CN114635200B

CN114635200B - Tubular nanofiber material, negative electrode plate and lithium metal battery

Info

Publication number: CN114635200B
Application number: CN202210241984.7A
Authority: CN
Inventors: 林小萍; 陈茂华; 谢远森
Original assignee: Ningde Amperex Technology Ltd
Current assignee: Ningde Amperex Technology Ltd
Priority date: 2022-03-11
Filing date: 2022-03-11
Publication date: 2023-12-22
Anticipated expiration: 2042-03-11
Also published as: CN114635200A

Abstract

The present application relates to a tubular nanofiber material, wherein the tubular nanofibers have a hollow tube extending axially along the nanofiber tube; the wall of the tubular nanofiber is distributed with a lithium-philic material; the two ends of the tubular nanofiber are of a closed structure. The application also relates to a negative electrode sheet comprising the tubular nanofiber material, and an electrochemical device and an electronic device.

Description

Tubular nanofiber material, negative electrode plate and lithium metal battery

Technical Field

The application relates to the technical field of energy storage, in particular to a tubular nanofiber material, a negative electrode plate and a lithium metal battery comprising the negative electrode plate.

Background

The lithium ion battery has the advantages of high energy density, high working voltage, low self-discharge rate, small volume, light weight and the like, and has wide application in the field of consumer electronics. With the current high-speed development of electric automobiles and mobile electronic devices, the requirements of lithium ion batteries on energy density, safety and cycle performance are increasingly high.

Lithium metal is the metal with the minimum relative atomic mass (6.94) and the lowest standard electrode potential (-3.045V) in all metal elements, has the theoretical specific capacity as high as 3860mAh/g, and is one of the metals with the maximum mass specific energy discovered at present. Therefore, the energy density and the operating voltage of the battery can be greatly improved by using lithium metal as the negative electrode material. However, lithium metal directly serves as a battery anode material, and has a large number of problems, such as high activity of the lithium metal, easiness in side reaction with substances in electrolyte, easiness in formation of dendrite and dead lithium, continuous volume expansion and shrinkage in the battery cycle process to destroy an electrode structure and a SEI (solid electrolyte interphase) film, reduction of cycle life and coulomb efficiency of the lithium metal battery, potential safety hazard generation and the like, and influences the application of the lithium metal in the anode.

Disclosure of Invention

The present application has been made in view of the above problems occurring in the prior art, and an object thereof is to provide a tubular nanofiber material to solve the above problems, namely, to reduce side reactions of lithium metal with an electrolyte, to suppress the generation of "dendrite" and "dead lithium", to solve interfacial peeling and SEI breakage caused during expansion-contraction, to improve cycle performance and capacity performance of a lithium metal battery, to reduce a volume expansion rate, and to improve coulombic efficiency thereof.

In order to achieve the above object, the present application provides a tubular nanofiber material, a negative electrode tab comprising the tubular nanofiber material, and a lithium metal battery comprising the negative electrode tab.

In one aspect, the present application provides a tubular nanofiber material, wherein the tubular nanofibers have a hollow tube extending axially along the nanofiber tube; the wall of the tubular nanofiber is distributed with a lithium-philic material; the two ends of the tubular nanofiber are of a closed structure.

In any embodiment, the tubular nanofiber material has an ionic conductivity greater than 10 ^-4 S/m。

In any embodiment, the content of the lithium-philic material is distributed in a manner of decreasing concentration from inside to outside of the tube along the radial direction of the tube wall of the tubular nanofiber material.

In any embodiment, the lithium-philic material is selected from the following:

(1) At least one of a metal simple substance and an alloy thereof, a metal oxide, a metal nitride, a metal sulfide or a metal carbide,

preferably, the metal simple substance and the alloy thereof comprise at least one of Ag, au, zn and the alloy thereof,

preferably, the metal oxide comprises TiO ₂ 、SiO ₂ 、ZnO、SnO ₂ 、Co ₃ O ₄ Or Fe (Fe) ₂ O ₃ At least one of the above-mentioned materials,

preferably, the metal nitrogenThe compound comprises Mo ₂ N ₃ ，

Preferably, the metal sulfide comprises MoS ₂ Or SnS ₂ At least one of the above-mentioned materials,

preferably, the metal carbide comprises FeC;

(2) At least one of a metal simple substance with a wettability functional group and an alloy, a metal oxide, a metal nitride, a metal sulfide or a metal carbide thereof, wherein the wettability functional group comprises at least one of a hydroxyl group, an ester group, a carboxyl group, an amino group and a sulfonic group,

preferably, the simple metal and alloys, metal oxides, metal nitrides, metal sulfides and metal carbides thereof are as defined in (1);

or alternatively

The lithiated material is formed from the tubular nanofiber material in combination with a wetting functional group, wherein the wetting functional group comprises at least one of a hydroxyl group, an ester group, a carboxyl group, an amino group, a sulfonic group.

In any embodiment, the weight percent of the lithium-philic material is 10 to 80 weight percent based on the total weight of the tubular nanofiber material.

In any embodiment, the tubular nanofiber material meets the following conditions:

(1) The diameter R of the tubular nanofibers is 100nm to 2 μm; and

(2) The wall thickness d of the tubular nanofibers is 50nm to 500nm.

In any embodiment, the diameter R, wall thickness d of the tubular nanofiber and porosity p of the tubular nanofiber satisfy the following relationship:

wherein the porosity p is 50% -85%.

In a second aspect, the present application provides a negative electrode sheet comprising a three-dimensional scaffold layer, wherein the three-dimensional scaffold layer comprises the tubular nanofiber material.

In any embodiment, the three-dimensional scaffold layer satisfies the following condition:

(1) The thickness of the three-dimensional skeleton layer is 30 μm to 200 μm, preferably 30 μm to 100 μm; and

(2) The three-dimensional framework layer has a porosity of 65% to 95%, preferably 70% to 90%.

In a third aspect, the present application provides a lithium metal battery comprising the negative electrode tab described above.

In a fourth aspect, the present application provides an electronic device comprising the lithium metal battery described above.

The tubular nanofiber material is of a closed tubular structure, and the wall of the tubular nanofiber material is distributed with the lithium-philic material, so that lithium metal can be deposited in a hollow structure of the wall of the tubular nanofiber material, and the deposition position and the deposition direction can be accurately controlled; meanwhile, lithium metal is deposited in the tubular structure, so that generation of dendrites and dead lithium can be restrained, and volume expansion is further slowed down; the fiber-enclosed tubular structure prevents electrolyte from entering, thereby avoiding contact between the electrolyte and deposited lithium and avoiding side reactions. Therefore, the tubular nanofiber material can be applied to the negative electrode, so that the capacity performance and the cycling stability of a lithium metal battery can be greatly improved, and the coulomb efficiency of the lithium metal battery can be improved.

Drawings

FIG. 1 is a scanning electron micrograph of a hollow structure of a tubular nanofiber of the present application;

FIG. 2 is a scanning electron micrograph of the capped structure of the tubular nanofibers of the present application;

FIG. 3 is a schematic structural view of a tubular nanofiber comprising a lithium-philic material of the present application;

FIG. 4 is a schematic diagram of a lithium metal deposition site in this application, where site 1 refers to the inner wall of the tubular nanofiber, site 2 refers to the outer wall of the tubular nanofiber (i.e., within the layer gap of the tubular nanofiber and the protective layer), and site 3 is the void between the tubular nanofibers;

Figure 5 is a schematic view of the diameter and wall thickness of the tubular nanofibers of the present application.

Detailed Description

For the purposes of making the objects, technical solutions and advantages of the present application more apparent, the technical solutions of the present application will be clearly and completely described in the following embodiments in conjunction with the present application, and it is apparent that the described embodiments are some embodiments of the present application, but not all embodiments. Based on the technical solution provided in the present application and the embodiments given, all other embodiments obtained by a person skilled in the art without making any inventive effort are within the scope of protection of the present application.

In this specification, unless specified or limited otherwise, relative terms such as: the terms "central," "longitudinal," "lateral," "front," "rear," "right," "left," "interior," "exterior," "lower," "upper," "horizontal," "vertical," "above," "below," "upper," "lower," "top," "bottom," and derivatives thereof (e.g., "horizontally," "downwardly," "upwardly," etc.) should be construed to refer to the directions as described in the discussion or as illustrated in the drawings. These relative terms are for convenience of description only and do not require that the present application be constructed or operated in a particular orientation.

Moreover, for ease of description, "first," "second," "third," etc. may be used herein to distinguish between different components of a figure or series of figures. The terms "first," "second," "third," and the like are not intended to describe corresponding components.

