Lithiation Mechanism Research Articles

Multi-electron reactions and chain conversion of amorphous cathodes to improve the specific capacity of rechargeable lithium batteries

This study explores the impact of the oxidation-reduction reaction process and Mo-V diatomic coupling on lithiation by introducing Mo2B as a reducing agent into the structure of V2O5-Li3PO4 glass. The results show that the mixed system simultaneously generated B2O3, MoO3 and VO2. With the increase of B2O3, the [BO3] triangle transformed into the [BO4] tetrahedron, accompanied by the boron anomaly effect, and V5+ transformed into V4+. 65V2O5-30Li3PO4-5BMo2 (VPBMo2) showed chain conversion with an excellent specific capacity (the first discharge specific capacity was 289.9 mAh g−1), rate performance, structural stability and had the highest electronic conductivity. The lithiation mechanism of the V-Mo coupling multi-electron reaction was found to increase the specific capacity of the lithium ion battery. According to DFT calculations, the VPBMo2 showed magnetism and became metallic. After Li adsorption, the peak density of states at the Fermi level to the guide band, indicating improved conductivity of the VPBMo2.

A novel Sb-Zn electrode with ingenious discharge mechanism towards high-energy-density and kinetically accelerated liquid metal battery

Liquid metal battery (LMB) has recently captured intensive attention for large-scale energy storage, originating from its attractive cost-efficiency, robust cyclability, and ultralong service lifetime. Nevertheless, realizing high energy density remains a great challenge. Herein, a novel dual-active Sb-Zn electrode is elaborately designed. A unique lithiation mechanism is demonstrated for the first time in LMB field. A ternary intermetallic compound LiZnSb is preferentially formed with a high discharge plateau at ca. 1.1 V, which is followed by a conversion reaction to Li3Sb and Zn at around 0.8 V and then a consecutive dissolution reaction of lithium in molten Zn, significantly ameliorating the voltage and capacity properties. Meanwhile, part Zn melts regenerate and disperse among discharge product layer, constructing rapid electron/lithium percolating networks in-situ, which accelerates the electrode reaction kinetics. As a result, the Li||Sb-Zn battery exhibits high average discharge voltage of 0.763 V at 100 mA cm−2 and superior rate performance (0.596 V at 1000 mA cm−2). Outstanding energy and power densities (290.6 Wh kg−1 and 239.66 W kg−1) are achieved, remarkably surpassing most reported LMBs and even comparable to Na-S battery. This work showcases an innovative electrochemistry system, opening a new avenue for high-performance LMBs.

Revealing the complex lithiation pathways and kinetics of core-shell NiO@CuO electrode

• Three-dimensional core-shell NiO@CuO electrode via simple phase separation strategy. • The NiO@CuO exhibits superior rate and stability performance. • The reaction kinetics and lithium pathways of the NiO@CuO electrode are revealed. • The chemomechanical simulation discloses the mechanical kinetics during lithium storage. Nanostructured composite electrodes with multiple active phases offer extraordinary performance that can be harnessed in future batteries. However, it is difficult to disclose the complicated reaction pathways. In this work, NiO@CuO core-shell nanocomposites are prepared and used as anodes for lithium-ion batteries, with superior rate and stability performance compared with single-phase CuO and NiO. Using a combination of in situ and ex situ electron microscopy, a two-stage lithiation reaction pathway on NiO@CuO is identified, with CuO reduced to Cu 2 O first and followed by the simultaneous reduction of both Cu 2 O and NiO to metals, resolving the existing inconsistency in literature. Chemomechanical simulation further discloses the key role of the core-shell structure in high cycling stability of NiO@CuO, which decreases the probability of cracking during the discharge-charge process. This work provides new insights to explore lithiation mechanisms and kinetics in novel electrodes, which contribute to further development of various electrode materials. Three-dimensional core-shell structured NiO@CuO nanoparticles deliver high lithium storage performance. By incorporating advanced electron microscopic analysis with chemomechanical simulation, complex lithiation reaction pathways, the reaction kinetics and capacity contributions for different species are fully revealed.

