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Semi-solid alkali metal electrodes enabling high critical current densities in solid electrolyte batteries

A Publisher Correction to this article was published on 31 March 2021

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The need for higher energy-density rechargeable batteries has generated interest in alkali metal electrodes paired with solid electrolytes. However, metal penetration and electrolyte fracture at low current densities have emerged as fundamental barriers. Here we show that for pure metals in the Li–Na–K system, the critical current densities scale inversely to mechanical deformation resistance. Furthermore, we demonstrate two electrode architectures in which the presence of a liquid phase enables high current densities while it preserves the shape retention and packaging advantages of solid electrodes. First, biphasic Na–K alloys show K+ critical current densities (with the K-β″-Al2O3 electrolyte) that exceed 15 mA cm‒2. Second, introducing a wetting interfacial film of Na–K liquid between Li metal and Li6.75La3Zr1.75Ta0.25O12 solid electrolyte doubles the critical current density and permits cycling at areal capacities that exceed 3.5 mAh cm‒2. These design approaches hold promise for overcoming electrochemomechanical stability issues that have heretofore limited the performance of solid-state metal batteries.

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Fig. 1: Overview of the electrochemical cells studied.
Fig. 2: Surface finish and microstructure of solid electrolytes studied.
Fig. 3: CCD for the metal penetration of solid electrolytes.
Fig. 4: Surfaces of positive and negative current collectors and solid electrolyte after cycling of the symmetric metal–solid electrolyte cells to short-circuit failure.
Fig. 5: CCD versus areal capacity for single-phase solid metals and semi-solid alloy mixtures.
Fig. 6: CCD versus electrochemical cell type and alkali metal yield stress.
Fig. 7: Compositional design for semi-solid alkali metal electrodes.

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We acknowledge support from the US Department of Energy, Office of Basic Energy Science, through award no. DE-SC0002633 (J. Vetrano, Program Manager). This work made use of the MRL MRSEC Shared Experimental Facilities at MIT, supported by the National Science Foundation under award no. DMR-1419807. We also acknowledge use of the MIT Nanomechanical Technology Laboratory (A. Schwartzman, Manager). We thank T. Swamy for helpful discussions, and N. Katorova and P. Morozova for assistance with alkali metal handling procedures. We acknowledge financial support from the MIT-Skoltech Next Generation Program, award no. 2016-1, for the portion of the work related to K metal. C.D.F. acknowledges the support of the National Science Foundation Graduate Research Fellowship under grant no. 1746932. M.P. acknowledges the support of the National Science Foundation under award no. DMR-1944674.

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Authors and Affiliations



Y.-M.C. and R.J.-Y.P. designed the study. R.J.-Y.P. prepared, measured and analysed the results from the electrochemical cells. C.M.E. measured the alkali metal wetting angles. C.D.F. measured the alkali metal mechanical properties. A.F.B. performed the image analysis of disassembled cells. P.G. calculated the Li–Na–K ternary phase diagram. All the authors contributed to writing the manuscript.

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Correspondence to Yet-Ming Chiang.

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Competing interests

Massachusetts Institute of Technology has filed for patents on the subject matter related to this article in which R.J.-Y.P., Y.-M.C., P.G. and V.V. are listed inventors.

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Peer review information Nature Energy thanks Qiang Zhang and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary information

Supplementary Information

Supplementary Tables 1–3, Figs. 1–12, discussion, methods and references.

Source data

Source Data Fig. 6

Microhardness data for Li, Na and K (10 independent measurements per metal).

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Park, R.JY., Eschler, C.M., Fincher, C.D. et al. Semi-solid alkali metal electrodes enabling high critical current densities in solid electrolyte batteries. Nat Energy 6, 314–322 (2021).

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