A ternary high-voltage lithium ion battery nonaqueous electrolyte and a lithium ion battery

Abstract

The application belongs to the technical field of lithium ion batteries, and discloses a ternary high-voltage lithium ion battery nonaqueous electrolyte and a lithium ion battery. The ternary high-voltage lithium ion battery nonaqueous electrolyte comprises a nonaqueous organic solvent, an electrolyte lithium salt and a film-forming additive, the film-forming additive comprises a cyano compound containing a silicon ether structure, and the cyano compound containing the silicon ether structure has a structural formula as shown in formula (I): wherein the substituents R1 and R2 are each independently selected from alkyl, alkenyl, fluoroalkyl, phenyl and cyanoxyl with 1-4 carbons. The lithium ion battery nonaqueous electrolyte has high energy density and high safety performance through optimization of a formula and under the joint action of various components in a unique combination, and is beneficial to meeting the demand of the electrolyte on cycle performance under high voltage.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, in particular to a ternary high-voltage lithium ion battery non-aqueous electrolyte and lithium ion battery. BACKGROUND

[0002] With the progress of science and technology, people's quality requirements for living environment are continuously improved, and the environmental pollution problems caused by the increasing depletion and consumption of fossil energy are becoming more and more serious, so the research and development of clean and renewable new energy have become a top priority. At present, a large number of new energy has been developed and used, such as solar energy, wind energy, tidal energy and geothermal energy, etc., but these energies are limited in time and space, and need to be properly converted and stored for use.

[0003] As a kind of green and environmental protection high-energy battery, lithium ion battery is the most ideal and potential rechargeable battery in the world. Compared with other batteries, it has a series of advantages such as no memory effect, fast charge and discharge, high energy density, long cycle life and no environmental pollution, so it is widely used in small electronic devices such as notebook computers, camcorders, mobile phones, electronic watches, etc. With the increasing demand for lithium ion battery capacity in pure electric vehicles, hybrid electric vehicles and portable energy storage devices, people expect to develop lithium ion batteries with higher energy density and power density to realize long-lasting endurance and energy storage. Increasing the working voltage can increase the energy density of lithium ion battery, but the electrochemical window of traditional carbonate electrolyte is narrow, and after the voltage is increased, on the one hand, the electrolyte itself will decompose; on the other hand, the oxidation ability of the positive electrode is enhanced under high voltage, a large amount of metal is dissolved, gas is precipitated, and the material phase changes, which makes the battery fail and even dangerous. The above problems limit the development of high-voltage lithium ion batteries. Therefore, it is necessary to develop electrolyte resistant to high pressure. SUMMARY

[0004] The purpose of the present application is to overcome the shortcomings of the prior art, and to provide a ternary high-voltage lithium ion battery non-aqueous electrolyte and lithium ion battery. The ternary high-voltage lithium ion battery non-aqueous electrolyte of the present application has high energy density and high safety performance by optimizing the formula and under the joint action of a unique combination of multiple components, which is beneficial to meet the demand of electrolyte for cycle performance under high voltage.

[0005] To achieve the purpose of the present application, the ternary high-voltage lithium ion battery non-aqueous electrolyte of the present application comprises non-aqueous organic solvent, electrolyte lithium salt and film-forming additive, the film-forming additive comprises a cyano compound containing a siloxane structure, and the cyano compound containing a siloxane structure has a structural formula as shown in formula (I):

[0006]

[0007] wherein the substituents R1, R2 are each independently selected from the group consisting of alkyl, alkenyl, fluoroalkyl, phenyl and cyanooxy groups having 1-4 carbons.

[0008] Further, in some embodiments of the present application, the siloxane ether structure cyan compound is selected from at least one of the following compounds represented by the following structural formula:

[0009]

[0010] Further, in some embodiments of the present application, the mass percentage of the siloxane ether structure cyan compound in the electrolyte is 0.1-0.3%.

[0011] Further, in some embodiments of the present application, the film-forming additive further comprises at least one of 1,3-propane sulfone lactone (PS), fluoroethylene carbonate (FEC), lithium difluoro oxalate borate (LiDFOB).

[0012] Further, in some embodiments of the present application, the mass percentage of the 1,3-propane sulfone lactone (PS), fluoroethylene carbonate (FEC), lithium difluoro oxalate borate (LiDFOB) in the electrolyte is 0.5-5%.

