Aminosilane-based additive and lithium-ion battery electrolyte containing the same

Abstract

The application discloses an amino silane additive, which comprises a compound with a structural formula as shown in formula (I). The application also discloses a lithium ion battery electrolyte and a lithium ion battery containing the additive. The amino silane additive of the application can inhibit the formation of HF in the electrolyte, effectively prevent the damage of HF to electrode materials and SEI films, and meanwhile, due to the fact that the silane additive is preferentially subjected to redox reaction to solvents during battery charging, a thick and uniform organic polymer film is formed at the negative electrode, the shortcomings of non-uniform film formation of a film forming additive are made up, and the cycle performance of the battery is improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and more particularly to an aminosilane additive and a lithium-ion battery electrolyte containing the additive. Background Technology

[0002] Lithium-ion batteries have advantages such as high energy density, long cycle life, and no memory effect, and are widely researched and applied. Currently, the main cathode materials for commercially available high-capacity lithium-ion batteries include lithium cobalt oxide, lithium manganese oxide, lithium nickel manganese oxide, and ternary materials. To meet the needs of portable electronic products and the sustainable operation of electric vehicles, lithium-ion batteries are required to have high energy density, high specific energy density, and long cycle life, which has kept them in the mainstream position in the market for a long time.

[0003] Electrolyte, as a crucial component of lithium-ion batteries, significantly impacts their performance. High water content in the electrolyte accelerates the catalytic decomposition of LiPF6, generating free acid and noticeably degrading battery performance. This is primarily manifested in the corrosion of the SEI film by HF, leading to the dissolution of the positive electrode material and consequently impairing battery cycle performance. Furthermore, during the production and storage of electrolytes, factors such as increased ambient humidity and deterioration of equipment sealing can all cause the water content to rise.

[0004] Currently, to remove water from electrolytes, inorganic compounds, isocyanates / thiocyanates, silazane compounds, and silane compounds are typically added. Inorganic dehydrating agents are mostly inorganic alkali metal oxides, such as CaO and MgO. After addition, they react with HF in the electrolyte. However, these substances remove HF slowly, and metal ions are easily reduced at the negative electrode, forming metal impurities and causing internal physical short circuits in the battery. Furthermore, inorganic alkali metal oxides are insoluble in electrolytes. Therefore, using alkali metal compounds as dehydrating agents is not suitable for the industrial application of organic electrolytes. Isocyanates / thiocyanates contain =N=C=O / =N=C=S groups, which can form polymers with free H+ in the electrolyte, generating amides that remove water. However, the reaction rate is slow, and the dehydration effect is not significant. Therefore, developing novel acid and water-removing electrolyte additives is of great importance. Summary of the Invention

[0005] Based on the technical problems existing in the background art, the present invention proposes an aminosilane additive and a lithium-ion battery electrolyte containing the additive.

[0006] This invention proposes an aminosilane additive, wherein the additive comprises at least one compound as shown in formula (I):

[0007]

[0008] In formula (I), R1 is selected from C1 to C3 alkyl, and R2 and R3 are independently selected from C1 to C5 alkyl, H, C1 to C3 alkoxy or phenyl.

[0009] Preferably, the additive is selected from at least one of the compounds shown in formulas (I-1) to (I-5):

[0010]

[0011]

[0012]

[0013] Taking the compound shown in formula (I-3) as an example, the reaction process and reaction conditions are specifically described as follows: First, benzene is added as a solvent in a three-necked flask. Under nitrogen protection, dichlorosilane and methanol are added dropwise simultaneously. During the dropwise addition, the mixture is cooled in an ice-water bath. After the dropwise addition is completed, the mixture is heated in an oil bath to 40°C and reacted for 40 min. Then, the mixture is heated to reflux and reacted for about 20 min to obtain dimethylsilane (CAS: 5314-52-3, which can also be purchased directly). At room temperature, dimethylsilane and chloropropane are added to an organic solvent to react and obtain propyldimethylsilane (Si-H addition reaction). Propyldimethylsilane and ethylenediamine are added to benzene solvent and heated to about 150°C to reflux and react to obtain the compound shown in formula (I-3), named diaminopropyldimethylsilane.

[0014] The synthesis procedures for the compounds shown in formulas (I-1) to (I-5) are as follows:

[0015]

[0016] Taking diaminopropyl dimethylsilane as an example, the mechanism of action is explained as follows:

[0017] Diaminopropyl dimethylsilane reacts with H2O and HF in the electrolyte to generate aminomethyl difluorosilane. The aminomethyl difluorosilane is further hydrolyzed to generate methyltrifluorosilane and NH3. In addition, -NH2 reacts with water to generate NH3. The synergistic effect of multiple functional groups effectively removes water and acid from the electrolyte.

[0018] A lithium-ion battery electrolyte comprising the aforementioned aminosilane additive.

