Solid electrolyte coating for high-nickel ternary positive electrode as well as preparation method and application of solid electrolyte coating

Abstract

The invention relates to a solid electrolyte coating for a high-nickel ternary positive electrode and a preparation method and application thereof, a functional coating is prepared on the surface of a positive electrode plate, and the functional coating comprises lithium titanium aluminum phosphate or similar oxides; the crystal structure of the oxide solid electrolyte has specific adsorption capacity on oxygen ions, effectively adsorbs free oxygen ions released by a positive electrode material under a thermal abuse condition, and inhibits a chain exothermic reaction; and the electronic insulation characteristic can construct an internal short-circuit barrier to ensure the thermal stability of the battery.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, and in particular relates to a solid electrolyte coating for high-nickel ternary cathodes, its preparation method, and its application. Background Technology

[0002] High-nickel ternary cathode materials (such as NCM811, NCA and LiNi with nickel content ≥90%) x Co-yMn-zO2 is a key material for improving the energy density of lithium-ion batteries. However, its inherent thermal and chemical instability severely restricts its safe application. High-nickel ternary cathode materials are prone to phase transition and release free oxygen under high voltage or high temperature conditions, triggering a violent exothermic reaction with the electrolyte, leading to thermal runaway. At the same time, violent interfacial side reactions and the dissolution of transition metal ions also exacerbate performance degradation and safety risks.

[0003] In existing technologies, a common improvement method is to coat the positive electrode surface, such as using oxide or fluoride coating layers. However, traditional coating materials are mostly insulators or semiconductors that block ions and electrons. Although they can isolate the positive electrode from the electrolyte to some extent, they often severely hinder lithium-ion transport, leading to increased internal resistance and deterioration of rate performance. In addition, traditional coating methods (such as solid-state sintering and atomic layer deposition) have limitations such as uneven coating, complex processes, high costs, or difficulty in large-scale production. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a solid electrolyte coating for high-nickel ternary cathodes, its preparation method, and its application.

[0005] The technical solution adopted in this invention is: a method for preparing a solid electrolyte coating for a high-nickel ternary cathode, wherein a slurry containing lithium titanium aluminum phosphate is prepared on the surface of the cathode material by microgravure printing and transfer coating process to form a solid electrolyte coating.

[0006] Preferably, the active ingredients in the slurry also include one or more of lithium lanthanum zirconium oxide, lithium lanthanum titanium oxide, and composite derivatives.

[0007] Preferably, the slurry includes the solvent N-methylpyrrolidone, and also includes a dispersant and / or a binder.

[0008] Preferably, the specific preparation method is as follows:

[0009] Step 1: Disperse the active ingredient containing lithium aluminum titanium phosphate in N-methylpyrrolidone to prepare a uniform slurry;

[0010] Step 2: Use microgravure printing equipment to coat the paste onto the surface of the positive electrode, and after drying, form a solid electrolyte coating.

[0011] Preferably, a solid electrolyte coating with a thickness of 2-10 μm is prepared on one side of the positive electrode sheet; or a solid electrolyte coating with a thickness of 6-14 μm is prepared on both sides of the positive electrode sheet.

[0012] Preferably, the lithium titanium aluminum phosphate has the general formula Li 1₊x Al x Ti 2₋x (PO4)3, where 0.1 < x < 0.5.

[0013] A method for preparing a solid electrolyte coating for a high-nickel ternary cathode, wherein the surface of the cathode is covered with a solid electrolyte coating.

[0014] Preferably, the positive electrode contains a high-nickel ternary positive electrode material, specifically LiNi. x Co_yMn_zO2 material, where x+y+z=1, x≥0.9.

[0015] A lithium secondary battery, comprising the positive electrode sheet as described in claim 7 or 8.

[0016] The advantages and positive effects of this invention are: it provides a solid electrolyte coating that can be used for the positive electrode of lithium batteries, especially suitable for high-nickel batteries, and can efficiently adsorb free oxygen. The solid electrolyte coating used for high-nickel ternary positive electrodes, its preparation method and application are also described. Furthermore, the solid electrolyte coating has good electronic insulation properties, which greatly improves the thermal stability of the battery. Attached Figure Description

[0017] Figure 1 Fully charged state DSC test results of commercial 9-series high-nickel cathode material powder;

[0018] Figure 2 Test results of the resistance of commercial 9-series high-nickel cathode. Detailed Implementation

[0019] The embodiments of the present invention will now be described with reference to the accompanying drawings.

