CN115663195B

CN115663195B - Silicon-based negative plate and preparation method thereof, lithium ion battery and electronic equipment

Info

Publication number: CN115663195B
Application number: CN202211653926.1A
Authority: CN
Inventors: 弓景耀
Original assignee: Bolu Tiancheng New Energy Technology Co ltd
Current assignee: Bolu Tiancheng New Energy Technology Co ltd
Priority date: 2022-12-22
Filing date: 2022-12-22
Publication date: 2023-03-10
Anticipated expiration: 2042-12-22
Also published as: CN115663195A

Abstract

The invention provides a silicon-based negative plate and a preparation method thereof, a lithium ion battery and electronic equipment, wherein the silicon-based negative plate comprises: a negative current collector; and a negative active material layer disposed on at least one side of the negative current collector, the negative active material layer including: a silicon-based negative electrode active material, a binder, and a conductive agent; wherein the binder is selected from one or more of polyacrylamide, beta-cyclodextrin, modified beta-cyclodextrin and polydopamine; the modified beta-cyclodextrin is obtained by modifying beta-cyclodextrin by using a fluorine-containing acrylate compound. The silicon-based negative plate can effectively improve the cycle performance and the rate capability of the lithium ion battery.

Description

Silicon-based negative plate and preparation method thereof, lithium ion battery and electronic equipment

Technical Field

The invention relates to the technical field of batteries, in particular to a silicon-based negative plate and a preparation method thereof, a lithium ion battery and electronic equipment.

Background

The lithium ion battery negative electrode material is used as an intercalation object of lithium ions, and the performance of the lithium ion battery negative electrode material directly determines the electrochemical performance of the lithium battery. Because the graphite material has rich resources and low price, the traditional negative electrode generally adopts the graphite material, but the development of the graphite negative electrode is severely limited by the low theoretical specific capacity of the graphite negative electrode. Si has higher theoretical capacity (3579 mAh/g Li) ₂₂ Si ₅ ) Low working voltage (0.4V vs Li/Li) ⁺ ) The advantages of resource richness, environmental friendliness and the like are distinguished from a plurality of cathode materials. Furthermore, the semiconductor industry is moving toward a mature stage which is beneficial for reducing the cost of processing Si.

However, during initial lithiation, the Si undergoes a severe volume expansion due to phase transition of crystalline silicon, and during delithiation, the Si undergoes a volume change of about 300% during lithiation/delithiation, and such a large volume fluctuation causes self-pulverization and breakage of Si particles during cycling, and separation of particles to lose electrochemical contact. The above fatal problem causes a sharp drop in reversible capacity in a short time. In addition, unstable Solid Electrolyte Interphase (SEI) formed on the Si negative electrode surface) Resulting in a large compromise in the Coulombic Efficiency (CE) and cycle stability of the lithium ion battery, i.e. exposure of new electrode surfaces to the electrolyte with a large change in the Si negative electrode volume during electrochemical cycling, resulting in continuous growth of new SEI which not only consumes a large amount of electrolyte and Li ⁺ And increase Li ⁺ The distance of diffusion, resulting in lower CE and material degradation.

In order to solve the above problems, those skilled in the art have proposed various methods such as design of the structure of the Si anode active material, development of a binder suitable for the silicon-based anode material, and the like. Among them, the structure of the Si negative active material has been designed with good progress, but since the preparation method is complicated and industrial mass production is difficult, it is important to develop a binder having good adhesion that can adapt to the volume change of Si particles in the field.

Patent CN107959027A discloses a preparation method of a silicon-based negative electrode binder of a lithium ion battery and a negative electrode sheet containing the binder, wherein the binder is prepared by the following method: ultrasonically dispersing graphite oxide in water to obtain a water dispersion of Graphene Oxide (GO) with the concentration of 0.5-5mg/mL, adding a modified SBR binder, wherein the mass ratio of GO to the modified SBR binder is 1-10-1. Although the binder has better conductivity, the acting force with Si groups is weaker, and the binder is easy to separate from the binder in the process of lithiation/delithiation of the Si groups, so that the cycle performance is reduced.

Patent CN 109722190A discloses a preparation method of a silicon-based negative electrode binder of a lithium battery and a binder thereof, and the preparation method comprises the steps of firstly preparing polyacrylate seed emulsion by adopting iodine transfer active radical miniemulsion polymerization, then adding a styrene monomer for continuous polymerization, and finally partially hydrolyzing the obtained block copolymer under an alkaline condition to obtain a polyethylene-polyacrylate-polyacrylic acid-polystyrene block copolymer binder. Although the adhesive has good adhesion, the block copolymer has high rigidity and cannot effectively control stress generated by volume change of the Si-based material, so that the cycle performance is reduced.

