Separator, electrochemical device and electronic device

Abstract

The present application discloses a separator, an electrochemical device and an electronic device. The separator of embodiments of the present application comprises a base membrane and a first coating arranged on at least one side of the base membrane, the first coating comprises polydopamine and an adhesive polymer, and the Young's modulus of the base membrane is 52-90 MPa. The separator has good structural stability and high mechanical strength, and the decrease in separator strength when the separator is immersed in an electrolyte and swells can be effectively mitigated, thereby improving the quick charging performance and the structural stability of an electrochemical device at a low temperature.

Description

Separating membranes, electrochemical devices and electronic devices

[0001] Cross-references to related applications

[0002] This application claims priority to Chinese Patent Application No. 202510181104.5, filed on February 19, 2025, entitled “Separation Membrane, Electrochemical Device and Electronic Device”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of batteries, and in particular to a separator, an electrochemical device, and an electronic device. Background Technology

[0004] Secondary batteries are reusable batteries that convert chemical energy into electrical energy through discharge and reverse charging processes, and are currently one of the main directions of energy storage research and development.

[0005] With increasingly diverse application scenarios, higher demands are being placed on the fast-charging performance and stability of rechargeable batteries in low-temperature environments, as well as their mechanical properties under extreme conditions such as high temperatures. In particular, lithium dendrites are prone to form on the negative electrode of rechargeable batteries in low-temperature environments, a problem that urgently needs to be addressed. Summary of the Invention

[0006] This application provides a separator membrane, an electrochemical device, and an electronic device. The separator membrane has good structural stability and high mechanical strength, which can effectively reduce the swelling of the separator membrane after it dissolves in the electrolyte, thereby improving the fast charging performance and structural stability of the electrochemical device at low temperatures.

[0007] In a first aspect, this application provides a separator membrane comprising a base membrane and a first coating disposed on at least one side of the base membrane, the first coating comprising polydopamine and an adhesive polymer, and the Young's modulus of the base membrane being 52 MPa to 90 MPa.

[0008] According to this application, the Young's modulus of the base film in the separator is 52 MPa to 90 MPa, and the first coating includes polydopamine. The polydopamine in the first coating can form a stable cross-linked structure with the binder polymer. This structure can promote the rapid transport of lithium ions at low temperatures, thereby improving the fast-charging performance of the electrochemical device at low temperatures. Furthermore, the sufficient Young's modulus of the base film allows the separator to possess certain mechanical strength and structural stability, preventing it from swelling after dissolving in the electrolyte and thus reducing its strength. Electrochemical devices containing this separator exhibit superior low-temperature fast-charging performance and structural stability. Additionally, the coating can stabilize the positive electrode active material, reduce metal dissolution from the positive electrode active material, and capture gas molecules generated by interfacial side reactions, thereby improving the intermittent cycling performance of the electrochemical device at high temperatures.

[0009] In some specific embodiments, the Young's modulus of the base film is 55 MPa to 70 MPa.

[0010] In the above specific embodiments, the Young's modulus of the base film is 55MPa to 70MPa, and the substrate has a suitable elastic deformation capability, which enables the separator to have good resistance to deformation under high and low temperature conditions. When in fast charging test, it can resist the battery deformation caused by material expansion, so that the separator and electrochemical device have stable structural performance and strength.

[0011] In some specific embodiments, the polydopamine in the first coating of the separator of this application satisfies at least one of the following: (1) the average molecular weight of the polydopamine is 120 kDa to 900 kDa; (2) the melting point of the polydopamine is 160°C to 220°C.

[0012] In the above specific embodiments, polydopamine satisfies any one of the above conditions. The polydopamine in the first coating can form a more stable cross-linked structure with the adhesive polymer, further improving the lithium ion transport speed at low temperatures, thereby further improving the fast charging performance of the electrochemical device at low temperatures.

[0013] In some specific embodiments, the first coating may further comprise inorganic ceramic particles, and / or the binder polymer may comprise dextrin.

[0014] In the above specific embodiments, the first coating may further include inorganic ceramic particles, and / or the binder polymer may include dextrin. The first coating has better flexibility and stability, thereby improving the low-temperature fast-charging performance and structural stability of the electrochemical device containing the separator.

[0015] In some specific embodiments, the adhesive polymer in the separator of this application includes dextrin, and based on the total mass of the first coating, the mass percentage of polydopamine in the first coating is Awt%, the mass percentage of dextrin in the first coating is Bwt%, and the separator satisfies: 0.02≤A / B≤2.

[0016] In the above specific embodiments, the separator membrane satisfies 0.02≤A / B≤2, and the resulting polydopamine coating has higher structural stability, giving the separator membrane a certain strength to resist structural deformation caused by the expansion of other materials during fast charging, thereby improving the fast charging performance and structural stability of the electrochemical device at low temperatures as well as its high-temperature intermittent cycling performance.

[0017] In some specific embodiments, the separator of this application may further include a second coating, which is disposed on both sides of the base film, and a first coating is disposed on at least one side outside the second coating, wherein the D90 of the particles in the second coating is 0.6 μm to 10 μm.

[0018] In the above specific embodiments, the D90 of the particles in the second coating of the separator is 0.6μm to 10μm. The separator has a certain supporting strength and resistance to deformation, and can also promote the migration of lithium ions, thereby improving the wetting ability of the electrolyte at high and low temperatures, reducing the purple spot lithium deposition at the interface, improving the fast charging performance at low temperatures, structural stability and high temperature intermittent cycling performance.

[0019] In some specific embodiments, the D90 of the particles in the second coating is 0.6 μm to 5 μm.

[0020] In the above specific embodiments, the particle D90 in the second coating of the separator of this application is 0.6μm to 5μm. The separator has more suitable support strength and resistance to deformation. In addition, when the D90 range is within the preferred range, it can further promote the migration of lithium ions, thereby improving the wetting ability of the electrolyte at high and low temperatures, reducing the purple spot lithium deposition at the interface, optimizing the fast charging performance at low temperature, structural stability and high temperature intermittent cycling performance.

[0021] In some specific embodiments, the separator of this application may further include a second coating, which is disposed on both sides of the base film, and a first coating is disposed on at least one side outside the second coating. The thickness of the first coating is C μm, and the D90 of the particles in the second coating is D μm. The separator satisfies: 0.06≤C / D≤10.

[0022] In the above specific embodiments, the separator satisfies 0.06 ≤ C / D ≤ 10, allowing it to better perform its isolation and insulation functions, effectively preventing direct contact between the positive and negative electrodes and reducing the risk of short circuits. Simultaneously, improving the mechanical properties and thermal stability of the separator helps enhance the safety of the electrochemical device. Furthermore, it facilitates the rapid transport of lithium ions within the battery, reducing resistance to lithium ion diffusion and thus improving the battery's charge and discharge efficiency.

[0023] In some specific embodiments, the separator of this application satisfies: 0.2≤C / D≤7.

[0024] In the above specific embodiments, the separator satisfies 0.2≤C / D≤7, and the separator has better mechanical properties and thermal stability, thereby further improving the safety of the electrochemical device.

[0025] In some specific embodiments, the first coating of the separator of this application satisfies at least one of the following: (1) the thickness of the first coating is 1 μm to 4 μm; (2) the porosity of the first coating is 30% to 65%; (3) the surface gloss of the base film is 1 GU to 5.5 GU; (4) based on the total mass of the first coating, the mass percentage of polydopamine in the first coating is Awt%, the thickness of the first coating is C μm, and the separator satisfies: 0.25≤A / C≤67.

[0026] In the above specific embodiments, the thickness of the first coating of the separator is 1μm to 4μm. The separator itself has suitable strength, thereby resisting structural deformation caused by the expansion of other materials during fast charging, thus improving fast charging performance and structural stability at low temperatures, as well as high-temperature intermittent cycling performance. When the thickness of the first coating is too thick, the energy density of the electrochemical device will decrease, and it may affect the wettability of the electrolyte. When the thickness of the first coating is too thin, it cannot stabilize the positive electrode active material, nor can it give the separator sufficient mechanical strength and structural stability. It is not easy to dissolve in the electrolyte and swell, leading to a decrease in the strength of the separator. Therefore, the electrochemical device containing this separator cannot exhibit excellent low-temperature fast charging performance and structural stability.

[0027] The porosity of the first coating of the separator is 30%–65%, maintaining good structural stability during battery cycling. This extends the separator's lifespan, thereby improving the overall cycle life of the battery. Simultaneously, it provides sufficient and suitable lithium-ion transport channels, allowing lithium ions to pass through the separator more smoothly during charging and discharging, improving battery charge / discharge efficiency, and thus increasing the battery's energy density and power density. If the porosity is too high, the first coating structure is not stable enough, leading to disordered lithium-ion transport paths and affecting the battery's charge / discharge efficiency and rate performance; if the porosity is too low, lithium-ion transport is hindered, slowing down the battery's charge / discharge rate and limiting its energy density.

[0028] The surface gloss of the base film of the separator ranges from 1 GU to 5.5 GU. The base film's surface has a certain degree of smoothness, allowing the coating to better integrate with the substrate, thereby improving the energy density of the electrochemical device. Higher substrate surface gloss results in a smoother surface, but excessively high gloss leads to less surface interaction between the coating and the substrate, increasing the difficulty of coating application. Conversely, excessively low gloss results in lower energy density for the electrochemical device, and the uneven surface increases safety risks and reduces the pass rate of the side extrusion test.

[0029] The separator meets the requirement of 0.25≤A / C≤67. The synergistic effect of the two can improve the mechanical strength of the separator, reduce the risk of the separator breaking or being damaged in the complex environment inside the battery, enhance the protective effect of the separator on the internal structure of the battery, improve the safety and service life of the battery, and at the same time, facilitate the transport of lithium ions in the separator, reduce the internal resistance of the battery, thereby improving the charging and discharging efficiency of the battery.

