Large-Scale Production of V6O13 Cathode Materials Assisted by

Sep 23, 2016 - Large-Scale Production of V6O13 Cathode Materials Assisted by ... in the initial specific capacity in comparison with commercial V6O13...
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Large-Scale Production of V6O13 Cathode Materials Assisted by Thermal Gravimetric Analysis−Infrared Spectroscopy Technology Han-Pu Liang,*,† Jian Du,†,‡ Timothy G. J. Jones,§ Nathan S. Lawrence,§ and Andrew W. Meredith§ †

Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao 266101, China University of Chinese Academy of Sciences, Beijing 100049, China § Schlumberger Cambridge Research, High Cross, Madingley Road, Cambridge CB3 0EL, U.K. ‡

S Supporting Information *

ABSTRACT: The kilogram-scale fabrication of V6O13 cathode materials has been notably assisted by in situ thermal gravimetric analysis (TGA)−infrared spectroscopy (IR) technology. This technology successfully identified a residue of ammonium metavanadate in commercial V6O13, which is consistent with the X-ray photoelectron spectroscopy result. Samples of V6O13 materials have been fabricated and characterized by TGA−IR, scanning electron microscopy, and X-ray diffraction. The initial testing results at 125 °C have shown that test cells containing the sample prepared at 500 °C show up to a 10% increase in the initial specific capacity in comparison with commercial V6O13. KEYWORDS: lithium-metal polymer battery, V6O13, TGA−IR, large-scale production, cathode materials g−1.7−9 However, the capacity is still subject to the specific capacity of the cathode materials in the cell system.10 V6O13 has been one of the most attractive cathode materials because of its unique crystal structure, high electrochemical capacity, and electronic conductivity since the pioneering work of Murphy and Christian in 1979.11 Theoretically, the maximum lithium uptake is eight lithium ions per formula unit, which can create more Li+ participation during lithium insertion and extraction, leading to a high theoretical specific capacity of 417 mAh g−1.12 In addition, V6O13 could undertake high rate charge and discharge because of the metallic character at room temperature.13,14 It appears difficult to obtain pure V6O13 because of its mixedvalent nature and the presence of multiple vanadium oxidation states (V2+, V3+, V4+, and V5+)15−21 although progress has been made on the fabrication of V6O13.22−26 It is essential to develop a simple and large-scale method to fabricate V6O13. In this letter, we report the kilogram-scale fabrication of V6O13 through thermal decomposition of ammonium metavanadate. The process was assisted by an in situ thermal

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t is well-known that several types of downhole equipment in the oilfield service, such as logging with drilling tools, measurement with drilling tools, and wireline logging tools, require the use of high-temperature batteries.1 The current widely used downhole batteries are nonrechargeable lithium thionyl chloride batteries.2 However, the toxic and corrosive nature of thionyl chloride causes environment and health issues upon disposal of the depleted batteries.3,4 In addition, as the oil industry moves to deeper reserves and the drilling time is increased, it becomes increasing important to develop rechargeable batteries to extend the downhole lifetime of the batteries. The downhole temperatures routinely range from 20 to 100 °C but can get as high as 200 °C. The current commonly used lithium-ion batteries contain flammable organic liquid electrolytes and are not suitable for such downhole high-temperature circumstances. Lithium-metal polymer rechargeable batteries have attracted considerable attention because of the advantages of high energy density, flame resistance, and thermal stability.5 These batteries use lithium metal as the anode and a polymer electrolyte instead of a flammable organic electrolyte.6 The merit of these systems is the high energy density associated with the high electrochemical factor of the lithium-metal electrode, which could offer a specific capacity of 3860 mAh © 2016 American Chemical Society

Received: August 28, 2016 Accepted: September 23, 2016 Published: September 23, 2016 25674

DOI: 10.1021/acsami.6b10832 ACS Appl. Mater. Interfaces 2016, 8, 25674−25679

Letter

ACS Applied Materials & Interfaces

Figure 1. (a) TGA profile and (b) 3D image of the IR spectra of commercial V6O13 supplied by Alfa Aesar. The weight of the sample is 20 mg, and the ramp rate is 20 °C min−1.

