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Silicon-graphite dual ion battery
At present, lithium-ion batteries have become the main energy conversion and storage equipment in the fields of portable electronic devices, electric vehicles, and renewable energy systems. Although the energy density of commercial lithium-ion batteries has increased, their manufacturing costs are high and it is not easy to recycle. It is difficult to meet the high energy density, low cost, and environmental protection of energy storage in portable electronic equipment, renewable clean energy, grid peaking, etc. Device performance requirements.
Recently, the team of Tang Yongbing, a researcher of the Functional Thin Film Materials Research Center of the Institute of Advanced Technology, Shenzhen Institute of Advanced Technology (hereinafter referred to as Shenzhen Advanced Institute) of the Chinese Academy of Sciences, and the team of Professor Zheng Zijian of the Hong Kong Polytechnic University, successfully developed a new silicon-graphite dual ion battery.
"The single voltage drop of this battery during the tens of thousands of bendings is only 0.0015%, and the capacity retention rate after 2000 cycles at 10 C rate is as high as 97%, which shows good application prospects in the field of flexible energy storage. Tang Yongbing introduced to the "China Science News". Related papers have been published in "Advanced Materials" (Advanced Materials).
Speaking of aluminum-graphite dual ion battery
In 2007, Tang Yongbing received his Ph.D. from the Institute of Metal Research, Chinese Academy of Sciences, and then went to the City University of Hong Kong for visiting research under the recommendation of his supervisor Cheng Huiming (elected member of the Chinese Academy of Sciences in 2013) and joined Shenzhen in September 2013. Advanced Institute.
"Teacher Cheng believes that only the development of new high-efficiency and low-cost energy storage devices and their key materials can really promote the development of non-lithium batteries such as sodium and potassium." Tang Yongbing told reporters that under the guidance of Cheng Huiming, he began to lead the team Engaged in research and development of new energy storage devices and materials. In March 2016, the team of Tang Yongbing published the first research achievement on aluminum-graphite dual-ion battery in "Advanced Energy Materials".
The previously reported dual-ion battery, because both positive and negative electrodes use graphite materials, the tap density of graphite is low, and the specific capacity as the positive and negative electrodes are not high, resulting in a low energy density of the double carbon battery. The development of dual-ion batteries is slow.
In this regard, the team of Tang Yongbing put forward the design idea of ​​the integration of active material / current collector. He introduced that compared with the existing traditional graphite anodes, alloyed metal anodes such as aluminum have a higher theoretical specific capacity and have advantages in improving energy density. "In addition, aluminum has excellent conductivity and ductility, and is inexpensive and abundant in reserves. Therefore, we have adopted an integrated design of aluminum foil as an active material and a conductive current collector to build a new aluminum-graphite dual ion battery."
In the follow-up research work, in order to improve the stability of the aluminum anode in the new battery, Tang Yongbing team also carried out the structure modification and interface adjustment of the aluminum anode, developed a three-dimensional porous aluminum / carbon anode, hollow interface structure of the aluminum anode, Carbon-coated nano aluminum anode, active material / current collector / separator integrated electrode, ultra-fast charge and discharge integrated flexible battery, etc.
"We have further expanded this new integrated design idea to a sodium, potassium, and calcium-based dual-ion battery system that does not rely on limited lithium resources, and opened up new ideas for the development of new, high-efficiency and low-cost energy storage devices." Tang Yongbing said.
Joint research to improve energy density
At present, the main technical difficulty of the dual-ion battery is that its operating voltage is higher (more than 4.2 volts), and the conventional carbonate-based electrolyte is easily oxidized and decomposed, resulting in a reduction in battery charging efficiency.
"It is urgent to design and develop a high-voltage electrolyte system to solve the gas production phenomenon and improve the charging efficiency of the dual-ion battery." Tang Yongbing said, "There are two main ways to increase its energy density. One is to develop a high-voltage system for the dual-ion system. Capacity positive and negative materials; The second is to develop a high-concentration electrolyte system to reduce the amount of electrolyte used to increase energy density. "
As far as the negative electrode is concerned, silicon has a high theoretical specific capacity and abundant reserves, making it an ideal negative electrode material for improving the energy density of dual-ion batteries. The problem also occurred, and Tang Yongbing's team found that the serious volume expansion of the silicon anode restricts its application in dual-ion batteries.
Although researchers have proposed various modifications such as nanometerization, porous structure, and composite structure, most of them use metal materials as current collectors. The rigid interface contact between the silicon negative electrode and the current collector causes interface stress concentration, resulting in interface cracking or even The peeling of the active material makes it difficult for the cycle performance to meet the actual application requirements.
In response to this, the team of Tang Yongbing proposed a flexible interface design strategy, intending to construct the silicon negative electrode on the surface of the flexible polymer fabric to effectively control the interface stress. He introduced: "To achieve a good interface construction of the silicon negative electrode on the surface of the flexible polymer, it is necessary to design an interface buffer layer with good conductivity between the two."
The team of Zheng Zijian has a good working foundation in the field of flexible conductive fabrics, so the two sides carried out joint research. The team of Zheng Zijian is mainly responsible for the preparation of flexible conductive fabrics to provide flexible conductive substrate materials for silicon negative electrodes; the team of Tang Yongbing uses flexible conductive fabrics as a base to carry out studies on the preparation of flexible silicon negative electrodes, battery assembly, in-situ stress and electrochemical performance tests jobs.
In addition, Tang Yongbing's team has also made a breakthrough in the research and development of high-concentration electrolytes, and has developed a high-concentration, high-voltage electrolyte system, which is expected to further improve the energy density and stability of dual-ion batteries.
Expect to put into demonstration applications as soon as possible
In recent years, the team of Tang Yongbing has carried out a series of research work in the field of energy material chemistry, especially new batteries, flexible batteries, and new cathode materials. In addition to the relevant research results listed above, the team also adopted a multi-ion hybrid strategy, by introducing a small amount of ions with high kinetic performance, the rate performance of battery systems such as sodium, potassium, and calcium ions was improved to improve sodium and potassium. , Calcium and other new battery system dynamic performance provides a new solution.
In addition, in order to develop high-efficiency, low-cost and environmentally friendly new cathode materials, Tang Yongbing's team also took the lead in the development of oxalate system, mixed polyanion system and other new cathode materials and their electrochemical reaction mechanism research work.
From the current development point of view, the future application field of dual ion batteries is mainly in the field of energy storage. Tang Yongbing is quite optimistic about the future of dual-ion batteries, such as household energy storage, UPS, communication base stations, distributed energy storage systems and other fields. But he said cautiously: "The future specific application of dual-ion batteries will also depend on whether the technology maturity can meet the technical requirements in related fields."
At present, the team of Tang Yongbing has jointly carried out research on the industrialization of dual-ion batteries with large local enterprises in Shenzhen, and has made the expected progress, and has entered the stage of pilot test verification. As the dual-ion battery technology continues to mature, he hopes that through efforts, the product will gradually expand from the application demonstration of small energy storage systems to the application of other energy storage systems in the next three to five years. (â– Our reporter Shen Chunlei trainee reporter Ding Ningning)
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