Electrolyte additive, electrolyte, battery

Abstract

The application relates to the technical field of electrolyte, in particular to an electrolyte additive, an electrolyte and a battery. The electrolyte additive has a structure shown in formula (1), the structure contains a nitrate radical and a carbon-oxygen-containing organic group, a nitrogen-containing SEI is formed through decomposition of the nitrate radical, the transmission of lithium ions in the SEI is accelerated, lithium deposition is more uniform, and the formation of lithium dendrites is reduced; the solubility of the additive in the electrolyte can be significantly increased through the carbon-oxygen-containing organic group, and the carbon-oxygen-containing organic group can decompose to generate an organic component, thereby enhancing the toughness of the SEI film; the decomposition of the electrolyte can be inhibited and the consumption of active lithium metal can be reduced by introducing the electrolyte additive into the electrolyte.

Description

Technical Field

[0001] This application relates to the technical field of electrolytes, and more particularly to electrolyte additives, electrolytes, and batteries. Background Technology

[0002] Various electrolyte strategies (high-concentration electrolytes, locally high-concentration electrolytes, fluorinated electrolytes, weakly solvated electrolytes, dual-salt electrolytes, sacrificial additives, etc.) have been reported to construct robust passivation layers to cope with the intense interfacial chemical reactions in lithium metal batteries. Among these, the use of sacrificial additives is a simple and effective method for modulating the physicochemical properties of the interface.

[0003] Sacrifice additives, such as LiNO3, have a certain positive effect on improving lithium battery performance; however, due to the low solubility of LiNO3 in the electrolyte, the concentration of LiNO3 is at a low level in the early stage of battery cycling. As the cycling time increases, the side reactions at the lithium anode interface increase, and LiNO3 will be consumed rapidly, thus affecting the battery cycle life and cycle performance. This cannot solve the problem that the limited additives will be consumed rapidly due to repeated damage and repair of SEI. Summary of the Invention

[0004] In view of this, this application provides an electrolyte additive having a structure as shown in formula (1) to at least partially solve the above-mentioned technical problems.

[0005] A first aspect of this application provides an electrolyte additive having a structure as shown in formula (1):

[0006]

[0007] Equation (1);

[0008] Wherein: R is at least one of the following: substituted or unsubstituted C1-C10 alkyl, substituted or unsubstituted C2-C10 alkenyl, substituted or unsubstituted C2-C10 alkynyl, substituted or unsubstituted C1-C10 alkoxy, substituted or unsubstituted C2-C10 alkoxycarbonyl, substituted or unsubstituted C2-C20 heterocyclic, substituted or unsubstituted C6-C12 aryl, and C3-C6 cycloalkyl;

[0009] n is an integer from 1 to 8.

[0010] According to a second aspect of this application, an electrolyte is provided, comprising a lithium salt, a solvent, and the electrolyte additives described in the first aspect above.

[0011] Optionally, the electrolyte additive is 0.1% to 15% by mass, based on the total mass of the electrolyte.

[0012] Optionally, the lithium salt is selected from one or more of lithium bisfluorosulfonylimide, lithium bis-trifluoromethylsulfonylimide, lithium bisfluorooxalate borate, lithium bisoxalate borate, lithium tetrafluoroborate, lithium hexafluorophosphate, lithium difluorophosphate, lithium difluorophosphate;

[0013] The mass percentage of the lithium salt is 5% to 35% based on the total mass of the electrolyte;

[0014] And / or, the solvent comprises a coordination type solvent and a non-coordination type solvent;

[0015] The mass percentage of the solvent is 64.9% to 94.9% based on the total mass of the electrolyte.

[0016] Optionally, the mass percentage of the electrolyte additive is 1% to 10%, the mass percentage of the lithium salt is 22% to 24%, and the mass percentage of the solvent is 66% to 77% based on the total mass of the electrolyte.

[0017] In a third aspect, the present application provides a battery comprising the electrolyte of the second aspect.

[0018] The electrolyte additive provided by the present application has a structure of formula (1), which contains a nitrate group and a carbon-oxygen-containing organic group. The formation of the SEI containing nitrogen through the decomposition of the nitrate group accelerates the transmission of lithium ions in the SEI, makes the lithium deposition more uniform, reduces the formation of lithium dendrites and reduces the consumption of active lithium ions. The carbon-oxygen-containing organic group can significantly increase the solubility of the additive in the electrolyte, and the carbon-oxygen-containing organic group can decompose to generate organic components, thereby enhancing the toughness of the SEI film. BRIEF DESCRIPTION OF DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0020] Figure 1 The schematic diagram of the lithium secondary battery cycle charge-discharge curve in Example 1 and Comparative Example 1.