In the description and claims of the present application, the terms "substantially," "substantially," and "about" are used to describe and illustrate minor variations. When used in connection with an event or circumstance, the terms can refer to instances where the event or circumstance occurs precisely and instances where it occurs to the close approximation. For example, when used in connection with a numerical value, the term can refer to a range of variation of less than or equal to ±10% of the numerical value, such as less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%.

Additionally, amounts, ratios, and other numerical values are sometimes presented herein in a range format. It is to be understood that such range format is used for convenience and brevity and should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited.

In the detailed description and claims, a list of items connected by the terms "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items a and B are listed, the phrase "at least one of a and B" means only a; only B; or A and B. In another example, if items A, B and C are listed, then the phrase "at least one of A, B and C" means only a; or only B; only C; a and B (excluding C); a and C (excluding B); b and C (excluding A); or A, B and C. Item a may comprise a single component or multiple components. Item B may comprise a single component or multiple components. Item C may comprise a single component or multiple components.

The "range" disclosed herein is defined in terms of lower and upper limits, with a given range being defined by the selection of a lower and an upper limit, the selected lower and upper limits defining the boundaries of the particular range. Ranges that are defined in this way can be inclusive or exclusive of the endpoints, and any combination can be made, i.e., any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, it is understood that ranges of 60-110 and 80-120 are also contemplated. Furthermore, if the minimum range values 1 and 2 are listed, and if the maximum range values 3,4 and 5 are listed, the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise indicated, the numerical range "a-b" represents a shorthand representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been listed throughout, and "0-5" is simply a shorthand representation of a combination of these values. When a certain parameter is expressed as an integer of 2 or more, it is disclosed that the parameter is, for example, an integer of 2, 3,4, 5, 6, 7, 8, 9, 10, 11, 12 or the like.

All embodiments and alternative embodiments of the present application may be combined with each other to form new solutions, unless specifically stated otherwise.

All technical features and optional technical features of the present application may be combined with each other to form new technical solutions, unless specified otherwise.

All steps of the present application may be performed sequentially or randomly, preferably sequentially, unless otherwise indicated. For example, the method comprises steps (a) and (b), meaning that the method may comprise steps (a) and (b) performed sequentially, or may comprise steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), may include steps (a), (c) and (b), may include steps (c), (a) and (b), and the like.

Reference herein to "comprising" and "including" means open ended, as well as closed ended, unless otherwise noted. For example, the terms "comprising" and "comprises" may mean that other components not listed may be included or included, or that only listed components may be included or included.

The terms "above", "below" as used in this application include the present number, e.g. "one or more" means one or more, "one or more of" a and B "means" a "," B "or" a and B ".

The term "or" is inclusive in this application, unless otherwise specified. For example, the phrase "a or B" means "a, B, or both a and B. More specifically, either of the following conditions satisfies the condition "a or B": a is true (or present) and B is false (or absent); a is false (or absent) and B is true (or present); or both A and B are true (or present).

Unless otherwise indicated, the amounts and percentages in the context of this application are by weight.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

In this application, a lithium metal battery generally includes a negative electrode tab, a positive electrode tab, a separator, and an electrolyte.

In this application, the positive pole piece includes positive current collector and sets up the positive pole rete at least one surface of positive current collector, the positive pole rete includes positive electrode active material. The positive electrode active material may be a positive electrode active material for a battery known in the art. As an example, the positive electrode active material may include at least one of the following materials: olivine structured lithium-containing phosphates, lithium transition metal oxides and their respective modified compounds. However, the present application is not limited to these materials, and other conventional materials that can be used as a battery positive electrode active material may be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (e.g., liCoO) ₂ ) Lithium nickel oxide (e.g. LiNiO) ₂ ) Lithium manganese oxide (e.g. LiMnO ₂ 、LiMn ₂ O ₄ ) Lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (e.g., liNi) _1/3 Co _1/3 Mn _1/3 O ₂ (also abbreviated as NCM 333), lithium nickel cobalt aluminum oxide (such as LiNi _0.85 Co _0.15 Al _0.05 O ₂ ) And at least one of its modified compounds and the like. Examples of olivine structured lithium-containing phosphates may include, but are not limited to, lithium iron phosphate (e.g., liFePO ₄ (also abbreviated as LFP)), composite material of lithium iron phosphate and carbon, and manganese lithium phosphate (such as LiMnPO) ₄ ) At least one of a composite material of lithium manganese phosphate and carbon, and a composite material of lithium manganese phosphate and carbon.

The positive electrode current collector has two surfaces opposite in the thickness direction thereof, and the positive electrode film layer is provided on either one or both of the two surfaces opposite to the positive electrode current collector. The positive electrode current collector can adopt a metal foil or a composite current collector, for example, as the metal foil, an aluminum foil can be adopted; the composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel alloy, titanium alloy, silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

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

In some embodiments, the positive electrode film layer further includes a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon nanotubes, graphene, and carbon nanofibers.

In some embodiments, the positive electrode sheet may be prepared by: dispersing the above components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; and (3) coating the positive electrode slurry on a positive electrode current collector, and obtaining a positive electrode plate after the procedures of drying, cold pressing and the like.

In the application, the negative electrode plate comprises a negative electrode current collector and a three-dimensional framework layer arranged on at least one surface of the negative electrode current collector and comprising the tubular nanofiber material.

As an example, the anode current collector has two surfaces opposing in its own thickness direction, and the three-dimensional skeleton layer is provided on either one or both of the two surfaces opposing the anode current collector.

In some embodiments, the negative electrode current collector may employ a metal foil or a composite current collector. For example, as the metal foil, copper foil may be used. The composite current collector may include a polymeric material base layer and a metal layer formed on at least one surface of the polymeric material base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel alloy, titanium alloy, silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

In some embodiments, the negative electrode tab further comprises a lithium metal layer between the negative electrode current collector and the three-dimensional scaffold layer. The lithium metal layer may be in a continuous form or a discontinuous form. The thickness of the lithium metal layer is not particularly limited either, and can be adjusted according to actual demands. For example, the lithium metal layer may have a thickness of 10 μm to 25 μm.

In some embodiments, the negative electrode tab may be pre-charged with lithium. When the lithium is pre-supplemented, cold pressing, hot pressing, electrochemical lithium supplementing or Physical Vapor Deposition (PVD) and other modes can be adopted; lithium metal powder may be used for the pre-lithium supplementation.

The negative electrode tab of the present application may be prepared according to methods conventional in the art. For example, the three-dimensional framework layer and the lithium metal layer are stacked in sequence and then placed on the surface of the negative electrode current collector, and then are stacked together in a rolling mode to obtain the negative electrode plate.

The electrolyte plays a role in ion conduction between the positive electrode plate and the negative electrode plate. In the present application, the type of the electrolyte is not particularly limited, and may be selected according to the need. For example, the electrolyte may be liquid, gel, or all solid.

In some embodiments, the electrolyte is an electrolyte. The electrolyte includes an electrolyte salt and a solvent.

In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis-fluorosulfonyl imide, lithium bis-trifluoromethanesulfonyl imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalato borate, lithium dioxaato borate, lithium difluorodioxaato phosphate lithium aluminate, lithium tetrachloroaluminate, lithium chloride, lithium fluoride, lithium perfluorobutyl sulfonate, and lithium tetrafluorooxalato phosphate.

In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methylethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1, 4-butyrolactone, sulfolane, dioxolane, dimethyl ether, dimethyl sulfone, methyl sulfone, and diethyl sulfone.

In some embodiments, the electrolyte further comprises an additive. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives capable of improving certain properties of the battery, such as additives that improve the overcharge performance of the battery, additives that improve the high or low temperature performance of the battery, and the like.

In the present application, the type of the separator is not particularly limited, and any known separator having good chemical stability and mechanical stability may be used. The material of the isolating film can be at least one selected from glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The separator may be a single-layer film or a multilayer composite film, and is not particularly limited. When the separator is a multilayer composite film, the materials of the respective layers may be the same or different, and are not particularly limited.

In the present application, the positive electrode sheet, the negative electrode sheet and the separator may be manufactured into an electrode assembly through a winding process or a lamination process.

In the present application, the lithium metal battery may include an outer package. The outer package may be used to encapsulate the electrode assembly and electrolyte described above.

In this application, the outer package of the lithium metal battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, or the like. The outer package of the lithium metal battery may also be a pouch, such as a pouch-type pouch. The material of the flexible bag may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

In the present application, the shape of the lithium metal battery is not particularly limited, and may be cylindrical, square, or any other shape.

In a lithium metal battery, lithium metal is used for a negative electrode plate, so that the energy density of the battery and the working voltage of the battery can be improved. However, in the process of battery charge-discharge cycle, side reaction is easy to occur between lithium metal and electrolyte, lithium dendrite is formed, and continuous expansion and contraction of pole piece volume are caused, so that internal impedance of the battery is increased, cycle performance and capacity performance of the lithium metal battery are reduced, and the battery has higher volume expansion rate.

