EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Solid state batteries (SSBs) are the most promising candidates to overcome safety and energy density drawbacks of conventional Li-ion batteries. Polyethylene(oxide) (PEO) mixed with lithium conductive salts is an excellent choice amongst the available solid electrolytes due to the processing into thin electrolyte layers with improved electrode/electrolyte interfacial contact. However, the heterogeneous nature of PEO-based electrodes, results in various resistive interfaces and interphases, jeopardizing the smooth performance of the cell, by decreasing the capacity, increasing the polarization and inhibiting fast rate cycling. Therefore, an important challenge of SSBs which require high-power and high-energy, is to decrease such resistive sources by improving ionic and electronic conductivity.

In this work we provide an evaluation of the electrochemical properties of PEO-based SSBs with electrodes optimized from a careful selection of active materials such as LiFePO4 (LFP) or Li4Ti5O12 (LTO) and electronic conductive additives with various morphologies such as carbon black and multi-walled carbon nanotubes. It is demonstrated that a rational and careful electrode design is the key to overcome important limitations of solid state batteries. The optimized electrodes exhibit an enhanced power capability and long cycling life. LTO electrodes exhibited high rate capability up to C/2 during 40 cycles and deliver the theoretical capacity during 140 cycles at C/20. LFP electrodes exhibit the theoretical capacity at 4 C and demonstrate 800 cycles at 2C with 80% depth-of-discharge and 100 % coulombic efficiency.

Besides, post-mortem studies on the ageing of the components were assessed by electrochemical impedance spectroscopy and scanning electron microscopy/EDAX mapping at the cross-section of the cells in order to provide insights on the sources of failure. It was found that the current density is closely tied to either dendrite formation or degradation of interfaces as main causes.