Walking into the National Wind and Solar Storage and Transmission
Demonstration Power Station in Zhangbei County, you can see rows of tall white
wind turbines and sparkling blue photovoltaic panels on the green grassland.
This is my country's largest wind and solar storage and transmission
demonstration project. It adopts the world's first wind and solar storage and
transmission combined power generation construction ideas and technical routes.
It is a "four-in-one" new energy comprehensive demonstration project integrating
wind power, photovoltaic, energy storage devices and intelligent power
transmission. .
This power station can "store" wind and light resources that are "difficult
to predict, control, and dispatch" and convert them into high-quality and
reliable green power for input into the grid, and can operate in "smooth
fluctuations" and "peak shaving and valley filling." Flexible switching between
modes allows the energy storage power station to maintain normal operation of
the grid through its internal self-starting capability when the external grid
power supply is lost.
The development of energy storage technology is one of the key core
technologies to promote new energy power generation and improve the security and
stability of the power grid. Among various types of electrochemical energy
storage technologies, lithium titanate batteries have the characteristics of
long cycle life and good safety performance, which are well suited for grid
energy storage application scenarios. However, the high cost of lithium titanate
batteries is not conducive to Large-scale energy storage applications.
In this regard, the China Electric Power Research Institute teamed up with
several units to jointly form a project team "Research and Development of
Low-Cost Lithium Titanate Batteries for Energy Storage and System Integration
Technology Development and Application". After years of research, the project
team proposed a lithium titanate battery material system and production process
reconstruction principles and technical solutions based on the original lithium
titanate battery to meet the needs of energy storage applications, and developed
a sub-micron Lithium titanate material. The lithium titanate battery for energy
storage developed in the project maintains the intrinsic characteristics of long
life while significantly reducing the cost. This project won the second prize in
the 2017 Beijing Science and Technology Award.
The next trend of new energy
Energy storage is considered to be the next trend in new energy. As a
forward-looking technology that will promote the development of the new energy
industry in the future, the energy storage industry will play a huge role in new
energy grid connection, new energy vehicles, smart grids, microgrids,
distributed energy systems, and home energy storage systems.
"The reason why energy storage is developed is that photovoltaic and wind
power generation are intermittent and unstable, so the cooperation of energy
storage systems is needed to provide stable and reliable power." Director of the
Energy Storage Battery Research Office of China Electric Power Research
Institute Yang Kai told reporters.
The use of large-scale energy storage technology can promote the
development of renewable energy, improve the security and stability of the power
grid, improve the quality of power supply, and effectively alleviate the
contradiction between power supply and demand.
Large-scale energy storage systems run through all aspects of power system
generation, transmission, distribution and use. Its application can not only
improve the performance of traditional power systems, but also bring revolution
to the planning, design, layout, operation management and use of power grids.
changes. In this sense, energy storage technology is a technological commanding
height of national strategic significance. The development of energy storage
technology is actually "storing the future."
A "wonderful flower" in lithium-ion batteries
It is understood that energy storage technology is mainly divided into
mechanical energy storage, electrochemical energy storage, electromagnetic
energy storage and phase change energy storage. In recent years, electrochemical
energy storage technology represented by lithium-ion batteries has the
characteristics of large energy scale, flexible location selection, and fast
response speed. It meets the technical needs of power systems and the
development trend of smart grids, and has been regarded as a research focus by
research institutions in various countries. Becoming the fastest growing power
system energy storage technology. Lithium-ion batteries are a kind of "rocking
chair battery". The positive and negative electrodes are composed of two
compounds or elements that can deintercalate lithium multiple times. During
charging, the positive electrode material is delithiated, lithium ions enter the
electrolyte, pass through the separator, and embed in the negative electrode. An
oxidation reaction occurs at the positive electrode, and the opposite occurs
during discharge.
Lithium-ion battery technology has been in a state of rapid development
with the research on battery electrode materials. It has now expanded from
lithium cobalt oxide batteries to the coexistence of various battery systems
such as ternary batteries, lithium manganate, lithium iron phosphate, and
lithium titanate. The new lithium-ion battery using lithium titanate as the
negative electrode breaks through the inherent limitations of graphite as the
negative electrode, and its performance is significantly better than that of
traditional lithium-ion batteries, making it one of the most promising energy
storage batteries. To this end, Yang Kai introduced to reporters the four major
advantages of lithium titanate batteries that can stand out:
Good safety and stability. Due to the high lithium insertion potential of
the lithium titanate anode material, the generation and precipitation of
metallic lithium is avoided during the charging process. Moreover, because its
equilibrium potential is higher than the reduction potential of most electrolyte
solvents, it does not react with the electrolyte and does not form solids. —The
liquid interface passivation film avoids the occurrence of many side reactions,
thus greatly improving safety. "Energy storage power stations are the same as
electric vehicles, safety and stability are the most important indicators." Yang
Kai said.
Excellent fast charging performance. Long charging times have always been
an insurmountable obstacle in the development of electric vehicles. Generally,
pure electric buses that use slow charging take at least 4 hours to charge, and
the charging time for many pure electric passenger cars is as long as 8 hours.
Lithium titanate batteries can be fully charged in about ten minutes, which is a
qualitative leap compared to traditional batteries.
