Porous Si Particles Research Articles

Effect of precursor morphology on the electrochemical performance of porous Si anodes prepared by magnesiothermic reduction

The magnesiothermic reduction of SiO2 to Si is a promising route for preparing high-energy-density Si-based anode materials for lithium-ion batteries. However, the effect of the initial morphological properties of SiO2 on the electrochemical performance of Si remains unclear. Herein, porous Si (PSi) particles were prepared from four different SiO2 precursors, namely, spherical SiO2 particles with diameters of 0.3 and 20 μm (denoted SiO2-0.3 and SiO2-20, respectively), fumed SiO2 powder (denoted SiO2-F), and well-ordered mesoporous SiO2 particles (denoted SiO2-K). Highly crystalline PSi particles were obtained after magnesiothermic reduction and subsequent HCl and HF etching. PSi prepared from SiO2-0.3 maintained its precursor morphology to some extent, whereas highly irregular Si particles were produced from SiO2-20, SiO2-F, and SiO2-K. Among the PSi particles, those prepared from SiO2-0.3 delivered the highest reversible capacity (1427 mAh g–1 at 0.1 A g–1) after 50 discharge–charge cycles. Because of the unique hierarchically porous morphology of PSi prepared from SiO2-0.3, the expansion of its electrode thickness was suppressed below 140 %. Moreover, owing to its nanosized Si domains and good electrode wetting, PSi prepared from SiO2-0.3 demonstrated improved electrochemical properties compared with those prepared from SiO2-F and SiO2-K.

Multi-functional double carbon shells coated boron-doped porous Si as anode materials for high-performance lithium-ion batteries

Various strategies have been devised to relieve the volume expansion and enhance the electronic conductivity of Si-based anode materials in LIBs. Herein, we have synthesized a novel double carbon shells coated boron-doped porous Si ([email protected] C) composite using low-cost industrial ferrosilicon alloys as raw materials through a modified ball milling combined with self-polymerization of dopamine hydrochloride and chemical vapor deposition process with acetylene. In this work, the boron-modified porous Si structure facilitates improved electron and Li+ kinetics. The inner flexible carbon can regulate the volume variation of Si during lithiation and enhance the particles’ electrical connectivity. Moreover, the outer rigid carbon promotes stable SEI formation and maintains structural integrity. This unique rigid-flexible double carbon structure, combined with the highly-capacity modified porous Si particles, render the composite to display outstanding electrochemical properties regarding both lithium storage capacity and cycling stability. As a result, the [email protected] C electrode displays a reversible capacity of 1105.8 mAh g−1 at 0.5 A g−1 over 300 cycles and excellent cyclic stability. This study provides a novel idea for producing low-cost and high-energy Si-based anode materials for LIBs.

Electrochemical Performance Enhancement of Micro-Sized Porous Si by Integrating with Nano-Sn and Carbonaceous Materials.

Silicon is investigated as one of the most prospective anode materials for next generation lithium ion batteries due to its superior theoretical capacity (3580 mAh g−1), but its commercial application is hindered by its inferior dynamic property and poor cyclic performance. Herein, we presented a facile method for preparing silicon/tin@graphite-amorphous carbon (Si/Sn@G–C) composite through hydrolyzing of SnCl2 on etched Fe–Si alloys, followed by ball milling mixture and carbon pyrolysis reduction processes. Structural characterization indicates that the nano-Sn decorated porous Si particles are coated by graphite and amorphous carbon. The addition of nano-Sn and carbonaceous materials can effectively improve the dynamic performance and the structure stability of the composite. As a result, it exhibits an initial columbic efficiency of 79% and a stable specific capacity of 825.5 mAh g−1 after 300 cycles at a current density of 1 A g−1. Besides, the Si/Sn@G–C composite exerts enhanced rate performance with 445 mAh g−1 retention at 5 A g−1. This work provides an approach to improve the electrochemical performance of Si anode materials through reasonable compositing with elements from the same family.

