A novel low-temperature solid-state route for nanostructured cubic garnet Li₇La₃Zr₂O₁₂ and its application to Li-ion battery

Abstract

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...

Reactive flash sintering of powders of four constituents into a single phase of a complex oxide in a few seconds below 700°C

“…Both higher and lower conductivities have been reported in the literature; they range from 0.001 mS cm -1 , 23 to 0.16 mS cm -1 , 24 to 0.99 mS cm -1 . The principal sophistication in flash is programming of the power supply which provided electrical voltage and current to the specimen.…”

Achieving high performance for aluminum stabilized Li 7 La 3 Zr 2 O 12 solid electrolytes for all solid‐state Li‐ion batteries: A thermodynamic point of view

“…The bands between 100 and 150 cm −1 were the vibrations of La cations where the wide band at about 640 cm −1 could be ascribed as Zr―O bond stretching. It has been recently reported that the Raman shift at 157 cm −1 was the characteristic peak of the tetragonal LLZO phase, and the shift at 289 cm −1 was continually decreased and disappeared when cubic LLZO phase was stabilized . The band at around 520 cm −1 was T 2g mode of Li 2 O and appeared first in the sample sintered at 1100°C …”

“…It has been recently reported that the Raman shift at 157 cm −1 was the characteristic peak of the tetragonal LLZO phase, and the shift at 289 cm −1 FIGURE 2 XRD patterns of wet and dry mixed precursors for solid-state LLZO synthesis was continually decreased and disappeared when cubic LLZO phase was stabilized. 16,17 The band at around 520 cm −1 was T 2g mode of Li 2 O and appeared first in the sample sintered at 1100°C. 18 The presence of Li 2 O in Figures 3 and 4 was believed to be due to the well-documented Li exclusion phenomenon during Al incorporation in cubic LLZO structure based on the reaction given below: 19 Li…”

Reducing the Interfacial Resistance in All‐Solid‐State Lithium Batteries Based on Oxide Ceramic Electrolytes

“…However, the solid‐solid contact of the electrolyte/electrode leads to a large Li + transmission resistance at the interface . Moreover, Li + ions also exhibit poor transport performance inside the solid electrode without a liquid electrolyte, which is not beneficial for the reaction of the electrode materials (low capacity) and fast charge/discharge (low rate performance) . Reducing the interfacial resistance is crucial to the commercial application of ASSLBs …”

“…[34][35][36] Moreover, Li + ions also exhibit poor transport performance inside the solid electrode without a liquid electrolyte, which is not beneficial for the reaction of the electrode materials (low capacity) and fast charge/discharge (low rate performance). [37][38][39] Reducing the interfacial resistance is crucial to the commercial application of ASSLBs. [40] In this review, we mainly summarize the strategies used to reduce the interfacial resistance in ASSLBs based on OCEs.…”