Electrolyte for lithium metal battery, lithium metal battery and electric device

Abstract

The invention relates to an electrolyte for a lithium metal battery, the lithium metal battery and a power utilization device, the electrolyte for the lithium metal battery comprises an organic solvent, the organic solvent comprises a phosphate ester compound, the phosphate ester compound comprises a silicon-containing group and at least one phosphate ester group, an oxygen atom of at least one phosphorus-oxygen single bond in the phosphate group is connected with a silicon atom of the silicon-containing group through a covalent single bond.

Description

Technical Field

[0001] The present application relates to an electrolyte for a lithium metal battery, a lithium metal battery and an electrical device. Background Art

[0002] Lithium metal batteries have properties such as high capacity and are therefore widely used in electronic devices such as mobile phones, laptops, electric vehicles, electric airplanes, electric boats, electric toy cars, electric toy boats, electric toy airplanes and electric tools, etc.

[0003] However, the low-temperature and high-temperature cycling performance of current lithium metal batteries is still poor. Summary of the invention

[0004] The present application provides an electrolyte for a lithium metal battery, a lithium metal battery and an electrical device. The low-temperature and high-temperature cycle performance of the lithium metal battery of the present application can be improved.

[0005] In the first aspect, an embodiment of the present application proposes an electrolyte for a lithium metal battery, wherein the electrolyte for a lithium metal battery includes an organic solvent, the organic solvent includes a phosphate compound, the phosphate compound includes a silicon-containing group and at least one phosphate group, and at least one oxygen atom of a phosphorus-oxygen single bond in the phosphate group is covalently bonded to a silicon atom of the silicon-containing group.

[0006] Therefore, the phosphate group in the embodiment of the present application can capture combustion free radicals such as hydrogen free radicals, hydroxyl free radicals, etc., thereby blocking the chain reaction of free radicals, making the combustion process unable to proceed due to the lack of combustion free radicals, reducing the risk of continuous combustion of the electrolyte, achieving flame retardancy or non-flammability of the electrolyte, and improving the thermal stability of the electrolyte, thereby improving the reliability of the use of lithium metal batteries. The oxygen atom in the phosphorus-oxygen single bond and the silicon atom in the silicon-containing group can be connected in the form of a covalent single bond to form a silicon-oxygen bond Si-O. The silicon-oxygen bond can participate in the formation of the SEI film, undergo a polymerization reaction to form an organic polymer, and increase the toughness of the SEI film. During the charging and discharging process of lithium metal, although the volume of lithium metal changes and exerts force on the SEI film, the SEI film is not easy to break due to its excellent toughness, which allows lithium metal to be deposited evenly and does not easily form lithium dendrites. Moreover, the above-mentioned organic polymer in the SEI film has strong reduction resistance and is not easy to decompose. The SEI film can play a good protective role on the negative electrode plate, reduce the risk of side reactions between lithium metal and electrolyte, and thus improve the low-temperature and high-temperature cycle performance of lithium metal batteries.

[0007] In some embodiments, at least one of the silicon-containing group and the phosphate group comprises an ether bond. The ether bond can participate in the film-forming reaction of the SEI film, further improving the stability of the SEI film, thereby improving the low-temperature and high-temperature cycle performance of the lithium metal battery.

[0008] In some embodiments, the phosphate compound includes a compound represented by formula A,

[0009]

[0010] In formula A,

[0011] R 1 To R 3 Each independently includes a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryl group, a substituted or unsubstituted aryloxy group, a substituted or unsubstituted phosphoxy group, a substituted or unsubstituted silane group, a substituted or unsubstituted siloxy group, a substituted or unsubstituted alkylsilyl group, a substituted or unsubstituted alkoxysilyl group, or a substituted or unsubstituted alkoxyalkylsilyl group;

[0012] Among them, R 1 To R 3 At least one of the above comprises a substituted or unsubstituted silane, a substituted or unsubstituted siloxy group, a substituted or unsubstituted alkylsilyl group, a substituted or unsubstituted alkoxysilyl group, or a substituted or unsubstituted alkoxyalkylsilyl group.

[0013] In some embodiments, the compound represented by Formula A includes at least one of the compounds represented by Formula A-Ia to the compounds represented by Formula A-IVb,

[0014]

[0015]

[0016] In some embodiments, the phosphate compound includes a compound represented by formula B,

[0017]

[0018] In formula B,

[0019] R 4 and R 5 Each independently includes a phosphite group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryl group, a substituted or unsubstituted aryloxy group, a substituted or unsubstituted phosphoryloxy group;

[0020] R 7 To R 10 Each independently includes a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryl group, a substituted or unsubstituted aryloxy group, and a substituted or unsubstituted phosphoryloxy group.

[0021] In some embodiments, the compound represented by Formula B includes at least one of the compounds represented by Formula B-1 to the compounds represented by Formula B-6.

[0022]

[0023] Therefore, the phosphate compound of the embodiment of the present application includes at least two phosphate groups, and at least two phosphate groups are connected by a silicon-containing group. As the content of the phosphate group increases, the flame retardant property of the electrolyte is improved.

[0024] In some embodiments, the phosphate compound includes a compound represented by Formula C,

[0025]

[0026] In formula C, R 6 including phosphite, substituted or unsubstituted alkyl, substituted or unsubstituted alkoxy, substituted or unsubstituted aryl, substituted or unsubstituted aryloxy, substituted or unsubstituted phosphoryloxy;

[0027] R 11 To R 16 Each independently includes a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryl group, a substituted or unsubstituted aryloxy group, and a substituted or unsubstituted phosphoryloxy group.

[0028] Therefore, the phosphate compound of the embodiment of the present application includes at least two phosphate groups, and at least two phosphate groups are connected by a silicon-containing group. As the content of the phosphate group increases, the flame retardant property of the electrolyte is improved.

[0029] In some embodiments, the compound represented by Formula C includes at least one of the compounds represented by Formula C-1 to the compounds represented by Formula C-3.

[0030]

[0031] In some embodiments, the volume content of the phosphate compound is ≥9% based on the total volume of the electrolyte; optionally, the volume content of the phosphate compound is 20% to 60%. The volume content of the phosphate compound within the above range can improve the flame retardant properties of the system, and the silicon-containing group and the phosphate group can work together to improve the toughness of the SEI film and improve the cycle performance and reliability of the lithium metal battery.

[0032] In some embodiments, the organic solvent further includes a nitrogen-containing ionic liquid; the nitrogen-containing ionic liquid can enhance the flame retardancy of the electrolyte.

[0033] In some embodiments, the nitrogen-containing ionic liquid includes a cation and an anion, the cation includes at least one of an amine cation, an imidazolium cation, a piperidinium cation, and a pyridinium cation, and the anion includes at least one of a trifluoromethylsulfonyl imide anion, a bisfluorosulfonyl imide anion, and a difluorooxalate borate anion.

[0034] In some embodiments, based on the total volume of the electrolyte, the ratio of the volume content of the phosphate compound to the volume content of the nitrogen-containing ionic liquid is 1:(0.1 to 9); optionally 1:(1 to 3). When the volume content ratio of the phosphate compound to the nitrogen-containing ionic liquid is within the above range, the flame retardant properties of the system can be further improved, the toughness of the SEI film can be improved, and the cycle performance and reliability of the lithium metal battery can be improved.

