Future super-capacity battery material staged ‘Three Kingdoms Kill’

Future super-capacity battery material staged 'Three Kingdoms Kill'

The supercapacitor is important consisting of 4 parts of electrodes, current fluids, electrolytes, and diaphragm, wherein electrode material is the most critical factor affecting performance and production cost of supercapacitors.. Research and development of high performance, low-cost electrode materials are important contents of supercapacitors research and development.

At present, there are many supercapacitor electrode materials important carbon materials, metal oxides (or hydroxides), conductive polymers, etc., and the commercialization of carbon materials and metal oxide electrode materials is relatively mature, and is the hot spot of current research..

1 What is a supercapacitor? Supercapacitors or Ultracapacitors, also known as electrochemical capacitors, is a new energy storage device between secondary batteries and conventional capacitors, and has high energy density of secondary battery and conventional capacitor power density. Advantages; In addition, supercapacitors also have a wide range of applications with high efficiency, high efficiency, high cycle life, wide temperature range, high safety, and extensive application prospects in the fields of electric vehicles, new energy power generations, information technology, aerospace..

The supercapacitor can also form a composite power system with the rechargeable battery, which can meet the high power requirements of electric vehicle start, acceleration, and climbing, and extend the recycling life of the charging battery, and achieve optimization of electric vehicle power system performance.. At present, the commercial production of supercapacitors has achieved a higher price, low energy density, which greatly limits the large-scale application of supercapacitors.

. The supercapacitor is important consisting of 4 parts of electrodes, current fluids, electrolytes, and diaphragm, wherein electrode material is the most critical factor affecting performance and production cost of supercapacitors..

Research and development of high performance, low-cost electrode materials are important contents of supercapacitors research and development. At present, there are many supercapacitor electrode materials important carbon materials, metal oxides (or hydroxides), conductive polymers, etc., and the commercialization of carbon materials and metal oxide electrode materials is relatively mature, and is the hot spot of current research.

. Therefore, this paper will focus on the latest research progress of high-performance electrode materials such as carbon material, metal oxide and its composites and commercial application prospects..

2 carbon materials as the latest research of supercapacitor electrode materials Developing plants, CNT, and mantannium, “killer” electrode materials? Carbon materials are currently studied and have the most widely used supercapacitor electrode materials, important include activated carbon, mold carbon, carbon nanotubes, activated carbon fibers, carbon gels, and graphene, etc.. The carbon material has a high conductivity, large specific surface area, good electrolyte infiltration, and the potential window width, but it is low than the capacitor is low.

. The carbon material is important to store energy in the electrode / solution interface, referred to as the duplex layer capacitor..

Increase the specific surface area of ​​the electrode active substance, you can add interface double-electrical layer area, thereby increasing the two-electric layer capacitance. Carbon nanotube carbon nanotubes are a pore structure that has been discovered in the early 1990s, a large specific surface area, suitable for electrolyte ion migration, and interactive winding to form a nanoma-scale web structure, therefore I have been considered a high power super capacitor ideal electrode material. Niu et al.

Earliestly reported the research of carbon nanotubes as a supercapacitor electrode material. They use catalytic pyrolysis to prepare hydrocarbons into multi-walled carbon nanotube film electrodes, in the H2SO4 electrolyte of 38% mass fraction and At different frequencies of 0.001 to 100 Hz, the specific capacitance reaches 50 to 110F / g, and its power density exceeds 8KW / kg.

. However, freely grown carbon nanotubes are different, orientation is messy, and even inclusions have amorphous carbon, it is difficult to purify, which improves the difficulty of its practical application..

Since the activated carbon has a stable service life, low price and large-scale industrial production foundation, it has been widely used in commercial supercapacitors.. In the 1960s, Becker applied for the first patent for the electrochemical capacitor of activated carbon material.

He was coated on the metal substrate, which was coated with a high ratio of activated carbon, and then impregnated in the H2SO4 solution, and doubled in the active carbon hole interface. Layer structure to store charge. Preparation of activated carbon’s raw material is very rich, coal, wood, nut shell, resin can be used to prepare activated carbon powder.

