The addition of tungsten has been reported to greatly improve the capacity retention of Ni‐rich layered oxide cathode materials in lithium‐ion batteries. In this work, Ni(OH)2 precursors, coated with WO3 and also W‐containing precursors prepared by co‐precipitation followed by heat treatment with LiOH·H2O, are studied. Structural analysi s and electron microscopy show that W is incorporated as amorphous LixWyOz phases concentrated in all the grain boundaries between the primary particles of LiNiO2 (LNO) and on the surface of the secondary particles. Tungsten does not substitute for Ni or Li in the LNO lattice no matter how W is added at the precursor synthesis stage. Scanning electron microscopy (SEM) images show that adding W greatly suppresses primary particle growth during synthesis. In agreement with previous literature reports, cycling test results show that 1% W added to LNO can greatly improve charge–discharge capacity retention while also delivering a high specific capacity. The LixWyOz amorphous phases act as coating layer on both the primary and secondary particles, restrict primary particle growth during synthesis and increase the resistance of the secondary particles to microcracking.

The development of an efficient electrocatalyst for hydrogen evolution reaction (HER) is essential to facilitate the practical application of water splitting. Here, we aim to develop an electrocatalyst, Ni/Ni­(OH)2/NiOOH, via electrodeposition technique on carbon cloth, which shows efficient activity and durability for HER in an alkaline medium. Phase purity and morphology of the electrodeposited catalyst are determined using powder X-ray diffraction and electron microscopic techniques. The compositional and thermal stability of the catalyst is checked using X-ray photoelectron spectroscopy and thermogravimetry analysis. Electrodeposited Ni/Ni­(OH)2/NiOOH material is an efficient, stable, and low-cost electrocatalyst for hydrogen evolution reaction in a 1.0 M KOH medium. The catalyst exhibits remarkable performance, achieving a current density of 10 mA/cm2 at a potential of −0.045 V vs reversible hydrogen electrode (RHE), and the Tafel slope value is 99.6 mV/dec. The overall electrocatalytic water splitting mechanism using Ni/Ni­(OH)2/NiOOH catalyst is well explained, where formation and desorption of OH– ion on the catalyst surface are significant at alkaline pH. The developed electrocatalyst shows significant durability up to 200 h in a negative potential window in a highly corrosive alkaline environment along with efficient activity. The electrocatalyst can generate 165.6 μmol of H2 in ∼145 min of reaction time with 81.5% faradic efficiency.

Ni-rich cathode materials suffer from poor capacity retention due to micro-cracking and interfacial reactivity with electrolyte. Addition of tungsten (W) to some Ni-rich materials can improve capacity retention. Here, a WO3 surface coating is applied on Ni-rich hydroxide precursors before heating with lithium hydroxide. After heating in oxygen, Ni-rich materials with any of the commonly used dopants (magnesium, aluminum, manganese, etc.) show a “universal” improvement in capacity retention. Experimental characterization and theoretical modelling showed W was concentrated in the grain boundaries between the primary grains of secondary particles of the layered oxides, and W is incorporated in amorphous LixWyOz phases rather than as a substituent in the LiNiO2 lattice. This self-infusion of W in the grain boundaries during synthesis also significantly restricts primary crystallite grain growth. Along with smaller primary grain size, the LixWyOz phases in the grain boundaries lead to improved resistance to microcracking and reduced surface or interfacial reactivity. Improving the intrinsic properties of primary grains through doping of Mg, Al, or Mn and reinforcing the secondary particle structure mechanically and chemically using W or a similar element, M, that forms LixMOy phases and does not substitute into LiNiO2 is a universal strategy to improve polycrystalline Ni-rich materials.

This work examined the impact of depth of discharge (DOD), C-rate, upper cut-off voltage (UCV), and temperature on the lifetime of single-crystal NMC811/Artificial Graphite (AG) cells. Cells were cycled at C/50, C/10, C/5, or C/3, and 25, 50, 75, or 100% DOD at room temperature (RT, 20. ± 2°C) or 40.0 ± 0.1°C. The UCVs were 4.06 or 4.20 V. After 12000 hours of cycling, experiments such as electrochemical impedance spectroscopy, Li-ion differential thermal analysis (DTA), ultrasonic mapping, X-ray fluorescence, differential capacity analysis, synchrotron computed tomography (CT) scans, and cross-section scanning electron microscopy (SEM) were carried out. We showed that capacity loss increased slightly with DOD and C-rate, and that cells with 4.06 V UCV have superior capacity retention and impedance control compared to 4.20 V. SEM, CT scans, and differential capacity analysis show that microcracking and positive electrode mass loss did not occur regardless of DOD, C-rate, or UCV. DTA and ultrasonic mapping showed no C-rate or DOD dependency for electrolyte changes or “unwetting.” A simple square-root time model was used to model SEI growth in 4.06 V UCV cells, and a cell design with impressive performance is demonstrated.

Reduction of the Co content in Ni-rich positive electrode materials is an intense research area of great interest. Despite high specific capacity, Co-free Ni-rich materials normally suffer from poor cycling performance. In this work, a Co-free precursor with a 16 μm Ni(OH)2 core and 1 μm Ni0.8Mn0.2(OH)2 shell was reacted with LiOH · H2O at 750 °C (CS-750) or 800 °C (CS-800). CS-750 was found to retain the well-defined core–shell structure after heating, while CS-800 became homogeneous in composition due to Ni/Mn interdiffusion at the higher temperature. Although both of materials exhibit higher specific capacity than LiNi0.8Mn0.1Co0.1O2 (NMC811) the charge-discharge capacity retention shows a dramatic difference. The cycling performance of CS-750 is equivalent to NMC811 samples, whereas CS-800 experiences significant capacity fade, suggesting the importance of a core–shell structure for Ni-rich materials with no Co. The electrical resistivity of CS-750 and CS-800 materials are comparable to NCA and are slightly lower than single crystal NMC811 suggesting that Co may not be essential to maintain good electrical properties. The authors believe CS-750 and related materials represent excellent Co-free options for high energy density Li-ion cells.