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Home > Development and Characterization of Limn 2 O 4 Based Cathode Materials for Lithium-Ion Batteries

Development and Characterization of Limn 2 O 4 Based Cathode Materials for Lithium-Ion Batteries

Thesis Info

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Author

Iqbal, Azhar

Program

PhD

Institute

University of Peshawar

City

Peshawar

Province

KPK

Country

Pakistan

Thesis Completing Year

2013

Thesis Completion Status

Completed

Subject

Chemistry

Language

English

Link

http://prr.hec.gov.pk/jspui/bitstream/123456789/2625/1/2695S.pdf

Added

2021-02-17 19:49:13

Modified

2024-03-24 20:25:49

ARI ID

1676725854048

Similar


Spinel LiMn 2 O 4 is one of the most attractive positive electrode materials for Li-ion rechargeable batteries. In the present study, six series of low content bi-metal doped LiMn 2 O 4 with nominal compositions of LiNi x Cr y Mn 2-x-y O 4 , LiLa x Zn y Mn 2-x-y O 4 , LiCu x Cr y Mn 2-x-y O 4 , LiCu x Zn y Mn 2-x-y O 4 , LiNi x Cu y Mn 2-x-y O 4 and LiNi x Zn y Mn 2-x-y O 4 (where x = y = 0.01-0.05) were prepared by the sol-gel method. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) confirmed the formation of the pure as well as the doped spinel LiMn 2 O 4 between 285 o C and 350 o C. However, well crystallized spinel phase verified from the X-ray diffraction studies was obtained at 750 o C. XRD measurements further confirmed that all the synthesized compounds crystallized as single phase products in the cubic spinel Fd3m space group. The results showed that doping LiMn 2 O 4 with such small amount of metals has not affected the original spinel structure. Inductively coupled plasma optical emission spectrometry (ICP-OES) findings agreed the used nominal compositions. Energy dispersive X-ray analysis (EDX) also confirmed the purity of all the synthesized samples. SEM and TEM images showed that unlike the pure LiMn 2 O 4 , all the doped samples exhibited uniform size with smooth faceted polyhedral particles. The average particle size ranges from about 42 nm to 250 nm. High resolution TEM images also demonstrated the highly crystalline nature of all the six doped series. Cyclic voltammetric studies indicated that all the synthesized samples showed two pairs of well-defined anodic and cathodic peaks at around 4.0 V that corresponded to the redox couple of Mn 3+ / Mn 4+ . However, for the doped samples, the oxidation and reduction peaks were much closer to each other. The peak current was increased and the peak width was narrowed, indicating the reduced polarization of the bi-metal doped LiMn 2 O 4 , resulting from the faster iiinsertion/ extraction of Li + ions into the spinel matrix. Electrochemical impedance spectroscopy (EIS) was employed to have an insight about the synergetic effect of the bi-metal doping on the electrochemical performance of spinel LiMn 2 O 4 . The Nyquist plots showed that the charge transfer resistance (R ct ) decreases upon doping with Ni-Cr, La-Zn, Cu-Cr, Cu-Zn, Ni-Cu and Ni- Zn. The observed faster kinetics of Li + ions is attributed to the enhanced conductivities of the doped samples. Galvanostatic charge/ discharge measurements performed between 3.0 and 4.8 V for all the samples showed two plateaus around 4.0 V and 4.1 V vs. Li/ Li + that clearly demonstrated that insertion/ extraction of Li + ions takes place in two steps. The improved cycling performance of all the doped samples over the investigated 100 charge/ discharge cycles indicated that low content bi-metal doping has stabilized the spinel LiMn 2 O 4 structure by suppressing Jahn- Teller distortion. Rate capability of the pure and doped samples was also evaluated. The cells for each material were charged to 4.8 V at constant low current rate (0.1 C) and discharged to 3.0 V at 0.1 C, 0.3 C, 0.5 C, 1 C, 2 C, and 5 C, respectively. Compared to the pure LiMn 2 O 4 which retained only 41% of the initial discharge capacity when cycled at high current rate of 5 C, the capacity retention at 5 C for the Ni-Cr, La-Zn, Cu-Cr, Cu-Zn, Ni-Cu and Ni-Zn doped samples (x = y = 0.01) was 82%, 78%, 81%, 67%, 62%, and 58%, respectively. Among the various synthesized bi-metal doped series, samples with the lowest doping metal contents LiM 0.01 M'' 0.01 Mn 1.98 O 4 (where M and M'' are the various doping metal cations used in this study) appeared to be the best composition both in terms of the initial discharge capacity as well as the rate capability.
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تدوین متن کے مدارج

