Electrolytes and batteries

Abstract

The application discloses electrolyte and battery, the electrolyte includes: electrolyte salt, solvent, first additive and second additive, the first additive is structural formula (1), the second additive is selected from at least one of structural formula (2) and structural formula (3). The first additive can form a film at the positive and negative electrode interface, the positive electrode interface is oxidized to generate a stable fluorophosphorus-based interface film, the interface film has low impedance and high stability, improves the stability of the positive electrode surface, inhibits the side reaction of electrolyte and active material, the first additive forms a film on the negative electrode side, and the second additive has a lower LUMO orbital, is easy to generate a stable interface film on the negative electrode, is richer in more conjugated double bonds than the interface film generated by the conventional acid anhydride structure, is easy to occur thermal polymerization under high temperature and extreme working conditions, protects the interface stability, the difluorophosphoric acid compound generated on the surface of the vinyl acid anhydride film has the characteristics of low impedance and high stability, improves the high-temperature safety performance of the battery while improving the cycle and low-temperature performance.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, specifically relating to an electrolyte and a battery. Background Technology

[0002] Lithium-ion batteries possess significant advantages such as high energy density, long cycle life, wide operating temperature range, and fast charging speed, making them widely used in 3C digital products, new energy vehicles, energy storage power stations, and aerospace. The electrolyte, acting as the lifeblood of the lithium-ion battery, plays a crucial role in transporting ions. Currently, lithium-ion batteries primarily use carbonate-based organic solvents, which have low stability at high temperatures. Under thermal shock and overcharge / overdischarge conditions, they fail, leading to severe battery combustion or even explosions, thus reducing the battery's high-temperature safety performance. Summary of the Invention

[0003] The purpose of this invention is to provide an electrolyte and a battery to solve the problem of low high-temperature safety performance of batteries.

[0004] In a first aspect, embodiments of the present invention provide an electrolyte, comprising:

[0005] Electrolyte salt, solvent, first additive and second additive, wherein the structural formula of the first additive is structural formula (1):

[0006]

[0007] Wherein, X is selected from alkyl with 1-5 carbon atoms, alkenyl with 1-5 carbon atoms, alkynyl with 1-5 carbon atoms, haloalkyl with 1-5 carbon atoms, haloalkenyl with 1-5 carbon atoms, haloalkynyl with 1-5 carbon atoms, nitrile with 1-5 carbon atoms, or halonitrile with 1-5 carbon atoms.

[0008] The structural formula of the second additive is selected from at least one of structural formula (2) and structural formula (3), and structural formula (2) and structural formula (3) are:

[0009]

[0010] R1, R2, R3, and R4 are independently selected from one of the following: hydrogen atom, halogen atom, alkyl group with 1 to 10 carbon atoms, alkenyl group with 1 to 10 carbon atoms, alkynyl group with 1 to 10 carbon atoms, fluoroalkyl group with 1 to 10 carbon atoms, fluoroalkenyl group with 1 to 10 carbon atoms, fluoroalkynyl group with 1 to 10 carbon atoms, nitrile group with 1 to 4 carbon atoms, or fluoronitrile group with 1 to 4 carbon atoms.

[0011] Optionally, the structural formula of the first additive is selected from at least one of structural formulas (A1) to (A4), wherein structural formulas (A1) to (A4) are:

[0012]

[0013] Optionally, the structural formula of the second additive is selected from at least one of structural formulas (B1) to (B4), wherein structural formulas (B1) to (B4) are:

[0014]

[0015] Optionally, the content of the first additive is 0.1-10% of the total mass of the electrolyte.

[0016] Optionally, the content of the second additive is 0.2-3% of the total mass of the electrolyte.

[0017] Optionally, the electrolyte further includes:

[0018] The third additive includes at least one selected from fluoroethylene carbonate, vinylene carbonate, 1,3-propanesulfonate lactone, vinyl sulfate, methanedisulfonate methylene, propylene sulfonate lactone, maleic anhydride, diethanolic anhydride, succinic anhydride, succinic anhydride, adiponitrile, ethylene glycol bis(propionitrile) ether, and hexanetrionitrile.

