Lithium metal capacitor and preparation method thereof

Abstract

The present application relates to the technical field of capacitors, and in particular to a lithium metal capacitor and a method for preparing the same. The lithium metal capacitor of the present application includes a positive electrode, a negative electrode, and a diaphragm and an electrolyte located between the positive electrode and the negative electrode. The positive electrode includes a positive electrode current collector and a positive electrode active material layer bonded to the surface of the positive electrode current collector. The positive electrode active material layer includes porous activated carbon, a conductive agent, and a binder. The surface of the positive electrode active material layer facing away from the positive electrode current collector is provided with a nanoscale metal oxide layer, and the negative electrode is lithium metal. The present application provides a nanoscale metal oxide layer as a protective layer on the surface of the positive electrode active material layer, so that the positive electrode has good high-voltage stability in the lithium metal capacitor. Such a positive electrode can make the device have electrochemical properties of high voltage and long cycle life, and has the characteristics of fast charging and discharging. Therefore, the present application has good application prospects in lithium metal capacitors as asymmetric supercapacitors.

Description

Technical Field

[0001] The present application belongs to the technical field of capacitors, and in particular, relates to a lithium metal capacitor and a preparation method thereof. Background Art

[0002] The electrode materials of lithium-ion capacitors (LICs) integrate battery-type electrodes and capacitor-type carbon electrodes, so they are expected to inherit the advantages of high specific energy of lithium-ion batteries (LIBs) and high specific power of electrochemical capacitors (ECs). However, the energy and cycle life of lithium-ion capacitors are approaching their limits, and there is still a big gap with the requirements of lithium-ion batteries.

[0003] According to different charge storage mechanisms, the battery-type electrodes of lithium-ion capacitors can generally be divided into three categories: insertion type, conversion type and alloy type. Lithium-ion insertion type electrode materials face the defect of low specific capacity, while the specific capacity of conversion type and alloy type electrode materials can exceed 1000mAh g -1 , and has a relatively low lithiation / delithiation voltage (<0.5V vs. Li / Li + ), which can significantly increase the specific capacity, broaden the voltage window of lithium-ion capacitors, and significantly increase the specific energy. However, the highest specific energy reported so far is still less than 280Wh kg -1 (Based on the active materials of positive and negative electrodes), so it is necessary to develop advanced electrode materials with high specific capacity and strong ion / electron transfer ability. Traditional capacitive electrode materials include activated carbon, graphene, carbon nanotubes (CNT), mesoporous carbon, and two-dimensional layered materials derived from transition metal carbon / nitrogen / carbonitride (MXene). Due to the large specific surface area, many active sites and defects, these materials are accompanied by side reactions with the electrolyte during operation, resulting in capacity decay.

[0004] However, lithium metal capacitors (LMCs) are new hybrid capacitors that use lithium metal to replace the traditional negative electrode and match the positive electrode such as activated carbon. Metal lithium has the highest theoretical specific capacity (3860mAh g -1 ) and the lowest redox potential (-3.04V), and is considered to be the most ideal negative electrode substitute in rechargeable batteries. This device can significantly improve the energy density of traditional lithium-ion capacitors, but its safety is relatively low.

[0005] Lithium metal capacitors have problems with lithium dendrite growth and flammability, so they are limited to a relatively low cycle life. At the same time, traditional capacitor-type activated carbon materials have a high specific surface area and relatively more defects. They are prone to side reactions with the electrolyte during long cycles, especially under high voltage, resulting in poor high-voltage cycle stability and difficulty in breaking through the 3V voltage. It is currently difficult to design these activated carbon electrode materials into asymmetric lithium metal capacitors with a high voltage window. Summary of the invention

[0006] The purpose of the present application is to provide a lithium metal capacitor and a preparation method thereof, aiming to solve the technical problem that the existing activated carbon modification effect is not ideal and is difficult to use in asymmetric lithium metal capacitors with high voltage windows.

[0007] In order to achieve the above application purpose, the technical solution adopted in this application is as follows:

[0008] In the first aspect, the present application provides a lithium metal capacitor, comprising a positive electrode, a negative electrode, and a separator and an electrolyte located between the positive electrode and the negative electrode, the positive electrode comprising a positive electrode collector and a positive electrode active material layer bonded to the surface of the positive electrode collector, the positive electrode active material layer comprising porous activated carbon, a conductive agent and a binder, a nanoscale metal oxide layer is provided on the surface of the positive electrode active material layer facing away from the positive electrode collector, and the negative electrode is lithium metal.

