A lithium metal negative electrode containing a lithium fluoride protective layer and a preparation method therefor, and a lithium metal battery

Abstract

To overcome the technical problems that the existing lithium oxide layer is unevenly distributed on the surface of lithium metal and is prone to generate lithium dendrites, the application provides a lithium metal negative electrode containing a lithium fluoride protective layer, a preparation method of the lithium metal negative electrode, and a lithium metal battery.The preparation method comprises the following steps: obtaining an etching solution, adding metal lithium into the etching solution for etching to obtain first structure lithium; obtaining an alkyl fluorinated amine solution, adding the first structure lithium into the alkyl fluorinated amine solution for reaction to obtain the lithium metal negative electrode containing the lithium fluoride protective layer; the etching solution contains an etching compound, and the etching compound comprises at least one of a phenyllithium compound, a naphthyllithium compound and a derivative thereof.The preparation method of the lithium metal negative electrode containing the lithium fluoride protective layer can effectively reduce the generation of lithium dendrites, further stabilize the lithium metal negative electrode, and improve the cycle performance and safety performance of the battery.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium metal negative electrodes, and in particular to a lithium metal negative electrode containing a lithium fluoride protective layer, a preparation method thereof, and a lithium metal battery. Background Art

[0002] Lithium metal is a highly reactive metallic element that readily reacts with oxygen in air to form lithium oxide. In battery manufacturing, lithium metal serves as the negative electrode. The lithium oxide layer on the surface of the lithium metal is unevenly distributed across the lithium metal surface. This unevenness leads to inconsistent electrochemical performance during the battery's charge and discharge processes. During this process, the deposition and deintercalation of lithium ions on the lithium metal negative electrode can easily generate lithium dendrites, which can easily penetrate the separator, causing a short circuit and leading to thermal runaway. Summary of the Invention

[0003] In response to the technical problem that the existing lithium oxide layer is unevenly distributed on the surface of lithium metal and lithium dendrites are easily generated, the present application provides a lithium metal negative electrode containing a lithium fluoride protective layer, a preparation method thereof, and a lithium metal battery.

[0004] In a first aspect, the present application provides a method for preparing a lithium metal negative electrode containing a lithium fluoride protective layer, comprising the following steps:

[0005] Obtaining an etching solution, adding metallic lithium to the etching solution for etching to obtain lithium of a first structure;

[0006] Obtaining an alkylamine fluoride solution, and adding the first structure lithium to the alkylamine fluoride solution to react to obtain a lithium metal negative electrode containing a lithium fluoride protective layer;

[0007] The etching solution contains an etching compound, and the etching compound includes at least one of phenyllithium compounds, naphthyllithium and derivatives thereof.

[0008] Preferably, obtaining the etching solution comprises the following steps:

[0009] dissolving the etching compound in an ether organic solvent and mixing the mixture to obtain the etching solution;

[0010] The molar concentration of the etching compound in the etching solution is 0.1-0.5 mol / L.

[0011] Preferably, the etching time is 1 to 30 minutes.

[0012] Preferably, the phenyllithium compound includes the compound shown in structural formula 1;

[0013]

[0014] wherein R1, R2, R3, R4, and R5 are each independently selected from at least one of H, a C1-C5 alkyl group which may be substituted or unsubstituted by halogen, a C1-C5 alkenyl group which may be substituted or unsubstituted by halogen, a halogen, a C1-C5 ester group which may be substituted or unsubstituted by halogen, and a C1-C5 alkoxy group which may be substituted or unsubstituted by halogen;

[0015] The naphthyl lithium and its derivatives include one or more of naphthyl lithium compounds, benzyl lithium compounds, and anthracenyl lithium compounds;

[0016] The naphthyl lithium compound includes the compound shown in structural formula 2,

[0017]

[0018] Among them, R 11 、R 12 、R 13 、R 14 、R 15 、R 16 、R 17 Each independently selected from at least one of H, halogen, C1~C5 alkyl group which may be substituted by halogen, and C1~C5 ester group which may be substituted by halogen;

[0019] The benzoyl lithium compound includes the compound shown in structural formula 3,

[0020]

[0021] Among them, R 21 、R 22 、R 23 、R 24 、R 25 、R 26 、R 27 、R 28 Each independently selected from at least one of H, halogen, C1~C5 alkyl group which may be substituted by halogen, and C1~C5 ester group which may be substituted by halogen;

[0022] The anthracene lithium compound includes a compound shown in structural formula 4,

[0023]

[0024] Among them, R 31 、R 32 、R 33 、R 34 、R 35 、R 36 、R 37 、R 38 、R 39Each is independently selected from at least one of H, halogen, C1~C5 alkyl group which may be substituted by halogen, and C1~C5 ester group which may be substituted by halogen.

[0025] Preferably, the alkylamine fluoride solution contains alkylamine fluoride, and the alkylamine fluoride includes the compound shown in structural formula 5,

[0026]

[0027] Wherein, R6, R7, R8, and R9 are each independently selected from a C1-C5 alkyl group which is substituted or unsubstituted by halogen.

