Electrolyte and secondary battery

Abstract

The invention discloses an electrolyte and a secondary battery, the electrolyte comprises a solvent, a lithium salt and a first additive, the first additive has any one of the following structural formula: a fluorocarbon group in the first additive can be subjected to an oxidation-reduction reaction prior to the solvent to form a lithium fluoride-rich high-conductivity electrode interface film; the amino group can react with residual moisture and hydrogen ions in a battery system, so that the effects of removing water and acid are achieved, and the stability of the whole battery system is improved; a pyridine group in the first additive has relatively high oxidation-reduction activity and can be subjected to oxidation reaction on the surface of a positive electrode prior to a solvent to form a stable interfacial film, so that oxygenolysis of the solvent is inhibited, long-term stability of the interfacial film of a positive electrode electrolyte is maintained, and a positive electrode material and an electrolyte can be effectively isolated; the electrolyte is prevented from directly contacting and corroding the positive electrode material, so that the dissolution of transition metal is inhibited.

Description

Technical Field

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

[0002] In order to meet the demand for longer driving range of electric vehicles, lithium-ion batteries need higher energy density. Since energy density is equal to the product of voltage and specific capacity, where mass energy density = average operating voltage × mass specific capacity and volume energy density = average operating voltage × volume specific capacity, increasing the operating voltage of lithium-ion batteries becomes an effective way to increase energy density. For example, compared with the lithium metal and lithium ion couple (Li + / Li), a voltage higher than 4.3V can make the cobalt element of the ternary material lithium-ion battery (referring to the lithium-ion battery using nickel-cobalt-manganese composite compound as the positive electrode active material) change from Co to 3+ Oxidized to Co 4+ , releasing more energy, thereby greatly improving the energy density of the battery.

[0003] However, traditional carbonate electrolytes have a narrow electrochemical window, with an operating voltage below 4.3V relative to the lithium metal and lithium ion pair. When the voltage exceeds 4.3V, the electrolyte itself is prone to decomposition, and side reactions between the cathode and the electrolyte intensify, leading to the dissolution of transition metals in the nickel-cobalt-manganese cathode material, further promoting electrolyte decomposition. Once the electrolyte decomposes, it can lead to a decline in many aspects of battery performance, such as capacity decay, shortened cycle life, decreased coulombic efficiency, and increased internal resistance. Furthermore, if the gases generated during the electrolyte decomposition accumulate to a certain level within the sealed battery casing, the excessive pressure can cause the battery to bulge or even rupture. If exposed to sparks or other ignition sources, combustion or explosion accidents are likely to occur, posing a serious threat to user safety.

[0004] To this end, the present application aims to propose a new electrolyte and secondary battery to solve the above problems. Summary of the Invention

[0005] The main purpose of the present invention is to provide an electrolyte and a secondary battery, aiming to solve the technical problem in the prior art of how to improve the operating voltage of ternary material lithium-ion batteries while inhibiting the decomposition of the electrolyte at high voltage and interfacial side reactions.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides an electrolyte, comprising a solvent, a lithium salt and a first additive, wherein the first additive has any one of the following structural formulas:

[0007]

[0008] wherein R1, R2, R3, and R4 contain at least one fluorine atom;

[0009] R1, R2, R3, R4, R5, R6, and R7 are each independently selected from hydrogen, halogen, cyano, boric acid, amino, imino, substituted or unsubstituted C1-C8 alkyl, substituted or unsubstituted C2-C8 alkenyl, substituted or unsubstituted C1-C8 alkoxy, substituted or unsubstituted alkoxycarbonyl, and substituted or unsubstituted C6-C 12 One of the aromatic groups.

[0010] Furthermore, the first additive is selected from one of the following structural formulas:

[0011]

[0012] Furthermore, the mass of the first additive accounts for 0.01% to 2.0% of the total mass of the electrolyte.

[0013] Furthermore, the mass of the lithium salt accounts for 10.0% to 20.0% of the total mass of the electrolyte.

[0014] Furthermore, the mass of the solvent accounts for 65.0% to 89.0% of the total mass of the electrolyte.

[0015] Furthermore, the lithium salt includes one or more of lithium hexafluorophosphate, lithium difluorophosphate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium difluorobis(oxalatophosphate), lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethylsulfonyl)imide.

[0016] Furthermore, the solvent includes one or more of ethylene carbonate, ethyl acrylate, methyl acrylate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate and methyl propyl carbonate.

[0017] Furthermore, the halogen includes one or more of fluorine, chlorine, bromine, and iodine; the alkyl includes one or more of methyl, ethyl, isopropyl, tert-butyl, hexyl, octyl, decyl, dodecyl, and heptadecyl;

[0018] The alkenyl group includes one or more of vinyl, propenyl, butenyl, hexenyl, octenyl, decenyl, dodecenyl, 9-heptadecenyl, 1,4-pentadienyl, 1,5-hexadienyl, 1,6-heptadienyl, 1,7-octadienyl, 1,8-nonadienyl, and 1,9-decadienyl; the alkoxy group includes one or more of methoxy, ethoxy, propoxy, butoxy, pentyloxy, heptyloxy, hexyloxy, octyloxy, decyloxy, and dodecyloxy;

[0019] The alkoxycarbonyl group includes one or more of methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, butoxycarbonyl, pentyloxycarbonyl, heptyloxycarbonyl, hexyloxycarbonyl, decyloxycarbonyl, dodecyloxycarbonyl, octyloxycarbonyl, palmitoyloxycarbonyl, and stearoyloxycarbonyl; the aryl group includes one or more of phenyl, p-tolyl, p-nitrophenyl, o-methoxyphenyl, m-methoxyphenyl, p-methoxyphenyl, and p-nitromethoxyphenyl;

[0020] The substitution groups of the substituted C1-C8 alkyl group, substituted C2-C8 alkenyl group, substituted C1-C8 alkoxy group, substituted alkoxycarbonyl group, and substituted C6-C 12 aryl group each independently include one or more of -NH2, -F, -Cl, -Br, -I, -OH, -COOH, -NO2, -SO3H, -CHO, -SH, and -CN.

