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

Abstract

The present invention provides a lithium-ion battery, comprising a positive electrode, a negative electrode, and an electrolyte. The positive electrode comprises a positive electrode active material containing a manganese element. The electrolyte comprises a lithium salt, a solvent, and an additive. The additive comprises a nitrile additive, an ester additive, and a lithium salt additive. The nitrile additive comprises succinonitrile, the ester additive comprises vinylene carbonate, the mass of succinonitrile: the mass of vinylene carbonate = 0.05 to 0.3:1, and the content of vinylene carbonate in the electrolyte does not exceed 2wt%. The ester additive further comprises vinyl sulfate, fluoroethylene carbonate, and 1,3-propane sultone. The lithium salt additive comprises at least one of lithium difluorophosphate, lithium bis(oxalatodifluorophosphate), and lithium bis(oxalatoborate). The lithium-ion battery provided by the present invention effectively suppresses the dissolution of manganese ions from the positive electrode active material by using an electrolyte that meets the above conditions, thereby improving the low-temperature performance and cycle output characteristics of the battery using the electrolyte.

Description

Technical Field

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

[0002] Lithium-ion batteries are currently the battery system with the best overall performance, boasting high specific energy, long cycle life, compact size, lightweight, no memory effect, and zero pollution. They are rapidly developing into a new generation of energy storage power sources, used to power information technology, electric and hybrid vehicles, specialized aerospace applications, and other fields. With the widespread use of electronic products, the industry is placing higher demands on the performance of lithium-ion batteries.

[0003] Manganese-containing cathode active materials have the advantages of high theoretical specific capacity, high safety characteristics and low cost, and have become a hot topic in lithium-ion battery research. However, manganese-containing cathode active materials have problems such as poor power characteristics of lithium-ion batteries, decreased cycle life, and reduced available capacity under low-temperature conditions. 3+ The existence of the John-Teller effect can easily lead to structural instability of the positive electrode active material during the charge and discharge process, resulting in a shorter cycle life.

[0004] Based on the above-mentioned defects of existing lithium-ion batteries, it is necessary to provide a lithium-ion battery that uses a positive electrode active material containing manganese elements and has good low-temperature performance and excellent cycle performance. 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, so as to enhance the cycle capacity retention rate and low-temperature 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, comprising a positive electrode, a negative electrode and an electrolyte, wherein the positive electrode comprises a positive electrode active material containing a manganese element, the electrolyte comprises a lithium salt, a solvent and an additive, the additive comprising a nitrile additive, an ester additive and a lithium salt additive; the nitrile additive comprises succinonitrile (SN); the ester additive comprises vinylene carbonate (VC), the mass of succinonitrile:the mass of vinylene carbonate=0.05-0.3:1, and the content of vinyl carbonate in the electrolyte does not exceed 2wt%; the ester additive further comprises vinyl sulfate (DTD), fluoroethylene carbonate (FEC) and 1,3-propane sultone (PS); the lithium salt additive comprises at least one of lithium difluorophosphate (LiPO2F2), lithium bis(oxalatodifluorophosphate) (LiDFOP) and lithium bis(oxalatoborate) (LiBOB). For example, the mass ratio of succinonitrile to vinylene carbonate is 0.05:1, 0.10:1, 0.15:1, 0.20:1, 0.25:1, and 0.30:1, and the content of vinylene carbonate in the electrolyte is 0.5 wt%, 1 wt%, 1.5 wt%, and 2 wt%.

[0007] The lithium-ion battery provided by the present invention effectively suppresses the dissolution of manganese ions from the positive electrode active material by adopting an electrolyte that meets the above conditions, thereby improving the low-temperature performance and cycle output characteristics of the battery using the electrolyte. First, during the operation of the battery, the above electrolyte can effectively reduce the manganese ions dissolved from the positive electrode, slow down the damage to the positive electrode structure, improve the cycle stability of the battery, and extend its service life. Secondly, the SEI film is composed of electrolyte decomposition products, so the composition of the electrolyte has a greater impact on the performance indicators of the SEI film. When an additive that meets the above requirements is selected, the electrolyte can promote the formation of a structurally stable SEI film on the surface of the negative electrode, reduce interfacial impedance, reduce adverse reactions between the electrolyte and the positive and negative electrodes, maintain the stability of the battery interface, help maintain the electrochemical performance of the battery in a low-temperature environment, and improve the energy output and cycle efficiency of the battery. Furthermore, by regulating the ratio of succinonitrile to vinylene carbonate in the electrolyte, the dissolution of manganese ions can be effectively suppressed, thereby reducing the manganese ion content in the electrolyte, effectively reducing the manganese ions that migrate to the negative electrode surface, and inhibiting the reduction of manganese ions to manganese metal at the negative electrode to form manganese deposits, thereby reducing the probability of manganese deposits piercing the SEI film, further maintaining the stability of the electrolyte interface, and optimizing the battery's cycle stability in low-temperature environments. In particular, this lithium-ion battery can maintain normal operation in environments ranging from -40°C to 55°C.

