阅读说明：本技术 一种适用于锌离子电池的纤维素隔膜及其应用 (Cellulose diaphragm suitable for zinc ion battery and application thereof ) 是由 崔光磊 葛雪松 赵井文 张伟华 宋富辰 徐红霞 于 2020-12-16 设计创作，主要内容包括：本发明涉及电化学储能领域,具体涉及一种适用于锌离子电池的纤维素隔膜及其应用。所述纤维素隔膜为以改性纤维素作为原料,经锌离子置换后成膜所得。本发明得到的纤维素隔膜经溶剂浸润后即可组装锌离子电池,无需外加锌盐,所组装锌离子电池的锌离子迁移数可达到0.86,可以有效提高电池的循环稳定性。此外该方法简单快速、成本低、环境友好,特别适宜于低成本大规模储能体系。(The invention relates to the field of electrochemical energy storage, in particular to a cellulose diaphragm suitable for a zinc ion battery and application thereof. The cellulose diaphragm is obtained by using modified cellulose as a raw material and forming a film after zinc ion replacement. The cellulose diaphragm obtained by the invention can be assembled into the zinc ion battery after being soaked by the solvent, no additional zinc salt is needed, the zinc ion transference number of the assembled zinc ion battery can reach 0.86, and the cycling stability of the battery can be effectively improved. In addition, the method is simple and quick, low in cost, environment-friendly and particularly suitable for a low-cost large-scale energy storage system.)

1. A cellulose separator suitable for use in a zinc ion battery, comprising: the cellulose diaphragm is obtained by using modified cellulose as a raw material and forming a film after zinc ion replacement.

2. The cellulose separator suitable for use in a zinc ion battery of claim 1, wherein: the modified cellulose is used as a raw material, and is subjected to zinc ion replacement with excessive zinc-containing compounds or simple substances in an acidic or neutral aqueous solution, and a film is formed after washing for later use.

3. The cellulose separator suitable for use in a zinc ion battery of claim 2, wherein: the modified cellulose should contain-COOH, -COONa, -COOK and-SO₃H、-SO₃Na、-SO₃K、-NO₂Na or-NO₂Any one or more functional groups of K; wherein the substitution degree of the modified cellulose is 0.15-3.

4. The cellulose separator suitable for use in a zinc ion battery of claim 2, wherein: the zinc-containing compound or the simple substance is selected from any one or combination of zinc sulfate, zinc nitrate, zinc chloride, zinc oxide, zinc trifluoromethanesulfonate, zinc sheet, zinc particles or zinc powder.

5. A cellulose separator suitable for use in a zinc ion battery according to any one of claims 1 to 3, wherein: the cellulose is selected from any one or combination of several of cellulose fibril, micron cellulose fiber and nanometer cellulose fiber.

6. Use of a cellulose membrane according to claim 1, characterized in that: use of the cellulose separator according to claim 1 as a separator in an aqueous zinc ion battery.

7. A zinc-ion battery, characterized by: comprising a positive electrode, the cellulose separator according to claim 1, and a negative electrode.

8. The zinc-ion battery of claim 7, wherein: soaking the cellulose diaphragm in a solvent for 10s-10h for later use; wherein the solvent is one or more of water, dimethyl sulfoxide, acetonitrile, N-dimethylformamide, N-dimethylacetamide, toluene or acetone.

9. The zinc-ion battery of claim 7, wherein: the positive electrode of the zinc ion battery is selected from manganese dioxide, Prussian blue, vanadium pentoxide and Mo₆S₈Iodine or bromine.

Technical Field

The invention relates to the field of electrochemical energy storage, in particular to a cellulose diaphragm suitable for a zinc ion battery and application thereof.

Background

In recent years, energy crisis and environmental crisis are becoming more severe, and rapid development of the large-scale energy storage fields such as electric vehicles and energy storage power grids is promoted. The lithium ion battery has the advantages of higher energy density, high working voltage, long cycle life, low self-discharge rate, no memory effect, quick charge and discharge, environmental friendliness and the like, and is widely applied to the field of new energy automobiles. However, many problems such as poor safety and high price of the lithium ion battery have been gradually revealed. Therefore, the search for a non-lithium chemical power source which is highly safe, inexpensive, and environmentally friendly has become an important research topic for domestic and foreign electrochemical workers.

