CN115692716A

CN115692716A - Binder for positive pole piece, positive pole piece and electrochemical device

Info

Publication number: CN115692716A
Application number: CN202211689680.3A
Authority: CN
Inventors: 周常通
Original assignee: Ningde Amperex Technology Ltd
Current assignee: Ningde Amperex Technology Ltd
Priority date: 2022-12-28
Filing date: 2022-12-28
Publication date: 2023-02-03
Anticipated expiration: 2042-12-28
Also published as: CN115692716B

Abstract

The application provides a binder for a positive pole piece, the positive pole piece and an electrochemical device. The adhesive comprises composite particles with a core-shell structure, the composite particles comprise a core and a shell layer arranged on the surface of at least part of the core, the core comprises conductive nano particles, the shell layer comprises a polymer, and monomers for forming the polymer comprise acrylic acid and acrylonitrile. The binder has good adhesive property, is applied to the positive pole piece, can improve the problem of the binder floating up in the preparation process of the positive pole piece, can ensure that good adhesive force exists between a positive active material layer and a current collector, is beneficial to the rapid diffusion of ions in the positive pole piece, reduces the resistance of the positive pole piece, and thus improves the multiplying power performance and the cycle performance of an electrochemical device.

Description

Binder for positive pole piece, positive pole piece and electrochemical device

Technical Field

The application relates to the technical field of electrochemistry, in particular to a binder for a positive pole piece, the positive pole piece and an electrochemical device.

Background

Electrochemical devices (lithium ion batteries) have many advantages such as high energy density, long cycle life, high nominal voltage, low self-discharge rate, small size, light weight, and have wide applications in the consumer electronics field. With the rapid development of electric vehicles and mobile electronic devices, people have increasingly high requirements on the dynamic performance, the cycle performance and the like of lithium ion batteries.

The lithium ion battery generally adopts expensive polyvinylidene fluoride (PVDF) as a positive electrode binder, and the oil-soluble binder can float upwards in the coating and drying processes of a positive electrode piece, so that the binding force between a positive electrode active material layer and a positive electrode current collector is poor, and the positive electrode active material layer is easy to fall off after being soaked by electrolyte. Meanwhile, the PVDF binder can excessively coat the positive active material due to polymer film formation in the using process, and the positive pole piece has high resistance to ion transmission and is not beneficial to ion diffusion, so that the resistance of the positive pole piece is high.

Disclosure of Invention

The application aims to provide a binder for a positive pole piece, the positive pole piece and an electrochemical device so as to improve the cohesiveness of the binder and reduce the resistance of the positive pole piece. The specific technical scheme is as follows:

a first aspect of the present application provides an adhesive for a positive electrode sheet, comprising composite particles having a core-shell structure, the composite particles comprising a core and a shell layer disposed on at least a portion of a surface of the core, the core comprising conductive nanoparticles, the shell layer comprising a polymer, monomers constituting the polymer comprising acrylic acid and acrylonitrile. The application provides a binder for positive pole piece is the river system binder, and it has good adhesive property, is applied to positive pole piece with the binder that this application provided, can improve the problem of binder come-up in positive pole piece preparation process, guarantees to have good adhesion stress between positive active material layer and the current collector, is favorable to the quick diffusion of positive pole piece mesonium simultaneously, reduces positive pole piece's resistance to improve electrochemical device's multiplying power performance and cyclicity ability.

In some embodiments herein, the monomers comprising the polymer further include ethyl methacrylate, 2-methoxyethyl 2-acrylate, and polyethylene glycol diacrylate. The monomer for forming the polymer is in the range, the glass transition temperature of the shell polymer of the adhesive can be further reduced, the adhesive property of the adhesive is further improved, good adhesive force between the positive active material layer and the current collector can be ensured, the adhesive can have excellent flexibility and proper swelling degree, the positive pole piece can have excellent flexibility and proper swelling degree, the resistance of the positive pole piece can be reduced, and the rate capability and the cycle performance of the electrochemical device can be improved.

In some embodiments of the present application, the radius of the core is r nm, the thickness of the shell is d nm,0.5 r.ltoreq.d.ltoreq.2r, and 100.ltoreq.2r.ltoreq.200. The radius of the core and the thickness of the shell layer are regulated and controlled to meet the relation, so that good adhesion between the positive active material layer and the current collector can be guaranteed, meanwhile, rapid diffusion of ions in the positive pole piece is facilitated, the resistance of the positive pole piece is reduced, and the rate capability and the cycle performance of the electrochemical device are improved.

In some embodiments of the present application, the mass ratio of conductive nanoparticles to polymer is 1 (0.5 to 15). By regulating the mass ratio of the conductive nanoparticles to the polymer within the range, the bonding effect of the shell layer polymer and the reinforcing effect of the conductive nanoparticles are better facilitated to be exerted, and the bonding property of the bonding agent is further improved, so that the positive active material layer and the current collector have good bonding force, and meanwhile, the rapid diffusion of ions in the positive pole piece is facilitated, the resistance of the positive pole piece is reduced, and the rate capability and the cycle performance of the electrochemical device are further improved.

In some embodiments herein, the acrylic acid is present in an amount of 15 to 25 weight percent, the acrylonitrile is present in an amount of 25 to 35 weight percent, the ethyl methacrylate is present in an amount of 5 to 45 weight percent, 2-methoxyethyl 2-acrylate is present in an amount of 4 to 45 weight percent, and the polyethylene glycol diacrylate is present in an amount of 2.0 to 4.0 weight percent, based on the weight of the polymer. By regulating the content of each monomer in the polymer within the range, the good adhesive force between the positive active material layer and the current collector can be ensured, the characteristics that ethyl methacrylate and 2-acrylic acid-2-methoxyethyl acrylate in the adhesive are taken as soft monomers and polyethylene glycol diacrylate is taken as a cross-linking agent can be exerted, so that the adhesive has excellent flexibility and proper swelling degree, and the positive pole piece has excellent flexibility and proper swelling degree.

In some embodiments of the present application, the binder meets at least one of the following characteristics: (1) the thickness of the shell layer is d nm, and d is more than or equal to 20 and less than or equal to 170; (2) the radius of the core is r nm, and the radius is more than or equal to 128 and less than or equal to 2r and less than or equal to 182; (3) The density of the conductive nano particles is more than or equal to 2.2g/cm ³ . The binder satisfies any of the above characteristics, and can further improve the adhesive strength between the active material layer and the current collector, thereby improving the rate performance and cycle performance of the electrochemical device.

In some embodiments of the present application, the diameter of the composite particle is 140nm to 500nm. By regulating the diameter of the composite particles within the range, the problems of instability, easy sedimentation and the like of the binder in the anode slurry can be solved, so that the binder is more uniformly distributed on the anode piece, the bonding strength among the anode active material particles is improved, and the good bonding force between the anode active material layer and the current collector is ensured.

In some embodiments of the present application, the conductive nanoparticles comprise silicon nanoparticles or carbon nanoparticles. The conductive nanoparticles within the range are selected, the conductivity of the conductive nanoparticles is superior to that of a polymer, the conductivity of the adhesive can be improved, the rigid supporting effect on the adhesive can be achieved, the excessive coating of the positive active material due to the film forming of the adhesive can be improved, gaps among the positive active materials are reserved, the rapid diffusion of ions in the positive active material and the positive pole piece infiltrated by electrolyte can be facilitated, the resistance of the positive pole piece is reduced, and the rate performance of the electrochemical device is improved.