[0019] Optionally, the content of the third additive is 0.1-15% of the total mass of the electrolyte.

[0020] Optionally, the electrolyte salt comprises:

[0021] At least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium difluorobis(oxalate) phosphate, lithium tetrafluoro(oxalate) phosphate, lithium oxalate phosphate, lithium bis(oxalate) borate, lithium difluoro(oxalate) borate, lithium tetrafluoroborate, and lithium difluorosulfonylimide.

[0022] Optionally, the solvent includes at least one of carbonates and carboxylic acid esters, wherein the carbonate includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate;

[0023] The carboxylic acid esters include at least one of ethyl propionate, propyl propionate, propyl acetate, n-butyl acetate, isobutyl acetate, n-pentyl acetate, isopentyl acetate, ethyl acetate, methyl butyrate, ethyl butyrate, and γ-butyrolactone.

[0024] Secondly, embodiments of the present invention provide a battery, comprising:

[0025] The electrolyte described in the above embodiments.

[0026] The electrolyte of this invention includes: an electrolyte salt, a solvent, a first additive, and a second additive. The first additive has the structural formula of (1), and the second additive has the structural formula selected from at least one of (2) and (3). The first additive is a difluorophosphazene compound, and the second additive is a vinyl anhydride compound. The difluorophosphazene compound can form a film at the interface between the positive and negative electrodes. The positive electrode interface is oxidized to generate a stable fluorophosphorus-based interface film. This interface film has low impedance and high stability. At the same time, the cyano group and the P element can inhibit excessive metal dissolution, improve the surface stability of the positive electrode, and inhibit the side reactions between the electrolyte and the active material. The film formation of the difluorophosphazene compound on the negative electrode side is slower than that of conventional additives, while the vinyl anhydride compound has a lower LUMO orbital, which makes it easy to generate a stable interface film at the negative electrode. The interface film generated by the conventional anhydride structure is richer in conjugated double bonds and is prone to thermal polymerization under high temperature and extreme conditions, thus protecting the interface stability. At the same time, the difluorophosphoric acid compound generated on the surface of the vinyl anhydride film has the characteristics of low impedance and high stability, which improves the high-temperature safety performance of the battery while improving the cycle and low-temperature performance. Detailed Implementation

[0027] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] The terms "first," "second," etc., used in the specification and claims of this invention are used to distinguish similar objects and are not used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that embodiments of the invention can be implemented in orders other than those described herein. Furthermore, in the specification and claims, "and / or" indicates at least one of the connected objects, and the character " / " generally indicates that the preceding and following objects are in an "or" relationship.

[0029] The electrolyte of this invention includes:

[0030] Electrolyte salt, solvent, first additive and second additive, wherein the structural formula of the first additive is structural formula (1):

[0031]

[0032] Wherein, X is selected from alkyl with 1-5 carbon atoms, alkenyl with 1-5 carbon atoms, alkynyl with 1-5 carbon atoms, haloalkyl with 1-5 carbon atoms, haloalkenyl with 1-5 carbon atoms, haloalkynyl with 1-5 carbon atoms, nitrile with 1-5 carbon atoms, or halonitrile with 1-5 carbon atoms.

[0033] The structural formula of the second additive is selected from at least one of structural formula (2) and structural formula (3), and structural formula (2) and structural formula (3) are:

[0034]

[0035] R1, R2, R3, and R4 are independently selected from one of the following: hydrogen atom, halogen atom, alkyl group with 1 to 10 carbon atoms, alkenyl group with 1 to 10 carbon atoms, alkynyl group with 1 to 10 carbon atoms, fluoroalkyl group with 1 to 10 carbon atoms, fluoroalkenyl group with 1 to 10 carbon atoms, fluoroalkynyl group with 1 to 10 carbon atoms, nitrile group with 1 to 4 carbon atoms, or fluoronitrile group with 1 to 4 carbon atoms. The second additive may be selected from structural formula (2) or structural formula (3), and the second additive may be selected from both structural formula (2) and structural formula (3).

