Secondary batteries based on earth-abundant sodium metal anodes are desirable for both stationary and portable electrical energy storage. Room-temperature sodium metal batteries are impractical today because morphological instability during recharge drives rough, dendritic electrodeposition. Chemical instability of liquid electrolytes also leads to premature cell failure as a result of parasitic reactions with the anode. Here we use joint density-functional theoretical analysis to show that the surface diffusion barrier for sodium ion transport is a sensitive function of the chemistry of solid–electrolyte interphase. In particular, we find that a sodium bromide interphase presents an exceptionally low energy barrier to ion transport, comparable to that of metallic magnesium. We evaluate this prediction by means of electrochemical measurements and direct visualization studies. These experiments reveal an approximately three-fold reduction in activation energy for ion transport at a sodium bromide interphase. Direct visualization of sodium electrodeposition confirms large improvements in stability of sodium deposition at sodium bromide-rich interphases.

A sodium metal anode protected by an ion-rich polymeric membrane exhibits enhanced stability and high-Columbic efficiency cycling. Formed in situ via electropolymerization of functional imidazolium-type ionic liquid monomers, the polymer membrane protects the metal against parasitic reactions with electrolyte and, for fundamental reasons, inhibits dendrite formation and growth. The effectiveness of the membrane is demonstrated using direct visualization of sodium electrodeposition.

Secondary batteries based on lithium are the most important energy storage technology for contemporary portable devices. The lithium ion battery (LIB) in widespread commercial use today is a compromise technology. It compromises high energy, high power, and design flexibility for long cell operating lifetimes and safety. Materials science, transport phenomena, and electrochemistry in the electrodes and electrolyte that constitute such batteries are areas of active study worldwide because significant improvements in storage capacity and cell lifetime are required to meet new demands, including the electrification of transportation and for powering emerging autonomous aircraft and robotics technologies. By replacing the carbonaceous host material used as the anode in an LIB with metallic lithium, rechargeable lithium metal batteries (LMBs) with higher storage capacity and compatibility with low-cost, high-energy, unlithiated cathodes such as sulfur, manganese dioxide, carbon dioxide, and oxygen become possible. Large-scale, commercial deployment of LMBs are today limited by safety concerns associated with unstable electrodeposition and lithium dendrite formation during cell recharge. LMBs are also limited by low cell operating lifetimes due to parasitic chemical reactions between the electrode and electrolyte. These concerns are greater in rechargeable batteries that utilize other, more earth abundant metals such as sodium and to some extent even aluminum. Inspired by early theoretical works, various strategies have been proposed for alleviating dendrite proliferation in LMBs. A commonly held view among these early studies is that a high modulus, solid-state electrolyte that facilitates fast ion transport, is nonflammable, and presents a strong-enough physical barrier to dendrite growth is a requirement for any commercial LMB. Unfortunately, poor room-temperature ionic conductivity, challenging processing, and the high cost of ceramic electrolytes that meet the modulus and stability requirements have to date proven to be insurmountable obstacles to progress. In this Account, we first review recent advances in continuum theory for dendrite growth and proliferation during metal electrodeposition. We show that the range of options for designing electrolytes and separators that stabilize electrodeposition is now substantially broader than one might imagine from previous literature accounts. In particular, separators designed at the nanoscale to constrain ion transport on length scales below a theory-defined cutoff, and structured electrolytes in which a fraction of anions are permanently immobilized to nanoparticles, to a polymer network or ceramic membrane are considered particularly promising for their ability to stabilize electrodeposition of lithium metal without compromising ionic conductivity or room temperature battery operation. We also review recent progress in designing surface passivation films for metallic lithium that facilitate fast deposition of lithium at the electrolyte/electrode interface and at the s...

Viscoelastic liquid electrolytes composed of ultrahigh molecular weight polymer solutions stabilize electrodeposition of metals by suppressing electroconvection.

Metal (based on Li, Na, Mg, or Al)-sulfur batteries are promising candidates for rechargeable electrochemical energy storage devices capable of high charge storage. However, the success of metal-sulfur battery technology calls for solutions of fundamental problems associated with the inherently complex solution chemistry and interfacial reactivity of sulfur and polysulfide species in commonly used electrolytes. It is understood that the dissolution and shuttling of polysulfides induce rapid capacity degradation, poor cycling stability and low efficiency of the cells. Herein, we report on the synthesis and transport properties of membranes containing sulfonate groups that are able to rectify transport of polysulfide species in liquid electrolytes. Comprised of a cross-linked polyethylene glycol (PEG) framework containing pendant SO 3 2-groups, the membranes facilitate electrolyte wetting and Li + ion transport, but are highly selective in preventing migration of negatively charged sulfur species (S n 2-) dissolved in liquid electrolytes.We argue that the ion rectifying properties originate from two sources, the small tortuous pores originating from cross-linking small PEG molecules and from repulsive electrostatic interactions between the pendant SO 3 2-groups and large migrating S n 2-species. Here we demonstrate the effectiveness of such membranes in Li-S batteries, wherein we find that the materials enable high-efficiency (>98%) cycling in additives-free electrolyte. Such membranes are also attractive in other electrochemical cell designs where they serve to decouple transport of positive and negative charged ions in the electrolyte to minimize polarization.