Lithium (Li) penetration through solid electrolytes (SEs) induces short circuits in Li solid‐state batteries (SSBs), which is a critical issue that hinders the development of high energy density SSBs. While cracking in ceramic SEs has been often shown to accompany Li penetration, the interplay between Li deposition and cracking remains elusive. Here, we constructed a mesoscale SSB inside a focused ion beam‐scanning electron microscope (FIB‐SEM) for in situ observation of Li deposition‐induced cracking in SEs at nanometer resolution. Our results revealed that Li propagated predominantly along transgranular cracks in a garnet Li6.4La3Zr1.4Ta0.6O12 (LLZTO). Cracks appeared to initiate from the interior of LLZTO beneath the electrode surface and then propagated by curving toward the LLZTO surface. The resulting bowl‐shaped cracks resemble those from hydraulic fracture caused by high fluid pressure on the surface of internal cracks, suggesting that the Li deposition‐induced pressure is the major driving force of crack initiation and propagation. The high pressure generated by Li deposition is further supported by in situ observation of the flow of filled Li between the crack flanks, causing crack widening and propagation. This work unveils the dynamic interplay between Li deposition and cracking in SEs and provides insight into the mitigation of Li dendrite penetration in SSBs.
The
two biggest promises of solid-state lithium (Li) metal batteries
(SSLMBs) are the suppression of Li dendrites by solid-state electrolyte
(SSE) and the realization of a high-energy-density Li anode. However,
LMBs have not met their expectations due to Li dendrite growth causing
short-circuiting. In fact, Li dendrites grow even more easily in SSE
than in liquid electrolyte, but the reason for this remains unclear.
Here we report in situ transmission electron microscopy
observations of Li dendrite penetration through SSE and “dead”
Li formation dynamics in SSLMBs. We show direct evidence that large
electrochemomechanical stress generates cracks in the SSE and drives
Li through the SSE directly. We revealed that fresh Li nucleation
sites emerged in every discharge cycle, creating new “dead”
Li in the following charging cycle and becoming the dominant Coulombic
efficiency decay mechanism in SSLMBs. These results indicate that
engineering flaw size and reducing electronic conductivity in SSEs
are essential to improve the performance of SSLMBs.
Akin
to Li, Na deposits in a dendritic form to cause a short circuit
in Na metal batteries. However, the growth mechanisms and related
mechanical properties of Na dendrites remain largely unknown. Here
we report real-time characterizations of Na dendrite growth with concurrent
mechanical property measurements using an environmental transmission
electron microscopy–atomic force microscopy (ETEM-AFM) platform. In situ electrochemical plating produces Na deposits stabilized
with a thin Na2CO3 surface layer (referred to
as Na dendrites). These Na dendrites have characteristic dimensions
of a few hundred nanometers and exhibit different morphologies, including
nanorods, polyhedral nanocrystals, and nanospheres. In situ mechanical measurements show that the compressive and tensile strengths
of Na dendrites with a Na2CO3 surface layer
vary from 36 to >203 MPa, which are much larger than those of bulk
Na. In situ growth of Na dendrites under the combined
overpotential and mechanical confinement can generate high stress
in these Na deposits. These results provide new baseline data on the
electrochemical and mechanical behavior of Na dendrites, which have
implications for the development of Na metal batteries toward practical
energy-storage applications.
Layered cathode materials are commonly used in lithium and sodium ion batteries, but they are prone to degradation under electrochemical cycling during battery operation. Here we report a new type of degradation mechanism through the electrochemically induced mechanical buckling and delamination cracking of intercalation layers in a P2 Na 0.7 -Ni 0.3 Mn 0.6 Co 0.1 O 2 (Na-NMC) cathode material. Kinks form in the delaminated layers due to severe local bending, and each kink consists of a vertical array of dislocations, resulting from an easy slip between transition metal oxide layers. In situ mechanical compression experiments directly reveal the kink formation due to strong mechanical anisotropy parallel and perpendicular to the intercalation layers in single-crystal Na-NMC. In situ electrochemical experiments indicate that kinks form during the desodiation process. Our results unveil a new mechanism of electrochemically induced mechanical degradation stemming from weak interlayer bonding in layered cathode materials. This work has broad implications for the mitigation of degradation associated with irreversible interlayer slip in layered cathode materials.
Peanut-like hierarchical MnCO3 microcrystals assembled with floss-like nanowires are synthesized via a hydrothermal process and used as an active material for supercapacitors.
A highly ordered binderfree multi-layered hydrogenated TiO2-II phase nanowire array (ML-HTO) negative electrode for 2.4 V aqueous asymmetric supercapacitors with high active materials loading, high electrical and ionic conductivity is synthesized via a multi-step method.
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