The raw material is activated after modulation, and there are two types of chemical activation and physical activation.. Chemical activation is at temperatures of 500 to 700 ° C, using phosphoric acid, potassium hydroxide, sodium hydroxide and zinc chloride as activators; physical activation is generally referred to in oxidative atmosphere such as water vapor, carbon dioxide, and air.

Treatment of raw materials for carbon material at high temperature of 800 ~ 1200 ° C. The active carbon well structure prepared by the activation process typically has a hole diameter distribution having a wide dimensional span, including micropores (<2 nm), mesh (2 ~ 50 nm) and a large pore (50 nm)..

It should be pointed out that when the activated carbon is higher than the surface area of ​​3000 m2 / g, only relatively small specific capacitance (<11μF / cm2) can be obtained, which is smaller than the active carbon dual electrical layer than the capacitor theory (15 ~ 25μF / cm2), this Indicates that not all well structures have effective charge accumulation. Although the specific surface area is an important parameter in the performance of the two-layer capacitor, the hole distribution, the shape and structure, conductivity and surface functional modification of the hole can also affect the electrochemical properties of activated carbon materials..

Over-activation can result in large porosity, and also reduce the bulk density and conductivity of activated carbon, thereby reducing the volumetric energy density of activated carbon material; additionally, some active groups and suspension keys in the surface of activated carbon will make it an electrolyte The reaction activity has increased, and the performance of electrode material properties will also cause attenuation of electrode material material.. Therefore, the activated carbon material having a narrow pore dispensing and the mutually crosslinked pore structure, a short ion transmission distance, and the controllable surface chemical properties (such as surface tension, surface free energy, etc.

) will help improve supercapacitors. Energy density, while do not affect its power density and cycle life. At present, the first choice for commercial supercapacitor electrode materials is still activated carbon, but with other new carbon materials such as carbon nanotubes, graphene, etc.

, it is possible to replace activated carbon material in the future.. In recent years, the research of highly orderly carbon nanotube arrays has once again attracted attention, which directly grown directly on the current fluid, not only reduces the contact resistance between active substances and current flow, but also simplifies the electrode.

Preparation process. Activated carbon has been widely used in commercial supercapacitor production due to activated carbon has a stable service life, low price and large-scale industrial production basis..

In the 1960s, Becker applied for the first patent for the electrochemical capacitor of activated carbon material. He was coated on the metal substrate, which was coated with a high ratio of activated carbon, and then impregnated in the H2SO4 solution, and doubled in the active carbon hole interface. Layer structure to store charge.

Preparation of activated carbon’s raw material is very rich, coal, wood, nut shell, resin can be used to prepare activated carbon powder. The raw material is activated after modulation, and there are two types of chemical activation and physical activation..

Chemical activation is at temperatures of 500 to 700 ° C, using phosphoric acid, potassium hydroxide, sodium hydroxide and zinc chloride as activators; physical activation is generally referred to in oxidative atmosphere such as water vapor, carbon dioxide, and air. Treatment of raw materials for carbon material at high temperature of 800 ~ 1200 ° C. The active carbon well structure prepared by the activation process typically has a hole diameter distribution having a wide dimensional span, including micropores (<2 nm), mesh (2 ~ 50 nm) and a large pore (50 nm).

. It should be pointed out that when the activated carbon is higher than the surface area of ​​3000 m2 / g, only relatively small specific capacitance (<11μF / cm2) can be obtained, which is smaller than the active carbon dual electrical layer than the capacitor theory (15 ~ 25μF / cm2), this Indicates that not all well structures have effective charge accumulation. Although the specific surface area is an important parameter in the performance of the two-layer capacitor, the hole distribution, the shape and structure, conductivity and surface functional modification of the hole can also affect the electrochemical properties of activated carbon materials.

