A binder for sulfur-containing cathodes, and a method for preparing and using the same

Abstract

The application provides a preparation method of an adhesive for a sulfur-containing positive electrode, which is carried out in the following steps: (1) dissolving a cerium salt in deionized water, standing, and obtaining a cerium salt solution; (2) adding an adhesive precursor into deionized water to swell, and placing in a water bath to heat, so as to obtain a uniform adhesive precursor solution; (3) introducing the cerium salt solution prepared in the step (1) into the adhesive precursor solution prepared in the step (2) by using a drainage method, mixing uniformly, and carrying out a reaction under the condition of 60 DEG C and stirring, so as to obtain the adhesive product. The application further provides the adhesive prepared by using the above method, a sulfur-containing positive electrode prepared by using the adhesive, and a preparation method of the sulfur-containing positive electrode.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of lithium secondary batteries, in particular to a binder for sulfur-containing positive electrodes, and a preparation method and application thereof. BACKGROUND

[0002] Energy is the cornerstone and important productivity of human development so far, but with the progress of human industrial revolution and the rapid increase of population, the demand for sustainable clean energy is increasing. Therefore, the secondary energy storage battery system has entered the sight of people, and lithium-sulfur battery has stood out among the new generation of secondary batteries due to its high theoretical specific capacity. Sulfur as the positive active material and lithium as the negative electrode, the theoretical specific capacity is as high as 1675 mAh / g, and the sulfur element is abundant in reserves, widely sourced, and low in pollution, which has attracted widespread attention.

[0003] However, lithium-sulfur battery still has a certain distance from extensive industrialization. The reaction characteristics of elemental sulfur in the charging and discharging process result in that the actual specific capacity is much lower than the theoretical value. The electrochemical reaction of lithium-sulfur battery is very complex, and the reaction mechanism is liquid-solid-liquid reaction. Due to the complexity of the intermediate product composition of electrochemical reaction, the solubility in electrolyte is different, which causes irreversible multiple side reactions, which is collectively called shuttle effect. On the one hand, the shuttle effect brings the active material to the negative electrode, causing the loss of active material, on the other hand, it destroys the structure of the negative electrode, consumes the electrolyte, and reduces the coulombic efficiency of the battery. In addition, due to the volume change of the positive electrode, the electrode also has the risk of separation from the current collector and cracking.

[0004] The binder plays an important role in improving the performance of the battery, especially in maintaining the cycle life and capacity retention rate of the battery. High-performance binder should have high adhesion to the current collector and provide a good conductive network for the active material. Compared with the common lithium battery binders, polyvinylidene fluoride (PVDF) and polyethylene oxide (PEO), the natural binder has good water solubility, can complete the mixing, coating and drying process of the electrode in a shorter time, and has low price and minimal environmental pollution. It has a high application potential for continuous production of industrialization.

[0005] However, the natural binder usually shows poor cycle stability during use, and the electrode material prepared by coating is easy to powder and fall off.

[0006] Therefore, the present application is proposed. SUMMARY

[0007] The present application aims at introducing rare earth cerium ions by chelation and quickly completing the cross-linking process by utilizing the large number of functional groups on the surface of natural binders, thereby enhancing the adsorption capacity of polysulfides, the multi-charge / discharge intermediates of natural binders, and improving the mechanical strength of natural binders. Meanwhile, the rare earth cerium ion cross-linked protein binder prepared based on the above method provides a preparation process of high-performance sulfur-containing positive electrodes, so as to improve the charge / discharge specific capacity and cycle stability of the sulfur-containing positive electrodes and promote the wide industrial production of lithium-sulfur batteries.

[0008] In order to achieve the above-mentioned purpose, the present application first provides a preparation method of a binder for a sulfur-containing positive electrode, which is carried out in the following steps:

[0009] (1) Dissolve cerium salt in deionized water, and stand to obtain a cerium salt solution;

[0010] (2) Swell the binder precursor in deionized water, and heat in a water bath to prepare a uniform binder precursor solution;

[0011] (3) Introduce the cerium salt solution prepared in step (1) into the binder precursor solution prepared in step (2) by using a drainage method, mix uniformly, and react under 60℃ to obtain the binder product.

