According to foreign media reports, scientists at Stanford University in the United States have invented a new type of lithium-based electrolyte that may pave the way for the development of the next generation of pure electric vehicles. Researchers at Stanford University demonstrated that its new electrolyte design can improve the performance of lithium metal batteries, and lithium metal batteries are a promising technology that can power electric cars, laptops and other devices.
(Image source: Stanford University)
Yi Cui, a co-author of the study, said: "The energy density of most lithium-ion batteries used in electric vehicles is rapidly approaching the theoretical limit. Therefore, our research focuses on lithium metal batteries, which are lighter than lithium-ion batteries and have a unit weight. And volume provides more energy."
Lithium-ion batteries, which are widely used in various products such as smart phones and electric cars, have two electrodes, a cathode containing lithium and an anode usually made of graphite. When the battery is used and charged, the electrolyte solution will allow lithium ions to shuttle back and forth between the anode and cathode.
Compared with today's traditional lithium-ion batteries, lithium metal batteries can hold twice as much electricity per kilogram, and only need to replace graphite anodes with lithium metal to store more energy.
Another co-author of the study, Zhenan Bao, said: "For electric vehicles, lithium metal batteries are very promising, but their weight and volume are a big issue. During operation, the lithium metal anode will react with the liquid electrolyte. , Resulting in the growth of lithium microstructures called dendrites on the surface of the anode, leading to fire and failure of the battery."
Researchers have spent decades to solve the dendritic problem of lithium metal batteries.
(Image source: Stanford University)
Zhiao Yu, a co-author of the study and a graduate student in the Department of Chemistry, said: “The electrolyte has always been the Achilles’ heel of lithium metal batteries. We have adopted organic chemistry in our research to design and build stable batteries for such batteries in a reasonable manner. New battery electrolyte."
In this study, researchers explored whether a common, commercially available liquid electrolyte can be used to solve the stability problem.
Yu said: "We assume that adding fluorine atoms to electrolyte molecules will make the electrolyte more stable. Fluorine is a widely used element in the electrolyte of lithium batteries. We have used its ability to attract electrons to create a new molecule. Let the lithium metal anode play a good role in the electrolyte." As a result, a new synthetic compound, abbreviated as FDMB, was made, and it can be mass-produced.
Bao said: "The electrolyte design is becoming more and more peculiar. Although some have good results, the manufacturing cost is very high. However, FDMB molecules can be produced in large quantities and are very cheap."
The Stanford University team tested this new electrolyte in a lithium metal battery and the results were very good. After 420 charge and discharge cycles, the experimental battery still retains 90% of the initial power. In the laboratory, ordinary lithium metal batteries stop working after about 30 charge-discharge cycles.
The researchers also measured the efficiency of lithium ion transfer between anode and cathode during charge and discharge. This characteristic is called "coulombic efficiency (coulombic efficiency)."
Cui said: "If you charge 1,000 lithium ions, how many lithium ions can be recovered after discharge? Ideally, if the coulombic efficiency reaches 100%, you can recover 1,000. If you want to be commercially available, the coulomb of the battery The efficiency must reach 99.9%. In our research, half of the battery cells have a Coulomb efficiency of 99.52%, and all the battery cells have a Coulomb efficiency of 99.98%, which is incredible."
For lithium metal batteries that may be used in consumer electronics, the Stanford University research team also tested the application of FDMB electrolyte in anode-free lithium metal soft-pack batteries. This type of battery has been commercialized, and the cathode will provide lithium to the anode.
Hansen Wang, a co-author of the study and a graduate student in the Department of Materials Science and Engineering, said: "Our idea is to use only the lithium on the cathode side to reduce the weight of the battery. This anodeless battery can be charged and discharged before the capacity drops to 80%. 100 times, although it is not comparable to the same capacity lithium-ion battery (which can be charged and discharged for 500 to 1000 times), it is still one of the best non-anode batteries. Research results show that this battery can be widely used in various devices , Lightweight, anode-free batteries will become an attractive feature for drones and many consumer electronics products."
The U.S. Department of Energy is funding a large research group called Battery500 to implement lithium metal batteries, allowing automakers to build lighter and longer range electric vehicles. Part of the funding for the research also came from the group, which includes Stanford University and the SLAC National Accelerator Laboratory.
By improving the anode, electrolyte and other battery components, Battery500's goal is to increase the power of lithium metal batteries by nearly two times, from 180 Wh/kg in 2016 to 500 Wh/kg. A higher energy-to-weight ratio or higher "specific energy" is the key to solving the anxiety of electric car buyers.
Cui said: "The specific energy of the anodeless battery we built in the laboratory reached 325 Wh/kg, which is quite impressive. Our next step is to cooperate with other researchers at Battery500 to build a 500 Wh/kg close to the team’s goal. Kilograms of batteries."
In addition to having a longer cycle life and better stability, FDMB electrolyte is also less flammable than traditional electrolytes. (Yu Qiuyun)
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