Electrochemical device and electronic device

Abstract

The invention discloses an electrochemical device and an electronic device. The electrochemical device comprises a positive pole piece, a negative pole piece, an isolating membrane and electrolyte, the isolating membrane is arranged between the positive pole piece and the negative pole piece, and the isolating membrane comprises a base membrane and a first coating at least arranged on one side of the base membrane; the first coating comprises a fluorine-containing polymer, and the layered thickness of the fluorine-containing polymer is 2.2 nm to 4 nm; the electrolyte comprises an additive, and the additive comprises a phosphorus-containing additive. The safety performance at high temperature, the low-temperature floating charge performance and the intermittent cycle performance can be improved.

Description

Technical Field

[0001] The present application relates to the field of batteries, and particularly to an electrochemical device and an electronic device. Background Art

[0002] In today's energy field, secondary batteries are increasingly widely used, and their performance directly affects the use effect and safety of many devices. However, secondary batteries face many problems that need to be solved urgently in different temperature environments.

[0003] On the one hand, in a high-temperature environment, the existing separator coating materials are difficult to simultaneously achieve appropriate adhesiveness with the electrode plate and mechanical support of the separator at high temperatures, resulting in a significant reduction in battery performance. On the other hand, in a low-temperature environment, the floating charge performance and intermittent cycle performance of secondary batteries are poor. The insufficient adhesiveness between the separator and the electrode plate seriously affects the low-temperature performance of the battery.

[0004] Currently, the technical means adopted to solve the above problems have many limitations and cannot effectively balance the safety performance, low-temperature floating charge performance, and intermittent cycle performance of secondary batteries at high temperatures. Summary of the Invention

[0005] Embodiments of the present application provide an electrochemical device and an electronic device, which can improve the safety performance, low-temperature floating charge performance, and intermittent cycle performance at high temperatures.

[0006] In a first aspect, embodiments of the present application provide an electrochemical device, which includes a positive electrode plate, a negative electrode plate, a separator, and an electrolyte. The separator is disposed between the positive electrode plate and the negative electrode plate. The separator includes a base film and at least a first coating disposed on one side of the base film. The first coating includes a fluoropolymer, and the layered thickness of the fluoropolymer is 2.2 nm to 4 nm. The electrolyte includes an additive, and the additive includes a phosphorus-containing additive.

[0007] According to the present application, when a fluoropolymer is included in the first coating of the separator of the electrochemical device, the first coating material on the separator substrate can have an appropriate layered thickness, so that the separator coating material can exhibit appropriate adhesiveness between the separator and the electrode plate at high temperatures. Moreover, when the layered thickness meets 2.2 nm to 4 nm, the material can also provide certain mechanical support for the separator when it becomes a fluid state. When the electrolyte includes a phosphorus-containing additive, combined with the layered thickness of the fluoropolymer that meets the scope of the present application, it can provide higher mechanical stability for the separator material when the secondary battery is at a relatively high temperature, reduce the thermal shrinkage rate of the separator, and thus improve the test passing rate of the secondary battery during high-temperature drop. The phosphorus-containing additive in the electrolyte helps to maintain the adhesiveness of the binder in the first coating material, so as to maintain excellent adhesiveness between the separator and the electrode plate, thereby improving the low-temperature intermittent cycling performance of the secondary battery. At the same time, the phosphorus element can form a stable solid electrolyte interface film (SEI, Solid Electrolyte Interface) at the interface between the negative electrode and the electrolyte, and this interface film can effectively inhibit the redox reaction of the electrolyte at the interface, thereby improving the self-discharge behavior of the secondary battery and reducing the voltage drop of the secondary battery at low temperatures.

[0008] In some specific embodiments, the layered thickness of the fluoropolymer is 3 nm to 3.8 nm.

[0009] In this specific embodiment, when the layered thickness of the fluoropolymer is 3 nm to 3.8 nm, the bonding material can provide better mechanical support for the separator when it transforms into a fluid or semi-fluid state at high temperatures, thereby further improving the drop performance and low-temperature intermittent cycling performance of the secondary battery at high temperatures. At the same time, it can also further improve the self-discharge phenomenon at low temperatures and reduce the voltage drop at low temperatures.

[0010] In some specific embodiments, the fluoropolymer includes a polyvinylidene fluoride-hexafluoropropylene copolymer, and the polyvinylidene fluoride-hexafluoropropylene copolymer satisfies at least one of the following: (1) the average molecular weight of the polyvinylidene fluoride-hexafluoropropylene copolymer is 110 KDa to 140 KDa; (2) the volume resistivity of the polyvinylidene fluoride-hexafluoropropylene copolymer is 10 13 Ω·cm to 10 15 Ω·cm; (3) the dielectric strength of the polyvinylidene fluoride-hexafluoropropylene copolymer is 15 kV / mm to 45 kV / mm.

[0011] In this specific embodiment, when the average molecular weight of the polyvinylidene fluoride-hexafluoropropylene copolymer is 110 KDa to 140 KDa, it can improve the mechanical strength of the first coating. In a high-temperature environment, it helps the separator to better maintain its own structural stability, provides more reliable mechanical support for the separator, thereby further reducing the thermal shrinkage rate of the separator and enhancing the safety performance of the secondary battery. At the same time, the polyvinylidene fluoride-hexafluoropropylene copolymer can optimize the bonding effect between the separator and the electrode, improve the interfacial bonding force between the separator and the electrode, and enhance the intermittent cycling performance of the secondary battery in a low-temperature environment.

[0012] When the volume resistivity of the polyvinylidene fluoride-hexafluoropropylene copolymer is 1013 Ω·cm to 1015 Ω·cm, it can construct a good ion transport channel inside the secondary battery. During the charge and discharge process of the battery, it helps to accurately control the migration rate and direction of ions, ensure the efficient and stable transport of ions between the electrode and the electrolyte, thereby enhancing the charge and discharge efficiency of the battery and increasing the battery output power.

[0013] When the dielectric strength of the polyvinylidene fluoride-hexafluoropropylene copolymer is 15 kV / mm to 45 kV / mm, the polyvinylidene fluoride-hexafluoropropylene copolymer can withstand a greater electric field strength without being broken down, thereby ensuring the stable distribution of the internal electric field of the secondary battery. This helps to maintain the stability of the ion transport path, enabling ions to continuously and orderly shuttle between the electrode and the electrolyte, avoiding the obstruction of ion transport caused by electric field disorder, and thus enhancing the charge and discharge efficiency and stability of the secondary battery.

[0014] In some specific embodiments, the phosphorus-containing additive includes at least one of ethoxy(pentafluoro)cyclotriphosphazene, trimethyl phosphate, triphenyl phosphate, and trimethyl phosphite. Based on the total mass of the electrolyte, the mass percentage content of at least one of ethoxy(pentafluoro)cyclotriphosphazene, trimethyl phosphate, triphenyl phosphate, and trimethyl phosphite is C(%), and the electrochemical device satisfies: 3.2 ≤ C ≤ 9.8.

[0015] In this specific embodiment, when the phosphorus-containing additive includes at least one of ethoxy(pentafluoro)cyclotriphosphazene, trimethyl phosphate, triphenyl phosphate, and trimethyl phosphite and the electrochemical device satisfies: 3.2 ≤ C ≤ 9.8, when the secondary battery is in a relatively high-temperature situation, it can provide higher mechanical stability for the separator material, thereby improving the passing rate of the secondary battery during high-temperature drop, and is more helpful for maintaining the adhesiveness of the binder in the first coating material, so that a good adhesiveness is maintained between the separator and the electrode, thereby further improving the drop performance and low-temperature intermittent cycling performance of the secondary battery at high temperature, and at the same time can also further improve the self-discharge phenomenon at low temperature and reduce the voltage drop at low temperature.

[0016] In some specific embodiments, the layered thickness of the fluoropolymer is N (nm), the phosphorus-containing additive includes at least one of ethoxy(pentafluoro)cyclotriphosphazene, trimethyl phosphate, triphenyl phosphate, and trimethyl phosphite. Based on the total mass of the electrolyte, the mass percentage of at least one of ethoxy(pentafluoro)cyclotriphosphazene, trimethyl phosphate, triphenyl phosphate, and trimethyl phosphite is C (%). The electrochemical device satisfies: 0.3 ≤ N / C ≤ 1.

[0017] In this specific embodiment, the electrochemical device satisfies: 0.3 ≤ N / C ≤ 1. The separator can form a good bonding effect with the electrode at high temperatures, and at the same time provide certain mechanical support for the separator. It synergistically acts with at least one of ethoxy(pentafluoro)cyclotriphosphazene, trimethyl phosphate, triphenyl phosphate, and trimethyl phosphite. When the battery is in a high-temperature environment, it further stabilizes the coating structure, strengthens the adhesion between the separator and the electrode, enables the separator to maintain a stable form at high temperatures, effectively reduces the thermal shrinkage rate of the separator, greatly improves the passing rate of the secondary battery in tests such as high-temperature drop, and significantly enhances the high-temperature safety of the battery. At the same time, in a low-temperature environment, the two act synergistically to enhance the bonding performance of the binder in the coating, enabling the separator and the electrode to always maintain an excellent bonding state in a low-temperature environment, effectively improving the low-temperature intermittent cycling performance of the secondary battery, reducing the voltage drop of the battery at low temperatures, and improving the working efficiency and endurance of the battery in a low-temperature environment.

[0018] Moreover, the two act synergistically. During the cycling process, they can not only maintain good contact between the separator and the electrode, but also protect the electrode material, reduce the loss of the electrode material, thereby prolonging the cycle life of the secondary battery and improving the comprehensive performance of the battery.

[0019] In some specific embodiments, the separator may further include a second coating. The second coating includes β-chitin. Based on the total mass of the second coating, the mass percentage of β-chitin is M (%). The phosphorus-containing additive includes at least one of ethoxy(pentafluoro)cyclotriphosphazene, trimethyl phosphate, triphenyl phosphate, and trimethyl phosphite. Based on the total mass of the electrolyte, the mass percentage of at least one of ethoxy(pentafluoro)cyclotriphosphazene, trimethyl phosphate, triphenyl phosphate, and trimethyl phosphite is C (%). The electrochemical device satisfies: 0.6 ≤ M / C ≤ 3.5.

[0020] In this specific embodiment, when the electrochemical device satisfies 0.6 ≤ M / C ≤ 3.5, the second coating containing β-chitin can induce the uniform movement of lithium ions, thereby improving the capacity retention rate of the secondary battery in the low-temperature intermittent cycle test. At the same time, this material helps the phosphorus additives including ethoxy(pentafluoro)cyclotriphosphazene, trimethyl phosphate, triphenyl phosphate, and / or trimethyl phosphite to form a uniform and dense cathode-electrolyte interface (CEI) film, thereby improving the self-discharge phenomenon and reducing the low-temperature voltage drop. This material has excellent heat resistance, so it can absorb the heat at the interface during the high-temperature drop test and improve the passing rate of the high-temperature drop test.

