A lithium-ion battery and an electrical device using the same

Abstract

The present invention provides a lithium-ion battery and an electrical device using the same. The lithium-ion battery includes a positive electrode, a negative electrode, and an electrolyte. The active material of the positive electrode includes lithium iron manganese phosphate, and the electrolyte includes a thiophene-based additive. The chemical structure of the thiophene-based additive satisfies Formula I: at least one of the groups R1 to R4 includes at least one of an amino group, a thiophene group, a pyridyl group, an acetyl group, an amide group, and an ester group. Based on the total mass of the electrolyte, the content of the thiophene-based additive is 0.08 to 2.80 wt%. The lithium-ion battery has a high cycle capacity retention rate and good high-temperature storage performance.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and particularly to a lithium-ion battery and an electrical device using the same. Background Art

[0002] Compared with lead-acid batteries, nickel-cadmium batteries, and nickel-metal hydride batteries, lithium-ion batteries are widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power stations, as well as in fields such as postal and telecommunications, power tools, electric bicycles, electric motorcycles, electric vehicles, special equipment, and special aerospace due to their large energy density, high working voltage, long life, and environmental friendliness. With the widespread use of electronic products, the industry has put forward higher requirements for the cycle performance of lithium-ion batteries.

[0003] At present, lithium iron manganese phosphate is a lithium-ion secondary battery with very broad application prospects. And lithium iron phosphate has the advantages of high energy density, rich raw material resources, low cost, environmental friendliness, and high safety. However, at higher temperatures or high voltages, lithium iron manganese phosphate will undergo the John-Teller effect during the cell cycle, resulting in the distortion of trivalent manganese into divalent manganese, increasing the dissolution amount of manganese ions in the electrolyte. Manganese ions are easily migrated to the negative electrode side and reduced and deposited on the negative electrode surface, damaging the SEI film, accelerating side reactions, consuming a large amount of active lithium, affecting the battery cycle capacity. Moreover, the dissolution of manganese ions in lithium iron manganese phosphate will cause damage to the positive electrode structure, and also lead to high interfacial impedance and battery capacity attenuation, affecting the battery cycle stability.

[0004] As an important component of lithium-ion batteries, the electrolyte has become one of the most important factors affecting the electrical performance of lithium-ion batteries. Based on the above defects of existing lithium-ion batteries, it is necessary to optimize the electrolyte to reduce the free amount of manganese ions in the electrolyte, inhibit manganese deposition on the negative electrode, and prevent a large amount of manganese metal deposition on the negative electrode. Summary of the Invention

[0005] The purpose of the present invention is to provide a lithium-ion battery and an electrical device using the same to improve the cycle capacity retention rate and high-temperature storage performance of the lithium-ion battery and improve the battery output characteristics.

[0006] According to one aspect of the present invention, a lithium-ion battery is provided, which includes a positive electrode, a negative electrode, and an electrolyte. The active material of the positive electrode includes lithium iron manganese phosphate, and the electrolyte includes a thiophene-based additive. The chemical structure of the thiophene-based additive satisfies Formula I: At least one of the groups R1 to R4 includes at least one of an amino group, a thiophenyl group, a pyridyl group, an acetyl group, an amide group, and an ester group. Based on the total mass of the electrolyte, the content of the thiophene-based additive is 0.08 to 2.80 wt%. For example, the content of the thiophene-based additive is 0.08 wt%, 0.10 wt%, 0.25 wt%, 0.5 wt%, 0.75 wt%, 1.0 wt%, 1.25 wt%, 1.5 wt%, 1.75 wt%, 2.0 wt%, 2.50 wt%, 2.80 wt%, etc.

