Lithium ion battery and battery pack using the same

Abstract

The application provides a lithium ion battery and a battery pack using the same. x Co y M 1‑x‑y O2, wherein x is greater than or equal to 0.8, M includes at least one of Mn and Al, the active material of the negative electrode includes at least one of graphite and silicon-carbon, the electrolyte includes 2,4,6-tris(3,4,5-trifluorophenyl)boroxin, fluorinated ethylene carbonate, a lithium salt and a solvent, the lithium salt includes lithium hexafluorophosphate, the content of 2,4,6-tris(3,4,5-trifluorophenyl)boroxin is 0.2-3 wt% based on the total mass of the electrolyte, and the mass ratio of 2,4,6-tris(3,4,5-trifluorophenyl)boroxin to lithium hexafluorophosphate is 1:2.6-26. The lithium ion battery reduces the situation of a large amount of heat generated due to an unexpected reaction of the lithium ion battery by constructing a CEI film and a SEI film with stable structure and good thermal stability, avoids the short circuit of the positive and negative electrodes caused by the shrinkage, melting and collapse of the separator due to heat generation, and improves the overcharge resistance, safety and cycle stability of the battery device.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a lithium-ion battery and a battery pack using the same. Background Technology

[0002] Overcharging refers to forcibly charging a battery beyond its designed capacity. This leads to increased internal pressure, battery deformation, leakage, and performance degradation. Overcharging is particularly prevalent and difficult to overcome in large-capacity battery packs due to the imbalance in charging states among individual cells. When overcharging occurs, the battery's internal voltage experiences an abnormal increase, a precursor to thermal runaway. Thermal runaway is a chain reaction; once triggered, heat rapidly accumulates inside the battery, causing a sharp rise in temperature. This leads to irreversible changes in the structure of the electrode active materials and the decomposition of the electrolyte, generating even more heat and creating a vicious cycle. Ultimately, this can result in fires, explosions, and other safety hazards.

[0003] To prevent battery overcharging, industry professionals commonly improve the external structure of the battery casing by adding overcharge protection devices, such as current interruption devices (CID), explosion-proof safety valves (Vent), and PTC polymer switches installed inside the battery's safety cap. However, before the overcharge protection device cuts off the battery current, the internal temperature of the battery is already high. At this point, the internal separator often shrinks, melts, or collapses, causing a short circuit between the positive and negative electrodes. This leads to a rapid rise in battery temperature and triggers thermal runaway. Summary of the Invention

[0004] The purpose of this invention is to provide a lithium-ion battery and a battery pack using the same. This lithium-ion battery reduces the amount of heat generated by the battery due to unexpected reactions by constructing CEI and SEI films with stable structure and good thermal stability, thereby improving the battery device's overcharge resistance, safety and cycle stability.

[0005] 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 active material of the positive electrode comprises a nickel-cobalt compound LiNi. x Co y M 1-x-yO2, wherein x is greater than or equal to 0.8, M includes at least one of Mn and Al, the active material of the negative electrode includes at least one of graphite and silicon-carbon, the electrolyte includes 2,4,6-tris(3,4,5-trifluorophenyl)boroxin, fluorinated ethylene carbonate and a lithium salt, the lithium salt includes lithium hexafluorophosphate; the content of 2,4,6-tris(3,4,5-trifluorophenyl)boroxin is 0.2-3 wt% based on the total mass of the electrolyte, and the mass ratio of 2,4,6-tris(3,4,5-trifluorophenyl)boroxin to lithium hexafluorophosphate is 1:2.6-26.