[0036] The electrolyte salt may include at least one of the following: lithium hexafluorophosphate, lithium difluorophosphate, lithium difluorobis(oxalate)phosphate, lithium tetrafluoro(oxalate)phosphate, lithium oxalate phosphate, lithium bis(oxalate)borate, lithium difluoro(oxalate)borate, lithium tetrafluoroborate, and lithium difluorosulfonylimide. For example, the electrolyte salt may be lithium hexafluorophosphate, and may include lithium hexafluorophosphate, lithium difluorophosphate, and lithium difluorosulfonylimide. The specific type of lithium salt can be selected according to the actual situation. The solvent may include at least one of carbonates and carboxylic esters. Carbonates may include at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate. Carboxylic esters may include at least one of propyl acetate, n-butyl acetate, isobutyl acetate, n-pentyl acetate, isoamyl acetate, propyl propionate, ethyl propionate, methyl butyrate, γ-butyrolactone, and n-ethyl butyrate. For example, the solvent may include ethylene carbonate, propylene carbonate, propyl acetate, and propyl propionate. The specific type of solvent can be selected according to the actual situation.

[0037] The electrolyte of this invention includes: an electrolyte salt, a solvent, a first additive, and a second additive. The first additive has the structural formula of (1), and the second additive has the structural formula selected from at least one of (2) and (3). The first additive is a difluorophosphazene compound, and the second additive is a vinyl anhydride compound. The difluorophosphazene compound can form a film at the interface between the positive and negative electrodes. The positive electrode interface is oxidized to generate a stable fluorophosphorus-based interface film. This interface film has low impedance and high stability. At the same time, the cyano group and the P element can inhibit excessive metal dissolution, improve the surface stability of the positive electrode, and inhibit the side reactions between the electrolyte and the active material. The film formation of the difluorophosphazene compound on the negative electrode side is slower than that of conventional additives, while the vinyl anhydride compound has a lower LUMO orbital, which makes it easy to generate a stable interface film at the negative electrode. The interface film generated by the conventional anhydride structure is richer in conjugated double bonds, and it is easy to undergo thermal polymerization under high temperature and extreme conditions, thus protecting the interface stability. At the same time, the difluorophosphoric acid compound generated on the surface of the vinyl anhydride film has the characteristics of low impedance and high stability, which improves the high-temperature safety performance of the battery while improving the cycle and low-temperature performance.

[0038] In some embodiments, the structural formula of the first additive may be selected from at least one of structural formulas (A1) to (A4), wherein structural formulas (A1) to (A4) are:

[0039]

[0040] For example, the first additive may be selected from one or more of structural formulas (A1) to (A4). For example, the first additive may be selected from structural formula (A1) or structural formula (A4), or the first additive may be selected from structural formula (A2) and structural formula (A4). The specific selection can be made according to the actual situation.

[0041] In some embodiments, the structural formula of the second additive may be selected from at least one of structural formulas (B1) to (B4), wherein structural formulas (B1) to (B4) are:

[0042]

[0043] The second additive may be selected from one or more of structural formulas (B1) to (B4). The second additive may be selected from structural formulas (B1), (B3), or (B4). The second additive may be selected from structural formulas (B1) and (B3). The specific selection can be made according to actual needs.

[0044] Optionally, the content of the first additive can be 0.1-10% of the total mass of the electrolyte, and the content of the first additive can be 0.5-3% of the total mass of the electrolyte. For example, the content of the first additive can be 0.1%, 3%, 7% or 10% of the total mass of the electrolyte. The content of the first additive can be reasonably selected according to actual conditions.

[0045] Optionally, the content of the second additive can be 0.2-3% of the total mass of the electrolyte. For example, the content of the second additive can be 0.2%, 1%, 2% or 3% of the total mass of the electrolyte, and the content of the second additive can be reasonably selected according to actual conditions.

