Lithium metal negative electrode sheet, preparation method thereof, lithium battery and electrical equipment

Abstract

The present application provides a lithium metal negative electrode sheet, a preparation method thereof, a lithium battery and an electrical device. The lithium metal negative electrode sheet includes a current collector and a lithium metal layer, a LiF layer, a Li2CO3 layer and a LiCH2CH2OCO2Li layer that are sequentially stacked on the surface of the current collector. When the lithium metal negative electrode sheet is used in a lithium battery, the LiF layer and the Li2CO3 layer are close to the lithium metal layer, which can effectively prevent the growth of dendrites in the lithium metal layer; the LiCH2CH2OCO2Li layer is close to the electrolyte, which can well prevent solvent molecules in the electrolyte from entering and prevent the reaction between the solvent molecules and the metal lithium layer; thereby cooperating synergistically to improve the cycle performance and safety performance of the lithium metal battery.

Description

Technical Field

[0001] The present invention relates to the field of batteries, and particularly to a lithium metal negative electrode sheet, a preparation method thereof, a lithium battery, and an electrical device. Background Art

[0002] Due to its high specific energy, with a theoretical specific capacity of 3870 mAh / g, lithium metal batteries can provide a higher energy density than current lithium-ion batteries, and are one of the hotspots in current battery technology research. However, lithium metal is highly reactive and easily reacts with the electrolyte to generate dendrites. The growth of dendrites contacts the positive electrode to form a short circuit, causing safety problems in lithium metal batteries. At the same time, the reaction between lithium metal and the electrolyte causes the continuous consumption of lithium metal and the electrolyte during this process, ultimately resulting in low Coulomb efficiency and short cycle life of the lithium metal negative electrode during cycling. Therefore, it is necessary to passivate the surface of lithium metal to prevent the growth of dendrites and make lithium metal batteries have better cycle stability. However, the lithium metal negative electrode sheet obtained by traditional passivation treatment still has poor cycle performance when used in lithium metal batteries. Summary of the Invention

[0003] Based on this, it is necessary to provide a lithium metal negative electrode sheet with better cycle performance, a preparation method thereof, a lithium battery, and an electrical device.

[0004] In a first aspect of the present invention, a lithium metal negative electrode sheet is provided. The lithium metal negative electrode sheet includes a current collector and a lithium metal layer, a LiF layer, a Li2CO3 layer, and a LiCH2CH2OCO2Li layer that are sequentially stacked on the surface of the current collector.

[0005] In the above lithium metal negative electrode sheet, a lithium metal layer, a LiF layer, a Li2CO3 layer, and a LiCH2CH2OCO2Li layer are sequentially stacked on the surface of the current collector. Among them, the LiF layer and the Li2CO3 layer are close to the lithium metal layer and can effectively prevent the growth of dendrites in the lithium metal layer; the LiCH2CH2OCO2Li layer is close to the electrolyte and can effectively prevent solvent molecules in the electrolyte from entering, preventing the reaction between solvent molecules and the metal lithium layer; and thus, they cooperate synergistically to improve the cycle performance and safety performance of the lithium metal battery.

[0006] In any embodiment of the present application, the thicknesses of the LiF layer, the Li2CO3 layer, and the LiCH2CH2OCO2Li layer are independently set to 5 nm - 30 nm;

[0007] Optionally, the thicknesses of the LiF layer, the Li2CO3 layer, and the LiCH2CH2OCO2Li layer are independently set to 10 nm - 25 nm.

[0008] By regulating the thicknesses of the LiF layer, the Li2CO3 layer, and the LiCH2CH2OCO2Li layer, it is possible to effectively prevent dendrites from forming in the lithium metal layer and prevent electrolyte solvent molecules from reacting with the lithium metal layer, thereby improving the cycling performance of the lithium metal battery. At the same time, it is also possible to avoid excessive thicknesses of the LiF layer, the Li2CO3 layer, and the LiCH2CH2OCO2Li layer, reducing costs.

[0009] In any embodiment of the present application, the areal density of one side of the lithium metal layer is 2.67 g / m 2 ~13.35 g / m 2 .

[0010] In a second aspect of the present invention, there is provided a method for preparing the lithium metal negative electrode sheet of the first aspect, including the following steps:

[0011] Form the lithium metal layer on the surface of the current collector;

[0012] Form the LiF layer on the lithium metal layer;

[0013] Form the Li2CO3 layer on the LiF layer;

[0014] Form the LiCH2CH2OCO2Li layer on the Li2CO3 layer.

[0015] In any embodiment of the present application, the method for forming the LiF layer, the Li2CO3 layer, and the LiCH2CH2OCO2Li layer includes a magnetron sputtering method.

