A core–shell structure of polypyrrole grown on V2O5 nanoribbons as a high performance anode material for supercapacitors is fabricated using anionic dodecylbenzenesulfonate (DBS−) as surfactant. ...Benefiting from the nanoribbon morphology of V2O5, the improved charge‐transfer and polymeric coating effect of PPy, PPy@V2O5 nanocomposites exhibits high energy density, and excellent cycling and rate capability in K2SO4 aqueous electrolyte.
On discharge, the Li-O2 battery can form a Li2O2 film on the cathode surface, leading to low capacities, low rates and early cell death, or it can form Li2O2 particles in solution, leading to high ...capacities at relatively high rates and avoiding early cell death. Achieving discharge in solution is important and may be encouraged by the use of high donor or acceptor number solvents or salts that dissolve the LiO2 intermediate involved in the formation of Li2O2. However, the characteristics that make high donor or acceptor number solvents good (for example, high polarity) result in them being unstable towards LiO2 or Li2O2. Here we demonstrate that introduction of the additive 2,5-di-tert-butyl-1,4-benzoquinone (DBBQ) promotes solution phase formation of Li2O2 in low-polarity and weakly solvating electrolyte solutions. Importantly, it does so while simultaneously suppressing direct reduction to Li2O2 on the cathode surface, which would otherwise lead to Li2O2 film growth and premature cell death. It also halves the overpotential during discharge, increases the capacity 80- to 100-fold and enables rates >1 mA cmareal(-2) for cathodes with capacities of >4 mAh cmareal(-2). The DBBQ additive operates by a new mechanism that avoids the reactive LiO2 intermediate in solution.
Lithium-oxygen cells, in which lithium peroxide forms in solution rather than on the electrode surface, can sustain relatively high cycling rates but require redox mediators to charge. The mediators ...are oxidised at the electrode surface and then oxidise lithium peroxide stored in the cathode. The kinetics of lithium peroxide oxidation has received almost no attention and yet is crucial for the operation of the lithium-oxygen cell. It is essential that the molecules oxidise lithium peroxide sufficiently rapidly to sustain fast charging. Here, we investigate the kinetics of lithium peroxide oxidation by several different classes of redox mediators. We show that the reaction is not a simple outer-sphere electron transfer and that the steric structure of the mediator molecule plays an important role. The fastest mediator studied could sustain a charging current of up to 1.9 A cm
, based on a model for a porous electrode described here.
Li-metal batteries have been emerging as attractive technologies for electrical energy storage and conversion by virtue of the ultrahigh theoretical specific capacity of lithium. However, the ...undesirable Li-dendrite growth upon prolonged cycling gives rise to thermal runaway, inducing tremendous safety concerns that impede the development of the technology. In general, Li nucleation and growth behavior significantly changes when the operating condition is modified through modulating temperature or thermodynamic energy to produce regulated lithium depositions. Herein, this perspective takes these two key factors as an example to emphasize the importance of thermodynamic understandings of the Li-dendrite issue. The key challenges and corresponding strategies for designing advanced dendrite-free Li-metal anodes with respect to thermodynamic factors are also discussed as fundamental guidance for future development.
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The recent boom in electrical energy storage and conversion with high-energy density facilitates the exploration of Li-metal batteries. However, Li dissolution and nucleation are easily susceptible to thermodynamic conditions that induce dendrite growth, causing tremendous safety hazards, low energy density, and short lifespan. Nevertheless, a comprehensive understanding of the thermodynamic effects on lithium deposition and growth is still absent.
The development and latest research progress of thermodynamic-inducing factors regarding lithium nucleation and growth are systematically summarized from theory to experiment, especially focusing on thermodynamic energy, temperature, and related models. Strategies for designing a dendrite-free Li-metal anode through thermodynamic considerations, including structured anode, self-healing dendrite tactics, and electrode and electrolyte interface engineering are also discussed. We highlight the imperfections of present thermodynamic research and propose corresponding feasible solutions. Future work should evaluate each individual system on its own to integrate suitable models that combine with kinetics and other factors to find interrelated strategies to address the dendrite-growth issues under various conditions.
