Flexible lithium-free metal negative electrode current collector based on bimetal active site regulation and preparation method of flexible lithium-free metal negative electrode current collector

Abstract

The invention discloses a flexible lithium-free metal negative electrode current collector based on bimetal active site regulation and a preparation method thereof, and belongs to the technical field of lithium-free metal battery negative electrode current collector materials. The current collector is a flexible carbon nanofiber three-dimensional skeleton with CoNi bimetallic alloy active site in-situ regulation and control, CoNi alloy nanoparticles are uniformly dispersed in the interior and on the surface of the fiber, and the skeleton has a micro / mesoporous hierarchical porous structure, is rich in pyrrole nitrogen and Co / Ni-Nx coordination bonds, and has excellent lithium affinity, flexibility and mechanical stability. A composite precursor membrane is obtained through electrostatic spinning, and in-situ construction of CoNi bimetallic active sites and carbon nanofiber skeleton forming are achieved through pre-oxidation and carbonization. The current collector does not need an additional metal support, can be directly used as a lithium-free metal negative electrode current collector, guides lithium metal to be uniformly and compactly deposited, and effectively inhibits dendritic crystal growth and volume expansion. The lithium metal battery applying the current collector shows excellent electrochemical performance and has important application value in the field of high-energy density energy storage.

Description

A flexible lithium-free metal anode current collector based on bimetallic active site regulation and its preparation method Technical Field

[0001] This invention belongs to the technical field of lithium-free metal battery anode current collector materials, specifically relating to a flexible lithium-free metal anode current collector based on bimetallic active site regulation and its preparation method. Background Technology

[0002] High-energy-density energy storage technology is the core foundation supporting the development of new energy vehicles, portable electronic devices, and large-scale grid energy storage. Lithium-free metal anode systems, because they do not require pre-loading of lithium metal, can significantly improve battery energy density, simplify manufacturing processes, and reduce safety risks, making them a key development direction for next-generation high-energy-density batteries. Lithium metal, with its ultra-high theoretical specific capacity of 3860 mAh / g and extremely low electrochemical potential of -3.04 V (relative to the standard hydrogen electrode), remains the core active component of lithium-free anode systems. However, problems encountered during deposition / stripping, such as dendrite growth, instability of the solid electrolyte interphase (SEI) film, severe volume expansion, and low coulombic efficiency, seriously restrict the practical industrial application of lithium-free metal anode batteries.

[0003] Constructing three-dimensional carbon-based host materials is an effective strategy to solve the above problems. Among them, carbon nanofibers have become an ideal three-dimensional host matrix for lithium-free anode systems due to their advantages such as high specific surface area, good conductivity, and structural tunability. However, pure carbon nanofibers have poor lithiophilicity, resulting in uneven deposition of lithium metal after migration from the cathode, and it is still difficult to effectively suppress dendrites. In the existing technology, although single-metal doping modified carbon nanofibers can improve lithiophilicity to a certain extent, they have defects such as uneven distribution of active sites, weak binding force with carbon matrix, and insufficient control of lithium ion adsorption-desorption kinetics, which cannot simultaneously meet the core requirements of lithium deposition uniformity, interface stability, and long cycle life in lithium-free systems.

[0004] Bimetallic alloys, with their synergistic electronic effects and structural modulation advantages, exhibit unique potential in optimizing active sites. Co and Ni, as transition metals, possess lithium binding energies within a moderate range, preventing excessive lithium adsorption while promoting reversible lithium deposition / exfoliation. Furthermore, the strong interaction between the CoNi alloy and the nitrogen-doped carbon matrix facilitates uniform dispersion and structural stability of active sites. Pairing lithium-free metal anodes with such optimized host materials can further simplify battery structures, reduce costs, and increase energy density, meeting the development needs of next-generation energy storage devices. Therefore, developing a flexible carbon nanofiber current collector that achieves synergistic optimization of lithiophilic properties, pore structure, and mechanical properties through precise modulation of bimetallic active sites is crucial for promoting the practical application of lithium-free metal anode batteries and provides key support for breakthroughs in high-safety, high-energy-density energy storage technologies. Summary of the Invention

