A high-voltage lithium cobalt oxide lithium ion battery nonaqueous electrolyte and lithium ion battery

Abstract

The application belongs to the technical field of lithium ion batteries, and discloses a high-voltage lithium cobalt oxide lithium ion battery nonaqueous electrolyte and a lithium ion battery. The high-voltage lithium cobalt oxide 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 silicon cyano additive and other additives. The structure of the silicon cyano additive is shown in formula (I). Substituents R1, R2, R3 and R4 are each independently selected from alkyl, alkoxy, cyano and combinations thereof containing 1-6 carbons or silicon. The other additives comprise at least two of FEC, PS, HTCN, SN and DTD. The high-voltage lithium ion battery nonaqueous electrolyte is optimized in formula, and under the joint action of the unique combination of solvents and multiple additives, the electrolyte system has high energy density and high safety performance, which is beneficial to meet the demand of the electrolyte on the cycle performance under high voltage.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a high-voltage lithium cobalt oxide lithium-ion battery non-aqueous electrolyte and the lithium-ion battery itself. 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, there is a growing expectation to develop lithium-ion batteries with higher energy density and power density to achieve longer driving range and energy storage.

[0004] While increasing the operating voltage can improve the energy density of lithium-ion batteries, ordinary electrolytes suffer from drawbacks such as oxidation decomposition and gas evolution at high voltages. For example, traditional carbonate electrolytes have a narrow electrochemical window; as the voltage increases, the electrolyte itself decomposes. Furthermore, the increased oxidation capacity of the cathode under high voltage, along with significant metal dissolution, gas evolution, and material phase transitions, can lead to battery failure or even dangerous situations. These drawbacks limit the development of high-voltage lithium-ion batteries; therefore, it is necessary to develop electrolytes that can withstand high voltages. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the aforementioned background technology and provide a high-voltage non-aqueous electrolyte for lithium cobalt oxide lithium-ion batteries and a lithium-ion battery thereof. The high-voltage non-aqueous electrolyte of this invention, through optimized formulation and the combined effect of a unique combination of solvents and various additives, enables the electrolyte system to possess both high energy density and high safety performance, which is beneficial for meeting the requirements of electrolyte cycle performance under high voltage.

[0006] To achieve the objectives of this invention, the non-aqueous electrolyte for the high-voltage lithium cobalt oxide lithium-ion battery of this invention contains a non-aqueous organic solvent, an electrolyte lithium salt, and a film-forming additive. The film-forming additive contains silicon cyanide additives and other additives, and the structural formula of the silicon cyanide additive is shown in formula (I):

[0007]

[0008] The substituents R1, R2, R3 and R4 are each independently selected from alkyl, alkoxy, cyano groups and combinations thereof containing 1 to 6 carbons or silicon.

[0009] The other additives include at least two of the following: fluoroethylene carbonate (FEC), 1,3-propanesulfonate lactone (PS), hexanetrionitrile (HTCN), succinic acid (SN), and ethylene sulfate (DTD).

[0010] Preferably, in some embodiments of the present invention, the silane-cyanide additive is selected from at least one of the compounds shown in the following structural formulas:

[0011]

[0012] Preferably, the mass percentage of the silane-cyanide additive in the electrolyte is 0.2-5%.

[0013] Furthermore, in some embodiments of the present invention, the other additives include fluoroethylene carbonate (FEC), 1,3-propanesulfonate lactone (PS), hexanetrionitrile (HTCN), succinic acid (SN), and ethylene sulfate (DTD).

[0014] Preferably, in some embodiments of the present invention, the mass percentages of the fluoroethylene carbonate (FEC), 1,3-propanesulfonate lactone (PS), hexanetrionitrile (HTCN), succinic anionyl (SN), and ethylene sulfate (DTD) in the electrolyte are 6-11%, 2-4%, 1.5-2.5%, 1-2%, and 0.3-0.7%, respectively.

[0015] Furthermore, in some embodiments of the present invention, the lithium salt is lithium hexafluorophosphate.

[0016] Preferably, in some embodiments of the present invention, the lithium salt has a mass percentage of 10-20% in the electrolyte.

