All solid state batteries are widely investigated as next generation batteries because they do not suffer from leakage, volatilization, and flammability of liquid electrolyte. Both bulk type and thin film solid batteries have attract great attention. LiCoO₂ thin film has been commonly used as the cathode material for solid state batteries due to its high capacity, operating voltage and long cycle life. Because of the importance of the solid-solid interface for the performance of the battery and stability during cycling, i.e. its life time, the interface of substrate/LiCoO₂ and LiCoO₂/solid electrolyte during the preparation of the solid battery and possible intermediate products in the interlayer attract great attention recently. [1]

 The deposition parameters has a big influence on the film quality in terms of structure, morphology and electrochemical properties. In the case of layered LiCoO₂, lithium-ion diffusion rely on vacancy hopping mechanism within the lithium plane, showing a predominant two dimensional path. Therefore, different orientation of lattice could influence the intercalation properties of LiCoO₂ thin film deposited. [2] A primary challenge in all solid state battery is the difficulty of rapidly moving charge across solid/solid interface within the electrodes and across the electrode/electrolyte interface. The consecutive study on electrode and/or electrolyte has achieved great progress for the last decades. However, interfaces still dominate the interfacial impedance during electrochemical reaction. The optimization of interface of substrate/LiCoO₂ and LiCoO₂ /solid electrolyte could direct the further improvement of current all solid state batteries.  Both lithium ion mobility and electrochemical reaction of LiCoO₂ thin film with the solid electrolyte and the substrate are related to the interfacial resistance, which could be minimized through controlling growth orientation of LiCoO₂during deposition.[3] Therefore, the ionic transportation across solid/solid interface and electrode/electrolyte interface are increased, leading to improved electrochemical performance.

In this work, we optimize the deposition parameter to get high crystalline HT-LiCoO₂ with hexagonal structure and good electrochemical performance firstly. Next, we study on sputtering deposition of LiCoO₂ with different orientation in order to study the LiCoO₂/substrate and LiCoO₂/solid state electrolyte interface. The compositional (XPS), microstructural (XRD, Raman, SEM) and electrochemical properties of the sputtering LiCoO₂thin films with different orientation are investigated.  For the study of interface, we will adopt advanced technique to investigate the chemical/physical changes at the interface layers.

Reference

[1] Luntz, Alan C., et al. The journal of physical chemistry letters 6.22 (2015): 4599-4604.

[2] Bates, J. B., et al. Journal of The Electrochemical Society 147.1 (2000): 59-70.

[3] Yoon, Yongsub, et al. Journal of Power Sources226 (2013): 186-190.