CN117558926B

CN117558926B - Flexible high-safety lithium ion positive electrode current collector, battery positive electrode and battery

Info

Publication number: CN117558926B
Application number: CN202311854036.1A
Authority: CN
Inventors: 蔡明军; 李荐; 王利华; 尚雷; 刘斌
Original assignee: Zhejiang Huangneng New Energy Technology Co ltd
Current assignee: Zhejiang Huangneng New Energy Technology Co ltd
Priority date: 2023-12-29
Filing date: 2023-12-29
Publication date: 2024-04-26
Anticipated expiration: 2043-12-29
Also published as: CN117558926A

Abstract

The invention belongs to the technical field of battery materials, and provides a flexible high-safety lithium ion positive electrode current collector, a battery positive electrode and a battery, which comprise a flexible supporting layer, a heat conduction connecting layer and a metal conductive layer which are sequentially laminated; the flexible supporting layer consists of a nanocellulose matrix and MOFs crystals, wherein the nanocellulose matrix is a three-dimensional network structure formed by nanocellulose, and the MOFs crystals grow in situ in the three-dimensional network structure; the heat conduction connecting layer consists of a dopamine matrix and boron nitride nano-sheets dispersed in the dopamine matrix; the metal conductive layer is formed on the surface of the heat conduction connecting layer by adopting a physical vapor deposition process. The positive electrode current collector provided by the invention has a three-layer structure, and the flexible supporting layer provides enough strength and flexibility for the positive electrode current collector; the boron nitride nano-sheets are doped in the heat conduction connecting layer, so that the heat conduction performance of the positive current collector is improved; the quality of the positive electrode current collector is greatly reduced by the metal conductive layer.

Description

Flexible high-safety lithium ion positive electrode current collector, battery positive electrode and battery

Technical Field

The invention belongs to the technical field of battery materials, and relates to a flexible high-safety lithium ion positive electrode current collector, a battery positive electrode and a battery.

Background

Lithium ion batteries are being increasingly popularized in various technical fields as a secondary battery in an emerging new energy industry. The lithium ion battery comprises a positive electrode current collector, a negative electrode current collector, active substances attached to the positive electrode current collector and the negative electrode current collector, a diaphragm arranged between the positive electrode and the negative electrode, and electrolyte for infiltrating the two electrodes. The current collector refers to a metal aggregate for attaching positive and negative active substances of a battery, and a metal matrix such as copper foil and aluminum foil is adopted in the prior art.

However, the current copper foil and aluminum foil current collectors used at present have the following problems: (1) The metal matrix is directly used as a current collector of the lithium ion battery, so that the current collector is easy to oxidize in the use process, and impurities are generated to influence the performance of the lithium ion battery; (2) The metal matrix is directly used as a current collector of the lithium ion battery, and the metal matrix has limited conductivity so as to prevent lithium ion migration; (3) The metal matrix current collector is easy to tear in the manufacturing process of the lithium ion battery, so that the use effect of the metal matrix current collector is influenced by the fragments, and the safety of the lithium ion battery is influenced; (4) The metal matrix current collector is easy to generate burrs in the manufacturing process of the lithium ion battery, so that potential safety hazards are brought to the lithium ion battery; (5) The metal matrix is directly used as a current collector, and the surface of the metal matrix is smooth, so that the binding force between the metal matrix and active substances is poor, positive and negative active substances are caused to fall off, and the product quality of the lithium ion battery is affected.

In order to solve the defect that the metal matrix is directly used as the current collector of the lithium ion battery, a novel lithium ion positive electrode current collector is needed to be designed, and the defect that the metal matrix is used as the current collector can be effectively solved on the basis of meeting the traditional current collector conductive function.

Disclosure of Invention

Aiming at the defects existing in the prior art, the invention aims to provide a flexible high-safety lithium ion positive electrode current collector, a battery positive electrode and a battery, wherein the positive electrode current collector is of a three-layer structure, and the flexible supporting layer takes nano cellulose as a matrix to provide enough strength and flexibility for the positive electrode current collector; the boron nitride nano-sheets are doped in the heat conduction connecting layer, so that the heat conduction performance of the positive current collector is improved; the metal conductive layer greatly reduces the quality of the positive current collector while ensuring the conductivity of the positive current collector.

To achieve the purpose, the invention adopts the following technical scheme:

In a first aspect, the invention provides a flexible high-safety lithium ion positive electrode current collector, which comprises a flexible supporting layer, a heat conduction connecting layer and a metal conductive layer which are sequentially laminated;

The flexible supporting layer consists of a nanocellulose matrix and MOFs crystals, wherein the nanocellulose matrix is a compact three-dimensional network structure formed by nanocellulose, and the MOFs crystals grow in situ in the three-dimensional network structure;

the heat conduction connecting layer consists of a dopamine matrix and boron nitride nano-sheets dispersed in the dopamine matrix;

The metal conductive layer is formed on the surface of the heat conduction connecting layer by adopting a physical vapor deposition process.

The flexible high-safety lithium ion positive electrode current collector provided by the invention comprises a three-layer structure consisting of the flexible supporting layer, the heat conduction connecting layer and the metal conductive layer, wherein the flexible supporting layer takes nano cellulose as a matrix, so that the flexible high-safety lithium ion positive electrode current collector provides enough strength and flexibility for the positive electrode current collector; the boron nitride nano-sheets are doped in the heat conduction connecting layer, so that the heat conduction performance of the positive current collector is improved; the metal conductive layer greatly reduces the quality of the positive current collector while ensuring the conductivity of the positive current collector.

Firstly, the flexible support layer is utilized to enhance the mechanical workability of the positive electrode current collector, so that the positive electrode current collector has excellent flexibility and mechanical strength, and is not easy to produce crease or brittle failure in the process of multiple bending. And secondly, the polydopamine formed by self-polymerization of the dopamine is used as a dopamine matrix, the boron nitride nanosheets are used as fillers, so that a heat conduction connecting layer is formed, on one hand, the excellent heat conduction performance of the boron nitride nanosheets is utilized, the safety of the lithium ion battery in the charge and discharge process is improved, and on the other hand, the rough structure formed on the surface of the heat conduction connecting layer by the boron nitride nanosheets is utilized, a sufficient number of anchoring points are provided for the deposition of a subsequent metal conductive layer, and the interface strength between the heat conduction connecting layer and the metal conductive layer is further improved. And then, a metal conductive layer is formed on the surface of the heat conduction connecting layer by deposition through a physical vapor deposition process, so that the overall mass density of the current collector can be greatly reduced while the conductivity of the metal conductive layer is ensured, the quality of a lithium battery is greatly reduced, and the energy density of the lithium battery is improved.

The nanocellulose has higher specific surface area and larger length-diameter ratio, and can form a light porous flexible supporting layer with a three-dimensional network structure through physical winding action among fibers, so that the nanocellulose has excellent mechanical properties, and stable physicochemical properties can be maintained in electrolyte. In addition, the surface of the nanocellulose is provided with a large number of hydroxyl groups, which is favorable for in-situ growth and load fixation of MOFs crystals on the nanocellulose, so that the dispersion uniformity of the MOFs crystals in the flexible supporting layer is remarkably improved, and the MOFs crystals maintain the optimal performance. According to the invention, the nanocellulose and MOFs crystal are combined to prepare the flexible supporting layer with high porosity and a hierarchical pore structure, the flexible supporting layer is used as a flexible supporting substrate of a current collector, and rich electrolyte transmission channels are formed in the flexible supporting layer. In addition, the synergistic effect between the nanocellulose three-dimensional network structure formed after physical winding and MOFs crystal with a hierarchical porous structure endows the flexible support layer with excellent electrochemical performance and structural stability, and after the current collector provided by the invention is bent and folded for a plurality of times, the internal structure of the flexible support layer can still be kept stable and undeformed.

According to the positive electrode current collector provided by the invention, the heat conduction connecting layer is arranged on the basis of the flexible supporting layer, and the boron nitride nano sheet plays two technical effects in the positive electrode current collector, on one hand, the boron nitride nano sheet has a higher heat conduction coefficient, so that the positive electrode current collector is endowed with excellent heat conduction capability, the heat of the assembled lithium ion battery in the charging and discharging processes is uniformly conducted, the occurrence of a lithium precipitation phenomenon caused by heat focusing is avoided, and the safety of the lithium ion battery in application is ensured; on the other hand, the heat conduction connecting layer is formed by coating or soaking the surface of the flexible supporting layer, the nanoscale scale of the boron nitride nanosheets is utilized to improve the roughness of the surface of the flexible supporting layer, favorable conditions are provided for the deposition and adhesion of the subsequent metal conductive layer, the contact area between the flexible supporting layer and the metal conductive layer is increased, and the interface strength between the flexible supporting layer and the metal conductive layer is improved.

