Safety coating and preparation method therefor, and composite current collector

Abstract

A safety coating and a preparation method therefor, and a composite current collector. The safety coating is mainly prepared from a phosphate material, a conductive agent, a binder, and a solvent, wherein the phosphate material is a lithium manganese iron phosphate material doped with at least one of the metals Cr, Mg, Ti, Al, Zn, W, Nb, and Zr. By controlling the addition ratio of each raw material, the adhesion between the safety coating and a current collector substrate can be increased, and the peel strength between an active material layer and the safety coating can be effectively enhanced, such that the prepared safety coating can effectively improve the safety performance of batteries without changing the material system, electrode sheet performance, and product performance; and the safety coating has little impact on energy density, can achieve good long-term cycle and high-rate discharge effects of batteries, and is suitable for promotion and application.

Description

A safety coating, its preparation method, and a composite current collector

[0001] This application claims priority to Chinese Patent Application No. 202410507351.5, filed with the Chinese Patent Office on April 25, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the technical field of lithium-ion batteries, specifically to a safety coating and its preparation method and a composite current collector, and more particularly to a safety coating and its preparation method, and its application in the preparation of positive and / or negative electrode composite current collectors. Background Technology

[0003] Due to their high energy density, long cycle life, lack of memory effect, and environmental friendliness, lithium-ion batteries are widely used in portable electronic products, energy storage devices, and new energy vehicles. With the advent of the 5G era for mobile phones and the increasing demand for longer driving ranges in new energy vehicles, higher demands are being placed on the energy density of lithium-ion batteries. However, the higher the energy density of lithium-ion batteries, the worse their safety. The poor safety of these batteries has led to numerous spontaneous combustion and explosion incidents in electric and hybrid vehicles, severely hindering the development of lithium-ion batteries in the new energy field.

[0004] Safety hazards caused by the contact between the positive and negative electrodes of lithium-ion batteries have attracted much attention and have yet to be effectively addressed. Research indicates that adding a safety coating to isolate the positive and negative electrode contact, resulting in high impedance and low heat generation during short circuits, can effectively improve safety. Considering practical application requirements, the safety coating must significantly improve the safety performance of the battery cell while minimizing its impact on energy density. For example, Chinese patent application CN 113314717 A discloses a composite current collector, its preparation method, and its application. This method involves coating an aluminum foil with a 2-5 μm layer of lithium manganese iron phosphate. While this safety coating balances energy density and safety, its addition is detrimental to long-term cycling or high-rate discharge of the battery. Technical issues

[0005] In related technologies, the safety coating applied to the current collector cannot simultaneously ensure battery safety, minimize the impact on energy density, provide excellent long-term cycle performance, and achieve excellent high-rate discharge performance. Solution

[0006] In a first aspect, embodiments of this application provide a safety coating, which, by weight, is prepared from coating raw materials comprising: 30-50 parts of phosphate material, 1-5 parts of conductive agent, 10-30 parts of binder, and 10-20 parts of solvent; wherein the chemical formula of the phosphate material is LiFe.1-x-y Mn x M y PO4, wherein 0 < x < 1, 0 < y ≤ 0.1, 0 < x + y < 1, and M is selected from at least one of Cr, Mg, Ti, Al, Zn, W, Nb, and Zr.

[0007] Secondly, embodiments of this application provide a method for preparing a safety coating, comprising the following steps: first, mixing all coating raw materials to obtain a coating slurry, then coating the coating slurry onto the surface of a substrate, and after drying, obtaining a safety coating on the surface of the substrate.