[0028] Preferably, obtaining the alkylamine fluoride solution comprises the following steps:

[0029] The alkylamine fluoride is dissolved in an ether organic solvent and mixed uniformly to obtain the alkylamine fluoride solution; the concentration of the alkylamine fluoride in the alkylamine fluoride is 0.1-2 mol / L.

[0030] Preferably, the first structure lithium is added to the alkylamine fluoride solution for reaction, wherein the reaction time is 1 to 30 minutes.

[0031] In a second aspect, the present application provides a lithium metal negative electrode containing a lithium fluoride protective layer, which is prepared by the above-mentioned method for preparing a lithium metal negative electrode containing a lithium fluoride protective layer.

[0032] Preferably, the lithium metal negative electrode comprises a 110 crystal plane and a lithium fluoride protective layer, and the lithium fluoride protective layer is arranged on the surface of the 110 crystal plane;

[0033] And / or, the thickness of the lithium fluoride protective layer is 0.01-1 μm.

[0034] In a third aspect, the present application provides a lithium metal battery comprising a positive electrode, a negative electrode and an electrolyte, wherein the negative electrode is the lithium metal negative electrode containing a lithium fluoride protective layer as described above.

[0035] The present application provides a method for preparing a lithium metal negative electrode containing a lithium fluoride protective layer. The method comprises adding lithium metal to an etching solution for chemical etching to remove lithium oxide on the surface of the lithium metal and lithium metal on the 200 crystal planes of the surface layer, thereby exposing more 110 crystal planes that are less likely to produce lithium dendrites, thereby generating first-structure lithium. The first-structure lithium is added to an alkylamine fluoride solution, and the alkylamine fluoride reacts on the surface of the first-structure lithium to generate a lithium fluoride protective layer. The present application provides a method for preparing a lithium metal negative electrode containing a lithium fluoride protective layer. The method removes the 200 crystal planes that are prone to lithium dendrite formation and uses more 110 crystal planes that are less likely to produce lithium dendrites as the surface layer of the first-structure lithium, which can effectively reduce the formation of lithium dendrites. At the same time, a lithium fluoride protective layer is generated on the surface of the first-structure lithium, further stabilizing the lithium metal negative electrode, reducing the formation of dendrites, and improving the cycle performance and safety performance of the battery. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0037] In order to illustrate the technical solution of the present invention, specific embodiments are provided below.

[0038] In a first aspect, the present application provides a method for preparing a lithium metal anode containing a lithium fluoride protective layer, comprising the following steps:

[0039] Obtaining an etching solution, adding metallic lithium to the etching solution for etching to obtain lithium of a first structure;

[0040] Obtaining an alkylamine fluoride solution, and adding the first structure lithium to the alkylamine fluoride solution to react to obtain a lithium metal negative electrode containing a lithium fluoride protective layer;

[0041] The etching solution contains an etching compound, and the etching compound includes at least one of phenyllithium compounds, naphthyllithium and derivatives thereof.

[0042] As a typical electrodeposition process, the morphology of Li deposition essentially depends on the crystal structure. Lithium metal is a body-centered cubic (bcc) crystal. In the crystal structure of lithium metal, the 110 crystal plane (Li(110)), 200 crystal plane (Li(200)) and 211 crystal plane (Li(211)) are several common crystal planes; Li usually exhibits a low refractive index crystal plane (110) and high refractive index crystal planes (200) and (211). The Li atom migration barrier on the Li(110) crystal plane is lower than that on the other two crystal planes. Therefore, it is generally believed that the Li(110) crystal plane is less likely to grow dendrites than other crystal planes. Therefore, it is more likely for lithium to diffuse laterally on the Li(110) crystal plane, which helps to form a planar, dendrite-free lithium deposition. Therefore, constructing a (110) crystal plane-oriented Li deposition is an effective strategy to achieve high-performance lithium metal batteries.

[0043] Since there is a layer of non-uniform lithium oxide on the surface of the lithium metal currently produced, and the lithium metal at the interface with the lithium oxide is mostly (200) crystal plane, the (200) crystal plane is more likely to produce lithium dendrites. After extensive research, the inventors found that using an etching solution to remove the lithium oxide on the surface of the lithium metal and the lithium metal on the surface (200) crystal plane will expose more (110) crystal planes that are less likely to produce lithium dendrites. At the same time, a protective layer rich in lithium fluoride is generated on the surface of the (110) crystal plane to stabilize the lithium metal negative electrode and reduce the generation of lithium dendrites during the charging and discharging process of the lithium metal.

[0044] The first structure lithium is obtained by adding existing lithium metal to an etching solution and performing chemical etching. The etching solution can remove the lithium oxide on the surface of the lithium metal and the lithium metal on the (200) crystal plane of the surface layer, thereby obtaining the first structure lithium without a lithium oxide layer and a (200) crystal plane; at this time, the surface layer of the first structure lithium is a (110) crystal plane.

[0045] The etching solution contains etching compounds, including phenyllithium compounds, naphthyllithium, and their derivatives. The etching compounds react with lithium oxide to remove lithium oxide from the surface of the lithium metal. The lithium metal and the etching compounds undergo a lithiation reaction, with lithium atoms replacing hydrogen atoms in the etching compound to form an organic lithium compound, thereby removing the lithium metal from the (200) crystal plane of the surface layer.