[0021] Figure 2 The schematic diagram of the capacity retention rate of the lithium secondary battery in Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0022] Clearly, the described embodiments are only a part of all embodiments of the present application, rather than all embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative efforts are within the scope of the present application. In addition, it should be understood that the specific implementations described herein are merely intended for illustration and explanation of the present application and are not intended to limit the present application.

[0023] In the present application, the orientation words such as "upper" and "lower" generally refer to the upper and lower in the actual use or working state of the device, specifically the drawing surface direction in the drawings, and "inner" and "outer" refer to the outline of the device. In addition, in the description of the present application, the term "comprising" means "including but not limited to". The terms first, second, third, etc. are only used as labels and do not impose numerical requirements or establish an order.

[0024] In the present application, "and / or" describes the association relationship of the associated objects, which means that there can be three kinds of relationships, for example, A and / or B, which means that A exists alone, A and B exist together, and B exists alone. Wherein A and B can be singular or plural.

[0025] In the present application, "at least one" means one or more, and "multiple" means two or more. "One or more", "at least one of the following" or similar expressions mean any combination of these items, including any combination of single item or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can mean a, b, c, a-b (i.e. a and b), a-c, b-c, or a-b-c, where a, b, and c can be single or multiple.

[0026] Various embodiments of the present application can exist in the form of a range; it should be understood that the description in the form of a range is only for the convenience and brevity, and should not be understood as a hard limit on the scope of the present application; therefore, it should be considered that the described range has specifically disclosed all possible sub-ranges and single values within the range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the described range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. In addition, whenever a numerical range is indicated in the present text, it means that any cited number (fraction or integer) within the indicated range is included.

[0027] As used herein, the term "alkyl" refers to a straight-chain or branched-chain monovalent saturated hydrocarbon group (e.g., C1-C10 alkyl, where C1-C10 means that the group contains 1 to 10 carbon atoms). Illustratively, examples of alkyl groups include C1-C6 alkyl, C1-C4 alkyl, C1-C3 alkyl, C1-C2 alkyl, and the like.

[0028] Specifically, the alkyl of C1-C10 alkyl can be methyl, ethyl, n-propyl, isopropyl, n-butyl, t-butyl, isobutyl, sec-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, and the like.

[0029] As used herein, "alkenyl" refers to a straight-chain or branched-chain hydrocarbon group containing at least one carbon-carbon double bond, no carbon-carbon triple bonds, e.g., C2-C10 alkenyl, C2-C8 alkenyl, C2-C6 alkenyl, C2-C5 alkenyl, C2-C4 alkenyl, C2-C3 alkenyl; examples of alkenyl groups include ethenyl, 1-propenyl, 2-propenyl, 2-methyl-l- propenyl, 1-butenyl, and 2-butenyl.

[0030] As used herein, "alkynyl" refers to a straight-chain or branched-chain hydrocarbon group containing at least one carbon-carbon triple bond, e.g., C2-C10 alkynyl, C2-C8 alkynyl, C2-C6 alkynyl, C2-C5 alkynyl, C2-C4 alkynyl, C2-C3 alkynyl. Examples of alkynyl groups include ethynyl, 1-propynyl, 1-methyl-2-propynyl, 2-propynyl, 1-butynyl, and 2-butynyl.

[0031] As used herein, "alkoxy" refers to A-O-, where A is an alkyl group as described herein. Preferably, the alkoxy group is a C1-C6 alkoxy group, such as methoxy, ethoxy, and the like.

[0032] As used herein, "alkoxycarbonyl" refers to -C(=O)-OA, where A is an alkyl group as described herein. Preferably, the alkoxycarbonyl group is -C(=O)-OA, where A is a C1-C6 alkyl group, such as methoxycarbonyl (-C(=O)-OCH3), ethoxycarbonyl (-C(=O)-OCH2-CH3), and the like.

[0033] As used herein, "heterocyclyl" refers to a cyclic group having 3 or more ring atoms, which can be composed of C2-C20 carbon atoms and 1-3 heteroatoms selected from O, N, and S. In some embodiments, the heterocyclyl group has 3 to 20 ring atoms. In some embodiments, the heterocyclyl group has 3 to 10 ring atoms. Examples of heterocyclyl groups include tetrahydrofuranyl, pyranyl, piperidinyl, piperazinyl.

[0034] As used herein, "cycloalkyl" is a saturated or unsaturated carbocyclic ring having 3 or more ring carbon atoms. In some embodiments, the cycloalkyl group has 3 to 6 ring carbon atoms (C3-C6 cycloalkyl). In some particular embodiments, the cycloalkyl group has 5 to 6 ring carbon atoms (C5-C6 cycloalkyl). Examples of cycloalkyl groups include cyclopentyl, cyclohexyl, cyclopropyl, cyclobutyl.