[0012] Preferably or alternatively, the cerium salt is any one of cerium oxalate, cerium nitrate, cerium halide and cerium nitrate, and is preferably cerium nitrate.

[0013] Preferably or alternatively, the binder precursor is any one of carboxymethyl cellulose, sodium alginate, carboxymethyl chitosan, plant protein, animal protein and synthetic protein, and is preferably gelatin.

[0014] Preferably or alternatively, the solid content in the binder precursor solution is 1.96-10 wt.%, and is preferably 1.96 wt.%.

[0015] Preferably or alternatively, the temperature of the water bath heating in step (2) is 40-60℃, and is preferably 60℃.

[0016] Preferably or alternatively, the proportion of cerium ions in the solute in the binder solution prepared in step (3) is 4.76-20 wt.%.

[0017] Secondly, the present application further provides a binder for a sulfur-containing positive electrode, which is prepared by using the above preparation method.

[0018] Thirdly, the present application provides a sulfur-containing positive electrode, the raw materials of which include a conductive agent, a sulfur-containing active material and the above binder.

[0019] Preferably or alternatively, the sulfur-containing active substance is any one of sublimed sulfur, nano-material sulfur, organic sulfur.

[0020] Preferably or alternatively, the conductive agent is any one of acetylene black, carbon black, conductive graphite, carbon nanotube, graphene or binary and ternary conductive paste.

[0021] Finally, the application provides a preparation method of the above-mentioned sulfur-containing positive electrode, which is carried out in the following steps:

[0022] (1) mixing the binder, the conductive agent and the sulfur-containing active substance in a mass ratio of 6-10:24-35:55-70 by mass of solute to obtain a uniform slurry;

[0023] (2) coating the slurry prepared in step (1) on a current collector, standing at room temperature for shaping, drying and cutting to obtain the sulfur-containing positive electrode.

[0024] Preferably or alternatively, the mixing process in step (1) is any one of ball milling, grinding or magnetic stirring, preferably ball milling, and the mixing time is 4-6h, preferably 6h.

[0025] Preferably or alternatively, the current collector is any one of aluminum foil, carbon paper, carbon cloth, preferably aluminum foil.

[0026] Preferably or alternatively, in step (2), the shaping time is 1h, the drying temperature is 60℃ and the drying time is 24h.

[0027] Beneficial effects

[0028] The application successfully introduces rare earth cerium ions by chelation and quickly completes the cross-linking process by using a large number of functional groups on the surface of the natural binder precursor, thereby enhancing the adsorption capacity of the natural binder for polysulfide, a multi-charge / discharge intermediate, and improving the mechanical strength of the natural binder.

[0029] Meanwhile, the rare earth cerium ion cross-linked protein binder prepared by the above method provides a preparation process of a high-performance sulfur-containing positive electrode, and the prepared sulfur-containing positive electrode has high charge / discharge specific capacity and cycle stability, which is conducive to the widespread industrial production of lithium-sulfur batteries. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 The figure is the lithium polysulfide adsorption test data of effect example 1 and comparative example 2 of the application;

[0031] Figure 2 The figure is the charge / discharge performance test data of effect examples 1 and 2 and comparative examples 1, 2 and 3 of the application. DETAILED DESCRIPTION

[0032] For the purpose of facilitating the understanding of the present application, the present application will be described in further detail below in conjunction with the accompanying drawings and preferred experimental examples, but the scope of protection of the present application is not limited to the following specific examples.

[0033] Unless otherwise defined, all the professional terms used in the following are the same as the meanings commonly understood by the skilled in the art. The professional terms used in the present application are only for the purpose of describing the specific examples, and are not intended to limit the scope of protection of the present application.

[0034] Unless otherwise specified, the various raw materials, reagents, instruments and equipment used in the present application can be purchased on the market or can be prepared by the existing method.

[0035] Example 1

[0036] The present application provides a kind of binder for sulfur-containing positive electrode and the sulfur-containing positive electrode prepared using it.

