Fig. 4: Multimodal magnetic microscopy on batteries.

a Finite element simulations of a Li|Li₇La₃Zr₂O₁₂|Li_xCoO₂ solid-state battery with the Li_xCoO₂ positive electrode particles containing various lithiation states and a lithium metal dendrite forming in the Li₇La₃Zr₂O₁₂ electrolyte grain boundaries. The geometry is inspired by experimental studies^81,82 as described in Supplementary Section S3. Here, both the dendrite and part of the positive electrode particles are buried below the surface, as shown in the lower schematics. In the middle panels, we show the magnitude of the local current density ( | J | ) with 23.5 mA·cm⁻² nominal current applied as well as the out-of-plane component of the Ørsted magnetic field (B_z) the current produces 50 nm above the surface. In the upper two panels, we show the lithium metal locations and the lithium content of the Li_xCoO₂ particles in addition to the magnetic field produced by the paramagnetic components in an external field of 100 mT. b The simulated signal strengths and magnetometry detection limits as a function of the external magnetic field (B_ext) for the paramagnetic lithium metal and Li_xCoO₂ and the nominal current density (J_nominal) for the Ørsted magnetic field. c Magnetic stray fields from the Li_xCoO₂ particles at different distances between the nitrogen vacancy (NV) sensor and the surface of the positive electrode.