Battery cell and lithium ion secondary battery

Abstract

The invention relates to the field of lithium ion batteries, and discloses a battery cell and a lithium ion secondary battery. The battery cell comprises a diaphragm and an electrolyte, the mass content B of a lithium salt in the electrolyte is 8-18%, and the lithium salt comprises at least one of lithium hexafluorophosphate and lithium difluorophosphate; the diaphragm comprises a base membrane and a ceramic layer, the ceramic layer comprises SiO2, a Si-O bond in the SiO2 comprises a Q4 covalent bond structure, and the mass content A of the Q4 covalent bond structure is 26.4-89% by taking the mass of the Si element in the ceramic layer as a reference; 11.13 > = A / B > = 1.47. By adjusting the mass content A of the Q4 covalent bond structure in the diaphragm ceramic layer, the mass content B of the lithium salt in the electrolyte and the A / B value to be within the range, the rate capability, the cycle stability and the low-temperature discharge performance of the battery can be comprehensively improved.

Description

Technical Field

[0001] The present application relates to the technical field of lithium-ion batteries, and in particular to a battery cell and a lithium-ion secondary battery. Background Art

[0002] The rapid growth of markets such as electric vehicles and portable electronic devices is placing higher demands on the energy density, charge and discharge rates, and low-temperature performance of lithium-ion secondary batteries. The performance of lithium-ion secondary batteries depends heavily on the performance of their internal components, particularly the separator. As a key component in a battery, the separator not only isolates the positive and negative electrodes, preventing short circuits, but also influences the lithium-ion transmission efficiency and the overall kinetic performance of the battery.

[0003] Although traditional diaphragm materials meet basic needs to a certain extent, the transmission of lithium ions is limited under high-rate charge and discharge conditions, resulting in poor battery kinetics and limited rate performance. In particular, the reduced mobility of ions in the electrolyte in low-temperature environments further exacerbates this problem. Summary of the Invention

[0004] In view of this, the technical problem to be solved by this application is to overcome the shortcomings of existing battery cells in terms of cycle performance, rate performance and low-temperature discharge performance.

[0005] According to an embodiment of the present application, in a first aspect, the present application provides a battery cell comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte; the electrolyte comprises a lithium salt, and the lithium salt comprises at least one of lithium hexafluorophosphate and lithium difluorophosphate; based on the mass of the electrolyte, the mass content B of the lithium salt is 8%-18%; the separator comprises a base film and a ceramic layer provided on at least one side surface of the base film in a thickness direction, the ceramic layer comprises SiO2, and the Si-O bond in the SiO2 comprises Q 4 Covalent bond structure, based on the mass of Si element in the ceramic layer, the Q 4 The mass content A of the covalent bond structure is 26.4%-89% and satisfies: 11.13≥A / B≥1.47.

[0006] In some optional embodiments, the mass content C of the Si element in the ceramic layer is 16.8%-33.3%, satisfying: 4.16≥C / B≥0.93.

[0007] In some optional embodiments, the ceramic layer further includes P element, and the mass content of the P element in the ceramic layer is 0.2%-1.3%.

[0008] In some optional embodiments, the thickness of the ceramic layer is 0.5 μm-10 μm.

[0009] In some optional embodiments, the contact angle of the electrolyte on the surface of the ceramic layer is 10°-40°.

[0010] In some optional embodiments, the electrolyte further comprises ethylene carbonate, and the Raman spectrum of the electrolyte comprises a first characteristic peak and a second characteristic peak, wherein the Raman shift of the first characteristic peak is at 712.5 cm -1 -725cm -1 In the range, the Raman shift of the second characteristic peak is at 739cm -1 -752cm -1 In the range, the ratio of the peak areas of the first characteristic peak to the second characteristic peak is 0.8-1.5.

[0011] In some optional embodiments, the electrolyte further includes at least one of a nitrile additive and a sulfonate additive.

[0012] Specifically, the nitrile compounds include acetonitrile, malononitrile, succinonitrile, glutaronitrile, adiponitrile, 1,3,6-hexanetrinitrile, 1,3,5-pentanetrinitrile, ethylene glycol dipropylene glycol ether, hexafluorocyclotriphosphazene, pentafluoroethoxycyclotriphosphazene, pentafluorophenoxycyclotriphosphazene, 1,4-dicyano-2-butene, p-fluorobenzonitrile, p-methylbenzonitrile, 2-fluoroadiponitrile, 2,2-difluorosuccinonitrile, tricyanobenzene, acrylonitrile, crotononitrile, trans-butene dinitrile, trans-hexene dinitrile, 3-(trimethylsilyloxy)propionitrile, 1,3,4,6-hexane tetranitrile, 1,2,4,5-benzene tetranitrile, 2,3,5,6-pyrazine tetranitrile, sebacononitrile, azelaic acid dinitrile, dicyanobenzene, pyridine-3, At least one of 4-dicarbonitrile, 2,5-dicyanopyridine, 2,2,3,3-tetrafluorosuccinonitrile, tetrafluoroterephthalonitrile, 4-tetrahydrothiopyrylamide malononitrile, 1,4,5,6-tetrahydro-5,6-dioxo-2,3-pyrazine dicarbonitrile, 1,3,5-cyclohexane tricarbonitrile, 1,2,3-propane tricarbonitrile, glycerol tricarbonitrile, tris(3-cyanopropyl)phosphate, 1,1,3,3-propane tetracarbonitrile, 1,2,2,3-tetracyanopropane, 3-methyl-3-propyl-cyclopropane-1,1,2,2-tetracarbonitrile, 7,7,8,8-tetracyanoquinodimethane, tetracyanoethylene, bis(cyanoethoxy)ethane, tris(cyanoethoxy)propane, and tetra(cyanoethoxy)butane.

[0013] Specifically, the sulfonate additive includes at least one of 1,3-propane sultone, 1,3-propylene sultone, and methylene methanedisulfonate.

[0014] In some optional embodiments, the ceramic layer includes 10-78 parts by weight of ceramic particles, 1-10 parts by weight of a binder, and 0.5-2 parts by weight of a dispersant.

[0015] In some optional embodiments, the average particle size of the ceramic particles is 0.1 μm-5 μm.

[0016] In some optional embodiments, the ceramic particles include SiO2 particles, and the SiO2 particles include at least one of solid SiO2, porous SiO2, and hollow SiO2.

[0017] In some optional embodiments, the ceramic particles further include at least one of alumina and boehmite.

[0018] In some optional embodiments, the pore size of the porous SiO2 is 2nm-50nm.

