CN117673371B - A method for preparing a current collector for a negative electrode-free lithium metal battery, a current collector and applications thereof - Google Patents

Abstract

The invention relates to the technical field of new energy, in particular to a preparation method of a current collector for a cathode-free lithium metal battery, the current collector and application, wherein the preparation method comprises the following steps: under the protection of inert gas, uniformly dispersing the lithium-philic nano particles and an initiator in a mixed solution of N-vinyl pyrrolidone and N-cyanovinyl pyrrolidone to form slurry, uniformly coating the slurry on the surface of a metal current collector, and carrying out in-situ polymerization by heating to obtain the current collector for the non-negative electrode lithium metal battery. The dosage of the N-vinyl pyrrolidone accounts for 35-75% of the total mass of the slurry; the dosage of the N-cyanovinyl pyrrolidone accounts for 5-30% of the total mass of the slurry. The current collector obtained by the in-situ polymerization method can form a lithium-philic alloy site with the active lithium component in the battery formation process, and can induce uniform lithium deposition, thereby improving the coulomb efficiency of the battery and prolonging the cycle life of the battery.

Description

A method for preparing a current collector for a negative electrode-free lithium metal battery, a current collector and applications thereof

Technical Field

The invention relates to a method for preparing a current collector for a negative electrode-free lithium metal battery, the current collector and application thereof, and belongs to the field of new energy technology.

Background technique

The development of new high-energy-density secondary battery systems is an important part of ensuring my country's energy security and promoting the upgrading of my country's energy industry. The energy density of commercial lithium-ion batteries that are currently widely used is close to the theoretical upper limit, and new secondary battery systems with higher energy density are urgently needed to be developed. In recent years, lithium metal batteries assembled with low-potential, high-capacity metallic lithium instead of graphite negative electrodes have gradually attracted widespread attention from researchers. However, due to the high reactivity of metallic lithium, lithium metal batteries have extremely demanding requirements on the assembly environment of the battery. In addition, the manufacturing of metallic lithium foil is difficult, the storage cost is high, and the production safety issues are prominent, so it is currently difficult to achieve large-scale production of lithium metal batteries. At the same time, lithium metal batteries are prone to generate dendritic metallic lithium on the negative electrode side during the cycle process, and there is even a risk that lithium dendrites pierce the diaphragm to cause a short circuit in the battery and cause thermal runaway of the battery, which greatly limits the development and application of lithium metal batteries.

Negative electrode-free lithium metal batteries are expected to be an ideal solution to the above problems. Unlike ordinary lithium metal batteries, all lithium sources in this battery system are provided by positive electrode active materials, and there is no need to use active metallic lithium. Since there are no pre-set negative electrode active components in the battery system, the energy density of negative electrode-free lithium metal batteries is greatly improved compared to commercial lithium-ion batteries. At the same time, this battery system does not use highly active metallic lithium, so there is no need to maintain a strict assembly environment during the battery assembly process. It can be directly compatible with the production line of lithium-ion batteries and is easy to achieve large-scale industrial production. However, due to the poor affinity of commonly used metal current collectors (such as copper and nickel current collectors) with lithium, it is difficult to deposit metallic lithium on their surfaces, and it is easy to form dendrites that cause battery short circuits, which limits the application of negative electrode-free lithium metal batteries.

Chinese patent application CN114597421A discloses a negative electrode current collector for a lithium metal battery without a negative electrode, and a preparation method and application thereof. The preparation method of the negative electrode current collector is: mixing a binder and a conductive polymer with a solvent to obtain a slurry; then coating the slurry on the surface of a copper foil, and vacuum drying to obtain the negative electrode current collector, wherein the conductive polymer includes any one of polypyrrole and/or polyaniline or a combination of at least two. This preparation method requires first polymerizing a conductive polymer, then conducting the polymer through a solvent, adding a binder, and coating it on the surface of the copper foil, and then removing the solvent to obtain the negative electrode current collector. The preparation method is complicated and difficult to operate, and in actual operation, it is easy to cause the surface of the negative electrode current collector to have poor uniformity, resulting in poor battery consistency.

Summary of the invention

In view of the deficiencies in the prior art, the present invention provides a method for preparing a current collector for a negative electrode-free lithium metal battery, a current collector and an application thereof. The current collector can form lithium-philic alloy sites with active lithium components during the battery formation process, and can induce uniform lithium deposition, thereby improving the battery coulombic efficiency and extending the battery cycle life, thus solving the problem of poor safety and short service life of negative electrode-free lithium metal batteries.

