Lithium metal negative electrode containing lithium fluoride protective layer, preparation method of lithium metal negative electrode and lithium metal battery

Abstract

In order to solve the technical problems that an existing lithium oxide layer is not uniformly distributed on the surface of lithium metal and lithium dendrites are easily generated, the invention provides a lithium metal negative electrode containing a lithium fluoride protection layer, a preparation method of the lithium metal negative electrode and a lithium metal battery, and the preparation method comprises the following steps: obtaining an etching solution, and adding metal lithium into the etching solution for etching to obtain the lithium metal negative electrode containing the lithium fluoride protection layer. First structure lithium is obtained; an alkyl amine fluoride solution is obtained, the first structure lithium is added into the alkyl amine fluoride solution for a reaction, and the lithium metal negative electrode containing a lithium fluoride protection layer is obtained after the reaction; the etching liquid contains an etching compound, and the etching compound comprises at least one of phenyl lithium compounds, naphthyl lithium and derivatives thereof. According to the preparation method of the lithium metal negative electrode containing the lithium fluoride protection layer, generation of lithium dendrites can be effectively reduced, the lithium metal negative electrode is further stabilized, and the cycle performance and the safety performance of the battery are improved.

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 very active metal element, which easily reacts with oxygen in the air to form lithium oxide. In battery manufacturing, lithium metal is used as the negative electrode. The lithium oxide layer on the surface of lithium metal is unevenly distributed on the surface of lithium metal. This unevenness will lead to inconsistent electrochemical performance of the battery during the charging and discharging process. During the charging and discharging process of the battery, the deposition and deintercalation of lithium ions on the lithium metal negative electrode are prone to produce lithium dendrites. Lithium dendrites can easily penetrate the diaphragm, causing battery short circuit and thermal runaway. Summary of the invention

[0003] In order to solve 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: Obtaining an etching solution, adding metallic lithium into the etching solution for etching to obtain lithium of a first structure; Obtaining an alkyl amine fluoride solution, adding the first structure lithium into the alkyl amine fluoride solution to react to obtain a lithium metal negative electrode containing a lithium fluoride protective layer; The etching solution contains etching compounds, and the etching compounds include at least one of phenyl lithium compounds, naphthyl lithium and derivatives thereof.

[0005] Preferably, obtaining the etching solution comprises the following steps: Dissolving the etching compound in an ether organic solvent and mixing them evenly to obtain the etching solution; The molar concentration of the etching compound in the etching solution is 0.1-0.5 mol / L.

[0006] Preferably, the etching time is 1 to 30 minutes.

[0007] Preferably, the phenyl lithium compound includes the compound shown in structural formula 1; Wherein, R1, R2, R3, R4, and R5 are each independently selected from at least one of H, C1-C5 alkyl substituted or unsubstituted by halogen, C1-C5 alkenyl substituted or unsubstituted by halogen, halogen, C1-C5 ester group substituted or unsubstituted by halogen, and C1-C5 alkoxy group substituted or unsubstituted by halogen; The naphthyl lithium and its derivatives include one or more of naphthyl lithium compounds, benzyl lithium compounds, and anthracene lithium compounds; The naphthyl lithium compound includes a 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 substituted or unsubstituted by halogen, and C1~C5 ester substituted or unsubstituted by halogen; The phenyllithium compound includes a 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 substituted or unsubstituted by halogen, and C1~C5 ester substituted or unsubstituted 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 substituted or unsubstituted by halogen, and C1~C5 ester substituted or unsubstituted by halogen.

[0008] Preferably, the alkyl amine fluoride solution contains alkyl amine fluoride, and the alkyl amine fluoride includes a compound represented by 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.

[0009] Preferably, obtaining the alkyl amine fluoride solution comprises the following steps: The alkyl amine fluoride is dissolved in an ether organic solvent and mixed evenly to obtain the alkyl amine fluoride solution; the concentration of the alkyl amine fluoride contained in the alkyl amine fluoride is 0.1-2 mol / L.

[0010] Preferably, the first structure lithium is added to the alkyl amine fluoride solution for reaction, wherein the reaction time is 1 to 30 minutes.

[0011] 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.