[0021] Furthermore, the electrolyte further includes a second additive, and the mass of the second additive accounts for 1.0% to 15.0% of the total mass of the electrolyte. ,

[0022] Furthermore, the second additive includes one or more of fluoroethylene carbonate, vinylene carbonate, ethylene sulfate, ethylene sulfite, sulfolane, tetravinylsilane, triallyl isocyanurate, triphenyl phosphate, trimethyl phosphate, tetrafluorophenyl acetate, and methylene methanedisulfonate.

[0023] On the one hand, the present invention provides a secondary battery, including a positive electrode sheet, an electrolyte, a separator, and a negative electrode sheet, wherein the electrolyte is the electrolyte described in any one of the above. !>

[0024] Furthermore, the positive electrode sheet includes an active material, and the active material is a ternary layered oxide positive electrode material with a general formula of LiNi x Co y Mn 1-x-y O2, where 0 < x < 1 and 0 < y < 1; the negative electrode sheet includes one or more of a metallic lithium negative electrode sheet, a metallic lithium alloy negative electrode sheet, a graphite negative electrode sheet, a silicon-based negative electrode sheet, a silicon-graphite composite negative electrode sheet, and a copper foil lithium-free negative electrode sheet; the separator includes one or more of a woven membrane, a non-woven membrane, a microporous membrane, a composite membrane, separator paper, a rolled membrane, a single-layer polypropylene membrane, a single-layer polyethylene membrane, PP + ceramic coating, PE + ceramic coating, double-layer PP / PE, three-layer PP / PE / PP, a polyester membrane, a cellulose membrane, a polyimide membrane, a polyamide membrane, a spandex membrane, and an aramid membrane.

[0025] Beneficial effects:

[0026] Compared with the prior art, an electrolyte in an embodiment of the present application includes a solvent, a lithium salt, and a first additive. The fluorine atoms in the first additive have high electronegativity and a small atomic radius, so that the fluorocarbon segments self-assemble on the interface in the liquid, thereby reducing the interfacial tension and improving the spreading ability of the electrolyte on the electrode surface. At the same time, the fluorocarbon group has high chemical stability and is not easily oxidized or reduced under high voltage conditions, ensuring that the first additive does not easily participate in unnecessary side reactions, but rather undergoes redox reactions before the solvent to form a high-conductivity electrode interface film rich in lithium fluoride. The amino group can react with residual water and hydrogen ions in the battery system, thereby achieving the effect of removing water and acid, which is beneficial to improving the stability of the entire battery system. The pyridine group in the first additive has a relatively high redox activity and can undergo oxidation reactions before the solvent on the positive electrode surface to form a stable interface film, inhibiting the oxidative decomposition of the organic solvent, maintaining the long-term stability of the CEI film, and effectively isolating the positive electrode material from the electrolyte, preventing the electrolyte from directly contacting and corroding the positive electrode material, thereby inhibiting the dissolution of transition metals, and facilitating high-temperature storage of lithium ions under high-voltage working environments.

[0027] Compared to the prior art, a secondary battery in an embodiment of the present application includes any of the above-mentioned electrolytes. It is understood that the battery of the present application may include the above-mentioned first additive, and the battery of the present application may include all the technical features and technical effects of the above-mentioned batteries, which will not be repeated here. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a graph showing the capacity retention rate after 500 cycles of 1C / 1C from 2.8V to 4.4V at 25°C according to an embodiment of the present invention;

[0029] Figure 2 This is a data graph of capacity retention after 500 cycles of 1C / 1C from 2.8V to 4.4V at 45°C according to another embodiment of the present invention.

[0030] The purpose, features and advantages of the present invention will be further described with reference to the accompanying drawings and in conjunction with the embodiments. DETAILED DESCRIPTION

[0031] It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0032] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like to indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, which is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the said features. In the description of the present invention, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined.

[0033] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed connections, detachable connections, or integral connections; they may refer to mechanical connections, direct connections, or indirect connections through an intermediate medium; they may refer to internal communication between two components or the interaction between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0034] In the present invention, unless otherwise expressly specified or limited, a first feature being "above" or "below" a second feature may include the first and second features being in direct contact, or may include the first and second features being in contact not directly but through another feature between them. Furthermore, a first feature being "above," "above," and "above" a second feature may include the first feature being directly above or obliquely above the second feature, or may simply mean that the first feature is higher in level than the second feature. A first feature being "below," "below," and "below" a second feature may include the first feature being directly below or obliquely below the second feature, or may simply mean that the first feature is lower in level than the second feature.

[0035] In this application, "and / or" describes the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. A and B can be singular or plural.

