Despite the dominance of lithium‐ion batteries (LIBs) in today's battery market, they are not flawless. Accordingly, the battery community is striving to strengthen the global battery portfolio with ...alternative systems. One branch of this effort is research into aqueous rechargeable batteries (ARBs). The simplicity of this concept, as well as rising safety concerns in commercial LIBs, has attracted numerous ARB‐related investigations in the past decade. Such heightened interest calls for a critical assessment of the field, especially with respect to its current state and potential opportunities. This essay examines the reality of ARBs in terms of their current socio‐technological context, which has been formed through a long history of battery research and development, often intertwined with social demands of the time. Attention is directed toward rechargeable batteries, briefly discussing their history, chemistry, and applications. The emergence of LIBs and their quick rise to market dominance with the concurrent fall of primitive ARBs serves as context for evaluating the current reality for newly emerging ARBs. Assessing their current position in academia and the battery market allows us to identify future opportunities and hurdles for incorporating ARBs into the global battery portfolio.
The current academic/market position of aqueous rechargeable batteries is examined in terms of technical merit and practicality. This critical evaluation sheds light on the future direction of aqueous battery research, highlighting prospective chemistries and applications in a technologically demanding era.
Aqueous zinc ion batteries (AZIBs) are steadily gaining attention based on their attractive merits regarding cost and safety. However, there are many obstacles to overcome, especially in terms of ...finding suitable cathode materials and elucidating their reaction mechanisms. Here, a mixed‐valence vanadium oxide, V6O13, that functions as a stable cathode material in mildly acidic aqueous electrolytes is reported. Paired with a zinc metal anode, this material exhibits performance metrics of 360 mAh g−1 at 0.2 A g−1, 92% capacity retention after 2000 cycles, and 145 mAh g−1 at a current density of 24.0 A g−1. A combination of experiments and density functional theory calculations suggests that hydrated intercalation, where water molecules are cointercalated with Zn ions upon discharge, accounts for the aforementioned electrochemical performance. This intercalation mechanism facilitates Zn ion diffusion throughout the host lattice and electrode–electrolyte interface via electrostatic shielding and concurrent structural stabilization. Through a correlation of experimental data and theoretical calculations, the promise of utilizing hydrated intercalation as a means to achieve high‐performance AZIBs is demonstrated.
For hydrated intercalation in aqueous batteries, V6O13 is presented as a promising cathode for aqueous zinc ion batteries. Water cointercalation with zinc ions facilitates their insertion into the host lattice by mitigating the desolvation energy and shielding electrostatic interaction, resulting in significantly enhanced electrochemical performance in aqueous environments.
Despite the prevalence of lithium ion batteries in modern technology, the search for alternative electrochemical systems to complement the global battery portfolio is an ongoing effort. The search ...has resulted in numerous candidates, among which mildly acidic aqueous zinc ion batteries have recently garnered significant academic interest, mostly due to their inherent safety. As the anode is often fixed as zinc metal in these systems, most studies address the absence of a suitable cathode for reaction with zinc ions. This has led to aggressive research into viable intercalation cathodes, some of which have shown impressive results. However, many investigations often overlook the implications of the zinc metal anode, when in fact the anode is key to determining the energy density of the entire cell. In this regard, we aim to shed light on the importance of the zinc metal anode. This perspective offers a brief discussion of zinc electrochemistry in mildly acidic aqueous environments, along with an overview of recent efforts to improve the performance of zinc metal to extract key lessons for future research initiatives. Furthermore, we discuss the energy density ramifications of the zinc anode with respect to its weight and reversibility through simple calculations for numerous influential reports in the field. Finally, we offer some perspectives on the importance of optimizing zinc anodes as well as a future direction for developing high-performance aqueous zinc ion batteries.
This perspective discusses the main issues with Zn anodes and highlights recent strategies to improve their performance in aqueous zinc ion batteries.
Lithium-ion batteries with ever-increasing energy densities are needed for batteries for advanced devices and all-electric vehicles. Silicon has been highlighted as a promising anode material because ...of its superior specific capacity. During repeated charge-discharge cycles, silicon undergoes huge volume changes. This limits cycle life via particle pulverization and an unstable electrode-electrolyte interface, especially when the particle sizes are in the micrometer range. We show that the incorporation of 5 weight % polyrotaxane to conventional polyacrylic acid binder imparts extraordinary elasticity to the polymer network originating from the ring sliding motion of polyrotaxane. This binder combination keeps even pulverized silicon particles coalesced without disintegration, enabling stable cycle life for silicon microparticle anodes at commercial-level areal capacities.