Because the surface of the boron nitride nano-sheet lacks polar functional groups, interaction with the flexible supporting layer cannot be formed, and the interface compatibility between the two is poor, the self-polymerization of dopamine is used for coating the surface of the boron nitride nano-sheet; meanwhile, because of rich imino groups on the polydopamine molecular chain, the polydopamine can react with hydroxyl groups on nanocellulose molecules to form covalent bonds, and the coating of polydopamine on the boron nitride nanosheets improves the interface performance between the boron nitride nanosheets and the flexible supporting layer, so that on one hand, the peeling strength between the heat conducting connecting layer and the flexible supporting layer is improved, and the service life and stability of the positive electrode current collector are prolonged; on the other hand, the interface gap between the two is eliminated, so that the interface thermal resistance between the heat conduction connecting layer and the flexible supporting layer is reduced, the heat conduction efficiency of the positive electrode current collector is improved, and the heat generated by the positive electrode plate can be conducted to the flexible supporting layer through the heat conduction connecting layer as soon as possible.

As a preferred embodiment of the present invention, the mass fraction of the nanocellulose is 60 to 70wt%, for example, 60wt%, 61wt%, 62wt%, 63wt%, 64wt%, 65wt%, 66wt%, 67wt%, 68wt%, 69wt% or 70wt%, based on 100wt% of the total mass fraction of the flexible support layer, but not limited to the recited values, other non-recited values within the range of values are equally applicable, and the balance is MOFs crystals.

In some alternative examples, the thickness of the flexible support layer is 20-30 μm, for example, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, 26 μm, 27 μm, 28 μm, 29 μm, or 30 μm, but is not limited to the recited values, as other non-recited values within this range are equally applicable.

In some alternative examples, the mass fraction of the boron nitride nanoplatelets is 5-15wt%, such as 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, or 15wt%, based on 100wt% of the total mass fraction of the thermally conductive connection layer, but is not limited to the recited values, other non-recited values within the range of values are equally applicable, and the balance is dopamine.

In some alternative examples, the thermally conductive connection layer has a thickness of 1-10 μm, for example, 1 μm, 2 μm,3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm, but is not limited to the recited values, and other non-recited values within the range of values are equally applicable.

In some alternative examples, the surface roughness of the thermally conductive connection layer is 50-60 μm, for example, 50 μm, 51 μm, 52 μm, 53 μm, 54 μm, 55 μm, 56 μm, 57 μm, 58 μm, 59 μm or 60 μm, but is not limited to the recited values, and other non-recited values within the range of values are equally applicable.

In some alternative examples, the thickness of the metal conductive layer is 0.5-1.5 μm, which may be, for example, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, or 1.5 μm, but is not limited to the recited values, and other non-recited values within this range are equally applicable.

As a preferable technical scheme of the invention, the flexible supporting layer is prepared by the following method:

Dissolving metal salt and an organic ligand in an organic solvent to form a precursor solution, mixing the precursor solution with a nanocellulose solution for reaction to grow MOFs crystals on the nanocellulose surface in situ, and then sequentially centrifuging, filtering, washing and drying to obtain a composite support material;

And (II) dispersing the composite support material obtained in the step (I) in deionized water to obtain a precursor solution, carrying out filter pressing on the precursor solution, extruding water in the precursor solution to obtain a filter cake, and drying the filter cake to obtain the flexible support layer.

The MOFs crystal can grow in situ and is supported and fixed on the surface of the fiber mainly due to the combination of electrostatic adsorption and hydrogen bonding, on one hand, metal ions are firstly adsorbed on the surface of the charged fiber through the electrostatic adsorption, and meanwhile, the hydrogen bonding on the surface of the fiber and carboxyl in the organic ligand molecule react to form an ester bond, so that the organic ligand molecule and the metal ions can react on the surface of the fiber to obtain the MOFs crystal, and the MOFs crystal grows on the surface of the fiber in situ. On the other hand, when the precursor solution is added into the nanocellulose solution, hydroxyl groups on the surface of the fiber react with free metal ions through hydrogen bonding, so that in-situ growth and load fixation of MOFs crystals on the surface of the fiber are realized.

According to the invention, the flexible supporting layer is prepared by filter pressing, and the nano cellulose molecules which are partially dissolved in the solution are subjected to molecular rearrangement and recrystallization under the mechanical action of the filter pressing, so that a net structure is formed by physically winding fibers in a local area, MOFs crystals which grow on the surfaces of the fibers in situ are wrapped, so that the combination between the MOFs and the nano cellulose net structure is more stable, the MOFs are not easy to fall off, and the tensile strength of the flexible supporting layer can be enhanced while the loading capacity of the MOFs is improved.

In a preferred embodiment of the present invention, in the step (i), the metal salt includes any one or a combination of at least two of aluminum nitrate, zinc nitrate, cobalt nitrate, magnesium nitrate, copper acetate, aluminum acetate, zinc acetate, cobalt acetate, magnesium acetate, and copper acetate.

In some alternative examples, the organic ligand includes any one or a combination of at least two of trimesic acid, isophthalic acid, terephthalic acid, trimellitic acid, phenol, dimethyl succinic acid, biphenyl dicarboxylic acid, 2-methylimidazole.

In some alternative examples, the organic solvent includes any one or a combination of at least two of dimethylacetamide, dimethylformamide, dimethylsulfoxide, and N-methylpyrrolidone.

In some alternative examples, the concentration of the metal salt in the precursor solution is 0.1-1.5mmol/L, which may be 0.1mmol/L、0.2mmol/L、0.3mmol/L、0.4mmol/L、0.5mmol/L、0.6mmol/L、0.7mmol/L、0.8mmol/L、0.9mmol/L、1.0mmol/L、1.1mmol/L、1.2mmol/L、1.3mmol/L、1.4mmol/L or 1.5mmol/L, for example, but is not limited to the recited values, as other non-recited values within this range are equally applicable.

The Metal Organic Frameworks (MOFs) material has unique porous structure, high specific surface area and Lewis acidic sites, and the structural characteristics can provide lithium ion transmission channels and adsorb lithium salt anions, thereby being beneficial to realizing high-efficiency transmission of lithium ions, effectively inhibiting formation and growth of lithium dendrites and ensuring the safety of the lithium ion battery in the charge and discharge processes.

The active sites of a large amount of hydroxyl groups and a small amount of carboxyl groups contained in the nanocellulose can interact with metal ions, and the nanocellulose can play a synergistic effect with organic ligands to serve as chelating agents in the formation process of MOFs crystals, and form complexes with the metal ions through the hydroxyl groups and the carboxyl groups on nanocellulose molecules. After the MOFs crystal is nucleated in the nano-pores of the three-dimensional network structure of the nano-cellulose, the nano-cellulose forms hydrogen bonds and coordination bonds with the central metal ions and amino groups of the MOFs crystal, so that the MOFs crystal can be anchored in the nano-pores of the three-dimensional network structure of the nano-cellulose, and the MOFs crystal is encapsulated in the nano-pores after being subjected to pressure filtration and drying.

According to the invention, MOFs crystals are grown on cellulose nanofibers in situ, so that the MOFs crystals are uniformly dispersed in the nanocellulose substrate, and a communicated electrolyte transmission channel is formed in the nanocellulose substrate, so that the reaction rate between an active substance and an electrolyte is increased, and meanwhile, the rich mesoporous condition can provide more lithium ion intercalation points, can regulate internal stress generated in the charging and discharging processes, and is beneficial to improving the electrochemical performance of a lithium ion battery.

The number of intermolecular bonds is sharply increased along with the dissolution, regeneration and press filtration of the nanocellulose to form a more compact three-dimensional network structure, and meanwhile, the effective stress transmission at the interface can be ensured and the failure of the flexible supporting layer in the stretching process is delayed due to the fact that the phase separation is inhibited by good interface adhesion between the nanocellulose and MOFs crystals. Thereby greatly improving the mechanical properties of the flexible support layer.

The method particularly limits the concentration of the metal salt in the precursor solution to 0.1-1.5mmol/L, and when the concentration of the metal salt is lower than 0.1mmol/L, the number of MOFs crystals synthesized in situ is too low to form an effective lithium ion transmission channel, so that the electrochemical performance of the lithium ion battery is influenced; in addition, too low a content of MOFs crystals may result in an ineffective improvement of the mechanical properties of the flexible support layer. When the concentration of the metal salt exceeds 1.5mmol/L, the number of MOFs crystals synthesized in situ is too high, and the high content of MOFs crystals can cause serious particle agglomeration problems, so that the high-efficiency transmission of lithium ions can be hindered, and the mechanical strength of the flexible supporting layer can be further influenced.

In some alternative examples, the molar ratio of the metal salt to the organic ligand is 1 (0.5-10), for example, may be 1:0.5, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, or 1:10, but is not limited to the recited values, and other non-recited values within the range of values are equally applicable.

In some alternative examples, the nanocellulose solution has a mass fraction of 0.5-1.5wt%, for example, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1.0wt%, 1.1wt%, 1.2wt%, 1.3wt%, 1.4wt%, or 1.5wt%, but is not limited to the recited values, and other non-recited values within the range of values are equally applicable.