[0046] The alkylamine fluoride solution contains alkylamine fluoride and fluoride ions, which react with lithium metal to form lithium fluoride. Lithium fluoride is a water-insoluble solid and can form a stable solid electrolyte interface film on the lithium metal surface of the (110) crystal plane, which is the lithium fluoride protective layer. It helps to protect the lithium metal negative electrode, reduce direct contact with the electrolyte, and inhibit the formation of lithium dendrites.

[0047] The present application provides a method for preparing a lithium metal negative electrode containing a lithium fluoride protective layer. The method comprises adding lithium metal to an etching solution for chemical etching to remove lithium oxide on the surface of the lithium metal and lithium metal on the (200) crystal plane of the surface layer, thereby exposing more (110) crystal planes that are less likely to produce lithium dendrites, thereby generating first-structure lithium. The first-structure lithium is added to an alkylamine fluoride solution, and the alkylamine fluoride reacts on the surface of the first-structure lithium to generate a lithium fluoride protective layer. The present application provides a method for preparing a lithium metal negative electrode containing a lithium fluoride protective layer. The method removes the (200) crystal plane that is prone to lithium dendrite formation and uses more (110) crystal planes that are less likely to produce lithium dendrites as the surface layer of the first-structure lithium, thereby effectively reducing the formation of lithium dendrites. At the same time, a lithium fluoride protective layer is generated on the surface of the first-structure lithium, further stabilizing the lithium metal negative electrode, reducing the formation of dendrites, and improving the cycle performance and safety performance of the battery.

[0048] In some embodiments, obtaining the etching solution comprises the following steps:

[0049] The etching compound is dissolved in an ether organic solvent, and the mixture is mixed uniformly to obtain the etching solution.

[0050] Specifically, the etching compound is an organic compound, and the etching compound is dissolved in an ether organic solvent to obtain an etching solution. The ether organic solvent dissolves the etching compound, facilitating the reaction of the etching compound with lithium oxide and metallic lithium.

[0051] In some embodiments, the ether organic solvent includes but is not limited to diethyl ether, tetrahydrofuran, ethylene glycol dimethyl ether, propylene glycol methyl ether, ethylene glycol butyl ether, ethylene oxide, cyclopentyl methyl ether, butynediol dipropoxy ether, dipropylene glycol butyl ether, and the like.

[0052] In some embodiments, the molar concentration of the etching compound in the etching solution is 0.1-0.5 mol / L.

[0053] Specifically, the molar concentration of the etching compound in the etching solution is in the range of 0.1 to 0.5 mol / L, which facilitates the control of the etching compound to remove lithium oxide and lithium metal on the (200) crystal plane, while reducing the removal of lithium metal on the (110) crystal plane, thereby improving etching efficiency.

[0054] Specifically, the molar concentration of the etching compound in the etching solution can be 0.1 mol / L, 0.15 mol / L, 0.2, 0.3 mol / L, 0.4 mol / L or 0.5 mol / L, etc., as long as the molar concentration of the etching compound in the etching solution is within the range of 0.1-0.5 mol / L.

[0055] If the molar concentration of the etching compound in the etching solution is greater than 0.5 mol / L, the concentration of the etching solution is too high, the chemical etching rate is accelerated, and some lithium metal on the (110) crystal surface is removed, increasing production costs. If the molar concentration of the etching compound in the etching solution is too low, the etching rate of the etching solution is low, the etching time is increased, and the etching efficiency is reduced.

[0056] In some preferred embodiments, the molar concentration of the etching compound in the etching solution is 0.2-0.3 mol / L.

[0057] Specifically, the molar concentration of the etching compound is in the range of 0.2 to 0.3 mol / L, which is beneficial for removing the lithium oxide layer and the (200) crystal plane, while reducing the removal of lithium metal on the (110) crystal plane.

[0058] In some embodiments, the etching time is 1 to 30 minutes.

[0059] Specifically, the etching time is controlled within the range of 1 to 30 minutes, the etching time is short, the etching efficiency is improved, and the etching thickness can also be controlled, reducing the lithium metal removed from the 100 crystal surface.

[0060] In some preferred embodiments, the etching time is 15 to 25 minutes.

[0061] Specifically, the etching time is within the range of 15 to 25 minutes. While improving the etching efficiency, it can also further reduce the removal of lithium metal on the (110) crystal plane, thereby improving production efficiency and reducing costs.

[0062] Further preferably, the molar concentration of the etching compound in the etching solution is 0.2~0.3 mol / L, and the etching time is in the range of 5~10 min, which can not only effectively improve the etching efficiency, effectively remove the lithium oxide layer on the surface of the lithium metal and the lithium metal on the (200) crystal plane, but also reduce the removal of lithium metal on the (110) crystal plane, thereby reducing production costs.

[0063] In some embodiments, the etching thickness is 0.05-1.0 μm.

[0064] Specifically, adding metallic lithium to the etching solution for etching can remove lithium oxide and the surface 200-degree crystal planes on the lithium metal surface. The etching thickness is controlled within the range of 0.05-1.0 μm to reduce the etching of more 110-degree crystal planes. During the etching process, existing characterization methods such as XPS, TOF-SIMs, and Cryo-TEM can be used to test the surface crystal structure and determine whether the surface 200-degree crystal planes have been removed.

