A method for preparing a nitrogen-doped reduced graphene oxide / cellulose asymmetrically modified separator for lithium-sulfur batteries
By coating both sides of the lithium-sulfur battery separator with nitrogen-doped reduced graphene oxide and cellulose, the problems of lithium polysulfide shuttle and lithium metal dendrite growth were solved, improving the battery's discharge specific capacity and cycle stability, simplifying the manufacturing process and reducing costs.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- UNIV OF SCI & TECH OF CHINA
- Filing Date
- 2024-11-22
- Publication Date
- 2026-06-30
AI Technical Summary
Existing lithium-sulfur battery separator materials are unable to effectively suppress lithium polysulfide shuttle and lithium metal dendrite growth simultaneously, resulting in limited battery performance.
A nitrogen-doped reduced graphene oxide/cellulose asymmetric modified membrane was used. By coating the positive electrode side of the membrane with nitrogen-doped reduced graphene oxide, lithium polysulfide conversion was adsorbed and catalyzed, while cellulose was coated on the negative electrode side to inhibit dendrite growth.
It achieves high discharge specific capacity and cycle stability, simplifies the preparation process and reduces costs, and has the potential for large-scale application.
Smart Images
Figure CN119481574B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of lithium-sulfur battery separator materials, specifically relating to a method for preparing a nitrogen-doped reduced graphene oxide / cellulose asymmetric modified separator for lithium-sulfur batteries. Background Technology
[0002] With economic development, society's demand for energy is gradually increasing, and the relationship between humans and energy is becoming closer. Utilizing secondary batteries to achieve efficient energy conversion and utilization is a current research hotspot. Lithium-ion batteries, as a type of secondary battery, have been widely used in electric vehicles, portable devices, and other fields; however, their relatively low theoretical energy density limits their further development. Lithium-sulfur batteries, as a new type of secondary battery, are considered to have great development potential due to their low cost, high discharge platform, high theoretical capacity, and high energy density.
[0003] Currently, the main materials for modifying lithium-sulfur battery separators include carbon materials, polymer materials, and inorganic catalyst materials. Among these, carbon materials are considered a candidate due to their advantages such as light weight, porosity, high specific surface area, and high conductivity. However, due to the non-polar nature of carbon materials, it is difficult to capture lithium polysulfides through chemical interactions; they can only suppress lithium polysulfide shuttle through physical mechanisms. Simple heteroatom doping of carbon materials can adsorb and catalyze the conversion of lithium polysulfides. Modification of the lithium metal anode side typically requires complex material preparation processes and the introduction of large amounts of active materials to suppress dendrite growth. These problems severely limit the development and practical application of lithium-sulfur batteries, thus urgently requiring the development of a modified separator that is simple to prepare and can simultaneously address the problems of both the positive and negative electrodes. Summary of the Invention
[0004] To address the aforementioned problems in lithium-sulfur batteries, this invention provides a method for preparing a nitrogen-doped reduced graphene oxide / cellulose asymmetric modified separator for lithium-sulfur batteries. The modified separator prepared by this method has advantages such as low cost, simple preparation process, and excellent structural stability. The assembled battery exhibits good cycle stability and high discharge specific capacity, thus possessing potential for large-scale electrochemical energy storage applications.
[0005] The present invention discloses a method for preparing a nitrogen-doped reduced graphene oxide / cellulose asymmetric modified membrane, comprising the following steps:
[0006] Step 1: Disperse graphite powder and sodium nitrate in deionized water, add concentrated sulfuric acid solution, and then add potassium permanganate powder; then heat the mixture, and after the reaction is complete, add excess hydrogen peroxide solution to the system to remove unreacted potassium permanganate, wash repeatedly with deionized water until the pH of the upper solution reaches a weakly acidic value; freeze-dry the washed product to obtain graphene oxide powder.
[0007] Step 2: Dissolve ammonium chloride in deionized water to obtain an ammonium chloride solution; add the graphene oxide powder obtained in Step 1 to the ammonium chloride solution and stir ultrasonically; freeze-dry the resulting product to obtain a mixed powder of graphene oxide and ammonium chloride.
