Rodrigo Villegas Salvatierra

Lithium Batteries with Nearly Maximum Metal Storage

The drive for significant advancement in battery capacity and energy density inspired a revisit to the use of Li metal anodes. We report the use of a seamless graphene-carbon nanotube (GCNT) electrode to reversibly store Li metal with complete dendrite formation suppression. The GCNT-Li capacity of 3351 mAh g-1GCNT-Li approaches that of bare Li metal (3861 mAh g-1Li), indicating the low contributing mass of GCNT, while yielding a practical areal capacity up to 4 mAh cm-2 and cycle stability. A full battery based on GCNT-Li/sulfurized carbon (SC) is demonstrated with high energy density (752 Wh kg-1 total electrodes, where total electrodes = GCNT-Li + SC + binder), high areal capacity (2 mAh cm-2), and cyclability (80% retention at >500 cycles) and is free of Li polysulfides and dendrites that would cause severe capacity fade.

Three-Dimensional Printed Graphene Foams

An automated metal powder three-dimensional (3D) printing method for in situ synthesis of free-standing 3D graphene foams (GFs) was successfully modeled by manually placing a mixture of Ni and sucrose onto a platform and then using a commercial CO2 laser to convert the Ni/sucrose mixture into 3D GFs. The sucrose acted as the solid carbon source for graphene, and the sintered Ni metal acted as the catalyst and template for graphene growth. This simple and efficient method combines powder metallurgy templating with 3D printing techniques and enables direct in situ 3D printing of GFs with no high-temperature furnace or lengthy growth process required. The 3D printed GFs show high-porosity (∼99.3%), low-density (∼0.015g cm-3), high-quality, and multilayered graphene features. The GFs have an electrical conductivity of ∼8.7 S cm-1, a remarkable storage modulus of ∼11 kPa, and a high damping capacity of ∼0.06. These excellent physical properties of 3D printed GFs indicate potential applications in fields requiring rapid design and manufacturing of 3D carbon materials, for example, energy storage devices, damping materials, and sound absorption.

Graphene Carbon Nanotube Carpets Grown Using Binary Catalysts for High-Performance Lithium-Ion Capacitors

Here we show that a versatile binary catalyst solution of Fe3O4/AlOx nanoparticles enables homogeneous growth of single to few-walled carbon nanotube (CNT) carpets from three-dimensional carbon-based substrates, moving past existing two-dimensional limited growth methods. The binary catalyst is composed of amorphous AlOx nanoclusters over Fe3O4 crystalline nanoparticles, facilitating the creation of seamless junctions between the CNTs and the underlying carbon platform. The resulting graphene-CNT (GCNT) structure is a high-density CNT carpet ohmically connected to the carbon substrate, an important feature for advanced carbon electronics. As a demonstration of the utility of this approach, we use GCNTs as anodes and cathodes in binder-free lithium-ion capacitors, producing stable devices with high-energy densities (∼120 Wh kg-1), high-power density capabilities (∼20,500 W kg-1 at 29 Wh kg-1), and a large operating voltage window (4.3 to 0.01 V).

Ultrafast Charging High Capacity Asphalt–Lithium Metal Batteries

Li metal has been considered an outstanding candidate for anode materials in Li-ion batteries (LIBs) due to its exceedingly high specific capacity and extremely low electrochemical potential, but addressing the problem of Li dendrite formation has remained a challenge for its practical rechargeable applications. In this work, we used a porous carbon material made from asphalt (Asp), specifically untreated gilsonite, as an inexpensive host material for Li plating. The ultrahigh surface area of >3000 m2/g (by BET, N2) of the porous carbon ensures that Li was deposited on the surface of the Asp particles, as determined by scanning electron microscopy, to form Asp-Li. Graphene nanoribbons (GNRs) were added to enhance the conductivity of the host material at high current densities, to produce Asp-GNR-Li. Asp-GNR-Li has demonstrated remarkable rate performance from 5 A/gLi (1.3C) to 40 A/gLi (10.4C) with Coulombic efficiencies >96%. Stable cycling was achieved for more than 500 cycles at 5 A/gLi, and the areal capacity reached up to 9.4 mAh/cm2 at a highest discharging/charging rate of 20 mA/cm2 that was 10× faster than that of typical LIBs, suggesting use in ultrafast charging systems. Full batteries were also built combining the Asp-GNR-Li anodes with a sulfurized carbon cathode that possessed both high power density (1322 W/kg) and high energy density (943 Wh/kg).

Three-Dimensional Rebar Graphene

Free-standing robust three-dimensional (3D) rebar graphene foams (GFs) were developed by a powder metallurgy template method with multiwalled carbon nanotubes (MWCNTs) as a reinforcing bar, sintered Ni skeletons as a template and catalyst, and sucrose as a solid carbon source. As a reinforcement and bridge between different graphene sheets and carbon shells, MWCNTs improved the thermostability, storage modulus (290.1 kPa) and conductivity (21.82 S cm-1) of 3D GF resulting in a high porosity and structurally stable 3D rebar GF. The 3D rebar GF can support >3150× the foams weight with no irreversible height change, and shows only a ∼25% irreversible height change after loading >8500× the foams weight. The 3D rebar GF also shows stable performance as a highly porous electrode in lithium ion capacitors (LICs) with an energy density of 32 Wh kg-1. After 500 cycles of testing at a high current density of 6.50 mA cm-2, the LIC shows 78% energy density retention. These properties indicate promising applications with 3D rebar GFs in devices requiring stable mechanical and electrochemical properties.

