Electrolyte and lithium ion battery

Abstract

The invention discloses an electrolyte and a lithium ion battery, the electrolyte comprises an organic solvent, a lithium salt, a first additive and a second additive, the first additive comprises an additive A and an additive B, the additive A comprises a benzene ring, a sulfonate group and an alkynyl group, the additive B comprises cresol diphenyl ester, and the battery comprises a positive electrode, a negative electrode and the electrolyte. The positive electrode includes a positive active material and the negative electrode includes a negative active material. And the positive electrode active material is lithium manganate. Compared with the prior art, by adding the first additive, the compactness and the stability of a CEI film on the surface of the positive electrode can be improved, the protection on positive electrode lithium manganate is enhanced, the side reaction of the positive electrode and an electrolyte caused by high-temperature decomposition of the CEI film is avoided, and the influence of manganese ion dissolution at high temperature on the battery performance is further reduced; and the high-temperature cycle performance of the lithium manganate battery is improved.

Description

Technical Field

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

[0002] Lithium manganese oxide material (LiMn 2 O 4 ) is widely considered to be a potential lithium-ion battery cathode active material due to its low cost, environmental protection and high voltage platform. However, lithium manganese oxide has structural distortion problems caused by the Jahn-Teller effect, resulting in poor cycle performance. At the same time, LiPF in the electrolyte 6 With H 2 The hydrofluoric acid (HF) generated by the reaction of O will accelerate the dissolution of manganese, seriously affecting the capacity retention rate of the battery. Especially under high temperature conditions, the dissolution rate of manganese increases significantly, further reducing the high temperature performance of lithium manganese oxide.

[0003] Recent studies have shown that by adding electrolyte additives to improve the solid electrolyte interface of the battery, the dissolution of manganese can be effectively inhibited, thereby significantly improving the performance of lithium manganese oxide batteries. However, although the existing commonly used electrolyte film-forming additives can form a CEI film on the positive electrode surface, most CEI films are easily decomposed at high temperatures and cannot effectively prevent the dissolution of manganese, resulting in the battery's performance in high-temperature cycles is still not ideal.

[0004] Therefore, there is an urgent need for an electrolyte and a lithium-ion battery to solve the above problems. Summary of the invention

[0005] In view of this, the present invention discloses an electrolyte and a lithium-ion battery, which improves the protection of the positive and negative electrodes at high temperatures, thereby helping to improve the high-temperature cycle performance of lithium manganese oxide batteries. The technical solution of the present invention is implemented as follows:

[0006] The first aspect of the present invention discloses an electrolyte, comprising an organic solvent, a lithium salt, a first additive and a second additive;

[0007] Wherein, the first additive includes additive A and additive B;

[0008] Additive A includes a benzene ring, a sulfonate group and an alkynyl group, and additive B includes diphenyl cresol;

[0009] The structural formula of additive A is as follows:

[0010]

[0011] Wherein, R includes any one of C1 to C4 hydrocarbon groups.

[0012] Specifically, R in the additive A further includes an alkynyl group.

[0013] Optionally, the mass ratio of the additive A to the additive B is (1-1.5):1.

[0014] Optionally, the mass percentage of the first additive in the electrolyte is 1.0% to 2.0%.

[0015] Specifically, the second additive includes methylene cyclomethanedisulfonate, vinylene carbonate and a lithium salt additive.

[0016] Optionally, the lithium salt additive includes at least one of lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium difluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonylimide), and lithium bis(trifluoromethanesulfonylimide).

[0017] Optionally, the mass ratio of methylene cyclohexane disulfonate, vinylene carbonate and lithium difluorooxalatoborate is (0.05-0.15):(0.5-1.5):(0.3-0.7).

[0018] Specifically, the total mass of the second additive accounts for 2% of the total mass of the electrolyte.

[0019] Optionally, the organic solvent includes ethylene carbonate, diethyl carbonate, or ethyl methyl carbonate.

[0020] Specifically, the lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl imide) and lithium bis(fluorosulfonyl imide).

