The morphologies that metal electrodeposits form during the earliest stages of electrodeposition are known to play a critical role in the recharge of electrochemical cells that use metals as anodes. Here we report results from a combined theoretical and experimental study of the early stage nucleation and growth of electrodeposited lithium at liquid–solid interfaces. The spatial characteristics of lithium electrodeposits are studied via scanning electron microscopy (SEM) in tandem with image analysis. Comparisons of Li nucleation and growth in multiple electrolytes provide a comprehensive picture of the initial nucleation and growth dynamics. We report that ion diffusion in the bulk electrolyte and through the solid electrolyte interphase (SEI) formed spontaneously on the metal play equally important roles in regulating  Li nucleation and growth. We show further that the underlying physics dictating bulk and surface diffusion are similar across a range of electrolyte chemistries and measurement conditions, and that fluorinated electrolytes produce a distinct flattening of Li electrodeposits at low rates. These observations are rationalized using X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS), and contact angle goniometry to probe the interfacial chemistry and dynamics. Our results show that high interfacial energy and high surface ion diffusivity are necessary for uniform Li plating.

Electrochemical cells based on alkali metal anodes are receiving intensive scientific interest as potentially transformative technology platforms for electrical energy storage. Chemical, morphological, mechanical and hydrodynamic instabilities at the metal anode produce uneven metal electrodeposition and poor anode reversibility, which, are among the many known challenges that limit progress. Here, we report that solid-state electrolytes based on crosslinked polymer networks can address all of these challenges in cells based on lithium metal anodes. By means of transport and electrochemical analyses, we show that manipulating thermodynamic interactions between polymer segments covalently anchored in the network and “free” segments belonging to an oligomeric electrolyte hosted in the network pores, one can facilely create hybrid electrolytes that simultaneously exhibit liquid-like barriers to ion transport and solid-like resistance to morphological and hydrodynamic instability.

Lithium metal is a promising anode for energy-dense batteries but is hindered by poor reversibility caused by continuous chemical and electrochemical degradation. Here we find that by increasing the Li plating capacity to high values (e.g., 10–50 mAh cm−2), Li deposits undergo a morphological transition to produce dense structures, composed of large grains with dominantly (110)Li crystallographic facets. The resultant Li metal electrodes manifest fast kinetics for lithium stripping/plating processes with higher exchange current density, but simultaneously exhibit elevated electrochemical stability towards the electrolyte. Detailed analysis of these findings reveal that parasitic electrochemical reactions are the major reason for poor Li reversibility, and that the degradation rate from parasitic electroreduction of electrolyte components is about an order of magnitude faster than from chemical reactions. The high-capacity Li electrodes provide a straightforward strategy for interrogating the solid electrolyte interphase (SEI) on Li —with unprecedented, high signal to noise. We find that an inorganic rich SEI is formed and is primarily concentrated around the edges of lithium particles. Our findings provide straightforward, but powerful approaches for enhancing the reversibility of Li and for fundamental studies of the interphases formed in liquid and solid-state electrolytes using readily accessible analytical tools.

Metallic sodium is receiving renewed interest as a battery anode material because the metal is earthabundant, inexpensive, and offers a high specific storage capacity (1166 mAh/g at-2.71 V vs the This article is protected by copyright. All rights reserved. 2 standard hydrogen potential). Unlike metallic lithium, the case for Na as the anode in rechargeable batteries has already been demonstrated on a commercial scale in high-temperature Na||S and Na||NiCl 2 secondary batteries, which increases interest. We investigate the reversibility of room temperature sodium anodes in galvanostatic plating/stripping reactions using in-situ optical visualization and galvanostatic polarization measurements. It is discovered that electronic disconnection of mossy metallic Na deposits (-orphaning‖) is a dominant source of anode irreversibility in liquid electrolytes. The disconnection is shown by means of direct visualization studies to be triggered by a root-breakage process during the stripping cycle. As a further step towards electrode designs that are able to accommodate the fragile Na deposits, electrodeposition of Na is demonstrated in non-planar electrode architectures which provide continuous and morphology agnostic access to the metal at all stages of electrochemical cycling. On this basis, we report nonplanar Na electrodes which exhibit exceptionally high levels of reversibility (Coulombic Efficiency > 99.6% for 1mAh/cm 2 Na throughput) in room-temperature, liquid electrolytes.

Reversible electrodeposition of metals at liquid‐solid interfaces is a requirement for long cycle life in rechargeable batteries that utilize metals as anodes. The process has been studied extensively from the perspective of the electrochemical transformations that impact reversibility, however, the fundamental challenges associated with maintaining morphological control when a intrinsically crystalline solid metal phase emerges from an electrolyte solution have been less studied, but provide important opportunities for progress. A crystal growth stabilization method to reshape the initial growth and orientation of crystalline metal electrodeposits is proposed here. The method takes advantage of polymer‐salt complexes (PEG‐Zn2+‐aX−) (a = 1,2,3) formed spontaneously in aqueous electrolytes containing zinc (Zn2+) and halide (X−) ions to regulate electro‐crystallization of Zn. It is shown that when X = Iodine (I), the complexes facilitate electrodeposition of Zn in a hexagonal closest packed morphology with preferential orientation of the (002) plane parallel to the electrode surface. This facilitates exceptional morphological control of Zn electrodeposition at planar substrates and leads to high anode reversibility and unprecedented cycle life. Preliminary studies of the practical benefits of the approach are demonstrated in Zn‐I2 full battery cells, designed in both coin cell and single‐flow battery cell configurations.