LR1130 battery.Principles of high-speed rail battery technology

　　Principles of high-speed rail battery technology

　　At present, countries around the world are taking different measures to develop new energy sources for automobiles and further reduce the pollution caused by automobile exhaust gas to the environment. Some new energy sources are constantly being used in modern automobiles, such as natural gas, hydrogen energy, electric energy, fuel Batteries, etc., and fuel cells are a research direction that various automobile manufacturers and scientific research institutions are focusing on. Among the current fuel cell technologies, there is a new battery technology - iron battery technology. Currently, there are two types of iron batteries being studied at home and abroad: high-speed iron batteries and lithium-iron batteries. High-speed iron battery is a new chemical battery made of synthetic stable ferrate (K2FeO4, BaFeO4, etc.) as the cathode material of high-speed iron battery. It has the characteristics of high energy density, small size, light weight, long life, and no pollution; The other is lithium iron battery, mainly iron phosphate battery, with an open circuit voltage of 1.78V-1.83V and a working voltage of 1.2V-1.5V, which is 0.2-0.4V higher than other primary batteries, and the discharge is stable, pollution-free and safe. , excellent performance.

　　Introduction to high-speed rail battery technology When high-speed rail is used as the cathode material of the battery, the electrode reaction is a three-electron reaction. The potential and energy of the battery are higher than those of traditional zinc-manganese batteries. Moreover, this material is cheap and non-polluting to the environment, so it has attracted widespread attention from the electrochemical community. Ferrate material can obtain 3 electrons in the battery reaction, so it has a relatively high capacity. As can be seen from Table 1, the theoretical capacity of lithium ferrate is as high as 601Ah/kg. The theoretical capacity of barium ferrate is also 313Ah/kg. The capacity of MnO2 is 308Ah/kg. High-speed rail primary batteries can be formed by using ferrate as the cathode material to replace MnO2 in commercial zinc-manganese batteries. The battery reaction is: MFeO4+3/2Zn→1/2Fe2O3+1/2ZnO+MznO2. Figure 1 is a comparison of the discharge curves of potassium ferrate-zinc batteries and zinc-manganese batteries. No. 7 battery is discharged at a constant current at a current density of 0.5mA/cm2, and the average discharge voltage of the K2FeO4 cathode material to Zn is 1.58V. This voltage is 24% higher than the average discharge voltage of zinc-manganese batteries (1.27V), and the discharge capacity of the former is 32% higher than that of the latter. Under the above conditions, its discharge efficiency is 85%. Compared with traditional zinc-manganese batteries, high-speed rail primary batteries have the advantages of high voltage (OpV: 1.9V), high energy (1.55Wh, AAA), no electrolyte consumption, and no environmental pollution.

　　High-speed rail battery electrolyte and commonly used negative electrode materials In high-speed rail batteries, there are many materials that can be used as battery negative electrodes, including zinc, aluminum, iron, cadmium and magnesium.

　　1. Zinc (Zn) According to the metallic properties of zinc, its equilibrium potential is relatively negative and its electrochemical equivalent is high, so its specific energy and specific power are relatively high. Moreover, zinc has good discharge performance, is cheap and has abundant sources. It is widely used in chemical power supplies. The current application forms mainly include Zn-MnO2 batteries and Zn-air batteries. In alkaline solution, in addition to the formation of zincate, the final product of the zinc electrode reaction is mainly solid phase zinc oxide: Zn+2OH-→Zn(OH)2+2eZn(OH)2+2OH-→Zn(OH) 42-Zn(OH)42-→ZnO+H2O+2OH-The total reaction is: Zn+2OH-→ZnO+H2O+2e For zinc anode, it has certain advantages in application in high-speed iron batteries, because zinc electrode is used as anode material There is relatively mature theory and process accumulation in alkaline solutions. When studying Zn-MFeO4 batteries, there are many technologies that can be used for reference in terms of corrosion inhibitors, conductive agents, separators, current collectors, and manufacturing processes.

