Lithium metal electrode modified with artificial solid electrolyte interface layer, preparation method therefor and use thereof, and lithium metal battery

Abstract

The present application relates to the technical field of secondary batteries. Disclosed are a lithium metal electrode modified with an artificial solid electrolyte interface (ASEI) layer, a preparation method therefor and the use thereof, and a lithium metal battery. In the lithium metal electrode provided by the present application, the surface of lithium metal is modified with an ASEI layer, and the ASEI has the characteristic of a high-density grain boundary structure. In the present application, the ASEI having a high-density grain boundary structure is constructed on the surface of lithium metal, and by increasing the density of a grain boundary to accelerate the transfer speed of lithium ions, increase the ionic conductivity of the surface of the lithium metal and reduce the impedance of the ASEI, energy consumption caused by the lithium ions crossing the grain boundary can be effectively avoided, and more uniform deposition of the lithium ions can be induced, thereby inhibiting the growth of dendrites; therefore, the charging and discharging requirements of a high-rate lithium-dendrite-free lithium metal battery are met, and the cycle life is prolonged.

Description

An artificial solid-liquid interface layer modified lithium metal electrode, a preparation method and application thereof, and a lithium metal battery TECHNICAL FIELD

[0001] The present application relates to the technical field of secondary batteries, in particular to an artificial solid-liquid interface layer modified lithium metal electrode, a preparation method and application thereof, and a lithium metal battery. BACKGROUND

[0002] With the wide popularity of electronic devices, electric vehicles and other fields, people's demand for high-efficiency and high-energy-density batteries is increasing, so it is necessary to develop new battery technologies to meet the above-mentioned needs. Among them, lithium metal batteries are attracting attention because of their higher energy density. In the lithium metal battery system, the lithium metal has a high capacity of 3860 mAh / g (11 times higher than graphite), and the redox potential is as low as-3.04 V compared with the standard hydrogen electrode, which also means that the discharge voltage platform is higher. According to theoretical calculations, if the graphite negative electrode in the battery is replaced by lithium metal, the volume ED gain of the battery can be increased by 62%, and the weight ED gain can be increased by 45% at most, which means that lithium metal batteries can store more energy under the same volume and weight, and electric vehicles, mobile phones and other devices will have longer battery life. However, in practical applications, lithium metal batteries face many challenges, such as impractical rate performance, unsafe cycling conditions and limited cycle life, etc.

[0003] In related technologies, interface protection is one of the important strategies to stabilize lithium metal. Researchers mostly start from lithium metal materials and strive to develop new artificial solid electrolyte interfaces (ASEI) for modification to solve the above-mentioned problems. However, the ASEI crystals prepared by conventional methods have large crystal size, low grain boundary density, high ASEI impedance, and lithium ions need to overcome a large energy barrier to transfer from the electrolyte to the negative electrode surface, which is slow, which also leads to uneven deposition of lithium ions on the negative electrode, easy to cause the disorderly growth of dendrites, and ultimately also shortens the cycle life of the battery.

[0004] Therefore, it is of great significance to solve the problems of large ASEI crystal size, low grain boundary density and high impedance, provide an artificial solid-liquid interface modification that can effectively accelerate the transfer speed of lithium ions and reduce the impedance of ASEI, inhibit the growth of dendrites, and thus improve the cycle life of the battery.

[0005] SUMMARY

[0006] The present application aims to at least solve one of the technical problems existing in the prior art. To this end, the present application provides a lithium metal electrode with an artificial solid-liquid interface layer, a preparation method and application thereof, and a lithium metal battery, aiming to solve the problems of large ASEI crystal size, low grain boundary density, and large impedance in the current lithium metal electrode material.

[0007] In a first aspect of the present application, a lithium metal electrode is provided, comprising metal lithium and an artificial solid-liquid interface layer modified on the surface of the metal lithium; the composition of the artificial solid-liquid interface layer comprises N elements and one or more of Zr elements, F elements, P elements, and S elements; the grain size of the artificial solid-liquid interface layer ranges from 10 to 18 nm; and the impedance of the artificial solid-liquid interface layer ranges from 30 to 100 Ω.

[0008] The lithium metal electrode according to the embodiments of the present application has at least the following beneficial effects: the lithium metal electrode provided by the present application is modified with an artificial solid-liquid interface (ASEI) layer on the surface of the metal lithium, and the ASEI has a high-density grain boundary structure. The grain boundary is the interface between grains with different structures or orientations. On the grain boundary, the atomic arrangement changes from one orientation to another, so the atomic arrangement at the grain boundary is in a transition state and has irregularity. Such irregular grain boundaries are important channels for lithium ions to cross the ASEI and reach the surface of the lithium metal for reversible reaction during the charging and discharging of the lithium metal battery: in the crystal interior, the atomic arrangement is regular, and lithium ions mainly diffuse through the vacancies and interstitials in the crystal lattice in solid phase, with a relatively slow rate; while the atomic arrangement at the grain boundary is irregular, with more defects and vacancies, and lithium ions can use these defects and vacancies for multi-dimensional diffusion, with a faster rate. Therefore, in most cases, the transfer rate of lithium ions at the grain boundary is much higher than that in the crystal interior. The present application constructs an ASEI with a high-density grain boundary structure on the surface of the metal lithium, accelerates the transfer rate of lithium ions by increasing the grain boundary density, improves the ionic conductivity of the lithium metal surface, reduces the impedance of the ASEI, effectively avoids the energy consumption of lithium ions crossing the grain boundary, induces more uniform lithium ion deposition, inhibits dendrite growth, and thus meets the charging and discharging requirements of the lithium metal battery with large rate and no lithium dendrites, and improves the cycle life.

