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Broadening the portfolio of cathode active materials for Li-ion battery applications is now more important than ever. Recent focus on enabling diversity and security in supply chains, as well as concerns over sustainability of a massively growing energy storage market, have put emphasis on enabling more Earth-abundant cathode materials as an attractive strategy. With respect to relatively near-term options, manganese-based cathodes are particularly interesting. Herein we discuss some of the challenges associated with advancing the development of manganese-based oxides and, in particular, those that take advantage of complex local structures and/or over-lithiated compositions. Discussion centers on the representative, lithium- and manganese-rich class of cathodes and considerations to future development are given that range from the atomic-scale to the electrode level. [ABSTRACT FROM AUTHOR]

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]

Lithium- and manganese-rich (LMR) materials provide cost and environmental advantages to other competing cathodes based on nickel or cobalt chemistries. Within the LMR family, layered-layered-spinel (LLS) cathodes have unique properties, detailed herein, that address several of the challenges faced in large-scale implementation of LMR cathodes. This paper details how a LLS//graphite system was considerably improved by combining optimization strategies. First, a cathode surface-treatment process was optimized. Interestingly, cathodes surface-treated at a low temperature (~100°C) exhibited the best results. The optimized LLS cathode was tested vs. graphite using small amounts of lithium difluoro(oxalate)borate electrolyte additive. The combined approach improved various aspects of the electrochemical performance (e.g., impedance, cycle life, and coulombic efficiency) more than each strategy used alone by mitigating Mn dissolution from the cathode and the ensuing deposition on the anode. The report describes a unique method to improve the performance of practically relevant LMR//graphite cells. [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]

The work herein reports on studies aimed at exploring the correlation between electrolyte volume and electrochemical performance of full cell, pouch-cells consisting of graphite/Li1.02Ni0.50Mn0.29Co0.19O2 (NMC-532) as the electrodes and 1.2 M LiPF6 in ethylene carbonate:ethylmethyl carbonate (EC:EMC) as the electrolyte. It is demonstrated that a minimum electrolyte volume factor of 1.9 times the total pore volume of cell components (cathode, anode, and separator) is needed for long-term cyclability and low impedance. Less electrolyte results in an increase of the measured ohmic resistances. Increased resistance ratios for charge transfer and passivation layers at cathode, relative to initial values, were 1.5-2.0 after 100 cycles. At the cathode, the resistance from charge transfer was 2-3 times higher than for passivation layers. Differential voltage analysis showed that anodes were less delithiated after discharging as the cells were cycled. [ABSTRACT FROM AUTHOR]

Manganese dissolution from metal-oxide cathodes, and subsequent deposition at graphitic anodes, are considered to be key causes of capacity fade in lithium-ion batteries. The Mn2+ redox state is thought to be the major solvated Mn species, but its coordination environment is not well understood. Herein, we present the effects of Mn2+-containing electrolytes (Mn(PF6)2 and Mn(TFSI)²) on the performance of lithium-iron-phosphate//graphite (LFP//Gr) cells. Clear differences in first-cycle capacities and subsequent cycling efficiencies depending on the associated counter-ion indicate that the Mn coordination environment has a profound effect on the associated electrochemical degradation mechanisms. [ABSTRACT FROM AUTHOR]

Coin-cells are often the test format of choice for laboratories engaged in battery research and development as they provide a convenient platform for rapid testing of new materials on a small scale. However, reliable, reproducible data via the coin-cell format is inherently difficult, particularly in the full-cell configuration. In addition, statistical evaluation to prove the consistency and reliability of such data is often neglected. Herein we report on several studies aimed at formalizing physical process parameters and coin-cell construction related to full cells. Statistical analysis and performance benchmarking approaches are advocated as a means to more confidently track changes in cell performance. We show that trends in the electrochemical data obtained from coin-cells can be reliable and informative when standardized approaches are implemented in a consistent manner. [ABSTRACT FROM AUTHOR]

Lithium- and manganese-rich (LMR) transition metal oxide cathodes are of interest for lithium-ion battery applications due to their increased energy density and decreased cost. However, the advantages in energy density and cost are offset, in part, due to the phenomena of voltage fade. Specifically, the voltage profiles (voltage as a function of capacity) of LMR cathodes transform from a high energy configuration to a lower energy configuration as they are repeatedly charged (Li removed) and discharged (Li inserted). We propose a physical model of voltage fade that accounts for the emergence of a low voltage Li phase due to the introduction of transition metal ion defects within a parent Li phase. The phenomenological model was re-cast in a general form and experimental LMR charge profiles were de-convoluted to extract the evolutionary behavior of various components of LMR capacitance profiles. Evolution of the voltage fade component was found to follow a universal growth curve with a maximal voltage fade capacity of ≈20% of the initial total capacity. [ABSTRACT FROM AUTHOR]

High energy densities of lithium-rich transition metal oxides cannot be sufficiently maintained on cycling due to high-voltage first-cycle activation and the subsequent structural changes. These changes can be seen as a continuous decrease of the average voltage with cycling, known as voltage fade. Electrochemical and chemical insertion of protons has been reported suggesting that protons generated in the electrolyte could be involved in electrochemical cycling which could play a similar role in the "Li2MnO3 component" of lithium rich transition metal oxides. Here, electrochemical insertion of structural protons, changes in lithium occupancy at various states of charge, and changes in local structure have been investigated via a combination of local probes including solid state NMR, X-ray absorption spectroscopy and first principle calculations. While significant evidence is found for the deposition of non-structural proton-bearing species on electrodes, which accumulate with extensive cycling, structural proton insertion is not found to be a significant process directly effecting voltage fade. The electrochemical activity of disordered Li2MnO3, synthesized at low temperature, is also investigated and its Li removal/insertion properties measured quantitatively with NMR. Major reordering of Li sites and subsequent local structural transitions are observed by NMR and are found to be synchronous with voltage fade. [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]

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]

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]