Lithium battery separator, lithium ion battery and electric device

Abstract

The application belongs to the technical field of lithium ion battery separators, and particularly relates to a lithium battery separator, a lithium ion battery and an electric device, which comprises a base film PE and a functional coating layer facing a positive electrode side surface; the functional coating layer comprises inorganic heat-resistant particles and a binder; the inorganic heat-resistant particles are physical mixed powders of yttria-stabilized zirconia and monoclinic zirconia; the doping amount of yttria in the yttria-stabilized zirconia is 3-5 mol%; the mass ratio of the yttria-stabilized zirconia to the monoclinic zirconia is 1:1-4:1; the solid electrolyte is at least one of lithium lanthanum zirconium oxide, lithium lanthanum titanium oxide or a sulfide type solid electrolyte, and the addition amount is 5-20% of the total weight of the functional coating layer; the composite functional coating layer further comprises a crosslinking agent, the crosslinking agent is a polyurethane crosslinking agent or an epoxy crosslinking agent, and the addition amount is 0.5-2% of the total weight of the functional coating layer.

Description

Technical Field

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

[0002] With the widespread application of high-nickel ternary cathodes in power batteries, their inherent poor thermal stability, aggravated high-voltage interface side reactions, and dendrite puncture risk have become core bottlenecks restricting battery safety and cycle life. While traditional single-layer ceramic separators (such as boehmite / Al2O3 coatings) can improve thermal stability, they have three limitations: first, the dehydration reaction of boehmite causes coating pulverization, with a thermal shrinkage rate still >3% at 180℃; second, a single ceramic component cannot simultaneously achieve ion conductivity and dendrite resistance; and third, homogeneous coatings cannot adapt to the differentiated requirements of positive and negative electrodes. Especially during high-voltage cycling, the rapid increase in positive electrode interface resistance and the uncontrollable growth of lithium dendrites lead to accelerated capacity decay.

[0003] Therefore, overcoming the penetration defect of lithium dendrites in single-layer ceramic separators is a technical problem that urgently needs to be solved in this field.

[0004] It should be noted that the information disclosed in this background section is only for understanding the background technology of the present application concept, and therefore, the above description is not considered to constitute prior art information. Summary of the Invention

[0005] This disclosure provides at least one lithium battery separator, a lithium-ion battery, and an electrical device.

[0006] In a first aspect, embodiments of this disclosure provide a lithium battery separator, comprising: a base film PE and a functional coating facing the positive electrode side surface; the functional coating comprises inorganic heat-resistant particles and a binder; the inorganic heat-resistant particles are a physical mixture powder of yttrium-stabilized zirconium oxide and monoclinic zirconium oxide; wherein the doping amount of yttrium oxide in the yttrium-stabilized zirconium oxide is 3-5 mol%; the mass ratio of the yttrium-stabilized zirconium oxide to the monoclinic zirconium oxide is 1:1 to 4:1; the solid electrolyte is at least one of lithium lanthanum zirconium oxide, lithium lanthanum titanium oxide, or sulfide-type solid electrolyte, and its addition amount is 5-20% of the total weight of the functional coating; the composite functional coating further comprises a crosslinking agent, the crosslinking agent being a polyurethane crosslinking agent or an epoxy crosslinking agent, and its addition amount is 0.5-2% of the total weight of the functional coating.

[0007] In one alternative embodiment, the adhesive comprises at least one of polyvinylidene fluoride, polyimide, and polyetherimide; the adhesive accounts for 3 to 10% of the total weight of the functional coating.

[0008] In one optional embodiment, the functional coating has a thickness of 2–6 μm and a porosity of 45–55%.

[0009] In one optional embodiment, the lithium battery separator has a electrolyte absorption rate of [missing information] at 25°C.

[0010] ≥260%.

[0011] In one optional embodiment, the lithium battery separator has an ionic conductivity ≥1.8 mS / cm at 25°C.

[0012] In one alternative embodiment, the contact angle of the diaphragm with the electrolyte at 25°C is ≤25°.

[0013] In one optional embodiment, the diaphragm, after being heat-treated at 180°C for 1 hour, exhibits a longitudinal shrinkage rate ≤2.5% and a transverse shrinkage rate ≤2.2%.

