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Among lithium transition metal oxides used as intercalation electrodes for rechargeable lithium batteries, LiCoO 2 is considered to be the most stable in the ␣-NaFeO 2 structure type. It has previously been believed that cation ordering is unaffected by repeated electrochemical removal and insertion. We have conducted direct observations, at the particle scale, of damage and cation disorder induced in LiCoO 2 cathodes by electrochemical cycling. Using transmission electron microscopy imaging and electron diffraction, it was found that (i) individual LiCoO 2 particles in a cathode cycled from 2.5 to 4.35 V against a Li anode are subject to widely varying degrees of damage; (ii) cycling induces severe strain, high defect densities, and occasional fracture of particles; and (iii) 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 2-based rechargeable lithium batteries.

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LiAlyCO1−yO2 solid solutions of α‐NaFeO2 structure type have been synthesized from homogeneous hydroxide precursors. X‐ray powder diffraction and scanning transmission electron microscopy show that single‐phase solid solutions are formed up to y ≈ 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 [Ceder et al., Nature, 392, 694 (1998)], while capacity fade was significant during cycling at room temperature. However, both the absolute capacity and cycleability were improved at 55°C. © 1999 The Electrochemical Society. All rights reserved.

The ability to store energy on the electric grid would greatly improve its efficiency and reliability while enabling the integration of intermittent renewable energy technologies (such as wind and solar) into baseload supply. Batteries have long been considered strong candidate solutions owing to their small spatial footprint, mechanical simplicity and flexibility in siting. However, the barrier to widespread adoption of batteries is their high cost. Here we describe a lithium-antimony-lead liquid metal battery that potentially meets the performance specifications for stationary energy storage applications. This Li||Sb-Pb battery comprises a liquid lithium negative electrode, a molten salt electrolyte, and a liquid antimony-lead alloy positive electrode, which self-segregate by density into three distinct layers owing to the immiscibility of the contiguous salt and metal phases. The all-liquid construction confers the advantages of higher current density, longer cycle life and simpler manufacturing of large-scale storage systems (because no membranes or separators are involved) relative to those of conventional batteries. At charge-discharge current densities of 275 milliamperes per square centimetre, the cells cycled at 450 degrees Celsius with 98 per cent Coulombic efficiency and 73 per cent round-trip energy efficiency. To provide evidence of their high power capability, the cells were discharged and charged at current densities as high as 1,000 milliamperes per square centimetre. Measured capacity loss after operation for 1,800 hours (more than 450 charge-discharge cycles at 100 per cent depth of discharge) projects retention of over 85 per cent of initial capacity after ten years of daily cycling. Our results demonstrate that alloying a high-melting-point, high-voltage metal (antimony) with a low-melting-point, low-cost metal (lead) advantageously decreases the operating temperature while maintaining a high cell voltage. Apart from the fact that this finding puts us on a desirable cost trajectory, this approach may well be more broadly applicable to other battery chemistries.

Microphase separated block copolymers consisting of an amorphous poly͑ethylene oxide͒ ͑PEO͒-based polymer covalently bound to a second polymer offer a highly attractive avenue to achieving both dimensional stability and high ionic conductivity in polymer electrolytes for solid-state rechargeable lithium batteries. However, due to the strong thermodynamic incompatibility typically found for most polymer pairs, the disordered, liquid state of the copolymer can rarely be achieved without the incorporation of a solvent, which complicates processing. Herein, we report the design of new block copolymer electrolytes based on poly͑methyl methacrylate͒, PMMA, and poly͑oligo oxyethylene methacrylate͒, POEM, which are segmentally mixed at elevated temperatures appropriate for melt processing, while exhibiting a microphase separated ͑ordered͒ morphology at ambient temperature. Although pure PMMA-b-POEM is segmentally mixed at all temperatures, it is shown that microphase separation in these materials can be induced in a controlled manner by the incorporation of even limited amounts of lithium trifluoromethane sulfonate (LiCF 3 SO 3 ), a salt commonly employed to render PEO ionically conductive. Such ''salt-induced'' microphase separation suggests a simple method for designing new solid polymer electrolytes combining high ionic conductivities with excellent dimensional stability and improved processing flexibility.

For nearly 20 years, poly(ethylene oxide)-based materials have been researched for use as electrolytes in solid-state rechargeable 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 temperature) 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 55ЊC. A solid-state rechargeable lithium battery was constructed by laminating lithium metal, BCE, and a composite cathode composed of particles of LiAl 0.25 Mn 0.75 O 2 (monoclinic), carbon black, and graphite in a BCE binder. Cycle testing showed the Li/BCE/LiAl 0.25 Mn 0.75 O 2 battery to have a high reversible capacity and good capacity retention. Li/BCE/Al cells have been cycled at temperatures as low as Ϫ20ЊC.

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