Panasonic succeeded in the visualization of the two-dimensional distribution of the lithium ions (Li-ions) in the LiCoO2 cathode for the first time in the world, in a big step toward commercialization of the next-generation batteries.
All-solid-state Li-ion batteries are expected to offer high safety and high energy density, mainly because of their tolerance to higher temperatures, avoiding the use of materials in current batteries that may be dangerous or toxic. Solid-state battery technology is also believed to allow for faster recharging for electric cars. In addition, higher voltage and longer cycle life is possible with solid-state batteries.
All-solid-state Li-ion batteries do not have the disadvantages of conventional batteries liquid electrolyte batteries, making them suitable for future installations in the electric cars.
However, the Li-ions' very high transport resistance at the interface between the electrode and the solid electrolyte is preventing commercialization of all-solid-state Li-ion batteries.
It has been important to is visualize the movement of the Li-ions in the batteries in order to solve designs issues. However, because of the batteries' reactions generated locoregionally in the nanometer (one-billionth of a meter) scale and low detection sensitivity of Li, a light element, the nanoscale movement of the Li-ions during the charging and discharging processes could not have been visualized.
Working in collaboration with Japan Fine Ceramics Center and Nagoya University, Panasonic achieved the visualization of the lithium ion during charging and discharging of an all-solid-state lithium ion battery. The researchers used a scanning transmission electron microscope (STEM), an electron energy-loss spectroscopy (EELS) and advanced image analysis techniques (multivariate analysis techniques). As the spectrum contains signals caused by Li, multivariate analysis techniques contributed to the clear capturing of the weak Li signals in nanometer scale.
The observation showsed that ununiformly distributed Li in the LiCoO2 cathode had effects also on movement of the Li-ions during the charging and discharging processes. It was also found that the Li-ion concentration was low and lots of Co3O4 coexisted around the interface near the solid electrolyte.
STEM is an electron microscope that detects scattered transmitted electrons and produces images by scanning two-dimensionally the surface of a sample with a beam of electrons narrowed to 0.1nm order. It can be used for evaluation and analysis of the locoregional atomic structure.
EELS is the method that enables analyzing the state of elements and electrons in the material by measuring the energy that is lost when electrons transmit the inside of a sample. It is a monitoring technique that is effective for detection of the light elements such as lithium.
Panasonic says that designing the batteries with reduced Li-ion interface resistance will be possible by feeding back this monitoring results into the all-solid-state battery designing process. As a result, the ultrahigh-performance all-solid-state batteries where the Li-ions can move smoothly can be realized.
In addition, as the STEM-EELS measurement and advanced image analysis techniques having been developed this time can also be applied to the other secondary batteries (such as the all-solid-state lithium ion batteries using the sulfide solid electrolyte, the sodium ion, the magnesium-ion, etc.), in a huge contribution to commercialization of various types of the all-solid-state batteries.