Battery monomer and full-tab cylindrical lithium ion battery

Abstract

The invention discloses a battery monomer and a full-tab cylindrical lithium ion battery, and belongs to the technical field of batteries. In the battery monomer, an active material layer of a positive plate and / or a negative plate at least comprises a first sub-layer positioned on one side close to an isolating membrane and a second sub-layer positioned on one side close to a current collector along the thickness direction; the average porosity of the first sub-layer is 25%-45%, and the ion transmission tortuosity is 1.5-3.0; the average porosity of the second sub-layer is 15%-30%, and the ion transmission tortuosity is 2.5-6.0; the average porosity of the first sub-layer is higher than that of the second sub-layer, the ion transmission tortuosity of the first sub-layer is smaller than that of the second sub-layer, and the thickness of the first sub-layer accounts for 20%-60% of the total thickness of the active material layer. The battery monomer has the advantages of favorable high-temperature cycle life, favorable high-temperature storage stability and lower impedance.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically, to a single battery cell and a cylindrical lithium-ion battery with all tabs. Background Technology

[0002] Under high-temperature cycling and storage conditions, all-tab cylindrical lithium-ion batteries are prone to coupled failures caused by accelerated interfacial side reactions and increased internal resistance. On the one hand, high temperatures significantly increase the rate of positive electrode electrolyte oxidation and decomposition and lithium salt side reactions, leading to CEI thickening, compositional inhomogeneity, and pore blockage. On the other hand, during high-temperature storage, the electrolyte redistributes within the electrode pore structure, and localized electrolyte shortages and accumulated salt concentration differences increase ion transport resistance, thereby amplifying polarization and accelerating interfacial film formation. For all-tab cylindrical structures, the core end face and outer periphery are more susceptible to local pressure field changes due to thermal expansion, stress relaxation, and trace gas generation, further causing uneven wetting and impedance drift.

[0003] Traditional strategies for improving high-temperature performance often rely on enhancing the electrolyte's film-forming ability or adding a thermally stable coating to the diaphragm. However, these often lead to deterioration in kinetics and an increase in DCIR, making it difficult to simultaneously achieve high-temperature cycle life, high-temperature storage stability, and low-impedance kinetics.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a single battery cell and a cylindrical lithium-ion battery with all tabs to solve or improve at least one of the above-mentioned technical problems.

[0006] This invention can be implemented as follows: In a first aspect, the present invention provides a battery cell including a positive electrode, a negative electrode, a separator, and an electrolyte. The active material layer of the positive electrode and / or the negative electrode includes at least a first sublayer and a second sublayer along the thickness direction. The first sublayer is located on the side close to the separator, and the second sublayer is located on the side close to the current collector. The first sublayer has an average porosity of 25%–45% and an ion transport tortuosity of 1.5–3.0; the second sublayer has an average porosity of 15%–30% and an ion transport tortuosity of 2.5–6.0; the average porosity of the first sublayer is higher than that of the second sublayer, the ion transport tortuosity of the first sublayer is lower than that of the second sublayer, and the thickness of the first sublayer accounts for 20%–60% of the total thickness of the active material layer.

[0007] In an optional embodiment, the difference between the average porosity of the first sublayer and the average porosity of the second sublayer is ≥5 percentage points; and / or, the difference between the ion transport tortuosity of the first sublayer and the ion transport tortuosity of the second sublayer is ≥0.5.

[0008] In an optional embodiment, the average porosity of the first sublayer is 28% to 45%, and the ion transport tortuosity is 1.6 to 2.6; the average porosity of the second sublayer is 15% to 22%, and the ion transport tortuosity is 4.0 to 5.5; the thickness of the first sublayer accounts for 30% to 55% of the total thickness of the active material layer.

[0009] In an optional implementation, the volumetric pore size D of the first sublayer is... 50 The volumetric pore size D of the second sublayer is larger than that of the second sublayer. 50 .

[0010] In an optional implementation, the volumetric pore size D of the first sublayer is... 50 The volume distribution aperture D of the second sublayer 50 The difference is ≥0.05μm.

[0011] In an optional implementation, the volumetric pore size D of the first sublayer is... 50 The pore size is 0.25 μm to 0.80 μm, and / or the volumetric pore size D of the second sublayer is... 50 The range is 0.10μm to 0.45μm.

[0012] In an optional embodiment, the first sublayer and the second sublayer are formed by step coating and / or multiple roll forming. When formed by roll forming, the roll forming pressure of the second sub-layer is greater than that of the first sub-layer.

[0013] In an optional implementation, a pore-forming agent is added during the formation of the first sublayer to obtain a porous structure.

[0014] In an optional embodiment, the pore-forming agent includes at least one of ammonium bicarbonate, ammonium carbonate, and volatile organic particles.

[0015] In an optional embodiment, the first sublayer comprises a wetting-retaining component having at least one of the following characteristics: Feature 1: The wetting and retaining components include at least one of polymers containing carboxyl, hydroxyl, or ether oxygen polar groups, or their salts, and / or hydrophilic inorganic particles; Feature 2: The mass fraction of the wetting and retaining component in the first sublayer is 0.05%~1.50%; preferably, the mass fraction of the wetting and retaining component in the first sublayer is 0.10%~1.20%; Feature 3: Within a thickness range of 0-20 μm near the separator of the first sublayer, the content of the wetting and retaining component is W1; within a thickness range of 0-20 μm near the current collector of the first sublayer, the content of the wetting and retaining component is W2; W1 > W2; preferably, W1:W2 ≥ 1.3, more preferably, W1:W2 is 1.30-2.20; preferably, W1 is 0.15wt%-1.20wt%, and / or, W2 is 0.10wt%-0.90wt%.

[0016] In an optional embodiment, the electrolyte has at least one of the following characteristics: Feature 4: The dynamic viscosity of the electrolyte at 25°C is 1.5 mPa·s to 4.0 mPa·s; preferably, the dynamic viscosity of the electrolyte at 25°C is 1.6 mPa·s to 3.8 mPa·s. Feature 5: The apparent contact angle of the electrolyte with the first sublayer is not greater than 25°; preferably, the apparent contact angle of the electrolyte with the first sublayer is 15°~23°; Feature 6: The wetting time of the electrolyte in the first sublayer is 2s to 60s; preferably, the wetting time of the electrolyte in the first sublayer is 6s to 40s.

[0017] In an optional embodiment, the battery cell is a cylindrical battery cell with multiple tabs, and the positive electrode and the negative electrode are wound together to form a core. An insulating limiting structure is provided on at least one end face and / or the outer periphery of the core. The insulating limiting structure includes at least one of insulating tape, insulating edge tape, end face insulating ring and insulating sleeve.

[0018] In an optional embodiment, the insulating limiting structure has at least one of the following features: Feature 7: The thickness of the insulating limiting structure is 10μm~80μm; preferably, the thickness of the insulating limiting structure is 20μm~70μm; Feature 8: The coverage width of the insulation limiting structure in the axial direction of the winding core is 0.5mm to 5.0mm; preferably, the coverage width of the insulation limiting structure in the axial direction of the winding core is 1.0mm to 5.0mm. Feature 9: The insulation limiting structure has a coverage angle of at least 180° on the outer periphery of the core, preferably 360° full coverage.

[0019] In an optional embodiment, the separator includes a polyolefin-based membrane and an inorganic coating disposed on at least one side of the polyolefin-based membrane; the inorganic coating has at least one of the following characteristics: Feature 10: The inorganic components in the inorganic coating include at least one of Al2O3, AlOOH, and SiO2; Feature 11: The binder phase in the inorganic coating is a non-fluorinated polymer; Feature 12: The average thickness of the inorganic coating on one side is 0.8 μm to 2.8 μm; Feature 13: The inorganic coating does not contain fluorinated organic particles.

[0020] In an optional embodiment, the negative electrode has at least one of the following characteristics: Feature 14: The compaction density of the negative electrode is 1.2 g / cm³. 3 Up to 1.7 g / cm 3 ; Feature 15: The ratio of the capacity of the negative electrode to the capacity of the positive electrode is 1.02~1.20.

[0021] In a second aspect, the present invention provides a cylindrical lithium-ion battery with multiple tabs, including a cylindrical shell, an end cap assembly, and a core and electrolyte disposed within the shell. The core includes an electrode assembly formed by winding a positive electrode sheet, a negative electrode sheet, and a separator, and the battery is a single battery cell of any of the aforementioned embodiments.

[0022] In an optional embodiment, the all-tab cylindrical lithium-ion battery further includes at least one of the following features: Feature 16: The capacity retention rate of the all-tab cylindrical lithium-ion battery is no less than 95% after 7 days of storage at 60℃; Feature 17: The capacity retention rate of the all-tab cylindrical lithium-ion battery is no less than 90% after 200 cycles at 60℃; Feature 18: The DCIR growth rate of all-tab cylindrical lithium-ion batteries does not exceed 20%.