[0019] In some optional embodiments, the pore size of the hollow SiO2 is 50nm-500nm.

[0020] In some optional embodiments, the binder includes polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyimide, polyacrylonitrile, polymethyl (meth)acrylate, aramid resin, poly (meth)acrylic acid, styrene-butadiene rubber, polyvinyl alcohol, polyvinyl acetate, carboxymethyl cellulose, sodium carboxymethyl cellulose, carboxyethyl cellulose, polyacrylamide, phenolic resin, epoxy resin, water-based polyurethane, ethylene-vinyl acetate copolymer, polyacrylic copolymer, lithium polystyrene sulfonate, water-based silicone resin, nitrile-polyvinyl chloride blend, styrene acrylic latex, pure styrene latex or at least one of the blended or copolymerized polymers derived from the aforementioned polymer modifications.

[0021] In some optional embodiments, the dispersant includes at least one of multi-branched alcohol, triethyl phosphate, polyethylene glycol, fluorinated polyethylene oxide, polyethylene oxide, stearic acid, sodium dodecylbenzene sulfonate, sodium hexadecyl sulfonate, fatty acid glyceride, sorbitan fatty acid ester, and polysorbate.

[0022] In some optional embodiments, the diaphragm further includes a glue layer, which is arranged on both side surfaces of the base film in the thickness direction, and the ceramic layer is located between the glue layer and the base film; the ratio of the area of ​​the glue layer to the area of ​​one side surface of the base film is 0.1-0.5.

[0023] In some optional embodiments, the adhesive layer includes adhesive particles and a wetting agent; the adhesive particles include polyvinylidene fluoride and polymethyl methacrylate in a mass ratio of 2-5:1, the average particle size of the polyvinylidene fluoride is 0.6μm-1.0μm, and the average particle size of the polymethyl methacrylate is 4μm-6μm.

[0024] In some optional embodiments, the wetting agent includes at least one of ethylene oxide, nonylphenol polyoxyethylene ether, and polyoxyethylene polyoxypropylene block copolymer.

[0025] In some optional embodiments, the base film has a thickness of 3 μm-20 μm.

[0026] And / or, the base film includes at least one of polyethylene, polypropylene, polyimide, polyacrylonitrile, and polyethersulfone.

[0027] According to an embodiment of the present application, in a second aspect, the present application further provides a lithium-ion secondary battery, comprising the battery cell described in the first aspect.

[0028] The technical solution of this application has the following advantages:

[0029] The battery cell provided by the present application includes a diaphragm and an electrolyte, wherein the electrolyte includes a lithium salt, the mass content B of the lithium salt in the electrolyte is 8%-18%, and the lithium salt includes at least one of lithium hexafluorophosphate and lithium difluorophosphate; the diaphragm includes a base film and a ceramic layer provided on at least one side surface in the thickness direction of the base film, the ceramic layer includes SiO2, and the Si-O bond in SiO2 includes Q 4 Covalent bond structure, Q is calculated based on the mass of Si element in the ceramic layer 4 The mass content of the covalent bond structure A is 26.4%-89% and satisfies 11.13≥A / B≥1.47. 4 When the mass content A of the covalent bond structure, the mass content B of the lithium salt in the electrolyte, and the value of A / B are within the above ranges, the battery's rate performance, cycle stability, and low-temperature discharge performance can be comprehensively improved.

[0030] Additional aspects and advantages of the embodiments of the present application will be described and shown in part in the subsequent description, or explained through the implementation of the embodiments of the present application. DETAILED DESCRIPTION

[0031] The following examples are provided to further better understand the present application, but are not limited to the best implementation mode described herein, and do not limit the content and protection scope of the present application. Any product identical or similar to the present application obtained by anyone under the inspiration of the present application or by combining the features of the present application with other prior arts shall fall within the scope of protection of the present application.

[0032] In order to solve the shortcomings of battery cells in related technologies in terms of cycle performance, rate performance and low-temperature discharge performance, this application proposes the following technical solutions.

[0033] According to a first aspect of the present application, a battery cell is provided, comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte; the electrolyte comprises a lithium salt, and the lithium salt comprises at least one of lithium hexafluorophosphate (LiPF6) and lithium difluorophosphate (LiPO2F2); based on the mass of the electrolyte, the mass content B of the lithium salt is 8%-18%; the separator comprises a base film and a ceramic layer provided on at least one side surface of the base film in a thickness direction, the ceramic layer comprises SiO2, and the Si-O bond in the SiO2 comprises Q 4 Covalent bond structure, based on the mass of Si element in the ceramic layer, the Q 4 The mass content A of the covalent bond structure is 26.4%-89% and satisfies: 11.13≥A / B≥1.47.

[0034] This study found that by introducing Q into the ceramic layer of the diaphragm 4 The mass content of covalent bond structure A is in the range of 26.4%-89%. This type of SiO2 has stable chemical properties, porous structure and rich surface functional groups, which can react with anions in the electrolyte (such as PF6 - PO2F2 - ) undergo electrostatic interactions, hydrogen bonding, and chemical adsorption, significantly capturing anions. At the same time, the relationship between A and the mass content of lithium salt in the electrolyte, B, is regulated to satisfy 11.13 ≥ A / B ≥ 1.47. This, on the one hand, effectively reduces the migration of anions in the diaphragm, provides more transport channels for lithium ions, significantly increases the number of lithium ion transfers, and thus improves the diaphragm dynamics; on the other hand, it also increases the dissociation degree of lithium salt in the electrolyte, thereby improving the ionic conductivity of the diaphragm, allowing the battery to maintain good performance under high-rate charge and discharge conditions.

[0035] Furthermore, the SiO2 in the diaphragm ceramic layer does not solvate with the ethylene carbonate (EC) in the electrolyte. This not only allows more EC to form solvated lithium, promoting the dissociation of lithium salts, allowing more active lithium to migrate and improving the diaphragm dynamics, but also does not change the solvation structure of the electrolyte, helping to form a stable solid electrolyte interface (SEI) film, preventing direct contact between the electrolyte and the negative electrode material, and reducing the occurrence of side reactions. Furthermore, the ceramic layer containing SiO2 can effectively slow down the coagulation trend of ions in the electrolyte in low-temperature environments, maintain high ion mobility, and improve the low-temperature discharge performance of the battery.

