M. Anji Reddy

Batteries based on fluoride shuttle

In search of new concepts to build batteries with high energy densities, electrochemical cells based on metal fluorides may be promising. Herein, we report the demonstration of secondary battery cells based on fluoride shuttle. In fluoride ion batteries, fluoride anion acts as charge transfer ion between a metal/metal fluoride pair where it will react with metal or evolve from metal fluoride depending on the flow of current.

Lithium Intercalation into Nanocrystalline Brookite TiO2

Lithium intercalation in phase-pure nanocrystalline brookite TiO 2 is demonstrated for the first time. Galvanostatic studies show that 0.9 Li per formula unit can be intercalated into this phase in initial discharge. Ex situ X-ray diffraction studies on the electrodes at different levels of lithium intercalation show that the structure is stable toward lithium intercalation and deintercation. In the initial charge, an irreversible capacity loss is observed. However, on further cycling, the phase shows excellent cycling behavior. A reversible capacity of 170 mAhg -1 is observed even after 40 cycles.

Single step transformation of sulphur to Li2S2/Li2S in Li-S batteries

Lithium-sulphur batteries have generated tremendous research interest due to their high theoretical energy density and potential cost-effectiveness. The commercial realization of Li-S batteries is still hampered by reduced cycle life associated with the formation of electrolyte soluble higher-order polysulphide (Li2Sx, x = 4–8) intermediates, leading to capacity fading, self-discharge, and a multistep voltage profile. Herein, we have realized a practical approach towards a direct transformation of sulphur to Li2S2/Li2S in lithium-sulphur batteries by alteration of the reaction pathway. A coconut shell derived ultramicroporous carbon-sulphur composite cathode has been used as reaction directing template for the sulphur. The lithiation/delithiation and capacity fading mechanism of microporous carbon confined sulphur composite was revealed by analyzing the subsurface using X-ray photoelectron spectroscopy. No higher-order polysulphides were detected in the electrolyte, on the surface, and in the subsurface of the cathode composite. The altered reaction pathway is reflected by a single-step profile in the discharge/charge of a lithium-sulphur cell.

Crystallite Size Constraints on Lithium Insertion into Brookite TiO2

We demonstrate lithium insertion into brookite in the nanophase regime. The extent of lithium insertion is significantly influenced by the crystallite size. A maximum of can be inserted into 10 nm size crystallites and the extent of lithium insertion is low (0.23 Li) in 33 nm crystallites. The reversibility decreases with an increase in crystallite size. The contrasting behavior of brookite and rutile suggests that the structural features of brookite may play an important role in determining Li insertion behavior.

Solid Electrolytes for Fluoride Ion Batteries: Ionic Conductivity in Polycrystalline Tysonite-Type Fluorides

Batteries based on a fluoride shuttle (fluoride ion battery, FIB) can theoretically provide high energy densities and can thus be considered as an interesting alternative to Li-ion batteries. Large improvements are still needed regarding their actual performance, in particular for the ionic conductivity of the solid electrolyte. At the current state of the art, two types of fluoride families can be considered for electrolyte applications: alkaline-earth fluorides having a fluorite-type structure and rare-earth fluorides having a tysonite-type structure. As regard to the latter, high ionic conductivities have been reported for doped LaF3 single crystals. However, polycrystalline materials would be easier to implement in a FIB due to practical reasons in the cell manufacturing. Hence, we have analyzed in detail the ionic conductivity of La(1-y)Ba(y)F(3-y) (0 ≤ y ≤ 0.15) solid solutions prepared by ball milling. The combination of DC and AC conductivity analyses provides a better understanding of the conduction mechanism in tysonite-type fluorides with a blocking effect of the grain boundaries. Heat treatment of the electrolyte material was performed and leads to an improvement of the ionic conductivity. This confirms the detrimental effect of grain boundaries and opens new route for the development of solid electrolytes for FIB with high ionic conductivities.

