A positive electrode of a capacitive battery based on the synergistic energy storage effect on the body surface

Abstract

The present invention discloses a positive electrode of a capacitive battery based on the synergistic energy storage effect on the body surface, belonging to the technical field of lithium-ion batteries. The positive electrode of the capacitive battery based on the synergistic energy storage effect on the body surface includes a composite positive electrode material, and the composite positive electrode material is obtained by mixing a positive electrode active material and activated carbon with a mass ratio of 80-95:5-20 through supercritical carbon dioxide fluid gradient pressure mixing. The supercritical carbon dioxide fluid gradient pressure mixing includes a first stage and a second stage. The first stage is carried out under a pressure condition higher than 7.3 MPa, and the second stage is carried out under a pressure condition lower than 7.3 MPa. The method of the present invention can improve the battery power density and cycle performance on the premise of ensuring simple process, low cost, green environmental protection and no increase in pollution. Moreover, the method of the present invention has good universality and is applicable to various lithium-ion battery positive electrode materials.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and particularly to a positive electrode of a capacitive battery based on the body surface collaborative energy storage effect. Background Art

[0002] With the development of the lithium-ion battery industry, lithium-ion batteries have become necessities in human social life. Lithium-ion batteries have the advantages of high energy density, high power density, and good cycle performance. However, in the fields of rail transit, distributed energy storage power stations, starting power supplies, electric tractors, etc., lithium-ion batteries cannot be widely used. Therefore, it is very crucial to develop lithium-ion batteries with higher power density and energy density.

[0003] Activated carbon is a porous carbon material. Due to its characteristics such as developed pore structure, large specific surface area, and strong adsorption ability, it shows good application prospects as an electrode material in energy storage materials. The shape of activated carbon is mainly granular, and the pore size distribution is mostly micropores. The preparation process is simple and the cost is low. Usually, biomass raw materials such as coconut shells and fruit shells or by-products such as coal and petroleum are used as precursors and obtained through high-temperature carbonization-activation or activation-high-pressure pyrolysis and other post-treatments. The structural characteristics of activated carbon, such as pore structure, microcrystalline structure, surface chemical structure and state, have a significant impact on its electrochemical performance.

[0004] Currently, the main methods to improve the energy density and power density of lithium-ion batteries are doping and coating the positive electrode material / negative electrode material. For example, the Chinese patent document with the publication number CN103943824A discloses a ternary composite positive electrode material for lithium-ion batteries doped with rare earth elements. This invention uses a wet method to prepare a ternary material precursor doped with rare earth element Gd, and then uses a solid-phase sintering method to dope F in the material to improve the energy density of the lithium-ion battery. The Chinese patent document with the publication number CN105186000A discloses a preparation method of a specific activated carbon material. In this invention, after processes such as heat treatment with dilute nitric acid on the activated carbon material, it is used as the positive electrode of a lithium-ion battery, which can improve the energy density of the lithium-ion battery. The Chinese patent document with the publication number CN115000369A discloses a positive electrode material, which includes a single-crystal ternary low-cobalt material and lithium cobaltate. The mass ratio of the single-crystal ternary low-cobalt material to lithium cobaltate is 0.90 - 0.99:0.01 - 0.10. The doping of lithium cobaltate in this positive electrode material can significantly improve the transmission ability of lithium ions in the solid phase and improve the power performance of the battery. The Chinese patent document with the publication number CN114229920A discloses a positive electrode material, including a positive electrode active material partially or entirely coated with a coating layer, where the coating layer includes a composite of selenium and an ion-conductive polymer. This invention can effectively alleviate the oxygen release of the positive electrode material by setting a specific coating layer and maintain the high energy density of the lithium-ion battery.

[0005] However, all of these methods have problems such as complex processes, high costs, and increased environmental pollution. SUMMARY OF THE INVENTION

[0006] The present invention provides a positive electrode of a capacitive battery based on the synergistic energy storage effect on the body surface. Its preparation method is simple and environmentally friendly. By utilizing the synergistic effect between the positive electrode active material and activated carbon and the capacitive characteristics of activated carbon itself, the power density and cycle performance of the battery are improved.

[0007] The specific technical solution adopted is as follows:

[0008] A positive electrode of a capacitive battery based on the synergistic energy storage effect on the body surface, comprising a composite positive electrode material, wherein the composite positive electrode material is obtained by mixing a positive electrode active material and activated carbon with a mass ratio of 80 - 95:5 - 20 through supercritical carbon dioxide fluid gradient pressure mixing;

[0009] The positive electrode active material includes at least one of lithium cobaltate, lithium manganate, lithium iron phosphate, and lithium nickel cobalt manganate;

[0010] The supercritical carbon dioxide fluid gradient pressure mixing includes a first stage and a second stage. The first stage is carried out under a pressure condition higher than 7.3 MPa, and the second stage is carried out under a pressure condition lower than 7.3 MPa.