[0035] In some embodiments, the electrolyte further includes a lithium salt, and the lithium salt includes at least one of lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, and lithium difluorooxalatoborate; the molar concentration of the lithium salt is 0.1 mol / L to 4 mol / L; optionally 1.8 mol / L to 2.2 mol / L. The lithium salt is used in combination with the above-mentioned organic solvent to form an SEI film containing inorganic components such as lithium fluoride on the negative electrode sheet, which can further improve the structural stability of the SEI film, thereby improving the cycle performance of the lithium metal battery.

[0036] In a second aspect, the embodiments of the present application further provide a lithium metal battery, the lithium metal battery comprising an electrolyte for a lithium metal battery as in any embodiment of the first aspect of the present application.

[0037] In some embodiments, the lithium metal battery further comprises a positive electrode sheet, the positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer disposed on at least one side of the positive electrode current collector, the positive electrode film layer comprises a positive electrode active material, and the positive electrode active material comprises a composition formula of Li a Ni b Co c M d O e A f Compounds and modified compounds thereof, 0.8≤a≤1.2, 0.5≤b<1, 0<c<1, 0<d<1, 1≤e≤2, 0≤f≤1, M includes at least one of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and A includes at least one of N, F, S and Cl.

[0038] In some embodiments, the battery further includes a negative electrode sheet, the negative electrode sheet including a negative current collector.

[0039] In some embodiments, the negative electrode plate includes a negative electrode current collector and a negative electrode film layer disposed on at least one side of the negative electrode current collector, the negative electrode film layer includes lithium metal or a lithium metal alloy, the lithium metal alloy includes lithium metal and a non-lithium element, and the non-lithium element includes at least one of tin, zinc, aluminum, magnesium, silver, gold, gallium, indium, foil, boron, carbon and silicon.

[0040] In a third aspect, an embodiment of the present application further proposes an electrical device, which includes a lithium metal battery as in any embodiment of the second aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments of the present application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the drawings without paying creative work.

[0042] Figure 1 It is a schematic diagram of one embodiment of the lithium metal battery of the present application.

[0043] Figure 2 yes Figure 1 An exploded schematic diagram of an embodiment of a lithium metal battery.

[0044] Figure 3 It is a schematic diagram of an embodiment of a battery module of the present application.

[0045] Figure 4 It is a schematic diagram of an embodiment of the battery pack of the present application.

[0046] Figure 5 yes Figure 4 An exploded schematic diagram of an embodiment of a battery pack is shown.

[0047] Figure 6 It is a schematic diagram of an embodiment of an electrical device including the lithium metal battery of the present application as a power source.

[0048] The drawings are not necessarily drawn to scale.

[0049] The following are the descriptions of the reference numerals:

[0050] 1. Battery pack; 2. Upper box; 3. Lower box; 4. Battery module;

[0051] 5. lithium metal battery; 51. housing; 52. electrode assembly;

[0052] 53. Cover plate;

[0053] 6. Electrical equipment. DETAILED DESCRIPTION

[0054] Hereinafter, the embodiments of the lithium metal battery electrolyte, lithium metal battery and electrical device of the present application will be specifically disclosed with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0055] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0056] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0057] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0058] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, a method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, a method may also include step (c), which means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0059] A lithium metal battery includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode sheet, a negative electrode sheet and a separator. The separator is located between the positive electrode sheet and the negative electrode sheet to isolate the positive electrode sheet from the negative electrode sheet.

[0060] Lithium metal batteries achieve energy storage and discharge through the stripping and deposition of lithium metal. Specifically, during the charging process of lithium metal batteries, lithium ions are released from the positive electrode active material of the positive electrode plate, pass through the isolation membrane through the electrolyte, and pass through the solid electrolyte interface (Solid Electrolyte Interface, SEI) membrane, and then deposited and reduced to lithium metal on the surface of the negative electrode plate, thereby generating a current concentration difference in the external circuit; during the discharge process of lithium metal batteries, the lithium metal on the surface of the negative electrode plate loses electrons to the external circuit, and the lithium metal forms lithium ions that are released into the electrolyte and migrate to the positive electrode active material through the electrolyte.

[0061] During the charge and discharge cycle of lithium metal batteries, the volume of lithium metal changes. For example, during the charging process, the volume of lithium metal expands. The expanded lithium metal may cause the SEI film to be destroyed. Lithium ions pass through the damaged area of ​​the SEI film and deposit irregularly on the negative electrode surface, causing the growth of lithium dendrites. The lithium dendrites may pierce the isolation membrane and contact the positive electrode plate, causing a short circuit, triggering thermal runaway, and deteriorating the reliability of the lithium metal battery.

[0062] In order to improve the reliability of lithium metal batteries, the relevant technology considers adding flame retardants, such as phosphate compounds, to the electrolyte. Phosphate compounds have the advantages of low viscosity, low melting point, low cost and high flame retardancy, and are widely used in flame retardant system electrolytes; however, phosphate compounds are difficult to form a stable SEI film on the surface of the negative electrode plate, and cannot effectively alleviate the growth of lithium dendrites; and lithium metal is prone to side reactions with the electrolyte, causing the lithium metal and the electrolyte to be consumed, and phosphate compounds have poor reduction resistance and are easily decomposed at the negative electrode plate, which is not conducive to improving the low-temperature and high-temperature cycle performance of lithium metal batteries.

[0063] In view of the above problems, the embodiments of the present application further improve the composition of the electrolyte, and improve the performance of the SEI film and the flame retardant properties of the electrolyte by selecting specific organic solvents. Specifically, the organic solvent includes a phosphate compound, which has good flame retardant properties and can improve the flame retardant effect of the electrolyte and the reliability of the lithium metal battery. The phosphate compound includes a silicon-containing group and at least one phosphate group, and the oxygen atom of at least one phosphorus-oxygen single bond in the phosphate group is covalently bonded to the silicon atom of the silicon-containing group to form a silicon-oxygen bond. The silicon-oxygen bond can undergo a polymerization reaction on the surface of the negative electrode to form a tough SEI film. The SEI film is not easy to break and can reduce the formation of lithium dendrites. The SEI film can provide good protection for the negative electrode plate, reduce the risk of side reactions between lithium metal and the electrolyte, and improve the low-temperature and high-temperature cycle performance of the lithium metal battery.

[0064] Next, the technical solution of this application is described in detail.

[0065] Electrolyte for lithium metal batteries

[0066] In a first aspect, an embodiment of the present application provides an electrolyte for a lithium metal battery.

[0067] The electrolyte for lithium metal battery includes an organic solvent, the organic solvent includes a phosphate compound, the phosphate compound includes a silicon-containing group and at least one phosphate group, and at least one oxygen atom of a phosphorus-oxygen single bond in the phosphate group is connected to a silicon atom of the silicon-containing group by a covalent single bond.

[0068] The skeleton structure of phosphate compounds is a phosphate group. The hydrogen atoms on the phosphate group can be replaced by other groups, such as silicon-containing groups. The phosphate group can improve the flame retardant properties of the system. The combined effect of the silicon-containing group and the phosphate group can improve the toughness of the SEI film and enhance the cycle performance and reliability of lithium metal batteries.

[0069] Although the mechanism is not clear, the mechanism of action of this application is speculated to be as follows:

[0070] Phosphate groups can capture combustion free radicals such as hydrogen radicals, hydroxyl radicals, etc., thereby blocking the chain reaction of free radicals, making the combustion process unable to proceed due to the lack of combustion free radicals, reducing the risk of continuous combustion of the electrolyte, making the electrolyte difficult to burn or non-flammable, and improving the thermal stability of the electrolyte, thereby improving the reliability of lithium metal batteries.