The technical solution of the present invention to solve the above technical problems is as follows: a method for preparing a current collector for a negative electrode-free lithium metal battery, the preparation method comprising:

Under the protection of inert gas, lithium-philic nanoparticles and initiators are uniformly dispersed in a mixed solution of N-vinyl pyrrolidone and N-cyanovinyl pyrrolidone to form a slurry, and the slurry is uniformly coated on the surface of the metal current collector and in-situ polymerized by heating to obtain a current collector for a negative electrode-free lithium metal battery.

Furthermore, the lithium-philic nanoparticles are selected from at least one of nano-silver powder, nano-tin powder, nano-zinc powder, nano-silver oxide, nano-tin dioxide, and nano-zinc oxide.

Furthermore, the initiator is selected from at least one of azobisisobutyronitrile and phthaloyl peroxide, and the amount of the initiator is 0.08-0.20% of the total mass of the slurry.

Preferably, the initiator is azobisisobutyronitrile.

Furthermore, the metal current collector is one of a copper current collector and a nickel current collector.

Furthermore, the particle size of the lithium-philic nanoparticles is 50-100 nm, and the amount of the lithium-philic nanoparticles is 15-40% of the total mass of the slurry.

Furthermore, further, the amount of N-vinyl pyrrolidone accounts for 35-75% of the total mass of the slurry; the amount of N-cyanovinyl pyrrolidone accounts for 5-30% of the total mass of the slurry.

Furthermore, the temperature of the heating in-situ polymerization is 60-120° C., and the heating in-situ polymerization time is 1-5 h.

Furthermore, the coating method used to uniformly coat the slurry on the surface of the metal current collector is a doctor blade coating method or a spin coating method.

The present invention also discloses a current collector for a negative electrode-free lithium metal battery, wherein the current collector is prepared by the preparation method of the present invention.

The present invention also discloses an application of a current collector for a negative electrode-free lithium metal battery, wherein the current collector is applied to the negative electrode-free lithium metal battery.

The beneficial effects of the present invention are:

(1) The preparation method of the present invention utilizes the concept of in-situ polymerization to introduce N-cyanovinylpyrrolidone containing a strongly polar cyano structure into N-vinylpyrrolidone, thereby enhancing the bonding strength between the lithium-philic nanoparticles and the current collector, ensuring that the active material does not fall off, thereby improving the cycle life of the battery. At the same time, N-cyanovinylpyrrolidone can also avoid the crystallization phenomenon after the polymerization of N-vinylpyrrolidone.

(2) The current collector obtained by the preparation method of the present invention using the in-situ polymerization method can form lithium-philic alloy sites with active lithium components during the battery formation process. The nucleation barrier of lithium deposition on the current collector is much lower than that of the metal current collector, so it can induce uniform lithium deposition, thereby improving the battery coulombic efficiency and extending the battery cycle life.

(3) The current collector prepared by the in-situ polymerization method of the present invention can reduce the contact between the electrolyte and the metal current collector and the lithium deposition product, inhibit the side reaction on the negative electrode side, thereby reducing the loss of lithium source and thus extending the service life of the battery. At the same time, the polymer obtained by in-situ polymerization of the mixed solution of N-vinyl pyrrolidone and N-cyanovinyl pyrrolidone can inhibit the growth of lithium dendrites through physical suppression, reducing the risk of dendritic lithium piercing the diaphragm and causing a short circuit in the battery.

(4) The current collector preparation method of the present invention has a simple process and low cost, can be directly used in a lithium-ion battery electrode production line, and is suitable for large-scale industrial production.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a graph showing the coulombic efficiency and cycle stability of a negative electrode-free lithium metal battery prepared in Example 1 of the present invention;

FIG2 is a first cycle capacity-voltage curve of a negative electrode-free lithium metal battery prepared in Example 2 of the present invention;

FIG3 is an optical photograph of the slurry prepared in Example 3 of the present invention;

FIG4 is a scanning electron microscope photograph of the current collector prepared in Example 4 of the present invention;

FIG5 is a scanning electron microscope photograph of metallic lithium deposition on the negative electrode side of the negative electrode-free lithium metal battery prepared in Example 5 of the present invention after the first charge;

6 is a scanning electron microscope photograph of the surface of the modified nickel current collector after the first discharge of the negative electrode-free lithium metal battery prepared in Example 6 of the present invention.