[0021] The second aspect of the present invention discloses a lithium-ion battery, comprising: a positive electrode, a negative electrode and an electrolyte; wherein the electrolyte is any one of the electrolytes disclosed in the first aspect above, and the positive electrode comprises a positive electrode active material, and the positive electrode active material is lithium manganate.

[0022] The advantages of the present invention are as follows:

[0023] In the present invention, by adding additives A and additive B to the electrolyte, a dense and stable CEI film can be formed on the surface of the positive electrode. The film layer can effectively isolate the positive electrode active material from the electrolyte to prevent side reactions, and is not easy to decompose at high temperatures, thereby ensuring the protection of the positive electrode at high temperatures, so that the cycle stability of the lithium manganese oxide battery at high temperatures is significantly improved, and the capacity retention rate during high-temperature storage is significantly improved. DETAILED DESCRIPTION

[0024] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] Unless otherwise defined, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by technicians in the technical field to which the present invention belongs; the terms used in the specific implementation methods are only for the purpose of describing specific embodiments and are not intended to limit the present invention; the terms "including" and "having" in the description and claims of the present invention and any variations thereof are intended to cover non-exclusive inclusions.

[0026] In the description of the specific implementation methods of the present invention, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present invention, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.

[0027] Reference to "embodiments" in the present invention means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present invention. The appearance of the phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described in the present invention may be combined with other embodiments.

[0028] In the description of the embodiments of the present invention, the term "and / or" is only a description of the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in the present invention generally indicates that the associated objects before and after are in an "or" relationship.

[0029] It should be noted that, for the convenience of description, in the following embodiments, all identical technical features are marked with the same symbols.

[0030] In the field of batteries, lithium manganese oxide materials (LiMn 2 O 4 ) has the advantages of low cost, environmental protection and high voltage platform, and is widely regarded as a potential lithium-ion battery positive electrode active material. However, lithium manganese oxide has structural distortion problems caused by the Jahn-Teller effect, resulting in poor cycle performance. At the same time, LiPF in the electrolyte 6 With H2 The hydrofluoric acid (HF) generated by the reaction of O will accelerate the dissolution of manganese, seriously affecting the capacity retention rate of the battery. Especially under high temperature conditions, the dissolution rate of manganese increases significantly, further reducing the high temperature performance of lithium manganese oxide.

[0031] The prior art adds additives to the electrolyte to form a CEI film on the positive electrode surface to protect the positive electrode and inhibit the dissolution of manganese. However, most CEI films are still easy to decompose at high temperatures and cannot effectively prevent the dissolution of manganese, and the effect of improving the high-temperature cycle performance of lithium manganate batteries is still unsatisfactory.

[0032] Therefore, the present application provides an electrolyte and a battery for improving the high temperature cycle performance of lithium manganese oxide.

[0033] The embodiments of the present invention will be described in more detail below by way of examples. It should be noted that the embodiments of the present invention are not limited to these examples.

[0034] The first aspect of the present invention discloses an electrolyte comprising an organic solvent, a lithium salt, a first additive and a second additive.

[0035] The first additive includes additive A and additive B, additive A includes a benzene ring, a sulfonate group and an alkynyl group, and additive B includes diphenyl cresol.

[0036] The structural formula of additive A is as follows:

[0037]

[0038] Wherein, R includes any one of C1 to C4 hydrocarbon groups.

[0039] Through the above arrangement, the benzene ring and alkynyl group in additive A can participate in the CEI film formation on the positive electrode surface, and the HOMO energy level of additive B is significantly higher than that of common solvents, and can form a CEI film on the positive electrode with additive A first, so that the CEI film can be formed on the positive electrode before the electrolyte and the positive electrode have a side reaction of dissolving manganese ions, isolating the positive electrode from the electrolyte, protecting the positive electrode surface, and preventing the positive electrode from being corroded. In addition, additive B forms a CEI film containing a P compound on the positive electrode, which helps to improve the quality of the CEI film, forms a dense and stable CEI film on the positive electrode surface, and prevents the CEI film from decomposing in a high temperature environment, thereby helping to improve the high temperature performance of lithium manganese oxide batteries.

