Composite negative electrode current collector, preparation method and application

Abstract

The invention discloses a composite negative electrode current collector, a preparation method and application, the composite negative electrode current collector comprises a substrate layer and a graphene oxide layer coated on the surface of the substrate layer, the graphene oxide layer is a porous layer, the lithium ion conductivity of the graphene oxide layer is greater than or equal to 10 <-4 > S / cm, and the electronic conductivity of the graphene oxide layer is less than or equal to 10 <-8 > S / cm. The graphene oxide layer promotes uniform deposition of lithium ions by virtue of high lithium ion conductivity, and the insulation characteristic (the electronic conductivity is less than or equal to 10 <-8 > S / cm) of the graphene oxide layer inhibits electron conduction, so that lithium is prevented from being deposited at an unexpected position, the cycle performance and coulombic efficiency of the battery are improved, and the service life of the battery is remarkably prolonged.

Description

Technical Field

[0001] The present invention relates to the field of lithium metal batteries without a negative electrode, and in particular to a composite negative electrode current collector, a preparation method and an application thereof. Background Art

[0002] A lithium metal battery without a negative electrode is a high-energy density battery system that completely abandons a pre-set lithium metal negative electrode and relies only on the positive electrode active material to provide a lithium source. Its core principle is that during the first charging process, lithium ions are removed from the positive electrode (such as high-nickel ternary materials, lithium cobaltate, etc.), pass through the electrolyte, and are in-situ reduced to metallic lithium on the surface of the negative electrode current collector to form a lithium negative electrode. During subsequent charge and discharge processes, lithium is reversibly deposited / stripped between the current collector and the positive electrode. Compared with traditional lithium metal batteries, the design without a negative electrode significantly simplifies the battery structure, and the theoretical energy density can be increased by 30% - 50%. At the same time, it reduces the material cost and is compatible with existing lithium-ion battery production lines.

[0003] However, the commercialization of this technology is limited by the core contradiction of the negative electrode current collector: Although traditional copper and aluminum current collectors have high electronic conductivity, their surface lithium-phobicity results in a high lithium nucleation barrier. The lithium metal deposited for the first time is distributed in a dendritic or island-like shape, causing local electric field distortion and electrolyte decomposition. At the same time, the high electronic conductivity of the current collector promotes the preferential reduction of lithium ions on its surface rather than uniformly diffusing to the entire electrode interface, resulting in uneven lithium layer thickness and dead lithium accumulation, and a sharp decline in capacity during the cycling process. Summary of the Invention

[0004] In order to overcome the defects in the prior art, the first object of the present invention is to provide a composite negative electrode current collector, the second object of the present invention is to provide a preparation method of the above composite negative electrode current collector, the third object of the present invention is a lithium metal battery without a negative electrode including the above composite negative electrode current collector, and the third object of the present invention is to provide an electrical device including the above lithium metal battery without a negative electrode.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] In a first aspect, a composite negative electrode current collector includes a base layer and a graphene oxide layer coated on the surface of the base layer. The graphene oxide layer is a porous layer, and its lithium ion conductivity ≥ 10 -4 S / cm, and the electronic conductivity ≤ 10 -8 S / cm.

[0007] The porous structure of the graphene oxide layer provides a large number of uniform nucleation sites for lithium ion deposition, guides the uniform deposition of lithium ions, and effectively inhibits the formation of lithium dendrites. At the same time, the high lithium ion conductivity (≥ 10 -4(S / cm) enables lithium ions to diffuse rapidly and uniformly to the surface of the current collector, reducing the local lithium ion concentration difference and avoiding the growth of lithium dendrites caused by uneven concentration; while the low electronic conductivity (≤10 -8 (S / cm) prevents electrons from conducting on the surface of the graphene oxide layer, forcing lithium ions to obtain electrons and be reduced and deposited only at the substrate interface, further ensuring the uniformity and controllability of lithium deposition.