[0071] The oxygen atom in the phosphorus-oxygen single bond and the silicon atom in the silicon-containing group can be connected in the form of a covalent single bond to form a silicon-oxygen bond Si-O. The silicon-oxygen bond can participate in the formation of the SEI film, undergo a polymerization reaction to form an organic polymer, and increase the toughness of the SEI film. During the charging and discharging process of lithium metal, although the volume of lithium metal changes and exerts force on the SEI film, the SEI film is not easy to break due to its excellent toughness, which allows lithium metal to be deposited evenly and does not easily form lithium dendrites. Moreover, the above-mentioned organic polymer in the SEI film has strong reduction resistance and is not easy to decompose. The SEI film can play a good protective role on the negative electrode plate, reduce the risk of side reactions between lithium metal and electrolyte, and thus improve the low-temperature and high-temperature cycle performance of lithium metal batteries.

[0072] In some embodiments, the silicon-containing group may include a silicon-oxygen bond Si-O, and the phosphate compound contains multiple silicon-oxygen bonds, which can further improve the toughness of the SEI film and further improve the low-temperature and high-temperature cycle performance of the lithium metal battery; it can also further improve the solubility of lithium salts and improve the kinetic performance of the battery.

[0073] In some embodiments, the phosphate compound further includes an ether bond, specifically, the silicon-containing group may include an ether bond; and / or the phosphate group may include an ether bond. The ether bond can participate in the film-forming reaction of the SEI film, further improving the stability of the SEI film, thereby improving the low-temperature and high-temperature cycle performance of the lithium metal battery.

[0074] The phosphate compound may include at least one phosphate group, such as one, two, three or four. The specific structure of the phosphate compound is described below.

[0075] In some embodiments, the phosphate compound includes a compound represented by formula A,

[0076]

[0077] In formula A,

[0078] R 1 To R 3 Each independently includes a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryl group, a substituted or unsubstituted aryloxy group, a substituted or unsubstituted phosphoxy group, a substituted or unsubstituted silane group, a substituted or unsubstituted siloxy group, a substituted or unsubstituted alkylsilyl group, a substituted or unsubstituted alkoxysilyl group, or a substituted or unsubstituted alkoxyalkylsilyl group;

[0079] Among them, R 1 To R 3At least one of the silicon-containing groups includes a silicon-containing group, and the specific silicon-containing group may include a substituted or unsubstituted silane, a substituted or unsubstituted siloxy group, a substituted or unsubstituted alkylsilicon group, a substituted or unsubstituted alkoxysilicon group, or a substituted or unsubstituted alkoxyalkylsilicon group.

[0080] In some embodiments, R 1 To R 3 Each independently includes a substituted or unsubstituted C1 to C6 alkyl group, a substituted or unsubstituted C1 to C6 alkoxy group, a substituted or unsubstituted C1 to C6 aryl group, a substituted or unsubstituted C1 to C6 aryloxy group, a substituted or unsubstituted C1 to C6 phosphoxy group, a substituted or unsubstituted C1 to C6 silane group, a substituted or unsubstituted C1 to C6 siloxy group, a substituted or unsubstituted C1 to C6 alkylsilyl group, a substituted or unsubstituted C1 to C6 alkoxysilyl group, or a substituted or unsubstituted C1 to C6 alkoxyalkylsilyl group.

[0081] When the above groups are substituted, the substituted groups include at least one of halogen atoms, sulfur atoms, and mercapto groups; halogen atoms can be selected. Halogen atoms such as fluorine atoms can reduce the hydrogen content in the system and further reduce the flammability of the electrolyte; and because fluorine atoms have a strong electron-withdrawing effect, they help to form an excellent SEI film at the interface of the negative electrode plate, which can improve the compatibility between the electrolyte and the negative electrode plate, so that the cycle performance of the lithium metal battery is further improved.

[0082] In some embodiments, R 1 To R 3 One of them includes a silicon-containing group. In the process of the silicon-containing group participating in the formation of the SEI film, the steric hindrance is small, which is conducive to the formation of the SEI film.

[0083] Illustratively, the compound represented by formula A includes at least one of the compounds represented by formula A-Ia to the compounds represented by formula A-Id,

[0084]

[0085] In some embodiments, R 1 To R 3 At least two of them include silicon-containing groups, and specific silicon-containing groups may include substituted or unsubstituted silane, substituted or unsubstituted siloxy, substituted or unsubstituted alkylsilicon, substituted or unsubstituted alkoxysilicon, or substituted or unsubstituted alkoxyalkylsilicon. The more silicon-containing groups there are in the phosphate ester compound, the stronger the toughness of the SEI film formed by it, and the more conducive it is to improving the structural stability of the SEI film and the protection performance of the negative electrode, thereby improving the cycle performance of the lithium metal battery.

[0086] In some embodiments, R 1 To R3 Two of them include silicon-containing groups. As the silicon content increases, the number of silicon-oxygen bonds increases, the film-forming performance of the SEI film is better, and it also helps to improve the coulombic efficiency of the battery.

[0087] Illustratively, the compound represented by formula A includes at least one of the compounds represented by formula A-IIa to the compounds represented by formula A-IIj,

[0088]

[0089] In some embodiments, R 1 To R 3 All three include silicon-containing groups.

[0090] Illustratively, the compound represented by formula A includes at least one of the compounds represented by formula A-IIIa to the compounds represented by formula A-IIIt,

[0091]

[0092] In some embodiments, the phosphate ester compound includes a fluorine atom.

[0093] Illustratively, the compound represented by formula A includes at least one of the compound represented by formula A-IVa and the compound represented by formula A-IVb,

[0094]

[0095] In some embodiments, the phosphate compound includes at least two phosphate groups, and at least two phosphate groups are connected by a silicon-containing group. As the content of the phosphate group increases, the flame retardant property of the electrolyte improves.

[0096] In some embodiments, the phosphate compound includes a compound represented by formula B,

[0097]

[0098] In formula B,

[0099] R 4 and R 5 Each independently includes a phosphite group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryl group, a substituted or unsubstituted aryloxy group, a substituted or unsubstituted phosphoryloxy group;

[0100] R 7 To R 10Each independently includes a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryl group, a substituted or unsubstituted aryloxy group, and a substituted or unsubstituted phosphoryloxy group.

[0101] Phosphite groups contain phosphorus atoms, which can further enhance the flame retardant effect.

[0102] In some embodiments, R 4 and R 5 Each independently includes a phosphite group, a substituted or unsubstituted C1 to C6 alkyl group, a substituted or unsubstituted C1 to C6 alkoxy group, a substituted or unsubstituted C1 to C6 aryl group, a substituted or unsubstituted C1 to C6 aryloxy group, and a substituted or unsubstituted phosphoryloxy group.

[0103] In some embodiments, R 7 To R 10 Each independently includes a substituted or unsubstituted C1 to C6 alkyl group, a substituted or unsubstituted C1 to C6 alkoxy group, a substituted or unsubstituted C1 to C6 aryl group, a substituted or unsubstituted C1 to C6 aryloxy group, and a substituted or unsubstituted phosphoryloxy group.

[0104] When the above groups are substituted, the substituted groups include at least one of halogen atoms, sulfur atoms, and mercapto groups; halogen atoms can be selected. Halogen atoms such as fluorine atoms can reduce the hydrogen content in the system and further reduce the flammability of the electrolyte; and because fluorine atoms have a strong electron-withdrawing effect, they help to form an excellent SEI film at the interface of the negative electrode plate, which can improve the compatibility between the electrolyte and the negative electrode plate, so that the cycle performance of the lithium metal battery is further improved.