[0036] Various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity and should not be understood as a hard limitation on the scope of the present application; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numbers within the range. For example, the description of a range from 1 to 6 should be considered to have 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 range, such as 1, 2, 3, 4, 5 and 6, which applies regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0037] In the present application, "aryl or aromatic group" refers to an aromatic hydrocarbon group derived from an aromatic ring compound by removing a hydrogen atom, which may be a monocyclic aromatic group, a condensed aromatic group, or a polycyclic aromatic group. For polycyclic rings, at least one is an aromatic ring system. For example, "substituted or unsubstituted aryl having 6 to 40 ring atoms" refers to an aromatic group containing 6 to 40 ring atoms, preferably a substituted or unsubstituted aryl having 6 to 30 ring atoms, more preferably a substituted or unsubstituted aryl having 6 to 18 ring atoms, and particularly preferably a substituted or unsubstituted aryl having 6 to 14 ring atoms; suitable examples include, but are not limited to, phenyl, biphenyl, terphenyl, naphthyl, anthracenyl, phenanthrenyl, fluoranthenyl, triphenylene, pyrenyl, perylenyl, naphthphenyl, fluorenyl, perylene, acenaphthenyl, and their derivatives. It is understood that multiple aromatic groups may be interrupted by short non-aromatic units (e.g., <10% non-H atoms, such as C, N, or O atoms). Specifically, acenaphthene, fluorene, or 9,9-diarylfluorene, triarylamine, and diaryl ether systems are also included in the definition of aromatic groups. The heteroatom in the heterocyclic ring is one or more of oxygen, sulfur, nitrogen, and phosphorus atoms.

[0038] In a first aspect, embodiments of the present application provide an electrolyte and a battery, including a solvent, a lithium salt, and a first additive, wherein the first additive has any one of the following structural formulas:

[0039]

[0040] wherein R1, R2, R3, and R4 contain at least one fluorine atom;

[0041] R1, R2, R3, and R4 are each independently selected from hydrogen, halogen, cyano, boric acid, amino, imino, substituted or unsubstituted C1-C8 alkyl, substituted or unsubstituted C2-C8 alkenyl, substituted or unsubstituted C1-C8 alkoxy, substituted or unsubstituted alkoxycarbonyl, and substituted or unsubstituted C6-C 12 One of the aromatic groups.

[0042] In this embodiment, the structural formula of the first additive includes a pyridine ring (a six-membered heterocyclic ring containing a nitrogen atom replacing a carbon atom in the benzene ring). The unshared electron pair on the nitrogen atom participates in the formation of the π electron system, making the pyridine ring aromatic and more likely to lose electrons than the benzene ring. The electronegativity of the nitrogen atom is greater than that of the carbon atom, so it can attract more electron density, resulting in an uneven distribution of electrons on the pyridine ring. This asymmetric electron distribution makes the pyridine ring more susceptible to oxidation, has a higher redox potential, and can begin to lose electrons at a lower voltage, that is, undergo an oxidation reaction. Compared with other components in the electrolyte, under high voltage conditions, the pyridine ring is more likely to undergo preferential oxidation on the positive electrode surface. This preferential oxidation behavior enables the pyridine group to quickly form a stable interface film (also known as CEI film: cathode electrolyte interphase: positive electrode electrolyte interface film) on the surface of the positive electrode material, effectively isolating the positive electrode material from direct contact with the electrolyte.

[0043] It should be noted that in the embodiments of the present application, high voltage or high operating voltage refers to a voltage higher than 4.3V relative to the lithium metal and lithium ion electrode pair; low voltage or low operating voltage refers to a voltage lower than 4.3V relative to the lithium metal and lithium ion electrode pair.

[0044] In this embodiment, the amino group can react with residual water and hydrogen ions in the battery system, thereby removing water and acid, which helps improve the stability of the entire battery system. Specifically, the amino group is a good nucleophile that can react with the hydrogen atoms in water molecules to remove water. At the same time, the amino group is a weakly basic group that can accept one or more protons (i.e., H+), thereby neutralizing acidic substances in the environment and forming corresponding salts, which can remove acid from the battery system.

[0045] In the above embodiment, the fluorine atom has a high electronegativity and a small atomic radius, which allows the fluorocarbon chain segments to self-assemble on the interface in the liquid, thereby reducing the interfacial tension, which is beneficial to improving the spreading ability of the electrolyte on the electrode surface; at the same time, the fluorocarbon group has a high chemical stability and is not easily oxidized or reduced under high voltage conditions, ensuring that the first additive does not easily participate in unnecessary side reactions, but instead undergoes redox reactions before the solvent, forming a high-conductivity electrode interface film rich in lithium fluoride, thereby ensuring the stability of the electrode.

[0046] In the above embodiment, the solvent is a non-aqueous organic solvent, including one or more of ethylene carbonate, ethyl acrylate, methyl acrylate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate and methyl propyl carbonate. In the present application embodiment, the organic compound is non-aqueous or contains only a trace of moisture. Exemplary, it can be that the ethylene carbonate water organic solvent refers to a carbonate substance that does not contain free esters, propylene carbonate and diethyl carbonate, or it can be ethers such as tetrahydrofuran and dioxolane, or it can be acetonitrile, dimethyl sulfoxide, cyclopentane and fluoroethylene carbonate. Specifically, it can be one of the above examples, or it can be a variety of combinations, and the present embodiment does not specifically limit it.