[0008] Uniform lithium deposition greatly reduces the generation of "dead lithium" and reduces the loss of active lithium during the charge-discharge cycle of the battery. This enables the battery to maintain a high capacity retention rate and extend the cycle life of the battery.

[0009] Inhibiting the growth of lithium dendrites can effectively avoid the risk of battery short circuit caused by dendrites piercing the separator, significantly improving the safety performance of the battery. At the same time, the porous structure of the graphene oxide layer can also buffer the volume change during the lithium deposition and stripping process, reducing the damage to the electrode structure, and further ensuring the safety and stability of the battery during use.

[0010] The porous graphene oxide layer increases the contact area between the current collector and the electrolyte, helps the infiltration of the electrolyte, and optimizes the ion transport at the electrode / electrolyte interface. In addition, the functional groups on its surface interact with the electrolyte to form a stable solid electrolyte interface (SEI) film, reducing the interface resistance and improving the charge-discharge efficiency of the battery.

[0011] The structure of this composite negative current collector is relatively simple and has a certain compatibility with the selection of the base layer material. A suitable base layer, such as copper foil or other conductive materials, can be selected according to different application scenarios, which is convenient for combination with the existing battery manufacturing process.

[0012] Preferably, the surface of the graphene oxide layer contains at least one functional group of carboxyl, hydroxyl or epoxy group.

[0013] The functional groups on the surface of graphene oxide have strong polarity and can form hydrogen bonds or other interactions with polar molecules in the electrolyte, thereby reducing the surface tension between the electrolyte and the graphene oxide layer and improving the wettability of the electrolyte on the surface of the current collector. Good wettability enables the electrolyte to spread more uniformly on the surface of the current collector, ensuring the uniform distribution of lithium ions throughout the electrode and creating conditions for subsequent uniform lithium deposition.

[0014] The oxygen atoms in the functional groups have lone pairs of electrons and can complex with lithium ions, providing an additional transport channel for lithium ions. This complexation - decomplexation process helps the migration of lithium ions in the graphene oxide layer. Combining with the high lithium ion conductivity of the graphene oxide layer itself, it further accelerates the diffusion rate of lithium ions, enables lithium ions to reach the deposition site more efficiently, reduces the local oversaturation of lithium ion concentration, and inhibits the formation of lithium dendrites.

[0015] During the first charge and discharge process of the battery, these functional groups can react chemically with lithium salts (such as LiPF6) in the electrolyte and participate in the formation of the solid electrolyte interface (SEI) film. The formed SEI film has good ionic conductivity and stability, which can effectively inhibit the continuous decomposition of the electrolyte, protect the electrode materials, and extend the cycle life of the battery. For example, carboxyl and hydroxyl functional groups react with LiPF6 to form an SEI film rich in components such as LiF and Li2O, which improves the performance of the SEI film.

[0016] Functional groups can enhance the interaction between the graphene oxide layer and the substrate layer through chemical bonds or hydrogen bonds. This helps maintain the structural integrity of the graphene oxide layer during the charge and discharge process, buffers the volume change caused by lithium deposition and stripping, and prevents the graphene oxide layer from falling off the substrate layer or its own structure from being damaged, thereby ensuring the long-term stability and reliability of the composite negative electrode current collector.

[0017] Preferably, the thickness of the graphene oxide layer is 1 to 10 μm. Setting the thickness of the graphene oxide layer to 1 to 10 μm is the result of comprehensive consideration of performance and process. From the performance point of view, this thickness range is crucial to maintaining the balance of key characteristics of the graphene oxide layer. The appropriate thickness can effectively block electronic conduction, guide lithium ions to be reduced at the substrate interface, and inhibit the longitudinal growth of dendrites. If the thickness is less than 1 μm, the electronic insulation is poor, it is difficult to block electrons, and it is easy to cause surface lithium deposition and dendrite formation; while if it is greater than 10 μm, although the electronic insulation is enhanced, the ion transfer resistance increases, which may cause local lithium ion aggregation and promote dendrite formation. In terms of preparation technology, common coating methods such as spin coating and spray coating show good operability and repeatability when the thickness is controlled at 1 to 10 μm. By adjusting parameters such as spin coating speed, time, and concentration of graphene oxide dispersion, the thickness can be accurately controlled, which facilitates large-scale production. In addition, this thickness range takes into account both cost and efficiency while ensuring battery performance. A too thick graphene oxide layer will increase the amount of material used and the preparation time, raising costs; a too thin graphene oxide layer will not be able to fully exert its performance advantages, leading to a decline in the overall performance of the battery. The thickness range of 1 to 10 μm achieves an optimal balance between cost and performance.