Development of new anode composite materials for fluoride ion batteries

Due to their high theoretical energy density values, Fluoride Ion Batteries (FIB) are interesting alternatives to Li-ion batteries. Recently, results have been reported on the reversible charge and discharge of such systems using a solid electrolyte, various metal fluorides as cathode materials and Ce metal as the anode. The work in the present study is focused on the development of new anode materials which do not contain Li. To facilitate cell preparation and material handling, cells were prepared in the discharged state with Bi or Cu as the cathode material and CeF3, CaF2 or MgF2 as potential anode materials. The charge and discharge mechanisms were examined by detailed ex situ X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) experiments. The best cycling performances were obtained with MgF2 but prepared in the half-discharged state (i.e. mixed with Mg), thus forming a composite that could provide better interface contacts between the different reactive phases. The results showed that apart from choosing carefully the electrode active materials, it is also important to optimise the architecture of the electrodes.

VOCl as a Cathode for Rechargeable Chloride Ion Batteries.

A novel room temperature rechargeable battery with VOCl cathode, lithium anode, and chloride ion transporting liquid electrolyte is described. The cell is based on the reversible transfer of chloride ions between the two electrodes. The VOCl cathode delivered an initial discharge capacity of 189 mAh g(-1) . A reversible capacity of 113 mAh g(-1) was retained even after 100 cycles when cycled at a high current density of 522 mA g(-1) . Such high cycling stability was achieved in chloride ion batteries for the first time, demonstrating the practicality of the system beyond a proof of concept model. The electrochemical reaction mechanism of the VOCl electrode in the chloride ion cell was investigated in detail by ex situ X-ray diffraction (XRD), infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The results confirm reversible deintercalation-intercalation of chloride ions in the VOCl electrode.

Improving the Energy Density and Power Density of CFx by Mechanical Milling: A Primary Lithium Battery Electrode

The effect of high energy ball milling on the electrochemical performance of graphite fluoride (CFx) was investigated. A significant improvement was observed in both energy density and power density. The volumetric energy density was increased up to a factor of 3 with ball milled materials compared with pristine materials. The gravimetric energy density was increased up to a factor of 2, depending on the discharge rates. At 6C the ball milled material still delivered 40% of its nominal capacity, whereas the pristine material did not exhibit any capacity any more. We achieved the power density of 9860 W/kg with a gravimetric energy density of 800 Wh/kg for the optimized material.

Influence of particle size and fluorination ratio of CFx precursor compounds on the electrochemical performance of C–FeF2 nanocomposites for reversible lithium storage

Summary Systematical studies of the electrochemical performance of CFx-derived carbon–FeF2 nanocomposites for reversible lithium storage are presented. The conversion cathode materials were synthesized by a simple one-pot synthesis, which enables a reactive intercalation of nanoscale Fe particles in a CFx matrix, and the reaction of these components to an electrically conductive C–FeF2 compound. The pretreatment and the structure of the utilized CFx precursors play a crucial role in the synthesis and influence the electrochemical behavior of the conversion cathode material. The particle size of the CFx precursor particles was varied by ball milling as well as by choosing different C/F ratios. The investigations led to optimized C–FeF2 conversion cathode materials that showed specific capacities of 436 mAh/g at 40 °C after 25 cycles. The composites were characterized by Raman spectroscopy, X-Ray diffraction measurements, electron energy loss spectroscopy and TEM measurements. The electrochemical performances of the materials were tested by galvanostatic measurements.

Mechanical Milling Assisted Synthesis and Electrochemical Performance of High Capacity LiFeBO3 for Lithium Batteries.

Borate chemistry offers attractive features for iron based polyanionic compounds. For battery applications, lithium iron borate has been proposed as cathode material because it has the lightest polyanionic framework that offers a high theoretical capacity. Moreover, it shows promising characteristics with an element combination that is favorable in terms of sustainability, toxicity, and costs. However, the system is also associated with a challenging chemistry, which is the major reason for the slow progress in its further development as a battery material. The two major challenges in the synthesis of LiFeBO3 are in obtaining phase purity and high electrochemical activity. Herein, we report a facile and scalable synthesis strategy for highly pure and electrochemically active LiFeBO3 by circumventing stability issues related to Fe(2+) oxidation state by the right choice of the precursor and experimental conditions. Additionally, we carried out a Mössbauer spectroscopic study of electrochemical charged and charged-discharged LiFeBO3 and reported a lithium diffusion coefficient of 5.56 × 10(-14) cm(2) s(-1) for the first time.