Rechargeable Mg battery has been considered a major candidate as a beyond lithium ion battery technology, which is apparent through the tremendous works done in the field over the past decades. The challenges for realization of Mg battery are complicated, multidisciplinary, and the tremendous work done to overcome these challenges is very hard to organize in a regular review paper. Additionally, we claim that organization of the huge amount of information accumulated by the great scientific progress achieved by various groups in the field will shed the light on the unexplored research domains and give clear perspectives and guidelines for next breakthrough to take place. In this Perspective, we provide a convenient map of Mg battery research in a form of radar chart of Mg electrolytes, which evaluates the electrolyte under the important components of Mg batteries. The presented radar charts visualize the accumulated knowledge on Mg battery and allow for navigation of not only the current research state but also future perspective of Mg battery at a glance.

Three-dimensional thin-film solid-state batteries (3D TSSB) were proposed by Long et al. in 2004 as a structure-based approach to simultaneously increase energy and power densities. Here, we report experimental realization of fully conformal 3D TSSBs, demonstrating the simultaneous power-and-energy benefits of 3D structuring. All active battery components-electrodes, solid electrolyte, and current collectors-were deposited by atomic layer deposition (ALD) onto standard CMOS processable silicon wafers microfabricated to form arrays of deep pores with aspect ratios up to approximately 10. The cells utilize an electrochemically prelithiated LiVO cathode, a very thin (40-100 nm) LiPON solid electrolyte, and a SnN anode. The fabrication process occurs entirely at or below 250 °C, promising compatibility with a variety of substrates as well as integrated circuits. The multilayer battery structure enabled all-ALD solid-state cells to deliver 37 μAh/cm·μm (normalized to cathode thickness) with only 0.02% per-cycle capacity loss. Conformal fabrication of full cells over 3D substrates increased the areal discharge capacity by an order of magnitude while simulteneously improving power performance, a trend consistent with a finite element model. This work shows that the exceptional conformality of ALD, combined with conventional semiconductor fabrication methods, provides an avenue for the successful realization of long-sought 3D TSSBs which provide power performance scaling in regimes inaccessible to planar form factor cells.

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Rechargeable magnesium (Mg) batteries are promising beyond Li-ion technologies due to their high volumetric capacity (3832 mAh cm −3 ) and high natural abundance. Nonetheless, the Mg metal anode is incompatible with most conventional electrolytes, which leads to the formation of an ionically passivating layer, and it also suffers from growth of dendrites similar to Li, which can cause failure of the cells. In this study, 1,3-dioxolane (DOL) was electrochemically polymerized to form a thin, Mg 2+ -conducting elastomeric artificial solid electrolyte interphase (ASEI) layer by pretreating Mg metal anodes. This protective ASEI layer enables excellent cyclability of Mg−Mg symmetric cells at high current density over 400 h at a stable, low overpotential (0.50 V vs Mg 2+ / Mg) without cell short-circuiting, while untreated pristine Mg symmetric cells quickly failed. Surface chemistry analysis by X-ray photoelectron spectroscopy showed that the poly-DOL component in the elastomer was well preserved postcycling.

Batteries based on magnesium chemistry are being widely investigated as an alternative energy storage system to replace lithium-ion batteries. Mg batteries have multiple challenges, especially on the cathode side. The divalent Mg ion has slow insertion kinetics in many metal oxide cathodes conventionally used in Li-ion batteries. One solution that has been explored is adding water molecules into an organic electrolyte, which has been shown to aid in Mg insertion and improve performance of manganese oxide (MnO) cathodes. While there have been studies on Mg insertion mechanisms into MnO in solely aqueous or organic electrolytes for some crystalline MnO polymorphs, our work is focused on water-containing organic electrolyte, where an HO to Mg ratio of 6 : 1 is present. In this study, we report results based on ex situ XPS experiments, including both angle resolved and depth profiling studies to assess the surface reactions and determine the mechanism of Mg insertion into an amorphous, electrodeposited MnO cathode. We propose that in this mixed electrolyte system, there is a combined insertion/conversion reaction mechanism whereby Mg and HO molecules co-insert into the MnO structure and a reaction between HO and Mg creates an observable Mg(OH) layer at the surface of the MnO. A more full understanding of the role of the water molecules is important to aid in the future design of cathode materials, especially when determining potential ways to integrate metal oxides in Mg batteries.

Among the many emerging technologies under investigation as alternatives to the successful Lithium-ion battery, the magnesium battery is promising due to the wide availability of magnesium, its high volumetric capacity, and the possibility for safety improvements. One of the largest challenges facing rechargeable magnesium batteries is the formation of a passivation layer at the Mg metal anode interface when reactive species in the electrolyte are reduced at the electrode-electrolyte interface. To control the solid electrolyte interphase in Lithium batteries, protective layers called artificial solid electrolyte interphase (ASEI) layers have been successful in improving Li metal anode performance. The approach of protecting Mg metal anodes from electrolyte degradation has been demonstrated by fewer studies in the literature than Li systems. In this work, we discuss the properties of Al2O3 thin films deposited using atomic layer deposition as an artificial solid electrolyte interphase at the Mg anode. Our results demonstrate that Al2O3 does prevent electrolyte degradation due to the reductive nature of Mg. However, undesirable properties such as defects and layer breakdown lead to Mg growth that causes soft-shorting. The soft-shorting occurs with and without the protection layer, indicating the ALD layer does not prevent it and hinders Al2O3 from being an ideal candidate for a protection layer. Crucial effects of this layer on Mg electrochemistry at the interface were observed, including growth of Mg deposits leading to soft-shorting of the cell whose morphology showed a dependence on the Al2O3 layer. These results may provide guidelines for the future design and development of protective ASEI layers for Mg anodes.

Mg2+ ions in electrolytes can catalyze the polymerization of 1,3-dioxolane to form poly-DOL while anion pairs affect their capability.

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