A modified diaphragm for inhibiting lithium-oxygen battery redox medium shuttling and a preparation method and application thereof

Abstract

The present application relates to a kind of modified diaphragm for inhibiting lithium-oxygen battery redox medium shuttle and its preparation method and application, with feather as raw material, by crosslinking and high-temperature carbonization, the fibrous carbon nanomaterial of obtained.The carbon nanomaterial provided by the present application has fibrous structure, and the fibrous reticular structure formed by it can effectively block the shuttle behavior of redox medium.Using the carbon nanomaterial of the present application, the modified diaphragm for lithium-oxygen battery is designed, effectively solve the shuttle behavior of redox medium in lithium-oxygen battery, can improve the reversibility and cycle stability of lithium-oxygen battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of nanomaterials and lithium-oxygen batteries, and particularly relates to a modified diaphragm for inhibiting redox mediator shuttling of a lithium-oxygen battery and a preparation method and application thereof. BACKGROUND

[0002] The electrification of existing transportation systems using renewable energy sources such as solar and wind energy will greatly improve our environment and energy security. At present, electric vehicles are mainly based on lithium ion batteries (LIBs), however, its low capacity, high cost and so on continue to limit its practical application, among which Li-O2 batteries have attracted considerable attention due to their high theoretical energy density (~3500 W h kg -1 ) and other advantages. However, the current lithium-oxygen battery is faced with serious obstacles such as slow reaction kinetics and undesirable parasitic reactions.

[0003] In recent years, molecular catalysts, namely redox mediators (RMs), are considered as an advanced solution to catalyze the oxygen electrochemistry of Li-O2 batteries. Specifically, RMs act as electron-hole 'carriers' to facilitate the electrochemical reactions of Li-O2 batteries by transferring electrons between O2 / Li2O2 and the cathode. However, the redox shuttling of RMs leads to corrosion of the Li anode and loss of RM catalytic activity, which in turn leads to poor sustainability of the battery.

[0004] The diaphragm is the most important core component in the lithium-oxygen battery except for the positive and negative electrodes, which plays a role in preventing the positive and negative electrodes from contacting and providing a channel for lithium ion transmission. Therefore, by modifying the diaphragm to inhibit the behavior of redox mediator shuttling in the lithium-oxygen battery, the reversibility and cycle stability of the battery can be improved. SUMMARY

[0005] Therefore, the present application provides a modified diaphragm for inhibiting redox mediator shuttling of a lithium-oxygen battery and a preparation method and application thereof, which uses feathers as raw materials to prepare a fibrous carbon nanomaterial, and modifies the diaphragm of the lithium-oxygen battery, which can effectively inhibit the shuttling effect of the redox mediator and improve the reversibility and cycle stability of the lithium-oxygen battery.

[0006] In order to achieve the above-mentioned application purposes, the present application provides the following technical solutions:

[0007] A preparation method of a fibrous carbon nanomaterial, comprising the following steps:

[0008] cleaning and drying the feathers;

[0009] crosslinking the dried feathers under a protective atmosphere;

[0010] carbonizing the crosslinked feathers under a protective atmosphere.

[0011] In the preferred embodiment of the present application, the feather includes but is not limited to duck feather and goose feather; the drying temperature is 40-90℃, and the time is 12-24h.

[0012] In the preferred embodiment of the present application, in the cross-linking step, the protective atmosphere is nitrogen, the cross-linking treatment temperature is 200-240℃, the holding time is 1-3h, the temperature rising rate to the pre-oxidation setting treatment temperature is 3-5℃ / min; and after the holding ends, the temperature is naturally lowered to room temperature.

[0013] In the preferred embodiment of the present application, in the carbonization step, the protective atmosphere is nitrogen, the carbonization treatment temperature is 400-500℃, the holding time is 1-2h, the temperature rising rate to the carbonization treatment temperature is 3-5℃ / min, and after the holding ends, the temperature is naturally lowered to room temperature.

[0014] The present application also protects the fibrous carbon nanomaterial prepared by the above preparation method. The fibrous carbon nanomaterial is used for modifying the separator of the lithium-oxygen battery.

[0015] The present application also protects a modified separator, which includes a separator and a modified layer arranged on the surface of the separator; the components of the modified layer include a conductive agent, a binder and the fibrous carbon nanomaterial of the above scheme.