In some embodiments of the present application, the binder satisfies at least one of the following characteristics: (1) the glass transition temperature of the binder is from 20 ℃ to 50 ℃; (2) The density of the binder is 1g/cm ³ To 1.6g/cm ³ (ii) a (3) The solid content of the aqueous dispersion of the binder is 5 to 50%, the viscosity of the aqueous dispersion of the binder is 50 to 200 mPas, and the Zeta potential of the aqueous dispersion of the binder is-50 to-40 mV. By passingThe glass transition temperature of the binder is regulated and controlled within the range, the binder has good cohesiveness, and meanwhile, the positive pole piece has good flexibility, so that the processability of the positive pole piece is improved. By regulating and controlling the density of the binder and the solid content, viscosity and Zeta potential of the aqueous dispersion of the binder within the above ranges, the problem that the binder floats upwards in the preparation process of the positive pole piece can be further improved, so that the binder is uniformly distributed on the positive pole piece, and the good binding power between the positive active material layer and the current collector can be ensured.

A second aspect of the present application provides a positive electrode sheet, which 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, the positive electrode active material layer including a positive electrode active material and the binder provided by the first aspect of the present application. The binder that this application first aspect provided has good adhesion strength, is applied to positive pole piece with the binder that this application provided, can guarantee to have good adhesion strength between positive active material layer and the current collector, can reduce the resistance of positive pole piece simultaneously to the positive pole piece that this application provided has good structural stability and lower resistance, and then improves electrochemical device's multiplying power performance and cyclicity.

In some embodiments of the present application, the binder is present in an amount of 0.8 to 3.0% by mass based on the mass of the positive electrode active material layer, and the adhesive force between the positive electrode active material layer and the positive electrode current collector is 14.5 to 19N/m. When the content of the binder and the binding power between the positive active material layer and the positive current collector are within the above ranges, the positive pole piece has good structural stability and lower resistance, and the rate capability and the cycle performance of the electrochemical device are favorably improved.

A third aspect of the present application provides an electrochemical device comprising the positive electrode sheet provided by the second aspect of the present application. The positive pole piece that the second aspect of this application provided has good structural stability and lower resistance to the electrochemical device that this application provided has good rate performance and cyclicity ability.

A fourth aspect of the present application provides an electronic device comprising the electrochemical device provided by the third aspect of the present application. The electrochemical device provided by the application has good rate performance and cycle performance, so that the electronic device has a long service life.

The beneficial effect of this application:

the application provides a binder for a positive pole piece, the positive pole piece and an electrochemical device. The adhesive comprises composite particles with a core-shell structure, the composite particles comprise a core and a shell layer arranged on at least part of the surface of the core, the core comprises conductive nano particles, the shell layer comprises a polymer, and monomers for forming the polymer comprise acrylic acid and acrylonitrile. The binder has good adhesive property, is applied to the positive pole piece, can improve the problem of the binder floating up in the preparation process of the positive pole piece, can ensure that good adhesive force exists between a positive active material layer and a current collector, is beneficial to the rapid diffusion of ions in the positive pole piece, reduces the resistance of the positive pole piece, and thus improves the multiplying power performance and the cycle performance of an electrochemical device.

Of course, not all advantages described above need to be achieved at the same time in the practice of any one product or method of the present application.

Drawings

In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present application, and it is also obvious for a person skilled in the art to obtain other embodiments according to the drawings.

FIG. 1 is a schematic diagram of a process for forming a composite particle having a core-shell structure;

FIG. 2 is a scanning electron micrograph of the binders prepared in examples 1 to 5 of the present application;

FIG. 3 is a transmission electron micrograph of the binders prepared in examples 1 to 5 of the present application.

Detailed Description

The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all of the embodiments. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments in the present application are within the scope of protection of the present application.

In the embodiments of the present application, the present application is explained by taking a lithium ion battery as an example of an electrochemical device, but the electrochemical device of the present application is not limited to a lithium ion battery.

A first aspect of the present application provides an adhesive for a positive electrode sheet, which includes composite particles having a core-shell structure, the composite particles including a core and a shell layer disposed on at least a portion of a surface of the core, the core including conductive nanoparticles, the shell layer including a polymer, monomers constituting the polymer including acrylic acid and acrylonitrile. In the present application, the shell layer may be provided on a part of the surface or the entire surface of the core, and the present application does not particularly limit this as long as the object of the present application can be achieved. In the present application, the monomers constituting the polymer include acrylic acid and acrylonitrile, that is, the above polymer is obtained by polymerizing a polymerization system including acrylic acid and acrylonitrile as monomers.

The application provides a binder for positive pole piece is water system binder, and on the one hand, the density of core-shell structure composite particles can be increased to the conductive nanoparticles as the core, and the polymer surface negative charge amount as the shell layer is high simultaneously, and the electrostatic repulsion that forms maintains the relative stability of binder at thick liquids interface position, can effectively improve the problem of binder come-up in positive pole piece preparation process for binder evenly distributed on positive pole piece can guarantee to have good adhesion between positive active material layer and the fluid collector. The shell polymer has a lower glass transition temperature, and is softened to form a film to realize an adhesion effect, and the conductive nanoparticles can play a reinforcing role in the film forming process of the adhesive to further improve the adhesion of the adhesive; on the other hand, the conductive nanoparticles can conduct electricity, can also play a role in rigid support of the binder, can effectively improve excessive coating of the anode active material due to binder film formation, and reserve gaps among anode active material particles, thereby being beneficial to rapid diffusion of ions in the anode active material and the anode pole piece infiltrated by electrolyte. Therefore, the binder has good adhesive property, is applied to the positive pole piece, can improve the floating problem of the binder in the preparation process of the positive pole piece, can ensure that a positive active material layer and a current collector have good adhesive force, is beneficial to the rapid diffusion of ions in the positive pole piece, reduces the resistance of the positive pole piece, and improves the rate capability and the cycle performance of an electrochemical device.

In some embodiments of the present application, the radius of the core is r nm, the thickness of the shell is d nm,0.5 r. Ltoreq. D.ltoreq.2r, and 100. Ltoreq. 2r.ltoreq.200, preferably 128. Ltoreq. 2r.ltoreq.182. For example, the diameter 2r nm of the core may be 100nm, 120nm, 140nm, 160nm, 180nm, 200nm, or a range of any two of these values. The radius of the core and the thickness of the shell layer are regulated to meet the relational expression, so that good adhesion force between the positive active material layer and the current collector can be guaranteed, meanwhile, rapid diffusion of ions in the positive pole piece is facilitated, the resistance of the positive pole piece is reduced, and the rate capability and the cycle performance of the electrochemical device are improved.

In some embodiments herein, the mass ratio of conductive nanoparticles to polymer is 1 (0.5 to 15). For example, the mass ratio of the conductive nanoparticles to the polymer can be 1. By regulating the mass ratio of the conductive nanoparticles to the polymer within the range, the bonding effect of the shell layer polymer and the reinforcing effect of the conductive nanoparticles are more favorably exerted, and the bonding property of the bonding agent is further improved, so that the positive active material layer and the current collector have good bonding force, and meanwhile, the positive active material layer and the current collector are favorable for the rapid diffusion of ions in the positive pole piece, the resistance of the positive pole piece is reduced, and the rate capability and the cycle performance of the electrochemical device are further improved.