[0008] Step 3: The mixed powder of graphene oxide and ammonium chloride obtained in Step 2 is subjected to high-temperature heat treatment under a nitrogen atmosphere. After natural cooling to room temperature, nitrogen-doped reduced graphene oxide, denoted as N-rGO, is obtained and used as the active material on the positive electrode side of the modified separator.
[0009] Step 4: Use commercially available cellulose powder, denoted as CF, as the active material on the negative electrode side of the modified membrane.
[0010] Step 5: The nitrogen-doped reduced graphene oxide obtained in Step 3 is used as the active material and mixed with binder and Ketjen black in a certain proportion, and coated on one side of the membrane; the cellulose obtained in Step 4 is used as the active material and mixed with binder and coated on the other side of the membrane to prepare a nitrogen-doped reduced graphene oxide / cellulose asymmetric modified membrane, denoted as N-rGO@PP@CF.
[0011] Preferably, in step 1, the concentration of concentrated sulfuric acid is 95.0~98.0%; the ratio of graphite powder, sodium nitrate, potassium permanganate, deionized water, and concentrated sulfuric acid solution is 2.0~2.5 g : 1.2~1.5 g : 8.0~10.0 g : 120~150 mL : 50~60 mL. The concentration of hydrogen peroxide is ≥30.0%.
[0012] Preferably, in step 1, the heating reaction temperature is 80°C and the reaction time is 2 h.
[0013] Preferably, in step 1, the solution is washed with deionized water until the pH of the supernatant solution reaches 3.0-4.0.
[0014] Preferably, in step 2, the ratio of graphene oxide, ammonium chloride and deionized water is 0.8~1.0 g: 4.0~5.0 g: 80~100 mL.
[0015] Preferably, in step 2, the ultrasonic stirring time is 4-5 hours.
[0016] Preferably, in step 3, the heat treatment temperature is 600~800℃, the heat treatment time is 1~2 h, and the heating rate is 5℃ / min.
[0017] Preferably, in step 5, the mass ratio of nitrogen-doped reduced graphene oxide, binder, and Ketjen black is 8:1:1; the mass ratio of cellulose to binder is 4:1. The binder is polyvinylidene fluoride.
[0018] Preferably, in step 5, the diaphragm is a commercially available polypropylene (PP) diaphragm, and the coating thickness of the slurry on both sides of the diaphragm is ≤3μm.
[0019] The present invention also provides a lithium-sulfur battery, which is obtained by assembling the nitrogen-doped reduced graphene oxide / cellulose asymmetric modified separator.
[0020] Compared with the prior art, the beneficial effects of the present invention are reflected in:
[0021] This invention prepares an asymmetric modified separator by coating active materials on both sides of the separator. Nitrogen-doped reduced graphene oxide is coated on the positive electrode side of the separator to adsorb and catalyze the conversion of lithium polysulfides, while cellulose is coated on the negative electrode side to achieve uniform lithium metal deposition and inhibit dendrite growth. Unlike traditional modified separators, the asymmetric modified separator can interact with both the positive and negative electrodes simultaneously, thus the assembled battery has high discharge specific capacity and cycle stability.
[0022] The preparation process of this invention is simple and low-cost, and has the potential for large-scale production, which contributes to the development of high-performance lithium-sulfur batteries. Attached Figure Description
[0023] Figure 1 This is a scanning electron microscope (SEM) image of the CF (Chemical Fiber) of Embodiment 1 of the present invention. From... Figure 1 As can be seen, CF exhibits a three-dimensional structure.
[0024] Figure 2 This is a scanning electron microscope (SEM) image of N-rGO prepared in Example 2 of this invention. From... Figure 2 As can be seen, N-rGO has a two-dimensional lamellar structure with a size of approximately 5~20 μm.
[0025] Figure 3 This is a high-resolution transmission electron microscope image of N-rGO prepared in Example 2 of this invention. From... Figure 3 As can be seen, N-rGO exhibits a two-dimensional lamellar structure, indicating that graphite was effectively exfoliated.
[0026] Figure 4 This is an elemental distribution diagram of N-rGO prepared in Example 2 of this invention. From... Figure 4As can be seen, C, N, and O are uniformly distributed on N-rGO.