The lithiation onset of amorphous silicon thin-film electrodes

The lithiation onset of amorphous silicon (a-silicon) films up to 10% state of charge (SOC) is characterized by a Li+-uptake region around 0.5 V vs a Li reference electrode. In the literature, this is commonly attributed to surface processes such as the formation of a solid electrolyte interphase layer and/or the reduction of the surface native oxide, and more seldom to bulk processes such as reduction of oxygen contaminations inside the silicon film and to silicon lithiation. This work presents evidence that this process is associated with the lithiation of elemental silicon using electrochemical and non-electrochemical measurements and including a discussion of literature data. Cyclic voltammetry performed on pre-lithiated a-silicon and a-silicon films with different oxygen concentrations and with different film thicknesses reveals a lithiation process that is not associated with the reduction of oxygen. Elemental depth-profiling with secondary ion mass spectrometry (SIMS) reveals a two-phase lithiation mechanism at the lithiation onset, which sharply delimits non-lithiated silicon from a Li-poor phase of constant Li content (Li0.3Si). The published operando neutron reflectometry data suggest that this is also the case for oxygen-free Si single crystal wafers. SIMS measurements further show that the whole a-silicon thin film is converted into the Li-poor phase. This phase remains stable in the vicinity of the current collector even at 100% SOC, indicating that mechanical stress may play an important role.

Unexpected reversible crystalline/amorphous (de)lithiation transformations enabling fast (dis)charge of high-capacity anatase mesocrystal anode

High-power, fast-charging capability is an urgent issue for the development of advanced Li-ion batteries (LIBs) for electrified mobility applications. An anatase titanium oxide mesocrystal (TOM) Li-ion battery (LIB) anode comprising extremely small (3–5 nm) and crystallographically coherent nanocrystallite subunits demonstrate a high specific capacity (up to 225 mAh g-1) and extraordinary rate capability and cycle stability under stressful currents (83 % capacity retention after 9000 cycles at 10 C rate, 1 C = 168 mA g-1), considerably outperforming the conventional nanocrystalline titanium oxide (TO) electrode. The investigation of the underlying (de)lithiation mechanism using synchrotron X-ray analyses and density functional theory calculations reveals a novel crystalline–amorphous–crystalline pathway for TOM involving an amorphous phase existing within a Li stoichiometry range approximately LixTiO2, x = 0.2–0.9. The combination of structure amorphization and existing of a fast inter-grain diffusion network inherent to the hierarchical interior of mesocrystal empowers the TOM electrode with orders-of-magnitude higher diffusion rates as compared with the TO electrode. The single-crystal-like crystallographic coherence of the (de)lithiation end-products enables favorable chemo-mechanical stability to avert particle cracking during high-rate cycling. The study indicates a potential new direction for engineering cycle-stable fast-charging electrode materials.

C-Rate Capability of Ion-Beam Sputter Deposited Silicon, Carbon and Silicon/Carbon Multilayer Thin Films for Li-Ion Batteries

Silicon is highly desired as high-energy density active Li storage material in Li-ion batteries, but usually does not withstand extended cycling. This work examines the C-rate capability up to Li plating and the long term cycling for ion-beam sputter-deposited amorphous (Si/C) × 10 multilayers (MLs) (with individual layer thicknesses between 5 and 27 nm), as well as for amorphous silicon and carbon single layers (with film thicknesses between 14 and 230 nm). Differential capacity plots were analyzed to examine the lithiation and delithiation mechanism. The silicon single-layers are stable for the first five cycles only, with a behavior of thinner films similar to supercapacitors. The carbon single layers show good cycling stability but also low capacities similar to graphite. The combination of silicon and carbon within Si/C MLs improved capacity and cycling behavior. The Li+ insertion and extraction process from the Si/C MLs is reversible and dominated by silicon. It coincides even at high currents (10C) and after hundreds of cycles with that of the thicker silicon film at its initial cycles. The MLs combine the positive property of carbon (reversible cycling) and of silicon (high capacity). Thinner carbon layers in the ML increase the silicon capacity for all cycles. The topic of irreversible Li-losses is discussed.