[0021] In some specific embodiments, the phosphorus-containing additive includes lithium difluorophosphate. Based on the total mass of the electrolyte, the mass percentage of lithium difluorophosphate is D (%). The electrochemical device satisfies 0.03 ≤ D ≤ 0.9.

[0022] In this specific embodiment, when the phosphorus-containing additive includes lithium difluorophosphate and the electrochemical device satisfies 0.03 ≤ D ≤ 0.9, lithium difluorophosphate can form a uniform and dense CEI film at the interface between the positive electrode and the electrolyte. This interface film can effectively inhibit the redox reaction of the electrolyte at the interface, reduce the formation of interface by-products, thereby improving the self-discharge behavior of the secondary battery and reducing the voltage drop of the secondary battery at low temperature.

[0023] In some specific embodiments, the electrochemical device satisfies 0.03 ≤ D ≤ 0.6.

[0024] In this specific embodiment, lithium difluorophosphate can form a uniform, dense and thin cathode solid electrolyte interface film at the interface between the positive electrode and the electrolyte. This interface film can better inhibit the redox reaction of the electrolyte at the interface, reduce the formation of interface by-products, thereby improving the self-discharge behavior of the secondary battery and reducing the voltage drop of the secondary battery at low temperature.

[0025] In some specific embodiments, the first coating may further include a surfactant. The surfactant includes at least one of perfluoroalkyl triethylene oxide methyl ether, polyoxyethylene alkyl ether, polyoxyethylene fatty acid ester, polyoxyethylene alkylphenol ether, and sorbitan aliphatic ester.

[0026] In this specific embodiment, when the first coating includes a surfactant, it can improve the wettability between the first coating and the electrolyte, enhance the interaction between the electrolyte and the first coating. While strengthening the adhesion between the separator and the electrode, it can also promote more uniform heat conduction inside the battery, effectively alleviate the phenomenon of local overheating, keep the separator in a more stable form at high temperatures, further reduce the thermal shrinkage rate of the separator, and improve the safety and reliability of the secondary battery in a high-temperature environment. In a low-temperature environment, the surfactant helps to lower the freezing point of the electrolyte and improve the fluidity of the electrolyte at low temperatures. Combined with the effect of the phosphorus-containing additive in promoting ion conduction, it can further increase the migration rate of ions in the electrolyte at low temperatures. At the same time, the surfactant can enhance the activity of the binder in the first coating in a low-temperature environment, making the adhesion state between the separator and the electrode more stable at low temperatures. It effectively improves the low-temperature intermittent cycling performance of the secondary battery and reduces the voltage drop of the secondary battery at low temperatures.

[0027] In some specific embodiments, the bulk density of the first coating is 0.5 g / cm 3 ~20 g / cm 3 .

[0028] In this specific embodiment, when the bulk density of the first coating is 0.5 g / cm 3 ~20 g / cm 3 , it helps to construct a good ion transport channel, which will neither cause chaotic ion transport paths due to excessive looseness nor hinder ion migration due to excessive tightness, effectively reducing the battery polarization phenomenon, lowering the battery internal resistance, and improving the charge-discharge efficiency and output voltage of the battery. Further, in a low-temperature environment, this bulk density can cooperate with the effect of the phosphorus-containing additive in promoting ion conduction, improve the migration rate of ions in the electrolyte at low temperatures, and effectively improve the low-temperature intermittent cycling performance of the secondary battery and reduce the voltage drop of the battery at low temperatures.

[0029] In some specific embodiments, the electrochemical device satisfies at least one of the following: (1) The base film includes a crosslinked polyolefin resin, and the crosslinked polyolefin resin includes a silicon-containing organic group; (2) The surface glossiness of the base film is G (GU), where 0 < G ≤ 5; (3) The separator may further include chromium element, and based on the total mass of the separator, the content of the chromium element is 0.2 ppm to 18 ppm.

[0030] In this specific embodiment, when the base film includes a crosslinked polyolefin resin and the crosslinked polyolefin resin includes a silicon-containing organic group, the wettability of the electrolyte to the adjacent electrode sheet material can be further improved. In the low-temperature intermittent cycle test, even during intermittent charge and discharge, sufficient lithium ion sources can be provided in a timely manner for the material exchange between the positive and negative electrodes, thereby improving the low-temperature intermittent cycle performance of the secondary battery. At the same time, this material is beneficial for the flame retardant additive containing phosphorus in the electrolyte to play a flame retardant role, thereby improving the passing rate of the drop test of the secondary battery at high temperature. In addition, this material can help the phosphorus-containing additive form a more stable solid electrolyte interface film on the negative electrode, thereby reducing interfacial side reactions and improving the self-discharge phenomenon of the secondary battery at low temperature and reducing the voltage drop.

[0031] When the surface gloss of the base film of the separator satisfies 0 < G ≤ 5, the surface of the base film has a certain flatness, so that the coating can better fit with the substrate, thereby improving the energy density of the electrochemical device. The higher the surface gloss of the substrate, the flatter the surface. However, when the gloss is too high, the surface force between the coating and the substrate is less, and the difficulty of coating the coating increases; when the gloss is too low, the energy density of the electrochemical device is low, and due to the overly uneven surface, the safety risk of the electrochemical device increases, and the passing rate of the high-temperature drop test of the electrochemical device decreases.

[0032] When the separator includes chromium element and the content of chromium element is 0.2 ppm to 18 ppm, the chromium element can improve the mechanical strength of the separator. Chromium atoms can form chemical bonds or strengthen intermolecular forces with the base material of the separator, such as polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), etc. In a high-temperature environment, this strengthening effect makes the separator not easily deformed and better maintains its own structure. The chromium element, the layered thickness of the fluorine-containing polymer, and the phosphorus-containing additive act synergistically to enhance the adhesion stability between the separator and the electrode sheet at high temperature. In tests such as high-temperature drop, the chromium-containing separator can effectively reduce the thermal shrinkage rate and improve the safety and reliability of the secondary battery under high-temperature conditions.

[0033] In some specific embodiments, based on the total mass of the separator, the content of chromium element is 0.2 ppm to 10 ppm.

[0034] In this specific embodiment, when the content of chromium element is 0.2 ppm to 10 ppm, the adhesion stability between the separator and the electrode sheet at high temperature can be further enhanced. The chromium-containing separator can effectively reduce the thermal shrinkage rate and improve the safety and reliability of the secondary battery under high-temperature conditions.

[0035] In some specific embodiments, the electrochemical device satisfies at least one of the following: (1) The additive may further include lithium difluoro(oxalato)borate, lithium bis(trifluoromethanesulfonyl)imide, and / or lithium difluorophosphate. Based on the total mass of the electrolyte, the mass percentage content of lithium difluoro(oxalato)borate, lithium bis(trifluoromethanesulfonyl)imide, and / or lithium difluorophosphate is X (%), and 0.02 ≤ X ≤ 4.4; (2) The additive may further include 1,3-propane sultone. Based on the total mass of the electrolyte, the mass percentage content of 1,3-propane sultone is Y (%), and 0.25 ≤ Y ≤ 4; (3) The additive may further include vinylene carbonate. Based on the total mass of the electrolyte, the mass percentage content of vinylene carbonate is A (%), and 0.12 ≤ A ≤ 3.3; (4) The additive may further include a fluorinated linear asymmetric carbonate. Based on the total mass of the electrolyte, the mass percentage content of the fluorinated linear asymmetric carbonate is B (%), and 2 ≤ B ≤ 28; (5) The electrolyte includes propyl propionate and / or ethyl propionate. Based on the total mass of the electrolyte, the mass percentage content of propyl propionate and / or ethyl propionate is E (%), and 26 ≤ E ≤ 40.

[0036] In this specific embodiment, when the electrolyte of the electrochemical device includes lithium difluoro(oxalato)borate, lithium bis(trifluoromethanesulfonyl)imide, or lithium difluorophosphate and satisfies 0.02 ≤ X ≤ 4.4, lithium difluoro(oxalato)borate can promote the activation of propyl propionate, thereby further promoting the circulation of lithium ions in the electrolyte, improving the low-temperature fast charging performance of the electrochemical device, and reducing the voltage drop at high temperatures.

[0037] When the electrolyte of the electrochemical device includes 1,3-propane sultone and satisfies 0.25 ≤ Y ≤ 4, 1,3-propane sultone can form a more stable SEI film on the surface of the positive electrode material, improving the low-temperature fast charging performance of the electrochemical device.

[0038] When the electrolyte of the electrochemical device contains vinylene carbonate and 0.12 ≤ A ≤ 3.3, vinylene carbonate can form a more uniform and dense SEI film on the surface of the negative electrode material, further improving the low-temperature fast charging performance of the electrochemical device.

[0039] When the electrolyte of the electrochemical device includes a fluorinated linear asymmetric carbonate and satisfies 2 ≤ B ≤ 28, the fluorinated linear asymmetric carbonate can participate in the construction of the SEI film, and the formed SEI film is denser and more stable. The presence of fluorine atoms enhances the protection of the SEI film on the electrode, effectively inhibits the side reaction between the electrolyte and the negative electrode material, prevents the continuous consumption of active lithium, and improves the Coulomb efficiency of the battery. Moreover, the fluorinated linear asymmetric carbonate helps to stabilize the CEI film, and synergistically with the phosphorus-containing additive, further inhibits the redox reaction at the interface between the positive electrode and the electrolyte, reduces the corrosion and degradation of the electrode material, maintains the stability of the structure of the positive electrode material, thereby ensuring the capacity retention rate of the battery during long-term cycling and extending the cycle life of the battery.

[0040] When the electrolyte of the electrochemical device includes and 26 ≤ E ≤ 40, propyl propionate and / or ethyl propionate further promote the circulation of lithium ions in the electrolyte, improve the low-temperature fast charging performance of the electrochemical device and reduce the voltage drop at high temperatures.

[0041] In some specific embodiments, the electrochemical device satisfies at least one of the following: (1) 0.25 ≤ Y ≤ 1.8; (2) 0.12 ≤ A ≤ 2; (3) the fluorinated linear asymmetric carbonate includes at least one of dimethyl fluorocarbonate, diethyl fluorocarbonate, and fluoromethyl ethyl carbonate.

[0042] In this specific embodiment, when the electrochemical device satisfies at least one of the above conditions, the low-temperature fast charging performance of the electrochemical device can be further improved.

[0043] In a second aspect, an embodiment of the present application provides an electronic device, and the electronic device includes the electrochemical device of the first aspect. Specific Embodiments

[0044] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below. Apparently, the described embodiments are some, but not all, of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts shall fall within the protection scope of the present application.