[0035] As used herein, "aryl" refers to a monocyclic, bicyclic, or tricyclic aromatic group containing 6 to 12 carbon atoms, i.e., C6-C12 aryl. Examples of aryl groups include phenyl, naphthyl, indenyl, azulenyl, biphenyl, and biphenylenyl.

[0036] The current research found that the solubility of some additives such as LiNO3 in the electrolyte is low, which causes the additive concentration to be at a low concentration level at the initial stage of battery cycle. With the extension of cycle time, the lithium negative electrode interface side reaction increases, and the additive will be quickly consumed, thereby affecting the battery cycle life and cycle performance, and the problem of rapid consumption of limited additives caused by repeated destruction and repair of SEI cannot be solved.

[0037] To this end, the first aspect of the present application provides an electrolyte additive, the electrolyte additive has a structure as shown in formula (1):

[0038]

[0039] Formula (1);

[0040] Wherein: R is at least one of substituted or unsubstituted C1-C10 alkyl, substituted or unsubstituted C2-C10 alkenyl, substituted or unsubstituted C2-C10 alkynyl, substituted or unsubstituted C1-C10 alkoxy, substituted or unsubstituted C2-C10 alkoxycarbonyl, substituted or unsubstituted C2-C20 heterocyclic group, substituted or unsubstituted C6-C12 aryl;

[0041] n is an integer from 1 to 8, such as 1, 2, 3, 4, 5, 6, 7, or 8.

[0042] By the above technical solution, the compound with the structure shown in formula (1) is used as an electrolyte additive, the structure contains a nitrate group and a carbon-oxygen-containing organic group, the solubility of the electrolyte additive in the electrolyte can be significantly increased through the carbon-oxygen-containing organic group, the electrolyte additive is introduced into the electrolyte, the electrolyte additive can be maintained at a high concentration at the initial stage of battery cycle, and as the cycle time is delayed, even if the electrolyte additive is consumed quickly, the concentration of the electrolyte additive is reduced to a certain extent, but still maintained at a high concentration content, ensuring the cycle life and cycle performance of the battery; at the same time, the nitrate ion participates in the formation of an interface film with high ion conductivity, and the organic component can be generated by decomposing the carbon-oxygen-containing organic group, the organic component can enhance the toughness of the interface film, the interface film can promote the uniform deposition and densification of lithium by regulating the migration path and deposition behavior of lithium ions. In this process, the stability of the interface film reduces the non-uniformity of the local current density, reduces the generation of dendrites and isolated lithium. At the same time, the chemical inertness of the interface film inhibits the side reaction of the electrolyte and inhibits the decomposition of lithium salt and solvent; the high ion conductivity of the interface film can make the lithium deposit uniformly and densely, thereby significantly reducing the mass accumulation of dead lithium.

[0043] The application does not limit the source of the electrolyte additive with the structure of formula (1), which can be a commercial product or prepared by a known method.

[0044] In some examples, the substituent is selected from halogen or C1-C4 alkyl, such as F, Cl, Br, I, preferably F or Cl; C1-C4 alkyl, including methyl, ethyl, propyl, butyl, preferably methyl or ethyl.

[0045] In some examples, n is an integer from 1 to 6, for example n = 1, 2, 3, 4, 5, 6, 7 or 8, and n is preferably 1 or 2.

[0046] In some examples, R is at least one of a substituted or unsubstituted C1-C8 alkoxy group or a substituted or unsubstituted C2-C10 heterocyclic group. For example, the C1-C8 alkoxy group includes C2 alkoxy (ethoxy), C3 alkoxy (such as n-propoxy, isopropoxy), C4 alkoxy (such as n-butoxy, isobutoxy, sec-butoxy, tert-butoxy), C5 alkoxy, C6 alkoxy, C7 alkoxy, C8 alkoxy, C9 alkoxy or C10 alkoxy;

[0047] For example, the C2-C10 heterocyclic group includes tetrahydrofuryl, pyrrolyl, thienyl, thiazolyl, pyridyl, indolyl, quinolyl, carbazolyl, oxacyclopropyl.

[0048] In some examples, the electrolyte additive is selected from at least one of the following compounds 1 to 8:

[0049] .

[0050] For example, the CAS number of compound 1 is 87-33-2; the CAS number of compound 2 is 59331-87-2; the CAS number of compound 3 is 88097-96-5; the CAS number of compound 4 is 88097-95-4; the CAS number of compound 5 is 28079-67-6; the CAS number of compound 6 is 874674-36-9; the CAS number of compound 7 is 62796-21-8; and the CAS number of compound 8 is 22703-81-7.

[0051] The source of the electrolyte additive described above is not limited in the present application, and can be a commercially available product or prepared by a known method.

