High-safety lithium ion battery

Abstract

The invention belongs to the technical field of batteries, and particularly relates to a high-safety lithium ion battery which comprises a positive electrode, a negative electrode, a diaphragm and an electrolyte, the electrolyte comprises a boron-containing lithium salt additive and an additive shown as a structural formula 1, in the structural formula 1, at least one of R2, R3, R4 and R5 is a halogen atom,-CF3,-COCH3,-COCF3,-COOCH3,-NHCOCF3,-NO2,-COH,-SO3H,-CCl3 and a maleimide group, and in the structural formula 1, at least one of R2, R3, R4 and R5 is a halogen atom,-CF3,-COCF3,-COOCH3,-NHCOCF3,-NO2,-COH,-SO3H,-CCl3 and a maleimide group. The rest are respectively and independently selected from H, alkyl or halogenated alkyl of C1-C12, cycloalkyl or halogenated cycloalkyl of C5-C7, alkenyl or halogenated alkenyl of C2-C12, alkoxy or halogenated alkoxy of C1-C12, aromatic hydrocarbon and derivatives thereof; r1 is selected from H, alkyl or halogenated alkyl of C1-C12, naphthenic base or halogenated naphthenic base of C5-C7, alkenyl or halogenated alkenyl of C2-C12, alkoxy or halogenated alkoxy of C1-C12, and aromatic hydrocarbon group. According to the invention, the overcharge and thermal runaway risks are reduced, the safety performance of the lithium ion battery is improved, and the battery performance is not obviously degraded.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion batteries, and particularly relates to a high-safety lithium ion battery. BACKGROUND

[0002] Lithium ion batteries are widely used in electronic products, new energy vehicles and other fields due to high energy density, high power output and long service life. With the increasing demand for energy density of terminals, lithium ion batteries gradually develop towards high voltage, and some positive electrode materials such as ternary NCM and lithium manganate also develop towards high nickel content or doping of nickel elements. However, the safety is decreased, which cannot meet the application in the field of electric vehicles.

[0003] At present, the safety protection of lithium ion batteries mainly focuses on preventing lithium ion overcharge and preventing thermal runaway in two main directions, and the modification of the material end, especially the electrolyte end, is more mainstream. For overcharge protection, the electrolyte end will select overcharge protection additives for protection, such as diphenyl BP, cyclohexylbenzene CHB, etc., which generates a high-resistance interface by high-voltage ring-opening polymerization to block the current and prevent overcharge; for thermal runaway, the main way is to remove free radicals to block thermal runaway, such as using phosphate solvents. However, whether it is an overcharge protection additive or a solvent for blocking thermal runaway, the performance of the battery is obviously deteriorated, and the function is single, the overcharge protection additive has a slight effect on thermal runaway, and the solvent or additive for blocking thermal runaway is difficult to prevent overcharge, so it is difficult to have large-scale commercial application. Therefore, a solution is needed in the material end, which does not significantly deteriorate the performance of the battery, but can improve the safety performance in multiple aspects. SUMMARY

[0004] Therefore, the purpose of the application is to provide a high-safety lithium ion battery to solve the technical problem that the overcharge protection and thermal runaway blocking additives in the prior art obviously deteriorate the performance of the battery, and the function is single, and the safety cannot meet the application in the field of electric vehicles.

[0005] To achieve the above purpose, the technical scheme provided by the application is as follows:

[0006] A high-safety lithium ion battery, comprising a positive electrode, a negative electrode, a separator and an electrolyte, wherein the electrolyte comprises a boron-containing lithium salt additive and an additive as shown in structural formula 1:

[0007]

[0008] Structural formula 1,

[0009] wherein at least one of R2, R3, R4, R5 is selected from a halogen atom, -CF3, -COCH3, -COCF3, -COOCH3, -NHCOCF3, -NO2, -COH, -SO3H, -CCl3, a maleimide group, and the rest are each independently selected from H, C1-C12 alkyl or halogenated alkyl, C5-C7 cycloalkyl or halogenated cycloalkyl, C2-C12 alkenyl or halogenated alkenyl, C1-C12 alkoxy or halogenated alkoxy, aromatic hydrocarbon group and derivatives thereof;

[0010] R1 is selected from H, C1-C12 alkyl or halogenated alkyl, C5-C7 cycloalkyl or halogenated cycloalkyl, C2-C12 alkenyl or halogenated alkenyl, C1-C12 alkoxy or halogenated alkoxy, aromatic hydrocarbon group and derivatives thereof;

[0011] The diaphragm comprises a base film and a ceramic layer on at least one side surface of the base film, and the ceramic layer comprises a ceramic material.

