Keegan R. Adair

Carbon nanofiber-based nanostructures for lithium-ion and sodium-ion batteries

Carbon nanofibers (CNFs) belong to a class of one-dimensional (1D) carbonaceous materials with excellent electronic conductivity, leading to their use as conductive additives in electrode materials for lithium-ion batteries (LIBs) and sodium-ion batteries (NIBs). Additionally, CNFs show excellent lithium- and sodium-storage performance when used directly as anode materials via template and activation strategies to produce numerous intercalation sites. In the case of the non-carbon electrodes for LIBs & NIBs, CNFs are capable of functioning as electron conducting and porous substrates to enhance the overall electronic & ionic conductivity and stabilizing the structures of electrodes during cycling, facilitating the improvement of the electrochemical performance of non-carbon anode and cathode materials. In this review, we present a comprehensive summary of the recent progress of CNF application in LIBs and NIBs, focusing on the structural evolution and the resulting improvements in electrochemical performance and demonstrating the importance of advancements in CNF-based electrode materials.

Atomic Layer Deposition of Lithium Niobium Oxides as Potential Solid-State Electrolytes for Lithium-Ion Batteries

The development of solid-state electrolytes by atomic layer deposition (ALD) holds unparalleled advantages toward the fabrication of next-generation solid-state batteries. Lithium niobium oxide (LNO) thin films with well-controlled film thickness and composition were successfully deposited by ALD at a deposition temperature of 235 °C using lithium tert-butoxide and niobium ethoxide as Li and Nb sources, respectively. Furthermore, incorporation of higher Li content was achieved by increasing the Li-to-Nb subcycle ratio. In addition, detailed X-ray absorption near edge structure studies of the amorphous LNO thin films on the Nb L-edge revealed the existence of Nb as Nb5+ in a distorted octahedral structure. The octahedrons in niobium oxide thin films experienced severe distortions, which could be gradually alleviated upon the introduction of Li atoms into the thin films. The ionic conductivities of the as-prepared LNO thin films were also measured, with the highest value achieving 6.39 × 10-8 S cm-1 at 303 K with an activation energy of 0.62 eV.

Structural Design of Lithium–Sulfur Batteries: From Fundamental Research to Practical Application

Lithium–sulfur (Li–S) batteries have been considered as one of the most promising energy storage devices that have the potential to deliver energy densities that supersede that of state-of-the-art lithium ion batteries. Due to their high theoretical energy density and cost-effectiveness, Li–S batteries have received great attention and have made great progress in the last few years. However, the insurmountable gap between fundamental research and practical application is still a major stumbling block that has hindered the commercialization of Li–S batteries. This review provides insight from an engineering point of view to discuss the reasonable structural design and parameters for the application of Li–S batteries. Firstly, a systematic analysis of various parameters (sulfur loading, electrolyte/sulfur (E/S) ratio, discharge capacity, discharge voltage, Li excess percentage, sulfur content, etc.) that influence the gravimetric energy density, volumetric energy density and cost is investigated. Through comparing and analyzing the statistical information collected from recent Li–S publications to find the shortcomings of Li–S technology, we supply potential strategies aimed at addressing the major issues that are still needed to be overcome. Finally, potential future directions and prospects in the engineering of Li–S batteries are discussed.Graphical Abstract

Aligning the binder effect on sodium–air batteries

Sodium–air batteries are attracting increasing research interest due to their high theoretical energy density and environmentally benign characteristics. Although sodium–air batteries share a similar concept, design, and composition when compared with their lithium–air counterparts, they still show many differences in their electrochemical behaviors and mechanisms. In the present work, the employment of four different types of polymers as binders in air electrodes for sodium–air batteries is presented, while the electrochemical and physical characterizations are carried out. Insights into how polymer binders impact the reaction mechanisms and formation of superoxide/peroxide species of sodium–air batteries from the view of their functional groups are revealed.

Carbon coated bimetallic sulfide nanodots/carbon nanorod heterostructure enabling long-life lithium-ion batteries

Exploitation of high capacity and long-life anode materials is essential for the development of lithium-ion batteries (LIBs) with high energy density. Metal sulfides have shown great potential as anode materials for LIBs due to their high theoretical specific capacity and excellent electronic properties and therefore they are considered as excellent candidates for anode materials. However, structural degradation during cycling and polysulfide dissolution has limited their practical application. In this work, we design a unique 0D/1D heterostructure of carbon coated iron–nickel sulfide nanodots/carbon nanorod through simultaneous decomposition and sulfidation of a bi-metal organic framework template. The resultant nanodots/nanorod heterostructure allows for fast ion/electron transport kinetics, suppresses polysulfide dissolution and ensures structural integrity during the lithiation/delithiation process. Consequently, this carbon coated iron–nickel sulfide nanodots/carbon nanorod structure exhibits a high specific capacity (851.3 mA h g−1 at 0.5C after 200 cycles) and an excellent cycling stability (484.7 mA h g−1 after 1000 cycles at a high rate of 4C).

Multi-functional nanowall arrays with unrestricted Li+ transport channels and integrated conductive network for high-areal-capacity Li-S batteries

The rational design of cathode hosts with superior polysulfide (PS) confinement properties, excellent Li+/e− transport and improved cyclability is of the utmost importance for high-areal-capacity lithium–sulfur (Li–S) batteries. Herein, multi-functional nanowall arrays (MNWAs) combining the aforementioned properties are fabricated to improve the electrochemical performance of Li–S batteries with high areal sulfur loadings. The integrated conductive networks and top-down vertically aligned Li+ transport channels are beneficial to Li+/e− transport, resulting in high rate performance with a discharge capacity of 620 mA h g−1 at a high current density of 9.6 mA cm−2 for 4 mg cm−2 sulfur-loaded S/MNWA electrodes. Additionally, the strong PS shuttling suppression via the synergetic effects of physical confinement and chemical adsorption leads to Li–S batteries with a sulfur loading of 10 mg cm−2 capable of delivering a high areal capacity of 12.4 mA h cm−2 with a high capacity retention of nearly 85% for over 100 cycles. Whats more, the Li–S batteries assembled with 4 mg cm−2 sulfur-loaded S/MNWA electrodes show an ultra-low capacity decay of 0.07% per cycle over 400 cycles at 3.2 mA cm−2.