[0005] The purpose of this invention is to overcome the defects of existing lithium metal anode current collectors in anode-free lithium metal batteries, such as poor lithium deposition uniformity, difficulty in suppressing dendrite growth, insufficient cycle stability, and poor flexibility. This invention provides a flexible lithium-free metal anode current collector based on bimetallic active site regulation and its preparation method. To achieve the above objective, this invention adopts the following technical solution: A flexible lithium-free metal anode current collector based on bimetallic active site regulation, wherein the current collector is a flexible three-dimensional framework of carbon nanofibers with in-situ regulated CoNi bimetallic alloy active sites. The carbon nanofibers have a diameter of 250~350nm, and CoNi alloy nanoparticles serve as core bimetallic active sites uniformly dispersed inside and on the surface of the carbon nanofibers. The three-dimensional framework has a hierarchical porous structure dominated by micro / mesopores. The abundant pyrrole nitrogen and CoNi-N coordination bonds inside give it excellent lithium affinity. After multiple bends, it does not break or experience performance degradation, exhibiting both excellent flexibility and mechanical stability.

[0006] The above-mentioned method for preparing a flexible lithium-free metal anode current collector based on bimetallic active site regulation includes the following steps: a) Preparation of bimetallic precursor spinning solution: Polyacrylonitrile, cobalt nitrate and nickel nitrate are dissolved in N,N-dimethylformamide in proportion, and stirred at 60°C for 6-8 h until completely dissolved to obtain a uniform and stable bimetallic precursor spinning solution; wherein the mass percentage of polyacrylonitrile to N,N-dimethylformamide is 5-15 wt%, the molar ratio of cobalt nitrate to nickel nitrate is 1:2-2:1, and the total mass of the two and the mass percentage of N,N-dimethylformamide are 3-8 wt%; b) Preparation of composite precursor film: The spinning solution obtained in step a) is injected into the syringe of an electrospinning device, the distance between the spinning needle and the receiver is set to 12-18 cm, the injection speed is 0.5-1.5 mL / h, the receiver rotation speed is 1000-1500 r / min, and an application of... Electrospinning was performed at a voltage of 15~20kV to collect polyacrylonitrile / cobalt-nickel salt composite precursor membranes; c) Pre-oxidation stabilization treatment: The composite precursor membranes were placed in a muffle furnace and heated to 260~290℃ at a heating rate of 5~8℃ / min in an air atmosphere, held for 2~3h, and naturally cooled to room temperature to achieve polymer chain cyclization and structural stabilization, resulting in a pre-oxidized fiber membrane; d) Carbonization and bimetallic active site construction: The pre-oxidized fiber membranes were transferred to a tube furnace and argon or nitrogen gas was introduced (flow rate 80~100mL / min), heated to 700~800℃ at a heating rate of 5~8℃ / min, and held for 2~3h. Cobalt-nickel ions were reduced in situ to form CoNi alloy nanoparticle bimetallic active sites, while polyacrylonitrile was carbonized to form a carbon nanofiber skeleton. The membranes were then cooled to room temperature with the furnace to obtain a flexible lithium-free metal anode current collector based on bimetallic active site regulation.

[0007] This invention also protects the application of the aforementioned current collector in lithium metal batteries. The current collector serves as a three-dimensional host for the lithium metal anode. The active sites of the CoNi bimetallic alloy regulate the lithium-ion adsorption and nucleation process, guiding the uniform deposition of lithium metal on the microporous structure and surface of the carbon nanofiber framework, forming a dendrite-free composite lithium metal anode. This current collector does not require additional metal current collector support and can be directly used as the anode current collector for lithium metal batteries, adapting to the assembly requirements of button batteries and flexible anode-free lithium metal batteries.