Therefore, it is required to develop a binder having good adhesion and capable of adapting to the volume change of the Si-based active material for preparing the silicon-based negative electrode sheet.

Disclosure of Invention

The invention provides a silicon-based negative plate, a preparation method thereof, a lithium ion battery and electronic equipment.

In a first aspect, the present invention provides a silicon-based negative electrode plate, including:

a negative current collector; and

a negative active material layer disposed on at least one side of the negative current collector, the negative active material layer including: a silicon-based negative electrode active material, a binder, and a conductive agent;

wherein the binder is selected from one or more of polyacrylamide, beta-cyclodextrin, modified beta-cyclodextrin and polydopamine;

the modified beta-cyclodextrin is obtained by modifying beta-cyclodextrin by using a fluorine-containing acrylate compound.

According to the technical scheme, the adhesive suitable for the silicon-based negative electrode active material is used, so that the interaction among the silicon-based negative electrode active material, the adhesive and the current collector is enhanced, a cross-linked network structure formed by all components in the adhesive can effectively relieve mechanical stress caused by silicon expansion, and meanwhile, a cross-linked network mechanism formed by the adhesive and the adhesive are connected with the silicon-based negative electrode active material through a large number of hydrogen bonds, so that the silicon-based negative electrode plate has a good self-repairing effect, and therefore, a smooth electric/ionic conduction path can be ensured, and the cycle performance and the rate capability of a lithium ion battery can be effectively improved.

In some embodiments of the present invention, the binder is a mixture of 1:0.5 to 3:0.01 to 0.1 parts of polyacrylamide, modified beta-cyclodextrin and dopamine.

In some embodiments of the invention, the method for preparing the modified beta-cyclodextrin comprises the following steps:

s1, dissolving beta-cyclodextrin in water to obtain a beta-cyclodextrin aqueous solution;

s2, respectively adding potassium persulfate, acrylic ester, a fluorine-containing acrylate compound and propionyl peroxide into the beta-cyclodextrin aqueous solution, and reacting to obtain the modified beta-cyclodextrin.

In some embodiments of the present invention, the S2 specifically includes:

s21, adding potassium persulfate into the beta-cyclodextrin aqueous solution to react to obtain an activated beta-cyclodextrin aqueous solution;

s22, adding acrylate and fluorine-containing acrylate compounds into the activated beta-cyclodextrin aqueous solution to react to obtain a pre-reaction mixed solution;

s23, adding propionyl peroxide (di) into the pre-reaction mixed solution for reaction, and drying to obtain the modified beta-cyclodextrin.

In some embodiments of the present invention, the silicon-based negative active material is one or more of nano silicon powder, silicon oxide, silicon-carbon composite, and silicon-lithium alloy.

In some embodiments of the present invention, the conductive agent is selected from one or more of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

In some embodiments of the present invention, the negative active material layer includes, in mass percent: 40% -80% of a silicon-based negative electrode active material, 10% -30% of a binder and 10% -30% of a conductive agent.

In a second aspect, the invention provides a preparation method of a silicon-based negative electrode plate, which comprises the following steps:

mixing the silicon-based negative electrode active material, the binder and the conductive agent in the silicon-based negative electrode plate according to any one of the embodiments of the first aspect in a solvent to obtain negative electrode slurry;

and coating the negative electrode slurry on a negative electrode current collector to obtain the silicon-based negative electrode plate.

In a third aspect, the present invention provides a lithium ion battery, comprising:

the silicon-based negative electrode plate according to any embodiment of the first aspect or the silicon-based negative electrode plate obtained by the preparation method according to any embodiment of the second aspect.

In a fourth aspect, the present invention provides an electronic device, comprising:

the lithium ion battery of any embodiment of the third aspect.

Detailed Description

The examples or embodiments are described in a progressive arrangement throughout this specification, each with emphasis on illustrating differences from the other examples.

In the description of the present specification, references to the description of the terms "one embodiment," "some embodiments," "an illustrative embodiment," "an example," "a specific example," or "some examples" or the like, mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present invention. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of the feature. In the description of the present invention, "a plurality" means at least two, e.g., two, three, etc., unless specifically limited otherwise.

At present, the most common negative electrode material of lithium ion batteries on the market is a graphite negative electrode, but the graphite negative electrode can only store one lithium ion per 6 carbon atoms, so the specific capacity is low, and in order to further improve the specific capacity of the negative electrode material, the negative electrode material which stores more lithium ions per unit mass or unit volume has been studied, wherein a Si-based negative electrode material is one of the most promising negative electrode materials.

