Dual-function lithium-ion battery electrolyte additive and lithium-ion battery

Abstract

The present invention relates to the field of lithium-ion batteries and discloses a dual-function lithium-ion battery electrolyte additive and a lithium-ion battery. The additive comprises an additive, wherein the additive is a compound represented by Formula I, a compound represented by Formula II, or a compound represented by Formula III. Compared to other components of the electrolyte, the additive has a higher highest occupied molecular orbital energy level and can be oxidized earlier, forming a positive electrode electrolyte interphase on the positive electrode surface, thereby reducing HF corrosion of the positive electrode. Furthermore, compared to other components of the electrolyte, the additive of the present invention also has a lower unoccupied molecular orbital level and can be reduced earlier, forming a solid electrolyte interface on the negative electrode surface. The passivation of the graphite surface by the solid electrolyte interface can impart good dynamic stability to the active material surface and ensure good battery cycle performance. The electrolyte additive also introduces a phosphate group, which imparts excellent flame retardancy.

Description

Technical Field

[0001] The present invention relates to the field of lithium ion batteries, and in particular to a dual-function lithium ion battery electrolyte additive. Background Art

[0002] Lithium-ion batteries, with their high theoretical energy density, portability, and durability, have shown great application prospects in a variety of fields, including electric vehicles, aerospace, and portable electronic products. Due to the popularity of lithium-ion batteries, research on lithium-ion battery electrolytes has gradually come into people's field of vision. Current lithium-ion battery electrolyte additives contain only a single functional group component and are generally unable to meet the various performance requirements of the battery. In practical applications, it is necessary to add different types of additives to meet the requirements of commercial battery use through synergistic effects between additives. To this end, the present invention proposes a dual-functional lithium-ion battery electrolyte additive. Summary of the Invention

[0003] (1) Technical problems solved

[0004] In view of the shortcomings of the existing technology, the present invention provides a dual-function lithium-ion battery electrolyte additive and a lithium-ion battery to solve the problem that the current lithium-ion battery electrolyte additive has a single function.

[0005] (2) Technical solution

[0006] To achieve the above-mentioned purpose, the present invention provides the following technical solutions:

[0007] A dual-function lithium-ion battery electrolytic additive comprises an additive, wherein the additive is a compound represented by formula I, a compound represented by formula II, or a compound represented by formula III.

[0008]

[0009] Preferably, the additive is at least two of the compounds represented by formula I, the compounds represented by formula II, or the compounds represented by formula III.

[0010] Preferably, the electrolyte further comprises a basic electrolyte, and the amount of the additive added accounts for 1% to 1% by mass of the basic electrolyte.

[0011] Preferably, the basic electrolyte comprises a lithium salt and an organic solvent.

[0012] Preferably, the lithium salt includes at least one of lithium hexafluorophosphate, lithium trifluoromethanesulfonate, lithium tetrafluoroborate, and lithium difluorooxalatoborate.

[0013] Preferably, the organic solvent includes at least one of carbonate, phosphate, carboxylate, ether solvent, nitrile solvent or sulfone solvent.

[0014] A lithium ion battery, the electrolyte of which includes the above-mentioned dual-function lithium ion battery electrolyte additive.

[0015] (3) Beneficial effects

[0016] Compared with the prior art, the dual-function lithium-ion battery electrolyte additive provided by the present invention has the following beneficial effects:

[0017] 1. This bifunctional lithium-ion battery electrolyte additive has a higher highest occupied molecular orbital (HOMO) energy level than other components of the electrolyte, allowing it to be oxidized prematurely, forming a cathode electrolyte interphase (CEI) on the positive electrode surface, thereby reducing HF corrosion of the positive electrode. Furthermore, compared to other components of the electrolyte, the additive of the present invention also has a lower unoccupied molecular orbital (LUMO) energy level, allowing it to be reduced prematurely, forming a solid electrolyte interface (SEI) on the negative electrode surface. The passivation of the graphite surface by the solid electrolyte interface can impart good dynamic stability to the active material surface and ensure good battery cycle performance. The electrolyte additive also introduces phosphate groups, giving it excellent flame retardant properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of room temperature cycling performance of batteries prepared in Examples 1-7 of the present invention and Comparative Example 1;