[0006] LiNi x Co y M 1-x-y O2 includes lithium nickel cobalt aluminum oxide (NCA) material and lithium nickel cobalt manganese oxide (NCM) material, not only has the advantages of high reversible specific capacity and low material cost, but also has high structural stability and safety, thereby improving the cycle stability of the battery using the nickel cobalt compound. Therefore, the nickel cobalt compound is one of the most popular materials in the commercialized cathode material. With the increase of nickel content in the cathode active material, the nickel cobalt compound provides higher specific capacity, but at the same time, the capacity retention rate and thermal stability are sacrificed. The above lithium ion battery uses a nickel cobalt compound with high nickel content as the active material of the cathode, and the nickel cobalt compound with high nickel content will rapidly react with the electrolyte under overcharge conditions. By using 2,4,6-tris(3,4,5-trifluorophenyl)boroxin (TTFPB) and fluorinated ethylene carbonate (FEC) as additives and lithium hexafluorophosphate as a lithium salt, a structure-stable and thermally stable CEI film and SEI film can be constructed, thereby inhibiting the oxidative decomposition of the electrolyte under high pressure and high temperature conditions, and reducing the loss of the cathode active material and the anode active material under overcharge conditions. Thus, the amount of heat generated due to unintended reactions in the battery is reduced, thereby reducing the probability of shrinkage, melting or collapse of the separator due to overheating, thereby improving the safety performance of the battery device using the electrolyte. The battery device can withstand a voltage higher than the normal charging upper limit voltage during charging, and can tolerate overcharging to a certain extent, thereby reducing the safety risk caused by improper charging.

[0007] On the one hand, 2,4,6-tris(3,4,5-trifluorophenyl)boroxin (TTFPB) and lithium hexafluorophosphate (LiPF6) in the electrolyte interact with each other and can jointly participate in the formation of the CEI film. When the feeding amount of 2,4,6-tris(3,4,5-trifluorophenyl)boroxin and lithium hexafluorophosphate meets the above requirements, the anion PF6 - can rapidly decompose at a low oxidation potential to form an inner surface rich in LiF and an outer surface rich in LiB xO y The CEI film of this structure has excellent mechanical strength, thermal stability and uniformity, which helps to reduce the internal temperature rise of the battery, and also can improve the cycle stability of the positive electrode material and reduce the electrochemical unintended reaction at high voltage. On the other hand, the fluoroethylene carbonate (FEC) in the electrolyte can form a stable SEI film rich in LiF, and the fluoroethylene carbonate has less effect on 2,4,6-tris (3,4,5-trifluorophenyl) cycloboroxane and lithium hexafluorophosphate. At the same time, under overcharge conditions, lithium dendrites are formed by lithium stripping from the graphite negative electrode, and the SEI film formed by fluoroethylene carbonate can effectively inhibit the growth of lithium dendrites, reduce the risk of short circuit caused by lithium dendrites penetrating the separator, and also reduce unintended reactions with the electrolyte, thereby reducing heat generation. Therefore, by introducing the above-mentioned additives and lithium salt into the electrolyte, the structure of the SEI film and the CEI film of the battery device using the electrolyte can be promoted to build a stable structure, reduce the case of a large amount of heat generation in the battery due to unintended reactions, improve the overcharge resistance of the battery device, and improve the safety and cycle stability of the battery device.

[0008] Preferably, the nickel-cobalt compound comprises lithium nickel cobalt aluminate LiNi x Co y Al 1-x-y O2, wherein x≥0.8.

[0009] Preferably, the nickel-cobalt compound comprises LiNi 0.8 Co 0.15 Al 0.05 O2.

[0010] Preferably, the lithium salt further comprises at least one of lithium bis(trifluoromethylsulfonyl)imide, lithium bisfluorosulfonylimide, lithium difluoro(oxalato)borate, lithium bis(oxalato)borate, lithium tetracyanoborate, lithium difluorobis(malonato)borate, lithium bisphenylborate, lithium bis(salicylate) diborate.

[0011] Preferably, the content of the lithium salt is 8-15wt% based on the total mass of the electrolyte. When the content of the lithium salt in the electrolyte is within the above range, the chemical stability and ionic conductivity of the electrolyte can be improved, and the cycle stability of the battery device using the electrolyte can be improved.

[0012] Preferably, the solvent comprises at least one of vinylene carbonate, propylene carbonate, γ-butyrolactone, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, dipropyl carbonate, and a carbonic acid ester synthesized from a linear or branched aliphatic monool having 3 to 8 carbon atoms and carbonic acid. Among them, vinylene carbonate, propylene carbonate, γ-butyrolactone, and butylene carbonate belong to cyclic carbonic acid esters, and dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, dipropyl carbonate, and a carbonic acid ester synthesized from a linear or branched aliphatic monool having 3 to 8 carbon atoms and carbonic acid belong to chain carbonic acid esters. That is, the solvent selected for the electrolyte solution comprises a cyclic carbonic acid ester and / or a chain carbonic acid ester.

[0013] Preferably, the solvent comprises vinylene carbonate (EC), dimethyl carbonate (DMC), and ethylmethyl carbonate (EMC).

