Transition metal oxides as lithium-free cathodes for solid-state lithium metal batteries

Solid-state lithium metal batteries (LMBs) receive increasing attentions worldwide due to their safety and high energy density. Herein, the practical application of conversion reaction-type transition metal oxides (TMOs, Fe2O3, Mn2O3 or CuO) as Li-free cathodes for solid-state LMBs is demonstrated for the first time, employing poly (ethylene oxide) (PEO), lithium garnet Li6.4La3Zr1.4Ta0.6O12 or Li1.5Al0.5Ge1.5(PO3)(4) solid-state electrolytes (SSEs). The cathodes embody good interfacial compatibility with the SSEs, ensuring the excellent electrochemical performance of the TMOs/SSEs/Li solid-state cells. The as-prepared Fe2O3/PEO/Li cell measured at 60 degrees C delivers a high discharge capacity of 990 mAh g(-1) at 10 mA g(-1), which is comparable to the Fe2O3 liquid cell. When cycling at 200 mA g(-1), a stable capacity of 733 mAh g(-1) is achieved at the 1,100th cycle for the Fe2O3/ PEO/Li cell, while the Fe2O3 liquid cell only sustains 860 cycles until failure. In order to further demonstrate the application feasibility, stable cycling of the Fe2O3/PEO/Li cells with high mass loading of 2.83 mg cm(-2) and thus high areal capacity of 1.67 mAh cm(-2) or with limited Li usage (150% in excess) is preliminarily achieved. In addition, the Fe2O3/PEO/Li pouch cells are assembled, which exhibit satisfied electrochemical performance. Moreover, poly(vinylidene difluoride) (PVDF)-based solid polymer electrolye is employed to make the Fe2O3 solid-state cell work at 30 degrees C successfully. These results convince the great promise of TMOs in future highenergy-density solid-state LMBs.