We report a method for in situ atomic-scale observation of electrochemical delithiation in a working all-solid-state battery using a state-of-the-art chip based in situ transmission electron microscopy (TEM) holder and focused ion beam milling to prepare an all-solid-state lithium-ion battery sample. A battery consisting of LiCoO2 cathode, LLZO solid state electrolyte and gold anode was constructed, delithiated and observed in an aberration corrected scanning transmission electron microscope at atomic scale. We found that the pristine single crystal LiCoO2 became nanosized polycrystal connected by coherent twin boundaries and antiphase domain boundaries after high voltage delithiation. This is different from liquid electrolyte batteries, where a series of phase transitions take place at LiCoO2 cathode during delithiation. Both grain boundaries become more energy favorable along with extraction of lithium ions through theoretical calculation. We also proposed a lithium migration pathway before and after polycrystallization. This new methodology could stimulate atomic scale in situ scanning/TEM studies of battery materials and provide important mechanistic insight for designing better all-solid-state battery.

Density functional theory simulations and experimental studies were performed to investigate the interfacial properties, including lithium ion migration kinetics, between lithium metal anode and solid electrolyte Li10GeP2S12(LGPS). The LGPS[001] plane was chosen as the studied surface because the easiest Li+ migration pathway is along this direction. The electronic structure of the surface states indicated that the electrochemical stability was reduced at both the PS4- and GeS4-teminated surfaces. For the interface cases, the equilibrium interfacial structures of lithium metal against the PS4-terminated LGPS[001] surface (Li/PS4–LGPS) and the GeS4-terminated LGPS[001] surface (Li/GeS4–LGPS) were revealed based on the structural relaxation and adhesion energy analysis. Solid electrolyte interphases were expected to be formed at both Li/PS4–LGPS and Li/GeS4–LGPS interfaces, resulting in an unstable state of interface and large interfacial resistance, which was verified by the EIS results of the Li/LGPS/Li cell. In addition, the simulations of the migration kinetics show that the energy barriers for Li+ crossing the Li/GeS4–LGPS interface were relatively low compared with the Li/PS4–LGPS interface. This may contribute to the formation of Ge-rich phases at the Li/LGPS interface, which can tune the interfacial structures to improve the ionic conductivity for future all-solid-state batteries. This work will offer a thorough understanding of the Li/LGPS interface, including local structures, electronic states and Li+ diffusion behaviors in all-solid-state batteries.

•Building the PLS modelling on QSAR formulation of cathode volume change in LIBs based on ab-initio calculation data.•Investigating the factors related to the volume change within 28 oxide cathodes including with spinel- and layered-structure.•Assigning the variables those make major contributions to the volume change during delithiation.•Exhibiting the promising future of the virtual screening and combinatorial design of low-strain cathode materials for LIBs.In this paper, we report a method through the combination of ab-initio calculations and partial least squares (PLS) analysis to develop the Quantitative Structure –Activity Relationship (QSAR) formulations of cathode volume changes in lithium ion batteries. The PLS analysis is based on ab-initio calculation data of 14 oxide cathodes with spinel structure LiX2O4 and 14 oxide cathodes with layered-structure LiXO2 (X = Ti, V, Cr, Mn, Fe, Co, Ni, Nb, Mo, Ru, Rh, Pd, Ta, Ir). Five types of descriptors, describing the characteristics of each compound from crystal structure, element, composition, local distortion and electronic level, with 34 factors in total, are adopted to obtain the QSAR formulation. According to the variable importance in projection analysis, the radius of X4+ ion, and the X octahedron descriptors make major contributions to the volume change of cathode during delithiation. The analysis is hopefully applied to the virtual screening and combinatorial design of low-strain cathode materials for lithium ion batteries.Download high-res image (249KB)Download full-size image

Solid state electrolytes with high Li ion conduction are vital to the development of all-solid-state lithium batteries. Lithium thiophosphate Li3PS4 is the parent material of a series of Li superionic conductors Li10MX2S12 (M = Ge, Sn,…; X = P, Si,…), and β-Li3PS4 shows relatively high ionic conductivity itself, though it is not room-temperature stable. The positive effects of introducing O dopants into β-Li3PS4 to stabilize the crystal phase and improve the ionic conducting behaviour are revealed in this study. With the aid of first-principles density functional theory (DFT) computations and quasi-empirical bond-valence calculations, the effects of O doping at different concentrations on the properties of β-Li3PS4 is thoroughly investigated from the aspects of lattice structures, electronic structures, ionic transport properties, the interface stability against Li and the thermodynamic stability. An oxygen-driven transition from two-dimensional to three-dimensional transport behaviour is found and the oxygen dopants play the role as a connector of 2D paths. Based on all these simulation results, hopefully our research can provide a new strategy for the modification of lithium thiophosphate solid electrolytes.

Li2MnO3 component plays a key role in Li-rich Mn-based layered materials (mLi2MnO3·nLiMO2, M = Mn, Ni, Co, etc.) for achieving unusually high lithium storage capacity. However, detailed lithium storage mechanism in Li2MnO3, such as structure evolution and charge compensation are still not very clear. In this work, the redox mechanism, the delithiation process, the kinetics of lithium diffusion, and the oxygen stability of Li2MnO3 are investigated through density functional calculations. The ground-state Li/vacancy configurations of Li2–xMnO3(0 ≤ x ≤ 1) at five Li concentrations are determined, from which the delithiation potential is calculated as ∼4.6 V vs Li+/Li, and the charge compensation during Li removal is contributed mainly by oxygen. According to the Li/vacancy configuration in each ground state, the sequence of lithium removal is suggested from an energetic view. Both the Li+ in the lithium layer and in the transition-metal layer can be extracted. The first-principles molecular dynamics (FPMD) simulations indicate that the lithium layer is the main diffusion plane in this material, while the Li+ in the transition-metal LiMn2 layer can migrate into the lithium layer first, and then diffuse through the lithium plane or move back to the LiMn2 layer. The energy barriers of such migrations are in the range of 0.51–0.84 eV, according to the calculations with the nudged elastic band method. The release of O2 gas from Li2–xMnO3(0 ≤ x ≤ 1) happens spontaneously if x ≥ 0.5, from the point of view of enthalpy change. Further understanding on the evolution of oxygen in Li2–xMnO3 with x ≥ 0.5 is needed to find a way to stabilize the structure during electrochemical cycles.Keywords: density functional theory calculations; lithium ion diffusion; lithium manganese oxide; oxygen release;

Solid state electrolytes with high Li ion conduction are vital to the development of all-solid-state lithium batteries. Lithium thiophosphate Li3PS4 is the parent material of a series of Li superionic conductors Li10MX2S12 (M = Ge, Sn,…; X = P, Si,…), and β-Li3PS4 shows relatively high ionic conductivity itself, though it is not room-temperature stable. The positive effects of introducing O dopants into β-Li3PS4 to stabilize the crystal phase and improve the ionic conducting behaviour are revealed in this study. With the aid of first-principles density functional theory (DFT) computations and quasi-empirical bond-valence calculations, the effects of O doping at different concentrations on the properties of β-Li3PS4 is thoroughly investigated from the aspects of lattice structures, electronic structures, ionic transport properties, the interface stability against Li and the thermodynamic stability. An oxygen-driven transition from two-dimensional to three-dimensional transport behaviour is found and the oxygen dopants play the role as a connector of 2D paths. Based on all these simulation results, hopefully our research can provide a new strategy for the modification of lithium thiophosphate solid electrolytes.