[0008] Preferably, based on the total weight of the electrolyte, the content of the ester additive is 3-4 wt %, for example, the content of the ester additive is 3 wt %, 3.5 wt %, or 4 wt %.

[0009] Preferably, the content of the lithium salt additive is 1-3 wt % based on the total mass of the electrolyte, for example, 1 wt %, 1.5 wt %, 2 wt %, 2.5 wt %, or 3 wt %.

[0010] Preferably, the mass ratio of nitrile additives, ester additives, and lithium salt additives is 0.01-1.5:2.5-5:1.5-2.5. For example, the mass ratio of nitrile additives, ester additives, and lithium salt additives is 0.01:2.5:1.5, 0.5:3.5:1.8, 0.3:3.8:2, 1:4.5:2.5, and 1.5:5:2.5. By comprehensively regulating the content of nitrile additives, ester additives, and lithium salt additives in the electrolyte, the stability of the electrolyte interface can be improved, the chemical reactions within the battery can be more stable, and the battery's cycling performance and kinetic performance can be improved while ensuring good low-temperature performance.

[0011] More preferably, the mass ratio of the nitrile additive, the ester additive and the lithium salt additive is 0.3:3.8:2.

[0012] Preferably, in the ester additive, the mass ratio of vinylene carbonate, vinyl sulfate, fluoroethylene carbonate, and 1,3-propane sultone is 1-3:0.2-0.7:0.1-0.5:0.5-1.5. Preferably, the mass ratio of vinylene carbonate, vinyl sulfate, fluoroethylene carbonate, and 1,3-propane sultone is 1:0.7:0.1:1.5, 2:0.5:0.3:1, or 3:0.2:0.5:0.5. When the mass ratio of the ester additive falls within the above-mentioned mass ratio range, it can not only promote the formation of the SEI film in the first cycle, but also the structural stability and flexibility of the formed SEI film are good, which is beneficial to reduce the possibility of SEI film rupture caused by the volume expansion of the negative electrode material or the deposition of manganese ions on the negative electrode surface during the lithium ion deintercalation process, inhibit the side reaction of the electrolyte, effectively reduce the loss of active lithium, and reduce the polarization resistance growth rate of the battery containing it during the cyclic charge and discharge process, thereby improving the electrochemical performance of the battery.

[0013] Preferably, the lithium salt additive includes lithium difluorophosphate, lithium bis(oxalato)difluorophosphate and lithium bis(oxalato)borate.

[0014] Preferably, in the lithium salt additive, the mass ratio of lithium difluorophosphate, lithium bisoxalatodifluorophosphate and lithium bisoxalatoborate is 0.5-1.0:0.5-1.5:0.1-0.5. Preferably, the mass ratio of lithium difluorophosphate, lithium bisoxalatodifluorophosphate and lithium bisoxalatoborate is 0.5.0:1.5:0.5, 0.7:1:0.3, 0.5:0.5:0.1. When the mass ratio of the lithium salt additive falls within the above mass ratio range, it can improve the transport performance of lithium ions in the SEI film, which is beneficial to the lithium deintercalation of the negative electrode, and can reduce the interfacial impedance of the SEI film, slowing down the aging of the SEI film during the battery cycle. In addition, the lithium salt additive can participate in the film formation process of the positive and negative electrodes, and can effectively improve the film formation performance and thermal stability of the positive and negative electrodes.

[0015] More preferably, in the lithium salt additive, the mass ratio of lithium difluorophosphate, lithium bisoxalatodifluorophosphate and lithium bisoxalatoborate is 0.7:1:0.3.

