Method for preparing ultrathin lithium air battery positive electrode in rolling mode

Abstract

The invention belongs to the field of lithium air battery preparation, and particularly relates to a method for preparing an ultrathin lithium air battery positive electrode in a rolling mode. According to the technical scheme, the method for preparing the ultra-thin lithium air battery positive electrode in the rolling mode is characterized in that a material for preparing the ultra-thin lithium air battery positive electrode is a mixture of a carbon base and an additive; and the ultrathin lithium air battery positive electrode is prepared in a rolling mode of a roller press. The method for preparing the ultrathin lithium air battery positive electrode in the rolling mode is safe, convenient and economical, and the problems that coating is not uniform, and slurry is too thick or too thin can be solved.

Description

Technical Field

[0001] The invention belongs to the field of lithium-air battery preparation, and in particular relates to a method for preparing an ultra-thin lithium-air battery positive electrode by rolling. Background Art

[0002] With the rapid development of industrialization, primary energy (fossil energy) has been drastically reduced, and the use of fossil energy has brought about many environmental problems. Adjusting the energy structure is currently the primary energy strategic goal of countries around the world.

[0003] Lithium-air batteries have attracted much attention as a new generation of highly promising power battery systems. They may provide a feasible solution to break through the current bottleneck of electric vehicle endurance and have extremely broad application prospects in aerospace, military and other fields. Taking into account factors such as operating voltage, theoretical energy density and specific capacity, lithium-oxygen batteries have obvious advantages over other metal-air batteries and have received very wide attention in recent years.

[0004] Lithium-oxygen batteries are mainly composed of negative electrode shells, spring washers, steel sheets, glass fiber membranes, electrolytes, positive electrode sheets and positive electrode shells. The positive electrode sheet is one of the important components of lithium-oxygen batteries. It mainly provides a place for reaction for lithium-oxygen batteries. Although as a reaction site, the type and number of catalytic groups on the electrode surface and the structure of the electrode itself have a significant impact on the reversibility of the electrochemical reaction and the integrity of the battery.

[0005] However, there are still many problems in the application of lithium-air batteries, and the selection of electrode materials and optimization of structure are considered to be effective means to solve these problems. At present, many types of materials have been applied to air cathodes, such as carbon materials, oxides and coordination polymers. Among them, carbon materials have the advantages of large specific surface area, good conductivity, strong stability and controllability, and have become the most promising type of lithium-air battery cathode material. Since the microscopic pore structure of the cathode material will affect the diffusion of oxygen at the air electrode interface and the diffusion of the electrolyte in the air electrode, it will ultimately greatly affect the performance of the lithium-air battery. Therefore, choosing a reasonable carbon material and designing a reasonable structural design optimization can better exert the performance of the lithium-oxygen battery.

[0006] The energy of lithium-oxygen battery is converted into Li + It flows through the electrolyte to the positive electrode, where it reacts with oxygen in the air. In order to make the reaction more complete during the entire reaction process, optimization can be performed from the positive electrode side. In the process of preparing the positive electrode, the catalyst doped in the positive electrode is often changed, and the microstructure is changed by changing the positive electrode material. However, it is not so easy to change the catalyst doped in the positive electrode and change the material. In the process of positive electrode optimization, it is not only possible to optimize from a microscopic aspect, but also to adjust the mass transfer process of the positive electrode by changing the positive electrode structure (thickness, stacking), thereby improving the performance of the positive electrode. The mass transfer optimization process is achieved by changing the thickness of the positive electrode sheet. After reducing the thickness of the positive electrode, the oxygen transmission path can be shortened, thereby improving the reaction efficiency of the battery.

[0007] The existing technology for preparing positive electrode materials requires a coating process, which requires a day of stirring preparation of the materials and the slurry is prone to being too thick or too thin during the stirring process, which is difficult to control. Summary of the invention

[0008] The invention provides a method for preparing an ultra-thin lithium-air battery positive electrode by rolling, which is safe, convenient and economical, and can avoid the problems of uneven coating and excessively thick or thin slurry.

[0009] The technical solution of the present invention is as follows:

[0010] A method for preparing an ultra-thin lithium-air battery positive electrode by rolling, wherein the material for preparing the ultra-thin lithium-air battery positive electrode is a mixture of a carbon base and an additive; the ultra-thin lithium-air battery positive electrode is prepared by rolling with a roller press.

[0011] Furthermore, in the method for preparing an ultra-thin lithium-air battery positive electrode by rolling, the carbon base is graphene, single-walled carbon nanotubes, multi-walled carbon nanotubes, acetylene black, mesoporous carbon and / or Ketjen carbon.

