Over time, the loss of oxygen in the lithium ion electrode will impair battery performance

　　We know that a lithium-ion battery is essentially a chemical battery, so it is necessary to carefully and extremely accurately measure changes in material properties during research.

　　The picture shows: SLAC and Stanford University scientists have carried out detailed, nanometer-level measurements on how the oxygen that constitutes the electrodes of lithium-ion batteries can leak out. In the picture, the red spheres are oxygen atoms that ooze out, and the purple spheres are metal ions.

　　As we all know, when lithium ions flow in the process of charging and discharging, the voltage of the battery will drop, and various components will also be very slightly lost. Over time, the accumulation of these losses will cause the battery's energy storage to easily decrease by 10-15%. During the battery charge and discharge cycle, researchers at the SLAC National Acceleration Laboratory (a national laboratory under the U.S. Department of Energy, operated and managed by Stanford University) discovered that a very small amount of oxygen leaked out. They made very detailed measurements of this ultra-slow process.

　　Ph.D Peter Csernica of Stanford University said: "In the experiment in collaboration with Associate Professor Will Chueh, we measured a very small amount of oxygen outflow over hundreds of cycles, the rate is very slow, which is why it is difficult to find." Researchers have found that sometimes, as lithium moves back and forth, oxygen atoms are lost among the billions of particles that make up each electrode. It is difficult to measure these oxygen losses. Csernica said: "The total amount of oxygen loss reached 6% in more than 500 charge and discharge cycles. This is not a small number, but if you try to measure the amount of oxygen loss in each charge and discharge cycle, it is about 1‰. "

　　The traditional view is that the loss of oxygen only comes from the surface of the nanoparticles. SLAC researchers are studying how oxygen loss changes the chemical properties and structure of particles, rather than trying to directly measure the rate of oxygen loss. The research team concluded: The initial loss of oxygen starts from the surface, and then slowly flows out from the inside. When the nanoparticles are condensed into a whole to form a larger cluster, those near the center will lose less oxygen than the surface.

　　Chueh pointed out another very important issue: how the loss of oxygen atoms affects other materials. Chueh said: "This is actually a big mystery. Imagine that the atoms in a nanoparticle are like closely packed spheres. If you keep taking out oxygen atoms, everything will collapse due to structural changes." The research team said: “From the aspect of electrode structure, it is impossible to directly image. We have carried out computer simulations and calculations with other types of experimental observations and various oxygen loss scenarios. The results show that holes do exist, but the material does not the structure collapses and densification occur. This shows from another perspective that the loss of oxygen will lead to a gradual decrease in battery power." Chueh said: "When oxygen seeps out, the surrounding manganese atoms, nickel atoms and cobalt atoms also move with it. All atoms deviate from the ideal position. The chemical changes caused by the recombination of this metal ion with the loss of oxygen will gradually reduce the voltage and efficiency of the battery over time. We have known these surface phenomena for a long time, but I don’t know the real root cause."

　　Lithium-ion battery (LIB) has become the main energy storage solution in modern social life. Among them, lithium iron phosphate batteries are a perfect substitute for lead-acid batteries and are the first choice for grid-connected peak shaving, off-grid energy storage, photovoltaic energy storage, UPS, data center and other industries.