Nano-Si Anode Research Articles

Deciphering the degradation mechanisms of nano-Si and micro-SiO anodes in lithium-ion battery full-cells using distribution relaxation times analysis

Silicon (Si) and silicon monoxide (SiO) have attracted great interest as next-generation anode materials for lithium-ion batteries (LiBs) due to their high energy density. However, their commercialization has been hindered by rapid capacity fading, which stems from mechanical degradation (e.g., cracking and delamination) and the aggressive formation of solid electrolyte interphase (SEI) layer. While understanding these degradation mechanisms in batteries necessitates in-operando measurement techniques, very few non-destructive analytical methods have been documented in literature. This paper highlights the effectiveness of combined electrochemical impedance spectroscopy (EIS) and distribution of relaxation times (DRT) techniques in performing systematic characterization of LiNi0.6Mn0.2Co0.2O2 (NMC)/nano-Si and NMC/micro-SiO full-cells. The systematic design of experiments enabled the separate deconvolution of anode and cathode aging using symmetrical cells. This approach offered a clear understanding of the overall degradation mechanisms in the full-cells. The major impedance sources in the NMC/nano-Si full-cell were anode contact impedance, resulting from mechanical degradation of Si, and cathode charge transfer impedance, due to significant lithium loss and consequently deeper extraction of lithium ions in NMC. In contrast, micro-SiO anodes exhibited less electrode-level degradation, as evidenced by SEM images and relatively stable impedance behaviors during extended cycling, which strongly corroborate its superior capacity retention (66 % at 300th cycle) compared to that of nano-Si anode in full-cells (26.5 % at 300th cycle).

Creating value added nano silicon anodes from end-of-life photovoltaic modules: recovery, nano structuring, and the impact of ball milling and binder on its electrochemical performance

Recovery of silicon from end-of-life photovoltaic (PV) modules, purification, conversion to nano silicon (nano-Si), and subsequent application as an anode in lithium-ion batteries is challenging but can significantly influence the circular economy. Currently, a complete technology consisting of cross-contamination-free recovery of silicon wafers from end-of-life PV modules, a low-cost environmentally friendly purification process of the recovered PV silicon, a high yield conversion process of the recovered PV silicon into nano-Si, and its subsequent application in lithium-ion batteries is unavailable. This study provides a complete package including cross-contamination-free recovery, economical purification, reliable conversion to nano-Si, and efficient application of the end-of-life PV nano-Si in lithium-ion batteries. Hydrofluoric acid-free recovery and purification processes are demonstrated which can deliver large quantities of high-purity (≥ 99) silicon. In addition, the subsequent ball milling process produces very distinct nano-Si with different shapes and sizes. This study also creates a very effective nano-Si anode through in-situ crosslinking of water-soluble carboxymethyl cellulose and poly (acrylic acid) precursors. The integration of distinct PV nano-Si and water-soluble carboxymethyl cellulose-poly (acrylic acid) crosslink binder opens distinct possibilities to develop silicon-based practical anode for next generation low-cost lithium-ion batteries to power cell phones to electric vehicles.

Calcium silicate composited nano-Si anode with low expansion and high performance for lithium-ion batteries

Calcium silicate composited nano-Si anode with low expansion and high performance for lithium-ion batteries

F-doped Carbon Coated Nano-Si Anode with High Capacity: Preparation by Gaseous Fluorination and Performance for Lithium Storage

F-doped Carbon Coated Nano-Si Anode with High Capacity: Preparation by Gaseous Fluorination and Performance for Lithium Storage

In-situ migration of Ni induced crystallization to boost the initial coulombic efficiency of nano Si anode for lithium ion batteries

Silicon (Si) has attracted enormous attention as next-generation anode material for lithium-ion batteries (LIBs) because of its ultra-high capacity. However, the practical application of Si is limited by its low initial coulombic efficiency (ICE) and unstable cycle performance. Here, a Ni-doped highly crystalline porous Si (Ni–CPSi) was prepared through facile magnesiothermic reduction and acid treatment. The enhanced crystallinity of Si effectively decreases the structural defects and suppresses the adverse side reactions. With moderate surface area and porous structure, the side reactions and volumetric expansion of Si during cycling are mitigated. Ni doping in Si crystal lattice further contributes to the enhancement of overall conductivity. As a result, the synthesized Ni–CPSi delivers a high ICE of 83.59%, and a superb rate capability of 682.8 mAh g−1 at 8.4 A g−1. In addition, Ni–CPSi anode achieves ultralong cycle life of 904.5 mAh g−1 at 4.2 A g−1 after 1000 cycles.