Through a number of experiments, the inventors found that the above problems can be significantly improved when the negative electrode sheet comprises the following materials: a tubular nanofiber material, wherein the tubular nanofibers have a hollow tube extending axially along the nanofiber tube; the wall of the tubular nanofiber is distributed with a lithium-philic material; the two ends of the tubular nanofiber are of a closed structure.

A first aspect of the present application provides a tubular nanofiber material, wherein the tubular nanofibers have a hollow tube extending axially along the nanofiber tube; the wall of the tubular nanofiber is distributed with a lithium-philic material; the two ends of the tubular nanofiber are of a closed structure.

The formation of the closed structure at both ends of the tubular nanofibers of the present application is preferably formed by coating the nanofibers with at least one protective layer. The thickness of the protective layer can be controlled by controlling the concentration of the raw materials forming the protective layer; the protective layer is too thin, and in the lithium metal deposition and stripping process, the situation of cracking is very easy to occur, side reaction between lithium metal and electrolyte is likely to occur, and the protective layer is too thick, and the energy barrier required by lithium ions penetrating through the protective layer is higher, so that part of lithium metal cannot be deposited on the wall of the tubular nanofiber. Suitable protective layers therefore have a thickness of 10nm to 500nm, with a preferred protective layer thickness of 50nm to 200nm.

The fiber with two ends not closed can lead electrolyte to flow in the fiber tube, and a great amount of metal lithium is deposited in gaps among the fibers to cause side reaction between the electrolyte and the deposited lithium, so that the cycle performance and the coulombic efficiency of the lithium metal battery are reduced. In the present application, preferably, at least 98% or more of the ends of the tubular nanofibers in the tubular nanofiber material are closed structures, more preferably 99% or more, and most preferably 100% of the ends of the tubular nanofibers are closed structures.

In one embodiment of the present application, the tubular nanofiber material has an ionic conductivity greater than 10 ^-4 S/m, preferably greater than 5 x 10 ^-4 S/m。

In one embodiment of the present application, the tubular nanofibers can be made using polypyrrolidone, polymethyl methacrylate, polyethylene oxide, polypropylene oxide, polyvinyl alcohol, or polystyrene.

In one embodiment of the present application, wherein the weight percent of the lithium-philic material is distributed progressively from inside to outside along the radial direction of the tubular nanofiber material wall, based on the total weight of the tubular nanofiber material. That is, the concentration of the lithium-philic material is higher at the inner wall of the nanofiber material than at the outer wall of the nanofiber material. Preferably at least 70 wt%, more preferably 80 wt% or more, even more preferably 90 wt% or more, even 95 wt% or more of the lithium-philic material is distributed on the inner wall of the nanofibrous tube. In the case where both ends of the tubular nanofiber formed with the cladding protective layer are closed, the lithium-philic material is distributed within the inner wall of the nanofiber material tube wall and the interlayer between the tubular nanofiber and the protective layer (i.e., distributed on the outer wall of the tubular nanofiber).

In one embodiment of the present application, the lithium-philic material is selected from the following:

preferably, the metal nitride comprises Mo ₂ N ₃ ，

preferably, the metal carbide comprises FeC;

or alternatively

(3) Taking the tubular nanofiber material with wetting functional groups as a lithium-philic material, wherein the wetting functional groups comprise at least one of hydroxyl groups, ester groups, carboxyl groups, amino groups and sulfonic groups; or (b)

Any mixture of the above-mentioned lithium-philic materials.

In this application, the lithium-philic material includes a source material that can form the above-described lithium-philic material under the conditions of preparing the tubular nanofiber material. For example, forming SiO ₂ Alkyl silicate esters of (a) such as tetraethyl silicate; formation of TiO ₂ For example tetrabutyl titanate.

In case said tubular nanofiber material having wetting functional groups is used as a lithium philic material, for example, an amino-bound tubular nanofiber material may be obtained from the treatment of nanofibers in step (3) of the method as described below. For example, after the second nanofibers are treated at high temperature to form carbon nanofibers, the material is soaked in 10-20wt% aqueous ammonia solution and then dried at a temperature above 60 ℃, thereby binding amino functional groups on the surface of the material.

In one embodiment of the present application, the weight percentage of the lithium-philic material is 10 to 80 wt%, preferably 25 to 75 wt%, more preferably 30 to 70 wt%, even more preferably 30 to 65 wt%, most preferably 32 to 60 wt%, based on the total weight of the tubular nanofiber material.

The inventor finds that when the content of the lithium-philic material in the tubular nanofiber with two closed ends is low, lithium ions cannot be well led into the hollow tube of the fiber to deposit, part of lithium metal is deposited in gaps among the tubular nanofiber, and the part of deposited lithium is easy to react with electrolyte in a side way; when the content of the lithium-philic material is too high, although the lithium ion affinity driving force reaches the maximum, the content of the nanofiber material is too low, so that the stability of the skeleton structure is insufficient, the skeleton structure may collapse in the lithium deposition and lithium stripping processes, and the cycle performance of the lithium metal battery is adversely affected. When no lithium-philic material is distributed in the tubular nanofiber material, the energy difference of lithium ions penetrating into the hollow structure is reduced, so that the lithium ions cannot penetrate; therefore, lithium metal is deposited in the gaps between the tubular nanofibers, side reactions with the electrolyte and volume expansion of the pole pieces cannot be well controlled, and adverse effects are generated on the cycle performance and capacity performance of the lithium metal battery. The weight percentage content of the lithium-philic material in the above range can obtain a lithium metal battery having superior performance.

In one embodiment of the present application, the tubular nanofiber material meets the following conditions:

(1) The diameter R of the tubular nanofibers is 100nm to 2 μm; preferably 600nm to 1.6. Mu.m, particularly preferably 1.2 μm to 1.5. Mu.m, and

(2) The wall thickness d of the tubular nanofiber is 50nm to 500nm; preferably from 80nm to 200nm, particularly preferably from 110nm to 150. Mu.m.

The inventors found that the larger diameter of the tubular nanofibers, the relatively larger wall thickness of the fibers, resulted in an increase in the energy required for lithium ions to deposit into the tube through the tube wall, so that for too large a diameter, some of the metallic lithium deposits in the interstices between the fibers, causing side reactions to occur with the electrolyte; when the fiber diameter is smaller, the fiber wall thickness is relatively reduced, a large amount of deposited lithium enters the tube in the metal lithium deposition process, but the thinner tube wall is broken, so that lithium metal is deposited between the fibers to cause side reaction, and the performance improvement of the lithium metal battery is affected. Tubular nanofiber diameters and wall thicknesses within the above ranges can achieve good lithium metal battery performance.

In one embodiment of the present application, the diameter R, the wall thickness d of the tubular nanofiber and the porosity p of the tubular nanofiber satisfy the following relationship:

Wherein the porosity p is 50% to 85% (i.e., where p represents a value between 0.5 and 0.85), preferably 60% to 80%; the value of (R-2 d)/d is preferably greater than 5, more preferably greater than 7, particularly preferably greater than 7.5. The porosity was measured using a fully automatic mercury porosimeter (model AutoPore V9610) and the porosity p was measured before the tubular nanofibers formed a structure with both ends closed.

Without being bound by any theory, the inventors have found that the tubular nanofibers satisfying the above relation can be advantageously combined with a lithium-philic material to achieve deposition of lithium metal in the hollow structure of the tube wall, achieving precise control of the deposition position and deposition direction of lithium metal.

The present application also relates to a method for preparing said tubular nanofibres, comprising the steps of:

(1) Forming a first nanofiber from the polymer a solution by an electrospinning process;

(2) Standing the first nanofiber for more than 24 hours, and then heating and drying, preferably drying under vacuum, to obtain a second nanofiber;

(3) Treating the second nanofiber at a high temperature in a nitrogen atmosphere to form a carbon nanofiber;

(4) Immersing the fibers obtained in step (2) or (3) in a solution of polymer B, followed by drying at elevated temperature, preferably under vacuum, to obtain a tubular nanofiber material.

In the application, the tubular nanofiber material obtained in the step (4) is a layered three-dimensional framework material which can be used in the negative electrode plate.

In step (1) of the above process, polymer a is selected from conductive polymers such as polypyrrolidone, polymethyl methacrylate, polyethylene oxide, polypropylene oxide, polyvinyl alcohol or polystyrene having a number average molecular weight of 100,000-2,000,000 and used in a concentration of 10 to 40% by weight, and the solvent used is selected from ketones, amides, ethers, esters, halogenated hydrocarbons, aromatic hydrocarbons, or mixtures thereof such as N, N-dimethylformamide, ethanol and acetone.