[0047] In the above embodiment, the lithium salt is used to provide lithium ions for the electrolyte. The fluorine atoms in the first additive have high electronegativity and small atomic radius, which allows the fluorocarbon segments to self-assemble at the interface in the liquid, thereby reducing the interfacial tension and improving the spreading ability of the electrolyte on the electrode surface. At the same time, the fluorocarbon groups have high chemical stability and are not easily oxidized or reduced under high voltage conditions. This ensures that the first additive does not easily participate in unnecessary side reactions, but instead undergoes redox reactions before the solvent, forming a highly conductive electrode interface film rich in lithium fluoride. The amino groups can react with residual water and hydrogen ions in the battery system, thereby removing water and acid, which is beneficial to improving the stability of the entire battery system. The pyridine groups in the first additive have relatively high redox activity and can undergo oxidation reactions before the solvent on the positive electrode surface, forming a stable interface film, inhibiting the oxidative decomposition of the organic solvent, maintaining the long-term stability of the solid electrolyte interface film, and effectively isolating the positive electrode material from the electrolyte, preventing the electrolyte from directly contacting and corroding the positive electrode material, thereby inhibiting the dissolution of transition metals and improving the high-temperature storage and high-temperature cycling performance of lithium ions under high-voltage working environments.

[0048] In one embodiment, the first additive is selected from one of the following structural formulas:

[0049]

[0050] in, 2-fluoro-5-aminopyridine. In this embodiment, 2-fluoro-5-aminopyridine can be prepared by itself or purchased. Exemplarily, 2-fluoro-5-aminopyridine can be prepared by the following route: first, 2-fluoro-3-cyanopyridine is prepared by a halogenation reaction of 3-cyanopyridine and a fluorinating agent (such as KF), then 2-fluoro-5-nitropyridine is generated by a nitration reaction of 2-fluoro-3-cyanopyridine and a nitrating agent (such as a mixture of concentrated sulfuric acid and concentrated nitric acid), and finally 2-fluoro-5-nitropyridine is prepared by a nitration reaction of 2-fluoro-5-nitropyridine and a reducing agent (S n The nitro group was reduced to an amino group by a reduction reaction of Cl2 to prepare the target product 2-fluoro-5-aminopyridine.

[0051] It is 3-amino-1-2-4-5-fluoropyridine, which can be prepared by oneself or purchased, and will not be described in detail here.

[0052] In one embodiment, the mass of the first additive accounts for 0.01% to 2.0% of the total mass of the electrolyte. The mass of the lithium salt accounts for 10.0% to 20.0% of the total mass of the electrolyte. The mass of the solvent accounts for 65.0% to 89.0% of the total mass of the electrolyte. The electrolyte also includes a second additive, the mass of which accounts for 1.0% to 15.0% of the total mass of the electrolyte.

[0053] Exemplarily, the proportion of the first additive to the total mass of the electrolyte can be 0.1%, 0.5%, 1.0%, or 2.0%. Exemplarily, the proportion of the mass of the lithium salt to the total mass of the electrolyte can be 10%, 12.5%, or 20%. Exemplarily, the proportion of the mass of the solvent to the total mass of the electrolyte can be 65%, 70%, 75%, 80%, or 89%.

[0054] The present application does not impose any specific restrictions on the type of the second additive, which can be determined based on actual design requirements, such as improving various performance requirements of electrolysis.

[0055] Exemplarily, the second additive includes one or more of fluoroethylene carbonate, vinylene carbonate, vinyl sulfate, vinyl sulfite, cyclopentane, tetravinylsilane, triallyl isocyanurate, triphenyl phosphate, trimethyl phosphate, tetrafluorophenyl acetate, and methylene methanedisulfonate.

[0056] In the above embodiment, the proportion of the second additive was set to 1.0% to 15.0% based on experimental results. This is to ensure that the second additive can fully optimize battery performance without affecting the basic properties of the electrolyte. This avoids potential negative effects caused by excessive concentration. In actual applications, the specific addition ratio needs to be adjusted according to the specific design requirements and application scenarios of the battery.

[0057] In the above embodiment, within the mass ratio range, the lithium salt and the additive can be uniformly dispersed in the solvent.

[0058] In one embodiment, the lithium salt includes an organic salt and / or an inorganic salt, specifically including one or more of lithium hexafluorophosphate, lithium difluorophosphate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium difluorobis(oxalatophosphate), lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethylsulfonyl)imide.

[0059] In this embodiment, the organic salt refers to a compound composed of one or more organic cations or anions. Exemplary organic salts include lithium dioxalatoborate, lithium difluorooxalatoborate, lithium difluorobisoxalatophosphate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethylsulfonyl)imide. Inorganic salts refer to compounds composed of metal cations (such as lithium ions Li + ) and non-metallic anions (such as halogen ions such as fluorine, chlorine, bromine, iodine, or other simple anions). They do not contain complex organic molecular structures. Exemplary inorganic salts include lithium hexafluorophosphate and lithium difluorophosphate.