[0012] 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; And / or, the thickness of the lithium fluoride protective layer is 0.01-1 μm.

[0013] 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.

[0014] The method for preparing a lithium metal negative electrode containing a lithium fluoride protective layer provided in the present application includes adding metallic lithium to an etching solution for chemical etching, removing lithium oxide on the surface of the metallic lithium and lithium metal on the 200 crystal plane of the surface layer, thereby exposing more 110 crystal planes that are not prone to lithium dendrites, and generating lithium of the first structure; the first structure lithium is added to an alkyl amine fluoride solution, and the alkyl amine fluoride reacts on the surface of the first structure lithium to generate a lithium fluoride protective layer. The method for preparing a lithium metal negative electrode containing a lithium fluoride protective layer provided in the present application includes removing the 200 crystal plane that is prone to generate lithium dendrites, and using more 110 crystal planes that are not prone to generate lithium dendrites as the surface layer of the first structure lithium, which can effectively reduce the generation of lithium dendrites, and at the same time generating a lithium fluoride protective layer on the surface of the first structure lithium, further stabilizing the lithium metal negative electrode, reducing the generation of dendrites, and improving the cycle performance and safety performance of the battery. DETAILED DESCRIPTION

[0015] In order to make the purpose, technical solution 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 used to limit the present invention.

[0016] In order to illustrate the technical solution of the present invention, specific embodiments are provided below for illustration.

[0017] 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: Obtaining an etching solution, adding metallic lithium into the etching solution for etching to obtain lithium of a first structure; Obtaining an alkyl amine fluoride solution, adding the first structure lithium into the alkyl amine fluoride solution to react to obtain a lithium metal negative electrode containing a lithium fluoride protective layer; The etching solution contains etching compounds, and the etching compounds include at least one of phenyl lithium compounds, naphthyl lithium and derivatives thereof.

[0018] 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 easier for lithium to diffuse and migrate 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.

[0019] 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 prone to 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 (200) crystal plane on the surface 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.

[0020] The first structure lithium is obtained by adding existing lithium metal into an etching solution for 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.

[0021] The etching solution contains etching compounds, including phenyl lithium compounds, naphthyl lithium and their derivatives. The etching compounds react with lithium oxide to remove lithium oxide on the surface of lithium metal. Lithium metal and the etching compounds undergo a lithiation reaction, and lithium atoms replace hydrogen atoms in the etching compounds to generate organic lithium compounds, thereby removing lithium metal on the (200) crystal plane of the surface.

[0022] 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, namely, a lithium fluoride protective layer, which helps to protect the lithium metal negative electrode, reduce direct contact with the electrolyte, and inhibit the formation of lithium dendrites.

[0023] The method for preparing a lithium metal negative electrode containing a lithium fluoride protective layer provided by the present application includes adding metallic lithium to an etching solution for chemical etching to remove lithium oxide on the surface of the metallic lithium and lithium metal on the (200) crystal plane of the surface layer, thereby exposing more (110) crystal planes that are not prone to lithium dendrites, and generating lithium of the first structure; the first structure lithium is added to an alkyl amine fluoride solution, and the alkyl amine fluoride reacts on the surface of the first structure lithium to generate a lithium fluoride protective layer. The method for preparing a lithium metal negative electrode containing a lithium fluoride protective layer provided by the present application includes removing the (200) crystal plane that is prone to generate lithium dendrites, and using more (110) crystal planes that are not prone to generate lithium dendrites as the surface layer of the first structure lithium, which can effectively reduce the generation of lithium dendrites, and at the same time generate a lithium fluoride protective layer on the surface of the first structure lithium, further stabilizing the lithium metal negative electrode, reducing the generation of dendrites, and improving the cycle performance and safety performance of the battery.

[0024] In some embodiments, obtaining the etching solution comprises the following steps: The etching compound is dissolved in an ether organic solvent and mixed evenly to obtain the etching solution.

[0025] 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 plays a role in dissolving the etching compound, which facilitates the reaction of the etching compound with lithium oxide and metallic lithium.

[0026] 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.

[0027] In some embodiments, the molar concentration of the etching compound in the etching solution is 0.1-0.5 mol / L.

[0028] Specifically, the molar concentration of the etching compound in the etching solution is in the range of 0.1-0.5 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.

