Structural and Surface Modifications of LiFePO[sub 4] Olivine Particles and Their Electrochemical Properties

Abstract

LiFePO 4 -based olivine compounds were prepared by the usual ceramic method, where some modifications were carried out in order to improve the electrical conductivity of the cathode compound. Considering that the cathode is made up of electrochemical active particles and a nonactive polymer binder, two different methods were applied. The first one is related to the improvement of the interparticle conduction, and the other is the enhancement of the conductivity in the active particle itself. The former was attained with thermal decomposition of an organic additive ͑pyrene͒ during the sample preparation process, and the precipitated carbon was investigated with Raman spectroscopy. The bulk conductivity of the olivine was improved with a partial substitution of Fe 2+ with Mn 2+ , where the holes were incorporated into the valence band. These modifications significantly altered the electrochemical properties of the olivine cathode: large specific capacity ͑Ͼ140 mAh/g͒ and small capacity fading. Although the importance of carbon deposition was confirmed as reported elsewhere, the structural modification effect was also more important than the surface one. The result will contribute to reduce carbon content of LiFePO 4 -based positive electrodes, which is important for their practical use.

Modeling the Effects of the Cathode Composition of a Lithium Iron Phosphate Battery on the Discharge Behavior

“…Despite the numerous advantages of LFP, its low electronic and ionic conductivities seriously limit its rate capability [2][3][4]. To overcome these limitations, many studies have been carried out, including particle size reduction [5][6][7], coating [8][9][10], and doping [11][12][13]. Even though the proper fabrication process of LFP has been identified, the composition of a LFP cathode consisting of active material, conductive additives, and binders should be optimized in order to tailor the LFP battery to a specific application.…”

Developments in Nanostructured Cathode Materials for High‐Performance Lithium‐Ion Batteries

“…Pioneering work on carbon-coated LiFePO 4 was carried out by Ravet et al [114,115] Sucrose was used as one carbon source [115] and was added on the initial hydrothermal samples [116] or during pyrolysis. [117] Other methods include thermal decomposition of pyrene [118] or citric-acid-based sol-gel processing. [119] It should be noted that the electrochemical properties Raman spectroscopy and H/C ratios determined from elemental analysis.…”

LiMnPO[sub 4] as an Advanced Cathode Material for Rechargeable Lithium Batteries

“…2 Among them, LiMnPO 4 is of particular interest as it offers the advantages of a flat discharge voltage profile at 4.1 V vs Li/Li + , the expected safety features, and an abundance of the relevant elements in the earth's crust. [1][2][3][4][5][6] Hence, LiMnPO 4 can be an ideal substitute for the commonly used cathode material, LiCoO 2 , which is expensive, toxic, and demonstrates problematic safety features. The three-dimensional framework of the olivine structure is stabilized by the strong covalent bonds between the oxygen and the P 5+ ions, resulting in PO 4 3− tetrahedral polyanions.…”

“…This indicates that LiMPO 4 electrodes may demonstrate better stability and capacity retention during prolonged cycling as compared to lithiated transition-metal oxide cathode materials such as LiCoO 2 , LiNiO 2 , LiMnO 2 , and LiMn 2 O 4 . However, LiMPO 4 compounds and LiMnPO 4 , in particular, suffer from poor electronic and ionic ͑Li + ͒ conductivity, which means a limited rate capability ͑especially at low temperatures͒. 1,4 Nevertheless, LiFePO 4 is now recognized as one of the most promising cathode materials due to the availability of a variety of synthetic routes for the production of nanoparticles coated by conducting phases ͑e.g., carbon͒.…”

“…However, LiMPO 4 compounds and LiMnPO 4 , in particular, suffer from poor electronic and ionic ͑Li + ͒ conductivity, which means a limited rate capability ͑especially at low temperatures͒. 1,4 Nevertheless, LiFePO 4 is now recognized as one of the most promising cathode materials due to the availability of a variety of synthetic routes for the production of nanoparticles coated by conducting phases ͑e.g., carbon͒. [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] The use of nanoparticles as the active mass helps to overcome kinetic problems due to the short diffusion length for ionic transport and a relatively high surface area, which promotes fast interfacial charge transfer.…”