In some embodiments herein, the acrylic acid is present in an amount of 15 to 25 weight percent, the acrylonitrile is present in an amount of 25 to 35 weight percent, the ethyl methacrylate is present in an amount of 5 to 45 weight percent, the 2-methoxyethyl 2-acrylate is present in an amount of 4 to 45 weight percent, and the polyethylene glycol diacrylate is present in an amount of 2.0 to 4.0 weight percent, based on the weight of the polymer. Preferably, based on the mass of the polymer, the mass percentage of acrylic acid is 17% to 22%, the mass percentage of acrylonitrile is 27% to 32%, the mass percentage of ethyl methacrylate is 25% to 35%, the mass percentage of 2-methoxyethyl 2-acrylate is 15% to 25%, and the mass percentage of polyethylene glycol diacrylate is 2% to 4%. For example, the acrylic acid may be 15%, 18%, 19%, 20%, 21%, 23%, 25% by mass or a range of any two of these values, the acrylonitrile may be 25%, 28%, 29%, 30%, 31%, 33%, 35% by mass or a range of any two of these values, the ethyl methacrylate may be 5%, 10%, 20%, 25%, 30%, 35%, 40%, 45% by mass or a range of any two of these values, the 2-methoxyethyl 2-acrylate may be 4%, 10%, 20%, 25%, 30%, 35%, 40%, 45% by mass or a range of any two of these values, and the polyethylene glycol diacrylate may be 2.0%, 2.5%, 3.0%, 3.5%, 4.0% by mass or a range of any two of these values. By regulating the content of each monomer in the polymer within the range, the good adhesive force between the positive active material layer and the current collector can be ensured, and the characteristics that ethyl methacrylate and 2-acrylic acid-2-methoxyethyl ester in the adhesive are taken as soft monomers and polyethylene glycol diacrylate is taken as a cross-linking agent can be exerted, so that the adhesive has excellent flexibility and proper swelling degree, and the positive pole piece has excellent flexibility and proper swelling degree.

In some embodiments of the present application, the shell layer has a thickness d nm, 20. Ltoreq. D.ltoreq.170. For example, the shell layer may have a thickness of 20nm, 40nm, 60nm, 80nm, 100nm, 120nm, 140nm, 170nm, or any two of these ranges. By regulating the thickness of the shell layer within the range, the adhesive property of the adhesive is improved, the resistance of the positive pole piece is reduced, and the rate capability and the cycle performance of the electrochemical device are improved.

In some embodiments of the present application, the density of the conductive nanoparticles is 2.2g/cm or more ³ Preferably 2.2g/cm ³ To 2.7g/cm ³ . By regulating the density of the conductive nanoparticles within the range, the problem that the adhesive floats upwards in the preparation process of the positive pole piece can be further improved, so that the adhesive is uniformly distributed on the positive pole piece, and the positive active material layer and the current collector can be ensured to have good adhesive force.

In some embodiments of the present application, the composite particles have a diameter of 140nm to 500nm. For example, the diameter of the composite particle may be 140nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm, or a range of any two of these values. By regulating the diameter of the composite particles within the range, the problems of instability, easy sedimentation and the like of the binder in the anode slurry can be further improved, so that the binder is more uniformly distributed on the anode plate, the bonding strength between the anode active materials is improved, and the good bonding force between the anode active material layer and the current collector can be ensured.

In some embodiments of the present application, the conductive nanoparticles comprise silicon nanoparticles (Si NPs) or carbon nanoparticles (C NPs). By selecting the conductive nanoparticles within the range, the conductivity of the conductive nanoparticles is superior to that of a polymer, so that the conductivity of the binder can be improved, the rigid supporting effect on the binder can be achieved, the excessive coating of the positive active material due to the binder film forming can be improved, the gap between the positive active materials can be reserved, the electrolyte can be favorably infiltrated into the positive active material and the ions in the positive pole piece can be rapidly diffused, the resistance of the positive pole piece can be reduced, and the rate capability of the electrochemical device can be improved.

The silicon nanoparticles herein further include a doping element including at least one of phosphorus or boron, and the mass percentage of the doping element herein is not particularly limited as long as the silicon nanoparticles can have good conductivity, for example, the mass percentage of the doping element is 5% to 20% based on the mass of the silicon nanoparticles.

In some embodiments herein, the glass transition temperature of the binder is from 20 ℃ to 50 ℃, preferably from 20 ℃ to 45 ℃. For example, the glass transition temperature of the binder can be 20 ℃, 25 ℃,30 ℃, 35 ℃, 40 ℃, 45 ℃, 50 ℃ or any two of these ranges. By regulating the glass transition temperature of the binder to be within the range, the binder has good cohesiveness, and meanwhile, the positive pole piece has good flexibility, thereby being beneficial to improving the processability of the positive pole piece.

In some embodiments of the present application, the binder has a density of 1g/cm ³ To 1.6g/cm ³ . For example, the binder may have a density of 1g/cm ³ 、1.2g/cm ³ 、1.3g/cm ³ 、1.4g/cm ³ 、1.5g/cm ³ 、1.6g/cm ³ Or a range of any two of the above. The density of the binder is regulated within the range, so that the problem that the binder floats upwards in the preparation process of the positive pole piece is improved, the binder is uniformly distributed on the positive pole piece, and the good binding power between the positive active material layer and the current collector can be ensured.

In some embodiments of the present application, the aqueous dispersion of the binder has a solid content of 5% to 50%, the viscosity of the aqueous dispersion of the binder is 50mPa · s to 200mPa · s, and the Zeta potential of the aqueous dispersion of the binder is-50 mV to-40 mV; preferably, the aqueous dispersion of the binder has a solid content of 10 to 45%, a viscosity of 70 to 180 mPas, and a Zeta potential of-49 to-42 mV. For example, the aqueous dispersion of the binder may have a solids content of 5%, 15%, 25%, 30%, 35%, 45%, 50%, or any two of these values, a viscosity of 50 mPas, 80 mPas, 100 mPas, 130 mPas, 150 mPas, 170 mPas, 200 mPas, or any two of these values, and a Zeta potential of-50 mV, -48mV, -46mV, -45mV, -44mV, -41mV, -40mV, or any two of these values. By regulating the solid content, viscosity and Zeta potential of the aqueous dispersion of the binder to be within the ranges, the problem that the binder floats upwards in the preparation process of the positive pole piece can be further solved, so that the binder is uniformly distributed on the positive pole piece, and the good binding power between the positive active material layer and the current collector can be ensured.

The method for preparing the binder is not particularly limited as long as the object of the present application can be achieved, and for example, as shown in fig. 1, the binder may be prepared by grafting double bonds to the surface of the core 11 using the conductive nanoparticles, and copolymerizing monomers of the polymer to obtain the composite particle 10 having a core-shell structure, the composite particle 10 including the core 11 and the polymer shell 12 disposed on at least a portion of the surface of the core 11, and the surface of the composite particle 10 having a high surface negative charge due to carboxyl anions ionized by the polymer shell 12 and an electronegative initiator adsorbed to the surface of the polymer shell 12, which is indicated by "-" in fig. 1. The preparation method of the binder may include, but is not limited to, the following steps: dispersing conductive nanoparticles in absolute ethyl alcohol, adding a silane coupling agent, stirring at room temperature for reaction, reacting with the silane coupling agent to graft double bonds on the surfaces of the conductive nanoparticles to obtain an ethanol dispersion liquid of modified conductive nanoparticles, and cleaning to obtain the modified conductive nanoparticles, wherein the ratio of the mass of the conductive nanoparticles to the volume of the absolute ethyl alcohol is 1g (40-60) mL; the silane coupling agent is present in an amount of 0.05 to 2 volume percent based on the volume of the absolute ethyl alcohol. And then dispersing the modified conductive nanoparticles in deionized water to obtain an aqueous dispersion of the modified conductive nanoparticles, adding an anionic surfactant into the aqueous dispersion of the modified conductive nanoparticles, and uniformly mixing, wherein the mass percentage of the anionic surfactant is 0.1-1% based on the mass of the modified carbon nanoparticles. Adding acrylic acid, acrylonitrile, ethyl methacrylate, 2-acrylic acid-2-methoxyethyl ester and polyethylene glycol diacrylate, heating to 60-80 ℃ under the conditions of mechanical stirring and nitrogen protection, adding an initiator for copolymerization reaction, and reacting for 3-7 h to obtain the aqueous dispersion of the composite particles with the core-shell structure, namely the aqueous dispersion of the binder, wherein the mass percentage of the initiator is 0.3-1.5% based on the mass of the monomers of the polymer. The mass of the modified conductive nanoparticles in the aqueous dispersion of the modified conductive nanoparticles is substantially the same as that of the conductive nanoparticles.