[0013] Further, in some embodiments of the present application, the electrolyte lithium salt is selected from a mixture of one or more of lithium hexafluorophosphate and lithium bisfluorosulfonimide, lithium bis(trifluoromethanesulfonimide), lithium difluorobis(oxalato)phosphate, lithium difluorophosphate.

[0014] Further, in some embodiments of the present application, the mass percentage of the electrolyte lithium salt in the electrolyte is 10-20%.

[0015] Further, in some embodiments of the present application, the non-aqueous organic solvent is selected from a mixture of one or more of ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl propionate, propyl propionate.

[0016] In another aspect, the present application also provides a ternary high-voltage lithium ion battery, which comprises a positive electrode, a negative electrode, a separator and the aforementioned ternary high-voltage lithium ion battery non-aqueous electrolyte of the present application.

[0017] Further, in some embodiments of the present application, the active material of the positive electrode is a ternary NCM material; the material of the negative electrode is one or more of natural graphite, artificial graphite, lithium titanate, silicon-oxygen negative electrode, silicon negative electrode.

[0018] Further, in some embodiments of the present application, the upper cut-off voltage of the lithium ion battery is 4.35-4.5V.

[0019] Compared with the prior art, the present application has the advantages of:

[0020] (1) In the high-voltage lithium ion battery non-aqueous electrolyte of the present application, the functional groups contained in the cyano compound with a siloxane structure of a specific structural formula form a stable phosphate CEI film at high voltage on the positive electrode, inhibit the side reaction of the positive electrode and the electrolyte, optimize the aqueous acid environment, and ensure the thermal stability of the battery and improve the high-voltage performance of the battery.

[0021] (2) The high-voltage lithium ion battery non-aqueous electrolyte of the present application can ensure excellent cycle performance of the high-voltage lithium ion battery by optimizing the formula, improving the solvent, and combining the synergistic effect of the cyano compound with a siloxane structure of a specific structural formula, mixed lithium salt, and other additives, so that the electrolyte system has high energy density and high stability. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical scheme and advantages of the present application more clear and explicit, the present application is further described in detail below in combination with examples. Additional aspects and advantages of the present application will be partially given in the following description, partially will become apparent from the following description, or will be understood by the practice of the present application. It should be understood that the following description is only used to explain the present application, and is not used to limit the present application.

[0023] The terms "comprising", "including", "having" "with" or any other variation thereof, as used in the present application, are intended to cover non-exclusive inclusions. For example, a composition, step, method, article, or apparatus that comprises a list of elements is not necessarily limited to those elements, but can include other elements not explicitly listed or inherent to such composition, step, method, article, or apparatus.

[0024] When a range, a preferred range, or a range defined by a series of upper preferred values and lower preferred values is used to express an equivalent, a concentration, or other value or parameter, it should be understood that all ranges formed by any pairings of any range upper limit or preferred value with any range lower limit or preferred value are specifically disclosed, regardless of whether the range is disclosed separately. For example, when the range "1 to 5" is disclosed, the described range should be interpreted as including the range "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5", etc. When a numerical range is described herein, unless otherwise stated, the range is intended to include its end values and all integers and fractions within the range.

[0025] The singular form includes the plural discussion object, unless the context clearly indicates otherwise. "Optional" or "any one" means that the matter or event described thereafter can occur or not occur, and the description includes the case where the event occurs and the case where 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 structures of the silyl ether-containing cyano compounds in the examples and comparative examples are as follows:

[0029] The structural formula for M1 is:

[0030]

[0031] The structural formula for M2 is:

[0032]

[0033] The structural formula for M3 is:

[0034]

[0035] The structural formula for M4 is:

[0036]

[0037] The structural formula for M5 is:

[0038]

[0039] Example 1

[0040] Preparation of electrolyte: In an argon-filled glove box (oxygen content ≤ 1 ppm, water content ≤ 1 ppm), ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), propyl propionate (PP) were mixed uniformly in a volume ratio of 10:20:10:60 to obtain a mixed solution, then 11% lithium hexafluorophosphate (LiPF6), 1% lithium difluorophosphate (LiPO2F2) and 3% lithium bisfluorosulfonylimide (LiFSI) based on the total mass of the electrolyte were added to the mixed solution, followed by adding 0.2% of the siloxane structure cyan compound M1 based on the total mass of the electrolyte, 4% of 1,3-propane sultone (PS) based on the total mass of the electrolyte, 3% of fluoroethylene carbonate (FEC) based on the total mass of the electrolyte, 1% of lithium difluoro(oxalato)borate (LiDFOB) based on the total mass of the electrolyte to the mixed solution, and stirring to completely dissolve, to obtain the electrolyte of Example 1.

