Lynden A. Archer

Porous Hollow Carbon@Sulfur Composites for High‐Power Lithium–Sulfur Batteries

C @ S nanocomposites based on mesoporous hollow carbon capsules were prepared by a template approach. Their excellent properties as a cathode material in a lithium secondary battery of S-sequestration of elemental sulfur in the carbon capsules, a restricted polysulfide shuttling and an improved electron transport on sulfur are attributed.

Constructing Hierarchical Spheres from Large Ultrathin Anatase TiO2 Nanosheets with Nearly 100% Exposed (001) Facets for Fast Reversible Lithium Storage

Synthesis of nanocrystals with exposed high-energy facets is a well-known challenge in many fields of science and technology. The higher reactivity of these facets simultaneously makes them desirable catalysts for sluggish chemical reactions and leads to their small populations in an equilibrated crystal. Using anatase TiO(2) as an example, we demonstrate a facile approach for creating high-surface-area stable nanosheets comprising nearly 100% exposed (001) facets. Our approach relies on spontaneous assembly of the nanosheets into three-dimensional hierarchical spheres, which stabilizes them from collapse. We show that the high surface density of exposed TiO(2) (001) facets leads to fast lithium insertion/deinsertion processes in batteries that mimic features seen in high-power electrochemical capacitors.

Stable lithium electrodeposition in liquid and nanoporous solid electrolytes

Rechargeable lithium, sodium and aluminium metal-based batteries are among the most versatile platforms for high-energy, cost-effective electrochemical energy storage. Non-uniform metal deposition and dendrite formation on the negative electrode during repeated cycles of charge and discharge are major hurdles to commercialization of energy-storage devices based on each of these chemistries. A long-held view is that unstable electrodeposition is a consequence of inherent characteristics of these metals and their inability to form uniform electrodeposits on surfaces with inevitable defects. We report on electrodeposition of lithium in simple liquid electrolytes and in nanoporous solids infused with liquid electrolytes. We find that simple liquid electrolytes reinforced with halogenated salt blends exhibit stable long-term cycling at room temperature, often with no signs of deposition instabilities over hundreds of cycles of charge and discharge and thousands of operating hours. We rationalize these observations with the help of surface energy data for the electrolyte/lithium interface and impedance analysis of the interface during different stages of cell operation. Our findings provide support for an important recent theoretical prediction that the surface mobility of lithium is significantly enhanced in the presence of lithium halide salts. Our results also show that a high electrolyte modulus is unnecessary for stable electrodeposition of lithium.

Thermal formation of mesoporous single-crystal Co3O4 nano-needles and their lithium storage properties

In this work, we report the simple solid-state formation of mesoporous Co3O4 nano-needles with a 3D single-crystalline framework. The synthesis is based on controlled thermal oxidative decomposition and re-crystallization of precursor β-Co(OH)2 nano-needles. Importantly, after thermal treatment, the needle-like morphology can be completely preserved, despite the fact that there is a large volume contraction accompanying the process: β-Co(OH)2 → Co3O4. Because of the intrinsic crystal contraction, a highly mesoporous structure with high specific surface area has been simultaneously created. The textual properties can be easily tailored by varying the annealing temperature between 200–400 °C. Interestingly, thermal re-crystallization at higher temperatures leads to the formation of a perfect 3D single-crystalline framework. Thus derived mesoporous Co3O4 nano-needles serve as a good model system for the study of lithium storage properties. The optimized sample manifests very low initial irreversible loss (21%), ultrahigh capacity, and excellent cycling performance. For example, a reversible capacity of 1079 mA h g−1 can be maintained after 50 cycles. The superior electrochemical performance and ease of synthesis may suggest their practical use in lithium-ion batteries.

SnO2 hollow structures and TiO2 nanosheets for lithium-ion batteries

As an important energy storage platform for portable electronics, lithium-ion batteries (LIBs) have been challenged by steadily growing demands for better performance, improved safety, and enhanced reliability. A variety of nanomaterials has emerged with good electrochemical properties and can be regarded as promising electrode materials for LIBs. In this feature article, we will specifically discuss two nanomaterials systems with unique structures, which show particular promise as anode materials for LIBs: tin dioxide (SnO2) hollow spheres and anatase titanium dioxide (TiO2) nanosheets (NSs) with exposed (001) high-energy facets. For both systems, we survey approaches for synthesizing the unique nanostructured materials required for improved LIB performance and subsequently review their lithium storage properties. By focusing on SnO2 and TiO2, we seek to provide rational understanding of the relationship between proper nanostructuring and enhanced physicochemical properties of the active anode material in LIBs; hopefully uncovering new possibilities to generate advanced materials for next generation rechargeable batteries.

