阅读说明：本技术 锂负极保护层及其制备方法和应用 (Lithium negative electrode protective layer and preparation method and application thereof ) 是由 伽龙 戚孝群 李可嘉 严超 于 2021-07-28 设计创作，主要内容包括：本发明提供一种锂负极保护层及其制备方法和应用,属于锂电池技术领域,锂负极保护层的制备方法在于：将锂盐、丙烯酸酯类单体、交联剂、光引发剂按比例均匀混合,得到透明的前驱体溶液；在惰性气氛下,将所述前驱体溶液滴加到金属锂表面,通过紫外固化即可形成保护层；本发明的锂负极保护层的厚度小于0.5μm。本发明将锂盐、丙烯酸酯类单体、交联剂在光引发剂的作用下制备形成离子电导弹性体,该离子电导弹性体作为锂负极保护层,可以有效增强金属锂负极的循环稳定性,并且不会影响电池整体的质量和体积能量密度的发挥。(The invention provides a lithium negative electrode protective layer and a preparation method and application thereof, belonging to the technical field of lithium batteries, wherein the preparation method of the lithium negative electrode protective layer comprises the following steps: uniformly mixing lithium salt, acrylate monomer, cross-linking agent and photoinitiator in proportion to obtain transparent precursor solution; dropwise adding the precursor solution to the surface of the metal lithium in an inert atmosphere, and forming a protective layer through ultraviolet curing; the thickness of the lithium negative electrode protective layer of the present invention is less than 0.5 μm. According to the invention, the lithium salt, the acrylate monomer and the cross-linking agent are prepared into the ionic conduction elastomer under the action of the photoinitiator, and the ionic conduction elastomer is used as the lithium negative electrode protective layer, so that the cycling stability of the metal lithium negative electrode can be effectively enhanced, and the overall quality and the volume energy density of the battery are not influenced.)

1. The preparation method of the lithium negative electrode protective layer is characterized by comprising the following steps of:

uniformly mixing lithium salt, acrylate monomer, cross-linking agent and photoinitiator in proportion to obtain transparent precursor solution;

and dropwise adding the precursor solution to the surface of the metal lithium in an inert atmosphere, and carrying out ultraviolet curing to form the protective layer.

2. The method for preparing the lithium negative electrode protective layer according to claim 1, wherein the concentration of the lithium salt in the precursor solution is 0.1-2M, and the molar ratio of the photoinitiator, the crosslinking agent and the acrylate monomer is 0.01-0.1:0.001-0.01: 1.

3. The method for preparing the lithium negative electrode protective layer according to claim 1, wherein the lithium salt is selected from one or more of lithium bistrifluoromethanesulfonimide, lithium bisfluorosulfonimide, lithium hexafluorophosphate, and lithium perchlorate.

4. The method for preparing the lithium negative electrode protective layer according to claim 1, wherein the acrylate monomer is selected from one or more of ethyl acrylate, propyl acrylate and butyl acrylate.

5. The method of claim 1, wherein the cross-linking agent is polyethylene glycol diacrylate.

6. The method for preparing a lithium negative electrode protective layer according to claim 1, wherein the photoinitiator is one or more selected from the group consisting of 2-hydroxy-methylphenylpropane-1-one and 1-hydroxycyclohexylbenzophenone.

7. The method of preparing the lithium negative electrode protective layer according to claim 1, wherein the forming of the precursor solution is performed at 20 to 40 ℃.

8. The method for preparing the lithium negative electrode protective layer according to claim 1, wherein the parameters of the ultraviolet curing are as follows: the wavelength is 395nm, and the curing time is 10-100 min.

9. The lithium negative electrode protective layer, characterized by being produced by the production method according to any one of claims 1 to 8, and having a thickness of less than 0.5 μm.

10. Use of the lithium negative electrode protective layer according to claim 9 in a negative electrode material for a lithium battery.

Technical Field

The invention belongs to the field of lithium batteries, and particularly relates to a lithium negative electrode protective layer.

