New materials hold the key to fundamental advances in energy conversion and storage, both of which are vital in order to meet the challenge of global warming and the finite nature of fossil fuels. Nanomaterials in particular offer unique properties or combinations of properties as electrodes and electrolytes in a range of energy devices. This review describes some recent developments in the discovery of nanoelectrolytes and nanoelectrodes for lithium batteries, fuel cells and supercapacitors. The advantages and disadvantages of the nanoscale in materials design for such devices are highlighted.

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Nanostructured materials for advanced energy conversion and storage devices

Energy storage is more important today than at any time in human history. Future generations of rechargeable lithium batteries are required to power portable electronic devices (cellphones, laptop computers etc.), store electricity from renewable sources, and as a vital component in new hybrid electric vehicles. To achieve the increase in energy and power density essential to meet the future challenges of energy storage, new materials chemistry, and especially new nanomaterials chemistry, is essential. We must find ways of synthesizing new nanomaterials with new properties or combinations of properties, for use as electrodes and electrolytes in lithium batteries. Herein we review some of the recent scientific advances in nanomaterials, and especially in nanostructured materials, for rechargeable lithium-ion batteries.

Nanomaterials for rechargeable lithium batteries

Li-ion battery materials: present and future

Lithium (Li) metal is an ideal anode material for rechargeable batteries due to its extremely high theoretical specific capacity (3860 mA h g−1), low density (0.59 g cm−3) and the lowest negative electrochemical potential (−3.040 V vs. the standard hydrogen electrode). Unfortunately, uncontrollable dendritic Li growth and limited Coulombic efficiency during Li deposition/stripping inherent in these batteries have prevented their practical applications over the past 40 years. With the emergence of post-Li-ion batteries, safe and efficient operation of Li metal anodes has become an enabling technology which may determine the fate of several promising candidates for the next generation energy storage systems, including rechargeable Li–air batteries, Li–S batteries, and Li metal batteries which utilize intercalation compounds as cathodes. In this paper, various factors that affect the morphology and Coulombic efficiency of Li metal anodes have been analyzed. Technologies utilized to characterize the morphology of Li deposition and the results obtained by modelling of Li dendrite growth have also been reviewed. Finally, recent development and urgent need in this field are discussed.

Lithium metal anodes for rechargeable batteries

Nano- and bulk-silicon-based insertion anodes for lithium-ion secondary cells

Among lithium transition metal oxides used as intercalation electrodes for rechargeable lithium batteries, LiCoO{sub 2} is considered to be the most stable in the {alpha}-NaFeO{sub 2} structure type. It has previously been believed that cation ordering is unaffected by repeated electrochemical removal and insertion. The authors have conducted direct observations, at the particle scale, of damage and cation disorder induced in LiCoO{sub 2} cathodes by electrochemical cycling. Using transmission electron microscopy imaging and electron diffraction, it was found that (1) individual LiCoO{sub 2} particles in a cathode cycled from 1.5 to 4.35 V against a Li anode are subject to widely varying degrees of damage; (2) cycling induces severe strain, high defect densities, and occasional fracture of particles; and (3) severely strained particles exhibit two types of cation disorder, defects on octahedral site layers (including cation substitutions and vacancies) as well as a partial transformation to spinel tetrahedral site ordering. The damage and cation disorder are localized and have not been detected by conventional bulk characterization techniques such as X-ray or neutron diffraction. Cumulative damage of this nature may be responsible for property degradation during overcharging or in long-term cycling of LiCoO{sub 2}-based rechargeable lithium batteries.

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TEM Study of Electrochemical Cycling‐Induced Damage and Disorder in LiCoO2 Cathodes for Rechargeable Lithium Batteries

Electrochemically-driven solid-state amorphization in lithium-silicon alloys and implications for lithium storage

For nearly 20 years, poly(ethylene oxide)-based materials have been researched for use as electrolytes in solid-state rechargeab le lithium batteries. Technical obstacles to commercialization derive from the inability to satisfy simultaneously the electrical and mechanical performance requirements: high ionic conductivity along with resistance to flow. Herein, the synthesis and characterization of a series of poly(lauryl methacrylate)- b-poly[oligo(oxyethylene) methacrylate]-based block copolymer electrolytes (BCEs) are reported. With both blocks in the rubbery state (i.e., having glass transition temperatures well below room temperatu re) these materials exhibit improved conductivities over those of glassy-rubbery block copolymer systems. Dynamic rheological testing verifies that these materials are dimensionally stable, whereas cyclic voltammetry shows them to be electrochemically stable over a wide potential window, i.e., up to 5 V at 55 8C. A solid-state rechargeable lithium battery was constructed by laminating lithium metal, BCE, and a composite cathode composed of particles of LiAl0.25Mn0.75O2 (monoclinic), carbon black, and graphite in a BCE binder. Cycle testing showed the Li/BCE/LiAl0.25Mn0.75O2 battery to have a high reversible capacity and good capacity

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Rubbery Block Copolymer Electrolytes for Solid‐State Rechargeable Lithium Batteries

Electrochemically-driven solid-state amorphization in lithium–metal anodes

LiAl{sub y}Co{sub 1{minus}y}O{sub 2} solid solutions of {alpha}-NaFeO{sub 2} structure type have been synthesized from homogeneous hydroxide precursors. X-ray powder diffraction and scanning transmission electron microscopy show that a single-phase solid solutions are formed up to y {approx} 0.5 at 800 C in air. Electrochemical tests using nonaqueous liquid electrolyte cells shows that the open-circuit voltage and working voltage increase with Al content as predicted by ab initio calculations, while capacity fade was significant during cycling at room temperature. However, both the absolute capacity and cyclability were improved at 55 C.

Young-Il Jang

Papers

TEM Study of Electrochemical Cycling‐Induced Damage and Disorder in LiCoO2 Cathodes for Rechargeable Lithium Batteries

Electrochemically-driven solid-state amorphization in lithium-silicon alloys and implications for lithium storage

Rubbery Block Copolymer Electrolytes for Solid‐State Rechargeable Lithium Batteries

Electrochemically-driven solid-state amorphization in lithium–metal anodes

LiAl y Co1 − y O 2 ( R 3̄m ) Intercalation Cathode for Rechargeable Lithium Batteries