[0105] In some embodiments, the compound represented by Formula B includes at least one of the compounds represented by Formula B-1 to the compounds represented by Formula B-6.

[0106]

[0107]

[0108] In some embodiments, the phosphate compound includes three phosphate groups, and the three phosphate groups are connected by a silicon-containing group. As the content of the phosphate groups increases, the flame retardant property of the electrolyte is improved.

[0109] In some embodiments, the phosphate compound includes a compound represented by Formula C,

[0110]

[0111] In formula C, R 6including phosphite, substituted or unsubstituted alkyl, substituted or unsubstituted alkoxy, substituted or unsubstituted aryl, substituted or unsubstituted aryloxy, substituted or unsubstituted phosphoryloxy;

[0112] R 11 To R 16 Each independently includes a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryl group, a substituted or unsubstituted aryloxy group, and a substituted or unsubstituted phosphoryloxy group.

[0113] Phosphite groups contain phosphorus atoms, which can further enhance the flame retardant effect.

[0114] In some embodiments, R 6 Including phosphite, substituted or unsubstituted C1 to C6 alkyl, substituted or unsubstituted C1 to C6 alkoxy, substituted or unsubstituted C1 to C6 aryl, substituted or unsubstituted C1 to C6 aryloxy, substituted or unsubstituted phosphoryloxy.

[0115] In some embodiments, R 11 To R 16 Each independently includes a substituted or unsubstituted C1 to C6 alkyl group, a substituted or unsubstituted C1 to C6 alkoxy group, a substituted or unsubstituted C1 to C6 aryl group, a substituted or unsubstituted C1 to C6 aryloxy group, and a substituted or unsubstituted phosphoryloxy group.

[0116] When the above groups are substituted, the substituted groups include at least one of halogen atoms, sulfur atoms, and mercapto groups; halogen atoms can be selected. Halogen atoms such as fluorine atoms can reduce the hydrogen content in the system and further reduce the flammability of the electrolyte; and because fluorine atoms have a strong electron-withdrawing effect, they help to form an excellent SEI film at the interface of the negative electrode plate, which can improve the compatibility between the electrolyte and the negative electrode plate, so that the cycle performance of the lithium metal battery is further improved.

[0117] In some embodiments, the compound represented by Formula C includes at least one of the compounds represented by Formula C-1 to the compounds represented by Formula C-3.

[0118]

[0119] The above-mentioned phosphate compounds can be obtained commercially or synthesized according to conventional methods. The preparation of the compound represented by formula A-IIIa is used as an example for illustration.

[0120] Hexamethyldisiloxane and phosphoric acid are added to the reaction kettle, and a dehydration reaction is carried out under the conditions of heating, stirring and reflux condensation. The conditions of the dehydration reaction are: temperature 100°C, time 5 hours, pressure 1.0 MPa; then 1-trimethylsilylpyrrolidine is added for distillation reaction, and the generated amine is distilled off during the reaction. The reaction liquid is finely filtered and vacuum distilled to obtain the compound represented by formula A-IIIa. The distillation conditions are temperature 200°C, time 10 hours, and pressure 1.0 MPa. The molar ratio of hexamethyldisiloxane, phosphoric acid and 1-trimethylsilylpyrrolidine is 3:1:3.

[0121] In some embodiments, based on the total volume of the electrolyte, the volume content of the phosphate compound is less than 100%, and the volume content of the phosphate compound is ≥9%; optionally, the volume content of the phosphate compound is 20% to 60%. The volume content of the phosphate compound within the above range can improve the flame retardant properties of the system, and the silicon-containing group and the phosphate group can work together to improve the toughness of the SEI film and improve the cycle performance and reliability of the lithium metal battery.

[0122] For example, based on the total volume of the electrolyte, the volume content of the phosphate ester compound can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, 101%, 102%, 103%, 104%, 105%, 106%, 107%, 108%, 109%, 110%, 111%, 112%, 113%, 114%, 115%, 116%, 117%, 118%, %, 45%, 50%, 55%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90% or a range consisting of any two of the above values.

[0123] In some embodiments, the electrolyte further comprises a nitrogen-containing ionic liquid. The nitrogen-containing ionic liquid can enhance the flame retardancy of the electrolyte.

[0124] In some embodiments, the nitrogen-containing ionic liquid includes cations and anions, the cations include at least one of amine cations, imidazolium cations, piperidinium cations, and pyridinium cations, and the anions include at least one of trifluoromethylsulfonyl imide anions, bisfluorosulfonyl imide anions, and difluorooxalate borate anions. Optionally, the anions include at least one of difluorooxalate borate anions. The above-mentioned nitrogen-containing ionic liquid can provide a large amount of anions to form an anion-derived SEI film, further improving the performance of the SEI film, thereby further improving the cycle performance.

[0125] In some embodiments, based on the total volume of the electrolyte, the volume content of the nitrogen-containing ionic liquid is ≤91%; optionally, the volume content of the nitrogen-containing ionic liquid is 40% to 80%. When the volume content of the nitrogen-containing ionic liquid is within the above range, the flame retardancy of the electrolyte can be further improved.

[0126] Illustratively, the volume content of the nitrogen-containing ionic liquid can be 40%, 45%, 50%, 55%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, or a range consisting of any two of the above values.

[0127] In some embodiments, the ratio of the volume content of the phosphate compound to the volume content of the nitrogen-containing ionic liquid is 1:(0.1 to 9); optionally 1:(1 to 3). When the volume content ratio of the phosphate compound to the nitrogen-containing ionic liquid is within the above range, the flame retardant performance of the system can be further improved, the toughness of the SEI film can be improved, and the cycle performance and reliability of the lithium metal battery can be improved.

[0128] Illustratively, the ratio of the volume content of the phosphate compound to the volume content of the nitrogen-containing ionic liquid can be 1:0.1, 1:0.5, 1:1, 1:1.01, 1:1.05, 1:1.1, 1:1.2, 1:1.5, 1:1.8, 1:2, 1:2.2, 1:2.5, 1:2.8, 1:3, 1:3.2, 1:3.5, 1:3.8, 1:4, 1:4.2, 1:4.5, 1:4.8, 1:5, 1:5.2, 1:5.5, 1:5.8, 1:6, 1:6.2, 1:6.5, 1:6.8, 1:7, 1:7.2, 1:7.5, 1:7.8, 1:8, 1:8.2, 1:8.5, 1:8.8, 1:9 or a range consisting of any two of the above values.

[0129] In some embodiments, the electrolyte further includes a lithium salt, and the lithium salt includes at least one of lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, and lithium difluorooxalate borate. The lithium salt is used in combination with the above-mentioned organic solvent to form a SEI film containing an inorganic component such as lithium fluoride on the negative electrode sheet, which can further improve the structural stability of the SEI film, thereby improving the cycle performance of the lithium metal battery.

[0130] In some embodiments, the molar concentration of the lithium salt is 0.1 mol / L to 4 mol / L; optionally 1.8 mol / L to 2.2 mol / L. The above concentration of lithium salt is conducive to decomposing on the surface of the negative electrode to form lithium fluoride, increasing the content of lithium fluoride in the SEI film, further improving the structural stability of the SEI film, and thus further improving the cycle performance of the lithium metal battery. In addition, the above organic solvent has excellent lithium salt solubility, which is conducive to the dissociation of ions in the lithium salt and the increase of the migration rate of lithium ions.