[0029] 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, 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.

[0030] 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.

[0031] In some preferred embodiments, the molar concentration of the etching compound in the etching solution is 0.2-0.3 mol / L.

[0032] Specifically, the molar concentration of the etching compound is in the range of 0.2-0.3 mol / L, which is beneficial to remove the lithium oxide layer and the (200) crystal plane, while reducing the removal of lithium metal on the (110) crystal plane.

[0033] In some embodiments, the etching time is 1 to 30 minutes.

[0034] 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.

[0035] In some preferred embodiments, the etching time is 15 to 25 minutes.

[0036] 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.

[0037] 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 the lithium metal on the (110) crystal plane, thereby reducing the production cost.

[0038] In some embodiments, the etching thickness is 0.05-1.0 μm.

[0039] Specifically, adding metallic lithium to the etching solution for etching can remove the lithium oxide on the surface of the metallic lithium and the 200 crystal plane of the surface layer, and controlling the etching thickness within the range of 0.05-1.0 μm is to reduce the etching of more 110 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 plane structure to determine whether the surface 200 crystal plane is removed.

[0040] In some embodiments, the phenyl lithium compound includes a compound represented by structural formula 1; Wherein, R1, R2, R3, R4, and R5 are each independently selected from at least one of H, C1~C5 alkyl substituted or unsubstituted by halogen, C1~C5 alkenyl substituted or unsubstituted by halogen, halogen, C1~C5 ester group substituted or unsubstituted by halogen, and C1~C5 alkoxy group substituted or unsubstituted by halogen.

[0041] Specifically, when R1, R2, R3, R4, and R5 are independently selected from H, the compound shown in structural formula 1 is phenyllithium. Halogen includes elements such as F, Cl, Br, and I. A C1-C5 alkyl group substituted with a halogen means that one or two or more hydrogen atoms in the alkyl group are replaced by a halogen, and an unsubstituted C1-C5 alkyl group means that the hydrogen atoms in the alkyl group are not replaced by a halogen. An alkyl group having 1 to 5 carbon atoms includes a straight-chain C1-C5 alkyl group, or a branched C1-C5 alkyl group, and the alkyl group may be a methyl group, an ethyl group, a propyl group, a butyl group, an isobutyl group, and the like. An alkenyl group having C1-C5 includes a straight-chain alkenyl group having 1 to 5 carbon atoms, or a branched alkenyl group having 1 to 5 carbon atoms, such as vinyl, propenyl, butenyl, 3-methyl-1-butenyl, and the like. The ester groups of C1 to C5 include straight-chain ester groups with 1 to 5 carbon atoms or branched ester groups with 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. The alkoxy groups of C1 to C5 include straight-chain alkoxy groups with 1 to 5 carbon atoms or branched alkoxy groups with 1 to 5 carbon atoms, such as methoxy, ethoxy, propoxy, butoxy and pentoxy, etc.

[0042] In some embodiments, the naphthyl lithium and its derivatives include one or more of naphthyl lithium compounds, benzyl lithium compounds, and anthracene lithium compounds.

[0043] In some embodiments, the naphthyl lithium compound includes a compound represented by structural formula 2, 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 substituted or unsubstituted by halogen, and C1~C5 ester substituted or unsubstituted by halogen.

[0044] 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.

[0045] In some embodiments, the phenyllithium compound includes a 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 is independently selected from at least one of H, halogen, C1~C5 alkyl substituted or unsubstituted by halogen, and C1~C5 ester substituted or unsubstituted by halogen.

[0046] 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 hydride.

[0047] In some embodiments, the anthracene lithium compound includes a compound represented by 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 substituted or unsubstituted by halogen, and C1~C5 ester substituted or unsubstituted by halogen.

[0048] Specifically, when R 31 , R 32 , R 33 , 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 anthracene lithium.

[0049] In some embodiments, the alkyl amine fluoride solution contains alkyl amine fluoride, and the alkyl amine fluoride includes a compound represented by structural formula 2, Wherein, R6, R7, R8, and R9 are each independently selected from a C1-C5 alkyl group which is substituted or unsubstituted by halogen.

[0050] Specifically, the alkyl fluorinated amine 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 structural lithium to generate lithium fluoride.

