A lithium-ion battery

Abstract

The application provides a lithium ion battery, comprising a nonaqueous electrolyte and a winding type pole core, the surface tension of the nonaqueous electrolyte is gamma, gamma < 25 mN / m; and / or the viscosity of the nonaqueous electrolyte is eta, eta < 1.8 mPa.s; the winding type pole core comprises a diaphragm, the diaphragm comprises a base film and a functional layer, the functional layer is arranged on at least one side surface of the base film; the functional layer comprises a plurality of hydrophilic coating layers and a plurality of hydrophobic coating layers, the plurality of hydrophobic coating layers are arranged at intervals, one hydrophilic coating layer is arranged between every two adjacent hydrophobic coating layers, or one hydrophobic coating layer is arranged between every two adjacent hydrophilic coating layers; and the connection between the hydrophilic coating layer and the hydrophobic coating layer, the edge of the hydrophilic coating layer and the edge of the hydrophobic coating layer at least partially coincide; the winding type pole core comprises a flat area and a circular arc area, the hydrophilic coating layer is located in the circular arc area, and the hydrophobic coating layer is located in the flat area. The lithium ion battery provided by the application solves the problem of circular arc lithium analysis and improves the cycle life of the battery.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, specifically relating to a lithium-ion battery. Background Technology

[0002] Lithium-ion batteries, as highly efficient energy storage carriers, have been widely used in consumer electronics, electric vehicles, and energy storage systems. Existing lithium-ion batteries include electrode cores, manufactured using either stacked or wound processes. Among these, the wound electrode core structure has become one of the mainstream product forms due to its advantages such as high energy density and mature manufacturing technology. However, this wound electrode core structure generally suffers from a key technical problem under long-term cycling, especially under high-rate charge-discharge conditions: lithium deposition easily occurs at the curved negative electrode. Lithium deposition not only leads to irreversible loss of active lithium, causing accelerated capacity decay, but more seriously, the deposited lithium dendrites may puncture the separator, causing internal short circuits and posing a serious safety hazard.

[0003] To address the issue of lithium plating at the curved negative electrode, the industry has proposed various technical solutions, including improvements to the separator. The most common approach is to coat the separator with ceramic or polymer coatings, aiming to enhance its mechanical strength, thermal stability, or electrolyte affinity. Improvements to the separator often focus on developing new coating materials (such as using highly absorbent materials) or achieving uniform, integral coating.

[0004] These solutions have the following problems: First, while they improve the overall performance of the separator to some extent, they fail to fundamentally solve the core contradiction of varying electrolyte requirements in different areas within the battery cell. Second, they represent a passive, localized electrolyte storage strategy, the effectiveness of which depends on the liquid absorption capacity and swelling volume of the coating material itself, and they do not address the fundamental need for dynamic electrolyte migration from enriched to depleted areas within the battery cell. The problem of uneven electrolyte distribution within the battery cell persists.

[0005] Therefore, the problem of lithium plating at the arc of wound cells remains a key bottleneck restricting their fast charging performance and long cycle life. Summary of the Invention

[0006] To address the problem of lithium deposition in the arc-shaped negative electrode area of ​​existing wound electrode cores, this application provides a lithium-ion battery.

[0007] To solve the above-mentioned technical problems, in a first aspect, this application provides a lithium-ion battery, including a non-aqueous electrolyte and a wound electrode core, wherein the surface tension of the non-aqueous electrolyte is γ, γ < 25 mN / m; and / or, the viscosity of the non-aqueous electrolyte is η, η < 1.8 mPa·s; The wound electrode core includes a diaphragm, the diaphragm includes a base film and a functional layer, the functional layer being disposed on at least one surface of the base film; The functional layer includes multiple hydrophilic coatings and multiple hydrophobic coatings. The multiple hydrophobic coatings are spaced apart, with one hydrophilic coating between each pair of adjacent hydrophobic coatings, or one hydrophobic coating between each pair of adjacent hydrophilic coatings; and at the junction of the hydrophilic coating and the hydrophobic coating, the edge of the hydrophilic coating at least partially overlaps with the edge of the hydrophobic coating. The wound electrode core includes a flat region and an arc region, with the hydrophilic coating located in the arc region and the hydrophobic coating located in the flat region.

[0008] Preferably, the contact angle between the hydrophilic coating and the non-aqueous electrolyte is θ1, where θ1 < 15°; And / or, the contact angle between the hydrophobic coating and the non-aqueous electrolyte is θ2, where θ2 > 35°.

[0009] Preferably, the contact angle between the hydrophobic coating and the non-aqueous electrolyte is θ2, and the contact angle between the hydrophilic coating and the non-aqueous electrolyte is θ1, where θ2-θ1≥15°.

[0010] Preferably, the porosity of the hydrophilic coating is P1, 65% ≤ P1 ≤ 80%; And / or, the porosity of the hydrophobic coating is P2, where P2 ≤ 50%.

[0011] Preferably, the porosity of the hydrophilic coating is P1, the porosity of the hydrophobic coating is P2, and P1 / P2 ≥ 1.5.

[0012] Preferably, the tortuosity of the hydrophilic coating on one side of the base film is τ1, where τ1 < 2.0; And / or, the tortuosity of the base film and the hydrophobic coating disposed on one side of the base film is τ2, where τ2 > 3.0.

[0013] Preferably, the hydrophilic coating comprises hydrophilic particles, which include hydrophilic particles of a first size and hydrophilic particles of a second size. A plurality of micropores and a plurality of mesopores are disposed between the first size hydrophilic particles and the second size hydrophilic particles. The average pore size of the micropores is 2 nm to 50 nm, and the average pore size of the mesopores is 50 nm to 200 nm.

[0014] Preferably, the mass ratio of the first-size hydrophilic particles to the second-size hydrophilic particles is (60-70):(30-40).

[0015] Preferably, the D50 particle size range of the first-size hydrophilic particles is 100nm-300nm, and the D50 particle size range of the second-size hydrophilic particles is 10nm-30nm.

[0016] Preferably, the hydrophilic particles include hydrophilic ceramic particles; The hydrophobic coating comprises a hydrophobic polymer, which includes a fluoropolymer, and the fluoropolymer includes at least one of polyvinylidene fluoride copolymer, polytetrafluoroethylene (PTFE), and perfluorosulfonic acid resin.

[0017] Preferably, the thickness of the hydrophilic coating is 3μm to 6μm, and the thickness of the hydrophobic coating is 1μm to 3μm.

[0018] Preferably, the method for preparing the diaphragm includes the following steps: Hydrophilic particles, a first binder, and a first solvent are mixed evenly to obtain a first slurry containing hydrophilic particles; the mass ratio of the hydrophilic particles to the first binder is (90~98):(10~2); the solid content of the first slurry is 30%~50%. A second slurry containing a hydrophobic polymer is obtained, wherein the solid content of the second slurry is 15% to 40%. The second slurry is applied intermittently to at least one side of the base film, dried to obtain a hydrophobic coating, and the first slurry is applied between each two adjacent hydrophobic coatings, dried to obtain a hydrophilic coating; or the first slurry is applied intermittently to at least one side of the base film, dried to obtain a hydrophilic coating, and the second slurry is applied between each two adjacent hydrophilic coatings, dried to obtain a hydrophobic coating. Furthermore, at the junction of the hydrophilic coating and the hydrophobic coating, the edge of the hydrophilic coating and the edge of the hydrophobic coating at least partially overlap, and the membrane is obtained by drying.

[0019] Preferably, the non-aqueous electrolyte includes additives; the additives include fluorocarbonate additives, linear siloxane additives, and perfluoropolyether additives, wherein the mass content of the fluorocarbonate additives in the non-aqueous electrolyte is 3% to 10%; The linear siloxane additive in the non-aqueous electrolyte has a mass content of 1% to 3%; The mass content of the perfluoropolyether additive in the non-aqueous electrolyte is 0.2% to 2%.

[0020] Preferably, the non-aqueous electrolyte further includes a lithium salt, which includes lithium hexafluorophosphate and lithium difluorosulfonylimide; In the non-aqueous electrolyte, the molar concentration of lithium hexafluorophosphate is n1, and the molar concentration of lithium difluorosulfonylimide is n2, with n1:n2 being (10~12):(1~3).

[0021] Preferably, n1 is 1.0 mol / L to 1.2 mol / L; n2 is 0.1 mol / L to 0.3 mol / L.

[0022] The lithium-ion battery provided in this application has the following effects: 1) Multiple hydrophobic coatings are spaced apart, and a hydrophilic coating is provided between each two adjacent hydrophobic coatings, or a hydrophobic coating is provided between each two adjacent hydrophilic coatings; and at the connection between the hydrophilic coating and the hydrophobic coating, the edge of the hydrophilic coating and the edge of the hydrophobic coating at least partially overlap. The above structure can form a wetting gradient between the hydrophilic coating and the hydrophobic coating, generate a sufficient interfacial energy difference, and drive the electrolyte to flow directionally from the region of the hydrophobic coating to the region of the hydrophilic coating, thereby achieving dynamic balance of the electrolyte. 2) A hydrophobic coating is set in the flat area of ​​the electrode core, and a hydrophilic coating is set in the arc area of ​​the electrode core. The hydrophilic coating, driven by capillary force and regulated by interfacial energy, enables the electrolyte to preferentially migrate and reside in the arc area of ​​the wound electrode core (corresponding to the hydrophobic coating area) to the arc area of ​​the wound electrode core (corresponding to the hydrophilic coating area). Through the synergistic effect of multi-level capillary effect, intelligent directional distribution of electrolyte is achieved, thereby solving the problem of electrolyte shortage at the arc of the battery during long cycle, fundamentally solving the problem of lithium plating at the arc of the wound cell, and improving the fast charging performance and cycle life of the battery. 3) This application limits the surface tension γ of the non-aqueous electrolyte to <25mN / m; and / or reduces the viscosity η of the electrolyte to <1.8 mPa▪s, thereby reducing the resistance of the electrolyte itself, which is equivalent to directly reducing the resistance of the entire system, increasing the migration rate of lithium ions, and amplifying the driving force difference caused by the difference in contact angle between the hydrophilic coating and the hydrophobic coating. This allows the electrolyte to generate stronger and faster capillary wetting when it encounters the hydrophilic coating, and the non-aqueous electrolyte is more violently "absorbed" into the hydrophilic coating region, thereby achieving efficient directional migration of the electrolyte and effectively solving the problem of lithium deposition in the arc region of the battery. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the cross-sectional structure of a diaphragm provided in this application; Figure 2 This is a schematic diagram of the negative electrode sheet after disassembly of the battery in Example 1 after 500 cycles at room temperature. Figure 3 This is a schematic diagram of the negative electrode sheet after disassembly of the battery in Example 26 after 500 cycles at room temperature. Figure 4 This is a schematic diagram of the negative electrode plate after disassembly of the battery in Comparative Example 3 after 500 cycles at room temperature. Figure 5 This is a top view schematic diagram of a diaphragm provided in this application; Figure 6 This is a schematic diagram of a wound pole core provided in this application; Figure 7 yes Figure 6 A schematic diagram of the diaphragm cross-section structure in one of the circular arc areas plus a part of the straight area.