[0014] Secondly, embodiments of this disclosure also provide a lithium-ion battery, including a positive electrode, a negative electrode, an electrolyte, and a lithium battery separator as described above; wherein the positive electrode includes a positive electrode active material with the chemical formula [chemical formula missing].

[0015] LiNi x Co y Mn z O2 constitutes the NCM ternary cathode material and satisfies x+y+z=1, x≥0.8; the anode includes a negative electrode active material, including at least one of artificial graphite, natural graphite, silicon-oxygen materials and silicon-carbon materials.

[0016] In one optional embodiment, the lithium-ion battery retains ≥86% of its capacity after 600 cycles at 25°C and 1C charge / discharge conditions.

[0017] Thirdly, embodiments of this disclosure also provide an electrical device, including: a charge / discharge control module, and a lithium-ion battery as described above, controlled by the charge / discharge control module.

[0018] The beneficial effects of this invention are that the lithium battery separator, lithium-ion battery, and power device, through the design of an asymmetric functional coating on the positive electrode side, innovatively adopt a physical hybrid system of yttrium-stabilized zirconium oxide (YSZ) and monoclinic zirconium oxide (ZrO2). The ultra-high melting point of YSZ inhibits thermal shrinkage, and the phase change toughening effect of ZrO2 resists dendrite penetration. Combined with a solid electrolyte, it constructs additional solid-state ion migration channels, forming a solid-liquid synergistic lithium-conducting effect with the liquid electrolyte. By optimizing the binder ratio and coating thickness, while ensuring ionic conductivity and electrolyte wettability, it achieves a capacity retention rate of ≥86% after 600 cycles in a high-nickel system, providing a reference for the synergistic effect of high energy density and high safety.

[0019] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention are realized and obtained through the structures particularly pointed out in the description.

[0020] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described in detail below. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] As used herein, the phrases “in one embodiment,” “according to one embodiment,” “in some embodiments,” etc., generally refer to the fact that a particular feature, structure, or characteristic following the phrase can be included in at least one embodiment of this disclosure. Therefore, a particular feature, structure, or characteristic can be included in more than one embodiment of this disclosure, such that these phrases do not necessarily refer to the same embodiment. As used herein, the terms “example,” “exemplary,” etc., are used to “serve as an example, instance, or illustration.” Any implementation, aspect, or design described herein as “example” or “exemplary” is not necessarily to be construed as preferred or superior to other implementations, aspects, or designs. Rather, the use of the terms “example,” “exemplary,” etc., is intended to present concepts in a specific manner.

[0023] In this document, as used herein, expressions such as “at least one of…” modify the entire list of elements when following a list of elements, rather than individual elements in the list. For example, the expression “at least one of a, b, and c” should be understood to include only a, only b, only c, both a and b, both a and c, both b and c, or all of a, b, and c.

[0024] The terminology used herein is for the purpose of describing specific exemplary configurations only and is not intended to be limiting. As used herein, the singular articles “a,” “an,” and “the” may also be intended to include plural forms unless otherwise clearly stated herein. The terms “comprising,” “including,” and “having” are inclusive and thus specify the presence of features, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and / or combinations thereof. The method steps, processes, and operations described herein should not be construed as requiring them to be performed in the specific order discussed or shown, unless specifically identified as such. Additional or alternative steps may be employed.

[0025] The following describes some embodiments of the present invention in detail. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0026] This disclosure provides a lithium battery separator, comprising: a base film PE and a functional coating facing the positive electrode side surface; the functional coating comprises inorganic heat-resistant particles and a binder; the inorganic heat-resistant particles are a physical mixture powder of yttrium-stabilized zirconium oxide and monoclinic zirconium oxide; wherein the doping amount of yttrium oxide in the yttrium-stabilized zirconium oxide is 3-5 mol%; the mass ratio of the yttrium-stabilized zirconium oxide to the monoclinic zirconium oxide is 1:1 to 4:1; the solid electrolyte is at least one of lithium lanthanum zirconium oxide (LLZO), lithium lanthanum titanium oxide (LLTO), or sulfide-type solid electrolyte, and its addition amount is 5-20% of the total weight of the functional coating; the composite functional coating further comprises a crosslinking agent, the crosslinking agent being a polyurethane crosslinking agent or an epoxy crosslinking agent, and its addition amount is 0.5-2% of the total weight of the functional coating.