Small angle neutron scattering and its application in battery systems

Small angle neutron scattering is a powerful, non-destructive technique that can provide both structural and compositional information. Recently, it has been applied to the field of battery research and has helped elucidate some of the phenomena that are traditionally difficult to probe, including lithiation mechanisms, solid electrolyte interface formation/composition, and electrode microstructure. Specific components of interest can be selectively probed through the application of targeted experiments, contrast variation, and specific composition/structural models gained from complementary data from other analytical techniques.

ToF-SIMS Li Depth Profiling of Pure and Methylated Amorphous Silicon Electrodes After Their Partial Lithiation.

Pure (a-Si:H) and methylated [a-Si0.95(CH3)0.05:H] amorphous silicon thin films were analyzed by time-of-flight secondary ion mass spectrometry after partial lithiation. Depth profiling gives insights into the lithiation mechanism of the material, enabling us to study the detailed biphasic process in the first lithiation process. Lithiation induces swelling and roughening of the active layer. In both a-Si:H and a-Si0.95(CH3)0.05:H, no measurable Li diffusion was observed after stopping current-induced lithiation. After applying the same lithiation charges, distinct Li profiles were observed for these two materials. Unlike a-Si:H, the Li concentration drops slowly from the heavily lithiated region to the non-lithiated region in a-Si0.95(CH3)0.05:H. This apparent progressive transition between the lithiated and lithium-free regions is attributed to the presence of nanovoids inside the material. When their concentration is high enough, these nanovoids constitute favorable quasi-percolating paths for lithium during the first lithiation. A specific model was developed to simulate the Li depth profiles, fully supporting this hypothesis.

New organic electrode materials for lithium batteries produced by condensation of cyclohexanehexone with p-phenylenediamine

The redox-active materials based on the condensation product of cyclohexanehexone with p-phenylenediamine (PTDA) were synthesized. The effect of the reactant ratios (1: n, n = 1, 2, 3) on the morphology and electrochemical properties of the resulting polymers PTDA1-PTDA3 was analyzed. In the case of PTDA3, a regular network crosslinked by CN-C bonds is formed resulting in a significant increase in the practical capacity of this material from 160 to 285 mAh g−1 corresponding to a three-electron redox process. Quantum-chemical modeling was performed to clarify the peculiarities of the lithiation mechanism. It is shown that the best sites for lithium cation coordination are adjacent oxygen and nitrogen atoms or two nitrogen atoms. For all polymer structures, sequential redox lithiation-delithiation processes have been established.

Comprehensive Approach to Investigate the De‐/Lithiation Mechanism of Fe‐Doped SnO2 as Lithium‐Ion Anode Material

AbstractIron‐doped tin oxide (Sn0.9Fe0.1O2), and specifically carbon‐coated Sn0.9Fe0.1O2 (Sn0.9Fe0.1O2‐C) provides high reversible capacity and a reasonably low de‐/lithiation potential owing to the combined conversion and alloying mechanism. The initial (quasi‐)amorphization during the first lithiation, however, renders an in‐depth understanding of the reaction mechanism challenging. Herein, a comprehensive investigation via a set of highly complementary characterization techniques is reported, including operando X‐ray diffraction, ex situ 119Sn and 57Fe Mössbauer spectroscopy, ex situ 7Li NMR spectroscopy, operando isothermal microcalorimetry (IMC) of Li‖Sn0.9Fe0.1O2‐C coin cells, and electrochemical microcalorimetry of single Sn0.9Fe0.1O2‐C electrodes. The combination of these advanced techniques allows for detailed insights into the lithiation and delithiation mechanism and the potential determining processes, despite the (quasi‐) amorphous nature of the active material after the initial lithiation.