[0052] According to a second aspect of the present application, an electrolyte is provided, which comprises the electrolyte additive described above. By introducing the electrolyte additive into the electrolyte, the electrolyte additive forms a solid electrolyte interface film rich in nitrogen elements on the surface of the lithium salt, promotes the rapid transport of lithium ions and the uniform deposition of lithium, and can inhibit the decomposition of the electrolyte and reduce the consumption of active lithium metal.

[0053] In some embodiments, the mass percentage of the electrolyte additive is 0.1% to 15% based on the total mass of the electrolyte. Within this mass percentage range, the electrolyte additive can be dissolved in the electrolyte, and the nitrate group in the electrolyte additive can decompose to form a nitrogen-rich interface layer, and the organic group can decompose to form an organic compound-rich interface layer, thereby reducing the consumption of active lithium metal and improving the cycle life of the battery. For example, the mass percentage of the electrolyte additive can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, or a range between any two of the above values.

[0054] In some embodiments, the electrolyte further comprises a lithium salt, which provides migratable lithium ions and transfers electric charges between the positive and negative electrodes to realize the charge and discharge cycle of the battery. The lithium salt is selected from commonly used lithium salts in electrolytes, such as one or more selected from lithium bisfluorosulfonylimide (LiFSI), lithium bis-trifluoromethylsulfonylimide (LiTFSI), lithium bisfluorooxalate borate (LiDFOB), lithium bisoxalate borate (LiBOB), lithium tetrafluoroborate (LiBF4), lithium hexafluorophosphate (LiPF6), lithium difluorooxalate phosphate (LiDFOP), and lithium difluorophosphate (LiDFP).

[0055] In some examples, the mass percentage of the lithium salt is 5% to 35% based on the total mass of the electrolyte, within the mass percentage range, the lithium salt can provide more migratable lithium ions to achieve higher ionic conductivity. Illustratively, the mass percentage of the lithium salt can be 5%, 6%, 7%, 8%, 9%, 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%, and a range value between any two of the above values.

[0056] In some embodiments, the electrolyte further comprises a solvent capable of dissolving the lithium salt and facilitating the dissociation of the lithium salt into free ions, thereby ensuring that the electrolyte has sufficient ionic conductivity. The solvent includes a coordinating solvent and a non-coordinating solvent; wherein the coordinating solvent is, for example, selected from one or more of ethylene glycol dimethyl ether (DME), ethylene glycol diethyl ether (DEE), 1,3-dimethoxypropane (DMP), dimethoxymethane (DMM), tetrahydrofuran (THF), tetrahydropyran (THP), 1,3-dioxolane (DOL), dimethyl carbonate (DMC), ethylene carbonate (EC), fluoroethylene carbonate (FEC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC);

[0057] wherein the non-coordinating solvent is, for example, selected from one or more of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), 2,2,2-trifluoroethyl ether (BTFE), 1,1,1,2,2,3,4,5,5,5-decafluoropentane (HFC), heptafluoroalkane (SFE), and tris(trifluoroethoxy)methane (TFEO).

[0058] In some examples, the mass percentage of the solvent is 64.9% to 94.9% based on the total mass of the electrolyte, within the mass percentage range, the solvent can better dissolve the lithium salt and the electrolyte additives, and the mass percentage of the solvent can be 64.9%, 65%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 77%, 78%, 82%, 83%, 88%, 91%, 92%, 93%, 74.5%, 85.2%, 86.1%, 94.9%, and a range value between any two of the above values.

[0059] The application does not specifically limit the preparation method of the electrolyte, and illustratively, the preparation method of the electrolyte described above includes the following steps:

[0060] S1, under the protection of an inert gas, adding a lithium salt to a configuration container, then adding a coordinating solvent to the configuration container and mixing uniformly;

[0061] S2, add non-coordinating solvent to the configuration container and mix uniformly;

[0062] S3, add additive to the configuration container and mix uniformly to obtain electrolyte.

[0063] According to the third aspect of the application, a battery is provided, comprising the electrolyte described above. The battery comprises a lithium ion battery.

[0064] Hereinafter, the electrolyte additive, electrolyte and battery provided by the application are described in detail through specific examples.

[0065] I. Examples

[0066] Example 1

[0067] 1.1, an electrolyte, comprising:

[0068] The electrolyte additive is compound 1, and the mass percentage is 5%;

[0069]

[0070] The lithium salt is lithium bisfluorosulfonylimide (LiFSI), and the mass percentage is 24%;

[0071] The coordinating solvent is ethylene glycol dimethyl ether (DME), and the mass percentage is 21%;

[0072] The non-coordinating solvent is 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE), and the mass percentage is 50%.