Long cycle life. Compared with the graphite material commonly used in
traditional lithium-ion batteries, the skeleton structure of lithium titanate
material hardly shrinks or expands during the process of charging and
discharging lithium. It is called a "zero strain" material and avoids the
detachment of general electrode materials. / The problem of electrode structure
damage caused by unit cell volume strain when lithium ions are inserted, so it
has very excellent cycle performance. According to experimental data, the
average cycle life of ordinary lithium iron phosphate batteries is 4,000-6,000
times, while the cycle life of lithium titanate batteries can reach more than
25,000 times.
Good performance in wide temperature range. Generally, electric vehicles
will have problems charging and discharging at -10°C. Lithium titanate batteries
have good wide-temperature resistance and strong durability. They can be charged
and discharged normally at -40°C to 70°C, whether in the frozen north. Even in
the hot south, the vehicle will not be affected by battery "shock", eliminating
users' worries.
It is precisely based on these advantages that lithium titanate batteries
have become a dazzling "wonder" in the development journey of lithium-ion
battery technology.
Technology restructuring reduces costs
The original lithium titanate battery was developed to meet the needs of
electric vehicle power batteries. Although internationally advanced lithium
titanate battery companies have begun to get involved in the field of electric
energy storage, there has not been a titanium titanate battery specifically
designed and developed for large-scale energy storage applications. Lithium acid
battery.
"The main problem faced by lithium titanate batteries in large-scale
applications is cost. At the beginning of the project development, its price was
4-6 times that of lithium iron phosphate batteries." Yang Kai said that the
price of lithium titanate batteries remains high. Although the performance is
significantly better than existing lithium-ion batteries, economic factors have
greatly limited the market promotion of lithium titanate batteries.
Therefore, in order to realize large-scale energy storage applications of
lithium titanate batteries, it is necessary to carry out technical
reconstruction on the basis of existing lithium titanate batteries for electric
vehicles, including technical reconstruction of material systems, battery
design, production processes, etc. While ensuring the long-life intrinsic
characteristics of lithium titanate batteries, the cost is significantly
reduced.
"We are not building a tall building from the ground, but based on the
lithium titanate battery technology for electric vehicles, we have carried out a
technical reconstruction of the lithium titanate battery technology for electric
vehicles with the goal of meeting the needs of energy storage applications."
Yang Kai said .
It is impossible for any technology to be comprehensive, and it is only
necessary to find the balance point between various technical indicators.
"Energy storage batteries do not have high rate requirements, and the
discharge rate only needs to reach 5C." Yang Kai said, "Energy storage batteries
are generally placed in rooms where the temperature is relatively constant, and
the requirements for temperature adaptability do not need to be too high.
"Giving up some performance and choosing low cost has become the most important
choice."
The project team conducted a cost analysis on lithium titanate batteries
and found that the source of the high cost of this battery lies in the material.
"Lithium titanate batteries use nanomaterials, and the material synthesis
process and battery preparation process are complicated."
Because nanomaterials have strong water absorption, the production process
must reduce the ambient humidity, increase dehumidification of the factory, and
increase drying procedures, which will significantly increase energy
consumption. In this regard, the project team decided to work on nanomaterials.
After repeated trials, they finally replaced nanometer lithium titanate
materials with low-cost sub-micron lithium titanate materials, and based on
this, established a lithium titanate battery material system for energy storage.
Through experiments, when the material particle size is 0.8 microns, it can not
only ensure long life, but also reduce the harsh conditions of production
process control, thereby reducing costs. At the same time, the laminated
flexible packaging structure, which has advantages in performance, manufacturing
process, and cost, is also used to replace the ring structure and cylindrical
structure.
"0.8 microns is a balance value. Any increase in particle size will affect
battery life." Yang Kai said.
This is to reduce battery costs from the reconstruction of materials and
battery structures. On the other hand, it is to carry out technical
reconstruction of homogenization, pre-coating current collectors, environmental
control, battery manufacturing processes and other links to reduce battery
costs.
"In the past, in the homogenization process of electrode materials, the
conventional mixing process was to add solvent first and then dry it, which
consumes a lot of energy. The R&D team changed this process to a
high-viscosity mixing process to reduce the amount of solvent used." Yang Kai
explain.
In the electrode production process, the project team changed the imported
pre-coated current collector to a self-developed pre-coated current collector;
in the battery production process, the two tasks of coil drying before coating
and cell drying before liquid injection were eliminated. Drying process. In the
environmental control process of battery production, the ambient humidity is
relaxed from 10% to 30%. "Generally, the humidity of nanomaterials should be
controlled below 10%, and that of lithium iron phosphate is 30%. We used
submicron materials to make batteries in a humidity environment of 30%, and
found that the battery life was almost not affected." Yang Kai said, "After
Tests have shown that the cycle life of lithium titanate batteries exceeds
16,000 times, and the battery cost has dropped by 30%."
It is understood that in addition to being applied in the "National Wind
and Solar Storage and Transmission Demonstration Project", the relevant research
results of this project will also play an important role in the 2022 Winter
Olympics held in Beijing-Zhangjiakou and the development of Beijing's electric
vehicle industry. .
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