阅读说明：本技术 一种锂金属电池隔膜及其制备方法和锂金属电池 (Lithium metal battery diaphragm and preparation method thereof and lithium metal battery ) 是由 王宝 张玉娇 赵婕 于 2021-08-19 设计创作，主要内容包括：本发明提供一种锂金属电池隔膜及其制备方法和锂金属电池,所述锂金属电池隔膜包括隔膜和涂覆于隔膜一侧的改性层,所述改性层的制备原料包括富勒烯衍生物、导电材料和粘结剂。本发明的锂金属电池隔膜具有较高的机械性能和离子电导率,当其用于锂金属电池时,可以提高锂金属电池的安全性和长周期稳定性。(The invention provides a lithium metal battery diaphragm, a preparation method thereof and a lithium metal battery. The lithium metal battery diaphragm of the invention has higher mechanical property and ionic conductivity, and when the lithium metal battery diaphragm is used for a lithium metal battery, the safety and the long-period stability of the lithium metal battery can be improved.)

1. The lithium metal battery diaphragm is characterized by comprising a diaphragm and a modified layer coated on one side of the diaphragm, wherein the modified layer is prepared from fullerene derivatives, a conductive material and a binder.

2. The lithium metal battery separator according to claim 1, wherein the thickness of the modified layer is 10-30 μm, preferably 16 μm;

preferably, the mass ratio of the fullerene derivative to the conductive material to the binder is (9-x): x:1, wherein x is 1-3;

preferably, the value of x is 1.

3. The lithium metal battery separator according to claim 1 or 2, wherein the fullerene derivative has a chemical formula of C₆₀-(OLi)_nWherein the value of n is 1-15.

4. The lithium metal battery separator according to any of claims 1-3, wherein the conductive material comprises any one or a combination of at least two of conductive carbon black, Ketjen black, conductive carbon nanotubes, or graphene, preferably conductive carbon black;

preferably, the binder comprises polyvinylidene fluoride.

5. The lithium metal battery separator according to any of claims 1 to 4, wherein the separator is selected from any of a polypropylene separator, a polyethylene separator, a glass fiber separator or a polyvinylidene fluoride separator, preferably a polypropylene separator.

6. The method of preparing a lithium metal battery separator according to any one of claims 1 to 5, comprising the steps of:

(1) dissolving the fullerene derivative, the conductive material and the binder in the formula ratio in a solvent, and stirring to obtain a mixed solution;

(2) and (3) coating the mixed solution obtained in the step (1) on one side of a diaphragm to obtain a modified layer, and drying to obtain the lithium metal battery diaphragm.

7. The method of claim 6, wherein the solvent comprises N-methylpyrrolidone;

preferably, the stirring time of the step (1) is 12-18 h;

preferably, the drying in step (2) is performed in a vacuum oven;

preferably, the drying temperature in the step (2) is 50-80 ℃, and the drying time is 8-24 h.

8. A lithium metal battery comprising a positive electrode material, a negative electrode material, an electrolyte, and the lithium metal battery separator of any one of claims 1-5.

9. The lithium metal battery of claim 8, wherein the modified layer of the lithium metal battery separator faces the side of the negative electrode material.

10. The lithium metal battery of claim 8 or 9, wherein the positive electrode material comprises any one of lithium metal, sulfur, lithium iron phosphate, lithium cobaltate, lithium manganate, ternary nickel cobalt manganese, or ternary nickel cobalt aluminum, preferably lithium metal or ternary nickel cobalt manganese;

preferably, the anode material is lithium metal.

Technical Field

The invention belongs to the field of secondary batteries, and relates to a lithium metal battery diaphragm, a preparation method thereof and a lithium metal battery.

