T. D. Hatchard

Thermal Model of Cylindrical and Prismatic Lithium-Ion Cells

Oven exposure testing is a standard benchmark that Li-ion cells must pass in order to he approved for sale by regulating bodies. In order to test the safety of new cell designs or electrode materials, manufacturers must make small test hatches of cells. This can be both costly and time consuming. Using reaction kinetics that have been developed for electrode materials with electrolyte exposed to high temperature, and thermal properties of cells from the literature, a predictive model for oven exposure testing has been developed. The model predictions are compared to oven exposure test results for E-One/Moli Energy, Canada, 18650 LiCoO 2 /graphite cells and shown to be in good agreement. The model can predict the response of new cell sizes and electrode materials to oven exposure testing without actually producing any cells. This is illustrated with a number of examples: (i) increasing the specific surface area of the graphite electrode; (ii) using LiMn 2 O 4 or other cathode substitutes instead of LiCoO 2 ; (iii) varying the diameter of cylindrical cells; and (iv) varying the thickness of prismatic cells.

Design and Testing of a 64-Channel Combinatorial Electrochemical Cell

Design, testing, and performance of a 64-channel combinatorial electrochemical cell are described. This cell is used for high-throughput screening of materials for use as Li-ion rechargeable battery electrodes. Our sealedcell has 64 separate positive electrodes and Li foil for the reference and counter electrodes. This combinatorial electrochemical cell was designed to complement our existing combinatorial materials science infrastructure. Using the combinatorial electrochemical cell decreases the time and labor associated with test cell assembly, improves the repeatability of our assembly procedure, and increases the number of compositions we can test in a given amount of time. In this paper, we demonstrate that the results from the combinatorial electrochemical cell and from conventional 2325 coin-type test cells, containing electrodes of sputtered films prepared in the same sputtering run, are identical for electrodes of the same composition.

Electrochemical Performance of SiAlSn Films Prepared by Combinatorial Sputtering

Amorphous alloys of Si and Sn exhibit large specific and volumetric capacities when cycled electrochemically vs. lithium. To improve the electrochemical performance of these materials, we explore here the effect of A1 additions to the alloys. Combinatorial films of Si 1 - x - y Al x Sn y were prepared by magnetron sputtering and then analyzed for structure, composition, and electrochemical performance. If the film is amorphous, the voltage-capacity behavior of the Li/Si 1 - x - y Al x Sn y cell is smooth and the differential capacity vs. potential shows no sharp peaks, indicating homogeneous insertion of lithium. If the film contains crystalline material, the voltage-capacity relation shows plateaus and peaks are seen in the differential capacity, indicating inhomogeneous insertion of lithium. If the film is amorphous, capacity retention is generally good, while films containing crystalline material have poor capacity retention. A summary of specific capacity and reversible capacity as a function of composition is presented.

Study of the Electrochemical Performance of Sputtered Si1 − x Sn x Films

Amorphous alloys of Si and Sn exhibit large specific and volumetric capacities when cycled electrochemically vs. lithium. Combinatorial films of a-Si 1-x Sn x in the range 0 < x < 0.45 have been prepared by magnetron sputtering. These films have been analyzed for structure, composition, and electrochemical performance. The composition range was chosen to ensure that the films would be amorphous. No sharp peaks are seen in the cyclic voltammograms of these films, indicating homogeneous insertion of lithium. Reversible capacities as high as 3500 mAh/g have been attained and capacity retention is generally good. There appears to be no correlation between composition and capacity retention in the range 0 < x < 0.45 in a-Si 1-x Sn x .

Design and Testing of a Low-Cost Multichannel Pseudopotentiostat for Quantitative Combinatorial Electrochemical Measurements on Large Electrode Arrays

We describe a simple multichannel pseudopotentiostat based on appropriately chosen resistors, a programmable voltage source, and a scanning multimeter. Our first pseudopotentiostat can perform cyclic voltammetry on 64 channels of a combinatorial electrochemical cell that has 64 working electrodes and common counter and reference electrodes. The performance of the pseudopotentiostat and a 100 channel Scribner model 900B multichannel microelectrode analyzer (MMA) are compared on the same channels of the same cell. We find that for experiments on arrays of lithium-insertion electrodes, the pseudopotentiostat provides equivalent information to the MMA at about 20% the cost. The cost benefits are more significant as the number of channels increases so we believe this represents a good strategy for measurement systems to be used in quantitative combinatorial electrochemistry studies of large arrays.