[0073] 1.2, a preparation method of the electrolyte described above, comprising the following steps:

[0074] S1, under the protection of inert gas, add lithium salt to the configuration container, then add coordinating solvent to the configuration container and mix uniformly;

[0075] S2, add non-coordinating solvent to the configuration container and mix uniformly;

[0076] S3, add electrolyte additive to the configuration container and mix uniformly to obtain electrolyte.

[0077] Example 2

[0078] Compared with example 1, the difference lies in that compound 2 is used as electrolyte additive.

[0079]

[0080] Example 3

[0081] Compared with Example 1, the difference lies in that the electrolyte additive uses compound 3.

[0082]

[0083] Example 4

[0084] Compared with Example 1, the difference lies in that the electrolyte additive uses compound 4.

[0085]

[0086] Example 5

[0087] Compared with Example 1, the difference lies in that the electrolyte additive uses compound 5.

[0088]

[0089] Example 6

[0090] Compared with Example 1, the difference lies in that the electrolyte additive uses compound 6.

[0091]

[0092] Example 7

[0093] Compared with Example 1, the difference lies in that the electrolyte additive uses compound 7.

[0094]

[0095] Example 8

[0096] Compared with Example 1, the difference lies in that the electrolyte additive uses compound 8.

[0097]

[0098] Example 9

[0099] Compared with Example 1, the difference lies in that the electrolyte includes:

[0100] An electrolyte additive, compound 1 is used, with a mass percentage of 5%;

[0101] A lithium salt: lithium bisfluorosulfonylimide (LiFSI) is used, with a mass percentage of 22%;

[0102] And lithium bisfluorosulfonylimide (LiTFSI), with a mass percentage of 2%;

[0103] A complex solvent: diethylene glycol diethyl ether (DEE) is used, with a mass percentage of 21%;

[0104] Non-coordinating solvent, 2,2,2-trifluoroethylether (BTFE) at 50% by mass.

[0105] Example 10

[0106] Compared to Example 1, the electrolyte includes:

[0107] Electrolyte additive, Compound 1 at 5% by mass;

[0108] Lithium salt: lithium bisfluorosulfonyl oxide borate (LiFSI) at 22% by mass;

[0109] and lithium tetrafluoroborate (LiBF4) at 2% by mass;

[0110] Coordinating solvent, ethylene glycol diethyl ether (DEE) at 21% by mass;

[0111] Non-coordinating solvent, 1,1,1,2,2,3,4,5,5,5-decafluoropentane (HFC) at 50% by mass.

[0112] Example 11

[0113] Compared to Example 1, the electrolyte includes:

[0114] Electrolyte additive, Compound 1 at 5% by mass;

[0115] Lithium salt: lithium bisfluorosulfonyl oxide borate (LiDFOB) at 17% by mass;

[0116] lithium bisoxalato borate (LiBOB) at 1% by mass;

[0117] and lithium difluorophosphate (LiDFP) at 2% by mass;

[0118] Coordinating solvent, ethylene glycol dimethyl ether (DME) at 25% by mass;

[0119] Non-coordinating solvent, tris(trifluoroethoxy)methane (TFEO) at 50% by mass.

[0120] Example 12

[0121] Compared to Example 1, the electrolyte includes:

[0122] Electrolyte additive, Compound 1 at 5% by mass;

[0123] Lithium salt: lithium bisfluorosulphate (LiFSI) at 20% by mass;

[0124] Lithium salt: lithium bisfluorosulphate (LiFSI) at 20% by mass;

[0125] Lithium salt: lithium bisfluorosulphate (LiFSI) at 20% by mass;

[0126] Coordinating solvent: ethylene glycol dimethyl ether (EMC) at 25% by mass;

[0127] Fluoroethylene carbonate (FEC) at 28% by mass;

[0128] Dimethyl carbonate (DMC) at 22% by mass.

[0129] Example 13

[0130] Compared to Example 1, the electrolyte comprises:

[0131] Electrolyte additive: compound 1 at 5% by mass;

[0132] Lithium salt: lithium bisfluorosulphate (LiFSI) at 20% by mass;

[0133] Lithium salt: lithium bisfluorosulphate (LiFSI) at 20% by mass;

[0134] Coordinating solvent: dimethyl carbonate (DMC) at 44% by mass;

[0135] Fluoroethylene carbonate (FEC) at 35% by mass.

[0136] Example 14

[0137] Compared to Example 1, the electrolyte comprises:

[0138] Electrolyte additive: compound 1 at 5% by mass;

[0139] Lithium salt: lithium bisfluorosulphate (LiFSI) at 20% by mass;

[0140] Lithium salt: lithium bisfluorosulphate (LiFSI) at 20% by mass;

[0141] Coordinating solvent: 1,3-dimethoxypropane (DMP) at 24% by mass;

[0142] Non-coordinating solvent: heptafluoroalkane (SFE) at 50% by mass.