[0045] As used in the present application, the terms "include", "contain", and "comprise" are used in their open, non-limiting sense.

[0046] In addition, sometimes quantities, ratios, and other numerical values are presented in a range format in this text. It should be understood that such range formats are for convenience and brevity, and should be understood flexibly, including not only the explicitly specified numerical values as range limits, but also all individual numerical values or sub-ranges covered within the said range, as if each numerical value and sub-range were explicitly specified.

[0047] In the specific embodiments and the claims, a list of items connected by terms such as "one or more of", "one or more in", "at least one of", or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A or B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, or C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may include a single element or multiple elements. Item B may include a single element or multiple elements. Item C may include a single element or multiple elements.

[0048] In today's energy field, secondary batteries are increasingly widely used, and their performance directly affects the use effects and safety of many devices. However, secondary batteries face many problems that need to be solved urgently in different temperature environments.

[0049] In a high-temperature environment, the safety performance of secondary batteries is severely tested. On the one hand, the adhesiveness between the separator and the electrode is unstable, and the thermal shrinkage rate of the separator is relatively high, which greatly affects the passing rate of the secondary battery in extreme cases such as high-temperature drop, and is prone to cause safety hazards. On the other hand, existing separator coating materials are difficult to simultaneously achieve appropriate adhesiveness with the electrode and mechanical support of the separator at high temperatures, resulting in a significant reduction in battery performance. In addition, in a high-temperature environment, the high-temperature mechanical performance and high-temperature floating charge performance of the battery are crucial. High temperature will cause the internal materials of the battery to expand and deform. If the mechanical performance is insufficient, it is extremely easy to cause serious safety problems such as shell rupture and internal short circuit; for battery systems in a floating charge state for a long time, such as uninterruptible power supplies (UPS), poor high-temperature floating charge performance will lead to increased self-discharge, shortened life, increased maintenance costs and replacement frequencies.

[0050] In a low-temperature environment, the floating charge performance and intermittent cycle performance of secondary batteries are poor. The insufficient adhesiveness between the separator and the electrode seriously affects the low-temperature intermittent cycle performance of the battery. At the same time, the electrolyte is prone to redox reactions at the negative electrode and the interface, resulting in increased self-discharge behavior of the battery, obvious voltage drop at low temperatures, and further reducing the use efficiency and life of the battery.

[0051] Currently, the technical means adopted to solve the above problems have many limitations and cannot effectively balance the safety performance of secondary batteries at high temperatures, the low-temperature floating charge performance, and the intermittent cycle performance.

[0052] Based on the above problems, embodiments of the present application provide an electrochemical device and an electronic device, which can improve the safety performance, low-temperature floating charge performance, and intermittent cycle performance at high temperatures.

[0053] The following provides a detailed description of the embodiments of the present application.

[0054] Electrochemical device

[0055] In a first aspect, embodiments of the present application provide an electrochemical device, which includes a positive electrode plate, a negative electrode plate, a separator, and an electrolyte. The separator is disposed between the positive electrode plate and the negative electrode plate. The separator includes a base film and at least a first coating disposed on one side of the base film; the first coating includes a fluoropolymer, and the layer thickness of the fluoropolymer is 2.2 nm to 4 nm; the electrolyte includes an additive, and the additive includes a phosphorus-containing additive.

[0056] For example, the layer thickness of the fluoropolymer can be 2.2 nm, 2.3 nm, 2.4 nm, 2.5 nm, 2.6 nm, 2.7 nm, 2.8 nm, 2.9 nm, 3 nm, 3.1 nm, 3.2 nm, 3.3 nm, 3.4 nm, 3.5 nm, 3.6 nm, 3.7 nm, 3.8 nm, 3.9 nm, 4 nm, or a range composed of any of the above values.

[0057] Optionally, the layer thickness of the fluoropolymer can be 2.3 nm to 4 nm, 2.4 nm to 4 nm, 2.5 nm to 4 nm, 2.6 nm to 4 nm, 2.7 nm to 4 nm, 2.8 nm to 4 nm, 2.9 nm to 4 nm, 3 nm to 4 nm, 3 nm to 3.9 nm, 3 nm to 3.8 nm.

[0058] As an example, the fluoropolymer can be one or more of poly(vinylidene fluoride-hexafluoropropylene) copolymer, poly(vinylidene fluoride-trifluoroethylene) copolymer, and poly(vinylidene fluoride-chlorotrifluoroethylene) copolymer.

[0059] According to the present application, when a fluoropolymer is included in the first coating of the separator of the electrochemical device, the first coating material on the separator substrate can have an appropriate layer thickness, so that the separator coating material can exhibit an appropriate adhesion between the separator and the electrode plate at high temperature. And when the layer thickness meets 2.2 nm to 4 nm, when the material becomes a fluid state, it can also provide certain mechanical support for the overall separator. When the electrolyte includes a phosphorus-containing additive, combined with the layer thickness of the fluoropolymer that meets the scope of the present application, it can provide higher mechanical stability for the separator material when the secondary battery is at a relatively high temperature, reduce the thermal shrinkage rate of the separator, and thus improve the passing rate of the secondary battery in the high-temperature drop test. The phosphorus-containing additive in the electrolyte helps to maintain the adhesiveness of the binder in the first coating material, so that an excellent adhesion is maintained between the separator and the electrode plate, thereby improving the low-temperature intermittent cycling performance of the secondary battery. At the same time, the phosphorus element can form a stable solid electrolyte interface film (SEI, Solid Electrolyte Interface) at the interface between the negative electrode and the electrolyte. This interface film can effectively inhibit the redox reaction of the electrolyte at the interface, thereby improving the self-discharge behavior of the secondary battery and reducing the voltage drop of the secondary battery at low temperature.

[0060] It should be noted that the definition of the layer thickness of the fluoropolymer is the total height of the sheet crystal form when the polymer chains of the fluoropolymer form a sheet crystal form. The layer thickness of the fluoropolymer and the phosphorus-containing additive in the electrolyte can both be detected by methods and instruments known in the art. For example, the separator and the electrolyte can be obtained by disassembling the electrochemical device, and the first coating can be further disassembled from the separator. The transmission electron microscope (TEM) is used for detection. The separator sample with the first coating containing the fluoropolymer is properly pretreated, such as cut into a suitable size. Subsequently, it is placed in the TEM. By selecting an appropriate magnification, from the TEM image, the layer thickness of the fluoropolymer can be directly measured. The ion chromatography (IC) is used for testing. Some components in the electrolyte (such as lithium salts) are qualitatively analyzed by the retention time, and the corresponding types and mass percentage contents are calculated by the peak area; the gas chromatography-mass spectrometry (GC-MS) is used to detect the types and mass percentage contents of some components (such as organic solvents) in the electrolyte.

[0061] In some embodiments, the fluoropolymer includes a polyvinylidene fluoride - hexafluoropropylene copolymer, and the polyvinylidene fluoride - hexafluoropropylene copolymer satisfies at least one of the following: (1) The average molecular weight of the polyvinylidene fluoride - hexafluoropropylene copolymer is 110KDa to 140KDa. For example, it can be 110KDa, 115KDa, 120KDa, 125KDa, 130KDa, 135KDa, 140KDa, or a range composed of any of the above values; (2) The volume resistivity of the polyvinylidene fluoride - hexafluoropropylene copolymer is 10 13 Ω·cm to 10^15 Ω·cm. For example, it can be 10 13 Ω·cm, 2×10 13 Ω·cm, 5×10 13 Ω·cm, 8×10 13 Ω·cm, 10 14 Ω·cm, 2×10 14 Ω·cm, 5×10 14 Ω·cm, 8×10 14 Ω·cm, 10 15 Ω·cm, or a range composed of any of the above values; (3) The dielectric strength of the polyvinylidene fluoride - hexafluoropropylene copolymer is 15kV / mm to 45Kv / mm. For example, it can be 15kV / mm, 18kV / mm, 20kV / mm, 22kV / mm, 25kV / mm, 28kV / mm, 30kV / mm, 32kV / mm, 35kV / mm, 38kV / mm, 40kV / mm, 42kV / mm, 45kV / mm, or a range composed of any of the above values.

[0062] In the above embodiments, when the average molecular weight of the polyvinylidene fluoride - hexafluoropropylene copolymer is 110KDa to 140KDa, it can improve the mechanical strength of the first coating. In a high - temperature environment, it helps the separator to better maintain its own structural stability, provides more reliable mechanical support for the separator, thereby further reducing the thermal shrinkage rate of the separator and enhancing the safety performance of the secondary battery. At the same time, the polyvinylidene fluoride - hexafluoropropylene copolymer can optimize the bonding effect between the separator and the electrode, improve the interfacial bonding force between the separator and the electrode, and enhance the intermittent cycling performance of the secondary battery in a low - temperature environment.

[0063] When the volume resistivity of the polyvinylidene fluoride - hexafluoropropylene copolymer is 10 13 Ω·cm to 10 15 Ω·cm, it can build a good ion - transport channel inside the secondary battery. During the charging and discharging process of the battery, it helps to accurately control the migration rate and direction of ions, ensures the efficient and stable transport of ions between the electrode and the electrolyte, thereby enhancing the charging and discharging efficiency of the battery and increasing the battery output power.

[0064] When the dielectric strength of the poly(vinylidene fluoride - hexafluoropropylene) copolymer is 15 kV / mm to 45 kV / mm, the poly(vinylidene fluoride - hexafluoropropylene) copolymer can withstand a greater electric field strength without breakdown, thus ensuring a stable distribution of the internal electric field of the secondary battery. This helps to maintain the stability of the ion transport path, enabling ions to continuously and orderly shuttle between the electrode and the electrolyte, avoiding the hindrance of ion transport caused by electric field disorder, and thereby improving the charging and discharging efficiency and stability of the secondary battery.

[0065] It should be noted that the average molecular weight, volume resistivity, and dielectric strength of PVDF - HFP can all be detected using methods and instruments known in the art. For example, the separator and electrolyte can be obtained by disassembling the electrochemical device. The separator can be further disassembled to obtain the first coating and then PVDF - HFP. Using gel permeation chromatography (GPC), PVDF - HFP is dissolved in a suitable solvent to prepare a solution with a certain concentration. Then the solution is injected into the GPC instrument, and a suitable chromatographic column and mobile phase are selected for separation. Finally, the content of components with different molecular weights is detected by a differential refractive index detector, ultraviolet detector, etc., and the average molecular weight is calculated by data processing software; using the four - probe method, the PVDF - HFP sample is placed on a suitable test bench to ensure that the sample surface is flat and in good contact with the probes. The parameters of the four - probe tester are adjusted, the voltage value between the four probes is measured and recorded, and the volume resistivity is calculated through a formula; using the breakdown voltage test method, with a breakdown voltage tester, the sample is installed between the test electrodes. According to the characteristics of the sample and the requirements of relevant standards, parameters such as the appropriate voltage - rising rate and test environmental conditions are set. The test instrument is started, and the voltage is gradually increased at the set rate. Observe the state of the sample. When the sample breaks down, the instrument will automatically record the breakdown voltage value at this time. According to the measured breakdown voltage and the sample thickness, the dielectric strength is calculated by substituting into the formula.