[0008] Thirdly, embodiments of this application provide a composite current collector, including a current collector substrate and a safety coating disposed on two opposing surfaces of the current collector substrate. The safety coating is the aforementioned safety coating, wherein the thickness of the current collector substrate is 10~15μm and the thickness of the safety coating is 2~5μm. Beneficial effects

[0009] 1. The safety coating provided in this application is mainly prepared from phosphate materials, conductive agents, binders, and solvents. The phosphate material is lithium iron manganese phosphate material doped with at least one metal selected from Cr, Mg, Ti, Al, Zn, W, Nb, and Zr. By controlling the addition ratio of each raw material, the tightness between the safety coating and the current collector substrate can be increased, which can effectively improve the peel force between the active material layer and the safety coating. When the battery cell experiences short circuits caused by needle penetration, extrusion, etc., direct contact between the positive electrode aluminum foil and the negative electrode copper foil can be effectively avoided. This allows the preparation of the safety coating to effectively improve the safety performance of the battery without changing the material system, electrode performance, or product performance. Moreover, the safety coating has little impact on energy density and can enable the battery to achieve excellent effects of long-term cycling and high-rate discharge, making it easy to promote and apply.

[0010] 2. This application provides a method for preparing a safety coating, which mainly includes mixing all raw materials to obtain a coating slurry, then applying the coating slurry to the surface of a substrate, and drying it to obtain a safety coating on the substrate surface. The preparation method is simple, easy to operate, and convenient for widespread application.

[0011] 3. This application provides a composite current collector with a safety coating. The safety coating is applied to the surface of the current collector substrate. By adding the safety coating, the positive and negative electrodes of the prepared battery are isolated, and the battery has high impedance and low heat generation during short circuit, which can effectively improve battery safety. At the same time, it can also ensure high electrochemical performance of the battery.

[0012] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0013] In some embodiments of this application, M is Mg, and the addition of magnesium makes the safety layer exhibit better safety performance.

[0014] In some embodiments of this application, the phosphate material has a D99 ≤ 10 μm and / or a D50 ≤ 8 μm. Alternatively, the phosphate material has a D99 of 2 μm to 10 μm and a D50 of 2 μm to 8 μm. Alternatively, the phosphate material has a D99 of 5 μm to 10 μm and a D50 of 5 μm to 8 μm.

[0015] In some embodiments of this application, the raw material for the safety coating further includes 1 to 10 parts of a fast ion conductor, wherein the fast ion conductor has an ionic conductivity ≥10. -6 S·cm -1 Through extensive experimental research, the inventors discovered that by adding a specific amount of fast-ion conductor, the safety coating can maintain excellent safety performance while also ensuring superior long-term cycle life and high-rate discharge performance of the battery. Furthermore, the research found that controlling the ionic conductivity of the fast-ion conductor to ≥10... -6 S·cm -1 It can show a good performance improvement effect, but the ionic conductivity decreases and the improvement effect is not obvious.

[0016] In some embodiments of this application, the fast ion conductor is an inorganic compound, a monocrystalline or polycrystalline organic compound, or a solid electrolyte. In some embodiments of this application, the fast ion conductor is selected from at least one of AgI, Ag2S, CuBr, and SrBr2.

[0017] In some embodiments of this application, the ratio of fast ion conductor to phosphate material is 0.03 to 0.2:1.

[0018] Through experimental research, the inventors discovered that the ratio of fast ion conductors to phosphate materials has a close influence on the safety and electrical performance of batteries. Within a suitable range, better technical results can be achieved.

[0019] In some embodiments of this application, the ratio of fast ion conductor to phosphate material is 0.15 to 0.2:1.

[0020] In some embodiments of this application, the coating material further includes 10-20 parts of ceramic particles. In some specific embodiments, the ceramic particles are at least one selected from boehmite, magnesium oxide, titanium oxide, zirconium oxide, silicon oxide, and yttrium oxide. The ceramic particles in the coating exhibit a certain degree of chemical inertness, are not easily thermally decomposed, and have a certain flame-retardant effect. Simultaneously, the ceramic particles can reduce the power consumption during a short circuit in the battery cell, thereby improving battery safety.

[0021] In some embodiments of this application, the conductive agent is at least one selected from graphene, carbon nanotubes, conductive carbon black, and carbon microspheres, which helps to improve the overall conductivity of the battery. And / or the binder is an oil-based or water-based polymeric binder. Specifically, the binder is not limited to at least one selected from carboxymethyl cellulose, acrylic acid, styrene, butadiene, polyvinylidene fluoride, and polyacrylate. And / or the solvent is N-methylpyrrolidone and / or water.

[0022] In some embodiments of this application, the substrate is at least one of microporous aluminum foil and mesh aluminum foil.

