Electrolyte additive, electrolyte, and battery

Abstract

An electrolyte additive, an electrolyte, and a battery. The electrolyte additive comprises a first additive and a second additive. The first additive comprises a compound represented by formula (I). In formula (I), R1 is at least one F-substituted C1-C6 linear alkyl group. The second additive comprises an unsaturated carbonate substance.

Description

Electrolyte additive, electrolyte and battery

[0001] Priority information

[0002] The present application claims priority to the Chinese patent application No. 2024112365274, filed on September 4, 2024, entitled "Electrolyte additive, electrolyte and battery", and its entire content is incorporated herein by reference. TECHNICAL FIELD

[0003] The present application relates to the technical field of batteries, in particular to an electrolyte additive, an electrolyte and a battery. BACKGROUND

[0004] Lithium ion batteries have high specific energy, large specific power and long cycle life, and have been widely used in new energy vehicle power battery field. With the increasing requirements of new energy vehicles on driving range, charging speed and application scene adaptability, it is urgent to improve the fast charging cycle performance and stability of lithium ion batteries under high pressure and high temperature.

[0005] However, increasing the operating voltage of lithium ion batteries usually exacerbates the dissolution of transition metal ions in the positive electrode material and the electrolyte side reaction, which in turn leads to the collapse of the positive electrode material structure and the deposition of electrolyte byproducts on the electrode surface, ultimately causing the lithium battery to fail due to capacity decay and impedance increase. At the same time, the impedance increase problem seriously affects the fast charging performance of lithium ion batteries. Under high temperature conditions, the decomposition of lithium hexafluorophosphate is intensified, and the phosphorus pentafluoride (PF5) generated by it will catalyze the decomposition of carbonate-based solvents in the electrolyte, leading to a serious capacity decay during high-temperature storage and exacerbating the safety risks of battery use.

[0006] DISCLOSURE

[0007] The present application aims to at least partially solve one of the technical problems in the related art. To this end, one object of the present application is to provide an electrolyte additive, an electrolyte and a battery. The electrolyte additive added to the battery can significantly improve the storage performance and fast charging cycle performance of the battery under high temperature and high pressure conditions.

[0008] The first aspect of the present application provides an electrolyte additive. According to embodiments of the present application, the electrolyte additive comprises a first additive and a second additive;

[0009] The first additive comprises a compound represented by Formula I:

[0010] In Formula I, R1 is at least one F-substituted C1-C6 linear alkyl group;

[0011] The second additive comprises an unsaturated carbonate compound.

[0012] The first additive and the second additive are used in cooperation to improve the storage performance and the cycle performance of the lithium ion battery under high temperature and high pressure.

[0013] For the first additive, the compound of formula I is prone to the following decomposition reaction when attacked by electrons due to the greater electronegativity of fluorine substituting the straight-chain alkyl group of C1-C6:

[0014] The S-F bond on the decomposition product B is prone to break and form a stable LiF interface film component, and the molecule of formula I can continue to react to form a fluorinated alkyl-rich, S-element inorganic interface film component after losing one F atom. The electrode-electrolyte interface formed through the above process has excellent stability, good mechanical strength and good ionic conductivity, which can improve the storage performance and cycle performance of the lithium ion battery under high temperature and high pressure. However, the F - may be free in the electrolyte to form HF, which further corrodes the positive active material, leading to ion dissolution and structure damage of the positive active material, and further leading to capacity attenuation of the lithium ion battery under high temperature and high pressure.

[0015] The second additive is an unsaturated carbonate substance, which can form a long carbon chain polymer type interface film component after the opening of the unsaturated bond, and the attachment of the long carbon chain polymer type interface film component on the positive electrode surface can improve the stability of the positive electrode-electrolyte interface, inhibit the corrosion of HF on the positive electrode material, and thus improve the capacity retention rate of high temperature storage and reduce the thickness expansion rate of high temperature storage. However, with the progress of the charging-discharging process in the cycle, the long carbon chain polymer will be more and more at the electrode-electrolyte interface, and agglomeration and crystallization will occur between the chain segments, resulting in obvious brittleness of the interface film. The flexibility of the interface film cannot adapt to the electrode expansion in the later cycle, leading to the rupture of the interface film and the problem of large DCR value in the later cycle. The negative effect of the long carbon chain polymer is more obvious in the fast charging cycle. The first additive can significantly reduce the DCR value (Direct Current Resistance) in the later stage of fast charging cycle, because the decomposition product A of the first additive can regulate the formation of PEO-like structure (PEO-like structure refers to a polymer having similar chemical structure and properties to polyethylene oxide (PEO)) of the unsaturated carbonate additive, and the grafted benzene ring can destroy the regularity of the PEO-like molecule, increase the free path of the molecular chain, increase the flexibility of the interface, reduce the repair of the film in the later cycle, and thus reduce the DCR value in the later cycle and improve the cycle performance.

[0016] In the compound of formula I, R1may be a straight-chain alkyl group of C1-C6 partially substituted by F, or a straight-chain alkyl group of C1-C6 fully substituted by F.

[0017] According to the embodiments of the present application, the electrolyte additive described above can further have the following additional technical features:

[0018] In some embodiments of the present application, R1is a straight-chain alkyl group of C1-C5 fully substituted by F.