[0023] The beneficial effects of this invention include: In this invention, the active material layer is configured with a pore structure gradient in the thickness direction. The average porosity of the first sublayer is defined as 25%~45%, and the ion transport tortuosity is defined as 1.5~3.0. The average porosity of the second sublayer is defined as 15%~30%, and the ion transport tortuosity is defined as 2.5~6.0. The average porosity of the first sublayer is higher than that of the second sublayer, and the ion transport tortuosity of the first sublayer is lower than that of the second sublayer. The thickness of the first sublayer accounts for 20%~60% of the total thickness of the active material layer.

[0024] The pore structure gradient along the thickness of the active material layer affects the uniformity of ion flux distribution under high-temperature conditions, thus influencing the spatial concentration of interfacial side reactions and the impedance growth rate. If the first and second sublayers are homogeneous, the effective ion conductivity and polarization distribution on the separator side and the current collector side will be difficult to control. This makes it easier to form localized high overpotential regions during high-temperature cycling and storage, accelerating electrolyte oxidation and salt decomposition reactions. The CEI (concentration-exchange interphase) film on the negative electrode surface exhibits faster thickening and stronger inhomogeneity, leading to a decrease in cycle capacity retention and a significant increase in the DC internal resistance (DCIR) growth rate. Furthermore, if the average porosity of the first sublayer is less than 25% and the ion transport tortuosity is greater than 3.0, while the thickness of the first sublayer accounts for less than 20% of the total thickness of the active material layer, there will be insufficient low-resistivity ion channels on the membrane side. Concentration polarization will be prominent at high temperatures, leading to continuous CEI formation and increased pore blockage, resulting in accelerated impedance growth. If the average porosity of the first sublayer is higher than 45% and the ion transport tortuosity is lower than 1.5, while the thickness of the first sublayer accounts for more than 60% of the total thickness of the active material layer, the rate capability and low impedance may not necessarily be improved; instead, DCIR may increase and high-temperature lifetime may deteriorate. If the porosity of the second sublayer is lower than 15% and the ion transport tortuosity is higher than 6.0, strong concentration polarization accumulation is likely to occur, and side reactions will still be concentrated on the membrane side at high temperatures, making it difficult to fundamentally suppress impedance growth and capacity decay. If the porosity of the second sublayer is higher than 30% and the ion transport tortuosity is lower than 2.5, and the second sublayer is too porous, there is a risk of "improved transport but increased structural and interface costs." Attached Figure Description

[0025] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a schematic diagram of the negative electrode sheet in Example 1.

[0027] Icons: 10 - First sublayer; 20 - Second sublayer; 30 - Current collector; 40 - Positive electrode. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0029] The following is a detailed description of the battery cell and the all-tab cylindrical lithium-ion battery provided by the present invention.

[0030] The present invention provides a battery cell comprising a positive electrode, a negative electrode, a separator, and an electrolyte.

[0031] Positive electrode plate, negative electrode plate The active material layer of the positive electrode and / or negative electrode includes at least a first sublayer and a second sublayer along the thickness direction, wherein the first sublayer is located on the side closer to the separator and the second sublayer is located on the side closer to the current collector.

[0032] The pore structure gradient along the thickness direction of the active material layer affects the uniformity of ion flux distribution under high-temperature conditions, thereby influencing the spatial concentration of interfacial side reactions and the impedance growth rate. If the first and second sublayers are homogeneous, the effective ion conductivity and polarization distribution on the separator side and the current collector side will be difficult to control. This makes it easier to form localized high overpotential regions during high-temperature cycling and storage, accelerating electrolyte oxidation and salt decomposition reactions. The electrolytic interface film (CEI) on the negative electrode surface exhibits faster thickening and stronger inhomogeneity, leading to a decrease in cycle capacity retention and a significant increase in the DC internal resistance (DCIR) growth rate. Therefore, in this invention, the active material layer is configured with a pore structure gradient along its thickness direction.

[0033] In some optional embodiments, the average porosity of the first sublayer is 25% to 45% and the ion transport tortuosity is 1.5 to 3.0; the average porosity of the second sublayer is 15% to 30% and the ion transport tortuosity is 2.5 to 6.0; and the average porosity of the first sublayer is higher than that of the second sublayer, the ion transport tortuosity of the first sublayer is less than that of the second sublayer, and the thickness of the first sublayer accounts for 20% to 60% of the total thickness of the active material layer.

[0034] The average porosity of the first sublayer can be 25%, 28%, 30%, 32%, 35%, 38%, 40%, 42%, or 45%, or other values ​​within the range of 25% to 45%.

[0035] The ion transport tortuosity of the first sublayer can be 1.5, 1.8, 2.0, 2.2, 2.5, 2.8 or 3.0, or other values ​​in the range of 1.5 to 3.0.

[0036] The percentage of the thickness of the first sublayer to the total thickness of the active material layer can be 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, or 60%, or other values ​​within the range of 20% to 60%.

[0037] The average porosity of the second sublayer can be 15%, 18%, 20%, 22%, 25%, 28%, or 30%, or other values ​​within the range of 15% to 30%.

[0038] The ion transport tortuosity of the second sublayer can be 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5 or 6.0, or other values ​​in the range of 2.5 to 6.0.

[0039] If the average porosity of the first sublayer is less than 25% and the ion transport tortuosity is greater than 3.0, and the thickness of the first sublayer accounts for less than 20% of the total thickness of the active material layer, it will lead to insufficient low-resistivity ion channels on the membrane side, prominent concentration polarization at high temperatures, and increased continuous formation of the interfacial film and pore blockage, resulting in accelerated impedance growth. If the average porosity of the first sublayer is greater than 45% and the ion transport tortuosity is less than 1.5, and the thickness of the first sublayer accounts for more than 60% of the total thickness of the active material layer, it is likely to cause the following: First, an overly loose and thick first sublayer will significantly increase the electrolyte retention and the contact area between the electrolyte and the high-potential positive electrode surface. At the same time, the exposed interface between the carbon conductive agent and the binder will increase, making electrolyte oxidation, by-product deposition, and gas generation more likely to occur at high temperatures. This will make the CEI thicker on the membrane side and more prone to pore blockage and "secondary growth" phenomena, which will manifest as increased impedance drift in the long term. Second, a decrease in solid volume fraction weakens particle contact and electronic pathway continuity, and reduces structural strength and compressive stability. Under winding and cyclic stress, microcracks, contact degradation, or local collapse are more likely to occur, leading to an increase in charge transfer impedance and ohmic components. The overall result is that rate capability and low impedance may not be further improved; instead, DCIR may increase and high-temperature lifespan may deteriorate.

[0040] If the porosity of the second sublayer is less than 15% and the ion transport tortuosity is greater than 6.0, and the second sublayer is close to the current collector side, if its porosity is too low and its tortuosity is too high, the ion supply in the thickness direction will be significantly limited at the bottom layer, resulting in a decrease in the utilization rate of deep active materials and a further concentration of reaction current towards the membrane side. Even if the ion transport of the first sublayer on the membrane side is faster, there will still be a stronger concentration polarization accumulation overall, and the side reactions at high temperatures will still be concentrated on the membrane side, and the increase in impedance and capacity decay will not be fundamentally suppressed. If the porosity of the second sublayer is greater than 30% and the ion transport tortuosity is less than 2.5, if the second sublayer is too loose, it will bring the risk of "improved transport but increased structural and interface costs": First, the structural support and anchoring effect near the current collector side will decrease, and the interparticle contact and bonding network will be more prone to degradation under thermal expansion and contraction and cyclic stress, resulting in an increase in contact resistance with the current collector or local debonding, manifested as an increase in DCIR and a decrease in consistency. Secondly, the electrolyte can penetrate deeper into the current collector interface and deep pores, which may enhance the side reactions of the current collector at high temperatures, such as corrosion of the aluminum current collector interface on the positive electrode side, decomposition of binder and deposition of salt decomposition by-products.

[0041] In some preferred embodiments, the difference between the average porosity of the first sublayer and the average porosity of the second sublayer is ≥5 percentage points. The difference between the ion transport tortuosity of the first sublayer and the ion transport tortuosity of the second sublayer is ≥0.5. By setting the difference between the average porosity of the first and second sublayers to ≥5 percentage points, a designable electrolyte phase volume fraction gradient can be established in the thickness direction, resulting in a more continuous electrolyte wetting channel and higher effective ion conductivity near the separator side, reducing concentration polarization and electrolyte phase potential drop in the separator-side inlet region; simultaneously, maintaining a lower porosity on the current collector side improves the solid phase skeleton volume fraction and structural stability, thereby suppressing excessive concentration of reaction current on the separator side and reducing side reactions during high-temperature cycling and high-temperature storage. By setting the difference between the ion transport tortuosity of the first sublayer and the ion transport tortuosity of the second sublayer to ≥0.5%, an effective diffusion coefficient difference can be formed in the thickness direction, giving the diaphragm side lower ion transport tortuosity and higher diffusion capacity, reducing local overpotential. At the same time, the higher tortuosity on the current collector side can limit the excessive penetration of the electrolyte phase and local side reactions, promoting a more uniform distribution of the reaction current in the thickness direction. This reduces the non-uniform thickening of the interface film caused by electrolyte oxidation and lithium salt decomposition at high temperatures, slows down the rate of increase in DC internal resistance, and improves the capacity retention rate.