Detailed ways

The specific implementation of the present invention is described in detail below. The present invention can be implemented in many other ways than those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention, so the present invention is not limited by the specific embodiments disclosed.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which the present invention belongs. The terms used are only for describing specific embodiments and are not intended to limit the present invention.

A method for preparing a current collector for a negative electrode-free lithium metal battery, the preparation method comprising:

Under the protection of inert gas, lithium-philic nanoparticles and initiators are uniformly dispersed in a mixed solution of N-vinyl pyrrolidone and N-cyanovinyl pyrrolidone to form a slurry, and the slurry is uniformly coated on the surface of the metal current collector and in-situ polymerized by heating to obtain a current collector for a negative electrode-free lithium metal battery.

The structural formulas of N-vinyl pyrrolidone and N-cyanovinyl pyrrolidone are shown in Formula I and Formula II:

Formula I;

Formula II.

Specifically, the lithium-philic nanoparticles are selected from at least one of nano-silver powder, nano-tin powder, nano-zinc powder, nano-silver oxide, nano-tin dioxide, and nano-zinc oxide.

Specifically, the initiator is selected from at least one of azobisisobutyronitrile and phthaloyl peroxide.

Specifically, the metal current collector is one of a copper current collector and a nickel current collector.

Specifically, the particle size of the lithium-philic nanoparticles is 50-100 nm, and the amount of the lithium-philic nanoparticles is 15-40% of the total mass of the slurry.

Specifically, the amount of the initiator is 0.08-0.20% of the total mass of the slurry.

Specifically, the amount of N-vinyl pyrrolidone accounts for 35-75% of the total mass of the slurry; the amount of N-cyanovinyl pyrrolidone accounts for 5-30% of the total mass of the slurry.

Specifically, the temperature of the in-situ polymerization is 60-120° C., and the in-situ polymerization time is 1-5 hours. Under this in-situ polymerization time, complete polymerization can be ensured, while preventing the polymer from aging due to long-term heating. The in-situ polymerization temperature and in-situ polymerization time defined in the present invention are more conducive to obtaining a current collector with excellent application effect.

Specifically, the coating method used to uniformly coat the slurry on the surface of the metal current collector is a doctor blade coating method or a spin coating method.

More specifically, the blade thickness used in the blade coating method is 50 μm; the rotation speed used in the spin coating method is 4000 rpm, and the coating time is 90 s.

More specifically, the slurry preparation process can be carried out in a glove box and the temperature can be maintained at 15-35°C.

More specifically, the stirring speed during the preparation of the slurry is 200-600 rpm, preferably 450 rpm; the stirring time is 0.5-5 h, preferably 2 h.

When the current collector for the negative electrode-free lithium metal battery prepared in the embodiment of the present invention is subjected to a performance test, a negative electrode-free lithium metal battery is assembled with a lithium iron phosphate electrode as a positive electrode for a full battery test, wherein the specific composition of the negative electrode-free lithium metal battery is:

Commercial carbon-coated lithium iron phosphate is mixed with conductive carbon black (Super P), carbon nanotubes (CNT), and polyvinylidene fluoride in a weight ratio of 93:2:2:3, and N-methylpyrrolidone is added and stirred evenly to form a positive electrode slurry. Coating is performed according to a single-sided surface density of 27 mg/ ^cm2 , vacuum drying at 100°C for 12 hours, and then rolling and cutting are performed to form a positive electrode sheet; the corresponding negative electrode sheet is prepared according to the preparation method of the current collector for a negative electrode-free lithium metal battery provided by the patent of this invention.

The positive and negative electrodes were separated by a polypropylene (PP) ceramic separator, where a ceramic coating (1 μm boehmite ceramic coating) was applied on the side of the ceramic separator facing the negative current collector, and then wound into a battery cell, packaged in an aluminum-plastic film, and vacuum-baked at 100°C for 48 hours. The electrolyte of trifluoroethanol carbonate (TFEC)/diethyl carbonate (DEC)/fluoroethylene carbonate (FEC) containing 1.0 mol/L LiPF ₆ (lithium hexafluorophosphate) and 0.1 mol/L LiODFB (lithium difluorooxalate borate) was injected, where the volume ratio of PC/DEC/FEC was 2:1:1, and the battery was sealed. After the injection, the battery was placed in an open circuit at 45°C for 48 hours to allow the electrolyte to completely penetrate.

