Lithium ion battery additive and lithium ion battery

Abstract

The invention relates to the technical field of lithium ion batteries, in particular to a lithium ion battery additive A, a lithium ion battery additive B and a lithium ion battery. The additive A has a compound as shown in a formula I, and in the formula I, R1-R4 are independently selected from hydrogen, C1-C5 alkyl, C2-C5 alkyl containing C = C, or a group containing an acrylate group, an acrylamide group, a borate group, an amino group, an isocyanate group and a hydroxyl group; r < 5 > to R < 8 > are respectively and independently selected from hydrogen, halogen, hydroxyl, C1-C5 alkyl and C2-C5 alkyl containing C = C. The additive provided by the invention can effectively improve the thermal safety of the battery and reduce the heat release rate and release amount of thermal runaway on the premise of not influencing the cycle life and rate performance of the lithium ion battery; # imgabs0 #

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and particularly relates to a lithium-ion battery additive A, a lithium-ion battery additive B, and a lithium-ion battery. Background Art

[0002] Due to advantages such as large energy density, high output power, long cycle life, and low environmental pollution, lithium-ion batteries are currently widely used in fields such as portable electronic devices, power tools, and electric vehicles. However, under abnormal conditions such as short circuit, overcharge, high temperature, extrusion, collision, and puncture, lithium-ion batteries are very likely to catch fire and explode, thus causing serious harm, especially for ternary batteries with high energy density. Therefore, the safety issue of lithium-ion batteries greatly restricts the large-scale popularization and application of lithium-ion batteries.

[0003] In order to improve the thermal safety performance of batteries, people have tried to make improvements from many aspects, including coating the positive electrode with inorganic dielectric materials (such as alumina), high heat-resistant organic materials, etc. to improve the thermal stability of the positive electrode material, coating the current collector surface with positive temperature coefficient thermosensitive materials, developing high heat-resistant separators, developing overcharge additives, composite current collectors, etc. Generally, the following technical means are adopted:

[0004] (1) A PTC material layer is separately provided between the current collector of the battery and the electrode active material layer. However, the coating on the current collector surface may be damaged by the solvent of the positive electrode material to be coated and the stress of rolling, increasing the internal resistance of the battery under normal conditions;

[0005] (2) Using polymer materials such as PET / PP as the intermediate layer base film, through processes such as vacuum coating, a composite material formed by stacking double-layer copper / aluminum conductive layers on both sides of the base film is obtained. The advantages of different materials can be maximally combined through the combination of different materials. The composite current collector has a "sandwich" structure of "metal - PET / PP polymer material - metal"; however, the composite current collector technology is still immature and will increase the internal resistance of the battery;

[0006] (3) For polyimide-based high heat-resistant separator technology, the electrochemical stability of the material itself is insufficient. In addition, the porosity, pore diameter, etc. cannot be controlled, which may lead to relatively large self-discharge of the battery, etc.;

[0007] (4) Coating the positive electrode with maleimide-based materials to generate a thermally insulating material with good heat resistance under high-temperature conditions; however, the polymerization reaction between maleimide double bonds is slow, the reaction temperature is high > 200 °C, and it is difficult to control the residual amount of maleimide double bonds during the preparation process.

[0008] Although many methods have been proposed in the prior art to improve the safety of batteries, there is still no very effective solution to significantly improve the thermal safety performance of high-energy-density lithium batteries while maintaining the performance of lithium batteries because it is impossible to take into account the advantages of long cycle life and high energy density of lithium-ion batteries. Therefore, it is indeed necessary to develop a technology that can improve battery safety. Summary of the Invention

[0009] The object of the present invention is to overcome the above technical problems and provide a lithium-ion battery additive A, a lithium-ion battery additive B, and a lithium-ion battery. Without affecting the cycle life and rate performance of the lithium-ion battery, the additive A and / or the additive B can effectively improve the thermal safety of the battery and reduce the heat release rate and release amount of thermal runaway.

[0010] To achieve the above object, in the first aspect of the present invention, a lithium-ion battery additive A is provided, and the additive A has a compound represented by Formula I.

[0011]

[0012] In Formula I, R1-R4 are each independently selected from hydrogen, a C1-C5 alkyl group, a C2-C5 hydrocarbon group containing C═C, or a group containing an acrylate group, an acrylamide group, a borate group, an amine group, an isocyanate group, or a hydroxyl group; R5-R8 are each independently selected from hydrogen, a halogen, a hydroxyl group, a C1-C5 alkyl group, or a C2-C5 hydrocarbon group containing C═C.