Background

Lithium metal is used as a negative electrode material due to its ultrahigh theoretical specific capacity (3860mAh g)^-1) And lowThe standard electrochemical potential (-3.040V vs standard hydrogen electrode) is in wide interest. However, Lithium Metal Batteries (LMBs) have hindered their commercial use during repeated charge and discharge due to the growth of lithium dendrites and low coulombic efficiency. Li dendrites can penetrate the membrane causing internal short circuits causing severe thermal runaway and explosion risks. In addition, the thermodynamic instability of lithium metal causes irreversible continuous reaction of lithium with an electrolyte, and since a solid electrolyte interface phase (SEI) containing Li is continuously formed on the surface of the Li metal with the consumption of Li and an organic electrolyte, the loss of Li is inevitably caused in an electrochemical process, thereby causing a short cycle life, and therefore, it is urgent to improve the safety and long-cycle stability of LMB.

The separator plays a crucial role in the electrochemical performance of the battery, and the design of the modified separator is one of the most effective and important strategies for solving the lithium dendrite problem. The modification of the separator is mainly to prevent the proliferation and growth of dendrites by coating ceramic and polymer, and the coatings can improve the mechanical strength of the composite separator and also can inhibit dendrites through reaction with Li. However, in contrast to charge transfer on electrodes, Li⁺The transport speed in the electrolyte is much slower. Therefore, Li is generally considered⁺Transport is Li⁺Determination of the deposition Process Rate, in other words if Li⁺Is able to pass uniformly through the membrane and transfer to the Li surface, a long-cycle stable dendrite-free LMB can be obtained.

Carbon-based materials, such as hollow carbon nanospheres, graphene, and fullerene, have excellent passivation properties, ionic conductivity, and mechanical strength and toughness. Passivation can protect Li metal, while defects in carbon-based materials provide a pathway for Li ion migration. Moreover, the derivative group can further improve the lithium ion conductivity of the lithium ion battery and meet the requirements of high mechanical property and high ionic conductivity. Compared with other carbon materials, the fullerene has poor conductivity and hydrophobicity, and is more suitable for the metallic lithium negative electrode.

CN110190326A discloses application of fullerene derivative as electrolyte additive and corresponding metal batteryAdded to the electrolyte of the metal battery. According to the invention, the fullerene derivative is introduced into the electrolyte of the metal battery as an electrolyte additive, and the corresponding metal battery is obtained, so that on one hand, the fullerene derivative can react with the metal cathode to generate a stable passivation film in situ, thereby preventing the metal cathode from directly contacting with the electrolyte, reducing the consumption of metal and prolonging the cycle life of the battery, and on the other hand, the fullerene after reaction can be deposited on the surface of the metal cathode to ensure that the metal is uniformly deposited, thereby reducing the generation of dendrites and improving the safety performance of the battery. However, the invention modifies the electrolyte, does not relate to the modification of the separator, and the SEI of the invention may also contain other inorganic substances (LiF, Li)₂CO₃Etc.), while the ionic conductivity of each inorganic substance is different, resulting in non-uniform deposition of lithium ions on the surface of lithium metal to generate lithium dendrites.

Accordingly, in the art, it is desired to develop a lithium metal battery separator which can improve the safety and long-term stability of a lithium metal battery when applied to the lithium metal battery.

Disclosure of Invention

In view of the defects of the prior art, the invention aims to provide a lithium metal battery diaphragm, a preparation method thereof and a lithium metal battery. The lithium metal battery diaphragm of the invention has higher mechanical property and ionic conductivity, and when the lithium metal battery diaphragm is used for a lithium metal battery, the safety and the long-period stability of the lithium metal battery can be improved.

In order to achieve the purpose, the invention adopts the following technical scheme:

in a first aspect, the invention provides a lithium metal battery diaphragm, which comprises a diaphragm and a modified layer coated on one side of the diaphragm, wherein raw materials for preparing the modified layer comprise a fullerene derivative, a conductive material and a binder.

In the invention, the membrane is modified by adopting a material taking the fullerene derivative as a main body, so that the mechanical strength of the membrane can be improved, and the ionic conductivity of the membrane can be improved.

