Lithium-rich Li[Li x M 1−x ]O 2 (M = Ni, Mn, Co) materials have been claimed to be two phase by some researchers and to be one phase by others when all the available lithium is extracted electrochemically. To clear up this confusion, the Li-rich samples [Li[Li 0.12 (Ni 0.5 Mn 0.5 ) 0.88 ]O 2 and Li-[Li 0.23 (Ni 0.2 Mn 0.8 ) 0.77 ]O 2 with different particle sizes were synthesized for in situ X-ray diffraction experiments. In situ X-ray diffraction measurements revealed two-phase behavior of 10 μm particles and one-phase behavior for samples with submicrometer particles. The phase separation in samples with large particles agrees with literature proposals of oxygen release from a surface layer and the observation of distinct surface and bulk phases. The small particle samples are so small that they are entirely composed of the surface phase found in the large particle samples. These results strongly suggest that the size of particles can significantly affect the structural evolution testing and electrochemical performance of the Li-and Mn-rich materials. It is proposed that the surface phase continuously grows during charge−discharge cycling, which leads to voltage fade in large particle samples. Meanwhile, in situ X-ray diffraction measurements were also performed for the layered Li−Ni−Mn−Co oxides with varying nickel contents, including NMC811 (LiNi 0.8 Mn 0.1 Co 0.1 O 2 ), NMC442 (LiNi 0.42 Mn 0.42 Co 0.16 O 2 ), [Li[Li 0.12 (Ni 0.5 Mn 0.5 ) 0.88 ]O 2 , and Li[Li 0.23 (Ni 0.2 Mn 0.8 ) 0.77 ]O 2 . Samples with higher nickel content showed much faster contraction of unit cell volume as a function of cell voltage, which suggests that the core−shell structures with a nickel-rich core (e.g., NMC811) and a Mn-rich shell (e.g., Li 1.23 Ni 0.154 Mn 0.616 O 2 ) should not crack during charge−discharge cycling.

Li [Ni 0.42 Mn 0.42 Co 0.16 ]O 2 (NMC442)/graphite pouch cells demonstrate superb performance at high voltage when ethylene carbonate (EC)-free electrolytes, using a solvent mixture that is >95% ethyl methyl carbonate (EMC) and between 2 and 5% of an "enabler", are used. The "enablers", required to passivate graphite during formation, can be vinylene carbonate (VC), methylene-ethylene carbonate (MEC), fluoroethylene carbonate (FEC) or difluoro ethylene carbonate (DiFEC), among others. In order to optimize the amount of "enabler" added to EMC, gas chromatography coupled with mass spectrometry (GC-MS) was used to track the consumption of "enabler" during the formation step. Storage tests, electrochemical impedance spectroscopy (EIS), ultrahigh precision coulometry (UHPC), long-term cycling, differential voltage analysis and isothermal microcalorimetry were used to determine the optimum amount of enabler to add to the cells. It was found that the graphite negative electrode cannot be fully passivated when the amount of "enabler" is too low resulting in gas production and capacity fade. Using excess "enabler" can cause large impedance and gas production in most cases. The choice of "enabler" also impacts cell performance. A solvent blend of 5% FEC with 95% EMC (by weight) provides the best combination of properties in NMC442/graphite cells operated to 4.4 V. It is our opinion that the experiments and their interpretation presented here represent a primer for the design of EC-free electrolytes. Lithium-ion batteries (LIB) are now widely used in electrified vehicles and energy storage systems.1 These applications require longer calendar and cycle lifetime as well as higher energy density. In order to increase the energy density of LIB, researchers focus on developing electrode materials with high specific capacity that may involve charging to increased upper cutoff potentials.2,3

Core–shell structure positive electrode materials, based on layered Li–Ni–Mn–Co oxides, could be the next generation of positive electrode materials for high energy density lithium-ion batteries. Diffusion of the transition metal cations between the core and shell phases occurs during sintering, which can significantly affect the final core–shell (CS) properties. However, the interdiffusion constants have never been measured. Laminar pellets of the pure core phase and pure shell phase were pressed in contact and then heated to measure the interdiffusivity of the transition metals at various temperatures. The diffusion couples Ni3+/Co3+, Co3+/Mn4+, and Ni3+/Mn4+ were measured by analyzing composition versus position, with respect to the initial interface between the core and shell phase pellets. The transition metal composition profiles were measured with energy dispersive spectroscopy (EDS) line scans. This is the first time interdiffusion constants have been reported in the layered cathode materials to our knowledge. At 900 °C, Ni3+/Co3+ has the highest interdiffusivity, D, of ∼4.7 × 10–12 cm2/s, while Ni3+/Mn4+ has the lowest of ∼0.1 × 10–12 cm2/s. The activation energy barriers for Ni3+/Co3+, Co3+/Mn4+, and Ni3+/Mn4+ interdiffusion were determined from Arrhenius plots of D vs 1/T. Simulations of diffusion in spherical core–shell materials were performed to show how knowledge of the interdiffusion constants can guide rational design of practical core–shell materials.

