Lithium Ion Diffusion Coefficient Research Articles

Mo-doping modulated cationic vacancy in Zn3V2O8 with enhanced electrochemical performance for lithium-ion batteries

Given diverse redox reactions and abundant raw materials, Zn3V2O8 with high specific capacity is considered as a potential anode material for lithium-ion batteries. Same as other transition metal oxides, Zn3V2O8 suffers from infertile conductivity, sluggish ion diffusion and fast capacity loss derived from volume expansion during discharge/charge process, further hindering its application. In this work, a novel Mo doped Zn3V2O8 (Zn3V2-xMo5x/6O8) anode material with cationic vacancy (V vacancy) has been designed through a facile sol-gel method. It is found that a small Mo-doping amount has nearly no influence on the crystal structure, morphology and element valence states of Zn3V2O8. Mo doped Zn3V2O8 samples possess smaller charge transfer resistance and higher lithium ion diffusion coefficient. The results of electrochemical performance illustrate that Mo doped Zn3V2O8 can deliver higher reversible specific capacities and better rate capability compared with Zn3V2O8, which can be ascribed to the introduction of V vacancy. In particular, when Mo-doping amount is set as 0.03, the obtained Zn3V1.97Mo0.025O8 exhibits a reversible capacity of 481.1 mAh g−1 after 600 cycles at 1 A g−1. It is believed that this work could provide an effective and feasible strategy to construct high performance transition metal vanadate anode materials for lithium-ion batteries.

Effects of Ti4+ doping on electrochemical properties of LiNi0.815Co0.15Al0.035O2 cathode materials

The high nickel ternary cathode materials LiNi0.815Co0.15Al0.035O2 (NCA) have been widely used in Li-ion batteries due to their high energy density, low cost, and little environmental pollution. However, it suffers from rapid capacity degradation and poor charging rate. In this work, Ti4+ doping NCA cathode materials are prepared by the high-temperature solid-state method. The results show that 0.5%Ti-NCA has a lower cationic mixing degree and better cycling performance. The capacity retention rate of 100 cycles is 98.91% and 96.59% at current densities of 0.5 C and 1.0 C, respectively. The CV and EIS test results show that 0.5%Ti-NCA has lower polarization and higher lithium ion diffusion coefficient DLi+(8.43×10−14 cm2/S) after 100 cycles, while Pure-NCA only has 6.92×10−15 cm2/S, which effectively enhances the electrochemical properties of NCA cathode materials.

Thermal Studies of Lithium-Ion Cells: Ensuring Safe and Efficient Energy Storage

This work investigated the impact of temperature on the diffusion of lithium ions within cells. To achieve this, electrochemical impedance spectroscopy (EIS) analysis was conducted at various temperatures across three distinct cells. These cells utilized an electrode composed of corn starch meringue and were paired with three different electrolytes. Notably, one electrolyte included an additional 5% of starch. The objective of this study extends beyond merely determining resistance from graphical representations; it also entails performing a kinetic analysis of specific systems, with a particular emphasis on elucidating the significance of the lithium-ion diffusion coefficient as a critical parameter. The cell with 1 M LiPF6 in the EC/DMC/DEC electrolyte and corn starch-based electrode exhibited the most horizontally oriented Warburg curve, representing the smallest angle.

Enhanced diffusion kinetics in Y-doped SnO2 anodes for low-temperature lithium-ion batteries: A combined theoretical and experimental study

In recent years, there has been an increasing demand for lithium-ion batteries suitable for low temperatures in various fields. SnO2, with its high theoretical specific capacity, has emerged as an ideal candidate for low-temperature lithium-ion batteries. However, tin oxide exhibits inherent issues such as poor conductivity and limited cycle reversibility. Enhancing the diffusion rate of lithium ions in tin oxide is crucial for improving its low-temperature performance. We use first-principles calculations based on Density Functional Theory (DFT) to investigate the doping models of various transition metal elements (Sc, Y, Ti, Zr, V, Nb, Gr, Mo, Mn, Fe, Co, Ni) with a rational ratio of 4 % in SnO2. The results indicate that Y doping decreases the band gap of SnO2 by 0.253 eV, leading to a significant reduction in the Li-ion diffusion barrier of α-Sn. Furthermore, the synthesized SnO2 doped with Y (Y-SnO2) electrode exhibited excellent cyclic stability as an anode and achieved a high reversible capacity of 672 mAh g−1 at −10°C, surpassing that of the pure SnO2 (450 mAh g−1). Moreover, it demonstrated a higher diffusion coefficient of lithium ions and lower charge transfer impedance at both low and room temperatures.

Comprehensive Study of Ti and Ta Co-Doping in Ni-Rich Cathode Material LiNi0.8Mn0.1Co0.1O2 Towards Improving the Electrochemical Performance.