[0024] The reference numerals in the attached figures are explained as follows: 1. Separator; 101. Base membrane; 102. Hydrophilic coating; 103. Hydrophobic coating; 2. Positive electrode; 3. Negative electrode. Detailed Implementation

[0025] To make the technical problems solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0026] like Figure 1-7 As shown, in a first aspect, this application provides a lithium-ion battery, including a non-aqueous electrolyte and a wound electrode core, wherein the surface tension of the non-aqueous electrolyte is γ, γ < 25 mN / m; and / or, the viscosity of the non-aqueous electrolyte is η, η < 1.8 mPa·s; The wound electrode core includes a diaphragm 1, which includes a base film 101 and a functional layer, wherein the functional layer is disposed on at least one side surface of the base film 101; The functional layer includes multiple hydrophilic coatings 102 and multiple hydrophobic coatings 103. The multiple hydrophobic coatings 103 are spaced apart, with one hydrophilic coating 102 between each pair of adjacent hydrophobic coatings 103, or one hydrophobic coating 103 between each pair of adjacent hydrophilic coatings 102; and at the junction of the hydrophilic coating 102 and the hydrophobic coating 103, the edge of the hydrophilic coating 102 at least partially overlaps with the edge of the hydrophobic coating 103. The wound electrode core includes a flat region and an arc region, the hydrophilic coating 102 is located in the arc region, and the hydrophobic coating 103 is located in the flat region.

[0027] like Figure 1 As shown, a hydrophobic coating 103 is disposed between two adjacent hydrophilic coatings 102. The two adjacent hydrophilic coatings 102 are defined as a first hydrophilic coating and a second hydrophilic coating, and the hydrophobic coating 103 located between the first and second hydrophilic coatings is defined as the first hydrophobic coating. The edge of the first hydrophilic coating near the first hydrophobic coating is connected to and at least partially overlaps with the edge of the first hydrophobic coating; preferably, at least half the length of the edge of the first hydrophobic coating overlaps. The edge of the second hydrophilic coating near the first hydrophobic coating is connected to and at least partially overlaps with the edge of the first hydrophobic coating; preferably, at least half the length of the edge of the first hydrophobic coating overlaps.

[0028] The arrangement of the plurality of hydrophilic coatings 102 and the plurality of hydrophobic coatings 103 in the functional coating can also be such that a hydrophobic coating 103 is provided between every two adjacent hydrophilic coatings 102. For example, two adjacent hydrophilic coatings 102 can be defined as a third hydrophilic coating and a fourth hydrophilic coating, and the hydrophobic coating 103 located between the first third hydrophilic coating and the fourth hydrophilic coating can be defined as a second hydrophobic coating. The edge of the third hydrophilic coating near the second hydrophobic coating is connected to and at least partially overlaps with the edge of the second hydrophobic coating; preferably, at least half the length of the edge of the second hydrophobic coating overlaps. The edge of the fourth hydrophilic coating near the second hydrophobic coating is connected to and at least partially overlaps with the other edge of the second hydrophobic coating; preferably, at least half the length of the edge of the second hydrophobic coating overlaps.

[0029] Specifically, hydrophilic coating 102 refers to a coating containing hydrophilic materials. Hydrophilic materials are those containing hydrophilic groups that readily interact with polar molecules such as water molecules (e.g., forming hydrogen bonds), can be wetted by polar substances such as water, and are readily miscible with polar substances such as water. Hydrophilic groups include hydroxyl, carboxyl, amino, and sulfonic acid groups, which readily form stable interactions with polar molecules such as water molecules.

[0030] Hydrophobic coating 103 refers to a coating containing hydrophobic materials. Hydrophobic materials are those containing hydrophobic groups, which make it difficult for them to interact effectively with water molecules, are not easily wetted by water, are poorly soluble in water, and are easily separated from water. Hydrophobic groups include hydrocarbon groups such as alkyl and aryl groups.

[0031] The hydrophobic coating 103 is readily soluble in nonpolar solvents. The hydrophilic coating 102 is readily soluble in polar solvents. The organic solvents contained in the electrolyte, most of which are polar organic solvents, and the lithium ions and some anions after the lithium salt dissociation are also polar ions, which can form ion-dipole and dipole-dipole interactions with the polar functional groups on the surface of the hydrophilic coating 102, thereby enhancing the affinity of the hydrophilic coating 102 for the electrolyte.

[0032] The surface tension of the non-aqueous electrolyte is γ, where γ < 25 mN / m; And / or, the viscosity of the non-aqueous electrolyte is η, where η < 1.8 mPa·s.

[0033] Specifically, the surface tension of conventional electrolytes is around 32 mN / m-35 mN / m, while this application limits the surface tension γ of the non-aqueous electrolyte to <25 mN / m. This directly reduces the resistance of the entire system and amplifies the difference in driving force caused by the contact angle difference between the hydrophilic coating 102 and the hydrophobic coating 103. This allows the electrolyte to generate stronger and faster capillary wetting when it encounters the hydrophilic coating 102, and the non-aqueous electrolyte is more violently "drawn" into the hydrophilic coating 102 region, thereby achieving efficient directional migration of the electrolyte.

[0034] Compared to the conventional electrolyte viscosity of approximately 2.0 mPa·s, this application reduces the electrolyte viscosity η to <1.8 mPa·s, thereby reducing the electrolyte's own resistance, increasing the lithium ion migration rate, and greatly enhancing the electrolyte flow and ion migration rate within the porous structure of the membrane 1, which is key to achieving rapid response.

[0035] Specifically, the hydrophobic coating 103 is disposed in the flat region of the electrode core, and the hydrophilic coating 102 is disposed in the arc region of the electrode core. The hydrophilic coating 102, driven by capillary force and controlled by interfacial energy, enables the electrolyte to preferentially migrate and reside in the flat region of the wound electrode core (corresponding to the region of the hydrophobic coating 103) to the arc region of the wound electrode core (corresponding to the region of the hydrophilic coating 102).

[0036] The lithium-ion battery provided in this application has the following effects: 1) Multiple hydrophobic coatings 103 are spaced apart, and a hydrophilic coating 102 is provided between each two adjacent hydrophobic coatings 103, or a hydrophobic coating 103 is provided between each two adjacent hydrophilic coatings 102; and at the connection between the hydrophilic coating 102 and the hydrophobic coating 103, the edge of the hydrophilic coating 102 and the edge of the hydrophobic coating 103 at least partially overlap. The above structure can form a wetting gradient between the hydrophilic coating 102 and the hydrophobic coating 103, generate sufficient interfacial energy difference, and drive the electrolyte to flow directionally from the region of the hydrophobic coating 103 to the region of the hydrophilic coating 102, thereby achieving dynamic balance of the electrolyte. 2) A hydrophobic coating 103 is set in the flat area of ​​the electrode core, and a hydrophilic coating 102 is set in the arc area of ​​the electrode core. The hydrophilic coating 102, driven by capillary force and controlled by interfacial energy, enables the electrolyte to preferentially migrate and reside in the flat area of ​​the wound electrode core (corresponding to the area of ​​the hydrophobic coating 103) to the arc area of ​​the wound electrode core (corresponding to the area of ​​the hydrophilic coating 102). Through the synergistic effect of multi-level capillary effect, the electrolyte is intelligently distributed in a directional manner, thereby solving the problem of electrolyte shortage at the arc of the battery during long cycle, fundamentally solving the problem of lithium plating at the arc of the wound cell, and improving the fast charging performance and cycle life of the battery. 3) This application limits the surface tension γ of the non-aqueous electrolyte to <25 mN / m; and / or reduces the viscosity η of the electrolyte to <1.8 mPa▪s, thereby reducing the resistance of the electrolyte itself, which is equivalent to directly reducing the resistance of the entire system, increasing the migration rate of lithium ions, and amplifying the driving force difference caused by the contact angle difference between the hydrophilic coating 102 and the hydrophobic coating 103. This allows the electrolyte to generate stronger and faster capillary wetting when it encounters the hydrophilic coating 102, and the non-aqueous electrolyte is more violently "absorbed" into the hydrophilic coating 102 region, thereby achieving efficient directional migration of the electrolyte and effectively solving the lithium deposition problem in the arc region of the battery.

[0037] In some embodiments, the contact angle between the hydrophilic coating 102 and the non-aqueous electrolyte is θ1, where θ1 < 15°.

[0038] Specifically, by limiting the contact angle θ1 between the hydrophilic coating 102 and the non-aqueous electrolyte to less than 15°, and through capillary force driving and interfacial energy regulation, the electrolyte can preferentially migrate and reside in the straight area of ​​the wound electrode core (corresponding to the hydrophobic coating 103 area) to the arc area of ​​the wound electrode core (corresponding to the hydrophilic coating 102 area). This effectively achieves the directional migration and effective locking of the electrolyte to the arc area of ​​the wound electrode core (corresponding to the hydrophilic coating 102 area), thereby solving the problem of electrolyte shortage at the arc of the battery during long cycles, fundamentally solving the problem of lithium plating at the arc of the wound cell, and improving the fast charging performance and cycle life of the battery.

[0039] If θ1 is greater than or equal to 15°, the wettability of the hydrophilic coating 102 is insufficient, the capillary force is weakened, and it is unable to overcome the electrolyte discharge caused by mechanical stress. The electrolyte is difficult to effectively fill the pores at the arc of the wound electrode core, the problem of electrolyte drying in the arc area still exists, the lithium ion transport impedance in the arc area is still large, lithium ion insertion is hindered, and the risk of lithium plating is significantly increased.

[0040] In a specific embodiment, the value of θ1 can be 14°, 13°, 12°, 10°, 8°, 9°, 7°, 6°, 5°, 4°, 3°, 2°, 1°, 0° or any combination thereof.

