Lithium metal battery

Abstract

The invention relates to the technical field of lithium metal batteries, in particular to a lithium metal battery which comprises a positive plate, a negative plate, a diaphragm and electrolyte, the diaphragm is used for isolating the positive plate from the negative plate, the negative plate comprises lithium metal and a LiX coating loaded on the surface of the lithium metal, and X is at least one of Cl, Br and I; in the electrolyte, the concentration of the lithium salt is not higher than 0.6 mol / kg. The surface-treated lithium metal negative electrode (a protective layer containing LiCl or LiBr or LiI) is cooperated with the low-concentration electrolyte to react on a solid-liquid phase interface in the first charging and discharging process of the lithium metal battery, and the SEI is generated on the lithium metal negative electrode in situ, so that compared with the beneficial component LiF of the conventional SEI, the SEI has the advantages that the service life of the SEI is prolonged, and the service life of the SEI is prolonged. The bihalide SEI effectively improves the ionic conductivity under the condition that the mechanical stability is not influenced, and the cycle life of the lithium metal battery is effectively prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and in particular to a lithium metal battery. Background Art

[0002] With the rapid development of electronic products, the increasingly prominent energy crisis and the continuous expansion of related application fields, humans hope to obtain secondary battery systems with higher energy density and good cycle performance. Lithium metal anode has become the most promising anode for high energy density battery systems due to its low electrode potential and high theoretical specific capacity. In actual use, lithium metal has problems such as low coulombic efficiency and short cycle life, and dendrites will be deposited during the charge and discharge process, causing short circuits in the battery and even overheating and explosion of the battery. These problems have greatly limited the practical application of lithium metal anodes.

[0003] The commonly used methods at present are: 1) modifying the solid electrolyte to increase the mechanical modulus to hinder the growth of lithium dendrites; 2) alloying to reduce the reactivity of metallic lithium; 3) designing and modifying the artificial SEI film to prevent further reaction between metallic lithium and electrolyte, etc. In lithium batteries, the performance of the SEI film covering the surface of the lithium electrode directly determines the electrochemical behavior of the lithium electrode. Therefore, the reasonable design of the modified artificial SEI film to prevent the growth of lithium dendrites is considered to be one of the most effective methods to stabilize the metallic lithium negative electrode.

[0004] The use of electrolytes with high lithium salt concentrations (>2.5 mol / kg) is conducive to building a stable solid electrolyte interface (SEI), and has a good effect in inhibiting electrolyte decomposition and lithium dendrite growth, and has become a research hotspot in the battery field in recent years. However, higher lithium salt concentrations will cause the cost of electrolytes to increase exponentially, the viscosity of the system to increase, and the low temperature and fast charging performance to be affected, limiting the practical application of related technologies. Summary of the invention

[0005] In view of the problems existing in the high-concentration electrolyte of the existing lithium metal battery mentioned in the background technology, the present invention provides a lithium metal battery, which improves the cycle performance of the lithium metal battery by combining a lithium-containing halide layer on the lithium metal negative electrode with a low-concentration electrolyte.

[0006] In order to achieve the above-mentioned object, the present invention provides a lithium metal battery, comprising a positive electrode sheet, a negative electrode sheet, a separator for isolating the positive electrode sheet and the negative electrode sheet, and an electrolyte, wherein the negative electrode sheet comprises lithium metal and a LiX coating loaded on the surface of the lithium metal, where X is at least one of Cl, Br, and I; in the electrolyte, the lithium salt concentration is not higher than 0.6 mol / kg.

[0007] Preferably, the method for preparing the negative electrode sheet comprises: contacting a solution of a Lewis acid containing Cl, Br or I with a lithium metal sheet, then washing with an organic solvent, and drying to obtain the negative electrode sheet.

[0008] Through the above technical scheme, the present invention adopts a surface-treated lithium metal negative electrode (containing a protective layer of LiCl, LiBr or LiI) in conjunction with a low-concentration electrolyte, and a reaction occurs at the solid-liquid interface during the first charge and discharge process of the lithium metal battery, and a dihalide SEI is generated in situ on the lithium metal negative electrode. Compared with the conventional SEI beneficial component LiF, the dihalide SEI effectively improves the ionic conductivity without affecting the mechanical stability, thereby effectively improving the cycle life of the lithium metal battery.