Layered Ni-rich oxides (LiNi1-x-yCoxMnyO2) cathode materials are of current interest in high-energy-demanding applications, such as electric vehicles because of high discharge capacity and high intercalation potential. Here, the effect of co-doping a small amount of Ti and Ta on the crystal structure, morphology, and electrochemical properties of high Ni-rich cathode material LiNi0.8Mn0.1Co0.1-x-yTixTayO2 (0.0≤x+y≤0.2) was systematically investigated. This work demonstrates that an optimum level of Ti and Ta doping is beneficial towards enhancing electrochemical performance. The optimal Ti4+ and Ta5+ co-doped cathode LiNi0.8Mn0.1Co0.09Ti0.005Ta0.005O2 exhibits a superior initial discharge capacity of 161.1 mAh g-1 at 1 C, and excellent capacity retention of 87.1 % after 250 cycles, compared to the pristine sample that exhibits only 59.8 % capacity retention. Moreover, the lithium-ion diffusion coefficients for the co-doped cathode after the 3rd and 50th cycles are 9.9×10-10 cm2 s-1 and 9.3×10-10 cm2 s-1 respectively, which is higher than that of the pristine cathode (3.3×10-10 cm2 s-1 and 2.5×10-10 cm2 s-1 respectively). Based on these studies, we conclude that Ti and Ta co-doping enhances structural stability by mitigating irreversible phase transformation, improving Li-ion kinetics by expanding interlayer spacing, and nanosizing primary particles, thereby stabilizing high-nickel cathode materials and significantly enhancing cyclability.

Boosting both electronic and ionic conductivities via incorporation of molybdenum for LiFe0.5Mn0.5PO4 cathode in lithium-ion batteries

As the EV and ESS markets expand, there is a growing interest in LiFexMn1-xPO4 (LFMP) cathode materials amidst the increasing demand for LIBs. The LFMP cathode material is cost-effective and structurally stable; however, it has the drawback of low conductivity. Therefore, the development of an LFMP cathode material with high ionic/electronic conductivity is essential for high-stability and high-C-rate LIB applications. We propose a carbon-coated LFMP cathode material with Mo placed at the Fe and Mn sites. The samples were synthesized using a solvothermal method. Mo contributes to enhanced Li-ion diffusion and charge transfer rates. The XRD Rietveld refinement results showed elongated Li–O bonds within the Mo-doped LFMP/C, which accelerated the Li+ ion diffusion. Through SEM, TEM–EDS mapping, and XPS analysis we have confirmed the properties and morphology of the material. The electrochemical evaluation of the material was conducted using galvanostatic charge-discharge, CV, and EIS methods. Based on these tests, Mo incorporation not only increased the capacity but also enhanced the rate performance, reduced the voltage polarization, and improved the lithium-ion diffusion coefficient. Based on the 3.7 V additional plateau, which is attributed to the sluggish kinetics of Mn3+, Mo6+ played a role in enhancing the kinetic behavior of Mn3+. Low-temperature performance tests demonstrated that the Mo-doped samples exhibited high energy density, cycle retention, and superior ionic conductivity. In summary, an appropriate amount of Mo doping is effective for improving the electrochemical performance of LFMP, making it a promising cathode material.

Novel LiFePO4/very-few-layer-graphene (LFP/VFLG) composites to improve structural and electrochemical properties of lithium-ion battery cathode

LiFePO4/Very-few-layer-graphene (LFP/VFLG) composites have been prepared using the sol-gel method for lithium-ion battery cathode. VFLG dominated by 1∼3 layers was obtained from an economical and environmentally benign process. Structural properties of LFP/VFLG composites were studied using Fourier-transform infrared spectra (FTIR) spectroscopy, X-ray diffractometry (XRD), high-resolution transmission electron microscopy (HRTEM) and Raman spectroscopy, while the electrochemical performance was measured using galvanostatic discharge, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) tests. The FTIR analysis confirmed that incorporating VFLG neither affected the chemical structure of LiFePO4 nor initiated any side reactions during the LiFePO4 formation reaction. The XRD results showed that LFP/VFLG composites had better lattice parameters, crystallinity, and phase purity than LiFePO4 without VFLG addition. The Raman spectroscopy analysis indicated that LFP/VFLG composites had a lower disorder in the carbon arrangement. HRTEM results indicated that a VFLG was successfully wrapped around the LFP particle offers a versatile way to enhanced electrochemical performance of LFP/VFLG composites. The galvanostatic discharge profiles showed an enhancing specific discharge capacity of up to 58.3% after incorporating VFLG. The cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) tests revealed that LFP/VFLG delivered small polarization, low inner resistance, high electrochemical reaction reversibility, and high lithium-ion diffusion coefficient. VFLG is a promising additive to improve the structural and electrochemical properties of the LiFePO4 cathode of lithium-ion batteries.