[0007] By introducing a thiophene-based additive that meets the above requirements into the electrolyte, the present invention can improve the cycling stability of the positive electrode and the negative electrode. The thiophene-based additive simultaneously includes a thiophene ring structure and the above-mentioned specific group containing nitrogen, sulfur, and / or oxygen elements with a lone pair electron number, and the above-mentioned specific group is directly connected to the thiophene ring. Thus, by using the elements with a lone pair electron number in the thiophene-based additive to complex with the manganese ions dissolved from the positive electrode material, the content of manganese ions in the electrolyte can be effectively reduced, thereby reducing the side reactions occurring between the manganese ions and the electrolyte. It can also prevent the migration of manganese ions to the surface of the negative electrode, reduce the damage caused by manganese ions to the SEI film of the negative electrode, inhibit the reduction of manganese ions to manganese metal at the negative electrode, reduce the deposition amount of manganese metal at the negative electrode, inhibit the dissolution of manganese ions, enhance the diffusion of lithium ions in the positive electrode, reduce battery polarization, and also reduce the free amount of manganese ions in the electrolyte, thereby preventing a large amount of manganese metal deposition on the negative electrode, and thus achieving the purpose of simultaneously improving the stability of the positive electrode and the negative electrode during battery cycling and enhancing the cycle capacity retention rate of the lithium-ion battery. On the other hand, the thiophene-based additive within the above content range can promote the formation of the SEI film on the surface of the negative electrode and enhance the structural stability of the SEI film, thereby reducing the interfacial impedance, improving the battery cycling performance, delaying the aging of the negative electrode, and extending the cycle life of the battery using this electrolyte. In particular, after high-temperature storage, the manganese element in the positive electrode material is more likely to undergo a disproportionation reaction and dissolve into the electrolyte in the form of manganese ions; and the electrolyte provided by the present invention also has good heat resistance. In a high-temperature environment, the thiophene-based additive can still form a complex with good stability with manganese ions, and the SEI film formed by the thiophene-based additive still has good mechanical properties, improving the high-temperature cycling and high-temperature storage performance of the battery and enhancing the capacity retention rate.

[0008] Preferably, the number of elements with a lone pair electron in the thiophene-based additive is not less than 2.

[0009] Preferably, R1 to R4 can be independently selected from at least one of a hydrogen atom, a methyl group, an ethyl group, a cyclopentyl group, a cyclohexyl group, a phenyl group, an amino group, a thiophenyl group, a pyridyl group, an acetyl group, a carboxamide group, and an ester group; and / or, R1 and R2, R2 and R3, or R3 and R4 independently form a ring, the ring is a 4- to 6-membered ring, the 4- to 6-membered ring includes a cycloalkane and / or a heterocycle, the heterocycle is a heterocycle containing O, S, or N, and the cycloalkane is at least one of a cycloalkane, a cycloolefin, and benzene.

[0010] Preferably, the chemical structure of the thiophene-based additive includes at least one of cyclopentanothiophene, tetrahydrobenzothiophene, and benzothiophene.

[0011] Preferably, the number of elements with lone pair electrons in the thiophene-based additive is not more than 4. The above thiophene-based additive has higher reactivity with manganese ions, and the obtained complex has higher chemical stability, effectively reducing the free amount of manganese ions in the electrolyte.

[0012] Preferably, the number of elements with lone pair electrons in the thiophene-based additive is 4.

[0013] Preferably, calculated by molar ratio, in the thiophene-based additive, nitrogen element: sulfur element: oxygen element = 2:1:1. Through long-term experiments and verification, it is found that when the molar ratio of nitrogen element, sulfur element, and oxygen element in the thiophene-based additive satisfies the above ratio, the bond energy of the coordination bond in the complex formed by the thiophene-based additive and manganese ions is larger, and the stability of the complex is higher, which helps to reduce the content of manganese deposition on the negative electrode, avoid the destruction of the negative electrode SEI film by manganese ions, and further reduce the consumption of active lithium, thereby improving the cycle stability of the battery using this electrolyte. In particular, the combination of the above thiophene-based additive and an ester-based additive can effectively inhibit the volume expansion of the negative electrode active material and effectively slow down the battery aging.

[0014] Preferably, the thiophene-based additive includes 2-amino-5,6-dihydro-cyclopentanothiophene-3-carboxamide.

[0015] Preferably, in the electrolyte, the mass ratio of the thiophene-based additive to the ester-based additive is 0.08 to 2.80:1.0 to 3.5. During the charge and discharge process of the battery, the volume of the negative electrode active material is likely to change, and the conventional negative electrode SEI film will break with the volume change of the negative electrode active material, resulting in a decrease in battery capacity. When the mass ratio of the thiophene-based additive to the ester-based additive falls within the above range, it can promote the formation of an inorganic film rich in anion derivatives and a dense and stable organic polymer SEI film on the negative electrode surface. This SEI film has excellent flexibility, mechanical properties, and low interfacial impedance, can adapt to the volume change of the negative electrode active material, effectively isolate the direct contact between the negative electrode and the electrolyte, reduce the consumption of the electrolyte and lithium ions and side reactions, and effectively improve the battery capacity.

