1,721,052 research outputs found
Physical and electrochemical study of halide-modified activated carbons
No full textThe current thesis aims to improve the electrochemical capacity of activated carbon electrodes, which enjoy prominent position in commercial electrochemical capacitors. Our approach was to develop electrochemical capacity by developing faradaic pseudocapacitance in carbon through a novel mechanochemical modification using iodine and bromine.
Various commercial carbons were mechanochemically modified via solid-state iodation and vapour phase iodine-incorporation. The halidation-induced changes in the structure, composition, morphology, electrical and electrochemical properties of carbon materials were studied using different characterization techniques encompassing XRD, XRF, XPS, Raman spectroscopy, BET study, TEM, SAXS and electrochemical testing followed by an intensive battery of physical and electrochemical characterization. The introduction of iodine into carbon system led to the formation of polyiodide species that were preferentially reacted within the micropore voids within the carbon leading to the development of a faradaic reaction at 3.1V. In spite of the lower surface area of modified carbon, we observed manyfold increase in its electrochemical capacity. Parallel inception of non-faradaic development and faradaic pseudocapacitive reaction led to promising gravimetric, surface area normalized and volumetric capacity in iodated carbons. With promising electrochemical improvement post halidation process, the chemical halidation method was extended to different class of carbons and halides. Carbons ranging from amorphous (activated) carbons to crystalline carbons (graphites, fluorographites) were iodine-modified to gain further insight on the local graphite-iodine chemical interaction. In addition, the effect of pore size distribution on chemical iodation process was studied by using in-house fabricated microporous carbon. A comparative study of commercial mesoporous carbons and in-house fabricated microporous carbons showed higher iodine-uptake ability and larger volumetric capacity development in case of microporous carbons. For halides, bromine was also tested in activated carbons, which showed similar set of physical and electrochemical modification, but to a smaller degree.
Carbon-polyhalide nanocomposites form a very interesting system both for fundamental research and as new electrode systems for asymmetric hybrid capacitor and low-voltage high power battery type applications.Ph.D.Includes bibliographical references.by Prabeer Barpand
Alluaudite Class of High-Voltage Cathodes for Sodium-Ion Battery Applications: A Synthesis, Structure, Property Correlation Study
No full textThe work presented in this thesis demonstrates
alluaudites as a niche class of compounds forming the
rich treasure house of sodium insertion hosts. The
potential of this open frame-worked alluaudites is
immense and further research will open up newer
domains of applications. The current thesis work has also elucidated in-depth crystal/ magnetic structure analysis
and Rietveld refinement of these novel compounds by combining X-ray, neutron and
synchrotron diffraction techniques. It has also explored the synthesis of various metastable
phases and polymorphism at different synthetic conditions to gauge their structural and
electrochemical propertie
Electrochemical Behavior of Mn-based Oxide Cathode Materials for Alkali-ion Batteries: Study of Cationic and Anionic Redox Reactions
No full textBetter batteries are being developed in response to the growing demand for clean energy in
order to replace conventional fossil fuels with renewable energy for affordable and long-term
energy storage. Lithium-ion batteries have long dominated the markets for electronic goods
and electric vehicles. Alternative monovalent (Na+/K+) metal-ion batteries are being
investigated in light of the diminishing Li sources. The discovery of suitable cathode materials
with effective electrochemical performance is essential for the development of these post-Li-
ion batteries. A variety of oxide materials have been investigated in this effort because of their
high specific capacities, environmental friendliness, and simplicity of synthesis. Oxide
compounds can be found in a variety of structures, including layered structures, spinel
structures, and tunnels with one to three-dimensional diffusion pathways. My research focuses
on examining different insertion compounds for secondary batteries that are based on oxides.