[0009] In one embodiment, the thickness of the nano-scale metal oxide layer is 0.5-5 nm.

[0010] In one embodiment, the metal oxide in the nano-scale metal oxide layer is selected from any one of aluminum oxide, titanium dioxide, aluminum oxide doped with zinc oxide, zinc oxide and MnCo2O4.

[0011] In one embodiment, the pore size of the porous activated carbon is 0.5 to 10 nm;

[0012] And / or, the specific surface area of ​​the porous activated carbon is 1000 to 3000 m 2 / g.

[0013] In one embodiment, the mass ratio of the porous activated carbon, the conductive agent and the binder is 80-90:8-12:2-8.

[0014] In a second aspect, the present application provides a method for preparing a lithium metal capacitor, comprising the following steps:

[0015] According to the composition of the lithium metal capacitor of the present application, a positive electrode, a negative electrode, a separator and an electrolyte in the lithium metal capacitor are provided;

[0016] The positive electrode, the negative electrode, the separator and the electrolyte are assembled to obtain a lithium metal capacitor.

[0017] In one embodiment, the method for preparing the positive electrode includes:

[0018] A positive electrode slurry containing porous activated carbon, a conductive agent and a binder is prepared, and then the positive electrode slurry is coated on a positive electrode current collector and dried to obtain a positive electrode active material layer;

[0019] Atomic layer deposition technology is used to deposit a nano-scale metal oxide layer on the surface of the positive electrode active material layer.

[0020] In one embodiment, a method for preparing porous activated carbon includes:

[0021] The biomass precursor is crushed, sieved, and then pre-carbonized to obtain a pre-carbonized product;

[0022] The pre-carbonized product is placed in an alkaline solution for chemical etching, and then dried to obtain an etching powder;

[0023] The etched powder is calcined at an elevated temperature, and then the calcined product is acid-washed and water-washed to obtain porous activated carbon.

[0024] In one embodiment, the biomass precursor is selected from at least one of radish shell, green tea leaves, pitaya peel, and coconut shell;

[0025] and / or, the pre-carbonization treatment comprises heating the temperature to 480-520° C. at a heating rate of 4-6° C. / min and then maintaining the temperature for 0.5-1.5 h;

[0026] And / or, the alkali solution is selected from any one of a sodium hydroxide solution and a potassium hydroxide solution;

[0027] and / or, the chemical etching treatment includes heating at 80 to 120° C. for 10 to 14 hours;

[0028] And / or, the temperature-raising calcination includes raising the temperature to 380-420° C. at a heating rate of 4-6° C. / min, keeping the temperature for 1-2 hours, and then continuing to raise the temperature to 750-850° C. at a heating rate of 4-6° C. / min, and keeping the temperature for 1-3 hours.

[0029] In one embodiment, the step of depositing a nanoscale metal oxide layer on the surface of the positive electrode active layer using an atomic layer deposition technique comprises placing a positive electrode current collector having a positive electrode active material layer formed on the surface thereof in an atomic layer deposition apparatus and performing 5 to 50 pulse cycles as follows:

[0030] The metal organic compound molecules are exposed to metal organic compound molecules for 0.1 to 0.2 s, and argon gas is purged for 0.1 to 0.2 s; the metal organic compound molecules are metal organic compound molecules corresponding to any one metal selected from aluminum, titanium, zinc, cobalt and manganese.

[0031] The lithium metal capacitor provided in the first aspect of the present application has a unique nanoscale metal oxide layer on the surface of the positive electrode active material layer of the positive electrode facing away from the positive electrode current collector to achieve modification of the positive electrode active material layer, that is, the nanoscale metal oxide layer is deposited on the surface of the positive electrode active material layer of the porous activated carbon as a protective layer. Such a positive electrode has good high-voltage stability in a lithium metal capacitor. Using the positive electrode in a lithium metal capacitor of an asymmetric supercapacitor can make the device have electrochemical properties of high voltage and long cycle life, and has the characteristics of fast charging and discharging. Therefore, the present application has good application prospects in lithium metal capacitors as an asymmetric supercapacitor.