[0016] Preferably, the mass ratio of the fibrous carbon nanomaterial, the conductive agent and the binder is 1-3:1-3:1.

[0017] The present application also protects a preparation method of the modified separator of the above scheme, which includes the following steps:

[0018] Mixing the fibrous carbon nanomaterial with the conductive agent, the binder and the solvent to obtain a fibrous carbon nanomaterial slurry;

[0019] Drying the fibrous carbon nanomaterial slurry after being coated on the surface of the separator to obtain the modified separator.

[0020] The present application also protects a lithium-oxygen battery, which includes a metal lithium negative electrode sheet, a positive electrode, a separator and an electrolyte, and the separator is the modified separator of the above scheme or the modified separator prepared by the preparation method of the above scheme.

[0021] Compared with the prior art, the present application has the following beneficial effects:

[0022] Down feather fiber is a natural green protein fiber, so it is expected to prepare a fibrous carbon nanomaterial with a large specific surface area, a fiber network structure and long-range conductive properties, and therefore various kinds of feathers (duck feather, goose feather, etc.) can be used as raw materials of the present application. Through analysis of TG-DTG, it can be concluded that there are three stages in the decomposition of duck feather, including removal of water and small molecules, pre-carbonization and carbonization process, so in order to maintain the natural fiber morphology, the present application selects the method of first crosslinking to maintain the stability of the fiber morphology, and then carbonizing to prepare the target material. However, too high crosslinking or carbonization temperature is easy to cause the aggregation of the material to form carbon spheres, so the present application obtains the target material by adjusting different experimental conditions.

[0023] The present application first crosslinks the raw material in a protective atmosphere, so that the fibers are pre-crosslinked and shaped, and then carbonized to obtain fibrous carbon nanomaterial. The raw material used in the present application is a natural biological material, which has good adsorption and biodegradability. After carbonization, the fibrous carbon nanomaterial exhibits a large specific surface area, and the fibers are crosslinked during the pre-crosslinking and shaping process. The long-range structure of the composite material can be maintained after carbonization, and the network structure can effectively inhibit the shuttle of the oxidation-reduction medium, improve the long-cycle stability and safety of the lithium-oxygen battery, and improve the coulombic efficiency.

[0024] The carbon nanomaterial provided by the present application has a fibrous structure, and the fibrous network structure formed thereby can effectively block the shuttle behavior of the oxidation-reduction medium. The fibrous carbon nanomaterial is used to modify a commercial separator, which is applied in a lithium-oxygen battery. The results show that the lithium-oxygen battery using the modified separator of the fibrous carbon nanomaterial has higher capacity and coulombic efficiency. The carbon nanomaterial of the present application is used to design a modified separator for lithium-oxygen batteries, which effectively solves the shuttle behavior of the oxidation-reduction medium in the lithium-oxygen battery, and can improve the reversibility and cycle stability of the lithium-oxygen battery. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 TG, DTG diagrams of duck feather carbon of Example 1;

[0026] Figure 2 SEM diagram of the fibrous carbon nanomaterial prepared in Example 1;

[0027] Figure 3 Discharge capacity comparison diagram of the lithium-oxygen batteries assembled by using the modified separator and the ordinary separator in Example 1;

[0028] Figure 4 Coulombic efficiency comparison diagram of the lithium-oxygen batteries assembled by using the modified separator and the ordinary separator in Example 1. DETAILED DESCRIPTION

[0029] The present application provides a preparation method of fibrous carbon nanomaterial, which comprises the following steps:

[0030] The duck feather is washed and dried;

[0031] The dried duck feather is cross-linked under a protective atmosphere;

[0032] The cross-linked duck feather is carbonized under a protective atmosphere.

[0033] In the present application, all the raw material components are commercially available products well known to those skilled in the art, unless otherwise specified.

[0034] Example 1

[0035] (1) Preparation of fibrous carbon nanomaterials:

[0036] An appropriate amount of duck feather is washed with ultrapure water and then dried in an oven at 60°C for 24h.