[0018] Further preferably, a lithium-philic layer is provided between the base layer and the graphene oxide layer, and the lithium-philic layer comprises lithium-philic nanoparticles and a binder.

[0019] The lithiophilic nanoparticles in the lithiophilic layer, through alloying, reducing interfacial energy and charge adsorption, greatly reduce the energy barrier that lithium needs to overcome when it begins to deposit on the surface of the substrate layer, that is, reduce the lithium nucleation overpotential, making it easier for lithium to nucleate uniformly on the surface of the substrate layer, reducing the initial formation of lithium dendrites. The lithiophilic nanoparticles are evenly distributed in the binder, and many uniform nucleation sites are constructed on the surface of the substrate layer. These sites provide orderly deposition locations for lithium ions, guide lithium ions to gather regularly on the surface of the lithiophilic layer, avoid random deposition, and promote uniform deposition of lithium. The binder firmly binds the lithiophilic nanoparticles and is closely connected to the substrate layer, enhancing the bonding force between the lithiophilic layer and the substrate layer. During the battery charging and discharging process, in the face of the stress generated by lithium deposition and stripping, the lithiophilic layer can firmly adhere to the substrate layer to maintain the stability of the composite negative electrode current collector structure.

[0020] The lithium-philic layer creates good starting conditions for lithium deposition by reducing the nucleation overpotential and providing uniform nucleation sites. The graphene oxide layer, with its high lithium ion conductivity, promotes the rapid and uniform diffusion of lithium ions to the nucleation sites of the lithium-philic layer. The two work together to ensure uniform nucleation and uniform distribution of surrounding lithium ions during lithium deposition, avoiding excessive local lithium concentration that causes dendrite growth.

[0021] The lithium-philic nanoparticles in the lithium-philic layer may have electronic conduction risks, while the electronic insulation of the graphene oxide layer can effectively block the migration of electrons to the surface, forcing lithium ions to obtain electrons and reduce and deposit only at the interface between the substrate and the lithium-philic layer. At the same time, the high ionic conductivity of the graphene oxide layer ensures that lithium ions can smoothly pass through the layer to reach the interface of the lithium-philic layer to participate in the reaction, synergistically inhibiting the longitudinal growth of dendrites.

[0022] The structure of the lithium-philic layer has a certain flexibility, which can buffer the micro-strain caused by lithium deposition. The porous structure of the graphene oxide layer can absorb the macroscopic volume change and prevent the coating from cracking due to the volume change of lithium. The two work together to maintain the structural integrity of the composite current collector during the cycle.

[0023] Preferably, the lithium-philic nanoparticles are selected from at least one of zinc, tin, magnesium, silicon, indium, gold, silver or their oxides.

[0024] The binder is selected from at least one of polydopamine, polyvinylidene fluoride, carboxymethyl cellulose, styrene-butadiene rubber, polyvinyl pyrrolidone, polymethyl methacrylate, polyacrylonitrile, polyacrylic acid, polyvinyl alcohol, sodium alginate, β-cyclodextrin polymer, polypropylene emulsion and polytetrafluoroethylene.

[0025] Preferably, the thickness of the lithium-philic layer is 1 to 10 μm. The thickness of the lithium-philic layer is set to 1 to 10 μm mainly based on comprehensive considerations of battery performance, structural stability, and feasibility of the preparation process. In actual production, it can be adjusted according to different application environments.