[0023] In another typical embodiment of this application, an application of a safety coating in the preparation of a composite current collector is provided, wherein the safety coating is applied to the surface of the current collector substrate.

[0024] Specifically, the composite current collector is either a positive electrode composite current collector or a negative electrode composite current collector.

[0025] This application provides the application of safety coatings in the preparation of positive electrode composite current collectors and / or negative electrode composite current collectors. By coating the surface of the current collector substrate with a safety coating, the prepared battery achieves isolation between the positive and negative electrodes, high impedance and low heat generation during short circuits, effectively improving battery safety, while also ensuring high electrochemical performance of the battery.

[0026] In another typical embodiment of this application, an electrode is provided, the electrode comprising the above-described composite current collector.

[0027] In another typical embodiment of this application, a lithium-ion battery is provided, which includes the aforementioned electrode.

[0028] In the following examples, the phosphate material has a D99 ≤ 10 μm and a D50 ≤ 8 μm. The solvent is N-methylpyrrolidone and / or water to completely dissolve the other raw materials. Example

[0029] Safety Coating

[0030] Phosphate materials LiFe 0.72 Mn 0.2 Mg 0.08PO4 is 40 parts; conductive agent: graphene is 3 parts; binder: carboxymethyl cellulose is 20 parts; solvent is 15 parts; among which, the D99 of the phosphate material is 10 μm and the D50 is 8 μm.

[0031] Preparation of positive electrode composite current collector

[0032] Phosphate material, conductive agent, binder and solvent are mixed and stirred evenly to obtain a safety coating slurry.

[0033] Aluminum foil with a thickness of 12 μm was soaked in acetone and ethanol for 5 min, then ultrasonically cleaned with deionized water for 30 min, and then soaked in 0.1 mol / L acetic acid solution for 5 min to remove surface oxides. It was then vacuum dried for later use.

[0034] The coating slurry was applied to the two opposite surfaces of a clean and dried aluminum foil, and then dried to obtain a composite current collector with a safety coating thickness of 3 μm. Example

[0035] Safety Coating

[0036] Phosphate materials LiFe 0.6 Mn 0.3 Mg 0.05 Cr 0.05 PO4 is 30 parts; conductive agent: conductive carbon black is 1 part; binder: acrylic acid is 10 parts; solvent is 10 parts; ceramic particles are 10 parts; the phosphate material has a D99 of 9 μm and a D50 of 8 μm.

[0037] Preparation of positive electrode composite current collector

[0038] Phosphate materials, conductive agents, binders, ceramic particles, and solvents are mixed and stirred evenly to obtain a safety coating slurry.

[0039] Aluminum foil with a thickness of 12 μm was soaked in acetone and ethanol for 5 min, then ultrasonically cleaned with deionized water for 30 min, and then soaked in 0.1 mol / L acetic acid solution for 5 min to remove surface oxides. It was then vacuum dried for later use.

[0040] The coating slurry was applied to the two opposite surfaces of a clean and dried aluminum foil, and then dried to obtain a composite current collector with a safety coating thickness of 3 μm. Example

[0041] Safety Coating

[0042] Phosphate materials LiFe 0.5 Mn 0.4 Mg 0.06 Zn 0.04PO4 is 50 parts; conductive agent: carbon nanotubes are 5 parts; binder: styrene is 30 parts; solvent is 20 parts; ceramic particles are 20 parts; the phosphate material has a D99 of 10 μm and a D50 of 6 μm.

[0043] Preparation of positive electrode composite current collector

[0044] Phosphate materials, conductive agents, ceramic particles, binders, and solvents are mixed and stirred evenly to obtain a safety coating slurry.

[0045] Aluminum foil with a thickness of 12 μm was soaked in acetone and ethanol for 5 min, then ultrasonically cleaned with deionized water for 30 min, and then soaked in 0.1 mol / L acetic acid solution for 5 min to remove surface oxides. It was then vacuum dried for later use.

