Sintering Effects on the Resistivity of LiNi1/3Mn1/3Co1/3O2/Ceramic-Solid-Electrolyte Interface in an All-Solid-State Battery

Abstract

Introduction Rechargeable all-solid-state-lithium batteries (SSBs) with oxide-based electrolytes are expected to be one of the new generation of energy storage devices because of their high energy density and sufficient safety. However, one of the problems SSBs is large interfacial resistance between electrode and solid electrolyte. Factors of interfacial resistance are attributed to high contact resistance due to solid-solid interface, formation of mutual diffusion layer at the interface [1, 2], and formation of space charge layer at the interface [3, 4]. In these cases, electrolyte/electrode interfacial modification by ionic conductive or dielectric materials has been suggested to as an effective method. On the other hand, effect of electrode/solid electrolyte sintering temperature on interfacial resistance has been not really investigated. In this work, we deposited LiNi1/3Mn1/3Co1/3O2 (NMC) films on Li1+x+yAlyTi2−ySixP3−xO12 (LATP) sheets by pulse laser deposition (PLD) at different temperatures. We also investigated the interface structure and electrochemical properties. Experimental NMC films were deposited on one side of LATP sheet by PLD at 700 and 900 °C (hereinafter NMC-7 and NMC-9, respectively) (150 nm in thickness). Electrochemical properties of LATP/NMC half-cells were measured by cyclic voltammetry (CV) and AC impedance spectroscopy. The bare side of LATP and lithium as reference and counter electrodes in half cell were immersed in propylene carbonate containing 1 mol dm-3 LiClO4. Also, structure analyses were carried out by XRD and TEM. Results and Discussion Fig. 1(a) shows CVs of fabricated half-cells measured at 1 mV s-1. A LATP/NMC-7 half cell shows a pair of oxidation and reduction peaks at 3.90 V and 3.68 V while no redox reactions were observed in a LATP/NMC-9 half cell. LATP/NMC interfacial resistivities in LATP/NMC-7 and NMC-9 half cells were estimated to be 750 Ω cm2 and >40000 Ω cm2, respectively. This result indicates that NMC-9 have high resistive LATP/NMC interface. Fig. 1(b) shows a cross-sectional TEM image of LATP/NMC-9 interface and EDS line profiles along the yellow arrow. Ni, Mn, and Co concentrations were constant in the NMC-9 region near the intersurface. However, Co and Ni concentrations increase and decrease near the interface. This elemental distributions were not observed in LATP/NMC-7 interface where Ni, Mn, and Co concentrations were constant through the NMC-7 region. Therefore, another phase formed at NMC near the interface, resulting in high interfacial resistance. Detailed interfacial structure will be discussed in the session. Acknowledgement This work was supported by JST-ALCA.