Composite current collector for anode-free lithium metal battery and preparation method therefor, and anode-free lithium metal battery

Abstract

A composite current collector for an anode-free lithium metal battery and a preparation method therefor, and an anode-free lithium metal battery. The composite current collector for an anode-free lithium metal battery comprises: a base film; an electrically conductive layer, which is arranged on at least one side surface of the base film; and a surface modification layer, which is arranged on the side surface of the conductive layer that is away from the base film, wherein the material of the surface modification layer comprises a hydroxyapatite-based compound. By means of constructing, on the surface of a composite current collector, a surface modification layer including a hydroxyapatite-based composite, the repulsion of an anode to free-state anions is effectively relieved, such that sufficient anion derivatives are generated at an electrolyte-anode interface to stabilize the electrolyte-anode interface; and the generated stable interface can reduce desolvation energy barriers of lithium ions, accelerate the transmission dynamics of the interface, and effectively suppress the generation of "dead lithium" and lithium dendrites, thereby prolonging the cycle life of a lithium metal battery.

Description

A composite current collector for a negative electrode-free lithium metal battery, a preparation method thereof, and a negative electrode-free lithium metal battery Technical Field

[0001] The present application relates to the field of battery technology, for example, a composite current collector for a negative electrode-free lithium metal battery, a preparation method thereof, and a negative electrode-free lithium metal battery. Background Art

[0002] At present, composite current collectors based on polymer films have received widespread attention and application in the new energy industry. The preparation of this composite current collector usually adopts the method of physical vapor deposition (PVD) to deposit a layer of metal on a polymer film (such as polyester, polyolefin, etc.), thereby preparing a composite current collector with good conductivity. Compared with traditional current collectors, composite current collectors based on polymer films have the characteristics of low cost, light weight, and good internal insulation. These characteristics enable the composite current collector to reduce the cost of the battery and improve the energy density and safety of the battery when used in the battery.

[0003] Lithium metal batteries, known for their high energy density, continue to attract attention as a promising next-generation advanced energy storage technology. In particular, anode-free lithium metal batteries, which eliminate the use of initial anode active materials, can push the full battery energy density to the extreme, exceeding 450Wh·kg. -1 , is considered the ultimate choice for high-energy-density lithium metal batteries. In particular, applying composite current collectors to anode-free lithium metal batteries can further highlight the advantages of high energy density of anode-free lithium metal batteries.

[0004] However, for negative electrode-free lithium metal batteries, due to the lack of protection from negative electrode active materials or compensation for excess active lithium, and the occurrence of problems such as "dead lithium" and lithium dendrites caused by the instability of the negative electrode interface during the cycle, the cycle performance of negative electrode-free lithium metal batteries is poor, which limits the large-scale application of negative electrode-free lithium metal batteries.

[0005] Therefore, how to avoid the poor cycle performance problem of negative electrode-free lithium metal batteries and improve the cycle life of lithium metal batteries is a technical problem that needs to be solved urgently.

[0006] Summary of the Invention

[0007] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0008] The present application provides a composite current collector for a negative electrode-free lithium metal battery, a preparation method thereof, and a negative electrode-free lithium metal battery. By constructing a surface modification layer made of a hydroxyapatite-based composite material on the surface of the composite current collector, the present application effectively alleviates the negative electrode's repulsion of free anions, thereby generating sufficient anion derivatives at the electrolyte-negative electrode interface to stabilize the electrolyte-negative electrode interface. The generated stable interface can reduce the lithium ion desolvation energy barrier, accelerate interfacial transport kinetics, and effectively suppress the generation of "dead lithium" and lithium dendrites, thereby improving the cycle life of the lithium metal battery.

[0009] In a first aspect, the present application provides a composite current collector for a negative electrode-free lithium metal battery, the composite current collector for a negative electrode-free lithium metal battery comprising:

[0010] basement membrane;

[0011] A conductive layer provided on at least one surface of the base film;

[0012] A surface modification layer is provided on a surface of the conductive layer on a side relatively far from the base film, wherein a material of the surface modification layer includes a hydroxyapatite-based composite.

[0013] The present application constructs a surface modification layer on the surface of the composite current collector, the material of which is a hydroxyapatite-based composite. The electrostatic force between the phosphate in the hydroxyapatite-based composite and the lithium ions is strong, thereby forming a local lithium ion-enriched area, increasing the probability of interaction between anions and lithium ions, and forming more lithium ion coordinated anions. This modification layer helps to alleviate the negative electrode's repulsion of free anions, stabilize the electrolyte-negative electrode interface, and the generated stable interface can reduce the lithium ion desolvation energy barrier, accelerate the interface transport kinetics, and effectively inhibit the generation of "dead lithium" and lithium dendrites, thereby improving the cycle life of the lithium metal battery.