[0042] In some more preferred embodiments, the average porosity of the first sublayer is 28%~45% (e.g., 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44% or 45%, etc.), and the ion transport tortuosity is 1.6~2.6 (e.g., 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5 or 2.6, etc.); the average porosity of the second sublayer is 15%~22% (… For example, 15%, 16%, 17%, 18%, 19%, 20%, 21% or 22%, etc.); ion transport tortuosity of 4.0~5.5 (such as 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5.0, 5.1, 5.2, 5.3, 5.4 or 5.5, etc.); the thickness of the first sublayer accounts for 30%~55% of the total thickness of the active material layer (such as 30%, 32%, 35%, 38%, 40%, 42%, 45%, 48%, 50%, 52% or 55%, etc.). Under the preferred conditions described above, the first sublayer on the separator side provides higher porosity and lower tortuosity to form a low-resistivity ion inlet and a uniform wetting retention channel, significantly reducing concentration polarization in the thickness direction and suppressing local concentration of reactive current on the separator side. The second sublayer on the current collector side improves the continuity and structural stability of the solid-phase framework through lower porosity and higher tortuosity, reducing electrolyte retention in deep pores and the expansion of side reaction active sites. This results in slower interfacial film growth and a lower DC internal resistance growth rate during high-temperature cycling and storage, while also considering volumetric energy density and processing stability. The thickness of the first sublayer accounts for 30% to 55% of the total thickness of the active material layer, achieving a balance between "establishing a low-resistivity inlet channel" and "effective loading and structural support retention," avoiding impedance fluctuations and reliability risks caused by insufficient or excessively porous inlet channels.

[0043] In some alternative implementations, the volumetric pore size D of the first sublayer is... 50 The volumetric pore size D of the second sublayer is larger than that of the second sublayer. 50 In some preferred embodiments, the volumetric pore size D of the first sublayer is... 50 The volume distribution aperture D of the second sublayer 50 The difference is ≥0.05 μm. In some preferred embodiments, the volumetric pore size D of the first sublayer is... 50 The pore size D of the second sublayer is 0.25 μm to 0.80 μm. 50 The pore size is 0.10 μm to 0.45 μm, and the volumetric pore size D of the first sublayer is... 50 The volume distribution aperture D of the second sublayer 50 The difference is ≥0.05μm. This is achieved by adjusting the volumetric pore size D of the first sublayer.50 The volume distribution aperture D of the second sublayer 50 Set to the above range, and make the volume distribution aperture D of the first sublayer... 50 The volume distribution aperture D of the second sublayer 50 With a difference ≥0.05μm, a pore structure with lower inlet resistance and stronger wettability can be established on the separator side, reducing inlet polarization of ion supply in the thickness direction and promoting uniformity of reaction current. At the same time, the smaller pore size on the current collector side helps to improve the stability of the solid-phase skeleton and reduce the retention of deep electrolyte and the expansion of side reaction active regions, thereby slowing down the thickening of the interface film and pore blockage during high-temperature cycling and storage, reducing the impedance growth rate and improving capacity retention and consistency.

[0044] In some alternative embodiments, the first sublayer and the second sublayer can be formed by step coating and / or multiple roll forming. When formed by roll forming, the roll forming pressure corresponding to the second sublayer is greater than the roll forming pressure corresponding to the first sublayer, so that the density of the second sublayer is higher than that of the first sublayer, thereby ensuring that the average porosity of the second sublayer is lower than that of the first sublayer.

[0045] In some alternative embodiments, a pore-forming agent may be added during the formation of the first sublayer to form a porous structure. The pore-forming agent may, by way of example but not limitation, include at least one of ammonium bicarbonate, ammonium carbonate, and volatile organic particles.

[0046] Furthermore, the inventors proposed through research that the wetting and retaining components enriched on the surface of the first sublayer affect the wetting and retaining capacity of the electrolyte in the membrane side pore structure and the stability of the ion channels after high-temperature storage. If the first sublayer does not contain a wetting and retaining component, localized liquid shortages and salt concentration gradient accumulation are likely to occur during high-temperature storage, reducing the effective electrolyte integral number within the channels, leading to a decrease in equivalent ionic conductivity, and making the charge transfer process and solvation structure at the interface more unstable, thereby accelerating CEI thickening and resistance increase, manifested as a decrease in cycle capacity retention and a significant increase in DCIR. Based on this, the first sublayer of the present invention includes a wetting and retaining component.

[0047] In some alternative embodiments, the wetting-retaining component may include at least one of polymers containing carboxyl, hydroxyl, or ether oxygen polar groups, or their salts, and / or hydrophilic inorganic particles. For example, the wetting-retaining component may include at least one of PVP and K30.

[0048] In some optional embodiments, the mass fraction of the wetting and retaining component in the first sublayer can be 0.05% to 1.50%, such as 0.05%, 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.2%, or 1.5%, or other values ​​within the range of 0.05% to 1.50%. Preferably, the mass fraction of the wetting and retaining component in the first sublayer can be 0.10% to 1.20%, such as 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, or 1.2%, or other values ​​within the range of 0.10% to 1.20%.

[0049] In some optional embodiments, the content of the wetting and retaining component is W1 in the 0-20 μm thickness range of the first sublayer near the separator side; the content of the wetting and retaining component is W2 in the 0-20 μm thickness range of the first sublayer near the current collector side; W1 > W2. Preferably, W1:W2 ≥ 1.3. In some more preferred embodiments, the value of W1 is 0.15wt%~1.20wt%, the value of W2 is 0.10wt%~0.90wt%, and the W1:W2 ratio is 1.30~2.20.

[0050] If the mass fraction of the wetting and retaining component in the first sublayer is less than 0.05% and W1:W2 < 1.3, it will lead to insufficient wetting and retaining capacity. Under high-temperature conditions, the electrolyte distribution will be more prone to migration over time, resulting in an increased interfacial film formation rate and more obvious in-plane inhomogeneity, and accelerated impedance growth. If the mass fraction of the wetting and retaining component in the first sublayer is greater than 1.5% and W1:W2 > 1.3, even if W1:W2 is not less than 1.3, excessively high polar polymers / salts or lyophilic particles may still increase local solvation binding and viscoelastic resistance, and increase the effective diffusion resistance within the pores. At the same time, it may induce stronger swelling, ion complexation, or enhanced interaction with lithium salts / solvents at high temperatures, leading to increased interfacial polarization, decreased rate performance, or increased DCIR. By controlling W1, W2, and W1:W2 within the aforementioned optimal ranges, a stable hydrophilic retaining phase and continuous wetting channels can be established on the membrane side, reducing localized electrolyte depletion and concentration polarization caused by electrolyte redistribution under high-temperature storage. At the same time, it avoids the increased solvation binding and pore mass transfer resistance caused by excessive wetting retaining components, allowing ion flux to be more uniformly distributed in the thickness and in-plane directions, thereby reducing side reactions, slowing down the rate of interfacial film thickening and pore blockage, and improving the high-temperature cycling capacity retention and consistency.

[0051] In some alternative embodiments, the compaction density of the negative electrode can be 1.2 g / cm³. 3 Up to 1.7 g / cm 3 For example, 1.2g / cm 31.3 g / cm 3 1.4 g / cm 3 1.5 g / cm 3 1.6 g / cm 3 Or 1.7 g / cm 3 The value can also be 1.2 g / cm³. 3 Up to 1.7 g / cm 3 Other values ​​within the range. This is achieved by controlling the compaction density of the negative electrode at 1.2 g / cm³. 3 Up to 1.7 g / cm 3 A balance can be achieved between electrolyte wetting and ion transport channels, particle contact and electronic pathway continuity, and cyclic expansion buffer space: too low compaction will lead to an increase in specific surface area and side reaction interface, increased SEI formation and electrolyte consumption, and greater impedance drift; too high compaction will reduce porosity and increase tortuosity, resulting in insufficient wetting and enhanced concentration polarization, thereby increasing the risk of lithium plating under fast charging and low temperature conditions and increasing DCIR.

[0052] In some alternative implementations, the ratio of the capacity of the negative electrode to the capacity of the positive electrode can be 1.02 to 1.20, such as 1.02, 1.05, 1.1, 1.15, or 1.2, or other values ​​within the range of 1.02 to 1.20. By controlling the ratio of the capacity of the negative electrode to the capacity of the positive electrode within the range of 1.02 to 1.20, a balance can be achieved between suppressing lithium plating on the negative electrode and avoiding energy density loss caused by excessive negative electrode: when the ratio is too low, the negative electrode at the end of charging is more likely to approach the lithium plating potential, especially at high rates or low temperatures, increasing the risk of lithium plating and leading to a rapid increase in impedance; when the ratio is too high, although the risk of lithium plating can be reduced, it will reduce the utilization rate of the positive electrode and increase the volumetric energy density loss caused by ineffective excess negative electrode. At the same time, excessive capacity redundancy may cause more obvious self-discharge and accumulation of interface side reactions under high-temperature storage, thereby affecting impedance consistency.

[0053] Electrolyte The viscosity and wettability of the electrolyte determine its wetting rate, replenishment capacity, and ion migration resistance in the high-porosity, low-torsional structure of the first sublayer, which in turn affect the polarization level and interfacial film thickening rate under high-temperature cycling and high-temperature storage.