The metal zinc has good electrochemical activity (the electrode potential is-0.763V Vs SHE), is rich in reserve in the earth crust, is a secondary battery energy storage material with low cost and high safety, and draws more and more attention of researchers. The water-based secondary battery assembled by taking zinc as the negative electrode is environment-friendly, high in safety and capable of being directly packaged in an air environment, and is one of the most potential substitutes of the lithium ion battery.

The separator has an important influence on the performance of the whole battery system, but the related research in the field of aqueous zinc ion batteries is relatively few. For a qualified water-based zinc ion battery separator, the separator has the advantages of good hydrophilicity, high porosity, uniform pore size distribution, good mechanical properties, high ionic conductivity, high zinc ion migration number and the like. At present, the commonly used diaphragm of the water-based zinc ion battery is mainly glass fiber and filter paper. The glass fiber has good hydrophilicity, but the pore diameter is large, so that the glass fiber is easily punctured by zinc dendrite growing on the negative electrode, and the short circuit of the battery is caused. In addition, glass fibers are brittle and have limited application in some flexible battery applications. The filter paper has an irregular pore structure and is unevenly distributed, resulting in different degrees of electrolyte wetting, which can lead to the build-up growth of zinc dendrites. The two diaphragms are only used as framework supporting materials in the using process, the effect of blocking the positive electrode and the negative electrode and preventing short circuit is achieved, zinc salt needs to be additionally added when the battery is assembled, the cost is increased, and the zinc ion transference number of the whole battery system is low due to the fact that the positive ions and the negative ions of the zinc salt can freely move, and the electrochemical performance of the zinc ion battery is affected. Research by the Chen army and the like discovers that a nafion membrane has abundant sulfonic acid groups, can be used as a single-ion conductor after being replaced by zinc ions, and improves the electrochemical performance of a water-based zinc-ion battery. However, nafion membranes are expensive, not environmentally friendly materials, and not suitable for large-scale applications. Zhoujiang et al disclose a zinc alginate-based polymer composite gel electrolyte membrane in patent CN 110085925A, which is environment-friendly, but because free zinc salt is not removed, the transference number of zinc ions is not high, and when the zinc alginate-based polymer composite gel electrolyte membrane is applied to a water system zinc ion battery, the zinc alginate-based composite membrane is in a gel state under a water system, and has no abundant porous structure, thereby influencing the mechanical property and the ionic conductivity of the membrane.

Disclosure of Invention

The invention aims to provide a cellulose diaphragm and application thereof in a zinc ion battery.

In order to achieve the purpose, the invention adopts the technical scheme that:

the cellulose diaphragm is obtained by using modified cellulose as a raw material and forming a film after zinc ion replacement.

The modified cellulose is used as a raw material, and is subjected to zinc ion replacement with excessive zinc-containing compounds or simple substances in an acidic or neutral aqueous solution, and a film is formed after washing for later use; wherein the molar ratio of zinc added to the cellulose repeat units should be greater than 1.

The modified cellulose should contain-COOH, -COONa, -COOK and-SO₃H、-SO₃Na、-SO₃K、-NO₂Na or-NO₂Any one or more functional groups of K. Is preferably-SO₃H、-SO₃Na or-SO₃K. Wherein, the substitution degree of the modified cellulose is 0.15 to 3, preferably 0.5 to 1.5.

The zinc-containing compound or the simple substance is selected from any one or combination of zinc sulfate, zinc nitrate, zinc chloride, zinc oxide, zinc trifluoromethanesulfonate, zinc sheet, zinc particles or zinc powder. Preferably zinc sulfate, zinc oxide or zinc powder.

The cellulose is selected from any one or combination of several of cellulose fibril, micro cellulose fiber or nano cellulose fiber. Preferably nanocellulose and microfibrillated cellulose.

The diameter range of the nano cellulose fiber is 5-100nm, and the diameter range of the micron cellulose fiber is 100-1000 nm.

The pH of the acidic or neutral aqueous solution is 2-7; preferably 4 to 6; the acidic aqueous solution is one or a combination of more of dilute sulfuric acid, dilute hydrochloric acid, dilute acetic acid and citric acid aqueous solution; the neutral aqueous solution is deionized water.