[0009] According to a preferred embodiment of the present invention, a protective layer containing LiCl, LiBr or LiI is first grown in situ by contacting a lithium metal negative electrode sheet with a solution containing a Lewis acid, and then a low-concentration electrolyte is reacted at the solid-liquid interface during the first charge and discharge process of the lithium metal battery to generate a dihalide SEI in situ on the lithium metal negative electrode. Compared with the conventional SEI beneficial component LiF phase, the in-situ dihalide SEI effectively improves the ionic conductivity without affecting the mechanical stability, and effectively improves the cycle life of the lithium metal battery. The low-concentration lithium salt system not only has low viscosity and good wettability with the positive and negative electrodes, but also can reduce production costs, and has considerable application prospects.

[0010] The present invention can apply low-cost and low-viscosity low-lithium salt concentration electrolyte to lithium metal batteries, significantly improving the safety, stability and electrochemical stability of the lithium metal negative electrode during use. DETAILED DESCRIPTION

[0011] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0012] The present invention provides a lithium metal battery, comprising a positive electrode sheet, a negative electrode sheet, a diaphragm for isolating the positive electrode sheet and the negative electrode sheet, and an electrolyte, wherein the negative electrode sheet comprises lithium metal and a LiX coating loaded on the surface of the lithium metal, wherein X is at least one of Cl, Br, and I; and in the electrolyte, the lithium salt concentration is not higher than 0.6 mol / kg. The present invention adopts a surface-treated lithium metal negative electrode (containing a protective layer of LiCl, LiBr, or LiI) in coordination with a low-concentration electrolyte, and reacts at the solid-liquid interface during the first charge and discharge process of the lithium metal battery, and generates a dihalide SEI in situ on the lithium metal negative electrode. Compared with the conventional SEI beneficial component LiF, the dihalide SEI effectively improves the ionic conductivity without affecting the mechanical stability, and effectively improves the cycle life of the lithium metal battery.

[0013] In the present invention, the lithium metal sheet is used as the negative electrode sheet, and the surface facing the separator includes a LiX-loaded coating.

[0014] In the present invention, the concentration of the lithium salt in the electrolyte can be selected in a wide range. According to a preferred embodiment of the present invention, the concentration of the lithium salt in the electrolyte is 0.2-0.6 mol / kg, preferably 0.4-0.5 mol / kg.

[0015] In the present invention, the lithium salt concentration of 0.2-0.6 mol / kg means that each kg of electrolyte contains 0.2-0.6 mol of lithium salt.

[0016] In the present invention, in the electrolyte, the types of lithium salts can be selected from a wide range. According to a preferred embodiment of the present invention, the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium perchlorate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide and lithium tetrafluoroborate.

[0017] According to a preferred embodiment of the present invention, the lithium salt is selected from at least two of lithium hexafluorophosphate, lithium perchlorate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium bis(trifluoromethylsulfonyl)imide and lithium bis(fluorosulfonyl)imide and lithium tetrafluoroborate, and the concentration of the single lithium salt is 0.1 mol / kg-0.4 mol / kg; it is beneficial to improve the cycle performance.

[0018] According to a preferred embodiment of the present invention, in the electrolyte, the lithium salt is a mixture of lithium bis(trifluoromethylsulfonyl)imide or lithium bis(fluorosulfonyl)imide and lithium difluorooxalate borate, and preferably the molar ratio of lithium bis(trifluoromethylsulfonyl)imide or lithium bis(fluorosulfonyl)imide to lithium difluorooxalate borate is 1-5:1; which is beneficial to further improve the cycle performance.

[0019] In the present invention, the types of solvents can be selected in a wide range, and conventional anhydrous solvents in the field can be used in the present invention. According to a preferred embodiment of the present invention, in the electrolyte, the solvent is selected from one or more of propylene carbonate, ethyl methyl carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, fluoroethylene carbonate, fluoropropylene carbonate, fluorodiethyl carbonate and fluoromethyl ethyl carbonate, γ-butyrolactone, and cyclopentane sulfone; preferably, it is a mixed solvent of ethylene carbonate, fluoroethylene carbonate, and ethyl methyl carbonate, and more preferably, the mass ratio of ethylene carbonate, fluoroethylene carbonate, and ethyl methyl carbonate is 0.5-3:1:1-5.

[0020] In the present invention, in-situ growth of a protective layer containing LiCl or LiBr or LiI is beneficial to further improve the cycle performance. According to a preferred embodiment of the present invention, the method for preparing the negative electrode sheet includes:

[0021] A solution of Lewis acid containing Cl, Br or I is brought into contact with a lithium metal sheet, which is then washed with an organic solvent and dried to obtain the negative electrode sheet.

[0022] In the present invention, the solution is brought into contact with one side of a lithium metal sheet, and the Lewis acid reacts with Li to in-situ grow a protective layer containing LiCl, LiBr or LiI.