[0027] Figure 5 This is the X-ray photoelectron spectrum of N-rGO prepared in Example 2 of this invention. From... Figure 5 As can be seen, the peaks of the N 1s spectrum at 398.36, 399.30 and 401.32 eV correspond to pyridine nitrogen, pyrrole nitrogen and graphitic nitrogen, respectively.
[0028] Figure 6 This is a cycle performance diagram of a symmetrical battery assembled from CF@PP@CF prepared in Example 1 of this invention. From... Figure 6 As can be seen from the data, the battery assembled using the CF@PP@CF separator achieves a performance of 1 mA / cm². 2 Current density and 1 mAh / cm 2 It can cycle stably for 950 hours at its capacity.
[0029] Figure 7 This is a morphology image of the lithium anode after cycling of a symmetrical battery assembled from CF@PP@CF prepared in Example 1 of this invention. Figure 7 As can be seen from the data, the battery assembled using the CF@PP@CF separator achieves a performance of 2 mA / cm². 2 Current density and 1 mAh / cm 2 After cycling 100 times at the specified capacity, it was found that no obvious dendrites were formed on the surface of the lithium metal anode after cycling, and the lithium metal deposition was relatively uniform and dense.
[0030] Figure 8 This is the electrochemical impedance spectroscopy of a symmetrical battery assembled from the CF@PP@CF prepared in Example 1 of this invention. From... Figure 8 As can be seen, the battery assembled using the CF@PP@CF separator has a lower charge transfer impedance.
[0031] Figure 9 These are optical photographs and ultraviolet images of N-rGO and rGO after adsorbing Li₂S₆, as described in Examples 2 and 3 of this invention. Figure 9 As can be seen, both N-rGO and rGO have adsorption effects on Li2S6, but N-rGO has a stronger adsorption effect on Li2S6.
[0032] Figure 10 This is a cross-sectional view of the diaphragm modified according to Embodiment 4 of the present invention. From... Figure 10 As can be seen, N-rGO and CF were coated on both sides of the diaphragm with a coating thickness of less than 3 μm.
[0033] Figure 11This is a cyclic voltammogram of a full cell assembled from N-rGO@PP@CF prepared in Example 4 and rGO@PP@CF prepared in Example 5. From... Figure 11 As can be seen, the battery assembled using the N-rGO@PP@CF separator has a higher current density and lower voltage hysteresis compared to the battery assembled using the rGO@PP@CF separator.
[0034] Figure 12 This is a cycle performance graph of a full cell assembled from N-rGO@PP prepared in Example 2 and rGO@PP prepared in Example 3 of this invention. From... Figure 12 As can be seen, the battery assembled using N-rGO@PP separator has a higher discharge specific capacity than the battery assembled using rGO@PP separator, indicating that N-rGO has a stronger adsorption and catalytic effect on lithium polysulfides than rGO.
[0035] Figure 13 This is a cycle performance graph of a full cell assembled from N-rGO@PP@CF prepared in Example 4 and rGO@PP@CF prepared in Example 5 of this invention. From... Figure 13 As can be seen, the battery assembled using the N-rGO@PP@CF separator has a higher discharge specific capacity compared to the battery assembled using the rGO@PP@CF separator. Figure 12 In terms of performance, the membrane modified with CF has better performance, indicating that CF can reduce the contact area between lithium polysulfide and the anode by uniformly depositing lithium metal anode, thereby reducing the loss of active material.
[0036] Figure 14 This is a rate performance graph of a full cell assembled from N-rGO@PP@CF prepared in Example 4 and rGO@PP@CF prepared in Example 5 of this invention. From... Figure 14 As can be seen, the battery assembled using the N-rGO@PP@CF separator has a higher discharge specific capacity at different currents compared to the battery assembled using the rGO@PP@CF separator.
