Coating diaphragm for lithium battery as well as preparation method and application of coating diaphragm

Abstract

The invention discloses a coating diaphragm for a lithium battery as well as a preparation method and application of the coating diaphragm, and belongs to the technical field of lithium batteries. The coating diaphragm for the lithium battery comprises a diaphragm base material and a coating material arranged on the surface of the diaphragm base material, the coating material comprises a compound obtained by removing small molecules from a metal salt and caffeic acid through a copolycondensation reaction in a solvent I environment, and the preparation method of the coating material comprises the following steps: reacting caffeic acid powder with the metal salt to generate compound powder, dissolving the compound powder, coating the surface of the commercial polyolefin diaphragm with the compound powder, and drying. The coating diaphragm for the lithium battery can promote uniform distribution of current density, promote uniform deposition of lithium and inhibit dendritic crystal growth of a lithium negative electrode, and is expected to further improve the electrochemical performance of the lithium battery.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium batteries, and particularly relates to a coated separator for lithium batteries and a preparation method and application thereof. BACKGROUND

[0002] Lithium metal has a high theoretical specific capacity (3860 mAh / g) and a low redox potential (-3.045 V vs. standard hydrogen electrode), and is considered as a potential next-generation high-energy-density secondary battery. However, the lithium metal has high reactivity, is prone to side reactions with electrolytes, and affects the cycle stability of the battery; meanwhile, uneven deposition of lithium ions is prone to cause growth of dendrites, and the formation of lithium dendrites can pierce the separator to cause internal short circuit of the battery, affecting the interface stability of the battery and causing capacity attenuation of the battery. These problems limit the development and application of lithium batteries.

[0003] The separator is located between the positive and negative electrodes of the battery and is the main path for ion transmission. Modification of the separator can improve the ion transmission characteristics of the battery. Uniform ion transmission helps to reduce the unevenness of ion concentration distribution and current density distribution, and is conducive to slowing down the formation of dendrites, thereby improving the rate performance, service life and safety of the battery. SUMMARY

[0004] To solve the problem of uneven deposition of lithium ions causing growth of lithium dendrites and affecting the performance of the battery in the prior art of lithium batteries, the application provides a coated separator for lithium batteries and a preparation technical solution. The coated separator prepared by simple coating modification can actively regulate the lithium ion flux compared with the commercial polyolefin separator, promote the uniform distribution of current density on the electrode surface, thereby inducing uniform nucleation and deposition of lithium, effectively inhibiting the growth of lithium dendrites, and significantly improving the cycle stability and safety performance of the lithium battery.

[0005] The application adopts the following technical solutions: According to a first aspect of the application, a coated separator for lithium batteries is provided, which comprises a separator substrate and a coating material arranged on the surface of the separator substrate. The coating material comprises a compound obtained by removing small molecules from a metal salt and a caffeic acid through a co-condensation reaction in a solvent I environment.

[0006] Optionally, the metal is a transition metal.

[0007] Optionally, the small molecules are selected from at least one of hydrogen chloride, nitric acid, sulfuric acid, water, isopropanol, butanol, ethylene glycol, and ethanol.

[0008] The compound of the metal and the caffeic acid is a compound generated by the reaction of the caffeic acid and the metal salt. The metal salt is an organic metal salt liquid or an inorganic metal salt soluble in an organic solvent.

[0009] Optionally, the metal is selected from at least one of zinc, copper, zirconium, titanium, cobalt.

[0010] According to a second aspect of the present application, a preparation method of the coating separator for lithium battery is provided, comprising the following steps: S1, dissolving caffeic acid powder in an organic solvent I to obtain a raw material solution, then adding a metal salt into the raw material solution, stirring and reacting, and then filtering to obtain a compound powder; S2, dissolving the compound powder in an organic solvent II to obtain a coating solution, coating the coating solution on the surface of a separator substrate, and drying to form a film to obtain the coating separator for lithium battery.

[0011] Optionally, in step S1, the adding of the metal salt into the raw material solution comprises: adding an organic metal salt liquid into the raw material solution; and / or adding an organic solution of an inorganic metal salt into the raw material solution.

