[2017-07-11]How do some batteries do not break when extended?

Information

When you are charging a battery or using it, it is not only the current flowing, but also the material inside the battery. The material inside the battery moves from one electrode to the other as the current is generated, which causes the electrode to shrink or swell. In fact, why the more fragile electrode material can still remain unbroken under the cyclical tension and contraction tension, which is a mystery that can't find an answer for a long time.

This problem seems to have finally been answered. A team of researchers from MIT, the University of Southern Denmark, Rice University and the Argonne National Laboratory has been able to determine that this secret is hidden in the molecular structure of the electrode. When these electrode materials are in a normal crystalline state, the internal atoms are arranged in a regular and regular manner; while during charging and discharging, the electrode structure is converted into an amorphous state, so that the material can adapt to changes in the volume level. Jiang Yeming, a professor of materials science and engineering at MIT, and an article published by eight graduate students, including Xiang Kai and Xing Wenting, in the academic journal Nano Letters, suggest that this discovery may have an impact on the structural design of batteries in the future, and even lead to new Actuator.

Scientists may have discovered that fragile electrodes are still not broken under cyclic expansion and contraction tension under charge and discharge conditions.

In theory, when you use a lithium-ion battery center as a fulcrum and extend in the direction of the two poles, Jiang Yeming said, "It will sway like a swing." During this process, the battery will continue to charge and discharge. The ions in the battery shuttle back and forth, accompanied by expansion and contraction of mass and volume, which is determined by the electrode material. "From about 1%, all the way to 300% of the silicon material can be stretched." Jiang Yeming said.

The study also looked at another battery, the sodium ion battery. Scientists have studied a class of substances that have the potential to become a positive (cathode) material for batteries. These substances are called phosphating minerals, especially sodium iron tetraphosphide (NaFePO4). They found that the volume change of this material can be fine-tuned over a wide range - not only controlling the expansion and contraction of matter, but also controlling the mechanical processes during this period. In some components, the expansion proceeds slowly, but in other components it can achieve a sudden increase.

“In these minerals series,” Jiang Yeming said, “we can make a slow, step-by-step response,” which ranges from failure to any charging to very high levels of electricity. On the other hand, this reaction process sometimes appears to be “quite intense,” as shown by the reaction of sodium iron phosphide in the reaction, which changes the full 17% capacity in the chemical reaction.

“According to our understanding, compounds with such a weak structure will rupture in this case, and there will be no more than 1% volume change,” Jiang Yeming said. “So what is the adaptation of these materials in the face of volume changes? Our findings, to a certain extent, are like the morphological changes in crystals that have become irregular glass." Rather than keeping the structure that was originally tightly arranged.

“We think the mechanism here will be widely used for similar compounds,” he said, adding that the discovery may represent “the discovery of a new way of making sluggish materials that might help the battery.” Once sluggish When the substance reacts, its volume change will be slow and not very sudden, so "the battery may be more long-lived," Jiang Yeming said.

Jiang Yeming said the discovery could provide a new tool for those who want to invent a long-life, high-performance battery. This may also allow volume change reactions to be applied to actual situations, such as robotic actuators or implantable devices that have drug infusion capabilities.

The research team plans to continue to work on the research to find a simpler way to synthesize this phosphating material and to further determine if more of the same crystalline compounds have the same phase transition properties.

The study is "a significant discovery that combines information on the electrochemical, mechanical, and battery-state crystalline structures," said William Chueh, assistant professor of materials science and engineering at Stanford University. Did not participate in the study.

“The electrode material in a lithium battery expands and contracts during charging and discharging, and often exhibits an asymmetry in a single molecule. If the reaction process cannot be carried out, the electrode material will crack and eventually cause damage to the battery. This is like Pour hot water into a cold ceramic cup," Chueh said. The study "redefined the strain-eliminating mechanism involving large volumetric transformations in which materials transition from solid-state crystal structures to amorphous structures rather than cracking."

He said the discovery "may lead scientists to re-examine potential battery electrode materials that were rejected because of large-area deformation during charging and discharging. It will also lead engineers to produce more sophisticated predictable models. So to design a new generation of batteries."

Other members of the research team include Dorthe Ravnsbaek from the University of Southern Denmark and MIT, Li Zheng from MIT, Hong Liang and Tang Ming from Rice University in Texas, and Kamila Wiaderek and Olaf Borkiewicz from Argonne National Laboratory. Karena Chapman and Peter Chupas. The experiment was supported by the US Department of Energy.

News source: Materials provided by the MIT Press Office, formerly author David L. Chandler.

Note: In order to adapt to the length of the news, the original text has been modified as appropriate.

Original source: Click to go

Previous: [2017-06-27]Towards a new era of all-solid lithium batteries

Next: None

Previous: [2017-06-27]Towards a new era of all-solid lithium batteries

Next: None

搜索