Science - USA (2022-02-18)

the reversible capacity of Li//SAMsC//LFP
recovers to 163 mA·hour g−^1 , indicating ex-
cellent rate performance (Fig. 5D). In addition,
SAMs can be employed to boost the perform-
ance of cells with highly concentrated electro-
lytes (HCEs). The SAMsC-based full cell with a
higher concentration of LiTFSI generates more
LiF in the SEI, thus rendering a prolonged life
span of the battery under the HCE condition

(fig. S33). Using another typical unstable

cathode, the Li//SAMsC//LiNi0.8Co0.1Mn0.1O 2

(NCM811) full cell also has enhanced cyclabil-

ity (fig. S34) and rate performance (fig. S35).

The potential practical application of SAMs

is further demonstrated in pouch cells. The

pristine Li//LFP pouch cell with a N/P ratio

of ~5 manifests rapid capacity decay toward

battery failure, whereas the Li//SAMsC//LFP

pouch cell exhibits much better cycling stabil-

ity, with an extended cycle life under similar

conditions (fig. S36). The improved cycle life

proves the substantial advantages of the LiF-

rich SEI originating from the surface dipole–

directed degradation of Li salts.

With the use of a SAM-grafted separator, we

have demonstrated a strategy to regulate elec-

trolyte degradation for constructing stable

LMBs. Comprehensive simulations and char-

acterizations reveal the critical role of ordered

polar carboxyl groups in promoting the cleav-

age of C–F bonds to generate a LiF-rich SEI

involving dipole moment–induced excess elec-

trons. The LiF-enriched SEI is beneficial for

stabilizing the Li/electrolyte interface, thus

substantially inhibiting the formation of Li

dendrites and boosting the life span of the Li

anode. This long-established SAMs technique

based on surface chemistry provides a solution

to uncontrollable electrolyte degradation and

SEI formation in batteries. With SAM-grafted

separators, full cells of LMBs exhibit enhanced

cyclability even under stringent conditions.

This facile strategy can potentially be extended

to other electrode systems by tailoring the

molecular structures of SAMs to build better

energy devices.

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744 18 FEBRUARY 2022•VOL 375 ISSUE 6582 science.orgSCIENCE

Fig. 5. Electrochemical performance of symmetric half cells and full cells equipped with SAMs.
(AandB) Galvanostatic discharge and charge voltage curves of the symmetric coin cells at (A) 1 mA cm−^2
with an areal capacity of 1 mA·hour cm−^2 and at (B) 5 mA cm−^2 with an areal capacity of 5 mA·hour cm−^2.
(C) Long-term cycling performance of the batteries using a Li-deposited Cu anode (10 mA·hour cm−^2 ),
aLFPcathode(3.2mA·hourcm−^2 ), and a LiTFSI-containing ether-based electrolyte (60ml) at a current
density of 1 C (1 C = 170 mA g−^1 ). (D) Rate performance of Li//LFP, Li//SAMsA//LFP, and Li//SAMsC//
LFP full cells with a N/P ratio of 3.5. (E) Discharge and charge voltage profiles of a Li//SAMsC//LFP
full cell at different current densities.

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