[0023] According to a preferred embodiment of the present invention, the preparation of the negative electrode sheet is carried out under an inert gas atmosphere; the inert gas may be one or more of argon, nitrogen, and helium.

[0024] In the present invention, the concentration of the Lewis acid in the solution can be selected in a wide range. According to a preferred embodiment of the present invention, the concentration of the Lewis acid is 0.1-2 mol / kg, that is, the Lewis acid content is 0.1-2 mol per kilogram of solution.

[0025] In the present invention, the ratio of the amount of lithium metal sheet to the solution can be selected in a wide range. According to a preferred embodiment of the present invention, per 1 cm 2 15-60 μL of the solution was applied to the lithium metal sheet.

[0026] In the present invention, the contact time between the solution and the Lewis acid can be selected in a wide range. According to a preferred embodiment of the present invention, the contact time is 20-100 seconds.

[0027] In the present invention, there is no particular limitation on the drying conditions, as long as the lithium is not oxidized and the organic solvent is removed. According to a preferred embodiment of the present invention, the drying conditions include: drying under vacuum or inert gas atmosphere at a temperature of 25-35°C; the reaction time can be reasonably adjusted according to actual needs, preferably, the time is 24-78h.

[0028] In the present invention, the solvent in the solution can be selected from a wide range of types. According to a preferred embodiment of the present invention, the solvent in the solution is selected from one or more of cyclic carbonate solvents, linear carbonate solvents and ether solvents.

[0029] According to a preferred embodiment of the present invention, the cyclic carbonate solvent is ethylene carbonate and / or propylene carbonate; the chain carbonate solvent is at least one of ethyl methyl carbonate, dimethyl carbonate and diethyl carbonate.

[0030] According to a preferred embodiment of the present invention, the ether solvent is at least one of 1,3-dioxolane, ethylene glycol dimethyl ether and tetrahydrofuran.

[0031] According to a preferred embodiment of the present invention, the organic solvent is selected from one or more ether solvents, preferably at least one of 1,3-dioxolane, ethylene glycol dimethyl ether and tetrahydrofuran, more preferably tetrahydrofuran.

[0032] According to a preferred embodiment of the present invention, the Lewis acid is selected from one or more of ZnCl2, CuCl2, CuI2, FeCl3, AlCl3, AlBr3 and AlI3.

[0033] In the present invention, there is no particular limitation on the type of material of the positive electrode sheet, which may be any existing positive electrode active material in the art. According to a preferred embodiment of the present invention, in the positive electrode sheet, the positive electrode active material is selected from one or more of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium cobalt oxide and lithium iron phosphate.

[0034] In the present invention, there is no particular limitation on the type of the separator, which may be a conventional separator in the art, for example, a polyolefin separator.

[0035] In order to further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0036] The raw materials used in the following examples and comparative examples, unless otherwise specified, are all disclosed in the prior art, for example, they can be directly purchased or prepared according to the preparation method disclosed in the prior art.

[0037] Preparation Example 1

[0038] (1) In a glove box filled with argon, 0.681 g of ZnCl2 was added to 5 g of 1,3-dioxolane and stirred for 4 h to obtain a mixed solution;

[0039] (2) Add the mixed solution obtained in step 1 dropwise onto the surface of the lithium metal negative electrode, with a volume of 1 cm 2 45 μL of the mixed solution was added dropwise onto the lithium metal sheet and kept for 30 s;

[0040] (3) The lithium metal sheet treated in step (2) was washed with tetrahydrofuran and dried under vacuum at 25° C. for 48 h to obtain a negative electrode sheet.

[0041] Preparation Example 2

[0042] (1) In a glove box filled with argon, 0.134 g of AlBr3 was added to 5 g of tetrahydrofuran and stirred for 4 h to obtain a mixed solution;

[0043] (2) Add the mixed solution obtained in step 1 dropwise onto the surface of the lithium metal negative electrode, with a volume of 1 cm 260 μL of the mixed solution was added dropwise onto the lithium metal sheet and kept for 100 s;

[0044] (3) The lithium metal sheet treated in step (2) was washed with tetrahydrofuran and dried under vacuum at 30° C. for 64 h to obtain a negative electrode sheet.

[0045] Preparation Example 3

[0046] (1) In a glove box filled with argon, add 1.9 g of CuI2 to 5 g of ethyl methyl carbonate and stir for 4 h to obtain a mixed solution;

[0047] (2) Add the mixed solution obtained in step 1 dropwise onto the surface of the lithium metal negative electrode, with a volume of 1 cm 2 15 μL of the mixture was added dropwise onto the lithium metal sheet and kept for 15 s;

[0048] (3) The lithium metal sheet treated in step (2) was washed with tetrahydrofuran and dried under vacuum at 35° C. for 24 h to obtain a negative electrode sheet.

