Arthur J. Kahaian

Structural fatigue in spinel electrodes in high voltage (4 V) Li/Li{sub x}Mn{sub 2}O{sub 4} cells.

Evidence of structural fatigue has been detected at the surface of discharged Li{sub x}[Mn{sub 2}]O{sub 4} spinel electrodes in (4 V) Li/Li{sub x}[Mn{sub 2}]O{sub 4} cells. Under nonequilibrium conditions, domains of tetragonal Li{sub 2}[Mn{sub 2}]O{sub 4} coexist with cubic Li[Mn{sub 2}]O{sub 4}, even at 500mV above the thermodynamic voltage expected for the onset of the tetragonal phase. The presence of Li{sub 2}[Mn{sub 2}]O{sub 4} on the particle surface may contribute to some of the capacity fade observed during cycling of Li/Li{sub x}[Mn{sub 2}]O{sub 4} cells.

Development of a high-power lithium-ion battery

Safety is a key concern for a high-power energy storage system such as will be required in a hybrid vehicle. Present lithium-ion technology, which uses a carbon/graphite negative electrode, lacks inherent safety for two main reasons: (1) carbon/graphite intercalates lithium at near lithium potential, and (2) there is no end-of-charge indicator in the voltage profile that can signal the onset of catastrophic oxygen evolution from the cathode (LiCoO{sub 2}). Our approach to solving these safety/life problems is to replace the graphite/carbon negative electrode with an electrode that exhibits stronger two-phase behavior further away from lithium potential, such as Li{sub 4}Ti{sub 5}O{sub 12}. Cycle-life and pulse-power capability data are presented in accordance with the Partnership for a New Generation of Vehicles (PNGV) test procedures, as well as a full-scale design based on a spreadsheet model.

Intermetallic insertion electrodes derived from NiAs-, Ni2In-, and Li2CuSn-type structures for lithium-ion batteries

The implications of designing intermetallic insertion electrodes for lithium-ion cells are discussed in terms of materials with the NiAs-, Ni2In-, and Li2CuSn-type structures. Specific reference is made to a recent announcement that lithium can be inserted topotactically into η-Cu6Sn5 at approximately 400 mV above the potential of metallic lithium. These materials hold promise for developing a new family of electrode structures to replace carbon as the negative electrode in state-of-the-art lithium-ion cells.

Structural fatigue in spinel electrodes in Li/Lix[Mn2]O4 cells

Evidence of structural fatigue has been detected at the surface of discharged Li{sub x}[Mn{sub 2}]O{sub 4} spinel electrodes in Li/Li{sub x}[Mn{sub 2}]O{sub 4} cells. Transmission electron microscopy has revealed a degradation of the structural integrity of Li[Mn{sub 2}]O{sub 4} crystals in electrodes that were cycled between 3.3 and 2.2 V, where the transformation from cubic Li[Mn{sub 2}]O{sub 4} to tetragonal Li{sub 2}[Mn{sub 2}]O{sub 4} is expected. It has also been observed in cells cycled at voltages above the 3 V plateau that domains of tetragonal Li{sub 2}[Mn{sub 2}]O{sub 4} coexist with cubic Li[Mn{sub 2}]O{sub 4}, even at 500 mV above the thermodynamic voltage expected for the onset of the tetragonal phase. It is proposed that the presence of Li{sub 2}[Mn{sub 2}]O{sub 4} on the particle surface may contribute to some of the capacity fade observed during cycling of Li/Li{sub x}[Mn{sub 2}]O{sub 4} cells.

Stabilization of insertion electrodes for lithium batteries

Abstract This paper discusses the techniques that are being employed to stabilize LiMn2O4 spinel and composite LixMnO2 positive electrodes. The critical role that spinel domains play in stabilizing these electrodes for operation at both 4 V and 3 V is highlighted. The concept of using an intermetallic electrode MM′ where M is an active alloying element and M′ is an inactive element (or elements) is proposed as an alternative negative electrode (to carbon) for lithium-ion cells. An analogy to metal oxide insertion electrodes, such as MnO2, in which Mn is the electrochemically active ion and O is the inactive ion, is made. Performance data are given for the copper–tin electrode system, which includes the intermetallic phases eta-Cu6Sn5 and Li2CuSn.

ELECTROCHEMICAL PERFORMANCE OF Ni/Cu-METALLIZED & CARBON-COATED GRAPHITES FOR LITHIUM BATTERIES

Synthetic and natural graphites were metallized with Cu or Ni using a fluidized bed coating and annealing process. With this method, crystalline nanometer-sized metal islands (~ 50 nm diameter) were deposited onto the surface of graphite. Post-metallization, the graphite materials were cycled in lithium coin cells to determine their electrochemical properties in a propylene carbonate (PC) solvent based electrolyte. Better cycling performance (316 mAh/g active graphite, 20 th cycle; 26% irreversible capacity) was obtained with the Cu-coated graphites versus Ni-coated or uncoated types (247 mAh/g, 20 th cycle; 62% irreversible capacity) in a 30% PC blend electrolyte at 50°C. The Cu nanosized deposits help to mediate charge transfer into the graphite particle via improved particle to particle contacts (electrical connectivity) and may contribute to improve kinetics of lithium ion insertion into the graphene layers by assisted Li-Cu interdiffusion. Further, Cu may act as a de-solvation catalyst to remove PCcoordinated molecules from Li cations allowing Li insertion into grapheme layers and overall improved electrochemical performance. Carbon-coated graphite electrodes prepared by a vapor deposition process, show superior performance versus the uncoated graphite in a PC electrolyte system. Coated graphites are under investigation as possible new anodes for high-power lithium-ion battery applications.