[0046] In embodiments of the present invention, the electrolyte may further include:

[0047] The third additive may include at least one of the following: fluoroethylene carbonate (FEC), vinylene carbonate (VC), 1,3-propanesulfonate lactone (PS), vinyl sulfate (DTD), methanedisulfonate methylene ester (MMDS), propenesulfonate lactone (PST), maleic anhydride, diethanolamine anhydride, succinic anhydride, succinic anhydride, succinic anhydride (SN), adiponitrile (ADN), ethylene glycol bis(propionitrile) ether (EGBE), and hexanetrionitrile (HTCN). For example, the third additive may include fluoroethylene carbonate, or fluoroethylene carbonate and 1,3-propanesulfonate lactone, depending on the specific application.

[0048] Optionally, the content of the third additive can be 0.1-15% of the total mass of the electrolyte. For example, the content of the third additive can be 0.1%, 5%, 10% or 15% of the total mass of the electrolyte, and the content of the third additive can be reasonably selected according to actual needs.

[0049] Optionally, the electrolyte salt may include:

[0050] The electrolyte salt can be at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium difluorobis(oxalate)phosphate, lithium tetrafluoro(oxalate)phosphate, lithium oxalate phosphate, lithium bis(oxalate)borate, lithium difluoro(oxalate)borate, lithium tetrafluoroborate, and lithium difluorosulfonylimide. For example, the electrolyte salt can be lithium hexafluorophosphate, and may include at least one of lithium hexafluorophosphate, lithium difluorophosphate, and lithium difluorosulfonylimide. The specific type and content of the electrolyte salt can be selected reasonably according to actual needs. The content of the electrolyte salt can be 10-15% of the total mass of the electrolyte.

[0051] Optionally, the solvent may include at least one of carbonates and carboxylic acid esters, wherein the carbonate includes at least one of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate, diethyl carbonate (DEC), and methyl ethyl carbonate; for example, the carbonate may include ethylene carbonate, propylene carbonate, and dimethyl carbonate.

[0052] The carboxylic acid ester may include at least one of ethyl propionate (EP), propyl propionate (PP), propyl acetate, n-butyl acetate, isobutyl acetate, n-amyl acetate, isoamyl acetate, ethyl acetate (EA), methyl butyrate, ethyl butyrate (EB), and γ-butyrolactone (GBL). For example, the carboxylic acid ester may include ethyl propionate, propyl propionate, propyl acetate, methyl butyrate, and ethyl butyrate. The solvent may include ethylene carbonate, propylene carbonate, ethyl propionate, propyl propionate, propyl acetate, and n-butyl acetate. The specific type and content of the solvent can be reasonably selected according to the actual situation. The solvent can be an organic solvent, and the solvent content can be 20% to 60% of the total mass of the electrolyte.

[0053] The battery of this invention includes:

[0054] The electrolyte described in the above embodiments. Batteries using the electrolyte described in the above embodiments can improve high-temperature safety performance, as well as cycle and low-temperature performance.

[0055] The battery can be a lithium-ion battery, and the battery can include a positive electrode, a negative electrode, a separator between the positive electrode and the negative electrode, and an electrolyte. The electrolyte can be the electrolyte described in the above embodiments.

[0056] The present invention will be further described below with reference to specific embodiments.

[0057] Example 1

[0058] Positive electrode preparation:

[0059] Lithium cobalt oxide (LCO), polyvinylidene fluoride (PVDF), conductive carbon black, and single-walled carbon nanotubes were mixed in a weight ratio of 97.2:1.5:1.2:0.1. N-methylpyrrolidone (NMP) was added, and the mixture was stirred under vacuum until a homogeneous and fluid positive electrode slurry was formed. The positive electrode slurry was uniformly coated onto a current collector aluminum foil. The coated aluminum foil was baked in an oven with five different temperature gradients, and then dried in an oven at 120°C for 8 hours. Finally, it was rolled and slit to obtain the desired positive electrode sheet.

