Synthesis of a Polyanion Cathode Material, Li[sub 2]Co[sub 2](MoO[sub 4])[sub 3], and Its Electrochemical Properties for Lithium Batteries

Abstract

High voltage redox properties of a polyanion material, Li 2 Co 2 (MoO 4 ) 3 , as positive electrode was demonstrated against lithium for the first time. The orthorhombic structure showed reversible extraction and insertion cycles of lithium at a potential of ca. 4.9 V vs. Li ϩ /Li as well as 1.5 V. The former potential was attributed to Co 2ϩ /Co 3ϩ and the latter to Mo 6ϩ /Mo 5ϩ . The reason for the change in charge/discharge curves after the first charge is clearly demonstrated by the structural changes ͑monoclinic, P2/m) caused by electrochemical extraction and insertion of lithium as deduced from the ex situ X-ray diffraction analysis on the cycled electrode pellet.Information and communication technology ͑ICT͒ occupies a place of pride in our modern society. Various mobile electronic appliances have become inseparable commodities of our daily life. Lithium rechargeable batteries are promising systems of stationary and portable energy storage for renewable energy systems in the 21st century. Although rechargeable Li-ion technology has been commercialized for more than a decade, the research trend in today's lithium-ion batteries is to improve the working voltage ͑energy density͒ and capacity to cope with power hungry devices. The needs of portable power obviously require investigation of new electrode materials. In this context, the search for new cathode materials is inevitable and various types of new materials are being investigated. [1][2][3][4] A step ahead in new materials development is an interesting class of polyanion based sodium superionic conductor ͑NASICON͒ framework type lithiated transition metal oxides that show tremendous potential for use in rechargeable lithium batteries. Recent report in the above category is the development of transition metal compounds with ordered olivine and/or modified olivines, and also the rhombohedral NASICON structure containing the polyanion, (PO 4 ). [3][4][5] The open three-dimensional ͑3D͒ crystal structure in these framework type compounds facilitates easy diffusion of smaller alkali cations like lithium. Many lithium containing compounds incorporating polyanions such as olivine type LiMЈXO 4 (MЈ ϭ transition metal and X ϭ P, Mo, W, S͒ and NASICON-type Li x M 2 Ј(XO 4 ) 3 (MЈ ϭ Ti, Fe, V and X ϭ P, As, Mo, W, S͒ have been reported. 6-12 Despite their inherent insulating nature ͑low electronic conductivity͒, 13,14 tremendous interest has been shown to understand the Li ϩ insertion/extraction behavior of these materials because of their potential application in new generation lithium batteries.Lithium insertion properties of lithium-free phases of Fe 2 (XO 4 ) 3 (X ϭ Mo, W, and S͒ and Ni 2 (MoO 4 ) 3 have been studied. [6][7][8]15 Gaubicher et al. 2 and Andersson et al. 12 have investigated the effect of insertion of additional lithium into Li 3 V 2 (PO 4 ) 3 and Li 3 Fe 2 (PO 4 ) 3 . Nevertheless, according to our knowledge, lithium extraction/insertion from and into Li 2 M 2 Ј(XO 4 ) 3 ͓MЈ ϭ Mn, Ni, and Co and X ϭ Mo and W͔ lithiated phases has not been studi...

The Adaptable Lyonsite Structure

“…High electrical conductivity was first observed for Li 2 Cu 2 A C H T U N G T R E N N U N G (MoO 4 ) 3 in 1981, [52] and a significant effort has since been made to investigate the conductivity of many of the molybdates. [19,[53][54][55][56][57][58] The lyonsite structure fits the criteria for NASICON ion conductors owing to the arrangement of the isolated (MO 4 ) nÀ polyanion tetrahedra. A review of various families of A x B y A C H T U N G T R E N N U N G (MoO 4 ) z molybdate families discusses the ionic conduction of lyonsite type molybdates.…”

Nano-sized copper tungstate thin films as positive electrodes for rechargeable Li batteries

“…Molybdates and vanadates are the typical ones, which have been widely investigated as posi- * Corresponding author. tive electrodes for rechargeable lithium cells [3][4][5][6][7][8]. Unlike the phosphate [9][10][11][12], where the polyanion PO 4 3− serves only as a structural framework and is not electrochemically active, the materials based on Mo-O and V-O polyanions provide additional capacity due to the expected redox activity of Mo 6+ /Mo 4+ and V 5+ /V 4+ .…”

New molybdate Li2Co2−x Nix (MoO4)3 (0⩽x⩽2) materials with a lyonsite structure: X-ray diffraction and Raman spectroscopy studies

“…Thus, it is revealed now that the open framework-type polyanion family of compounds with the general formula Li 2 M 2 (MoO 4 ) 3 (M = transition metal) indeed exemplifies the topotactic extraction/insertion of Li + within the framework [27]. The compounds Li 2 M 2 (MoO 4 ) 3 and Li 3 M(MoO 4 ) 3 (M = Fe, Co, Ni) are isostructural and attracted recently attention, because of their ability for reversible Li insertion [26][27][28]. They crystallize in a lyonsite-type structure, which was first described for the Na, Co-containing molybdate with NaCo 2.31 (-MoO 4 ) 3 stoichiometry [29].…”