[0016] Optionally, the process conditions of the magnetron sputtering method include: a background vacuum degree of 4×10 -5 Pa~6×10 -5 Pa, a sputtering gas pressure of 0.2 Pa~0.4 Pa, a distance between the target and the substrate of 40 mm~60 mm, and a sputtering power of 4.5 kW~6.5 kW.

[0017] Forming the LiF layer, the Li2CO3 layer, and the LiCH2CH2OCO2Li layer on the lithium metal layer by the magnetron sputtering method is conducive to forming a regular laminated structure on the surface of the lithium metal layer; moreover, directly forming the LiF layer, the Li2CO3 layer, and the LiCH2CH2OCO2Li layer on the lithium metal layer can avoid the consumption of the lithium metal layer and avoid damaging the battery performance.

[0018] In any embodiment of the present application, the preparation method of the LiCH2CH2OCO2Li includes the following steps: mixing metallic lithium and ethylene carbonate and stirring, reacting under the condition of 140 °C~160 °C, and drying after the reaction is completed to obtain LiCH2CH2OCO2Li.

[0019] Optionally, the preparation method of the LiCH2CH2OCO2Li satisfies at least one of the following conditions:

[0020] (1) The mass ratio of the ethylene carbonate to the metallic lithium is (7 - 8):1;

[0021] (2) The rotation speed of the stirring is 150 r / min - 250 r / min;

[0022] (3) The reaction time ≥ 24 h;

[0023] (4) The drying is distillation drying, and the temperature of the distillation drying is 250°C - 260°C.

[0024] In the third aspect of the present application, there is provided a lithium battery including the lithium metal negative electrode sheet of the first aspect or the lithium metal negative electrode sheet prepared by the preparation method of the second aspect.

[0025] In the fourth aspect of the present application, there is provided an electrical device including the lithium battery of the third aspect.

[0026] The above description is only an overview of the technical solution of the present application. In order to be able to understand the technical means of the present application more clearly, it can be implemented according to the content of the specification. And in order to make the above and other objects, features and advantages of the present application more obvious and understandable, the following specifically gives the specific embodiments of the present application. Description of the Drawings

[0027] Figure 1 It is a schematic structural diagram of a lithium metal negative electrode sheet of an embodiment.

[0028] Description of the reference numerals:

[0029] 10 - Current collector, 20 - Lithium metal layer, 30 - LiF layer, 40 - Li2CO3 layer, 50 - LiCH2CH2OCO2Li layer. Detailed Embodiments

[0030] For the convenience of understanding the present invention, the present invention will be described more comprehensively below with reference to the relevant drawings. The preferred embodiments of the present invention are given in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure content of the present invention more thorough and comprehensive.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field to which this invention belongs. The terms used in the description of the present invention herein are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0032] Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the present application. The phrase does not necessarily refer to the same embodiment at every occurrence in the specification, nor is it an independent or alternative embodiment mutually exclusive of other embodiments. Those skilled in the art will explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments.

[0033] In the description of the embodiments of the present application, the orientation or positional relationship indicated by technical terms such as "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the embodiments of the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation to the embodiments of the present application.

[0034] In a lithium metal negative electrode sheet, lithium metal is extremely likely to react with solvent molecules in the electrolyte, and lithium metal dendrites are generated, posing a safety hazard to lithium batteries. More importantly, the cycle performance of lithium batteries is reduced. In traditional technologies, surface treatment of an ultra-thin lithium metal foil is carried out by using argon plasma in an atmosphere containing a small amount of carbon dioxide to form a lithium carbonate passivation layer on the surface of the lithium metal foil layer, thereby preventing the reaction between the lithium metal negative electrode sheet and the electrolyte. However, the protection effect of such a single-layer passivation protection layer is limited, and a single inorganic salt layer cannot prevent the reaction between solvent molecules and the lithium metal layer. The inventors of the present application have found through research that a specific inorganic salt layer and an organic salt layer are sequentially formed on the surface of the lithium metal layer. The inorganic salt LiF layer and Li2CO3 layer are close to the lithium metal layer and can prevent the growth of lithium dendrites; the organic salt LiCH2CH2OCO2Li layer is close to the electrolyte and can prevent solvent molecules from entering, preventing the reaction between solvent molecules and the metal lithium layer; and thus, through synergistic cooperation, the specific capacity after 50 cycles of the lithium battery is effectively increased, and the cycle performance of the lithium battery is improved.

[0035] One embodiment of the present application provides a lithium metal negative electrode sheet, as Figure 1As shown in the figure, the above-mentioned lithium metal negative electrode sheet includes a current collector 10, and a lithium metal layer 20, a LiF layer 30, a Li2CO3 layer 40, and a LiCH2CH2OCO2Li layer 50 that are sequentially stacked on the surface of the current collector.

