Lithium Ion Diffusion Coefficient Research Articles

Lithium Storage Mechanism: A Review of Perylene Diimide N-Substituted with a 1,2,4-Triazol-3-yl Ring for Organic Cathode Materials.

The demand for lithium-ion batteries (LIBs) has increased rapidly. However, commercial inorganic-based cathode materials have a low theoretical capacity and inherent disadvantages, such as high cost and toxicity. Redox-active organic cathodes with a high theoretical capacity, eco-friendly properties, and sustainability have been developed to overcome these limitations. Herein, perylene diimide derivatives N-substituted with 1,2,4-triazol-3-yl rings (PDI-3AT) were developed to apply as a cathode material for LIBs. The PDI-3AT cathode exhibited discharge capacities of 85.2 mAh g-1 (50 mA g-1 over 100 cycles) and 64.5 mAh g-1 (500 mA g-1 over 1000 cycles) with ratios to the theoretical capacities of 84 and 64%, respectively. Electrochemical kinetics analysis showed capacitive behaviors of the PDI-3AT cathode with efficient pathways for lithium-ion transport. Also, the activation step of the PDI-3AT cathode was demonstrated by improving the charge transfer resistance and lithium-ion diffusion coefficient during the initial few charge-discharge cycles. Furthermore, DFT calculations at the B3LYP/6-311+G** level and ex situ analysis of various charge states of the PDI-3AT electrode using attenuated total reflection Fourier transform infrared (ATR FT-IR) analysis, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) were conducted for the further study of the lithium-ion storage mechanism. The results showed that the lithiation process formed the lithium enolate (═C-O-Li) coordinated with the N atoms of the 1,2,4-triazole ring. It is expected that our study results will encourage the production and use of redox-active perylene diimide derivatives as next-generation cathode materials.

A 2D montmorillonite-carbon nanotube interconnected porous network that prevents polysulfide shuttling

A commercial polypropylene (PP) separator was modified by a one-dimensional carbon nanotube (CNT) and two-dimensional montmorillonite (MMT) hybrid material (CNT-MMT). Because of the high electron conductivity of the CNTs, and the strong polysulfide (LiPS) adsorption ability and easy lithium ion transport through MMT, the interconnected porous CNT-MMT interlayer with excellent structural integrity strongly suppresses LiPS shuttling while maintaining high lithium-ion transport, producing a high utilization of the active sulfur. Lithium-sulfur batteries assembled with this interlayer have a high lithium-ion diffusion coefficient, a high discharge capacity and stable cycling performance. They had an initial specific capacity of 1 373 mAh g−1 at 0.1 C, and a stable cycling performance with a low decay rate of 0.062% per cycle at 1 C after 500 cycles.

Sustainable recovery of LiCoO2 from spent lithium-ion batteries: Simplicity, scalability, and superior electrochemical performance

In light of the ecological ramifications and material consumption stemming from exhausted lithium-ion batteries, an exigent requirement persists for efficient and expansible recycling techniques. Herein, we investigate an innovative expedited method to directly regenerate and enhance spent LiCoO2 (SLCO). The profoundly discharged SLCO powders, featuring an unimpaired crystal lattice, are isolated. These powders are then amalgamated with Li, Ni, and Mn precursors. Subsequent heating at elevated temperatures yields LNMO-SLCO, effecting the direct regeneration of LCO, accompanied by a synergistic re-lithiation process and the application of a LiNi0.5Mn1.5O4 (LNMO) coating, all achieved in a single step. The homogeneously thin spinel LNMO coating layer (10–15 nm) bestows upon LNMO-SLCO an enhanced cycling performance and charge–discharge rate capacity when benchmarked against SLCO and commercial LiCoO2 (CLCO). Evidently, at 0.1C, 0.5C, and 2C rates, LNMO-SLCO delivers discharge capacities of 214.4 mAh g−1, 187.4 mAh g−1, and 144.1 mAh g−1, respectively. Notably, it sustains 77.68 % of its original capacity following 100 cycles at 0.5 C. The merits of LNMO-SLCO are corroborated through cyclic voltammetry and electrochemical impedance spectroscopy, affirming its reduced charge transfer resistance and augmented lithium-ion solid phase diffusion coefficient. This endeavor stands as the foremost documented instance of a direct approach to SLCO reconstruction involving LNMO coating, culminating in the formation of LNMO-SLCO, characterized by sustained high-voltage cycling performance. The outlined re-lithiation and LNMO coating stratagem proffer valuable insights for the scalable, high-value recycling of SLCO, while remaining transposable to other spent cathode materials.