Li dissolution and nucleation are easily susceptible to thermodynamic conditions that induce dendrite growth, giving rise to thermal runaway and causing tremendous safety hazards. Here, Gao et al. systematically summarize the progress in thermodynamic effects on lithium formation from theory to experiment and highlight the imperfections of present thermodynamic research as well as propose corresponding feasible solutions. This review provides a fundamental guidance for future development of dendrite-free Li-metal anodes.
The solid electrolyte interphase (SEI), a complex layer that forms over the surface of electrodes exposed to battery electrolyte, has a central influence on the structural evolution of the electrode ...during battery operation. For lithium metallic anodes, tailoring this SEI is regarded as one of the most effective avenues for ensuring consistent cycling behavior, and thus practical efficiencies. While fluoride‐rich interphases in particular seem beneficial, how they alter the structural dynamics of lithium plating and stripping to promote efficiency remains only partly understood. Here, operando liquid‐cell transmission electron microscopy is used to investigate the nanoscale structural evolution of lithium electrodeposition and dissolution at the electrode surface across fluoride‐poor and fluoride‐rich interphases. The in situ imaging of lithium cycling reveals that a fluoride‐rich SEI yields a denser Li structure that is particularly amenable to uniform stripping, thus suppressing lithium detachment and isolation. By combination with quantitative composition analysis via mass spectrometry, it is identified that the fluoride‐rich SEI suppresses overall lithium loss through drastically reducing the quantity of dead Li formation and preventing electrolyte decomposition. These findings highlight the importance of appropriately tailoring the SEI for facilitating consistent and uniform lithium dissolution, and its potent role in governing the plated lithium's structure.
The composition of the solid electrolyte interphase (SEI) layer in batteries can be manipulated to improve performance, yet remains challenging to understand. In this work, in situ transmission electron microscopy is used to directly image electrodes as they are cycled, revealing the role that a fluoride‐rich SEI layer has for promoting improved cycling performance.
The application of redox mediators has been considered as a promising strategy to boost the performance of aprotic Li‐O2 batteries. However, the issues brought with redox mediators, especially on the ...Li anode side have been overlooked. Here, we propose a facile approach of preparing a gel polymer membrane that not only allow uniform Li plating/stripping with large current densities over extended cycling but also inhibit the diffusion of redox mediators and avoid redox shuttling, self‐discharge, and internal short‐circuiting. More importantly, the gel polymer membrane prevents the penetration of O2 and superoxide intermediates from the Li anode. Therefore, it ensures the successful application of both lithium anode and redox mediators in Li‐O2 batteries to achieve the desired high capacity and rate performance. Meanwhile, it helps understand the benefit and problems of added redox mediators and reactive oxygen species so that the performance of such Li‐O2 batteries can be truly evaluated.
We prepared a gel polymer membrane that could prohibit the redox shuttle of redox mediators as well as the penetration of oxygen related species. This not only protects the lithium negative electrode but also improves the performance of the lithium oxygen batteries.
Abstract
Solid‐state lithium batteries may provide increased energy density and improved safety compared with Li‐ion technology. However, in a solid‐state composite cathode, mechanical degradation ...due to repeated cathode volume changes during cycling may occur, which may be partially mitigated by applying a significant, but often impractical, uniaxial stack pressure. Herein, we compare the behavior of composite electrodes based on Li
4
Ti
5
O
12
(LTO) (negligible volume change) and Nb
2
O
5
(+4% expansion) cycled at different stack pressures. The initial LTO capacity and retention are not affected by pressure but for Nb
2
O
5
, they are significantly lower when a stack pressure of <2 MPa is applied, due to inter‐particle cracking and solid‐solid contact loss because of cyclic volume changes. This work confirms the importance of cathode mechanical stability and the stack pressures for long‐term cyclability for solid‐state batteries. This suggests that low volume‐change cathode materials or a proper buffer layer are required for solid‐state batteries, especially at low stack pressures.
