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

Abstract

The present application relates to an electrolyte for a lithium metal battery, a lithium metal battery and an electric device. The electrolyte for a lithium metal battery comprises an organic solvent, wherein the organic solvent comprises a phosphate compound that comprises a silicon-containing group and at least one phosphate group, an oxygen atom of at least one phosphorus-oxygen single bond in the phosphate group being connected to a silicon atom of the silicon-containing group via a covalent single bond.

Description

Lithium metal battery electrolyte, lithium metal battery and electrical device

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application No. 202311562654.9, filed on November 22, 2023, entitled “Electrolyte for lithium metal batteries, lithium metal batteries and electrical devices,” the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present application relates to an electrolyte for a lithium metal battery, a lithium metal battery and an electrical device. Background Art

[0004] Lithium metal batteries have high capacity and other characteristics, so they are 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 power tools, etc.

[0005] However, the low-temperature and high-temperature cycling performance of current lithium metal batteries is still poor.

[0006] Summary of the Invention

[0007] 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.

[0008] In a 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 the oxygen atom of at least one phosphorus-oxygen single bond in the phosphate group is covalently connected to the silicon atom of the silicon-containing group by a single bond.

[0009] Therefore, the phosphate group in the embodiment of the present application 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 the lithium metal battery. 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 polymerization reaction to form organic polymers, 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 can make the lithium metal deposited evenly and is not easy to form lithium dendrites. Moreover, the above-mentioned organic polymers in the SEI film have strong reduction resistance and are not easy to decompose. The SEI film can play a good protective role on the negative electrode sheet, reduce the risk of side reactions between lithium metal and electrolyte, and thus improve the low-temperature and high-temperature cycle performance of the lithium metal battery.

[0010] 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 formation reaction of the SEI film, further improving the stability of the SEI film, thereby enhancing the low-temperature and high-temperature cycling performance of the lithium metal battery.

[0011] In some embodiments, the phosphate compound includes a compound represented by formula A,

[0012] In formula A,

[0013] R1 to R3 each independently include 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 phosphino 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;

[0014] Wherein, at least one of R1 to R3 includes 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.

[0015] 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,

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

[0017] In formula B,

[0018] R4 and R5 each independently include 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, or a substituted or unsubstituted phosphoryloxy group;

[0019] R7 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 phosphorusoxy group.

[0020] 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.

[0021] Thus, the phosphate compound of the embodiment of the present application includes at least two phosphate groups, and the at least two phosphate groups are connected by a silicon-containing group. As the content of the phosphate groups increases, the flame retardant properties of the electrolyte are improved.

[0022] In some embodiments, the phosphate compound includes a compound represented by Formula C,

[0023] In formula C, R6 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, or a substituted or unsubstituted phosphoxy group;

[0024] 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 phosphorusoxy group.

[0025] Thus, the phosphate compound of the embodiment of the present application includes at least two phosphate groups, and the at least two phosphate groups are connected by a silicon-containing group. As the content of the phosphate groups increases, the flame retardant properties of the electrolyte are improved.

[0026] 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.

[0027] In some embodiments, the volume content of the phosphate ester compound is ≥ 9% based on the total volume of the electrolyte; alternatively, the volume content of the phosphate ester compound is 20% to 60%. A volume content of the phosphate ester compound within this range can enhance the flame retardancy of the system. The silicon-containing groups and phosphate ester groups work together to improve the toughness of the SEI film, enhancing the cycling performance and reliability of the lithium metal battery.

[0028] 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.

[0029] 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 difluorooxalatoborate anion.

[0030] 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). A ratio of the volume content of the phosphate compound to the nitrogen-containing ionic liquid within the above range can further enhance the flame retardancy of the system, improve the toughness of the SEI film, and enhance the cycling performance and reliability of the lithium metal battery.

[0031] In some embodiments, the electrolyte further includes a lithium salt, including 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, and optionally 1.8 mol / L to 2.2 mol / L. The lithium salt, when used in conjunction with the aforementioned organic solvent, can also form an organic electrolyte interface (SEI) film containing inorganic components, such as lithium fluoride, on the negative electrode sheet, further improving the structural stability of the SEI film and thereby improving the cycling performance of the lithium metal battery.

