Silicon-based negative electrode binder and preparation method thereof, silicon-based negative electrode and battery

Abstract

The invention provides a silicon-based negative electrode adhesive and a preparation method thereof, a silicon-based negative electrode and a battery, and belongs to the technical field of lithium ion battery production, the silicon-based negative electrode adhesive comprises a three-dimensional cross-linked network structure; the silicon-based negative electrode adhesive is prepared by a cross-linking reaction of a polydopamine surface modified carbon nanotube and polyacrylic acid. The silicon-based negative electrode adhesive provided by the invention has a three-dimensional cross-linked network structure, can effectively limit volume expansion of a silicon-based negative electrode in a circulation process, is beneficial to protecting the integrity of a whole electrode structure and improves the cycle performance of a battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion battery production, in particular to a silicon-based negative electrode binder and a preparation method thereof, a silicon-based negative electrode and a battery. BACKGROUND

[0002] Lithium ion secondary batteries have the advantages of high voltage, high capacity, long cycle life, environmental friendliness, etc., making them have broad application prospects in portable electronic devices, electric vehicles, energy storage, national defense industry, etc., and have become a research hotspot in the development of new energy industries in recent years. In recent years, with the vigorous development of electric vehicles and large power grids, people have put forward higher requirements for the energy density of lithium ion batteries. Although the traditional graphite negative electrode has good cycle stability, its theoretical specific capacity is low, which does not meet the development requirements of high-energy-density lithium ion batteries. Silicon-based negative electrodes have higher specific capacity and play an important role in high-energy-density batteries. However, silicon-based negative electrode materials have the problem of large volume change during the cycle process, which leads to instability of the SEI film, resulting in rapid cycle decay, which hinders its wide application.

[0003] In the prior art, PAA is commonly used as a binder for silicon-based negative electrodes and can form covalent bonds with the surface of silicon-based materials, which can alleviate the volume expansion of silicon-based negative electrodes to a certain extent. However, the one-dimensional linear molecular structure has limited effect on the expansion of silicon-based negative electrodes, and therefore, there is an urgent need for a technical solution to solve the above problems. SUMMARY

[0004] To solve the above technical problems, a technical solution is proposed in the present application, which improves the problem of excessive volume change of silicon-based negative electrodes during the cycle process by using a silicon-based negative electrode binder with a three-dimensional cross-linked network structure, thereby improving the cycle performance of lithium ion batteries. The technical solution of the present application is realized as follows:

[0005] The first aspect of the present application discloses a silicon-based negative electrode binder, which comprises a three-dimensional cross-linked network structure.

[0006] The silicon-based negative electrode binder is prepared by cross-linking reaction of polydopamine surface-modified carbon nanotubes and polyacrylic acid.

[0007] In an embodiment, the carbon nanotubes include single-walled carbon nanotubes and multi-walled carbon nanotubes.

[0008] The second aspect of the present application discloses a preparation method of a silicon-based negative electrode binder, which is used to prepare the silicon-based negative electrode binder disclosed in the first aspect of the present application, and the method comprises the following steps:

[0009] The carbon nanotubes and dopamine hydrochloride are added into a Tris-HCl buffer solution, stirred for 12-24 hours, centrifuged, washed, and freeze-dried to obtain the polydopamine surface-modified carbon nanotubes.

[0010] The polydopamine surface-modified carbon nanotubes are dispersed in water to form a dispersion liquid, polyacrylic acid is dispersed in water to form a glue solution, and then the glue solution and the dispersion liquid are mixed and crosslinked to form a silicon-based negative electrode binder with a three-dimensional crosslinked network structure.

[0011] In an embodiment, the mass ratio of the carbon nanotubes to the dopamine hydrochloride is (1:5) to (5:1).

[0012] In an embodiment, the mass ratio of the polydopamine-modified carbon nanotubes to the polyacrylic acid is (1:5) to (5:1).

[0013] In an embodiment, the mass fraction of the dispersion liquid is 0.01% to 5%.

[0014] In an embodiment, the mass fraction of the glue solution is 0.01% to 10%.

[0015] The third aspect of the present application discloses a silicon-based negative electrode, which comprises a negative electrode current collector, a negative electrode active material layer arranged on the surface of the negative electrode current collector, and a first conductive agent; further comprising the silicon-based negative electrode binder disclosed in the first aspect of the present application and a first binder.

[0016] In an embodiment, the first binder comprises at least one of sodium carboxymethyl cellulose, polyacrylic acid, polyacrylate, and styrene-butadiene rubber.

[0017] The fourth aspect of the present application discloses a battery, which comprises a positive electrode, a separator, and a negative electrode, wherein the negative electrode is the silicon-based negative electrode disclosed in the third aspect of the present application.