Electrochemical Study on Porous Silicon Anodes in Sulfide-Based All-Solid-State Lithium-Ion Batteries: II

All-solid-state lithium-ion battery (LIB) with high safety and reliability is the dominant power source for electric and hybrid vehicles. Here, to meet the energy demands of near-future automobile technology, the anode materials should possess high energy density and long cycle life. Though Si with a high theoretical capacity (4200 mAh g-1) is the most attractive choice, there are few applications for the all-solid-state LIBs. This is because the large volumetric fluctuation (>300%) in lithiation/delithiation causes the drastic capacity loss and low coulombic efficiency. Very recently, sulfide-based all-solid-state LIBs with porous Si composite anodes have exhibited high capacity retention [1]. We proposed the following mechanisms to consistently explain the experimental results [2]: (a) the volumetric expansion is buffered by the shrinkage of Si pores and (b) the stress arising from the Si particles is relieved by the elastic deformation of solid electrolyte (SE). In the present study, to provide further insight into these findings, the electrochemical characteristics were evaluated for the porous Si composite anodes with different SEs.Porous Si particles were prepared through air-oxidation demagnesiation of Mg2Si. The details have been described in our previous paper [1]. Anode composites were comprised of Si particles, SE, and acetylene black. Here Li3PS4 (LPS) and Li10GeP2S12 (LGPS) were adopted as sulfide-based SE. In an electric insulation tube, the anode composite and LPS powder were pressed to make two-layered pellet. As the counter electrode, Li-In foil was attached on the SE side. Finally, the three-layered pellet was compressed using stainless-steel disks. AC impedance of the half-cells thus prepared was measured in the range from 0.002 to 1 MHz.Figure 1 shows the cycle characteristics of LPS- and LPGS-cells. The LPS composite anode cell exhibited an initial discharge capacity of 1240 mAh g-1. On the other hand, a discharge capacity of 924 mAh g-1, which was about 30% lower than that of LPS-cell, was observed in the LGPS-cell. The maximum discharge capacity was 1532 mAh g-1 for LPS-cell and 1269 mAh g-1 for LGPS-cells, respectively. As the results, the capacity retention of LPS-cell was calculated as 95% at 50th cycle, compared to 83% in LGPS-cell. It is worthy to note that these values were extremely larger than those of non-porous Si anode cells. As shown in Cole-Cole plots, Figure 2, in the LPS composite anode cell, there was few changes in the arc size between 1st and 5th cycles. On the other hand, the arc of LPGS-cell became large with the increase of cycle number.The Young's modulus of LPS is known to be about 10% lower than that of LGPS [3]. Based on this fact, the above results are described as follows. Though the volumetric expansion is buffered by the shrinkage of pores, the porous Si particles slightly become large during lithiation. In LPS-cell, the stress should be relieved by the elasticity of surrounding SE. On the other hand, in LPGS with higher rigidity, voids are probably formed between the Si particles and the deformed SE, resulting in the lower capacity retention and higher interfacial resistance. In these considerations, we should note that LGPS with narrow potential window is prone to decompose in long cycles.

Silicon-Aluminum-Alloy-Derived Porous Silicon/Carbon As Anode Materials for Lithium Ion Batteries

Nowadays, most of countries in the world promote energy saving and carbon emission reduction. The development of electric vehicles (EVs) is one of the main solution to reduce the carbon emission. Lithium ion batteries (LIBs) have higher energy density than other secondary batteries so they serve as the most popular energy storage device for EVs. However, the capacity of commercial graphite anode material is limited to ~372 mA h g-1 which is hard to meet the high-energy demand for long-range EVs. Silicon with highest theoretical capacity of 4200 mA h g-1 has been considered as the next-generation anode material. Despite the high capacity, the severe volume change of silicon during charge and discharge processes leads to the peeling-off of the active materials from the current collector. Therefore, the capacity retention of Si is poor. Porous structure and carbon coating are two major methods applying for improving the capacity retention of Si.In our work, we utilized Si-Al alloys as precursors to synthesize micro-size porous Si anode materials by acidic treatment. Besides, carbon was coated on the porous Si particles to increase the electronic conductivity. Si-Al alloys are commercial available so this micro-size porous Si/C anode material can be mass-produced. High capacity around 1000 mA h g-1 could be achieved with good capacity retention. It indicates that the micro-sized porous Si/C is a promising LIB anode materials for electric vehicle application.

