Li-ion Insertion Research Articles

An Atomic View of Cation Diffusion Pathways from Single-Crystal Topochemical Transformations.

The diffusion pathways of Li-ions as they traverse cathode structures in the course of insertion reactions underpin many questions fundamental to the functionality of Li-ion batteries. Much current knowledge derives from computational models or the imaging of lithiation behavior at larger length scales; however, it remains difficult to experimentally image Li-ion diffusion at the atomistic level. Here, by using topochemical Li-ion insertion and extraction to induce single-crystal-to-single-crystal transformations in a tunnel-structured V2 O5 polymorph, coupled with operando powder X-ray diffraction, we leverage single-crystal X-ray diffraction to identify the sequence of lattice interstitial sites preferred by Li-ions to high depths of discharge, and use electron density maps to create a snapshot of ion diffusion in a metastable phase. Our methods enable the atomistic imaging of Li-ions in this cathode material in kinetic states and provide an experimentally validated angstrom-level 3D picture of atomic pathways thus far only conjectured through DFT calculations.

Peapod-like MnO@Hollow carbon nanofibers film as self-standing electrode for Li-Ion capacitors with enhanced rate capacity

Lithium ion capacitors (LICs), combining with the advantages of supercapacitors and batteries, are considered as one of the most attractive energy storage devices. The key point of constructing high-performance LICs is to address the sluggish kinetics behavior of battery-type anode. Herein, we demonstrate that nano-MnO with low Li-ion insertion voltage and fast kinetics can be favorably used for LICs. Self-standing hollow carbon-encapsulated MnO nanofibers film (MnO@HCF) is synthesized through a morphology-inheritance route, exhibiting high electrical conductivity, good structural stability, and continuous open channels to facilitate electrolyte ion transportation. Such a synergistic structure endows MnO@HCF with excellent electrochemical properties including a considerably enhanced capacity of 586.8 mAh g−1 at a current density of 0.1 A g−1. The LIC based on the MnO@HCF anode and activated carbon cathode deliver a high energy density of 87.4 Wh kg−1 at 215 W kg−1, under a high mass loading of 7.1 mg cm−2. Even at an ultrahigh power density of 10750 W kg−1, the energy density can still reach 50.6 Wh kg−1. Additionally, the LIC exhibits a remarkable capacity retention of 98.6% after 3000 cycles at 1075 W kg−1.

Stressed Lattice Creating New Electric Field for Photoelectrocatalysis

To improve the water splitting performance of photoelectrode, Wang’s group borrowed the lithiation mechanism of Li-ion battery to create ordered lattice strain in the electrode. The stressed lattice induced by Li-ion insertion generates a polarized electric field in the bulk, which greatly improves the bulky charge separation and transfer capability and remarkably promotes the photoelectrocatalytic water splitting. This work paves a new avenue for photoelectrochemical water splitting towards efficient solar hydrogen production. The related work was published in Nature Communications on May 1, 2020.

Mechanically Reinforced Localized Structure Design to Stabilize Solid-Electrolyte Interface of the Composited Electrode of Si Nanoparticles and TiO2 Nanotubes.

Silicon anode with extremely high theoretical specific capacity (≈4200 mAh g-1 ), experiences huge volume changes during Li-ion insertion and extraction, causing mechanical fracture of Si particles and the growth of a solid-electrolyte interface (SEI), which results in a rapid capacity fading of Si electrodes. Herein, a mechanically reinforced localized structure is designed for carbon-coated Si nanoparticles (C@Si) via elongated TiO2 nanotubes networks toward stabilizing Si electrode via alleviating mechanical strain and stabilizing the SEI layer. Benefited from the rational localized structure design, the carbon-coated Si nanoparticles/TiO2 nanotubes composited electrode (C@Si/TiNT) exhibits an ideal electrode thickness swelling, which is lower than 1% after the first cycle and increases to about 6.6% even after 1600 cycles. While for traditional C@Si/carbon nanotube composited electrode, the initial swelling ratio is about 16.7% and reaches ≈190% after 1600 cycles. As a result, the C@Si/TiNT electrode exhibits an outstanding capacity of 1510 mAh g-1 at 0.1 A g-1 with high rate capability and long-time cycling performance with 95% capacity retention after 1600 cycles. The rational design on mechanically reinforced localized structure for silicon electrode will provide a versatile platform to solve the current bottlenecks for other alloyed-type electrode materials with large volume expansion toward practical applications.

Solvated Ion Intercalation in Graphite: Sodium and Beyond.