[0018] The present application has the following beneficial technical effects:

[0019] The silicon-based negative electrode composite binder provided by the present application has a three-dimensional crosslinked network structure, which can effectively limit the volume expansion of the silicon-based negative electrode during the cycle process, is conducive to protecting the integrity of the entire electrode structure, and improves the cycle performance of the battery. DETAILED DESCRIPTION

[0020] The technical solutions of the present application will be described clearly and completely below in combination with the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used in the detailed description of the application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application; the terms "comprising," "including," and "having," and variations thereof, as used in the specification and claims of this application, are intended to be open-ended and to mean that the stated component is present, but not excluding the presence of other components.

[0022] In the description of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "a plurality of" is two or more, unless otherwise explicitly and specifically limited.

[0023] In the present application, the phrase "embodiments" means that the specific features, structures or characteristics described in conjunction with the embodiments can be included in at least one embodiment of the present application. The appearance of this phrase at various places in the specification does not necessarily mean the same embodiment, nor is it an independent or alternative embodiment to other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described in the present application can be combined with other embodiments.

[0024] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship between the associated objects, which means that there can be three relationships, for example, A and / or B, which can represent the three cases of A alone, A and B together, and B alone. In addition, the character " / " in the present application generally represents a "or" relationship between the front and rear associated objects.

[0025] Throughout this disclosure, numerical expressions are approximate measures of a range or limit to encompass minor deviations and embodiments having about the stated value as well as embodiments having the stated exact value. Except in the working examples provided at the end of the detailed description, all numerical values of parameters (e.g., amounts or conditions) in this specification (including the claims) should be understood as being modified in all instances by the term “about” whether or not “about” actually appears before the numerical value. “About” indicates that the stated numerical value

[0026] In addition, the disclosure of ranges includes all values and further subdivisions between the stated range limits, including the range limits and sub-ranges as given.

[0027] In the prior art, polyacrylic acid (PAA) as a commonly used adhesive for silicon-based anodes can form covalent bonds with the surface of silicon-based materials and to some extent can alleviate the volume expansion of silicon-based anodes, but the one-dimensional linear molecular structure has limited effect on the restriction of the expansion of silicon-based anodes.

[0028] To solve the above problems, the present application provides a technical solution.

[0029] The first aspect of the present application discloses a silicon-based anode adhesive, which comprises a three-dimensional cross-linked network structure.

[0030] The silicon-based anode adhesive is a cross-linked combination of polydopamine surface-modified carbon nanotubes and polyacrylic acid.

[0031] The silicon-based anode composite adhesive provided by the present application has a three-dimensional cross-linked network structure, which can effectively limit the volume expansion of the silicon-based anode during the cycle process, is conducive to protecting the integrity of the entire electrode structure, and improves the cycle performance of the battery.

[0032] It can be understood that the carbon nanotube surface is inert and cannot directly react with the polyacrylic acid. The polydopamine is introduced on the surface of the carbon nanotube to introduce a high-activity reaction site. The surface of the polydopamine contains catechol and amino groups, which can react with the groups on the polyacrylic acid to prepare a three-dimensional cross-linked network. Compared with the one-dimensional linear molecular structure of the polyacrylic acid, the silicon-based negative electrode composite adhesive with the three-dimensional cross-linked network structure can more effectively improve the expansion behavior of the silicon negative electrode in the cycle process, thereby improving the cycle performance of the battery. Moreover, the carbon nanotube is added to provide a rigid network for the adhesive, which can more effectively bind the silicon material to avoid expansion.

[0033] In some embodiments, the carbon nanotube includes a single-walled carbon nanotube and a multi-walled carbon nanotube.

[0034] The second aspect of the present application discloses a preparation method of a silicon-based negative electrode adhesive. The method is used for preparing the silicon-based negative electrode adhesive disclosed in the first aspect of the present application. The method includes the following steps:

[0035] The carbon nanotube and the dopamine hydrochloride are added into a Tris-HCl buffer solution, stirred and reacted for 12-24 hours, centrifuged, washed, and freeze-dried to obtain the polydopamine surface-modified carbon nanotube. For example, the stirring and reaction time can be selected as 12 hours, 14 hours, 15 hours, 18 hours, 20 hours, 22 hours, 24 hours, etc. The above list is only an example and is not limited. The centrifugation, washing, and freeze-drying operations are all common knowledge in the art, and thus will not be described in detail. It can be understood that the Tris-HCl buffer solution is prepared by mixing “tris-hydroxymethyl aminomethane (Tris)” and “hydrochloric acid (HCl)” in a certain proportion, and the pH value is 8.5.

[0036] The polydopamine surface-modified carbon nanotube is dispersed in water to form a dispersion liquid, the polyacrylic acid is dispersed in water to form a glue solution, and then the glue solution and the dispersion liquid are mixed and cross-linked to form the silicon-based negative electrode adhesive with a three-dimensional cross-linked network structure.

[0037] In some embodiments, the mass ratio of the carbon nanotube to the dopamine hydrochloride is (1:5)-(5:1).