[0012] Further, the additive shown in the structural formula 1 comprises at least one of the following compounds:

[0013] Compound 1 Compound 2 Compound 3

[0014]

[0015] Compound 4 Compound 5 Compound 6

[0016]

[0017] Compound 7 Compound 8 Compound 9

[0018]

[0019] Compound 10 Compound 11 Compound 12.

[0020] Further, the boron-containing lithium salt additive is one or more of lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium tetraphenylborate, lithium chloroborane.

[0021] Further, the content of the additive shown in the structural formula 1 is 0.05-5% based on 100% of the total weight of the electrolyte.

[0022] Furthermore, based on the total weight of the electrolyte (100%), the content of the boron-containing lithium salt additive is 0.05-3%.

[0023] Furthermore, the positive electrode includes a positive electrode material layer containing a positive electrode active material, wherein the positive electrode active material is LiNi. x M y O z M contains one or more of the elements Co, Mn, Al, Fe, Cu, Sb, Na, Mg, Ti, Zr, K, and Nb, and 0.5 ≤ x < 1, 0 < y ≤ 2, and 2 ≤ z ≤ 4.

[0024] Furthermore, the negative electrode includes a negative electrode material layer comprising a negative electrode active material, wherein the negative electrode active material is selected from one or more of carbon materials and silicon-based materials; and / or,

[0025] The carbon material is one or more of the following: artificial graphite, natural graphite, composite graphite, graphene, and hard carbon; and / or,

[0026] The silicon-based material is one or more of silicon materials, silicon oxide materials, and silicon carbon materials.

[0027] The electrolyte further includes auxiliary additives, which are one or more selected from vinylene carbonate, fluoroethylene carbonate, vinyl sulfate, and lithium difluorophosphate; and / or,

[0028] The content of the auxiliary additives is 0.05-5% based on the total weight of the electrolyte (100%).

[0029] Furthermore, the ceramic material is at least one selected from alumina, silicon oxide, barium oxide, zirconium oxide, titanium oxide, magnesium oxide, magnesium hydroxide, boron nitride, aluminum nitride, magnesium nitride, zeolite, and boehmite.

[0030] Furthermore, the thickness of the ceramic layer is 1 to 5 micrometers.

[0031] The beneficial effects of this invention are as follows:

[0032] The high-safety lithium-ion battery provided by this invention has an additive shown in Structural Formula 1 that can respond to both temperature and voltage. When the temperature or voltage rises rapidly, the additive shown in Structural Formula 1 can rapidly polymerize at the positive electrode interface to generate a thermally stable and insulating resin gel, which effectively suppresses chemical crosstalk and electrochemical reactions between the positive and negative electrodes, significantly increases the thermal runaway critical temperature of the battery, and improves the safety performance of the battery.

[0033] During the first charge and discharge cycle of this high-safety lithium-ion battery, the additive shown in Formula 1 undergoes a small amount of polymerization, forming a uniform, LiF-rich, and high-temperature-resistant CEI / SEI composition, thereby helping to improve the battery's high-temperature calendar life. However, if the additive shown in Formula 1 polymerizes excessively during the first charge cycle at higher concentrations, it can still degrade the battery's initial impedance. The boron-containing lithium salt additive, with its free radical scavenging effect, can inhibit some of the polymerization of the additive shown in Formula 1 during the first charge cycle, mitigating the degradation of battery impedance caused by the additive shown in Formula 1.

[0034] The ceramic-coated separator significantly inhibits thermal shrinkage under high-temperature conditions, thereby significantly increasing the upper limit of the separator's operating temperature and thus raising the battery's thermal runaway temperature. The auxiliary additives can form an interfacial film during the first charge, further reducing the polymerization of the additives shown in Structural Formula 1 under normal operating conditions, thereby reducing impedance and enhancing the safety performance improvement effect of the additives shown in Structural Formula 1. Simultaneously, it further improves capacity retention and gas generation under high-temperature storage.

