Preparation method and application of a temperature-sensitive methylated chitin

Abstract

The present invention discloses a preparation method and application of thermosensitive methylated chitin. First, chitin is dissolved in an alkali / urea or alkali solution, and a methylation reagent is added to the chitin aqueous solution at a low temperature, followed by mixing and stirring for reaction. Then, it is neutralized with acid, dialyzed, and freeze-dried to obtain thermosensitive methylated chitin. The preparation process of this method is simple, the reaction conditions are mild, and the gel transition point of the product is in the range of 15 to 85 °C. Among them, the methylated chitin with a low transition temperature can be used as an injectable hydrogel and a drug carrier material. The methylated chitin with a high transition temperature can effectively increase the resistance during the thermal runaway of the aqueous battery, playing a role in thermal self-protection. Moreover, compared with common synthetic polymer thermosensitive polymer materials, methylated chitin can form a stable gel with a polymer concentration as low as 1 wt% to 3 wt%. At the same time, methylated chitin has better degradation performance, does not use organic additives, and is more environmentally friendly when the aqueous battery is discarded.

Description

Technical Field

[0001] The present invention belongs to the technical field of new materials, and relates to a temperature-sensitive methylated chitin material, specifically to a preparation method and application of temperature-sensitive methylated chitin, specifically for injectable hydrogels, drug carrier materials, and temperature-sensitive electrolytes. Background Art

[0002] Chitin is a natural polymer, and its biosynthesis ranks second only to cellulose in nature. It is widely available and inexpensive. Water-soluble chitin derivatives are one of the most attractive chitin derivatives because the poor solubility of chitin in most solvents limits its applications. Obtaining water-soluble chitin materials through modification can endow them with new properties and improve their application value. Among them, temperature-sensitive carboxymethyl chitin, temperature-sensitive hydroxypropyl chitin, etc. have been reported, and injectable hydrogels can be prepared. When their transition temperature is relatively low, they gel in situ in the body and have wide applications in injectable hydrogels and drug carrier materials. For example, they can be used to make dressings that promote skin regeneration and reduce scar formation. Among them, temperature-sensitive hydroxypropyl chitin also has temperature-sensitive reversible characteristics, but there is no report on temperature-sensitive methylated chitin yet.

[0003] With the rapid development of the electronics field and the continuous increase in people's demands, the demand for high-energy-density and high-power batteries has gradually increased. However, they also bring many safety problems that cannot be ignored. Under extreme conditions such as sudden temperature increase, external mechanical shock, overcharge / discharge, and short circuit, etc., it is easy to cause local high temperature in aqueous zinc-ion batteries, and in severe cases, it may cause fire or even explosion. Traditional thermal runaway control methods (such as fans and coolants) increase the complexity of the system and require additional energy supply; physical methods such as thermal fuses and functional cut-off separators respond slowly and irreversibly. Obviously, the above methods cannot suppress the thermal runaway phenomenon quickly, effectively, and reversibly. Therefore, there is an urgent need for a new method to solve this problem. Thermoresponsive polymer hydrogels based on sol-gel transitions can maintain good solution properties at low or room temperature and can rapidly form gels when the temperature runs out of control and exceeds the critical temperature, thereby hindering the movement of ions in the system [Shi Y, Ha H, Al-Sudani A, et al. Thermoplastic elastomer-enabled smart electrolyte for thermoresponsive self-protection of electrochemical energy storage devices [J]. Advanced Materials, 2016, 28(36): 7921-7928]. Common thermosensitive polymers such as poly(N-isopropylacrylamide) (PNIPAM) and thermosensitive carboxymethyl chitin (CN103601819A), thermosensitive hydroxypropyl chitin (CN103951764A) have low transition temperatures (LCST is 32 °C), while in fact, the general operating temperature of electrochemical energy storage devices is greater than 32 °C, so they do not have practical application value in electrochemical energy storage devices; in addition, for actual battery applications, thermosensitive materials with different transition temperatures are required at different operating temperatures, while it is difficult to adjust the transition temperature of thermosensitive materials in the existing technology, especially difficult to adjust in a large range, making it necessary to search for new materials again when designing electrochemical energy storage devices with different operating temperatures. Based on this, it is of great significance to study new thermoresponsive electrolytes with higher intelligent transition temperatures.These methods have been reported as more proactive and effective strategies for preventing thermal runaway in aqueous zinc-ion batteries [Mo F, Li H, Pei Z, et al. A smart safe rechargeable zinc ion battery based on sol-gel transition electrolytes [J]. Science Bulletin, 2018, 63(16): 1077-1086; Yang P, Feng C, Liu Y, et al. Thermal self-protection of zinc-ion batteries enabled by smart hygroscopic hydrogel electrolytes [J]. Advanced Energy Materials, 2020, 10(48): 2002898]. However, there is no report on thermosensitive methylated chitin in this regard yet. Summary of the Invention

[0004] One of the objectives of the present invention is to overcome the limitations in the application of chitin, and to provide a thermosensitive methylated chitin structure and its preparation method. The reaction conditions are simple, the yield is high, the degree of deacetylation is relatively low, and the degree of substitution is uniformly controllable. The thermosensitive transition temperature is controlled by the controllable degree of substitution.