[0026] In a second aspect, a method for preparing the above-mentioned composite negative current collector includes the following steps:

[0027] Coat the surface of the base layer with a graphene oxide dispersion liquid, and after drying, form a graphene oxide layer to obtain the composite negative current collector.

[0028] A method for preparing the above-mentioned composite negative current collector includes the following steps:

[0029] Coat the surface of the base layer with a lithiumophilic layer slurry, and after drying, form a lithiumophilic layer. The lithiumophilic layer slurry includes lithiumophilic nanoparticles and a binder;

[0030] Coat the surface of the lithiumophilic layer with a graphene oxide dispersion liquid, and after drying, form a graphene oxide layer to obtain the composite negative current collector.

[0031] Preferably, the preparation method includes the following steps:

[0032] Base layer pretreatment: Select a copper foil as the base layer, wash it with a 1M hydrochloric acid solution to remove surface oxides, then rinse it with acetone to remove oil stains and impurities, and dry it for later use.

[0033] Preparation of lithiumophilic layer slurry: Mix lithiumophilic nanoparticles such as zinc and tin with binders such as polydopamine and polyvinylidene fluoride in proportion, add an appropriate amount of solvent, and perform ultrasonic dispersion to form a uniform lithiumophilic layer slurry. The mass concentration of lithiumophilic nanoparticles in the lithiumophilic layer slurry is 1 - 3 mg / mL.

[0034] Coating and drying of the lithiumophilic layer: Use the spin coating or spraying method to coat the lithiumophilic layer slurry on the surface of the pretreated base layer. When spin coating, control the rotation speed at 3000 - 4000 rpm and the time at 80 - 120 seconds; when spraying, adjust the pressure and distance. After coating, dry it in an oven at 60 - 80 °C to form a lithiumophilic layer.

[0035] Preparation of graphene oxide dispersion liquid: Add graphene oxide powder to solvents such as ethanol, and perform ultrasonic treatment for 6 - 12 hours to prepare a graphene oxide dispersion liquid with a concentration of 2 - 5 mg / mL.

[0036] Coating and drying of the graphene oxide layer: Coat the graphene oxide dispersion liquid on the surface of the lithiumophilic layer, with a spin coating rotation speed of 3000 - 4000 rpm and a time of 80 - 120 seconds. After coating, dry it under vacuum conditions at 70 - 90 °C to obtain the composite negative current collector.

[0037] In a third aspect, a lithium metal battery without a negative electrode having a composite negative current collector includes a positive electrode, a composite negative current collector, a separator, and an electrolyte.

[0038] Preferably, the positive electrode material is selected from one or more of lithium cobaltate, lithium manganate, ternary nickel cobalt manganese oxide, lithium nickel manganate, lithium iron phosphate, and lithium manganese iron phosphate. Further preferably, the positive electrode material is ternary nickel cobalt manganese oxide. These materials can release lithium ions during battery charging and receive lithium ions for re-embedding during discharging, and are the key part for providing a lithium source.

[0039] Preferably, the separator is selected from polypropylene and polyethylene separators. Further preferably, the separator is a polypropylene separator. The main function of the separator is to separate the positive and negative electrodes to prevent short circuits, while allowing lithium ions to pass through to ensure the smoothness of the ion conduction path inside the battery.

[0040] Preferably, the organic solvent of the electrolyte can be selected from one or more of organic esters, ethers, sulfones, or nitrile solvents, preferably organic ester solvents, more preferably one or more of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, 1,4-butyrolactone, methyl formate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, ethyl butyrate, methyl difluoroacetate, ethyl difluoroacetate, methyl trifluoroethyl carbonate, or bis(2,2,2-trifluoroethyl) carbonate. The electrolyte also contains a lithium salt, such as lithium hexafluorophosphate (LiPF6), which provides a carrier for lithium ions to ensure ion transport inside the battery and enables the battery to carry out charge and discharge reactions normally.