[0041] It should be noted that the contact angle θ1 between the hydrophilic coating 102 and the non-aqueous electrolyte refers to the angle formed by the tangent on the surface of the electrolyte droplet and the contact surface between the electrolyte and the hydrophilic coating 102 at the intersection of the three phases: electrolyte (liquid phase), hydrophilic coating 102 (solid phase), and air (gas phase).

[0042] In some preferred embodiments, θ1 < 10°.

[0043] Specifically, the contact angle θ1 between the hydrophilic coating 102 and the non-aqueous electrolyte is preferably less than 10°. The hydrophilic coating 102 has stronger hydrophilicity and capillary driving force, which is conducive to the preferential directional migration and residence of more electrolyte from the flat area of ​​the wound electrode core (corresponding to the hydrophobic coating 103 area) to the arc area of ​​the wound electrode core (corresponding to the hydrophilic coating 102 area). This increases the electrolyte content in the arc area, reduces the lithium-ion transport impedance, and improves the lithium-ion insertion rate, fundamentally solving the problem of lithium plating in the arc area of ​​the wound cell and improving the fast charging performance and cycle life of the battery.

[0044] In some embodiments, the contact angle between the hydrophobic coating 103 and the non-aqueous electrolyte is θ2, where θ2 > 35°.

[0045] Specifically, the contact angle θ2 between the hydrophobic coating 103 and the non-aqueous electrolyte is greater than 35°, which has the following effects: 1) Suppressing excessive electrolyte retention: The hydrophobic coating 103 is hydrophobic, and its surface can reduce the accumulation of electrolyte in the flat area of ​​the wound electrode core, promoting the migration of electrolyte to the high-demand arc area of ​​the wound electrode core. 2) Forming a wetting gradient with the hydrophilic coating 102: A significant contact angle difference is formed with the hydrophilic coating 102, generating a sufficient interfacial energy difference, driving the electrolyte to flow directionally from the area of ​​the hydrophobic coating 103 to the area of ​​the hydrophilic coating 102, achieving dynamic equilibrium.

[0046] If θ2 is less than or equal to 35°, the hydrophobicity of the hydrophobic coating 103 decreases, making the hydrophobic coating 103 also hydrophilic. The wetting gradient between the hydrophobic coating 103 and the hydrophilic coating 102 decreases, the capillary driving force decreases, the electrolyte cannot effectively migrate to the arc region of the wound electrode core, the distribution tends to be uniform, the arc region may still lack electrolyte, and the arc region in the battery still has the problem of lithium plating.

[0047] In a specific embodiment, the value of θ2 can be 36°, 38°, 40°, 45°, 50°, 55°, 60°, 70°, 80°, 90° or any combination thereof.

[0048] It should be noted that the contact angle θ2 between the hydrophobic coating 103 and the non-aqueous electrolyte refers to the angle formed by the tangent on the surface of the electrolyte droplet and the contact surface between the electrolyte and the hydrophobic coating 103 at the intersection of the three phases: electrolyte (liquid phase), hydrophobic coating 103 (solid phase), and air (gas phase).

[0049] In some preferred embodiments, θ2 > 40°.

[0050] Specifically, it is preferable that the contact angle θ2 between the hydrophobic coating 103 and the non-aqueous electrolyte is greater than 40°. This reduces the attraction of the hydrophobic coating 103 to the electrolyte, increases the contact angle difference between the hydrophobic coating 103 and the hydrophilic coating 102, generates a sufficient interfacial energy difference, and is more conducive to driving the electrolyte to flow directionally from the region of the hydrophobic coating 103 to the region of the hydrophilic coating 102, achieving dynamic balance and improving the lithium deposition problem of the negative electrode 3 in the arc region.

[0051] In some embodiments, the contact angle between the hydrophobic coating 103 and the non-aqueous electrolyte is θ2, and the contact angle between the hydrophilic coating 102 and the electrolyte is θ1, where θ2-θ1≥15°.

[0052] Specifically, by limiting the range of θ2-θ1≥15°, the surface energy difference between the hydrophobic coating 103 and the hydrophilic coating 102 is increased, which can generate a capillary force sufficient to overcome the viscous resistance inside the electrolyte and drive its directional flow. This drives the electrolyte to flow directionally from the region of the hydrophobic coating 103 to the region of the hydrophilic coating 102, achieving dynamic balance and improving the lithium deposition problem of the negative electrode 3 in the arc region.

[0053] When θ2-θ1<15°, the driving force generated by the gradient between the hydrophobic coating 103 and the hydrophilic coating 102 is too weak to effectively counteract the influence of other factors inside the cell (such as electrolyte gravity, electrode pressure, pumping effect during cycling, etc.) on electrolyte distribution, resulting in insignificant electrolyte directional migration effect.

[0054] In some preferred embodiments, the contact angle between the hydrophobic coating 103 and the non-aqueous electrolyte is θ2, and the contact angle between the hydrophilic coating 102 and the non-aqueous electrolyte is θ1, where 15°≤θ2-θ1≤45°.

[0055] Specifically, within the range of 15°≤θ2-θ1≤45°, the surface energy difference between the hydrophobic coating 103 and the hydrophilic coating 102 is relatively large, which has a capillary force to drive their directional flow, driving the electrolyte to flow directionally from the region of the hydrophobic coating 103 to the region of the hydrophilic coating 102, effectively improving the lithium deposition problem of the negative electrode 3 in the arc region.

[0056] When θ2-θ1 is greater than 45°, excessive capillary force may cause the electrolyte to be excessively "drawn" into the arc area, resulting in a relative lack of electrolyte in the flat area. The wettability difference between the hydrophilic coating 102 and the hydrophobic coating 103 is too large, affecting the formation of the electrode interface film, leading to an increase in electrode interface impedance and lithium plating on the negative electrode 3. Under the mechanical stress of long-term battery cycling, unstable mechanical contact may occur between the interfaces, affecting the adhesion between the active coating and the current collector in the electrode, and affecting the cycle performance of the battery.

[0057] In some embodiments, the porosity of the hydrophilic coating 102 is P1, where 65% ≤ P1 ≤ 80%; And / or, the porosity of the hydrophobic coating 103 is P2, where P2 ≤ 50%.

[0058] Specifically, the porosity P1 of the hydrophilic coating 102 satisfies 65%≤P1≤80%. The larger porosity of the hydrophilic coating 102 is beneficial for storing more electrolyte, thereby allowing more electrolyte to exist in the hydrophilic coating 102, reducing the migration resistance of lithium ions, increasing the electrolyte storage capacity in the wound electrode core, and solving the lithium plating problem of the negative electrode 3.

[0059] If the porosity of the hydrophilic coating 102 is too low, the amount of electrolyte stored will be small. Combined with the mechanical stress in the arc region of the wound electrode core, the amount of electrolyte in the arc region will be small, and lithium plating will occur in the negative electrode 3.

[0060] The porosity P2 of the hydrophobic coating 103 is ≤50%. The small porosity of the hydrophobic coating 103 means that the amount of electrolyte stored in the hydrophobic coating 103 is small. Combined with the low affinity of the hydrophobic coating 103 for the electrolyte, it is beneficial for the electrolyte in the flat area of ​​the wound electrode core to migrate to the arc area, thereby achieving a dynamic balance of electrolyte in the arc area and the flat area.

[0061] If the porosity of the hydrophobic coating 103 is too high, the amount of electrolyte stored in the hydrophobic coating 103 will be high, increasing the migration resistance of the electrolyte. Even if there is an interfacial energy difference between the hydrophobic coating 103 and the hydrophilic coating 102, the amount of electrolyte migrating to the hydrophilic coating 102 will be reduced, the amount of electrolyte stored in the arc region will be small, and lithium will be deposited on the negative electrode 3.

[0062] In specific embodiments, the value of P1 can be 65%, 68%, 70%, 72%, 75%, 76%, 78%, 80%, etc. In specific embodiments, the value of P2 can be 50%, 48%, 45%, 43%, 40%, 35%, 30%, 32%, 20%, 25%, 15%, etc.

[0063] In some preferred embodiments, 70% ≤ P1 ≤ 80%.

[0064] Specifically, the porosity P1 of the hydrophilic coating 102 satisfies 70%≤P1≤80%. The high porosity of the hydrophilic coating 102 results in a high electrolyte storage capacity, which can increase the electrolyte storage capacity in the arc region of the wound electrode core and solve the lithium plating problem of the negative electrode 3 in the arc region.

[0065] In some embodiments, the porosity of the hydrophilic coating 102 is P1, the porosity of the hydrophobic coating 103 is P2, and P1 / P2 ≥ 1.5.

[0066] Specifically, P1 / P2≥1.5 limits the ratio of the porosity of the hydrophilic coating 102 to that of the hydrophobic coating 103, ensuring that the porosity of the hydrophilic coating 102 is significantly greater than that of the hydrophobic coating 103. This correspondingly limits the electrolyte storage capacity of the arc-shaped separator 1 of the wound electrode core to be greater than that of the separator 1 in the flat region. This creates a physical advantage for the "directional storage" and "rapid replenishment" of electrolyte in the arc-shaped region, ensuring that the arc-shaped region has sufficient electrolyte and solving the lithium plating problem of the negative electrode 3 in the arc-shaped region.

[0067] In some preferred embodiments, P1 / P2 ≥ 1.8.

[0068] Specifically, P1 / P2≥1.8, the large difference in porosity between the hydrophilic coating 102 and the hydrophobic coating 103 is beneficial for the directional storage of electrolyte in the hydrophilic coating 102, increasing the electrolyte storage capacity in the arc region, enabling rapid replenishment of electrolyte during battery charging and discharging, and solving the lithium plating problem of the negative electrode 3 in the arc region.

[0069] In some preferred embodiments, 1.5 ≤ P1 / P2 ≤ 2.0.

[0070] Specifically, by satisfying the condition 1.5≤P1 / P2≤2.0, while ensuring sufficient electrolyte storage in the arc region, the adhesion between the electrode and the separator 1 can be achieved, reducing lithium deposition in the arc region of the negative electrode 3 and improving the battery cycle performance.

[0071] For further optimization, 1.8 ≤ P1 / P2 ≤ 2.0.

[0072] Specifically, if the condition 1.8≤P1 / P2≤2.0 is met, the negative electrode in the arc region will not deposit lithium, and the battery will have good fast charging performance and better cycle performance.

[0073] In some embodiments, the tortuosity of the hydrophilic coating 102 is τ1, where τ1 < 2.0; And / or, the tortuosity of the hydrophobic coating 103 is τ2, where τ2 > 3.0.