[0046] The coating slurry was applied to the two opposite surfaces of a clean and dried aluminum foil, and then dried to obtain a composite current collector with a safety coating thickness of 3 μm. Example

[0047] Safety Coating

[0048] Phosphate materials LiFe 0.72 Mn 0.2 Mg 0.08 The composition consists of 40 parts PO4; 3 parts graphene as a conductive agent; 20 parts carboxymethyl cellulose as a binder; 15 parts solvent; and 6 parts fast ion conductor AgI. The phosphate material has a D99 of 6 μm and a D50 of 6 μm. The fast ion conductor has an ionic conductivity of 10⁻⁶. -6 S·cm -1 .

[0049] Preparation of positive electrode composite current collector

[0050] Phosphate materials, conductive agents, fast ion conductors, binders, and solvents are mixed and stirred evenly to obtain a safety coating slurry.

[0051] Aluminum foil with a thickness of 12 μm was soaked in acetone and ethanol for 5 min, then ultrasonically cleaned with deionized water for 30 min, and then soaked in 0.1 mol / L acetic acid solution for 5 min to remove surface oxides. It was then vacuum dried for later use.

[0052] The coating slurry was applied to the two opposite surfaces of a clean and dried aluminum foil, and then dried to obtain a composite current collector with a safety coating thickness of 3 μm. Example

[0053] Safety Coating

[0054] Phosphate materials LiFe 0.44Mn 0.5 Ti 0.03 Al 0.03 The composition includes: 30 parts PO4; 1 part conductive agent (conductive carbon black); 10 parts binder (acrylic acid); 10 parts solvent; 10 parts ceramic particles; and 1 part fast ion conductor AgI. The phosphate material has a D99 of 9 μm, a D50 of 8 μm, and an ionic conductivity of 10⁻⁶. -5 S·cm -1 .

[0055] Preparation of positive electrode composite current collector

[0056] Phosphate materials, conductive agents, ceramic particles, fast ion conductors, binders, and solvents are mixed and stirred evenly to obtain a safety coating slurry.

[0057] Aluminum foil with a thickness of 12 μm was soaked in acetone and ethanol for 5 min, then ultrasonically cleaned with deionized water for 30 min, and then soaked in 0.1 mol / L acetic acid solution for 5 min to remove surface oxides. It was then vacuum dried for later use.

[0058] The coating slurry was applied to the two opposite surfaces of a clean and dried aluminum foil, and then dried to obtain a composite current collector with a safety coating thickness of 3 μm. Example

[0059] Safety Coating

[0060] Phosphate materials LiFe 0.8 Mn 0.1 W 0.03 Zr 0.07 The composition of the phosphate material is as follows: 50 parts PO4; 5 parts conductive agent: carbon nanotubes; 30 parts binder: styrene; 20 parts solvent; 20 parts ceramic particles; and 10 parts fast ion conductor AgI. The phosphate material has a D99 of 8 μm, a D50 of 7 μm, and an ionic conductivity of 10⁻⁶. -6 S·cm -1 .

[0061] Preparation of positive electrode composite current collector

[0062] Phosphate materials, conductive agents, ceramic particles, fast ion conductors, binders, and solvents are mixed and stirred evenly to obtain a safety coating slurry.

[0063] Aluminum foil with a thickness of 12 μm was soaked in acetone and ethanol for 5 min, then ultrasonically cleaned with deionized water for 30 min, and then soaked in 0.1 mol / L acetic acid solution for 5 min to remove surface oxides. It was then vacuum dried for later use.

[0064] The coating slurry was applied to the two opposite surfaces of a clean and dried aluminum foil, and then dried to obtain a composite current collector with a safety coating thickness of 3 μm.

[0065] Comparative Example 1 did not use a safety coating compared to Example 1.

[0066] Aluminum foil with a thickness of 12 μm was soaked in acetone and ethanol for 5 min, then ultrasonically cleaned with deionized water for 30 min, and then soaked in acetic acid solution with a concentration of 0.1 mol / L for 5 min to remove surface oxides. After vacuum drying, it was ready for use as a positive electrode current collector.

