An electrolyte and a battery including the electrolyte

Abstract

The present invention belongs to the technical field of batteries, and particularly relates to an electrolyte and a battery including the electrolyte. A first additive is added to the electrolyte provided by the present invention. The first additive has a lower highest occupied molecular orbital (HOMO), which makes it have extremely strong oxidation resistance and high positive electrode stability. At the same time, the first additive has a lower lowest unoccupied molecular orbital (LUMO), which enables it to preferentially undergo a reduction reaction on the surface of the negative electrode. Further, the sulfonyl group (-S(=O)2-) and -C=N- in its structure can both participate in film formation, significantly improving the film formation stability. Moreover, the SEI film rich in -N- and -S- structures can not only improve the lithium ion transfer rate and stabilize the interfacial impedance, but also the introduction of N and S heteroatoms has better high-temperature stability compared with the interfacial film structure of carbonates. Therefore, while improving the high-temperature cycle and storage performance, the low-temperature discharge performance is also taken into account.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries, and particularly relates to an electrolyte and a battery including the electrolyte. Background Art

[0002] As one of the important constituent materials of lithium-ion batteries, the electrolyte only accounts for 5% - 10% of the total production cost of lithium-ion batteries, but plays a crucial role in the performance of lithium-ion batteries, and is one of the key materials for lithium-ion batteries to achieve high energy density and high voltage.

[0003] Lithium-ion batteries have the advantages of high energy density, high working voltage, long cycle life, and fast charging speed, and are highly concerned by researchers. However, with the continuous development of lithium-ion battery technology and the continuous improvement of market and customer requirements for the performance of lithium-ion batteries, lithium-ion batteries must have better cycle storage performance to meet market and customer needs. However, the working voltage of commercial lithium cobalt oxide batteries has developed from 4.2V to nearly 4.5V now. With the continuous increase of the working voltage of commercial lithium cobalt oxide batteries, the redox side reactions of the electrolyte on the positive and negative electrode surfaces are aggravated, and at the same time, a large number of side reactions lead to the continuous increase of the impedance of lithium-ion batteries; therefore, the cycle performance, storage performance, and low-temperature performance of the battery are significantly deteriorated, and in severe cases, the battery will generate gas and expand, resulting in safety problems.

[0004] At present, in order to inhibit the occurrence of side reactions of the electrolyte at high voltage, researchers add additives that can form a stable protective film on the positive and negative electrodes to inhibit the side reactions between the electrolyte and the materials. However, the impedance of the protective film formed by the existing additives is relatively large, seriously affecting the performance balance of lithium-ion batteries. Therefore, how to form a stable protective film while taking into account the cycle storage and low-temperature performance of lithium batteries has become the research focus. Summary of the Invention

[0005] The purpose of the present invention is to improve the deficiencies of the existing technology and provide an electrolyte and a battery including the electrolyte. While improving the normal-temperature cycle performance, high-temperature cycle performance, and high-temperature storage performance of the battery, the electrolyte can also well take into account the low-temperature discharge performance of the battery.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] An electrolyte, comprising an electrolyte salt, an organic solvent, and a first additive; the first additive is selected from at least one of heterocyclic compounds containing oxygen, sulfur, and nitrogen.

[0008] According to an embodiment of the present invention, the heterocyclic compound containing oxygen, sulfur and nitrogen contains at least one nitrogen atom, one oxygen atom and one sulfur atom on the ring. Specifically, the heterocyclic compound containing oxygen, sulfur and nitrogen contains at least one nitrogen atom, two oxygen atoms and two sulfur atoms on the ring.

[0009] According to an embodiment of the present invention, the sulfur atom exists in the form of a sulfonyl group (-S(=O)2-).

[0010] According to an embodiment of the present invention, the first additive is selected from at least one compound having the structure shown in Formula I:

[0011]

[0012] Wherein, R1 is selected from a hydrogen atom, a halogen, a substituted or unsubstituted C 6～12 aryl, a substituted or unsubstituted C 1～10 alkyl, a substituted or unsubstituted C 2～10 alkoxy, a substituted or unsubstituted C 2～10 alkenyl; the substituent is a halogen, a C 1～10 alkyl.