Tuning the pH value of electrospinning precursor to synthesize Fe2O3/MoO2/Fe2(MoO4)3 as anode for lithium-ion batteries to boost the reaction kinetics and energy/power density performance

In this work, a simple strategy for the synthesis of Fe2O3/MoO2/Fe2(MoO4)3 anode material was proposed, which controls the surface tension and viscosity of electrospinning precursor by adjusting its pH value, and optimizes the structure and morphology of the product. Compared with the Fe2(MoO4)3, the Fe2O3/MoO2/Fe2(MoO4)3 heterostructure not only effectively reduces the deactivation of the electrode material, but also increases the insertion sites of lithium-ions. Meanwhile, the built-in electric field generated near the heterointerface increases the diffusion coefficient of lithium-ions and improves the interfacial reaction kinetics. The sample obtained at a pH value of 1.85 exhibits the best electrochemical performance. The battery maintained a high reversible capacity (1014.2 mAh·g−1) after 480 cycles at 1000 mA·g−1, with an average specific capacity decrease rate of only 0.035 % per cycle. The mechanism of improving reaction kinetics and lithium storage performance by heterostructures has been proposed. Based on the interfaces confined effect of heterostructures and the formation of built-in electric fields, this work provides a strategy to adjust the spinning behavior by changing the pH value of precursors to achieve product structure optimization and electrochemical performance improvement, which will provide strong support for the research of high power/energy densities LIBs.

Effect of rapid thermal annealing on the charge storage kinetics of conductive N-doped SnO2 thin film anodes for Li-ion batteries

This study focuses on the fabrication of a flexible thin film electrode composed of N-doped tin oxide (SnO2: N). The fabrication process involves sputtering SnO2 onto a Cu foil sheet using radio frequency (RF) magnetron sputtering, conducted under an N2 atmosphere. The deposited thin films are subsequently exposed to annealing treatment using rapid thermal annealing (RTA) at temperatures ranging from 200 to 400 °C. The primary objective of this study is to get an understanding of the effects of N-doping, annealing temperature on the growth of SnO2: N. as well as the influence of film thickness on the crystallographic state. We evaluate their thin-film anode performance for lithium-ion batteries (LIBs). The specific capacity of the as-deposited SnO2 thin films standing at 859 mAh g−1 when measured at 1 mA g−1. This enhanced capacity is attributed to the limited crystal growth in ultrathin SnO2, a factor that effectively combats electrode degradation while simultaneously improving the lithium-ion diffusion coefficient and electron kinetics of the electrode. However, the SnO2: N film that undergoes annealing at 400 °C demonstrates remarkable cyclic retention, reaching 82 %. This improvement is due to the enhanced electrical conductivity resulting from annealing, which prevents the aggregation of tin (Sn) and effectively accommodates the volume changes that occur in prolonged cycles. Additionally, this synchronized approach involving sputtering and RTA is proving to be a simple, efficient, and scalable method. It holds the potential to emerge as a valuable strategy to produce anode materials for lithium-ion batteries.