[0041] Fourthly, an electrical device includes the above-mentioned lithium metal-free battery without a negative electrode.

[0042] Due to the application of the above technical solutions, the present invention has the following advantages compared with the prior art:

[0043] 1. The lithiophilic layer effectively reduces the lithium nucleation overpotential and provides uniform nucleation sites, while the graphene oxide layer promotes the uniform deposition of lithium ions by virtue of its high lithium ion conductivity. Its insulating property (electronic conductivity ≤ 10 -8 S / cm) inhibits electron conduction and avoids lithium deposition at unexpected positions, synergistically improving the battery cycle performance and Coulomb efficiency with the lithiophilic layer, and significantly extending the battery service life.

[0044] 2. It effectively inhibits the growth of lithium dendrites, avoids the short circuit caused by dendrites piercing the separator, and greatly improves the safety of battery use. The insulating property of the graphene oxide layer further reduces the safety risk caused by abnormal electron conduction.

[0045] 3. The layers act synergistically to maintain the stability of the battery structure, buffer the volume change of lithium deposition / stripping, and enhance the stability of the electrode / electrolyte interface.

[0046] 4. The two-step spin coating method is used to coat the lithiumophilic layer and the graphene oxide layer respectively, which can accurately control the thickness and quality of each layer. Coating the lithiumophilic layer first ensures its tight bonding with the substrate, and then coating the graphene oxide layer can optimize the interfacial properties. Moreover, this process is compatible with existing production lines and does not require large-scale equipment modification, further reducing costs.

[0047] To make the above and other objects, features, and advantages of the present invention more obvious and understandable, the following specifically provides preferred embodiments and, in conjunction with the accompanying drawings, makes a detailed description as follows. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] To more clearly illustrate the technical solutions in the embodiments of the present invention or in the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0049] Figure 1 It is a schematic diagram of lithium nucleation and deposition on the current collector of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0050] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0051] Embodiment 1:

[0052] This embodiment discloses a composite negative electrode current collector, including a base layer and a graphene oxide layer (GO coating) coated on the surface of the base layer. The graphene oxide layer is a porous layer, and its lithium ion conductivity ≥ 10 -4 S / cm, and the electron conductivity ≤ 10 -8 S / cm.

[0053] The lithium ion conductivity measures the bulk resistance of the symmetric cell (Li|GO layer|Li) through electrochemical impedance spectroscopy (EIS), and calculates the conductivity in combination with the thickness. The electron conductivity directly measures the transverse resistivity of the GO layer by the four-probe method or the van der Pauw method.

[0054] The surface of the graphene oxide layer contains at least one functional group among carboxyl, hydroxyl, or epoxy groups. The thickness of the graphene oxide layer is 1 - 10 μm.

[0055] In a preferred embodiment, a lithium-philic layer is further provided between the base layer and the graphene oxide layer, and the lithium-philic layer comprises lithium-philic nanoparticles and a binder.

[0056] The lithium-philic nanoparticles are selected from at least one of zinc, tin, magnesium, silicon, indium, gold, silver or their oxides, and the binder is selected from at least one of polydopamine, polyvinylidene fluoride, carboxymethyl cellulose, styrene-butadiene rubber, polyvinylpyrrolidone, polymethyl methacrylate, polyacrylonitrile, polyacrylic acid, polyvinyl alcohol, sodium alginate, β-cyclodextrin polymer, polypropylene emulsion, polytetrafluoroethylene. When the lithium-philic nanoparticles are selected from zinc and the binder is selected from polydopamine, poly-dopamine-coated zinc nanoparticles (Zn@PDA) can be formed.

[0057] The thickness of the lithium-philic layer is 1-10 μm.