[0032] The preparation method of the lithium metal capacitor provided in the second aspect of the present application is to assemble the positive electrode, negative electrode, diaphragm and electrolyte in the lithium metal capacitor. In the lithium metal capacitor assembled in this way, a thin, uniform and dense nanoscale metal oxide layer is formed on the surface of the positive electrode active material layer of the positive electrode as a protective layer. The nanoscale metal oxide layer can inhibit the oxygen-containing functional groups with high surface activity of the porous activated carbon. The lithium metal capacitor obtained by such a preparation method has good energy density and high-voltage cycle stability as an asymmetric supercapacitor. Moreover, the process conditions of the preparation method are simple and mild, and the industrial production of lithium metal capacitors can be realized. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0034] Figure 1 is a schematic diagram of the structure of a lithium metal capacitor provided in an embodiment of the present application; wherein the Figure 1 The reference numerals are as follows: 1-positive electrode, 11-positive electrode current collector, 12-positive electrode active layer, 13-nanoscale metal oxide layer, 2-negative electrode, 3-separator, 4-electrolyte;

[0035] Figure 2 It is a schematic diagram of the preparation process of porous activated carbon in the electrode material provided in the embodiment of the present application;

[0036] Figure 3 is a scanning electron microscope (SEM) schematic diagram of the porous activated carbon MJ5 prepared in the example of the present application;

[0037] Figure 4 Schematic diagram of pore size distribution of porous activated carbon MJ5 prepared in the embodiment of the present application;

[0038] Figure 5: is a schematic diagram of X-ray photoelectron spectroscopy (XPS) fitting of the porous activated carbon MJ5 prepared in the embodiment of the present application;

[0039] Figure 6 This is a comparison chart of the rate performance of the lithium metal capacitor before and after the ALD modification of the porous activated carbon in the lithium metal capacitor provided in the embodiment of the present application;

[0040] Figure 7 This is a comparison chart of the long cycle life performance of lithium metal capacitors before and after ALD modification of porous activated carbon in the lithium metal capacitor provided in the examples of the present application. DETAILED DESCRIPTION

[0041] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application more clearly understood, the present application is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0042] In this application, the term "and / or" describes the association relationship of associated objects, indicating that there may be three relationships. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. A and B can be singular or plural. The character " / " generally indicates that the associated objects are in an "or" relationship.

[0043] In the present application, "at least one" means one or more, "more than one" means two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single or plural items.

[0044] It should be understood that in the various embodiments of the present application, the size of the serial numbers of the above-mentioned processes does not mean the order of execution, some or all of the steps can be executed in parallel or sequentially, and the execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0045] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms "a", "said" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings.

[0046] The weight of the relevant components mentioned in the specification of the embodiments of the present application can not only refer to the specific content of each component, but also represent the proportional relationship of the weights of the components. Therefore, as long as the content of the relevant components is proportionally enlarged or reduced according to the specification of the embodiments of the present application, it is within the scope disclosed in the specification of the embodiments of the present application. Specifically, the mass described in the specification of the embodiments of the present application can be μg, mg, g, kg and other mass units known in the chemical industry. The room temperature in this application can be 25-27°C.

[0047] The terms "first" and "second" are used only for descriptive purposes to distinguish objects such as substances from each other, and should not be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. For example, without departing from the scope of the embodiments of the present application, the first XX may also be referred to as the second XX, and similarly, the second XX may also be referred to as the first XX. Thus, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features.

[0048] In a first aspect, an embodiment of the present application provides a lithium metal capacitor, such as Figure 1 As shown, the lithium metal capacitor includes a positive electrode 1, a negative electrode 2, and a separator 3 and an electrolyte 4 located between the positive electrode 1 and the negative electrode 2. The positive electrode 1 includes a positive electrode collector 11 and a positive electrode active material layer 12 bonded to the surface of the positive electrode collector 11. The positive electrode active material layer 12 includes porous activated carbon, a conductive agent and a binder. The surface of the positive electrode active material layer 12 facing away from the positive electrode collector 11 is provided with a nanoscale metal oxide layer 13. The negative electrode 2 is lithium metal.

[0049] The lithium metal capacitor provided in the embodiment of the present application has a unique nanoscale metal oxide layer 13 on the surface of the positive electrode active material layer 12 of the positive electrode 1 facing away from the positive electrode current collector 11, thereby modifying the positive electrode active material layer 12, that is, depositing the nanoscale metal oxide layer 13 on the surface of the positive electrode active material layer 12 of the porous activated carbon as a protective layer. Such a positive electrode 1 has good high-voltage stability in the lithium metal capacitor. Using the positive electrode 1 in the lithium metal capacitor of the asymmetric supercapacitor can make the device have electrochemical properties of high voltage and long cycle life, and has the characteristics of fast charging and discharging. Therefore, the embodiment of the present application has a good application prospect in the lithium metal capacitor as an asymmetric supercapacitor.

