A lithium metal negative electrode carbon-based host material and a preparation method thereof

Abstract

The application provides a preparation method of a lithium metal negative electrode carbon-based host material, and belongs to the technical field of lithium batteries, and comprises the following steps: adding polytetrafluoroethylene concentrated dispersion liquid into a mixed solution of polyvinyl alcohol solution and boric acid solution and uniformly mixing; then adding magnesium acetate tetrahydrate and deionized water and uniformly mixing; performing electrostatic spinning to obtain an original silk film, and performing pre-oxidation treatment and carbonization treatment on the original silk film to obtain the lithium metal negative electrode carbon-based host material of magnesium fluoride nanodot covalent bonding honeycomb-like carbon nanofiber. The precursor solution is converted into a nanofiber film through the electrostatic spinning technology, and the lithium metal negative electrode carbon-based host material is obtained by combining a subsequent heat treatment process. The host material contains honeycomb-like holes, effectively increases the specific surface area, reduces the local current density, inhibits the generation of lithium dendrites, simultaneously, the ultra-small magnesium fluoride nanodots are uniformly loaded on the surface of the carbon skeleton, reduces the lithium nucleation energy barrier, and promotes the uniform deposition of lithium.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium batteries, and particularly relates to a lithium metal negative electrode carbon-based host material and a preparation method thereof. BACKGROUND

[0002] Lithium metal has ultra-high theoretical specific capacity, the lowest redox potential, and a relatively low density, and is considered to be the holy grail negative electrode of the next generation of high-energy-density batteries. However, the dendrite growth, volume expansion, and unstable interface structure of the lithium metal negative electrode during the battery cycle seriously hinder its practical application. In order to realize the commercial application of the lithium metal negative electrode as soon as possible, the academic and industrial circles have proposed strategies such as artificial protective layer, solid-state electrolyte, new type of separator, and host material to protect the lithium metal negative electrode, so as to improve the electrochemical reversibility and long cycle stability of the lithium metal battery.

[0003] Compared with other strategies, the host material can accommodate metal lithium due to sufficient internal pores, thereby effectively inhibiting the volume expansion phenomenon of the lithium metal negative electrode during the cycle process, and the specific surface area of the host material is large, so as to reduce the local current density of the electrode and thereby inhibit the dendrite growth. Among them, the carbon-based host material has been widely concerned due to the advantages of lighter mass, stronger structure adjustability, and various synthesis methods. However, it is difficult to accurately control the lithium deposition behavior due to the strong lithium-phobicity of the carbon material.

[0004] Studies have shown that the modification of carbon materials with lithiumophilic species can significantly enhance the lithiumophilicity of carbon materials. For example, the Chinese invention patent with the application publication number CN109841797A discloses a high-performance composite lithium metal negative electrode material based on graphene and a preparation method thereof. The host material is prepared by uniformly mixing magnesium fluoride, zinc fluoride, and graphene oxide solution, using the filtration method to prepare a graphene-based composite host material, and then using the melt lithium filling method to prepare a composite lithium metal negative electrode. Although these methods realize the compounding of lithiumophilic species and carbon materials, the simple physical combination makes the bonding force between the lithiumophilic species and the carbon substrate poor, resulting in the migration and aggregation of the lithiumophilic species during the repeated lithium deposition / stripping process, which is difficult to induce the directional deposition of lithium, causing the generation of lithium dendrites and even safety problems. Therefore, it is urgent to develop a host material in which the lithiumophilic species and the carbon substrate are tightly combined. SUMMARY

[0005] The present application aims at the technical problems existing in the prior art, and provides a lithium metal negative electrode carbon-based host material and a preparation method thereof. The prepared novel magnesium fluoride nanodot covalent bonding honeycomb-like carbon nanofiber lithium metal host material has excellent lithium affinity and good structural stability, realizes long-term stable deposition of lithium metal, and effectively prolongs the cycle life of the lithium metal battery. The host material contains honeycomb-like pores, effectively increases the specific surface area, reduces the local current density, and inhibits the generation of lithium dendrites. At the same time, the ultra-small magnesium fluoride nanodots are uniformly loaded on the surface of the carbon skeleton, reducing the lithium nucleation energy barrier and promoting the uniform deposition of lithium. More importantly, there is a covalent bond between the magnesium fluoride and the honeycomb-like carbon skeleton, which significantly prolongs the cycle life of the composite lithium metal negative electrode based on the host material.