[0013] According to an embodiment of the present invention, R1 is selected from a hydrogen atom, a halogen, a substituted or unsubstituted C 6～10 aryl, a substituted or unsubstituted C 1～6 alkyl, a substituted or unsubstituted C 2～6 alkoxy, a substituted or unsubstituted C 2～6 alkenyl; the substituent is a halogen, a C 1～6 alkyl.

[0014] According to an embodiment of the present invention, R1 is selected from a hydrogen atom, a halogen, a substituted or unsubstituted C 6～8 aryl, a substituted or unsubstituted C 1～3 alkyl, a substituted or unsubstituted C 2～3 alkoxy, a substituted or unsubstituted C 2～3 alkenyl; the substituent is fluorine, a C 1～3 alkyl.

[0015] According to an embodiment of the present invention, R1 is selected from a hydrogen atom, fluorine, phenyl, methyl, and fluorine-substituted methyl.

[0016] According to an embodiment of the present invention, the compound having the structural formula shown in Formula I specifically includes at least one of the compounds having the following structural formulas:

[0017]

[0018] According to an embodiment of the present invention, the first additive can be prepared by methods known in the art or obtained by commercial purchase.

[0019] According to an embodiment of the present invention, the mass of the first additive accounts for 0.1-10 wt% of the total mass of the electrolyte, preferably 0.3-3 wt%, for example, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1 wt%, 1.2 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.8 wt%, 2 wt%, 2.5 wt%, 2.6 wt%, 2.8 wt%, 3 wt%, 3.4 wt%, 3.7 wt%, 3.9 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt% or 10 wt%.

[0020] According to an embodiment of the present invention, the electrolyte salt includes at least one of lithium salts, sodium salts, potassium salts, etc.

[0021] According to an embodiment of the present invention, the lithium salt is selected from at least one of lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiPF2O2), lithium difluorobis(oxalato)phosphate (LiPF2(C2O4)2), lithium tetrafluorooxalate phosphate (LiPF4C2O4), lithium oxalate phosphate (LiPO2C2O4), lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiODFB), lithium tetrafluoroborate (LiBF4), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium bis(fluorosulfonyl)imide (LiFSI).

[0022] According to an embodiment of the present invention, the mass of the electrolyte salt accounts for 10 wt%-15 wt% of the total mass of the electrolyte, for example, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt% or 15 wt%.

[0023] According to an embodiment of the present invention, the lithium salt is selected from lithium hexafluorophosphate (LiPF6) and lithium difluoro(oxalato)borate (LiODFB); preferably, the mass percentage content of lithium hexafluorophosphate (LiPF6) is 13.75 wt%; the mass percentage content of lithium difluoro(oxalato)borate (LiODFB) is 0.5 wt%.

[0024] According to an embodiment of the present invention, the organic solvent is selected from at least one of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl propionate (EP), propyl propionate (PP), ethyl acetate (EA), ethyl n-butyrate (EB) and γ-butyrolactone (GBL).

[0025] According to an embodiment of the present invention, the mass of the organic solvent accounts for 20 wt% to 60 wt% of the total mass of the electrolyte, such as 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, 55 wt% or 60 wt%.

[0026] According to an embodiment of the present invention, the electrolyte further includes a second additive, and the second additive is selected from at least one of fluoroethylene carbonate (FEC), vinylene carbonate (VC), 1,3 - propane sultone (PS), divinyl sulfate (DTD), methylene methanedisulfonate (MMDS), propylene sultone (PST), maleic anhydride, diglycolic anhydride, succinic anhydride, butanedinitrile (SN), adiponitrile (ADN), ethylene glycol bis(propionitrile) ether (EGBE), and hexane trinitrile (HTCN).

[0027] According to an embodiment of the present invention, the mass of the second additive accounts for 0.1 wt% to 15 wt% of the total mass of the electrolyte, such as 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1 wt%, 1.2 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.8 wt%, 2 wt%, 2.5 wt%, 2.6 wt%, 2.8 wt%, 3 wt%, 3.4 wt%, 3.7 wt%, 3.9 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt% or 15 wt%.

[0028] The present invention also provides a battery, and the battery includes the above - mentioned electrolyte.

[0029] According to an embodiment of the present invention, the battery is a lithium - ion battery.