(De)Lithiation and Strain Mechanism in Crystalline Ge Nanoparticles.

Germanium is a promising active material for high energy density anodes in Li-ion batteries thanks to its good Li-ion conduction and mechanical properties. However, a deep understanding of the (de)lithiation mechanism of Ge requires advanced characterizations to correlate structural and chemical evolution during charge and discharge. Here we report a combined operando X-ray diffraction (XRD) and ex situ 7Li solid-state NMR investigation performed on crystalline germanium nanoparticles (c-Ge Nps) based anodes during partial and complete cycling at C/10 versus Li metal. High-resolution XRD data, acquired along three successive partial cycles, revealed the formation process of crystalline core-amorphous shell particles and their associated strain behavior, demonstrating the reversibility of the c-Ge lattice strain, unlike what is observed in the crystalline silicon nanoparticles. Moreover, the crystalline and amorphous lithiated phases formed during a complete lithiation cycle are identified. Amorphous Li7Ge3 and Li7Ge2 are formed successively, followed by the appearance of crystalline Li15Ge4 (c-Li15Ge4) at the end of lithiation. These results highlight the enhanced mechanical properties of germanium compared to silicon, which can mitigate pulverization and increase structural stability, in the perspective for developing high-performance anodes.

Li+ additive accelerated structural transformation of MoS2 cathodes for performance-enhancing rechargeable Mg2+ batteries

Rechargeable magnesium ion batteries (MIBs) with intercalation materials as the cathode are found to offer better performance in Li+ based electrolytes. Herein, we compare the electrochemical performance of MIBs using all-phenyl complex (APC) electrolytes before and after adding Li+ additives with layered MoS2 cathodes. We coincidentally describe the lithiation mechanism that leads to a phase transition whereby Li+ additives accelerate a MoS2 structural transformation from 2H to 1T which accounts for the superior battery performance (150 mAh/g, around two times the capacity of that without Li+ additives). In this process, MoS2 is partly exfoliated into single-layer nanosheets during cycle as evidenced by operando electrochemical synchrotron X-ray diffraction, ex situ X-ray photoelectron spectroscopy and scanning electron microscopy analyses. Accordingly, electrochemical cells with pre-exfoliated MoS2 nanosheets (liquid phase exfoliation) require fewer activation cycles (50 cycles, a quart of the cycles that using pristine MoS2) in APC electrolyte and better rate performance. Our work thus provides new insight in designing high-performance rechargeable MIBs by optimizing the intercalation cathodes using Li+ additives.

Synergistic Effect of Co and Mn Co-Doping on SnO2 Lithium-Ion Anodes

The incorporation of transition metals (TMs) such as Co, Fe, and Mn into SnO2 substantially improves the reversibility of the conversion and the alloying reaction when used as a negative electrode active material in lithium-ion batteries. Moreover, it was shown that the specific benefits of different TM dopants can be combined when introducing more than one dopant into the SnO2 lattice. Herein, a careful characterization of Co and Mn co-doped SnO2 via transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy and X-ray diffraction including Rietveld refinement is reported. Based on this in-depth investigation of the crystal structure and the distribution of the two TM dopants within the lattice, an ex situ X-ray photoelectron spectroscopy and ex situ X-ray absorption spectroscopy were performed to better understand the de-/lithiation mechanism and the synergistic impact of the Co and Mn co-doping. The results specifically suggest that the antithetical redox behaviour of the two dopants might play a decisive role for the enhanced reversibility of the de-/lithiation reaction.