To obtain the highest energy density, lithium ion batteries based on layered Li-Ni-Mn-Co oxides need to be charged to above 4.5 V without sacrificing lifetime. Lithium-rich core-shell (CS) structured positive electrodes having a high energy density core material with poor stability against the electrolyte can be protected by a thin layer of a stable shell material. In this work, the effects of the initial shell thickness, sintering temperature and interdiffusion during sintering on the electrochemical performance of CS cathodes were studied for the first time to our knowledge. Full cell coin cells of selected CS samples with electrolyte additives showed good capacity retention. This work will help guide the design of next generation positive electrode materials using CS and coating strategies. Lithium ion batteries (LIBs) with high energy density, low cost as well as long-life time are required for large scale adoption of electric vehicles. The layered Li-Ni-Mn-Co oxides (NMC) are excellent positive electrodes candidates for cost effective LIBs.1,2 A large operating voltage window (charge to 4.5 V and above in full cells against graphite) is needed to increase the energy density and minimal electrolyte oxidation is required so the life-time of the cells will not be sacrificed.3 Besides the development of novel electrolyte systems using additives or new solvents, 3-11 coatings on the positive electrode material can minimize electrolyte oxidation in high voltage cells. 12-16However, thick coatings (higher than 3 wt%) with inactive oxides on NMC materials significantly decrease the energy density and rate capability of the cells and thus these coatings are usually incomplete with nano-particles scattered on the NMC surface. 12,13Core-shell (CS) structured positive electrode materials based on NMC could be the next generation of positive electrode materials for high energy density lithium-ion batteries. This is because a high energy core material with poor stability against the electrolyte can be protected by a thin layer of a stable and active shell material with lower Ni and higher Mn content.17 Core-shell or gradient LiNi x Mn y Co z O 2 (x + y + z = 1) materials for voltages lower than 4.4 V were first developed by Y. K. Sun's group. [18][19][20] These have a high Ni content in the core and increasing Mn content from the core to the surface, with a maximum Mn content on the surface of ∼50%. In our previous report, 17,21 Li-rich and Mn-rich materials 22,23 were used as the protecting shell for voltages above 4.5 V. It was shown that the Li-rich and Mn-rich shell protected the Ni-rich core from reactions with the electrolyte while the Ni-rich core rendered a high and stable average voltage. 21Diffusion of the cations between the core and shell phases occurs during sintering to prepare the NMC core-shell oxide.24 Although much research on CS and gradient NMC materials have been reported, there are no detailed studies of how interdiffusion during sintering affects the final composition, structure and electrochemical...

A special type of hydrous MnO 2 /Fe 2 O 3 nanocomposite was prepared using a two-step precipitation method. Fe 2 O 3 •xH 2 O nanoparticles, precipitated from Fe(NO 3 ) 3 and NH 3 • H 2 O, were proposed to be embedded into the mesoporous network of MnO 2 , which was synthesized by the aqueous reaction between KMnO 4 and glucose. The nanocomposite with an equal Mn/Fe molar ratio shows strong synergy, with a specific surface area of 388 m 2 /g, much larger than those of individual MnO 2 or Fe 2 O 3 •xH 2 O samples. As a result, this nanocomposite exhibited the highest adsorption capacity for NH 3 and SO 2 . The isolation of Fe 2 O 3 •xH 2 O by MnO 2 , leading to mitigated aggregation of Fe 2 O 3 •xH 2 O nanoparticles, was characterized by transmission electron microscopy, powder X-ray diffraction, and vibrational spectra. X-ray absorption spectroscopy was used to study the interaction between Fe 2 O 3 •xH 2 O and MnO 2 after the formation of composites. This typical method for the preparation of nanocomposites proved to be effective to improve porosity, as demonstrated by N 2 adsorption isotherms and small-angle X-ray scattering. KEYWORDS: MnO 2 , Fe 2 O 3 •xH 2 O, nanocomposite, BET surface area, dynamic flow test, respirators