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Earth-abundant, sustainable cathode chemistries based on Mn are increasingly attractive for enabling a broader portfolio of cathode oxides. The well-known class of lithium- and manganese-rich cathodes still represents very viable options. However, despite the important work on understanding the mechanisms of voltage fade, hysteresis, and oxygen activity, relatively little attention has been given to understanding the impedance characteristics of these electrodes. In particular, an anomalous rise in area specific impedance at lower states of charge, as well as overall impedance rise and surface damage due to electrolyte interactions, represent critical barriers to implementation. This work presents a comprehensive study of impedance behavior in cobalt-free, lithium- and manganese-rich electrodes. The use of a robust surface treatment allows for long-term behavior to be probed in the absence of surface damage, capacity loss, and impedance rise due to electrolyte interactions. The anomalous rise in impedance could not be correlated to surface changes, or surface phase formation, but could be directly correlated with the bulk processes of voltage fade and voltage hysteresis. The activated material can be explained as a percolating network of higher-voltage, layered-type sites having facile Li diffusion. Interspersed throughout this network are lower-voltage, disordered sites that represent a significant barrier. [ABSTRACT FROM AUTHOR]

Preformation of graphite electrodes, in a highly fluorinated electrolyte, show exemplary performance when incorporated into LiNi0.5Mn0.3Co0.2O2//graphite cells (NMC//Gr) containing a traditional organic electrolyte. NMC//Gr cells, using preformed graphite electrodes, showed enhanced capacity and power retention as well as improved coulombic efficiencies. The increased performance was only observed with the use of specific electrolytes during the preforming step, where graphite electrodes, when preformed with the baseline organic carbonate electrolyte, did not show the same benefits. The identity of the preforming electrolyte was also observed to influence electrode crosstalk, where compounds generated at one electrode can affect the opposite electrode. The work herein presents both physical and electrochemical evidence of electrode crosstalk and reveals the beneficial effect of the preforming procedure in limiting the associated degradation mechanisms thereof. The insights gained may lead to new methodologies for the design of electrochemically robust interfaces that can enable high-voltage, lithium-ion batteries. [ABSTRACT FROM AUTHOR]

Composite electrode structures with layered and spinel components have been investigated to evaluate the possibility of arresting or suppressing the voltage fade observed on cycling high capacity, lithium- and manganese-rich 'layered-layered' xLi2MnO3 • (l-x)LiMO2 (M=Mn, Ni, Co) electrodes in lithium cells. Control of the spinel content in 'layered-layered-spinel' electrode materials and regulating the electrochemical voltage window of the lithium cells enables a capacity of approximately 190 mAh/g with little voltage fade. The results bode well for enhancing the electrochemical properties and structural stability of composite electrode structures on long-term cycling in lithium-ion batteries. [ABSTRACT FROM AUTHOR]

The results of a detailed structuralinvestigation on the influenceof cooling rates in the synthesis of lithium- and manganese-rich 0.5Li2MnO3·0.5LiCoO2composite electrodematerials, which are of interest for Li-ion battery applications,are presented. It is shown that a low-temperature, intermediate firingstep, often employed in cathode synthesis, yields a minor secondarycomponent representing a polydisperse distribution of lattice parameters,not found in the absence of low-temperature treatments. However, regardlessof the heating and cooling conditions employed, all samples presenttwo distinctly different local environments as evidenced by X-rayabsorption fine structure spectroscopy (XAFS) and nuclear magneticresonance (NMR) analysis. Transmission electron microscopy (TEM) datashow discrete domain structures that are consistent with the XAFSand NMR findings. Furthermore, high resolution synchrotron X-ray diffraction(HR-XRD), as well as the XAFS and NMR data show no discernible differencesbetween sample sets heated in similar fashion and subsequently cooledat different rates. The results contradict recent reports, using X-raydiffraction, that rapidly quenched samples of the same compositionare true solid solutions. This apparent discrepancy is assigned, inpart, to the inherent nature of conventional diffraction, which firmlyelucidates the average long-range structure but does not capture thelocal domain microstructure of these nanocomposite materials. Thecombined use of HR-XRD, XAFS, NMR, and TEM data indicate that chargeordering, which is initiated at relatively low temperatures, is thedominant force that produces a nanoscale, inhomogeneous compositestructure, irrespective of the cooling rate. [ABSTRACT FROM AUTHOR]

Structural and electrochemical data of xLi2MnO3∙(1-x)LiMn0.5Ni0.5O2 electrodes, as a function of Li2MnO3 content, x, are presented. Three distinct processes have been identified and tracked during extended electrochemical cycling. In addition to the standard intercalation behavior typical of layered metal oxide electrodes, two additional electrochemical phenomena, manifest as hysteresis and continuous voltage fade, are found to be directly related to one another. These two processes are a consequence of the Li2MnO3 component in the electrochemical reaction. This finding, coupled to X-ray absorption data, reveals that lithium and manganese ordering plays a significant role in the voltage degradation mechanisms of high-capacity lithium-and manganese-rich composite electrode structures. In general, all xLi2MnO3∙(1-x)(LiMO2 (M = Mn, Ni, Co) electrode materials possess this feature and are subject to similar degradation after activation (>4.5 V) and during high voltage (>4.0 V) cycling. The data highlight the practical importance of limiting the amount of Li2MnO3 and/or the extent of activation in these composite structures, thereby providing electrode stability to counteract voltage fade and hysteresis. [ABSTRACT FROM AUTHOR]