[0050] In one embodiment, the thickness of the nano-scale metal oxide layer 13 on the surface of the positive electrode 1 is 0.5 to 5 nm; for example, 1 nm, 2 nm, 3 nm, 4 nm, etc. The nano-scale metal oxide layer within this thickness range can provide good protection for the porous activated carbon. Furthermore, the metal oxide in the nano-scale metal oxide layer is selected from any one of aluminum oxide, titanium dioxide, aluminum oxide doped with zinc oxide, zinc oxide, and MnCo2O4. Specifically, it can be a nano-scale aluminum oxide layer, a nano-scale titanium dioxide layer, or a nano-scale zinc oxide layer, etc.

[0051] In one embodiment, the pore size of the porous activated carbon in the positive electrode active material layer 12 is 0.5 to 10 nm; more preferably, the pore size of the porous activated carbon is 1 to 6 nm; specifically, the pore size distribution of the porous activated carbon is between less than 2 nm (micropores) and 2-6 nm (mesopores). When such a rich mesoporous and microporous structure is used in an asymmetric lithium metal capacitor, the electrolyte ions in the electrolyte can be better embedded / released.

[0052] In one embodiment, the specific surface area of ​​the porous activated carbon in the positive electrode 1 is 1000-3000 m 2 / g; for example, it can be 1000m 2 / g、1500m 2 / g, 2000m 2 / g、2500m 2 / g、2800m 2 / g, etc. The positive electrode active material layer formed by the porous activated carbon within the above specific surface area range can well deposit a nano-scale metal oxide layer on the surface.

[0053] In one embodiment, the mass ratio of porous activated carbon, conductive agent and binder in the positive electrode 1 is 80-90:8-12:2-8. Specifically, the electrode slurry containing porous activated carbon, conductive agent and binder can be prepared according to the above ratio, and then the electrode slurry is scraped on the positive electrode collector and dried to obtain the positive electrode active layer. The conductive agent can be carbon black, etc., the binder can be polyvinylidene fluoride, etc., and the positive electrode collector can be aluminum foil, etc.

[0054] In one embodiment, the electrolyte is an electrolyte containing a lithium salt. The lithium salt may be lithium tetrafluoroborate (LiBF4), lithium hexafluorophosphate (LiPF6), a new lithium salt lithium bis(fluorosulfonyl)imide (LiFSI), etc. The solvent may be a commonly used carbonate solvent, including propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), etc. The diaphragm may be a diaphragm commonly used in supercapacitors, including one or more of a biomass-based diaphragm, a synthetic polymer-based diaphragm, and an inorganic composite diaphragm.

[0055] Specifically, a lithium metal capacitor includes a positive electrode, a negative electrode, a separator and an electrolyte located between the positive electrode and the negative electrode. The positive electrode includes a positive electrode current collector and a positive electrode active material layer bonded to the surface of the positive electrode current collector. The positive electrode active material layer includes porous activated carbon, a conductive agent and a binder. A nanoscale metal oxide layer is provided on the surface of the positive electrode active material layer close to the separator. The negative electrode is lithium metal. The nanoscale metal oxide layer can be deposited as a thin film using atomic layer deposition (ALD). The film thickness can be controlled at a specific scale to promote dense film deposition, which enables lithium metal capacitor devices to have better electrochemical performance of high voltage and long cycle life.

[0056] A second aspect of the embodiment of the present application provides a method for preparing a lithium metal capacitor, the method comprising the following steps:

[0057] S01: According to the composition of the lithium metal capacitor of the embodiment of the present application, a positive electrode, a negative electrode, a separator and an electrolyte in the lithium metal capacitor are provided;

[0058] S02: Assemble the positive electrode, the negative electrode, the separator and the electrolyte to obtain a lithium metal capacitor.

[0059] The preparation method of the lithium metal capacitor provided in the embodiment of the present application is to assemble the positive electrode, the negative electrode, the separator and the electrolyte in the lithium metal capacitor. In the lithium metal capacitor assembled in this way, a thin, uniform and dense nanoscale metal oxide layer is formed on the surface of the positive electrode active material layer of the positive electrode as a protective layer. The nanoscale metal oxide layer can inhibit the oxygen-containing functional groups with high surface activity of the porous activated carbon. The lithium metal capacitor obtained by such a preparation method has good energy density and high-voltage cycle stability as an asymmetric supercapacitor. Moreover, the process conditions of the preparation method are simple and mild, and the industrial production of lithium metal capacitors can be realized.

