Transition Metal Fluoride Cathode Materials for Rechargeable Lithium Cells

Transcription

1 Transition Metal Fluoride Cathode Materials for Rechargeable Lithium Cells by Wishvender Behl and Jeffrey Read ARL-TR-5698 September 2011 Approved for public release; distribution unlimited.

2 NOTICES Disclaimers The findings in this report are not to be construed as an official Department of the Army position unless so designated by other authorized documents. Citation of manufacturer s or trade names does not constitute an official endorsement or approval of the use thereof. Destroy this report when it is no longer needed. Do not return it to the originator.

3 Army Research Laboratory Adelphi, MD ARL-TR-5698 September 2011 Transition Metal Fluoride Cathode Materials for Rechargeable Lithium Cells Wishvender Behl and Jeffrey Read Sensors and Electron Devices Directorate, ARL Approved for public release; distribution unlimited.

4 REPORT DOCUMENTATION PAGE Form Approved OMB No Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing the burden, to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports ( ), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. 1. REPORT DATE (DD-MM-YYYY) September REPORT TYPE Final 4. TITLE AND SUBTITLE Transition Metal Fluoride Cathode Materials for Rechargeable Lithium Cells 3. DATES COVERED (From - To) 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) Wishvender Behl and Jeffrey Read 5d. PROJECT NUMBER 5e. TASK NUMBER 5f. WORK UNIT NUMBER 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) U.S. Army Research Laboratory ATTN: RDRL-SED-C 2800 Powder Mill Road Adelphi MD PERFORMING ORGANIZATION REPORT NUMBER ARL-TR SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR S ACRONYM(S) 11. SPONSOR/MONITOR'S REPORT NUMBER(S) 12. DISTRIBUTION/AVAILABILITY STATEMENT Approved for public release; distribution unlimited. 13. SUPPLEMENTARY NOTES 14. ABSTRACT This report describes a study of the lithium (Li)/transition metal fluoride cells using nanocomposites of carbon with cobalt or manganese fluorides as cathode materials. The nanocomposite cathode materials were prepared by high energy milling of carbon and metal fluorides. It was, however, found that cobalt trifluoride reacted with carbon during the high energy milling process to form carbon fluoride. The Li/cobalt fluoride cells were, therefore, studied by using nanocomposite cathodes prepared by high energy milling of carbon, cobalt metal, and lithium fluoride or cathodes prepared by mixing carbon and cobalt trifluoride without subjecting the mixture to the high energy milling process. The charge-discharge characteristics of lithium/transition metal fluoride cells were studied at 22 and 50 C using a 1 molar solution of lithium hexafluorophosphate in sulfolane as the electrolyte. The cells were found to be electrochemically reversible but could not be completely charged due to simultaneous oxidation of the electrolyte at potentials above ~4.5 V. 15. SUBJECT TERMS Cobalt fluoride, manganese fluoride, lithium, lithium cells 16. SECURITY CLASSIFICATION OF: a. REPORT Unclassified b. ABSTRACT Unclassified c. THIS PAGE Unclassified 17. LIMITATION OF ABSTRACT UU ii 18. NUMBER OF PAGES 20 19a. NAME OF RESPONSIBLE PERSON Wishvender Behl 19b. TELEPHONE NUMBER (Include area code) (301) Standard Form 298 (Rev. 8/98) Prescribed by ANSI Std. Z39.18

5 Contents List of Figures List of Tables iv iv 1. Introduction 1 2. Experimental 1 3. Results and Discussion High Energy Milling Li/Cobalt Fluoride Cells Li/C-Manganese Trifluoride Cells Li/C-Manganese Difluoride Cells Conclusions References 12 Distribution List 13 iii

