The continuously rising importance of batteries to power portable electronic equipment and, more recently, electric and the resulting ambition to steadily improve the energy density of the battery cells has triggered a renewed interest in lithium-metal batteries (LMBs) in the past years^1,2. Towards this goal, the design of the electrolyte is of critical importance with regard to the pronounced reduction potential of the lithium-metal negative electrode, while simultaneously a sufficient stability towards high-energy positive electrodes with a de-/lithiation potential beyond 4 V has to be ensured³. Among the different electrolyte systems, polymer electrolytes have received particular attention owing to their suitable mechanical properties, thermal stability, and, not least, the proven commercial relevance in such systems³.

Herein, a novel single-ion conducting polymer electrolyte is reported that is characterized by high ionic conductivity and a sufficiently wide electrochemical stability window, allowing for the stable cycling of Li||NCM₆₂₂ and Li||NCM₈₁₁ cells. The high ionic conductivity is the result of adding small organic molecules of high dielectric constant that are supporting the Li⁺ charge transport, also referred to as “molecular transporters”^4,5. In fact, when optimizing the molecular composition of these molecular transporters embedded in the new single-ion conducting polymer electrolyte, an enhanced capacity retention of greater than 82% after 200 cycles has been obtained for Li||NCM₈₁₁ cells at 0.2C and 40 °C (Figure 1) thanks to a superior ionic conductivity of 0.45 mS cm^-1 in combination with an electrochemical stability exceeding 4.8 V, rendering this novel polymer electrolyte very suitable for the realization of safe high-performance LMBs.

References

1. Liu, B., J.-G. Zhang, and W. Xu, Advancing lithium metal batteries. Joule, 2018. 2(5): p. 833-845.
2. Wang, J., et al., Improving cyclability of Li metal batteries at elevated temperatures and its origin revealed by cryo-electron microscopy. Nature Energy, 2019. 4(8): p. 664-670.
3. Kalhoff, J., et al., Safer electrolytes for lithium‐ion batteries: state of the art and perspectives. ChemSusChem, 2015. 8(13): p. 2154-2175.
4. Nguyen, H.-D., et al., Nanostructured multi-block copolymer single-ion conductors for safer high-performance lithium batteries. Energy & environmental science, 2018. 11(11): p. 3298-3309.
5. Chen, Z., et al., High-energy lithium batteries based on single-ion conducting polymer electrolytes and Li[Ni_0.8Co_0.1Mn_0.1]O₂ cathodes. Nano Energy, 2020. 77: p. 105129.