High-ionic-conductivity lithium polyacrylate gel for lithium ion battery and preparation method of high-ionic-conductivity lithium polyacrylate gel

Abstract

The invention belongs to the technical field of functional polymer materials and electrochemistry, and discloses high-ionic-conductivity lithium polyacrylate gel for a lithium ion battery and a preparation method thereof.The preparation method comprises the steps that pre-alkalization polymerization is combined with ion exchange, firstly, a pre-alkalization sodium acrylate solution is formed through a controllable alkalization acrylic acid monomer, and then the pre-alkalization sodium acrylate solution is prepared; adding a cross-linking agent and an initiator, carrying out gradient heating polymerization and post-curing to obtain a sodium polyacrylate gel matrix, and then realizing replacement of sodium ions to lithium ions through multi-step ion exchange to finally obtain the lithium polyacrylate ion gel. The polyacrylic acid lithium ion gel with high ionic conductivity has a uniform and compact three-dimensional network structure and high ionic conductivity, is suitable for being used as a flexible solid electrolyte of a lithium ion battery, especially a solid-state battery or a semi-solid-state battery, and has important application value and industrialization potential.

Description

Technical Field

[0001] This invention belongs to the field of functional polymer materials and electrochemical technology, specifically relating to a high ionic conductivity lithium polyacrylate gel for lithium-ion batteries and its preparation method. Background Technology

[0002] The demand for safe and high-performance gel electrolytes is increasingly urgent for lithium-ion batteries, especially solid-state or semi-solid-state batteries. Traditional liquid electrolytes pose safety hazards such as leakage and combustion, while some solid-state electrolytes face the problem of high interfacial impedance.

[0003] Gel electrolytes combine the high ionic conductivity of liquid electrolytes with the stability of solid electrolytes, making them an ideal solution. Polyacrylic acid (PAA) is an excellent matrix for preparing ionogels due to the large number of dissociable carboxyl groups in its molecular chain. Currently, studies have reported zinc and sodium ion gels based on PAA, mainly used in supercapacitors or sensors; however, the application of PAA gels for lithium-ion conduction, especially as solid electrolytes in lithium batteries, still faces challenges.

[0004] The main challenges are: first, lithium ions have different coordination capabilities than zinc ions, and achieving uniform and efficient lithium ion loading in a PAA network through a simple process is crucial; second, the ionic conductivity and mechanical strength of the gel need to be balanced to meet practical application requirements. Existing methods may be complex or result in gels with insufficient ionic conductivity.

[0005] Therefore, developing a simple process for preparing PAA lithium-ion gels with high ionic conductivity is of great significance for advancing the development of lithium-ion batteries, especially semi-solid and solid-state lithium-ion battery devices. Summary of the Invention

[0006] The purpose of this invention is to provide a high ionic conductivity lithium polyacrylate gel for lithium-ion batteries and its preparation method. The preparation method is based on a pre-alkalization polymerization-ion exchange strategy, which is simple and efficient, and can achieve uniform and efficient loading of lithium ions in the polyacrylate network, thereby obtaining a gel electrolyte with high ionic conductivity.

[0007] The technical solution adopted in this invention is as follows:

[0008] This invention provides a method for preparing high ionic conductivity lithium polyacrylate gel for lithium-ion batteries, the preparation method comprising the following steps:

[0009] 1) Mix acrylic acid with deionized water, add alkali solution for pre-alkalization to obtain a pre-alkalized acrylate mixed solution;

[0010] 2) Add chemical crosslinking agent and thermal initiator to the pre-alkalized acrylate mixed solution for dispersion, deoxygenation and molding treatment. After molding, heat up to carry out polymerization reaction. After the reaction is completed, solidify to obtain gel matrix;

[0011] 3) The gel matrix is ​​immersed in a lithium salt solution for ion exchange. After the exchange is completed, it is washed and dried to obtain lithium polyacrylate lithium gel for lithium-ion batteries. The ionic conductivity of the high ionic conductivity lithium polyacrylate lithium gel for lithium-ion batteries is ≥0.05 mS / cm.

[0012] In the above preparation method, step 2) can also be replaced by: adding an ionic conductivity enhancer, a chemical crosslinking agent and a thermal initiator to a pre-alkalized acrylate mixed solution, then dispersing, deoxygenating and molding, heating up to carry out a polymerization reaction after molding, and solidifying to obtain a gel matrix after the reaction is completed.

