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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