[0009] In the present application, the grain size of the artificial solid-liquid interface layer ranges from 10 to 18 nm, and the impedance ranges from 30 to 100 Ω. A decrease in grain size can increase the grain boundary density, and a too large grain size can decrease the grain boundary density, thereby reducing the migration rate of lithium ions. The present application can provide a grain size as low as 10 nm. The smaller the impedance, the more conducive to the migration of lithium ions; the larger the impedance, the slower the migration rate of lithium ions in the ASEI, which ultimately affects the deposition of lithium metal and the cycle life. The impedance of the ASEI provided by the present application can be as low as 30 Ω.

[0010] In some embodiments of the present application, when the composition of the artificial solid-liquid interface layer comprises N element and Zr element, the ratio of the content of the Zr element to the content of the N element (Zr / N) ranges from 0.25 to 0.45.

[0011] In some embodiments of the present application, when the composition of the artificial solid-liquid interface layer comprises N element and F element, the ratio of the content of the F element to the content of the N element (F / N) ranges from 0.5 to 2.

[0012] In some embodiments of the present application, when the composition of the artificial solid-liquid interface layer comprises N element and P element, the ratio of the content of the P element to the content of the N element (P / N) ranges from 0.5 to 2.

[0013] In some embodiments of the present application, when the composition of the artificial solid-liquid interface layer comprises N element and S element, the ratio of the content of the S element to the content of the N element (S / N) ranges from 0.4 to 1.

[0014] In some embodiments of the present application, when the composition of the artificial solid-liquid interface layer comprises N element and multiple elements selected from Zr element, F element, P element and S element, the ratio of the total content of the multiple elements to the content of the N element ranges from 0.25 to 2. For example, when the composition of the ASEI comprises N element, Zr element, F element, P element and S element, the range of (Zr+F+P+S) / N is 0.25 to 2.

[0015] In the present application, the element ratio of the ASEI product can be obtained by mapping test. When the solute is single, the range of Zr / N is 0.25 to 0.45, the range of F / N is 0.5 to 2, the range of P / N is 0.5 to 2, and the ratio of S / N is 0.4 to 1. When the solute is not single, the element content is related to the composition ratio of the solute, and the range of (Zr+F+P+S) / N is 0.25 to 2.

[0016] In some embodiments of the present application, the composition of the artificial solid-liquid interface layer comprises lithium nitride, and further comprises one or more of lithium nitrate, zirconium oxide, lithium fluoride, lithium phosphate, lithium oxide, lithium dodecylbenzenesulfonate, and lithium hydroxide.

[0017] In a second aspect of the present application, a preparation method of a lithium metal electrode modified by an artificial solid-liquid interface layer is provided, comprising the steps of:

[0018] S1, coating a predetermined concentration of a modification solution on the surface of the metal lithium under a protective gas atmosphere;

[0019] S2, after the solvent of the modification liquid is completely volatilized, the metal lithium coated with the modification liquid on the surface is placed in a nitrogen atmosphere, and is left to stand at a predetermined temperature for a predetermined time, to obtain a lithium metal electrode modified by an artificial solid-liquid interface layer;

[0020] The solute of the modification liquid comprises one or more of zirconyl nitrate, ammonium fluoride, phosphoric acid, and dodecylbenzenesulfonic acid.

[0021] The preparation method of the lithium metal electrode modified by the artificial solid-liquid interface layer according to the embodiments of the present application has at least the following beneficial effects: the present application proposes an artificial solid-liquid interface (ASEI) modification method for a lithium metal electrode: a certain amount of modification liquid is coated on the surface of metal lithium in a protective gas atmosphere, after the solvent of the modification liquid is completely volatilized, the metal lithium is placed in a nitrogen atmosphere, and is left to stand in a certain temperature environment, finally a lithium metal electrode coated with ASEI is obtained, and the ASEI has the characteristics of a high-density grain boundary structure. The grain boundary is the interface between grains with different structures or orientations. On the grain boundary, the atomic arrangement changes from one orientation to another, so the atomic arrangement at the grain boundary is in a transition state and has irregularity. Such irregular grain boundaries are important channels for lithium ions to pass through the ASEI and reach the surface of the lithium metal to undergo reversible reactions during charging and discharging of the lithium metal battery: in the crystal, the atomic arrangement is regular, and lithium ions mainly diffuse through vacancies and interstitials in the crystal lattice in solid phase, and the rate is relatively slow; while the atomic arrangement at the grain boundary is irregular, and there are more defects and vacancies, so lithium ions can use these defects and vacancies for multidimensional diffusion, and the rate is relatively fast. Therefore, in most cases, the transfer rate of lithium ions at the grain boundary is much higher than that in the crystal. Therefore, the method provided in the present application constructs an ASEI with a high-density grain boundary structure on the surface of the metal lithium, accelerates the transfer speed of lithium ions by increasing the grain boundary density, improves the ionic conductivity of the surface of the lithium metal, reduces the impedance of the ASEI, can effectively avoid the energy consumption of lithium ions passing through the grain boundary, induces more uniform lithium ion deposition, inhibits dendrite growth, and thus meets the charging and discharging requirements of the lithium metal battery with large rate and no lithium dendrites, and improves the cycle life.