Electrochemical Study on Porous Silicon Anodes in Sulfide-Based All-Solid-State Lithium-Ion Batteries

All-solid-state lithium-ion battery (LIB) with high safety and reliability is the dominant power source for electric and hybrid vehicles. To meet the energy demands of near-future automobile technology, the anode materials should possess high energy density and long cycle life. Though Si with a high theoretical capacity (4200 mAh g-1) is the most attractive choice, there are few applications for the all-solid-state LIBs. This is because the large volumetric fluctuation (>300%) in lithiation/delithiation causes the drastic capacity loss and low coulombic efficiency. Very recently, we have found that sulfide-based all-solid-state LIBs with porous Si anodes exhibited high capacity retention [1,2]. In the present study, the electrochemical impedance was measured to provide further insight into the stable cyclability. Porous Si particles were prepared through air-oxidation demagnesiation of Mg2Si. The details have been described in our previous paper [1]. Commercially available non-porous Si particles were also used as a reference active material. Anode composite was comprised of Si particles, Li3PS4 solid electrolyte (SE), and acetylene black. We adopted two mixing methods, ball milling and mortar milling, to vary the dispersion degree of Si particles. In an electric insulation tube, the anode composite and SE powder were pressed to make two-layered pellet. As the counter electrode, Li-In foil was attached on the SE side. Finally, the three-layered pellet was compressed using stainless-steel disks. AC impedance of the half-cells thus prepared was measured in the range from 2×10-3 to 1×106 Hz. The ball-milled porous Si anode cells exhibited the capacity retention over 80% up to 150 cycles. In contrast, the lower retention, 40%, was observed for the mortar-milled porous Si anode cells. The ball-milled and mortar-milled non-porous Si anode cells possessed the poorer cycle stability with the capacity retention of 10% or less. As shown in the Cole-Cole plots, in the ball-milled porous Si anode cell, there was few changes in the arc size between 1st and 20th cycles. On the other hand, the arc of the mortar-milled porous Si anode cell became gradually large with the increase of cycle number. In addition, huge arcs were observed in the non-porous Si anode cells, regardless of the mixing method. The experimental results described above can be explained as follows. By utilizing the ball milling, Si particles are highly dispersed in the SE matrix. In this case, a lot of pores on the porous Si surface are exposed to the electrolyte. As the result, surface electrolyte interface (SEI) is easily formed at 1st cycle. However, SEI become hardly thick with the increase of charge/discharge cycle. This is because SE possesses high stability and low fluidity. In addition, the volumetric expansion is buffered by the shrinkage of Si pores. Therefore, the slight stress arising from the Si particles is relieved by the elastic deformation of SE. These findings strongly suggest that almost constant interfacial resistance causes the cycle stability of the ball-milled porous Si anode cells.

Gel-Mediated Electrospray Assembly of Silica Supraparticles for Sustained Drug Delivery.

Supraparticles (SPs) composed of smaller colloidal particles provide a platform for the long-term, controlled release of therapeutics in biomedical applications. However, current synthesis methods used to achieve high drug loading and those involving biocompatible materials are often tedious and low throughput, thereby limiting the translation of SPs to diverse applications. Herein, we present a simple, effective, and automatable alginate-mediated electrospray technique for the assembly of robust spherical silica SPs (Si-SPs) for long-term (>4 months) drug delivery. The Si-SPs are composed of either porous or nonporous primary Si particles within a decomposable alginate matrix. The size and shape of the Si-SPs can be tailored by controlling the concentrations of alginate and silica primary particles used and key electrospraying parameters, such as flow rate, voltage, and collector distance. Furthermore, the performance (including drug loading kinetics, loading capacity, loading efficiency, and drug release) of the Si-SPs can be tuned by changing the porosity of the primary particles and through the retention or removal (via calcination) of the alginate matrix. The structure and morphology of the Si-SPs were characterized by electron microscopy, dynamic light scattering, N2 adsorption-desorption analysis, and X-ray photoelectron spectroscopy. The cytotoxicity and degradability of the Si-SPs were also examined. Drug loading kinetics and loading capacity for six different types of Si-SPs, using a model protein drug (fluorescently labeled lysozyme), demonstrate that Si-SPs prepared from primary silica particles with large pores can load significant amounts of lysozyme (∼10 μg per SP) and exhibit sustained, long-term release of more than 150 days. Our experiments show that Si-SPs can be produced through a gel-mediated electrospray technique that is robust and automatable (important for clinical translation and commercialization) and that they present a promising platform for long-term drug delivery.