Background

Since its birth, lithium ion batteries have been widely used in various portable electronic devices, electric vehicles, and other fields, but with the rapid development and urgent needs of new industrial technologies, development of battery systems with higher energy density is required. The metallic lithium has very high theoretical specific capacity (3860 mAh.g)^-1) And the lowest electrochemical potential (-3.04V, vs H) relative to a standard hydrogen electrode₂H), and is therefore an extremely desirable anode material.

However, for the metallic lithium negative electrode, the formation and uncontrollable growth of lithium dendrites, volume change caused by metallic lithium, and other problems during charging and discharging not only cause the destruction of the original solid electrolyte interface film (SEI), but also expose more fresh lithium in the electrolyte, affect the cycle life and coulombic efficiency of the battery, and even cause serious safety problems. Therefore, solving these problems is of great significance for the development of next-generation battery systems.

At present, the methods for improving the stability of the lithium metal negative electrode mainly include the following methods: introducing an artificial interface protective layer, modifying electrolyte, designing a metal lithium cathode with a novel structure and the like.

The artificial interface protective layer can effectively promote the uniform deposition of the lithium metal cathode under high surface capacity by constructing the protective layer on the surface of the lithium metal in advance. In response to this strategy, professor Donghai Wang et al improved the SEI layer of lithium metal anodes by preparing a crosslinked multifunctional sulfur-containing polymer protective layer (ACS Energy lett.4(2019) 1271); professor Jia-Qi Huang et al constructed Li_6.75La₃Zr_1.75Ta_0.25O₁₂The composite protective layer of/Li-Nafion regulates the deposition behavior of lithium ions (adv. Mater.31(2019) 1808392)). Chinese patent CN 111430668A discloses a composite film for a lithium ion battery negative electrode protection layer, which effectively reduces the generation of "dead lithium".

In the process of implementing the invention, the inventor finds that the prior art has at least the following defects:

artificial interfacial protection layers constructed in the prior art generally have a large thickness (>5 μm), and although effective in enhancing the stability of a lithium metal anode, they also cause a loss in the overall volume and mass energy density of the battery and an increase in the internal impedance of the battery.

Disclosure of Invention

Based on the above background problems, the present invention aims to provide a method for preparing a lithium negative electrode protection layer, which can prepare a protection layer with a thickness of less than 0.5 μm, does not affect the overall quality and the volume energy density of a battery, and can reduce the interface impedance of the battery; another object of the present invention is to provide a lithium negative electrode protective layer and applications thereof.

In order to achieve the above object, on one hand, the embodiment of the present invention provides a technical solution:

the preparation method of the lithium negative electrode protective layer comprises the following steps:

uniformly mixing lithium salt, acrylate monomer, cross-linking agent and photoinitiator in proportion to obtain transparent precursor solution;

and dropwise adding the precursor solution to the surface of the metal lithium in an inert atmosphere, and carrying out ultraviolet curing to form the protective layer.

Further, the concentration of lithium salt in the precursor solution is 0.1-2M, and the molar ratio of the photoinitiator, the cross-linking agent and the acrylate monomer is 0.01-0.1:0.001-0.01: 1.

Further, the lithium salt is selected from one or more of lithium bis (trifluoromethanesulfonyl) imide, lithium bis (fluorosulfonyl) imide, lithium hexafluorophosphate and lithium perchlorate.

Further, the acrylic ester monomer is selected from one or more of ethyl acrylate, propyl acrylate and butyl acrylate.

Further, the cross-linking agent is polyethylene glycol diacrylate.

Further, the photoinitiator is selected from one or more of 2-hydroxy-methyl phenyl propane-1-ketone and 1-hydroxy cyclohexyl benzophenone.

Further, the formation of the precursor solution is performed at 20-40 ℃.

Further, the parameters of the ultraviolet curing are as follows: the wavelength is 395nm, and the curing time is 10-100 min.

The invention selects the acrylate as a monomer, generates the polyacrylate after polymerization, and has stronger adhesive force with a metal lithium matrix, thereby forming a stable protective layer on the surface of the metal lithium.