Insights into phosphorus doping on the structure and electrochemical performance of Li2FeSiO4/C nano-composites

Li2FeSiO4 is one of the most promising cathode materials for lithium ion batteries due to its high theoretical capacity. However, the low electrical conductivity and low lithium-ion diffusion coefficient restrict its practical applications. Hetero-ion doping distinctly affect the crystal and electrochemical properties of Li2FeSiO4 based materials. Herein, phosphorus (P) doped Li2FeSiO4/C nano-composites (Li1.95FeSi0.95P0.05O4/C, abbreviated as LFSPC) and Li2FeSiO4/C nano-composites (LFSC) were synthesized and investigated as cathode material for lithium ion batteries. XRD and XPS analyses indicate that P has been doped in the crystal Li2FeSiO4. SEM results prove that the particle size of LFSPC is smaller than that of LFSC. These features make LFSPC exhibit better electrochemical performance over LFSC. The discharge capacity of LFSPC at 0.1C is as high as 218.1 mAh/g, higher than that of LFSC (144.0 mAh/g). The capacity retention ratio for LFSPC after 200 cycles at 1C is 85 %, higher than that of LFSC (78 %). In addition, LFSPC deliver larger rate performance, lower charge transfer resistance and larger lithium-ion diffusion coefficient.

Mitigation of charge heterogeneity by uniform in situ coating enables stable cycling of LiCoO2 at 4.6V

LiCoO2 is a predominant cathode for lithium-ion batteries of portable electronics owing to its merit of high volumetric energy density. Nevertheless, it experiences rapid capacity deterioration under high voltages, concomitant with structural degradation and numerous intragranular cracks. Coating has been recognized as an efficacious strategy to ameliorate the decline in cycling performance of LiCoO2 at high voltages. Hence, a systematic elucidation of the precise mechanisms underlying the mitigation of structural degradation via coating layers assumes paramount importance in the context of advancing the next generation of high-voltage LiCoO2. In this work, the intricate interrelation among lithium-ion diffusion coefficients, charge heterogeneity, and crack distribution is explicated through techniques inclusive of galvanostatic intermittent titration technique (GITT), finite element analysis (FEA), and X-ray computed tomography (XCT). A robustly stable lithium-ion-conducting coating material serves the function of curtailing the occurrence of surface passivation layers, achieved by diminishing side reactions between the LiCoO2 and the electrolyte; while a uniform coating ensures a homogeneous lithium-ion flux, thereby mitigating charge heterogeneity and the resultant mechanical strain as well as intragranular cracks. Both are important elements that collectively allow the coating to effectively protect the surface from structural degradation, thus achieving superior performances upon high-voltage charging.

Achieving CoAl2O4@Li1.2Ni0.13Co0.13Mn0.54O2 with Long Cyclic and High-Rate Performance via Citric Acid Combustion Method

Lithium-rich manganese-based cathode materials (LNCM) have high specific capacities and operating voltages. However, they also have intractable deficiencies such as low capacity retention and unsatisfactory rate capability. Herein, CoAl2O4 with spinel structure and chemically stable is adopted to decorate the surface of LNCM to modify the cyclic and high-rate performance of final product. 3CoAl2O4@LNCM synthesized by self combustion of citric acid shows the best electrochemical properties such as lower voltage drop (4.7 mV per cycle) and higher capacity retention of 81.33% (1 C) after 100 cycles, which is exceed to bare LNCM (7.7 mV per cycle, 47.65%). Besides, the charge transfer resistance R ct of the modified sample is lower, and its lithium ion diffusion coefficient D Li + is higher. Consequently, 3CoAl2O4@LNCM is able to demonstrate high rate performance, whereby a capacity retention of 65.84% (5 C) is achieved after 100 cycles. The improved electrochemical properties of 3CoAl2O4@LNCM because of the 3D diffusion channel of CoAl2O4 benefits lithium ion diffusion; and the chemical stability of CoAl2O4 enhances the corrosion resistance of LNCM bulk to the electrolyte. As such, this results in the suppression of TM ion dissolution, and the enhancement of cyclic stability and initial coulomb efficiency.

MIL-53(Fe) anode for lithium-ion batteries with the capacity self-activation effect based on electrochemically induced crystalline-to-amorphization transformation

The relationship between structural changes and electrochemical properties of flexible metal-organic framework materials is a striking phenomenon. We synthesized a highly ordered flexible metal-organic framework called MIL-53(Fe) as an anode for lithium-ion batteries. MIL-53(Fe) 's cyclic performance exhibits capacity self-activation traits. At 100 mA g−1 current density, the specific discharge capacity of 100 cycles is 931.23 mAh g−1, the coulomb efficiency is 98.53%, and the capacity retention rate is 92.60%. The evolution of MIL-53(Fe) throughout the cycle was observed using X-ray diffraction, Raman spectroscopy, and high-resolution transmission electron microscopy. It was discovered that the structure of MIL-53(Fe) experienced an electrochemically induced transition from a crystalline state to an amorphous state. After amorphous conversion, the electrochemical transfer impedance of the material is reduced from 177.2 Ω to 40.6 Ω, the diffusion coefficient of lithium-ion is increased from 3.32 × 10−14 cm2/s to 1.10 × 10−13 cm2/s, and the mass transfer capacity is improved. The results show that MIL-53(Fe) has unique electrochemical properties, and the feasibility of amorphous transition as a mechanism to enhance the electrochemical properties is found.