[0014] As an optional technical solution of the present application, the hydroxyapatite-based composite includes a hydroxyapatite compound, a binder and a conductive agent.

[0015] It should be noted that the present application does not specifically limit the type of binder. For example, it can be one or more of polyvinylidene fluoride (PVDF), carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyvinyl pyrrolidone (PVP), polymethyl methacrylate (PMMA), polyacrylonitrile (PAN), polyacrylic acid (PAA), polyvinyl alcohol (PVA), sodium alginate (Alg), β-cyclodextrin polymer (β-CDp), polypropylene emulsion (LA132) or polytetrafluoroethylene (PTFE).

[0016] It should be noted that the present application does not specifically limit the type of conductive agent. For example, it can be carbon nanomaterials, such as graphene, carbon nanotubes, carbon fibers, carbon nanoquantum dots, etc.

[0017] In one embodiment, the hydroxyapatite compound includes at least one ion-doped modified hydroxyapatite.

[0018] In the present application, ion doping of hydroxyapatite helps to improve the structural stability and dispersibility of hydroxyapatite, enhance its stability and uniform dispersion in the modified layer, and thus enhance the performance of the modified layer.

[0019] It should be noted that ion doping is achieved by replacing calcium ions in hydroxyapatite.

[0020] In one embodiment, in the ion-doped modified hydroxyapatite, the doped ions include any one or a combination of at least two of lithium ions, copper ions, magnesium ions, zinc ions, or strontium ions, and lithium ions can be selected.

[0021] In the present application, lithium ion-doped hydroxyapatite can replenish lithium during the battery cycle, thereby improving the cycle stability of the battery.

[0022] In one embodiment, the ion doping amount of the ion-doped modified hydroxyapatite is 0-5 wt.% of the total mass of the ion-doped modified hydroxyapatite, for example, it can be 0 wt.%, 1 wt.%, 2 wt.%, 3 wt.%, 4 wt.% or 5 wt.%.

[0023] In the present application, if the doping amount of ions is too much, it is not conducive to the crystallization of hydroxyapatite, reduces its structural stability, and leads to reduced stability of the modified layer.

[0024] In one embodiment, the average particle size of the hydroxyapatite compound is ≤100 nm, for example, it can be 100 nm, 80 nm, 60 nm, 40 nm or 20 nm, and can be optionally 30-60 nm.

[0025] In the present application, if the average particle size of the hydroxyapatite compound is too large, it is difficult to disperse evenly, which affects the uniformity of the surface modification layer and leads to poor performance.

[0026] In one embodiment, the aspect ratio of the hydroxyapatite compound is 5-50, for example, 5, 10, 15, 20, 25, 30, 35, 40, 45 or 50.

[0027] In this application, increasing the aspect ratio can promote the formation of a network structure between hydroxyapatite, the binder, and the conductive agent, promote the formation of a stable electrolyte-negative electrode interface, reduce the lithium ion desolvation energy barrier, accelerate the interfacial transport dynamics, and effectively inhibit the generation of "dead lithium" and lithium dendrites, thereby improving the cycle life of lithium metal batteries. However, if the aspect ratio is too high, it will not be easy to evenly disperse in the modified layer, resulting in a decrease in the battery's cycle life.

[0028] In one embodiment, the mass ratio of the hydroxyapatite compound, the binder and the conductive agent is (70-90): (1-5): (9-25), wherein the selection range of the hydroxyapatite compound "70-90" can be, for example, 70wt.%, 75wt.%, 80wt.%, 85wt.% or 90wt.%, etc., the selection range of the binder "1-5" can be, for example, 1wt.%, 2wt.%, 3wt.%, 4wt.% or 5wt.%, etc., and the selection range of the conductive agent "9-25" can be, for example, 10wt.%, 15wt.%, 20wt.%, 23wt.% or 25wt.%, etc.

[0029] As an optional technical solution of the present application, the surface modification layer is a porous structure.

[0030] In the present application, the surface modification layer of the porous structure helps to achieve the insertion and removal of lithium ions, improves the interface stability, and promotes the improvement of the cycle performance of the battery based on the composite current collector.

[0031] In one embodiment, the average pore size of the surface modification layer is 0.1-5 μm, for example, 0.1 μm, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm or 5 μm.

[0032] In the present application, if the average pore size of the surface modification layer is too small, the resistance to lithium ion insertion and removal is large, resulting in poor cycle performance of the battery based on the composite current collector; if the average pore size of the surface modification layer is too large, the interface stability away from the pore-non-pore peripheral area is poor, resulting in poor cycle performance of the battery based on the composite current collector.

[0033] In one embodiment, the porosity of the surface modification layer is ≥40%, for example, it can be 40%, 60%, 80% or 90%, etc., and can be optionally 40-80%.