Reversible intercalation of guest ions in graphite is the key feature utilized in modern battery technology. In particular, the capability of Li-ion insertion into graphite enabled the successful launch of commercial Li-ion batteries 30 years ago. On the road to explore graphite as a universal anode for post Li-ion batteries, the conventional intercalation chemistry is being revisited, and recent findings indicate that an alternative intercalation chemistry involving the insertion of solvated ions, designated as co-intercalation, could overcome some of the obstacles presented by the conventional intercalation of graphite. As an example, the intercalation of Na ions into graphite for Na-ion batteries has been perceived as being thermodynamically impossible; however, recent work has revealed that a large amount of Na ions can be reversibly inserted in graphite through solvated-Na-ion co-intercalation reactions. More recently, it has been extensively demonstrated that with appropriate electrolyte selection, not only Na ions but also other ions such as Li, K, Mg, and Ca ions can be co-intercalated into a graphite electrode, resulting in high capacities and power capabilities. The co-intercalation reaction shares a lot in common with the conventional intercalation chemistry but also differs in many respects, which has attracted tremendous research efforts in terms of both fundamentals and practical applications. Herein, we aim to review the progress made in understanding the solvated-ion intercalation mechanisms in graphite and to comprehensively summarize the state-of-the-art achievements by surveying the correlations among the guest ions, co-intercalation conditions, and electrochemical performance of batteries. In addition, the advantages and challenges related to the practical application of graphite undergoing co-intercalation reactions are presented.

High-performance lithium battery driven by hybrid lithium storage mechanism in 3D architectured carbonized eggshell membrane anode

The increasing demand for large-capacity lithium batteries requires new anode materials satisfying both high capacity and long-life cycles. Here, a free-standing, binder-free, and environmentally friendly carbonized eggshell membrane (CEM) anode with a highly conductive interwoven network is presented for the use in high-performance lithium batteries. Highly porous and naturally doped nitrogen in CEM structure enables a unique hybrid Li storage mechanism where the effective insertion of Li ions and highly uniform Li metal deposition occur without Li dendrites formation. By employing a three-dimensionally architectured CEM anode, an areal capacity as high as 10 mA h cm−2 (357.2 A h L−1 in volumetric capacity) is achieved with an average Coulombic efficiency of 97.6% over 1300 h. The CEM anode also exhibits high Li-ion diffusivity, stable voltage hysteresis, and excellent cycling performance even after 1000 cycles at 0.5C, making it an environmentally sustainable electrode material for high-performance Li-ion batteries.

Analytical Measurements to Elucidate Structural Behavior of 2,5-Dimethoxy-1,4-benzoquinone During Charge and Discharge.

Organic compounds as electrode materials can contribute to sustainability because they are nontoxic and environmentally abundant. The working mechanism during charge–discharge for reported organic compounds as electrode materials is yet to be completely understood. In this study, the structural behavior of 2,5‐dimethoxy‐1,4‐benzoquinone (DMBQ) during charge—discharge is investigated by using NMR spectroscopy, energy‐dispersive X‐ray spectroscopy, magnetic measurements, operando Raman spectroscopy, and operando X‐ray diffraction. For both lithium and sodium systems, DMBQ works as a cathode accompanied with the insertion and deinsertion of Li and Na ions during charge—discharge processes. The DMBQ sample is found to be in two‐phase coexistence state at the higher voltage plateau, and the radical monoanion and dianion phases have no long‐distance ordering. These structures reversibly change into the original neutral phase with long‐distance ordering. These techniques can show the charge–discharge mechanism and the factors that determine the deterioration of organic batteries, thus guiding the design of future high‐performance organic batteries.

Anodic lithium ion battery material with negative thermal expansion

Negative thermal expansion materials will effectively counteract possible severe expansion and contraction due to the insertion and extraction of Li ions in lithium ion batteries. Herein, negative thermal expansion ZrScMo2VO12 and its carbon-coating composites are prepared as electrode material in lithium ion batteries by a heating treatment route. The galvanostatic charge/discharge process, cyclic voltammetry measurement and electrochemical impedance spectroscopy are tested to relate their thermal expansion and electrochemical properties. The initial specific capacity reaching 1062 mA h g-1 at the current density of 0.2 A g-1 is obtained with ideal negative thermal expansion properties. The reversible specific capacity still remains stable at 310 mA h g-1 for that material coated with carbon after 100 cycles. The corresponding theoretical simulations and in situ XRD patterns propose a Li ion storage mechanism based on Li ion insertion process in open framework structure. As a proof-of-concept research, this work paves a way to the promising application of negative thermal expansion materials in lithium ion batteries and other energy storage systems.

