Dendrite formation in silicon anodes of lithium-ion batteries

Materials descriptors of machine learning to boost development of lithium-ion batteries

Traditional methods for developing new materials are no longer sufficient to meet the needs of the human energy transition. Machine learning (ML) artificial intelligence (AI) and advancements have caused materials scientists to realize that using AI/ML to accelerate the development of new materials for batteries is a powerful potential tool. Although the use of certain fixed properties of materials as descriptors to act as a bridge between the two separate disciplines of AI and materials chemistry has been widely investigated, many of the descriptors lack universality and accuracy due to a lack of understanding of the mechanisms by which AI/ML operates. Therefore, understanding the underlying operational mechanisms and learning logic of AI/ML has become mandatory for materials scientists to develop more accurate descriptors. To address those challenges, this paper reviews previous work on AI, machine learning and materials descriptors and introduces the basic logic of AI and machine learning to help materials developers understand their operational mechanisms. Meanwhile, the paper also compares the accuracy of different descriptors and their advantages and disadvantages and highlights the great potential value of accurate descriptors in AI/machine learning applications for battery research, as well as the challenges of developing accurate material descriptors.

Fe3 C/nanocarbon-Enabled Lithium Dendrite Mitigation in Lithium-Sulfur batteries

Lithium dendrite-induced short circuits and material loss are two major obstacles to the commercialization of lithium-sulfur (Li-S) batteries. Here, a nanocarbon composite consisting of cotton-derived Fe3 C-encapsulated multiwalled carbon nanotubes (Fe3 C-MWCNTs) and graphene effectively traps polysulfides to suppress lithium dendrite growth is reported. Machine learning combined with molecular dynamics (MD) simulations unveils a new polysulfide-induced lithium dendrite formation mechanism: the migration of polysulfides away from the anode drags out lithium protrusions through localized lattice distortion of the lithium anode and traps lithium ions in the surrounding electrolyte, leading to lithium dendrite formation. The Li-S battery, constructed using the composite of cotton-derived Fe3 C-MWCNTs and graphene that serves as both the sulfur host and the anode interlayer, exhibits exceptional cycling stability, impressive capacity retention, and effective mitigation of lithium dendrite formation. The findings offer valuable strategies to prevent lithium dendrite formation and enhance understanding of lithium dendrite growth in Li-S batteries.

Li, Na, K, Mg, Zn, Al, and Ca Anode Interface Chemistries Developed by Solid-State Electrolytes

Solid-state batteries (SSBs) have received significant attention due to their high energy density, reversible cycle life, and safe operations relative to commercial Li-ion batteries using flammable liquid electrolytes. This review presents the fundamentals, structures, thermodynamics, chemistries, and electrochemical kinetics of desirable solid electrolyte interphase (SEI) required to meet the practical requirements of reversible anodes. Theoretical and experimental insights for metal nucleation, deposition, and stripping for the reversible cycling of metal anodes are provided. Ion transport mechanisms and state-of-the-art solid-state electrolytes (SEs) are discussed for realizing high-performance cells. The interface challenges and strategies are also concerned with the integration of SEs, anodes, and cathodes for large-scale SSBs in terms of physical/chemical contacts, space-charge layer, interdiffusion, lattice-mismatch, dendritic growth, chemical reactivity of SEI, current collectors, and thermal instability. The recent innovations for anode interface chemistries developed by SEs are highlighted with monovalent (lithium (Li+ ), sodium (Na+ ), potassium (K+ )) and multivalent (magnesium (Mg2+ ), zinc (Zn2+ ), aluminum (Al3+ ), calcium (Ca2+ )) cation carriers (i.e., lithium-metal, lithium-sulfur, sodium-metal, potassium-ion, magnesium-ion, zinc-metal, aluminum-ion, and calcium-ion batteries) compared to those of liquid counterparts.