[0016] Preferably, the electrolyte further includes an ester additive, and the ester additive includes at least one of vinylene carbonate (VC), ethylene sulfite (ES), divinyl sulfate (DTD), 1,3 - propane sultone (1,3 - PS), and propylene sultone (PST). By introducing the ester additive into the electrolyte, during the battery cycling process, the ester additive combined with the above - mentioned thiophene additive can make the SEI film formed on the battery have good flexibility and mechanical strength, thereby reducing the possibility of the SEI film being damaged or cracked, and effectively inhibiting the volume expansion rate of the negative electrode material, and effectively improving the cycling performance of the battery.

[0017] Preferably, in the electrolyte, the mass ratio of the thiophene additive to the ester additive is 0.08 - 2.80:1.0 - 3.5. For example, the mass ratio of the thiophene additive to the ester additive is 0.08:3.5, 0.20:3.0, 0.5:2.5, 1.0:2.0, 1.5:1.5, 2.0:1.25, 2.8:1.0. By regulating the mass ratio of the thiophene additive to the ester additive in the electrolyte, the structural stability of the SEI film formed on the battery can be further improved, the damage of the SEI film can be reduced, and the electrolyte loss caused by further contact between the electrolyte and the electrode can be reduced.

[0018] Preferably, based on the total mass of the electrolyte, the content of the thiophene additive is 0.10 - 1.80 wt%. When the addition amount of the thiophene additive in the electrolyte is within the above - mentioned range, the prepared lithium - ion battery has excellent high - temperature storage performance and cycling performance, and can still maintain an excellent battery available capacity after high - temperature storage and after 1200 - cycle charge - discharge experiments.

[0019] Preferably, based on the total mass of the electrolyte, the content of the ester additive is 1.00 - 3.50 wt%. For example, the content of the ester additive is 1.00 wt%, 1.50 wt%, 2.00 wt%, 2.50 wt%, 3.00 wt%, 3.50 wt%. Introducing the ester additive with the above - mentioned content range into the electrolyte can improve the film - forming performance of the electrolyte, reduce the interfacial impedance, and improve the battery cycling performance.

[0020] Preferably, the ester additive includes at least one of divinyl sulfate and vinylene carbonate. When this ester additive is used in combination with the above - mentioned thiophene additive, it can promote the formation of a dense, flexible and low - impedance SEI film on the electrode surface of the electrolyte, which can form a tight structural layer without increasing the battery impedance, inhibit the co - intercalation and reduction decomposition of the electrolyte on the electrode, and improve the cycling performance of the lithium - ion battery.

[0021] Preferably, the ester additive includes vinylene carbonate, and based on the total mass of the electrolyte, the content of vinylene carbonate is 2.50 wt%.

[0022] Preferably, the electrolyte further includes a lithium salt, and based on the total mass of the electrolyte, the content of the lithium salt is 10.50 - 13.00 wt%. For example, the content of the lithium salt is 10.50 wt%, 11.00 wt%, 11.50 wt%, 12.00 wt%, 12.50 wt%, 13.00 wt%.

[0023] Preferably, the lithium salt includes lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide, and the mass ratio of lithium hexafluorophosphate to lithium bis(fluorosulfonyl)imide is 10.5 - 12:0.5 - 2. By using a combination of lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI), the conductivity of the electrolyte can be improved, and the transport efficiency of lithium ions can be enhanced, thereby improving the battery output characteristics and extending the battery service life.

[0024] Preferably, the electrolyte further includes an organic solvent, and the organic solvent includes at least one of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). The above organic solvents have good compatibility with the thiophene-based additive and the ester additive, can reduce side reactions during battery cycling, and improve the battery cycle capacity retention rate.

[0025] Preferably, the organic solvent includes at least three of ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC).

[0026] Preferably, the electrolyte further includes an organic solvent, and the organic solvent includes ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC).

[0027] Preferably, calculated by mass ratio, ethylene carbonate:dimethyl carbonate:ethyl methyl carbonate = 2 - 3:4 - 4.5:1.5 - 2. The electrolyte using the organic solvent with the above mass ratio can improve the battery cycle characteristics and cycle capacity retention rate of the battery after high-temperature storage.

[0028] Preferably, the active material of the negative electrode includes at least one of natural graphite, artificial graphite, and silicon carbon.

[0029] Preferably, the active material of the negative electrode includes artificial graphite.

[0030] Preferably, the lithium ion battery further includes a separator disposed between the positive electrode and the negative electrode, and the separator includes at least one of polypropylene, polyvinylidene fluoride, polytetrafluoroethylene, polyacrylonitrile, and polyethylene.

[0031] Preferably, the separator comprises polypropylene.

[0032] According to another aspect of the present invention, there is provided an electrical device including the above lithium-ion battery. Detailed implementation manners

[0033] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0034] Embodiment 1

[0035] This embodiment provides a lithium-ion battery, which includes a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and also includes an electrolyte.