[0040] In addition, the sulfonate group in additive A can form an SEI film at the negative electrode, inhibiting the dissolution of manganese from causing side effects on the negative electrode surface. Through this setting, while protecting the positive electrode and inhibiting the dissolution of manganese, the negative electrode is also protected to prevent the manganese ions in the electrolyte from affecting the negative electrode. This double-sided protection method can further improve the high-temperature performance of the battery and prevent capacity decay.

[0041] In some embodiments, R in additive A further comprises an alkynyl group.

[0042] Through this setting, the alkynyl group has a higher reactivity, which enables the alkynyl group to form a uniform CEI film with good mechanical properties on the positive electrode surface. By increasing the alkynyl group, the mechanical properties and uniformity of the CEI film can be further improved, thereby alleviating the phenomenon of high-temperature manganese ion dissolution and improving the electrochemical performance of the battery at high temperature.

[0043] In some embodiments, the mass ratio of additive A to additive B is (1-1.5):1.

[0044] In some embodiments, the mass percentage of the first additive in the electrolyte is 1.0% to 2.0%.

[0045] In specific applications, in addition to the end points of 1.0% and 2.0% in the mass percentage range, any value in the above mass percentage range can be selected, such as 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, etc.

[0046] In some embodiments, the second additive includes at least one of methylene cyclohexanedisulfonate, vinyl sulfite, vinyl sulfate, 1,3-propylene sultone, 4-methylethylene sulfate, bisfluoroethylene carbonate, fluoroethylene carbonate, 1,3-propane sultone, vinylene carbonate, vinyl ethylene carbonate, and a lithium salt additive.

[0047] Specifically, the lithium salt additive includes at least one of lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium difluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonylimide), and lithium bis(trifluoromethanesulfonylimide).

[0048] The term "at least one" in the present invention refers to selecting one of the materials listed above, or selecting a mixture of two of the materials listed above, but is not limited to two. A person skilled in the art may select a greater number. The method may be freely implemented within the scope of understanding of a person skilled in the art. The present invention does not impose any limitation on this.

[0049] Through the above-mentioned arrangement, a second additive is added to the electrolyte, and the second additive can work together with the first additive to form a protective film (SEI film and CEI film) on the surface of the positive electrode and the surface of the negative electrode, and the formed SEI and CEI films have high density and stability, which can further improve the quality of the negative electrode SEI film and the negative electrode CEI film.

[0050] In addition, during the first charge and discharge cycle of the battery, the lithium salt additive in the second additive and the additive B with a higher HOMO energy level work together to further accelerate the formation of a stable CEI film on the positive electrode surface during the first charge and discharge, protecting the positive electrode active material, so that only Li+ can shuttle back and forth from the SEI film during the subsequent charge and discharge process, avoiding the dissolution of Mn3+ in the positive electrode active material into the electrolyte. It not only protects the positive electrode active material, but also prevents the electrolyte from being continuously oxidized and reduced, improving the cycle stability of lithium manganese oxide lithium ions.

[0051] In some preferred examples, the second additive is selected from methylene cyclohexane disulfonate, vinylene carbonate and lithium difluorooxalate borate.

[0052] In some embodiments, the mass ratio of methylene cyclohexane disulfonate, vinylene carbonate and lithium difluorooxalatoborate in the second additive is (0.05-0.15):(0.5-1.5):(0.3-0.7).

[0053] In some embodiments, the total mass of the second additive accounts for 2% of the total mass of the electrolyte.

[0054] In some embodiments, the organic solvent includes at least one of carbonates, carboxylates, and aromatic hydrocarbons.

[0055] In some embodiments, the carbonate includes halogenated carbonate and / or non-halogenated carbonate.

[0056] In some embodiments, the halogenated carbonate includes any one or a combination of at least two of fluoroethylene carbonate, bisfluoropropylene carbonate, trifluoroethyl methyl carbonate, trifluoromethylethylene carbonate, 4-trifluoromethylethylene carbonate, chloroethylene carbonate, di(2,2,2-trifluoroethyl) carbonate, or 1,1,1,3,3,3-hexafluoroisopropyl acrylate.