6 List of Figures Figure 1. Typical discharge curve of the Li/LiPF 6 -sulfolane electrolyte/cof 3 cell at a constant current of 0.5 ma at 22 C....3 Figure 2. Typical charge-discharge curves of Li cell using a nanomixture of carbon-cobalt metal-lithium fluoride as the cathode material at a constant current of 0.1 ma at 22 C....5 Figure 3. Typical voltage-time curve obtained on cycling of the Li/1M LiPF 6 -sulfolane/c- MnF 3 cell at 22 C at a constant current of 0.1 ma....6 Figure 4. Typical voltage-time curve obtained on cycling of the Li/1M LiPF 6 -sulfolane/ C- MnF 3 cell at 50 C at a constant current of 0.1 ma....6 Figure 5. Typical voltage-time curve obtained on cycling of the Li/LiPF 6 -sulfolane/c-mnf 3 cell at 22 C at a constant current of 0.05 ma....7 Figure 6. Cathode capacities for the Mn 3+ /Mn 2+ step in Li/C-MnF 3 cells on charge (Δ) and discharge (O) as a function of cycle number at 22 C....8 Figure 7. Typical voltage-time curve obtained on cycling of the Li/1M LiPF 6 -sulfolane/ C- MnF 2 cell at 22 C at a constant current of 0.09 ma....9 Figure 8. Typical voltage-time curve obtained on cycling of the Li/1M LiPF 6 -sulfolane/c- MnF 2 cell at 50 C at a constant current of 0.09 ma....9 Figure 9. Cathode capacities in Li/C-MnF 2 cells on charge (Δ) and discharge (O) as a function of cycle number at 22 C List of Tables Table 1. Theoretical energy densities of selected Li/metal fluoride cells....1 iv

7 1. Introduction Transition metal fluorides are highly energetic materials (1), but have not attracted much attention in the past as cathode materials for rechargeable lithium (Li) cells due to their insulating nature and poor reversible capacities (2). Recently, it has been found (3, 4) that the reversible capacity of iron trifluoride (FeF 3 ) can be significantly improved by using carbon-iron trifluoride (C-FeF 3 ) nanocomposites as cathodes in Li cells. The nanocomposites were prepared by high energy milling of C and FeF 3 mixtures. The C-FeF 3 nanocomposite cathodes yielded reversible capacities of ~600 mah/g in lithium cells at 70 C. Li cells with other transition metal trifluorides such as cobalt trifluoride (CoF 3 ) and manganese trifluoride (MnF 3 ) as positive electrodes can also provide high cell voltages and high energy densities (table 1) based on the thermodynamic data (5, 6). It was the purpose of this study to find if the use of carbon-cof 3 and carbon-mnf 3 nanocomposites as cathodes in Li cells can also provide high reversible capacities. The charge-discharge characteristics of Li/CoF 3, Li/C-Co-LiF,Li/C-MnF 3, and Li/C-MnF 2 cells were investigated and the results are summarized in this report. Table 1. Theoretical energy densities of selected Li/metal fluoride cells. Metal fluoride CoF 3 CoF 2 CoF 3 /CoF 2 FeF 3 FeF 2 FeF 3 /FeF 2 MnF 3 MnF 2 MnF 3 /MnF 2 Cell potential (V) Th. Energy Density (Wh/kg) Experimental CoF 3 (99%), CoF 2 (98%), cobalt nanopowder (98%), MnF 3 (98%) and MnF 2 (99%), LiF (99.98%) and graphite powder (99.9%) were obtained from Alfa Aesar. Super P carbon black (MMM Carbon Belgium), Kynar 2801 poly (vinylidene difluoride) polymer (Elf Atochem), dibutylphthalate (Aldrich 99%+), lithium foil (FMC Lithium), and a battery separator (Celgard 3401) were used as received. 1