[0016] Preferably, the additive content is 5-8wt% based on the total weight of the electrolyte. For example, the additive content is 5wt%, 6wt%, 7wt%, or 8wt%. When the additive content in the electrolyte is within the above range, the resulting lithium-ion battery has excellent low-temperature output performance and cycle performance, and can still maintain excellent battery capacity retention in low-temperature operating environments.

[0017] Preferably, the lithium salt includes at least one of lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI); the concentration of the lithium salt in the electrolyte is 0.5 to 1.5 mol / L. For example, the concentration of the lithium salt in the electrolyte is 0.5 mol / L, 1 mol / L, and 1.5 mol / L. By selecting the above-mentioned mixed lithium salt and regulating the concentration of the lithium salt in the electrolyte, on the one hand, the number of free lithium ions in the electrolyte can be increased, the migration efficiency of lithium ions can be promoted, and the current transmission speed can be increased. On the other hand, the electrolyte prepared by combining the lithium salt with the above-mentioned additives has good thermal stability and low viscosity characteristics. The electrolyte has good wettability to the positive and negative electrodes, which is beneficial to improving the battery dynamics, further reducing the internal resistance of the battery, and improving the output performance of the battery.

[0018] More preferably, the concentration of the lithium salt in the electrolyte is 1 mol / L.

[0019] Preferably, the lithium salt includes lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI).

[0020] Preferably, the mass ratio of lithium hexafluorophosphate to lithium bis(fluorosulfonyl)imide in the lithium salt is 0.8-1.2:0.8-1.2. For example, the mass ratio of lithium hexafluorophosphate to lithium bis(fluorosulfonyl)imide is 0.8:1.2, 0.9:1.1, 1:1, 1.1:0.9, or 1.2:0.8. Optimizing the mass ratio of lithium hexafluorophosphate to lithium bis(fluorosulfonyl)imide in this manner can improve the conductivity of the electrolyte and the efficiency of lithium ion transport, thereby alleviating lithium plating at the negative electrode, improving battery output characteristics, and extending battery life.

[0021] More preferably, in the lithium salt, the mass ratio of lithium hexafluorophosphate to lithium bis(fluorosulfonyl)imide is 1:1.

[0022] Preferably, the solvent includes at least one of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC).

[0023] Preferably, the solvent includes ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC). By selecting the above-mentioned composite organic solvent as the solvent in the electrolyte, not only can the compatibility between the additives, lithium salts and solvents in the electrolyte be improved, but it is also conducive to the formation of an electrolyte system with high dielectric constant, low viscosity and low melting point. In particular, when the mass ratio of nitrile additives, ester additives and lithium salt additives in the electrolyte falls within the range of 0.01-1.5:2.5-5:1.5-2.5, the SEI film formed has a low solubility in the above-mentioned composite organic solvent and can exist stably. Moreover, the above-mentioned composite organic solvent is more difficult to pass through the SEI film, which is conducive to preventing the co-embedding of the solvent, thereby avoiding damage to the negative electrode material due to the co-embedding of the solvent and improving the service life of the battery.

[0024] Preferably, in the solvent, the mass ratio of ethylene carbonate, propylene carbonate, dimethyl carbonate, and ethyl methyl carbonate is 0.8-1.2:0.8-1.2:2.5-3.5:1.6-1.8. For example, the mass ratio of ethylene carbonate, propylene carbonate, dimethyl carbonate, and ethyl methyl carbonate is 0.8:1.2:2.5:1.6, 1:1:3:1.7, or 1.2:0.8:3.5:1.8.

[0025] More preferably, the mass ratio of ethylene carbonate, propylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in the solvent is 1:1:3:1.6 to 1.8. For example, the mass ratio of ethylene carbonate, propylene carbonate, dimethyl carbonate, and ethyl methyl carbonate is 1:1:3:1.6, 1:1:3:1.7, or 1:1:3:1.8.

[0026] Preferably, the positive electrode active material includes lithium iron manganese phosphate. 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, abundant raw material resources, low cost, environmental friendliness, and high safety. Under normal circumstances, lithium iron manganese phosphate will undergo the John-Teller effect during the battery cell cycle, which increases the amount of manganese ions dissolved in the electrolyte, affecting the battery cycle capacity. By selecting the above-mentioned electrolyte and the lithium iron manganese phosphate positive electrode active material, the dissolution of manganese ions can be effectively inhibited, thereby reducing the content of manganese ions in the electrolyte, and improving the low-temperature performance and cycle performance of the battery while meeting the high energy density of the battery.