A flexible micro/nanostructured Si microsphere cross-linked by highly-elastic carbon nanotubes toward enhanced lithium ion battery anodes

Inspired by the carbon nanotubes (CNTs) with high elasticity, we design a flexible conductive Si/CNT composite where the CNTs are in situ grown in the porous Si particles with mesoscale porosity to solve the problems facing high capacity Si-based anodes. The Si/CNT composite with CNTs in situ grown into the Si wall and mesoscale porosity has advantages in several aspects, including improving the electron transport within the Si particle, holding the Si domains together without getting pulverized, and exhibiting excellent mechanical properties. As a result, the as-obtained Si/CNT composites delivers a reversible capacity of 1275.5 mA h g-1 at 0.2 A g-1 after 100 cycles and a capacity of 715.5 mA h g-1 at 1 A g-1 after 400 cycles. When assembled with the Si/CNT composite as anode and commercial LiCoO2 as cathode, the full cell delivers a reversible capacity of 127.4 mA h g−1 with a working potential beyond 3.0 V based on the cathode active material. The enhanced performance could be attributed to the flexible conductive microstructured design, which can significantly improve conductivity, stabilize SEI film, and maintain the integrity of the porous Si-based electrodes.

Highly porous coral-like silicon particles synthesized by an ultra-simple thermal-reduction method

The highly porous coral-like Si particles have been successfully synthesized using an ultra-simple Mg-thermal-reduction method in air.

PEDOT/PSS-Coated Porous Silicon as anode of lithium-Ion Batteries

Silicon (Si) has been regarded as the most promising anode material of lithium-ion batteries (LIBs) because of its super-high theoretical capacity. However, dramatic volume variations during cycling of lithiation/de-lithiation will trigger electrode pulverization, disruption and structural failure of solid electrolyte interface (SEI), and the according poor cycling performance as well. Nanolization, composite with buffer material and special microstructure design of silicon based materialsare the most common strategy to alleviate the volume change effects[1-2]. The given electrode material design are usually with high-cost, complicated process and low volume specific capacity. In this work, the porous Si in the size of several micrometers are synthesized by Metal-assisted chemical etching(MaCE) method, in which micro-sized Si particles is locally etched in the isopropyl alcohol solution containing AgNO3 and HF[3]. The resulting porous Si is subsequently coated with a thin PEDOT/PSS layer. PSS is used in dispersing porous Si particles well into an aqueous solution and then tethering EDOT monomer onto the surface of porous Si particles to facilitate the formation of a uniform PEDOT coating [4].Fig. 1. SEM image of porous Si (a) and porous Si@PEDOT/PSS(b).Figure 1 shows that the pore size in the as synthesized silicon particles is below 200nm, and the PEDOT/PSS is uniformed coated on the silicon particle surface. This unique micron sized core-shell structure is considered to contribute to cycle stability and rate capability. The micron size silicon particles will help the realization of favorable volume specific capacity. The suitable sized pores in the silicon will be enough to accommodate the volume change resulting from lithiation. And the PEDOT/PSS coating is used to shield the silicon from the direct contact to electrolyte and inhabit the repeated rupture and reconstruction of SEI during volume change charge/discharge cycling. The detailed electrochemical performance of this silicon electrode material will be reported in meeting poster session. Acknowledgement Financial support by the National Science Foundation of China (21473128 and 21373154) is gratefully acknowledged.

Three-Dimensional Porous Si and SiO2 with In Situ Decorated Carbon Nanotubes As Anode Materials for Li-ion Batteries.