[0013] In the present invention, without special instructions, the lithium-ion battery additive A is simply referred to as additive A; similarly, the lithium-ion battery additive B is simply referred to as additive B.

[0014] In the second aspect of the present invention, a lithium-ion battery additive B is provided. The additive B contains at least one additive A provided in the first aspect and a polymerization monomer.

[0015] Preferably, the polymerization monomer is selected from double-bonded polymerization monomers and / or isocyanate monomers.

[0016] In the third aspect of the present invention, a lithium-ion battery is provided. The lithium-ion battery contains a polymerization product of the additive A provided in the first aspect and / or a polymerization product of the additive B provided in the second aspect.

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] (1) In the present invention, an additive having a thermally responsive benzocyclobutene structure is introduced into the battery electrode / separator / electrolyte. During normal operation of the battery, the polymer of this structure can maintain electrochemical inertness and does not interfere with the electrochemical performance of the battery.

[0019] (2) In the case of thermal runaway of the battery, the temperature of the battery cell increases, and the additive provided by the present invention will undergo a ring-opening - thermal polymerization reaction to obtain an electronically insulating layer with high heat resistance, blocking the short circuit between the positive and negative electrodes and the side reaction between the active material and the electrolyte, thereby enhancing the thermal safety of the battery. Description of the Drawings

[0020] Figure 1(a)-1(b) is the ordinary DSC curve obtained from the test of the sample in Test Example 2;

[0021] Figure 2 is the high - voltage DSC reaction curve of the fully - charged positive electrode and electrolyte of the batteries in Examples 3, 6 and Comparative Examples 1 - 2. Detailed Embodiments

[0022] In the ranges disclosed herein, the endpoints and any values are not limited to the precise ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0023] The first aspect of the present invention provides a lithium - ion battery additive A, and the additive A has a compound represented by Formula I,

[0024]

[0025] In Formula I, R1 - R4 are each independently selected from hydrogen, C1 - C5 alkyl, C2 - C5 hydrocarbon group containing C═C, or a group containing acrylate group, acrylamide group, borate group, amino group, isocyanate group, or hydroxyl group; R5 - R8 are each independently selected from hydrogen, halogen, hydroxyl, C1 - C5 alkyl, C2 - C5 hydrocarbon group containing C═C.

[0026] In some embodiments of the present invention, preferably, in Formula I, at least one of R1 - R4 is selected from chemically reactive functional groups; it means that among R1 - R4, there can be 1 selected from functional groups capable of undergoing chemical reactions, or 2 or 3, or even 4. In the present invention, without special circumstances, the chemically reactive functional group is selected from functional groups capable of undergoing chemical reactions.

[0027] In some embodiments of the present invention, further preferably, in Formula I, any one of R1 - R4 is selected from chemically reactive functional groups, for example, R1, R2, R3, R4; more preferably, in Formula I, R2 or R3 is selected from chemically reactive functional groups.

[0028] In the present invention, unless otherwise specified, a C2-C5 hydrocarbon group containing C═C refers to a C2-C5 hydrocarbon group containing a C═C double bond. As for the number of C═C double bonds, the present invention will not elaborate on this.

[0029] In some embodiments of the present invention, preferably, in Formula I, at least one of R1-R4 is selected from groups containing alkenyl, acrylate group, acrylamide group, borate group, amine group, isocyanate group, and hydroxyl group, preferably selected from alkenyl, boric acid group, amine group, isocyanate group, and hydroxyl group. In the present invention, alkenyl includes, but is not limited to, vinyl, propenyl, etc.

[0030] In some embodiments of the present invention, further preferably, in Formula I, any one of R1-R4 is selected from groups containing alkenyl, acrylate group, acrylamide group, borate group, amine group, isocyanate group, and hydroxyl group, more preferably selected from alkenyl, boric acid group, amine group, isocyanate group, and hydroxyl group.

[0031] In some embodiments of the present invention, preferably, in Formula I, any three of R1-R4 are each independently selected from hydrogen, C1-C5 alkyl, and halogen, preferably selected from hydrogen, C1-C3 alkyl, and halogen, more preferably selected from hydrogen, C1-C3 alkyl.

