The graphite felt is normally classified into asphaltic based graphite felt, PAN based graphite felt &rayon-based graphite felt. The mainly application is electric conduction in the photovoltaic industry, as the heat retaining material, thermal insulation material for the smelting furnace and vacuum furnace, and in chemical industry it could be the filtration material.

　　The carbon/ graphite felt is made of oxidized PAN short cut fiber. And after opening, carding,

　　lapping, needling,it is made into a certain density and thickness. Some excellent performances such as high purity, soft texture, No dus and chemical corrosion resistance will be obtained by

　　special carbonization and graphitization process .The carbon/graphite felt can improve the current

　　density of the liquid flow battery, and it has the protective effect on the corrosion resistance of the bipolar plate and is mainly used as the electrode of the liquid flow battery industry.

　　The graphite felt is formed after above 2000℃ high temperature treatment under inert gas or vacuum.The polypropylene cyano is the major raw material. The polypropylene cyano carbon felt or rayon-based carbon feltis cuttd into the specific dimension, and loaded into the graphite vessel after rolled. The graphite vessel will be setted in the high temperature furnace, protected in vacuum or by high pure inert gas. It's heated up to 2200-2500℃ with the heating rate 100-300℃/h, then get the final product after naturally cooled to 100℃.

　　PAN Based Carbon Felt is used in high temperature insulation in resistance or induction heated vacuum furnaces and inert gas furnaces. Made of carbon or graphite fibers, these materials have low thermal conductivity and vapor pressure. it is considerably less expensive and more effective than metallic radiation shields and may be used to replace them, with power savings of up to 75%. The low specific heat and low density permit rapid heating and cooling of furnaces.

　　The electrode material is one of the key materials for vanadium redox flow battery. Due to the large surface area and good stability, the graphite felt is dominant. However, the graphite felt material has poor hydrophilicity, and its electrochemical activity is not good enough. This paper on the graphite felt electrode respectively chromic acid oxidation method, mixed acid electrochemical oxidation method and hydrothermal ammoniation method for processing vanadium redox flow battery to improve its activity, the main conclusions are as follows: after chromic acid oxidation, hydrophilicity and electrochemical activity of the Shi Mozhan electrode increased, the optimum processing time is 5 h. In the 10 to 70mA/cm2, the battery with the graphite felt after the treatment with the chromate has a good charge discharge performance.

　　The efficiency of the battery voltage is about 90.9% and the energy efficiency is up to 79.4% at mA/cm2. FT-IR and SEM show that the carbon fiber processing after the oxygen functional groups increased and the surface gully increased, the former increased the number of active sites on surface of carbon fiber in VO2+/VO2+ electrode reaction, which increases the contact area of vanadium ion and electrode. The hydrophilicity and electrochemical activity of the graphite felt electrode were obviously enhanced after the electrochemical anodization of sulfuric acid and phosphoric acid. The optimum treatment conditions were as follows: the current density was 50 mA/cm2 and the treatment time was 4min. The processing of graphite felt is loaded into the cell, showing good charge and discharge performance in 10 to 50 in mA/cm2, 20 in mA/cm2, the battery voltage efficiency of 88.2%, energy efficiency reached 79.6%. FT-IR and SEM tests showed that the oxygen functional groups on the surface of carbon fiber increased, and the surface roughness increased. The results of XRD show that the crystallite size and the space between the carbon fibers decrease, which indicates that the electrochemical oxidation etching the graphite crystallites in the outer layer, which is the reason for the increase of the surface roughness of the carbon fiber. For the first time put forward 180 degrees in the hydrothermal ammoniation of graphite felt electrode, hydrophilicity and electrochemical activity of treated graphite felt electrode increased, the optimum processing time is 15 H.

　　The processing of graphite felt is loaded into the battery, charge and discharge can be stabilized in 20 to 60 in the range of mA/cm2. In 20mA/cm2, the voltage efficiency can reach 83.7% and the energy efficiency is up to 85.3%. The reason lies in the improvement of electrode active carbon fiber surface increased nitrogen content of functional groups and nitrogen functional groups to enhance the positive charge density of the alkaline carbon fiber and its adjacent carbon atoms, to speed up the transfer speed of vanadium ions and electrons in the electrode / solution interface, improve the vanadium ion diffusion process, reduces the electron transfer resistance.