8 A Spex CertiPrep 8000-D mixing mill was used for high-energy milling of transition metal fluorides and acetylene carbon black. Transition metal fluorides were thoroughly mixed in an argon-filled dry box with 15 wt.% acetylene carbon black (50% compressed), which was previously vacuum dried overnight at 100 C. The mixture was then transferred in a milling jar and placed on the mixing mill and milled for 3 h with 30-min cooling periods after each hour of milling. The C-MnF 3 nanocomposite cathodes were made by mixing a 1-g sample of the milled powder with 25 wt.% Teflon-acetylene carbon black (50:50) binder. About 0.04 g of this cathode mix was spread and pressed on a nickel grid and used as the cathode. The C-MnF 2 nanocomposite cathodes were made by mixing a 0.5-g sample of the milled powder with ~4-5 wt.% Super P carbon black, 12wt.% Kynar and ~1.4 g of methyl ethyl ketone (MEK) to form a slurry. The slurry was doctor-bladed onto an aluminum foil and dried at 70 C in a dry room. Then, ½-in discs were cut out of the dried sheet and used as cathode in coin cells. It was not possible to prepare C-CoF 3 nanocomposite cathodes by high energy milling of the constituents since CoF 3 was found to react with carbon during the milling process to form C x F (see section 3). Li/CoF 3 cells were, therefore, studied by using a mixture of cobalt fluoride and carbon as the cathode material without subjecting the mixture to high energy milling. To make these cathodes, CoF 3 was mixed with 25 wt.% acetylene carbon black (50% compressed) and 10 wt.% Teflon-acetylene carbon black (50:50) binder. About 0.1 g of this cathode mix was spread and pressed on a nickel grid and used as the cathode. Some Li/cobalt fluoride cells were fabricated in the discharged state by using a nano-mixture of cobalt metal, lithium fluoride, and carbon as the cathode material. To prepare these cathodes, lithium fluoride was mixed with 25 wt.% acetylene carbon black and subjected to high energy milling for 1 h and then thoroughly mixed using a rolling mill with 60 wt.% nanophase cobalt metal powder (Alfa Aesar). The cathodes were then made using Teflon binder as described above. The discharge/charge characteristics of Li/transition metal fluorides cells were studied at ambient temperatures and at 50 C in coin cells. The coin cells were fabricated using a Li metal anode covered with two layers of microporous polypropylene separators soaked in a 1 M solution of LiPF 6 in sulfolane. The cathode disc prepared as described above was then placed on top of the separator and the coin cell sealed using a Hohsen Corp. crimp sealer. The coin cells were cycled using a Maccor series 4000 battery cycler. 2

9 3. Results and Discussion 3.1 High Energy Milling The technique of high energy milling was employed to prepare carbon-transition metal fluoride nanocomposites. The high energy milling can result in the dehalogenation of the transition metal fluorides and a possible reaction with carbon to form carbon fluorides resulting in reduced cathode capacities. The x-ray analysis of the milled metal fluoride-carbon mixtures indicated that whereas no such reaction occurred between carbon and manganese fluorides, CoF 3 reacted with carbon to form carbon fluoride according to the reaction: x C + CoF 3 C x F + CoF 2 (1) This was, however, not unexpected since the free energy change for the above reaction for x=1 was calculated to be 55.6 KJ/mole of CoF 3 from the thermodynamic data (5, 7). In a separate experiment, 1 g of graphite or acetylene carbon black was mixed with 15 g of cobalt fluoride and milled for 3 h. The milled mixture was then treated with 1 M of warm sulfuric acid to remove cobalt difluoride and unreacted cobalt trifluoride and filtered. The residue was repeatedly washed with warm distilled water and vacuum dried at 110 C. The chemical analysis of the residue indicated it to be C 0.6 F. Thus, the high energy milling of carbon with CoF 3 provides a new method to synthesize carbon sub-fluorides at room temperature (8, 9). 3.2 Li/Cobalt Fluoride Cells A typical discharge curve for the Li/CoF 3 cell is shown in figure OCV 4.0 Voltage, V Time, Hours Figure 1. Typical discharge curve of the Li/LiPF 6 -sulfolane electrolyte/cof 3 cell at a constant current of 0.5 ma at 22 C. 3

10 The theoretical cell potentials for lithium/cobalt fluoride cells for stepwise reduction of CoF 3 to CoF 2 and cobalt metal according to reactions and CoF 3 + Li CoF 2 + LiF (2) CoF 2 + 2Li Co + 2 LiF (3) are calculated to be 5.14 and 2.85 V, respectively, from the thermodynamic data (5). Shah et al. (10) have described the use of CoF 3 as cathode material in primary Li cells and reported open circuit potentials of ~5 V. In the present studies, Li/CoF 3 cells exhibited an open circuit voltage (OCV) of ~4.5 V, which continued to drop with time. The lower open circuit potential and its decrease with time may be attributed to the presence of small amounts of moisture and/or a slow reaction of cobalt fluoride with the electrolyte. Upon discharge, the discharge curves exhibited a sloping plateau beginning at ~3 V followed by a flat plateau at ~2.2 V. These plateaus may be attributed to the reduction of CoF 3 to CoF 2 followed by the reduction of CoF 2 to cobalt metal according to the equations 2 and 3. Li/cobalt fluoride cells were also fabricated in the discharged state using a nanomixture of nanophase cobalt metal powder, acetylene carbon black, and lithium fluoride as the cathode material and a 1 M solution of lithium hexafluorophosphate in sulfolane as the electrolyte. The use of Co- LiF nanocomposite thin films as cathode materials has been earlier reported by Zhou et al. (11). The cathode and the coin cells were fabricated as described in the experimental section. The cells were cycled between 1.5 and 6.0 V. Since the theoretically calculated potential for Reaction II for the conversion of CoF 2 to CoF 3 (5.14 V) is close to the anodic oxidation limit of the electrolyte, it was feared that the solvent may be oxidized before the charging limit of 6 V is reached. To prevent substantial oxidation of solvent, a capacity cut-off limit corresponding to the cathode capacity was set for the charging cycle. A typical charge-discharge curve for the first cycle is shown in figure 2. It is seen that the cell potential quickly rises to a potential of ~4.3 V and shows a small plateau before slowly increasing to ~5.1 V. The potential did not increase further and the charging of the cell was stopped due to the cathode capacity limit. Thus, at potentials above 5 V, substantial oxidation of the electrolyte solvent occurs and interferes with the formation of CoF 3 from CoF 2. 4