The binder provided by the application is a water-based binder, the aqueous dispersion of the binder prepared by the method can be directly mixed with components such as a positive electrode active material and a positive electrode conductive agent to prepare positive electrode slurry, and the aqueous dispersion of the binder can also be separated and dried to obtain solid composite particles to be stored for later use, and the solid composite particles are dispersed in deionized water when the binder is used. The present application is not particularly limited thereto as long as the object of the present application can be achieved. The present application does not particularly limit the method of the above separation and dispersion as long as the object of the present application can be achieved.

In the present application, the conductive nanoparticles of different particle diameters are obtained by purchase, and the radius r of the core of the composite particle can be controlled by using the conductive nanoparticles of different particle diameters as the core. Generally, the mass ratio of the conductive nanoparticles to the polymer can be varied to control the thickness of the shell layer. For example, decreasing the mass ratio of conductive nanoparticles to polymer increases the thickness of the shell layer; the mass ratio of the conductive nano particles to the polymer is increased, and the thickness of the shell layer is reduced.

In the present application, the conductive nanoparticles include silicon nanoparticles or carbon nanoparticles, both of which are commercially available conventional substances, and the source thereof is not particularly limited as long as the object of the present application can be achieved. In general, the surface of silicon nanoparticles or carbon nanoparticles contains hydroxyl functional groups, and the modified conductive nanoparticles with double bonds grafted on the surface can be obtained by modifying the silicon nanoparticles or the carbon nanoparticles through a silane coupling agent, so that the copolymerization process of polymers on the surface of a core is facilitated. The above silane coupling agent includes, but is not limited to, at least one of Vinyltrichlorosilane (VTC), vinyltrimethoxysilane (VTMO), vinyltriethoxysilane (VTEO), gamma-methacryloxypropyltrimethoxysilane (gamma-MPS), and vinyltris- (beta-methoxyethoxy) silane (VTS). The anionic surfactant includes, but is not limited to, at least one of sodium lauryl sulfate, ammonium lauryl sulfate, or sodium lauryl alcohol polyoxyethylene ether sulfate.

In the present application, the polyethylene glycol diacrylate as a monomer of the polymer is generally low in molecular weight, and the molecular weight is not particularly limited in the present application as long as the object of the present application can be achieved, for example, the weight average molecular weight (Mw) of the polyethylene glycol diacrylate may be 150 to 1000, for example, the weight average molecular weight of the polyethylene glycol diacrylate may be 150, 250, 400, 500, 600, 800, 1000, or a range consisting of any two values thereof, and the characteristics of the polyethylene glycol diacrylate as a cross-linking agent in the monomer of the polymer may be better exerted, so that the binder has more excellent flexibility and more suitable swelling degree, thereby further improving the flexibility and swelling degree of the positive electrode plate.

In the present application, the polymer is obtained by monomer copolymerization, and the initiator for the copolymerization is not particularly limited as long as the object of the present application can be achieved, and illustratively, the initiator may include, but is not limited to, potassium persulfate (K) ₂ S ₂ O ₈ ) Sodium persulfate (Na) ₂ S ₂ O ₈ ) Ammonium persulfate ((NH) ₄ ) ₂ S ₂ O ₈ ) Or azodiisobutyramidine hydrochloride. The initiator is adsorbed on the surface of a shell layer in the copolymerization process, so that the shell layer of the adhesive has higher surface negative charges, and the position of the adhesive on the interface of the slurry is further increasedThe relative stability of the positive pole piece and the problem that the adhesive floats upwards in the preparation process of the positive pole piece are improved, so that good adhesive force between the positive active material layer and the current collector can be ensured.

A second aspect of the present application provides a positive electrode sheet, which includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, the positive active material layer including a positive active material and the binder provided in the first aspect of the present application. The binder that this application first aspect provided has good adhesion strength, is applied to positive pole piece with the binder that this application provided, can guarantee to have good adhesion strength between positive active material layer and the current collector, can reduce the resistance of positive pole piece simultaneously to the positive pole piece that this application provided has good structural stability and lower resistance, and then improves electrochemical device's multiplying power performance and cyclicity.

In some embodiments of the present application, the binder is present in an amount of 0.8 to 3.0% by mass based on the mass of the positive electrode active material layer, and the adhesive force between the positive electrode active material layer and the positive electrode current collector is 14.5 to 19N/m. For example, the binder may be present in an amount of 0.8%, 1.0%, 2.0%, 2.5%, 3.0% by mass or in any two of the above ranges, and the adhesion between the positive electrode active material layer and the positive electrode current collector may be 14.5N/m, 16N/m, 17N/m, 18N/m, 19N/m or in any two of the above ranges. When the content of the binder and the binding power between the positive active material layer and the positive current collector are within the above range, the positive pole piece has good structural stability and lower resistance, and is beneficial to improving the rate capability and the cycle performance of the electrochemical device.

The present application is not particularly limited as long as the object of the present application can be achieved. For example, the positive electrode current collector may include an aluminum foil, an aluminum alloy foil, or a composite current collector (e.g., an aluminum carbon composite current collector), or the like. The present application does not particularly limit the thickness of the positive electrode current collector as long as the object of the present application can be achieved. For example, the thickness of the positive electrode current collector is 5 μm to 20 μm.

The kind of the positive electrode active material is not particularly limited as long as the object of the present application can be achieved. For example, the positive electrode active material may include at least one of lithium Nickel Cobalt Manganese (NCM), lithium nickel cobalt aluminate, lithium iron phosphate, a lithium rich manganese based material, lithium cobaltate, lithium manganese oxide, lithium iron manganese phosphate, or the like. The type of NCM is not particularly limited in the present application as long as the object of the present application can be achieved, and for example, at least one of NCM811, NCM622, NCM523, and NCM111 may be included. In the present application, the positive electrode active material may further include a non-metal element, for example, the non-metal element includes at least one of fluorine, phosphorus, boron, chlorine, or the like, which can further improve the stability of the positive electrode active material. The present application does not particularly limit the thickness of the positive electrode active material layer as long as the object of the present application can be achieved. For example, the thickness of the single-sided positive electrode active material layer is 30 μm to 120 μm.

In the present application, the positive electrode active material layer may be provided on one surface in the thickness direction of the positive electrode current collector, and may also be provided on both surfaces in the thickness direction of the positive electrode current collector. The "surface" herein may be the entire region of the positive electrode current collector or a partial region of the positive electrode current collector, and the present application is not particularly limited as long as the object of the present application can be achieved.