[0036] It can be seen that the present invention adjusts the Q 4The mass content A of the covalent bond structure, the mass content B of the lithium salt in the electrolyte, and the value of A / B are within the above ranges, which can comprehensively improve the rate performance, cycle stability, and low-temperature discharge performance of the battery. If the value of A / B exceeds 11.13, the excessively high content of Q 4 The covalent bond structure will lead to poor thermal conductivity of the diaphragm, which is easy to cause local heat accumulation in the diaphragm, and then lead to local damage of the diaphragm, which is prone to short circuit risk and is not conducive to the rate performance and cycle performance of the battery; when the A / B value is less than 1.47, the Q 4 The covalent bond structure content is insufficient, and it is unable to effectively capture anions and stabilize the SEI film, resulting in a decrease in the degree of lithium salt dissociation, a decrease in the ion conductivity of the diaphragm, and a change in the electrolyte structure. It is also difficult for the electrolyte to maintain high ion activity in a low-temperature environment, thereby affecting the battery's rate performance, cycle performance, and low-temperature discharge performance.

[0037] It should be noted that the Q 4 The mass content A of the covalent bond structure is obtained by testing the solid-state NMR silicon spectrum of the diaphragm. In the silicon spectrum, the peaks with chemical shifts near -80ppm, -90ppm, -100ppm, and -110ppm are derived from the covalent bonds of the silicon atoms Si(OSi)(OH)3, Si(OSi)2(OH)2, Si(OSi)3(OH), and Si(OSi)4 structures, respectively, and are named Q 1 , Q 2 , Q 3 , Q 4 Covalent bond structure. 4 The high proportion of covalent bond structure indicates that the Si-O bond is stable and the diaphragm can better capture anions in the electrolyte.

[0038] For example, the Q in the diaphragm ceramic layer 4 The mass content A of the covalent bond structure can be 26.4%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 89%, etc., or a value within the range formed by any two of the above values.

[0039] Exemplarily, the mass content B of the lithium salt in the electrolyte can be 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, etc., or a value within the range of any two of the above values.

[0040] For example, the Q in the diaphragm ceramic layer 4The ratio A / B of the mass content A of the covalent bond structure to the mass content B of the lithium salt in the electrolyte can be, for example, 1.47, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11.13, etc., or a value within the range of any two of the above values.

[0041] Furthermore, in some embodiments, the mass content C of the Si element in the ceramic layer is 16.8%-33.3%, and the mass content B of the lithium salt in the electrolyte satisfies the relationship: 4.16≥C / B≥0.93. By adjusting the mass content C of the Si element in the ceramic layer to be within the range of 16.8%-33.3%, it is possible to ensure that the diaphragm ceramic layer has a sufficiently high content of Q 4 The covalent bond structure can effectively capture anions in the electrolyte and stabilize the SEI film, improve the dissociation degree of lithium salts and the ion conductivity of the diaphragm, maintain the electrolyte structure, and keep the high ion activity of the electrolyte at low temperatures, thereby improving the battery's rate performance, cycle performance and low-temperature discharge performance.

[0042] If the C / B value exceeds 4.16, it means that the Si content in the ceramic layer is too high, and the Q 4 The covalent bond structure content is too high, resulting in poor thermal conductivity of the diaphragm, which is prone to local heat accumulation in the diaphragm, and then leads to local damage of the diaphragm, which is prone to short circuit risk and is not conducive to the rate performance and cycle performance of the battery; when the C / B value is less than 0.93, the Si content in the ceramic layer is too small, that is, Q 4 The content of covalent bond structure is insufficient, which cannot effectively capture anions and stabilize the SEI film, resulting in a decrease in the degree of lithium salt dissociation, a decrease in the ion conductivity of the diaphragm, and a change in the electrolyte structure. It is also difficult for the electrolyte to maintain high ion activity in a low-temperature environment, thereby affecting the battery's rate performance, cycle performance, and low-temperature discharge performance.

[0043] Exemplarily, the mass content C of the Si element in the ceramic layer can be, for example, 16.8%, 20%, 22%, 24%, 26%, 28%, 30%, 32%, 33.3%, etc., or a value within the range formed by any two of the above values.

[0044] Illustratively, the ratio C / B of the mass content C of the Si element in the ceramic layer to the mass content B of the lithium salt in the electrolyte can be 0.93, 1.25, 1.5, 1.75, 2, 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.16, etc., or a value within the range of any two of the above values.

[0045] The diaphragm was disassembled from the battery cell of the present application and washed with N,N-dimethylacetamide (DMAc) several times to remove the electrolyte on the surface and inside the diaphragm. Then, X-ray photoelectron spectroscopy (XPS) was used for testing. The results showed that P element could be detected in the ceramic layer of the diaphragm, and the mass content of P element was 0.2%-1.3% based on the mass of the ceramic layer. This shows that the ceramic layer of the diaphragm of the present application can indeed capture anions in the electrolyte (such as PF6 - PO2F2 - ).

[0046] It is understandable that when the content of P in the ceramic layer exceeds 1.3%, it indicates that the Q 4 Too much covalent bond structure leads to poor thermal conductivity of the diaphragm, which can easily cause local heat accumulation in the diaphragm, leading to local damage of the diaphragm, and the risk of short circuit, which is also not conducive to the rate performance and cycle performance of the battery; when the content of P element in the ceramic layer is less than 0.2%, it means that Q in SiO2 4 The content of covalent bond structure is too small to effectively capture anions and stabilize the SEI film, resulting in a decrease in the degree of lithium salt dissociation, a decrease in the ion conductivity of the diaphragm, and a change in the electrolyte structure. It is also difficult for the electrolyte to maintain high ion activity in a low-temperature environment, thereby affecting the battery's rate performance, cycle performance, and low-temperature discharge performance.

[0047] Exemplarily, the mass content of the P element in the ceramic layer can be 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, etc., or a value within the range formed by any two of the above values.

[0048] In some embodiments, the thickness of the ceramic layer is 0.5 μm-10 μm. In this way, on the one hand, the good mechanical strength of the separator can be ensured, effectively preventing the penetration of lithium dendrites and reducing the risk of short circuit; on the other hand, it can also ensure that the ceramic layer has sufficient content of Si elements and Q 4 The covalent bond structure effectively captures anions in the electrolyte and stabilizes the SEI film, thereby improving the dissociation degree of lithium salts and the ion conductivity of the diaphragm, maintaining the electrolyte structure, and maintaining high ion activity of the electrolyte at low temperatures, thereby improving the battery's rate performance, cycle performance, and low-temperature discharge performance.