[0074] Specifically, tortuosity (τ) = actual penetration path length (L) a The apparent thickness (L0) of the coating essentially describes the degree of tortuosity, interlacing, and meandering of the pore channels inside the coating. The pores of the coating are not vertically penetrating straight cylindrical channels, but rather a tortuous, interconnected, and interlaced network pore structure formed by the coating. Lithium ions and electrolytes must be transported along these tortuous channels, and the degree of tortuosity is a quantitative characterization of the "degree of tortuosity of the transport path".

[0075] The tortuosity τ1 of the hydrophilic coating 102 is less than 2.0. The smaller the tortuosity, the faster the electrolyte wetting rate, the shorter the actual penetration path length of lithium ions, and the smaller the transmission resistance of lithium ions. This improves the transmission rate of lithium ions, the electrolyte wetting rate, and the electrolyte retention capacity of the hydrophilic coating 102, solves the lithium deposition problem of the negative electrode 3 caused by lithium ion congestion, and improves the battery cycle performance.

[0076] The tortuosity τ2 of the hydrophobic coating 103 is greater than 3.0. The slightly larger tortuosity results in a lower electrolyte wetting rate, which is beneficial for the electrolyte portion in the hydrophobic coating 103 region to effectively migrate to the hydrophilic coating 102 region, thereby increasing the electrolyte retention in the hydrophilic coating 102 region.

[0077] In some embodiments, the hydrophilic coating 102 includes hydrophilic particles, which include hydrophilic particles of a first size and hydrophilic particles of a second size. A plurality of micropores and a plurality of mesopores are disposed between the first size hydrophilic particles and the second size hydrophilic particles. The average pore size of the micropores is 2 nm to 50 nm, and the average pore size of the mesopores is 50 nm to 200 nm.

[0078] Specifically, the hydrophilic coating 102 contains hydrophilic particles of two different particle size ranges. Multiple micropores and mesopores are formed between the first and second size hydrophilic particles, creating a bimodal pore size distribution. During battery charging and discharging, lithium ions rapidly converge into the arc-shaped region through the mesopore channels. Simultaneously, the electrolyte stored in the micropores continuously releases lithium ions to replenish the electrolyte through concentration gradient and capillary action. This collectively ensures a sufficient supply of lithium ions in the arc-shaped region of the wound electrode core, fundamentally improving the intercalation kinetics and suppressing lithium deposition on the electrode.

[0079] The first and second size hydrophilic particles, through the distribution of particles of different sizes, form mesopores and micropores. The different pore sizes enable a fine division of labor and synergy of functions, thereby simultaneously optimizing the two key links of electrolyte storage and transportation.

[0080] In specific embodiments, the average pore size of the micropores can be 2nm, 5nm, 10nm, 8nm, 12nm, 15nm, 20nm, 25nm, 30nm, 40nm, 50nm, 32nm, 35nm, 38nm, 42nm, 45nm, etc.

[0081] The average pore size of the mesopores can be 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 120nm, 140nm, 150nm, 160nm, 170nm, 180nm, 190nm, 200nm, etc.

[0082] In some embodiments, the D50 particle size of the first-size hydrophilic particles is 100nm-300nm, and the D50 particle size of the second-size hydrophilic particles is 10nm-30nm.

[0083] Specifically, in the hydrophilic coating 102, hydrophilic particles of the first size are stacked to form mesopores with an average pore size in the range of 50nm to 200nm, and hydrophilic particles of the second size fill the spaces between the mesopores to form micropores with an average pore size in the range of 2nm to 50nm.

[0084] In some embodiments, the mass ratio of the first-size hydrophilic particle to the second-size hydrophilic particle is (60-70):(30-40).

[0085] In specific embodiments, the mass ratio of the first-size hydrophilic particles to the second-size hydrophilic particles can be 60:40, 30:70, 62:38, 64:36, 65:35, 67:33, 68:32, 69:31, etc.

[0086] When the mass ratio of the first-size hydrophilic particles to the second-size hydrophilic particles is within the above range, it is beneficial to control the formation of micropores with an average pore size of 2nm to 50nm and mesopores with an average pore size of 50nm to 200nm, thereby improving the migration rate of lithium ions and alleviating the lithium deposition problem in the arc region.

[0087] In some embodiments, the hydrophilic particles include hydrophilic ceramic particles; The hydrophobic coating 103 includes a hydrophobic polymer, which includes a fluoropolymer, and the fluoropolymer includes at least one of polyvinylidene fluoride copolymer, polytetrafluoroethylene (PTFE), and perfluorosulfonic acid resin.

[0088] Specifically, hydrophilic ceramic particles refer to ceramic particles that have been modified to be hydrophilic using existing modification methods. These methods can include chemical methods such as oxidation modification, grafting, and co-precipitation; or physical methods such as dissolution and soaking, and blending and coating.

[0089] The hydrophilic modifiers used in hydrophilic modification include at least one of aminosilane coupling agents, epoxy-containing silane coupling agents, and sodium aluminate. Hydrophilic ceramic particles can be obtained by purchase.

[0090] The hydrophobic coating 103 is made of the aforementioned fluoropolymer, which is beneficial for forming a hydrophobic coating 103 with a contact angle >35° with the non-aqueous electrolyte, thereby reducing the adsorption force on the electrolyte.

[0091] In some embodiments, the ceramic particles include at least one of alumina, boehmite, titanium dioxide, and silicon dioxide.

[0092] In some embodiments, the base film 101 includes at least one of PP, PE, PP / PE, PP / PE / PP, polyester base film 101, polyimide base film 101, and aramid.

[0093] PE stands for polyethylene, and PP stands for polypropylene.

[0094] In some embodiments, the thickness of the hydrophilic coating 102 is 3 μm to 6 μm, and the thickness of the hydrophobic coating 103 is 1 μm to 3 μm.

[0095] The thickness of the hydrophilic coating 102 is within the above range to ensure the formation of a stable bimodal porous structure and provide sufficient electrolyte storage space; the thickness of the hydrophobic coating 103 is within the above range to minimize ion transport impedance while maintaining a stable hydrophobic interface.

[0096] In a specific embodiment, the thickness of the hydrophilic coating 102 can be 3μm, 3.2μm, 3.5μm, 3.6μm, 3.9μm, 4.0μm, 4.3μm, 4.5μm, 4.8μm, 5.0μm, 5.2μm, 5.5μm, 5.8μm, 6.0μm, or any two of the above.

[0097] The thickness of the hydrophobic coating 103 can be 1, 1.2 μm, 1.4 μm, 1.5 μm, 1.7 μm, 1.9 μm, 2.0 μm, 2.2 μm, 2.3 μm, 2.5 μm, 2.7 μm, 2.8 μm, 2.9 μm, 3.0 μm, or any two of the above.

[0098] In some preferred embodiments, the thickness of the hydrophilic coating 102 is 4 μm to 6 μm, and the thickness of the hydrophobic coating 103 is 1 μm to 2 μm.

[0099] The thickness of the hydrophilic coating 102 and the thickness of the hydrophobic coating 103 are within the above-mentioned preferred range, which is beneficial for storing sufficient electrolyte in the arc region and effectively solves the problem of lithium deposition in the arc region.

[0100] In some embodiments, the method for preparing the diaphragm 1 includes the following steps: Hydrophilic particles, a first binder, and a first solvent are mixed evenly to obtain a first slurry containing hydrophilic particles; the mass ratio of the hydrophilic particles to the first binder is (90~98):(10~2); the solid content of the first slurry is 30%~50%. A second slurry containing a hydrophobic polymer is obtained, wherein the solid content of the second slurry is 15% to 40%. The second slurry is applied intermittently to at least one side surface of the base film 101 and dried to obtain a hydrophobic coating 103. The first slurry is then applied between each adjacent pair of hydrophobic coatings 103 and dried to obtain a hydrophilic coating 102. Alternatively, the first slurry is applied intermittently to at least one side surface of the base film 101 and dried to obtain a hydrophilic coating 102. The second slurry is then applied between each adjacent pair of hydrophilic coatings 102 and dried to obtain a hydrophobic coating 103. Furthermore, at the junction of the hydrophilic coating 102 and the hydrophobic coating 103, the edge of the hydrophilic coating 102 and the edge of the hydrophobic coating 103 at least partially overlap, and the membrane 1 is obtained by drying.

[0101] Specifically, the second slurry is applied intermittently to at least one side surface of the base film 101 and dried to obtain a hydrophobic coating 103. The first slurry is applied between each two adjacent hydrophobic coatings 103 and dried to obtain a hydrophilic coating 102, thus forming a structure in which a hydrophilic coating 102 is provided between each two adjacent hydrophobic coatings 103.

[0102] The first slurry is applied intermittently to at least one side surface of the base film 101 and dried to obtain a hydrophilic coating 102. The second slurry is applied between each two adjacent hydrophilic coatings 102 and dried to obtain a hydrophobic coating 103, thus forming a structure in which a hydrophobic coating 103 is provided between each two adjacent hydrophilic coatings 102.

[0103] The method for preparing the separator 1 provided in this application is simple. The resulting separator 1 can form an electrolyte wetting gradient between the hydrophilic coating 102 and the hydrophobic coating 103, generating a sufficient interfacial energy difference. This allows the electrolyte to flow directionally from the region of the hydrophobic coating 103 to the region of the hydrophilic coating 102, achieving dynamic equilibrium of the electrolyte. When used in a wound electrode core, the hydrophilic coating 102 is located in the arc region, and the hydrophobic coating 103 is located in the flat region. Through the synergistic effect of multi-level capillary action, intelligent directional distribution of the electrolyte is achieved, thereby solving the problem of electrolyte scarcity at the arc region of the battery during long cycles. This fundamentally solves the problem of lithium plating at the arc region of wound cells, improving the fast-charging performance and cycle life of the battery.

[0104] By controlling the mass ratio of hydrophilic particles to the first binder and the solid content of the first slurry within the above range, the contact angle, porosity, and tortuosity of the hydrophilic coating 102 with the non-aqueous electrolyte can be adjusted within the range of this application by adjusting the amount of hydrophilic particles and the first binder, and the distribution structure of the hydrophilic particles and the first binder. This is beneficial to driving the electrolyte to flow directionally from the region of the hydrophobic coating 103 to the region of the hydrophilic coating 102, thereby achieving dynamic balance of the electrolyte.

[0105] In specific embodiments, the mass ratio of hydrophilic particles to the first binder can be in the following ranges: (90~92): (10~8), (92~94): (8~6), (94~96): (6~4), or (96~98): (4~2).

