One-Step Hydrothermal Synthesis of SnO2@Carbon Composites with Super Lithium Ions Storage Performances.

Tin oxide (SnO2) based anode materials for lithium ion batteries (LIBs) have drawn much attention for their high theoretical capacity and energy density, but suffer from a large volume change and resulting a rapid capacity fading during charging/discharging cycles. To optimize the status, herein, SnO2/carbon composites are synthesized using SnCl4 · 5H2O and glucose with different mass ratio as raw materials via a simple one-step hydrothermal process, following calcination under Ar gas atmosphere. As comparison, pure SnO2 is synthesized as the same as SnO2/carbon composites without glucose and calcination in air. The electrochemical impedance spectroscopy (EIS) measurements were used to investigate the lithium ions storage behavior in pure SnO2 and the SnO2@carbon composites. The EIS results indicate that pure SnO2 has much larger electronic transfer resistance and smaller diffusion coefficient of Li+ resulting worst electrochemical performances, while carbon can substantially enhance the electronic conductivity of the composites and resulting better cycle stability and rate capability of the composite anodes. Moreover, the stability and capacity of the composites are different from each other due to diverse carbon content, surface area and particle size, in which, SnO2-24%C exhibits better lithium storage performances. The initial discharge/charge capacities are up to 1650 and 890 mAh g-1 at the current density of 0.2 A g-1, and the reversible capacity even still maintains at 800 mAh g-1 after 60 cycles. The super electrochemical performances are attributed to that the proper content of carbon clusters as a support can buffer volume expansion of SnO2 during cycling, enhance the electrode conductivity and accelerate the diffusion of Li+ ions in the composite. The results implying that the composite with proper carbon content has a wide application prospect for anode material of LIBs.

A Spinel Tin Ferrite with High Lattice-Oxygen Anchored on Graphene-like Porous Carbon Networks for Lithium-Ion Batteries with Super Cycle Stability and Ultra-fast Rate Performances.

A new type of nano-SnFe2O4 with stable lattice-oxygen and abundant surface defects anchored on ultra-thin graphene-like porous carbon networks (SFO@C) is prepared for the first time by an interesting freezing crystallization salt template method. The functional composite has excellent rate performance and long-term cycle stability for lithium-ion battery (LIB) anodes due to the stable structure, improved conductivity, and shortened migrating distance for lithium-ions, which are derived from the higher lattice-oxygen of SnFe2O4, abundant porous carbon networks and surface defects, and smaller nanoparticles. Under the ultra-high current density of 10, 15, and 20 A g-1 cycling for 1000 times, the SFO@C can provide high reversible capacities of 522.2, 362.5, and 361.1 mAh g-1, respectively. The lithium-ion storage mechanism of the composite was systematically studied for the first time by in situ X-ray diffraction (XRD), ex situ XRD and scanning electron microscopy (SEM), and density functional theory (DFT) calculations. The results indicate that the existence of Li2O and metallic Fe during the lithiation/delithiation process is a key reason for reducing the initial lithium-ion storage reversibility but increasing the rate performance and capacity stability in the subsequent cycles. DFT calculations show that lithium-ions are more easily adsorbed on the (111) crystal plane with a much lower adsorption energy of -7.61 eV than other planes, and the Fe element is the main acceptor of electrons. Moreover, the kinetics investigation indicates that the lithium-ion intercalation and deintercalation in SFO@C are mainly controlled by the pseudocapacitance behavior, which is favorable to enhancing the rate performance. The research provides a new strategy for designing LIB electrode materials with a stable structure and outstanding lithium-ion storage performance.

Synergistic effects of flake-like ZnO/SnFe2O4/nitrogen-doped carbon composites on structural stability and electrochemical behavior for lithium-ion batteries.

In order to improve the electrochemical performance and relieve volume expansion of pure SnFe2O4 anode for lithium-ion batteries (LIBs), we synthesized a novel ZnO/SnFe2O4/nitrogen-doped carbon composites (ZSFO/NC) with flake-like polyhedron morphology by using ZIF-8 as a sacrificial template. Remarkably, it exhibited an initial charge/discharge capacities of 1078.3/1507.5 mAh g-1 with a high initial coulombic efficiency (ICE) of 71.2%, and maintained a steady charge/discharge capacities of 1495.7/1511.8 mAh g-1 at 0.2 A g-1 after 300 cycles. The excellent rate performance of 435.6 mAh g-1 at a higher current density of 10.0 A g-1 and superior reversible capacity of 532.3/536.2 mAh g-1 after 500 cycles at 2.0 A g-1 were obtained. It revealed that the nitrogen-doped carbon matrix and peculiar structure of ZSFO/NC not only effectively buffered large volume expansion upon (de)lithiation through the synergistic interface action between ZnO, SnFe2O4 and NC, but also improved capacity of the composite by large contribution of surface pseudo-capacitance. The excellent charge-discharge performance showed that ZSFO/NC composite has a great potential for LIBs due to the synergistic effect of the multi-components.

Comparative Study of Electrochemical Performance of SnO2 Anodes with Different Nanostructures for Lithium-Ion Batteries.

Powders composed of SnO2 nanostructures including microporous nanospheres, mesoporous nanospheres and nanosheets were synthesized by the direct hydrothermal hydrolyzation of SnCl4, hydrothermal hydrolyzation of SnCl4 using glucose as a soft template and precipitation of SnCl2 ∙ 2H20 using oxalic acid as a precipitant, respectively. The electrochemical performance of the three samples used as the anode of a lithium ion battery was determined using galvanostatic discharge/charge tests and electrochemical impedance spectroscopy. Among of them, the anode composed of microporous SnO2 nanospheres demonstrated outstanding initial discharge and charge capacities of 2480 and 1510 mAh g-1, respectively, with a coulombic efficiency of 60.9% at a current density of 78 mA g-1 (0.1 C). In addition, high initial discharge and charge capacities of 1398 mAh g-1 and 950 mAh g-1, respectively, with a coulombic efficiency of 67.95% were obtained even at a high current density of 550 mA g-1 (0.7 C). Moreover, a reversible capacity of 500 mAh g-1 with a coulombic efficiency of 99.95% was attained even after 50 discharging/charging cycles at 550 mA g-1 (0.7 C). This superior electrochemical performance of the SnO2 anodes can be attributed to the large specific surface area (172.7 m2 g-1), small crystal size (approximately 15 nm) and the interstitial microporous pores (<2 nm) of the particles, which favored lithium-ion diffusion and insertion/desertion at the surface of SnO2 and decreased the polarization and the volume expansion of SnO2. Moreover, the resistance of the cell and Li+ diffusion coefficient were studied by electrochemical impedance spectroscopy.