Cu-Substituted NiF₂ as a Cathode Material for Li-Ion Batteries

Metal fluorides usually have a large electronegativity and are promising electrode materials for high-power lithium-ion batteries. However, like other conversion-reaction-based materials, large volumetric expansions and large capacity losses in cycling are the major issues for metal fluorides. Here, we explore substitution of Ni with Cu for binary NiF2 and its effects on the electrochemical properties. By in situ transmission electron microscopy, the structural evolutions of several ternary metal fluorides with different Cu/Ni ratios are observed and correlated with their electrochemical properties. With increased Cu substitution from 0 to 25 wt %, the areal expansion during the first lithiation is reduced. Meanwhile, the fluorine loss (due to reaction irreversibility) in the delithiation cycle is also reduced. This provides an explanation for the advantage of Cu substitution for improved cycling stability and capacity. We believe that our observations provide insight into the development of better ternary metal fluorides as cathodes for high power density lithium-ion batteries

Cu-Substituted NiF₂ as a Cathode Material for Li-Ion Batteries

Metal fluorides usually have a large electronegativity and are promising electrode materials for high-power lithium-ion batteries. However, like other conversion-reaction-based materials, large volumetric expansions and large capacity losses in cycling are the major issues for metal fluorides. Here, we explore substitution of Ni with Cu for binary NiF2 and its effects on the electrochemical properties. By in situ transmission electron microscopy, the structural evolutions of several ternary metal fluorides with different Cu/Ni ratios are observed and correlated with their electrochemical properties. With increased Cu substitution from 0 to 25 wt %, the areal expansion during the first lithiation is reduced. Meanwhile, the fluorine loss (due to reaction irreversibility) in the delithiation cycle is also reduced. This provides an explanation for the advantage of Cu substitution for improved cycling stability and capacity. We believe that our observations provide insight into the development of better ternary metal fluorides as cathodes for high power density lithium-ion batteries

Cu-Substituted NiF₂ as a Cathode Material for Li-Ion Batteries

Metal fluorides usually have a large electronegativity and are promising electrode materials for high-power lithium-ion batteries. However, like other conversion-reaction-based materials, large volumetric expansions and large capacity losses in cycling are the major issues for metal fluorides. Here, we explore substitution of Ni with Cu for binary NiF2 and its effects on the electrochemical properties. By in situ transmission electron microscopy, the structural evolutions of several ternary metal fluorides with different Cu/Ni ratios are observed and correlated with their electrochemical properties. With increased Cu substitution from 0 to 25 wt %, the areal expansion during the first lithiation is reduced. Meanwhile, the fluorine loss (due to reaction irreversibility) in the delithiation cycle is also reduced. This provides an explanation for the advantage of Cu substitution for improved cycling stability and capacity. We believe that our observations provide insight into the development of better ternary metal fluorides as cathodes for high power density lithium-ion batteries

Cu-Substituted NiF₂ as a Cathode Material for Li-Ion Batteries

Metal fluorides usually have a large electronegativity and are promising electrode materials for high-power lithium-ion batteries. However, like other conversion-reaction-based materials, large volumetric expansions and large capacity losses in cycling are the major issues for metal fluorides. Here, we explore substitution of Ni with Cu for binary NiF2 and its effects on the electrochemical properties. By in situ transmission electron microscopy, the structural evolutions of several ternary metal fluorides with different Cu/Ni ratios are observed and correlated with their electrochemical properties. With increased Cu substitution from 0 to 25 wt %, the areal expansion during the first lithiation is reduced. Meanwhile, the fluorine loss (due to reaction irreversibility) in the delithiation cycle is also reduced. This provides an explanation for the advantage of Cu substitution for improved cycling stability and capacity. We believe that our observations provide insight into the development of better ternary metal fluorides as cathodes for high power density lithium-ion batteries

Cu-Substituted NiF₂ as a Cathode Material for Li-Ion Batteries

Metal fluorides usually have a large electronegativity and are promising electrode materials for high-power lithium-ion batteries. However, like other conversion-reaction-based materials, large volumetric expansions and large capacity losses in cycling are the major issues for metal fluorides. Here, we explore substitution of Ni with Cu for binary NiF2 and its effects on the electrochemical properties. By in situ transmission electron microscopy, the structural evolutions of several ternary metal fluorides with different Cu/Ni ratios are observed and correlated with their electrochemical properties. With increased Cu substitution from 0 to 25 wt %, the areal expansion during the first lithiation is reduced. Meanwhile, the fluorine loss (due to reaction irreversibility) in the delithiation cycle is also reduced. This provides an explanation for the advantage of Cu substitution for improved cycling stability and capacity. We believe that our observations provide insight into the development of better ternary metal fluorides as cathodes for high power density lithium-ion batteries

