Evaluation of Metal Phosphide Nanocrystals as Anode Materials for Na-ion Batteries

Sodium-ion batteries (SIBs) are potential low-cost alternatives to lithium-ion batteries (LIBs) because of the much greater natural abundance of sodium salts. However, developing high-performance electrode materials for SIBs is a challenging task, especially due to the ?50% larger ionic radius of the Na+ ion compared to Li+, leading to vastly different electrochemical behavior. Metal phosphides such as FeP, CoP, NiP2, and CuP2 remain unexplored as electrode materials for SIBs, despite their high theoretical charge storage capacities of 900–1300 mAh g–1. Here we report on the synthesis of metal phosphide nanocrystals (NCs) and discuss their electrochemical properties as anode materials for SIBs, as well as for LIBs. We also compare the electrochemical characteristics of phosphides with their corresponding sulfides, using the environmentally benign iron compounds, FeP and FeS2, as a case study. We show that despite the appealing initial charge storage capacities of up to 1200 mAh g–1, enabled by effective nanosizing of the active electrode materials, further work toward optimization of the electrode/electrolyte pair is needed to improve the electrochemical performance upon cycling

An overview and prospective on Al and Al-ion battery technologies

Aluminum batteries are considered compelling electrochemical energy storage systems because of the natural abundance of aluminum, the high charge storage capacity of aluminum of 2980 mA h g−1/8046 mA h cm−3, and the sufficiently low redox potential of Al3+/Al. Several electrochemical storage technologies based on aluminum have been proposed so far. This review classifies the types of reported Al-batteries into two main groups: aqueous (Al-ion, and Al-air) and non-aqueous (aluminum graphite dual-ion, Al-organic dual-ion, Al-ion, and Al-sulfur). Specific focus is given to Al electrolyte chemistry based on chloroaluminate melts, deep eutectic solvents, polymers, and “chlorine-free” formulations

Laser Patterning of High‐Mass‐Loading Graphite Anodes for High‐​Performance Li‐​Ion Batteries

Given the ongoing efforts to build Li-ion batteries with higher volumetric energy and power densities, the research on enhancing Li-ion transport within compressed high-mass-loading electrodes at fast cycling conditions is imperative. In this work, we show that the rate capability of graphite electrodes with high areal capacity of 4.5 mAh cm2 and density of 1.79 g cm3 (15% of porosity) can be considerably improved by laser patterning, namely by the fabrication of arrays of vertically aligned channels serving as diffusion paths for rapid Li-ion transport. Resultant laser patterned graphite electrodes delivered enhanced volumetric capacity as compared to that of non-patterned electrodes (450 vs. 396 mAh cm3 at C/2 rate). The reduction of the total steady-state concentration drop within the graphite electrodes after their patterning was also assessed

SnP nanocrystals as anode materials for Na-ion batteries

Tin monophosphide is a layered material consisting of Sn-P-P-Sn sandwiches that are stacked on top of each other to form a three dimensional crystallographic structure. Its composition and crystal structure makes it an excellent candidate anode material for sodium-ion batteries (SIBs). However, SnP is yet to be explored for such and other applications due to its challenging synthesis. In the present work, we report the synthesis of SnP nanocrystals (NCs) from the reaction of hexamethylphosphorous triamide (HMPT) and a tin phosphonate prepared from tin oxalate and a long chain phosphonic acid. SnP NCs obtained from this reaction displayed a spherical geometry and a trigonal crystallographic phase with a superstructure attributed to ordered diphosphorus pairs. Such NCs were mixed with carbon black and used as anode materials in SIBs. SIBs based on SnP NCs and sodium(i) bis(fluorosulfonyl)imide (NaFSI) electrolyte displayed a high reversible capacity of 600 mA h g at a current density of 100 mA g and cycling stability for over 200 cycles. Their excellent cycling performance is associated with both the small size of the crystal domains and the particular composition and phase of SnP which prevent mechanical disintegration and major phase separation during sodiation and desodiation cycles. These results demonstrate SnP to be an attractive anode material for sodium ion batteries

Extending the high-voltage operation of Graphite/NCM811 cells by constructing a robust electrode/electrolyte interphase layer

The cycling life of layered Ni-rich LiNi$_{1-x-y}$CoxMn$_y$O$_2$ (NCM, 1-x-y ≥ 0.8) is typically extended by restricting the upper cut-off voltage during cycling to below 4.2 V, sacrificing, however, the untapped additional capacity above the cut-off voltage. To make this additional capacity available, we investigate graphite/LiNi$_{0·8}$Co$_{0·1}$Mn$_{0·1}$O$_2$ cells cycled to high upper cut-off voltages up to 4.5 V at high electrode areal capacities of 4.8 mAh/cm$^2$ in a standard electrolyte consisting of 1 M lithium hexafluorophosphate (LiPF$_6$) in ethylene carbonate and ethylene methyl carbonate (ethylene carbonate:ethylene methyl carbonate = 3:7 vol% + 2% vinylene carbonate). Although the initial capacity reaches 190 mAh/g, the capacity retention after 300 cycles to 4.5 V is only 66%. Employing a combination of tris(trimethylsilyl)phosphite and lithium difluoro(oxalato)borate as electrolyte additives, we demonstrate excellent capacity retention of 85% after 300 cycles to 4.5 V. Moreover, graphite/LiNi$_{0·8}$Co$_{0·}$1Mn$_{0·1}$O$_2$ cells with additives show improved capacity retention also at elevated temperatures of 60 °C. A detailed post-mortem analysis reveals the formation of a compact and LiF-rich and B-containing cathode/electrolyte interphase layer on the LiNi$_{0·8}$Co$_{0·1}$Mn$_{0·1}$O$_2$ particles cycled with tris(trimethylsilyl)phosphite and lithium difluoro(oxalato)borate additives, substantially suppressing the transition metal dissolution and the cation-disordered layer formation on the exposed particles\u27 surface

