Electrolytes and batteries

Abstract

This invention discloses an electrolyte and a battery. The electrolyte comprises an electrolyte, a solvent, and a first additive, the first additive having the structural formula (1). The first additive contains silicon-based phosphate groups, which have low oxidation and reduction potentials. It can generate an inorganic interface film rich in P and Si at the positive and negative electrodes. The generated interface helps to reduce the interfacial impedance of the positive and negative electrodes. Cyclic phosphates have good high-voltage stability. The generated phosphate compounds can suppress excessive ion deposition during the high-voltage positive electrode phase transition, providing better protection for the positive and negative electrode interfaces and improving high-voltage cycle performance. The polycyclic phosphate structure can capture hydroxyl radicals and hydrogen radicals generated by the electrolyte at high temperatures, preventing the diffusion reaction of hydrocarbon radicals. At the same time, the silicon-based structure can generate a stable thermally stable film at the positive and negative electrode interfaces. The generated high-thermal-stability inorganic thermal insulation protective layer can reduce the flammability of the electrolyte and significantly improve the safety performance of the battery.

Description

Technical Field

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

[0002] With the development of the new energy industry, lithium-ion batteries have become a key research area. However, their safety remains a significant drawback. Numerous safety incidents involving power tools and digital products have led to a negative market reaction to lithium-ion batteries. Furthermore, the increasing market demand, particularly for fast charging, high voltage, and high energy density, poses a greater challenge to lithium battery safety. The electrolyte, a crucial component of lithium-ion batteries, plays a decisive role in performance. Liquid electrolytes, however, suffer from insufficient stability and are prone to reacting with active materials, resulting in low safety performance of lithium-ion batteries. Summary of the Invention

[0003] The purpose of this invention is to provide an electrolyte and a battery to solve the problem of low safety performance caused by insufficient electrolyte stability.

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

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

[0006]

[0007] Wherein, at least one of R1, R2, R3, and R4 is structural formula (2); when R1 is structural formula (2), R2, R3, and R4 are each independently selected from one of hydrogen atom, halogen atom, aryl, olefin, and alkyl with 1 to 5 carbon atoms, alkenyl with 1 to 5 carbon atoms, fluoroalkyl with 1 to 5 carbon atoms, fluoroalkenyl with 1 to 5 carbon atoms, alkoxy with 1 to 5 carbon atoms, nitrile with 1 to 4 carbon atoms, and fluoronitrile with 1 to 4 carbon atoms;

[0008] When R1 and R2 are of structural formula (2), R3 and R4 are each independently selected from one of the following: hydrogen atom, halogen atom, aryl, olefin, and alkyl with 1 to 5 carbon atoms, alkenyl with 1 to 5 carbon atoms, fluoroalkyl with 1 to 5 carbon atoms, fluoroalkenyl with 1 to 5 carbon atoms, alkoxy with 1 to 5 carbon atoms, nitrile with 1 to 4 carbon atoms, and fluoronitrile with 1 to 4 carbon atoms;

[0009] When R1, R2, and R3 are of structural formula (2), R4 includes at least one of nitrile group, fluoronitrile group, and structural formula (2);

[0010] The structural formula of structural formula (2) is:

[0011]

[0012] R5 is an O atom or an S atom.

[0013] Optionally, the structural formula of the first additive is selected from at least one of structural formulas (A1) to (A12), wherein structural formulas (A1) to (A12) are:

[0014]

[0015]

[0016]

[0017] Optionally, the content of the first additive is 0.1-10% of the total mass of the electrolyte.

[0018] Optionally, the electrolyte further includes:

[0019] The second additive includes at least one of fluoroethylene carbonate, 1,3-propane sulfonate lactone, ethylene sulfate, propylene sulfonate lactone, maleic anhydride, citrate anhydride, succinic anhydride, succinic anhydride, succinic nitrile, adiponitrile, ethylene glycol bis(propionitrile) ether, and hexanetrionitrile.

[0020] Optionally, the content of the second additive is 0.1-15% of the total mass of the electrolyte.

[0021] Optionally, the mass content of the first additive in the electrolyte is less than the mass content of the second additive in the electrolyte.

[0022] Optionally, the electrolyte comprises:

[0023] 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.

[0024] Optionally, the content of the electrolyte is 10-15% of the total mass of the electrolyte.

[0025] 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;

[0026] The carboxylic acid ester includes at least one of propyl acetate, n-butyl acetate, isobutyl acetate, n-pentyl acetate, isopentyl acetate, propyl propionate, ethyl propionate, ethyl acetate, methyl butyrate, γ-butyrolactone, and ethyl butyrate.