[0012] Optionally, the adding of the metal salt into the raw material solution is in the form of dropwise adding. The dropwise adding is conducive to avoiding the formation of particles with inconsistent sizes due to excessively high local concentration, and thus promoting the reaction to be more complete.

[0013] Optionally, the organic metal salt is selected from at least one of metal alcoholates of zinc, copper, zirconium, titanium, and cobalt.

[0014] Optionally, the inorganic metal salt is selected from at least one of inorganic salts of zinc, copper, zirconium, titanium, and cobalt which are soluble in the organic solvent I.

[0015] Optionally, the organic metal salt is selected from at least one of zirconium n-propoxide, zirconium n-butoxide, tetraisopropyl titanate, titanium isopropoxide, and tetrabutyl titanate; preferably, the tetrabutyl titanate.

[0016] Optionally, the inorganic metal salt is selected from at least one of zinc acetate, copper nitrate, copper sulfate, zirconium chloride, cobalt nitrate, and cobalt chloride.

[0017] Optionally, in step S1, the solvent I is selected from at least one of methanol, ethanol, diethyl ether, benzene, and chloroform; preferably, the methanol.

[0018] Optionally, in step S2, the solvent II is selected from at least one of methanol, ethanol, and dichloromethane; preferably, the methanol.

[0019] Optionally, in step S1, the stirring and reacting is performed under the following conditions: a temperature of 15-30°C, and a stirring time of 30-90 min.

[0020] Optionally, in step S2, the coating method is selected from dip coating.

[0021] Optionally, in step S2, the coating time is 5 to 15 minutes.

[0022] Optionally, the drying film formation conditions include: a drying temperature of 50~60℃ and a drying time of 5~8 h.

[0023] Optionally, in step S2, the material of the diaphragm substrate is selected from polyethylene or polypropylene.

[0024] According to a third aspect of this application, the application of the above-described coated separator for lithium batteries or the coated separator for lithium batteries obtained according to the above-described preparation method in the preparation of lithium metal batteries is provided.

[0025] Optionally, the lithium metal battery includes a lithium metal negative electrode, a liquid organic electrolyte, a positive electrode, and a separator; wherein the separator is selected from the coated separators used in lithium batteries.

[0026] The beneficial effects that this application can produce include: The lithium battery coated separator provided in this application is not only simple to manufacture, has a short preparation cycle, and low cost, but also significantly improves the electrochemical performance, safety, and cycle stability of the battery by optimizing the ion transport path and suppressing lithium dendrite growth, providing a new technical solution for the development of high-performance lithium batteries. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the preparation process of the CA-Ti coated membrane in Example 1 of this application; Figure 2 Atomic force microscopy images of the commercial polyolefin separator and the prepared CA-Ti@PP coated separator in Test Example 1 of this application are compared. Figure 3 The images are scanning electron microscope (SEM) images of lithium metal deposition morphologies of two Li||Cu half-cells based on commercial polyolefin separators and CA-Ti@PP coated separators, as shown in Test Example 2 of this application. The scale bar is 10 μm. (a) shows the lithium metal deposition morphology of the half-cell assembled with commercial polyolefin separator PP, and (b) shows the lithium metal deposition morphology of the half-cell assembled with modified separator CA-Ti@PP. Figure 4 The commercial polyolefin separator and the CA-Ti@PP coated separator in Test Example 2 of this application have a discharge capacity of 0.5 mAh cm⁻¹. -2 The current density is 1 mA cm⁻¹ -2 Cyclic performance of lithium-ion symmetric batteries under test conditions; Figure 5The lithium-ion symmetric battery using a commercial polyolefin separator and a CA-Ti@PP coated separator in Test Example 2 of this application achieved a discharge capacity of 0.5 mAh cm⁻¹. -2 The current density is 1 mA cm⁻¹ -2 The surface morphology of lithium metal after 100 cycles under test conditions, with a scale of 10 μm, where (a) is a commercial polyolefin separator (PP) and (b) is a CA-Ti@PP coated separator. Figure 6 Rate cycling diagrams of lithium metal batteries with lithium iron phosphate (LFP) cathodes using commercial polyolefin separators and CA-Ti@PP coated separators in Test Example 2 of this application; Figure 7 The following is a diagram showing the evaluation results of the interfacial bonding performance between the CA-Ti@PP coated membrane and the polypropylene base in Test Example 3 of this application: Initial state: (a) without electrolyte immersion, (c) original coated membrane; Aging state: (b) immersed in electrolyte for 10 days, (d) coated membrane immersed for 10 days. Figure 8 The commercial polyolefin separator and the CA-Zr@PP coated separator in Test Example 3 of this application have a discharge capacity of 0.5 mAh cm⁻¹. -2 The current density is 1 mA cm⁻¹ -2 Cyclic performance of lithium symmetric batteries under test conditions. Detailed Implementation