[0041] Examples 2-12

[0042] Examples 2-12 are also specific examples of electrolyte preparation, except that the composition and ratio of each component of the electrolyte are added as shown in Table 1, and other parameters and preparation methods are the same as Example 1. The electrolyte formula is shown in Table 1.

[0043] Comparative Examples 1-9

[0044] Comparative Examples 1-9 are the same as Example 1 except that the composition and ratio of each component of the electrolyte are added as shown in Table 1. The electrolyte formula is shown in Table 1.

[0045] Table 1 Electrolyte composition of examples and comparative examples

[0046]

[0047]

[0048]

[0049] Note: The content of each component in the lithium salt is the mass percentage in the electrolyte;

[0050] The content of the siloxane structure cyan compound is the mass percentage in the electrolyte;

[0051] The content of each component in the other additives is the mass percentage in the electrolyte;

[0052] The ratio of each component in the solvent is mass ratio.

[0053] Preparation of ternary battery:

[0054] The positive active material NCM622, conductive agent acetylene black, and binder polyvinylidene fluoride were mixed in a mass ratio of 95:3:2 in an N-methylpyrrolidone system, and then uniformly stirred to obtain a mixture. The mixture was coated on an aluminum foil, dried, and cold-pressed to obtain a positive electrode sheet.

[0055] The negative active material artificial graphite, conductive agent super carbon black, thickening agent sodium carboxymethyl cellulose, and binder styrene-butadiene rubber were mixed in a mass ratio of 95:1:2:2 in a deionized water solvent system, and then uniformly stirred to obtain a mixture. The mixture was coated on a copper foil, dried, and cold-pressed to obtain a negative electrode sheet.

[0056] A polyethylene film was used as a base film, and a nano-aluminum oxide coating was coated on the base film as a separator.

[0057] The positive electrode sheet, the separator, and the negative electrode sheet were stacked in order, with the separator between the positive and negative electrode sheets to play a separating role, and were wound to obtain a bare battery cell. The bare battery cell was placed in an outer package, injected with the prepared electrolyte, and subjected to processes such as packaging, standing, formation, aging, secondary packaging, and capacity distribution to obtain an NCM622 / graphite lithium ion battery.

[0058] Performance test of lithium ion battery

[0059] (1) Normal temperature cycle performance test: at 25℃, the above-mentioned ternary / graphite lithium ion battery was charged at 1C constant current and constant voltage to 4.35V, and the cutoff current was 0.05C, and then discharged at 1C constant current to 3.0V, respectively. After 500 cycles of charge / discharge, the cycle capacity retention rate at the 500th week was calculated. The calculation formula is:

[0060] The capacity retention rate at the 500th week = the cycle discharge capacity at the 500th week / the cycle discharge capacity at the first week x 100%.

[0061] (2) High-temperature storage performance at 60℃: the above-mentioned ternary / graphite lithium ion battery was charged and discharged at 1C at room temperature once, and the cutoff current was 0.05C. The initial capacity was recorded. Then it was fully charged at 1C constant current and constant voltage, and the initial thickness and initial internal resistance of the battery were tested. The fully charged battery was stored in a constant temperature environment at 60℃ for 14 days, and the thermal expansion rate was calculated. After the battery cooled to room temperature for 6h, it was discharged at 1C to 3.0V, and the remaining capacity of the battery was recorded. The battery capacity remaining rate was calculated, and the calculation formula is:

[0062] The battery thermal expansion rate (%) = (thermal thickness-initial thickness) / initial thickness x 100%;

[0063] The battery capacity remaining rate (%) = remaining capacity / initial capacity x 100%;

[0064] The battery capacity recovery rate (%) = recovery capacity / initial capacity x 100%

