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Elektroda interkalacyjna w ogniwie litowym z niewodnym roztworem elektrolitu. [Cz.] 1. Dwutlenek manganu i tlenki litowo-manganowe

Bełtowska-Brzezińska M., Kozik T., Jaworska H.

Wiadomości Chemiczne

2001

[Z] 55, 3-4

289-329

Lithium batteries of various types have found use in portable electronic devices and are also considered for application in electric or hybrid vehicles because of their high operating voltage and energy density. Among a number of materials examined as the positive electrode in lithium batteries with organic electrolyte solution, much attention has been paid to transition metal oxides, in particular to manganese dioxide and its lithiated derivatives. Electrochemical studies have proved that these compounds are able to accommodate or remove Li+ ions in parallel with the electron injection or extraction thus changing the oxidation state of manganese (IV/III) upon the solid state redox reaction. The capacity and power density of intercalation electrodes varies with the crystallographic and electronic structure of their solid phase, electrode thickness and porosity as well as the chemical nature and conductivity of the electrolyte solution. The kinetics of the electrochemical intercalation-deintercalation of Li+ ions is mostly limited by the diffusion of these ions into or from the host matrix. Another limitation comes from an electrolyte depletion in pores of the electrode material during the discharge, as the rate of the Li+ ions transport from the bulk electrolyte is lower in comparison with the charge transfer rate at the electrode/electrolyte interface. The diffusion model for nonporous and porous intercalation electrodes quite well describes the surface and bulk distribution of Li+ ions in the solid phase as well as in the pore electrolyte, as a function of the discharge rate and discharge degree. The experimental characteristics of MnO2 and compounds of the Li-Mn-O system, obtained at various electrode thickness, particle size and charge-discharge density has confirmed the theoretical predictions. Manganese dioxide (g-MnO2) electrodes having discharge capacity of 220-270 Ah/kg at Eť3 V vs. Li/Li+ show a limited rechargeability on charge-discharge cycling in secondary lithium cells. As evidenced by XRD-ray patterns this is due to anisotropic expansion and contraction of the crystallographic unit cell at the average manganese valence of about +3.5. A significantly higher cycling efficiency can be achieved with MnO2(CDMO) and Li-Mn-O spinel phases, providing a three-dimensional interstitial space for Li+ ions transport. The cubic close-packed structure of the stoichiometric LiMn2O4 remains almost unchanged upon deintercalation to l-MnO2 and subsequent reintercalation to x ť 1 in the potential range E ť 4 V (vs. Li/Li+). One can obtain the rechargeable capacity of 125 Ah/kg at moderate current rates owing to the relatively fast solid state diffusion of Li+ ions for 0< x <1. Two further potential plateau's at E ť 3 V and E ť 1 V correspond to the intercalation degree of 1< x <2 and 2< x <4 upon a cubic-tetragonal and tetragonal-trygonal phase transition, respectively. The identification of three distinct regions in the potential-composition (E-x) curves at makes the basis for spinel electrodes application in energy storage devices. In the last years, several overlithiated and defect spinel phases of the general formula (...) have been used in the so-called "lithium-ion" batteries with the carbon based negative electrode. Alternative lihium-ion batteries contain two transition metal oxides having different intercalation potentials. Quite recently, a family of mixed spinel oxides Li (...) has been proposed for the positive electrode, Li[Li0,33Ti1,67]O4 as the negative electrode. Future improvement of the charge-discharge performance of spinel electrodes for primary and secondary lithium batteries can be expected under a complex optimisation of the synthesis methods, the electrode mophology, porosity and thickness. Furthermore, the advanced batteries require the high conductivity electrolyte-solvent systems, stable in the potential range of at least 0 to 5V.