The nano cellulose mainly comprises cellulose nano fibers and cellulose nano crystals, wherein the cellulose nano fibers are of fiber filament structures with high length-diameter ratio, and the cellulose nano crystals are of rod-shaped structures. In order to form a flexible support layer having a tunnel structure, the present invention preferably employs cellulose nanofibers.

The mass fraction of the nano cellulose solution is particularly limited to 0.5-1.5wt%, and due to the high length-diameter ratio of cellulose nano fibers, when the solid content of the nano cellulose solution is too high, the nano cellulose solution is in a gel state, so that the dispersibility of metal salt and organic ligand in the nano cellulose solution is influenced, and MOFs crystals obtained by reaction are easily distributed unevenly in a flexible supporting layer. However, when the solid content of the nano cellulose solution is too low, the nano cellulose content in the flexible supporting layer is low, and a sufficient number of electrolyte transmission channels cannot be formed; meanwhile, the water content in the nanocellulose solution is too high, so that the energy consumption and time required by filter pressing are greatly increased, and the production efficiency of the flexible supporting layer is reduced.

It should be noted that the cellulose nanofiber used in the present invention may be prepared by using the currently disclosed prior art or a new technology not disclosed, and the present invention is not particularly limited and limited thereto. The currently common preparation methods include physical methods and chemical methods.

In some alternative examples, the temperature of the mixing reaction is 100-150 ℃, such as 100 ℃, 105 ℃, 110 ℃, 115 ℃, 120 ℃, 125 ℃, 130 ℃, 135 ℃, 140 ℃, 145 ℃, or 150 ℃, although not limited to the recited values, other non-recited values within the range are equally applicable.

In some alternative examples, the mixing reaction may be carried out for a period of time ranging from 10 to 20 hours, such as 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, 16 hours, 17 hours, 18 hours, 19 hours, or 20 hours, although not limited to the recited values, and other non-recited values within the range are equally applicable.

In some alternative examples, the mass fraction of the precursor solution in step (ii) is 1-10wt%, such as 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, or 10wt%, but is not limited to the recited values, and other non-recited values within the range of values are equally applicable.

In some alternative examples, the pressure of the press filtration is 1-5MPa, for example, 1.0MPa, 1.5MPa, 2.0MPa, 2.5MPa, 3.0MPa, 3.5MPa, 4.0MPa, 4.5MPa, or 5.0MPa, but is not limited to the recited values, and other non-recited values within the range are equally applicable.

In some alternative examples, the time of the press filtration is 10-20min, for example, 10min, 11min, 12min, 13min, 14min, 15min, 16min, 17min, 18min, 19min or 20min, but not limited to the recited values, and other non-recited values within the range are equally applicable.

In some alternative examples, the drying temperature is 80-120 ℃, such as 80 ℃, 85 ℃,90 ℃,95 ℃, 100 ℃, 105 ℃, 110 ℃, 115 ℃, or 120 ℃, but is not limited to the recited values, and other non-recited values within the range of values are equally applicable.

In some alternative examples, the drying time is 20-30min, for example, 20min, 21min, 22min, 23min, 24min, 25min, 26min, 27min, 28min, 29min, or 30min, but not limited to the recited values, and other non-recited values within the range are equally applicable.

As a preferable technical scheme of the invention, the heat conduction connecting layer is prepared by adopting the following method:

dispersing dopamine and boron nitride nano-sheets in a Tirs-HCl buffer solution and performing ultrasonic dispersion treatment to obtain a dopamine/boron nitride nano-sheet suspension;

And immersing the flexible supporting layer in the dopamine/boron nitride nanosheet suspension, taking out and drying after a period of time to form the heat conduction connecting layer on the surface of the flexible supporting layer.

As a preferred embodiment of the present invention, the pH of the Tirs-HCl buffer is 8-9, and may be, for example, 8.0, 8.1, 8.2, 8.3, 8.4, 8.5, 8.6, 8.7, 8.8, 8.9 or 9.0, but is not limited to the values recited, and other values not recited in the range are equally applicable.

In some alternative examples, the concentration of dopamine in the dopamine/boron nitride nanosheet suspension is 0.5-1.5g/L, and may be, for example, 0.5g/L, 0.6g/L, 0.7g/L, 0.8g/L, 0.9g/L, 1.0g/L, 1.1g/L, 1.2g/L, 1.3g/L, 1.4g/L, or 1.5g/L, although not limited to the recited values, as other non-recited values within this range of values may be equally suitable.

The concentration of dopamine in the dopamine/boron nitride nanosheet suspension is particularly limited to be 0.5-1.5g/L, and on one hand, when the concentration of dopamine is higher than 1.5g/L, the heat conduction efficiency of the heat conduction connecting layer is reduced, and the phonon is lost when passing through the heat conduction connecting layer due to mismatch of phonon vibration frequencies between polydopamine and boron nitride nanosheets; the higher the concentration of dopamine is, the larger the thickness of the formed heat conduction connecting layer is, the more phonon loss is, and finally the heat conduction performance of the heat conduction connecting layer is reduced; in addition, since polydopamine itself is a poor conductor of heat, the interfacial thermal resistance between boron nitride nanoplatelets is also increased when the concentration of dopamine is too high. On the other hand, the invention realizes the coating of the boron nitride nano-sheets through the self-polymerization of the dopamine, thereby ensuring that the boron nitride nano-sheets have good dispersibility in the dopamine/boron nitride nano-sheet suspension, and the better the dispersibility is, the smaller the contact area between the boron nitride nano-sheets is, thereby reducing the interface thermal resistance between the boron nitride nano-sheets and being beneficial to the internal conduction of heat in the heat conduction connecting layer; therefore, when the concentration of dopamine is lower than 0.5g/L, effective coating of the boron nitride nano-sheets cannot be formed, so that serious agglomeration of the boron nitride nano-sheets is caused, and the full play of the heat conducting property of the boron nitride nano-sheets is affected.

In some alternative examples, the concentration of boron nitride nanoplatelets in the dopamine/boron nitride nanoplatelet suspension is between 0.05 and 0.1g/L, and may be, for example, 0.05g/L, 0.055g/L, 0.06g/L, 0.065g/L, 0.07g/L, 0.075g/L, 0.08g/L, 0.085g/L, 0.09g/L, 0.095g/L, or 0.1g/L, although not limited to the recited values, as other non-recited values within this range of values are equally applicable.

The invention particularly limits the concentration of the boron nitride nano-sheets in the dopamine/boron nitride nano-sheet suspension to 0.05-0.1g/L, and when the concentration of the boron nitride nano-sheets is lower than 0.05g/L, the advantage of high heat conductivity of the boron nitride nano-sheets cannot be effectively exerted on one hand; on the other hand, the rough structure is formed on the surface of the heat conduction connecting layer by means of the boron nitride nano-sheets, so that anchoring sites are provided for subsequent metal physical vapor deposition, the interface strength between the heat conduction connecting layer and the metal conductive layer is further enhanced, when the concentration of the boron nitride nano-sheets is too low, a sufficient number of rough structures cannot be formed on the surface of the heat conduction connecting layer, and the interface bonding strength between the metal conductive layer formed by subsequent deposition and the heat conduction connecting layer is further influenced. When the concentration of the boron nitride nano-sheets is higher than 0.1g/L, the boron nitride nano-sheets can generate serious agglomeration phenomenon in the dopamine/boron nitride nano-sheet suspension, so that the interface thermal resistance between the boron nitride nano-sheets is improved, and the heat cannot be smoothly conducted; the flexible supporting layer and the heat conduction connecting layer cannot be tightly attached to each other, so that the interface bonding strength between the flexible supporting layer and the heat conduction connecting layer is affected; meanwhile, particles formed after the boron nitride nano-sheets are agglomerated can also cause stress concentration phenomenon in the heat conduction connecting layer, so that the mechanical property of the positive electrode current collector is affected.

In some alternative examples, the ultrasonic power 600-700W of the ultrasonic dispersion treatment may be 600W, 610W, 620W, 630W, 640W, 650W, 660W, 670W, 680W, 690W or 700W, for example, but is not limited to the recited values, and other non-recited values within the range of values are equally applicable.

In some alternative examples, the time of the ultrasonic dispersion treatment is 20-30min, for example, 20min, 21min, 22min, 23min, 24min, 25min, 26min, 27min, 28min, 29min or 30min, but not limited to the recited values, and other non-recited values within the range of values are equally applicable.

In some alternative examples, the flexible support layer is immersed in the dopamine/boron nitride nanosheet suspension at a temperature of 20-30 ℃, such as 20 ℃, 21 ℃, 22 ℃, 23 ℃, 24 ℃, 25 ℃, 26 ℃, 27 ℃, 28 ℃, 29 ℃ or 30 ℃, but is not limited to the recited values, as other non-recited values within the range of values are equally applicable.

In some alternative examples, the flexible support layer is immersed in the dopamine/boron nitride nanosheet suspension for a period of time ranging from 6 to 12 hours, such as 6.0 hours, 6.5 hours, 7.0 hours, 7.5 hours, 8.0 hours, 8.5 hours, 9.0 hours, 9.5 hours, 10.0 hours, 10.5 hours, 11.0 hours, 11.5 hours, or 12.0 hours, although not limited to the recited values, as well as other non-recited values within this range of values.

