Abstract
To develop a high-density and long-life lithium-ion battery, a technology is needed that allows non-destructive visualization of the spatial distribution of deteriorated parts after cycle test. In the present study, we measured the distribution of the magnetic field leaking from the lithium-ion battery during its operation. Based on the measurement results, we evaluated the spatial distribution of electric current density that corresponds to the reaction rate of the active material and the ion diffusion rate in the electrolyte solution inside a battery using the electric current reconstruction process. With respect to the changes in the internal state of the lithium-ion battery associated with cycle deterioration, we successfully visualized the part where the electrical conductivity has changed that is the deteriorated part causing the battery capacity to decrease inside the lithium-ion battery.
Highlights
Because of their high energy density and long life, lithiumion batteries are widely used in electric vehicles, hybrid electric vehicles, mobile phones, etc
Lithium-ion batteries, are known for forming dendritic lithium crystals, which deposit on negative electrodes during charging.1–4) Dendrites degrade the performance of the negative electrode and cause capacity deterioration.5–8) In addition, it has been reported that some overgrown dendrites penetrate separators, which causes short circuits that results in serious accidents such as ignition and burning of the organic solvent.9–12) Observation of the negative electrode crosssection using synchrotron hard X-ray microtomography 1)
We used a laminated single-layer lithium-ion battery having an electrode size of 80 mm × 240 mm
Summary
Because of their high energy density and long life, lithiumion batteries are widely used in electric vehicles, hybrid electric vehicles, mobile phones, etc. The methods for observing the non-uniformity of reactions include three-dimensional structural analysis using X-ray tomography,20,21) visualization of the lithium ions distribution using X-ray Absorption Spectroscopy,22–24) energy dispersive X-ray spectroscopy for element mapping,). In this study, in contrast to the mentioned methods, by using a magnetic sensor we measured the distribution of magnetic field generated by the currents during operation of a lithium-ion battery. Based on these results, we developed a method to visualize the conductivity distribution inside a lithium-ion battery using the analytical relation between the solution of the current in a battery and the magnetic field it induces. This paper deals with a non-destructive visualization of changes in conductivity
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