Solid-state lithium batteries (SSLBs), which are regarded as one promising next-generation battery technology, are drawing increasing attentions due to the improved safety, enhanced capacities, and the broader operation temperature window, compared with the state-of-the-art lithium ion batteries (LIBs). LIBs as well as SSLBs are usually evaluated by cost, safety, and performance indicators including specific energy, energy density and cycle life, but rarely by their environmental impact, i.e. the sustainability. To specify, the sustainability of battery refers to the battery that is manufactured from green materials by sustainable processes. With this regard, developing an aqueous processing route for SSLBs is thereby of great interest. In this work, a sustainable, water-based processing route for the garnet-supported SSLB featuring a LiFePO₄ (LFP)-polyethylene oxide (PEO) composite cathode is presented.

The garnet-structured thin separator¹ is prepared by tape-casting an aqueous slurry containing Al/Ta co-substituted Li₇La₃Zr₂O₁₂ (LLZO) solid electrolyte, methylcellulose binder and other harmless plasticizers. After sintering, the free-standing ceramic separator with a low thickness of 105 µm has a high total conductivity of 0.15 mS cm^-1 at room temperature. The formation of the high-conductive cubic LLZO phase is enabled by a reversible Li⁺/H⁺ exchange reaction² involved in this process. Furthermore, this garnet separator exhibits outstanding stability against lithium metal, which enables the use of this high-capacity anode material in SSLBs. Water-based tape casting is also applied to fabricate a LFP-PEO composite cathode³. After optimizing the composition of the cathode, the full cell delivers a high capacity of 136 mAh g^-1 with a high coulombic efficiency over 99% at moderate areal loadings of 0.37 mAh cm^-2 and current density of 50 µA cm^-2.

In summary, we demonstrated a sustainable water-based processing route for garnet-supported SSLBs with LFP cathode, avoiding the harmful organic solvents commonly used in the conventional production. The prepared full cell exhibits comparable performance as the ones prepared in conventional ways. Hence, the here presented water-based fabrication route provides a baseline for further improvements and pushes SSLBs further towards sustainable battery production.

References

1. Ye, R.; Tsai, C.-L.; Ihrig, M.; Sevinc, S.; Rosen, M.; Dashjav, E.; Sohn, Y. J.; Figgemeier, E.; Finsterbusch, M., Water-based fabrication of garnet-based solid electrolyte separators for solid-state lithium batteries. Green Chemistry 2020, 22, 4952-4961.
2. Ye, R.; Ihrig, M.; Imanishi, N.; Finsterbusch, M.; Figgemeier, E., A Review on Li+/H+ Exchange in Garnet Solid Electrolytes: From Instability against Humidity to Sustainable Processing in Water. ChemSusChem 2021, 14 (20), 4397-4407.
3. Ye, R.; Hamzelui, N.; Ihrig, M.; Finsterbusch, M.; Figgemeier, E., in preparation.