[0019] In some embodiments of the present application, the first additive comprises at least one of a compound of formula I-1, a compound of formula I-2, a compound of formula I-3, a compound of formula I-4, a compound of formula I-5, and a compound of formula I-6; wherein:

[0020] The compound of formula I-1 is The compound of formula I-2 is The compound of formula I-3 is The compound of formula I-4 is The compound of formula I-5 is The compound of formula I-6 is

[0021] In some embodiments of the present application, the first additive comprises at least one of a compound of formula I-1, a compound of formula I-2, a compound of formula I-3, and a compound of formula I-4; wherein:

[0022] The compound of formula I-1 is The compound of formula I-2 is The compound of formula I-3 is The compound of formula I-4 is

[0023] In some embodiments of the present application, the second additive comprises at least one of a compound of formula II-1, a compound of formula II-2, a compound of formula II-3, a compound of formula II-4, a compound of formula II-5, and a compound of formula II-6; wherein,

[0024] The compound of formula II-1 is The compound of formula II-2 is The compound of formula II-3 is The compound of formula II-4 is The compound of formula II-5 is The compound of formula II-6 is

[0025] In some embodiments of the present application, the mass ratio of the first additive and the second additive is 1:(0.03-20).

[0026] In some embodiments of the present application, the mass ratio of the first additive and the second additive is 1:(0.05-15).

[0027] In some embodiments of the present application, the mass ratio of the first additive and the second additive is 1:(1-8).

[0028] In some embodiments of the present application, the auxiliary additive comprises at least one of fluoroethylene carbonate, 1,3-propene sultone, 1,3-propane sultone, and lithium difluorophosphate.

[0029] The second aspect of the present application provides an electrolyte, comprising the electrolyte additive described above.

[0030] The electrolyte provided by the embodiments of the present application contains the electrolyte additive described above, and the first additive and the second additive synergistically act to improve the storage performance and cycle performance of the lithium ion battery under high-temperature and high-pressure conditions.

[0031] In some embodiments of the present application, the electrolyte satisfies at least one of the following (1)-(3) based on the total mass of the electrolyte:

[0032] (1) the mass percentage of the first additive is 0.1%-2%;

[0033] (2) the mass percentage of the second additive is 0.1%-3%;

[0034] (3) the mass percentage of the auxiliary additive is 0.1%-3%.

[0035] The third aspect of the present application provides a battery, comprising the electrolyte described above.

[0036] The battery provided by the embodiments of the present application contains the electrolyte described above and exhibits good storage performance and cycle performance under high-temperature and high-pressure conditions.

[0037] In some embodiments of the present application, the battery further comprises a positive electrode sheet, a negative electrode sheet, and a separator.

[0038] The positive electrode active material used in the positive electrode sheet comprises LiNi a Co b M c O2 or LiFePO4; wherein M comprises at least one of Mn, Al, Ti, V, Fe, Zn, V, Zr, Ce, Cr, and Cu, a+b+c=1, 0.1≤a≤0.8, 0.1≤b≤0.2, 0.1≤c≤0.3.

[0039] Additional aspects and advantages of the present application will be in part apparent and in part expressly stated below. DETAILED DESCRIPTION

[0040] The following description is provided in relation to exemplary embodiments of the present application, and it is to be appreciated that modifications and improvements can be made by those skilled in the art without departing from the principles of the present application, and such modifications and improvements are to be considered within the scope of the present application.

[0041] In one aspect of the present application, the embodiments of the present application provide an electrolyte additive, comprising a first additive and a second additive;

[0042] The first additive comprises a compound shown in Formula I:

[0043] In Formula I, R1 is at least one F-substituted C1-C6 linear alkyl;

[0044] The second additive comprises an unsaturated carbonate.

[0045] The embodiments of the present application adopt the synergistic effect of the first additive and the second additive, so as to improve the storage performance and cycle performance of the lithium ion battery under high temperature and high pressure conditions.

[0046] For the first additive, since the electronegativity of the F-substituted C1-C6 linear alkyl is large, the compound molecule shown in Formula I is prone to the following decomposition reaction when subjected to electron attack:

[0047] The S-F bond on the decomposition product B is prone to break and form a stable LiF interface film component, and the molecule of Formula I can continue to react to form a fluorinated alkyl-rich, S-element inorganic interface film component after losing one F atom. The electrode-electrolyte interface formed through the above process has excellent stability, good mechanical strength and good ionic conductivity, and can improve the storage performance and cycle performance of the lithium ion battery under high temperature and high pressure conditions. However, the F - may be free in the electrolyte to form HF, which further corrodes the positive active material, leading to ion dissolution and structure damage of the positive active material, and further leading to capacity attenuation of the lithium ion battery under high temperature and high pressure.

[0048] The second additive is an unsaturated carbonate substance, which can form an interface film component of long carbon chain polymer type after the opening of the unsaturated bond, which is attached to the surface of the positive electrode and can improve the stability of the positive electrode-electrolyte interface, and can inhibit the corrosion of HF to the positive electrode material, thereby improving the capacity retention rate of high-temperature storage and reducing the thickness expansion rate of high-temperature storage. However, with the progress of the charging-discharging process in the cycle, the long carbon chain polymer will be more and more at the electrode-electrolyte interface, and the agglomeration and crystallization between the chain segments will occur, resulting in the interface film showing obvious brittleness. The flexibility of the interface film cannot adapt to the electrode expansion in the later stage of the cycle, resulting in the problem of interface film rupture, which leads to a large DCR value in the later stage of the cycle. The negative effect is more obvious in the fast charging cycle process. The first additive can significantly reduce the DCR value (Direct Current Resistance) in the later stage of the fast charging cycle, because the decomposition product A of the first additive can regulate the formation of the PEO-like structure of the unsaturated carbonate additive (the PEO-like structure refers to a polymer having a similar chemical structure and properties to polyethylene oxide (PEO)), and the grafted benzene ring can destroy the regularity of the PEO-like molecule, increase the free path of the molecular chain, increase the flexibility of the interface, reduce the repair of the film in the later stage of the cycle, and thus reduce the DCR value in the later stage of the cycle and improve the cycle performance.

