Enhanced Durability of a Lithium Ion Secondary Battery Using Solid Electrolyte LICGCTM

Abstract

Lithium Ion Conducting Glass Ceramic (LICGCTM) with a NASICON type structure was developed using industrial glass melting methods and functions as a solid lithium ion electrolyte.1-3) The ionic conductivity of the glass ceramic with Li1+x+yAlxTi2–xSiyP3–yO12 specific composition has values equal to or greater than 1×10-3 Scm-1 at room temperature. The NASICON type structure of LICGCTM was formed and crystalized in the starting bulk amorphous glass during heat treatment. The resulting glass ceramic has high chemical resistance and does not lose weight in boiling distilled water. The ionic conductivity of this electrolyte does not deteriorate, even if soaked in an aqueous of Li salt solution4-5. These characteristics indicate LICGCTM might be used to partially replace organic electrolytes and to enhance the properties of lithium ion secondary batteries.The effects of using LICGCTM in powder form as a cathode additive for lithium ion secondary batteries were investigated by OHARA is presented in this paper. LICGCTM powder of a controlled particle size, 0.4μm(D50), was prepared to fit into the inter-particle gaps of active materials generally used in a cathode. The cathode slurry was prepared by mixing standard cathode component materials (active material, carbon, binder) with LICGCTM powder and NMP. The slurry was then coated onto Al foil to form the cathode. The electrochemical performance of the NMC cathode, when evaluated in a half cell, indicated a capacity increase of 21% at 3C discharge and a reduced charging time of 20% at CC-CV condition, compared to a standard cathode with equal capacity. A full cell was fabricated using the cathode containing the LICGCTM powder additive and a carbon anode. The DC resistance of the full cell at DOD50 was decreased by more than 20%. We confirmed that LICGCTM powder when used as a cathode additive is effective in enhancing the performance of lithium ion secondary batteries. OHARA proceeded to evaluate battery retention capacity at 60℃. At this temperature, the charge and discharge cycle numbers of a lithium ion battery containing 1% LICGCTM powder in the NMC cathode increased by 4 times, at the point where the retention capacity is typically decreased by 10%, and the battery capacity at 300 cycles was increased by 14%. In the case of a lithium ion battery containing 1% LICGCTM powder additive in the LCO cathode at 60℃, the retention capacity was increased by 13% at 300 cycles. It was determined the 1% LICGCTM powder additive in the cathode inhibits the generation of the resistive layer and X-ray absorption spectroscopy (XAS, Ritsumeikan Univ. SR center) indicated the improved surface state of the LCO active material resulted in longer battery lifetime. OHARA’s results indicate that cathodes containing LICGCTM glass ceramic electrolyte powder can significantly improve battery retention capacity, by controlling the degradation of the cathode, when charging and exposed at high temperature.