[0035] The high-safety lithium-ion battery of this invention meets the high energy density requirements of end users for lithium-ion batteries while reducing the risk of overcharging and thermal runaway, significantly improving the safety performance of lithium-ion batteries without significantly degrading battery performance. It overcomes the shortcomings of Ni-containing cathode materials, whose safety performance is reduced due to structural mixing and other reasons, which limits their application in the market. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of the invention clearer, the technical solutions will be described more clearly and in detail below with reference to comparative examples and embodiments of the invention. Obviously, the described embodiments are only a part of the invention, not all of them. Other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort should fall within the protection scope of the invention.

[0037] This invention provides a high-safety lithium-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte comprises a boron-containing lithium salt additive and an additive as shown in structural formula 1:

[0038]

[0039] Structural Formula 1,

[0040] Wherein, at least one of R2, R3, R4, and R5 is selected from halogen atoms, -CF3, -COCH3, -COCF3, -COOCH3, -NHCOCF3, -NO2, -COH, -SO3H, -CCl3, maleimide groups, and the rest are each independently selected from H, C1-C12 alkyl or haloalkyl, C5-C7 cycloalkyl or halocycloalkyl, C2-C12 alkenyl or haloalkenyl, C1-C12 alkoxy or haloalkoxy, aromatic hydrocarbon groups and their derivatives;

[0041] R1 is selected from H, C1-C12 alkyl or haloalkyl, C5-C7 cycloalkyl or halocycloalkyl, C2-C12 alkenyl or haloalkenyl, C1-C12 alkoxy or haloalkoxy, aromatic hydrocarbon groups and their derivatives.

[0042] The diaphragm includes a base membrane and a ceramic layer located on at least one side of the base membrane, the ceramic layer comprising a ceramic material.

[0043] Specifically, the compound shown in structural formula 1 includes any one of the compounds in Table 1:

[0044] Table 1

[0045] Specifically, the preparation method of compound 2 shown in structural formula 1 is as follows:

[0046] Step 1: Synthesize N,N-dimethylethanolamine by reacting aniline and paraformaldehyde in a specific ratio with 1,4-dioxane (under alkaline conditions; heating at 40°C).

[0047]

[0048] Step 2: Dissolve p-trifluoromethylphenol in 1,4-dioxane, then mix with N,N-dimethylethanolamine and stir while heating to obtain compound 2 (alkaline conditions; heating at 90°C).

[0049]

[0050] After the reactants have cooled, the solvent is removed by rotary evaporation, followed by washing in dichloromethane and sodium chloride aqueous solution, and then drying to obtain the product.

[0051] To obtain other compounds, simply replace aniline with... Replace trifluoromethylphenol with R1, R2, R3, R4, and R5 can be selected from the above groups.

[0052] The high-safety lithium-ion battery provided by this invention can achieve dual response to temperature and voltage by adding the additive shown in Structural Formula 1 to the electrolyte. When the temperature or voltage rises rapidly, the additive shown in Structural Formula 1 can rapidly polymerize at the positive electrode interface to generate a thermally stable and insulating resin gel, effectively suppressing chemical crosstalk and electrochemical reactions between the positive and negative electrodes, significantly increasing the battery's thermal runaway critical temperature, and improving the battery's safety performance.

[0053] During the first charge and discharge of the battery, the additive shown in Formula 1 undergoes a small amount of polymerization, forming a uniform, LiF-rich, and high-temperature-resistant CEI / SEI composition, thereby helping to improve the battery's high-temperature calendar life. However, if the additive shown in Formula 1 polymerizes excessively during the first charge at higher concentrations, it can still degrade the battery's initial impedance. Boron-containing lithium salt additives, on the other hand, possess a certain free radical scavenging effect, which can inhibit some of the polymerization of the additive shown in Formula 1 during the first charge, mitigating the degradation of battery impedance caused by the additive shown in Formula 1.