In the step (1) of the above method, the parameters of the electrospinning method are: the negative pressure is-4 kV, the positive pressure is 12-20kV, the liquid inlet rate is 0.1-0.3mL/h, and the distance between the collecting plate and the needle head is 15cm-20cm; the rotational speed of the collecting drum is 1500-3000rpm.

In step (1) of the above process, the polymer a solution further comprises an auxiliary glacial acetic acid (99 mass%) for accelerating the hydrolysis in an amount of 10 to 20% by weight, based on the total weight of the polymer a solution, calculated as pure glacial acetic acid.

In step (2) of the above method, the first nanofiber membrane is left to stand for 24-48 hours at normal temperature at a relative humidity of 35% or more, preferably 35% -80%; and then dried under vacuum at 70-90 ℃ for more than 10 hours.

In step (3) of the above method, the temperature is raised to 800 ℃ or higher at a constant rate, for example, 5-8 ℃ per minute, and the drying is performed for 6 hours or longer.

In step (4) of the above method, the polymer B may be the same as or different from the polymer A. In the present application, the type of the polymer B is not particularly limited, and the polymer B may be selected so long as it can satisfy the both-end closed structure forming the tubular nanofiber, thereby achieving the effect of improving the cycle and safety performance of the battery. In the present application, examples of the polymer B may be selected from polyvinylidene chloride, polyacrylonitrile, polyethylene oxide (PEO), polymethyl methacrylate (PMMA), and phenolic resin, for example, having a number average molecular weight of 100,000-2,000,000; the concentration is 1-5wt%; the solvent used is selected from ketones, ethers, esters, halogenated hydrocarbons, aromatic hydrocarbons, or mixtures thereof, such as N-methylpyrrolidone, ethanol and acetone.

Preferably, the concentration of the solution of polymer B is 2-4wt%, preferably 2.5-3.5wt%, polymer B as coating material, the concentration of the solution affecting the thickness of the coating layer; the coating layer formed by the lower concentration of the solution is thinner, and the cracking condition is easy to occur in the process of depositing and stripping lithium metal, so that side reaction is caused; the higher concentration of the coating material solution forms a thicker coating and the lithium ions have a high energy barrier to traverse, so that some of the lithium metal is deposited in the interstices between the tubular nanofibers. Therefore, the proper concentration of the coating material solution is selected to form the proper thickness of the coating layer, so that the cycle performance and the capacity performance of the lithium metal battery can be improved, and the volume expansion rate of the lithium metal battery can be reduced.

In step (4) of the above method, immersing the fibers in the polymer B solution for more than 10 minutes; and then dried under vacuum at 70-90 ℃ for more than 10 hours.

In this application, the molecular weight of the polymer used is determined by Gel Permeation Chromatography (GPC).

A second aspect of the present application provides a negative electrode tab, comprising a negative electrode current collector and a three-dimensional framework layer located on the negative electrode current collector, wherein the three-dimensional framework layer comprises the tubular nanofiber material described above. The three-dimensional skeleton layer includes a single-layer structure layer or a multi-layer structure layer formed by stacking single-layer structure layers, for example, 2 layers, 3 layers, or 4 layers. The single-layer structure layer has a three-dimensional interpenetrating network structure formed by stacking the tubular nanofiber materials.

In this application, the negative pole piece can be single face structure, also can be double-sided structure, and wherein single face structure is only set up this application in one side of current collector three-dimensional framework layer, and double-sided structure is all set up this application in the both sides of current collector three-dimensional framework layer.

In one embodiment of the present application, the three-dimensional scaffold layer satisfies the following condition:

(1) The thickness of the three-dimensional skeleton layer is 30 μm to 200 μm, preferably 30 μm to 100 μm; more preferably 30 μm to 80 μm, and

(2) The three-dimensional scaffold layer has a porosity of 65% to 95%, preferably 70% to 90%, more preferably 75% to 88%.

In this application, the porosity of the three-dimensional scaffold layer is based on the sum of the pores of the tubular fibers themselves and the pores between the tubular fibers in the scaffold layer. When the gaps in the three-dimensional framework layer are small, the space for accommodating and depositing lithium in the three-dimensional framework layer is limited, and lithium metal deposition sites cannot be controlled well, so that the performance of the lithium metal battery is adversely affected. When the tubular nanofiber does not have a hollow structure, the void ratio of the three-dimensional framework layer is reduced, and lithium metal deposition can partially enter the void between the fibers, so that side reactions of lithium metal and electrolyte occur, thereby influencing the cycle performance and the volume expansion ratio of the lithium metal battery. When the porosity of the three-dimensional framework layer is in the above range, good lithium metal battery performance is obtained. In addition, the thickness of the three-dimensional framework layer also affects the performance of the lithium metal battery, when the thickness of the three-dimensional framework layer is low, the pores of the three-dimensional framework layer cannot fully contain deposited lithium, lithium metal is partially deposited on the top of the pole piece, side reactions can be caused, the cycle performance of the lithium metal battery is affected, and the excessive thickness of the three-dimensional framework layer can reduce the energy density of the lithium metal battery. A thickness in the above range can obtain good lithium metal battery performance. In the electrostatic spinning process, a three-dimensional framework layer formed by tubular fibers with different thicknesses is obtained by controlling the spinning time.

In the application, the three-dimensional framework layers with different porosities can be obtained by controlling the processing conditions, the process parameters and the composition and the content of raw materials in the electrostatic spinning process. In the present application, if the three-dimensional skeleton layer includes a multi-layered structure, the thickness of the three-dimensional skeleton layer as described in the above condition (1) refers to the total thickness of the three-dimensional skeleton layer.

A third aspect of the present application provides a lithium metal battery, including the negative electrode tab.

In a fourth aspect, the present application provides an electronic device, including the lithium metal battery, where the electronic device is, for example, a mobile phone, a game console, a computer, a radio recorder, or the like.

The application may be implemented as follows:

1. a tubular nanofiber material, wherein the tubular nanofibers have a hollow tube extending axially along the nanofiber tube; the wall of the tubular nanofiber is distributed with a lithium-philic material; two ends of the tubular nanofiber are of a closed structure; the tubular nanofiber is preferably formed with a protective coating in a closed structure at both ends.

2. In one embodiment of the present application, the tubular nanofiber material has an ionic conductivity greater than 10 ^-4 S/m。

3. In one embodiment of the present application, wherein the weight percentage of the lithium-philic material is distributed in decreasing amounts from inside to outside along the radial direction of the tubular nanofiber material wall, preferably at least 70 weight percent, more preferably 80 weight percent or more, even more preferably 90 weight percent or more of the lithium-philic material is distributed on the inner nanofiber tube wall, based on the total weight of the tubular nanofiber material.

4. In one embodiment of the present application, the lithium-philic material is selected from the following:

preferably, the metal nitride comprises Mo ₂ N ₃ ，

preferably, the metal carbide comprises FeC;

or alternatively

(3) The tubular nanofiber material having a wetting functional group, wherein the wetting functional group comprises at least one of a hydroxyl group, an ester group, a carboxyl group, an amino group, a sulfonic group;

or a mixture of the above-mentioned lithium-philic materials.

5. In one embodiment of the present application, the weight percentage of the lithium philic material is 10 to 80 wt%, preferably 25 to 75 wt%, more preferably 30 to 70 wt%, even more preferably 30 to 65 wt%, most preferably 32 to 60 wt%, based on the total weight of the tubular nanofiber material.

6. In one embodiment of the present application, the tubular nanofiber material meets the following conditions:

(1) The diameter R of the tubular nanofibers is 100nm to 2 μm; and

(2) The wall thickness d of the tubular nanofibers is 50nm to 500nm.

7. In one embodiment of the present application, the diameter R, the wall thickness d of the tubular nanofiber and the porosity p of the tubular nanofiber satisfy the following relationship:

wherein the porosity p is 50% to 85%, preferably 60% to 80%, and the value of (R-2 d)/d is greater than 5, preferably greater than 7, particularly preferably greater than 7.5.

8. In one embodiment of the present application, the method of preparing a tubular nanofiber comprises the steps of:

9. In one embodiment of the present application, the concentration of the polymer B solution is from 1 to 5% by weight, preferably from 2 to 4% by weight, more preferably from 2.5 to 3.5% by weight.

10. A negative electrode tab comprising a negative electrode current collector and a three-dimensional scaffold layer on the negative electrode current collector, wherein the three-dimensional scaffold layer comprises the tubular nanofiber material of any one of embodiments 1-9.