[0058] See Figure 1 As shown in the schematic diagram of lithium nucleation and deposition on the coated current collector. The copper foil surface has lithium-phobicity and heterogeneity, resulting in a large nucleation barrier for the lithium metal coating on the bare copper surface, and thus a relatively high overpotential, making the deposition of lithium ions on the copper foil surface random and uneven. As can be seen from Figure 1 (a), after a long time of cycling, dendritic lithium dendrites are formed by lithium deposition.

[0059] If a lithium-philic material is used as a nanocrystal seed to pretreat the bare copper, the nucleation barrier of lithium can be reduced, promoting uniform lithium deposition. As Figure 1 (b) shows, for the copper current collector coated with lithium-philic Zn@PDA, its lithium nucleation energy barrier is relatively low, and during repeated cycling, the growth of lithium dendrites is uniform and the number is small.

[0060] When a GO coating is applied on Zn@PDA, this coating has ion-conducting and electrical insulating properties, and at the same time improves the wettability of the composite current collector to the electrolyte. Therefore, as Figure 1 (c) shows, on the copper foil with a matrix composed of lithium-philic zinc nanoparticles and coated with GO, the nucleation overpotential is reduced to the lowest, and the lithium deposition presents a smooth and dense state.

[0061] This embodiment also discloses a preparation method of the above composite negative current collector, including the following steps:

[0062] Synthesis of polydopamine (PDA): PDA is prepared by the self-polymerization of dopamine (DA). Take 400 mg of dopamine, dissolve it in 10 mM, pH = 8.5 tris(hydroxymethyl)aminomethane hydrochloride (Tris-HCl) buffer solution, and mechanically stir at room temperature for 6 hours to form a solution with a concentration of 2 mg / mL. Subsequently, the solution is centrifuged and washed successively with ethanol and deionized water to obtain PDA.

[0063] Synthesis of polydopamine-coated zinc nanoparticles (Zn@PDA): 10 mg of PDA was dispersed in 10 ml of deionized water by ultrasonic wave. Then, a 2 mg / ml ZnNO3 solution was added successively, and 1% sodium citrate (Na3C6H5O7) was further added. The mixture was stirred in a water bath at 60 °C. After the reaction, it was centrifuged and washed with deionized water. Finally, the synthesized Zn@PDA was dispersed in deionized water.

[0064] Preparation of graphene oxide suspension: First, monolayer graphene oxide (GO) was placed in an oven filled with argon at 60 °C for 12 hours to remove moisture. Then, 0.025 g of the treated GO was dispersed in ethanol by ultrasonic wave for 6 hours to obtain a solution with a concentration of 2.5 mg / mL. Subsequently, it was continuously stirred for 12 hours to obtain a uniform graphene oxide suspension without conductive and binder materials.

[0065] Preparation of Zn@PDA-GO coated copper electrode: The copper foil was cut into discs with a diameter of 19 mm, washed with 1 M hydrochloric acid and acetone to remove surface contaminants, and dried to be used as a control and a coating substrate. A two-step coating method was adopted. First, Zn@PDA was coated with a spin coater at a speed of 3800 rpm for 100 seconds, and then dried in an oven after coating. Then, the graphene oxide suspension was coated on the surface of Zn@PDA, and the surface uniformity and thickness of the film were optimized by adjusting the concentrations of Zn@PDA and the graphene oxide suspension. Finally, the coated copper current collector was placed in a vacuum oven at 80 °C to dry the solvent. The composite negative current collector (Cu|Zn@PDA-GO) was obtained. Before assembling the battery, the dried electrode was transferred to a glove box where the oxygen and moisture levels were both maintained below 0.1 ppm and left standing for 12 hours.

