A power type lithium ion battery electrolyte and its preparation method and battery

Abstract

A power-type lithium-ion battery electrolyte has the following formula: 3-5 parts of a film-forming additive; 12-20 parts of a lithium salt; and 75-85 parts of a non-aqueous organic solvent. The film-forming additive consists of lithium difluorophosphate, lithium difluorobisoxalatophosphate, tributyl borate, sultone, and a carbonate compound. The mass ratio of lithium difluorophosphate to lithium difluorobisoxalatophosphate is 0.3-2; the mass ratio of tributyl borate to lithium difluorophosphate is 0.5-2; and the mass ratio of sultone to carbonate compound is 0.5-3. The carbonate compound accounts for 0.5%-2% of the total mass of the electrolyte. The carbonate compound is vinylene carbonate or fluoroethylene carbonate. The lithium salt is lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl imide), lithium bis(fluorosulfonyl imide), and lithium difluorooxalatoborate. The film-forming additive used in the present invention effectively improves the low-temperature film-forming characteristics of the battery cell, which is manifested in excellent low-temperature rate performance. It still exhibits excellent electrochemical performance under the discharge pulse conditions of ‑30° and 15C, which well meets the low-temperature start-stop goals of the new energy vehicle market.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium ion batteries. Background Art

[0002] The new energy market is experiencing enormous demand, with 12 / 48V start-stop and auxiliary systems attracting widespread attention. These high-power lithium-ion batteries place high demands on the electrolyte's low-temperature performance. Currently, approaches to improving low-temperature performance include adding low-temperature additives to increase ionic conductivity or modifying lithium salt composition to lower the desolvation barrier. However, these approaches primarily focus on the battery's low-rate, low-temperature charge and discharge capabilities, making them difficult to meet the low-temperature electrochemical performance requirements of start-stop power supplies under high-current pulses. Summary of the Invention

[0003] The purpose of the present invention is to overcome the shortcomings of the existing technology in the low-temperature performance of lithium-ion battery electrolytes, especially the low-temperature electrochemical performance under large current pulses, and to provide a start-stop low-temperature power lithium-ion battery electrolyte with good film-forming characteristics and excellent low-temperature performance.

[0004] The inventors have discovered that the low-temperature performance of lithium ions is closely related to their transport capabilities within the battery system. In addition to the ionic conductivity and desolvation barrier of lithium ions in low-temperature environments, the migration capabilities of lithium ions within the negative electrode SEI film should also be considered. The migration capabilities of lithium ions within the negative electrode SEI film are related to the composition and thickness of the negative electrode SEI film. This technical solution significantly improves the migration capabilities of lithium ions within the negative electrode SEI film by adding a film-forming additive to generate a negative electrode SEI film with lower impedance and thinner thickness, thereby enhancing the low-temperature performance of lithium ions.

[0005] The technical solution adopted by the present invention is: a power type lithium ion battery electrolyte, the formula of which includes the following raw materials in parts by weight:

[0006] 3-5 parts of film-forming additives;

[0007] 12-20 parts of lithium salt;

[0008] 75-85 parts of non-aqueous organic solvent;

[0009] The film-forming additives are composed of lithium difluorophosphate (LiDFP), lithium difluorobis(oxalatophosphate) (LiDFOP), tributyl borate (TBB), 1,3-propane sultone (PS), and carbonate compounds; the mass ratio of lithium difluorophosphate (LiDFP) to lithium difluorobis(oxalatophosphate) (LiDFOP) is 0.3-2; the mass ratio of tributyl borate (TBB) to lithium difluorophosphate (LiDFP) is 0.5-2; the mass ratio of 1,3-propane sultone (PS) to carbonate compounds is 0.5-3; and the carbonate compounds account for 0.5%-2% of the total mass of the electrolyte.

[0010] The carbonate compound is one or both of vinylene carbonate (VC) and fluoroethylene carbonate (FEC).

[0011] The lithium salt is one or a combination of lithium hexafluorophosphate (LiPF6), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium difluorooxalatoborate (LiDFOB).

[0012] The non-aqueous organic solvent is an ester solvent.

[0013] The ester solvent is a combination of two or more of ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC).

[0014] The present invention also provides a method for preparing the above-mentioned power-type lithium-ion battery electrolyte, comprising the following steps: weighing a film-forming additive, a lithium salt, and an organic solvent according to a formula; adding the film-forming additive to the organic solvent in a glove box filled with argon, with moisture <1 ppm and oxygen <1 ppm; then slowly adding the lithium salt and stirring until completely dissolved to obtain the power-type lithium-ion battery electrolyte.