[0106] In a specific embodiment, the solid content of the first slurry can be: 30%, 32%, 35%, 37%, 39%, 40%, 42%, 43%, 45%, 47%, 48%, 50%, or any two of the above.

[0107] By controlling the solid content of the second slurry within the above-mentioned range, the contact angle, porosity, and tortuosity of the hydrophobic coating 103 with the non-aqueous electrolyte are within the scope of this application. The adsorption force of the hydrophobic coating 103 on the electrolyte is weak, which promotes the migration of the electrolyte to the side of the hydrophilic coating 102.

[0108] In a specific embodiment, the solid content of the second slurry can be: 15%, 17%, 20%, 22%, 25%, 28%, 30%, 33%, 35%, 37%, 40%, or any two of the above.

[0109] In some embodiments, the first solvent comprises deionized water.

[0110] In some embodiments, the first adhesive includes at least one of styrene-butadiene rubber, polyvinyl alcohol, polyacrylic acid, sodium carboxymethyl cellulose, and polyacrylates.

[0111] Polyacrylates are water-based polyacrylates. Water-based polyacrylates include polyacrylate emulsions, styrene-acrylate copolymer emulsions, ammonium polyacrylates, and sodium polyacrylates.

[0112] In some embodiments, obtaining a second slurry containing a hydrophobic polymer includes the following steps: The hydrophobic polymer and the second solvent are mixed evenly to obtain the second slurry; The solid content of the second slurry is 15% to 40%.

[0113] In some embodiments, the second solvent includes at least one of N-methylpyrrolidone, dimethylacetamide, dimethylformamide, acetone, and tetrahydrofuran.

[0114] The coating process used in the above coating includes one of the following: gravure roller coating, slot extrusion coating with precision mask, or high-precision spraying.

[0115] In some embodiments, the non-aqueous electrolyte includes additives; The additives include fluorocarbonate additives, linear siloxane additives, and perfluoropolyether additives, wherein the mass content of the fluorocarbonate additives in the non-aqueous electrolyte is 3% to 10%. The linear siloxane additive in the non-aqueous electrolyte has a mass content of 1% to 3%; The mass content of the perfluoropolyether additive in the non-aqueous electrolyte is 0.2% to 2%.

[0116] Specifically, the mass content of fluorocarbonate additives ranges from 3% to 10%, the mass content of linear siloxane additives ranges from 1% to 3%, and the mass content of perfluoropolyether additives ranges from 0.2% to 2%. All of these are beneficial for reducing the surface tension of the electrolyte and reducing the migration resistance of lithium ions. The electrolyte and the separator 1 work together to achieve efficient directional migration of the electrolyte, effectively solving the lithium deposition problem of the negative electrode 3 in the arc region, and improving the battery cycle performance and fast charging performance.

[0117] In specific embodiments, the mass content of fluorocarbonate additives can be 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, etc.

[0118] The mass content of linear siloxane additives can be 1%, 1.2%, 1.5%, 1.7%, 2.0%, 2.3%, 2.5%, 2.8%, 3.0%, etc.

[0119] The mass content of perfluoropolyether additives can be 0.2%, 0.4%, 0.5%, 0.8%, 1.0%, 1.3%, 1.5%, 1.7%, 1.9%, 2.0%, or any two of the above.

[0120] In some preferred embodiments, the fluorocarbonate additive in the non-aqueous electrolyte has a mass content of 5% to 10%.

[0121] Specifically, when the mass content of fluorocarbonate additives is within the above-mentioned preferred range, it is more beneficial to reduce the surface tension of the electrolyte, increase the migration rate of the electrolyte to the hydrophilic coating 102, and effectively solve the problem of lithium deposition on the negative electrode 3.

[0122] In some preferred embodiments, the linear siloxane additive in the non-aqueous electrolyte has a mass content of 1% to 2%.

[0123] Specifically, when the mass content of linear siloxane additives is within the above-mentioned preferred range, it is more beneficial to reduce the surface tension of the electrolyte, increase the migration rate of the electrolyte to the hydrophilic coating 102, and effectively solve the problem of lithium deposition on the negative electrode 3.

[0124] In some embodiments, the fluorocarbonate additives include fluorocyclic carbonate additives, which include at least one of fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), propylene trifluorocarbonate (TFPC), fluorobutylene carbonate (FBC), and trifluoromethyl ethylene carbonate (TFC). The linear siloxane additives include at least one of hexamethyldisiloxane (HMDSO), octamethyltrisiloxane (OMTSO), decamethyltetrasiloxane (DMTSO), tetramethyldisiloxane (TMDSO), heptamethyltrisiloxane (HMTSO), tris(trimethylsiloxy)methylsilane (M3T), and divinyltetramethyldisiloxane. The perfluoropolyether additives include at least one of the following: perfluoropolyether alcohol (PFPE-OH), perfluoropolyether acyl fluoride (PFPE-COF), perfluoropolyether diol (PFPE-(OH)2), perfluoropolyether carboxylic acid (PFPE-COOH), perfluoropolyether methyl ester (PFPE-COOCH3), perfluoropolyether (meth) acrylate, perfluoropolyether triethoxysilane (PFPE-Si(OEt)3), perfluoropolyether phosphate ester (PFPE-PO4), and perfluoropolyether amide (PFPE-CONH2).

[0125] Specifically, fluorocarbonate additives, linear siloxane additives, and perfluoropolyether additives are selected from the above categories, which helps to reduce the surface tension of the electrolyte, reduce the migration resistance of lithium ions, and facilitate the efficient directional migration of the electrolyte.

[0126] In some embodiments, the electrolyte further includes auxiliary additives, which include nitrile additives, specifically at least one selected from acetonitrile, butyronitrile, propionitrile, succinic anionyl nitrile, isobutyronitrile, glutaronitrile, adiponitrile, and malononitrile. The mass content of the nitrile additives in the non-aqueous electrolyte is 0.5% to 5%.

[0127] In some embodiments, the non-aqueous electrolyte further includes an organic solvent, which includes a low-viscosity carboxylic acid ester solvent, and the low-viscosity carboxylic acid ester solvent includes at least one of methyl formate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, and ethyl butyrate. In the non-aqueous electrolyte, the mass content of the low-viscosity carboxylic acid ester solvent is 5% to 30%.

[0128] Specifically, the non-aqueous electrolyte contains low-viscosity carboxylic acid ester solvents, and the content meets the above range, which helps to reduce the surface tension of the electrolyte and improve the directional migration ability of the electrolyte.

[0129] In specific embodiments, the mass content of the low-viscosity carboxylic acid ester solvent can be 5%, 8%, 10%, 12%, 13%, 15%, 17%, 19%, 20%, 22%, 23%, 24%, 25%, 27%, 28%, 29%, 30%, etc.

[0130] In some embodiments, the organic solvent also includes carbonate solvents.

[0131] The carbonate solvents include at least one of ethylene carbonate, butenyl carbonate, pentenyl carbonate, methyl ethyl carbonate, diethyl carbonate, dipropyl carbonate, propylene carbonate, vinylene carbonate, dimethyl carbonate, and methyl propyl carbonate.

[0132] The organic solvent also includes one or more of 1,4-butyrolactone and tetrahydrofuran.

[0133] In some embodiments, the non-aqueous electrolyte further includes a fluorinated surfactant, which includes at least one of anionic fluorinated surfactants, cationic fluorinated surfactants, amphoteric fluorinated surfactants, and nonionic fluorinated surfactants. In the non-aqueous electrolyte, the mass content of the fluorinated surfactant is 0.01% to 1%.

[0134] Specifically, the presence of fluorinated surfactants in non-aqueous electrolytes, with the content meeting the above-mentioned range, helps to reduce the surface tension of the electrolyte and improve its directional migration ability.

[0135] In specific embodiments, the mass content of the fluorinated surfactant can be 0.01%, 0.05%, 0.08%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.8%, 0.9%, 1.0%, etc.

[0136] In some embodiments, the non-aqueous electrolyte further includes a lithium salt, which includes lithium hexafluorophosphate and lithium difluorosulfonylimide; In the non-aqueous electrolyte, the molar concentration of lithium hexafluorophosphate is n1, and the molar concentration of lithium difluorosulfonylimide is n2, with n1:n2 being (10~12):(1~3).

[0137] Specifically, the lithium salts include lithium hexafluorophosphate and lithium difluorosulfonylimide, and n1:n2 satisfies the range of (10~12):(1~3), which can effectively ensure the high ionic conductivity of the electrolyte, improve the conductivity of lithium ions, improve the battery cycle performance, and work in synergy with the separator 1 to increase the electrolyte content in the arc region and solve the lithium deposition problem of the negative electrode 3 in the arc region.

[0138] In specific embodiments, the ratio of n1:n2 can be 10:1, 10:2, 10:3, 11:1, 11:2, 11:3, 12:1, 12:2, 12:3, etc.

[0139] In some embodiments, n1 is 1.0 mol / L to 1.2 mol / L; n2 is 0.1 mol / L to 0.3 mol / L.

[0140] Specifically, n1 and n2 within the above range effectively ensure the high ionic conductivity of the electrolyte, improve the conductivity of lithium ions, improve battery cycle performance, and solve the problem of lithium deposition in the arc region.

[0141] In specific embodiments, the value of n1 can be 1 mol / L, 1.02 mol / L, 1.05 mol / L, 1.07 mol / L, 1.1 mol / L, 1.13 mol / L, 1.15 mol / L, 1.18 mol / L, 1.2 mol / L, etc.

[0142] The value of n2 can be 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.25 mol / L, 0.3 mol / L, etc.

[0143] It should be noted that the aforementioned positive electrode 2 and negative electrode 3 are existing technologies. For example, positive electrode 2 includes a positive current collector and a positive active material layer. The positive active material layer includes a positive conductive agent, a positive active material, and a positive binder. The positive conductive agent includes one or more of acetylene black, conductive carbon black, carbon fiber, carbon nanotubes, and Ketjen black. The positive active material includes one or more of lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, and lithium nickel cobalt manganese oxide.

[0144] The positive electrode binder includes one or more of polyvinylidene fluoride, polyacrylonitrile, polytetrafluoroethylene, polyvinyl alcohol, and polyurethane.

[0145] The negative electrode sheet 3 includes a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder.

[0146] The negative electrode active material includes one or more of graphite, hard carbon materials, silicon materials, silicon carbon materials, and silicon oxides.

[0147] The negative electrode binder includes one or more of the following: styrene-butadiene rubber, polyvinylidene fluoride, polytetrafluoroethylene, fluorinated rubber, polyurethane, polyacrylic acid, sodium polyacrylate, polyvinyl alcohol, alginate, and sodium alginate.