[0020] This invention relates to a solid electrolyte coating for high-nickel ternary cathodes, its preparation method, and its application. A functional coating is prepared on the surface of the cathode sheet, comprising lithium aluminum titanium phosphate or similar oxides. The crystal structure of this oxide solid electrolyte coating exhibits a specific adsorption capacity for oxygen ions, effectively adsorbing free oxygen ions released by the cathode material under thermal abuse conditions and suppressing chain exothermic reactions. Its electronic insulation properties can construct an internal short-circuit barrier, ensuring the thermal stability of the battery.

[0021] In preparation, a functional coating slurry is first prepared. The active ingredient includes lithium titanium aluminum phosphate, and may also include at least one of lithium lanthanum zirconium oxide, lithium lanthanum titanium oxide, and composite derivatives. In some embodiments of the present invention, the general formula of lithium titanium aluminum phosphate is Li. 1₊ x Al x Ti 2₋x (PO4)3 (0.1 < x < 0.5), in addition to the active ingredients, the functional coating slurry also includes solvents and additives. The solvent is N-methylpyrrolidone, and the additives may include dispersants and / or binders. The dispersant may be PVP, and the binder may be polyvinylidene fluoride. The additives can improve the slurry properties and further improve the performance of the functional coating.

[0022] To better utilize the functional coating and control its thickness, the functional coating can be prepared on the surface of the positive electrode using a microgravure printing-transfer coating process. The coating can be prepared on the surface of the positive electrode, either on one side with a thickness of 2-10 μm, preferably 3-7 μm, or on both sides, forming a dense, continuous film with a thickness of 6-14 μm. Furthermore, the positive electrode including the functional coating can be assembled to form a battery.

[0023] In slurry preparation, oxide solid electrolyte powder, additives, and N-methylpyrrolidone solvent are mixed and mechanically dispersed to form a uniform slurry. Using a microgravure coating device, the slurry is quantitatively transferred to a coating roller or belt via a precisely controlled gravure roller (cell volume of 5-50 cm³ / m²), and then uniformly coated onto the surface of a high-nickel ternary cathode sheet through pressure contact. The coated electrode sheet is then transported to a drying oven and dried at 80-150℃, preferably 100-120℃, to evaporate the NMP solvent, allowing the solid electrolyte particles to form a dense coating that firmly adheres to the cathode material surface. Microgravure printing technology ensures an ultra-thin, uniform, and controllable coating thickness; the excellent lithium-ion conductivity of the solid electrolyte material itself avoids a significant impact on battery rate performance; and single-sided coating minimizes the negative impact on battery energy density while maintaining functionality.

[0024] This solid electrolyte coating is particularly suitable for high-nickel lithium batteries. It can be applied to the surface of a high-nickel ternary cathode, which is then further assembled into a high-safety lithium secondary battery. When the high-nickel cathode decomposes and releases free oxygen under abuse conditions, this coating effectively captures these highly reactive oxygen species, delaying or preventing their violent reaction with the electrolyte, significantly improving the battery's thermal stability. Commercial 9-series high-nickel cathode material powder without the solid electrolyte coating exhibits a large exothermic peak in its full-charge DSC test, while the same cathode material powder coated with the solid electrolyte coating does not show a significant exothermic peak in its full-charge DSC test. This solid electrolyte coating is an excellent electronic insulator, significantly increasing the electronic resistance of the cathode sheet. When the positive and negative electrodes come into physical contact due to separator damage or other reasons, the coating prevents electron conduction, thus preventing the formation of a large-current short-circuit loop and avoiding localized rapid temperature rise, improving the battery's safety under mechanical abuse conditions. In lithium battery fabrication, the solid electrolyte coating is first prepared on the cathode, and then the cathode is assembled with the negative electrode, separator, and electrolyte to form a lithium battery.