Example 1

Preparation of a current collector for a negative electrode-free lithium metal battery:

1) Under nitrogen protection, 1500 mg of nano-silver powder, 7 mg of azobisisobutyronitrile, 3000 mg of N-vinyl pyrrolidone and 500 mg of N-cyanovinyl pyrrolidone were placed in a screw-cap bottle and stirred with a magnetic stirrer at 450 rpm for 2.0 h to form a gray-black slurry in which the diameter of the nano-silver powder was 70 nm.

2) The slurry prepared in step 1) is evenly coated on the surface of the metal current collector and heat-dried and polymerized at 80°C for 3.0 hours to obtain a modified current collector. The metal current collector is a copper current collector, and the slurry coating method is a blade coating method. The blade thickness used in the blade coating method is 50 μm.

FIG1 is a graph of the coulombic efficiency and cycle stability of the negative electrode-free lithium metal battery prepared in this embodiment, wherein the curve of ■ in FIG1 is the discharge specific capacity curve of the negative electrode-free lithium metal battery prepared in this embodiment at different cycle numbers, and the curve of □ in FIG1 is the coulombic efficiency curve of the negative electrode-free lithium metal battery prepared in this embodiment at different cycle numbers. The slurry prepared in this embodiment is uniform and fine, and is gray-black; the surface modified coating of the copper current collector is flat, and the polymer matrix and the inorganic filler are evenly distributed; the negative electrode-free lithium metal battery is assembled with the lithium iron phosphate electrode as the positive electrode for full battery testing, and the battery first cycle discharge specific capacity is 151.33 mAh g ^-1 , and the first cycle coulombic efficiency is 94.00%; it can be seen from FIG1 that the coulombic efficiency is close to 100% during the cycle, and there is still a capacity retention rate of 73.96% after 50 cycles; after the battery is charged, the lithium deposition morphology on the surface of the copper current collector is dense, no lithium dendrites are generated, and the modified coating can still be evenly attached to the surface of the copper current collector after the battery is discharged.

Example 2

Preparation of a current collector for a negative electrode-free lithium metal battery:

1) Under nitrogen protection, 1000 mg of nano-tin powder, 5 mg of azobisisobutyronitrile, 3300 mg of N-vinyl pyrrolidone and 700 mg of N-cyanovinyl pyrrolidone were placed in a screw-capped bottle, and magnetically stirred at 450 rpm for 2.0 h to form a silver-grey slurry; the diameter of the nano-tin powder was 60 nm.

2) The slurry prepared in step 1) is evenly coated on the surface of the metal current collector and heat-dried and polymerized at 90°C for 4.0 hours to obtain a modified current collector. The metal current collector is a copper current collector, and the slurry coating method is a spin coating method. The rotation speed used in the spin coating method is 4000 rpm and the coating time is 90 s.

FIG2 is the first cycle capacity-voltage curve of the negative electrode-free lithium metal battery prepared in this embodiment. The upward trend curve in FIG2 is the battery specific capacity-voltage curve during charging, and the downward trend curve in FIG2 is the battery specific capacity-voltage curve during discharge. The slurry prepared in this embodiment is uniform and fine, and is silver-gray; the surface modified coating of the copper current collector is flat, and the polymer matrix and the inorganic filler are evenly distributed; the negative electrode-free lithium metal battery is assembled with the lithium iron phosphate electrode as the positive electrode for full battery testing. As can be seen from FIG2, the battery first cycle discharge specific capacity is 148.2 mAh g ^-1 , and the first cycle coulomb efficiency is 90.75%; the coulomb efficiency during the cycle is close to 100%, and there is still a capacity retention rate of 70.59% after 50 cycles; after the battery is charged, the lithium deposition morphology on the surface of the copper current collector is dense, no lithium dendrites are generated, and the modified coating can still be evenly attached to the surface of the copper current collector after the battery is discharged.

Example 3

Preparation of a current collector for a negative electrode-free lithium metal battery:

1) Under nitrogen protection, 1000 mg of nano silver oxide, 5 mg of azobisisobutyronitrile, 3000 mg of N-vinyl pyrrolidone and 1000 mg of N-cyanovinyl pyrrolidone were placed in a screw-mouth bottle, and stirred at 450 rpm for 2.0 h to form a silver-grey slurry. The diameter of the nano silver oxide was 70 nm.

