Preparation method and application of polyacrylamide / carboxylated chitosan / ionic liquid hydrogel composite material

Abstract

The invention provides a preparation method and application of a polyacrylamide / carboxylated chitosan / ionic liquid (PAM / CCS / ionic liquid) hydrogel composite material, and belongs to the technical field of hydrogel materials. Dispersion liquid of ionic liquid, carboxylated chitosan, acrylamide and zinc salt is subjected to polymerization reaction under the condition that an initiator and a cross-linking agent are added, and then the PAM / CCS / ionic liquid hydrogel composite material is prepared in situ. The preparation method provided by the invention is simple and efficient, and the obtained PAM / CCS / ionic liquid hydrogel composite material has high ionic conductivity, excellent mechanical properties and wider applicable temperature range. When the PAM / CCS / ionic liquid hydrogel composite material prepared by the method provided by the invention is used as a gel electrolyte of a zinc storage device, excellent electrochemical performance is shown.

Description

Technical Field

[0001] The present invention belongs to the field of electrochemical energy storage materials, and particularly relates to a preparation method of acrylamide / carboxylated chitosan / ionic liquid (PAM / CCS / ionic liquid hydrogel composite material) and its application in zinc storage. Background Art

[0002] Aqueous zinc-ion batteries (ZIBs) and zinc-ion hybrid capacitors (ZHCS) have the advantages of high safety, low cost, environmental friendliness, etc., and have been widely used in the field of large-scale energy storage. From a practical perspective, an ideal battery system should have a relatively high potential plateau and excellent cycle stability. However, problems such as the decomposition of aqueous electrolytes at high potentials, uneven zinc deposition, side reactions (hydrogen evolution reaction) caused by free water molecules in the electrolyte, corrosion, and narrow operating temperature seriously hinder the development of ZIBs and ZHCS. To solve the above problems, researchers have proposed common strategies such as electrolyte additives, "water-in-salt" electrolytes, and hydrogel electrolytes. Due to the thermodynamic instability of zinc metal, electrolyte additives cannot completely inhibit water decomposition in weakly acidic solutions. High-concentration "water-in-salt" electrolytes have poor ionic conductivity. Compared with electrolyte additives and "water-in-salt" electrolytes, hydrogel electrolytes have a three-dimensional network framework, and the rich functional groups of hydrogels can form strong intermolecular hydrogen bond networks with water molecules, reducing the activity of free water and inhibiting side reactions such as hydrogen evolution reaction, and are considered a promising practical application method. The strong hydrogen bond network formed between the hydrogel and water molecules destroys the hydrogen bond between free water molecules, lowers the freezing point of water, and expands the operating temperature range. However, under extreme operating conditions, trace amounts of water molecules may still freeze or react with the zinc anode, thus having a negative impact on the overall performance of the battery. Summary of the Invention

[0003] The object of the present invention is to provide a PAM / CCS / ionic liquid hydrogel composite material with excellent mechanical strength, low-temperature tolerance and good interfacial chemical properties, a preparation method thereof and an application thereof in zinc storage devices. The PAM / CCS / ionic liquid hydrogel composite material provided by the present invention can withstand different environmental temperature conditions, and the preparation method is simple and efficient. In the present invention, an ionic liquid is introduced into the PAM / CCS hydrogel electrolyte to reduce the water activity, improve the low-temperature durability and enhance the mechanical properties of the polymer. In particular, the hydrogen bond sites on the imidazole ring of the ionic liquid can preferentially form coordination bonds with water, destroying the strong hydrogen bond interaction between water molecules, thereby reorganizing the hydrogen bond network structure of the gel electrolyte, changing it from the strong hydrogen bond network of the PAM hydrogel to the weak hydrogen bond network of the PAM / CCS / ionic liquid hydrogel. This is conducive to reducing the activity of free water and inhibiting side reactions such as hydrogen evolution reaction, thereby improving the electrochemical performance of the zinc storage device assembled with the PAM / CCS / ionic liquid hydrogel composite material as the electrolyte.

[0004] The PAM / CCS / ionic liquid hydrogel composite material prepared by the present invention has the following characteristics. It is composed of an ionic liquid, CCS (carboxylated chitosan), PAM and a zinc salt, has a flexible and interconnected porous structure, the tensile stress is between 50 and 100 kPa, and the compressive stress is between 50 and 300 kPa. The PAM / CCS / ionic liquid hydrogel also exhibits a high ionic conductivity, up to 3 - 5 S m -1 .