[0022] In some embodiments of the present application, the solute of the modification liquid comprises one or more of zirconyl nitrate, ammonium fluoride, phosphoric acid, and dodecylbenzenesulfonic acid (DBSA), and is preferably zirconyl nitrate.

[0023] In some embodiments of the present application, the solvent of the modification liquid comprises one or more of dimethyl sulfoxide (DMSO), ethylene carbonate (EC), methyl ethyl carbonate (EMC), acetonitrile (ACN), and methanol.

[0024] The main component of the ASEI generated by the present application is inorganic crystal material, and according to the different modification liquid formula (solute + solvent), the main component of the ASEI can include one or more of lithium nitrate, zirconium oxide, lithium fluoride, lithium phosphate, lithium oxide, lithium dodecylbenzenesulfonate, and lithium hydroxide in addition to lithium nitride. The solute of the modification liquid is preferably zirconyl nitrate, because zirconyl nitrate reacts with lithium metal to form various compounds, including a large amount of lithium nitride (Li3N), which has extremely high ionic conductivity, is conducive to the rapid transfer of lithium ions in the deposition stripping process, and reduces the charge transfer impedance. Therefore, compared with other solutes, the ASEI generated by zirconyl nitrate is conducive to reducing the charge transfer impedance and can exhibit lower SEI impedance in electrical performance.

[0025] In some embodiments of the present application, the grain size of the artificial solid-liquid interface layer ranges from 10 to 18 nm, and the impedance ranges from 30 to 100 Ω. Reducing the grain size can increase the grain boundary density, and excessively large grain size can reduce the grain boundary density, thereby reducing the migration rate of lithium ions. The present application can provide a grain size as low as 10 nm. The smaller the impedance, the more conducive to lithium ion migration; the larger the impedance, the slower the migration rate of lithium ions in the ASEI, which ultimately affects the lithium metal deposition and cycle life. The ASEI provided by the present application can have an impedance as low as 30 Ω.

[0026] In some embodiments of the present application, the composition of the artificial solid-liquid interface layer includes lithium nitride and one or more of lithium nitrate, zirconium oxide, lithium fluoride, lithium phosphate, lithium oxide, lithium dodecylbenzenesulfonate, and lithium hydroxide.

[0027] In the present application, the elemental composition of the ASEI is different according to the different solutes of the modification liquid in the preparation process. The characteristic elements of zirconyl nitrate are Zr and N, the characteristic element of ammonium fluoride is F, the characteristic element of phosphoric acid is P, and the characteristic element of dodecylbenzenesulfonic acid is S. These characteristic elements will remain on the surface of the lithium metal in the form of compounds after preliminary treatment. The lithium metal after preliminary treatment is placed in a nitrogen atmosphere, and lithium nitride will be generated on the surface of the lithium metal, and the content of N element will increase.

[0028] In some embodiments of the present application, when the composition of the artificial solid-liquid interface layer includes N element and Zr element, the ratio of the content of Zr element to the content of N element (Zr / N) ranges from 0.25 to 0.45.

[0029] In some embodiments of the present application, when the composition of the artificial solid-liquid interface layer includes N element and F element, the ratio of the content of F element to the content of N element (F / N) ranges from 0.5 to 2.

[0030] In some embodiments of the present application, when the composition of the artificial solid-liquid interface layer comprises N element and P element, the ratio of the content of P element to the content of N element (P / N) ranges from 0.5 to 2.

[0031] In some embodiments of the present application, when the composition of the artificial solid-liquid interface layer comprises N element and S element, the ratio of the content of S element to the content of N element (S / N) ranges from 0.4 to 1.

[0032] In some embodiments of the present application, when the composition of the artificial solid-liquid interface layer comprises N element and multiple elements selected from Zr element, F element, P element and S element, the ratio of the total content of the multiple elements to the content of N element ranges from 0.25 to 2. For example, when the composition of ASEI comprises N element, Zr element, F element, P element and S element, the ratio of (Zr+F+P+S) / N ranges from 0.25 to 2.

[0033] In the present application, the element ratio of ASEI product can be obtained by mapping test. When the solute is single, the ratio of Zr / N ranges from 0.25 to 0.45, the ratio of F / N ranges from 0.5 to 2, the ratio of P / N ranges from 0.5 to 2, and the ratio of S / N ranges from 0.4 to 1. When the solute is not single, the element content is related to the composition ratio of solute, and the ratio of (Zr+F+P+S) / N ranges from 0.25 to 2.

