Opportunities and Challenges in the Development of Cathode Materials for Rechargeable Mg Batteries

Recent years have seen an intense and renewed interest in the Mg battery research, naming Mg-S the ≫Holy Grail≪ battery, and expectations that Mg battery system will be able to compete and surpass Li-ion batteries in a matter of years. Considerable progress has been achieved in the field of Mg electrolytes, where several new electrolytes with improved electrochemical performance and favorable chemical properties (non-corrosive, non-nucleophilic) were synthesized. Development in the field of cathodes remains a bit more elusive, with inorganic, sulfur, and organic cathodes all showing their upsides and downsides. This review highlights the recent progress in the field of Mg battery cathodes, paying a special attention to the performance and comparison of the different types of the cathodes. It also aims to define advantages and key challenges in the development of each type of cathodes and finally specific questions that should be addressed in the future research

Advances in understanding Li battery mechanisms using impedance spectroscopy

The use of impedance spectroscopy in the field of modern batteries is demonstrated on three systems: lithium ion batteries represented by lithium iron phosphate (LFP) and lithium cobalt oxide (LCO) electrodes, a porous carbon cathode in contact with polysulfides and a metallic lithium anode exhibiting dendritic growth. In all cases, systematic experiments are shown where the type and composition of electrochemical cell is varied in order to identify the main processes contributing to the impedance response. The experiments are upgraded with appropriate models, using mainly the transmission line approach. The approach allows establishment of clear correlations between the composition and morphology of electrodes on one hand and the measured impedance features on the other. As the transmission line models are based on the use of physically well-defined elements, the approach allows a quantitative description of the main processes (diffusion, reaction, migration across films and contacts) taking place in modern battery electrodes

Fluorinated reduced graphene oxide as a protective layer on the metallic lithium for application in the high energy batteries

International audienceMetallic lithium is considered to be one of the most promising anode materials since it offers high volumetric and gravimetric energy densities when combined with high-voltage or high-capacity cathodes. However, the main impediment to the practical applications of metallic lithium is its unstable solid electrolyte interface (SEI), which results in constant lithium consumption for the formation of fresh SEI, together with lithium dendritic growth during electrochemical cycling. Here we present the electrochemical performance of a fluorinated reduced graphene oxide interlayer (FGI) on the metallic lithium surface, tested in lithium symmetrical cells and in combination with two different cathode materials. The FGI on the metallic lithium exhibit two roles, firstly it acts as a Li-ion conductive layer and electronic insulator and secondly, it effectively suppresses the formation of high surface area lithium (HSAL). An enhanced electrochemical performance of the full cell battery system with two different types of cathodes was shown in the carbonate or in the ether based electrolytes. The presented results indicate a potential application in future secondary Li-metal batteries

The Role of Cellulose Based Separator in Lithium Sulfur Batteries

International audienceIn this work, abundant and environmentally friendly nano-fibrillated (NFC) cellulose is used for fabrication of porous separator membranes according to the procedure adopted from papermaking industry. As-prepared NFC separators were characterized in terms of thickness, porosity, wettability, electrochemical stability and electrochemical performance in lithium-sulfur and Li-symmetrical pouch cells and compared to a commercial Celgard 2320 separator membrane. Results demonstrated that morphology and electrochemical performance of NFC separator outperforms the conventional polyolefin separator. Due to exceptional interplay between lithium metal and cellulose, this research provides a self-standing NFC separator that can be used besides the lithium-sulfur also in other lithium metal battery configurations

Mechanism of Li2S formation and dissolution in Lithium-Sulphur batteries

Insufficient understanding of the mechanism that reversibly converts sulphur into lithium sulphide (Li2S) via soluble polysulphides (PS) hampers the realization of high performance lithium-sulphur cells. Typically Li2S formation is explained by direct electroreduction of a PS to Li2S; however, this is not consistent with the size of the insulating Li2S deposits. Here, we use in situ small and wide angle X-ray scattering (SAXS/WAXS) to track the growth and dissolution of crystalline and amorphous deposits from atomic to sub-micron scales during charge and discharge. Stochastic modelling based on the SAXS data allows quantification of the chemical phase evolution during discharge and charge. We show that Li2S deposits predominantly via disproportionation of transient, solid Li2S2 to form primary Li2S crystallites and solid Li2S4 particles. We further demonstrate that this process happens in reverse during charge. These findings show that the discharge capacity and rate capability in Li-S battery cathodes are therefore limited by mass transport through the increasingly tortuous network of Li2S / Li2S4 / carbon pores rather than electron transport through a passivating surface film

LiFePO4 nanocrystals synthesis by hydrothermal reduction method

The nanocrystals of LiFePO4 a cathode material for Li-ion batteries were synthesized by simple one – pot combined colloidal hydrothermal reduction approach. The influences of surfactant ratios on nanocrystal formation are investigated. Also extent of surface modification and agglomeration is assessed. The electrochemical performance of material is investigated on as prepared samples and on samples with carbonized surface layer. The XRD, TEM, SEM, FTIR, laser diffraction PSA, magnetic measurements and galvanostatic cycling are performed characterization techniques

Sol-gel synthesis of Li2FeSiO4/C

Lithium transition-metal orthosilicates with general formula Li2MSiO4 (M = Fe, Mn, Co, etc.) have attracted a lot of interest due to their potentially high theoretical capacities arising from the possibility of the extraction of two Li-ions per formula unit. Li2FeSiO4 takes prominent position among this family of compounds due to its structural stability and natural abundance of iron. In this study, Li2FeSiO4/C composite was synthesized by simple method which involves rapid heating, short high-temperature delay, and subsequent quenching. Starting materials were Li2CO3, Fe(NO3)3·9H2O, Si(OC2H5)4 (TEOS) and water-soluble methylcellulose. Precursor preparation is based on the sol-gel processing and provides homogenous mixing at the molecular level. Structural analysis, morphology examination and electrochemical test of thus obtained powder were performed

The Li2FeSiO4 / c composites obtained from cellulose gel

In this study, monoclinic polymorph of Li2FeSiO4 (space group P21/n) in composite with carbon has been synthesized by sol-gel method followed by rapid heating, short high-temperature delay, and subsequent quenching. Three composites were made with 3, 9 and 14 weight percent of the carbon. The effect of the carbon on structure, morphology and electrochemical performance of the prepared composites has been examined by X-ray diffractometry, scanning electron microscopy and galvanostatic cycling

Operando characterization of batteries using x-ray absorption spectroscopy: advances at the beamline XAFS at synchrotron Elettra

International audience; X-ray absorption spectroscopy is a synchrotron radiation based technique that is able to provide information on both local structure and electronic properties in a chemically selective manner. It can be used to characterize the dynamic processes that govern the electrochemical energy storage in batteries, and to shed light on the redox chemistry and changes in structure during galvanostatic cycling to design cathode materials with improved properties. Operando XAS studies have been performed at beamline XAFS at Elettra on different systems. For Li-ion batteries, a multiedge approach revealed the role of the different cathode components during the charge and discharge of the battery. In addition, Li-S batteries for automotive applications were studied. Operando sulfur K-edge XANES and EXAFS analysis was used to characterize the redox chemistry of sulfur, and to relate the electrochemical mechanism to its local structure