[0005] Another objective of the present invention is to provide a preparation method and use of a safe aqueous electrolyte. A safe aqueous electrolyte is prepared with controllable thermosensitive methylated chitin, and the gelation transition temperature can be accurately adjusted as needed, so as to prepare a safe electrolyte. When the ambient temperature of the electrolyte exceeds the set value, the resistance value can be increased, thereby cutting off the circuit cycle of the electrolyte and achieving safety protection.

[0006] The present invention provides a thermosensitive methylated chitin, and its structural formula is as follows:

[0007]

[0008] R1 is any one of NH2, NHCH3, N(CH3)2, N(CH3)3 + ;

[0009] R2 is H or CH3;

[0010] R3 is H or CH3;

[0011] And among R2, R2 and R3, at least one contains CH3;

[0012] n is a positive integer;

[0013] The degree of acetylation of the thermosensitive methylated chitin is 0.78 - 0.90, and the degree of methylation substitution is 0.40 - 0.64.

[0014] Preferably, n ranges from 100 to 10,000; most preferably 200 to 2,000.

[0015] The methylated chitin aqueous solution prepared with the above thermosensitive methylated chitin has reversible temperature sensitivity: it is prepared into an aqueous solution at 2 - 20°C, and after being stirred evenly, it spontaneously undergoes physical cross-linking above the transition temperature to transform into a methylated chitin hydrogel; then it can be restored to a flowing liquid below the transition temperature. The thermosensitive transition temperature of the methylated chitin is 15 - 85°C, and the specific transition temperature is adjusted by the degree of acetylation and the degree of methylation substitution.

[0016] The present invention provides a one-step preparation method of thermosensitive methylated chitin, including the following steps:

[0017] S1. Dissolve the chitin raw material at low temperature to form a homogeneous alkaline chitin aqueous solution;

[0018] S2. Slowly add the methylation reagent to the alkaline chitin aqueous solution at low temperature and stir to make it undergo a homogeneous reaction;

[0019] S3. Neutralize the reaction solution to neutral, then dialyze and dry to obtain the thermosensitive methylated chitin.

[0020] Preferably, the dissolution method in step S1 is: add the chitin raw material to an aqueous solution of alkali and urea, mix evenly at low temperature, freeze at -32 to -18°C for 6 - 96 hours, and then stir at 2 - 25°C to obtain a homogeneous alkaline urea aqueous solution of chitin.

[0021] Preferably, the reaction parameters in step S2 are: the homogeneous reaction time for adding the methylation reagent at low temperature is 18 - 108 hours, and the reaction temperature is 2 - 15°C. Finally, after acid neutralization, dialysis, and freeze-drying, a methylated chitin sponge is obtained.

[0022] Preferably, the degree of deacetylation of the chitin raw material is less than 20%, and the weight-average molecular weight is 5×10 4 ~5×10 6 .

[0023] More preferably, the degree of deacetylation of the chitin raw material is less than 10%.

[0024] Preferably, the alkali is one or more of sodium hydroxide, potassium hydroxide, and lithium hydroxide, the concentration of the alkali is 5 - 30 wt%, and the concentration of the urea is 0 - 15 wt% (excluding 0).

[0025] More preferably, the base is sodium hydroxide, the concentration of the base is 8-11 wt% (mass fraction, the same hereinafter) of the chitin raw material, and the concentration of the urea is 2-4 wt% of the chitin raw material.

[0026] Preferably, the methylation reagent is any one or a mixture of several of fluoromethane, chloromethane, bromomethane, iodomethane, and dimethyl sulfate, and the ratio of the addition amount of the methylation reagent to the number of moles of the chitin structural unit is 5:1-20:1;

[0027] More preferably, the methylation reagent is iodomethane, and the ratio of the addition amount (number of moles) to the number of moles of the chitin structural unit is 8:1-15:1.

[0028] Preferably, in step S3, after neutralization with dilute acid, dialysis is carried out for 6-168 hours, and the drying time is 6-72 hours.

[0029] Preferably, the dilute acid is one or several of hydrochloric acid, sulfuric acid, formic acid, acetic acid, and nitric acid, the concentration of the dilute acid is 0.1-3 mol / L, and the drying method is one or several of freeze-drying, drying, and vacuum drying.

[0030] More preferably, the dilute acid is hydrochloric acid or acetic acid, the concentration of the dilute acid is 0.5-1 mol / L, and the drying method is freeze-drying.

[0031] The present invention also provides a two-step preparation method of thermosensitive methylated chitin, comprising the following steps:

[0032] Step (1) Prepare the primary product, and the specific method is as follows:

[0033] Step 1.1: Dissolve the chitin raw material at low temperature to form a homogeneous chitin alkaline aqueous solution;

[0034] Step 1.2: Slowly add the methylation reagent to the chitin alkaline aqueous solution at low temperature and stir to make it fully react homogeneously;

[0035] Step 1.3: Neutralize the reaction solution to neutrality, then dialyze and dry to obtain the primary product.