[0034] In the present application, if the porosity of the surface modification layer is too small, local lithium ion enrichment is not easy, the probability of interaction between anions and lithium ions is reduced, resulting in instability of the electrolyte-negative electrode interface, and failure to effectively suppress the generation of "dead lithium" and lithium dendrites, causing the cycle life of the lithium metal battery to decrease; if the porosity of the surface modification layer is greater than 80%, the mechanical stability of the modification layer deteriorates, and defects are easily formed during the cycle process, resulting in a decrease in the cycle life of the battery.

[0035] As an optional technical solution of the present application, the thickness of the surface modification layer on one side is 50-1000 nm, for example, it can be 50 nm, 100 nm, 300 nm, 500 nm, 700 nm or 900 nm, etc., and can be optionally 100-500 nm.

[0036] In the present application, if the thickness of the surface modification layer is too small, the cycle performance of the battery based on the composite current collector will not be significantly improved; if the thickness of the surface modification layer is too large, the resistance to lithium ion insertion and removal will be large, resulting in poor cycle performance of the battery based on the composite current collector.

[0037] As an optional technical solution of the present application, the material of the conductive layer includes metallic copper and / or copper alloy.

[0038] In the present application, the function of the conductive layer is to provide conductivity for the composite current collector.

[0039] In one embodiment, the copper alloy comprises a copper-lithium alloy.

[0040] In the present application, the copper-lithium alloy can supplement the lithium source during the use of the battery and improve the battery performance.

[0041] In one embodiment, the thickness of the conductive layer on one side is 0.5-3 μm, for example, 0.5 μm, 0.8 μm, 0.9 μm, 1 μm, 1.1 μm, 1.2 μm, 2 μm, 2.5 μm or 3 μm.

[0042] In one embodiment, the base film is a polymer film, and the material of the polymer film includes any one or a combination of at least two of polyethylene terephthalate (PET), polypropylene (PP), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), polyethylene (PE), polypropylene, polyvinyl chloride (PVC), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyphenylene sulfide (PPS), polyphenylene oxide (PPO), polystyrene (PS) or polyimide (PI).

[0043] In one embodiment, the base film has a thickness of 1-10 μm, for example, 1 μm, 3 μm, 15 μm, 7 μm or 9 μm.

[0044] In the present application, a base film with a thickness of 1-10 μm can take into account both the difficulty of the preparation process and the cost.

[0045] As an optional technical solution of the present application, an adhesive layer is further provided between the base film and the conductive layer.

[0046] In the present application, the role of the adhesive layer is to enhance the adhesive force between the base film and the conductive layer.

[0047] In one embodiment, the material of the bonding layer includes any one or a combination of at least two of aluminum oxide, silicon oxide, titanium oxide, nickel, chromium, titanium, nickel-chromium alloy, nickel-chromium-copper alloy, silicon-aluminum alloy, polyacrylic acid, polyacrylate, polyacrylamide or polyurethane.

[0048] In one embodiment, the thickness of the adhesive layer on one side is 1-100 nm, for example, 1 nm, 10 nm, 30 nm, 50 nm, 70 nm or 90 nm.

[0049] In a second aspect, the present application provides a method for preparing a composite current collector for a negative electrode-free lithium metal battery as described in the first aspect, the preparation method comprising the following steps:

[0050] (1) preparing a conductive layer on at least one surface of the base film to obtain a composite film having a conductive layer;

[0051] (2) coating the hydroxyapatite-based composite on the surface of the conductive layer, and drying to obtain the composite current collector for the negative electrode-free lithium metal battery.

[0052] The preparation method provided in this application is simple, easy to operate, and suitable for large-scale promotion.

[0053] It should be noted that the present application does not limit the preparation method of the base film. For example, it can be a melt-extrusion-biaxial stretching method.

[0054] As an optional technical solution of the present application, the method for preparing the conductive layer in step (1) includes any one of physical vapor deposition, electroplating or chemical plating, or a combination of at least two of them.

[0055] In one embodiment, the specific steps of coating in step (2) include:

[0056] A hydroxyapatite compound, a binder, a conductive agent and a pore-forming agent are mixed in an organic solvent to obtain a mixture, and then the mixture is coated on the surface of the conductive layer.

[0057] In one embodiment, based on the mass of the mixture, the mass fraction of the pore former is 5-15 wt.%, for example, 5 wt.%, 10 wt.%, or 15 wt.%.

[0058] In one embodiment, the pore former includes metallic aluminum and / or aluminum oxide.

[0059] In one embodiment, the average particle size of the pore former is 0.1-5 μm, for example, 0.1 μm, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm or 5 μm.

