The electrode kinetics of Li-ion batteries, which are important for battery utilization in electric vehicles, are affected by the grain size, crystal orientation, and surface structure of electrode materials. However, the kinetic influences of the grain interior structure and element segregation are poorly understood, especially for Li-rich layered oxides with complex crystalline structures and unclear electrochemical phenomena. In this work, cross-sectional thin transmission electron microscopy specimens are "anatomized" from pristine Li1.2Mn0.567Ni0.167Co0.067O2 powders using a new argon ion slicer technique. Utilizing advanced microscopy techniques, the interior configuration of a single grain, multiple monocrystal-like domains, and nickel-segregated domain boundaries are clearly revealed; furthermore, a randomly distributed atomic-resolution Li2MnO3-like with an intergrown LiTMO2 (TM = transitional metals) "twin domain" is demonstrated to exist in each domain. Further theoretical calculations based on the Li2MnO3-like crystal domain boundary model reveal that Li(+) migration in the Li2MnO3-like structure with domain boundaries is sluggish, especially when the nickel is segregated in domain boundaries. Our work uncovers the complex configuration of the crystalline grain interior and provides a conceptual advance in our understanding of the electrochemical performance of several compounds for Li-ion batteries.

We propose a new sealed battery operating on a redox reaction between an oxide (O2−) and a peroxide (O22−) with its theoretical specific energy of 2570 Wh kg−1 (897 mAh g−1, 2.87 V) and demonstrate that a Co-doped Li2O cathode exhibits a reversible capacity over 190 mAh g−1, a high rate capability, and a good cyclability with a superconcentrated lithium bis(fluorosulfonyl)amide electrolyte in acetonitrile. The reversible capacity is largely dominated by the O2−/O22− redox reaction between oxide and peroxide with some contribution of the Co2+/Co3+ redox reaction.

Atomic-scale defects strongly influence the electrical and optical properties of materials, and their impact can be more pronounced in localized dimensions. Here, we directly demonstrate that strain triggers the formation of oxygen vacancies in complex oxides by examining the tilt boundary of SrTiO3 bicrystals. Through transmission electron microscopy and electron energy loss spectroscopy, we identify strains along the tilt boundary and oxygen vacancies in the strain-imposed regions between dislocation cores. First-principles calculations support that strains, irrespective of their type or sign, lower the formation energy of oxygen vacancies, thereby enhancing vacancy formation. Finally, current-voltage measurements confirm that such oxygen vacancies at the strained boundary result in a decrease of the nonlinearity of the I-V curve as well as the resistivity. Our results strongly indicate that oxygen vacancies are preferentially formed and are segregated at the regions where strains accumulate, such as heterogeneous interfaces and grain boundaries.

For the intercalation type cathode in lithium-ion batteries, the structural framework of electrode is expected to remain unchanged during lithium insertion and extraction. Unfavorable phase transition in electrode materials, which has been frequently observed, modifies the structural framework, which leads to capacity loss and voltage decay. Here, we track atoms motion/shift in lithium manganese oxide during a phase transition from spinel to rocksalt by using atomically resolved aberration corrected scanning transmission electron microscopy and spectroscopy. We find that when given energy, the transition metal cation can readily hop between oxygen tetrahedral and octahedral sites in oxygen deficient lithium manganese oxide similar to lithium diffusion behavior, which leaves the anion structure framework almost unchanged. During this phase transition, the intermediate state, migration length, and atomic structure of phase boundaries are revealed, and the mechanism is discussed. Our observations help us to understand the past experimental phenomena and provide useful information to stabilize the structure of electrode materials and thus improve the cycling life of lithium-ion batteries.

The plastic deformation process of a SrTiO3 single crystal has been dynamically and microscopically observed by in situ nanoindentation in a transmission electron microscope. The plastic deformation of SrTiO3 was found to proceed by dislocation slips even at room temperatures under the present experimental condition, and the dynamic behavior of dislocations such as nucleation, propagation, and annihilation have been clearly captured. The detailed dislocation analyses revealed that the activated slip system is 〈110〉{11¯0} type, which is consistent with the results of macroscopic deformation experiments reported so far. The mechanisms of dislocation behavior are discussed based on the experimentally obtained results.

Polycrystalline MnAl co-doped ZnO ceramics were prepared by sintering in air. Increasing Mn dopant concentration led to an increase of the ZnO lattice constants indicating substitution of Mn on the Zn sublattice. A Mn-rich spinel secondary phase was also detected within grains and at grain boundaries. The addition of the Al dopant led to an initial reduction in grain size while the addition of Mn led to an increase in grain size. Thermoelectric property measurements revealed that Al doping led to a large initial increase in electrical conductivity and increasing Mn dopant addition resulted in electrical conductivity reduction. The absolute value of the Seebeck coefficient was largely unaffected at low Mn doping levels; however, an increase was observed for high Mn doping levels. The thermal conductivity showed a marked decrease with increasing Mn concentration, indicating the effectiveness of Mn dopant substitution for Zn to reduce the thermal conductivity by point defect scattering. Overall, the maximum ZT was achieved for the Zn 0.99 Al 0.01 O sample (ZT = 0.07 at 750°C) and increasing Mn doping led to a decrease of ZT due to the increased resistivity caused by alloy scattering and secondary phase formation.

In fracture processes, grain boundaries behave as preferential paths for crack propagation. These grain boundary fractures proceed by the atomic-bond rupture within the grain boundary cores, and thus grain boundary structures have crucial influence on the fracture properties. However, the relationship between grain boundary structures and atomic fracture processes has been a matter of conjecture, especially in the case of dopant-segregated grain boundaries which have complicated local structures and chemistries. Here, we determine the atomic-bond breaking path within a dopant-segregated Al 2 O 3 grain boundary core, via atomic-scale observations of the as-fractured surface and the crack tip introduced by in situ nanoindentation experiments inside a transmission electron microscope. Our observations show that the atomic fracture path is selected to produce less coordination-deficient oxygen polyhedra of dopant cations, which is rationalised using first-principles calculations. The present findings indicate that the atomic coordination geometry at the grain boundary core affects the fracture processes.

At present, significant research efforts are being devoted both to identifying means of upgrading existing batteries, including lithium ion types, and also to developing alternate technologies, such as sodium ion, metal-air, and lithium-sulfur batteries. In addition, new battery systems incorporating novel electrode reactions are being identified. One such system utilizes the reaction of electrolyte ions with oxygen atoms reversibly extracted and reinserted topotactically from cathode materials. Batteries based on this system allow the use of various anode materials, such as lithium and sodium, without the requirement to develop new cathode intercalation materials. In the present study, this concept is employed and a new battery based on a CaFeO3 cathode with a sodium anode is demonstrated.