[0032] In a specific embodiment of the present invention, in Formula I, R2 is selected from groups containing alkenyl, acrylate group, acrylamide group, borate group, amine group, isocyanate group, and hydroxyl group, preferably selected from alkenyl, boric acid group, amine group, isocyanate group, and hydroxyl group; R1, R3, and R4 are each independently selected from hydrogen, C1-C5 alkyl, and halogen, preferably selected from hydrogen, C1-C3 alkyl, and halogen, more preferably selected from hydrogen, C1-C3 alkyl.

[0033] In another specific embodiment of the present invention, in Formula I, R3 is selected from groups containing alkenyl, acrylate group, acrylamide group, borate group, amine group, isocyanate group, and hydroxyl group, preferably selected from alkenyl, boric acid group, amine group, isocyanate group, and hydroxyl group; R1, R2, and R4 are each independently selected from hydrogen, C1-C5 alkyl, and halogen, preferably selected from hydrogen, C1-C3 alkyl, and halogen, more preferably selected from hydrogen, C1-C3 alkyl.

[0034] In some embodiments of the present invention, preferably, in Formula I, R5-R8 are each independently selected from hydrogen, halogen, hydroxyl group, and C1-C5 alkyl, preferably selected from hydrogen, C1-C3 hydrocarbon group, and halogen, more preferably selected from hydrogen, C1-C3 hydrocarbon group.

[0035] In the present invention, unless otherwise specified, the C1-C5 hydrocarbyl group includes both unsubstituted C1-C5 hydrocarbyl groups (i.e., C1-C5 hydrocarbyl groups) and substituted C1-C5 hydrocarbyl groups. In the present invention, the C1-C5 hydrocarbyl group includes, but is not limited to, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, n-pentyl, etc.; the substituting groups in the substituted C1-C5 hydrocarbyl group are selected from halogen, mercapto, hydroxyl, etc.

[0036] In the present invention, there is a wide range of choices for the source of additive A satisfying the above formula I structure. It can be obtained by purchase or by self-preparation.

[0037] The second aspect of the present invention provides a lithium-ion battery additive B, which contains at least one additive A provided in the first aspect and a polymerizable monomer.

[0038] In the present invention, unless otherwise specified, in addition to additive A and the polymerizable monomer, additive B may further contain other components. Preferably, additive B consists of additive A and the polymerizable monomer. In the present invention, in additive B, the type of additive A can be one or more.

[0039] In some embodiments of the present invention, preferably, the molar ratio of additive A to the polymerizable monomer is 1:0.1-10, for example, 1:0.1, 1:0.5, 1:1, 1:1.5, 1:2, 1:3, 1:4, 1:5, 1:8, 1:10, and any value within the range composed of any two numerical values, preferably 1:0.1-5.

[0040] In some embodiments of the present invention, preferably, the polymerizable monomer is selected from double-bond-containing polymerizable monomers and / or isocyanate monomers.

[0041] In some embodiments of the present invention, preferably, when the polymerization monomer is selected from double-bond polymerization monomers, the double-bond polymerization monomers are selected from at least one of methyl methacrylate, pentaerythritol tetramethacrylate, propylene glycol dimethacrylate, 1,3-butanediol dimethacrylate, 1,3-butanediol diacrylate, neopentyl glycol diacrylate, 1,4-butanediol diacrylate, 1,4-butanediol dimethacrylate, 1,5-pentanediol diacrylate, 1,6-hexanediol dimethacrylate, 1,10-decanediol diacrylate, 1,10-decanediol dimethacrylate, ethylene glycol dimethacrylate, pentaerythritol tetraacrylate, triethylene glycol dimethacrylate, triethylene glycol diacrylate, dipropylene glycol diacrylate, diethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, tetraethylene glycol diacrylate, tris(2-acryloyloxyethyl) isocyanurate, triallyl cyanurate, cyclohexanedimethanol diacrylate, cyclohexanedimethanol dimethacrylate, 2-[(trimethylsilyl)oxy]-1,3-propanediyl bis(2-methylacrylate), glycerol trimethacrylate, 2-butene-1,4-dimethacrylate, 2,2',2”-nitrilotriethanol trimethacrylate, 2,2,6,6-tetrabromobisphenol A dimethacrylate, 1-methyl-1,2-ethanediyl diacrylate, 2-(phosphonyloxy)propane-1,3-diyl dimethacrylate, 3-methyl-1,5-pentanediyl diacrylate.