When the lithium metal battery separator is used in a lithium metal battery, lithium gold is present during charging and dischargingThe modified layer in the battery separator can be mixed with Li⁺Reaction preferentially produces Li₂And O, inducing the formation of uniform SEI (solid electrolyte interphase) components, so that a uniform passivation film is formed on the surface of the negative electrode, and the effects of protecting Li metal and preventing dendritic crystal growth are achieved, thereby improving the safety and long-period stability of the lithium metal battery.

Preferably, the thickness of the modification layer is 10-30 μm, such as 10 μm, 12 μm, 13 μm, 16 μm, 18 μm, 20 μm, 22 μm, 23 μm, 25 μm, 28 μm or 30 μm, etc., preferably 16 μm.

If the thickness of the modified layer is less than 10 μm, it may result in low mechanical strength of a passivation layer formed at the negative electrode, and if the thickness of the modified layer is greater than 30 μm, it may result in slow transport of lithium ions in the lithium metal battery separator, and decrease of ionic conductivity of the lithium metal battery separator, thereby resulting in deterioration of electrochemical performance of the lithium metal battery.

Preferably, the mass ratio of the fullerene derivative to the conductive material to the binder is (9-x): x:1, wherein x is 1-3, such as 1, 1.2, 1.3, 1.5, 1.8, 2, 2.3, 2.5, 2.8 or 3.

If the value of x is less than 1, the content of the fullerene derivative is larger, the content of the conductive material is smaller, so that the liquidity of the modified layer mixed liquid is larger, and the modified layer mixed liquid cannot be fully attached to the diaphragm, so that the loading capacity of the fullerene derivative is reduced; if the value of x is more than 3, the ratio of the fullerene derivative is too small, the fullerene derivative cannot be fully contacted with the metal lithium, and cannot be fully reacted at the negative electrode and induced to generate a passivation layer with sufficient mechanical strength, so that the electrochemical performance of the lithium metal battery is not improved.

Preferably, the value of x is 1.

Preferably, the fullerene derivative has the chemical formula C₆₀-(OLi)_nWherein the value of n is 1-15, and the value of n cannot be accurately controlled in the actual preparation process, which is a range.

The fullerene derivative is coated on the diaphragm, so that the mechanical property of the diaphragm is firstly improved, and the possibility of penetration of lithium dendrites is reduced. Next, the fullerene derivative of the present invention contains-OLiDuring discharge-OLi will react with Li⁺Reaction to form Li₂O, improving the uniformity of the SEI composition. Thus, Li₂The generation of O can ensure the uniformity of lithium deposition on the surface of the lithium metal and reduce the nucleation and growth of lithium dendrites.

C₆₀-(OLi)_nThe preparation method can refer to the prior art (Peng Q, Gang C, Mizuseki H, et al. hydrogen storage capacity of C₆₀(OM)₁₂(M＝Li and Na)clusters[J]The method in Journal of Chemical Physics,2009,131(21): 353), for example, can be prepared by the following method: first using hydrogen peroxide (H)₂O₂) Oxide C₆₀Oxidizing C with potassium hydroxide₆₀Finally, the lithium ion exchange potassium ion reaction is carried out to obtain C₆₀-(OLi)_n。

Preferably, the conductive material comprises any one or a combination of at least two of conductive carbon black, ketjen black, conductive carbon nanotubes or graphene, preferably conductive carbon black.

Preferably, the binder comprises polyvinylidene fluoride (PVDF).

According to the preferable technical scheme, the adhesive is polyvinylidene fluoride, and the polyvinylidene fluoride not only plays the role of the adhesive, but also plays the role of ion conduction and is connected with C₆₀-(OLi)_nThe ionic conductivity of the lithium metal battery separator can be further improved by matching the lithium metal battery separator with the lithium metal battery separator.

Preferably, the separator is selected from any one of a polypropylene (PP) separator, a Polyethylene (PE) separator, a glass fiber separator, or a PVDF separator, preferably a PP separator.