[0034] The element ratio can directly reflect the reaction degree of the front and rear processes, that is, the composition of ASEI. Taking Zr / N as an example: the first process will generate LiZrO(NO3)2, and at this time the Zr / N is theoretically 0.5; the second process will generate Li3N on the surface of lithium metal, and as the reaction degree deepens, the ratio of Zr / N will decrease. When the ratio of Zr / N is too high, it indicates that the reaction degree of the second process is low, and when the ratio of Zr / N is too low, it indicates that a large amount of Li3N is covered on the surface of lithium metal, and in both cases a good high-density grain boundary structure cannot be formed. The same is true for the ratios of F / N, P / N, S / N and (Zr+F+P+S) / N. In order to form a high-density grain boundary structure, the ratios should be within a suitable range.

[0035] In some embodiments of the present application, the concentration of the modification solution is 0.02% to 0.2% (wt%), preferably 0.05 to 0.15 wt%, and more preferably about 0.1 wt%. The modification solution used in the present application is a low-concentration modification solution with a concentration of 0.02 to 0.2 wt%. When the concentration is too low (less than 0.02 wt%), the modification effect cannot be achieved; when the concentration is too high, the surface of the lithium metal is completely covered by the generated inorganic salts, and the active sites for the reaction between lithium metal and nitrogen gas in the next process cannot be provided. In the present application, the low-concentration modification solution in the above range is scraped onto the surface of the lithium metal in a dry protective gas atmosphere, and after the solvent of the modification solution is completely volatilized, the lithium metal is placed in a nitrogen atmosphere and left to stand for several hours in a certain temperature environment. Finally, the lithium metal coated with ASEI is obtained, and the ASEI has the characteristic of high-density grain boundary structure.

[0036] In some embodiments of the present application, the amount of the modification solution used is 20 to 80 μL / cm 2 , preferably 40 to 60 μL / cm 2 , and more preferably about 50 μL / cm 2 . When the amount of the modification solution used is too low, the modification solution cannot completely wet the surface of the lithium metal, resulting in incomplete and uneven modification reaction; when the amount of the modification solution used is too high, the surface of the lithium metal is completely covered by the generated inorganic salts, and the active sites for the reaction between lithium metal and nitrogen gas in the next process cannot be provided.

[0037] In some embodiments of the present application, the lithium metal is further subjected to surface polishing treatment before being coated with the modification solution. The surface of the lithium metal should be polished before modification to remove surface oxides, so that the modification effect can be better controlled by the modification solution, and the uncontrollable factors in the experiment can be reduced.

[0038] In some embodiments of the present application, the coating method of the modification solution is scraping, spraying, spinning or other conventional coating methods, as long as the uniform distribution of the modification solution on the modification surface can be ensured. Scraping is preferred.

[0039] In some embodiments of the present application, in step S1, the protective gas can be nitrogen or an inert gas (such as argon, etc.).

[0040] In some embodiments of the present application, the predetermined temperature is 0 to 100°C, preferably 30 to 80°C, and more preferably about 50°C. The temperature has an important influence on the nitridation reaction of lithium metal. When the temperature is too low, the crystal size of the product lithium nitride is large, and it is difficult to construct ASEI with high-density grain boundary structure; when the temperature is too high, the lithium nitride is decomposed, and nitrogen gas and reduced lithium metal are released. Therefore, the present application selects the standing temperature to be 0 to 100°C.

[0041] In some embodiments of the present application, the predetermined time is 1-12 h, preferably 2-12 h. When the standing time is too short, the lithium nitride generated by the reaction fails to completely cover the active sites of the lithium metal, and the ASEI has structural defects. When the standing time exceeds 12 hours, the nitriding reaction has been completed. Therefore, the standing time in the present application is preferably 1-12 h.

[0042] In some embodiments of the present application, the metal lithium coated with the modification solution is placed in a high-purity nitrogen atmosphere. Preferably, the purity of the high-purity nitrogen is ≥99%.

[0043] In step S2 of the present application, the metal lithium coated with the modification solution is placed in a high-purity nitrogen atmosphere (purity ≥99%) and is allowed to stand at a temperature of 0-100°C for 1-12 hours. Under this condition, the metal lithium reacts with nitrogen to generate lithium metal nitride, i.e., lithium nitride (Li3N), and the chemical reaction equation is 6Li+N2→2Li3N. The product is usually purple or red. This is mainly because the metal lithium has strong reducing property and reacts with nitrogen to generate lithium metal nitride, and finally generates lithium metal coated with high-density grain boundary structure ASEI.