Here, a thorough investigation of various oxide cathodes for metal-ion batteries will be
presented, demonstrating the connection between electrochemical performance and phase
transition. The work is presented in three chapters. Phase pure Na0.44MnO2 compound was
synthesized by using facile solution combustion method taking low-cost nitrates and urea as
precursors. This compound has a 3D tunnel structure and was studied as a host for Li-, Na-,
and K-ion batteries. Following that, phase pure Li0.44MnO2 was synthesized using molten salt
and underlying redox mechanism were explained. The electrochemical activity of layered P2-
oxides
type
[Na0.7Mn0.6Ni0.3Co0.1O2,
Na0.7(Li1/18Mn11/18Ni3/18Fe2/181/18)O2-xNa2MoO4] will be reported. High reversible capacity
over 140 mAh/g, involving both cationic and anionic redox activity, will be demonstrated along
with the effect of cation doping in improving overall performance. Many oxides exhibit
polymorphic phase transition. Li0.44MnO2 was found to undergo tunnel to spinel phase
transition upon annealing with onset point of 463 °C. This phase transition will be depicted
combining in-situ X-ray diffraction, in-situ Raman spectroscopy and in-situ transmission
electron microscopy.MHR
Exploration of Ti-based Anodes for Rechargeable Alkali-ion Batteries And Hybrid-ion Capacitors
No full textFrom 600 B.C. till 1700 A.D., electricity remained the least understood form of energy and was considered "Magical." In the 18th century A.D., the electricity that mysteriously struck
Franklin as he arduously flew a kite directly into a thunderstorm was also thought to be "indwelling" inside all living beings by Galvani when he saw a dead frog's leg jolt upon scalpel
touch. In this period, for the first time, electricity was bottled in its transient static (electronic) form inside a Leyden jar and in permanent (ionic) form between a "pile" of a brine-soaked
copper-zinc discs, designed by a pragmatic Volta. Improved "pile"s enabled major fundamental findings ranging from water splitting to numerous element discoveries in the 20th century
before Plante introduced the lead-acid rechargeable batteries in 1859. Surprisingly, these rechargeable batteries were used in clean, silent, and swift starting electric cars as early as 1900
by Edison, the inventor of the electric bulb. Gasoline took over as the energy source with the advent of post-world war V8 internal combustion engines by Rolls Royce and the electric
starters by Kettering. Recently, electric cars have returned to limelight highlighting the need for economic and high-performance batteries to topple the incessant usage of gasoline-powered
automobiles. Weber and Kummer's sodium-sulfur battery (1967) followed by Arab's oil embargo (1973) slingshot original research activity on rechargeable non-aqueous batteries by
Huggins, Schollhörn, Murphy, Hagenmuller, and other pioneers. The key idea was to dump fossils and sustainably collect and (electrochemically) store energy in fuel cells, batteries, or
capacitors from renewable sources like solar, wind, ocean, and others that are scattered in space and unpredictable/intermittent in time. This sense of urgency bore pivotal output by
Whittingham and Armand on intercalation, Goodenough on LiCoO2 cathode, Yazami and Yoshino on carbon anodes. These enabled SONY's first commercial Lithium-Ion Battery (LIB)
in 1991, which powered the portable industry's take-off. LIBs, even to date, remain the undisputed power source for high energy portable electronics, safe automotive, and cheap gridlevel applications that have penetrated our lives. SONY's LIB gift kickstarted arduous research and industry activity in energy storage. While the cathode and the electrolyte that underlie the
maximum cost in a battery are feverishly researched, it was the anode that blocked the gateway to the first commercial LIB. Carbon as amorphous coal may be a polluting energy source, but as layered graphite is the cheapest and most widely used anode material in the LIBs. The energy of lithium does not significantly drop (unstable) inside the layered graphite anode compared to
a vast energy drop (stable) in the cathode. Although this energy difference of lithium results in the highest energy density batteries when graphite is used, it is far from being the holy grail of
anode materials. For example, while graphite is the preferred anode in Li- and K-ion batteries, it is inactive in sodium-ion batteries. Further, its low voltage operation risks fire hazards during
accidental overcharge or high current conditions. It is a severe setback in the present scenario where a global uprising towards using earth-abundant materials has catapult research and
industry activity in the Sodium-Ion Battery (NIB) space. Following this, spearheaded by the 1.55 V spinel Li4Ti5O12 (LTO), Ti-based anodes are safe and can be used in fast-charge
applications. Along with the LiFePO4 (LFP) safe cathode, the LTO anode results in a 2 V battery that lasted for 30000 cycles at 15C fast charging conditions while retaining over 90%
capacity. Building on the titanium chemistry, three stories of Ti-based anodes for rechargeable batteries and Hybrid-Ion Capacitors (HIC) are hereby discussed. They are inspired by spinel
Li4Ti5O12, mineralogy, and potentially new directions in Ti-chemistry to design new anodes.