[0005] In order to achieve the above-mentioned invention object, the present invention provides the following technical solutions: The present invention provides a preparation method of a PAM / CCS / ionic liquid hydrogel composite material, comprising the following steps: (1) Dissolve CCS in deionized water, and then heat until completely dissolved; (stir, magnetic stirrer) (2) Uniformly disperse the ionic liquid, acrylamide and zinc salt in the solution of step (1); (3) After cooling down the solution in step (2), add a crosslinking agent and an initiator, stir evenly, and carry out a thermal initiation polymerization reaction. The polymerization temperature is 50 °C to 80 °C, and the polymerization time is 0.5 h to 4 h to obtain a PAM / CCS / ionic liquid hydrogel composite material.

[0006] Preferably, the ionic liquid includes 1-methylimidazole trifluoromethanesulfonate, 1-butyl-3-methylimidazole acetate, 1-methyl-2-ethylimidazole bromide, 1-methyl-2-ethylimidazole sulfite and N-butylpyridinium bromide.

[0007] Preferably, the zinc salts in the step (2) include ZnSO4, ZnCl2, Zn(ClO4)2, Zn(CH3COO)2, Zn(BF4)2 and Zn(CF3SO3)2; the crosslinking agents in the step (3) include N,N N,N'-methylenebisacrylamide, diethylene glycol divinyl ether and 1,3-propanediol diacrylate; the initiators in the step (3) include ammonium persulfate, azoisobutyronitrile and 4-cyanovaleric acid.

[0008] Preferably, the concentration of carboxylated chitosan in the step (1) is 0.005 - 0.01 g / mL.

[0009] Preferably, the concentration of acrylamide in the step (2) is 0.05 - 1 g / mL.

[0010] Preferably, the concentration of ionic liquids in the step (2) is 0.1 - 0.5 g / mL, and the concentration of zinc salts is 0.5 - 2 mol / L.

[0011] Preferably, the addition amount of the initiator in the step (3) is 1 - 5% of the mass of acrylamide, and the addition amount of the crosslinking agent is 0.1 - 0.5% of the mass of acrylamide.

[0012] Preferably, the temperature of the thermal initiation polymerization reaction in the step (3) is 50 °C - 80 °C, and the polymerization time is 0.5 h - 3 h.

[0013] The present invention also provides a PAM / CCS / ionic liquid hydrogel composite material prepared by the preparation method described in the above technical solution and its applications in zinc ion hybrid capacitors and electrolyte materials for zinc ion batteries. Description of the Drawings

[0014] Figure 1 It is the SEM (scanning electron microscope) image of the sample prepared in Example 1; Figure 2 It is the ionic conductivity diagram of the sample prepared in Example 1; Figure 3 It is the mechanical tensile curve of the sample prepared in Example 1; Figure 4 It is the mechanical compression cycle curve of the sample prepared in Example 1; Figure 5 It is the electrochemical rate performance curve of the quasi-solid-state zinc-vanadium battery composed of the sample prepared in Example 1; Figure 6 It is the electrochemical cycle performance curve of the quasi-solid-state zinc-vanadium battery composed of the sample prepared in Example 1.

[0015] Figure 7 It is the ionic conductivity diagram of the sample prepared in Comparative Example 1; Figure 8 The mechanical tensile curve of the sample prepared in Comparative Example 1; Figure 9 The mechanical compression curve of the sample prepared in Comparative Example 1 Figure 10 The electrochemical rate performance curve of the quasi-solid-state zinc-vanadium battery composed of the sample prepared in Comparative Example 1; Figure 11 The electrochemical cycling performance curve of the quasi-solid-state zinc-vanadium battery composed of the sample prepared in Comparative Example 1. Specific embodiments

[0016] The present invention provides a method for preparing a PAM / CCS / ionic liquid hydrogel composite material, comprising the following steps: (1) Dissolve CCS in deionized water, and then heat until completely dissolved; (stir, magnetic stirrer) (2) Uniformly disperse the ionic liquid, acrylamide, and zinc salt in the solution of step (1); (3) After cooling down the solution in step (2), add a crosslinking agent and an initiator, stir evenly, and carry out a thermal initiation polymerization reaction at a polymerization temperature of 50 °C to 80 °C and a polymerization time of 0.5 h to 4 h to obtain a PAM / CCS / ionic liquid hydrogel composite material.