[0028] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0029] Unless otherwise specified, all raw materials used in the embodiments of this application were purchased through commercial channels.

[0030] Unless otherwise specified, all test methods are standard and all instrument settings are those recommended by the manufacturer.

[0031] The lithium metal symmetric battery assembled during the performance testing process in this application embodiment includes a lithium metal electrode, an electrolyte, and a separator. The lithium metal electrode and electrolyte are well known to those skilled in the art. The separator in this application embodiment is a CA-M@PP separator, where M refers to metal.

[0032] The lithium metal full battery assembled during the performance testing process in this application embodiment includes a lithium metal anode, a cathode, an electrolyte, and a separator. The lithium metal anode, cathode, and electrolyte are well known to those skilled in the art, and the separator is a CA-M@PP separator prepared in this application embodiment.

[0033] Example 1 A schematic diagram of the preparation process of the coated diaphragm in this embodiment is shown below. Figure 1 As shown, the specific steps are as follows: Step 1: Preparation of titanium caffeate compound powder First, 0.92 g of caffeic acid (CA) was added to 13 g of anhydrous methanol and completely dissolved. Then, 0.58 g of tetrabutyl titanate (Ti(Bu)4) was added dropwise and the mixture was magnetically stirred at room temperature for 30 min. The resulting mixture was then filtered to obtain titanium caffeate compound powder.

[0034] Step 2: Preparation of CA-Ti@PP coated membrane All the caffeic acid titanium compound powder obtained in step 1 was dissolved in 40g of anhydrous methanol, and excess solute was removed by filtration to obtain a coating solution. A commercial polypropylene (PP) membrane was ultrasonically dipped into the coating solution for 10min, hung to dry at room temperature, and then vacuum dried at 60℃ for 6h to remove the solvent, resulting in a coated membrane labeled CA-Ti@PP.

[0035] Test Example 1 The thickness of the CA-Ti@PP coated separator prepared in Example 1 was tested. Figure 2 The atomic force microscopy (AFM) images of the CA-Ti@PP coated membrane prepared in Example 1 of this application are compared with those of a commercial polypropylene (PP) membrane. The height difference in the AFM images indicates that the coating thickness is approximately 460 nm.

[0036] Test Example 2 The following performance tests were performed on the CA-Ti@PP coated membrane prepared in Example 1: A Li||Cu half-cell was assembled using a CA-Ti@PP coated membrane, with lithium metal as the counter electrode and copper as the working electrode. The electrolyte was prepared by dissolving 1 M LiPF6 (lithium hexafluorophosphate) in a 1:1:1 molar ratio of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC). A Li||Cu half-cell assembled with a commercial polypropylene (PP) membrane was used as a control. Tests were conducted under constant current discharge conditions as follows: at 1 mA cm⁻¹ -2 Deposition experiments were conducted using current density, with a deposition capacity of 1 mAh / cm³. -2 The morphology of lithium metal deposited on copper sheets was observed using a scanning electron microscope.

[0037] Figure 3Scanning electron microscope (SEM) images show the lithium metal deposition morphology of two Li||Cu half-cells: one using a commercial polyolefin (PP) separator and the other using a CA-Ti coated separator. The SEM images reveal that the cell using the CA-Ti coated separator exhibits a smooth, uniform lithium layer, while the cell using an uncoated commercial PP separator shows severe surface cracks and localized lithium accumulation. Therefore, compared to conventional commercial PP separators, the improved coated separator promotes more uniform lithium deposition and effectively reduces lithium dendrite formation. This uniform deposition is crucial for maintaining the structural integrity of the negative electrode and preventing short circuits that could lead to battery failure.