[0066] In some embodiments, the phosphorus - containing additive includes at least one of ethoxy(pentafluoro)cyclotriphosphazene, trimethyl phosphate, triphenyl phosphate, and trimethyl phosphite. Based on the total mass of the electrolyte, the mass percentage content of at least one of ethoxy(pentafluoro)cyclotriphosphazene, trimethyl phosphate, triphenyl phosphate, and trimethyl phosphite is C (%). The electrochemical device satisfies: 3.2 ≤ C ≤ 9.8. For example, C can be 3.2, 3.5, 3.8, 4, 4.2, 4.5, 4.8, 5, 5.2, 5.5, 5.8, 6, 6.2, 6.5, 6.8, 7, 7.2, 7.5, 7.8, 8, 8.2, 8.5, 8.8, 9, 9.2, 9.5, 9.8, 4, or a range composed of any of the above values.

[0067] In the above embodiments, the phosphorus-containing additive includes at least one of ethoxy(pentafluoro)cyclotriphosphazene, trimethyl phosphate, triphenyl phosphate, and trimethyl phosphite, and when the electrochemical device satisfies 3.2 ≤ C ≤ 9.8, when the secondary battery is in a relatively high temperature condition, it can provide higher mechanical stability for the separator material, thereby improving the passing rate of the secondary battery during high-temperature drop, and is more conducive to maintaining the adhesiveness of the binder in the first coating material, so that a good adhesiveness is maintained between the separator and the electrode sheet, thereby further improving the drop performance and low-temperature intermittent cycling performance of the secondary battery at high temperature, and at the same time can further improve the self-discharge phenomenon at low temperature and reduce the voltage drop at low temperature.

[0068] In some embodiments, the layer thickness of the fluoropolymer is N (nm), and at least one of ethoxy(pentafluoro)cyclotriphosphazene, trimethyl phosphate, triphenyl phosphate, and trimethyl phosphite, based on the total mass of the electrolyte, the mass percentage content of at least one of ethoxy(pentafluoro)cyclotriphosphazene, trimethyl phosphate, triphenyl phosphate, and trimethyl phosphite is C (%). The electrochemical device satisfies 0.3 ≤ N / C ≤ 1. For example, N / C can be 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, or a range composed of any of the above values.

[0069] In the above embodiments, when the electrochemical device satisfies 0.3 ≤ N / C ≤ 1, the separator can form a good adhesion effect with the electrode sheet at high temperature, and at the same time provide certain mechanical support for the separator. In cooperation with ethoxy(pentafluoro)cyclotriphosphazene, when the battery is in a high-temperature environment, the coating structure is further stabilized, the adhesiveness between the separator and the electrode sheet is strengthened, so that the separator maintains a stable form at high temperature, effectively reducing the thermal shrinkage rate of the separator, and greatly improving the passing rate of the secondary battery in tests such as high-temperature drop, and significantly enhancing the high-temperature safety of the battery. At the same time, in a low-temperature environment, the two work together to enhance the adhesive performance of the binder in the coating, so that the separator and the electrode sheet always maintain an excellent adhesive state in a low-temperature environment, effectively improving the low-temperature intermittent cycling performance of the secondary battery, reducing the voltage drop of the battery at low temperature, and improving the working efficiency and endurance of the battery in a low-temperature environment.

[0070] Moreover, the two work together. During the cycling process, they can not only maintain good contact between the separator and the electrode sheet, but also protect the electrode material, reduce the loss of the electrode material, thereby prolonging the cycle service life of the secondary battery and improving the comprehensive performance of the battery.

[0071] In some embodiments, the separator membrane may further include a second coating, the second coating includes β-chitin, and based on the total mass of the second coating, the mass percentage of β-chitin is M(%), the phosphorus-containing additive includes at least one of ethoxy(pentafluoro)cyclotriphosphazene, trimethyl phosphate, triphenyl phosphate, and trimethyl phosphite. Based on the total mass of the electrolyte, the mass percentage of at least one of ethoxy(pentafluoro)cyclotriphosphazene, trimethyl phosphate, triphenyl phosphate, and trimethyl phosphite is C(%), and the electrochemical device satisfies: 0.6 ≤ M / C ≤ 3.5.

[0072] For example, M / C can be 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3, 3.1, 3.2, 3.3, 3.4, 3.5, or a range composed of any of the above values.

[0073] As an example, based on the total mass of the second coating, the mass percentage of β-chitin is M(%), 3 ≤ M ≤ 15. For example, it can be 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, or a range composed of any of the above values.

[0074] In the above embodiments, when the electrochemical device satisfies: 0.6 ≤ M / C ≤ 3.5, the second coating containing β-chitin can induce the uniform movement of lithium ions, thereby improving the capacity retention rate of the secondary battery in the low-temperature intermittent cycle test. At the same time, this material helps the uniform and dense formation of the cathode solid electrolyte interface film (CEI) of ethoxy(pentafluoro)cyclotriphosphazene, thereby improving the self-discharge phenomenon and reducing the low-temperature voltage drop. This material has excellent heat resistance, so it can absorb the heat at the interface during the high-temperature drop test and improve the passing rate of the high-temperature drop test.

[0075] It should be noted that β-chitin in the second coating can be detected by methods and instruments known in the art. For example, the separator membrane and the electrolyte can be obtained by disassembling the electrochemical device, the second coating can be further disassembled from the separator membrane, and then β-chitin can be separated from the second coating. Using gel permeation chromatography (GPC) method, dissolve β-chitin in the coating in a suitable solvent, make it into a solution and then inject it into the GPC instrument. Using tetrahydrofuran, chloroform, etc. as the mobile phase, detect through a differential refractive index detector or a multi-angle laser light scattering detector, etc., and calculate the content of β-chitin according to the standard curve and software analysis.

[0076] In some embodiments, the phosphorus-containing additive includes lithium difluorophosphate. Based on the total mass of the electrolyte, the mass percentage of lithium difluorophosphate is D (%), and the electrochemical device satisfies: 0.03 ≤ D ≤ 0.9. For example, D can be 0.03, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, or a range composed of any of the above values.

[0077] Optionally, 0.03 ≤ D ≤ 0.85, 0.03 ≤ D ≤ 0.8, 0.03 ≤ D ≤ 0.75, 0.03 ≤ D ≤ 0.7, 0.03 ≤ D ≤ 0.65, 0.03 ≤ D ≤ 0.6.

[0078] In the above embodiments, when the phosphorus-containing additive includes lithium difluorophosphate and the electrochemical device satisfies: 0.03 ≤ D ≤ 0.9, lithium difluorophosphate can form a uniform and dense CEI at the interface between the positive electrode and the electrolyte. This interface film can effectively inhibit the redox reaction of the electrolyte at the interface, reduce the formation of interface by-products, thereby improving the self-discharge behavior of the secondary battery and reducing the voltage drop of the secondary battery at low temperatures.

[0079] In some embodiments, the first coating may further include a surfactant, and the surfactant includes at least one of perfluoroalkyl triepoxyethane methyl ether, polyoxyethylene alkyl ether, polyoxyethylene fatty acid ester, polyoxyethylene alkylphenol ether, and sorbitan aliphatic ester.

[0080] In the above embodiments, when the first coating includes a surfactant, it can optimize the wettability between the first coating and the electrolyte, enhance the interaction between the electrolyte and the first coating, further strengthen the adhesion between the separator and the electrode sheet, and also promote more uniform heat conduction inside the battery, effectively alleviating the phenomenon of local overheating, keeping the separator in a more stable form at high temperatures, further reducing the thermal shrinkage rate of the separator, and improving the safety and reliability of the secondary battery in a high-temperature environment. In a low-temperature environment, the surfactant helps to lower the freezing point of the electrolyte and improve the fluidity of the electrolyte at low temperatures. Combined with the role of the phosphorus-containing additive in promoting ion conduction, it can further increase the migration rate of ions in the electrolyte at low temperatures. At the same time, the surfactant can enhance the activity of the binder in the first coating in a low-temperature environment, making the adhesion state between the separator and the electrode sheet more stable at low temperatures. It effectively improves the low-temperature intermittent cycle performance of the secondary battery and reduces the voltage drop of the secondary battery at low temperatures.

[0081] It should be noted that the surfactant in the first coating can be detected by methods and instruments known in the art. For example, the separator and electrolyte can be obtained by disassembling the electrochemical device, and the first coating can be obtained by further disassembling the separator. The types and mass percentage contents of some components in the first coating can be detected by a gas chromatography-mass spectrometry (GC-MS).

[0082] In some embodiments, the bulk density of the first coating is 0.5 g / cm 3 ~20 g / cm 3 . For example, it can be 0.5 g / cm 3 , 1 g / cm 3 , 2 g / cm 3 , 5 g / cm 3 , 8 g / cm 3 , 10 g / cm 3 , 12 g / cm 3 , 15 g / cm 3 , 18 g / cm 3 , 20 g / cm 3 , or a range composed of any of the above values.

[0083] In the above embodiments, when the bulk density of the first coating is 0.5 g / cm 3 ~20 g / cm 3 , it is helpful to construct a good ion transport channel, which will neither cause chaotic ion transport paths due to being too loose nor hinder ion migration due to being too tight, effectively reducing the battery polarization phenomenon, lowering the battery internal resistance, and improving the charge and discharge efficiency and output voltage of the battery. Further, in a low-temperature environment, this bulk density can cooperate with the role of the phosphorus-containing additive in promoting ion conduction, improving the migration rate of ions in the electrolyte at low temperature, effectively improving the low-temperature intermittent cycle performance of the secondary battery, and reducing the voltage drop of the battery at low temperature.

[0084] It should be noted that the bulk density in the first coating can be detected by methods and instruments known in the art. For example, the separator and electrolyte can be obtained by disassembling the electrochemical device, and the first coating can be obtained by further disassembling the separator. The gas displacement method can be used, and a gas with a known volume and pressure is used to displace gases such as air in the coating under certain conditions. The true volume of the coating is calculated by measuring the change in gas volume, thereby obtaining the bulk density.

[0085] In some embodiments, the electrochemical device satisfies at least one of the following: (1) the base film comprises a crosslinked polyolefin resin, and the crosslinked polyolefin resin comprises a silicon-containing organic group; (2) the surface glossiness of the base film is G (GU), where 0 < G ≤ 5; (3) the separator film may further comprise chromium element, and based on the total mass of the separator film, the content of the chromium element is 0.2 ppm to 18 ppm.