However, the biggest disadvantage of the Si-based negative electrode material is that it undergoes a volume change of 300% during lithiation/delithiation, even though the volume change of the current silicon-based negative electrode material is about 200%, and such a large volume fluctuation causes self-pulverization and cracking of the Si material, which in turn causes particle separation to lose electrochemical basis, resulting in significant reduction in cycle performance and rate performance.

In the prior art, the performance of the silicon-based anode active material is improved mainly by optimizing the structure of the silicon-based anode active material, and the influence of volume change on the material is reduced by technologies such as a core-shell structure, an eggshell structure, a silicon nanowire and silicon nanocrystallization, but the methods are high in cost and are not suitable for large-scale industrial production. Therefore, the invention starts with the selection of the binder in the negative plate, designs the binder capable of effectively controlling the influence of the volume change of the silicon-based material on the electric/ionic conduction path, and the silicon-based negative plate prepared by using the binder still has complete electric/ionic conduction path after multiple charge-discharge cycles, thereby being capable of preparing the lithium ion battery with good cycle performance and rate capability.

a negative current collector; and

set up in the negative pole active material layer of at least one side of negative pole mass flow body, negative pole active material layer includes: a silicon-based negative electrode active material, a binder, and a conductive agent;

wherein, the binder is selected from one or more of polyacrylamide, beta-cyclodextrin, modified beta-cyclodextrin and polydopamine;

the modified beta-cyclodextrin is obtained by modifying beta-cyclodextrin with a fluorine-containing acrylate compound selected from the group consisting of 2- (perfluoro-3-methylbutyl) ethacrylic acid, 2- (perfluorobutyl) acrylic acid, 2- (perfluorobutyl) ethacrylic acid ester, and 2- (perfluorohexyl) ethylmethacrylate. One or more of them.

According to the technical scheme, the adhesive suitable for the silicon-based negative electrode active material is used, so that the interaction among the silicon-based negative electrode active material, the adhesive and the current collector is enhanced, a cross-linked network structure formed by all components in the adhesive can effectively reduce mechanical stress caused by silicon expansion, and meanwhile, a cross-linked network mechanism formed by the adhesive and the adhesive are connected with the silicon-based negative electrode active material through a large number of hydrogen bonds, so that the silicon-based negative electrode plate has a good self-repairing function, and therefore, a smooth electric/ionic conducting path can be ensured, and the cycle performance and the rate capability of a lithium ion battery can be effectively improved.

In the technical scheme of the invention, polyacrylamide and beta-cyclodextrin are selected as binders at first, and a large number of hydrogen bonds are formed by utilizing a large number of amido bonds in the polyacrylamide and hydroxyl groups of the beta-cyclodextrin and hydroxyl groups on the surface of a silicon-based negative electrode material to form a cross-linked network structure. Meanwhile, the polyacrylamide has high Young modulus, so that the volume of the negative active material layer can be guaranteed not to deform when the volume of the silicon-based negative material changes, the molecular weight of the beta-cyclodextrin is low, and the beta-cyclodextrin can move in a cross-linked network when the volume of the silicon-based negative material changes, so that the change of the internal stress of the negative active material layer is dispersed, the negative active material layer is prevented from being broken, and a good electric/ionic conduction path is guaranteed. On the other hand, a large number of lone-pair electrons in polyacrylamide and beta-cyclodextrin and a cyclic structure of the beta-cyclodextrin can promote the transfer of lithium ions, so that the cycle performance and the rate capability of the lithium ion battery are improved.

In subsequent experiments, it is found that although polyacrylamide and beta-cyclodextrin are used as a binder to effectively control the influence of volume change of a silicon-based negative active material on a negative active material layer in the charge and discharge processes, the acting force of the binder and the silicon-based active material is mainly formed by hydrogen bonds with hydroxyl on the surface of the silicon-based active material, the magnitude of the acting force has a great relationship with the number of hydroxyl on the surface of the silicon-based active material, when the number of hydroxyl on the surface of the silicon-based active material is small, the acting force of the binder and the silicon-based active material is weak, and when the charge and discharge rate is high, the weak acting force cannot adapt to the volume change speed of the silicon-based active material, so that the performance is reduced.

Through analysis, the main component of the active material layer generating stress release for volume change is beta-cyclodextrin, so that the beta-cyclodextrin is further modified, and the main modification thought is to enhance the acting force of the silicon-based active material, so that the beta-cyclodextrin is grafted with the chain segment with the F atom, on one hand, the hydrogen bond acting force formed by the F atom and the hydroxyl group is stronger, and on the other hand, the F atom and Si have stronger acting force.