[0057] In some embodiments, the non-halogenated carbonate includes any one of ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, or ethyl methyl carbonate, or a combination of at least two thereof.

[0058] In some embodiments, the carboxylate includes a halogenated carboxylate and / or a non-halogenated carboxylate.

[0059] In some embodiments, the halogenated carboxylic acid ester includes any one of propyl fluorobutyrate, propyl fluoroacetate, ethyl fluoroacetate, isopropyl fluoroacetate, butyl fluoropropionate, isopropyl fluoropropionate, ethyl fluorobutyrate, methyl fluoropropionate, ethyl fluoropropionate, or propyl fluoropropionate, or a combination of at least two thereof.

[0060] In some embodiments, the non-halogenated carboxylic acid ester includes any one or a combination of at least two of ethyl acetate, methyl acetate, propyl butyrate, propyl acetate, isopropyl acetate, butyl propionate, isopropyl propionate, ethyl butyrate, methyl propionate, ethyl propionate or propyl propionate.

[0061] In some embodiments, the aromatic hydrocarbon includes a halogenated aromatic hydrocarbon and / or a non-halogenated aromatic hydrocarbon.

[0062] In some embodiments, the halogenated aromatic hydrocarbon includes any one or a combination of at least two of monofluorobenzene, difluorobenzene, 1,3,5-trifluorobenzene, trifluorotoluene, 2-fluorotoluene, or 2,4-dichlorotrifluorotoluene.

[0063] In some embodiments, the non-halogenated aromatic hydrocarbon includes at least one of benzene, toluene, xylene, styrene, biphenyl, phenol, and naphthalene.

[0064] In a preferred embodiment, the organic solvent includes ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0065] In a preferred embodiment, the mass ratio of ethylene carbonate, diethyl carbonate and ethyl methyl carbonate is 0.1:1:0.5

[0066] In some embodiments, the lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl imide), and lithium bis(fluorosulfonyl imide).

[0067] The second aspect of the present invention discloses a lithium-ion battery, comprising: a positive electrode, a negative electrode and an electrolyte, wherein the electrolyte is any one of the electrolytes disclosed in the first aspect above, and the positive electrode comprises a positive electrode active material, and the positive electrode active material is lithium manganate.

[0068] In some embodiments, the positive electrode includes a positive electrode current collector and a positive electrode active layer disposed on the positive electrode current collector, and the positive electrode active layer includes a positive electrode active material.

[0069] In some embodiments, the positive electrode current collector may be an aluminum (Al) foil, but is not limited thereto.

[0070] In some embodiments, the positive electrode active layer includes a binder, which can improve the bonding between the positive electrode active material particles and also improve the bonding between the positive electrode active layer and the positive electrode current collector.

[0071] In some embodiments, non-limiting examples of binders include polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, and the like.

[0072] In some embodiments, the positive electrode active layer includes a conductive agent so that the electrode has a certain conductivity. The conductive agent may include any conductive material as long as it does not cause chemical changes. Non-limiting examples of conductive materials include carbon-based materials (e.g., natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.), metal-based materials (e.g., metal powder, metal fiber, etc., including, for example, copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives) and mixtures thereof.

[0073] In some embodiments, the negative electrode includes a negative electrode current collector and a negative electrode active layer disposed on the negative electrode current collector, and the negative electrode active layer includes a negative electrode active material.

[0074] In the present invention, the specific types of negative electrode active materials are not subject to specific restrictions and can be selected according to demand. Specifically, the negative electrode active material is selected from one or more of natural graphite, artificial graphite, mesophase microcarbon beads (referred to as MCMB), hard carbon, soft carbon, silicon, silicon-carbon composites, Li-Sn alloys, Li-Sn-O alloys, Sn, SnO, SnO2, spinel-structured lithiated TiO2-Li4Ti5O12, and Li-Al alloys. Non-limiting examples of carbon materials include crystalline carbon, amorphous carbon, and mixtures thereof. Crystalline carbon can be amorphous or flaky, flake-shaped, spherical or fibrous natural graphite or artificial graphite. Amorphous carbon can be soft carbon, hard carbon, mesophase pitch carbide, calcined coke, etc.