First Principles Study of Layered CrGeTe3 as Lithium Intercalation Compound

There have been unprecedented research efforts to produce efficient and sustainable electrode materials for lithium-ion batteries (LIB). The research efforts to increase energy density, life cycle, safety, and rate-capability are still in progress. This work is carried out to explore the prospects of a new anode material CrGeTe3 for use in LIB studied via first-principles predictions. The investigation of Li: CrGeTe3 system and lithiation mechanism in the proposed material pointed out its suitability for lithium intercalation compound. The energy-profiling at highly symmetry points in the host structure revealed that BGe-Cr is most favorable energy site for lithiation in the material. The maximum value of the lithium insertion voltage is 3.41 V and the storage capacity is 620.60 mAh g−1. The diffusion barrier faced by lithium atom is 0.27 eV which is the minimum value, while moving along the x-axis within the top and middle hexagonal rings. The steric interaction of Li with Ge and Te atoms pointed structural reliability and hence stable operation of the anode to address capacity fading problems in LIB.

Lithiation and Magnesiation Mechanism of VOCl: First-Principles Moleculardynamics Simulation

The layered metal oxide VOCl is a kind of promising electrode material for rechargeable batteries. It is the first time that the thermodynamic, electronic, and kinetic properties of lithiated and magnesiated VOCl were systematically investigated. The upper limit of Li and Mg topological intercalation into VOCl is xLi = 1 and xMg = 0.5, respectively. Beyond the critical value, further lithiation and magnesiation will cause the phase evolution of layered VOCl. Upon lithiation, four discharge plateaus are observed at 2.10, 2.23, 1.62 and 1.23 V vs Li+/Li in the concentration range of 0 ≤ xLi ≤ 1. Upon magnesiation, the average voltage reaches 1.10 V vs Mg2+/Mg in the concentration range of 0 ≤ xMg ≤ 0.25, which are consistent with the experimental values. The pair correlation function (PCF) diagrams display the formation of V metal at high concentration of xLi and xMg, proving the occurrence of conversion reaction. The diffusion energy barriers of Li ions and Mg ions in VOCl are 0.22 and 0.72 eV, respectively, which are much lower than those of other intercalation materials. The layered VOCl bulk is a high-rate capability cathode material for lithium-ion battery. Based on the thermodynamic/kinetic properties and the AIMD simulation results, the electrochemical mechanism of layered VOCl is an intercalation-conversion reaction during the lithiated and magnesiated processes. The conversion-type cathodes have the potential to circumvent the sluggish solid-state Mg diffusion and improves the performance of Mg rechargeable batteries with high-energy density and high-rate capability.

Intrinsic electrochemical activity of Ni in Ni3Sn4 anode accommodating high capacity and mechanical stability for fast-charging lithium-ion batteries

Fast interfacial kinetics derived from bicontinuous three-dimensional (3D) architecture is a strategic feature for achieving fast-charging lithium-ion batteries (LIBs). One of the main reasons is its large active surface and short diffusion path. Yet, understanding of unusual electrochemical properties still remain great challenge due to its complexity. In this study, we proposed a nickel–tin compound (Ni3Sn4) supported by 3D Nickel scaffolds as main frame because the Ni3Sn4 clearly offers a higher reversible capacity and stable cycling performance than bare tin (Sn). In order to verify the role of Ni, atomic-scale simulation based on density functional theory systematically addressed to the reaction mechanism and structural evolution of Ni3Sn4 during the lithiation process. Our findings are that Ni enables Ni3Sn4 to possess higher mechanical stability in terms of reactive flow stress, subsequently lead to improve Li storage capability. This study elucidates an understanding of the lithiation mechanism of Ni3Sn4 and provides a new perspective for the design of high-capacity and high-power 3D anodes for fast-charging LIBs.

