3 research outputs found
Spinodal Decomposition Method for Structuring Germanium–Carbon Li-Ion Battery Anodes
To increase the energy density of lithium-ion batteries
(LIBs),
high-capacity anodes which alloy with Li ions at a low voltage against
Li/Li+ have been actively pursued. So far, Si has been
studied the most extensively because of its high specific capacity
and cost efficiency; however, Ge is an interesting alternative. While
the theoretical specific capacity of Ge (1600 mAh g–1) is only half that of Si, its density is more than twice as high
(Ge, 5.3 g cm–3; Si, 2.33 g cm–3), and therefore the charge stored per volume is better than that
of Si. In addition, Ge has a 400 times higher ionic diffusivity and
4 orders of magnitude higher electronic conductivity compared to Si.
However, similarly to Si, Ge needs to be structured in order to manage
stresses induced during lithiation and many reports have achieved
sufficient areal loadings to be commercially viable. In this work,
spinodal decomposition is used to make secondary particles of about
2 μm in diameter that consist of a mixture of ∼30 nm
Ge nanoparticles embedded in a carbon matrix. The secondary structure
of these germanium–carbon particles allows for specific capacities
of over 1100 mAh g−1 and a capacity retention of
91.8% after 100 cycles. Finally, high packing densities of ∼1.67
g cm–3 are achieved in blended electrodes by creating
a bimodal size distribution with natural graphite
Does Heat Play a Role in the Observed Behavior of Aqueous Photobatteries?
Light-rechargeable photobatteries have emerged as an
elegant solution
to address the intermittency of solar irradiation by harvesting and
storing solar energy directly through a battery electrode. Recently,
a number of compact two-electrode photobatteries have been proposed,
showing increases in capacity and open-circuit voltage upon illumination.
Here, we analyze the thermal contributions to this increase in capacity
under galvanostatic and photocharging conditions in two promising
photoactive cathode materials, V2O5 and LiMn2O4. We propose an improved cell and experimental
design and perform temperature-controlled photoelectrochemical measurements
using these materials as photocathodes. We show that the photoenhanced
capacities of these materials under 1 sun irradiation can be attributed
mostly to thermal effects. Using operando reflection
spectroscopy, we show that the spectral behavior of the photocathode
changes as a function of the state of charge, resulting in changing
optical absorption properties. Through this technique, we show that
the band gap of V2O5 vanishes after continued
zinc ion intercalation, making it unsuitable as a photocathode beyond
a certain discharge voltage. These results and experimental techniques
will enable the rational selection and testing of materials for next-generation
photo-rechargeable systems
Does Heat Play a Role in the Observed Behavior of Aqueous Photobatteries?
Light-rechargeable photobatteries have emerged as an
elegant solution
to address the intermittency of solar irradiation by harvesting and
storing solar energy directly through a battery electrode. Recently,
a number of compact two-electrode photobatteries have been proposed,
showing increases in capacity and open-circuit voltage upon illumination.
Here, we analyze the thermal contributions to this increase in capacity
under galvanostatic and photocharging conditions in two promising
photoactive cathode materials, V2O5 and LiMn2O4. We propose an improved cell and experimental
design and perform temperature-controlled photoelectrochemical measurements
using these materials as photocathodes. We show that the photoenhanced
capacities of these materials under 1 sun irradiation can be attributed
mostly to thermal effects. Using operando reflection
spectroscopy, we show that the spectral behavior of the photocathode
changes as a function of the state of charge, resulting in changing
optical absorption properties. Through this technique, we show that
the band gap of V2O5 vanishes after continued
zinc ion intercalation, making it unsuitable as a photocathode beyond
a certain discharge voltage. These results and experimental techniques
will enable the rational selection and testing of materials for next-generation
photo-rechargeable systems