Comparative study of the electrochemical performances of different polyolefin separators in lithium/sulfur batteries

Lithium/sulfur batteries (LSBs) have drawn the broad attention of researchers in recent years. Separator is an indispensable part of the battery design, which functions as a physical barrier for the electrode as well as an electrolyte reservoir for ionic transport. However, a comprehensive comparison and analysis of the performance of commonly used separators in LSBs are still lacking. In this study, systematic electrochemical performances of LSBs with four kinds of commonly used polyolefin separators Celgard 2400, Celgard 2500, Celgard 2320, and XuRan E-10 were investigated. Physicochemical experimental results showed that the Celgard 2400 separator has good thermal stability, better electrolyte uptake (∼93.1 %) and displays excellent mechanical property with longitudinal and transverse tensile strength of 31.3 N and 4.5 N, respectively. The battery with Celgard 2400 separator presents the lowest shuttle current density (4.28×10−2 mA cm−2), good electrochemical reaction kinetics and the highest lithium ion diffusion coefficient (10−10 cm2 s−1).

Study of Performance Graphene Oxide Modification of LiFePO4/C Material for The Cathode of Li-Ion Batteries

The need for energy storage is increasing rapidly along with technological development. Lithium ion batteries are one of the energy storages that are in great demand due to their high specific capacity and energy density, discharge voltage of 3.4 volts, and environmental friendliness. LiFePO4 is a lithium-ion battery cathode material with a high specific capacity of 170 mAh/g and a discharge voltage of about 3.4 V, thermal stability, high energy density, environmentally friendly, and easy to obtain. However, it has low electrical conductivity and poor ion diffusion, which hinders energy storage. Carbon modification is a method that has the advantage of reducing particle size and preventing agglomeration in nanoparticles, so this method is widely researched to improve lithium ion diffusion coefficient and conductivity in lithium ion batteries. This study aims to describe the effect of GO modification on the characterization of LiFePO4/C-GO composite material and LiFePO4/C-GO composite material battery performance as a lithium ion battery cathode material. In this study, it can be seen that the addition of GO in LiFePO4 cathode material can improve battery performance. The LiFePO4/C-GO-10 cathode obtained the most effective results with the lowest Rct value of 95.21 Ω and the highest conductivity value of 14.3×10-6 S/cm indicating the best electron transport. The Rct value decreased with the addition of GO, and the conductivity value increased with the addition of GO.

High ionic conductivity and critical current density of Li7−xLa2.95Yb0.05Zr2−xTaxO12 solid electrolyte by modulation of Li+ distribution

Safety concerns caused by organic liquid electrolyte in lithium battery might limit its application. Li7La3Zr2O12 is a promising electrolyte for solid-state lithium batteries due to its high ionic conductivity and interfacial stability with lithium. The influence of Ta doping on the structure, transport property and ionic conductivity of Li7−xLa2.95Yb0.05Zr2−xTaxO12 (0 ≤ x ≤ 0.2) has been investigated. Ta drives some Li ions from 24d to 96 h site and simultaneously optimizes the size of Li ion transport pathway. This structure modification increases the mobility, jump rate, and diffusion coefficient of lithium ion. Besides, the densification and grain contact have also been enhanced. The ionic conductivity of Li6.85La2.95Yb0.05Zr1.85Ta0.15O12 reaches 1.07 × 10−3 S cm−1 at 30 °C. The solid-state battery assembled with Li6.85La2.95Yb0.05Zr1.85Ta0.15O12 exhibits high critical current density of 1.1 mA cm−2 and discharge capacity of 166.7 mAh g−1, indicating that Li6.85La2.95Yb0.05Zr1.85Ta0.15O12 is a competitive solid electrolyte for solid-state lithium batteries.