[0025] During battery electrode manufacturing, metallic foreign objects that affect safety (such as Fe and Cu shavings) are typically dark or black, while the solid electrolyte functional coating is grayish-white. When these foreign objects land on the grayish-white coating surface, they create a striking color contrast, making it extremely easy and precise to identify and locate these defective electrodes using machine vision inspection systems or manual visual inspection. These defective electrodes can then be removed before assembly into batteries. This characteristic controls the risk of internal short circuits introduced by metallic foreign objects at the source, significantly improving the overall reliability and consistency of battery products.

[0026] Solid electrolyte functional coatings not only significantly improve the safety of high-nickel ternary batteries through their free oxygen adsorption and electronic insulation properties (such as passing rigorous needle penetration tests), but also greatly improve the efficiency of foreign object detection during the manufacturing process due to their unique color. Thus, they provide dual protection for the reliability and safety of high-energy-density lithium secondary batteries at both the material and manufacturing levels.

[0027] The present invention will now be described with reference to the accompanying drawings. Experimental methods not specifically described in terms of operation steps are performed in accordance with the corresponding product manuals. Unless otherwise specified, the instruments, reagents, and consumables used in the embodiments can be purchased from commercial companies.

[0028] Example 1: Preparation of LATP Coating Slurry

[0029] 90 parts by weight of lithium aluminum titanium phosphate powder (average particle size D50 of 1.0 μm), 5 parts by weight of polyvinylidene fluoride binder, and 5 parts by weight of polyvinylpyrrolidone dispersant were premixed in a high-speed mixer for 30 minutes. The mixed powder was then slowly added to a planetary mixer containing 400 parts by weight of N-methylpyrrolidone solvent. The mixture was first stirred at a low speed of 500 rpm for 30 minutes, then switched to a high speed of 2000 rpm for 120 minutes until a uniform, fine slurry without obvious agglomerates was obtained. The viscosity of the slurry was measured to be 2500 mPa·s (25℃).

[0030] Example 2: Preparation of a 9-series high-nickel ternary cathode with LATP coating

[0031] Commercially produced 9-series high-nickel ternary cathode (LiNi0.9Co0. 05 Mn0. 05 O2 active material was coated onto aluminum foil (with an areal density of 20-40 mg / cm²) as the substrate. A microgravure coating machine was used, employing a gravure roller with a cell volume of 20 cm³ / m². The slurry prepared in Example 1 was injected into the coating head, and precisely metered by the gravure roller, the slurry was transferred to the coating roller. The pressure between the coating roller and the positive electrode was controlled at 0.2 MPa, and the linear speed at 2 m / min, ensuring the slurry was uniformly coated onto the surface of the active material on the positive electrode. The coated electrode was immediately placed in a three-stage drying oven, with the three temperatures set to 80℃, 100℃, and 120℃, respectively, for a total drying time of 15 minutes.

[0032] After drying, the electrode sheets are lightly pressed using a roller press (compaction density controlled at 3.4 g / cm³), and then slit for later use. Scanning electron microscopy measurements show that the single-layer thickness of the obtained LATP coating is 4.0 ± 0.5 μm, and the coating is continuous, dense, and completely covers the positive electrode active material particles.

[0033] Comparative Example 1: Uncoated 9-series high-nickel ternary cathode

[0034] The same substrate as in Example 2 was used, but without LATP coating.

[0035] Example 3: Assembly and performance testing of a 60Ah pouch cell

[0036] The fully charged DSC of the positive electrodes prepared in Example 2 and Comparative Example 1 were tested respectively, and the results are as follows: Figure 1As shown, the commercially available 9-series high-nickel cathode material powder without a solid electrolyte coating exhibits a large exothermic peak in the fully charged DSC test, while the same cathode material powder coated with a solid electrolyte coating does not show a significant exothermic peak in the fully charged DSC test; this coating can significantly improve thermal stability. Further testing of the cathode resistors prepared in Example 2 and Comparative Example 1 yielded the following results: Figure 2 As shown, the electronic resistance of the positive electrode with a solid electrolyte coating is significantly improved.

