A nonaqueous electrolyte for ternary high-nickel lithium ion batteries and a lithium ion battery containing the electrolyte

Abstract

The application belongs to the technical field of lithium ion batteries, and discloses a ternary high-nickel lithium ion battery nonaqueous electrolyte and a lithium ion battery containing the electrolyte. The ternary high-nickel lithium ion battery nonaqueous electrolyte contains a nonaqueous organic solvent, an electrolyte lithium salt and an additive, the additive contains a sulfur-containing additive and other film-forming additives, the structure of the sulfur-containing additive is shown in formula (I), and the high-nickel lithium ion battery nonaqueous electrolyte is optimized in formula, and under the joint action of a plurality of components in a unique combination, the electrolyte system has high energy density and long service life, and is beneficial to meeting the demand of the electrolyte on cycle performance and high-temperature storage performance in the high-nickel system.

Description

Technical Field

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

[0002] With technological advancements, people's demands for the quality of their living environment are constantly increasing. Meanwhile, the environmental pollution problems caused by the depletion and consumption of fossil fuels are becoming increasingly serious, making the research and development of clean and renewable energy sources an urgent priority. Currently, a large number of new energy sources have been developed and utilized, such as solar, wind, tidal, and geothermal energy. However, these energy sources are limited in time and space, requiring appropriate conversion and storage before they can be used.

[0003] Lithium-ion batteries, as a green and environmentally friendly high-energy battery, are currently the most ideal and promising rechargeable batteries in the world. Compared with other batteries, they have a series of advantages such as no memory effect, rapid charging and discharging, high energy density, long cycle life, and no environmental pollution. Therefore, they are widely used in small electronic devices such as laptops, cameras, mobile phones, and smartwatches. With the increasing demands on lithium-ion battery capacity from pure electric vehicles, hybrid vehicles, and portable energy storage devices, people are looking forward to developing lithium-ion batteries with higher energy density and power density to achieve longer driving range and energy storage. Increasing the nickel content in the battery's positive electrode material can improve the battery's energy density, but with the increase of nickel content, the stability of the positive electrode material decreases. The increase of Ni worsens cycle performance and thermal stability, leads to uneven surface reactions during charging and discharging, and results in a large proportion of Ni4+ in the reaction products. + This causes the material to become oxidizing, slowly oxidizing the electrolyte and releasing gas in the process. Therefore, it is necessary to develop an electrolyte suitable for high-nickel systems. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the aforementioned background technology and provide a non-aqueous electrolyte for ternary high-nickel lithium-ion batteries and a lithium-ion battery containing this electrolyte. The non-aqueous electrolyte for high-nickel lithium-ion batteries of this invention, through optimized formulation and the combined effect of a unique combination of multiple components, enables the electrolyte system to possess both high energy density and long lifespan, which is beneficial for meeting the requirements of electrolyte in high-nickel systems for cycle performance and high-temperature storage performance.

[0005] To achieve the above objectives, the non-aqueous electrolyte of the ternary high-nickel lithium-ion battery of the present invention comprises a non-aqueous organic solvent, an electrolyte lithium salt, and additives, wherein the additives include sulfur-containing additives and other film-forming additives; the structure of the sulfur-containing additives is shown in formula (I):

[0006]

[0007] Among them, R1, R2, and R3 are each independently selected from hydrogen atoms, fluorine atoms, nitrile groups, fluoroalkyl groups, silyl ether groups, and boron fluoride groups;

[0008] The other film-forming additives are selected from at least one of vinylene carbonate (VC), fluoroethylene carbonate (FEC), vinylene carbonate (VEC), 1,3-propanesulfonate lactone (PS), propylene sulfonate lactone (PST), butene sulfonate lactone (BS), methane disulfonate methylene ester (MMDS), vinyl sulfate (DTD), lithium difluorooxalate borate (LiDFOB), and lithium difluorobis(oxalate) phosphate (LiDFOP).