[0012] Furthermore, in the method for preparing an ultra-thin lithium-air battery positive electrode by rolling, the additive is manganese dioxide, ruthenium dioxide, iron manganese oxide, cobalt oxide, nickel dioxide and / or cerium dioxide.

[0013] Furthermore, the method for preparing an ultra-thin lithium-air battery positive electrode by rolling comprises the following steps:

[0014] 1) Weigh a certain amount of multi-walled carbon nanotubes and manganese dioxide on an electronic scale and add them to a beaker, the mass ratio of multi-walled carbon nanotubes to manganese dioxide being 3:1, and mix the two evenly with a glass rod;

[0015] 2) Take a disposable rubber-tipped dropper and draw PTFE emulsion into the beaker, the mass ratio of multi-walled carbon nanotubes to PTFE emulsion is 4:1;

[0016] 3) Pour the materials in the beaker into the agate mortar and mix evenly, adding a small amount of alcohol to moisten it until the mixture is crushed into a dough-like substance;

[0017] 4) adding the dough-like substance into a roller press, and preparing positive electrode sheets of different thicknesses by adjusting different gears;

[0018] 5) placing the positive electrode sheet in air to dry for 4-8 hours;

[0019] 6) sending the dried positive electrode sheet into a tube furnace for sintering, when the temperature of the tube furnace is raised to 240°C and maintained for one hour, the temperature is then raised to 340°C and maintained for one hour before stopping heating; after cooling to room temperature in air, taking out the fired positive electrode sheet;

[0020] 7) Use a hydraulic slicer to cut the positive electrode sheet into a circle with a diameter of 16 mm.

[0021] Furthermore, in the method for preparing an ultra-thin lithium-air battery positive electrode by roller pressing, the thickness of the positive electrode sheet is 80-300 μm.

[0022] The beneficial effects of the present invention are as follows: the present invention has a greater advantage than the traditional positive electrode in the product deposition of the lithium oxygen battery, can effectively improve the discharge capacity of the lithium oxygen battery, and can adjust the thickness and pore parameters of the positive electrode according to demand. The rolling preparation method has a short cycle, does not require high preliminary work preparation of materials, does not have excessive requirements for the preparation of materials, and can more efficiently prepare ultra-thin positive electrode sheets with higher efficiency. The prepared ultra-thin positive electrode sheet has better flexibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a low-magnification scanning electron microscope image of the positive electrode surface;

[0024] Figure 2 This is a high-magnification scanning electron microscope image of the positive electrode surface;

[0025] Figure 3 This is a low-magnification scanning electron microscope image of the cross section of the positive electrode sheet;

[0026] Figure 4 This is a high-magnification scanning electron microscope image of the cross section of the positive electrode;

[0027] Figure 5 It is the electrochemical impedance spectrum of the positive electrode;

[0028] Figure 6 This is the cyclic voltammetry (CV) test diagram of the positive electrode;

[0029] Figure 7 This is a deep discharge test diagram of a battery with a positive electrode installed. DETAILED DESCRIPTION

[0030] A method for preparing an ultra-thin lithium-air battery positive electrode by rolling, specifically comprising the following steps:

[0031] 1) Weigh a certain amount of multi-walled carbon nanotubes (MWCNT) and manganese dioxide on an electronic scale and add them to a beaker, the mass ratio of multi-walled carbon nanotubes to manganese dioxide being 3:1, and mix the two evenly with a glass rod;

[0032] 2) Take a disposable rubber-tipped dropper and draw PTFE emulsion into the beaker, the mass ratio of multi-walled carbon nanotubes to PTFE emulsion is 4:1;

[0033] 3) Pour the materials in the beaker into the agate mortar and mix evenly, adding a small amount of alcohol to moisten it until the mixture is crushed into a dough-like substance;

[0034] 4) adding the dough-like substance into a roller press, and preparing positive electrode sheets of different thicknesses by adjusting different gears, wherein the thickness of the positive electrode sheet is 80-300 μm;

[0035] 5) placing the positive electrode sheet in air to dry for 6 hours;

[0036] 6) sending the dried positive electrode sheet into a tube furnace for sintering, when the temperature of the tube furnace is raised to 240°C and maintained for one hour, the temperature is then raised to 340°C and maintained for one hour before stopping heating; after cooling to room temperature in air, taking out the fired positive electrode sheet;

[0037] 7) The positive electrode sheet was cut into a circular shape with a diameter of 16 mm using a hydraulic slicer T-06 (produced in Shenzhen).