[0060] As an optional technical solution of the present application, the preparation method comprises the following steps:

[0061] (1) preparing a base film with a thickness of 1-10 μm, and then depositing a bonding layer with a thickness of 1-100 nm on both sides of the base film to obtain a composite film with a bonding layer;

[0062] (2) depositing a conductive layer with a thickness of 0.5-3 μm on both sides of the composite film to obtain a composite film containing a conductive layer and an adhesive layer;

[0063] (3) A hydroxyapatite compound, a conductive agent, a binder and a pore-forming agent are dispersed in an organic solvent to obtain a mixture, and the mixture is then coated on the surfaces of the conductive layers on both sides of the composite membrane, and then dried at 60-90°C (for example, 60°C, 70°C, 80°C or 90°C, etc.). After the mixture is dried, it is placed in a sodium hydroxide solution for removal of the pore-forming agent for 5-30 minutes (for example, 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes or 30 minutes, etc.), and then washed with water 2-3 times (for example, 2 times or 3 times), and finally dried at 60-90°C (for example, 60°C, 70°C, 80°C or 90°C, etc.) to obtain the composite current collector for the negative electrode-free lithium metal battery.

[0064] In a third aspect, the present application provides a negative electrode-free lithium metal battery, which includes a composite current collector for a negative electrode-free lithium metal battery as described in the first aspect, or a composite current collector for a negative electrode-free lithium metal battery prepared according to the preparation method described in the second aspect.

[0065] The numerical range described in this application includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to limited space and for the sake of simplicity, this application no longer exhaustively lists the specific point values ​​included in the range.

[0066] Compared with the related art, this application has the following beneficial effects:

[0067] (1) The present application constructs a surface modification layer on the surface of the composite current collector, the material of which is a hydroxyapatite-based composite. The electrostatic force between the phosphate in the hydroxyapatite-based composite and the lithium ions is strong, thereby forming a local lithium ion enrichment area, increasing the probability of interaction between anions and lithium ions, and forming more lithium ion coordinated anions. This modification layer helps to alleviate the negative electrode's rejection of free anions, stabilize the electrolyte-negative electrode interface, and the generated stable interface can reduce the lithium ion desolvation energy barrier, accelerate the interface transmission kinetics, and effectively inhibit the generation of "dead lithium" and lithium dendrites, thereby improving the cycle life of the lithium metal battery.

[0068] (2) The preparation method provided in this application is simple, easy to operate, and suitable for large-scale promotion.

[0069] Still other aspects will become apparent upon reading and understanding the accompanying drawings and detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0070] The accompanying drawings are used to provide a further understanding of the technical solution of this article and constitute a part of the specification. Together with the embodiments of this application, they are used to explain the technical solution of this article and do not constitute a limitation on the technical solution of this article.

[0071] FIG1 is a schematic diagram of the structure of the composite current collector prepared in Example 1 of the present application.

[0072] Among them, 1-base film; 2-first adhesive layer; 3-second adhesive layer; 4-first conductive layer; 5-second conductive layer; 6-first surface modification layer; 7-second surface modification layer. DETAILED DESCRIPTION

[0073] The technical solution of the present application is further described below through specific implementation methods. Those skilled in the art should understand that the embodiments are only used to help understand the present application and should not be regarded as specific limitations of the present application.

[0074] Example 1

[0075] This embodiment provides a composite current collector for a negative electrode-free lithium metal battery. The structural schematic diagram of the composite current collector is shown in FIG1 . The composite current collector for a negative electrode-free lithium metal battery is sequentially stacked with a second surface modification layer 7, a second conductive layer 5, a second bonding layer 3, a base film 1, a first bonding layer 2, a first conductive layer 4, and a first surface modification layer 6.

[0076] The first surface modification layer 6 and the second surface modification layer 7 are both made of a hydroxyapatite-based composite, which includes hydroxyapatite (non-ion-doped) with an average diameter of 50 nm and an aspect ratio of 30, a binder PVDF, a conductive agent graphene, and a pore-forming agent alumina (with an average particle size of 1 μm), and the mass ratio of hydroxyapatite, PVDF, and graphene is 80:2:18.

[0077] The thickness of the first surface modification layer 6 and the second surface modification layer 7 are both 200 nm, the average pore diameter of the first surface modification layer 6 and the second surface modification layer 7 are both 1 μm, and the porosity is both 60%;

[0078] The first conductive layer 4 and the second conductive layer 5 are both metal copper layers, and the thickness is 1 μm;

[0079] The first bonding layer 2 and the second bonding layer 3 are both made of nickel-chromium alloy, and both have a thickness of 5 nm;

[0080] The base film 1 is a PET film with a thickness of 4.5 μm.