In the present application, the positive electrode active material layer further includes a positive electrode conductive agent, and the present application is not particularly limited as long as the object of the present application can be achieved, and for example, the positive electrode conductive agent may include, but is not limited to, at least one of conductive carbon black (Super P), carbon Nanotubes (CNTs), carbon fibers, graphene, a metal material, or a conductive polymer, and the carbon nanotubes may include, but is not limited to, single-walled carbon nanotubes and/or multi-walled carbon nanotubes. The carbon fibers may include, but are not limited to, vapor Grown Carbon Fibers (VGCF) and/or carbon nanofibers. The metal material may include, but is not limited to, metal fibers, and specifically, the metal may include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The above-mentioned conductive polymer may include, but is not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole. In the present application, the content of the conductive agent is 0.5 to 5% by mass based on the mass of the positive electrode active material layer.

A third aspect of the present application provides an electrochemical device comprising the positive electrode sheet provided in the second aspect of the present application. The positive pole piece that the second aspect of this application provided has good structural stability and lower resistance to the electrochemical device that this application provided has good rate performance and cyclicity ability.

The electrochemical device further comprises a negative pole piece, wherein the negative pole piece comprises a negative pole current collector and a negative pole active material layer arranged on at least one surface of the negative pole current collector. In the present application, the negative electrode active material layer may be provided on one surface in the thickness direction of the negative electrode current collector, and may also be provided on both surfaces in the thickness direction of the negative electrode current collector. The "surface" herein may be the entire region of the negative electrode current collector or a partial region of the negative electrode current collector, and the present application is not particularly limited as long as the object of the present application can be achieved. The present application does not particularly limit the thickness of the anode active material layer as long as the object of the present application can be achieved. For example, the thickness of the single-sided anode active material layer may be 30 μm to 160 μm.

The present application is not particularly limited as long as the object of the present application can be achieved. For example, the negative electrode current collector may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or composite current collectors (e.g., carbon copper composite current collectors, nickel copper composite current collectors, titanium copper composite current collectors), and the like. The present application does not particularly limit the thickness of the negative electrode current collector as long as the object of the present application can be achieved. For example, the thickness of the negative electrode current collector is 4 μm to 10 μm.

In the present application, the anode active material layer includes an anode active material, and the present application does not particularly limit the anode active material as long as the object of the present application can be achieved, and may include, for example, but not limited to, graphite, mesophase micro carbon spheres (MCMB), hard carbon, soft carbon, li-Sn alloy, li-Sn-O alloy, sn, snO, and the like ₂ Lithium titanate Li of spinel structure ₄ Ti ₅ O ₁₂ In Li-Al alloy or metallic lithium, etcAt least one of (1). The negative electrode active material layer may further include a negative electrode conductive agent, which is not particularly limited as long as the purpose of the present application can be achieved, and may include, but is not limited to, at least one of conductive carbon black (Super P), carbon Nanotubes (CNTs), carbon fibers, graphene, a metal material, or a conductive polymer, and the carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and/or multi-walled carbon nanotubes. The carbon fibers may include, but are not limited to, vapor Grown Carbon Fibers (VGCF) and/or carbon nanofibers. The metal material may include, but is not limited to, metal powder and/or metal fiber, and specifically, the metal may include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The above-mentioned conductive polymer may include, but is not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole.

In the present application, the negative electrode active material layer may further include a negative electrode binder, and the negative electrode binder is not particularly limited as long as the object of the present application can be achieved, and for example, the binder for the positive electrode sheet provided in the first aspect of the present application may be included, and at least one of polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, an ethylene oxide-containing polymer, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyacrylic acid, styrene-butadiene rubber, acryl-styrene-butadiene rubber, epoxy resin, or nylon may also be included.

In the present application, the electrochemical device further includes an electrolyte including a lithium salt and a non-aqueous solvent. The lithium salt may include LiPF ₆ 、LiBF ₄ 、LiClO ₄ 、LiB(C ₆ H ₅ ) ₄ 、LiCH ₃ SO ₃ 、LiCF ₃ SO ₃ 、LiN(SO ₂ CF ₃ ) ₂ 、LiC(SO ₂ CF ₃ ) ₃ 、Li ₂ SiF ₆ At least one of lithium bis (oxalato) borate (LiBOB) or lithium difluoro borate. The concentration of the lithium salt in the electrolyte is not particularly limited hereinAs long as the object of the present application can be achieved. For example, the concentration of the lithium salt in the electrolyte is 0.9mol/L to 1.5mol/L, and illustratively, the concentration of the lithium salt in the electrolyte may be 0.9mol/L, 1.0mol/L, 1.1mol/L, 1.3mol/L, 1.5mol/L, or a range consisting of any two of the above values. The non-aqueous solvent is not particularly limited as long as the object of the present application can be achieved, and may include, for example, but not limited to, at least one of a carbonate compound, a carboxylate compound, an ether compound, or other organic solvent. The carbonate compound may include, but is not limited to, at least one of a chain carbonate compound, a cyclic carbonate compound, or a fluoro carbonate compound. The above chain carbonate compound may include, but is not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl Propyl Carbonate (MPC), ethyl Propyl Carbonate (EPC), or Methyl Ethyl Carbonate (MEC). The above cyclic carbonate may include, but is not limited to, at least one of Ethylene Carbonate (EC), propylene Carbonate (PC), butylene Carbonate (BC), or Vinyl Ethylene Carbonate (VEC). The fluoro carbonate compound may include, but is not limited to, at least one of fluoroethylene carbonate (FEC), 1, 2-difluoroethylene carbonate, 1, 2-trifluoroethylene carbonate, 1, 2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1, 2-difluoro-1-methylethylene carbonate, 1, 2-trifluoro-2-methylethylene carbonate, or trifluoromethyl ethylene carbonate. The above carboxylic acid ester compound may include, but is not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ -butyrolactone, decalactone, valerolactone, or caprolactone. The above ether compound may include, but is not limited to, at least one of dibutyl ether, tetraglyme, diglyme, 1, 2-dimethoxyethane, 1, 2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. Such other organic solvents may include, but are not limited to, dimethyl sulfoxide, 1, 2-dioxolane, sulfolane, methylsulfolane, 1, 3-dimethyl-2-imidazolidinone, N-methyl-at least one of 2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate or trioctyl phosphate. The content of the nonaqueous solvent in the electrolyte solution may be 70% to 90% by mass, and may be, for example, 70%, 75%, 80%, 86%, 88%, 90% or any range therebetween.

The electrochemical device of the present application further includes a separator, which is not particularly limited as long as the object of the present application can be achieved, and for example, the material of the separator may include, but is not limited to, at least one of Polyethylene (PE), polypropylene (PP), polyolefin (PO) based separator mainly based on polytetrafluoroethylene, polyester film (e.g., polyethylene terephthalate (PET) film), cellulose film, polyimide film (PI), polyamide film (PA), spandex or aramid film, and the like. The type of the separator may include, but is not limited to, at least one of a woven film, a non-woven film (non-woven fabric), a microporous film, a composite film, a rolled film, or a spun film, etc. The separation membrane of the present application may have a porous structure, and the size of the pore diameter is not particularly limited as long as the object of the present application can be achieved, and for example, the size of the pore diameter may be 0.01 μm to 1 μm. In the present application, the thickness of the separator is not particularly limited as long as the object of the present application can be achieved, and for example, the thickness may be 5 μm to 500 μm.