2) The slurry prepared in step 1) is evenly coated on the surface of the metal current collector and heat-dried and polymerized at 90°C for 4.0 hours to obtain a modified current collector. The metal current collector is a nickel current collector, and the slurry coating method is a spin coating method. The rotation speed used in the spin coating method is 4000 rpm and the coating time is 90 s.

Figure 3 is an optical photograph of the slurry for metal current collector modification prepared in this embodiment. The slurry prepared in this embodiment is uniform and fine, and is gray-black in color; the modified coating on the surface of the nickel current collector is flat, and the polymer matrix and the inorganic filler are evenly distributed; the full battery test is performed by assembling a negative electrode-free lithium metal battery with a lithium iron phosphate electrode as the counter electrode, and the battery's first cycle discharge capacity is 150.3 mAh g ^-1 , and the first cycle coulomb efficiency is 91.15%; the coulomb efficiency is close to 100% during the cycle, and there is still a capacity retention rate of 73.28% after 50 cycles; after the battery is charged, the lithium deposition morphology on the surface of the nickel current collector is dense, no lithium dendrites are generated, and the modified coating can still be evenly attached to the surface of the nickel current collector after the battery is discharged.

Example 4

Preparation of a current collector for a negative electrode-free lithium metal battery:

1) Under nitrogen protection, 1200 mg of nano zinc oxide, 5 mg of azobisisobutyronitrile, 3000 mg of N-vinyl pyrrolidone and 800 mg of N-cyanovinyl pyrrolidone were placed in a screw-mouth bottle, and stirred at 450 rpm for 2.0 h to form a white slurry. The diameter of the nano zinc oxide was 60 nm.

2) The slurry prepared in step 1) is evenly coated on the surface of the metal current collector and heat-dried and polymerized at 80°C for 4.0 hours to obtain a modified current collector. The metal current collector is a nickel current collector, and the slurry coating method is a blade coating method. The blade thickness used in the blade coating method is 50 μm.

Figure 4 is a scanning electron microscope photo of the modified metal current collector prepared in this embodiment. The slurry prepared in this embodiment is uniform and fine, and is white; the modified coating on the surface of the nickel current collector is flat, and the polymer matrix and the inorganic filler are evenly distributed; the full battery test is performed by assembling a negative electrode-free lithium metal battery with a lithium iron phosphate electrode as the positive electrode, and the battery first cycle discharge capacity is 146.7 mAh g ^-1 , and the first cycle coulomb efficiency is 88.54%; the coulomb efficiency is close to 100% during the cycle, and there is still a capacity retention rate of 69.36% after 50 cycles; after the battery is charged, the lithium deposition morphology on the surface of the nickel current collector is dense, no lithium dendrites are generated, and the modified coating can still be evenly attached to the surface of the nickel current collector after the battery is discharged.

Example 5

Preparation of a current collector for a negative electrode-free lithium metal battery:

1) Under nitrogen protection, 1000 mg of nano-tin dioxide, 5 mg of azobisisobutyronitrile, 3500 mg of N-vinyl pyrrolidone and 500 mg of N-cyanovinyl pyrrolidone were placed in a screw-mouth bottle, and stirred at 450 rpm for 2.0 h to form an off-white slurry. The diameter of the nano-tin dioxide was 80 nm.

2) The slurry prepared in step 1) is evenly coated on the surface of the metal current collector and heat-dried and polymerized at 80°C for 4.0 hours to obtain a modified metal current collector. The metal current collector is a copper current collector, and the slurry coating method is a blade coating method. The blade thickness used in the blade coating method is 50 μm.

Figure 5 is a scanning electron microscope photo of the metal lithium deposition on the negative electrode side of the negative electrode-free lithium metal battery prepared in this embodiment after the first charge. The slurry prepared in this embodiment is uniform and fine, and is grayish white; the modified coating on the surface of the copper current collector is flat, and the polymer matrix and the inorganic filler are evenly distributed; the negative electrode-free lithium metal battery is assembled with the lithium iron phosphate electrode as the positive electrode for full battery testing, and the battery first cycle discharge capacity is 149.78 mAh g ^-1 , and the first cycle coulomb efficiency is 90.14%; the coulomb efficiency is close to 100% during the cycle, and there is still a capacity retention rate of 73.35% after 50 cycles; after the battery is charged, the lithium deposition morphology on the surface of the copper current collector is dense, no lithium dendrites are generated, and the modified coating can still be evenly attached to the surface of the copper current collector after the battery is discharged.