[0081] This embodiment also provides a method for preparing the composite current collector for the negative electrode-free lithium metal battery, the preparation method comprising the following steps:

[0082] (1) A PET film with a thickness of 4.5 μm was prepared by a melt-extrusion-biaxial stretching method, and then a nickel-chromium alloy layer with a thickness of 5 nm was deposited on both sides of the PET film to obtain a composite film having a nickel-chromium alloy layer. The specific process conditions were: a nickel-chromium target (purity: 99.99%) was used as the target material, a power of 5 kW, an argon flow rate of 50 mL / min, a coating vacuum of 0.08 Pa, and a coating time of 1 s.

[0083] (2) The composite film having the nickel-chromium alloy layer is placed in a magnetron sputtering machine by a magnetron sputtering method, and a copper layer with a thickness of 50 nm is deposited on both sides of the composite film. The specific process conditions are: a copper target (purity: 99.99%) is used as the target material, the power is 12 kW, the argon flow rate is 50 mL / min, the coating vacuum is 0.08 Pa, and the coating time is 5 s; then the copper layer is electroplated by electroplating. The specific process conditions are: the electroplating solution includes 100 g / L copper sulfate, 120 g / L sulfuric acid, 46 mg / L HCl (hydrochloric acid), 15 mg / L sodium 3-mercapto-1-propane sulfonate, 0.6 mg / L 2-mercaptopyridine, and 100 mg / L polyethylene glycol (average molecular weight is 10,000). The temperature of the electroplating solution is 25°C, and the average cathode current density is 1.5 A / dm 2, the electroplating time is 5 minutes, and a metal copper layer with a thickness of 1 μm is prepared to obtain a composite film containing a metal copper layer and a nickel-chromium alloy layer; (3) hydroxyapatite (without ion doping), PVDF, graphene and alumina are dispersed in an organic solvent N-methylpyrrolidone to obtain a mixture with a solid content of 20wt.%, including solid phase 1 and solid phase 2, solid phase 1 includes hydroxyapatite (without ion doping), PVDF and graphene, and solid phase 2 is alumina, and alumina accounts for 10wt.% of the mass of the mixture; the mixture is coated on the surface of the metal copper layer on both sides of the composite film by a scraper to a thickness of 1 μm, and then dried in an oven at 80°C to obtain a coating with a thickness of 200nm, and then the composite film with the coating on the surface is placed in a sodium hydroxide solution with a mass fraction of 1wt.% for removal of alumina, the immersion time is 10 minutes, followed by washing with pure water twice, and finally drying in an oven at 80°C to obtain the composite current collector for the negative electrode-free lithium metal battery.

[0084] Example 2

[0085] The difference between this embodiment and Example 1 is that the first conductive layer and the second conductive layer are both copper-lithium alloy layers, and the specific process conditions are: a copper-lithium alloy target (the mass ratio of copper and lithium in the copper-lithium alloy is 9:1) is used as the target material, the power is 13kW, the argon flow rate is 60mL / min, the coating vacuum is 0.1Pa, and the coating time is 80s.

[0086] The rest of the preparation methods and parameters remained the same as in Example 1.

[0087] Example 3

[0088] The difference between this embodiment and embodiment 1 is that in step (3), the hydroxyapatite (non-ion doped) is replaced by hydroxyapatite modified by lithium ion doping, and the doping amount is 2%.

[0089] The rest of the preparation methods and parameters remained the same as in Example 1.

[0090] Example 4

[0091] The difference between this embodiment and embodiment 1 is that the hydroxyapatite (non-ion doped) in step (3) is replaced by hydroxyapatite modified by copper ion doping, and the doping amount is 2%.

[0092] The rest of the preparation methods and parameters remained the same as in Example 1.

[0093] Example 5

[0094] The difference between this embodiment and embodiment 1 is that the graphene in step (3) is replaced by carbon nanotubes.

[0095] The rest of the preparation methods and parameters remained the same as in Example 1.

[0096] Example 6

[0097] The difference between this embodiment and embodiment 1 is that PVDF is replaced by CMC in step (3).

[0098] The rest of the preparation methods and parameters remained the same as in Example 1.

[0099] Example 7

[0100] The difference between this embodiment and embodiment 1 is that in step (3), the mass ratio of hydroxyapatite (without ion doping), PVDF and graphene is 70:5:25.

[0101] The rest of the preparation methods and parameters remained the same as in Example 1.

[0102] Example 8

[0103] The difference between this embodiment and embodiment 1 is that in step (3), the mass ratio of hydroxyapatite (without ion doping), PVDF and graphene is 90:1:9.

[0104] The rest of the preparation methods and parameters remained the same as in Example 1.

[0105] Example 9

[0106] The difference between this embodiment and embodiment 1 is that the average particle size of the aluminum oxide in step (3) is adjusted to 0.1 μm, so that the average pore size of the surface modification layer is 0.1 μm.