Silicon (Si) anode is among the most promising candidates for the next-generation high-capacity electrodes in Li-ion batteries owing to its unparalleled theoretical capacity (4200 mA h g
−1
for Li
...4.4
Si) that is approximately 10 times higher than that of commercialized graphitic anodes (372 mA h g
−1
for LiC
6
). The battery community has witnessed substantial advances in research on new polymeric binders for silicon anodes mainly due to the shortcomings of conventional binders such as polyvinylidene difluoride (PVDF) to address problems caused by the massive volume change of Si (300%) upon (de)lithiation. Unlike conventional battery electrodes, polymeric binders have been shown to play an active role in silicon anodes to alleviate various capacity decay pathways. While the initial focus in binder research was primarily to maintain the electrode morphology, it has been recently shown that polymeric binders can in fact help to stabilize cracked Si microparticles along with the solid-electrolyte-interphase (SEI) layer, thus substantially improving the electrochemical performance. In this review article, we aim to provide an in-depth analysis and molecular-level design principles of polymeric binders for silicon anodes in terms of their chemical structure, superstructure, and supramolecular interactions to achieve good electrochemical performance. We further highlight that supramolecular chemistry offers practical tools to address challenging problems associated with emerging electrode materials in rechargeable batteries.
Polymeric binders with supramolecular inter-chain interactions can effectively accommodate the volume expansion of silicon (Si) anodes and thus extend their cycle lives markedly, offering an insight in binder design for emerging electrodes that undergo large volume expansion.
The unparalleled theoretical specific energy of lithium–sulfur (Li–S) batteries has attracted considerable research interest from within the battery community. However, most of the long cycling ...results attained thus far relies on using a large amount of electrolyte in the cell, which adversely affects the specific energy of Li–S batteries. This shortcoming originates from the low solubility of polysulfides in the electrolyte. Here, 1,3‐dimethyl‐2‐imidazolidinone (DMI) is reported as a new high donor electrolyte for Li–S batteries. The high solubility of polysulfides in DMI and its activation of a new reaction route, which engages the sulfur radical (S3•−), enables the efficient utilization of sulfur as reflected in the specific capacity of 1595 mAh g−1 under lean electrolyte conditions of 5 μLelectrolyte mgsulfur−1. Moreover, the addition of LiNO3 stabilizes the lithium metal interface, thereby elevating the cycling performance to one of the highest known for high donor electrolytes in Li–S cells. These engineered high donor electrolytes are expected to advance Li–S batteries to cover a wide range of practical applications, particularly by incorporating established strategies to realize the reversibility of lithium metal electrodes.
1,3‐Dimethyl‐2‐imidazolidinone (DMI) is reported as a promising high donor electrolyte for Li–S batteries. DMI, in which polysulfides are highly soluble, allows cell operation under lean electrolyte conditions and diversifies reaction routes involving the sulfur radical. The addition of LiNO3 stabilizes the interface with the Li metal anode, achieving superior cyclability under lean electrolyte conditions of 5 μLelectrolyte mgsulfur−1.
A covalent triazine framework (CTF) with embedded polymeric sulfur and a high sulfur content of 62 wt % was synthesized under catalyst‐ and solvent‐free reaction conditions from 1,4‐dicyanobenzene ...and elemental sulfur. Our synthetic approach introduces a new way of preparing CTFs under environmentally benign conditions by the direct utilization of elemental sulfur. The homogeneous sulfur distribution is due to the in situ formation of the framework structure, and chemical sulfur impregnation within the micropores of CTF effectively suppresses the dissolution of polysulfides into the electrolyte. Furthermore, the triazine framework facilitates electron and ion transport, which leads to a high‐performance lithium–sulfur battery.
Elemental stabilization: A covalent triazine framework (CTF) with chemically embedded polymeric sulfur (S‐CTF) was synthesized under catalyst‐ and solvent‐free reaction conditions from 1,4‐dicyanobenzene and elemental sulfur. This material was used as a robust cathode for high‐performance lithium–sulfur batteries with very good cycling stabilities.
