The creation of a suitable inorganic colloidal nanocrystal ink for use in a scalable coating process is a key step in the development of low-cost solar cells. Here, we present a facile solution synthesis of chalcopyrite CuInSe 2 nanocrystals and demonstrate that inks based on these nanocrystals can be used to create simple solar cells, with our first cells exhibiting an efficiency of 3.2% under AM1.5 illumination. We also report the first solution synthesis of uniform hexagonal shaped single crystals CuInSe 2 nanorings by altering the synthesis parameter.

A combination of cryogenic electron microscopy and cryogenic focused ion beam enabled the characterization of the interface between Li metal and lithium phosphorous oxynitride, one of the well-known interfaces to exhibit exemplary electrochemical stability with a lithium metal anode. The probed structural and chemical information leads to a more comprehensive understanding of the underlying cause for the interfacial stability and its formation mechanism.

A self-passivating Li2ZrO3 layer with a thickness of 5–10 nm, which uniformly encapsulates the surfaces of LiNiO2 cathode particles, is spontaneously formed by introducing excess Zr (1.4 atom %). A thin layer of Li2ZrO3 on the surface is converted into a stable impedance-lowering solid–electrolyte interphase layer during subsequent cycles. The Zr-doped LiNiO2 cathode with an initial discharge capacity of 233 mA·h·g–1 exhibited significantly improved capacity retention (86% after 100 cycles) and thermal stability, compared to the undoped LiNiO2. While the spontaneously formed Zr-rich coating layer provides surface protection, the Zr ions in the LiNiO2 lattice delay the detrimental phase transition occurring in the deeply charged state of LiNiO2 and partially suppress the anisotropic strain emerging from the phase transition. Further optimization of the proposed simultaneous coating and doping strategy can mitigate the inherent structural instability of the LiNiO2 cathode, making it a promising high-energy-density cathode for electric vehicles.

A remarkable reduction in electronic conductivity in the core region rather than on the surface of secondary particles is proposed as a capacity-fading mechanism of a Ni-rich cathode. This result is confirmed by analyzing the electronic conductivity of the secondary particles of Li[Ni 0.98 Co 0.01 Mn 0.01 ]-O 2 using the scanning spreading resistance microscopy (SSRM) mode of atomic force microscopy. SSRM analysis reveals that a much thicker rocksalt phase, which is transformed from the original layered structure, on the surface of the primary particles in the core region electronically insulates the entire volume of the primary particles from the neighboring particles. Li intercalation−deintercalation is not achievable in the electronically insulated primary particles. Thus, visualization of the local electronic conductivity in the secondary particles confirms that the loss of electronic conductivity in the core region of the secondary particle is a key factor in the capacity fading of a Ni-rich cathode for lithium ion batteries.

Lithium-ion batteries with high energy density, long cycle life, and appropriate safety levels are necessary to facilitate the penetration of electrified transportation systems into the automobile market.

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A series of Ni-rich Li[Ni x Co (1−x)/2 Mn (1−x)/2 ]O 2 (x = 0.9, 0.92, 0.94, 0.96, 0.98, and 1.0) (NCM) cathodes are prepared to study their capacity fading behaviors. The intrinsic trade-off between the capacity gain and compromised cycling stability is observed for layered cathodes with x ≥ 0.9. The initial specific capacities of LiNiO 2 and Li[Ni 0.9 Co 0.05 Mn 0.05 ]O 2 are 245 mAh g −1 (91% of the theoretical capacity) and 230 mAh g −1 , and their corresponding capacity retentions are 72.5% and 88.4%. However, the capacity retention characteristic deteriorates at an increasingly faster rate for x > 0.95, in contrast with the nearly linear increase of specific capacity. The fast capacity fading stems from the chemical attack of the cathode by the electrolyte infiltrated through the microcracks, resulting from the mechanical instability inflicted by the anisotropic internal strain caused by the H2 ⇆ H3 phase transition. Thus, the capacity fading of the NCM cathodes for x > 0.9 critically depends on the extent of the H2 → H3 phase transition. Retardation or protraction of the H2 ⇆ H3 phase transition by engineering the microstructure should improve the cycle life of these highly Ni-enriched NCM cathodes. KEYWORDS: Ni-rich layered Li[Ni x Co y Mn 1−x−y ]O 2 cathode, capacity fading mechanism, microcracks, high-energy density, lithium-ion batteries

Fabrication of conductive nanoparticle films is observed in Cu–Ag core-shell nanoparticles by fast diffusion of Ag at 220 °C from particle surfaces, leading to the formation of sintered necks of Ag at the initial particle-particle contacts. Transmission electron microscopy showed that the necks were pure Ag and that particle surfaces away from the contacts were nearly Ag-free. The extent of neck formation is controllable by the choice of initial Ag thickness. Analysis of the thermodynamics of the Ag–Cu system and the relative diffusivities of Ag and Cu provide criteria for fabrication of other core-shell two-phase systems by the same mechanism.