[0019] Preferably, the lithium-ion battery electrolyte further includes lithium salt, film-forming additives, and organic solvents.

[0020] Preferably, the aminosilane additive accounts for 0.05-12% of the total mass of the electrolyte.

[0021] Preferably, the lithium salt accounts for 10-15% of the total mass of the electrolyte; the lithium salt is at least one selected from lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorooxalate borate, and lithium difluorosulfonylimide.

[0022] Preferably, the film-forming additive accounts for 0.1-2% of the total mass of the electrolyte; the film-forming additive is at least one selected from vinylene carbonate, fluoroethylene carbonate, ethylene ethylene carbonate, ethylene sulfite, vinyl sulfite, ethylene sulfate, 1,2,6-oxodithiophene-2,2,6,6-tetraoxide, methane disulfonate, and lithium bis(oxalato)borate.

[0023] Preferably, the organic solvent is at least one selected from ethylene carbonate, propylene carbonate, methyl ethyl carbonate, dimethyl carbonate, butene carbonate, diethyl carbonate, propyl acetate, ethyl propionate, and propyl propionate.

[0024] Preferably, the lithium-ion battery electrolyte comprises the following components by mass percentage: 10-15% lithium salt, 0.1-2% film-forming additive, 0.05-12% aminosilane additive, and the balance being an organic solvent.

[0025] A lithium-ion battery includes a positive electrode, a negative electrode, a separator, and a lithium-ion battery electrolyte.

[0026] Preferably, the active material of the positive electrode is selected from any one of lithium cobalt oxide, lithium manganese oxide, nickel-cobalt-manganese ternary materials, nickel-cobalt-aluminum ternary materials, and spinel nickel-manganese lithium oxide materials.

[0027] Preferably, the active material of the negative electrode is selected from either graphite or silicon dioxide.

[0028] The beneficial effects of this invention are as follows:

[0029] This invention adds aminosilane compounds to the electrolyte, which can inhibit the formation of HF in the electrolyte, effectively preventing HF from damaging the electrode materials and SEI film. Simultaneously, because silane additives preferentially undergo redox reactions over the solvent during battery charging, they form a uniformly thick organic polymer film at the negative electrode, compensating for the uneven film formation of film-forming additives and improving the battery's cycle performance. Furthermore, the aminosilane additives of this invention also possess a high LUMO energy level, enabling preferential film formation at the positive electrode and significantly improving the battery's high-temperature cycle performance. Attached Figure Description

[0030] Figures 1-5 The NMR spectra of the compounds represented by formulas (I-1) to (I-5) proposed in this invention are shown.

[0031] Figure 6The cycling performance of batteries assembled with the electrolytes of Example 3, Comparative Example 2, and Comparative Example 3 at 45°C.

[0032] Figure 7 The HOMU and LUMO energy levels are for dimethoxydimethylsilane, N,N-diethyltrimethylsilaneamine, and aminosilane compounds represented by formula (I-3). Detailed Implementation

[0033] The technical solution of the present invention will now be described in detail through specific embodiments.

[0034] Example 1

[0035] A lithium-ion battery electrolyte comprises the following components in weight percentages: 14% lithium hexafluorophosphate, 5% aminosilane compound of formula (I-1), 0.5% fluoroethylene carbonate, 0.5% vinylene carbonate, and the balance being an organic solvent.

[0036] Preparation of lithium-ion batteries:

[0037] (1) Preparation of positive electrode sheet: The positive electrode active material, conductive agent and binder are mixed in a mass ratio of 98:1:1, N-methylpyrrolidone is added, and the mixture is stirred and mixed thoroughly to form a uniform positive electrode slurry. The slurry is then uniformly coated on an aluminum foil with a thickness of 15 micrometers and dried to obtain the positive electrode sheet.

[0038] (2) Preparation of negative electrode sheet: Graphite, conductive agent, binder and thickener are mixed in a mass ratio of 96:1:2:1, deionized water is added, and the mixture is stirred and mixed thoroughly to form a uniform negative electrode slurry. The slurry is then uniformly coated on a copper foil with a thickness of 8 micrometers and dried to obtain the negative electrode sheet.

[0039] (3) Battery assembly: In a dry environment with the dew point controlled below -40°C, the positive electrode, separator, and negative electrode are stacked in sequence to ensure that the separator completely separates the positive and negative electrodes. Then, the electrode is wound to form a core and sealed in an aluminum-plastic film of a fixed size using adhesive tabs to form a soft-pack battery to be injected with electrolyte. Then, the lithium-ion battery electrolyte is injected into the soft-pack battery, followed by sealing, formation, aging, and capacity testing to obtain the experimental battery for testing.

[0040] Example 2

[0041] A lithium-ion battery electrolyte comprises the following components in weight percentages: 14% lithium hexafluorophosphate, 5% aminosilane compound of formula (I-2), 0.5% fluoroethylene carbonate, 0.5% vinylene carbonate, and the balance being an organic solvent.

