Donald R. Vissers

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.

Reduction Mechanisms of Ethylene, Propylene, and Vinylethylene Carbonates A Quantum Chemical Study

Quantum chemical methods have been used to study reduction mechanisms of ethylene carbonate (EC), propylene carbonate (PC), and vinylethylene carbonate (VEC), in electrolyte solutions. The feasibility of direct two-electron reduction of these species was assessed, and no barrier to reaction was found for the formation of Li2CO3 and 1,4-butadiene from VEC. In contrast EC and PC have barriers to reaction on the order of 0.5 eV. The ready formation of Li{sub 2}CO{sub 3} when VEC is reduced may explain why it acts as a good passivating agent in lithium-ion cells.

Factors responsible for impedance rise in high power lithium ion batteries

Abstract High-power, 18,650 lithium-ion cells have been designed and fabricated in order to understand the factors limiting the calendar life of the lithium-ion system. Each cell consisted of a LiNi0.8Co0.2O2 positive electrode, a blend of MCMB-6 and SFG-6 carbon negative electrode, and a LiPF6 in EC:DEC (1:1) electrolyte. These cells, which initially meet the power requirement set by the partnership for a new generation of vehicles (PNGV), were subjected to accelerated calendar life and cycle life testing. After testing at elevated temperatures, the cells experienced a significant impedance rise and loss of power. The fade rate of power in these cells was dependent of the state of charge and the temperature of testing. Micro-reference electrode and ac-impedance studies on symmetrical cells have confirmed that the interfacial resistance at the positive electrode was the main reason behind the impedance rise in the high power cell.

Flame-retardant additives for lithium-ion batteries

Abstract To enhance the resistance of lithium-ion battery components to ignition and to reduce the flammability of the electrolyte with minimal effect on performance, we added flame-retardant additives to the electrolyte. The flame retardants were selected from a group of organic phosphate compounds, triphenylphosphate (TPP) and tributylphosphate (TBP), to provide superior thermal safety in lithium-ion cells at the fully charged state. The cycling characteristics of the lithium-ion cells containing flame-retardant additives were found to be similar or superior to the cells that contained no additives. Horizontal burning tests of electrolytes were carried out in a flame test chamber referenced by Underwriters Laboratories (UL) test standard 94 (UL 94) and ASTM D4986-98 to evaluate the electrolyes’ flammability characteristics. The thermal stability characteristics of the electrodes and electrolytes with and without flame-retardant additives were investigated by accelerating rate calorimetry (ARC). Negative electrode samples with electrolytes containing flame-retardant additives revealed less heat generation and higher-onset decomposition temperatures. The results disclose that the thermal safety of lithium-ion cells can be improved by incorporating small amounts of suitable additives such as triphenylphosphate and tributylphosphate to the electrolyte.

Structural and electrochemical studies of α-manganese dioxide (α-MnO2)

Abstract The structural and electrochemical properties of α -MnO 2 , prepared by acid digestion of Mn 2 O 3 , and its lithiated derivatives x Li 2 O · MnO 2 (0 ≤ x ≤ 0.25) have been investigated as insertion compounds in the search for new and viable cathode materials for rechargeable 3 V batteries. The α -MnO 2 product fabricated by this technique contains water within the large (2 × 2) channels of the structure; the water can be removed from the α -MnO 2 framework without degradation of the structure, and then at least partially replaced by Li 2 O (lithium oxide). The Li 2 O-doped α -MnO 2 electrodes, described generically as x Li 2 O · MnO 2 , stabilize the structure and provide higher capacities on cycling than the parent material. The structures of these α -MnO 2 -type electrode materials are described, and electrochemical data are presented for both liquid electrolyte and polymer electrolyte Li/ α -MnO 2 and Li/ x Li 2 O · MnO 2 cells.

The thermal stability of lithium-manganese-oxide spinel phases☆

The thermal stability of stoichiometric spinel phases in the system Li{sub 1+{delta}}Mn{sub 2{minus}{delta}}O{sub 4} (0 {le} {delta} {le} 0.33) has been investigated by high-temperature powder X-ray diffraction, differential thermal analysis, and thermogravimetric analysis. At elevated temperatures, the lithium-manganese-oxide spinels undergo phase changes by loss of oxygen and lithia (Li{sub 2}O). The data highlight the importance of temperature control when synthesizing lithium-manganese-oxide spinel compounds.

Performance Characteristics of Solid Lithium‐Aluminum Alloy Electrodes

Lithium--aluminum alloy electrodes have shown a great deal of promise for meeting the performance requirements of negative electrodes in batteries for off-peak energy storage in utility networks and for vehicle propulsion. To develop negative electrodes that meet the cell performance goals, the effects of a number of variables on the lithium--aluminum electrode performance were determined. Investigations were conducted to determine the effects of volume fraction electrolyte in the electrode, electrode thickness, fabrication technique, lithium concentration in the Li--Al alloy, and current collector in the electrode. Electrochemically formed Li--Al electrodes that are 0.32 cm thick, have an electrolyte volume fraction of 0.2 in the charged state, and contain about 2 percent stainless steel wire current collector demonstrated the performance goals for the negative electrodes in a Li--Al/FeS/sub 2/ electric automobile battery. For electrode thicknesses greater than or equal to 0.64 cm, vibratorily loaded pyrometallurgical Li--Al electrodes with porous metallic current collectors demonstrated the highest lithium utilization and capacity density over a wide range of discharge current densities and met the performance goals for negative electrodes in a Li--Al/FeS/sub 2/ off-peak energy storage battery. (8 figures, 3 tables)