[0038] like Figure 1 As shown, the multi-walled carbon nanotubes on the surface of the positive electrode are evenly interwoven, which can not only load the catalyst MnO2 well but also have a good mass transfer effect; Figure 2 As shown in Figure 1, under high magnification of the surface of the positive electrode, it can be seen that MnO2 particles are embedded in the multi-walled carbon nanotubes; Figure 3 As shown in the figure, the cross section of the positive electrode sheet is relatively flat, without bumps and unevenness, and the thickness is only 102.4μm. The thin positive electrode sheet can increase the oxygen transmission rate and shorten the mass transfer path, thereby allowing the reaction to occur more thoroughly. Figure 4 As shown, at a high magnification of the cross-section of the positive electrode sheet, it can be seen that MnO2 is evenly attached to the multi-walled carbon nanotubes, which can provide a better catalytic effect for the battery's charge and discharge reactions.

[0039] Electrode performance test: Figure 5As shown in the electrochemical impedance spectrum (EIS), before discharge, it has a very small initial ohmic impedance of only 10.21Ω, and a charge transfer impedance of 35.2Ω. The smaller impedance can provide a higher discharge platform for the battery discharge process, so that the battery can have a higher discharge capacity. Under the conditions of a current of 0.2mA and a capacity of 1mAh, after 10 cycles, the initial ohmic impedance is only 41Ω, and the charge transfer impedance is 124.5Ω, which improves the battery's charge and discharge cycle performance.

[0040] Cyclic voltammetry (CV) tests are used to determine the redox potential of battery materials, which is a key parameter for electron transfer during battery charge and discharge. CV was tested before discharge and after full electrical cycling, with a scan voltage range of 2V to 4.5V and test temperatures at room temperature. Figure 6 As shown, the reduction peak is around 3.8 V, and the peak value is only 0.5 A / g. A smaller peak will lead to an easier reaction process.

[0041] Battery discharge performance test: at a current density of 0.1 mA / cm 2 The discharge capacity that can be achieved is 27400mAh / g. Figure 7 As shown, when the current density is 0.2 mA / cm 2 The prepared positive electrode sheet showed excellent discharge capacity. The current applied when testing the discharge depth was 0.1 mA / cm 2 and 0.2mA / cm 2 , the discharge capacity is 27mAh / cm 2 and 17.3 mAh / cm 2 .

Claims

1. A method for preparing an ultra-thin lithium-air battery positive electrode by roller pressing, characterized in that: The material for preparing the positive electrode of the ultra-thin lithium-air battery is a mixture of a carbon base and an additive; the ultra-thin positive electrode of the lithium-air battery is prepared by rolling with a roller press.

2. The method for preparing an ultra-thin lithium-air battery positive electrode by rolling according to claim 1, characterized in that: The carbon base is graphene, single-walled carbon nanotube, multi-walled carbon nanotube, acetylene black, mesoporous carbon and / or Ketjen carbon.

3. The method for preparing an ultra-thin lithium-air battery positive electrode by rolling according to claim 2, characterized in that: The additive is manganese dioxide, ruthenium dioxide, iron manganese oxide, cobalt oxide, nickel dioxide and / or cerium dioxide.

4. The method for preparing an ultra-thin lithium-air battery positive electrode by rolling according to claim 3, characterized in that: The specific steps include: 1) Weigh a certain amount of multi-walled carbon nanotubes and manganese dioxide on an electronic scale and add them to a beaker, the mass ratio of multi-walled carbon nanotubes to manganese dioxide being 3:1, and mix the two evenly with a glass rod; 2) Take a disposable rubber-tipped dropper and draw PTFE emulsion into the beaker, the mass ratio of multi-walled carbon nanotubes to PTFE emulsion is 4:1; 3) Pour the materials in the beaker into the agate mortar and mix evenly, adding a small amount of alcohol to moisten it until the mixture is crushed into a dough-like substance; 4) adding the dough-like substance into a roller press, and preparing positive electrode sheets of different thicknesses by adjusting different gears; 5) placing the positive electrode sheet in air to dry for 4-8 hours; 6) sending the dried positive electrode sheet into a tube furnace for sintering, when the temperature of the tube furnace is raised to 240°C and maintained for one hour, the temperature is then raised to 340°C and maintained for one hour before stopping heating; after cooling to room temperature in air, taking out the fired positive electrode sheet; 7) Use a hydraulic slicer to cut the positive electrode sheet into a circle with a diameter of 16 mm.

5. The method for preparing an ultra-thin lithium-air battery positive electrode by rolling according to claim 4, characterized in that: The thickness of the positive electrode sheet is 80-300 μm.

Images