Further, as is well known to those skilled in the art, the current collector of the negative electrode tab generally uses metallic copper. The polyacrylamide, the beta-cyclodextrin and the modified beta-cyclodextrin are used as the binder, and although the silicon-based negative electrode material layer and the current collector have better adhesive property in the early stage, after the silicon-based negative electrode plate is assembled into a battery, the adhesive property of the silicon-based negative electrode material layer and the current collector is easily reduced and even the silicon-based negative electrode material layer and the current collector fall off under the long-time soaking and charging and discharging circulation in electrolyte.

In contrast, the invention utilizes the characteristic of dopamine autopolymerization, dopamine with a certain concentration is added into negative active slurry in the process of preparing a negative plate, the negative active slurry is coated on the surface of a negative current collector for in-situ polymerization, and because the dopamine has good metal coordination effect, a layer of polydopamine film can be formed on the surface of the metal current collector, so a large amount of amino and hydroxyl groups can exist on the surface of the metal current collector, the polydopamine film can interact with polyacrylamide, beta-cyclodextrin and modified beta-cyclodextrin in a binder, and the polydopamine layer is relatively stable, so that the obtained negative active material layer and the current collector also have good cohesiveness, on the other hand, the polydopamine layer is accumulated through a large amount of pi-pi conjugation effect and hydrogen bonding effect, and has relatively good conductivity, so the conductivity of the negative plate cannot be influenced by the polydopamine layer with proper thickness. Thereby further improving the cycle performance and rate capability of the lithium battery.

It should be noted that, in the technical solution of the present invention, the types of the negative current collector, the types of the silicon-based active material, the conductive agent, the types of the fluorine-containing acrylate compound, and the specific preparation method of the modified β -cyclodextrin are not further limited, and any solution that does not depart from the technical concept of the technical solution of the present invention falls within the protection scope of the present invention.

In some embodiments of the present invention, the fluoroacrylate compound is selected from one or more of 2- (perfluoro-3-methylbutyl) ethacrylic acid, 2- (perfluorobutyl) acrylic acid, 2- (perfluorobutyl) ethacrylate, and 2- (perfluorohexyl) ethylmethacrylate.

The above is merely exemplary, and it is within the scope of the present invention for a person skilled in the art to select other specific types of fluoroacrylate compounds without any inventive effort. It should be noted that, in order to ensure a certain mobility of the modified β -cyclodextrin in the negative electrode active material layer, the grafted segment and the branched chain of the segment are not likely to be too long, which may affect the self-healing property of the negative electrode material layer.

In some embodiments of the invention, the binder is present in a mass ratio of 1:0.5 to 3:0.01 to 0.1 of polyacrylamide, modified beta-cyclodextrin and dopamine.

In some embodiments, the mass ratio of the polyacrylamide, the modified beta-cyclodextrin and the dopamine in the binder is specifically defined, and the obtained binder has the best stability of the silicon-based negative electrode sheet in the charge and discharge processes, so that the cycle performance and rate performance of the lithium battery are better.

The method comprises the steps of adding the modified beta-cyclodextrin into a binder, coating the modified beta-cyclodextrin on the surface of a negative current collector after adding the modified beta-cyclodextrin into negative active slurry, and covering the modified beta-cyclodextrin on the surface of the negative current collector after self-polymerization to form a polydopamine layer, wherein a small part of polydopamine layer interacts with other components in the negative active layer.

In addition, as can be seen from the above ratio, the mass fraction of dopamine in the binder is minimized because dopamine has a strong self-polymerizing ability, and excessive addition increases the crosslinking density of the negative electrode active material layer, which in turn decreases the cycle performance and rate performance of the battery, and therefore the content of dopamine in the binder should be controlled.

In some embodiments of the invention, a method of preparing a modified beta-cyclodextrin comprises the steps of:

In some embodiments, the preparation method of the modified beta-cyclodextrin is provided, and the fluorine-containing acrylate compound can be smoothly grafted on the beta-cyclodextrin, so that the acting force of the modified beta-cyclodextrin and the silicon-based negative electrode active material is improved. It is worth to be noted that the added reaction monomer not only contains the fluorine-containing acrylate compound, but also contains the acrylate, because the fluorine-containing side chain is not easy to be soaked by the electrolyte, so that the ionic conductivity of the negative active material layer is reduced, and therefore, a certain amount of acrylate needs to be added, so that the binder has good electrolyte affinity.

In some embodiments of the invention, the mass fraction of the aqueous solution of beta-cyclodextrin in S1 is 5% to 10%.