[0017] Furthermore, in some embodiments of the present invention, the other additives also include lithium difluorooxalate borate; preferably, the mass percentage of lithium difluorooxalate borate in the electrolyte is 0.2-0.4%.

[0018] Preferably, in some embodiments of the present invention, the lithium salt is lithium hexafluorophosphate, and the other additives include fluoroethylene carbonate (FEC), 1,3-propanesulfonate lactone (PS), hexanetrionitrile (HTCN), succinate (SN), vinyl sulfate (DTD), and lithium difluorooxalate borate; more preferably, the mass percentages of fluoroethylene carbonate (FEC), 1,3-propanesulfonate lactone (PS), hexanetrionitrile (HTCN), succinate (SN), vinyl sulfate (DTD), and lithium difluorooxalate borate in the electrolyte are 9-11%, 2-4%, 1.5-2.5%, 1-2%, 0.4-0.6%, and 0.2-0.4%, respectively.

[0019] Furthermore, in some embodiments of the present invention, the other additives also include lithium difluorooxalate borate, lithium dioxalate borate, and vinylene carbonate (VC); preferably, the mass percentages of lithium difluorooxalate borate, lithium dioxalate borate, and vinylene carbonate (VC) in the electrolyte are 0.2-0.4%, 0.1-0.3%, and 0.1-0.3%, respectively.

[0020] Preferably, in some embodiments of the present invention, the lithium salt is lithium hexafluorophosphate, and the other additives include fluoroethylene carbonate (FEC), 1,3-propanesulfonate lactone (PS), hexanetrionitrile (HTCN), succinate (SN), vinyl sulfate (DTD), lithium difluorooxalate borate, lithium dioxalate borate, and vinylene carbonate (VC); more preferably, the mass percentages of fluoroethylene carbonate (FEC), 1,3-propanesulfonate lactone (PS), hexanetrionitrile (HTCN), succinate (SN), vinyl sulfate (DTD), lithium difluorooxalate borate, lithium dioxalate borate, and vinylene carbonate (VC) in the electrolyte are 6-8%, 2-4%, 1.5-2.5%, 1.5-2.5%, 0.4-0.6%, 0.2-0.4%, 0.1-0.3%, and 0.1-0.3%, respectively.

[0021] Furthermore, in some embodiments of the present invention, the non-aqueous organic solvent comprises ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and propyl propionate (PP); preferably, the ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and propyl propionate (PP) are mixed uniformly in a mass ratio of 5-15:10-20:40-50:25-35.

[0022] On the other hand, the present invention also provides a high-voltage lithium-ion battery, the high-voltage lithium-ion battery comprising a positive electrode, a negative electrode, a separator, and the aforementioned high-voltage lithium-ion battery non-aqueous electrolyte of the present invention.

[0023] Furthermore, the active material of the positive electrode is lithium cobalt oxide; the negative electrode material is one or more of natural graphite, artificial graphite, silicon-oxygen negative electrode, and silicon negative electrode.

[0024] Preferably, the upper limit cutoff voltage of the lithium-ion battery is 4.5V.

[0025] Compared with the prior art, the advantages of the present invention are as follows:

[0026] (1) The silicon-cyanide additives with specific structural formulas in the non-aqueous electrolyte of the high-voltage lithium-ion battery of the present invention can form an organic-inorganic composite interface film containing N at the positive and negative electrodes. By introducing silicon elements, they play an anchoring role, suppressing the complete oxidation of cyano functional groups under high voltage and the cross-reduction reaction with the negative electrode, thus avoiding battery deterioration.

[0027] (2) The silicon-cyanide additives with specific structural formulas in the electrolyte of the present invention introduce silicon elements, which can also improve the wettability of the electrolyte. At the same time, the cyano group plays a role in removing water and inhibiting acid, stabilizing the positive electrode and reducing side reactions, ultimately improving the electrochemical performance of high-voltage lithium-ion batteries.

[0028] (3) The high-voltage lithium-ion battery non-aqueous electrolyte of the present invention, through optimized formulation and improved solvent, combined with the combined effect of silicon cyanide additives with specific structures and other additives, can ensure that the high-voltage lithium-ion battery obtains excellent cycle performance, and make the electrolyte system have both high energy density and high stability. Detailed Implementation

[0029] 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.