Thermal Stability of the Li ( Ni0.8Co0.15Al0.05 ) O2 Cathode in the Presence of Cell Components

The Li(Ni 0.8 Co 0.15 Al 0.05 )O 2 cathode, a potential candidate for hybrid electric vehicle applications, has been electrochemically charged in powder form without a carbon additive and binder. The thermal stability of the resulting Lio.53(Ni 0.8 Co 0.15 Al 0.05 )O 2 powder was studied by thermal gravimetric analysis (TGA), gas chromatography/mass spectrometry, and X-ray diffraction techniques under different gas flows. The transformation of Li 0.53 (Ni 0.8 Co 0.15 Al 0.05 )O 2 -layered material to the NiO-type structure material and/or to nickel metal was correlated to the oxidizing/reducing properties of the TGA gas flow under which the thermal decomposition of the Li 0.53 (Ni 0.8 Co 0.15 Al 0.05 )O 2 occurred. Differential scanning calorimetry measurements were performed on Li 0.53 (Ni 0.8 Co 0.15 Al 0.05 )0 2 powder in the presence of solvent, salt, or binder independently. The reactivity at 170°C between Li 0,53 (Ni 0.8 Co 0.15 Al 0,05 )O 2 and ethylene carbonate (EC) solvent was found to be dependent on the Li 0.53 (Ni 0.8 Co 0.15 Al 0.05 )O 2 oxide/EC weight ratio. The exothermic reaction observed in the presence of other solvents was not greatly affected, as long as the oxide/solvent weight ratios were kept very close to one another. The LiPF 6 salt, when added to the charged oxide powder, was found to shift the exothermic reaction to 220°C when it was dissolved in the electrolyte and 270°C when it was added in the solid form. When polyvinylidene fluoride binder was added to Li 0.53 (Ni 0.8 Co 0.15 Al 0.05 )O 3 powder, the exothermic reaction occurred at high temperatures (340°C). The initiation of the exothermic reaction has been primarily attributed to the oxidation of the electrolyte by the oxygen gas released from Li 0.53 (Ni 0.8 Co 0.15 Al 0.05 )O 2 after the collapse of its layered structure.

High temperature lithium/sulfide batteries

Bipolar LiAl/FeS and LiAl/FeS2 batteries are being developed for electric vehicle (EV) applications by Argonne National Laboratory. Current technology employs a two-phase Li alloy negative electrode, low melting point LiCl—rich LiClLiBrKBr molten salt electrolyte, and either an FeS or an upper-plateau (UP) FeS2 positive electrode. These components are assembled in an “electrolyte-starved” bipolar cell configuration. Use of the two-phase Li alloy (α + β LiAl and Li5Al5Fe2) negative electrode provides in situ overcharge tolerance that renders the bipolar design viable. Employing LiCl rich LiClLiBrKBr electrolyte in “electrolyte-starved” cells achieves low-burdened cells that possess low area-specific impedance; comparable to that of flooded cells using LiClLiBrKBr eutectic electrolyte. The combination of dense U.P. FeS2 electrodes and low-melting electrolyte produces a stable and reversible couple, achieving over 1000 cycles in flooded cells, with high power capabilities. In addition, a family of stable chalcogenide ceramic/sealant materials was developed that produce high-strength bonds between a variety of metals and ceramics, which renders lithium/iron sulfide bipolar stacks practical. Bipolar LiAl/FeS and LiAl/FeS2 cells and four-cell stacks using these seals are being built and tested in the 13 cm diameter size for EV applications. To date, LiAl/FeS cells have achieved 240 W kg−1 power at 80% depth of discharge (DOD) and 130 Wh kg−1 energy at the 25 W kg−1 rate. LiAl/FeS2 cells have attained 400 W kg−1 power at 80% DOD and 180 Wh kg−1 energy at the 30 W kg−1 rate. When cell performance characteristics are used to model full-scale EV and hybrid vehicle (HV) batteries, they are projected to meet or exceed the performance requirements for a large variety of EV and HV applications.

In Situ Thermal Study of Li1 + x [ Ni1 ∕ 3Co1 ∕ 3Mn1 ∕ 3 ] 1 − x O2 Using Isothermal Micro-clorimetric Techniques

Li 1+x [Ni 1/3 Co 1/3 Mn 1/3 ] 1-x O 2 /Li half-cells were investigated using isothermal microcalorimetry (IMC), and the results were quantitatively analyzed. The entropy change (dEldT) calculated based on the IMC results during the charging process has the small range from -0.06 mV to -0.12 mV/K, which agrees with the experimental results. The small dE/dT values could explain why Li 1+x [N 1/3 Co 1/3 Mn 1/3 ] 1-x O 2 has better thermal stability than that of other nickel based layered oxide such as LiNiO 2, LiNi 1-x Co x O 2 , and LiNi 1-x Co y Al z O 2 . Furthermore, the heat flow rate during the discharge process was also calculated from the cells irreversible heat and the cell entropy change. The calculated values fit well the experimental data from the IMC results. This study also suggests the optimum voltage window of the operation of the cell based on Li 1+x [Ni 1/3 Co 1/3 Mn 1/3 ] 1-x O 2 cathode is between 4.1 and 3.5 V due to both, the self-discharge of the cell at higher voltages and the higher impedance of the cell in lower voltage regions.