[0027] Secondly, embodiments of the present invention provide a battery, comprising:

[0028] The electrolyte described in the above embodiments.

[0029] The electrolyte of this invention includes: an electrolyte, a solvent, and a first additive. The first additive has the structural formula (1). The first additive, containing silicon-based phosphate groups, has a low oxidation potential and a low reduction potential. It can generate an inorganic interface film rich in P and Si at the positive and negative electrodes. The generated interface helps reduce the interfacial impedance of the positive and negative electrodes. Furthermore, the cyclic phosphate ester exhibits good high-voltage stability. The generated phosphate ester compound can suppress excessive ion deposition during the high-voltage positive electrode phase transition, providing better protection for the positive and negative electrode interfaces and improving high-voltage cycle performance. The polycyclic phosphate ester structure can capture hydroxyl radicals and hydrogen radicals generated in the electrolyte at high temperatures, preventing hydrocarbon radical diffusion reactions. Simultaneously, the silicon-based structure can generate a stable thermally stable film at the positive and negative electrode interfaces. The generated high-thermal-stability inorganic thermal insulation protective layer can reduce the flammability of the electrolyte and significantly improve the battery's safety performance. Detailed Implementation

[0030] 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.

[0031] 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.

[0032] The electrolyte of this invention includes:

[0033] Electrolyte, solvent, and first additive, wherein the structural formula of the first additive is structural formula (1):

[0034]

[0035] Wherein, at least one of R1, R2, R3, and R4 is structural formula (2); when R1 is structural formula (2), R2, R3, and R4 are each independently selected from one of hydrogen atom, halogen atom, aryl, olefin, and alkyl with 1 to 5 carbon atoms, alkenyl with 1 to 5 carbon atoms, fluoroalkyl with 1 to 5 carbon atoms, fluoroalkenyl with 1 to 5 carbon atoms, alkoxy with 1 to 5 carbon atoms, nitrile with 1 to 4 carbon atoms, and fluoronitrile with 1 to 4 carbon atoms;

[0036] When R1 and R2 are of structural formula (2), R3 and R4 are each independently selected from one of the following: hydrogen atom, halogen atom, aryl, olefin, and alkyl with 1 to 5 carbon atoms, alkenyl with 1 to 5 carbon atoms, fluoroalkyl with 1 to 5 carbon atoms, fluoroalkenyl with 1 to 5 carbon atoms, alkoxy with 1 to 5 carbon atoms, nitrile with 1 to 4 carbon atoms, and fluoronitrile with 1 to 4 carbon atoms;

[0037] When R1, R2, and R3 are of structural formula (2), R4 includes at least one of nitrile group, fluoronitrile group, and structural formula (2), and the structural formula of structural formula (2) is:

[0038]

[0039] R5 is an O atom or an S atom.

[0040] The electrolyte may include 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, lithium bis(fluorosulfonyl)imide, and lithium bis(fluorosulfonyl)imide. For example, the electrolyte may be lithium hexafluorophosphate, and may include lithium hexafluorophosphate, lithium difluorophosphate, and lithium bis(fluorosulfonyl)imide; the specific lithium salt can be selected according to the actual situation. The solvent may include at least one of carbonates and carboxylic esters, wherein the carbonate includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate; the carboxylic ester includes 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.

[0041] The electrolyte of this invention includes: an electrolyte, a solvent, and a first additive. The first additive has the structural formula (1). The first additive, containing silicon-based phosphate groups, has a low oxidation potential and a low reduction potential. It can generate an inorganic interface film rich in P and Si at the positive and negative electrodes. The generated interface helps reduce the interfacial impedance of the positive and negative electrodes. Furthermore, the cyclic phosphate ester exhibits good high-voltage stability. The generated phosphate ester compound can suppress excessive ion deposition during the high-voltage positive electrode phase transition, providing better protection for the positive and negative electrode interfaces and improving high-voltage cycle performance. The polycyclic phosphate ester structure can capture hydroxyl radicals and hydrogen radicals generated in the electrolyte at high temperatures, preventing hydrocarbon radical diffusion reactions. Simultaneously, the silicon-based structure can generate a stable thermally stable film at the positive and negative electrode interfaces. The generated high-thermal-stability inorganic thermal insulation protective layer can reduce the flammability of the electrolyte, significantly improving battery safety performance and enhancing high-temperature cycle performance.

