Lithium ion battery high-voltage electrolyte and lithium ion battery

Abstract

The invention belongs to the technical field of lithium ion batteries, and particularly relates to a lithium ion battery high-voltage electrolyte and a lithium ion battery. The high-voltage electrolyte comprises a lithium salt, a first additive, a second additive, an auxiliary additive and an organic solvent, the first additive is a sulfur-containing siloxy boric acid ester derivative, and the second additive is a benzofuran boric acid ester derivative. Borate groups and benzofuran groups in the first additive and the second additive can promote generation of CEI and SEI protective films on the surfaces of a positive electrode and a negative electrode, the stability of the material is enhanced, electrolyte decomposition is inhibited, and the high-voltage performance of the lithium battery is improved; the trimethylsiloxy group can remove HF in the system, can reduce the corrosion to the positive and negative electrode interface of the battery, and improves the cycle performance of the battery; boron and sulfur atoms in the additive can significantly reduce the internal resistance of the battery and improve the performance of the high-voltage battery at low temperature.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium ion batteries, and in particular relates to a lithium ion battery high voltage electrolyte and a lithium ion battery. Background Art

[0002] With the rapid development of the new energy vehicle industry, people have put forward higher requirements on the performance of new energy vehicles such as cruising range and safety. In order to meet the growing customer demand, developing lithium-ion batteries with higher energy density and better safety performance is one of the important goals of the current lithium battery industry.

[0003] The high-energy-density lithium-ion batteries that are currently widely used are usually transition metal oxides with high nickel content, such as high-nickel ternary positive electrode materials. The charge cutoff voltage of the above materials is usually greater than 4.2 V. The general electrolyte system is prone to oxidative decomposition under this voltage range, and the formed CEI and SEI films cannot protect the positive and negative electrode materials well, and the positive and negative electrode material structures are prone to be destroyed, resulting in reduced coulombic efficiency and rapid capacity decay of lithium batteries. In severe cases, there may even be safety issues such as battery bulging and fire. Therefore, the development of new high-voltage resistant lithium-ion electrolytes is one of the keys to the development of high-energy-density lithium-ion batteries.

[0004] In lithium-ion batteries, borate additives can decompose oxidatively before the electrolyte to construct CEI and SEI membranes to protect the electrodes. At the same time, borate additives can complex with anions to inhibit anion decomposition, so borate additives have good application prospects. However, traditional borate additives are often ineffective in improving the low-temperature performance of batteries or even slightly deteriorate. Therefore, optimizing the structure of borate additives and providing a high-voltage resistant electrolyte that improves the low-temperature performance of batteries is an important issue in this field. Summary of the invention

[0005] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a lithium ion battery electrolyte and a lithium ion battery. The lithium ion battery electrolyte provided by the present invention can not only solve the problem that the electrolyte is easy to decompose under high pressure, but also improve the technical problem that the high-voltage electrolyte in the prior art has poor low-temperature performance.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solutions: In a first aspect, the present invention provides a lithium ion battery electrolyte, comprising a lithium salt, a first additive, a second additive, a common additive and an organic solvent, wherein the first additive is a sulfur-containing siloxy borate derivative; and the second additive is a benzofuran borate derivative.

[0007] Preferably, the structural formula of the first additive is as shown in formula (1): .

[0008] Among them, R1, R2, and R3 are any one of a hydrogen atom, a chlorine atom, a fluorine atom, a substituted or unsubstituted C1~C3 alkyl group, and a substituted or unsubstituted aryl group; the substituted groups include chlorine atoms, fluorine atoms, carbonyl groups, and ester groups; and the aromatic rings include benzene, furan, and thiophene.

[0009] Preferably, the first additive contains at least one sulfur-containing siloxy borate derivative selected from Compounds 1-3.

[0010]

[0011] Preferably, the amount of the first additive added is 0.1-2% of the total mass of the electrolyte.