A high-capacity Si anode is always accompanied by very large volume expansion and structural collapse during the lithium-ion insertion/extraction process. To stabilize the structure of the Si anode, magnesium vapor thermal reduction has been used to synthesize porous Si and SiO2 (pSS) particles, followed by in situ growth of carbon nanotubes (CNTs) in pSS pores through a chemical vapor deposition (CVD) process. Field-emission scanning electron microscopy and high-resolution transmission electron microscopy have shown that the final product (pSS/CNTs) possesses adequate void space intertwined by uniformly distributed CNTs and inactive silica in particle form. pSS/CNTs with such an elaborate structural design deliver improved electrochemical performance, with better coulombic efficiency (70% at the first cycle), cycling capability (1200 mAh g-1 at 0.5 A g-1 after 200 cycles), and rate capability (1984, 1654, 1385, 1072, and 800 mAh g-1 at current densities of 0.1, 0.2, 0.5, 1, and 2 A g-1, respectively), compared to pSS and porous Si/CNTs. These merits of pSS/CNTs are attributed to the capability of void space to absorb the volume changes and that of the silica to confine the excessive lithiation expansion of the Si anode. In addition, CNTs have interwound the particles, leading to significant enhancement of electronic conductivity before and after Si-anode pulverization. This simple and scalable strategy makes it easy to expand the application to manufacturing other alloy anode materials.

Cost-effective approach for structural evolution of Si-based multicomponent for Li-ion battery anodes

Al2O3passivated porous Si particles with novel electrochemical properties were successfully demonstrated as outstanding anodes.

In Situ and Ex Situ TEM Study of Lithiation Behaviours of Porous Silicon Nanostructures.

In this work, we study the lithiation behaviours of both porous silicon (Si) nanoparticles and porous Si nanowires by in situ and ex situ transmission electron microscopy (TEM) and compare them with solid Si nanoparticles and nanowires. The in situ TEM observation reveals that the critical fracture diameter of porous Si particles reaches up to 1.52 μm, which is much larger than the previously reported 150 nm for crystalline Si nanoparticles and 870 nm for amorphous Si nanoparticles. After full lithiation, solid Si nanoparticles and nanowires transform to crystalline Li15Si4 phase while porous Si nanoparticles and nanowires transform to amorphous LixSi phase, which is due to the effect of domain size on the stability of Li15Si4 as revealed by the first-principle molecular dynamic simulation. Ex situ TEM characterization is conducted to further investigate the structural evolution of porous and solid Si nanoparticles during the cycling process, which confirms that the porous Si nanoparticles exhibit better capability to suppress pore evolution than solid Si nanoparticles. The investigation of structural evolution and phase transition of porous Si nanoparticles and nanowires during the lithiation process reveal that they are more desirable as lithium-ion battery anode materials than solid Si nanoparticles and nanowires.

Fabrication of Porous Si Particles by Barrel Anode Etching

Porous Si particles were prepared by the barrel anode etching of small Si particles. The depth of the holes formed on the surface of the Si particles could be controlled by changing the anode etching time. The process reported here allows high-throughput preparation of small porous Si particles with controlled geometrical surface structures. The obtained porous Si particles can be applied in various types of functional devices.

High Performance Porous Silicon Anodes By Chemical Etching Metal Si Alloy Powders

We describe a simple process for prepare three-dimensional porous silicon powders by acid etching process. Subsequently, the aluminum-silicon alloy particles were chemically etched to synthesize porous silicon particles, without changing the chemical and physical properties of Si. The silicon monoxide-coated porous silicon anodes exhibited excellent electrochemical properties, including a high specific capacity and a high rate capability. High electrochemical performance of porous silicon powder could be attributed to its porous structure, which provides enough tiny space to buffer the huge volume change of Si anode during charging and discharging processes. The firm connection between Si nanobars in spongy porous structure prevented the breakdown of porous Si particles. This easy acid etching process for preparing high performance porous Si material is simple and inexpensive, effective way for a rich variety of applications, including lithium-ion batteries.

A Silicon-Graphene Electrode with Multilayered Structure for High Performance Lithium-Ion Batteries

A silicon-graphene electrode composed of porous Si and reduced graphene oxide with multilayered structure was synthesized from bulk Si particles through inexpensive electroless etching and graphene self-encapsulating approach. The prepared composite electrode presents superior electrochemical performance with a discharge capacity of 1026 mAh/g tested at 1A/g and good retention rate. The columbic efficiencies are about 99% during the whole cycling process. The electrode was extensively characterized and it is found that the superior performance attributes to the novel multilayered structure with porous Si particles encapsulated, which effectively accommodate the large volume change during the lithiation/delithiation process and provide increased electrical conductivity. This facile approach offers an alternative route to construct promising low cost Si electrode for future industrial applications.

