Analysis of the advantages and disadvantages of the four major CR1220 battery 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 hydrogen fuel cell system is refilled with hydrogen at the hydrogen refueling station; the midstream is the production of key components such as the battery stack, integrating the battery stack and accessories to form a hydrogen fuel cell system; at the downstream application level, there are mainly three directions: transportation, portable power supply and fixed power supply.

2. Comparison of the advantages and disadvantages of power batteries At present, 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 they need external charging, while hydrogen fuel cell vehicles need external hydrogen refueling, and aluminum-air batteries need to replenish aluminum plates and electrolytes.

Comparison of advantages and disadvantages of four technical routes 1 Characteristics of hydrogen fuel cells

(1) Good environmental compatibility Hydrogen fuel cells provide efficient and clean energy. The amount of water they emit is not only small, but also very clean, so there is no water pollution problem. At the same time, because fuel cells do not need to convert heat energy into mechanical energy like engines, but directly convert chemical energy into electrical energy and heat energy, the energy conversion efficiency is high and the noise is low.

(2) Good operating performance Hydrogen fuel cell power generation does not require complex and large configuration equipment, and the battery stack can be assembled modularly. For example, a 4.5MW power generation device can be composed of 460 battery modules, and its power plant occupies a much smaller area than 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. They can be built in phases according to actual needs. At the same time, hydrogen fuel cells have high operating quality and excellent characteristics in dealing with rapid changes in load (such as peak load). They can be converted from low power to rated power within seconds.

(3) High-efficiency output performance Hydrogen fuel cells convert the energy stored in fuel into electricity and heat when working, with an efficiency of over 40% in converting electricity, while steam turbines can only convert 1/3 into electricity.

(4) Flexible structural characteristics Hydrogen fuel cells are very flexible to assemble and easy to adjust in terms of power. Compared with traditional engines, hydrogen fuel cells are easy to build and relatively easy to control the power grid due to their good modularity. Hydrogen fuel cells can easily adjust output power and voltage by increasing or decreasing the number of cells without increasing infrastructure investment. This feature of fuel cells improves system stability. (5) Wide sources of hydrogen Hydrogen, as a secondary energy source, can be obtained in a variety of ways, such as coal-to-hydrogen, natural gas reforming, water electrolysis, etc. When fossil energy is exhausted, hydrogen will become the world's main fuel and energy. The use of solar energy to electrolyze water to produce hydrogen does not emit carbon in the process, so hydrogen can be considered the ultimate energy source. (6) Existing bottlenecks From the current development perspective, the popularization of hydrogen fuel cells has encountered certain bottlenecks, such as the high cost of the battery itself and the lack of popularization of infrastructure. 2 Characteristics of lithium-ion batteries

(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 the lithium iron phosphate single cell, which is widely used, is 3.2V, which is three times that of nickel-hydrogen batteries and twice that of lead-acid batteries. (2) High specific energy The energy density of lithium-ion power batteries for passenger cars is currently close to 200Wh/kg, and it is expected to reach 300Wh/kg in 2020.

(3) Short battery life Due to the constraints of electrochemical material characteristics, the number of cycles of lithium-ion batteries has not made a breakthrough. Taking lithium iron phosphate as an example, the number of cycles of a single cell can reach more than 2,000 times, but only more than 1,000 times after being grouped. It cannot meet the requirement of the 8-year operation period of public transportation.

(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 with less pollution to the environment. However, in fact, because its positive and negative electrode materials and electrolyte contain metals such as nickel and manganese, the United States has classified lithium-ion batteries as batteries that are toxic and harmful, including flammable, leaching toxicity, corrosiveness, and reactivity. It is the battery that contains the most toxic substances among all types of batteries. In addition, its recycling and reuse process is relatively complicated, resulting in high costs. Therefore, the current recycling and reuse 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 lithium iron phosphate battery, the mainstream product of power batteries for buses, as an example, the price is about 2,500 yuan/kWh. With the popularization of electric vehicles, it is expected to drop to less than 1,000 yuan/kWh in 2020. Due to the limitation of the number of cycles after the single battery is assembled, buses usually need to replace batteries in about 3 years, which puts a lot of pressure on the cost of the operating unit.

(6) A large impact on the power grid. First, with the large-scale application of pure electric vehicles, the harmonic interference of charging equipment on the power grid will be prominent due to the large charging demand, affecting the power supply quality of the power grid; secondly, during fast charging, due to the high charging rate, the charging power is high (50kW for passenger cars and 150~250kW for buses), which has a large 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 mileage of less than 200km.

3 Characteristics of supercapacitors

(1) Extremely high charge and discharge rate Supercapacitors have a high power density and can discharge hundreds to thousands of amperes of current in a short time. The charging speed is fast and the charging process can be completed 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 The loss of supercapacitors in the charging and discharging process is extremely small, so in theory its cycle life is infinite, and in reality it can reach more than 100,000 times, which is 10~100 times higher than that of batteries.

(3) Good low-temperature performance Most of the charge transfer that occurs during the charging and discharging process of supercapacitors occurs on the surface of the electrode active material, so the capacity decay with temperature is very small, while the capacity decay of lithium-ion batteries at low temperatures is even as high as 70%.

(4) Low energy density 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 source of electric vehicles. Most of them are used as auxiliary power sources, mainly for quick start devices and brake energy recovery devices.

4 Characteristics of aluminum-air batteries

(1) Low material cost and high energy density The negative active material of aluminum-air batteries is abundant metal aluminum, which is cheap and environmentally friendly. The positive active material is oxygen in the air, and the positive capacity is virtually 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 precipitation are important obstacles to the marketization of metal-air batteries. The improvement of aluminum-air battery performance has encountered a great bottleneck. It is still in the laboratory stage and there is still a long way to go before commercial promotion.

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