Modeling and simulation in rate performance of solid-state lithium-ion batteries at low temperatures

Solid-state lithium-ion batteries (SSBs) not only improve the energy density of batteries, but also solve the unavoidable battery safety problems of liquid electrolytes. However, the rate capability of SSBs cannot meet the needs of practical applications due to the defects of low ionic conductivity and slow reaction rate of solid-solid interface, which becomes one of the bottlenecks restricting its development. Moreover, SSBs usually suffer from capacity reduction and security problems under low temperatures. This paper established a two-dimensional model of SSBs based on a multi-physical field simulation software, and studied the rate performance of SSBs under low temperatures. The distribution of lithium ion concentration in both electrolyte and cathode, diffusion coefficient of lithium ion and high rate discharge behavior of SSBs at low temperature were discussed in details. The simulation results exhibit that the rate capability of SSBs at low temperature can be improved by appropriately reducing the thickness of solid-state electrolyte. When the electrolyte thickness is fixed as 0.6 μm, the discharge capacities decrease from 0.345 Ah m−2 to 0.343 Ah m−2 as the discharge rates increase from 3C to 8C, together with a high capacity retention ratio of 99.5 %. Besides, SSBs can still maintain a high and flat discharge platform even at the high rate of 8C. This study proposes a method to improve the rate performance of solid state battery at low working temperatures, which has a theoretical guiding significance and engineering value for the structure design of SSBs.

Revealing the surface modification effect on Li-ion insertion into Ni-rich NCM cathode material by cyclic voltammetry

This article presents a new approach to the determination of electrochemical parameters characterizing the degradation behavior of electrodes based on LiNi0.85Co0.10Mn0.05O2 (Ni-rich NCM) using the method of cyclic voltammetry with a linear scan of the electrode potential (CV). To establish the relationship between electrochemical, structural, and morphological characteristics, XRD, synchrotron XRD (SXRD) in the operando mode, and SEM were used. The results of the galvanostatic intermittent titration technique (GITT) and electrochemical impedance spectroscopy (EIS) were used to verify the CV data. The features of the irreversible phase transition in NCM during the first cycle of extraction-insertion of lithium ions and its influence on the further behavior of the material during cycling were studied. It was found that the nature of the slope variation of capacity and coulomb efficiency dependences on the cycle number with an increase in the electrode potential scan rate is a criterion for the ratio of reversible and irreversible components of the electrode capacity degradation. Reversible electrode capacity degradation is due to the difference between the diffusion coefficients of lithium ions in the anodic and cathodic processes, irreversible degradation is due to the structural degradation of the material. For NCM samples with different particle surface conditions (with different composition of Cathode Electrolyte Interphase (CEI)) the values of Li+ ions diffusion coefficient (D) for each stage of the intercalation process were found in the range 4.5·10−14 – 1.2·10−13 cm2·s−1 for the anodic process, 1.7·10−14 – 5.6·10−14 cm2·s−1 for the cathodic process. It has been established that the reversible and irreversible degradation components of electrodes based on Ni-rich NCM in the potential range corresponding to the H2-H3/H3-H2 interphase transition correlate with each other. Therefore, the difference in D values in the anodic and cathodic processes, which correspond to the current peaks of the cyclic voltammogram in this region, is a criterion for the irreversible degradation of the material’s capacity: the greater the difference in the D values for these peaks, the higher the irreversible degradation of the material’s capacity.

Phase field modeling of lithium deposition in porous lithium metal anodes

Fabricating the structured lithium metal anode is an effective method to improve the cycling performance and severe safety problem of the lithium metal anode for commercial application. In this work, we have employed an electrochemical phase field (PF) model to simulate the non-uniform lithium deposition in porous lithium metal anodes. Four factors have been investigated to facilitate homogeneous lithium deposition and increase the capacity for the inside-pore lithium deposition, including 1) the porosity of the lithium metal anode, 2) the diffusion coefficient of lithium ion, 3) the reaction constant for lithium deposition and 4) structured electrode with a gradient of porosity. We have found that the inside-pore lithium deposition can be improved by increasing the diffusion coefficient lithium ion and designing a lithium metal anode with a gradient of reaction constants and a gradient of porosity. These results provide some new thoughts for the development of high-performance lithium metal anodes.

