A Ruthenium-based / Cobalt-based-MOCPs Pyrolysis-Derived Nanomaterial and Its Application in Lithium-Air Batteries

Abstract

The present invention provides a ruthenium-based / cobalt-based - MOCPs pyrolysis-derived nanomaterial and its application in a lithium-air battery, belonging to the field of battery technology. The nanomaterial provided by the present invention is denoted as Ru / Co@N-C and is obtained by high-temperature carbonization of n the nanomaterial. Among them, the ruthenium-based content in Ru / Co@N-C is about 0.8-5.0 wt%, and the cobalt-based content is about 15-30 wt%. When the composite material is used as a catalyst for a lithium-air battery, it has the advantages of facilitating the migration of oxygen and lithium ions in the electrolyte, improving the catalytic activities of OER and ORR in the lithium-air battery, reducing the overpotential of the lithium-air battery, and improving the cycle stability of the battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries, and particularly relates to a ruthenium-based / cobalt-based-MOCPs pyrolysis-derived nanomaterial and its application in a lithium-air battery. Background Art

[0002] Energy storage devices with high energy density and long cycle life have attracted extensive attention in the new energy industry in recent years. Among them, rechargeable secondary lithium-ion batteries are widely used in portable electronic devices such as mobile phones, laptop computers, and digital cameras due to their low self-discharge, wide working range, long cycle life, and other advantages. Some lithium-ion batteries have even been used as power batteries for electric vehicles and achieved commercial production. However, the energy density of current lithium-ion batteries is generally not high, so the driving range of electric vehicles is far from comparable to that of ordinary vehicles. Therefore, developing a new power system with higher energy density to achieve a leap in the driving range of electric vehicles has become one of the current research hotspots in the energy field.

[0003] Among many battery energy storage systems, the organic electrolyte-based lithium-air battery has attracted wide attention due to its extremely high theoretical energy density. The charge and discharge process of the organic lithium-air battery is based on the following reversible redox reaction: 2Li + O2 ↔ Li2O2 (E0 = 2.96V vs Li / Li + ). However, at present, the lithium-air battery still faces many challenges, such as slow redox reactions usually resulting in problems such as low specific capacity, high overpotential, and poor cycle stability. Moreover, the discharge product (Li2O2) of the lithium-air battery is not easily dissolved and has poor conductivity, and it is extremely easy to block the catalytic electrode, thus making the battery unable to work. Therefore, designing a porous catalyst with high catalytic activity is extremely important for the lithium-air battery.

[0004] At present, lithium-air battery catalysts with high catalytic activity, such as carbon materials, carbon-free materials, composites of metals and metal oxides with carbon materials, etc., have received extensive attention. Among them, carbon materials (such as carbon nanotubes, mesoporous carbon, and graphene, etc.) with excellent electrical conductivity, low mass density, ultra-high specific surface area, and abundant pores are the most commonly used catalysts for lithium-air batteries. However, the catalytic activity of carbon materials for the oxygen evolution reaction (OER) is poor and side reactions are likely to occur during the charge and discharge process, thus severely restricting their practical application in lithium-air batteries. In 2012, Bruce's team tried to use non-carbon materials such as nanoporous gold as catalysts for lithium-air batteries, which improved the battery performance to a certain extent. However, the high cost and high mass density of these non-carbon material catalysts make it difficult for them to be widely used in lithium-air batteries. Carbon materials loaded with metal oxides have become catalysts for lithium-air batteries due to their advantages such as low cost, good catalytic activity, and relatively high stability. In 2013, Kim's team dispersed metal oxide Co3O4 nanofibers on graphene oxide as a catalyst for lithium-air batteries, greatly improving the battery's electrochemical performance. However, during the cycling process, these metal particles serving as active sites are prone to agglomeration and even detachment from the carbon materials. Metal-organic complex polymers (MOCPs) have the potential to become catalysts for lithium-air batteries due to their advantages such as high porosity, high specific surface area, and sufficient open metal sites. However, the surface electron conductivity of these MOCPs materials is very limited and they need to be mixed with a large amount of carbon materials, which will cause serious side reactions in lithium-air batteries. The pyrolysis derivative materials of MOCPs can not only retain the main advantages of the original MOCPs but also significantly enhance their electrical conductivity, thus arousing great research interest. However, the carbon materials exposed on the surface of MOCPs derivatives can still trigger serious side reactions. On the other hand, studies have shown that some noble metal nanoparticles can effectively inhibit side reactions in lithium-air batteries. For example, loading or embedding ruthenium-based nanoparticles on carbon materials (such as carbon nanotubes, carbon black, porous carbon, graphene, etc.) can significantly reduce the charge and discharge overpotential of lithium-air batteries and enhance the battery's reversibility. However, the high cost of noble metals limits their use, so it is very necessary to design highly catalytic porous catalysts with low-content noble metal embedding to improve the performance of lithium-air batteries. Summary of the Invention