[0036] In any embodiment of the present application, the above-mentioned current collector can be selected from copper foil, steel sheet or steel mesh;

[0037] In any embodiment of the present application, the thickness of the above-mentioned copper foil is 6 μm to 10 μm; the thickness of the above-mentioned steel sheet is 8 μm to 12 μm; the thickness of the steel mesh is 8 μm to 12 μm, and the mesh aperture is 200 mesh.

[0038] It can be understood that the above-mentioned lithium metal layer, LiF layer, Li2CO3 layer and LiCH2CH2OCO2Li layer can be sequentially stacked only on one surface of the current collector, or the above-mentioned lithium metal layer, LiF layer, Li2CO3 layer and LiCH2CH2OCO2Li layer can be sequentially stacked on both surfaces of the current collector.

[0039] In the above-mentioned lithium metal negative electrode sheet, a lithium metal layer, a LiF layer, a Li2CO3 layer and a LiCH2CH2OCO2Li layer are sequentially stacked on the surface of the current collector. Among them, the LiF layer and the Li2CO3 layer are close to the lithium metal layer, which can effectively prevent the growth of dendrites in the lithium metal layer; the LiCH2CH2OCO2Li layer is close to the electrolyte, which can well prevent solvent molecules in the electrolyte from entering, and prevent the reaction between the solvent molecules and the metal lithium layer; thereby cooperating with each other to improve the cycle performance and safety performance of the lithium metal battery.

[0040] The inventors of the present application also found during the experiment that in the battery material, when the voltage reaches a certain value, a series of physical and chemical changes will occur on the negative electrode surface, and Li reacts with EC, DMC, trace water, HF, etc. + to form substances such as LiOH, Li2CO3, LiF, LiCH2CH2OCO2Li, CH3OCO2Li, etc. These substances cover the negative electrode surface to form a SEI film. The SEI film has a multi-layer structure. Inorganic substances such as lithium carbonate are close to the negative electrode material, and organic substances such as alkyl lithium fat are close to the electrolyte. This film acts as an intermediate phase between the electrode material and the electrolyte, has the properties of a solid electrolyte, and only allows lithium ions to pass freely, preventing solvent molecules from passing through and insulating electrons. However, the SEI film formed by the above method does not have the sequentially stacked film layer structure of the present application, the protection effect on the negative electrode sheet is not very ideal, and the cycle performance of the battery is low.

[0041] In any embodiment of the present application, the thicknesses of the above-mentioned LiF layer, Li2CO3 layer, and LiCH2CH2OCO2Li layer are independently set to be 5 nm - 30 nm. Further, the thicknesses of the LiF layer, Li2CO3 layer, and LiCH2CH2OCO2Li layer are independently set to be 10 nm - 25 nm.

[0042] By controlling the thicknesses of the LiF layer, Li2CO3 layer, and LiCH2CH2OCO2Li layer, it is possible to effectively prevent the formation of dendrites in the lithium metal layer and prevent the reaction between the electrolyte solvent molecules and the lithium metal layer, improving the cycling performance of the lithium metal battery. At the same time, it is possible to avoid the excessive thickness of the LiF layer, Li2CO3 layer, and LiCH2CH2OCO2Li layer, reducing costs.

[0043] In the above "5 nm - 30 nm", the values include the minimum and maximum values of this range, as well as each value between such minimum and maximum values. Specific examples include, but are not limited to, the point values in the embodiments and: 6 nm, 7 nm, 8 nm, 9 nm, 11 nm, 12 nm, 13 nm, 14 nm, 16 nm, 17 nm, 18 nm, 19 nm, 21 nm, 22 nm, 23 nm, 24 nm, 26 nm, 27 nm, 28 nm, 29 nm.

[0044] In any embodiment of the present application, the areal density per side of the lithium metal layer is 2.67 g / m 2 ~13.35 g / m 2 . The areal density per side refers to the areal density of the lithium metal layer formed on one side surface of the current collector.

[0045] It can be understood that when the lithium metal layer, LiF layer, Li2CO3 layer, and LiCH2CH2OCO2Li layer are laminated on both side surfaces of the current collector, the areal density per side values of the lithium metal layers formed on both side surfaces of the current collector are consistent, and the areal density per side of the lithium metal layer on the surface of the current collector is 2.67 g / m 2 ~13.35 g / m 2 ; when the lithium metal layer, LiF layer, Li2CO3 layer, and LiCH2CH2OCO2Li layer are sequentially laminated only on one side surface of the current collector, the areal density per side of the lithium metal layer on the surface of the current collector is 2.67 g / m 2 ~13.35 g / m 2 .

