Isolation of Solid Solution Phases in Size‐Controlled Li_xFePO₄ at Room Temperature

Abstract

State‐of‐the‐art LiFePO4 technology has now opened the door for lithium ion batteries to take their place in large‐scale applications such as plug‐in hybrid vehicles. A high level of safety, significant cost reduction, and huge power generation are on the verge of being guaranteed for the most advanced energy storage system. The room‐temperature phase diagram is essential to understand the facile electrode reaction of LixFePO4 (0 < x < 1), but it has not been fully understood. Here, intermediate solid solution phases close to x = 0 and x = 1 have been isolated at room temperature. Size‐dependent modification of the phase diagram, as well as the systematic variation of lattice parameters inside the solid‐solution compositional domain closely related to the electrochemical redox potential, are demonstrated. These experimental results reveal that the excess capacity that has been observed above and below the two‐phase equilibrium potential is largely due to the bulk solid solution, and thus support the size‐dependent miscibility gap model.

Response to “unsupported claims of ultrafast charging of Li-ion batteries”

“…We deal with each of these arguments in turn. Undoubtedly, exposure to air can extract Li from the surface and thereby create Fe 3+ as shown by some of the authors of the Comment as well as by others [7,8]. We do not dispute this but argue that Fe 3+ in our materials is already present in the asmade material.…”

Systematic Studies on “Abundant” Battery Materials: Identification and Reaction Mechanisms

“…6). 11 Thermodynamically, the dependence can be explained by the increasing contribution of the elastic energy induced along coherent two-phase interphase in the smaller particles by a factor of r ³ A(x)/V(x), where r is the particle radius, A(x) is the interface area, and V(x) is the particle volume.…”

Effect of Li4Ti5O12 Particle Size on the Performance of Lithium Ion Battery Electrodes at High C-Rates and Low Temperatures

“…Reduction of the voltage plateau domain has been observed in all these materials when particle size is reduced to nanosize. In case of LiFePO4 which also exhibits a two phase lithium insertion reaction this is associated with the reduction of the miscibility gap due to strain and interface energy between the end members LiαFePO4 and Li1-βFePO4 13 . However, as LTO is a zero strain material the origin of the curved voltage plateaus is different and it is suggested to result from different environments in the surface region and bulk 11 .…”