The washing method is selected from any one or more of dialysis, centrifugation, suction filtration or filtration.

The application of the cellulose diaphragm is to use the cellulose diaphragm as a diaphragm in a water-based zinc ion battery.

The zinc ion battery consists of a positive electrode, the cellulose diaphragm and a negative electrode.

Soaking the cellulose diaphragm in a solvent for 10s-10h for later use; wherein the solvent is one or more of water, dimethyl sulfoxide, acetonitrile, N-dimethylformamide, N-dimethylacetamide, toluene or acetone.

The positive electrode of the zinc ion battery is selected from manganese dioxide, Prussian blue, vanadium pentoxide and Mo₆S₈Iodine or bromine.

The zinc ion battery comprises any one of a button cell battery, a soft package battery, a blade battery or a cylindrical battery.

The invention has the beneficial effects that:

the raw material of the cellulose diaphragm is selected from cellulose, the source is wide, the cost is low, the environment is friendly, the cellulose diaphragm has better mechanical property, after modification treatment, the obtained cellulose diaphragm does not need to be added with zinc salt additionally, and the use method is simple. And after the cellulose diaphragm is soaked by a water system solvent, the cellulose diaphragm can not be dissolved and obviously swelled, the pore structure in the diaphragm can be well maintained, a rapid channel is provided for migration of zinc ions, and higher ionic conductivity is obtained. The water system zinc ion battery assembled by the diaphragm has high zinc ion migration number, can effectively inhibit the growth of zinc dendrite, improves the cycling stability of the battery, is environment-friendly, has low cost and is particularly suitable for the field of large-scale energy storage.

Drawings

FIG. 1a is a transmission electron microscope image of carboxymethyl nanocellulose zinc in example 1.

FIG. 1b is a cross-sectional scanning electron microscope image of the carboxymethyl nanocellulose zinc separator in example 1.

Fig. 2 is a stress-strain curve of the carboxymethyl nanocellulose zinc film of example 1 and the cellulose-based filter paper of comparative example 2.

Fig. 3 is a graph of the zinc ion transport number test results for the assembled zinc-on-zinc cell of example 1.

FIG. 4 shows the zinc-on-zinc cell assembled in example 1 and comparative example 2 at 5mA/cm²Lower polarization long cycle curve.

Fig. 5 is a graph showing the results of a zinc ion transport number test for the assembled zinc-on-zinc cell of comparative example 1.

Fig. 6 is a graph showing the results of the zinc ion transport number test for the assembled zinc-on-zinc cell of comparative example 2.

FIG. 7 is a charge/discharge curve of a battery assembled in example 2 using Prussian blue as a positive electrode at a current density of 50 mAh/g.

FIG. 8 shows the specific charge/discharge capacity and coulombic efficiency of the first 100 cycles of the example 2 using Prussian blue as the positive electrode at a current density of 50 mAh/g.

FIG. 9 shows a value V in example 3₂O₅The charge-discharge curve of the battery assembled by the positive electrode is under the current density of 50 mAh/g.

Fig. 10 is a plot of electrochemical window of an assembled zinc-on-titanium cell using titanium foil as the working electrode in example 4.

Fig. 11 is a polarization curve for the assembled zinc versus zinc cell of example 4 at different current densities.

Detailed Description

The present invention will be described in further detail with reference to specific examples. It is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments, and all other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention are within the protection scope of the present invention without any inventive work.

The environment-friendly low-cost modified cellulose diaphragm obtained by the invention takes cellulose with excellent mechanical property and strong hydrophilicity as a raw material, and the modified cellulose diaphragm is subjected to zinc ion replacement; the obtained cellulose diaphragm can be directly assembled into a zinc ion battery after being soaked by a water system solvent without adding zinc salt additionally, and the battery has very high zinc ion migration number, can effectively inhibit the growth of zinc dendrite and improves the circulation stability. The obtained cellulose diaphragm slightly swells but does not dissolve in a water system solvent, and a good pore structure is maintained, so that the battery has high ionic conductivity. Meanwhile, the cellulose diaphragm has good transparency and certain flexibility, and can be applied to flexible batteries, implantable batteries, transparent batteries and the like.