[0046] In the above "2.67 g / m 2 ~13.35 g / m 2 ", the values include the minimum and maximum values of this range, as well as each value between such minimum and maximum values. Specific examples include, but are not limited to, the point values in the embodiments and: 2.68 g / m2 , 2.70 g / m 2 , 2.72 g / m 2 , 2.75 g / m 2 , 2.80 g / m 2 , 2.85 g / m 2 , 2.90 g / m 2 , 2.95 g / m 2 , 3.0 g / m 2 , 3.50 g / m 2 , 4.00 g / m 2 , 4.50 g / m 2 , 5.00 g / m 2 , 5.50 g / m 2 , 6.0 g / m 2 , 6.50 g / m 2 , 7.00 g / m 2 , 7.50 g / m 2 , 8.00 g / m 2 , 8.50 g / m 2 , 9.00 g / m 2 , 9.50 g / m 2 , 10.00 g / m 2 , 10.50 g / m 2 , 11.00 g / m 2 , 12.00 g / m 2 , 12.50 g / m 2 , 13.00 g / m 2 , 13.35 g / m 2 。

[0047] If the single-sided surface density of the lithium metal layer on the current collector surface is set too low, the foil will be exposed, and if it is too high, the cost will increase.

[0048] One embodiment of the present application provides a method for preparing the above-mentioned lithium metal negative electrode sheet, which includes the following steps:

[0049] Form the lithium metal layer on the surface of the current collector;

[0050] Form the LiF layer on the lithium metal layer;

[0051] Form the Li2CO3 layer on the LiF layer;

[0052] Form the LiCH2CH2OCO2Li layer on the Li2CO3 layer.

[0053] In any embodiment of the present application, the method for forming the above-mentioned LiF layer, Li2CO3 layer, and LiCH2CH2OCO2Li layer includes a magnetron sputtering method. The present application uses a magnetron sputtering method to form a sequentially stacked LiF layer, Li2CO3 layer, and LiCH2CH2OCO2Li layer on the lithium metal negative electrode sheet. This structure is regular, which can effectively prevent the formation of dendrites in the lithium metal layer and avoid the reaction between the solvent molecules in the electrolyte and lithium. In addition, the present application directly forms the LiF layer, Li2CO3 layer, and LiCH2CH2OCO2Li layer on the surface of the lithium metal by using a magnetron sputtering method, avoiding the consumption of the lithium metal layer on the negative electrode sheet in the traditional method, which is beneficial to improving the specific capacity of the lithium metal battery and extending the cycle life of the lithium metal battery.

[0054] Further, the process conditions of the above magnetron sputtering method include: a background vacuum degree of 4×10 -5 Pa to 6×10 - 5 Pa, a sputtering gas pressure of 0.2 Pa to 0.4 Pa, a distance between the target and the substrate of 40 mm to 60 mm, and a sputtering power of 4.5 kW to 6.5 kW.

[0055] In the method for preparing the above lithium metal negative electrode sheet of the present application, the preparation method of the raw material of the LiCH2CH2OCO2Li layer includes the following steps:

[0056] Mix metallic lithium and ethylene carbonate and stir, react under the condition of 140°C to 160°C. After the reaction is completed, perform distillation drying to obtain LiCH2CH2OCO2Li.

[0057] In any embodiment of the present application, the mass ratio of the above ethylene carbonate to metallic lithium is (7 to 8):1.

[0058] In any embodiment of the present application, when mixing metallic lithium and ethylene carbonate and stirring, the stirring speed is 150 r / min to 250 r / min.

[0059] In any embodiment of the present application, under the condition of 140°C to 160°C, the reaction time of metallic lithium and ethylene carbonate is ≥24 h. Further, under the condition of 145°C to 155°C, the reaction time is 24 h to 32 h.

[0060] In any embodiment of the present application, the above drying is distillation drying, and the distillation drying temperature is 250°C to 260°C.

[0061] One embodiment of the present application provides a lithium battery, which includes the lithium metal negative electrode sheet described in the above embodiment or the lithium metal negative electrode sheet prepared by the above preparation method.

[0062] In any embodiment of the present application, the above lithium battery further includes a positive electrode sheet and a separator film.

[0063] In any embodiment of the present application, the thickness of the above positive electrode sheet is 130 μm to 136 μm.

[0064] One embodiment of the present application provides a method for preparing the positive electrode sheet in the above lithium battery, including the following steps:

[0065] Mix the positive electrode active material, binder, conductive agent, and solvent to obtain a positive electrode slurry. Coat the positive electrode slurry on both surfaces of the positive electrode substrate, and after drying, perform rolling treatment to obtain the positive electrode sheet.

