A lithium ion battery electrolyte and a lithium ion battery containing the electrolyte

Abstract

The application belongs to the technical field of lithium ion batteries, and discloses a lithium ion battery electrolyte and a lithium ion battery containing the electrolyte. The lithium ion battery electrolyte comprises a non-aqueous organic solvent, a lithium salt and an additive, wherein the additive comprises a conventional additive and a compound A, and the structure of the compound A is shown in formula (I): wherein R is independently selected from one of an alkyl group with 1-4 carbons, an alkenyl group, an isocyanate group, a fluorinated alkyl group, a phenyl group, a silicon group and a substituted product thereof. The lithium ion battery electrolyte fully plays the performance of the lithium ion battery and prolongs the calendar and cycle life of the lithium ion battery through optimization of a formula, especially under the synergistic effect of a unique combination of a mixed lithium salt, a negative electrode film-forming additive, a positive electrode protection additive and the compound A with a specific structure.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a lithium-ion battery electrolyte and a lithium-ion battery containing the electrolyte. Background Technology

[0002] High energy density is the eternal pursuit of lithium-ion batteries. Thanks to the successful commercialization of lithium-ion batteries, their energy density has been significantly improved. However, current lithium-ion batteries still cannot meet the growing demands of electric vehicles and portable electronic devices. To achieve higher energy density in commercial ternary lithium-ion batteries, there are two main paths: one is to gradually increase the proportion of nickel in the ternary cathode material, and the other is to steadily increase the cutoff voltage of the cathode material. However, both approaches place higher demands on the stability of the electrolyte: high nickel content in the cathode material affects the stability of the electrolyte under high-temperature conditions, and continuous charging and discharging can easily lead to gas generation; conventional electrolytes are prone to side reactions with the cathode material surface at high voltages, affecting the performance of high-voltage ternary cathode materials. To address these issues, in addition to utilizing the synergistic combination of conventional additives, it is also necessary to develop novel film-forming additives. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the aforementioned background technology and to provide a lithium-ion battery electrolyte and a lithium-ion battery containing the electrolyte. The lithium-ion battery electrolyte of this invention, through optimized formulation and the synergistic effect of a unique combination of multiple components, effectively solves the high-temperature storage performance and cycle performance issues of lithium-ion batteries. This results in an electrolyte system with both high energy density and high safety performance, which is beneficial for meeting the requirements of high-temperature storage performance and safety performance of electrolytes, thereby improving the electrochemical performance of lithium-ion batteries.

[0004] To achieve the above objectives, the lithium-ion battery electrolyte of the present invention comprises a non-aqueous organic solvent, a lithium salt, and additives, wherein the additives include conventional additives and compound A, and the structure of compound A is shown in formula (I):

[0005]

[0006] R is independently selected from one of alkyl, alkenyl, isocyanate, fluoroalkyl, phenyl, silyl and their substitutes, which have 1 to 4 carbon atoms.

[0007] Furthermore, in some embodiments of the present invention, compound A is selected from at least one of the compounds shown in the following structural formulas:

[0008]

[0009] Preferably, in some embodiments of the present invention, the content of the compound A additive is 0.5 to 1.0% of the total mass of the lithium-ion battery electrolyte.

[0010] Furthermore, in some embodiments of the present invention, the lithium-ion battery electrolyte also contains other additives, which are selected from at least one of fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinyl sulfate (DTD), 1,3-propanesulfonate lactone (PS), 1,3-propenesulfonate lactone (PST), tris(trimethylsilyl)borate (TMSB), tris(trimethylsilyl)phosphate (TMSP), tetravinylsilane (TVS), and citralic anhydride (CA).

[0011] Preferably, in some embodiments of the present invention, the content of the other additives is 0.5 to 3.0% of the total mass of the lithium-ion battery electrolyte.

[0012] Furthermore, in some embodiments of the present invention, the lithium salt is selected from at least two of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiDFP), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(oxalate-borate) (LiBOB), lithium di(fluorooxalate-borate) (LiDFOB), lithium tetrafluorooxalate-phosphate (LiOTFP), and lithium di(fluorobis(oxalate-borate)) (LiDFOP).

