Ph. D. Thesis Colloquium
Name: Mr. Ajeet Kumar Rana
Research Supervisor: Prof. Naga Phani B. Aetukuri
Title: Understanding Interfacial Processes in High-Purity and High-Density Garnet-Based Lithium Metal Batteries
Date and Time: Friday, 16th October 2026 at 11:00 a.m.
Venue: Rajarshi Bhattacharyya Memorial Lecture Hall, Chemical Sciences Building
Abstract:
Solid-state Li-metal batteries employing solid electrolytes (SEs) offer higher energy densities while still being safer compared to conventional liquid-electrolyte based batteries [1]. Among various SEs, garnet Li7La3Zr2O12 (LLZO) is often preferred due to its high ionic conductivity (0.1 – 1 mS cm-1) and wide electrochemical stability window (5 – 6 V vs Li+/Li) [2], [3]. However, lithium dendrite growth in LLZO electrolytes leading to cell failure is commonly reported by many research groups [4], [5]. A microscopic understanding of interfacial and bulk properties that lead to dendrite growth in LLZO are still not fully understood.
In this work, we address some of these challenges by first establishing a protocol to synthesize high-purity (~99 %) and high-density (~98 %) Li6.4La3Zr1.4Ta0.6O12 (LLZTO) solid electrolyte. We show that high-purity and high-density in LLZTO can be simultaneously realized using conventional cold-pressing (60–65 MPa) followed by pressure-less sintering [6]. We successfully synthesized electrolytes that exhibited high ionic conductivity of up to 1 mS cm-1 and with critical current densities for lithium dendrite growth approaching 1 mA cm-2. High critical current densities are essential for solid-state batteries that are resilient lithium dendrite growth. In this talk, we will discuss the origins of impurities and in LLZTO and their correlation with poor sinter densities, ionic conductivity and critical current density.
Next, we will discuss an impedance spectroscopy-based approach that we developed to probe Li/LLZTO interfaces under varying external stimuli such as deposition potential, pressure and temperature. The developed methodology can perform operando impedance measurements to frequencies of up to 10 MHz while being amenable for the application of pressures of up to 400 MPa over a temperature range of room temperature to 140 ºC. Using this set-up, we first deconvolute the various interfacial processes employing a variable-amplitude impedance spectroscopy approach coupled with distribution of relaxation times (DRT) analysis. We will discuss how the non-linearity of the charge-transfer (CT) process helped deconvolute the CT process from the other interfacial processes such as electrode-electrolyte constriction and mass transfer polarization [7]. We will also discuss the application of this approach for measuring degradation in electrolyte/cathode interfaces in solid-state full cells with SE/cathode interfacing enabled by liquid electrolytes. Our work establishes an operando electrochemical approach for measuring and characterizing solid-solid electrode/electrolyte interfaces without the need for ex-situ microscopy or synchrotron techniques that are often cumbersome and time-consuming.
Finally, we will discuss a chemical modification approach that selectively forms LiF at sub-surface grain boundaries of LLZTO electrolytes. We show that this approach mitigates the oft-reported lithium growth along grain boundaries in LLZTO-based electrolytes [8]. Remarkably, the grain boundary modification with LiF enabled a transition from an intergranular to a transgranular Li-filamentation mode with a concomitant 3-fold increase in critical current density [9]. We will discuss the driving forces for this transition in lithium filamentation mode and its utility in realizing solid electrolytes with higher resilience to lithium dendrite growth.
References:
[1] J. Janek and W. G. Zeier, “A solid future for battery development,” Nat. Energy, vol. 1, no. 9, p. 16141, Sep. 2016.
[2] R. Murugan, V. Thangadurai, and W. Weppner, “Fast Lithium Ion Conduction in Garnet‐Type Li7 La3 Zr2 O12,” Angew Chem Int Ed, vol. 46, no. 41, pp. 7778–7781, Oct. 2007.
[3] T. Thompson et al., “Electrochemical Window of the Li-Ion Solid Electrolyte Li7La3Zr2O12,” ACS Energy Lett., vol. 2, no. 2, pp. 462–468, Feb. 2017.
[4] V. Raj, V. Venturi, V. R. Kankanallu, B. Kuiri, V. Viswanathan, and N. P. B. Aetukuri, “Direct correlation between void formation and lithium dendrite growth in solid-state electrolytes with interlayers,” Nat. Mater., vol. 21, no. 9, pp. 1050–1056, Sep. 2022.
[5] V. Raj et al., “Dendrite Growth—Microstructure—Stress—Interrelations in Garnet Solid‐State Electrolyte,” Adv. Energy Mater., vol. 14, no. 15, p. 2303062, Apr. 2024.
[6] A. K. Rana et al. (Manuscript under review).
[7] A. K. Rana et al. (Manuscript under preparation).
[8] V. Raj, N. P. B. Aetukuri, and J. Nanda, “Solid state lithium metal batteries – Issues and challenges at the lithium-solid electrolyte interface,” Curr. Opin. Solid State Mater. Sci., vol. 26, no. 4, p. 100999, Aug. 2022.
[9] A. K. Rana et al., “Intergranular to transgranular lithium filamentation in a garnet solid-state electrolyte,” J. Mater. Chem. A, p. 10.1039.D6TA00099A, 2026.