[0049] Preparation Example 4

[0050] According to the method of Preparation Example 1, except that Lewis acid is not added, 1,3-dioxolane is used to treat the lithium metal negative electrode sheet, specifically:

[0051] (1) 5 g of 1,3-dioxolane was added dropwise to the surface of the lithium metal negative electrode, with a volume of 1 cm 2 45 μL of the mixed solution was added dropwise onto the lithium metal sheet and kept for 30 s;

[0052] (2) The lithium metal sheet treated in step (1) was washed with tetrahydrofuran and dried under vacuum at 25° C. for 48 h to obtain a negative electrode sheet.

[0053] Example 1

[0054] Electrolyte and composition: ethylene carbonate, fluoroethylene carbonate, and ethyl methyl carbonate in a mass ratio of 3:2:5 as solvent, lithium salt and concentration: 0.4 mol / kg lithium bis(trifluoromethylsulfonyl)imide and 0.1 mol / kg lithium difluorooxalate borate.

[0055] The button cell shell, copper sheet, separator, negative electrode sheet prepared in Preparation Example 1, and electrolyte were assembled into a lithium copper half-cell and charged at 1 mA.cm -2 The coulombic efficiency test was carried out at a current density of . The test results are shown in Table 2.

[0056] Example 2

[0057] The electrolyte and its composition: ethylene carbonate, fluoroethylene carbonate and ethyl methyl carbonate are used as solvents in a mass ratio of 1:2:7, and the lithium salt and its concentration are: 0.3 mol / kg lithium hexafluorophosphate + 0.1 mol / kg lithium difluorooxalate borate.

[0058] The button cell shell, copper sheet, separator, negative electrode sheet prepared in Preparation Example 2, and electrolyte were assembled into a lithium copper half-cell and charged at 1 mA.cm -2 The coulombic efficiency test was carried out at a current density of . The test results are shown in Table 2.

[0059] Example 3

[0060] The method of Example 1 is used, except that the negative electrode sheet is the negative electrode sheet prepared in Preparation Example 3, and the lithium salt concentration in the electrolyte is: 0.4 mol / kg lithium bis(trifluoromethylsulfonyl)imide+0.2 mol / kg lithium hexafluorophosphate; the other conditions are the same as Example 1. The test results are shown in Table 2.

[0061] Comparative Example 1

[0062] The method of Example 1 was followed, except that the negative electrode sheet was the negative electrode sheet prepared in Preparation Example 4, and the other conditions were the same as in Example 1. The test results are shown in Table 2.

[0063] Embodiment 4-10

[0064] According to the method of Example 1, the type or concentration of lithium salt in the electrolyte was changed, as shown in Table 1.

[0065] Table 1

[0066]

[0067]

[0068] Comparative Example 2

[0069] The method of Example 1 is followed, except that the lithium salt and concentration in the electrolyte are: 0.8 mol / kg lithium bis(trifluoromethylsulfonyl)imide and 0.2 mol / kg lithium difluorooxalatoborate, and the other conditions are the same as those of Example 1. The test results are shown in Table 2.

[0070] Comparative Example 3

[0071] The method of Example 1 is used, except that the concentration of lithium salt in the electrolyte is 1 mol / kg lithium hexafluorophosphate, and the other conditions are the same as those of Example 1. The test results are shown in Table 2.

[0072] Comparative Example 4

[0073] Electrolyte and composition: ethylene carbonate, fluoroethylene carbonate, and ethyl methyl carbonate in a mass ratio of 3:2:5 as solvent, and lithium salt and concentration: 0.8 mol / kg lithium bis(trifluoromethylsulfonyl)imide and 0.2 mol / kg lithium difluorooxalatoborate.

[0074] The button cell shell, copper sheet, separator, negative electrode sheet prepared in Preparation Example 4, and electrolyte were assembled into a lithium copper half-cell and charged at 1 mA.cm -2 The coulombic efficiency test was carried out at a current density of . The test results are shown in Table 2.

[0075] Comparative Example 5

[0076] The electrolyte and its composition: ethylene carbonate, fluoroethylene carbonate and ethyl methyl carbonate are used as solvents in a mass ratio of 3:2:5, and the lithium salt and its concentration are: 1 mol / kg lithium hexafluorophosphate.

