Chemical Communications Blog

Lithium-ion batteries are indispensable for powering a number of electronics (e.g. cell phones, laptops and even electric vehicles) used in the modern society. The key components of a lithium-ion battery are its two electrodes (anode and cathode) because they largely dictate the amount of electrical energy (measured by a parameter called “capacity”) the battery can hold. Increasing the capacity as well as prolonging the lifetime of lithium-ion batteries are practically desirable. Material scientists worldwide are searching for electrode materials to achieve the goal.

In the past decade, a diverse array of metal oxides has been developed as lithium-ion battery anodes with promising performance. These anodes have exhibited considerably higher capacity (~1000 mAh/g) than the current commercial anode material, graphite (372 mAh/g). However, two major drawbacks of metal oxides, namely the limited electrical conductivity and the short lifetime, impede their feasibility for practical applications. While the poor electrical conductivity is an intrinsic physical property of most metal oxides, their short life time is caused by the large volumetric deformation during charge and discharge processes. The deformation will eventually trigger pulverization of electrodes and lead to loss of capacity. Therefore, developing novel strategies that manage to turn metal oxides to viable electrode candidates with satisfying lifetime becomes necessary.

Now writing in Chemical Communications, a research group led by Professor Liqiang Mai and Professor Qi Li from Wuhan University of Technology, China demonstrated a metal oxide-carbon composite anode that exhibited both high capacity and super-long lifetime. The structure of this composite is a “cube-in-tube” configuration (Figure 1): the manganese oxide nanoparticle-embedded carbon “tubes” encapsulate the CoSnO₃ (a binary metal oxide) “cubes”. This unique composite electrode delivered a maximal capacity of 960 mAh/g at a current density of 0.1 A/g (Figure 2a), around three times higher than the theoretical capacity of graphite. More impressively, as shown in Figure 2b, the electrode displayed outstanding stability with ~99% of capacity retained after 1500 consecutive charge and discharge cycles (roughly equivalent to four years’ use), much higher than those of the current commercial products and other laboratory-developed composites.

Figure 1. Schematic of the synthesis strategy and the morphology of the “cube-in-tube” metal oxide-carbon composite lithium-ion battery electrode.

Figure 2. (a) Plot of capacity at different current densities; (b) The stability performance evaluated at 2 A/g.

The authors attributed the electrode’s excellent durability to two reasons. Firstly, the hollow structures (both the “tube” and the “cube”) provide adequate empty space to accommodate volumetric change of metal oxides. Secondly, the soft nature of carbon renders its ability to serve as a mechanical buffer layer. Both aspects reduce the possibility of structural pulverization and promote long lifetime.

To find out more please read:

Facile Electrospinning Formation of Carbon-confined Metal Oxide Cube-in-tube Nanostructures for Stable Lithium Storage

Ziang Liu, Ruiting Guo, Jiashen Meng, Xiong Liu, Xuanpeng Wang, Qi Li, Liqiang Mai

DOI: 10.1039/C7CC0327A

About the author:

Tianyu Liu is a Ph.D. in chemistry graduated from University of California-Santa Cruz, United States. He is passionate about scientific communication to introduce cutting-edge researches to both the general public and the scientists with diverse research expertise. He is a web writer for the Chem. Commun. and Chem. Sci. blog websites. More information about him can be found at http://liutianyuresearch.weebly.com/.

All of the referee-recommended articles below are free to access until 5th August 2017.

Chemically individual armoured bioreporter bacteria used for the in vivo sensing of ultra-trace toxic metal ions
Zhijun Zhang, Enguo Ju, Wei Bing, Zhenzhen Wang, Jinsong Rena and Xiaogang Qu
Chem. Commun., 2017, Advance Article
DOI: 10.1039/C7CC03794E, Communication

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Expeditious synthesis of pyrano[2,3,4-de]quinolines via Rh(III)-catalyzed cascade C–H activation/annulation/lactonization of quinolin-4-ol with alkynes
Gang Liao, Hong Song, Xue-Song Yinab and Bing-Feng Shi
Chem. Commun., 2017, Advance Article
DOI:  10.1039/C7CC04113F, Communication

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Autonomously propelled microscavengers for precious metal recovery
Sarvesh Kumar Srivastava, Mariana Medina-Sáncheza and Oliver G. Schmidta
Chem. Commun., 2017, Advance Article
DOI: 10.1039/C7CC02605F, Communication

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Aromatic stacking – a key step in nucleation
Aurora J. Cruz-Cabeza, Roger J. Davey, Sharlinda Salim Sachithananthan, Rebecca Smith, Sin Kim Tang, Thomas Vetter and Yan Xiao
Chem. Commun., 2017, Advance Article
DOI: 10.1039/C7CC02423A, Communication

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Hexagonal boron nitride nanosheets as a multifunctional background-free matrix to detect small molecules and complicated samples by MALDI mass spectrometry
Jianing Wang, Jie Sun, Jiyun Wang, Huihui Liu, Jinjuan Xue and Zongxiu Nie
Chem. Commun., 2017, Advance Article
DOI: 10.1039/C7CC02957H, Communication

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Faradaic oxygen evolution from SrTiO3 under nano- and femto-second pulsed light excitation
D. J. Aschaffenburg, X. Chen and T. Cuk
Chem. Commun., 2017,53, 7254-7257
DOI: 10.1039/C7CC03061D, Communication

Written by Tianyu Liu, University of California, Santa Cruz

Batteries are indispensable components that are powering a diverse array of electronics used almost every day. In recent years, due to the mass production of rechargeable electronics such as cell phones and electric vehicles, the need for reliable and economically viable batteries is rapidly increasing. Lithium-ion batteries represent a dominated rechargeable battery category that has been commercialized since early 1990s. However, the uneven distribution and high cost of lithium pose concerns on the sustainability of lithium-ion batteries.