[0143] Example 15

[0144] and Example 1 except that the electrolyte includes:

[0145] an electrolyte additive of Compound 1 at 5% by mass;

[0146] a lithium salt of lithium bisfluorosulfonylimide (LiFSI) at 20% by mass;

[0147] a coordinating solvent of ethylene glycol diethyl ether (DME) at 12% by mass;

[0148] and 1,3-dioxolane (DOL) at 13% by mass;

[0149] a non-coordinating solvent of 1,1,1,2,2,3,4,5,5,5-decafluoropentane (HFC) at 50% by mass.

[0150] Example 16

[0151] and Example 1 except that the electrolyte includes:

[0152] an electrolyte additive of Compound 1 at 5% by mass;

[0153] a lithium salt of lithium bisfluorosulfonylimide (LiFSI) at 20% by mass;

[0154] a coordinating solvent of tetrahydropryan (THP) at 25% by mass;

[0155] and tetrahydrofuran (TMP) at 5% by mass;

[0156] a non-coordinating solvent of 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE) at 45% by mass.

[0157] Example 17

[0158] and Example 1 except that the electrolyte includes:

[0159] an electrolyte additive of Compound 1 at 0.1% by mass;

[0160] a lithium salt of lithium bisfluorosulfonylimide (LiFSI) at 5% by mass;

[0161] a coordinating solvent of ethylene glycol diethyl ether (DME) at 24.9% by mass;

[0162] The non-coordinative solvent is 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE) with a mass percentage of 70%.

[0163] Example 18

[0164] Compared with Example 1, the difference is that the electrolyte includes:

[0165] The electrolyte additive is compound 1 with a mass percentage of 15%;

[0166] The lithium salt is lithium bisfluorosulfonylimide (LiFSI) with a mass percentage of 35%;

[0167] The coordinating solvent is ethylene glycol dimethyl ether (DME) with a mass percentage of 30%;

[0168] The non-coordinative solvent is 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE) with a mass percentage of 20%.

[0169] Example 19

[0170] Compared with Example 1, the difference is that the mass percentage of compound 1 in the electrolyte additive is 1%, the mass percentage of lithium bisfluorosulfonylimide (LiFSI) is 24%, the mass percentage of ethylene glycol dimethyl ether (DME) is 25%, and the mass percentage of 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE) is 50%.

[0171] Example 20

[0172] Compared with Example 1, the difference is that the mass percentage of compound 1 in the electrolyte additive is 10%, the mass percentage of lithium bisfluorosulfonylimide (LiFSI) is 24%, the mass percentage of ethylene glycol dimethyl ether (DME) is 21%, and the mass percentage of 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE) is 45%.

[0173] It is found during the preparation process that in Examples 1 to 20, the electrolyte additive in the electrolyte is completely dissolved.

[0174] II. Comparative Examples

[0175] Comparative Example 1

[0176] Compared with Example 1, the difference is that compound 1 is not added in the electrolyte.

[0177] Comparative Example 2

[0178] Compared with Example 9, the difference is that compound 1 is not added in the electrolyte.

[0179] Comparative Example 3

[0180] The difference compared with Example 10 is that no compound 1 is added in the electrolyte.

[0181] Comparative Example 4

[0182] The difference compared with Example 13 is that the electrolyte comprises:

[0183] LiNO3, 15% by mass;

[0184] Lithium salt: lithium bisfluorosulfonylimide (LiFSI), 35% by mass;

[0185] Coordination type solvent: ethylene glycol diethyl ether (DME), 30% by mass;

[0186] Non-coordination type solvent: 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE), 20% by mass.

[0187] It is found during preparation that LiNO3 cannot be completely dissolved in the electrolyte.

[0188] Comparative Example 5

[0189] The difference compared with Example 14 is that the electrolyte comprises:

[0190] LiNO3, 1% by mass;

[0191] Lithium salt: lithium bisfluorosulfonylimide (LiFSI), 24% by mass;

[0192] Coordination type solvent: ethylene glycol dimethyl ether (DME), 25% by mass;

[0193] Non-coordination type solvent: 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE), 50% by mass.

[0194] It is found during preparation that LiNO3 cannot be completely dissolved in the electrolyte.

[0195] III. Experimental Examples

[0196] 1. The electrolytes in Examples 1 to 20 and Comparative Examples 1 to 5 are assembled into Li||NCM811 soft pack batteries in an argon atmosphere.

[0197] 2. Test method

[0198] (1) 25 °C cycle performance test: the batteries prepared in each example and comparative example were charged at 0.2C constant current and constant voltage to 4.2V at 25 °C, and then discharged at 0.5C constant current to 3.0V, which was 1 cycle. The cycle number when the battery reached 80% SOH was recorded.