[0075] In some embodiments, metal elements and metal compounds can also be selected as negative electrode active materials, such as compounds containing metals or metalloids such as Li, Ag, Al, Bi, Cu, Ga, Ge, In, Ni, Pb, Sb, Si, Sn, Sr, and Zn.

[0076] In some embodiments, the negative electrode active layer may include a binder; the binder improves the bonding between negative electrode active material particles and the bonding between the negative electrode active material and the current collector.

[0077] In some embodiments, non-limiting examples of binders include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, and the like.

[0078] In some embodiments, the negative electrode active layer can be obtained by coating a negative electrode slurry on a negative electrode current collector and then drying the negative electrode slurry, wherein the negative electrode slurry includes at least a negative electrode active material and a negative electrode binder. When an aqueous solvent is used as a liquid medium for forming the negative electrode slurry, a thickener is preferably used for slurrying, and the thickener can generally be used to adjust the viscosity of the slurry.

[0079] In some embodiments, the aforementioned viscosity enhancer may be one or more of the following: carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, and salts thereof.

[0080] In some embodiments, the mass proportion of the thickener in the negative electrode slurry can be 0.1%-5%, for example, 0.1%, 0.2%, 0.5%, 0.6%, 1%, 2%, 3%, 4%, 5%, etc., preferably 0.5%-3%, and more preferably 0.6%-2%.

[0081] In some embodiments, the negative electrode active layer includes a conductive material so that the electrode has conductivity. The conductive material may include any conductive material as long as it does not cause chemical changes. Non-limiting examples of conductive materials include carbon-based materials (e.g., natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.), metal-based materials (e.g., metal powder, metal fiber, etc., such as copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives) and mixtures thereof.

[0082] In some embodiments, the negative electrode current collector can be selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

[0083] In some embodiments, the lithium ion battery of the present invention further comprises a separator disposed between the positive electrode and the negative electrode, and the separator can insulate and protect the positive electrode and the negative electrode to prevent the positive and negative electrodes from contacting and causing a short circuit. The material and shape of the separator used in the lithium ion battery of the present invention are not particularly limited, and it can be any technology disclosed in the prior art.

[0084] In some embodiments, the separator includes a polymer or an inorganic substance formed of a material that is stable to the electrolyte of the present application.

[0085] In some embodiments, the separator may include a substrate layer and a surface treatment layer. The substrate layer is a non-woven fabric, a film or a composite film with a porous structure, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate and polyimide.

[0086] The embodiments of the present invention will be described in more detail below through examples and comparative examples, wherein all examples and comparative examples are lithium ion battery sample groups prepared by the same process.

[0087] It should be noted that the embodiments of the present invention are not limited to these examples.

[0088] Example 1

[0089] The preparation process of this embodiment is as follows:

[0090] 1. Preparation of electrolyte

[0091] First, ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) are added into a container and mixed for 30 minutes to form an organic solvent. In terms of the total mass percentage of the organic solvent, the mass percentage of ethylene carbonate (EC) in the organic solvent is 20%, the mass percentage of diethyl carbonate (DEC) is 30%, and the mass percentage of ethyl methyl carbonate (EMC) is 50%.

[0092] Then slowly add lithium salt to the organic solvent and continue stirring for 30 minutes. The lithium salt includes a certain proportion of lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI), so that the concentration of lithium hexafluorophosphate (LiPF6) in the electrolyte is 0.9 mol / L and the concentration of lithium bis(fluorosulfonyl)imide (LiFSI) in the electrolyte is 0.3 mol / L.

[0093] Then, lithium salt additive lithium difluorooxalate borate was added, and the mixture was stirred for 30 minutes to make the solution uniform. Then, a certain ratio of methylene disulfonate (MMDS) and vinylene carbonate (VC) was added, and the mixture was stirred for 30 minutes to make the solution uniform.