[0030] Secondly, this application provides an electrochemical device, including a positive electrode, a negative electrode, an electrolyte, and a separator membrane as described in the first aspect. The separator membrane is disposed between the positive and negative electrode, and the electrolyte includes a lithium salt and a non-aqueous solvent. This electrochemical device exhibits superior low-temperature fast-charging performance and structural stability.

[0031] In some specific embodiments, the electrolyte of the electrochemical device of this application satisfies at least one of the following: (1) the lithium salt includes at least one of lithium difluorooxalate borate, lithium bis(trifluoromethanesulfonyl)imide, and lithium difluorophosphate, and the mass percentage of lithium difluorooxalate borate, lithium bis(trifluoromethanesulfonyl)imide, or lithium difluorophosphate in the electrolyte is 0.01wt% to 4.5wt% based on the total mass of the electrolyte; (2) the lithium salt includes lithium difluorooxalate borate, lithium bis(trifluoromethanesulfonyl)imide, and lithium difluorophosphate. At least one of the following, based on the total mass of the electrolyte, the mass percentage of lithium difluorooxalate borate, lithium bis(trifluoromethanesulfonyl)imide or lithium difluorophosphate in the electrolyte is Fwt%, based on the total mass of the first coating, the mass percentage of polydopamine in the first coating is Awt%, and the electrochemical device satisfies: 6≤A / F≤3330; (3) the non-aqueous solvent includes propyl propionate, based on the total mass of the electrolyte, the mass percentage of propyl propionate in the electrolyte is 20wt% to 45wt%.

[0032] In the above specific embodiments, the electrolyte of the electrochemical device satisfies the following mass percentage requirements: lithium difluorooxalate borate, lithium bis(trifluoromethanesulfonyl)imide, or lithium difluorophosphate has a mass percentage of 0.01wt% to 4.5wt% and / or propyl propionate has a mass percentage of 20wt% to 45wt%. Lithium difluorooxalate borate can promote the activation of propyl propionate, thereby further promoting the flow 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.

[0033] The electrochemical device satisfies 6 ≤ A / F ≤ 3330. Polydopamine works synergistically with at least one of lithium difluorooxalate borate, lithium bis(trifluoromethanesulfonyl)imide, and lithium difluorophosphate to stabilize the internal interface of the battery, reduce the increase in interfacial resistance, and improve the long-term cycle performance of the battery. Simultaneously, polydopamine improves the interfacial compatibility between the separator and the electrolyte, while the stable solid electrolyte interface (SEI) film formed by lithium difluorooxalate borate, lithium bis(trifluoromethanesulfonyl)imide, or lithium difluorophosphate helps to further stabilize the electrode / electrolyte interface. The combined effect of these two factors further stabilizes the internal interface of the battery, reduces the increase in interfacial resistance, and improves the long-term cycle performance of the battery.

[0034] In some specific embodiments, the electrolyte of the electrochemical device of this application includes propyl propionate and lithium bis(fluorosulfonyl)imide; based on the total mass of the electrolyte, the mass percentage of propyl propionate in the electrolyte is Gwt%, the mass percentage of lithium bis(fluorosulfonyl)imide is Hwt%, and the electrochemical device satisfies: 0.02≤H / G≤0.48.

[0035] In the above specific embodiments, the electrochemical device satisfies 0.02≤H / G≤0.48, which can improve the viscosity of the electrolyte, thereby improving the safety of low-temperature fast charging and overcurrent, while reducing the increase in impedance value obtained by high-temperature electrochemical impedance spectroscopy (EIS) testing.

[0036] In some specific embodiments, the electrochemical device of this application satisfies: 0.02≤H / G≤0.3.

[0037] In the above specific embodiments, the electrochemical device satisfies 0.02≤H / G≤0.3, which can further improve the viscosity of the electrolyte, thereby improving the low-temperature fast charging performance and overcurrent safety, while further reducing the increase in impedance value obtained by high-temperature EIS testing.

[0038] In some specific embodiments, the electrolyte of the electrochemical device of this application may further include additives, including at least one selected from 1,3-propanesulfonate lactone, ethylene ethylene carbonate, ethylene sulfate, and 1,2,3-tris(2-cyanoxy)propane.

[0039] In the above specific embodiments, 1,3-propanesulfonate lactone, ethylene ethylene carbonate, ethylene sulfate, and 1,2,3-tris(2-cyanoxy)propane are used as electrolyte additives to isolate the electrodes from the solvent, preventing electrode damage. Simultaneously, they inhibit electrolyte decomposition, reduce battery material loss, and effectively extend battery life. Furthermore, they reduce battery internal resistance, optimize charge-discharge performance, and improve the battery's rate performance and low-temperature charge-discharge performance. In addition, under high-temperature conditions, they reduce gas generation and battery expansion, lower the self-discharge rate, improve the battery's high-temperature cycle and storage performance, and significantly enhance battery safety.

[0040] In some specific embodiments, the electrochemical device of this application satisfies at least one of the following: (1) the additive includes 1,3-propanesulfonate lactone, and the mass percentage of 1,3-propanesulfonate lactone in the electrolyte is 0.2 wt% to 3.5 wt% based on the total mass of the electrolyte; (2) the additive includes ethylene carbonate, and the mass percentage of ethylene carbonate in the electrolyte is 0.1 wt% to 3.5 wt% based on the total mass of the electrolyte; (3) the additive includes vinyl sulfate, and the mass percentage of vinyl sulfate in the electrolyte is [missing information]. 0.1wt%~3.5wt%; (4) The additives include 1,2,3-tris(2-cyanoxy)propane, and the mass percentage of 1,2,3-tris(2-cyanoxy)propane in the electrolyte is 0.1wt%~2.8wt% based on the total mass of the electrolyte; (5) The additives include 1,3-propanesulfonic acid lactone, and the mass percentage of 1,3-propanesulfonic acid lactone is Iwt% based on the total mass of the electrolyte; the mass percentage of polydopamine in the first coating is Awt% based on the total mass of the first coating; the electrochemical device satisfies: 8≤A / I≤334.

[0041] In the above specific embodiments, the electrolyte of the electrochemical device contains 1,3-propanesulfonate lactone and satisfies the mass percentage of 1,3-propanesulfonate lactone in the electrolyte being 0.2wt% to 3.5wt%. 1,3-propanesulfonate lactone can form a stable SEI film on the surface of the positive electrode material, thereby improving the low-temperature fast charging performance and overcurrent safety of the electrochemical device.

[0042] The electrolyte of the electrochemical device contains ethylene ethylene carbonate and the mass percentage of ethylene ethylene carbonate in the electrolyte is 0.1wt% to 3.5wt%. Ethylene ethylene carbonate can form a uniform and dense SEI film on the surface of the negative electrode material, improving the low-temperature fast charging performance and overcurrent safety of the electrochemical device.

[0043] The electrolyte of the electrochemical device contains vinyl sulfate and the mass percentage of vinyl sulfate in the electrolyte is 0.1wt% to 3.5wt%. Vinyl sulfate can form a denser SEI film on the surface of the negative electrode material and capture gas molecules generated by side reactions at the interface between the negative electrode and the electrolyte, thereby improving the low-temperature fast charging performance and overcurrent safety of the electrochemical device.

[0044] The electrolyte of the electrochemical device contains 1,2,3-tris(2-cyanoxy)propane, and the mass percentage of 1,2,3-tris(2-cyanoxy)propane in the electrolyte is 0.1wt% to 2.8wt%. 1,2,3-tris(2-cyanoxy)propane can improve the viscosity of the electrolyte and is conducive to the formation of a stable positive electrode electrolyte interface (CEI film), thereby improving low-temperature fast charging, overcurrent safety, and reducing the increase in impedance value obtained by high-temperature EIS testing.

[0045] The electrochemical device satisfies 8 ≤ A / I ≤ 334. Polydopamine and 1,3-propanesulfonate synergistically enhance the bonding force between the various components inside the battery, making the battery structure more robust and able to withstand volume changes and mechanical stress during charging and discharging, reducing interface separation and structural damage. Furthermore, it optimizes the lithium-ion transport path between the separator and the electrolyte, making lithium-ion transport more efficient, reducing ion migration resistance during battery charging and discharging, and improving the battery's charge / discharge efficiency and power performance.

[0046] In some specific embodiments, the electrochemical device satisfies at least one of the following: (1) the additive includes 1,3-propanesulfonate lactone, and the mass percentage of 1,3-propanesulfonate lactone in the electrolyte is 0.2 wt% to 2 wt% based on the total mass of the electrolyte; (2) the additive includes ethylene carbonate, and the mass percentage of ethylene carbonate in the electrolyte is 0.1 wt% to 1.8 wt% based on the total mass of the electrolyte; (3) the additive includes vinyl sulfate, and the mass percentage of vinyl sulfate in the electrolyte is 0.1 wt% to 2.5 wt% based on the total mass of the electrolyte.

[0047] In the above specific embodiments, the electrolyte of the electrochemical device contains 1,3-propanesulfonate lactone and satisfies the mass percentage of 1,3-propanesulfonate lactone in the electrolyte being 0.2wt% to 2wt%. 1,3-propanesulfonate lactone can form a more stable SEI film on the surface of the positive electrode material, further improving the low-temperature fast charging performance and overcurrent safety of the electrochemical device.

[0048] The electrolyte of the electrochemical device contains ethylene ethylene carbonate and the mass percentage of ethylene ethylene carbonate in the electrolyte is 0.1wt% to 1.8wt%. Ethylene ethylene 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 and overcurrent safety of the electrochemical device.

[0049] The electrolyte of the electrochemical device contains vinyl sulfate and the mass percentage of vinyl sulfate in the electrolyte is 0.1wt% to 2.5wt%. Vinyl sulfate can form a denser SEI film on the surface of the negative electrode material and capture gas molecules generated by side reactions at the interface between the negative electrode and the electrolyte, thereby improving the low-temperature fast charging performance and overcurrent safety of the electrochemical device.

[0050] In some specific embodiments, the electrode bonding strength between the separator and the negative electrode of the electrochemical device is 1.8gf / 15mm≤T≤3.6gf / 15mm.