[0030] 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.

[0031] The conjunction "composed of..." excludes any unspecified elements, steps, or components. If used in a claim, this phrase makes the claim closed, excluding materials other than those described, except for associated conventional impurities. When the phrase "composed of..." appears in a clause of the body of a claim rather than immediately following it, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] The structural formulas of the silicon-cyanide additives in the embodiments and comparative examples of this invention are as follows:

[0036] The structural formula for M1 is:

[0037]

[0038] The structural formula for M2 is:

[0039]

[0040] The structural formula for M3 is:

[0041]

[0042] The structural formula for M4 is:

[0043]

[0044] The structural formula for M5 is:

[0045]

[0046] Example 1

[0047] Preparation of electrolyte: In an argon-filled glove box (oxygen content ≤1ppm, water content ≤1ppm), ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and propyl propionate (PP) were mixed uniformly in a mass ratio of 10:15:45:30 to obtain a mixed solution. Then, lithium hexafluorophosphate (LiPF6) at 15% of the total mass of the electrolyte was added to the mixed solution. Subsequently, silane-cyanide additive M1 at 0.2% of the total mass of the electrolyte, 1,3-propanesulfonate lactone (PS) at 4% of the total mass of the electrolyte, fluoroethylene carbonate (FEC) at 10% of the total mass of the electrolyte, hexanetrionitrile (HTCN) at 2% of the total mass of the electrolyte, succinic anhydride (SN) at 1.5% of the total mass of the electrolyte, and ethylene sulfate (DTD) at 0.5% of the total mass of the electrolyte were added to the mixed solution and stirred until completely dissolved to obtain the electrolyte of Example 1.

[0048] Example 2-11

[0049] 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.

[0050] Comparative Examples 1-7

[0051] Comparative Examples 1-7 were identical to Example 1 except that the electrolyte components were added in the proportions shown in Table 1.

[0052] Table 1. Electrolyte composition of the examples and comparative examples.

[0053]

[0054]

[0055] Note: The content of each component in lithium salt is the mass percentage in the electrolyte;

[0056] The content of silicon-cyanide additives is the mass percentage in the electrolyte;

[0057] The content of each component in other additives is the mass percentage in the electrolyte;

[0058] The proportions of each component in the solvent are by mass.

[0059] Preparation of lithium cobalt oxide batteries:

[0060] The positive electrode active material LiCoO2, the conductive agent acetylene black, and the binder polyvinylidene fluoride are thoroughly mixed 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 the positive electrode sheet.

[0061] The negative electrode active material AG, conductive agent super carbon black, thickener sodium carboxymethyl cellulose, and binder styrene-butadiene rubber are thoroughly mixed 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.

[0062] Polyethylene is used as the base membrane, and a nano-alumina coating is coated on the base membrane to serve as a separator.

[0063] 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 a lithium cobalt oxide graphite lithium-ion battery.

[0064] Lithium-ion battery performance testing

[0065] (1) Room temperature cycling performance test: At 25℃, the above LiCoO2 / graphite lithium-ion batteries were charged to 4.5V at a constant current and constant voltage of 1C, with a cutoff current of 0.05C. Then, they were discharged to 3.0V at a constant current of 1C. After 500 charge / discharge cycles, the capacity retention rate at the 500th cycle was calculated. The calculation formula is as follows:

[0066] Capacity retention rate at week 500 = Week 500 cycle discharge capacity / Week 1 cycle discharge capacity × 100%.

[0067] (2) High-temperature storage performance at 60℃: The above-mentioned LiCoO2 / graphite lithium-ion battery was charged and discharged once at 1C at room temperature, with a cutoff current of 0.05C, and 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 of 60℃ for 14 days, and the thermal expansion rate was calculated. After the battery cooled to room temperature for 6 hours, it was discharged at 1C to 3.0V, and the remaining capacity of the battery was recorded. The remaining capacity rate of the battery was calculated using the following formula:

[0068] Battery thermal expansion rate (%) = (thermal thickness - initial thickness) / initial thickness × 100%;

[0069] Battery capacity remaining rate (%) = Remaining capacity / Initial capacity × 100%;

