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 according to
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 the characteristics of electrochemical materials,
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 metallic
aluminum, which is cheap and environmentally friendly. The positive active
material is oxygen in the air, and the positive capacity is 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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