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.

We report that a solid‐state battery architecture enables the reversible, four electron storage of fully utilized solvothermally synthesized cubic‐FeS2 (pyrite). With a sulfide based glass electrolyte we successfully confine electro‐active species and permit the safe use of a lithium metal anode. These FeS2/Li solid‐state cells deliver a theoretical specific capacity of 894 mAh g−1 at 60 °C. We find that nanoparticles of orthorhombic‐FeS2 (marcasite) are generated upon recharge at 30–60 °C which explains a coincident change in rate kinetics.

The molecular-layer deposition of a flexible coating onto Si electrodes produces high-capacity Si nanocomposite anodes. Using a reaction cascade based on inorganic trimethylaluminum and organic glycerol precursors, conventional nano-Si electrodes undergo surface modifications, resulting in anodes that can be cycled over 100 times with capacities of nearly 900 mA h g(-1) and Coulombic efficiencies in excess of 99%.

By cyclizing commercially available polyacrylonitrile (PAN), we show that it is possible to conformally coat nanoparticles of Si with a conjugated polymer. We utilize cyclized-PAN both as a binder and conductive additive because of its good mechanical resiliency to accommodate silicon's (Si) large expansion as well as its good ionic and electronic conductivity. By the 150 th cycle, our nano-Si/cyclized-PAN composite anodes exhibit a specifi c charge capacity of nearly 1500 mAh g − 1 with a coulombic efficiency (CE) approaching 100%. Because Si is naturally abundant and has such a high achievable specifi c capacity, [ 1 , 2 ] the next generation of Lithium-ion batteries will inevitably incorporate an advanced Si based anode like that presented here. At room temperature, Si can accommodate 3.75 mole Li per mole of Si (Li 15 Si 4 ) for a theoretical capacity of 3579 mAh g − 1 . [ 3 , 4 ] Despite these advantages, progress towards a commercially viable Si anode has been impeded by Si's rapid capacity fade, poor ionic transport and low CE.Rapid capacity fade is a primary cause for the delay of Si's commercialization. At room temperature, a volume expansion of 300% occurs upon full lithiation to Li 15 Si 4 . [5][6][7] Such a massive volumetric change can result in cracking and pulverization of the Si particles, which then leads to the interruption of electronic transport pathways and the electrochemical isolation of pulverized particles. [ 2 ] To better accommodate the large stresses and strains generated upon lithiation, utilization of nanoparticles, nanowires, and 3D nano-porous structures have been studied. Nano-Si based structures have the added benefi t of reducing the average Li + diffusion length into Si for faster charge and discharge rates. [8][9][10] However, nano-Si structures often suffer from poor CE due to the continual formation of a solid electrolyte interphase (SEI) layer at the large nano-Si/electrolyte interface. Adding to the frustration, many of these clever nano-Si based engineering solutions are rarely appropriate for commercialization because they may require expensive synthesis techniques. [11][12][13][14][15] Yet, recent work has shown that Si-C nano-composites may be promising candidates for viable, inexpensive, stable and effi cient high capacity anodes. Si-C conventional composites are typically prepared by carbonizing precursors [16][17][18] or by mechanically mixing Si with carbon. [ 19 , 20 ] The result are composites of Si particles embedded in carbon matrices. Unfortunately, these carbon matrices cannot accommodate Si's large volumetric changes because of their tendency for brittle failure. Cracking of these carbon matrices during cycling interrupts electronic conduction pathways and exposes fresh Si to the electrolyte which results in further SEI formation. Several studies using electronically conductive polymer based matrices or coatings have demonstrated better results. [21][22][23][24][25] For example, G. Liu et al. developed a cathodically (n-type) doped polymer binder that mai...

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Whether attempting to eliminate parasitic Li metal plating on graphite (and other Li-ion anodes) or enabling stable, uniform Li metal formation in 'anode-free' Li battery configurations, the detection and characterization (morphology, microstructure, chemistry) of Li that cannot be reversibly cycled is essential to understand the behavior and degradation of rechargeable batteries. In this review, various approaches used to detect and characterize the formation of Li in batteries are discussed. Each technique has its unique set of advantages and limitations, and works towards solving only part of the full puzzle of battery degradation. Going forward, multimodal characterization holds the most promise towards addressing two pressing concerns in the implementation of the next generation of batteries in the transportation sector (viz. reducing recharging times and increasing the available capacity per recharge without sacrificing cycle life). Such characterizations involve combining several techniques (experimental-and/or modeling-based) in order to exploit their respective advantages and allow a more comprehensive view of cell degradation and the role of Li metal formation in it. It is also discussed which individual techniques, or combinations thereof, can be implemented in real-world battery management systems on-board electric vehicles for early detection of potential battery degradation that would lead to failure.

In spite of significant interest toward solid-state electrolytes owing to their superior safety in comparison to liquid-based electrolytes, sluggish ion diffusion and high interfacial resistance