[0060] Among them, the preparation method of the positive electrode includes: preparing a positive electrode slurry containing porous activated carbon, a conductive agent and a binder, and then coating the positive electrode slurry on the positive electrode current collector for drying to obtain a positive electrode active material layer; using atomic layer deposition technology to deposit a nano-scale metal oxide layer on the surface of the positive electrode active material layer. The embodiment of the present application uses atomic layer deposition technology to deposit a nano-scale metal oxide layer on the surface of the positive electrode active material layer of the porous activated carbon, so that a thin, uniform and dense protective layer can be formed on the surface of the porous activated carbon. The nano-scale metal oxide layer can inhibit the highly active oxygen-containing functional groups on the surface of the porous activated carbon. The positive electrode obtained by such a preparation method is used in an asymmetric lithium metal capacitor, which can improve the energy density and high-voltage cycle stability of the device. Moreover, the process conditions of the preparation method are simple and mild, and the obtained electrode material product has a high yield and high purity, which meets the requirements of green production and emission.

[0061] Furthermore, the pore size of the porous activated carbon can be 0.5 to 10 nm, and the specific surface area of ​​the porous activated carbon can be 1000 to 3000 m 2 In one embodiment, the method for preparing porous activated carbon comprises:

[0062] S011: crushing and sieving the biomass precursor, and then pre-carbonizing it to obtain a pre-carbonized product;

[0063] S012: placing the pre-carbonized product in an alkali solution for chemical etching, and then drying to obtain an etching powder;

[0064] S013: calcining the etched powder at a high temperature, and then acid-washing and water-washing the calcined product to obtain porous activated carbon.

[0065] like Figure 2 As shown, the biomass precursor is first washed with water and then dried, and then crushed and sieved, and the sieved powder is further pre-carbonized, and the pre-carbonized product is chemically activated, that is, the pre-carbonized product is placed in an alkaline solution for chemical etching, and then dried to obtain an etched powder; the etched powder is calcined at a temperature, including two heating processes, namely, the first stage heating (heating rate of 4 to 6 ° C / min to 380 to 420 ° C, heat preservation for 1 to 2 hours) and the second stage heating (then continue to heat at a rate of 4 to 6 ° C / min to 750 to 850 ° C, heat preservation for 1 to 3 hours), and then the calcined product is acid-washed and washed with water until the pH value is approximately equal to 7 to obtain a porous activated carbon product (which can be represented by MJ5). The preparation method can obtain porous activated carbon with a fiber structure of 3D hollow hierarchical pores. The pore size of the obtained porous activated carbon can be in the range of 0.5 to 10 nm, and the specific surface area of ​​the porous activated carbon can be in the range of 1000 to 3000 m 2 / g range.

[0066] Furthermore, the biomass precursor can be selected from at least one of radish shell, green tea leaves, dragon fruit peel, and coconut shell; the pre-carbonization treatment includes heating the temperature to 480-520°C at a heating rate of 4-6°C / min, and then keeping it warm for 0.5-1.5h; the chemical etching treatment includes heating at 80-120°C for 10-14h; the temperature rise calcination includes heating the temperature to 380-420°C at a heating rate of 4-6°C / min, keeping it warm for 1-2h, and then continuing to heat the temperature to 750-850°C at a heating rate of 4-6°C / min, and keeping it warm for 1-3h.

[0067] Furthermore, the alkaline solution in the chemical etching treatment is selected from any one of a sodium hydroxide solution and a potassium hydroxide solution; the acid in the pickling treatment can be hydrochloric acid, which can be washed 1-3 times, and the water washing can be washed 1-3 times with deionized water until the pH value is approximately equal to 7.

[0068] Furthermore, atomic layer deposition technology is used to deposit a nanoscale metal oxide layer on the surface of the positive electrode active material layer of the porous activated carbon. When atomic layer deposition of the nanoscale metal oxide layer is performed on the surface of the positive electrode active material layer of the porous activated carbon, the precursor can be a metal organic compound corresponding to the metal and high performance liquid chromatography grade water.

[0069] In one embodiment, the step of depositing a nanoscale metal oxide layer on the surface of the positive electrode active layer using atomic layer deposition technology includes placing the positive electrode current collector with a positive electrode active material layer formed on the surface in an atomic layer deposition device and performing 5 to 50 pulse cycles as follows: exposure to metal organic compound molecules for 0.1 to 0.2 seconds, argon purge for 0.1 to 0.2 seconds, exposure to water molecules for 0.1 to 0.2 seconds, and argon purge for 0.1 to 0.2 seconds; wherein the metal organic compound molecules are metal organic compound molecules corresponding to any one of aluminum, titanium, zinc, cobalt and manganese. Thus, a nanoscale aluminum oxide layer, a nanoscale titanium dioxide layer, and a nanoscale zinc oxide layer can be obtained respectively. In the above pulse cycle process, generally each cycle can grow Therefore, after 5 to 50 pulse cycles, a nanoscale metal oxide layer with a thickness of about 0.5 to 5 nm can be obtained, thereby obtaining a positive electrode (which can be represented by ALD-MJ5).