[0054] The use of ceramic coating on the separator can significantly suppress the thermal shrinkage of the separator under high temperature conditions, thereby significantly increasing the upper limit of the separator's operating temperature and thus raising the thermal runaway temperature of the battery.

[0055] Specifically, as one embodiment of the present invention, the content of the additive shown in structural formula 1 is 0.05-5% based on 100% of the total weight of the electrolyte. Preferably, the content of the additive shown in structural formula 1 is 0.1-3%. More specifically, the content of the additive shown in structural formula 1 is within any two of the following ranges: 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.6%, 0.8%, 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.2%, 2.4%, 2.6%, 2.8%, 3.0%, 3.2%, 3.4%, 4.0%, 4.5%, 5.0%.

[0056] Specifically, in one embodiment of the present invention, the content of the boron-containing lithium salt additive is 0.05-3% based on 100% of the total weight of the electrolyte. Preferably, the content of the boron-containing lithium salt additive is 0.2-2%. More specifically, the content of the boron-containing lithium salt additive is in the range of any two of the following: 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.6%, 0.8%, 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.2%, 2.4%, 2.6%, 2.8%, 3.0%.

[0057] Specifically, as one embodiment of the present invention, the boron-containing lithium salt additive is one or more of lithium tetrafluoroborate B1, lithium bis(oxalate)borate B2, lithium difluorooxalateborate B3, lithium tetraphenylborate B4, and lithium chloroborane B5.

[0058] The electrolyte also includes an organic solvent selected from one or more of the following: ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, fluoroethylene carbonate, γ-butyrolactone, sulfolane, dimethyl sulfone, ethyl acetate, ethyl propionate, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, and triethylene glycol dimethyl ether.

[0059] Specifically, in one embodiment of the present invention, the positive electrode includes a positive electrode material layer containing a positive electrode active material, wherein the positive electrode active material is LiNi. x M y O z M contains one or more of the elements Co, Mn, Al, Fe, Cu, Sb, Na, Mg, Ti, Zr, K, and Nb, and 0.5 ≤ x < 1, 0 < y ≤ 2, and 2 ≤ z ≤ 4.

[0060] Ni-containing cathode materials can provide high capacity, meeting the high energy density requirements of end-user lithium-ion batteries. This invention improves the safety performance of lithium-ion batteries and reduces the risks of overcharging and thermal runaway by adding the additive shown in Structural Formula 1 and boron-containing lithium salt additives to the electrolyte, without significantly degrading battery performance. This overcomes the drawback of Ni-containing cathode materials, where the safety performance is reduced due to structural mixing, limiting their market application.

[0061] Specifically, as one embodiment of the present invention, the negative electrode includes a negative electrode material layer comprising a negative electrode active material, wherein the negative electrode active material is selected from one or more of carbon materials and silicon-based materials; and / or,

[0062] The carbon material is one or more of the following: artificial graphite, natural graphite, composite graphite, graphene, and hard carbon; and / or,

[0063] The silicon-based material is one or more of silicon materials, silicon oxide materials, and silicon carbon materials.

[0064] Preferably, the carbon material is artificial graphite; the silicon material is nano-silicon; and the silicon oxide material is SiO2. β Materials, where 0 ≤ β < 2;

[0065] More specifically, the silicon-carbon material is a silicon-based material containing silicon and carbon materials, and / or containing SiO2. αThe carbon material is selected from one or more of artificial graphite, natural graphite, composite graphite, graphene, and hard carbon, wherein 0 ≤ α < 2. Preferably, the silicon-carbon material is a silicon-based material of artificial graphite.

[0066] The electrolyte further includes auxiliary additives, which are one or more selected from vinylene carbonate C1, fluoroethylene carbonate C2, ethylene sulfate C3, and lithium difluorophosphate C4; and / or,

[0067] The content of the auxiliary additive is 0.05-5% based on 100% of the total weight of the electrolyte. Preferably, the content is 0.1-5%; more preferably, the content is 0.1-2%. Specifically, the content of any one optional substance in the auxiliary additive can be 0.05%, 0.08%, 0.1%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.5%, 5%, or any combination of these values.

[0068] The auxiliary additives can form an interfacial film during the first charge, further reducing the polymerization of the additives shown in Formula 1.

