Carbon confined GeO2 hollow spheres for stable rechargeable Na ion batteries†

Germanium (Ge) based nanomaterials are regarded as promising high-capacity anode materials for Na ion batteries, but suffer fast capacity fading problems caused by the alloying/de-alloying reactions of Na–Ge. Herein, we report a new method for preparing highly dispersed GeO₂ by using molecular-level ionic liquids (ILs) as carbon sources. In the obtained GeO₂@C composite material, GeO₂ exhibits hollow spherical morphology and is uniformly distributed in the carbon matrix. The as-prepared GeO₂@C exhibits improved Na ion storage performances including high reversible capacity (577 mA h g⁻¹ at 0.1C), rate property (270 mA h g⁻¹ at 3C), and high capacity retention (82.3% after 500 cycles). The improved electrochemical performance could be attributed to the unique nanostructure of GeO₂@C, the synergistic effect between GeO₂ hollow spheres and the carbon matrix ensures the anode material effectively alleviates the volume expansion and the particle agglomeration problems.

We report a new method for preparing dispersed GeO₂ by using molecular-level ionic liquids as carbon sources. In the obtained GeO₂@C composite material, GeO₂ exhibits hollow spherical morphology and is uniformly distributed in the carbon matrix.

Facile synthesis of Si/Ge/graphite@C composite with improved tap density and electrochemical performance

Nanoengineering is one of the most effective methods to promote the lithium storage performance of silicon material, which suffers from huge volume changes and poor reaction kinetics during cycling. However, the commercial application of nanostructured silicon is hindered by its high manufacturing cost and low tap density. Herein, a Si/Ge/graphite@C composite was successfully synthesized by ball-milling with subsequent calcination. By introducing Ge, graphite and an amorphous carbon coating, both tap density and electrochemical performance are improved significantly. Benefiting from the synergetic effects of the above components, the Si/Ge/graphite@C composite delivers a reversibility capacity of 474 mA h g-1 at 0.2 A g-1 and stable capacity retention.

A Novel Tin-Bonded Silicon Anode for Lithium-Ion Batteries

Poor cyclic stability and low rate performance due to dramatic volume change and low intrinsic electronic conductivity are the two key issues needing to be urgently solved in silicon (Si)-based anodes for lithium-ion batteries. Herein, a novel tin (Sn)-bonded Si anode is proposed for the first time. Sn, which has a high electronic conductivity, is used to bond the Si-anode material and copper (Cu) current collector together using a hot-pressed method with a temperature slightly above the melting point of Sn. The cycling performance of the electrode is studied using a galvanostatic method. Nanoindentation and peeling tests are conducted to measure the mechanical strength of the electrodes. Direct current polarization and galvanostatic intermittent titration techniques are applied to assess the conductivity of the composites. Electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy are conducted to evaluate the effect of the coating layer on the cycling ability of the composites. The Sn-bonded Si anodes show superior cycling stability and high rate performance with an improved initial Coulombic efficiency. Analyses reveal that the low-melting-point Sn helps to markedly improve the electronic conductivity of the electrodes and serves as a metallic binder as well to enhance the adhesive strength of the electrode. It is hopeful that this novel Sn-bonded Si anode provides a new insight for the development of advanced Si-based anodes for LIBs.