In addition, β -cyclodextrin has low solubility in water at room temperature, and needs to be dissolved by heating and stirring.

In some embodiments of the invention, the reaction temperature in S2 is 80 to 90 ℃.

In some embodiments of the present invention, in S2, the mass ratio of the β -cyclodextrin, the acrylate, and the fluorine-containing acrylate compound is 10:1 to 3:0.5 to 1.5.

In some embodiments, when the mass ratio of the beta-cyclodextrin to the acrylate to the fluorine-containing acrylate compound is 10:1 to 3: when the reaction temperature is 0.5 to 1.5, the obtained modified beta-cyclodextrin has good acting force with a silicon-based active material and also has good electrolyte affinity.

In some embodiments of the invention, in S2, the acrylate is specifically ethyl acrylate.

In some embodiments of the present invention, S2 specifically includes:

In some embodiments of the invention, in S21, the mass fraction of the potassium persulfate in the activated β -cyclodextrin aqueous solution is 0.1% to 1%.

In some embodiments of the invention, in S21, the amount of propionyl (di) peroxide added is 0.1% to 1% of the mass of the pre-reaction mixture.

In some embodiments of the present invention, the negative electrode active material layer may further include other auxiliaries, such as a thickener, for example, sodium carboxymethyl cellulose, and the like.

It should be noted that the present invention is not limited to the above materials, and other known materials that can be used as the silicon-based negative electrode active material, the conductive agent, and the thickener may also be used in the silicon-based negative electrode sheet of the present invention.

In some embodiments of the present invention, the negative electrode current collector has two surfaces opposite in a thickness direction thereof, and the negative electrode active material layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

As the negative electrode collector, a metal foil or a porous metal plate, for example, a foil or a porous plate using a metal such as copper, nickel, titanium, or iron, or an alloy thereof, may be used. As an example, the negative current collector is a copper foil.

The silicon-based negative electrode sheet of the present invention does not exclude additional functional layers other than the negative electrode active material layer. For example, in certain embodiments, the silicon-based negative electrode sheet of the present invention further comprises a conductive undercoat layer interposed between the negative electrode current collector and the negative electrode active material layer, disposed on the surface of the negative electrode current collector.

and coating the negative electrode slurry on a negative electrode current collector to obtain the silicon-based negative plate.

The silicon-based negative plate can be prepared according to the conventional method in the field. The solvent can be deionized water, the solid content in the negative electrode slurry is 30-80 wt%, and the silicon-based negative electrode sheet is obtained by coating the negative electrode slurry on a negative electrode current collector, drying, cold pressing, cutting into pieces, cutting and drying.

In some embodiments of the invention, the lithium ion battery further comprises: the positive plate, the isolating membrane and the electrolyte.

In some embodiments of the present invention, the silicon-based negative electrode sheet, the positive electrode sheet, and the separator may be manufactured into an electrode assembly through a winding process or a lamination process.

The lithium ion battery of the invention also comprises an outer package for packaging the electrode assembly and the electrolyte. In some embodiments, the outer package may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, or the like, or a soft bag, such as a soft bag. The soft bag can be made of plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT) and polybutylene succinate (PBS).

[ Positive plate ]

The materials, composition and manufacturing method of the positive electrode sheet used in the lithium ion battery of the present invention may include any known techniques in the art.

The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector and including a positive electrode active material. As an example, the positive electrode current collector has two surfaces opposite in its own thickness direction, and the positive electrode active material layer is provided on either or both of the two surfaces opposite to the positive electrode current collector.

In some embodiments of the present invention, the positive electrode active material layer includes a positive electrode active material, and the specific kind of the positive electrode active material is not particularly limited and may be selected as desired. For example, the positive active material may include one or more of lithium transition metal oxide, olivine-structured lithium-containing phosphate, and respective modified compounds thereof. In the lithium ion battery of the present invention, the modified compound of each positive electrode active material may be a compound obtained by modifying the positive electrode active material by doping, surface coating, or both doping and surface coating.

In some embodiments of the present invention, the positive electrode active material layer further optionally includes a conductive agent. As an example, the conductive agent may be selected from one or more of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

In some embodiments of the invention, the positive electrode active material layer further optionally includes a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluoroacrylate resin.

In some embodiments of the present invention, the positive electrode current collector may employ a metal foil or a composite current collector. As an example of the metal foil, an aluminum foil may be used as the positive electrode current collector. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. By way of example, the metal material may be selected from one or more of aluminum, aluminum alloy, nickel alloy, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may be selected from polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, and the like.