[0066] In any embodiment of the present application, the mass ratio of the positive electrode active material, binder, and conductive agent is (97 - 99):(0.5 - 1.5):(0.5 - 1.5).

[0067] In any embodiment of the present application, the above positive electrode substrate includes aluminum foil; the thickness of the aluminum foil is 10 μm to 14 μm.

[0068] In any embodiment of the present application, the above positive electrode active material includes, but is not limited to, one or more of LiCoO2, LiNi 0.8 Co 0.1 Mn 0.1 O2 and NCM ternary materials.

[0069] In any embodiment of the present application, the above binder includes, but is not limited to, PVDF (polyvinylidene fluoride).

[0070] In any embodiment of the present application, the above solvent includes, but is not limited to, NMP (N-methylpyrrolidone).

[0071] In any embodiment of the present application, the above conductive agent is selected from at least one of graphene, conductive carbon black, and conductive graphite without limitation.

[0072] In any embodiment of the present application, the solid content of the above positive electrode slurry is 72% to 80%.

[0073] In any embodiment of the present application, the viscosity of the above positive electrode slurry is 6000 mPa·s to 9000 mPa·s.

[0074] If the solid content of the positive electrode slurry is too low, it is not easy to dry the electrode sheet. If the solid content is too high, it is not easy to uniformly stir the slurry.

[0075] One embodiment of the present application provides an electrical device, which includes the lithium battery in the above embodiment.

[0076] The present invention will be described below in conjunction with specific embodiments, but the present invention is not limited to the following embodiments. It should be understood that the attached claims summarize the scope of the present invention. Under the guidance of the concept of the present invention, those skilled in the art should realize that certain changes made to the various embodiments of the present invention will be covered by the spirit and scope of the claims of the present invention.

[0077] The following are specific embodiments.

[0078] The raw materials used in the following examples and comparative examples are as follows:

[0079] Negative electrode substrate: copper foil; Negative electrode active material: metal lithium foil; Positive electrode substrate: aluminum foil; Conductive agent: graphene (Pas1004 from Hongna (Dongguan) New Materials Technology Co., Ltd.); Positive electrode active material: NCM (811), Binder: PVDF (US Solvay 5130); Solvent: NMP (Maiqi Chemical Co., Ltd.); Diaphragm: (12μm wet method from Shanghai Enjie New Materials Technology Co., Ltd.); Electrolyte: DJ6056YI from Hunan Dajing New Materials Co., Ltd.;

[0080] Magnetron sputtering equipment: JCP200 magnetron sputtering coating machine from Beijing Techno Technology Co., Ltd.;

[0081] LiF, Li2CO3: purchased from Nanjing Chemical Reagent Co., Ltd., specification: 4N 100g;

[0082] Ethylene carbonate: Shandong Jinyueyuan New Materials Co., Ltd.; Metal lithium: Tianjin Zhongneng Lithium Co., Ltd., particles with a diameter of 3mm-5mm and a length of 5mm-10mm; LiOH: analytically pure from Tianjin Komiou Chemical Reagent Co., Ltd.; Li2O: analytically pure from Aladdin; CH3OLi: analytically pure from Aladdin.

[0083] Example 1

[0084] Preparation method of LiCH2CH2OCO2Li:

[0085] Place a 250mL three-necked round-bottomed quartz flask in a heating inner sleeve of a digital temperature-controlled magnetic device, weigh 88g of ethylene carbonate and transfer it into the three-necked round-bottomed quartz flask, stir the magnetic device at a speed of 200r / min, weigh 12g of metallic lithium and slowly transfer it into the three-necked round-bottomed quartz flask, stir for 1h, set the temperature of the digital temperature-controlled magnetic device to 150℃, and the reaction time is 24h;

[0086] Place a three-necked round-bottomed quartz flask on a distillation apparatus and set the distillation temperature to 250°C until all the liquid material is distilled. The dry material in the three-necked round-bottomed quartz flask is LiCH2CH2OCO2Li.

[0087] Example 2

[0088] (1) Preparation of the positive electrode sheet:

[0089] S1: Mix NCM(811), PVDF, and conductive agent in a mass ratio of 98:1:1 in the solvent NMP to obtain a positive electrode slurry with a solid content of 76% and a viscosity of 7800 mPa·s;

[0090] S2: Coat the above positive electrode slurry evenly on both sides of an aluminum foil with a thickness of 12 μm at a coating amount of 442 mg / cm 2 . After drying, perform rolling treatment to obtain a positive electrode sheet with a thickness of 133 μm;

[0091] (2) Preparation of the negative electrode sheet:

[0092] S1: Form a lithium metal layer on the surface of the current collector

[0093] Prepare a lithium metal foil in an argon drying atmosphere with a water content of less than 1 ppm and an oxygen content of less than 1 ppm. Uniformly bond the lithium metal foil on both side surfaces of a copper foil with a thickness of 8 μm by a rolling method. The areal density of the lithium metal layer on the surface of the copper foil is 2.67 g / m 2 .

