Lightweight Carbon-Metal-Based Fabric Anode for Lithium-Ion Batteries.

Lithium-ion battery electrodes are typically manufactured via slurry casting, which involves mixing active material particles, conductive carbon, and a polymeric binder in a solvent, followed by casting and drying the coating on current collectors (Al or Cu). These electrodes are functional but still limited in terms of pore network percolation, electronic connectivity, and mechanical stability, leading to poor electron/ion conductivities and mechanical integrity upon cycling, which result in battery degradation. To address this, we fabricate trichome-like carbon-iron fabrics via a combination of electrospinning and pyrolysis. Compared with slurry cast Fe2O3 and graphite-based electrodes, the carbon-iron fabric (CMF) electrode provides enhanced high-rate capacity (10C and above) and stability, for both half cell and full cell testing (the latter with a standard lithium nickel manganese oxide (LNMO) cathode). Further, the CMFs are free-standing and lightweight; therefore, future investigation may include scaling this as an anode material for pouch cells and 18,650 cylindrical batteries.

Monitoring state of charge and volume expansion in lithium-ion batteries: an approach using surface mounted thin-film graphene sensors.

Accurate monitoring of battery cell state of charge (SoC) and state of health (SoH) is vital to the safe and effective operation of rechargeable battery systems such as those in electric vehicles yet remains a challenge while the system is in use. A new surface-mounted sensor enabling simple and rapid monitoring of lithium-ion battery cell SoC and SoH is demonstrated. Small changes in cell volume brought about by the expansion and contraction of electrode materials during charge and discharge are detected through monitoring the changes in electrical resistance of a graphene film in the sensor. The relationship between sensor resistance and cell SoC/voltage was extracted, enabling rapid SoC determination without interruption to cell operation. The sensor was also capable of detecting early indications of irreversible cell expansion due to common cell failure modes, enabling mitigating steps to be taken to avoid catastrophic cell failure.

Enhancing the performance of germanium nanowire anodes for Li-ion batteries by direct growth on textured copper.

Herein, textured Cu foil is presented as an attractive current collector substrate for directly grown Ge nanowire (NW) anodes. Compared to planar stainless steel (SS) current collectors, textured Cu led to an increase in achievable mass loading, removal of the requirement for a catalyst deposition step, improved adhesion of the active material and dramatically enhanced capacity retention. When SS and textured Cu foil based anodes with similar areal loadings (∼1.4 mA h cm-2) were compared, the capacity after 250 cycles for textured Cu was 2.7 times higher than the SS anode, illustrating the key role of the current collector.

Axial Si-Ge Heterostructure Nanowires as Lithium-Ion Battery Anodes.

Here, we report the application of axially heterostructured nanowires consisting of alternating segments of silicon and germanium with a tin seed as lithium-ion battery anodes. During repeated lithiation and delithiation, the heterostructures completely rearrange into a porous network of homogeneously alloyed Si1- xGe x ligaments. The transformation was characterized through ex situ TEM, STEM, and Raman spectroscopy. Electrochemical analysis was conducted on the heterostructure nanowires with discharge capacities in excess of 1180 mAh/g for 400 cycles (C/5) and capacities of up to 613 mAh/g exhibited at a rate of 10 C.

Investigation into the Selenization Mechanisms of Wurtzite CZTS Nanorods.

Here, we report the first detailed investigation into the selenization mechanism of thin films of wurtzite copper zinc tin sulfide (CZTS) nanorods (NRs), giving particular emphasis to the role of the long-chain organic ligands surrounding each NR. During selenization, the NRs undergo a selenium-mediated phase change from wurtzite to kesterite, concurrent with the replacement of sulfur with selenium in the lattice and in situ grain growth, along with the recrystallization of larger copper zinc tin selenide kesterite grains on top of the existing film. By utilizing a facile ligand removal technique, we demonstrate that the formation of a large-grain overlayer is achievable without the presence of ligands. In addition, we demonstrate an elegant ligand-exchange-based method for controlling the thickness of the fine-grain layer. This report emphasizes the key role played by ligands in determining the structural evolution of CZTS nanocrystal films during selenization, necessitating the identification of optimal ligand chemistries and processing conditions for desirable grain growth.

Complete assembly of Cu2ZnSnS4 (CZTS) nanorods at substrate interfaces using a combination of self and directed organisation.

Here we report the two-stage assembly of semiconductor nanorods at substrates. The nanorods preassemble into 2D discs by self-organisation and these discs are deposited into conformal layers at substrates using electric field assembly. The intermediate self-assembly step can be eliminated by carrying out a judicious ligand exchange allowing selectivity for dimensional control of layer formation from nanorod building blocks in one two and three dimensions.