[0012] Preferably, the structural formula of the second additive is as shown in formula (2):

[0013] Among them, R4, R5, R6, and R7 are any one of a hydrogen atom, a chlorine atom, a fluorine atom, a substituted or unsubstituted C1~C3 alkyl group, and a substituted or unsubstituted aryl group; the substituted groups include chlorine atoms, fluorine atoms, carbonyl groups, and ester groups; and the aromatic rings include benzene, furan, and thiophene.

[0014] Preferably, the second additive benzofuran borate derivative is at least one selected from compounds 4-6.

[0015]

[0016] Preferably, the amount of the second additive added is 0.1-2% of the total mass of the electrolyte.

[0017] Preferably, the commonly used additive is at least one of vinylene carbonate, 1,3-propylene sultone, and vinyl sulfate.

[0018] Preferably, the mass of the commonly used additives is 0.1-5% of the total mass of the electrolyte.

[0019] Preferably, the lithium salt is at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluorosulfonyl)imide, lithium tetrafluoroborate, lithium difluorophosphate, lithium difluorooxalate and lithium perchlorate.

[0020] Preferably, the mass of the lithium salt is 10% to 20% of the total mass of the electrolyte.

[0021] Preferably, the organic solvent is at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, fluoroethylene carbonate and ethyl acetate.

[0022] On the other hand, the present invention provides a high-voltage lithium-ion battery, comprising a negative electrode sheet, a positive electrode sheet, a separator disposed between the negative electrode sheet and the positive electrode sheet, and the electrolyte described in the first aspect.

[0023] Preferably, the positive electrode sheet comprises a positive electrode material, and the positive electrode material is LiNi x Co y Mn (1-x-y) , where 0≤x≤1, 0≤y≤1.

[0024] Preferably, the negative electrode material is selected from any one of natural graphite, artificial graphite, soft carbon, hard carbon and silicon.

[0025] Compared with the existing technology, the present invention has the following technical advantages: The two types of borate derivative additives provided by the present invention have a variety of different functional groups and functions. First, the borate group is more easily oxidized to form a film on the surface of the positive and negative electrodes under the electron-withdrawing induction effect of the thiophene or benzofuran group, thereby preventing the metal ions of the positive and negative electrodes from being precipitated and stabilizing the electrode structure. Second, the benzofuran group is prone to free radical polymerization reaction, and a dense polymer film is formed on the surface of the ternary positive electrode material and the surface of the negative electrode, thereby inhibiting the decomposition of the electrolyte and improving the surface properties of the electrode material. Third, the thiophene group also participates in the film formation, and the sulfur atom therein greatly enhances the conductivity of the SEI / CEI film, reduces the battery impedance, and improves the performance of the battery at low temperatures. Fourth, the trimethylsilyl group can remove residual moisture and hydrogen fluoride in the electrolyte, and at the same time can prevent the electrode from being attacked by nucleophilic fluorides by other fluorides, thereby maintaining the stability of the lithium-ion battery under high-voltage circulation.

[0026] The lithium ion battery provided by the present invention, which contains the high-voltage electrolyte, can maintain a relatively high battery capacity after multiple cycles at a high charge cut-off voltage, and its effective discharge capacity is significantly improved, especially at low temperatures. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0028] Example 1 This embodiment provides a high-voltage lithium-ion battery electrolyte, including lithium hexafluorophosphate, a first additive, a second additive, a common additive and a solvent, the first additive is compound 1, the second additive is compound 4, the common additive is vinylene carbonate, and the solvent is dimethyl carbonate, vinyl carbonate and fluoroethylene carbonate.

[0029] In the above electrolyte, based on the total mass of the electrolyte as 100%, the mass proportion of lithium hexafluorophosphate is 13%; the mass proportion of the first additive compound 1 is 0.5%; the mass proportion of the second additive compound 4 is 0.5%; the mass proportion of vinylene carbonate is 1%; the mass ratio of dimethyl carbonate, ethylene carbonate and fluoroethylene carbonate is 5:4:1, and the mass proportion of the solvent is 85%.