Capacitive deionization (CDI) that engages porous carbon electrodes constitutes one of the well‐established energy‐efficient desalination methods. However, improvement in desalination performance, ...including ion removal capacity, ion removal rate, and charge efficiency remains requisite for a wide range of applications. Herein, an ion‐exchange membrane‐free asymmetric CDI is introduced by pairing a metal organic framework (MOF), namely, K0.03CuFe(CN)60.65·0.43H2O and porous carbon. The exclusive intercalation of cations into the MOF prevents the reverse adsorption of co‐ions (anions), thus significantly improving ion removal capacity (23.2 mg g−1) and charge efficiency (75.8%). Moreover, by utilizing the advantage of the MOF that diverse mono‐ and divalent cations can be stored in the narrow redox potential range, the asymmetric CDI allows simultaneous capture of mono‐ and divalent cations, thus achieving omnivalent cation removal. Moreover, cations are intercalated in the hydrated forms without a discrete phase transition of the host structure, facilitating rapid desalination by reducing the desolvation energy penalty, which results in a high ion removal rate of 0.24 mg g−1 s−1. This study offers a new design principle in CDI: the integration of a crystal structure with large ionic channels that enable hydrated intercalation of multivalent ions in a fast and exclusive manner.
An asymmetric capacitive deionization is demonstrated by pairing metal organic framework (MOF) and activated carbon electrodes. The exclusive intercalation of various mono‐ and divalent cations into the MOF prevents the reverse adsorption of co‐ions (anions), improving charge efficiency and ion removal capacity significantly. Furthermore, the hydrated intercalation of cations without phase transition facilitates fast desalination.
Aqueous zinc (Zn)-ion batteries are gaining considerable attention as grid-scale energy storage systems due to their advantages in rate performance, cost, and safety. Here, we report a layered ...manganese oxide that contains a high content of crystal water (∼10 wt%) as an aqueous zinc battery cathode. The interlayer crystal water can effectively screen the electrostatic interactions between Zn
2+
ions and the host framework to facilitate Zn
2+
diffusion while sustaining the host framework for prolonged cycles. By virtue of these 'water' effects, this material exhibits a high reversible capacity of 350 mA h g
−1
at 100 mA g
−1
, along with decent cycling and rate performance, in a two-electrode cell configuration. Density functional theory (DFT) calculations and extended X-ray absorption fine structure (EXAFS) analyses jointly reveal that upon Zn
2+
ion intercalation, a stable inner-sphere Zn-complex coordinated with water molecules is formed, followed by the formation of a Zn-Mn dumbbell structure, which gives a clue for the observed electrochemical performance. This work unveils the useful function of crystal water in enhancing the key electrochemical performance of emerging divalent battery electrodes.
Crystal water improves electrochemical performance of the layered manganese oxide for aqueous rechargeable zinc batteries.
Lithium–sulfur (Li–S) batteries continue to be considered promising post‐lithium‐ion batteries owing to their high theoretical energy density. In pursuit of a Li–S cell with long‐term cyclability, ...most studies thus far have relied on using ether‐based electrolytes. However, their limited ability to dissolve polysulfides requires a high electrolyte‐to‐sulfur ratio, which impairs the achievable specific energy. Recently, the battery community found high donor electrolytes to be a potential solution to this shortcoming because their high solubility toward polysulfides enables a cell to operate under lean electrolyte conditions. Despite the increasing number of promising outcomes with high donor electrolytes, a critical hurdle related to stability of the lithium‐metal counter electrode needs to be overcome. This review provides an overview of recent efforts pertaining to high donor electrolytes in Li–S batteries and is intended to raise interest from within the community. Furthermore, based on analogous efforts in the lithium‐air battery field, strategies for protecting the lithium metal electrode are proposed. It is predicted that high donor electrolytes will be elevated to a higher status in the field of Li–S batteries, with the hope that either existing or upcoming strategies will, to a fair extent, mitigate the degradation of the lithium–metal interface.
H. Shin, M. Baek, A. Gupta, K. Char, A. Manthiram, J. W. Choi
High donor electrolytes for lithium–sulfur batteries have drawn increasing attention due to their high solubility of polysulfides that is beneficial for the specific energy density of a cell. This review summarizes pros and cons of high donor electrolytes in Li–S batteries and suggests viable approaches to overcome the fatal interfacial issue with the Li‐metal electrode.
PDF