Application of two-dimensional lamellar lithium titanate in lithium-ion anode batteries

Lithium titanate exhibits effective suppression of lithium metal plating and lithium dendrite formation, attributed to its high lithium ion diffusion coefficient and a relatively high discharge plateau of 1.55 V (vs. Li+/Li). It is considered a zero-strain material, displaying minimal lattice size changes during lithium intercalation and deintercalation processes. The focus of this study was to obtain titanium dioxide through the calcination of selected MXene (Ti2C), and then mix it with lithium carbonate in a specific lithium-titanium ratio to generate lithium titanate. Spinel lithium titanate synthesized via solid-state method retained the sheet-like structure and excellent conductivity characteristics of MXene. Because its sheet structure provides a larger specific surface area for the electrode and enhances ion migration, it shows excellent electrochemical performance. The reaction mechanism was studied by in-situ Raman and variable speed CV. It was found that the reaction mechanism was pseudocapacitance plus lithium ion deintercalation. The obtained structure exhibited excellent electrochemical performance, making it suitable for applications in lithium-ion batteries.

Preparation of High‐Power Lithium Fluoride Carbon Battery via Microstructural Modulation of Ketjen Black

Ketjen black fluoride (KBF‐2) material, a novel carbon fluoride cathode nanomaterial, is fabricated through a pregrinding treatment followed by a fluorination process for lithium primary batteries. The ketjen black material as the carbon precursors provides a 3D spherical structure with a high‐specific surface area. In addition, the pregrinding treatment results in several cracks in the spherical KBF‐2 particles. The effects of cracks on the fluorine content ratio under the same fluorination process conditions, diffusion coefficient of lithium ions, rate performance, and power density performance are investigated. At an extremely high current density of 4.5 A g−1(at a 6 C rate), the discharge capacity retention is 52.09%, which is a breakthrough for the series of fluoride cathode materials. Moreover, the KBF‐2 cathode is evaluated in a 10 Ah KBF‐2/Li primary pouch cell and demonstrated a high gravimetric energy density of 573.70 Wh kg−1 at a 0.5 C rate, and the discharge duration time reached 624 s under a constant specific power of 1,500 W kg−1. These factors contribute to the remarkable energy density performance and power output stability, particularly at high current densities.

A high performance TiO2 anode modified by germanium and oxygen vacancies for lithium-ion batteries

A TiO2 anode modified by germanium and oxygen vacancies was fabricated using a hydrothermal method with an autoclave at 180 °C, followed by reduction sintering at 600 °C for 5 h in a reducing atmosphere. Germanium was obtained and distributed uniformly on the surface of the anatase TiO2 particles. Oxygen vacancies were identified on the TiO2 surface by electron paramagnetic resonance and X-ray photoelectron spectroscopy. The specific capacity of the Ge@TiO2−x anode was 510 mAh g−1 after 550 charge-discharge cycles. The charge transfer and electrolyte impedance of Ge@TiO2−x were smaller than those of the initial TiO2. The lithium-ion diffusion coefficient in Ge@TiO2−x was 7.87 × 10−13 cm2·s−1, which was significantly higher than that of a commercial TiO2 anode. The germanium and oxygen vacancies in TiO2 provided more active sites for the transport of lithium ions and electrons, thereby reducing the energy barrier, accelerating the charge transfer of lithium ions and enhancing the conductivity and capacity of the Ge@TiO2−x anode.

Electronic structure and lithium ion diffusion in nitrogen-doped Li2FeSiO4: First-principles study

As a typical orthosilicate material, Li2FeSiO4 has become a potential candidate for the cathode materials of next-generation advanced lithium-ion batteries. However, low electronic/ionic conductivity and slow diffusion rate of lithium ions limit its practical application in the field of lithium-ion batteries. Element doping is an effective and simple strategy to improve the electrical and electrochemical performance of Li2FeSiO4. In this work, electronic structure and lithium ion diffusion of nitrogen doped Li2FeSiO4 were studied by first-principles calculations. The band gap of Li16Fe8Si8O31N (0.331 eV) is smaller than that of Li16Fe8Si8O30N2 (0.712 eV), which indicates a better electronic conductivity. Results of mean square displacement confirm that lithium ion could diffuse in two-dimensional path in Li2FeSiO4 along the a-axis and c-axis. Additionally, nitrogen doping reduces the energy barrier and improves the diffusion of lithium ions. Diffusion coefficient of lithium ion and the ionic conductivity is 4 and 5 orders of magnitude larger than that of intrinsic system, respectively.