[0037] 0.045g of cerium nitrate hexahydrate (crystalline water is not included in the proportion of cerium nitrate (Ce (NO3) 3)) is weighed and dissolved in 0.955mL of deionized water to obtain a cerium nitrate solution.

[0038] 0.167g of gelatin is weighed and added to 8.833mL of deionized water, and left for 30 minutes to allow the gelatin particles to swell fully, and heated in a water bath at 60°C to obtain a uniform gelatin solution.

[0039] The prepared cerium nitrate solution is introduced into the prepared gelatin solution by using the drainage method, and stirred at 60°C for 1h to obtain a binder solution with a solid content of 2wt.%.

[0040] 3.5g of the above binder solution, 0.3g of acetylene black and 0.63g of sulfur are weighed, and a planetary ball mill is used to mill for 6h, the prepared slurry is coated on an aluminum foil, and after shaping at room temperature for 1h, it is dried at 60°C for 24h to remove moisture, and cut into a sulfur-containing positive electrode with Φ = 12mm.

[0041] Example 2

[0042] The present application provides a kind of binder for sulfur-containing positive electrode and the sulfur-containing positive electrode prepared using it.

[0043] 0.024g of cerium nitrate hexahydrate is weighed and dissolved in 0.976mL of deionized water to obtain a cerium nitrate solution.

[0044] 0.182g of gelatin is weighed and added to 8.818mL of deionized water, and left for 30 minutes to allow the gelatin particles to swell fully, and heated in a water bath at 60°C to obtain a uniform gelatin solution.

[0045] The prepared cerium nitrate solution was introduced into the prepared gelatin solution by using a drainage method, and was reacted at 60 °C for 1 h under stirring to obtain a binder solution with a solid content of 2 wt.%.

[0046] The above binder solution was weighed at 3.5 g, acetylene black was weighed at 0.3 g, and sulfur was weighed at 0.63 g. The prepared slurry was coated on an aluminum foil, and was dried at 60 °C for 24 h after being shaped at room temperature for 1 h to remove water. A sulfur-containing positive electrode with a diameter of Φ = 12 mm was cut.

[0047] Comparative Example 1

[0048] The present comparative example provides a binder for a sulfur-containing positive electrode and a sulfur-containing positive electrode prepared using the same.

[0049] Cerium nitrate hexahydrate was weighed at 0.089 g and dissolved in 0.911 mL of deionized water to obtain a cerium nitrate solution.

[0050] Gelatin was weighed at 0.133 g and added to 8.867 mL of deionized water. The gelatin particles were allowed to swell for 30 minutes, and a uniform gelatin solution was obtained by heating in a water bath at 60 °C.

[0051] The prepared cerium nitrate solution was introduced into the prepared gelatin solution by using a drainage method, and was reacted at 60 °C for 1 h under stirring to obtain a binder solution with a solid content of 2 wt.%.

[0052] The above binder solution was weighed at 3.5 g, acetylene black was weighed at 0.3 g, and sulfur was weighed at 0.63 g. The prepared slurry was coated on an aluminum foil, and was dried at 60 °C for 24 h after being shaped at room temperature for 1 h to remove water. A sulfur-containing positive electrode with a diameter of Φ = 12 mm was cut.

[0053] Comparative Example 2

[0054] The present comparative example provides a sulfur-containing positive electrode.

[0055] Gelatin was weighed at 0.200 g and added to 9.800 mL of deionized water. The gelatin particles were allowed to swell for 30 minutes, and a uniform gelatin solution was obtained by heating in a water bath at 60 °C. The solid content of the gelatin solution was 2 wt.%.

[0056] The above binder solution was weighed at 3.5 g, acetylene black was weighed at 0.3 g, and sulfur was weighed at 0.63 g. The prepared slurry was coated on an aluminum foil, and was dried at 60 °C for 24 h after being shaped at room temperature for 1 h to remove water. A sulfur-containing positive electrode with a diameter of Φ = 12 mm was cut.

[0057] Comparative Example 3

[0058] The present comparative example provides a sulfur-containing positive electrode.