[0148] The negative electrode conductive agent includes one or more of acetylene black, conductive carbon black, carbon fiber, carbon nanotubes, and Ketjen black.

[0149] The contact angle θ1 between the hydrophilic coating 102 and the electrolyte, and the contact angle θ2 between the hydrophobic coating 103 and the electrolyte, were obtained by measuring the contact angle using a contact angle measuring instrument.

[0150] The contact angle can be obtained using the following test method: obtain a test electrolyte with an EC / DMC / EMC volume ratio of 1:1:1; use a contact angle measuring instrument to place the sample on the test platform and let the test electrolyte drip naturally onto the sample surface. After the droplet shape is completely stable, take five test points of the droplet, test the contact angle values ​​of the test points, and take the average value.

[0151] The porosity of the hydrophilic coating 102 and the porosity of the hydrophobic coating 103 can be obtained by commonly used methods such as impregnation, mercury porosimetry, and gas adsorption.

[0152] If the immersion method is used, the following method can be used to test: Weigh the dry weight of the sample (m). 干 Immerse the sample in a test electrolyte solution with an EC / DMC / EMC volume ratio of 1:1:1 for 5-10 minutes. Remove the sample and allow excess immersion solution to drip off naturally. Weigh the wet weight (m). 湿 The porosity of the sample = (m 湿 -m 干 / Test electrolyte density.

[0153] The tortuosity τ1 of the hydrophilic coating 102 and the tortuosity τ2 of the hydrophobic coating 103 are tested. The test methods for τ1 and τ2 are as follows.

[0154] The cross-sectional microstructure image of the functional coating of the diaphragm 1 was obtained by high-resolution scanning electron microscopy. The pores and skeleton were binarized by image processing software, the geometric topology of the pore network was extracted, and the geometric tortuosity was calculated.

[0155] In this invention, the tortuosity of the hydrophilic coating 102 and the hydrophobic coating 103 is determined using scanning electron microscopy-image analysis. The specific steps are as follows: (1) Sample preparation: From the gradient functional membrane 1 prepared in the example, samples containing only the hydrophilic coating 102 (size ≥ 5 mm × 5 mm) and samples containing only the hydrophobic coating 103 (size ≥ 5 mm × 5 mm) are cut out respectively. The samples are brittlely fractured in liquid nitrogen to obtain a flat cross-section; or a deformation-free cross-section is prepared using an ion beam cutter (IM4000Plus type) with a cutting accuracy of ±10 nm.

[0156] (2) Image acquisition: The cross sections of the hydrophilic coating 102 and the hydrophobic coating 103 were imaged using a field emission scanning electron microscope. ≥5 fields of view were randomly selected for each functional area, with a magnification of 10,000× and an image resolution better than 10 nm / pixel. Each field of view contained the complete coating thickness direction.

[0157] (3) Image processing: The acquired SEM images were preprocessed using image analysis software (Olympus Stream 2.4), including contrast enhancement and noise filtering. The Otsu method was used to automatically determine the grayscale threshold and binarize the image into a porous phase (white) and a skeleton phase (black). Mis-segmented regions caused by charging effects or contamination were manually corrected.

[0158] (4) Tortuosity calculation: The pore skeleton centerline extraction algorithm is used to identify the continuous pore channels along the thickness direction and extract the actual path length L of each channel. eThe ratio of the tortuosity τ to the geometric thickness L of the coating (read directly from the SEM image scale) is the tortuosity τ of the channel. e / L. For each functional area, no fewer than 100 independent channels are counted, and their arithmetic mean is taken as the tortuosity test result of that functional area.

[0159] The specific embodiments of the present invention will be further explained and illustrated below through examples, but this does not mean that the scope of protection of the present invention is limited to the scope described in the examples.

[0160] Example 1 S1: Preparation of diaphragm 1 S11: Obtain the first slurry Hydrophilic particles and styrene-butadiene rubber in a weight ratio of 94:6 were mixed evenly, then added to deionized water and mixed evenly to obtain the first slurry. The solid content of the first slurry was 40%.

[0161] The hydrophilic particles are hydrophilic particles with a first diameter and hydrophilic particles with a second diameter. Both the first diameter and the second diameter hydrophilic particles are selected from hydrophilically modified nano-silica particles and obtained by purchase. The hydrophilic modifier used for hydrophilic modification is an aminosilane coupling agent.

[0162] The mass ratio of the first-size hydrophilic particles to the second-size hydrophilic particles is 65:35. The D50 particle size of the first-size hydrophilic particles is 200 nm, and the D50 particle size of the second-size hydrophilic particles is 20 nm.

[0163] S12: Obtain the second slurry Polyvinylidene fluoride (PVDF) polymer was dissolved in N-methylpyrrolidone (NMP) solvent and mixed evenly to obtain a second slurry with a solid content of 30%.

[0164] S13: Preparation of diaphragm 1 The base film 101 is selected from PE and has a thickness of 5μm. The base film 101 is subjected to corona treatment to enhance adhesion.

[0165] Using a slot extrusion coating machine, the second slurry prepared in step S12 is applied to one side surface of the base film 101 at intervals, with a coating thickness of 3 μm, and then dried at 80°C to obtain a hydrophobic coating 103. The first slurry prepared in step S11 is coated between every two adjacent hydrophobic coatings 103 with a coating thickness of 5 μm, and then dried at 80°C. At the junction of the hydrophilic coating 102 and the hydrophobic coating 103, the edge of the hydrophilic coating 102 and the edge of the hydrophobic coating 103 at least partially overlap, thus obtaining the diaphragm 1.

[0166] The contact angle between the hydrophobic coating 103 and the electrolyte is θ2 = 45°. The contact angle between the hydrophilic coating 102 and the electrolyte is θ1 = 12°. θ2 - θ1 = 33°.

[0167] In the hydrophilic coating 102, hydrophilic particles of a first size are stacked to form mesopores with an average pore size of 150 nm, and hydrophilic particles of a second size fill the spaces between the mesopores to form micropores with an average pore size of 15 nm.

[0168] The porosity P1 of the hydrophilic coating 102 and the porosity P2 of the hydrophobic coating 103 were tested. The tortuosity τ1 of the hydrophilic coating 102 and the tortuosity τ2 of the hydrophobic coating 103 were tested.

[0169] P1 is 70%, P2 is 45%, τ1 is 1.8, and τ2 is 3.5.

[0170] In the diaphragm 1, the thickness of the hydrophilic coating 102 is 4 μm, and the thickness of the hydrophobic coating 103 is 3 μm.

[0171] S2: Preparation of positive electrode 2 Lithium cobalt oxide, conductive carbon black, and polyvinylidene fluoride were mixed evenly at a mass ratio of 97%:1.5%:1.5%, and then NMP was added and mixed evenly to obtain a positive electrode slurry. The positive electrode slurry was coated on both sides of an aluminum foil, dried, and rolled to obtain positive electrode sheet 2.

[0172] S3: Preparation of negative electrode 3 Graphite, SP, styrene-butadiene rubber, and carboxymethyl cellulose were mixed evenly in a mass ratio of 96.3:1.0:1.3:1.2, and deionized water was added and stirred evenly to obtain the negative electrode slurry.

[0173] The negative electrode slurry is coated on both sides of the copper foil, and then dried and rolled to obtain the negative electrode sheet 3.

[0174] S4: Electrolyte Preparation Ethylene carbonate, methyl ethyl carbonate, diethyl carbonate, and propyl propionate were mixed uniformly in a volume ratio of 3:4:2:1. Then, additives including fluoroethylene carbonate, hexamethyldisiloxane, adiponitrile, perfluoropolyether acyl fluoride, lithium hexafluorophosphate, and lithium bis(fluorosulfonyl)imide were added and mixed uniformly to obtain the electrolyte. In the electrolyte, the mass content of fluoroethylene carbonate was 8%, hexamethyldisiloxane was 2%, adiponitrile was 1%, and perfluoropolyether acyl fluoride was 1%; the molar concentration of lithium hexafluorophosphate was 1.1 mol / L, and the molar concentration of lithium bis(fluorosulfonyl)imide was 0.2 mol / L.

[0175] The surface tension γ of the electrolyte tested was 24.5 mN / m, the viscosity η was 1.65 mPa·s, and the conductivity was 9.5 mS / cm.

[0176] S5: Manufacturing Lithium-ion Batteries The positive electrode 2 prepared in step S2, the negative electrode 3 prepared in step S3, and the separator 1 prepared in step S1 are wound together to obtain a wound electrode core. The hydrophilic coating 102 in the separator 1 is disposed in the arc region of the wound electrode core, and the hydrophobic coating 103 is disposed in the straight region of the wound electrode core.

[0177] A lithium-ion battery is made by combining a wound electrode core with an aluminum-plastic film, followed by processes such as liquid injection and formation.

[0178] Examples 2 to 9 Most of the steps in Examples 2-9 are the same as those in Example 1. The difference is that in step S11 of this example, the mass ratio of hydrophilic particles to styrene-butadiene rubber is different, the solid content of the first slurry is different, and the corresponding θ1, θ2-θ1, P1, P2, τ1, τ2 are different, as shown in Table 1.

[0179] Table 1 Examples 10-19 Examples 10-19 are mostly the same as Example 1, except that the mass ratio of the first-size hydrophilic particles to the second-size hydrophilic particles is different, the D50 particle size of the first-size hydrophilic particles and the D50 particle size of the second-size hydrophilic particles are different, P1, P2, τ1, and τ2 are different, and the average pore size of the mesopores and the average pore size of the micropores are different, as shown in Table 2.

[0180] Table 2 Example 20 Most of the steps in this embodiment are the same as those in Embodiment 1. The difference is that the hydrophilic particles used in step S11 are hydrophilic modified alumina. The rest are the same as in Embodiment 1, where θ2=46°, θ1=10°, P1=72%, P2=44%, τ1=1.7, and τ2=3.6.

[0181] Example 21 Example 21 is largely the same as Example 1, except that in step S4, the mass content of fluoroethylene carbonate is 3%, the mass content of hexamethyldisiloxane is 1%, and the mass content of perfluoropolyether additives is 0.5%. The rest is the same as in Example 1. The surface tension γ of the electrolyte was tested to be 24.9 mN / m, the viscosity η was 1.75 mPa·s, and the conductivity was 9.2 mS / cm.

