1

[0091] (1) Preparation of conductive binder I:

[0092]

[0093] A compound containing diamino and carboxyl groups has the structural formula , where m = 1, and the diamino-terminated compound is , where n = 2. They are dissolved in water together in a ratio of 4:3 to obtain mixture I. A mixture of formaldehyde and acetaldehyde is added dropwise to mixture I under an ice-water bath condition and stirred to mix evenly. Then acetic acid is added, and the mixture is heated to 100 °C and reacted for 2 h to obtain mixture II;

[0094] Aniline and potassium persulfate are added to mixture II, and the mixture is heated to 100 °C and reacted for 2 h to obtain mixture III; among them, , and aniline are in a ratio of 4:3:3, and the ratio of aniline to potassium persulfate is 1:0.1. Mixture III is obtained through cooling, reduced-pressure distillation, and washing processes to obtain a polymer containing acetate counteranions;

[0095] The polymer containing acetate counteranions is dissolved in water and added dropwise to an aqueous solution of lithium bis(trifluoromethanesulfonyl)imide to react to form a precipitate;

[0096] The precipitate is obtained through washing and drying processes to obtain an electrode binder, and the structural formula can be expressed as

[0097] (2) Preparation of half-cell

[0098] Nanosilicon powder, carbon black (Super-P), and conductive binder I are dispersed in water in a mass ratio of 90:2:8. After being ground evenly in a mortar, the slurry is coated on a copper foil with a coater, and the thickness of the coated slurry is 100 μm; it is left to dry at room temperature, cut into a circular piece with a diameter of 13 mm with a slicer, and the circular piece is placed in a vacuum drying oven at 80 °C and dried for 12 h, and taken out when the temperature drops to room temperature after drying to obtain a nanosilicon negative electrode;

[0099] The nanosilicon negative electrode is transferred to a glove box filled with argon (content O 2 ≤0.5 ppm, H 2O ≤ 0.5 ppm), weigh each nanosilicon anode sheet in a glove box, record the weighed mass, use a lithium metal sheet as the counter electrode, and 1 mol / L LiPF 6 An EC / DMC / DEC (v / v / v = 1 / 1 / 1) solution is used as the electrolyte, and a CR2025 coin-type half-cell is assembled in a glove box.

[0100] Example 2

[0101] The difference between this example and Example 1 is that the structural formula of conductive binder II is:

[0102] Example 3

[0103] The difference between this example and Example 1 is that the structural formula of conductive binder III is:

[0104]

[0105] Example 4

[0106] The difference between this example and Example 1 is that the structural formula of conductive binder IV is:

[0107]

[0108] Example 5

[0109] The difference between this example and Example 1 is that the structural formula of conductive binder V is:

[0110]

[0111] Example 6

[0112] The difference between this example and Example 1 is that the structural formula of conductive binder VI is:

[0113]

[0114] Example 7

[0115] The difference between this example and Example 1 is that the structural formula of conductive binder VII is:

[0116]

[0117] Example 8

[0118] The difference between this example and Example 1 is that the structural formula of conductive binder VIII is:

[0119]

[0120] Example 9

[0121] This example is different from Example 1 in that the structural formula of the conductive binder IX is:

[0122]

[0123] Comparative Example 1

[0124] This comparative example is different from Example 1 in that the electrode binder is PAA (polyacrylic acid).

[0125] Comparative Example 2

[0126] This comparative example is different from Example 1 in that the structural formula of the electrode binder is as follows:

[0127]

[0128] The value of a makes the molecular weight of the polymer 50,000 - 500,000

[0129] Comparative Example 3

[0130] This comparative example is different from Example 1 in that the structural formula of the electrode binder is as follows:

[0131]

[0132] The value of b makes the molecular weight of the polymer 50,000 - 500,000

[0133] Comparative Example 4

[0134] This comparative example is different from Example 1 in that the structural formula of the electrode binder is as follows:

[0135]

[0136] The value of c makes the molecular weight of the polymer 50,000 - 500,000

[0137] Comparative Example 5

[0138] This comparative example is different from Example 1 in that the structural formula of the electrode binder is as follows:

[0139]

[0140] Comparative Example 6

[0141] This comparative example is different from Example 1 in that the structural formula of the electrode binder is as follows:

[0142]

[0143] Comparative Example 7

[0144] The difference between this comparative example and Example 1 is that the structural formula of the electrode binder is as follows:

[0145] The lithium batteries prepared in the above examples and comparative examples were subjected to the following performance tests to characterize the electrochemical performance of the conductive binder.

[0146] The test process is as follows: 10 batteries prepared in Examples 1-9 and Comparative Examples 1-7 were each taken, and a constant current charge-discharge cycle test was carried out on a LAND CT2001C secondary battery performance detection device under the condition of 25±1°C. The test conditions were: the discharge cut-off voltage was 0.01V, the charge cut-off voltage was 1.5V, first charge and discharge cycles were carried out 3 times at a current density of 100mA / g, and then charge and discharge cycles were carried out at a current density of 500mA / g. The test results are shown in Table 1.

[0147] Table 1 Performance test results of the half-cells prepared in Examples 1-9 and Comparative Examples 1-7

[0148]

[0149] From the results shown in Table 1, it can be obtained that:

[0150] According to the test results of Examples 1-9 and Comparative Example 1, it can be obtained that the half-cells prepared in Examples 1-9 are superior to the half-cells prepared in Comparative Example 1 in terms of battery capacity and cycle performance, indicating that the conductive binder prepared in the examples of the present invention is beneficial to improving the performance of lithium batteries compared with traditional binders.