[0066] This example also discloses a lithium metal battery without a negative electrode, which includes the following preparation steps: NCM811 was selected as the positive electrode material, and the above-prepared composite negative current collector (Cu|Zn@PDA-GO) was used as the negative current collector. The mass loading of Zn@PDA is 0.150 mg / cm 2 , which means that during the preparation of the composite negative current collector, the mass of polydopamine-coated zinc nanoparticles (Zn@PDA) loaded on the surface of each square centimeter of the current collector (such as copper foil) is 0.150 mg. The mass loading of GO is 0.134 mg / cm 2. Celgard 2325 (a battery separator produced by Celgard, USA) was used as the separator. Ethylene carbonate (EC) and diethyl carbonate (DEC) were fully mixed at a volume ratio of 1:1 as the organic solvent. Lithium hexafluorophosphate (LiPF6) was added to this organic solvent, and 5 wt% fluoroethylene carbonate (FEC) was added to prepare a 1 M LiPF6 solution. Subsequently, a coin cell was assembled in a glove box filled with argon and with the contents of H2O and O2 both less than 0.1 ppm.

[0067] The Chinese name of NCM811 is lithium nickel cobalt manganese oxide (8:1:1), which is a kind of cathode material for ternary lithium-ion batteries. Among them, "811" represents the molar ratio of three elements, nickel (Ni), cobalt (Co), and manganese (Mn), being 8:1:1.

[0068] Example 2:

[0069] This example discloses a lithium metal battery without a negative electrode, and its preparation steps are the same as those of Example 1, except that: the mass loading of Zn@PDA in the composite negative electrode current collector (Cu|Zn@PDA-GO) is 0.125 mg / cm 2 .

[0070] Example 3:

[0071] This example discloses a lithium metal battery without a negative electrode, and its preparation steps are the same as those of Example 1, except that: the mass loading of Zn@PDA in the composite negative electrode current collector (Cu|Zn@PDA-GO) is 0.195 mg / cm 2 .

[0072] Comparative Example 1:

[0073] This example discloses a lithium metal battery without a negative electrode, and its preparation steps are the same as those of Example 1, except that: a bare copper is used as the negative electrode current collector.

[0074] Comparative Example 2:

[0075] This example discloses a lithium metal battery without a negative electrode, and its preparation steps are the same as those of Example 1, except that: the negative electrode current collector is Cu|Zn@PDA.

[0076] Comparative Example 3:

[0077] This example discloses a lithium metal battery without a negative electrode, and its preparation steps are the same as those of Example 1, except that: the negative electrode current collector is Cu|ZnNPs (the current collector is a copper foil and the lithiumophilic layer is zinc nanoparticles).

[0078] The lithium metal batteries without a negative electrode of Examples 1 - 3 and Comparative Examples 1 - 3 were tested, and the test steps are as follows:

[0079] The current density of the non-aqueous lithium metal battery with NCM811 as the positive electrode is 0.5 mA / cm 2 , and it is cycled within the voltage range of 2.5 and 4.2 V to obtain data such as the number of cycles and capacity retention rate. The current density is 0.5 mA / cm 2 , the cycling voltage range is 2.5 - 4.2 V. By testing the initial voltage curve of the lithium-copper half-cell on different Cu current collectors, the nucleation overpotential of each current collector can be obtained, and the Coulombic efficiency can be obtained through the cycling curve of the lithium-copper half-cell.

[0080] Table 1 Cycling performance of non-aqueous lithium metal batteries assembled with different current collectors

[0081]

[0082]

[0083] As shown in Table 1, the rapid capacity decay of the bare copper||NMC battery is caused by the inhomogeneity, lithium-phobicity, and roughness of the bare copper electrode surface, accompanied by inhomogeneous initial lithium nucleation and uncontrolled lithium deposition. The capacity decays rapidly with the number of cycles and the polarization increases rapidly. Compared with the battery assembled with bare Cu, the batteries assembled with Cu|Zn@PDA and Cu|Zn@PDA-GO show lower nucleation barriers (i.e., lower overpotentials), higher capacity retention rates, and higher Coulombic efficiencies. Due to the synergistic effect of the excellent ionic conductivity of GO and the high lithium-philicity of Zn@PDA, the battery with the Cu|Zn@PDA-GO current collector shows the lowest overpotential and the best cycling performance.

