Lithium ion battery electrolyte, lithium ion battery and electric device

Abstract

The application provides a lithium ion battery electrolyte, a lithium ion battery and a power utilization device, and belongs to the technical field of lithium ion battery manufacturing. The electrolyte comprises a solvent, a lithium salt and an additive, the additive comprises a fluoropyridine compound, a tetra-vinyl compound and an isocyanate compound; wherein the mass percentage of the fluoropyridine compound in the electrolyte is 0.1-2%, the mass percentage of the tetra-vinyl compound in the electrolyte is 0.1-2%, and the mass percentage of the isocyanate compound in the electrolyte is 0.05-1%. The use of the electrolyte can improve the problems of poor cycle performance and storage performance of the corresponding lithium ion battery under high-temperature and high-pressure conditions.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion battery manufacturing, in particular to a lithium ion battery electrolyte, a lithium ion battery and an electric device. BACKGROUND

[0002] Since the commercialization of lithium ion secondary batteries in 1991, as their applications have been continuously expanded from portable electronic devices to electric vehicles and energy storage power grids, people's demand for battery energy density has also increased, and it is increasingly urgent to seek a breakthrough in this key performance indicator. High-voltage spinel-type lithium nickel manganese oxide LiNi 0.5 Mn 1.5 O4(LNMO) electrode is a kind of extremely potential positive electrode material due to its high charge-discharge platform (4.7-4.8V), suitable ionic conductivity (10 -4 S / cm) and fast lithium ion transport kinetics (10 -9 cm -2 / S -1 ). The theoretical specific capacity of the LNMO positive electrode is 147mAh / g, and the battery assembled based on the electrode is expected to achieve an energy density of more than 250Wh / kg, while the cost of LNMO particles is only about 21000 US dollars per ton, and its cost-effectiveness can be comparable or even superior to the current commercialized power battery positive electrode, which has good application prospects. However, the current battery system based on the LNMO electrode has the problem of poor cycle performance and storage performance under high temperature and high pressure conditions in actual application, which further affects the application and promotion of this type of battery. SUMMARY

[0003] The purpose of the present application is to provide a lithium ion battery electrolyte, a lithium ion battery and an electric device, the use of which can improve the problem of poor cycle performance and storage performance of the corresponding lithium ion battery under high temperature and high pressure conditions.

[0004] Embodiments of the present application are implemented as follows:

[0005] In a first aspect, the embodiments of the present application provide a lithium ion battery electrolyte, which comprises a solvent, a lithium salt and an additive, and the additive comprises a fluoropyridine compound, a tetra-vinyl compound and an isocyanate compound; wherein the mass percentage of the fluoropyridine compound in the electrolyte is 0.1-2%, the mass percentage of the tetra-vinyl compound in the electrolyte is 0.1-2%, and the mass percentage of the isocyanate compound in the electrolyte is 0.05-1%.

[0006] In the technical solution, the electrolyte contains three different functional additives. Specifically, the fluoropyridine compound mainly functions as a negative electrode film-forming additive, can generate an SEI film rich in lithium nitride and lithium fluoride at the negative electrode, lithium fluoride and lithium nitride are inorganic compounds, have excellent stability in organic solvents, are not easy to decompose, and have certain resistance to free acid in the electrolyte, so as to alleviate the erosion of trace acid in the electrolyte on the negative electrode SEI film, thereby ensuring the long-term stability of the negative electrode interface; the tetra-vinyl compound mainly functions as a positive electrode film-forming additive, can generate a dense oxide CEI film at the positive electrode, the film layer has excellent electrochemical stability, can effectively prevent the electrolyte from reacting with the positive electrode material during the cycle process, so as to alleviate the erosion of the electrolyte on the positive electrode CEI film, thereby ensuring the long-term stability of the positive electrode interface; the isocyanate compound mainly functions as an acid-removing agent, can remove trace acid in the electrolyte, so as to alleviate the corrosion of trace acid in the electrolyte on the positive and negative electrode materials under high temperature and high pressure conditions, obviously reduce the gas production of the battery, and also can greatly improve the stability of the electrolyte working at high voltage. By adopting three specific types of functional components and limiting the amount of the three functional components in a specific range, the lithium ion battery corresponding to the electrolyte has excellent cycle performance and storage performance under high temperature and high pressure conditions.

[0007] In some optional embodiments, the lithium ion battery electrolyte satisfies at least one of the following conditions A-C:

[0008] A. The mass percentage of the fluoropyridine compound in the electrolyte is 0.3-1%.

