Polyaniline/Polyoxometalate Hybrid Nanofibers as Cathode for Lithium Ion Batteries with Improved Lithium Storage Capacity

Hybrid nanofibers of polyaniline/polyoxometalate are synthesized via a facile interfacial polymerization method for the first time, and evaluated as a cathode material for lithium ion batteries. The hybrid nanofibers with 100 nm diameter consisted of phosphomolybdic acid polyanion, [PMo₁₂O₄₀]^3–, and polyaniline matrix. Their 1D geometry improves the utilization of electrode materials and accommodates the volume change during cycling, which enables the significant improvement in lithium storage capacity and capacity retentions. The phosphomolybdic acid polyanions not only exhibit a large theoretical capacity of about 270 mAh g^–1, but also reduce the charge transfer resistance of electrode leading to the enhanced reversible capacity and rate capability. The polyaniline/polyoxometalate nanofibers delivered a remarkably improved electrochemical performance in terms of lithium storage capacity (183.4 mAh g^–1 at 0.1C rate), cycling stability (80.7% capacity retention after 50 cycles), and rate capability (94.2 mAh g^–1 at 2C rate) compared to polyaniline nanofibers and bulk polyaniline/polyoxometalate hybrid

Dominant Factors Governing the Rate Capability of a TiO₂ Nanotube Anode for High Power Lithium Ion Batteries

Titanium dioxide (TiO₂) is one of the most promising anode materials for lithium ion batteries due to low cost and structural stability during Li insertion/extraction. However, its poor rate capability limits its practical use. Although various approaches have been explored to overcome this problem, previous reports have mainly focused on the enhancement of both the electronic conductivity and the kinetic associated with lithium in the composite film of active material/conducting agent/binder. Here, we systematically explore the effect of the contact resistance between a current collector and a composite film of active material/conducting agent/binder on the rate capability of a TiO₂-based electrode. The vertically aligned TiO₂ nanotubes arrays, directly grown on the current collector, with sealed cap and unsealed cap, and conventional randomly oriented TiO₂ nanotubes electrodes were prepared for this study. The vertically aligned TiO₂ nanotubes array electrode with unsealed cap showed superior performance with six times higher capacity at 10 C rate compared to conventional randomly oriented TiO₂ nanotubes electrode with 10 wt % conducting agent. On the basis of the detailed experimental results and associated theoretical analysis, we demonstrate that the reduction of the contact resistance between electrode and current collector plays an important role in improving the electronic conductivity of the overall electrode system

Si/Ge Double-Layered Nanotube Array as a Lithium Ion Battery Anode

Problems related to tremendous volume changes associated with cycling and the low electron conductivity and ion diffusivity of Si represent major obstacles to its use in high-capacity anodes for lithium ion batteries. We have developed a group IVA based nanotube heterostructure array, consisting of a high-capacity Si inner layer and a highly conductive Ge outer layer, to yield both favorable mechanics and kinetics in battery applications. This type of Si/Ge double-layered nanotube array electrode exhibits improved electrochemical performances over the analogous homogeneous Si system, including stable capacity retention (85% after 50 cycles) and doubled capacity at a 3<i>C</i> rate. These results stem from reduced maximum hoop strain in the nanotubes, supported by theoretical mechanics modeling, and lowered activation energy barrier for Li diffusion. This electrode technology creates opportunities in the development of group IVA nanotube heterostructures for next generation lithium ion batteries