Ion-Dynamics in Materials for Future Solid State Energy Devices
One of the most important scientific problems to solve for our modern society is how to convert and store clean energy. In order to accomplish a paradigm shift in this field, we need to understand the fundamental dynamical processes that govern the transfer of energy on an atomic scale. For future energy devices like solid-state batteries (SSB) as well as solid-oxide fuel cells (SOFC), this means understanding and controlling the complex mechanisms of ion diffusion in solid matter. Only recently, developments of state-of-the-art large scale experimental facilities e.g. neutron/muon spallation sources as well as free electron lasers, have opened new possibilities for studying such intrinsic material properties in a straightforward manner. I have in a collaboration with Toyota Central Research and Development Laboratories in Japan, developed a novel method that utilizes the muon-spin rotation/relaxation (m+SR) technique to probe the microscopic ion self-diffusion constant (Dion) with high accuracy [1]. I will give a brief introduction to the method itself as well as summarize our extensive m+SR studies of Li-ion diffusion in a wide range of battery cathode materials [2-6].
In the field of rechargeable batteries, strong interest has recently been raised to find a replacement for traditional Li-ion technology. The main reason is that such batteries are rather expensive and in addition the extraction of lithium metal is problematic from an environmental point of view due to its high reactivity and relatively low abundance in the Earth’s crust (only 20 ppm). One option to avoid these drawbacks may be to replace lithium (Li) with sodium (Na) in the electrode materials. Sodium is similar to lithium in its chemical properties, but approximately 1000 times more abundant in the Earth’s crust (26’000 ppm) as well as in the form of salt (NaCl) in normal seawater (15’000 ppm). This makes sodium based batteries potentially more environmental friendly and easier to recycle as well as up to five times less expensive.
Currently the most common Li-ion cathode material is LiCoO2, where the Na-analog consequently is NaCoO2, making this compound a logical first step towards the development of Na-ion batteries. To understand the Na-ion diffusion process in this material, we have performed high-resolution neutron diffraction (ND) measurements as a function of temperature. Our data display a two-step "melting" of the Na-ion planes, involving an intriguing crossover from 1D-to-2D Na-diffusion channels [7]. Further, it is evident that the onset and evolution of ion-diffusion is intrinsically linked to a series of subtle structural transitions, which unlocks the diffusion pathways. Finally, we have also performed m+SR [8] and pressure-dependent neutron scattering measurements [9], which reveal novel and functional possibilities for tuning Na-ion diffusion using lattice-strains. In summary, our current research has established a novel and detailed insight into the ion-diffusion mechanisms in these compounds. This allows us to actively consider targeted tuning and smart design of energy related materials for the use in future solid state devices with optimized performance.
In the field of rechargeable batteries, strong interest has recently been raised to find a replacement for traditional Li-ion technology. The main reason is that such batteries are rather expensive and in addition the extraction of lithium metal is problematic from an environmental point of view due to its high reactivity and relatively low abundance in the Earth’s crust (only 20 ppm). One option to avoid these drawbacks may be to replace lithium (Li) with sodium (Na) in the electrode materials. Sodium is similar to lithium in its chemical properties, but approximately 1000 times more abundant in the Earth’s crust (26’000 ppm) as well as in the form of salt (NaCl) in normal seawater (15’000 ppm). This makes sodium based batteries potentially more environmental friendly and easier to recycle as well as up to five times less expensive.
Currently the most common Li-ion cathode material is LiCoO2, where the Na-analog consequently is NaCoO2, making this compound a logical first step towards the development of Na-ion batteries. To understand the Na-ion diffusion process in this material, we have performed high-resolution neutron diffraction (ND) measurements as a function of temperature. Our data display a two-step "melting" of the Na-ion planes, involving an intriguing crossover from 1D-to-2D Na-diffusion channels [7]. Further, it is evident that the onset and evolution of ion-diffusion is intrinsically linked to a series of subtle structural transitions, which unlocks the diffusion pathways. Finally, we have also performed m+SR [8] and pressure-dependent neutron scattering measurements [9], which reveal novel and functional possibilities for tuning Na-ion diffusion using lattice-strains. In summary, our current research has established a novel and detailed insight into the ion-diffusion mechanisms in these compounds. This allows us to actively consider targeted tuning and smart design of energy related materials for the use in future solid state devices with optimized performance.
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- ICMP (Arnaud Magrez and Raphaël Butté)
Contact
- Arnaud Magrez