[0036] Step (2) Prepare the final product, and the specific method is as follows:

[0037] Step 2.1: Dissolve the primary product obtained in step 1.3 in an alkaline aqueous solution to obtain a homogeneous solution of the primary product;

[0038] Step 2.2: Then slowly add the methylation reagent to the homogeneous solution of the primary product and mix and stir for reaction;

[0039] Step 2.3: Neutralize the reaction solution with acid, dialyze, and dry it to obtain thermosensitive methylated chitin as the final product.

[0040] Preferably, the specific method in Step 1.1 is: Add the chitin raw material into an aqueous solution of alkali / urea and mix evenly at low temperature, freeze at -32 to -18 °C for 6 to 96 hours, and then stir at 2 to 25 °C to obtain a homogeneous alkaline urea aqueous solution of chitin.

[0041] Preferably, the specific method in Step 1.2 is: Add the methylation reagent at low temperature and react homogeneously for 2 to 72 hours, and the reaction temperature is 2 to 30 °C.

[0042] Preferably, the degree of deacetylation of the chitin raw material in Step 1.1 is less than 20%, and the weight-average molecular weight is 5×10 4 ~5×10 6 .

[0043] More preferably, the degree of deacetylation of the chitin raw material is less than 10%.

[0044] Preferably, the alkali in Step 1.2 is one or more of sodium hydroxide, potassium hydroxide, and lithium hydroxide, the concentration of the alkali is 5 to 30 wt%, and the concentration of the urea is 0 to 15 wt%.

[0045] More preferably, the alkali is sodium hydroxide, the concentration of the alkali is 8 to 11 wt%, and the concentration of the urea is 2 to 4 wt%.

[0046] Preferably, the specific method in Step 2.1 is: Dissolve the primary product in (1) in an aqueous alkali solution with a concentration of 10 to 25 wt% at -30 to -20 °C to obtain a homogeneous solution of the primary product.

[0047] Preferably, the specific method in Step 2.2 is: Slowly add the methylation reagent to the homogeneous solution of the primary product, mix and stir, and react at room temperature for 4 to 24 hours.

[0048] Preferably, the specific method in Step 2.3 is: Neutralize with dilute acid, dialyze for 6 to 168 hours, and dry to obtain the final product.

[0049] Preferably, the alkali in Step 2.1 is one or more of sodium hydroxide, potassium hydroxide, and lithium hydroxide, and the concentration of the alkali is 5 to 30 wt%.

[0050] Preferably, the methylation reagent in Steps (1) and (2) is any one or a mixture of several of fluoromethane, chloromethane, bromomethane, iodomethane, and dimethyl sulfate, and the ratio of the addition amount of the methylation reagent to the molar number of the chitin structural unit is 5:1 to 20:1;

[0051] More preferably, the methylation reagent is methyl iodide, and the ratio of the addition amount to the number of moles of the chitin structural unit is 8:1 to 10:1.

[0052] Preferably, in steps (1) and (2), after neutralization with dilute acid, dialysis is carried out for 6 to 168 hours, and the drying time is 6 to 72 hours.

[0053] Preferably, in steps (1) and (2), the dilute acid is one or more of hydrochloric acid, sulfuric acid, formic acid, acetic acid, and nitric acid, the concentration of the dilute acid is 0.1 to 3 mol / L, and the drying method is one or more of freeze-drying, drying, and vacuum drying.

[0054] More preferably, the dilute acid is hydrochloric acid or acetic acid, the concentration of the dilute acid is 0.5 to 1 mol / L, and the drying method is freeze-drying.

[0055] The present invention also provides a use of the thermosensitive methylated chitin prepared above with a thermosensitive transition temperature lower than 33 °C, for artificial tears, injectable hydrogels, and drug carrier materials.

[0056] The thermosensitive methylated chitin with a thermosensitive transition temperature higher than 33 °C can be used to prepare a safe aqueous electrolyte.

[0057] A method for preparing a safe aqueous electrolyte includes the following steps:

[0058] S100. At a low temperature, the above-mentioned thermosensitive methylated chitin is formulated into an aqueous solution;

[0059] S200. An electrolyte salt is added to the aqueous solution of the thermosensitive methylated chitin prepared in step S100 and stirred until completely dissolved to prepare a thermosensitive electrolyte; when the electrolyte usage environment exceeds the set safety temperature, the thermosensitive electrolyte changes from a water-soluble system to a gel system with a large resistance.

[0060] Preferably, the low temperature in step S100 is 2 to 20 °C.

[0061] Preferably, in step S100, the concentration of the aqueous solution is 1 to 3 wt% (mass concentration).

[0062] Preferably, in step S200, the electrolyte salt is zinc sulfate and manganese sulfate.

[0063] Preferably, in step S200, in the thermosensitive electrolyte, the concentrations of zinc sulfate and manganese sulfate are 0.1 to 2 mol / L and 0.01 to 0.2 mol / L respectively.

[0064] The present invention also provides a use of a safe aqueous electrolyte for the electrolyte of a battery or an electrolytic cell.

[0065] Preferably, when zinc sulfate and manganese sulfate are added, an aqueous temperature-sensitive electrolyte is obtained, which can increase the battery resistance and reduce the electrolyte conductivity when the battery temperature rises abnormally or thermal runaway occurs, so as to play a role in thermal self-protection.

