Seoung-Bum Son

Reversible High‐Capacity Si Nanocomposite Anodes for Lithium‐ion Batteries Enabled by Molecular Layer Deposition

The molecular-layer deposition of a flexible coating onto Si electrodes produces high-capacity Si nanocomposite anodes. Using a reaction cascade based on inorganic trimethylaluminum and organic glycerol precursors, conventional nano-Si electrodes undergo surface modifications, resulting in anodes that can be cycled over 100 times with capacities of nearly 900 mA h g(-1) and Coulombic efficiencies in excess of 99%.

Effect of pores in hollow carbon nanofibers on their negative electrode properties for a lithium rechargeable battery.

The effect of pores in hollow carbon nanofibers (HCNFs) on their electrochemical performance is investigated because the carbon shell itself acts as a reservoir for accommodating Li-ions through intercalation and simultaneously becomes a transport medium through which Li-ions migrate into the core materials in HCNFs. Porous HCNFs (pHCNFs) are prepared by the coaxial electrospinning of a sacrificial core solution and an emulsified shell solution containing sacrificial islands for pore generation. After a thermal treatment, a systematic study is carried out to relate the resulting pore size in pHCNFs to the sacrificial islands in the emulsified shell. As the pores are introduced in pHCNFs, their initial capacity and reversible capacity rate are proved to increase significantly to 1003 mAhg(-1) and 61.8%, respectively, compared to those (653 mAhg(-1) and 53.9%) of nonporous HCNFs. The increased pore size and expanded graphene layers are believed to facilitate lithium insertion/extraction behavior.

Hierarchical Porous Framework of Si‐Based Electrodes for Minimal Volumetric Expansion

A tunable hierarchical porous framework is fabricated to house the volumetric changes outputted by Si. The nSi@cPAN/cPAN electrodes only expand by 14.3% at full initial lithiation and remain within 23% expansion from its uncycled state after 20 cycles with remarkable cycling stability and high coulombic efficiencies in excess of 99.5%.

Structure and Reactivity of Alucone-Coated Films on Si and LixSiy Surfaces

Coating silicon particles with a suitable thin film has appeared as a possible solution to accommodate the swelling of silicon upon lithiation and its posterior cracking and pulverization during cycling of Li-ion batteries. In particular, aluminum alkoxide (alucone) films have been recently deposited over Si anodes, and the lithiation and electrochemical behavior of the system have been characterized. However, some questions remain regarding the lithium molecular migration mechanisms through the film and the electronic properties of the alucone film. Here we use density functional theory, ab initio molecular dynamics simulations, and Greens function theory to examine the film formation, lithiation, and reactivity in contact with an electrolyte solution. It is found that the film is composed of Al-O complexes with 3-O or 4-O coordination. During lithiation, Li atoms bind very strongly to the O atoms in the most energetically favorable sites. After the film is irreversibly saturated with Li atoms, it becomes electronically conductive. The ethylene carbonate molecules in liquid phase are found to be reduced at the surface of the Li-saturated alucone film following similar electron transfer mechanisms as found previously for lithiated silicon anodes. The theoretical results are in agreement with those from morphology and electrochemical analyses.

An artificial interphase enables reversible magnesium chemistry in carbonate electrolytes

Magnesium-based batteries possess potential advantages over their lithium counterparts. However, reversible Mg chemistry requires a thermodynamically stable electrolyte at low potential, which is usually achieved with corrosive components and at the expense of stability against oxidation. In lithium-ion batteries the conflict between the cathodic and anodic stabilities of the electrolytes is resolved by forming an anode interphase that shields the electrolyte from being reduced. This strategy cannot be applied to Mg batteries because divalent Mg2+ cannot penetrate such interphases. Here, we engineer an artificial Mg2+-conductive interphase on the Mg anode surface, which successfully decouples the anodic and cathodic requirements for electrolytes and demonstrate highly reversible Mg chemistry in oxidation-resistant electrolytes. The artificial interphase enables the reversible cycling of a Mg/V2O5 full-cell in the water-containing, carbonate-based electrolyte. This approach provides a new avenue not only for Mg but also for other multivalent-cation batteries facing the same problems, taking a step towards their use in energy-storage applications.Mg-based batteries possess potential advantages over their lithium counterparts; however, the use of reversible oxidation-resistant, carbonate-based electrolytes has been hindered because of their undesirable electrochemical reduction reactions. Now, by engineering a Mg2+-conductive artificial interphase on a Mg electrode surface, which prevents such reactivity, highly reversible Mg deposition/stripping in carbonate-based electrolytes has been demonstrated.