[0060] Negative electrode preparation:

[0061] A certain proportion of graphite (anode active material), sodium carboxymethyl cellulose (CMC-Na) (thickener), styrene-butadiene rubber (binder), and acetylene black (conductive agent) were mixed in a weight ratio of 97:1:1:1. Deionized water was added, and the mixture was stirred in a vacuum mixer to obtain a cathode slurry. The cathode slurry was uniformly coated onto a high-strength carbon-coated copper foil to obtain an electrode sheet. The obtained electrode sheet was dried at room temperature and then transferred to an 80°C oven for 10 hours. After that, it was rolled and slit to obtain a cathode sheet.

[0062] Electrolyte preparation:

[0063] In a glove box filled with inert gas (H2O < 10 ppm, O2 < 5 ppm), ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate were mixed at a mass ratio of EC:PC:DEC = 1:2:4. Then, lithium hexafluorophosphate (LiPF6) at 13.75 wt% of the total electrolyte weight was slowly added to the mixture. After passing tests for moisture and free acid, a basic electrolyte was obtained. Different amounts of the first and second additives listed in Table 1, along with 8 wt% fluoroethylene carbonate and 2 wt% hexanetrionitrile, were added to the basic electrolyte to obtain the corresponding electrolytes.

[0064] Battery manufacturing:

[0065] Stack the prepared positive electrode, separator (9-micron thick PP film), and negative electrode in sequence, ensuring that the separator is between the positive and negative electrodes to provide isolation. Place the bare cell in the aluminum-plastic film outer packaging, inject the prepared electrolyte into the dried battery, and then encapsulate, let stand, form, shape, and perform capacity testing to complete the preparation of the lithium-ion soft pack battery.

[0066] Examples 2-16 and Comparative Examples 1-8 differ from Example 1 in the content of the first and second additives in the electrolyte. The specific substances and their contents are shown in Table 1 below.

[0067] Table 1. Electrolyte composition and content in the examples and comparative examples.

[0068]

[0069]

[0070] Performance testing

[0071] The lithium-ion batteries obtained in Examples 1-16 and Comparative Examples 1-8 were subjected to relevant performance tests.

[0072] (1) High-temperature cycle performance test: At 45℃, the battery after capacity grading was charged to 4.48V at a constant current and constant voltage of 0.7C, with a cutoff current of 0.05C, and then discharged to 3.0V at a constant current of 0.5C. This cycle was repeated for 500 charge-discharge cycles. The capacity retention rate at the 500th cycle was calculated using the following formula:

[0073] 500-week cycle capacity retention (%) = (500-week cycle discharge capacity / initial cycle discharge capacity) × 100%.

[0074] (2) Thermal shock performance: Under 25℃ ambient conditions, discharge to 3.0V with a given current of 0.2C; rest for 5 minutes; charge to 4.48V with a charging current of 0.2C. When the cell voltage reaches 4.48V, switch to constant voltage charging at 4.48V until the charging current is less than or equal to the given cutoff current of 0.05C; after resting for 1 hour, put the cell into an oven. The oven temperature rises to 135±2℃ at a rate of 5±2℃ / min and is maintained for 30 minutes before stopping. The judgment criterion is that the cell does not catch fire or explode.

[0075] (3) Low-temperature discharge performance test: Under 25℃ conditions, the capacity-graded battery was discharged at 0.5C to 3.0V and left to stand for 5 minutes; then charged at 0.2C to 4.45V. When the cell voltage reached 4.45V, it was switched to constant voltage charging at 4.45V until the charging current was less than or equal to the given cutoff current of 0.05C, and left to stand for 5 minutes; the fully charged cell was transferred to a high-low temperature chamber, set to -10℃, and left to stand for 120 minutes after the chamber temperature was reached; then discharged at 0.2C to the cutoff voltage of 3.0V and left to stand for 5 minutes; then the high-low temperature chamber temperature was adjusted to 25℃±3℃, and left to stand for 60 minutes after the chamber temperature was reached; charged at 0.2C to 4.45V. When the cell voltage reached 4.45V, it was switched to constant voltage charging at 4.45V until the charging current was less than or equal to the given cutoff current of 0.05C; left to stand for 5 minutes; the capacity retention rate at -10℃ low-temperature discharge of 3.0V was calculated. The calculation formula is as follows:

[0076] -10℃ discharge to 3.0V capacity retention rate (%) = (-10℃ discharge capacity to 3.0V / 25℃ discharge capacity to 3.0V) × 100%.