[0011] During the rapid charge and discharge process of the battery, activated carbon can buffer the impact of large current on the positive electrode active material through its rapid response, slowing down the decay rate of the positive electrode active material. The present invention uses supercritical carbon dioxide fluid to disperse and shear the positive electrode active material and activated carbon, and physically mixes the positive electrode active material and activated carbon through the characteristics of high mass transfer, low surface tension, and strong permeability of supercritical carbon dioxide fluid, realizing the particle size dispersion regulation of the battery-type positive electrode active material and the capacitive activated carbon material, meeting the synergistic energy storage requirements on the body surface of the composite positive electrode material. Compared with the traditional mixing method, it increases the contact area between the positive electrode active material and activated carbon, improves the dispersion uniformity of the powder, can establish a rapid electron transfer channel between components, synergistically combines the double-layer charging process and the Faraday reaction, better realizes synergistic energy storage, and produces excellent rate performance and cycle performance.

[0012] Preferably, the particle size of the positive electrode active material is 5 - 10 μm; the particle size of the activated carbon is 5 - 10 μm, the micropore volume is 0.6 - 1.0 mL / g, and the specific surface area is 1500 - 2300 m 2 / / g. Under the above parameters, the contact between the positive electrode active material and activated carbon will be more sufficient, improving the conductivity. The larger the micropore volume and specific surface area of activated carbon, the higher the adsorption capacity exerted, which is more conducive to synergistic energy storage on the body surface.

[0013] Preferably, the temperature for the gradient pressure mixing of supercritical carbon dioxide fluid is 40 - 60°C, and the flow rate of the supercritical carbon dioxide fluid is 30 - 40 L / h.

[0014] Preferably, during the gradient pressure mixing of supercritical carbon dioxide fluid, the pressure in the first stage is 12 - 20 MPa and the time is 40 - 60 min; the pressure in the second stage is 6.5 - 7.2 MPa and the time is 5 - 10 min. If the parameters of the gradient pressure mixing of supercritical carbon dioxide fluid are not within the above ranges, there will be a phenomenon that the positive active material and activated carbon are not tightly combined and a small amount of agglomeration still exists, resulting in delamination during the subsequent wet coating process and affecting the electrochemical performance of the material.

[0015] The number of repetitions of the gradient pressure mixing of the supercritical carbon dioxide fluid is 2 - 3 times. By repeatedly converting between carbon dioxide gas below the supercritical state and supercritical carbon dioxide fluid in the present invention, the dispersion effect of the powder can be improved, the phenomenon of agglomeration can be avoided, and the performance of the composite positive electrode material can be enhanced.

[0016] Preferably, the positive electrode of the capacitive battery based on the body surface synergistic energy storage effect further includes a conductive agent and a positive electrode binder. The conductive agent includes acetylene black, Super - P, carbon nanotubes or graphene, and the positive electrode binder includes polyvinylidene fluoride.

[0017] The preparation method of the positive electrode of the capacitive battery based on the body surface synergistic energy storage effect is as follows: Mix the composite positive electrode material, conductive agent, and positive electrode binder according to a mass ratio of 80 - 90:5 - 10:5 - 10, then add a positive electrode solvent, and prepare a positive electrode slurry with a solid content of 20 - 33 wt% by ball milling. Coat the positive electrode slurry on a current collector and dry it to obtain the positive electrode of the capacitive battery based on the body surface synergistic energy storage effect.

[0018] The present invention also provides a capacitive battery, including the positive electrode of the capacitive battery based on the body surface synergistic energy storage effect, a negative electrode, and a separator.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] (1) By using supercritical carbon dioxide fluid to disperse and shear - mix the positive active material and activated carbon, the present invention can improve the battery power density and cycle performance on the premise of ensuring simple process, low cost, green environmental protection, and no additional pollution. Moreover, the method of the present invention has good universality and is applicable to various lithium - ion battery positive electrode materials.

[0021] (2) Compared with the traditional mixing method, the specific supercritical carbon dioxide fluid gradient pressure mixing method of the present invention improves the dispersion uniformity of the powder materials, avoids the phenomenon of agglomeration, increases the contact area between the cathode active material and the activated carbon, can establish a rapid electron transfer channel between the components, synergistically combines the electric double layer charging process and the Faraday reaction, better realizes synergistic energy storage, and generates excellent rate performance and cycling performance.