[0005] In view of this, the present application provides a ruthenium-based / cobalt-based-MOCPs ( n [Ru / Co(PPD)(BTA)]) pyrolysis derivative, which is denoted as Ru / Co@N-C. When applied to lithium-air batteries, it has advantages such as good catalytic activity for OER and ORR, low overpotential, and high cycle stability of the battery.

[0006] The specific technical solution of this application is as follows:

[0007] This application provides a pyrolysis derivative of ruthenium-based / cobalt-based-MOCPs ([Ru / Co(PPD)(BTA)] n ), and this material is denoted as Ru / Co@N-C, which is a composite material formed on a porous nitrogen-doped carbon material embedded with ruthenium-based / cobalt-based nanoparticles;

[0008] The porous nitrogen-doped carbon material embedded with cobalt-based is obtained by high-temperature carbonization of [Ru / Co(PPD)(BTA)] n nanomaterials.

[0009] The specific surface area of the Ru / Co@N-C is 180 - 300 m 2 / g.

[0010] The pore size of the Ru / Co@N-C is mainly 0.5 - 4 nm.

[0011] The mass fraction of ruthenium-based nanoparticles in the Ru / Co@N-C is 0.4 - 6.0 wt%, and further, it can be preferably 1.5 - 4.0 wt%, for example, 2.0 wt%.

[0012] This application provides a pyrolysis derivative of ruthenium-based / cobalt-based-MOCPs ([Ru / Co(PPD)(BTA)] n ), and this material is denoted as Ru / Co@N-C, which is a composite material formed on a porous nitrogen-doped carbon material embedded with ruthenium-based / cobalt-based nanoparticles; after the pyrolysis of this composite material, through XRD and SEM tests, its morphology has not changed significantly. The highly graphitized carbon contained therein improves the electron transferability of the material.

[0013] This application also provides a preparation method of the above composite material, including the following steps: Carbonize [Ru / Co(PPD)(BTA)] n nanomaterials at high temperature to obtain a derivative, denoted as Ru / Co@N-C.

[0014] Preferably, the temperature of the high-temperature carbonization is 600°C - 1200°C, preferably 700°C - 1000°C, for example, 750°C.

[0015] Preferably, the heating rate of the high-temperature carbonization is 2°C - 10°C / minute, preferably 5°C / minute.

[0016] Preferably, the time of the high-temperature carbonization is 2 - 6 hours, preferably 4 hours.

[0017] According to an embodiment of the present invention, the preparation method of the Ru / Co@N-C further includes the preparation of Co@N-C, which specifically includes the following steps: [Co(PPD)(BTA)] n The nanomaterial is carbonized in a nitrogen atmosphere and cooled to obtain Co@N-C.

[0018] Preferably, the cobalt-containing metal salt or hydrate of the metal salt is selected from cobalt-containing halides / nitrates / carbonates / sulfates or their hydrates, etc., preferably cobalt nitrate and its hydrate;

[0019] Preferably, the ruthenium-containing metal salt or hydrate of the metal salt is selected from ruthenium-containing halides or their hydrates, or ruthenium-containing nitrates and their hydrates, preferably ruthenium-containing halides and their hydrates, such as ruthenium chloride hydrate.

[0020] Preferably, the temperature of the carbonization is 600°C to 1200°C, preferably 700°C to 1000°C, such as 750°C.

[0021] Preferably, the heating rate of the carbonization is 2°C to 10°C per minute, preferably 5°C per minute.

[0022] Preferably, the time of the carbonization is 2 to 6 hours, preferably 4 hours.

[0023] The present application also provides the use of the above-mentioned Ru / Co@N-C as a catalyst, such as a catalyst for a lithium-air battery.

[0024] The present application also provides a battery, including the above-mentioned Ru / Co@N-C composite material.

[0025] According to an embodiment of the present application, the battery is a lithium-air battery.

[0026] According to an embodiment of the present application, the Ru / Co@N-C is included in the air electrode of the lithium-air battery.