[0070] The present invention uses atomic layer deposition (ALD) to deposit thin films. It plays a unique role in controlling the thickness of the film at a certain scale and promoting the dense deposition of the film on nanoparticles. The embodiment of the present application uses atomic layer deposition technology to deposit a nanoscale metal oxide layer coating on the surface of the positive electrode active material layer of the porous activated carbon, providing a thinner, uniform and dense protective layer, suppressing the oxygen-containing functional groups with higher surface activity of the porous activated carbon, and assembling such a positive electrode with a lithium metal negative electrode into an asymmetric lithium metal capacitor, thereby improving the energy density and high-voltage cycle stability of the overall device. Specifically, the constructed asymmetric lithium metal capacitor achieves electrochemical properties of high voltage (≥3.5V, such as 3.5~4.5V) and long cycle life (≥5000 times, such as 5000~6000 times).

[0071] The lithium metal capacitor provided in the embodiment of the present application is an asymmetric supercapacitor, which uses a unique positive electrode. Based on the protective effect of the nano-scale metal oxide layer on the surface of the positive electrode, the lithium metal capacitor of the embodiment of the present application has electrochemical properties of high voltage and long cycle life, and has the characteristics of fast charging and discharging, which can be used in a variety of fast charging and discharging application scenarios, such as new energy smart trams, smart grids, rail transit, etc. In one embodiment, the lithium metal capacitor includes a positive electrode, a negative electrode, and a diaphragm and an electrolyte between the positive electrode and the negative electrode, the negative electrode is lithium metal (Li Metal), the positive electrode includes a positive electrode current collector and a positive electrode active layer located at the positive electrode current collector, and the surface of the positive electrode active layer can be atomically deposited with a nano-scale metal oxide layer. The embodiment of the present application uses atomic layer deposition technology to deposit a nano-scale metal oxide layer on the surface of the positive electrode active layer of porous activated carbon to obtain a lithium metal capacitor for protection, which can improve the operating voltage and electrochemical stability of the lithium metal capacitor, and is combined with a lithium metal negative electrode to obtain a lithium metal capacitor with a high voltage and a long cycle life. Specifically, the positive electrode active material layer of the lithium metal capacitor contains a certain proportion of porous activated carbon, a conductive agent, and a binder.

[0072] The following describes the invention in conjunction with specific embodiments.

[0073] Example 1

[0074] A method for preparing porous activated carbon as an electrode material comprises the following steps:

[0075] Step 1: wash the radish shell with deionized water and dry it at 100°C for 12 hours, crush it with a grinder and pass it through a 300-mesh sieve, weigh 10g of the precursor powder for pre-carbonization: heat it to 500°C at a heating rate of 5°C / min and keep it for 1 hour, then naturally cool it to room temperature to obtain a pre-carbonized product, with a yield of about 60%.

[0076] Step 2: weigh 6 g of the pre-carbonized product and 30 g of potassium hydroxide (KOH) powder (alkali-carbon ratio 5:1), dissolve the potassium hydroxide powder in water to prepare a potassium hydroxide aqueous solution. The potassium hydroxide aqueous solution and the pre-carbonized product are fully mixed, heated at 100° C. and stirred for 12 h, and dried to obtain a powder.

[0077] Step 3, place the dried powder into a tubular furnace and heat it to 400°C at a heating rate of 5°C / min for 1.5 hours, then continue to heat it to 800°C at a heating rate of 5°C / min for 2 hours. Naturally cool to room temperature to obtain 2g of product with a yield of about 33-35%. The product is then placed in a 1mol / L hydrochloric acid solution and stirred at 90°C, washed three times, each time for 2 hours. Subsequently, wash with deionized water 2-3 times until the pH value is approximately equal to 7, and finally obtain activated carbon with a fiber structure of 3D hollow hierarchical pores, named MJ5.

[0078] Structural characterization

[0079] Figure 3 The scanning electron microscope images of porous activated carbon MJ5, where a shows an obvious 3D hollow carbon fiber structure, and b is Figure 3 In the partial enlarged view of a, it can be clearly observed that there are abundant mesopores and micropores. Therefore, the porous activated carbon MJ5 synthesized in the embodiment of the present application has abundant hierarchical pore structures.