There is considerable interest in multivalent cation batteries, such as those based on magnesium, calcium or aluminium. Most attention has focused on magnesium. In all cases the metal anode ...represents a significant challenge. Recent work has shown that calcium can be plated and stripped, but only at elevated temperatures, 75 to 100 °C, with small capacities, typically 0.165 mAh cm
, and accompanied by significant side reactions. Here we demonstrate that calcium can be plated and stripped at room temperature with capacities of 1 mAh cm
at a rate of 1 mA cm
, with low polarization (∼100 mV) and in excess of 50 cycles. The dominant product is calcium, accompanied by a small amount of CaH
that forms by reaction between the deposited calcium and the electrolyte, Ca(BH
)
in tetrahydrofuran (THF). This occurs in preference to the reactions which take place in most electrolyte solutions forming CaCO
, Ca(OH)
and calcium alkoxides, and normally terminate the electrochemistry. The CaH
protects the calcium metal at open circuit. Although this work does not solve all the problems of calcium as an anode in calcium-ion batteries, it does demonstrate that significant quantities of calcium can be plated and stripped at room temperature with low polarization.
A sodium‐ion battery operating at room temperature is of great interest for large‐scale stationary energy storage because of its intrinsic cost advantage. However, the development of a high capacity ...cathode with high energy density remains a great challenge. In this work, sodium super ionic conductor‐structured Na3V2−xCrx(PO4)3 is achieved through the sol–gel method; Na3V1.5Cr0.5(PO4)3 is demonstrated to have a capacity of 150 mAh g−1 with reversible three‐electron redox reactions after insertion of a Na+, consistent with the redox couples of V2+/3+, V3+/4+, and V4+/5+. Moreover, a symmetric sodium‐ion full cell utilizing Na3V1.5Cr0.5(PO4)3 as both the cathode and anode exhibits an excellent rate capability and cyclability with a capacity of 70 mAh g−1 at 1 A g−1. Ex situ X‐ray diffraction analysis and in situ impedance measurements are performed to reveal the sodium storage mechanism and the structural evolution during cycling.
The rationally designed Na3V1.5Cr0.5(PO4)3 shows a capacity of 150 mAh g−1 and reversible three‐electron redox reactions, consistent with the redox couples of V2+/3+, V3+/4+, and V4+/5+. A symmetric sodium‐ion cell with a high capacity of 120 mA g−1 is achieved, with Na3V1.5Cr0.5(PO4)3 both as the anode and cathode, demonstrating it as a competitive electrode material for sodium‐ion batteries.
Intercalation transition metal oxides (ITMO) have attracted great attention as lithium-ion battery negative electrodes due to high operation safety, high capacity and rapid ion intercalation. ...However, the intrinsic low electron conductivity plagues the lifetime and cell performance of the ITMO negative electrode. Here we design a new carbon-emcoating architecture through single CO
2
activation treatment as demonstrated by the Nb
2
O
5
/C nanohybrid. Triple structure engineering of the carbon-emcoating Nb
2
O
5
/C nanohybrid is achieved in terms of porosity, composition, and crystallographic phase. The carbon-embedding Nb
2
O
5
/C nanohybrids show superior cycling and rate performance compared with the conventional carbon coating, with reversible capacity of 387 mA h g
−1
at 0.2 C and 92% of capacity retained after 500 cycles at 1 C. Differential electrochemical mass spectrometry (DEMS) indicates that the carbon emcoated Nb
2
O
5
nanohybrids present less gas evolution than commercial lithium titanate oxide during cycling. The unique carbon-emcoating technique can be universally applied to other ITMO negative electrodes to achieve high electrochemical performance.
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