Cathode Materials For Li Batteries Research Articles

Li 2MnSiO 4 as a potential Li-battery cathode material

Recently we synthesized and preliminary characterized a new material for potential use in Li-battery cathodes: Li 2MnSiO 4. Although its theoretical capacity is about 330 mAh g −1, the actual measurements showed a much smaller value (about 120 mAh g −1). One of the reasons for the poor performance could be the poor electronic conductivity (<10 −14 S cm −1 at RT) causing a huge polarization during charge–discharge. However, in the present paper we show that reducing the particle size down to the range of 20–50 nm and additional particle embedment into a carbon phase does not significantly improve the electrochemistry of Li 2MnSiO 4. Observations of structural changes during the first charge shows a complete loss of peaks when reaching the nominal composition of ca. Li 1MnSiO 4. The peaks are not recovered during subsequent cycling. It is supposed that extraction of Li causes significant structural changes so that the resulting material is only able to reversibly exchange a limited amount of Li.

Mass and charge transport in hierarchically organized storage materials. Example: Porous active materials with nanocoated walls of pores

To enhance the kinetics of poorly conducting cathode materials for Li batteries, the authors have proposed a number of strategies based on crushing the active material into nanopowder and embedding the powder into a carbon-based web or coating. Using the well-elaborated example of LiFePO4, we demonstrate that the same goal can be achieved with a different approach where the active material remains in a form of large (1–20 μm) single crystals. Instead of crushing the material, we make it porous—with average pore size around 50 nm and pore surface area of 25 m 2/g. The walls of the pores (but also the outer surfaces of crystals) are covered with ca. 1-nm-thick carbon film. Most surprisingly, such a unique nanoarchitecture can be prepared using a simple sol–gel based procedure including a single heat treatment. The crucial part is the selection of appropriate carbon precursor. For example, citric acid decomposes quite vigorously into gases and solid carbon at temperatures up to ca. 450 °C. This range matches exactly the first solidification of LiFePO 4. Thus, the evolving gases can create an interconnected web of pores while the solid parts (carbon) are deposited simultaneously on the walls of pores. We further show that a carbon content of less than 3% is already sufficient for surpassing the percolation threshold with respect to surface conductivity of carbon. Using more carbon can decrease the rate performance so a fine balance is required in this respect. Most importantly, carbonization at a temperature of slightly less than 700 °C is sufficient to achieve a composite conductivity of the order of 10 − 2 S cm − 2 —more than sufficient for good cathode kinetics. In the end, we show new evidence that the phase that is responsible for high conductivity of LiFePO 4–C composites is indeed the carbon phase.

Study of Various (“Super Iron”) MFeO4 Compounds in Li Salt Solutions as Potential Cathode Materials for Li Batteries

In this work we studied the possibility of using “super iron” compounds, including , and as potential cathode materials for rechargeable Li batteries, and their behavior in several nonaqueous Li salt solutions. Classic electrochemical techniques, such as cyclic voltammetry and chronopotentiometry combined with X-ray photoelectron spectroscopy, X-ray diffraction, Mössbauer spectroscopy, atomic adsorption, atomic emission, in situ and ex situ atomic force microscopy imaging, and diffuse reflectance Fourier Transform infrared spectroscopy were used in order to obtain a full picture of the electrochemical behavior of these compounds. compounds such as and are reduced in the presence of Li ions to compounds. , and or BaO are formed in amorphous or nanocrystalline structures. The reaction is partially reversible, i.e., compounds can be reformed by oxidation. The mechanisms of the lithiation–delithiation of these systems and what limited their reversibility are discussed.

Electrochemical performance of Li 2FeSiO 4 as a new Li-battery cathode material

Phase-pure lithium iron silicate (Li 2FeSiO 4) has been prepared successfully. Its ambient temperature structure has been determined by X-ray diffraction and its electrochemical performance characterised at 60 °C. The resulting cyclic voltammogram suggests a phase transition to a more stable structure after the first cycle. This could involve a structural ordering process from a solid-solution to a long-range-ordered structure. The initial charge capacity of 165 mAh/g (99% of the theoretical value) stabilises after a few cycles to around 140 mAh/g (84% of the theoretical value).

ChemInform Abstract: LiCuxMn2‐xO4 Spinels (0.1 ≤ x ≤ 0.5): A New Class of Cathode Materials for Li Batteries. Part 2. In situ Measurements.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform Abstract: LiMn2‐xCuxO4 Spinels (0.1 ≤ x ≤ 0.5): A New Class of 5 V Cathode Materials for Li Batteries. Part 1. Electrochemical, Structural, and Spectroscopic Studies.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

LiMn2 − xCux O 4 Spinels (0.1 ⩽ x ⩽ 0.5): A new Class of 5 V Cathode Materials for Li Batteries: I. Electrochemical, Structural, and Spectroscopic Studies

A series of electroactive spinel compounds, (0.1 ⩽ x ⩽ 0.5), has been studied by crystallographic, spectroscopic, and electrochemical methods and by electron microscopy. These spinels are nearly identical in structure to cubic and successfully undergo reversible Li intercalation. The electrochemical data show a remarkable reversible electrochemical process at 4.9 V which is attributed to the oxidation of to . The inclusion of Cu in the spinel structure enhances the electrochemical stability of these materials upon cycling. The initial capacity of spinels decreases with increasing x from 130 mAh/g in (x = 0) to 70 mAh/g in “” (x = 0.5). The data also show slight shifts to higher voltage for the delithiation reaction that normally occurs at 4.1 V in standard electrodes (1 ⩾ x ⩾ 0) corresponding to the oxidation of to . Although the powder X‐ray diffraction pattern of “” shows a single‐phase spinel product, neutron diffraction data show a small but significant quantity of an impurity phase, the composition and structure of which could not be identified. X‐ray absorption spectroscopy was used to gather information about the oxidation states of the manganese and copper ions. The composition of the spinel component in the was determined from X‐ray diffraction and X‐ray absorption near‐edge spectroscopy to be , suggesting to a best approximation that the impurity in the sample was a lithium‐copper‐oxide phase. The substitution of manganese by copper enhances the reactivity of the spinel structure toward hydrogen: the compounds are more easily reduced at moderate temperature (∼200°C) than .

Electrochemical properties of non-stoichiometric V 6O 13

Non-stoichiometric V 6O 13±0.2 (VO y ) prepared by thermal decomposition of NH 4VO 3 in N 2 atmosphere is investigated cathode material for Li batteries. The maximum lithium composition is found to be Li 2 y-3 VO y . The emf vs composition relationship of Li/Li x VO 2.144 is determined in the interval 0 < x < 1.3, yielding a theoretical energy density of 890 Wh kg −1. The kinetics and reversibility of the VO y electrode is investigated by cyclic voltammetry and cycling of test cells. The lithium diffusion coefficient and the electronic conductivity of the oxide is found to decrease with increasing lithium content. The cyclability of very thin electrodes is found to be excellent, but inferior results are obtained with practical cells, presumably due to degradation of electrode structure.