[0032] In a second aspect, an embodiment of the present application further proposes a lithium metal battery, which includes an electrolyte for a lithium metal battery as in any embodiment of the first aspect of the present application.

[0033] In some embodiments, the lithium metal battery further comprises a positive electrode sheet, the positive electrode sheet comprising 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 comprising a positive electrode active material, the positive electrode active material comprising a composition formula of Li a Ni b Co c M d O e A fCompounds 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.

[0034] In some embodiments, the battery further comprises a negative electrode sheet, and the negative electrode sheet comprises a negative current collector.

[0035] 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.

[0036] 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

[0037] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. 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 creative work.

[0038] FIG1 is a schematic diagram of an embodiment of a lithium metal battery of the present application.

[0039] FIG. 2 is an exploded schematic diagram of an embodiment of the lithium metal battery of FIG. 1 .

[0040] FIG3 is a schematic diagram of an embodiment of a battery module of the present application.

[0041] FIG4 is a schematic diagram of an embodiment of a battery pack of the present application.

[0042] FIG. 5 is an exploded schematic diagram of the embodiment of the battery pack shown in FIG. 4 .

[0043] FIG6 is a schematic diagram of an embodiment of an electric device including the lithium metal battery of the present application as a power source.

[0044] The drawings are not necessarily drawn to scale.

[0045] The reference numerals are as follows: 1. battery pack; 2. upper case; 3. lower case; 4. battery module; 5. lithium metal battery; 51. housing; 52. electrode assembly; 53. cover plate; 6. electrical device. DETAILED DESCRIPTION

[0046] Below, the embodiments of the lithium metal battery electrolyte, lithium metal battery, and electrical device of the present application are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be 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 understanding by those skilled in the art. In addition, the drawings and the following description 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.

[0047] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and 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 special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this 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 all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this 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.

[0048] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0049] 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.

[0050] 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 indicates 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 further include step (c), which indicates 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.

[0051] 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.

[0052] 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 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 are 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 and is released into the electrolyte, and migrates to the positive active material through the electrolyte.

[0053] 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. Lithium dendrites may pierce the isolation membrane and contact the positive electrode sheet, causing a short circuit, triggering thermal runaway, and deteriorating the reliability of the lithium metal battery.

[0054] In order to improve the reliability of lithium metal batteries, relevant technologies consider adding flame retardants to the electrolyte, such as phosphate compounds. 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, 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, which is not conducive to improving the low-temperature and high-temperature cycle performance of lithium metal batteries.

[0055] 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. The phosphate compound has good flame retardant properties, can improve the flame retardant effect of the electrolyte, and improve 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 connected 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; and the SEI film can form 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.

[0056] Next, the technical solution of this application is described in detail.

[0057] Electrolyte for lithium metal batteries

[0058] In a first aspect, an embodiment of the present application provides an electrolyte for a lithium metal battery.

[0059] The electrolyte for the 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 the oxygen atom of at least one phosphorus-oxygen single bond in the phosphate group is covalently connected to the silicon atom of the silicon-containing group via a single bond.

[0060] 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 silicon-containing groups and phosphate groups can improve the toughness of the SEI film and enhance the cycle performance and reliability of lithium metal batteries.

[0061] Although the mechanism is not clear, the mechanism of action of this application is speculated to be as follows:

[0062] 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.

[0063] 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 polymerization reaction to form organic polymers, 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 can make the lithium metal deposited evenly and is not easy to form lithium dendrites. Moreover, the above-mentioned organic polymers in the SEI film have strong reduction resistance and are not easy to decompose. The SEI film can play a good protective role on the negative electrode sheet, reduce the risk of side reactions between lithium metal and electrolyte, and thus improve the low-temperature and high-temperature cycle performance of the lithium metal battery.

[0064] 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 enhance the toughness of the SEI film and further enhance the low-temperature and high-temperature cycle performance of the lithium metal battery; it can also further enhance the solubility of lithium salts and enhance the kinetic performance of the battery.

