Materials for All-Solid-State Lithium Ion Batteries

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Materials for All-Solid-State Lithium Ion Batteries Sumaletha Narayanan, Lina Truong, and Venkataraman Thangadurai* University of Calgary, 2500 University Drive, Calgary, Alberta, T2N 1N4, Canada. ABSTRACT Garnet-type electrolytes are currently receiving much attention for applications in Li-ion batteries, as they possess high ionic conductivity and chemical stability. Doping the garnet structure has proved to be a good way to improve the Li ion conductivity and stability. The present study includes effects of Y- doping in Li5La3Nb2O12 on Li ion conductivity and stability of “Li5+2xLa3Nb2-xYxO12” (0.05 ≤ x ≤ 0.75) under various environments, as well as chemical stability studies of Li5+xBaxLa3-xM2O12 (M = Nb, Ta) in water. “Li6.5La3Nb1.25Y0.75O12” showed a very high ionic conductivity of 2.7 х 10-4 Scm-1 at 25 °C, which is comparable to the highest value reported for garnet-type compounds, e.g., Li7La3Zr2O12. The selected members show very good stability against high temperatures, water, Li battery cathode Li2CoMn3O8 and carbon. The Li5+xBaxLa3-xNb2O12 garnets have shown to readily undergo an ion-exchange (proton) reaction under water treatment at room temperature; however, the Ta-based garnet appears to exhibit considerably higher stability under the same conditions. INTRODUCTION Rechargeable Li-ion batteries play a major role in the field of energy storage and are used for variety of applications, ranging from portable electronics to electric vehicles. The higher volumetric and gravimetric energy densities make them superior among other known batteries, including lead acids, and Ni-metal hydrides. The current Li ion batteries contain flammable organic solvents incorporated with an organic polymer and Li salts as the electrolyte, Li-C as the anode and LiCoO2 as the cathode. Several safety concerns exist such as leakage problems and fire hazards associated with organic solvents. The use of all-solid-state batteries by replacing the liquid with a solid state electrolyte would be much safer. Ceramic materials with different crystal structures such as A-site deficient perovskites, NASICON (sodium super ionic conductor) structured phosphates, and LIPON (lithium phosphorous oxynitride) were previously investigated and the conductivity results for some important solid electrolytes are shown in Figure 1 [1-5]. Surprisingly, none of these materials show high ionic conductivity and chemical stability electrodes as well as high electrochemical stability window. Solid (metal oxide) electrolytes with high total (bulk + grain-boundary) ionic conductivity > 10-3 Scm-1 and high electrochemical stability have potential to replace the polymer electrolytes in current Li ion batteries. It is generally believed that all-solid-state Li ion batteries using ceramic electrolytes are potentially safer and will provide higher energy densities.

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20 0

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T ( C)

-1

log10σ (Scm )

-1 -2 -3 -4 Li0.34La0.51TiO2.94 (LLT)

-5

Li3N Li1.3Ti1.7Al0.3(PO4)3 (NASICON -type)

-6 -7

Li14ZnGe4O16 (LISICON) Li2.9PO3.3N0.46 (LIPON)

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