[0042] The preparation method of the lithium-ion battery is the same as in Example 1.

[0043] Example 3

[0044] A lithium-ion battery electrolyte comprises the following components in weight percentages: 14% lithium hexafluorophosphate, 5% aminosilane compound of formula (I-3), 0.5% fluoroethylene carbonate, 0.5% vinylene carbonate, and the balance being an organic solvent.

[0045] The preparation method of the lithium-ion battery is the same as in Example 1.

[0046] Example 4

[0047] A lithium-ion battery electrolyte comprises the following components in weight percentages: 14% lithium hexafluorophosphate, 5% aminosilane compounds of formula (I-5), 0.5% fluoroethylene carbonate, 0.5% vinylene carbonate, and the balance being an organic solvent.

[0048] The preparation method of the lithium-ion battery is the same as in Example 1.

[0049] Example 5

[0050] A lithium-ion battery electrolyte comprises the following components in the indicated mass percentages: 14% lithium hexafluorophosphate, 1% aminosilane compound of formula (I-3), 0.5% fluoroethylene carbonate, 0.5% vinylene carbonate, and the balance being an organic solvent.

[0051] The preparation method of the lithium-ion battery is the same as in Example 1.

[0052] Example 6

[0053] A lithium-ion battery electrolyte comprises the following components in weight percentages: 14% lithium hexafluorophosphate, 2% aminosilane compound of formula (I-3), 0.5% fluoroethylene carbonate, 0.5% vinylene carbonate, and the balance being an organic solvent.

[0054] The preparation method of the lithium-ion battery is the same as in Example 1.

[0055] Example 7

[0056] A lithium-ion battery electrolyte comprises the following components in weight percentages: 14% lithium hexafluorophosphate, 6% aminosilane compound of formula (I-3), 0.5% fluoroethylene carbonate, 0.5% vinylene carbonate, and the balance being an organic solvent.

[0057] The preparation method of the lithium-ion battery is the same as in Example 1.

[0058] Example 8

[0059] A lithium-ion battery electrolyte comprises the following components in the indicated mass percentages: 14% lithium hexafluorophosphate, 8% aminosilane compound of formula (I-3), 0.5% fluoroethylene carbonate, 0.5% vinylene carbonate, and the balance being an organic solvent.

[0060] The preparation method of the lithium-ion battery is the same as in Example 1.

[0061] Comparative Example 1

[0062] A lithium-ion battery electrolyte comprises the following components in weight percentages: 14% lithium hexafluorophosphate, 0.5% fluoroethylene carbonate, 0.5% vinylene carbonate, and the balance being an organic solvent.

[0063] The preparation method of the lithium-ion battery is the same as in Example 1.

[0064] Comparative Example 2

[0065] A lithium-ion battery electrolyte comprises the following components in weight percentages: 14% lithium hexafluorophosphate, 5% dimethoxydimethylsilane (containing Si-O), 0.5% fluoroethylene carbonate, 0.5% vinylene carbonate, and the balance being an organic solvent.

[0066] Comparative Example 3

[0067] A lithium-ion battery electrolyte comprises the following components in weight percentages: 14% lithium hexafluorophosphate, 5% N,N-diethyltrimethylsilaneamine (containing Si-N), 0.5% fluoroethylene carbonate, 0.5% vinylene carbonate, and the balance being an organic solvent.

[0068] The following tests were performed on the batteries assembled in the examples and comparative examples:

[0069] Test 1: Composition and Compatibility Test

[0070] Take the assembled lithium-ion battery described above, charge it to 3.0V at a constant current of 0.02C, let it stand for 5 minutes, charge it to 3.3V at a constant current of 0.05C, let it rest for 5 minutes, and finally charge it to 3.8V at a constant current of 0.1C to complete the formation test. Charge the battery to 4.25V at a constant current and constant voltage of 0.1C, discharge it to 2.5V at 0.33C, and then charge and discharge it three times each at 0.33C and 1.0C to complete the capacity grading. The charging is constant current and constant voltage charging, and the discharging is constant current discharging.

[0071] Test 2: Room Temperature Cycling Experiment

[0072] Take the assembled lithium-ion battery described above, record the average 0.33C discharge capacity as the reference capacity C0, charge it at a constant current of 0.5C0 to the 4.25V limit voltage, then switch to constant voltage charging until the charging current is ≤0.05C0, let it stand for 30 minutes, then discharge it at 1.0C0 to the cutoff voltage of 2.5V, let it stand for 30 minutes, and perform the charge and discharge test according to the above procedure for more than 100 cycles.