[0151] According to the test results of Examples 1-5, it can be obtained that the half-cells of Examples 1-5 all have high capacity and excellent cycle performance. Therefore, the value range of the molar ratio of the carboxyl chain segment, PEG chain segment and polyaniline chain segment in the polymer of the examples of the present application is beneficial to the conductive binder having good adhesion performance, ion conduction performance and conductivity.

[0152] According to the test results of Example 1, Examples 6-7 and Examples 8-9, it can be obtained that the half-cells prepared with the value ranges of m, n, and p in the conductive binder of the examples of the present application all have high capacity and good cycle performance.

[0153] According to the test results of Example 1 and Comparative Examples 2-7, it can be obtained that the half-cells prepared in Example 1 are superior to the half-cells prepared in Comparative Examples 2-7 in terms of battery capacity and cycling performance. Among them, the polymer in Example 1 contains three chain segments, the polymers in Comparative Examples 2-4 only include one of the chain segments, and Comparative Examples 5-7 only include two of the chain segments. Therefore, it can be known that the reason why the polymer disclosed in this application can improve the performance of the battery lies in the synergistic effect of the carboxyl chain segment, PEG chain segment and polyaniline chain segment, so that the conductive binder has excellent adhesion performance, ion conduction performance and electrical conductivity, can bind tightly with silicon, improve the stability of silicon particles, and at the same time can adapt to the volume change of silicon particles, improve the stability of the silicon negative electrode during charge and discharge; and is conducive to conducting lithium ions and reducing polarization; in addition, the good adhesion and electrical conductivity enable the silicon negative electrode to always maintain electrical connection, avoid the formation of "dead silicon", and thus improve the cycling service life of the silicon negative electrode.

[0154] The above description is only a preferred embodiment of the present application and an explanation of the applied technical principles. Those skilled in the art should understand that the scope of the invention involved in the present application is not limited to the technical solutions formed by the specific combination of the above technical features, and should also cover other technical solutions formed by any combination of the above technical features or their equivalent features without departing from the inventive concept. For example, the technical solutions formed by mutually replacing the above features with the (but not limited to) technical features with similar functions disclosed in the present application.

Claims

1. A conductive binder, characterized in that, the structural formula of the conductive binder is as follows: wherein, R is selected from one of bis(trifluoromethylsulfonyl)imide anion, bis(fluorosulfonyl)imide anion, perchlorate anion, hexafluorophosphate anion, hexafluoroarsenate anion, tetrafluoroborate anion, bis(oxalato)borate anion, difluoro(oxalato)borate anion or trifluoromethanesulfonate anion; m is an integer from 1 to 20; n is an integer from 1 to 100; x, y and z are the molar ratios of the corresponding segments in the whole polymer, and x + y + z equals 1.0; 0.1 ≤ x ≤ 0.9, 0.05 ≤ y ≤ 0.45, 0.05 ≤ z ≤ 0.45; p is the molar ratio of reduced polyaniline in the whole polyaniline segment, 0.2 ≤ p ≤ 0.

8.

2. The conductive binder according to claim 1, characterized in that, 0.2 ≤ x ≤ 0.6, 0.2 ≤ y ≤ 0.4, 0.2 ≤ z ≤ 0.

4.

3. The conductive binder according to claim 1 or 2, characterized in that, the molecular weight of the conductive binder is 1000 - 1000000.

4. The conductive binder according to claim 3, characterized in that, the molecular weight of the conductive binder is 50000 - 500000.

5. A preparation method of the conductive binder according to any one of claims 1 - 4, characterized in that, it includes the following process: Dissolve the compound containing diamino and carboxyl groups, and PEG capped with diamino in a solvent to obtain a mixed solution I. Dropwise add the mixed solution of formaldehyde and acetaldehyde to the mixed solution I, and after adding an acid solution, heat and react to obtain a mixed solution II; Add aniline and an initiator to the mixed solution II, heat and react to obtain a mixed solution III. Subject the mixed solution III to cooling, distillation and washing processes in sequence to obtain a polymer containing an acid root counter anion; Add the polymer containing the acid root counter anion to an aqueous solution of an anion exchanger for ion exchange to obtain a precipitate; Subject the precipitate to washing and drying processes to obtain the conductive binder.

6. The method according to claim 5, characterized in that, the structural formula of the compound containing diamino and carboxyl groups is as follows: wherein, m is any integer between 1 and 20.

7. The method according to claim 5, characterized in that, the solvent is any one of water, N - methylpyrrolidone, N - methylformamide, N - methylacetamide, N,N - dimethylformamide, N,N - dimethylacetamide, sulfolane or dimethyl sulfoxide.

8. The method according to claim 5, characterized in that, the acid solution is any one of acetic acid, hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid.

9. The method according to claim 5, characterized in that, the initiator is any one of azobisisobutyronitrile, azobisisoheptonitrile, dimethyl azobisisobutyrate, benzoyl peroxide, tert - butyl peroxybenzoate, benzophenone, diphenyl ketone, methyl o - benzoylbenzoate, potassium persulfate, ammonium persulfate, potassium dichromate, hydrogen peroxide, ferric chloride.

10. The method according to claim 5, characterized in that, The conditions for the heating reaction are as follows: the heating temperature is 80°C to 100°C, and the reaction time is 0.5 h to 4 h.

11. A silicon negative electrode for a lithium battery, comprising: a current collector and a silicon active material layer formed on the surface of the current collector, characterized in that the silicon active material layer comprises the conductive binder according to any one of claims 1-4.

12. A lithium battery, characterized in that it comprises the silicon negative electrode for a lithium battery according to claim 11.

13. A vehicle, characterized in that it comprises the lithium battery according to claim 12.

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