20 research outputs found
<i>In Situ</i> Transmission Electron Microscopy Observation of the Conversion Mechanism of Fe<sub>2</sub>O<sub>3</sub>/Graphene Anode during Lithiation–Delithiation Processes
Transition metal oxides have attracted tremendous attention as anode materials for lithium ion batteries (LIBs) recently. However, their electrochemical processes and fundamental mechanisms remain unclear. Here we report the direct observation of the dynamic behaviors and the conversion mechanism of Fe<sub>2</sub>O<sub>3</sub>/graphene in LIBs by <i>in situ</i> transmission electron microscopy (TEM). Upon lithiation, the Fe<sub>2</sub>O<sub>3</sub> nanoparticles showed obvious volume expansion and morphological changes, and the surfaces of the electrode were covered by a nanocrystalline Li<sub>2</sub>O layer. Single-crystalline Fe<sub>2</sub>O<sub>3</sub> nanoparticles were found to transform to multicrystalline nanoparticles consisting of many Fe nanograins embedded in Li<sub>2</sub>O matrix. Surprisingly, the delithiated product was not Fe<sub>2</sub>O<sub>3</sub> but FeO, accounting for the irreversible electrochemical process and the large capacity fading of the anode material in the first cycle. The charge–discharge processes of Fe<sub>2</sub>O<sub>3</sub> in LIBs are different from previously recognized mechanism, and are found to be a fully reversible electrochemical phase conversion between Fe and FeO nanograins accompanying the formation and disappearance of the Li<sub>2</sub>O layer. The macroscopic electrochemical performance of Fe<sub>2</sub>O<sub>3</sub>/graphene was further correlated with the microcosmic <i>in situ</i> TEM results
In Situ Transmission Electron Microscopy Observation of the Lithiation–Delithiation Conversion Behavior of CuO/Graphene Anode
The electrochemical conversion behavior
of metal oxides as well
as its influence on the lithium-storage performance remains unclear.
In this paper, we studied the dynamic electrochemical conversion process
of CuO/graphene as anode by in situ transmission electron microscopy.
The microscopic conversion behavior of the electrode was further correlated
with its macroscopic lithium-storage properties. During the first
lithiation, the porous CuO nanoparticles transformed to numerous Cu
nanograins (2–3 nm) embedded in Li<sub>2</sub>O matrix. The
porous spaces were found to be favorable for accommodating the volume
expansion during lithium insertion. Two types of irreversible processes
were revealed during the lithiation–delithiation cycles. First,
the nature of the charge–discharge process of CuO anode is
a reversible phase conversion between Cu<sub>2</sub>O and Cu nanograins.
The delithiation reaction cannot recover the electrode to its pristine
structure (CuO), which is responsible for about ∼55% of the
capacity fading in the first cycle. Second, there is a severe nanograin
aggregation during the initial conversion cycles, which leads to low
Coulombic efficiency. This finding could also account for the electrochemical
behaviors of other transition metal oxide anodes that operate with
similar electrochemical conversion mechanism
<i>In Situ</i> Transmission Electron Microscopy Observation of the Conversion Mechanism of Fe<sub>2</sub>O<sub>3</sub>/Graphene Anode during Lithiation–Delithiation Processes
Transition metal oxides have attracted tremendous attention as anode materials for lithium ion batteries (LIBs) recently. However, their electrochemical processes and fundamental mechanisms remain unclear. Here we report the direct observation of the dynamic behaviors and the conversion mechanism of Fe<sub>2</sub>O<sub>3</sub>/graphene in LIBs by <i>in situ</i> transmission electron microscopy (TEM). Upon lithiation, the Fe<sub>2</sub>O<sub>3</sub> nanoparticles showed obvious volume expansion and morphological changes, and the surfaces of the electrode were covered by a nanocrystalline Li<sub>2</sub>O layer. Single-crystalline Fe<sub>2</sub>O<sub>3</sub> nanoparticles were found to transform to multicrystalline nanoparticles consisting of many Fe nanograins embedded in Li<sub>2</sub>O matrix. Surprisingly, the delithiated product was not Fe<sub>2</sub>O<sub>3</sub> but FeO, accounting for the irreversible electrochemical process and the large capacity fading of the anode material in the first cycle. The charge–discharge processes of Fe<sub>2</sub>O<sub>3</sub> in LIBs are different from previously recognized mechanism, and are found to be a fully reversible electrochemical phase conversion between Fe and FeO nanograins accompanying the formation and disappearance of the Li<sub>2</sub>O layer. The macroscopic electrochemical performance of Fe<sub>2</sub>O<sub>3</sub>/graphene was further correlated with the microcosmic <i>in situ</i> TEM results