[0042] In some embodiments of the present invention, preferably, when the polymerization monomer is selected from isocyanate monomers, the isocyanate monomers are selected from at least one of toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), naphthalene 1,5-diisocyanate, hexamethylene diisocyanate (HDI), xylylene diisocyanate (XDI), isophorone diisocyanate (IPDI), dicyclohexylmethane-4,4'-diisocyanate (HMDI), tetramethylxylylene diisocyanate (TMXDI).

[0043] The third aspect of the present invention provides a lithium-ion battery, which contains the polymerization product of additive A provided in the first aspect and / or the polymerization product of additive B provided in the second aspect.

[0044] In the present invention, unless otherwise specified, the lithium-ion battery includes: a positive electrode sheet, a negative electrode sheet, a separator, an electrolyte, and the polymerization product of additive A and / or the polymerization product of additive B.

[0045] In some embodiments of the present invention, preferably, the polymerization product is loaded on the surface and / or inside of the electrode sheet in the lithium-ion battery, the surface of the separator, and the electrolyte.

[0046] In some embodiments of the present invention, preferably, the polymerization product is prepared by a polymerization reaction of the additive A and / or additive B. In the present invention, the polymerization reaction includes, but is not limited to, in-situ polymerization reaction, etc. Specifically, in an inert atmosphere, the additive A and / or additive B undergoes a polymerization reaction in the presence of an initiator to obtain the polymerization product. In the present invention, the polymerization product can be a homopolymer or a copolymer.

[0047] In the present invention, the inert atmosphere includes, but is not limited to, nitrogen atmosphere, helium atmosphere, argon atmosphere, neon atmosphere, etc.

[0048] In the first specific embodiment of the present invention, preferably, when the polymerization product is loaded on the surface of the electrode sheet, the additive A and / or additive B is directly coated on the surface of the electrode sheet and dried.

[0049] In the second specific embodiment of the present invention, preferably, when the polymerization product is loaded inside the electrode sheet, the additive A and / or additive B is blended in the electrode paste, coated on the current collector, and dried and compacted in sequence.

[0050] In the third specific embodiment of the present invention, preferably, when the polymerization product is loaded on the surface of the separator, the additive A and / or additive B is directly coated on the surface of the separator and dried.

[0051] In some embodiments of the present invention, preferably, based on the total weight of the active material in the electrode sheet, the content of the additive A and / or additive B is 0.1 - 10 wt%, for example, 0.1 wt%, 0.5 wt%, 0.8 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, and any value within the range composed of any two numerical values, preferably 0.1 - 5 wt%. In the present invention, the total weight of the active material in the electrode sheet refers to the sum of the weights of the positive electrode material / negative electrode material, conductive agent, and binder.

[0052] In some embodiments of the present invention, preferably, based on the total weight of the electrolyte, the content of additive A and / or additive B is 0.1-70 wt%, for example, 0.1 wt%, 0.5 wt%, 0.8 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, and any value within the range composed of any two numerical values, preferably 1-30 wt%. When the content is less than 1 wt%, due to too little material, its improvement effect on the thermal safety of the battery cannot be observed; when the content is greater than 30 wt%, due to its poor ionic conductivity, the internal resistance of the battery increases and the rate performance deteriorates.

[0053] In some embodiments of the present invention, preferably, the mass ratio of additive A and / or additive B to the initiator is 100:0.01-5, preferably 1:0.01-2.

[0054] In the present invention, there is a wide selection range for the type of the initiator. Preferably, the initiator is selected from at least one of azobisisobutyronitrile, azobisisoheptonitrile, dimethyl azobisisobutyrate, dibutyltin, tributyltin, triphenyltin, and stannous octoate.

[0055] In some embodiments of the present invention, preferably, the temperature of the polymerization reaction is 0-100 °C, preferably 35-80 °C. During the polymerization process, the benzocyclobutene structure does not participate in the reaction.

[0056] In some embodiments of the present invention, preferably, when the lithium-ion battery is thermally out of control, the four-membered ring structure in the benzocyclic four-membered ring in Formula I undergoes a ring-opening reaction to generate a material with high thermal stability, Tg≥300 °C, which can effectively prevent further internal short circuit inside the battery and side reactions between the active material and the electrolyte.

