[China Aluminum Network] Currently, there are four main technical routes for power sources for transportation: lithium-ion batteries, hydrogen fuel cells, super capacitors, and aluminum air batteries. Lithium-ion batteries, supercapacitors and hydrogen fuel cells are widely used, while aluminum-air batteries are still in the laboratory research stage. In terms of energy supply, lithium-ion batteries and supercapacitors are suitable for pure electric vehicles, but external charging is required. Hydrogen fuel cell vehicles require external hydrogen filling. Aluminum air batteries need to be supplemented with aluminum plates and electrolytes.
1. Characteristics of Hydrogen Fuel Cells (1) Good environmental compatibility Hydrogen fuel cells provide highly efficient and clean energy. The amount of water discharged is not only small but also very clean, so there is no water pollution problem. At the same time, because the fuel cell does not need to convert thermal energy into mechanical energy like an engine, it directly converts chemical energy into electrical energy and thermal energy, and has high energy conversion efficiency and low noise.
(2) Good operation performance Hydrogen fuel cell power generation does not require complicated and large configuration equipment, and the battery stack can be modularly assembled. For example, a 4.5MW power plant can have 460 battery components, and its power plant covers much less space than a thermal power plant. Hydrogen fuel cells are suitable as distributed power generation devices. In addition, compared with firepower, hydropower, and nuclear power generation, the construction period of hydrogen fuel cell power plants is short, and expansion is easy. It can be constructed in phases according to actual needs. At the same time, the operation quality of the hydrogen fuel cell is high, and it is excellent in response to rapid changes in the load (eg, peak load) and can be switched from low power to rated power in a few seconds.
(3) High-efficiency output performance When the hydrogen fuel cell is working, the energy stored in the fuel is converted into electricity and heat, and the efficiency of converting electric energy is above 40%, and only 1/3 of the steam turbine can be converted into electricity.
(4) Flexible structural characteristics The assembly of hydrogen fuel cells is very flexible and the power is easily configurable. Compared with conventional engines, the good modularity of hydrogen fuel cells can be achieved by increasing or decreasing the number of single cells without increasing the investment in infrastructure. The number of chips can easily achieve the adjustment of output power and voltage, so it is easy to build, and it is easier to control the power grid. This feature of the fuel cell improves system stability.
(5) Sources of hydrogen Hydrogen is widely used as a secondary energy source and can be obtained in various ways, such as hydrogen production from coal, hydrogen production from natural gas reforming, and hydrogen production from electrolyzed water. When fossil energy is depleted, hydrogen will become the world's main fuel and energy. The use of solar electrolysis to produce hydrogen does not produce carbon emissions during the process. It can be assumed that hydrogen is an energy source.
(6) Existing bottlenecks From the current stage of development, the popularization of hydrogen fuel cells has encountered certain bottlenecks, such as the high cost of the battery itself and the inaccessibility of the infrastructure.
2. Characteristics of Lithium Ion Battery (1) Voltage Platform Lithium Ion Battery Due to the different anode and cathode materials, the working voltage range of the single cell is 3.7~4V, in which the operating voltage of lithium iron phosphate single cell battery with large application scale is used. This is 3.2V, which is 3 times that of a nickel-metal hydride battery and 2 times that of a lead-acid battery.
(2) Specific energy The current energy density of lithium-ion battery for passenger cars is close to 200Wh/kg, and is expected to reach 300Wh/kg by 2020.
(3) Short battery life Due to the restriction of electrochemical material characteristics, there is no breakthrough in the number of cycles of lithium-ion batteries. Taking lithium iron phosphate as an example, the number of cycle times of single-cell batteries can reach more than 2,000 times and only 1,000 times after group formation. . Failed to meet the 8-year deadline for bus operations.
(4) Larger impact on the environment Lithium-ion batteries use light-metal lithium. Although they do not contain mercury, lead, and other harmful heavy metals, they are considered to be green batteries and have less environmental pollution. However, in reality, because the positive and negative electrode materials and electrolytes contain nickel, manganese, and other metal substances, the United States has classified lithium ion batteries as a battery containing flammable, leaching toxic, corrosive, and reactive toxic and harmful substances. It is a battery with many types of batteries containing toxic substances, and because the recycling and recycling process is relatively complicated and the cost is relatively high, the current recycling rate is not high, and the used batteries have a greater impact on the environment.
(5) The cost is still high. The initial cost of lithium-ion battery acquisition is high. Take the example of Lithium Iron Phosphate battery, the mainstream product of the Power Battery for buses as an example. The price is about 2500 yuan/kWh. With the popularization of electric vehicles, it is expected to be in 2020. Reduced to less than 1000 yuan/kWh. Due to the restrictions on the number of cycles after the unit cells are grouped, the buses usually need to be replaced in about 3 years, and the operation unit has a higher cost pressure.
(6) Large impact on the power grid The first large-scale application of pure electric vehicles, due to the greater demand for charging, harmonic interference of the charging equipment on the power grid will be prominent, affecting the power quality of the power grid; Second, in the fast charge, due to the large The rate of charge is higher, so the charging power is higher (50 kW for passenger cars and 150 to 250 kW for passenger cars), which has a greater impact on the power grid.
Therefore, based on the current technology level of lithium-ion batteries, its application in electric vehicles is mainly in short-haul pure electric vehicles with a mileage of less than 200 km.
3. Supercapacitor characteristics (1) Extremely high charge/discharge rate Supercapacitors have a high power density and can emit currents of several hundred to several thousand amps in a short period of time. The charging speed is fast and can be within tens of seconds to several minutes. The charging process is completed within. Super capacitor buses and trams use this feature to complete charging in a short period of time to drive the vehicle forward.
(2) Long cycle life The supercapacitor has a very small loss during charge and discharge. Therefore, in theory, the cycle life is infinite. Actually it can reach more than 100,000 times, which is 10 to 100 times higher than the battery.
(3) Good low-temperature performance Most of the charge transfer during charging and discharging of the supercapacitor is performed on the surface of the electrode active material, so the capacity decays very little with temperature, and the capacity attenuation of lithium-ion batteries is usually as high as 70% at low temperatures. .
(4) Energy density is too low One of the bottlenecks of supercapacitor applications is that the energy density is too low, only about 1/20 of a lithium ion battery, and about 10Wh/kg. Therefore, it cannot be used as the main power source of electric vehicles, and is mostly used as an auxiliary power source, and is mainly used for a quick start device and a brake energy recovery device.
4. Characteristics of aluminum air battery (1) Low material cost and high energy density The negative electrode active material of aluminum air battery is rich in metal aluminum, which is cheap and environmentally friendly. The positive electrode active material is oxygen in the air, and the positive electrode capacity can be seen as infinite. . Therefore, the aluminum air battery has the advantages of light weight, small size and long service life.
(2) The key technology has not made breakthroughs, and the problem of polarization of the air electrode in the laboratory and the precipitation of aluminum hydroxide has not yet emerged. This is an important obstacle to the marketization of metal air batteries, and the performance improvement of aluminum air batteries has encountered a major bottleneck. It is still in the laboratory stage and there is still a long way to go from commercialization to promotion.