In a second aspect, the present invention provides a method for preparing the lithium metal battery separator of the first aspect, the method comprising the steps of:

(1) dissolving the fullerene derivative, the conductive material and the binder in the formula ratio in a solvent, and stirring to obtain a mixed solution;

(2) and (2) uniformly coating the mixed solution obtained in the step (1) on one side of a diaphragm to obtain a modified layer, and drying to obtain the lithium metal battery diaphragm.

In the invention, the preparation method of the lithium metal battery diaphragm is simple, green and environment-friendly, and is suitable for large-scale production.

Preferably, the solvent comprises N-methylpyrrolidone (NMP).

Preferably, the stirring time in step (1) is 12-18h, such as 12h, 13h, 14h, 15h, 16h, 17h or 18h, etc.

Preferably, the drying in step (2) is performed in a vacuum oven.

Preferably, the temperature for drying in step (2) is 50-80 ℃, such as 50 ℃, 55 ℃, 60 ℃, 65 ℃, 70 ℃, 75 ℃ or 80 ℃ and the like, and the time for drying is 8-24h, such as 8h, 10h, 12h, 14h, 16h, 18h, 20h, 22h or 24h and the like.

In a third aspect, the present invention provides a lithium metal battery comprising a positive electrode material, a negative electrode material, an electrolyte, and the lithium metal battery separator of the first aspect.

In the invention, when the lithium metal battery diaphragm is used for the lithium metal battery, the lithium metal battery diaphragm can induce to generate an SEI film with uniform components in the charging and discharging processes, so that a layer of uniform passivation film is formed on the surface of a negative electrode, and the effects of protecting Li metal and preventing dendritic crystal growth are achieved, thereby improving the safety and long-period stability of the lithium metal battery.

Taking a lithium metal symmetrical battery as an example, the invention can obviously prevent the growth of dendritic crystals, improve the mechanical strength of the composite diaphragm, inhibit the dendritic crystals through the reaction with Li and increase the cycle stability of the lithium metal battery.

The electrical property and the cycling stability of the lithium metal battery prepared by the method are obviously improved, and the safety and the cycling stability of the next generation lithium metal battery are obviously improved.

Preferably, the modified layer of the lithium metal battery separator faces the side of the anode material.

Preferably, the positive electrode material includes any one of lithium metal, sulfur, lithium iron phosphate, lithium cobaltate, lithium manganate, nickel cobalt manganese ternary or nickel cobalt aluminum ternary, preferably lithium metal or nickel cobalt manganese ternary.

Preferably, the anode material is lithium metal.

As a preferable technical scheme of the invention, the negative electrode material is lithium metal, the negative electrode material and the fullerene derivative both contain lithium, and-OLi and Li can react in the charging and discharging process⁺Reaction to form Li₂O, improving the uniformity of the SEI composition.

The specific components of the electrolyte solution are not particularly limited in the present invention, and, for example, lithium hexafluorophosphate (LiPF) may be used₆) Dissolving in a mixed solution of diethyl carbonate (DEC) and Ethylene Carbonate (EC) in a volume ratio of 1:1 to obtain LiPF₆The concentration in the mixed solution was 1 mol/L.

Compared with the prior art, the invention has the following beneficial effects:

the lithium metal battery diaphragm prepared by the fullerene derivative modified diaphragm has higher mechanical strength and ionic conductivity. When the lithium metal battery diaphragm is used for a lithium metal battery, the lithium metal battery diaphragm can induce to generate an SEI film with uniform components in the charging and discharging processes, so that a uniform passivation film is formed on the surface of a negative electrode, the effects of protecting Li metal and preventing dendritic crystal growth are achieved, and the safety and the long-period stability of the lithium metal battery are improved (the capacity retention rate after 1C cycle of 500 cycles is 75% -81%).

Drawings

Fig. 1 is a surface SEM image of a lithium metal battery separator provided in example 1.

Fig. 2 is a side SEM image of the lithium metal battery separator provided in example 1.