[0006] The technical scheme adopted by the present application is: a preparation method of a lithium metal negative electrode carbon-based host material, comprising the following steps:

[0007] Step 1: polyvinyl alcohol is added to deionized water, and after stirring and dissolving, a polyvinyl alcohol solution is obtained;

[0008] Step 2: boric acid is added to deionized water, and after stirring and dissolving, a boric acid solution is obtained;

[0009] Step 3: the boric acid solution obtained in step 2 is added to the polyvinyl alcohol solution obtained in step 1 and stirred uniformly to obtain a mixed solution;

[0010] Step 4: polytetrafluoroethylene concentrated dispersion liquid is added to the mixed solution of step 3, and stirring is continued until the mixture is uniform;

[0011] Step 5: magnesium acetate tetrahydrate is added to the mixed solution obtained in step 4, and deionized water is added to continue stirring until the mixture is uniform;

[0012] Step 6: electrospinning is performed on the mixed solution of step 5 to obtain a raw silk film;

[0013] Step 7: the raw silk film obtained in step 6 is subjected to pre-oxidation treatment in an air atmosphere to obtain a pre-oxidized fiber film;

[0014] Step 8: the pre-oxidized fiber film obtained in step 7 is subjected to carbonization treatment in an argon atmosphere to obtain a lithium metal negative electrode carbon-based host material of magnesium fluoride nanodot covalent bonding honeycomb-like carbon nanofiber.

[0015] Further, the mass fraction of polyvinyl alcohol in the polyvinyl alcohol solution is 10-15%, and the mass fraction of boric acid in the boric acid solution is 3-5%. In step 3, 0-100 μL of boric acid solution is added to 7 g of polyvinyl alcohol solution.

[0016] Further, the amount of boric acid solution used is 26 μL.

[0017] Further, in step 1, the dissolving temperature is 90℃.

[0018] Further, in step 4, the adding amount of the polytetrafluoroethylene concentrated dispersion solution is 5-15g.

[0019] Further, in step 5, the adding amount of the magnesium acetate tetrahydrate is 0.1-2g, and the adding amount of the ionized water is 1mL.

[0020] Further, in step 6, the electrospinning takes the following parameters: the distance between the needle tip and the receiver is 10-20cm, the applied voltage is 20-35kV, the injection pump rate is 0.8-1.5mL / h, the collector rotation speed is 300-800rpm, the cabin temperature is 25-35℃, and the cabin relative humidity is 40-60RH%.

[0021] Further, in step 7, the heating rate is 1-5℃ / min, the holding temperature is 200-300℃, and the holding time is 1-3h.

[0022] Further, in step 8, the heating rate is 1-5℃ / min, the holding temperature is 600-800℃, and the holding time is 1-3h.

[0023] The technical scheme adopted by the present application is: a lithium metal negative electrode carbon-based host material is prepared by the preparation method of the lithium metal negative electrode carbon-based host material.

[0024] Synthesis principle: the precursor solution is converted into a nanofiber membrane by electrospinning technology, and combined with the subsequent heat treatment process to obtain a magnesium fluoride nanodot covalent bonding honeycomb-like carbon nanofiber lithium metal negative electrode carbon-based host material. The polytetrafluoroethylene particles are pyrolyzed to form a honeycomb-like pore structure during carbonization, and at the same time, the polytetrafluoroethylene and magnesium acetate tetrahydrate undergo in-situ solid-phase reaction to generate MgF2 nanodots. In this process, the F element in the polytetrafluoroethylene is doped into the carbon fiber in-situ, forming fluorine-doped carbon, and bonding with magnesium atoms, anchoring the MgF2 nanodots on the surface of the honeycomb-like carbon nanofiber through Mg-F bonds, and finally forming a magnesium fluoride nanodot covalent bonding honeycomb-like carbon nanofiber lithium metal host material.