　　Graphite felt has good stability, the unit cost of large surface area, good permeability of the advantages of electrode materials used in direct methanol fuel cell flow, but because of its poor hydrophilicity, electrochemical activity is not high, which greatly limits its application. Therefore, we try to improve the electrochemical properties of carbon atoms by changing the electronic structure of carbon atoms. Although the nitrogen doped graphite felt has been reported sporadically, the research on the nitrogen doped graphite felt used as the cathode of direct flow methanol fuel cell is still in the blank.

　　With the energy and environmental problems become more and more prominent, the research and development of green, pollution-free new energy has been attached great importance by the enterprises and the government. Fuel cell is a kind of clean energy which can directly convert the chemical energy into electric energy.

　　The graphite felt has the advantages of good stability, large surface area per unit cost and good fluid permeability, but its application is limited because of its poor hydrophilicity and low electrochemical activity. Therefore, it is hoped that the surface treatment can improve its electrochemical performance. Commonly used acid treatment, heat treatment, electrochemical oxidation, rare earth ion modification methods.

　　The electrode material is one of the key factors to restrict the development of the liquid flow battery. It needs to meet the requirements of high conductivity, large surface area, high selectivity to a specific reaction, good electrochemical activity, good chemical stability and so on. The main researches are metal, composite and carbon. The metal electrode has good conductivity, excellent mechanical properties, high electrochemical activity, but the stability in the anode region is poor and expensive, it is not suitable for large-scale applications; composite electrode material is a polymer and conductive carbon mixing, drying and tabletting after prepared, while improving the conductivity, oxidation but the need to overcome the polymer at high temperature; carbon electrode mainly include carbon cloth, graphite, carbon fiber and graphite felt, good stability and low cost, but the graphite, carbon fiber and carbon cloth used as electrode, a few cycles, the electrode surface is damaged, only the graphite felt electrode is the present study is more and more widely used as electrode material.

　　Graphite felt comprehensive performance is the best of the electrode used in battery.but it still need to do some activation treatment to improve the activity.

　　The commonly used method:heat treatment,acid treatment, electrochemistry treatment etc.

　　The heat treatment of graphite felt is to put it into the heating equipment, like muffle furnace,to make it oxidation around the surface.

　　Some scholars have found that if put the un-modified graphite felt into the H2SO4 solution,the surface of the graphite felt is hydrophobic,and it need about 48h to be complete wetting.under 200℃ heating environment,and after that,the wetting time can be reduce to about 30h,and with the heating temperature increasing,the graphite felt is easier to be wetting.

　　Under the heating temperature at 400℃ in the air environment for 30h,then make the graphite felt used in the vanadium redox flow battery,we could found that,the heating treatment can apparently improve the electrochemistry property of the graphite felt,and can make the energy conversion efficiency of the battery increase from about 70% to 89%.

　　We could also have a comparation between the modified graphite felt and the un-modifified ones,we could found that the absorption rate of un-modified graphite felt is mearly about 3.2g/g,but the modifified ones,under 400 ℃ environment for 2h,can reach about 10g/g absorption rate.

　　The reason that heating treatment can improve the graphite felt activation is mainly the heating treatment can improve the directional arrangement of the graphitization,and make the electric resistance come down apparently.

　　after the experiment and testing,an appropriate condition can make the graphite felt with a minimum electric resistance,make it used in the vanadium battery pack,during the charging and discharging process,the coulomb efficiency can reach more than 90%.

　　All vanadium redox flow battery, using vanadium ion solution as positive and negative electrode active material, the cathode is V (IV) /V (V) of V cathode, (II) /V (III) on the electric potential difference, the standard is about 1.25 V. The battery has the advantages of large capacity, long service life, deep discharge and no damage to the battery, and can realize the instantaneous recharging. At present, the development of vanadium battery is hindered by the electrode material, and the electrode material target is PAN base felt.

　　At present, the production of PAN carbon felt is mainly used as thermal insulation material, the conductivity and electrochemical activity can not meet the requirements of the battery. The effect of heat treatment temperature on the graphitization of graphite felt was further studied.

　　In the heat treatment of graphite felt, the optimum temperature of heat treatment is about 550 DEG C, and the Shi Mozhan resistance is the lowest and the exchange current is the maximum. In the process of charging and discharging, the coulomb efficiency can reach more than 90% by using the graphite felt electrode prepared by the optimum temperature.

　　Electrode material is one of the key materials for all vanadium redox flow batteries. Due to the large surface area and good stability, the graphite felt is dominant. However, the graphite felt material has poor hydrophilicity, and its electrochemical activity is not good enough. This paper on the graphite felt electrode respectively chromic acid oxidation method, mixed acid electrochemical oxidation method and hydrothermal ammoniation method for processing vanadium redox flow battery to improve its activity.

