Analysis of lithium battery and aluminum air battery power battery technology

At present, there are four main technical routes for transportation power sources: lithium ion batteries, hydrogen fuel cells, super capacitors and aluminum air batteries. Lithium-ion batteries, supercapacitors and hydrogen fuel cells are widely used, and aluminum-air batteries are still in the laboratory research stage. For energy replenishment, 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 additional aluminum plates and electrolytes.

1. Hydrogen fuel cell characteristics

(1) Good environmental compatibility

Hydrogen fuel cells provide efficient and clean energy, and the water they emit is not only small but also very clean, so there is no water pollution problem. At the same time, since the fuel cell does not need to convert thermal energy into mechanical energy like the engine, it directly converts chemical energy into electrical energy and thermal energy, and has high energy conversion efficiency and low noise.

(2) Good operating performance

Hydrogen fuel cells generate electricity and do not require complicated and large configuration equipment. The stack can be assembled modularly. For example, a 4.5 MW power plant can have 460 battery packs, and its power plant area is much smaller than that of a thermal power plant. A hydrogen fuel cell is suitable as a distributed power generation device. In addition, compared with firepower, hydropower and nuclear power generation, the construction period of hydrogen fuel cell power plants is short, and the expansion is easy. It can be built in stages according to actual needs. At the same time, the operation quality of the hydrogen fuel cell is high, and the rapid change of the load (such as the peak load) is excellent, and the power can be changed from the low power to the rated power in a few seconds.

(3) Efficient output performance

Hydrogen fuel cells work to convert the energy stored in the fuel into electricity and heat. The efficiency of converting electrical energy is above 40%, and only 1/3 of the steam turbine can be converted into electricity.

(4) Flexible structural characteristics

Hydrogen fuel cell assembly is very flexible, and the power is easy to adjust. Compared with the traditional engine, the good modularity of the hydrogen fuel cell can be easily achieved by increasing or decreasing the number of cells without increasing the infrastructure investment. The adjustment of power and voltage is easy to construct, and it is easier to control the power grid. This feature of the fuel cell improves system stability.

(5) a wide range of sources of hydrogen

Hydrogen as a secondary energy source can be obtained in various ways, such as hydrogen production from coal, hydrogen production from natural gas reforming, hydrogen production from electrolyzed water, and the like. When fossil energy is exhausted, hydrogen will become the world's main fuel and energy. The use of solar electrolysis water to produce hydrogen, there is no carbon emissions in the process, it can be considered that hydrogen is the ultimate energy source.

(6) Bottlenecks that exist

From the perspective of current development, the popularity of hydrogen fuel cells has encountered certain bottlenecks, such as the high cost of the battery itself and the lack of infrastructure.

2, lithium ion battery characteristics

(1) Voltage platform

Due to the different positive and negative materials used in lithium-ion batteries, the operating voltage range of single cells is 3.7~4V, and the operating voltage of lithium iron phosphate single battery is 3.2V, which is 3 times that of nickel-hydrogen battery. 2 times that of lead-acid batteries.

(2) specific energy

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

(3) Short battery life

Due to the limitations of electrochemical materials, the number of cycles of lithium-ion batteries has not been broken. Taking lithium iron phosphate as an example, the number of cycles of single cells can reach more than 2000 times, and only 1000 times after grouping. Unable to meet the eight-year deadline for bus operation.

(4) Great 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 to be green batteries and have less environmental pollution. However, in fact, due to its positive and negative materials, the electrolyte contains nickel, manganese and other metal materials, the United States has classified lithium-ion batteries as a kind of battery containing flammable, leaching toxicity, corrosive, reactive and other toxic and harmful. At present, various types of batteries contain the most toxic substances, and because of the complicated process of recycling and recycling, the cost is high, so the current recycling rate is not high, and the discarded batteries have a great impact on the environment.

(5) The cost is still high

The initial purchase cost of lithium-ion batteries is high. For example, the current price of Lithium Iron Phosphate Batteries for bus batteries is about 2,500 yuan / kWh. With the popularity of electric vehicles, it is expected to be reduced to less than 1,000 yuan / kWh in 2020. . Due to the restriction of the number of cycles after the cells are grouped, the bus usually needs to be replaced in about 3 years, and the operating unit cost pressure is large.

(6) Great impact on the power grid

First of all, the large-scale application of pure electric vehicles, due to the large charging demand, the harmonic interference of the charging equipment to the power grid will be prominent, affecting the power quality of the power grid; secondly, in the fast charging, because of the large rate of charging, the charging power is higher (The passenger car is 50kW, the passenger car is about 150~250kW), and the load on the power grid is greatly impacted.

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

3, super capacitor characteristics

(1) Very high charge and discharge rate

The supercapacitor has a high power density and can discharge hundreds to thousands of amperes in a short period of time. The charging speed is fast and the charging process can be completed in several tens of seconds to several minutes. Supercapacitor buses and trams use this feature to complete charging in a short period of time and drive the vehicle forward.

(2) long cycle life

The charging and discharging process of the super capacitor is extremely small, so in theory its cycle life is infinite, actually up to 100,000 times, 10 to 100 times higher than the battery.

(3) better low temperature performance

Most of the charge transfer that occurs during charging and discharging of supercapacitors is carried out on the surface of the electrode active material, so the capacity decays very little with temperature, and the capacity of the lithium ion battery is usually as high as 70% at low temperatures.

(4) The energy density is too low

One of the bottlenecks in supercapacitor applications is that the energy density is too low, only about 1/20 of a lithium-ion battery, about 10Wh/kg. Therefore, it cannot be used as the main power source for electric vehicles, and is mostly used as an auxiliary power source, mainly for quick start devices and brake energy recovery devices.

4, aluminum air battery characteristics

(1) Low material cost and high energy density

The anode active material of the aluminum air battery is rich in metal aluminum, which is cheap and environmentally friendly. The positive active material is oxygen in the air, and the positive electrode capacity can be infinitely large. Therefore, the aluminum air battery has the advantages of light weight, small volume and long service life.

(2) No breakthroughs in key technologies, not yet out of the laboratory

The problems of air electrode polarization and aluminum hydroxide deposition are important obstacles affecting the marketization of metal-air batteries. The performance improvement of aluminum-air batteries encounters a large bottleneck. It is still in the laboratory stage, and there is still a long way to go from commercialization.
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