[0051] In the above specific embodiments, the electrochemical device satisfies the electrode bonding strength between the separator and the negative electrode sheet being 1.8gf / 15mm≤T≤3.6gf / 15mm. This ensures that the separator and the negative electrode sheet are not easily separated during side extrusion testing, thus giving the electrochemical device a certain structural strength and high-temperature cycling stability.

[0052] In some specific embodiments, the electrode bonding strength between the separator and the negative electrode sheet is T gf / 15mm, and the electrochemical device satisfies: 15≤X / T≤43.

[0053] In the above specific embodiments, the electrochemical device satisfies 15≤X / T≤43. The separator has a certain degree of flexibility to adapt to changes in electrode volume while maintaining good adhesion to the negative electrode, preventing separation of the separator from the electrode and maintaining the stability of the battery's internal structure. Simultaneously, the stable adhesion between the separator and the negative electrode helps maintain the stability of the ion transport channel. During charging and discharging, lithium ions can pass more smoothly through the interface between the separator and the negative electrode, reducing ion transport obstacles, lowering the battery's internal resistance, and thus improving the battery's charging and discharging efficiency and power performance.

[0054] Thirdly, this application provides an electronic device, including the electrochemical device described above. Detailed Implementation

[0055] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0056] As used in this application, the terms “comprising,” “containing,” and “including” are used in their open, non-restrictive sense.

[0057] Additionally, quantities, ratios, and other numerical values ​​are sometimes presented in range format in this document. It should be understood that such range format is for convenience and brevity and should be interpreted flexibly to include not only the numerical values ​​explicitly specified as range limits, but also all individual numerical values ​​or subranges covered within the range, as if each numerical value and subrange were explicitly specified.

[0058] In the detailed description and claims, a list of items connected by the terms "one or more of," "one or more of," "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 contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements.

[0059] In the structure of a secondary battery, the separator plays an indispensable role. On the one hand, it prevents direct contact between the positive and negative electrodes, avoiding the risk of short circuits; on the other hand, it allows ions to pass through, maintaining the electrochemical reactions inside the battery.

[0060] With technological advancements, the application scenarios for rechargeable batteries are constantly expanding, encompassing everyday electronic devices, electric vehicles, and energy storage power stations. Different application scenarios place stringent demands on the performance of rechargeable batteries. In low-temperature environments, such as the starting and range extension of electric vehicles in cold winters, and the stable operation of outdoor electronic devices, higher requirements are placed on the fast-charging performance and stability of rechargeable batteries. However, at low temperatures, lithium dendrites are prone to form on the negative electrode of rechargeable batteries. The presence of lithium dendrites not only reduces the battery's charging and discharging efficiency but may also penetrate the separator, causing a short circuit and thus affecting the battery's safety and lifespan.

[0061] Meanwhile, under extreme conditions such as high temperatures, such as the continuous operation of energy storage power stations during hot summers, secondary batteries need to possess excellent mechanical properties to ensure stable operation. The mechanical strength and thermal stability of the separator play a crucial role in the performance of secondary batteries under these extreme conditions. Therefore, developing high-performance separators that can meet the performance requirements of secondary batteries under various complex operating conditions has become an important problem that urgently needs to be solved in the current battery field.

[0062] Based on the above problems, this application provides a separator, an electrochemical device, and an electronic device. The separator has good structural stability and high mechanical strength, which can effectively reduce the problem of the separator swelling after dissolving in the electrolyte, thereby improving the fast charging performance and structural stability of the electrochemical device at low temperatures.

[0063] The embodiments of this application will be described in detail below.

[0064] Separating membrane

[0065] In a first aspect, embodiments of this application provide a separator membrane, which includes a base membrane and a first coating disposed on at least one side of the base membrane. The first coating includes polydopamine and an adhesive polymer, and the Young's modulus of the base membrane is X MPa, where 52 ≤ X ≤ 90.

[0066] For example, X can be 52, 55, 58, 60, 62, 65, 68, 70, 72, 75, 78, 80, 82, 85, 88, 90, or any range of the above values.

[0067] Optional, 55≤X≤90, 55≤X≤88, 55≤X≤86, 55≤X≤84, 55≤X≤82, 55≤X≤80, 55≤X≤78, 55≤X≤76, 55≤X≤74, 55≤X≤72, 55≤X≤70.

[0068] According to this application, when the Young's modulus of the base film in the separator satisfies 52≤X≤90, and the first coating includes polydopamine and a binder polymer, the polydopamine in the first coating can form a stable cross-linked structure with the binder polymer. This structure can promote the rapid transport of lithium ions at low temperatures, thereby improving the fast-charging performance of the electrochemical device at low temperatures. Furthermore, the Young's modulus of the base film ensures that the separator possesses certain mechanical strength and structural stability, preventing swelling after dissolution in the electrolyte and thus reducing the separator's strength. Electrochemical devices containing this separator exhibit superior low-temperature fast-charging performance and structural stability. Additionally, this coating can stabilize the positive electrode active material, reduce metal dissolution from the positive electrode active material, and capture gas molecules generated by interfacial side reactions, thereby improving the intermittent cycling performance of the electrochemical device at high temperatures.

[0069] It should be noted that the Young's modulus of the base film and the polydopamine in the first coating can both be detected using methods and instruments known in the art. For example, the base film can be obtained by disassembling the electrochemical device to obtain the separator, and then further disassembling it. Using the method specified in JIS K7127, a suitable tensile speed is set according to the material properties and standard requirements, and a tensile testing machine is started to apply tensile force to the sample. During the tensile process, the testing machine automatically records the tensile force and the corresponding elongation of the sample at different times, calculates the stress and strain, and then obtains the Young's modulus of the base film. The first coating can be dissolved in a suitable solvent, and the specific soluble components and the mass percentage of each component in the first coating can be detected using gas chromatography-mass spectrometry (GC-MS).

[0070] In some embodiments, the polydopamine in the first coating of the separator of this application satisfies at least one of the following: (1) the average molecular weight of the polydopamine is 120 kDa to 900 kDa, for example, it can be 120 kDa, 150 kDa, 180 kDa, 200 kDa, 250 kDa, 300 kDa, 350 kDa, 400 kDa, 450 kDa, 500 kDa, 550 kDa, 600 kDa, 650 kDa, 700 kDa, 750 kDa, 800 kDa, 850 kDa, 900 kDa, or any of the above values; (2) the melting point of the polydopamine is 160°C to 220°C, for example, it can be 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, or any of the above values.

[0071] It should be noted that the average molecular weight and melting point of polydopamine can be detected using methods and instruments known in the art. For example, polydopamine can be obtained by disassembling an electrochemical device to obtain a separating membrane, which can then be further disassembled and separated. Using gel permeation chromatography (GPC), the solution is injected into the GPC instrument, and a suitable column and mobile phase are selected. By comparing with a standard curve, the average molecular weight of polydopamine can be determined. Alternatively, differential scanning calorimetry (DSC) can be used. An appropriate amount of polydopamine sample is placed in the sample cell of the DSC instrument, and an equal mass of a reference material (such as alumina) is placed in the reference cell. The sample and reference cells are then placed in the DSC instrument, and the temperature is increased at a certain rate (e.g., 5℃ / min, 10℃ / min, etc.). The instrument records the change in heat flow rate between the sample and the reference material throughout the heating process. By analyzing the obtained DSC curve, the position and temperature of the endothermic peak are determined, thereby identifying the melting point of polydopamine.

[0072] According to this embodiment, polydopamine satisfies any of the above conditions. The polydopamine in the first coating can form a more stable cross-linked structure with the adhesive polymer, further improving the lithium-ion transport speed at low temperatures, thereby further improving the fast-charging performance of the electrochemical device at low temperatures.

[0073] In some embodiments, the first coating may also be in inorganic ceramic particles, and / or the binder polymer may include dextrin. The inclusion of dextrin and / or inorganic ceramic particles in the first coating provides better flexibility and stability, thereby improving the low-temperature fast-charging performance and structural stability of the electrochemical device containing the separator.

[0074] In some embodiments, the adhesive polymer in the separator of this application includes dextrin, and based on the total mass of the first coating, the mass percentage of polydopamine in the first coating is Awt%, the mass percentage of dextrin in the first coating is Bwt%, and the separator satisfies: 0.02≤A / B≤2.

[0075] For example, A / B can be 0.02, 0.05, 0.08, 0.1, 0.2, 0.5, 0.8, 1, 1.2, 1.5, 1.8, 2, or any of the above values.

[0076] According to this embodiment, the separator membrane satisfies 0.02≤A / B≤2, and the resulting polydopamine coating has higher structural stability, giving the separator membrane a certain strength to resist structural deformation caused by the expansion of other materials during fast charging, thereby improving the fast charging performance and structural stability of the electrochemical device at low temperatures as well as its high-temperature intermittent cycling performance.

[0077] In some embodiments, the separator of this application may further include a second coating, which is disposed on both sides of the base film, and a first coating is disposed on at least one side outside the second coating. The particle D90 of the particles in the second coating is Dμm, where 0.6 ≤ D ≤ 10. For example, D can be 0.6, 0.8, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, or any range of the above values.

[0078] Optional values ​​are: 0.6≤D≤9.5, 0.6≤D≤9, 0.6≤D≤8.5, 0.6≤D≤8, 0.6≤D≤7.5, 0.6≤D≤7, 0.6≤D≤6.5, and 0.6≤D≤6.

[0079] According to this embodiment, the particles in the second coating of the separator satisfy 0.6≤D≤10. The separator has a certain supporting strength and resistance to deformation, and can also promote the migration of lithium ions, thereby improving the wetting ability of the electrolyte at high and low temperatures, reducing the purple spot lithium deposition at the interface, improving the fast charging performance at low temperatures, structural stability and high temperature intermittent cycling performance.

[0080] In some embodiments, the separator of this application may further include a second coating, which is disposed on both sides of the base film, and a first coating is disposed on at least one side outside the second coating. The thickness of the first coating is C μm, and the D90 of the particles in the second coating is D μm. The separator satisfies: 0.06 ≤ C / D ≤ 10. For example, C / D can be 0.06, 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, or any range of the above values.