[0049] In the compound represented by formula I, R1 can be a straight-chain alkyl group of C1-C6 partially substituted with F, or a straight-chain alkyl group of C1-C6 fully substituted with F.

[0050] In some embodiments of the present application, R1 is a straight-chain alkyl group of C1-C5 fully substituted with F.

[0051] In the embodiments of the present application, R1 satisfies the above conditions, and the perfluoroalkyl group R1 has a large electronegativity. When the molecule of the compound represented by formula I is attacked by electrons, the S-F bond on the decomposition product B-SO2F decomposed from the molecule is easy to break and form a stable LiF interface film component. After losing one F atom, the molecule of the compound represented by formula I can continue to react to form an interface film component rich in fluoroalkyl and S element inorganic matter. The electrode-electrolyte interface formed through the above process has excellent stability, good mechanical strength and good ionic conductivity, which can improve the storage performance and cycle performance of the lithium ion battery under high temperature and high pressure conditions; at the same time, it is beneficial to reduce the DCR value in the later stage of the fast charging cycle and improve the cycle performance of the battery.

[0052] In some embodiments of the present application, the first additive comprises at least one of a compound represented by formula I-1, a compound represented by formula I-2, a compound represented by formula I-3, a compound represented by formula I-4, a compound represented by formula I-5, and a compound represented by formula I-6; wherein:

[0053] The compound represented by formula I-1 is The compound shown as formula I-2 is The compound shown as formula I-3 is The compound shown as formula I-4 is The compound shown as formula I-5 is The compound shown as formula I-6 is

[0054] In some embodiments of the present application, the first additive comprises at least one of the compounds shown as formula I-1, formula I-2, formula I-3 and formula I-4; wherein:

[0055] The compound shown as formula I-1 is The compound shown as formula I-2 is The compound shown as formula I-3 is The compound shown as formula I-4 is

[0056] In the embodiments of the present application, the first additive is selected to comprise at least one of the above four compounds. Based on the high electronegativity of the perfluoroalkyl group R1, the electrode-electrolyte interface formed has excellent stability, good mechanical strength and good ionic conductivity, which can improve the storage performance and cycle performance of the lithium ion battery under high temperature and high pressure conditions, reduce the DCR value in the later stage of fast charging cycle, and improve the cycle performance of the battery. However, as the number of carbons in the fluoroalkyl group R1 increases, the molecular steric hindrance of the compound of formula I increases, which may make it more difficult to participate in the formation of the electrode-electrolyte interface film, and ultimately cannot guarantee the quality of the electrode-electrolyte interface film. At the same time, when the number of carbons in R1 exceeds 4, the steric hindrance problem caused by the long carbon chain in the electrode-electrolyte interface will affect the conduction of lithium ions, resulting in a decrease in the ability to inhibit the change of DCR in the later stage of cycle.

[0057] In some embodiments of the present application, the second additive comprises at least one of the compounds shown as formula II-1, formula II-2, formula II-3, formula II-4, formula II-5 and formula II-6; wherein,

[0058] The compound shown as formula II-1 is The compound shown as formula II-2 is The compound shown as formula II-3 is The compound shown as formula II-4 is The compound shown as formula II-5 is The compound shown as formula II-6 is

[0059] In the embodiments of the present application, the second additive is selected to include at least one of the above six compounds, which is conducive to protecting the positive electrode material, improving the capacity retention rate of high-temperature storage, and reducing the thickness expansion rate of high-temperature storage.

[0060] In some embodiments of the present application, the mass ratio of the first additive to the second additive is 1:(0.03-20). In specific examples, the mass ratio of the first additive to the second additive is 1:0.03, 1:0.05, 1:0.1, 1:0.5, 1:1, 1:5, 1:10, 1:15, 1:20, etc. Specifically, as the mass ratio of the first additive to the second additive decreases, for example, as the amount of the second additive increases based on the first additive as a benchmark "1", the positive electrode interface film formed tends to increase in thickness, and the corresponding interface impedance tends to increase, and the battery tends to decrease in lithium ion transmission capacity in the later stage of the cycle; as the mass ratio of the first additive to the second additive increases, for example, as the amount of the second additive decreases based on the first additive as a benchmark "1", the long-chain polymer type interface film component of the positive electrode interface tends to decrease, and the improvement effect on the stability of the positive electrode interface and the resistance to HF corrosion tends to decrease.

[0061] In the embodiments of the present application, the first additive and the second additive satisfy the above mass ratio condition, on the one hand, avoiding the increase of the DCR value of the lithium ion battery in the later stage of the long cycle, leading to the decrease of the long cycle performance; on the other hand, avoiding the decrease of the high-temperature storage performance, leading to the decrease of the capacity recovery rate in the later stage of the storage.

