Cycle stability of conversion-type iron fluoride lithium battery cathode at elevated temperatures in polymer electrolyte composites


Metal fluoride conversion cathodes offer a pathway towards developing lower-cost Li-ion batteries. Unfortunately, such cathodes suffer from extremely poor performance at elevated temperatures, which may prevent their use in large-scale energy storage applications. Here we report that replacing commonly used organic electrolytes with solid polymer electrolytes may overcome this hurdle. We demonstrate long-cycle stability for over 300 cycles at 50 °C attained in high-capacity (>450 mAh g−1) FeF2 cathodes. The absence of liquid solvents reduced electrolyte decomposition, while mechanical properties of the solid polymer electrolyte enhanced cathode structural stability. Our findings suggest that the formation of an elastic, thin and homogeneous cathode electrolyte interphase layer on active particles is a key for stable performance. The successful operation of metal fluorides at elevated temperatures opens a new avenue for their practical applications and future successful commercialization.

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Fig. 1: Advantages of robust and elastic solid CEI on MF particles.
Fig. 2: The fabrication process steps and corresponding morphology of the cathode.
Fig. 3: Characterization of the synthesized and fabricated materials.
Fig. 4: The electrochemical performance of the all-solid-state batteries with ICNT@FeF2 cathodes.
Fig. 5: Characterization of the cycled FeF2 particles.

Data availability

The data used in this study are available from the authors upon reasonable request.


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This project was largely supported by the Army Research Office (grant No. W911NF17-1-0053). The authors also wish to acknowledge fellowship support of Q. Huang and X. Ren by the China Scholarship Council.

Author information

Q.H. contributed to the synthesis and electrochemical testing. Q.H., X.R., A.M., A.-Y.S., Y.X. and D.K. contributed to sample characterizations. K.T., Q.H. and G.Y. discussed and interpreted the experimental results. Q.H., K.T. and G.Y. wrote the paper. G.Y. conceived the idea.

Correspondence to Gleb Yushin.

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