Example 6

Preparation of a current collector for a negative electrode-free lithium metal battery:

1) Under nitrogen protection, 1000 mg of nano zinc powder, 5 mg of azobisisobutyronitrile, 3600 mg of N-vinyl pyrrolidone and 400 mg of N-cyanovinyl pyrrolidone were placed in a screw-cap bottle, and stirred at 450 rpm for 2.0 h to form an off-white slurry. The diameter of the nano zinc powder was 70 nm.

2) The slurry prepared in step 1) is evenly coated on the surface of the metal current collector and heat-dried and polymerized at 70°C for 5.0 hours to obtain a modified current collector. The metal current collector is a nickel current collector, and the slurry coating method is a spin coating method. The rotation speed used in the spin coating method is 4000 rpm and the coating time is 90 s.

Figure 6 is a scanning electron microscope photo of the surface of the modified nickel current collector after the first discharge of the negative electrode-free lithium metal battery prepared in this embodiment. The slurry prepared in this embodiment is uniform and fine, and is off-white; the modified coating on the surface of the nickel current collector is flat, and the polymer matrix and the inorganic filler are evenly distributed; the negative electrode-free lithium metal battery is assembled with lithium iron phosphate electrode as the positive electrode for full battery testing, and the battery first cycle discharge capacity is 147.53 mAh g ^-1 , and the first cycle coulomb efficiency is 90.47%; the coulomb efficiency is close to 100% during the cycle, and there is still a capacity retention rate of 72.68% after 50 cycles; after the battery is charged, the lithium deposition morphology on the surface of the nickel current collector is dense, no lithium dendrites are generated, and the modified coating can still be evenly attached to the surface of the nickel current collector after the battery is discharged.

Example 7

Preparation of a current collector for a negative electrode-free lithium metal battery:

1) Under nitrogen protection, 850 mg of nano zinc powder, 10 mg of azobisisobutyronitrile, 3800 mg of N-vinyl pyrrolidone and 450 mg of N-cyanovinyl pyrrolidone were placed in a screw-cap bottle and stirred with a magnetic stirrer at 450 rpm for 2.0 h to form a gray-black slurry, in which the diameter of the nano zinc powder was 70 nm.

2) Under nitrogen protection, the slurry prepared in step 1) is evenly coated on the surface of the metal current collector and heat-dried and polymerized at 60°C for 5.0 hours to obtain a modified current collector. The metal current collector is a copper current collector, and the slurry coating method is a blade coating method. The blade thickness used in the blade coating method is 50 μm.

The slurry prepared in this embodiment is uniform and fine, and is gray-black in color; the modified coating on the surface of the copper current collector is flat, and the polymer matrix and the inorganic filler are evenly distributed; a full-battery test is performed on a negative-electrode-free lithium metal battery assembled with a lithium iron phosphate electrode as the positive electrode, and the battery has a first-cycle discharge capacity of 150.63 mAh g ^-1 and a first-cycle coulomb efficiency of 93.00%; the coulomb efficiency is close to 100% during the cycle, and there is still a capacity retention rate of 73.06% after 50 cycles; after the battery is charged, the lithium deposition morphology on the surface of the copper current collector is dense, no lithium dendrites are generated, and the modified coating can still be evenly attached to the surface of the copper current collector after the battery is discharged.

Example 8

Preparation of a current collector for a negative electrode-free lithium metal battery:

1) Under nitrogen protection, 800 mg of nano-tin dioxide, 8 mg of azobisisobutyronitrile, 2000 mg of N-vinyl pyrrolidone and 1200 mg of N-cyanovinyl pyrrolidone were placed in a screw-mouth bottle, and stirred at 450 rpm for 2.0 h to form an off-white slurry. The diameter of the nano-tin dioxide was 80 nm.

2) The slurry prepared in step 1) is evenly coated on the surface of the metal current collector and heat-dried and polymerized at 120°C for 1.0h to obtain a modified current collector. The metal current collector is a nickel current collector, and the slurry coating method is a spin coating method. The rotation speed used in the spin coating method is 4000 rpm and the coating time is 90 s.

