Final Report Summary - LICRYSTG (Single-crystalline Lithium-based model systems of future materials for electrochemical energy storage and data storage)
Li-based olivine phosphates exhibit an enormous potential for applications. One the one hand, their cyclability and high-temperature stability renders them the next-generation cathode materials for Li-ion batteries. In addition, they exhibit complex ordering phenomena and large magnetoelectric effects. The interest in olivine phosphates has been further boosted by the recent discovery of unusual ferrotoroidic domains which are supposed to be relevant for data storage applications. In both fields, the detailed knowledge on the fundamental properties is mandatory for optimizing the material with respect to application. However, since single crystals of this species are extremely rare due to, e.g. high volatility of Li, information on the fundamental parameters is often missing.
The overall aim of the project was hence to provide missing experimental data on this promising class of materials. The scientific approach was to grow high-quality single crystals which enable investigating relevant anisotropic materials paramaters. In particular, measurements e.g. of the anisotropic Li-diffusion along the various crystallographic directions is an important input to theoretical models on battery performance and aging.
In the project the following subtasks were successfully addressed:
1. Growth of high-quality single crystals such as LiFePO4, LiMnPO4, LiCoPO4, LiMn1-xNixPO4, LiFe0.5Mn0.5PO4 single crystals by using the unique high-pressure TSFZ furnace equipped in the host institution KIP Heidelberg. This subtask also included understanding of the growth process in detail in order to optimize the growth parameters.
3. Detailed characterization of the crystals by X-ray diffraction, polarization images, chemical analysis, and Laue back scattering, and orientation, before further measurements.
4. Studies of Li-diffusion, local structural, structural and magnetic properties. This included studies of Mn-induced local disorder in LiMnPO4 by NMR and high-energy x-ray diffraction which show why the Mn-based olivine exhibits relatively poor electrochemical properties. In addition, the single crystal structures of the abovementioned crystals were refined. Thermal expansion and magnetostriction studies of the abovementioned crystals provide information on the structural changes and magneto-elasic coupling. These data are supported by specific heat and magnetisation studies which provide further information on the crystals quality and electronic properties. The magnetic phase diagrams were established. In the particular case of LiCoPO4, NMR and EPR studies provided information on short-range magnetic order at high temperature. For selected crystals, diffusion parameters of anisotropic Li-diffusion along the main crystallographic axes were determined.
In the course of the project it turned out that the phononic specific heat background is not reported in the literature with high precision but only estimated. Therefore, LiMgPO4 polycrystals were synthesised and studied as non-magnetic analog for NMR and specific heat.
4. Studies of ferrotoroidic domains for potential applications in data storage in the orientated samples by optical second harmonic generation (SHG) method were done at ETH Zurich. The materials under study are low-Ni-doped LiMnPO4 which provides information on the local environment and electronic structure of a few Ni-dopants in a matrix not showing ferrotoroidal behavior. This work is still in progress.
In addition to the original work plan, a few items have been done which extend the original schedule:
- Growth of Li7La3Zr2O12 by the flux method
- Synthesis and growth of LiFeBO3
- Synthesis and electrochemical studies on nanoscaled Li(Fe,Mn,Co)PO4
- Crystal growth of LiMAO3 (M = Fe, Mn, Co, A = B, V)
- Synthesis of LiMgPO4 polycrystals
- Crystals growth of Li2CuO2 under pressure
Deviations from the original work plan:
- Delithiation of single crystals which is very time-demanding has not yet been done. First studies turned our to be non-encouraging regarding the feasibility. Further work is scheduled for the next months.
- Instead of impurity doping of LiMnPO4 and LiFePO4 with Si, a series of single cyrstals with various transition metal doping has been produced.