[0009] Preferably, in some embodiments of the present invention, the sulfur-containing additive is selected from at least one of the compounds shown in the following structural formulas:

[0010]

[0011] Preferably, the sulfur-containing additive is present in the non-aqueous electrolyte of the ternary high-nickel lithium-ion battery at a mass percentage of 0.1-0.2%.

[0012] Preferably, in some embodiments of the present invention, the other film-forming additives include vinylene carbonate (VC), and also include at least one of lithium difluorooxalatoborate (LiDFOB), 1,3-propanesulfonate lactone (PS), methanedisulfonate methylene ester (MMDS), vinyl sulfate (DTD), and lithium difluorobis(oxalato)phosphate (LiDFOP).

[0013] More preferably, in some embodiments of the present invention, the other film-forming additives include vinylene carbonate (VC), and also include at least one of lithium difluorooxalate borate (LiDFOB), vinyl sulfate (DTD), and lithium difluorobis(oxalate) phosphate (LiDFOP).

[0014] Furthermore, in some embodiments of the present invention, the other film-forming additives have a mass percentage of 0.2-2% in the electrolyte.

[0015] Furthermore, in some embodiments of the present invention, the electrolyte lithium salt is selected from at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium tetrafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide.

[0016] Preferably, in some embodiments of the present invention, the electrolyte lithium salt is lithium hexafluorophosphate or lithium difluorosulfonylimide.

[0017] Furthermore, in some embodiments of the present invention, the mass percentage of the electrolyte lithium salt in the electrolyte is 12-18%.

[0018] Furthermore, in some embodiments of the present invention, the non-aqueous organic solvent is selected from two or more mixtures of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, and dimethyl carbonate.

[0019] On the other hand, the present invention also provides a high-nickel lithium-ion battery, which includes a positive electrode, a negative electrode, a separator, and the aforementioned ternary high-nickel lithium-ion battery non-aqueous electrolyte.

[0020] Furthermore, the active material of the positive electrode is LiNi. 1-x-y Co x Mn y Al z Where 0≤x≤1, 0≤y≤1, 0≤z≤1, 0≤x+y+z≤1; the negative electrode material is one or more of natural graphite, artificial graphite, lithium titanate, graphite negative electrode, and silicon negative electrode.

[0021] Furthermore, the upper limit cutoff voltage of the high-nickel lithium-ion battery is 4.35-4.5V.

[0022] Compared with the prior art, the advantages of the present invention are as follows:

[0023] (1) In the non-aqueous electrolyte of the high-nickel lithium-ion battery of the present invention, the sulfur-containing additive with a specific structural formula has a higher reduction potential than ethylene carbonate, vinylene carbonate and fluoroethylene carbonate. It preferentially undergoes a reduction reaction on the graphite negative electrode surface to form a stable and dense SEI film, which reduces the impedance of the SEI film and the subsequent electrolyte loss due to the poor density of the SEI film, reduces side reactions and prolongs the battery life. At the same time, its decomposition products modify the positive electrode CEI film, reduce the reactivity of Ni on the surface, inhibit the electrolyte oxidation of the positive electrode, improve the decomposition behavior of the electrolyte, and thus improve the cycle life.

[0024] (2) In the non-aqueous electrolyte of the high-nickel lithium-ion battery of the present invention, sulfur-containing additives with specific structures preferentially decompose on the negative electrode surface to form an excellent solid electrolyte membrane, which enriches the chemical composition of the SEI membrane, adjusts the impedance, and improves the high-temperature storage and cycle performance of the battery.