[0014] Preferably, the mass ratio of vinylene carbonate (EC), dimethyl carbonate (DMC), and ethylmethyl carbonate (EMC) is 2 to 2.5: 5 to 5.5: 2.5 to 3.

[0015] Preferably, the mass ratio of vinylene carbonate (EC), dimethyl carbonate (DMC), and ethylmethyl carbonate (EMC) is 2.3: 5.1: 2.6.

[0016] Preferably, the content of the solvent is 70 to 90 wt% based on the total mass of the electrolyte solution.

[0017] Preferably, the content of the fluorinated vinylene carbonate is 0.2 to 9 wt% based on the total mass of the electrolyte solution. The fluorinated vinylene carbonate within the above content range can promote the electrolyte solution to form a dense, flexible, and low-resistance SEI film on the surface of the negative electrode, facilitate the rapid exchange reaction of charges on the surface of the electrode, improve the cycle performance of the battery, delay the aging of the battery, and prolong the cycle life of the battery without limiting the functions of other components in the electrolyte solution.

[0018] Preferably, the content of the 2,4,6-tris(3,4,5-trifluorophenyl)boroxin is 2wt% and the content of the fluoroethylene carbonate is 7wt% based on the total mass of the electrolyte. The lithium ion battery has good overcharge resistance, can prevent battery failure and potential safety accidents, also helps to maintain the state of health of the battery and maintain its long-term electrochemical performance, creating more progress space for the development of new energy field. Preferably, after the electrolyte is injected into the lithium ion battery, the lithium ion battery after injection is placed in the condition of 22-28℃ for 20-28 hours, and then charged at a current size of I1 for 80-120 minutes, I1≤0.1C, then the lithium ion battery is placed in the condition of 50-70℃ for 20-28 hours, and then the lithium ion battery is placed in the condition of 22-28℃ for 8-16 hours; S2. The lithium ion battery is charged at a current size of I2 to an upper limit voltage U1, and the cutoff current is 90-110mA, wherein 0.4C≤I2≤0.6C, 4.0V≤U1≤4.5V. The lithium ion battery using the above electrolyte and the above formation operation can promote the electrolyte to form a CEI film and a SEI film with good mechanical properties, good structural stability and good thermal stability. First, a lower current is used in the first charging process of constant current charging at I1, and high-temperature standing is performed; the purpose is to age the battery and promote the conversion of part of the organic components in the SEI film to inorganic components to form a more compact and stable SEI film; at the same time, fluoroethylene carbonate (FEC) also participates in the film formation reaction of the SEI film at this stage. Then, in the second charging process of constant current and constant voltage charging at I2, the battery is charged in constant current mode until the battery voltage reaches the upper limit voltage U1, and then converted to constant voltage mode until the charging current drops to the cutoff current, ensuring that the battery is fully charged, to ensure that 2,4,6-tris(3,4,5-trifluorophenyl)boroxin (TTFPB) and lithium hexafluorophosphate (LiPF6) form a structurally stable CEI film.

[0019] Preferably, after S2 is completed, the following operation is further included: S3. The lithium ion battery is discharged at a current size of I3 to a lower limit voltage U2, 0.9C≤I3≤1.1C, 2.0V≤U2≤3.0V. Through the discharging operation in S3, the lithium ion battery is in a low voltage state, thereby reducing the side reactions of the lithium ion battery and improving the storage stability of the lithium ion battery.

[0020] Preferably, S3 further includes performing capacity sorting on the lithium ion battery.

[0021] Preferably, S1 further includes: winding the positive electrode, the separator and the negative electrode in sequence on a winding machine to obtain a winding core, placing the winding core in a cylindrical steel shell, and then performing a liquid injection operation on the cylindrical steel shell.