[0062] In some embodiments of the present application, the mass ratio of the first additive to the second additive is 1:(0.05-15). In specific examples, the mass ratio of the first additive to the second additive is 1:0.05, 1:0.06, 1:0.07, 1:0.08, 1:0.09, 1:0.1, 1:0.2, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, etc.

[0063] In some embodiments of the present application, the mass ratio of the first additive to the second additive is 1:(1-8). In specific examples, the mass ratio of the first additive to the second additive is 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5, 1:5.5, 1:6, 1:6.5, 1:7, 1:7.5, 1:8, etc.

[0064] In the embodiments of the present application, the first additive and the second additive meet the above mass ratio condition, which is beneficial to fully exert the synergistic effect of the first additive and the second additive, and improve the electrochemical performance of the battery under high temperature and high pressure conditions.

[0065] In some embodiments of the present application, an auxiliary additive is further included, and the auxiliary additive includes at least one of fluoroethylene carbonate, 1,3-propylene sulfone lactone, 1,3-propane sulfone lactone and lithium difluorophosphate.

[0066] The electrolyte provided in the embodiments of the present application can further include other auxiliary additives. When the first additive, the second additive and the auxiliary additive are used together, the effect is better. On the one hand, the auxiliary additive can participate in the formation of a stable interface film in the formation stage, which can further improve the performance of the lithium ion battery. On the other hand, the addition of the auxiliary additive can reduce the consumption of the first additive and the second additive in the formation and capacity test stage, so that the electrode-electrolyte interface film can be better repaired in 3C fast charging cycles, to further form a stable interface film, and improve the electrochemical performance of the battery under high temperature and high pressure conditions.

[0067] The second aspect of the embodiments of the present application provides an electrolyte, which includes the electrolyte additive described above.

[0068] The electrolyte provided in the embodiments of the present application includes the electrolyte additive described above, and the first additive and the second additive can exert synergistic effect, which can improve the storage performance and cycle performance of the lithium ion battery under high temperature and high pressure conditions.

[0069] In some embodiments of the present application, based on the total mass of the electrolyte, the electrolyte meets at least one of the following (1) to (3):

[0070] (1) The mass percentage of the first additive is 0.1% to 2%;

[0071] (2) The mass percentage of the second additive is 0.1% to 3%;

[0072] (3) The mass percentage of the auxiliary additive is 0.1% to 3%.

[0073] In the embodiments of the present application, the mass percentage of the first additive is 0.1% to 2%. Within this range, the first additive can play an active role, and the electrode-electrolyte interface formed has excellent stability, good mechanical strength and good ionic conductivity, which can improve the storage performance and cycle performance of the lithium ion battery under high temperature and high pressure conditions. At the same time, it is beneficial to significantly reduce the DCR value in the later stage of fast charging cycle and improve the cycle performance of the battery. In addition, as the amount of the first additive added to the electrolyte decreases, the interface film component of the PEO-like structure formed tends to decrease, and the improvement effect on the problem of large interface impedance in the later stage of battery cycle tends to decrease; as the amount of the first additive added to the electrolyte increases, the F - tends to increase, and the phenomenon of obvious side reaction of the electrolyte under high temperature conditions tends to increase, which makes the improvement effect on the high temperature performance of the battery tend to decrease. In specific examples, the mass percentage of the first additive is 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9% or 2%, etc.

[0074] In the embodiments of the present application, the mass percentage of the second additive is 0.1% to 3%. Within this range, the second additive can play an active role. The unsaturated carbonate substance can form a long carbon chain polymer type interface film component after the unsaturated bond is opened, which can improve the stability of the positive electrode-electrolyte interface and inhibit the erosion of HF to the positive electrode material, thereby improving the capacity retention rate of high temperature storage and reducing the thickness expansion rate of high temperature storage. In addition, as the amount of the second additive added to the electrolyte decreases, the long carbon chain polymer type interface film component formed tends to decrease, which affects the stability of the positive electrode and makes the improvement effect on the high temperature performance of the battery tend to decrease; as the amount of the second additive added to the electrolyte increases, the interface film impedance tends to increase, and the synergistic effect of the first additive and the second additive weakens, which makes the improvement effect on the problem of increased impedance in the later stage of battery cycle tend to decrease. In specific examples, the mass percentage of the second additive is 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3%, etc.

[0075] In the embodiments of the present application, the mass percentage of the auxiliary additive is 0.1% to 3%. In specific examples, the mass percentage of the auxiliary additive is 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, etc.

[0076] In the embodiments of the present application, the auxiliary additive can be used, which has the ability to well control the stability of the electrode-electrolyte interface film; and the mass percentage of the auxiliary additive meets the above conditions, which can further optimize the interface stability, and is beneficial to better improve the negative effects of the first additive by-product on the battery.

[0077] The third aspect of the embodiments of the present application provides a battery comprising the above-mentioned electrolyte.

[0078] The battery provided by the embodiments of the present application comprises the above-mentioned electrolyte, and has good storage performance and cycle performance under high temperature and high pressure conditions.

[0079] In some embodiments of the present application, the battery further comprises a positive electrode sheet, a negative electrode sheet, and a separator.

[0080] The positive electrode active material used in the positive electrode sheet includes LiNi a Co b M c O2 or LiFePO4; wherein M includes at least one of Mn, Al, Ti, V, Fe, Zn, V, Zr, Ce, Cr, and Cu, a+b+c=1, 0.1≤a≤0.8, 0.1≤b≤0.2, 0.1≤c≤0.3.