[0066] The present invention also provides a preparation method of a zinc ion battery, comprising the following steps:

[0067] Prepare a battery positive electrode sheet;

[0068] Assemble the battery positive electrode sheet, negative electrode, and separator together to form a battery. During the assembly process, a safety aqueous electrolyte is coated on the surface of the separator to obtain a thermally affected battery.

[0069] Preferably, the preparation method of the battery positive electrode sheet is as follows:

[0070] Mix the active substance α-MnO2, acetylene black, and polyvinylidene fluoride (PVDF) in an N-methylpyrrolidone (NMP) solvent, and continue stirring to form a uniform slurry; coat the slurry on a metal foil, and cut it into electrode sheets after drying;

[0071] Preferably, the negative electrode is a zinc sheet, and the separator is a glass fiber.

[0072] Preferably, the battery positive electrode sheet is cut into a circular shape and assembled into a button battery.

[0073] Advantages of the present invention:

[0074] Compared with the prior art, the present invention has the following beneficial effects:

[0075] (1) The present invention discloses a thermosensitive methylated chitin with a low degree of deacetylation and a homogeneous preparation method thereof. The preparation method has simple process, easy control of the reaction process, uniform substitution degree of the product, high yield and low degree of deacetylation of the product.

[0076] (2) The thermosensitive methylated chitin prepared by the method of the present invention can be dissolved in water to form a transparent solution at low temperature (0-20 °C). This solution can form a gel during the heating process and return to a solution when cooled. By changing the reaction conditions, thermosensitive methylated chitin materials with different substitution degrees and different transition temperatures can be obtained. When the transition temperature is below body temperature, it can be used in biomedical fields such as artificial tears, injectable hydrogels, and drug carrier materials, while only when the transition temperature is relatively high can it be used for self-protection during thermal runaway in electrochemical energy storage devices.

[0077] (3) The present invention prepares a safety aqueous electrolyte based on thermosensitive methylated chitin, which can act as an electrolyte for an aqueous zinc ion battery. When the battery temperature rises abnormally or gets out of control, it can spontaneously gel to increase the circuit resistance and reduce the electrolyte conductivity, playing a role in thermal self-protection.

[0078] (4) After the temperature-sensitive methylated chitin prepared by the present invention is configured into a solution, the gel transition temperature can be freely adjusted within a relatively wide temperature range, and the transition temperature is highly correlated with the concentration and substitution degree of the temperature-sensitive methylated chitin. The substitution degree has a relatively large relationship with the reaction time. By adjusting the concentration or substitution degree, the gel transition temperature can be adjusted to the required set temperature, so as to achieve precise control of the gel transition temperature. Description of the Drawings

[0079] The present invention will be further described with reference to the accompanying drawings, but the embodiments in the drawings do not constitute any limitation to the present invention.

[0080] Figure 1 1H NMR spectra of MCH-5, MCH-6, MCH-7 and MCH-8 prepared in Example 1 in 20% DCl / D2O respectively 1 1H NMR spectra.

[0081] Figure 2 Sol-gel transition process diagram of 3 wt% aqueous solution of MCH-2 prepared in Example 3 during the heating and cooling cycle from 2 to 37 °C.

[0082] Figure 3 Temperature sensitivity test diagrams of methylated chitin with different substitution degrees in Example 3, where Figure 3 (a) is the test result diagram of the rheological transition point of MCH-2 solution at a concentration of 3 wt%, Figure 3 (b) is the test result diagram of the rheological transition point of MCH-5 solution at a concentration of 3 wt%, Figure 3 (c) is the test result diagram of the rheological transition point of MCH-6 solution at a concentration of 3 wt%, Figure 3 (d) is the test result diagram of the rheological transition point of MCH-7 solution at a concentration of 3 wt%.

[0083] Figure 4 Test result diagrams of the rheological sol-gel-sol transition process of the MCH-2 solution prepared in Example 3 at different concentrations (from top to bottom are 1 wt%, 2 wt% and 3 wt%). Among them, Figure 4 (a) is the test result diagram of the rheological sol-gel-sol transition process of 1 wt% concentration MCH-2 solution, Figure 4 (b) is the test result diagram of the rheological sol-gel-sol transition process of 2 wt% concentration MCH-2 solution, Figure 4 (c) is the test result diagram of the rheological sol-gel-sol transition process of 3 wt% concentration MCH-2 solution.

[0084] Figure 5The figure of the thermosensitive electrolyte (ZM-MCH-a) prepared in Example 4 at different temperatures.

[0085] Figure 6 The cyclic voltammogram of the zinc-ion battery based on the thermosensitive electrolyte (ZM-MCH-a) in Example 6.

[0086] Figure 7 a is the electrochemical impedance spectrum and its equivalent circuit diagram (inset) of the zinc-ion battery based on the thermosensitive electrolyte (ZM-MCH-a) in Example 6;

[0087] Figure 7 b is the R s (Combined internal resistance) variation trend graph with temperature.

