A scalable and cost‐effective process is used to electroplate metallic Zn seeds on stainless steel substrates. Si and Ge nanowires (NWs) are subsequently grown by placing the electroplated substrates in the solution phase of a refluxing organic solvent at temperatures >430 °C and injecting the respective liquid precursors. The native oxide layer formed on reactive metals such as Zn can obstruct NW growth and is removed in situ by injecting the reducing agent LiBH4. The findings show that the use of Zn as a catalyst produces defect‐rich Si NWs that can be extended to the synthesis of Si–Ge axial heterostructure NWs with an atomically abrupt Si–Ge interface. As an anode material, the as grown Zn seeded Si NWs yield an initial discharge capacity of 1772 mAh g−1 and a high capacity retention of 85% after 100 cycles with the active participation of both Si and Zn during cycling. Notably, the Zn seeds actively participate in the Li‐cycling activities by incorporating into the Si NWs body via a Li‐assisted welding process, resulting in restructuring the NWs into a highly porous network structure that maintains a stable cycling performance.
expansion during charge (300% when fully lithiated). [9][10][11][12][13] The build-up of mechanical stress through expansion of the active layer causes a loss of electrical contact with the non-expanding current collector, exacerbating capacity fade. Nanostructuring can alleviate mechanical stress build-up through smaller particle sizes, structural porosity and void spaces. [9,10] Nanoparticles (NPs), [14][15][16][17] nanowires (NWs), [18][19][20][21][22][23][24][25] and nanotubes (NTs) [26][27][28][29] are the most widely used morphologies, allowing for structural relaxation through shortened diffusion channels, increased porosity and larger surface area to volume ratios.Cu is the optimal current collector for lithium-ion battery anodes, due to its superior electrical conductivity over stainless steel (SS) and other carbon-based substrates. However, direct growth of Si on Cu yields electrochemically inactive CuSi compounds. [30][31][32] Alternatively, slurry-based Si electrodes suffer from issues of capacity fade as harsh expansion leads to electrical contact loss with the current collector. [33][34][35] Also, issues of capacity fade are heightened for thicker slurry layers, behaving similarly to bulk Si. [36,37] Si composites with graphite have gained huge popularity over recent years, synergistically combining the high lithiation capacity of Si with the low cost, stability, and scalability of carbon. [38][39][40][41][42] Graphite incorporation can alleviate instability issues common with Si-rich electrodes. [43,44] Karuppiah et al. demonstrated impressive long-term stability of slurry-based electrodes of Si NWs directly grown on graphite, retaining 87% capacity after 250 cycles versus Li metal. [44] Similarly, Datta et al. found that Si/graphite stability could be further enhanced through amorphous carbon coating, removing direct contact between Si and the electrolyte, and delivering a stable capacity of 660 mAh g −1 . [45] Slurry-based composites allow for high achievable Si loadings while maintaining anode stability. However, thick slurry layers suffer from poor fast-rate performance and inactive slurry additions negatively impact energy density. [46][47][48][49] The incorporation of Si into metallic or carbonbased frameworks like Mxenes, [50,51] graphene, [52,53] CNTs, [54,55] and CNFs [56,57] has allowed considerable improvements in cell stability, although the continued presence of inactive slurry components increases dead weight. Directly grown electrodes offer a multitude of advantages over slurry-based configurations, however, achieving stable performance of high loading binder-free Si electrodes has historically been difficult.High loading (>1.6 mg cm −2 ) of Si nanowires (NWs) is achieved by seeding the growth from a dense array of Cu 15 Si 4 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 bolst...
Here we report the use of 1D SixGe1-x (x = 0.25, 0.5, 0.75) alloy nanowires (NWs) as anode materials for Na-ion batteries (NIB). The strategy involves the synthesis of crystalline...
The electrochemical performance of Ge, an alloying anode in the form of directly grown nanowires (NWs), in Li-ion full cells (vs LiCoO 2 ) was analyzed over a wide temperature range (−40 to 40 °C). LiCoO 2 ||Ge cells in a standard electrolyte exhibited specific capacities 30× and 50× those of LiCoO 2 ||C cells at −20 and −40 °C, respectively. We further show that propylene carbonate addition further improved the low-temperature performance of LiCoO 2 ||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 LiCoO 2 ||C cells did not allow for any gains in performance. Interestingly, the capacity retention of LiCoO 2 ||Ge improved at low temperatures due to delayed amorphization of crystalline NWs, suppressing complete lithiation and high-order Li 15 Ge 4 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.
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