The Formation of Layered Double Hydroxide Phases in the Coprecipitation Syntheses of [Ni0.80Co0.15](1−x)/0.95Alx(OH)2(anionn−)x/n (x = 0–0.2, n = 1, 2)

One-Step Solid-State Synthesis of Ni-Rich Cathode Materials for Lithium-Ion Batteries

Ni-rich cathodes are expected to serve as critical materials for high-energy lithium-ion batteries. Increasing the Ni content can effectively improve the energy density but usually leads to more complex synthesis conditions, thus limiting its development. In this work, a simple one-step solid-state process for synthesizing Ni-rich ternary cathode materials NCA (LiNi_0.9Co_0.05Al_0.05O₂) was presented, and the synthesis conditions were systematically studied. It was found that the synthesis conditions have a substantial impact on electrochemical performance. Furthermore, the cathode materials produced through a one-step solid-state process exhibited excellent cycling stability, maintaining 97.2% of their capacity after 100 cycles at a rate of 1 C. The results show that a one-step solid-state method can successfully synthesize Ni-rich ternary cathode material, which has great potential for application. Optimizing the synthesis conditions also provides valuable ideas for the commercial synthesis of Ni-rich cathode materials.

Layered Double Hydroxide-Based Gas Sensors for VOC Detection at Room Temperature

Miniaturized low-cost sensors for volatile organic compounds (VOCs) have the potentiality to become a fundamental tool for indoor and outdoor air quality monitoring, to significantly improve everyday life. Layered double hydroxides (LDHs) belong to the class of anionic clays and are largely employed for NO x detection, while few results are reported on VOCs. In this work, a novel LDH coprecipitation method is proposed. For the first time, a study comparing four LDHs (ZnAl-Cl, ZnFe-Cl, ZnAl-NO3, and MgAl-NO3) is carried out to investigate the sensing performances. As explored through several microscopy and spectroscopy analyses, LDHs show a morphology characterized by a large surface area and a three-dimensional hierarchical flowerlike architecture with micro- and nanopores that induce a fast diffusion and highly effective surface interaction of the target gases. The fabricated sensors, operating at room temperature, are able to reversibly and selectively detect acetone, ethanol, ammonia, and chlorine vapors, reaching significant sensing response values up to 6% at 21 °C. The results demonstrate that by changing the LDHs' composition, it is possible to modulate the sensitivity and selectivity of the sensor, helping the discrimination of different analytes, and the consequent integration on a sensor array paves the way for electronic nose development.

Ni-Rich Layered Oxide with Preferred Orientation (110) Plane as a Stable Cathode Material for High-Energy Lithium-Ion Batteries

The cathode, a crucial constituent part of Li-ion batteries, determines the output voltage and integral energy density of batteries to a great extent. Among them, Ni-rich LiNi_xCo_yMn_zO₂ (x + y + z = 1, x ≥ 0.6) layered transition metal oxides possess a higher capacity and lower cost as compared to LiCoO₂, which have stimulated widespread interests. However, the wide application of Ni-rich cathodes is seriously hampered by their poor diffusion dynamics and severe voltage drops. To moderate these problems, a nanobrick Ni-rich layered LiNi_0.6Co_0.2Mn_0.2O₂ cathode with a preferred orientation (110) facet was designed and successfully synthesized via a modified co-precipitation route. The galvanostatic intermittent titration technique (GITT) and electrochemical impedance spectroscopy (EIS) analysis of LiNi_0.6Co_0.2Mn_0.2O₂ reveal its superior kinetic performance endowing outstanding rate performance and long-term cycle stability, especially the voltage drop being as small as 67.7 mV at a current density of 0.5 C for 200 cycles. Due to its unique architecture, dramatically shortened ion/electron diffusion distance, and more unimpeded Li-ion transmission pathways, the current nanostructured LiNi_0.6Co_0.2Mn_0.2O₂ cathode enhances the Li-ion diffusion dynamics and suppresses the voltage drop, thus resulting in superior electrochemical performance.

Concentration Gradient-Driven Aluminum Diffusion in a Single-Step Coprecipitation of a Compositionally Graded Precursor for LiNi0.8Co0.135Al0.065O2 with Mitigated Irreversibility of H2 ↔ H3 Phase Transition

LiNi_1-x-yCo_xAl_yO₂ (NCA) possessing a nano-/micro hierarchical architecture delivers a high specific capacity of 200 mAh/g with an upper cutoff voltage of 4.4 V. However, the structural reconstruction due to the irreversibility of the H2 ↔ H3 phase transition at higher voltage increases the initial irreversible capacity loss and charge-transfer impedance and reduces the performance at higher C-rates. Structural and electrochemical stability can be achieved by reducing the nickel content and increasing the electrochemically inactive aluminum at the surface. Nonetheless, getting an aluminum concentration gradient in NCA-(OH)₂ is difficult owing to the difference in the solubility constant and reaction kinetics of Al(OH)₃ compared to that of NiCo-(OH)₂. Hence, we have exploited the high diffusion of nano-Al(OH)₃ driven by the concentration gradient of Al across the hierarchical hydroxide structure and synthesized LiNi_0.8Co_0.135Al_0.065O₂ (NCA) with reduced Ni and increased Al at the surface. The process of formation of a concentration gradient was analyzed by X-ray diffraction, Fourier transform infrared spectroscopy, and cross-sectional elemental mapping. The concentration-graded NCA exhibited superior electrochemical performance compared to its pristine counterpart. The graded NCA shows excellent reversibility of the H2 ↔ H3 phase, leading to low impedance development, confirming the reduced surface reconstruction during the initial cycles. Therefore, the specific capacity of graded NCA is 65% higher than that of pristine NCA at 10 C. Both in half-cell and in full-cell configurations, the graded NCA exhibited superior first cycle reversibility and specific capacity. Specifically, in the full-cell configuration, the capacity retention of graded NCA is 91.5%, while that of pristine NCA is 83% after 150 cycles when cycled between 3 and 4.3 V. Further, the capacity loss reduces to 1% even after 500 cycles when the upper cutoff voltage is reduced to 4.2 V in the case of graded NCA.