Predictive Molecular Models for Charged Materials Systems: From Energy Materials to Biomacromolecules

Electrostatic interactions play a dominant role in charged materials systems. Understanding the complex correlation between macroscopic properties with microscopic structures is of critical importance to develop rational design strategies for advanced materials. But the complexity of this challenging task is augmented by interfaces present in the charged materials systems, such as electrode-electrolyte interfaces or biological membranes. Over the last decades, predictive molecular simulations that are founded in fundamental physics and optimized for charged interfacial systems have proven their value in providing molecular understanding of physicochemical properties and functional mechanisms for diverse materials. Novel design strategies utilizing predictive models have been suggested as promising route for the rational design of materials with tailored properties. Here, an overview of recent advances in the understanding of charged interfacial systems aided by predictive molecular simulations is presented. Focusing on three types of charged interfaces found in energy materials and biomacromolecules, how the molecular models characterize ion structure, charge transport, morphology relation to the environment, and the thermodynamics/kinetics of molecular binding at the interfaces is discussed. The critical analysis brings two prominent field of energy materials and biological science under common perspective, to stimulate crossover in both research field that have been largely separated.

Designing Versatile Polymers for Lithium-Ion Battery Applications: A Review

Solid-state electrolytes are a promising family of materials for the next generation of high-energy rechargeable lithium batteries. Polymer electrolytes (PEs) have been widely investigated due to their main advantages, which include easy processability, high safety, good mechanical flexibility, and low weight. This review presents recent scientific advances in the design of versatile polymer-based electrolytes and composite electrolytes, underlining the current limitations and remaining challenges while highlighting their technical accomplishments. The recent advances in PEs as a promising application in structural batteries are also emphasized.

Cycling-induced structural damage/degradation of electrode materials-microscopic viewpoint

Most analyses of the mechanical deformation of electrode materials of lithium-ion battery in the framework of continuum mechanics suggest the occurring of structural damage/degradation during the de-lithiation phase and cannot explain the lithiation-induced damage/degradation in electrode materials, as observed experimentally. In this work, we present first-principle analysis of the interaction between two adjacent silicon atoms from the Stillinger-Weber two-body potential and obtain the critical separation between the two silicon atoms for the rupture of Si-Si bonds. Simple calculation of the engineering-tensile strain for the formation of Li-Si intermetallic compounds from the lithiation of silicon reveals that cracking and cavitation in lithiated silicon can occur due to the formation of Li-Si intermetallic compounds. Assuming the proportionality between the net mass flux across the tip surface of a slit crack and the migration rate of the crack tip, we develop analytical formulas for the growth and healing of the slit crack controlled by lithiation and de-lithiation, respectively. It is the combinational effects of the state of charge, the radius of curvature of the crack tip and local electromotive force that determine the cycling-induced growth and healing of surface cracks in lithiated silicon.

Growth Mechanism of Micro/Nano Metal Dendrites and Cumulative Strategies for Countering Its Impacts in Metal Ion Batteries: A Review

Metal-ion batteries are capable of delivering high energy density with a longer lifespan. However, they are subject to several issues limiting their utilization. One critical impediment is the budding and extension of solid protuberances on the anodic surface, which hinders the cell functionalities. These protuberances expand continuously during the cyclic processes, extending through the separator sheath and leading to electrical shorting. The progression of a protrusion relies on a number of in situ and ex situ factors that can be evaluated theoretically through modeling or via laboratory experimentation. However, it is essential to identify the dynamics and mechanism of protrusion outgrowth. This review article explores recent advances in alleviating metal dendrites in battery systems, specifically alkali metals. In detail, we address the challenges associated with battery breakdown, including the underlying mechanism of dendrite generation and swelling. We discuss the feasible solutions to mitigate the dendrites, as well as their pros and cons, highlighting future research directions. It is of great importance to analyze dendrite suppression within a pragmatic framework with synergy in order to discover a unique solution to ensure the viability of present (Li) and future-generation batteries (Na and K) for commercial use.

Production of high-energy Li-ion batteries comprising silicon-containing anodes and insertion-type cathodes

Rechargeable Li-based battery technologies utilising silicon, silicon-based, and Si-derivative anodes coupled with high-capacity/high-voltage insertion-type cathodes have reaped significant interest from both academic and industrial sectors. This stems from their practically achievable energy density, offering a new avenue towards the mass-market adoption of electric vehicles and renewable energy sources. Nevertheless, such high-energy systems are limited by their complex chemistry and intrinsic drawbacks. From this perspective, we present the progress, current status, prevailing challenges and mitigating strategies of Li-based battery systems comprising silicon-containing anodes and insertion-type cathodes. This is accompanied by an assessment of their potential to meet the targets for evolving volume- and weight-sensitive applications such as electro-mobility.