As a preferable technical scheme of the invention, the metal conductive layer is prepared by the following method:

Placing a composite layer consisting of the flexible supporting layer and the heat conducting connecting layer on a conveyor belt in a coating cavity, wherein the heat conducting connecting layer faces upwards; fixing a metal target above the conveyor belt, vacuumizing the inside of the coating cavity and introducing argon into the coating cavity; the conveyor belt drives the composite layer to continuously move at a constant speed, and the coating equipment acts on the metal target material to deposit a metal conductive layer on the surface of the heat-conducting connecting layer.

The metal target is any one or the combination of at least two of a copper target, an aluminum target, a nickel target and a zinc target.

As a preferred embodiment of the present invention, the vertical distance between the metal target and the thermally conductive connection layer is 50-100mm, and may be, for example, 50mm, 55mm, 60mm, 65mm, 70mm, 75mm, 80mm, 85mm, 90mm, 95mm or 100mm, but is not limited to the recited values, and other non-recited values within the range of values are equally applicable.

In some alternative examples, the vacuum level of the coating chamber is 1.0X10 ^-4-3.0×10^-3 Pa, which may be 1×10^-4、3×10^-4、5×10^-4、7×10^-4、9×10^-4、1×10^-3、1.5×10^-3、2×10^-3、2.5×10^-3 or 3X 10 ^-3, for example, but is not limited to the recited values, and other non-recited values within the range are equally applicable.

In some alternative examples, the argon gas flow is 50-60SCCM, which may be, for example, 50SCCM, 51SCCM, 52SCCM, 53SCCM, 54SCCM, 55SCCM, 56SCCM, 57SCCM, 58SCCM, 59SCCM, or 60SCCM, but is not limited to the recited values, and other non-recited values within the range of values are equally applicable.

In some alternative examples, the conveyor belt may have a conveying speed of 1-5cm/min, such as 1.0cm/min, 1.5cm/min, 2.0cm/min, 2.5cm/min, 3.0cm/min, 3.5cm/min, 4.0cm/min, 4.5cm/min, or 5.0cm/min, although not limited to the recited values, and other non-recited values within this range of values may be equally applicable.

In some alternative examples, the average power density of the metal target surface is 10-20W/cm ², which may be 10W/cm²、11W/cm²、12W/cm²、13W/cm²、14W/cm²、15W/cm²、16W/cm²、17W/cm²、18W/cm²、19W/cm² or 20W/cm ², for example, but is not limited to the recited values, and other non-recited values within this range are equally applicable.

In some alternative examples, the average current density of the metal target surface is 30-40mA/cm ², which may be 30mA/cm²、31mA/cm²、32mA/cm²、33mA/cm²、34mA/cm²、35mA/cm²、36mA/cm²、37mA/cm²、38mA/cm²、39mA/cm² or 40mA/cm ², for example, but is not limited to the recited values, and other non-recited values within this range are equally applicable.

The invention provides a preparation method of a flexible high-safety lithium ion positive electrode current collector, which comprises the following steps of:

(1) Dissolving metal salt and an organic ligand in an organic solvent according to a molar ratio of 1 (0.5-10) to form a precursor solution, mixing the precursor solution with 0.5-1.5wt% of nano cellulose solution, reacting for 10-20h at 100-150 ℃ to grow MOFs crystals on the surface of the nano cellulose, and sequentially centrifuging, filtering, washing and drying to obtain a composite support material;

(2) Dispersing the composite support material obtained in the step (1) in deionized water to obtain a precursor solution with the weight percent of 1-10%, press-filtering the precursor solution for 10-20min under the pressure filtration of 1-5MPa, extruding water in the precursor solution to obtain a filter cake, and drying the filter cake at 80-120 ℃ for 20-30min to obtain a flexible support layer;

(3) Dispersing dopamine and boron nitride nano-sheets in Tirs-HCl buffer solution (pH value is 8-9) and carrying out ultrasonic dispersion treatment for 20-30min, wherein the adopted ultrasonic power is 600-700W, and the dopamine/boron nitride nano-sheet suspension is obtained, wherein the concentration of dopamine is 0.5-1.5g/L, and the concentration of boron nitride nano-sheets is 0.05-0.1g/L; soaking the flexible supporting layer obtained in the step (2) in dopamine/boron nitride nanosheet suspension at 20-30 ℃ for 6-12h, and then taking out and drying to form a heat conduction connecting layer on the surface of the flexible supporting layer;

(4) Placing a composite layer consisting of the flexible supporting layer and the heat conducting connecting layer on a conveyor belt in a coating cavity, wherein the heat conducting connecting layer faces upwards; fixing a metal target above a conveyor belt, wherein the vertical distance between the metal target and a heat conduction connecting layer is 50-100mm, vacuumizing the interior of a coating cavity to 1.0 multiplied by 10 ^-4-3.0×10^-3 Pa, and simultaneously introducing argon into the coating cavity at the flow rate of 50-60 SCCM; the conveyor belt drives the composite layer to advance at a uniform speed with a moving speed of 1-5cm/min, the coating equipment acts on the metal target, the average power density of the surface of the metal target is 10-20W/cm ², and the average current density is 30-40mA/cm ², so that a metal conductive layer is deposited on the surface of the heat-conducting connecting layer.

The invention also provides a flexible high-safety lithium ion positive electrode current collector, which comprises a flexible supporting layer, a heat conduction connecting layer and a metal electric conduction layer which are sequentially stacked. The thickness of the flexible supporting layer is 20-30 mu m, the thickness of the heat conducting connecting layer is 1-10 mu m, and the thickness of the metal conductive layer is 0.5-1.5 mu m.

The flexible supporting layer is composed of a nanocellulose matrix and MOFs crystals, the nanocellulose matrix is a compact three-dimensional network structure formed by nanocellulose, and the MOFs crystals grow in situ in the three-dimensional network structure. The mass fraction of the nanocellulose is 60-70wt% based on 100wt% of the total mass fraction of the flexible support layer, and the balance is MOFs crystal.

The heat conduction connecting layer consists of a dopamine matrix and boron nitride nano-sheets dispersed in the dopamine matrix, wherein the mass fraction of the boron nitride nano-sheets is 5-15wt% based on the total mass fraction of the heat conduction connecting layer of 100wt%, and the balance of the dopamine. The surface roughness of the heat conducting connection layer is 50-60 mu m.

In a second aspect, the present invention provides a battery positive electrode including a positive electrode current collector and a positive electrode active layer formed on a surface of the positive electrode current collector; the positive current collector is the flexible high-safety lithium ion positive current collector in the first aspect.

In a third aspect, the invention provides a battery, the battery comprises a shell and a battery core positioned in the shell, the battery core comprises a battery positive electrode, a diaphragm and a battery negative electrode which are sequentially stacked, and the battery positive electrode is the battery positive electrode in the second aspect.

Compared with the prior art, the invention has the beneficial effects that:

Drawings

FIG. 1 is a flow chart of the preparation process of the positive electrode current collector provided in examples 1-13 of the present invention;

fig. 2 is a schematic structural diagram of a positive electrode current collector according to embodiments 1 to 13 of the present invention;

fig. 3 is a physical picture of the positive current collector provided in embodiment 1 of the present invention under different bending degrees;

FIG. 4 is a cross-sectional electron micrograph of a flexible support layer according to example 1 of the present invention;

FIG. 5 is an electron micrograph of MOFs crystals prepared in example 1 of the present invention;

wherein, 1-a flexible support layer; 2-a thermally conductive connection layer; 3-metal conductive layer.

Detailed Description

The technical scheme of the application is described in detail below with reference to specific embodiments and attached drawings. The examples described herein are specific embodiments of the present application for illustrating the concept of the present application; the description is intended to be illustrative and exemplary in nature and should not be construed as limiting the scope of the application in its aspects. In addition to the embodiments described herein, those skilled in the art can adopt other obvious solutions based on the disclosure of the claims and the specification thereof, including those adopting any obvious substitutions and modifications to the embodiments described herein.