The positive electrode sheet of the present invention can be prepared according to a conventional method in the art. For example, the positive electrode active material layer is generally formed by coating a positive electrode slurry on a positive electrode current collector, drying, and cold pressing. The positive electrode slurry is generally formed by dispersing a positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring them uniformly. The solvent may be N-methylpyrrolidone (NMP), but is not limited thereto.

The positive electrode sheet of the present invention does not exclude additional functional layers other than the positive electrode active material layer. For example, in some embodiments, the positive electrode sheet of the present invention further includes a conductive undercoat layer (composed of, for example, a conductive agent and a binder) interposed between the positive electrode current collector and the positive electrode active material layer and provided on the surface of the positive electrode current collector. In some other embodiments, the positive electrode sheet of the present invention further includes a protective layer covering the surface of the positive electrode active material layer.

[ ELECTROLYTE ]

The electrolyte plays a role in conducting active ions between the positive plate and the negative plate. The electrolyte that can be used in the lithium ion battery of the present invention may be an electrolyte known in the art.

In some embodiments of the present invention, the electrolyte includes an organic solvent, a lithium salt, and an optional additive, and the types of the organic solvent, the lithium salt, and the additive are not particularly limited and may be selected as needed.

In some embodiments of the invention, the lithium salt includes, by way of example and not limitation, liPF ₆ (lithium hexafluorophosphate), liBF ₄ Lithium tetrafluoroborate (LiClO), liClO ₄ (lithium perchlorate), liFSI (lithium bis-fluorosulfonylimide), liTFSI (lithium bis-trifluoromethanesulfonylimide), liTFS (lithium trifluoromethanesulfonate), liDFOB (lithium difluorooxalato borate), liBOB (lithium dioxaoxalato borate), liPO ₂ F ₂ (lithium difluorophosphate), liDFOP (lithium difluorooxalate phosphate) and LiTFOP (lithium tetrafluorooxalate phosphate). The lithium salt may be used alone or in combination of two or more.

In some embodiments of the present invention, the organic solvent includes, by way of example and not limitation, at least one of Ethylene Carbonate (EC), propylene Carbonate (PC), ethyl Methyl Carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl Propyl Carbonate (MPC), ethyl Propyl Carbonate (EPC), butylene Carbonate (BC), fluoroethylene carbonate (FEC), methyl Formate (MF), methyl Acetate (MA), ethyl Acetate (EA), propyl Acetate (PA), methyl Propionate (MP), ethyl Propionate (EP), propyl Propionate (PP), methyl Butyrate (MB), ethyl Butyrate (EB), 1, 4-butyrolactone (GBL), sulfolane (SF), dimethylsulfone (MSM), methylethylsulfone (EMS), and diethylsulfone (ESE). The organic solvent may be used alone or in combination of two or more. Alternatively, two or more of the above organic solvents are used at the same time.

In some embodiments of the present invention, the additives may include a negative electrode film-forming additive, a positive electrode film-forming additive, and may further include an additive capable of improving certain properties of the battery, such as an additive for improving overcharge properties of the battery, an additive for improving high-temperature or low-temperature properties of the battery, and the like.

By way of example, the additive includes, but is not limited to, at least one of fluoroethylene carbonate (FEC), vinylene Carbonate (VC), vinyl Ethylene Carbonate (VEC), vinyl sulfate (DTD), propylene sulfate, vinyl sulfite (ES), 1, 3-Propanesultone (PS), 1, 3-Propanesultone (PST), sulfonate cyclic quaternary ammonium salts, succinic anhydride, succinonitrile (SN), adiponitrile (AND), tris (trimethylsilane) phosphate (TMSP), tris (trimethylsilane) borate (TMSB).

The electrolyte may be prepared according to a method conventional in the art. For example, an organic solvent, a lithium salt, and an optional additive may be uniformly mixed to obtain an electrolyte. The adding sequence of the materials is not particularly limited, for example, lithium salt and optional additives are added into an organic solvent and uniformly mixed to obtain an electrolyte; or, firstly, adding the lithium salt into the organic solvent, then adding the optional additive into the organic solvent, and uniformly mixing to obtain the electrolyte.

[ isolating film ]

The isolating membrane is arranged between the positive plate and the silicon-based negative plate, mainly plays a role in preventing the short circuit of the positive plate and the negative plate and can enable active ions to pass through. The type of the separator is not particularly limited in the present invention, and any known separator having a porous structure and good chemical and mechanical stability may be used.