Revealing the Phase-Transition Dynamics and Mechanism in a Spinel Li4Ti5O12 Anode Material through in Situ Electron Microscopy.

Spinel Li4Ti5O12 is considered as a promising anode material for long-life lithium-ion batteries because of the negligible volumetric variation during the insertion and extraction of Li ions. Phase transition is an inevitable process during the migration of Li ions, and the transition process and mechanism need detailed investigation down to the atomic scale. In this study, we investigated the behavior and mechanism on the phase transition of Li4Ti5O12 through in situ transmission electron microscopy (TEM). It has been found that the spinel-structured Li4Ti5O12 was gradually transformed to a rock salt structure under electron beam irradiation. A sharp interface with an epitaxial relationship was observed between the transformed rock salt phase and the parent spinel phase. Furthermore, the heterostructure with different crystal structures of Li4Ti5O12 has been precisely tailored with electron beam irradiation. Our detailed in situ TEM results and theoretical calculations led to unprecedented level on the understanding of phase-transition mechanism in Li4Ti5O12. This study demonstrates a possible approach to precisely engineer the crystal structure of materials and to realize a well-designed heterostructure in electrode materials.

Continuous Energy Harvesting and Motion Sensing from Flexible Electrochemical Nanogenerators: Toward Smart and Multifunctional Textiles.

Here, we demonstrate the utilization of biocompatible Prussian blue (PB) active coatings onto polyester-carbon nanotube (CNT) threads to enable a fiber-based platform for both power harvesting and continuous motion sensing. First, we show experimental evidence supporting that the mechanistic power generating mechanical-electrochemical coupling in an electrochemical generator (ECG) is best achieved with K-ion insertion, in contrast to the expected preference for Li-ion insertion for batteries. We then construct KPB fibers and demonstrate power generation in an ECG device up to 3.8 μW/cm2 at low frequencies relevant to human motion in either an aqueous or polymer gel electrolyte media. Further, by stitching these yarns into gloves or arm sleeves, our results show the continuous monitoring of finger or arm motion, respectively, during slow and repetitive human motion. Overall, our work demonstrates an ECG platform that overcomes the performance and integration barriers toward combined textile integration and human motion sensing while leveraging common materials and understanding extending from alkali metal-ion batteries.

Tailoring porous structure and graphitic degree of seaweed-derived carbons for high-rate performance lithium-ion batteries

Hierarchical porous carbons embedded with graphitic domains were synthesized by carbonization of seaweeds with a catalytic graphitization strategy. The Ni2+ ions are pre-chelated with seaweeds precursor (porphyra) to enable a catalyst confined graphitization process and to provide mesopores template. Carbonization temperature is significant in tailoring graphitic degree and porosity structure of porphyra-derived carbons (PDCs). The PDCs carbonized at 900 °C (PDC-900) show favorable features for electrochemical energy storage, which balance the specific surface area (515.7 mm2g-1), degree of graphitization (ID/IG = 0.78), expand graphite interlayer spacing (∼0.342 nm), and N-doping (2.13 wt%). These unique features of PDC-900 not only can supply abundant sites for the storage and insertion of Li ions, but also can facilitate rapid mass transport of electrons and Li ions. Thus, PDC-900 shows remarkable reversible capacity (950 mAhg−1 at 0.1 C), excellent rate capability (352 mAhg−1 at 10 Ag-1), and superior cycling performance (348 mAhg−1 at 5 Ag-1 after 3000 cycles), when used as an anode material for lithium ion batteries.

Improving rate capacity and cycling stability of Si-anode lithium ion battery by using copper nanowire as conductive additive

Measures of using carbon nanomaterials as conductive additives or coating carbon are popularly taken to relieve the huge volume expansion of Si-anode. However, these measures usually lead to the consumption of lithium ions and excessive formation of unstable solid-electrolyte interface film, resulting in a low initial coulombic efficiency (ICE), unsatisfied capacity and cycling stability. To address this issue, copper nanowire (CuNW) with high electrical conductivity is used instead of acetylene black as an inactive conductive additive for Si-anode in this study. Compared with Si anode with acetylene black conductive additive, the Si-anode with the CuNW conductive additive exhibits a significantly improved rate capacity (1686.9 mA h g−1 at 1 C) and cycling stability (capacity retention of ∼88.2% after 100 cycles), and a higher ICE of ∼93.1%. The improved performance can be attributed to the one-dimensional characteristic and excellent electrical conductivity of the CuNW, which can construct robust and effective conducting networks in the Si-anode, maintain efficient electron transfer pathways and significantly reduces the cell resistance. Furthermore, the CuNW is inactive to Li ions insertion and extraction and can reduce the irreversible reactions with electrolyte and the consumption of lithium ions, leading to the high ICE.