[0027] Preferably, the active material of the negative electrode includes at least one of graphite and silicon carbon.

[0028] Preferably, the active material of the negative electrode includes graphite.

[0029] Preferably, the lithium-ion battery further comprises a separator disposed between the positive electrode and the negative electrode, and the separator comprises at least one of polypropylene, polyvinylidene fluoride, polytetrafluoroethylene, polyacrylonitrile, and polyethylene.

[0030] Preferably, the membrane comprises polyethylene.

[0031] According to another aspect of the present invention, there is provided an electrical device comprising the above-mentioned lithium-ion battery. DETAILED DESCRIPTION

[0032] In order to enable those skilled in the art to better understand the technical solutions of 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 embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0033] Example 1

[0034] This embodiment provides a lithium-ion battery, including a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte.

[0035] (1) Electrolyte:

[0036] The composition of the electrolyte is shown in Table 1:

[0037] Table 1. Raw material composition for preparing electrolyte of the battery provided in Example 1

[0038]

[0039]

[0040] Note: The ratios appearing in Table 1 are mass ratios, such as "lithium hexafluorophosphate: lithium bisfluorosulfonyl imide = 1:1", which means the mass ratio of lithium hexafluorophosphate to lithium bisfluorosulfonyl imide is 1:1; and so on, such as "ethylene carbonate: propylene carbonate: dimethyl carbonate: ethyl methyl carbonate = 1:1:3:1.67", which means the mass ratio of ethylene carbonate, propylene carbonate, dimethyl carbonate, and ethyl methyl carbonate is 1:1:3:1.67, and they are mixed and matched as the organic solvent.

[0041] Prepare the raw materials according to the above composition and prepare the electrolyte according to the following steps: first mix the solvent evenly under an environment of temperature 20-25°C, humidity ≤1%, oxygen content ≤1ppm, and water content ≤0.1ppm, then add lithium salt and additives to the solvent, and mix evenly to obtain the electrolyte.

[0042] (2) Lithium-ion batteries:

[0043] Lithium manganese iron phosphate is used as the positive electrode active material, graphite is used as the negative electrode active material, and PE+OBS separator is used as the separator. The positive electrode, separator and negative electrode are stacked in order, and a battery cell is obtained through a lamination process. The battery cell is placed in an outer packaging shell and dried. The electrolyte is injected according to the electrolyte injection coefficient of 4.4g / Ah. After vacuum packaging, standing, formation, and capacity division processes, a lithium-ion battery is obtained.

[0044] Example 2

[0045] This example uses the preparation method provided in Example 1 to prepare a lithium-ion battery. The difference between this example and Example 1 is that during the preparation of the electrolyte, the amounts of succinonitrile and solvent were adjusted so that the mass ratio of succinonitrile to vinylene carbonate was 0.3:1. The remaining raw material ratios and preparation method were strictly consistent with those in Example 1.

[0046] Example 3

[0047] This example uses the preparation method provided in Example 1 to prepare a lithium-ion battery. This example differs from Example 1 in that, during the preparation of the electrolyte, an equal mass of lithium difluorophosphate is used instead of the lithium salt additive in Example 1. That is, this example uses a single lithium salt additive. The remaining raw material ratios and preparation method remain strictly consistent with those in Example 1.

[0048] Example 4

[0049] This example uses the preparation method provided in Example 1 to prepare a lithium-ion battery. This example differs from Example 1 in that an equal mass of lithium bis(oxalato)difluorophosphate is used in place of the lithium salt additive in Example 1 during the preparation of the electrolyte. That is, this example uses a single lithium salt additive. The remaining raw material ratios and preparation method remain strictly consistent with those in Example 1.

[0050] Example 5

[0051] This example uses the preparation method provided in Example 1 to prepare a lithium-ion battery. This example differs from Example 1 in that an equal mass of lithium bis(oxalatoborate) is used in place of the lithium salt additive in Example 1 during the preparation of the electrolyte. This example uses a single lithium salt additive. The remaining raw material ratios and preparation method remain identical to those in Example 1.

