Sensitive magnetometry reveals inhomogeneities in charge storage and weak transient internal currents in Li-ion cells

Abstract

The ever-increasing demand for high-capacity rechargeable batteries highlights the need for sensitive and accurate diagnostic technology for determining the state of a cell, for identifying and localizing defects, and for sensing capacity loss mechanisms. Here, we leverage atomic magnetometry to map the weak induced magnetic fields around Li-ion battery cells in a magnetically shielded environment. The ability to rapidly measure cells nondestructively allows testing even commercial cells in their actual operating conditions, as a function of state of charge. These measurements provide maps of the magnetic susceptibility of the cell, which follow trends characteristic for the battery materials under study upon discharge. In particular, hot spots of charge storage are identified. In addition, the measurements reveal the capability to measure transient internal current effects, at a level of μA, which are shown to be dependent upon the state of charge. These effects highlight noncontact battery characterization opportunities. The diagnostic power of this technique could be used for the assessment of cells in research, quality control, or during operation, and could help uncover details of charge storage and failure processes in cells.

Interference in Atomic Magnetometry

“…Furthermore, we uncover a novel interference effect in magnetometers due to the contributions from different detection paths to the observed signal. Our work could be immediately applied to characterize the interference effect in applications such as biomagnetic measurements [ 45 ] and battery diagnostics [ 41 ] using atomic magnetometers, and allows for high‐accuracy measurements of magnetic fields. A promising application is using arrays of high‐sensitivity atomic magnetometers to monitor the faint magnetic‐field signals from human brain activities.…”

“…[ 40 ] Moreover, without the prior knowledge of the hidden systematic effect, it would reduce the accuracy of atomic magnetometers in locating the magnetic field sources, such as for diagnosing the brain electrophysiological symptom [ 17,38,39 ] and defects in Li‐ion battery cells. [ 41 ] Therefore, there is a pressing need for a subtle analysis of the relevant physical processes and achieving a precise detection model in atomic magnetometry.…”

Rechargeable Batteries from the Perspective of the Electron Spin

“…8b). 64 This diagnostic technique is in principle scalable and could be adapted to screen larger commercial-type cell designs, such as those used in the electric car industry, in their target form factors. Importantly, this method could provide detailed spatial information about the battery state, and possible internal defects and damage, without compromising the cell.…”

Photo Rechargeable Li‐Ion Batteries Using Nanorod Heterostructure Electrodes

“…After a complete discharge (till it reaches ≈0.01 V), the battery voltage was allowed to equilibrate (Figure 3a, yellow area). [41] After the voltage stabilization (at ≈2.42 V), a red LED light having a power density of 50 mW cm −2 is turned on. The voltage enhancement is visible during the exposure of light as shown in Figure 3a (red area, enhanced up to 2.83 V within 4.7 h).…”