11 6 OCV 5 Voltage, V OCV Time, Hours Figure 2. Typical charge-discharge curves of Li cell using a nanomixture of carbon-cobalt metal-lithium fluoride as the cathode material at a constant current of 0.1 ma at 22 C. Thus, on discontinuing the charge, the cell open circuit potential is ~4.5 V similar to the cell open circuit potential exhibited by Li/CoF 3 cells described above indicating that the formation of CoF 3 had occurred during the charging process. However, on starting the discharge cycle, the voltage-time curves showed a sloping region, as also observed in Li/CoF 3 cells described above, for the reduction of CoF 3 to CoF 2 followed by a flat voltage plateau at ~2.2 V for the reduction of CoF 2 to cobalt metal. It, therefore, seems that the solvent oxidation had essentially consumed the charge at potentials above ~5 V and only a fraction of the charge was consumed for the oxidation of CoF 2 to CoF 3 during the charging cycle according to conversion reaction II. 3.3 Li/C-Manganese Trifluoride Cells Typical voltage time curves for the Li/C-MnF 3 cells obtained at room temperature and at 50 C are presented in figures 3 and 4, respectively. The Li/C-MnF 3 cells exhibited open circuit potentials of ~4.3 V, which is slightly higher than V calculated from the thermodynamic data (5, 6) according to the cell reaction given by equation 4. 5

12 5 4 Cell Voltage, V Time, hrs. Figure 3. Typical voltage-time curve obtained on cycling of the Li/1M LiPF 6 -sulfolane/c-mnf 3 cell at 22 C at a constant current of 0.1 ma. 5 4 Cell Voltage, V Time, hrs. Figure 4. Typical voltage-time curve obtained on cycling of the Li/1M LiPF 6 -sulfolane/ C-MnF 3 cell at 50 C at a constant current of 0.1 ma. During the first discharge, the voltage-time curves exhibited two plateaus beginning at ~4 V and ~1.4 V, respectively. These voltage plateaus may be ascribed to the stepwise reduction of MnF 3 to MnF 2 and then to manganese metal, as represented by equations 4 and 5 and MnF 3 + Li MnF 2 + (4) 6

13 MnF 2 + 2Li Mn + 2 LiF (5) After the first discharge, the Li/C-MnF3 cell was charged to 4.4 V at a constant current of 0.1 ma followed by a constant voltage charge until the current decreased to 0.01 ma. The charge curve showed a distinct plateau beginning at ~2 V corresponding to the reformation of MnF 2 as represented by the reverse reaction of equation 5. The charging of the cell was continued up to a voltage of 4.4 V to regenerate MnF 3 as represented by the reverse reaction of equation 4. On subsequent discharge, the voltage-time curves exhibited only a sloping discharge for the Mn +3 Mn +2 reaction but a distinct lower voltage plateau for the Mn +2 Mn 0 reaction as was also observed in the initial discharge. The Li/C-MnF 3 cells delivered cathode capacities of ~300 mah/g at 22 C and 500 mah/g at 50 C in the initial discharge but continued to fade during the following cycles. In order to further study the reversibility of the Mn +3 Mn +2 reaction, the Li/C-MnF 3 coin cells were cycled in the upper voltage region between 4.4 V and 2.0 V. Typical voltage-time plots obtained for the first three cycles at room temperature at a discharge/charge current of 0.05 ma are shown in figure Cell Voltage, V Time, hrs. Figure 5. Typical voltage-time curve obtained on cycling of the Li/LiPF 6 -sulfolane/c-mnf 3 cell at 22 C at a constant current of 0.05 ma. It is seen that after the initial discharge, Li/C-MnF 3 cells can be recharged and MnF 2 converted back to MnF 3. The constant current charge was followed by constant voltage charge at 4.4 V till the charging current decreased by a factor of 10. Thus on the following discharge, voltage-time plots exhibit a high voltage plateau for the conversion reaction represented by equation 4. However, the discharge capacity was much less than the capacity obtained during the initial 7