[0042] In some embodiments, the structural formula of the first additive may be selected from at least one of structural formulas (A1) to (A12), wherein structural formulas (A1) to (A12) are:

[0043]

[0044]

[0045]

[0046] The structural formula of the first additive can be selected from one or more of structural formulas (A1) to (A12). For example, the structural formula of the first additive can be selected from structural formula (A1) or structural formula (A3). The structural formula of the first additive can be selected from structural formula (A1), structural formula (A2) and structural formula (A3), and can be reasonably selected according to actual needs.

[0047] Optionally, the content of the first additive can be 0.1-10% of the total mass of the electrolyte. Alternatively, 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%, 0.5%, 3%, 7% or 10% of the total mass of the electrolyte. The specific content of the first additive can be selected according to actual conditions.

[0048] In some embodiments, the electrolyte may further include a second additive, which includes at least one of the following: fluoroethylene carbonate, 1,3-propanesulfonate lactone, vinyl sulfate, propylene sulfonate lactone, maleic anhydride, citrate anhydride, succinic anhydride, succinic anhydride, succinic nitrile, adiponitrile, ethylene glycol bis(propionitrile) ether, and hexanetrionitrile. For example, the electrolyte may also include fluoroethylene carbonate, and other additives may be added as needed. The second additive includes fluoroethylene carbonate (FEC). Fluoroethylene carbonate has a better synergistic effect with the first additive. The first additive mainly generates inorganic components and has a limited interfacial protection capability. When it works synergistically with FEC, it generates organic components such as LiF and lithium carbonate, which regulate the interfacial composition and further improve stability.

[0049] Optionally, the content of the second additive can be 0.1-15% of the total mass of the electrolyte. For example, the content of the second additive can be 0.1%, 5%, 10% or 15% of the total mass of the electrolyte. The specific content of the second additive can be selected according to actual needs.

[0050] In some embodiments, the mass content of the first additive in the electrolyte is less than the mass content of the second additive in the electrolyte. For example, the first additive has the structural formula (A3), the second additive is fluoroethylene carbonate, the mass content of the first additive in the electrolyte is 1.5% of the total mass of the electrolyte, and the mass content of the second additive in the electrolyte is 6% of the total mass of the electrolyte; or the mass content of the first additive in the electrolyte is 2% of the total mass of the electrolyte, and the mass content of the second additive in the electrolyte is 8% of the total mass of the electrolyte. The specific mass contents of the first additive and the second additive can be selected according to actual needs.

[0051] Optionally, the electrolyte may include 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 may be lithium hexafluorophosphate, and may include lithium hexafluorophosphate and lithium difluorosulfonylimide; the specific type of electrolyte can be selected as needed.

[0052] Optionally, the content of the electrolyte is 10-15% of the total mass of the electrolyte. For example, the content of the electrolyte is 10% or 15% of the total mass of the electrolyte. The specific type and content of the electrolyte can be reasonably selected according to the actual situation.

[0053] In some embodiments, the solvent may include at least one of carbonates and carboxylic esters. The carbonate may include 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 and propylene carbonate. The carboxylic ester may include at least one of propyl acetate, n-butyl acetate, isobutyl acetate, n-amyl acetate, isoamyl acetate, propyl propionate (PP), ethyl propionate (EP), ethyl acetate (EA), methyl butyrate, γ-butyrolactone (GBL), and ethyl butyrate (EB); for example, the carboxylic ester may include propyl acetate, propyl propionate, and ethyl propionate. The solvent may include ethylene carbonate, propylene carbonate, propyl acetate, n-butyl acetate, propyl propionate, and ethyl propionate. The solvent content may be 20-60% of the total mass of the electrolyte, and the specific type and amount of solvent can be reasonably selected as needed.

[0054] The battery of this invention includes:

[0055] The electrolyte described in the above embodiments. Batteries using the electrolyte described in the above embodiments have high safety.

[0056] The present invention will be further described below with reference to some 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, methyl ethyl carbonate, and diethyl carbonate were mixed in a mass ratio of EC:PC:DEC = 1:2:4. Then, lithium hexafluorophosphate (LiPF6) was slowly added to the mixed solution at 13.75 wt% of the total electrolyte weight. After passing the tests for moisture and free acid, the basic electrolyte was obtained. Different components were added to the basic electrolyte, and the specific contents of the components are shown in Table 1.

[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 1-2 differ from Example 1 in the content of each substance in the electrolyte. The specific substances and their contents are shown in Table 1 below.