Chapter 1 reinforces the need for Ti-based anodes. Under the backdrop of the terawatt challenge, different primary sources of energy (e.g., fossil, oil, and coal) are discussed,
emphasizing the need for renewable energy generation and storage in batteries in the (electro)chemical form. The evolution of the batteries and their current demand in automobiles
is portrayed. Different anode operation mechanisms and their hybrid combination are outlined. Pressing topics relating to anodes like metal anode, risks with the use of graphite, the reason
for its inactivity for NIB, formation of the Solid Electrolyte Interphase (SEI), and the anode roadblock to commercialization of LIB are discussed. Finally, some critical works relating to
HIC and existing Ti-based anodes operating on different charge storage mechanisms are portrayed, setting the stage for the thesis work.
Chapter 2 focuses on the experimental procedures used for carrying out the thesis research. The preparative methods discussed include ball milling, dry, wet, and ion exchange routes.
Different physicochemical, spectroscopy, microscopy, and diffraction techniques have been described. The preparation of electrode coatings, cell assembly, and different electrochemical
testing techniques (galvanostatic, potentiodynamic, impedance etc.) are outlined. A description of high-temperature bulk ionic conductivity measurements, calculation of lithium migration
pathway, and their energy barrier by Bond Valence Site Energy (BVSE) method is provided.
Chapter 3 is inspired from spinel LTO and revolves around a closely related group of titanates, MLi2Ti6O14 (M = 2Na, Sr, Ba, Pb) (MLTO), first reported by the Amine and Shu groups. The
relation of MLTO to popular battery materials having a different dimensionality of (non)mobile structural units is discussed. BVSE calculations show how M influences the Li+ migration
pathways and their energy barriers. Bulk high-temperature conductivity measurements indicate the transition points of the dimensionality of lithium flow. The electrochemical performance
of combustion synthesized MLTO family of compounds is outlined. MLTO inserts lithium involving a Ti(IV)/Ti(III) redox change in a flat profile at 1.2-1.4 V that is slightly lower than
Li4Ti5O12. Divalent MLTOs deliver up to four electron capacities (100 – 160 mAh/g) with an additional low voltage slope region, while NaLTO shows less than 80 mAh/g (2 electrons).
The lower capacity of NaLTO is due to filled interlayer space, while it is half-filled for the divalent MLTOs. Hence, the MLTO structure's capacity becomes space-constrained, and the
theoretical capacity (220 – 283 mAh/g) for all six-lithium transfer is out of reach. Following the battery study, MLTOs were tested versus Activated Carbon (A.C.) for the first time in
asymmetric Lithium-Ion Capacitors (LIC) (100 mAh/g, 1-3 V). The role of the M-ion is emphasized while understanding the differences in electrochemical performance of MLTO.
MLTOs were first loaded with lithium (discharged) before assembling them in MLTOs/AC LIC hybrids. A.C. cathode rapidly adsorbs PF6- ions with a capacitor like slopy profile (40
mAh/g), while MLTOs (de)intercalate Li+ (100 mAh/g, 1-2 V) at Ti redox potential. This chapter confirms MLi2Ti6O14 (M = 2Na, Sr, Ba, Pb) titanates as versatile electrodes for both
secondary batteries and hybrid-ion capacitors.
