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Sodium-ion storage technologies are promising candidates for large-scale grid systems due to the abundance and low cost of sodium. However, compared to well-understood lithium-ion storage mechanisms, sodium-ion storage remains relatively unexplored. Herein, we systematically determine the sodium-ion storage properties of anatase titanium dioxide (TiO2(A)). During the initial sodiation process, a thin surface layer (~3 to 5 nm) of crystalline TiO2(A) becomes amorphous but still undergoes Ti4+/Ti3+ redox reactions. A model explaining the role of the amorphous layer and the dependence of the specific capacity on the size of TiO2(A) nanoparticles is proposed. Amorphous nanoparticles of ~10 nm seem to be optimum in terms of achieving high specific capacity, on the order of 200 mAh g-1, at high charge/discharge rates. Kinetic studies of TiO2(A) nanoparticles indicate that sodium-ion storage is due to a surface-redox mechanism that is not dependent on nanoparticle size in contrast to the lithiation of TiO2(A) which is a diffusion-limited intercalation process. The surface-redox properties of TiO2(A) result in excellent rate capability, cycling stability and low overpotentials. Moreover, tailoring the surface-redox mechanism enables thick electrodes of TiO2(A) to retain high rate properties, and represents a promising direction for high-power sodium-ion storage.

Conversion-type transition-metal phosphide anode materials with high theoretical capacity usually suffer from low-rate capability and severe capacity decay, which are mainly caused by their inferior electronic conductivities and large volumetric variations together with the poor reversibility of discharge product (Li3P), impeding their practical applications. Herein, guided by density functional theory calculations, these obstacles are simultaneously mitigated by confining amorphous FeP nanoparticles into ultrathin 3D interconnected P-doped porous carbon nanosheets (denoted as FeP@CNs) via a facile approach, forming an intriguing 3D flake-CNs-like configuration. As an anode for lithium-ion batteries (LIBs), the resulting FeP@CNs electrode not only reaches a high reversible capacity (837 mA h g-1 after 300 cycles at 0.2 A g-1) and an exceptional rate capability (403 mA h g-1 at 16 A g-1) but also exhibits extraordinary durability (2500 cycles, 563 mA h g-1 at 4 A g-1, 98% capacity retention). By combining DFT calculations, in situ transmission electron microscopy, and a suite of ex situ microscopic and spectroscopic techniques, we show that the superior performances of FeP@CNs anode originate from its prominent structural and compositional merits, which render fast electron/ion-transport kinetics and abundant active sites (amorphous FeP nanoparticles and structural defects in P-doped CNs) for charge storage, promote the reversibility of conversion reactions, and buffer the volume variations while preventing pulverization/aggregation of FeP during cycling, thus enabling a high rate and highly durable lithium storage. Furthermore, a full cell composed of the prelithiated FeP@CNs anode and commercial LiFePO4 cathode exhibits impressive rate performance while maintaining superior cycling stability. This work fundamentally and experimentally presents a facile and effective structural engineering strategy for markedly improving the performance of conversion-type anodes for advanced LIBs.

Sodium metal anodes have received considerable attention due to their high theoretical capacity, low reduction potential, and natural abundance in sodium batteries. Nevertheless, uneven sodium ion (Na+) deposition accelerates uncontrolled dendrite growth and an unstable solid electrolyte interphase (SEI) layer hinders Na+ diffusion, which eventually leads to short circuits and potential safety hazards. Herein, a multiphase artificial interphase layer composed of sodium bismuth alloy (BiNa3) and sodium chloride (NaCl) is applied to improve the interface stability of sodium metal anodes. Theoretical calculations and experimental results demonstrate that the BiNa3 alloy with good sodiophilic properties can function as nucleation sites to lower the nucleation barrier, induce uniform Na+ flux, and guide dendrite-free Na deposition. Meanwhile, a NaCl compound with high ionic conductivity can lower the Na+ diffusion barrier and improve diffusion kinetics. As a result, the assembled symmetric cells with a sodium metal anode modified by using a multiphase artificial interphase layer exhibit a remarkable cycling performance of 1200 h with a low overpotential of 20 mV at 3 mA cm−2 and 3 mA h cm−2. The full battery assembled with the Na3V2(PO4)3 cathode retains an ultrahigh capacity of 99 mA h g−1 even after 1000 cycles at 5C. The design strategy for a multiphase artificial interphase layer can provide insight into developing high-performance and dendrite-free sodium metal batteries. [ABSTRACT FROM AUTHOR]

Lithium (Li) metal has emerged as a viable alternative anode material to address the current energy density shortfalls in Li batteries. However, its integration into widespread implementation remains somewhat constrained due to the substandard reversibility issues and safety concerns arising from erratic Li deposition. To effectively tackle these obstacles, considerable endeavors have been exerted to modulate the morphology of Li deposition. Nevertheless, it is exceedingly challenging for Li nuclei that tend to dendritic growth thermodynamically to transform into dense Li morphologies during their growth process. Therefore, it is crucial to understand what influences the formation process of Li nuclei and how to improve the state of Li nuclei. Herein, Li nucleation mechanisms involving mass transport across the solid electrolyte interface from electrolyte to electrode and electrode interfacial reactions are elucidated. Inspired by the understanding of Li nucleation, the corresponding design principles, including enhancing and homogenizing mass transport, stabilizing solid electrolyte interface film, and regulating surface interaction/selection, are summarized for optimizing Li nucleation and further inducing dendrite‐free Li deposition. In light of the competition among these design principles, a perspective on the existing challenges and opportunities for further promoting the application of Li metal batteries is proposed. [ABSTRACT FROM AUTHOR]