Example 1

The embodiment provides a preparation method of a flexible high-safety lithium ion positive electrode current collector, as shown in fig. 1, comprising the following steps:

(1) Dissolving cobalt nitrate and 2-methylimidazole in dimethylacetamide according to a molar ratio of 1:0.5 to form a precursor solution, wherein the concentration of the cobalt nitrate in the precursor solution is 0.1mmol/L, mixing the precursor solution with 0.5wt% of cellulose nanofiber solution, reacting for 20 hours at 100 ℃ to grow MOFs crystals on the surface of the cellulose nanofiber in situ, and sequentially centrifuging, filtering, washing and drying to obtain a composite support material;

(2) Dispersing the composite support material obtained in the step (1) in deionized water to obtain a precursor solution with the weight percent of 1%, carrying out filter pressing on the precursor solution for 20min under the filter pressing condition of 1MPa, extruding water in the precursor solution to obtain a filter cake, and drying the filter cake at 80 ℃ for 30min to obtain a flexible support layer 1;

(3) Dispersing dopamine and boron nitride nano-sheets in a Tirs-HCl buffer solution (pH value is 8) and carrying out ultrasonic dispersion treatment for 20min, wherein the adopted ultrasonic power is 700W, and a dopamine/boron nitride nano-sheet suspension is obtained, wherein the concentration of dopamine is 0.5g/L, and the concentration of boron nitride nano-sheets is 0.05g/L; immersing the flexible supporting layer 1 obtained in the step (2) in dopamine/boron nitride nanosheet suspension at 20 ℃ for 12 hours, and then taking out and drying to form a heat-conducting connecting layer 2 on the surface of the flexible supporting layer 1;

(4) Placing a composite layer consisting of the flexible supporting layer 1 and the heat conducting connecting layer 2 on a conveyor belt in a coating cavity, wherein the heat conducting connecting layer 2 faces upwards; fixing a metal target above a conveyor belt, wherein the vertical distance between the metal target and the heat conduction connecting layer 2 is 50mm, vacuumizing the interior of a coating cavity to 1.0 multiplied by 10 ^-4 Pa, and simultaneously introducing argon into the coating cavity at a flow rate of 50 SCCM; the conveyor belt drives the composite layer to advance at a uniform speed with a moving speed of 1cm/min, the coating equipment acts on the metal target, the average power density of the surface of the metal target is 10W/cm ², and the average current density is 30mA/cm ², so that a metal conductive layer 3 is deposited on the surface of the heat-conducting connecting layer 2.

The embodiment also provides a flexible high-safety lithium ion positive electrode current collector, which comprises a flexible supporting layer 1, a heat conduction connecting layer 2 and a metal conductive layer 3 which are sequentially stacked as shown in fig. 2. The thickness of the flexible supporting layer 1 is 20 μm, the thickness of the heat conducting connection layer 2 is 1 μm, and the thickness of the metal conductive layer 3 is 0.5 μm.

The flexible supporting layer 1 is composed of a nanocellulose matrix and MOFs crystals, wherein the nanocellulose matrix is a compact three-dimensional network structure formed by nanocellulose, and the MOFs crystals grow in situ in the three-dimensional network structure. The mass fraction of nanocellulose is 60wt% based on 100wt% of the total mass fraction of the flexible support layer 1, the balance being MOFs crystals.

The heat conduction connecting layer 2 consists of a dopamine matrix and boron nitride nano-sheets dispersed in the dopamine matrix, wherein the mass fraction of the boron nitride nano-sheets is 5wt% based on the total mass fraction of the heat conduction connecting layer 2 of 100wt%, and the balance is dopamine. The surface roughness of the thermally conductive connection layer 2 was 50.6 μm.

The positive current collector prepared in this example was subjected to a bending test, and the test result is shown in fig. 3. It can be seen from fig. 3 that the positive current collector does not break or wrinkle after being bent at different angles, so that it can be demonstrated that the positive current collector prepared in this example has excellent flexibility.

The microscopic profile of the cross section of the flexible supporting layer 1 prepared in this example is shown in fig. 4, and it can be seen from fig. 4 that MOFs crystals are uniformly dispersed in a three-dimensional network structure formed by cross winding cellulose nanofibers.

The MOFs crystal prepared in the embodiment is a ZIF-67 crystal and consists of a metal drill center and 2-methylimidazole. The microscopic morphology is shown in fig. 5, and as can be seen from fig. 5, the in-situ synthesized ZIF-67 crystal of the embodiment has a relatively uniform size and is rhombic dodecahedron.

Example 2

(1) Zinc nitrate and terephthalic acid are dissolved in dimethylformamide according to a molar ratio of 1:1 to form a precursor solution, the concentration of the zinc nitrate in the precursor solution is 0.5mmol/L, the precursor solution is mixed with 0.8wt% of cellulose nanofiber solution, the mixture is reacted for 18 hours at 110 ℃ to grow MOFs crystals on the surface of the cellulose nanofiber in situ, and then the composite support material is obtained after centrifugation, filtration, washing and drying are sequentially carried out;

(2) Dispersing the composite support material obtained in the step (1) in deionized water to obtain a precursor solution with the concentration of 3wt%, press-filtering the precursor solution for 18min under the pressure filtration of 2MPa, extruding water in the precursor solution to obtain a filter cake, and drying the filter cake at 90 ℃ for 28min to obtain a flexible support layer 1;

(3) Dispersing dopamine and boron nitride nano-sheets in a Tirs-HCl buffer solution (pH value is 8.3) and carrying out ultrasonic dispersion treatment for 22min, wherein the adopted ultrasonic power is 680W, and a dopamine/boron nitride nano-sheet suspension is obtained, wherein the concentration of dopamine is 0.8g/L, and the concentration of boron nitride nano-sheets is 0.06g/L; immersing the flexible supporting layer 1 obtained in the step (2) in a dopamine/boron nitride nanosheet suspension at 23 ℃ for 10 hours, and then taking out and drying to form a heat-conducting connecting layer 2 on the surface of the flexible supporting layer 1;

(4) Placing a composite layer consisting of the flexible supporting layer 1 and the heat conducting connecting layer 2 on a conveyor belt in a coating cavity, wherein the heat conducting connecting layer 2 faces upwards; fixing a metal target above a conveyor belt, wherein the vertical distance between the metal target and the heat conduction connecting layer 2 is 60mm, vacuumizing the interior of a coating cavity to 5.0 multiplied by 10 ^-4 Pa, and simultaneously introducing argon into the coating cavity at the flow rate of 52 SCCM; the conveyor belt drives the composite layer to advance at a constant speed with a moving speed of 2cm/min, the coating equipment acts on the metal target, the average power density of the surface of the metal target is 12W/cm ², and the average current density is 32mA/cm ², so that a metal conductive layer 3 is deposited on the surface of the heat-conducting connecting layer 2.

The embodiment also provides a flexible high-safety lithium ion positive electrode current collector, which comprises a flexible supporting layer 1, a heat conduction connecting layer 2 and a metal conductive layer 3 which are sequentially stacked as shown in fig. 2. The thickness of the flexible supporting layer 1 is 22 μm, the thickness of the heat conducting connection layer 2 is 3 μm, and the thickness of the metal conductive layer 3 is 0.8 μm.

The flexible supporting layer 1 is composed of a nanocellulose matrix and MOFs crystals, wherein the nanocellulose matrix is a compact three-dimensional network structure formed by nanocellulose, and the MOFs crystals grow in situ in the three-dimensional network structure. The mass fraction of nanocellulose was 62wt%, calculated as 100wt% of the total mass fraction of the flexible support layer 1, the remainder being MOFs crystals.

The heat conduction connecting layer 2 consists of a dopamine matrix and boron nitride nano-sheets dispersed in the dopamine matrix, wherein the mass fraction of the boron nitride nano-sheets is 8wt% based on the total mass fraction of the heat conduction connecting layer 2 of 100wt%, and the balance is dopamine. The surface roughness of the thermally conductive connection layer 2 was 52.3 μm.

Example 3

(1) Dissolving magnesium nitrate and isophthalic acid in dimethyl sulfoxide according to a molar ratio of 1:5 to form a precursor solution, mixing the precursor solution with 1wt% of cellulose nanofiber solution, reacting for 15 hours at 120 ℃ to grow MOFs crystals on the surface of the cellulose nanofiber in situ, and sequentially centrifuging, filtering, washing and drying to obtain a composite support material;

(2) Dispersing the composite support material obtained in the step (1) in deionized water to obtain a precursor solution with the concentration of 5wt%, press-filtering the precursor solution for 15min under the pressure filtration of 3MPa, extruding water in the precursor solution to obtain a filter cake, and drying the filter cake at 100 ℃ for 25min to obtain a flexible support layer 1;

(3) Dispersing dopamine and boron nitride nano-sheets in a Tirs-HCl buffer solution (pH value is 8.5) and carrying out ultrasonic dispersion treatment for 25min, wherein the adopted ultrasonic power is 650W, and the dopamine/boron nitride nano-sheet suspension is obtained, wherein the concentration of the dopamine is 1g/L, and the concentration of the boron nitride nano-sheets is 0.07g/L; soaking the flexible supporting layer 1 obtained in the step (2) in dopamine/boron nitride nanosheet suspension at 25 ℃ for 8 hours, and then taking out and drying to form a heat-conducting connecting layer 2 on the surface of the flexible supporting layer 1;

(4) Placing a composite layer consisting of the flexible supporting layer 1 and the heat conducting connecting layer 2 on a conveyor belt in a coating cavity, wherein the heat conducting connecting layer 2 faces upwards; fixing a metal target above a conveyor belt, wherein the vertical distance between the metal target and the heat conduction connecting layer 2 is 70mm, vacuumizing the interior of a coating cavity to 1.0 multiplied by 10 ^-3 Pa, and simultaneously introducing argon into the coating cavity at a flow rate of 55 SCCM; the conveyor belt drives the composite layer to advance at a constant speed at a moving speed of 3cm/min, the coating equipment acts on the metal target, the average power density of the surface of the metal target is 15W/cm ², and the average current density is 35mA/cm ², so that a metal conductive layer 3 is deposited on the surface of the heat-conducting connecting layer 2.