[0019] Figure 2 This is a schematic diagram of the acupuncture test results of an embodiment of the present invention;

[0020] Figure 3 This is a schematic diagram of cyclic voltammetry test results according to an embodiment of the present invention;

[0021] Figure 4 This is a schematic diagram of the SEM scanning electron microscope test results of an embodiment of the present invention. DETAILED DESCRIPTION

[0022] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0023] Example

[0024] See also Figure 1-4The bifunctional lithium-ion battery electrolyte additive provided by the embodiment of the present invention includes an additive, wherein the additive is a compound represented by Formula I, a compound represented by Formula II, or a compound represented by Formula III. Specifically, each compound is: 1) a compound represented by Formula I; or 2) a compound represented by Formula II; or 3) a compound represented by Formula III; or 4) at least two of the compounds represented by Formula I, the compounds represented by Formula II, or the compounds represented by Formula III.

[0025]

[0026] The lithium-ion battery electrolyte provided by the present invention further comprises a base electrolyte and an electrolyte additive. The amount of the electrolyte additive added accounts for 1% to 1% by weight of the lithium-ion battery electrolyte. Specifically, the base electrolyte comprises a lithium salt and an organic solvent, the lithium salt comprising at least one of lithium hexafluorophosphate, lithium trifluoromethanesulfonate, lithium tetrafluoroborate, and lithium difluorooxalatoborate, and the organic solvent comprising at least one of a carbonate, a phosphate, a carboxylate, an ether solvent, a nitrile solvent, or a sulfone solvent.

[0027] An embodiment of the present invention further provides a lithium ion battery comprising a positive electrode, a negative electrode, a separator and an electrolyte, wherein the electrolyte is a lithium ion electrolyte containing the bifunctional lithium ion battery electrolyte additive.

[0028] The active material of the positive electrode material can be selected from composite lithium metal oxides containing three elements: nickel, cobalt and manganese, such as LiNi 0.8 Mn 0.1 Co 0.1 O2.

[0029] The active material in the negative electrode material can be selected from at least one of metallic lithium, lithium alloy, and SiO / Gr. Example 1

[0030] (1) Preparation of electrolyte

[0031] Compound ① was dissolved in a basic electrolyte as an electrolyte additive, wherein the organic solvent in the basic electrolyte was EC / DMC / EMC (volume ratio was 1:1:1), the lithium salt was 1 mol / L LiPF6, and the addition ratio of compound ① was 0.5%.

[0032] The structural formula of compound ① is as follows:

[0033]

[0034] (2) Preparation of positive electrode sheet

[0035] The nickel-cobalt-manganese ternary material (LiNi 0.8 Mn 0.1 Co 0.1O2), conductive carbon black (Super-P) and a binder polyvinylidene fluoride (PVDF) containing N-methyl-2-pyrrolidone (NMP) were mixed in a mass ratio of 8:1:1 and stirred for 0.5 h using a magnetic stirrer to obtain a positive electrode slurry. The positive electrode slurry was evenly coated on one side of a clean aluminum foil surface, dried, and cut into pieces to obtain the positive electrode sheet for testing.

[0036] (3) Preparation of button half-cell

[0037] In a glove box with a moisture and oxygen content of less than 10 ppm and filled with argon, a CR2032 button cell was assembled using the positive electrode sheet in (2) and a lithium sheet as the negative electrode, the electrolyte in (1) was added, and a polyethylene separator with a thickness of 25 μm was used.

[0038] (4) Button battery electrochemical performance test

[0039] The room temperature cycle performance test was carried out for 100 cycles by charging to 4.2V at a constant current of 1.0C and then discharging to 2.5V at a constant current. The room temperature cycle performance data is shown in Figure 1 .