[0030] According to an embodiment of the present invention, the battery includes a positive electrode sheet, a negative electrode sheet, a separator disposed between the positive electrode sheet and the negative electrode sheet, and the above - mentioned electrolyte.

[0031] Advantages of the present invention:

[0032] A first additive is added to the electrolyte provided by the present invention. The first additive has a lower highest occupied molecular orbital (HOMO), which gives it extremely strong oxidation resistance and high positive electrode stability. At the same time, the first additive has a lower lowest unoccupied molecular orbital (LUMO), which enables it to preferentially undergo a reduction reaction on the surface of the negative electrode. Further, the sulfonyl group (-S(=O)2-) and -C=N- in its structure can both participate in film formation, significantly improving the film formation stability. The SEI film rich in -N- and -S- structures can not only enhance the lithium ion transfer rate and stabilize the interfacial impedance, but also the introduction of N and S heteroatoms has better high temperature stability compared to the interfacial film structure of carbonates. Therefore, while improving the high temperature cycle and storage performance, the low temperature discharge performance is also taken into account. Detailed Embodiments

[0033] The following will further elaborate on the present invention in conjunction with specific embodiments. It should be understood that the following embodiments are only for illustrative and explanatory purposes of the present invention and should not be construed as limiting the protection scope of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0034] Unless otherwise specified, the experimental methods used in the following embodiments are all conventional methods; the reagents, materials, etc. used in the following embodiments can all be obtained from commercial channels unless otherwise specified.

[0035] The preparation method of the lithium ion battery includes:

[0036] [Preparation of Positive Electrode Sheet]

[0037] The positive electrode active material lithium cobaltate (LCO), binder polyvinylidene fluoride (PVDF), conductive carbon black, and single-walled carbon nanotubes are mixed according to a weight ratio of 97.2:1.5:1.2:0.1, and N-methylpyrrolidone (NMP) is added and stirred under a vacuum mixer until the mixed system becomes a homogeneous and flowable positive electrode slurry; the positive electrode slurry is uniformly coated on the current collector aluminum foil; the above-coated aluminum foil is baked in an oven with 5 different temperature gradients and then dried in an oven at 120°C for 8 h, and then obtained the required positive electrode sheet through rolling and slitting.

[0038] [Preparation of Negative Electrode Sheet]

[0039] The negative electrode active material graphite, thickener sodium carboxymethyl cellulose (CMC-Na), binder styrene-butadiene rubber, and conductive agent acetylene black are mixed according to a weight ratio of 97:1:1:1, and deionized water is added to obtain a negative electrode slurry under a vacuum mixer; the negative electrode slurry is uniformly coated on a high-strength carbon-coated copper foil to obtain a pole piece; the obtained pole piece is air-dried at room temperature and then transferred to an oven at 80°C for 10 h, and then obtained the negative electrode sheet through rolling and slitting.

[0040] [Electrolyte Preparation]

[0041] In a glove box filled with inert gas (H2O < 10 ppm, O2 < 5 ppm), organic solvents are mixed in a specific mass ratio, and then lithium salt, the first additive, and the second additive are slowly added to the mixed solution. After passing the moisture and free acid tests, the electrolyte is obtained. The specific composition of the electrolyte is shown in Table 1.

[0042] [Manufacture of Battery]

[0043] The prepared positive electrode sheet, separator (9-micron-thick PP film), and negative electrode sheet are stacked in sequence, ensuring that the separator is between the positive and negative electrode sheets to play an isolation role. The bare battery core is placed in an aluminum-plastic film outer package, and the prepared electrolyte is injected into the dried battery. After encapsulation, standing, formation, shaping, and grading, the preparation of the lithium-ion soft-pack battery is completed.

[0044] Examples 1 to 14 and Comparative Examples 1 to 4 are prepared according to the above preparation method. The differences between each example and comparative example are only the substances and their contents in the electrolyte, and the specific substances and contents are as shown in Table 1 below.

[0045] Table 1 Electrolyte Compositions of Examples and Comparative Examples

[0046]

[0047]

[0048] Performance Test

[0049] Relevant performance tests are carried out on the lithium-ion batteries and their electrolytes obtained from the above examples and comparative examples.