[0027] In some embodiments, specifically, the binder includes at least one of polyvinylidene fluoride (PVDF), polyimide (PI), and polyetherimide (PEI); the binder accounts for 3 to 10% of the total weight of the functional coating.

[0028] In some embodiments, specifically, the thickness of the functional coating is 2–6 μm and the porosity is 45–55%.

[0029] In some embodiments, specifically, the lithium battery separator has an electrolyte absorption rate of ≥260% at 25°C.

[0030] In some embodiments, specifically, the lithium battery separator has an ionic conductivity ≥1.8 mS / cm at 25°C.

[0031] In some embodiments, specifically, the contact angle of the diaphragm with the electrolyte at 25°C is ≤25°.

[0032] In some embodiments, specifically, after heat treatment at 180°C for 1 hour, the diaphragm exhibits a longitudinal shrinkage rate ≤2.5% and a transverse shrinkage rate ≤2.2%.

[0033] This disclosure also provides a lithium-ion battery, including a positive electrode, a negative electrode, an electrolyte, and a lithium battery separator as described above; wherein the positive electrode includes a positive electrode active material with the chemical formula LiNi. x Co y Mn z O2 constitutes the NCM ternary cathode material and satisfies x+y+z=1, x≥0.8; the anode includes a negative electrode active material, including at least one of artificial graphite, natural graphite, silicon-oxygen materials and silicon-carbon materials.

[0034] In some embodiments, specifically, the lithium-ion battery retains ≥86% of its capacity after 600 cycles at 25°C and 1C charge / discharge conditions.

[0035] This disclosure also provides an electrical device, including: a charge / discharge control module, and a lithium-ion battery as described above, controlled by the charge / discharge control module.

[0036] The battery fabrication method is tested, taking Example 1 as an example:

[0037] 1. Method for manufacturing positive electrode plates:

[0038] The positive electrode active material (high-nickel ternary material LiNi) 0.8 Co 0.1 Mn 0.1 O2), conductive carbon black (conductive agent), and polyvinylidene fluoride (PVDF) (binder) were mixed in a mass ratio of 96:2:2. Then, N-methylpyrrolidone (NMP) was added, and the mixture was stirred and homogenized to form a stable positive electrode slurry with a solid content of 70%. The positive electrode slurry was then uniformly coated onto a 12μm aluminum foil as the positive electrode current collector. After drying and cold pressing, the positive electrode sheet was obtained with a compaction density of 3.4 g / cm³. 3 .

[0039] 2. Method for manufacturing negative electrode plates:

[0040] Artificial graphite, silicon carbide material, conductive carbon nanotubes, thickener sodium carboxymethyl cellulose (CMC), and binder polyacrylic acid (PAA) were mixed in a mass ratio of 86:10:1.5:1:1.5. Deionized water was then added and the mixture was stirred to form a uniform and stable negative electrode slurry with a solid content of 40%. The negative electrode slurry was uniformly coated onto an 8μm thick copper foil as the negative electrode current collector. After drying and cold pressing, the negative electrode sheet was obtained with a compaction density of 1.6 g / cm³. 3 .

[0041] 3. Preparation of electrolyte:

[0042] An electrolyte was prepared by mixing lithium salt lithium hexafluorophosphate (LiPF6), organic solvents ethylene carbonate (EC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), ethylene sulfate (DTD), and vinylene carbonate (VC) in a mass percentage ratio of 10.0:20.0:55.0:2.0:8.0:5.0.

[0043] 4. Preparation of the diaphragm

[0044] YSZ (4 mol% Y₂O₃) and monoclinic ZrO₂ were mixed at a mass ratio of 1:1 to prepare inorganic heat-resistant particles. LLZO (lithium lanthanum zirconium oxide) solid electrolyte powder, comprising 10% of the total powder (inorganic particles + solid electrolyte) mass, was added. The powder mixture was dry-mixed for 30 min. PVDF binder, comprising 5% of the total solid mass (inorganic particles + solid electrolyte + binder), and polyurethane crosslinking agent, were added. The mixture was ball-milled with NMP solvent for 12 h to adjust the slurry solid content to 35%. A wet film of a specific thickness was coated onto the positive electrode side of a 12 μm PE base film, and after drying at 100 °C for 5 min, a 4.0 μm functional coating was obtained.