Chapter 4 attempts to unravel new Ti-based anode materials using mineralogy, beyond conventional exploration using lab-based synthetic or computational databases. Three Ti-based
minerals, (i) Narsarsukite Na2TiOSi4O10, (ii) Freudenbergite NaMTi3O8 (M = Al, Fe), and (iii) Priderite Na1.7Cr1.7Ti6.3O16, could insert lithium and sodium thereby working as anodes for
metal-ion batteries and capacitors. Solid-state synthesized Narsarsukite (de)inserts one lithium (at C/2) using a Ti(IV)/Ti(III) redox giving near theoretical capacity (70 mAh/g) with 80%
capacity retention after 200 cycles. Due to its unique tetragonal I4/m structure consisting of open tunnels of rigid silicate units, Narsarsukite could deliver 50% capacity at a high 50C rate.
The Freudenbergites have a theoretical capacity of 220-250 mAh/g. Pure solution combustion synthesized phases were tested for lithium and sodium insertion (0.01 to 2.5 V). While AlFreudenbergite showed low capacities for the first-time lithium insertion, Fe-Freudenbergite delivered 200 mAh/g and 70 mAh/g for the unannealed and annealed phases, respectively.
Unannealed Fe- Freudenbergite showed moderate Na de-insertion capacity (140 mAh/g) while annealed Fe-Freudenbergite yielded high capacity (180 mAh/g till 100 cycles). Mössbauer
spectroscopy was performed at different states of charge, hoping to see Fe(0) in order to reinforce a conversion reaction and refute the earlier proposed sodium intercalation reaction.
This claim is based on initial cues from work by the Greenblatt, Cava and Murphy group at the Bell Labs in the 1980s. They found a two-lithium insertion limit for alkali-free FeV3O8, which
is a crystallographic rigid shear structure exactly like NaFeTi3O8. Obviously, NaFeTi3O8 already hosting structural sodium cannot topotactically insert three more sodiums. Further, the
Fe-freudenbergite was tested vs. A.C. in sodium-ion capacitor (80 mAh/g at 50 mA/g, 0-3 V).[NaxCrxTi(8-x)O16 (x=1.7)] (NCTOq) Priderite mineral was prepared using solid-state synthesis
by quenching at 1350 oC. It crystallizes in a hollandite-type (I4/m) structure with three types of sodium present in the tunnels, one of which uniquely and favorably sits at the closest spaced
oxygen site bottlenecks. These structure types are usually stabilized by larger cations and do not occur for sodium compounds. Furnace-cooled samples (1350 oC) result in a mixture of
Rutile, Freudenbergite, and Priderite phases, while low temperature (900 oC) annealing forms pure Freudenbergite phase. Electrochemical performance of ball-milled NCTOq samples was
evaluated. Capacity values of 130 mAh/g and 60 mAh/g were observed vs. lithium and sodium (0.01 V to 2.5 V, 10 mA/g) after correcting for charge storage in binder and carbon additives.
XPS analysis confirmed the presence of Ti(IV)/Ti(III) redox activity. The NCTOq samples were pre-lithiated, balanced, and were used in Li-ion and Na-ion capacitors with Activated
Carbon. Based on the active material weight, ~100 Wh/kg energy density was observed in halfcell and hybrid-ion capacitor configurations. On a broader note, this chapter highlights possible
exploitation of vast mineralogical database to design potential Ti-based anode materials.