[0040] Example 2

[0041] The difference between this embodiment and embodiment 1 is that, (1) in the preparation of the electrolyte, the addition ratio of compound ① is 1%, and the remaining operations are carried out according to the same steps as in embodiment 1 to prepare the electrode and perform the electrochemical performance test. The obtained room temperature cycle performance data are shown in FIG. Figure 1 .

[0042] Example 3

[0043] The difference between this embodiment and embodiment 1 is that, (1) in the preparation of the electrolyte, compound ② is used as an additive, and the remaining operations are carried out according to the same steps as in embodiment 1 to prepare the electrode and perform the electrochemical performance test. The obtained room temperature cycle performance data are shown in FIG. Figure 1 .

[0044] The structural formula of compound ② is as follows:

[0045]

[0046] Example 4

[0047] The difference between this embodiment and embodiment 3 is that, (1) in the preparation of the electrolyte, the addition ratio of compound ② is 1%, and the remaining operations are carried out according to the same steps as in embodiment 1 to prepare the electrode and perform the electrochemical performance test. The obtained room temperature cycle performance data are shown in FIG. Figure 1 .

[0048] Example 5

[0049] The difference between this embodiment and embodiment 1 is that, (1) in the preparation of the electrolyte, compound ③ is used as an additive, and the remaining operations are carried out according to the same steps as in embodiment 1 to prepare the electrode and perform the electrochemical performance test. The obtained room temperature cycle performance data are shown in FIG. Figure 1 .

[0050] The structural formula of compound ③ is as follows:

[0051]

[0052] Example 6

[0053] The difference between this embodiment and embodiment 5 is that, (1) in the preparation of the electrolyte, the addition ratio of compound ③ is 1%, and the remaining operations are carried out according to the same steps as in embodiment 1 to prepare the electrode and perform the electrochemical performance test. The obtained room temperature cycle performance data are shown in FIG. Figure 1 .

[0054] Example 7

[0055] The difference between this embodiment and embodiment 1 is that, (1) in the preparation of the electrolyte, compound ② and compound ③ are mixed in a ratio of 1:1 as an additive, and the addition ratio is 1%. The remaining operations are carried out according to the same steps as in embodiment 1 to prepare the electrode and perform the electrochemical performance test. The obtained room temperature cycle performance data are shown in FIG. Figure 1 .

[0056] Comparative Example 1

[0057] The difference between this comparative example and Example 1 is that no lithium salt electrolyte additive is added. The remaining operations are carried out according to the same steps as Example 1 to prepare the electrode and perform electrochemical performance tests. The obtained room temperature cycle performance data are shown in FIG. Figure 1 .

[0058] Table 1 Battery performance results with different additives

[0059] Example 100 cycle capacity retention rate Comparative Example 1 83,58％ Example 1 85,07％ Example 2 87,92％ Example 3 88,46％ Example 4 92,42％ Example 5 88,36％ Example 6 85,21％ Example 7 87,25％

[0060] As can be seen from Table 1, compared with the comparative example, after 100 cycles, the capacity retention rate of the embodiment has increased to varying degrees, all of which are higher than 85%, indicating that the addition of the additive having anhydride and phosphoric acid group structures can effectively improve the antioxidant stability of the electrolyte and is a multifunctional additive for improving the long cycle life of the battery.

[0061] <Test Example>

[0062] Electrolyte additive performance test

[0063] Test samples: Example 1, Comparative Example 1

[0064] In order to verify the flame retardant function of the electrolyte additive ① and its role in improving the cycle performance of the lithium nickel cobalt manganese oxide button battery, the lithium nickel cobalt manganese oxide button battery was subjected to a needle penetration test and a cyclic voltammetry test, and the positive electrode of the lithium nickel cobalt manganese oxide button battery after the cycle was subjected to a SEM scanning electron microscopy test.