[0060] In one embodiment, the halogen includes one or more of fluorine, chlorine, bromine, and iodine; and / or

[0061] The alkyl group includes one or more of methyl, ethyl, isopropyl, tert-butyl, hexyl, octyl, decyl, dodecyl, and heptadecyl; and / or

[0062] The alkenyl group includes one or more of vinyl, propenyl, butenyl, hexenyl, octenyl, decenyl, dodecenyl, 9-heptadecenyl, 1,4-pentadienyl, 1,5-hexadienyl, 1,6-heptadienyl, 1,7-octadienyl, 1,8-nonadienyl, and 1,9-decadienyl; and / or

[0063] The alkoxy group includes one or more of methoxy, ethoxy, propoxy, butoxy, pentyloxy, heptyloxy, hexyloxy, octyloxy, decyloxy and dodecyloxy; and / or

[0064] The alkoxycarbonyl group includes one or more of methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, butoxycarbonyl, pentyloxycarbonyl, heptyloxycarbonyl, hexyloxycarbonyl, decyloxycarbonyl, dodecyloxycarbonyl, octyloxycarbonyl, palmityloxycarbonyl and stearyloxycarbonyl; and / or

[0065] The aryl group includes one or more of phenyl, p-tolyl, p-nitrophenyl, o-methoxyphenyl, m-methoxyphenyl, p-methoxyphenyl, and p-nitromethoxyphenyl; and / or

[0066] The substituted C1-C8 alkyl, substituted C2-C8 alkenyl, substituted C1-C8 alkoxy, substituted alkoxycarbonyl and substituted C6-C 12 The substituent groups of the aryl group independently include one or more of -NH2, -F, -Cl, -Br, -I, -OH, -COOH, -NO2, -SO3H, -CHO, -SH, and -CN.

[0067] It is understandable that the substituent group refers to the substituent in a substituted alkyl or heteroalkyl, substituted alkenyl or heteroalkenyl, substituted alkynyl or heteroalkynyl, substituted alkoxy, substituted acyloxy, substituted alkoxycarbonyl, substituted heterocyclic group, or substituted aryl.

[0068] The present application also provides a secondary battery, including a positive electrode sheet, an electrolyte, a separator, and a negative electrode sheet, wherein the electrolyte is the electrolyte described in any one of the above.

[0069] During the charging process of the battery, an external power source drives electrons to flow from the negative electrode sheet to the positive electrode sheet, while ions move in the electrolyte towards the positive electrode sheet. During the discharging process of the battery, redox reactions occur between the positive and negative electrode materials, electrons flow from the positive electrode sheet to the negative electrode sheet, and ions move from the positive electrode sheet to the negative electrode sheet. This process enables the battery to achieve the conversion between chemical energy and electrical energy.

[0070] The separator is a permeable membrane located between the positive electrode sheet and the negative electrode sheet. Its main function is to keep the positive electrode sheet and the negative electrode sheet separated to prevent battery short - circuit. At the same time, the separator also needs to allow charge carriers to pass through to ensure the closure of the chemical battery circuit. The separator is usually a polymer membrane with micropores, which needs to have certain chemical and electrochemical stability towards the electrolyte and electrode materials, and also needs to have sufficient mechanical strength to withstand the stress during battery assembly.

[0071] The electrolyte is the liquid medium responsible for transferring ions in the battery, and its working principle is to enable redox reactions between the positive and negative electrode materials. The performance of the electrolyte directly affects the charge - discharge efficiency and cycle life of the battery. During the battery cycle, the electrolyte will undergo a series of reactions with the surface of the negative electrode to form a SEI film (SEI: Solid Electrolyte Interfac, solid electrolyte interface film). The formation and properties of the SEI film have an important impact on the performance and life of the battery. On the one hand, the SEI film can prevent the direct contact between the electrode surface and the electrolyte, avoiding the reaction between the solute and solvent in the electrolyte and the electrode, thus improving the stability of the electrochemical energy storage device. On the other hand, the SEI film also plays a role in ion transport. By selectively conducting cations and blocking the diffusion of solvents and anions, it promotes the ion transport balance between the positive and negative electrodes.

[0072] In one embodiment, the positive electrode sheet includes an active material, and the active material is a ternary layered oxide positive electrode material with a general formula of LiNi x Co y Mn 1-x-y O2, where 0 < x < 1 and 0 < y < 1; the negative electrode sheet includes one or more of a metallic lithium negative electrode sheet, a metallic lithium alloy negative electrode sheet, a graphite negative electrode sheet, a silicon - based negative electrode sheet, a silicon - graphite composite negative electrode sheet, and a copper foil lithium - free negative electrode sheet.

[0073] For example, lithium alloy negative electrode plates can include alloys of lithium with tin, silicon, aluminum, etc.; graphite negative electrode plates include natural graphite and artificial graphite. In actual use, the voltage platform and capacity of the material can be adjusted by varying the ratio of nickel (Ni), cobalt (Co), and manganese (Mn), thereby optimizing the battery's energy density to a certain extent.

[0074] The present application will be described in detail below through specific examples. The following examples are only some examples of the present application and are not limitations of the present application.

[0075] Example 1:

[0076] This embodiment provides an electrolyte solution comprising a solvent, a lithium salt and a first additive, wherein the first additive has a structural formula of

[0077] The preparation method of the electrolyte comprises:

[0078] In an argon-filled glove box (moisture <10 ppm, oxygen <1 ppm), ethylene carbonate, ethyl methyl carbonate, and propylene carbonate were mixed in a mass ratio of 30:60:10 to obtain a solvent; 12.5% ​​lithium hexafluorophosphate was added to the solvent, and the components were mixed by stirring to obtain a lithium salt;

[0079] 0.5% of lithium bisfluorosulfonamide, 0.8% of lithium difluorophosphate, 0.5% of vinylene carbonate, 0.5% of ethylene carbonate and 0.8% of trimethyl phosphate are mixed to obtain a second additive;

[0080] 12.5% ​​of lithium hexafluorophosphate (lithium salt) is added to the solvent and mixed evenly, then the second additive is added to the solvent and mixed evenly, and finally 0.01% of the first additive is added to the solvent and mixed evenly to obtain an electrolyte.