[0084] From the result comparison in Table 1, it is found that the battery assembled with the Cu|ZnNPs current collector without PDA (Comparative Example 3) shows faster capacity decay than the battery assembled with Cu@Zn@PDA (Comparative Example 2). This is due to the better lithium-philic property of the Cu@PDA coating, which can be used as a nucleation seed to promote the uniformity of the initial nucleation behavior. In addition, when the loading of the Zn@PDA coating is low (Example 2), the battery shows better electrochemical performance than the bare copper, but relatively poorer electrochemical performance compared with the samples with higher loading. The results show that the higher the mass loading, the more materials can be used as nucleation seeds, but too high a mass loading (Example 3) leads to a relatively rough surface and ineffective uniformity of ZnNPs on the copper substrate. Therefore, medium mass loading (Example 1) shows relatively high Coulombic efficiency and capacity retention rate.

[0085] In the present invention, specific embodiments are used to elaborate on the principles and implementation manners of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manners and application scopes. In summary, the content of this specification should not be construed as a limitation to the present invention.

Claims

1. A composite negative electrode current collector, characterized in that, It includes a base layer and a graphene oxide layer coated on the surface of the base layer. The graphene oxide layer is a porous layer with a lithium ion conductivity ≥ 10 -4 S / cm and an electron conductivity ≤ 10 -8 S / cm.

2. The composite negative current collector according to claim 1, wherein The surface of the graphene oxide layer contains at least one functional group among carboxyl groups, hydroxyl groups or epoxy groups.

3. The composite negative electrode current collector according to claim 1, wherein The thickness of the graphene oxide layer is 1 to 10 μm.

4. The composite negative electrode current collector according to claim 1, wherein A lithiumophilic layer is further provided between the base layer and the graphene oxide layer, and the lithiumophilic layer includes lithiumophilic nanoparticles and a binder.

5. The composite negative current collector according to claim 4, wherein The lithiumophilic nanoparticles are selected from at least one of zinc, tin, magnesium, silicon, indium, gold, silver or their oxides, and the binder is selected from at least one of polydopamine, polyvinylidene fluoride, carboxymethyl cellulose, styrene-butadiene rubber, polyvinylpyrrolidone, polymethyl methacrylate, polyacrylonitrile, polyacrylic acid, polyvinyl alcohol, sodium alginate, β-cyclodextrin polymer, polypropylene emulsion, polytetrafluoroethylene.

6. The composite negative current collector according to claim 5, wherein, The thickness of the lithiumophilic layer is 1 to 10 μm.

7. A method for preparing a composite negative current collector according to any one of claims 1 to 3, characterized in that, Comprising the following steps: Coating a graphene oxide dispersion on the surface of the base layer, and drying to form a graphene oxide layer, thereby obtaining the composite negative electrode current collector.

8. A method for preparing a composite negative current collector according to any one of claims 4 to 6, characterized in that, Comprising the following steps: Coating a lithiumophilic layer slurry on the surface of the base layer, and drying to form a lithiumophilic layer, wherein the lithiumophilic layer slurry includes lithiumophilic nanoparticles and a binder; Coating a graphene oxide dispersion on the surface of the lithiumophilic layer, and drying to form a graphene oxide layer, thereby obtaining the composite negative electrode current collector.

9. The preparation method according to claim 8, characterized in that, The coating is carried out by spin coating, with a rotation speed of 3000 to 4000 rpm and a coating time of 80 to 120 seconds.

10. The preparation method according to claim 8, characterized in that, The concentration of the graphene oxide dispersion is 2 to 5 mg / mL, and the mass concentration of the lithiumophilic nanoparticles in the lithiumophilic layer slurry is 1 to 3 mg / mL.

11. A non-aqueous lithium metal battery having the composite negative current collector according to any one of claims 1 to 6, characterized in that, Comprising a positive electrode, a composite negative electrode current collector, a separator and an electrolyte.

12. An electrical device, characterized in that, Comprising the non-aqueous lithium metal battery according to claim 11.

Images