[0094] S2: Form a LiF layer on the lithium metal layer

[0095] Use a vacuum magnetron sputtering method (the specific process conditions of the vacuum magnetron sputtering method are: background vacuum degree 5×10 -5 Pa, sputtering gas pressure 0.3 Pa, distance between the target and the substrate 50 mm, sputtering power 5.5 kW) to deposit LiF on the lithium metal layer to form a LiF layer with a single-sided thickness of 5 nm.

[0096] S3: Form a Li2CO3 layer on the LiF layer

[0097] Use a vacuum magnetron sputtering method (the specific process conditions of the vacuum magnetron sputtering method are: background vacuum degree 5×10 -5 Pa, sputtering gas pressure 0.3 Pa, distance between the target and the substrate 50 mm, sputtering power 5.5 kW) to deposit Li2CO3 on the surface of the LiF layer to form a Li2CO3 layer with a single-sided thickness of 5 nm.

[0098] S4: Use a vacuum magnetron sputtering method (the specific process conditions of the vacuum magnetron sputtering method are: background vacuum degree 5×10 - 5Pa, the sputtering pressure is 0.3 Pa, the distance between the target and the substrate is 50 mm, and the sputtering power is 5.5 kW) The LiCH2CH2OCO2Li prepared in Example 1 was plated on the surface of the Li2CO3 layer to form a Li2CO3 layer with a single-sided thickness of 5 nm.

[0099] (3) Button cell preparation:

[0100] The positive electrode sheet, negative electrode sheet and commercially available separator prepared by the above method were wound, assembled into a core, put into a shell, filled with liquid, and sealed to make a 1254 button cell.

[0101] Example 3

[0102] Example 3 is basically the same as Example 2, except that: in the preparation of the negative electrode sheet, the single-sided coating thicknesses of LiF, Li2CO3, and LiCH2CH2OCO2Li are independently 10 nm.

[0103] Example 4

[0104] Example 4 is basically the same as Example 2, except that:

[0105] in the preparation of the negative electrode sheet, the single-sided coating thicknesses of LiF, Li2CO3, and LiCH2CH2OCO2Li are independently 15 nm.

[0106] Example 5

[0107] Example 5 is basically the same as Example 2, except that:

[0108] in the preparation of the negative electrode sheet, the single-sided coating thicknesses of LiF, Li2CO3, and LiCH2CH2OCO2Li are independently 20 nm.

[0109] Example 6

[0110] Example 6 is basically the same as Example 2, except that:

[0111] in the preparation of the negative electrode sheet, the single-sided coating thicknesses of LiF, Li2CO3, and LiCH2CH2OCO2Li are independently 25 nm.

[0112] Example 7

[0113] Example 7 is basically the same as Example 2, except that:

[0114] in the preparation of the negative electrode sheet, the single-sided coating thicknesses of LiF, Li2CO3, and LiCH2CH2OCO2Li are independently 30 nm.

[0115] Comparative Example 1

[0116] Comparative Example 1 is basically the same as Example 2, except that:

[0117] In the preparation of the negative electrode sheet in Comparative Example 1, no LiF layer, Li2CO3 layer, or LiCH2CH2OCO2Li layer is plated on the lithium metal layer.

[0118] Comparative Example 2

[0119] Comparative Example 2 is basically the same as Example 5, except that:

[0120] In the preparation of the negative electrode sheet in Comparative Example 2, no LiF layer is plated on the lithium metal layer, and the thickness of the Li2CO3 layer is 40 nm.

[0121] Comparative Example 3

[0122] Comparative Example 3 is basically the same as Example 5, except that:

[0123] In the preparation of the negative electrode sheet in Comparative Example 3, no Li2CO3 layer is plated on the lithium metal layer, and the thickness of the LiF layer is 40 nm.

[0124] Comparative Example 4

[0125] Comparative Example 4 is basically the same as Example 5, except that:

[0126] In the preparation of the negative electrode sheet in Comparative Example 4, the LiCH2CH2OCO2Li layer is plated in the S2 step, and the single-sided coating thickness is 60 nm; no LiF layer and Li2CO3 layer are plated.

