Yoon Seok Jung

Ultrathin Direct Atomic Layer Deposition on Composite Electrodes for Highly Durable and Safe Li‐Ion Batteries

Abstract : In order to employ Li-ion batteries (LIBs) in next-generation hybrid electric and/or plug-in hybrid electric vehicles (HEVs and PHEVs), LIBs must satisfy many requirements: electrodes with long lifetimes (fabricated from inexpensive environmentally benign materials), stability over a wide temperature range, high energy density, and high rate capability. Establishing long-term durability while operating at realistic temperatures (5000 charge-depleting cycles, 15 year calendar life, and a range from -46 deg C to +66 deg C) for a battery that does not fail catastrophically remains a significant challenge. Recently, surface modifications of electrode materials have been explored as viable paths to improve the performance of LIBs for vehicular applications. Here we clearly demonstrate that conformal ultrathin protective coating by inactive metal oxide without disrupting inter-particle electronic pathway can be realized by atomic layer deposition (ALD) directly performed on a composite electrode, which leads to significant improvement of both long-term durability and safety of NG anode. Also ALD coatings are significantly more promising than efforts that have been previously reported.

Ultrathin coatings on nano-LiCoO2 for Li-ion vehicular applications.

To deploy Li-ion batteries in next-generation vehicles, it is essential to develop electrodes with durability, high energy density, and high power. Here we report a breakthrough in controlled full-electrode nanoscale coatings that enables nanosized materials to cycle with durable high energy and remarkable rate performance. The nanoparticle electrodes are coated with Al(2)O(3) using atomic layer deposition (ALD). The coated nano-LiCoO(2) electrodes with 2 ALD cycles deliver a discharge capacity of 133 mAh/g with currents of 1400 mA/g (7.8C), corresponding to a 250% improvement in reversible capacity compared to bare nanoparticles (br-nLCO), when cycled at this high rate. The simple ALD process is broadly applicable and provides new opportunities for the battery industry to design other novel nanostructured electrodes that are highly durable even while cycling at high rate.

Enhanced Stability of LiCoO2 Cathodes in Lithium-Ion Batteries Using Surface Modification by Atomic Layer Deposition

Ultrathin atomic layer deposition (ALD) coatings enhance the performance of lithium-ion batteries (LIBs). Previous studies have demonstrated that LiCoO 2 cathode powders coated with metal oxides with thicknesses of ∼100 to 1000 A grown using wet chemical techniques improved LIB performance. In this study, LiCoO 2 powders were coated with conformal Al 2 O 3 ALD films with thicknesses of only ∼ 3 to 4 A established using two ALD cycles. The coated LiCoO 2 powders exhibited a capacity retention of 89% after 120 charge-discharge cycles in the 3.3-4.5 V (vs Li/Li + ) range. In contrast, the bare LiCoO 2 powders displayed only a 45% capacity retention. Al 2 O 3 ALD films coated directly on the composite electrode also produced improved capacity retention. This dramatic improvement may result from the ultrathin Al 2 O 3 ALD film acting to minimize Co dissolution or reduce surface electrolyte reactions. Similar experiments with ultrathin ZnO ALD films did not display enhanced performance.

Tin Phosphide as a Promising Anode Material for Na‐Ion Batteries

Sn4 P3 is introduced for the first time as an anode material for Na-ion batteries. Sn4 P3 delivers a high reversible capacity of 718 mA h g(-1), and shows very stable cycle performance with negligible capa-city fading over 100 cycles, which is attributed to the confinement effect of Sn nanocrystallites in the amorphous phosphorus matrix during cycling.

Using Atomic Layer Deposition to Hinder Solvent Decomposition in Lithium Ion Batteries: First-Principles Modeling and Experimental Studies

Passivating lithium ion (Li) battery electrode surfaces to prevent electrolyte decomposition is critical for battery operations. Recent work on conformal atomic layer deposition (ALD) coating of anodes and cathodes has shown significant technological promise. ALD further provides well-characterized model platforms for understanding electrolyte decomposition initiated by electron tunneling through a passivating layer. First-principles calculations reveal two regimes of electron transfer to adsorbed ethylene carbonate molecules (EC, a main component of commercial electrolyte), depending on whether the electrode is alumina coated. On bare Li metal electrode surfaces, EC accepts electrons and decomposes within picoseconds. In contrast, constrained density functional theory calculations in an ultrahigh vacuum setting show that, with the oxide coating, e(-) tunneling to the adsorbed EC falls within the nonadiabatic regime. Here the molecular reorganization energy, computed in the harmonic approximation, plays a key role in slowing down electron transfer. Ab initio molecular dynamics simulations conducted at liquid EC electrode interfaces are consistent with the view that reactions and electron transfer occur right at the interface. Microgravimetric measurements demonstrate that the ALD coating decreases electrolyte decomposition and corroborates the theoretical predictions.