[0088] Figure 8 a is the relationship graph between the brightness of the LED lamp and the electrolyte temperature when the thermosensitive electrolyte solution (ZM-MCH-b) is connected in series to the circuit containing the LED lamp in Example 6;

[0089] Figure 8 b is the conductivity of ZM-MCH-b at different temperatures. Detailed implementation manners

[0090] To make the present invention easier to understand, the following further illustrates the implementation manners of the present invention in conjunction with specific embodiments. The following embodiments are only used to illustrate the present invention and do not limit the claims.

[0091] Example 1 Two-step preparation of methylated chitin

[0092] (1) Take 4 g of purified chitin and stir it to disperse in 200 g of an aqueous solution containing 11 wt% NaOH / 4 wt% urea that has been pre-frozen, freeze it at -30 °C for 6 h, take it out and mechanically stir to thaw it at room temperature, repeat the freeze-thaw process 2 times to obtain a transparent chitin solution. Place the chitin solution (200 g, 2 wt%) at 2 °C, and slowly add 27.9 g of methyl iodide during mechanical stirring to keep the reactants well mixed. Then raise the temperature to 5 °C and react for 6 h; finally raise the temperature to 15 °C and react for 24 h. Cool the system to 2 °C, and adjust the pH value of the system to 7.4 with 1 M hydrochloric acid. Dialyze with deionized water for 5 days to remove small molecules such as urea, residual methyl iodide, and salts in the solution, and freeze-dry to obtain a sponge-like primary product MCH-0.

[0093] (2) Redissolve the above-mentioned (1) sponge MCH-0 (500 mg) in 25 mL of 20 wt% aqueous NaOH solution, control the temperature at -20 to -30 °C to obtain a clear MCH-0 solution with a concentration of 2 wt%. Slowly add 3.5 g of methyl iodide to the MCH-0 solution, and mechanically stir it at 20 °C or 25 °C for 4-10 h according to the conditions in Table 1. Adjust the pH value of the system to 7.4 with 1 M hydrochloric acid. Dialyze with deionized water for 5 days to remove small molecules such as urea, residual methyl iodide, and salts in the solution, and freeze-dry to obtain sponge-like methylated chitin, denoted as MCH-5 to MCH-8 respectively. Their 1 1H NMR spectra are as Figure 1 shown. The total degree of O-methyl substitution DS on the carbon atoms at the third and sixth positions is calculated according to nuclear magnetic resonance o-methyl and the degree of acetylation DA. It can be seen from Table 1 that the product yield is relatively high and the degree of acetylation DA can be maintained above 76%.

[0094] Table 1. Preparation of methylated chitin under different conditions

[0095] Sample Reaction Time (h) <![CDATA[DS o-methyl > DA Yield (%) MCH-2 4* 0.46 0.83 89 MCH-5 4# 0.52 0.81 93 MCH-6 6# 0.56 0.79 92 MCH-7 8# 0.64 0.78 92 MCH-8 10# 0.71 0.76 89

[0096] where * indicates that the reaction temperature is 20 °C and # indicates that the reaction temperature is 25 °C. All products have good water solubility (1 wt%).

[0097] In this example, the base used can be replaced by one or a mixture of potassium hydroxide and lithium hydroxide, which has no obvious effect on the reaction and treatment; hydrochloric acid can be replaced by one or a mixture of sulfuric acid, formic acid, acetic acid, and nitric acid during neutralization, and different concentrations have no effect; the methylation reagent methyl iodide can also be replaced by one or a mixture of chloromethane, bromomethane, dimethyl sulfate, and dimethyl carbonate, which has no obvious effect on the methylation process, except that the required reaction time is different; the freeze-drying treatment can be replaced by drying or vacuum drying, which has no effect on the product.

[0098] When the polymer concentration in the MCH-8 aqueous solution reaches 4 wt% in this example, no obvious gel system can be formed within the range of 2-85 °C, and it becomes difficult to dissolve MCH-8 at higher concentrations, indicating that there is no thermosensitivity when the degree of substitution is relatively high.

[0099] Example 2 One-step preparation of methylated chitin

[0100] Take 4 g of purified chitin and stir it to disperse in 200 g of an aqueous solution containing 11 wt% NaOH / 4 wt% urea that has been pre-frozen. Freeze it at -30 °C for 6 h, take it out and thaw it by mechanical stirring at room temperature. Repeat the freeze-thaw process twice to obtain a transparent chitin solution. Place the chitin solution (200 g, 2 wt%) at 2 °C, and slowly add 27.9 g of iodomethane during mechanical stirring, keeping the reactants well mixed. Then raise the temperature to 5 °C and react for 12 - 72 h, then add another 27.9 g of iodomethane and raise the temperature to 10 °C and continue to react for 6 - 36 h. Adjust the pH value of the system to 7.4 with 1 M hydrochloric acid. Dialyze with deionized water for 5 days to remove small molecules such as urea, residual iodomethane, and salts in the solution, and freeze-dry to obtain a series of sponge-like methylated chitins. Among these methylated chitins, the methylated chitin with thermosensitive properties has an acetylation degree of 0.81 - 0.90 and a methylation substitution degree of 0.40 - 0.62.

[0101] From Example 1 and Example 2, it can be seen that the acetylation degree range of the thermosensitive methylated chitin is 0.78 - 0.90, and the methylation substitution degree range is 0.40 - 0.64.