Coordination induced electron redistribution to achieve highly reversible Li-ion insertion chemistry in metal-organic frameworks.

Herein, the coordination-induced increase in the electron density of fused C6 rings in MOFs as high performance anode materials for Li+ ion batteries is described. Zn-PTCA is able to deliver a high specific capacity of 700 mA h g-1 at 50 mA g-1 and exhibits excellent cycle performance over 1100 cycles and good rate capability.

Effect of Temperature on The Kinetics of Electrochemical Insertion of Li-Ions into a Graphite Electrode Studied by Kinetic Monte Carlo

The effect of temperature on the kinetics of electrochemical insertion/removal of lithium in graphite is analyzed by kinetic Monte Carlo methods. Different electrochemical techniques are simulated at different temperatures and responses are compared with experimental results. Simulated voltammograms show, similarly to experiment, how the behavior of the system becomes closer to equilibrium as temperature increases. Calculated chronoamperometric profiles show a different qualitative behavior in the current at different temperatures, especially in the Cottrell representation peaks, explained in terms of the relative importance of diffusive versus charge transfer processes at different temperatures. Results at room temperature are in good agreement with experiment, and we further evaluate trends at elevated temperature that have not yet been described in experimental or theoretical works. Exchange current densities for different degrees of lithium intercalation at different temperatures are predicted using potentiostatic simulations, showing an Arrhenius-type relationship. The dependence of the exchange current on electrolyte composition is simulated by investigating the effect of different activation energy barriers at different temperatures. The influence of temperature on diffusion coefficients as a function of lithiation fraction in graphite is simulated and related to Arrhenius plots, explaining the experimentally observed changes in diffusion phenomena with lithium composition and temperature.

Ge2Sb2Se5 Glass as High-capacity Promising Lithium-ion Battery Anode

Conventional alloying and conversion Li-host anode materials have been extensively studied as high capacity lithium ion battery anodes. However, they suffer continuous volume change during each charge-discharge process, triggering the electrode pulverization and loss of their capacity upon cycling. Interestingly, investigations on glass materials as Li-host anodes are less prevalent, although their disorder structure can help to accommodate their volumetric expansion and maintain the anisotropic particle arrangement with a better distribution during Li-ion insertion and extraction. Here, we report attributes of a promising candidate chalcogenide glass material, Ge2Sb2Se5, which exhibits a reversible high capacity of 626 mAh g−1 at a 0.5 C-rate, displays a capacity retention of 80% with a coulombic efficiency of >99% after 100 cycles. The resulting material performance is explained by a proposed lithiation mechanism in which lithium ions are alloyed with Se atoms at high potential, followed by the lithiation of Sb and Ge as the potential decreases during the discharge process. DFT calculation suggests an optimized glassy cell unit of Ge2Sb2Se5 with an energy gap of 0.14 eV, proposing a possible arrangement of atoms with short range order, in which the large variation of the nearest neighbor distances in Ge2Sb2Se5 can promote its stable anodic performance.

Redox Catalytic and Quasi-Solid Sulfur Conversion for High-Capacity Lean Lithium Sulfur Batteries.

The practical deployment of lithium sulfur batteries demands stable cycling of high loading and dense sulfur cathodes under lean electrolyte conditions, which is very difficult to realize. We describe here a strategy of fabricating extremely dense sulfur cathodes, designed by integrating Mo6S8 nanoparticles as a multifunctional mediator with a Li-ion conducting binder and a high-performance Fe3O4@N-carbon sulfur host. The Mo6S8 nanoparticles have substantially faster Li-ion insertion kinetics compared with sulfur, and the produced LixMo6S8 particles have spontaneous redox reactivity with relevant polysulfide species (such as Li4Mo6S8 + Li2S4 ↔ Li3Mo6S8 + Li2S, ΔG = -84 kJ mol-1), which deliver a true redox catalytic sulfur conversion mechanism. In addition, LixMo6S8 particles strongly absorb polysulfide during battery cycling, which provides a quasi-solid sulfur conversion pathway and almost eliminated polysulfide dissolution. Such a pathway not only promotes growth of uniform Li2S that can be readily charged back with nearly no overpotential, but also mitigates the polysulfide-induced Li metal corrosion issue. The combination of these benefits enables stable and high capacity cycling of dense sulfur cathodes under a low electrolyte to sulfur ratio (4.2 μL mg-1), as demonstrated with cathodes with volumetric capacities of at least 1.3 Ah cm-3 and capacity retentions of ∼80% for 300 cycles. Furthermore, stable cycling of batteries under a practically relevant N/P ratio of 2.4 is also demonstrated.