Mg2Si promoted magnesio-mechanical reduction of silica into silicon nanoparticles for high-performance Li-ion batteries

In this study, we report a scalable magnesio-mechanical reduction method to prepare high quality silicon nanoparticles with good lithium storage performance using low cost starting materials. Although the reaction of Mg and silica is thermodynamically highly favorable, direct reaction using commercial Mg powder by mechanical milling at room temperature is difficult. However, by adding of 5 ​wt % Mg2Si, silica nanoparticles can be reduced into Si nanoparticles using commercial Mg as the reductant by mechanical milling at 250 ​rpm in 5 ​h. Mechanism study suggests that Mg2Si can effectively break the surface oxide layer of Mg due to its high rigidity modules and create fresh Mg surface to initiate the reaction. The obtained Si nanoparticles and Si@C composites exhibit excellent lithium storage performance comparable to that of the state-of-the-art nano-Si anode materials.

Electrochemical Performance of an Ultrathin Surface Oxide-Modulated Nano-Si Anode Confined in a Graphite Matrix for Highly Reversible Lithium-Ion Batteries.

Si-based anode materials have attracted considerable attention for use in high-capacity lithium-ion batteries (LIBs), but their practical application is hindered by huge volume changes and structural instabilities that occur during lithiation/delithiation and low-conductivity. In this regard, we report a novel Si-nanocomposite by modulating the ultrathin surface oxide of nano-Si at a low temperature and highly conductive graphene-graphite matrix. The Si nanoparticles are synthesized by high-energy mechanical milling of micro-Si. The prepared Si/SiOx@C nanocomposite electrode delivers a high-discharge capacity of 1355 mAh g-1@300th cycle with an average Coulombic efficiency of 99.5% and a discharge capacity retention of ∼88% at 1C-rate (500 mA g-1). Remarkably, the nanocomposite exhibits a high initial Coulombic efficiency of ∼87% and excellent charge/discharge rate performance in the range of 0.5-5C. Moreover, a comparative investigation of the three different electrodes nano-Si, Si/SiOx, and Si/SiOx@C are presented. The exceptional electrochemical performance of Si/SiOx@C is owing to the nanosized silicon and ultrathin SiOx followed by a high-conductivity graphene-graphite matrix, since such a nanostructure is beneficial to suppress the volume changes of silicon, maintain the structural integrity, and enhance the charge transfer during cycling. The proposed nanocomposite and the synthesis method are novel, facile, and cost-effective. Consequently, the Si/SiOx@C nanocomposite can be a promising candidate for widespread application in next-generation LIB anodes.

Highly efficient synthesis of nano-Si anode material for Li-ion batteries by a ball-milling assisted low-temperature aluminothermic reduction

A nano-sized Si anode material was synthesized by a novel and highly efficient route of ball-milling assisted low-temperature aluminothermic reduction at 150–180 °C in a eutectic NaCl/KCl/AlCl3 mixture, using white carbon black and coarse-grained Al powder as the starting materials. After extending the duration of ball-milling assisted aluminothermic reduction to 10 h, the obtained Si yield reached as high as 94%. The synthesized nano-Si mainly consisted of irregular porous agglomerates constructed by ultrafine primary particles with a particle size less than 50 nm. The nano-Si anode showed a superior electrochemical performance. Its maximum discharge and charge capacities at a current density of 0.05 A g−1 were 3075 and 2597 mAh g−1, respectively, leading to a high initial Coulumbic efficiency of 84.5%. The nano-Si anode exhibited reversible capacities of 2458 mAh g−1 at 0.2 A g−1, and of 1169 mAh g−1 at a high current density of 5 A g−1. After cycling at 1 A g−1 for 400 cycles, it still delivered a high reversible capacity of 804 mAh g−1. The synthetic strategy, which is not only facile and highly efficient, but also low-cost and environmentally benign, is thus promising to be applied for mass production of nano-Si anode materials for next-generation Li-ion batteries.

