TEM Studies: The Key for Understanding the Origin of the 3.3 V and 4.5 V Steps Observed in LiMn2O4-based Spinels

✍ Scribed by L. Dupont; M. Hervieu; G. Rousse; C. Masquelier; M.R. Palacı́n; Y. Chabre; J.M. Tarascon

• Publisher: Elsevier Science
• Year: 2000
• Tongue: English
• Weight: 994 KB
• Volume: 155
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.2000.8940

✦ Synopsis

Transmission electron microscopy (TEM) measurements were performed on electrochemically partially delithiated prepared spinel Li 1؊x Mn 2 O 4 samples. The potential+composition pro5le of LiMn 2 O 4 exhibits (besides the two plateaus at 4.05 and 4.1 V) two additional redox steps of identical capacity at 4.5 and 3.3/3.95 V. We found by TEM studies that these extra steps are the signature of a reversible phase transition between LiMn 2 O 4 spinel type structure and a new Li 1؊x Mn 2 O 4 double hexagonal (DH) type structure (a+5.8 A > , c+8.9 A > , P6 3 mc). The latter is isotypic with DH LiFeSnO 4 . Selected area electron di4raction (SAED) and high-resolution transmission electron microscopy (HRTEM) made it possible to identify the mechanism by which this cubic+DH phase transition occurs within a particle. Based on the structural 5ndings the origin as well as the similar electrochemical capacity of the 3.3/3.95 and 4.5 V anomalies are explained.