[0081] In some embodiments of the present application, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer.

[0082] Further, the positive electrode active material layer includes a positive electrode active material, and the positive electrode active material includes LiNi a Co b M c O2 or LiFePO4; wherein M includes at least one of Mn, Al, Ti, V, Fe, Zn, V, Zr, Ce, Cr, and Cu, a+b+c=1, 0.1≤a≤0.8, 0.1≤b≤0.2, 0.1≤c≤0.3.

[0083] Further, the positive electrode active material includes lithium nickel cobalt manganese oxide (such as NCM811, NCM622, NCM613, NCM523, NCM111) or LiFePO 4。

[0084] When the positive active material is a nickel-cobalt-manganese ternary material, structural phase change easily occurs under high voltage (>4.3 V) and high rate (>2 C) charging, which promotes the occurrence of oxygen evolution reaction and transition metal ion dissolution, leading to the decrease of electrolyte stability, the acceleration of lithium salt and solvent decomposition, and the problem of poor cycle performance under high-voltage fast charging. By matching the additive of the application, the high-voltage stability of the nickel-cobalt-manganese ternary positive electrode surface can be improved, and the thermal stability of the electrode-electrolyte interface can be improved, thereby improving the 3C fast charging cycle performance at room temperature and the high-temperature storage performance.

[0085] When the positive active material is LiFePO4, although the battery system using the positive electrode itself has certain thermal stability, the poor ion conductivity of the LiFePO4 system leads to poor fast charging cycle performance of the LiFePO4 system lithium battery. By matching the additive of the application, the ion conduction at the electrode-electrolyte interface can be improved, and the conduction of lithium ions on the SEI and CEI can be promoted, thereby significantly improving the fast charging cycle performance.

[0086] Further, the positive current collector includes a metal foil or a composite positive current collector. For example, the metal foil can be an aluminum foil. The composite positive current collector can include a polymer material base layer and a metal layer formed on at least one side surface of the polymer material base layer. For example, the composite negative current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, etc.) on a polymer material base material (such as a polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc. base material). As an example, the positive current collector has two surfaces opposite in the thickness direction thereof, and the positive active material layer is provided on any one or both of the two opposite surfaces of the positive current collector.

[0087] The application will be described in detail below with reference to specific examples, and it should be noted that these examples are merely descriptive and do not limit the application in any way. The reagents used in the examples are all from Aladdin Biochem Technology Co., Ltd.

[0088] Example 1

[0089] 1. Preparation of electrolyte: In an argon glove box with water content <10 ppm, oxygen content <1 ppm, non-aqueous organic solvents ethylene carbonate, methyl ethyl carbonate and dimethyl carbonate are mixed uniformly according to the mass ratio of 3:5:2 (ratio 3 / 5 / 2), then the first additive compound represented by formula I-1 and the second additive compound represented by formula II-1 are added and mixed uniformly, and then lithium salt lithium hexafluorophosphate is added, dissolved and mixed uniformly to obtain the electrolyte; wherein, based on the mass of the electrolyte, the mass percentage of lithium salt lithium hexafluorophosphate is 12.5%, the mass percentage of the first additive compound represented by formula I-1 is 1%, the mass percentage of the second additive compound represented by formula II-1 is 0.01%, and the balance is non-aqueous organic solvent 87.39%.

[0090] 2. Preparation of positive electrode sheet: the positive electrode active material LiNi 0.6 Co 0.1 Mn 0.3 O2, the binder polyvinylidene fluoride (PVDF), and the conductive agent carbon black are mixed uniformly according to the mass ratio of 97:1.2:1.8, N-methyl pyrrolidone (NMP) is added as a solvent, and stirring is performed under the action of a vacuum stirrer until the mixed system becomes a positive electrode slurry with uniform fluidity, and the solid content of the positive electrode slurry is 65wt%; the positive electrode slurry is uniformly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 1.8μm, and the coating amount is 2.5g / m 2 ; drying at 85℃, the positive electrode sheet with a single positive electrode material layer; then repeat the above steps on the other surface of the aluminum foil, i.e. obtain the positive electrode sheet with double positive electrode material layers; after drying at 85℃, cold pressing, edge cutting, sheet cutting, striping, and after striping, drying at 85℃ under vacuum for 4 hours, welding the tabs to obtain the positive electrode sheet with a specification of 258mm×200mm for standby use; wherein, the thickness of the single positive electrode material layer is 45μm.

[0091] 3. Preparation of negative electrode sheet: the negative electrode active material artificial graphite, the conductive agent carbon black, the thickening agent sodium carboxymethyl cellulose (CMC), and the adhesive styrene butadiene rubber (SBR) are mixed according to the mass ratio of 95.8:1.2:1.5:1.5, and deionized water is added to obtain a negative electrode slurry with a solid content of 50wt% under the action of a vacuum stirrer; the negative electrode slurry is uniformly coated on one surface of a negative electrode current collector copper foil with a thickness of 8μm, and the coating amount is 1.5g / m 2 ; drying at 85℃, the negative electrode sheet with a single negative electrode material layer; then repeat the above steps on the other surface of the copper foil, i.e. obtain the negative electrode sheet with double negative electrode material layers; after drying at 85℃, cold pressing, edge cutting, sheet cutting, striping, and after striping, drying at 85℃ under vacuum for 4 hours, welding the tabs to obtain the negative electrode sheet with a specification of 260mm×198mm for standby use; wherein, the thickness of the single negative electrode material layer is 50μm.