[0036] (1) Electrolyte:

[0037] The composition of the electrolyte is shown in Table 1:

[0038] Table 1. Raw material composition for preparing the electrolyte in Embodiment 1

[0039]

[0040]

[0041] Note: The ratios shown in Table 1 are mass ratios. For example, "dimethyl carbonate: ethyl methyl carbonate: ethylene carbonate = 3:4.5:2.5", that is, the mass ratio of dimethyl carbonate, ethyl methyl carbonate and ethylene carbonate is 3:4.5:2.5, and they are mixed and used as an organic solvent.

[0042] Among them, the CAS number of 2-(2-thienyl)pyridine is 3319-99-1, and its structural formula is shown in Formula II:

[0043] Prepare materials according to the above raw material composition, and prepare the electrolyte according to the following steps: In a glove box filled with argon, first mix the organic solvents evenly, and then add lithium salt, ester additives, and thiophene additives to the organic solvents, and mix evenly to obtain the electrolyte.

[0044] (2) Positive electrode:

[0045] The positive electrode includes a positive current collector and a positive active coating. The positive active coating includes the positive active material lithium iron manganese phosphate (LiFeMnPO4), the conductive agent carbon black (SP), the conductive agent carbon nanotube (CNT), and the positive binder polyvinylidene fluoride (PVDF). In the positive active coating, the mass ratio of LiFeMnPO4, SP, CNT, and PVDF is 96.0:2.0:0.5:1.5, and the solid content of the positive binder is 1.327%.

[0046] Prepare materials according to the above raw material composition, and prepare the positive electrode according to the following steps:

[0047] S1. Mix the positive active material, the conductive agent SP, and the solvent N-methylpyrrolidone (NMP) evenly; then sequentially add the conductive agent CNT and the positive binder into the reaction system to obtain a positive electrode slurry; then add the solvent NMP to the positive electrode slurry to adjust the viscosity of the positive electrode slurry so that the viscosity of the positive electrode slurry is 15000 ± 3000 mPa·s and the fineness is ≤ 10 μm.

[0048] S2. Coat the positive electrode slurry on the surface of the positive current collector, dry it to obtain a positive active coating, and then perform post-treatment operations such as cold pressing and cutting to obtain the positive electrode.

[0049] (3) Negative electrode:

[0050] The negative electrode includes a negative current collector and a negative active coating. The negative active coating includes the negative active material graphite, the conductive agent carbon black (SP), the negative binder carboxymethyl cellulose (CMC), and the aqueous dispersant styrene-butadiene rubber (SBR). In the negative active coating, the mass ratio of graphite, SP, CMC, and SBR is 96.5:1.5:1.2:0.8, and the solid content of the negative binder is 8.0%.

[0051] Prepare materials according to the above raw material composition, and prepare the negative electrode according to the following steps:

[0052] S1. Mix the negative active material, the conductive agent SP, and the solvent N-methylpyrrolidone (NMP) evenly; then add the negative binder to the reaction system in batches, then add deionized water to the reaction system to adjust the viscosity of the reaction system, and finally add the aqueous dispersant SBR to obtain a negative electrode slurry, so that the viscosity of the negative electrode slurry is 4000 ± 1500 mPa·s and the fineness is ≤ 15 μm.

[0053] S2. Coat the negative electrode slurry on the surface of the negative current collector, dry it to obtain a negative active coating, and then perform post-treatment operations such as cold pressing and cutting to obtain the positive electrode.

[0054] (4) Lithium-ion battery:

[0055] Stack the positive electrode, separator, and negative electrode in sequence, and obtain an electrode assembly through the stacking process. Place the electrode assembly in an outer packaging case, dry it, inject electrolyte at an injection coefficient of 5.8 g / Ah, and obtain a lithium-ion battery through vacuum packaging, standing, formation, and grading processes.

[0056] Example 2

[0057] In this example, a lithium-ion battery was prepared with reference to the preparation method provided in Example 1. The difference between this example and Example 1 is that: during the preparation of the electrolyte, an equal mass of bithiophene was used to replace the thiophene additive used in Example 1. The other raw material ratios and preparation methods were strictly the same as those in Example 1.

[0058] Among them, the CAS number of bithiophene is 492-97-7, and its structural formula is as shown in Formula III:

[0059] Example 3

[0060] In this example, a lithium-ion battery was prepared with reference to the preparation method provided in Example 1. The difference between this example and Example 1 is that: during the preparation of the electrolyte, an equal mass of 2-acetylthiophene was used to replace the thiophene additive used in Example 1. The other raw material ratios and preparation methods were strictly the same as those in Example 1.