The electrochemical device of the present application is not particularly limited, and may include any device in which electrochemical reactions occur. In one embodiment of the present application, an electrochemical device may include, but is not limited to: a lithium ion secondary battery (lithium ion battery), a lithium polymer secondary battery, a lithium ion polymer secondary battery, or the like. In one embodiment, the structure of the electrode assembly includes a winding type structure, a lamination type structure, or the like.

The process for preparing the electrochemical device of the present application is well known to those skilled in the art, and the present application is not particularly limited, and for example, may include, but is not limited to, the following steps: stacking the positive pole piece, the isolating membrane and the negative pole piece in sequence, winding, folding and the like according to needs to obtain an electrode assembly with a winding structure, putting the electrode assembly into a packaging bag, injecting electrolyte into the packaging bag and sealing the packaging bag to obtain the electrochemical device; or, stacking the positive pole piece, the isolating membrane and the negative pole piece in sequence, fixing four corners of the whole lamination structure by using an adhesive tape to obtain an electrode assembly of the lamination structure, placing the electrode assembly into a packaging bag, injecting electrolyte into the packaging bag and sealing the packaging bag to obtain the electrochemical device. In addition, an overcurrent prevention element, a guide plate, or the like may be placed in the packaging bag as necessary to prevent a pressure rise or overcharge/discharge inside the electrochemical device. The application has no limitation to the packaging bag, and the person skilled in the art can select the packaging bag according to actual needs as long as the purpose of the application can be achieved. For example, a plastic-aluminum film package can be used.

A fourth aspect of the present application provides an electronic device comprising the electrochemical device provided by the third aspect of the present application. The electrochemical device that this application provided has good rate performance and cycling performance to the electron device of this application has longer life.

The electronic device of the present application is not particularly limited, and may be any electronic device known in the art. In some embodiments, 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 telephone, a portable facsimile machine, a portable copier, a portable printer, a headphone, a video recorder, a liquid crystal television, a handheld cleaner, a portable CD player, a mini-disc, a transceiver, an electronic organizer, 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 or lithium ion capacitor, and the like.

Examples

Hereinafter, embodiments of the present application will be described in more detail with reference to examples and comparative examples. Various tests and evaluations were carried out according to the following methods. Unless otherwise specified, "part" and "%" are based on mass.

Test method and apparatus

Scanning Electron Microscope (SEM) testing

The microscopic morphology of the binder was observed by scanning electron microscopy and the diameters of 200 individual composite particles were counted and the average calculated and reported as the diameter of the composite particle.

Transmission Electron Microscopy (TEM) test

Observing the microscopic morphology of the binder through a transmission electron microscope, counting the diameters of the cores and the thicknesses of the shell layers in 50 single composite particles, calculating the average value to obtain the diameter 2r of the core and the thickness d of the shell layer, and further calculating the radius r of the core.

Viscosity measurement

The viscosity of the aqueous dispersion of the binder was measured using a digital rotational viscometer (Shanghai Jingtian electronics, ltd., LVDV-1), and an appropriate spindle and rotational speed were selected depending on the aqueous dispersion of the binder to be measured. And slowly inclining the rotor, putting the rotor into the aqueous dispersion of the adhesive for soaking to prevent bubbles from being generated at the bottom of the rotor, starting a rotary viscometer, reading when the readings are unchanged after three minutes by using the liquid level of the aqueous dispersion of the adhesive, and recording the viscosity of the aqueous dispersion of the adhesive as the viscosity of the aqueous dispersion of the adhesive, wherein the unit of the viscosity is mPas.

Potential testing

The Zeta potential of the aqueous binder dispersion was tested using a potentiometric analyzer (marwen, zetasizer Nano ZS-90), the aqueous binder dispersion of the sample was diluted with water to a transparent state, the sample was slowly pushed into the sample cell using a sample injector, and placed into the instrument. The test was repeated 15 times at a constant temperature of 25 ℃ and the results were recorded and the average value calculated and reported as the Zeta potential in mV of the aqueous dispersion of the binder.

Density test

The density of the composite particles (i.e., the binder powder samples) was measured using a powder density tester (inteno, ET-320). Firstly weighing the mass of the composite particles in the air, then weighing the mass of the composite particles in the water, and finally pressing an 'ENTER' key after a stable symbol at the upper left corner of a display screen of a powder density tester is displayed, wherein the density of a binder powder sample is directly displayed on the screen, and the unit is g/cm ³ 。

Glass transition temperature test

The glass transition temperature (Tg) of the binder was measured by Differential Scanning Calorimetry (DSC), and a 5mg sample of the binder was taken and the Tg of the binder was determined by analyzing the DSC curve at a ramp rate of 5 deg.C/min from-20 deg.C to 100 deg.C.

Adhesion test

And taking the rolled positive pole piece, and punching the sample by using a sample cutting die to obtain a test sample strip with the width of 20mm and the length of 100 mm. The surface of the steel plate was wiped clean with alcohol, and double-sided tape (nitto. No. 5000ns) having a width of 20mm and a length of 55mm to 70mm was attached to the steel plate. The test specimen was attached to a double-sided adhesive with the test side facing down and no air bubbles were generated. A paper tape with the width equal to that of the test sample strip and the length of 55mm to 70mm is connected and fixed with one end of the test sample strip through wrinkle glue (high-viscosity beautiful line paper), and a press roller with the mass of 2kg is pushed by a hand to roll on the test sample strip back and forth for 4 times to obtain a test sample.

The test was performed using a tensile machine power supply (san si, instron 3365). Fixing a test sample on a test bench, turning up the paper tape at 90 degrees, fixing the paper tape through a clamp, then starting to pull the paper tape by a pulling machine at the speed of 10mm/min until the positive active material layer on the surface of the double-sided adhesive tape is separated from the positive current collector, and then finishing the test, and storing test data. The average value of the tensile force in the plateau region was taken as the adhesion between the positive electrode active material layer and the positive electrode current collector, and the unit was N/m.

Resistance test of positive pole piece

And testing the resistance of the positive pole piece by using a diaphragm resistance meter (energy science and technology). Before testing, the test probe of the diaphragm resistance meter is wiped clean by alcohol, and then the pressure and the resistance are reset to zero. The cut positive pole piece (60 multiplied by 80 mm) is flatly placed on a sample carrying table, then the sample table is placed in a testing cavity, 12 different positions of each pole piece sample are tested, and then the average value is calculated to obtain the resistance of the positive pole piece, wherein the unit is omega.

Rate capability test

In an environment of 25 ℃, charging the lithium ion battery to 4.45V at a constant current of 0.7C (multiplying power), and then charging at a constant voltage until the cut-off current is 0.025C; then, constant current discharge was performed at a discharge current of 0.2C until the cut-off voltage was 3.0V, and the discharge capacity at 0.2C was recorded. Then, the above charging process was repeated, constant current discharge was performed at a discharge current of 2C until the cut-off voltage was 3.0V, and the 2C discharge capacity was recorded. Rate capability =2C discharge capacity/0.2C discharge capacity × 100%.