موضوع6:تدوین متن کے مدارج
فراہمی متن:
کسی کتاب کی تدوین کے لیے اس کے جملہ قلمی اور مطبوعہ نسخے فراہم کرنے چاہییں۔چونکہ عملا ایسا مشکل ہے اس لیے اہم نسخوں سے مدد لینا کافی ہے۔
ترتیب متن:
ماخذات کو زبانی،فکری اور موضوعاتی ترتیب دینا
تصحیح متن:
متن جب مصنف کی منشاء کے قریب نہ ہو تو محقق اسے منشائے مصنف تک پہنچانے کی کوشش کرتا ہے۔اس کوشش کو تصحیح متن کہا جاتا ہے۔متن کی تصحیح کا کام چونکہ بہت ذمہ داری کا ہوتا ہے اس لیے یہاں تساہل نہیں برتا جا سکتا۔
تحقیق متن:
تحقیق کے اصولوں کو عمل میں لائیں جو ماخذ ہم تک پہنچا ہے یہ کتنا مستند ہے۔مخطوطے کی پوری طرح چھان بین کریں۔اس کے عہد کے پیرامیٹر ز سے اس کی جانچ کریں۔اگر دو نسخوں میں ایک ہی مقام پر دو مختلف قراتیں ہوں تو کس کو ترجیح دی جائے ؟ متنی نقاد کو ہر قرات کے بارے میں مثبت یا منفی رائے دیتے ہوئے بہت سوجھ بوجھ سے کام لینا چاہیے۔ دونوں صورتوں میں اس پر بہت بڑی ذمہ داری عائد ہوتی ہے :
۱۔ اگر ایک نسخے میں قرآت میں ایسا لفظ استعمال ہوا ہے جو مصنف کے عہد میں رائج نہیں تھا یا کم رائج تھا یا اس کا تلفظ مختلف تھا اور دوسرے نسخے کی قرآت اس عہد سے زیادہ قریب ہے تو دوسری قرآت کو ترجیح دی جائے گی۔
۲۔ ایک بامعنی قرآت کو بے معنی قرآت پر ترجیح دی جائے گی۔
۳۔ اگر کسی قرآت میں ایک یا ایک سے زیادہ الفاظ زائد ہیں تودوسری قرآت قابل ترجیح ہوگی۔
۴۔ اگر کسی قرآت میں ایک یا ایک سے زیادہ الفاظ حذف ہیں تو دوسری قرآت کو ترجیح دی جائے گی۔
۵۔ اگر ایک قرآت بامعنی ہے لیکن سیاق وسباق کے مطابق نہیں ہے تو دوسری کو ترجیح...

Image of Islam Western Media: An Overview of Studies About Portrayal of Islam and Islamic World 1971-2001

ABSTRACT: This article presents an over view of studies conducted by the various scholars about portrayal of Islam and Islamic world during the time period (1971-2001) . It is claimed that mainstream media of west and US have been disseminating false information about Islamic world since the several decades. Due to the distorted images, developed and manipulated by the media, Islam is the name of negativity in the west. It is generally believed that western and United States mainstream media often misrepresents and inaccurately interprets/portrays Islam, Islamic world and its manifestation. After conducting in depth analysis of various studies regarding portrayal of Islamic world prior the incident of 9/11, it was found that elite media in the United States including the newspapers: Like New York Times and Washington post; the magazines: like Time and News Week, electronic media including: like ABC, CBS, NBS & CNN have been highlighting Islamic world in negative and unfavorable manner. It is said this anti Islamic campaign has reached to enormous proportion with the demise of communism. The that negative image of Islamic country is primarily a conspiracy of American foreign office to invent a new bogy and enemy to fill vacuum created by the collapse of soviet Union and world wide desperation of communism, particularly demise of communism in former USSR

Evaluation of Biological Potential, Elemental Profiling and Gcms Based Metabolomics of Some Selected Grasses of Bahawalpur, Punjab Province, Pakistan

