Abstract
For the next generation Li-battery anode materials LiFePO4, the forming of the solid solution phase LixFePO4 and the related charge/discharge mechanism are the high light topics recently. In the paper, ab-initio calculation was applied to study the formation and electronic structure of the solid solution of LixFePO4, and a Charge/Discharge model of LiFePO4 was set up based on the calculation results. Due to the high formation energy, LixFePO4 separates into FePO4 and LiFePO4 in bulk system under room temperature. The single solid solution phase LixFePO4 could exists in the nanoscale particle, and it is due to that the relative larger lattice mismatch energy. The nanoscale particle materials should have a good rating performance due to the forming of LixFePO4 in solid solution phase, of which the partially occupied state and the small energy gap between the VBM and the defect state could improve the intrinsic electronic conductivity. In bulk materials, the medium region, which is composed of LixFePO4, is very narrow between the two phases FePO4 and LiFePO4. There is a electron potential well in the region, of which the bottom is at the side of LixFePO4 (x<0.5). The number of electron in the well highly affects the lithium insertion and extraction. In order to efficiently transfer the electron between the potential well and the out circuit, an electron conductor network or layer should be coated on the LiFePO4 particle.
Highlights
As an alternative generation cathode materials of lithium ion batteries, LiFePO4 have several advantages compared with conventional cathodes: lower cost, more safety, lower toxicity, and a reasonable high potential
The first problem has been solve by adding the conductive phase, typically carbon, which led to a room temperature capacity up to 160 mAhg-1. [1,2,3,4,5,6,7,8] The second problem is mainly attributed to the FePO4/LiFePO4 two-phase charge/discharge mechanism which is firstly mentioned by Yamada and co-workers. [9, 10]
The theoretical studies reported by Morgan et al, [11] Ouyang et al [12] and Islam et al [13] showed that LiFePO4 is an one-dimensional ionic conductor, and the lithium ions only migrate along the [10] direction, and the conclusion was confirmed with the neutron diffraction technique by Nishimura et al
Summary
Email address: To cite this article: Jun Yu, Shaorui Sun. A Theoretical Study of the Solid Solution Phases of LixFePO4. Received: November 2, 2020; Accepted: November 16, 2020; Published: November 24, 2020
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