[0107] The rest of the preparation methods and parameters remained the same as in Example 1.

[0108] Example 10

[0109] The difference between this embodiment and embodiment 1 is that the average particle size of the aluminum oxide in step (3) is adjusted to 5 μm, so that the average pore size of the surface modification layer is 5 μm.

[0110] The rest of the preparation methods and parameters remained the same as in Example 1.

[0111] Example 11

[0112] The difference between this embodiment and embodiment 1 is that the porosity of the surface modified layer is 40% by adjusting the content of aluminum oxide in the mixture of step (3) to 6 wt.% and the content of solid phase 1 to 14 wt.%.

[0113] The rest of the preparation methods and parameters remained the same as in Example 1.

[0114] Example 12

[0115] The difference between this embodiment and embodiment 1 is that the porosity of the surface modified layer is 80% by adjusting the content of aluminum oxide in the mixture of step (3) to 14 wt.% and the content of solid phase 1 to 6 wt.%.

[0116] The rest of the preparation methods and parameters remained the same as in Example 1.

[0117] Example 13

[0118] The difference between this embodiment and embodiment 1 is that the thickness of the mixture on the surface of the metal copper layer on both sides of the composite film is adjusted to 250 nm, so that the thickness of the surface modification layer is 50 nm.

[0119] The rest of the preparation methods and parameters remained the same as in Example 1.

[0120] Example 14

[0121] The difference between this embodiment and embodiment 1 is that the thickness of the mixture on the surface of the metal copper layer on both sides of the composite film is adjusted to 5000 nm, so that the thickness of the surface modification layer is 1000 nm.

[0122] The rest of the preparation methods and parameters remained the same as in Example 1.

[0123] Example 15

[0124] The difference between this embodiment and embodiment 1 is that the content of aluminum oxide in the mixture of step (3) is adjusted to 18 wt.%, and the content of solid phase 1 is adjusted to 2 wt.%.

[0125] The rest of the preparation methods and parameters remained the same as in Example 1.

[0126] Example 16

[0127] The difference between this embodiment and embodiment 1 is that the average pore size of the aluminum oxide in step (3) is adjusted to 0.08 μm, so that the average pore size of the surface modification layer is 0.08 μm.

[0128] The rest of the preparation methods and parameters remained the same as in Example 1.

[0129] Example 17

[0130] The difference between this embodiment and embodiment 1 is that the average pore size of the aluminum oxide in step (3) is adjusted to 6 μm, so that the average pore size of the surface modification layer is 6 μm.

[0131] The rest of the preparation methods and parameters remained the same as in Example 1.

[0132] Example 18

[0133] The difference between this embodiment and embodiment 1 is that the content of aluminum oxide in the mixture of step (3) is adjusted to 4 wt.%, and the content of solid phase 1 is adjusted to 16 wt.%, so that the porosity of the surface modified layer is 30%.

[0134] The rest of the preparation methods and parameters remained the same as in Example 1.

[0135] Example 19

[0136] The difference between this embodiment and embodiment 1 is that the thickness of the mixture on the surface of the metal copper layer on both sides of the composite film is adjusted to 150 nm, so that the thickness of the surface modification layer is 30 nm.

[0137] The rest of the preparation methods and parameters remained the same as in Example 1.

[0138] Example 20

[0139] The difference between this embodiment and embodiment 1 is that the thickness of the mixture on the surface of the metal copper layer on both sides of the composite film is adjusted to 6000 nm, so that the thickness of the surface modification layer is 1200 nm.

[0140] The rest of the preparation methods and parameters remained the same as in Example 1.

[0141] Example 21

[0142] The difference between this embodiment and embodiment 1 is that the aspect ratio of hydroxyapatite is 60.

[0143] The rest of the preparation methods and parameters remained the same as in Example 1.

[0144] Comparative Example 1

[0145] The difference between this comparative example and Example 1 is that no surface modification layer is provided, that is, step (3) is not performed.

[0146] The rest of the preparation methods and parameters remained the same as in Example 1.

[0147] Performance Testing

[0148] The composite current collectors prepared in the above examples and comparative examples were made into negative electrode-free lithium metal batteries, and the cycle performance tests were carried out.

[0149] Preparation of a negative electrode-free lithium metal battery: For the positive electrode, the positive electrode current collector is aluminum foil (thickness of 12 μm), and the positive electrode material is lithium iron phosphate; for the negative electrode, the negative electrode current collector is provided by the above embodiment and comparative example; for the separator, a polypropylene separator (thickness of 20 μm) is used; for the electrolyte, the electrolyte includes 1 mol·L -1% lithium bis(trifluoromethanesulfonyl)imide and 2wt.% lithium nitrate, the electrolyte solvent includes 1,2-dimethoxymethane and 1,3-dioxolane, the volume ratio of the two is 1:1; using the above materials, a negative electrode-free lithium metal battery is assembled, and the battery capacity is 1Ah.