[0067] Table 1. Components and contents in the examples and comparative examples.

[0068]

[0069] The lithium-ion batteries obtained in Examples 1-16 and Comparative Examples 1-2 were subjected to relevant performance tests.

[0070] (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:

[0071] 500-week cycle capacity retention (%) = (500-week cycle discharge capacity / initial cycle discharge capacity) × 100%.

[0072] (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 4.48V constant voltage charging 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 132±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.

[0073] (3) Overcharge test: Under 25℃ environmental conditions, the battery after capacity division is constant current 2C to 6.0V. The judgment standard is that it does not catch fire or explode.

[0074] (4) DCR (DC impedance) test: At room temperature (23℃±3℃), constant current and constant voltage of 0.5C to 4.48V, cut-off current of 0.02C, then discharge at 0.1C for 9h (adjusted to 10% SOC), then discharge at 0.1C for 10s, record the end voltage V1, discharge at 1C for 1s, and record the end voltage V2.

[0075] DCR calculation formula: DCR=(V1-V2) / (1C-0.1C).

[0076] Table 2 shows the battery performance tests in the examples and comparative examples.

[0077]

[0078]

[0079] As can be seen from the test results of Comparative Examples 1-2 and Examples 1-16 in Table 2, the compound additive A with the structure of structural formula (1) in the examples can effectively improve the cycle and safety performance of lithium-ion batteries.

[0080] A comparison of the examples and the embodiments shows that the additive with structural formula (1) can improve the normal and high temperature cycling performance and DCR;

[0081] Comparison of Examples 1-2 and Examples 1-16 shows that the additive with structural formula (1) can improve thermal shock and overcharge performance, and the higher the amount added, the more significant the improvement effect. The negative electrode film-forming additive FEC has a better synergistic effect with the additive with structural formula (1). The additive with structural formula (1) mainly generates inorganic components and has a single interface protection capability. When it works synergistically with FEC, it generates organic components such as LiF and lithium carbonate, which adjust the interface components, further improves stability, and has better performance.

[0082] In this embodiment of the invention, the first additive contains silicon-based phosphate groups, which can generate an inorganic interface film rich in P and Si at the positive and negative electrodes. The generated interface helps reduce the interfacial impedance of the positive and negative electrodes, and the cyclic phosphate ester has good high-voltage stability. The generated phosphate ester compound can suppress excessive ion deposition during the high-voltage positive electrode phase transition, providing better protection for the positive and negative electrode interfaces and improving high-voltage cycle performance. The polycyclic phosphate ester structure can capture hydroxyl radicals and hydrogen radicals generated in the electrolyte at high temperatures, preventing hydrocarbon radical diffusion reactions. At the same time, the silicon-based structure can also generate a stable thermally stable film at the positive and negative electrode interfaces. The generated high-thermal-stability inorganic thermal insulation protective layer can reduce the flammability of the electrolyte and significantly improve the safety performance of the battery.

[0083] 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, solvent, and first additive, wherein the structural formula of the first additive is selected from at least one of structural formulas (A1) to (A4) and (A6) to (A12), and the structural formulas (A1) to (A4) and (A6) to (A12) are as follows: ； ； ； 。 2. The electrolyte according to claim 1, characterized in that, The content of the first additive is 0.1-10% of the total mass of the electrolyte.

3. The electrolyte according to any one of claims 1-2, characterized in that, Also includes: The second additive includes at least one of fluoroethylene carbonate, 1,3-propane sulfonate lactone, ethylene sulfate, propylene sulfonate lactone, maleic anhydride, citrate anhydride, succinic anhydride, succinic anhydride, succinic nitrile, adiponitrile, ethylene glycol bis(propionitrile) ether, and hexanetrionitrile.

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

5. The electrolyte according to claim 3, characterized in that, The mass content of the first additive in the electrolyte is less than the mass content of the second additive in the electrolyte.

6. The electrolyte according to claim 1, characterized in that, The electrolyte 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.

7. The electrolyte according to claim 6, characterized in that, The content of the electrolyte is 10-15% of the total mass of the electrolyte.

8. 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 ester includes at least one of propyl acetate, n-butyl acetate, isobutyl acetate, n-pentyl acetate, isopentyl acetate, propyl propionate, ethyl propionate, ethyl acetate, methyl butyrate, γ-butyrolactone, and ethyl butyrate.

9. A battery, characterized in that, include: The electrolyte according to any one of claims 1-8.