[0025] Compared with the prior art, the present application has the following beneficial effects:

[0026] 1. The fluorinated magnesium nanodots of the present application are uniformly and densely distributed on the surface of the honeycomb-like carbon nanofibers, successfully enhancing the lithium affinity of the host material, and realizing the controllable and rapid preparation of dense and uniform composite lithium metal negative electrode by the melt lithium infusion method; and the covalent bond between the fluorinated magnesium nanodots and the honeycomb-like carbon skeleton makes the MgF2 sites maintain good spatial distribution stability during the melt lithium infusion process, avoiding the migration and agglomeration of lithium-affinity sites during the melt lithium infusion process.

[0027] 3. The lithium metal host material based on the covalent bonding of fluorinated magnesium nanodots and honeycomb-like carbon nanofibers in the composite lithium negative electrode of the present application uniformly disperses lithium-magnesium alloy as a lithium deposition active site, inducing a targeted dendrite-free deposition mode of lithium.

[0028] 4. The present application has abundant gaps between the fiber skeletons, which provide sufficient buffer space for lithium deposition / exfoliation behavior, effectively relieving the volume fluctuation during electrode cycling, and avoiding the collapse and pulverization of the lithium negative electrode structure.

[0029] 5. The fluorinated magnesium of the present application also plays a regulatory role in the lithium metal interface composition during melt lithium infusion, forming LiF with high mechanical strength, inhibiting the fragmentation of the solid-state electrolyte interface layer caused by long-term cycling, and reducing the consumption of electrolyte and active lithium.

[0030] 6. The synthesis and preparation method of the present application is simple, fast and low in cost, and has good practical application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 is the XRD spectrum of the host material of Example 1 of the present application;

[0032] Figure 2 is the XPS spectrum of the host material of Example 1 of the present application;

[0033] Figure 3 is the SEM image of the host material of Example 1 of the present application;

[0034] Figure 4 is the full battery cycle performance test based on the host material in Example 1 of the present application;

[0035] Figure 5 is the SEM image of the host material of Example 2 of the present application;

[0036] Figure 6 is the full battery cycle performance test based on the host material in Example 2 of the present application;

[0037] Figure 7 is the SEM image of the host material of Example 3 of the present application;

[0038] Figure 8is the full battery cycle performance test based on the host material in Example 3 of the present application.

[0039] Figure 9 is the SEM image of the host material of Example 4 of the present application;

[0040] Figure 10 is the full battery cycle performance test based on the host material in Example 4 of the present application;

[0041] Figure 11 is the SEM image of the host material of Example 5 of the present application;

[0042] Figure 12 is the full battery cycle performance test based on the host material in Example 6 of the present application. DETAILED DESCRIPTION

[0043] In order for those skilled in the art to better understand the technical solutions of the present application, the present application will be described in detail below in combination with the drawings and specific examples.

[0044] Example 1

[0045] The embodiment of the present application provides a preparation method of a lithium metal negative electrode carbon-based host material, which comprises the following steps:

[0046] Step 1: polyvinyl alcohol is added in deionized water, and after stirring and dissolving at 90℃, a polyvinyl alcohol solution with a polyvinyl alcohol mass fraction of 15% is obtained;

[0047] Step 2: boric acid is added in deionized water, and after stirring and dissolving, a boric acid solution with a boric acid mass fraction of 4% is obtained;

[0048] Step 3: 26μL of the boric acid solution obtained in Step 2 is added to 7g of the polyvinyl alcohol solution obtained in Step 1 and stirred uniformly to obtain a mixed solution;

[0049] Step 4: 10.5g of polytetrafluoroethylene concentrated dispersion liquid is added to the mixed solution of Step 3, and continues to be stirred until mixed uniformly;

[0050] Step 5: 1g of magnesium acetate tetrahydrate is added to the mixed solution obtained in Step 4, and 1mL of deionized water is added to continue stirring until mixed uniformly;