[0199] (2) Dead lithium mass

[0200] In lithium metal batteries, hydrogen-gas chromatography titration (H2-GCT) can be used to quantify dead lithium (‘dead lithium’ wrapped by SEI), the core principle of which is to use dead lithium to react with water to generate hydrogen (H2), and the volume of H2 is accurately measured by gas chromatography (GC), and then the mass of dead lithium is calculated. The specific operation steps are as follows:

[0201] S1. The cycled lithium metal negative electrode was cut into a 14mm diameter disc, exposing the fresh edge of active lithium (metallic lithium not wrapped by SEI). The disc was immersed in a diphenyl / THF solution (6wt% diphenyl), and left to stand at room temperature for 36-48 hours to dissolve the active lithium. The residual dead lithium (SEI-wrapped lithium) remained intact due to the chemical stability of SEI in diphenyl / THF. The disc containing dead lithium was separated and rinsed with THF to remove residual diphenyl / THF solution, and then transferred to a gas-tight glass bottle after drying.

[0202] S2. Deionized water was injected into the glass bottle using a gas-tight syringe, and after sealing, it was shaken to facilitate contact between the SEI-wrapped dead lithium and water (SEI partially dissolves in water, releasing internal lithium to participate in the reaction). Dead lithium reacts with water:

[0203] The volume of H2 generated is proportional to the mass of dead lithium.

[0204] S3. The entire process was carried out in an argon (Ar) atmosphere glove box, and the generated H2 was collected in a vacuum aluminum foil bag using a gas-tight syringe. Ensure that Ar is used as an internal standard gas with a constant volume for subsequent calibration.

[0205] S4. Use a gas chromatograph for detection, use the thermal conductivity difference between H2 and carrier gas (Ar) to detect the signal, use a thermal conductivity detector (TCD) to detect the concentration of H2, record the ratio of H2 peak area to Ar peak area, and substitute into the calibration curve to calculate the amount of substance of H2, and then convert the mass of dead lithium (1 mol H2 corresponds to 2 mol Li), the calculation formula is: dead lithium mass = (nH2 x 2 x 6.941) / 1; repeat the measurement 3 times to take the average value. The test results are summarized in Table 1.

[0206] Table 1

[0207]

[0208] From Example 1 to Example 20, Comparative Example 1 to Comparative Example 5 and Table 1, it can be seen that:

[0209] (1) Comparative Example 1 and Example 1

[0210] Comparative Example 1 does not add an electrolyte additive, i.e., does not add compound 1, to the electrolyte, while in Example 1, 5% by mass of compound 1 based on the total mass of the electrolyte is added as an electrolyte additive; from Table 1, the cycle performance (@80%SOH) of Example 1 reaches 380 cls, which is much higher than the cycle performance (@80%SOH) of Comparative Example 1, which is 201 cls, and the dead lithium mass (@50 cls) of Example 1 is only 1.58 mg cm -3 , which is much smaller than 2.99 mg cm -3 of Comparative Example 1; the cycle performance of Example 1 is significantly improved and the dead lithium mass is reduced; it can be seen that in Example 1, the nitrate group in compound 1 can decompose to form a nitrogen-rich interface layer, and the organic group can decompose to form an organic compound-rich interface layer, effectively reducing the consumption of active lithium metal and significantly improving the cycle life of the battery.

[0211] In combination with Figure 1 and Figure 2 , it can be seen that the soft pack battery prepared by using the electrolyte of Example 1 has a capacity retention rate of more than 80% after 380 cycles, while the soft pack battery prepared by using the electrolyte of Comparative Example 1 has a capacity retention rate of 80% after 201 cycles; under the condition of consistent capacity retention rate, the cycle number of the soft pack battery of Comparative Example 1 is significantly reduced, which shows that by adding compound 1 in Example 1, the cycle number of the battery can be improved.

[0212] Similarly, Comparative Example 2 and Example 9, Comparative Example 2 also does not add an electrolyte additive, and the cycle performance of Comparative Example 2 is significantly reduced and the dead lithium mass is significantly increased; Comparative Example 3 and Example 10, Comparative Example 3 also does not add an electrolyte additive, and the cycle performance of Comparative Example 3 is significantly reduced and the dead lithium mass is significantly increased;

[0213] (2) Example 1 to Example 20

[0214] From Table 1, it can be seen that in Examples 1 to 20, by using compounds 1 to 8 as electrolyte additives, the mass content of the electrolyte additive is 0.1% to 15%, in combination with a lithium salt, a coordination type solvent and a non-coordination type solvent, the battery prepared has a cycle performance (@80%SOH) ≥ 238 cls and a dead lithium mass ≤ 2.57 mg cm -3, the cycle performance (@80%SOH) of 222 cls, the dead lithium mass of 2.70 mg cm -3 It can be seen that the batteries prepared in Examples 1 to 20 have good cycle performance and the dead lithium mass is significantly reduced.

