Search

Oxygen participation, arising from increased transition metal–oxygen covalency during delithiation, is considered essential for the description of charge compensation in conventional layered oxides. The advent of high-resolution mapping of the O K-edge resonant inelastic X-ray scattering (RIXS) provides an opportunity to revisit the onset and extent of oxygen participation. Combining RIXS with an array of structural and electronic probes for the family of Ni-rich LiNi0.8Co0.2−yAlyO2cathodes, we identify common charge compensation regimes that are assigned to formal transition metal redox (<4.25 V) and oxygen participation through covalency (>4.25 V). From O K-edge RIXS maps, we find the emergence of a sharp RIXS feature in these systems when approaching full delithiation, which has previously been associated with lattice oxidized oxygen in alkali-rich systems. The lack of transition metal redox signatures and strong covalency at these high degrees of delithiation suggest this RIXS feature is similarly attributed to lattice oxygen charge compensation as in the alkali-rich systems. The RIXS feature's evolution with state of charge in conventional layered oxides is evidence that this feature reflects the depopulation of occupied O 2p states associated with oxygen participation.

Practical utilization of energy densities near the theoretical limit for R3̅mlayered oxide positive electrode materials is dependent on the stability of the electrochemical performance of these materials at or near full delithiation. To develop new chemistries and novel approaches toward the improvement of the electrochemical performance of these materials at such high states of charge, a robust understanding of the failure mechanisms limiting current materials is necessary. Thorough analysis of LixCo1–yAlyO2and LixNi1–yAlyO2as well as LixNi0.8Co0.2O2and LixNi0.8Co0.15Al0.05O2(1 ≥ x≥ 0 and 0.2 ≥ y≥ 0) enabled the identification of key relationships between the transition metal chemistry of the electrode, its structural stability, and cycling characteristics at or near complete delithiation (4.75 V). Extensive characterization of these materials was achieved by a multitude of physical and electrochemical techniques to investigate the relative importance of surface vs bulk phenomena. The resulting insights derived from these analyses highlight the importance of the intrinsic structural and mechanical stability of the electrode when highly delithiated and establish guidelines for identifying positive electrode materials with improved high state of charge performance. Particularly important is the contrasting electrochemical impact of Al substitution into LiCoO2- and LiNiO2-based materials, which is shown to likely arise from the enhanced propensity for Al ions to migrate to the tetrahedral site in Co-rich compounds at high states of delithiation.

For layered oxide cathodes, aluminum doping has widely been shown to improve performance, particularly at high degrees of delithiation. While this has led to increased interest in Al-doped systems, including LiNi0.8Co0.15Al0.05O2 (NCA), the aluminum surface environment has not been thoroughly investigated. Using hard x-ray photoelectron spectroscopy measurements of the Al 1s core region for NCA electrodes, we examined the evolution of the surface aluminum environment under electrochemical and thermal stress. By correlating the aluminum environment to transition metal reduction and electrolyte decomposition, we provide further insight into the cathode-electrolyte interface layer. A remarkable finding is that Al-O coatings in LiPF6 electrolyte mimic the evolution observed for the aluminum surface environment in doped layered oxides.

The current Li-ion battery technology has reached its maturity and incremental improvements in energy density can not meet the increasing demand for more energy and power for portable electronic applications. Stabilized Lithium Metal Powder (SLMPTM) is an enabling material and technology that creates opportunities for more choices of active materials to be used in Li-ion batteries resulting in systems with improved performance in energy, safety and possibly cost. In this work we have discussed the initial results for SLMP stability in selected solvents. Material has been incorporated into Li-ion cells and results indicate that SLMP could be used as an independent source of lithium. Examples of using SLMP to improve the first cycle efficiency in silicon composite material and of Li-ion cell built with non-lithium providing cathode, such as the first Li-ion battery fabricated with a metal fluoride, are discussed. Approaches for synthesis of tin and silicon nanocomposites are presented.

For layered oxide cathodes, aluminum doping has widely been shown to improve performance, particularly at high degrees of delithiation. While this has led to increased interest in Al-doped systems, including LiNi0.8Co0.15Al0.05O2(NCA), the aluminum surface environment has not been thoroughly investigated. Using hard x-ray photoelectron spectroscopy measurements of the Al 1s core region for NCA electrodes, we examined the evolution of the surface aluminum environment under electrochemical and thermal stress. By correlating the aluminum environment to transition metal reduction and electrolyte decomposition, we provide further insight into the cathode-electrolyte interface layer. A remarkable finding is that Al-O coatings in LiPF6electrolyte mimic the evolution observed for the aluminum surface environment in doped layered oxides.

The current Li-ion battery technology has reached its maturity and incremental improvements in energy density can not meet the increasing demand for more energy and power for portable electronic applications. Stabilized Lithium Metal Powder (SLMPTM) is an enabling material and technology that creates opportunities for more choices of active materials to be used in Li-ion batteries resulting in systems with improved performance in energy, safety and possibly cost. In this work we have discussed the initial results for SLMP stability in selected solvents. Material has been incorporated into Li-ion cells and results indicate that SLMP could be used as an independent source of lithium. Examples of using SLMP to improve the first cycle efficiency in silicon composite material and of Li-ion cell built with non-lithium providing cathode, such as the first Li-ion battery fabricated with a metal fluoride, are discussed. Approaches for synthesis of tin and silicon nanocomposites are presented.