[0086] For example, G can be 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, or a range composed of any of the above values. The content of the chromium element can be 0.2 ppm, 0.5 ppm, 1 ppm, 2 ppm, 3 ppm, 4 ppm, 5 ppm, 6 ppm, 7 ppm, 8 ppm, 9 ppm, 10 ppm, 11 ppm, 12 ppm, 13 ppm, 14 ppm, 15 ppm, 16 ppm, 17 ppm, 18 ppm, or a range composed of any of the above values.

[0087] For example, the chromium element can be distributed on the inorganic particles of the ceramic layer of the separator film or in the adhesive layer of the separator film.

[0088] Optionally, the content of the chromium element is 0.2 ppm to 17 ppm, 0.2 ppm to 16 ppm, 0.2 ppm to 15 ppm, 0.2 ppm to 14 ppm, 0.2 ppm to 13 ppm, 0.2 ppm to 12 ppm, 0.2 ppm to 11 ppm, 0.2 ppm to 10 ppm.

[0089] In the above embodiments, when the base film comprises a crosslinked polyolefin resin and the crosslinked polyolefin resin comprises a silicon-containing organic group, the wettability of the electrolyte to the adjacent electrode sheet material can be further improved. In the low-temperature intermittent cycle test, even during intermittent charge and discharge, it can provide sufficient lithium ion sources for the material exchange between the positive and negative electrodes in time, thereby improving the low-temperature intermittent cycle performance of the secondary battery. At the same time, this material is beneficial for the flame retardant effect of the phosphorus-containing additives in the electrolyte, thereby improving the passing rate of the drop test of the secondary battery at high temperature. In addition, this material can help the phosphorus-containing additives form a more stable solid electrolyte interface film on the negative electrode, thereby reducing the interfacial side reactions and improving the self-discharge phenomenon of the secondary battery at low temperature and reducing the voltage drop.

[0090] When the surface gloss of the base film of the separator film satisfies 0 < G ≤ 5, the surface of the base film has a certain flatness, so that the coating can better fit with the substrate, thereby improving the energy density of the electrochemical device. The higher the surface gloss of the substrate, the flatter the surface. However, when the gloss is too high, the surface force between the coating and the substrate is less, and the difficulty of coating the coating increases; when the gloss is too low, the energy density of the electrochemical device is low, and due to the overly uneven surface, the safety risk of the electrochemical device increases, and the passing rate of the high-temperature drop test of the electrochemical device decreases.

[0091] When the separator film contains chromium element and the content of chromium element is 0.2 ppm to 18 ppm, the chromium element can improve the mechanical strength of the separator film. Chromium atoms can form chemical bonds or strengthen the intermolecular forces with the base material of the separator film, such as polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), etc. In a high-temperature environment, this strengthening effect makes the separator film not easily deformed and better maintains its own structure. The chromium element, the layered thickness of PVDF-HFP, and the phosphorus-containing additive act synergistically to enhance the adhesion stability between the separator film and the electrode sheet at high temperatures. In tests such as high-temperature drop, the chromium-containing separator film can effectively reduce the thermal shrinkage rate and improve the safety and reliability of the secondary battery under high-temperature conditions.

[0092] It should be noted that the silicon-containing organic groups in the crosslinked polyolefin resin, the surface gloss of the base film, and the chromium element in the separator film can all be detected by methods and instruments known in the art. For example, the separator film can be obtained by disassembling the electrochemical device, and the base film can be further disassembled from the separator film. For example, infrared spectroscopy can be used to cut the base film into appropriate sizes for measurement to obtain an infrared spectrogram, and the presence and relative content of the organosilicon group can be judged according to the position and intensity of the characteristic absorption peaks; the "micro-TRI-gloss-s" manufactured by BYK company can be used to measure the surface gloss at a 60° reflection angle; for example, inductively coupled plasma mass spectrometry (ICP-MS) can be used. First, the elements in the separator film are ionized by ICP, and then the ions are analyzed and detected by a mass spectrometer.

[0093] In some specific embodiments, the electrochemical device satisfies at least one of the following: (1) The additive may further include lithium difluoro(oxalato)borate, lithium bis(trifluoromethanesulfonyl)imide, and / or lithium difluorophosphate. Based on the total mass of the electrolyte, the mass percentage content of lithium difluoro(oxalato)borate, lithium bis(trifluoromethanesulfonyl)imide, and / or lithium difluorophosphate is X (%), and 0.02 ≤ X ≤ 4.4; (2) The additive may further include 1,3-propane sultone. Based on the total mass of the electrolyte, the mass percentage content of 1,3-propane sultone is Y (%), and 0.25 ≤ Y ≤ 4; (3) The additive may further include vinylene carbonate. Based on the total mass of the electrolyte, the mass percentage content of vinylene carbonate is A (%), and 0.12 ≤ A ≤ 3.3; (4) The additive may further include a fluorinated linear asymmetric carbonate. Based on the total mass of the electrolyte, the mass percentage content of the fluorinated linear asymmetric carbonate is B (%), and 2 ≤ B ≤ 28; (5) The electrolyte includes propyl propionate and / or ethyl propionate. Based on the total mass of the electrolyte, the mass percentage content of propyl propionate and / or ethyl propionate is E (%), and 26 ≤ E ≤ 40.

[0094] For example, X can be 0.02, 0.05, 0.1, 0.5, 1, 1.5, 2, 1.5, 2.5, 3, 3.5, 4, 4.4, or a range composed of any of the above values. Y can be 0.25, 0.5, 0.8, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4, or a range composed of any of the above values. A can be 0.12, 0.2, 0.5, 0.8, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.3, or a range composed of any of the above values. B can be 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, or a range composed of any of the above values. E can be 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, or a range composed of any of the above values.

[0095] Optionally, 0.25 ≤ Y ≤ 3.8, 0.25 ≤ Y ≤ 3.6, 0.25 ≤ Y ≤ 3.4, 0.25 ≤ Y ≤ 3.2, 0.25 ≤ Y ≤ 3, 0.25 ≤ Y ≤ 2.8, 0.25 ≤ Y ≤ 2.6, 0.25 ≤ Y ≤ 2.4, 0.25 ≤ Y ≤ 2.2, 0.25 ≤ Y ≤ 2, 0.25 ≤ Y ≤ 1.8.

[0096] Optionally, 0.12 ≤ A ≤ 3.3, 0.12 ≤ A ≤ 3.2, 0.12 ≤ A ≤ 3.1, 0.12 ≤ A ≤ 3, 0.12 ≤ A ≤ 2.9, 0.12 ≤ A ≤ 2.8, 0.12 ≤ A ≤ 2.7, 0.12 ≤ A ≤ 2.6, 0.12 ≤ A ≤ 2.5, 0.12 ≤ A ≤ 2.4, 0.12 ≤ A ≤ 2.3, 0.12 ≤ A ≤ 2.2, 0.12 ≤ A ≤ 2.1, 0.12 ≤ A ≤ 2.

[0097] Optionally, the fluorinated linear asymmetric carbonate includes at least one of dimethyl fluorocarbonate, diethyl fluorocarbonate and ethyl methyl fluorocarbonate.

[0098] In the above embodiments, when the electrolyte of the electrochemical device includes lithium difluoro(oxalato)borate, lithium bis(trifluoromethanesulfonyl)imide or lithium difluorophosphate and 0.02 ≤ X ≤ 4.4, lithium difluoro(oxalato)borate can promote the activation of propyl propionate, thereby further promoting the circulation of lithium ions in the electrolyte, improving the low-temperature fast charging performance of the electrochemical device and reducing the voltage drop at high temperatures.

[0099] When the electrolyte of the electrochemical device includes 1,3-propane sultone and 0.25 ≤ Y ≤ 4, 1,3-propane sultone can form a more stable SEI film on the surface of the positive electrode material, improving the low-temperature fast charging performance of the electrochemical device.

[0100] When the electrolyte of the electrochemical device contains vinylene carbonate and 0.12 ≤ A ≤ 3.3, vinylene carbonate can form a more uniform and dense SEI film on the surface of the negative electrode material, further improving the low-temperature fast charging performance of the electrochemical device.

[0101] When the electrolyte of the electrochemical device includes fluorinated linear asymmetric carbonate and 2 ≤ B ≤ 28, the fluorinated linear asymmetric carbonate can participate in the construction of the SEI film, and the formed SEI film is denser and more stable. The presence of fluorine atoms enhances the protection of the SEI film on the electrode, effectively inhibits the side reaction between the electrolyte and the negative electrode material, prevents the continuous consumption of active lithium, and improves the Coulomb efficiency of the battery. In addition, the fluorinated linear asymmetric carbonate helps to stabilize the CEI film, and synergistically with the phosphorus-containing additive, further inhibits the redox reaction at the interface between the positive electrode and the electrolyte, reduces the corrosion and degradation of the electrode material, and maintains the stability of the positive electrode material structure, thereby ensuring the capacity retention rate of the battery during long-term cycling and extending the cycle life of the battery.

[0102] When the electrolyte of the electrochemical device includes and 26 ≤ E ≤ 40, propyl propionate and / or ethyl propionate further promote the circulation of lithium ions in the electrolyte, improving the low-temperature fast charging performance of the electrochemical device and reducing the voltage drop at high temperatures.

[0103] The following embodiments can enable those skilled in the art to understand the present application more comprehensively, but do not limit the present application in any way.

[0104] In some embodiments, the types of additives included in the electrolyte may further include vinylene sulfate (DTD), vinylene sulfite (VC), 1,3 - propanesultone, and may further include methyl fluoromethyl carbonate, methyl difluoromethyl carbonate, methyl trifluoromethyl carbonate, methyl trifluoroethyl carbonate, or bis(trifluoroethyl) carbonate.

[0105] In some embodiments, in addition to LiFSI and LiPO2F2, the electrolyte may further include ionizable lithium salts. The ionizable lithium salts include at least one of LiPF6, LiSbF6, LiAsF6, LiClO4, LiN(C2F5SO2)2, CF3SO3Li, LiC(CF3SO2)3, or LiC4BO8. There is no special limitation on the concentration of the ionizable lithium salts in the electrolyte. It is preferably 0.5 mol / L or more, more preferably 0.8 mol / L or more, and further preferably 1.0 mol / L or more. Additionally, it is preferably 3 mol / L or less, more preferably 2 mol / L or less, and further preferably 1.7 mol / L or less. If the concentration of these ionizable lithium salts is too low, it may result in insufficient mobile lithium ions in the electrolyte. On the other hand, if the concentration of these ionizable lithium salts is too high, it may cause an increase in the viscosity of the electrolyte, leading to an increase in the electrolyte impedance and a decrease in the lithium ion migration rate, thereby possibly reducing the performance of the electrochemical device.