[0057] In some embodiments of the present invention, preferably, when the lithium-ion battery is in a thermally out-of-control state, the four-membered ring structure of the benzocyclic four-membered ring of additive A and / or additive B undergoes a ring-opening thermal polymerization reaction to obtain an insulating thermal polymerization product.

[0058] The present invention will be described in detail below through examples.

[0059] Example 1

[0060] The battery includes a positive electrode sheet, a separator, a negative electrode sheet, and a semi-gel electrolyte;

[0061] (1) Preparation of the positive electrode sheet: Take NCM811 positive electrode main material, conductive carbon black, and PVDF, and add them to a stirring tank according to the mass ratio of pure substances of 97:1.5:1.5:0.5. Add 30 wt% of NMP, stir and disperse evenly to obtain a positive electrode slurry. Then use a coater to coat the positive electrode slurry on aluminum foil, dry it at 80 °C for 2 h, and then compact it with a roll press to obtain the positive electrode sheet;

[0062] (2) Preparation of the electrolyte: In a glove box, add dimethyl carbonate, diethyl carbonate, and ethylene carbonate with a volume ratio of 1:1:1, 1.2 mol / L of lithium hexafluorophosphate, add 5 wt% of vinylene carbonate and 2 wt% of ethylene sulfite as film-forming additives, stir and mix evenly to obtain the electrolyte. Add 2.5 wt% of A1 and 2.5 wt% of hexanediol dimethacrylate as cross-linking agents, add 0.05 wt% of azobisisobutyronitrile, and stir and mix evenly.

[0063] Among them, the above additive A1 is selected from vinylbenzocyclobutene, R2 is selected from vinyl, and R1 and R3-R8 are all selected from hydrogen;

[0064] (3) Button cell assembly: Cut the positive electrode sheet into a 12 mm diameter round sheet. Select a 16 μm polypropylene microporous diaphragm with a diameter of 16.2 mm. Use a lithium sheet with a diameter of 16 mm and a thickness of 450 μm as the negative electrode. Add 90 μL of the above electrolyte, and assemble it into a button cell in a glove box, let it stand and soak for 12 h, and cure it at 70 °C for 2 h to obtain the lithium-ion battery S1.

[0065] Example 2

[0066] According to the method of Example 1, the difference is that

[0067] In step (2), adjust it to add 5 wt% of A1, 5 wt% of hexanediol dimethacrylate as a cross-linking agent, add 0.05 wt% of azobisisobutyronitrile, and stir and mix evenly

[0068] Under the same other conditions, obtain the lithium-ion battery S2.

[0069] Example 3

[0070] According to the method of Example 1, the difference is that

[0071] In step (2), adjust it to add 7.5 wt% of A1, 7.5 wt% of hexanediol dimethacrylate as a cross-linking agent, add 0.05 wt% of azobisisobutyronitrile, and stir and mix evenly.

[0072] Under the same other conditions, obtain the lithium-ion battery S3.

[0073] Example 4

[0074] According to the method of Example 1, the difference is that

[0075] In step (2), it is adjusted to add 10 wt% of A1, 10 wt% of hexanediol dimethacrylate as a crosslinking agent, add 0.05 wt% of azobisisobutyronitrile, and stir and mix evenly.

[0076] Under the same other conditions, a lithium-ion battery S4 is obtained.

[0077] Example 5

[0078] According to the method of Example 1, the difference is that

[0079] In step (2), it is adjusted to add 15 wt% of A1, 15 wt% of hexanediol dimethacrylate as a crosslinking agent, add 0.05 wt% of azobisisobutyronitrile, and stir and mix evenly.

[0080] Under the same other conditions, a lithium-ion battery S5 is obtained.