[0013] In step 1) of the above preparation method, the volume ratio of acrylic acid, deionized water and alkali solution is 3.5-3.8:5:5, the alkali solution is either an aqueous solution of sodium hydroxide or an aqueous solution of potassium hydroxide, and the molar concentration of the alkali solution is 16-18 mol / L.

[0014] In step 1) of the above preparation method, the pH of the pre-alkalized acrylate mixed solution is 7.5-9.0.

[0015] In step 2) of the above preparation method, the chemical crosslinking agent is one or more of N,N-methylenebisacrylamide (MBAA), ethylene glycol dimethacrylate, triethylene glycol dimethacrylate, 1,3-butanediol dimethacrylate, or neopentyl glycol dimethacrylate, and the amount of the chemical crosslinking agent is 0.08%-0.12% of the mass of acrylic acid; the thermal initiator is one or more of ammonium persulfate (APS), benzoyl peroxide, azobisisobutyronitrile, or potassium persulfate, and the amount of the thermal initiator is 1.0%-1.5% of the mass of acrylic acid.

[0016] In step 2) of the above preparation method, the deoxygenation refers to passing an inert gas into the pre-alkalized acrylate mixed solution to remove dissolved oxygen in the mixed solution, wherein the inert gas is one or more of nitrogen or argon.

[0017] In step 2) of the above preparation method, the ionic conductivity enhancer is one or more of nano-titanium dioxide, nano-zirconia, or silane coupling agent-modified nano-titanium dioxide. The particle size of the nano-titanium dioxide and nano-zirconia is 20-30 nm, and the amount of the ionic conductivity enhancer is 0.5%-3% of the mass of acrylic acid. Preferably, the silane coupling agent-modified nano-titanium dioxide is nano-titanium dioxide modified with silane coupling agent KH-550. The preparation method steps are as follows:

[0018] 10g of nano-TiO2 powder was prepared into 50g·L -1 The suspension, with deionized water as solvent, was adjusted to pH 4.0 with 5% acetic acid solution. It was dispersed at 800 rpm for 30 min and then ultrasonically dispersed for 30 min. It was then transferred to a three-necked flask, 2 g of silane coupling agent KH-550 was added, and the reaction was carried out in a constant temperature water bath at 80°C for 4 h. The solid was then filtered, washed, and separated, extracted with anhydrous ethanol for 6 h, dried at 100°C for 12 h, and pulverized to obtain modified nano-titanium dioxide.

[0019] Preferably, the surface of the mold used for molding is silanized using KH-550.

[0020] In step 2) of the above preparation method, the heating procedure for the polymerization reaction is as follows:

[0021] Phase 1: Maintain at 40-50℃ for 0.5-1 hour;

[0022] Second stage: Maintain 60-70℃ for 1.5-3 hours;

[0023] The first stage of polymerization forms a preliminary network structure, while the second stage of polymerization completes the full cross-linking reaction.

[0024] Preferably, the curing temperature is 75-85℃, the curing time is 1-2h, and the pressure is 0.05-0.1atm.

[0025] In step 3) of the above preparation method, the molar concentration of the lithium salt solution is 1.5-3.0 mol / L, the solute of the lithium salt solution is one or more of lithium chloride, lithium perchlorate, lithium hexafluorophosphate, or lithium bis(trifluoromethanesulfonyl)imide, and the solvent of the lithium salt solution is one or more of deionized water or organic solvent, wherein the organic solvent is one or more of N-methylpyrrolidone, dimethyl sulfoxide, or acetonitrile; further, the solvent of the lithium salt solution is a mixture of water and organic solvent, wherein the volume ratio of deionized water to organic solvent is 1:0.2-1.

[0026] In step 3) of the above preparation method, the temperature of the ion exchange is 25-45℃ and the time is 24-72h; preferably, the lithium salt solution is replaced every 8 hours, and the ion exchange is continuously stirred to promote mass transfer.

[0027] In step 3) of the above preparation method, the drying temperature is 40℃, the drying pressure is 0.05-0.1 atm, and the drying time is 6-12h.