[0030] This embodiment provides a method for manufacturing a high-voltage lithium-ion battery: Preparation method of electrolyte: In a glove box with water and oxygen content less than 0.01 ppm, first weigh a corresponding mass of solvent and mix them, then weigh a corresponding mass of lithium hexafluorophosphate and add it to the solvent and stir evenly, then weigh a corresponding mass of the first additive, the second additive and vinylene carbonate in turn, and add them to the above electrolyte and stir evenly to obtain the high-voltage lithium-ion battery electrolyte.

[0031] Preparation method of positive electrode sheet: After the positive electrode material LiNi8Co1Mn1 is mixed with Super P and N-methylpyrrolidone, PVDF is added and stirred overnight to obtain positive electrode slurry; the slurry is evenly coated on aluminum foil and vacuumed at 100 o After drying at C for 8 h, cut into round electrodes for later use.

[0032] Preparation method of negative electrode sheet: Same as the preparation method of positive electrode sheet, graphite is selected as the negative electrode material, and the current collector aluminum foil is replaced with copper foil.

[0033] In a glove box, the prepared positive electrode sheet, negative electrode sheet, separator and the electrolyte in the above embodiment are assembled into a button battery.

[0034] Example 2 The difference between this embodiment and embodiment 1 is that the mass proportion of the first additive compound 1 is 0.2%; the mass proportion of the second additive compound 4 is 0.2%; and the rest is the same as embodiment 1.

[0035] Example 3 The difference between this embodiment and embodiment 1 is that the mass proportion of the first additive compound 1 is 1%; the mass proportion of the second additive compound 4 is 1%; and the rest is the same as embodiment 1.

[0036] Example 4 The difference between this embodiment and embodiment 1 is that the first additive is compound 2 and the second additive is compound 4; the rest is the same as embodiment 1.

[0037] Example 5 The difference between this embodiment and embodiment 1 is that the first additive is compound 3 and the second additive is compound 4; the rest is the same as embodiment 1.

[0038] Example 6 The difference between this embodiment and embodiment 1 is that the first additive is compound 1 and the second additive is compound 5; the rest is the same as embodiment 1.

[0039] Example 7 The difference between this embodiment and embodiment 1 is that the first additive is compound 2 and the second additive is compound 5; the rest is the same as embodiment 1.

[0040] Example 8 The difference between this embodiment and embodiment 1 is that the first additive is compound 3 and the second additive is compound 5; the rest is the same as embodiment 1.

[0041] Example 9 The difference between this embodiment and embodiment 1 is that the first additive is compound 1 and the second additive is compound 6; the rest is the same as embodiment 1.

[0042] Example 10 The difference between this embodiment and embodiment 1 is that the first additive is compound 2 and the second additive is compound 6; the rest is the same as embodiment 1.

[0043] Embodiment 11 The difference between this embodiment and embodiment 1 is that the first additive is compound 3 and the second additive is compound 6; the rest is the same as embodiment 1.

[0044] Comparative Example 1 The difference between this embodiment and embodiment 1 is that the first additive compound 1 is not added to the electrolyte; the rest is the same as embodiment 1.

[0045] Comparative Example 2 The difference between this embodiment and embodiment 1 is that the second additive compound 4 is not added to the electrolyte; the rest is the same as embodiment 1.

[0046] Comparative Example 3 The difference between this embodiment and the embodiment 1 is that the first additive compound 1 and the second additive compound 4 are not added to the electrolyte; the rest is the same as the embodiment 1.

[0047] Test conditions: The assembled lithium-ion batteries were o C and -40 o The electrochemical performance test was carried out at 25 °C, and the battery charge and discharge voltage range was 2.0-4.7 V. Normal temperature cycle performance evaluation: 25 o C, 0.5C, 2.0-4.7V cycle 100 times, calculate its capacity retention rate. Low temperature performance evaluation: -40o C, 0.2C, 2.0-4.7V for 100 cycles, and calculate its capacity retention rate.

[0048] The test results of Examples 1-11 and Comparative Examples 1-3 are as follows: Table 1

[0049] It can be seen from Table 1 that the lithium ion battery provided by Example 1 of the present invention has the best normal temperature and low temperature cycle performance.