[0008] Invention Principle: This invention achieves in-situ construction and uniform dispersion of CoNi bimetallic active sites in carbon nanofibers through electrospinning combined with a pre-oxidation-carbonization process. During carbonization, cobalt nitrate and nickel nitrate in the spinning pretreatment solution are reduced by the carbon matrix, forming CoNi alloy nanoparticles with highly lithiophilic activity and bimetallic active sites. Simultaneously, polyacrylonitrile carbonization forms a three-dimensionally interconnected carbon nanofiber framework. A stable Co / Ni-N bimetallic active site is formed between the CoNi bimetallic active site and the carbon matrix. x The carbon nanofiber framework simultaneously induces the formation of numerous pyrrole nitrogen active sites on the carbon nanofiber surface, significantly enhancing the material's lithiophilicity. The three-dimensionally interconnected micro / mesoporous hierarchical porous structure reduces local current density, homogenizes lithium-ion flux, and alleviates volume expansion. The flexible carbon nanofiber framework ensures the current collector's excellent mechanical properties and processing adaptability. These three elements work synergistically to achieve uniform and dense lithium metal deposition, effectively suppressing lithium dendrite growth and improving the cycle stability and safety of lithium metal batteries.

[0009] Beneficial Effects: This invention utilizes the CoNi bimetallic active site regulation to synergistically regulate pyrrole nitrogen and Co / Ni-N. x A multi-element lithiophilic active site system is constructed, significantly reducing the lithium nucleation overpotential (down to 18mV), achieving uniform and dense lithium metal deposition, and fundamentally inhibiting lithium dendrite growth. The continuous and interconnected micro-mesoporous structure inside the current collector provides ample space for lithium metal deposition, with a volume expansion rate of only 57% during cycling, far lower than traditional carbon nanofibers and single-metal doped materials, effectively mitigating volume fluctuations in the lithium metal anode. An integrated electrospinning-pre-oxidation-carbonization process is adopted to achieve in-situ uniform dispersion of bimetallic active sites. The process is simple, scalable, requires no complex post-processing steps, and has low production costs and high preparation efficiency. The current collector has excellent flexibility and mechanical stability, showing no breakage or performance degradation after multiple bends, and can meet the preparation requirements of flexible anode-free lithium metal batteries, significantly expanding the application scenarios of lithium metal batteries. Lithium metal batteries using this current collector exhibit excellent electrochemical performance: half-cell performance at 1 mA cm⁻¹ - It can stably cycle for more than 400 cycles at current density with an average coulombic efficiency of 99.1%; the electrodeless full cell assembled with LiFePO4 cathode retains 96.8% capacity after 200 cycles at 1C rate, demonstrating outstanding practical application value. Attached Figure Description

[0010] Figure 1 shows the SEM and HRTEM images of the current collectors prepared in Example 1 (a, b), Comparative Examples 1-1 (c, d), Comparative Examples 1-2 (e, f), and Comparative Examples 1-3 (g, h) of the present invention.

[0011] Figure 2 shows the XRD patterns of the current collectors prepared in Example 1, Comparative Example 1-1, Comparative Example 1-2 and Comparative Example 1-3 of the present invention.

[0012] Figure 3 shows the Co2pXPS, Ni2pXPS, and N1sXPS spectra of the current collectors prepared in Example 1, Comparative Example 1-1, Comparative Example 1-2, and Comparative Example 1-3 of this invention.

[0013] Figure 4 shows the current collector assembled half-cells prepared in Example 2, Comparative Example 2-1, Comparative Example 2-2, and Comparative Example 2-3 of the present invention at 1 mA / cm². -2 1mAhcm -2 The Coulomb efficiency curve is shown below.

[0014] Figure 5 shows the specific capacity curves of the current collectors and lithium iron phosphate assembled full cells prepared in Examples 3, 3-1, 3-2 and 3-3 of the present invention at a 1C rate. Detailed Implementation