[0038] Assemble Li||Li symmetric cells using CA-Ti@PP coated separators (in) Figures 4-5 The same designation is CA-Ti@PP. Lithium metal is used as both the counter and working electrodes. The electrolyte is prepared by dissolving 1 M LiPF6 (lithium hexafluorophosphate) in a 1:1:1 molar ratio of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC). A Li||Li symmetric cell with the same electrolyte, assembled using a commercially available polypropylene (PP) membrane, is also described. Figures 4-5 For comparison, the sample (also labeled PP) was subjected to long-cycle testing under constant current charge-discharge conditions at a current density of 1 mA cm⁻¹. -2 The discharge capacity is 0.5mAh cm⁻¹ -2 With a cutoff voltage of 0.5V, the results are as follows: Figures 4 to 5 As shown, Figure 4 This figure shows the long-cycle voltage curves of two Li||Li symmetric cells using CA-Ti@PP coated separators and commercial polypropylene (PP) separators. The figure demonstrates that the CA-Ti@PP coated separator exhibits lower polarization voltage and excellent cycle stability during long-term cycling, indicating its significant advantages in suppressing lithium dendrite growth and improving battery safety. Figure 5 Scanning electron microscopy (SEM) images show the lithium metal deposition morphology of the negative electrode in two Li||Li symmetric batteries using CA-Ti@PP coated separators and commercial polypropylene (PP) separators. Compared with the traditional PP separator, the improved separator promotes more uniform lithium deposition, thereby slowing down the growth of lithium dendrites and improving battery safety performance.

[0039] Lithium metal batteries are assembled using CA-Ti@PP coated separators (in) Figure 6 The battery, labeled CA-Ti@PP, uses lithium iron phosphate (LFP) as the positive electrode and lithium metal as the negative electrode. The electrolyte is prepared by dissolving 1 M lithium hexafluorophosphate (LiPF6) in a 1:1:1 molar ratio of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC). It is a lithium metal battery assembled with a commercially available polypropylene (PP) separator.Figure 6 For comparison, the PP membrane is used. At 25°C, the assembled coin-type lithium metal batteries were left to stand and cycled 5 times each at five different rates: 0.1C, 0.2C, 0.5C, 1C, and 0.5C. The rate cycling graphs of two lithium metal batteries using lithium iron phosphate (LFP) as the cathode, one using a CA-Ti@PP coated separator and the other using a commercial polypropylene (PP) separator, are shown in the figure. Figure 6 As shown in the figure, the results indicate that the rate performance of the coated diaphragm prepared in this application is superior to that of commercially available polypropylene (PP) diaphragms.

[0040] Test Example 3: Evaluation of the adhesion between the coating and the separator substrate for lithium batteries.

[0041] The CA-Ti@PP coated membrane prepared in Example 1 was irradiated under ultraviolet light for 90 seconds using the dip-coating method. After the light treatment, the coated membrane sample was vertically immersed in a dimethyl carbonate reagent bottle and left to stand for 10 days. The interfacial bonding strength between the coating and the polypropylene substrate was systematically evaluated by periodically observing changes in coating integrity (including the degree of peeling and dissolution). Experimental results showed that the CA-Ti@PP coated membrane did not exhibit peeling or dissolution after immersion in dimethyl carbonate for 10 days (as shown in the attached figure). Figure 7 As shown in the figure, it confirms that a stable interfacial bond is formed between it and the polypropylene substrate.

[0042] Example 2 Step 1: Prepare zirconium caffeate compound powder: First, 0.49 g of caffeic acid (CA) was added to 11 g of anhydrous methanol and completely dissolved. Then, 0.34 g of zirconium butoxide was added dropwise, and the mixture was magnetically stirred at room temperature for 30 min. The resulting mixture was then filtered to obtain titanium caffeate compound powder.

[0043] Step 2: Preparation of CA-Zr@PP coated membrane: All the caffeic acid titanium compound powder obtained in step S1 was dissolved in 25g of anhydrous methanol, and excess solute was removed by filtration to obtain a coating solution. A commercial polypropylene (PP) membrane was ultrasonically coated in the coating solution for 10min, hung to dry at room temperature, and then vacuum dried at 60℃ for 6h to remove the solvent, resulting in a coated membrane labeled CA-Zr@PP.