[0081] Optional values ​​are: 0.1≤C / D≤10, 0.2≤C / D≤10, 0.2≤C / D≤9.5, 0.2≤C / D≤9, 0.2≤C / D≤8.5, 0.2≤C / D≤8, 0.2≤C / D≤7.5, and 0.2≤C / D≤7.

[0082] According to this embodiment, the separator satisfies 0.06 ≤ C / D ≤ 10, allowing it to better perform its isolation and insulation functions, effectively preventing direct contact between the positive and negative electrodes and reducing the risk of short circuits. Simultaneously, improving the mechanical properties and thermal stability of the separator helps enhance the safety of the electrochemical device. Furthermore, it facilitates the rapid transport of lithium ions within the battery, reducing resistance to lithium ion diffusion and thus improving the battery's charge and discharge efficiency.

[0083] In some embodiments, the first coating of the separator of this application satisfies at least one of the following: (1) the thickness of the first coating is C μm, 1≤C≤4, for example, it can be 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4, or any combination of the above values; (2) the porosity of the first coating is 30% to 65%, for example, it can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, or any combination of the above values; (3) the surface gloss of the base film is E. GU, 1≤E≤5.5, for example, E can be 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4, 4.2, 4.5, 4.8, 5, 5.2, 5.5, or any of the above values; (4) Based on the total mass of the first coating, the mass percentage of polydopamine in the first coating is Awt%, the thickness of the first coating is Cμm, and the isolation membrane satisfies: 0.25≤A / C≤67, for example, A / C can be 0.25, 1, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 67, or any of the above values.

[0084] According to this embodiment, the first coating of the separator satisfies 1≤C≤4, and the separator itself has suitable strength, thereby resisting structural deformation caused by the expansion of other materials during fast charging, thus improving fast charging performance and structural stability at low temperatures as well as high-temperature intermittent cycling performance. When the thickness of the first coating is too thick, the energy density of the electrochemical device will decrease, and it may affect the wettability of the electrolyte. When the thickness of the first coating is too thin, it cannot stabilize the positive electrode active material, nor can it give the separator sufficient mechanical strength and structural stability. It is not easy to dissolve in the electrolyte and swell, resulting in a decrease in the strength of the separator. Therefore, the electrochemical device containing this separator cannot exhibit excellent low-temperature fast charging performance and structural stability.

[0085] The porosity of the first coating of the separator is 30%–65%, maintaining good structural stability during battery cycling. This extends the separator's lifespan, thereby improving the overall cycle life of the battery. Simultaneously, it provides sufficient and suitable lithium-ion transport channels, allowing lithium ions to pass through the separator more smoothly during charging and discharging, improving battery charge / discharge efficiency, and thus increasing the battery's energy density and power density. If the porosity is too high, the first coating structure is not stable enough, leading to disordered lithium-ion transport paths and affecting the battery's charge / discharge efficiency and rate performance; if the porosity is too low, lithium-ion transport is hindered, slowing down the battery's charge / discharge rate and limiting its energy density.

[0086] The base film of the separator meets the requirement of 1≤E≤5.5, and its surface has a certain degree of smoothness, which allows the coating to better integrate with the substrate, thereby improving the energy density of the electrochemical device. Higher substrate surface gloss results in a smoother surface, but excessively high gloss leads to less surface interaction between the coating and the substrate, increasing the difficulty of coating application. Conversely, excessively low gloss results in lower energy density of the electrochemical device, and the uneven surface increases safety risks and reduces the pass rate of side extrusion tests.

[0087] The separator meets the requirement of 0.25≤A / C≤67. The synergistic effect of the two can improve the mechanical strength of the separator, reduce the risk of the separator breaking or being damaged in the complex environment inside the battery, enhance the protective effect of the separator on the internal structure of the battery, improve the safety and service life of the battery, and at the same time, facilitate the transport of lithium ions in the separator, reduce the internal resistance of the battery, thereby improving the charging and discharging efficiency of the battery.

[0088] It should be noted that the thickness C of the first coating can be measured using methods and instruments known in the art. For example, the separator can be obtained by disassembling the electrochemical device, and a flat cross-sectional sample can be prepared by slicing the separator using scanning electron microscopy (SEM). The sample is then placed in the SEM device, and a high-resolution cross-sectional image is obtained by selecting an appropriate accelerating voltage and scanning parameters. The thickness of the first coating can be directly measured on the image using the image processing software provided with the SEM.

[0089] The surface gloss of the base film can be detected using methods and instruments known in the art. For example, the electrochemical device can be disassembled to obtain the separator, and the base film can be obtained by disassembling the separator. The surface gloss can then be measured at a 60° reflection angle using a "micro-TRI-gloss-s" manufactured by BYK.

[0090] The porosity of the first coating can be detected using methods and instruments known in the art. For example, an isolation membrane can be obtained by disassembling an electrochemical device, and the first coating can be obtained by disassembling the isolation membrane. Then, a gas adsorption method is used to perform vacuum degassing at a certain temperature to remove impurities and gases adsorbed on the surface. The sample is then placed in the sample tube of a gas adsorption instrument, the instrument is cooled to about liquid nitrogen temperature (77K), nitrogen gas at different pressures is introduced, and the amount of nitrogen adsorbed is measured. By analyzing the adsorption isotherms, the specific surface area of ​​the sample is calculated using methods such as the BET equation, and the porosity is calculated using relevant models. Alternatively, scanning electron microscopy (SEM) combined with image analysis can be used to appropriately process the first coating, such as by coating, to increase the conductivity of the sample and the image quality. The sample is then placed in a scanning electron microscope, and an appropriate magnification and imaging parameters are selected to obtain an SEM image of the coating. Import the SEM image into image analysis software. Through threshold setting, binarization and other operations, the pores are distinguished from the coating substrate. The software will automatically calculate parameters such as the area and number of pores, and then obtain the porosity.

[0091] Electrochemical device

[0092] Secondly, this application provides an electrochemical device, including a positive electrode, a negative electrode, an electrolyte, and a separator membrane as described in the first aspect. The separator membrane is disposed between the positive and negative electrode, and the electrolyte includes a lithium salt and a non-aqueous solvent. This electrochemical device exhibits superior low-temperature fast-charging performance and structural stability.

[0093] In some specific embodiments, the electrolyte of the electrochemical device of this application satisfies at least one of the following: (1) the lithium salt includes at least one of lithium difluorooxalate borate, lithium bis(trifluoromethanesulfonyl)imide, and lithium difluorophosphate, and the mass percentage of lithium difluorooxalate borate, lithium bis(trifluoromethanesulfonyl)imide, or lithium difluorophosphate in the electrolyte is Fwt%, 0.01≤F≤4.5, for example, F can be 0.01, 0.05, 0.1, 0.5, 1, 1.5, 2, 1.5, 2.5, 3, 3.5, 4, 4.5, or any range of the above values; (2) the lithium salt includes at least one of lithium difluorooxalate borate, lithium bis(trifluoromethanesulfonyl)imide, and lithium difluorophosphate, and the mass percentage of lithium difluorooxalate borate, lithium bis(trifluoromethanesulfonyl)imide, or lithium difluorophosphate in the electrolyte is Fwt%, 0.01≤F≤4.5, for example, F can be 0.01, 0.05, 0.1, 0.5, 1, 1.5, 2, 1.5, 2.5, 3, 3.5, 4, 4.5, or any range of the above values; The mass percentage of lithium fluorophosphate is Fwt%, and the mass percentage of polydopamine in the first coating is Awt%, based on the total mass of the first coating. The electrochemical device satisfies: 6≤A / F≤3330, for example, A / F can be 6, 50, 100, 300, 500, 700, 1000, 1200, 1500, 1800, 2000, 2200, 2500, 2800, 3000, 3200, 3330, or any of the above values; (3) The non-aqueous solvent includes propyl propionate, and the mass percentage of propyl propionate in the electrolyte is Gwt%, based on the total mass of the electrolyte, 20≤G≤45, for example, G can be 20, 22, 25, 28, 30, 32, 35, 38, 40, 42, 45, or any of the above values.

[0094] According to this embodiment, the electrolyte of the electrochemical device satisfies 0.01≤F≤4.5 and / or 20≤G≤45. Lithium difluorooxalate borate, lithium bis(trifluoromethanesulfonyl)imide, or lithium difluorophosphate can promote the activation of propyl propionate, thereby further promoting the flow 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.

[0095] The electrochemical device satisfies 6 ≤ A / F ≤ 3330. Polydopamine, in synergy with at least one of lithium difluorooxalate borate, lithium bis(trifluoromethanesulfonyl)imide, and lithium difluorophosphate, makes the internal interface of the battery more stable, reduces the increase in interface resistance, and improves the long-term cycle performance of the battery. Simultaneously, polydopamine improves the interfacial compatibility between the separator and the electrolyte, while the stable solid electrolyte interface (SEI film) formed by lithium difluorooxalate borate, lithium bis(trifluoromethanesulfonyl)imide, or lithium difluorophosphate helps to further stabilize the electrode / electrolyte interface. The combined effect of these two factors makes the internal interface of the battery more stable, reduces the increase in interface resistance, and improves the long-term cycle performance of the battery.

[0096] It should be noted that the mass percentage of lithium difluorooxalate borate in the electrolyte can be detected using methods or instruments known in the art. For example, the electrochemical device can be disassembled, the electrolyte obtained by centrifugation, and tested using ion chromatography (IC). The retention time can be used to qualitatively identify some components (such as lithium salts) in the electrolyte, and the corresponding mass percentage can be calculated by peak area. Gas chromatography-mass spectrometry (GC-MS) can be used to detect the mass percentage of some components (such as organic solvents) in the electrolyte.