[0065] 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 formation reaction of the SEI film, further improving the stability of the SEI film, thereby enhancing the low-temperature and high-temperature cycling performance of the lithium metal battery.

[0066] 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.

[0067] In some embodiments, the phosphate compound includes a compound represented by formula A,

[0068] In formula A,

[0069] R1 to R3 each independently include 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 phosphino 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;

[0070] Among them, at least one of R1 to R3 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.

[0071] In some embodiments, R1 to R3 each independently include 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.

[0072] When the above-mentioned groups are substituted, the substituents include at least one of halogen atoms, sulfur atoms, and thiol groups; halogen atoms are optional. Halogen atoms, such as fluorine atoms, can reduce the hydrogen content in the system, further reducing the flammability of the electrolyte. Furthermore, due to their strong electron-withdrawing effect, fluorine atoms help form a good SEI film at the interface of the negative electrode, improving the compatibility between the electrolyte and the negative electrode, thereby further enhancing the cycling performance of lithium metal batteries.

[0073] In some embodiments, one of R1 to R3 includes a silicon-containing group. The silicon-containing group has a small steric hindrance in the process of forming the SEI film, which is conducive to the formation of the SEI film.

[0074] 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,

[0075] In some embodiments, at least two of R1 to R3 include silicon-containing groups, specifically substituted or unsubstituted silane, substituted or unsubstituted siloxy, substituted or unsubstituted alkylsilyl, substituted or unsubstituted alkoxysilyl, or substituted or unsubstituted alkoxyalkylsilyl. The greater the number of silicon-containing groups in the phosphate ester compound, the stronger the toughness of the SEI film formed with them, which is more conducive to improving the structural stability of the SEI film and the protection of the negative electrode, thereby improving the cycling performance of the lithium metal battery.

[0076] In some embodiments, two of R1 to R3 include silicon-containing groups. As the silicon content increases, the number of silicon-oxygen bonds increases, the SEI film has better film-forming properties, and also helps to improve the coulombic efficiency of the battery.

[0077] 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,

[0078] In some embodiments, three of R1 to R3 include silicon-containing groups.

[0079] 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,

[0080] In some embodiments, the phosphate compound includes a fluorine atom.

[0081] 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,

[0082] In some embodiments, the phosphate compound includes at least two phosphate groups, and the at least two phosphate groups are connected by a silicon-containing group. As the content of the phosphate groups increases, the flame retardant properties of the electrolyte improve.

[0083] In some embodiments, the phosphate compound includes a compound represented by Formula B,

[0084] In formula B,

[0085] R4 and R5 each independently include 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, or a substituted or unsubstituted phosphoryloxy group;

[0086] R7 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 phosphorusoxy group.

[0087] Phosphite groups contain phosphorus atoms, which can further enhance the flame retardant effect.

[0088] In some embodiments, R4 and R5 each independently include 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, or a substituted or unsubstituted phosphinoyl group.

[0089] In some embodiments, R7 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.

[0090] When the above-mentioned groups are substituted, the substituents include at least one of halogen atoms, sulfur atoms, and thiol groups; halogen atoms are optional. Halogen atoms, such as fluorine atoms, can reduce the hydrogen content in the system, further reducing the flammability of the electrolyte. Furthermore, due to their strong electron-withdrawing effect, fluorine atoms help form a good SEI film at the interface of the negative electrode, improving the compatibility between the electrolyte and the negative electrode, thereby further enhancing the cycling performance of lithium metal batteries.

[0091] 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.

[0092] In some embodiments, the phosphate compound includes three phosphate groups connected by a silicon-containing group. As the content of the phosphate groups increases, the flame retardant properties of the electrolyte improve.

[0093] In some embodiments, the phosphate compound includes a compound represented by Formula C,

[0094] In formula C, R6 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, or a substituted or unsubstituted phosphoxy group;

[0095] 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 phosphorusoxy group.

[0096] Phosphite groups contain phosphorus atoms, which can further enhance the flame retardant effect.

