Search

Novellithium metal polymer solid state batteries with nano C-LiFePO4and nano Li1.2V3O8counter-electrodes(average particle size 200 nm) were studied for the first time byin situ SEM and impedance during cycling. The kinetics of Li-motionduring cycling is analyzed self-consistently together with the electrochemicalproperties. We show that the cycling life of the nano Li1.2V3O8is limited by the dissolution of the vanadiumin the electrolyte, which explains the choice of nano C-LiFePO4(1300 cycles at 100% DOD): with this olivine, no dissolutionis observed. In combination with lithium metal, at high loading andwith a stable SEI an ultrahigh energy density battery was thus newlydeveloped in our laboratory. [ABSTRACT FROM AUTHOR]

3d-metal fluorosulphates that have a tavorite-type structure (e.g., LiFeSO4F) were recently reported as attractive positive electrode candidates for future Li-ion batteries aimed at large volume markets. These new fluorosulphates had to be synthesized via ionothermal synthesis owing to both their thermal instability at temperatures greater than 300 °C and their water solubility. In an attempt to depart from ionothermal synthesis, low-temperature solid-state reactions and solvothermal processes were successfully tried. The latter technique, which is reported herein, proceeds with water as the solvent and has led to a new family of fluorosulphates NaMSO4F·2H2O that crystallize in a monoclinic unit cell (SG =P21/m)similar to the uklonskovite-type structure earlier proposed for NaMgSO4F·2H2O. These new phases show no electrochemical activity with either Li or Na metal and have room temperature ionic conductivities on the order of 1 × 10−9S cm−1. Additionally, we have discovered the feasibility, upon controlled dehydration of the NaMSO4F.2H2O phases, to prepare NaMSO4F phases adopting a derived tavorite-type structure and displaying ionic conductivities around 10−7S cm−1. Finally, this finding opens the possibility to achieve Li-based fluorosulphates via two-step synthetic pathways. [ABSTRACT FROM AUTHOR]

Fluoride-based materials have regained interest within the field of Li-ion batteries largely due to the advent of nanosizing which has transformed the insulating insertion compounds into attractive electrode materials. Herein we demonstrate the effectiveness of ionothermal synthesis in the preparation of nanometric LiFePO4F and LiTiPO4F phases with structures isotopic to tavorite LiFePO4(OH) at temperatures of only 260 °C, while temperatures of 600−700 °C are required to obtain coarse powders via the ceramic method. However, the redox-active phases, which are obtained in a high state of division, have lower redox voltages than LiFePO4despite the presence of fluorine. Additionally, LiTiPO4F shows staircase charge/discharge profiles with Ti2/3+and Ti3/4+couples. Though quite unusual in lithium intercalation oxides, a hint of a Li-driven Fe3/4+transition has been detected in LiFePO4F. [ABSTRACT FROM AUTHOR]

As opposed to ceramic methods, low-temperature solvothermal-hydrothermal methods using liquid media as reaction support are less energy demanding to design new electrode materials; therefore, they tend to replace ceramic routes. Here, we report the use of ionic liquids as both solvent and template to enable the growth of LiFePO4(LFP) powders with controlled size and morphology at temperatures at least 200 °C lower than those required for conventional ceramic methods, while showing excellent electrochemical performances versus lithium. An inherent advantage to the use of ionic liquids lies in the feasibility of carrying out the reaction at atmospheric pressure. Besides, the recovery of the powders from the reacting medium is particularly easy, as are the effluents and ionic liquid recycling. Additionally, it is shown that ionic liquids can be used as a structural directing agent to orient crystal growth and obtain powders adopting a single morphology. Needless to say, such a new approach, which is not specific to LiFePO4, offers great opportunities for the low-temperature synthesis of new electrode materials. [ABSTRACT FROM AUTHOR]

The recent infatuation for LiFePO 4as positive electrode material in Li-ion batteries has prompted a renewed interest in olivine-type structures, with a view to enhance their conduction properties. We show that the dual substitution of Li for Fe and of P for Si in the olivine LiFePO 4phase leads to a complete solid solution Li 1− xFe 1+ xP 1− xSi xO 4as deduced from combined X-ray diffraction, Mössbauer, and NMR experiments. Our findings challenge the common belief that the anionic network cannot be substituted. Moreover, it is found that such a substitution promotes Li intersite mixing between the olivine M1 and M2 sites. Such mixing, together with the worsening of the conducting properties of the dually substituted samples, is believed to be responsible for the poor electrochemical performances of the member’s series. Beyond x= 0.20, the samples were electrochemically inactive. While the current materials are disappointing application-wise, such a study provides clues to the rich chemistry remaining to be unveiled with olivine-type structures in particular and polyanionic compounds in general. [ABSTRACT FROM AUTHOR]