Could λ-Ti3O5 with lamellar and channel microstructure characteristics determine the excellent properties of LIBs? The first-principles study of λ-Ti3O5 lithiation mechanism

While people are searching for potential electrode materials for Li-ion batteries (LIBs), it is controversial whether the microstructure is a critical factor of electrochemistry property. λ-Ti3O5 is an example due to its lamellar and channel microstructure characteristics to discuss whether the microstructure characteristic is the critical factor of properties of LIBs. The intercalation/de-intercalation mechanisms and diffusion behavior of Li-ion in λ-Ti3O5 are studied by DFT. The binding energies with the different number of Li-ions are from − 3.1 to − 2.2 eV, and the volume changes are from 0.1% to 1.3%, indicating λ-Ti3O5 is stable during lithiation. The supercell and (001) slab of λ-Ti3O5 is constructed to investigate the diffusion behaviors of Li-ion in bulk and Li-ion escaping from the system, respectively. The former energy barriers are about 1.0 eV, and the latter energy barriers are above 2.0 eV, suggesting it is difficult for Li-ion to diffuse in or escape from the system. It presumably can be inferred that the microstructure is not the critical factor of diffusion property for electrode materials. More studies are needed to optimize the performance of λ-Ti3O5 as an electrode material, such as interionic distance and strength of bonding.

Li–Se batteries: Insights to the confined structure of selenium in hierarchical porous carbon and discharge mechanism in the carbonate electrolyte

Confining selenium in porous carbon hosts is an effective strategy to improve the performance of Li–Se batteries. The structure of confined Se and the corresponding lithiation mechanism remain to be clarified yet. In this work, Se@CISC-58 composite material was prepared based on hierarchical porous carbon CISC-58 with same content of mesopores and micropores, and then used for cathode material of Li–Se batteries. The selenium loaded in Se@CISC-58 takes Sex chain structure rather than the cyclic Se8, as evidenced by both 77Se MAS NMR and EPR experiments. In particular, the free radical signals in EPR changes adaptively with the discharge-charge cycling. Ex-stiu EPR and in-stiu 7Li NMR techniques further confirmed the stepwise reaction mechanism of Sex chains in the carbonate-based electrolytes. To better understand the discharge process of selenium, NMR in combination with DFT calculations are utilized to assign the polyselenides engaged in discharge process. We have found that polyselenides represented by Li2Se2 were generated during the discharge of selenium in the carbonate-based electrolytes.

Cation reordering instead of phase transitions: Origins and implications of contrasting lithiation mechanisms in 1D ζ- and 2D α-V2O5

Substantial improvements in cycle life, rate performance, accessible voltage, and reversible capacity are required to realize the promise of Li-ion batteries in full measure. Here, we have examined insertion electrodes of the same composition (V2O5) prepared according to the same electrode specifications and comprising particles with similar dimensions and geometries that differ only in terms of their atomic connectivity and crystal structure, specifically two-dimensional (2D) layered α-V2O5 that crystallizes in an orthorhombic space group and one-dimensional (1D) tunnel-structured ζ-V2O5 crystallized in a monoclinic space group. By using particles of similar dimensions, we have disentangled the role of specific structural motifs and atomistic diffusion pathways in affecting electrochemical performance by mapping the dynamical evolution of lithiation-induced structural modifications using ex situ scanning transmission X-ray microscopy, operando synchrotron X-ray diffraction measurements, and phase-field modeling. We find the operation of sharply divergent mechanisms to accommodate increasing concentrations of Li-ions: a series of distortive phase transformations that result in puckering and expansion of interlayer spacing in layered α-V2O5, as compared with cation reordering along interstitial sites in tunnel-structured ζ-V2O5 By alleviating distortive phase transformations, the ζ-V2O5 cathode shows reduced voltage hysteresis, increased Li-ion diffusivity, alleviation of stress gradients, and improved capacity retention. The findings demonstrate that alternative lithiation mechanisms can be accessed in metastable compounds by dint of their reconfigured atomic connectivity and can unlock substantially improved electrochemical performance not accessible in the thermodynamically stable phase.

Silicon carbide (SiC) derived from agricultural waste potentially competitive with silicon anodes

Silicon carbide derived from rice hull ash reveals, on long-term cycling, capacity increases to >900 mA h g−1 without significant volume changes. Lithiation mechanisms and the extraordinary capacity increment origins were assessed in detail.