[0044] Test Example 3 The following performance tests were performed on the CA-Zr@PP coated membrane prepared in Example 2: Assemble Li||Li symmetric cells using CA-Zr@PP coated separators ( Figure 8The electrode is labeled CA-Zr@PP, with lithium metal as the counter and working electrodes. The electrolyte is prepared by dissolving 1 M LiPF6 (lithium hexafluorophosphate) in a 1:1:1 molar ratio of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC). A Li||Li symmetric cell with the same electrolyte, assembled using a commercially available polypropylene (PP) membrane, was also tested. Figure 8 (marked as PP) was used for comparison. Long-cycle testing was performed under constant current charge-discharge conditions with a current density of 1 mA cm⁻¹. -2 The discharge capacity is 0.5mAh cm⁻¹ -2 With a cutoff voltage of 0.5V, the results are as follows: Figure 8 As shown in the figure, compared to commercial polypropylene (PP) separators, the CA-Zr@PP coated separator exhibits lower polarization voltage and superior cycle stability during long-term cycling, demonstrating its significant advantages in suppressing lithium dendrite growth and improving battery safety.

[0045] As can be seen from the above examples, the coated membrane obtained by CA-M modification can produce higher performance lithium batteries compared to commercial polypropylene (PP) membranes.

[0046] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A coated separator for lithium batteries, characterized in that, The coating separator for lithium battery comprises a separator substrate and a coating material arranged on the surface of the separator substrate; The coating material comprises a compound obtained by removing small molecules from a copolycondensation reaction of a metal salt and a caffeic acid in a solvent I environment.

2. The coated separator for lithium batteries according to claim 1, characterized in that, The small molecules are selected from at least one of hydrogen chloride, nitric acid, sulfuric acid, water, isopropanol, butanol, ethylene glycol, and ethanol. Preferably, the metal is selected from at least one of zinc, copper, zirconium, titanium, and cobalt.

3. The method for producing a coated separator for lithium batteries according to claim 1 or 2, characterized in that, The method comprises the following steps: S1. Dissolving caffeic acid powder in an organic solvent I to obtain a raw material solution, then adding a metal salt to the raw material solution, stirring and reacting, and filtering to obtain a compound powder; S2. Dissolving the compound powder in an organic solvent II to obtain a coating solution, coating the coating solution on the surface of a separator substrate, and drying to form a film to obtain the coating separator for lithium battery.

4. The production method according to claim 3, characterized by, In step S1, the addition of the metal salt to the raw material solution comprises: adding an organic metal salt liquid to the raw material solution; and / or adding an organic solution of an inorganic metal salt to the raw material solution.

5. The preparation method according to claim 4, characterized in that, The organic metal salt is selected from at least one of metal alkoxides of zinc, copper, zirconium, titanium, and cobalt; Preferably, the inorganic metal salt is selected from at least one of inorganic salts of zinc, copper, zirconium, titanium, and cobalt that are soluble in the organic solvent I.

6. The preparation method according to claim 4, characterized in that, The organic metal salt is selected from at least one of zirconium n-propoxide, zirconium n-butoxide, tetraisopropyl titanate, titanium isopropoxide, and tetrabutyl titanate. Preferably, the inorganic metal salt is selected from at least one of zinc acetate, copper nitrate, copper sulfate, zirconium chloride, cobalt nitrate, and cobalt chloride.

7. The preparation method according to claim 3, characterized in that, In step S1, the solvent I is selected from at least one of methanol, ethanol, diethyl ether, benzene, and chloroform. Preferably, in step S2, the solvent II is selected from at least one of methanol, ethanol, and dichloromethane.

8. The preparation method according to claim 3, characterized in that, In step S1, the stirring and reaction conditions include a temperature of 15-30°C and a stirring time of 30-90 min.

9. The preparation method according to claim 3, characterized in that, In step S2, the material of the separator substrate is selected from polyethylene or polypropylene.

10. Use of the coating separator for lithium battery of claim 1 or 2 or the coating separator for lithium battery prepared by the method of any one of claims 3 to 8 in the preparation of a lithium metal battery.

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