[0028] This invention provides a lithium polyacrylate gel prepared using the above-described preparation method.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] 1. By employing a "sodium / potassium ion preloading-lithium ion exchange" pathway, efficient and uniform distribution of lithium ions in the PAA three-dimensional network is ensured. This overcomes the challenges of strong lithium ion coordination ability and the tendency for direct polymerization to lead to local aggregation, achieving high-density and uniform distribution of Li⁺ in the gel network. This is because a large number of carboxyl groups on the polyacrylic acid molecular chain interact with Li⁺. + The strong coordination of the lithium ions provides a fast lithium-ion conduction channel, ultimately resulting in a lithium polyacrylate gel electrolyte with high ionic conductivity.

[0031] 2. The preparation method described is mild, simple, reproducible, and easy to scale up, and has significant industrialization potential. Attached Figure Description

[0032] Figure 1 The EIS test spectra of Examples 1-3 and Comparative Example 1 are shown below; Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. 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.

[0034] Unless otherwise specified, all test materials and reagents used in the following examples are commercially available.

[0035] The nano-titanium dioxide used in the following examples and comparative examples has a particle size range of 20-30 nm. The nano-titanium dioxide modified with the silane coupling agent KH550 is prepared by the following steps:

[0036] 10g of nano-TiO2 powder was prepared into 50g·L -1 The suspension, with deionized water as the solvent, was adjusted to pH 4.0 with 5% acetic acid solution. It was dispersed at 800 rpm for 30 min and then ultrasonically dispersed for 30 min. It was then transferred to a three-necked flask, and 2 g of silane coupling agent KH-550 was added. The flask was placed in a constant temperature water bath to maintain the reaction temperature at 80°C for 4 h. The solid was then filtered, washed, and separated, and extracted with anhydrous ethanol for 6 h. It was then dried at 100°C for 12 h and pulverized to obtain silane coupling agent modified nano-titanium dioxide.

[0037] Example 1

[0038] A method for preparing high ionic conductivity lithium polyacrylate gel for lithium-ion batteries, the preparation method steps are as follows:

[0039] 1) Measure 3.6 mL of acrylic acid and 5 mL of deionized water into a 50 mL three-necked flask and place the flask in an ice-water bath. Turn on the magnetic stirrer and set the speed to 300 rpm. Use a constant pressure dropping funnel to slowly add 5 mL of 18 M NaOH solution, controlling the dropping rate to be completed within 8 minutes. After the addition is complete, remove the ice-water bath and continue stirring until the solution returns to room temperature to obtain a pre-alkalized acrylate mixed solution. The pH value of the solution was measured to be 8.2.

[0040] 2) Add 3.8 mg MBAA and 55 mg APS sequentially to the above pre-alkalized acrylate mixed solution and stir until completely dissolved. Transfer the mixture to an ultrasonic processor and sonicate at 200W for 10 minutes. Then, continuously purge the liquid surface with nitrogen gas for 15 minutes to remove oxygen. Pour the solution into a mold consisting of two glass plates and a 1 mm thick silicone pad. Place the mold in a programmed temperature oven and raise the temperature from 25°C to 45°C at a rate of 1.5°C / min, and hold for 45 minutes. Then raise the temperature to 60°C at the same rate and hold for 2 hours. After polymerization, remove the gel and place it in an 80°C vacuum drying oven. Dry and cure at 0.05 atm for 1.5 hours to obtain a transparent gel matrix.

[0041] 3) The gel matrix was immersed in 100 mL of 2.0 mol / L LiCl aqueous solution and ion exchange was carried out by shaking at 100 rpm in a constant temperature water bath at 35℃. The solution was replaced every 12 hours for a total of 48 hours. After the exchange was completed, the gel was removed and rinsed three times with deionized water. Then it was dried in a vacuum drying oven at 40℃ at 0.05 atm for 8 hours to obtain high ionic conductivity lithium polyacrylate gel for lithium-ion batteries, labeled as Li-PAA-1.

[0042] Example 2

[0043] A method for preparing high ionic conductivity lithium polyacrylate gel for lithium-ion batteries, the preparation method steps are as follows:

[0044] The difference between this embodiment and Example 1 is that the amount of acrylic acid used in step 1) of Example 1 is changed from 3.6 mL to 3.5 mL, the molar concentration of sodium hydroxide solution is changed from 18M to 17M, and the addition of 3.8 mg MBAA and 55 mg APS to the pre-alkalized acrylate mixed solution in step 2) is replaced by the addition of 30 mg of nano-titanium dioxide powder modified with silane coupling agent KH-550, 3.8 mg MBAA and 55 mg APS to the pre-alkalized acrylate mixed solution. The rest is the same as in Example 1, and the product is labeled as Li-PAA-2.