[0049] When the thickness of the ceramic layer is too large, the permeability of the diaphragm becomes poor, which is not conducive to the volume energy density, cycle performance and rate performance of the battery; on the contrary, if the thickness of the ceramic layer is too small, the strength of the diaphragm is reduced, and the Si element and Q in the ceramic layer are 4The content of covalent bond structure also decreases, which makes it impossible to effectively capture anions and stabilize the SEI film, resulting in a decrease in the degree of lithium salt dissociation, a decrease in the ion conductivity of the diaphragm, and a change in the electrolyte structure. It is also difficult for the electrolyte to maintain high ion activity in a low temperature environment, thereby affecting the battery's rate performance, cycle performance, and low-temperature discharge performance.

[0050] The thickness of the ceramic layer can be obtained by photographing a SEM cross-section of the diaphragm. For example, the thickness of the ceramic layer can be 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, or the like, or a value within a range formed by any two of the foregoing values.

[0051] In some embodiments, the ceramic layer includes 10-78 parts by weight of ceramic particles, 1-10 parts by weight of a binder, and 0.5-2 parts by weight of a dispersant. Adding an appropriate amount of a binder can improve the film-forming properties and mechanical strength of the ceramic layer, ensure that the ceramic layer can be more tightly bonded to the surface of the base film, and prevent the ceramic layer from falling off during the battery cycle, thereby ensuring the cycle stability and safety of the battery. The role of the dispersant is to ensure that the ceramic particles can be evenly dispersed in the ceramic layer, so that the ceramic layer has the ability to more effectively capture anions in the electrolyte, thereby ensuring the battery's rate performance, cycle performance, low-temperature discharge performance, and safety.

[0052] The ceramic layer is prepared by coating a slurry including ceramic particles on at least one side surface in the thickness direction of the base film; specifically, the method comprises the following steps: mixing ceramic particles with deionized water in a mass ratio of 10-78:10-88.5, adding the above-mentioned binder and dispersant in parts by weight, stirring evenly to obtain a ceramic slurry, coating the ceramic slurry on at least one side surface in the thickness direction of the base film, and drying to obtain a ceramic layer.

[0053] It is understood that the thickness of the ceramic layer is closely related to the average particle size of the ceramic particles, and the average particle size of the ceramic particles determines the minimum thickness of the ceramic layer. In some embodiments, the average particle size of the ceramic particles is 0.1 μm-5 μm, thereby ensuring that the ceramic layer has an appropriate thickness. This can ensure good mechanical strength of the diaphragm, effectively prevent the penetration of lithium dendrites, and reduce the risk of short circuits; on the other hand, it can also ensure that the ceramic layer has sufficient content of Si elements and Q 4 The covalent bond structure effectively captures anions in the electrolyte and stabilizes the SEI film, thereby improving the dissociation degree of lithium salts and the ion conductivity of the diaphragm, maintaining the electrolyte structure, and maintaining high ion activity of the electrolyte at low temperatures, thereby improving the battery's rate performance, cycle performance, and low-temperature discharge performance.

[0054] The average particle size of the ceramic particles can be measured by a laser particle size analyzer. For example, the average particle size of the ceramic particles can be 0.1 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, or a value within a range formed by any two of the above values.

[0055] For example, the ceramic particles can be SiO2 particles or a mixture of SiO2 particles with alumina and / or boehmite. Alumina and boehmite have excellent thermal stability. When combined with SiO2 particles to form a ceramic layer, they can reduce costs while ensuring battery safety during charge and discharge.

[0056] The SiO2 particles include at least one of solid SiO2, porous SiO2, and hollow SiO2. The porous SiO2 has a pore size of 2nm-50nm, as measured by nitrogen adsorption-desorption testing. The hollow SiO2 has a pore size of 50nm-500nm, as measured by mercury porosimetry. Hollow particles are particles with a hollow structure containing pores. The pore size of hollow particles refers to the diameter of the pores within the particle.

[0057] SiO2 particles with porous or hollow structures have a large specific surface area and can provide more action sites to capture anions in the electrolyte, thereby reducing the membrane surface resistance and improving the membrane dynamics.

[0058] As an example, the binder includes polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyimide, polyacrylonitrile, polymethyl (meth)acrylate, aramid resin, poly (meth)acrylic acid, styrene-butadiene rubber, polyvinyl alcohol, polyvinyl acetate, carboxymethyl cellulose, sodium carboxymethyl cellulose, carboxyethyl cellulose, polyacrylamide, phenolic resin, epoxy resin, water-based polyurethane, ethylene-vinyl acetate copolymer, polyacrylic copolymer, lithium polystyrene sulfonate, water-based silicone resin, nitrile-polyvinyl chloride blend, styrene acrylic latex, pure styrene latex or at least one of the blended or copolymerized polymers derived from the modified aforementioned polymers.

[0059] As an example, the dispersant includes at least one of multi-branched alcohol, triethyl phosphate, polyethylene glycol, fluorinated polyethylene oxide, polyethylene oxide, stearic acid, sodium dodecylbenzene sulfonate, sodium hexadecyl sulfonate, fatty acid glyceride, sorbitan fatty acid ester, and polysorbate.

[0060] In some embodiments, the contact angle of the electrolyte on the surface of the ceramic layer is 10°-40°. This ensures good wettability of the electrolyte to the separator and low interfacial impedance between the electrolyte and the separator, thereby improving the battery's liquid retention and cycle performance.

[0061] The contact angle of the electrolyte on the surface of the ceramic layer can be measured by a contact angle meter. For example, the contact angle can be 10°, 15°, 20°, 25°, 30°, 35°, 40°, or a value within a range formed by any two of the above values.

[0062] In some embodiments, the electrolyte further comprises ethylene carbonate (EC), which has a strong polarity and can react with Li + coordination, forming a stable solvation shell, weakening the Li + With anions (such as PF6 - PO2F2 - ) between the Coulomb force, promoting the dissociation of lithium salts and increasing the free Li + The concentration of Li + Migration efficiency. And, at the electrode interface + It is easier to remove the solvation shell, reduce interfacial impedance, and increase the charge and discharge rate. Especially on the negative electrode surface, the solvation shell of EC will preferentially undergo reduction decomposition to form a lithium-rich SEI film, which can effectively prevent the continuous decomposition of the electrolyte and reduce lithium dendrite growth and side reactions.

[0063] Furthermore, the Raman spectrum of the electrolyte includes a first characteristic peak and a second characteristic peak, wherein the Raman shift of the first characteristic peak is at 712.5 cm -1 -725cm -1 In the range, the Raman shift of the second characteristic peak is at 739cm -1 -752cm -1 In the range, the ratio of the peak areas of the first characteristic peak to the second characteristic peak is 0.8-1.5, which can ensure that the rate performance of the lithium-ion secondary battery reaches the best.

