Probing Capacity Trends in MLi2_2Ti6_6O14_{14} Lithium-Ion Battery Anodes Using Calorimetric Studies

Due to higher packing density, lower working potential, and area specific impedance, the MLi$_2$Ti$_6$O$_{14}$ (M = 2Na, Sr, Ba, and Pb) titanate family is a potential alternative to zero-strain Li$_4$Ti$_5$O$_{12}$ anodes used commercially in Li-ion batteries. However, the exact lithiation mechanism in these compounds remains unclear. Despite its structural similarity, MLi$_2$Ti$_6$O$_{14}$ behaves differently depending on charge and size of the metal ion, hosting 1.3, 2.7, 2.9, and 4.4 Li per formula unit, giving charge capacity values from 60 to 160 mAh/g in contrast to the theoretical capacity trend. However, high-temperature oxide melt solution calorimetry measurements confirm strong correlation between thermodynamic stability and the observed capacity. The main factors controlling energetics are strong acid–base interactions between basic oxides MO, Li$_2$O and acidic TiO$_2$, size of the cation, and compressive strain. Accordingly, the energetic stability diminishes in the order Na$_2$Li$_2$Ti$_6$O$_{14}$ > BaLi$_2$Ti$_6$O$_{14}$ > SrLi$_2$Ti$_6$O$_{14}$ > PbLi$_2$Ti$_6$O$_{14}$. This sequence is similar to that in many other oxide systems. This work exhibits that thermodynamic systematics can serve as guidelines for the choice of composition for building better batteries

First principles investigation of anionic redox in bisulfate lithium battery cathodes

The search for an alternative high-voltage polyanionic cathode material for Li-ion batteries is vital to improve the energy densities beyond the state-of-the-art, where sulfate frameworks form an important class of high-voltage cathode materials due to the strong inductive effect of the S$^{6+}$ ion. Here, we have investigated the mechanism of cationic and/or anionic redox in Li$_x$M(SO$_4$)$_2$ frameworks (M = Mn, Fe, Co, and Ni and 0 $\leq$ x $\leq$ 2) using density functional calculations. Specifically, we have used a combination of Hubbard $U$ corrected strongly constrained and appropriately normed (SCAN+$U$) and generalized gradient approximation (GGA+$U$) functionals to explore the thermodynamic (polymorph stability), electrochemical (intercalation voltage), geometric (bond lengths), and electronic (band gaps, magnetic moments, charge populations, etc.) properties of the bisulfate frameworks considered. Importantly, we find that the anionic (cationic) redox process is dominant throughout delithiation in the Ni (Mn) bisulfate, as verified using our calculated projected density of states, bond lengths, and on-site magnetic moments. On the other hand, in Fe and Co bisulfates, cationic redox dominates the initial delithiation (1 $\leq$ x $\leq$ 2), while anionic redox dominates subsequent delithiation (0 $\leq$ x $\leq$ 2). In addition, evaluation of the crystal overlap Hamilton population reveals insignificant bonding between oxidizing O atoms throughout the delithiation process in the Ni bisulfate, indicating robust battery performance that is resistant to irreversible oxygen evolution. Finally, we observe both GGA+$U$ and SCAN+$U$ predictions are in qualitative agreement for the various properties predicted. Our work should open new avenues for exploring lattice oxygen redox in novel high voltage polyanionic cathodes, especially using the SCAN+$U$ functional.Comment: Draft and supporting information included, 40 pages tota

A 3.8-V earth-abundant sodium battery electrode

Rechargeable lithium batteries have ushered the wireless revolution over last two decades and are now matured to enable green automobiles. However, the growing concern on scarcity and large-scale applications of lithium resources have steered effort to realize sustainable sodium-ion batteries, ​Na and ​Fe being abundant and low-cost charge carrier and redox centre, respectively. However, their performance is limited owing to low operating voltage and sluggish kinetics. Here we report a hitherto-unknown material with entirely new composition and structure with the first alluaudite-type sulphate framework, Na2Fe2(SO4)3, registering the highest-ever Fe3+/Fe2+ redox potential at 3.8 V (versus ​Na, and hence 4.1 V versus ​Li) along with fast rate kinetics. Rare-metal-free Na-ion rechargeable battery system compatible with the present Li-ion battery is now in realistic scope without sacrificing high energy density and high power, and paves way for discovery of new earth-abundant sustainable cathodes for large-scale batteries.UTokyo Research掲載「新物質発見で電池のレアメタル使用ゼロに」 URI: http://www.u-tokyo.ac.jp/ja/utokyo-research/research-news/materials-discovery-for-earth-abundant-battery/UTokyo Research "Materials discovery for earth-abundant battery" URI: http://www.u-tokyo.ac.jp/en/utokyo-research/research-news/materials-discovery-for-earth-abundant-battery

