Improving the performance of silicon monoxide anodes via tuning a multiple pre-doping system: a first-principles study.

Silicon monoxide is a potentially viable anode material for high-performance lithium-ion batteries (LIBs). However, a low initial coulombic efficiency and large volume expansion limit its commercial application. Pre-lithiation is an efficient solution, but is expensive because of limited "pre-lithiation" sources. In this work, we theoretically investigated a novel multiple pre-doping SiO system (Li-NaMg-SiO). By comparing its lithiation behavior to that of the traditional Li-doping system (Li-SiO), we revealed the different doping effects during lithiation. Similar to the traditional Li-doping system, the insertion of Na and Mg disintegrates the Si-O host matrix to form Na-O and Mg-O bonds and active Si clusters. At the end of lithiation, the O-Li coordination number (CN) tends to saturate at CNO-Li ≈ 5 in Li-Na-SiO, Li-Mg-SiO, and Li-NaMg-SiO systems, while the value of CNO-Li in the Li-SiO system is more than 6, which suggests that there are reorganizations between Li, Na, and Mg in the silicate matrix. Doping sources of both Na and Mg can prevent the active Li ions from being trapped by O-Li bonds and increase the initial coulombic efficiency. From the density of states (DOS), we notice that all the different pre-doping systems have similar electronic structures, and they can be expected to undergo the same lithiation process. Furthermore, the higher ion-conductivity and smaller volume expansion during the lithiation process characterized by root mean square deviation (RMSD) and volume analysis prove the advantages of the binary doping system (Li-NaMg-SiO) for the improvement of cycle stability for Si-based materials. These advantages benefit from the loose and amorphous structures of doping systems during lithiation. Our work highlights the doping effects of multiple sources and the promotion of "inert compounds" on the entire lithiation process, which provide valuable insight for high-performance anode design.

Scalable Synthesis of Pore-Rich Si/C@C Core-Shell-Structured Microspheres for Practical Long-Life Lithium-Ion Battery Anodes.

Silicon/carbon (Si/C) composites have rightfully earned the attention as anode candidates for high-energy-density lithium-ion batteries (LIBs) owing to their advantageous capacity and superior cycling stability, yet their practical application remains a significant challenge. In this study, we report the large-scale synthesis of an intriguing micro/nanostructured pore-rich Si/C microsphere consisting of Si nanoparticles tightly immobilized onto a micron-sized cross-linked C matrix that is coated by a thin C layer (denoted P-Si/C@C) using a low-cost spray-drying approach and a chemical vapor deposition process with inorganic salts as pore-forming agents. The as-obtained P-Si/C@C composite has high porosity that provides sufficient inner voids to alleviate the huge volume expansion of Si. The outer smooth and robust C shells strengthen the stability of the entire structure and the solid-electrolyte interphase. Si nanoparticles embedded in a microsized cross-linked C matrix show excellent electrical conductivity and superior structural stability. By virtue of structural advantages, the as-fabricated P-Si/C@C anode displays a high initial Coulombic efficiency of 89.8%, a high reversible capacity of 1269.6 mAh g-1 at 100 mA g-1, and excellent cycle performance with a capacity of 708.6 mAh g-1 and 87.1% capacity retention after 820 cycles at 1000 mA g-1, outperforming the reported results of Si/C composite anodes. Furthermore, a low electrode swelling of 18.1% at a high areal capacity of 3.8 mAh cm-2 can be obtained. When assembled into a practical 3.2 Ah cylindrical cell, extraordinary long cycling life with a capacity retention of 81.4% even after 1200 cycles at 1C (3.2 A) and excellent rate performance are achieved, indicating significant advantages for long-life power batteries in electric vehicles.

Structure and conductivity enhanced treble-shelled porous silicon as an anode for high-performance lithium-ion batteries.

Silicon is regarded as the next generation anode material for lithium-ion batteries because of its high specific capacity, low intercalation potential and abundant reserves. However, huge volume changes during the lithiation and delithiation processes and low electrical conductivity obstruct the practical applications of silicon anodes. In this study, a treble-shelled porous silicon (TS-P-Si) structure was synthesized via a three-step approach. The TS-P-Si anode delivered a capacity of 858.94 mA h g-1 and a capacity retention of 87.8% (753.99 mA h g-1) after being subjected to 400 cycles at a current density of 400 mA g-1. The good cycling performance was due to the unique structure of the inner silicon oxide layer, middle silver nano-particle layer and outer carbon layer, leading to a good conductivity and a decreased volume change of this silicon-based anode.

Facile Synthesis of Amorphous Ge Supported by Ni Nanopyramid Arrays as an Anode Material for Sodium-Ion Batteries.

In this work, we introduce Ni nanopyramid arrays (NPAs) supported amorphous Ge anode architecture and demonstrate its effective improvement in sodium storage properties. The Ni-Ge NPAs are prepared by facile electrodeposition and sputtering method, which eliminates the need for any binder or conductive additive when used as a Na-ion battery anode. The electrodes display stable cycling performance and enhanced rate capabilities in contrast with planar Ge electrodes, which can be owing to the rational design of the architectured electrodes and firm bonding between current collector and active material (i. e. Ni and Ge, respectively). To validate improvement of nanostructures on electrochemical performance, sodium insertion behavior of crystalline Ge derived from Mg2Ge precursor has been investigated, in which limited but effective enhancement of sodium storage properties are realized by introducing porous nanostructure in crystalline Ge. These results show that elaborately designed configuration of Ge electrodes may be a promising anode for Na-ion battery applications.

Walnut-structure Si-G/C materials with high coulombic efficiency for long-life lithium ion batteries.

Nano-sized silicon is a potential high energy density anode material for lithium ion batteries. However, the practical use of a nano-Si anode is still challenging due to its low coulombic efficiency, poor scalability and cycling stability. Herein, a Si/graphite/carbon (Si-G/C) composite with a core-shell structure was fabricated by a facile two-step chemical process, stirring-evaporating followed by heat treatment. The composite structure consists of a graphite core, coated first by silicon and then amorphous carbon, which was decomposed by pitch. The as-prepared Si-G/C composite anode demonstrates a first cycle capacity of about 650 mA h g-1, over 90% coulombic efficiency, and high capacity retention of 96.7% after 50 cycles. When paired with a commercial NCA cathode, superior cycling stability with more than 81% capacity retention was achieved for 1200 cycles. These results demonstrate that such a core-shell Si-G/C composite is a promising anode material for high energy Li-ion batteries.

Assembling CoSn3 nanoparticles on multiwalled carbon nanotubes with enhanced lithium storage properties.

CoSn(3) nanoparticles have been successfully assembled on noncovalently poly(diallyldimethylammonium chloride)-functionalized multiwalled carbon nanotubes (MWCNTs) via a chemical reduction method in a polyol system. The influences of the surface functionality and the reaction temperature on the synthesis of uniform CoSn(3)-MWCNTs nanohybrids have been investigated. The as-synthesized CoSn(3)-MWCNTs nanohybrids have been applied as anodes for lithium-ion batteries, and show better lithium storage performance compared to the bare CoSn(3) nanoparticles and MWCNTs. The combining of MWCNTs that can hinder the agglomeration and enhance the electronic conductivity of the active materials is responsible for the enhanced cyclic performance.