Fig. 3 is Li C of the lithium symmetric battery provided in embodiment 1₆₀-(OLi)_nA lithium plating and lithium removal behavior diagram of/PP | Li.

Fig. 4 is a lithium metal battery NCM811| | C provided in embodiment 1₆₀-(OLi)_nand/PP | Li circulation performance diagram.

Fig. 5 is a side SEM image of the lithium metal battery separator provided in example 3.

Fig. 6 is a side SEM image of the lithium metal battery separator provided in example 4.

Fig. 7 is a lithium plating and lithium removal behavior diagram of the lithium symmetric battery Li | | | PP | | Li provided in embodiment 1.

Detailed Description

The technical solution of the present invention is further explained by the following embodiments. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.

The electrolyte used in the examples and the comparative examples of the invention is LiPF₆Dissolving in mixed solution of DEC and EC with the volume ratio of 1:1 to obtain LiPF₆The concentration in the mixed solution was 1 mol/L. The NCM811 used in the examples and comparative examples of the present invention means that the main component is nickel (Ni) cobalt (Co) manganese (Mn), and 811 represents the ratio of the three components of Ni, Co and Mn of 0.8:0.1: 0.1.

Example 1

The lithium metal battery diaphragm comprises a diaphragm and a modified layer coated on one side of the diaphragm, and the modified layer is prepared from fullerene derivatives, a conductive material and a binder in a mass ratio of 8:1: 1.

Wherein the thickness of the modified layer is 16 μm, and the chemical formula of the fullerene derivative is C₆₀-(OLi)_nThe value of n is 1-15, the conductive material is conductive carbon black Super-P, the binder is PVDF, and the diaphragm is a PP diaphragm.

The preparation method comprises the following steps:

(1) dissolving the fullerene derivative, the conductive material and the binder in the formula ratio in NMP, and stirring for 12h to obtain a mixed solution;

(2) coating the mixed solution obtained in the step (1) on one side of a diaphragm to obtain a modified layer, and putting the diaphragm coated with the modified layer into a vacuum oven at 50 ℃ to bake for 12h to obtain the lithium metal battery diaphragm.

The lithium metal battery separator prepared in this example was cut according to the size of the desired assembled battery.

The lithium metal battery separator prepared in example 1 was subjected to a Scanning Electron Microscope (SEM) test, and its surface scanning topography and side scanning topography were respectively shown in fig. 1 and 2, and it can be seen from fig. 2 that the thickness of the modified layer was 16 μm.

The lithium metal battery diaphragm, the lithium sheet, the electrolyte and the lithium metal prepared in the example 1 are assembled into the lithium symmetrical battery Li | | C₆₀-(OLi)₁₂The results of the tests on the lithium plating and lithium removal of the lithium symmetric battery are shown in FIG. 3, when the current density is 0.1mA cm^-2The lithium symmetric battery can stably cycle for more than 1000 times and can keep low overpotential.

The lithium metal battery separator, the lithium sheet, the electrolyte, the ternary NCM811 and the lithium metal prepared in example 1 were assembled into a lithium metal battery NCM811| | C₆₀-(OLi)₁₂The result of testing 500 cycles of the Li under the condition of 1C is shown in figure 4, and it can be seen that the stable state can be kept even if the cycle is carried out under the high current density, and the capacity retention rate can reach 81% after 500 cycles.

Example 2

The lithium metal battery diaphragm comprises a diaphragm and a modified layer coated on one side of the diaphragm, and the modified layer is prepared from fullerene derivatives, a conductive material and a binder in a mass ratio of 6:3: 1.

Wherein the thickness of the modified layer is 16 μm, and the chemical formula of the fullerene derivative is C₆₀-(OLi)_nThe value of n is 1-15, the conductive material is conductive carbon black Super-P, the binder is PVDF, and the diaphragm is a PP diaphragm.