[0065] In some embodiments, the phenyllithium compound includes the compound shown in structural formula 1;

[0066]

[0067] Wherein, R1, R2, R3, R4, and R5 are each independently selected from at least one of H, C1-C5 alkyl groups which may be substituted or unsubstituted by halogen, C1-C5 alkenyl groups which may be substituted or unsubstituted by halogen, halogen, C1-C5 ester groups which may be substituted or unsubstituted by halogen, and C1-C5 alkoxy groups which may be substituted or unsubstituted by halogen.

[0068] Specifically, when R1, R2, R3, R4, and R5 are each independently selected from H, the compound represented by Structural Formula 1 is phenyllithium. Halogens include elements such as F, Cl, Br, and I. A C1-C5 alkyl group substituted with a halogen refers to an alkyl group in which one, two, or more hydrogen atoms are replaced by a halogen, and an unsubstituted C1-C5 alkyl group refers to an alkyl group in which no hydrogen atoms are replaced by a halogen. An alkyl group having 1 to 5 carbon atoms includes a linear C1-C5 alkyl group or a branched C1-C5 alkyl group, and the alkyl group may be a methyl group, ethyl group, propyl group, butyl group, isobutyl group, or the like. A C1-C5 alkenyl group includes a linear alkenyl group having 1 to 5 carbon atoms or a branched alkenyl group having 1 to 5 carbon atoms, such as ethenyl, propenyl, butenyl, and 3-methyl-1-butenyl. C1-C5 ester groups include linear ester groups having 1 to 5 carbon atoms or branched ester groups having 1 to 5 carbon atoms, such as methyl formate, ethyl formate, methyl acetate, propyl formate, isopropyl formate, ethyl acetate, propyl acetate, methyl propionate, butyl formate, isobutyl formate, propyl acetate, isopropyl acetate, ethyl propionate, methyl propionate, methyl butyrate, methyl isobutyrate, etc. C1-C5 alkoxy groups include linear alkoxy groups having 1 to 5 carbon atoms or branched alkoxy groups having 1 to 5 carbon atoms, such as methoxy, ethoxy, propoxy, butoxy, and pentoxy, etc.

[0069] In some embodiments, the naphthyl lithium and its derivatives include one or more of naphthyl lithium compounds, benzyl lithium compounds, and anthracenyl lithium compounds.

[0070] In some embodiments, the naphthyl lithium compound includes a compound represented by structural formula 2,

[0071]

[0072] Among them, R 11 、R 12 、R 13 、R 14 、R 15 、R 16 、R 17 Each is independently selected from at least one of H, halogen, C1~C5 alkyl group which may be substituted by halogen, and C1~C5 ester group which may be substituted by halogen.

[0073] Specifically, when R 11 、R 12 、R 13 、R 14 、R 15 、R 16 、R 17 When each is independently selected from H, the compound represented by structural formula 2 is naphthyl lithium.

[0074] In some embodiments, the benzothiophene lithium compound includes a compound represented by structural formula 3,

[0075]

[0076] Among them, R 21 、R 22 、R 23 、R 24 、R 25 、R 26 、R 27 、R 28 Each is independently selected from at least one of H, halogen, C1~C5 alkyl group which may be substituted by halogen, and C1~C5 ester group which may be substituted by halogen.

[0077] Specifically, when R 21 、R 22 、R 23 、R 24 、R 25 、R 26 、R 27 、R 28 When each is independently selected from H, the compound shown in structural formula 3 is lithium mercaptan.

[0078] In some embodiments, the anthracene lithium compound includes a compound represented by structural formula 4,

[0079]

[0080] Among them, R 31 、R 32 、R 33 、R 34 、R 35 、R 36 、R 37 、R 38 、R 39 Each is independently selected from at least one of H, halogen, C1~C5 alkyl group which may be substituted by halogen, and C1~C5 ester group which may be substituted by halogen.

[0081] Specifically, when R 31 、R 32 、R33 、R 34 、R 35 、R 36 、R 37 、R 38 、R 39 When each is independently selected from H, the compound represented by structural formula 4 is anthracenyl lithium.

[0082] In some embodiments, the alkylamine fluoride solution contains alkylamine fluoride, and the alkylamine fluoride includes the compound represented by structural formula 2.

[0083]

[0084] Wherein, R6, R7, R8, and R9 are each independently selected from a C1-C5 alkyl group which is substituted or unsubstituted by halogen.

[0085] Specifically, the alkylamine fluoride includes a compound shown in structural formula 5, which contains a quaternary ammonium cation and a fluoride ion. The fluoride ion reacts with the first structure lithium to generate lithium fluoride.

[0086] In some preferred embodiments, the alkylamine fluoride includes at least one of tetrabutylamine fluoride, tetramethylamine fluoride, tetraethylamine fluoride, and tetrapropylamine fluoride.

[0087] In some embodiments, the alkylamine fluoride is dissolved in an ether organic solvent and mixed uniformly to obtain the alkylamine fluoride solution.

[0088] Specifically, the ether organic solvent is used to dissolve the alkylamine fluoride to facilitate the reaction of the alkylamine fluoride and the lithium metal.