[0061] Among them, the CAS number of 2-acetylthiophene is 88-15-3, and its structural formula is as shown in Formula IV:

[0062] Example 4

[0063] In this example, a lithium-ion battery was prepared with reference to the preparation method provided in Example 1. The difference between this example and Example 1 is that: during the preparation of the electrolyte, an equal mass of 3-methylthiophene-2-carboxamide was used to replace the thiophene additive used in Example 1. The other raw material ratios and preparation methods were strictly the same as those in Example 1.

[0064] Among them, the CAS number of 3-methylthiophene-2-carboxamide is 76655-99-7, and its structural formula is as shown in Formula V:

[0065] Example 5

[0066] In this example, a lithium-ion battery was prepared with reference to the preparation method provided in Example 1. The difference between this example and Example 1 is that: during the preparation of the electrolyte, an equal mass of 2-amino-5,6-dihydro-cyclopenta[b]thiophene-3-carboxamide was used to replace the thiophene additive used in Example 1. The other raw material ratios and preparation methods were strictly the same as those in Example 1.

[0067] Among them, the CAS number of 2-amino-5,6-dihydro-cyclopentathiophene-3-carboxamide is 77651-38-8, and its structural formula is shown in Formula VI:

[0068] Example 6

[0069] This example refers to the preparation method provided in Example 1 to prepare a lithium ion battery. The difference between this example and Example 1 is that in the process of preparing the electrolyte, an equal mass of 5-carbamoylthiocyanate is used.

[0070] Phenyl-2-carboxylic acid methyl ester replaces the thiophene additive used in Example 1. The remaining raw material ratios and preparation methods are strictly consistent with those in Example 1.

[0071] Among them, the CAS number of 5-carbamoylthiophene-2-carboxylic acid methyl ester is 1206087-41-3, and its structural formula is shown in Formula VII:

[0072] Example 7

[0073] This example refers to the preparation method provided in Example 5 to prepare a lithium ion battery. The difference between this example and Example 5 is that in the process of preparing the electrolyte, the content of the thiophene additive and the organic solvent in the electrolyte is adjusted so that the mass percentage of the thiophene additive in the electrolyte is 0.08%. The rest of the raw material ratios and preparation methods are strictly consistent with those in Example 5.

[0074] Example 8

[0075] This example refers to the preparation method provided in Example 5 to prepare a lithium ion battery. The difference between this example and Example 5 is that in the process of preparing the electrolyte, the content of the thiophene additive and the organic solvent in the electrolyte is adjusted so that the mass percentage of the thiophene additive in the electrolyte is 1.80%. The rest of the raw material ratios and preparation methods are strictly consistent with those in Example 5.

[0076] Example 9

[0077] This example refers to the preparation method provided in Example 5 to prepare a lithium ion battery. The difference between this example and Example 5 is that in the process of preparing the electrolyte, the content of the thiophene additive and the organic solvent in the electrolyte is adjusted so that the mass percentage of the thiophene additive in the electrolyte is 2.80%. The rest of the raw material ratios and preparation methods are strictly consistent with those in Example 5.

[0078] Example 10

[0079] This example refers to the preparation method provided in Example 5 to prepare a lithium-ion battery. The difference between this example and Example 5 is that during the preparation of the electrolyte, lithium hexafluorophosphate of equal mass is used instead of lithium bis(fluorosulfonyl)imide used in Example 5, and the mass percentage of the lithium salt in the electrolyte in this example is the same as that of the lithium salt in the electrolyte in Example 5. The ratios of the remaining raw materials and the preparation method are strictly the same as those in Example 5.

[0080] Example 11

[0081] This example refers to the preparation method provided in Example 5 to prepare a lithium-ion battery. The difference between this example and Example 5 is that during the preparation of the electrolyte, 1,3 - propane sultone (1,3-PS) of equal mass is used instead of the ester additive used in Example 5. The ratios of the remaining raw materials and the preparation method are strictly the same as those in Example 5.

[0082] Example 12

[0083] This example refers to the preparation method provided in Example 5 to prepare a lithium-ion battery. The difference between this example and Example 5 is that during the preparation of the electrolyte, an organic solvent of equal mass is used instead of the ester additive used in Example 5. The ratios of the remaining raw materials and the preparation method are strictly the same as those in Example 5.