[0097] In some embodiments, R6 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, or a substituted or unsubstituted phosphinoyl group.

[0098] 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.

[0099] When the above-mentioned groups are substituted, the substituents include at least one of halogen atoms, sulfur atoms, and thiol groups; halogen atoms are optional. Halogen atoms, such as fluorine atoms, can reduce the hydrogen content in the system, further reducing the flammability of the electrolyte. Furthermore, due to their strong electron-withdrawing effect, fluorine atoms help form a good SEI film at the interface of the negative electrode, improving the compatibility between the electrolyte and the negative electrode, thereby further enhancing the cycling performance of lithium metal batteries.

[0100] 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.

[0101] The above-mentioned phosphate compounds can be purchased commercially or synthesized according to conventional methods. The preparation of the compound represented by formula A-IIIa is used as an example for illustration.

[0102] Hexamethyldisiloxane and phosphoric acid were added to a reactor and dehydration reaction was carried out under heating, stirring, and reflux condensation conditions. The dehydration reaction conditions were: temperature 100°C, time 5 hours, and pressure 1.0 MPa. 1-Trimethylsilylpyrrolidine was then added and distilled to remove the generated amine. The reaction solution was then subjected to precision filtration and vacuum distillation to obtain the compound represented by Formula A-IIIa. The distillation conditions were: temperature 200°C, time 10 hours, and pressure 1.0 MPa. The molar ratio of hexamethyldisiloxane, phosphoric acid, and 1-trimethylsilylpyrrolidine was 3:1:3.

[0103] In some embodiments, the volume content of the phosphate compound is less than 100% based on the total volume of the electrolyte, and the volume content of the phosphate compound is ≥9%. Optionally, the volume content of the phosphate compound is 20% to 60%. A volume content of the phosphate compound within this range can enhance the flame retardancy of the system. The silicon-containing groups and phosphate groups work together to improve the toughness of the SEI film, enhancing the cycling performance and reliability of the lithium metal battery.

[0104] For example, based on the total volume of the electrolyte, the volume content of the phosphate 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.

[0105] In some embodiments, the electrolyte further comprises a nitrogen-containing ionic liquid, which can enhance the flame retardancy of the electrolyte.

[0106] In some embodiments, the nitrogen-containing ionic liquid includes cations and anions, wherein the cations include at least one of an amine cation, an imidazolium cation, a piperidinium cation, and a pyridinium cation, and the anions include at least one of a trifluoromethylsulfonyl imide anion, a bisfluorosulfonyl imide anion, and a difluorooxalatoborate anion. Alternatively, the anions include at least one of a difluorooxalatoborate anion. These nitrogen-containing ionic liquids can provide a large amount of anions, forming an anion-derived SEI film, further improving the performance of the SEI film, thereby further improving the cycling performance.

[0107] In some embodiments, the volume content of the nitrogen-containing ionic liquid is ≤ 91% based on the total volume of the electrolyte; alternatively, 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 enhanced.

[0108] For example, 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.

[0109] 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 retardancy of the system can be further enhanced, the toughness of the SEI film can be improved, and the cycling performance and reliability of the lithium metal battery can be improved.

[0110] 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.

[0111] In some embodiments, the electrolyte further includes a lithium salt, including at least one of lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, and lithium difluorooxalatoborate. The lithium salt, when used in conjunction with the aforementioned organic solvent, can also form an SEI film containing an inorganic component, such as lithium fluoride, on the negative electrode sheet, further improving the structural stability of the SEI film and thereby improving the cycling performance of the lithium metal battery.

[0112] 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. This concentration of lithium salt facilitates the decomposition of lithium fluoride on the surface of the negative electrode, increasing the lithium fluoride content in the SEI film and further improving the structural stability of the SEI film, thereby further improving the cycling performance of the lithium metal battery. Furthermore, the aforementioned organic solvent has excellent lithium salt solubility, facilitating the dissociation of ions in the lithium salt and enhancing the migration rate of lithium ions.

[0113] 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.