[0025] (3) The non-aqueous electrolyte of the high-nickel lithium-ion battery of the present invention, through optimized formulation, under the combined effect of carbonate solvent that improves the electrode / electrolyte interface, sulfur-containing compounds with specific structures, mixed lithium salts, and other additives, can ensure that the high-nickel lithium-ion battery obtains excellent cycle performance and high-temperature storage performance, so that the battery system has both high energy density and high stability, thereby improving the electrochemical performance of the high-nickel lithium-ion battery. Detailed Implementation

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] The structures of the sulfur-containing compounds in the examples and comparative examples are as follows:

[0033] The structural formula for M1 is:

[0034]

[0035] The structural formula for M2 is:

[0036]

[0037] The structural formula for M3 is:

[0038]

[0039] The structural formula for M4 is:

[0040]

[0041] The structural formula for M5 is:

[0042]

[0043] The structural formula for M6 is:

[0044]

[0045] The abbreviated names of some chemical substances in the examples and comparative examples are as follows:

[0046] EC (ethylene carbonate), FEC (fluoroethylene carbonate), 1,2-difluoroethylene carbonate (DFEC), EMC (methyl ethyl carbonate), DEC (diethyl carbonate), EP (ethyl propionate), FEMC (fluoromethyl ethyl carbonate), LiFSI (lithium bis(fluorosulfonyl)imide), LiTFSI (lithium bis(trifluoromethanesulfonyl)imide), LiDFOB (lithium difluorooxalate borate), LiDFOP (lithium difluorobis(oxalate phosphate), VEC (vinyl vinyl carbonate), PS (1,3-propanesulfonate lactone), PST (propylene sulfonate lactone), BS (butene sulfonate lactone), MMDS (methylene disulfonate), DTD (ethylene sulfate).

[0047] Example 1

[0048] Preparation of electrolyte: In an argon-filled glove box (oxygen content ≤1ppm, water content ≤1ppm), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed uniformly in a mass ratio of 30:50:20 to obtain a mixed solution. Then, lithium hexafluorophosphate (LiPF6) at 14% of the total electrolyte mass and LiFSI at 1% of the total electrolyte mass were added to the mixed solution. Subsequently, sulfur-containing compound M1 at 0.1% of the total electrolyte mass, VC at 0.2% of the total electrolyte mass, and LiDFOB at 1% of the total electrolyte mass were added to the mixed solution. The mixture was stirred until completely dissolved to obtain the electrolyte of Example 1.

[0049] Example 2-11

[0050] Examples 2-11 are also specific examples of electrolyte preparation. Except that the composition ratio of each electrolyte component is added as shown in Table 1, the other parameters and preparation methods are the same as in Example 1. The specific electrolyte formula is shown in Table 1.

[0051] Comparative Examples 1-16

[0052] Comparative Examples 1-16 were identical to Example 1 except that the electrolyte components were added in the proportions shown in Table 1. Specific electrolyte formulations are shown in Table 1.

[0053] Table 1 Electrolyte composition of the examples and comparative examples

[0054]

[0055]

[0056]

[0057] Note: The content of each component in lithium salt is the mass percentage in the electrolyte;

[0058] The content of sulfur-containing compounds is the mass percentage in the electrolyte;

[0059] The content of each component in other additives is the mass percentage in the electrolyte;

[0060] The proportions of each component in the solvent are by mass.

[0061] LiNi 0.8 Co 0.1 Mn 0.1 Preparation of O2 / graphite lithium-ion batteries:

[0062] LiNi, the positive electrode active material 0.8 Co 0.1 Mn 0.1O2, conductive agent acetylene black, and binder polyvinylidene fluoride are mixed thoroughly in an N-methylpyrrolidone system at a mass ratio of 95:3:2. The mixture is then coated onto aluminum foil, dried, and cold-pressed to obtain a positive electrode sheet.

[0063] The negative electrode active material artificial graphite, conductive agent super carbon black, thickener sodium carboxymethyl cellulose, and binder styrene-butadiene rubber are mixed evenly in a deionized water solvent system at a mass ratio of 95:1:2:2. The mixture is then coated onto copper foil, dried, and cold-pressed to obtain the negative electrode sheet.

[0064] A polyethylene base membrane is used, and a nano-alumina coating is coated on the base membrane to serve as a separator.