[0045] 5. Assembly of lithium-ion batteries:

[0046] The positive and negative electrode sheets are rolled and slit respectively, and then wound together with the separator to obtain a 21700 cylindrical battery core. The battery core is then welded to the connecting piece and installed into the battery casing. After completing the liquid injection, sealing and formation processes, the lithium-ion battery of Example 1 is obtained. The casing of the lithium-ion battery is cylindrical with the following dimensions: diameter: 21.0 mm, length: 70.0 mm.

[0047] Example 2

[0048] The mass ratio of YSZ:ZrO2 was adjusted to 4:1, the amount of LLZO added was 5%, and the rest was the same as in Example 1.

[0049] Example 3

[0050] The mass ratio of YSZ:ZrO2 was adjusted to 4:1, the amount of LLZO added was 20%, and the rest was the same as in Example 1.

[0051] Example 4:

[0052] The binder was replaced with polyimide (PI), and the crosslinking agent was adjusted accordingly to be a model suitable for PI. The rest was the same as in Example 1.

[0053] Example 5:

[0054] The binder was replaced with polyetherimide (PEI), and the crosslinking agent was adjusted accordingly to be a type compatible with PEI. The rest was the same as in Example 1.

[0055] Example 6:

[0056] Reduce the PVDF ratio to 3wt%, and the rest is the same as in Example 1.

[0057] Example 7:

[0058] Increase the PVDF ratio to 10 wt%, and the rest is the same as in Example 1.

[0059] Example 8:

[0060] The coating thickness was adjusted to 2.0 μm, and the rest was the same as in Example 1.

[0061] Example 9:

[0062] The coating thickness was adjusted to 6.0 μm, and the rest was the same as in Example 1.

[0063] Example 10:

[0064] The sulfide-type solid electrolyte (LPSCl) was used instead of LLZO. The preparation process was carried out under an inert atmosphere, and the remaining steps were the same as in Example 1.

[0065] Comparative Example 1:

[0066] No solid electrolyte was added (LLZO addition was 0%), and the rest was the same as in Example 1.

[0067] Comparative Example 2:

[0068] The mass ratio of YSZ:ZrO2 was adjusted to 0.8:1, and the rest was the same as in Example 1.

[0069] Comparative Example 3:

[0070] The mass ratio of YSZ:ZrO2 was adjusted to 5:1, and the rest was the same as in Example 1.

[0071] Comparative Example 4:

[0072] The PVDF ratio was reduced to 2 wt%, and the rest was the same as in Example 1.

[0073] Comparative Example 5:

[0074] The PVDF ratio was increased to 12 wt%, and the rest was the same as in Example 1.

[0075] Comparative Example 6:

[0076] The coating thickness was reduced to 1.5 μm, and the rest was the same as in Example 1.

[0077] Comparative Example 7:

[0078] The coating thickness was increased to 7.0 μm, and the rest was the same as in Example 1.

[0079] Comparative Example 8:

[0080] The amount of LLZO added was increased to 25%, and the rest was the same as in Example 1.

[0081] Method for determining diaphragm liquid absorption rate:

[0082] Cut the diaphragm into small circular pieces with a diameter of 14 mm, immerse them in the electrolyte until the mass no longer changes, and measure the mass before and after immersion. The mass before immersion is recorded as M1, and the mass after immersion is recorded as M2. The liquid absorption rate is calculated as (M2-M1) / M1×100%.

[0083] Methods for determining ionic conductivity:

[0084] (1) Sample preparation: The prepared three-layer composite membrane was immersed in an electrolyte (such as 1M LiPF6, EC / DEC = 1:1, v / v) for at least 12 hours to ensure sufficient wetting.

[0085] (2) Assemble a symmetrical cell: In an inert atmosphere (such as a glove box), two stainless steel electrodes (SS) are sandwiched with a membrane that has been wetted with electrolyte to form an SS|membrane|SS symmetrical structure, which is an impedance testing device with "no active electrode".

[0086] (3) Test equipment and parameters: Use an electrochemical workstation to perform AC impedance testing (EIS). The test conditions are as follows: frequency range: 1MHz~0.1Hz, AC disturbance voltage: 5~10mV, test temperature: 60℃ (temperature can be controlled by a constant temperature chamber).