[0009] B. The mass percentage of the tetra-vinyl compound in the electrolyte is 0.3-1%.

[0010] C. The mass percentage of the isocyanate compound in the electrolyte is 0.05-0.5%.

[0011] In some optional embodiments, the lithium ion battery electrolyte satisfies at least one of the following conditions A-C:

[0012] D. The mass percentage of the fluoropyridine compound in the electrolyte is 0.3-0.5%.

[0013] E. The mass percentage of the tetra-vinyl compound in the electrolyte is 0.3-0.5%.

[0014] F. The mass percentage of the isocyanate compound in the electrolyte is 0.1-0.3%.

[0015] In the technical solution, the use amount of the three functional components is step by step limited in a specific range, so that each functional component has a more appropriate amount, so that the three functional components can play a better effect, and then the corresponding lithium ion battery has more excellent cycle performance and storage performance under high temperature and high pressure conditions; when the use amount of fluoropyridine compounds, tetra-vinyl compounds and isocyanate compounds is limited in the range of 0.3-0.5%, 0.3-0.5% and 0.1-0.3% respectively, the cycle performance and storage performance of the corresponding battery under high temperature and high pressure conditions are improved more significantly.

[0016] In some optional embodiments, the fluoropyridine compound includes at least one of 2-fluoropyridine, 2,4-difluoropyridine, 2,5-difluoropyridine, 2,6-difluoropyridine and 2,4,6-trifluoropyridine.

[0017] In the technical solution, a specific type of fluoropyridine compound is used, which can better adapt to many other components in the electrolyte, thereby better maintaining the stability of the negative electrode interface without affecting the action of the other functional components.

[0018] In some optional embodiments, the tetra-vinyl compound includes at least one of tetra-vinyl tin, tetra-vinyl silane and tetra-vinyl tetramethylcyclotetrasiloxane.

[0019] In the technical solution, a specific type of tetra-vinyl compound is used, which can better adapt to many other components in the electrolyte, thereby better maintaining the stability of the positive electrode interface without affecting the action of the other functional components.

[0020] In some optional embodiments, the isocyanate compound includes at least one of hexamethylene diisocyanate, phenylene diisocyanate and tolyl isocyanate.

[0021] In the technical solution, a specific type of isocyanate compound is used, which can better adapt to many other components in the electrolyte, thereby more thoroughly removing trace amounts of acid in the electrolyte without affecting the action of the other functional components.

[0022] In some optional embodiments, the solvent includes a fluorinated solvent, and the fluorinated solvent includes at least one of cyclic fluorinated ethylene carbonate, fluorinated propylene carbonate and fluorinated methyl ethyl carbonate.

[0023] In the technical solution, the solvent is a fluorine-containing solvent, and the type of the solvent is limited in a specific range, so that multiple additives with specific functions can exist stably in the electrolyte and be well compounded together, and thus the whole electrolyte system is more suitable for high-temperature and high-pressure application conditions. Accordingly, the battery corresponding to the electrolyte has more excellent cycle performance and storage performance under high-temperature and high-pressure conditions.

[0024] In some optional embodiments, the lithium salt includes at least one of lithium hexafluorophosphate and lithium bisfluorosulfonylimide.

[0025] Optionally, the mass percentage of the lithium salt in the electrolyte is 10-16%.

[0026] In the technical solution, the lithium salt of the specific type has the advantages of good compatibility and adaptability, so that the whole electrolyte system is more stable, and thus is more suitable for high-temperature and high-pressure application conditions.

[0027] Further, the amount of the lithium salt is limited in a specific range, so that the inherent function of the lithium salt can be better exerted without affecting the effects of numerous other functional components.

[0028] In some optional embodiments, the electrolyte further includes an auxiliary additive, and the auxiliary additive includes at least one of lithium difluoro(oxalato)phosphate, lithium tetrafluoro(oxalato)phosphate, and lithium difluoro(oxalato)borate.

[0029] Optionally, the mass percentage of the auxiliary additive in the electrolyte is 0.2-1%.

[0030] In the technical solution, the specific type of auxiliary additive is added to the electrolyte, and the auxiliary additive is combined with the three specific functional additives, so that the battery corresponding to the electrolyte has more excellent cycle performance and storage performance under high-temperature and high-pressure conditions.

[0031] Further, the amount of the auxiliary additive is limited in a specific range, so that the function of the auxiliary additive can be better exerted without affecting the effects of numerous other functional components.