[0084] Example 13

[0085] This example refers to the preparation method provided in Example 5 to prepare a lithium-ion battery. The difference between this example and Example 5 is that during the preparation of the electrolyte, the contents of the ester additive and the organic solvent are adjusted so that the mass ratio of the ester additive in the electrolyte is 0.8%. The ratios of the remaining raw materials and the preparation method are strictly the same as those in Example 5.

[0086] Example 14

[0087] This example refers to the preparation method provided in Example 5 to prepare a lithium-ion battery. The difference between this example and Example 5 is that during the preparation of the electrolyte, the contents of the ester additive and the organic solvent are adjusted so that the mass ratio of the ester additive in the electrolyte is 1.0%. The ratios of the remaining raw materials and the preparation method are strictly the same as those in Example 5.

[0088] Example 15

[0089] This example refers to the preparation method provided in Example 5 to prepare a lithium-ion battery. The difference between this example and Example 5 is that during the preparation of the electrolyte, the contents of the ester additive and the organic solvent are adjusted so that the mass ratio of the ester additive in the electrolyte is 3.5%. The ratios of the remaining raw materials and the preparation method are strictly the same as those in Example 5.

[0090] Comparative Example 1

[0091] In this example, a lithium-ion battery was prepared with reference to the preparation method provided in Example 5. The difference between this example and Example 5 is that during the preparation of the electrolyte, an equal mass of organic solvent was used to replace the thiophene-based additive used in Example 5, which is equivalent to the electrolyte obtained in this comparative example not containing the thiophene-based additive. The other raw material ratios and preparation methods were strictly the same as those in Example 5.

[0092] Comparative Example 2

[0093] In this example, a lithium-ion battery was prepared with reference to the preparation method provided in Example 5. The difference between this example and Example 5 is that during the preparation of the electrolyte, an equal mass of thiophene was used to replace the thiophene-based additive used in Example 5. The other raw material ratios and preparation methods were strictly the same as those in Example 5.

[0094] Among them, the CAS number of thiophene is 110 - 02 - 1, and its structural formula is shown as Formula VIII:

[0095] Comparative Example 3

[0096] In this example, a lithium-ion battery was prepared with reference to the preparation method provided in Example 5. The difference between this example and Example 5 is that during the preparation of the electrolyte, an equal mass of 4,6 - dimethyldibenzothiophene was used to replace the thiophene-based additive used in Example 5. The other raw material ratios and preparation methods were strictly the same as those in Example 5.

[0097] Among them, the CAS number of 4,6 - dimethyldibenzothiophene is 1207 - 12 - 1, and its structural formula is shown as Formula IX:

[0098]

[0099] Comparative Example 4

[0100] In this example, a lithium-ion battery was prepared with reference to the preparation method provided in Example 5. The difference between this example and Example 5 is that during the preparation of the electrolyte, the contents of the thiophene-based additive and the organic solvent in the electrolyte were adjusted so that the mass percentage of the thiophene-based additive in the electrolyte was 3.0%. The other raw material ratios and preparation methods were strictly the same as those in Example 5.

[0101] Comparative Example 5

[0102] This example refers to the preparation method provided in Example 5 to prepare a lithium-ion battery. The difference between this example and Example 5 is that during the preparation of the electrolyte, the contents of the thiophene additive and the organic solvent in the electrolyte are adjusted so that the mass percentage of the thiophene additive in the electrolyte is 0.05%. The other raw material ratios and preparation methods are strictly the same as those in Example 5.

[0103] Test Example

[0104] Test subjects: The lithium-ion batteries provided in Examples 1 to 12 and Comparative Examples 1 to 5.

[0105] Test items and test methods:

[0106] (1) Cycling performance: The test subjects are charged at a constant current and constant voltage of 1.0C to 4.5V at 25°C, left standing for 5 min, and then discharged at 0.1C to 2.5V. The discharged capacity is recorded as the initial capacity. Then, they are charged at a constant current and constant voltage of 1.0C to 4.5V again, and the initial volume of the battery is recorded. The test subjects are charged and discharged at 1C at 45°C, with the voltage range of 2.5 to 4.5V, and charged and discharged 1200 times. The discharge capacity of the 1200th cycle is recorded, the capacity retention rate is calculated, the battery is taken out, and the volume of the battery after 1200 cycles is recorded. Among them, the capacity retention rate (%) = (discharge capacity of the 1200th cycle / initial capacity) × 100%, and the volume change rate (%) = (volume after cycling - initial volume) / initial volume × 100%.