[0087] Formula for calculating electrical conductivity:

[0088] Where: σ is the ionic conductivity (S / cm), L is the membrane thickness (cm), R is the high-frequency semicircular intercept in the Nyquist plot (Ω), and A is the effective area of ​​the peripheral electrode (cm²). 2 ).

[0089] Method for measuring diaphragm contact angle:

[0090] A micro-electrolyte (EC:DMC = 1:1) of 2-5 μL was dropped onto the treated and cleaned diaphragm surface using a micro-syringe. A side view image of the droplet was taken, and the droplet profile was fitted using software (such as the Young-Laplace equation or ellipse fitting method). The contact angle was calculated after the baseline was automatically detected.

[0091] Method for determining the heat shrinkage rate of diaphragms:

[0092] Cut the diaphragm into rectangular samples of 10mm × 100mm. Lay the samples flat between A4 sheets of paper to prevent high-temperature curling. Place them in an oven with a temperature control accuracy of ±1℃, set the temperature to 180℃, heat for 1 hour without external force, and then cool to room temperature. Use a vernier caliper (accuracy 0.01mm) or a laser rangefinder to measure the initial length L0 and the length L1 after heating, respectively. Calculate the shrinkage rate according to the formula (L0-L1) / L0×100%. Three samples should be tested in each direction and the average value should be taken. If the deviation exceeds 5%, the test should be repeated.

[0093] Cyclic performance testing methods:

[0094] The lithium battery was placed in a 25°C constant temperature chamber for 6 hours and tested according to the following steps:

[0095] (1) First round of constant current and constant voltage charging: Charge at a constant current of 0.1C to 4.2V, then switch to constant voltage charging until the current drops to 0.1C.

[0096] (2) Let it stand for 30 minutes after charging is complete.

[0097] (3) Perform constant current discharge, and discharge to 2.5V at a rate of 0.1C.

[0098] (4) Cyclic charge and discharge process: Charge at a constant current rate of 1C to 4.2V. Let stand for 30 minutes again. Discharge at a constant current rate of 1C to 2.5V.

[0099] (5) Repeat the above charging and discharging process for a total of 600 cycles.

[0100] The discharge capacities Q1 and Q600 of the battery after 1 cycle and 600 cycles were statistically analyzed, and the capacity retention rate of the battery was calculated as: Q600 / Q1×100%.

[0101] Specifically, the test performance results of Examples 1-8 and Comparative Examples 1-6 are shown in Table 1 below.

[0102] Table 1

[0103]

[0104] Examples 1-3 and Comparative Example 1 show that the amount of solid electrolyte (LLZO) added has a significant impact on the membrane performance.

[0105] Comparative Example 1, without the addition of LLZO, relies entirely on the liquid electrolyte absorbed by the coating pores for ion conduction. The ion conduction path is relatively simple and easily constrained by interfacial side reactions and changes in pore structure. Therefore, the ionic conductivity is relatively low (1.95 mS / cm), and the interfacial impedance is large during cycling, resulting in a low capacity retention rate (82.5%).

[0106] The performance improvement in Example 2 (with the addition of 5% LLZO) is crucial. The introduction of LLZO particles creates additional solid-state ion migration channels within the existing porous coating, forming a "solid-liquid synergistic" lithium conduction effect with the liquid electrolyte. This dual-channel mode significantly reduces the transport resistance of lithium ions in the separator, thereby greatly improving the bulk ionic conductivity (2.30 mS / cm), reducing polarization during battery charge and discharge, and ultimately resulting in excellent cycle life (89.5%).

[0107] Example 1 (with the addition of 10% LLZO) represents an optimal balance. This addition amount allows the LLZO particles to form a more continuous and effective ion conduction network in the coating without severely damaging the porous structure of the coating, and has no negative impact on electrolyte preservation and wettability. Therefore, the overall performance (ionic conductivity 2.25 mS / cm, capacity retention 88.7%) is optimal.

[0108] Example 3 (with the addition of 20% LLZO) further improved the ionic conductivity (2.35 mS / cm), but the addition of excess filler began to slightly clog the coating pores, possibly sacrificing some liquid uptake. However, its positive contribution to ion transport still dominated, and the cycling performance (89.8%) remained excellent. This comparison clearly demonstrates that the introduction of LLZO is the core of the performance leap, fundamentally improving transport kinetics by providing solid-state ion channels.