[0059] Take 0.200 g of vinylidene fluoride (PVDF) and add it to 9.800 g of N-methyl pyrrolidone (NMP) to obtain a uniform PVDF solution by magnetic stirring.

[0060] Take 3.5 g of the above binder solution, a certain amount of NMP, 0.3 g of acetylene black, and 0.63 g of sulfur, mix them using magnetic stirring for 48 h, coat the prepared slurry on an aluminum foil, dry it for a week after shaping at room temperature to remove water, and cut it into a sulfur-containing positive electrode with a diameter of Φ = 12 mm.

[0061] Effect Example 1

[0062] Take the binder solution prepared in Example 1 and Comparative Example 2, respectively, and freeze-dry to obtain dried binder solids. Take 20 mg of the binder solids in a 15 mL transparent glass vial, and in an oxygen-free and water-free glove box, add 4 mL of an electrolyte base mixed in equal volumes of 1,3-dioxolane (DOL) and ethylene glycol dimethyl ether (DME) to it. Add 40 μL of lithium polysulfide electrolyte with a concentration of 0.167 mol / L (its composition is Li2S6) to the electrolyte base, and after standing for 4 h, measure the adsorption capacity for polysulfides using a UV spectrophotometer.

[0063] The absorbance curves of Example 1 group, Comparative Example 2 group, and the blank group are shown in Figure 1 .

[0064] As can be seen from Figure 1 , the intensity of the lithium polysulfide absorption peak at a wavelength of about 300 nm can represent the content of lithium polysulfide in the supernatant of each experimental group. Therefore, the content of lithium polysulfide in the supernatant of Example 1 group is significantly lower than that of Comparative Example 2 group, i.e., the adsorption capacity of Example 1 group for polysulfides is better than that of Comparative Example 2 group. Therefore, it can be further inferred that after cross-linking with rare earth cerium ions, the adsorption capacity of the natural binder for polysulfides has been effectively improved, which not only effectively improves the energy density of the sulfur-containing positive electrode side, but also ensures its cycle stability, and is an effective means to improve the electrochemical activity of the natural binder.

[0065] Effect Example 2

[0066] Take the sulfur-containing positive electrodes prepared in Examples 1, 2, and Comparative Examples 1, 2, and 3, respectively, to assemble lithium-sulfur batteries.

[0067] The assembly process was carried out in an oxygen-free and water-free glove box, the shell was selected 2325 button cell shell, the positive electrode was selected from the above-mentioned examples and comparative examples, the negative electrode was ordinary metal lithium foil with Φ = 16 mm, the separator was ordinary commercial separator Celgard2325 with Φ = 19 mm, and 40 μL of electrolyte (containing 1 M lithium bis (trifluoromethylsulfonyl) imide (LiTFSI) and 0.4 M lithium nitrate (LiNO3)) was added, and the battery was used for subsequent test after standing for 10 h after assembly.

[0068] The cycle performance of each battery was tested on a charge-discharge device, and the specific test conditions were as follows: the charge-discharge test was carried out at a current density of 0.5 C, and the test results are shown in Figure 2 .

[0069] From Figure 2 It can be seen that the stable cycle capacity of the material of Example 1 is 920 mAh / g after 100 charge-discharge cycles at a current density of 0.5 C (1 C = 1675 mAh / g), and the average coulombic efficiency is greater than 99%;

[0070] The stable cycle capacity of the material of Example 2 is 900 mAh / g after 100 charge-discharge cycles at a current density of 0.5 C (1 C = 1675 mAh / g);

[0071] The stable cycle capacity of the material of Comparative Example 1 is 810 mAh / g after 100 charge-discharge cycles at a current density of 0.5 C (1 C = 1675 mAh / g);

[0072] The stable cycle capacity of the material of Comparative Example 2 is 790 mAh / g after 100 charge-discharge cycles at a current density of 0.5 C (1 C = 1675 mAh / g);

[0073] The stable cycle capacity of the material of Comparative Example 2 is 690 mAh / g after 100 charge-discharge cycles at a current density of 0.5 C (1 C = 1675 mAh / g).