11. In one embodiment of the present application, wherein the three-dimensional scaffold layer satisfies the following condition:

(1) The thickness of the three-dimensional skeleton layer is 30 μm to 200 μm, preferably 30 μm to 100 μm, more preferably 30 μm to 80 μm; and

12. In one embodiment of the present application, the method for preparing the negative electrode sheet comprises the steps of:

(4) Immersing the fibers obtained in step (2) or (3) in a solution of polymer B, followed by drying at elevated temperature, preferably under vacuum, to obtain a tubular nanofiber material;

(5) And applying the tubular nanofiber material to the current collector to form a three-dimensional framework layer so as to obtain the negative electrode plate.

13. A lithium metal battery comprising the negative electrode tab of any one of embodiments 10-12.

14. An electronic device comprising the lithium metal battery of embodiment 13.

Examples

Other advantages and effects of the present application will become apparent to those skilled in the art from the present disclosure, when the following description of the present application is taken in conjunction with the accompanying drawings. The present application may be embodied or carried out in other specific embodiments, and the details of the present application may be modified or changed from various points of view and applications without departing from the spirit of the present application.

It should be noted that, the illustrations 1-5 provided in the present embodiment merely illustrate the basic concepts of the present application by way of illustration, and only show the illustrations of the components related to the present application, and not limit the number, shape, size, manufacturing method and process window of the components in actual implementation, and the form, number and proportion of each component in actual implementation may be arbitrarily changed, and the layout of the components may be more complex. The process conditions involved in the examples can be reasonably varied within the effective window and achieve the effects disclosed herein.

Experimental raw materials:

the polymeric materials used in the examples were all purchased from Sigma, with polyvinylpyrrolidone having a molecular weight (Mn) of 130 ten thousand; polyvinylidene fluoride with a molecular weight (Mn) of 36 ten thousand; polyacrylonitrile, molecular weight (Mn) 15 ten thousand; polymethyl methacrylate, molecular weight (Mn) 12 ten thousand; polyethylene oxide having a molecular weight (Mn) of 15 ten thousand.

The following raw materials used in the examples were all purchased from Sigma: tetraethyl silicate, tetrabutyl titanate, lithium iron phosphate, absolute ethyl alcohol, glacial acetic acid, N-methylpyrrolidone, dioxolane, dimethyl ether and lithium bistrifluoromethane sulfonyl imide.

Example 1

1. Preparation of negative pole piece

Preparation of tubular nanofiber material (i.e., three-dimensional scaffold layer):

the preparation of the hollow three-dimensional framework layer of the contained tubular nanofiber comprises the following steps: 2g of polyvinylpyrrolidone (PVP) was dissolved in 10g of absolute ethanol and stirred for 4 hours, then 2g of glacial acetic acid (99% by weight), 3.5g of tetraethyl silicate and 1g of tetrabutyl titanate were added and stirring was continued for 2 hours until the solution became a homogeneous clear state. Transferring the solution into a needle cylinder for electrostatic spinning, wherein the parameters of the electrostatic spinning process are as follows: the negative pressure is-4 kV, the positive pressure is 18kV, the liquid inlet rate is 0.3mL/h, the distance between the collecting plate and the needle head is 20cm, the rotating speed of the collecting roller is 2000rpm, and the spinning time is 12 hours. The material obtained by spinning is kept stand for 24 hours at 20 ℃ and relative humidity of 50 percent, and then is transferred to a vacuum drying oven to be dried for 12 hours at 80 ℃; then, the temperature is raised to 800 ℃ per minute in a tube furnace under the nitrogen atmosphere for 6 hours, and a three-dimensional framework layer with hollow tubular nanofibers is obtained.

The preparation of the three-dimensional framework layer with two closed ends of the contained tubular nanofiber comprises the following steps: preparing an N-methyl pyrrolidone (NMP) solution of polyvinylidene fluoride (PVDF) with the concentration of 3 weight percent, soaking the hollow tubular nanofiber material prepared in the above into the PVDF solution, and standing for 10 minutes; and then transferring the anode plate to a vacuum drying oven for vacuum drying at 80 ℃ for 12 hours to obtain the three-dimensional framework layer applicable to the anode plate.

And stacking the three-dimensional framework layer, the lithium foil and the negative current collector copper foil in sequence, and cold pressing to form a negative electrode plate. And then, cold pressing and lithium supplementing the negative electrode plate, wherein the thickness of a lithium supplementing layer is 20 mu m, and directly punching and cutting into a circular sheet with the diameter of (18 mm) for later use.

In this example, the content of the lithium-philic material in the three-dimensional skeleton layer was 32 wt%, the thickness of the three-dimensional skeleton layer was 60 μm, the thickness of the lithium foil was 20 μm, the thickness of the copper foil was 12 μm, and the porosity of the three-dimensional skeleton layer was 85%.

2. Preparation of positive pole piece

Lithium iron phosphate (LiFePO) as a cathode active material ₄ ) The conductive carbon black (Super P) and polyvinylidene fluoride (PVDF) are mixed according to the weight ratio of 97.5:1.0:1.5, then added into N-methyl pyrrolidone (NMP) serving as a solvent, prepared into slurry with the solid content of 75 weight percent, and stirred until uniform. Uniformly coating the slurry on an aluminum foil of a positive current collector, and drying at 90 ℃ to obtain a positive pole piece with the load capacity of 1mAh/cm ² . The pole piece is cut into (14 mm) specifications for standby.

3. Preparation of electrolyte

In dry argon atmosphere, first mixing dioxolane and dimethyl ether in a volume ratio of 1:1, and then adding lithium bistrifluoromethane sulfonyl imide into an organic solvent to dissolve and mix uniformly, thus obtaining the electrolyte with the lithium salt concentration of 1M.

4. Preparation of lithium metal batteries

Polyethylene (PE) with the thickness of 15 mu m is selected as a separation film, the positive pole piece, the separation film and the negative pole piece are sequentially wound into a battery core, then the battery core is filled into an aluminum plastic film, electrolyte is injected, and the battery is assembled into a button cell for testing.

Example 2

The same preparation as in example 1 was carried out, except that: the tubular nanofibers contained in example 2 were prepared as a three-dimensional scaffold layer with both ends closed as follows:

an N-methylpyrrolidone solution of Polyacrylonitrile (PAN) was used at a concentration of 3% by weight.

Example 3

The same preparation as in example 1 was carried out, except that: the solution for forming the three-dimensional skeleton layer of the negative electrode sheet in example 3 was prepared as follows:

2.8g of polyvinylpyrrolidone (PVP) was dissolved in 10g of absolute ethanol and stirred for 4 hours, then 2g of glacial acetic acid (99% by weight), 3.5g of tetraethyl silicate and 1g of tetrabutyl titanate were added and stirring was continued for 2 hours until the solution became a homogeneous clear state.

In this example, the content of the lithium-philic material in the three-dimensional skeleton layer was 25 wt%, the thickness of the three-dimensional skeleton layer was 60 μm, the thickness of the lithium foil was 20 μm, the thickness of the copper foil was 12 μm, and the porosity of the three-dimensional skeleton layer was 85%.

Example 4

The same preparation as in example 1 was carried out, except that: the solution for forming the three-dimensional skeleton layer of the negative electrode sheet in example 4 was prepared as follows:

2.8g of polyvinylpyrrolidone (PVP) was dissolved in 10g of absolute ethanol and stirred for 4 hours, then 1g of glacial acetic acid (99% by weight), 1.75g of tetraethyl silicate and 0.5g of tetrabutyl titanate were added and stirring was continued for 2 hours until the solution became a homogeneous clear state.

In this example, the content of the lithium-philic material in the three-dimensional skeleton layer was 10 wt%, the thickness of the three-dimensional skeleton layer was 60 μm, the thickness of the lithium foil was 20 μm, the thickness of the copper foil was 12 μm, and the porosity of the three-dimensional skeleton layer was 85%.

Example 5

The same preparation as in example 1 was carried out, except that: the solution for forming the three-dimensional skeleton layer of the negative electrode sheet in example 5 was prepared as follows:

1.5g polyvinylpyrrolidone (PVP) was dissolved in 15g absolute ethanol and stirred for 4 hours, then 5g glacial acetic acid (99 wt%), 8.75g tetraethyl silicate and 2.5g tetrabutyl titanate were added and stirring was continued for 2 hours until the solution became a homogeneous clear state.

In this example, the content of the lithium-philic material in the three-dimensional skeleton layer was 70 wt%, the thickness of the three-dimensional skeleton layer was 60 μm, the thickness of the lithium foil was 20 μm, the thickness of the copper foil was 12 μm, and the porosity of the three-dimensional skeleton layer was 85%.