[0092] 4. Battery Fabrication: The prepared positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to act as a separator. They are then wound, with the positive tab connected to the positive electrode and the negative tab connected to the negative electrode, resulting in an electrode assembly. The electrode assembly is placed in an aluminum foil packaging bag, with the positive and negative tabs extended from the inside to the outside of the bag. Moisture is removed at 80°C, and the electrolyte prepared above is injected, with an injection coefficient of 3.0 g / Ah. After vacuum sealing, formation, aging, and capacity testing, a lithium-ion battery is obtained. The formation upper limit voltage is 4.4V, the formation temperature is 45℃, and the formation resting time is 24h; the aging temperature is 45℃, and the aging resting time is 24h; the capacity test involves charging to 4.4V at 0.2C, resting for 5 minutes, and then discharging to 3.0V at 0.2C, followed by repeating the above steps at 0.5C and 1C.

[0093] Examples 2-35

[0094] The preparation methods used in Examples 2-35 are the same as those in Example 1, and the composition and amount of each raw material are shown in Table 1-1.

[0095] Example 36

[0096] Example 36 uses the same preparation method as Example 1, with the positive electrode active material LiNi 0.6 Co 0.1 Mn 0.3 O2 replaced with LiNi 0.5 Co 0.2 Mn 0.3 The composition and dosage of each raw material for O2 are shown in Table 1-1.

[0097] Example 37

[0098] 1. Preparation of electrolyte: In an argon atmosphere glove box with a water content <10ppm and an oxygen content <1ppm, non-aqueous organic solvents ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate are added and mixed evenly in a mass ratio of 3:5:2 (ratio 3 / 5 / 2). Then, the compound shown in the first additive formula I-1 and the compound shown in the second additive formula II-1 are added and mixed evenly. Finally, lithium salt lithium hexafluorophosphate is added, dissolved, and mixed evenly to obtain the electrolyte. Based on the mass of the electrolyte, the mass percentage of lithium salt lithium hexafluorophosphate is 12.5%, the mass percentage of the compound shown in the first additive formula I-1 is 0.1%, the mass percentage of the compound shown in the second additive formula II-1 is 3%, and the balance is 84.40% non-aqueous organic solvent.

[0099] 2. Preparation of the positive electrode sheet: the positive electrode active material LiFePO4, the binder polyvinylidene fluoride (PVDF), and the conductive agent carbon black are mixed uniformly in a mass ratio of 96:2:2, N-methyl pyrrolidone (NMP) is added as a solvent, and stirring is performed under the action of a vacuum stirrer until the mixed system becomes a positive electrode slurry with uniform fluidity. The solid content of the positive electrode slurry is 0.65; the positive electrode slurry is uniformly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 1.8 μm, and the coating amount is 2.2 g / m 2 , and the positive electrode sheet with a single-sided positive electrode material layer is obtained; the above steps are repeated on the other surface of the aluminum foil, i.e., the positive electrode sheet with a double-sided positive electrode material layer is obtained; after drying at 85°C, cold pressing, edge cutting, sheet cutting, and strip cutting are performed, the strip is dried at 85°C under vacuum for 4 hours, and the tab is welded to obtain a positive electrode sheet with a size of 258 mm x 200 mm for standby use; the thickness of the single-sided positive electrode material layer is 90 μm.

[0100] 3. Preparation of the negative electrode sheet: the negative electrode active material artificial graphite, the conductive agent carbon black, the thickening agent sodium carboxymethyl cellulose (CMC), and the binder styrene-butadiene rubber (SBR) are mixed in a mass ratio of 95.8:1.2:1.5:1.5, deionized water is added, and a negative electrode slurry with a solid content of 50 wt% is obtained under the action of a vacuum stirrer; the negative electrode slurry is uniformly coated on one surface of a negative electrode current collector copper foil with a thickness of 8 μm, and the coating amount is 1.5 g / m 2 , and the negative electrode sheet with a single-sided negative electrode material layer is obtained; the above steps are repeated on the other surface of the copper foil, i.e., the negative electrode sheet with a double-sided negative electrode material layer is obtained; after drying at 85°C, cold pressing, edge cutting, sheet cutting, and strip cutting are performed, the strip is dried at 85°C under vacuum for 4 hours, and the tab is welded to obtain a negative electrode sheet with a size of 260 mm x 198 mm for standby use; the thickness of the single-sided negative electrode material layer is 60 μm.

[0101] 4. Preparation of the battery: the positive electrode sheet, the separator, and the negative electrode sheet prepared above are stacked in order with the separator between the positive electrode sheet and the negative electrode sheet to play a role of isolation, then are wound, the positive lug is connected to the positive electrode sheet, and the negative lug is connected to the negative electrode sheet to obtain an electrode assembly. The electrode assembly is put into an aluminum foil packaging bag, and the positive lug and the negative lug are led out from the inside space of the aluminum foil packaging bag to the outside space of the aluminum foil packaging bag, water is removed at 80°C, the electrolyte prepared above is injected, the injection coefficient is 3.0 g / Ah, and the lithium ion battery is obtained through processes such as vacuum packaging, formation, aging, and capacity distribution. The upper limit voltage of formation is 3.65 V, the formation temperature is 45°C, and the standing time of formation is 24 h; the aging temperature is 45°C, and the standing time of aging is 24 h; the capacity distribution is 0.2 C charged to 3.65 V, left for 5 minutes, then discharged to 2.0 V at 0.2 C, and then the above steps are repeated at 0.5 C and 1 C.