[0069] More specifically, the base membrane is at least one of polypropylene (PP), polyethylene (PE), aramid, polyester, cellulose, polyimide, and polyamide. Preferably, the base membrane is selected from a PP / PE / PP three-layer composite membrane.

[0070] Specifically, in one embodiment of the present invention, the ceramic material is at least one selected from alumina, silicon oxide, barium oxide, zirconium oxide, titanium oxide, magnesium oxide, magnesium hydroxide, boron nitride, aluminum nitride, magnesium nitride, zeolite, and boehmite. Preferably, the ceramic layer is selected from alumina.

[0071] More specifically, the thickness of the ceramic layer is 1 to 5 micrometers.

[0072] The present invention will be further explained and illustrated below through specific embodiments.

[0073] Unless otherwise specified, all reagents, materials, and instruments used in the following description are conventional reagents, materials, and instruments, all of which are commercially available. The reagents involved can also be synthesized using conventional synthetic methods. Unless otherwise specified, the methods in the examples are conventional methods in the art. Monomers conforming to this invention are commercially available.

[0074] The additives used in each example and comparative example were selected from the compounds in Table 2.

[0075] Table 2

[0076] Example 1

[0077] (1) Cathode preparation: The cathode active material LiNi was mixed in a mass ratio of 96.2:1.5:0.5:1.8. 0.8 Co 0.1 Mn 0.1 O2, conductive carbon black, carbon nanotube conductive agent and binder polyvinylidene fluoride are dispersed in N-methyl-2-pyrrolidone to obtain a positive electrode slurry. The positive electrode slurry is uniformly coated on both sides of an aluminum foil, and after drying, calendering and vacuum drying, aluminum leads are welded on using an ultrasonic welding machine to obtain a positive electrode plate. The coating thickness is between 60-140 μm.

[0078] (2) Negative electrode preparation: Artificial graphite, conductive carbon black, styrene-butadiene rubber binder and carboxymethyl cellulose are mixed in a mass ratio of 95.2:1:2.4:1.4 and dispersed in deionized water to obtain a negative electrode slurry. The negative electrode slurry is coated on both sides of copper foil, dried, rolled and vacuum dried, and nickel leads are welded on using an ultrasonic welding machine to obtain the negative electrode.

[0079] (3) Electrolyte preparation: Ethyl carbonate, ethyl methyl carbonate and dimethyl carbonate are mixed in a volume ratio of EC:EMC:DMC = 30:40:30. After mixing, lithium hexafluorophosphate with a concentration of 1.05 mol / L is added, along with the additives shown in structural formula 1, boron-containing lithium salt additives, and auxiliary additives of 0.5% vinylene carbonate, 0.7% lithium difluorophosphate and 1.5% ethylene sulfate.

[0080] (4) Separator preparation: The separator is made of a 15-micron base membrane composed of polypropylene, polyethylene and polypropylene, with 2-micron alumina ceramic particles coated on the base membrane.

[0081] (5) Battery assembly: Place a separator between the positive plate and the negative plate, then wind the sandwich structure composed of the positive plate, the negative plate and the separator, flatten the wound body and put it into a square aluminum-plastic shell, weld the lead wires of the positive and negative electrodes to the nickel tabs and aluminum tabs respectively, seal the opening and vacuum to obtain the cell to be injected with liquid.

[0082] The electrolyte prepared above is injected into the cell through the injection hole, ensuring that the electrolyte fills all the gaps in the cell. Then, the first charge is performed according to the following steps: constant current charging at 0.05C for 3 hours, constant current charging at 0.2C for 2 hours, constant current charging at 0.5C for 2 hours, resting for 1 hour, shaping and sealing, and then further charging at a constant current of 0.2C to 4.25V, resting for 0.5 hours, and then discharging at a constant current of 0.2C to 3.0V.

[0083] Example 2-44

[0084] The main differences between Examples 2-44 and Example 1 are: the types and contents of additives shown in Structure 1, the types and contents of boron-containing lithium salt additives, the types and contents of auxiliary additives, and the type of ceramic layer; all other steps are the same. See Table 1 for details.