[0054] In some alternative embodiments, the dynamic viscosity of the electrolyte at 25°C can be from 1.5 mPa·s to 4.0 mPa·s, such as 1.5 mPa·s, 2.0 mPa·s, 2.5 mPa·s, 3.0 mPa·s, 3.5 mPa·s, or 4.0 mPa·s, or other values ​​within the range of 1.5 mPa·s to 4.0 mPa·s. Preferably, the dynamic viscosity of the electrolyte at 25°C is from 1.6 mPa·s to 3.8 mPa·s.

[0055] In some alternative embodiments, the apparent contact angle of the electrolyte with the first sublayer is no greater than 25°. Preferably, the apparent contact angle of the electrolyte with the first sublayer can be 15° to 23°, such as 15°, 16°, 17°, 18°, 19°, 20°, 21°, 22° or 23°, or other values ​​within the range of 15° to 23°.

[0056] In some optional embodiments, the wetting time of the electrolyte on the first sublayer can be 2s to 60s, such as 2s, 5s, 10s, 15s, 20s, 25s, 30s, 35s, 40s, 45s, 50s, 55s, or 60s, or other values ​​within the range of 2s to 60s. Preferably, the wetting time of the electrolyte on the first sublayer can be 6s to 40s.

[0057] If the dynamic viscosity of the electrolyte is higher than 4.0 mPa·s, the apparent contact angle is greater than 23°, and the wetting time is longer than 60s, the diaphragm side channels are prone to insufficient wetting and local drying and concentration polarization are more likely to occur during high-temperature processes. This leads to a significant increase in ion transport resistance, and the decomposition of electrolyte and CEI generation at the interface are amplified by polarization, which in turn leads to a significant decrease in cycle capacity retention and a significant increase in DCIR growth rate. If the dynamic viscosity of the electrolyte at 25°C is less than 1.5 mPa·s, the apparent contact angle is less than 15°, and the wetting time is less than 2 s, although the initial wetting is sufficient, the excessively rapid penetration and higher electrolyte accessibility will increase the amount of electrolyte retained in the electrode channels and make it easier for solvent evaporation and gas phase migration to occur at high temperatures. At the same time, the frequency of contact between the electrolyte and the exposed interface of the conductive agent / binder in the deep layer of the electrode increases, which increases the reaction area and effective reaction probability of electrolyte oxidation and lithium salt decomposition. In addition, low viscosity systems are often accompanied by lower coordination viscosity damping and weaker solvation binding, which makes it easier to induce solvation structure rearrangement and diversification of side reaction pathways at high temperatures. This results in a looser CEI component and more significant dissolution and redeposition, which manifests as increased impedance drift and increased risk of gas generation after high-temperature storage, thereby affecting the maintenance and consistency of cycle capacity.

[0058] In a preferred embodiment of the present invention, by controlling the dynamic viscosity of the electrolyte at 25°C to 1.6 mPa·s to 3.8 mPa·s, the apparent contact angle to 15° to 23°, and the wetting time to 6 s to 40 s, the wetting and transport effects can be significantly improved, reducing ionic resistance (Rion) and alleviating high-temperature polarization. Furthermore, if the dynamic viscosity of the electrolyte is too low, the solvation structure may be more prone to fluctuation at high temperatures, increasing the accessibility of side reactions.

[0059] In some alternative embodiments, the battery cell is a cylindrical battery cell with multiple tabs, and the positive and negative electrode sheets are wound together to form a core, with an insulating limiting structure provided on at least one end face and / or the outer periphery of the core.

[0060] It should be noted that in all-tab cylindrical batteries, the core undergoes thermal expansion, stress relaxation, and geometric changes due to possible trace gas generation during high-temperature cycling and storage. The end face edges and outer periphery are more prone to relative displacement, increased burr risk, or reduced insulation margin with the casing. Therefore, this invention specifically provides an insulating limiting structure on at least one end face and / or outer periphery of the core to solve or improve the above problems. Without an insulating limiting structure, the core end face and outer periphery lack effective insulation limiting and isolation, making it easier for abnormal self-discharge channels or micro-short circuit trigger points to form in local areas, leading to increased impedance drift and DCIR growth, while also resulting in poor high-temperature cycling consistency.

[0061] In some alternative embodiments, the insulating limiting structure may, by way of example but not limitation, include at least one of insulating tape, insulating edge banding, end face insulating ring, and insulating sleeve. The material used to prepare the insulating limiting structure may include at least one of polyimide film, polyethylene terephthalate film, and polypropylene film.

[0062] In some optional embodiments, the thickness (radial direction) of the insulating limiting structure can be 10 μm to 80 μm, such as 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, or 80 μm, or other values ​​within the range of 10 μm to 80 μm. Preferably, the thickness of the insulating limiting structure is 20 μm to 70 μm.

[0063] In some optional embodiments, the coverage width of the insulating limiting structure in the axial direction of the winding core can be 0.5mm to 5.0mm, such as 0.5mm, 1.0mm, 1.5mm, 2.0mm, 2.5mm, 3.0mm, 3.5mm, 4.0mm, 4.5mm, or 5.0mm, or other values ​​within the range of 0.5mm to 5.0mm. Preferably, the coverage width of the insulating limiting structure in the axial direction of the winding core is 1.0mm to 5.0mm.

[0064] In some alternative embodiments, the insulation limiting structure covers the outer periphery of the core at an angle of at least 180°. Preferably, the insulation limiting structure provides 360° full coverage of the outer periphery of the core.

[0065] If the thickness of the insulating limiting structure is less than 10μm and the axial coverage width is less than 0.5mm, it is more prone to local insulation failure under high temperature mechanical stress and core expansion and contraction. If the thickness of the insulating limiting structure is greater than 80μm and the coverage width is greater than 5.0mm, the insulating limiting structure will occupy the electrolyte penetration and buffer space on the end face and the outer periphery and change the local pressure field, resulting in poor ion supply and heat transfer conditions in the edge area.

[0066]

Isolation Film

[0067] In some alternative embodiments, the inorganic components in the inorganic coating may, by way of example but not by way of limitation, include at least one of Al2O3, AlOOH and SiO2.

[0068] In some alternative embodiments, the binder phase in the inorganic coating is a non-fluorinated polymer.

[0069] In some alternative embodiments, the average thickness of the inorganic coating on one side can be 0.8 μm to 2.8 μm, such as 0.8 μm, 1 μm, 1.2 μm, 1.5 μm, 1.8 μm, 2.0 μm, 2.5 μm or 2.8 μm, or other values ​​within the range of 0.8 μm to 2.8 μm.

[0070] In some alternative implementations, the inorganic coating does not contain fluorinated organic particles.

[0071] It should be noted that the thickness of the inorganic coating on the membrane and the binder phase system affect the thermal stability, wetting behavior, and equivalent tortuosity of the membrane pore structure, thereby affecting the stability of ion channels and impedance growth at high temperatures. If the average thickness of the inorganic coating on one side is less than 0.8 μm, the membrane's ability to support the pore structure and inhibit shrinkage in a high-temperature environment will decrease, the pore morphology will be more prone to evolution, resulting in increased local ion transport resistance and impedance growth. If the average thickness of the inorganic coating on one side is greater than 2.8 μm, although the thermal stability is stronger, the pores of the coating itself are longer and more likely to exhibit a densification trend, increasing the equivalent ion path length, causing Rion to rise and inducing higher polarization. In addition, if the inorganic coating includes a fluorinated binder phase and introduces fluorinated organic particles, it will change the pore structure and surface energy of the inorganic coating, making it more prone to coating densification or decreased pore connectivity at high temperatures. The synergistic wetting with the high porosity structure of the first sublayer is disrupted, interfacial polarization and side reactions are amplified, leading to a decrease in cycling capacity retention and a significant increase in DCIR.

[0072] As mentioned above, the battery cell that meets the above-mentioned structural features of this application can have good high-temperature cycle life, high-temperature storage stability and low impedance.

[0073] In addition, the present invention also provides a cylindrical lithium-ion battery with full tabs, which includes a cylindrical shell, an end cap assembly, and a core and electrolyte disposed in the shell. The core includes an electrode assembly formed by winding a positive electrode sheet, a negative electrode sheet and a separator, and the battery is the aforementioned battery cell.

[0074] In some optional implementations, the capacity retention rate of the all-tab cylindrical lithium-ion battery is not less than 95% after being stored at 60°C for 7 days, such as 95.5% to 97%.

[0075] In some alternative implementations, the capacity retention rate of the all-tab cylindrical lithium-ion battery is not less than 90% after 200 cycles at 60°C, such as 90% to 92%.

[0076] In some alternative implementations, the DCIR growth rate of the all-tab cylindrical lithium-ion battery does not exceed 20%, such as 15% to 20%.