[0106] In some embodiments, the electrolyte may further include at least one of fluoroethers, fluorinated ethylene carbonate, or ether solvents. In some embodiments, the electrolyte may further include a non - aqueous solvent. The non - aqueous solvent may be a carbonate compound, a carboxylate compound, an ether compound, other organic solvents, or a combination thereof.

[0107] In addition to chain - like carbonate compounds, the carbonate compounds may further include cyclic carbonate compounds, fluorinated carbonate compounds, or a combination thereof.

[0108] In addition to diethyl carbonate (DEC) defined in this application, examples of chain carbonate compounds may include ethyl propionate (EP), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), and combinations thereof. Examples of cyclic carbonate compounds are ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene ethylene carbonate (VEC), or combinations thereof. Examples of fluorinated carbonate compounds are fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, trifluoromethyl ethylene carbonate, or combinations thereof.

[0109] Examples of carboxylic acid ester compounds are methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolide, valerolactone, mevalonolactone, caprolactone, methyl formate, or combinations thereof.

[0110] Examples of ether compounds are dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, or combinations thereof.

[0111] Examples of other organic solvents are dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphate esters, or combinations thereof.

[0112] This application also provides an electrochemical device including the above electrolyte. In some embodiments, the electrochemical device further includes a positive electrode plate, a negative electrode plate, and a separator, wherein the positive electrode plate and the negative electrode plate are separated by the separator disposed therebetween. In some embodiments, the positive electrode plate includes a positive current collector and a positive active material layer disposed on the positive current collector. The positive active material layer may include a positive active material and an additive. The negative electrode plate includes a negative current collector and a negative active material layer disposed on the negative current collector. The negative active material layer may include a negative active material.

[0113] In some embodiments, the negative electrode sheet may include a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector. The negative electrode active material layer may be disposed on one or both sides of the negative electrode current collector. In some embodiments, the negative electrode current collector may be at least one of a copper foil, a nickel foil, or a carbon-based current collector. In some embodiments, the thickness of the negative electrode current collector may be from 1 μm to 200 μm. In some embodiments, the negative electrode active material layer may be coated only on a partial region of the negative electrode current collector. In some embodiments, the thickness of the negative electrode active material layer may be from 10 μm to 500 μm. It should be understood that these are merely exemplary, and other suitable thicknesses may be employed.

[0114] In some embodiments, as described above, the negative electrode active material layer includes a negative electrode active material. In some embodiments, the negative electrode active material includes at least one of natural graphite, artificial graphite, or a silicon-based material. In some embodiments, the silicon-based material includes at least one of silicon, a silicon oxide compound, a silicon carbide compound, or a silicon alloy.

[0115] In some embodiments, the negative electrode active material layer may further include a negative electrode conductive agent and / or a negative electrode binder. The negative electrode conductive agent may include at least one of carbon black, acetylene black, Ketjen black, graphene, carbon nanotubes, or carbon fibers. In some embodiments, the negative electrode binder may include at least one of carboxymethyl cellulose (CMC), polyacrylic acid, polyacrylate, polyacrylate ester, polyvinylpyrrolidone, polyimide, polysiloxane, or styrene-butadiene rubber. It should be understood that the materials disclosed above are merely exemplary, and the negative electrode active material layer may be made of any other suitable materials. In some embodiments, the mass ratio of the negative electrode active material, the negative electrode conductive agent, and the negative electrode binder in the negative electrode active material layer may be (80-99):(0.5-10):(0.5-10). It should be understood that this is merely exemplary and does not limit the present application.

[0116] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector. The positive electrode active material layer may be located on one or both sides of the positive electrode current collector. In some embodiments, the positive electrode current collector may be an aluminum foil. Of course, other positive electrode current collectors commonly used in the art may also be employed. In some embodiments, the thickness of the positive electrode current collector may be from 1 μm to 200 μm. In some embodiments, the positive electrode active material layer may be coated only on a partial region of the positive electrode current collector. In some embodiments, the thickness of the positive electrode active material layer may be from 20 μm to 490 μm. Further preferably, the thickness may be from 20 μm to 400 μm. Still further, it may be from 40 μm to 120 μm. Even further, it may be from 40 μm to 90 μm.

[0117] In some embodiments, as described above, the positive electrode active material layer includes a positive electrode active material. In some embodiments, the positive electrode active material may include at least one of lithium cobaltate, lithium manganate, lithium iron phosphate, lithium manganese iron phosphate, lithium nickel cobalt manganate, lithium nickel cobalt aluminate, or lithium nickel manganate, and the above positive electrode active materials may be subjected to doping and / or coating treatments. Further preferably, the positive electrode active material is lithium cobaltate or lithium iron phosphate.

[0118] In some embodiments, the surface of the positive electrode material includes lithium phosphate and / or lithium niobate, and the mass ratio of the two is 1:3 to 1:1, and the thickness of the covering layer is 1 μm to 1.8 μm.

[0119] In some embodiments, the surface of the positive electrode material includes lithium dihydrogen phosphate or aluminum dihydrogen phosphate, and based on the total mass of the positive electrode active material layer, the mass percentage content of lithium dihydrogen phosphate or aluminum dihydrogen phosphate is M%, where 5 ≤ M ≤ 20.

[0120] In some embodiments, the substrate of the separator includes at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid. For example, polyethylene includes at least one selected from high-density polyethylene, low-density polyethylene, or ultra-high molecular weight polyethylene. In particular, polyethylene and polypropylene play a good role in preventing short circuits and can improve the safety of the battery through the shut-off effect. In some embodiments, the overall thickness of the separator is in the range of about 3 μm to 480 μm.

[0121] In some embodiments, the surface of the separator membrane may further include a porous layer, which is disposed on at least one surface of the separator membrane. The porous layer includes inorganic particles and a binder. The inorganic particles are selected from at least one of aluminum oxide (Al2O3), silicon dioxide (SiO2), magnesium oxide (MgO), titanium dioxide (TiO2), hafnium dioxide (HfO2), tin dioxide (SnO2), cerium dioxide (CeO2), nickel oxide (NiO), zinc oxide (ZnO), calcium oxide (CaO), zirconium dioxide (ZrO2), yttrium oxide (Y2O3), silicon carbide (SiC), boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. In some embodiments, the pores of the separator membrane have a diameter in the range of about 0.01 μm to 1 μm. The binder of the porous layer is selected from at least one of polyvinylidene fluoride, vinylidene fluoride - hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate salt, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyethylene ether, polytetrafluoroethylene, or polyhexafluoropropylene. The porous layer on the surface of the separator membrane can improve the heat resistance, oxidation resistance, and electrolyte infiltration performance of the separator membrane, and enhance the adhesion between the separator membrane and the electrode sheet. One surface of the separator may further include one of a high melting point crystalline polymer or a high temperature resistant amorphous polymer. The high temperature resistant resin includes at least one of polypropylene, poly-4-methylpentene, polytetrafluoroethylene, polyvinylidene fluoride, and cycloolefin copolymer. The high melting point crystalline polymer includes at least one of polypropylene, poly-4-methylpentene, polytetrafluoroethylene, or polyvinylidene fluoride, and the high temperature resistant amorphous polymer includes cycloolefin copolymer. Based on the mass of the polyolefin porous substrate, the mass percentage content z of the high temperature resistant resin is 2.5% to 9%. For example, the mass percentage content z of the high temperature resistant resin is 2.5%, 3%, 5%, 7%, 8%, 9%, or a range composed of any two of these values. When adding the above-mentioned types of high temperature resistant resins to the polyolefin porous substrate and regulating the mass percentage content of the high temperature resistant resin within the above range, it is beneficial to increase the melting rupture temperature of the separator, improve the strength, and the high temperature performance of the electrochemical device.

[0122] In some embodiments, the electrochemical device is a lithium-ion battery, but the present application is not limited thereto.

[0123] In some embodiments of the present application, taking a lithium-ion battery as an example, the positive electrode sheet, the separator membrane, and the negative electrode sheet are wound or stacked in sequence to form an electrode assembly, and then are installed in a housing such as an aluminum-plastic film for encapsulation, electrolyte is injected, formed, and encapsulated to make a lithium-ion battery.

[0124] Electronic device

[0125] Embodiments of the present application also provide electronic devices including the above-mentioned electrochemical devices. The electronic devices of the embodiments of the present application are not particularly limited, and they can be any electronic devices known in the prior art. In some embodiments, the electronic device can include, but is not limited to, a laptop computer, a pen-input computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD TV, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery and a lithium-ion capacitor, etc.

[0126] Testing section

[0127] (1) Voltage drop test of lithium-ion battery at low temperature:

[0128] At -10°C, the lithium-ion battery is charged to 4.3V at 1C constant current, then charged to 0.05C at constant voltage, and then discharged to 2.0V at 1C constant current, left to stand for 5 minutes, and then the voltage is tested as the pre-storage voltage. After storing at -20°C for 24 hours, the voltage is re-tested as the post-storage voltage. The voltage drop of the lithium-ion battery is calculated according to the following formula: voltage drop = pre-storage voltage - post-storage voltage.

[0129] (2) Capacity retention test after 200 cycles of intermittent cycling at -10°C:

[0130] At -10°C, the lithium-ion battery was allowed to stand for 30 minutes; it was charged to 4.3V at a constant current of 0.5C, and charged to 0.05C at a constant voltage of 4.3V; the battery was allowed to stand in a 60°C environment for 24 hours; the battery was cross-current discharged to 3.0V at a rate of 0.5C, and the battery discharge capacity was recorded; this was a complete intermittent charge and discharge cycle, and the battery was charged and discharged 200 times in the same way.

[0131] Capacity retention rate (%) of the lithium ion battery after the 200th cycle = discharge capacity at the 200th cycle / initial discharge capacity×100%.

[0132] (3) Capacity retention test after 400 cycles of intermittent cycling at -15°C:

[0133] The lithium-ion battery is left standing for 30 minutes at -15°C; it is charged at a constant current of 0.5C until 4.3V and then charged at a constant voltage of 4.3V until 0.05C; the battery is left standing in an environment at 60°C for 24 hours; the battery is discharged at a constant current of 0.5C until 3.0V, and the discharge capacity of the battery is recorded; this is a complete intermittent charge-discharge cycle, and the battery is charged and discharged in the same way for 400 cycles.

[0134] The capacity retention rate (%) after the 400th cycle of the lithium-ion battery = the discharge capacity of the 400th cycle / the first discharge capacity × 100%.

