Though Li 2 MnO 3 was originally considered to be electrochemically inert, its observed activation has spawned a new class of Li-rich layered compounds that deliver capacities beyond the traditional transition-metal redox limit. Despite progress in our understanding of oxygen redox in Li-rich compounds, the underlying origin of the initial charge capacity of Li 2 MnO 3 remains hotly contested. To resolve this issue, we review all possible charge compensation mechanisms including bulk oxygen redox, oxidation of Mn 4+ , and surface degradation for Li 2 MnO 3 cathodes displaying capacities exceeding 350 mAh g −1 . Using elemental and orbital selective X-ray spectroscopy techniques, we rule out oxidation of Mn 4+ and bulk oxygen redox during activation of Li 2 MnO 3 . Quantitative gas-evolution and titration studies reveal that O 2 and CO 2 release accounted for a large fraction of the observed capacity during activation with minor contributions from reduced Mn species on the surface. These studies reveal that, although Li 2 MnO 3 is considered critical for promoting bulk anionic redox in Li-rich layered oxides, Li 2 MnO 3 by itself does not exhibit bulk oxygen redox or manganese oxidation beyond its initial Mn 4+ valence.

Nickel-rich layered metal oxide LiNi 1−y−z Mn y Co z O 2 (1 − y − z ≥ 0.8) materials are the most promising cathodes for next-generation lithium-ion batteries in electric vehicles. However, they lose more than 10% of their capacity on the first cycle, and interfacial/structural instability causes capacity fading. Coating and substitution are possible direct and effective solutions to solve these challenges. In this Letter, Nb coating and Nb substitution on LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC811) is easily produced through a scalable wet chemistry method followed by sintering from 400 to 800 °C. A Li-free Nb oxide treatment is found to remove surface impurities forming a LiNbO 3 /Li 3 NbO 4 surface coating, to reduce the first capacity loss and to improve the rate performance. Nb substitution stabilizes the structure, as evidenced by less heat evolution on heating, thus providing better long cycling stability with a 93.2% capacity retention after 250 cycles.

The high nickel layered mixed metal oxides, such as LiNi z Co y Mn 1−z-y−q Al q O 2 , are the most utilized cathode materials in Li-ion batteries for electric vehicles due to their high energy density. However, as the nickel content increases, they suffer from poor capacity retention and from voltage fading due to interfacial/ structural instability. In this paper, a series of Nb-coated/substituted LiNi 0.9 Co 0.05 Mn 0.05 O 2 (NMC 9055) were synthesized by reacting the Nb precursors, Ni 0.9 Co 0.05 Mn 0.05 (OH) 2 , and LiOH. Nb is found in the NMC structure and also on the grain boundaries between the primary particles. These Nb-modified materials showed improved capacity retention and charge/discharge voltage profiles over the untreated material; the capacity retention was 86.4% (0.7 Nb-NMC 9055) vs 93.5% (1.4 Nb-NMC 9055) vs 99.7% (2.1 Nb-NMC 9055) vs 75.3% (NMC 9055) after 200 cycles and nearly no voltage fading (1.4 Nb-NMC 9055 and 2.1 Nb-NMC 9055) during cycling. High-angle annular dark-field (HAADF) scanning transition electron microscopy (STEM) images showed that the added niobium (Li−Nb−O phase) is located in the boundaries between the primary particles. This transferred obvious interparticles/intraparticles cracking into tiny intraparticles cracking, which benefits the release of strain/stress, maintains the mechanical integrity of secondary particles, and inhibits the structural transformation from the layer structure to rock-salt phase supported by large reduced charge transfer resistance, thus enhancing the electrochemical performance of NMC 9055.

Nickel-rich layered oxides, such as LiNi0.8Mn0.1Co0.1O2 (NMC 811), are considered as one of the most promising candidates for the next-generation cathode because of their high energy densities and relatively low cost. However, the poor first Coulombic efficiency of NMC 811 leads to around a 15% capacity loss in the first cycle at a cut-off voltage of 4.4 V. Moreover, the structure degradation during cycling results in capacity fading and safety concerns, due to potential oxygen loss after charging. Here, with aluminum substitution for manganese through a developed continuous co-precipitation approach, the electrochemical performance of NMC 811 cathodes has been greatly enhanced. Among different Al% substituted samples, LiNi0.8Mn0.06Co0.1Al0.04O2 cathodes reduced by 50% the first capacity loss of pristine NMC 811(18.0 vs 35.9 mAh g−1) and improved the capacity retention from 81.4 to 96.4% after 60 cycles at 0.5C in the voltage range of 2.8–4.4 V.

Mn2+ activated ZnS (ZnS:Mn2+) nanoparticles biotin matrix have been synthesized by chemical co-precipitation route. X-ray diffraction (XRD) results confirmed single phase zinc blend structure with crystallite sizes ranging from 1.5 to 1.9 nm. The small particle sizes are believed to have single domain crystallites because of quantum confinement of particles in the biotin matrix. Scanning electron microscopy (SEM) analysis shows smooth and polygon shape potato like morphology having cluster size varying from 77μm to 182μm. Optical measurement shows the band gap of 3.85 eV which has been blue shifted and is accredit to the quantum size effect. The particle size estimated for this gap is to be 2.03 nm and is good agreement with sizes obtained from XRD. The luminescence feature of the as synthesized sample was also reported. The photoluminescence (PL) spectra shows two wide peaks centred at 408 nm and 520 nm respectively. The first emission at 408 nm with short time is attributed to the defects of ZnS while another peak at 520 nm attributed in green emission due to the elemental sulphur species on the surface of zinc sulphide. The both emissions are blue shifted and are attributed to the small particle sizes. The well known manganese related orange-red emission peak cantered at 590 nm has not been observed and is completely quenched that confirmed that the Mn2+ ions have been allocated outside the ZnS crystals. A new emission at 338 nm appears to have radiative transitions from the defect level to the acceptor levels. Thus, by using suitable activator and capping molecule, we are able to stabilize the growth of nanoparticles at room temperature, thereby enhance the structural and opto-electronic properties.