[0077] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0078] In this paper, "average porosity" refers to the percentage of pore volume in the total volume of the electrode active material layer (or its first / second sublayer), obtained through micron-CT three-dimensional reconstruction analysis. Sample preparation: 10mm × 10mm samples were cut from the electrode sheet for micron-CT three-dimensional reconstruction analysis. Scanning conditions: Micron-CT spatial resolution 1.0μm / voxel; accelerating voltage and current were set according to equipment standards; consistency was maintained for samples from the same batch. Layer statistics: Slices were prepared along the thickness direction with a layer thickness of 20μm (or divided according to sublayer thickness boundaries), and the pore volume fraction of the first and second sublayers was calculated separately; the "average porosity" of each layer is the average of the pore phase volume fractions of all voxels in that layer.

[0079] In this paper, "ion transport tortuosity" refers to the degree of tortuosity of the equivalent transport path of ions in a porous network under electrolyte-filled channels, used to characterize the geometric constraint of pore structure on ion transport; τ is dimensionless and is calculated through micron-scale CT reconstruction. Using the same micron-scale CT three-dimensional segmentation results as the porosity, the effective diffusion coefficient Deff (machine fitting output) of the porous network in the thickness direction is calculated, and τ is obtained using the equivalent form of the relation Deff / D0=ε / τ, where ε is the porosity and D0 is the free diffusion coefficient (set to 1); Layered output: according to the same thickness as the porosity (e.g., one layer every 20 μm or according to the sublayer boundary), the average τ values ​​of the first sublayer and the second sublayer are given respectively.

[0080] In this article, "volume distribution aperture D" 50 "Through mercury porosimetry."

[0081] In this paper, the contents of wetting and maintaining components, as well as W1 and W2, were analyzed by TOF-SIMS depth profile and characterized by normalized characteristic ion intensities.

[0082] The test method for "electrode compaction density" in this article can be described as follows: Electrodes that have been washed with dimethyl carbonate and vacuum dried are cut into six standard-sized square samples (2.0cm × 2.0cm). Next, the active material on both sides of three of these square samples is removed, and they are rinsed with ethanol, dried, weighed, and their average mass M1 is calculated. Simultaneously, the average thickness L1 of the samples is measured using a micrometer. Then, the mass of the remaining three square samples is weighed, and their average mass M2 is calculated. The average thickness L2 of the samples is also measured. The thickness of the electrode is calculated as L2 - L1 (in cm). The compaction density of the electrode is then calculated. Unit: g / cm 3 .

[0083] In this article, "dynamic viscosity of electrolyte at 25℃" refers to the shear viscosity of electrolyte under constant temperature conditions of 25℃, with the unit being mPa·s. It is measured by a rotational rheometer (or rotational viscometer) at a constant shear rate of 25℃.

[0084] In this paper, the "apparent contact angle of the electrolyte to the first sublayer" is the static apparent contact angle measured at a specified time point after the electrolyte is dropped onto the surface of the first sublayer to form a droplet. It is measured by titration using a contact angle measuring instrument.

[0085] Example 1 This embodiment provides a fully tabbed cylindrical lithium-ion battery. A schematic diagram of the positive electrode structure in this fully tabbed cylindrical lithium-ion battery is shown below. Figure 1 As shown, the preparation method of this all-tab cylindrical lithium-ion battery includes: S1: Prepare the second sublayer 20.

[0086] To prepare 1000g of positive electrode second sublayer slurry with a solid content of 65wt%, 13.0g of PVDF was added to a portion of NMP (approximately 65wt% of the total NMP), and stirred at 40℃~60℃ until completely dissolved to obtain a PVDF / NMP solution. 9.75g of Super P and 1.95g of CNT were added to the above PVDF / NMP solution, and the conductive phase was homogenized using high-speed dispersion or three-roll milling. Subsequently, 625.3g of NCM811 was gradually added under medium-speed stirring until homogeneous. The remaining NMP was then added, and the mixture was degassed under vacuum for later use.

[0087] The second sublayer slurry of the positive electrode was coated onto the current collector 30 (aluminum foil) to form a wet film of the second sublayer. The wet film of the second sublayer was dried in stages (pre-drying at 60℃ for 10 min, drying at 90℃ for 20 min, and drying at 115℃ for 15 min), followed by rolling at a rolling temperature of 45℃ and a rolling speed of 0.3 m / min. The linear pressure of the first rolling was 80 kN / m, and the linear pressure of the second rolling was 120 kN / m, resulting in: an average porosity ε2 = 22%, an ion transport tortuosity τ2 = 4.0, and a volume distribution pore size D. 50 The second sublayer 20 is 0.25 μm thick.

[0088] S2: Prepare the first sublayer 10.

[0089] Preparation of 1000g of positive electrode first sublayer slurry with a solid content of 65wt%: 13.0g of PVDF was added to a portion of NMP (approximately 65wt% of the total NMP), and stirred at 40℃~60℃ until completely dissolved to obtain a PVDF / NMP solution. 9.75g of Super P and 1.95g of CNT were added to the above PVDF / NMP solution, and high-speed dispersion or three-roll milling was used to ensure uniform conductive phase. Wetting and maintaining component solution (making the amount of PVP solids 3.9g) and 1.3g of SiO2 were added, and mixed at low speed. Subsequently, 616.2g of NCM811 was gradually added under medium-speed stirring, followed by the remaining NMP, and stirred until homogeneous. Vacuum degassing was then performed for later use. Finally, 9.1g of NH4HCO3 was added, and low-shear short-time mixing was used to avoid excessive breakage of the pore-forming agent and premature decomposition and gas release. Vacuum degassing was then performed. The preparation of the wetting and maintaining component solution includes: adding 10.0g PVP to 90.0g NMP under stirring conditions at 25℃~35℃, stirring until completely dissolved, to obtain a wetting and maintaining component solution with a concentration of 10wt%.

[0090] The first sublayer slurry of the positive electrode was coated onto the surface of the compacted second sublayer 20 to form a wet film of the first sublayer. The wet film of the first sublayer was dried in stages (pre-drying at 60℃ and venting for 10 min, drying at 90℃ for 20 min, and fully drying at 115℃ for 20 min to promote the decomposition of NH4HCO3 to release gas and form pores). Then it was rolled at a rolling temperature of 45℃ and a rolling speed of 0.3 m / min. The linear pressure of the first rolling was 50 kN / m, and the linear pressure of the second rolling was 90 kN / m. The resulting material had an average porosity ε1=35%, ion transport tortuosity τ1=2.0, a total active material layer thickness f1=40%, a wetting retention component mass fraction W1=0.60 wt% in the first sublayer 10, a W1:W2 ratio of 1.5, and a volume distribution pore size D. 50 The first sublayer 10 is 0.35 μm thick, which is then used to obtain the positive electrode 40.

[0091] S3: Prepare the inorganic coating for the diaphragm.

[0092] 98g of Al2O3 and 2g of non-fluorinated binder phase (PAA / CMC system) were mixed with water to form an aqueous ceramic slurry with a solid content of 2wt%. The aqueous ceramic slurry was coated on one side of a polyolefin-based film, and the dry film thickness was controlled at 1.5μm. The film was then dried and cured at 100℃.

[0093] S4: Prepare the electrolyte.

[0094] Solvent system (volume ratio): EC:EMC:DEC:EA = 20:55:20:5.

[0095] Lithium salt: LiPF6 1.0 mol / L.

[0096] In a dry environment, solvents were mixed in a volume ratio, LiPF6 was added to dissolve the mixture, and the solution was filtered to obtain an electrolyte with a dynamic viscosity η of 2.5 mPa·s at 25 °C. The electrolyte was then immersed in the surface of the first sublayer for 10 s to achieve an apparent contact angle θ of 18° on the first sublayer surface.

[0097] S5: Prepare the negative electrode sheet.

[0098] The negative electrode sheet comprises a negative current collector copper foil and a negative electrode coating material coated on both sides of the copper foil. By mass percentage, the negative electrode coating material comprises 10.0% deposited silicon carbon, 86.0% graphite, 0.75% conductive agent, 0.75% conductive carbon black, 1.0% thickener sodium carboxymethyl cellulose (CMC), 0.75% binder polyacrylic acid (PAA), and 0.75% binder styrene-butadiene rubber (SBR). These substances are added to deionized water and stirred to form the negative electrode coating material, with a solid content of 42 wt%. The negative electrode coating material is then coated onto both sides of the negative current collector (copper foil), dried, and cold-pressed to form the negative electrode sheet with a compaction density of 1.5 g / cm³. 3 .

[0099] S5: Assemble lithium-ion batteries.

[0100] After the positive electrode sheet 40 and the negative electrode sheet are respectively rolled and slit, they are wound together with the separator according to the set process to form a 21700 cylindrical battery core. After the core is formed and before it is installed into the metal battery casing, an insulating limiting structure is set on the outer periphery of the core to form a stable insulating gap between the core and the inner surface of the metal casing and to limit the circumferential movement of the core.

[0101] The aforementioned insulating limiting structure is a ring-shaped insulating tape formed of polyimide film. This insulating limiting structure has a radial thickness of 30 μm; its axial coverage width is 2.0 mm, located along the outer periphery of the core; and its coverage angle along the core's outer periphery is 360°, forming a closed ring around the core's outer periphery to achieve full circumferential coverage. This insulating limiting structure is assembled as follows: a 30 μm thick, 2.0 mm wide polyimide film is attached around the core's outer periphery, overlapping at both ends to form a continuous closed ring; the overlap length is 1.0 mm, and it is fixed with an electrolyte-resistant adhesive to ensure no displacement or warping during formation and high-temperature cycling.