[0015] The film-forming additives are composed of lithium difluorophosphate (LiDFP), lithium difluorobis(oxalatophosphate) (LiDFOP), tributyl borate (TBB), 1,3-propane sultone (PS), and carbonate compounds; the mass ratio of lithium difluorophosphate (LiDFP) to lithium difluorobis(oxalatophosphate) (LiDFOP) is 0.3-2; the mass ratio of tributyl borate (TBB) to lithium difluorophosphate (LiDFP) is 0.5-2; the mass ratio of 1,3-propane sultone (PS) to carbonate compounds is 0.5-3; and the carbonate compounds account for 0.5%-2% of the total mass of the electrolyte.

[0016] The carbonate compound is one or both of vinylene carbonate (VC) and fluoroethylene carbonate (FEC).

[0017] The present invention also provides a power type lithium ion battery, comprising a battery core formed by stacking and winding a positive electrode sheet, a separator, and a negative electrode sheet in sequence, and an electrolyte, wherein the electrolyte is the above-mentioned power type lithium ion battery electrolyte.

[0018] The positive electrode active material on the positive electrode sheet is at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, and lithium nickel manganese oxide, which accounts for 94.5%-97% of the total mass of the positive electrode material.

[0019] Compared with the prior art, the beneficial effect of the present invention is that the film-forming additives used in the present invention effectively improve the low-temperature film-forming characteristics of the battery cell, which is manifested in excellent low-temperature rate performance. It still exhibits excellent electrochemical performance under the discharge pulse conditions of -30° and 15C, and well meets the low-temperature start-stop goals of the new energy vehicle market. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a graph showing the low-temperature rate performance of battery cells equipped with different electrolytes at -10°C and different pulse discharge conditions.

[0021] Figure 2 This is a graph showing the low-temperature rate performance of battery cells equipped with different electrolytes at -30°C and different pulse discharge conditions. DETAILED DESCRIPTION

[0022] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is in no way intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without carrying out creative work are within the scope of protection of the present invention.

[0023] Technologies, methods, and apparatus known to ordinary technicians in the relevant field may not be discussed in detail, but where appropriate, such technologies, methods, and apparatus should be considered part of the authorization specification.

[0024] Example 1

[0025] Preparation of electrolyte: In a glove box filled with argon, with moisture <1 ppm and oxygen <1 ppm, ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate are mixed uniformly in a mass ratio of 18:32:32, 0.5% by mass of lithium difluorophosphate, 1% by mass of lithium difluorobisoxalatophosphate, 1% by mass of tributyl borate, 1% by mass of 1,3-propane sultone and 0.5% by mass of vinylene carbonate are added to the mixed solution, and then 9% by mass of lithium hexafluorophosphate and 5% by mass of lithium bis(fluorosulfonyl)imide are slowly added and stirred until completely dissolved to obtain a lithium-ion battery electrolyte;

[0026] Preparation of a lithium-ion battery: After fully stirring the positive electrode active material lithium nickel cobalt manganese oxide, conductive carbon fiber, and binder polyvinylidene fluoride in a 1-methylpyrrolidone solvent at a mass ratio of 96:2:2, the mixture is evenly coated on aluminum foil, dried, and cold-pressed to obtain a positive electrode plate; after fully stirring the negative electrode active material graphite, conductive agent acetylene black, binder styrene butadiene rubber, and thickener sodium carboxymethyl cellulose in a deionized water solvent system at a mass ratio of 96:2:1:1, the mixture is evenly coated on copper foil, dried, and cold-pressed to obtain a negative electrode plate; the separator is a polyethylene film coated with a 2μm nano-aluminum oxide coating; the positive electrode plate, separator, and negative electrode plate are stacked in sequence and then wound to obtain a bare battery cell, which is injected with the electrolyte described in step 1 and packaged to obtain a square aluminum shell lithium-ion battery.

[0027] Example 2

[0028] Preparation of electrolyte: In a glove box filled with argon, with moisture <1 ppm and oxygen <1 ppm, ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate are mixed uniformly in a mass ratio of 15:30:30, 0.5% by mass of lithium difluorophosphate, 1.5% by mass of lithium difluorobisoxalatophosphate, 1% by mass of tributyl borate, 1% by mass of 1,3-propane sultone and 1% by mass of vinylene carbonate are added to the mixed solution, and then 15% by mass of lithium hexafluorophosphate and 5% by mass of lithium bis(fluorosulfonyl)imide are slowly added and stirred until completely dissolved to obtain a lithium-ion battery electrolyte;