[0013] Preferably, in some embodiments of the present invention, the content of the lithium salt is 15-17% of the total mass of the lithium-ion battery electrolyte.

[0014] Furthermore, in some embodiments of the present invention, the non-aqueous organic solvent is one or more of chain carbonates and cyclic carbonates.

[0015] Preferably, in some embodiments of the present invention, the cyclic carbonate is one or more of ethylene carbonate and propylene carbonate; the chain carbonate is one or more of ethyl methyl carbonate, dimethyl carbonate, and diethyl carbonate.

[0016] More preferably, in some embodiments of the present invention, the non-aqueous organic solvent is a mixture of ethylene carbonate (EC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC).

[0017] On the other hand, the present invention also provides a lithium-ion battery, the lithium-ion battery comprising a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and the lithium-ion battery electrolyte.

[0018] Preferably, in some embodiments of the present invention, the positive electrode sheet includes a positive current collector and a positive electrode film on the surface of the positive current collector, the positive electrode film including a positive electrode active material, a conductive agent and a binder, wherein the positive electrode active material is LiNi. 1-x-y-z Co x Mn y Al z O2, lithium nickel manganese oxide, lithium cobalt oxide, lithium-rich manganese-based solid solution, lithium manganese oxide, wherein: 0≤x≤1, 0≤y≤1, 0≤z≤1 and 0≤x+y+z≤1, and the negative electrode active material is artificial graphite, lithium metal, coated natural graphite, silicon-carbon negative electrode, silicon negative electrode.

[0019] Compared with the prior art, the advantages of the present invention are as follows:

[0020] (1) On the one hand, the compound A with a specific structure in the lithium-ion battery electrolyte of the present invention can preferentially EC-reduced into a stable SEI film at the negative electrode, and the film-forming impedance is low; on the other hand, the additive containing a trimethylsilyl structure in compound A can combine with the trace amounts of HF and moisture released by the electrolyte under high temperature conditions, thus mitigating the damage to the electrode material.

[0021] (2) The lithium-ion battery electrolyte of the present invention, through optimized formulation, especially through the synergistic effect of a unique combination of mixed lithium salts, negative electrode film-forming additives, positive electrode protective additives and compound A with a specific structure, fully utilizes the performance of lithium-ion batteries and extends the calendar and cycle life of lithium-ion batteries. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. Additional aspects and advantages of this invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. It should be understood that the following description is merely illustrative and not intended to limit the invention.

[0023] The terms “comprising,” “including,” “having,” “containing,” or any other variations thereof, as used herein, are intended to cover a non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0024] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1 to 5” is disclosed, the described range should be interpreted as including the ranges “1 to 4”, “1 to 3”, “1 to 2”, “1 to 2 and 4 to 5”, “1 to 3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range.

[0025] The singular form includes the plural objects of discussion unless the context clearly indicates otherwise. "Optional" or "any one" means that the matter or event described thereafter may or may not occur, and the description includes both the possibility that the event occurs and the possibility that the event does not occur.

[0026] The indefinite articles “a” and “an” preceding an element or component of this invention do not impose any limitation on the quantity (i.e., number of times) of the element or component. Therefore, “an” or “a” should be interpreted as including one or at least one, and the singular form of an element or component also includes the plural form, unless the quantity clearly refers only to the singular form.

[0027] Furthermore, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., described below refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms are not necessarily directed at the same embodiment or example. Moreover, the technical features involved in the various embodiments of the present invention can be combined with each other as long as they do not conflict with each other.

