Rechargeable Li-ion batteries are currently being explored for high-power applications such as electric vehicles. However, in order to deploy Li-ion batteries in next-generation vehicles, it is essential to develop electrodes made from durable, nontoxic, and inexpensive materials with a high charge/discharge rate and a high reversible capacity. Transition metal oxides such as Fe

Magnesium-based batteries possess potential advantages over their lithium counterparts. However, reversible Mg chemistry requires a thermodynamically stable electrolyte at low potential, which is usually achieved with corrosive components and at the expense of stability against oxidation. In lithium-ion batteries the conflict between the cathodic and anodic stabilities of the electrolytes is resolved by forming an anode interphase that shields the electrolyte from being reduced. This strategy cannot be applied to Mg batteries because divalent Mg cannot penetrate such interphases. Here, we engineer an artificial Mg-conductive interphase on the Mg anode surface, which successfully decouples the anodic and cathodic requirements for electrolytes and demonstrate highly reversible Mg chemistry in oxidation-resistant electrolytes. The artificial interphase enables the reversible cycling of a Mg/VO full-cell in the water-containing, carbonate-based electrolyte. This approach provides a new avenue not only for Mg but also for other multivalent-cation batteries facing the same problems, taking a step towards their use in energy-storage applications.

The performance of battery materials is largely governed by structural and chemical evolutions during electrochemical reactions. Therefore, resolving spatially dependent reaction pathways could enlighten mechanistic understanding, and enable rational design for rechargeable battery materials. Here, we present a phase evolution panorama via spectroscopic and three-dimensional imaging at multiple states of charge for an anode material (that is, nickel oxide nanosheets) in lithium-ion batteries. We reconstruct the threedimensional lithiation/delithiation fronts and find that, in a fully electrolyte immersion environment, phase conversion can nucleate from spatially distant locations on the same slab of material. In addition, the architecture of a lithiated nickel oxide is a bent porous metallic framework. Furthermore, anode-electrolyte interphase is found to be dynamically evolving upon charging and discharging. The present study has implications for resolving the inhomogeneity of the general electrochemically driven phase transition (for example, intercalation reactions) and for the origin of inhomogeneous charge distribution in large-format battery electrodes.

Solid-state electrolytes such as Li2S-P2S5 compounds are promising materials that could enable Li metal anodes. However, many solid-state electrolytes are unstable against metallic lithium, and little is known about the chemical evolution of these interfaces during cycling, hindering the rational design of these materials. In this work, operando X-ray photoelectron spectroscopy and real-time in situ Auger electron spectroscopy mapping are developed to probe the formation and evolution of the Li/Li2S-P2S5 solid-electrolyte interphase during electrochemical cycling, and to measure individual overpotentials associated with specific interphase constituents. Results for the Li/Li2S-P2S5 system reveal that electrochemically driving Li+ to the surface leads to phase decomposition into Li2S and Li3P. Additionally, oxygen contamination within the Li2S-P2S5 leads initially to Li3PO4 phase segregation, and subsequently to Li2O formation. The spatially non-uniform distribution of these phases, coupled with differences in their ionic conductivities, have important implications for the overall properties and performance of the solid-electrolyte interphase.

Solid-state batteries utilizing Li metal anodes have the potential to enable improved performance (specific energy >500 Wh/kg, energy density >1,500 Wh/L), safety, recyclability, and potentially lower cost (< $100/kWh) compared to advanced Li-ion systems. 1,2 These improvements are critical for the widespread adoption of electric vehicles and trucks and could create a short haul electric aviation industry. [1][2][3] Expectations for solid-state batteries are high, but there are significant materials and processing challenges to overcome.On May 15 th , 2020, Oak Ridge National Laboratory (ORNL) hosted a 6-hour, national online workshop to discuss recent advances and prominent obstacles to realizing solid-state Li metal batteries. The workshop included more than 30 experts from national laboratories, universities, and companies, all of whom have worked on solid-state batteries for multiple years. The participants' consensus is that, although recent progress on solid-state batteries is exciting, much has yet to be researched, discovered, scaled, and developed. Our goal was to examine the issues and identify the most pressing needs and most significant opportunities. The organizers asked workshop participants to present their views by articulating fundamental knowledge gaps for materials and processing science, mechanical behavior and battery architectures critical to advancing solid-state battery technology. The organizers used this input to set the workshop agenda. The group also considered what would incentivize the adoption of US manufacturing and how to accelerate and focus research attention for the benefit of the US energy, climate, and economic interests. The participants identified pros and cons for sulfide, oxide, and polymerbased solid-state batteries and identified common science gaps among the different chemistries. Addressing these common science gaps may reveal the most promising systems to pursue in the future.