[0022] According to another aspect of the present application, a battery pack is provided, comprising a plurality of batteries, the battery comprising the above lithium ion battery. Since the voltage and stored energy of the lithium ion battery cell is limited, it is difficult to directly meet the demand of higher voltage, larger power of the electrical appliances, so in most cases, the lithium ion battery is not the battery cell directly providing energy for the electrical appliances, but a battery pack composed of several, dozens, hundreds or even thousands of single battery cells through series connection, parallel connection and other ways to obtain high enough voltage and energy to meet the power demand of different electrical appliances. According to the existing lithium ion battery production process, the uniformity problem of lithium ion battery cannot be fundamentally solved, that is, there will be differences in capacity, internal resistance and other aspects among the single battery cells in the same battery pack. Therefore, when the battery pack works, part of the lithium ion battery will be in overcharge, overdischarge and other abnormal working conditions. By applying the above electrolyte, the overcharge resistance of the lithium ion battery can be improved, thereby improving the safety performance of the battery pack, preventing thermal runaway, and even causing fire and explosion. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 The 16A overcharge test curve schematic diagram of the battery pack composed of the lithium ion battery provided for Example 1;

[0024] Figure 2 The 16A overcharge test curve schematic diagram of the battery pack composed of the lithium ion battery provided for Comparative Example 1. DETAILED DESCRIPTION

[0025] In order to enable persons skilled in the art to better understand the technical solutions in the present application, the technical solutions of the present application will be described clearly and completely below in combination with the drawings of the embodiments and examples of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by persons skilled in the art without creative labor should belong to the protection scope of the present application.

[0026] Example 1

[0027] The present embodiment provides a lithium ion battery, comprising a positive electrode, a negative electrode and a separator between the positive electrode and the negative electrode, further comprising an electrolyte.

[0028] (1) Electrolyte:

[0029] The composition of the electrolyte is shown in Table 1:

[0030] Table 1. Composition of raw materials for preparing electrolyte in Example 1

[0031]

[0032]

[0033] Note: The ratio appearing in Table 1 is a mass ratio, such as "ethylene carbonate: dimethyl carbonate: methyl ethyl carbonate = 2.3:5.1:2.6", that is, the mass ratio of ethylene carbonate, dimethyl carbonate, and methyl ethyl carbonate is 2.3:5.1:2.6, and the mixture is used as a solvent.

[0034] The CAS number of 2,4,6-tris(3,4,5-trifluorophenyl)boroxin is 223440-94-6, and the mass ratio of 2,4,6-tris(3,4,5-trifluorophenyl)boroxin to lithium hexafluorophosphate can be calculated from the above table as 1:5.

[0035] According to the above raw material composition, the electrolyte is prepared according to the following steps: in an argon-filled glove box, first mix the solvent uniformly, then add lithium salt and additives to the solvent, and mix uniformly to obtain the electrolyte.

[0036] (2) Positive electrode:

[0037] The positive electrode includes a positive electrode current collector and a positive electrode active coating, and the positive electrode active coating includes a positive electrode active material lithium nickel cobalt aluminum oxide (LiNi 0.8 Co 0.15 Al 0.05 O2, NCA).

[0038] (3) Negative electrode:

[0039] The negative electrode includes a negative electrode current collector and a negative electrode active coating, and the negative electrode active coating includes a negative electrode active material graphite and silicon carbon.

[0040] (4) Separator:

[0041] The separator includes a substrate and a separation coating, the substrate is selected from a PE substrate, and the separation coating is an Al2O3 ceramic coating.

[0042] (5) Lithium ion battery (cylindrical battery):

[0043] S1. The positive electrode, the separator, and the negative electrode are sequentially wound on a winding machine to obtain a winding core, the winding core is placed in a cylindrical steel shell, the above electrolyte is injected according to an electrolyte injection coefficient of 6.3g / 4Ah, vacuum packaging is performed, and the lithium ion battery is statically placed at 25±3℃ for 24 hours. Then, the lithium ion battery is charged at a constant current (CC) of I1 for 108 minutes, I1 = 0.1C (1C = 4Ah). Then, the lithium ion battery is statically placed at 60℃ for 24 hours, and the lithium ion battery is statically placed at 25±3℃ for 12 hours.

[0044] S2. The lithium ion battery is charged at a constant current and constant voltage of I2 to an upper limit voltage U1, I2 = 0.5C, U1 = 4.2V, and the cutoff current is 100mA.

[0045] S3. Then discharge to the lower limit voltage U2 with the current size of I3 constant current; I3 = 1C, U2 = 2.5V. The lithium ion battery is sorted to obtain the lithium ion battery.