[0037] The positive electrodes prepared in Example 2 and Comparative Example 1 were assembled into batteries. The negative electrode used was a commercially available lithium metal negative electrode (40-60 μm thick), the separator was a polyethylene separator coated with Al2O3 ceramic, and the electrolyte was a commercially available high-nickel lithium metal battery electrolyte. The above components were stacked, packaged, injected with electrolyte, pre-sealed, formed (two 0.1C charge-discharge cycles), and capacity tested using conventional processes to obtain a soft-pack lithium secondary battery with a rated capacity of 60 Ah. The battery containing the LATP coating was designated as experimental battery A, and the battery without the LATP coating was designated as control battery B.

[0038] The prepared experimental battery A and control battery B were subjected to needle penetration safety tests. The test conditions followed GB / T 31485-2015 standard. The battery was at 100% SOC (fully charged) when a 3mm diameter high-temperature resistant steel needle was inserted into the battery at a speed of 25mm / s from a direction perpendicular to the battery electrodes (the needle penetration point was at the geometric center). Control battery B rapidly ignited and exploded after needle penetration, while experimental battery A maintained a voltage of 4.27V after needle penetration without igniting or exploding.

[0039] Example 4: Comparative Experiment on Foreign Object Detection of Positive Electrode Sheets with LATP Coating

[0040] In the electrode manufacturing workshop, 100 uncoated positive electrode sheets (dark black) prepared according to the method of Comparative Example 1 and 100 LATP coated positive electrode sheets (grayish white) prepared according to the method of Example 2 were taken respectively, and black iron powder particles with a size of 100-150 μm (simulating metal foreign objects) were randomly sprinkled on their surfaces.

[0041] The same industrial machine vision inspection system was used to inspect both types of electrodes. Comparing the inspection results, on the uncoated black positive electrode, the vision system detected iron powder in ~85% of cases, indicating some missed detections; on the LATP-coated grayish-white positive electrode, the vision system detected iron powder in as high as ~99%, with almost all of it being identified and removed.

[0042] The embodiments of the present invention have been described in detail above, but the content described is only a preferred embodiment of the present invention and should not be considered as limiting the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the patent coverage of the present invention.

Claims

1. A method for the preparation of a solid state electrolyte coating for high nickel ternary cathodes, characterized by: A slurry containing lithium aluminum titanium phosphate is prepared on the surface of the positive electrode material by a microgravure printing and transfer coating process to form a solid-state electrolyte coating.

2. The method of claim 1, wherein: The active ingredients in the slurry also include one or more of lithium lanthanum zirconium oxide, lithium lanthanum titanium oxide and composite derivatives.

3. The method of claim 1, wherein: The slurry includes a solvent N-methyl pyrrolidone, and also includes a dispersant and / or a binder.

4. The method of claim 1-3 for the preparation of solid state electrolyte coating for high nickel ternary cathode, characterized in that: The specific preparation method is as follows: Step 1: The active ingredients containing lithium aluminum titanium phosphate are dispersed in N-methyl pyrrolidone to prepare a uniform slurry; Step 2: The slurry is coated on the surface of the positive electrode sheet using a microgravure printing device, and after drying, a solid-state electrolyte coating is formed.

5. The method of claim 4, wherein: The solid-state electrolyte coating is prepared on one side of the positive electrode sheet, with a thickness of 2-10 μm; or the solid-state electrolyte coating is prepared on both sides of the positive electrode sheet, with a thickness of 6-14 μm.

6. The method of claim 5, wherein: Titanium aluminum lithium phosphate has the general formula Li 1₊x Al x Ti 2₋x (PO4)3, where 0.1 < x < 0.

5.

7. A positive electrode sheet characterized by comprising: The surface is covered with a solid-state electrolyte coating for high-nickel ternary positive electrodes prepared by the method for preparing a solid-state electrolyte coating according to any one of claims 1-6.

8. The cathode electrode of claim 7, wherein: The positive electrode sheet contains a high-nickel ternary positive electrode material, specifically LiNi x Co_yMn_zO2 material, where x+y+z=1, x≥0.

9.

9. A lithium secondary battery, characterized by: The positive electrode sheet includes the positive electrode sheet according to claim 7 or 8.

Images