[0073] Test 3: 45℃ High Temperature Cyclic Test

[0074] Take the assembled lithium-ion battery described above, record the average 0.33C discharge capacity as the reference capacity C0, charge it at a constant current of 0.5C0 to a limit voltage of 4.25V, then switch to constant voltage charging until the charging current is ≤0.05C0, let it stand for 30 minutes, then discharge it at 1.0C0 to the cutoff voltage of 2.8V, let it stand for 30 minutes, and perform charge and discharge experiments according to the above procedure for more than 100 cycles.

[0075] Battery initial efficiency calculation method: (formation charge capacity + first charge capacity during capacity grading) / (first discharge capacity during capacity grading) 8 × 100%; Capacity retention rate calculation method: (discharge capacity per cycle) / (average of the first five cycles) × 100%.

[0076] The test results are shown in Table 1. Figure 2 As shown:

[0077] Table 1

[0078]

[0079]

[0080] The above-mentioned acid-removing additives containing Si-O structures primarily function by allowing the lone pair electrons of oxygen atoms to readily react with H+ through acid-base interactions. + In addition, Si has a high affinity for F- and can remove the separated F. The Si-N structure has a similar effect to the Si-O structure. Furthermore, -NH and -NH2 have a certain scavenging effect on H+.

[0081] Comparing the data of Examples 1, 2, 3, and 4 in Table 2 with Comparative Example 1, Examples 1, 2, 3, and 4 all showed improvements in battery performance, with Example 3 showing the most significant improvement. This is because the aminosilane additives used in Examples 2 and 4 contain Si-H in their structural formula, which generates additional H during the reaction. +Example 1 has one less Si-O bond than Example 3, resulting in a reduced acid removal effect and lower cycle performance compared to Example 3. Comparing Examples 3, 5, 6, 7, and 8, it can be observed that the effect of compound concentration on battery performance generally shows an initial increase followed by a decrease. This is because if the compound concentration is too low, the acid removal effect is not obvious, while if the compound concentration is too high, the thickness of the SEI film formed by the additive increases, leading to higher internal resistance.

[0082] Comparing the cycling performance of Example 3, Comparative Example 2, and Comparative Example 3 at 45°C, the results are as follows: Figure 6 As shown in the figure. It can be seen that the aminosilane additives of the present invention greatly improve the cycle performance of the battery at high temperatures due to the synergistic effect of multiple functional groups. The HOMU and LUMO energy levels of dimethoxydimethylsilane (containing Si-O), N,N-diethyltrimethylsilaneamine (containing Si-N), and aminosilane compounds shown in formula (I-3) were calculated using the B3P86 model based on density functional theory (DFT), and the results are as follows. Figure 7 As shown, the structure of equation (I-3) has a high LUMO energy level, indicating that this structure can preferentially form a film on the positive electrode, thus improving the high-temperature cycling performance of the battery.

[0083] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A lithium-ion battery electrolyte, characterized in that, The amino silane additive comprises at least one compound as shown in formula (I): The amino silane additive comprises at least one compound as shown in formula (I): In formula (I), R1 is selected from C1-C3 alkyl, and R2 and R3 are independently selected from C1-C5 alkyl, H, C1-C3 alkoxy or phenyl.

2. The electrolyte for lithium ion batteries according to claim 1, characterized in that, The amino silane additive is selected from at least one of the compounds as shown in formula (I-1) to formula (I-5):

3. The electrolyte for lithium ion batteries according to claim 1, characterized in that, The lithium salt, the film forming additive and the organic solvent are also included.

4. The electrolyte for lithium ion batteries according to claim 1, characterized in that, The amino silane additive accounts for 0.05-12% of the total mass of the lithium ion battery electrolyte.

5. The electrolyte for lithium ion batteries according to claim 3, characterized in that, The lithium salt accounts for 10-15% of the total mass of the lithium ion battery electrolyte; the lithium salt is at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluoro(oxalato)borate and lithium bis(fluorosulfonyl)imide.

6. The electrolyte for lithium ion batteries according to claim 3, characterized in that, The film forming additive accounts for 0.1-2% of the total mass of the lithium ion battery electrolyte; the film forming additive is at least one of vinylene carbonate, fluoroethylene carbonate, vinyl ethylene carbonate, vinyl sulfite, vinyl sulfite, vinyl sulfate, 1,2,6-oxadithiophene-2,2,6,6-tetraoxide, methylene methane disulfonate and lithium bis(oxalato)borate.

7. The electrolyte for lithium ion batteries according to claim 3, characterized in that, The organic solvent is at least one of vinyl carbonate, propylene carbonate, methyl ethyl carbonate, dimethyl carbonate, butylene carbonate, diethyl carbonate, propyl acetate, ethyl propionate and propyl propionate.

8. A lithium-ion battery, characterized by The lithium ion battery electrolyte comprises a positive electrode, a negative electrode, a separator and the lithium ion battery electrolyte according to any one of claims 1-7.

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