14 discharge and continued to decrease in the subsequent cycles. The decrease in capacity on cycling may be partially due to the incomplete charging of MnF 2 to MnF 3 at 4.4 V. Thus, the plots of cathode capacities on charge and discharge presented in figure 6 show that the cathode capacity on discharge is significantly smaller than the cathode capacity on charge. It seems that during the charging cycle, oxidation of MnF 2 is simultaneously accompanied by the oxidation of the electrolyte solvent resulting in incomplete charging of MnF 2 to MnF Li/C-Manganese Difluoride Cells Typical voltage-time curves for Li/C-MnF 2 cells at ambient temperatures and 50 C at a C/100 rate are presented in figures 6 and 7, respectively. The thermodynamic potential of the cell according to the cell reaction represented by equation 5 is calculated (5, 6) to be V. Initially, the cells exhibited an open circuit potential of ~3.2 to 3.4 V. However, after partial discharge, the open circuit potential was found to be ~1.95 V. The Li/C-MnF 2 cells were cycled between 3.0 and 0.9 V. During the first discharge at ambient temperature, these cells exhibited a voltage plateau beginning at ~1.2 V corresponding to the reduction of MnF 2 to manganese metal as represented by the conversion reaction shown in equation 5. At the end of first discharge, the cell was charged to 3.0 V at a constant current 0f 0.09 ma and then the potential maintained at 3 V until the charging current decreased to 1/10 of its value. During the subsequent discharge, the cells again showed a discharge plateau corresponding to conversion reaction represented by equation 2. The discharge plateau voltage, however, was slightly higher during subsequent discharge cycles than during the first discharge. Cathode Capacity, mah/g of MnF Cycle Number Figure 6. Cathode capacities for the Mn 3+ /Mn 2+ step in Li/C-MnF 3 cells on charge (Δ) and discharge (O) as a function of cycle number at 22 C. 8

15 Cell Voltage, V Time, Hrs. Figure 7. Typical voltage-time curve obtained on cycling of the Li/1M LiPF 6 -sulfolane/ C-MnF 2 cell at 22 C at a constant current of 0.09 ma. The Li/C-MnF 2 cells exhibited similar discharge/charge behavior at 50 C (figure 8) as observed at room temperature. The discharge plateaus voltages were found to be slightly higher at 50 C than those observed at room temperature. The Li/C-MnF 2 cells delivered initial cathode capacities of ~250 and ~400 mah/g at 22 and 50 C, respectively, but continued to fade during the following cycles. The Li/C-MnF 2 cells were cycled between 3.0 and 0.9 V and the plots of cathode capacities on charge and discharge are presented in figure Cell Voltage, V Time, Hrs. Figure 8. Typical voltage-time curve obtained on cycling of the Li/1M LiPF 6 -sulfolane/c-mnf 2 cell at 50 C at a constant current of 0.09 ma. 9