[0102] Thermosensitivity test of methylated chitin in Example 3

[0103] Observe the thermosensitive reversible property of methylated chitin by the inversion method: Prepare an aqueous solution with a concentration of 3 wt% of MCH-2 at low temperature with deionized water. As Figure 2 , the aqueous solution of MCH-2 is a flowable liquid at 2 °C, forms a gel when heated to 37 °C, and finally returns to a flowable liquid when cooled to 2 °C, indicating that the MCH-2 hydrogel has thermosensitive reversibility.

[0104] Effect of different substitution degrees on the sol-gel transition point: The temperature sensitivities of MCH-2, MCH-5, MCH-6, and MCH-7 were studied using a rheometer. The storage modulus (G') represents the elastic behavior of the system, and the loss modulus (G") represents the viscous behavior of the system. The intersection point of the storage modulus (G') and the loss modulus (G″) is defined as the sol-gel transition point. MCH-2 with a concentration of 3 wt% ( Figure 3 a), MCH-5 ( Figure 3 b), MCH-6 ( Figure 3 c) and MCH-7 ( Figure 3d) The G' and G" of the aqueous solution start to intersect to form gels at 22 °C, 42 °C, 58 °C and 73 °C respectively, indicating that at the same concentration, with the increase of the degree of methyl substitution, the sol-gel transition point increases from 22 °C to 73 °C. When the degree of substitution further increases, the aqueous solution of MCH-8 with a concentration of 3 wt% has no intersection of G' and G" in the range of 2 - 80 °C, and it cannot form a stable gel system in the range of 2 - 80 °C.

[0105] Effect of different concentrations on the sol-gel transition point: The temperature sensitivity of MCH-2 solutions with different polymer concentrations was studied using a rheometer. As Figure 4 a - c are aqueous solutions of MCH-2 with concentrations of 1 wt%, 2 wt% and 3 wt% respectively, and their gel transition points are 65 °C, 43 °C and 22 °C respectively. The reason is that with the increase of the concentration of the MCH-2 aqueous solution, the number of hydrophobic groups on the polymer chain increases, the collision probability increases, and it is easier to form a hydrophobic core. Therefore, the MCH-2 aqueous solution with a high concentration has a lower gel transition point.

[0106] The gel transition point of the MCH aqueous solution has a great relationship with both the polymer concentration and the degree of substitution. By changing the degree of substitution and concentration of MCH, MCH aqueous solutions with a transition point range of 15 - 85 °C can be obtained. For example, when the concentration of the MCH-2 aqueous solution is 4 wt%, the gel transition point can be reduced to 15 °C; when the polymer concentration in the MCH-7 aqueous solution is reduced to 2 wt%, its gel transition point can be increased to 85 °C.

[0107] Example 4 Preparation of thermosensitive electrolyte

[0108] 30 mg of MCH-7 was dissolved in 1000 mg of distilled water at 4 °C, and then ZnSO4 and MnSO4 powders were added thereto to make the concentration of ZnSO4 2 mol / L and the concentration of MnSO4 0.1 mol / L, and the temperature was raised to 25 °C and stirred to dissolve. Finally, a thermosensitive electrolyte was obtained and recorded as ZM-MCH-a. The gel-sol transition diagram of this thermosensitive electrolyte in the range of 25 - 60 °C is as Figure 5 shown. Another 30 mg of MCH-7 was dissolved in 1000 mg of distilled water at 4 °C, ZnSO4 with a concentration of 0.2 mol / L and MnSO4 with a concentration of 0.01 mol / L were added, and the temperature was raised to 25 °C and stirred to dissolve. Finally, a thermosensitive electrolyte was obtained and recorded as ZM-MCH-b.

[0109] Example 5 Assembly of zinc ion battery

[0110] The active material α-MnO2, acetylene black, and polyvinylidene fluoride (PVDF) were mixed in an N-methylpyrrolidone (NMP) solvent at a mass ratio of 8:1:1, and stirring was continued to form a homogeneous slurry. Then, the slurry was coated on a stainless steel foil using a square coater and ensured to be thin and uniform. Finally, the steel foil was dried in vacuum at 75 °C for 12 hours and cut into discs with a radius of 8 mm. Using this α-MnO2 disc as the positive electrode, a zinc sheet as the negative electrode, and a glass fiber as the separator, a zinc-ion button battery (CR2032) was formed by adding spring pieces and washers. ZM-MCH-a and ZM (without adding MCH-7 and with the same concentrations of zinc sulfate and manganese sulfate as ZM-MCH-a) were added to the surface of the separator to form a thermoresponsive zinc-ion button battery and a common zinc-ion button battery.

[0111] Example 6 Electrochemical Performance Test of the Battery

[0112] The electrochemical performance was tested using a battery test system (CT 4008, Neware) in the voltage range of 0.9 V to 1.9 V. Cyclic voltammetry (CV) curves were measured at the same scan rate on an electrochemical workstation (CHI660D, Shanghai Chenhua Instrument Co., Ltd.) in the range of 0.9 - 1.9 V. Electrochemical impedance spectroscopy (EIS) data were collected at 5 mV from 100 kHz to 10 mHz.