[0085] Comparative Examples 1-3

[0086] The comparative examples are used to illustrate the lithium battery disclosed in this invention, including most of the operating steps in Example 1, with the only difference being the composition of the electrolyte and the presence or absence of a ceramic layer.

[0087] Table 1

[0088] Performance testing: The lithium-ion batteries prepared in the above examples and comparative examples were subjected to the following tests.

[0089] (1) Initial DCIR

[0090] The battery was placed in a 25°C constant temperature test chamber and left to stand for 4 hours. Then, it was run at a constant temperature, charged at 0.5 C to the upper limit voltage, with a cutoff current of 0.05 C, left to stand for 10 minutes, and then discharged at a constant current of 0.5 C with a cutoff capacity of 0.5 C. After standing for 30 minutes, it was discharged at a constant current of 2 C I for 10 seconds, and the discharge start voltage U1 and discharge cutoff voltage U2 were recorded.

[0091] Initial DCIR = (U1-U2) / I*1000, in milliohms.

[0092] (2) High-temperature storage capacity retention rate

[0093] At room temperature, the battery is charged at a constant current and constant voltage of 0.5 C to the upper limit voltage, with a cutoff voltage of 0.05 C. It is then allowed to rest for 5 minutes, followed by a constant current discharge at 0.5 C to 3.0 V, and a rest for 5 minutes. This cycle is repeated twice, with the discharge capacity of the last cycle as the initial value V. The battery is then charged at a constant current and constant voltage of 0.5 C to the upper limit voltage, with a cutoff voltage of 0.05 C. It is then placed in a 60℃ constant temperature test chamber for n days before being tested. The discharge capacity at a constant current of 0.5 C to 3.0 V is recorded as Vn.

[0094] High-temperature gas production rate over n days = (Vn - Vinitial) / Vinitial * 100%.

[0095] (3) Thermal shock test

[0096] Charge the batteries to 4.25V using a constant current and constant voltage method at 0.5C, with a cutoff current of 0.05C. Two batteries are used in each group. The batteries are placed in an explosion-proof test chamber and heated from room temperature at a rate of 5℃ / min, with an upper limit of 250℃. Temperature changes during heating are monitored, and the average temperature at which the batteries ignite and explode is recorded.

[0097] (4) Overcharge test

[0098] The battery was placed in an explosion-proof test chamber and charged at a constant current of 1C until it was cut off at 10V. The temperature change during overcharging was monitored, and the highest temperature of the battery during overcharging was recorded.

[0099] Table 2 shows the performance of the lithium-ion batteries prepared in Examples 1-11 and Comparative Examples 1-3.

[0100] Table 2

[0101] As shown in Table 2, the test results of Examples 1-11 and Comparative Examples 1-3 indicate that Example 1 introduced additive compound 2 (shown in Structural Formula 1), lithium difluorooxalate borate B3, and alumina ceramic layer. The initial DCIR of the lithium-ion battery in Example 1 was 35.7 milliohms, the capacity retention rate after 30 days of high-temperature storage was 92.3%, the gas production rate was 4.3%, the ignition temperature in the thermal shock test was 182°C, and the maximum temperature in the overcharge test was 72°C. In contrast, Comparative Example 2, which did not use the compound shown in Structural Formula 1, had a capacity retention rate of 87.2% after 30 days of high-temperature storage, a gas production rate of 21.4%, and an ignition temperature of only 154°C in the thermal shock test. It also ignited directly in the overcharge test, which was significantly worse than Example 1. This is because the additive shown in Structural Formula 1 can rapidly polymerize at the positive electrode interface under thermal and voltage abuse, generating a thermally stable and insulating resin gel. This effectively suppresses chemical crosstalk and electrochemical reactions between the positive and negative electrodes, significantly increasing the battery's thermal runaway critical temperature and improving battery safety. Simultaneously, the polymerization of a small amount of the additive shown in Structural Formula 1 facilitates the formation of a uniform, LiF-rich, and high-temperature-resistant CEI / SEI composition, thereby contributing to improved high-temperature calendar life of the battery. In Comparative Example 1, without the use of lithium difluorooxalate borate B3, the DCIR is 44.3 milliohms, and the ignition temperature during thermal shock testing is 173°C, with the highest overcharge test temperature rising to 85°C. This is due to the boron-containing lithium salt additive, boron difluorooxalate borate. Lithium oxide has a certain free radical scavenging effect. Under normal battery operating conditions, it inhibits the polymerization of some additives shown in Structural Formula 1, alleviates the degradation of battery impedance caused by additives shown in Structural Formula 1, and prevents the polymerization of additives shown in Structural Formula 1 under normal battery operating conditions. It also helps to improve the protective effect of additives shown in Structural Formula 1 under thermal abuse and voltage abuse conditions. In Comparative Example 3, without the use of a separator with ceramic material coating, the ignition temperature in the thermal shock test decreased to 171°C, and the maximum temperature in the overcharge test increased to 77°C. This is because the separator with ceramic material coating can significantly inhibit the thermal shrinkage of the separator under high temperature environment, which significantly increases the upper limit of the separator's operating temperature and further improves the thermal runaway temperature of the battery.