[0032] In a second aspect, the embodiments of the present application provide a lithium ion battery, which includes a shell, an electrode assembly, and the electrolyte provided in the first aspect. The electrode assembly is accommodated in the shell, and the electrolyte is accommodated in the shell.

[0033] In the technical solution, the lithium ion battery includes the electrolyte provided in the first aspect, so that the lithium ion battery has more excellent cycle performance and storage performance under high-temperature and high-pressure conditions.

[0034] In some optional embodiments, in the battery positive electrode of the electrode assembly, the positive active material includes spinel-type lithium nickel manganese oxide.

[0035] In the technical solution, the spinel-type lithium nickel manganese oxide is used as the positive active material, so that the lithium ion battery is more suitable for high-temperature and high-pressure application conditions.

[0036] In some optional embodiments, in the battery negative electrode of the electrode assembly, the negative active material includes at least one of metal lithium, graphite, soft carbon, hard carbon, silicon, silicon oxide compounds and silicon-carbon composites.

[0037] In the technical solution, the applicable types of the negative active material are more, and more embodiments can be implemented, so that the technical solution provided by the application is facilitated to be popularized and applied.

[0038] In a third aspect, the embodiments of the application provide a power consumption device including the lithium ion battery provided in the second aspect. BRIEF DESCRIPTION OF DRAWINGS

[0039] In order to more clearly illustrate the technical solutions of the embodiments of the application, the drawings needed in the embodiments will be briefly introduced as follows. It should be understood that the following drawings only show some of the embodiments of the application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0040] Figure 1 A film formation curve diagram of the positive electrode film formation additive provided by the embodiments of the application;

[0041] Figure 2 A film formation curve diagram of the negative electrode film formation additive provided by the embodiments of the application;

[0042] Figure 3 An acid removal curve diagram of the acid removal agent provided by the embodiments of the application. DETAILED DESCRIPTION

[0043] In order to make the purpose, technical solutions and advantages of the embodiments of the application more clear, the technical solutions in the embodiments of the application will be clearly and completely described below. If the specific conditions are not specified in the embodiments, the conventional conditions or the conditions recommended by the manufacturer are used. If the reagents or instruments used are not specified by the manufacturer, they are all conventional products that can be purchased on the market.

[0044] It should be noted that in the present application, "and / or", such as "feature 1 and / or feature 2", means that it can be "feature 1" alone, "feature 2" alone, or "feature 1" plus "feature 2". The three cases.

[0045] In addition, in the description of the present application, unless otherwise specified, the meaning of "multiple" in "one or more" refers to two or more; the range of "value a ~ value b" includes both end values "a" and "b", and the "unit of measurement" in "value a ~ value b + unit of measurement" represents the "unit of measurement" of both "value a" and "value b".

[0046] Currently, the battery system based on the LNMO electrode has the problems of poor cycle performance and storage performance under high temperature and high pressure conditions in practical application, which is mainly caused by the following aspects.

[0047] (1) The traditional carbonate electrolyte has serious oxidative decomposition under high pressure conditions, and the by-products generated will further affect the formation of the solid-state electrolyte interface film.

[0048] (2) The dissolution of Mn / Ni ions causes the destruction of the LNMO crystal structure, generates an interface side reaction, and leads to an increase in the internal impedance of the battery.

[0049] (3) The trace water in the battery will react with LiPF6 to produce HF, and then HF will attack the LNMO particles, causing the dissolution of transition metal ions to intensify, and at the same time, it will also cause more gas to be generated in the electrolyte, thereby affecting the performance of the corresponding battery.

[0050] The inventors found that by optimizing the electrolyte formula of the LNMO battery system, specifically, selecting specific types of positive electrode film-forming additives, negative electrode film-forming additives, and acid scavengers for compounding, and with the combined action of multiple functional components, the problems of poor cycle performance and storage performance of the corresponding lithium ion battery under high temperature and high pressure conditions can be improved.

[0051] The lithium ion battery electrolyte, lithium ion battery and electric equipment of the embodiments of the present application are described below.

[0052] In a first aspect, the embodiments of the present application provide a lithium ion battery electrolyte, the electrolyte comprising a solvent, a lithium salt and an additive, the additive comprising a fluoropyridine compound, a tetra-vinyl compound and an isocyanate compound; wherein the mass percentage of the fluoropyridine compound in the electrolyte is 0.1-2%, the mass percentage of the tetra-vinyl compound in the electrolyte is 0.1-2%, and the mass percentage of the isocyanate compound in the electrolyte is 0.05-1%.