Water‐Soluble Inorganic Binders for Lithium‐Ion and Sodium‐Ion Batteries

Inorganic materials form an emerging class of water-soluble binders for battery applications. Their favourable physicochemical properties, such as intrinsic ionic conductivity, high thermal stability (>1000 °C), and compatibility to coat a diverse range of electrode materials make them useful binders for lithium-ion and sodium-ion batteries. Li and Na containing phosphates and silicates are attractive choices as multifunctional inorganic aqueous binders (IABs). This review discusses these binders\u27 structural, thermal, and ionic properties, followed by exploiting their ionically conducting nature for all-solid-state batteries. Subsequently, the application of these compounds as binders and surface coating agents for different anodes and cathodes in lithium-ion and sodium-ion batteries is discussed. Eventually, a first evaluation of their environmental impacts and economic aspects is presented as well

Greener, Safer and Better Performing Aqueous Binder for Positive Electrode Manufacturing of Sodium Ion Batteries

P2-type cobalt-free MnNi-based layered oxides are promising cathode materials for sodium-ion batteries (SIBs) due to their high reversible capacity and well chemical stability. However, the phase transformations during repeated (dis)charge steps lead to rapid capacity decay and deteriorated Na+ diffusion kinetics. Moreover, the electrode manufacturing based on polyvinylidene difluoride (PVDF) binder system has been reported with severely defluorination issue as well as the energy intensive and expensive process due to the use of toxic and volatile N-methyl-2-pyrrolidone (NMP) solvent. It calls for designing a sustainable, better performing, and cost-effective binder for positive electrode manufacturing. In this work, we investigated inorganic sodium metasilicate (SMS) as a viable binder in conjunction with P2-Na0.67Mn0.55Ni0.25Fe0.1Ti0.1O2 (NMNFT) cathode material for SIBs. The NMNFT-SMS electrode delivered a superior electrochemical performance compared to carboxy methylcellulose (CMC) and PVDF based electrodes with a reversible capacity of ~161 mAh/g and retaining ~83 % after 200 cycles. Lower cell impedance and faster Na+ diffusion was also observed in this binder system. Meanwhile, with the assistance of TEM technique, SMS is suggested to form a uniform and stable nanoscale layer over the cathode particle surface, protecting the particle from exfoliation/cracking due to electrolyte attack. It effectively maintained the electrode connectivity and suppressed early phase transitions during cycling as confirmed by operando XRD study. With these findings, SMS binder can be proposed as a powerful multifunctional binder to enable positive electrode manufacturing of SIBs and to overall reduce battery manufacturing costs

Sulfate Chemistry for High-Voltage Insertion Materials: Synthetic, Structural and Electrochemical Insights

Rechargeable batteries based on Li and Na ions have been growing leaps and bounds since their inception in the 1970s. They enjoy significant attention from both the fundamental science point of view and practical applications ranging from portable electronics to hybrid vehicles and grid storage. The steady demand for building better batteries calls for discovery, optimisation and implementation of novel positive insertion (cathode) materials. In this quest, chemists have tried to unravel many future cathode materials by taking into consideration their eco-friendly synthesis, material/process economy, high energy density, safety, easy handling and sustainability. Interestingly, sulfate-based cathodes offer a good combination of sustainable syntheses and high energy density owing to their high-voltage operation, stemming from electronegative SO42- units. This review delivers a sneak peak at the recent advances in the discovery and development of sulfate-containing cathode materials by focusing on their synthesis, crystal structure and electrochemical performance. Several family of cathodes are independently discussed. They are 1) fluorosulfates AMSO(4)F], 2) bihydrated fluorosulfates AMSO(4)F2H(2)O], 3) hydroxysulfate AMSO(4)OH], 4) bisulfates A(2)M(SO4)(2)], 5) hydrated bisulfates A(2)M(SO4)(2)nH(2)O], 6) oxysulfates Fe-2(SO4)(2)O] and 7) polysulfates A(2)M(2)(SO4)(3)]. A comparative study of these sulfate-based cathodes has been provided to offer an outlook on the future development of high-voltage polyanionic cathode materials for next-generation batteries

Physical and electrochemical study of halide-modified activated carbons

The 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

Pursuit of Sustainable Iron-Based Sodium Battery Cathodes: Two Case Studies

Rechargeable 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

The 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