[0064] It should be noted that testing the electrolyte composition using a Raman spectrometer involves loading a treated electrolyte sample into the Raman spectrometer's sample chamber, activating the spectrometer, irradiating the sample with a laser beam to stimulate Raman scattering, and collecting the scattered light using the spectrometer's spectral system, converting it into Raman spectral data. In the electrolyte's Raman spectrum, the first characteristic peak is attributed to the ring vibration of EC, and the second characteristic peak is attributed to the symmetric stretching vibration of the anion.

[0065] If the peak area ratio of the first characteristic peak to the second characteristic peak in the Raman spectrum of the electrolyte is less than 0.8, it indicates that the EC content relative to the anion is too low, which is not conducive to the solvation of lithium ions, thereby affecting the rate performance of the battery. When the peak area ratio of the first characteristic peak to the second characteristic peak is greater than 1.5, it indicates that the EC content relative to the anion is too high, increasing the viscosity of the electrolyte, reducing ion mobility, and hindering lithium ion migration, which is also not conducive to the rate performance of the battery. For example, the peak area ratio of the first characteristic peak to the second characteristic peak in the Raman spectrum of the electrolyte can be 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, etc., or a value within the range of any two of the above values.

[0066] In some embodiments, the electrolyte further includes at least one of a nitrile additive, a sulfonate additive, and a fluorinated cyclic carbonate additive.

[0067] Nitrile additives have a high dielectric constant and can effectively promote the dissociation of lithium salts and increase the concentration of free lithium ions. In addition, the viscosity of nitrile additives is usually lower than that of carbonate solvents. Therefore, they can reduce the overall viscosity of the electrolyte, improve the efficiency of ion migration, and significantly improve the conductivity, especially the conductivity in low-temperature environments, which is beneficial to improving the low-temperature discharge performance, rate and cycle performance of the battery.

[0068] For example, the nitrile compounds include acetonitrile, malononitrile, succinonitrile, glutaronitrile, adiponitrile, 1,3,6-hexanetrinitrile, 1,3,5-pentanetrinitrile, ethylene glycol bispropionitrile ether, hexafluorocyclotriphosphazene, pentafluoroethoxycyclotriphosphazene, pentafluorophenoxycyclotriphosphazene, 1,4-dicyano-2-butene, p-fluorobenzonitrile, p-methylbenzonitrile, 2-fluoroadiponitrile, 2,2-difluorosuccinonitrile, tricyanobenzene, acrylonitrile, crotononitrile, trans-butenedicononitrile, trans-hexenedicononitrile, 3-(trimethylsilyloxy)propionitrile, 1,3,4,6-hexanetetranitrile, 1,2,4,5-benzenetetracarbonitrile, 2,3,5,6-pyrazinetetranitrile, sebacononitrile, azelaic acid dicyanobenzene, pyridine-3- ,4-dinitrile, 2,5-dicyanopyridine, 2,2,3,3-tetrafluorosuccinonitrile, tetrafluoroterephthalonitrile, 4-tetrahydrothiopyranylmalononitrile, 1,4,5,6-tetrahydro-5,6-dioxo-2,3-pyrazinedicarbonitrile, 1,3,5-cyclohexanetricarbonitrile, 1,2,3-propanetricarbonitrile, glyceroltricarbonitrile, tris(3-cyanopropyl)phosphate, 1,1,3,3-propanetetracarbonitrile, 1,2,2,3-tetracyanopropane, 3-methyl-3-propyl-cyclopropane-1,1,2,2-tetracarbonitrile, 7,7,8,8-tetracyanoquinodimethane, tetracyanoethylene, di(cyanoethoxy)ethane, tris(cyanoethoxy)propane, tetra(cyanoethoxy)butane.

[0069] Sulfonate additives have strong polarity and can promote the dissociation of lithium salts and increase the concentration of free lithium ions. At the same time, the low freezing point and low viscosity of sulfonates enable them to maintain a high ion migration rate at low temperatures (such as -30°C), which is beneficial to the low-temperature discharge performance of the battery. Sulfonates can also participate in the formation of SEI film, enhance the interfacial passivation ability, and inhibit the continuous decomposition of the electrolyte. The flexible sulfur-containing SEI film can better adapt to the volume changes of the silicon-based negative electrode, reduce electrode pulverization, and improve cycle stability.

[0070] Exemplarily, the sulfonate additive includes at least one of 1,3-propane sultone (PS), 1,3-propylene sultone, and methylene methanedisulfonate.

[0071] Adding a fluorinated cyclic carbonate to the electrolyte will generate a fluorinated elastic SEI film upon decomposition, which can better adapt to the volume expansion of the silicon-based negative electrode and extend the cycle life. Exemplarily, the fluorinated cyclic carbonate can be fluorinated ethylene carbonate (FEC).

[0072] In some embodiments, the separator further includes a glue layer disposed on both sides of the base film in the thickness direction, with the ceramic layer positioned between the glue layer and the base film. The ratio of the area of ​​the glue layer to the area of ​​one side of the base film is 0.1-0.5. This prevents the glue layer from obstructing the separator pores, ensuring high dynamic performance of the separator and thus improving the battery's cycle and rate performance.

[0073] Illustratively, the ratio of the area of ​​the adhesive layer to the area of ​​the surface of one side of the base film can be 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, etc., or a value within the range of any two of the above values.

[0074] It should be noted that the test method for the ratio of the area of ​​the adhesive layer to the area of ​​one side of the base film includes: at any size, the percentage of the sum of the areas of all coating points in the test area to the area of ​​the test area, and the test is performed using a Keyence microscope.

[0075] Specifically, in some embodiments, the adhesive layer includes adhesive particles and a wetting agent, wherein the adhesive particles include polyvinylidene fluoride (PVDF) and polymethyl methacrylate (PMMA) in a mass ratio of 2-5:1, the average particle size of the polyvinylidene fluoride is 0.6μm-1.0μm, and the average particle size of the polymethyl methacrylate is 4μm-6μm.

[0076] Mixing small-particle PVDF with large-particle PMMA in a ratio of 2-5:1 helps form a uniform pore structure, allowing the diaphragm to maintain good air permeability and ion conductivity efficiency, thereby improving the battery's cycle and rate performance. When the mass ratio of PVDF to PMMA is greater than 5, excessive small particles will clog the pores, reducing the diaphragm's air permeability and ion conductivity efficiency, affecting the battery's cycle and rate performance; when the mass ratio of PVDF to PMMA is less than 2, excessive large particles will lead to poor adhesion between the diaphragm and the electrode, reducing the battery's cycle and rate performance, as well as safety.