[0081] Example 6

[0082] The battery includes a positive electrode sheet, a separator, a negative electrode sheet, and a semi-gel electrolyte;

[0083] (1) Preparation of the positive electrode sheet: Weigh a certain amount of polyvinylidene fluoride (PVDF), add NMP, and prepare a 7 wt% colloidal solution; take the NCM811 positive electrode main material, conductive carbon black, PVDF, and additive A1 and add them to the stirring tank according to a pure substance mass ratio of 92:1.5:1.5:5 (PVDF is the pure substance mass, not the solution mass), stir evenly, then add azobisisobutyronitrile, mix evenly to obtain a positive electrode slurry, and then use a coater to coat the positive electrode slurry on aluminum foil, dry it at 80 °C for 2 h, and then compact it with a roll press to obtain the positive electrode sheet;

[0084] Among them, the above additive A1 is selected from vinylbenzocyclobutene, R2 is selected from vinyl, and R1 and R3-R8 are all selected from hydrogen; the mass ratio of the above additive A1 to azobisisobutyronitrile is 100:1;

[0085] (2) Preparation of the electrolyte: In a glove box, add dimethyl carbonate, diethyl carbonate, ethylene carbonate with a volume ratio of 1:1:1, 1.2 mol / L lithium hexafluorophosphate, add 5 wt% of fluoroethylene carbonate and 2 wt% of vinylene carbonate as film-forming additives, stir and mix evenly to obtain the electrolyte;

[0086] (3) Coin cell assembly: The positive electrode sheet was punched into a circular sheet with a diameter of 12 mm. A 16-μm polypropylene microporous diaphragm with a diameter of 16.2 mm was selected. A lithium sheet with a diameter of 16 mm and a thickness of 450 μm was used as the negative electrode sheet. 90 μL of the above electrolyte was added, and a coin-type battery was assembled in a glove box as lithium-ion battery S6.

[0087] Example 7

[0088] According to the method of Example 6, the difference is that

[0089] In step (1), additive A1 was replaced with additive A2, and isophorone diisocyanate was added; wherein, additive A2 was selected from 4-aminobenzocyclobutene, R2 was selected from amino group, R1, R 3、 R4 and R5-R8 were all selected from hydrogen; the molar ratio of additive A2 to isophorone diisocyanate was 1:1;

[0090] Under the same other conditions, lithium-ion battery S7 was obtained.

[0091] Example 8

[0092] (1) Preparation of macromolecular polymer: 5 mmol of styrene and 2 mmol of additive A1 (selected from vinylbenzocyclobutene, R2 was selected from vinyl group, and R1 and R3-R8 were all selected from hydrogen) were taken, and toluene was added to prepare a solution with a mass fraction of 10 wt%. 1 wt% of azobisisobutyronitrile based on the mass of the monomer was added. Under an inert gas atmosphere, the temperature was raised to 60 °C, and the polymerization reaction was stirred for 12 h; the reaction was stopped, the polymerization solution was precipitated in methanol, stirred and washed, dried, and then redissolved in toluene and precipitated in methanol twice to obtain a copolymer P1 of styrene and vinylbenzocyclobutene;

[0093] Positive electrode sheet preparation: Weigh a certain amount of polyvinylidene fluoride (PVDF), add NMP to prepare a 7 wt% colloidal solution; take NCM811 positive electrode main material, conductive carbon black, PVDF and copolymer P1 and add them to the stirring tank according to a pure substance mass ratio of 92:1.5:1.5:5 (PVDF is the mass of the pure substance, not the mass of the solution), stir and mix evenly to obtain the positive electrode slurry, and then use a coater to coat the positive electrode slurry on the aluminum foil, dry at 80 °C for 2 h, and then roll press to compact to obtain the positive electrode sheet;

[0094] (2) Electrolyte preparation: In a glove box, dimethyl carbonate, diethyl carbonate, ethylene carbonate with a volume ratio of 1:1:1, 1.2 mol / L lithium hexafluorophosphate, 5 wt% of fluoroethylene carbonate and 2 wt% of vinylene carbonate were added as film-forming additives, and stirred and mixed evenly to obtain the electrolyte;

[0095] (3) Button cell assembly: The positive electrode sheet was punched into a circular sheet with a diameter of 12 mm. The separator was a 16-μm polypropylene microporous separator with a diameter of 16.2 mm. The negative electrode sheet was a lithium sheet with a diameter of 16 mm and a thickness of 450 μm. 90 μL of the above electrolyte was added, and a button cell was assembled in a glove box as the lithium-ion battery S8.

[0096] Comparative Example 1

[0097] According to the method of Example 1, except that the preparation of the electrolyte was slightly adjusted:

[0098] In a glove box, dimethyl carbonate, diethyl carbonate, and ethylene carbonate with a volume ratio of 1:1:1, 1.2 mol / L of lithium hexafluorophosphate, 5 wt% of fluoroethylene carbonate, and 2 wt% of vinylene carbonate were added as film-forming additives, and stirred and mixed evenly to obtain an electrolyte;

[0099] Under the same other conditions, the lithium-ion battery DS1 was obtained.

