Mg2+ ion-catalyzed polymerization of 1,3-dioxolane in battery electrolytes.

Electrolyte salts with Mg2+ and Al3+ Lewis acidic cations demonstrate polymerization of 1,3-dioxolane. The speed and extent of the reaction depends on coordination of the anion with the Mg2+ cation catalyst. Weakly coordinating anions such as TFSI- aid faster polymerization while strongly coordinating anions such as ClO4- hinder the polymerization.

Impact of pore size, interconnections, and dynamic conductivity on the electrochemistry of vanadium pentoxide in well defined porous structures.

Considering the tortuous, random porous nanostructures existing in many battery electrodes, it is essential to understand electronic and ionic behaviors in such a confined nanoscale porous geometry in which electron and ion transports can change dynamically. Here, we have carefully designed three dimensional (3D) interconnected porous electrode structures and performed experiments to probe how the ion and electron transport is impacted within these controlled geometries. By using anodized aluminum oxide as a template, we were able to fabricate both 1D array electrodes and 3D electrodes with varying numbers of interconnections, utilizing vanadium oxide (V2O5) as the active material. We demonstrate that the inherent properties of the electrode material in combination with the structural properties of the electrodes can both positively and negatively impact electrochemical characteristics. Most notably, electrodes with seven interconnecting layers in their structure had 19.7% less capacity at 25C than electrodes with zero interconnecting layers, demonstrating the negative effect of interconnections combined with poor electronic conductivity of V2O5 upon lithiation beyond one Li insertion. These results indicate that a careful consideration of the material and structural properties is needed for the design of high performance battery systems.

Three-Dimensional Solid-State Lithium-Ion Batteries Fabricated by Conformal Vapor-Phase Chemistry.

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 LiV2O5 cathode, a very thin (40-100 nm) Li2PO2N solid electrolyte, and a SnN x 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/cm2·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.

Investigation of the water-stimulated Mg2+ insertion mechanism in an electrodeposited MnO2 cathode using X-ray photoelectron spectroscopy.

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 (MnO2) cathodes. While there have been studies on Mg insertion mechanisms into MnO2 in solely aqueous or organic electrolytes for some crystalline MnO2 polymorphs, our work is focused on water-containing organic electrolyte, where an H2O 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 MnO2 cathode. We propose that in this mixed electrolyte system, there is a combined insertion/conversion reaction mechanism whereby Mg and H2O molecules co-insert into the MnO2 structure and a reaction between H2O and Mg creates an observable Mg(OH)2 layer at the surface of the MnO2. 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.

Mapping the Challenges of Magnesium Battery.

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.