[0046] Example 2

[0047] In this embodiment, a lithium ion battery is prepared by referring to the preparation method provided in Example 1, and the difference between this embodiment and Example 1 is that, in the process of preparing the electrolyte, the addition amount of 2,4,6-tris(3,4,5-trifluorophenyl)boroxin, the solvent and the lithium salt is adjusted, specifically, the content of 2,4,6-tris(3,4,5-trifluorophenyl)boroxin is 0.5wt%. The lithium salt includes lithium hexafluorophosphate and lithium difluoro(oxalato)borate, wherein the content of lithium hexafluorophosphate is 2.5wt%, and the content of lithium difluoro(oxalato)borate is 7.5wt%. The remaining formulation materials and the preparation method are strictly consistent with those of Example 1, especially the mass ratio of 2,4,6-tris(3,4,5-trifluorophenyl)boroxin to lithium hexafluorophosphate is strictly consistent with that of Example 1.

[0048] Example 3

[0049] In this embodiment, a lithium ion battery is prepared by referring to the preparation method provided in Example 1, and the difference between this embodiment and Example 1 is that, in the process of preparing the electrolyte, the addition amount of 2,4,6-tris(3,4,5-trifluorophenyl)boroxin, the lithium salt and the solvent is adjusted, specifically, the content of 2,4,6-tris(3,4,5-trifluorophenyl)boroxin is 3wt%, and the content of lithium hexafluorophosphate is 15wt%. The remaining formulation materials and the preparation method are strictly consistent with those of Example 1, especially the mass ratio of 2,4,6-tris(3,4,5-trifluorophenyl)boroxin to lithium hexafluorophosphate is strictly consistent with that of Example 1.

[0050] Example 4

[0051] In this embodiment, a lithium ion battery is prepared by referring to the preparation method provided in Example 1, and the difference between this embodiment and Example 1 is that, in the process of preparing the electrolyte, the type of lithium salt is adjusted, and the mass ratio of 2,4,6-tris(3,4,5-trifluorophenyl)boroxin to lithium hexafluorophosphate is 1:2.6. Specifically, the lithium salt includes lithium hexafluorophosphate and lithium difluoro(oxalato)borate, the content of lithium hexafluorophosphate is 5.2wt%, and the content of lithium difluoro(oxalato)borate is 4.8wt%. The remaining formulation materials and the preparation method are strictly consistent with those of Example 1.

[0052] In particular, in practical applications, at least one of lithium bis(trifluoromethylsulfonyl)imide, lithium bisfluorosulfonylimide, lithium bis(oxalato)borate, lithium tetracyanoborate, lithium difluorobis(malonato)borate, lithium bisphenylborate, lithium bis(salicylato)diborate can be used instead of lithium difluoro(oxalato)borate in the present embodiment.

[0053] Example 5

[0054] The present embodiment refers to the preparation method provided in Example 1 to prepare a lithium ion battery. The difference between the present embodiment and Example 1 is that in the process of preparing the electrolyte, the contents of 2,4,6-tris(3,4,5-trifluorophenyl)boroxin, lithium salt and solvent are adjusted so that the mass ratio of 2,4,6-tris(3,4,5-trifluorophenyl)boroxin to lithium hexafluorophosphate is 1:26. Specifically, the content of 2,4,6-tris(3,4,5-trifluorophenyl)boroxin is 0.4wt%, and the content of lithium hexafluorophosphate is 10.4wt%. The remaining formulation materials and preparation methods are strictly consistent with those of Example 1.

[0055] Example 6

[0056] The present embodiment refers to the preparation method provided in Example 1 to prepare a lithium ion battery. The difference between the present embodiment and Example 1 is that in the process of preparing the lithium ion battery, the size of I2 is adjusted to 0.3C, and the remaining formulation materials and preparation methods are strictly consistent with those of Example 1.

[0057] Example 7

[0058] The present embodiment refers to the preparation method provided in Example 1 to prepare a lithium ion battery. The difference between the present embodiment and Example 1 is that in the process of preparing the lithium ion battery, the size of I2 is adjusted to 0.7C, and the remaining formulation materials and preparation methods are strictly consistent with those of Example 1.

[0059] Example 8

[0060] The present embodiment refers to the preparation method provided in Example 1 to prepare a lithium ion battery. The difference between the present embodiment and Example 1 is that in the process of preparing the lithium ion battery, the size of I3 is adjusted to 0.8C, and the remaining formulation materials and preparation methods are strictly consistent with those of Example 1.

