438
12 Localized or Spatially Selective Electrodeposition Methods
12.2.4 In Situ TEM Studies of Nanostructures Related
to Batteries
In situ TEM studies gained recently an important role in the investigation of various
nanostructures that are produced electrochemically in various battery constituents,
especially in lithium ion batteries [45]. It has long been known that Li is prone to
develop dendrites upon battery charging that are not consumed upon the battery
discharge. This leads to the formation of a direct electrical contact between the
electrodes upon battery cycling, causing an obvious battery failure. The details of
the lithium growth and dissolution process were revealed with in situ TEM studies
[46, 47]. In accord with general nucleation and growth theories, it was directly imaged
that higher Li deposition rate tends to lead to a dendrite-rich growth. The spatially
selective dissolution of the Li dendrites near their root results in separated Li needles
that can contribute to the battery failure.
Lithium growth and dissolution is always coupled with the formation of a layer
around the cathode called the solid electrolyte interface (SEI). SEI is produced during
the partial solvent reduction and has a protective nature against the spontaneous
reaction between Li and the solution components, making possible Li
+ ion transfer
at the same time. The competition between Li growth/dissolution and SEI-related
electrochemical processed has been shown to regulate the overall electrochemical
behaviour of Li electrodes [48, 49]. The direct in situ imaging of SEI in sealed thinlayer cells revealed the thickness distribution of SEI, the nature of the processes
due to the breaks in a fragile SEI layer and the impact of bubble formation under
the SEI. It is practically impossible to study such processes ex situ due to the very
high reactivity of lithium. The study of intercalation-type electrodes in lithium ion
batteries can also be performed with in situ TEM. Here, the volume and structural
change of the lithiation/de-lithiation gained the major interest [50, 51].
Unlike in Li batteries, in Mg batteries the dissolution of the metal is the problematic part of the battery operation. Magnesium forms a smooth deposit with no dendrite
formation, but the dominant anodic process is the formation of an organometallic
compound that passivates the remaining metallic magnesium underneath. A combination of direct in situ TEM and scanning transmission X-ray microscopy (STXM)
was successfully applied for revealing the details of the electrochemical behaviour
of magnesium under typical battery conditions [52].
12.2.5 Chemical Changes in Thin-Layer Cells Induced
by the Electron Beam
Electron beam in an in situ TEM cell can be used, besides imaging, for the modification of electrochemical processes or for the initiation of electron-transfer reactions
(i.e., reduction of ions). The term used for such processes is focused electron-beaminduced deposition using bulk liquid precursors (LP-EBID). Although such processes
12 Localized or Spatially Selective Electrodeposition Methods
12.2.4 In Situ TEM Studies of Nanostructures Related
to Batteries
In situ TEM studies gained recently an important role in the investigation of various
nanostructures that are produced electrochemically in various battery constituents,
especially in lithium ion batteries [45]. It has long been known that Li is prone to
develop dendrites upon battery charging that are not consumed upon the battery
discharge. This leads to the formation of a direct electrical contact between the
electrodes upon battery cycling, causing an obvious battery failure. The details of
the lithium growth and dissolution process were revealed with in situ TEM studies
[46, 47]. In accord with general nucleation and growth theories, it was directly imaged
that higher Li deposition rate tends to lead to a dendrite-rich growth. The spatially
selective dissolution of the Li dendrites near their root results in separated Li needles
that can contribute to the battery failure.
Lithium growth and dissolution is always coupled with the formation of a layer
around the cathode called the solid electrolyte interface (SEI). SEI is produced during
the partial solvent reduction and has a protective nature against the spontaneous
reaction between Li and the solution components, making possible Li
+ ion transfer
at the same time. The competition between Li growth/dissolution and SEI-related
electrochemical processed has been shown to regulate the overall electrochemical
behaviour of Li electrodes [48, 49]. The direct in situ imaging of SEI in sealed thinlayer cells revealed the thickness distribution of SEI, the nature of the processes
due to the breaks in a fragile SEI layer and the impact of bubble formation under
the SEI. It is practically impossible to study such processes ex situ due to the very
high reactivity of lithium. The study of intercalation-type electrodes in lithium ion
batteries can also be performed with in situ TEM. Here, the volume and structural
change of the lithiation/de-lithiation gained the major interest [50, 51].
Unlike in Li batteries, in Mg batteries the dissolution of the metal is the problematic part of the battery operation. Magnesium forms a smooth deposit with no dendrite
formation, but the dominant anodic process is the formation of an organometallic
compound that passivates the remaining metallic magnesium underneath. A combination of direct in situ TEM and scanning transmission X-ray microscopy (STXM)
was successfully applied for revealing the details of the electrochemical behaviour
of magnesium under typical battery conditions [52].
12.2.5 Chemical Changes in Thin-Layer Cells Induced
by the Electron Beam
Electron beam in an in situ TEM cell can be used, besides imaging, for the modification of electrochemical processes or for the initiation of electron-transfer reactions
(i.e., reduction of ions). The term used for such processes is focused electron-beaminduced deposition using bulk liquid precursors (LP-EBID). Although such processes