Cycle performance test

The cycle performance was evaluated by the cycle capacity retention rate of the lithium ion battery. Placing the formed lithium ion battery in a constant temperature environment of 25 ℃, charging to 4.45V at a constant current of 0.7C, then charging to a cut-off current of 0.05C at a constant voltage, standing for 3min after full charge, then discharging to 3.0V at 0.5C, and recording the discharge capacity as D ₀ Then, 0.7C charge/0.5C discharge was performed for cycle test for 500 cycles, and the discharge capacity after the 500 th cycle was measured as D ₁ The retention ratio (%) of the cycle capacity after 500 cycles of the lithium ion battery at normal temperature (25 ℃) = D ₁ /D ₀ ×100%。

Examples 1 to 1

< preparation of Binder >

Dispersing 100nm carbon nanoparticles (C NPs) in absolute ethyl alcohol, adding 0.1vol% Vinyl Trichlorosilane (VTC), and stirring for 30min at the conditions of room temperature of 25 ℃ and rotation speed of 800rpm to obtain an ethanol dispersion liquid of the modified carbon nanoparticles. After washing and centrifuging by using ethanol for 3 times, dispersing the modified carbon nano particles in deionized water to obtain a modified carbon nano particle water dispersion with the mass fraction of 5%. Wherein the density of the carbon nanoparticles is 2.3g/cm ³ . The ratio of the mass of the carbon nanoparticles to the volume of the absolute ethyl alcohol is 1g; the volume percent VTC was 0.1% based on the volume of absolute ethanol.

Adding the modified carbon nanoparticle aqueous dispersion with the mass fraction of 5% and 0.4% of sodium dodecyl sulfate into a four-neck flask, uniformly stirring and mixing, then adding the monomer acrylic acid, acrylonitrile, ethyl methacrylate, 2-acrylic acid-2-methoxyethyl ester and polyethylene glycol diacrylate (Mw is 200) of the polymer according to the mass ratio of 19.6Potassium persulfate (K) as the oxidizing agent ₂ S ₂ O ₈ ) And reacting for 5 hours to obtain the aqueous dispersion of the composite particles with the core-shell structure, namely the aqueous dispersion of the binder. Wherein the mass ratio of the modified carbon nanoparticles to the monomers of the polymer is 1; the mass percentage of initiator is 1% based on the mass of the monomers of the polymer. The aqueous dispersion of the binder had a solid content of 14%, a viscosity of 80 mPas and a Zeta potential of-48 mV.

< preparation of Positive electrode sheet >

The positive electrode active material lithium cobaltate (LiCoO) ₂ ) Dispersing the conductive carbon black and the aqueous dispersion of the prepared binder in deionized water, and uniformly stirring to obtain slurry with the solid content of 72wt%, wherein LiCoO is contained in the solid component ₂ The mass ratio of the conductive carbon black to the binder is 96. And uniformly coating the positive electrode slurry on one surface of a positive electrode current collector aluminum foil with the thickness of 9 mu m, and drying at 120 ℃ to obtain a positive electrode piece with a positive electrode active material layer with the thickness of 110 mu m and single-side coated with the positive electrode active material. And then, repeating the steps on the other surface of the aluminum foil of the positive current collector to obtain the positive pole piece with the positive active material coated on the two surfaces. After coating, the positive pole piece is subjected to cold pressing and is cut into sheets with the specification of 74mm multiplied by 867mm for standby.

< preparation of negative electrode sheet >

Mixing graphite serving as a negative electrode active material, styrene butadiene rubber and sodium carboxymethylcellulose according to a mass ratio of 97.5. And uniformly coating the negative electrode slurry on one surface of a negative electrode current collector copper foil with the thickness of 6 mu m, drying at 120 ℃ to obtain a negative electrode piece with a 150 mu m negative electrode active material layer and a single-side negative electrode active material layer, and repeating the steps on the other surface of the negative electrode current collector copper foil to obtain the negative electrode piece with the double-side negative electrode active material layer. And after coating, carrying out cold pressing on the negative pole piece, and cutting the negative pole piece into sheets with the specification of 78mm multiplied by 875mm for later use.

< preparation of electrolytic solution >

In a dry argon atmosphere glove box, organic solvents of diethyl carbonate (DEC), ethylene Carbonate (EC), propylene Carbonate (PC) were mixed at a mass ratio of 1 ₆ ) Dissolving and mixing uniformly to obtain LiPF ₆ The concentration of (3) is 1.15 mol/L.

< isolation film >

A porous polyethylene film (supplied from Celgard) having a thickness of 16 μm was used as the separator.

< preparation of lithium ion Battery >

And (3) stacking the prepared positive pole piece, the prepared isolating film and the prepared negative pole piece in sequence to enable the isolating film to be positioned between the positive pole piece and the negative pole piece to play an isolating role, and then winding to obtain the electrode assembly. And after welding the electrode lugs, putting the electrode assembly into an aluminum plastic film packaging shell, placing the aluminum plastic film packaging shell in a vacuum oven at the temperature of 80 ℃ for drying for 12 hours to remove moisture, injecting the prepared electrolyte, and performing vacuum packaging, standing, formation (0.02C constant current charging to 3.5V, 0.1C constant current charging to 3.9V), capacity, shaping and other processes to obtain the lithium ion battery.

Examples 1-2 to examples 1-23

The examples were conducted in the same manner as in example 1-1 except that the parameters were adjusted as shown in Table 1.

Example 2-1

The examples were the same as examples 1 to 7 except that the parameters were adjusted as shown in Table 3.

Comparative example 1

The procedure of example 1-1 was repeated, except that PVDF (type: akema HSV 900), a commercially available oil-based binder, was used in place of the binder.

Comparative example 2

The procedure of example 1-1 was repeated, except that commercially available polyvinylpyrrolidone (Mw =40000, sigma-aldrich) was used in place of the binder.

Comparative example 3

The same as in example 1-1 was repeated, except that a commercially available water-based adhesive (type: yindele 136D) was used in place of the adhesive.

Comparative example 4

The procedure of example 1-1 was repeated, except that a commercially available polyvinyl imidazole (Mw =400000, inokay) was used in place of the binder.

The relevant parameters and performance tests for each example and each comparative example are shown in tables 1,2 and 3.

TABLE 1

Note: the density of the Si NPs in examples 1-12 was 2.3g/cm ³ 。

TABLE 2

Fig. 2 and fig. 3 are scanning electron micrographs and transmission electron micrographs of the binders prepared in examples 1 to 5 of the present application, respectively, and it can be seen that the binder provided in the present application is a composite particle with a core-shell structure, the composite particle is a nano-sized bead, the structure is regular, the size distribution is uniform, and the polymer shell layer is uniformly present on the surface of the conductive nanoparticle.

As can be seen from examples 1-1 to 1-23 and comparative examples 1 to 4, the lithium ion battery in the example of the present application includes the positive electrode sheet, and when the positive electrode sheet includes the binder provided by the present application, the binding force between the positive electrode active material layer and the current collector is large, the resistance of the positive electrode sheet is smaller, and the lithium ion battery has higher rate capability and cycle capacity retention rate. Therefore, the adhesive provided by the embodiment of the application is applied to the positive pole piece, so that good adhesive force between the positive active material layer and the current collector can be ensured, meanwhile, the positive pole piece has lower resistance, and the lithium ion battery prepared by adopting the positive pole piece provided by the application has good rate capability and cycle performance.

The types of monomers that make up the polymer often affect the rate capability and cycling performance of lithium ion batteries. It can be seen from examples 1-1 to 1-23 that the binder of the monomers comprising acrylic acid, acrylonitrile, ethyl methacrylate, 2-methoxyethyl acrylate and polyethylene glycol diacrylate as the constituent polymers has a lower glass transition temperature, and when the binder is applied to the positive electrode plate, the positive electrode active material layer and the current collector have better binding power, and the positive electrode plate has lower resistance.