Regarding training activities, the fellow has become acquainted to a variety of new experimental techniques:
- High-pressure TSFZ-growth of single crystals
- Microwave-assisted hydrothermal synthesis
- Mouting Li-ion batteries
- Cyclic Voltammetry and GPCL studies
The project has been implemented as expected and there were no critical issues from the management point of view. The abovementioned adjustments to the original work plan reflect progress in knowledge gained within the project and in the literature. Direct management activities have not been funded by the grant. The original time schedule was adjusted according to family needs of the fellow. We are thankful to the Commission and to the Administration that these family needs were thoughtfully supported.
The overall aim of the project was hence to provide missing experimental data on this promising class of materials. The scientific approach was to grow high-quality single crystals which enable investigating relevant anisotropic materials paramaters. In particular, measurements e.g. of the anisotropic Li-diffusion along the various crystallographic directions is an important input to theoretical models on battery performance and aging.
In the project the following subtasks were successfully addressed:
1. Growth of high-quality single crystals such as LiFePO4, LiMnPO4, LiCoPO4, LiMn1-xNixPO4, LiFe0.5Mn0.5PO4 single crystals by using the unique high-pressure TSFZ furnace equipped in the host institution KIP Heidelberg. This subtask also included understanding of the growth process in detail in order to optimize the growth parameters.
3. Detailed characterization of the crystals by X-ray diffraction, polarization images, chemical analysis, and Laue back scattering, and orientation, before further measurements.
4. Studies of Li-diffusion, local structural, structural and magnetic properties. This included studies of Mn-induced local disorder in LiMnPO4 by NMR and high-energy x-ray diffraction which show why the Mn-based olivine exhibits relatively poor electrochemical properties. In addition, the single crystal structures of the abovementioned crystals were refined. Thermal expansion and magnetostriction studies of the abovementioned crystals provide information on the structural changes and magneto-elasic coupling. These data are supported by specific heat and magnetisation studies which provide further information on the crystals quality and electronic properties. The magnetic phase diagrams were established. In the particular case of LiCoPO4, NMR and EPR studies provided information on short-range magnetic order at high temperature. For selected crystals, diffusion parameters of anisotropic Li-diffusion along the main crystallographic axes were determined.
In the course of the project it turned out that the phononic specific heat background is not reported in the literature with high precision but only estimated. Therefore, LiMgPO4 polycrystals were synthesised and studied as non-magnetic analog for NMR and specific heat.
4. Studies of ferrotoroidic domains for potential applications in data storage in the orientated samples by optical second harmonic generation (SHG) method were done at ETH Zurich. The materials under study are low-Ni-doped LiMnPO4 which provides information on the local environment and electronic structure of a few Ni-dopants in a matrix not showing ferrotoroidal behavior. This work is still in progress.
In addition to the original work plan, a few items have been done which extend the original schedule:
- Growth of Li7La3Zr2O12 by the flux method
- Synthesis and growth of LiFeBO3
- Synthesis and electrochemical studies on nanoscaled Li(Fe,Mn,Co)PO4
- Crystal growth of LiMAO3 (M = Fe, Mn, Co, A = B, V)
- Synthesis of LiMgPO4 polycrystals
- Crystals growth of Li2CuO2 under pressure
Deviations from the original work plan:
- Delithiation of single crystals which is very time-demanding has not yet been done. First studies turned our to be non-encouraging regarding the feasibility. Further work is scheduled for the next months.
- Instead of impurity doping of LiMnPO4 and LiFePO4 with Si, a series of single cyrstals with various transition metal doping has been produced.
Regarding training activities, the fellow has become acquainted to a variety of new experimental techniques:
- High-pressure TSFZ-growth of single crystals
- Microwave-assisted hydrothermal synthesis
- Mouting Li-ion batteries
- Cyclic Voltammetry and GPCL studies
The project has been implemented as expected and there were no critical issues from the management point of view. The abovementioned adjustments to the original work plan reflect progress in knowledge gained within the project and in the literature. Direct management activities have not been funded by the grant. The original time schedule was adjusted according to family needs of the fellow. We are thankful to the Commission and to the Administration that these family needs were thoughtfully supported.