Lithiation Mechanism Research Articles

Reversible Iron Oxyfluoride (FeOF)-Graphene Composites as Sustainable Cathodes for High Energy Density Lithium Batteries

Two large barriers are impeding the wide implementation of battery electric vehicles, namely driving-range and cost, primarily due to the low specific capacity/energy and high cost of mono-valence cathodes (e.g. LiNi0.8Co0.1Mn0.1O2) used in lithium-ion batteries. Iron is the ideal element of choice for cathode materials considering its abundance, low cost and toxicity. Two fundamental challenges, in particular, the poor reversibility of (de)lithiation and low electronic conductivity, prevent those iron based high specific capacity/energy multi-valence conversion cathodes from practical applications. In this work, we have developed a sustainable FeOF nanocomposite with extraordinary performance. In particular, we were able to reach the theoretical specific capacity of 621 mAh·g-1 and 1,124 Wh·kg-1 specific energy (2.1-valence change/2.1 Li+ stored per unit) and more than 100 cycles with 80% capacity retention at 0.1C (realizing the reversible (de)lithiation), which is 3 times of the specific capacity, and 2 times of the specific energy of current mono-valence intercalation LiCoO2 respectively (i.e., 145 mAh·g-1 and 551 Wh·kg-1). This is the result of an effective approach, combing the nanostructured FeOF with graphene sheets to solve these challenges, realized by (1) making the (de)lithiation reversible by immobilizing FeOF nanoparticles and the discharge products of Fe nanoparticle and LiF over the graphene surface, and sandwiching them between graphene sheets to prevent them from migration and dissolution into electrolytes and (2) providing the inter-particle electric conductivity. In situ high energy synchrotron X-ray absorption spectroscopy (XAS) reveals that this new FeOF composite has a different but reversible (de)lithiation mechanism. Importantly, it demonstrated that introducing small amount of graphene can create new materials with desired properties, opening a new avenue for altering the (de)lithiation process. Such extraordinary performance represents a significant breakthrough in developing the sustainable conversion materials for replacing the intercalation compounds, eventually overcoming the driving range and cost barriers.

Thermodynamics of multi-sublattice battery active materials: from an extended regular solution theory to a phase-field model of LiMnyFe1-yPO4

Phase separation during the lithiation of redox-active materials is a critical factor affecting battery performance, including energy density, charging rates, and cycle life. Accurate physical descriptions of these materials are necessary for understanding underlying lithiation mechanisms, performance limitations, and optimizing energy storage devices. This work presents an extended regular solution model that captures mutual interactions between sublattices of multi-sublattice battery materials, typically synthesized by metal substitution. We apply the model to phospho-olivine materials and demonstrate its quantitative accuracy in predicting the composition-dependent redox shift of the plateaus of LiMnyFe1-yPO4 (LFMP), LiCoyFe1-yPO4 (LFCP), LiCoxMnyFe1-x-yPO4 (LFMCP), as well as their phase separation behavior. Furthermore, we develop a phase-field model of LFMP that consistently matches experimental data and identifies LiMn0.4Fe0.6PO4 as a superior composition that favors a solid solution phase transition, making it ideal for high-power applications.

Molten salt synthesis, morphology modulation, and lithiation mechanism of high entropy oxide for robust lithium storage

High entropy oxides (HEOs) with ideal element tunability and enticing entropy-driven stability have exhibited unprecedented application potential in electrochemical lithium storage. However, the general control of dimension and morphology remains a major challenge. Here, scalable HEO morphology modulation is implemented through a salt-assisted strategy, which is achieved by regulating the solubility of reactants and the selective adsorption of salt ions on specific crystal planes. The electrochemical properties, lithiation mechanism, and structure evolution of composition- and morphology-dependent HEO anode are examined in detail. More importantly, the potential advantages of HEOs as electrode materials are evaluated from both theoretical and experimental aspects. Benefiting from the high oxygen vacancy concentration, narrow band gap, and structure durability induced by the multi-element synergy, HEO anode delivers desirable reversible capacity and reaction kinetics. In particular, Mg is evidenced to serve as a structural sustainer that significantly inhibits the volume expansion and retains the rock salt lattice. These new perspectives are expected to open a window of opportunity to compositionally/morphologically engineer high-performance HEO electrodes.

