Combined dynamic nuclear polarization and electron paramagnetic resonance at 0.34 T to investigate electrochemical lithium deposition on copper

Despite extensive research conducted on plating and dendrite formation in lithium batteries, themolecular formation processes are not yet fully understood. Electron paramagnetic resonance (EPR)sensitively detects metallic Li species but misses non-paramagnetic ones. Nuclear magneticresonance (NMR) is chemically selective, yet exhibits low sensitivity under low-field conditions.Dynamic nuclear polarization (DNP) overcomes this by transferring electron spin polarization tonuclei. Here, correlative EPR and DNP-enhanced 7Li NMR of lithium on copper is demonstratedusing a custom setup operating at 0.34 T with a sweepable electromagnet. DNP experiments wereconducted in pulsed mode to minimize sample heating. The resulting enhanced 7Li NMR signal allowsthe observation of electrochemically deposited lithium on copper, harvested from a Cu vs. Li cell, withan enhancement ϵ > 400. By changing the magnetic field strength by a few Gauss, the saturationof the conduction EPR transition was varied, leading to an altered Knight shift of metallic 7Li. Thecorresponding change of the DNP-polarized 7Li chemical shifts in the range from 240 ppm to 80 ppmallowed an indirect, saturation-based distinction of EPR species. Moreover, an enhancement ϵ by afactor of about 2 of the 1H signal from the surrounding electrolyte of electrochemically depositedlithium was observed, indicating the potential to investigate the solid–electrolyte interface (SEI). Thesetup employed a battery cell housing developed for EPR, demonstrating its suitability for in operandoexperiments in the future.