The slurry prepared in this embodiment is uniform and fine, and is off-white in color; the modified coating on the surface of the nickel current collector is flat, and the polymer matrix and the inorganic filler are evenly distributed; a full-battery test is performed on a negative-electrode-free lithium metal battery assembled with a lithium iron phosphate electrode as the positive electrode, and the battery has a first-cycle discharge capacity of 149.63 mAh g ^-1 and a first-cycle coulomb efficiency of 93.57%; the coulomb efficiency is close to 100% during the cycle, and there is still a capacity retention rate of 73.88% after 50 cycles; after the battery is charged, the lithium deposition morphology on the surface of the nickel current collector is dense, no lithium dendrites are generated, and the modified coating can still be evenly attached to the surface of the nickel current collector after the battery is discharged.

Example 9

Preparation of a current collector for a negative electrode-free lithium metal battery:

1) Under nitrogen protection, 2000 mg of nano silver powder, 5 mg of azobisisobutyronitrile, 2000 mg of N-vinyl pyrrolidone and 1500 mg of N-cyanovinyl pyrrolidone were placed in a screw-mouth bottle, and stirred at 450 rpm for 2.0 h to form a white slurry. The diameter of the nano silver powder was 60 nm.

2) The slurry prepared in step 1) is evenly coated on the surface of the metal current collector and heat-dried and polymerized at 80°C for 4.0 hours to obtain a modified current collector. The metal current collector is a nickel current collector, and the slurry coating method is a blade coating method. The blade thickness used in the blade coating method is 50 μm.

The slurry prepared in this embodiment is uniform and fine, and is white in color; the modified coating on the surface of the nickel current collector is flat, and the polymer matrix and the inorganic filler are evenly distributed; a full-battery test is performed on a negative-electrode-free lithium metal battery assembled with a lithium iron phosphate electrode as the positive electrode, and the battery has a first-cycle discharge capacity of 150.2 mAh g ^-1 and a first-cycle coulomb efficiency of 92.65%; the coulomb efficiency is close to 100% during the cycle, and there is still a capacity retention rate of 73.22% after 50 cycles; after the battery is charged, the lithium deposition morphology on the surface of the nickel current collector is dense, no lithium dendrites are generated, and the modified coating can still be evenly attached to the surface of the nickel current collector after the battery is discharged.

Comparative Example 1

The current collector was prepared in the same manner as in Example 1, except that 4000 mg of N-vinyl pyrrolidone was directly added instead of N-cyanovinyl pyrrolidone.

In this comparative example 1, a negative electrode-free lithium metal battery was assembled with lithium iron phosphate electrode as the positive electrode for full battery testing. The battery had a first-cycle discharge capacity of 115.25 mAh g ^-1 and a first-cycle coulomb efficiency of 87.00%. The coulomb efficiency during the cycle was about 91%, and after 50 cycles, the capacity retention rate was 52.33%.

From the comparison of the data of Comparative Example 1 and Example 1, it can be seen that if N-cyanovinyl pyrrolidone is not added to the slurry, the battery performance will decrease when the prepared current collector is applied to the battery. This is because in the in-situ polymerization process, N-vinyl pyrrolidone and N-cyanovinyl pyrrolidone act as both inorganic lithium-philic nanoparticle dispersants and binders. When N-vinyl pyrrolidone is used alone, its polymerization degree is too high, resulting in a decrease in the bonding performance between the formed polymer and the metal current collector. However, when an appropriate amount of cyanovinyl pyrrolidone containing a cyano strong electron-withdrawing group is introduced, it can play a role in regulating the in-situ polymerization degree and at the same time enhance the bonding performance between the polymer and the current collector.

Comparative Example 2

The current collector was prepared by the same method as in Example 1, except that the amount of N-cyanovinylpyrrolidone added was increased, i.e., step 1) was: 1500 mg of nano silver powder, 7 mg of azobisisobutyronitrile, 1800 mg of N-vinylpyrrolidone and 1700 mg of N-cyanovinylpyrrolidone were placed in a screw-mouth bottle, magnetically stirred at 450 rpm, stirred and dispersed for 2.0 h to form a gray-black slurry, wherein the diameter of the nano silver powder was 70 nm. Step 2) was the same as in Example 1.

In this comparative example 2, a negative electrode-free lithium metal battery was assembled with lithium iron phosphate electrode as the positive electrode for full battery testing. The battery had a first-cycle discharge capacity of 118.98 mAh g ^-1 and a first-cycle coulomb efficiency of 86.00%. The coulomb efficiency during the cycle was about 93%, and the capacity retention rate was 48.47% after 50 cycles.