[0080] Figure 4 The BET test results of porous activated carbon MJ5 show that the pore size distribution of MJ5 is between less than 2nm (micropores) and 2-6nm (mesopores).

[0081] Figure 5 The XPS fitting diagram of porous activated carbon MJ5 shows that the element content of MJ5 is 92.2% C and 7.8% O. Porous activated carbon MJ5 is mainly composed of carbon and oxygen elements, and contains C=O, CO, and COC functional groups, which help to improve surface wettability and pseudocapacitance.

[0082] Example 2

[0083] A lithium metal capacitor comprises a positive electrode, a negative electrode, and a separator and an electrolyte located between the positive electrode and the negative electrode, wherein the negative electrode is lithium metal, the positive electrode comprises a positive electrode current collector (i.e., aluminum foil) and a positive electrode active material layer bonded to the surface of the positive electrode current collector, and an atomic layer deposition nano aluminum oxide layer is formed on the surface of the positive electrode active material layer; the positive electrode active material in the positive electrode is the porous activated carbon MJ5 prepared in Example 1 of the present application. The preparation method of the lithium metal capacitor comprises the following steps:

[0084] Step 1: The MJ5 prepared in Example 1 is fully mixed with the conductive agent carbon black (Super P), and then the binder polyvinylidene fluoride (PVDF) and N-methylpyrrolidone (NMP) solvent are added to mix and prepare a uniform electrode slurry, wherein the mass ratio of ALD-MJ5: conductive agent: binder is controlled to be 85:10:5. Then the electrode slurry is scraped onto aluminum foil, and the electrode loading is controlled to be 12 mg / cm 2 about, and then drying to obtain a positive electrode sheet with a positive electrode active material layer formed on the surface;

[0085] Step 2: Atomic layer deposition is used to coat the surface of the positive electrode active material layer with a nano-scale aluminum oxide layer. The nano-scale aluminum oxide layer coating uses trimethylaluminum (TMA) and HPLC grade water as precursors. 20 cycles are performed on the surface of the positive electrode active material layer (each cycle grows ), the reaction sequence in each deposition cycle is: (i) exposing the positive electrode active material layer containing activated carbon MJ5 to TMA for 0.2s; (ii) blowing argon to remove unreacted precursors and by-products for 0.2s; (iii) exposing activated carbon MJ5 to water for 0.2s; and (iv) blowing argon to remove unreacted precursors and by-products for 0.2s. The temperature of the entire reaction process is 120℃. Finally, a positive electrode with a nano-scale aluminum oxide layer on the surface was obtained, named ALD-MJ5. The dried positive electrode sheet was punched into a φ12mm circular positive electrode and dried in a vacuum oven at 120℃ for 12h. The dried positive electrode was weighed and set aside.

[0086] Step 3, in the order of negative electrode shell, negative electrode (i.e., lithium metal), diaphragm, positive electrode (including ALD-MJ5), flat gasket, spring sheet, and positive electrode shell from bottom to top, add an electrolyte with a concentration of 1 mol / L (solute is LiPF6, and the solvent is ethylene carbonate EC and dimethyl carbonate DMC in a volume ratio of 1:1) in a glove box filled with argon with a water and oxygen content of ≤0.1ppm, assemble and package, and obtain a button-type lithium metal capacitor with model R2302.

[0087] Performance Testing

[0088] The obtained lithium metal capacitor was left standing at room temperature for 24 hours before electrochemical performance testing.

[0089] Figure 6 The comparison of the rate performance of lithium metal capacitors corresponding to the unmodified porous activated carbon MJ5 and the ALD-MJ5 deposited with nano-scale aluminum oxide layer at room temperature 25°C, with a current density of 0.1A g -1 -5A g -1 , the operating voltage is 1.5-4.2 V. The specific capacity of both devices decays to varying degrees with the increase of current density, and the lithium metal capacitor rate corresponding to the ALD-MJ5 electrode modified by ALD is significantly better than that of the unmodified MJ5, which is related to the aluminum oxide layer increasing the conductivity and reducing the impedance of the electrode material.