[0051] Step 6: the mixed solution of Step 5 is taken up with a syringe and placed in a push pump, the push rate is set to 1mL / h, the distance between the needle and the receiver is 15cm, the applied voltage is 30kV, the collector speed is 500rpm, the cabin temperature is controlled at 30℃, the relative humidity in the cabin is controlled at 40RH%, electrospinning is carried out, and a raw silk film is obtained;

[0052] Step 7: The raw fiber film obtained in step 6 is subjected to pre-oxidation treatment in an air atmosphere, the pre-oxidation temperature is controlled at 280℃, the holding time is 2h, and the heating rate is 2℃ / min, to obtain a pre-oxidized fiber film;

[0053] Step 8: The pre-oxidized fiber film obtained in step 7 is subjected to carbonization treatment in an argon atmosphere, the carbonization temperature is controlled at 600℃, the holding time is 2h, and the heating rate is 5℃ / min, to obtain a lithium metal anode carbon-based host material of magnesium fluoride nanodots covalently bonded to honeycomb carbon nanofibers.

[0054] Figure 1 FIG. 1 is an XRD spectrum of the host material of the inventive example 1, indicating that the nanodots loaded on the surface of the honeycomb carbon nanofiber are magnesium fluoride.

[0055] Figure 2 FIG. 2 is an XPS spectrum of the host material of the inventive example 1, from which it can be seen that the peaks at 686.2eV and 688.2eV in the F 1s spectrum correspond to Mg-F bonds and C-F bonds, respectively, proving that magnesium fluoride is successfully covalently bonded to the honeycomb carbon nanofiber framework. Due to the presence of covalent bonds, the magnesium fluoride nanodots covalently bonded to the honeycomb carbon nanofiber host material remain stable in morphology during the lithium melt filling process, avoiding the migration and aggregation of the nanodots, and the formation of uniformly distributed lithium-magnesium alloys effectively induces the deposition behavior of lithium, thereby improving the electrochemical performance of the lithium metal battery.

[0056] Figure 3 FIG. 3 is an SEM image of the host material of the inventive example 1, from which it can be observed that the carbon nanofiber contains a large number of honeycomb pore structures, effectively increasing the specific surface area of the host material, thereby reducing the local current density and inhibiting the generation of dendrites. At the same time, the fiber surface is uniformly loaded with ultra-small magnesium fluoride nanodots, enhancing the affinity of the host material for metal lithium, effectively promoting the realization of lithium melt filling and reducing the nucleation barrier of lithium, thereby inducing the deposition behavior of lithium.

[0057] In order to investigate the electrochemical performance of the composite anode based on the lithium metal anode carbon-based host material of magnesium fluoride nanodots covalently bonded to honeycomb carbon nanofibers, the prepared host material was verified as follows: a lithium sheet was heated to a molten state at 300℃, the host material in step 8 was contacted with the liquid lithium, and the liquid lithium spontaneously immersed into the host material, and a composite lithium metal anode was obtained after cooling. Based on the composite lithium metal anode and a lithium iron phosphate positive electrode to form a full battery, Figure 4 FIG. 4 is a full battery cycle performance graph of example 1, and the full battery has a discharge specific capacity of 146.3mAh g -1 after 200 cycles at a current density of 0.5C (1C=170mA g -1 ).

[0058] Example 2

[0059] The embodiment of the present application provides a preparation method of a lithium metal negative electrode carbon-based host material, which comprises the following steps:

[0060] Step 1: polyvinyl alcohol is added into deionized water, and after stirring and dissolving at 90 DEG C, a polyvinyl alcohol solution with a mass fraction of 15% of polyvinyl alcohol is obtained;

[0061] Step 2: boric acid is added into deionized water, and after stirring and dissolving, a boric acid solution with a mass fraction of 4% of boric acid is obtained;

[0062] Step 3: 26 μL of the boric acid solution obtained in step 2 is added into 7 g of the polyvinyl alcohol solution obtained in step 1 and stirred uniformly to obtain a mixed solution;