[0114] The qualitative and quantitative determination of each substance or element in this application can be performed using appropriate equipment and methods known to those skilled in the art. The relevant detection methods can refer to domestic and international detection standards, domestic and international enterprise standards, etc., and those skilled in the art can also adapt certain detection steps / instrument parameters, etc., based on the accuracy of the detection, to obtain more accurate detection results. A single detection method can be used for qualitative or quantitative determination, or several detection methods can be used in combination for qualitative or quantitative determination.

[0115] The types and contents of inorganic components / lithium salt concentrations in the electrolyte are well known in the art and can be detected using 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 according to standard JY / T020-1996 "General Rules for Ion Chromatography Analysis Methods". In the embodiments of the present application, a freshly prepared electrolyte can be taken as a sample, or a battery that has been fully discharged (discharged to the lower cut-off voltage so that the battery's state of charge is approximately 0%) can be reversely disassembled, and the free electrolyte obtained from the battery can be used as a sample for detection using ion chromatography analysis.

[0116] The types and contents of organic components in the electrolyte are well known in the art and can be detected using 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" for qualitative and quantitative analysis of organic components in the electrolyte by gas chromatography. In the embodiments of the present application, a freshly prepared electrolyte can be taken as a sample, or a battery that has been fully discharged (discharged to the lower cutoff voltage so that the battery's state of charge is approximately 0%) can be reversely disassembled, and the free electrolyte obtained from the battery can be used as a sample for detection using ion chromatography.

[0117] lithium metal batteries

[0118] In a second aspect, an embodiment of the present application proposes a lithium metal battery.

[0119] [Negative electrode]

[0120] In some embodiments, the lithium metal battery includes a negative electrode plate.

[0121] 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.

[0122] 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.

[0123] The negative electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, 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, a copper alloy, nickel, a nickel alloy, titanium, a titanium alloy, silver, and a 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).

[0124] The negative electrode plate does not exclude additional functional layers. For example, in some embodiments, the negative electrode plate of the embodiments of the present application further includes a conductive layer (e.g., 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 embodiments of the present application further includes a protective layer covering the surface of the negative electrode current collector.

[0125] Optionally, the negative electrode plate may further include a conductive layer disposed on at least one side of the negative electrode current collector, wherein the conductive layer includes 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.

[0126] Optionally, the conductive layer may further include a negative electrode binder. For example, the negative electrode binder may include at least one of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based 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).

[0127] 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 facing each other in the thickness direction of the negative electrode current collector, and the negative electrode film layer is disposed on either or both of the two facing surfaces of the negative electrode current collector. The negative electrode film layer may include lithium metal or a lithium metal alloy, wherein the lithium metal alloy includes lithium metal and a non-lithium element, wherein the non-lithium element includes at least one of tin (Sn), zinc (Zn), aluminum (Al), magnesium (Mg), silver (Ag), gold (Au), gallium (Ga), indium (In), platinum (Pt), boron (B), carbon (C), and silicon (Si).

[0128] The material of the negative electrode current collector is as described above and will not be repeated here.

[0129] The negative electrode plate does not exclude additional functional layers. For example, in some embodiments, the negative electrode plate of the embodiments of the present application further includes a conductive layer (e.g., 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 embodiments of the present application further includes a protective layer covering the surface of the negative electrode current collector.

[0130] Optionally, the negative electrode plate may further include a conductive layer disposed between the negative electrode current collector and the lithium metal layer. The conductive layer may include a negative electrode conductive agent. The material of the negative electrode conductive agent is as described above and will not be further described here. Further, 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 further described here.

[0131] [Positive electrode]

[0132] In some embodiments, the lithium metal battery may further include a positive electrode sheet.

[0133] 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 comprising a positive electrode active material. For example, the positive electrode current collector may have two opposing surfaces in its thickness direction, and the positive electrode film layer may be disposed on either or both of the two opposing surfaces of the positive electrode current collector.

[0134] The positive electrode active material may be a positive electrode active material for lithium metal batteries 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 lithium nickel manganate, lithium-rich spinel lithium manganate, and lithium nickel manganate, etc.).

[0135] 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.

[0136] 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.