Aluminum electrolytes for Al dual-ion batteries

In the search for sustainable energy storage systems, aluminum dual-ion batteries have recently attracted considerable attention due to their low cost, safety, high energy density (up to 70 kWh kg−1), energy efficiency (80–90%) and long cycling life (thousands of cycles and potentially more), which are needed attributes for grid-level stationary energy storage. Overall, such batteries are composed of aluminum foil as the anode and various types of carbonaceous and organic substances as the cathode, which are immersed in an aluminum electrolyte that supports efficient and dendrite-free aluminum electroplating/stripping upon cycling. Here, we review current research pursuits and present the limitations of aluminum electrolytes for aluminum dual-ion batteries. Particular emphasis is given to the aluminum plating/stripping mechanism in aluminum electrolytes, and its contribution to the total charge storage electrolyte capacity. To this end, we survey the prospects of these stationary storage systems, emphasizing the practical hurdles of aluminum electrolytes that remain to be addressed

On Achievable Gravimetric and Volumetric Energy Densities of Al Dual-Ion Batteries

ISSN:2380-819

Perspective on design and technical challenges of Li-garnet solid-state batteries

Solid-state Li-ion batteries based on Li-garnet Li7La3Zr2O12 (LLZO) electrolyte have seen rapid advances in recent years. These solid-state systems are poised to address the urgent need for safe, non-flammable, and temperature-tolerant energy storage batteries that concomitantly possess improved energy densities and the cycle life as compared to conventional liquid-electrolyte-based counterparts. In this vision article, we review present research pursuits and discuss the limitations in the employment of LLZO solid-state electrolyte (SSE) for solid-state Li-ion batteries. Particular emphasis is given to the discussion of pros and cons of current methodologies in the fabrication of solid-state cathodes, LLZO SSE, and Li metal anode layers. Furthermore, we discuss the contributions of the LLZO thickness, cathode areal capacity, and LLZO content in the solid-state cathode on the energy density of Li-garnet solid-state batteries, summarizing their required values for matching the energy densities of conventional Li-ion systems. Finally, we highlight challenges that must be addressed in the move towards eventual commercialization of Li-garnet solid-state batteries.ISSN:1468-6996ISSN:1878-551

The Pitfalls in Nonaqueous Electrochemistry of Al-Ion and Al Dual-Ion Batteries

The quest for cost-effective and TWh-scale stationary energy storage systems has caused a surge of research on novel post-Li-ion batteries that consist solely of abundant chemical elements. Nonaqueous Al batteries, inter alia, are appealing as an inexpensive electrochemical technology owing to the high natural abundance of aluminum. A critical assessment of the literature on Al batteries, however, points to numerous misconceptions in this field. The latter is primarily linked to the false assessment of the charge storage redox reactions occurring upon cycling of Al batteries. To ensure the constructive progress of Al batteries, in this essay, the current scientific understanding of the operational mechanisms of two commonly studied Al battery systems, Al-ion and Al dual-ion batteries are summarized. Furthermore, the main pitfalls in interpretation and reporting of the electrochemical performance of Al cathode materials and cell-level energy densities of Al batteries are clarified along with core challenges currently limiting their development. Toward this end, the subject of the charge storage balancing of Al dual-ion batteries is discussed

AlCl3‐Saturated Ionic Liquid Anolyte with an Excess of AlCl3 for Al–Graphite Dual‐Ion Batteries

Al–graphite dual‐ion batteries (AGDIBs) represent a compelling battery concept for large‐scale stationary storage of electricity in view of their safety, low cost, long cycling life, and high energy efficiency (80–90 %). However, at present, the deployment of AGDIBs is intrinsically limited by their low cell‐level energy density as a result of the non‐rocking‐chair operation principle and, consequently, the need for large quantities of acidic chloroaluminate ionic liquid (IL) anolytes as a reservoir of Al2Cl7− ions required for AGDIB operation. Thus far, AGDIBs have commonly employed IL anolytes with moderate acidity (AlCl3/Lewis base molar ratio of 1.3), which corresponds to charge‐storage anolyte capacity of ca. 19 mAh g−1, eventually resulting in low cell‐level energy densities of 20–30 Wh kg−1. In this work, we present an AGDIB utilizing an AlCl3‐saturated IL anolyte, containing an excess of AlCl3 powder for maintaining constant acidity during operation, leading to a theoretical capacity of 52 mAh g−1. The resultant AGDIB possesses an energy density of 59.1 Wh kg−1, along with a high energy efficiency of 85 % and an average discharge voltage of 1.71 V