[0063] Step 4: 10.5 g of polytetrafluoroethylene concentrated dispersion liquid is added into the mixed solution in step 3, and stirring is continued until the mixture is uniformly mixed;

[0064] Step 5: 0.75 g of magnesium acetate tetrahydrate is added into the mixed solution obtained in step 4, and 1 mL of deionized water is added to continue stirring until the mixture is uniformly mixed;

[0065] Step 6: the mixed solution in step 5 is taken by a syringe and placed in a push pump, the push rate is set to 1 mL / h, the distance between the needle and the receiver is 15 cm, the applied voltage is 20 kV, the collector rotation speed is 500 rpm, the cabin temperature is controlled at 30 DEG C, the relative humidity in the cabin is controlled at 40 RH%, electrostatic spinning is carried out, and a raw silk film is obtained;

[0066] Step 7: the raw silk film obtained in step 6 is subjected to pre-oxidation treatment in an air atmosphere, the pre-oxidation temperature is controlled at 280 DEG C, the holding time is 2 h, and the heating rate is 2 DEG C / min, and a pre-oxidized fiber film is obtained;

[0067] Step 8: the pre-oxidized fiber film obtained in step 7 is subjected to carbonization treatment in an argon atmosphere, the carbonization temperature is controlled at 600 DEG C, the holding time is 2 h, and the heating rate is 5 DEG C / min, and a lithium metal negative electrode carbon-based host material of magnesium fluoride nanodot covalently bonded honeycomb-like carbon nanofiber is obtained.

[0068] Figure 5 The SEM image of the host material of the inventive example 2, from the figure, it can be observed that the carbon nanofiber contains a large number of honeycomb-like pore structures, which effectively increases the specific surface area of the host material, thereby reducing the local current density and inhibiting the generation of dendrites. At the same time, the fiber surface is uniformly loaded with ultra-small magnesium fluoride nanodots, which enhances the affinity of the host material to metal lithium, effectively promotes the realization of molten lithium filling and reduces the nucleation barrier of lithium, thereby inducing the deposition behavior of lithium.

[0069] In order to investigate the electrochemical performance of the composite negative electrode based on the lithium metal negative electrode carbon-based host material covalently bonded with magnesium fluoride nanodots and honeycomb carbon nanofibers, the prepared host material is verified, as follows: the lithium sheet is heated to a molten state at 300 DEG C, the host material in step 8 is contacted with liquid lithium, and the liquid lithium spontaneously immerses into the host material, and the composite lithium metal negative electrode is obtained after cooling. Based on the composite lithium metal negative electrode and the lithium iron phosphate positive electrode to form a full battery, Figure 6 The full battery cycle performance graph of Example 2 is shown in Figure 2, and the discharge specific capacity is 137.4 mAh g after 200 cycles at a current density of 0.5 C. -1 .

[0070] Example 3

[0071] The embodiment of the present application provides a preparation method of a lithium metal negative electrode carbon-based host material, which comprises the following steps:

[0072] Step 1: polyvinyl alcohol is added to deionized water, and after stirring and dissolving at 90 DEG C, a polyvinyl alcohol solution with a polyvinyl alcohol mass fraction of 15% is obtained;

[0073] Step 2: boric acid is added to deionized water, and after stirring and dissolving, a boric acid solution with a boric acid mass fraction of 4% is obtained;

[0074] Step 3: 26 μL of the boric acid solution obtained in step 2 is added to 7 g of the polyvinyl alcohol solution obtained in step 1 and stirred uniformly to obtain a mixed solution;

[0075] Step 4: 10.5 g of polytetrafluoroethylene concentrated dispersion liquid is added to the mixed solution of step 3, and stirring is continued until the mixture is uniform;

[0076] Step 5: 0.75 g of magnesium acetate tetrahydrate is added to the mixed solution obtained in step 4, and 1 mL of deionized water is added to continue stirring until the mixture is uniform;