[0182] Example 22 Most of the steps in this embodiment are the same as those in Example 1, except that in step S4, the mass content of fluoroethylene carbonate is 10%, the mass content of hexamethyldisiloxane is 3%, and the mass content of perfluoropolyether additives is 2%. The rest are the same as in Example 1. The surface tension γ of the above electrolyte was tested to be 24.8 mN / m, the viscosity η was 1.68 mPa·s, and the conductivity was 9.4 mS / cm.

[0183] Example 23 Most of the steps in this embodiment are the same as those in Example 1, except that in step S4, the mass content of fluoroethylene carbonate is 5%, the mass content of hexamethyldisiloxane is 2%, and the mass content of perfluoropolyether additives is 1%. The rest are the same as in Example 1. The surface tension γ of the above electrolyte was tested to be 24.2 mN / m, the viscosity η was 1.62 mPa·s, and the conductivity was 9.6 mS / cm.

[0184] Example 24 Most of the steps in this embodiment are the same as those in Example 1, except that in step S4, the molar concentration of lithium hexafluorophosphate is 1.0 mol / L and the molar concentration of lithium difluorosulfonylimide is 0.1 mol / L. The rest is the same as in Example 1. The surface tension γ of the above electrolyte was tested to be 24.8 mN / m, the viscosity η was 1.68 mPa·s, and the conductivity was 9.1 mS / cm.

[0185] Example 25 Most of the steps in this embodiment are the same as those in Example 1, except that in step S4, the molar concentration of lithium hexafluorophosphate is 1.2 mol / L and the molar concentration of lithium difluorosulfonylimide is 0.3 mol / L. The rest is the same as in Example 1. The surface tension of the electrolyte was tested to be 24.2 mN / m, the viscosity η was 1.72 mPa·s, and the conductivity was 9.8 mS / cm.

[0186] Example 26 Most of the steps in this embodiment are the same as those in Example 1, except that in step S4, the molar concentration of lithium hexafluorophosphate is 1.0 mol / L and the molar concentration of lithium difluorosulfonylimide is 0.4 mol / L. The rest is the same as in Example 1. The surface tension γ of the above electrolyte was tested to be 24.5 mN / m, the viscosity η was 1.78 mPa·s, and the conductivity was 9.2 mS / cm.

[0187] Comparative Example 1 Most of the steps in this comparative example are the same as those in Example 1, except that Comparative Example 1 omits step S1 and uses a PE-based membrane 1; the rest is the same as in Example 1. The PE-based membrane has a porosity of 45%, a contact angle with the electrolyte of 62°, and a tortuosity of 3.8.

[0188] Comparative Example 2 Most of the steps in this comparative example are the same as those in Example 1, except that in Comparative Example 2, the membrane 1 is without step S11, and the hydrophilic coating 102 is not prepared in step S13. Only the second slurry is coated on the surface of the PE base film. The rest is the same as in Example 1. The membrane in Comparative Example 2 has a porosity of 42%, a contact angle with the electrolyte of 45°, and a tortuosity of 3.4.

[0189] Comparative Example 3 Most of the steps in this comparative example are the same as those in Example 1, except that Comparative Example 3 omits step S1, and the diaphragm 1 used is a commercially available diaphragm 1 with a ceramic coating. The rest is the same as in Example 1. The diaphragm 1 of Comparative Example 3 has a porosity of 45%, a contact angle with the electrolyte of 35°, and a tortuosity of 3.0.

[0190] Comparative Example 4 This comparative example is largely the same as Example 1, except that in step S4, the mass content of fluoroethylene carbonate is 2%, the mass content of hexamethyldisiloxane is 0.5%, and the mass content of perfluoropolyether additives is 0.1%. The rest is the same as in Example 1. The surface tension γ of the above electrolyte was tested to be 28.5 mN / m, the viscosity η was 1.85 mPa·s, and the conductivity was 8.8 mS / cm.

[0191] Comparative Example 5 This comparative example is largely the same as Example 1, except that in step S4, the mass content of fluoroethylene carbonate is 12%, the mass content of hexamethyldisiloxane is 4%, and the mass content of perfluoropolyether additives is 2.5%. The rest is the same as in Example 1. The surface tension γ of the electrolyte was tested to be 24.5 mN / m, the viscosity η was 1.92 mPa·s, and the conductivity was 8.9 mS / cm.

[0192] Comparative Example 6 This comparative example is largely the same as Example 1, except that in step S4, no surface tension reducing additives are added (fluorinated ethylene carbonate, hexamethyldisiloxane, and perfluoropolyether acyl fluoride are all omitted), and only the basic solvent and lithium salt are used; the rest is the same as in Example 1. The surface tension γ of the above electrolyte was tested to be 32.5 mN / m, the viscosity η was 2.10 mPa·s, and the conductivity was 8.5 mS / cm.

[0193] Comparative Example 7 This comparative example is largely the same as Example 1, except that in step S4, the molar concentration of lithium hexafluorophosphate is 0.8 mol / L and the molar concentration of lithium difluorosulfonylimide is 0.3 mol / L. The rest is the same as in Example 1. The surface tension γ of the above electrolyte was tested to be 25.1 mN / m, the viscosity η was 1.65 mPa·s, and the conductivity was 8.5 mS / cm.

[0194] Test methods (1) The contact angle test method is as follows: Obtain a test electrolyte with an EC / DMC / EMC volume ratio of 1:1:1; using a contact angle meter, place the sample on the test platform and allow the test electrolyte to drip naturally onto the sample surface. Once the droplet shape is completely stable, take five test points of the droplet, measure the contact angle values ​​at each test point, and take the average value.

[0195] (2) P1 and P2 were tested using the immersion method: Weigh the sample dry weight m 干 Immerse the sample in a test electrolyte solution with an EC / DMC / EMC volume ratio of 1:1:1 for 5-10 minutes. Remove the sample and allow excess immersion solution to drip off naturally. Weigh the wet weight (m). 湿 The porosity of the sample = (m 湿 -m 干 / Test electrolyte density.

[0196] (3) Test τ1 and τ2.

[0197] Battery performance test: The batteries prepared in the above embodiments and comparative examples were subjected to the following tests. (1) Cyclic life test at 25℃: The battery prepared above was placed at room temperature of 25°C and charged to 4.45V with a constant current of 3C. Then it was charged at a constant voltage of 4.45V with a cutoff current of 0.05C. Then it was discharged to 3.0V with a constant current of 1C. After 300 cycles, the capacity retention rate was recorded. The capacity retention rate = discharge capacity of the 500th cycle C2 / average discharge capacity of the 1st to 3rd cycles C1 × 100%.

[0198] After 300 cycles, the battery was fully charged and disassembled to observe whether lithium plating had occurred on the negative electrode 3 in the arc-shaped area. The method for determining whether lithium plating had occurred is as follows: No lithium plating: No lithium plating in the arc-shaped negative electrode 3.

[0199] Slight lithium plating: The total area of ​​lithium plating in the arc-shaped negative electrode 3 is less than 5% of the total area of ​​the arc-shaped negative electrode 3.

[0200] Severe lithium plating: The total area of ​​lithium plating in the arc-shaped negative electrode 3 is greater than or equal to 5% of the total area of ​​the arc-shaped negative electrode 3.

[0201] Table 3 Continued from Table 3 As shown in Tables 1-3, comparing Example 1 and Comparative Examples 1-3, the separator 1 used in Comparative Example 1 is a PE-based membrane, the separator 1 used in Comparative Example 2 has a hydrophobic coating 103 coated on the surface of the PE-based membrane, and the separator 1 used in Comparative Example 3 has a ceramic coating coated on the surface of the PE-based membrane. In the batteries of Comparative Examples 1-3, the negative electrode 3 exhibits severe lithium plating and low capacity retention during room temperature cycling. This indicates that in the lithium-ion battery provided in this application, multiple hydrophobic coatings 103 are spaced apart in the functional layer of the separator 1, with a hydrophilic coating 102 between each two adjacent hydrophobic coatings 103, or a hydrophobic coating 103 between each two adjacent hydrophilic coatings 102; and the connection between the hydrophilic coating 102 and the hydrophobic coating 103 is... At the junction, the edge of the hydrophilic coating 102 at least partially overlaps with the edge of the hydrophobic coating 103, which can form a wetting gradient between the hydrophilic coating 102 and the hydrophobic coating 103, generating a sufficient interfacial energy difference. This drives the electrolyte to flow directionally from the region of the hydrophobic coating 103 to the region of the hydrophilic coating 102, achieving dynamic balance of the electrolyte. This enables the electrolyte to preferentially migrate and reside in the straight area of ​​the wound electrode core (corresponding to the region of the hydrophobic coating 103) to the arc area of ​​the wound electrode core (corresponding to the region of the hydrophilic coating 102). Through the synergistic effect of multi-level capillary action, intelligent directional distribution of the electrolyte is achieved, thereby solving the problem of electrolyte scarcity at the arc of the battery during long cycles, fundamentally solving the problem of lithium plating at the arc of the wound cell, and improving the fast charging performance and cycle life of the battery.

[0202] Comparing Examples 1-3 with Examples 4 and 5, in Example 4, θ1 is equal to 15°, which does not satisfy θ1 < 15°. The wettability of the hydrophilic coating 102 is insufficient, and the electrolyte cannot effectively fill the pores at the arc of the wound electrode core. The problem of electrolyte drying in the arc area still exists, and lithium plating occurs on the negative electrode 3. In Comparative Example 5, θ2 is equal to 35°, which does not satisfy θ2 > 35°. The wetting gradient between the hydrophobic coating 103 and the hydrophilic coating 102 is reduced, the capillary driving force is reduced, and the electrolyte cannot effectively migrate to the arc area of ​​the wound electrode core. The distribution tends to be uniform, but the arc area may still lack electrolyte, and the problem of lithium plating still exists in the arc area of ​​the battery. This indicates that the contact angle θ2 between the hydrophobic coating 103 and the non-aqueous electrolyte is greater than 35°, while the contact angle θ1 between the hydrophilic coating 102 and the non-aqueous electrolyte is less than 15°. Through capillary force and interfacial energy regulation, the electrolyte can preferentially migrate and reside in the arc area of ​​the wound electrode core from the flat area. This solves the problem of electrolyte shortage at the arc area of ​​the battery during long cycles, fundamentally solves the problem of lithium plating at the arc of the wound cell, and improves the fast charging performance and cycle life of the battery.

[0203] Comparing Examples 1-3 and 7-8, it is shown that θ1 < 10° and θ2 > 40° are more conducive to driving the electrolyte to flow directionally from the region of hydrophobic coating 103 to the region of hydrophilic coating 102, achieving dynamic balance, improving the lithium deposition problem of the negative electrode 3 in the arc region, and further improving the cycle capacity retention rate of the battery.