[0053] In the present application, the electrolyte contains three different functional additives. Specifically, the fluoropyridine compound mainly functions as a negative electrode film-forming additive, can generate an SEI film rich in lithium nitride and lithium fluoride at the negative electrode, lithium fluoride and lithium nitride are inorganic compounds, have excellent stability in organic solvents, are not easy to decompose, and have certain resistance to free acid in the electrolyte, so as to alleviate the erosion of trace acid in the electrolyte on the negative electrode SEI film, thereby ensuring the long-term stability of the negative electrode interface; the tetra-vinyl compound mainly functions as a positive electrode film-forming additive, can generate a dense oxide CEI film at the positive electrode, the film layer has excellent electrochemical stability, can effectively prevent side reactions between the electrolyte and the positive electrode material during the cycle process, so as to alleviate the erosion of the electrolyte on the positive electrode CEI film, thereby ensuring the long-term stability of the positive electrode interface; the isocyanate compound mainly functions as an acid scavenger, can remove trace acid in the electrolyte, so as to alleviate the corrosion of trace acid in the electrolyte on the positive and negative electrode materials under high temperature and high pressure conditions, significantly reduce the gas production of the battery, and also can greatly improve the stability of the electrolyte working at high voltage.

[0054] It should be noted that only from the single function, the types of positive electrode film forming additives, negative electrode film forming additives and acid scavengers are relatively rich, but due to the large difference in physical and chemical properties of different types of compounds, most of the different types of additives have incompatibility problems in the process of compounding, which further leads to limited performance improvement of the corresponding battery, and even the performance is difficult to improve. This is also the reason why few multi-functional additives are compounded at present, especially when the number of additive components is three or more. At the same time, even if the additive combination that can be compounded is determined, the function of the additive is closely related to its content in the electrolyte, especially for this multi-functional additive compounded system. Specifically, if the amount of fluoropyridine compound is too much, it will make the SEI film formed on the negative electrode too thick, leading to increased interface impedance, affecting the cycle and storage performance; if the amount of tetra-vinyl compound is too much, it will make the CEI film formed on the positive electrode too thick, affecting the lithium extraction process of the battery, and also leading to poor cycle performance; if the amount of isocyanate compound is too much, it will react with lithium salt, affecting the cycle performance of the battery; in addition, the total amount of additives in the electrolyte also needs to be controlled, otherwise it will affect the basic function and overall stability of the electrolyte, which also increases the difficulty of determining the amount of each functional additive. In this application, researchers select a plurality of additive components that can be well compounded and limit the amount of each component to a specific range, which can overcome the difficulty of using multi-component additives, so that the lithium ion battery corresponding to the electrolyte has excellent cycle performance and storage performance under high temperature and high pressure conditions.

[0055] As an example, the lithium ion battery electrolyte satisfies at least one of the following conditions A-C:

[0056] A. The mass percentage of fluoropyridine compound in the electrolyte is 0.3-1%, for example, but not limited to, any one of the mass percentages of 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9% and 1% or a range value between any two of them.

[0057] B. The mass percentage of tetra-vinyl compound in the electrolyte is 0.3-1%, for example, but not limited to, any one of the mass percentages of 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9% and 1% or a range value between any two of them.

[0058] C. The mass percentage of isocyanate compound in the electrolyte is 0.05-0.5%, for example, but not limited to, any one of the mass percentages of 0.05%, 0.1%, 0.2%, 0.3%, 0.4% and 0.5% or a range value between any two of them.

[0059] As an example, the lithium ion battery electrolyte satisfies at least one of the following conditions A-C:

[0060] The mass percentage of D fluoropyridine compound in the electrolyte is 0.3-0.5%, for example but not limited to any one of the point values of 0.3%, 0.35%, 0.4%, 0.45% and 0.5% or a range value between any two of them.

[0061] The mass percentage of E tetraethenyl compound in the electrolyte is 0.3-0.5%, for example but not limited to any one of the point values of 0.3%, 0.35%, 0.4%, 0.45% and 0.5% or a range value between any two of them.

[0062] The mass percentage of F isocyanate compound in the electrolyte is 0.1-0.3%, for example but not limited to any one of the point values of 0.1%, 0.15%, 0.2%, 0.25% and 0.3% or a range value between any two of them.