[0089] Ether organic solvents include, but are not limited to, diethyl ether, tetrahydrofuran, ethylene glycol dimethyl ether, propylene glycol methyl ether, ethylene glycol butyl ether, ethylene oxide, cyclopentyl methyl ether, butynediol dipropoxy ether, dipropylene glycol butyl ether, and the like.

[0090] In some embodiments, the concentration of the alkyl amine fluoride in the alkyl amine fluoride is 0.1-2 mol / L.

[0091] Specifically, controlling the concentration of alkylamine fluoride within the range of 0.1 to 2 mol / L is conducive to forming a lithium fluoride protective layer on the surface of the first structure lithium. The lithium fluoride protective layer is an inorganic solid electrolyte interface film, which helps to protect the lithium metal negative electrode, reduce direct contact with the electrolyte, and inhibit the formation of lithium dendrites.

[0092] Specifically, the concentration of the alkyl amine fluoride contained in the alkyl amine fluoride can be 0.1 mol / L, 0.2 mol / L, 0.4 mol / L, 0.5 mol / L, 0.7 mol / L, 0.9 mol / L, 1.0 mol / L, 1.3 mol / L, 1.5 mol / L, 1.8 mol / L, 2.0 mol / L, etc., as long as the concentration of the alkyl amine fluoride is within the range of 0.1 to 2 mol / L.

[0093] In some preferred embodiments, the concentration of the alkyl amine fluoride in the alkyl amine fluoride is 0.8-1.2 mol / L.

[0094] Specifically, the concentration of the alkyl amine fluoride contained in the alkyl amine fluoride is in the range of 0.8~1.2 mol / L, which helps to form a lithium fluoride protective layer of moderate thickness on the surface of the first structure lithium without affecting the extraction and embedding of lithium ions. At the same time, it also reduces the contact between the lithium metal negative electrode and the electrolyte, and inhibits the formation of lithium dendrites.

[0095] In some embodiments, the first structure lithium is added to the alkylamine fluoride solution for reaction, wherein the reaction time is 1 to 30 minutes.

[0096] Specifically, the first structure lithium is added into the alkylamine fluoride solution for reaction, and the reaction time is controlled to be 1 to 30 minutes, so that a lithium fluoride layer can be formed on the surface of the first structure lithium.

[0097] In some preferred embodiments, the reaction time is 5 to 30 minutes.

[0098] Specifically, controlling the reaction time within the range of 5 to 30 minutes helps to form a lithium fluoride protective layer of moderate thickness on the surface of the first structure lithium, effectively inhibiting the formation of lithium dendrites.

[0099] In a second aspect, the present application provides a lithium metal negative electrode containing a lithium fluoride protective layer, which is prepared by the above-mentioned method for preparing a lithium metal negative electrode containing a lithium fluoride protective layer.

[0100] The lithium metal negative electrode provided by the present application, which contains a lithium fluoride protective layer, is free of unevenly distributed lithium oxide and (200) crystal planes that are prone to the formation of lithium dendrites, and can reduce the formation of lithium dendrites. A lithium fluoride protective layer is formed on the surface of the (110) crystal planes that are less likely to form lithium dendrites, which can further stabilize the lithium metal negative electrode, reduce the formation of dendrites, and improve the cycle performance and safety performance of the battery.

[0101] In some embodiments, it includes a (110) crystal plane and a lithium fluoride protective layer, and the lithium fluoride protective layer is disposed on the surface of the (110) crystal plane.

[0102] Specifically, the (110) crystal plane is a crystal plane that is not prone to the formation of lithium dendrites, and can reduce the formation of lithium dendrites on the surface of the lithium metal negative electrode. The lithium fluoride protective layer is arranged on the surface of the (110) crystal plane. The lithium fluoride protective layer has high stability and can further improve the stability of the lithium metal negative electrode, reduce the reaction between the lithium metal negative electrode and the electrolyte, and inhibit the formation of lithium dendrites.

[0103] In some embodiments, the thickness of the lithium fluoride protective layer is 0.05-1 μm.

[0104] Specifically, the thickness of the lithium fluoride protective layer is limited to 0.05~1μm, which can not only protect the lithium metal negative electrode, reduce the reaction between the lithium metal negative electrode and the electrolyte, and inhibit the formation of lithium dendrites; at the same time, it can not only increase the thickness of the lithium metal negative electrode significantly, but also not affect the battery energy density.

[0105] In a third aspect, the present application provides a lithium metal battery comprising a positive electrode, a negative electrode and an electrolyte, wherein the negative electrode is the lithium metal negative electrode containing a lithium fluoride protective layer as described above.

[0106] The lithium metal battery provided in the present application contains the above-mentioned lithium fluoride protective layer, which reduces the reaction between the lithium metal negative electrode and the electrolyte, inhibits the formation of lithium dendrites, and improves the cycle performance and safety performance of the battery.

[0107] In some embodiments, the positive electrode includes a positive electrode active material, which is a commonly used material, such as lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, a ternary material, or other novel positive electrode materials. The electrolyte is also known in the art and will not be described in detail here.

[0108] The present invention is further described below with reference to the following examples.

[0109] Example 1

[0110] A method for preparing a lithium metal negative electrode containing a lithium fluoride protective layer comprises the following steps:

[0111] The ether organic solvent is ethylene glycol dimethyl ether solvent, the etching compound is naphthyl lithium, and the alkylamine fluoride is tetrabutylamine fluoride.