[0077] PVDF particles and PMMA particles in the adhesive layer can be distinguished by the following method: randomly take 100 polymer particles within any 100μm*100μm area on the surface of the adhesive layer. Among them, large-sized PMMA particles are polymer particles with a particle size >1μm, while polymer particles with a size ≤1μm are small-sized PVDF particles.

[0078] Exemplarily, the mass ratio of PVDF to PMMA is 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, etc., or a value within the range formed by any two of the above values.

[0079] The average particle size of PVDF and PMMA can be obtained by laser particle size analyzer. For example, the average particle size of PVDF can be 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, etc., or a value within the range formed by any two of the above values. For example, the average particle size of PMMA can be 4 μm, 4.2 μm, 4.5 μm, 4.7 μm, 5 μm, 5.2 μm, 5.5 μm, 5.7 μm, 6 μm, etc., or a value within the range formed by any two of the above values.

[0080] The wetting agent includes at least one of ethylene oxide, nonylphenol polyoxyethylene ether, and polyoxyethylene-polyoxypropylene block copolymer. Adding the wetting agent to the adhesive layer can reduce the surface energy of the separator, facilitate lithium ion migration, and thus improve the battery's cycle and rate performance.

[0081] In some embodiments, the base film has a thickness of 3 μm to 20 μm. The thickness of the base film affects the overall thickness of the separator. Using a base film of this thickness to manufacture the separator can ensure high mechanical strength and lithium ion transfer rate of the separator, thereby ensuring the cycle and rate performance of the battery.

[0082] The thickness of the base film can be measured by observing a cross section of the base film using a scanning electron microscope (SEM). For example, the thickness of the base film can be 3 μm, 5 μm, 7.5 μm, 10 μm, 12.5 μm, 15 μm, 17.5 μm, 20 μm, or a value within a range formed by any two of the above values.

[0083] The base film includes at least one of polyethylene, polypropylene, polyimide, polyacrylonitrile, and polyethersulfone.

[0084] According to a second aspect of the present application, a lithium-ion secondary battery is provided, comprising the battery cell described in the first aspect. The lithium-ion secondary battery assembled using the battery cell can simultaneously have good cycle performance, rate performance, safety, and low-temperature discharge performance.

[0085] The present application is further described in detail below with reference to specific examples. These examples are not to be construed as limiting the scope of protection claimed in this application. Where specific experimental procedures or conditions are not specified in the Examples and Comparative Examples, the procedures or conditions of conventional experimental procedures described in the literature in this field can be followed. Where the manufacturer of the reagents or instruments used is not specified, they are all commercially available conventional reagent products.

[0086] Example 1

[0087] This embodiment provides a method for preparing a lithium-ion secondary battery, comprising the following steps:

[0088] Positive electrode preparation:

[0089] Lithium cobalt oxide, PVDF binder, and conductive carbon material (Super P: carbon nanotubes = 2:1, weight ratio) were mixed in N-methylpyrrolidone (NMP) solvent at a weight ratio of 95.5:2:2.5. A blender was used to continuously stir the mixture into a uniform, fluid cathode slurry. The slurry was then coated on both sides of a 10μm-thick aluminum foil with a 2% elongation, dried in a 120°C vacuum oven for 6 hours, and then rolled and slit to produce the cathode sheets.

[0090] Negative electrode preparation:

[0091] Graphite, conductive carbon black (Super P), sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber were mixed in a water solvent at a weight ratio of 98:1:0.5:0.5 and continuously stirred in a blender to form a uniform, fluid negative electrode slurry. The slurry was then coated on both sides of a 10μm-thick current collector copper foil and dried in a 120°C vacuum oven for 6 hours. The negative electrode sheets were then rolled and slit.

[0092] Electrolyte preparation:

[0093] In an argon-filled glove box (moisture <1ppm, oxygen <1ppm), ethylene carbonate, propylene carbonate, propyl propionate, and ethyl propionate solvents were mixed into a uniform solvent in a mass ratio of 15:15:50:20. Additives (1,3-propane sultone, 1,3,6-hexane trinitrile, and fluoroethylene carbonate) and LiPF6 were slowly added and stirred evenly to form an electrolyte.

[0094] Based on the mass of the electrolyte, the content of LiPF6 is 15.5 wt%, the content of 1,3-propane sultone is 2 wt%, the content of 1,3,6-hexane trinitrile is 3 wt%, and the content of fluoroethylene carbonate is 10 wt%.

[0095] Diaphragm preparation:

[0096] Using the sol-gel method, ethyl orthosilicate is hydrolyzed under acidic or alkaline conditions to generate Si(OH)4, and the hydroxyl groups condense to form a Si-O-Si network; by adjusting the aging time and baking temperature, Q 4 Porous SiO2 particles with a covalent bond structure content of 81%.

[0097] Ceramic particles, a binder, and a dispersant, polyethylene glycol, were added to an appropriate amount of deionized water in a mass ratio of 93:5:2. The mixture was stirred at 300 rpm for 2 hours to form a ceramic slurry. The ceramic particles consisted of SiO2 and alumina particles prepared in the above steps in a mass ratio of 37.5:55.5, and the binder consisted of polyvinylidene fluoride and sodium carboxymethyl cellulose in a mass ratio of 3:1. The ceramic slurry was then coated onto the first surface of the base film using a gravure roller and dried in a multi-section oven at 60°C to form a 2μm thick ceramic layer.

[0098] 800 parts by weight of small-particle (0.8 μm) polyvinylidene fluoride and 200 parts by weight of large-particle (5.2 μm) polymethyl methacrylate were mixed, and 10 parts by weight of polyacrylate, 1 part by weight of ethylene oxide, and 3000 parts by weight of deionized water were added and stirred to obtain a mixed solution. Using a dot-coating technique, the mixed solution was applied to the second side surface of the base film and the surface of the ceramic layer facing away from the base film, and then dried to obtain a diaphragm.

[0099] Lithium-ion secondary battery preparation:

[0100] The prepared positive electrode sheet, separator, and negative electrode sheet are wound to prepare a bare cell; the bare cell is then placed in an aluminum-plastic film, and the prepared electrolyte is injected into the dried bare cell. After vacuum packaging, room temperature standing, and high-temperature formation, a lithium-ion secondary battery is obtained.