[0063] In this embodiment, the amount of the three functional components is step by step limited in a specific range, so that each functional component has a more appropriate amount, so that the three functional components can play a better effect, and thus the corresponding lithium ion battery has more excellent cycle performance and storage performance under high temperature and high pressure conditions; wherein when the amounts of fluoropyridine compound, tetraethenyl compound and isocyanate compound are limited in the ranges of 0.3-0.5%, 0.3-0.5% and 0.1-0.3% respectively, the cycle performance and storage performance of the corresponding battery under high temperature and high pressure conditions are more significantly improved.

[0064] It should be noted that there are many specific types of fluoropyridine compounds, tetraethenyl compounds and isocyanate compounds. For the same type of additive, there are also differences in physical and chemical properties between different types of compounds. Considering the compounding effect of multiple components, the type of each functional additive can be adjusted.

[0065] As an example, the fluoropyridine compound includes at least one of 2-fluoropyridine, 2,4-difluoropyridine, 2,5-difluoropyridine, 2,6-difluoropyridine and 2,4,6-trifluoropyridine.

[0066] In this embodiment, a specific type of fluoropyridine compound is used, which can better adapt to many other components in the electrolyte, thereby better maintaining the stability of the negative electrode interface without affecting the action of the other functional components.

[0067] As an example, the tetra-vinyl compound includes at least one of tetra-vinyl tin, tetra-vinyl silane, and tetra-vinyl tetramethyl cyclotetrasiloxane.

[0068] In this embodiment, a specific type of tetra-vinyl compound is used, which can better adapt to many other components in the electrolyte, thereby better maintaining the stability of the positive electrode interface without affecting the action of other functional components.

[0069] As an example, the isocyanate compound includes at least one of hexamethylene diisocyanate, phenylene diisocyanate, and tolyl isocyanate.

[0070] In this embodiment, a specific type of isocyanate compound is used, which can better adapt to many other components in the electrolyte, thereby more thoroughly removing trace amounts of acid in the electrolyte without affecting the action of other functional components.

[0071] It should be noted that for the current high-pressure electrolyte, a high-pressure resistant fluorinated solvent is usually used as the electrolyte. However, due to the large number of functional additive components in the electrolyte, the stability of different functional additives in the solvent may differ, and therefore, in consideration of the overall stability of the electrolyte, the type of fluorinated solvent can be adjusted.

[0072] As an example, the solvent includes a fluorinated solvent, and the fluorinated solvent includes at least one of cyclic fluorinated ethylene carbonate, fluorinated propylene carbonate, and fluorinated methyl ethyl carbonate.

[0073] In this embodiment, the solvent is a fluorinated solvent and the type of the solvent is limited to a specific range, so that a plurality of specific functional additives can stably exist in the electrolyte and be better compounded together, thereby making the entire electrolyte system more suitable for high-temperature and high-pressure application conditions. Accordingly, the battery corresponding to the electrolyte has more excellent cycle performance and storage performance under high-temperature and high-pressure conditions.

[0074] As an example, the lithium salt includes at least one of lithium hexafluorophosphate and lithium bisfluorosulfonylimide.

[0075] In this embodiment, a specific type of lithium salt is used, which has the advantages of compatibility and adaptability, so that the entire electrolyte system is more stable, thereby being more suitable for high-temperature and high-pressure application conditions.

[0076] As an example, the mass percentage of the lithium salt in the electrolyte is 10-16%, such as but not limited to any one of 10%, 11%, 12%, 13%, 14%, 15%, and 16%, or a range value between any two of them.

[0077] In this embodiment, the amount of lithium salt is further limited in a specific range, which can better exert the inherent function of lithium salt without affecting the effects of many other functional components.

[0078] As an example, the electrolyte further includes an auxiliary additive, and the auxiliary additive includes at least one of lithium difluoro(oxalato)phosphate, lithium tetrafluoro(oxalato)phosphate, and lithium difluoro(oxalato)borate.

[0079] In this embodiment, a specific type of auxiliary additive is added to the electrolyte, and the auxiliary additive is combined with the three specific functional additives, so that the corresponding battery of the electrolyte has more excellent cycle performance and storage performance under high temperature and high pressure conditions.

[0080] As an example, the mass percentage of the auxiliary additive in the electrolyte is 0.2-1%, such as but not limited to any one of 0.2%, 0.4%, 0.6%, 0.8%, and 1%, or a range value between any two of them.