[0204] Comparing Examples 1-3, 7-8 and Examples 4-6, 9, even if the conditions θ1<15°, θ2>35°, 65%≤P1≤80%, and P2≤50% are met, P1 / P2 does not satisfy P1 / P2≥1.5. After 300 cycles, lithium plating occurs on the negative electrode 3, and the battery's cycle capacity retention is low. This indicates that while satisfying θ1<15°, θ2>35°, 65%≤P1≤80%, and P2≤50%, satisfying P1 / P2≥1.5 results in a high cycle capacity retention, effectively solving the lithium plating problem on the negative electrode 3.

[0205] Comparing Examples 1-3 with Examples 4 and 9, it is shown that satisfying τ1 < 2.0 improves the liquid retention capacity of the hydrophilic coating 102, solves the lithium plating problem of the negative electrode 3 caused by lithium-ion congestion, and improves the battery cycle performance. Satisfying τ2 > 3.0 facilitates the effective migration of electrolyte in the hydrophobic coating 103 region to the hydrophilic coating 102 region, increases the electrolyte retention capacity in the hydrophilic coating 102 region, and improves the battery cycle performance.

[0206] Comparing Examples 1, 12-16 and Examples 10-11, 17-19, the mass ratio of the first-size hydrophilic particles to the second-size hydrophilic particles is in the range of (60-70):(30-40). The porosity P1 of the resulting hydrophilic coating 102 satisfies the condition 65%≤P1≤80%, and the porosity P2 of the hydrophobic coating 103 satisfies the condition P2≤50%, as well as the condition P1 / P2≥1.5. The average pore size of the micropores is in the range of 2nm~50nm, and the average pore size of the mesopores is in the range of 50nm~200nm. The resulting battery has a high cycle capacity retention rate, can cycle for 300 cycles at room temperature, and has no lithium plating on the negative electrode 3, effectively solving the lithium plating problem of the negative electrode 3.

[0207] A comparison of Example 1 and Example 20 shows that as long as the hydrophilic particles in the hydrophilic coating 102 are hydrophilic ceramic particles, they can improve the problem of lithium deposition in the arc region of the negative electrode 3 and improve the cycle performance of the battery.

[0208] Comparing Examples 1, 21-23, and Comparative Examples 4-6, in Comparative Example 5, the mass content of fluorocarbonate additives was greater than 3%~10%, the mass content of linear siloxane additives was greater than 1%~3%, and the mass content of perfluoropolyether additives was greater than 0.2%~2%, resulting in an electrolyte viscosity greater than 1.8 mPa·s. In Comparative Example 4, the mass content of fluorocarbonate additives was less than 3%~10%, the mass content of linear siloxane additives was less than 1%~3%, and the mass content of perfluoropolyether additives was less than 0.2%~2%. When the mass content of the additive is less than 0.2% to 2%, the surface tension γ of the resulting electrolyte is greater than 25 mN / m. Comparative Example 6 does not contain any additives to reduce surface tension, resulting in an excessively high surface tension and viscosity of the electrolyte. The batteries in Comparative Examples 4-6 have low cycle capacity retention and severe lithium plating. This indicates that while the separator 1 meets the functional requirements of this application, the electrolyte must also meet the conditions of γ < 25 mN / m and η < 1.8 mPa·s to obtain a battery with high cycle capacity retention and solve the lithium plating problem in the arc region of the negative electrode 3.

[0209] Comparing Examples 1, 24-25, and Examples 26 with Comparative Example 7, the molar concentration of lithium hexafluorophosphate in Comparative Example 7 was not in the range of 1.0 mol / L to 1.2 mol / L, and the electrolyte did not meet the conditions of γ < 25 mN / m and η < 1.8 mPa·s. This resulted in severe lithium plating on the negative electrode 3 and a decrease in battery cycle capacity retention. In Example 26, the molar concentration of lithium difluorosulfonylimide was not in the range of 0.1 mol / L to 0.3 mol / L, and the negative electrode 3 showed slight lithium plating, resulting in a low battery cycle capacity retention. This indicates that when the molar concentration of lithium hexafluorophosphate in the electrolyte is within the range of 1.0 mol / L to 1.2 mol / L, and the molar concentration of lithium difluorosulfonylimide is within the range of 0.1 mol / L to 0.3 mol / L, and the electrolyte meets the conditions of γ < 25 mN / m and η < 1.8 mPa·s, the resulting battery exhibits a high cycle capacity retention. After 300 cycles, no lithium plating occurs in the arc region of the negative electrode 3.

[0210] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A lithium-ion battery, characterized in that, It includes a non-aqueous electrolyte and a wound electrode core, wherein the surface tension of the non-aqueous electrolyte is γ, γ < 25 mN / m; and / or, the viscosity of the non-aqueous electrolyte is η, η < 1.8 mPa·s; The wound electrode core includes a diaphragm (1), the diaphragm (1) includes a base film (101) and a functional layer, the functional layer being disposed on at least one side surface of the base film (101); The functional layer includes multiple hydrophilic coatings (102) and multiple hydrophobic coatings (103). The multiple hydrophobic coatings (103) are spaced apart, and a hydrophilic coating (102) is provided between each two adjacent hydrophobic coatings (103), or a hydrophobic coating (103) is provided between each two adjacent hydrophilic coatings (102). At the junction of the hydrophilic coating (102) and the hydrophobic coating (103), the edge of the hydrophilic coating (102) and the edge of the hydrophobic coating (103) at least partially overlap. The wound electrode core includes a flat region and an arc region, the hydrophilic coating (102) is located in the arc region, and the hydrophobic coating (103) is located in the flat region.

2. The lithium-ion battery according to claim 1, characterized in that, The contact angle between the hydrophilic coating (102) and the non-aqueous electrolyte is θ1, where θ1 < 15°; And / or, the contact angle between the hydrophobic coating (103) and the non-aqueous electrolyte is θ2, where θ2 > 35°.

3. The lithium-ion battery according to claim 1 or 2, characterized in that, The contact angle between the hydrophobic coating (103) and the non-aqueous electrolyte is θ2, and the contact angle between the hydrophilic coating (102) and the non-aqueous electrolyte is θ1, where θ2-θ1≥15°.

4. The lithium-ion battery according to claim 1, characterized in that, The porosity of the hydrophilic coating (102) is P1, 65%≤P1≤80%; And / or, the porosity of the hydrophobic coating (103) is P2, where P2 ≤ 50%.

5. The lithium-ion battery according to claim 1 or 4, characterized in that, The porosity of the hydrophilic coating (102) is P1, and the porosity of the hydrophobic coating (103) is P2, with P1 / P2 ≥ 1.

5.

6. The lithium-ion battery according to claim 1, characterized in that, The tortuosity of the hydrophilic coating (102) is τ1, where τ1 < 2.0; And / or, the tortuosity of the hydrophobic coating (103) is τ2, where τ2 > 3.

0.

7. The lithium-ion battery according to claim 1, characterized in that, The hydrophilic coating (102) includes hydrophilic particles, which include hydrophilic particles of a first size and hydrophilic particles of a second size. Multiple micropores and multiple mesopores are provided between the first size hydrophilic particles and the second size hydrophilic particles. The average pore size of the micropores is 2nm~50nm, and the average pore size of the mesopores is 50nm~200nm.

8. The lithium-ion battery according to claim 7, characterized in that, The mass ratio of the first-size hydrophilic particles to the second-size hydrophilic particles is (60-70):(30-40).

9. The lithium-ion battery according to claim 7, characterized in that, The D50 particle size range of the first-size hydrophilic particles is 100nm-300nm, and the D50 particle size range of the second-size hydrophilic particles is 10nm-30nm.

10. The lithium-ion battery according to claim 7, characterized in that, The hydrophilic particles include hydrophilic ceramic particles; The hydrophobic coating (103) includes a hydrophobic polymer, which includes a fluoropolymer, and the fluoropolymer includes at least one of polyvinylidene fluoride copolymer, polytetrafluoroethylene (PTFE), and perfluorosulfonic acid resin.

11. The lithium-ion battery according to claim 1, characterized in that, The thickness of the hydrophilic coating (102) is 3μm to 6μm, and the thickness of the hydrophobic coating (103) is 1μm to 3μm.

12. The lithium-ion battery according to claim 1, characterized in that, The method for preparing the diaphragm includes the following steps: Hydrophilic particles, a first binder, and a first solvent are mixed evenly to obtain a first slurry containing hydrophilic particles; the mass ratio of the hydrophilic particles to the first binder is (90~98):(10~2); the solid content of the first slurry is 30%~50%. A second slurry containing a hydrophobic polymer is obtained, wherein the solid content of the second slurry is 15% to 40%. The second slurry is applied intermittently to at least one side surface of the base film (101), dried to obtain a hydrophobic coating (103), and the first slurry is applied between each adjacent two hydrophobic coatings (103), dried to obtain a hydrophilic coating (102); or the first slurry is applied intermittently to at least one side surface of the base film (101), dried to obtain a hydrophilic coating (102), and the second slurry is applied between each adjacent two hydrophilic coatings (102), dried to obtain a hydrophobic coating (103). Furthermore, at the junction of the hydrophilic coating (102) and the hydrophobic coating (103), the edge of the hydrophilic coating (102) and the edge of the hydrophobic coating (103) at least partially overlap, and the membrane (1) is obtained by drying.

13. The lithium-ion battery according to claim 1, characterized in that, The non-aqueous electrolyte includes additives; the additives include fluorocarbonate additives, linear siloxane additives, and perfluoropolyether additives, wherein the mass content of the fluorocarbonate additives in the non-aqueous electrolyte is 3% to 10%; The linear siloxane additive in the non-aqueous electrolyte has a mass content of 1% to 3%; The mass content of the perfluoropolyether additive in the non-aqueous electrolyte is 0.2% to 2%.

14. The lithium-ion battery according to claim 1, characterized in that, The non-aqueous electrolyte also includes lithium salts, including lithium hexafluorophosphate and lithium difluorosulfonylimide. In the non-aqueous electrolyte, the molar concentration of lithium hexafluorophosphate is n1, and the molar concentration of lithium difluorosulfonylimide is n2, with n1:n2 being (10~12):(1~3).

15. The lithium-ion battery according to claim 14, characterized in that, n1 is 1.0 mol / L to 1.2 mol / L; n2 is 0.1 mol / L to 0.3 mol / L.

Images