[0127] Comparative Example 5

[0128] Comparative Example 5 is basically the same as Example 5, except that:

[0129] In the preparation of the negative electrode sheet in Comparative Example 5, LiF is plated in the S2 step with a single-sided coating thickness of 30 nm; Li2CO3 is plated in the S3 step with a single-sided coating thickness of 30 nm; and the LiCH2CH2OCO2Li layer is not plated in the S4 step.

[0130] Comparative Example 6

[0131] Comparative Example 6 is basically the same as Example 5, except that:

[0132] In the preparation of the negative electrode sheet in Comparative Example 6, the LiCH2CH2OCO2Li layer is plated in the S2 step; the LiF layer is plated in the S3 step; and the Li2CO3 layer is plated in the S4 step, and the single-sided thickness of each coating is 20 nm.

[0133] Comparative Example 7

[0134] Comparative Example 7 is basically the same as Example 5, except that LiOH is used instead of LiF.

[0135] Comparative Example 8

[0136] Comparative Example 8 is basically the same as Example 5, except that Li2O is used to replace Li2CO3.

[0137] Comparative Example 9

[0138] Comparative Example 9 is basically the same as Example 5, except that CH3OLi is used to replace LiCH2CH2OCO2Li.

[0139] The parameters of the above examples and comparative examples are shown in Table 1.

[0140] Table 1

[0141]

[0142] Test Example 1 Electrochemical Performance Test

[0143] The internal resistance of the button cell was tested using a battery internal resistance tester.

[0144] Under the condition of a current density of 0.5C, the capacity of the button cell was tested, and the gram capacity = the capacity of the button cell / the weight of the electrode active material.

[0145] Under the condition of a current density of 0.5C, the button cell was charged and discharged for 50 cycles, and the cycle performance of the button cell was tested. The results are shown in Table 1, and the gram capacity in Table 1 refers to the discharge gram capacity.

[0146] Table 2

[0147]

[0148] As can be seen from Table 1, in Comparative Example 1, LiF, Li2CO3, and LiCH2CH2OCO2Li were not plated, and the first-week gram capacity and the capacity retention rate after 50 cycles were the lowest. From Example 2 to Example 4, the coating thickness increased from 5nm to 15nm, the first-week gram capacity increased from 191.86 mAh / g to 201.65 mAh / g, and the capacity retention rate after 50 cycles increased from 97.37% to 99.62%. This is because the thickness of the protective layer on the lithium metal layer increased, and LiF and Li2CO3 played a good role in hindering the dendritic growth of lithium metal, and LiCH2CH2OCO2Li played a good role in hindering the entry of solvent molecules, achieving the protection of the lithium metal layer and further improving the cycle performance of the lithium metal battery.

[0149] As can be seen from Examples 4 - 7, when the coating thickness continued to increase, the increase in the first-week gram capacity and the capacity retention rate after 50 cycles was no longer obvious, because the protective layer of the coating reached the optimal value.

[0150] In Comparative Example 2, only Li2CO3 was coated on the inorganic layer, and in Comparative Example 3, only LiF was coated on the inorganic layer. The initial specific capacity and the retention rate of the specific capacity after 50 cycles were inferior to those of Example 5. In Comparative Example 4, only the LiCH2CH2OCO2Li layer was coated, and in Comparative Example 5, only the LiF layer and the Li2CO3 layer were coated. The initial specific capacity and the retention rate of the specific capacity after 50 cycles were inferior to those of Example 5. In Comparative Example 6, the LiCH2CH2OCO2Li layer was plated first, and then the LiF layer and the Li2CO3 layer were plated. Although the coating thickness was the same as that of Example 5, the initial specific capacity and the retention rate of the specific capacity after 50 cycles were inferior to those of Example 5, indicating that only by sequentially forming the LiF layer, the Li2CO3 layer, and the LiCH2CH2OCO2Li layer on the lithium metal surface can the lithium metal surface be well protected.

[0151] Compared with Example 5, in Comparative Example 7, the LiF layer was replaced with LiOH, in Comparative Example 8, the Li2CO3 layer was replaced with Li2O, and in Comparative Example 9, the LiCH2CH2OCO2Li layer was replaced with CH3OLi. The initial specific capacity and the retention rate of the specific capacity after 50 cycles of Examples 7 - 9 were inferior to those of Example 5, indicating that the specific structure layers of sequentially forming the LiF layer, the Li2CO3 layer, and the LiCH2CH2OCO2Li layer on the lithium metal surface in this application have a better protective effect on the lithium metal surface.

[0152] Test Example 2 Cycle Performance Test

[0153] The button cell was charged and discharged under a current density of 0.5C, and the number of cycles when the capacity retention rate of the button cell was 80% was tested. When the button cell was charged and discharged until the capacity retention rate was 80%, it was disassembled to observe whether there was lithium dendrite powder on the surface of the composite negative electrode. The results are shown in Table 3.