Sn-Carbon Core-Shell Powder for Anode in Lithium Secondary Batteries

bMaterials Laboratroy, Samsung Advanced Institute of Technology, Suwon, 440-600, Korea Spherical Sn-carbon core-shell powder was synthesized through a resorcinol-formaldehyde ~RF! microemulsion polymerization performed in the presence of hydrophobized Sn nanoparticles. The Sn-carbon core-shell structure was found to greatly enhance the cycle life compared to the mixture of Sn and spherical carbon when evaluated as the anode in lithium-ion batteries. A core-shell powder containing 20 wt % Sn showed 69% capacity retention at the 40th cycle when cycled between 0 and 2.0 V ~vs Li/Li + ! at a constant current of 40 mA g ˛1 . The mixture of 20 wt % Sn nanopowder and 80 wt % spherical carbon powder exhibited only 10% capacity retention in the same test condition. It is believed that the improved cyclability achieved with the core-shell powder is largely attributed to the inhibition of aggregation between Sn nanoparticles. The marginal polarization due to an intimate electrical contact made between Sn core and carbon shell is an additional advantageous feature achieved with this electrode.

Conformal Surface Coatings to Enable High Volume Expansion Li-Ion Anode Materials

An alumina surface coating is demonstrated to improve electrochemical performance of MoO(3) nanoparticles as high capacity/high-volume expansion anodes for Li-ion batteries. Thin, conformal surface coatings were grown using atomic layer deposition (ALD) that relies on self-limiting surface reactions. ALD coatings were tested on both individual nanoparticles and prefabricated electrodes containing conductive additive and binder. The coated and non-coated materials were characterized using transmission electron microscopy, energy-dispersive X-ray spectroscopy, electrochemical impedance spectroscopy, and galvanostatic charge/discharge cycling. Importantly, increased stability and capacity retention was only observed when the fully fabricated electrode was coated. The alumina layer both improves the adhesion of the entire electrode, during volume expansion/contraction and protects the nanoparticle surfaces. Coating the entire electrode also allows for an important carbothermal reduction process that occurs during electrode pre-heat treatment. ALD is thus demonstrated as a novel and necessary method that may be employed to coat the tortuous network of a battery electrode.

Solution-Processable Glass LiI-Li4SnS4 Superionic Conductors for All-Solid-State Li-Ion Batteries

A new, highly conductive (4.1 × 10(-4) S cm(-1) at 30 °C), highly deformable, and dry-air-stable glass 0.4LiI-0.6Li4 SnS4 is prepared using a homogeneous methanol solution. The solution process enables the wetting of any exposed surface of the active materials with highly conductive solidified electrolytes (0.4LiI-0.6Li4 SnS4), resulting in considerable improvements in the electrochemical performance of these electrodes over conventional mixture electrodes.

Bendable and Thin Sulfide Solid Electrolyte Film: A New Electrolyte Opportunity for Free-Standing and Stackable High-Energy All-Solid-State Lithium-Ion Batteries

Bulk-type all-solid-state lithium batteries (ASLBs) are considered a promising candidate to outperform the conventional lithium-ion batteries. Unfortunately, the current technology level of ASLBs is in a stage of infancy in terms of cell-based (not electrode-material-based) energy densities and scalable fabrication. Here, we report on the first ever bendable and thin sulfide solid electrolyte films reinforced with a mechanically compliant poly(paraphenylene terephthalamide) nonwoven (NW) scaffold, which enables the fabrication of free-standing and stackable ASLBs with high energy density and high rate capabilities. The ASLB, using a thin (∼70 μm) NW-reinforced SE film, exhibits a 3-fold increase of the cell-energy-density compared to that of a conventional cell without the NW scaffold.

Na3SbS4: A Solution Processable Sodium Superionic Conductor for All‐Solid‐State Sodium‐Ion Batteries

All-solid-state sodium-ion batteries that operate at room temperature are attractive candidates for use in large-scale energy storage systems. However, materials innovation in solid electrolytes is imperative to fulfill multiple requirements, including high conductivity, functional synthesis protocols for achieving intimate ionic contact with active materials, and air stability. A new, highly conductive (1.1 mS cm(-1) at 25 °C, Ea =0.20 eV) and dry air stable sodium superionic conductor, tetragonal Na3 SbS4 , is described. Importantly, Na3 SbS4 can be prepared by scalable solution processes using methanol or water, and it exhibits high conductivities of 0.1-0.3 mS cm(-1) . The solution-processed, highly conductive solidified Na3 SbS4 electrolyte coated on an active material (NaCrO2 ) demonstrates dramatically improved electrochemical performance in all-solid-state batteries.