The embodiment also provides a flexible high-safety lithium ion positive electrode current collector, which comprises a flexible supporting layer 1, a heat conduction connecting layer 2 and a metal conductive layer 3 which are sequentially stacked as shown in fig. 2. The thickness of the flexible supporting layer 1 is 25 μm, the thickness of the heat conducting connection layer 2 is 5 μm, and the thickness of the metal conductive layer 3 is 1 μm.

The flexible supporting layer 1 is composed of a nanocellulose matrix and MOFs crystals, wherein the nanocellulose matrix is a compact three-dimensional network structure formed by nanocellulose, and the MOFs crystals grow in situ in the three-dimensional network structure. The mass fraction of nanocellulose is 65wt% based on 100wt% of the total mass fraction of the flexible support layer 1, the balance being MOFs crystals.

The heat conduction connecting layer 2 consists of a dopamine matrix and boron nitride nano-sheets dispersed in the dopamine matrix, wherein the mass fraction of the boron nitride nano-sheets is 10% by weight based on the total mass fraction of the heat conduction connecting layer 2 of 100% by weight, and the balance is dopamine. The surface roughness of the thermally conductive connection layer 2 was 55.6 μm.

Example 4

(1) Dissolving cobalt acetate and terephthalic acid in N-methyl pyrrolidone according to a molar ratio of 1:7 to form a precursor solution, wherein the concentration of cobalt acetate in the precursor solution is 1.3mmol/L, mixing the precursor solution with 1.2wt% of cellulose nanofiber solution, reacting at 130 ℃ for 12 hours to grow MOFs crystals on the surface of the cellulose nanofiber in situ, and sequentially centrifuging, filtering, washing and drying to obtain a composite support material;

(2) Dispersing the composite support material obtained in the step (1) in deionized water to obtain a precursor solution with the concentration of 7wt%, press-filtering the precursor solution for 12min under the pressure filtration of 4MPa, extruding water in the precursor solution to obtain a filter cake, and drying the filter cake at 110 ℃ for 23min to obtain a flexible support layer 1;

(3) Dispersing dopamine and boron nitride nano-sheets in a Tirs-HCl buffer solution (pH value is 8.8) and carrying out ultrasonic dispersion treatment for 28min, wherein the adopted ultrasonic power is 620W, and the dopamine/boron nitride nano-sheet suspension is obtained, wherein the concentration of the dopamine is 1.2g/L, and the concentration of the boron nitride nano-sheets is 0.08g/L; immersing the flexible supporting layer 1 obtained in the step (2) in dopamine/boron nitride nanosheet suspension at 28 ℃ for 7 hours, and then taking out and drying to form a heat-conducting connecting layer 2 on the surface of the flexible supporting layer 1;

(4) Placing a composite layer consisting of the flexible supporting layer 1 and the heat conducting connecting layer 2 on a conveyor belt in a coating cavity, wherein the heat conducting connecting layer 2 faces upwards; fixing a metal target above a conveyor belt, wherein the vertical distance between the metal target and the heat conduction connecting layer 2 is 80mm, vacuumizing the interior of a coating cavity to 2.0 multiplied by 10 ^-3 Pa, and simultaneously introducing argon into the coating cavity at the flow rate of 58 SCCM; the conveyor belt drives the composite layer to advance at a constant speed with a moving speed of 4cm/min, the coating equipment acts on the metal target, the average power density of the surface of the metal target is 18W/cm ², and the average current density is 38mA/cm ², so that a metal conductive layer 3 is deposited on the surface of the heat-conducting connecting layer 2.

The embodiment also provides a flexible high-safety lithium ion positive electrode current collector, which comprises a flexible supporting layer 1, a heat conduction connecting layer 2 and a metal conductive layer 3 which are sequentially stacked as shown in fig. 2. The thickness of the flexible supporting layer 1 was 28 μm, the thickness of the heat conductive connecting layer 2 was 7 μm, and the thickness of the metal conductive layer 3 was 1.2 μm.

The flexible supporting layer 1 is composed of a nanocellulose matrix and MOFs crystals, wherein the nanocellulose matrix is a compact three-dimensional network structure formed by nanocellulose, and the MOFs crystals grow in situ in the three-dimensional network structure. The mass fraction of nanocellulose was 67wt%, with the balance being MOFs crystals, based on 100wt% of the total mass fraction of the flexible support layer 1.

The heat conduction connecting layer 2 consists of a dopamine matrix and boron nitride nano-sheets dispersed in the dopamine matrix, wherein the mass fraction of the boron nitride nano-sheets is 12wt% based on the total mass fraction of the heat conduction connecting layer 2 of 100wt%, and the balance is dopamine. The surface roughness of the thermally conductive connection layer 2 was 57.4 μm.

Example 5

(1) Dissolving zinc acetate and trimesic acid in dimethylacetamide according to a molar ratio of 1:10 to form a precursor solution, mixing the precursor solution with 1.5wt% of cellulose nanofiber solution, reacting for 10 hours at 150 ℃ to grow MOFs crystals on the surface of the cellulose nanofiber in situ, and sequentially centrifuging, filtering, washing and drying to obtain a composite support material;

(2) Dispersing the composite support material obtained in the step (1) in deionized water to obtain a precursor solution with the concentration of 10wt%, press-filtering the precursor solution for 10min under the pressure filtration of 5MPa, extruding water in the precursor solution to obtain a filter cake, and drying the filter cake at 120 ℃ for 20min to obtain a flexible support layer 1;

(3) Dispersing dopamine and boron nitride nano-sheets in a Tirs-HCl buffer solution (pH value is 9) and carrying out ultrasonic dispersion treatment for 30min, wherein the adopted ultrasonic power is 600W, and a dopamine/boron nitride nano-sheet suspension is obtained, wherein the concentration of the dopamine is 1.5g/L, and the concentration of the boron nitride nano-sheets is 0.1g/L; soaking the flexible supporting layer 1 obtained in the step (2) in dopamine/boron nitride nanosheet suspension at 30 ℃ for 6 hours, and then taking out and drying to form a heat-conducting connecting layer 2 on the surface of the flexible supporting layer 1;

(4) Placing a composite layer consisting of the flexible supporting layer 1 and the heat conducting connecting layer 2 on a conveyor belt in a coating cavity, wherein the heat conducting connecting layer 2 faces upwards; fixing a metal target above a conveyor belt, wherein the vertical distance between the metal target and the heat conduction connecting layer 2 is 100mm, vacuumizing the interior of a coating cavity to 3.0 multiplied by 10 ^-3 Pa, and simultaneously introducing argon into the coating cavity at a flow rate of 60 SCCM; the conveyor belt drives the composite layer to advance at a constant speed at a moving speed of 5cm/min, the coating equipment acts on the metal target, the average power density of the surface of the metal target is 20W/cm ², and the average current density is 40mA/cm ², so that a metal conductive layer 3 is deposited on the surface of the heat-conducting connecting layer 2.

The embodiment also provides a flexible high-safety lithium ion positive electrode current collector, which comprises a flexible supporting layer 1, a heat conduction connecting layer 2 and a metal conductive layer 3 which are sequentially stacked as shown in fig. 2. The thickness of the flexible supporting layer 1 is 30 μm, the thickness of the heat conducting connection layer 2 is 10 μm, and the thickness of the metal conductive layer 3 is 1.5 μm.

The flexible supporting layer 1 is composed of a nanocellulose matrix and MOFs crystals, wherein the nanocellulose matrix is a compact three-dimensional network structure formed by nanocellulose, and the MOFs crystals grow in situ in the three-dimensional network structure. The mass fraction of nanocellulose is 70wt% based on 100wt% of the total mass fraction of the flexible support layer 1, the balance being MOFs crystals.

The heat conduction connecting layer 2 consists of a dopamine matrix and boron nitride nano-sheets dispersed in the dopamine matrix, wherein the mass fraction of the boron nitride nano-sheets is 15wt% based on the total mass fraction of the heat conduction connecting layer 2 of 100wt%, and the balance is dopamine. The surface roughness of the thermally conductive connection layer 2 was 59.7 μm.

Example 6

The present embodiment provides a method for preparing a flexible high-safety lithium ion positive electrode current collector, which is different from embodiment 1 in that in step (1), the concentration of cobalt nitrate in the precursor solution is 0.05mmol/L, and other process parameters and operation steps are the same as embodiment 1.

Example 7

The present embodiment provides a method for preparing a flexible high-safety lithium ion positive electrode current collector, which is different from embodiment 1 in that in step (1), the concentration of cobalt nitrate in the precursor solution is 2mmol/L, and other process parameters and operation steps are the same as those in embodiment 1.

Example 8

The present embodiment provides a method for preparing a flexible high-safety lithium ion positive electrode current collector, which is different from embodiment 1 in that in step (1), the mass fraction of the cellulose nanofiber solution is 0.2wt%, and other process parameters and operation steps are the same as those in embodiment 1.