High-Throughput Single-Nanoparticle-Level Imaging of Electrochemical Ion Insertion Reactions.

Nanoparticle electrodes are attractive for electrochemical energy storage applications because their nanoscale dimensions decrease ion transport distances and generally increase ion insertion/extraction efficiency. However, nanoparticles vary in size, shape, defect density, and surface composition, which warrants their investigation at the single-nanoparticle level. Here we demonstrate a nondestructive high-throughput electro-optical imaging approach to quantitatively measure electrochemical ion insertion reactions at the single-nanoparticle level. Electro-optical measurements relate the optical density change of a nanoparticle to redox changes of elements in the particle under working electrochemical conditions. We benchmarked this technique by studying Li-ion insertion in hexagonal tungsten oxide (h-WO3) nanorods during chronoamperometry and cyclic voltammetry. Interestingly, the optically detected current response revealed underlying processes that are hidden in the conventional electrochemical current measurements. This imaging technique may be applied to 13 nm particles and a wide range of electrochemical systems such as electrochromic smart windows, batteries, solid oxide fuel cells, and sensors.

Hollow α‐Fe2O3 Nanotubes Embedded in Graphene Aerogel as High‐Performance Anode Material for Lithium‐Ion Batteries

AbstractHematite, with the higher theoretical capacity, as one of the most promising alternatives attract great attention in lithium‐ion batteries (LIBs). However, it is suffers from severe volume expansion and shrinkage during the insertion and extraction of Li ions. Here novel 3D graphene aerogel load with hollow Fe2O3 nanotubes was synthesized with the help of polyvinyl pyrrolidone (PVP) and N‐Methyl pyrrolidone (NMP) by a simple hydrothermal method. Serving as an anode material for LIBs, this composite manifested great cycle performance of high columbic efficiency (97%∼99%), high specific discharged capacity (1512 mAh g−1 at 100 mA g−1) and high rate capability (280 mAh g−1 at 5 A g−1). The superior performance of the material mainly depends on the interaction of graphene sheets and hollow Fe2O3 nanotubes. The 3D framework affords shorter diffusion distance for Li ions and enormous area to accommodate the volume expansion during the insertion/extraction of Li ions. Herein, this composite demonstrates a new way to modify the morphology of Fe2O3 and displays high efficiency and good performance as the anode of LIBs.

Fast lithiation of NiO investigated by in situ transmission electron microscopy

As a lithium-ion battery anode material, NiO has attracted a lot of attention owing to its excellent theoretical capacity. In this work, the dynamic lithiation process of NiO nanoplates and nanoparticles was investigated by in situ transmission electron microscopy (TEM). The morphology evolution, phase transformation, and electrochemical reaction of NiO during the lithiation process have been probed in real time by in situ TEM combined with selected area electron diffraction and electron energy loss spectroscopy technologies. We found that the insertion of Li-ions led to huge volume expansion of NiO, resulting in structural changes and breakdown. Li2O formed during lithiation hinders electron transportation through NiO due to its low conductivity, which causes poor cycling performance of NiO. Our findings provide valuable theoretical guidance for the modification of NiO as anode material for next generation high-performance lithium-ion batteries.

Femtosecond Laser Processing of Thick Film Cathodes and Its Impact on Lithium-Ion Diffusion Kinetics

Quantitative experiments of lithiation/delithiation rates were considered for a better understanding of electrochemical intercalation/deintercalation processes in laser structured thick film cathodes. Besides galvanostatic cycling for evaluation of specific discharge capacities, a suitable quantitative approach for determining the rate of Li-ion insertion in the active material and the rate of Li-ion transport in the electrolyte is expressed by chemical diffusion coefficient values. For this purpose, the galvanostatic intermittent titration technique has been involved. It could be shown that laser structured electrodes provide an enhanced chemical diffusion coefficient and an improved capacity retention at high charging and discharging rates.