　　The reason lies in the improvement of electrode active carbon fiber surface increased nitrogen content of functional groups and nitrogen functional groups to enhance the positive charge density of the alkaline carbon fiber and its adjacent carbon atoms, accelerate the electrode / solution interface of vanadium ion and electron transfer rate, improve the vanadium ion diffusion process, reduces the electron transfer resistance.

　　Flow battery is to achieve large-scale renewable energy application of new green secondary battery two, the performance of electrode materials has important significance for the practical application of the flow battery, PAN based graphite felt electrode material is the preferred flow battery, in order to further improve the hydrophilicity and electrochemical activity of the modified Shi Mozhan electrode materials, graphite related research in recent years the carpet has become a hot spot.

　　Energy storage technology is very conducive to the balance between energy production and consumption between the control in power, plays an important role in the integration of renewable energy and other areas, as one of the electrochemical energy storage technology flow battery, the redox flow battery, with current conversion capability, flexible structure design, reasonable cost, operation simple, is a new type of green two battery suitable for large scale electricity storage.

　　Carbon fiber, also called graphite felt, is made of carbon fiber after pre oxidation by lapping process of acupuncture, felt body made of carbonization process, graphite felt is a low strength carbon fiber products, has the advantages of low density, low linear expansion coefficient, low thermal capacity, small thermal conductivity, high temperature resistance thermal shock resistance, strong resistance, chemical corrosion resistance and excellent high temperature, is widely used in industry, energy industry, auto industry, chemical and environmental protection.

　　Graphite felt is the first choice of electrode material for liquid flow battery, but its electrochemical activity and hydrophilicity can not fully meet the requirements of liquid flow battery.

　　The electrochemical activity of graphite felt is not high and the poor hydrophilicity, so graphite felt modification has become an important means to improve the properties of electrode materials, the modified method is mainly to increase the graphite felt surface oxygen and deposited on the Shi Mozhan surface catalytic material, and surface morphology of carbon felt, produce different effects of chemical composition and electrochemical performance, and improve the properties of liquid flow battery.

　　The bipolar plate used therein are required to achieve higher electrical conductivity due to the requirements for redox flow batteries have become more and more stringent in recent years.and thus A bipolar plate composed of an electrically conductive composite achieves a higher electrical conductivity by increasing the conductive filler content in the material.

　　Graphite was used as one of the main bipolar plate material in redox flow batteries due to its high electrical conductivity ,low weight and good chemical stability in the past.Graphite blocks were produced by sintering process and plates were machined to desired sizes.The main limitation of this method was the porosity of produced graphite plates.

　　At present, our company provides a bipolar plate for a redox flow battery , the bipolar late including an electrically conductive composite prepared by mixing a thermoplastic resin ,a carbonaceous material selected from graphite and carbon black ,and a carbon nano-tube.

　　Our current business is extended from the overall solution of the material to the manufacture of bipolar plates, and thus provides the following three VRB assembly services:

　　1).The bipolar plate (we can provide punch service. The thickness of the bipolar plate now can be processed are 0.6/0.8/1.0 /1.2/1.3mm.

　　2).The composite of the bipolar plate and the electrode, the advantage is that the electrode felt is fully combined with the felt in the plate, it greatly reduces the theoretical value of the contact resistance to the felt.

　　3).The bipolar plate ,the electrode and outline border. Three in one frame after embedding flow

　　box (precision injection), it’s the way which improve the reliability greatly compared with the above 1 and 2.

　　Although the density of carbon fiber is lower than that of aluminum, its strength is higher than that of steel. Carbon fiber is not only the inherent "hard" characteristic of carbon materials, but also the machinability of textile fiber.

　　A carbon fiber woven graphite felt has good conductivity, mechanical properties, electrochemical reaction activity, acid resistance, corrosion resistance and oxidation resistance, is a good electrode material, compared with metal, graphite powder and various electrode materials, more suitable for the electrode storage battery.

　　At present, the domestic production of graphite felt is mainly used to make thermal insulation material, and its conductivity and electrochemical activity can not meet the requirements of the use of battery electrode materials, therefore, the need for carbon fiber felt surface treatment. The commonly used surface treatment methods include heat treatment, acid treatment and electrochemical oxidation treatment.