[0015] Example 1: Preparation of a flexible lithium metal anode current collector based on bimetallic active site regulation: a) Preparation of bimetallic precursor spinning solution: 10 mL of N,N-dimethylformamide was placed in a beaker, and 1.0 g of polyacrylonitrile (relative molecular mass 150,000) and 0.31 g of cobalt nitrate (Co(NO3)2) were added. 6H2O) and 0.31g nickel nitrate (Ni(NO3)2) a) Dissolve the bimetallic precursor in 6H2O by stirring at 60℃ for 8 hours until completely dissolved to obtain a uniform and transparent bimetallic precursor spinning solution; b) Preparation of composite precursor membrane: Inject the spinning precursor solution into the syringe of the electrospinning equipment, set the distance between the spinning needle and the receiver to 15cm, the injection speed to 1.0mL / h, the receiver rotation speed to 1200r / min, apply a voltage of 18kV, and perform electrospinning to collect the polyacrylonitrile / cobalt-nickel salt composite precursor membrane; c) Pre-oxidation stabilization treatment: Place the composite precursor membrane in a muffle furnace. In the furnace, the temperature was raised to 270°C at a rate of 3°C / min under an air atmosphere, held for 2.5 h, and then naturally cooled to room temperature to obtain a pre-oxidized fiber membrane; d) Carbonization and construction of bimetallic active sites: The pre-oxidized fiber membrane was transferred to a tube furnace, argon gas was introduced (flow rate 100 mL / min), and the temperature was raised to 800°C at a rate of 5°C / min, held for 2 h, and then cooled to room temperature with the furnace to obtain a flexible lithium metal anode current collector based on bimetallic active site regulation (denoted as CoNi-CNF).

[0016] Preparation of pure carbon nanofiber current collector (CNF) in Comparative Example 1-1: Except for the absence of cobalt nitrate and nickel nitrate in the spinning precursor solution, the other preparation steps were exactly the same as in Example 1.

[0017] Preparation of Co monometallic doped carbon nanofiber current collectors (denoted as Co-CNF) in Comparative Examples 1-2: Except for the addition of only 0.62g of cobalt nitrate (without adding nickel nitrate) to the spinning precursor solution, the other preparation steps were exactly the same as in Example 1.

[0018] Preparation of Ni-CNF (Ni monometallic active site doped carbon nanofiber current collector): Except for the addition of only 0.62g of nickel nitrate (without adding cobalt nitrate) to the spinning precursor solution, the other preparation steps were exactly the same as in Example 1.

[0019] As shown in Figures 1-3, Example 1 exhibits significant structural advantages compared to Comparative Examples 1-1, 1-2, and 1-3. SEM observation revealed that the CNF surface was smooth and lacked active sites. Co-CNF and Ni-CNF showed metal particle aggregation and large fluctuations in fiber diameter, while CN-CNF exhibited uniform fiber diameter (250~350nm), a continuous three-dimensional framework, and no obvious particle aggregation. HRTEM confirmed that CNF was a completely amorphous structure. Co-CNF and Ni-CNF showed metal particle aggregation and were prone to inducing dendrite nucleation, while CN-CNF formed uniformly embedded CoNi alloy nanoparticles (111) with a lattice spacing of 0.216nm, demonstrating excellent dispersibility. XRD patterns showed that the diffraction peaks of CN-CNF exhibited characteristic shifts due to the formation of the CoNi alloy, indicating that the carbon matrix crystal structure was appropriately regulated, avoiding structural disorder caused by single metal doping and functional loss of pure carbon. XPS analysis showed that CN-CNF had a pyrrole nitrogen content (26.8%) and a Co / Ni-N ratio of 26.8%.x The bonding strength is superior to that of single-metal samples, and the surface electron cloud distribution is more uniform. CN-CNF achieves uniform dispersion of active sites, synergistic optimization of crystal structure, and regulation of surface chemical environment through bimetallic alloying, solving the key problems of insufficient lithiophilicity of pure carbon nanofibers and particle agglomeration in single-metal doped samples, and providing a structural basis for uniform lithium deposition and dendrite suppression.

[0020] Example 2: To test the lithium deposition / stripping efficiency of the CN-CNF material in Example 1, a half-cell was assembled for testing. CN-CNF was used as the positive electrode, and metallic lithium as the negative electrode. The electrolyte was 1M LiTFSI dissolved in DOL / DME = 1:1, with 2wt% lithium nitrate added. The battery was assembled using a Model 2032 button cell in an argon-protected glove box. The test conditions were 1 mA / cm². -2 1mAhcm -2 Its coulomb efficiency curve is shown in Figure 4.