[0065] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The cells are then wound to obtain a bare cell. The bare cell is placed in an outer packaging, injected with the prepared electrolyte, and undergoes processes such as encapsulation, formation, aging, secondary encapsulation, and capacity testing to obtain the NCM811 graphite lithium-ion battery.

[0066] Lithium-ion battery performance testing

[0067] (1) Room temperature cycling performance test: At 25℃, the above LiNi 0.8 Co 0.1 Mn 0.1 The O2 / graphite lithium-ion battery was charged at 1C constant current and constant voltage to 4.35V, with a cutoff current of 0.05C, and then discharged at 1C constant current to 3.0V. The capacity retention rate was calculated after 500 charge / discharge cycles. The calculation formula is as follows:

[0068] Capacity retention rate at week 500 = Week 500 cycle discharge capacity / Week 1 cycle discharge capacity × 100%.

[0069] (2) High-temperature storage performance at 60℃: The above-mentioned LiNi was stored at room temperature. 0.8 Co 0.1 Mn 0.1 The O2 / graphite lithium-ion battery was charged and discharged once at 1C with a cutoff current of 0.05C, and the initial capacity was recorded. It was then fully charged at 1C with constant current and constant voltage, and the initial thickness and internal resistance of the battery were measured. The fully charged battery was stored in a constant temperature environment of 60℃ for 14 days, and the thermal thickness was measured, and the thermal expansion rate was calculated. After the battery cooled to room temperature for 6 hours, the cold thickness, voltage, and internal resistance were measured. It was then discharged at 1C to 3.0V, and the remaining capacity was recorded. The remaining capacity rate of the battery was calculated using the following formula:

[0070] Battery thermal expansion rate (%) = (thermal thickness - initial thickness) / initial thickness × 100%;

[0071] Battery capacity remaining rate (%) = Remaining capacity / Initial capacity × 100%;

[0072] Battery capacity recovery rate (%) = Recovered capacity / Initial capacity × 100%

[0073] Table 2 Battery performance of each embodiment and comparative example

[0074]

[0075]

[0076] For LiNi 0.8 Co 0.1 Mn 0.1 O2 / graphite system lithium-ion battery:

[0077] As can be seen from Examples 1-11 and Comparative Examples 1-16, the lithium-ion batteries using the electrolyte of Examples 1-11 exhibit superior room-temperature cycle performance and high-temperature storage performance compared to the lithium-ion batteries of Comparative Examples 1-16. Specifically, M1, due to the improved wetting and oxidation resistance of the fluorinated groups; M4, due to the stabilizing effect of the cyano groups on the positive electrode; and M6, due to the reduced impedance and stabilization of the positive electrode, thus improving cycle stability, each have advantages in DCR performance and cycle storage. Through optimized formulation, the combined effect of multiple components in a unique combination, particularly the combined use of sulfur-containing additives with specific structures and other additives, ensures that the high-capacity NCM811-graphite lithium-ion battery possesses long cycle life and excellent high-temperature storage performance. Specifically:

[0078] Comparing Examples 1-11 with Comparative Examples 7-13, it was found that the battery performance using the combined VC / LiDFOB and the sulfur-containing additive was superior to other single-additive groups, proving the excellent performance of the sulfur-containing additive and VC / LiDFOB co-forming film. Comparing only Comparative Examples 7-13, it was found that the performance of the group using only the sulfur-containing additive was slightly weaker when each additive was used alone, proving that the combined use of the sulfur-containing additive and VC / LiDFOB brings a significant performance improvement to the battery. Because the co-forming film is relatively dense in this case, the film formation at the positive electrode results in a higher sulfur content at the active sites, reducing the catalytic activity of nickel, cobalt, and manganese, especially M3. This reduces the direct contact between the highly active nickel at the positive electrode and the electrolyte, thereby reducing gas production.