[0135] (4) Pass rate test of the drop test:

[0136] Under the environmental conditions of 55°C, record the open-circuit voltage and internal resistance of the battery (the test instrument is a voltage and resistance tester, manufacturer: Dongguan Lijia Precision Instruments Co., Ltd., model: LNG-SY1-0020-DQ); 2) Place the battery in the fixture bin, and use an automatic drop device to drop the fixture bin with the battery from a height of 1m to the cement floor in turn with the bottom surface, left side, right side, back side, front side, and top surface of the fixture bin as one round of landing; a total of 3 rounds, that is, 18 times, are dropped in one cycle; 3) Then drop it from a height of 1.5m to the cement floor in turn with the bottom surface, left side, right side, back side, front side, and top surface of the fixture bin as one round of landing; a total of 3 rounds, that is, 18 times, are dropped in one cycle; 4) Measure the voltage of the battery after each round of dropping. When the battery catches fire or leaks liquid, stop dropping; otherwise, continue dropping; 5) Record the voltage and internal resistance of the battery. If the voltage drop is <10mV within 24 hours and the battery packaging bag is not opened or broken, and the battery does not catch fire, leak liquid, or explode, it is judged that the battery passes the drop test; otherwise, it is considered to fail. The pass rate of the drop test = (the number of products passing the drop test ÷ the total number of products participating in the drop test) × 100%.

[0137] (5) Capacity retention rate test of 300 cycles of high-temperature floating charge:

[0138] Place the lithium-ion battery in a 25°C constant-temperature oven and leave it standing for 30 minutes to make the lithium-ion battery reach a constant temperature. Charge it at a constant current of 1C until the voltage reaches 4.3V, and then charge it at a constant voltage until the current reaches 0.05C, and record the charging capacity of the first cycle at this time. Transfer the tested lithium-ion battery to a 45°C constant-temperature oven and continuously charge it at a current of 1C for 60 days, and record the charging capacity of the last cycle. Calculate the charging capacity retention rate during the floating charge test of the lithium-ion battery as an index to evaluate the floating charge performance of the lithium-ion battery. The floating charge capacity retention rate = (the charging capacity after 60 days of floating charge - the charging capacity of the first cycle) / the charging capacity of the first cycle × 100%.

[0139] (6) Pass rate test of the high-temperature side extrusion test:

[0140] At 45 °C, it is charged at a constant current of 0.5 C rate until 4.4 V, and then charged at a constant voltage until 0.05 C. Using the UL1642 test standard, the side extrusion force is 13 kN. The side extrusion test is carried out on the lithium-ion secondary battery, and 20 lithium-ion secondary batteries are tested in each group, and the passing rate of the side extrusion test of the lithium-ion secondary battery is calculated.

[0141] (7) Component test of the electrolyte: The components of the electrolyte are tested by GC-MS and combined with the external standard method for testing.

[0142] (8) Substrate smoothness test: Use "micro-TRI-gloss-s" manufactured by BYK to measure the surface glossiness (GU value) at a 60° reflection angle.

[0143] Example

[0144] The following examples more specifically describe the content disclosed in the present application. These examples are only for illustrative purposes, because various modifications and changes within the scope of the present application are obvious to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on weight, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further treatment, and the instruments used in the examples are all commercially available.

[0145] Example 1-1

[0146] Positive electrode: Lithium cobaltate, acetylene black, and polyvinylidene fluoride are mixed in a weight ratio of 88:6:6 and added to N-methylpyrrolidone, and stirred into a homogeneous slurry. The slurry is stirred, coated, dried, roll-pressed, and spot-welded with electrode tabs to obtain the battery positive electrode.

[0147] Negative electrode: Weigh 100 g of negative electrode active material (artificial graphite with a particle size of 10 μm), 1 g of conductive agent (carbon black), and 4 g of binder (styrene-butadiene rubber, SBR), add them to 3 g of N-methylpyrrolidone and 100 g of water to form a negative electrode slurry. The negative electrode slurry is stirred, coated, dried, roll-pressed, and spot-welded with electrode tabs to obtain the battery negative electrode.

[0148] Electrolyte: In a glove box filled with argon, ethylene carbonate: diethyl carbonate: ethyl methyl carbonate are mixed in a mass ratio of 1:2:1, and 1,3-propane sultone accounting for 1% of the total mass of the electrolyte, vinylene carbonate accounting for 1% of the total mass of the electrolyte, difluoroethyl carbonate accounting for 6% of the total mass of the electrolyte, lithium difluoro(oxalato)borate accounting for 1% of the total mass of the electrolyte, and propyl propionate accounting for 35% of the total mass of the electrolyte are added. A certain amount of lithium hexafluorophosphate is added so that the mass percentage of lithium hexafluorophosphate in the electrolyte is finally 9%.

[0149] Separator membrane:

[0150] Select an 8-μm-thick polyethylene (PE, porosity 40%) microporous membrane. Add cellulose nanocrystals (diameter: 10 nm, length: 200 nm, Young's modulus: 70 GPa, MAINE) to water and disperse to prepare a dispersion. After impregnating the porous polymer substrate with the dispersion, dry it with a hot air gun at 60 °C. The loading amount of cellulose nanocrystals on the porous polymer substrate is 9 g / m 2 . Manufacture a separator substrate with a thickness of 9 μm. Coat a layer of silane compound QHL 607 before coating the inorganic coating.

[0151] Prepare a solution by dissolving β-chitin (Glycosyn, β-chitin) in HFIP (1,1,1,3,3,3-hexafluoro-2-propanol) at a concentration of 0.8 wt%. Disperse boehmite with a volume average particle size Dv50 of 1.5 μm, binder polyacrylate, and β-chitin in deionized water according to a mass ratio of 85:10:5 to form an inorganic coating slurry with a solid content of 38%; use a microgravure coating method to uniformly coat the inorganic coating slurry on one side of an 8-μm-thick PE porous substrate, and obtain an inorganic coating (the second coating) after drying in an oven. The thickness of the inorganic coating is 1.5 μm.

[0152] Preparation of the first coating (coated on the second coating facing the negative electrode side):

[0153] Add a polyvinylidene fluoride-hexafluoropropylene copolymer with a number average molecular weight of 110,000 Da to a stirrer; add wetting agent dimethyl silicone and surfactant polyoxyethylene alkyl ether to the stirrer, then add deionized water and stir to adjust the viscosity of the slurry to 35 mPa·s and the solid content to 7% to obtain the first coating slurry. Uniformly coat the first coating slurry on the inorganic coating, and obtain the first coating after drying in an oven. The coating weight of the first coating slurry is 1 mg / 5000 mm 2 . The thickness of the first coating is 1.5 μm. The mass ratio of polyvinylidene fluoride-hexafluoropropylene copolymer, sodium carboxymethyl cellulose, and dimethyl silicone is 94:1.5:4.5, and the dosage of surfactant polyoxyethylene alkyl ether is 2.8% of the total mass of the slurry.

[0154] Lithium-ion battery: Stack the positive electrode sheet, separator membrane, and negative electrode sheet in sequence, with the separator membrane between the positive electrode sheet and the negative electrode sheet to play a role in isolation, and wind to obtain an electrode assembly. After welding the tabs, place the electrode assembly in an outer packaging aluminum-plastic film, remove moisture at 80 °C, inject the above electrolyte, and obtain a lithium-ion battery through processes such as vacuum packaging, standing, forming, shaping, and capacity testing.

[0155] Examples 1-2 to 1-29, Comparative Examples 1 to 4

[0156] The preparation of the lithium-ion battery was substantially the same as that of Example 1-1, except that the layer thickness of the polyvinylidene fluoride-hexafluoropropylene copolymer, the content of ethoxy(pentafluoro)cyclotriphosphazene in the electrolyte, N / C, the content of lithium difluorophosphate in the electrolyte, the types of groups contained on the crosslinked polyolefin, and the surface gloss of the base film were different. The specific parameters are shown in Table 1.

[0157] The lithium-ion battery was subjected to a performance retention rate test of 200 intermittent cycles at -10°C, a low-temperature voltage drop test, and a passing rate test of a high-temperature drop test. The results are shown in Table 1.

[0158] Table 1

[0159]

[0160] According to Table 1, compared with the comparative examples, in each example, the low-temperature voltage drop of the lithium-ion battery decreased, and the passing rate of the high-temperature drop test and the performance retention rate of 200 intermittent cycles at -10°C were significantly improved. The first coating of the separator of the electrochemical device includes a polyvinylidene fluoride-hexafluoropropylene copolymer, and the layer thickness of the polyvinylidene fluoride-hexafluoropropylene copolymer is 2.2 nm to 4 nm; and the electrolyte includes an additive. When the additive includes a phosphorus-containing additive, the lithium-ion battery has good low-temperature performance and high-temperature safety.

[0161] On this basis, according to Examples 1-3 to 1-5, when the layer thickness of the polyvinylidene fluoride-hexafluoropropylene copolymer is 3 nm to 3.8 nm, the lithium-ion battery has better low-temperature performance and high-temperature safety.

[0162] According to Examples 1-7 to 1-13, when the lithium-ion battery satisfies 3.2 ≤ C ≤ 9.8, the lithium-ion battery has better low-temperature performance and high-temperature safety.

[0163] According to each example and the comparative examples, when the lithium-ion battery satisfies 0.3 ≤ N / C ≤ 1, the polyvinylidene fluoride-hexafluoropropylene copolymer and ethoxy(pentafluoro)cyclotriphosphazene have a synergistic effect to improve the low-temperature performance and high-temperature safety of the lithium-ion battery.

[0164] According to Examples 1-14 to 1-20, when the lithium-ion battery satisfies 0.03 ≤ D ≤ 0.9, the lithium-ion battery has better low-temperature performance and high-temperature safety.

[0165] On this basis, according to Examples 1-14 to 1-17, when the lithium-ion battery satisfies 0.03 ≤ D ≤ 0.6, the lithium-ion battery has better low-temperature performance and high-temperature safety.

[0166] According to the examples and comparative examples, when the base film includes a crosslinked polyolefin resin and the crosslinked polyolefin resin includes a silicon-containing organic group, the low-temperature performance and high-temperature safety of the lithium-ion battery can be improved.

[0167] According to Examples 1-21 to 1-26, when 0 < G ≤ 5 for the lithium-ion battery, the lithium-ion battery has good low-temperature performance and high-temperature safety.

[0168] According to Examples 1-2, 1-28, and 1-29, when the lithium-ion battery contains both ethoxy(pentafluoro)cyclotriphosphazene and lithium difluorophosphate, it has better low-temperature performance and high-temperature safety.

[0169] Examples 2-1 to 2-7

[0170] The preparation of the lithium-ion battery is substantially the same as that of Example 1-1, except that the parameters of the polyvinylidene fluoride-hexafluoropropylene copolymer are different. For details, see Table 2.

[0171] Table 2

[0172]

[0173]

[0174] According to Table 2, when the number-average molecular weight, volume resistivity, and dielectric strength of the polyvinylidene fluoride-hexafluoropropylene copolymer are controlled within the scope of this application, the lithium-ion battery has good low-temperature performance and high-temperature stability.