[0137] 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.

[0138] 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.

[0139] 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.

[0140] Illustratively, e can 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.

[0141] 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.

[0142] 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, 0.70, 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, 0.91, 0.92 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.

[0143] 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, 0.70, 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, 0.99, 0.91, 0.92 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.

[0144] 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, 0.70, 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, 0.99, 0.91, 0.92 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.

[0145] 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.

[0146] 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.

[0147] 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 O2(NCM333),LiNi 0.8 Co 0.1 Mn 0.1O2(NCM811) and LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523),LiNi 0.6 Co 0.2 Mn 0.2 O2、LiNi 0.85 Co 0.15 Al 0.05 O2、LiNi 0.80 Co 0.15 Al 0.05 One or more of O2.

[0148] For example, the composition formula of the olivine-type phosphate active material is: Li x A y Me 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 material includes one or more of LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4.

[0149] 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 active materials of the spinel structure include LiMn2O4, LiNi0.5 Mn 1.5 O4、LiCr 0.3 Mn 1.7 O4、Li 1.1 Al 0.1 Mn 1.9 O4, Li2Mn2O4 and Li 1.5 One or more of Mn2O4.

[0150] In the embodiments 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 a transition metal element, and for example, the coating modification may be performed by coating a carbon layer on the surface of the material.

[0151] The charge and discharge 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 varies at different discharge states. The molar content of Li in the examples of positive electrode active materials in the embodiments of this application refers to the initial state of the material, i.e., the state before the material is added. When the positive electrode active material is used in a battery system, the molar content of Li may change after charge and discharge cycles.

[0152] In the examples of the positive electrode active materials in the embodiments of the present application, the molar content of oxygen O is only a theoretical value. Lattice oxygen release will cause the molar content of oxygen O to change. In practice, the molar content of oxygen O will fluctuate.

[0153] In some embodiments, the positive electrode film layer may further optionally include a positive electrode conductive agent. The present embodiments do not particularly limit the type of the positive electrode conductive agent. By way of example, the positive 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. In some embodiments, the mass percentage of the positive electrode conductive agent based on the total mass of the positive electrode film layer is ≤5%.

[0154] In some embodiments, the positive electrode film layer may further optionally include a positive electrode binder. The embodiments of the present application do not particularly limit the type of positive electrode binder. As an example, the positive electrode binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylic resin. In some embodiments, based on the total mass of the positive electrode film layer, the mass percentage of the positive electrode binder is ≤5%.

[0155] 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 layer and a metal material layer formed on at least one surface of the polymer material base layer. 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 layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0156] The positive electrode film is typically formed by coating a positive electrode slurry onto a positive electrode current collector, drying it, and cold pressing it. The positive electrode slurry is typically formed by dispersing the positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring them uniformly. The solvent can be, but is not limited to, N-methylpyrrolidone (NMP).

[0157] [Isolation film]

[0158] In some embodiments, the lithium metal battery may further include a separator.

[0159] The embodiments of the present application have no particular limitation on the type of isolation membrane, and any known isolation membrane with a porous structure having good chemical stability and mechanical stability can be selected.

[0160] In some embodiments, the material of the separator may include at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0161] In some embodiments, the positive electrode sheet, the separator, and the negative electrode sheet may be formed into an electrode assembly through a winding process and / or a lamination process.

[0162] In some embodiments, the lithium metal battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0163] 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 pouch-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).

[0164] The embodiment of the present application has no particular limitation on the shape of the lithium metal battery, which can be cylindrical, square or any other shape. FIG1 shows a lithium metal battery 5 with a square structure as an example.

[0165] In some embodiments, as shown in FIG2 , the outer packaging 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 separator may be formed into 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 impregnated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the lithium metal battery 5 may be one or more, which can be adjusted according to demand.

[0166] The preparation method of the lithium metal battery of the embodiments of the present application is well known. In some embodiments, a positive electrode sheet, a separator, a negative electrode sheet, and an 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. The electrode assembly is placed in an outer packaging, dried, and then injected with electrolyte. The lithium metal battery is obtained through vacuum packaging, static standing, chemical formation, and shaping processes.