[0097] In some embodiments, the electrolyte of the electrochemical device of this application comprises propyl propionate and lithium bisfluorosulfonylimide; based on the total mass of the electrolyte, the mass percentage of propyl propionate in the electrolyte is Gwt%, and the mass percentage of lithium bisfluorosulfonylimide is Hwt%, and the electrochemical device satisfies: 0.02 ≤ H / G ≤ 0.48. For example, H / G can be 0.02, 0.05, 0.08, 0.1, 0.12, 0.15, 0.18, 0.2, 0.22, 0.25, 0.28, 0.3, 0.32, 0.35, 0.38, 0.4, 0.42, 0.45, 0.48, or any range of the above values.

[0098] Optionally, 0.02≤H / G≤0.46, 0.02≤H / G≤0.44, 0.02≤H / G≤0.42, 0.02≤H / G≤0.4, 0.02≤H / G≤0.38, 0.02≤H / G≤0.36, 0.02≤H / G≤0.34, 0.02≤H / G≤0.32, and 0.02≤H / G≤0.3.

[0099] According to this embodiment, the electrochemical device satisfies 0.02≤H / G≤0.48, which can improve the viscosity of the electrolyte, thereby improving the safety of low-temperature fast charging and overcurrent, while reducing the increase in impedance value obtained by high-temperature EIS testing.

[0100] In some embodiments, the electrolyte of the electrochemical device of this application may further include additives, including at least one of 1,3-propanesulfonate lactone, ethylene ethylene carbonate, ethylene sulfate, and 1,2,3-tris(2-cyanoxy)propane.

[0101] According to this embodiment, 1,3-propanesulfonate lactone, ethylene ethylene carbonate, ethylene sulfate, and 1,2,3-tris(2-cyanoxy)propane are used as electrolyte additives to isolate the electrodes from the solvent, preventing electrode damage. Simultaneously, they inhibit electrolyte decomposition, reduce battery material loss, and effectively extend battery life. Furthermore, they reduce battery internal resistance, optimize charge-discharge performance, and improve the battery's rate performance and low-temperature charge-discharge performance. In addition, under high-temperature conditions, they reduce gas generation and battery expansion, lower the self-discharge rate, improve the battery's high-temperature cycle and storage performance, and significantly enhance battery safety.

[0102] In some specific embodiments, the electrochemical device of this application satisfies at least one of the following: (1) the additive includes 1,3-propanesulfonic acid lactone, and the mass percentage of 1,3-propanesulfonic acid lactone in the electrolyte is 1 wt%, 0.2 ≤ 1 ≤ 3.5, for example, 1 can be 0.2, 0.5, 0.8, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, or any range of the above values; (2) the additive includes ethylene ethylene carbonate, and the mass percentage of 1,3-propanesulfonic acid lactone in the electrolyte is 1 wt%, based on the total mass of the electrolyte. The mass percentage of ethylene carbonate in the electrolyte is Jwt%, 0.1≤J≤3.5, for example, J can be 0.1, 0.2, 0.5, 0.8, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, or any range of the above values; (3) The additives include vinyl sulfate, and the mass percentage of vinyl sulfate in the electrolyte is Kwt%, based on the total mass of the electrolyte, 0.1≤K≤3.5, for example, K can be 0.1, 0.2, 0.5, 0. .8, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, or any of the above values; (4) The additive includes 1,2,3-tris(2-cyanoxy)propane, and the mass percentage of 1,2,3-tris(2-cyanoxy)propane in the electrolyte is Lwt%, based on the total mass of the electrolyte, 0.1≤L≤2.8, for example, L can be 0.1, 0.2, 0.5, 0.8, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, or any of the above values. (5) The additives include 1,3-propanesulfonic acid lactone, with a mass percentage of 1 wt% based on the total mass of the electrolyte, and a mass percentage of A wt% of polydopamine in the first coating based on the total mass of the first coating. The electrochemical device satisfies: 8 ≤ A / I ≤ 334, for example, A / F can be 8, 20, 50, 80, 100, 120, 150, 180, 200, 220, 250, 280, 300, 320, 334, or any of the above-mentioned ranges of values.

[0103] Optional values ​​are: 0.2≤I≤3.2, 0.2≤I≤3, 0.2≤I≤2.8, 0.2≤I≤2.6, 0.2≤I≤2.4, 0.2≤I≤2.2, and 0.2≤I≤2.

[0104] Optional values ​​are: 0.1≤J≤3.4, 0.1≤J≤3.2, 0.1≤J≤3, 0.1≤J≤2.8, 0.1≤J≤2.6, 0.1≤J≤2.4, 0.1≤J≤2.2, 0.1≤J≤2, and 0.1≤J≤1.8.

[0105] Optional values ​​are: 0.1≤K≤3.4, 0.1≤K≤3.3, 0.1≤K≤3.2, 0.1≤K≤3.1, 0.1≤K≤3, 0.1≤K≤2.9, 0.1≤K≤2.8, 0.1≤K≤2.7, 0.1≤K≤2.6, and 0.1≤K≤2.5.

[0106] In this embodiment, the electrolyte of the electrochemical device contains 1,3-propanesulfonic acid lactone and satisfies 0.2≤I≤3.5. 1,3-propanesulfonic acid lactone can form a stable SEI film on the surface of the positive electrode material, thereby improving the low-temperature fast charging performance and overcurrent safety of the electrochemical device.

[0107] The electrolyte of the electrochemical device contains ethylene ethylene carbonate and satisfies 0.1≤J≤3.5. Ethylene ethylene carbonate can form a uniform and dense SEI film on the surface of the negative electrode material, improving the low-temperature fast charging performance and overcurrent safety of the electrochemical device.

[0108] The electrolyte of the electrochemical device contains vinyl sulfate and satisfies 0.1≤K≤3.5. Vinyl sulfate can form a denser SEI film on the surface of the negative electrode material and capture gas molecules generated by side reactions at the interface between the negative electrode and the electrolyte, thereby improving the low-temperature fast charging performance and overcurrent safety of the electrochemical device.

[0109] The electrolyte of the electrochemical device contains 1,2,3-tris(2-cyanoxy)propane and satisfies 0.1≤L≤2.8. 1,2,3-tris(2-cyanoxy)propane can improve the viscosity of the electrolyte and is conducive to the formation of a stable interfacial CEI film, thereby improving low-temperature fast charging, overcurrent safety and reducing the increase in impedance value obtained by high-temperature EIS test.

[0110] The electrochemical device satisfies 8 ≤ A / I ≤ 334. Polydopamine and 1,3-propanesulfonate synergistically enhance the bonding force between the various components inside the battery, making the battery structure more robust and able to withstand volume changes and mechanical stress during charging and discharging, reducing interface separation and structural damage. Furthermore, it optimizes the lithium-ion transport path between the separator and the electrolyte, making lithium-ion transport more efficient, reducing ion migration resistance during battery charging and discharging, and improving the battery's charging and discharging efficiency and power performance.

[0111] In some embodiments, the electrode bonding strength between the separator and the negative electrode plate of the electrochemical device is T gf / 15mm, where 1.8 ≤ T ≤ 3.6. For example, T can be 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, 3.6, or any range of the above values.

[0112] According to this embodiment, the electrochemical device satisfies 1.8≤T≤3.6, which makes it less likely for the separator and the negative electrode to separate during side extrusion testing, thus giving the electrochemical device a certain structural strength and high-temperature cycling stability. Furthermore, during heating testing, the corner areas of the electrochemical device tend to separate, thereby improving the structural stability of the device.

[0113] It should be noted that the electrode adhesion strength between the separator and the negative electrode sheet can be tested using methods and equipment known in the art. For example, one end of the sample can be fixed to the upper clamp of a testing machine, and the separator at the other end can be separated from the negative electrode sheet and fixed to the lower clamp. The tensile speed of the testing machine can be set, and the machine can be started to perform a peel test. The testing machine automatically records the force-displacement curve during the peel process, and the average force value of the stable segment of the curve can be taken as the peel force. The adhesion strength can be calculated according to the formula. Another example is to laminate the separator onto a 200 μm thick carbon sheet with the adhesive layer of the separator facing the carbon sheet. The adhesion strength is measured by compressing the separator at 80°C, using a hot press at 20 MPa for 30 seconds, and then peeling the separator at 180°C according to ASTM D903 using a UTM device to obtain the adhesion strength.

[0114] In some embodiments, the electrode bonding strength between the separator and the negative electrode is T gf / 15 mm, and the electrochemical device satisfies: 15 ≤ X / T ≤ 43. For example, X / T can be 15, 18, 20, 22, 25, 28, 30, 32, 35, 38, 40, 43, or any range of the above values.

[0115] In this embodiment, the electrochemical device satisfies 15 ≤ X / T ≤ 43. The separator has both sufficient flexibility to adapt to changes in electrode volume and good adhesion to the negative electrode, preventing separation and maintaining the stability of the battery's internal structure. Simultaneously, the stable adhesion between the separator and the negative electrode helps maintain the stability of the ion transport channels. During charging and discharging, lithium ions can pass more smoothly through the interface between the separator and the negative electrode, reducing ion transport obstacles, lowering the battery's internal resistance, and thus improving the battery's charging and discharging efficiency and power performance.

[0116] In some embodiments, the electrochemical device further includes a positive electrode, a negative electrode, and a separator, wherein the positive electrode and the negative electrode are separated by the separator disposed therebetween. In some embodiments, the positive electrode includes a positive current collector and a positive active material layer disposed on the positive current collector, the positive active material layer including a positive active material; the negative electrode includes a negative current collector and a negative active material layer disposed on the negative current collector, the negative active material layer including a negative active material.

[0117] 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 copper foil, nickel foil, or carbon-based current collector. In some embodiments, the thickness of the negative electrode current collector may be 1 μm to 200 μm. In some embodiments, the negative electrode active material layer may be coated only on a portion of the negative electrode current collector. In some embodiments, the thickness of the negative electrode active material layer may be 10 μm to 500 μm. It should be understood that these are merely exemplary, and other suitable thicknesses may be used.

