Margaretha Hendrina Rossouw

Spinel Electrodes from the Li‐Mn‐O System for Rechargeable Lithium Battery Applications

The electrochemical and structural properties of spinel phases in the Li-Mn-O system are discussed as insertion electrodes for rechargeable lithium batteries. In this paper the performance of button-type cells containing electrodes from the Li{sub 2}O yMnO{sub 2} system, e.g., the stoichiometric spinel Li{sub 4}Mn{sup 5}O{sub 12}(y = 2.5) and the defect spinel Li{sub 2}Mn{sub 4}O{sub 9}(y = 4.0), is highlighted and compared with a cell containing a standard LiMn{sub 2}O{sub 4} spinel electrode.

Structural aspects of lithium-manganese-oxide electrodes for rechargeable lithium batteries

The structural characteristics of “LixMnOy” electrodes, prepared by reacting manganese oxides with lithium salts at 400°C–900°C, for ambient temperature, rechargeable lithium cells have been determined by powder X-ray and neutron diffraction studies. The identification of structure types and cyclic voltammetry data show that the rechargeability of the “LixMnOy” electrodes in Li“LixMnOy” cells can be attributed predominantly to a spinel component of the system LixMn2−zO4 (0≤x≤1.33 and 0≤z≤0.33) which includes the spinel phases LiMn2O4, Li2Mn4O9 and Li4Mn5O12.

Alpha manganese dioxide for lithium batteries: A structural and electrochemical study

Abstract A highly crystalline α-MnO 2 phase has been synthesised by acid treatment of Li 2 MnO 3 . A neutron-diffraction study has shown that the stoichiometry of this phase is A 0.36 Mn 0.91 O 2 (or MnO 2 ·0.2A 2 O) where A refers predominantly to H + ions and a very minor concentration of Li + ions. Heat-treatment at 300°C leaves a virtually anhydrous α-MnO 2 product. The absence of any foreign cation such as K + , Na + or Rb + within the channels of the structure has raised the possibility of utilizing the α-MnO 2 framework as a high performance electrode for secondary lithium cells. Preliminary electrochemical data indicate that capacities in excess of 200 mAh/g are achievable from these α-MnO 2 electrodes in room-temperature lithium cells. Cyclic voltammograms show that lithium is inserted into α-MnO 2 in a two-step process and that this process is reversible.

Lithium manganese oxides from Li2MnO3 for rechargeable lithium battery applications

Electrochemically active lithium-manganese-oxide phases have been synthesized by chemical leaching of Li2O from the rock salt phase Li2MnO3 (Li2O.MnO2) with acid at 25°C. Preliminary electrochemical tests have shown that capacities of approximately 200 mAh/g based on the mass of the lithium-manganese oxide electrode can be obtained in room-temperature lithium cells, and that capacities in excess of 140 mAh/g can be achieved on cycling. Although a detailed structure analysis of an extensively delithiated sample has not yet been undertaken, it is believed that it may be a novel layered lithium-manganese oxide compound Li2−xMnO3−x2 (0<x<2) with a cubic-close-packed oxygen anion array in which some of the Li+ ions are ionexchanged with H+ ions. Heat-treatment of an extensively delithiated Li2MnO3 sample at 300°C in air transforms the product to a γβ−MnO2 type phase, whereas delithiated samples that still contain an appreciable amount of lithium transform on heating to a two-phase product of Li2MnO3 and a compound with a spinel-related structure.

Ramsdellite-MnO2 for lithium batteries: the ramsdellite to spinel transformation

A pure and highly crystalline form of ramsdellite-MnO2 has been synthesized by acid treatment of the spinels LiMn2O4 and Li2Mn4O9 at 95°C. Although the ramsdellite—MnO2 framework remains intact on lithiation at 70°C, the hexagonally-close-packed oxygen array buckles towards a cubic-close-packed structure to accommodate the inserted lithium ions. The reaction is reversible but the instability of the structure on cycling limits the utility of ramsdellite-MnO2 as a rechargeable electrode in lithium cells. The ramsdellite structure can be stabilized by reaction with LiOH or LiNO3 at 300–400°C; this reaction, which displaces manganese ions from the MnO2 framework into interstitial octahedral sites generates spinel-related domains that coexist with the lithiated ramsdellite phase. At 300°C, under vacuum, the lithiated ramsdellite phase Li0.5MnO2 transforms to the spinel LiMn2O4; at 300–400°C, in air, it oxidizes slowly and transforms to a defect spinel LiMn2O4+δ (0 < δ ⩽ 0.5) via an intermediate compound. A mechanism for the ramsdellite—spinel transition is proposed.

Defect spinels in the system Li2O.yMnO2 (y>2.5): A neutron-diffraction study and electrochemical characterization of Li2Mn4O9

Abstract The structure of the defect spinel Li2Mn4O9 which is a component of the system Li2O.yMnO2 (y = 4.0) has been determined by neutron diffraction analysis; it has the spinel notation (Li0.89□0.11) [Mn1.78□0.22]O4. The electrochemical properties of Li2Mn4O9 when used as an insertion electrode in rechargeable room-temperature lithium cells have been evaluated.

The versatility of MnO2 for lithium battery applications

Manganese dioxide has for many years found widespread use as a cathode material in aqueous Leclanche, zinc chloride and alkaline cells and, more recently, in nonaqueous lithium cells. However, despite the large number of polymorphic structures that exist in the manganese dioxide family, the battery industry has used y-MnOz exclusively as the positive electrode in these cells. With the advent of rechargeable lithium battery technology, research efforts have demonstrated that other MnO, structures, when processed in the correct way, provide attractive electrochemical properties for lithium cells. In this paper, some recent advances that have been made in MnOz materials technology are discussed, for example, in the development of cr-MnOz, layered-MnO,, spine]-related L&O -yMnO* 01.2.5) and ramsdellite-MnO, materials. An attempt has been made to clarify issues relating to the structural features of ‘CDMO’-type materials that are prepared by the reaction of r_MnO, with LiNOB (or LiOH) at 300400 “C.

Synthesis of highly crystalline ramsdellite MnO2 and its lithiated derivative Li0.9MnO2

A method for the synthesis of highly crystalline ramsdellite MnO2 is described. Chemical lithiation of the highly crystalline material gave the derivative Li0.9MnO2 which has potential application in electrochemical cells.