Most commercial rechargeable lithium-ion batteries deliver energy densities far below their theoretical values. The key problem determining these limitations are the slow electrode process kinetics, low ionic diffusion and low electronic conductivity, particularly at the electrode-electrolyte interfaces. Mastering control of these interfaces is identified as a grand challenge in battery research, even more important than designing new electrode and electrolyte materials.

All-solid-state microbatteries facilitate miniaturization, which will create more flexibility for the design of stand-alone microelectronic devices with enhanced applicability due to the avoided leakage risks. However, the successful application of all-solid-state microbatteries depends strongly on the enhancement of energy density and lifetime. The cycle-life and lifetime are dependent on the nature of the interfaces between the electrodes and electrolyte, whereas safety is a function of the stability of the electrode materials and interfaces. Therefore, perfect control on the interfacial properties between the electrodes and electrolyte is needed, but remains a great challenge.

The crystal structure of the electrode, electrolyte matrix and their interfaces will determine the lithium diffusion mechanism within the complete structure, which will eventually be crucial for the battery performance. To study the variation in electrochemical properties for the different crystalline directions in the spinel crystal structure of the LiMn₂O₄ cathode material, thin films have been grown by pulsed laser deposition. Control over the deposition parameters (temperature, pressure, etc.) in combination with variation in crystal orientation of the Nb-doped SrTiO₃ substrates (e.g. (001), (111) and (110)) enabled the formation of single crystalline LiMn₂O₄ thin films.

The local variations in surface morphology and phase composition have been analyzed by Atomic Force Microscopy (AFM) and X-Ray Photoelectron Spectroscopy (XPS), while the variations in structural properties have been characterized by X-ray Diffraction (XRD). Electrochemical performance was studied by impedance spectroscopy.

In our study we have investigated the relation between the electrochemical performance and the crystal orientation in LiMn₂O₄ cathode thin films. This provides important insight for the subsequent creation of solid-state cathode/electrolyte interfaces with controlled crystal structures for optimal interfacial properties.