[0102] Examples 38-39

[0103] The preparation method used in Examples 38-39 is the same as that in Example 37, and the compositions and amounts of the raw materials are shown in Tables 1-2.

[0104] Comparative Examples 1-4

[0105] The preparation method used in Comparative Examples 1-4 is the same as that in Example 1, and the compositions and amounts of the raw materials are shown in Tables 1-2.

[0106] Table 1-1: Compositions and amounts of raw materials used in each example and comparative example

[0107] Table 1-2: Compositions and amounts of raw materials used in each example and comparative example

[0108] Note:

[0109] 1. In Table 1-1 and Table 1-2:

[0110] The compound represented by Formula I-1 is The compound represented by Formula I-2 is The compound represented by Formula I-3 is The compound represented by Formula I-4 is The compound represented by Formula I-5 is The compound represented by Formula I-6 is

[0111] 2. In Table 1:

[0112] The compound represented by Formula II-1 is The compound represented by Formula II-2 is The compound shown in Formula II-3 is The compound shown in Formula II-4 is The compound shown in Formula II-5 is The compound shown in Formula II-6 is

[0113] Performance test

[0114] I. Test method

[0115] 1. Test method of nickel-cobalt-manganese system of Examples 1-36 and Comparative Examples 1-4:

[0116] ① Normal temperature cycle performance test:

[0117] The lithium ion battery was placed in a 25°C constant temperature test box and allowed to stand for 30 minutes, so that the lithium ion battery reached a constant temperature. Charged to 4.4V at 3.0C constant current, then charged to the cut-off current of 0.05C constant voltage, and allowed to stand for 30 minutes, discharged to 3.0V at 1.0C constant current, and recorded as the discharge capacity C0. The above steps were repeated until the capacity decayed to 80% C0, and the cycle number was recorded, i.e. the normal temperature cycle number.

[0118] ② High temperature stability test:

[0119] The lithium ion battery was placed in a 25°C constant temperature test box and allowed to stand for 30 minutes, so that the lithium ion battery reached a constant temperature. Charged to 4.4V at 3.0C constant current, then charged to the cut-off current of 0.05C constant voltage, and allowed to stand for 30 minutes, discharged to 3.0V at 1.0C constant current, and recorded as the discharge capacity C0. The above steps were repeated until the capacity decayed to 80% C0, and the cycle number was recorded, i.e. the normal temperature cycle number.

[0120] ③ Direct current resistance (DCR) test of 3C cycle at normal temperature to 500 cycles:

[0121] The lithium ion battery was placed in a 25°C constant temperature test box and allowed to stand for 30 minutes, then the lithium ion battery was charged to a voltage of 4.4V at 3.0C constant current, then discharged at 1.0C constant current for 30 minutes and allowed to stand for 1h, then discharged at a current I1 corresponding to a rate of 2.0C for 10s, and recorded the corresponding voltage V1. The direct current resistance (DCR) of the lithium ion battery at 50% state of charge (SOC), i.e. DCR = V1 / I1, unit: mΩ.

[0122] 2. Test method of lithium iron phosphate system of Examples 37-39:

[0123] ① Normal temperature cycle performance test:

[0124] The lithium ion battery was placed in a 25℃ constant temperature test box and rested for 30 minutes, so that the lithium ion battery reached constant temperature. Charged to 3.65V at 3.0C constant current, then charged to 0.05C cutoff current at constant voltage, rested for 30 minutes, discharged to 2.0V at 1.0C constant current, and recorded as discharge capacity C0. Cycle with this step until the capacity decays to 80% C0, and record the cycle number, i.e. normal temperature cycle number.

[0125] ② High temperature stability test:

[0126] The lithium ion battery was placed in a 25℃ constant temperature test box and rested for 30 minutes, so that the lithium ion battery reached constant temperature. Charged to 3.65V at 1.0C constant current, then charged to 0.05C cutoff current at constant voltage, rested for 10 minutes, discharged to 2.0V at 1.0C constant current, and recorded as discharge capacity C2. The lithium ion battery was again placed in a 25℃ constant temperature test box and rested for 30 minutes, so that the lithium ion battery reached constant temperature. Charged to 3.65V at 1.0C constant current, then charged to 0.05C cutoff current at constant voltage, and then the lithium ion battery was transferred to 60℃ for 15 days. Then discharged to 2.0V at 1.0C constant current, and recorded as discharge capacity C3. The high temperature storage capacity retention rate of 60℃ storage for 15 days = C3 / C2 x 100%.

[0127] ③ Normal temperature 3C cycle to 500 cycles direct current resistance (DCR) test:

[0128] The lithium ion battery was placed in a 25℃ constant temperature test box and rested for 30 minutes, then the lithium ion battery was charged to 3.65V at 3.0C constant current, then discharged for 30 minutes at 1.0C constant current and rested for 1h, then discharged at 2.0C rate corresponding current I1 for 10s, and recorded the corresponding voltage as V1. The direct current resistance (DCR) of the lithium ion battery at 50% state of charge (SOC), i.e. DCR = V1 / I1, unit mΩ.