[0167] 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.

[0168] Figure 3 is a schematic diagram of an exemplary battery module 4. As shown in Figure 3 , within the battery module 4, multiple lithium metal batteries 5 may be arranged sequentially along the length of the battery module 4. Of course, any other arrangement is also possible. Furthermore, the multiple lithium metal batteries 5 may be secured using fasteners.

[0169] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of lithium metal batteries 5 are received in the receiving space.

[0170] 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.

[0171] Figures 4 and 5 are schematic diagrams of an exemplary battery pack 1. As shown in Figures 4 and 5, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 covers the lower case 3 and forms an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0172] Electrical devices

[0173] A third aspect of the embodiments of the present application provides an electrical device, wherein the electrical device 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 may 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, a satellite, an energy storage system, etc.

[0174] Electrical devices can choose lithium metal batteries, battery modules or battery packs according to their usage requirements.

[0175] FIG6 is a 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. To meet the high power and high energy density requirements of the electric device 6, a battery pack or battery module may be used.

[0176] As another example, an electric device may be a mobile phone, a tablet computer, a laptop computer, etc. Such an electric device is usually required to be lightweight and thin, and may use a lithium metal battery as a power source.

[0177] Example

[0178] The following examples describe the disclosure of the present invention in more detail. These examples are intended for illustrative purposes only, as various modifications and variations within the scope of the disclosure of the present invention will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by 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.

[0179] Example 1

[0180] 1. Preparation of positive electrode sheet

[0181] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer. The positive electrode current collector is an aluminum foil with a thickness of 10 μm. The positive electrode film layer includes a positive electrode slurry (the solvent is N-methylpyrrolidone NMP) uniformly coated on the surface of the positive electrode current collector aluminum foil, and a film layer formed after 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) with a weight ratio of 98:1:1.

[0182] The positive electrode active material includes a composition formula of LiNi 0.8 Co 0.1 Mn 0.1 Compound of O2(NCM811).

[0183] 2. Preparation of negative electrode sheet

[0184] 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. The lithium metal foil with a thickness of 50 μm is pressed on both sides of the copper foil by roller pressing.

[0185] 3. Isolation film

[0186] The isolation film is a polyethylene film layer.

[0187] 4. Preparation of electrolyte

[0188] The electrolyte includes an organic solvent and a lithium salt.

[0189] 5. Preparation of lithium metal batteries

[0190] The above-mentioned positive electrode sheet, isolation membrane, and lithium metal negative electrode are stacked in order, so that the isolation membrane is placed 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 laminated lithium metal battery is obtained.

[0191] Example 2 to Example 9

[0192] A lithium metal battery was prepared using a method similar to that of Example 1. Unlike Example 1, the electrolyte components of Examples 2 to 9 were different from those of Example 1. In particular, the volume ratio of the phosphate compound to the nitrogen-containing ionic liquid was adjusted in Examples 2 to 9.

[0193] Comparative Examples 1 to 3

[0194] 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 Comparative Examples 1 to 3 were different from those of Example 1.

[0195] Performance Testing

[0196] 1. Room temperature cycle test of lithium metal batteries

[0197] The ambient temperature for the lithium metal battery room temperature cycle was set at 25°C, and the charge and discharge cycles were performed at a rate of 0.5C (i.e., 70mA). The charge and discharge cutoff voltages were set at 4.3V and 2.8V, respectively.

[0198] When the discharge capacity decays to 80% of the initial discharge capacity, the battery life is considered to be over.

[0199] 2. High cycle test of lithium metal batteries

[0200] The ambient temperature for high-temperature cycling of the lithium metal battery was set at 60°C, and the charge and discharge cycles were performed at a rate of 0.5C (i.e., 70 mA). The charge and discharge cutoff voltages were set at 4.3V and 2.8V, respectively.

[0201] When the discharge capacity decays to 80% of the initial discharge capacity, the battery life is considered to be over.

[0202] Test results

[0203] The test results are shown in Table 1.