[0027] According to an embodiment of the present application, the air electrode of the lithium-air battery further includes a conductive agent Ketjen black KB and a binder polyvinylidene fluoride PVDF.

[0028] According to an embodiment of the present application, the mass ratio of Ru / Co@N-C, conductive agent and binder in the lithium-air electrode is (8 to 0):(1 to 9):1.

[0029] According to an embodiment of the present application, the lithium battery further includes an electrolyte, and the electrolyte is selected from an organic solution of a lithium salt, or a solution formed by dissolving a lithium salt in an ionic liquid.

[0030] According to an embodiment of the present application, the lithium salt is selected from lithium bis(trifluoromethanesulfonyl)imide (LTFSI), lithium perchlorate (LiClO4), or lithium trifluoromethanesulfonate (LiCF3SO3).

[0031] According to an embodiment of the present application, the battery further includes a negative electrode, and the negative electrode is selected from lithium foils.

[0032] When the composite material of the present application is used as a catalyst for a lithium-air battery, the prepared lithium-air battery is subjected to cyclic charge and discharge tests at a current density of 250 mA / g. It has a porous structure with sufficient porosity, which is beneficial to the migration of oxygen and lithium ions in the electrolyte. The specific discharge capacity in the first cycle can reach about 15000 mAh / g. At the same time, the composite material contains a large number of uniformly doped non-metal element (N) or metal element (Ru or Co) active catalytic sites. When the composite material is used as a catalyst for a lithium-air battery, the catalytic activities of OER and ORR in the lithium-air battery are improved. And the uniformly distributed ruthenium-based nanoparticles in Ru / Co@N-C effectively reduce the overpotential of the lithium-air battery and improve the cycle stability of the battery.

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0034] 1. The present invention provides a novel ruthenium-based / cobalt-based-MOCPs ([Ru / Co(PPD)(BTA)] n ), a pyrolysis-derived material (Ru / Co@N-C), and its preparation method and use. The highly graphitized carbon contained in the composite material improves the electron transferability of the material. When the composite material is used as a catalyst for a lithium-air battery, it has a porous structure with sufficient porosity, which is beneficial to the migration of oxygen and lithium ions in the electrolyte.

[0035] 2. The ruthenium-based / cobalt-based-MOCPs ([Ru / Co(PPD)(BTA)] n ), a pyrolysis-derived material (Ru / Co@N-C), prepared by the present invention contains a large number of uniformly doped non-metal element (N) or metal element (Ru or Co) active catalytic sites. When the composite material is used as a catalyst for a lithium-air battery, the catalytic activities of OER and ORR in the lithium-air battery are improved. And the uniformly distributed ruthenium-based nanoparticles in Ru / Co@N-C effectively reduce the overpotential of the lithium-air battery and improve the cycle stability of the battery.

[0036] In the present invention, LTFSI represents lithium bis(trifluoromethanesulfonyl)imide; LiClO4 represents lithium perchlorate; LiCF3SO3 represents lithium trifluoromethanesulfonate. Description of the Drawings

[0037] Figure 1Powder XRD data of Ru / Co@N-C and Co@N-C.

[0038] Figure 2 SEM characterization of Ru / Co@N-C and Co@N-C.

[0039] Figure 3 BET tests of Ru / Co@N-C and Co@N-C.

[0040] Figure 4 Comparison chart of voltage cycling stability curves of lithium-air batteries in Examples 3 and 4 at a current density of 250 mA / g and a cut-off charge-discharge specific capacity of 500 mA / g (wherein, Ru / Co@N-C represents a lithium-air battery prepared with Ru / Co@N-C as the catalyst; Co@N-C represents a lithium-air battery prepared with Co@N-C as the catalyst).

[0041] Figure 5 Comparison chart of complete charge-discharge curves of lithium-air batteries in Examples 3 and 4 at a current density of 250 mA / g (wherein, Ru / Co@N-C represents a lithium-air battery prepared with Ru / Co@N-C as the catalyst; Co@N-C represents a lithium-air battery prepared with Co@N-C as the catalyst). Detailed implementation mode

[0042] The technical solutions of the present invention will be further described in detail below in conjunction with specific embodiments. It should be understood that the following embodiments are only for illustrative and explanatory purposes of the present invention, and should not be construed as limiting the protection scope of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0043] Unless otherwise specified, the raw materials and reagents used in the following examples are all commercially available products, or can be prepared by known methods.