[0050] (1) High-temperature cycle performance test: At 45 °C, the graded battery is charged at a constant current of 0.7C and a constant voltage of 4.48V until the cut-off current is 0.05C, and then discharged at a constant current of 0.5C to 3.0V. This cycle is repeated. After 500 charge-discharge cycles, the capacity retention rate of the 500th cycle is calculated. The calculation formula is as follows:

[0051] Capacity retention rate of the 500th cycle (%) = (Discharge capacity of the 500th cycle / Discharge capacity of the first cycle) × 100%.

[0052] (2) Room-temperature cycle performance test: At 25 °C, the graded battery is charged at a constant current of 0.7C and a constant voltage of 4.48V until the cut-off current is 0.05C, and then discharged at a constant current of 0.5C to 3.0V. This cycle is repeated. After 500 charge-discharge cycles, the capacity retention rate of the 500th cycle is calculated. The calculation formula is as follows:

[0053] Retention rate of capacity after 500 - week cycling (%) = (Discharge capacity after 500 - week cycling / Discharge capacity of the first cycle) × 100%.

[0054] (3) High - temperature storage test at 85°C for 6 h: Place the battery at room temperature and charge and discharge it at 0.5C once (4.48V - 3.0V), record the discharge capacity C0 before storage. Then charge the battery at constant current and constant voltage to 4.48V full charge state. Use a PPG battery thickness gauge (500g) to measure the thickness d1 of the battery before high - temperature storage. Place the battery in an 85°C constant - temperature oven for 6 h. After storage, take out the battery and measure the thickness d2 of the battery after storage, and calculate the thickness expansion rate of the battery after 85°C storage for 6 h. After the battery cools at room temperature for 24 h, discharge the battery at 0.5C to 3.0V again, then charge it at 0.5C constant current and constant voltage to 4.48V, record the discharge capacity C1 and charge capacity C2 after storage, and calculate the remaining rate and recovery rate of the capacity after 85°C storage for 6 h. The calculation formulas are as follows:

[0055] Thickness expansion rate after 85°C storage for 6 h = (d2 - d1) / d1 * 100%;

[0056] Remaining rate of capacity after 85°C storage for 6 h = C1 / C0 * 100%;

[0057] Recovery rate of capacity after 85°C storage for 6 h = C2 / C0 * 100%.

[0058] (4) Low - temperature discharge performance test: Under the environmental condition of 25°C, discharge the binned battery at 0.5C to 3.0V and set it aside for 5 min; then charge it at 0.2C to 4.48V. When the cell voltage reaches 4.48V, change to constant - voltage charging at 4.48V until the charging current is less than or equal to the given cut - off current 0.05C, and set it aside for 5 min; transfer the fully - charged cell to a high - and - low - temperature chamber, set the temperature to - 10°C, and after the chamber temperature reaches, set it aside for 120 min; then discharge it at 0.2C to the cut - off voltage 3.0V and set it aside for 5 min; then adjust the temperature of the high - and - low - temperature chamber to 25°C ± 3°C, and after the chamber temperature reaches, set it aside for 60 min; charge it at 0.2C to 4.48V. When the cell voltage reaches 4.48V, change to constant - voltage charging at 4.48V until the charging current is less than or equal to the given cut - off current 0.05C; set it aside for 5 min; calculate the capacity retention rate of discharging at 3.0V at - 10°C. The calculation formula is as follows:

[0059] Capacity retention rate of discharging at 3.0V at - 10°C (%) = (Discharge capacity of discharging to 3.0V at - 10°C / Discharge capacity of discharging to 3.0V at 25°C) × 100%.

[0060] Table 2 Performance test results of the batteries in the examples and comparative examples

[0061]

[0062]

[0063] From the comparison of the test results of Comparative Examples 1-4 and Examples 1-14 in Table 2, it can be seen that:

[0064] The compounds with the structure shown in Formula I in Examples 1-14 can effectively improve the normal temperature and high temperature cycle performance and the 85°C high temperature storage performance of lithium-ion batteries, effectively inhibit gas generation, improve the remaining recovery capacity after high temperature storage of lithium-ion batteries, and there is no significant difference in low temperature discharge. It can be seen that while improving the cycle storage performance, the low temperature performance of lithium batteries is well considered;

[0065] The compounds with the structure shown in Formula I have good film-forming performance, and both can effectively improve the cycle performance of lithium batteries with the lithium salt type film-forming additive LiODFB. The combined effect is more significant. Compared with LiODFB, the compounds with the structure shown in Formula I can inhibit gas generation while improving the cycle performance and effectively improve the storage performance.

