Keith D. Kepler

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.

Li x Cu6Sn5 ( 0 < x < 13 ) : An Intermetallic Insertion Electrode for Rechargeable Lithium Batteries

It has been discovered that lithium can be inserted into the intermetallic compound Cu{sub 6}Sn{sub 5} in a two-phase reaction to yield the product Li{sub x}Cu{sub 6}Sn{sub 5} (x{approx}13). This finding has important implications for designing new intermetallic insertion electrodes (anodes) for rechargeable lithium batteries. The theoretical capacity of Li{sub x}Cu{sub 6}Sn{sub 5} derived from the eta-phase, {eta}-Cu{sub 6}Sn{sub 5}, with a NiAs-type structure is 358 mAh/g for x{sub max}=13, which corresponds to a fully lithiated composition Li{sub 2.17}CuSn{sub 0.83}; this capacity is close to the theoretical capacity of lithiated graphite LiC{sub 6} (372 mAh/g). The reaction occurs at approximately 0.4 V vs. lithium metal. The best cycling efficiency is obtained when the end voltage is restricted to 200 mV above the potential of lithium metal. A mechanism is proposed for the insertion of lithium into {eta}-Cu{sub 6}Sn{sub 5}.It has been discovered that lithium can be inserted into the intermetallic compound in a two‐phase reaction to yield the product . This finding has important implications for designing new intermetallic insertion electrodes (anodes) for rechargeable lithium batteries. The theoretical capacity of derived from the eta‐phase, , with a structure is for , which corresponds to a fully lithiated composition ; this capacity is close to the theoretical capacity of lithiated graphite . The reaction occurs at approximately vs. lithium metal. The best cycling efficiency is obtained when the end voltage is restricted to above the potential of lithium metal. A mechanism is proposed for the insertion of lithium into . ©1999 The Electrochemical Society

Li{sub x}Cu{sub 6}Sn{sub 5} (0

It has been discovered that lithium can be inserted into the intermetallic compound Cu{sub 6}Sn{sub 5} in a two-phase reaction to yield the product Li{sub x}Cu{sub 6}Sn{sub 5} (x{approx}13). This finding has important implications for designing new intermetallic insertion electrodes (anodes) for rechargeable lithium batteries. The theoretical capacity of Li{sub x}Cu{sub 6}Sn{sub 5} derived from the eta-phase, {eta}-Cu{sub 6}Sn{sub 5}, with a NiAs-type structure is 358 mAh/g for x{sub max}=13, which corresponds to a fully lithiated composition Li{sub 2.17}CuSn{sub 0.83}; this capacity is close to the theoretical capacity of lithiated graphite LiC{sub 6} (372 mAh/g). The reaction occurs at approximately 0.4 V vs. lithium metal. The best cycling efficiency is obtained when the end voltage is restricted to 200 mV above the potential of lithium metal. A mechanism is proposed for the insertion of lithium into {eta}-Cu{sub 6}Sn{sub 5}.It has been discovered that lithium can be inserted into the intermetallic compound in a two‐phase reaction to yield the product . This finding has important implications for designing new intermetallic insertion electrodes (anodes) for rechargeable lithium batteries. The theoretical capacity of derived from the eta‐phase, , with a structure is for , which corresponds to a fully lithiated composition ; this capacity is close to the theoretical capacity of lithiated graphite . The reaction occurs at approximately vs. lithium metal. The best cycling efficiency is obtained when the end voltage is restricted to above the potential of lithium metal. A mechanism is proposed for the insertion of lithium into . ©1999 The Electrochemical Society

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.

Copper–tin anodes for rechargeable lithium batteries: an example of the matrix effect in an intermetallic system

Lithium batteries are typically constructed from a lithium cobalt oxide cathode and a carbon anode. We have investigated intermetallic anode materials based on tin, which can provide a high capacity at a slightly higher voltage (400 mV) than metallic lithium and thus reduce the safety concerns associated with the carbon anode. In particular, we have investigated the copper-tin system at around the composition Cu{sub 6}Sn{sub 5} and have determined the effect on cycling and capacity of electrodes with various ratios of copper to tin. Anode compositions that are slightly copper rich (Cu{sub 6}Sn{sub 4}) were found to exhibit greater utilization of the tin than those with the stoichiometric bronze ratio (Cu{sub 6}Sn{sub 5}) or those having a slight excess of tin (Cu{sub 6}Sn{sub 6}). The differences in electrochemical behavior are explained in terms of an inert matrix 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.

NiAs- versus zinc-blende-type intermetallic insertion electrodes for lithium batteries: lithium extraction from Li2CuSn

Abstract The extraction of lithium from Li2CuSn with a lithiated zinc-blende-type structure has been investigated both chemically and electrochemically. The data show that the resulting LixCuSn (x≈0) product has a NiAs-related structure similar to that of Cu6Sn5 (CuSn0.83). The Li2CuSn structure is described in detail; this structure type has important implications for designing new intermetallic insertion electrodes with zinc-blende-type structures.