　　The operation of heat treatment in air atmosphere, and after the heat treatment,the conductive ability of graphite felt has been improved, in the heat treatment of graphite felt, if the temperature is too low, resulting in electrochemical active graphite felt low, unable to meet the requirements of use as electrode materials; but if the heat treatment temperature is too high, it will cause the graphite felt surface etching, serious excessive oxidation, fiber breakage and breakage, resulting in the the electrical conductivity and mechanical properties decreased sharply, seriously affecting their life.

　　With the heat treatment temperature increased gradually from 450 degrees to 600 degrees Celsius, the impurities of graphite felt surface are gradually disappear, with the further oxidation of the holes, grooves and other defects; carbon fiber structure with the oxidation degree also changed gradually from the turbostratic structure of two dimensional ordered structure transformation three.

　　Polyacrylonitrile (PAN) based graphite felt , made of PAN precursor in an inert gas in high temperature and antipyretic have a variety of forms, such as continuous products, carbon fiber, short carbon fiber and short carbon fiber. It has many applications in engineering because of its excellent physical and chemical properties and electrical conductivity. Continuous carbon fibers are often used in resin matrix composites as reinforcements.

　　The most widely used short cut carbon fiber is a small amount of chopped carbon fiber mixed with concrete, forming carbon fiber concrete, which has a variety of functional characteristics such as pressure sensitivity, temperature sensitivity, thermoelectric and electrothermal effects. Based on the above features, carbon fiber reinforced concrete materials can be used in the temperature and deformation self diagnosis and adaptive aspects of concrete structures, such as intelligent deicing and snow melting system of concrete pavement [5]. But the production process of continuous carbon fiber is relatively complex, the price is higher; and the short cut carbon fiber mixed with concrete, need the chopped carbon fiber completely uniformly dispersed in the concrete, it is a big problem in materials, the functional properties of carbon fiber reinforced concrete material is affected, especially the heating effects the size based conductive network formation in carbon fiber, namely by carbon fiber components reduce the concrete resistance and Joule heat.

　　Graphite felt is a soft cloth formed by the bonding of chopped carbon fibers, and each fiber forms a conductive network with each other. In the concrete smart materials, because the carbon fiber felt easily cut into the desired shape size, sample only need to be paved in concrete.

　　PAN based graphite felt with electrothermal effect good and stable; the thermal efficiency of carbon fiber of different types are different, therefore, can choose the optimal thickness, to achieve efficient and economic purposes; in a certain temperature range, the temperature stability of PAN based graphite felt the rise and the input power is proportional to the input power can be selected according to the need the temperature rise; graphite felt with a temperature sensitive effect, linear resistivity increased with the temperature of graphite felt decreases, this effect can be used for temperature detection structure; combined with temperature sensitive effect and heating effect, is expected to realize the adaptive temperature regulating structure.

　　Ammonia decomposition produced by urea nitrogen doping on graphite felt, preparation of nitrogen doped graphite felt, compared with nitrogen doped graphite felt and graphite felt has more excellent electrochemical performance, and doping temperature and doping time have influence on the electrochemical activity of graphite felt.

　　Proton exchange membrane fuel cell (PEMFC) has many advantages, such as high power density, low working temperature, fast start and long service life, but hydrogen storage is used as fuel.

　　Graphite felt is the main cathode material of direct flow methanol fuel cell, and its performance is very important for direct flow methanol fuel cell. Graphite felt has the advantages of good stability, large surface area under unit cost, good fluid permeability, etc. but its application is limited because of its poor hydrophilicity and low electrochemical activity.

　　Commonly used acid treatment, heat treatment, electrochemical oxidation, nitrogen doping and other methods. Due to nitrogen doping not only improves the surface chemical activity of graphite felt, but also on the electronic structure of regulation, so in recent years, nitrogen doped graphite felt in many electrochemical devices exhibited electrocatalytic properties better than graphite felt no nitrogen doping of this study is based on previous achievements.

　　The ammonia produced by hydrolysis of urea by nitrogen doping treatment on graphite felt, has an important influence on the electrochemical activity of the cathode temperature,nitrogen doping does not change the crystal structure of graphite felt, but will affect the crystallite parameter.

　　there will not be much affected the overall morphology of nitrogen doped under certain conditions on the graphite felt mat, the nitrogen content of graphite are improved in nitrogen doped after nitrogen increased mainly pyrrolic nitrogen and pyridine type nitrogen, indicating the increase of no contribution even inhibit the electrochemical activity of graphite nitrogen on graphite felt, pyrrolic nitrogen and pyridine type nitrogen is the main reason to enhance the electrochemical activity of graphite felt the.