From the comparison of the data of Comparative Example 2 and Example 1, it can be seen that if too much N-cyanovinyl pyrrolidone is added to the slurry, the battery performance will also be reduced. Because the amount of N-cyanovinyl pyrrolidone is too much, due to the structural limitations of N-cyanovinyl pyrrolidone, the compound polymer is too low and the inorganic electrophilic nanoparticles cannot be completely coated and bonded to the metal current collector, resulting in a reduction in battery performance.

Comparative Example 3

Preparation of a current collector for a negative electrode-free lithium metal battery:

1) Preparation of polymer

3000 mg of N-vinyl pyrrolidone, 500 mg of N-cyanovinyl pyrrolidone and 7 mg of azobisisobutyronitrile were polymerized at 80° C. The polymerization time was 3.0 h to obtain a polymer.

2) Preparation of slurry

The polymer was dissolved in N-methylpyrrolidone, and 1500 mg of nano silver powder was added and dispersed evenly to obtain a slurry.

3) Preparation of current collector

The slurry is evenly coated on the surface of the copper current collector and then dried to obtain the current collector.

In this comparative example 4, a negative electrode-free lithium metal battery was assembled with lithium iron phosphate electrode as the positive electrode for full battery testing. The battery had a first-cycle discharge capacity of 140.02 mAh g ^-1 and a first-cycle coulomb efficiency of 89.00%. The coulomb efficiency during the cycle was about 96%, and after 50 cycles, the capacity retention rate was 63.54%.

From the comparison of the data of Comparative Example 3 and Example 1, it can be seen that the current collector prepared by the in-situ polymerization method of the present invention in Example 1 has a better application effect in the battery, because the polymer generated by the in-situ polymerization method is more uniform, thereby improving the consistency of the battery. The traditional method of Comparative Example 3 is prone to the problem of unevenness between the polymer and the lithium-philic nanoparticles, thereby affecting the application effect in the battery, and the preparation method is cumbersome and has poor repeatability.

The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are exhaustively listed. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

For those skilled in the art, several modifications and improvements may be made without departing from the concept of the present invention, all of which belong to the protection scope of the present invention. The protection scope of the present invention shall be based on the attached claims.

Claims (9)

1. A method for preparing a current collector for a negative electrode-free lithium metal battery, characterized in that the preparation method is: Under the protection of inert gas, the lithium-philic nanoparticles and the initiator are uniformly dispersed in a mixed solution of N-vinyl pyrrolidone and N-cyanovinyl pyrrolidone to form a slurry, and the slurry is uniformly coated on the surface of the metal current collector and in-situ polymerized by heating to obtain a current collector for a negative electrode-free lithium metal battery; the structural formula of the N-cyanovinyl pyrrolidone is: ; The lithium-philic nanoparticles are selected from at least one of nano silver powder, nano tin powder, nano zinc powder, nano silver oxide, nano tin dioxide and nano zinc oxide. 2. The method for preparing a current collector for a negative electrode-free lithium metal battery according to claim 1, wherein the initiator is selected from at least one of azobisisobutyronitrile and phthaloyl peroxide; The amount of the initiator is 0.08-0.20% of the total mass of the slurry. 3. The method for preparing a current collector for a negative electrode-free lithium metal battery according to claim 1, wherein the metal current collector is one of a copper current collector and a nickel current collector. 4. A method for preparing a current collector for a negative electrode-free lithium metal battery according to claim 1, characterized in that the particle size of the lithium-philic nanoparticles is 50-100 nm, and the amount of the lithium-philic nanoparticles is 15-40% of the total mass of the slurry. 5. According to claim 1, a method for preparing a current collector for a negative electrode-free lithium metal battery is characterized in that the amount of N-vinyl pyrrolidone accounts for 35-75% of the total mass of the slurry; the amount of N-cyanovinyl pyrrolidone accounts for 5-30% of the total mass of the slurry. 6. A method for preparing a current collector for a negative electrode-free lithium metal battery according to claim 1, characterized in that the temperature of the heating in-situ polymerization is 60-120°C, and the heating in-situ polymerization time is 1-5h. 7. A method for preparing a current collector for a negative electrode-free lithium metal battery according to claim 1, characterized in that the coating method used to evenly coat the slurry on the surface of the metal current collector is a doctor blade coating method or a spin coating method. 8. A current collector for a negative electrode-free lithium metal battery, characterized in that the current collector is prepared by the preparation method according to any one of claims 1 to 7. 9. An application of a current collector for a negative electrode-free lithium metal battery, characterized in that the current collector according to claim 8 is applied to a negative electrode-free lithium metal battery.