Li and Na metals have the highest theoretical anode capacity for Li/Na batteries, but the operational safety hazards stemming from uncontrolled growth of Li/Na dendrites and unstable electrode-electrolyte interfaces hinder their real-world applications. Recently, the emergence of 3D conductive scaffolds aimed at mitigating the dendritic growth to improve the cycling stability has gained traction. However, while achieving 3D scaffolds that are conducive to completely prevent dendritic Li/Na is challenging, the routes proposed to fabricate 3D scaffolds to date are often complex and expensive. This not only leads to suboptimal battery performance but can make the manufacturing nearly unachievable, compromising their commercial viability. We herein introduce a facile and single-step route to honeycomb-like 3D porous Ni@Cu scaffolds via a hydrogen bubble dynamic template (HBDT) electrodeposition method. The current collectors fabricated by this method offer highly stable cycling performance of Li plating/stripping (> 300 cycles at 0.5 mAh cm-2 and over 200 cycles at 1.0 mAh cm-2), attributed to their ability to effectively accommodate Li/Na deposits in their porous networks and to delocalize the charge distribution. The beneficial role of LiNO3 as an electrolyte additive in improving the mechanical integrity of solid electrolyte interface (SEI) and mechanistic insights into how the 3D porous structure facilitates Li/Na plating/stripping are comprehensively presented. Finally, with an outstanding cycling performance of reversible Na deposition (over 240, 110 and 50 cycles for 0.5, 1.0 and 2.0 mAh cm-2 at 1.0 mA cm-2), our findings open new doors to expedite the development of Li/Na metal battery technology.

Batteries. ChemRxiv. Preprint. Operando X-ray diffraction (XRD) is a valuable tool for studying secondary battery materials as it allows for the direct correlation of electrochemical behavior with structural changes of crystalline active materials. This is especially true for the lithium-sulfur chemistry, in which energy storage capability depends on the complex growth and dissolution kinetics of lithium sulfide (Li2S) and sulfur (S8) during discharge and charge, respectively. In this work, we present a novel development of this method through combining operando XRD with simultaneous and continuous resistance measurement using an Intermittent Current Interruption (ICI) method. We show that a coefficient of diffusion resistance, which reflects the transport properties in the sulfur/carbon composite electrode, can be determined from analysis of each current interruption. Its relationship to the established Warburg impedance model is validated theoretically and experimentally. We also demonstrate for an optimized electrode formulation and cell construction that the diffusion resistance increases sharply at the discharge end point, which is consistent with the blocking of pores in the carbon host matrix. The combination of XRD with ICI allows for a direct correlation of structural changes with not only electrochemical properties but also energy loss processes at a non-equilibrium state, and therefore is a valuable technique for the study of a wide range of energy storage chemistries. File list (2) download file view on ChemRxiv Manuscript.docx (3.06 MiB) download file view on ChemRxiv Supporting Information.pdf (720.53 KiB)

The high-theoretical-capacity (∼170 mAh/g) Prussian white (PW), Na x Fe[Fe(CN) 6 ] y · n H 2 O, is one of the most promising candidates for Na-ion batteries on the cusp of commercialization. However, it has limitations such as high variability of reported stable practical capacity and cycling stability. A key factor that has been identified to affect the performance of PW is water content in the structure. However, the impact of airborne moisture exposure on the electrochemical performance of PW and the chemical mechanisms leading to performance decay have not yet been explored. Herein, we for the first time systematically studied the influence of humidity on the structural and electrochemical properties of monoclinic hydrated (M-PW) and rhombohedral dehydrated (R-PW) Prussian white. It is identified that moisture-driven capacity fading proceeds via two steps, first by sodium from the bulk material reacting with moisture at the surface to form sodium hydroxide and partial oxidation of Fe 2+ to Fe 3+ . The sodium hydroxide creates a basic environment at the surface of the PW particles, leading to decomposition to Na 4 [Fe(CN) 6 ] and iron oxides. Although the first process leads to loss of capacity, which can be reversed, the second stage of degradation is irreversible. Over time, both processes lead to the formation of a passivating surface layer, which prevents both reversible and irreversible capacity losses. This study thus presents a significant step toward understanding the large performance variations presented in the literature for PW. From this study, strategies aimed at limiting moisture-driven degradation can be designed and their efficacy assessed.

Lithium-rich materials, such as Li 1.2 Ni 0.2 Mn 0.6 O 2 , exhibit capacities not limited by transition metal redox, through the reversible oxidation of oxide anions. Here we offer detailed insight into the degree of oxygen redox as a function of depth within the material as it is charged and cycled. Energy-tuned photoelectron spectroscopy is used as a powerful, yet highly sensitive technique to probe electronic states of oxygen and transition metals from the top few nanometers at the near-surface through to the bulk of the particles. Two discrete oxygen species are identified, O nÀ and O 2À , where n < 2, confirming our previous model that oxidation generates localised hole states on O upon charging. This is in contrast to the oxygen redox inactive high voltage spinel LiNi 0.5 Mn 1.5 O 4 , for which no O nÀ species is detected. The depth profile results demonstrate a concentration gradient exists for O nÀ from the surface through to the bulk, indicating a preferential surface oxidation of the layered oxide particles. This is highly consistent with the already well-established core-shell model for such materials. Ab initio calculations reaffirm the electronic structure differences observed experimentally between the surface and bulk, while modelling of delithiated structures shows good agreement between experimental and calculated binding energies for O nÀ .