[0038] In specific applications, the mass ratio of the carbon nanotube to the dopamine hydrochloride can be selected as 1:5, 2:5, 3:5, 4:5, 5:5, 2:1, 3:1, 4:1, 5:1, etc. The above list is only an example and is not limited. Those skilled in the art can freely implement any value within the range of (1:5)-(5:1) according to actual needs.

[0039] In some embodiments, the mass ratio of the polydopamine-modified carbon nanotube to the polyacrylic acid is (1:5)-(5:1).

[0040] In specific applications, the mass ratio of the polydopamine modified carbon nanotube and the polyacrylic acid can be 1:5, 2:5, 3:5, 4:5, 5:5, 2:1, 3:1, 4:1, 5:1, etc.

[0041] In some embodiments, the mass fraction of the dispersion is 0.01% to 5%. It can be understood that the mass fraction here refers to the mass ratio of the mass of the solute to the mass of the solvent.

[0042] When the mass fraction of the dispersion exceeds 5%, the dispersion has a high solid content, and the material is prone to agglomeration and difficult to disperse uniformly.

[0043] In specific applications, the mass fraction of the dispersion can be 0.01%, 0.02%, 0.05%, 0.08%, 0.1%, 0.2%, 0.5%, 0.8%, 1.0%, 1.2%, 1.5%, 2.0%, 2.2%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5%, etc. The above listed values are only examples and are not limiting. Those skilled in the art can freely implement any value within the range of 0.01% to 5% according to actual needs.

[0044] In some embodiments, the mass fraction of the dispersion is 0.01% to 5%.

[0045] In specific applications, the mass fraction of the dispersion can be 0.01%, 0.02%, 0.05%, 0.08%, 0.1%, 0.2%, 0.5%, 0.8%, 1.0%, 1.2%, 1.5%, 2.0%, 2.2%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5%, 6%, 7%, 8%, 10%, etc. The above listed values are only examples and are not limiting. Those skilled in the art can freely implement any value within the range of 0.01% to 10% according to actual needs.

[0046] When the mass fraction of the dispersion exceeds 10%, the viscosity of the glue solution is large, the flowability is poor, and the carbon nanotube dispersion and the glue solution are not easy to mix uniformly.

[0047] The third aspect of the present application discloses a silicon-based negative electrode, which comprises a negative electrode current collector, a negative electrode active material layer arranged on the surface of the negative electrode current collector, and a first conductive agent. The silicon-based negative electrode further comprises the silicon-based negative electrode binder disclosed in the first aspect of the present application and a first binder.

[0048] The first binder comprises at least one of sodium carboxymethyl cellulose, polyacrylic acid, polyacrylate, and butadiene styrene rubber.

[0049] The "at least one" in the present application refers to that one element can be selected from the above-mentioned elements as the technical solution implementation, or two or more mixed elements can be selected as the technical solution implementation. Since the listed elements have similar physical and chemical properties, the mixing of each other will not affect the physical and chemical properties, and the person skilled in the art can freely implement according to the actual situation.

[0050] In some embodiments, the negative active material in the negative active material layer includes at least one of a silicon-oxygen material, a silicon-carbon composite material, and a silicon nanowire. Exemplarily, the silicon-oxygen material includes SiO, SiO x (0 < x < 2); the silicon-carbon composite material includes silicon / graphite composite material, silicon / hard carbon composite material, silicon / soft carbon composite material, porous silicon-carbon material, silicon-carbon core-shell material, etc.

[0051] In some embodiments, the first conductive agent includes at least one of conductive carbon black, acetylene black, conductive carbon fiber, graphene, carbon nanotube, and ketjen black.

[0052] In some embodiments, the third aspect of the application discloses a silicon-based negative electrode prepared by the following method; including the following steps:

[0053] Mixing the negative active material, the silicon-based negative electrode binder, the first binder, the first conductive agent, and water to obtain a negative electrode slurry, coating the negative electrode slurry on a negative electrode current collector, and then drying, rolling, and die cutting to obtain a silicon-based negative electrode.

[0054] The fourth aspect of the application discloses an electrochemical device, which includes a positive electrode, a separator, and a negative electrode, wherein the negative electrode is the silicon-based negative electrode disclosed in the third aspect of the application.

[0055] In some embodiments, the positive electrode includes a positive electrode current collector and a positive active material layer disposed on the positive electrode current collector.

[0056] In some preferred embodiments, the positive active material layer is disposed on both sides of the positive electrode current collector.

[0057] In some embodiments, the positive active material layer includes a positive active material, and the positive active material includes a compound that reversibly intercalates and deintercalates lithium ions.

[0058] In some embodiments, the positive active material contains one or more transition metal cations, such as manganese (Mn), nickel (Ni), cobalt (Co), chromium (Cr), iron (Fe), vanadium (V), and combinations thereof.