[0029] Preparation of a lithium-ion battery: After fully stirring the positive electrode active material lithium nickel cobalt manganese oxide, conductive carbon fiber, and binder polyvinylidene fluoride in a 1-methylpyrrolidone solvent at a mass ratio of 95:2.5:2.5, the mixture is evenly coated on aluminum foil, dried, and cold pressed to obtain a positive electrode plate; after fully stirring the negative electrode active material graphite, conductive agent acetylene black, binder styrene butadiene rubber, and thickener sodium carboxymethyl cellulose in a deionized water solvent system at a mass ratio of 96:2:1:1, the mixture is evenly coated on copper foil, dried, and cold pressed to obtain a negative electrode plate; the separator is a polyethylene film coated with a 2μm nano-aluminum oxide coating; the positive electrode plate, separator, and negative electrode plate are stacked in sequence and then wound to obtain a bare battery cell, which is injected with the electrolyte described in step 1 and packaged to obtain a square aluminum shell lithium-ion battery.

[0030] Example 3

[0031] Preparation of electrolyte: In a glove box filled with argon, with moisture <1 ppm and oxygen <1 ppm, ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate are uniformly mixed in a mass ratio of 15:32:32, 1% by mass of lithium difluorophosphate, 0.5% by mass of lithium difluorobisoxalatophosphate, 0.5% by mass of tributyl borate, 1% by mass of 1,3-propane sultone and 1% by mass of vinylene carbonate are added to the mixed solution, and then 12% by mass of lithium hexafluorophosphate and 5% by mass of lithium bis(fluorosulfonyl)imide are slowly added and stirred until completely dissolved to obtain a lithium-ion battery electrolyte;

[0032] Preparation of a lithium-ion battery: After fully stirring the positive electrode active material lithium nickel cobalt manganese oxide, conductive carbon fiber, and binder polyvinylidene fluoride in a 1-methylpyrrolidone solvent at a mass ratio of 97:1.5:1.5, the mixture is evenly coated on aluminum foil, dried, and cold-pressed to obtain a positive electrode plate; after fully stirring the negative electrode active material graphite, conductive agent acetylene black, binder styrene butadiene rubber, and thickener sodium carboxymethyl cellulose in a deionized water solvent system at a mass ratio of 96:2:1:1, the mixture is evenly coated on copper foil, dried, and cold-pressed to obtain a negative electrode plate; the separator is a polyethylene film coated with a 2μm nano-aluminum oxide coating; the positive electrode plate, separator, and negative electrode plate are stacked in sequence and then wound to obtain a bare battery cell, which is injected with the electrolyte described in step 1 and packaged to obtain a square aluminum shell lithium-ion battery.

[0033] Comparative Example 1

[0034] Preparation of electrolyte: In a glove box filled with argon and containing less than 1 ppm of moisture and less than 1 ppm of oxygen, ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate were mixed in a mass ratio of 18:32:32. 13% by mass of lithium hexafluorophosphate and 5% by mass of lithium bis(fluorosulfonyl)imide were then slowly added and stirred until completely dissolved to obtain a lithium-ion battery electrolyte.

[0035] Preparation of a lithium-ion battery: After fully stirring the positive electrode active material lithium nickel cobalt manganese oxide, conductive carbon fiber, and binder polyvinylidene fluoride in a 1-methylpyrrolidone solvent at a mass ratio of 96:2:2, the mixture is evenly coated on aluminum foil, dried, and cold-pressed to obtain a positive electrode plate; after fully stirring the negative electrode active material graphite, conductive agent acetylene black, binder styrene butadiene rubber, and thickener sodium carboxymethyl cellulose in a deionized water solvent system at a mass ratio of 96:2:1:1, the mixture is evenly coated on copper foil, dried, and cold-pressed to obtain a negative electrode plate; the separator is a polyethylene film coated with a 2μm nano-aluminum oxide coating; the positive electrode plate, separator, and negative electrode plate are stacked in sequence and then wound to obtain a bare battery cell, which is injected with the electrolyte described in step 1 and packaged to obtain a square aluminum shell lithium-ion battery.

[0036] like Figure 1As shown, under the conditions of -10°C and 270A maximum pulse discharge, the lowest voltage limit of the battery cell in Example 1 is 3.42V, which is higher than the lowest voltage limit value (3.31V) of the battery cell in Comparative Example 1.

[0037] Comparative Example 2

[0038] Preparation of electrolyte: In a glove box filled with argon and containing less than 1 ppm of moisture and less than 1 ppm of oxygen, ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate were mixed in a mass ratio of 20:30:30. Then, 15% by mass of lithium hexafluorophosphate and 5% by mass of lithium bis(fluorosulfonyl)imide were slowly added and stirred until completely dissolved to obtain a lithium-ion battery electrolyte.