[0112] S1: Dissolve naphthyl lithium in ethylene glycol dimethyl ether solvent, mix well to prepare an etching solution with a concentration of 0.3 mol / L, then immerse a commercially available metal lithium sheet in the above-mentioned etching solution with a volume of 100 mL for chemical etching. The etching time is 15 minutes and the etching thickness is 0.75 μm. After the etching is completed, the first structure lithium is obtained.

[0113] S2: Tetrabutylammonium fluoride was dissolved in ethylene glycol dimethyl ether solvent, and the mixture was evenly mixed to prepare a tetrabutylammonium fluoride solution with a concentration of 1.0 mol / L. A volume of 100 mL of tetrabutylammonium fluoride solution was taken, and then the first structure lithium obtained in step S1 was immersed in the tetrabutylammonium fluoride solution to react for 17 minutes. A lithium fluoride protective layer was formed on the surface of the first structure lithium to obtain a lithium metal negative electrode containing a lithium fluoride protective layer, wherein the thickness of the lithium fluoride protective layer was 0.8 μm.

[0114] Example 2

[0115] Most of the steps of this embodiment are the same as those of embodiment 1, except that in step S1, naphthyl lithium is dissolved in ethylene glycol dimethyl ether solvent, mixed evenly to prepare an etching solution with a concentration of 0.1 mol / L, the etching time is 30 min, and the etching thickness is 0.2 μm.

[0116] Example 3

[0117] Most of the steps of this embodiment are the same as those of embodiment 1, except that in step S1, naphthyl lithium is dissolved in ethylene glycol dimethyl ether solvent, mixed evenly to prepare an etching solution with a concentration of 0.5 mol / L, the etching time is 20 min, and the etching thickness is 1 μm.

[0118] Example 4

[0119] Most of the steps of this embodiment are the same as those of embodiment 1, except that in step S1, naphthyl lithium is dissolved in ethylene glycol dimethyl ether solvent, mixed evenly to prepare an etching solution with a concentration of 0.2 mol / L, the etching time is 20 min, and the etching thickness is 0.6 μm.

[0120] Example 5

[0121] Most of the steps of this embodiment are the same as those of embodiment 1, except that in step S1, naphthyl lithium is dissolved in ethylene glycol dimethyl ether solvent, mixed evenly to prepare an etching solution with a concentration of 0.05 mol / L, the etching time is 30 min, and the etching thickness is 0.05 μm.

[0122] Example 6

[0123] Most of the steps of this embodiment are the same as those of embodiment 1, except that in step S1, naphthyl lithium is dissolved in ethylene glycol dimethyl ether solvent, mixed evenly to prepare an etching solution with a concentration of 0.6 mol / L, the etching time is 20 min, and the etching thickness is 1.4 μm.

[0124] Example 7

[0125] This example shares most of the same steps as Example 1, with the following exceptions: In step S2, tetrabutylammonium fluoride was dissolved in ethylene glycol dimethyl ether solvent and mixed uniformly to form a 0.1 mol / L tetrabutylammonium fluoride solution. The reaction time was 30 minutes. A lithium metal anode containing a lithium fluoride protective layer having a thickness of 0.02 μm was obtained.

[0126] Example 8

[0127] This example shares most of the same steps as Example 1, with the following exceptions: In step S2, tetrabutylammonium fluoride was dissolved in ethylene glycol dimethyl ether solvent and mixed uniformly to form a 2.0 mol / L tetrabutylammonium fluoride solution. The reaction time was 30 minutes. A lithium metal anode containing a lithium fluoride protective layer having a thickness of 1.0 μm was obtained.

[0128] Example 9

[0129] This example shares most of the same steps as Example 1, with the following exceptions: In step S2, tetrabutylammonium fluoride was dissolved in ethylene glycol dimethyl ether solvent and mixed uniformly to form a tetrabutylammonium fluoride solution with a concentration of 0.06 mol / L. The reaction time was 30 minutes. A lithium metal anode containing a lithium fluoride protective layer having a thickness of 0.005 μm was obtained.

[0130] Example 10

[0131] This example shares most of the same steps as Example 1, with the following exceptions: In step S2, tetrabutylammonium fluoride was dissolved in ethylene glycol dimethyl ether solvent and mixed uniformly to form a 2.2 mol / L tetrabutylammonium fluoride solution. The reaction time was 30 minutes. A lithium metal anode containing a lithium fluoride protective layer having a thickness of 1.2 μm was obtained.

[0132] Example 11

[0133] Most of the steps in this embodiment are the same as those in embodiment 1, except that in step S1, the ether organic solvent is tetrahydrofuran, and the etching compound is anthracenyl lithium and In step S2, the alkylamine fluoride is tetramethylamine fluoride. In step S1, the etching thickness is 0.7 μm.

[0134] Example 12

[0135] Most of the steps in this embodiment are the same as those in embodiment 1, except that in step S1, the ether organic solvent is tetrahydrofuran, and the etching compound is phenyllithium and In step S2, the alkylamine fluoride is tetraethylamine fluoride. In step S1, the etching thickness is 0.73 μm.