. Over-activation can result in large porosity, and also reduce the bulk density and conductivity of activated carbon, thereby reducing the volumetric energy density of activated carbon material; additionally, some active groups and suspension keys in the surface of activated carbon will make it an electrolyte The reaction activity has increased, and the performance of electrode material properties will also cause attenuation of electrode material material..

Therefore, the activated carbon material having a narrow pore dispensing and the mutually crosslinked pore structure, a short ion transmission distance, and the controllable surface chemical properties (such as surface tension, surface free energy, etc.) will help improve supercapacitors. Energy density, while do not affect its power density and cycle life.

At present, the first choice for commercial supercapacitor electrode materials is still activated carbon, but with other new carbon materials such as carbon nanotubes, graphene, etc., it is possible to replace activated carbon material in the future..

GEIM, British Scientist GEIM, discovered a single-layer graphite film composed of carbon atoms in 2004, graphene (Graphene). Graphie is not only the thinner of known materials, but also very hard. As a single, it transmits electrons at room temperature is the fastest in all conductor known.

. Carbon nanotubes and graphene are representatives of one-dimensional nanomaterials and two-dimensional nanomaterials, each of which has complementarity in structural and performance..

From now on, graphene has a more excellent characteristic, such as high conductivity and thermal conductivity (5000W / m˙K), high carrier mobility (2 × 105 cm2 / v˙s), free electron movement Space, high strength and stiffness (Yang’s modulus of approximately 1.0TPa), high theoretical specific surface area (2600m2 / g), etc..

Therefore, graphene has broad application prospects in the field of single electronics, ultra-sensitive sensors, electrode materials, pharmaceutical carriers.. Using the high-specific surface area of ​​graphene material and high conductivity, etc.

, it is desirable to obtain a lower price of low and superior performance supercapacitor electrode materials.. 3 Metal oxide as a supercapacitor electrode material is an important metal oxide is important to store energy by electrode active substance at the electrode surface and near surface.

. The working principle is the same, but the charge and discharge behavior is similar to the conventional capacity, so the magazine caile capacitor. Farase tallery capacitance has a relatively high capacity, 10 to 100 times the two-electric layer capacitance.

Accelerate the electrochemical reaction rate of electrode active substance and increase the utilization of electrode active substances, which is an effective way to improve metal oxide supercapacitor than capacitance.. The ruthenium oxide material for cerium oxide is used as a supercapacitor electrode material has a higher capacitance, good conductivity, and a very stable conductivity in the electrolyte, and is the best supercapacitor electrode material.

. US Army Research Laboratory reported that the amorphous hydrated oxide ratio capacitance was as high as 768F / g, and the energy density based on electrode material was 26.7Wh / kg.

. At present, the United States has used cerium oxide materials for aerospace and science and other important areas..

However, ruthenium resources are limited, and the price is very expensive, it is difficult to apply. In order to further improve performance and reduce costs, all domestic and foreign are actively looking for other low-cost metal oxide electrode materials..

Studies have shown that manganese dioxide, cobalt oxide, nickel oxide, iron oxide and vanadium oxide, etc. have electrochemical properties similar to cerium oxide, wherein manganese dioxide is one of more electrode materials..

Manganese dioxide manganese dioxide material has a significant advantage that the price is low, the environment is environmentally friendly and the electrochemical working window (more than 1000mV above the water solution system, and the ruthenium oxide electrode material is equivalent). More importantly, the manganese dioxide supercapacitor can employ a neutral electrolyte solution (such as Na2SO4 aqueous solution, KCl aqueous solution, etc.), unlike other metal oxides or carbon-based supercapacitors, the electrolyte of strong acid or strong alkali, which makes Mandioxide supercapacitor assembly and use more secure and convenient.

Further, the nanotechnology is applied to the field of supercapacitor electrode materials, and the electrochemical activity can be greatly improved by high specific surface area, short ion diffusion distance and electron transport distance using the nano-manganese dioxide electrode material.. In 1999, Goodenough et al.

