Recovery of porous silicon from waste crystalline silicon solar panels for high-performance lithium-ion battery anodes

A low-cost and easy-available silicon (Si) feedstock is of great significance for developing high-performance lithium-ion battery (LIB) anode materials. Herein, we employ waste crystalline Si solar panels as silicon raw materials, and transform micro-sized Si (m-Si) into porous Si (p-Si) by an alloying/dealloying approach in molten salt where Li⁺ was first reduced and simultaneously alloyed with m-Si to generate Li-Si alloy at the cathode. Subsequently, the as-prepared Li-Si alloy served as the anode in the same molten salt to release Li⁺ into the molten salt, resulting in the production of p-Si by taking advantage of the volume expansion/contraction effect. In the whole process, Li⁺ was shuttled between the electrodes in molten LiCl-KCl, without consuming Li salt. The obtained p-Si was applied as an anode in a half-type LIBs that delivered a capacity of 2427.7 mAh g^-1 at 1 A g^-1 after 200 cycles with a capacity retention rate of 91.5% (1383.3 mAh g^-1 after 500 cycles). Overall, this work offers a straightforward way to convent waste Si panels to high-performance Si anodes for LIBs, giving retired Si a second life and alleviating greenhouse gas emissions caused by Si production.

Design Strategies of Si/C Composite Anode for Lithium-Ion Batteries

Silicon-based materials that have higher theoretical specific capacity than other conventional anodes, such as carbon materials, Li₂ TiO₃ materials and Sn-based materials, become a hot topic in research of lithium-ion battery (LIB). However, the low conductivity and large volume expansion of silicon-based materials hinders the commercialization of silicon-based materials. Until recent years, these issues are alleviated by the combination of carbon-based materials. In this review, the preparation of Si/C materials by different synthetic methods in the past decade is reviewed along with their respective advantages and disadvantages. In addition, Si/C materials formed by silicon and different carbon-based materials is summarized, where the influences of carbons on the electrochemical performance of silicon are emphasized. Lastly, future research direction in the material design and optimization of Si/C materials is proposed to fill the current gap in the development of efficient Si/C anode for LIBs.

Yolk-Shell Carbon Nanospheres with Controlled Structure and Composition by Self-Activation and Air Activation

Yolk-shell carbon nanospheres (YSCNs) have raised a great deal of interest due to the synergistic advantages over their counterparts. However, it is still difficult to precisely regulate the morphology, porosity, and composition of YSCNs. Here, N-doped porous YSCNs were synthesized via an in situ self-activation by pyrolysis of polypyrrole encapsulated hyper-cross-linked polystyrene (HPS@PPy) core-shell nanospheres, followed by a mild air activation treatment. During the self-activation process, the polypyrrole shell of HPS@PPy provided a confinement effect for the morphology transformation from the core-shell to the yolk-shell structure. The air activation exhibited simultaneous control over porosity and composition. The preparation parameters, such as shell thickness and air activation conditions, were modified to optimize the structure and surface composition of YSCNs to achieve optimal electrochemical performances.

Synergic effects of the decoration of nickel oxide nanoparticles on silicon for enhanced electrochemical performance in LIBs

Significant efforts continue to be directed toward the construction of anode materials with high specific capacity and long cycling stability for lithium-ion batteries (LIBs). In this context, silicon is preferred due to its high capacity even though it has a problem of excessive volume expansion during electrochemical reactions as well as poor cyclability due to a reduction in conductivity. Hence, the hybridization of silicon with suitable materials could be a promising approach to overcome the abovementioned problems. Herein, we demonstrate the uniform decoration of nickel oxide (NiO) nanoparticles (15-20 nm) on silicon nanosheets using bis(cyclopentadienyl) nickel(ii) (C₁₀H₁₀Ni) at low temperatures, taking advantage of the presence of two unpaired electrons in an antibonding orbital in the cyclopentadienyl group. The formation and growth mechanism are discussed in detail. The electrochemical study of the nanocomposite revealed an initial delithiation capacity of 2507 mA h g^-1 with a reversible capacity of 2162 mA h g^-1, having 86% retention and better cycling stability for up to 500 cycles. At the optimum concentration, NiO nanoparticles facilitate Li⁺-ion adsorption, which in turn accelerates the transport of Li⁺-ions to active sites of silicon. The Warburg coefficient and Li⁺-ion diffusion at the electrodes confirm the enhancement in the charge transfer process at the electrode/electrolyte interface with NiO nanoparticles. Further, the NiO nanoparticles with uniform distribution suppress the agglomeration of Si nanosheets and provide sufficient space to accommodate a volume change in Si during cycling, which also reduces the diffusion path length of the Li-ions. It also helps to strengthen the mechanical stability, which might be helpful in preventing the cracking of silicon due to volume expansion and maintains the Li-ion transport pathway of the active material, resulting in enhanced cycling stability. Due to the synergic effect between NiO nanoparticles and Si sheets, the nanocomposite delivers high reversible capacity.

Enhanced Stability Lithium-Ion Battery Based on Optimized Graphene/Si Nanocomposites by Templated Assembly

Considering the sharp increase in energy demand, Si-based composites have shown promise as high-performance anodes for lithium-ion batteries during the last few years. However, a significant volume change of Si during repetitive cycles may cause technical and security problems that limit the particular application. Here, an optimized reduced graphene oxide/silicon (RGO/Si) composite with excellent stability has been fabricated via a facile templated self-assembly strategy. The active silicon nanoparticles were uniformly supported by graphene that can further form a three-dimensional network to buffer the volume change of Si and produce a stable solid-electrolyte interphase film due to the increased specific surface area and enhanced intermolecular interaction, resulting in an increase of electrical conductivity and structural stability. As the anode electrode material of lithium-ion batteries, the optimized 10RGO/Si-600 composite showed a reversible high capacity of 2317 mA h/g with an initial efficiency of 93.2% and a quite high capacity retention of 85% after 100 cycles at 0.1 A/g rate. Especially, it still displayed a specific capacity of 728 mA h/g after 100 cycles at a reasonably high current density of 2 A/g. This study has proposed the optimized method for developing advanced graphene/Si nanocomposites for enhanced cycling stability lithium-ion batteries.

In Situ Synthesis of Multilayer Carbon Matrix Decorated with Copper Particles: Enhancing the Performance of Si as Anode for Li-Ion Batteries

A 3D structured composite was designed to improve the conductivity and to ease the volume problems of Si anode during cycling for lithium-ions batteries. An in situ method via a controllable gelation process was explored to fabricate the 3D composite of a multilayer carbon matrix toughened by cross-linked carbon nanotubes (CNTs) and decorated with conductive Cu agents. Structurally, a bifunctional carbon shell was formed on the surface of Si to improve the conductivity but alleviate side reactions. Cu particles as conducting agents decorated in the carbon matrix are also used to further improve the conductivity. The volume issue of Si particles can be effectively released via toughening the carbon matrix through the multilayered structure and cross-linked CNTs. Moreover, the carbon matrix might prevent silicon particles from agglomeration. Consequently, the Si@C@Cu composite is expected to exhibit benign electrochemical performances with a commendable capacity of 1500 mAh g^-1 (900 cycles, 1 A g^-1) and a high rate performance (1035 mAh g^-1, 4 A g^-1). The D_Li⁺ ranging from 10^-11 to 10^-9 cm^-2 s^-1 of the Si@C@Cu anode is obtained via the GITT test, which is higher than most reported data.