[0102] Subsequently, the battery core is fixed to the prefabricated connecting piece by welding and then installed into the metal battery casing. After completing key processes such as electrolyte injection, sealing, and formation, a lithium-ion battery is produced. This lithium-ion battery adopts a cylindrical casing with external dimensions of 21.0 mm in diameter and 70.0 mm in length, conforming to the 21700 standard specification.

[0103] Example 2 The difference between this embodiment and Embodiment 1 is that this embodiment only reduces the amount of pore-forming agent in the first sublayer and increases the rolling pressure of the first sublayer, so that the average porosity of the first sublayer is 28% and the ion transport tortuosity is 2.6; the average porosity of the second sublayer is 22% and the ion transport tortuosity is 4.0; the thickness of the first sublayer accounts for 30% of the total thickness of the active material layer. Everything else is the same as in Embodiment 1.

[0104] Example 3 The difference between this embodiment and Embodiment 1 is that this embodiment only increases the amount of pore-forming agent in the first sublayer and decreases the rolling pressure of the first sublayer, while increasing the rolling pressure of the second sublayer, so that the average porosity of the first sublayer is 45% and the ion transport tortuosity is 1.6; the average porosity of the second sublayer is 15% and the ion transport tortuosity is 5.5; and the thickness of the first sublayer accounts for 55% of the total thickness of the active material layer. Everything else is the same as in Embodiment 1.

[0105] Example 4 The difference between this embodiment and Embodiment 1 is that this embodiment only reduces the amount of pore-forming agent in the first sublayer and increases the rolling pressure of the first sublayer, while reducing the proportion of wet film thickness in the first sublayer partition coating; resulting in an average porosity of 25% and an ion transport tortuosity of 2.9 for the first sublayer; an average porosity of 22% and an ion transport tortuosity of 4.0 for the second sublayer; and the thickness of the first sublayer accounts for 20% of the total thickness of the active material layer. Everything else is the same as in Embodiment 1.

[0106] Example 5 The difference between this embodiment and Embodiment 1 is that this embodiment only increases the amount of pore-forming agent in the first sublayer and reduces the rolling pressure of the first sublayer, while increasing the proportion of wet film thickness in the first sublayer partition coating and increasing the rolling pressure of the second sublayer, adjusting the proportion of the first sublayer thickness to the total thickness of the active material layer to 60%; at the same time, the rolling pressure of the second sublayer is increased to form a denser structure; resulting in an average porosity of 45% and an ion transport tortuosity of 1.6 for the first sublayer; an average porosity of 15% and an ion transport tortuosity of 6.0 for the second sublayer; and the thickness of the first sublayer accounting for 60% of the total thickness of the active material layer. Everything else is the same as in Embodiment 1.

[0107] Comparative Example 1 The difference between this comparative example and Example 1 is that this comparative example omits the step-by-step coating and multiple rolling processes, resulting in a uniform single-layer structure of the active material layer with an average porosity of 25% and an ion transport tortuosity of 3.5. All other aspects are the same as in Example 1.

[0108] Comparative Example 2 The difference between this comparative example and Example 1 is that this comparative example further reduces the amount of pore-forming agent in the first sublayer and further increases the rolling pressure of the first sublayer, while further reducing the proportion of wet film thickness in the first sublayer partition coating, so that the average porosity of the first sublayer is 22% and the ion transport tortuosity is 3.2; the average porosity of the second sublayer is 22% and the ion transport tortuosity is 4.0; and the thickness of the first sublayer accounts for 15% of the total thickness of the active material layer. Everything else is the same as in Example 1.

[0109] Example 6 The difference between this embodiment and Embodiment 1 is that this embodiment only reduces the amount of wetting-retaining component added in the first sublayer and weakens the surface enrichment, so that the mass fraction of the wetting-retaining component in the first sublayer is 0.1% and the W1:W2 ratio is 1.2. Everything else is the same as in Embodiment 1.

[0110] Example 7 The difference between this embodiment and Embodiment 1 is that this embodiment only increases the amount of wetting-retaining component added in the first sublayer and enhances the enrichment in the surface layer, so that the mass fraction of the wetting-retaining component in the first sublayer is 1.20 wt% and the W1:W2 ratio is 1.8. Everything else is the same as in Embodiment 1.

[0111] Example 8 The difference between this embodiment and Embodiment 1 is that this embodiment only reduces the amount of wetting and retaining component added in the first sublayer, so that the mass fraction of the wetting and retaining component in the first sublayer is 0.05 wt%, and the W1:W2 ratio is 1.30. Everything else is the same as in Embodiment 1.

[0112] Example 9 The difference between this embodiment and Embodiment 1 is that this embodiment only increases the amount of wetting and retaining component added to the first sublayer, so that the mass fraction of the wetting and retaining component in the first sublayer is 1.50 wt%, and the W1:W2 ratio is 2.20. Everything else is the same as in Embodiment 1.

[0113] Comparative Example 3 The difference between this comparative example and Example 1 is that this comparative example only omits the wetting retention component and its enrichment process in the first sublayer, so that the mass fraction of the wetting retention component in the first sublayer is 0, and W1:W2 is 0. Everything else is the same as in Example 1.

[0114] Example 10 The difference between this embodiment and Embodiment 1 is that this embodiment only increases the proportion of low-viscosity co-solvent and decreases the proportion of high-viscosity solvent, so that the dynamic viscosity of the electrolyte at 25°C is 1.6 mPa·s, the apparent contact angle of the electrolyte with the first sublayer is 15°, and the wetting time of the electrolyte with the first sublayer is 6 s. Everything else is the same as in Embodiment 1.

[0115] Example 11 The difference between this embodiment and Embodiment 1 is that this embodiment only reduces the proportion of low-viscosity co-solvent and increases the proportion of high-viscosity solvent, so that the dynamic viscosity of the electrolyte at 25°C is 3.8 mPa·s, the apparent contact angle of the electrolyte with the first sublayer is 23°, and the wetting time of the electrolyte with the first sublayer is 40 s. Everything else is the same as in Embodiment 1.

[0116] Example 12 The difference between this embodiment and Embodiment 1 is that in this embodiment, only the solvent system ratio and lithium salt concentration are adjusted to achieve a dynamic viscosity of 1.5 mPa·s for the electrolyte at 25°C, an apparent contact angle of 15° for the electrolyte on the first sublayer, and a wetting time of 2 s for the electrolyte on the first sublayer. Everything else is the same as in Embodiment 1.

[0117] Example 13 The difference between this embodiment and Embodiment 1 is that in this embodiment, only the solvent system ratio and lithium salt concentration are adjusted to achieve a dynamic viscosity of 4.0 mPa·s for the electrolyte at 25°C, an apparent contact angle of 23° for the electrolyte on the first sublayer, and a wetting time of 60 s for the electrolyte on the first sublayer. Everything else is the same as in Embodiment 1.

[0118] Comparative Example 4 The difference between this comparative example and Example 1 is that this comparative example uses only a high-viscosity solvent system and does not perform wettability control, so that the dynamic viscosity of the electrolyte at 25°C is 6.0 mPa·s, the apparent contact angle of the electrolyte with the first sublayer is 35°, and the wetting time of the electrolyte with the first sublayer is 120 s. Everything else is the same as in Example 1.

[0119] Example 14 The difference between this embodiment and Embodiment 1 is that this embodiment only reduces the thickness and axial coverage width of the insulating limiting structure of the full-tab cylindrical core, so that the thickness of the insulating limiting structure is 20μm, the axial coverage width of the insulating limiting structure of the core is 1.0mm, and the coverage angle of the insulating limiting structure on the outer periphery of the core is 360°. Everything else is the same as in Embodiment 1.

[0120] Example 15 The difference between this embodiment and Embodiment 1 is that this embodiment only increases the thickness and axial coverage width of the insulating limiting structure of the full-tab cylindrical core, so that the thickness of the insulating limiting structure is 70μm, the axial coverage width of the insulating limiting structure of the core is 5.0mm, and the coverage angle of the insulating limiting structure on the outer periphery of the core is 360°. Everything else is the same as in Embodiment 1.

[0121] Example 16 The difference between this embodiment and Embodiment 1 is that this embodiment only adjusts the structural dimensions of the insulating component of the top cover assembly or the insulating limiting component inside the housing, so that the radial thickness of the insulating limiting structure is 10 μm. Everything else is the same as in Embodiment 1.

[0122] Example 17 The difference between this embodiment and Embodiment 1 is that this embodiment only adjusts the structural dimensions of the insulating component of the top cover assembly or the insulating limiting component inside the housing, so that the radial thickness of the insulating limiting structure is 80 μm. Everything else is the same as in Embodiment 1.

[0123] Comparative Example 5 The difference between this comparative example and Example 1 is that this comparative example only omits the insulation limiting structure of the full-tab cylindrical core. Everything else is the same as Example 1.

[0124] Comparative Example 6 The difference between this comparative example and Example 1 is that this comparative example only adjusts the structural dimensions of the insulating component of the top cover assembly or the insulating limiting component inside the housing, so that the radial thickness of the insulating limiting structure is 5 μm. Everything else is the same as in Example 1.