Matching silicon-based anodes with sulfide-based solid-state electrolytes for Li-ion batteries

Thanks to their high ionic conductivity and appropriate mechanical properties, sulfide-based solid electrolytes (SSE) are increasingly studied for a use in all-solid-state batteries (ASSBs). Silicon is abundant, non toxic and has a high theoretical capacity, and therefore is a promising active material in ASSBs. We first study the compatibility between two different solid electrolytes with similar ionic conductivity, Li10SnP2S12 (LSnPS) and Li6PS5Cl (LPSCl), and micron-sized silicon based anode. LPSCl appears to be less reactive than LSnPS and it is then used to determine the most appropriate silicon size and shape for efficient cycling. Two silicon materials are compared, micron-sized silicon particles (μSi) and silicon nanowires (SiNWs). Energy Dispersive X-ray spectroscopy (EDX) mapping of the composite powders shows a better dispersion of the SiNWs in the LPSCl matrix. Galvanostatic cycling and Electrochemical Impedance Spectroscopy (EIS) measurements highlight the greater compatibility of SiNWs compared to μSi in ASSBs with a high specific delithiation capacity of 2600 mAh/gSi at the first cycle, while limiting the polarization and maintaining a relatively stable lithiation mechanism during cycling.

MAS NMR and DFT study of electrochemical performance of silicon nanoparticle as anodes for Li-ion batteries

In this work we have investigated the effect of slurry pH on the lithiation mechanism of silicon nanoparticle (SiNP) anodes in lithium-ion batteries. To this end, we have used a combination of lithium (7Li) and silicon (29Si) magic angle spinning nuclear magnetic resonance (MAS NMR), density functional theory (DFT), and electrochemical charge–discharge cycling. The NMR results show that different lithiation mechanisms are present depending on the pH. An acidic slurry facilitates the lithiation of SiNP, whereas a basic slurry oxidises the SiNP to form a shell of SiO/SiO2, which must be cracked before Si lithiation becomes relevant. In a basic slurry, the leading process during the first cycle is the reaction of Li+ and SiO/SiO2 to form lithium silicates. Consequently, this intermediate step leads to a greater capacity loss in the basic media than in the acidic one.

New perspectives on spatial dynamics of lithiation and lithium plating in graphite/silicon composite anodes

Huge volume expansion, unstable SEI-film evolution and uncontrollable Li plating remain challenging issues for achieving high energy-density and fast charging graphite/silicon anodes. Unfortunately, less reports on Li plating in graphite/silicon anodes have been found up to now. Herein, for the first time, we report that the interfacial polarization of silicon dominates the co-lithiation process with graphite, thus determining the preferential Li-plating sites and SEI film evolution. Interestingly, the disturbance of local electrochemical potential due to consecutive volume variation of silicon upon cycling, indeed keep Li plating sites changing and deteriorate the battery performances. In a typical case of silicon, global electrochemical potential-equilibrium of electrons in silicon can be achieved by regulating Li-ion diffusion kinetic in silicon, thus delaying Li-plating on graphite. Comparing to commercial silicon, P-type photovoltaic silicon exhibits weaker disturbance of local electrochemical potential upon volume variation, resulting in smaller change in Li-plating sites and smaller re-growth SEI film. Therefore, our findings propose a new perspective on the competitive lithiation mechanism and Li plating for graphite/silicon anodes which is highly desirable for designing high-capacity and fast-charging graphite/silicon.