[0050] It can be seen from Examples 1, 2 and 3 that the cycle performance of the lithium-ion battery at room temperature and low temperature can be optimized by optimizing the addition amounts of the first additive and the second additive.

[0051] It can be seen from Example 1 and Examples 4-11 that the substituent groups in the structures of the first additive and the second additive have a great influence on the cycle performance of the lithium-ion battery at room temperature and low temperature.

[0052] It can be seen from Example 1 and Comparative Examples 1-3 that adding sulfur-containing siloxy borate derivatives or benzofuran borate derivatives can improve the capacity retention rate of the battery at room temperature and low temperature, and the effect of adding both additives is greater than the effect of adding any one additive.

[0053] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be considered exemplary and non-restrictive in all respects, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims be included in the present invention.

[0054] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A lithium ion battery high voltage electrolyte, characterized in that: The invention comprises a lithium salt, a first additive, a second additive and an organic solvent, wherein the first additive is a sulfur-containing siloxy borate derivative; and the second additive is a benzofuran borate derivative.

2. The lithium ion battery high voltage electrolyte according to claim 1, characterized in that: The first additive is a sulfur-containing siloxy borate derivative, and its structure is as follows: Wherein, R1, R2, and R3 are any one of a hydrogen atom, a chlorine atom, a fluorine atom, a substituted or unsubstituted C1-C3 alkyl group, and a substituted or unsubstituted aryl group; The substituted groups include chlorine atoms, fluorine atoms, carbonyl groups, and ester groups; The aromatic rings include benzene, furan, and thiophene; The mass of the first additive is 0.1-2% of the total mass of the electrolyte.

3. The lithium ion battery high voltage electrolyte according to claim 1, characterized in that: The second additive is a benzofuran borate derivative, and its structure is as follows: Wherein, R4, R5, R6, and R7 are any one of a hydrogen atom, a chlorine atom, a fluorine atom, a substituted or unsubstituted C1-C3 alkyl group, and a substituted or unsubstituted aryl group; The substituted groups include chlorine atoms, fluorine atoms, carbonyl groups, and ester groups; The aromatic rings include benzene, furan, and thiophene; The mass of the second additive is 0.1-2% of the total mass of the electrolyte.

4. The lithium ion battery high voltage electrolyte according to claim 1, characterized in that: The lithium salt is at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluorosulfonyl)imide, lithium tetrafluoroborate, lithium difluorophosphate, lithium difluorooxalate, and lithium perchlorate, and the mass of the lithium salt is 10% to 20% of the total mass of the electrolyte.

5. The lithium ion battery high voltage electrolyte according to claim 1, characterized in that: The high-voltage electrolyte also includes common additives, which include at least one of vinylene carbonate, 1,3-propylene sultone, and vinyl sulfate. The mass of the common additives is 0.1-5% of the total mass of the electrolyte.

6. The lithium ion battery high voltage electrolyte according to claim 1, characterized in that: The organic solvent is at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, fluoroethylene carbonate and ethyl acetate.

7. The lithium ion battery high voltage electrolyte according to any one of claims 1 to 6, characterized in that: The charging cut-off voltage of the high-voltage electrolyte reaches 4.7V.

8. A low temperature resistant lithium ion battery high voltage electrolyte, characterized in that: The electrolyte is the electrolyte according to any one of claims 1 to 7.

9. A lithium ion battery, characterized in that: The invention comprises a negative electrode sheet, a positive electrode sheet, a separator arranged between the negative electrode sheet and the positive electrode sheet, and the electrolyte according to any one of claims 1 to 7.

10. The lithium ion battery according to claim 9, characterized in that The positive electrode sheet includes a positive electrode material, and the positive electrode material includes LiNi x Co y Mn (1-x-y) , wherein 0≤x≤1, 0≤y≤1; the negative electrode material is selected from any one of natural graphite, artificial graphite, soft carbon, hard carbon, and silicon.

Images