Donald R. Sadoway

Identification of cathode materials for lithium batteries guided by first-principles calculations

Lithium batteries have the highest energy density of all rechargeable batteries and are favoured in applications where low weight or small volume are desired — for example, laptop computers, cellular telephones and electric vehicles. One of the limitations of present commercial lithium batteries is the high cost of the LiCoO2 cathode material. Searches for a replacement material that, like LiCoO2, intercalates lithium ions reversibly have covered most of the known lithium/transition-metal oxides, but the number of possible mixtures of these is almost limitless, making an empirical search labourious and expensive. Here we show that first-principles calculations can instead direct the search for possible cathode materials. Through such calculations we identify a large class of new candidate materials in which non-transition metals are substituted for transition metals. The replacement with non-transition metals is driven by the realization that oxygen, rather than transition-metal ions, function as the electron acceptor upon insertion of Li. For one such material, Li(Co,Al)O2, we predict and verify experimentally that aluminium substitution raises the cell voltage while decreasing both the density of the material and its cost.

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

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.

Rubbery Block Copolymer Electrolytes for Solid‐State Rechargeable Lithium Batteries

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

Melt-Formable Block Copolymer Electrolytes for Lithium Rechargeable Batteries

Microphase separated block copolymers consisting of an amorphous poly(ethylene oxide) (PEO)-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 he achieved without the incorporation of a solyent, which complicates processing, Herein, we report the design of new block copolymer electrolytes based on poly(methyl methacrylate), PMMA, and poly(oligo oxycthylene methacrylate), POEM, which are segmentally mixed at elevated temperatures appropriate for melt processing, while exhibiting a mierophase separated (ordered) morphology at ambient temperature. Although pure PMMA-b-POEM is segmentally mixed at all temperatures, it is shown that mierophase 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.

Magnesium−Antimony Liquid Metal Battery for Stationary Energy Storage

Batteries are an attractive option for grid-scale energy storage applications because of their small footprint and flexible siting. A high-temperature (700 °C) magnesium-antimony (Mg||Sb) liquid metal battery comprising a negative electrode of Mg, a molten salt electrolyte (MgCl(2)-KCl-NaCl), and a positive electrode of Sb is proposed and characterized. Because of the immiscibility of the contiguous salt and metal phases, they stratify by density into three distinct layers. Cells were cycled at rates ranging from 50 to 200 mA/cm(2) and demonstrated up to 69% DC-DC energy efficiency. The self-segregating nature of the battery components and the use of low-cost materials results in a promising technology for stationary energy storage applications.

Electrochemical Cycling‐Induced Spinel Formation in High‐Charge‐Capacity Orthorhombic LiMnO2

Li{sub x}Mn{sub 2}O{sub 4} spinel normally undergoes a transformation from its cubic to tetragonal phase when x exceeds 1 due to a collective Jahn-Teller distortion, resulting in poor cyclability when both the 4 and 3 V intercalation plateaus are utilized. In this study, the authors show that this transformation is suppressed in spinels of composition up to x {approx} 2 obtained through the electrochemical cycling of orthorhombic LiMnO{sub 2}. X-ray diffraction, transmission electron microscopy, and high-resolution electron microscopy studies together show the cycling produces a cubic spinel containing partial tetrahedral cation site occupancy and a nanodomain structure (20 to 50 nm size) within parent single-crystalline oxide particles. This structure is responsible for the cycling stability of electrochemically produced spinel. The reversible capacity (272 mAh/g) and energy density (853 Wh/kg) achieved at a low charge-discharge rate (3.33 mA/g) in the present samples are the highest among crystalline LiMnO{sub 2} materials reported to date.

