Manganites of transition and/or post-transition metals, AMn 2 O 4 (where A was Co, Ni or Zn), were synthesized by a simple and easily scalable co-precipitation route and were evaluated as anode materials for Li-ion batteries. The obtained powders were characterized by SEM, TEM, and XRD techniques. Battery cycling showed that ZnMn 2 O 4 exhibited the best performance (discharge capacity, cycling, and rate capability) compared to the two other manganites and their corresponding simple oxides. Further studies on the effect of different sintering temperatures (from 400 to 1000 C) on particle size were performed, and it is found that the size of the particles had a significant effect on the performance of the batteries. The optimum particle size for ZnMn 2 O 4 is found to be 75-150 nm. In addition, the use of water-soluble and environmentally friendly binders, such as lithium and sodium salts of carboxymethlycellulose, greatly improved the performance of the batteries compared to the conventional binder, PVDF. Finally, ZnMn 2 O 4 powder sintered at 800 C (<150 nm) and the use of the in-house synthesized lithium salt of carboxymethlycellulose (LiCMC) binder gave the best battery performance: a capacity of 690 mA h g À1 (3450 mA h mL À1 ) at C/10, along with good rate capability and excellent capacity retention (88%).
Large LiMn 1.5 Ni 0.5 O 4 single crystals in plate shape with (112) surface facets and octahedral shape with (111) surface facets were obtained by molten-salt synthesis. The presence of transition-metal ordering in both samples was independently confirmed by SAED, FTIR, NMR, and electrochemical studies, demonstrating the excellent capability of each technique in distinguishing the ordered and disordered phases. The apparent chemical diffusion minima during Li extraction and insertion were correlated with the occurrence of the first-order phase transition, implying that phase boundary movement limits Li transport in the spinel cathodes. Despite a more ordered structure, nearly ten times less Mn 3+ content, and increased two-phase boundary movement during delithiation and relithiation, the octahedral crystals exhibited superior rate capability and a larger chemical diffusion coefficient, suggesting the kinetic preeminence of (111) surface facets over (112). The dominating effect of particle morphology and the importance of morphology design in achieving optimal performance of the LiMn 1.5 Ni 0.5 O 4 spinel are clearly demonstrated for the first time.
Although Li- and Mn-rich transition metal oxides have been extensively studied as high-capacity cathode materials for Li-ion batteries, the crystal structure of these materials in their pristine state is not yet fully understood. Here we apply complementary electron microscopy and spectroscopy techniques at multi-length scale on well-formed Li1.2(Ni0.13Mn0.54Co0.13)O2 crystals with two different morphologies as well as two commercially available materials with similar compositions, and unambiguously describe the structural make-up of these samples. Systematically observing the entire primary particles along multiple zone axes reveals that they are consistently made up of a single phase, save for rare localized defects and a thin surface layer on certain crystallographic facets. More specifically, we show the bulk of the oxides can be described as an aperiodic crystal consisting of randomly stacked domains that correspond to three variants of monoclinic structure, while the surface is composed of a Co- and/or Ni-rich spinel with antisite defects.
Micrometer-sized LiNi x Mn2–x O4 (0.3 ≤ x ≤ 0.5) single crystals with (111) surface facets were synthesized and characterized by 6Li magic angle spinning nuclear magnetic resonance, Fourier transform infrared spectroscopy, and electrochemical studies. All three techniques were sensitive to cation disorder and the corroborated results showed that structural ordering improves with x. The transition from the ordered to the disordered spinel was triggered by an increase in Mn3+ content, which was accomplished either by a change in chemical composition or postsynthesis thermal treatment. Disordering led to increased solid solution behavior, reduced two-phase transformation domains, and improved transport properties during Li extraction and insertion. Further increasing Mn3+ content in already disordered structure extends the solid solution domain and eliminates the presence of phase II; however, this has limited effect on rate capability. The study demonstrates the dominant role of structural ordering in morphology-controlled LiMn1.5Ni0.5O4, and it reveals that the kinetic significance of Mn3+ lies in its ability in triggering structural disordering. The rate performance of the spinels is not directly proportional to the Mn3+ content or the domain size of solid solution transformation in samples where two-phase transition is also present.
High voltage spinel LiMn1.5Ni0.5normalO4 has been synthesized by a modified Pechini sol–gel method and has been characterized by transmission electron microscopy, X-ray diffraction (XRD), and electrochemical methods. The synthesized materials are porous structures of nanosized crystallites ranging in size from 21 to over 400 nm depending on the sintering temperature used. The XRD patterns of the materials were assigned to the disordered spinel structure of the space group Fd3m . The Li-ion batteries assembled using the synthesized cathode materials showed significant capacity fade for samples sintered at 500°C , while for those sintered at 800°C the capacity fade was low. Impedance spectroscopy, Fourier transform IR spectroscopy, and X-ray photoelectron spectroscopy were used to determine the compositions of the cathode electrolyte interphase (CEI). Impedance spectroscopy confirmed the spontaneous formation of the CEI on LiMn1.5Ni0.5normalO4 and that its thickness grows on cycling. After more than 100 cycles, it is found that the CEI film is composed of polycarbonates, polyether, LiF, and LixPOynormalFz salts. The composition of the organic layer was the same regardless of the capacity fade.
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