RESUMEN
Germanium nanowire (GeNW) electrodes have shown great promise as high-power, fast-charging alternatives to silicon-based electrodes, owing to their vastly improved Li ion diffusion, electron mobility and ionic conductivity. Formation of the solid electrolyte interphase (SEI) on the anode surface is critical to electrode performance and stability but is not completely understood for NW anodes. Here, a systematic study characterizing pristine and cycled GeNWs in charged and discharged states with SEI layer present and removed is performed using Kelvin probe force microscopy in air. Correlating changes in the morphology of the GeNW anodes with contact potential difference mapping at different cycles provides insight into SEI layer formation and growth, and the effect of the SEI on battery performance.
RESUMEN
The electrochemical performance of Ge, an alloying anode in the form of directly grown nanowires (NWs), in Li-ion full cells (vs LiCoO2) was analyzed over a wide temperature range (-40 to 40 °C). LiCoO2||Ge cells in a standard electrolyte exhibited specific capacities 30× and 50× those of LiCoO2||C cells at -20 and -40 °C, respectively. We further show that propylene carbonate addition further improved the low-temperature performance of LiCoO2||Ge cells, achieving a specific capacity of 1091 mA h g-1 after 400 cycles when charged/discharged at -20 °C. At 40 °C, an additive mixture of ethyl methyl carbonate and lithium bis(oxalato)borate stabilized the capacity fade from 0.22 to 0.07% cycle-1. Similar electrolyte additives in LiCoO2||C cells did not allow for any gains in performance. Interestingly, the capacity retention of LiCoO2||Ge improved at low temperatures due to delayed amorphization of crystalline NWs, suppressing complete lithiation and high-order Li15Ge4 phase formation. The results show that alloying anodes in suitably configured electrolytes can deliver high performance at the extremes of temperature ranges where electric vehicles operate, conditions that are currently not viable for commercial batteries without energy-inefficient temperature regulation.
RESUMEN
High loading (>1.6 mg cm-2 ) of Si nanowires (NWs) is achieved by seeding the growth from a dense array of Cu15 Si4 NWs using tin seeds. A one-pot synthetic approach involves the direct growth of CuSi NWs on Cu foil that acts as a textured surface for Sn adhesion and Si NW nucleation. The high achievable Si NW loading is enabled by the high surface area of CuSi NWs and bolstered by secondary growth of Si NWs as branches from both Si and CuSi NW stems, forming a dense Si active layer, interconnected with an electrically conducting CuSi array (denoted Si/CuSi). When employed as Li-ion battery anodes, the Si/CuSi nest structure demonstrates impressive rate performance, reaching 4.1 mAh cm-2 at C/20, 3.1 mAh cm-2 at C/5, and 0.8 mAh cm-2 at 6C. Also, Si/CuSi shows remarkable long-term stability, delivering a stable areal capacity of 2.2 mAh cm-2 after 300 cycles. Overall, complete anode fabrication is achieved within a single reaction by employing an inexpensive Sn powder approach.
RESUMEN
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 (â¼1.4 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.