[0154] Table 3

[0155]

[0156]

[0157] As can be seen from Table 2, in Comparative Example 1, the LiF layer, Li2CO3 layer, and LiCH2CH2OCO2Li layer were not coated. The battery failed after 134 weeks of cycling, and there were powdery lithium dendrite substances on the surface of the separator. In Comparative Example 4, only the LiCH2CH2OCO2Li layer was coated. In Comparative Example 5, only the LiF layer and Li2CO3 layer were coated. In Comparative Example 6, the LiCH2CH2OCO2Li layer was first plated, and then the LiF layer and Li2CO3 layer were plated. There were slight powdery lithium dendrite substances on the surface of the separator, indicating that an ordered coating of the LiF layer, Li2CO3 layer, and LiCH2CH2OCO2Li layer was formed on the surface of the lithium metal layer in sequence. The LiF layer and Li2CO3 layer close to the lithium metal layer can prevent the growth of dendrites in the lithium metal layer, while the LiCH2CH2OCO2Li layer close to the electrolyte can prevent solvent molecules from entering and prevent the reaction between solvent molecules and the metal lithium layer. A single LiF layer or Li2CO3 layer cannot prevent the reaction between solvent molecules and the lithium layer; a single LiCH2CH2OCO2Li layer cannot prevent the growth of lithium dendrites either.

[0158] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered to be within the scope described in this specification.

[0159] The above-described embodiments only represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the invention patent should be subject to the appended claims.

Claims

1. A lithium metal negative electrode sheet, characterized in that, It includes a current collector and a lithium metal layer, a LiF layer, a Li2CO3 layer, and a LiCH2CH2OCO2Li layer that are sequentially stacked on the surface of the current collector.

2. The lithium metal negative electrode sheet according to claim 1, wherein, The thicknesses of the LiF layer, the Li2CO3 layer, and the LiCH2CH2OCO2Li layer are independently set to be 5 nm - 30 nm respectively.

3. The lithium metal negative electrode sheet according to claim 1, wherein The lithium metal negative electrode sheet satisfies at least one of the following conditions: (1) The areal density of one side of the lithium metal layer is 2.67 g / m 2 ~13.35 g / m 2 ; (2) The thicknesses of the LiF layer, the Li2CO3 layer, and the LiCH2CH2OCO2Li layer are independently set to be 10 nm - 25 nm respectively.

4. The preparation method of the lithium metal negative electrode sheet according to any one of claims 1 to 3, characterized in that, It includes the following steps: Form the lithium metal layer on the surface of the current collector; Form the LiF layer on the lithium metal layer; Form the Li2CO3 layer on the LiF layer; Form the LiCH2CH2OCO2Li layer on the Li2CO3 layer.

5. The preparation method of the lithium metal negative electrode sheet according to claim 4, characterized in that, The method for forming the LiF layer, the Li2CO3 layer, and the LiCH2CH2OCO2Li layer includes a magnetron sputtering method.

6. The preparation method of the lithium metal negative electrode sheet according to claim 5, characterized in that, The process conditions of the magnetron sputtering method include: the background vacuum degree is 4×10 -5 Pa to 6×10 -5 Pa, the sputtering gas pressure is 0.2 Pa to 0.4 Pa, the distance between the target and the substrate is 40 mm to 60 mm, and the sputtering power is 4.5 kW to 6.5 kW.

7. The preparation method of the lithium metal negative electrode sheet according to any one of claims 4 to 6, characterized in that, The preparation method of the raw material of the LiCH2CH2OCO2Li layer includes the following steps: Mix metallic lithium and ethylene carbonate and stir, react under the condition of 140 °C - 160 °C, and after the reaction is completed, perform drying to obtain LiCH2CH2OCO2Li.

8. The preparation method of the lithium metal negative electrode sheet according to claim 7, wherein, The preparation method of the raw material of the LiCH2CH2OCO2Li layer satisfies at least one of the following conditions: (1) The mass ratio of the ethylene carbonate to the metallic lithium is (7 - 8):1; (2) The rotation speed of the stirring is 150 r / min - 250 r / min; (3) The reaction time ≥ 24 h; (4) The drying is distillation drying, and the temperature of the distillation drying is 250 °C - 260 °C.

9. A lithium battery, characterized in that, It includes the lithium metal negative electrode sheet according to any one of claims 1 - 3 or the lithium metal negative electrode sheet prepared by the preparation method according to any one of claims 4 - 8.

10. An electrical device, characterized in that, It includes the lithium battery according to claim 9.

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