[0067] Comparative Example 2 uses a lithium iron manganese phosphate material as the safety coating compared to Example 1, but otherwise it is the same as Example 1, as detailed below:

[0068] Safety Coating

[0069] Phosphate materials LiFe 0.8 Mn 0.2 PO 4 The total amount of the active ingredient is 40 parts; the conductive agent is 3 parts of graphene; the binder is 20 parts of carboxymethyl cellulose; and the solvent is 15 parts.

[0070] Preparation of positive electrode composite current collector

[0071] Phosphate material, conductive agent, binder and solvent are mixed and stirred evenly to obtain a safety coating slurry.

[0072] Aluminum foil with a thickness of 12 μm was soaked in acetone and ethanol for 5 min, then ultrasonically cleaned with deionized water for 30 min, and then soaked in 0.1 mol / L acetic acid solution for 5 min to remove surface oxides. It was then vacuum dried for later use.

[0073] The coating slurry was applied to the two opposite surfaces of a clean and dried aluminum foil, and then dried to obtain a composite current collector with a safety coating thickness of 3 μm.

[0074] Compared to Example 4, Comparative Example 3 changed the proportion of fast ion conductors added, as follows:

[0075] Safety Coating

[0076] Phosphate materials LiFe 0.72 Mn 0.2 Mg 0.08 PO 4 The total amount of the active ingredient is 36.8 parts; the conductive agent is 3 parts of graphene; the binder is 20 parts of carboxymethyl cellulose; the solvent is 15 parts; and the fast ion conductor AgI is 9.2 parts.

[0077] Preparation of positive electrode composite current collector

[0078] Phosphate materials, conductive agents, fast ion conductors, binders, and solvents are mixed and stirred evenly to obtain a safety coating slurry.

[0079] Aluminum foil with a thickness of 12 μm was soaked in acetone and ethanol for 5 min, then ultrasonically cleaned with deionized water for 30 min, and then soaked in 0.1 mol / L acetic acid solution for 5 min to remove surface oxides. It was then vacuum dried for later use.

[0080] The coating slurry was applied to the two opposite surfaces of a clean and dried aluminum foil, and then dried to obtain a composite current collector with a safety coating thickness of 3 μm.

[0081] Comparative Example 4 changed the y-value compared to Example 1, specifically as follows:

[0082] Safety Coating

[0083] Phosphate materials LiFe 0.6 Mn 0.2 Mg 0.2 PO4: 40 parts; conductive agent: graphene: 3 parts; binder: carboxymethyl cellulose: 20 parts; solvent: 15 parts.

[0084] Preparation of positive electrode composite current collector

[0085] Phosphate material, conductive agent, binder and solvent are mixed and stirred evenly to obtain a safety coating slurry.

[0086] Aluminum foil with a thickness of 12 μm was soaked in acetone and ethanol for 5 min, then ultrasonically cleaned with deionized water for 30 min, and then soaked in 0.1 mol / L acetic acid solution for 5 min to remove surface oxides. It was then vacuum dried for later use.

[0087] The coating slurry was applied to the two opposite surfaces of a clean and dried aluminum foil, and then dried to obtain a composite current collector with a safety coating thickness of 3 μm.

[0088] Subsequent testing revealed that excessive metal doping can lead to structural instability and material failure in phosphate materials.

[0089] (1) The positive electrode active material (NCM811): conductive carbon black SP: binder PVDF are mixed in a mass ratio of 90:5:5. After mixing with NMP as solvent, the slurry is prepared with an areal density of 170 g / m³. 2 The current collectors obtained in Examples 1-6 and Comparative Examples 1-3 were coated and dried under vacuum at 90 °C to obtain positive electrode sheets. The electrode sheet peel strength and film resistance were tested for positive electrode sheets using different current collectors.

[0090] (2) The obtained positive electrode sheet was combined with the graphite negative electrode (graphite:SP:CMC:SBR=94:2:2:2) to form a soft pack battery with a capacity of 1.2 Ah. The energy density of the battery and the maximum temperature rise during the nail penetration process were tested.

[0091] Cyclic performance test

[0092] At 25 °C, the lithium-ion batteries prepared in each embodiment and comparative example were charged to 3.6 V at a constant power of 0.6 P, allowed to rest for 10 min, and then discharged to 2.4 V at a constant power of 0.6 P, and allowed to rest for 10 min. This constitutes one charge-discharge cycle. The capacity retention rate of the battery after 300 charge / discharge cycles was calculated.