[0131] Illustratively, the molar concentration of the lithium salt can be 0.1 mol / L, 0.2 mol / L, 0.5 mol / L, 0.8 mol / L, 1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.5 mol / L, 1.8 mol / L, 2 mol / L, 2.2 mol / L, 2.5 mol / L, 2.8 mol / L, 3 mol / L, 3.2 mol / L, 3.5 mol / L, 3.8 mol / L, 4 mol / L, or a range consisting of any two of the above values.

[0132] The qualitative and quantitative determination of each substance or element in this application can be carried out using appropriate equipment and methods known to those skilled in the art. The relevant detection methods can refer to domestic and foreign detection standards, domestic and foreign enterprise standards, etc., and those skilled in the art can also adaptively change certain detection steps / instrument parameters, etc. from the perspective of detection accuracy to obtain more accurate detection results. One detection method can be used for qualitative or quantitative determination, or several detection methods can be used in combination for qualitative or quantitative determination.

[0133] The types and contents of the inorganic components / lithium salt concentrations in the electrolyte are well known in the art and can be detected by equipment and methods well known in the art. For example, the inorganic components / lithium salt concentrations in the electrolyte can be qualitatively or quantitatively analyzed by ion chromatography analysis methods with reference to the standard JY / T020-1996 "General Rules for Ion Chromatography Analysis Methods". In the embodiments of the present application, a newly prepared electrolyte can be taken as a sample, or a battery that has been fully discharged (discharged to the lower limit cut-off voltage so that the battery is charged to about 0% SOC) can be reversely disassembled, and the free electrolyte obtained from the battery is used as a sample, and the ion chromatography analysis method is used for detection.

[0134] The type and content of organic components in the electrolyte are well known in the art and can be detected by equipment and methods well known in the art. For example, reference can be made to GB / T9722-2006 "General Rules for Gas Chromatography of Chemical Reagents" to perform qualitative and quantitative analysis of organic components in the electrolyte by gas chromatography. In the embodiments of the present application, a newly prepared electrolyte can be taken as a sample, or a battery that has been fully discharged (discharged to the lower limit cut-off voltage so that the battery's charged state is about 0% SOC) can be reversely disassembled, and the free electrolyte obtained from the battery can be used as a sample, and the ion chromatography analysis method can be used for detection.

[0135] Lithium Metal Batteries

[0136] In a second aspect, an embodiment of the present application proposes a lithium metal battery.

[0137] [Negative electrode]

[0138] In some embodiments, the lithium metal battery includes a negative electrode sheet.

[0139] The negative electrode plate and the above-mentioned electrolyte are combined, and the phosphate compounds in the electrolyte can form a SEI film containing silicon polymer on the surface of the negative electrode plate, thereby improving the toughness of the SEI film, reducing the risk of SEI film rupture, significantly improving the uniformity of lithium metal deposition, improving the interface performance of the negative electrode plate, and improving the cycle performance of the lithium metal battery.

[0140] In some embodiments, the negative electrode plate may include a negative electrode current collector. During the charging process of the lithium metal battery, lithium ions can be deposited on the surface of the negative electrode current collector to form a lithium metal layer; during the discharge process of the lithium metal battery, the lithium metal layer loses electrons to form lithium ions, which migrate to the positive electrode active material.

[0141] The negative electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, a copper foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include at least one of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. As an example, the polymer material base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS) and polyethylene (PE).

[0142] The negative electrode plate does not exclude additional functional layers. For example, in some embodiments, the negative electrode plate of the embodiment of the present application further includes a conductive layer (for example, composed of a conductive agent and a binder) disposed on the surface of the negative electrode current collector. In other embodiments, the negative electrode plate of the embodiment of the present application further includes a protective layer covering the surface of the negative electrode current collector.

[0143] Optionally, the negative electrode plate may further include a conductive layer disposed on at least one side of the negative electrode current collector, the conductive layer including a negative electrode conductive agent. As an example, the negative electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0144] Further optionally, the conductive layer may further include a negative electrode binder. As an example, the negative electrode binder may include at least one of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, aqueous acrylic resin (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0145] In other embodiments, the negative electrode sheet may include a negative electrode current collector and a negative electrode film layer disposed on at least one side of the negative electrode current collector. For example, the negative electrode current collector has two surfaces opposite to each other in the thickness direction thereof, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector. The negative electrode film layer may include lithium metal or a lithium metal alloy, the lithium metal alloy including lithium metal and a non-lithium single substance, and the non-lithium single substance including at least one of tin (Sn), zinc (Zn), aluminum (Al), magnesium (Mg), silver (Ag), gold (Au), gallium (Ga), indium (In), foil (Pt), boron (B), carbon (C) and silicon (Si).

[0146] The material of the negative electrode current collector is as described above and will not be repeated here.

[0147] The negative electrode plate does not exclude additional functional layers. For example, in some embodiments, the negative electrode plate of the embodiment of the present application further includes a conductive layer (for example, composed of a conductive agent and a binder) disposed on the surface of the negative electrode current collector. In other embodiments, the negative electrode plate of the embodiment of the present application further includes a protective layer covering the surface of the negative electrode current collector.

[0148] Optionally, the negative electrode plate may further include a conductive layer, the conductive layer is disposed between the negative electrode current collector and the lithium metal layer, the conductive layer includes a negative electrode conductive agent, the material of the negative electrode conductive agent is as described above, and will not be repeated here. Further optionally, the conductive layer may further include a negative electrode binder, the material of the negative electrode binder is as described above, and will not be repeated here.

[0149] [Positive electrode]

[0150] In some embodiments, the lithium metal battery may further include a positive electrode sheet.

[0151] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector and including a positive electrode active material. For example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0152] The positive electrode active material may be a positive electrode active material for a lithium metal battery known in the art. As an example, the positive electrode active material may include at least one of the following materials: a layered positive electrode active material (e.g., ternary, lithium nickelate / sodium, lithium cobaltate / sodium, lithium manganate / sodium, lithium-rich / sodium layered and rock salt phase layered materials), an olivine-type phosphate active material, a spinel structured positive electrode active material (e.g., spinel lithium manganate, spinel nickel lithium manganate, lithium-rich spinel lithium manganate, and lithium nickel lithium manganate, etc.).

[0153] For example, the layered structure positive electrode active material composition formula is Li a Ni b Co c M d O e A f Compounds and modified compounds thereof, 0.8≤a≤1.2, 0.5≤b<1, 0<c<1, 0<d<1, 1≤e≤2, 0≤f≤1, M includes at least one of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and A includes at least one of N, F, S and Cl.

[0154] Illustratively, a can be 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1, 1.1, 1.2, or a range consisting of any two of the above values.

[0155] Illustratively, b can be 0.50, 0.52, 0.55, 0.58, 0.60, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, 0.70, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, or a range consisting of any two of the above values.

[0156] For example, c can be 0.01, 0.02, 0.05, 0.08, 0.10, 0.12, 0.15, 0.18, 0.20, 0.22, 0.25, 0.28, 0.30, 0.32, 0.35, 0.38, 0.40, 0.42, 0.45, 0.48, 0.50, 0.52, 0.55, 0.58, 0.60, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68 8, 0.69, 0.70, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99 or a range consisting of any two of the above values.

[0157] For example, d can be 0.01, 0.02, 0.05, 0.08, 0.10, 0.12, 0.15, 0.18, 0.20, 0.22, 0.25, 0.28, 0.30, 0.32, 0.35, 0.38, 0.40, 0.42, 0.45, 0.48, 0.50, 0.52, 0.55, 0.58, 0.60, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68 8, 0.69, 0.70, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99 or a range consisting of any two of the above values.