[0215] (3) Comparison between Comparative Example 4 and Example 13

[0216] In Comparative Example 4, LiNO3 is used as an electrolyte additive, and the mass percentage is 15%; while in Example 13, Compound 1 is used as an electrolyte additive, and the mass percentage is 15%. The mass percentage of the electrolyte additive in Example 13 and Comparative Example 4 is the same, but the cycle performance (@80%SOH) of Comparative Example 4 is only 176 cls, which is much smaller than 264 cls of Example 13. The dead lithium mass (@50 cls) of Comparative Example 4 is as high as 3.41 mg cm -3 which is much greater than 2.55 mg cm -3 of Example 13. It can be seen that when LiNO3 is used as an electrolyte additive, the cycle performance of the battery is significantly poorer and the dead lithium mass is significantly higher.

[0217] The solubility of LiNO3 in the electrolyte is low, and LiNO3 is not fully dissolved in Comparative Example 4. The inventors speculate that as the cycle time is prolonged, the lithium negative electrode interface side reaction increases, and LiNO3 will be quickly consumed, thereby affecting the cycle life and cycle performance of the battery. While the present application uses Compound 1 as an electrolyte additive, Compound 1 has good solubility in the electrolyte. In the early stage of battery cycling, the electrolyte additive can be maintained at a high concentration. As the cycle time is delayed, even if the electrolyte additive is quickly consumed, the concentration of the electrolyte additive is reduced to a certain extent, but it still maintains a high concentration, ensuring the cycle life and cycle performance of the battery. Therefore, compared with Comparative Example 4, the battery of Example 13 has better cycle performance and significantly less dead lithium mass.

[0218] (4) Comparison between Comparative Example 5 and Example 14

[0219] In Comparative Example 5, LiNO3 is used as an electrolyte additive, and the mass percentage is 1%; while in Example 14, Compound 1 is used as an electrolyte additive, and the mass percentage is 1%. The mass percentage of the electrolyte additive in Example 14 and Comparative Example 5 is the same, but the cycle performance (@80%SOH) of Comparative Example 5 is 231 cls, which is less than 355 cls of Example 14. The dead lithium mass (@50 cls) of Comparative Example 5 is 2.65 mg cm -3 which is greater than 1.71 mg cm -3It can be seen that the cycle performance of the battery is obviously poorer and the dead lithium mass is obviously higher when LiNO3 is used as an electrolyte additive.

[0220] In Comparative Example 5, LiNO3 is not fully dissolved. The inventors speculate that as the cycle time is prolonged, the lithium negative electrode interface side reaction increases, LiNO3 is quickly consumed, thereby affecting the cycle life and cycle performance of the battery. In the present application, compound 1 is used as an electrolyte additive. Compound 1 has good solubility in the electrolyte, so compared with Comparative Example 5, the battery of Example 14 has better cycle performance and significantly less dead lithium mass.

[0221] The electrolyte additive, electrolyte, and battery provided by the embodiments of the present application are described in detail above. The principles and implementation modes of the present application are described by applying specific examples in this document. The above description of the embodiments is only used to help understand the method of the present application and its core idea; at the same time, for those skilled in the art, according to the idea of the present application, the specific implementation mode and application range will be changed; in summary, the content of the specification should not be understood as a limitation of the present application.

Claims

1. An electrolyte, characterized by, The lithium salt, the solvent, and the electrolyte additive; The electrolyte additive is selected from at least one of the following compounds: ； The lithium salt is selected from one or more of lithium bisfluorosulfonylimide, lithium bisfluorooxalate borate, and lithium bisoxalate borate; The solvent includes a complexing solvent and a non-complexing solvent; The cycle number at which the battery including the electrolyte reaches a capacity retention rate of 80% is greater than or equal to 238 cycles, and the dead lithium mass of the battery after 50 cycles is less than or equal to 2.57 mg / cm 3 .

2. The electrolyte according to claim 1, characterized in that, The mass percentage of the electrolyte additive is 0.1% to 15% based on the total mass of the electrolyte.

3. The electrolyte of claim 2, wherein, The mass percentage of the lithium salt is 5% to 35% based on the total mass of the electrolyte; The mass percentage of the lithium salt is 5% to 35% based on the total mass of the electrolyte; The mass percentage of the lithium salt is 5% to 35% based on the total mass of the electrolyte.

4. The electrolyte according to claim 3, characterized in that The mass percentage of the electrolyte additive is 1% to 10%, the mass percentage of the lithium salt is 22% to 24%, and the mass percentage of the solvent is 66% to 77% based on the total mass of the electrolyte.

5. A battery, characterized by The battery is a lithium ion battery.

6. The battery of claim 5, wherein, The battery is a lithium ion battery.

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