[0074] The natural binder has more functional groups in the side chain, which can fix polysulfides to a certain extent, and can improve the energy density of the lithium-sulfur battery cathode to a certain extent, but the specific capacity and cycle stability still have a large space for improvement. By using cerium ion crosslinking, the fixing effect of polysulfides on the positive side can be effectively improved, and the energy density and cycle stability of the lithium-sulfur full battery can be improved. Although the amount of cerium ions introduced is related to the fixing ability of polysulfides, too much high-valent metal ions will inevitably destroy the natural molecular structure, making it impossible to maintain the structural stability of the battery cathode, resulting in little difference in cycle performance between Comparative Example 1 and Comparative Example 2.

[0075] As can be seen from the above, the rare earth cerium ion crosslinked protein binder prepared by the above method has high electrochemical activity, and the lithium-sulfur battery cathode prepared has high charge-discharge specific capacity and cycle stability, which is conducive to the widespread industrial production of lithium-sulfur batteries.

[0076] Finally, it should be pointed out that: the above examples are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for preparing a binder for a sulfur-containing positive electrode, characterized by, The following steps are taken: (1) Dissolve cerium salt in deionized water, stand, and obtain cerium salt solution; (2) Add the binder precursor to deionized water to swell, and place in a water bath to heat, and prepare a uniform binder precursor solution; (3) Introduce the cerium salt solution prepared in step (1) into the binder precursor solution prepared in step (2) by using a drainage method, mix, and react under 60℃ heat preservation and stirring, and obtain the binder. The binder precursor is any one of carboxymethyl cellulose, sodium alginate, carboxymethyl chitosan, plant protein, animal protein, and synthetic protein.

2. The production method according to claim 1, characterized by, The cerium salt is any one of cerium oxalate, cerium nitrate, cerium halide, and cerium nitrate.

3. The preparation method according to claim 1, characterized in that, The cerium salt is cerium nitrate.

4. The method of claim 1, wherein, The binder precursor is gelatin.

5. The preparation method according to claim 1, characterized in that, The solid content in the binder precursor solution is 1.96-10 wt.%.

6. The method of claim 1, wherein, The solid content in the binder precursor solution is 1.96 wt.%.

7. The preparation method according to claim 1, characterized in that, The temperature of water bath heating in step (2) is 40-60℃.

8. The method of claim 1, wherein, The temperature of water bath heating in step (2) is 60℃.

9. The method of claim 1, wherein, The proportion of cerium ions in the prepared binder solution in step (3) is 4.76-20 wt.%.

10. A binder for a sulfur-containing positive electrode, characterized by, The binder is prepared by using the preparation method in any one of claims 1-9.

11. A sulfur-containing positive electrode, characterized by comprising: The raw materials of the sulfur-containing positive electrode include a conductive agent, a sulfur-containing active material, and the binder in claim 10.

12. The sulfur-containing cathode of claim 11, wherein, The sulfur-containing active material is any one of sublimed sulfur, nano-material sulfur, and organic sulfur.

13. The sulfur-containing cathode of claim 11, wherein, The conductive agent is any one of acetylene black, carbon black, conductive graphite, carbon nanotubes, graphene, or binary and ternary conductive paste.

14. A method of producing a sulfur-containing positive electrode as claimed in any one of claims 11 to 13, characterized by, The following steps are taken: (1) Mix the binder, the conductive agent, and the sulfur-containing active material in a mass ratio of 6-10:24-35:55-70, and obtain a uniform slurry; (2) Coat the slurry prepared in step (1) on a current collector, stand at room temperature to shape, dry, and cut to obtain the sulfur-containing positive electrode.

15. The method of claim 14, wherein, The mixing process in step (1) is any one of ball milling, grinding, or magnetic stirring, and the mixing time is 4-6h.

16. The method of claim 14, wherein, The mixing process in step (1) is ball milling. The mixing time is 6h.

17. The method of claim 14, wherein, The current collector is any one of aluminum foil, carbon paper, and carbon cloth.

18. The method of claim 14, wherein, The current collector is aluminum foil.

19. The method of claim 14, wherein, In step (2), the shaping time is 1h, the drying temperature is 60℃, and the drying time is 24h.

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