[0158] Illustratively, e may be 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, or a range consisting of any two of the above values.

[0159] For example, f can be 0, 0.01, 0.02, 0.05, 0.08, 0.10, 0.12, 0.15, 0.18, 0.20, 0.22, 0.25, 0.28, 0.30, 0.32, 0.35, 0.38, 0.40, 0.42, 0.45, 0.48, 0.50, 0.52, 0.55, 0.58, 0.60, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 8, 0.69, 0.70, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1 or a range consisting of any two of the above values.

[0160] Optionally, 0<a<1; further optionally, 0.8≤a<1. a can be 0.01, 0.02, 0.05, 0.08, 0.10, 0.12, 0.15, 0.18, 0.20, 0.22, 0.25, 0.28, 0.30, 0.32, 0.35, 0.38, 0.40, 0.42, 0.45, 0.48, 0.50, 0.52, 0.55, 0.58, 0.60, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0. .69, 0.70, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1 or a range consisting of any two of the above values.

[0161] Optionally, 0<b<1. b can be 0.01, 0.02, 0.05, 0.08, 0.10, 0.12, 0.15, 0.18, 0.20, 0.22, 0.25, 0.28, 0.30, 0.32, 0.35, 0.38, 0.40, 0.42, 0.45, 0.48, 0.50, 0.52, 0.55, 0.58, 0.60, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0. .69, 0.70, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1 or a range consisting of any two of the above values.

[0162] Optionally, 0<c<1. c can be 0.01, 0.02, 0.05, 0.08, 0.10, 0.12, 0.15, 0.18, 0.20, 0.22, 0.25, 0.28, 0.30, 0.32, 0.35, 0.38, 0.40, 0.42, 0.45, 0.48, 0.50, 0.52, 0.55, 0.58, 0.60, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0. .69, 0.70, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1 or a range consisting of any two of the above values.

[0163] Optionally, 0.1≤a+b+c<1. a+b+c can be 0.10, 0.12, 0.15, 0.18, 0.20, 0.22, 0.25, 0.28, 0.30, 0.32, 0.35, 0.38, 0.40, 0.42, 0.45, 0.48, 0.50, 0.52, 0.55, 0.58, 0.60, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, 0.7 0, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99 or a range consisting of any two of the above values.

[0164] z can be 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5 or a range consisting of any two of the above values.

[0165] Specifically, the layered structure positive electrode active material may include lithium cobalt oxide LCO, lithium nickel oxide LNO, lithium manganese oxide LMO, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 (NCM333), LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811) and LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O 2 、LiNi 0.85 Co 0.15 Al 0.05 O 2 、LiNi 0.80 Co 0.15 Al 0.05 O 2 One or more of .

[0166] Exemplarily, the composition formula of the olivine phosphate active material is: Li x A yMe a M b P 1-c X c Y z , wherein 0≤x≤1.3, 0≤y≤1.3, and 0.9≤x+y≤1.3; 0.9≤a≤1.5, 0≤b≤0.5, and 0.9≤a+b≤1.5; 0≤c≤0.5; 3≤z≤5; A is selected from one or more of Na, K, and Mg; Me is selected from one or more of Mn, Fe, Co, and Ni; M is selected from one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; X is selected from one or more of S, Si, Cl, B, C, and N; and Y is selected from one or more of O and F. Specifically, the olivine-type phosphate active materials include LiFePO 4 、LiMnPO 4 、LiNiPO 4 , and LiCoPO 4 One or more of .

[0167] For example, the composition formula of the positive electrode active material of the spinel structure is: Li x A y Mn a M 2-a Y z , wherein 0≤x≤2, 0≤y≤1, and 0.9≤x+y≤2; 0.5≤a≤2; 3≤z≤5; A is selected from one or more of Na, K, and Mg; M is selected from one or more of Ni, Co, B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; and Y is selected from one or more of O and F. Specifically, the positive electrode active materials of the spinel structure include LiMn 2 O 4 、LiNi 0.5 Mn 1.5 O 4 、LiCr 0.3 Mn 1.7 O 4 , Li 1.1 Al 0.1 Mn 1.9 O 4 , Li 2 Mn 2 O 4 and Li 1.5 Mn 2 O4 One or more of .

[0168] In the embodiment of the present application, each of the above-mentioned positive electrode active materials may also be a modified compound, and the modified compound may be a doping modification and / or surface coating modification of the positive electrode active material. For example, the doping modification may be performed by doping with transition metal elements, and for example, the coating modification may be performed by coating a carbon layer on the surface of the material.

[0169] The charging and discharging process of lithium metal batteries is accompanied by the deintercalation and consumption of active ions such as Li. The molar content of Li in lithium metal batteries is different when they are discharged to different states. In the examples of positive electrode active materials in the embodiments of the present application, the molar content of Li is the initial state of the material, that is, the state before feeding. The positive electrode active material is used in the battery system, and the molar content of Li may change after charge and discharge cycles.

[0170] In the list of positive electrode active materials in the embodiments of the present application, the molar content of oxygen O is only a theoretical value. The release of oxygen from the lattice will cause the molar content of oxygen O to change. In reality, the molar content of oxygen O will fluctuate.

[0171] In some embodiments, the positive electrode film layer may further include a positive electrode conductive agent. The present application embodiment has no particular restrictions on the type of the positive electrode conductive agent. As an example, the positive electrode conductive agent includes at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers. In some embodiments, based on the total mass of the positive electrode film layer, the mass percentage of the positive electrode conductive agent is ≤5%.

[0172] In some embodiments, the positive electrode film layer may also optionally include a positive electrode binder. The present application embodiment has no particular restrictions on the type of positive electrode binder. As an example, the positive electrode binder may include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and at least one of fluorine-containing acrylic resins. In some embodiments, based on the total mass of the positive electrode film layer, the mass percentage of the positive electrode binder is ≤5%.

[0173] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil may be used. The composite current collector may include a polymer material base and a metal material layer formed on at least one surface of the polymer material base. As an example, the metal material of the metal material layer may include at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. As an example, the polymer material base may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS) and polyethylene (PE).

[0174] The positive electrode film layer is usually formed by coating the positive electrode slurry on the positive electrode current collector, drying and cold pressing. The positive electrode slurry is usually formed by dispersing the positive electrode active material, optional conductive agent, optional binder and any other components in a solvent and stirring them uniformly. The solvent can be N-methylpyrrolidone (NMP), but is not limited thereto.

[0175] [Isolation film]

[0176] In some embodiments, the lithium metal battery may further include a separator.

[0177] The embodiments of the present application have no particular restrictions on the type of isolation membrane, and any known porous isolation membrane with good chemical stability and mechanical stability can be selected.

[0178] In some embodiments, the material of the isolation membrane may include at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane may be a single-layer film or a multi-layer composite film, without particular limitation. When the isolation membrane is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0179] In some embodiments, the positive electrode sheet, the separator, and the negative electrode sheet may be formed into an electrode assembly by a winding process and / or a lamination process.

[0180] In some embodiments, the lithium metal battery may include an outer packaging, which may be used to encapsulate the electrode assembly and the electrolyte.

[0181] In some embodiments, the outer packaging of the lithium metal battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the lithium metal battery can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT) and polybutylene succinate (PBS).

[0182] The embodiment of the present application has no particular limitation on the shape of the lithium metal battery, which may be cylindrical, square or any other shape. Figure 1 A lithium metal battery 5 having a square structure is used as an example.