[0044] Example 1 [Co(PPD)(BTA)] n Preparation of nanomaterial derivative (Co@N-C)

[0045] The precursor [Co(PPD)(BTA)] n The nanomaterials were ground evenly, placed in a flowing nitrogen atmosphere, carbonized at a heating rate of 5 °C / minute to 750 °C for 4 hours, and cooled to room temperature to obtain black powder Co@N-C. After XRD and SEM tests, the detection results are as Figure 1 and 2 shown, and the results show that [Co(PPD)(BTA)] nAfter the pyrolysis of the nanomaterial, the morphology of its derivative Co@N-C did not change significantly. The specific surface area of Co@N-C was 217.8 m 2 / g as measured by BET, and the pore size was mainly 1.6 nm ( Figure 3 ).

[0046] Example 2 [Ru / Co(PPD)(BTA)] n Derivative of nanomaterial (Ru / Co@N-C)

[0047] The precursor [Ru / Co(PPD)(BTA)] n nanomaterial was ground evenly and placed in a flowing nitrogen atmosphere. It was carbonized at 750 °C for 4 hours at a heating rate of 5 °C per minute and then cooled to room temperature to obtain a black powder Ru / Co@N-C. After XRD and SEM tests, the test results are as Figure 1 and 2 shown. The results show that after the pyrolysis of the [Ru / Co(PPD)(BTA)] n nanomaterial, the morphology of its derivative Ru / Co@N-C did not change significantly. The specific surface area of Co@N-C was 230.6 m 2 / g as measured by BET, and the pore size was mainly 1.6 nm ( Figure 3 ). By ICP test, the content of ruthenium-based in Ru / Co@N-C was measured to be about 2 wt%, and the content of cobalt-based was about 24 wt%.

[0048] Example 3

[0049] The [Co(PPD)(BTA)] n nanomaterial derivative (Co@N-C) prepared in Example 1 above was used as a catalyst to prepare a lithium-air battery.

[0050] The preparation steps for the corresponding air electrode are as follows:

[0051] (1) The [Co(PPD)(BTA)] n nanomaterial derivative (Co@N-C), Ketjenblack (KB, Shenzhen Kejing), and the binder polyvinylidene fluoride (PVDF, Shenzhen Kejing) were mixed in a mass ratio of 80:10:10. N-methylpyrrolidone (NMP, Shenzhen Kejing) was added dropwise and stirred into a uniform slurry, and then the slurry was evenly coated on a carbon paper current collector to form the air electrode of the lithium-air battery;

[0052] (2) The coated carbon paper was cut according to the specifications and paired with lithium metal sheets to assemble a lithium-air battery in an argon-filled glove box. The separator used was a commercial lithium-ion battery separator Celgard 2400, and the electrolyte was a tetraethylene glycol dimethyl ether (TEGDME) electrolyte containing 1 M LTFSI. The assembled lithium-air battery was subjected to charge-discharge tests at different current densities on a LAND CT2001A model blue electrochemical workstation;

[0053] (3) The prepared lithium-air battery was subjected to cyclic charge-discharge tests at a current density of 250 mA / g, and the charge-discharge depth was controlled at 500 mAh / g. After 720 hours of cycling, the discharge terminal voltage dropped below 2 V (see Figure 4 ). With a cut-off discharge voltage of 2.0 V and a current density of 250 mA / g, the specific discharge capacity in the first cycle was only about 8000 mAh / g (see Figure 5 ).

[0054] Example 4

[0055] The [Ru / Co(PPD)(BTA)] n nanomaterial derivative (Ru / Co@N-C) prepared in Example 2 above was used as a catalyst to prepare a lithium-air battery.

[0056] The preparation steps for the corresponding air electrode are as follows:

[0057] (1) [Ru / Co(PPD)(BTA)] n The nanomaterial derivative (Ru / Co@N-C), Ketjenblack (KB, Shenzhen Kejing), and binder polyvinylidene fluoride (PVDF, Shenzhen Kejing) were mixed in a mass ratio of 80:10:10, and N-methylpyrrolidone (NMP, Shenzhen Kejing) was added dropwise and stirred into a uniform slurry. Then the slurry was evenly coated on a carbon paper current collector to form the air electrode of the lithium-air battery;