Since the last decade, a number of scientists have shifted their attention to metal-ion batteries with more abundant and inexpensive metals than lithium, such as sodium and potassium. Change of ions calls for the need of seeking electrode materials with suitable structures that are able to host sodium or potassium ions. Most recently, Naguib and coworkers from Oak Ridge National Laboratory in USA and Purdue University in USA have identified a new two-dimensional material belonging to the MXene family that exhibits promising performance as an electrode for potassium-ion batteries. Their works has been published in Chem. Commun.

MXenes are a group of two-dimensional transition metal carbides and carbonitrides (Figure a) with chemical formula Mn+1XnTz; where M, X and Tz stand for an early transition metal element (e.g., Ti, V, Cr), carbon and/or nitrogen, and termination element (usually O, OH or F), respectively. Based on previous theoretical studies, MXenes are predicted to be capable of hosting potassium ions. In this work, Naguib et al. first synthesized one of the MXenes, Ti3CNOF, and experimentally investigated its energy storage performance.

The researchers first synthesized the Ti3CNOF powder by a wet etching process of its precursor. The obtained powder was then blended with other additives (including carbon black powder and polymer binders) and cast onto a piece of copper foil to prepare the electrode. The Ti3CNOF electrode delivered a high capacity (a measure for amount of energy that can be stored) of 710 mAh/g in the first discharging process and retained 75 mAh/g after 100 charge and discharge cycles (Figure b). In addition, the researchers gauged the charge storage mechanism of the synthesized Ti3CNOF using X-ray diffraction and X-ray photoelectron spectroscopy. The key conclusion is that potassium ions are able to intercalate in between layers of Ti3CNOF without triggering any phase change (Figure c). This mechanism is similar with lithium-ion intercalation into graphite.

Though the capacity performance reported here is not as outstanding as other graphene-based electrodes, this work provides the encouraging potential of MXenes serving as potassium-ion battery electrodes. Exploring other MXenes and modifying Ti3CNOF demonstrated here are expected to further enhance the charge storage performance of MXene-based potassium-ion batteries.

To find out more please read:
Electrochemical Performance of MXenes as K-ion Battery Anodes
Michael Naguib, Ryan A. Adams, Yunpu Zhao, Dmitry Zemlyanov, Arvind Varma, Jagjit Nanda, Vilas G. Pol.
DOI: 10.1039/C7CC02026K

About the author:
Tianyu Liu is a Ph.D. in chemistry from University of California-Santa Cruz. He is passionate about scientific communication to introduce cutting-edge researches to both the general public and the scientists with diverse research expertise. He is a web writer for the Chem. Commun. and Chem. Sci. blog websites. More information about him can be found at http://liutianyuresearch.weebly.com/.

Written by Tianyu Liu, University of California, Santa Cruz

Chitosan is a polysaccharide derived from chitin, a second most abundant bio-polymer on earth that consists of the shells of crustaceans (such as shrimps and crabs). It is a commonly used bio-compatible material for bio-medical applications such as drug delivery.

Previous studies have shown that chitosan is pH sensitive in water: it forms a viscous solution at low pH values and becomes insoluble at high pH values. Preliminary investigations suggest that such pH responsiveness is associated with the protonation and de-protonation processes of the amine groups on the chitosan polymer chain (the red box in Figure a). However, there still lacks fundamental understanding on how the pH affects the behavior of chitosan.

Now writing in Chem. Commun., Xu and Matysiak from University of Maryland, USA provided us new insights on the chitosan’s pH responsiveness at the molecular level. They adopted a method called “coarse-grained molecular simulation” to illustrate the self-assembly behaviors of chitosan polymer chains at different pH values. Unlike atomistic molecular simulations that focus on individual atoms of a molecule, the coarse-grained molecular simulation treats a group of atoms as one ensemble and probes the collective behavior of each ensemble (Figure a and b). This simulation technique demands less time than the atomistic counterparts without significantly reducing the simulation accuracy. It is suitable for characterizing polymers composed of thousands of atoms, such as chitosan.

The key discovery of this work is that the chitosan polymer chains can adopt different configurations at different pH values. At high pH values, each chain tends to crosslink perpendicularly with adjacent chains. The crosslinking reaction propagates and eventually builds up a three-dimensional dense chain network (Figure c). At low pH values, the protonated amine groups favor parallel crosslinking. Thus, each chain aligns in parallel with each other, which leads to a loosely-packed structure (Figure d). The perpendicularly cross-linked configuration reduces the solubility of chitosan in water but renders robustness and elasticity of the chitosan networks. The parallel cross-linked morphology increases water solubility but decreases the elasticity of the chitosan assembly. These conclusions obtained by the simulation are consistent with experimental results.

To find out more please read:
Effect of pH on Chitosan Hydrogel Polymer Network Structure
Hongcheng Xu and Silvina Matysiak
DOI: 10.1039/C7CC01826F

About the author:
Tianyu Liu is a Ph.D. in chemistry from University of California-Santa Cruz. He is passionate about scientific communication to introduce cutting-edge researches to both the general public and the scientists with diverse research expertise. He is a web writer for the Chem. Commun. and Chem. Sci. blog websites. More information about him can be found at http://liutianyuresearch.weebly.com/