[0066] The compounds with the structure shown in Formula I in the appropriate range (0.3-3 wt%) consider the low temperature performance while improving the cycle and high temperature storage performance. When the addition amount is excessive, the low temperature discharge performance will deteriorate. This may be due to the increase in the addition amount, resulting in a denser film-forming and an increase in the interfacial impedance, leading to the deterioration of the low temperature performance.

[0067] In summary, it can be seen that the lithium-ion battery electrolyte provided by the present invention and the lithium-ion battery using this electrolyte consider the low temperature performance while effectively improving the normal temperature and high temperature cycle and high temperature storage performance, showing extremely high application potential.

[0068] The above describes the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An electrolyte, characterized in that, It includes an electrolyte salt, an organic solvent and a first additive; the first additive is selected from at least one compound having the structure shown in Formula I: Among them, R1 is selected from a hydrogen atom, a halogen, a substituted or unsubstituted C 6～12 aryl, a substituted or unsubstituted C 1～10 alkyl, a substituted or unsubstituted C 2～10 alkoxy, a substituted or unsubstituted C 2～10 alkenyl; the substituent is a halogen, C 1～10 alkyl.

2. The electrolyte according to claim 1, characterized in that, R1 is selected from a hydrogen atom, a halogen, a substituted or unsubstituted C 6～10 aryl, a substituted or unsubstituted C 1～6 alkyl, a substituted or unsubstituted C 2～6 alkoxy, a substituted or unsubstituted C 2～6 alkenyl; the substituent is a halogen, a C 1～6 alkyl.

3. The electrolyte according to claim 2, wherein, R1 is selected from a hydrogen atom, a halogen, a substituted or unsubstituted C 6～8 aryl, a substituted or unsubstituted C 1～3 alkyl, a substituted or unsubstituted C 2～3 alkoxy, a substituted or unsubstituted C 2～3 alkenyl; the substituent is fluorine, C 1～3 alkyl.

4. The electrolyte according to claim 3, characterized in that, R1 is selected from a hydrogen atom, fluorine, phenyl, methyl, fluorine-substituted methyl.

5. The electrolyte according to claim 1, wherein The compound having the structure shown in Formula I includes at least one of the compounds having the following structural formulas:

6. The electrolyte according to any one of claims 1-5, characterized in that, The mass of the first additive accounts for 0.1 wt% to 10 wt% of the total mass of the electrolyte.

7. The electrolyte according to claim 6, characterized in that, The mass of the first additive accounts for 0.3 to 3 wt% of the total mass of the electrolyte.

8. The electrolyte according to any one of claims 1-5, characterized in that, The electrolyte further includes a second additive, and the second additive is selected from at least one of fluoroethylene carbonate (FEC), vinylene carbonate (VC), 1,3-propane sultone (PS), ethylene sulfate (DTD), methylene methanedisulfonate (MMDS), propylene sultone (PST), maleic anhydride, diglycolic anhydride, succinic anhydride, butanedinitrile (SN), adiponitrile (ADN), ethylene glycol bis(propionitrile) ether (EGBE), and hexane trinitrile (HTCN).

9. The electrolyte according to claim 8, wherein, The mass of the second additive accounts for 0.1 wt% to 15 wt% of the total mass of the electrolyte.

10. The electrolyte according to claim 6, wherein, The electrolyte further includes a second additive, and the second additive is selected from at least one of fluoroethylene carbonate (FEC), vinylene carbonate (VC), 1,3-propane sultone (PS), ethylene sulfate (DTD), methylene methanedisulfonate (MMDS), propylene sultone (PST), maleic anhydride, diglycolic anhydride, succinic anhydride, butanedinitrile (SN), adiponitrile (ADN), ethylene glycol bis(propionitrile) ether (EGBE), and hexane trinitrile (HTCN).

11. The electrolyte according to claim 10, wherein The mass of the second additive accounts for 0.1 wt% to 15 wt% of the total mass of the electrolyte.

12. A battery, characterized in that, The battery includes the electrolyte according to any one of claims 1-11.

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