Influence of Laser Structuring and Calendering of Graphite Anodes on Electrode Properties and Cell Performance

Abstract

The influence of calendering and laser structuring on the pore structure and electrochemical performance of electrodes is reported. Graphite anodes of varying bulk porosity were micro structured with pulsed laser radiation. Using scanning electron microscopy and energy-dispersive X-ray spectroscopy, laser structuring was found to release superficial pore clogging caused by calendering and to result in binder agglomerates on the electrode surfaces. Structured electrodes showed higher porosities than their unstructured counterparts due to a thickness increase and material removal, but no significant change in the pore size distribution was detected using mercury intrusion porosimetry. Electrochemical impedance spectra of symmetric battery cells revealed increasing ionic resistances and tortuosities for decreasing electrode porosities. Laser structuring significantly reduced the underlying lithium-ion diffusion limitations at all porosity levels. In a discharge rate test, performance deteriorations at high currents were found to be amplified by calendering and could be diminished by electrode structuring. The performance improvements by laser structuring moved towards lower C-rates for stronger compressed anodes. Despite their growth in thickness and porosity, laser structured graphite anodes showed a higher volumetric energy density at high currents than unstructured electrodes, which demonstrates the potential of electrode structuring for highly compressed anodes.

Structured aqueous processed lignin-based NMC cathodes for energy-dense LIBs with improved rate capability

“…The cathode coating presumably expanded abruptly upon the laser irradiation and released tension introduced into the electrode coating during the calendering process. 55…”

“…The cathode coating presumably expanded abruptly upon the laser irradiation and released tension introduced into the electrode coating during the calendering process. 55 The spring-back effect is seen aer laser structuring; therefore, it increases the bulk porosity of the calendered Targray electrodes aer structuring. The spring back effect increases the bulk porosity from 23.8% to 29.5% for the laser-structured cathode when using the new thickness (97 mm) in the porosity calculation.…”

“…51 An extensive review of these processes is available in the study undertaken by Usseglio-Viretta et al 52 Multiple researchers are developing techniques to reduce the solid diffusion path in anodes and cathodes by increasing the active particle surface area with smaller particles, [53][54][55] or by structuring the electrode surface area with microchannels. 36,[55][56][57][58] The surface-induced structures will lower the tortuosity pathways for facile Li + -transport deep into the electrode, limit electrolyte concentration gradients, and reduce the electrochemical overpotential that leads to Li-plating. These features will eventuate higher rate capabilities.…”

“…tortuosity), and therefore a low Li + -conductivity, compared to the cathode with mainly spherical transition metal oxide particles. 55,56 However, structuring is compatible with most known cathode chemistries, such as LiFePO 2 (LFP), [59][60][61] LiMnO 2 (LMO), 62 and LiNiMnCoO 2 (NMC). 26,53,57,58,63 When comparing different variations of unstructured and structured electrodes in full cells, it is found that structuring both electrode coatings 58 or only the cathode 57 is preferred for optimal cycling performance at high C-rates.…”

“…tortuosity), and therefore a low Li + -conductivity, compared to the cathode with mainly spherical transition metal oxide particles. 55,56 However, structuring is compatible with most known cathode chemistries, such as LiFePO 2 (LFP), 59–61 LiMnO 2 (LMO), 62 and LiNiMnCoO 2 (NMC). 26,53,57,58,63…”