Chapter 5 explores two new directions in Ti-based anodes bearing tremendous promise; one opens research gateways to innumerable structures containing an alloying element, another
unveils a new lithium insertion mechanism for battery materials. Venturing beyond the unstable lead halide perovskites famous in solar cells, stable and ubiquitous lead titanate and lead
zirconate perovskites were tested as battery anodes for the first time. Just four years after SONY's introduction of Li-ion battery (circa 1991), in a 1995 patent, Fuji Photo Film Co.
announced a Sn-based Amorphous Tin Composite Oxide (ATCO) glass delivering four times volumetric and two times gravimetric anode energy density than graphite. Enlightened by this,xii
there was a deep dive in research activity over the next decade into all materials having the Sn alloying center, including some having the perovskite-type ABO3 structure. Focusing on Pb
alloying center in perovskite frameworks, PbTiO3 and PbZrO3 are presented as potential anode materials for the first time as a glimpse into many potential ABO3 battery materials. Following
the structural breakdown of PbTiO3 in the first irreversible conversion cycle, Pb alloying and TiO2 insertion led to reversible capacities up to 400 mAh/g for Li/Na (nearly 4e-/mol) and 180
mAh/g for K (nearly 2e-/mol) in the first cycle. De-alloyed Pb particles were observed from TEM images after de-lithiation at the end of the charge. Perovskite family (and their
derivatives) can be put on anvil to develop high-capacity battery anode materials. In the second new direction, following the lowest 0.3 V Na2Ti3O7 NIB anode, we explore PbTi3O7 titanate
anode for the first time. Capacities of 300-400 mAh/g (in LIB/NIB) were observed via different electrochemical mechanisms. Large Na+ irreversibly converts PbTi3O7 to Pb and TiO2. These
reversible alloys (NaxPb) convert (Pb/PbO2) and intercalate (TiO2/NaxTiO2) like PX-PbTiO3. On the contrary, small Li+ intercalates, displacing Pb as metal, in PbTi3O7 at low voltages like
previously studied reversible Cu/Ag extrusion reactions studied in the 2000s by Thackeray and Tarascon. Pb metal stores more lithium forming various alloys. All reactions are reversible
leading to parent PbTi3O7 structure at the end of the charge. It shows the first example of reversible conversion-alloying-displacement reaction in Ti-based anode materials. Chapter 6 provides a summary of the entire thesis work outlining possible future directions to expand the rich playground of titanium-based battery anode materials
Investigation on AxMn3O7 Class of Layered Oxides as Versatile Battery Cathodes: Structure and Electrochemistry
No full textRechargeable battery technologies have been the spotlight of global scientific research in the quest to address steadily growing energy demand. Currently, Li-ion batteries have unanimously occupied consumer electronic sector. Most of these batteries are majorly based on two transition elements, Cobalt (Co) and Nickel (Ni), in popular cathodes like LiCoO2 and LiNi1/3Mn1/3Co1/3O2 (NMC). The resource constraints of Co and Ni have paved away for alternate transition metal redox chemistry. In this scenario, manganese based layered materials offer promise owing to their low-cost, resource-friendly nature with high operational safety. The cathode (positive electrode) forms the central component accounting for over 35% of the net cost of battery. The current work revolves around the rational design of high energy density cathode materials synergizing “Synthesis-Structure-Electrochemistry-Mechanism” of economic A2Mn3O7 (A= Li, Na, K, and Zn) class of insertion materials. Triclinic Na2Mn3O7 (P-1, #2) consists of defective (vacant sites) infinite [Mn3O7]-2¥ layers with two distinct Na-sites. The flexibility of variable Mn oxidation states triggers polymorphism and rich crystal chemistry. The Mn+4 oxidation state specifies the ability of layered Na2Mn3O7 to accommodate foreign intercalating alkali-ions with active Mn+4/Mn+3/Mn+2 redox couples. Owing to the low bond valence site energy (BVSE) of the two Na-sites (0.27 eV) in Na2Mn3O7, they can be easily exchanged using simple soft-chemistry techniques. This work demonstrates Na2Mn3O7 as a versatile cathode for secondary Li-ion and post-Li-ion batterie