[0077] Step 6: the mixed solution of step 5 is taken with a syringe and placed in a push pump, the push rate is set to 1 mL / h, the distance between the needle and the receiver is 15 cm, the applied voltage is 35 kV, the collector speed is 500 rpm, the cabin temperature is controlled at 30 DEG C, and the relative humidity in the cabin is controlled at 40 RH%, electrospinning is carried out, and a raw silk film is obtained;

[0078] Step 7: the raw silk film obtained in step 6 is subjected to pre-oxidation treatment in an air atmosphere, the pre-oxidation temperature is controlled at 280 DEG C, the holding time is 2 h, the heating rate is 2 DEG C / min, and a pre-oxidized fiber film is obtained;

[0079] Step 8: The pre-oxidized fiber membrane obtained in step 7 is subjected to carbonization treatment in an argon atmosphere, the carbonization temperature is controlled to be 600 DEG C, the holding time is 2h, and the heating rate is 2 DEG C / min, to obtain a lithium metal negative electrode carbon-based host material of magnesium fluoride nanodots covalently bonded to honeycomb carbon nanofibers.

[0080] Figure 7 The SEM image of the host material of the application embodiment 3, from which it can be observed that the carbon nanofibers contain a large number of honeycomb pore structures, effectively increasing the specific surface area of the host material, thereby reducing the local current density and inhibiting the generation of dendrites. At the same time, the fiber surface is uniformly loaded with ultra-small magnesium fluoride nanodots, enhancing the affinity of the host material to metal lithium, effectively promoting the realization of molten lithium infusion and reducing the nucleation barrier of lithium, thereby inducing the deposition behavior of lithium.

[0081] In order to investigate the electrochemical performance of the composite negative electrode based on the lithium metal negative electrode carbon-based host material of magnesium fluoride nanodots covalently bonded to honeycomb carbon nanofibers, the prepared host material is verified, as follows: the lithium sheet is heated to a molten state at 300 DEG C, the host material in step 8 is contacted with liquid lithium, and the liquid lithium spontaneously infuses into the host material, and after cooling, a composite lithium metal negative electrode is obtained. Based on the composite lithium metal negative electrode and the lithium iron phosphate positive electrode to form a full battery, Figure 8 The full battery cycle performance chart of example 3, the discharge specific capacity is 119.5mAh g -1 .

[0082] Example 4

[0083] The application embodiment provides a preparation method of a lithium metal negative electrode carbon-based host material, which comprises the following steps:

[0084] Step 1: polyvinyl alcohol is added to deionized water, and after stirring and dissolving at 90 DEG C, a polyvinyl alcohol solution with a polyvinyl alcohol mass fraction of 15% is obtained;

[0085] Step 2: boric acid is added to deionized water, and after stirring and dissolving, a boric acid solution with a boric acid mass fraction of 4% is obtained;

[0086] Step 3: 10 μL of the boric acid solution obtained in step 2 is added to 7g of the polyvinyl alcohol solution obtained in step 1 and stirred uniformly to obtain a mixed solution;

[0087] Step 4: 10.5g of polytetrafluoroethylene concentrated dispersion liquid is added to the mixed solution of step 3, and stirring is continued until the mixture is uniform;

[0088] Step 5: 0.5g of magnesium acetate tetrahydrate is added to the mixed solution obtained in step 4, and 1mL of deionized water is added to continue stirring until the mixture is uniform;

[0089] Step 6: The mixed solution of step 5 is taken up with a syringe and placed in a push pump, the push rate is set to 1 mL / h, the distance between the needle and the receiver is 15 cm, the applied voltage is 30 kV, the collector speed is 500 rpm, the cabin temperature is controlled at 30 DEG C, the relative humidity in the cabin is controlled at 40 RH%, electrostatic spinning is carried out to obtain a raw silk film;

[0090] Step 7: The raw silk film obtained in step 6 is subjected to pre-oxidation treatment in an air atmosphere, the pre-oxidation temperature is controlled at 280 DEG C, the holding time is 2 h, and the heating rate is 2 DEG C / min, to obtain a pre-oxidized fiber film;

[0091] Step 8: The pre-oxidized fiber film obtained in step 7 is subjected to carbonization treatment in an argon atmosphere, the carbonization temperature is controlled at 600 DEG C, the holding time is 2 h, and the heating rate is 5 DEG C / min, to obtain a lithium metal negative electrode carbon-based host material covalently bonded with magnesium fluoride nanodots.

