Joon Ha Chang

Atomic visualization of a non-equilibrium sodiation pathway in copper sulfide

Sodium ion batteries have been considered a promising alternative to lithium ion batteries for large-scale energy storage owing to their low cost and high natural abundance. However, the commercialization of this device is hindered by the lack of suitable anodes with an optimized morphology that ensure high capacity and cycling stability of a battery. Here, we not only demonstrate that copper sulfide nanoplates exhibit close-to-theoretical capacity (~560 mAh g–1) and long-term cyclability, but also reveal that their sodiation follows a non-equilibrium reaction route, which involves successive crystallographic tuning. By employing in situ transmission electron microscopy, we examine the atomic structures of four distinct sodiation phases of copper sulfide nanoplates including a metastable phase and discover that the discharge profile of copper sulfide directly reflects the observed phase evolutions. Our work provides detailed insight into the sodiation process of the high-performance intercalation–conversion anode material.Copper sulfide allows for high-performance sodium ion storage, yet its sodiation mechanism is poorly understood. Here, the authors examine the atomic structures of sodiated phases via in situ transmission electron microscopy, showing a non-equilibrium reaction pathway.

In Situ High-Resolution Transmission Electron Microscopy (TEM) Observation of Sn Nanoparticles on SnO2 Nanotubes Under Lithiation

We trace Sn nanoparticles (NPs) produced from SnO2 nanotubes (NTs) during lithiation initialized by high energy e-beam irradiation. The growth dynamics of Sn NPs is visualized in liquid electrolytes by graphene liquid cell transmission electron microscopy. The observation reveals that Sn NPs grow on the surface of SnO2 NTs via coalescence and the final shape of agglomerated NPs is governed by surface energy of the Sn NPs and the interfacial energy between Sn NPs and SnO2 NTs. Our result will likely benefit more rational material design of the ideal interface for facile ion insertion.

In Situ Transmission Electron Microscopy Graphene Liquid Cell on Chemical Sodiation of Nickel Oxide Nanoparticle

Sodium-ion batteries (SIBs) are highly treated to be the complementary alternatives to lithium ion batteries (LIBs) with response to the abundance of cost-effective sodium material. Both sodium and lithium belong to the same main group, showing most similar chemical characteristics although Na has relatively large ionic radius compared to lithium, which limits its electrochemical performance [1]. For SIBs to fulfil its promise of being alternative to LIBs, there is a necessity to innovate effective and appropriate strategies to design various electrodes materials with functional structures [2]. Among the widely studied electrodes are the transition metal oxides (TMOs) as they exhibit high theoretical capacities for sodium storage via similar mechanisms to lithium [3].

The Effect of Electron Beam Dosage in the Decomposition Behavior of Electrolytes Encapsulated Inside the Graphene Sheets Based on In Situ TEM Observation

Real-time observation on the dynamics inside the battery can be an ideal way to obtain fundamental understanding about electrochemical reactions that can lead to rational design of electrode materials for the rechargeable batteries. In particular, in situ transmission electron microscopy (TEM) is the most suitable platform observing such dynamics as it can analyse the morphological, phase, electronic, and even chemical structure of respective elements [1].

In Situ TEM Observation on the Agglomeration of Nanoparticles in the Interface of SnO 2

Direct observation of nanoparticles in high resolution has attracted considerable attention, as it can provide the fundamental understanding that is crucial to manufacturing the nanoscale materials that have different morphologies (e.g. sizes and shapes). Recently, very feasible in situ TEM platform called ‘graphene liquid cell’ (GLC) has been developed, which is easy to fabricate while maintaining high resolution imaging to better understand the dynamics of nanoparticles [1].

In Situ TEM Observation on the Growth and Agglomeration of Propylene Carbonate-based Electrolytes During Sodiation with Graphene Liquid Cell

Since the first publication in Science in 2012 [1], graphene liquid cell (GLC) has attracted considerable attention with subsequent research works as it can be easily fabricated and can be used for observation in conventional transmission electron microscopy (TEM) without further modification. As nanoscience is significantly progressing each year, there is increasing demand for understanding more detailed processes of how growth and reorganization of nanoparticles or nanocrystals occur in the liquid solution.