Figure 2. (a) XPS survey and high-resolution (b) C 1s, (c) V 2p, (d) O 1s, and (e) N 1s spectra of commercial V6O13.

ammonia bands, respectively, according to the spectrum library supplied by Nicolet. This suggests that the main weight loss can be attributed to water vapor at the beginning of the process. With the process of heating up commercial V6O13, ammonia is found to be unexpectedly present in the exhausted gas. The presence of ammonia could be attributed to the presence of a residue of the ammonium metavanadate precursor in commercial V6O13. The low- and high-magnification SEM images, EDS spectrum, and element composition of commercial V6O13 are shown in Figure S1a−d, respectively. However, it should be noted that the nitrogen element is absent from the EDS spectrum and element composition in Figure S1. In order to further investigate the element composition of commercial V6O13, X-ray photoelectron spectroscopy (XPS)

gravimetric analysis (TGA)−infrared spectroscopy (IR) technology, which might be able to simultaneously analyze the exhausted gas during the decomposition process. The testing results at 125 °C show that V6O13 fabricated at 500 °C shows up to a 10% increase in the initial specific capacity compared to the commercial material. Figure 1a shows the TGA profile of commercial V6O13, from which about 3.42% weight loss was observed. The exhausted gas from this thermal decomposition process has been further investigated by this in situ IR technique. The obtained 3D image of the IR spectra is given in Figure 1b. As is evident from Figure 1b, the upward pointing peaks in the range of 1300− 2000 cm−1 and the bands in the range of 870−1160 cm−1, indicated by arrows, can be attributed to water vapor and 25675

DOI: 10.1021/acsami.6b10832 ACS Appl. Mater. Interfaces 2016, 8, 25674−25679

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ACS Applied Materials & Interfaces

Figure 3. (a) TGA profile, (b) 3D image of the IR spectra, and (c) DSC curve of ammonium metavanadate. The green line is the weight change, and the blue curve is the derivative with respect to temperature.

consistent with the TGA results. The differential scanning calorimetric (DSC) curve of ammonium metavanadate is shown in Figure 3c. The DSC measurement further indicates the presence of three decomposition processes, including two endothermic steps and one exothermic step. On the basis of the DSC and TGA−IR analysis of thermal decomposition of ammonium metavanadate, a target temperature of 400 °C was initially set up to fabricate V6O13 in the tube furnace, where argon gas was used to prevent the oxidation of V6O13. The X-ray diffraction (XRD) pattern of the corresponding V6O13 sample (red curve) is illustrated in Figure 4. It is evident from Figure 4 that the diffraction peaks in the spectrum can be well-indexed to the monoclinic crystal structure of V6O13 according to JCPDS 43-1050, which is shown in Figure 4. The XRD pattern of commercial V6O13 is shown as the green curve in Figure 4. It should be mentioned

was used to analyze the surface chemistry of several atomic layers of the commercial V6O13 sample. The XPS survey and high-resolution C 1s, V 2p, O 1s, and N 1s spectra of commercial V6O13 are shown in Figure 2. The XPS survey spectrum in Figure 2a suggests the presence of carbon, vanadium, oxygen, and nitrogen elements because most peaks can be assigned to electrons from different orbitals of these elements. This is further confirmed by the high-resolution C 1s, V 2p, O 1s, and N 1s spectra in parts b−e of Figure 2, respectively. The presence of the nitrogen element in the XPS spectra is consistent with the TGA−IR result, from which the presence of ammonia in commercial V6O13 was found. As indicated from the above TGA−IR and XPS analysis, a residue of the ammonium metavanadate precursor is present in commercial V6O13 supplied by Alfa Aesar. It would be beneficial if the V6O13 material could be fabricated and compared with the commercial samples in order to understand the material effect on the performance of the battery. The preparation process of V6O13 normally involves thermal decomposition of an ammonium metavanadate precursor in an inert gas. The in situ TGA−IR technique has been carried out in order to better understand this thermal decomposition process. Figure 3a shows the TGA profile of ammonium metavanadate, which suggests that the rate of mass loss decreases significantly above 400 °C. In addition, three major decomposition processes are found at temperatures of 225, 317, and 377 °C, which was in agreement with the previous report.25 The total mass loss during the decomposition process is observed to be about 24.15%. The 3D image of the IR spectra of ammonium metavanadate is shown in Figure 3b, in which the upward pointing peaks indicated by arrows can be attributed to ammonia and water according to the spectrum library. It is worth noting that three major decomposition processes are observed along the time axis, which was