[0044] In related art, there are also patents that attempt to prepare two or more grain boundaries to inhibit the growth of lithium dendrites, thereby improving the stability and cycle life of the lithium metal negative electrode, such as Chinese patent CN202311554323.0. However, the above scheme essentially wants to use lithium salt inorganic matter with high mechanical strength to construct a solid-state electrolyte layer to induce plastic deformation of the dendrites to inhibit the growth of the dendrites. Unlike the above, the present application uses in-situ modification to obtain a high-density grain boundary. Because only the in-situ modification method (i.e., the solute of the modification solution needs to react with lithium metal) can make the lithium salt closely adhere to the lithium metal, the high-density grain boundary ASEI obtained can effectively improve the ionic conductivity of the lithium metal surface, induce more uniform lithium ion deposition, and thus achieve the charging and discharging requirements of the lithium metal battery with large current and no lithium dendrites. Since lithium nitride has extremely high ionic conductivity (10 -3 S / cm), which is much higher than other lithium salts, and the simple path to generate lithium nitride is to introduce nitrogen to react with lithium metal, therefore, the technical scheme adopted in the present application is not only simple and convenient, but also obtains lithium metal coated with high-density grain boundary structure ASEI.

[0045] In a third aspect of the present application, a lithium metal electrode as described in any one of the above or a lithium metal electrode obtained by the preparation method as described in any one of the above is used in the preparation of a lithium metal secondary battery.

[0046] In a fourth aspect of the present application, a lithium metal battery comprises a lithium metal electrode as described in any one of the above or a lithium metal electrode obtained by the preparation method as described in any one of the above.

[0047] In some embodiments of the present application, the lithium metal electrode is used as a negative electrode. The above-mentioned electrode as a negative electrode can exhibit higher rate performance and long cycle life after being assembled into a battery, and has extremely wide application prospects in the field of secondary batteries.

[0048] In some embodiments of the present application, the lithium metal battery further comprises a positive electrode, a separator and an electrolyte.

[0049] Since the lithium metal battery (LMB) uses the lithium metal electrode with the artificial solid-liquid interface modification according to the above-mentioned embodiments, it at least has all the beneficial effects brought by the technical solutions of the above-mentioned embodiments. That is, the lithium metal negative electrode surface ion conductivity is effectively improved, more uniform lithium ion deposition is induced, and the large rate, lithium dendrite-free lithium metal battery charging and discharging requirements are realized, which has extremely wide application prospects in the field of secondary batteries.

[0050] In some embodiments of the present application, the material of the positive electrode can be oxygen, elemental sulfur, metal oxide and other commonly used lithium metal battery positive electrode materials in the art, which are not limited herein.

[0051] In some embodiments of the present application, the separator is arranged between the positive electrode and the negative electrode, and the electrolyte infiltrates the positive electrode, the negative electrode and the separator.

[0052] In some embodiments of the present application, the material of the separator includes at least one of polyethylene, polypropylene and polyvinylidene fluoride. In actual production, the material and structure of the separator are not strictly limited, for example, the above materials can be stacked to form a multi-layer structure, or the above materials can be mixed to form a single-layer structure, or a single material can form a single-layer structure; as long as it can play the basic role of the separator.

[0053] In some embodiments of the present application, the electrolyte includes an electrolyte salt and an organic solvent. The electrolyte salt includes lithium hexafluorophosphate. The organic solvent includes at least one of a carbonate solvent and a carboxylic acid ester solvent.

[0054] In some embodiments of the present application, the carbonate solvent includes at least one of ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC).

[0055] In some embodiments of the present application, the carboxylic acid ester solvent includes propyl propionate (PP).

[0056] In some embodiments of the present application, in the electrolyte, the concentration of the electrolyte salt is 0.8-1.5 mol / L.

[0057] In some embodiments of the present application, the amount of liquid electrolyte in the lithium ion battery is 6.05-9.65 g / 5 Ah. For example, it can be 7.2-7.95 g / 5 Ah.

[0058] In a fifth aspect of the present application, the above lithium metal battery is applied in an energy storage device, an electrical device or an electronic device. DETAILED DESCRIPTION

[0059] The concept and the resulting technical effects of the present application will be described below in conjunction with embodiments. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments of the present application. Based on the embodiments of the present application, other embodiments obtained by those skilled in the art without creative effort fall within the scope of the present application.

[0060] In the description of the present application, the description of the terms "one embodiment", "some embodiments", "exemplary embodiment", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the exemplary description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0061] In the description of the present application, unless otherwise specified, the numerical range "a-b" represents a shorthand representation of any real combination between a and b, where a and b are real numbers. Unless otherwise specified, each reaction or operation step can be carried out in sequence or not in sequence. Preferably, the reaction method in the present application is carried out in sequence.

[0062] In the following examples, the specific techniques or conditions not otherwise described are carried out according to the techniques or conditions described in the literature in the art or according to the product instructions. All reagents or instruments not otherwise specified are conventional products that can be obtained commercially.

[0063] Example 1

[0064] In a dry argon atmosphere, 50 μL of zirconyl nitrate / dimethyl sulfoxide modification solution with a concentration of 0.1 wt% was scraped on the surface of lithium metal (the surface area of lithium metal was 1 cm 2, the surface of the lithium metal is polished in advance to remove surface oxides), after the solvent dimethyl sulfoxide is completely volatilized, the lithium metal is placed in a nitrogen atmosphere and left to stand in a temperature environment of 50°C for 2 hours, and finally the lithium metal coated with ASEI of high-density grain boundary structure is obtained, and the main components of the ASEI are lithium nitride, lithium oxide, lithium nitrate and zirconium oxide.