Example 9

The present embodiment provides a method for preparing a flexible high-safety lithium ion positive electrode current collector, which is different from embodiment 1 in that in step (1), the mass fraction of the cellulose nanofiber solution is 1.8wt%, and other process parameters and operation steps are the same as those in embodiment 1.

Example 10

The present embodiment provides a method for preparing a flexible high-safety lithium ion positive electrode current collector, which is different from embodiment 1 in that in step (3), the concentration of dopamine in the dopamine/boron nitride nanosheet suspension is 0.1g/L, and other process parameters and operation steps are the same as those in embodiment 1.

Example 11

The present embodiment provides a method for preparing a flexible high-safety lithium ion positive electrode current collector, which is different from embodiment 1 in that in step (3), the concentration of dopamine in the dopamine/boron nitride nanosheet suspension is 2g/L, and other process parameters and operation steps are the same as those in embodiment 1.

Example 12

The present embodiment provides a method for preparing a flexible high-safety lithium ion positive electrode current collector, which is different from embodiment 1 in that in step (3), the concentration of the boron nitride nano-sheets of the dopamine/boron nitride nano-sheet suspension is 0.01g/L, and other process parameters and operation steps are the same as those of embodiment 1.

Example 13

The present embodiment provides a method for preparing a flexible high-safety lithium ion positive electrode current collector, which is different from embodiment 1 in that in step (3), the concentration of the boron nitride nano-sheets of the dopamine/boron nitride nano-sheet suspension is 0.15g/L, and other process parameters and operation steps are the same as those of embodiment 1.

Comparative example 1

The preparation method of the flexible high-safety lithium ion positive electrode current collector provided in the embodiment is different from that of the embodiment 1 in that the step (1) is omitted, the cellulose nanofiber solution with the weight percentage of 0.5% is subjected to pressure filtration in the step (2) to obtain the flexible supporting layer 1, other process parameters and operation steps are the same as those of the embodiment 1, and the finally prepared flexible supporting layer 1 only consists of cellulose nanofibers and does not contain MOFs crystal materials.

Comparative example 2

The present embodiment provides a method for preparing a flexible high-safety lithium ion positive electrode current collector, which is different from embodiment 1 in that step (3) is omitted, in step (4), a metal conductive layer 3 is directly deposited on the surface of the flexible supporting layer 1 obtained in step (2), other process parameters and operation steps are the same as those of embodiment 1, and finally the prepared positive electrode current collector does not contain a heat conduction connecting layer 2.

The positive electrode current collectors provided in examples 1 to 13 and comparative examples 1 to 2 were tested for tensile strength, elongation at break, thermal conductivity and resistivity change rate as follows:

(1) Tensile strength and elongation at break: cutting a positive electrode current collector into a strip-shaped sample with the length of 100mm multiplied by 10mm, fixing two ends of the sample on a clamp of a tensile testing machine, setting the tensile speed to be 50mm/min, starting the tensile testing machine until the sample is broken, and reading the tensile strength and the breaking elongation displayed on the tensile testing machine, wherein the test result is shown in Table 1;

(2) Thermal conductivity coefficient: the heat conductivity coefficient of the positive electrode current collector is tested by referring to GB/T10297-2015 heat conductivity coefficient measurement hot wire method of nonmetallic solid material, and the test result is shown in Table 1;

(3) Resistivity change rate: the positive current collector is bent 10000 times with a bending radius of 0.5cm and 180 degrees, the resistance value of the positive current collector before and after bending is measured by a resistance measuring instrument, the resistance value before bending is recorded as R ₀, the resistance value after bending is recorded as R ₁, The calculation results are shown in Table 1.

The positive electrode current collectors provided in examples 1 to 13 and comparative examples 1 to 2 were assembled into lithium ion batteries by the following assembly process:

(1) Mixing ternary positive electrode material NCM, polyvinylidene fluoride and acetylene black, dissolving in N-methyl pyrrolidone, and mixing to obtain positive electrode active slurry; the total mass fraction of the positive electrode active slurry is 100wt%, wherein the mass fraction of the ternary positive electrode material NCM is 94wt%, the mass fraction of polyvinylidene fluoride is 3wt%, and the mass fraction of acetylene black is 3wt%;

(2) Coating the positive electrode active slurry obtained in the step (1) on the surfaces of the positive electrode current collectors provided in the examples 1-13 and the comparative examples 1-2, wherein the coating thickness is 0.15mm, and then drying the positive electrode current collector coated with the positive electrode active slurry in a vacuum oven at 120 ℃ to obtain a positive electrode piece;

(3) Mixing negative electrode material graphite, PVDF and acetylene black, dissolving the mixture in N-methylpyrrolidone, and mixing to obtain negative electrode active slurry; the total mass fraction of the cathode active slurry is 100wt%, wherein the mass fraction of graphite is 94wt%, the mass fraction of polyvinylidene fluoride is 3wt%, and the mass fraction of acetylene black is 3wt%;

(4) Coating the negative electrode active slurry obtained in the step (3) on the surface of a negative electrode current collector (copper foil) with the thickness of 10 mu m, wherein the coating thickness is 0.08mm, and then drying the negative electrode current collector coated with the negative electrode active slurry in a vacuum oven at the temperature of 100 ℃ to obtain a negative electrode plate;

(5) And (3) sequentially stacking the positive electrode plate obtained in the step (2), the polypropylene porous diaphragm and the negative electrode plate obtained in the step (4), winding to form an electric core, placing the electric core into a shell, packaging through a top cover, injecting electrolyte into the shell through a liquid injection port on the top cover in a glove box, and obtaining the lithium ion battery, wherein the electrolyte is lmol/L LiPF6/EC+DEC+DMC (the volume ratio of EC, DEC and DMC is 1:1:1).

According to the method, assembling the non-bent positive current collector and the positive current collector bent 10000 times into a lithium ion battery, testing the capacity retention rate of the lithium ion battery before and after bending the positive current collector, wherein the testing process is as follows:

Charging and discharging the lithium ion battery once under the test conditions of 1C charging and 1C discharging, carrying out 50 times of charging and discharging cycles in total, testing the battery capacity of the lithium ion battery after 50 times of charging and discharging cycles, recording the capacity test value of the lithium ion battery adopting the unbent positive electrode current collector as C ₀, recording the capacity test value of the lithium ion battery adopting the bent positive electrode current collector as C ₁, The test results are shown in Table 1.

The positive electrode current collectors provided in examples 1 to 13 and comparative examples 1 to 2 were assembled into lithium ion batteries and then fully charged, the lithium ion batteries were subjected to a needling test, the test method was referred to GB/T31485-2015 for safety requirements and test methods for Power storage batteries for electric vehicles, 10 lithium ion batteries were taken for the needling test in the same example or comparative example, and the needling passing rate is shown in Table 1.

TABLE 1

As can be seen from the test data provided in examples 1 to 5, the positive electrode current collector provided by the invention has excellent mechanical properties, heat conduction properties and safety, and the resistance change rate is still less than 0.5% after 10000 times of bending; the positive current collector provided by the invention is assembled into the lithium ion battery after being bent 10000 times, and the capacity retention rate can still reach more than 95%.

From the test data provided in examples 1, 6 and 7, it can be seen that the capacity retention rate of the lithium ion battery assembled using the positive electrode current collector prepared in example 6 is lower than that of example 1, because the concentration of the metal salt in the precursor solution in example 6 is too low, resulting in too low the number of MOFs crystals synthesized in situ, so that an effective lithium ion transmission channel cannot be formed, resulting in a decrease in the capacity retention rate of the assembled lithium ion battery. The tensile strength and elongation at break of the positive electrode current collector prepared in example 7 are lower than those of example 1, and this is because the concentration of the metal salt in the precursor solution in example 7 is too high, so that the MOFs crystals generated by the reaction are too many, serious particle agglomeration problem is generated, and the stress concentration phenomenon occurs in the flexible supporting layer 1, so that the overall mechanical strength of the positive electrode current collector is affected.

As can be seen from the test data provided in examples 1, 8 and 9, the capacity retention rate of the lithium ion battery assembled by using the positive electrode current collector prepared in example 8 is lower than that of example 1, because the concentration of the cellulose nanofiber solution in example 8 is too low, so that the content of nanocellulose in the flexible support layer 1 formed after press filtration is low, a sufficient number of electrolyte transmission channels cannot be formed, and the capacity retention rate of the lithium ion battery is affected. The tensile strength and elongation at break of the positive electrode current collector prepared in example 9 are lower than those of example 1, and because the concentration and viscosity of the cellulose nanofiber solution in example 9 are too high, the metal salt and the organic ligand cannot be uniformly dispersed in the cellulose nanofiber solution, so that the reaction-generated MOFs crystals are agglomerated, and the stress concentration phenomenon occurs in the flexible supporting layer 1, so that the integral mechanical strength of the positive electrode current collector is affected.