[0113] As Figure 6 shown, the addition of methylated chitin has little effect on the electrochemical performance of the battery and almost no effect on its charge-discharge process; as Figure 7 shown in a, for the ZM-MCH-a electrolyte, when the temperature is heated from 25 °C to 75 °C, the diameter of the semicircle fitted in the high-frequency region of the EIS spectrum gradually increases, indicating that the impedance is gradually increasing, which is contrary to that of general electrolytes. The diameter of the semicircle after fitting is the charge transfer resistance R ct undergoes a mutation at about 45 °C to 60 °C, which is similar to the result in the rheological test, rising sharply from 1483 Ω at 45 °C to 4342 Ω at 55 °C. According to the data analysis of the fitting circuit, the change trend of the impedance R s (combined internal resistance) is as Figure 7 shown in b, the impedance R s increases from 54.6 Ω at 45 °C to 212.7 Ω at 55 °C. As Figure 8As shown in the figure, we connected ZM-MCH-b into a series circuit containing a light-emitting diode through a zinc sheet, a copper sheet and an external power supply. The solution was kept for 30 s at each temperature before testing. The results showed that as the temperature increased from 20 °C to 80 °C, the brightness of the light-emitting diode gradually decreased, and at the same time, the ionic conductivity of the ZM-MCH-b solution also gradually decreased. This indicates that as the temperature increases, the formation of a gel in the ZM-MCH-b solution will cause its resistance to gradually increase and the current in the circuit to gradually decrease. These results all show that the gelation transition of this temperature-sensitive electrolyte can restrict the movement of conductive ions, causing the battery resistance to increase rapidly and weakening the current to achieve the function of thermal runaway self-protection.

[0114] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A preparation method of a safe aqueous electrolyte, characterized in that, It includes the following steps: S100. At low temperature, prepare a water solution of thermosensitive methylated chitin; S200. Add an electrolyte salt to the thermosensitive methylated chitin water solution prepared in step S100, and stir until completely dissolved to prepare a thermosensitive electrolyte; when the usage environment of the electrolyte exceeds the set safety temperature, the thermosensitive electrolyte changes from a water-soluble system to a gel system with high resistance; The preparation method of the thermosensitive methylated chitin includes the following steps: S1. Dissolve the chitin raw material at low temperature to form a homogeneous alkaline chitin water solution; S2. Slowly add the methylation reagent to the alkaline chitin water solution at low temperature and stir to make it fully undergo a homogeneous reaction; S3. Neutralize the reaction solution to neutrality, then dialyze and dry to obtain thermosensitive methylated chitin; the degree of acetylation of the thermosensitive methylated chitin is 0.78 - 0.90, and the degree of methylation substitution is 0.40 - 0.

64.

2. The preparation method of the safe aqueous electrolyte according to claim 1, characterized in that In step S1, the specific dissolution method is as follows: Add the chitin raw material to an aqueous solution of alkali and urea, mix evenly at low temperature, freeze at -32 to -18 °C for 6 to 96 hours, and then stir at 2 to 25 °C to obtain a homogeneous alkaline urea water solution of chitin.

3. The preparation method of the safe aqueous electrolyte according to claim 1, characterized in that, In step S2, the reaction parameters of the homogeneous reaction are: the homogeneous reaction time is 18 to 108 hours, and the reaction temperature is 2 to 15 °C.

4. The preparation method of the safe aqueous electrolyte according to claim 1, characterized in that, The ratio of the addition amount of the methylation reagent to the molar number of the chitin structural unit is 5:1 to 20:

1.

5. The preparation method of the safe aqueous electrolyte according to claim 1, characterized in that, The degree of deacetylation of the chitin raw material is less than 20%, and the weight-average molecular weight is 5×10 4 ~ 5×10 6 .

6. The preparation method of the safe aqueous electrolyte according to claim 2, characterized in that, The alkali is one or more of sodium hydroxide, potassium hydroxide, and lithium hydroxide, and the concentration of the alkali is 5 - 30 wt%.

7. The preparation method of the safe aqueous electrolyte according to claim 2, wherein, The concentration of the urea is 0 - 15 wt%, not including 0.

8. The preparation method of the safe aqueous electrolyte according to claim 1, characterized in that, The methylation reagent is any one or a mixture of several of fluoromethane, chloromethane, bromomethane, iodomethane, dimethyl sulfate, and dimethyl carbonate.

9. The preparation method of the safe aqueous electrolyte according to claim 1, wherein The drying method is freeze-drying or drying.

10. A preparation method of a safe aqueous electrolyte, characterized in that, It includes the following steps: S100. At low temperature, prepare a water solution of thermosensitive methylated chitin; S200. Add an electrolyte salt to the thermosensitive methylated chitin water solution prepared in step S100, and stir until completely dissolved to prepare a thermosensitive electrolyte; when the usage environment of the electrolyte exceeds the set safety temperature, the thermosensitive electrolyte changes from a water-soluble system to a gel system with high resistance; The preparation method of the thermosensitive methylated chitin includes the following steps: Step (1) Prepare the primary product, and the specific method is as follows: Step 1.