[0094] Finally, a certain amount of the first additive is added and stirred for about 1 hour to complete the preparation of the electrolyte. In this embodiment, the additive A in the first additive is propargyl benzenesulfonate, wherein the R group is -CH2-. The ratio of the additive A propargyl benzenesulfonate and the additive B diphenyl cresol phosphate is 2:1.

[0095] Taking the mass of the electrolyte as 100%, the mass proportion of the first additive in the electrolyte is 1%; in the second additive, the mass proportion of ethylene carbonate is 0.1%, the mass proportion of diethyl carbonate is 1%, and the mass proportion of methyl ethyl carbonate is 0.5%.

[0096] In this embodiment, the structural formula of additive A is as follows:

[0097]

[0098] 2. Preparation of positive electrode

[0099] The positive electrode active material lithium manganese oxide, the conductive agent superconducting carbon (Super-P), and the binder polyvinylidene fluoride (PVDF) are mixed evenly in a mass ratio of 90:7:3 to form a positive electrode slurry, the positive electrode slurry is coated on both surfaces of the current collector aluminum foil, and dried at 100°C to form a positive electrode active material layer, and then cold pressed, trimmed, cut into pieces, and slit into strips to form a lithium-ion battery positive electrode.

[0100] 3. Preparation of negative electrode

[0101] The negative electrode active material graphite, conductive agent superconducting carbon (Super-P), binder sodium carboxymethyl cellulose (CMC), binder styrene butadiene rubber (SBR) are made into negative electrode slurry at a mass ratio of 96.5:1.0:1.0:1.5, coated on the current collector copper foil and dried at 90°C to form a negative electrode active material layer, and then cold pressed, trimmed, cut into pieces, and slit, and then the negative electrode of the lithium-ion battery is made. .

[0102] 4. Preparation of batteries

[0103] The positive and negative electrodes prepared above are stacked crosswise, and a separator is inserted between adjacent positive and negative electrodes to form a battery core. The battery core is placed in a battery case, and a battery top cover is set on the open end of the case to seal the battery core in the battery case. Then, the electrolyte prepared above is injected into the battery case through the injection hole on the battery top cover to make the electrolyte infiltrate the battery core. Finally, the injection hole is sealed to make a lithium-ion battery.

[0104] Example 2

[0105] 1. Preparation of electrolyte

[0106] The preparation method of the electrolyte provided in this embodiment is the same as the steps of Example 1, except that the ratio of additive A propargyl benzenesulfonate and additive B diphenyl cresol phosphate is 1:1; the mass proportion of the first additive in the electrolyte is 1.5%.

[0107] 2. Preparation of positive electrode

[0108] The preparation method of the positive electrode provided in this embodiment is the same as that of embodiment 1 in each step.

[0109] 3. Preparation of negative electrode

[0110] The preparation method of the negative electrode provided in this embodiment is the same as that of Embodiment 1 in each step.

[0111] 4. Preparation of batteries

[0112] The preparation method of the battery provided in this embodiment is the same as that of embodiment 1 in each step.

[0113] Example 3

[0114] 1. Preparation of electrolyte

[0115] The preparation method of the electrolyte provided in this embodiment is the same as the steps of Example 1, except that the ratio of the additive A propargyl benzenesulfonate and the additive B diphenyl cresol phosphate is 1.3:1; and the mass proportion of the first additive in the electrolyte is 1.5%.

[0116] 2. Preparation of positive electrode

[0117] The preparation method of the positive electrode provided in this embodiment is the same as that of embodiment 1 in each step.

[0118] 3. Preparation of negative electrode

[0119] The preparation method of the negative electrode provided in this embodiment is the same as that of Embodiment 1 in each step.

[0120] 4. Preparation of batteries

[0121] The preparation method of the battery provided in this embodiment is the same as that of embodiment 1 in each step.

[0122] Example 4

[0123] 1. Preparation of electrolyte

[0124] The preparation method of the electrolyte provided in this embodiment is the same as the steps of Example 1, except that the ratio of the additive A propargyl benzenesulfonate and the additive B diphenyl cresol phosphate is 1.5:1; and the mass proportion of the first additive in the electrolyte is 1.5%.