[0065] Table 2 Battery performance of examples and comparative examples

[0066]

[0067] From the examples 1-10 and the comparative examples 1-9, it can be seen that the lithium ion battery using the electrolyte of the examples 1-10 has better normal temperature cycle performance and high temperature storage performance than the lithium ion battery of the comparative examples 1-9. This is because the high voltage lithium ion battery non-aqueous electrolyte of the present application can stabilize the CEI film and reduce the electrolyte oxidation rate on the positive electrode surface at high voltage by optimizing the formula and the combined action of various components in a unique combination, especially by the combined use of the cyan compound containing a siloxane structure with a specific structural formula and other additives, thereby ensuring that the high-capacity ternary-graphite battery has long cycle life and excellent high-temperature storage performance. At the same time, the optimal addition amount of the cyan compound containing a siloxane structure is 0.2%-0.3%. Exactly, the optimal addition amount of M1, M5 is 0.3%, and M2, M3, M4 have advantages and disadvantages at different addition amounts.

[0068] The data of the comparative example 1-5 which only adds the cyan compound containing a siloxane structure shows that the formula with only the cyan compound containing a siloxane structure has limited effect; and the capacity retention rate of the comparative example 6 without adding the cyan compound containing a siloxane structure is slightly lower than that of the example after 500 cycles at normal temperature, which shows that the CEI interface film formed by the cyan compound containing a siloxane structure is more excellent and stable, and can improve the cycle performance of the battery. At the same time, the comparison of several different substituent groups of cyan compounds containing a siloxane structure shows that M1, M2, M3, M5 can form a CEI film with low impedance and high quality, and have good cycle performance and low DCR; M4 has excellent storage performance and small gas production.

[0069] Those skilled in the art will readily understand that the above description is only examples of the present application and is not intended to limit the present application, and any modifications, equivalent replacements and improvements made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A non-aqueous electrolyte for a ternary high-voltage lithium-ion battery, characterized in that, The non-aqueous electrolyte of the ternary high-voltage lithium-ion battery comprises a non-aqueous organic solvent, an electrolyte lithium salt, and a film-forming additive. The electrolyte lithium salt is lithium hexafluorophosphate and other lithium salts, wherein the other lithium salts are one or a mixture of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium difluorobis(oxalate)phosphate, and lithium difluorophosphate. The film-forming additive comprises a cyano compound with a silicon ether structure, wherein the cyano compound with a silicon ether structure is selected from at least one of the compounds shown in the following structural formulas:

2. The non-aqueous electrolyte for a ternary high-voltage lithium-ion battery according to claim 1, characterized in that, The mass percentage of the silyl ether-structured cyano compound in the electrolyte is 0.1-0.3%.

3. The non-aqueous electrolyte for a ternary high-voltage lithium-ion battery according to claim 1, characterized in that, The film-forming additive also contains at least one of 1,3-propanesulfonate lactone, fluoroethylene carbonate, and lithium difluorooxalate borate.

4. The non-aqueous electrolyte for a ternary high-voltage lithium-ion battery according to claim 3, characterized in that, The mass percentage of 1,3-propanesulfonate lactone, fluoroethylene carbonate, and lithium difluorooxalate borate in the electrolyte is 0.5-5%.

5. The non-aqueous electrolyte for a ternary high-voltage lithium-ion battery according to claim 1, characterized in that, The mass percentage of the electrolyte lithium salt in the electrolyte is 10-20%.

6. The non-aqueous electrolyte for a ternary high-voltage lithium-ion battery according to claim 1, characterized in that, The non-aqueous organic solvent is selected from one or more of ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl propionate, and propyl propionate.

7. A ternary high-voltage lithium-ion battery, characterized in that, The ternary high-voltage lithium-ion battery includes a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte as described in any one of claims 1-6.

8. The ternary high-voltage lithium-ion battery according to claim 7, characterized in that, The active material of the positive electrode is a ternary NCM material; the material of the negative electrode is one or more of natural graphite, artificial graphite, lithium titanate, silicon-oxygen negative electrode, and silicon negative electrode.

9. The ternary high-voltage lithium-ion battery according to claim 7, characterized in that, The upper limit cutoff voltage of the lithium-ion battery is 4.35-4.5V.

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