Nanoscopic scale studies of LiFePO4 as cathode material in lithium-ion batteries for HEV application

Abstract

International audienceWe present a review of the structural properties of LiFePO4. Depending on the mode of preparation, different impurities can poison this material. These impurities are identified and a quantitative estimate of their concentrations is deduced from the combination of X-ray diffraction analysis, Fourier transform infrared spectroscopy, Raman spectroscopy, and magnetic measurements. An optimized preparation provides samples with carbon-coated particles free of any impurity phase, insuring structural stability and electrochemical performance that justify the use of this material as a cathode element a new generation of lithium secondary batteries

Graphene-modified LiFePO4 cathode for lithium ion battery beyond theoretical capacity

“…The outstanding cycling performance is attributed to the highly conductive few-layers graphene homogenously distributed around cLFP particles, which serve as a fast path for electron migration during the charge/discharge processes 18 . It is known that electron transfer in sp 2 carbon is more effective than in sp 3 amorphous carbon 34,35 . The electrons are capable of spreading to the entire surface of the EG/cLPF particles through the EG sheets during charge/discharge, improving the kinetics and reversibility of the lithium insertion/extraction cycles.…”

Nanotechnology for Energy Storage

“…The dramatic effect of the small grain-size material (<20 nm) on increasing the electrochemical activity (capacity) has been established recently for the lithium extraction/insertion reactions of LiCrO 2 electrodes. On the other hand, nanoparticles with a relatively high surface area may be reactive with electrolyte solutions based on alkyl carbonate solvents and LiPF 6 (which unavoidably contain detrimental contaminants such as HF, trace water, PF 5 and POF 3 ). Possible reactions with solution species may develop undesirable detrimental side reactions (especially on the high surface area particles) leading to the passivation phenomena and high electrode impedance.…”

“…First of all, the iron in the surface layer is trivalent. A significant amount of Fe 3+ is systematically detected in LiFePO 4 by M€ ossbauer experiments although they do not give any information on their location [5]. The magnetic properties are the first evidence that these Fe 3+ ions are localized in the surface layer.…”

“…That is why they can be used as a probe of any defect or impurity in its vicinity. This strategy was successful for the bulk [5], but also for the surface [77], with which we are concerned hereunder.…”

“…Nanoparticles, as well as more tailored nanostructures, are being explored and exploited to enhance rate, even for materials with poor intrinsic electronic conductivity such as olivine frameworks. For such a compound, by preparing the materials at the nanoscale form and by carbon coating, high rate are achievable [5]. In addition, the small electronic conductivity of the olivine particles that results from a two-phase FePO 4 /LiFePO 4 reaction has led to coating of the particles with a thin layer that is conductive of both electrons and Li, usually an amorphous carbon layer [6].…”