[0125] 2. Preparation of positive electrode

[0126] The preparation method of the positive electrode provided in this embodiment is the same as that of embodiment 1 in each step.

[0127] 3. Preparation of negative electrode

[0128] The preparation method of the negative electrode provided in this embodiment is the same as that of Embodiment 1 in each step.

[0129] 4. Preparation of batteries

[0130] The preparation method of the battery provided in this embodiment is the same as that of embodiment 1 in each step.

[0131] Example 5

[0132] 1. Preparation of electrolyte

[0133] The preparation method of the electrolyte provided in this embodiment is the same as the steps of Example 1, except that the ratio of the additive A propargyl benzenesulfonate and the additive B diphenyl cresol phosphate is 1:1; and the mass proportion of the first additive in the electrolyte is 1.7%.

[0134] 2. Preparation of positive electrode

[0135] The preparation method of the positive electrode provided in this embodiment is the same as that of embodiment 1 in each step.

[0136] 3. Preparation of negative electrode

[0137] The preparation method of the negative electrode provided in this embodiment is the same as that of Embodiment 1 in each step.

[0138] 4. Preparation of batteries

[0139] The preparation method of the battery provided in this embodiment is the same as that of embodiment 1 in each step.

[0140] Example 6

[0141] 1. Preparation of electrolyte

[0142] The preparation method of the electrolyte provided in this embodiment is the same as the steps of Example 1, except that the ratio of the additive A propargyl benzenesulfonate and the additive B diphenyl cresol phosphate is 1:1; and the mass proportion of the first additive in the electrolyte is 2%.

[0143] 2. Preparation of positive electrode

[0144] The preparation method of the positive electrode provided in this embodiment is the same as that of embodiment 1 in each step.

[0145] 3. Preparation of negative electrode

[0146] The preparation method of the negative electrode provided in this embodiment is the same as that of Embodiment 1 in each step.

[0147] 4. Preparation of batteries

[0148] The preparation method of the battery provided in this embodiment is the same as that of embodiment 1 in each step.

[0149] Comparative Example 1

[0150] 1. Preparation of electrolyte

[0151] The preparation method of the electrolyte provided in this embodiment is the same as the steps of Embodiment 1, except that the first additive is not added to the electrolyte.

[0152] 2. Preparation of positive electrode

[0153] The preparation method of the positive electrode provided in this embodiment is the same as that of embodiment 1 in each step.

[0154] 3. Preparation of negative electrode

[0155] The preparation method of the negative electrode provided in this embodiment is the same as that of Embodiment 1 in each step.

[0156] 4. Preparation of batteries

[0157] The preparation method of the battery provided in this embodiment is the same as that of embodiment 1 in each step.

[0158] Comparative Example 2

[0159] 1. Preparation of electrolyte

[0160] The preparation method of the electrolyte provided in this embodiment is the same as the steps of Embodiment 1, except that the first additive in the electrolyte only includes the additive A propargyl benzenesulfonate.

[0161] 2. Preparation of positive electrode

[0162] The preparation method of the positive electrode provided in this embodiment is the same as that of embodiment 1 in each step.

[0163] 3. Preparation of negative electrode

[0164] The preparation method of the negative electrode provided in this embodiment is the same as that of Embodiment 1 in each step.

[0165] 4. Preparation of batteries

[0166] The preparation method of the battery provided in this embodiment is the same as that of embodiment 1 in each step.

[0167] Comparative Example 3

[0168] 1. Preparation of electrolyte

[0169] The preparation method of the electrolyte provided in this embodiment is the same as the steps of Embodiment 1, except that the first additive in the electrolyte only includes the additive B diphenyl cresol phosphate.

[0170] 2. Preparation of positive electrode

[0171] The preparation method of the positive electrode provided in this embodiment is the same as that of embodiment 1 in each step.

[0172] 3. Preparation of negative electrode

[0173] The preparation method of the negative electrode provided in this embodiment is the same as that of Embodiment 1 in each step.

[0174] 4. Preparation of batteries

[0175] The preparation method of the battery provided in this embodiment is the same as that of embodiment 1 in each step.