[0081] The preparation method of a lithium-ion battery includes:

[0082] LiNi 00.6 Co 0.1 Mn 0.3 The O2 positive electrode active material is used as the positive electrode material, and the conductive agent carbon black and the binder carbon nanotubes are dissolved in N-methylpyrrolidone solvent at a mass ratio of 96:2:2. After being fully stirred and mixed, the solid content is controlled at 68% to obtain a positive electrode slurry;

[0083] The positive electrode slurry was coated on a 13 μm thick aluminum foil positive electrode current collector, and then rolled, dried, and punched to obtain a positive electrode sheet.

[0084] The artificial graphite negative electrode active material is used as the negative electrode material, and is dissolved in a deionized water solvent at a mass ratio of 96:2:1:1 with a conductive agent carbon black, a binder styrene-butadiene rubber, and a thickener sodium carboxymethyl cellulose. After being fully stirred and mixed, the solid content is controlled at 50% to obtain a negative electrode slurry.

[0085] The negative electrode slurry was coated on a 6 μm thick copper foil negative electrode current collector, and then rolled, dried, and punched to obtain a negative electrode sheet.

[0086] A polyethylene (PE) base film is used and a nano-aluminum oxide coating is coated on the base film to obtain a diaphragm;

[0087] The negative electrode sheet, positive electrode sheet and separator are stacked, encapsulated in an aluminum-plastic film, and injected with the prepared electrolyte. The process is then followed by encapsulation, activation, formation, aging, secondary encapsulation and capacity division to obtain a lithium-ion battery.

[0088] Example 2:

[0089] This embodiment is substantially the same as embodiment 1, with the only difference being that in this embodiment, the first additive is added to the solvent at a ratio of 0.05% and mixed evenly to obtain an electrolyte.

[0090] Example 3:

[0091] This embodiment is substantially the same as embodiment 1, with the only difference being that in this embodiment, the first additive is added to the solvent at a ratio of 0.1% and mixed evenly to obtain an electrolyte.

[0092] Example 4:

[0093] This embodiment is substantially the same as embodiment 1, with the only difference being that in this embodiment, the first additive is added to the solvent at a ratio of 0.5% and mixed evenly to obtain an electrolyte.

[0094] Example 5:

[0095] This embodiment is substantially the same as embodiment 1, with the only difference being that in this embodiment, the first additive is added to the solvent at a ratio of 1.0% and mixed evenly to obtain an electrolyte.

[0096] Example 6:

[0097] This embodiment is substantially the same as embodiment 1, with the only difference being that in this embodiment, the first additive is added to the solvent at a ratio of 1.5% and mixed evenly to obtain an electrolyte.

[0098] Example 7:

[0099] This embodiment is substantially the same as embodiment 1, except that in this embodiment, 12.5% ​​lithium hexafluorophosphate (lithium salt) is added to the solvent and mixed evenly; and the first additive is added to the solvent at a ratio of 2.0% and mixed evenly to obtain an electrolyte.

[0100] Example 8:

[0101] This embodiment is basically the same as embodiment 4, except that the first additive is replaced by and uniformly mixing 5.0% of lithium bisfluorosulfonamide, 5.0% of lithium difluorophosphate, 0.5% of vinylene carbonate, 0.5% of ethylene carbonate and 0.4% of trimethyl phosphate to obtain a second additive.

[0102] Example 9:

[0103] This embodiment is basically the same as embodiment 5, except that the first additive is replaced by and uniformly mixing 0.2% of lithium bisfluorosulfonamide, 0.3% of lithium difluorophosphate, 0.1% of vinylene carbonate, 0.1% of ethylene carbonate and 0.3% of trimethyl phosphate to obtain a second additive.

[0104] Example 10:

[0105] This embodiment is substantially the same as embodiment 5, with the only difference being that, in this embodiment, 10.0% lithium hexafluorophosphate (lithium salt) is added to the solvent and mixed uniformly.

[0106] Example 11:

[0107] This embodiment is substantially the same as embodiment 5, with the only difference being that in this embodiment, 20.0% lithium hexafluorophosphate (lithium salt) is added to the solvent and mixed uniformly.

[0108] Example 12:

[0109] This embodiment is basically the same as Example 2, except that, in this embodiment, the first additive is added to the solvent at a ratio of 1.0% and mixed evenly to obtain an electrolyte, and 0.5% of lithium bisfluorosulfonamide, 0.8% of lithium difluorophosphate, 0.5% of vinylene carbonate, 0.5% of ethylene carbonate, 0.8% of trimethyl phosphate and 0.3% of lithium difluorobisoxalatophosphate are mixed evenly to obtain a second additive;

[0110] Comparative Example 1:

[0111] This embodiment is substantially the same as embodiment 1, with the only difference being that in this embodiment, the first additive is added to the solvent at a ratio of 0.0% and mixed evenly to obtain an electrolyte.