[0052] Example 6

[0053] This example uses the preparation method provided in Example 1 to prepare a lithium-ion battery. This example differs from Example 1 in that, during the preparation of the electrolyte, a mixed lithium salt additive of equal masses of lithium difluorophosphate and lithium bis(oxalate)difluorophosphate was used instead of the lithium salt additive in Example 1, with the mass ratio of lithium difluorophosphate to lithium bis(oxalate)difluorophosphate being 0.7:1. The remaining raw material ratios and preparation method remained strictly consistent with those in Example 1.

[0054] Example 7

[0055] This example uses the preparation method provided in Example 1 to prepare a lithium-ion battery. This example differs from Example 1 in that, during the preparation of the electrolyte, a mixed lithium salt additive of equal masses of lithium difluorophosphate and lithium bis(oxalatoborate) is used instead of the lithium salt additive in Example 1, with the mass ratio of lithium difluorophosphate to lithium bis(oxalatoborate) being 0.7:0.3. The remaining raw material ratios and preparation method remain strictly consistent with those in Example 1.

[0056] Example 8

[0057] This example uses the preparation method provided in Example 1 to prepare a lithium-ion battery. This example differs from Example 1 in that, during the preparation of the electrolyte, a mixed lithium salt additive of equal masses of lithium bis(oxalatodifluorophosphate) and lithium bis(oxalatoborate) is used instead of the lithium salt additive in Example 1, with the mass ratio of lithium bis(oxalatodifluorophosphate) to lithium bis(oxalatoborate) being 1:0.3. The remaining raw material ratios and preparation method remain strictly consistent with those in Example 1.

[0058] Example 9

[0059] This example uses the preparation method provided in Example 1 to prepare a lithium-ion battery. The difference between this example and Example 1 is that during the preparation of the electrolyte, an equal mass of lithium hexafluorophosphate is used instead of the lithium bis(fluorosulfonyl)imide used in Example 1. The remaining raw material ratios and preparation method remain strictly consistent with those in Example 1.

[0060] Example 10

[0061] This example uses the preparation method provided in Example 1 to prepare a lithium-ion battery. The difference between this example and Example 1 is that during the preparation of the electrolyte, an equal mass of lithium bis(fluorosulfonyl)imide is used instead of the lithium hexafluorophosphate in Example 1. The remaining raw material ratios and preparation method are strictly consistent with those in Example 1.

[0062] Comparative Example 1

[0063] This comparative example uses the preparation method provided in Example 1 to prepare a lithium-ion battery. This comparative example differs from Example 1 in that an equal amount of solvent is used in place of the fluoroethylene carbonate used in Example 1 during the preparation of the electrolyte. The remaining raw material ratios and preparation method remain strictly consistent with those in Example 1.

[0064] Comparative Example 2

[0065] This comparative example uses the preparation method provided in Example 1 to prepare a lithium-ion battery. The difference between this comparative example and Example 1 is that during the preparation of the electrolyte, the amounts of ethylene carbonate, succinonitrile, and solvent were adjusted so that the content of ethylene carbonate in the electrolyte was 3 wt %, and the mass ratio of succinonitrile to ethylene carbonate was consistent with that in Example 1. The remaining raw material ratios and preparation method remained strictly consistent with those in Example 1.

[0066] Comparative Example 3

[0067] This comparative example uses the preparation method provided in Example 1 to prepare a lithium-ion battery. This comparative example differs from Example 1 in that an equal amount of lithium tetrafluoroborate is used in place of the lithium salt additive in Example 1 during the preparation of the electrolyte. The remaining raw material ratios and preparation method remain strictly consistent with those in Example 1.

[0068] Comparative Example 4

[0069] This comparative example uses the preparation method provided in Example 1 to prepare a lithium-ion battery. The difference between this comparative example and Example 1 is that during the preparation of the electrolyte, the contents of succinonitrile and vinylene carbonate in the electrolyte were adjusted to achieve a mass ratio of succinonitrile to vinylene carbonate of 0.03:1. The remaining raw material ratios and preparation method remained strictly consistent with those in Example 1.

[0070] Comparative Example 5

[0071] This comparative example uses the preparation method provided in Example 1 to prepare a lithium-ion battery. This comparative example differs from Example 1 in that, during the preparation of the electrolyte, the contents of succinonitrile and vinylene carbonate in the electrolyte were adjusted to achieve a mass ratio of succinonitrile to vinylene carbonate of 0.4:1. The remaining raw material ratios and preparation method remained strictly consistent with those in Example 1.

