•A mesoporous Si@C/graphite material is prepared via an accessible route on Al-Si alloy.•The material shows a much higher initial coulombic efficiency.•The stable cycling performances can be ascribed to the porous structure, the amorphous carbon layer and the graphite.A mesoporous Si@amorphous carbon/graphite (Si@C/G) material is synthesized by acid etching technique on a low-cost Al-Si alloy followed by ball-milling and heat treatment process. The Galvanostatic charge/discharge tests prove that the specific anodes hold a high gravimetric capacity of 919.0 mAh g−1 after 150 cycles. In addition, benefiting from the addition of the graphite, a relatively high initial coulombic efficiency of 78.4% is achieved. The physical-chemical properties are characterized by SEM, XRD, XPS, TEM and N2 sorption methods, revealing that the mesoporous Si is coated by amorphous carbon layer, ca. 20 nm. The mesoporous structure of Si can refrain the volume expansion of hybrid material during the lithium insertion/extraction process and can create efficient channels for the fast transport of Li+, and the outer carbon layer and graphite can increase the electroconductibility of the anode material. This low-cost Si@C/G hybrid material with improved electrochemical properties via a simple and applicable synthesis process on Al-Si alloy is prospective for scalable production in commercial lithium ion batteries.Download high-res image (330KB)Download full-size image

•SiO-C composite is prepared by a low-cost and simple method.•Pre-milling of graphite makes the components disperse more evenly.•Pre-milling of graphite enhances the conductivity of the SiO-C composite.•Cycling performance is improved by pre-milling of graphite.•Li4SiO4 and amorphous Si as the products of the 1st cycle are verified by HRTEM.A SiO/graphite/amorphous carbon (SiO-C) hybrid anode with superior electrochemical performance is successfully realized by using a low-cost and simple method. Here, we apply a pretreatment of commercialized graphite by ball-milling to realize evenly dispersion of the components and good effect of carbon coating, thus resulting in excellent cycling stability. Specifically, the as-prepared sample shows a high reversible capacity of 850 mA h g−1 after 100 cycles at 100 mA g−1 and excellent rate capability of 730 mA h g−1 even at 500 mA h g−1. Additionally, a relatively high initial coulombic efficiency of 77% is delivered among SiO-based anode materials. High-resolution transmission electron microscope (HRTEM) technique is used to further visually verify the conversion behavior of SiO in the first cycle: scattered amorphous silicon particles with size about 5 nm and irreversible Li4SiO4 as the detected resultants. The result of electrochemical impedance spectroscopy (EIS) reveals that the polarization resistance (Rp) decreases with pre-treated graphite. This work presents a facile approach to prepare Si-based anode material for new generation lithium-ion batteries with high energy density and more insights into the conversion behavior of SiO.

•Si/Li2TiO3 nanocomposite is prepared by sol–gel method.•A buffer matrix of Li–Ti–O ternary phase ensures good cyclic performance.•The lithiation and delithiation behaviors at different potentials are investigated.•Si/Li2TiO3 composite indicates excellent electrochemical performance than pure Si.Silicon/lithium titanate (Si/Li2TiO3) nanocomposite is successfully prepared through the combination of a sol–gel approach with a high-temperature treatment as well as a high energy ball milling process. The structure and morphology of the composite are characterized by the X-ray diffraction (XRD), scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM) analysis reveals Si particles are coated by the uniform disordered Li2TiO3 layer with a thickness of about 5 nm. The investigation in cycling performances demonstrates that Si/Li2TiO3 exhibits the improved cycling stability, with specific capacity of 471.0 mA h g−1 after 50 cycles and the capacity retention is 31.5%, much higher than pure Si. Compared with pure Si, Si/Li2TiO3 shows better rate-capability, a reversible capacity of 315.2 mA h g−1 at 0.8 A g−1 is maintained. The higher ionic conductivity of Li2TiO3 is responsible for the improved rate performance. In addition, the results derived from XRD, the cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) indicate that lithium ions could react reversibly with Si, and electrochemically less active Li2TiO3 turns into the Li–Ti–O ternary phase, which acts as a buffer matrix in the Si/Li2TiO3 composite, thus improving the reversibility of electrode.

A cost-efficient and scalable method is designed to prepare a SiOx–C composite with superior cyclability and excellent rate performance. The glucose addition in a two-step way induces a hierarchical structure, where individual SiOx nanoparticles are wrapped by a conductive carbon layer and these agglomerated particles are further wrapped by a carbon shell functioning as an electrolyte blocking layer. Instrumental analysis indicates that the SiOx domains are comprised of SiO2 and SiO. The SiOx–C anode exhibits a high reversible specific capacity of 674.8 mA h g−1 after 100 cycles at 100 mA g−1 with a capacity retention of about 83.5%. The excellent electrochemical performance is due to the hierarchical structure, the well-dispersed conductive carbon network, and the Li2O and Li4SiO4 generated in the initial discharge process, all of which can immensely relieve the volume expansion induced by the lithiation of silicon. This hierarchical SiOx–C composite has a promising prospect of practical application given its adequate storage capacity, good cycling stability, commercially available materials and simple equipment.