[0059] In some embodiments, the positive electrode active material is one of a layered oxide, a spinel, and a polyanion. For example, the layered oxide (e.g., a rock-salt layered oxide) includes one or more lithium-based positive electrode active materials selected from the group consisting of LiCoO2(LCO), LiNi x Mn y Co 1-x-y O2(wherein 0≤x≤1 and 0≤y≤1), LiNi 1-x-y Co x Al y O2(wherein 0≤x≤1 and 0≤y≤1), LiNi x Mn 1-x O2(wherein 0≤x≤1), and Li 1+x MO2(wherein M is one of Mn, Ni, Co, and Al and 0≤x≤1). The spinel includes one or more lithium-based positive electrode active materials selected from the group consisting of LiMn2O4(LMO) and LiNi x Mn 1.5 O4. The olivine-type includes one or more lithium-based positive electrode active materials LiMPO4(wherein M is at least one of Fe, Ni, Co, and Mn). The polyanion cation includes, for example, a phosphate such as LiV2(PO4) 24 and / or a silicate such as LiFeSiO4.

[0060] In some embodiments, the mass of the positive electrode active material is 60% to 95% of the mass of the positive electrode active material layer.

[0061] In some embodiments, the positive electrode active material layer includes a binder. The binder improves the binding of the positive electrode active material particles to each other and also improves the binding of the positive electrode active material layer to the positive electrode current collector.

[0062] In some embodiments, non-limiting examples of the binder include polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene butadiene rubber, acrylated styrene butadiene rubber, epoxy resin, nylon, and the like.

[0063] In some embodiments, the mass of the binder is 0.1% to 20% of the mass of the positive electrode active material layer.

[0064] In some embodiments, the positive electrode active material layer includes a conductive agent, thereby imparting electrical conductivity to the electrode. The conductive agent can include any electrically conductive material, so long as it does not cause chemical changes. Non-limiting examples of conductive materials include carbon-based materials (e.g., natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fibers, etc.), metal-based materials (e.g., metal powders, metal fibers, etc., including, for example, copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives), and mixtures thereof.

[0065] In some embodiments, the conductive agent has a mass that is 0.1% to 20% of the mass of the positive electrode active material layer.

[0066] In some embodiments, the positive electrode active material layer provided herein further includes a fast ion conductor for improving the ionic conductivity of the positive electrode active material layer. The present application does not limit the type of fast ion conductor, which can be an oxide solid-state electrolyte, a sulfide solid-state electrolyte, a halide solid-state electrolyte, a lithium salt, etc.

[0067] In some embodiments, the oxide solid-state electrolyte can include one or more of garnet ceramics, LISICON-type oxides, NASICON-type oxides, and perovskite-type ceramics. For example, the one or more garnet ceramics can be selected from the group including Li 6.5 La 24 Zr 1.75 Te 0.25 O 12 , Li7La 24 Zr2O 12 , Li 6.2 Ga 0.24 La 2.95 Rb 0.05 Zr2O 12 , Li 6.85 La 2.9 Ca 0.1 Zr 1.75 Nb 0.25 O 12 , Li 6.25 Al 0.25 La 24 Zr2O 12 , Li 6.75 La 24 Zr 1.75 Nb 0.25 O 12 , Li 6.75 La 24 Zr 1.75 Nb 0.25 O 12 , and combinations thereof. The one or more LISICON-type oxides can be selected from the group including Li 6.75 La 24 Zr 1.75 Nb 0.25 O 12 , Li 6.75 La 24 Zr 1.75 Nb 0.25 O 12 , and combinations thereof. The one or more LISICON-type oxides can be selected from the group including Li14 Zn(GeO4)4, Li 24+x (P 1-x Si x )O4 (where 0 < x < 1), Li 24+x Ge x V 1-x O4 (where 0 < x < 1) and combinations thereof. One or more NASICON-type oxides can be selected from the group including LiMM'(PO4) 24 where M and M' are independently selected from the group consisting of Al, Ge, Ti, Sn, Hf, Zr, and La. For example: in certain variations, one or more NASICON-type oxides can be selected from the group including Li 1+x Al x Ge 2-x (PO4) 24 (LAGP) (where 0 < x < 2), Li 1+x Al x Ti 2-x (PO4) 24 (LATP) (where 0 < x < 2), Li 1+x Y x Zr2-x(PO4)24 (LYZP) (where 0 < x < 2), Li 1.24 Al 0.24 Ti 1.7 (PO4) 24 , LiTi2(PO4) 24 , LiGeTi(PO4) 24 , LiGe2(PO4) 24 , LiHf2(PO4) 24 and combinations thereof. One or more perovskite-type ceramics can be selected from the group including Li 24.24 La 0.524 TiO 24 , LiSr 1.65 Zr 1.24 Ta 1.7 O9, Li 2x-y Sr 1-x Ta y Zr 1-y O 24 (where x = 0.75y and 0.60 < y < 0.75), Li 24 / 8 Sr 7 / 16 Nb 24 / 4 Zr 1 / 4 O 24 , Li 24x La (2 / 24-x) TiO 24(where 0 < x < 0.25) and combinations thereof. In one variation, the one or more oxide-based materials can have an ionic conductivity greater than or equal to about 10 -5 S / cm to less than or equal to about 10 -1 S / cm.