[0051] In some preferred embodiments, the alkylamine fluoride includes at least one of tetrabutylamine fluoride, tetramethylamine fluoride, tetraethylamine fluoride, and tetrapropylamine fluoride.

[0052] In some embodiments, the alkyl amine fluoride is dissolved in an ether organic solvent and mixed evenly to obtain the alkyl amine fluoride solution.

[0053] Specifically, the ether organic solvent is used to dissolve the alkyl amine fluoride to facilitate the reaction of the alkyl amine fluoride and lithium metal.

[0054] The 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.

[0055] In some embodiments, the concentration of the alkyl amine fluoride contained in the alkyl amine fluoride is 0.1-2 mol / L.

[0056] Specifically, controlling the concentration of the alkyl fluoride amine within the range of 0.1-2 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.

[0057] Specifically, the concentration of the alkyl fluoride amine contained in the alkyl fluoride amine 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 fluoride amine is within the range of 0.1~2 mol / L.

[0058] In some preferred embodiments, the concentration of the alkyl amine fluoride contained in the alkyl amine fluoride is 0.8-1.2 mol / L.

[0059] 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.

[0060] In some embodiments, the first structure lithium is added to the alkyl amine fluoride solution for reaction, wherein the reaction time is 1 to 30 minutes.

[0061] Specifically, the first structure lithium is added into the alkyl amine 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.

[0062] In some preferred embodiments, the reaction time is 5 to 30 minutes.

[0063] Specifically, controlling the reaction time within the range of 5 to 30 minutes is helpful to form a lithium fluoride protective layer with a moderate thickness on the surface of the first structure lithium, thereby effectively inhibiting the formation of lithium dendrites.

[0064] 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.

[0065] The lithium metal negative electrode containing a lithium fluoride protective layer provided in the present application has no unevenly distributed lithium oxide and no (200) crystal plane that is easy to generate lithium dendrites, which can reduce the generation of lithium dendrites; a layer of lithium fluoride protective layer is generated on the surface of the (110) crystal plane that is less likely to generate lithium dendrites, which can further stabilize the lithium metal negative electrode, reduce the generation of dendrites, and improve the cycle performance and safety performance of the battery.

[0066] 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.

[0067] Specifically, the (110) crystal plane is a crystal plane that is not prone to the generation of lithium dendrites, and can reduce the generation 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 generation of lithium dendrites.

[0068] In some embodiments, the thickness of the lithium fluoride protective layer is 0.05-1 μm.

[0069] Specifically, the thickness of the lithium fluoride protective layer is limited to 0.05~1μm, which can 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 too much, but also does not affect the battery energy density.

[0070] 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.

[0071] 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.

[0072] 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, ternary materials or other new positive electrode materials. The electrolyte is also a prior art and will not be described in detail here.

[0073] The present invention is further described below by way of examples.

[0074] Example 1 A method for preparing a lithium metal negative electrode containing a lithium fluoride protective layer comprises the following steps: The ether organic solvent is ethylene glycol dimethyl ether solvent, the etching compound is naphthyl lithium, and the alkyl amine fluoride is tetrabutyl amine fluoride.

[0075] S1: dissolving naphthyl lithium in ethylene glycol dimethyl ether solvent, mixing evenly to prepare an etching solution with a concentration of 0.3 mol / L, and then immersing 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 min, the etching thickness is 0.75 μm, and the first structure lithium is obtained after the etching is completed.

[0076] S2: dissolving tetrabutylammonium fluoride in ethylene glycol dimethyl ether solvent, mixing evenly to prepare a tetrabutylammonium fluoride solution with a concentration of 1.0 mol / L, taking a 100 mL volume of the tetrabutylammonium fluoride solution, and then immersing the first structure lithium obtained in step S1 into the tetrabutylammonium fluoride solution to react for 17 min, generating a lithium fluoride protective layer on the surface of the first structure lithium, and obtaining a lithium metal negative electrode containing a lithium fluoride protective layer, wherein the thickness of the lithium fluoride protective layer is 0.8 μm.

[0077] Example 2 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.

[0078] Example 3 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.

[0079] Example 4 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.

[0080] Example 5 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.