Example 6

The same preparation as in example 1 was carried out, except that: the solution for forming the three-dimensional framework layer of the negative electrode sheet in example 6 was prepared as follows:

3g of polyvinylpyrrolidone (PVP) was dissolved in 10g of absolute ethanol and stirred for 4 hours, then 3g of glacial acetic acid (99% by weight), 5.25g of tetraethyl silicate and 1.5g of tetrabutyl titanate were added and stirring was continued for 2 hours until the solution became a homogeneous clear state.

In this example, the content of the lithium-philic material in the three-dimensional skeleton layer was 32 wt%, the thickness of the three-dimensional skeleton layer was 60 μm, the thickness of the lithium foil was 20 μm, the thickness of the copper foil was 12 μm, and the porosity of the three-dimensional skeleton layer was 65%.

Comparative example 7

The same preparation as in example 1 was carried out, except that: the parameters of the electrostatic spinning process for forming the three-dimensional framework layer of the negative electrode sheet in comparative example 7 were:

the negative pressure is-4 kV, the positive pressure is 18kV, the liquid inlet rate is 0.3mL/h, the distance between the collecting plate and the needle head is 20cm, the rotating speed of the collecting roller is 2000rpm, and the spinning time is 12 hours. Transferring the material obtained by spinning into a vacuum drying oven, and vacuum drying at 80 ℃ for 12 hours; then, the temperature is raised to 800 ℃ per minute in a tube furnace under the nitrogen atmosphere for 6 hours, and a three-dimensional framework layer with hollow tubular nanofibers is obtained.

In this example, the content of the lithium-philic material in the three-dimensional skeleton layer was 32 wt%, the thickness of the three-dimensional skeleton layer was 60 μm, the thickness of the lithium foil was 20 μm, the thickness of the copper foil was 12 μm, and the porosity of the three-dimensional skeleton layer was 30%.

Comparative example 8

The same preparation as in example 1 was carried out, except that: the solution forming the three-dimensional skeleton layer of the negative electrode sheet in comparative example 8 was prepared as follows:

3.2g of polyvinylpyrrolidone (PVP) was dissolved in 10g of absolute ethanol and stirred for 4 hours, then 3.2g of glacial acetic acid (99% by weight), 5.6g of tetraethyl silicate and 1.6g of tetrabutyl titanate were added and stirring was continued for 2 hours until the solution became a homogeneous clear state.

In this example, the content of the lithium-philic material in the three-dimensional skeleton layer was 32 wt%, the thickness of the three-dimensional skeleton layer was 60 μm, the thickness of the lithium foil was 20 μm, the thickness of the copper foil was 12 μm, and the porosity of the three-dimensional skeleton layer was 50%.

Comparative example 9

The same preparation as in example 1 was carried out, except that: the solution forming the three-dimensional skeleton layer of the negative electrode sheet in comparative example 9 was prepared as follows:

3.5g polyvinylpyrrolidone (PVP) was dissolved in 10g absolute ethanol and stirred for 4 hours, then 3.2g glacial acetic acid (99 wt%), 6.13g tetraethyl silicate and 1.75g tetrabutyl titanate were added and stirring was continued for 2 hours until the solution became a homogeneous clear state.

In this example, the content of the lithium-philic material in the three-dimensional skeleton layer was 32 wt%, the thickness of the three-dimensional skeleton layer was 60 μm, the thickness of the lithium foil was 20 μm, the thickness of the copper foil was 12 μm, and the porosity of the three-dimensional skeleton layer was 35%.

Example 10

The same preparation as in example 1 was carried out, except that: the tubular nanofibers contained in example 10 were prepared as a three-dimensional scaffold layer with both ends closed as follows:

an N-methylpyrrolidone (NMP) solution of polyvinylidene fluoride (PVDF) was used at a concentration of 1% by weight.

Example 11

The same preparation as in example 1 was carried out, except that: the tubular nanofibers contained in example 11 were prepared as a three-dimensional scaffold layer with both ends closed as follows:

an N-methylpyrrolidone (NMP) solution of polyvinylidene fluoride (PVDF) was used at a concentration of 5% by weight.

Comparative example 12

The same preparation as in example 1 was carried out, except that: the parameters of the electrospinning process for forming the three-dimensional framework layer of the negative electrode sheet in comparative example 12 were:

the negative pressure is-4 kV, the positive pressure is 18kV, the liquid inlet rate is 0.3mL/h, the distance between the collecting plate and the needle head is 20cm, the rotating speed of the collecting roller is 2000rpm, and the spinning time is 4 hours. The material obtained by spinning is kept stand for 24 hours at 20 ℃ and relative humidity of 50 percent, and then is transferred to a vacuum drying oven to be dried for 12 hours at 80 ℃; then, the temperature is raised to 800 ℃ per minute in a tube furnace under the nitrogen atmosphere for 6 hours, and a three-dimensional framework layer with hollow tubular nanofibers is obtained.

In this example, the content of the lithium-philic material in the three-dimensional skeleton layer was 32 wt%, the thickness of the three-dimensional skeleton layer was 20 μm, the thickness of the lithium foil was 20 μm, the thickness of the copper foil was 12 μm, and the porosity of the three-dimensional skeleton layer was 85%.

Example 13

The same preparation as in example 1 was carried out, except that: the parameters of the electrospinning process for forming the three-dimensional framework layer of the negative electrode sheet in example 13 were:

the negative pressure is-4 kV, the positive pressure is 18kV, the liquid inlet rate is 0.3mL/h, the distance between the collecting plate and the needle head is 20cm, the rotating speed of the collecting roller is 2000rpm, and the spinning time is 18 hours. The material obtained by spinning is kept stand for 24 hours at 20 ℃ and relative humidity of 50 percent, and then is transferred to a vacuum drying oven to be dried for 12 hours at 80 ℃; then, the temperature is raised to 800 ℃ per minute in a tube furnace under the nitrogen atmosphere for 6 hours, and a three-dimensional framework layer with hollow tubular nanofibers is obtained.

In this example, the content of the lithium-philic material in the three-dimensional skeleton layer was 32 wt%, the thickness of the three-dimensional skeleton layer was 100 μm, the thickness of the lithium foil was 20 μm, the thickness of the copper foil was 12 μm, and the porosity of the three-dimensional skeleton layer was 85%.

Example 14

The same preparation as in example 1 was carried out, except that: the parameters of the electrospinning process for forming the three-dimensional framework layer of the negative electrode sheet in example 14 were:

the negative pressure is-4 kV, the positive pressure is 18kV, the liquid inlet rate is 0.3mL/h, the distance between the collecting plate and the needle head is 20cm, the rotating speed of the collecting roller is 2000rpm, and the spinning time is 28 hours. The material obtained by spinning is kept stand for 24 hours at 20 ℃ and relative humidity of 50 percent, and then is transferred to a vacuum drying oven to be dried for 12 hours at 80 ℃; then, the temperature is raised to 800 ℃ per minute in a tube furnace under the nitrogen atmosphere for 6 hours, and a three-dimensional framework layer with hollow tubular nanofibers is obtained.

In this example, the content of the lithium-philic material in the three-dimensional skeleton layer was 32 wt%, the thickness of the three-dimensional skeleton layer was 200 μm, the thickness of the lithium foil was 20 μm, the thickness of the copper foil was 12 μm, and the porosity of the three-dimensional skeleton layer was 85%.

Comparative example 15

The same preparation as in example 1 was carried out, except that: the solution for forming the three-dimensional skeleton layer of the negative electrode sheet in comparative example 15 was prepared as follows:

2g of polyvinylpyrrolidone (PVP) and 1g of polymethyl methacrylate (PMMA) were dissolved in 10g of absolute ethanol and stirred for 6h until the solution formed a homogeneous clear state.

In this example, the content of the lithium-philic material in the three-dimensional skeleton layer was 0 wt%, the thickness of the three-dimensional skeleton layer was 60 μm, the thickness of the lithium foil was 20 μm, the thickness of the copper foil was 12 μm, and the porosity of the three-dimensional skeleton layer was 85%.

Example 16

The same preparation as in example 1 was carried out, except that: the solution and electrospinning process parameters for forming the three-dimensional scaffold layer of the negative electrode sheet in example 16 were as follows:

preparation of tubular nanofiber material: 2.5g polyvinylpyrrolidone (PVP) was dissolved in 10g absolute ethanol and stirred for 4 hours, then 2g glacial acetic acid (99 wt%), 4g tetraethyl silicate and 1.2g tetrabutyl titanate were added and stirring was continued for 2 hours until the solution became a homogeneous clear state.