[0068] In some embodiments, the sulfide solid-state electrolyte can include one or more sulfide-based materials selected from the group including Li2S-P2S5, Li2S-P2S5-MS x (where M is Si, Ge, and Sn and 0 < x < 2), Li 24.4 Si 0.4 P 0.6 S4, Li 10 GeP2S 11.7 O 0.24 , Li 9.6 P 24 S 12 , Li7P 24 S 11 , Li9P 24 S9O 24 , Li 10.245 Si 1.245 P 1.65 S 12 , Li 9.81 Sn 0.81 P 2.19 S 12 , Li 10 (Si 0.5 Ge 0.5 )P2S 12 , Li(Ge 0.5 Sn 0.5 )P2S 12 , Li 10 GeP2S 12 (LGPS), Li6PS5X (where X is CI, Br, or I), Li7P2S8I, Li 10.245 Ge 1.245 P 1.65 S 12 , Li 24.25 Ge 0.25 P 0.75 S4, Li 10 SnP2S 12 , Li 10 SiP2S 12 , Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.24Li2S-P2S5, (1-x)P2S5-xLi2S (where 0.5≤x≤0.7), and combinations thereof. In one variation, one or more of the sulfide-based materials can have an ionic conductivity greater than or equal to about 10-3S / cm to less than or equal to about 1 S / cm. -7 S / cm to less than or equal to about 1 S / cm.

[0069] In some embodiments, the halide solid-state electrolyte includes Li a M b X c N d wherein M includes a base metal element, such as one or more combinations of Zr, Hf, In, Sc, Y, La, Ce, Pr, Nb, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and M further includes a doping metal element, such as one or more combinations of Nb, Ta, Al, La, Mg, Ca, Ba, Ag, used in conjunction with the aforementioned base metal element; X includes one or more combinations of F, Cl, Br, I; N includes one or more combinations of O, S, and a+mb=c+nd is satisfied, where m and n are the weighted valence of M and N, respectively, and 1≤a≤4.

[0070] In some embodiments, the halide solid-state electrolyte particles can be at least one of Li2ZrCl6, Li2ZrCl5F, Li2ZrCl4F2, Li2ZrCl3F3, Li2ZrCl2F4, Li2ZrClF5, Li3InCl6, Li3YCl6, Li2HfCl6, LiInBr4, Li3InBr6, Li3LaI6, Li3LuCl6, Li3ErCl6. 5.5 O 0.25

[0071] In some embodiments, the lithium salt includes at least one of LiNbO3, Li4Ti5O12, Li2TiO3, LiAlO2, LiTaO3, LiMoO3, Li2RuO3, or Li2WO4. 12

[0072] In some embodiments, the fast ion conductor has a mass that is 1-20% of the mass of the positive active material layer; preferably 5-20%.

[0073] In some embodiments, the positive current collector includes a metal material that can conduct electrons, and illustratively, the positive current collector includes at least one of Al, Ni, tin, copper, stainless steel.

[0074] In some embodiments, the aluminum foil surface can be anodized to form a nanoscale aluminum oxide layer to enhance its corrosion resistance and interfacial bonding with the positive material.

[0075] ​​In some embodiments, the aluminum alloy foil can include trace amounts of titanium (Ti) or silicon (Si) elements to improve mechanical strength and high-temperature stability.

[0076] In some embodiments, the aluminum foil can also be a carbon-coated aluminum foil.

[0077] In some embodiments, the separator separates the negative electrode and the positive electrode and provides a path for movement of lithium ions. Any separator can be used without particular limitation, as long as it is a commonly used separator. A separator having excellent electrolyte moisture content and low resistance to ion movement in the electrolyte is preferred. A porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminate structure having two or more layers thereof, can be used. A typical porous nonwoven fabric, for example, a nonwoven fabric formed of glass fibers having a high melting point, polyethylene terephthalate fibers, or the like, can also be used. In addition, a coated separator film containing a ceramic component or a polymeric material can also be used to ensure heat resistance or mechanical strength, and can be selectively used in a single-layer or multi-layer structure.

[0078] In some embodiments, the battery further includes an electrolyte including a solvent, an electrolyte salt, and an electrolyte additive.

[0079] In some embodiments, the solvent includes a non-aqueous organic solvent.

[0080] In some embodiments, the solvent includes one or more of a carbonate-based solvent, a carboxylate-based solvent, and an aromatic hydrocarbon-based solvent.

[0081] In some embodiments, the carbonate-based solvent includes a halogenated carbonate and / or a non-halogenated carbonate.

[0082] In some embodiments, the halogenated carbonate includes one or more of fluoroethylene carbonate, bisfluoropropylene carbonate, trifluoroethylmethyl carbonate, trifluoromethylvinylene carbonate, 4-trifluoromethylvinylene carbonate, chloroethylene carbonate, bis(2,2,2-trifluoroethyl) carbonate, or 1,1,1,3,3,3-hexafluoroisopropyl propiolate.