[0101] The preparation methods of Examples 2 to 23 and Comparative Examples 1 to 5 are basically the same as those of Example 1. The differences are shown in Tables 1 and 2. 4 The mass content of the covalent bond structure, B is the mass content of the lithium salt, C is the mass content of the Si element in the ceramic layer, and the Raman peak area ratio is the ratio of the peak area of ​​the first characteristic peak to the second characteristic peak in the Raman spectrum of the electrolyte.

[0102] Table 1

[0103]

[0104]

[0105] Table 2

[0106]

[0107]

[0108] Test Case

[0109] 1. Rate performance test

[0110] At 25±3°C, charge the lithium-ion secondary battery at a constant current and voltage of 1C to 4.53V, cut off at 0.05C, and then discharge at a constant current of 0.5C to 3.0V. Record the initial discharge capacity as C0. Then charge at 1C to 4.53V, then charge at a constant voltage of 0.05C to cut off. Let it rest for 30 minutes, then discharge at a constant rate of 5C to 3.0V. Record the discharge capacity as C1. Calculate the capacity retention: C = C1 / C0 * 100%.

[0111] 2. Low temperature discharge performance test

[0112] Test the sample's voltage, internal resistance, and thickness at 25±5°C, then allow to rest for 10 minutes. Discharge at 0.2C to the lower voltage limit and allow to rest for 10 minutes. Charge at 0.7C to 4.5V, cut off at 0.025C, allow to rest for 10 minutes, discharge at 0.2C to the lower voltage limit, allow to rest for 10 minutes, and calibrate the initial capacity (Q0). Charge at 0.7C to the upper voltage limit, cut off at 0.025C, and allow to rest for 10 minutes. Allow to rest at -10±2°C for 4 hours, and discharge at 0.4C to the lower voltage limit at this temperature. Calculate the low-temperature discharge capacity (Q1), with a capacity retention ratio of Q1 / Q0*100%.

[0113] 3. Cycle performance test

[0114] At 45°C ± 2°C, the lithium-ion secondary battery was charged at a constant current and constant voltage of 0.7C to 4.53V, cut off at 0.05C, and the initial thickness P0 was recorded. It was then discharged at a constant current of 0.2C to 3.0V, with the initial discharge capacity recorded as C0. It rested for 10 minutes. The cycling system was as follows: charged at a constant current and constant voltage of 3C to 4.25V, cut off at 2C, switched to a constant current and constant voltage of 2C to 4.48V, cut off at 1.5C, switched to a constant current and constant voltage of 1.5C to 4.53V, cut off at 0.18C, rested for 5 minutes, and discharged at 0.7C to 3.0V. After 400T of cycling, it was charged at a constant current and constant voltage of 0.7C to 4.53V, cut off at 0.05C, and the final thickness P1 was recorded. It was then discharged at a constant current of 0.2C to 3.0V, with the initial discharge capacity recorded as C1. Calculate the capacity retention rate: C = C1 / C0*100%, and the thickness expansion rate: P = (P1-P0) / P0*100%.

[0115] 4. Furnace temperature test

[0116] The battery cell is fully charged to the upper limit of 4.5V. The cell is then placed in an oven and heated at a rate of 5±2°C / min to the set target temperature of 130°C. The temperature is then maintained for 60 minutes before the test is complete. The cell passes if it does not catch fire or explode. If the temperature continues to rise until it catches fire or explodes, the test fails. Twenty samples are tested to see if each passes this test.

[0117] The above test results are shown in Table 3.

[0118] Table 3

[0119]

[0120]

[0121] Combining Tables 1 to 3, it can be seen that compared with Comparative Examples 1 to 5, the Q content of the diaphragm ceramic layer of Examples 1 to 23 is 4The mass content A of the covalent bond structure and the mass content B of the lithium salt in the electrolyte satisfy 11.13≥A / B≥1.47, thus showing good rate, high temperature cycle and low temperature discharge performance and thermal safety. Among them, the Si element content in the diaphragm ceramic layer of Example 7 and Example 10 is relatively high, resulting in a large C / B value, poor thermal conductivity of the diaphragm, and thus affecting the thermal safety of the battery; on the contrary, the Si element content in the diaphragm ceramic layer of Example 9 is relatively low, resulting in a C / B value that is too small, which is not conducive to the rate, high temperature cycle and low temperature discharge performance of the battery. The diaphragm ceramic layer of Example 13 is formed by the accumulation of small-sized ceramic particles, which causes the diaphragm dynamics to deteriorate, thereby affecting the rate, high temperature cycle and low temperature discharge performance of the battery; a diaphragm ceramic layer that is too thin (such as Example 14) or too thick (such as Example 15) will affect the battery performance, especially when the diaphragm ceramic layer is too thin, it will also aggravate the thermal safety risk of the battery. Furthermore, a mass ratio of small PVDF particles to large PMMA particles in the diaphragm adhesive layer that is too small (such as in Example 18) or too large (such as in Example 19) will also have an adverse effect on battery performance, especially when the mass ratio is too small, it will also reduce the thermal safety of the battery.

[0122] Comparative Example 1 Compared with Example 3, the Q 4 The mass content of the covalent bond structure increases, resulting in an excessively large A / B value. Although this helps improve the rate and high-temperature cycle performance of the battery, it seriously affects the low-temperature discharge performance and thermal safety of the battery due to the poor thermal conductivity of the diaphragm. 4 The mass content of the covalent bond structure decreases, resulting in a too small A / B value and an increase in the internal resistance of the battery, which significantly deteriorates the battery's rate, high-temperature cycle and low-temperature discharge performance.

[0123] Compared to Example 4, the electrolyte in Comparative Example 3 has an excessively high lithium salt content, an excessively low A / B ratio, and numerous interfacial side reactions, severely impacting the battery's rate capability, high-temperature cycling, low-temperature discharge performance, and thermal safety. Furthermore, compared to Example 1, the electrolyte in Comparative Example 4 has an excessively low lithium salt content and an excessively high A / B ratio, similarly detrimental to battery performance.

[0124] Compared with Example 1, the diaphragm ceramic layer of Comparative Example 5 does not contain silicon dioxide, but only aluminum oxide particles. The battery has good thermal safety, but cannot improve the battery's rate, high-temperature cycle and low-temperature discharge performance.

[0125] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of this application.