[0037] Figure 15 This is a charge-discharge curve of a full cell assembled from the N-rGO@PP@CF prepared in Example 4 of this invention. From... Figure 15 As can be seen, the battery assembled using the N-rGO@PP@CF separator has a stable discharge plateau under different currents. Detailed Implementation
[0038] To further illustrate the present invention, the following describes in detail, with reference to embodiments, a method for preparing a nitrogen-doped reduced graphene oxide / cellulose asymmetric modified separator for lithium-sulfur batteries provided by the present invention. The described embodiments are some, but not all, of the embodiments of the present invention. Example 1:
[0039] In this embodiment, the cellulose / cellulose-modified membrane is prepared according to the following steps:
[0040] Step 1: Use commercially available cellulose powder, denoted as CF, as the active material for the positive and negative electrode sides of the modified membrane.
[0041] Step 2: The CF and polyvinylidene fluoride obtained in Step 1 are mixed at a mass ratio of 4:1 to prepare a slurry, which is then coated on both sides of the membrane to finally prepare a cellulose / cellulose modified membrane, denoted as CF@PP@CF. Example 2:
[0042] In this embodiment, a nitrogen-doped reduced graphene oxide modified membrane was prepared according to the following steps:
[0043] Step 1: Place 2.5 g of graphite powder and 1.5 g of sodium nitrate in a round-bottom flask, and add 150 mL of deionized water. Measure 60 mL of concentrated sulfuric acid and slowly pour it into the flask under ice-water bath conditions, while continuously stirring and maintaining a low temperature. When the reaction system no longer releases heat significantly, add 10 g of potassium permanganate to the flask. Subsequently, heat the mixture to 80°C and maintain this temperature for 2 h. After the reaction is complete, allow it to cool to room temperature, then add excess hydrogen peroxide solution to the flask to remove any unconsumed potassium permanganate. Wash repeatedly with deionized water until the pH of the supernatant reaches 3.0–4.0. Freeze-dry the washed product to obtain graphene oxide powder.
[0044] Step 2: Disperse 1 g of graphene oxide powder in 100 mL of deionized water, add 5 g of ammonium chloride, stir ultrasonically for 5 h, and freeze-dry the resulting product for 3 days to obtain a mixed powder of graphene oxide and ammonium chloride.
[0045] Step 3: Place the mixed powder of graphene oxide and ammonium chloride in a tube furnace at 800℃ under a nitrogen atmosphere and hold for 2 h at a heating rate of 5℃ / min. After naturally cooling to room temperature, nitrogen-doped reduced graphene oxide, denoted as N-rGO, is obtained and used as the active material on the positive electrode side of the modified separator.
[0046] Step 4: Prepare a slurry using N-rGO obtained in Step 3, polyvinylidene fluoride and Ketjen Black in a mass ratio of 8:1:1, and coat it on one side of the diaphragm, denoted as N-rGO@PP. Example 3:
[0047] In this embodiment, the reduced graphene oxide modified membrane was prepared according to the following steps:
[0048] Step 1: Place 2.5 g of graphite powder and 1.5 g of sodium nitrate in a round-bottom flask, and add 150 mL of deionized water. Measure 60 mL of concentrated sulfuric acid and slowly pour it into the flask under ice-water bath conditions, while continuously stirring and maintaining a low temperature. When the reaction system no longer releases heat significantly, add 10 g of potassium permanganate to the flask. Subsequently, heat the mixture to 80°C and maintain this temperature for 2 h. After the reaction is complete, allow it to cool to room temperature, then add excess hydrogen peroxide solution to the flask to remove any unconsumed potassium permanganate. Wash repeatedly with deionized water until the pH of the supernatant reaches 3.0–4.0. Freeze-dry the washed product to obtain graphene oxide powder.
[0049] Step 2: Place the graphene oxide powder in a tube furnace under a nitrogen atmosphere at 800℃ and hold for 2 h at a heating rate of 5℃ / min. After naturally cooling to room temperature, reduced graphene oxide, denoted as rGO, is obtained and used as the active material on the positive electrode side of the modified separator.
