Many potential consumers are deterred by the short range and high cost of
electric vehicles.
The energy density of lithium-ion power batteries has become a bottleneck
for its industrialization. For this reason, the United States, Japan, South
Korea and other countries have formulated relevant industrial policies, all of
which aim at "energy density reaching 300Wh/kg in 2020." Recently, with the
support of national key projects, the R&D team of CATL New Energy Technology
Co., Ltd. has conquered key core technologies such as high-nickel ternary
materials and silicon-carbon anode materials, and has taken the lead in
developing a specific energy (mass energy density) of 304Wh/kg. The battery
sample won the first prize in this international competition.
Open up the "two channels of Ren and Du" and make up for the shortcomings
of cathode materials
Lithium-ion power batteries are currently the most widely used new energy
vehicle power batteries and are the core part of new energy vehicles. Its
advantages lie in high energy density and long cycle life. Its technical
difficulties lie in high stability and safety requirements and complex
preparation process. This core production technology has always been in the
hands of a few countries in the world.
The energy density of a battery refers to the electrical energy released by
the average unit volume or mass of the battery. "The current increase in energy
density has become the biggest bottleneck restricting the development of
lithium-ion batteries, which are facing many world-class problems." Wu Kai,
chief scientist of CATL, said that battery manufacturers can achieve the effect
of power expansion by increasing battery size, but battery capacity Core
"getting fat" or "growing taller" only treats the symptoms, not the root
cause.
What exactly limits the energy density of lithium batteries?
Wu Kai said that the chemical system behind the battery is the main reason.
Generally speaking, the four parts of a lithium battery are very critical:
positive electrode, negative electrode, electrolyte, and diaphragm. The positive
and negative electrodes are where chemical reactions occur, which are equivalent
to the "Ren and Du meridians" of the human body.
Since the energy density of the current negative electrode material is much
greater than that of the positive electrode, the positive electrode material has
become the "short board of the barrel" - the lower limit of energy density of
lithium-ion batteries depends on the positive electrode material, so increasing
energy density requires continuous upgrading of positive electrode materials.
However, the development of high-nickel materials in my country started late,
the technology accumulation is relatively weak, and the preparation technology
and equipment conditions are relatively backward.
"The stable supply of high-performance high-nickel cathode materials in
batches is one of the key technical difficulties in the development of
high-specific energy power batteries." Wu Kai said. To this end, CATL relies on
major scientific research such as the National Engineering Research Center and
the Fujian Provincial Key Laboratory. The platform, through collaborative
development with upstream and downstream partners in the industry chain,
optimizes raw material synthesis process conditions, improves structural
stability, adjusts microstructure, controls material morphology and size
distribution, and gradually realizes the large-scale production and application
of domestic high-nickel materials. .
Compared with similar materials from Japanese and Korean competitors, the
current domestic high-nickel materials have the characteristics of high
reversible capacity, high compaction density, and relatively stable surface and
bulk structures. They will break the Japanese and Korean technology monopoly and
improve the technical level of the domestic industrial chain and The core
competitiveness of domestic power batteries has eliminated the “first obstacle”
on the road to innovation.
Subvert the tradition and solve the shortcomings of negative electrode
materials
The negative electrode material is also one of the core materials of
lithium-ion batteries. Currently, graphite is mostly used as the negative
electrode material. As the demand for cruising range continues to escalate,
traditional graphite anodes can no longer meet market expectations for battery
energy density.
According to calculations, the specific capacity of silicon-based anode
materials can be up to 10 times that of graphite anodes, and it is regarded as a
"substitute" for the latter. The application of traditional silicon-based
materials mainly uses carbon coating technology, which is to compound a layer of
carbon material on the surface of silicon materials. Wu Kai said that due to the
volume change of the silicon material during charging and discharging as high as
300%, the surface-coated carbon material will break and fall off after multiple
cycles, and the protective effect on the silicon material will be greatly
weakened, resulting in poor battery cycle performance.
This world-class problem has plagued the industry like a "ghost" for the
past 10 years.
CATL abandoned traditional carbon coating technology and turned to research
on artificial electrolyte interface film coating technology. It took more than 2
years to apply this technology to the preparation of silicon materials, and
developed a new artificial electrolyte interface film-coated silicon-carbon
composite anode material with independent intellectual property rights. Its
cycle performance is significantly better than that of foreign products,
breaking the innovation path. The "second stumbling block".
“Compared with carbon materials, the artificial electrolyte interface film
has stronger binding force with silicon materials, better elasticity, is not
easily broken or pulverized, and plays a very good protective role for silicon
materials, so it can greatly increase the silicon content during cycles. The
interface stability of the material will improve the cycle life of the battery."
Wu Kai said that this move will promote our country to fully master core
technologies such as material modification and precursor synthesis, and realize
the localization of key material technologies to provide silicon carbon The
gradual commercial promotion and application of composite anodes provides an
important guarantee.
Perfect "slimming", the first to use special grade "7 series aluminum"
When energy consumption remains unchanged and volume and weight are
limited, the cruising range of new energy vehicles mainly depends on the energy
density of the battery pack.
"This tests the researchers' ability to 'slim down' the battery pack." Wu
Kai said that for the first time, CATL applied special grade "7 series aluminum"
to the lower box of the battery pack. "7 series aluminum", the "combat aluminum"
among aluminum, is often used to make aircraft landing gears and has the
characteristics of lightness, strength and safety.
Wu Kai told reporters that the application of "7 series aluminum" also has
many risks, especially the phenomenon of stress corrosion (metal materials break
in certain specific media due to the combined action of corrosive media and
stress).
"The industry generally believes that this is a technical difficulty of '7
series aluminum', and even a technical forbidden area." Wu Kai said that for
this reason, they have controlled the stress corrosion index at the highest
level in the industry through hundreds of experiments and related process
improvements. . At present, CATL has successfully developed the "7 Series
Aluminum" lower box and has put it into mass production.
So far, the company's lightweight design of the battery pack's lower box
has been at the world's leading level. This new energy density power battery can
increase the load capacity (total power of the battery) by about 50% on the
existing basis of the B-class pure electric car battery compartment without
adding additional space; the energy of the vehicle-mounted power battery system
Increase by 50%; the weight of the entire vehicle can be reduced by 250
kilograms on the existing basis, increasing the driving range of this model to
more than 600 kilometers under standard operating conditions.
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