[0175] According to Examples 1-1, 2-1 to 2-3, when the number-average molecular weight of the polyvinylidene fluoride-hexafluoropropylene copolymer is 110 KDa to 140 KDa, the lithium-ion battery has good low-temperature performance and high-temperature stability.

[0176] According to Examples 1-1, 2-5 to 2-7, the volume resistivity of the polyvinylidene fluoride-hexafluoropropylene copolymer is 10 13 Ω·cm to 10 15 Ω·cm and / or the dielectric strength is 15 Kv / mm to 45 Kv / mm, the lithium-ion battery has good low-temperature performance and high-temperature stability.

[0177] Examples 3-1 to 3-55

[0178] The preparation of the lithium-ion battery is substantially the same as that of Example 1-1, except that the content of β-chitin in the second coating, M / C, the content of lithium difluoro(oxalato)borate, 1,3-propane sultone, vinylene carbonate, fluorinated linear asymmetric carbonate and propyl propionate in the electrolyte, the type of fluorinated linear asymmetric carbonate and the packing density of the first coating are different. The specific parameters are shown in Table 3.

[0179] The lithium-ion battery was tested for the capacity retention rate after 300 cycles of high-temperature floating charge, the passing rate of the high-temperature side extrusion test, and the capacity retention rate after 400 intermittent cycles at -15°C. The results are shown in Table 3.

[0180]

[0181]

[0182]

[0183]

[0184]

[0185] As can be seen from Table 3, when the electrochemical device meets any one of the content of β-chitin in the second coating, M / C, the content of lithium difluoro(oxalato)borate, 1,3-propane sultone, vinylene carbonate, fluorinated linear asymmetric carbonate and propyl propionate in the electrolyte, the type of fluorinated linear asymmetric carbonate and the packing density of the first coating in this application, the lithium-ion battery has good low-temperature and high-temperature performance.

[0186] According to Example 1-1, Example 3-1 to Example 3-9, when the content of chromium element is 0.2 ppm to 18 ppm based on the total mass of the separator in the lithium-ion battery, the lithium-ion battery has good low-temperature and high-temperature performance.

[0187] On this basis, according to Example 3-1 to 3-5, when the content of chromium element is 0.2 ppm to 10 ppm based on the total mass of the separator in the lithium-ion battery, the lithium-ion battery has better low-temperature and high-temperature performance.

[0188] According to Example 1-1, Example 3-10 to Example 3-15, when the lithium-ion battery satisfies 0.02 ≤ X ≤ 4.4, the lithium-ion battery has good low-temperature and high-temperature performance.

[0189] According to Example 1-1, Example 3-16 to Example 3-22, when the lithium-ion battery satisfies 0.25 ≤ Y ≤ 4, the lithium-ion battery has good low-temperature and high-temperature performance.

[0190] On this basis, according to Examples 3-16 to 3-18, it can be seen that when 0.25 ≤ Y ≤ 4, the lithium-ion battery has good low-temperature performance and high-temperature performance.

[0191] According to Examples 1-1, 3-23 to 3-30, it can be seen that when 0.12 ≤ A ≤ 3.3, the lithium-ion battery has good low-temperature performance and high-temperature performance.

[0192] On this basis, according to Examples 3-23 to 3-26, it can be seen that when 0.12 ≤ A ≤ 2, the lithium-ion battery has good low-temperature performance and high-temperature performance.

[0193] According to each example, when the electrolyte of the lithium-ion battery contains fluorinated linear asymmetric carbonate, polyvinylidene fluoride-hexafluoropropylene copolymer and ethoxy(pentafluoro)cyclotriphosphazene have a synergistic effect to improve the low-temperature performance and high-temperature safety of the lithium-ion battery.

[0194] On this basis, according to Examples 1-1, 3-31 to 3-36, it can be seen that when 2 ≤ B ≤ 28, the lithium-ion battery has good low-temperature performance and high-temperature performance.

[0195] According to Examples 1-1, 3-37 to 3-43, the packing density of the first coating in the separator of the lithium-ion battery satisfies 0.5 g / cm 3 ~20 g / cm 3 , the lithium-ion battery has good low-temperature performance and high-temperature performance.

[0196] According to Examples 1-1, 3-44 to 3-48, it can be seen that when 26 ≤ E ≤ 40, the lithium-ion battery has good low-temperature performance and high-temperature performance.

[0197] According to Examples 1-1, 3-51 to 3-55, it can be seen that when 0.6 ≤ M / C ≤ 3.5, the lithium-ion battery has good low-temperature performance and high-temperature performance.

[0198] Although the present application has been described with reference to the preferred embodiments, various improvements can be made to it and components therein can be replaced with equivalents without departing from the scope of the present application. In particular, as long as there is no structural conflict, the technical features mentioned in each embodiment can be combined in any way. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. An electrochemical device, characterized in that, The electrochemical device includes a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. The separator is disposed between the positive electrode sheet and the negative electrode sheet. The separator includes a base film and at least a first coating disposed on one side of the base film; The first coating includes a fluoropolymer, and the layered thickness of the fluoropolymer is 2.2 nm to 4 nm; The electrolyte includes an additive, and the additive includes a phosphorus-containing additive.

2. The electrochemical device according to claim 1, wherein The layered thickness of the fluoropolymer is 3 nm to 3.8 nm.

3. The electrochemical device according to claim 1, characterized in that, The fluoropolymer includes a poly(vinylidene fluoride - hexafluoropropylene) copolymer, and the poly(vinylidene fluoride - hexafluoropropylene) copolymer satisfies at least one of the following: (1) The average molecular weight of the poly(vinylidene fluoride - hexafluoropropylene) copolymer is 110 KDa to 140 KDa; (2) The volume resistivity of the polyvinylidene fluoride - hexafluoropropylene copolymer is 10 13 Ω·cm to 10 15 Ω·cm; (3) The dielectric strength of the poly(vinylidene fluoride - hexafluoropropylene) copolymer is 15 kV / mm to 45 kV / mm.

4. The electrochemical device according to claim 1, wherein The phosphorus-containing additive includes at least one of ethoxy(pentafluoro)cyclotriphosphazene, trimethyl phosphate, triphenyl phosphate, and trimethyl phosphite. Based on the total mass of the electrolyte, the mass percentage content of at least one of ethoxy(pentafluoro)cyclotriphosphazene, trimethyl phosphate, triphenyl phosphate, and trimethyl phosphite is C (%). The electrochemical device satisfies: 3.2 ≤ C ≤ 9.

8.

5. The electrochemical device according to claim 1, characterized in that, The layered thickness of the fluoropolymer is N (nm), the phosphorus-containing additive includes at least one of ethoxy(pentafluoro)cyclotriphosphazene, trimethyl phosphate, triphenyl phosphate, and trimethyl phosphite. Based on the total mass of the electrolyte, the mass percentage content of at least one of ethoxy(pentafluoro)cyclotriphosphazene, trimethyl phosphate, triphenyl phosphate, and trimethyl phosphite is C (%). The electrochemical device satisfies: 0.3 ≤ N / C ≤ 1.

6. The electrochemical device according to claim 1, characterized in that, The separator further includes a second coating, the second coating includes β-chitin, based on the total mass of the second coating, the mass percentage content of β-chitin is M (%). The phosphorus-containing additive includes at least one of ethoxy(pentafluoro)cyclotriphosphazene, trimethyl phosphate, triphenyl phosphate, and trimethyl phosphite. Based on the total mass of the electrolyte, the mass percentage content of at least one of ethoxy(pentafluoro)cyclotriphosphazene, trimethyl phosphate, triphenyl phosphate, and trimethyl phosphite is C (%). The electrochemical device satisfies: 0.6 ≤ M / C ≤ 3.

5.

7. The electrochemical device according to claim 1, wherein The phosphorus-containing additive includes lithium difluorophosphate. Based on the total mass of the electrolyte, the mass percentage content of lithium difluorophosphate is D (%). The electrochemical device satisfies: 0.03 ≤ D ≤ 0.

9.

8. The electrochemical device according to claim 7, wherein The electrochemical device satisfies: 0.03 ≤ D ≤ 0.

6.

9. The electrochemical device according to any one of claims 1-8, characterized in that, The first coating further includes a surfactant, and the surfactant includes at least one of perfluoroalkyl triethylene oxide methyl ether, polyoxyethylene alkyl ether, polyoxyethylene fatty acid ester, polyoxyethylene alkylphenol ether, and sorbitan aliphatic ester.

10. The electrochemical device according to any one of claims 1-8, characterized in that, The bulk density of the first coating is 0.5 g / cm 3 to 20 g / cm 3 .

11. The electrochemical device according to any one of claims 1-8, characterized in that, The electrochemical device satisfies at least one of the following: (1) The base film includes a crosslinked polyolefin resin, and the crosslinked polyolefin resin includes a silicon-containing organic group; (2) The surface glossiness of the base film is G (GU), where 0 < G ≤ 5; (3) The separator film further includes chromium element, and based on the total mass of the separator film, the content of the chromium element is 0.2 ppm to 18 ppm.

12. The electrochemical device according to claim 11, wherein, Based on the total mass of the separator film, the content of the chromium element is 0.2 ppm to 10 ppm.

13. The electrochemical device according to any one of claims 1-8, characterized in that, The electrochemical device satisfies at least one of the following: (1) The additive further includes lithium difluoro(oxalato)borate, lithium bis(trifluoromethanesulfonyl)imide and / or lithium difluorophosphate. Based on the total mass of the electrolyte, the mass percentage content of lithium difluoro(oxalato)borate, lithium bis(trifluoromethanesulfonyl)imide and / or lithium difluorophosphate is X (%), where 0.02 ≤ X ≤ 4.4; (2) The additive further includes 1,3 - propane sultone. Based on the total mass of the electrolyte, the mass percentage content of 1,3 - propane sultone is Y (%), where 0.25 ≤ Y ≤ 4; (3) The additive further includes vinylene carbonate. Based on the total mass of the electrolyte, the mass percentage content of vinylene carbonate is A (%), where 0.12 ≤ A ≤ 3.3; (4) The additive further includes a fluorinated linear asymmetric carbonate. Based on the total mass of the electrolyte, the mass percentage content of the fluorinated linear asymmetric carbonate is B (%), where 2 ≤ B ≤ 28; (5) The electrolyte includes propyl propionate and / or ethyl propionate. Based on the total mass of the electrolyte, the mass percentage content of propyl propionate and / or ethyl propionate is E (%), where 26 ≤ E ≤ 40.

14. The electrochemical device according to claim 13, characterized in that, The electrochemical device satisfies at least one of the following: (1)0.25≤Y≤1.8； (2)0.12≤A≤2； (3) The fluorinated linear asymmetric carbonate includes at least one of dimethyl fluorocarbonate, diethyl fluorocarbonate and fluoromethyl ethyl carbonate.

15. An electronic device, characterized in that, Comprising the electrochemical device according to any one of claims 1 - 14.

Images