16 Cathode Capacity, mah/g of MnF Cycle Number Figure 9. Cathode capacities in Li/C-MnF 2 cells on charge (Δ) and discharge (O) as a function of cycle number at 22 C. It is seen that the Li/C-MnF 2 cells exhibit capacity fade upon cycling, which may be partially attributed to a slight solubility of MnF 2 in the electrolyte. However, cathode capacities on discharge were found to be quite close to the cathode capacity on charge, indicating good coulombic efficiency and reversibility for the Mn +2 to Mn 0 reaction in Li/C-MnF 2 cells. 4. Conclusions The use of carbon-transition metal fluorides nanocomposites as cathode material in Li cells was investigated. The carbon metal fluoride nanocomposites were prepared by high energy milling of carbon and metal fluorides. It was found that it was not possible to make C-CoF 3 nanocomposites as CoF 3 reacted with carbon to form C x F and CoF 2 during the milling process. It was, however, possible to prepare carbon-cobalt metal-lithium fluoride nanocomposite and carbon-manganese fluoride nanocomposite cathodes by high energy milling of the components. Li cells using a nanocomposite of carbon-cobalt metal-lithium fluoride as the cathode were found to be rechargeable and exhibited a flat plateau on charge at ~4.3 V for the formation of CoF 2. However, the conversion of CoF 2 to CoF 3 was hindered due to the simultaneous solvent oxidation occurring at potentials above ~4.5 V. On subsequent discharge, the cells exhibited a sloping plateau for the reduction of CoF 3 to CoF 2 and a flat plateau for the reduction of CoF 2 to 10

17 cobalt metal. The discharge curves were similar to the discharge curves obtained with Li/CoF 3 cells where the CoF 3 cathodes were prepared without subjecting C-CoF 3 mixtures to the high energy milling process. Li/C-MnF 2 cells using nanocomposite C-MnF 2 as cathode material exhibited a discharge voltage plateau for the reduction of Mn +2 to Mn 0 and delivered cathode capacities in excess of 200 mah/g of MnF 2 at ambient temperatures. Li/C-MnF 3 cells using nanocomposite C-MnF 3 exhibited an additional discharge voltage plateau corresponding to the reduction of Mn +3 to Mn +2 followed by the voltage plateau for the reduction of Mn +2 to Mn 0. Both cells could be recharged at room temperature as well as at 50 C, but exhibited capacity fade upon cycling. 11

18 5. References 1. Hong, L.; Balaya, P.; Maier, J. J.Electrochem. Soc. 2003, 150, A Arai, H.; Okada, S.; Sakurai, Y.; Yamaki J. J. Power Sources 1997, 68, Badway, F.; Pereira, N.; Consandey, F.; Amatucci, G. G. J.Electrochem. Soc. 2003, 150, A Badway, F.; Consandey, F.; Pereira, N.; Amatucci. G. G. J. Electrochem. Soc. 2003, 150, A Journal of Physical and Chemical Reference Data, NIST-JANAF Tables, Monograpph 9, 4th Edition, Malcolm J. Chase, Jr., Editor., Bariu, I. Thermochemical Data of Pure Substances, VCH Publishers, New York (1995). 7. Valerga, A. J.; Badachhape, R. B.; Parks, G. D.; Kamarchik, P.; Wood, J. L.; Margrave, J. L. Research and Development Technical Report, AD , contract no.daab07-73-c- 0056, U.S. Army Electronics Command, Fort Monmouth, NJ, Read, J. A.; Behl, W. K. Electrochemical and Solid-State Letters 2998, 12, A16 9. Behl, W. K.; Read, J. A. Mechanochemical Synthesis Of Carbon Fluorides And And Electrochemical Cell Using the Synthesized Carbon Fluorides, U.S. Patent Application No. 12/877,153, Sept. 8, Shah, P. M.; Kroninberg, M. L.; Bis, R. F.; Warburton, D. L.; Bytella, J. J.; Meshri, D. T. Electrochemical Power Cells and Method of Improving Electrochemical Cell Performance, U.S. Patent No. 6,218,055 B1, April 17, Zhou, Y.; Liu, W., Xue, M.; Yu, L.; Wu, C.; Wu, X.; Fu, Z. Electrochem. and Solid State Letters 2006, 9, A

19 NO. OF COPIES ORGANIZATION 1 ADMNSTR DEFNS TECHL INFO CTR ATTN DTIC OCP 8725 JOHN J KINGMAN RD STE 0944 FT BELVOIR VA US ARMY RSRCH LAB ATTN IMNE ALC HRR MAIL & RECORDS MGMT ATTN RDRL CIO LL TECHL LIB ATTN RDRL CIO MT TECHL PUB ATTN RDRL SED E J SHAFFER ATTN RDRL SED C C LUNDGREN R JOW S GILMAN JEFFREY READ WISHVENDER BEHL (4 copies) ADELPHI MD CERDEC HDQ ATTN EDWARD PLICHTA 5100 MAGAZINE ROAD ABERDEEN PROVING GROUND MD TOTAL: 14 (1 PDF, 13 HCs) 13

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