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Recent years have seen a rapid growth of interest by the scientific and engineering communities in the thermal properties of materials. Heat removal has become a crucial issue for continuing progress in the electronic industry, and thermal conduction in low-dimensional structures has revealed truly intriguing features. Carbon allotropes and their derivatives occupy a unique place in terms of their ability to conduct heat. The room-temperature thermal conductivity of carbon materials span an extraordinary large range--of over five orders of magnitude--from the lowest in amorphous carbons to the highest in graphene and carbon nanotubes. Here, I review the thermal properties of carbon materials focusing on recent results for graphene, carbon nanotubes and nanostructured carbon materials with different degrees of disorder. Special attention is given to the unusual size dependence of heat conduction in two-dimensional crystals and, specifically, in graphene. I also describe the prospects of applications of graphene and carbon materials for thermal management of electronics.

Thermal properties of graphene and nanostructured carbon materials

Li-ion battery materials: present and future

The lithium metal battery is strongly considered to be one of the most promising candidates for high-energy-density energy storage devices in our modern and technology-based society. However, uncontrollable lithium dendrite growth induces poor cycling efficiency and severe safety concerns, dragging lithium metal batteries out of practical applications. This review presents a comprehensive overview of the lithium metal anode and its dendritic lithium growth. First, the working principles and technical challenges of a lithium metal anode are underscored. Specific attention is paid to the mechanistic understandings and quantitative models for solid electrolyte interphase (SEI) formation, lithium dendrite nucleation, and growth. On the basis of previous theoretical understanding and analysis, recently proposed strategies to suppress dendrite growth of lithium metal anode and some other metal anodes are reviewed. A section dedicated to the potential of full-cell lithium metal batteries for practical applicatio...

Toward Safe Lithium Metal Anode in Rechargeable Batteries: A Review.

Recent years witnessed a rapid growth of interest of scientific and engineering communities to thermal properties of materials. Carbon allotropes and derivatives occupy a unique place in terms of their ability to conduct heat. The room-temperature thermal conductivity of carbon materials span an extraordinary large range – of over five orders of magnitude – from the lowest in amorphous carbons to the highest in graphene and carbon nanotubes. I review thermal and thermoelectric properties of carbon materials focusing on recent results for graphene, carbon nanotubes and nanostructured carbon materials with different degrees of disorder. A special attention is given to the unusual size dependence of heat conduction in two-dimensional crystals and, specifically, in graphene. I also describe prospects of applications of graphene and carbon materials for thermal management of electronics.

Thermal Properties of Graphene, Carbon Nanotubes and Nanostructured Carbon Materials

A composite of silicon and tin is prepared as a negative electrode composition with increased lithium insertion capacity and durability for use with a metal current collector in cells of a lithium-ion battery. This electrode material is formed such that the silicon is present as a distinct amorphous phase in a matrix phase of crystalline tin. While the tin phase provides electron conductivity, both phases accommodate the insertion and extraction of lithium in the operation of the cell and both phases interact in minimizing mechanical damage to the material as the cell experiences repeated charge and discharge cycles. In general, roughly equal atomic proportions of the tin and silicon are used in forming the phase separated composite electrode material.

Phase separated silicon-tin composite as negative electrode material for lithium-ion batteries

Surface coatings as artificial solid electrolyte interphases have been actively pursued as an effective way to improve the cycle efficiency of nanostructured Si electrodes for high energy density lithium ion batteries, where the mechanical stability of the surface coatings on Si is as critical as Si itself. However, the chemical composition and mechanical property change of coating materials during the lithiation and delithiation process imposed a grand challenge to design coating/Si nanostructure as an integrated electrode system. In our work, we first developed reactive force field (ReaxFF) parameters for Li–Si–Al–O materials to simulate the lithiation process of Si-core/Al2O3-shell and Si-core/SiO2-shell nanostructures. With reactive dynamics simulations, we were able to simultaneously track and correlate the lithiation rate, compositional change, mechanical property evolution, stress distributions, and fracture. A new mechanics model based on these varying properties was developed to determine how to stabilize the coating with a critical size ratio. Furthermore, we discovered that the self-accelerating Li diffusion in Al2O3 coating forms a well-defined Li concentration gradient, leading to an elastic modulus gradient, which effectively avoids local stress concentration and mitigates crack propagation. Based on these results, we propose a modulus gradient coating, softer outside, harder inside, as the most efficient coating to protect the Si electrode surface and improve its current efficiency.

Self-generated concentration and modulus gradient coating design to protect Si nano-wire electrodes during lithiation

An electrode material for use in an electrochemical cell, like a lithium-ion battery, is provided. The electrode material may be a negative electrode comprising graphite, silicon, silicon-alloys, or tin-alloys, for example. By avoiding deposition of transition metals, the battery substantially avoids charge capacity fade during operation. The surface coating is particularly useful with negative electrodes to minimize or prevent deposition of transition metals thereon in the electrochemical cell. The coating has a thickness of less than or equal to about 40 nm. Methods for making such materials and using such coatings to minimize transition metal deposition in electrochemical cells are likewise provided.

Ultrathin surface coating on negative electrodes to prevent transition metal deposition and methods for making and use thereof

An example of a flexible membrane includes a porous membrane and a solid electrolyte coating formed on at least a portion of a surface of the porous membrane, in pores of the porous membrane, or both on the surface and in the pores. The solid electrolyte coating includes i) a polymer chain or ii) an inorganic ionically conductive material. The polymer chain or the inorganic material includes a group to interact or react with a polysulfide through covalent bonding or supramolecular interaction.

Flexible membranes and coated electrodes for lithium based batteries

The gravimetric and volumetric efficiency of lithium ion batteries may be increased if high capacity materials like tin and silicon may be employed as the lithium-accepting host in the negative electrode of the battery. But both tin and silicon, when fully charged with lithium, undergo expansions of up to 300% and generate appreciable internal stresses which have potential to spall off material from the electrode on each discharge-charge cycle, resulting in a progressive reduction in battery capacity, also known as battery fade. A method of reinforcing such electrode materials by incorporating within them fiber reinforcements or shaped, elongated reinforcements fabricated of shape memory alloy is described. Electrode materials incorporating such reinforcements are less prone to damage under applied stress and so less prone to battery fade.

Xingcheng Xiao

Papers

Phase separated silicon-tin composite as negative electrode material for lithium-ion batteries

Self-generated concentration and modulus gradient coating design to protect Si nano-wire electrodes during lithiation

Ultrathin surface coating on negative electrodes to prevent transition metal deposition and methods for making and use thereof

Flexible membranes and coated electrodes for lithium based batteries

Reinforced battery electrodes