Hybrid MoS2/h-BN Nanofillers As Synergic Heat Dissipation and Reinforcement Additives in Epoxy Nanocomposites

Two-dimensional (2D) nanomaterials as molybdenum disulfide (MoS2), hexagonal boron nitride (h-BN), and their hybrid (MoS2/h-BN) were employed as fillers to improve the physical properties of epoxy composites. Nanocomposites were produced in different concentrations and studied in their microstructure, mechanical and thermal properties. The hybrid 2D mixture imparted efficient reinforcement to the epoxy leading to increases of up to 95% in tensile strength, 60% in ultimate strain, and 58% in Youngs modulus. Moreover, an enhancement of 203% in thermal conductivity was achieved for the hybrid composite as compared to the pure polymer. The incorporation of MoS2/h-BN mixture nanofillers in epoxy resulted in nanocomposites with multifunctional characteristics for applications that require high mechanical and thermal performance.

Lightweight Hexagonal Boron Nitride Foam for CO2 Absorption

Weak van der Waals forces between inert hexagonal boron nitride (h-BN) nanosheets make it easy for them to slide over each other, resulting in an unstable structure in macroscopic dimensions. Creating interconnections between these inert nanosheets can remarkably enhance their mechanical properties. However, controlled design of such interconnections remains a fundamental problem for many applications of h-BN foams. In this work, a scalable in situ freeze-drying synthesis of low-density, lightweight 3D macroscopic structures made of h-BN nanosheets chemically connected by poly(vinyl alcohol) (PVA) molecules via chemical cross-link is demonstrated. Unlike pristine h-BN foam which disintegrates upon handling after freeze-drying, h-BN/PVA foams exhibit stable mechanical integrity in addition to high porosity and large surface area. Fully atomistic simulations are used to understand the interactions between h-BN nanosheets and PVA molecules. In addition, the h-BN/PVA foam is investigated as a possible CO2 absorption and as laser irradiation protection material.

Mechanical Properties of Ultralow Density Graphene Oxide/Polydimethylsiloxane Foams

Low-density, highly porous graphene/graphene oxide (GO) based-foams have shown high performance in energy absorption applications, even under high compressive deformations. In general, foams are very effective as energy dissipative materials and have been widely used in many areas such as automotive, aerospace and biomedical industries. In the case of graphene-based foams, the good mechanical properties are mainly attributed to the intrinsic graphene and/or GO electronic and mechanical properties. Despite the attractive physical properties of graphene/GO based-foams, their structural and thermal stabilities are still a problem for some applications. For instance, they are easily degraded when placed in flowing solutions, either by the collapsing of their layers or just by structural disintegration into small pieces. Recently, a new and scalable synthetic approach to produce low-density 3D macroscopic GO structure interconnected with polydimethylsiloxane (PDMS) polymeric chains (pGO) was proposed. A controlled amount of PDMS is infused into the freeze-dried foam resulting into a very rigid structure with improved mechanical properties, such as tensile plasticity and toughness. The PDMS wets the graphene oxide sheets and acts like a glue bonding PDMS and GO sheets. In order to obtain further insights on mechanisms behind the enhanced mechanical pGO response we carried out fully atomistic molecular dynamics (MD) simulations. Based on MD results, we build up a structural model that can explain the experimentally observed mechanical behavior.

Suppressing Li Metal Dendrites Through a Solid Li‐Ion Backup Layer

The growing demand for sustainable and off-grid energy storage is reviving the attempts to use Li metal as the anode in the next generation of batteries. However, the use of Li anodes is hampered due to the growth of Li dendrites upon charging and discharging, which compromises the life and safety of the battery. Here, it is shown that lithiated multiwall carbon nanotubes (Li-MWCNTs) act as a controlled Li diffusion interface that suppresses the growth of Li dendrites by regulating the Li+ ion flux during charge/discharge cycling at current densities between 2 and 4 mA cm-2 . A full Li-S cell is fabricated to showcase the versatility of the protected Li anode with the Li-MWCNT interface, where the full cells could support pulse discharges at high currents and over 450 cycles at different rates with coulombic efficiencies close to 99.9%. This work indicates that carbon materials in lithiated forms can be an effective and simple approach to the stabilization of Li metal anodes.

Tip-Sonicated Red Phosphorus-Graphene Nanoribbon Composite for Full Lithium-Ion Batteries

Red phosphorus (RP) is considered a promising anode material for lithium-ion batteries (LIBs) due to its high energy density and low cost. Although RP is electrically insulating, researchers have reduced its particle size and added conductive fillers to improve the electrochemical activity of RP. Here, we report a method for making <1 μm sized RP under ambient conditions by using tip sonication. A specific surfactant solution was used to stabilize the dispersion of <1 μm sized RP. Graphene nanoribbons (GNRs) were added to improve the conductivity. The RP-GNR composite achieved nearly maximum capacity at 0.1C and showed a capacity retention of 96% after 216 cycles at 0.4 C in the half-cell. When combined with a LiCoO2 cathode, the full cell delivered a total capacity of 86 mAh/g after 200 cycles at 0.4C. This study has demonstrated the fabrication of high-performance LIBs using RP in a safe, convenient, and cost-effective manner, and the method might be extended for the preparation of other battery or catalyst materials that are difficult to acquire through bottom-up or top-down approaches.