[0100] Comparative Example 2

[0101] According to the method of Example 1, except that

[0102] In step (2), additive A1 was not added to the above electrolyte, and the addition ratio of diethylene glycol dimethacrylate was adjusted to 15 wt%.

[0103] Under the same other conditions, the lithium-ion battery DS2 was obtained.

[0104] Test Example 1

[0105] The above examples and comparative examples were tested for their electrochemical performance. The test conditions included: using a Blue Electric battery test system at 25 °C, and performing charge and discharge cycle tests on the above lithium-ion batteries in the voltage range of 2.75 V - 4.2 V. The test procedure was: charge and discharge at 0.1C / 0.1C for 2 cycles, and cycle at 0.3C / 0.3C. The test results are all listed in Table 1.

[0106] Table 1

[0107]

[0108] Based on the data in Table 1, it can be seen that by adding additive A and / or additive B by blending in the positive electrode sheet or adding in the electrolyte, there is no obvious difference in the capacity performance of the lithium-ion battery compared with Comparative Examples 1 - 2, which proves that the introduction of additive A and / or additive B has little effect on the cycle of the battery. At a high addition ratio, the battery capacity performance slightly decreases, probably because it causes a slight decrease in the ionic conductivity of the electrolyte.

[0109] Test Example 2

[0110] Common DSC test method: Add 10 wt% of vinylbenzocyclobutene or hexanediol dimethacrylate to PC (LiPF6 with a lithium salt concentration of 1 mol / L), stir and mix evenly, and in-situ cure at 70 °C for 2 h to obtain a white gel; Take 5 mg of the gel respectively, use DSC test, at a rate of 5 °C / min, heat up from 25 °C to 300 °C, and observe the exothermic situation.

[0111] In Test Example 2, the DSC curve of using vinylbenzocyclobutene is shown in Figure 1(a), and the DSC curve of using hexanediol dimethacrylate is shown in Figure 1(b). As can be seen from Figure 1(a) and Figure 1(b), the additive A1 (vinylbenzocyclobutene) containing benzocyclobutene structure has an exothermic reaction peak at 190 - 230 °C, proving that it undergoes a thermal curing reaction at high temperature; while no reaction peak appears in the test using hexanediol dimethacrylate.

[0112] Test Example 3

[0113] High-pressure DSC test method: Take the assembled lithium-ion battery, charge it to 4.2 V at a charging rate of 0.3 C, disassemble the coin cell in the glove box, take out the positive electrode sheet, wash it 3 times with DMC to remove the residual electrolyte, dry it naturally, and scrape off the positive electrode powder with a spatula; Take 3 mg of the positive electrode powder into a gold-plated high-pressure crucible, add 3 mg of the electrolyte, seal it, and heat it up to 400 °C at a rate of 5 °C / min, and compare and observe the reaction conditions of different samples.

[0114] The high-pressure DSC reaction curves of the fully charged positive electrodes of the batteries in Examples 3 and 6 and Comparative Examples 1 - 2 are as Figure 2 shown. As Figure 2 can be seen, the exothermic peak temperatures of DSC in Example 3 and Example 6 are 238 °C and 240 °C respectively, and the heat release amounts are 1137 J / g and 1187 J / g respectively; while for Comparative Example 1 with pure electrolyte and Comparative Example 2 with added hexanediol dimethacrylate, their exothermic peak temperatures are 230 °C and 232 °C respectively, and the heat release amounts are 1312 J / g and 1298 J / g respectively. Compared with Comparative Examples 1 - 2, Examples 3 and 6 can effectively improve the thermal safety of the battery, reduce the side reaction temperature between the positive electrode and the electrolyte, and reduce the heat release rate and release amount of thermal runaway. It proves the effectiveness of this additive in improving the thermal safety of the battery.

[0115] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. An additive A for lithium-ion batteries, characterized in that, The additive A has a compound represented by Formula I. In Formula I, R1-R4 are each independently selected from hydrogen, C1-C5 alkyl, C2-C5 hydrocarbon group containing C═C, or a group containing acrylate group, acrylamide group, borate group, amine group, isocyanate group, hydroxyl group; R5-R8 are each independently selected from hydrogen, halogen, hydroxyl group, C1-C5 alkyl, C2-C5 hydrocarbon group containing C═C.