As can be seen from the test data provided in example 1, example 10 and example 11, the thermal conductivity and the needling passing rate of the positive electrode current collector prepared in example 10 are lower than those of example 1, and this is because the concentration of dopamine in the dopamine/boron nitride nanosheet suspension in example 10 is too low to form an effective coating on the boron nitride nanosheets, so that serious agglomeration of the boron nitride nanosheets occurs, the exertion of the thermal conductivity of the boron nitride nanosheets is affected, and the safety of the lithium ion battery is further affected. The heat conductivity coefficient and the needling passing rate of the positive electrode current collector prepared in example 11 are lower than those of example 1, because the concentration of dopamine in the dopamine/boron nitride nanosheet suspension in example 11 is too high, the formed heat conduction connecting layer 2 is too thick, phonon loss is increased, heat conduction efficiency is reduced, and the safety of the lithium ion battery is further affected.

As can be seen from the test data provided in examples 1, 12 and 13, the tensile strength, elongation at break, thermal conductivity and needling pass rate of the positive electrode current collector prepared in example 12 are all lower than those of example 1, because the concentration of the boron nitride nano-sheets in the dopamine/boron nitride nano-sheet suspension in example 12 is too low, on one hand, the excellent thermal conductivity of the boron nitride nano-sheets cannot be fully exerted, and thus the thermal conductivity of the positive electrode current collector is reduced; on the other hand, the number of the surface roughness structures of the heat conduction connecting layer 2 is reduced, the deposition anchoring effect of the subsequent metal conductive layer 3 on the surface of the heat conduction connecting layer 2 is affected, and the interface bonding strength between the heat conduction connecting layer 2 and the metal conductive layer 3 is further reduced, so that the tensile strength and the elongation at break of the positive electrode current collector are affected. The tensile strength, elongation at break, thermal conductivity and needling passing rate of the positive electrode current collector prepared in example 13 are all lower than those of example 1, because the concentration of the boron nitride nano-sheets of the dopamine/boron nitride nano-sheet suspension in example 13 is too high, so that serious agglomeration phenomenon of the boron nitride nano-sheets in a dopamine matrix occurs, stress concentration occurs in the thermally conductive connecting layer 2, and the tensile strength and elongation at break of the positive electrode current collector are further affected; in addition, as the agglomeration phenomenon of the boron nitride nano sheets is aggravated, the interface thermal resistance between the boron nitride nano sheets is improved, heat cannot be smoothly conducted, and finally the heat conductivity coefficient of the positive electrode current collector is reduced.

As can be seen from the test data provided in example 1 and comparative example 1, the invention can greatly improve the mechanical properties and electrolyte wettability of the positive electrode current collector by synthesizing the MOFs crystal on the nanocellulose in situ, so that the electrochemical properties of the assembled lithium ion battery are greatly improved.

As can be seen from the test data provided in the embodiment 1 and the comparative example 2, the heat conduction performance of the positive electrode current collector can be improved on one hand and the safety of the lithium ion battery in the charging and discharging process can be greatly improved by arranging the heat conduction connecting layer 2 between the flexible supporting layer 1 and the metal conductive layer 3; on the other hand can be as the tie layer between flexible supporting layer 1 and the metal conducting layer 3, improved flexible supporting layer 1, heat conduction tie layer 2 and the metal conducting layer 3 three layer construction's wholeness, and then strengthened the whole mechanical strength of anodal electric current collector.

The applicant declares that the above is only a specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and it should be apparent to those skilled in the art that any changes or substitutions that are easily conceivable within the technical scope of the present invention disclosed by the present invention fall within the scope of the present invention and the disclosure.

Claims

1. The flexible high-safety lithium ion positive electrode current collector is characterized by comprising a flexible supporting layer, a heat conduction connecting layer and a metal conductive layer which are sequentially laminated;

the heat conduction connecting layer consists of a polydopamine matrix and boron nitride nano-sheets dispersed in the polydopamine matrix;

the metal conductive layer is formed on the surface of the heat conduction connecting layer by adopting a physical vapor deposition process;

the flexible supporting layer is prepared by the following method:

Dissolving metal salt and an organic ligand in an organic solvent to form a precursor solution, mixing the precursor solution with a nanocellulose solution for reaction to grow MOFs crystals on the nanocellulose surface in situ, and then sequentially centrifuging, filtering, washing and drying to obtain a composite support material; the concentration of the metal salt in the precursor solution is 0.1-1.5mmol/L; the mass fraction of the nano cellulose solution is 0.5-1.5wt%;

Dispersing the composite support material obtained in the step (I) in deionized water to obtain a precursor solution, performing filter pressing on the precursor solution, extruding water in the precursor solution to obtain a filter cake, and drying the filter cake to obtain the flexible support layer;

The heat conduction connecting layer is prepared by the following method:

dispersing dopamine and boron nitride nano-sheets in a Tirs-HCl buffer solution and performing ultrasonic dispersion treatment, wherein the concentration of the dopamine is 0.5-1.5g/L, and the concentration of the boron nitride nano-sheets is 0.05-0.1g/L, so as to obtain polydopamine/boron nitride nano-sheet suspension;

And immersing the flexible supporting layer in the polydopamine/boron nitride nanosheet suspension, taking out and drying after a period of time to form the heat conduction connecting layer on the surface of the flexible supporting layer.

2. The flexible high-safety lithium ion positive electrode current collector according to claim 1, wherein the mass fraction of the nanocellulose is 60-70wt% based on 100wt% of the total mass fraction of the flexible support layer, and the balance is MOFs crystals;

the thickness of the flexible supporting layer is 20-30 mu m;

The mass fraction of the boron nitride nano-sheet is 5-15wt% calculated by the total mass fraction of the heat conduction connecting layer being 100wt%, and the rest is polydopamine;

the thickness of the heat conduction connecting layer is 1-10 mu m;

the surface roughness of the heat conduction connecting layer is 50-60 mu m;

the thickness of the metal conductive layer is 0.5-1.5 mu m.

3. The flexible high-safety lithium ion positive electrode current collector according to claim 1, wherein in the step (i), the metal salt comprises any one or a combination of at least two of aluminum nitrate, zinc nitrate, cobalt nitrate, magnesium nitrate, copper acetate, aluminum acetate, zinc acetate, cobalt acetate, magnesium acetate, and copper acetate;

The organic ligand comprises any one or a combination of at least two of trimesic acid, isophthalic acid, terephthalic acid, trimellitic acid, phenol, dimethyl succinic acid, biphenyl acid and 2-methylimidazole;

The organic solvent comprises any one or a combination of at least two of dimethylacetamide, dimethylformamide, dimethyl sulfoxide and N-methylpyrrolidone;

the molar ratio of the metal salt to the organic ligand is 1 (0.5-10);

the temperature of the mixing reaction is 100-150 ℃;

the time of the mixing reaction is 10-20h;

in the step (II), the mass fraction of the precursor solution is 1-10wt%;

the pressure of the filter pressing is 1-5MPa;

The filter pressing time is 10-20min;

the drying temperature is 80-120 ℃;

the drying time is 20-30min.

4. The flexible high-safety lithium ion positive electrode current collector according to claim 1, wherein the pH value of the Tirs-HCl buffer is 8-9;

the ultrasonic power of the ultrasonic dispersion treatment is 600-700W;

The ultrasonic dispersion treatment time is 20-30min;

the soaking temperature of the flexible supporting layer in the polydopamine/boron nitride nanosheet suspension is 20-30 ℃;

The soaking time of the flexible supporting layer in the polydopamine/boron nitride nanosheet suspension is 6-12h.

5. The flexible high-safety lithium ion positive electrode current collector according to claim 1, wherein the metal conductive layer is prepared by the following method:

Placing a composite layer consisting of the flexible supporting layer and the heat conducting connecting layer on a conveyor belt in a coating cavity, wherein the heat conducting connecting layer faces upwards; fixing a metal target above the conveyor belt, vacuumizing the inside of the coating cavity and introducing argon into the coating cavity; the conveyor belt drives the composite layer to continuously move at a constant speed, and the coating equipment acts on the metal target material to deposit a metal conductive layer on the surface of the heat-conducting connecting layer;

6. The flexible high-safety lithium ion positive electrode current collector according to claim 5, wherein a vertical distance between the metal target and the heat conducting connection layer is 50-100mm;

The vacuum degree of the film coating chamber is 1.0 multiplied by 10 ^-4-3.0×10^-3 Pa;

The flow of the argon is 50-60SCCM;

The transmission speed of the conveyor belt is 1-5cm/min;

the average power density of the surface of the metal target is 10-20W/cm ²;

The average current density of the surface of the metal target material is 30-40mA/cm ².

7. A battery positive electrode, characterized in that the battery positive electrode comprises a positive electrode current collector and a positive electrode active layer formed on the surface of the positive electrode current collector;

the positive electrode current collector is the flexible high-safety lithium ion positive electrode current collector according to any one of claims 1 to 6.

8. A battery, characterized in that the battery comprises a shell and a battery core positioned in the shell, wherein the battery core comprises a battery positive electrode, a diaphragm and a battery negative electrode which are sequentially stacked, and the battery positive electrode is the battery positive electrode of claim 7.