The preparation method comprises the following steps:

(1) dissolving the fullerene derivative, the conductive material and the binder in the formula ratio in NMP, and stirring for 12h to obtain a mixed solution;

(2) coating the mixed solution obtained in the step (1) on one side of a diaphragm to obtain a modified layer, and putting the diaphragm coated with the modified layer into a vacuum oven at 50 ℃ to bake for 12h to obtain the lithium metal battery diaphragm.

The lithium metal battery separator prepared in this example was cut according to the size of the desired assembled battery.

The lithium metal battery separator, the lithium sheet and the battery prepared in example 2 were usedThe electrolyte and lithium metal are jointly assembled into the lithium symmetrical battery Li C₆₀-(OLi)_nThe method comprises the steps of/PP | Li, testing the lithium plating and lithium removing behaviors of the lithium symmetrical battery, and testing the current density of 0.1mA cm^-2The lithium symmetric battery can stably cycle for more than 1000 times and can keep low overpotential.

The lithium metal battery separator, the lithium sheet, the electrolyte, the ternary NCM811 and the lithium metal prepared in example 2 are assembled into the lithium metal battery NCM811| | C₆₀-(OLi)_nThe result of testing 500 cycles of Li under 1C was that it could be kept in a steady state even when cycled at such high current densities.

Example 3

In this example, a lithium metal battery separator was provided, which was different from example 1 only in that the thickness of the modified layer was 10 μm, and the other conditions were the same as in example 1.

The lithium metal battery separator prepared in this example was cut according to the size of the desired assembled battery.

When the lithium metal battery separator prepared in example 3 was subjected to a Scanning Electron Microscope (SEM) test and its side-scan morphology is shown in fig. 5, it can be seen that the thickness of the modified layer was 10 μm.

The lithium metal battery separator prepared in example 3 was assembled into a lithium metal battery NCM 811C in the same manner as in example 1₆₀-(OLi)_n/PP||Li。

Example 4

A lithium metal battery separator was provided in this example, which was different from example 1 only in that the thickness of the modified layer was 25 μm, and the other conditions were the same as in example 1.

The lithium metal battery separator prepared in this example was cut according to the size of the desired assembled battery.

When the lithium metal battery separator prepared in example 4 was subjected to a Scanning Electron Microscope (SEM) test and its side-scan morphology is shown in fig. 6, it can be seen that the thickness of the modified layer was 25 μm.

Lithium metal battery separator prepared in example 4 was prepared as in the example1 into a lithium metal battery NCM 811C₆₀-(OLi)_n/PP||Li。

Example 5

In this example, a lithium metal battery separator was provided, and the only difference between this example and example 1 was that the conductive material in the raw material for the modified layer was ketjen black, and the other conditions were the same as in example 1.

The lithium metal battery separator prepared in this example was cut according to the size of the desired assembled battery.

The lithium metal battery separator prepared in example 5 was assembled into a lithium metal battery NCM 811C in the same manner as in example 1₆₀-(OLi)_n/PP||Li。

Example 6

In this example, a lithium metal battery separator was provided, which was different from example 1 only in that the thickness of the modified layer was 8 μm, and the other conditions were the same as in example 1.

The lithium metal battery separator prepared in this example was cut according to the size of the desired assembled battery.

The lithium metal battery separator prepared in this example was assembled into a lithium metal battery NCM 811C in the manner of example 1₆₀-(OLi)_n/PP||Li。

Example 7

A lithium metal battery separator was provided in this example, which was different from example 1 only in that the thickness of the modified layer was 33 μm, and the other conditions were the same as in example 1.

The lithium metal battery separator prepared in this example was cut according to the size of the desired assembled battery.

The lithium metal battery separator prepared in this example was assembled into a lithium metal battery NCM 811C in the manner of example 1₆₀-(OLi)_n/PP||Li。

Example 8

In this example, a lithium metal battery separator was provided, and the only difference between this example and example 1 was that the raw materials for preparing the modified layer included fullerene derivatives, conductive carbon black Super-P, and PVDF in a mass ratio of 5:4:1, and the other conditions were the same as in example 1.