[0050] Step 3: Prepare a slurry using the rGO obtained in Step 2, polyvinylidene fluoride and Ketjen black in a mass ratio of 8:1:1, and coat it on one side of the diaphragm, denoted as rGO@PP. Example 4:
[0051] In this embodiment, a nitrogen-doped reduced graphene oxide / cellulose asymmetric modified membrane was prepared according to the following steps:
[0052] Step 1: Place 2.5 g of graphite powder and 1.5 g of sodium nitrate in a round-bottom flask, and add 150 mL of deionized water. Measure 60 mL of concentrated sulfuric acid and slowly pour it into the flask under ice-water bath conditions, while continuously stirring and maintaining a low temperature. When the reaction system no longer releases heat significantly, add 10 g of potassium permanganate to the flask. Subsequently, heat the mixture to 80°C and maintain this temperature for 2 h. After the reaction is complete, allow it to cool to room temperature, then add excess hydrogen peroxide solution to the flask to remove any unconsumed potassium permanganate. Wash repeatedly with deionized water until the pH of the supernatant reaches 3.0–4.0. Freeze-dry the washed product to obtain graphene oxide powder.
[0053] Step 2: Disperse 1 g of graphene oxide powder in 100 mL of deionized water, add 5 g of ammonium chloride, stir ultrasonically for 5 h, and freeze-dry the resulting product for 3 days to obtain a mixed powder of graphene oxide and ammonium chloride.
[0054] Step 3: Place the mixed powder of graphene oxide and ammonium chloride in a tube furnace at 800℃ under a nitrogen atmosphere and hold for 2 h at a heating rate of 5℃ / min. After naturally cooling to room temperature, nitrogen-doped reduced graphene oxide, denoted as N-rGO, is obtained and used as the active material on the positive electrode side of the modified separator.
[0055] Step 4: Use commercially available cellulose powder, denoted as CF, as the active material on the negative electrode side of the modified membrane.
[0056] Step 5: Prepare a slurry using N-rGO obtained in Step 3, polyvinylidene fluoride, and Ketjen Black at a mass ratio of 8:1:1, and coat it on one side of the membrane; prepare a slurry using CF obtained in Step 4 and polyvinylidene fluoride at a mass ratio of 4:1, and coat it on the other side of the membrane. Finally, a nitrogen-doped reduced graphene oxide / cellulose asymmetric modified membrane is prepared, denoted as N-rGO@PP@CF. Example 5:
[0057] In this embodiment, the reduced graphene oxide / cellulose asymmetric modified membrane was prepared according to the following steps:
[0058] Step 1: Place 2.5 g of graphite powder and 1.5 g of sodium nitrate in a round-bottom flask, and add 150 mL of deionized water. Measure 60 mL of concentrated sulfuric acid and slowly pour it into the flask under ice-water bath conditions, while continuously stirring and maintaining a low temperature. When the reaction system no longer releases heat significantly, add 10 g of potassium permanganate to the flask. Subsequently, heat the mixture to 80°C and maintain this temperature for 2 h. After the reaction is complete, allow it to cool to room temperature, then add excess hydrogen peroxide solution to the flask to remove any unconsumed potassium permanganate. Wash repeatedly with deionized water until the pH of the supernatant reaches 3.0–4.0. Freeze-dry the washed product to obtain graphene oxide powder.
[0059] Step 2: Place the graphene oxide powder in a tube furnace under a nitrogen atmosphere at 800℃ and hold for 2 h at a heating rate of 5℃ / min. After naturally cooling to room temperature, reduced graphene oxide, denoted as rGO, is obtained and used as the active material on the positive electrode side of the modified separator.
[0060] Step 3: Use commercially available cellulose powder, denoted as CF, as the active material on the negative electrode side of the modified membrane.
[0061] Step 4: Prepare a slurry using rGO obtained in Step 2, polyvinylidene fluoride, and Ketjen black at a mass ratio of 8:1:1, and coat it on one side of the membrane; prepare a slurry using CF obtained in Step 3 and polyvinylidene fluoride at a mass ratio of 4:1, and coat it on the other side of the membrane. Finally, a reduced graphene oxide / cellulose asymmetric modified membrane is prepared, denoted as rGO@PP@CF.
[0062] This paper describes a full cell that uses sulfur as the positive electrode material, lithium metal as the negative electrode, and the example cell as the separator, assembled into a battery. A symmetrical cell uses lithium metal as both the positive and negative electrodes, and the example cell as the separator, assembled into a battery.