In some embodiments of the present invention, the material of the isolation film may be selected from one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride, but is not limited thereto. The separating film can be a single-layer film or a multi-layer composite film. When the isolating membrane is a multilayer composite film, the materials of all layers are the same or different. In some embodiment modes, a ceramic coating and a metal oxide coating can be further arranged on the isolation film.

the lithium ion battery of any of the embodiments of the third aspect.

The electronic device of the present invention is not particularly limited, and may be any electronic device known in the art. In some embodiments of the present invention, the electronic device may include, but is not limited to, a notebook computer, a pen-input computer, a mobile computer, an electronic book player, a portable phone, a portable facsimile, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, a liquid crystal television, a handheld cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notebook, a calculator, a memory card, a portable recorder, a radio, a backup power source, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a lighting fixture, a toy, a game machine, a clock, an electric tool, a flashlight, a camera, a large-sized household battery, a lithium ion capacitor, and the like.

The present disclosure is more particularly described in the following examples that are intended as illustrations only, since various modifications and changes within the scope of the present disclosure will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are on a mass basis, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further treatment, and the instruments used in the examples are commercially available.

The nano silicon powder has the average particle size of 80nm and is purchased from Shanghai lane field nano materials Co., ltd;

the electrochemical performance characterization method comprises the following steps:

assembling the battery: button cells were assembled in an Ar-filled glove box using lithium foil as the counter and reference electrodes, and 1.0mol/L LiPF ₆ Dissolving in a solvent with the volume ratio of 1:1:1 ethylene carbonate, dimethyl carbonate and diethyl carbonate (by volume) and fluoroethylene carbonate as electrolytes, 7 μm thick film as separator. Constant current charge-discharge cycling tests were conducted on a battery tester at room temperature of 0.01 to 1.2V.

And (3) testing charge and discharge cycles of the lithium ion battery: the assembled half cell is connected into a blue test system, the test mode is constant current charge-discharge circulation at room temperature,the voltage range of charging and discharging is 0.01-1.2V (vs Li/Li) ⁺ ) The procedure was first to activate charge and discharge at 400mA/g, and then to perform 100 charge and discharge cycles at 1000mA/g, and the residual capacity after 100 charge and discharge cycles was measured.

And (3) testing the rate performance of the battery: the test pattern at room temperature was: 400 Under the current density of 800, 1600, 3200 and 6400mA/g, each current density circulates for 5 circles, and finally returns to the current density of 400mA/g, and the voltage range of the battery is 0.01 to 1.2V (vs Li/Li) ⁺ ) The discharge capacity at this time was measured.

Example 1

Preparing a silicon-based negative plate:

mixing nano silicon powder, a conductive agent super P and a binder according to the weight ratio of 6:2:2, and dispersing in deionized water to obtain the cathode slurry with the solid content of 50%.

Coating the negative electrode slurry on a copper foil with a smooth single surface by using a scraper, placing the coated wet copper foil in a vacuum drying oven for drying for 12 hours at the temperature of 80 ℃, and cutting the dried pole piece into a circular piece with the diameter of 12mm by using a manual slicer after drying to obtain the silicon-based negative electrode piece.

Wherein the binder is prepared from the following components in a mass ratio of 1:2:0.01 of a mixture of polyacrylamide, modified beta-cyclodextrin and dopamine.

The preparation method of the modified beta-cyclodextrin comprises the following steps:

dissolving 10g of beta-cyclodextrin in 100mL of deionized water at 85 ℃ to obtain a beta-cyclodextrin aqueous solution;

adding 0.5g of potassium persulfate into the beta-cyclodextrin aqueous solution at 85 ℃ to react for 10min to obtain an activated beta-cyclodextrin aqueous solution;

adding 3g of ethyl acrylate and 1g of 2- (perfluorobutyl) acrylic acid into the activated beta-cyclodextrin aqueous solution at 85 ℃ to react for 1 hour to obtain a pre-reaction mixed solution;

adding 0.5g of (di) propionyl peroxide into the pre-reaction mixed solution at 85 ℃ for reaction for 2h, and then drying in vacuum at 80 ℃ for 12h to obtain the modified beta-cyclodextrin.

The silicon-based negative plate is assembled into a battery, and subjected to charge-discharge cycle test and rate performance test, and the results are shown in table 1.

Example 2

Preparing a silicon-based negative plate:

mixing nano silicon powder, a conductive agent super P and a binder according to the ratio of 6:2:2, and dispersing in deionized water to obtain the cathode slurry with the solid content of 50%.

Coating the negative electrode slurry on a copper foil with a smooth single surface by using a scraper, placing the coated wet copper foil in a vacuum drying oven for drying for 12 hours at the temperature of 80 ℃, and cutting the dried pole piece into a wafer with the diameter of 12mm by using a manual slicer after drying to obtain the silicon-based negative electrode piece.

