[en] Highlights: • Long-term ambient storage leads to poor cycling stability of NMC-811. • Electrochemically inactive species were formed during ambient storage. • Mechanisms driving the effect of moisture on NMC-811 materials were identified. • Humid storage promotes the structural deterioration of NMC-811. -- Abstract: High-Ni cathode materials are prone to reactivity and instability upon exposure to ambient levels of humidity. This has implications for the storage and processing of cathodes for Li-ion batteries (LIBs), in order to avoid any premature degradation of the material prior to operation. NMC-811 materials were subjected to differing degrees of exposure to ambient humidity, in order to establish the impact this would have on electrochemical performance. This study used a combination of physical, chemical and electrochemical methods to investigate the operational effects that moisture can have on the battery accordingly. Longer-term cycling, d-SIMS and microscopy were used to characterise the degradation phenomena and relating to capacity fade. Post-mortem analysis revealed that the structural breakdown of the secondary particles is a dominant factor that influences charge transfer resistance increases. The study highlights the criticality of how high Ni materials are handled during storage and processing, in order to mitigate premature degradation events during operation.

[en] Highlights: • High surface area nano-structured Nb₂O₅ created via a simple hydrothermal method. • Anisotropically crystalline Nb₂O₅ related to T-structure characterised electrochemically. • Anisotropically crystalline, T and H- Nb₂O₅ capable of cycling to rates of 100 C. • H-Nb₂O₅ presented as a high rate anode without the need for carbon integration. • All materials have high current stability tested at 20C over 200 cycles. -- Abstract: Orthorhombic niobium pentoxide (T-Nb₂O₅) is known to be an effective anode material for Li-ion batteries (LIBs) with very high rate capability, but the other Nb₂O₅ polymorphs and non-crystalline phases have lacked thorough exploration. A simple hydrothermal mechanism is used to produce an anisotropically crystalline ‘as-synthesised material’, which has not previously been characterised electrochemically. The as-synthesised material is heat-treated to produce T-Nb₂O₅ at 600°C and monoclinic (H-) Nb₂O₅ at 1000°C. We present electrochemical properties for all of these materials. Collectively we report rate sweeps and demonstrate high current stability (20 C-rate capability) and a long life span, up to 200 cycles. We propose the H-phase as a high rate anode when prepared via an anisotropically crystalline precursor, as it is able to demonstrate 60 % capacity retention after 200 cycles at a notably high current flux of 20 C. Such high rates results are rare for this material without integration with carbon materials. For the anisotropically crystalline Nb₂O₅ material, we achieve cycling rates up to 100 C with 80% capacity recovery upon current reduction, representing an important discovery in the development of very high rate anode materials.

[en] While silicon-based negative electrode materials have been extensively studied, to develop high capacity lithium-ion batteries (LIBs), implementing a large-scale production method that can be easily transferred to industry, has been a crucial challenge. Here, a scalable wet-jet milling method was developed to prepare a silicon-graphene hybrid material to be used as negative electrode in LIBs. This synthesized composite, when used as an anode in lithium cells, demonstrated high Li ion storage capacity, long cycling stability and high-rate capability. In particular, the electrode exhibited a reversible discharge capacity exceeding 1763 mAh g⁻¹ after 450 cycles with a capacity retention of 98% and a coulombic efficiency of 99.85% (with a current density of 358 mA g⁻¹). This significantly supersedes the performance of a Si-dominant electrode structures. The capacity fade rate after 450 cycles was only 0.005% per cycle in the 0.05–1 V range. This superior electrochemical performance is ascribed to the highly layered, silicon-graphene porous structure, as investigated via focused ion beam in conjunction with scanning electron microscopy tomography. The hybrid electrode could retain 89% of its porosity (under a current density of 358 mA g⁻¹) after 200 cycles compared with only 35% in a Si-dominant electrode. Moreover, this morphology can not only accommodate the large volume strains from active silicon particles, but also maintains robust electrical connectivity. This confers faster transportation of electrons and ions with significant permeation of electrolyte within the electrode. Physicochemical characterisations were performed to further correlate the electrochemical performance with the microstructural dynamics. The excellent performance of the hybrid material along with the scalability of the synthesizing process is a step forward to realize high capacity/energy density LIBs for multiple device applications. (paper)