[0150] Cycle performance test: The negative electrode-free lithium metal battery prepared above was placed in a cycle performance test device, and a charge and discharge cycle experiment was carried out at a rate of 0.2C and a cycle charge and discharge voltage range of 3.0V-3.8V. The battery capacity retention rate after 100 cycles of charge and discharge was recorded.

[0151] The test results are shown in Table 1.

[0152] Table 1

[0153] analyze:

[0154] As can be seen from the above table, compared with traditional composite copper current collectors, the composite copper current collector provided by the present application can significantly improve the cycle performance of the battery when used in a negative electrode-free lithium metal battery.

[0155] It can be seen from the data results of Example 1 and Example 2 that the use of copper-lithium alloy as the conductive layer can replenish the lithium source during the use of the battery and improve the battery performance.

[0156] It can be seen from the data results of Example 1 and Examples 3-4 that ion doping of hydroxyapatite helps to improve the structural stability and dispersibility of hydroxyapatite, enhance its stability and uniform dispersion in the modified layer, thereby improving the performance of the modified layer and improving the battery cycle performance.

[0157] It can be seen from the data results of Example 1, Example 15 and Example 18 that if the content of aluminum oxide in the mixture is too little, the porosity of the surface modification layer is too small, and local lithium ion enrichment is not easy, which reduces the probability of interaction between anions and lithium ions, resulting in instability of the electrolyte-negative electrode interface, and cannot effectively inhibit the generation of "dead lithium" and lithium dendrites, causing the cycle life of the lithium metal battery to be reduced; if the content of aluminum oxide in the mixture is too high, the porosity of the surface modification layer is greater than the optional range, the mechanical stability of the modification layer deteriorates, and defects are easily formed during the cycle process, resulting in a reduced cycle life of the battery.

[0158] It can be seen from the data results of Example 1 and Examples 16-17 that if the average pore size of the surface modification layer is too small, the resistance to lithium ion insertion and removal is large, resulting in poor cycle performance of the battery based on the composite current collector; if the average pore size of the surface modification layer is too large, the interface stability away from the pore-non-pore peripheral area is poor, resulting in poor cycle performance of the battery based on the composite current collector.

[0159] It can be seen from the data results of Example 1 and Examples 19-20 that if the thickness of the surface modification layer is too small, the cycle performance of the battery based on the composite current collector will not be significantly improved; if the thickness of the surface modification layer is too large, the resistance to lithium ion insertion and removal will be large, resulting in poor cycle performance of the battery based on the composite current collector.

[0160] It can be seen from the data results of Example 1 and Example 21 that if the aspect ratio of hydroxyapatite is not too high, it will not be easy to be uniformly dispersed in the modified layer, resulting in a poor cycle life of the battery.

[0161] It can be seen from the data results of Example 1 and Comparative Example 1 that if a surface modification layer is not provided on the surface of the composite current collector, it is difficult to alleviate the negative electrode's rejection of free anions, the generation of "dead lithium" and lithium dendrites cannot be effectively suppressed, and the cycle life of the lithium metal battery is significantly deteriorated.

[0162] The applicant declares that while the above-mentioned embodiments are used to illustrate the process of the present application, the present application is not limited to the above-mentioned process steps, which does not mean that the present application must rely on the above-mentioned process steps in order to be implemented. Those skilled in the art should understand that any improvements to the present application, equivalent replacements for the raw materials used in the present application, addition of auxiliary components, and selection of specific methods, etc., fall within the scope of protection and disclosure of the present application.

Claims

1. A composite current collector for a negative electrode-free lithium metal battery, wherein: The composite current collector for the negative electrode-free lithium metal battery comprises: Basement membrane; A conductive layer disposed on at least one surface of the base film; A surface modification layer is disposed on a surface of the conductive layer on a side relatively far from the base film, wherein a material of the surface modification layer includes a hydroxyapatite-based composite.

2. The composite current collector for a negative electrode-free lithium metal battery according to claim 1, wherein: The hydroxyapatite-based composite comprises a hydroxyapatite compound, a binder and a conductive agent.

3. The composite current collector for a negative electrode-free lithium metal battery according to claim 1 or 2, wherein: The hydroxyapatite compound includes at least one ion-doped modified hydroxyapatite.

4. The composite current collector for a negative electrode-free lithium metal battery according to claim 3, wherein: In the ion-doped modified hydroxyapatite, the doped ions include any one of lithium ions, copper ions, magnesium ions, zinc ions or strontium ions, or a combination of at least two of them.