[0118] In some embodiments, as described above, the negative electrode active material layer comprises a negative electrode active material. In some embodiments, the negative electrode active material comprises at least one of natural graphite, artificial graphite, or a silicon-based material. In some embodiments, the silicon-based material comprises at least one of silicon, silicon oxides, silicon carbide compounds, or silicon alloys.

[0119] 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, 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 use any other suitable material. In some embodiments, the mass ratio of the negative electrode active material, negative electrode conductive agent, and 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 not intended to limit the scope of this application.

[0120] In some embodiments, the positive electrode includes a positive current collector and a positive active material layer disposed on the positive current collector. The positive active material layer may be located on one or both sides of the positive current collector. In some embodiments, the positive current collector may be aluminum foil, but other positive current collectors commonly used in the art may also be used. In some embodiments, the thickness of the positive current collector may be 1 μm to 200 μm. In some embodiments, the positive active material layer may be coated only on a portion of the positive current collector. In some embodiments, the thickness of the positive active material layer may be 10 μm to 500 μm. It should be understood that these are merely exemplary, and other suitable thicknesses may be used.

[0121] 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 cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, or lithium nickel manganese oxide, and the above-mentioned positive electrode active material may be doped and / or coated.

[0122] In some embodiments, the surface of the positive electrode material includes lithium phosphate and / or lithium niobate, with a mass ratio of 1:5 to 1:1, and the thickness of the capping layer is 1 μm to 2 μm.

[0123] In some embodiments, the positive electrode active material layer further includes a positive electrode binder and a positive electrode conductive agent. In some embodiments, the positive electrode binder may include at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, styrene-acrylate copolymer, styrene-butadiene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinyl acetate, polyvinylpyrrolidone, polyvinyl ether, polytetrafluoroethylene, or polyhexafluoropropylene. In some embodiments, the positive electrode conductive agent may include at least one of conductive carbon black, acetylene black, Ketjen black, graphene, carbon nanotubes, or carbon fibers.

[0124] In this application, the electrochemical device includes an electrolyte, which comprises a lithium salt and a non-aqueous solvent. This application does not impose any particular limitation on the lithium salt, as long as it achieves the purpose of this application. For example, the lithium salt may include, but is not limited to, at least one of LiPF6, LiBF4, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalato)borate (LiBOB), or lithium difluoroborate. This application does not impose any particular limitation on the content of the lithium salt in the electrolyte, as long as it achieves the purpose of this application. For example, based on the mass of the electrolyte, the mass percentage of the lithium salt is 5% to 23%, for example, the concentration of the lithium salt in the electrolyte may be 5%, 8%, 12%, 16%, 20%, 23%, or a range consisting of any two of the above values. This application does not impose any particular limitation on non-aqueous solvents, as long as they can achieve the purpose of this application. For example, non-aqueous solvents may include, but are not limited to, at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, or other organic solvents. The aforementioned carbonate compounds may include, but are not limited to, at least one of chain carbonate compounds, cyclic carbonate compounds, or fluorinated carbonate compounds. The aforementioned chain carbonate compounds may include, but are not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or methyl ethyl carbonate (MEC). The aforementioned cyclic carbonates may include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), or vinyl ethylene carbonate (VEC). Fluorocarbonate compounds may include, but are not limited to, at least one of 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, or trifluoromethylethylene carbonate. The aforementioned carboxylic acid ester compounds may include, but are not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valproic acid lactone, or caprolactone. The aforementioned ether compounds may include, but are not limited to, at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. The aforementioned other organic solvents may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate.This application does not impose any particular restrictions on the content of non-aqueous solvents in the electrolyte, as long as the purpose of this application can be achieved.

[0125] In some embodiments, the separator comprises at least one selected from 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. Polyethylene and polypropylene, in particular, are effective in preventing short circuits and can improve battery safety through a turn-off effect. In some embodiments, the thickness of the separator is in the range of about 3 μm to 480 μm.

[0126] In some embodiments, the separator has a porous layer, the binder of which is selected from at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyvinyl ether, polytetrafluoroethylene, or polyhexafluoropropylene. The porous layer on the surface of the separator can improve its heat resistance, oxidation resistance, and electrolyte wetting properties, and enhance the adhesion between the separator and the electrode. The separator may also include a high-melting-point crystalline polymer or a high-temperature resistant amorphous polymer. The high-temperature resistant resin includes at least one of polypropylene, poly4-methylpentene, polytetrafluoroethylene, polyvinylidene fluoride, and cyclic olefin copolymers. The high-melting-point crystalline polymer includes at least one of polypropylene, poly4-methylpentene, polytetrafluoroethylene, or polyvinylidene fluoride, and the high-temperature resistant amorphous polymer includes cyclic olefin copolymers. Based on the mass of the polyolefin porous substrate, the mass percentage Z of the high-temperature resistant resin is 2% to 10%. For example, the mass percentage Z of the high-temperature resistant resin is 2%, 3%, 5%, 7%, 8%, 10%, or a range consisting of any two of these values. When the aforementioned high-temperature resistant resins are added to a polyolefin porous substrate and the mass percentage of the high-temperature resistant resin is controlled within the above range, it is beneficial to increase the melt-burst temperature of the diaphragm, thereby improving its strength and the high-temperature performance of the electrochemical device.

[0127] In some embodiments, the electrochemical device is a lithium-ion battery, but this application is not limited thereto.

[0128] In some embodiments of this application, taking a lithium-ion battery as an example, the positive electrode sheet, the separator, and the negative electrode sheet are wound or stacked in sequence to form an electrode assembly, which is then encapsulated in a housing such as an aluminum-plastic film, injected with electrolyte, formed, and encapsulated to produce a lithium-ion battery.

[0129] Embodiments of this application also provide electronic devices including the aforementioned electrochemical apparatus. The electronic devices in these embodiments are not particularly limited and can be any electronic device known in the prior art. In some embodiments, the electronic device may include, but is not limited to, laptops, pen-based computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.

[0130] The following are some specific embodiments and comparative examples to better illustrate this application, wherein a lithium-ion battery is used as an example.

[0131] Example 1-1

[0132] Positive electrode: Lithium cobalt oxide, acetylene black, and polyvinylidene fluoride are mixed in a weight ratio of 88:6:6 and added to N-methylpyrrolidone. The mixture is stirred into a homogeneous slurry. The slurry is then stirred, coated, dried, rolled, and spot-welded with tabs to obtain the positive electrode of the battery.

[0133] Negative electrode: Weigh 100g of negative electrode active material (artificial graphite with a particle size of 10μm), 1g of conductive agent (carbon black), and 4g of binder (styrene-butadiene rubber, SBR), add them to 3g of N-methylpyrrolidone and 100g of water to form a negative electrode slurry. The negative electrode slurry is stirred, coated, dried, rolled, and spot-welded with tabs to obtain the battery negative electrode.

[0134] Electrolyte: In an argon-filled glove box, ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate are mixed in a mass ratio of 3:4:3. Lithium difluorooxalate borate (4.5% of the total electrolyte mass) and propyl propionate (20% of the total electrolyte mass) are added. A certain amount of lithium hexafluorophosphate is also added to make the final lithium salt concentration in the electrolyte 8.5%.

[0135] Separating membrane:

[0136] A 7 μm thick polyethylene (PE, 30% porosity) microporous membrane was used. Cellulose nanocrystals (diameter: 10 nm, length: 200 nm, Young's modulus: 70 GPa, MAINE) were added to water and dispersed to prepare a dispersion. The porous polymer substrate was impregnated with the dispersion and then air-dried at 60°C using a hot air gun. The loading of cellulose nanocrystals on the porous polymer substrate was 9 g / m². A 9 μm thick membrane substrate was then fabricated.

[0137] Boehmite with a D90 of 7 μm and polyacrylate binder were dispersed in deionized water at a mass ratio of 88:12 to form an inorganic coating slurry with a solid content of 38%. The slurry was coated onto the two surfaces of the negative electrode ring by gravure roller coating at a speed of 0.6 m / min and dried by blowing hot air at 120°C at a wind speed of 0.5 m / sec, thereby forming a second coating with a thickness of 2 μm that adheres to the surface of the PE substrate.

[0138] Organic coating preparation (coated onto the second coating facing the negative electrode side):

[0139] Polymer particles of the first polymer (propylene-based monomer) with a melt index of 10 g / 10 min and polymer particles of the second polymer (vinylidene fluoride-based monomer) with a melt index of 2 g / 10 min were added to a stirrer at a 1:1 molar ratio and stirred until homogeneous. Sodium carboxymethyl cellulose was added to the stirrer and stirred until homogeneous. Dimethylsiloxane, a wetting agent, was added to the stirrer, followed by deionized water and stirring. The viscosity of the slurry was adjusted to 38 mPa·s and the solid content to 5%, resulting in an organic coating slurry. The organic coating slurry was uniformly applied to the second coating (the side of the separator facing the anode / negative electrode) and dried in an oven to obtain the first coating. The coating weight of the first coating slurry was 1.5 mg / 5000 mm². The thickness of the first coating was 3 μm. The mass ratio of the first polymer, the second polymer, sodium carboxymethyl cellulose, and dimethylsiloxane was 75:20:0.7:4.3.

[0140] Preparation of polydopamine coating (first coating) (coated on the second coating facing the positive electrode side)

[0141] At room temperature (25°C), dopamine was added at a concentration of 2 mg / mL and dextrin at a concentration of 50 mg / mL to an alkaline buffer solution (20 mM Tris-HCl buffer). After adjusting the final dopamine to dextrin ratio to 1:2, the petri dish was opened to prepare a dopamine and dextrin solution with a dissolved oxygen content of 8 ppm and a pH of 8. The pre-separated membrane was immersed in the solution for 48 hours and then dried at 60°C for 15 hours to prepare a membrane with a total thickness of 15 μm (13 μm for the remaining portion of the separator and 2 μm for the polydopamine coating), containing a polydopamine to dextrin weight ratio of 1:2.

