Financial Associated Press (Shanghai, editor Huang Junzhi)-in order to explore more promising lithium batteries, scientists have focused on metal anodes based on pure lithium rather than the commonly used mixed materials. At the same time, in order to overcome its poor performance at low temperatures, scientists in this field have been "racking their brains" and have made some breakthroughs.
The (UCSD) team at the University of California, San Diego is reportedly trying to develop a battery that can charge Discharge at extremely low temperatures, which usually requires an additional heating system, but this time they are focusing on electrolytes, which rely on weak binding properties to release unprecedented performance in cold conditions.
It is understood that compared with the currently used graphite / copper mixed anode, pure lithium metal anode has excellent energy density, so it is considered to be a promising technology. In the face of such a big difference, some battery researchers even describe lithium metal as a "dream material" and see it as the key to breaking the bottleneck of energy density.
As a solution that carries lithium ions back and forth between the poles of the battery during the cycle, the importance of electrolytes in a battery is self-evident. The goal of the UCSD team is to develop an electrolyte that does not freeze, allowing lithium ions to move in cold environments.
Specifically, the researchers tested two types of electrolytes, one of which binds firmly to ions and the other much weaker, to verify which is more suitable for low-temperature conditions.
It was found that at-60 ℃ (- 76 degrees Fahrenheit), this group of experimental batteries with firmly bonded electrolytes could only last two cycles, and then stopped working. In contrast, batteries using weakly bound electrolytes can run smoothly after 50 cycles and maintain a capacity of 76%. If the operating temperature is changed to-40 °C (- 40 °F), this scheme can even maintain 84% capacity.
"We found that the binding of lithium ions to electrolytes and the structures occupied by ions in electrolytes are strongly related to their performance at low temperatures," said John Holoubek, lead author of the study.
It is worth mentioning that further studies on such proof-of-concept batteries also show that weakly bound electrolytes allow ions to be deposited more evenly on the battery anode, while strongly bound electrolytes lead to bulk and needle-like deposition (dendrites). This is another focus for scientists studying lithium-metal batteries, which can quickly lead to serious failures such as short circuits and failures.
"understanding the interaction between lithium ions and electrolytes at the atomic level can not only improve the low temperature performance of lithium batteries, but also help prevent the formation of dendrites," the researchers said.
Based on these findings, the team built a prototype of lithium-metal battery with sulfur-based cathode and weakly bound electrolyte. It is said that this equipment is expected to play an important role in areas such as outer space exploration and deep-sea exploration.
"the significance of this work is actually twofold," the researchers said. From a scientific point of view, it offers the opposite of conventional wisdom. Technically, this is the first lithium-metal battery that can be recharged at ultra-low temperatures, and it can also provide considerable energy density at full operation at-60 degrees Celsius. These two aspects provide a complete solution for cryogenic batteries.
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