Example 1

Weighing 5g (diameter is 10-15nm, length is 500-1000nm) of sodium carboxymethylcellulose with substitution degree of 1.0, ultrasonically dispersing in 100mL of deionized water, adjusting pH to 3-4 with 0.1mol/L dilute sulfuric acid, adding 32.2g (0.2mol) of ZnSO₄Mechanically stirring for 24h, and then removing free salt by a repeated centrifugation-washing method to prepare the carboxymethyl nano-cellulose zinc, wherein a transmission electron microscope photo of the carboxymethyl nano-cellulose zinc is shown in figure 1 a. As can be seen from FIG. 1a, the diameter of the carboxymethyl nanocellulose zinc is 10-15nm, and the length is 500-1000nm, which shows that the morphology and the size are basically kept unchanged before and after the zinc ion replacement. Then the film was filtered by suction to form a film, which was naturally dried to a film thickness of 40 μm, and the cross section of the film was measured by scanning electron microscopy as shown in FIG. 1 b. As can be seen from FIG. 1b, the film is a layered structure, in sectionThe cross section of one nano cellulose fiber can be clearly seen, and the film has higher porosity.

The tensile properties of the film were tested after equilibration for 24 hours at 50% RH, as shown in fig. 2, the tensile strength of which was 208MPa, much higher than 15MPa for the comparative cellulose-based filter paper.

The membrane was punched into a wafer, soaked in deionized water for 1 minute, and the excess water on the surface was blotted up with filter paper and tested for ionic conductivity of 10 mS/cm. Then assembling a zinc-zinc battery, testing the zinc ion migration number, and calculating the zinc ion migration number to be 0.86 at 5mA/cm according to the result in the figure 3²The polarization stability of zinc to zinc cells was tested at current densities of (a) and the results are shown in fig. 4, where the cells can be cycled stably for over 100 cycles.

Comparative example 1

Weighing 5g (diameter 10-15nm, length 500-1000nm) of sodium carboxymethylcellulose with substitution degree of 0.05, ultrasonically dispersing in 100mL of deionized water, adjusting pH to 3-4 with 0.1mol/L dilute sulfuric acid, adding 32.2g (0.2mol) of ZnSO₄Mechanically stirring for 24h, then removing free salt by a repeated centrifugation-washing method to prepare the carboxymethyl nano-cellulose zinc (the diameter is 10-15nm, the length is 500-1000nm), then filtering the carboxymethyl nano-cellulose zinc to form a film by suction, and naturally drying the film, wherein the thickness of the obtained film is 40 microns. The membrane was punched into a wafer, soaked in deionized water for 1 minute, and the excess water on the surface was blotted up with filter paper and tested for ionic conductivity of 2 mS/cm. Then assembling the zinc-zinc battery, testing the zinc ion migration number, and calculating the zinc ion migration number to be 0.70 according to the result of the figure 5.

From the comparison, compared with the example 1, the substitution degree has no obvious influence on the size and the shape before and after the sodium carboxymethylcellulose replaces the zinc ions, a good porous structure after film formation and infiltration can be ensured, but the substitution degree has obvious influence on the ionic conductivity and the zinc ion migration number (the ionic conductivity is reduced from 10mS/cm to 2 mS/cm). The reason is that the substitution degree directly affects the content of zinc ions after replacement, the ionic conductivity is reduced after the content of the zinc ions is reduced, and the adverse effect of protons in water on the transference number of the zinc ions becomes obvious, so that the transference number of the zinc ions is reduced.

Comparative example 2

Punching cellulose-based filter paper into a wafer at 1.0mol/L ZnSO₄Soaking for 1 minute, sucking off excessive water on the surface, and testing the ionic conductivity to be 8 mS/cm. Then assembling a zinc-zinc battery, testing the zinc ion migration number, and calculating according to the result of figure 6 to obtain the zinc ion migration number which is only 0.40 and is 5mA/cm²The polarization stability of zinc to zinc cells was tested at current densities of (a) and the results are shown in fig. 4, with the cells showing short circuits after 30 cycles.

As can be seen from the above comparison, compared to example 1, the ion conductivity of the battery assembled by directly using unmodified cellulose-based filter paper as a separator is not much different from that of the example, but since zinc sulfate solution is used as an electrolyte, both zinc ions and sulfate radicals therein can freely move, resulting in a decrease in the transference number of zinc ions from 0.86 of the example to 0.4. In addition, compared with example 1, the zinc ion battery assembled by using cellulose-based filter paper has short circuit after 30 cycles under the same current density, which is mainly caused by lower zinc ion migration number and uneven wetting of electrolyte.