[0093] The capacity retention rate (%) of a lithium-ion battery after 300 cycles = discharge capacity of the 300th cycle / discharge capacity of the 2nd cycle × 100%.

[0094] High-rate discharge performance test

[0095] At 25±2 ℃, the battery was left to rest for 10 min, and then cyclically charged at 0.5C / 0.5C for 6 cycles. The battery was then charged at 0.5C constant current and constant voltage. The battery was left to rest at 25±2 ℃ for 10 min. The battery was then discharged at 3C current until the battery voltage reached 2.0 V and then the discharge energy efficiency was recorded.

[0096] The test results are shown in Table 1.

[0097] Table 1

[0098] The test results above show that the technical solutions of this application used in Examples 1-6 can effectively improve the peel strength between the active material layer and the safety coating, with a peel strength of up to 0.65 N / 30 mm and an energy density of up to 230 Wh / kg. The maximum temperature rise during the needle-punching process is below 40 °C. Examples 4-6, in particular, show even more significant effects due to the addition of fast ion conductors.

[0099] Comparing the test data of Comparative Examples 1-4 with the test data of the Examples, it can be seen that coating the current collector substrate with metal-doped lithium iron manganese phosphate material and controlling the addition ratio of each raw material can not only effectively improve the safety performance of the battery and have little impact on the energy density, but also enable the battery to achieve long-term cycling and high-rate discharge, which is convenient for widespread application.

[0100] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A safety coating, wherein, The safety coating is prepared from coating raw materials in parts by weight, the coating raw materials comprising: Phosphate material 30-50 parts; conductive agent 1-5 parts; binder 10-30 parts; solvent 10-20 parts; The chemical formula of the phosphate material is LiFe. 1-x-y Mn x M y PO4, wherein 0 < x < 1, 0 < y ≤ 0.1, 0 < x + y < 1, and M is selected from at least one of Cr, Mg, Ti, Al, Zn, W, Nb, and Zr.

2. The safety coating according to claim 1, wherein, M is Mg.

3. The safety coating according to claim 1 or 2, wherein, The phosphate material has a D99 ≤ 10 μm and / or a D50 ≤ 8 μm.

4. The safety coating according to any one of claims 1 to 3, wherein, The coating material also includes 1 to 10 parts of a fast ion conductor, wherein the fast ion conductor has an ionic conductivity ≥10. -6 S·cm -1 .

5. The safety coating according to claim 4, wherein, The mass ratio of the fast ion conductor to the phosphate material is 0.03~0.2:

1.

6. The safety coating according to claim 5, wherein, The mass ratio of the fast ion conductor to the phosphate material is 0.15~0.2:

1.

7. The safety coating according to any one of claims 1 to 6, wherein, The coating material also includes 10 to 20 parts of ceramic particles.

8. The safety coating according to any one of claims 1 to 7, wherein, The conductive agent is selected from at least one of graphene, carbon nanotubes, conductive carbon black and carbon microspheres; and / or the binder is selected from at least one of carboxymethyl cellulose, acrylic acid, styrene, butadiene, polyvinylidene fluoride and polyacrylate; and / or the solvent is N-methylpyrrolidone and / or water.

9. A method for preparing the safety coating according to any one of claims 1 to 8, wherein, Includes the following steps: First, all coating materials are mixed to obtain a coating slurry. Then, the coating slurry is applied to the surface of the substrate and dried to obtain a safety coating on the substrate surface.

10. A composite current collector, comprising a current collector substrate and a safety coating disposed on two opposing surfaces of the current collector substrate, wherein, The safety coating is the safety coating according to any one of claims 1 to 8, wherein the thickness of the current collector substrate is 10 to 15 μm, and the thickness of the safety coating is 2 to 5 μm.

11. An electrode comprising a current collector, wherein the current collector is the composite current collector of claim 10.

12. A lithium-ion battery, comprising electrodes, wherein, The electrode is the electrode as described in claim 11.

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