A Comparison Between the High Temperature Electrode /Electrolyte Reactions of Li x CoO2 and Li x Mn2 O 4

Accelerating rate calorimetry (ARC) is used to compare the reactions between Li x CoO 2 (4.2 V) or Li x Mn 2 O 4 (4.2 V) and an equal mass of 1 M LiPF 6 (ethylene carbonate/diethyl carbonate) electrolyte. The ARC results show that under these conditions, the self-heating rates and hence thermal power are significantly larger for Li x Mn 2 O 4 than for Li x CoO 2 . This result is not consistent with the results of oven exposure tests on 18650 size cells using the same materials, where higher temperatures are needed to initiate thermal runaway for cells with Li x Mn 2 O 4 cathodes The amount of reaction heat generated by the reaction of Li x CoO 2 with 1 M electrolyte is independent of the electrode/electrolyte mass ratio (at least for the first reaction process), while that generated by the reaction of Li x Mn 2 O 4 with electrolyte increases with electrolyte amount. ARC experiments using an approximate 1:6 electrolyte to electrode mass ratio, which mirrors the conditions found in 18650 cells, demonstrate that Li x CoO 2 is much more reactive than Li x Mn 2 O 4 , as is observed in commercial cells The work presented here suggests that the safety of Li-ion cells using LiMn 2 O 4 cathodes can be improved by decreasing the positive electrode porosity.

A Comparison of the Reactions of the SiSn, SiAg, and SiZn Binary Systems with L3i

Alloys of Si with elements such as Sn, Ag, or Zn may exhibit large specific and volumetric capacities when cycled electrochemically vs lithium. Combinatorial films of Si 1 - x M x in the range 0 < x < ∼ 0.60 have been prepared by magnetron sputtering. where M is Sn, Ag, or Zn. These films have been analyzed for structure, composition, and electrochemical performance. The electrochemical performance of the film is found to be dependent on the element M as well as the amount, x, of the element in the film. The three Si-based binary systems are compared in terms of phases formed, amorphous vs crystalline structure, and capacity retention. It is found that electrodes which remain as a single amorphous phase during insertion and removal of Li exhibit superior capacity retention as compared to electrodes that form multiple or crystalline phases.

In Situ 119Sn Mössbauer Effect Study of the Reaction of Lithium with Si Using a Sn Probe

The reaction of lithium with amorphous Si was studied by 119 Sn Mossbauer effect spectroscopy using small amounts of Sn as probe atoms. Two powder samples, amolphous-Si 87 Sn 13 and amolphous-Si 93 Sn 7 , were prepared by magnetron sputtering and investigated using in situ and ex situ Mossbauer spectroscopy. There are two gently sloping plateaus in the voltage vs capacity of Li/Si cells whose origin has never been explained. There is a clear step between these plateaus at ∼2.3 Li atoms per Si atom, or Li 2.3 Si. The step between the plateaus is found to correlate with dramatic changes in the Mossbauer effect spectra with x in Li x Si at x ≈ 2.3, which suggest the step occurs at the point when each Si atom is surrounded only by Li atom first neighbors. The changes in the Mossbauer spectra during the delithiation of the Li/Si-Sn cells also give clues about electrode failure mechanisms.

Combinatorial investigations of advanced Li-ion rechargeable battery electrode materials

Future advances in Li-ion rechargeable battery performance are strongly linked to improved electrode materials. Candidate materials for the negative electrode of the future generally contain multiple elements and broad composition ranges. There are surprisingly few published accounts of combinatorial investigations of Li-ion rechargeable battery electrode materials. This paper describes the combinatorial infrastructure of the Dahn group at Dalhousie University as it relates to other published accounts in the search for advanced Li-ion rechargeable battery negative electrode materials. Sample data sets are provided for various material systems. Special attention is paid to start-up and operational costs to encourage other groups to adopt combinatorial methods in this and other fields.

Electrochemical Reaction of the SiAg Binary System with Li

Si and Si-based alloys are promising candidates for use as negative electrode materials in Li-ion batteries because of their large specific capacities of up to ten times that of graphite. The phases that form during the insertion of Li in the electrode material can have a significant impact on the capacity retention of the material. A series of studies have been performed on the reaction of Li with Si 1 - x M x films over wide composition ranges, where M is an element that itself alloys with Li. This is the first in a series of three papers that will present the results of these studies for a variety of elements, M. This paper presents the results obtained for the reaction of Li with Si 1 - x Ag x films along with a simple model of the structure changes in the films during the insertion and removal of Li.