Case Examination on Volume Expansion of Crystalline Si Nanoparticles under Sodiation: In Situ TEM Study Using Graphene Liquid Cells

Silicon nanoparticles are very famous as the best anode material for batteries because of its high theoretical capacity [1]. This material has been proved to have effective performance in lithium ion batteries. Due to some limitations in lithium ion batteries such as scarcity of lithium and high cost, the need has been made to search the alternative candidate to lithium [2,3]. Sodium ion batteries have been extensively considered to be among the promising alternative candidates to lithium ion battery as they are accompanied with desirable properties such as abundant of sodium resources, low cost and low toxicity. Moreover. Sodium and lithium show most similar chemical characteristics. Although sodium has higher ionic radius (0.98Å) than lithium (0.68Å), this leads to scientific challenges in optimizing and discovering anode material for sodium ion batteries. However, significant problem arises when silicon is used in the sodium ion batteries, because most previous ex situ studies reported that crystalline silicon is inactive when used as anode material in sodium ion battery [4-6]. Nevertheless, recent ex situ study proved the possibility of sodiation of silicon nanoparticles for both amorphous and crystalline phases with a volume expansion of 28.4% and initial sodiation/desodiation 1027 mAh g and 270 mAh g at a current density of 20 mA g [7]. This study is contrary to the previous studies, and it is currently controversial as to whether sodium actually reacts with Si and whether volume expansion does occur. Understanding whether volume expansion truly occurs in Si is crucially important as it is the indication that sodiation process truly takes place, and opens up new opportunities to use Si as the viable anode material for sodium ion batteries.

Structural Integrity of SnO 2 Nanotubes During Sodiation Examined by in Situ TEM Observation with Graphene Liquid Cell

Morphological evolutions and volume expansions of electrode materials that can be potentially applied for energy storage devices are critical issues as they trigger loss of electric contact and subsequent pulverization that lead to capacity decay and shorter cycle life. At the same time, understanding the morphological dynamics of electrode materials upon lithiation and sodiation is crucial to further suggest superior material designs that can best modify such structures.

In Situ TEM Observation on Formation of Uniform Amorphous Layer on SnO 2 Nanotube

Interfacial reactions at electrolyte/electrode boundary are crucially important for the performance of lithium-ion batteries (LIBs) as they are one of influencing parameters in the transport of electrons and Li ions to the electrodes [1,2]. Taking into account that these interfacial reactions are important, a number of studies utilizing Fourier Transform Infrared spectroscopy (FTIR) analysis and x-ray photoelectron spectroscopy (XPS) have been reported in this subject [3,4]. However, limitations exist as there they are based on ex situ analysis, where they were examined in the electrode that was stripped off from the electrochemical cell and underwent washing process, where some variables exist [5]. To overcome these limitations, in situ analysis was adopted beyond the simple research on the morphology and composition of the final products, in order to fully understand the mechanisms occurring at interfacial layers.

In Situ TEM Study on the Growth Process of Amorphous Layer on SnO 2 Nanoparticle During Sodiation on Real Time Scale

As the secondary rechargeable batteries, lithium-ion batteries (LIBs) have been commercialized, to some extent, in different applications, such as electric vehicle (EV), cell phones, cameras, and other small-scale electronic devices [1,2]. Nevertheless, relatively scarce amount of lithium (Li) present in the world can significantly downplay its commercialization in the far future, because there is increasing demand for large-scale electric grid or energy storage system that can be devised in a costeffective way. In order to overcome the limited Li resources, different alternative batteries have been suggested. [2] Among them, sodium-ion battery (SIB) has become one of main feasible and practical candidates mainly due to the abundance and cheap cost that sodium (Na) can offer, compared with Li.