Cu-Substituted NiF₂ as a Cathode Material for Li-Ion Batteries

Metal fluorides usually have a large electronegativity and are promising electrode materials for high-power lithium-ion batteries. However, like other conversion-reaction-based materials, large volumetric expansions and large capacity losses in cycling are the major issues for metal fluorides. Here, we explore substitution of Ni with Cu for binary NiF2 and its effects on the electrochemical properties. By in situ transmission electron microscopy, the structural evolutions of several ternary metal fluorides with different Cu/Ni ratios are observed and correlated with their electrochemical properties. With increased Cu substitution from 0 to 25 wt %, the areal expansion during the first lithiation is reduced. Meanwhile, the fluorine loss (due to reaction irreversibility) in the delithiation cycle is also reduced. This provides an explanation for the advantage of Cu substitution for improved cycling stability and capacity. We believe that our observations provide insight into the development of better ternary metal fluorides as cathodes for high power density lithium-ion batteries

Reversible Photomodulation of Two-Dimensional Electron Gas in LaAlO₃/SrTiO₃ Heterostructures

Long-lived photoinduced conductance changes in LaAlO3/SrTiO3 (LAO/STO) heterostructures enable their use in optoelectronic memory applications. However, it remains challenging to quench the persistent photoconductivity (PPC) instantly and reproducibly, which limits the reversible optoelectronic switching. Herein, we demonstrate a reversible photomodulation of two-dimensional electron gas (2DEG) in LAO/STO heterostructures with high reproducibility. By irradiating UV pulses, the 2DEG at the LAO/STO interface is gradually transformed to the PPC state. Notably, the PPC can be completely removed by water treatment when two key requirements are met: (1) the moderate oxygen deficiency in STO and (2) the minimal band edge fluctuation at the interface. Through our X-ray photoelectron spectroscopy and electrical noise analysis, we reveal that the reproducible change in the conductivity of 2DEG is directly attributed to the surface-driven electron relaxation in the STO. Our results provide a stepping-stone toward developing optically tunable memristive devices based on oxide 2DEG systems

Investigating Series and Parallel Oxide Memtransistors for Tunable Weight Update Properties

Currently, analog in-memory computing, employing memristors into a crossbar array architecture (CAA), is the leading system among available neuromorphic hardware. This study presents a highly tunable synaptic weight update based on a multiterminal memtransistor device as a solution for nonlinear synaptic operations and crosstalk issues in CAA memristors, which are long-standing challenges in neuromorphic hardware applications. To explore an effective device structure for tunable weight update properties, a memtransistor device with a series and parallel structure functioning by interface type and oxygen migration is fabricated using a ZnO channel layer and an amorphous TiO2 memristor. The series memtransistor device exhibits a significant tunable weight update property at the gate knob; thus, it simultaneously can function as a selector (accelerating and inhibiting weight update) in the CAA and tune and ultimately improve the linearity of the potentiation and depression curves. Neuromorphic hardware based on tunable synaptic weight update functions provides advantageous features for accuracy and crosstalk issues. Using the Fashion-MNIST pattern recognition simulation, the tuned weight update properties are obtained by three different write and read condition combinations, and the results are close to ideal accuracy

Exchange Coupling in Soft Magnetic Nanostructures and Its Direct Effect on Their Theranostic Properties

Exchange coupling between hard and soft magnetic materials at the nanoscale exhibits novel or improved physical properties for energy and data storage applications. Recently, exchange coupling has also been explored in core/shell magnetic nanostructures (MNS) composed of hard and soft magnetic spinel ferrites, but applications have been limited in biomedicine due to the presence of “toxic” cobalt based ferrites as hard magnetic component. We report core/shell MNS where both core and shell components are soft magnetic ferrites (Fe₃O₄, MnFe₂O₄, and Zn_0.2Mn_0.8Fe₂O₄) and show that exchange coupling still exists due to the difference in their anisotropy. The physical properties (saturation magnetization, susceptibility, anisotropy, <i>r</i>₂ relaxivity, and specific absorption rate) of core/shell MNS are compared with the same size single phase counterparts which excludes any size dependent effect and gives the direct effect of exchange coupling. After optimization of core and shell components and their proportions, we have shown that a core/shell MNS shows significantly higher contrast enhancement and thermal activation properties than their single phase counterparts due to exchange coupling between core and shell ferrites. Our finding provides a novel way to improve theranostic properties of spinel ferrite based MNS while maintaining their biocompatibility