Research ArticleMATERIALS SCIENCE

A new approach to both high safety and high performance of lithium-ion batteries

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Science Advances  28 Feb 2020:
Vol. 6, no. 9, eaay7633
DOI: 10.1126/sciadv.aay7633
  • Fig. 1 Principles and advantages of a SEB versus a conventional LIB.

    DCR is shown to vary with the inverse of temperature for both batteries, where the upper curve for the passivated SEB is always safer due to higher DCR. The SEB can, however, achieve a similar power output to the LIB by thermal stimulation before operation, shown as going from point b to c.

  • Fig. 2 Experimental comparison between LIB and SEB and mechanism explanation.

    (A) Nyquist plots showing measured charge-transfer resistances of SEB cells versus the baseline LIB cell. (B) Schematic showing the in situ formed interfacial layers on the surface of graphite and NCM particles. The enhanced SEI layer on graphite slows down EC transport though the film and suppresses further SEI growth. The CEI layer hinders EC oxidation with lattice oxygen over the NCM surface at high temperatures or high voltages. (C and D) Cell voltage and temperature evolutions during nail penetration of a SEB cell and the baseline LIB cell along with qualitative temperature distributions. Both cells are 2.8-Ah pouch cells composed of the same graphite anode and NMC622 cathode materials. The baseline LIB cell is filled with a standard electrolyte: 1 M LiPF6 in EC/EMC (3/7 wt) + 2 wt % VC. The SEB cell has the electrolyte of 1 M LiPF6 in EC/EMC (1/9 wt) + 2 wt % VC with TAP as electrolyte additive. RT, room temperature.

  • Fig. 3 Temperature dependence of cell power performance.

    (A and B) DCRs of discharge and charge, respectively, at 50% SOC for SEB cells versus the baseline LIB cell. (C) Relative discharge power (DCRbaseline@RT/DCR) of a SEB cell versus the baseline LIB cell. (D) Relative reactivity (Rct,baseline@RT/Rct) of a SEB cell versus the baseline LIB cell, showing that SEB cells operated at appropriate elevated temperatures, e.g., SEB-3 at 50°C, can deliver sufficient power at all ambient temperatures (labeled as line a), that SEB cells are 5× safer and less aging at room temperature (labeled as line b), and that SEB cells are 2.6× less prone to thermal runaway at 60°C (labeled as line c).

  • Fig. 4 Comparison of cycling stability at 60°C.

    (A and B) Capacity retention and DCR of the SEB cells versus the baseline LIB cell during cycling at 60°C. The cells are charged with CCCV protocol at 1 C to 4.2 V with a cutoff current of C/20 and then discharged at 1 C to 2.8 V. (C and D) Discharge curves of the fresh SEB cell versus aged cell.

  • Fig. 5 SEM micrographs of the pristine, aged electrodes for the baseline and SEB-3 cells.

    (A) Pristine anode. (B) Pristine cathode. (C) Baseline anode after 50 cycles. (D) Baseline cathode after 50 cycles. (E) Baseline anode after 956 cycles. (F) Baseline cathode after 956 cycles. (G) SEB-3 anode after 50 cycles. (H) SEB-3 cathode after 50 cycles. (I) SEB-3 anode after 4021 cycles. (J) SEB-3 cathode after 4021 cycles. ETD, Everhart-Thornley Detector; HV, electron accelerating voltage; WD, working distance; HFW, horizontal field width.

  • Fig. 6 XPS core spectra comparison for aged baseline and SEB-3 electrodes.

    The graphite and NCM622 electrodes are taken from the baseline cell after 956 cycles and the SEB-3 cell after 4021 cycles.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/6/9/eaay7633/DC1

    Fig. S1. Cycling behavior of LIB and SEB under over-charge conditions.

    Fig. S2. Calendar life testing for LIB and SEB.

    Fig. S3. Comparison of cell discharge performance.

    Fig. S4. Optical comparison of fresh and aged electrodes.

    Fig. S5. Elemental concentration of EEI layers.

    Fig. S6. Discharge curves of the fresh baseline cell versus the aged cell.

    Fig. S7. Comparison of C-rate discharge curves for the baseline LIB cell and the three SEB cells at room temperature.

  • Supplementary Materials

    This PDF file includes:

    • Fig. S1. Cycling behavior of LIB and SEB under over-charge conditions.
    • Fig. S2. Calendar life testing for LIB and SEB.
    • Fig. S3. Comparison of cell discharge performance.
    • Fig. S4. Optical comparison of fresh and aged electrodes.
    • Fig. S5. Elemental concentration of EEI layers.
    • Fig. S6. Discharge curves of the fresh baseline cell versus the aged cell.
    • Fig. S7. Comparison of C-rate discharge curves for the baseline LIB cell and the three SEB cells at room temperature.

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