The lithium metal battery separator prepared in this example was cut according to the size of the desired assembled battery.

The lithium metal battery separator prepared in this example was assembled into a lithium metal battery NCM 811C in the manner of example 1₆₀-(OLi)_n/PP||Li。

Comparative example 1

In this comparative example, an original PP separator (i.e., not including a modified layer) was provided.

The PP diaphragm, the lithium sheet, the electrolyte and the lithium metal provided in the comparative example 1 are assembled together to form Li | PP | Li of the lithium symmetric battery, and the lithium plating and lithium removal behaviors of the lithium symmetric battery are tested, and the result is shown in FIG. 7, when the current density is 0.1mA cm^-2The lithium symmetric battery can only cycle about 100 times with high overpotential, and then the battery cannot continue to operate.

A lithium metal battery NCM811| | | PP | | | Li was assembled in the manner of example 1, and the specific discharge capacity and the capacity retention rate after the cycle of the lithium metal battery were tested, and the results are shown in table 1.

Lithium metal batteries NCM 811. DELTA.C as provided in examples 1 to 8₆₀-(OLi)_nThe performance of the/PP | Li and the NCM811| PP | Li of the lithium metal battery provided by the proportion 1 are tested, and the test method is as follows:

(1) standing the assembled lithium metal battery for 24 hours, and then respectively carrying out cycle performance test at the multiplying power of 0.5C and 3C, wherein the test voltage is 1.5-3.0V, the number of test turns is 100 turns, and the discharge specific capacity after 100 turns is obtained;

(2) and standing the assembled lithium metal battery for 24 hours, and then carrying out a cycle performance test at a multiplying power of 1C, wherein the test voltage is 1.5-3.0V, the number of test turns is 500, and the discharge specific capacity and the capacity retention rate after 500 turns are obtained.

The results of the performance tests are shown in table 1.

TABLE 1

As can be seen from Table 1, the lithium metal batteries provided in examples 1 to 5 have good rate capability (the specific discharge capacity after 100 cycles of 0.5C cycle: 196-210mAh/g, the specific discharge capacity after 100 cycles of 3C cycle: 144-163mAh/g, and the specific discharge capacity after 500 cycles of 1C cycle: 177-194mAh/g) and good cycle stability (the capacity retention rate after 500 cycles of 1C cycle: 75% -81%), and the safety performance of the lithium metal batteries is improved.

Compared with example 1, the specific discharge capacity of the lithium metal battery provided by examples 6-8 after cycling at 0.5C, 1C or 3C is obviously reduced, and the capacity retention rate of the lithium metal battery after cycling at 1C for 500 cycles is also obviously reduced, because the thickness of the modified layer in example 6 is too small, the mechanical strength of the passivation layer generated on the negative electrode is low, and the improvement of the electrochemical performance of the lithium metal battery is not facilitated; the thickness of the modified layer in embodiment 7 is too large, which affects the quality and thickness of the whole battery, increases the internal resistance, and reduces the reaction specific capacity of the battery; the fullerene derivative in example 8 is too small in mass, and the fullerene derivative does not sufficiently contact with metallic lithium, and does not sufficiently react with a negative electrode to induce a passivation layer having sufficient mechanical strength, which is disadvantageous for improving the electrochemical performance of a lithium metal battery.

The rate performance and cycle stability of the lithium metal battery provided in comparative example 1 were significantly deteriorated compared to example 1, which further demonstrates that the fullerene derivative can help to suppress lithium dendrites, thereby improving the electrochemical stability of the lithium metal battery.

The applicant states that the present invention is illustrated by the above examples to the lithium metal battery separator, the method of preparing the same, and the lithium metal battery of the present invention, but the present invention is not limited to the above examples, i.e., it is not meant that the present invention must be implemented by the above examples. It will be apparent to those skilled in the art that any modification of the present invention, equivalent substitutions of selected materials and additions of auxiliary components, selection of specific modes and the like, which are within the scope and disclosure of the present invention, are contemplated by the present invention.