[2017-06-19]The battery “capacity decay” chemical cause was confirmed

Jun 19, 2017 | XTAR

It is well known that the cycle life of batteries is limited.


When manganese ions (gray) are pulled out of the battery positive (blue), they react with the electrolyte (gold) near the battery’s negative electrode, trapping lithium ions (green/yellow)
    When a battery enters the “aging” stage, scientists will name the phenomenon of weakening its performance as “capacity decay.” The “capacity attenuation” phenomenon indicates a phenomenon in which the battery capacity gradually decreases as the number of times the battery is charged increases. A mobile phone can last for a whole day when it is first used, but it can only last for several hours after two years. The reason for this phenomenon is the capacity decay.
    So what if scientists can reduce the process of capacity decay and let the battery age in a more elegant way?
    Researchers at the US Department of Energy’s Argonne National Laboratory released an article in the Electrochemical Society, saying that they have successfully confirmed a major cause of capacity decay in high-energy lithium-ion batteries.
    For lithium batteries, the batteries we use in laptops, smart phones, and connected hybrid vehicles, the capacity is closely linked to the amount of lithium ions that can be switched back and forth between the two poles during charging and discharging.
    The back-and-forth conversion of lithium ions is excited by a specific transition metal, which changes the oxidation state of ions when lithium ions flow in the positive electrode of the primary battery. However, during the battery cycle, some of the ions, especially the manganese ions, are stripped out of the positive electrode of the cell and eventually attached to the negative electrode material of the cell.
    Once near the negative electrode of the cell, these metal ions will interact in the “solid electrolyte membrane” region of the cell. The solid electrolyte membrane is formed by a reaction between a highly active anode and a liquid electrolyte that moves back and forth with lithium ions. For each electrolyte molecule that decomposes in a process called a reduction reaction, lithium ions are trapped in the mesophase. As more and more lithium ions are trapped in the mesophase, the energy storage capacity of the battery will gradually decrease.
    On the solid electrolyte membrane, some of the molecules are not completely reduced, which means that they can receive more electrons and combine with more lithium ions. These particles are like flammable materials waiting for a fire.
    When these manganese ions are attached to the surface of these particles, they are like fireworks scattered on flammable materials: these lithium ions are a powerful catalyst for chemical reactions that do not completely degrade molecules, and more will be in the process. The lithium ion is trapped in the mesophase.
    “The amount of manganese ions attached to the negative electrode of the battery is closely related to the amount of lithium ions trapped,” said Daniel Abraham, a Argonne laboratory scientist and co-author of the study. “Since we have now figured out that lithium ions have been The mechanism behind sleep and capacity decay, we can start looking for ways to solve the problem.”
Source: Materials provided by Argonne National Laboratory, former author Jared Sagoff.
Note: In order to adapt to the length of the news, the original text has been modified as appropriate.
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