[0017] In the present invention, the concentration of acrylamide is preferably 0.05 - 1 g / mL, more preferably 0.1 - 0.3 g / mL. If the concentration of acrylamide is too low, the degree of crosslinking will be too low and it is not easy to form a gel. If the concentration of acrylamide is too high, the solution will be too thick and premature polymerization is likely to occur, resulting in uneven polymerization. The present invention has no limitation on the source of acrylamide, and those well-known to those skilled in the art can be selected.

[0018] In the present invention, the concentration of the ionic liquid is 0.1 - 0.5 g / mL, more preferably 0.1 - 0.2 g / mL. If the concentration of the ionic liquid is too low, the improvement effect of ionic conductivity will be poor. If the concentration of the ionic liquid is too high, the ionic conductivity will decrease.

[0019] In the present invention, the ionic liquid is preferably an ionic liquid that is easily soluble in water, which is beneficial to the uniform formation of the hydrogel.

[0020] In the present invention, the degree of polymerization of CCS is preferably 500 - 2000, more preferably 800 - 1200, and the degree of carboxylation is preferably 60 - 90%, more preferably 75 - 85%. The degree of polymerization and the degree of carboxylation affect the solubility of carboxymethyl chitosan in water, and thus affect the uniformity of the hydrogel.

[0021] In the present invention, the addition amount of the initiator is 1% to 5% of the mass of acrylamide, more preferably 2.5% to 3.5% of the mass of acrylamide. When the addition amount of the initiator is too small, the reaction cannot occur. When it is too much, over-initiation occurs, causing the glue to lose its flexibility. The addition amount of the cross-linking agent is 0.1% to 0.5% of the mass of acrylamide, more preferably 0.2% to 0.4% of the mass of acrylamide. When the addition amount of the cross-linking agent is too low, insufficient cross-linking occurs. When it is too high, over-cross-linking occurs, and the hydrogel material becomes hard.

[0022] In the present invention, the temperature of the thermal initiation polymerization reaction is 50 °C to 80 °C, more preferably 60 °C to 70 °C. If the temperature is too low, the polymerization reaction cannot occur smoothly. If the temperature is too high, the glue will denature. The polymerization time is 0.5 h to 4 h, more preferably 2 h to 3 h. If the polymerization time is too short, the polymerization reaction is insufficient. If the polymerization time is too long, over-initiation occurs, causing the glue to denature.

[0023] The present invention also provides the application of the PAM / CCS / ionic liquid hydrogel composite material described in the above technical solution as a gel electrolyte in a zinc storage device.

[0024] Next, the technical solutions in the present invention will be clearly and completely described in conjunction with the embodiments in the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention. Embodiment

[0025] At room temperature, 0.05 g of CCS was dissolved in 10 mL of deionized water at 90 °C, and then stirred until completely dissolved. Then, 2 g of acrylamide, 0.1 g of 1-methylimidazole trifluoromethanesulfonate, and 2.88 g of ZnSO4 were added to the above solution and stirred evenly. After the homogeneous solution was cooled to room temperature, 0.006 g N,N -Dimethylbisacrylamide and 0.06 g of ammonium persulfate were dispersed in deionized water and stirred evenly. After a homogeneous solution was formed, a thermal initiation polymerization reaction was carried out at a constant temperature of 60 °C to obtain a PAM / CCS / ionic liquid polymer hydrogel electrolyte.

[0026] The morphology of the hydrogel was characterized by SEM, and the results are as Figure 1 shown. It can be seen from Figure 1 that the hydrogel material has a rich pore structure. The ionic conductivity of the hydrogel was measured using a Chenhua electrochemical workstation 660E, as Figure 2 shown. It can be seen that the ionic conductivity of the hydrogel is 4.8 S m -1。The tensile and compressive properties were tested using a universal tensile tester. The results showed that the tensile stress of the hydrogel was 75.1 kPa and the compressive stress was 71.8 kPa ( Figure 3 and Figure 4 ).

