The ongoing electrification of the transportation sector is triggering a continuous search for batteries with higher energy density. One approach to achieve this goal is the transition to lithium-metal anodes. However, the practical implementation brings about severe safety issues such as the dendritic deposition and growth of metallic lithium and the consequent risk of accidental short circuiting of the cell, resulting in a thermal runaway.¹ Solid-state electrolytes such as polymers are considered a viable strategy to overcome this issue, especially single-ion conducting polymers, owing to the absence of the detrimental reversed cell polarization, the uniform Li⁺ flux, and frequently higher limiting current densities.^2,3 In fact, the latter is of utmost importance for the fast charging of battery cells as well as the eventual power density. So far, however, the cycling performance at high dis-/charge rates and high current densities for battery cells comprising a polymer electrolyte remained little investigated and commonly non-satisfactory.

Here, we report the development of a polysiloxane-based single-ion conducting polymer electrolyte (PSiOM) with a Li⁺ conductivity exceeding 10⁻⁴ S cm⁻¹ at ambient temperature and excellent stability towards both lithium metal and high-energy LiNi_0.8Co_0.1Mn_0.1O₂ (NMC₈₁₁) as the active material for the positive electrode. This new polymer electrolyte enables dendrite-free lithium deposition, thanks to the formation of a suitable electrode|electrolyte interface and interphase and the uniform Li⁺ flux. Moreover, PSiOM allows for an outstanding capacity retention of, e.g., 90% at 1C and 86% at 2C after 300 cycles and rapid charging and discharging at C rates as high as 5C. It is important to note that we used reasonable active material mass loadings for these tests (>7 mg cm^-2), which means that the current densities applied were up to 7.20 mA cm⁻² at 40 °C and 2.88 mA cm⁻² at 20 °C. To the best of our knowledge, these current densities are among the highest reported so far for polymer-based electrolytes.

References

(1) Kalhoff, J.; Eshetu, G. G.; Bresser, D.; Passerini, S. Safer Electrolytes for Lithium-Ion Batteries: State of the Art and Perspectives. ChemSusChem 2015, 8 (13), 2154–2175.

(2) Zhang, H.; Li, C.; Piszcz, M.; Coya, E.; Rojo, T.; Rodriguez-Martinez, L. M.; Armand, M.; Zhou, Z. Single Lithium-Ion Conducting Solid Polymer Electrolytes: Advances and Perspectives. Chemical Society Reviews 2017, 46 (3), 797–815.

(3) Nguyen, H.-D.; Kim, G.-T.; Shi, J.; Paillard, E.; Judeinstein, P.; Lyonnard, S.; Bresser, D.; Iojoiu, C. Nanostructured Multi-Block Copolymer Single-Ion Conductors for Safer High-Performance Lithium Batteries. Energy & Environmental Science 2018, 11 (11), 3298–3309.