Face-centered-cubic lithium crystals formed in mesopores of carbon nanofiber electrodes.

In the foreseeable future, there will be a sharp increase in the demand for flexible Li-ion batteries. One of the most important components of such batteries will be a freestanding electrode, because the traditional electrodes are easily damaged by repeated deformations. The mechanical sustainability of carbon-based freestanding electrodes subjected to repeated electrochemical reactions with Li ions is investigated via nanotensile tests of individual hollow carbon nanofibers (HCNFs). Surprisingly, the mechanical properties of such electrodes are improved by repeated electrochemical reactions with Li ions, which is contrary to the conventional wisdom that the mechanical sustainability of carbon-based electrodes should be degraded by repeated electrochemical reactions. Microscopic studies reveal a reinforcing mechanism behind this improvement, namely, that inserted Li ions form irreversible face-centered-cubic (FCC) crystals within HCNF cavities, which can reinforce the carbonaceous matrix as strong second-phase particles. These FCC Li crystals formed within the carbon matrix create tremendous potential for HCNFs as freestanding electrodes for flexible batteries, but they also contribute to the irreversible (and thus low) capacity of HCNFs.

Pd effect on reliability of Ag bonding wires in microelectronic devices in high-humidity environments

We investigated the effect of Pd concentration in Pd-doped Ag wires on the humidity reliability and interfacial corrosion characteristics between Ag wire and Al metallization. Additionally, we confirmed no corrosion problem between Ag wire and noble metal (Pd, Au) metallization, even after a pressure cooker test (PCT). The chemical composition of the tested Ag wires was pure Ag, Ag-1wt% Pd and Ag-3wt% Pd. These wires were bonded to Al and noble metal (Au, Pd) metallization using a thermo-sonic bonder. The interfaces were characterized by focused ion beam (FIB), high resolution transmission electron microscope (HRTEM) and energy dispersive X-ray spectroscopy (EDS). The interface corrosion of Pd doped Ag wires was significantly reduced as the Pd concentration in the Ag wires increased. Furthermore, the Ag wires on the noble metal (Au, Pd) metallization exhibited stable reliability during the PCT.

Systematic Investigation of the Alucone-Coating Enhancement on Silicon Anodes

Polyvinylidene fluoride (PVDF) is the most popular binder in commercial lithium-ion batteries but is incompatible with a silicon (Si) anode because it fails to maintain the mechanical integrity of the Si electrode upon cycling. Herein, an alucone coating synthesized by molecular layer deposition has been applied on the laminated electrode fabricated with PVDF to systematically study the sole impact of the surface modification on the electrochemical and mechanical properties of the Si electrode, without the interference of other functional polymer binders. The enhanced mechanical properties of the coated electrodes, confirmed by mechanical characterization, can help accommodate the repeated volume fluctuations, preserve the electrode structure during electrochemical reactions, and thereby, leading to a remarkable improvement of the electrochemical performance. Owing to the alucone coating, the Si electrodes achieve highly reversible cycling performance with a specific capacity of 1490 mA h g-1 (0.90 mA h cm-2) as compared to 550 mA h g-1 (0.19 mA h cm-2) observed in the uncoated Si electrode. This research elucidates the important role of surface modification in stabilizing the cycling performance and enabling a high level of material utilization at high mass loading. It also provides insights for the future development of Si anodes.