Wherein the binder is prepared from the following components in a mass ratio of 1:2 and beta-cyclodextrin.

Example 3

Preparing a silicon-based negative plate:

Wherein the binder is prepared from the following components in a mass ratio of 1:2 and a modified beta-cyclodextrin.

adding 0.5g of potassium persulfate into the beta-cyclodextrin aqueous solution at 85 ℃ to react for 10min to obtain activated beta-cyclodextrin aqueous solution;

Example 4

Preparing a silicon-based negative plate:

Wherein the binder is prepared from the following components in percentage by mass of 1:2:0.01 of a mixture of polyacrylamide, beta-cyclodextrin and dopamine.

Comparative example 1

Preparing a silicon-based negative plate:

mixing nano silicon powder, conductive agent super P and sodium carboxymethyl cellulose according to the weight ratio of 6:2:2, and dispersing in deionized water to obtain the cathode slurry with the solid content of 50%.

TABLE 1

As can be seen from the results in table 1, the silicon-based negative electrode sheet obtained in example 1 has very good cycle performance and rate capability, and it is also demonstrated that the use of the binder in the example can significantly improve the high capacity electrode having a large volume variation. The cycle performance and the rate performance of each embodiment are higher than those of a comparative example, which shows that compared with the prior art that sodium carboxymethylcellulose is used as a binder compounded by polyacrylamide and beta-cyclodextrin, the binder has a better effect of adapting to the volume change of a silicon-based negative electrode active material, can be mainly attributed to the fact that polyacrylamide has higher Young modulus, can ensure that the volume of the negative electrode active material layer is not deformed when the volume of the silicon-based negative electrode material is changed, and the beta-cyclodextrin can move in a cross-linked network when the volume of the silicon-based negative electrode material is changed, so that the change of the internal stress of the negative electrode active material layer is dispersed, and the negative electrode active material layer is prevented from being broken, thereby ensuring a good electric/ionic conduction path. On the other hand, a large number of lone-pair electrons in polyacrylamide and beta-cyclodextrin and a cyclic structure of the beta-cyclodextrin can promote the transfer of lithium ions, so that the cycle performance and the rate capability of the lithium ion battery are improved.

Meanwhile, by comparing the results of the examples, the acting force of the modified beta-cyclodextrin and the silicon-based negative electrode active material is stronger, and when the nano silicon powder is used as the negative electrode active material, the stability of the silicon-based negative electrode sheet can be obviously improved by using the modified beta-cyclodextrin, so that the cycle performance and the rate capability of the lithium ion battery are improved. And a proper amount of dopamine is added, so that the acting force among the adhesive, the silicon-based negative electrode active material and the negative electrode current collector is improved, the stability of the silicon-based negative electrode plate is improved, and the cycle performance and the rate capability of the lithium ion battery are improved.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and these modifications or substitutions do not depart from the spirit of the corresponding technical solutions of the embodiments of the present invention.

Claims

1. A silicon-based negative plate is characterized by comprising:

a negative current collector; and

wherein the adhesive is prepared from the following components in a mass ratio of 1:0.5 to 3:0.01 to 0.1 of a mixture of polyacrylamide, modified beta-cyclodextrin and dopamine;

2. The silicon-based negative electrode plate according to claim 1, wherein the preparation method of the modified beta-cyclodextrin comprises the following steps:

3. The silicon-based negative electrode plate according to claim 2, wherein S2 specifically comprises:

4. The silicon-based negative electrode plate according to claim 1, wherein the silicon-based negative electrode active material is one or more of nano silicon powder, silicon oxide, a silicon-carbon composite and a silicon-lithium alloy.

5. The silicon-based negative electrode plate according to claim 1, wherein the conductive agent is one or more selected from superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

6. The silicon-based negative electrode sheet according to any one of claims 1 to 5, wherein the negative electrode active material layer comprises the following components in percentage by mass: 40% -80% of a silicon-based negative electrode active material, 10% -30% of a binder and 10% -30% of a conductive agent.

7. The preparation method of the silicon-based negative plate is characterized by comprising the following steps of:

mixing the silicon-based negative electrode active material, the binder and the conductive agent in the silicon-based negative electrode sheet of any one of claims 1 to 6 in a solvent to obtain negative electrode slurry;

8. A lithium ion battery, comprising:

the silicon-based negative electrode sheet as defined in any one of claims 1 to 6 or the silicon-based negative electrode sheet obtained by the preparation method as defined in claim 7.

9. An electronic device, comprising:

the lithium ion battery of claim 8.