[0183] In some embodiments, Figure 2 As shown, the outer package may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 is used to cover the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation film can form an electrode assembly 52 through a winding process and / or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the lithium metal battery 5 can be one or more, which can be adjusted according to demand.

[0184] The preparation method of the lithium metal battery of the embodiment of the present application is well known. In some embodiments, the positive electrode sheet, the separator, the negative electrode sheet and the electrolyte can be assembled to form a lithium metal battery. As an example, the positive electrode sheet, the separator, and the negative electrode sheet can be formed into an electrode assembly through a winding process and / or a lamination process, and the electrode assembly is placed in an outer package, and the electrolyte is injected after drying, and the lithium metal battery is obtained through vacuum packaging, standing, forming, shaping and other processes.

[0185] In some embodiments of the present application, the lithium metal batteries according to the present application can be assembled into a battery module. The number of lithium metal batteries contained in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0186] Figure 3 FIG. 4 is a schematic diagram of a battery module 4 as an example. Figure 3 As shown, in the battery module 4, the plurality of lithium metal batteries 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of lithium metal batteries 5 may be fixed by fasteners.

[0187] Optionally, the battery module 4 may further include a housing having a housing space, and the plurality of lithium metal batteries 5 are accommodated in the housing space.

[0188] In some embodiments, the battery modules described above may also be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0189] Figure 4 and Figure 5 FIG. 1 is a schematic diagram of a battery pack 1 as an example. Figure 4 and Figure 5As shown, the battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3, wherein the upper box body 2 is used to cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 may be arranged in the battery box in any manner.

[0190] Electrical devices

[0191] The third aspect of the embodiments of the present application provides an electrical device, which includes at least one of the lithium metal battery, battery module or battery pack of the embodiments of the present application. The lithium metal battery, battery module or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device can be, but is not limited to, a mobile device (such as a mobile phone, a laptop computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc.

[0192] Electrical devices can select lithium metal batteries, battery modules or battery packs according to their usage requirements.

[0193] Figure 6 Schematic diagram of an exemplary electric device 6. The electric device 6 is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the requirements of the electric device 6 for high power and high energy density, a battery pack or a battery module may be used.

[0194] As another example, the electric device may be a mobile phone, a tablet computer, a laptop computer, etc. The electric device is usually required to be light and thin, and a lithium metal battery may be used as a power source.

[0195] Example

[0196] The following examples more specifically describe the contents disclosed in the embodiments of the present application, and these examples are only for illustrative purposes, because it is obvious to those skilled in the art that various modifications and changes are made within the scope of the disclosure of the embodiments of the present application. Unless otherwise stated, all parts, percentages and ratios reported in the following examples are based on mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further processing, and the instruments used in the examples are commercially available.

[0197] Example 1

[0198] 1. Preparation of positive electrode sheet

[0199] The positive electrode sheet includes a positive electrode collector and a positive electrode film layer. The positive electrode collector is an aluminum foil with a thickness of 10 μm. The positive electrode film layer includes a film layer formed by uniformly coating a positive electrode slurry (the solvent is N-methylpyrrolidone NMP) on the surface of the positive electrode collector aluminum foil, drying, and cold pressing. The positive electrode film layer includes a positive electrode active material, a conductive agent acetylene black, and a binder polyvinylidene fluoride (PVDF) in a weight ratio of 98:1:1.

[0200] The positive electrode active material includes a composition formula of LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811) compound.

[0201] 2. Preparation of negative electrode sheet

[0202] The negative electrode plate includes a negative electrode current collector and a lithium metal foil. The negative electrode current collector is a copper foil with a thickness of 13 μm. A lithium metal foil with a thickness of 50 μm is pressed on both sides of the copper foil by rolling.

[0203] 3. Isolation film

[0204] The isolation film is a polyethylene film layer.

[0205] 4. Preparation of electrolyte

[0206] The electrolyte includes an organic solvent and a lithium salt.

[0207] 5. Preparation of lithium metal batteries

[0208] The positive electrode sheet, the isolation film, and the lithium metal negative electrode are stacked in order, so that the isolation film is located between the positive electrode sheet and the lithium metal negative electrode to play an isolating role, thereby obtaining an electrode assembly; the electrode assembly is placed in an outer packaging shell, and after drying, the electrolyte is injected, and after vacuum packaging, standing, forming, shaping and other processes, a stacked lithium metal battery is obtained.

[0209] Example 2 to Example 9

[0210] A lithium metal battery was prepared by a method similar to that of Example 1. The difference from Example 1 is that the electrolyte components of Examples 2 to 9 are different from those of Example 1, and Examples 2 to 9 particularly adjust the volume ratio of the phosphate compound and the nitrogen-containing ionic liquid.

[0211] Comparative Example 1 to Comparative Example 3

[0212] A lithium metal battery was prepared by a method similar to that of Example 1. The difference from Example 1 is that the electrolyte components of Comparative Examples 1 to 3 are different from those of Example 1.

[0213] Performance Testing

[0214] 1. Room temperature cycle test of lithium metal batteries

[0215] The ambient temperature of the lithium metal battery room temperature cycle was set at 25°C, and the charge and discharge cycle was performed at a rate of 0.5C (i.e., 70 mA). The cut-off voltages for charge and discharge were set at 4.3V and 2.8V, respectively.

[0216] When the discharge capacity decays to 80% of the initial discharge capacity, the battery life is considered to be over.

[0217] 2. High cycle test of lithium metal batteries

[0218] The ambient temperature of the lithium metal battery high temperature cycle was set at 60°C, and the charge and discharge cycle was performed at a rate of 0.5C (i.e., 70 mA). The cut-off voltages for charge and discharge were set at 4.3V and 2.8V, respectively.

[0219] When the discharge capacity decays to 80% of the initial discharge capacity, the battery life is considered to be over.

[0220] Test Results

[0221] The test results are shown in Table 1.

[0222] Table 1

[0223]

[0224] In Table 1,

[0225] “-” means that such substance is not added or the parameter here is meaningless.

[0226] “2M” means that the amount of substance of the lithium salt is 2 mol / L.

[0227] As can be seen from Table 1, the organic solvent of the electrolyte in Comparative Example 1 includes a phosphate ester solvent (trimethyl phosphate), but the phosphate ester solvent does not contain silicon atoms. Since the organic solvent can react with lithium metal, it is difficult to form a stable SEI film on the surface of the negative electrode, resulting in poor battery cycle performance.

[0228] The organic solvent of the electrolyte in Comparative Example 2 includes a siloxane solvent (dimethoxydimethylsilane). This type of solvent has high stability at room temperature, which is beneficial to improving the cycle performance of the battery. However, it has poor stability at high temperatures and the battery cycle performance decays rapidly.

[0229] Compared with Comparative Examples 1 and 2, in Comparative Example 3, a phosphate ester solvent and a siloxane solvent are mixed as the organic solvent of the electrolyte. The phosphate ester solvent can improve the thermal stability and has a certain improvement on the high-temperature cycle performance of the battery, but the improvement effect still cannot meet the use requirements; and the organic solvent has limited effect on improving the low-temperature cycle performance of the battery.

[0230] Compared with Comparative Example 3, Example 1 uses a phosphate compound containing a silicon-containing group as an organic solvent. The organic solvent can form a silicon-containing polymer on the surface of the negative electrode plate, which can improve the toughness of the SEI film. The SEI film is not easy to break and can induce uniform deposition of lithium metal. The SEI film has good stability, such as good reduction resistance, and can provide good protection for the negative electrode plate, thereby significantly improving the low-temperature and high-temperature cycle performance of the lithium metal battery.