[0092] Figure 9 The SEM image of the host material of the present application is shown in Figure 4, from which it can be observed that the carbon nanofiber contains a large number of honeycomb-like pore structures, effectively increasing the specific surface area of the host material, thereby reducing the local current density and inhibiting the generation of dendrites. At the same time, the fiber surface is uniformly loaded with ultra-small magnesium fluoride nanodots, enhancing the affinity of the host material for metal lithium, effectively promoting the realization of molten lithium infusion and reducing the nucleation barrier of lithium, thereby inducing lithium deposition behavior.

[0093] In order to investigate the electrochemical performance of the composite anode based on the lithium metal negative electrode carbon-based host material covalently bonded with magnesium fluoride nanodots, the prepared host material was verified as follows: the lithium sheet was heated to a molten state at 300 DEG C, the host material in step 8 was contacted with the liquid lithium, and the liquid lithium spontaneously immersed into the host material, and a composite lithium metal anode was obtained after cooling. Based on the composite lithium metal anode and the lithium iron phosphate positive electrode, Figure 10 Figure 2 is a cycle performance graph of the full battery of Example 4, and the discharge specific capacity is 97.9 mAh g -1 .

[0094] Example 5

[0095] The present application provides a preparation method of a lithium metal negative electrode carbon-based host material, which comprises the following steps:

[0096] Step 1: Polyvinyl alcohol is added to deionized water, and after stirring and dissolving at 90 DEG C, a polyvinyl alcohol solution with a polyvinyl alcohol mass fraction of 15% is obtained;

[0097] Step 2: Add boric acid into deionized water, after stirring and dissolving, a boric acid solution with a mass fraction of 4% of boric acid is obtained;

[0098] Step 3: Add 10 μL of the boric acid solution obtained in step 2 into 7 g of the polyvinyl alcohol solution obtained in step 1 and stir until uniform to obtain a mixed solution;

[0099] Step 4: Add 10.5 g of a concentrated polytetrafluoroethylene dispersion into the mixed solution of step 3 and continue stirring until uniform;

[0100] Step 5: Add 1 g of magnesium acetate tetrahydrate into the mixed solution obtained in step 4 and add 1 mL of deionized water and continue stirring until uniform;

[0101] Step 6: Take the mixed solution of step 5 with a syringe and place it in a push pump, the push rate is set to 1 mL / h, the distance between the needle and the receiver is 15 cm, the applied voltage is 25 kV, the collector rotation speed is 500 rpm, the cabin temperature is controlled at 30°C, the relative humidity in the cabin is controlled at 40 RH%, electrospinning is performed to obtain a raw silk film;

[0102] Step 7: Perform pre-oxidation treatment on the raw silk film obtained in step 6 in an air atmosphere, control the pre-oxidation temperature to be 280°C, the holding time to be 2 h, and the heating rate to be 2°C / min to obtain a pre-oxidized fiber film;

[0103] Step 8: Perform carbonization treatment on the pre-oxidized fiber film obtained in step 7 in an argon atmosphere, control the carbonization temperature to be 600°C, the holding time to be 2 h, and the heating rate to be 5°C / min to obtain a lithium metal negative electrode carbon-based host material covalently bonded with magnesium fluoride nanodots.

[0104] Figure 11 The SEM image of the host material is the SEM image of the inventive example 5, from which it can be observed that the carbon nanofiber contains a large number of honeycomb-like pore structures, effectively increasing the specific surface area of the host material, thereby reducing the local current density and inhibiting the generation of dendrites. At the same time, the fiber surface is uniformly loaded with ultra-small magnesium fluoride nanodots, enhancing the affinity of the host material to metal lithium, effectively promoting the realization of molten lithium infusion and reducing the nucleation barrier of lithium, thereby inducing the deposition behavior of lithium.