[0039] Preparation of a lithium-ion battery: After fully stirring the positive electrode active material lithium nickel cobalt manganese oxide, conductive carbon fiber, and binder polyvinylidene fluoride in a 1-methylpyrrolidone solvent at a mass ratio of 95:2.5:2.5, the mixture is evenly coated on aluminum foil, dried, and cold pressed to obtain a positive electrode plate; after fully stirring the negative electrode active material graphite, conductive agent acetylene black, binder styrene butadiene rubber, and thickener sodium carboxymethyl cellulose in a deionized water solvent system at a mass ratio of 96:2:1:1, the mixture is evenly coated on copper foil, dried, and cold pressed to obtain a negative electrode plate; the separator is a polyethylene film coated with a 2μm nano-aluminum oxide coating; the positive electrode plate, separator, and negative electrode plate are stacked in sequence and then wound to obtain a bare battery cell, which is injected with the electrolyte described in step 1 and packaged to obtain a square aluminum shell lithium-ion battery.

[0040] like Figure 2 As shown, under the conditions of -30°C and 270A maximum pulse discharge, the lowest voltage limit of the battery cell in Example 1 is 2.60V, which is higher than the lowest voltage limit value (2.15V) of the battery cell in Comparative Example 2.

[0041] The above description is merely an exemplary embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A power lithium-ion battery electrolyte, characterized in that: Its formula includes the following raw materials in parts by weight: 3-5 parts of film-forming additives; 12-20 parts of lithium salt; 75-85 parts of non-aqueous organic solvent; The film-forming additives are composed of lithium difluorophosphate (LiDFP), lithium difluorobisoxalatophosphate (LiDFOP), tributyl borate (TBB), 1,3-propane sultone (PS), and carbonate compounds; the mass ratio of lithium difluorophosphate (LiDFP) to lithium difluorobisoxalatophosphate (LiDFOP) is 0.3-2; the mass ratio of tributyl borate (TBB) to lithium difluorophosphate (LiDFP) is 0.5-2; the mass ratio of 1,3-propane sultone (PS) to carbonate compounds is 0.5-3; and the carbonate compounds account for 0.5%-2% of the total mass of the electrolyte; The carbonate compound is one or both of vinylene carbonate (VC) and fluoroethylene carbonate (FEC).

2. The power type lithium ion battery electrolyte according to claim 1, characterized in that: The lithium salt is one or a combination of lithium hexafluorophosphate (LiPF6), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium difluorooxalatoborate (LiDFOB).

3. The power type lithium ion battery electrolyte according to claim 1, characterized in that: The non-aqueous organic solvent is an ester solvent.

4. The power type lithium ion battery electrolyte according to claim 3, characterized in that: The ester solvent is a combination of two or more of ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC).

5. A method for preparing a power-type lithium-ion battery electrolyte according to any one of claims 1 to 4, characterized in that: The following steps are involved: The film-forming additive, lithium salt and organic solvent are weighed according to the formula. In a glove box filled with argon, moisture <1ppm and oxygen <1ppm, the film-forming additive is added to the organic solvent, and then the lithium salt is slowly added and stirred until completely dissolved to obtain a power-type lithium-ion battery electrolyte.

6. The method for preparing a power type lithium ion battery electrolyte according to claim 5, wherein: The film-forming additives are composed of lithium difluorophosphate (LiDFP), lithium difluorobis(oxalatophosphate) (LiDFOP), tributyl borate (TBB), 1,3-propane sultone (PS), and carbonate compounds; the mass ratio of lithium difluorophosphate (LiDFP) to lithium difluorobis(oxalatophosphate) (LiDFOP) is 0.3-2; the mass ratio of tributyl borate (TBB) to lithium difluorophosphate (LiDFP) is 0.5-2; the mass ratio of 1,3-propane sultone (PS) to carbonate compounds is 0.5-3; and the carbonate compounds account for 0.5%-2% of the total mass of the electrolyte.

7. The method for preparing a power type lithium ion battery electrolyte according to claim 6, characterized in that: The carbonate compound is one or both of vinylene carbonate (VC) and fluoroethylene carbonate (FEC).

8. A power lithium-ion battery comprising a battery cell formed by stacking and winding a positive electrode sheet, a separator, and a negative electrode sheet in sequence, and an electrolyte, characterized in that: The electrolyte is the power lithium-ion battery electrolyte according to any one of claims 1 to 5.

9. The power type lithium ion battery according to claim 8, characterized in that: The positive electrode active material on the positive electrode sheet is at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, and lithium nickel manganese oxide, which accounts for 94.5%-97% of the total mass of the positive electrode material.

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