[0081] Example 6 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.

[0082] Example 7 Most of the steps of this embodiment are the same as those of embodiment 1, except that in step S2, tetrabutylammonium fluoride is dissolved in ethylene glycol dimethyl ether solvent, mixed evenly to prepare a tetrabutylammonium fluoride solution with a concentration of 0.1 mol / L, and the reaction time is 30 min. A lithium metal negative electrode containing a lithium fluoride protective layer is obtained, and the thickness of the lithium fluoride protective layer is 0.02 μm.

[0083] Example 8 Most of the steps of this embodiment are the same as those of embodiment 1, except that in step S2, tetrabutylammonium fluoride is dissolved in ethylene glycol dimethyl ether solvent, mixed evenly to prepare a tetrabutylammonium fluoride solution with a concentration of 2.0 mol / L, and the reaction time is 30 min. A lithium metal negative electrode containing a lithium fluoride protective layer is obtained, and the thickness of the lithium fluoride protective layer is 1.0 μm.

[0084] Example 9 Most of the steps of this embodiment are the same as those of embodiment 1, except that in step S2, tetrabutylammonium fluoride is dissolved in ethylene glycol dimethyl ether solvent, mixed evenly to prepare a tetrabutylammonium fluoride solution with a concentration of 0.06 mol / L, and the reaction time is 30 min. A lithium metal negative electrode containing a lithium fluoride protective layer is obtained, and the thickness of the lithium fluoride protective layer is 0.005 μm.

[0085] Example 10 Most of the steps of this embodiment are the same as those of embodiment 1, except that in step S2, tetrabutylammonium fluoride is dissolved in ethylene glycol dimethyl ether solvent, mixed evenly to prepare a tetrabutylammonium fluoride solution with a concentration of 2.2 mol / L, and the reaction time is 30 min. A lithium metal negative electrode containing a lithium fluoride protective layer is obtained, and the thickness of the lithium fluoride protective layer is 1.2 μm.

[0086] Embodiment 11 Most of the steps of this embodiment are the same as those of embodiment 1, except that in step S1, the ether organic solvent is tetrahydrofuran, and the etching compound is anthracene lithium and In step S2, the alkylamine fluoride is tetramethylamine fluoride. In step S1, the etching thickness is 0.7 μm.

[0087] Example 12 Most of the steps of this embodiment are the same as those of embodiment 1, except that in step S1, the ether organic solvent is tetrahydrofuran, and the etching compound is phenyl lithium and In step S2, the alkylamine fluoride is tetraethylamine fluoride. In step S1, the etching thickness is 0.73 μm.

[0088] Embodiment 13 Most of the steps of this embodiment are the same as those of embodiment 1, except that in step S1, the ether organic solvent is tetrahydrofuran, and the etching compound is lithium mercapto, In step S2, the alkylamine fluoride is tetrapropylamine fluoride. In step S1, the etching thickness is 0.78 μm.

[0089] Comparative Example 1 The negative electrode of this comparative example is an existing commercially available lithium metal negative electrode, which is not subjected to etching treatment and has no lithium fluoride protective layer provided on the surface of the lithium metal.

[0090] Comparative Example 2 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 metal lithium 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.

[0091] Comparative Example 3 This comparative example has the same steps as Example 1, except that there is no step S1 and only step S2 is included. A lithium metal negative electrode containing a lithium fluoride protective layer is obtained, and an uneven lithium fluoride protective layer is generated.

[0092] 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.

[0093] Lithium metal battery performance test: (1) Room temperature cycle performance test method: At room temperature 25℃±2, charge at 1C constant current to 4.4V, then charge at 4.4V constant voltage to 0.05C cutoff, then discharge at 1C constant current to 3.0V, and cycle for 300 cycles to test the battery capacity retention rate. The specific test results are shown in Table 1.

[0094] Lithium dendrite test After the 300th cycle according to the method in (1), the fully charged lithium metal battery is disassembled to observe whether there are deposited lithium dendrites on the surface of the lithium metal negative electrode sheet. If lithium dendrites are generated, the ratio of the generated area of ​​the lithium dendrites to the area of ​​the entire lithium metal negative electrode sheet is observed.