[0107] (2) High-temperature storage performance: The test subjects are charged at a constant current and constant voltage of 1.0C to 4.5V at 25°C, left standing for 5 min, and then discharged at 0.1C to 2.5V. The discharged capacity is recorded as the initial capacity. Then, they are charged at a constant current and constant voltage of 1.0C to 4.5V again, and the initial volume of the battery is recorded. The test subjects are stored under the condition of 60°C ± 2°C, open-circuit stored for 90 days, then the battery is taken out, the volume of the battery in the hot state is recorded, and after standing at room temperature for 2 h, the battery core is charged and discharged at 1.0C, the discharge capacity is recorded, and then the capacity retention rate is calculated. Among them, the capacity retention rate (%) = discharge capacity after storage / initial capacity × 100%, and the volume change rate (%) = (volume after storage - initial volume) / initial volume × 100%.

[0108] (3) Negative electrode manganese deposition amount: Charge the test object at a constant current and constant voltage of 1.0C to 4.5V at 25°C, let it stand for 5 minutes, then discharge it to 2.5V at 0.1C. Then disassemble and take out the negative electrode plate, soak it in dimethyl carbonate and dry it, weigh to calculate the weight of the negative electrode active material, and measure the content of manganese in the negative electrode by inductively coupled plasma atomic emission spectrometry, which is recorded as the initial negative electrode manganese deposition amount. Then, take down the battery cells that have been cycled 1200 times and stored for 90 days in (1) and (2) above and discharge them to 2.5V, then disassemble and take out the negative electrode plate, soak it in dimethyl carbonate and dry it, weigh to calculate the weight of the negative electrode active material, and measure the content of manganese in the negative electrode by inductively coupled plasma atomic emission spectrometry.

[0109] Test results: The composition of the electrolyte provided by the test object is shown in Table 2, and the test results are shown in Table 3.

[0110] Table 2. Composition of the electrolytes provided by each test object

[0111]

[0112]

[0113]

[0114]

[0115] Note: In Examples 1-9, Examples 11-15, and Comparative Examples 1-5, a mixed lithium salt composed of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide in a mass ratio of 11.25:1.5 is used. In Example 10, a single lithium salt of lithium hexafluorophosphate is used.

[0116] Table 3. Test results of various performance of this test example

[0117]

[0118]

[0119] Result analysis:

[0120] Comparing the test results of Examples 1-15 and Comparative Examples 1-5 in Table 2, it can be found that the comprehensive performance of the batteries provided by Examples 1-15 is better than that of the batteries provided by Comparative Examples 1-5. Among them, in the batteries provided by Examples 1-15, the electrolyte provided by Example 5 can effectively reduce the negative electrode manganese deposition, and the provided battery has the best cycle characteristics and high-temperature storage performance.

[0121] By comparing the comprehensive performance of Examples 1-6 with that of Comparative Examples 1-3, it can be found that as the number of elements with lone pair electrons in the thiophene-based additive increases, the measured negative electrode manganese deposition amount and volume expansion rate of the battery show a trend of first decreasing and then increasing, while the cycle capacity retention rate and high-temperature storage performance of the battery show a trend of first increasing and then decreasing. Compared with the batteries of Comparative Examples 1-3, the batteries provided in Examples 1-6 have lower negative electrode manganese deposition amount and volume expansion rate, and higher cycle capacity retention rate after 1200 cycles and / or after high-temperature storage. This shows that when using a thiophene-based additive with no less than 2 elements with lone pair electrons, the activity of complexation between the thiophene-based additive and manganese ions can be effectively improved, the content of manganese ions in the electrolyte can be effectively reduced, thereby reducing the side reactions occurring between manganese ions and the electrolyte, and improving the cycle performance of the battery. From the performance indicators of Comparative Examples 1-3 in Table 3, it can be seen that the corresponding negative electrode manganese deposition amount of Comparative Examples 1-3 is relatively high and the cycle performance of the battery is poor because the electrolytes provided do not use thiophene-based additives or use thiophene-based compounds containing only 1 element with lone pair electrons as thiophene-based additives, resulting in the cycle performance and high-temperature storage performance of the batteries in Comparative Examples 1-3 being inferior to those of the batteries in Examples 1-6. Among them, compared with the thiophene-based additive used in Comparative Example 3, the thiophene-based additive used in Comparative Example 2 has a smaller steric hindrance. Therefore, the complexation activity of the thiophene-based additive with manganese ions in Comparative Example 2 is higher than that in Comparative Example 3, which is reflected in the manganese deposition amount of Comparative Example 2 during cycling at 45 °C and storage at 60 °C being lower than the performance indicators of Comparative Example 3.