[0081] In this embodiment, the amount of auxiliary additive is further limited in a specific range, which can better exert the function of auxiliary additive without affecting the effects of many other functional components.

[0082] It should be noted that the functional components in the electrolyte that are not specifically mentioned or limited in the amount can be set according to the conventional selection in the art.

[0083] In a second aspect, the embodiments of the present application provide a lithium ion battery, which includes a shell, an electrode assembly, and an electrolyte as provided in the first aspect. The electrode assembly is contained in the shell; and the electrolyte is contained in the shell.

[0084] In the present application, the lithium ion battery includes the electrolyte as provided in the first aspect, so that it has more excellent cycle performance and storage performance under high temperature and high pressure conditions.

[0085] As an example, in the battery positive electrode of the electrode assembly, the positive electrode active material includes spinel lithium nickel manganese oxide, specifically LiNi 0.5 Mn 1.5 O4.

[0086] In this embodiment, the spinel lithium nickel manganese oxide is used as the positive electrode active material, so that the lithium ion battery is more suitable for high temperature and high pressure application conditions.

[0087] As an example, in the battery negative electrode of the electrode assembly, the negative electrode active material includes at least one of metal lithium, graphite, soft carbon, hard carbon, silicon, silicon oxide compound, and silicon-carbon composite.

[0088] In this embodiment, there are many applicable types of negative electrode active materials, and many possible implementation schemes, which facilitates the promotion and application of the technical solutions provided in this application.

[0089] It should be noted that, for lithium-ion batteries, structures that are not specifically described or limited can be set according to conventional choices in the field.

[0090] Thirdly, embodiments of this application provide an electrical device including a lithium-ion battery as provided in the second aspect of the embodiments.

[0091] It should be noted that there are no restrictions on the type of electrical equipment, such as mobile phones, portable devices, laptops, electric vehicles, electric cars, ships, spacecraft, electric toys, energy storage devices, and power tools.

[0092] The features and performance of this application will be further described in detail below with reference to the embodiments.

[0093] Example 1

[0094] This application provides a method for preparing a lithium-ion electrolyte, comprising the following steps:

[0095] Lithium salt was added to an organic solvent and stirred until homogeneous to obtain an electrolyte intermediate. Then, additives were added to the electrolyte intermediate and mixed to obtain the electrolyte. For the specific formulation designs of Example 1 and subsequent examples and comparative examples, please refer to Table 1.

[0096] Table 1 Electrolyte formulations for each embodiment and comparative example.

[0097]

[0098]

[0099]

[0100]

[0101] In Table 1, “—” indicates that no solvent is added; the amount of solvent used is the remainder after subtracting the amounts of other components from 100.

[0102] Experimental Example 1

[0103] Performance testing of negative electrode film-forming additives

[0104] Test method:

[0105] The electrolytes prepared in Comparative Examples 1 and 6 were used as test samples. These samples were then assembled into lithium-ion batteries (see Example 4 for battery assembly instructions). The batteries were charged to 4.8V at a constant current of 0.05C at room temperature. The voltage was plotted on the x-axis, and the data was plotted on the d-axis.Q d V The data is plotted on the vertical axis and then drawn into a chart to obtain the corresponding film formation curve.

[0106] See Figure 1 It is known that after adding the negative electrode film-forming additive provided in the embodiments of this application to the electrolyte, the former begins to form an SEI film at around 2.5V, while the latter does not show film formation, compared to the latter without the addition of the negative electrode film-forming additive.

[0107] Experimental Example 2

[0108] Performance testing of cathode film-forming additives

[0109] Test method:

[0110] The electrolytes prepared in Comparative Examples 1 and 5 were used as test samples. These samples were then assembled into lithium-ion batteries (see Example 4 for battery assembly instructions). The batteries were charged to 4.8V at a constant current of 0.05C at room temperature. The voltage was plotted on the x-axis, and the data was plotted on the d-axis. Q d V The data is plotted on the vertical axis and then drawn into a chart to obtain the corresponding film formation curve.

[0111] See Figure 2 It is known that after adding the positive electrode film-forming additive provided in the embodiments of this application to the electrolyte, the former begins to form a CEI film at around 4.2V, while the latter does not show film formation, compared to the latter without the addition of the positive electrode film-forming additive.