[0102] As can be seen from the test results in Table 2, the present invention uses a ceramic material coated separator and controls the content of additives as shown in Formula 1 within a certain range. This allows for the generation of a thermally uniform, LiF-rich, and high-temperature resistant CEI / SEI component at the positive electrode interface when the temperature or voltage rises rapidly. This effectively suppresses chemical crosstalk and electrochemical reactions between the positive and negative electrodes, significantly increases the thermal runaway critical temperature of the battery, and improves the battery's safety performance.

[0103] Comparing Examples 1-9 with Examples 10-11, Example 10 has a low content of Structural Formula 1, which does not significantly improve the capacity retention rate and gas production rate under high temperature storage, nor does it improve safety performance. Example 11 has a high content of Structural Formula 1, which leads to severe self-polymerization, resulting in severe deterioration of initial impedance and deterioration of capacity retention rate under high temperature storage.

[0104] Table 3 shows the performance of the lithium-ion batteries prepared in Examples 12-22.

[0105] Table 3

[0106] As can be seen from the test results in Table 3, the different types of compounds of structural formula 1 used in this invention can all generate thermally uniform, LiF-rich and high-temperature resistant CEI / SEI components at the positive electrode interface when the temperature or voltage rises rapidly. This helps to improve the high-temperature calendar life of the battery, improve the capacity retention rate and gas generation rate during high-temperature storage, and enhance safety performance.

[0107] Table 4 shows the performance of the lithium-ion batteries prepared in Examples 23-32.

[0108] Table 4

[0109] As shown in the test results of Examples 23-30 in Table 4, the present invention, by controlling the content of boron-containing lithium salt additive within a certain range, can inhibit the polymerization of some additives shown in Structural Formula 1 during the first charge, thus alleviating the degradation of battery impedance caused by the additives shown in Structural Formula 1. As shown in the test results of Examples 31-32, when the content of boron-containing lithium salt additive is too low, it is preferentially consumed during the first charge, failing to clear the free radicals generated by the additives shown in Structural Formula 1, and thus failing to inhibit the polymerization of the additives shown in Structural Formula 1, resulting in a higher impedance; when the content is too high, the initial impedance is significantly degraded.

[0110] Table 5 shows the performance of the lithium-ion batteries prepared in Examples 33-36.

[0111] Table 5

[0112] As can be seen from the test results of Examples 33-34 in Table 5, different types of boron-containing lithium salt additives can inhibit the polymerization of some additives shown in Structural Formula 1 during the first charging process, and alleviate the degradation of battery impedance caused by the additives shown in Structural Formula 1.

[0113] Table 6 shows the performance of the lithium-ion batteries prepared in Examples 37-40.

[0114] Table 6

[0115] As shown in Table 6, the test results of Examples 37-39 indicate that different types of auxiliary additives can all form an interfacial film during the first charge, further reducing the polymerization of the additive shown in Structural Formula 1 under normal operating conditions, thereby reducing impedance and improving the safety performance of the additive shown in Structural Formula 1. Simultaneously, it further improves capacity retention and gas generation under high-temperature storage. Example 40 did not contain any auxiliary additives, therefore its initial DCIR was high, and its gas generation rate was also higher than that of Examples 37-39.