[0045] Example 3

[0046] A method for preparing high ionic conductivity lithium polyacrylate gel for lithium-ion batteries, the preparation method steps are as follows:

[0047] The difference between this embodiment and Example 1 is that the amount of acrylic acid used in step 1) of Example 1 is changed from 3.6 mL to 3.8 mL, the molar concentration of sodium hydroxide solution is changed from 18M to 16M, and the 100 mL of 2.0 mol / L LiCl aqueous solution in step 3) of Example 1 is replaced with a mixed solution of 2.0 mol / L lithium bis(trifluoromethanesulfonylimide) in N-methylpyrrolidone and water, wherein the volume ratio of N-methylpyrrolidone to water is 1:2. The rest is the same as in Example 1, and the product is labeled as Li-PAA-3.

[0048] Comparative Example 1

[0049] A method for preparing lithium polyacrylate gel, the preparation method steps are as follows:

[0050] The difference between this embodiment and Example 1 is that step 1) is omitted, and the addition of 3.8 mg MBAA and 55 mg APS to the pre-alkalized acrylate mixed solution in step 2) is replaced by adding 3.6 mL acrylic acid, 5 mL deionized water, 3.8 mg MBAA, 55 mg APS and 3.6 g NaOH powder to a 50 mL three-necked flask in an ice-water bath. The ice-water bath is then removed and the mixture is stirred continuously until completely dissolved. Subsequent operations are the same as in Example 1, and the resulting product is labeled C-Li-PAA-1.

[0051] Test Example 1

[0052] Ionic conductivity is one of the key indicators of conductive materials used in lithium-ion batteries. To simulate the application effect of the prepared materials in lithium-ion batteries, the ionic conductivity of the gels obtained in the above examples and comparative examples was tested using an electrochemical workstation.

[0053] The gels prepared in each example and comparative example were made into circular discs with a diameter of 1 cm and a thickness of 0.1 cm. The gel samples were sandwiched between two identical stainless steel discs to ensure good contact. They were then placed in a CR2032 button cell mold, and appropriate pressure was applied to ensure stable contact. Conductivity tests were performed at 25°C, and the EIS spectra were obtained as follows: Figure 1 As shown in Table 1, the ionic conductivity of each embodiment and comparative example is as follows:

[0054] Sample Name Rb(Ω) diameter cm Thickness (cm) Ionic conductivity S / cm Example 1 2523.51 1 0.1 0.000051 Example 2 1238.16 1 0.1 0.000103 Example 3 1023.51 1 0.1 0.000124 Comparative Example 1 4500.00 1 0.1 0.000028

[0055] As shown in the table above, the gels prepared in each example have significantly better ionic conductivity than Comparative Example 1. Specifically, the ionic conductivity of Example 1 is 1.82 times that of Comparative Example 1, demonstrating that the pre-alkalization process is crucial for constructing a regular and efficient ion transport channel. Comparative Example 1, lacking a pre-alkalization step, has defects in its polymer network, hindering the rapid migration of lithium ions. Example 2 introduces nano-titanium dioxide on the basis of pre-alkalization, achieving an ionic conductivity of 0.000103 S / cm, which is twice that of Example 1 and 3.7 times that of Comparative Example 1. This is partly due to the additional ion transport path provided by the nanoparticles, and partly because the interaction between the nanoparticles and the polymer chains may have optimized the network structure and reduced the resistance to ion migration. This indicates that the nanocomposite strategy and the pre-alkalization process have a significant synergistic effect, working together to significantly improve ionic conductivity.

[0056] Example 3, using a mixed solvent system of N-methylpyrrolidone and water for ion exchange, achieved a highest ionic conductivity of 0.000124 S / cm, which is 4.5 times that of Comparative Example 1. This is attributed to the swelling effect of the organic solvent on the gel network, which allows the large-sized LiTFSI lithium salt to diffuse more fully into the gel and bind to the carboxyl sites, thereby achieving a higher carrier concentration and migration efficiency. This result demonstrates that optimizing the ion exchange medium is an effective means to further improve the performance of the product of this invention.