[0037] The above duck feather is subjected to pre-oxidation and shaping treatment in a tube furnace, the temperature range of the heating process is room temperature to 220°C, the heating rate is 3°C / min, the holding time at 220°C is 2h, after holding, carbonization treatment is performed in the tube furnace, the temperature range of the heating process is 220°C to 450°C, the heating rate is 3°C / min, the holding time at 450°C is 1h, after holding, the material is taken out after natural cooling to 50°C, fibrous carbon nanomaterials are obtained, and grinding treatment is performed thereon for collection.

[0038] Before preparation, TG and DTG analysis of duck feather carbon under a protective atmosphere shows that there are two obvious stages of mass change at different heating rates, so they are divided into three stages, the first stage is the removal of free and bound water molecules, the second stage is the pre-carbonization process, and the third stage is the carbonization process, the temperature being 450-500°C. Therefore, the present application selects 220°C as the pre-carbonization process temperature, and 450 and 500°C as the carbonization process temperatures, respectively. The SEM results show that the fibrous morphology is more complete at a carbonization temperature of 450°C.

[0039] Figure 2 The SEM image of the fibrous carbon nanomaterials prepared in this example, as shown in FIG. 1, shows that the obtained nanocarbon material has a clear fibrous structure. Figure 2

[0040] (2) Preparation of modified separator:

[0041] ​The fibrous carbon nanomaterial prepared above is mixed with conductive agent acetylene black and binder polyvinylidene fluoride, the mixing time is 24 h, and the mixture is dissolved in a solvent N,N-dimethylformamide (DMF) solution to obtain a uniformly dispersed slurry; the mass ratio of the collagen-based fibrous carbon-hydroxyapatite nanocomposite, the conductive agent acetylene black (AB) and the binder polyvinylidene fluoride (PVDF) is 4:4:2, so that the mass concentration of polyvinylidene fluoride in the finally obtained slurry is 2 wt%.

[0042] The uniformly dispersed slurry prepared above is coated on the surface of a commercial PP separator by using a coater with a height of 120 μm. The obtained coated separator is transferred to a vacuum drying oven for drying to remove the excess solvent, the drying temperature is 60 °C, the drying time is 24 h, and the separator is cut into small round pieces with a diameter of 16 mm by using a dicing machine.

[0043] (3) Assembly of lithium-oxygen battery

[0044] The separator above is assembled into a self-made mold battery with a common metal lithium sheet negative electrode and a sulfur positive electrode sheet in a glove box, and the electrolyte is diethylene glycol dimethyl ether (Diglyme) containing 0.5 M (2,2,6,6-tetramethylpiperidinoxide) TEMPO, 0.5 M lithium bis (trifluoromethanesulfonyl) imide (LiTFSI) additive.

[0045] (4) Electrochemical performance test of lithium-oxygen battery

[0046] The lithium-oxygen battery is subjected to a cycle performance test on a charge-discharge device, and the test conditions are 0.5 mA cm -2 , and the test results are shown in Figures 3-4 .

[0047] Figure 3 FIG. 2 is a comparison chart of discharge capacity of lithium-oxygen batteries assembled with modified separators and ordinary separators, Figure 4 FIG. 3 is a comparison chart of coulombic efficiency of lithium-oxygen batteries assembled with modified separators and ordinary separators.

[0048] As can be seen from the data in Figures 3-4 , compared with the lithium-oxygen battery assembled with the ordinary separator, the lithium-oxygen battery assembled with the modified separator prepared by using the fibrous carbon nanomaterial has higher discharge capacity and more stable cycle efficiency, which indicates that the modification of the separator by using the fibrous carbon nanomaterial of the application can effectively inhibit the shuttle effect of the redox medium and improve the coulombic efficiency and cycle performance of the lithium-oxygen battery.

[0049] Example 2

[0050] (1) Preparation of fibrous carbon nanomaterial:

[0051] Take the appropriate amount of duck feather and clean it with ultrapure water, then dry it in a 60℃ oven for 24h.

[0052] The above duck feather was subjected to pre-oxidation and shaping treatment in a tube furnace, the temperature range of the heating process was room temperature to 220℃, the heating rate was 3℃ / min, and the holding time at 220℃ was 2h. After holding, carbonization treatment was carried out in the tube furnace, the temperature range of the heating process was 220℃ to 500℃, the heating rate was 3℃ / min, and the holding time at 500℃ was 1h. After holding, the material was taken out after natural cooling to 50℃, and a fibrous carbon nanomaterial was obtained, which was then ground and collected for use.

