Performance of cells containing SAMs under
stringent conditions
Reversible Li plating and stripping are evaluated
by testing symmetric cells. The symmetric cell
with carboxyl group–terminated SAMs (SAMsC)
exhibits steady cyclability over 1000 cycles for
more than 2500 hours, with a small over-
potential of 40 mV (Fig. 5A). By contrast, the
symmetric cell with Al 2 O 3 exhibits a much
larger overpotential (75 mV for 700 hours), with
greatly reduced cycle life. Even when the cur-
rent density and areal capacity are increased
to 5 mA cm−^2 and 5 mA·hour cm−^2 , respectively,
the symmetric cell with SAMsC can still be
steadily cycled over 600 hours (Fig. 5B). For
the full cell tests, coin cells with a LiFePO 4 (LFP)
cathode and a Li anode (Li foil or Li-deposited
Cu) are evaluated at a current density of 1 C
in a LiTFSI-containing ether electrolyte in
the presence of SAMsC and amino group–
terminated SAMs (SAMsA). The Li//SAMsC//
LFP cell can be cycled steadily over 1000 cycles,
with a capacity retention of 92.8% (fig. S31).
Notably, the full cell of Li//SAMsC//LFP under
a low capacity ratio of the negative electrode to
the positive electrode (N/P ratio of ~3) can still
exhibit an enhanced life span over 450 cycles,
with a capacity retention above 80% and anaverage CE above 99.9% (Fig. 5C), indicative
of a promising strategy to boost high–energy
density LMBs (table S2). Even if the ratio of
electrolyte weight to cathode capacity is further
decreased to below 5 g A−^1 ·hour−^1 with lean
electrolyte conditions (15ml), the full cell of
Li//SAMsC//LFP shows marked cycling sta-
bility, with little capacity loss over 270 cycles
(fig. S32). The Li//SAMsC//LFP full cell also
delivers higher discharge specific capacities
(163 to 137 mA·hour g−^1 ) at current densities
ranging from 0.2 to 3 C (Fig. 5, D and E) than
the Li//LFP and Li//SAMsA//LFP cells. After
the current density is reduced back to 0.5 C,SCIENCEscience.org 18 FEBRUARY 2022•VOL 375 ISSUE 6582 743
Fig. 4. Cryo-TEM visualization of the Li deposits and SEI nanostructures.
(A) Morphology of Li plated on a Cu grid in the presence of Al 2 O 3 -OOC(CH 2 ) 2 COOH.
(B) Cryo-STEM image of Li deposit in the presence of Al 2 O 3 -OOC(CH 2 ) 2 COOH
and (C) corresponding elemental distributions of C, O, F, and S. (D) Elemental mass
ratios of the SEIs formed in three cells equipped with Al 2 O 3 , Al 2 O 3 -OOC(CH 2 ) 2 NH 2 , and
Al 2 O 3 -OOC(CH 2 ) 2 COOH. (E) Enlarged TEM image of the Li/Al 2 O 3 -OOC(CH 2 ) 2 COOH
interface, where the typical mosaic SEI structure and the incorporated crystalline
regions are shown. (Inset) Corresponding fast Fourier transform with yellow circle
indexed to LiF, 2.32 Å (PDF#45-1460); red circle indexed to Li, 2.48 Å (PDF#15-0401);
white circle indexed to Li 2 O, 2.66 Å (PDF#12-0254); and blue circle indexed to
LiOH,4.35Å(PDF#32-0564).(FtoI) HRTEM images of (F) Li, (G) LiOH, (H) Li 2 O, and
(I) LiF nanocrystals with long-rangeÐordered lattices.RESEARCH | RESEARCH ARTICLES