[0057] Comparative Example 1, due to the omission of step 1 and the absence of pre-alkalization treatment, exhibits significantly lower conductivity than the examples.

[0058] In summary, this invention has successfully prepared a lithium polyacrylate gel electrolyte with significantly better ionic conductivity than traditional methods through a pre-alkalization core process combined with a nanocomposite and exchange medium optimization strategy. This material is expected to improve the conductivity of lithium-ion batteries, especially solid-state or semi-solid-state batteries.

[0059] It should be noted that the above embodiments are merely some preferred embodiments of the present invention, and not all embodiments. Obviously, based on the above embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0060] The above description of the embodiments is intended to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for preparing a high ionic conductivity lithium polyacrylate gel for lithium-ion batteries, characterized in that, The preparation method steps are as follows: 1) Mix acrylic acid with deionized water, add alkali solution for pre-alkalization to obtain a pre-alkalized acrylate mixed solution; 2) Add chemical crosslinking agent and thermal initiator to the pre-alkalized acrylate mixed solution, then perform dispersion, deoxygenation and molding treatment, and heat up to carry out polymerization reaction after molding. After the reaction is completed, solidify to obtain gel matrix; 3) The gel matrix is ​​immersed in a lithium salt solution for ion exchange. After the exchange is completed, it is washed and dried to obtain a high ionic conductivity lithium polyacrylate gel for lithium-ion batteries. The ionic conductivity of the high ionic conductivity lithium polyacrylate gel for lithium-ion batteries is ≥0.05mS / cm.

2. The preparation method according to claim 1, characterized in that, Replace step 2) with adding an ionic conductivity enhancer, a chemical crosslinking agent, and a thermal initiator to the pre-alkalized acrylate mixed solution, followed by dispersion, deoxygenation, and molding. After molding, heat the solution to carry out a polymerization reaction, and solidify the solution after the reaction to obtain a gel matrix.

3. The preparation method according to claim 1 or 2, characterized in that, In step 1), the volume ratio of acrylic acid, deionized water and alkali solution is 3.5-3.8:5:5, and the alkali solution is either an aqueous solution of sodium hydroxide or an aqueous solution of potassium hydroxide, with a molar concentration of 16-18 mol / L.

4. The preparation method according to claim 1 or 2, characterized in that, In step 2), the chemical crosslinking agent is one or more of N,N-methylenebisacrylamide, ethylene glycol dimethacrylate, triethylene glycol dimethacrylate, 1,3-butanediol dimethacrylate, or neopentyl glycol dimethacrylate, and the amount of the chemical crosslinking agent is 0.08%-0.12% of the mass of acrylic acid; the thermal initiator is one or more of ammonium persulfate, benzoyl peroxide, azobisisobutyronitrile, or potassium persulfate, and the amount of the thermal initiator is 1.0%-1.5% of the mass of acrylic acid.

5. The preparation method according to claim 2, characterized in that, The ionic conductivity enhancer mentioned in step 2) is one or more of nano-titanium dioxide, nano-zirconia, or silane coupling agent modified nano-titanium dioxide, and the amount of the ionic conductivity enhancer is 0.5%-3% of the mass of acrylic acid.

6. The preparation method according to claim 1 or 2, characterized in that, The heating procedure for the polymerization reaction described in step 2) is as follows: Phase 1: Maintain at 40-50℃ for 0.5-1 hour; Second stage: Maintain 60-70℃ for 1.5-3 hours.

7. The preparation method according to claim 1 or 2, characterized in that, In step 3), the molar concentration of the lithium salt solution is 1.5-3.0 mol / L, the solute of the lithium salt solution is one or more of lithium chloride, lithium perchlorate, lithium hexafluorophosphate or lithium bis(trifluoromethanesulfonylimide), and the solvent of the lithium salt solution is one or more of deionized water or organic solvent, wherein the organic solvent is one or more of N-methylpyrrolidone, dimethyl sulfoxide or acetonitrile.

8. The preparation method according to claim 7, characterized in that, The solvent for the lithium salt solution is a mixture of deionized water and organic solvent, with a volume ratio of deionized water to organic solvent of 1:0.2-1.

9. The preparation method according to claim 1 or 2, characterized in that, The ion exchange in step 3) is performed at a temperature of 25-45℃ for 24-72 hours.

10. A lithium polyacrylate gel prepared by the preparation method as described in claim 1 or 2.

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