[Paper Review] Design Principles for Self-forming Interfaces Enabling Stable Lithium Metal Anodes

Yingying Zhu, Vikram Pande+6 more|arXiv (Cornell University)|Mar 22, 2019

Advancements in Battery Materials65 references66 citations

TL;DR

This study identifies ionicity and compactness as key descriptors for designing stable solid-electrolyte interphases (SEIs) on lithium metal anodes, enabling high Coulombic efficiency and dendrite-free plating. By engineering an SEI rich in LiF, Li2CO3, and Li2SO3, the authors achieve stable cycling of thin Li metal anodes (20–50 µm) in full cells with LiCoO2 cathodes, exceeding 240 cycles at 0.2C/0.5C rates with 80% capacity retention.

ABSTRACT

The path toward Li-ion batteries with higher energy-densities will likely involve use of thin lithium metal (Li) anode (<50 $\mu$m in thickness), whose cyclability today remains limited by dendrite formation and low Coulombic efficiency. Previous studies have shown that the solid-electrolyte-interface (SEI) of Li metal plays a crucial role in Li electrodeposition and stripping. However, design rules for optimal SEIs on lithium metal are not well-established. Here, using integrated experimental and modeling studies on a series of structurally-similar SEI-modifying compounds as model systems, we reveal the relationship between SEI compositions, Li deposition morphology and coulombic efficiency, and identify two key descriptors (ionicity and compactness) for high performance SEIs through integrated experimental and modeling studies. Using this understanding, we design a highly ionic and compact SEI that shows excellent cycling performance in LiCoO$_2$-Li full cells at practical current densities. Our results provide guidance for the rational selection and optimization of SEI modifiers to further improve Li metal anodes.

Motivation & Objective

• To address the critical challenge of low Coulombic efficiency and dendrite formation in thin lithium metal anodes.
• To establish rational design rules for solid-electrolyte interphases (SEIs) that enable stable lithium plating and stripping.
• To demonstrate high-performance cycling of thin Li metal anodes (20–50 µm) in practical full-cell configurations with LiCoO2 cathodes.
• To identify universal descriptors—ionicity and compactness—that predict high-performance SEI compositions.

Proposed method

• Integrated experimental and density functional theory (DFT) modeling on a series of structurally similar SEI-modifying compounds.
• Quantitative analysis of SEI composition effects on lithium deposition morphology and Coulombic efficiency.
• Use of DFT to calculate Bader charges and volumes, assessing charge transfer and reactivity of solvent molecules and ions on Li surfaces.
• Systematic variation of electrolyte components to form SEIs enriched in LiF, Li2CO3, and Li2SO3 with high ionicity and compactness.
• Full-cell testing of LiCoO2-Li cells with 20–50 µm Li anodes at practical C-rates (0.2C charge/0.5C discharge).
• Derivation of theoretical relationships between Coulombic efficiency, Li excess (Fp), and cycle life using Equations [1]–[3] to predict performance.

Experimental results

Research questions

• RQ1 How do SEI composition and microstructure influence lithium deposition morphology and Coulombic efficiency in thin lithium metal anodes?
• RQ2 What are the fundamental descriptors that predict high-performance SEIs for lithium metal anodes?
• RQ3 Can a highly ionic and compact SEI suppress dendrite formation and improve Coulombic efficiency in practical full cells?
• RQ4 What is the impact of Li metal thickness and Coulombic efficiency on the cycle life and energy density of full batteries?
• RQ5 Can the identified design principles enable stable cycling of thin Li metal anodes (20–50 µm) at practical current densities?

Key findings

• A highly ionic and compact SEI enriched with LiF, Li2CO3, and Li2SO3 enables dendrite-free lithium plating and stripping.
• Full cells with 50 µm Li anodes and LiCoO2 cathodes achieve >240 cycles with 80% capacity retention at 0.2C charge/0.5C discharge.
• Even 20 µm Li anodes achieve 130 cycles under the same conditions, demonstrating viability of ultra-thin anodes.
• Theoretical modeling predicts that a Coulombic efficiency of 99.9% enables over 1000 cycles in an anode-free configuration.
• Ionicity and compactness are identified as the two key descriptors for high-performance SEIs, enabling rational design beyond trial-and-error.
• DFT calculations confirm that LiF passivates the Li surface, reducing further reactivity with electrolyte, and that charge transfer to solvent is minimized on such surfaces.