We present a novel approach to the solid-state synthesis of garnet-type cubic Li7La3Zr2O12 (c-LLZO) nanostructured particles with 1.0 mass% Al at 750 o C within 3 h. In contrast to conventional solid-state processes, a highly reactive precursor was prepared in two steps: (i) by homogenizing the stoichiometric mixture without Li, and (ii) subsequent addition of Li in the form of an ethanolic solution of lithium acetate. The actual composition determined by ICP analysis was Li6.61La3Zr2Al0.13O11.98. Sintering these nanoparticles at 1100 o C for 3 h in air after cold isostatic pressing brought a dense ceramic pellet with a relative density of 90.5%. The corresponding ionic conductivity with Au electrodes was 1.6 × 10 −4 S cm −1 at room temperature. To study its electrochemical behavior as an electrolyte, a model cell of Li//(1M LiPF6 + c-LLZO)//LiCoO2 configuration was constructed. Cyclic voltammetry of the cell delivered one set of redox couple with narrow voltage separation (15 mV) with a Li + diffusion coefficient at room temperature of about 2 × 10 −11 cm 2 s −1 at the interface between LiCoO2 and 1M LiPF6 + c-LLZO. The cell received an average discharge capacity of 64.4, 60.3, 56.1, 51.9 and 46.9µAh cm −2 µm −1 at discharge rates 0.5C, 1C, 2C, 4C and 6C, respectively. The cell exhibited complete oxidation and reduction reactions with an average initial discharge capacity of about 64 µAh cm −2 µm −1 , which is 92.7 % of LiCoO2 theoretical value.These observations indicate the applicability of the present c-LLZO as an electrolyte for a solid-state Li-ion battery. IntroductionA lithium ion battery (LIB) with higher safety and affordability is of utmost importance for better utilization of renewable energy and high-energy electric vehicles. 1,2 Stringent requirements are highenergy density, long cycle life with improved safety, reliability and leakage-free properties in wider operating temperature regimes, enabling a cost-effective process. In current battery technology, we have relatively promising electrode materials in terms of higher energy density and structural stability. On the other hand, we still use flammable, volatile and unstable organic solvents based electrolytes containing Li-salts with polymer separator in all types of conventional Li-ion batteries. These electrolytes not only cause irreversible capacity losses due to the formation of solid-electrolyte interphases (SEI), but also limit the safety of the batteries. Solidstate electrolytes (SSE) with fast Li-ion diffusion were recognized as promising alternative, addressing better thermal and chemical stabilities and opening a wider operational temperature window. 3 For the high-performance SSE, however, great challenges remain, such as: (i) increase in the ionic conductivity and (ii) optimization of fabrication processes. 4 Within the variety of SSE including lithium superionic conductor (LISICON), thio-LISICON or sodium superionic conductor (NASICON), garnet-type c-LLZO is regarded as one of the most promising SSE due to its high ionic conductivity...

Built-in electric field (BIEF)-induced charge transfer in planar and bulk junctions has significantly improved electrochemical performance in current and advanced energy storage devices such as lithium, sodium, and aluminum batteries. In this study, fuel cells with different junctions based on semiconductor membranes were designed in thin-film planar, bulk planar, and bulk heterojunction (BHJ) configurations to investigate the BIEF effects on their electrochemical performance. These semiconductor membrane fuel cells were constructed with p-type LiCoO2 and n-type SnO2 sandwiched between Ni0.8Co0.15Al0.05LiO2 (NCAL) electrode semiconductors. At 600 °C, the fuel cells with bulk heterojunction (BHJ), bulk planar p–n junction, and thin-film planar p–n junction deliver remarkable peak power densities of 0.82, 0.61, and 0.28 W/cm2 in H2/air operation, respectively. The band structures were determined and the charge transport properties and device operation were investigated. Our results show that the semiconductor membrane-based devices are a good alternative to replace the conventional electrolyte membrane fuel cells for the next generation of fuel-to-electricity conversion technology.

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