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Crystalline-Amorphous Core−Shell Silicon Nanowires for High Capacity and High Current Battery Electrodes
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2008
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Silicon NanowiresEngineeringHigh CapacityChemical EngineeringCore-shell NanowiresNanoelectronicsSodium BatteryMaterials ScienceElectrical EngineeringLarge Volume ChangeBattery Electrode MaterialsNanotechnologyAdvanced Electrode MaterialLithium-ion BatteryLithium-ion BatteriesEnergy StorageSolid-state BatteryElectrochemistryElectric BatteryApplied PhysicsCathode MaterialsElectrochemical Energy StorageBatteriesAnode Materials
Silicon offers the highest known anode capacity (~4200 mAh g⁻¹) but its large volume change during lithiation causes pulverization and capacity fading, limiting practical use. The study proposes nanoscale hierarchical core‑shell silicon nanowires as a novel strategy to mitigate these volume‑change issues. Silicon crystalline‑amorphous core‑shell nanowires were synthesized in a single step on stainless‑steel collectors, with crystalline cores providing mechanical support and conductivity and amorphous shells serving as Li⁺ storage sites. The resulting electrodes deliver ~1000 mAh g⁻¹ with ~90 % capacity retention after 100 cycles and achieve high‑rate performance of 6.8 A g⁻¹, roughly 20× that of carbon at a 1 h rate.
Silicon is an attractive alloy-type anode material for lithium ion batteries because of its highest known capacity (4200 mAh/g). However silicon's large volume change upon lithium insertion and extraction, which causes pulverization and capacity fading, has limited its applications. Designing nanoscale hierarchical structures is a novel approach to address the issues associated with the large volume changes. In this letter, we introduce a core-shell design of silicon nanowires for highpower and long-life lithium battery electrodes. Silicon crystalline-amorphous core-shell nanowires were grown directly on stainless steel current collectors by a simple one-step synthesis. Amorphous Si shells instead of crystalline Si cores can be selected to be electrochemically active due to the difference of their lithiation potentials. Therefore, crystalline Si cores function as a stable mechanical support and an efficient electrical conducting pathway while amorphous shells store Li(+) ions. We demonstrate here that these core-shell nanowires have high charge storage capacity ( approximately 1000 mAh/g, 3 times of carbon) with approximately 90% capacity retention over 100 cycles. They also show excellent electrochemical performance at high rate charging and discharging (6.8 A/g, approximately 20 times of carbon at 1 h rate).