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Extra storage capacity in transition metal oxide lithium-ion batteries revealed by in situ magnetometry


In lithium-ion batteries (LIBs), many promising electrodes that are based on transition metal oxides exhibit anomalously high storage capacities beyond their theoretical values. Although this phenomenon has been widely reported, the underlying physicochemical mechanism in such materials remains elusive and is still a matter of debate. In this work, we use in situ magnetometry to demonstrate the existence of strong surface capacitance on metal nanoparticles, and to show that a large number of spin-polarized electrons can be stored in the already-reduced metallic nanoparticles (that are formed during discharge at low potentials in transition metal oxide LIBs), which is consistent with a space charge mechanism. Through quantification of the surface capacitance by the variation in magnetism, we further show that this charge capacity of the surface is the dominant source of the extra capacity in the Fe3O4/Li model system, and that it also exists in CoO, NiO, FeF2 and Fe2N systems. The space charge mechanism revealed by in situ magnetometry can therefore be generalized to a broad range of transition metal compounds for which a large electron density of states is accessible, and provides pivotal guidance for creating advanced energy storage systems.

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Fig. 1: Characterization of the Fe3O4 electrode.
Fig. 2: In situ XRD and magnetic monitoring characterizations.
Fig. 3: In situ observation of the phase transformation and magnetic response.
Fig. 4: Electrochemical performance and in situ magnetic characterization in the potential window of 0.01–1 V.
Fig. 5: Schematic of surface capacitance with spin-polarized electrons at the Fe/Li2O interface.

Data availability

All data supporting the findings of this study are included in the paper and its Supplementary Information files. Source data are available from the corresponding authors upon reasonable request.


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Q.L. and H.L. acknowledge support from the National Science Foundation of China (grant nos. 11504192, 51804173, 11434006 and 51673103), National Basic Research Program of China (no. 2015CB921502), National Key R&D Program of China (no. 2017YFA0303604), National Science Foundation of Shandong Province (no. ZR2018BB030), Science and Technology Program in Qingdao City (nos. 18-2-2-22-jch and 16-5-12-jch) and Youth Innovation Promotion Association of the Chinese Academy of Sciences (no. 2018008). G.Y. acknowledges financial support from a Welch Foundation award (no. F-1861), Sloan Research Fellowship and Camille Dreyfus Teacher-Scholar award. G.-X.M. acknowledges support from the Natural Sciences and Engineering Research Council of Canada (Discovery Grant no. RGPIN-04178) and Canada First Research Excellence Fund. J.S.M. acknowledges support from the National Science Foundation of the United States (grant no. DMR 1700137) and Office of Naval Research of the United States (grant no. N00014-16-1-2657).

Author information




Q.L., H.L., G.Y., G.-X.M. and J.S.M. conceived and designed the experiments. Q.X., Z.H., S.F. and X.S. carried out the synthesis and electrochemical tests. L.G. and Q.Z. performed STEM measurements. Q.L., H.L., X.W. and Q.X. carried out in situ magnetism measurements. G.-X.M., J.S.M., S.Y. and Y.L. assisted in the interpretation of the magnetization variation. H.L., Q.L., G.Y., Y.Z., C.G., G.-X.M. and J.S.M. analysed the data and co-wrote the paper. All authors discussed the experiments and final manuscript.

Corresponding authors

Correspondence to Qiang Li or Hongsen Li or Guo-Xing Miao or Guihua Yu.

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The authors declare no competing interests.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–23, discussion and refs. 1–8.

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Li, Q., Li, H., Xia, Q. et al. Extra storage capacity in transition metal oxide lithium-ion batteries revealed by in situ magnetometry. Nat. Mater. 20, 76–83 (2021).

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