<i>In Situ</i> Transmission Electron Microscopy Observation of the Conversion Mechanism of Fe<sub>2</sub>O<sub>3</sub>/Graphene Anode during Lithiation–Delithiation Processes
Transition metal oxides have attracted tremendous attention as anode materials for lithium ion batteries (LIBs) recently. However, their electrochemical processes and fundamental mechanisms remain unclear. Here we report the direct observation of the dynamic behaviors and the conversion mechanism of Fe<sub>2</sub>O<sub>3</sub>/graphene in LIBs by <i>in situ</i> transmission electron microscopy (TEM). Upon lithiation, the Fe<sub>2</sub>O<sub>3</sub> nanoparticles showed obvious volume expansion and morphological changes, and the surfaces of the electrode were covered by a nanocrystalline Li<sub>2</sub>O layer. Single-crystalline Fe<sub>2</sub>O<sub>3</sub> nanoparticles were found to transform to multicrystalline nanoparticles consisting of many Fe nanograins embedded in Li<sub>2</sub>O matrix. Surprisingly, the delithiated product was not Fe<sub>2</sub>O<sub>3</sub> but FeO, accounting for the irreversible electrochemical process and the large capacity fading of the anode material in the first cycle. The charge–discharge processes of Fe<sub>2</sub>O<sub>3</sub> in LIBs are different from previously recognized mechanism, and are found to be a fully reversible electrochemical phase conversion between Fe and FeO nanograins accompanying the formation and disappearance of the Li<sub>2</sub>O layer. The macroscopic electrochemical performance of Fe<sub>2</sub>O<sub>3</sub>/graphene was further correlated with the microcosmic <i>in situ</i> TEM results
<i>In Situ</i> Transmission Electron Microscopy Observation of the Conversion Mechanism of Fe<sub>2</sub>O<sub>3</sub>/Graphene Anode during Lithiation–Delithiation Processes
Transition metal oxides have attracted tremendous attention as anode materials for lithium ion batteries (LIBs) recently. However, their electrochemical processes and fundamental mechanisms remain unclear. Here we report the direct observation of the dynamic behaviors and the conversion mechanism of Fe<sub>2</sub>O<sub>3</sub>/graphene in LIBs by <i>in situ</i> transmission electron microscopy (TEM). Upon lithiation, the Fe<sub>2</sub>O<sub>3</sub> nanoparticles showed obvious volume expansion and morphological changes, and the surfaces of the electrode were covered by a nanocrystalline Li<sub>2</sub>O layer. Single-crystalline Fe<sub>2</sub>O<sub>3</sub> nanoparticles were found to transform to multicrystalline nanoparticles consisting of many Fe nanograins embedded in Li<sub>2</sub>O matrix. Surprisingly, the delithiated product was not Fe<sub>2</sub>O<sub>3</sub> but FeO, accounting for the irreversible electrochemical process and the large capacity fading of the anode material in the first cycle. The charge–discharge processes of Fe<sub>2</sub>O<sub>3</sub> in LIBs are different from previously recognized mechanism, and are found to be a fully reversible electrochemical phase conversion between Fe and FeO nanograins accompanying the formation and disappearance of the Li<sub>2</sub>O layer. The macroscopic electrochemical performance of Fe<sub>2</sub>O<sub>3</sub>/graphene was further correlated with the microcosmic <i>in situ</i> TEM results
Magnetic and Quantum Transport Properties of Small-Sized Transition-Metal-Pentalene Sandwich Cluster
The chemical bonds and magnetic and
quantum transport properties
of small-sized transition-metal-pentalene sandwich clusters TM<sub>2<i>n</i></sub>Pn<sub><i>n</i>+1</sub> (TM =
V, Cr, Mn, Co, and Ni; <i>n</i> = 1, 2) were investigated
by using density functional theory and nonequilibrium Green’s
function method. Theoretical results show that TM<sub>2<i>n</i></sub>Pn<sub><i>n</i>+1</sub> sandwiches have high stabilities.
