Thin film solid state Li-ion batteries have shown great promise for next generation energy storage devices. Their reduced dimensions, larger gravimetric specific capacity, rapid charge/discharge rates and long cycle life make them an attractive alternative to conventional battery technologies. Moreover, they possess additional benefits in the form of improved operational safety and compatibility with microfabrication technologies [1].

The current commercially available thin film solid state Li-ion batteries possess metallic Li as an anode, which limits their safety and environmental stability, thereby requiring it to be sealed from the environment.

Moreover, current technology allows only the use of amorphous LiPON as the thin film electrolyte because other materials show insufficient conductivity when processed as thin films. This not only limits the possible choices of electrode-electrolyte couplings but also preclude high temperature fabrication of the SSB heterostructure which is required for the growth of the electrodes but would lead to a crystallization of the LiPON layer.

Herein, we evaluate the suitability of an all-oxide Li-ion battery fabricated by pulsed laser deposition. For this purpose, we have employed Li₄Ti₅O₁₂ (LTO) as the anode, LiMn₂O₄ (LMO) as the cathode and Li_4-xGe_1-xP_xO₄ (LGPO) as the electrolyte. LTO exhibits a promising anodic electrochemical performance, with a stability window between 0 V and 5 V , as well as a low volumetric change during Li (de)intercalation [2, 3]. LMO is known for its non-toxicity, high redox potential and specific capacity (4.2 V and 145 mA.h/g) which makes an attractive cathodic layer candidate [4]. As a solid-state oxide electrolyte alternative to LiPON, LGPO exhibits a high ionic conductivity (up to 10^-6 S/cm) at room and high temperature (500 ^oC) regardless of its crystalline properties [5].

We investigate the structural, morphological and electrochemical properties of LTO and LMO, grown on Nb-doped SrTiO₃ substrates buffered with La-doped BaSnO₃ as a current collector in order to provide an improved matching of the lattice parameters and thereby reduce interfacial strain. Both layers are shown to grow epitaxially and can be cycled in liquid cells at high C rates (12C for cathode and 100C for anode). Moreover, LGPO thin films are confirmed to possess Li ion conductivities in the previously reported range.

Subsequently, we demonstrate the potential for the growth of a three-layer structure consisting of LTO, LGPO and LMO to form a complete thin film solid state Li-ion battery and demonstrate the capability for growth on Si substrates to make the fabrication of the complete heterostructure compatible with the conventional microfabrication methods.