5. The composite current collector for a negative electrode-free lithium metal battery according to claim 3 or 4, wherein: In the ion-doped modified hydroxyapatite, the doping amount of ions accounts for 0-5wt.% of the total mass of the ion-doped modified hydroxyapatite; Optionally, the average diameter of the hydroxyapatite compound is ≤100 nm, and may be 30-60 nm; Optionally, the aspect ratio of the hydroxyapatite compound is 5-50; Optionally, the mass ratio of the hydroxyapatite compound, the binder and the conductive agent is (70-90):(1-5):(9-25).

6. The composite current collector for a negative electrode-free lithium metal battery according to any one of claims 1 to 5, wherein: The surface modification layer is a porous structure; Optionally, the average pore size of the surface modification layer is 0.1-5 μm; Optionally, the porosity of the surface modification layer is ≥40%, and can be 40-80%.

7. The composite current collector for a negative electrode-free lithium metal battery according to any one of claims 1 to 6, wherein: The thickness of the surface modification layer on one side is 50-1000 nm, and can be optionally 100-500 nm.

8. The composite current collector for a negative electrode-free lithium metal battery according to any one of claims 1 to 7, wherein: The material of the conductive layer includes metallic copper and / or copper alloy; Optionally, the copper alloy comprises a copper-lithium alloy; Optionally, the thickness of the conductive layer on one side is 0.5-3 μm, and optionally 0.8-1.2 μm; Optionally, the base film is a polymer film, and the material of the polymer film includes any one or a combination of at least two of polyethylene terephthalate, polypropylene, polybutylene terephthalate, polyethylene naphthalate, polyethylene, polypropylene, polyvinyl chloride, polyvinylidene fluoride, polytetrafluoroethylene, polyphenylene sulfide, polyphenylene oxide, polystyrene or polyimide; Optionally, the base film has a thickness of 1-10 μm.

9. The composite current collector for a negative electrode-free lithium metal battery according to any one of claims 1 to 8, wherein: An adhesive layer is also provided between the base film and the conductive layer; Optionally, the material of the bonding layer includes any one or a combination of at least two of aluminum oxide, silicon oxide, titanium oxide, nickel, chromium, titanium, nickel-chromium alloy, nickel-chromium-copper alloy, silicon-aluminum alloy, polyacrylic acid, polyacrylate, polyacrylamide or polyurethane; Optionally, the thickness of the adhesive layer on one side is 1-100 nm.

10. A method for preparing a composite current collector for a negative electrode-free lithium metal battery according to any one of claims 1 to 9, comprising the following steps: (1) preparing a conductive layer on at least one surface of the base film to obtain a composite film having a conductive layer; (2) coating the hydroxyapatite-based composite on the surface of the conductive layer, and drying to obtain the composite current collector for the negative electrode-free lithium metal battery.

11. The preparation method according to claim 10, wherein: The preparation method of the conductive layer in step (1) includes any one of physical vapor deposition, electroplating or chemical plating, or a combination of at least two of them.

12. The preparation method according to claim 10 or 11, wherein: The specific steps of coating in step (2) include: A hydroxyapatite compound, a binder, a conductive agent and a pore-forming agent are mixed in an organic solvent to obtain a mixture, and then the mixture is coated on the surface of the conductive layer.

13. The preparation method according to claim 12, wherein: Based on the mass of the mixture, the mass fraction of the pore former is 5-15wt.%; Optionally, the pore former includes metallic aluminum and / or aluminum oxide; Optionally, the average particle size of the pore former is 0.1-5 μm.

14. The preparation method according to any one of claims 10 to 13, comprising the following steps: (1) preparing a base film with a thickness of 1-10 μm, and then depositing a bonding layer with a thickness of 1-100 nm on both sides of the base film to obtain a composite film with a bonding layer; (2) depositing a conductive layer with a thickness of 0.5-3 μm on both sides of the composite film to obtain a composite film containing a conductive layer and an adhesive layer; (3) A hydroxyapatite compound, a conductive agent, a binder and a pore-forming agent are dispersed in an organic solvent to obtain a mixture, and the mixture is then coated on the surface of the conductive layer on both sides of the composite membrane, and then dried at 60-90° C. After the mixture is dried, it is placed in a sodium hydroxide solution for 5-30 minutes to remove the pore-forming agent, and then washed with water for 2-3 times, and finally dried at 60-90° C. to obtain the composite current collector for the negative electrode-free lithium metal battery.

15. A negative electrode-free lithium metal battery, wherein: The negative electrode-free lithium metal battery comprises the composite current collector for a negative electrode-free lithium metal battery as described in any one of claims 1 to 9, or the composite current collector for a negative electrode-free lithium metal battery prepared by the preparation method according to any one of claims 10 to 14.

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