Study of the Electrochemical and Self-healing Processes of Galinstan as an Anode Material for Li-ion Batteries

Alloy electrodes are attracting a lot of interest in the field of Li-ion batteries due to their high energy density. However, they suffer from large volume expansion and contraction during lithiation and delithiation, leading to rapid pulverization and disconnection. A strategy to avoid this is to use self-healing materials. Ga-based liquid alloys have been studied as self-healing electrodes because of their capacity to store Li and their liquid state at room temperature. The so-called “galinstan” (Ga0.77In0.15Sn0.08) exhibits the lowest melting temperatures and has also been used to add self-healing properties in composite electrodes. Nevertheless, its lithiation mechanism and its practical capacity still remain unknown. Also, the reversibility of the lithiation, which is crucial to ensure the self-healing properties offered by the liquid metal, requires investigation. In this work, electrochemical measurements were coupled with XRD and SEM analyses to better understand the redox processes, structural and morphological properties of galinstan as an electrode material in Li-ion batteries. It was shown that only Ga and In would react with Li to form LiGa and LiIn. The reversibility of these reactions and thus the self-healing ability of galinstan was demonstrated through observation of its liquid state before and after electrochemical cycling.

Tin Metal Improves the Lithiation Kinetics of High-Capacity Silicon Anodes

Si-based anodes present a great promise for high energy density lithium-ion batteries. However, its commercialization is largely hindered by a grand challenge of a rapid capacity fade. Here, we demonstrate excellent cycling stability on a Si–Sn thin film electrode that outperforms pure Si or Sn counterpart under the similar conditions. Combined with the first-principles calculations, in situ transmission electron microscopy studies reveal a reduced volume expansion, increased conductivity, as well as dynamic rearrangement upon lithiation of the Si–Sn film. We attribute the improved lithiation kinetics to the formation of a conductive matrix that comprises a mosaic of nanostructured Sn, LiySn (specifically, Li7Sn2 develops around the lithiation potential of Si), and LixSi. This work provides an important advance in understanding the lithiation mechanism of Si-based anodes for next-generation lithium-ion batteries.

Sb-Cu alloy cathode with a novel lithiation mechanism of ternary intermetallic formation: Enabling high energy density and superior rate capability of liquid metal battery

Sb-Cu alloy cathode with a novel lithiation mechanism of ternary intermetallic formation: Enabling high energy density and superior rate capability of liquid metal battery

Development and Validation of a ReaxFF Reactive Force Field for Modeling Silicon–Carbon Composite Anode Materials in Lithium-Ion Batteries

Silicon–carbon (Si–C) nanocomposites have recently established themselves among the most promising next-generation anode materials for lithium (Li)-ion batteries. Indeed, combined Si and graphitic (sp2-C) phases exhibit high energy densities with reasonable electrochemical responses, while covalently bonded silicon carbide (SiC) compounds offer high mechanical stiffness to withstand structural degradation. However, to form and utilize a Si–C composite structure that effectively satisfies specific battery energy, power, and lifetime requirements, it is necessary to understand the underlying atomistic mechanisms at work within its individual phases and at their interfaces. Here, we develop and validate a reactive interatomic potential (ReaxFF) for the Li–Si–C system, trained and tested against a large, diverse collection of ab initio data. In conjunction with molecular dynamics and Monte Carlo simulations, our new force field links macroscale phenomena to the nanostructures of various hybrid Si–C systems in a wide range of lithiation, temperature, and stress conditions. As an illustration, it demonstrates that the high capacity of SiC (5882 mA h g–1) is caused by amorphous lithium carbides (e.g., a-Li4.4C), which soften the overall a-Li4.4(SiC)0.5 system while swelling it volumetrically up to 668%. Furthermore, our force field accurately depicts step-wise lithiation mechanisms and volume changes in Si–sp2-C composites throughout the lithiation domain of each host subsystem. It reveals the formation of a Li-rich interphase at their grain boundary, which favors their adhesion and increases the local Li (de)insertion voltage up to 1 V. These examples demonstrate the ability of the new Li–Si–C ReaxFF potential to provide atomistic-scale insights required for designing and optimizing a wide range of Si–C-based anode candidates for upcoming Li-ion battery technologies.