Capture and electrochemical conversion of CO2 to value-added carbon and oxygen by molten salt electrolysis

A molten salt electrochemical system comprising a eutectic mixture of Li–Na–K carbonates, a Ni cathode, and a SnO2 inert anode is proposed for the capture and electrochemical conversion of CO2. It is demonstrated that CO2 can be effectively captured by molten carbonates, and subsequently electrochemically split into amorphous carbon on the cathode, and oxygen gas at the anode. The carbon materials generated at the cathode exhibit high BET surface areas of more than 400 m2 g−1 and as such, represent value-added products for a variety of applications such as energy storage and pollutant adsorption. In the carbonate eutectic (500 °C), the presence of Li2CO3 is shown to be required for the deposition of carbon from the melt, wherein O2− or Li2O serves as the intermediate for CO2 capture and electrochemical conversion. SnO2 proved to be an effective anode for the electrochemical evolution of oxygen. Electrochemical reactions were found to proceed at relatively high current efficiencies, even though the current densities exceed 50 mA cm−2. The intrinsic nature of alkaline oxides for CO2 capture, the conversion of CO2 to value-added products, and the ability to drive the process with renewable energy sources such as solar power, enables the technology to be engineered for high flux capture and utilization of CO2.

Effect of Counter Ion Placement on Conductivity in Single-Ion Conducting Block Copolymer Electrolytes

Single-ion conducting block copolymer electrolytes were prepared in which counter ions were tethered to the polymer backbone to achieve a lithium transference number of unity. Through tailored anionic synthesis, the influence of counter ion placement on conductivity was investigated. Incorporating the anions outside the ion-conducting @poly~ethylene oxide!-based# block, such as in poly~lauryl methacrylate!-block-poly~lithium methacrylate!-block-poly@(oxyethylene) 9 methacrylate#, known as PLMA-bPLiMA-b-POEM, and P~LMA-r-LiMA!-b-POEM, caused lithium ions to dissociate from the carboxylate counter ions upon microphase separation of the POEM and PLMA blocks, yielding conductivities of 10 25 S/cm at 70°C. In contrast, incorporating anions into the conducting block, as in PLMA-b-P~LiMA-r-OEM!, rendered the majority of lithium ions immobile, resulting in conductivities one to two orders of magnitude lower over the range of temperatures studied for equivalent stoichiometries. Converting the carboxylate anion to one that effectively delocalized charge through complexation with the Lewis acid BF3 raised the conductivity of the latter system to values comparable to those of the other electrolyte architectures. Ion dissociation could thus be equivalently achieved by using a low charge density counter ion (COOBF3 2 ) or by spatially isolating the counter ion from the ion-conducting domains by microphase separation.

High Capacity, Temperature‐Stable Lithium Aluminum Manganese Oxide Cathodes for Rechargeable Batteries

Manganese oxides are of great interest as low cost and environmentally sound intercalation cathodes for rechargeable lithium ba tteries, but have suffered from limited capacity and instability upon cycling at the moderately high temperatures (50-70°C) encountered in many applications. Here, we show that Li xAl0.05Mn0.95O2 of both the monoclinic and orthorhombic ordered rock salt structures exhibit stable cycling and high discharge capacities at elevated temperatures, after an initial transient associated with a spinel like phase t ransformation. In cells utilizing Li anodes tested at 55°C, rechargeable capacities of 150 mAh/g for the orthorhombic and 200 mAh/g for t he monoclinic phase and energy densities ~500 Wh/kg were achieved over more than 100 cycles (2.0-4.4 V). At low current densities, cha rge capacities approached the theoretical limit. The temperature stability and excellent electrochemical performance, combined with nontoxicity and low raw materials cost, make these compounds attractive cathodes for advanced lithium batteries.

Rubbery Graft Copolymer Electrolytes for Solid-State, Thin-Film Lithium Batteries

Graft copolymer electrolytes (GCEs) of poly[(oxyethylene)9 methacrylate]-g-poly(dimethyl siloxane) (POEM-g-PDMS) (70:30) have been synthesized by simple free radical polymerization using a macromonomer route. Differentialscanning calorimetry, transmission electron microscopy, and small angle neutron scattering confirmed the material to be microphase-separated with a domain periodicity of ∼25 nm. Over the temperature range 290 200 cycles) at a discharge rate of 2/3 C and could be cycled (charged and discharged) at subambient temperature (0°C).