Strategies for improving the storage performance of silicon-based anodes in lithium-ion batteries

Silicon has attracted much attention as a promising anode material for lithium-ion batteries (LIBs) due to its high theoretical capacity and rich resource abundance. However, the practical battery use of Si is challenged by its low conductivity and drastic volume variation during the Li uptake/release process. Tremendous efforts have been made on shrinking the particle size of Si into nanoscale so that the volume variation could be accommodated. However, the bare nano-Si material would still pulverize upon (de)lithiation. Moreover, it shows an excessive surface area to invite unlimited growth of solid electrolyte interface that hinders the transportation of charge carriers, and an increased interparticle resistance. As a result, the Si nanoparticles gradually lose their electrical contact during the cycling process, which accounts for poor thermodynamic stability and sluggish kinetics of the anode reaction versus Li. To address these problems and improve the Li storage performance of nano-Si anode, proper structural design should be applied on the Si anode. In this perspective, we will briefly review some strategies for improving the electrochemistry versus Li of nano-Si materials and their derivatives, and show opinions on the optimal design of nanostructured Si anode for advanced LIBs.

Behaviour of Nanostructured Si-Based Anode Materials Studied By Atom Probe Tomography and Hard X-Ray Photoelectron Spectrocopy

Lithium-ion batteries (LIB) are considered for electric vehicles (EV) as well as for home or off-grid energy storage for example in combination with photovoltaics. These specific applications drive the research on high energy density, cost-effective, safe and environmental friendly battery materials. To obtain deeper insight into the reaction mechanisms advanced characterization such as in-situ TEM or in-situ XRD1 are often used in combination with simplified model systems. For LIB anodes Si has the highest specific capacity among all anode materials. However, the mechanical fatigue (lack of microstructural integrity) associated with large volume expansion of pure Si during the lithiation process has hindered their wider use for commercial applications so far. Also, there are a series of side reactions which happen at the surface forming the solid electrolyte interface (SEI). In this work we investigate the role of mechanically confined nanocrystalline Si particles being embedded in a SiTiNi matrix2. Samples are produced by melt-spinning from a rapidly solidified SiTiNi alloy. The ribbon exhibits a nanocomposite microstructure with nano-Si particles (~50-200 nm) as potential sites for Li-storage embedded in an amorphous matrix of SiTiNi (STN). Such alloys have shown potential for anode materials in high capacity Li-ion batteries. Systematic lithiation and de-lithiation cycles were performed and selected samples after different cycles were investigated using Atom Probe Tomography (APT) to understand the Li diffusion mechanism in and out of the Si particles. We consider Atom Probe Tomography as a powerful tool to understand the phase changes at an atomic level3. Aided by Focus Ion Beam (FIB), we can address the nm-scale element distribution in any local structure. On the other hand, Hard X-Ray Photoelectron Spectroscopy (HAXPES) is adopted for a detailed SEI study. The employed high energy X-ray beams can probe deeper information of core level photoemission [1] Bach, P.; Valencia-Jaime, I.; Ruett, U.; Gutowski, O.; Romero, A.H.; Renner, F.U. Chemistry of Materials (2016), doi: 10.1021/acs.chemmater.5b04719; Renner, F.U.; Kageyama, H.; Siroma, Z.; Shikano, M.; Schröder, S.; Gründer, Y.; Sakata, O. Gold Model Anodes for Li-Ion Batteries: Single Crystalline Systems Studied by In Situ X-ray Diffraction, Electrochim. Acta 2008, 53, 6064-6069. [2] Son et al. “A Highly Reversible Nano Si Anode Enabled by Mechanical Confinement in an Electrochemically Activated LiXTi4Ni4Si7 Matrix.” Advanced Energy Materials 2 (2012), 1226. [3] Diercks et al., Microscopy of Chemical and Mechanical Heterogeneities in Lithium Cobalt Oxide, Microscopy and Microanalysis 21 (2015), 523.

Atom Probe Tomography Study on Lithiation Behavior in Silicon Alloy Electrodes

With respect to its high specific capacity, silicon would be an ideal replacement for carbonaceous anodes in lithium-ion batteries. But the usage of silicon-based active materials has been hindered by its tremendous volume change and related problems during lithiation cycles. To mitigate the problems, the silicon particles are often used as (expensive) nanoparticles, or some recent strategies include confined Si precipitates embedded in a matrix material. Among others, for example, Si/Ti4Ni4Si7 (STN) has been recently proposed [1]. However, the lithiation mechanisms remain poorly understood for either pure silicon or silicon alloys, due to the silicon (and silicon alloy) amorphization induced by lithiation. We consider Atom Probe Tomography (APT) as a powerful tool [2] to understand the mechanisms of lithium insertion and interaction in silicon alloy electrodes. APT is enabling for a sub-micron sample prepared by Focused Ion Beam (FIB) to address the elemental distribution at the atomic level. Our results propose a strong contribution of interfaces in such nano-scale Si alloys [3]. In the discharged state we revealed a core-shell structure with the formation of a Li-rich shell surrounding a pure silicon core. Hereby, not only an accurate composition of this shell is determined by APT, but also the lithium atom position in the matrix is provided. We believe that this study will be beneficial not only for silicon alloys, but also for understanding pure silicon lithiation mechanisms. [1] Son et al. “A Highly Reversible Nano-Si Anode Enabled by Mechanical Confinement in an Electrochemically Activated LiXTi4Ni4Si7 Matrix.” Advanced Energy Materials 2 (2012), 1226. [2] Diercks et al., Microscopy of Chemical and Mechanical Heterogeneities in Lithium Cobalt Oxide, Microscopy and Microanalysis 21 (2015), 523. [3] Y.Zheng, KG. Pradeep, F.U. Renner et al., to be published. Figure 1. The atom probe tomography reconstruction of Silicon atoms in pristine Si/Si7Ti4Ni4. Figure 1