Lithium–Sulfur Battery Cathode Enabled by Lithium–Nitrile Interaction

Lithium sulfide is a promising cathode material for high-energy lithium ion batteries because, unlike elemental sulfur, it obviates the need for metallic lithium anodes. Like elemental sulfur, however, a successful lithium sulfide cathode requires an inherent mechanism for preventing lithium polysulfide dissolution and shuttling during electrochemical cycling. A new scheme is proposed to create composites based on lithium sulfide uniformly dispersed in a carbon host, which serve to sequester polysulfides. The synthesis methodology makes use of interactions between lithium ions in solution and nitrile groups uniformly distributed along the chain backbone of a polymer precursor (e.g., polyacrylonitrile), to control the distribution of lithium sulfide in the host material. The Li(2)S-carbon composites obtained by carbonizing the precursor are evaluated as cathode materials in a half-cell lithium battery, and are shown to yield high galvanic charge/discharge capacities and excellent Coulombic efficiency, demonstrating the effectiveness of the architecture in homogeneously distributing Li(2)S and in sequestering lithium polysulfides.

Ionic Liquid‐Nanoparticle Hybrid Electrolytes and their Application in Secondary Lithium‐Metal Batteries

Ionic liquid-tethered nanoparticle hybrid electrolytes comprised of silica nanoparticles densely grafted with imidazolium-based ionic liquid chains are shown to retard lithium dendrite growth in rechargeable batteries with metallic lithium anodes. The electrolytes are demonstrated in full cell studies using both high-energy Li/MoS(2) and high-power Li/TiO(2) secondary batteries.

Enhanced Li–S Batteries Using Amine-Functionalized Carbon Nanotubes in the Cathode

The rechargeable lithium-sulfur (Li-S) battery is an attractive platform for high-energy, low-cost electrochemical energy storage. Practical Li-S cells are limited by several fundamental issues, including the low conductivity of sulfur and its reduction compounds with Li and the dissolution of long-chain lithium polysulfides (LiPS) into the electrolyte. We report on an approach that allows high-performance sulfur-carbon cathodes to be designed based on tethering polyethylenimine (PEI) polymers bearing large numbers of amine groups in every molecular unit to hydroxyl- and carboxyl-functionalized multiwall carbon nanotubes. Significantly, for the first time we show by means of direct dissolution kinetics measurements that the incorporation of CNT-PEI hybrids in a sulfur cathode stabilizes the cathode by both kinetic and thermodynamic processes. Composite sulfur cathodes based the CNT-PEI hybrids display high capacity at both low and high current rates, with capacity retention rates exceeding 90%. The attractive electrochemical performance of the materials is shown by means of DFT calculations and physical analysis to originate from three principal sources: (i) specific and strong interaction between sulfur species and amine groups in PEI; (ii) an interconnected conductive CNT substrate; and (iii) the combination of physical and thermal sequestration of LiPS provided by the CNT=PEI composite.

Ionic‐Liquid–Nanoparticle Hybrid Electrolytes: Applications in Lithium Metal Batteries

Development of rechargeable lithium metal battery (LMB) remains a challenge because of uneven lithium deposition during repeated cycles of charge and discharge. Ionic liquids have received intensive scientific interest as electrolytes because of their exceptional thermal and electrochemical stabilities. Ionic liquid and ionic-liquid-nanoparticle hybrid electrolytes based on 1-methy-3-propylimidazolium (IM) and 1-methy-3-propylpiperidinium (PP) have been synthesized and their ionic conductivity, electrochemical stability, mechanical properties, and ability to promote stable Li electrodeposition investigated. PP-based electrolytes were found to be more conductive and substantially more efficient in suppressing dendrite formation on cycled lithium anodes; as little as 11 wt % PP-IL in a PC-LiTFSI host produces more than a ten-fold increase in cell lifetime. Both PP- and IM-based nanoparticle hybrid electrolytes provide up to 10 000-fold improvements in cell lifetime than anticipated based on their mechanical modulus alone. Galvanostatic cycling measurements in Li/Li4 Ti5 O12 half cells using IL-nanoparticle hybrid electrolytes reveal more than 500 cycles of trouble-free operation and enhanced rate capability.

25th Anniversary Article: Polymer–Particle Composites: Phase Stability and Applications in Electrochemical Energy Storage

Polymer-particle composites are used in virtually every field of technology. When the particles approach nanometer dimensions, large interfacial regions are created. In favorable situations, the spatial distribution of these interfaces can be controlled to create new hybrid materials with physical and transport properties inaccessible in their constituents or poorly prepared mixtures. This review surveys progress in the last decade in understanding phase behavior, structure, and properties of nanoparticle-polymer composites. The review takes a decidedly polymers perspective and explores how physical and chemical approaches may be employed to create hybrids with controlled distribution of particles. Applications are studied in two contexts of contemporary interest: battery electrolytes and electrodes. In the former, the role of dispersed and aggregated particles on ion-transport is considered. In the latter, the polymer is employed in such small quantities that it has been historically given titles such as binder and carbon precursor that underscore its perceived secondary role. Considering the myriad functions the binder plays in an electrode, it is surprising that highly filled composites have not received more attention. Opportunities in this and related areas are highlighted where recent advances in synthesis and polymer science are inspiring new approaches, and where newcomers to the field could make important contributions.