[0083] In some embodiments, the non-halogenated carbonate includes one or more of ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, or methyl ethyl carbonate.

[0084] In some embodiments, the carboxylate-based solvent includes a halogenated carboxylate and / or a non-halogenated carboxylate.

[0085] In some embodiments, the halogenated carboxylic acid ester comprises one or more of fluorinated butyric acid propyl ester, fluorinated acetic acid propyl ester, fluorinated acetic acid ethyl ester, fluorinated acetic acid isopropyl ester, fluorinated propionic acid butyl ester, fluorinated propionic acid isopropyl ester, fluorinated butyric acid ethyl ester, fluorinated propionic acid methyl ester, fluorinated propionic acid ethyl ester, or fluorinated propionic acid propyl ester.

[0086] In some embodiments, the non-halogenated carboxylic acid ester comprises one or more of ethyl acetate, methyl acetate, propyl butyrate, propyl acetate, isopropyl acetate, butyl propionate, isopropyl propionate, ethyl butyrate, methyl propionate, ethyl propionate, or propyl propionate.

[0087] In some embodiments, the aromatic hydrocarbon-based solvent comprises a halogenated aromatic hydrocarbon and / or a non-halogenated aromatic hydrocarbon.

[0088] In some embodiments, the halogenated aromatic hydrocarbon comprises one or more of monofluorobenzene, difluorobenzene, 1,3,5-trifluorobenzene, trifluoromethylbenzene, 2-fluorotoluene, or 2,4-dichlorotrifluorotoluene.

[0089] In some embodiments, the electrolyte salt comprises one or more of lithium hexafluorophosphate (LiPF6), lithium hexafluoroarsenate (LiAsF6), lithium perchlorate (LiClO4), lithium bisfluorosulfonylimide (LiFSI), lithium tetrafluoroborate (LiBF4), and lithium bis-trifluoromethanesulfonimide (LiTFSI).

[0090] In some embodiments, the mass percentage of the electrolyte salt in the electrolyte is 0.5% to 20%, including but not limited to 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%.

[0091] In some embodiments, the electrolyte additive comprises one or more of a sulfonic acid lactone compound, a cyclic sulfate compound, a phosphate ester compound, and a borate ester compound.

[0092] In some embodiments, the mass percentage of the electrolyte additive in the electrolyte is 0.1% to 5%, including but not limited to 0.1%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%

[0093] In some embodiments, the sulfonic acid lactone compound is selected from one or more of 1,3-propane sultone, 1,4-butane sultone, propenyl-1,3-sulfonic acid lactone.

[0094] In some embodiments, the cyclic sulfate compound is selected from one or more of ethylene sulfate, 4-methyl ethylene sulfate, propylene sulfate.

[0095] In some embodiments, the phosphate ester compound is selected from at least one of a saturated phosphate ester compound and an unsaturated phosphate ester compound. The saturated phosphate ester compound includes tris(trimethylsilyl) phosphate; the unsaturated phosphate ester compound includes at least one of triallyl phosphate, triallyl phosphite, and hydroxyethyl methacrylate phosphate.

[0096] In some embodiments, the borate ester compound is selected from one or more of tris(trimethylsilyl) borate and tris(triethylsilyl) borate.

[0097] In some embodiments, the battery further comprises a solid-state electrolyte layer, the solid-state electrolyte layer comprises a solid-state electrolyte, the solid-state electrolyte comprises at least one of a polymer solid-state electrolyte, an oxide solid-state electrolyte, a sulfide solid-state electrolyte, a halide solid-state electrolyte, a hydride solid-state electrolyte, and a nitride solid-state electrolyte.

[0098] In order to more clearly understand the above objects, features and advantages of the present application, the schemes of the present application will be further described below. It should be noted that the embodiments of the present application and the features in the embodiments can be combined with each other without conflict.

[0099] In the following description, a large number of details are set forth in order to provide a thorough understanding of the present application, but the present application can also be implemented in other different manners from the description; obviously, the embodiments in the specification are only some embodiments of the present application, not all embodiments.

[0100] Embodiment 1: An electrochemical device comprising a positive electrode and a silicon-based negative electrode.

[0101] Preparation of a silicon-based negative electrode binder:

[0102] A single-walled carbon nanotube and dopamine hydrochloride were added to a Tris-HCl buffer solution (pH = 8.5) at a mass ratio of 1:1, stirred at room temperature for 12 h, and the reaction product was centrifuged and washed several times until the dispersion was neutral. After freeze-drying, polydopamine surface-modified carbon nanotubes were obtained.

[0103] The polydopamine surface-modified carbon nanotubes were added to water and ultrasonically dispersed for 1 h to obtain a dispersion of polydopamine surface-modified carbon nanotubes, and the mass fraction of the polydopamine surface-modified carbon nanotubes in the dispersion was 1%.

