High Voltage Solid State Batteries: Targeting High Energy Density with Polymer Composite Electrolytes

Solid State Batteries (SSBs) are the best candidates to overcome the safety and energy density drawbacks of conventional Li-ion. However, this technology is still relatively nascent in development and needs to offer competitive energy density so as to meet current demands of devices, especially those related to emerging electric vehicles. This work focuses on cell characteristics having the potential to reach 250 Wh kg ⁻¹ and 500 Wh l ⁻¹ in a manufacturing environment. The electrode and the solid electrolyte were carefully selected based on the results of theoretical energy density calculations, also taking into account the the scalability of their processing. The reported cells rely on a cathode which includes the high voltage active material NMC622, with loadings up to 1.6 mAh cm ⁻² , a composite electrolyte based on garnet-type oxide (Li ₇ La ₃ Zr ₂ O ₁₂ ) and poly(ethylene oxide) (PEO), and a Li metal anode. As a consequence of a particular conditioning, when cycled at 70 °C the cells delivered 91% of their theoretical capacity. To our knowledge, this is the first time that a PEO-based electrolyte has been successfully cycled with a high-voltage cathode. Pouch cells of 30 mAh have also been tested at 55 °C. These promising results highlight the feasibility of the industrial development of competitive SSBs.