[0061] Example 9

[0062] The present embodiment refers to the preparation method provided in Example 1 to prepare a lithium ion battery. The difference between the present embodiment and Example 1 is that in the process of preparing the lithium ion battery, the size of I3 is adjusted to 1.2C, and the remaining formulation materials and preparation methods are strictly consistent with those of Example 1.

[0063] Comparative Example 1

[0064] A lithium ion battery was prepared according to the preparation method provided in Example 1. The difference between the present comparative example and Example 1 is that, in the preparation of the electrolyte, the same mass of lithium salt was used instead of 2,4,6-tris(3,4,5-trifluorophenyl)boroxin and fluoroethylene carbonate in Example 1. The remaining formulation materials and preparation method were strictly consistent with Example 1.

[0065] Comparative Example 2

[0066] A lithium ion battery was prepared according to the preparation method provided in Example 1. The difference between the present comparative example and Example 1 is that, in the preparation of the electrolyte, the same mass of lithium salt was used instead of 2,4,6-tris(3,4,5-trifluorophenyl)boroxin and fluoroethylene carbonate in Example 1. The remaining formulation materials and preparation method were strictly consistent with Example 1.

[0067] Comparative Example 3

[0068] A lithium ion battery was prepared according to the preparation method provided in Example 1. The difference between the present comparative example and Example 1 is that, in the preparation of the electrolyte, the addition amount of 2,4,6-tris(3,4,5-trifluorophenyl)boroxin, solvent and lithium salt was adjusted. Specifically, the content of 2,4,6-tris(3,4,5-trifluorophenyl)boroxin was 0.1wt%. The lithium salt included lithium hexafluorophosphate and lithium difluoro(oxalato)borate, wherein the content of lithium hexafluorophosphate was 0.5wt%, and the content of lithium difluoro(oxalato)borate was 9.5wt%. The remaining formulation materials and preparation method were strictly consistent with Example 1, especially the mass ratio of 2,4,6-tris(3,4,5-trifluorophenyl)boroxin to lithium hexafluorophosphate was strictly consistent with Example 1.

[0069] Comparative Example 4

[0070] A lithium ion battery was prepared according to the preparation method provided in Example 1. The difference between the present comparative example and Example 1 is that, in the preparation of the electrolyte, the addition amount of 2,4,6-tris(3,4,5-trifluorophenyl)boroxin, lithium salt and solvent was adjusted. Specifically, the content of 2,4,6-tris(3,4,5-trifluorophenyl)boroxin was 3.5wt%, and the content of lithium hexafluorophosphate was 17.5wt%. The remaining formulation materials and preparation method were strictly consistent with Example 1, especially the mass ratio of 2,4,6-tris(3,4,5-trifluorophenyl)boroxin to lithium hexafluorophosphate was strictly consistent with Example 1.

[0071] Comparative Example 5

[0072] A lithium ion battery was prepared according to the preparation method provided in Example 1. The difference between the present example and Example 1 is that the type of lithium salt was adjusted during the preparation of the electrolyte, so that the mass ratio of 2,4,6-tris(3,4,5-trifluorophenyl)boroxin to lithium hexafluorophosphate was 1:2. Specifically, the lithium salt included lithium hexafluorophosphate and lithium difluoro(oxalato)borate, the content of lithium hexafluorophosphate was 4wt%, and the content of lithium difluoro(oxalato)borate was 6wt%. The remaining formulation materials and preparation method were strictly consistent with Example 1.

[0073] Specifically, in practical applications, at least one of lithium bis(trifluoromethylsulfonyl)imide, lithium bisfluorosulfonylimide, lithium bis(oxalato)borate, lithium tetracyanoborate, lithium difluorobis(malonato)borate, lithium bisphenylborate, and lithium bis(salicylato)diborate can be used instead of lithium difluoro(oxalato)borate in the present example.

[0074] Comparative Example 6

[0075] A lithium ion battery was prepared according to the preparation method provided in Example 1. The difference between the present example and Example 1 is that the content of 2,4,6-tris(3,4,5-trifluorophenyl)boroxin, lithium salt, and solvent was adjusted during the preparation of the electrolyte, so that the mass ratio of 2,4,6-tris(3,4,5-trifluorophenyl)boroxin to lithium hexafluorophosphate was 1:27. Specifically, the content of 2,4,6-tris(3,4,5-trifluorophenyl)boroxin was 0.5wt%, and the content of lithium hexafluorophosphate was 13.5wt%. The remaining formulation materials and preparation method were strictly consistent with Example 1.