[0125] Example 18 The difference between this embodiment and Embodiment 1 is that this embodiment only reduces the amount of sizing agent applied to the inorganic coating of the diaphragm, so that the average thickness of the inorganic coating on one side of the diaphragm is 0.8 μm, and the binder phase is a non-fluorinated polymer and does not contain fluorinated organic particles. Everything else is the same as in Embodiment 1.

[0126] Example 19 The difference between this embodiment and Embodiment 1 is that this embodiment only increases the amount of slurry applied to the inorganic coating of the diaphragm and extends the drying and curing time, so that the average thickness of the inorganic coating on one side of the diaphragm is 2.8 μm, and the binder phase is a non-fluorinated polymer and does not contain fluorinated organic particles. Everything else is the same as in Embodiment 1.

[0127] Comparative Example 7 The difference between this comparative example and Example 1 is that the inorganic coating binder phase of the diaphragm in this comparative example is replaced with a fluoropolymer and fluorinated organic particles are introduced. The average thickness of the inorganic coating on one side of the diaphragm is 1.5 μm. Everything else is the same as in Example 1.

[0128] Performance testing Electrochemical performance testing methods: Place the battery in a 45℃ constant temperature chamber for 6 hours and test it according to the following steps: Step (1) First round of constant current and constant voltage charging: Charge at a constant current of 0.1C to 4.25V, then switch to constant voltage charging until the current drops to 0.01C; Step (2) After charging is complete, let it stand for 30 minutes; Step (3) Perform constant current discharge at a rate of 0.33C to 2.5V, and record the reference capacitance C. 0.33 ; Step (4) Let it stand for another 30 minutes.

[0129] P1 represents the capacity retention rate at 60℃: The battery that has completed step (2) above is placed at 60℃ for 7 days, then at 25℃ for 2 hours, and then discharged at 0.33C to 2.5V. The capacity C is then measured. 60 P1=C 60 / C 0.33 ×100%.

[0130] P2 represents the capacity retention rate under 60℃ high-temperature cycling: The battery cell obtained in step (2) is placed in a 60℃ oven and left to stand for 6 hours. Then, it is charged and discharged at 1C for 200 cycles (2.5V~4.2V). Every 50 cycles, the cell is returned to 25℃ for a 0.33C discharge capacity retest. P2 = Capacity retested on the 200th cycle / C 0.33 ×100%.

[0131] P3 represents the DCIR growth rate: The cell obtained in step (2) is discharged at 0.1C for 5 hours at 25°C, left to stand for 30 minutes and the voltage V1 is recorded. Then, it is pulsed discharged at 3C rate (for discharge current ΔI) for 10 seconds and the voltage V2 is recorded. DCIR (1) = V0 - V1 / ΔI; After completing the P1 test, the battery cell was charged to 4.2V at 0.1C at 25℃, then discharged at 0.1C for 5h, and after standing for 30min, the voltage V3 was recorded. Then, it was pulsed discharged at 3C rate (for discharge current ΔI) for 10s, and the voltage V4 was recorded at this time. DCIR (2) = V3-V4 / ΔI.

[0132] P3= DCIR(2) / DCIR(1)×100%.

[0133] The test results are shown in Table 1.

[0134] Table 1 Test Results

[0135] As can be seen from Table 1: A. Comparing Examples 1-5 and Comparative Example 1, it can be seen that, compared with Examples 1-5, Comparative Example 1 has a uniform layer structure. The effective ionic conductivity and polarization distribution on the membrane side and the current collector side are difficult to control. During high-temperature cycling and storage, it is easier to form local high overpotential regions, which accelerates the oxidation and salt decomposition reactions of the electrolyte. The CEI shows faster thickening and stronger non-uniformity, resulting in a decrease in P2 and a significant increase in the DCIR growth rate.

[0136] Compared to Example 1, in Example 2, the porosity of the first sublayer is reduced to 28% and the tortuosity is increased to 2.6. At the same time, the thickness of the first sublayer is reduced to 30%, which will result in insufficient low-resistivity ion channels on the membrane side, more prominent concentration polarization at high temperatures, and increased continuous formation of the interface film and pore blockage, leading to faster impedance growth.

[0137] Compared to Example 1, the gradient in Example 3 is too strong, the porosity of the second sublayer drops to 15% and the tortuosity increases to 5.5, resulting in a bottleneck in ion supply in the thickness direction. Although the transport on the membrane side is faster, the overall ion flux is limited at the bottom layer, and polarization will still accumulate during the cycle.

[0138] Compared to Examples 1-5, Comparative Example 2 performed worse; and compared to Examples 1-3, Examples 4 and 5 performed worse, indicating that under the same conditions, the scheme that satisfies the following ranges can achieve better results: "the average porosity of the first sublayer is 28%-45%, the ion transport tortuosity is 1.6-2.6; the average porosity of the second sublayer is 15%-22%, the ion transport tortuosity is 4.0-5.5; and the thickness of the first sublayer accounts for 30%-55% of the total thickness of the active material layer".

[0139] B. Comparing Examples 1, 6-10 and Comparative Example 3, it can be seen that, compared with Examples 1 and 6-10, after the wetting and retaining component was removed in Comparative Example 3, the first sublayer is prone to local liquid shortage and salt concentration accumulation during the high-temperature storage stage. The effective electrolytic liquid integral number in the channel decreases, resulting in a decrease in equivalent ionic conductivity, and making the charge transfer process and solvation structure at the interface more unstable, thereby accelerating the thickening and resistance of CEI, which is manifested as a decrease in P1 and P2 and a significant increase in DCIR.

[0140] Compared to Example 1, Example 6 reduces the mass fraction of the wetting and retaining component in the first sublayer to 0.10 wt% and the W1:W2 ratio to 1.2, resulting in insufficient wetting and retaining capacity and buffering capacity. Under high temperature conditions, the electrolyte distribution is more likely to migrate over time, leading to an increased interfacial film formation rate and more obvious in-plane non-uniformity, and faster impedance growth.

[0141] Compared to Example 1, Example 7 increases the mass fraction of the wetting and retaining component in the first sublayer to 1.20 wt% and the W1:W2 ratio to 1.8. Although it provides stronger suppression of liquid shortage and concentration gradient during high-temperature storage, the excessively high polar component may increase local solvation binding and viscoelasticity, resulting in certain mass transfer resistance and interfacial polarization. The improvement in kinetics has a marginal effect.

[0142] Compared to Examples 1 and 6-7, Examples 8 and 9 showed worse results, indicating that under the same conditions, the scheme that satisfies the range of "the mass fraction of the wetting and retaining component in the first sublayer is 0.10%~1.20%, W1 is 0.15wt%~1.20wt%, W2 is 0.10wt%~0.90wt%, and W1:W2 is 1.30~2.20" can achieve better results.

[0143] C. Comparing Examples 1, 10-13 and Comparative Example 4, it can be seen that, compared with Examples 1 and 10-13, the dynamic viscosity of the electrolyte in Comparative Example 4 at 25°C increased to 6.0 mPa·s, the apparent contact angle of the first sublayer increased to 35°, and the wetting time of the first sublayer was extended to 120 s. This resulted in insufficient wetting of the membrane side channels and made it easier for local drying and concentration polarization to occur during high-temperature processes. The ion transport resistance increased significantly, and the electrolyte decomposition and CEI generation at the interface were amplified by polarization, leading to a significant decrease in P1 and P2 and a significant increase in the DCIR growth rate.

[0144] Compared to Example 1, the electrolyte of Example 10 has a reduced dynamic viscosity of 1.6 mPa·s at 25°C, a reduced contact angle of 15°, and a shortened wetting time of 6 s, which significantly improves wetting and transport, reduces Rion, and alleviates high-temperature polarization.

[0145] Compared to Example 1, the electrolyte in Example 11 has a dynamic viscosity of 3.8 mPa·s at 25°C and a wetting time of 40 s, which still results in a decrease in replenishment efficiency, more significant concentration accumulation during circulation, and a higher impedance increase than in Example 1.

[0146] Compared to Examples 1 and 10-11, Examples 12 and 13 showed worse results, indicating that under the same conditions, the solution that satisfies the following ranges can achieve better results: "the dynamic viscosity of the electrolyte at 25°C is 1.6 mPa·s to 3.8 mPa·s, the apparent contact angle of the electrolyte to the first sublayer is 15° to 23°, and the wetting time of the electrolyte to the first sublayer is 6 s to 40 s". D. Comparing Examples 1, 14-17 and Comparative Examples 5-6, it can be seen that, compared to Examples 1 and 14-17, after the insulation limiting structure was removed in Comparative Example 5, the core end face and the outer periphery lacked effective insulation limiting and isolation. This made it easier for abnormal self-discharge channels or micro-short circuit trigger points to form in local areas, resulting in increased impedance drift and DCIR growth, and worsened high-temperature cycling consistency.

[0147] Compared to Example 1, Example 14 reduces the thickness of the insulating limiting structure to 20 μm and the axial coverage width to 1.0 mm. Although it still has an insulating effect, the coverage margin for the end face edge is insufficient. Under high temperature mechanical stress and core expansion and contraction, it is more prone to local insulation failure, resulting in performance that is slightly inferior to Example 1.

