Chemomechanically Stable Ultrahigh-Ni Single-Crystalline Cathodes with Improved Oxygen Retention and Delayed Phase Degradations

The pressing demand in electrical vehicle (EV) markets for high-energy-density lithium-ion batteries (LIBs) requires further increasing the Ni content in high-Ni and low-Co cathodes. However, the commercialization of high-Ni cathodes is hindered by their intrinsic chemomechanical instabilities and fast capacity fade. The emerging single-crystalline strategy offers a promising solution, yet the operation and degradation mechanism of single-crystalline cathodes remain elusive, especially in the extremely challenging ultrahigh-Ni (Ni > 90%) regime whereby the phase transformation, oxygen loss, and mechanical instability are exacerbated with increased Ni content. Herein, we decipher the atomic-scale stabilization mechanism controlling the enhanced cycling performance of an ultrahigh-Ni single-crystalline cathode. We find that the charge/discharge inhomogeneity, the intergranular cracking, and oxygen-loss-related phase degradations that are prominent in ultrahigh-Ni polycrystalline cathodes are considerably suppressed in their single-crystalline counterparts, leading to improved chemomechanical and cycling stabilities of the single-crystalline cathodes. Our work offers important guidance for designing next-generation single-crystalline cathodes for high-capacity, long-life LIBs

Vaper Phase Polymerized PEDOT/Cellulose Paper Composite for Flexible Solid-State Supercapacitor

A flexible solid-state supercapacitor based on vapor phase polymerized (VPP) PEDOT into cellulose paper matrix (PEDOT/CP) was successfully fabricated. The PEDOT/CP composite material worked as both current collector and electrode in constructed test cells. It had a low sheet resistance of 14 Ω/square and survived the Scotch tape test for adhesion. It also showed excellent stability with no significant conductivity drop after 1000 cycles of bending. The PEDOT from electrode obtained the mass specific capacitance of 179 F/g at scan rate of 10 mV/s, which was among the highest specific capacitances ever reported. This high capacitance was attributed to the combination of the VPP technique and the porous fibrous structure of the cellulose matrix. The EDOT vapor penetrated and polymerized through the CP matrix made of nanometer to micrometer level CP fibers. The highest electrode volumetric capacitance achieved was 13.7 F/cm3. The whole device achieved an energy density of 0.76 mWh/cm3 and a power density of 0.01 W/cm3. Bending the supercapacitor to 90° or rotating to 45° caused no major change in capacitance. Owing to the all nonmetallic materials used to construct the supercapacitor, it can be easily disposed. The incineration of the supercapacitor does not release significant hazardous exhaust

Nonstoichiometry and Defects in Hydrothermally Synthesized ε‑LiVOPO₄

ε-LiVOPO4 has been synthesized through the hydrothermal method by adjusting the pH of the hydrothermal solution and the reaction temperature. This phase is formed between 180 and 220 °C, as diamond-like crystals around 10–15 μm in size. X-ray diffraction (XRD) analysis shows that hydrothermal ε-LiVOPO4 lattice parameters a and b linearly decrease, while c linearly increases when the synthesis temperature increases. Thermogravimetric analysis with mass spectroscopy reveals 1.5 to 0.5% water loss at about 350 °C for ε-LiVOPO4 synthesized at 180 and 220 °C, suggesting water or protons incorporation into the structure. Magnetic studies reveal ferrimagnetism in hydrothermal ε-LiVOPO4 below 10 K, as opposed to antiferromagnetic ordering below 14 K found in samples synthesized at high temperature. In-situ XRD upon heating of the hydrothermal ε-LiVOPO4 synthesized at 180, 200, and 220 °C reveals that the temperature dependences of their lattice parameters merge at about 500 °C; furthermore, at the same temperature the structure reversibly changes from triclinic to monoclinic. The lattice parameters and the magnetic properties of the hydrothermal samples heated to 750 °C are similar to those of solid-state synthesized ε-LiVOPO4. Based on structure and composition analysis, we suggest that hydrothermal samples can be described as an ε-Li1+xHyV1–zOPO4 (x, y, z < 0.1) solid solution. The electrochemical characterization of hydrothermal ε-LiVOPO4 reveals the first cycle capacity of about 300 mAh/g, which holds for about five cycles, gradually decreasing thereafter. The low-voltage region does not reveal voltage plateaus corresponding to Li1.5VOPO4 and Li1.75VOPO4 phases found in the solid-state material, further suggesting structural disorder in the low-temperature samples evidenced from the lattice parameters and the magnetic properties