Searching for Mechanically Superior Solid-State Electrolytes in Li-Ion Batteries via Data-Driven Approaches

Li-ion solid-state electrolytes (SSEs) have great potential, but their commercialization is limited due to interfacial contact stability issues and the formation and growth of dendrites. In this study, a machine learning regression algorithm was implemented to screen for mechanically superior SSEs among 17,619 candidates. Elasticity information (14,238 structures) was imported from an available database, and their machine learning descriptors were constructed using physiochemical and structural properties. A surrogate model for predicting the shear and bulk moduli exhibited R² values of 0.819 and 0.863, respectively. The constructed model was applied to predict the elastic properties of potential SSEs, and first-principles calculations were conducted for validation. Furthermore, the application of an active learning process, which reduced the prediction uncertainty, was clearly demonstrated to improve the R² score from approximately 0.6-0.8 by adding only 32-63% of new data sets depending on the type of modulus. We believe that the current model and additional data sets can accelerate the process of finding optimal SSEs to satisfy the mechanical conditions being sought.

Review on Li Deposition in Working Batteries: From Nucleation to Early Growth

Lithium (Li) metal is one of the most promising alternative anode materials of next-generation high-energy-density batteries demanded for advanced energy storage in the coming fourth industrial revolution. Nevertheless, disordered Li deposition easily causes short lifespan and safety concerns and thus severely hinders the practical applications of Li metal batteries. Tremendous efforts are devoted to understanding the mechanism for Li deposition, while the final deposition morphology tightly relies on the Li nucleation and early growth. Here, the recent progress in insightful and influential models proposed to understand the process of Li deposition from nucleation to early growth, including the heterogeneous model, surface diffusion model, crystallography model, space charge model, and Li-SEI model, are highlighted. Inspired by the abovementioned understanding on Li nucleation and early growth, diverse anode-design strategies, which contribute to better batteries with superior electrochemical performance and dendrite-free deposition behavior, are also summarized. This work broadens the horizon for practical Li metal batteries and also sheds light on more understanding of other important metal-based batteries involving the metal deposition process.

Analysis of an all-solid state nanobattery using molecular dynamics simulations under an external electric field

Present Li-ion battery (LIB) technology requires strong improvements in performance, energy capacity, charging-time, and cost to expand their application to e-mobility and grid storage. Li-metal is one of the most promising materials to replace commercial anodes such as graphite because of its 10 times higher specific capacity. However, Li-metal has high reactivity with commercial liquid electrolytes; thus, new solid materials are proposed to replace liquid electrolytes when Li-metal anodes are used. We present a theoretical analysis of the charging process in a full nanobattery, containing a LiCoO2 cathode, a Li7P2S8I solid-state electrolyte (SSE), a Li-metal anode as well as Al and Cu collectors for the cathode and anode, respectively. In addition, we added a Li3P/Li2S film as a solid electrolyte interphase (SEI) layer between the Li-anode and SSE. Thus, we focus this study on the SEI and SSE. We simulated the charging of the nanobattery with an external voltage by applying an electric field. We estimated temperature profiles within the nanobattery and analyzed Li-ion transport through the SSE and SEI. We observed a slight temperature rise at the SEI due to reactions forming PS3- and P2S74- fragments at the interfaces; however, this temperature profile changes due to the charging current under the presence of the external electric field ε = 0.75 V Å-1. Without the external field, the calculated open-circuit voltage (OCV) was 3.86 V for the battery, which is within the range of values of commercial cobalt-based LIBs. This voltage implies a spontaneous fall of available Li-ions from the anode to the cathode (during discharge). The charge of this nanobattery requires overcoming the OCV plus an additional voltage that determines the charging current. Thus, we applied an external potential able to neutralize the OCV, plus an additional 1.6 V to induce the transport of Li+ from the cathode up to the anode. Several interesting details about Li+ transport paths through the SSE and SEI are discussed.