1. Dissolve the chitin raw material at low temperature to form a homogeneous alkaline chitin water solution; Step 1.

2. Slowly add the methylation reagent to the alkaline chitin water solution at low temperature and stir to make it fully undergo a homogeneous reaction; Step 1.

3. Neutralize the reaction solution to neutrality, then dialyze and dry to obtain the primary product; Step (2) Prepare the final product, and the specific method is as follows: Step 2.

1. Dissolve the primary product obtained in step 1.3 in an alkaline water solution to obtain a homogeneous solution of the primary product; Step 2.

2. Then slowly add the methylation reagent to the homogeneous solution of the primary product, mix and stir for reaction; Step 2.3: Neutralize the reaction solution with acid, dialyze, and dry it to obtain thermosensitive methylated chitin as the final product. The degree of acetylation of the thermosensitive methylated chitin is 0.78 - 0.90, and the degree of methylation substitution is 0.40 - 0.

64.

11. The preparation method of the safe aqueous electrolyte according to claim 10, wherein, In Step 1.1, the specific dissolution method is as follows: Add the chitin raw material to an aqueous solution of alkali and urea, mix evenly at low temperature, freeze at -32 to -18 °C for 6 - 96 hours, and then stir at 2 - 25 °C to obtain a homogeneous aqueous solution of chitin alkaline urea.

12. The preparation method of the safe aqueous electrolyte according to claim 10, characterized in that, In Step 2.1, the specific dissolution method is as follows: Dissolve the primary product in an aqueous alkali solution with a mass concentration of 10 - 25% at -30 to -20 °C to obtain a homogeneous solution of the primary product.

13. The preparation method of the safe aqueous electrolyte according to claim 10, wherein, In Step 1.2, the reaction parameters are as follows: The reaction time is 2 - 72 hours, and the reaction temperature is 2 - 30 °C.

14. The preparation method of the safe aqueous electrolyte according to claim 10, characterized in that, In Step 2.2, the reaction parameters are as follows: The reaction time is 4 - 24 hours, and the reaction temperature is room temperature.

15. The preparation method of the safe aqueous electrolyte according to claim 10, wherein, The ratio of the addition amount of the methylation reagent to the molar number of the chitin structural unit is 5:1 - 20:

1.

16. The preparation method of the safe aqueous electrolyte according to claim 10, characterized in that, The degree of deacetylation of the chitin raw material is less than 20%, and the weight-average molecular weight is 5×10 4 ~ 5×10 6 .

17. The preparation method of the safe aqueous electrolyte according to claim 11, wherein The alkali is one or more of sodium hydroxide, potassium hydroxide, and lithium hydroxide, and the concentration of the alkali is 5 - 30 wt%.

18. The preparation method of the safe aqueous electrolyte according to claim 11, characterized in that, The concentration of the urea is 0 - 15 wt%, excluding 0.

19. The preparation method of the safe aqueous electrolyte according to claim 10, characterized in that, The methylation reagent is any one or a mixture of several of fluoromethane, chloromethane, bromomethane, iodomethane, dimethyl sulfate, and dimethyl carbonate.

20. The preparation method of the safe aqueous electrolyte according to claim 10, wherein, The drying method is freeze-drying or drying.

21. The preparation method of the safe aqueous electrolyte according to claim 1 or 10, characterized in that, The low temperature in Step S100 is 2 - 20 °C.

22. The preparation method of the safe aqueous electrolyte according to claim 1 or 10, characterized in that, In Step S100, the concentration of the aqueous solution is 1 - 3 wt%.

23. The preparation method of the safe aqueous electrolyte according to claim 1 or 10, characterized in that, In Step S200, the electrolyte salts are zinc sulfate and manganese sulfate.

24. The preparation method of the safe aqueous electrolyte according to claim 23, wherein In the thermosensitive electrolyte, the concentrations of zinc sulfate and manganese sulfate are 0.1 - 2 mol / L and 0.01 - 0.2 mol / L, respectively.

25. A safe aqueous electrolyte, characterized in that, Prepared by the preparation method described in Claim 1 or 10.

26. Use of the safety aqueous electrolyte according to claim 25, characterized in that, For use as the electrolyte of a battery or the electrolyte of an electrolytic cell.

27. A method for preparing a zinc-ion battery, characterized in that, Comprises the following steps: Prepare a battery positive electrode plate; Assemble the battery positive electrode plate, negative electrode, and separator together to form a battery. During the assembly process, coat the safety aqueous electrolyte described in Claim 25 on the surface of the separator to obtain a thermally affected battery.

28. The preparation method of the zinc ion battery according to claim 27, characterized in that, The preparation method of the battery positive electrode plate is as follows: Mix the active substance α-MnO2, acetylene black, and polyvinylidene fluoride in an N-methylpyrrolidone solvent, and continue to stir to form a homogeneous slurry; coat the slurry on a metal foil, and cut it into electrode plates after drying.

29. The preparation method of the zinc ion battery according to claim 27, wherein The negative electrode is a zinc sheet, and the separator is a glass fiber.

30. The preparation method of the zinc ion battery according to claim 27, wherein The battery positive electrode plate is cut into a circular shape and assembled into a button battery.

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