[0065] Example 2

[0066] In a dry argon atmosphere, 50 μL of 0.1 wt% zirconium oxynitrate / dimethyl sulfoxide modification solution was scraped on the surface of the lithium metal (the surface area of the lithium metal was 1 cm 2 , the surface of the lithium metal is polished in advance to remove surface oxides), after the solvent dimethyl sulfoxide is completely volatilized, the lithium metal is placed in a nitrogen atmosphere and left to stand in a temperature environment of 50°C for 2 hours, and finally the lithium metal coated with ASEI of high-density grain boundary structure is obtained, and the main components of the ASEI are lithium nitride, lithium oxide, lithium nitrate and zirconium oxide.

[0067] Example 3

[0068] In a dry argon atmosphere, 50 μL of 0.1 wt% zirconium oxynitrate / dimethyl sulfoxide modification solution was scraped on the surface of the lithium metal (the surface area of the lithium metal was 1 cm 2 , the surface of the lithium metal is polished in advance to remove surface oxides), after the solvent dimethyl sulfoxide is completely volatilized, the lithium metal is placed in a nitrogen atmosphere and left to stand in a temperature environment of 50°C for 2 hours, and finally the lithium metal coated with ASEI of high-density grain boundary structure is obtained, and the main components of the ASEI are lithium nitride, lithium oxide, lithium nitrate and zirconium oxide.

[0069] Example 4

[0070] In a dry argon atmosphere, 50 μL of 0.1 wt% zirconium oxynitrate / dimethyl sulfoxide modification solution was scraped on the surface of the lithium metal (the surface area of the lithium metal was 1 cm 2 , the surface of the lithium metal is polished in advance to remove surface oxides), after the solvent dimethyl sulfoxide is completely volatilized, the lithium metal is placed in a nitrogen atmosphere and left to stand in a temperature environment of 50°C for 2 hours, and finally the lithium metal coated with ASEI of high-density grain boundary structure is obtained, and the main components of the ASEI are lithium nitride, lithium oxide, lithium nitrate and zirconium oxide.

[0071] Example 5

[0072] In a dry argon atmosphere, 50 μL of 0.1 wt% zirconium oxynitrate / dimethyl sulfoxide modification solution was scraped on the surface of the lithium metal (the surface area of the lithium metal was 1 cm 2, surface polishing is performed in advance to remove surface oxides), after the solvent methanol is completely volatilized, the lithium metal is placed in a nitrogen atmosphere, and is left to stand in a temperature environment of 50°C for 2 hours, and finally lithium metal coated with ASEI of a high-density grain boundary structure is obtained, and the main component of the ASEI is lithium nitride and lithium fluoride.

[0073] Comparative Example 1

[0074] In a dry argon atmosphere, 100 μL of zirconium oxynitrate / dimethyl sulfoxide modification solution with a concentration of 0.1 wt% is scraped onto the surface of lithium metal (the surface area of the lithium metal is 1 cm 2 , surface polishing is performed in advance to remove surface oxides), after the solvent dimethyl sulfoxide is completely volatilized, the lithium metal is placed in a nitrogen atmosphere, and is left to stand in a temperature environment of 50°C for 2 hours, and finally lithium metal coated with ASEI is obtained.

[0075] Comparative Example 2

[0076] In a dry argon atmosphere, 50 μL of zirconium oxynitrate / dimethyl sulfoxide modification solution with a concentration of 0.3 wt% is scraped onto the surface of lithium metal (the surface area of the lithium metal is 1 cm 2 , surface polishing is performed in advance to remove surface oxides), after the solvent dimethyl sulfoxide is completely volatilized, the lithium metal is placed in a nitrogen atmosphere, and is left to stand in a temperature environment of 50°C for 2 hours, and finally lithium metal coated with ASEI is obtained.

[0077] Comparative Example 3

[0078] In a dry argon atmosphere, 50 μL of zirconium oxynitrate / dimethyl sulfoxide modification solution with a concentration of 0.1 wt% is scraped onto the surface of lithium metal (the surface area of the lithium metal is 1 cm 2 , surface polishing is performed in advance to remove surface oxides), after the solvent dimethyl sulfoxide is completely volatilized, the lithium metal is placed in a nitrogen atmosphere, and is left to stand in a temperature environment of 50°C for 0.5 hours, and finally lithium metal coated with ASEI is obtained.

[0079] Comparative Example 4

[0080] In a dry argon atmosphere, 50 μL of zirconium oxynitrate / dimethyl sulfoxide modification solution with a concentration of 0.1 wt% is scraped onto the surface of lithium metal (the surface area of the lithium metal is 1 cm 2 , surface polishing is performed in advance to remove surface oxides), after the solvent dimethyl sulfoxide is completely volatilized, the lithium metal is placed in a nitrogen atmosphere, and is left to stand in a temperature environment of 120°C for 2 hours, and finally lithium metal coated with ASEI is obtained.