[0112] Comparative Example 2:

[0113] This embodiment is basically the same as embodiment 12, with the only difference being that in this embodiment, the first additive is added to the solvent at a ratio of 0.0% and mixed evenly to obtain an electrolyte.

[0114] In order to more conveniently understand the specific differences between the above embodiments and comparative examples, the following Table 1 lists the composition of the electrolyte and the proportion of each component in each embodiment and comparative example.

[0115] Table 1 Electrolyte composition and proportions

[0116]

[0117]

[0118] Battery Test 1:

[0119] The battery capacity and internal resistance of the batteries prepared in Examples 1 to 12 and Comparative Examples 1 and 2 were tested, and the initial charge and discharge efficiency was calculated. The test equipment was a battery charge and discharge tester. During the test, the process steps of the battery charge and discharge tester were set as shown in Table 2 below:

[0120] Table 2 Battery charge and discharge tester working step test table A

[0121]

[0122] The test structure is shown in Table 3 below:

[0123] Table 3 Test results Table A

[0124]

[0125]

[0126] It should be noted that the data in Table 3 above are the average values ​​of test data of 10 lithium-ion batteries made in Examples 1 to 12 and Comparative Examples 1 and 2, respectively.

[0127] The following conclusions can be drawn from the test results in Table 3:

[0128] Compared with Comparative Example 1, the electrolytes of Examples 1 to 12 are applied to lithium-ion batteries, which improves the capacity of the lithium-ion batteries, improves the first efficiency of the lithium-ion batteries by about 1.5 to 3 percentage points, and reduces the DC internal resistance of the lithium-ion batteries by 5 to 10 percentage points. This proves that the electrolyte provided in the present application has a significant improvement effect on the capacity, first efficiency and reduction of the DC internal resistance of the lithium-ion batteries.

[0129] In Examples 1 to 7, the capacity and first effect of the lithium-ion battery show a trend of first increasing and then decreasing as the content of the first additive increases, and the overall data of the DC internal group shows an increasing trend during this process, and there are fluctuations in the data decrease. A lower proportion of the first additive, such as 0.01% to 0.05%, is not enough to fully form a stable interface film, while a higher proportion, such as 0.5% to 2.0%, will introduce too many side reactions or interfere with the uniformity of the electrolyte. The proportion of 0.1% can effectively utilize the preferential oxidation characteristics of the fluorocarbon group and the pyridine group to form a high conductivity interface film, and avoid the negative impact of excessive additives on the performance of the electrolyte. In Example 3, the internal resistance is 30.667mohm, which is slightly higher than that of Example 230.389mohm, but its capacity and first effect are more significantly improved, indicating that the conductivity and stability of the interface film are optimally balanced under this ratio. Therefore, in order to balance the above-mentioned capacity, DC internal resistance and first effect of the lithium battery, the amount of the first additive is not the more the better, and needs to be adjusted according to the actual design requirements of the battery.

[0130] Battery Test 2:

[0131] The batteries prepared in Examples 1 to 12 and Comparative Examples 1 and 2 were subjected to cyclic charge and discharge tests. The test equipment was a battery charge and discharge tester. During the test, the process steps of the battery charge and discharge tester were set as shown in Table 4 below:

[0132] Table 4 Battery charge and discharge tester working step test table B

[0133]

[0134] The test structure is shown in Table 5 below:

[0135] Table 5 Test results Table B

[0136]

[0137] It should be noted that the data in Table 5 above are the average values ​​of the test data of two lithium-ion batteries made in Examples 1 to 12 and Comparative Examples 1 and 2, respectively.

[0138] From the test results in Table 5, we can draw the following conclusions:

[0139] Compared with Comparative Example 1 and Comparative Example 2, when the electrolytes of Examples 1 to 12 are applied to lithium-ion batteries, the capacity retention rates after 500 cycles of 2.8V to 4.4V 1C / 1C at different temperatures are higher than those of Comparative Example 1 and Comparative Example 2, which significantly improves the cycle performance of the lithium-ion battery.

[0140] In order to understand the difference between the above data more clearly, this application provides the data graph of the capacity retention rate of Examples 1 and 3 and Comparative Example 1 at 25°C and 45°C respectively, from 2.8V to 4.4V 1C / 1C for 500 cycles. Figure 1 and Figure 2 , Figure 1 This is the data graph of capacity retention rate after 500 cycles of 2.8V to 4.4V 1C / 1C at 25°C. Figure 2 This is a data chart of capacity retention after 500 cycles of 2.8V to 4.4V 1C / 1C at 45°C. Figure 1 and Figure 2 It can be seen that as the number of cycles increases, the capacity of Comparative Example 1 shows a continuous and gradual downward trend, while Examples 1 and 3 still maintain a 100% capacity retention rate within the first 200 cycles, and fluctuate and decrease within a small range as a whole within 200 to 500 cycles. The curves of Examples 1 and 3 are both above that of Comparative Example 1, proving that the electrolyte provided in the examples of the present application significantly improves the cycle performance of lithium-ion batteries.