[0122] By comparing the performance indicators of Examples 5, 7-9 and Comparative Examples 4-5 in Table 3, it can be found that as the content of the thiophene-based additive in the electrolyte increases, the comprehensive performance of the lithium-ion battery shows a trend of first increasing and then decreasing. Compared with the batteries of Comparative Examples 4-5, the batteries of Examples 7-9 have higher capacity retention rate, better high-temperature storage performance and lower volume expansion rate. By comparing the performance indicators of the batteries provided in Example 5 and Example 10, it can be found that the comprehensive performance of the battery in Example 5 using a mixed lithium salt is better than that of the battery in Example 10 using a single lithium salt. Among them, the electrolyte applied in the battery provided in Comparative Example 4 contains a relatively large amount of thiophene-based additive, which increases the impedance of the battery and ultimately affects the normal cycle performance of the electrolyte, which is reflected in the relatively low cycle capacity retention rate of the battery in Comparative Example 4.

[0123] Furthermore, among the batteries of Example 5 and Examples 12 to 15, the battery of Example 12 exhibits a relatively high volume expansion rate. This indicates that the ester additive and the thiophene additive have a synergistic effect in the electrolyte, which can effectively inhibit the volume expansion of the negative electrode active material and effectively slow down the battery aging. As can be seen from Table 3, the performance indicators of the batteries of Example 5 and Examples 13 to 15 during cycling at 45 °C are relatively close. However, the performance indicators of the batteries of Example 5 and Examples 14 to 15 after high-temperature storage are better than those of Example 13. In particular, the amount of manganese deposition on the negative electrode after high-temperature storage in Example 5 and Examples 14 to 15 is lower than that in Example 13. Therefore, when the mass ratio of the thiophene additive to the ester additive falls within the range of 0.08 to 2.80:1.0 to 3.5, the structural stability of the SEI film formed by the battery can be further improved, the cycling characteristics of the battery can be enhanced, and the complexation of the thiophene compound with manganese ions can be promoted.

[0124] The above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A lithium-ion battery, characterized in that, It includes a positive electrode, a negative electrode and an electrolyte. The active material of the positive electrode includes lithium iron manganese phosphate. The electrolyte includes a thiophene-based additive, and the chemical structure of the thiophene-based additive satisfies Formula I: At least one of the groups R1 to R4 includes at least one of an amino group, a thiophenyl group, a pyridyl group, an acetyl group, an amide group, and an ester group. Based on the total mass of the electrolyte, the content of the thiophene-based additive is 0.08 to 2.80 wt%. The number of elements with lone pair electrons in the thiophene-based additive is not higher than 4. Calculated by molar ratio, in the thiophene-based additive, nitrogen element: sulfur element: oxygen element = 2:1:

1.

2. The lithium-ion battery according to claim 1, wherein In the chemical structure of the thiophene-based additive, the following conditions are satisfied: The R1 to R4 may independently be selected from at least one of a hydrogen atom, a methyl group, an ethyl group, a cyclopentyl group, a cyclohexyl group, a phenyl group, an amino group, a thiophenyl group, a pyridyl group, an acetyl group, a carboxamide group, and an ester group; And / or, R1 and R2, R2 and R3, or R3 and R4 are independently cyclized respectively, the ring is a 4- to 6-membered ring, the 4- to 6-membered ring includes a cycloalkane and / or a heterocycle, the heterocycle is a heterocycle containing O, S, or N, and the cycloalkane is at least one of a cycloalkane, a cycloolefin, and benzene.

3. The lithium-ion battery according to claim 1, characterized in that, The electrolyte further includes an ester-based additive, and the ester-based additive includes at least one of vinylene carbonate, ethylene sulfite, ethylene sulfate, 1,3-propane sultone, and propylene sultone.

4. The lithium ion battery according to claim 3, wherein In the electrolyte, the mass ratio of the thiophene-based additive to the ester-based additive is 0.08 to 2.80:1.0 to 3.

5.

5. The lithium ion battery according to claim 3, wherein The ester-based additive includes at least one of ethylene sulfate and vinylene carbonate.

6. The lithium-ion battery according to claim 1, characterized in that, The electrolyte further includes a lithium salt, and based on the total mass of the electrolyte, the content of the lithium salt is 10.50 to 13.00 wt%.

7. The lithium ion battery according to claim 6, characterized in that, The lithium salt includes lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide, and the mass ratio of the lithium hexafluorophosphate to the lithium bis(fluorosulfonyl)imide is 10.5 to 12:0.5 to 2.

8. An electrical device, comprising the lithium ion battery according to any one of claims 1 to 7.

Images