Interpretable Real-Time Modeling of the Diffusion Overpotential in Lithium Batteries

Fractional-order dynamics can form physically-interpretable equivalent-circuit models of the diffusion overpotential in lithium-ion batteries but have complex formulations in the time-domain. Meanwhile, resistor-capacitor circuits have simple implementations but little physical meaning. Thus we propose a discrete-time state-space diffusion model, named ‘receding-horizon diffusion’ (RHD). It combines physical interpretability with computational simplicity. Analogous to theWarburg element in impedance spectroscopy, the RHD constant is explicitly linked with the lithium ion diffusion coefficient. Fivefold validation of the RHD model using simulated and experimental from lithium NiMnCo and NiCoAl cells up to 3 C-rate, temperatures from 0 to 25°C, and wide ranges of states of health and charge. The model has less than 1% modelling error. Ohmic, charge-transfer, and diffusion overpotentials are tracked in real time. The RHD model could be integrated into battery management systems in electric vehicles and used in standard state estimation techniques.

Insight into the effect of thick graphite electrodes towards high-performance cylindrical Ni-rich NCA90 Li-ion batteries

This study explored the complex effect of graphite tortuosity on the electrochemical performance of Ni-rich NCA90 Li-ion batteries (LIBs). Different levels of graphite anode tortuosity were analyzed, revealing that low-tortuosity electrodes had better graphite utilization. The in-plane tortuosities of the graphite anode electrodes examined were 1.70, 1.94, 2.05, and 2.18, while their corresponding through-plane tortuosities were 4.74, 6.94, 8.19, and 9.80. In-operando X-ray diffraction and differential electrochemical mass spectrometry were employed to investigate the charge storage mechanism and gas evolution. The study revealed that while graphite electrode tortuosity impacted the amount of Li present in the lithiated graphite phase due to diffusion constraints, it did not affect gas generation. The Li-ion utilization in low-tortuosity electrodes was higher than that in high-tortuosity electrodes because of solid-diffusion limitations. Additionally, the galvanostatic intermittent titration technique (GITT) was employed to investigate a lithium-ion diffusion coefficient. Our results indicate that the lithium-ion diffusion coefficient exhibits a significant difference only during LiC6 phase transition. We also observed that the use of a lower tortuosity electrode leads to improved lithium-ion insertion. Consequently, graphite utilization is influenced by the porous electrode design. Safety tests adhering to UN38.3 guidelines verified battery safety. The study demonstrated the practical application of optimized NCA90 LIB cells with diverse graphite electrode tortuosities in a high-performance Lamborghini GoKart, paving the way for further advancements in Ni-rich LIB technology.

Leveraging Molecular Dynamics to Improve Porous Electrode Theory Modeling Predictions of Lithium-Ion Battery Cells