[0028] The structural characterization of compound A in the examples and comparative examples is as follows:

[0029]

[0030] Example 1

[0031] The lithium-ion battery electrolyte was prepared as follows: In an argon-filled glove box (moisture < 0.1 ppm, oxygen < 0.1 ppm), ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) were mixed uniformly in a mass ratio of 30:20:50 to obtain a mixed solution. Then, 13.5% of lithium hexafluorophosphate (LiPF6), 1.0% of lithium difluorophosphate (LiDFP), and 0.5% of lithium difluorobis(oxalato) phosphate (LiDFOP) based on the total mass of the electrolyte were added to the mixed solution and stirred until completely dissolved. Then, 0.5% of A9, 1% of ethylene sulfate (DTD), and 0.5% of 1,3-propenesulfonate lactone (PST) based on the total mass of the electrolyte were added and stirred uniformly to obtain the lithium-ion battery electrolyte of Example 1.

[0032] Example 2-14

[0033] Examples 2-14 are also specific examples of electrolytes. Except for the parameters in Table 1, the other parameters and preparation methods are the same as in Example 1.

[0034] Comparative Examples 1-5

[0035] In Comparative Examples 1-5, except for the parameters in Table 1, the other parameters and preparation methods are the same as in Example 1.

[0036] Table 1. Composition ratio of electrolyte components in Examples 1-14 and Comparative Examples 1-5

[0037]

[0038]

[0039] Note: Lithium salt concentration is the mass percentage in the electrolyte;

[0040] The content of compound A is its mass percentage in the electrolyte;

[0041] The content of each component in other additives is the mass percentage in the electrolyte;

[0042] The proportions of each component in the solvent are by mass.

[0043] Lithium-ion battery performance testing

[0044] Preparation of lithium-ion batteries:

[0045] LiNi, the positive electrode active material 0.6 Co 0.2 Mn 0.2O2 (622), conductive agent acetylene black, carbon nanotubes, and binder polyvinylidene fluoride (PVDF) were mixed in an N-methylpyrrolidone solvent system at a mass ratio of 95:2.8:0.2:2. The mixture was thoroughly stirred and homogenized in a nitrogen-filled dry environment, then coated onto an Al foil, dried, and cold-pressed to obtain a positive electrode sheet with a compaction density of 3.60 g / cm³. 3 .

[0046] The negative electrode active material graphite, conductive agent acetylene black, carbon nanotubes, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) were thoroughly mixed in a deionized water solvent system at a mass ratio of 96:1.8:0.2:1:1. This mixture was then coated onto Cu foil, dried, and cold-pressed to obtain the negative electrode sheet. A 14 μm polyethylene (PE) base film was used as the base film, and a 2 μm nano-alumina coating was coated onto the base film as a separator.

[0047] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes for isolation. The cells are then wound to obtain a bare battery cell. The bare battery cell is placed in an outer packaging, and the electrolyte prepared in each embodiment and comparative example is injected. The battery undergoes encapsulation, resting, formation, aging, secondary encapsulation, and capacity testing to obtain a high-nickel NCM622 / AG-4.3V ternary cathode material soft-pack lithium-ion battery. Performance tests were conducted on the batteries from each embodiment and comparative example. The test results are shown in Table 2.

[0048] 1) Room temperature cycling performance

[0049] Under normal temperature (25±2℃) conditions, the above-mentioned NCM622 battery was charged to 4.3V at 1C constant current and constant voltage, with a cutoff current of 0.05C; rested for 5 minutes, and then discharged to 3.0V at 1C constant current, and rested for 5 minutes. This charging and discharging cycle was repeated. When the cycle capacity reached 80% of the initial capacity, the cycle life of the battery was recorded.

[0050] 2) High-temperature cycling performance

[0051] Under high temperature (45℃) conditions, the above-mentioned NCM622 batteries were charged to 4.3V at 1C constant current and constant voltage, with a cutoff current of 0.05C; rested for 5 minutes, and then discharged to 3.0V at 1C constant current, and rested for 5 minutes. This charging and discharging cycle was repeated. When the cycle capacity reached 80% of the initial capacity, the cycle life of the battery was recorded.