Transferring the solution into a needle cylinder for electrostatic spinning, wherein the parameters of the electrostatic spinning process are as follows: the negative pressure is-4 kV, the positive pressure is 12kV, the liquid inlet rate is 0.3mL/h, the distance between the collecting plate and the needle head is 20cm, the rotating speed of the collecting roller is 2000rpm, and the spinning time is 12 hours. The material obtained by spinning is kept stand for 24 hours at 20 ℃ and relative humidity of 50 percent, and then is transferred to a vacuum drying oven to be dried for 12 hours at 80 ℃; then, the temperature is raised to 800 ℃ per minute in a tube furnace under the nitrogen atmosphere for 6 hours, and a three-dimensional framework layer with hollow tubular nanofibers is obtained.

Comparative example 17

The same preparation as in example 1 was carried out, except that: the solution and electrospinning process parameters for forming the three-dimensional scaffold layer of the negative electrode sheet in comparative example 17 were as follows:

preparation of tubular nanofiber material: 1.5g of polyvinylpyrrolidone (PVP) was dissolved in 10g of absolute ethanol and stirred for 4 hours, then 2g of glacial acetic acid (99% by weight), 3.5g of tetraethyl silicate and 1g of tetrabutyl titanate were added and stirring was continued for 2 hours until the solution became a homogeneous clear state.

Transferring the solution into a needle cylinder for electrostatic spinning, wherein the parameters of the electrostatic spinning process are as follows: the negative pressure is-4 kV, the positive pressure is 28kV, the liquid inlet rate is 0.3mL/h, the distance between the collecting plate and the needle head is 20cm, the rotating speed of the collecting roller is 2000rpm, and the spinning time is 12 hours. The material obtained by spinning is kept stand for 24 hours at 20 ℃ and relative humidity of 50 percent, and then is transferred to a vacuum drying oven to be dried for 12 hours at 80 ℃; then, the temperature is raised to 800 ℃ per minute in a tube furnace under the nitrogen atmosphere for 6 hours, and a three-dimensional framework layer with hollow tubular nanofibers is obtained.

Example 18

The same preparation as in example 1 was carried out, except that: the three-dimensional scaffold layer forming the negative electrode sheet in example 18 was prepared as follows:

preparation of solution 1: 2g of polyvinylpyrrolidone (PVP) was dissolved in 10g of absolute ethanol and stirred for 4 hours, then 2g of glacial acetic acid (99% by weight), 3.5g of tetraethyl silicate and 1g of tetrabutyl titanate were added and stirring was continued for 2 hours until the solution became a homogeneous clear state.

Preparation of solution 2: 2.8g of polyvinylpyrrolidone (PVP) was dissolved in 10g of absolute ethanol and stirred for 4 hours, then 2g of glacial acetic acid (99% by weight), 3.5g of tetraethyl silicate and 1g of tetrabutyl titanate were added and stirring was continued for 2 hours until the solution became a homogeneous clear state.

Transferring the solution 1 into a needle cylinder for electrostatic spinning, wherein the parameters of the electrostatic spinning process are as follows: negative pressure is-4 kV, positive pressure is 18kV, liquid inlet rate is 0.3mL/h, distance between a collecting plate and a needle head is 20cm, rotating speed of a collecting roller is 2000rpm, and spinning time is 6 hours (30 mu m thickness is formed); then transferring the solution 2 into a needle cylinder for electrostatic spinning, wherein the parameters of the electrostatic spinning process are as follows: the negative pressure is-4 kV, the positive pressure is 18kV, the liquid inlet rate is 0.3mL/h, the distance between the collecting plate and the needle head is 15-20cm, the rotating speed of the collecting roller is 2000rpm, and the spinning time is 6 hours (30 mu m thickness is formed). The material obtained by spinning is kept stand for 24 hours at 20 ℃ and relative humidity of 50 percent, and then is transferred to a vacuum drying oven to be dried for 12 hours at 80 ℃; then, the temperature is raised to 800 ℃ per minute in a tube furnace under the nitrogen atmosphere for 6 hours, and a three-dimensional framework layer with hollow tubular nanofibers is obtained.

In this example, the content of the lithium-philic material in the three-dimensional skeleton layer was 28 wt%, the thickness of the three-dimensional skeleton layer was 60 μm, the thickness of the lithium foil was 20 μm, the thickness of the copper foil was 12 μm, and the porosity of the three-dimensional skeleton layer was 85%.

Example 19

The same preparation as in example 1 was carried out, except that: the three-dimensional scaffold layer forming the negative electrode sheet in example 19 was prepared as follows:

Preparation of solution 2: 2g of polyvinylpyrrolidone (PVP) and 1g of polymethyl methacrylate (PMMA) were dissolved in 10g of absolute ethanol and stirred for 6h until the solution formed a homogeneous clear state.

In this example, the content of the lithium-philic material in the three-dimensional skeleton layer was 16 wt%, the thickness of the three-dimensional skeleton layer was 60 μm, the thickness of the lithium foil was 20 μm, the thickness of the copper foil was 12 μm, and the porosity of the three-dimensional skeleton layer was 85%.

Comparative example 20

The same preparation as in example 1 was carried out, except that: the three-dimensional scaffold layer forming the negative electrode tab in comparative example 20 was prepared as follows:

the hollow tubular nanofiber material prepared in example 1 (i.e., both ends were not closed) and the tubular nanofiber material both ends were combined with cold pressing at a weight ratio of 1:1 to form a pole piece.

In this example, the content of the lithium-philic material in the three-dimensional skeleton layer was 30 wt%, the thickness of the three-dimensional skeleton layer was 60 μm, the thickness of the lithium foil was 20 μm, the thickness of the copper foil was 12 μm, and the porosity of the three-dimensional skeleton layer was 85%.

Example 21

The same preparation as in example 1 was carried out, except that: the tubular fibers with both ends closed in the three-dimensional skeleton layer in example 21 were prepared as follows:

an N-methylpyrrolidone (NMP) solution of polyethylene oxide (PEO) was used at a concentration of 3% by weight.

Example 22

The same preparation as in example 1 was carried out, except that: the tubular fibers with closed ends in the three-dimensional scaffold layer in example 22 were prepared as follows:

a solution of polymethyl methacrylate (PMMA) in N-methylpyrrolidone (NMP) was used at a concentration of 3% by weight.

Comparative example 23

The same preparation as in example 1 was carried out, except that: the three-dimensional scaffold layer in comparative example 23 was not subjected to the step of preparing a tubular fiber with both ends closed.

In this comparative example, the content of the lithium-philic material in the three-dimensional skeleton layer was 32 wt%, the thickness of the three-dimensional skeleton layer was 60 μm, the thickness of the lithium foil was 20 μm, the thickness of the copper foil was 12 μm, and the porosity of the three-dimensional skeleton layer was 85%.

Comparative example 24

The same preparation as in example 1 was carried out, except that: the solution forming the three-dimensional skeleton layer of the negative electrode sheet in comparative example 24 was prepared as follows: 2g of polyvinylpyrrolidone (PVP) and 1g of polymethyl methacrylate (PMMA) are dissolved in 10g of absolute ethanol and stirred for 6 hours until the solution forms a uniform and clear state; and the step of preparing the tubular fiber with both ends closed is not performed.

In this comparative example, the content of the lithium-philic material in the three-dimensional skeleton layer was 0 wt%, the thickness of the three-dimensional skeleton layer was 60 μm, the thickness of the lithium foil was 20 μm, the thickness of the copper foil was 12 μm, and the porosity of the three-dimensional skeleton layer was 85%.

Comparative example 25

The same preparation as in example 1 was carried out, except that: the three-dimensional scaffold layer in comparative example 25 was not subjected to the step of preparing a tubular fiber with both ends closed.

In this comparative example, the content of the lithium-philic material in the three-dimensional skeleton layer was 32 wt%, the thickness of the three-dimensional skeleton layer was 60 μm, the thickness of the lithium foil was 20 μm, the thickness of the copper foil was 12 μm, and the porosity of the three-dimensional skeleton layer was 70%.

Comparative example 26

The difference from example 1 is that: the cathode pole piece is directly made of commercial lithium copper composite tape, wherein the lithium sheet is 20 mu m thick, the copper foil is 12 mu m thick, and the cathode pole piece is directly punched into a wafer with the diameter of 18mm for later use.

Three-dimensional framework layer structure characterization and lithium metal battery performance test method

1. Three-dimensional framework layer porosity test

The three-dimensional scaffold samples to be tested were placed into a fully automatic mercury porosimeter (model AutoPore V9610) and tested at a measured pressure of 30,000psi to give a porosity expressed as the porosity of the three-dimensional scaffold.

2. Thickness of three-dimensional skeleton layer

The thickness of the three-dimensional skeleton layer was measured by using a thickness meter (model number Mitutoyo7327, sanfeng, japan), 10 positions of the three-dimensional skeleton layer were selected to measure the thickness, the highest and lowest values were removed after the measurement, and an average value was calculated and recorded as the thickness of the three-dimensional skeleton layer.