Figure 4. XRD patterns of commercial and fabricated V6O13 at 400 and 500 °C. 25676

DOI: 10.1021/acsami.6b10832 ACS Appl. Mater. Interfaces 2016, 8, 25674−25679

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ACS Applied Materials & Interfaces

Figure 5. (a) TGA profile and (b) 3D image of the IR spectra of V6O13 fabricated at 500 °C.

Figure 6. SEM images of cathode composites containing (a) V6O13 fabricated at 500 °C and (b) commercial V6O13.

that the red curve of V6O13 prepared at 400 °C is very similar to the green curve of commercial V6O13, suggesting that commercial V6O13 might have been fabricated at around 400 °C because of the similar crystalline structure. V6O13 samples fabricated at a target temperature of 400 °C have been initially analyzed by the TGA−IR technique. The TGA profile and 3D spectral image are shown in Figure S2. It is evident from the TGA profile of the sample calcined at 400 °C, shown in Figure S2a, that the weight loss was only 1.5% in comparison with that of approximately 3.4% for commercial V6O13 in Figure 1a. However, the 3D image in Figure S2b still confirms the presence of a very small amount of ammonia, indicated by the red ellipse. Therefore, a higher target temperature of 500 °C and a holding time of 4 h were chosen. The TGA profile and 3D image are illustrated in Figure 5. The TGA profile in Figure 5a indicates a low amount of weight loss of 0.15%, and the 3D image in Figure 5b confirms the absence of ammonia bands, suggesting that pure V6O13 samples have been fabricated at higher calcination temperature. The XRD pattern of the V6O13 sample prepared at 500 °C is given as the blue curve in Figure 4. The diffraction peaks in the spectrum can be well-indexed to the monoclinic crystal structure of V6O13 according to JCPDS 43-1050. It has been difficult to obtain a pure phase of V6O13 because of the presence of multivalent vanadium oxide. Commercial V2O3, VO2, and V2O5 have been obtained from Aldrich, and the XRD patterns are detailed in Figure S3. These peaks in Figure S3 can be assigned to diffraction planes of vanadium oxides, and these samples can therefore be identified as V2O3, VO2, and V2O5 according to JCPDS 43-1051, 34-0187, and 41-1426, respectively. XRD has been demonstrated to be an effective

technique to identify the species of vanadium oxides through major diffraction peaks. The diffraction peaks at 25.14° and 26.58° can be assigned to the crystal planes of {110} and {003}, respectively. It is worth mentioning that the ratio of the diffraction peak intensity at 25.14−26.58° was about 4:3 in JCPDS 43-1050. In the case of the green curve of commercial V6O13 and the red curve of V6O13 fabricated at 400 °C, the ratio of these two peaks was far greater than 4:3. However, in the case of V6O13 fabricated at 500 °C, the ratio of the crystal planes of {110} and {003} was almost 4:3, which is very close to that of JCPDS 43-1050, indicating the successful preparation of V6O13. In order to further understand the effects of temperature on crystallinity, higher target temperatures, such as 600 and 700 °C, were chosen to fabricate V6O13. XRD patterns of V6O13 fabricated at 600 °C (red curve) and at 700 °C (green curve) are shown in Figure S4. It should be noted that the growth of the {003} crystal plane in comparison with the adjacent {110} crystal plane goes on as a function of the calcination temperature, and the peak intensity ratio was far below 4:3. The scanning electron microscopy (SEM) image of V6O13 fabricated at 700 °C in Figure S5 shows predominantly very large microsized platy particles. From the analyses of the XRD pattern and 3D image of the IR spectrum, it could be confirmed that V6O13 fabricated at 500 °C had no ammonium metavanadate residue and the crystal structure was nearly identical with that of JCPDS 43-1050. Therefore, V6O13 prepared at 500 °C has been studied as a cathode material and compared with commercial V6O13. The SEM images of cathode composites containing V6O13 fabricated at 500 °C and commercial V6O13 are shown in Figure 6a,b, respectively. It is evident from the SEM images that both 25677

