Advantages and disadvantages of the four major lithium battery 18650 3.7v technology routes

　　1. Hydrogen fuel cell industry chain

　　In the hydrogen fuel cell industry chain, the upstream is the production, transportation and storage of hydrogen, and the filling of hydrogen fuel cell systems with hydrogen at hydrogenation stations; the midstream is the production of key components such as stacks, and the stacks and accessories The two parts are integrated to form a hydrogen fuel cell system; at the downstream application level, there are three main directions: transportation, portable power supply and fixed power supply.

　　2. Comparison of advantages and disadvantages of power batteries

　　Currently, there are four main technical routes in terms of power sources for transportation: lithium-ion batteries, hydrogen fuel cells, supercapacitors and aluminum-air batteries. Among them, 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 require external charging, while hydrogen fuel cell vehicles require external hydrogen filling, and aluminum-air batteries require replenishing aluminum plates and electrolytes.

　　Comparison of advantages and disadvantages of four technical routes

　　1 Hydrogen fuel cell characteristics

　　(1) Good environmental compatibility

　　Hydrogen fuel cells provide efficient and clean energy. The water they emit 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, but directly converts chemical energy into electrical energy and thermal energy, it has high energy conversion efficiency and low noise.

　　(2) Good operating performance

　　Hydrogen fuel cell power generation does not require complex and bulky configuration equipment, and the battery stack can be assembled in a modular manner. For example, a 4.5MW power generation unit can be composed of 460 battery modules, and its power plant footprint is much smaller than that of a thermal power plant. Hydrogen fuel cells are suitable as distributed power generation devices. In addition, compared with thermal, hydropower and nuclear power generation, hydrogen fuel cell power plants have a short construction period and are easy to expand, and can be constructed in phases based on actual needs. At the same time, hydrogen fuel cells have high operating quality and excellent characteristics in responding to rapid changes in load (such as peak loads). They can convert from low power to rated power in a few seconds.

　　(3) Efficient output performance

　　When the hydrogen fuel cell works, it converts the energy stored in the fuel into electricity and heat. The efficiency of converting electrical energy is more than 40%, while 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 easy to adjust. Compared with traditional engines, due to the good modularity of hydrogen fuel cells, the output can be easily achieved by increasing or decreasing the number of single cells without increasing infrastructure investment. The power and voltage can be adjusted, so it is easy to build and it is relatively easy to control the power grid. This feature of fuel cells improves system stability.

　　(5) Hydrogen comes from a wide range of sources

　　As a secondary energy, hydrogen can be obtained through various methods, such as hydrogen production from coal, hydrogen production from natural gas reforming, hydrogen production from water electrolysis, etc. When fossil energy is exhausted, hydrogen will become the world's main fuel and energy source. The use of solar energy to electrolyze water to produce hydrogen has no carbon emissions during the process. Hydrogen can be considered the ultimate energy source.

　　(6) Existing bottlenecks

　　Judging 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 lack of popular infrastructure.

　　2 Lithium-ion battery characteristics

　　(1) Voltage platform

　　Due to the different positive and negative electrode materials used in lithium-ion batteries, the operating voltage range of its single cell is 3.7~4V. Among them, the operating voltage of lithium iron phosphate single cell, which is widely used, is 3.2V, which is three times that of nickel-metal hydride batteries. , 2 times that of lead-acid batteries.

　　(2) Larger than energy

　　The current energy density of passenger car lithium-ion power batteries is close to 200Wh/kg, and is expected to reach 300Wh/kg in 2020.

　　(3) Short battery life

　　Due to the constraints of electrochemical material characteristics, there has been no breakthrough in the number of cycles of lithium-ion batteries. Taking lithium iron phosphate as an example, the number of cycles of a single battery can reach more than 2,000 times, and the number of cycles in a group is only more than 1,000 times. Unable to meet the 8-year bus operation requirement.

　　(4) Large impact on the environment

　　Lithium-ion batteries use light metal lithium. Although they do not contain harmful heavy metals such as mercury and lead, they are considered green batteries and have less environmental pollution. But in fact, because its positive and negative electrode materials and electrolytes contain nickel, manganese and other metals, the United States has classified lithium-ion batteries as a battery that contains toxic and harmful properties such as flammability, leaching toxicity, corrosiveness, and reactivity. It is the battery that contains the most toxic substances among all types of batteries at present, and because its recycling process is more complicated and the cost is higher, the current recycling rate is not high, and discarded batteries have a greater impact on the environment.

　　(5) The cost is still high

　　The initial purchase cost of lithium-ion batteries is high. Taking the current mainstream product of power batteries for buses, lithium iron phosphate batteries, as an example, the price is about 2,500 yuan/kWh. With the popularity of electric vehicles, it is expected to drop to less than 1,000 yuan/kWh in 2020. . Due to the restriction of the number of cycles of a single battery after being assembled into a group, buses usually need to replace batteries in about 3 years, which puts great pressure on operating unit costs.

　　(6) Greater impact on the power grid

　　Firstly, due to the large-scale application of pure electric vehicles, due to the large charging demand, the harmonic interference of charging equipment on the power grid will be prominent, affecting the power supply quality of the power grid; secondly, during fast charging, due to high charging rates, the charging power is high (Passenger cars are around 50kW and buses are around 150~250kW), which has a greater impact on the load of the power grid.

　　Therefore, based on the current technical level of lithium-ion batteries, its application in electric vehicles is mainly in short-distance pure electric vehicles with a driving range of less than 200km.

　　3 Supercapacitor Characteristics

　　(1) Extremely high charge and discharge rate

　　Supercapacitors have high power density and can discharge hundreds to thousands of amps of current in a short period of time. They charge quickly and can complete the charging process in tens of seconds to minutes. Supercapacitor buses and trams use this feature to complete charging in a short time and drive the vehicle forward.

　　(2) Long cycle life

　　Supercapacitors have very little loss during charging and discharging, so their cycle life is theoretically infinite, and can actually last more than 100,000 times, which is 10 to 100 times longer than batteries.

　　(3) Better low temperature performance

　　Most of the charge transfer that occurs during the charging and discharging of supercapacitors occurs on the surface of the electrode active material, so the capacity attenuation with temperature is very small. In general, the capacity attenuation of lithium-ion batteries at low temperatures is even as high as 70%.

　　(4) Energy density is too low

　　One of the bottlenecks in the application of supercapacitors is that the energy density is too low, which is only about 1/20 of that of lithium-ion batteries, about 10Wh/kg. Therefore, it cannot be used as the main power supply of electric vehicles, but is mostly used as auxiliary power supply, mainly used for quick start devices and braking energy recovery devices.

　　4 Aluminum air battery characteristics

　　(1) Low material cost and high energy density

　　The negative active material of the aluminum-air battery is rich metal aluminum, which is cheap and environmentally friendly. The positive active material is oxygen in the air, and the positive capacity can be infinite. Therefore, aluminum-air batteries have the advantages of light weight, small size and long service life.

　　(2) Key technologies have not made breakthroughs and have not yet left the laboratory.

　　Problems such as air electrode polarization and aluminum hydroxide sedimentation are important obstacles affecting the marketization of metal-air batteries. The improvement of aluminum-air battery performance has encountered a big bottleneck. It is still in the laboratory stage, and there is still a long way to go before commercialization.

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