Singular Structural and Electrochemical Properties in Highly Defective LiFePO₄ Powders

Abstract

Highly defective LiFePO4 powders were synthesized via a modified version of the co-precipitation in aqueous medium method using oxidizing experimental conditions. A pure olivine phase containing 44 at.% of Fe 3+ is obtained after only 10 minutes at 108 °C, and the evolution of the structure and purity is followed during reaction. The nature of the native defects and their influence on the crystallographic structure and on the electrochemical reaction mechanisms are thoroughly studied by a combination of ex situ and in situ methods, using high-resolution transmission electron microscopy, inductive coupled plasma, X-ray diffraction and Mössbauer spectroscopy. The high concentration of defects induces a unit-cell volume 4 Å 3 smaller than that of stoichiometric LiFePO4, with a complete cationic redistribution over the M1 and M2 crystallographic sites, and a completely new electrochemical signature. A precise structural model during electrochemical operation of the pristine defective "LiFePO4" is built.

Accelerated Removal of Fe-Antisite Defects while Nanosizing Hydrothermal LiFePO4 with Ca2+

“…We also observed the formation of Fe 2 P 2 O 7 in this case, while no Fe 2 P 2 O 7 was observed in the LFP@C sample (Fe-antisite defect free) obtained after 5 h of synthesis. This impurity was already detected after carbon coating by Wang et al 18 at the surface of LiFePO 4 and recently by Masquelier et al 19 in deficient Li-ion LiFePO 4 structure. These results are in agreement with the observations by HAADF-STEM imaging ( Figure 6).…”

Electrochemical kinetics of nanostructure LiFePO 4 /graphitic carbon electrodes

“…Accordingly, the electrochemical signature can be assigned, in a first approach, to a pseudocapacitive behavior. This pseudocapacitive behavior is extrinsic in origin, since it is related to the presence of Fe 3+ defects in the structure [15,21,22]. The capacitive current observed below 2.5 V and beyond 3.4 V corresponds to the double-layer capacitance of the graphitic carbon shell, since no change in the oxidation state of Fe was observed [18]; it accounts for about 25% of the total capacity.…”

“…This means that the peak B (amorphous LFP) characteristic is associated with a fast, nondiffusionlimited, surface reaction such as observed for pseudocapacitive materials. Differently from MnO 2 [4,5], TiO 2 [6] or Nb 2 O 5 [16], this pseudocapacitive behavior is extrinsic in origin, since it is related to the presence of Fe 3+ defects in the structure [15,21,22]. To get further insights on the electrochemical reaction kinetics in the two different potential ranges (peaks A and B), we divided the total current into two contributions such as proposed by Dunn's group [15,16,26,27].…”

Direct regeneration of cathode materials from spent lithium iron phosphate batteries using a solid phase sintering method

“…1,2 Among the numerous cathode materials of lithium ion batteries, lithium iron phosphate (LiFePO 4 ) with a theoretical capacity of 170 mA h g À1 , a theoretical energy density of 550 W h kg À1 , high rate discharge, good cycle performance, stable structure and safety performance has become suitable for electric cars and other large energy requirements. [3][4][5][6][7][8] At present, the synthetic methods for LiFePO 4 mainly include high temperature solid state, microwave synthesis, hydrothermal synthesis, coprecipitation method, dry emulsion method, etc. [9][10][11] With the huge investment and policy support worldwide, electric car market will exhibit blowout development in the next few decades.…”