[0142] Preparation of lithium-ion batteries: The positive electrode sheet lithium iron phosphate, the separator, and the negative electrode sheet silicon-carbon negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. The electrode assembly is then wound up, and after welding the tabs, the electrode assembly is placed in an outer packaging aluminum-plastic film. After removing moisture at 80°C, the electrolyte is injected. After vacuum sealing, settling, formation, shaping, and capacity testing, the lithium-ion battery is obtained.

[0143] The testing method is as follows:

[0144] (1) Low temperature fast charging test method: At -10℃, the lithium-ion batteries prepared in the examples and comparative examples were subjected to constant current charging test at a rate of 2C. The rate charging capacity retention rate was calculated. The battery rate charging capacity retention rate at 2C = the capacity released after charging at a rate of 2C / the capacity released after charging at a rate of 0.5C.

[0145] (2) High temperature interval cycle test: The battery is placed in an environment of (50±3)℃ and left to stand for 3 hours. When the cell body reaches (50±3)℃, the battery is charged at a constant current of 1C to 4.25V, and then charged at a constant voltage of 4.25V to the cutoff current of 0.05C. The battery is left to stand at (50±3)℃ for a certain period of time, ensuring that the constant current and constant voltage charging time plus the standing time is 24 hours. Then the battery is discharged at 0.5C, and the initial energy E0 is recorded. This cycle is repeated. When the required number of cycles is reached, the energy of this discharge is taken as the energy of the battery E1, and the energy retention rate (%) is calculated. The energy retention rate (%) = E1 / E0 × 100%.

[0146] (3) Overcharge test pass rate: Under the condition of (45±5)℃, the discharged battery cell is charged with a constant current of 3.5C to 5.0V, and then switched to constant voltage charging. The charging time is limited to 6 hours or the charging is stopped when the battery surface temperature stabilizes (temperature difference ≤2℃ within 30min). Judgment criteria: The battery cell does not catch fire. Each example uses 5 parallel samples as a group for testing.

[0147] (4) Overcurrent safety test: At room temperature of 25°C, the secondary battery is charged with a constant current of 1C, and the battery state of charge (SOC) is charged from 10% to 30%. Then, the secondary battery is charged with a constant current of 1.5C, and the battery state of charge (SOC) is charged from 30% to 60%. Then, the secondary battery is charged with a constant current of 2C, and the battery state of charge (SOC) is charged from 60% to 90%. Then, the temperature of the secondary battery is monitored with a temperature measuring instrument.

[0148] The lower the measured temperature of the secondary battery, the better its performance. The secondary batteries are graded (A to D) based on their temperature test results, with the following grading criteria:

[0149] A: Temperature is less than 50℃;

[0150] B: The temperature is above 50℃ and below 55℃;

[0151] C: Temperature is above 55℃ and below 60℃;

[0152] D: Temperature greater than 60℃.

[0153] A rating of A indicates that the overcurrent safety test has been passed. The pass rate was calculated for each example / comparative example with 20 parallel samples.

[0154] (5) Side extrusion test: At 25°C, charge at a constant current rate of 0.5C to 4.4V, then charge at a constant voltage rate to 0.05C. The UL1642 test standard is adopted, with a side extrusion force of 13kN. Side extrusion tests are performed on lithium-ion secondary batteries, with 20 batteries tested in each group. The pass rate of the side extrusion test for lithium-ion secondary batteries is calculated.

[0155] (6) Drop test pass rate: Under 25℃ environmental conditions, record the open circuit voltage and internal resistance of the battery (testing instrument is a voltage and resistance tester, manufacturer: Dongguan Lijia Precision Instrument Co., Ltd., model: LNG-SY1-0020-DQ); place the battery in the clamping chamber, and use an automatic drop device to drop the clamping chamber with the battery from a position of 1m onto the cement floor in a series of drops, with the clamping chamber head bottom, left side, right side, back, front, and top surfaces as one round, for a total of 3 rounds, or 18 times; then... The battery is dropped sequentially from a height of 1.5m onto a concrete base, with the bottom, left, right, back, front, and top sides of the clamping head forming one round of drops. A total of 3 rounds (18 drops) are performed. The battery voltage is measured after each round of drops. Dropping stops if the battery catches fire or leaks; otherwise, it continues. The battery voltage and internal resistance are recorded. If the voltage drop is less than 10mV within 24 hours, the battery packaging is not broken or punctured, and the battery does not catch fire, leak, or explode, the battery passes the drop test; otherwise, it fails. The drop test pass rate (%) = (Number of products that passed the drop test ÷ Total number of products participating in the drop test) × 100%.

[0156] (7) Electrolyte composition test: GC-MS was used to test the electrolyte composition, and the external standard method was also used.

[0157] (8) Young's modulus test: The coating on the diaphragm was washed off, and the substrate sample was cut into rectangles 120 mm long and 10 mm wide as experimental samples. The orientation was adjusted so that the length of the diaphragm in the MD direction was 120 mm. A tensile testing machine (such as a Strograph R-3 manufactured by Toyo Seiki Co., Ltd. or other tensile testing machines that can be used to test Young's modulus) was used to conduct a tensile test in the MD direction of the diaphragm. The initial chuck distance was 50 mm, and the tensile speed was 500 mm / min. The Young's modulus is calculated by the tensile load at 1% elongation and the cross-sectional area of ​​the sample, calculated as tensile load (1% elongation) / cross-sectional area × 100. The results of each example / comparative example were obtained by testing three parallel experimental samples and taking the average value.

[0158] (9) Substrate smoothness test: The surface gloss (GU value) was measured using a “micro-TRI-gloss-s” manufactured by BYK at a reflection angle of 60°.

[0159] Examples 1-2 to 1-33 and Comparative Examples 1-1 to 1-2

[0160] The preparation of lithium-ion batteries is largely the same as in Examples 1-1, with the only differences being the Young's modulus X of the base film, the polydopamine content A in the first coating, the mass ratio of polydopamine to dextrin A / B, the thickness C and A / C of the first coating, the surface gloss E of the base film, the size D and C / D of the D90 of the particles in the second coating, and the electrode bonding strength T and X / T between the separator and the negative electrode sheet. Specific parameters are shown in Table 1.

[0161] Table 1

[0162] According to Table 1, compared with the comparative examples, the low-temperature fast-charge cycle retention rate, high-temperature intermittent cycle retention rate, and drop test pass rate of the lithium-ion batteries in each embodiment are significantly improved. When the first coating of the separator includes polydopamine and the Young's modulus of the separator base film meets the range of this application, the lithium-ion battery exhibits good low-temperature performance, high-temperature performance, and structural stability.

[0163] According to Examples 1-2, 1-3 and 1-33, the Young's modulus of the base film is 55≤X≤70, which indicates better low-temperature and high-temperature performance of the lithium-ion battery.

[0164] According to Examples 1-2, 1-6 to 1-8, and 1-23 to 1-24, the thickness of the first coating of the separator satisfies 1≤C≤4, and the lithium-ion battery has better low-temperature performance, high-temperature performance, and structural stability.

[0165] According to Examples 1-2, 1-9 to 1-16, when the mass ratio of polydopamine to dextrin in the first coating of the separator is 0.02 to 2, the lithium-ion battery exhibits good low-temperature performance, high-temperature performance, and structural stability.

[0166] According to Examples 1-2, 1-21 to 1-22 and 1-31 to 1-32, the surface gloss of the base film of the separator is such that 1≤E≤5.5, and the lithium-ion battery has better low-temperature performance, high-temperature performance and structural stability.

[0167] According to Examples 1-2, 1-17 to 1-20 and 1-29 to 1-30, the D90 of the particles in the second coating of the separator satisfies 0.6μm≤D≤10μm, and the lithium-ion battery has better low-temperature performance, high-temperature performance and structural stability.

[0168] Based on this, according to Examples 1-17 to 1-19, the D90 of the particles in the second coating of the separator satisfies 0.6μm≤D≤5μm, and the lithium-ion battery has better low-temperature performance, high-temperature performance and structural stability.

[0169] Based on this, according to Examples 1-17 to 1-19, the D90 of the particles in the second coating of the separator satisfies 0.6μm≤D≤5μm, and the lithium-ion battery has better high-temperature performance and structural stability.

[0170] Examples 2-1 to 2-12

[0171] The preparation of lithium-ion batteries is largely the same as in Examples 1-1, except that the average molecular weight, melting point, or porosity of the first coating of polydopamine are different. Specific parameters are shown in Table 2.

[0172] Table 2

[0173] According to Table 2, when the average molecular weight of polydopamine is 120 kDa to 900 kDa, the melting point of polydopamine is 160°C to 220°C, or the porosity of the first coating is 30% to 65%, the lithium-ion battery of this application has good pass rates for side extrusion tests, overcurrent safety tests, overcharge tests, and low-temperature fast charging cycle retention.

[0174] According to Examples 1-1, 2-1 to 2-4, 2-9 and 2-10, when the average molecular weight of polydopamine is 120 kDa to 900 kDa and / or the melting point of polydopamine is 160°C to 220°C, lithium-ion batteries have better structural stability, charging stability and low-temperature performance.

[0175] According to Examples 1-1, 2-5 to 2-8, 2-11 and 2-12, when the porosity of the first coating is 30% to 65%, the lithium-ion battery has better structural stability, charging stability and low-temperature performance.

[0176] Examples 3-1 to 3-34

[0177] The preparation of lithium-ion batteries is largely the same as in Examples 1-1, except that the contents of propyl propionate, lithium difluorooxalate borate, lithium difluorosulfonyl imide, 1,3-propanesulfonic acid lactone, ethylene carbonate, ethylene sulfate, and 1,2,3-tris(2-cyanoxy)propane in the electrolyte are different. Specific parameters are shown in Table 3.

[0178] Table 3

[0179] According to Table 3, when the electrolyte includes propyl propionate, lithium difluorooxalate borate, lithium difluorosulfonyl imide, 1,3-propanesulfonic acid lactone, ethylene carbonate, ethylene sulfate, and 1,2,3-tris(2-cyanoxy)propane, the lithium-ion battery of this application has better pass rates in side extrusion tests, overcurrent safety tests, overcharge tests, and low-temperature fast charge cycle retention.

