Overview of olivines in lithium batteries for green transportation and energy storage

Abstract

We present the progress on the physical chemistry of the olivine compounds since the pioneering work of Prof. John Goodenough. This progress has allowed LiFePO 4 to become the active cathode element of a new generation of Li-ion batteries that makes a breakthrough in the technology of the energy storage and electric transportation. This achievement is the fruit of about a decade of intensive research in the electrochemical community during which chemists, electrochemists, and physicists added there efforts to understand the properties of the material, to overcome the obstacles that were met on the way, and finally to reach the state of the art that allows its commercial use for worldwide applications in the industry today. These obstacles involved carbon coating, purification, control of the surface, the progressive decrease of the size of the particles down to nanoscale, and comprehensive investigation of surface effects. Nevertheless, heterogeneity in the quality of the product available on the market is damaging and may even be an obstacle to the development of new demanding technologies such as electric transportation. Emphasis is placed on the quality control that is needed to guarantee the reliability and the optimum electrochemical performance of this material as the active cathode element of Li-ion batteries. The route to increase the performance of Li-ion batteries with the other members of the family is also discussed. Since Prof. John Goodenough not only initiated the work but also played a major role in the research and development on these materials through the years, the present review is dedicated to him.

Electrochemical Performance and Delithiation/Lithiation Characteristics of Mixed LiFe1-yMyPO4(M= Co, Ni) Electrode Materials

“…Olivine-structured metal phosphates LiMPO 4 (M = Fe, Mn, Co, Ni) are an interesting material family to replace the layered metal oxides LiMO 2 as the positive electrode. [1][2][3][4] Their safety owing to their intrinsic structural stability is very tempting for large-scale batteries. The orthorhombic olivine structure (space group Pnma) is composed of LiO 6 and MO 6 octahedra and PO 4 tetrahedra, such that Li + -ion diffusion during lithiation/delithiation takes place only in one dimension, along the b axis.…”

“…[1][2][3][4] Their safety owing to their intrinsic structural stability is very tempting for large-scale batteries. The orthorhombic olivine structure (space group Pnma) is composed of LiO 6 and MO 6 octahedra and PO 4 tetrahedra, such that Li + -ion diffusion during lithiation/delithiation takes place only in one dimension, along the b axis. 3,5 The iron-based olivine LiFePO 4 is already commercially used in Li-ion batteries; it shows a theoretical capacity of 170 mAh g −1 , high safety and cycle stability, and is in addition cheap and environmentally friendly.…”

“…8,9 Existence of wider single-phase areas or formation of a metastable intermediate phase have been proposed for extreme conditions (elevated temperatures, 10 high current rates, 11 and nano-sized particles 12 ). The poor electronic and ionic conductivity properties of LiFePO 4 have been successfully overcome by decreasing the active material particle size and by coating the particles with a conductive carbon layer. 13,14 Also substituting iron with isovalent or aliovalent transition metal species has been reported to increase the conductivity and enhance the battery performance at low substitution levels.…”

“…However, in practice discharge capacities of typically only 100-120 mAh g −117, [19][20][21][22][23][24][25] or even less 18,[26][27][28][29] are achieved, and the capacity fade during continuous cycling has moreover been rapid. The reasonably poor electrochemical performance and its fast deterioration have been attributed to the low electronic conductivity (lower than for LiFePO 4 ), 30,31 slow Li + -ion diffusion, 32,33 possible irreversible structural changes while charging, 26 and to the electrolyte oxidation at high potentials 21,23 and possible hydrogen fluoride generation. 34 Furthermore, the fully-delithiated CoPO 4 phase is unstable in air and undergoes amorphization.…”

“…The reasonably poor electrochemical performance and its fast deterioration have been attributed to the low electronic conductivity (lower than for LiFePO 4 ), 30,31 slow Li + -ion diffusion, 32,33 possible irreversible structural changes while charging, 26 and to the electrolyte oxidation at high potentials 21,23 and possible hydrogen fluoride generation. 34 Furthermore, the fully-delithiated CoPO 4 phase is unstable in air and undergoes amorphization. 21 Unlike the one-step, two-phase reaction mechanism of LiFePO 4 , the delithiation/lithiation reaction of LiCoPO 4 proceeds in two steps, consisting of two two-phase regions, LiCoPO 4 ↔Li x CoPO 4 and Li x CoPO 4 ↔CoPO 4 , 21 the intermediate phase composition being found at x = 0.7 21,35 or x = 2/3, 23 although x = 0.2 -0.45 has been suggested as well.…”