The precursor solution disclosed by the invention has excellent wettability with the metal lithium, and when the precursor solution is dripped on the surface of the metal lithium, the precursor solution can be rapidly spread on the surface of the metal lithium, so that the prepared protective layer is very thin.

In addition, after the precursor solution is subjected to photocuring, the lithium salt and the polymer matrix can generate an ion-conductive elastomer, has an ion-conductive function and excellent ductility, and can effectively coat the surface of the metal lithium without cracking.

In another aspect, an embodiment of the present invention provides a lithium negative electrode protection layer, which is prepared by the above preparation method, and has a thickness of less than 0.5 μm.

In a third aspect, the embodiment of the invention also provides an application of the lithium negative electrode protection layer in a negative electrode material of a lithium battery.

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

1. according to the invention, lithium salt, acrylate monomer and cross-linking agent are prepared under the action of photoinitiator to form the ion-conducting elastomer, the ion-conducting elastomer is used as a lithium negative electrode protective layer, has the thickness of less than 0.5 μm, can effectively enhance the cycling stability of the metal lithium negative electrode, and does not influence the overall quality and volume energy density of the battery.

2. The protective layer has excellent mechanical properties and excellent stability with a carbonate electrolyte, and shows significant effects on improving deposition/stripping of metallic lithium and inhibiting growth of lithium dendrites in an ultrathin size.

Drawings

FIG. 1 is a Scanning Electron Microscope (SEM) cross-sectional view of a lithium metal negative electrode modified with a protective layer in example 1 of the present invention;

fig. 2 is a polarization diagram of symmetric cells in example 1 of the present invention and comparative example.

Detailed Description

In order to solve the problem that the conventional artificial interface protective layer is thick, the invention provides a lithium negative electrode protective layer with the thickness of less than 0.5 mu m, and the preparation method comprises the steps of uniformly mixing lithium salt, acrylate monomers, a cross-linking agent and a photoinitiator in proportion to obtain a transparent precursor solution; and dropwise adding the precursor solution to the surface of the metal lithium in an inert atmosphere, and carrying out ultraviolet curing to form the protective layer.

The ionic conduction elastomer can be formed by the method, and can effectively enhance the cycling stability of the metal lithium negative electrode without influencing the overall quality and the volume energy density of the battery when being used as a lithium negative electrode protective layer.

The invention will be elucidated by means of specific embodiments.

Example 1

The preparation method of the lithium negative electrode protective layer comprises the following steps:

(1) weighing 1.435g (5mmol) of lithium bistrifluoromethanesulfonylimide, 0.142g (0.694mmol, 0.01eq) of 1-hydroxycyclohexyl benzophenone and 0.042g (0.0694mmol, 0.001eq, average molecular weight 600) of polyethylene glycol diacrylate, adding the mixture into 10mL (69.4mmol, 1.0eq) of butyl acrylate, and stirring the mixture at 20 ℃ for 20 hours until the mixture is completely dissolved to obtain a precursor solution;

(2) and (2) in an argon atmosphere, dripping 3 μ L of the precursor solution obtained in the step (1) on the surface of the metal lithium, curing for 90min by using an ultraviolet lamp (395nm), and forming a protective layer on the surface of the metal lithium after the curing is finished, wherein the thickness of the protective layer is 0.27 μm, and an SEM image of the protective layer is shown in figure 1.

The lithium metal formed by the method of this example was used to assemble a symmetrical cell.

Example 2

The preparation method of the lithium negative electrode protective layer comprises the following steps:

(1) weighing 0.213g (2mmol) of lithium perchlorate, 1.438g (7.04mmol,0.1eq) of 1-hydroxycyclohexyl benzophenone and 0.085g (0.141mmol, 0.002eq, average molecular weight 600) of polyethylene glycol diacrylate, adding into 10mL (70.4mmol,1.0eq) of propyl acrylate, and stirring for 10h at 25 ℃ until complete dissolution to obtain a precursor solution;

(2) and (2) in an argon atmosphere, dropwise coating 3 mu L of the precursor solution obtained in the step (1) on the surface of the metal lithium, curing for 80min by using an ultraviolet lamp (395nm), and forming a protective layer on the surface of the metal lithium after the curing is finished, wherein the thickness of the protective layer is 0.15 mu m.