[0076] Test Example 1

[0077] Test objects: lithium ion batteries provided in Examples 1-9 and Comparative Examples 1-6.

[0078] Test items and test methods:

[0079] (1) Overcharge resistance: a single cell was discharged at 0.8A to 2.5V, then the cell was welded with a connecting piece (copper-tin alloy, thickness 0.25mm) to form a battery pack (5 strings 2 parallel, 5S2P), the positive and negative electrodes were connected to a power supply, and the battery was charged at a current of 16A and a voltage of 60V for 7 hours or until the voltage no longer increased. Record whether the battery pack showed thermal runaway and the maximum temperature of the battery pack during overcharging.

[0080] (2) Battery cycle performance:

[0081] At room temperature, the battery is discharged at a current of 0.8 A to 2.5 V, and then charged at a constant current of 6 A to 4.2 V to constant voltage charging, until the charging current decreases to 0.1 A, and then the charging is stopped. After charging, it is placed for 10 min. After standing for 1 hour, it is discharged at a current of 0.8 A to 2.5 V, and the initial discharge capacity is calculated (sampling points recorded: 30 s of charging, 60 s of standing after charging, 10 s of discharging, and 120 s of standing after discharging).

[0082] Then the following operations are performed:

[0083] a) At room temperature, the battery is discharged at a current of 0.8 A to 2.5 V, and then charged at a constant current of 4 A to 4.2 V to constant voltage charging, until the charging current decreases to 0.1 A, and then the charging is stopped. After charging, it is placed for 5 min, and then discharged at a current of 4 A to 2.5 V or 75 °C cutoff, and placed for 10 min;

[0084] b) Repeat step a for 500 cycles;

[0085] c) Record the discharge capacity, discharge energy and process temperature of each cycle (sampling points recorded: 30 s of charging, 60 s of standing after charging, 10 s of discharging, and 120 s of standing after discharging).

[0086] Test results: The test results are shown in Table 2. And the 16A overcharge overcharge test curve of the battery pack composed of the lithium ion battery provided by Example 1 is shown in Figure 1 The 16A overcharge overcharge test curve of the battery pack composed of the lithium ion battery provided by Comparative Example 1 is shown in Figure 2 .

[0087] Table 2. Test data measured in this test example

[0088]

[0089] Result analysis:

[0090] By comparing the test performances of Examples 1-9 and Comparative Examples 1-6 in Table 1, it can be found that, compared with Comparative Examples 1-6, the lithium ion batteries provided by Examples 1-9 not only have better overcharge resistance, are less likely to cause thermal runaway, but also have good cycle stability. Among them, the lithium ion battery provided by Example 1 has the best overcharge resistance and cycle capacity retention rate.

[0091] Compared with the lithium ion batteries provided by Comparative Examples 1-2 and Examples 1-9, it can be found that the lithium ion batteries provided by Examples 1-9 have better overcharge resistance, because 2,4,6-tris(3,4,5-trifluorophenyl)boroxin (TTFPB) and lithium hexafluorophosphate (LiPF6) in the electrolyte interact to form a CEI film with good mechanical properties and thermal stability.

[0092] Compared with the lithium ion batteries provided by Comparative Examples 3-4 and Examples 1-3, it can be found that the batteries provided by Examples 1-3 have better overcharge resistance and cycle stability. This shows that when the content of 2,4,6-tris(3,4,5-trifluorophenyl)boroxin is 0.2-3wt%, the lithium ion battery has better overcharge resistance and cycle stability.

[0093] Compared with the lithium ion batteries provided by Comparative Examples 5-6 and Examples 1, 4-5, it can be found that as the mass ratio of 2,4,6-tris(3,4,5-trifluorophenyl)boroxin (TTFPB) to lithium hexafluorophosphate (LiPF6) increases, the overcharge resistance and cycle stability of the lithium ion battery show a trend of first increasing and then decreasing. When the mass ratio of 2,4,6-tris(3,4,5-trifluorophenyl)boroxin to lithium hexafluorophosphate is 1:2.6-26, it is beneficial to form a CEI film with stable structure and good thermal stability in the lithium ion battery, which helps to reduce the internal temperature rise of the battery.