[0081] Comparative Example 5

[0082] In a dry argon atmosphere, 50 μL of zirconyl nitrate / dimethyl sulfoxide modification solution with a concentration of 0.1 wt% was scraped on the surface of lithium metal (the surface area of lithium metal was 1 cm 2 , surface polishing was performed in advance to remove surface oxides), and then 50 μL of ammonium fluoride / methanol modification solution with a concentration of 0.1 wt% was scraped on the surface of lithium metal after the solvent dimethyl sulfoxide was completely volatilized. After the solvent methanol was completely volatilized, the lithium metal coated with ASEI was finally obtained.

[0083] Performance test

[0084] 1. Grain boundary density test

[0085] The distribution of the inorganic crystal size of the modified lithium metal surface obtained by TEM test of Examples 1-5 and Comparative Examples 1-5 was tested, and the test method was as follows:

[0086] 1) After ASEI grew on the surface of lithium metal, a small amount of powder was scraped off with a scraper, and a suspension was prepared after dispersion with a dispersing agent and ultrasonic treatment;

[0087] 2) The suspension was dropped on a support film, and a sample was obtained after drying;

[0088] 3) TEM and HRTEM (high resolution transmission electron microscope) were performed on the sample to observe the lattice fringes, crystal size and grain boundaries of the sample.

[0089] The results are shown in Table 1, and the observation and statistical results show that the ASEI in the examples has a higher grain boundary density and a smaller internal crystal size.

[0090] 2. Lithium metal symmetrical battery EIS test

[0091] The lithium metal modified in Examples 1-5 and Comparative Examples 1-5 was cut into small round pieces of 16 mm, and two identical small round pieces were assembled into 2032 symmetrical batteries, wherein the electrolyte formula was 1M LiPF6 EC / EMC electrolyte, EC:EMC=3:7, and the separator was a 14 μm thick PE separator. At the same time, the 2032 symmetrical battery prepared by the same procedure without any treatment of the lithium metal was used as Comparative Example 6.

[0092] EIS test was performed on the lithium metal symmetrical batteries obtained in Examples 1-5 and Comparative Example 6 using an electrochemical workstation, and RSEI, i.e. the impedance of ASEI, was obtained by fitting the curve.

[0093] The EIS test instrument was a Shanghai Chenhua electrochemical workstation.

[0094] The test frequency was 10 -2 -10 5 Hz.

[0095] Equivalent circuit diagram:

[0096] The results are shown in Table 1. Among them, the lower the RSEI, the higher the ionic conductivity. It is found that lithium metal with high density of grain boundary ASEI has higher ionic conductivity.

[0097] 3. Cycle life ratio of lithium metal symmetric battery

[0098] The lithium metal modified in Examples 1-5 and Comparative Examples 1-5 was cut into 16mm small round pieces, and two of the same small round pieces were assembled into 2032 symmetric batteries, wherein the electrolyte formula was 1M LiPF6 EC / EMC electrolyte, EC:EMC=3:7, and the separator was a 14μm thick PE separator. At the same time, the 2032 symmetric battery prepared by the same procedure without any treatment of the lithium metal was used as Comparative Example 6.

[0099] The lithium metal symmetric batteries obtained in Examples 1-5 and Comparative Examples 1-6 were subjected to cycle life comparison, and the current density was set to 1mAh / cm 2 , the single charge capacity was 1mAh / cm 2 , the battery was subjected to charge-discharge cycle at room temperature until the polarization voltage was greater than 0.5V, and the cycle life of the symmetric battery of each example and comparative example was compared.

[0100] The test procedure is as follows:

[0101] 1) Stand for 5min;

[0102] 2) Constant current charge at 1mAh / cm 2 for 1h;

[0103] 3) Stand for 5min;

[0104] 4) Constant current discharge at 1mAh / cm 2 for 1h;

[0105] 5) Repeat 1-4 until the polarization voltage is >0.5V;

[0106] 6) End.

[0107] The test results are shown in Table 1.

[0108] Table 1

[0109] From the above Examples 1-4 and Comparative Examples 1-2, it can be seen that the amount and concentration of the modification solution mainly affect the amount of inorganic salts generated. When the amount or concentration is too high, the lithium metal surface will be completely covered by the generated inorganic salts, which cannot provide active sites for the reaction of lithium metal with nitrogen gas in the next process, thereby failing to form ASEI with a high-density grain boundary structure, resulting in an increase in average crystal size and RSEI, a decrease in ionic conductivity, and a decrease in cycle life. In addition, too high a concentration of the modification solution will also result in an increase in ASEI thickness, a longer migration path of lithium ions from the electrolyte to the surface of the negative electrode, and a decrease in migration rate, which is manifested in an increase in RSEI in impedance testing and a decrease in life in symmetric cell testing.

[0110] From the above Examples 1-4 and Comparative Example 3, it can be seen that the standing time in a nitrogen atmosphere mainly affects the generation of lithium nitride and the defect distribution of ASEI. When the standing time is too short, the generated lithium nitride does not completely cover the active sites of the lithium metal, and ASEI has structural defects.