[0053] (2) Preparation of modified separator:

[0054] The above-prepared fibrous carbon nanomaterial was mixed with conductive agent acetylene black and binder polyvinylidene fluoride for 24h, and then dissolved in solvent N,N-dimethylformamide (DMF) solution to obtain a uniformly dispersed slurry. The mass ratio of collagen-based fibrous carbon-hydroxyapatite nanocomposite, conductive agent acetylene black (AB), and binder polyvinylidene fluoride (PVDF) was 4:4:2, so that the mass concentration of polyvinylidene fluoride in the final obtained slurry was 2wt%.

[0055] The above-prepared uniformly dispersed slurry was coated on the surface of a commercial PP separator using a coater with a height of 120μm. The obtained coated separator was transferred to a vacuum drying oven for drying to remove excess solvent, the drying temperature was 60℃, and the drying time was 24h. The separator was then cut into small round pieces with a diameter of 16mm using a dicing machine.

[0056] (3) Assembly of lithium-oxygen battery

[0057] The above separator was assembled into a self-made mold battery with a common metal lithium sheet negative electrode and a sulfur positive electrode sheet in a glove box, and the electrolyte was diethylene glycol dimethyl ether (Diglyme) containing 0.5M 2,2,6,6-tetramethylpiperidine oxide (TEMPO) and 0.5M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) additives.

[0058] (4) Electrochemical performance test of lithium-oxygen battery

[0059] The lithium-oxygen battery was subjected to cycle performance test on a charge-discharge device, and the test conditions were 0.5mA cm -2 , and the test results showed that, compared with the lithium-oxygen battery using a common separator, the lithium-oxygen battery assembled with the modified separator prepared by the present application had higher discharge specific capacity and more stable cycle efficiency.

[0060] The above merely describes the preferred embodiments of the present application, and it should be pointed out that, for those skilled in the art, several improvements and refinements can be made without departing from the principles of the present application, and these improvements and refinements should also be considered as falling within the protection scope of the present application.

Claims

1. A modified separator for a lithium-oxygen battery, characterized in that, The modified separator comprises a diaphragm and a modified layer arranged on the surface of the diaphragm; the components of the modified layer comprise a conductive agent, a binder and a fibrous carbon nanomaterial, and the preparation method of the fibrous carbon nanomaterial comprises the following steps: The feather is cleaned and dried; The dried feather is crosslinked in a protective atmosphere; the crosslinking treatment temperature is 200-240℃; The crosslinked feather is carbonized in a protective atmosphere; the carbonization treatment temperature is 400-500℃.

2. The modified separator according to claim 1, wherein The feather comprises duck feather or goose feather; the drying temperature is 40-90℃, and the drying time is 12-24h.

3. The modified separator of claim 1, wherein, In the crosslinking step, the protective atmosphere is nitrogen, the holding time is 1-3h, the temperature is raised to the crosslinking treatment temperature at a rate of 3-5℃ / min, and the temperature is naturally lowered to room temperature after the holding.

4. The modified separator of claim 1, wherein In the carbonization step, the protective atmosphere is nitrogen, the holding time is 1-2h, the temperature is raised to the carbonization treatment temperature at a rate of 3-5℃ / min, and the temperature is naturally lowered to room temperature after the holding.

5. The modified separator of claim 1, wherein The mass ratio of the fibrous carbon nanomaterial, the conductive agent and the binder is 1-3:1-3:

1.

6. The method of producing a modified separator according to any one of claims 1 to 5, characterized by, The preparation method comprises the following steps: The fibrous carbon nanomaterial is mixed with a conductive agent, a binder and a solvent to obtain a fibrous carbon nanomaterial slurry; The fibrous carbon nanomaterial slurry is coated on the surface of a diaphragm and dried to obtain a modified diaphragm.

7. A lithium-oxygen battery, characterized by, The modified separator comprises a diaphragm and a modified layer arranged on the surface of the diaphragm; the components of the modified layer comprise a conductive agent, a binder and a fibrous carbon nanomaterial, and the preparation method of the fibrous carbon nanomaterial comprises the following steps:

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