[0094] Further, compared with the lithium ion batteries provided by Example 1 and Examples 6-9, it can be found that during the formation process, as the I2 current increases, the overcharge resistance of the lithium ion battery shows a trend of first increasing and then decreasing. Among them, the lithium ion batteries provided by Examples 1 and 7-8 have better overcharge resistance, because when I2 is in the range of 0.4C-0.6C, it is beneficial for 2,4,6-tris(3,4,5-trifluorophenyl)boroxin (TTFPB) and lithium hexafluorophosphate (LiPF6) to form a CEI film with good mechanical properties, thereby reducing the situation of a large amount of heat generated in the battery due to side reactions and improving the overcharge resistance of the lithium ion battery.

[0095] The above examples are only used to illustrate the technical solutions of the present application and not to limit the protection scope of the present application. Although the present application 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 application can be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present application.

Claims

1. A lithium-ion battery, characterized by, including a positive electrode, a negative electrode, and an electrolyte, an active material of the positive electrode includes a nickel-cobalt compound LiNi x Co y M 1-x-y O2, wherein x≥0.8, M includes at least one of Mn, Al, an active material of the negative electrode includes at least one of graphite, silicon-carbon, The electrolyte comprises 2,4,6-tris(3,4,5-trifluorophenyl)boroxin, fluorinated ethylene carbonate, lithium salt and solvent, wherein the lithium salt comprises lithium hexafluorophosphate; The content of the 2,4,6-tris(3,4,5-trifluorophenyl)boroxin is 0.2-3wt% based on the total mass of the electrolyte, and the mass ratio of the 2,4,6-tris(3,4,5-trifluorophenyl)boroxin to the lithium hexafluorophosphate is 1:2.6-26. The formation process of the lithium ion battery comprises the following operations: S1. After the electrolyte is injected into the lithium ion battery, the lithium ion battery after injection is placed in a condition of 22-28℃ for 20-28 hours, then the lithium ion battery is charged at a constant current of I1 for 80-120 minutes, I1≤0.1 C, then the lithium ion battery is placed in a condition of 50-70℃ for 20-28 hours, and then the lithium ion battery is placed in a condition of 22-28℃ for 8-16 hours; S2. The lithium ion battery is charged at a constant current and constant voltage of I2 to an upper limit voltage U1, and the cutoff current is 90-110mA, wherein 0.4C≤I2≤0.6C and 4.0V≤U1≤4.5V.

2. The lithium-ion battery of claim 1, wherein, The lithium salt further comprises at least one of lithium bis(trifluoromethylsulfonyl)imide, lithium bisfluorosulfonylimide, lithium difluoro(oxalato)borate, lithium bis(oxalato)borate, lithium tetracyanoborate, lithium difluorobis(malonato)borate, lithium bisphenylborate and lithium bis(salicylato)diborate.

3. The lithium-ion battery of claim 1, wherein the lithium-ion battery is a lithium-ion battery. The content of the lithium salt is 8-15wt% based on the total mass of the electrolyte.

4. The lithium-ion battery of claim 1, wherein the lithium-ion battery is a lithium-ion battery. The solvent comprises at least one of vinyl carbonate, propylene carbonate, γ-butyrolactone, butylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, dipropyl carbonate and carbonic acid ester synthesized from linear or branched aliphatic monohydric alcohol with carbon atom number of 3-8.

5. The lithium-ion battery of claim 4, wherein the lithium-ion battery is a lithium-ion battery. The solvent comprises vinyl carbonate, dimethyl carbonate and methyl ethyl carbonate.

6. The lithium-ion battery of claim 4, wherein the lithium-ion battery is a lithium-ion battery. The content of the solvent is 70-90wt% based on the total mass of the electrolyte.

7. The lithium-ion battery as described in claim 1, characterized in that, The content of the fluorinated ethylene carbonate is 0.2-9wt%.

8. The lithium-ion battery of claim 1, wherein, After the S2 is completed, the following operation is further included: S3. The lithium ion battery is discharged at a constant current of I3 to a lower limit voltage U2, wherein 0.9C≤I3≤1.1C and 2.0V≤U2≤3.0V.

9. A battery pack characterized by comprising: The battery comprises the lithium ion battery according to any one of claims 1-8.

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