The lithium metal formed by the method of this example was used to assemble a symmetrical cell.

Example 3

The preparation method of the lithium negative electrode protective layer comprises the following steps:

(1) weighing 3.74g (20mmol) of lithium bis (fluorosulfonyl) imide, 0.376g (1.84mmol, 0.02eq) of 1-hydroxycyclohexyl benzophenone and 0.276g (0.46mmol, 0.005eq, average molecular weight 600) of polyethylene glycol diacrylate, adding the mixture into 10mL (92.1mmol, 1.0eq) of ethyl acrylate, and stirring for 4h at 30 ℃ until the mixture is completely dissolved to obtain a precursor solution;

(2) and (2) in an argon atmosphere, dropwise coating 3 mu L of the precursor solution obtained in the step (1) on the surface of the metal lithium, curing for 70min by using an ultraviolet lamp (395nm), and forming a protective layer on the surface of the metal lithium after the curing is finished, wherein the thickness of the protective layer is 0.45 mu m.

The lithium metal formed by the method of this example was used to assemble a symmetrical cell.

Example 4

The preparation method of the lithium negative electrode protective layer comprises the following steps:

(1) weighing 1.52g (10mmol) of lithium hexafluorophosphate, 0.709g (3.47mmol, 0.05eq) of 1-hydroxycyclohexyl benzophenone and 0.416g (0.694mmol, 0.01eq, average molecular weight 600) of polyethylene glycol diacrylate, adding into 10mL (69.4mmol, 1.0eq) of butyl acrylate, and stirring for 15h at 35 ℃ until complete dissolution to obtain a precursor solution;

(2) and (2) in an argon atmosphere, dropwise coating 3 mu L of the precursor solution obtained in the step (1) on the surface of the metal lithium, curing for 60min by using an ultraviolet lamp (395nm), and forming a protective layer on the surface of the metal lithium after the curing is finished, wherein the thickness of the protective layer is 0.20 mu m.

The lithium metal formed by the method of this example was used to assemble a symmetrical cell.

Example 5

The preparation method of the lithium negative electrode protective layer comprises the following steps:

(1) weighing 2.87g (10mmol) of lithium bistrifluoromethanesulfonylimide, 1.438g (7.04mmol,0.1eq) of 2-hydroxy-methylphenylpropane-1-one and 0.422g (0.704mmol,0.01eq, average molecular weight 600) of polyethylene glycol diacrylate, adding into 10mL (70.4mmol,1.0eq) of propyl acrylate, and stirring at 40 ℃ for 10h until complete dissolution to obtain a precursor solution;

(2) and (2) in an argon atmosphere, dropwise coating 3 mu L of the precursor solution obtained in the step (1) on the surface of the metal lithium, curing for 50min by using an ultraviolet lamp (395nm), and forming a protective layer on the surface of the metal lithium after the curing is finished, wherein the thickness of the protective layer is 0.43 mu m.

The lithium metal formed by the method of this example was used to assemble a symmetrical cell.

Example 6

The preparation method of the lithium negative electrode protective layer comprises the following steps:

(1) weighing 0.532g (5mmol) of lithium perchlorate, 0.188g (0.921mmol, 0.01eq) of 2-hydroxy-methylphenylpropane-1-one and 0.276g (0.46mmol, 0.005eq, average molecular weight 600) of polyethylene glycol diacrylate, adding the mixture into 10mL (92.1mmol, 1.0eq) of ethyl acrylate, and stirring for 10 hours at 35 ℃ until the mixture is completely dissolved to obtain a precursor solution;

(2) and (2) in an argon atmosphere, dropwise coating 3 mu L of the precursor solution obtained in the step (1) on the surface of the metal lithium, curing for 40min by using an ultraviolet lamp (395nm), and forming a protective layer on the surface of the metal lithium after the curing is finished, wherein the thickness of the protective layer is 0.22 mu m.

The lithium metal formed by the method of this example was used to assemble a symmetrical cell.