[0072] Test Case

[0073] Test objects: the lithium-ion batteries provided in Examples 1 to 11, and the lithium-ion batteries provided in Comparative Examples 1 to 5.

[0074] Test items and test methods:

[0075] (1) Discharge capacity retention rate at different temperatures: The test object's battery was charged to 4.25V at 1 / 3C constant current and constant voltage at 25℃, with a cut-off current of 0.05C. After standing for 30 minutes, it was discharged to 2.5V at 1 / 3C. The discharged capacity was recorded as the initial capacity C0. Then, it was charged to 100% at 1 / 3C constant current and constant voltage (cut-off current 0.05C0). After the battery was left at different temperatures (represented by T, including -20℃, 0℃, 25℃, and 40℃) for 4 hours, it was discharged to 2.5V at 1 / 3C0 at the corresponding shelf temperature (-20℃, 0℃, 0℃, and 2.0V). The discharge capacity C1 was recorded and the discharge capacity retention rate was calculated. The specific calculation formula is: discharge capacity retention rate = (C1 / C0) * 100%.

[0076] (2) Negative electrode manganese deposition: The test object was charged at 1 / 3C constant current and constant voltage at 25°C to 4.25V, with a cut-off current of 0.05C. After standing for 30 minutes, it was discharged at 1 / 3C to 2.0V. The negative electrode was then disassembled and removed, soaked in dimethyl carbonate and dried, and the weight of the negative electrode active material was calculated by weighing. The manganese content of the negative electrode was measured by inductively coupled plasma atomic emission spectrometry, which was recorded as the initial negative electrode manganese deposition. The test object was then charged and discharged at 1C at 25°C, with a voltage range of 2.5 to 4.25V, for 500 charge and discharge cycles. After 500 cycles, the battery cell was removed and discharged to 2.0V. The negative electrode was then disassembled and removed, soaked in dimethyl carbonate and dried, and the weight of the negative electrode active material was calculated by weighing. The manganese content of the negative electrode was measured by inductively coupled plasma atomic emission spectrometry.

[0077] Test results: The composition of the electrolyte provided by the test subjects is shown in Table 2, and the test results are shown in Table 3.

[0078] Table 2. Composition of the electrolyte provided by each test subject

[0079]

[0080] Table 3. Performance test results of this test case

[0081]

[0082]

[0083] Result analysis:

[0084] Comparing the test results of Examples 1-11 with those of Comparative Examples 1-5 in Table 2 reveals that the overall performance of the batteries provided by Examples 1-11 is superior to that of the batteries provided by Comparative Examples 1-5. In the batteries provided by Examples 1-11, the electrolyte provided by Example 1 effectively reduces manganese deposition at the negative electrode and exhibits a high discharge capacity retention rate at low temperatures, with a capacity retention rate of 86.1% at -20°C. Batteries using this electrolyte exhibit excellent low-temperature cycling characteristics.

[0085] Comparing the comprehensive performance of Example 1 with that of Comparative Example 1, it can be found that compared with the battery of Comparative Example 1, the battery provided in Example 1 has a higher discharge capacity retention rate in a low temperature environment. This shows that when the electrolyte system simultaneously uses vinyl sulfate (DTD), fluoroethylene carbonate (FEC) and 1,3-propane sultone (PS), it can promote the formation of a structurally stable SEI film on the surface of the negative electrode, reduce the interfacial impedance, reduce the adverse reactions between the electrolyte and the positive and negative electrodes, maintain the stability of the battery interface, and help improve the electrochemical performance of the battery in a low temperature environment, and improve the energy output and cycle efficiency of the battery.

[0086] By comparing the comprehensive performance of Example 1 with that of Comparative Example 2, it can be found that compared with the battery of Comparative Example 2, the battery provided by Example 1 has a higher discharge capacity retention rate and a lower negative electrode manganese deposition amount under low temperature conditions. This shows that when the content of ethylene carbonate in the electrolyte does not exceed 2wt%, the electrolyte can effectively reduce the manganese ions dissolved from the positive electrode.