[0109] Examples 1-2 and Comparative Examples 2-3 show that the proportion of inorganic particles has a significant impact on membrane performance. The proportion of inorganic particles is crucial in determining the thermal stability of the coating.

[0110] In Comparative Example 2 (YSZ:ZrO2 = 0.8:1), the proportion of monoclinic zirconium oxide (ZrO2) was too high. Although the monoclinic phase itself has excellent heat resistance, it undergoes a reversible phase transition accompanied by volume change under temperature changes. This microscale instability may weaken the overall structural integrity of the coating, resulting in its thermal shrinkage rate (1.7% / 1.4%) not showing any advantage.

[0111] Example 1 (scale 1:1) achieved optimal performance synergy. Yttrium-stabilized zirconia (YSZ) has a stable cubic phase structure, while monoclinic zirconia (ZrO2) has extremely high thermal stability. When the two are physically mixed, they form a rigid and dimensionally stable composite framework that together resists shrinkage at high temperatures, resulting in excellent thermal shrinkage (1.5% / 1.2%).

[0112] Example 2 (ratio 4:1) further increased the proportion of YSZ, whose stable phase structure dominates in the coating, forming an extremely robust skeleton, thus exhibiting the best thermal dimensional stability (shrinkage rate 1.3% / 1.0%) in this series.

[0113] In contrast, Comparative Example 3 (5:1) had an excessively high YSZ ratio (outside the acceptable range). This could lead to poor particle size matching or changes in specific surface area, resulting in decreased slurry uniformity and reduced coating cohesion. Consequently, the binder could not adequately coat all the particles, ultimately causing the coating structure to become unstable at high temperatures, and the shrinkage rate to increase sharply (4.5% / 3.9%). This indicates that the two types of particles need to be blended in a specific ratio to achieve a synergistic effect of "1+1>2".

[0114] Examples 1, 6-7, and Comparative Examples 4-5 demonstrate the influence of the amount of binder (PVDF). The amount of binder directly determines the porosity and mechanical strength of the coating microstructure. Comparative Example 4 (2% PVDF) had a severely insufficient amount, failing to adequately coat and bond the inorganic particles and LLZO solid particles, resulting in a loose coating structure with poor cohesion. This structure not only has low strength but also excessively large pores and poor connectivity, making it unable to effectively lock in the electrolyte through capillary action. This manifests as a low electrolyte absorption rate (235%) and an increased contact angle (33°), leading to poor wettability.

[0115] Example 6 (PVDF 3%) achieved a higher porosity by minimizing the amount of binder occupying the pores while maintaining the basic integrity of the coating, thus exhibiting optimal liquid absorption (277%) and wettability (contact angle 20°). Example 1 (PVDF 5%) represents an ideal balance, providing strong adhesion to prevent powdering and material loss during cold pressing and winding, without excessively clogging ion transport channels.

[0116] The amount of PVDF 10% in Example 7 began to show negative effects. Excessive polymer covered part of the particle surface and blocked the micropores, resulting in a decrease in coating porosity. Consequently, there was an observable decrease in liquid absorption (263%) and wettability (contact angle 24°).

[0117] Comparative Example 5 (PVDF 12%) showed a severe over-addition. The large amount of binder formed a dense polymer film, severely clogging the porous structure of the coating and greatly hindering electrolyte wetting and lithium ion migration, leading to a comprehensive deterioration of all performance characteristics. This demonstrates that the amount of binder used needs to be appropriate; too much or too little will undermine the original design intent of the functional coating.

[0118] Examples 1, 8-9, and Comparative Examples 6-7 demonstrate that the thickness of the functional coating also affects the membrane performance. The coating thickness directly influences the balance between ion transport resistance and physical protection.

[0119] Comparative Example 6 (1.5 μm) had an excessively thin coating, which failed to form a continuous and complete protective layer on the base film surface. At high temperatures, the PE base film was more easily exposed to the thermal environment and underwent significant shrinkage (2.8% / 2.4%). Furthermore, the thin coating lacked sufficient ability to suppress lithium dendrites and had insufficient mechanical strength, resulting in poor cycle life (81.9%).