A multilayered silicon-reduced graphene oxide electrode for high performance lithium-ion batteries.

A multilayered structural silicon-reduced graphene oxide electrode with superior electrochemical performance was synthesized from bulk Si particles through inexpensive electroless etching and graphene self-encapsulating approach. The prepared composite electrode presents a stable charge-discharge performance with high rate, showing a reversible capacity of 2787 mAh g(-1) at a charging rate of 100 mA g(-1), and a stable capacity over 1000 mAh g(-1) was retained at 1 A g(-1) after 50 cycles with a high columbic efficiency of 99% during the whole cycling process. This superior performance can be attributed to its novel multilayered structure with porous Si particles encapsulated, which can effectively accommodate the large volume change during the lithiation process and provide increased electrical conductivity. This facile low-cost approach offers a promising route to develop an optimized carbon encapsulated Si electrode for future industrial applications.

Control of interfacial layers for high-performance porous Si lithium-ion battery anode.

We demonstrate a facile synthesis of micrometer-sized porous Si particles via copper-assisted chemical etching process. Subsequently, metal and/or metal silicide layers are introduced on the surface of porous Si particles using a simple chemical reduction process. Macroporous Si and metal/metal silicide-coated Si electrodes exhibit a high initial Coulombic efficiency of ∼90%. Reversible capacity of carbon-coated porous Si gradually decays after 80 cycles, while metal/metal silicide-coated porous Si electrodes show significantly improved cycling performance even after 100 cycles with a reversible capacity of >1500 mAh g(-1). We confirm that a stable solid-electrolyte interface layer is formed on metal/metal silicide-coated porous Si electrodes during cycling, leading to a highly stable cycling performance.

An easy way for preparing high performance porous silicon powder by acid etching Al–Si alloy powder for lithium ion battery

We developed a novel, simple method to prepare porous silicon powder by acid etching Al–Si alloy powder. .The morphology and structure of the as-obtained material were investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscope (TEM), and BET methods. It was found that the porous silicon powder (size about 15μm) had a spongy structure, consisting of silicon nanobars with diameter about 50nm and length of 1.5μm. Its specific surface area was 102.8m2g−1. The electrochemical properties of porous silicon electrode were evaluated by measuring voltammograms and charge and discharge curves. The porous silicon electrode with ratio of porous Si powder:Super P:binder=1:1:1 was tested in button style lithium/Si cell. It was found that due to its ability to promote the formation of primal SEI film on the surface of electrodes, additive fluoroethylene carbonate (FEC) had an effect to improve the charge and discharge cycle stability of porous silicon electrodes. In solution 1M LiPF6, EC:DMC=1:1 (V/V) containing 15% FEC, the first charge and discharge capacities of porous silicon electrode were 3450mAhg−1 Si and 2072mAhg−1 Si respectively, at current density 100mAg−1. The discharge capacity retained 66% as 1368mAhg−1 Si after 258 charge and discharge cycles. In 1M LiPF6/EC:DEC=1:1 (V/V) solution, the charge and discharge capacities of porous silicon electrode in first cycle were 3396mAhg−1 Si and 2537mAhg−1 Si respectively. At 69th cycle, the discharge capacity remained 59% as 1497mAhg−1 Si. The high electrochemical performance of porous silicon powder could be attributed to its porous structure, which provides enough tiny space to buffer the huge volume change of Si anode during charging and discharging processes. The nano-size Si bars benefited the diffusion process of lithium in Li–Si alloy. Moreover, the firm connection between Si nanobars in spongy porous structure prevented the breakdown of porous Si particles. This new advanced method for preparing high performance porous Si material is simple and inexpensive, presenting a promising prospect for practical application.

Fabrication of Porous Si Particles by Electrochemical Etching

Nanoporous Si particles were fabricated by the electrochemical etching of closely packed Si particles in an electrolyte containing HF. The geometrical structures of the obtained porous layers on the surface of the particles could be controlled by adjusting the preparation conditions. The process reported here is effective for the high-throughput preparation of nanoporous Si particles with controlled geometrical structures.