[0176] Comparative experiment:

[0177] The batteries of Examples 1-6 and Comparative Examples 1-3 were subjected to 55°C cycle test and 55°C storage test. The specific test methods are as follows:

[0178] 1. 55℃ cycle test: The battery is tested at 55℃, as follows: the divided battery is charged to 4.2V with 1C constant current and constant voltage, with a cut-off rate of 0.05C; then discharged to 3V with 1C constant current. After such charge / discharge cycles, the capacity retention rate after the target number of cycles is calculated to evaluate its cycle performance. Among them, the target number of cycles at 55℃ is 400 times.

[0179] 2. 55℃ storage test: Charge the divided battery to 4.2V with 1C constant current and constant voltage, with 0.05C as the cut-off rate; after being fully charged for 7 days, discharge it to 3V, and then perform a complete charge and discharge process again.

[0180] The test results are shown in the following table:

[0181]

[0182]

[0183] According to the above table, by comparing Example 1 with Comparative Example 1 and Comparative Example 2, Example 1 effectively improves the high temperature cycle performance and high temperature storage performance of the lithium manganese oxide battery by adding additive A and additive B to the electrolyte. The possible reason is that additive B has a higher HOMO energy level, and preferentially generates a CEI film at the positive electrode during the initial charge and discharge of the battery; and additive A has an acetylenic group with high reaction activity. Before the electrolyte reacts with the positive electrode, additive A and additive B jointly form a CEI film on the positive electrode surface to protect the positive electrode surface and effectively isolate the electrolyte from lithium manganese oxide. And additive B can generate a CEI film of a solder P compound, which can improve the compactness and stability of the CEI film, avoid the decomposition of the CEI film in a high temperature environment, and further improve the high temperature cycle performance and high temperature storage performance of the lithium manganese oxide battery. In addition, additive A also participates in the formation of an SEI film on the negative electrode surface, inhibiting the side effects of manganese ions on the negative electrode surface, and further improving battery performance.

[0184] It can be seen from Examples 2-4 that as the ratio of additive A in the first additive increases, the high temperature cycle performance and high temperature retention rate of the battery are improved.

[0185] It can be seen from Example 2, Example 5 and Example 6 that as the content of the first additive in the electrolyte increases, the high temperature cycle performance and high temperature retention rate of the battery are improved.

[0186] It should be pointed out that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. An electrolyte, characterized in that: comprising an organic solvent, a lithium salt, a first additive and a second additive; Wherein, the first additive includes additive A and additive B; Additive A includes a benzene ring, a sulfonate group and an alkynyl group, and additive B includes diphenyl cresol; The structural formula of additive A is as follows: Wherein, R includes any one of C1 to C4 hydrocarbon groups.

2. An electrolyte according to claim 1, characterized in that: The mass ratio of the additive A to the additive B is (1-1.5):

1.

3. An electrolyte according to claim 1, characterized in that: The mass percentage of the first additive in the electrolyte is 1.0% to 2.0%.

4. An electrolyte according to claim 1, characterized in that: The second additive includes methylene cyclomethanedisulfonate, vinylene carbonate and a lithium salt additive.

5. An electrolyte according to claim 4, characterized in that: The lithium salt additive includes at least one of lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium difluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonylimide), and lithium bis(trifluoromethanesulfonylimide).

6. An electrolyte according to claim 5, characterized in that: The mass ratio of the methylene cyclomethanedisulfonate, the vinylene carbonate and the lithium difluorooxalatoborate is (0.05-0.15):(0.5-1.5):(0.3-0.7).

7. An electrolyte according to claim 1, characterized in that: The total mass of the second additive accounts for 2% of the total mass of the electrolyte.

8. An electrolyte according to claim 1, characterized in that: The organic solvent includes ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate.

9. An electrolyte according to claim 1, characterized in that: The lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl imide) and lithium bis(fluorosulfonyl imide).

10. A lithium ion battery comprising: An electrolyte, a positive electrode and a negative electrode, characterized in that the electrolyte is the electrolyte described in any one of claims 1 to 9, the positive electrode comprises a positive electrode active material, and the positive electrode active material is lithium manganate.

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