[0052] 3) High-temperature storage performance

[0053] Under normal temperature (25±2℃) conditions, a lithium-ion battery is subjected to one 1C / 1C charge and discharge cycle (the discharge capacity is denoted as D). C0Then, the NCM622 / AG batteries were charged to 4.3V under constant current and constant voltage conditions at 1C. The fully charged lithium-ion batteries were then stored in a 60°C high-temperature chamber for 14 days and discharged at 1C under normal temperature conditions (the discharge capacity is denoted as D). C1 Then, under normal temperature conditions, perform 1C / 1C charging and discharging (discharge capacity denoted as D). C2 The following formulas are used to calculate the capacity retention rate and capacity recovery rate of lithium-ion batteries.

[0054] Seventh-day volume retention rate (%) = D C1 / D C0 ×100%;

[0055] Volume recovery rate on day 7 (%) = D C2 / D C0 ×100%;

[0056] Table 2. Performance test results of lithium-ion batteries in each comparative example and embodiment.

[0057]

[0058]

[0059] Compared to Comparative Examples 4 and 5, the lithium-ion batteries of Examples 1 and 2 showed significant improvements in room temperature and high temperature cycling performance, as well as high temperature storage performance. The comparative results indicate that the effect of additive compound A alone is not very significant, and that adding an appropriate amount of compound A is crucial to maximizing the performance of this additive.

[0060] As can be seen from the electrochemical performance of Comparative Examples 2 and 3 and Examples 1-14 in Table 2, the compound A additive described in this invention, when used in combination with other additives, has a better effect. This is mainly because the specific structure compound A described in this invention can preferentially form a film on the negative electrode surface, thereby improving the stability of the negative electrode. At the same time, other functional groups of this compound, such as isocyanate groups, help to improve the stability of the positive electrode protective layer and mitigate the damage of the electrolyte to the electrode material. Unsaturated groups also show good performance in high-temperature storage.

[0061] Those skilled in the art will readily understand that the above description is merely an embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A lithium-ion battery electrolyte, characterized in that, The lithium-ion battery electrolyte is composed of a non-aqueous organic solvent, a lithium salt, and additives. The additives consist of compound A and other additives, wherein compound A is selected from at least one of the compounds shown in the following structural formulas: The other additives are vinyl sulfate and 1,3-propenesulfonate lactone, or vinyl sulfate and tetravinylsilane, or fluorovinyl carbonate and tetravinylsilane, or vinyl sulfate and 1,3-propanesulfonate lactone.

2. The lithium-ion battery electrolyte according to claim 1, characterized in that, The content of the compound A additive is 0.5~1.0% of the total mass of the lithium-ion battery electrolyte.

3. The lithium-ion battery electrolyte according to claim 1, characterized in that, The content of the other additives is 0.5 to 3.0% of the total mass of the lithium-ion battery electrolyte.

4. The lithium-ion battery electrolyte according to claim 1, characterized in that, The lithium salt is selected from at least two of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorophosphate, lithium bisfluorosulfonylimide, lithium bis(oxalate)borate, lithium difluorooxalateborate, lithium tetrafluorooxalate phosphate, and lithium difluorobis(oxalate) phosphate.

5. The lithium-ion battery electrolyte according to claim 1 or 4, characterized in that, The lithium salt content is 15-17% of the total mass of the lithium-ion battery electrolyte.

6. The lithium-ion battery electrolyte according to claim 1, characterized in that, The non-aqueous organic solvent is one or more of chain carbonates and cyclic carbonates.

7. The lithium-ion battery electrolyte according to claim 6, characterized in that, The cyclic carbonate is one or more of ethylene carbonate and propylene carbonate; the chain carbonate is one or more of ethyl methyl carbonate, dimethyl carbonate, and diethyl carbonate.

8. The lithium-ion battery electrolyte according to claim 1, characterized in that, The non-aqueous organic solvent is a mixture of ethylene carbonate, diethyl carbonate, and methyl ethyl carbonate.

9. A lithium-ion battery, characterized in that, The lithium-ion battery includes a positive electrode, a negative electrode, a separator placed between the positive and negative electrodes, and the lithium-ion battery electrolyte according to any one of claims 1-8.

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