Ti3C2 MXene-derived Li4Ti5O12 nanoplates with in-situ formed carbon quantum dots for metal-ion battery anodes.

Two-dimensional (2D) material Ti3C2 MXenes have recently been used in electrode composites for lithium-ion batteries (LIBs) for their excellent electrical conductivity and accordion-like nanosheet morphology. However, Ti3C2 has low specific capacity and fast degradation rate upon cycling after inevitably coupling with surface species during synthesis. In this work, Ti3C2 is used as Ti-source for Li4Ti5O12 (LTO) and C-source for carbon quantum dots (CQDs) in a one-step hydrothermal process. The resultant LTO product (M-LTO) inherits the nanosheet morphology of Ti3C2 with uniformly anchored CQDs. The highly electronic conductive CQDs optimize the transmission path of ions which reduces the diffusion barrier of ions, and they further increase the density of states of the material which effectively improving the conductivity of M-LTO. Remarkable electrochemical performances including high initial specific capacity, long lifetime and excellent low temperature capacity are demonstrated for this type of electrode in LIBs, sodium ion batteries (SIBs) and lithium-magnesium ion hybrid batteries (LMIHBs). This paper offers a new strategy to the rapidly expanding research on the application of transition metal MXenes in electrodes for metal-ion batteries.

Identifying Element-Modulated Reactivity and Stability of the High-Voltage Spinel Cathode Materials via In Situ Time-Resolved X-Ray Diffraction.

Designing and identifying a dopant-involved material is quite significant, especially for battery science. LiNi0.5Mn1.5O4, being one of the most appealing candidates for high-potential lithium-ion batteries, has attracted immense attention and been investigated with Al or F dopants for its undesirable inherent structural challenges. Although the excellent performance of Al- or F-doped LiNi0.5Mn1.5O4 has been reported previously, the relationship between dopants, structural variation, and electrochemistry has not been fully identified. Hence, synchronous time-resolved XRD techniques are applied for identifying a guideline of the phase variations in cathodic (Al3+)- and anodic (F-)-substituted LiNi0.5Mn1.5O4, which revealed a three-phase evolution as a function of structural stability. Also, the Al-substituted materials exhibit excellent reactivity and stability, which can be clearly identified via the stable buffer phase existing in high power density or after long cycling due to the improvement in reaction kinetics of phase transition and the lithium-ion diffusion coefficient, just opposite to F doping. This provides a good guideline for identifying an element-modulated mechanism of reactivity or stability of materials science.

In situ synthesis of a high-performance bismuth oxide based composite cathode for low temperature solid oxide fuel cells.

Here, we report the design and fabrication of a cost-effective and high-performance composite (Bi0.75Y0.25)0.93Ce0.07O1.5±Î´-La0.8Sr0.2MnO3 cathode by an in situ synthesis strategy with single-step phase formation and microstructure assembly, which shows lower cathode polarization resistance and better oxygen reduction reaction activity than the conventional LSM-based cathodes for low temperature solid oxide fuel cells.

Understanding Structure-Activity Relationships in Sr1- xY xCoO3-δ through in Situ Neutron Diffraction and Electrochemical Measurements.

In this work, we report a systematic study on temperature-dependent local structural evolution, oxygen stoichiometry, and electrochemical properties of an oxygen-deficient perovskite Sr0.7Y0.3CoO3-δ (SYC30) for oxygen electrocatalysis. The obtained results are then closely compared with its analogue Sr0.9Y0.1CoO3-δ (SYC10) of different crystal structures to establish structure-activity relationships. The comparison shows that both SYC30 and SYC10 consist of alternate layers of oxygen-deficient Co1-polyhedra and oxygen-saturated Co2-octahedra with Co1-polyhedra being responsible for Vo•• migration. It is also found that the distribution and concentration of oxygen vacancies within the Co1-layer are, respectively, less symmetrical and lower in SYC30 than those in SYC10, making the former unfavorable for oxygen transport. A molecular orbital energy analysis reveals that the energy gap between Fermi level and O 2p level in the active Co1-polyhedra is larger in SYC30 than that in SYC10, further suggesting that SYC10 is a better oxide-ion conductor and thus a better electrocatalyst for oxygen reduction reaction, which is unambiguously confirmed by the subsequent electrochemical measurements.

A Combined Variable-Temperature Neutron Diffraction and Thermogravimetric Analysis Study on a Promising Oxygen Electrode, SrCo0.9Nb0.1O3-δ, for Reversible Solid Oxide Fuel Cells.

The present study investigates the temperature-structure-stoichiometry relationship of a promising oxygen electrode SrCo0.9Nb0.1O3-δ over a temperature (T) range from room temperature (RT) to 900 °C. The techniques employed are variable-temperature neutron diffraction (VTND) and thermogravimetric analysis (TGA). At T < 75 °C, VTND reveals a tetragonal (P4/mmm) structure with a G-type magnetic ordering. Above 75 °C, the nucleus structure remains the same, while the magnetic ordering disappears. A phase transition from tetragonal (P4/mmm) to cubic (Pm3̅m) is observed at 412 °C, where the two Co sites and three O sites in the P4/mmm phase converge to one equivalent site, respectively. The phase transition temperature coincides with the peak temperature of oxygen uptake obtained by TGA. It is also observed that the Nb dopant has no preferred Co site to occupy. The oxygen vacancies are mostly located at the O3 site surrounding the Co2 site in the P4/mmm structure. The intermediate-spin state of Co3+ at the Co2 site is responsible for the observed distortions of CoO6 octahedra, i.e., elongation of Co2O6 octahedra and shortening of Co1O6 octahedra along the c-axis, which is a phenomenon known as Jahn-Teller distortion. At high temperatures, large thermal displacement factor for O2- is observed with high concentration of oxygen vacancies, providing a structural environment favorable to high O2- conductivity in Nb-doped SrCoO3-based oxygen electrode materials.