The TM–TM bond order gradually decreases with the increase
of 3d electron number of TM atoms and TM<sub>2<i>n</i></sub>Pn<sub><i>n</i>+1</sub> could exhibit different spin states.
With Au as two electrodes, significant spin-filter capability was
observed in TM<sub>2<i>n</i></sub>Pn<sub><i>n</i>+1</sub>, and such a filter can be switched on/off by changing the
spin state. In addition, giant magnetoresistance was also found in
the systems. These interesting quantum transport properties indicate
that TM<sub>2<i>n</i></sub>Pn<sub><i>n</i>+1</sub> sandwiches are promising materials for designing molecular junction
with different functions
In Situ Transmission Electron Microscopy Observation of Electrochemical Behavior of CoS<sub>2</sub> in Lithium-Ion Battery
Metal sulfides are a type of potential anode materials for lithium-ion batteries (LIBs). However, their electrochemical behaviors and mechanism during the charge and discharge process remain unclear. In the present paper, we use CoS<sub>2</sub> as a model material to investigate their electrochemical process using in situ transmission electron microscopy (TEM). Two kinds of reaction behaviors are revealed. The pure CoS<sub>2</sub> particles show a side-to-side conversion process, in which large and anisotropic size expansion (47.1%) occurs that results in the formation of cracks and fractures in CoS<sub>2</sub> particles. In contrast, the CoS<sub>2</sub> particles anchored on reduced graphene oxide (rGO) sheets exhibit a core–shell conversion process involving small and homogeneous size expansion (28.6%) and few fractures, which attributes to the excellent Li<sup>+</sup> conductivity of rGO sheets and accounts for the improved cyclability. Single-crystalline CoS<sub>2</sub> particle converts to Co nanocrystals of 1–2 nm embedded within Li<sub>2</sub>S matrix after the first lithiation. The subsequent electrochemical reaction is a reversible phase conversion between Co/Li<sub>2</sub>S and CoS<sub>2</sub> nanocrystals. Our direct observations provide important mechanistic insight for developing high-performance conversion electrodes for LIBs
Microstructure Evolution and Conversion Mechanism of Mn<sub>3</sub>O<sub>4</sub> under Electrochemical Cyclings
Probing the microstructure evolution,
phase change, and fundamental conversion mechanism of anodes for lithium
ion batteries (LIBs) during lithiation–delithiation cycles
is important to gain insights into understanding how the electrode
works and thus how it can be improved. The electrochemical reaction
and phase evolution of Mn<sub>3</sub>O<sub>4</sub> during lithiation–delithiation
cycles remain unknown. To observe the real-time electrochemical behaviors
of Mn<sub>3</sub>O<sub>4</sub> during lithiation–delithiation
cycles, a nanosized LIB was constructed inside a transmission electron
microscope (TEM) using an individual Mn<sub>3</sub>O<sub>4</sub>/graphene
moiety as the anode. Upon the first lithiation, Mn<sub>3</sub>O<sub>4</sub> nanoparticles are lithiated into the crystallized Mn nanograins
embedded within the Li<sub>2</sub>O matrix. However, Mn and Li<sub>2</sub>O cannot be recovered to the original Mn<sub>3</sub>O<sub>4</sub> phase but to MnO after the first full delithiation, which
results in an irreversible phase transformation. Such incomplete conversion
reaction accounts for the huge capacity fading during the first cycle
of Mn<sub>3</sub>O<sub>4</sub>-based LIBs. Excellent cyclability between
Mn and MnO is also established during the subsequent lithiation–delithiation
cycles, which is beneficial to the capacity retention in real battery.