First studied the application of amorphous manganese dioxide electrode materials in supercapacitors.. They used a coprecipitation method to prepare a high-proportional surface area of ​​amorphous manganese dioxide material (303 m2 / g), in 2 mol / L KCl electrolyte, more than 203F / g than capacitance.

4 Composites as a supercapacitor electrode material research progress uses a composite material for supercapacitors in recent years, and improves the comprehensive performance of supercapacitors by utilizing synergies between components of the composite material.. Composite material is important carbon / metal oxide composite, carbon / conductive polymer composite, metal oxide / conductive polymer composite, etc.

. For the disadvantage of the carbon material (such as graphene material), the surface is modified with a metal oxide having a large Farased capacitor or a conductive polymer thereof, which can be greatly improved than the capacitance; the metal oxide ( For example, the conductivity of manganese dioxide material is compounded by composite, and its performance is also significantly improved, and the power characteristics are also improved..

The graphene composite WANG et al. Employs a Ni (OH) 2 nano sheet in graphene, in the KOH electrolyte of 1 mol / L, when the constant current charge current density is 2.8a / g.

Based on the composite quality of the composite material to 935F / g, Ni (OH) 2-based ratio is as high as 1335F / g (the potential window is -0.05 ~ 0.45V, the reference electrode is Ag / AGCL).

They also studied the difference between different preparation conditions and graphene precursor content of oxygen on composite ratio capacitance. When the scanning speed is 40 mV / s, it is employed in a graphene surface in situ growth Ni (OH) 2, graphene and Ni (OH) 2 Mechanical mixing and a method of growing Ni (OH) 2 on the surface of the oxide oxide surface, the specific capacitance of the composite material is 877F / g, respectively? 339F / G and 297F / g. The above results indicate that high-conductivity graphene contributes to a rapid and efficient charge transport between macro agglomeration Ni (OH) 2 and the current collector while accompanied by fast storage and release of energy.

. Manganese dioxide composites are poorly conductive due to manganese dioxide composites, poor conductivity is poor, and severely affect the electrochemical properties of manganese dioxide materials..

Therefore, the researchers use more doped or composite means to increase the conductivity of manganese dioxide materials.. Carbon nanotubes, mesoporous carbon, and recent carbon materials such as carbonaceous materials such as graphene and manganese dioxide have been reported; in addition, the composite of conductive polymer and manganese dioxide also caused great attention.

This organic-inorganic composite can give full play to the respective advantages of the two types of materials, greatly improves the overall performance of the electrodes.. 5 Prospects Super Capacitor As an emerging energy storage component with extremely broad market prospects, and high-performance electrode materials are the focus of current supercapacitor research.

. The supercapacitor needs to meet the demand for high energy / high power density, which must satisfy electric vehicle and renewable energy power generation. It is necessary to make the electrode material have high specific capacitance, large specific surface area, high conductivity, low cycle life and low cost.

. The aperture control of activated carbon is relatively difficult, lower than the surface area utilization; the price of carbon nanotubes is relatively expensive, it is difficult to purify, thereby greatly affect the actual application of carbon nanotubes in supercapacitors; graphene is a new type of carbon material, Have excellent conductivity and open surface structure, excellent energy storage characteristics. If it can achieve scale preparation, reduce cost, performance controllable, the graphene electrode material will have a tempting application prospect, and it is expected to go to industrialization in the near future.

. About cheap metal oxide-manganese dioxide, if it can effectively solve the problem of poor conductivity and cycle stability, the utilization of the electrode material will help realize large-scale applications of manganese dioxide supercapacitor..

On the other hand, the composite material is used as the electrode material, and the length of each material is avoided, that is, the “synergistic effect” is conducive to improving the integrated electrochemical properties of the material.. Currently, high-energy density, high-power density, and low-cost new composites (such as graphene-manganese dioxide composites, etc.

) are prepared at home and abroad.. However, in general, the synthesis method, use mechanism and electrochemical performance of composite materials are still in the development stage, and it is necessary to fully meet the requirements of practicalization, and it is still waiting for further in-depth research and material performance.

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