[0104] Polyacrylic acid was dissolved in water and mechanically stirred for 1 h to obtain a polyacrylic acid glue solution, and the mass fraction of the polyacrylic acid in the glue solution was 5%.

[0105] The dispersion liquid and the glue liquid are mixed according to the mass ratio of the polydopamine surface modified carbon nanotube to the polyacrylic acid 5:1, and after stirring and reaction, a silicon-based negative electrode adhesive is obtained.

[0106] Preparation of a silicon-based negative electrode:

[0107] The prepared silicon-based negative electrode adhesive, negative electrode active material, first adhesive, and first conductive agent are added into water in a certain proportion and uniformly dispersed to obtain a negative electrode active material slurry.

[0108] In the negative electrode active material slurry, the mass ratio of the negative electrode active material, the silicon-based negative electrode adhesive, the first adhesive, and the first conductive agent is 90:4:1:5.

[0109] The negative electrode active material is a mixture of graphite and silicon carbon, and the mass ratio of graphite to silicon carbon in the negative electrode active material is 50% and 50% respectively. The first conductive agent is conductive carbon black.

[0110] The first adhesive is a mixture of carboxymethyl cellulose sodium and butadiene rubber, and the weight ratio of the two is 1:1.

[0111] The negative electrode active material slurry is coated on the negative electrode current collector copper foil, and after drying, rolling and die cutting, a silicon-based negative electrode is obtained.

[0112] Preparation of a positive electrode:

[0113] The positive electrode active material lithium nickel cobalt manganese oxide, the second adhesive polyvinylidene fluoride, and the second conductive agent are mixed in the N-methyl pyrrolidone solvent and stirred for 60 min to form a positive electrode active material slurry. Then, the positive electrode active material slurry is coated on the positive electrode current collector aluminum foil, and after drying, rolling and die cutting, a positive electrode is obtained.

[0114] The second conductive agent is a mixture of conductive carbon black and carbon nanotubes, and the mass ratio of the two is 1:1.

[0115] The mass ratio of the positive electrode active material, the second adhesive, and the second conductive agent is 97:2:1.

[0116] Preparation of an electrochemical device:

[0117] The prepared positive electrode, PE separator, and silicon-based negative electrode are stacked to form a battery cell, and then a liquid electrolyte is injected to form an electrochemical device.

[0118] Example 2: An electrochemical device comprising a positive electrode and a silicon-based negative electrode.

[0119] The structure, preparation process, and raw materials of this example and example 1 are completely the same, and the only difference is that in this example, the mass ratio of single-walled carbon nanotubes to dopamine hydrochloride is 5:1.

[0120] Example 3: An electrochemical device comprising a positive electrode and a silicon-based negative electrode.

[0121] The structure, preparation process, and raw materials of this example and example 1 are completely the same, and the only difference is that in this example, the mass ratio of single-walled carbon nanotubes and dopamine hydrochloride is 1:5.

[0122] Example 4: An electrochemical device comprising a positive electrode and a silicon-based negative electrode.

[0123] The structure, preparation process, and raw materials of this example and example 1 are completely the same, and the only difference is that in this example, the mass ratio of polydopamine surface modified carbon nanotubes and polyacrylic acid is 1:1.

[0124] Example 5: An electrochemical device comprising a positive electrode and a silicon-based negative electrode.

[0125] The structure, preparation process, and raw materials of this example and example 1 are completely the same, and the only difference is that in this example, the mass ratio of polydopamine surface modified carbon nanotubes and polyacrylic acid is 1:5.

[0126] Example 6: An electrochemical device comprising a positive electrode and a silicon-based negative electrode.

[0127] The structure, preparation process, and raw materials of this example and example 1 are completely the same, and the only difference is that in this example, the mass ratio of polydopamine surface modified carbon nanotubes and polyacrylic acid is 1:9.

[0128] Example 7: An electrochemical device comprising a positive electrode and a silicon-based negative electrode.

[0129] The structure, preparation process, and raw materials of this example and example 1 are completely the same, and the only difference is that in this example, the mass ratio of single-walled carbon nanotubes and dopamine hydrochloride is 1:9.

[0130] Comparative Example 1: An electrochemical device comprising a positive electrode and a silicon-based negative electrode.

[0131] The structure, preparation process, and raw materials of this example and example 1 are completely the same, and the only difference is that in this example, the mass ratio of single-walled carbon nanotubes and dopamine hydrochloride is 1:9.

[0132] Comparative Example 2: An electrochemical device comprising a positive electrode and a silicon-based negative electrode.

[0133] The structure, preparation process, and raw materials of this example and example 1 are completely the same, and the only difference is that in this example, the mass ratio of single-walled carbon nanotubes and dopamine hydrochloride is 1:9.

[0134] Dopamine hydrochloride was dispersed in water to obtain a dispersion. The mass fraction of dopamine hydrochloride in the dispersion was 1%.

