Flexible and free-standing LiFePO4/TPU/SP cathode membrane prepared via phase separation process for lithium ion batteries

Construction of high elastic artificial SEI for air-stable and long-life lithium metal anode

Compared with other anode materials, Li metal anode has higher capacity density and lower electrode potential, which has been considered as one of the most promising anode materials. However, the unstable solid electrolyte interface (SEI) leads to Li dendrite growth and the infinite volumetric expansion of Li metal, which seriously hinders the stability and cycle life of Li metal batteries (LMBs). Here, a polyurethane elastomer (TPU) material with high elasticity and air stability is used as the artificial SEI of Li metal anode. Its designed synergistic effect of soft chain forging and hard chain segments not only gives TPU artificial SEI layer good electronic insulation, Li ion conductivity, Li dendrite growth inhibition, high elastic modulus and flexibility to adapt to Li volume expansion, but also has a significant air protection effect on the Li metal surface, so that the TPU coated Li foil will not occur obvious oxidation phenomenon after being placed in air for 45 min. The Li symmetric battery modified by TPU achieved a stable and long-term cycle performance of 1300 h at 1 mA/cm², it can also cycle stably at a high current density of 10 mA/cm². The Coulomb efficiency of the modified Li/Cu half-cell maintains at above 97% after 400 cycles. In addition, the full cell with LiFePO₄ cathode also delivers a very excellent long cycle stability with 90% capacity retention after 1500 cycles at 5 C. This surface modification strategy of SEI on lithium anode has has great research value and will help to improve the widely application of LMBs.

Ultrastable Interfacial Contacts Enabling Unimpeded Charge Transfer and Ion Diffusion in Flexible Lithium-Ion Batteries

Deteriorating interfacial contact under mechanical deformation induces large cracks and high charge transfer resistance, resulting in a severe capacity fading of flexible lithium-ion batteries (LIBs). Herein, an oxygen plasma treatment on a polymer separator combined with high-speed centrifugal spraying to construct ultrastable interfacial contacts is reported. With the treatment, abundant hydrophilic oxygen-containing functional groups are produced and ensure strong chemical adhesion between the separator and the active materials. With single walled carbon nanotubes (SWCNTs) sprayed onto the active materials, a dense thin film is formed as the current collector. Meanwhile, the centrifugal force caused by high-speed rotation together with van der Waals forces under fast evaporation produces a much closer interface between the current collector and the active materials. As a result of this ultrastable interfacial interaction, the integrated electrode shows no structural failure after 5000 bending cycles with the charge-transfer resistance as low as 35.8% and a Li-ion diffusion coefficient nearly 19 times of the untreated electrode. Flexible LIBs assembled with these integrated electrodes show excellent structural and electrochemical stability, and can work steadily under various deformed states and repeated bending. This work provides a new technique toward rational design of electrode configuration for flexible LIBs.

A novel Zr-MOF-based and polyaniline-coated UIO-67@Se@PANI composite cathode for lithium-selenium batteries

In this work, we synthesized a novel UIO-67@Se@PANI composite cathode material for Li-Se battery applications. Zr-MOFs (metal organic frameworks) were used as a support and a PANI (polyaniline) layer was employed as the coating. UIO-67@Se@PANI was expected to be one of the candidates for Li-Se batteries, with a high specific capacity of 248.3 mA h g^-1 at 1C (1C = 675 mA g^-1) after 100 cycles. In particular, stable capacities of 203.1 and 167.6 mA h g^-1 were received after 100 cycles at high rates of 2C and 5C, respectively. To explain such a good electrochemistry performance of the composite cathode material, multiple characterization methods were carried out. And that can be attributed to the sandwich-like structure of the UIO-67@Se@PANI composite and the fact that UIO-67 can provide unsaturated sites to tether the selenium effectively and the PANI layer can improve the electronic conductivity of the whole electrode significantly.