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A novel LiMn0.5Ni0.5O2 cathode with a predominant, partially-disordered lithiated-spinel structure has been prepared by a 'low temperature' (LT) synthesis. Li/LT-LiMn0.5Ni0.5O2 cells operate between 5.0 and 2.5 V with good cycling stability, yielding a capacity of 225 mA h g−1, principally by redox reactions on the nickel ions on distinct voltage plateaus at ∼3.6 V and ∼4.6 V. [ABSTRACT FROM AUTHOR]

The necessity of developing low-cobalt cathode oxides for lithium-ion batteries is increasingly apparent. The most popular strategy followed thus far in addressing this issue has been the development of LiNiO 2 -like, Ni-rich, layered LiMO 2 (M = Ni, Mn, Co; NMC) oxides with low Mn and Co contents, e.g., NMC-811. However, safety, cycle-life, and even cost could remain critical barriers to the success of such cathode materials. Herein an alternative to LiNiO 2 -based, low-cobalt cathodes is suggested based on modifications to the prototypical cobalt-free, layered oxide, LiNi 0.5 Mn 0.5 O 2. • Low cobalt oxides show promise for next generation, lithium-ion cathodes. • Nickel is limited to ~60% allowing increased contents of cheaper, abundant manganese. • Lithium/nickel exchange is limited even in the presence of substantial manganese. [ABSTRACT FROM AUTHOR]

High-energy, inexpensive and safe electrochemistries have been the main goals of lithium-ion battery research for many years. Historically, manganese-based cathodes have long been studied for their attractive cost and safety characteristics [1]. However, due to issues related to both surface and bulk instabilities, manganese-rich electrodes have yet to find substantial success in the high-energy lithium-ion battery market. With current trends in cathode chemistries leaning heavily toward Ni-rich compositions, the factors of cost and safety are again at the forefront of research and development efforts. This paper reports the recent progress made at Argonne National Laboratory (USA) to stabilize manganese-rich cathode structures and surfaces with a specific focus on composite materials with intergrown layered and spinel components; it presents an overview of their electrochemical properties in terms of capacity, energy, and cycle-life in cells with metallic lithium, graphite, and Li 4 Ti 5 O 12 anodes. These layered-spinel cathodes show promise as alternatives to highly nickel-rich electrode compositions, which bodes well for continued advances. • Mn-rich oxides show promise as competitive alternatives to Ni-rich cathodes. • Layered-layered-spinel electrodes offer high capacity and good rate capability. • Novel materials improve interfacial and cycling stability of Mn-rich cathodes. [ABSTRACT FROM AUTHOR]

Direct observations of structure-electrochemical activity relationships continue to be a key challenge in secondary battery research. 6Li magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy is the only structural probe currently available that can quantitatively characterize local lithium environments on the subnanometer scale that dominates the free energy for site occupation in lithium-ion (Li-ion) intercalation materials. In the present study, we use this local probe to gain new insights into the complex electrochemical behavior of activated 0.56Li2MnO3- 0.56LiMn0.5Ni0.5C>2, lithium- and manganese-rich transitionmetal (TM) oxide intercalation electrodes. We show direct evidence of path-dependent lithium site occupation, correlated to structural reorganization of the metal oxide and the electrochemical hysteresis, during lithium insertion and extraction. We report new 0.5Li resonances centered at ∼1600 ppm that are assigned to LiMn6-TMtet sites, specifically, a hyperfine shift related to a small fraction of re-entrant tetrahedral TMs (Mntet), located above or below lithium layers, coordinated to LiMn6 units. The intensity of the TM layer lithium sites correlated with tetrahedral TMs loses intensity after cycling, indicating limited reversibility of TM migrations upon cycling. These findings reveal that defect sites, even in dilute concentrations, can have a profound effect on the overall electrochemical behavior. [ABSTRACT FROM AUTHOR]

In this work, we report solution-based doping and coating strategies to improve the electrochemical performance of the Co-free layered oxide cathode LiNi 0.5 Mn 0.5 O 2 (NM-50/50). Small amounts of d0 dopants (e.g., Mo6+and Ti4+, 0.5–1 at. %) increase the cathode's specific capacity, cycling stability, and rate capability. For example, a Mo-doped cathode with the nominal composition LiNi 0.495 Mn 0.495 Mo 0.01 O 2 exhibits a high reversible capacity of 180 mA h/g at 20 mA/g compared to only 156 mA h/g for undoped NM-50/50. Effects of 1 at.% Mo dopant on the cathode structure were studied using a suite of characterization tools including X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy. These measurements demonstrate that Mo6+ dopant is enriched near the particle surface and improves the electrochemical performance of LiNi 0.5 Mn 0.5 O 2 by: (i) reducing Li+/Ni2+ cation mixing which facilitates Li+ transport, (ii) mitigating undesirable phase transformations near the cathode surface, and (iii) altering the cathode/electrolyte interfacial chemistry. This work also reports the use of an inorganic Mn 2 P 2 O 7 coating which enhances the cycling stability of Mo-doped NM-50/50, presumably through formation of a stable cathode electrolyte interphase (CEI) layer. Overall, the synthesis approaches reported herein are quite general and can potentially be expanded to other high voltage Li-ion battery cathodes. Image 1 • Synthesis of high capacity cobalt-free Ni–Mn cathodes with d0 dopants Mo and Ti. • Lower cation mixing on Mo doping from x-ray diffraction and electron microscopy. • Small Mo and Ti doping improve capacity retention and rate performance. • Mn 2 P 2 O 7 coating on surface provides higher cycling stability at high voltage. [ABSTRACT FROM AUTHOR]