[0136] Example 13

[0137] Most of the steps in this embodiment are the same as those in embodiment 1, except that in step S1, the ether organic solvent is tetrahydrofuran, the etching compound is lithium mercaptan, In step S2, the alkylamine fluoride is tetrapropylamine fluoride. In step S1, the etching thickness is 0.78 μm.

[0138] Comparative Example 1

[0139] The negative electrode of this comparative example is an existing commercially available lithium metal negative electrode, which has not been subjected to etching treatment and has not been provided with a lithium fluoride protective layer on the surface of the lithium metal.

[0140] Comparative Example 2

[0141] In this comparative example, an existing commercially available lithium metal sheet is directly immersed in a magnesium fluoride solution for 6 hours. After the immersion, the metal fluoride salt solution on the surface of the lithium metal sheet is dried to obtain a lithium metal negative electrode containing a lithium fluoride protective layer. The thickness of the generated lithium fluoride protective layer is 0.8 μm.

[0142] Comparative Example 3

[0143] This comparative example is similar to Example 1 in terms of the steps except that step S1 is omitted and only step S2 is included. A lithium metal negative electrode containing a lithium fluoride protective layer is obtained, and a non-uniform lithium fluoride protective layer is generated.

[0144] NCM811 was used as the positive electrode, the lithium metal negative electrode prepared in the above embodiments and comparative examples was used as the negative electrode, the separator was a PP separator, the battery used a commercially available electrolyte containing lithium hexafluorophosphate, and the lithium metal battery was prepared using existing technology.

[0145] Lithium metal battery performance test:

[0146] (1) Normal temperature cycle performance test method: At room temperature (25℃±2), charge the battery to 4.4V at a constant current of 1C, then charge the battery to 0.05C at a constant voltage of 4.4V, and then discharge the battery to 3.0V at a constant current of 1C. Repeat this cycle for 300 cycles to test the battery capacity retention rate. The specific test results are shown in Table 1.

[0147] Lithium dendrite test

[0148] The fully charged lithium metal battery after the 300th cycle according to the method in (1) was disassembled to observe whether there were deposited lithium dendrites on the surface of the lithium metal negative electrode. If there were lithium dendrites, the ratio of the area of ​​the lithium dendrites to the area of ​​the entire lithium metal negative electrode was observed.

[0149] Among them, the proportion of the area of ​​lithium dendrites to the area of ​​the entire lithium metal negative electrode sheet is less than 0.1%, which can be considered that no lithium dendrites are generated;

[0150] If the area of ​​the dendrite accounts for more than 0.1% and less than 10% of the area of ​​the entire lithium metal negative electrode sheet, it can be considered that lithium dendrites have been generated and the degree of lithium precipitation is slight;

[0151] If the area of ​​the dendrite accounts for 10% or more of the area of ​​the entire lithium metal negative electrode, it can be considered that lithium dendrites have been generated and the degree of lithium precipitation is serious; the specific test results are shown in Table 1.

[0152] Table 1

[0153]

[0154] From the test results in Table 1, it can be seen that Comparative Example 1 directly uses lithium metal as the negative electrode, the area of ​​lithium dendrites on the surface of the negative electrode accounts for a large proportion, and the degree of lithium plating on the lithium metal negative electrode is serious; Comparative Example 2 is immersed in a magnesium fluoride solution to form a lithium fluoride protective layer on the surface of the lithium metal. After the battery is cycled for 300 cycles, the negative electrode has slight lithium plating; Comparative Example 3 is not etched and is directly immersed in an alkyl amine fluoride solution. Due to the uneven lithium fluoride protective layer formed on the surface, the lithium metal negative electrode still has serious lithium plating, and the battery capacity remains low after 300 cycles; Example 1 is compared with Comparative Examples 1, 2, and 3 to illustrate that the etching solution is first used to remove the lithium oxide and 200 crystal planes on the surface of the lithium metal, and a lithium fluoride protective layer is formed on the 110 crystal plane surface where lithium dendrites are less likely to form, which can reduce the formation of dendrites and improve the cycle capacity retention rate and safety performance of the battery.

[0155] Comparing Examples 1-4 with Examples 5 and 6, the concentration of the etching solution is lower than 0.1 mol / L, the etching thickness is low, and some 200 crystal faces and lithium oxide may not be removed, and lithium plating is still serious; the concentration of the etching solution is greater than 0.5 mol / L, the 100 crystal face is etched away, and the battery cycle capacity retention rate is reduced; this shows that when the concentration of the etching solution is in the range of 0.1~0.5 mol / L, the generation of lithium dendrites is reduced, the proportion of lithium plating area is small, and the battery cycle capacity retention rate is high; when the concentration of the etching solution is in the range of 0.2~0.3 mol / L, the battery has a higher cycle capacity retention rate, and the area of ​​generated lithium dendrites accounts for a small proportion.

[0156] Comparing Examples 1, 7-8 and 9-10, when the concentration of the alkylamine fluoride solution is in the range of 0.1~2mol / L, the battery cycle capacity retention rate is high and the proportion of lithium dendrite area is small; when the concentration of the alkylamine fluoride solution is lower than 0.1mol / L, the thickness of the lithium fluoride protective layer is low, and the formation of lithium dendrites cannot be effectively reduced; when the concentration of the alkylamine fluoride solution is higher than 2.0mol / L, the thickness of the lithium fluoride protective layer is too thick, which affects the battery cycle capacity retention rate.