Solid electrolyte interphase formation between the Li0.29La0.57TiO3 solid-state electrolyte and a Li-metal anode: an ab initio molecular dynamics study

An ab initio molecular dynamics study of an electrochemical interface between a solid-state-electrolyte Li_0.29La_0.57TiO₃ and Li-metal is performed to analyze interphase formation and evolution when external electric fields of 0, 0.5, 1.0 and 2.0 V Å^-1 are applied. From this electrochemical stability analysis, it was concluded that lithium-oxide (Li₂O) and lanthanum-oxide (La₂O₃) phases were formed at the electrolyte/anode interphase. As the electric field increased, oxygen from the electrolyte diffused through the Li-metal anode, increasing the amount of O from deeper crystallographic planes of the electrolyte that reacted with Li and La. A strong reduction of Ti was expected from their Bader charge variation from +3.5 in the bulk to +2.5 at the interface. Due to the loss of Li atoms from the anode to form Li-oxide at the interphase, vacancies were created on the Li-metal, causing anode structure amorphization near the Li-oxide phase and keeping the rest of the anode structure as BCC. Therefore, the interface was unstable because of the continuous Li-oxide and La-oxide formation and growth, which were more pronounced when increasing the external electric field.

Tuning Two Interfaces with Fluoroethylene Carbonate Electrolytes for High-Performance Li/LCO Batteries

Various electrolytes have been reported to enhance the reversibility of Li-metal electrodes. However, for these electrolytes, concurrent and balanced control of Li-metal and positive electrode interfaces is a critical step toward fabrication of high-performance Li-metal batteries. Here, we report the tuning of Li-metal and lithium cobalt oxide (LCO) interfaces with fluoroethylene carbonate (FEC)-containing electrolytes to achieve high cycling stability of Li/LCO batteries. Reversibility of the Li-metal electrode is considerably enhanced for electrolytes with high FEC contents, confirming the positive effect of FEC on the stabilization of the Li-metal electrode. However, for FEC contents of 50 wt % and above, the discharge capacity is significantly reduced because of the formation of a passivation layer on the LCO cathodes. Using balanced tuning of the two interfaces, stable cycling over 350 cycles at 1.5 mA cm-2 is achieved for a Li/LCO cell with the 1 M LiPF6 FEC/DEC = 30/70 electrolyte. The enhanced reversibility of the Li-metal electrode is associated with the formation of LiF and polycarbonate in the FEC-derived solid electrolyte interface (SEI) layer. In addition, electrolytes with high FEC contents lead to lateral Li deposition on the sides of Li deposits and larger dimensions of rodlike Li deposits, suggesting the elastic and ion-conductive nature of the FEC-derived SEI layer.

Dendrite formation in Li-metal anodes: an atomistic molecular dynamics study

Lithium-metal is a desired material for anodes of Li-ion and beyond Li-ion batteries because of its large theoretical specific capacity of 3860 mA h g⁻¹ (the highest known so far), low density, and extremely low potential. Unfortunately, there are several problems that restrict the practical application of lithium-metal anodes, such as the formation of dendrites and reactivity with electrolytes. We present here a study of lithium dendrite formation on a Li-metal anode covered by a cracked solid electrolyte interface (SEI) of LiF in contact with a typical liquid electrolyte composed of 1 M LiPF₆ salt solvated in ethylene carbonate. The study uses classical molecular dynamics on a model nanobattery. We tested three ways to charge the nanobattery: (1) constant current at a rate of one Li⁺ per 0.4 ps, (2) pulse train 10 Li⁺ per 4 ps, and (3) constant number ions in the electrolyte: one Li⁺ enters the electrolyte from the cathode as one Li⁺ exits the electrolyte to the anode. We found that although the SEI does not interfere with the lithiation, the mere presence of a crack in the SEI boosts and guides dendrite formation at temperatures between 325 K and 410.7 K at any C-rate, being more favorable at 325 K than at 410.7 K. On the other hand, we find that a higher C-rate (2.2C) favors the lithium dendrite formation compared to a lower C-rate (1.6C). Thus the battery could store more energy in a safe way at a lower C-rate.

Lithium dendrites (blue) growing through the cracks of a SEI (orange) covering a Li-metal anode (blue) while lithiation by Li-ions (purple). The electrolyte is not shown.