2. The additive A according to claim 1, wherein In Formula I, at least one of R1-R4 is selected from chemically reactive functional groups. Preferably, in Formula I, any one of R1-R4 is selected from chemically reactive functional groups. More preferably, in Formula I, R2 or R3 is selected from chemically reactive functional groups.

3. The additive A according to claim 2, wherein, In Formula I, at least one of R1-R4 is selected from a group containing alkenyl, acrylate group, acrylamide group, borate group, amine group, isocyanate group, hydroxyl group. Preferably, in Formula I, any one of R1-R4 is selected from a group containing alkenyl, acrylate group, acrylamide group, borate group, amine group, isocyanate group, hydroxyl group. And / or, in Formula I, any three of R1-R4 are each independently selected from hydrogen, C1-C5 alkyl, halogen. And / or, in Formula I, R5-R8 are each independently selected from hydrogen, halogen, hydroxyl group, C1-C5 alkyl.

4. An additive B for lithium-ion batteries, characterized in that, The additive B contains at least one additive A as described in any one of claims 1-3, and a polymerizable monomer.

5. The additive B according to claim 4, wherein, The polymerizable monomer is selected from double bond-containing polymerizable monomers and / or isocyanate monomers. And / or, the molar ratio of the additive A to the polymerizable monomer is 1:0.1-10, preferably 1:0.1-5.

6. The additive B according to claim 5, wherein, The double bond-containing polymerizable monomers are selected from at least one of methyl methacrylate, pentaerythritol tetramethacrylate, propylene glycol dimethacrylate, 1,3-butanediol dimethacrylate, 1,3-butanediol diacrylate, neopentyl glycol diacrylate, 1,4-butanediol diacrylate, 1,4-butanediol dimethacrylate, 1,5-pentanediol diacrylate, 1,6-hexanediol dimethacrylate, 1,10-decanediol diacrylate, 1,10-decanediol dimethacrylate, ethylene glycol dimethacrylate, pentaerythritol tetraacrylate, triethylene glycol dimethacrylate, triethylene glycol diacrylate, dipropylene glycol diacrylate, diethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, tetraethylene glycol diacrylate, tris(2-acryloyloxyethyl) isocyanurate, triallyl cyanurate, cyclohexanedimethanol diacrylate, cyclohexanedimethanol dimethacrylate, 2-[(trimethylsilyl)oxy]-1,3-propanediyl bis(2-methylacrylate), glycerol trimethacrylate, 2-butene-1,4-dimethacrylate, 2,2',2”-nitrilotriethanol trimethacrylate, 2,2,6,6-tetrabromobisphenol A dimethacrylate, 1-methyl-1,2-ethanediyl diacrylate, 2-(phosphoryloxy)propane-1,3-diyl dimethacrylate, 3-methyl-1,5-pentanediyl diacrylate.

7. The additive B according to claim 5 or 6, wherein, The isocyanate monomer is selected from at least one of toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), naphthalene 1,5-diisocyanate, hexamethylene diisocyanate (HDI), xylylene diisocyanate (XDI), isophorone diisocyanate (IPDI), dicyclohexylmethane-4,4'-diisocyanate (HMDI), and tetramethylxylylene diisocyanate (TMXDI).

8. A lithium-ion battery, characterized in that, The lithium ion battery contains a polymerization product of the additive A described in any one of claims 1-3, and / or a polymerization product of the additive B described in any one of claims 4-7.

9. The lithium ion battery according to claim 8, wherein, The polymerization product is loaded on the surface and / or inside of the electrode sheet in the lithium ion battery, on the surface of the separator, and in the electrolyte; and / or, the polymerization product is prepared by a polymerization reaction of the additive A and / or the additive B; Preferably, in an inert atmosphere, the additive A and / or the additive B undergoes the polymerization reaction in the presence of an initiator to obtain the polymerization product.

10. The lithium ion battery according to claim 9, wherein, Based on the total weight of the active substances in the electrode sheet, the content of the additive A and / or the additive B is 0.1-10 wt%, preferably 0.1-5 wt%; Alternatively, based on the total weight of the electrolyte, the content of the additive A and / or the additive B is 0.1-70 wt%, preferably 1-30 wt%.

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