[0116] Table 7 shows the performance of the lithium-ion batteries prepared in Examples 41-44.

[0117] Table 7

[0118] As can be seen from the test results of Examples 41-44 in Table 7, lithium-ion batteries with low initial DCIR and high safety performance can still be obtained by using ceramic layers of different materials, which shows that the present invention has universality for different positive electrode active materials.

[0119] The examples above are merely illustrative of the invention and do not constitute a limitation on the scope of protection of the invention. Any design that is the same as or similar to the invention falls within the scope of protection of the invention.

Claims

1. A high safety lithium-ion battery, characterized in that, The battery includes a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte includes a lithium salt containing boron additive and an additive as shown in structural formula 1: Structure 1, wherein at least one of R2, R3, R4, and R5 is selected from a halogen atom, -CF3, -COCH3, -COCF3, -COOCH3, -NHCOCF3, -NO2, -COH, -SO3H, -CCl3, a maleimide group, and the rest are each independently selected from H, C1-C12 alkyl or halogenated alkyl, C5-C7 cycloalkyl or halogenated cycloalkyl, C2-C12 alkenyl or halogenated alkenyl, C1-C12 alkoxy or halogenated alkoxy, aromatic hydrocarbon group and derivatives thereof; R1 is selected from H, C1-C12 alkyl or halogenated alkyl, C5-C7 cycloalkyl or halogenated cycloalkyl, C2-C12 alkenyl or halogenated alkenyl, C1-C12 alkoxy or halogenated alkoxy, aromatic hydrocarbon group and derivatives thereof; The separator includes a base film and a ceramic layer on at least one side surface of the base film, and the ceramic layer includes a ceramic material.

2. The high safety lithium-ion battery according to claim 1, characterized in that, The additive as shown in structural formula 1 includes at least one of the following: Compound 1 Compound 2 Compound 3 Compound 4 Compound 5 Compound 6 Compound 7 Compound 8 Compound 9 Compound 10 Compound 11 Compound 12.

3. The high safety lithium-ion battery according to claim 1, wherein, The lithium salt containing boron additive is one or more of lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium tetraphenylborate, and lithium chloroborane.

4. The high safety lithium-ion battery of claim 1, wherein, The content of the additive as shown in structural formula 1 is 0.05-5% based on 100% of the total weight of the electrolyte.

5. The high safety lithium-ion battery of claim 1, wherein, The content of the lithium salt containing boron additive is 0.05-3% based on 100% of the total weight of the electrolyte.

6. The high safety lithium-ion battery of claim 1, wherein, The positive electrode includes a positive electrode material layer containing a positive electrode active material, the positive electrode active material being LiNi x M y O z wherein M contains one or more elements selected from the group consisting of Co, Mn, Al, Fe, Cu, Sb, Na, Mg, Ti, Zr, K, Nb, and 0.5 ≤ x < 1, 0 < y ≤ 2, and 2 ≤ z ≤ 4.

7. The high safety lithium-ion battery of claim 1, wherein, The negative electrode includes a negative electrode material layer containing a negative electrode active material, and the negative electrode active material is selected from one or more of carbon materials, silicon-based materials; and / or, The carbon material is one or more of artificial graphite, natural graphite, composite graphite, graphene, and hard carbon; and / or, The silicon-based material is one or more of silicon material, silicon oxide material, and silicon-carbon material.

8. The high safety lithium-ion battery of claim 1, wherein, The electrolyte further includes an auxiliary additive, and the auxiliary additive is one or more of vinylene carbonate, fluoroethylene carbonate, vinyl sulfate, and lithium difluorophosphate; and / or, The content of the auxiliary additive is 0.05-5% based on 100% of the total weight of the electrolyte.

9. The high safety lithium-ion battery of claim 1, wherein, The ceramic material is at least one of alumina, silica, barium oxide, zirconium oxide, titanium oxide, magnesium oxide, magnesium hydroxide, boron nitride, aluminum nitride, magnesium nitride, zeolite, and boehmite.

10. The high safety lithium-ion battery of claim 1, wherein, The thickness of the ceramic layer is 1-5 microns.

Images