Abstract: An electrochemical study of structurally-integrated xLi2MnO3•(1−x)LiMn0.5Ni0.5O2 ‘composite’ materials has been undertaken to investigate the stability of electrochemically-activated electrodes at the Li2MnO3-rich end of the Li2MnO3–LiMn0.5Ni0.5O2 tie-line, i.e., for 0.7≤ x ≤0.95. Excellent performance was observed for x =0.7 in lithium half-cells; comparable to activated electrodes that have significantly lower values of x and are traditionally the preferred materials of choice. Electrodes with higher manganese content (x ≥0.8) showed significantly reduced performance. Implications for stabilizing low-cost, manganese-rich, layered lithium-metal-oxide electrode materials are discussed. [Copyright &y& Elsevier]

The concept of embedding a spinel component in high capacity, composite xLi2MnO3•(1-x)LiMO2 (M = Mn, Ni) 'layered-layered' structures to improve their electrochemical properties and cycling stability bas been exploited. In this paper, we report the preparation and electrochemical characterization of three-component 'layered-layered-spinel' electrodes, synthesized by lowering the lithium content of a parent 'layered-layered' 0.3Li2MnO3•0.7LiMn0.5Ni0.5O2 material while maintaining a Mn:Ni ratio of 0.65:0.35; such compounds can be designated generically by the system, LixMn0.65Ni0.35Oy, for which the end members are 0.3Li2MnO3•0.7LiMn0.5Ni0.5O2 (x = 1.3; y = 2.3), in which the average manganese and nickel oxidation states are 4+ and 2+, respectively, and LiMn1.3Ni0.7O4 (x = 0.5; y = 2) in which the corresponding average oxidation states are expected to lie between 4+ and 3.77+ for Mn, and 2.57+ and 3+ for Ni, respectively. For this study, compounds with a lithium content of x = 1.3, i.e., the parent 'layered-layered' composition, and 1.25 were selected for detailed and comparative investigation, the latter value corresponding to a targeted spinel content of 6%. The beneficial effects of 1) using Mg2+ as a dopant ion and 2) treating the electrode particle surface with an acidic solution of AIF3 to enhance cycling stability, reduce first-cycle capacity loss, and to slow voltage decay on cycling are discussed. [ABSTRACT FROM AUTHOR]

A new approach to synthesizing high capacity lithium-metal-oxide cathodes for lithium-ion batteries from a Li2MnO3 precursor is described. The technique, which is simple and versatile, can be used to prepare a variety of integrated `composite' electrode structures, such as 'layered-layered' xLi2MnO3•(1-x)LiMO2, `layered-spinel' xLi2MnO3•(1-x)LiM2O4, `layered-rocksalt' xLi2MnO3• (1-x)MO and more complex arrangements, in which M is typically Mn, Ni, and/or Co. Early indications are that electrodes prepared by this method are effective in 1) countering the voltage decay that occurs on cycling `layered-layered' xLi2MnO3•(1-x)LiMO2 electrodes without compromising capacity, and 2) reducing the extent of electrochemical activation required above 4.5 V on the initial charge. In particular, a 0.5Li2MnO3•0.5LiMn0.5Ni0.5O2 electrode, after activation at 4.6 V, delivers a steady capacity of 245 mAh/g between 4.4 and 2.5 V at 15 mA/g (~C/15 rate) with little change to the voltage profile; a first cycle capacity loss of 12%, which is significantly less than usually observed for `layered-layered' electrodes, has been achieved with a manganese-rich 0.1Li2MnO3•0.9LiMn0.50Ni0.37Co0.13O2 electrode. These results have implications for enhancing the performance of the next generation of high-energy lithium-ion batteries. The flexibility of the method and the variation in electrochemical properties of various composite electrode structures and compositions are demonstrated. [ABSTRACT FROM AUTHOR]

Abstract: Electrochemical studies demonstrate a strong correlation between the phenomena of hysteresis and voltage fade in lithium- and manganese-rich layered transition-metal oxide electrodes. A mechanism is proposed that entails both the reversible and irreversible migration of transition metal ions. Their reversible migration to a metastable configuration, suggested to involve the occupation of tetrahedral sites in the lithium layer, is manifested as a 1V hysteresis in site energy for 10–15% of the lithium content. The irreversible migration of the transition metal ions through the metastable ‘hysteresis’ sites to localized and lower energy cubic environments results in the observed voltage fade phenomenon. [Copyright &y& Elsevier]