[0077] The button cell shell, copper sheet, separator, negative electrode sheet prepared in Preparation Example 4, and electrolyte were assembled into a lithium copper half-cell and charged at 1 mA.cm -2 The coulombic efficiency test was carried out at a current density of . The test results are shown in Table 2.

[0078] Table 2

[0079] serial number 250 cycles Coulomb efficiency (%) Example 1 94.3 Example 2 89.1 Example 3 90.3 Example 4 87.3 Example 5 86.7 Example 6 81.5 Example 7 85.4 Example 8 88.6 Example 9 86.5 Example 10 81.2 Comparative Example 1 69.9 Comparative Example 2 70.2 Comparative Example 3 72.4 Comparative Example 4 77.2 Comparative Example 5 80.6

[0080] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A lithium metal battery, comprising a positive electrode sheet, a negative electrode sheet, a separator for isolating the positive electrode sheet and the negative electrode sheet, and an electrolyte, characterized in that: The negative electrode sheet includes lithium metal and a LiX coating loaded on the surface of the lithium metal, wherein X is at least one of Cl, Br, and I; In the electrolyte, the lithium salt concentration is not higher than 0.6 mol / kg.

2. The lithium metal battery according to claim 1, wherein In the electrolyte, the lithium salt concentration is 0.2-0.6 mol / kg; In the electrolyte, the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium perchlorate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide and lithium tetrafluoroborate; Preferably, the lithium salt is selected from at least two of lithium hexafluorophosphate, lithium perchlorate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium bis(trifluoromethylsulfonyl)imide and lithium bis(fluorosulfonyl)imide and lithium tetrafluoroborate, and the concentration of the single lithium salt is 0.1 mol / kg-0.4 mol / kg.

3. The lithium metal battery according to claim 1 or 2, wherein: In the electrolyte, the lithium salt concentration is 0.4-0.5 mol / kg.

4. The lithium metal battery according to claim 1 or 2, wherein: In the electrolyte, the lithium salt is a mixture of lithium bis(trifluoromethylsulfonyl)imide or lithium bis(fluorosulfonyl)imide and lithium difluorooxalate borate, and preferably the molar ratio of lithium bis(trifluoromethylsulfonyl)imide or lithium bis(fluorosulfonyl)imide to lithium difluorooxalate borate is 1-5:

1.

5. The lithium metal battery according to claim 1 or 2, wherein: In the electrolyte, the solvent is selected from one or more of propylene carbonate, ethyl methyl carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, fluoroethylene carbonate, fluoropropylene carbonate, fluorodiethyl carbonate and fluoromethyl ethyl carbonate, γ-butyrolactone, and cyclopentane sulfone; preferably, it is a mixed solvent of ethylene carbonate, fluoroethylene carbonate, and ethyl methyl carbonate, and more preferably, the mass ratio of ethylene carbonate, fluoroethylene carbonate, and ethyl methyl carbonate is 0.5-3:1:1-5.

6. The lithium metal battery according to any one of claims 1 to 5, wherein: The method for preparing the negative electrode sheet comprises: A solution of Lewis acid containing Cl, Br or I is brought into contact with a lithium metal sheet, which is then washed with an organic solvent and dried to obtain the negative electrode sheet.

7. The lithium metal battery according to claim 6, wherein: In the solution, the concentration of Lewis acid is 0.1-2 mol / kg; and / or Every 1cm 2 Apply 15-60 μL of the solution to the lithium metal sheet; and / or The contact time is 20-100 seconds; and / or Drying conditions include: temperature of 25-35°C, drying under vacuum or inert gas atmosphere.

8. The lithium metal battery according to claim 6, wherein In the solution, the solvent is selected from one or more of cyclic carbonate solvents, chain carbonate solvents and ether solvents; Preferably, The cyclic carbonate solvent is ethylene carbonate and / or propylene carbonate; The chain carbonate solvent is at least one of ethyl methyl carbonate, dimethyl carbonate and diethyl carbonate; The ether solvent is at least one of 1,3-dioxolane, ethylene glycol dimethyl ether and tetrahydrofuran; and / or The organic solvent is selected from one or more ether solvents, preferably at least one of 1,3-dioxolane, ethylene glycol dimethyl ether and tetrahydrofuran, more preferably tetrahydrofuran.

9. The lithium metal battery according to claim 6, wherein: The Lewis acid is selected from one or more of ZnCl2, CuCl2, CuI2, FeCl3, AlCl3, AlBr3 and AlI3.

10. The lithium metal battery according to claim 1 or 2, wherein: In the positive electrode sheet, the positive electrode active material is selected from one or more of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium cobalt oxide and lithium iron phosphate.

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