[0027] Application Example 1 A zinc-ion battery was assembled with V2O5 as the positive electrode, Zn foil as the negative electrode, and the hydrogel electrolyte prepared in Example 1 as the separator and electrolyte, and assembled into a pouch soft-pack battery. The rate performance and cycling performance of the zinc-ion battery prepared in Application Example 1 were tested under the following conditions: constant current charge-discharge mode, cycling 15 times at current densities of 0.2, 0.5, 1, 2, and 5 A g -1 , and finally returning to 0.2 A g -1 . The discharge cut-off voltage was 0.3 V and the charge cut-off voltage was 1.5 V. The results are shown in Figure 5 and Figure 6 . It can be seen from Figure 5 that the specific capacities of the zinc-ion battery prepared in Application Example 1 at 0.2, 0.5, 1, 2, and 5 A g -1 were 326.8, 311.7, 300, 278.9, and 243.4 mAh g -1 , respectively, and the specific capacity when finally returning to 0.2 A g -1 was 334.8 mAh g -1 , indicating that it has good rate performance and electrochemical reversibility. It can be seen from Figure 6 that under the condition of 1 A g -1 , it can be stably cycled 1000 times with a capacity retention rate of 70.7%.

[0028] Comparative Example 1 0.05 g of CCS was dissolved in 10 mL of deionized water at 90 °C, and then stirred until completely dissolved. Then, 2 g of acrylamide and 2.88 g of ZnSO4 were weighed and added to the above solution, and stirred evenly. After the homogeneous solution was cooled to room temperature, 0.006 g of N,N-dimethylbisacrylamide and 0.06 g of ammonium persulfate were dispersed in deionized water and stirred evenly. After a homogeneous solution was formed, a thermal initiation polymerization reaction was carried out under a constant temperature condition of 60 °C to obtain a PAM / CCS polymer hydrogel electrolyte. The ionic conductivity of it was tested using a Chenhua electrochemical workstation 660E, as shown in Figure 7 . It can be seen that the ionic conductivity of the hydrogel was 3.1 S m -1 . The tensile and compressive properties were tested using a universal tensile tester. The results showed that the tensile stress of the hydrogel was 34.8 kPa and the compressive stress was 22.7 kPa ( Figure 8 andFigure 9 ) Comparative Application Example 1 Using V2O5 as the positive electrode, Zn foil as the negative electrode, and the hydrogel electrolyte prepared in Comparative Example 1 as the separator and electrolyte, a zinc-ion battery was assembled and fabricated into a pouch soft-pack battery. The rate performance and cycling performance of the zinc-ion battery prepared in Comparative Example 1 were tested under the following conditions: constant current charge-discharge mode, cycling 15 times at current densities of 0.2, 0.5, 1, 2, and 5 A g -1 , and finally returning to 0.2 A g -1 . The discharge cut-off voltage was 0.3 V, and the charge cut-off voltage was 1.5 V. The results are as shown in Figure 10 and Figure 11 . It can be seen from Figure 10 that the specific capacities of the zinc-ion battery prepared in Application Example 1 at 0.2, 0.5, 1, 2, and 5 A g -1 were 292.6, 276, 259.6, 242.1, and 196.8 mAh g -1 respectively, and the specific capacity when finally returning to 0.2 A g -1 was 297.7 mAh g -1 , indicating that it has good rate performance and electrochemical reversibility. It can be seen from Figure 11 that under the condition of 1 A g -1 , it can be stably cycled 1000 times with a capacity retention rate of 52.5%. Example

[0029] At room temperature, 0.05 g of CCS was dissolved in 10 mL of deionized water at 90 °C, and then stirred until completely dissolved. Subsequently, 2 g of acrylamide, 0.2 g of 1-butyl-3-methylimidazolium acetate, and 2.88 g of ZnSO4 were added to the above solution and stirred evenly. After the homogeneous solution was cooled to room temperature, 0.006 g of N,N-dimethylbisacrylamide and 0.06 g of ammonium persulfate were dispersed in deionized water and stirred evenly. After a homogeneous solution was formed, a thermal-initiated polymerization reaction was carried out under a constant temperature condition of 60 °C to obtain a PAM / CCS / ionic liquid polymer hydrogel electrolyte. Example