[0105] In order to investigate the electrochemical performance of the composite negative electrode based on the lithium metal negative electrode carbon-based host material covalently bonded with magnesium fluoride nanodots, the prepared host material was verified as follows: heat the lithium sheet to a molten state at 300°C, contact the host material in step 8 with the liquid lithium, and the liquid lithium will spontaneously immerse into the host material to obtain a composite lithium metal negative electrode. Based on the composite lithium metal negative electrode and the lithium iron phosphate positive electrode to form a full battery, Figure 12For the full cell cycle performance graph of Example 5, the discharge specific capacity after 200 cycles at 0.5 C current density was 106.2 mAh g -1 .

[0106] The above has been described in detail through examples, but the content described is only exemplary embodiments of the present application and cannot be considered to limit the scope of the implementation of the present application. The scope of protection of the present application is defined by the claims. Any similar technical solution that utilizes the technical solutions described in the present application or is inspired by the technical solutions of the present application within the spirit and protection scope of the present application, and achieves the above technical effects, or any equivalent changes and improvements to the scope of the application, shall still belong to the patent protection scope of the present application.

Claims

1. A method of preparing a carbon-based host material for a lithium metal anode, characterized by, The method comprises the following steps: Step 1: adding polyvinyl alcohol into deionized water to obtain a polyvinyl alcohol solution after stirring and dissolving; Step 2: adding boric acid into deionized water to obtain a boric acid solution after stirring and dissolving; Step 3: adding the boric acid solution obtained in Step 2 into the polyvinyl alcohol solution obtained in Step 1 and stirring uniformly to obtain a mixed solution; Step 4: adding a polytetrafluoroethylene concentrated dispersion into the mixed solution in Step 3 and continuing to stir until mixed uniformly; Step 5: adding magnesium acetate tetrahydrate into the mixed solution obtained in Step 4 and adding deionized water to continue stirring until mixed uniformly; Step 6: electrospinning the mixed solution in Step 5 to obtain a raw silk film; Step 7: pre-oxidizing the raw silk film obtained in Step 6 in an air atmosphere to obtain a pre-oxidized fiber film; Step 8: carbonizing the pre-oxidized fiber film obtained in Step 7 in an argon atmosphere to obtain a lithium metal negative electrode carbon-based host material with magnesium fluoride nanodots covalently bonded to honeycomb-shaped carbon nanofibers; The mass fraction of polyvinyl alcohol in the polyvinyl alcohol solution is 10-15%, and the mass fraction of boric acid in the boric acid solution is 3-5%; in Step 3, 0-100 μL of the boric acid solution is added into 7 g of the polyvinyl alcohol solution; The amount of the boric acid solution used is 26 μL; In Step 4, the amount of the polytetrafluoroethylene concentrated dispersion added is 5-15 g; In Step 5, the amount of magnesium acetate tetrahydrate added is 0.1-2 g, and the amount of deionized water added is 1 mL.

2. The method of claim 1, wherein the carbon-based host material is prepared by a process comprising: In Step 1, the dissolving temperature is 90°C.

3. The method of producing a lithium metal anode carbon host material according to claim 1, wherein In Step 6, the electrospinning is performed with the following parameters: the distance between the needle tip and the receiver is 10-20 cm, the applied voltage is 20-35 kV, the injection pump rate is 0.8-1.5 mL / h, the collector rotation speed is 300-800 rpm, the cabin temperature is 25-35°C, and the cabin relative humidity is 40-60 RH%.

4. The method of producing a lithium metal anode carbon host material according to claim 1, wherein In Step 7, the heating rate is 1-5°C / min, the holding temperature is 200-300°C, and the holding time is 1-3 h.

5. The method of producing a lithium metal anode carbon host material according to claim 1, wherein In Step 8, the heating rate is 1-5°C / min, the holding temperature is 600-800°C, and the holding time is 1-3 h.

6. A lithium metal negative electrode carbon-based host material prepared by the method according to any one of claims 1-5.

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