Example 7

The preparation method of the lithium negative electrode protective layer comprises the following steps:

(1) weighing 0.935g (5mmol) of lithium bis (fluorosulfonyl) imide, 0.709g (3.47mmol, 0.05eq) of 2-hydroxy-methylphenylpropane-1-one and 0.083g (0.139mmol, 0.002eq, average molecular weight 600) of polyethylene glycol diacrylate, adding into 10mL (69.4mmol, 1.0eq) of butyl acrylate, and stirring at 30 ℃ for 20h until complete dissolution to obtain a precursor solution;

(2) and (2) in an argon atmosphere, dropwise coating 3 mu L of the precursor solution obtained in the step (1) on the surface of the metal lithium, curing for 30min by using an ultraviolet lamp (395nm), and forming a protective layer on the surface of the metal lithium after the curing is finished, wherein the thickness of the protective layer is 0.30 mu m.

The lithium metal formed by the method of this example was used to assemble a symmetrical cell.

Example 8

The preparation method of the lithium negative electrode protective layer comprises the following steps:

(1) weighing 0.760g (5mmol) of lithium hexafluorophosphate, 0.288g (1.41mmol, 0.02eq) of 2-hydroxy-methylphenylpropane-1-one, and 0.042g (0.070mmol, 0.001eq, average molecular weight 600) of polyethylene glycol diacrylate, adding into 10mL (70.4mmol,1.0eq) of propyl acrylate, and stirring at 25 ℃ for 40h until complete dissolution to obtain a precursor solution;

(2) and (2) in an argon atmosphere, dropwise coating 3 mu L of the precursor solution obtained in the step (1) on the surface of the metal lithium, curing for 20min by using an ultraviolet lamp (395nm), and forming a protective layer on the surface of the metal lithium after the curing is finished, wherein the thickness of the protective layer is 0.26 mu m.

The lithium metal formed by the method of this example was used to assemble a symmetrical cell.

Comparative example

And assembling the symmetrical battery by adopting common lithium metal.

It is to be noted that the positive and negative electrodes of the symmetrical batteries of examples 1 to 8 and comparative example are lithium electrodes, and the lithium electrode of comparative example is the same size as the lithium electrode of examples 1 to 8, and the separators of the symmetrical batteries are all lithium electrodesThe electrolyte is a PP diaphragm and is carbonate electrolyte: 1.0M lithium hexafluorophosphate (LiPF)₆) + Ethylene Carbonate (EC) + dimethyl carbonate (DMC) + diethyl carbonate (DEC), where the volume ratio of EC: DMC: DEC is 1:1: 1.

The symmetric batteries of examples 1 to 8 and comparative example were assembled into a button cell type CR2032 in an argon-filled glove box, and the cell was left to stand for 12 hours and then subjected to charge and discharge tests on a Newwei CT-4008 tester, and the test results are shown in Table 1, wherein the polarization diagrams of the symmetric electrode of example 1 and the symmetric electrode of comparative example are shown in FIG. 2.

TABLE 1 comparison of polarization voltage after stabilization of symmetrical cells with cycling performance in examples 1-8 and comparative examples

As can be seen from Table 1, the polarization voltage of the symmetrical cell formed by the lithium metal modified by the protective layer in the present invention is lower in the carbonate electrolyte system, and is significantly smaller than that of the symmetrical cell formed by the lithium metal without the protective layer in the comparative example, wherein the polarization voltage is only 30mV in example 1, and >100mV in the comparative example.

The symmetric battery formed by the lithium metal modified by the protective layer in the invention has better cycling stability, and as can be seen from table 1 and fig. 2, the symmetric battery in example 1 can be stably cycled for more than 1000h, while the comparative example can only be stably cycled for less than 200 h.

In conclusion, the protective layer of the present invention can improve deposition/exfoliation of metallic lithium and inhibit growth of lithium dendrites, thereby significantly improving cycle performance of a battery and reducing polarization voltage of the battery.

It should be noted that, for those skilled in the art, various changes and modifications can be made without departing from the inventive concept of the present invention, and these changes and modifications belong to the protection scope of the present invention.