[0095] 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%, and it can be considered that no lithium dendrites are generated; 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 are generated and the degree of lithium precipitation is slight; 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 are generated and the degree of lithium precipitation is serious; the specific test results are shown in Table 1.

[0096] Table 1 From the test results in Table 1, it can be seen that in Comparative Example 1, lithium metal is directly used 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 deposition on the lithium metal negative electrode is serious; in Comparative Example 2, the battery is immersed in a magnesium fluoride solution to form a lithium fluoride protective layer on the surface of the lithium metal. After 300 cycles of the battery, the negative electrode has slight lithium deposition; in Comparative Example 3, no etching is performed, and the battery is directly immersed in an alkyl fluoride amine solution. Due to the uneven formation of a lithium fluoride protective layer on the surface, the lithium metal negative electrode still has serious lithium deposition, and the battery capacity remains low after 300 cycles; Example 1 is compared with Comparative Examples 1, 2, and 3 to illustrate that an etching solution is first used to remove lithium oxide and 200 crystal planes on the surface of the lithium metal, and a lithium fluoride protective layer is formed on the surface of the 110 crystal plane where lithium dendrites are less likely to be generated, which can reduce the formation of dendrites and improve the battery's cycle capacity retention rate and safety performance.

[0097] Compared with Examples 1-4 and 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 indicates 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 ​​the generated lithium dendrites accounts for a small proportion.

[0098] Comparing Examples 1, 7-8 and Examples 9-10, when the concentration of the alkyl amine fluoride solution is in the range of 0.1-2 mol / L, the battery cycle capacity retention rate is high and the lithium dendrite area accounts for a small proportion; when the concentration of the alkyl amine fluoride solution is lower than 0.1 mol / 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 alkyl amine fluoride solution is higher than 2.0 mol / L, the thickness of the lithium fluoride protective layer is too thick, which affects the battery cycle capacity retention rate.

[0099] Comparison between Example 1 and Examples 11-13 shows that the etching compound in the etching solution is selected from any one of phenyl lithium 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.

[0100] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them. Although the present invention has been described in detail with reference to the above embodiments, it should be understood by those skilled in the art that the technical solutions described in the above embodiments can still be modified, or some of the technical features can be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention, and should be included in the protection scope 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 into the etching solution for etching to obtain lithium of a first structure; Obtaining an alkyl amine fluoride solution, adding the first structure lithium into the alkyl amine fluoride solution to react to obtain a lithium metal negative electrode containing a lithium fluoride protective layer; The etching solution contains etching compounds, and the etching compounds include at least one of phenyl lithium compounds, naphthyl lithium and derivatives thereof.

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 them evenly 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, characterized in that: 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, C1-C5 alkyl substituted or unsubstituted by halogen, C1-C5 alkenyl substituted or unsubstituted by halogen, halogen, C1-C5 ester group substituted or unsubstituted by halogen, and C1-C5 alkoxy group substituted or unsubstituted by halogen; The naphthyl lithium and its derivatives include one or more of naphthyl lithium compounds, benzyl lithium compounds, and anthracene lithium compounds; The naphthyl lithium compound includes a 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 substituted or unsubstituted by halogen, and C1~C5 ester substituted or unsubstituted by halogen; The phenyllithium compound includes a 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 substituted or unsubstituted by halogen, and C1~C5 ester substituted or unsubstituted 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 substituted or unsubstituted by halogen, and C1~C5 ester substituted or unsubstituted by halogen.

5. The method for preparing a lithium metal negative electrode containing a lithium fluoride protective layer according to claim 1, characterized in that: The alkyl amine fluoride solution contains alkyl amine fluoride, and the alkyl amine fluoride includes a 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 alkyl amine fluoride solution comprises the following steps: The alkyl amine fluoride is dissolved in an ether organic solvent and mixed evenly to obtain the alkyl amine fluoride solution; the concentration of the alkyl amine fluoride contained in the alkyl amine fluoride 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 into the alkyl amine fluoride solution to react, 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 method for preparing a lithium metal negative electrode containing a lithium fluoride protective layer according to any one of claims 1 to 7 is used.

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, and 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 a lithium metal negative electrode containing a lithium fluoride protective layer as claimed in claim 8 or 9.

Images