[0030] At room temperature, 0.05 g of CCS was dissolved in 10 mL of deionized water at 90 °C, and then stirred until completely dissolved. Subsequently, 2 g of acrylamide, 0.1 g of 1-methyl-2-ethylimidazolium bromide, and 2.88 g of ZnSO4 were weighed and added to the above solution, and stirred evenly. After the homogeneous solution was cooled to room temperature, 0.006 g of N,N-dimethylbisacrylamide and 0.06 g of ammonium persulfate, which were dispersed in deionized water and stirred evenly, were added. After a homogeneous solution was formed, a thermal initiation polymerization reaction was carried out under the condition of constant temperature at 60 °C to obtain a PAM / CCS / ionic liquid polymer hydrogel electrolyte. Example

[0031] At room temperature, 0.05 g of CCS was dissolved in 10 mL of deionized water at 90 °C, and then stirred until completely dissolved. Subsequently, 2 g of acrylamide, 0.05 g of 1-methyl-2-ethylimidazolium sulfite, and 2.88 g of ZnSO4 were weighed and added to the above solution, and stirred evenly. After the homogeneous solution was cooled to room temperature, 0.006 g of N,N-dimethylbisacrylamide and 0.06 g of ammonium persulfate, which were dispersed in deionized water and stirred evenly, were added. After a homogeneous solution was formed, a thermal initiation polymerization reaction was carried out under the condition of constant temperature at 60 °C to obtain a PAM / CCS / ionic liquid polymer hydrogel electrolyte.

[0032] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A PAM / CCS / ionic liquid hydrogel composite material, characterized in that: The material is composed of ionic liquid, CCS (carboxylated chitosan), PAM and zinc salt, has a flexible, interconnected porous structure, a tensile stress between 50 and 100 kPa, and a compressive stress between 50 and 300 kPa.

2. A method for preparing a PAM / CCS / ionic liquid hydrogel composite material, comprising the following steps: (1) Dissolve CCS with a degree of polymerization of 500 to 2000 in deionized water and then heat until completely dissolved; (2) uniformly dispersing the ionic liquid, acrylamide and zinc salt in the solution of step (1); (3) After the solution in step (2) is cooled down, a cross-linking agent and an initiator are added, and after stirring evenly, a thermal polymerization reaction is initiated at a polymerization temperature of 50°C to 80°C and a polymerization time of 0.5 h to 4 h to obtain a PAM / CCS / ionic liquid hydrogel composite material.

3. The method for preparing the PAM / CCS / ionic liquid hydrogel composite material according to claim 2, characterized in that: The ionic liquid includes 1-methyl imidazolium trimethanesulfonate, 1-butyl-3-methyl imidazolium acetate, 1-methyl-2-ethyl imidazolium bromide, 1-methyl-2-ethyl imidazolium sulfinate and N-butyl pyridinium bromide.

4. The method for preparing the PAM / CCS / ionic liquid hydrogel composite material according to claim 2, characterized in that: The zinc salts include ZnSO4, ZnCl2, Zn(ClO4)2, Zn(CH3COO)2, Zn(BF4)2 and Zn(CF3SO3)2; the crosslinking agent includes N,N Dimethylbisacrylamide, diethylene glycol divinyl ether and 1,3-propylene glycol diacrylate; the initiator includes ammonium persulfate, azoisobutyronitrile and 4-cyanovaleric acid.

5. The method for preparing a PAM / CCS / ionic liquid hydrogel composite material according to claim 2, characterized in that: The concentration of acrylamide is 0.05~1 g / mL.

6. The method for preparing the PAM / CCS / ionic liquid hydrogel composite material according to claim 2, characterized in that: The concentration of the ionic liquid is 0.1~0.5 g / mL.

7. The method for preparing the PAM / CCS / ionic liquid hydrogel composite material according to claim 2, characterized in that: The concentration of CCS is 0.005~0.01 g / mL, and the concentration of zinc salt is 0.5~2 mol / L.

8. The method for preparing the PAM / CCS / ionic liquid hydrogel composite material according to claim 2, characterized in that: The added amount of the initiator is 1-5% of the mass of acrylamide, and the added amount of the cross-linking agent is 0.1-0.5% of the mass of acrylamide.

9. The PAM / CCS / ionic liquid hydrogel composite material prepared by the method according to any one of claims 2 to 8.

10. Use of the PAM / CCS / ionic liquid hydrogel composite material according to claim 1 or the PAM / CCS / ionic liquid hydrogel composite material obtained by the preparation method according to claim 9 as an electrolyte material for zinc ion hybrid capacitors and zinc ion batteries.

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