[0204] Table 1

[0205] In Table 1,

[0206] “-” means that such substance is not added or the parameter here is meaningless.

[0207] “2M” means that the amount of substance of the lithium salt is 2 mol / L.

[0208] As can be seen from Table 1, the organic solvent of the electrolyte in Comparative Example 1 includes a phosphate solvent (trimethyl phosphate), but the phosphate 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 cycle performance of the battery.

[0209] 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.

[0210] Compared with Comparative Examples 1 and 2, Comparative Example 3 mixes phosphate solvents and siloxane solvents as the organic solvent of the electrolyte. The phosphate 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.

[0211] Compared with Comparative Example 3, Example 1 uses a phosphate compound containing a silicon group as an organic solvent. The organic solvent can form a silicon-containing polymer on the surface of the negative electrode, 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, thereby significantly improving the low-temperature and high-temperature cycle performance of the lithium metal battery.

[0212] Compared to Example 1-1, Example 1 also adds nitrogen-containing ionic liquid Y (1-propyl-1-methylpyrrolidine bis(fluorosulfonyl)imide), which can work together with the organic solvent to exert a flame retardant effect and further improve 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 nitrogen-containing ionic liquid Y, the cycle performance of the lithium metal battery can be further improved.

[0213] Example 10 to Example 18

[0214] Lithium metal batteries were prepared using a method similar to that of Example 1. The difference from Example 1 was that the electrolyte components of Examples 10 to 18 were different from those of Example 1, and the materials of the organic solvents in the electrolytes were different.

[0215] The test results are shown in Table 2.

[0216] Table 2

[0217] It can be seen from Table 2 that by regulating the types of phosphate compounds including silicon groups, the low-temperature and high-temperature cycle performance of lithium metal batteries can be effectively regulated.

[0218] Example 19 to Example 21

[0219] Lithium metal batteries were prepared using a method similar to that of Example 1. Unlike Example 1, 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.

[0220] The test results are shown in Table 3.

[0221] Table 3

[0222] As shown in Table 3, 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.

[0223] Although illustrative embodiments have been shown 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, comprising an organic solvent, wherein the organic solvent comprises a phosphate compound, wherein the phosphate compound comprises a silicon-containing group and at least one phosphate group, wherein 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.

2. The electrolyte for lithium metal batteries according to claim 1, wherein At least one of the silicon-containing group and the phosphate group includes an ether bond.

3. The electrolyte for lithium metal batteries according to claim 1 or 2, wherein The phosphate compound includes a compound shown in formula A, In formula A, R1 to R3 each independently include 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; Wherein, at least one of R1 to R3 includes 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 lithium metal battery according to claim 3, wherein 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, 5. The electrolyte for lithium metal batteries according to any one of claims 1 to 4, wherein The phosphate compound includes a compound shown in formula B, In formula B, R4 and R5 each independently include 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, or a substituted or unsubstituted phosphoryloxy group; R7 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 lithium metal battery according to claim 5, wherein 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, 7. The electrolyte for lithium metal batteries according to any one of claims 1 to 6, wherein The phosphate compound includes a compound shown in formula C, In formula C, R6 includes 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 lithium metal batteries according to claim 7, wherein 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, 9. The electrolyte for lithium metal batteries according to any one of claims 1 to 8, wherein Based on the total volume of the electrolyte, the volume content of the phosphate compound is ≥9%; Optionally, the volume content of the phosphate compound is 20% to 60%.

10. The electrolyte for lithium metal batteries according to any one of claims 1 to 9, wherein The organic solvent also includes a nitrogen-containing ionic liquid; Optionally, 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 difluorooxalatoborate anions.

11. The electrolyte for lithium metal battery according to claim 10, wherein 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 lithium metal batteries according to any one of claims 1 to 11, wherein The electrolyte further includes a lithium salt, wherein 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.

13. A lithium metal battery, comprising the electrolyte for a lithium metal battery according to any one of claims 1 to 12.

14. The lithium metal battery according to claim 13, wherein 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, wherein: 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 comprising the battery according to any one of claims 13 to 15.

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