Preparation and Electrochemical Properties of Nano Si-C Composite

nanoSi-C composite was prepared using eletronspinning technique. The microstructure and morphology of the Si-C composite were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The electrochemical performances of the Si-C composite were tested by battery testing system. The results showed that the Si-C composite not only behaved high initial capacity but also good cycle performances. The reversible discharge capacity could remain at 860 mAhg-1 when current density was 50 mAg-1. The rate reversible capacity is much higher than that of pure nanoSi anode at same condition.

In situ Scanning electron microscope study and microstructural evolution of nano silicon anode for high energy Li-ion batteries

In situ and ex situ scanning electron microscopy of nano Si and SiO anode particles was carried out during the first cycles, and at various stages of charge. The particle size effects were explored in the range 0.1–20 μm, providing a new insight into the micro-structural evolution of the particles as a function of their size, and into the ‘mechanical’ resistance upon important volume change upon phase transformation of these anodes. For small particles, the failure of the battery comes from an electrochemical sintering that compacts the whole electrode, which results in its cracking. The particles keep their integrity when the discharge is stopped at a voltage 0.1 V, which corresponds to the chemical composition Li12Si7, while the particles are known to crack at deeper discharge up to Li22Si5. Replacing the Si particles by SiO particles in an attempt to avoid these structural effects did not help, because of the different chemical reactions during cycling, with the loss of oxygen.

Effect of oxide layer thickness to nano–Si anode for Li-ion batteries

Oxide thickness controlled amorphous SiO2/nano-Si core–shell structure anode for Li ion batteries was easily prepared by etching with NaOH solution using commercial nano-Si with a native oxide. Based on X-ray diffraction patterns and analysis of high resolution transmission microscope images, the electrode which consists of amorphous SiO2/amorphous Si/core crystalline Si after the first cycle showed a self-limiting reaction behavior. Due to this unique dual core–shell structure for a short diffusion path, a high reversible capacity of about 1800 mAh g−1 over 50 cycles and excellent rate capability could be achieved.

Nano-silicon composites using poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) as elastic polymermatrix and carbon source for lithium-ion battery anode

Nano-silicon composites, Si/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and Si/C, were prepared by an in situ chemical polymerization of 3,4-ethylenedioxythiophene (EDOT) with nano-Si particles in a PSS aqueous solution and subsequent carbonization of Si/PEDOT:PSS, respectively. The nano-Si particles were embedded in a shapeless PEDOT:PSS matrix and amorphous carbon in the corresponding composite. Energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) measurements revealed that 2.66 wt% of the element sulfur was doped in the carbon matrix for Si/C composite. Both the Si/PEDOT:PSS and Si/C composite electrodes exhibited higher initial coulombic efficiency and better cycling performance than the bare nano-Si anode. The Si/C composite showed the best electrochemical performance, retaining a specific capacity of 768 mA h g−1 and a Coloumbic efficiency of 99.2% after 80 cycles, with a very small initial capacity loss of 2.80% and a capacity fade of 0.48% per cycle.

The crystal structural evolution of nano-Si anode caused by lithium insertion and extraction at room temperature

The crystal structure and morphology of nanosized Si particles and wires after Li-insertion/extraction electrochemically have been studied by ex-situ XRD, Raman spectroscopy and electronic microscopy. It is confirmed that the insertion of lithium ions at room temperature destroys the crystal structure of Si gradually and leads to the formation of metastable amorphous Li–Si alloy. Furthermore, local ordered structure of Si can be restored after the partial extraction of lithium ions, which indicates the extraction of lithium ions promoting the recrystallization of amorphous Li-inserted Si. It was also observed that nanosized Si particles and wires were merged together after the insertion/extraction of lithium ions.