3. Cycle performance test

Charging the lithium metal battery to 3.7V at a constant current of 0.2C at 25 ℃, then charging the lithium metal battery to a constant voltage of 0.025C, wherein the lithium metal battery is in a full charge state, and recording the charge capacity at the moment, namely the 1 st charge capacity; after the lithium metal battery is kept stand for 5min, the constant current discharge is carried out at 0.5 ℃ to 2.55V, the lithium metal battery is kept stand for 5min, the lithium metal battery is a cyclic charge-discharge process, and the discharge capacity at the moment is recorded to be the 1 st-turn discharge capacity. And (3) carrying out a cyclic charge-discharge test on the lithium metal battery according to the method, recording the discharge capacity after each cycle until the discharge capacity of the lithium metal battery is attenuated to 80% of the discharge capacity of the 1 st cycle, stopping the test, and representing the cycle performance of the lithium metal battery by using the cycle number at the moment. The higher the number of cycles, the better the cycle performance of the lithium metal battery.

4. Diameter/wall thickness determination of tubular nanofiber material

Performing section cutting treatment on the three-dimensional framework layer by an ion beam section polishing instrument (CP instrument), and observing the section of the sample by a scanning electron microscope, wherein the section structure of single fiber is shown in figure 1; the cross section of ten fibers in the cross section of the sample is selected, the diameter and the wall thickness of the cross section are measured, and the average value is obtained. A schematic of the diameter and wall thickness of the individual fibers is shown in fig. 5.

5. Lithium metal deposition site determination

The method comprises the steps of carrying out section cutting treatment on a three-dimensional framework layer through an ion beam section polishing instrument (CP instrument), observing the section of a sample through a scanning electron microscope, and carrying out element analysis on the section of a tubular nanofiber material in the three-dimensional framework layer by utilizing an energy dispersion X-ray spectrometer arranged on the scanning electron microscope.

6. Content distribution of lithium-philic material along radial direction of tubular nanofiber material tube wall

The three-dimensional skeleton layer is subjected to section cutting treatment by an ion beam section polishing instrument (CP instrument), then the section of a sample is observed by a scanning electron microscope, the section of a tubular nanofiber material in the three-dimensional skeleton is subjected to element analysis by an energy dispersion X-ray spectrometer arranged on the scanning electron microscope, the specific element distribution can be seen, and the content distribution of a lithium-philic material along the radial direction of the wall of the tubular nanofiber material can be further characterized according to the quantitative element analysis.

7. Coulomb efficiency test

Charging the lithium metal battery to 3.7V at a constant current of 0.2C at 25 ℃, then charging the lithium metal battery to a constant voltage of 0.025C, wherein the lithium metal battery is in a full charge state, and recording the charge capacity at the moment, namely the 1 st charge capacity; after the lithium metal battery is kept stand for 5min, the constant current discharge is carried out at 0.5 ℃ to 2.55V, the lithium metal battery is kept stand for 5min, the lithium metal battery is a cyclic charge-discharge process, and the discharge capacity at the moment is recorded to be the 1 st-turn discharge capacity. And (3) carrying out a cyclic charge-discharge test on the lithium metal battery according to the method, recording the charge capacity and the discharge capacity after each cycle, stopping the test until the discharge capacity of the lithium metal battery is attenuated to 80% of the discharge capacity of the 1 st cycle, and taking the average value of the ratio of the discharge capacity and the charge capacity after each cycle as the coulomb efficiency of the lithium metal battery.

The coulombic efficiency of a lithium metal battery can characterize the capacity performance of the lithium metal battery. The higher the coulombic efficiency of the lithium metal battery, the better the capacity performance of the lithium metal battery.

8. Thickness expansion test

Charging the lithium metal battery to 3.7V at a constant current of 0.2C at 25 ℃, then charging the lithium metal battery to a constant voltage of 0.025C, wherein the lithium metal battery is in a full charge state, and recording the charge capacity at the moment, namely the 1 st charge capacity; after the lithium metal battery is kept stand for 5min, the constant current discharge is carried out at 0.5 ℃ to 2.55V, the lithium metal battery is kept stand for 5min, the lithium metal battery is a cyclic charge-discharge process, and the discharge capacity at the moment is recorded to be the 1 st-turn discharge capacity. Performing a cyclic charge-discharge test on the lithium metal battery according to the method, recording the discharge capacity after each cycle, and stopping the test until the discharge capacity of the lithium metal battery is attenuated to 80% of the discharge capacity of the 1 st cycle; disassembling the battery, taking out the negative electrode plate, immersing in a dimethyl carbonate solution, preparing a sample of the negative electrode plate by adopting an argon ion polishing (CP) method, observing the section of the negative electrode plate (namely, the section perpendicular to the direction of a negative electrode current collector) by using a scanning electron microscope, and obtaining the thickness of the section of the negative electrode plate after circulation and marking the thickness as T mu m; the cross-sectional thickness of the negative electrode tab was measured by the same method and recorded as T μm before assembling the lithium metal battery, and the thickness expansion ratio (%) = (T-T)/t×100% of the negative electrode tab.

The volume expansion condition of the negative electrode plate and the lithium metal battery can be represented by the thickness expansion rate of the negative electrode plate. The lower the thickness expansion rate of the negative electrode plate is, the lower the volume expansion rate of the negative electrode plate and the lithium metal battery is, which indicates that the battery has better cyclic expansion performance.

The test results of the examples and comparative examples of the present application are shown in the following tables 1 to 9, wherein the specific meanings of numerals 1, 2 and 3 referring to "metal deposition position" in each table are described with reference to fig. 4 and the accompanying drawings.

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The foregoing embodiments are merely illustrative of the principles of the present application and their effectiveness, and are not intended to limit the application. Modifications and variations may be made to the above-described embodiments by those of ordinary skill in the art without departing from the spirit and scope of the present application. Accordingly, it is intended that all equivalent modifications and variations which may be accomplished by persons skilled in the art without departing from the spirit and technical spirit of the disclosure be covered by the claims of this application.

Claims

1. A tubular nanofiber material, wherein the tubular nanofibers have a hollow tube extending axially along the nanofiber tube; the wall of the tubular nanofiber is provided with a lithium-philic material, wherein the weight percentage of the lithium-philic material is 10-80% by weight based on the total weight of the tubular nanofiber material, and the weight percentage of the lithium-philic material is distributed gradually from inside to outside of the tube along the radial direction of the wall of the tubular nanofiber material; two ends of the tubular nanofiber are of a closed structure; the tubular nanofiber material meets the following conditions:

(1) The diameter R of the tubular nanofibers is 100nm to 2 μm; and

(2) The wall thickness d of the tubular nanofiber is 50nm to 500nm;

the diameter R of the tubular nanofiber, the wall thickness d of the tube and the porosity p of the tubular nanofiber meet the following relation:

wherein the porosity p is 50% -85%.

2. The tubular nanofiber material of claim 1 having an ionic conductivity greater than 10 ^-4 S/m。

3. The tubular nanofiber material of claim 1, the lithium-philic material being selected from at least one of the following:

(2) At least one of a metal simple substance with a wetting functional group and an alloy thereof, a metal oxide, a metal nitride, a metal sulfide or a metal carbide, wherein the wetting functional group comprises at least one of a hydroxyl group, an ester group, a carboxyl group, an amino group and a sulfonic group; or (b)

(3) The tubular nanofiber material having a wetting functional group, wherein the wetting functional group comprises at least one of a hydroxyl group, an ester group, a carboxyl group, an amino group, a sulfonic group.

4. The tubular nanofiber material of claim 3, wherein the elemental metal and alloys thereof comprise at least one of Ag, au, zn and alloys thereof,

the metal oxide comprises at least one of TiO2, siO2, znO, snO2, co3O4 or Fe2O3,

the metal nitride includes Mo2N3,

the metal sulfide includes at least one of MoS2 or SnS2,

the metal carbide comprises FeC.

5. A negative electrode tab comprising a negative electrode current collector and a three-dimensional scaffold layer on the negative electrode current collector, wherein the three-dimensional scaffold layer comprises the tubular nanofiber material of any one of claims 1-4.

6. The negative electrode tab of claim 5 wherein the three-dimensional scaffold layer satisfies the following condition:

(1) The thickness of the three-dimensional framework layer is 30-200 μm; and

(2) The three-dimensional framework layer has a porosity of 65% to 95%.

7. The negative electrode tab of claim 5 wherein the three-dimensional scaffold layer satisfies the following condition:

(1) The thickness of the three-dimensional framework layer is 30-100 μm; and

(2) The three-dimensional framework layer has a porosity of 70% to 90%.

8. A lithium metal battery comprising the negative electrode tab according to any one of claims 5-7.