[0077] The battery test results in the examples and comparative examples are shown in Table 2.

[0078] Table 2 Battery test results in the examples and comparative examples.

[0079]

[0080] As can be seen from the comparative examples and embodiments in Table 2, the first additive and the second additive can effectively improve the thermal shock performance of lithium-ion batteries while also taking into account low-temperature performance and improving high-temperature cycle performance.

[0081] Difluorophosphazene compounds are more effective in improving thermal shock performance. Under thermal shock conditions, the phosphorus-containing low-resistivity film they generate has high stability, low heat generation, and can suppress free radical side reactions, thus improving thermal shock performance. Vinyl anhydride has a significant effect on improving cycle performance, and when combined with difluorophosphazene compounds, it has a significant effect on improving furnace temperature. The improvement in high-temperature cycle performance mainly comes from the better stability of the film structure formed by its anhydride and conjugated double bonds. Under thermal shock conditions, the bilayer film formed by it and difluorophosphazene compounds works synergistically. The phosphorus-containing cyano structure has high stability before the extreme temperature. At the extreme temperature, the conjugated double bonds undergo endothermic thermal polymerization, which further improves thermal shock stability, improves the high-temperature safety performance of the battery, and improves cycle and low-temperature performance.

[0082] The embodiments of the present invention have been described above. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims, and all of these forms are within the protection scope of the present invention.

Claims

1. An electrolyte, characterized in that, include: Electrolyte salts, solvents, first additive and second additive, The structural formula of the first additive is selected from at least one of structural formulas (A1) to (A4), and structural formulas (A1) to (A4) are as follows: Structural formula (A1) Structural formula (A2) Structural formula (A3). Structural formula (A4); The structural formula of the second additive is selected from at least one of structural formulas (B1) to (B4), and structural formulas (B1) to (B4) are as follows: Structural formula (B1) Structural formula (B2) Structural formula (B3). Structural formula (B4); The content of the first additive is 0.1-10% of the total mass of the electrolyte; The content of the second additive is 0.2-3% of the total mass of the electrolyte.

2. The electrolyte according to claim 1, characterized in that, Also includes: The third additive includes at least one selected from fluoroethylene carbonate, vinylene carbonate, 1,3-propanesulfonate lactone, vinyl sulfate, methanedisulfonate methylene, propylene sulfonate lactone, maleic anhydride, diethanolic anhydride, succinic anhydride, succinic anhydride, adiponitrile, ethylene glycol bis(propionitrile) ether, and hexanetrionitrile.

3. The electrolyte according to claim 2, characterized in that, The content of the third additive is 0.1-15% of the total mass of the electrolyte.

4. The electrolyte according to claim 1, characterized in that, The electrolyte salt includes: At least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium difluorobis(oxalate) phosphate, lithium tetrafluoro(oxalate) phosphate, lithium oxalate phosphate, lithium bis(oxalate) borate, lithium difluoro(oxalate) borate, lithium tetrafluoroborate, and lithium difluorosulfonylimide.

5. The electrolyte according to claim 1, characterized in that, The solvent includes at least one of carbonates and carboxylic acid esters, wherein the carbonate includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate; The carboxylic acid esters include at least one of ethyl propionate, propyl propionate, propyl acetate, n-butyl acetate, isobutyl acetate, n-pentyl acetate, isopentyl acetate, ethyl acetate, methyl butyrate, ethyl butyrate, and γ-butyrolactone.

6. A battery, characterized in that, include: The electrolyte according to any one of claims 1-5.

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