[0058] (2) The coated carbon paper was cut according to the specifications and paired with lithium metal sheets to assemble a lithium-air battery in an argon-filled glove box. The separator used was a commercial lithium-ion battery separator Celgard 2400, and the electrolyte was a tetraethylene glycol dimethyl ether (TEGDME) electrolyte containing 1 M LTFSI. The assembled lithium-air battery was subjected to charge-discharge tests at different current densities on a LAND CT2001A model blue electrochemical workstation;

[0059] (3) The prepared lithium-air battery was subjected to cyclic charge-discharge tests at a current density of 250 mA / g, and the charge-discharge depth was controlled at 500 mAh / g. After 1000 hours of cycling, the charge-discharge curve did not show obvious changes (see Figure 4). The cut-off discharge voltage is 2.0 V. At a current density of 250 mA / g, the initial discharge specific capacity can reach approximately 15000 mAh / g (see Figure 5 ).

[0060] The method of the present invention has been described through preferred embodiments. It is obvious that relevant personnel can make changes or appropriate alterations and combinations to the methods and applications described herein within the content, spirit, and scope of the present invention to implement and apply the technology of the present invention. Those skilled in the art can draw on the content of this article and appropriately improve the process parameters to achieve it. It should be particularly noted that all similar substitutions and alterations are obvious to those skilled in the art, and they are all considered to be included in the present invention.

Claims

1. A ruthenium-based / cobalt-based-MOCPs pyrolysis derivative material, denoted as Ru / Co@N-C, characterized in that, Comprising: A composite material formed by ruthenium-based / cobalt-based nanoparticles embedded in a porous nitrogen-doped carbon material, wherein the porous nitrogen-doped carbon material embedded with ruthenium-based / cobalt-based nanoparticles is obtained by high-temperature carbonization of [Ru / Co(PPD)(BTA)] n nanomaterials.

2. The ruthenium-based / cobalt-based-MOCPs pyrolysis derivative material according to claim 1, wherein The mass fraction of the ruthenium-based nanoparticles is 0.4 to 6.0 wt%.

3. The ruthenium-based / cobalt-based-MOCPs pyrolysis derivative material according to claim 2, wherein The mass fraction of the ruthenium-based nanoparticles is 1.5 to 4.0 wt%.

4. The ruthenium-based / cobalt-based-MOCPs pyrolysis derivative material according to claim 1, characterized in that, The specific surface area of the composite material is 180~300m 2 / g.

5. The ruthenium-based / cobalt-based-MOCPs pyrolysis derivative material according to claim 1, characterized in that, The pore size of the composite material is 0.5 to 4 nm.

6. The preparation method of the composite material Ru / Co@N-C according to any one of claims 1-5, characterized in that, Comprising the following steps: Carbonizing the [Ru / Co(PPD)(BTA)] n nanomaterials at high temperature yields ruthenium-based / cobalt-based-MOCPs derivatives.

7. The preparation method according to claim 6, characterized in that, The cobalt-containing metal salt or hydrate of the metal salt is selected from cobalt-containing halides, nitrates, carbonates, sulfates or their hydrates.

8. The preparation method according to claim 6, characterized in that, The cobalt-containing metal salt or hydrate of the metal salt is selected from cobalt-containing nitrates and their hydrates.

9. The preparation method according to claim 6, characterized in that, The ruthenium-containing metal salt or hydrate of the metal salt is selected from ruthenium-containing halides or their hydrates, or ruthenium-containing nitrates and their hydrates.

10. The preparation method according to claim 6, characterized in that, The ruthenium-containing metal salt or hydrate of the metal salt is selected from ruthenium-containing halides and their hydrates.

11. The preparation method according to claim 10, wherein The ruthenium-containing halide and its hydrate are selected from ruthenium chloride hydrate.

12. The preparation method according to claim 6, characterized in that, The temperature of high-temperature carbonization is 600 °C to 1200 °C. The composite material Ru / Co@N-C prepared by the preparation method according to any one of claims 6-12. Use of the composite material Ru / Co@N-C according to claim 13 as a catalyst.

15. The use according to claim 14, wherein The composite material Ru / Co@N-C as a catalyst for a lithium-air battery.

16. A lithium-air battery comprising the composite material Ru / Co@N-C according to claim 1.

17. The battery according to claim 16, wherein, The air electrode of the lithium-air battery further comprises a conductive agent Ketjen black KB and a binder polyvinylidene fluoride PVDF.

18. The battery according to claim 17, characterized in that, The mass ratio of Ru / Co@N-C, the conductive agent and the binder in the air electrode is (8 to 0):(1 to 9):1.

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