Electrochemical properties and facile preparation of hollow porous V2O5 microspheres for lithium-ion batteries

Vanadium pentoxide (V2O5) has shown great potential to be used in lithium-ion batteries (LIBs), but it has limited applications because it has cycle instability and poor rate capability, and its lithiation mechanism is not well understood. In this work, hollow porous V2O5 microspheres (HPVOM) were obtained by a facile poly(vinylpyrrolidone) and ethylene glycol-assisted soft-template solvothermal method. Half cells with HPVOM exhibited good capacity, rate capability, and stability, delivering 407.9 mAh g−1 at 1.0 A g−1 after 700 cycles. Furthermore, a LiFePO4/HPVOM full cell had a discharge capacity of 109.9 mAh g−1 after 150 cycles at 0.1 A g−1. Using an equivalent circuit model (ECM) and distribution of relaxation times (DRT), we found that the charge-transfer (including the solid-state interface resistance) and bulk resistances varied regularly with the charge/discharge state, while the electrolyte resistance was largely maintained. The bulk resistance finally vanished, indicative of dynamic activation. The method used to prepare the hollow microspheres, as well as the display of electrode kinetics via ECM and DRT, could be broadly applied in developing efficient electrodes for LIBs.

One-step method synthesis of cobalt-doped GeZn1.7ON1.8 particle for enhanced lithium-ion storage performance

The exploration of alternative anode materials to obtain the satisfactory lithium-ion storage performance is crucial for next-generation energy storage devices. Herein, the rational design of a completely new anode material is reported by a simple solid state reaction method, which follows an insertion-type lithiation mechanism, cobalt-doped GeZn1.7ON1.8 (Co-GeZn1.7ON1.8). The introduced cobalt increases the achievable capacity by more than 100%, originating from the additional space for the lithium-ion insertion. The Co-GeZn1.7ON1.8 particle anode delivered high capacity (861.4 mAh g−1 at 0.1 A g−1 after 200 cycles) and ultralong cycling stability (2000 cycles at 1.0 A g−1 with a maintained capacity of 435 mAh g−1), which represents outstanding comprehensive electrochemical performance. Electrochemical kinetic results confirms the existence of the pseudocapacitive and the reduced lithium-ion diffusion barrier in the Co-GeZn1.7ON1.8 particle anode. Furthermore, ex-situ XRD and XPS analyses corroborate the reversible intercalation electrochemical reaction mechanism of the Co-GeZn1.7ON1.8 anode. This study offers a new vision toward designing high-performance quaternary metallic oxynitrides-based materials for large-scale energy storage applications.

Recent developments in Nb‐based oxides with crystallographic shear structures as anode materials for high‐rate lithium‐ion energy storage

AbstractHigh‐power lithium‐ion batteries (LIBs) are required for a variety of technological applications, especially in the field of electric vehicles (EVs). Oxides based on niobium, titanium, and tungsten, and having crystallographic shear structures, are considered promising materials for high‐rate anodes of LIBs. The unique structures with open channels, multielectron redox processes, and a moderate potential window with a resulting solid electrolyte interface‐free interface provide them with rapid Li‐ion diffusion pathways, fairly high capacities, and high safety. In this review, the recent advancements in diverse crystallographic shear structure Nb‐based oxide anodes for fast Li‐ion energy storage are comprehensively presented, with a specific focus on the relationships between the crystal structures and electronic properties, lithiation mechanisms, kinetic properties, and electrochemical performance. The challenges in the design, optimization, and practical application of oxides with crystallographic shear structures are also discussed, together with strategies to overcome these challenges and prospects for the future.

Correction: Understanding the lithiation mechanism of Li2O-doped spinel high-entropy oxides as anode materials for Li-ion batteries

Correction for ‘Understanding the lithiation mechanism of Li2O-doped spinel high-entropy oxides as anode materials for Li-ion batteries’ by Renzong Hu et al., Energy Adv., 2023, https://doi.org/10.1039/D3YA00326D.

Understanding the electrochemical reaction mechanism to achieve excellent performance of the conversion-alloying Zn2SnO4 anode for Li-ion batteries

New insights into the (de-)lithiation mechanism of the Zn2SnO4 conversion-alloying anode material obtained by an industry-scalable method allowed preparing fully operational anodes for Li-ion full-cells through controlling the anode's working range.