[0063] The lithium-ion symmetric battery assembled in Example 1 can cycle stably for 950 h. The uniform morphology of the lithium metal anode after cycling indicates that CF has the effect of uniform lithium deposition and inhibiting lithium dendrite growth. Using the full cells assembled in Examples 2 and 3, performance results show that N-rGO has a stronger adsorption and catalytic effect on lithium polysulfides compared to rGO. Using the full cells assembled in Examples 4 and 5, the experimental results of electrochemical cyclic voltammetry, long-cycle, and rate performance show that N-rGO and CF can simultaneously interact with the positive and negative electrodes, thereby more effectively improving battery performance.
[0064] The above are merely exemplary embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. A method for preparing a nitrogen-doped reduced graphene oxide / cellulose asymmetric modified lithium-sulfur battery separator, characterized in that: A nitrogen-doped reduced graphene oxide / cellulose asymmetric modified separator was prepared by using nitrogen-doped reduced graphene oxide as the active material on the positive electrode side of the modified separator, mixing it with a binder and Ketjen black, and coating it on one side of the separator; and by using cellulose as the active material on the negative electrode side of the modified separator, mixing it with a binder and coating it on the other side of the separator. Includes the following steps: Step 1: Disperse graphite powder and sodium nitrate in deionized water, add concentrated sulfuric acid solution, and then add potassium permanganate powder; then heat the mixture, and after the reaction is complete, add excess hydrogen peroxide solution to the system to remove unreacted potassium permanganate, wash repeatedly with deionized water until the pH of the upper solution reaches a weakly acidic value; freeze-dry the washed product to obtain graphene oxide powder; Step 2: Dissolve ammonium chloride in deionized water to obtain an ammonium chloride solution; add the graphene oxide powder obtained in Step 1 to the ammonium chloride solution and stir ultrasonically; freeze-dry the resulting product to obtain a mixed powder of graphene oxide and ammonium chloride; Step 3: The mixed powder of graphene oxide and ammonium chloride obtained in Step 2 is subjected to high-temperature heat treatment under a nitrogen atmosphere. After natural cooling to room temperature, nitrogen-doped reduced graphene oxide, denoted as N-rGO, is obtained and used as the active material on the positive electrode side of the modified separator. Step 4: Use cellulose powder, denoted as CF, as the active material on the negative electrode side of the modified membrane; Step 5: The nitrogen-doped reduced graphene oxide obtained in Step 3 is mixed with binder and Ketjen black in a certain proportion and coated on one side of the membrane; cellulose is mixed with binder and coated on the other side of the membrane to prepare a nitrogen-doped reduced graphene oxide / cellulose asymmetric modified membrane, denoted as N-rGO@PP@CF. In step 2, the ratio of graphene oxide, ammonium chloride, and deionized water is 0.8~1.0 g: 4.0~5.0 g: 80~100 mL; In step 3, the heat treatment temperature is 600~800℃, the heat treatment time is 1~2 h, and the heating rate is 5℃ / min; In step 5, the coating thickness of the slurry on both sides of the diaphragm is ≤3μm.
2. The preparation method according to claim 1, characterized in that: In step 1, the ratio of graphite powder, sodium nitrate, potassium permanganate, deionized water, and concentrated sulfuric acid solution is 2.0~2.5 g: 1.2~1.5 g: 8.0~10.0 g: 120~150 mL: 50~60 mL.
3. The preparation method according to claim 1, characterized in that: In step 1, the heating reaction temperature is 80℃ and the reaction time is 2 h.
4. The preparation method according to claim 1, characterized in that: In step 1, wash with deionized water until the pH of the supernatant solution reaches 3.0-4.
0.
5. The preparation method according to claim 1, characterized in that: In step 5, the mass ratio of nitrogen-doped reduced graphene oxide, binder and Ketjen black is 8:1:1; the mass ratio of cellulose and binder is 4:
1.
6. A lithium-sulfur battery, assembled using a nitrogen-doped reduced graphene oxide / cellulose asymmetric modified lithium-sulfur battery separator prepared by any one of the preparation methods in claims 1-5.