[0022] (3) During the wet mixing process, due to the density difference between the cathode active material and the activated carbon, the stratification phenomenon of the active material and the activated carbon is likely to occur in the wet environment, which has an adverse effect on the performance of the composite electrode material. By supercritically mixing the cathode active material and the activated carbon, on the one hand, a three-dimensional ion transport network will be formed to accelerate the ion conduction. On the other hand, supercritical mixing enables the cathode active material and the activated carbon to have a tighter binding force under high pressure, avoiding the stratification phenomenon. Brief Description of the Drawings

[0023] Figure 1 SEM image of the surface of the cathode of the capacitive battery based on the body surface synergistic energy storage effect prepared in Example 1.

[0024] Figure 2 Schematic diagram of the synergistic effect between the cathode active material and the activated carbon. LCO represents lithium cobaltate, AC represents activated carbon, and electrolyte represents the electrolyte.

[0025] Figure 3 Rate performance curve of the capacitive battery prepared in Example 1.

[0026] Figure 4 Cycling performance curve of the capacitive battery prepared in Example 1.

[0027] Figure 5 Rate performance curve of the capacitive battery prepared in Example 2.

[0028] Figure 6 Rate performance curve of the capacitive battery prepared in Comparative Example 1.

[0029] Figure 7 Rate performance curve of the capacitive battery prepared in Comparative Example 2. Detailed Description of the Embodiments

[0030] The present invention will be further clarified below in conjunction with the embodiments and the drawings. It should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. The operation methods without specific conditions indicated in the following embodiments are usually carried out under conventional conditions or according to the conditions recommended by the manufacturer.

[0031] Example 1

[0032] 1.62 g of lithium cobaltate with a particle size of 5 μm and 0.18 g of activated carbon with a particle size of 5 μm, a pore volume of 0.94 mL / g, and a specific surface area of 2100 m 2 / g were added to an agate mortar and stirred and mixed. After stirring, they were added to a well-sealed crystallization kettle and sealed. A carbon dioxide gas cylinder was connected and the inlet valve was opened for supercritical carbon dioxide fluid gradient pressure mixing. The specific parameters were as follows: the temperature was 50 °C, the flow rate of the supercritical carbon dioxide fluid was 30 L / h, the pressure in the first stage was 15 MPa, and the time was 60 min; the pressure in the second stage was 7 MPa, and the time was 10 min; the above operations were repeated 3 times to obtain the composite cathode material powder.

[0033] The mixed composite cathode material, Super-P, and polyvinylidene fluoride were weighed according to a mass ratio of 90:5:5 and added to a ball mill jar. At the same time, an appropriate amount of the cathode solvent N-methylpyrrolidone (NMP) was added and ball milling was carried out in a planetary ball mill. The ball milling parameters were 300 r / min, 30 min / time, eight times of ball milling, and standing for 5 min after each ball milling to obtain a cathode slurry with a solid content of 33 wt%. Subsequently, the cathode slurry was coated on an aluminum foil current collector and placed in an oven to be dried at 110 °C for 12 h to obtain a cathode sheet with an activated carbon content of 10%. The surface SEM image of the cathode sheet is as Figure 1 shown. It can be seen that the distribution of lithium cobaltate and activated carbon on the surface of the cathode sheet is very uniform, in full contact with the conductive carbon black, constructing a good conductive network, and enabling better realization of body-surface collaborative energy storage.

[0034] The obtained cathode sheet was cut into electrode sheets with a diameter of 12 mm. A metal lithium sheet was used as the anode, a PP material was used as the separator, and LiPF 6 in EC / DMC (ethylene carbonate / dimethyl carbonate) was used as the electrolyte, and a coin cell was assembled using a 2016 battery case.

[0035] Figure 2 is a schematic diagram of the synergistic effect between the cathode active material LCO and activated carbon. Due to the different energy storage mechanisms of activated carbon and the cathode active material, the rate of change of the response potential is different. During charging, activated carbon responds quickly and has a high potential, and electrons transfer from the cathode active material to activated carbon, which is manifested as activated carbon charging the active material. The same is true for discharging. Thus, during the charge-discharge process, a rapid electron transfer channel is established between the two components, coordinating the electric double layer charging process and the Faraday reaction, thereby generating excellent rate performance and cycling performance. In addition, during the charging process, PF 6 - will accumulate on the surface of activated carbon. When it accumulates to a certain extent, the activated carbon at this time can be regarded as an ideal capacitor, showing obvious capacitance characteristics.