[0141] Compared with Comparative Examples 1 and 2, the cycle capacity retention rates of Examples 11 and 12 are relatively high. The capacity retention rates of Comparative Examples 1 and 2 are relatively high compared to those of Comparative Example 2. This is because 0.3% of lithium difluorobis(oxaloyl)phosphate was added to Comparative Example 2. When decomposed on the surface of the negative electrode, it can form an SEI film rich in lithium fluoride and organic components. Lithium fluoride can effectively inhibit the growth of lithium dendrites, reduce SEI film rupture, stabilize the SEI film, reduce continuous electrolyte decomposition, avoid activity loss, and improve the cycle capacity retention rate. At the same time, on the surface of the high-voltage positive electrode, lithium difluorobis(oxaloyl)phosphate can also form a CEI film through oxidative decomposition, which can inhibit the collapse of the positive electrode material structure and the oxidative decomposition of the electrolyte, slowing down the capacity decay. In Example 12, due to the reduction in the proportion of the first additive and the addition of 0.3% of lithium difluorobis(oxaloyl)phosphate, the cycle capacity retention rate is further improved under the synergistic effect of the first additive and lithium difluorobis(oxaloyl)phosphate.

[0142] The above description is only a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made by using the contents of the present invention description and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. An electrolyte, characterized in that: include: A solvent, a lithium salt, and a first additive, wherein the first additive has any one of the following structural formulas: wherein R1, R2, R3, and R4 contain at least one fluorine atom; R1, R2, R3, and R4 are each independently selected from hydrogen, halogen, cyano, boric acid, amino, imino, substituted or unsubstituted C1-C8 alkyl, substituted or unsubstituted C2-C8 alkenyl, substituted or unsubstituted C1-C8 alkoxy, substituted or unsubstituted alkoxycarbonyl, and substituted or unsubstituted C6-C 12 One of the aromatic groups.

2. The electrolyte according to claim 1, characterized in that The first additive is selected from one of the following structural formulas:

3. The electrolyte according to claim 1, characterized in that The mass of the first additive accounts for 0.01% to 2.0% of the total mass of the electrolyte.

4. The electrolyte according to claim 1, characterized in that The mass of the lithium salt accounts for 10.0% to 20.0% of the total mass of the electrolyte.

5. The electrolyte according to claim 1, characterized in that The mass of the solvent accounts for 65.0% to 89.0% of the total mass of the electrolyte.

6. The electrolyte according to claim 1, characterized in that The lithium salt includes one or more of lithium hexafluorophosphate, lithium difluorophosphate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium difluorobis(oxalatophosphate), lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethylsulfonyl)imide.

7. The electrolyte according to claim 1, characterized in that The solvent includes one or more of ethylene carbonate, ethyl acrylate, methyl acrylate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate and methyl propyl carbonate.

8. The electrolyte according to claim 1, characterized in that The halogen includes one or more of fluorine, chlorine, bromine and iodine; The alkyl group includes one or more of methyl, ethyl, isopropyl, tert-butyl, hexyl, octyl, decyl, dodecyl, and heptadecyl; The alkenyl group includes one or more of vinyl, propenyl, butenyl, hexenyl, octenyl, decenyl, dodecenyl, 9-heptadecenyl, 1,4-pentadienyl, 1,5-hexadienyl, 1,6-heptadienyl, 1,7-octadienyl, 1,8-nonadienyl, and 1,9-decadienyl; The alkoxy group includes one or more of methoxy, ethoxy, propoxy, butoxy, pentyloxy, heptyloxy, hexyloxy, octyloxy, decyloxy, and dodecyloxy; The alkoxycarbonyl group includes one or more of methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, butoxycarbonyl, pentyloxycarbonyl, heptyloxycarbonyl, hexyloxycarbonyl, decyloxycarbonyl, dodecyloxycarbonyl, octyloxycarbonyl, palmityloxycarbonyl, and stearyloxycarbonyl; the aryl group includes one or more of phenyl, p-tolyl, p-nitrophenyl, o-methoxyphenyl, m-methoxyphenyl, p-methoxyphenyl, and p-nitromethoxyphenyl; The substituted C1-C8 alkyl, substituted C2-C8 alkenyl, substituted C1-C8 alkoxy, substituted alkoxycarbonyl and substituted C6-C 12 The substituent groups of the aryl group independently include one or more of -NH2, -F, -Cl, -Br, -I, -OH, -COOH, -NO2, -SO3H, -CHO, -SH, and -CN.

9. The electrolyte according to claim 1, characterized in that The electrolyte further includes a second additive, and the mass of the second additive accounts for 1.0% to 15.0% of the total mass of the electrolyte.

10. The electrolyte according to claim 9, characterized in that The second additive includes one or more of fluoroethylene carbonate, vinylene carbonate, vinyl sulfate, vinyl sulfite, sulfolane, tetravinylsilane, triallyl isocyanurate, triphenyl phosphate, trimethyl phosphate, tetrafluorophenyl acetate, and methylene methanedisulfonate.

11. A secondary battery, characterized in that: The invention comprises a positive electrode sheet, an electrolyte, a separator and a negative electrode sheet, wherein the electrolyte is the electrolyte according to any one of claims 1 to 10.

12. The secondary battery according to claim 11, wherein The positive electrode sheet includes an active material, and the active material is a ternary layered oxide positive electrode material with a general composition formula of LiNi x Co y Mn 1-x-y O2, where 0 < x < 1 and 0 < y < 1; the negative electrode sheet includes one or more of a metallic lithium negative electrode sheet, a metallic lithium alloy negative electrode sheet, a graphite negative electrode sheet, a silicon-based negative electrode sheet, a silicon-graphite composite negative electrode sheet, and a copper foil lithium-free negative electrode sheet.

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