[0231] Compared with Example 1-1, Example 1 further adds nitrogen-containing ionic liquid Y (1-propyl-1-methylpyrrolidine bis(fluorosulfonyl)imide), which can cooperate with the organic solvent to exert a flame retardant effect and is conducive to further improving the cycle performance of the lithium metal battery. By adjusting the ratio of the phosphate compound and the nitrogen-containing ionic liquid Y or the type of the nitrogen-containing ionic liquid Y, the cycle performance of the lithium metal battery can be further improved.

[0232] Example 10 to Example 18

[0233] A lithium metal battery was prepared by a method similar to that of Example 1. The difference from Example 1 is that the electrolyte components of Examples 10 to 18 are different from those of Example 1, and the materials of the organic solvents in the electrolytes are different.

[0234] The test results are shown in Table 2.

[0235] Table 2

[0236]

[0237] It can be seen from Table 2 that the low-temperature and high-temperature cycle performance of lithium metal batteries can be effectively regulated by regulating the types of phosphate compounds including silicon groups.

[0238] Example 19 to Example 21

[0239] A lithium metal battery was prepared by a method similar to that of Example 1. The difference from Example 1 was that the electrolyte components of Examples 19 to 21 were different from those of Example 1, and at least one of the material and concentration of the lithium salt in the electrolyte was adjusted.

[0240] The test results are shown in Table 3.

[0241] Table 3

[0242]

[0243] It can be seen from Table 3 that the low-temperature and high-temperature cycle performance of lithium metal batteries can be effectively regulated by regulating at least one of the type and content of lithium salt.

[0244] Although illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments should not be construed as limitations on the present application, and that changes, substitutions and modifications may be made to the embodiments without departing from the spirit, principles and scope of the present application.

Claims

1. An electrolyte for a lithium metal battery, characterized in that, it includes an organic solvent, the organic solvent includes a phosphate compound, the phosphate compound includes a silicon-containing group and at least one phosphate group, and at least one oxygen atom of the phosphorus-oxygen single bond in the phosphate group is covalently bonded to the silicon atom of the silicon-containing group.

2. The electrolyte for a lithium metal battery according to claim 1, characterized in that, at least one of the silicon-containing group and the phosphate group contains an ether bond.

3. The electrolyte for a lithium metal battery according to claim 1 or 2, characterized in that, the phosphate compound includes a compound represented by formula A, in formula A, R 1 To R 3 Each independently includes a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryl group, a substituted or unsubstituted aryloxy group, a substituted or unsubstituted phosphoxy group, a substituted or unsubstituted silane group, a substituted or unsubstituted siloxy group, a substituted or unsubstituted alkylsilyl group, a substituted or unsubstituted alkoxysilyl group, or a substituted or unsubstituted alkoxyalkylsilyl group; Among them, R 1 To R 3 At least one of the above comprises a substituted or unsubstituted silane, a substituted or unsubstituted siloxy group, a substituted or unsubstituted alkylsilyl group, a substituted or unsubstituted alkoxysilyl group, or a substituted or unsubstituted alkoxyalkylsilyl group.

4. The electrolyte for a lithium metal battery according to claim 3, characterized in that, the compound represented by formula A includes at least one of the compounds represented by formula A-Ia to formula A-IVb.

5. The electrolyte for a lithium metal battery according to any one of claims 1 to 4, characterized in that, the phosphate compound includes a compound represented by formula B, in formula B, R 4 and R 5 Each independently includes a phosphite group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryl group, a substituted or unsubstituted aryloxy group, a substituted or unsubstituted phosphoryloxy group; R 7 To R 10 Each independently includes a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryl group, a substituted or unsubstituted aryloxy group, and a substituted or unsubstituted phosphoryloxy group.

6. The electrolyte for a lithium metal battery according to claim 5, characterized in that, the compound represented by formula B includes at least one of the compounds represented by formula B-1 to formula B-6.

7. The electrolyte for a lithium metal battery according to any one of claims 1 to 6, characterized in that, the phosphate compound includes a compound represented by formula C, In formula C, R 6 including phosphite, substituted or unsubstituted alkyl, substituted or unsubstituted alkoxy, substituted or unsubstituted aryl, substituted or unsubstituted aryloxy, substituted or unsubstituted phosphoryloxy; R 11 To R 16 Each independently includes a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryl group, a substituted or unsubstituted aryloxy group, and a substituted or unsubstituted phosphoryloxy group.

8. The electrolyte for a lithium metal battery according to claim 7, characterized in that, the compound represented by formula C includes at least one of the compounds represented by formula C-1 to formula C-3.

9. The electrolyte for a lithium metal battery according to any one of claims 1 to 8, characterized in that, based on the total volume of the electrolyte, the volume content of the phosphate compound ≥ 9%; Optionally, the volume content of the phosphate compound is 20% to 60%.

10. The electrolyte for a lithium metal battery according to any one of claims 1 to 9, characterized in that, the organic solvent further includes a nitrogen-containing ionic liquid; Optionally, the nitrogen-containing ionic liquid includes a cation and an anion, the cation includes at least one of an amine cation, an imidazole cation, a piperidine cation, and a pyridine cation, and the anion includes at least one of a trifluoromethylsulfonylimide anion, a bisfluorosulfonylimide anion, and a difluorooxalate borate anion.

11. The electrolyte for a lithium metal battery according to claim 10, characterized in that, based on the total volume of the electrolyte, the ratio of the volume content of the phosphate compound to the volume content of the nitrogen-containing ionic liquid is 1:(0.1 to 9); optionally 1:(1 to 3).

12. The electrolyte for a lithium metal battery according to any one of claims 1 to 11, characterized in that, the electrolyte further includes a lithium salt, and the lithium salt includes at least one of lithium bis(trifluoromethylsulfonyl)imide, lithium bisfluorosulfonylimide, and lithium difluorooxalate borate; The molar concentration of the lithium salt is 0.1 mol / L to 4 mol / L; optionally 1.8 mol / L to 2.2 mol / L.

13. A lithium metal battery, It is characterized in that The invention comprises the electrolyte for lithium metal battery as claimed in any one of claims 1 to 12.

14. The lithium metal battery according to claim 13, It is characterized in that The lithium metal battery further comprises a positive electrode sheet, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer disposed on at least one side of the positive electrode current collector, wherein the positive electrode film layer comprises a positive electrode active material, wherein the positive electrode active material comprises a composition formula of Li a Ni b Co c M d O e A f Compounds and modified compounds thereof, 0.8≤a≤1.2, 0.5≤b<1, 0<c<1, 0<d<1, 1≤e≤2, 0≤f≤1, M includes at least one of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and A includes at least one of N, F, S and Cl.

15. The lithium metal battery according to claim 13 or 14, It is characterized in that The battery also includes a negative electrode plate, The negative electrode plate includes a negative electrode current collector; or The negative electrode plate includes a negative electrode current collector and a negative electrode film layer arranged on at least one side of the negative electrode current collector, the negative electrode film layer includes lithium metal or a lithium metal alloy, the lithium metal alloy includes lithium metal and a non-lithium single substance, and the non-lithium single substance includes at least one of tin, zinc, aluminum, magnesium, silver, gold, gallium, indium, foil, boron, carbon and silicon.

16. An electrical device, It is characterized in that Comprising a battery as claimed in any one of claims 13 to 15.

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