Working principle diagram
Recently, James Flander, a professor at the University of California, San Diego, has developed a surface ultrasonic device, which can use ultrasonic waves to drive the electrolyte flow and improve the uniformity of ion distribution, thereby achieving rapid charging and improving the cycle life of the battery. Related papers were published in "Advanced Functional Materials".
From grid energy storage, intelligent robots to electric vehicles, rechargeable batteries are the key to its development. The energy density of the best lithium-ion batteries (240 watt-hours / kg) is only six times that of lead-acid batteries (40 watt-hours / kg). Their safety, rechargeability, specific capacity, and cycle life are all required. Continue to improve.
Lithium metal batteries with lithium metal as the negative electrode have an energy density of more than 500 watt-hours / kg, which is twice that of the best lithium-ion batteries, but lithium metal will produce dendrites during the cycle, resulting in a series of safety problems. This also hinders the commercial development of lithium metal batteries.
In this research, Flander looks forward to solving two fundamental problems that have hindered the development and progress of batteries for more than 50 years, namely long charging time and short cycle life. Especially to solve the more serious lithium dendrite problem, because the formation of dendrites further consumes the electrolyte and lithium anode.
In previous studies, it was proposed to apply external magnetic force to lithium metal batteries to suppress the continuous growth of dendrites through magnetohydrodynamics, but this method has high energy consumption and limited performance. At the same time, in the traditional chemical vapor deposition process, ultrasonic waves are used to drive the electrolyte flow and improve the uniformity of the ion distribution. However, ultrasonic equipment is bulky, inefficient, and electrochemically incompatible, making it unsuitable for practical applications.
In contrast, a surface ultrasonic device that is only the size of a nail can provide excellent power density, produce local extreme accelerations of 108 to 1010 m / s, and drive fluid flow rates up to 1 m / s, often used in biosensors and microfluidics Particle collection and other aspects. Standard UV etching and processing procedures can produce surface ultrasonic devices at low cost, depositing staggered metal electrodes on a low-loss single crystal piezoelectric lithium niobate substrate.
To this end, Flanders has developed a surface ultrasonic device to overcome the long-standing problems in lithium metal batteries. The device drives the electrolyte to fully flow between the electrode gaps to prevent the generation of dendrites and the depletion of the electrolyte as much as possible.
The flow driven by the acoustic wave (fluid) generated inside the surface ultrasonic device significantly reduces the concentration gradient of lithium ions in the electrolyte, and even in the case of rapid charging, uniform lithium deposition can be achieved. In addition, the power consumption of the surface ultrasonic device is about 10 mWh / cm2, which is relatively small compared to the charging itself. In the discharge process of lithium metal batteries, dendrites are not easy to form.
This paper devises a method that is not related to chemical substances to avoid ion depletion and dendrite growth in the electrolyte. The use of a small high-frequency ultrasonic device can effectively drive the electrolyte to produce a uniform ion flux distribution in the electrode gap, so that the potential position of dendrite growth remains stable within a specific distance of the ultrasonic source. This simple technology will help to improve the efficiency, utility and sustainability of the battery and can be used in current and future rechargeable batteries. (Li Huiyu)
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