The relationship between the radius of the core and the thickness of the shell layer generally affects the rate capability and cycle performance of the lithium ion battery. It can be seen from examples 1 to 3, examples 1 to 4, examples 1 to 10, and examples 1 to 11 that when the numerical values r and d corresponding to the radius of the core and the thickness of the shell layer satisfy the relation that d is not less than 2r and not more than 0.5r, the positive electrode sheet including the binder provided in the examples of the present application has a larger binding power between the positive electrode active material layer and the current collector, and the lithium ion battery manufactured by using the positive electrode sheet provided in the present application has better rate multiplying performance and cycle performance.

The monomer content of the polymer generally affects the rate capability and cycling performance of the lithium ion battery. From examples 1-6 to 1-8, and 1-14 to 1-18, it can be seen that when the binder having the monomer content of the polymer within the range of the present application is applied to a positive electrode plate, the positive electrode active material layer and the current collector have good binding power, and the resistance value of the positive electrode plate is low. Compared with examples 1-5 and examples 1-9, examples 1-6 to 1-8 show that when the binder with the monomeric polyethylene glycol diacrylate content of the polymer in the range of the present application is applied to the positive electrode plate, the positive electrode active material layer has better binding power with the current collector, and the positive electrode plate has lower resistance.

The type of conductive nanoparticles generally affects the rate capability and cycle performance of lithium ion batteries. It can be seen from examples 1-12 and examples 1-13 that when the binder with the types of conductive nanoparticles in the range of the present application is applied to a positive electrode sheet, the positive electrode active material layer and the current collector have good binding power, and the resistance value of the positive electrode sheet is low.

The diameter of the core typically affects the rate capability and cycling performance of the lithium ion battery. It can be seen from examples 1-1 to 1-23 that, when the binder having a core diameter within the range of the present application is applied to a positive electrode sheet, the positive electrode active material layer and the current collector have good binding power, and the positive electrode sheet has a low resistance value.

The thickness of the shell layer generally affects the rate capability and cycle performance of the lithium ion battery. From examples 1-1 to 1-23, it can be seen that when the binder having a shell layer thickness within the range of the present application is applied to a positive electrode sheet, the positive electrode active material layer and the current collector have good binding power, and the positive electrode sheet has a low resistance value.

The diameter of the composite particles generally affects the rate capability and cycling performance of the lithium ion battery. It can be seen from examples 1-19 and examples 1-20 that when the binder having the diameter of the composite particles within the range of the present application is applied to a positive electrode sheet, the positive electrode sheet has a higher binding power between a positive active material layer and a current collector, and a lower resistance.

The Tg of the binder typically affects the rate capability and cycling performance of the lithium ion battery. From examples 1-1 to 1-23, it can be seen that when the binder with Tg in the range of the present application is applied to a positive electrode sheet, the positive electrode active material layer and the current collector have better binding power, and the positive electrode sheet has lower resistance.

The density of the binder typically affects the rate capability and cycling performance of the lithium ion battery. It can be seen from examples 1-1 to 1-23 that when the binder having a density within the range of the present application is applied to a positive electrode plate, a better binding force is provided between a positive electrode active material layer and a current collector, and the positive electrode plate has a lower resistance.

The solid content of the aqueous dispersion of the binder and the corresponding viscosity and Zeta potential generally affect the cohesiveness and dispersibility of the binder, and thus the rate capability and cycle performance of the lithium ion battery. It can be seen from examples 1-1 to 1-23 that when the binder having a solid content of the aqueous dispersion of the binder, a corresponding viscosity and a Zeta potential within the range of the present application is applied to the positive electrode sheet, the positive electrode active material layer and the current collector have a good binding power, and the resistance value of the positive electrode sheet is low. The inventor conjectures that due to the carboxyl negative ions ionized by the shell polymer and the electronegative initiator adsorbed on the surface of the shell, the shell of the aqueous binder provided by the application has high surface negative charges, the electrostatic repulsion force formed by the shell polymer can maintain the relative stability of the binder at the interface position of slurry, the problem that the binder floats upwards in the preparation process of the positive pole piece can be effectively solved, the binder is uniformly distributed on the positive pole piece, the good binding power between the positive active material layer and the current collector can be ensured, and meanwhile, the positive pole piece has lower resistance, so that the lithium ion battery prepared by the positive pole piece provided by the application has good rate multiplying performance and cycle performance.

TABLE 3

The binder content generally affects the rate capability and cycle performance of lithium ion batteries. From examples 1-7 and 2-1, it can be seen that the positive electrode sheet with the binder content in the range of the present application has good binding power between the positive active material layer and the current collector, and meanwhile, the positive electrode sheet has low resistance.

It should be noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, or article that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, or article.

All the embodiments in the present specification are described in a related manner, and the same and similar parts among the embodiments may be referred to each other, and each embodiment focuses on the differences from the other embodiments.

The above description is only for the preferred embodiment of the present application and is not intended to limit the scope of the present application. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present application are included in the scope of protection of the present application.

Claims

1. An adhesive for a positive electrode sheet, comprising composite particles having a core-shell structure, the composite particles comprising a core and a shell layer disposed on at least a portion of a surface of the core, the core comprising conductive nanoparticles, the shell layer comprising a polymer, monomers constituting the polymer comprising acrylic acid and acrylonitrile.

2. The binder of claim 1, wherein the monomers comprising the polymer further comprise ethyl methacrylate, 2-methoxyethyl 2-acrylate, and polyethylene glycol diacrylate.

3. The binder of claim 1, wherein the radius of the core is r nm, the thickness of the shell layer is d nm,0.5r ≦ d ≦ 2r, and 100 ≦ 2r ≦ 200.

4. The binder of claim 1, wherein the mass ratio of the conductive nanoparticles to the polymer is 1 (0.5 to 15).

5. The adhesive according to claim 2, wherein the acrylic acid is 15 to 25% by mass, the acrylonitrile is 25 to 35% by mass, the ethyl methacrylate is 5 to 45% by mass, the 2-methoxyethyl 2-acrylate is 4 to 45% by mass, and the polyethylene glycol diacrylate is 2.0 to 4.0% by mass, based on the mass of the polymer.

6. The binder of claim 1, satisfying at least one of the following characteristics:

(1) The thickness of the shell layer is d nm, and d is more than or equal to 20 and less than or equal to 170;

(2) The radius of the core is r nm, and the radius is more than or equal to 128 and less than or equal to 2r and less than or equal to 182;

(3) The density of the conductive nano particles is more than or equal to 2.2g/cm ³ 。

7. The binder of claim 1, wherein the diameter of the composite particles is from 140nm to 500nm.

8. The binder of claim 1, wherein the conductive nanoparticles comprise silicon nanoparticles or carbon nanoparticles.

9. The binder of claim 1, satisfying at least one of the following characteristics:

(1) The glass transition temperature of the binder is from 20 ℃ to 50 ℃;

(2) The density of the binder is 1g/cm ³ To 1.6g/cm ³ ；

(3) The solid content of the aqueous dispersion of the binder is 5 to 50%, the viscosity of the aqueous dispersion of the binder is 50 to 200mPa s, and the Zeta potential of the aqueous dispersion of the binder is-50 to-40 mV.

10. A positive electrode sheet comprising a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, the positive electrode active material layer comprising a positive electrode active material and the binder of any one of claims 1 to 9.

11. The positive electrode sheet according to claim 10, wherein the binder is contained in an amount of 0.8 to 3.0% by mass based on the mass of the positive electrode active material layer, and the adhesion between the positive electrode active material layer and the positive electrode current collector is 14.5 to 19N/m.

12. An electrochemical device comprising the positive electrode sheet of any one of claims 10 to 11.

13. An electronic device comprising the electrochemical device of claim 12.