RESUMEN
Traditional dual-ion lithium salts have been widely used in solid polymer lithium-metal batteries (LMBs). Nevertheless, concentration polarization caused by uncontrolled migration of free anions has severely caused the growth of lithium dendrites. Although single-ion conductor polymers (SICP) have been developed to reduce concentration polarization, the poor ionic conductivity caused by low carrier concentration limits their application. Herein, a dual-salt quasi-solid polymer electrolyte (QSPE), containing the SICP network as a salt and traditional dual-ion lithium salt, is designed for retarding the movement of free anions and simultaneously providing sufficient effective carriers to alleviate concentration polarization. The dual salt network of this designed QSPE is prepared through in-situ crosslinking copolymerization of SICP monomer, regular ionic conductor, crosslinker with the presence of the dual-ion lithium salt, delivering a high lithium-ion transference number (0.75) and satisfactory ionic conductivity (1.16 × 10-3 S cm-1 at 30 °C). Comprehensive characterizations combined with theoretical calculation demonstrate that polyanions from SICP exerts a potential repulsive effect on the transport of free anions to reduce concentration polarization inhibiting lithium dendrites. As a consequence, the Li||LiFePO4 cell achieves a long-cycle stability for 2000 cycles and a 90% capacity retention at 30 °C. This work provides a new perspective for reducing concentration polarization and simultaneously enabling enough lithium-ions migration for high-performance polymer LMBs.
RESUMEN
Ionic-conductive polymers are appealing electrolyte materials for solid-state lithium-based batteries. However, these polymers are detrimentally affected by the electrochemically-inactive anion migration that limits the ionic conductivity and accelerates cell failure. To circumvent this issue, we propose the use of polyvinyl ferrocene (PVF) as positive electrode active material. The PVF acts as an anion-acceptor during redox processes, thus simultaneously setting anions and lithium ions as effective charge carriers. We report the testing of various Li||PVF lab-scale cells using polyethylene oxide (PEO) matrix and Li-containing salts with different anions. Interestingly, the cells using the PEO-lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) solid electrolyte deliver an initial capacity of 108 mAh g-1 at 100 µA cm-2 and 60 °C, and a discharge capacity retention of 70% (i.e., 70 mAh g-1) after 2800 cycles at 300 µA cm-2 and 60 °C. The Li|PEO-LiTFSI|PVF cells tested at 50 µA cm-2 and 30 °C can also deliver an initial discharge capacity of around 98 mAh g-1 with an electrolyte ionic conductivity in the order of 10-5 S cm-1.
RESUMEN
Porous titaniumniobium alloys of composition Ti-24Nb, Ti-35Nb and Ti-42Nb were synthesised by electro-deoxidation of sintered oxide discs of mixed TiO2 and Nb2O5 powders in molten CaCl2 at 1173â¯K, and characterised by XRD, SEM, EDX and residual oxygen analysis. At the lower Nb content a dual-phase α/ß-alloy was formed consisting of hexagonal close-packed and body-centred cubic Ti-Nb, whereas at the higher Nb contents a single-phase ß-alloy was formed of body-centred cubic Ti-Nb. The corrosion behaviour of the alloys prepared was assessed in Hanks' simulated body fluid solution at 310â¯K over extended periods of time. Potentiodynamic polarisation studies confirmed that the alloys exhibited passivation behaviour, and impedance studies revealed that the passive films formed on the surface of the alloys comprised a bi-layered structure. XPS analysis further proved that this contained hydroxyapatite at the top and native metal oxide underneath. The mechanical properties of the alloys were evaluated, and the elastic moduli and the Vickers hardness were both found to be in the range of that of bone. Overall, Ti-35Nb is proposed to be the best-suited candidate of the materials studied in regard to biomedical applications.