[0021] Comparative Example 2-1: To test the lithium deposition / stripping efficiency of the CNF material in Comparative Example 1-1, a half-cell was assembled for testing. CNF was used as the positive electrode, and lithium metal was used as the negative electrode. The other conditions were the same as in Example 2, and the coulombic efficiency curve is shown in Figure 4.

[0022] Comparative Example 2-2: To test the lithium deposition / stripping efficiency of the Co-CNF material in Comparative Examples 1-2, a half-cell was assembled for testing. Co-CNF was used as the positive electrode, and metallic lithium was used as the negative electrode. The other conditions were the same as in Example 2, and its coulombic efficiency curve is shown in Figure 4.

[0023] Comparative Examples 2-3: To test the lithium deposition / stripping efficiency of the Ni-CNF materials in Comparative Examples 1-3, half-cells were assembled for testing. Ni-CNF was used as the positive electrode, and metallic lithium as the negative electrode. The other conditions were the same as in Example 2, and the coulombic efficiency curves are shown in Figure 4.

[0024] As shown in Figure 4, CN-CNF exhibits significantly superior cycling stability and reversibility compared to CN, Co-CNF, and Ni-CNF. CN exhibits a sharp fluctuation in coulombic efficiency after 60 cycles, failing to achieve stable cycling. While Co-CNF and Ni-CNF show improved lithium affinity due to single-metal doping, they only achieve stable cycling for 230 and 210 cycles respectively, with average coulombic efficiencies of 98.0% and 93.4%. Furthermore, their coulombic efficiency continues to decline due to interface instability caused by metal particle aggregation. In contrast, CN-CNF, with its uniform dispersion of bimetallic active sites and Co / Ni-N... x The synergistic lithiophilic effect between the bond and pyrrole nitrogen achieves a high average coulombic efficiency of 99.1%, with stable cycling up to 400 cycles and minimal fluctuations in coulombic efficiency during cycling.

[0025] In Example 3, the CN-CNF material from Example 1 was first assembled into a half-cell and pre-cycled. Then, it was disassembled and used as the negative electrode to assemble a full cell with lithium iron phosphate. The electrolyte was 1M LiTFSI dissolved in DOL / DME = 1:1, with 2wt% lithium nitrate added. Battery assembly was performed using a 2032 button cell in an argon-protected glove box. Charge-discharge tests were conducted at 1C rate, and the results are shown in Figure 5.

[0026] Comparative Example 3-1: The CNF material from Comparative Example 1-1 was first assembled into a half-cell and pre-cycled. Then, it was disassembled and used as a negative electrode to assemble a full cell with lithium iron phosphate. The remaining conditions were the same as in Example 3. The results are shown in Figure 5.

[0027] Comparative Example 3-2: The Co-CNF material from Comparative Example 1-2 was first assembled into a half-cell and pre-cycled. Then, it was disassembled and used as a negative electrode to assemble a full cell with lithium iron phosphate. The remaining conditions were the same as in Example 3. The results are shown in Figure 5.

[0028] In Comparative Example 3-3, the Ni-CNF material from Comparative Example 1-3 was first assembled into a half-cell and pre-cycled. Then, it was disassembled and used as a negative electrode to assemble a full cell with lithium iron phosphate. The remaining conditions were the same as in Example 3. The results are shown in Figure 5.

[0029] As shown in Figure 5, CNF's capacity decays rapidly in the early stages of cycling, and it can no longer maintain an effective discharge capacity after 50 cycles. Co-CNF and Ni-CNF retain only about 85% of their capacity after 200 cycles. However, CN-CNF, relying on the uniform dispersion of bimetallic active sites, still retains 96.8% of its capacity after 200 cycles.