Understanding the lithiation mechanism of Li2O-doped spinel high-entropy oxides as anode materials for Li-ion batteries

This work proposes an Li2O-doping strategy for improving the lithium storage ability of a high-entropy oxide, and its lithiation process is investigated in detail, which may promote the further development of high-entropy oxide anodes.

Unveiling the (de-)lithiation mechanism of nano-sized LiMn2O4 allows the design of a cycling protocol for achieving long-term cycling stability

Operando XAS and XRD of nano-sized LiMn2O4 shed light on the (de-)lithiation and Jahn–Teller distortion mechanisms. The finding helps to design a cycling protocol, with periodic deep discharge to 2 V, leading to superior cycling performance at 4.3 V.

The Role of Oxygen in Lithiation and Solid Electrolyte Interphase Formation Processes in Silicon-Based Anodes

Silicon oxides (SiOx) have been considered as promising alternatives to pure Si in high energy anodes in lithium-ion batteries (LIBs) due to their improved cycling stability. However, their fundamental lithiation mechanism has not yet been systematically investigated, and potential collateral downsides remain unclear. In this work, we report on the role of oxygen in lithiation/delithiation and solid electrolyte interphase (SEI) formation processes in SiOx thin film model electrodes with different oxygen contents. We show that the SiOx anodes with higher oxygen content experience smaller volume change and form a thinner and more stable SEI, both of which are beneficial for cycling stability. However, these SiOx anodes also show an irreversible lithiation at around 0.7 V attributed to the reduction of Si oxides, leading to lower first cycle coulombic efficiency that is undesirable for practical applications. Overall, these results offer a balanced perspective on the advantages and disadvantages that oxygen brings to Si-based anodes in LIBs.

Probing Capacity Trends in MLi2Ti6O14 Lithium-Ion Battery Anodes Using Calorimetric Studies.

Due to higher packing density, lower working potential, and area specific impedance, the MLi2Ti6O14 (M = 2Na, Sr, Ba, and Pb) titanate family is a potential alternative to zero-strain Li4Ti5O12 anodes used commercially in Li-ion batteries. However, the exact lithiation mechanism in these compounds remains unclear. Despite its structural similarity, MLi2Ti6O14 behaves differently depending on charge and size of the metal ion, hosting 1.3, 2.7, 2.9, and 4.4 Li per formula unit, giving charge capacity values from 60 to 160 mAh/g in contrast to the theoretical capacity trend. However, high-temperature oxide melt solution calorimetry measurements confirm strong correlation between thermodynamic stability and the observed capacity. The main factors controlling energetics are strong acid-base interactions between basic oxides MO, Li2O and acidic TiO2, size of the cation, and compressive strain. Accordingly, the energetic stability diminishes in the order Na2Li2Ti6O14 > BaLi2Ti6O14 > SrLi2Ti6O14 > PbLi2Ti6O14. This sequence is similar to that in many other oxide systems. This work exhibits that thermodynamic systematics can serve as guidelines for the choice of composition for building better batteries.

Operando visualization of kinetically induced lithium heterogeneities in single-particle layered Ni-rich cathodes

<h2>Summary</h2> Understanding how lithium-ion dynamics affect the (de)lithiation mechanisms of state-of-the-art nickel-rich layered oxide cathodes is crucial to improve electrochemical performance. Here, we directly observe two distinct kinetically induced lithium heterogeneities within single-crystal LiNi_xMn_yCo_(1−x−y)O₂ (NMC) particles using recently developed <i>operando</i> optical microscopy, challenging the notion that uniform (de)lithiation occurs within individual particles. Upon delithiation, a rapid increase in lithium diffusivity at the beginning of charge results in particles with lithium-poor peripheries and lithium-rich cores. The slow ion diffusion at near-full lithiation states—and slow charge transfer kinetics—also leads to heterogeneity at the end of discharge, with a lithium-rich surface preventing complete lithiation. Finite-element modeling confirms that concentration-dependent diffusivity is necessary to reproduce these phenomena. Our results demonstrate how kinetic limitations cause significant first-cycle capacity losses in Ni-rich cathodes.