Advancing Next-generation Battery Research with Single Crystal XRD
The modern world relies upon high performance lithium-ion batteries. But to move towards a true net-zero world, batteries with improved storage capacity, conductivity, safety, and sustainable resource use are critical.
Single crystal XRD remains the most powerful technique for scientists to understand structure – property relationships of new materials for next-gen batteries.
SC-XRD and research into solid state fast ionic conductors
Fast ionic conductors are inorganic crystalline materials that exhibit ionic conductivity comparable to or higher than that in the liquid state. This property makes fast ionic conductors appealing for a variety of advanced technologies including solid-state batteries, fuel cells and gas sensors.
A comprehensive understanding of fast ionic conduction in crystalline solids can lead to generalized design rules for improved fast ionic conductors but this understanding is challenging to attain. The mechanism of ionic transport in solids is highly complex and intricately linked to the atomic structure of the crystalline solid.
Single crystal XRD is the technique of choice for the structural determination of fast-ionic conductors. Single-crystal diffraction data yields excellent data quality at d-spacing beyond 0.8 Å and reveals a level of structural details not achievable with other techniques.
SC-XRD is a well-established method offering standardised workflows and software-guided data processing to ensure high quality structures can be obtained quickly and easily.
Structural features and the physical properties they affect
- Accurate atomic coordinates of lattice
- Atomic coordinates of ions including light elements such as Li, Na and O
- Accurate determination of ion-site occupancies
- Anisotropic thermal parameters for light ions indicating ion transport pathways
- Lattice volume and parameters
- Detailed description of ion coordination sites
- Detailed insight into bottlenecks
- Description of higher order phenomena
SC-XRD provides uniquely detailed structural insight
Sub-picometer bond length accuracy
- Even for light atoms
- E.g Li – O bond length
1.9037(0.0017) Å
Unit cell parameters
- Database search
- Phase identification by XRPD
Connectivity
- Coordination environment
- Bond character
Structural Details
- Disorder
- Thermal Ellipsoids
- Higher Dimension Order
- Charge density
Composition
- Atom types
- Mixed sites
- Deficiencies
3D Arrangement
- Packing
- Channels
- Potential transport pathways
Application examples
Precise description of light ion coordination sites
NMC mixed metal oxides are commonly used as the cathode material in Li-ion batteries for mobile devices and EVs. There is particular interest in optimizing NMCs to reduce Co- and increase Ni-content to reduce costs and achieve higher capacity.
The structure shown here was determined ab initio from an individual crystallite of only 5 µm with excellent refinement statistics. The Li ions are clearly located between the layered structured with highly precise coordinates. The Li – O distance was determined to 2.1076(32) Å.
The single-crystal structure also provided very accurate mixed site occupation with the following occupancies Co₀.₀₂₀(₄)Mn₀.₀₄₀(₄)Ni₀.₈₆₀(₄)Li₀.₀₈₀(₄)(Li₀.₉₂₀(₄)Ni₀.₀₈₀(₄))O₂. Furthermore, the higher ADPs for Li indicate increased mobility.
Variable-temperature SC-XRD to understand the structural basis for ion migration bottlenecks
Garnet-type LLZO solid electrolytes exhibit promising ionic conductivity properties for all solid-state Li-metal batteries. However, their electrochemical stability in contact with the Li metal cathode is not sufficient for development of practical batteries. Various doped cubic phase LLZO derivatives have shown the required stability but are stable only at high temperatures, exhibiting transition to an unstable tetragonal phase at around 600°C 1. Development of cubic LLZO stable at ambient temperatures is critical for their practical use in batteries.
SC-XRD can provide a detailed understanding of the structure and driving forces behind the phase transitions required to develop better derivatives.
When a single crystal is not a single crystal
Isolating single crystals from solid state preparations can sometimes be a challenge. Being able to determine high-resolution single crystal structures when single crystals are not available is a great advantage.
APEX5 uses advanced routines to reliably process multiple lattices. This allows you take advantage of the detail in single crystal structures when you can only obtain agglomerates of multiple crystals.
Rapid phase identification from microgram powder samples
Bruker’s SC-XRD instruments feature high-intensity X-ray sources and the PHOTON III large area photon-counting detector. This enables fast data collection on microgram amounts of powders to identify phases when larger amounts are not readily available.
XRPD enables convenient confirmation on a single instrument that the crystal form determined by SC-XRD is that of the bulk sample.
Local disorder by pair distribution function analysis
Short-range structure can greatly affect ion transport through local distortion, site disorder and defects. Over the past decade pair distribution function analysis of X-ray total scattering data has become a mature method capable of accurately probing local structure.
The D8 VENTURE HE uses Mo or Ag radiation for maximum sample interaction. The PHOTON III detector is excellent for the accurate measurement of extremely weak signal. Together this enables the efficient collection of accurate total scattering.