Lithium-ion battery cell modeling using physics-based approaches such as porous electrode theory is a powerful tool for battery design and analysis. Performance metrics such as cell power and resistance can be quickly calculated in a pseudo-two-dimensional (P2D) framework and when coupled with thermal models, component level detail of heating and temperature rise can be evaluated1. For engineering of electric vehicle batteries, speed and fidelity of electrochemical models is paramount in a competitive landscape. Physics-based models allow for high fidelity but require detailed knowledge of the cell component material properties. Acquiring these material characteristics typically requires time-consuming and expensive experiments limiting the ability to quickly screen through cell designs. Therefore, engineering assumptions of the materials properties must be made based on prior tests or literature sources necessarily limiting model accuracy. One approach to improve model accuracy and circumvent costly experiments is to use atomistic modeling to calculate battery cell material properties such as kinetics, OCVs, and transport properties without the need of experiments2–4.In this contribution we use molecular dynamics to calculate electrolyte conductivity and lithium-ion diffusion coefficients for a commercial electrolyte. We first validate our MD modeling approach by reproducing experimental measures of electrolyte conductivity for several test systems. We then construct a porous electrode theory model using the computed electrolyte transport values for the commercial system. Using this model, cell resistance and power is calculated and compared to experimental values measured from small-format pouch cells using the same electrolyte. We show how the variability in the MD modeling impacts cell performance metrics and demonstrate the robustness of this approach to improve cell-level model accuracy.

Nickel-doped Nb18W16O93 nanowires with improved electrochemical properties for lithium-ion battery anodes

Recently, niobium tungsten oxide nanowires have been reported to be a promising anode material for lithium-ion batteries (LiBs). This material has demonstrated high theoretical capacity, significant structural stability, high power density, and environmental friendliness. Nonetheless, its low electronic conductivity is a significant drawback that needs to be addressed. More so, it is desirable to enhance its electrochemical performance to meet the needs of current energy applications. In this study, pristine and nickel-doped (Ni = 1 wt%, 3 wt%, 5 wt%) niobium tungsten oxide nanowires were fabricated using the electrospinning technique, followed by annealing. The effect of nickel doping content on the morphology, structure, and electrochemical performance of niobium tungsten oxide nanowires was investigated. The XRD results show that the Ni doping expanded the unit cell and enhanced the lithium-ion diffusion in the Nb18W16O93 nanowires. The electrochemical test results indicate that the 3 wt% nickel-doped condition exhibits remarkable capacity retention of 93.1% over 500 cycles at a high current rate of 5 C. Furthermore, the Ni doping significantly enhanced the electronic conductivity compared to the pristine Nb18W16O93 nanowires. The results obtained from the CV test also show that Ni doping lowered the polarization and increased the lithium-ion diffusion coefficient.

Two Birds One Stone: Graphene Assisted Reaction Kinetics and Ionic Conductivity in Phthalocyanine-Based Covalent Organic Framework Anodes for Lithium-ion Batteries.

This work reports a covalent organic framework composite structure (PMDA-NiPc-G), incorporating multiple-active carbonyls and graphene on the basis of the combination of phthalocyanine (NiPc(NH2 )4 ) containing a large π-conjugated system and pyromellitic dianhydride (PMDA) as the anode of lithium-ion batteries. Meanwhile, graphene is used as a dispersion medium to reduce the accumulation of bulk covalent organic frameworks (COFs) to obtain COFs with small-volume and few-layers, shortening the ion migration path and improving the diffusion rate of lithium ions in the two dimensional (2D) grid layered structure. PMDA-NiPc-G showed a lithium-ion diffusion coefficient (DLi + ) of 3.04 × 10-10 cm2 s-1 which is 3.6 times to that of its bulk form (0.84 × 10-10 cm2 s-1 ). Remarkably, this enables a large reversible capacity of 1290 mAhg-1 can be achieved after 300 cycles and almost no capacity fading in the next 300 cycles at 100mAg-1 . At a high areal capacity loading of ≈3 mAhcm-2 , full batteries assembled with LiNi0.8 Co0.1 Mn0.1 O2 (NCM-811) and LiFePO4 (LFP) cathodes showed 60.2% and 74.7% capacity retention at 1 C for 200 cycles. Astonishingly, the PMDA-NiPc-G/NCM-811 full battery exhibits ≈100% capacity retention after cycling at 0.2 C. Aided by the analysis of kinetic behavior of lithium storage and theoretical calculations, the capacity-enhancing mechanism and lithium storage mechanism of covalent organic frameworks are revealed. This work may lead to more research on designable, multifunctional COFs for electrochemical energy storage.