[0036] The assembled coin cell was subjected to relevant electrochemical tests on a Blue Power test system. The rate performance curve is as Figure 3 shown. At an ultra-high rate of 100 C, the battery prepared with this composite cathode material can still deliver a specific capacity of 60 mAh / g. The cycling performance curve is as Figure 4 shown. After 100 cycles, the cycling retention rate is 99.4%.

[0037] Example 2

[0038] 1.71 g of lithium cobaltate with a particle size of 5 μm and 0.09 g of activated carbon with a particle size of 5 μm, a pore volume of 0.94 mL / g, and a specific surface area of 2100 m 2 / g were added to an agate mortar and stirred and mixed. After stirring, they were added to a well-sealed crystallization kettle and sealed. A carbon dioxide gas cylinder was connected and the inlet valve was opened for supercritical carbon dioxide fluid gradient pressure mixing. The specific parameters are as follows: the temperature is 50 °C, the flow rate of the supercritical carbon dioxide fluid is 30 L / h, the pressure in the first stage is 15 MPa, and the time is 60 min; the pressure in the second stage is 7 MPa, and the time is 10 min; the above operations were repeated 3 times to obtain the composite cathode material powder.

[0039] The mixed composite cathode material, Super-P, and polyvinylidene fluoride were weighed according to a mass ratio of 90:5:5 and added to a ball milling tank. At the same time, an appropriate amount of NMP was added and ball milling was carried out in a planetary ball mill. The ball milling parameters were 300 r / min, 30 min / time, eight times of ball milling, and standing for 5 min after each ball milling to obtain a positive electrode slurry with a solid content of 33 wt%. Subsequently, the positive electrode slurry was coated on an aluminum foil current collector and placed in an oven to be dried at 110 °C for 12 h to obtain a positive electrode sheet with an activated carbon content of 5%.

[0040] The obtained positive electrode sheet was cut into electrode sheets with a diameter of 12 mm. Using a lithium metal sheet as the negative electrode, a PP material as the separator, and LiPF 6 in EC / DMC as the electrolyte, a coin cell was assembled using a 2016 battery case. Relevant electrochemical tests were carried out on a Blue Power test system. The rate performance curve is as Figure 5 shown. At an ultra-high rate of 100 C, the battery prepared with this composite cathode material can still deliver a specific capacity of 49 mAh / g.

[0041] Example 3

[0042] 1.62 g of lithium cobaltate with a particle size of 5 μm and 0.18 g of activated carbon with a particle size of 5 μm, a pore volume of 0.7 mL / g, and a specific surface area of 1600 m 2The activated carbon of [[ID=]] / g was added to an agate mortar and stirred. After stirring, it was added to a well-sealed crystallization kettle and sealed. Connect the carbon dioxide gas cylinder and open the inlet valve for supercritical carbon dioxide fluid gradient pressure mixing. The specific parameters are as follows: the temperature is 60 °C, the flow rate of the supercritical carbon dioxide fluid is 40 L / h, the pressure in the first stage is 17 MPa, and the time is 50 min; the pressure in the second stage is 7.2 MPa, and the time is 10 min; the above operations were repeated 3 times to obtain the composite cathode material powder.

[0043] The mixed composite cathode material, Super-P, and polyvinylidene fluoride were weighed according to a mass ratio of 90:5:5 and added to a ball mill jar. At the same time, an appropriate amount of the cathode solvent N-methylpyrrolidone (NMP) was added and ball milled in a planetary ball mill. The ball milling parameters were 300 r / min, 30 min / time, ball milled eight times, and left to stand for 5 min after each ball milling to obtain a cathode slurry with a solid content of 33 wt%. Subsequently, the cathode slurry was coated on an aluminum foil current collector and placed in an oven to dry at 110 °C for 12 h to obtain a cathode sheet with an activated carbon content of 10%.

[0044] Comparative Example 1

[0045] Lithium cobaltate, Super-P, and polyvinylidene fluoride were weighed according to a mass ratio of 90:5:5 and added to a ball mill jar. At the same time, an appropriate amount of NMP was added and ball milled in a planetary ball mill. The ball milling parameters were 300 r / min, 30 min / time, ball milled eight times, and left to stand for 5 min after each ball milling to obtain a cathode slurry with a solid content of 33 wt%. Subsequently, the cathode slurry was coated on an aluminum foil current collector and placed in an oven to dry at 110 °C for 12 h to obtain a P-LCO electrode sheet.