　　2. As the negative electrode of high-speed rail batteries, aluminum will encounter two problems: First, the self-corrosion problem of aluminum in alkaline solution. In strong alkaline solution, aluminum dissolves very quickly and generates a large amount of hydrogen. For ferrate, the hydrogen passing through the separator will accelerate the decomposition of ferrate; secondly, the deposits produced on the surface of aluminum during the anode process will prevent the reaction of the electrode, increase the anode overpotential, and reduce the voltage efficiency of the anode. . The above problems can be overcome through two approaches: alloying and electrolyte additives. By adding some elements to form binary or multi-element aluminum alloys, such as adding Ga, Sn, In and other metals, the composition and structure of aluminum surface deposits can be changed, the anodic potential of aluminum can be increased, and the ability of aluminum to resist self-corrosion can be enhanced.

　　Adding other substances to the electrolyte can also improve the crystal form of the electrode reaction product, thus inhibiting corrosion and increasing the anode potential. For example, adding In(OH)3 can effectively reduce corrosion, and adding Ga2O3, Na2SnO3 or sodium citrate can effectively activate the electrode.

　　3. The electrode reaction of iron as the negative electrode of the battery in alkaline solution is relatively complicated. Iron loses electrons to form stable +2-valent and +3-valent hydroxides, that is, Fe+nOH-→Fe(OH)n2-n+ 2eFe(OH)n2-n→Fe(OH)2+(n-2)OH-E°=-0.877V(vs.SHE)Fe(OH)2+OH-→Fe(OH)3+eE°= -0.56V (vs.SHE) Then, 2Fe(OH)3+Fe(OH)2→Fe3O4+4H2O In the alkaline solution, iron initially forms a +2-valent product, and the divalent iron forms Fe(OH) with the electrolyte The n2-n complex generates +3-valent iron when discharge continues, and Fe3O4 is formed by the interaction between +3-valent iron and +2-valent iron. When iron and ferrate form a battery, the open circuit voltage of the battery is about 1.5V, which varies slightly depending on the type of ferrate. It can be seen from the discharge curve of the iron electrode that the iron negative electrode has two discharge platforms during discharge. The first discharge platform corresponds to the conversion of Fe to Fe(OH)2; the second discharge platform corresponds to Fe(OH)2 /Fe(OH)3 reaction,

　　The voltage from the first discharge platform to the second discharge platform will decrease by about 0.3V. In fact, the discharge of the second platform is easily affected by many factors. For example, Fe(OH)3, the reaction product of the second discharge product and ferrate, will form Fe3O4 with Fe(OH)2, affecting the discharge of Fe(OH)2. The theoretical capacity of a single battery composed of iron negative electrode and potassium ferrate at the first discharge platform should be 285.3mAh/g. 4. When cadmium and ferrate form a battery, the theoretical value of the single cell open circuit voltage should be around 1.4V. The electrochemical equivalent of cadmium is 477mAh/g, and the theoretical capacity of the battery formed with K2FeO4 is 219mAh/g.

　　High-speed rail battery electrolyte

　　1. The cathode material of the aqueous solution system high-speed iron battery is ferrate, and the solubility of ferrate is relatively poor, and it is very unstable even in neutral or weakly alkaline aqueous solutions. Therefore, the aqueous solution system of a chemical power source using ferrate as the cathode material can only be a concentrated strong alkali aqueous solution. In alkaline aqueous solutions, there are many materials that can be used as battery negative electrodes, including zinc, aluminum, iron, cadmium and magnesium.

　　2. Non-aqueous ferrate is also very stable in some non-aqueous organic media such as acetonitrile, ethylene carbonate (EC), propylene carbonate (pC), ethylene glycol dimethyl ether (DEM) and tetrahydrofuran (THF). And it's almost insoluble.

　　This allows ferrate to be used as a positive electrode material for non-aqueous electrolyte batteries. The negative electrode material currently used in non-aqueous electrolytes is mainly lithium. Due to its small density, high potential, large electrochemical capacity, and good conductivity, lithium metal has the characteristics of high voltage and high specific energy, and is widely used in medicine, special equipment, navigation, and electronics.

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