Electrochemical stability of electrospun silicon/carbon nanofiber anode materials: a review

Silicon (Si) is regarded as a promising anode material owing to its high specific capacity and low lithiation potential. The large volume change and the pulverization of silicon during the lithiation/delithiation process hinder its direct energy storage application. This review focuses on the electrospun silicon/carbon (Si/C) nanofiber anode materials for lithium-ion batteries for long-term stable energy storage. Silicon is completely embedded in electrospinning-based carbon nanofibers to form electrospun Si/C nanofibers. It not only creates pore space to buffer silicon volume expansion, but also prevents direct contact between silicon and the electrolyte, consequently forming a stable solid electrolyte interface film. The electrospun Si/C nanofibers solve the pulverization issue of silicon to achieve improved cycling stability. Furthermore, the electrospun carbon nanofibers form a flexible conductive network for surrounding silicon by facilely introducing sacrificial polymers or template agents. The electrospun Si/C nanofibers ultimately promote the lithium-ion transport to achieve rate stability. The silicon source selection and microstructure regulation of the electrospun Si/C nanofibers are overviewed. The silicon sources include the direct utilization of silicon or silicon oxide particles as well as the indirect conversion of silicon-based precursors. The cycling stability regulation of various metal- and metal oxide-modified silicon composites and heterogeneous carbon material-decorated electrospun Si/C nanofibers is summarized. In addition, the microstructure designs of the electrospun Si/C nanofibers associated with the improvement of long-term capacity retention are overviewed. The main challenges in the electrospun Si/C nanofiber anode materials are summarized, and the future perspectives are also proposed.

Scalable Synthesis of SiOx-TiON Composite As an Ultrastable Anode for Li-Ion Half/Full Batteries

Among various anode materials, SiOx is regarded as the next generation of promising anode due to its advantages of high theoretical capacity with 2680 mA h g-1, low lithium voltage platform, and rich natural resources. However, the pure SiOx-based materials have slow lithium storage kinetics attributed to their low electron/ion conductive properties and the large volume change during lithiation/delithiation, restricting their practical application. Optimizing the SiOx material structures and the fabricating methods to mitigate these fatal defects and adapt to the market demand for energy density is critical. Hence, SiOx material with TiO1-xNx phase modification has been prepared by simple, low-cost, and scalable ball milling and then combined with nitridation. Consequently, based on the TiO1-xNx modified layer, which boosts high ionic/electronic conductivity, chemical stability, and excellent mechanical properties, the SiOx@TON-10 electrode shows highly stable lithium-ion storage performance for lithium-ion half/full batteries due to a stable solid-electrolyte interface layer, fast Li+ transport channel, and alleviative volumetric expansion, further verifying its practical feasibility and universal applicability.

Flexible electrodes with high areal capacity based on electrospun fiber mats

The ever-growing portable, flexible, and wearable devices impose new requirements from power sources. In contrast to gravitational metrics, areal metrics are more reliable performance indicators of energy storage systems for portable and wearable devices. For energy storage devices with high areal metrics, a high mass loading of the active species is generally required, which imposes formidable challenges on the current electrode fabrication technology. In this regard, integrated electrodes made by electrospinning technology have attracted increasing attention due to their high controllability, excellent mechanical strength, and flexibility. In addition, electrospun electrodes avoid the use of current collectors, conductive additives, and polymer binders, which can essentially increase the content of the active species in the electrodes as well as reduce the unnecessary physically contacted interfaces. In this review, the electrospinning technology for fabricating flexible and high areal capacity electrodes is first highlighted by comparing with the typical methods for this purpose. Then, the principles of electrospinning technology and the recent progress of electrospun electrodes with high areal capacity and flexibility are elaborately discussed. Finally, we address the future perspectives for the construction of high areal capacity electrodes using electrospinning technology to meet the increasing demands of flexible energy storage systems.

Tunable Synthesis of Hierarchical Yolk/Double-Shelled SiOx @TiO2 @C Nanospheres for High-Performance Lithium-Ion Batteries

This work reports the preparation of unique hierarchical yolk/double-shelled SiO_x @TiO₂ @C nanospheres with different voids by a facile sol-gel method combined with carbon coating. In the preparation process, SiO_x nanosphere is used as a hard template. Etch time of SiO_x yolk affects the morphology and electrochemical performance of SiO_x @TiO₂ @C. With the increase in etch time, the yolk/double-shelled SiO_x @TiO₂ @C with 15 and 30 nm voids and the TiO₂ @C hollow nanospheres are obtained. The yolk/double-shelled SiO_x @TiO₂ @C nanospheres exhibit remarkable lithium-ion battery performance as anodes, including high lithium storage capacity, outstanding rate capability, good reversibility, and stable long-term cycle life. The unique structure can accommodate the large volume change of the SiO_x yolk, provide a unique buffering space for the discharge/charge processes, improve the structural stability of the electrode material during repeated Li⁺ intercalation/deintercalation processes, and enhance the cycling stability. The SiO_x @TiO₂ @C with 30 nm void space exhibits a high discharge specific capacity of ≈1195.4 mA h g^-1 at the current density of 0.1 A g^-1 after 300 cycles and ≈701.1 mA h g^-1 at 1 A g^-1 for over 800 cycles. These results suggest that the proposed particle architecture is promising and may have potential applications in improving various high performance anode materials.

Carbon coated SiO nanoparticles embedded in hierarchical porous N-doped carbon nanosheets for enhanced lithium storage

Carbon coated SiO nanoparticles embedded in N-doped carbon nanosheets were synthesized via a scalable and cost-effective route, and exhibited enhanced cyclability and rate capability as an anode for lithium-ion batteries.