In SituObservation and Mechanism Investigation of Lattice Breathing in Vanadium Oxide Cathode

Abstract

As cathode materials in lithium-ion batteries, layered vanadium oxides have been extensively studied and used in many aspects varying from industrial production to our daily life, due to their excellent physical property and gorgeous lithium storage performance. During lithiation/delithiation, layered vanadium oxides such as V 2 O 5 xerogel (with a bilayer structure), undergoes "lattice breathing" which leads to the deactivation of electrode materials and fast capacity fading, which limits its large-scale application. In this work, VO x is used as the cathode material of lithium-ion batteries to study the "lattice breathing" phenomenon. The phase evolution has been observed and studied via in situ method. The X-ray diffraction (XRD) patterns show typical (001) diffraction peaks characteristic of vanadium oxide xerogel structure and also confirm the good crystallinity. This compound with crystal parameters of a＝4.56 Å, b＝14.87 Å, c＝12.38 Å, α＝117.26°, β＝96.02°, γ＝ 81.86°, forms a triclinic structure. Results of scanning electron microscope (SEM) and transmission electron microscope (TEM) further verify the layered structure of VO x . The thermo gravimetric analysis (TGA) at air and nitrogen atmosphere shows that the carbon content of the sample is about 2.4 wt% and the water content is about 2.1%. As lithium-ion battery cathode the initial discharge capacity of the compound is about 136 mA•h/g at a current density of 100 mA/g, with a capacity retention of 92.6% after 50 cycles. To study the lithium storage mechanism of VO x , electrochemical discharge/charge processes are further investigated by in situ XRD. It is found that the lattice plane diffraction displays three different stages linked during the insertion and deinsertion of lithium ions, indicating three solid solution reactions. During discharge process, the three diffraction changes show continuous shifts to higher diffraction angles, demonstrating three different continuous contraction processes with the insertion of lithium ions. Nevertheless, the evolution of the (001) peak is swift during the beginning and the end of discharge, in contrast to the slow deviation of the intermediate process. In the whole process, the diffraction pattern displays periodic changes, confirming the reversibility of the reaction process. The corresponding calculations of d 001 during the discharge/charge process prove the notable discontinuity between these three stages. In addition, cycling experiments conducted at the higher and the lower temperature indicate that the electrochemical performance of this compound is highly sensitive to temperature.

Pyrene-Based Conjugated Microporous Polymer as High Performance Electrode for Lithium-Ion Batteries

“…共沉淀-高温固相法制备了均匀微球形貌的高性能镍基 正极材料 LiNi 0.5 Co 0.2 Mn 0.3 O 2 ; Zhang 等 [6] 研究了层状钒 氧化物正极材料的充放电机理. 而锂离子电池负极材料 主要包括碳材料、金属及金属氧化物等 [7～9] .…”