Claims

1. A flexible lithium-free metal anode current collector based on bimetallic active site regulation, characterized in that, The current collector is a flexible three-dimensional carbon nanofiber framework with in-situ regulated CoNi bimetallic active sites. The carbon nanofibers have a diameter of 200~350nm. CoNi alloy nanoparticles are uniformly dispersed inside and on the surface of the carbon nanofibers as core bimetallic active sites. The three-dimensional framework has a hierarchical porous structure dominated by micro / mesoporous structures. The abundant pyrrole nitrogen and CoNi-N coordination bonds inside give it excellent lithium affinity. It does not break or degrade in performance after multiple bends, and has both excellent flexibility and mechanical stability.

2. The preparation method of the flexible lithium-free metal anode current collector based on bimetallic active site regulation according to claim 1, characterized in that, Includes the following steps: a) Preparation of bimetallic precursor spinning solution: Polyacrylonitrile, cobalt nitrate, and nickel nitrate were dissolved in N,N-dimethylformamide in a certain proportion. After stirring until completely dissolved, the solution was ultrasonically dispersed to obtain a uniform and stable bimetallic precursor spinning solution. b) Preparation of composite precursor membrane: The spinning solution obtained in step a) was formed by electrospinning, and a polyacrylonitrile / cobalt-nickel compound composite precursor membrane was collected. c) Pre-oxidation stabilization treatment: The composite precursor membrane obtained in step b) was subjected to gradient heating pre-oxidation in an air atmosphere to achieve polymer chain cyclization and structural stabilization, resulting in a pre-oxidized fiber membrane. d) Carbonization and construction of bimetallic active sites: The pre-oxidized fiber membrane obtained in step c) was carbonized at high temperature under inert gas protection. The cobalt-nickel compound was reduced in situ to form CoNi alloy nanoparticle bimetallic active sites. At the same time, the polyacrylonitrile was carbonized to form a carbon nanofiber skeleton, and finally a flexible lithium-free metal anode current collector based on bimetallic active site regulation was obtained.

3. The preparation method according to claim 2, characterized in that, In step a), the mass percentage of polyacrylonitrile to N,N-dimethylformamide is 5~15wt%; the molar ratio of cobalt nitrate to nickel nitrate is 1:2~2:1, and the total mass of the two to N,N-dimethylformamide is 3~8wt%.

4. The preparation method according to claim 2, characterized in that, In step b), the electrospinning process parameters are as follows: the distance between the spinning needle and the receiver is 12~18cm, the spinning solution injection speed is 0.5~1.5mL / h, the receiver rotation speed is 1000~1500r / min, and the applied voltage is 15~20kV.

5. The preparation method according to claim 2, characterized in that, In step c), the pre-oxidation process is as follows: the temperature is increased from room temperature to 260~290℃ at a heating rate of 5-8℃ / min, and held for 2~3 hours.

6. The preparation method according to claim 2, characterized in that, In step d), the carbonization process is as follows: under an argon or nitrogen atmosphere, the temperature is raised to 700-800℃ at a heating rate of 5-8℃ / min, and held for 2-3 hours, with an inert gas flow rate of 80-100mL / min.

7. The application of the flexible lithium-free metal anode current collector based on bimetallic active site regulation according to claim 1 or the carbon nanofibers prepared by any of the preparation methods of claims 2 to 6 in the anode current collector of lithium metal batteries.

8. The application according to claim 7, characterized in that, The current collector serves as the three-dimensional host of the lithium metal anode. The active sites of the CoNi bimetallic alloy regulate the lithium ion adsorption and nucleation process, guiding the uniform deposition of lithium metal on the micro / mesoporous structure and surface of the carbon nanofiber framework, forming a dendrite-free composite lithium metal anode.

9. The application according to claim 7, characterized in that, The current collector does not require additional metal current collector support and can be directly used as the negative electrode current collector of lithium metal batteries, adapting to the assembly requirements of button batteries and flexible lithium metal batteries.

10. The application according to claim 9, characterized in that, In the assembled lithium metal battery, the positive electrode is LiFePO4, the electrolyte is a 1M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) mixed solution of 1,3-dioxolane (DOL) / ethylene glycol dimethyl ether (DME) (volume ratio 1:1), and 2wt% lithium nitrate is added as an electrolyte additive.

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