[0065] Acupuncture experiment

[0066] The nickel manganese cobalt oxide lithium button half-cells assembled in Example 1 and Comparative Example 1 were subjected to needle penetration tests, and the changes in temperature and voltage were recorded. Figure 2 shown.

[0067] from Figure 2 It can be seen that the heating rate of the nickel manganese cobalt oxide button half-cell assembled in Example 1 is slower than that in Comparative Example 1, and the peak temperature is lower, which indicates that the electrolyte in Example 1 can effectively improve the temperature rise after the lithium ion battery is short-circuited.

[0068] Cyclic voltammetry test

[0069] The nickel manganese cobalt oxide lithium button half-cells assembled in Example 1 and Comparative Example 1 were tested at 0.05 mV s -1 Cyclic voltammetry test was performed. The results are as follows Figure 3 shown.

[0070] from Figure 3 It can be seen that the redox peak current of the nickel manganese cobalt oxide lithium button half-cell assembled in Example 1 is significantly higher than the redox peak current of Comparative Example 1, which indicates that the SEI film and CEI film generated by the electrolyte additive have higher ionic conductivity, which can achieve faster Li + Insertion / deinsertion kinetics.

[0071] SEM scanning electron microscope test

[0072] The present invention conducted a section scanning electron microscope test on the positive electrode materials of Comparative Example 1 and Example 1 after cycling. Figure 4 It can be seen that after cycling, both cathode materials develop microcracks along the grain boundaries, which spread in a zigzag pattern from the center of the particle to the surface, with the width of the microcracks gradually decreasing from the center of the particle to the surface. It can be seen that the microcracks generated in Comparative Example 1 after cycling are more numerous and longer than those in Example 1. The primary particle crystal structure in the cathode material of Example 1 shows no obvious fractures after cycling, and the primary particles remain densely packed near the surface.

[0073] The dual-function lithium-ion battery electrolyte additive and lithium-ion battery provided by the above-mentioned embodiments of the present invention have a higher highest occupied molecular orbital energy level than other components of the electrolyte, can be oxidized in advance, and form a positive electrode electrolyte interphase on the positive electrode surface, reducing HF corrosion of the positive electrode. Moreover, compared with other components of the electrolyte, the additive of the present invention also has a lower unoccupied molecular orbital, can be reduced in advance, and form a solid electrolyte interface on the negative electrode surface. The passivation of the graphite surface by the solid electrolyte interface can make the active material surface have good dynamic stability, while ensuring good battery cycle performance. At the same time, the electrolyte additive also introduces a phosphate group, which gives it excellent flame retardant properties.

[0074] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A dual-function lithium-ion battery electrolyte additive, characterized in that: The additive is a compound represented by formula I, a compound represented by formula II, or a compound represented by formula III:

2. The dual-function lithium-ion battery electrolyte additive according to claim 1, characterized in that: The additive is at least two of the compounds represented by formula I, the compounds represented by formula II, or the compounds represented by formula III.

3. An electrolyte comprising the dual-function lithium-ion battery electrolyte additive according to claim 1, characterized in that: The invention also includes a basic electrolyte, and the amount of the additive added to the basic electrolyte is no more than 1% by mass.

4. The electrolyte according to claim 3, characterized in that: The basic electrolyte includes a lithium salt and an organic solvent.

5. The electrolyte according to claim 4, characterized in that: The lithium salt includes at least one of lithium hexafluorophosphate, lithium trifluoromethanesulfonate, lithium tetrafluoroborate, and lithium difluorooxalatoborate.

6. The electrolyte according to claim 4, characterized in that: The organic solvent includes at least one of carbonate, phosphate, carboxylate, ether solvent, nitrile solvent or sulfone solvent.

7. A lithium-ion battery, characterized in that: The electrolyte comprises the bifunctional lithium ion battery electrolyte additive according to any one of claims 1 to 2.

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