Claims

1. A battery cell comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte; characterized in that: The electrolyte includes a lithium salt, wherein the lithium salt includes at least one of lithium hexafluorophosphate and lithium difluorophosphate; based on the mass of the electrolyte, the mass content B of the lithium salt is 8%-18%; The diaphragm includes a base film and a ceramic layer provided on at least one side surface of the base film in a thickness direction, wherein the ceramic layer includes SiO2, and the Si-O bond in the SiO2 includes Q 4 Covalent bond structure, based on the mass of Si element in the ceramic layer, the Q 4 The mass content A of the covalent bond structure is 26.4%-89%; Meets: 11.13≥A / B≥1.

47.

2. The battery cell according to claim 1, characterized in that The mass content C of Si element in the ceramic layer is 16.8%-33.3%, satisfying the following: 4.16≥C / B≥0.93; And / or, the ceramic layer further includes P element, and the mass content of P element in the ceramic layer is 0.2%-1.3%.

3. The battery cell according to claim 1, characterized in that The thickness of the ceramic layer is 0.5 μm-10 μm; And / or, the contact angle of the electrolyte on the surface of the ceramic layer is 10°-40°.

4. The battery cell according to claim 1, characterized in that The electrolyte also includes ethylene carbonate. The Raman spectrum of the electrolyte includes a first characteristic peak and a second characteristic peak. The Raman shift of the first characteristic peak is at 712.5 cm -1 -725cm -1 In the range, the Raman shift of the second characteristic peak is at 739cm -1 -752cm -1 In the range, the ratio of the peak areas of the first characteristic peak to the second characteristic peak is 0.8-1.5; Preferably, the electrolyte further comprises at least one of a nitrile additive and a sulfonate additive; More preferably, the nitrile compounds include acetonitrile, malononitrile, succinonitrile, glutaronitrile, adiponitrile, 1,3,6-hexanetrinitrile, 1,3,5-pentanetrinitrile, ethylene glycol dipropionitrile ether, hexafluorocyclotriphosphazene, pentafluoroethoxycyclotriphosphazene, pentafluorophenoxycyclotriphosphazene, 1,4-dicyano-2-butene, p-fluorobenzonitrile, p-methylbenzonitrile, 2-fluoroadiponitrile, 2,2-difluorosuccinonitrile, tricyanobenzene, acrylonitrile, crotononitrile, trans-butenedicononitrile, trans-hexenedicononitrile, 3-(trimethylsilyloxy)propionitrile, 1,3,4,6-hexanetetranitrile, 1,2,4,5-benzenetetracarbonitrile, 2,3,5,6-pyrazinetetranitrile, sebacononitrile, azelaic acid dicyanobenzene, pyridine-3- at least one of 1,4-dicarbonitrile, 2,5-dicyanopyridine, 2,2,3,3-tetrafluorosuccinonitrile, tetrafluoroterephthalonitrile, 4-tetrahydrothiopyranylmalononitrile, 1,4,5,6-tetrahydro-5,6-dioxo-2,3-pyrazinedicarbonitrile, 1,3,5-cyclohexanetricarbonitrile, 1,2,3-propanetricarbonitrile, glyceroltricarbonitrile, tris(3-cyanopropyl)phosphate, 1,1,3,3-propanetetracarbonitrile, 1,2,2,3-tetracyanopropane, 3-methyl-3-propyl-cyclopropane-1,1,2,2-tetracarbonitrile, 7,7,8,8-tetracyanoquinodimethane, tetracyanoethylene, di(cyanoethoxy)ethane, tris(cyanoethoxy)propane, and tetra(cyanoethoxy)butane; More preferably, the sulfonate additive includes at least one of 1,3-propane sultone, 1,3-propylene sultone, and methylene methanedisulfonate.

5. The battery cell according to any one of claims 1 to 4, characterized in that: The ceramic layer comprises 10-78 parts by weight of ceramic particles, 1-10 parts by weight of a binder, and 0.5-2 parts by weight of a dispersant; Preferably, the average particle size of the ceramic particles is 0.1 μm-5 μm; Preferably, the ceramic particles include SiO2 particles, and the SiO2 particles include at least one of solid SiO2, porous SiO2, and hollow SiO2.

6. The battery cell according to claim 5, characterized in that The ceramic particles further include at least one of alumina and boehmite; And / or, the pore size of the porous SiO2 is 2nm-50nm; and / or, the pore size of the hollow SiO2 is 50nm-500nm; And / or, the binder includes at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyimide, polyacrylonitrile, polymethyl (meth)acrylate, aramid resin, poly (meth)acrylic acid, styrene-butadiene rubber, polyvinyl alcohol, polyvinyl acetate, carboxymethyl cellulose, sodium carboxymethyl cellulose, carboxyethyl cellulose, polyacrylamide, phenolic resin, epoxy resin, water-based polyurethane, ethylene-vinyl acetate copolymer, polyacrylic copolymer, lithium polystyrene sulfonate, water-based silicone resin, nitrile-polyvinyl chloride blend, styrene-acrylic latex, pure styrene latex, or blends or copolymers derived from the aforementioned polymer modifications; And / or, the dispersant includes at least one of multi-branched alcohol, triethyl phosphate, polyethylene glycol, fluorinated polyethylene oxide, polyethylene oxide, stearic acid, sodium dodecylbenzene sulfonate, sodium hexadecyl sulfonate, fatty acid glyceride, sorbitan fatty acid ester, and polysorbate.

7. The battery cell according to any one of claims 1 to 4, characterized in that: The diaphragm also includes a glue layer, which is arranged on both side surfaces of the base film in the thickness direction, and the ceramic layer is located between the glue layer and the base film; the ratio of the area of ​​the glue layer to the area of ​​one side surface of the base film is 0.1-0.

5.

8. The battery cell according to claim 7, characterized in that The adhesive layer includes adhesive particles and a wetting agent; The rubber particles include polyvinylidene fluoride and polymethyl methacrylate in a mass ratio of 2-5:1, the average particle size of the polyvinylidene fluoride is 0.6 μm-1.0 μm, and the average particle size of the polymethyl methacrylate is 4 μm-6 μm; And / or, the wetting agent includes at least one of ethylene oxide, nonylphenol polyoxyethylene ether, and polyoxyethylene polyoxypropylene block copolymer.

9. The battery cell according to claim 1, characterized in that: The thickness of the base film is 3 μm-20 μm; And / or, the base film includes at least one of polyethylene, polypropylene, polyimide, polyacrylonitrile, and polyethersulfone.

10. A lithium ion secondary battery, characterized in that: The battery cell comprises the battery cell according to any one of claims 1 to 9.

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