[0148] Compared to Example 1, Example 15 increases the thickness of the insulating limiting structure to 70 μm and the coverage width to 5.0 mm, which improves the insulation margin but may occupy the electrolyte penetration and buffer space on the end face and the periphery and change the local pressure field, resulting in poorer ion supply and heat transfer conditions in the edge area.

[0149] Compared to Examples 1 and 14-17, Comparative Example 6 is worse; and compared to Examples 14-15, Examples 16 and 17 are worse, indicating that under the same conditions, the solution that meets the requirement of "the thickness of the insulating limiting structure is 20μm to 70μm" can achieve better results.

[0150] E. As can be seen from the comparison of Examples 1, 18-19 and Comparative Example 7, compared with Examples 1 and 18-19, Comparative Example 7 uses a fluorinated binder phase and introduces fluorinated organic particles, which significantly changes the pore structure and surface energy of the inorganic coating. Moreover, at high temperatures, the coating is more likely to become dense or the pore connectivity decreases. The synergistic wetting with the high porosity structure of the first sublayer is disrupted, and the interfacial polarization and side reactions are amplified, resulting in a decrease in P1 and P2 and a significant increase in DCIR.

[0151] Compared to Example 1, Example 18 thins the inorganic coating to 0.8 μm. The membrane's ability to support the pore structure and inhibit shrinkage decreases in a high-temperature environment, and the pore morphology is more prone to evolution, resulting in an increase in local ion transport resistance. The impedance growth is slightly higher than that of Example 1.

[0152] Compared to Example 1, Example 19 thickened the inorganic coating to 2.8 μm. Although it had stronger thermal stability, the coating itself had longer pores and was more likely to become denser. The equivalent ion path length increased, which increased Rion and caused higher polarization, resulting in a higher DCIR growth than in Example 1.

[0153] In summary, this invention constructs a thickness-direction pore structure gradient by using a high-porosity, low-torsion sublayer on the diaphragm side and a high-pressure solid sublayer on the current collector side, thereby reducing concentration polarization and local side reaction hotspots at high temperatures. Combined with the enrichment of wetting-retaining components on the surface layer and a low-viscosity, high-wetting electrolyte window, it suppresses electrolyte shortages and salt concentration differences during high-temperature storage. Furthermore, the non-fluorinated ceramic diaphragm boundary and the outer peripheral insulation limiting structure of the core end face reduce abnormal resistance increases and safety hazards at high temperatures, thus achieving low DCIR growth and excellent capacity retention.

[0154] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A battery cell, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, characterized in that, The active material layer of the positive electrode and / or the negative electrode includes at least a first sublayer and a second sublayer along the thickness direction, with the first sublayer located on the side closer to the separator and the second sublayer located on the side closer to the current collector. The first sublayer has an average porosity of 25% to 45% and an ion transport tortuosity of 1.5 to 3.0; the second sublayer has an average porosity of 15% to 30% and an ion transport tortuosity of 2.5 to 6.0; the average porosity of the first sublayer is higher than that of the second sublayer, the ion transport tortuosity of the first sublayer is lower than that of the second sublayer, and the thickness of the first sublayer accounts for 20% to 60% of the total thickness of the active material layer.

2. The battery cell according to claim 1, characterized in that, The difference between the average porosity of the first sublayer and the average porosity of the second sublayer is ≥5 percentage points; and / or, the difference between the ion transport tortuosity of the first sublayer and the ion transport tortuosity of the second sublayer is ≥0.

5. Preferably, the average porosity of the first sublayer is 28%~45% and the ion transport tortuosity is 1.6~2.6; the average porosity of the second sublayer is 15%~22% and the ion transport tortuosity is 4.0~5.5; and the thickness of the first sublayer accounts for 30%~55% of the total thickness of the active material layer.

3. The battery cell according to claim 1, characterized in that, The volume distribution aperture D of the first sublayer 50 The volume distribution pore size D of the second sublayer is larger than that of the second sublayer. 50 ; Preferably, the volumetric pore size D of the first sublayer is... 50 The volume distribution aperture D of the second sublayer 50 The difference is ≥0.05μm; Preferably, the volumetric pore size D of the first sublayer is... 50 The pore size is 0.25 μm to 0.80 μm, and / or the volumetric pore size D of the second sublayer is... 50 The range is 0.10μm to 0.45μm.

4. The battery cell according to claim 1, characterized in that, The first sublayer and the second sublayer are formed by step coating and / or multiple roll forming; When formed by roll forming, the roll forming pressure of the second sub-layer is greater than the roll forming pressure of the first sub-layer. Preferably, a pore-forming agent is added during the formation of the first sub-layer to obtain a porous structure; Preferably, the pore-forming agent includes at least one of ammonium bicarbonate, ammonium carbonate, and volatile organic particles.

5. The battery cell according to claim 1, characterized in that, The first sublayer comprises a wetting-retaining component, the wetting-retaining component having at least one of the following characteristics: Feature 1: The wetting and retaining component includes at least one of polymers containing carboxyl, hydroxyl, or ether oxygen polar groups, or their salts and / or hydrophilic inorganic particles; Feature 2: The mass fraction of the wetting and retaining component in the first sublayer is 0.05%~1.50%; preferably, the mass fraction of the wetting and retaining component in the first sublayer is 0.10%~1.20%; Feature 3: The content of the wetting and retaining component in the first sublayer within a thickness range of 0~20μm near the separator is W1; the content of the wetting and retaining component in the first sublayer within a thickness range of 0~20μm near the current collector is W2; W1>W2; preferably, W1:W2≥1.3, more preferably, W1:W2 is 1.30~2.20; preferably, W1 is 0.15wt%~1.20wt%, and / or, W2 is 0.10wt%~0.90wt%.

6. The battery cell according to claim 1, characterized in that, The electrolyte has at least one of the following characteristics: Feature 4: The dynamic viscosity of the electrolyte at 25°C is 1.5 mPa·s to 4.0 mPa·s; preferably, the dynamic viscosity of the electrolyte at 25°C is 1.6 mPa·s to 3.8 mPa·s. Feature 5: The apparent contact angle of the electrolyte with the first sublayer is not greater than 25°; preferably, the apparent contact angle of the electrolyte with the first sublayer is 15°~23°; Feature 6: The wetting time of the electrolyte on the first sublayer is 2s to 60s; preferably, the wetting time of the electrolyte on the first sublayer is 6s to 40s.

7. The battery cell according to any one of claims 1 to 6, characterized in that, The battery cell is a cylindrical battery cell with multiple tabs. The positive electrode and the negative electrode are wound together to form a core. An insulating limiting structure is provided on at least one end face and / or the outer periphery of the core. The insulating limiting structure includes at least one of insulating tape, insulating edge tape, end face insulating ring and insulating sleeve. Preferably, the insulating limiting structure has at least one of the following features: Feature 7: The thickness of the insulating limiting structure is 10μm~80μm; preferably, the thickness of the insulating limiting structure is 20μm~70μm; Feature 8: The coverage width of the insulating limiting structure in the axial direction of the winding core is 0.5mm to 5.0mm; preferably, the coverage width of the insulating limiting structure in the axial direction of the winding core is 1.0mm to 5.0mm. Feature 9: The insulation limiting structure has a coverage angle of at least 180° on the outer periphery of the core, preferably 360° full coverage.

8. The battery cell according to any one of claims 1 to 6, characterized in that, The separator membrane comprises a polyolefin-based membrane and an inorganic coating disposed on at least one side of the polyolefin-based membrane; the inorganic coating has at least one of the following characteristics: Feature 10: The inorganic components in the inorganic coating include at least one of Al2O3, AlOOH, and SiO2; Feature 11: The binder phase in the inorganic coating is a non-fluorinated polymer; Feature 12: The average thickness of the inorganic coating on one side is 0.8 μm to 2.8 μm; Feature 13: The inorganic coating does not contain fluorine-containing organic particles.

9. The battery cell according to any one of claims 1 to 6, characterized in that, The negative electrode has at least one of the following characteristics: Feature 14: The compaction density of the negative electrode sheet is 1.2 g / cm³. 3 Up to 1.7 g / cm 3 ; Feature 15: The ratio of the capacity of the negative electrode to the capacity of the positive electrode is 1.02 to 1.

20.

10. A cylindrical lithium-ion battery with multiple tabs, characterized in that, The battery includes a cylindrical shell, an end cap assembly, and a core and electrolyte disposed within the shell. The core includes an electrode assembly formed by winding a positive electrode sheet, a negative electrode sheet, and a separator. The battery is a single battery cell as described in any one of claims 1 to 9. Preferably, the all-tab cylindrical lithium-ion battery further includes at least one of the following features: Feature 16: The full-tab cylindrical lithium-ion battery retains no less than 95% of its capacity after being stored at 60°C for 7 days; Feature 17: The full-tab cylindrical lithium-ion battery retains no less than 90% of its capacity after 200 cycles at 60°C; Feature 18: The DCIR growth rate of the all-tab cylindrical lithium-ion battery does not exceed 20%.

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