[0090] Figure 7 The long cycle performance comparison of lithium metal capacitors corresponding to unmodified porous activated carbon MJ5 and ALD-MJ5 deposited with nano-scale aluminum oxide layer at room temperature 25°C, with a current density of 2A g -1, the working voltage is 1.5-4.2V. Although the coulombic efficiency of the two electrodes has been maintained at about 99.9%, the long cycle of the lithium metal capacitor corresponding to the ALD-MJ5 electrode modified by ALD is significantly better than that of the unmodified MJ5. The capacity retention rate of the lithium metal capacitor corresponding to the ALD-MJ5 electrode modified by ALD can still be maintained at 83.5% after 3000 cycles, while the unmodified MJ5 is only 66.1%.

[0091] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A lithium metal capacitor, comprising a positive electrode, a negative electrode, and a separator and an electrolyte located between the positive electrode and the negative electrode, characterized in that: The positive electrode comprises a positive electrode current collector and a positive electrode active material layer bonded to the surface of the positive electrode current collector, wherein the positive electrode active material layer comprises porous activated carbon, a conductive agent and a binder, and a nano-scale metal oxide layer is provided on the surface of the positive electrode active material layer away from the positive electrode current collector, and the negative electrode is lithium metal; wherein the porous activated carbon is a porous activated carbon with a fiber structure of 3D hollow hierarchical pores, the pore size distribution of the porous activated carbon is less than 2nm and 2-6nm, and the specific surface area of ​​the porous activated carbon is 1000~3000m 2 / g; the metal oxide in the nanoscale metal oxide layer is selected from aluminum oxide, the thickness of the nanoscale metal oxide layer is 0.5~5nm, and the nanoscale metal oxide layer is prepared by atomic layer deposition technology; and the maximum cyclic operating voltage of the lithium metal capacitor is 4.5V.

2. The lithium metal capacitor according to claim 1, characterized in that The mass ratio of the porous activated carbon, the conductive agent and the binder is 80-90:8-12:2-8.

3. A method for preparing a lithium metal capacitor, characterized in that: The steps include: According to the composition of the lithium metal capacitor according to any one of claims 1 to 2, providing a positive electrode, a negative electrode, a separator and an electrolyte in the lithium metal capacitor; The positive electrode, the negative electrode, the separator and the electrolyte are assembled to obtain the lithium metal capacitor.

4. The method for preparing a lithium metal capacitor according to claim 3, characterized in that: The preparation method of the positive electrode comprises: Preparing a positive electrode slurry containing the porous activated carbon, a conductive agent and a binder, and then coating the positive electrode slurry on a positive electrode current collector and performing drying treatment to obtain a positive electrode active material layer; A nanometer-scale metal oxide layer is deposited on the surface of the positive electrode active material layer by using atomic layer deposition technology.

5. The method for preparing a lithium metal capacitor according to claim 4, characterized in that: The preparation method of the porous activated carbon comprises: The biomass precursor is crushed, sieved, and then pre-carbonized to obtain a pre-carbonized product; The pre-carbonized product is placed in an alkaline solution for chemical etching, and then dried to obtain an etching powder; The etched powder is calcined at an elevated temperature, and then the calcined product is acid-washed and water-washed to obtain the porous activated carbon.

6. The method for preparing a lithium metal capacitor according to claim 5, characterized in that: The biomass precursor is selected from at least one of radish shell, green tea leaves, pitaya peel, and coconut shell; And / or, the pre-carbonization treatment includes heating the temperature to 480-520° C. at a heating rate of 4-6° C. / min, and then keeping the temperature for 0.5-1.5 h; And / or, the alkali solution is selected from any one of a sodium hydroxide solution and a potassium hydroxide solution; And / or, the chemical etching treatment includes heating at 80-120° C. for 10-14 h; And / or, the temperature-raising calcination includes raising the temperature to 380-420° C. at a heating rate of 4-6° C. / min, keeping the temperature for 1-2 hours, and then continuing to raise the temperature to 750-850° C. at a heating rate of 4-6° C. / min, and keeping the temperature for 1-3 hours.

7. The method for preparing a lithium metal capacitor according to claim 4, characterized in that: The step of depositing a nanoscale metal oxide layer on the surface of the positive electrode active layer by using an atomic layer deposition technique comprises placing a positive electrode current collector having the positive electrode active material layer formed on the surface thereof in an atomic layer deposition device and performing 5 to 50 pulse cycles as follows: The metal organic compound molecules are exposed to organic compound molecules for 0.1 to 0.2 seconds, and argon gas is purged for 0.1 to 0.2 seconds; the metal organic compound molecules are exposed to water molecules for 0.1 to 0.2 seconds, and argon gas is purged for 0.1 to 0.2 seconds; wherein the metal organic compound molecules are organic compound molecules corresponding to any one of aluminum, titanium, zinc, cobalt and manganese.

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