DOI: 10.1021/acsami.6b10832 ACS Appl. Mater. Interfaces 2016, 8, 25674−25679

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Figure 7. Discharge curves (1st, 5th, and 10th) of pouch cells containing (a) V6O13 fabricated at 500 °C and (b) commercial V6O13.

plausible explanation for this capacity fading is under investigation. It should be mentioned that these batteries were tested at 125 °C, suggesting that these cells can be used as power sources for well logging, testing, and drilling tools under high-temperature downhole conditions. In summary, we have demonstrated the large-scale production of V6O13 with a batch size of around 1 kg assisted by an in situ TGA−IR technology. The presence of ammonia in the commercial samples of V6O13 has been found using TGA− IR and is a residue of ammonium metavanadate. Samples of V6O13 with varying residue concentrations of the ammonium metavanadate precursor and improved crystallinity have been fabricated and characterized. This methodology has the potential to scale up. V6O13 fabricated at 500 °C has been tested as a cathode material at 125 °C. The initial specific capacity was 351 mAh g−1 and showed up to a 10% increase compared to commercial V6O13. This could be attributed to the fact that the lithium storage capability of V6O13 has been improved because of the removal of the ammonium metavanadate residue. The specific capacity is much higher than the theoretical capacity of other cathode materials, such as LiCoO2, LiMnO2, and LiFePO4. The testing results at 125 °C suggest that this type of lithium-metal polymer battery could be deployed as a high-temperature power source for downhole tools in oilfield application.

V6O13 samples have platy morphology and a size of 400 nm. Such a structure of composites could effectively reduce the transport length for electrons and ions and result in a high electrochemistry performance.27−29 It is worth noting that carbon additives are present in both SEM images and are around 50 nm in diameter. The electrochemical performances of both fabricated and commercial V6O13 were evaluated as cathode materials in pouch cells. Figure 7 compares the 1st, 5th, and 10th discharge curves of both fabricated and commercial V6O13. As is evident from the first discharge curve of the V6O13 sample prepared at 500 °C in Figure 7a, the structure of the voltage plateau is more pronounced than that of the commercial one in Figure 7b. Furthermore, the extent of the lowest voltage plateau is greater than that observed with the commercial material. The initial specific capacities of the fabricated and commercial materials were 351 and 319 mAh g−1, respectively, showing up as a 10% increase in the specific capacity compared to the commercial material. The improved capacity can be attributed to the absence of an impurity and better crystallinity of V6O13 fabricated at 500 °C. Upon cycling, the definition of the voltage plateau is lost because the relative amount of the capacity is observed at the lowest voltage plateau. Figure 8 shows the cycling performance of V6O13 fabricated at 500 °C. The initial discharge capacity of the V6O13 cathode is 351 mAh g−1. Upon cycling, the discharge capacity undergoes a relatively fast drop in the first 15 cycles and maintains a steady state during 15−40 cycle times. After 40 cycles, the reversible capacity of 211 mAh g−1 could be reserved, about 60.1% capacity of its initial capacity. The

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.6b10832. Experimental section, SEM images and EDS spectra of commercial V6O13, TGA−IR of V6O13 fabricated at 400 °C, XRD patterns of V2O3, VO2, V2O5, and V6O13 fabricated at 600 and 700 °C, and SEM image of V6O13 fabricated at 700 °C (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Author Contributions

The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes

Figure 8. Cycling performance of V6O13 fabricated at 500 °C and tested at 125 °C.

The authors declare no competing financial interest. 25678

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ACKNOWLEDGMENTS H.-P. L. is thankful for support from the “Hundred Talent Program” of Chinese Academy of Sciences (RENZI[2015] 70HAO).

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DOI: 10.1021/acsami.6b10832 ACS Appl. Mater. Interfaces 2016, 8, 25674−25679