Manganese phosphide anode material is successfully prepared by a high-temperature solid-phase synthesis process, and its phase structure changes during cycling are revealed in this work. The results derived from X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) combined with selection area electron diffraction (SAED) show that the prepared MnP powder has a single crystalline structure covered with an amorphous oxide layer. Galvanostatic charge/discharge test results indicate that in the voltage range between 0.01 V and 2.00 V at the current density of 50 mA g−1, the MnP anode delivers an initial lithiation and delithiation capacity of 1104 mAh g−1 and 870 mAh g−1, respectively. After 50 cycles, the retained capacity reaches 287 mAh g−1. XRD results indicate that the single crystalline MnP phase is transformed to an amorphous LixMnyPz phase during the initial lithiation process. During the following cycles, the content of the MnP phase is gradually reduced, and the content of the amorphous LixMnyPz phase is continuously accumulated. The amorphous LixMnyPz and Mn2P phases residued in the anode act as the buffer matrix for the MnP active material to suppress the decrease of the lithiation and delithiation capacity during cycling. This amorphous structure is believed to be responsible for the reversible lithiation and delithiation after decade cycles.Graphical abstractHighlights► MnP is prepared by a high-temperature solid-phase synthesis process. ► MnP powder has a single crystalline structure. ► MnP anode delivers a steady capacity after decade cycles. ► Amorphous phases are formed. ► Amorphous structure is responsible for the reversible capacity after decade cycles.

An MgH2 + 1 mol% Nb2O5 system was modified by heptane and acetone through a high-energy ball milling process, and their rehydrogenation performances were investigated. XRD results indicated that except MgH2 and Nb2O5 phases Mg and MgO phases existed after ball milling. The rehydrogenation results showed that after modification by heptane the capacity increased from 3.0 wt% and 4.2 wt% to 5.0 wt% and 5.5 wt% within 110 s at 523 K and 573 K, respectively. The hydriding rate increased from 0.08 wt%/s after 20 s to 0.22 wt%/s after 10 s at 523 K. However, after modification by acetone it only absorbed 1.8 wt% and 2.0 wt% of hydrogen even within 8000 s at 523 K and 573 K, respectively. Rietveld refinement results indicated that after modification by the heptane the content of MgO was reduced from 6.8 wt% to 4.2 wt%, while after the modification by the acetone the content of MgO was significantly increased from 6.8 wt% to 23.8 wt%. The difference in the rehydrogenation performance was believed to be attributed to the different contents of the MgO phase, which led to the difference in the contents of the MgH2 phase. It implied that the heptane acted as a solvent without oxygen element in it to prevent the MgH2 + Nb2O5 system from aggregation, crystallization and oxidation. It suggested heptane was suitable for the improvement of the rehydrogenation performance of MgH2 system.

An Li-Mg-N-H system has been synthesized from Mg(NH2)2 and LiH in the ratio 3:8 by a ball-milling process and its dehydrogenation/rehydrogenation properties at around 190°C were investigated. XRD, FTIR and TG results showed that the system was composed of an LiH phase and an amorphous Mg(NH2)2 phase with a purity of 90%. A reversible hydrogen storage capacity of 4.7% was observed during the first cycle and more than 90% of the stored hydrogen was desorbed within 100 min for each cycle. However, only 4.2% and 2.9%, respectively, of hydrogen was observed during two subsequent dehydrogenation cycles. In situ GC results showed that no NH3 could be observed during the dehydrogenation process. On the basis of the SEM and XRD results, the loss in hydrogen storage capacity can be mainly attributed to agglomeration, oxidation and crystallization of the materials.

An amorphous silicon film with an average thickness of up to 2 μm was deposited on copper foil by direct-circuit (dc) magnetron sputtering and coupled with commercial LiCoO2 cathode to fabricate cells. Their cycle performance and high rate capability at room temperature have been investigated. In the voltage range 2.5–3.9 V at the current density of 0.2C (0.11 mA cm−2), the lithiation and delithiation capacity of this cell was first increased to 0.55 mAh cm−2 within 80 cycles and maintained stable during the following cycles. After 300 cycles its capacity still retained 0.54 mAh cm−2. High-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) image indicated that the sputtered film could keep an amorphous structure although the volume expansion ratio during the lithiation and delithiation was still up to 300% after 300 cycles observed from scanning electron microscopy (SEM) image. This recovered amorphous structure was believed to be beneficial for the improvement of the cycle life of the cell. Rate performance showed that the cells had a promising high rate capability. At 30C, its lithiation/delithiation capacity remained 25% of that at 0.2C.

A cost-efficient and scalable method is designed to prepare a SiOx–C composite with superior cyclability and excellent rate performance. The glucose addition in a two-step way induces a hierarchical structure, where individual SiOx nanoparticles are wrapped by a conductive carbon layer and these agglomerated particles are further wrapped by a carbon shell functioning as an electrolyte blocking layer. Instrumental analysis indicates that the SiOx domains are comprised of SiO2 and SiO. The SiOx–C anode exhibits a high reversible specific capacity of 674.8 mA h g−1 after 100 cycles at 100 mA g−1 with a capacity retention of about 83.5%. The excellent electrochemical performance is due to the hierarchical structure, the well-dispersed conductive carbon network, and the Li2O and Li4SiO4 generated in the initial discharge process, all of which can immensely relieve the volume expansion induced by the lithiation of silicon. This hierarchical SiOx–C composite has a promising prospect of practical application given its adequate storage capacity, good cycling stability, commercially available materials and simple equipment.