Pakistan is enriched with natural flora comprising of unique wild and cultivated species utilized predominately by humans and animals. Bahawalpur region is in one of the nine divisions of the Punjab province in Pakistan established near the Sutlej River and comprises of many valuable species including grasses. Grasses possess remarkable economic and medicinal importance. All the cereal crops (maize, wheat, rice, barley) are also cultivated grasses. Many grasses are also used as a source of medicines as these are cheap, non-toxic and easily accessible. Hence, it is of keen interest to explore the native grasses of Bahawalpur region so that they can be used as a source of medicine and dietary fibre.In the present study, seventeen grasses were selected and their extracts were prepared in four solvents depending upon the polarity. Biological potential, elements and volatile compounds present in these extracts were evaluated. Initially, phytochemical tests were done to confirm the presence of different secondary metabolites. Total phenolic and flavonoid contents were determined spectrophotometrically which were detected in all extracts in varying concentrations. Highest phenolic contents were displayed in the methanol extracts of Ochthocloa compressa and Saccharum spontaneum (263.345 ± 16.35 mg GAE/g and 242.071 ± 20.63 mg GAE/g) while highest flavonoids contents were found in the ethanol extract of D. annulatum (47.023 mg QE/g) and the methanol extract of C. citratus (38.887 ± 2.19 mg QE/g). Antioxidant potential was determined via six different methods and the activity index was calculated. Results revealed that species which showed highest phenolic and flavonoid contents also exhibit highest antioxidant potential.Similarly, antimicrobial potential of all selected extracts was checked using disc diffusion assay which revealed somewhat weak to moderate antimicrobial potential against selected pathogens. So, cytotoxic potential was carried out to observe the toxicity potential of selected species. Among all species, O. compressa n-hexane extract showed highest cytotoxic potential with LC50 value of 2.80 µg/mL. All other species also displayed remarkable cytotoxic potential against brine shrimps. DNA damage protection assay was performed which revealed that ethanol and methanol extracts were more ix effective against DNA damage protection while acetone and n-hexane extracts did not show good activity. All inclusive, methanol extracts displayed significant biological potential as compared to the other extracts so they were further selected to examine antihemolytic potential of the plants. Methanol extracts of C. citratus (96.163 % inhibition), S. spontaneum (94.667 % inhibition), O. compressa (65.821 % inhibition) and D. annulatum (60.423 % inhibition) showed remarkable anti-hemolytic potential. Antihemolyticpotential of these species was found to be linked with the antioxidant potential and phenolic and flavonoid compounds. Strong anti-hemolytic and antioxidant activity of these plants suggests promising role in treating different diseases.Moreover, elemental profiling was done using ICP-MS and metabolomic studies were carried out using GC-MS. Results revealed the presence of seven essential and eighteen non-essential elements. Essential elements were found in decreasing order of potassium > magnesium > sodium > calcium > iron > manganese > zinc. Most of the non-essential elements were present within the permissible limit set by WHO which showed that the species are safe to use. GC-MS studies revealed the presence of more than 100 compounds in different concentrations. Decane (4.136 minutes) and m-cresol (5.46 minutes) were noted at minimum retention time in most of the species while Z-9hexadecenal (29.44 minutes) and 8, 11, 14-docosatrienoic acid, methyl ester (29.421 minutes) were identified at maximum retention time in most of the species. Total seventeen fatty acids and almost eighty-one different hydrocarbons were identified. Besides these, some monoterpenoids and diterpenoids were also detected in some species. Some of these compounds are known to possess cytotoxic potential while some of these compounds exhibit antimicrobial and antioxidant potential. Hence, these compounds are considerably involved in biological activities.In the end, individual organs of three species (S. halepense, D. annulatum and I. cylindrica) were investigated for further cell wall analysis. Acid-digestion of cell wall fractions revealed that xylose, arabinose, glucose and some traces of galactans are present more strongly in the aerial parts of selected species than the underground parts. Lichenase digestion confirmed that cellotrisoses exceeds cellotetroses and cellobioses in the cell wall of grasses. Dot-blot assay was done using eight commercial antibodies and comparison was made among dialysed and non-dialysed samples. Results revealed that x MLG, xylans, xyloglucans, arabinoxylan and glucoronoxylan were abundantly present in the sodium hydroxide extracts of non-dialysed samples while pachyman and mannan were not detected in significant concentrations. Some galactans were noted in the imidazole extracts of all fractions which showed the presence of pectins. Dialysed samples were not found effective to isolate hemi-celluloses from the fractions. Altogether, aerial parts possess more hemi-celluloses than the underground parts of plants.It is concluded that among all selected grass species, C. citratus, S. spontaneum, O. compressa and D. annulatum possess significant antioxidant, anti-hemolytic and cytotoxic potential. Overall, all species exhibited a variety of elements and compounds which are responsible for their biological activities. Moreover, these species can also be used as a biological marker. Cell wall analysis confirmed the presence of glycans in the aerial parts of plants which can be used as a dietary fibre and in different fibre industries. In future, in vivo studies should be carried out to confirm the medicinal value of these plants and compound isolation and microarray based profiling should be done to confirm the presence of non-volatile compounds and cell wall glycans.