[0180] According to Examples 1-1, 3-1 to 3-3, 3-26 and 3-27, when the content of propyl propionate in the electrolyte satisfies 20≤G≤45, the lithium-ion battery has better structural stability, charging stability and low-temperature performance.

[0181] According to Examples 1-1, 3-1 to 3-3, 3-34 and 3-35, when lithium difluorosulfonyl imide and propyl propionate in the electrolyte satisfy 0.02≤H / G≤0.48, the lithium-ion battery has better structural stability, charging stability and low-temperature performance.

[0182] Based on this, according to Examples 1-1, 3-1, and 3-2, when lithium difluorosulfonyl imide and propyl propionate in the electrolyte satisfy 0.02≤H / G≤0.3, the lithium-ion battery has better structural stability, charging stability, and low-temperature performance.

[0183] According to Examples 3-1, 3-4 to 3-8, and 3-28, when the content of lithium difluorooxalate borate in the electrolyte satisfies 0.01≤F≤4.5, the lithium-ion battery has better structural stability, charging stability, and low-temperature performance.

[0184] According to Examples 3-1, 3-9 to 3-13, 3-29 and 3-30, when the content of 1,3-propanesulfonic acid lactone in the electrolyte satisfies 0.2≤I≤3.5, the lithium-ion battery has better structural stability, charging stability and low-temperature performance.

[0185] Based on this, according to Examples 3-1, 3-9 to 3-11, it can be seen that when the content of 1,3-propanesulfonic acid lactone in the electrolyte satisfies 0.2≤I≤2, the lithium-ion battery has better structural stability, charging stability and low-temperature performance.

[0186] According to Examples 3-1, 3-14 to 3-17 and 3-31, when the content of ethylene ethylene carbonate in the electrolyte satisfies 0.1≤J≤3.5, the lithium-ion battery has better structural stability, charging stability and low-temperature performance.

[0187] Based on this, according to Examples 3-1, 3-12 to 3-14, when the content of ethylene ethylene carbonate in the electrolyte satisfies 0.1≤J≤1.8, the lithium-ion battery has better structural stability, charging stability and low-temperature performance.

[0188] According to Examples 3-1, 3-18 to 3-21 and 3-32, when the content of ethylene sulfate in the electrolyte satisfies 0.1≤K≤3.5, the lithium-ion battery has better structural stability, charging stability and low-temperature performance.

[0189] Based on this, according to Examples 3-1, 3-18 to 3-20, when the content of ethylene sulfate in the electrolyte satisfies 0.1≤K≤2.5, the lithium-ion battery has better structural stability, charging stability and low-temperature performance.

[0190] According to Examples 3-1, 3-22 to 3-25 and 3-33, when the content of 1,2,3-tris(2-cyanoxy)propane in the electrolyte satisfies 0.1 ≤ L ≤ 2.8, the lithium-ion battery has better structural stability, charging stability and low-temperature performance.

[0191] Although this application has been described with reference to preferred embodiments, various modifications can be made thereto and components can be replaced with equivalents without departing from the scope of this application. In particular, the technical features mentioned in the various embodiments can be combined in any manner, provided there is no structural conflict. This 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 isolation film, wherein, The separator includes a base film and a first coating disposed on at least one side of the base film. The first coating includes polydopamine and an adhesive polymer. The Young's modulus of the base film is 52 MPa to 90 MPa.

2. The separator film according to claim 1, wherein The Young's modulus of the base membrane is 55 MPa to 70 MPa.

3. The separator film according to claim 1, wherein The polydopamine must satisfy at least one of the following: (1) The average molecular weight of the polydopamine is 120 kDa to 900 kDa; (2) The melting point of the polydopamine is 160℃~220℃.

4. The separator film according to claim 1, wherein The first coating also includes inorganic ceramic particles and / or the binder polymer includes dextrin.

5. The separator film according to claim 1, wherein The adhesive polymer includes dextrin, and based on the total mass of the first coating, the mass percentage of polydopamine in the first coating is Awt%, the mass percentage of dextrin in the first coating is Bwt%, and the separator membrane satisfies: 0.02≤A / B≤2.

6. The separator film according to claim 1, wherein The isolation membrane further includes a second coating layer, which is disposed on both sides of the base membrane. The first coating layer is disposed on at least one side outside the second coating layer. The particles in the second coating layer have a D90 of 0.6 μm to 10 μm.

7. The separator film according to claim 6, wherein The particle D90 in the second coating is 0.6 μm to 5 μm.

8. The separator film according to claim 1, wherein The separator further includes a second coating layer disposed on both sides of the base film, and a first coating layer disposed on at least one side outside the second coating layer. The thickness of the first coating layer is C μm, and the D90 of the particles in the second coating layer is D μm. The separator satisfies the following condition: 0.06 ≤ C / D ≤ 10.

9. The separator film according to claim 8, wherein The isolation membrane satisfies the following condition: 0.2≤C / D≤7.

10. The separator film according to any one of claims 1 to 9, wherein The first coating satisfies at least one of the following: (1) The thickness of the first coating is 1 μm to 4 μm; (2) The porosity of the first coating is 30% to 65%; (3) The surface gloss of the base film is 1 GU to 5.5 GU; (4) Based on the total mass of the first coating, the mass percentage of polydopamine in the first coating is Awt%, the thickness of the first coating is Cμm, and the isolation membrane satisfies: 0.25≤A / C≤67.

11. An electrochemical device, wherein, It includes a positive electrode, a negative electrode, an electrolyte, and a separator as described in any one of claims 1-10, wherein the separator is disposed between the positive electrode and the negative electrode, and the electrolyte includes a lithium salt and a non-aqueous solvent.

12. The electrochemical device of claim 11, wherein, The electrolyte satisfies at least one of the following: (1) The lithium salt includes at least one of lithium difluorooxalate borate, lithium bis(trifluoromethanesulfonyl)imide and lithium difluorophosphate, and the mass percentage of lithium difluorooxalate borate, lithium bis(trifluoromethanesulfonyl)imide or lithium difluorophosphate in the electrolyte is 0.01wt% to 4.5wt% based on the total mass of the electrolyte. (2) The lithium salt includes at least one of lithium difluorooxalate borate, lithium bis(trifluoromethanesulfonyl)imide, and lithium difluorophosphate. Based on the total mass of the electrolyte, the mass percentage of lithium difluorooxalate borate, lithium bis(trifluoromethanesulfonyl)imide, or lithium difluorophosphate in the electrolyte is Fwt%. Based on the total mass of the first coating, the mass percentage of polydopamine in the first coating is Awt%. The electrochemical device satisfies: 6≤A / F≤3330. (3) The non-aqueous solvent includes propyl propionate, and the mass percentage of propyl propionate in the electrolyte is 20wt% to 45wt% based on the total mass of the electrolyte.

13. The electrochemical device of claim 11, wherein, The non-aqueous solvent includes propyl propionate, and the lithium salt includes lithium bis(fluorosulfonyl)imide; based on the total mass of the electrolyte, the mass percentage of propyl propionate in the electrolyte is Gwt%, the mass percentage of lithium bis(fluorosulfonyl)imide is Hwt%, and the electrochemical device satisfies: 0.02≤H / G≤0.

48.

14. The electrochemical device of claim 13, wherein, The electrochemical device satisfies the following condition: 0.02 ≤ H / G ≤ 0.

3.

15. The electrochemical device of claim 11, wherein, The electrolyte also includes additives, which include at least one of 1,3-propanesulfonate lactone, ethylene carbonate, vinyl sulfate, and 1,2,3-tris(2-cyanoxy)propane.

16. The electrochemical device of claim 15, wherein, The electrochemical device shall satisfy at least one of the following: (1) The additive includes 1,3-propanesulfonic acid lactone, and the mass percentage of 1,3-propanesulfonic acid lactone in the electrolyte is 0.2wt% to 3.5wt% based on the total mass of the electrolyte; (2) The additive includes ethylene carbonate, and the mass percentage of ethylene carbonate in the electrolyte is 0.1 wt% to 3.5 wt% based on the total mass of the electrolyte; (3) The additive includes vinyl sulfate, and the mass percentage of vinyl sulfate in the electrolyte is 0.1wt% to 3.5wt% based on the total mass of the electrolyte; (4) The additive includes 1,2,3-tris(2-cyanoxy)propane, and the mass percentage of 1,2,3-tris(2-cyanoxy)propane in the electrolyte is 0.1 wt% to 2.8 wt% based on the total mass of the electrolyte; (5) The additive includes 1,3-propanesulfonic acid lactone, and the mass percentage of 1,3-propanesulfonic acid lactone is 1 wt% based on the total mass of the electrolyte. The mass percentage of polydopamine in the first coating is A wt% based on the total mass of the first coating. The electrochemical device satisfies: 8 ≤ A / I ≤ 334.

17. The electrochemical device of claim 16, wherein, The electrochemical device satisfies at least one of the following: (1) The additive includes 1,3-propanesulfonic acid lactone, and the mass percentage of 1,3-propanesulfonic acid lactone is 0.2wt% to 2wt% based on the total mass of the electrolyte; (2) The additive includes ethylene carbonate, and the mass percentage of ethylene carbonate is 0.1 wt% to 1.8 wt% based on the total mass of the electrolyte; (3) the additive comprises vinylsulfate, the mass percentage of the vinylsulfate is 0.1wt%-2.5wt% based on the total mass of the electrolyte.

18. The electrochemical device of claim 11, wherein, The electrode adhesion strength between the separator film and the negative electrode sheet is 1.8gf / 15mm-3.6gf / 15mm.

19. The electrochemical device of claim 11, wherein, The Young's modulus of the base film is X MPa, the electrode adhesion strength between the separator film and the negative electrode sheet is T gf / 15mm, and the electrochemical device satisfies: 15≤X / T≤43.

20. An electronic device, comprising: The electrochemical device comprises the separator film according to any one of claims 11-19.

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