Example 2

Weighing 5g of bacterial cellulose sodium sulfonate film with the substitution degree of 0.5, fully soaking and swelling the bacterial cellulose sodium sulfonate film in 100mL of deionized water, then adjusting the pH of the system to be between 3 and 4 by using 0.1mol/L dilute sulfuric acid, and adding 32.2g (0.2mol) of ZnSO₄And mechanically stirring for 24 hours, and then repeatedly washing with deionized water to remove free zinc salts to prepare the bacterial cellulose zinc sulfonate membrane. The wet film was punched into a circular sheet, and excess water on the surface was blotted up with filter paper to test its ionic conductivity to be 8 mS/cm. Then, a battery is assembled by taking zinc as a negative electrode and prussian blue as a positive electrode, and a charge-discharge test is carried out under the current density of 50mAh/g, wherein the charge-discharge curve is shown in figure 7, and the cycle stability is shown in figure 8.

As can be seen from fig. 7, when prussian blue is used as the positive electrode, the assembled battery can be stably charged and discharged, and the specific capacity can reach 125 mAh/g. In addition, it can be seen from fig. 8 that the battery has very good long cycle stability, the average coulombic efficiency of the battery is greater than 99%, and the capacity retention rate of the battery after 100 cycles is greater than 80%.

Example 3

Weighing 5g of bacterial cellulose sodium sulfonate film with the substitution degree of 0.5, fully soaking and swelling the bacterial cellulose sodium sulfonate film in 100mL of deionized water, then adjusting the pH of the system to be between 3 and 4 by using 0.1mol/L dilute sulfuric acid, and adding 32.2g (0.2mol) of ZnSO₄And mechanically stirring for 24 hours, and then repeatedly washing with deionized water to remove free zinc salts to prepare the bacterial cellulose zinc sulfonate membrane. The wet film was punched into a circular sheet, and excess water on the surface was blotted up with filter paper to test its ionic conductivity to be 8 mS/cm. Then zinc as the negative electrode, V₂O₅For the positive electrode assembled battery, the charge and discharge test was performed at a current density of 50mAh/g, and the charge and discharge curve is shown in FIG. 9.

From FIG. 9, it can be seen that₂O₅When the lithium ion battery is used as a positive electrode material, the assembled battery can be stably charged and discharged, and the specific capacity can reach 200 mAh/g.

Example 4

Weighing 5g of sodium nanocellulose sulfonate with the substitution degree of 1.5, ultrasonically dispersing the sodium nanocellulose sulfonate in 100mL of deionized water, adjusting the pH value of the system to be between 3 and 4 by using 0.1mol/L dilute sulfuric acid, adding 2g of zinc oxide into the solution, mechanically stirring the solution for 24 hours, removing redundant zinc oxide by filtering the solution, removing free salt by using a centrifugation-washing method to prepare the zinc nanocellulose sulfonate, carrying out suction filtration to form a film, and naturally drying the film, wherein the thickness of the obtained film is 40 micrometers. The membrane was punched into a round piece, immersed in a mixed solvent (volume ratio 1:1) of water and N, N-Dimethylformamide (DMF) for 1 minute, and the excess liquid on the surface was blotted with filter paper to test its ionic conductivity to be 12 mS/cm. Then assembling a zinc-on-stainless steel battery, testing the electrochemical window of the zinc-on-stainless steel battery at a sweep rate of 1mV/s, and testing the electrochemical stability window to reach 2.5V as shown in FIG. 10; the polarization curves of the cells at different current densities were tested by assembling zinc versus zinc cells and the results are shown in fig. 11.

As can be seen from fig. 10, the nanocellulose zinc sulfonate membrane has better electrochemical stability in a mixed solvent system of water and DMF, the electrochemical window of the nanocellulose zinc sulfonate membrane can reach 2.5V, and the nanocellulose zinc sulfonate membrane can be matched with most zinc cathode materials for use. As can be seen from fig. 11, the zinc deposition and stripping of the zinc can be better performed on the zinc cell by the assembled zinc at different current densities, and the polarization voltage is small and is less than 0.1V.