[0070] Battery capacity recovery rate (%) = Recovered capacity / Initial capacity × 100%

[0071] Table 2 Battery performance of the examples and comparative examples

[0072]

[0073]

[0074] As can be seen from Examples 1-11 and Comparative Examples 1-7, the lithium-ion batteries using the electrolytes of Examples 1-11 exhibit superior room-temperature cycling performance, high-temperature cycling performance, and high-temperature storage performance compared to the lithium-ion batteries of Comparative Examples 1-7. This is because the high-voltage lithium-ion battery non-aqueous electrolyte of the present invention, through optimized formulation and the combined effect of multiple components in a unique combination, particularly through the combined use of silicon-cyanide additives with specific structural formulas and other additives, can stabilize the CEI film, reduce the electrolyte oxidation rate on the positive electrode surface under high voltage, and improve electrolyte wettability, thereby ensuring that the high-capacity lithium cobalt oxide-graphite battery possesses long cycle life and excellent high-temperature storage performance. Furthermore, the optimal addition amount of silicon-cyanide additives is 2%. Adjusting the content of fluoroethylene carbonate (FEC), sulfur-containing high-temperature additives (PS), and lithium salt additives further enhances the battery's high-temperature cycling and storage performance.

[0075] Comparative Examples 1-5 show that the combination of additives in the electrolyte enables the battery to have excellent electrochemical performance, and the lack of some additives will significantly affect the normal use of the battery. A comparison between Comparative Examples 6-7 and the examples shows that the introduction of silane-cyanide additives can further improve the stability of the battery, indicating that the CEI film formed by silane-cyanide additives is superior and can improve the overall performance of the battery. Furthermore, compared with several silane-cyanide additives with different substituents, additive M3 has superior overall performance.

[0076] 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 high-voltage lithium cobalt oxide lithium-ion batteries, characterized in that, The non-aqueous electrolyte of the high-voltage lithium cobalt oxide lithium-ion battery comprises a non-aqueous organic solvent, an electrolyte lithium salt, and a film-forming additive. The non-aqueous organic solvent comprises ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and propyl propionate (PP), which are uniformly mixed at a mass ratio of 5-15:10-20:40-50:25-35. The lithium salt is lithium hexafluorophosphate. The film-forming additive comprises silane-cyanide additives and other additives, wherein the silane-cyanide additives are selected from at least one compound shown in the following structural formulas: The silane-cyanide additives constitute 0.2-5% of the electrolyte by mass; the other additives include at least two of the following: fluoroethylene carbonate (FEC), 1,3-propanesulfonate lactone (PS), hexanetrionitrile (HTCN), succinate (SN), and vinyl sulfate (DTD); the other additives also include lithium difluorooxalate borate, lithium dioxalate borate, and vinylene carbonate (VC); the mass percentages of fluoroethylene carbonate (FEC), 1,3-propanesulfonate lactone (PS), hexanetrionitrile (HTCN), succinate (SN), vinyl sulfate (DTD), lithium difluorooxalate borate, lithium dioxalate borate, and vinylene carbonate (VC) in the electrolyte are 6-8%, 2-4%, 1.5-2.5%, 1.5-2.5%, 0.4-0.6%, 0.2-0.4%, 0.1-0.3%, and 0.1-0.3%, respectively.

2. The non-aqueous electrolyte for high-voltage lithium cobalt oxide lithium-ion batteries according to claim 1, characterized in that, The lithium salt has a mass percentage of 10-20% in the electrolyte.

3. A high-voltage lithium-ion battery, characterized in that, The high-voltage lithium-ion battery includes a positive electrode, a negative electrode, a separator, and the non-aqueous electrolyte for high-voltage lithium cobalt oxide lithium-ion batteries according to any one of claims 1-2.

4. The high-voltage lithium-ion battery according to claim 3, characterized in that, The active material of the positive electrode is lithium cobalt oxide; the negative electrode material is one or more of natural graphite, artificial graphite, silicon-oxygen negative electrode, and silicon negative electrode.

5. The high-voltage lithium-ion battery according to claim 3, characterized in that, The upper limit cutoff voltage of the lithium-ion battery is 4.5V.

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