[0120] Example 8 (2 μm) thickness provides basic thermal protection and dendrite suppression, but due to the thinness of the protective layer, its thermal stability margin is insufficient, and the ionic conductivity (2.20 mS / cm) is also slightly lower due to the slightly weaker continuity of the LLZO network.

[0121] Example 1 (4 μm) represents the optimal balance of performance. At this thickness, the functional layer formed by LLZO and inorganic particles is very continuous and robust, providing excellent thermal shielding (shrinkage rate 1.5% / 1.2%) and mechanical protection, while the ion transport path is not significantly prolonged, and the ionic conductivity (2.25 mS / cm) and cycling performance (88.7%) are both excellent.

[0122] Example 9 (6 μm) further increased the protection strength, but the thicker coating meant that lithium ions had to travel a longer solid-liquid mixed path, and the bulk resistance began to increase, which slightly offset the gain brought by LLZO, resulting in an inflection point in ionic conductivity (2.23 mS / cm) and cycle performance (88.3%).

[0123] In Comparative Example 7 (7 μm), the excessively thick coating exacerbated the internal resistance problem, resulting in a significant decrease in ionic conductivity (1.78 mS / cm). Furthermore, the thick coating generates greater internal stress during winding, affecting interfacial contact and making it more susceptible to peeling and overall shrinkage under thermal shock, leading to a comprehensive decline in performance.

[0124] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A lithium battery separator, characterized in that, include: A composite functional coating consisting of a PE base film and a surface facing the positive electrode. The composite functional coating comprises inorganic heat-resistant particles, a binder, and a solid electrolyte; The inorganic heat-resistant particles are a physical mixture of yttrium-stabilized zirconium oxide and monoclinic zirconium oxide powder, wherein the doping amount of yttrium oxide in the yttrium-stabilized zirconium oxide is 3-5 mol%, and the mass ratio of yttrium-stabilized zirconium oxide to monoclinic zirconium oxide is 1:1 to 4:

1. The solid electrolyte is at least one of lithium lanthanum zirconium oxide, lithium lanthanum titanium oxide, or sulfide-type solid electrolyte, and its addition amount is 5-20% of the total weight of the inorganic heat-resistant particles and the solid electrolyte. The composite functional coating also includes a crosslinking agent, which is a polyurethane crosslinking agent or an epoxy crosslinking agent, and its addition amount is 0.5% to 2% of the total weight of the inorganic heat-resistant particles, solid electrolyte and binder; The adhesive includes at least one of polyvinylidene fluoride, polyimide, and polyetherimide; The binder accounts for 3 to 10% of the total weight of the inorganic heat-resistant particles, solid electrolyte, and binder; The thickness of the composite functional coating is 2–6 μm.

2. The lithium battery separator as described in claim 1, characterized in that: The porosity of the composite functional coating is 45-55%.

3. The lithium battery separator as described in claim 1, characterized in that: The lithium battery separator has an electrolyte absorption rate of ≥260% at 25°C.

4. The lithium battery separator as described in claim 1, characterized in that: The lithium battery separator has an ionic conductivity ≥1.8 mS / cm at 25℃.

5. The lithium battery separator as described in claim 1, characterized in that: The contact angle of the diaphragm with the electrolyte is ≤25° at 25°C.

6. The lithium battery separator as described in claim 1, characterized in that: After heat treatment at 180°C for 1 hour, the diaphragm exhibits a longitudinal shrinkage rate of ≤2.5% and a transverse shrinkage rate of ≤2.2%.

7. A lithium-ion battery, characterized in that, Includes a positive electrode, a negative electrode, an electrolyte, and a lithium battery separator as described in any one of claims 1-6; The positive electrode includes a positive electrode active material with the chemical formula LiNi. x Co y Mn z O2 constitutes the NCM ternary cathode material and satisfies x+y+z=1, x≥0.8; The negative electrode includes a negative electrode active material, which includes at least one of artificial graphite, natural graphite, silicon-oxygen materials, and silicon-carbon materials.

8. The lithium-ion battery as described in claim 7, characterized in that, The lithium-ion battery retains ≥86% of its capacity after 600 cycles at 25°C and 1C charge / 1C discharge conditions.

9. An electrical device, characterized in that, include: A charge / discharge control module, and a lithium-ion battery as described in any one of claims 7 or 8 controlled by the charge / discharge control module.

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