Structural and Electrochemical Investigation of Fluoro(hydroxy)phosphate Based Cathode Materials for Secondary Batteries
No full textStructural and electrochemical investigation of LiFePO4OH hydroxyphosphate material. The synthesis and structure of this material is explained. The hydrothermally synthesized material crystallizes in triclinic structure with P-1 space group. The electrochemistry of this material was revisited in both aqueous and organic electrolytes. In organic commercial electrolyte, a stable discharge capacity of 140 mAh g-1 up to 60 cycles at a current density of 1 mA cm-2 was obtained making it the best-reported capacity for this material until date. Further, the material was tested in 21m LiTFSi + 7m LiOTf aqueous electrolyte in the potential window -1.0 to 1.0 V vs. Ag/AgCl reference electrode. It delivered a discharge capacity of 153 mAh g-1 with good cyclability. Notably, LiFePO4OH, which is reported as a cathode for LIBs in organic electrolyte, worked in the anodic range for aqueous LIBs. This is first time an iron based tavorite material was reported as an anode for aqueous LIBs. An electrochemical model was also developed to improve the performance of the material by employing various geometrical and kinetic parameters. It was further used to study the commercial aspects of the material. Though the redox potential of LiFePO4OH (2.4-2.6 V) is low as compared to commercial LiFePO4 (3.5 V) cathode, but it can still be a good option for stationary storage applications where high energy density is often not required. The possible future directions to explore fluoro(hydroxy)phosphate materials for electrochemical applications
Structural and Electrochemical Investigation of Bisulfate and Hydroxysulfate based Polyanionic Cathodes
No full textThe discovery of LiFePO4 cathode for Li-ion battery ushered intensive study on polyanionic high-voltage battery insertion materials. Polyanionic materials offer rich crystal chemistry, robust framework, voltage tunability, and high redox potential based on the inductive effect due to the polyanionic unit [(XO4)mn-, X = S, P, Si, W, Mo, etc.] [1]. Among them, SO4-based polyanionic systems have the advantage of higher redox potential and ease/versatility of low temperature synthesis. In this spirit, I have investigated bisulfate [A2-xM(SO4)2: A= Li, Na, K; x= 0,1] and hydroxysulfate [AMSO4OH: A = Li] type sulfate-based polyanionic frameworks. Few salient features of my thesis work are:
(i) Spray drying route was used to discover a metastable monoclinic polymorph of Li2NiII(SO4)2 (s.g. P21/c). As per first principle calculations, it can work as a 5.5 V (vs. Li+/Li) cathode for Li-ion battery coupling both cationic (Ni2+/Ni3+) and anionic (O-) redox activity. The crystal chemistry, phase stability landscape and the ground state magnetic structure (A-type Antiferromagnetic spin ordering) of this novel compound have been examined [2,3].
(ii) Mineralogical exploration and synthetic preparation of naturally found minerals are strategically used to unveil battery electrode materials. Following, saranchinaite Na2Cu(SO4)2 and its hydrated derivative kröhnkite Na2Cu(SO4)2.2H2O bisulfate minerals have been prepared using the facile spray drying synthesis route. The thermodynamic phase stability landscape has been explored along with the structural effects on the Na+ ion mobility. While the presence of Cu makes them unsuitable for insertion ion chemistry, they have been reported as potential conversion type battery electrodes [4].
(iii) The eldfellite NaVIII(SO4)2 (s.g. C2/m) is demonstrated as a versatile novel cathode material for both Li-ion (2.57 V, 80 mAh/g) and Na-ion (2.28 V, 70 mAh/g) battery at current rate of C/20 and based on solid solution reaction mechanism.
(iv) Hydrothermally prepared orthorhombic polymorph of FeIIISO4OH (s.g. Pnma) has been examined as a 3.2 V (110 mAh/g, C/20) Li-ion battery cathode. I have further demonstrated the first reversible Na-ion (de)insertion in monoclinic FeIIISO4OH at ~2.9 V based on solid solution reaction mechanism with a discharge capacity of 85 mAh/g (C/100) [5,6].