It provides an in-depth understanding of the phase evolution and conversion
mechanism of Mn<sub>3</sub>O<sub>4</sub> during lithiation–delithiation
and holds the promise of improving the capacity for the development
of durable, high-capacity, and high-rate anodes for LIBs
Microstructure Evolution and Conversion Mechanism of Mn<sub>3</sub>O<sub>4</sub> under Electrochemical Cyclings
Probing the microstructure evolution,
phase change, and fundamental conversion mechanism of anodes for lithium
ion batteries (LIBs) during lithiation–delithiation cycles
is important to gain insights into understanding how the electrode
works and thus how it can be improved. The electrochemical reaction
and phase evolution of Mn<sub>3</sub>O<sub>4</sub> during lithiation–delithiation
cycles remain unknown. To observe the real-time electrochemical behaviors
of Mn<sub>3</sub>O<sub>4</sub> during lithiation–delithiation
cycles, a nanosized LIB was constructed inside a transmission electron
microscope (TEM) using an individual Mn<sub>3</sub>O<sub>4</sub>/graphene
moiety as the anode. Upon the first lithiation, Mn<sub>3</sub>O<sub>4</sub> nanoparticles are lithiated into the crystallized Mn nanograins
embedded within the Li<sub>2</sub>O matrix. However, Mn and Li<sub>2</sub>O cannot be recovered to the original Mn<sub>3</sub>O<sub>4</sub> phase but to MnO after the first full delithiation, which
results in an irreversible phase transformation. Such incomplete conversion
reaction accounts for the huge capacity fading during the first cycle
of Mn<sub>3</sub>O<sub>4</sub>-based LIBs. Excellent cyclability between
Mn and MnO is also established during the subsequent lithiation–delithiation
cycles, which is beneficial to the capacity retention in real battery.
It provides an in-depth understanding of the phase evolution and conversion
mechanism of Mn<sub>3</sub>O<sub>4</sub> during lithiation–delithiation
and holds the promise of improving the capacity for the development
of durable, high-capacity, and high-rate anodes for LIBs
Microstructure Evolution and Conversion Mechanism of Mn<sub>3</sub>O<sub>4</sub> under Electrochemical Cyclings
Probing the microstructure evolution,
phase change, and fundamental conversion mechanism of anodes for lithium
ion batteries (LIBs) during lithiation–delithiation cycles
is important to gain insights into understanding how the electrode
works and thus how it can be improved. The electrochemical reaction
and phase evolution of Mn<sub>3</sub>O<sub>4</sub> during lithiation–delithiation
cycles remain unknown. To observe the real-time electrochemical behaviors
of Mn<sub>3</sub>O<sub>4</sub> during lithiation–delithiation
cycles, a nanosized LIB was constructed inside a transmission electron
microscope (TEM) using an individual Mn<sub>3</sub>O<sub>4</sub>/graphene
moiety as the anode. Upon the first lithiation, Mn<sub>3</sub>O<sub>4</sub> nanoparticles are lithiated into the crystallized Mn nanograins
embedded within the Li<sub>2</sub>O matrix. However, Mn and Li<sub>2</sub>O cannot be recovered to the original Mn<sub>3</sub>O<sub>4</sub> phase but to MnO after the first full delithiation, which
results in an irreversible phase transformation. Such incomplete conversion
reaction accounts for the huge capacity fading during the first cycle
of Mn<sub>3</sub>O<sub>4</sub>-based LIBs. Excellent cyclability between
Mn and MnO is also established during the subsequent lithiation–delithiation
cycles, which is beneficial to the capacity retention in real battery.
It provides an in-depth understanding of the phase evolution and conversion
mechanism of Mn<sub>3</sub>O<sub>4</sub> during lithiation–delithiation
and holds the promise of improving the capacity for the development
of durable, high-capacity, and high-rate anodes for LIBs