[0087] Comparing the comprehensive performance of Example 1, Examples 3-8, and Comparative Example 3, it can be found that compared with the battery of Comparative Example 3, the batteries provided by Example 1 and Examples 3-8 have lower negative electrode manganese deposition. This shows that when the lithium salt additive uses at least one of lithium difluorophosphate, lithium bisoxalate difluorophosphate, and lithium bisoxalate borate, it can effectively reduce the manganese ion concentration in the electrolyte system. Further, comparing the low-temperature cycle performance of Example 1 and Examples 3-8, it can be found that compared with Examples 3-5 using only a single lithium salt additive, the batteries provided by Example 1 and Examples 6-8 using a composite lithium salt additive have better discharge capacity under low-temperature conditions. Among them, the battery of Example 1 using three lithium salt additives has the best comprehensive performance. Any combination can be made. This shows that the use of a composite lithium salt additive including lithium difluorophosphate, lithium bisoxalate difluorophosphate, and lithium bisoxalate borate can produce a synergistic effect in lithium-ion batteries.

[0088] Comparing the comprehensive performance of Examples 1-2 with Comparative Examples 4-5 reveals that as the mass ratio of succinonitrile to vinylene carbonate increases, the negative electrode manganese deposition and volume expansion rate measured by the battery decrease, while the low-temperature discharge capacity retention of the battery increases. When the mass ratio of succinonitrile to vinylene carbonate is between 0.05 and 0.3:1, the manganese ion content in the electrolyte is effectively reduced, thereby reducing side reactions between the manganese ions and the electrolyte and improving the battery's cycling performance.

[0089] Comparing the comprehensive performance of Example 1 with that of Examples 9-10 in Table 2, it can be found that compared with Examples 9-10 using a single lithium salt, Example 1 using a compound lithium salt has a higher capacity retention rate. And during the experiment, it was found that

[0090] Compared to the electrolyte of Example 9, which uses LiPF6 as the lithium salt, the electrolyte provided by Example 1 has a moderate viscosity and a high lithium ion mobility, resulting in a higher capacity retention rate. Compared to the electrolyte of Example 10, which uses only LiFSI as the lithium salt, the electrolyte provided by Example 1 is less expensive and the aluminum foil is less susceptible to corrosion by the electrolyte, resulting in a longer battery cycle life.

[0091] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A lithium-ion battery, characterized in that: The invention comprises a positive electrode, a negative electrode and an electrolyte, wherein the positive electrode comprises a positive electrode active material containing a manganese element, the electrolyte comprises a lithium salt, a solvent and an additive, and the additive comprises a nitrile additive, an ester additive and a lithium salt additive; The nitrile additive includes succinonitrile, and the ester additive includes vinylene carbonate, wherein the weight of succinonitrile:the weight of vinylene carbonate is 0.05-0.3:1, and the content of vinylene carbonate in the electrolyte does not exceed 2wt%; The ester additives also include vinyl sulfate, fluoroethylene carbonate and 1,3-propane sultone; The lithium salt additives include lithium difluorophosphate, lithium bis(oxalato)difluorophosphate, and lithium bis(oxalato)borate.

2. The lithium-ion battery according to claim 1, wherein: The mass ratio of the nitrile additive, the ester additive and the lithium salt additive is 0.01-1.5:2.5-5:1.5-2.

5.

3. The lithium-ion battery according to claim 2, wherein: In the ester additive, the mass ratio of the vinylene carbonate, the vinyl sulfate, the fluoroethylene carbonate and the 1,3-propane sultone is 1-3:0.2-0.7:0.1-0.5:0.5-1.

5.

4. The lithium-ion battery according to claim 1, wherein In the lithium salt additive, the mass ratio of the lithium difluorophosphate, the lithium bis(oxalato)difluorophosphate, and the lithium bis(oxalato)borate is 0.5-1.0:0.5-1.5:0.1-0.

5.

5. The lithium-ion battery according to claim 1, wherein: Based on the total mass of the electrolyte, the content of the additive is 5-8 wt%.

6. The lithium-ion battery according to claim 1, wherein: The lithium salt includes at least one of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide; and the concentration of the lithium salt in the electrolyte is 0.5-1.5 mol / L.

7. The lithium-ion battery according to claim 1, wherein: The solvent includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, and ethyl methyl carbonate.

8. The lithium-ion battery according to any one of claims 1 to 7, wherein: The positive electrode active material includes lithium manganese iron phosphate.

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

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