[0135] Polyacrylic acid was dissolved in water and stirred mechanically for 1 h to obtain a polyacrylic acid glue solution. The mass fraction of polyacrylic acid in the glue solution was 5%.

[0136] The dispersion and the glue solution were mixed according to the mass ratio of dopamine hydrochloride to polyacrylic acid of 5:1, and a silicon-based negative electrode binder was obtained after stirring and reaction.

[0137] Comparative Example 3: An electrochemical device comprising a positive electrode and a silicon-based negative electrode.

[0138] The structure, preparation process, and raw materials of the present comparative example and Example 1 are basically the same, and the only difference is that in the present comparative example, the silicon-based negative electrode binder is prepared according to the following method:

[0139] Single-walled carbon nanotubes and dopamine hydrochloride were added to Tris-HCl buffer solution (pH = 8.5) according to a mass ratio of 1:1, stirred at room temperature for 12 h, and the reaction product was centrifuged and washed several times until the dispersion was neutral. After freeze-drying, polydopamine surface-modified carbon nanotubes were obtained, which were the silicon-based negative electrode binder of the present comparative example.

[0140] Comparative Experiment: Ten groups of samples were taken from Examples 1-7 and Comparative Examples 1-3, each group containing 30 samples. The following tests were performed on each group, and the average values were taken as the test results.

[0141] Cycle capacity test:

[0142] 1. The manganese ion battery sample was placed in an environment at 25±2℃, charged at 1C to the charge termination voltage of 4.2V, and the cutoff current was 0.05C. It was left for 1h;

[0143] 3. At an environment temperature of 25±2℃, the sample was discharged at 1C constant current to the lower limit voltage of 3.0V and left for 1h;

[0144] 4. Steps 2-3 were repeated for 500 cycles, and the capacity retention rate was calculated. Cycle capacity retention rate = nth cycle discharge capacity / first cycle discharge capacity x 100%.

[0145] The test results are shown in the following table:

[0146]

[0147]

[0148] According to the above table, introducing polydopamine on the surface of carbon nanotubes for surface modification and cross-linking reaction with polyacrylic acid can form a continuous and uniform semi-rigid three-dimensional network structure, can bind the volume change of silicon-based negative electrode in the cycle process, and the composite binder has self-repairing ability, can maintain the stability of the binder structure, thereby improving the cycle life of the battery.

[0149] In addition, according to examples 1-7, the capacity retention rate of the electrochemical device in examples 1-5 can reach more than 80% after 500 cycles, while examples 6 and 7 are less than 80%, therefore, the mass ratio of carbon nanotubes to dopamine hydrochloride is controlled in (1:5)~(5:1), and the mass ratio of polydopamine modified carbon nanotubes to polyacrylic acid is controlled in the range of (1:5)~(5:1) is the best.

[0150] It should be noted that the above only describes the preferred embodiments of the present application and is not intended to limit the present application, and any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A silicon-based negative electrode binder, characterized in that, Including a three-dimensional cross-linked network structure; The silicon-based negative electrode adhesive is prepared by the cross-linking reaction of polydopamine-modified carbon nanotubes with polyacrylic acid.

2. The adhesive according to claim 1, characterized in that, The carbon nanotubes include single-walled carbon nanotubes and multi-walled carbon nanotubes.

3. The method for preparing the silicon-based negative electrode adhesive as described in claim 1, characterized in that, The steps include the following: Carbon nanotubes and dopamine hydrochloride were added to Tris-HCl buffer and stirred for 12-24 hours. After centrifugation, washing and freeze-drying, polydopamine-modified carbon nanotubes were obtained. The polydopamine-modified carbon nanotubes are dispersed in water to form a dispersion, and polyacrylic acid is dispersed in water to form a gel. The gel and the dispersion are then mixed and crosslinked to form a silicon-based anode binder with a three-dimensional crosslinked network structure.

4. The method according to claim 3, characterized in that, The mass ratio of the carbon nanotubes to the dopamine hydrochloride is (1:5) to (5:1).

5. The method according to claim 3, characterized in that, The mass ratio of the polydopamine-modified carbon nanotubes to the polyacrylic acid is (1:5) to (5:1).

6. The method according to claim 3, characterized in that, The dispersion has a mass fraction of 0.01% to 5%.

7. The method according to claim 3, characterized in that, The mass fraction of the adhesive solution is 0.01% to 10%.

8. A silicon-based negative electrode, comprising a negative electrode current collector, a negative electrode active material layer disposed on the surface of the negative electrode current collector, and a first conductive agent; characterized in that, It also includes the silicon-based negative electrode binder and the first binder as described in claim 1.

9. The silicon-based negative electrode according to claim 8, characterized in that, The first adhesive includes at least one of sodium carboxymethyl cellulose, polyacrylic acid, polyacrylate, and styrene-butadiene rubber.

10. A battery, characterized in that, It includes a positive electrode, a separator, and a negative electrode, characterized in that the negative electrode is a silicon-based negative electrode as described in claim 8 or 9.

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