[0079] Despite the addition of a certain amount of sulfur-containing additives, the capacity retention rates of the batteries in Comparative Examples 14-16 at room temperature remained poor. The reason for this is that the high content of sulfur-containing additives in Comparative Examples 14-16 led to side reactions, affecting the quality of the positive electrode film formation. The resulting loose film was unable to provide adequate protection, and the dissolved transition metal ions caused electrolyte decomposition, resulting in irreversible capacity reduction. Combining Comparative Examples 1-6 and the various embodiments, the overall performance was superior when the amount of sulfur-containing additives added was 0.1%-0.2%, with 0.1% being the optimal amount.

[0080] Compared to Examples 1-6, Comparative Example 13, without the addition of sulfur-containing additives, showed a lower capacity retention and slightly higher DCR after 500 cycles at room temperature. This indicates that the interfacial film formed by the sulfur-containing additives is not only stable and thin but also has low impedance, thus improving cycling performance. In particular, the presence of F atoms in M1, cyano groups in M3, silicon groups in M4, and boron in M6 all modified the film formation of the additives to a certain extent, reducing impedance.

[0081] Regarding high-temperature storage performance, MMDS, DTD and the sulfur-containing additives in the examples have good compatibility, and the resulting film has high thermal stability, which makes up for the poor stability of nickel on the material surface at high temperatures. The FEC group exhibits gas generation, and the substituents of M2 and M3 show the best thermal stability.

[0082] In summary, the high-nickel lithium-ion battery non-aqueous electrolyte of the present invention, through improving the carbonate solvent at the electrode / electrolyte interface, combined with the combined effects of sulfur-containing compounds with specific structures, mixed lithium salt additives, and other conventional additives, can ensure high-nickel LiNi... 0.8 Co 0.1 Mn 0.1 O2 / graphite type lithium-ion batteries achieve excellent cycle performance and high-temperature storage performance.

[0083] 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 non-aqueous electrolyte for ternary high-nickel lithium-ion batteries, characterized in that, The non-aqueous electrolyte of the ternary high-nickel lithium-ion battery contains a non-aqueous organic solvent, an electrolyte lithium salt, and additives. The additives include sulfur-containing additives and other film-forming additives. The sulfur-containing additives are selected from at least one compound shown in the following structural formulas: The sulfur-containing additive is present in the non-aqueous electrolyte of the ternary high-nickel lithium-ion battery at a mass percentage of 0.1-0.2%. The other film-forming additives include vinylene carbonate (VC), and also include at least one of lithium difluorooxalate borate (LiDFOB), methane disulfonate (MMDS), vinyl sulfate (DTD), and lithium difluorobis(oxalate) phosphate (LiDFOP). The electrolyte lithium salt is lithium hexafluorophosphate and lithium difluorosulfonylimide.

2. The non-aqueous electrolyte for ternary high-nickel lithium-ion batteries according to claim 1, characterized in that, The other film-forming additives are present in the electrolyte at a mass percentage of 0.2-2%.

3. The non-aqueous electrolyte for a ternary high-nickel lithium-ion battery according to claim 1, characterized in that, The mass percentage of the electrolyte lithium salt in the electrolyte is 12-18%.

4. The non-aqueous electrolyte for a ternary high-nickel lithium-ion battery according to claim 1, characterized in that, The non-aqueous organic solvent is selected from two or more mixtures of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, and dimethyl carbonate.

5. A lithium-ion battery, characterized in that, The high-nickel lithium-ion battery includes a positive electrode, a negative electrode, a separator, and the ternary high-nickel lithium-ion battery non-aqueous electrolyte as described in any one of claims 1-4.

6. The lithium-ion battery according to claim 5, characterized in that, The active material of the positive electrode is LiNi1-x-yCoxMnyAlz, where 0≤x≤1, 0≤y≤1, 0≤z≤1, and 0≤x+y+z≤1; the negative electrode material is one or more of natural graphite, artificial graphite, lithium titanate, and silicon.

7. The lithium-ion battery according to claim 5, characterized in that, The upper limit cutoff voltage of the high-nickel lithium-ion battery is 4.35-4.5V.

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