[0157] Comparison between Example 1 and Examples 11-13 shows that the etching compound in the etching solution is selected from any one of phenyllithium compounds, naphthyl lithium, and naphthyl lithium derivatives, all of which have the effect of removing lithium oxide on the surface of metallic lithium and lithium metal on the 200 crystal plane of the surface.

[0158] The above embodiments are intended only to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they may still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein with equivalents. However, such modifications or replacements do not deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention and are intended to be included within the scope of protection of the present invention.

Claims

1. A method for preparing a lithium metal negative electrode containing a lithium fluoride protective layer, characterized in that: The following steps are involved: Obtaining an etching solution, adding metallic lithium to the etching solution for etching to obtain lithium of a first structure; Obtaining an alkylamine fluoride solution, and adding the first structure lithium to the alkylamine fluoride solution to react to obtain a lithium metal negative electrode containing a lithium fluoride protective layer; The etching solution contains an etching compound, and the etching compound includes at least one of a phenyllithium compound, a naphthyllithium compound, a mercaptan lithium compound, and an anthracene lithium compound.

2. The method for preparing a lithium metal negative electrode containing a lithium fluoride protective layer according to claim 1, characterized in that: Obtaining the etching solution comprises the following steps: dissolving the etching compound in an ether organic solvent and mixing the mixture to obtain the etching solution; The molar concentration of the etching compound in the etching solution is 0.1-0.5 mol / L.

3. The method for preparing a lithium metal negative electrode containing a lithium fluoride protective layer according to claim 1 or 2, characterized in that: The etching time is 1 to 30 minutes.

4. The method for preparing a lithium metal negative electrode containing a lithium fluoride protective layer according to claim 1, wherein: The phenyl lithium compound includes a compound shown in structural formula 1; wherein R1, R2, R3, R4, and R5 are each independently selected from at least one of H, a C1-C5 alkyl group which may be substituted or unsubstituted by halogen, a C1-C5 alkenyl group which may be substituted or unsubstituted by halogen, a halogen, a C1-C5 ester group which may be substituted or unsubstituted by halogen, and a C1-C5 alkoxy group which may be substituted or unsubstituted by halogen; The naphthyl lithium compound includes the compound shown in structural formula 2, Among them, R 11 、R 12 、R 13 、R 14 、R 15 、R 16 、R 17 Each independently selected from at least one of H, halogen, C1~C5 alkyl group which may be substituted by halogen, and C1~C5 ester group which may be substituted by halogen; The benzoyl lithium compound includes the compound shown in structural formula 3, Among them, R 21 、R 22 、R 23 、R 24 、R 25 、R 26 、R 27 、R 28 Each independently selected from at least one of H, halogen, C1~C5 alkyl group which may be substituted by halogen, and C1~C5 ester group which may be substituted by halogen; The anthracene lithium compound includes a compound shown in structural formula 4, Among them, R 31 、R 32 、R 33 、R 34 、R 35 、R 36 、R 37 、R 38 、R 39 Each is independently selected from at least one of H, halogen, C1~C5 alkyl group which may be substituted by halogen, and C1~C5 ester group which may be substituted by halogen.

5. The method for preparing a lithium metal negative electrode containing a lithium fluoride protective layer according to claim 1, wherein: The alkylamine fluoride solution contains alkylamine fluoride, and the alkylamine fluoride includes the compound shown in structural formula 5, Wherein, R6, R7, R8, and R9 are each independently selected from a C1-C5 alkyl group which is substituted or unsubstituted by halogen.

6. The method for preparing a lithium metal negative electrode containing a lithium fluoride protective layer according to claim 1, characterized in that: Obtaining an alkylamine fluoride solution comprises the following steps: The alkylamine fluoride is dissolved in an ether organic solvent and mixed uniformly to obtain the alkylamine fluoride solution; the concentration of the alkylamine fluoride in the alkylamine fluoride solution is 0.1-2 mol / L.

7. The method for preparing a lithium metal negative electrode containing a lithium fluoride protective layer according to claim 1 or 6, characterized in that: The first structure lithium is added to the alkylamine fluoride solution to carry out a reaction, wherein the reaction time is 1 to 30 minutes.

8. A lithium metal negative electrode containing a lithium fluoride protective layer, characterized in that: The negative electrode is prepared by the method for preparing a lithium metal negative electrode containing a lithium fluoride protective layer according to any one of claims 1 to 7.

9. The lithium metal negative electrode containing a lithium fluoride protective layer according to claim 8, characterized in that The lithium metal negative electrode comprises a 110 crystal plane and a lithium fluoride protective layer, wherein the lithium fluoride protective layer is arranged on the surface of the 110 crystal plane; And / or, the thickness of the lithium fluoride protective layer is 0.01-1 μm.

10. A lithium metal battery, characterized in that: The invention comprises a positive electrode, a negative electrode and an electrolyte, wherein the negative electrode is the lithium metal negative electrode containing a lithium fluoride protective layer as claimed in claim 8 or 9.

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