RESEARCH 

  A FIRST PRINCIPLES-BASED  STUDY FOR THE DEVELOPMENT OF ALL-SOLID-STATE ELECTROLYTES FOR SUSTAINABLE ELECTROCHEMICAL ENERGY STORAGE 

Developing energy-efficient materials to reduce global warming is a crucial problem for scientists and engineers in the twenty-first century. India's per capita oil consumption and carbon emissions have surged by more than 300% and 400%, respectively, over the last 40 years. In 2016, the government of India initiated one of the fastest-growing renewable energy programs to meet the Paris accord and cut carbon emissions. Our energy needs can only be addressed by judicious use of renewable energy sources and the development of new materials for electrical devices that consume less energy. 

Despite being inexpensive, liquid electrolytes used in consumer electronics batteries exhibit poor chemical and physical stability. For example, leakage of toxic organic solvents, high flammability, side reactions at the electrodes resulting in the formation of solid-electrolyteinterphase (SEI), which results in capacity loss, and short circuits caused by the formation of dense dendrites. Solid-state electrolytes (SSE) have emerged as promising candidates in this context because they exhibit excellent chemical and physical stability, perform satisfactorily as thin films, and inhibit dendrite formation while allowing selective conduction of lithium ions. 

In this context, SSEs are safe and also offer efficient utilization because of higher gravimetric and volumetric energy densities. Therefore, these systems are suitable for use in portable electronics and electronic vehicles. Adopting a trial-and-error based experimental strategy to determine the most appropriate material for a system from a large catalogue of alternatives may be both sluggish and expensive. Furthermore, essential material qualities like strength and conductivity are controlled by atomistic mechanisms. Thus, the emergence of computational modelling for these complex systems is fascinating and promising. Numerous materials can be screened using state-of-the-art computer simulations, and laboratory trials will focus on the most promising candidates.

Developing a novel good solid electrolyte is dependent on a variety of structural factors, including defects, composition, symmetry, decomposition energy, and thus on the performance characteristics of the electrolyte, including ionic conductivity, phase stability, chemical and electrochemical stability, and mechanical properties. 

Our research investigates the ionic transport mechanisms in disordered sulfide solid-state electrolytes, specifically Li10SiP2S12 (LSiPS) and Li10SnP2S12 (LSnPS). These materials are potential candidates for next-generation all-solid-state lithium-ion batteries due to their high ionic conductivity, structural stability, and cost-effectiveness compared to traditional LGPS-based electrolytes.

Key Highlights

Objective: To understand the role of disorder and cation substitution (Sn/Si) in enhancing lithium-ion mobility and electrochemical stability.

Approach: Employing advanced computational methods, including Car-Parrinello molecular dynamics in an NPT ensemble, to capture the complex behavior of disordered sublattices.

Research Insights

1. Material Design

Substitution of germanium with earth-abundant tin and silicon improves cost-effectiveness and interfacial stability.

Structural disorder in LSiPS and LSnPS enables diverse bonding environments, enhancing ionic mobility.

2. Computational Methodology

Framework: Ensemble statistics and variable cell relaxations to identify representative structures from billions of atomic configurations.

Techniques: Quantum ESPRESSO and Wannier90 for structural relaxations, band gap analysis, and ionic transport property calculations.

3. Transport Properties

Diffusivity and Conductivity: Enhanced lithium-ion transport with lower activation energies in Si-substituted systems.

Temperature Effects: High-temperature studies reveal additional diffusion pathways and reduced migration barriers.

4. Electrochemical Stability

LSiPS exhibits a wider band gap (2.4 eV) compared to LSnPS (2.0 eV), indicating superior electrochemical stability.

Wannier function analysis shows dynamic changes in chemical bonding states with temperature.

Impact and Future Directions

Advancements in Battery Technology: This research demonstrates the potential of sulfide-based solid electrolytes to replace liquid counterparts in all-solid-state batteries.

Future Work: Exploration of doping strategies, machine learning-driven molecular simulations, and long-term ionic mobility studies to optimize material performance.

Publications and Presentations

• V. Maithani, S. Das, and S. Mukherjee, “Cooperative Transport of Lithium in Disordered Li₁₀MP₂S₁₂ (M = Sn, Si) Electrolytes for Li-Ion Batteries,” Chemistry of Materials, 2024.

• A. Anuragi, A. Das, A. Baski, V. Maithani, and S. Mukherjee, "Machine Learning Predicted Inelasticity in Defective Two-Dimensional Transition Metal Dichalcogenides Using SHAP Analysis," Physical Chemistry Chemical Physics, 26, no. 21 (2024): 15316-15331.

• V. Maithani, S. Das, and S. Mukherjee, “Lithium Transport in Superionic Halide (LiGaXn) Solid electrolytes. (Submitted to Journal of Materials Chemistry A)

• V. Maithani, S. Mukherjee, “Advanced Insights into the Transport and Surface Characteristics of Li11AlP2S12 Solid-State Electrolytes. (Submitted to Applied Materials and interfaces)

• Presentation: CAMD-2024, Electronic Structure Theory and Materials Design, Technical University of Denmark, August 18-23, 2024, Topic: “Li-Transport and Temperature Dependent Elasticity in Disordered Li₁₀SiP₂S₁₂ Solid Electrolyte”

• Presentation: International Conference on 60 Years of DFT: Advancements in Theory & Computation, IIT Mandi, July 21-26, 2024, Topic: “Li Transport in Sulfide Solid-State Electrolytes”