[0046] The obtained P-LCO electrode sheet was cut into electrode sheets with a diameter of 12 mm. A metallic lithium sheet was used as the anode, a PP material was used as the separator, and LiPF 6 in EC / DMC was used as the electrolyte, and a coin cell was assembled using a 2016 battery case. Relevant electrochemical tests were carried out on a BlueTEC test system, and the rate performance curve is as Figure 6 shown. Starting from a rate of 15C, the capacity of this battery could no longer be exerted.

[0047] Comparative Example 2

[0048] 1.62 g of lithium cobaltate with a particle size of 5 μm, 0.18 g of which has a particle size of 5 μm, a pore volume of 0.94 mL / g, and a specific surface area of 2100 m 20.1 g of activated carbon, 0.1 g of Super-P, and 0.1 g of polyvinylidene fluoride were added to a ball milling jar. At the same time, an appropriate amount of NMP was added and ball milling was carried out in a planetary ball mill. The ball milling parameters were 300 r / min, 30 min / time, and ball milling was carried out eight times. After each ball milling, it was left standing for 5 min to obtain a positive electrode slurry with a solid content of 33 wt%. Subsequently, the positive electrode slurry was coated on an aluminum foil current collector and placed in an oven to be dried at 110 °C for 12 h to obtain a conventional positive electrode sheet with an activated carbon content of 10%.

[0049] The obtained conventional positive electrode sheet with an activated carbon content of 10% was cut into electrode sheets with a diameter of 12 mm. A metallic lithium sheet was used as the negative electrode, a PP material was used as the separator, and LiPF 6 in EC / DMC was used as the electrolyte, and a coin cell was assembled using a 2016 battery case. Relevant electrochemical tests were carried out on a BlueTEC test system, and the rate performance curve was as Figure 7 shown, and its rate performance was better than that of P-LCO but lower than that of Example 1.

[0050] The above-described embodiments have described the technical solutions of the present invention in detail. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the present invention. Any modifications, supplements, or substitutions in a similar manner made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A positive electrode of a capacitive battery based on the synergistic energy storage effect of the body surface, characterized in that, it includes a composite positive electrode material, and the composite positive electrode material is obtained by mixing a positive electrode active material and activated carbon with a mass ratio of 80-95:5-20 through supercritical carbon dioxide fluid gradient pressure mixing; the positive electrode active material includes at least one of lithium cobaltate, lithium manganate, lithium iron phosphate, and lithium nickel cobalt manganate; the supercritical carbon dioxide fluid gradient pressure mixing includes a first stage and a second stage. During the supercritical carbon dioxide fluid gradient pressure mixing process, the pressure in the first stage is 12-20 MPa, and the time is 40-60 min; the pressure in the second stage is 6.5-7.2 MPa, and the time is 5-10 min; the temperature of the supercritical carbon dioxide fluid gradient pressure mixing is 40-60 °C, and the flow rate of the supercritical carbon dioxide fluid is 30-40 L / h.

2. The positive electrode of the capacitive battery based on the synergistic energy storage effect of the body surface according to claim 1, characterized in that, the particle size of the positive electrode active material is 5-10 μm.

3. The positive electrode of the capacitive battery based on the synergistic energy storage effect of the body surface according to claim 1, characterized in that, The particle size of the activated carbon is 5 to 10 μm, the pore volume is 0.6 to 1.0 mL / g, and the specific surface area is 1500 to 2300 m 2 / g.

4. The positive electrode of the capacitive battery based on the synergistic energy storage effect of the body surface according to claim 1, characterized in that, the number of repetitions of the supercritical carbon dioxide fluid gradient pressure mixing is 2-3 times.

5. The positive electrode of the capacitive battery based on the synergistic energy storage effect of the body surface according to claim 1, characterized in that, the positive electrode of the capacitive battery based on the synergistic energy storage effect of the body surface further includes a conductive agent and a positive electrode binder. The conductive agent includes acetylene black, Super-P, carbon nanotubes or graphene, and the positive electrode binder includes polyvinylidene fluoride.

6. The positive electrode of the capacitive battery based on the synergistic energy storage effect of the body surface according to claim 5, characterized in that, the preparation method of the positive electrode of the capacitive battery based on the synergistic energy storage effect of the body surface is: mixing the composite positive electrode material, the conductive agent, and the positive electrode binder according to a mass ratio of 80-90:5-10:5-10, then adding a positive electrode solvent, and preparing a positive electrode slurry with a solid content of 20-33 wt% after ball milling. Coating the positive electrode slurry on a current collector and drying to obtain the positive electrode of the capacitive battery based on the synergistic energy storage effect of the body surface.

7. A capacitive battery, characterized in that, it includes the positive electrode of the capacitive battery based on the synergistic energy storage effect of the body surface according to claim 1, a negative electrode, and a separator.

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