[0112] Experimental Example 3

[0113] Performance testing of deacidifying agents

[0114] Test method:

[0115] The electrolytes prepared in Comparative Examples 1 and 7 were used as test samples and sealed in an oven at 45°C. At regular intervals, portions of the electrolyte samples were removed from a glove box filled with argon gas, and the free acid content in the electrolyte was tested using triethylamine potentiometric titration. The remaining electrolyte was then sealed and stored in the oven at 45°C. A graph was plotted with storage time on the x-axis and free acid content on the y-axis to obtain the change in electrolyte acidity over different storage times.

[0116] See Figure 3 It can be seen that after adding the acid remover provided in the embodiments of this application to the electrolyte, compared with the addition of the acid remover, the acid content in the mixed system corresponding to the former increases slowly and tends to be at a level, while the acid content in the mixed system corresponding to the latter increases significantly.

[0117] Test Example 4

[0118] Electrolyte electrical performance testing

[0119] Test method:

[0120] The electrolytes prepared in Examples 1-20 and Comparative Examples 1-10 were assembled into lithium-ion batteries and numbered accordingly. Then, the capacity retention rate of the lithium-ion batteries after 500 cycles at 45°C and the capacity retention rate, capacity recovery rate and thickness expansion rate after 7 days of storage at 60°C were tested.

[0121] in,

[0122] The assembly of lithium-ion batteries is carried out according to the following method:

[0123] S1 is mixed with LiNi at a mass ratio of 96.8:2.0:1.2 0.5 Mn 1.5 O4 (positive electrode active material), conductive carbon black (conductive agent), and polyvinylidene fluoride (binder) are dispersed in N-methyl-2-pyrrolidone to obtain a positive electrode slurry. Then, the positive electrode slurry is uniformly coated on both sides of an aluminum foil. Then, it is dried, rolled, and vacuum dried in sequence. After aluminum leads are welded on using an ultrasonic welding machine, a positive electrode sheet with a thickness of 125 μm is obtained.

[0124] S2 is mixed with graphite (negative electrode active material), conductive carbon black (conductive agent), styrene-butadiene rubber and carboxymethyl cellulose (binder) in a mass ratio of 95:1.5:1.5:2 and dispersed in deionized water to obtain a negative electrode slurry. Then, the negative electrode slurry is coated on both sides of a copper foil. Then, it is dried, rolled and vacuum dried in sequence, and nickel leads are welded on using an ultrasonic welding machine to obtain a negative electrode sheet with a thickness of 125μm.

[0125] S3 The prepared positive electrode sheet, separator (PE-coated ceramic separator, 20 μm thick) and negative electrode sheet are stacked in sequence and wound to prepare a bare cell. Then, the bare cell, the shell and the battery electrolyte group prepared in Examples 1-12 and Comparative Examples 1-9 are injected into the dried battery. After encapsulation, standing, formation, shaping and capacity testing, a lithium secondary battery is obtained.

[0126] The specific performance testing methods are as follows:

[0127] (1) Capacity retention test after 500 cycles at 45℃

[0128] Charge the battery at 45℃ with a constant current of 0.5C to 4.9V, then charge it with a constant voltage to the cutoff current of 0.05C. Then discharge the battery with a constant current of 0.5C. Record the discharge capacity as C0. Repeat the charge and discharge steps until the capacity decays to 80%. Record the cycle number n and the discharge capacity Cn. Cycle capacity retention rate = Cn / C0*100%.

[0129] (2) Capacity retention, capacity recovery and thickness expansion rate after storage at 60℃ for 7 days

[0130] The battery was charged at 25℃ with a constant current of 0.5C to 4.9V, and then charged at a constant voltage of 4.9V until the cutoff current of 0.05C. It was then discharged at a constant current of 0.5C, and the discharge capacity was recorded as C2. The battery was removed, and its initial thickness was measured using a thickness meter and recorded as T1. At 25℃, the battery was charged at a constant current of 0.5C to 4.9V, and then charged at a constant voltage of 4.9V until the cutoff current of 0.05C. The battery was then transferred to 60℃ and stored for 7 days, and its thickness after 7 days was measured using a thickness meter and recorded as T2. The battery was then discharged at a constant current of 0.5C, and the discharge capacity was recorded as C3. Then, it was charged and discharged once more at 0.5C, and the capacity was recorded as C4. The capacity retention rate after 7 days of storage at 60℃ is calculated as C3 / C2*100%, the capacity recovery rate after 7 days of storage at 60℃ is calculated as C4 / C2*100%, and the battery expansion rate is calculated as 100%*(T2T1) / T1.