Recent developments and insights into the understanding of Na metal anodes for Na-metal batteries

Rechargeable Na-based battery systems, including Na-ion batteries, room temperature Na–S, Na–O2, Na–CO2, and all-solid-state Na metal batteries, have attracted significant attention due to the high energy density, abundance, low cost, and suitable redox potential of Na metal. However, the Na metal anode faces several challenges, including: (1) the formation of Na dendrites and short circuiting; (2) low Coulombic efficiency (CE) and poor cycling performance; and (3) an infinite volume change due to its hostless nature. Furthermore, the issues associated with Na metal anodes have also been noticed in practical Na metal batteries (NMBs). In recent years, the importance of the Na metal anode has been highlighted and many studies have provided potential solutions to address the issues of its use. This review article focuses on the recent developments of Na metal anodes, including insight into the fundamental understanding of its electrochemical processes, novel characterization methods, approaches for protecting the anode and future perspectives. Our review will accelerate further improvement in the characterization and application of Na metal anodes for next-generation NMB systems.

In Situ Li3PS4 Solid-State Electrolyte Protection Layers for Superior Long-Life and High-Rate Lithium-Metal Anodes

A thin and adjustable Li3 PS4 (LPS) solid-state electrolyte protection layer on the surface of Li is proposed to address the dynamic plating/stripping process of Li metal. The LPS interlayer is formed by an in situ and self-limiting reaction between P4 S16 and Li in N-methyl-2-pyrrolidone. By increasing the concentration of P4 S16 , the thickness of the LPS layer can be adjusted up to 60 nm. Due to the high ionic conductivity and low electrochemical activity of Li3 PS4 , the intimate protection layer of LPS can not only prevent the formation of Li dendrites, but also reduces parasitic side reactions and improves the electrochemical performance. As a result, symmetric cells with the LPS protection layer can deliver stable Li plating/stripping for 2000 h. Full cells assembled with the LPS-protected Li exhibit two times higher capacity retention in Li-S batteries (≈800 mAh g-1 ) at 5 A g-1 for over 400 cycles compared to their bare Li counterparts. Furthermore, high rate performances can be achieved with Li-LPS/LiCoO2 cells, which are capable of cycling at rates as high as 20 C. This innovative and scalable approach to stabilizing the Li anode can serve as a basis for the development of next-generation high-performance lithium-metal batteries.

Designing High-Performance Nanostructured P2-type Cathode Based on a Template-free Modified Pechini Method for Sodium-Ion Batteries

Layered oxides are promising cathode materials for sodium-ion batteries because of their high theoretical capacities. However, many of these layered materials experience severe capacity decay when operated at high voltage (>4.25 V), hindering their practical application. It is essential to design high-voltage layered cathodes with improved stability for high-energy-density operation. Herein, nano P2-Na2/3(Mn0.54Ni0.13Co0.13)O2 (NCM) materials are synthesized using a modified Pechini method as a prospective high-voltage sodium storage component without any modification. The changes in the local ionic state around Ni, Mn, and Co ions with respect to the calcination temperature are recorded using X-ray absorption fine structure analysis. Among the electrodes, NCM fired at 850 °C (NCM-850) exhibits excellent electrochemical properties with an initial capacity and energy density of 148 mAh g–1 and 555 Wh kg–1, respectively, when cycled between 2 and 4.5 V at 160 mA g–1 along with improved cyclic stability after 100 charge/discharge cycles. In addition, the NCM-850 electrode is capable of maintaining a 75 mAh g–1 capacity even at a current density of 3200 mA g–1. In contrast, the cell fabricated with NCM obtained at 800 °C shows continuous capacity fading because of the formation of an impurity phase during the synthesis process. The obtained capacity, rate performance, and energy density along with prolonged cyclic life for the cell fabricated with the NCM-850 electrodes are some of the best reported values for sodium-ion batteries as compared to those of other p2-type sodium intercalating materials.

Stabilizing the Interface of NASICON Solid Electrolyte against Li Metal with Atomic Layer Deposition

Solid-state batteries have been considered as one of the most promising next-generation energy storage systems because of their high safety and energy density. Solid-state electrolytes are the key component of the solid-state battery, which exhibit high ionic conductivity, good chemical stability, and wide electrochemical windows. LATP [Li1.3Al0.3Ti1.7 (PO4)3] solid electrolyte has been widely investigated for its high ionic conductivity. Nevertheless, the chemical instability of LATP against Li metal has hindered its application in solid-state batteries. Here, we propose that atomic layer deposition (ALD) coating on LATP surfaces is able to stabilize the LATP/Li interface by reducing the side reactions. In comparison with bare LATP, the Al2O3-coated LATP by ALD exhibits a stable cycling behavior with smaller voltage hysteresis for 600 h, as well as small resistance. More importantly, on the basis of advanced characterizations such as high-resolution transmission electron spectroscope-electron energy loss spectroscopy, the lithium penetration into the LATP bulk and Ti4+ reduction are significantly limited. The results suggest that ALD is very effective in improving solid-state electrolyte/electrode interface stability.