[0111] From the above Examples 1-4 and Comparative Example 4, it can be seen that the standing temperature also has an important influence on the nitriding reaction of lithium metal. When the standing temperature is too high, the lithium nitride will decompose, release nitrogen gas, and reduce lithium metal, i.e., the nitriding reaction of lithium metal does not occur.

[0112] From the above Example 5, it can be seen that when the solute of the modification solution is changed from zirconyl nitrate to ammonium fluoride, RSEI is found to increase significantly, because the ionic conductivity of lithium fluoride generated by the reaction of the latter with lithium metal is lower than that of lithium nitride. In Comparative Example 5, low-concentration zirconyl nitrate solution and ammonium fluoride solution are used to modify lithium metal, respectively, without standing in a nitrogen environment, which also results in a significant increase in RSEI, which is also due to the lack of lithium nitride with high ionic conductivity.

[0113] The above examples only express several embodiments of the present application, and the description is more specific and detailed, but it cannot be understood as limiting the scope of the patent of the present application. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the present application, several modifications and improvements can be made, which are within the scope of protection of the present application.

Claims

1. A lithium metal electrode, comprising metal lithium and an artificial solid-liquid interface layer modified on the surface of the metal lithium; the composition of the artificial solid-liquid interface layer comprises N element and one or more of Zr element, F element, P element and S element; the grain size of the artificial solid-liquid interface layer ranges from 10 nm to 18 nm; the impedance of the artificial solid-liquid interface layer ranges from 30 Ω to 100 Ω.

2. The lithium metal electrode of claim 1, wherein, when the composition of the artificial solid-liquid interface layer comprises N element and Zr element, the ratio of the content of the Zr element to the content of the N element ranges from 0.25 to 0.45; and / or, when the composition of the artificial solid-liquid interface layer comprises N element and F element, the ratio of the content of the F element to the content of the N element ranges from 0.5 to 2; and / or, when the composition of the artificial solid-liquid interface layer comprises N element and P element, the ratio of the content of the P element to the content of the N element ranges from 0.5 to 2; and / or, when the composition of the artificial solid-liquid interface layer comprises N element and S element, the ratio of the content of the S element to the content of the N element ranges from 0.4 to 1; and / or, when the composition of the artificial solid-liquid interface layer comprises N element and multiple elements selected from Zr element, F element, P element and S element, the ratio of the total content of the multiple elements to the content of the N element ranges from 0.25 to 2.

3. The lithium metal electrode according to claim 1 or 2, wherein, the composition of the artificial solid-liquid interface layer comprises lithium nitride and one or more of lithium nitrate, zirconium oxide, lithium fluoride, lithium phosphate, lithium oxide, lithium dodecylbenzenesulfonate and lithium hydroxide. 4.A method for preparing an artificial solid-liquid interface layer modified lithium metal electrode, comprising the steps of: applying a predetermined concentration of a modification solution to the surface of metal lithium under a protective gas atmosphere; after the solvent of the modification solution is completely volatilized, placing the metal lithium with the modification solution coated on the surface in a nitrogen atmosphere, and standing at a predetermined temperature for a predetermined time to obtain an artificial solid-liquid interface layer modified lithium metal electrode; wherein the solute of the modification solution comprises one or more of zirconyl nitrate, ammonium fluoride, phosphoric acid and dodecylbenzenesulfonic acid.

5. The method of producing a lithium metal electrode modified with an artificial solid-liquid interface layer according to claim 4, wherein, the concentration of the modification solution is 0.02-0.2 wt%; And / or, the amount of the modifying liquid is 20-80 μL / cm 2 ; and / or, the solvent of the modification solution comprises one or more of dimethyl sulfoxide, ethylene carbonate, methyl ethyl carbonate, acetonitrile and methanol.

6. The method of producing a lithium metal electrode modified with an artificial solid-liquid interface layer according to claim 4, wherein, the predetermined temperature is 0-100℃; and / or, the predetermined time is 1-12 h; and / or, placing the metal lithium coated with the modification solution in a high-purity nitrogen atmosphere; preferably, the purity of the high-purity nitrogen is ≥99%.

7. The method of producing a lithium metal electrode modified with an artificial solid-liquid interface layer according to claim 4, wherein, the composition of the artificial solid-liquid interface layer comprises lithium nitride and one or more of lithium nitrate, zirconium oxide, lithium fluoride, lithium phosphate, lithium oxide, lithium dodecylbenzenesulfonate and lithium hydroxide. 8.Use of the lithium metal electrode according to any one of claims 1-3 or the lithium metal electrode prepared by the method according to any one of claims 4-7 in the preparation of a lithium metal secondary battery. 9.A lithium metal battery comprising the lithium metal electrode according to any one of claims 1-3 or the lithium metal electrode prepared by the method according to any one of claims 4-7.

10. Use of the lithium metal battery of claim 9 in an energy storage device, a power- consuming device, or an electronic device.

Images