Solid polymer electrolytes can be used to construct solid-state
lithium batteries (SSLBs) using lithium metals as the anode. However,
the lifespan and safety problems of SSLBs caused by lithium dendrite
growth have hindered their practical application. Here, we have designed
and prepared a rigid-flexible asymmetric solid electrolyte (ASE) that
is used in building SSLBs. The ASE can inhibit efficiently the growth
of lithium dendrites and lead to a long cycle life of SSLBs due to
the hierarchical structure of a combination of “polymer-in-ceramic”
(i.e., rigid ceramic layer of Li6.4La3Zr1.4Ta0.6O12) and “LiBOB-in-polymer”
(i.e., soft polymer-layer of polyethylene oxide and LiBOB components).
The results demonstrated that a symmetrical battery with ASE (Li|ASE|Li)
can be steadily cycled for more than 2000 h and yielded a flat plating/stripping
voltage profile under a current density of 0.1 mA cm–2. As a consequence, the SSLB of LiFePO4|ASE|Li delivered
a specific capacity of 155.1 mA h g–1 with a capacity
retention rate up to 90.2% after 200 cycles with the Coulombic efficiency
over 99.6% per cycle. This asymmetric structure combines the advantages
of ceramics and polymers, providing an ingenious solution for building
rigid and flexible solid electrolytes.
Based
on the analysis of systematic research (density functional theory
calculations, physical characterizations, and electrochemical performances),
here, we report a novel mixture surface modification layer of LiC6&LiF, which can enhance the lithium-ion diffusion and
decrease the local current density. This is beneficial to the improvement
of cycling stability. As a result, the Li@LiC6&LiF-5/NCM
half-cell possesses an excellent capacity retention of 94% after 100
cycles at 0.1C, with a capacity decay of only 0.06% per cycle. For
comparison, the capacity retention of a pristine Li/NCM cell is only
9.3% after 100 cycles. Our study confirms that compositing the high
ionic conductivity layer (e.g., LiC6&LiF for the first
time) is a promising avenue to stabilize lithium-metal anodes. From
this perspective, we concisely review recent discoveries in this field
and suggest possible new research directions for further development
of Li-metal batteries.
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