[0131] Table 2 Performance test statistics for each embodiment and comparative example

[0132]

[0133]

[0134] Referring to Table 2, the test results of Examples 1-20 and Comparative Examples 1-10 show that, when the three additives with specific functions provided in the embodiments of this application are used in combination, compared with the use of no additives, only some of the additives provided in the embodiments of this application, and other additives with the same function but different types, the lithium-ion batteries corresponding to the former have better cycle performance and storage performance under high temperature and high pressure conditions.

[0135] As can be seen from the test results of Examples 1 and 2, based on the compounding of the three specific functional additives provided in the embodiments of this application, further using the specific types of auxiliary additives provided in the embodiments of this application can enable the corresponding lithium-ion batteries to have better cycle performance and storage performance under high temperature and high pressure conditions.

[0136] The test results from Examples 1 and 3-6, Examples 1 and 9-12, and Examples 1 and 15-18 show that limiting the three specific functional additives to specific ranges step by step helps to improve the cycle performance and storage performance of the corresponding lithium-ion batteries under high temperature and high pressure conditions. In particular, when the amounts of fluoropyridine compounds, tetravinyl compounds, and isocyanate compounds are limited to the ranges of 0.3-0.5%, 0.3-0.5%, and 0.1-0.3%, respectively, the cycle performance and storage performance of the corresponding batteries under high temperature and high pressure conditions are significantly improved.

[0137] The test results from Examples 1 and 7-8, Examples 1 and 13-14, and Examples 1 and 19-20 show that when the types of the three functional additives are limited to a specific range, compared with other similar components that are not within the limited range, the lithium-ion batteries corresponding to the former have better cycle performance and storage performance under high temperature and high pressure conditions.

[0138] The embodiments described above are some, but not all, of the embodiments of this application. The detailed description of the embodiments of this application is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

Claims

1. A lithium-ion battery electrolyte, characterized in that, The electrolyte comprises a solvent, a lithium salt and an additive, the additive comprising a fluoropyridine compound, a tetra-vinyl compound and an isocyanate compound; The fluoropyridine compound has a mass percentage of 0.3-0.5% in the electrolyte, the tetra-vinyl compound has a mass percentage of 0.3-0.5% in the electrolyte, and the isocyanate compound has a mass percentage of 0.1-0.3% in the electrolyte. The fluoropyridine compound comprises at least one of 2-fluoropyridine, 2,4-difluoropyridine, 2,5-difluoropyridine, 2,6-difluoropyridine and 2,4,6-trifluoropyridine. The tetra-vinyl compound comprises at least one of tetra-vinyl tin and tetra-vinyl silane. The isocyanate compound comprises at least one of hexamethylene diisocyanate, phenylene diisocyanate and tolyl isocyanate.

2. The electrolyte for lithium ion batteries according to claim 1, characterized in that, The solvent comprises a fluorinated solvent, the fluorinated solvent comprising at least one of cyclic fluorinated ethylene carbonate, fluorinated propylene carbonate and fluorinated ethyl methyl carbonate.

3. The electrolyte for lithium ion batteries according to claim 1, characterized in that, The lithium salt comprises at least one of lithium hexafluorophosphate and lithium bisfluorosulfonylimide.

4. The electrolyte for lithium-ion batteries according to claim 3, characterized in that, The lithium salt has a mass percentage of 10-16% in the electrolyte.

5. The electrolyte for lithium ion batteries according to claim 1, wherein The electrolyte further comprises an auxiliary additive, the auxiliary additive comprising at least one of lithium difluoro(oxalato)phosphate, lithium tetrafluoro(oxalato)phosphate and lithium difluoro(oxalato)borate.

6. The electrolyte for lithium-ion batteries according to claim 5, characterized in that, The auxiliary additive has a mass percentage of 0.2-1% in the electrolyte.

7. A lithium-ion battery, characterized by It comprises: a housing; an electrode assembly accommodated in the housing; and the electrolyte as claimed in any one of claims 1-6 is accommodated in the housing. In a battery positive electrode of the electrode assembly, a positive active material comprises spinel lithium nickel manganese oxide.

8. The lithium-ion battery of claim 7, wherein, In a battery negative electrode of the electrode assembly, a negative active material comprises at least one of metallic lithium, graphite, soft carbon, hard carbon, silicon, silicon oxide compound and silicon-carbon composite.

9. The lithium-ion battery according to claim 7 or 8, characterized in that The electric device comprises the lithium ion battery as claimed in any one of claims 7-9.

10. An electric device, characterized by ​

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