[0129] II. Test results

[0130] Table 2 Performance test results of samples provided by each example and comparative example

[0131] As can be seen from Examples 1 to 39, when the mass ratio of the first additive is 0.1 to 2%, the mass ratio of the second additive is 0.1 to 3%, and the mass ratio of the first additive to the second additive is 1:(0.03 to 20), the normal temperature 3C fast charging cycle performance of the lithium ion battery can be improved, the DCR value in the later stage of 3C fast charging cycle can be obviously reduced, and the capacity retention rate after high-temperature storage can be obviously improved. The above technical effects can be attributed to the mutual synergy of the first additive and the second additive, which forms an electrode-electrolyte interface film with excellent stability and beneficial ion conductivity. Meanwhile, the interface film has a certain toughness, which can adapt to the electrode expansion in the fast charging cycle, thereby enhancing the electrode-electrolyte interface stability in the later stage of 3C fast charging cycle. When the mass ratio of the first additive to the second additive is preferably 1:(1 to 8), the effect is better. Whether the nickel-cobalt-manganese ternary material or the lithium iron phosphate material is used as the positive active material of the lithium ion battery, the above technical effects are embodied. As can be seen from the data in Examples 29 to 36, when the first additive, the second additive, and the auxiliary additive are used together, the effect is better than when the first additive and the second additive are used together. The reasons are as follows: on the one hand, the auxiliary additive can form a stable interface film in the formation stage, which can further improve the performance of the lithium ion battery; on the other hand, the addition of the auxiliary additive can reduce the consumption of the first additive and the second additive in the formation and capacity distribution stages, so that the electrode-electrolyte interface film can be better repaired in the 3C fast charging cycle. In Example 39, the content of the second additive is 4% (which is beyond the protection scope of the second additive mass ratio of 0.1 to 3% in the present application), and it can be found that the adjustment of the impedance problem caused by the second additive by the first additive is limited, that is, when the content of the second additive is too large, the impedance problem caused by the second additive cannot be inhibited by the first additive from the beginning to the end of the cycle, and finally the DCR in the later stage of 3C fast charging cycle cannot be measured.

[0132] The above examples only express several embodiments of the present application, and the description is more specific and detailed, but it cannot be understood as limiting the scope of the present application. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the present application, several modifications and improvements can be made, which are within the scope of the present application. Therefore, the protection scope of the present application should be subject to the appended claims.

Claims

1. An electrolyte additive, wherein, The first additive and the second additive are included. The first additive includes a compound represented by Formula I: In the formula I, R1 is at least one F-substituted C1-C6 linear alkyl; The second additive includes an unsaturated carbonate substance.

2. The electrolyte additive according to claim 1, wherein, The R1 is a C1-C5 linear alkyl group which is fully substituted with F.

3. The electrolyte additive according to claim 1 or 2, wherein, The first additive includes at least one of a compound shown in formula I-1, a compound shown in formula I-2, a compound shown in formula I-3, a compound shown in formula I-4, a compound shown in formula I-5, and a compound shown in formula I-6; wherein, The compound of formula I-1 is The compound of formula I-2 is The compound of formula I-3 is The compound represented by the formula I-4 is Compounds of formula I-5 are Compounds of formula I-6 are 4. The electrolyte additive according to any one of claims 1 to 3, wherein, The second additive includes at least one of a compound shown in formula II-1, a compound shown in formula II-2, a compound shown in formula II-3, a compound shown in formula II-4, a compound shown in formula II-5, and a compound shown in formula II-6; wherein, The compound represented by the formula II-1 is The compound represented by the formula II-2 is The compound represented by the formula II-3 is The compound represented by the formula II-4 is The compound represented by the formula II-5 is The compound represented by the formula II-6 is 5. The electrolyte additive according to any one of claims 1 to 4, wherein, The mass ratio of the first additive and the second additive is 1:(0.03-20).

6. The electrolyte additive according to claim 5, wherein, The mass ratio of the first additive and the second additive is 1:(0.05-15).

7. The electrolyte additive according to claim 5, wherein, The mass ratio of the first additive and the second additive is 1:(1-8).

8. The electrolyte additive according to any one of claims 1 to 7, wherein, The auxiliary additive includes at least one of fluoroethylene carbonate, 1,3-propylene sulfone lactone, 1,3-propane sulfone lactone, and lithium difluorophosphate.

9. An electrolyte, wherein, The electrolyte includes the electrolyte additive according to any one of claims 1-8.

10. The electrolyte of claim 9, wherein, The electrolyte satisfies at least one of the following (1)-(3) based on the total mass of the electrolyte: (1) the mass percentage of the first additive is 0.1%-2%; (2) the mass percentage of the second additive is 0.1%-3%; (3) the mass percentage of the auxiliary additive is 0.1%-3%.

11. A battery, wherein, The electrolyte includes the electrolyte according to claim 9 or 10.

12. The battery of claim 11, wherein, The electrolyte further includes a positive electrode sheet, a negative electrode sheet, and a separator. The positive electrode active material used in the positive electrode sheet includes LiNi a Co b M c O2 or LiFePO4; wherein M includes at least one of Mn, Al, Ti, V, Fe, Zn, V, Zr, Ce, Cr, and Cu, a+b+c=1, 0.1≤a≤0.8, 0.1≤b≤0.2, 0.1≤c≤0.3.

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