Overall, this work can be suitably placed in the materials science tetrahedron encompassed by “structure-property-processing-performance”. I will elaborate the above-mentioned sulfate based polyanionic battery insertion materials.Ministry of Human Resource Developmen
Swift Combustion Synthesis of PbLi2Ti6O14 Anode for Lithium-Ion Batteries: Diffusional and Electrochemical Investigation
No full textLead lithium titanate (PbLi2Ti6O14) was synthesized by combustion route restricting the annealing at 900 degrees C to just 1 minute. Rietveld analysis confirmed orthorhombic (Cmca) product phase with an average particle size similar to 200 nm and surface area of 2 m(2)/g forming secondary porous particles. From bond valence site energy (BVSE) calculations, 1 D ionic conduction was found along c axis with low activation energy (0.23 eV). AC conductivity analysis revealed a bulk conductivity of 2 x 10(-7) S. cm(-1) at room temperature and 1 x 10(-4) S. cm(-1) at 200 degrees C with a switch from extrinsic 1D to intrinsic 2D mechanism at 150. C. Li + diffusion coefficient was calculated to be in the order of 10(-12) cm(2). s(-1). More than 4 lithium (per f. u.) could be reversibly (de) inserted delivering capacity over 160 mAh/g with good cycling retention over 1000 cycles. With a feasible rapid synthesis, good diffusional and electrochemical behavior especially high rate capability, PbLi2Ti6O14 can act as a safe 1.35 V anode for rechargeable Li-ion batteries. (c) The Author(s) 2018. Published by ECS
Pursuit of Sustainable Iron-Based Sodium Battery Cathodes: Two Case Studies
No full textRechargeable batteries have been the torchbearer electrochemical energy storage devices empowering small-scale electronic gadgets to large-scale grid storage. Complementing the lithium-ion technology, sodium-ion batteries have emerged as viable economic alternatives in applications unrestricted by volume/weight. What is the best performance limit for new-age Na-ion batteries? This mission has unravelled suites of oxides and polyanionic positive insertion (cathode) compounds in the quest to realize high energy density. Economically and ecologically, iron-based cathodes are ideal for mass-scale dissemination of sodium batteries. This Perspective captures the progress of Fe-containing earth-abundant sodium battery cathodes with two best examples: (i) an oxide system delivering the highest capacity (similar to 200 mA h/g) and (ii) a polyanionic system showing the highest redox potential (3.8 V). Both develop very high energy density with commercial promise for large-scale applications. Here, the structural and electrochemical properties of these two cathodes are compared and contrasted to describe two alternate strategies to achieve the same goal, i.e., improved energy density in Fe-based sodium battery cathodes
Alluaudite Class of High Voltage Sodium Insertion Materials: An Interplay of Polymorphism and Magnetism
No full textThe research and development with sodium ion batteries has geared up manifold in last one decade, owing to their abundance, non-toxicity, uniform geographical distribution and electrochemical performance complimentary to lithium counterpart. This research often leads to various novel material discoveries such as Na2Fe2(SO4)(3) sodium insertion material, which has recently registered the highest-ever Fe3+/Fe2+ redox potential (3.8 V vs. Na) having excellent cyclability and rate kinetics. This basically belongs to a family of materials-Alluaudites Na2M2(SO4)(3) (M: Fe, Mn, Co, Ni). Such cathode insertion compounds are basically functional materials, involving redox active 3d transition metals that are often magnetic in nature. We have investigated the magnetic structure and properties of - Alluaudites Na2M2(SO4)(3). These alluaudite shows wide structural diversity and polymorphism. Employing various experimental methods involving diffraction, magnetic susceptibility, Mossbauer spectroscopy and low temperature neutron powder diffraction data we have explored the magnetic properties exhibited by the Alluaudite class of insertion materials
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