Boosting the cycle stability of nickel-rich ternary materials at high voltage by coating mixed conductor Li7.5La3Zr1.5Co0.5O12

Ni-rich NCM materials have the high electrochemical capacities and low costs. However, the disadvantage of poor cycle performance severely limits their large-scale use. In this work, the nanoscale ion-electron mix-conductor Li7.5La3Zr1.5Co0.5O12 was prepared by ball milling and used to directly mix LiNi0.83Co0.11Mn0.06O2. After annealing, a mixed conductive protective layer could be formed on the surface of the NCM. The coating layer can protect the structural integrity of the NCM particles during cycling. At a current density of 1C between 2.8 and 4.5 V, the modified sample exhibited a capacity of 196 mAh g−1, and the capacity retention rate was as high as 85.7 % after 200 cycles, which was a significant improvement of 23.8 % over the pristine sample. The lithium-ion diffusion coefficient is enhanced and the charge transfer resistance is reduced by the mixed conductor cladding. The modified material shows an excellent rate performance. The specific capacity at 5C was 181 mAh g−1. The proposed modification method is simple in process and suitable for large-scale applications. The method has reference significance for the modification of other cathode materials.

Interfacial polymerization achieved integration of pore size adjustment, electrostatic repulsion and physical adsorption into one to inhibit polysulfide shuttle for enhanced lithium–sulfur battery

The application of lithium-sulfur battery is seriously hindered by the shuttle of dissolved polysulfide between sulfur cathode and lithium anode, by which is not selectively inhibited by the conventional separator. Developing functional separator is considered as a preferred solution for this issue, but it is always challenged by the tedious preparation process. Herein, interfacial polymerization (IP) is employed to modify the surface property of ZrO2 nanoparticles embedded polyetherimide (PZ) based separator, and the integration of pore size adjustment, electrostatic repulsion and physical adsorption into one is facilely achieved to effectively inhibit the polysulfide shuttle. Consequently, the optimized PZ separator presents a high lithium-ion transference number (0.55) and diffusion coefficient (2.16 × 10−8 cm s−1). Compared with the pristine one, the electrochemical performance of the assembled lithium-sulfur battery is obviously enhanced, and an initial discharge specific capacity of 1242 mAh g−1 and a capacity retention of 68 % after 200 cycles are obtained.

Lithium-copolymerized polyimide cathodes for stable and fast lithium-ion storage

Organic materials as cathodes have attracted a lot of attention for lithium-ion batteries due to their structural designability and high theoretical capacity. However, most organic polymer cathode materials, such as π-conjugated polymers, have slow diffusion of lithium ions due to closely packed structures, resulting in inferior properties. Herein, we have synthesized lithium modified polyimides by condensation polymerization between 3,4,9,10-perylenetetracarboxylic acid dianhydride and 1,2-ethylenediamine in the presence of N-(2-aminoethyl)glycine lithium salt. The lithium-copolymerized polyimides exhibit lamellar structure and have increased specific surface area and therefore lead to enhanced lithium-ion diffusion coefficient and electronic conductivity. Lithium metal half cells employing lithium modified polyimide cathodes have a high discharge capacity of 138.3 mAh g−1 at a current density of 30 mA g−1 and good cycling stability with 71 % capacity retention at a current density of 1000 mA g−1 after 5000 cycles, which are much better than those employing general polyimides.

Molecular Dynamics Analysis of Lithium-Ion Transport Properties in All-Solid-State Lithium-Ion Battery

Lithium-ion batteries have been widely used in electronic products since their commercialization, but the use of liquid electrolytes carries safety risks of electrolyte volatilization, leakage, and corrosion. Meanwhile, solid-state electrolytes have the advantage of high safety performance compared with liquid electrolytes. Therefore, all-solid-state Lithium-ion batteries has become a new research topic. LiNi x Co y Mn z O2 (NCM, x+y+z =1) material have been used as a representative ternary compound cathode material in Lithium-ion batteries. However, understanding the influencing conditions during the transport of Lithium ions in NCM materials is incomplete and difficult to observe experimentally. Therefore, our goal is to understand the factors influencing Lithium-ion transport properties. In this work, molecular dynamics (MD) simulations of NCM materials were used to analyze the transport properties of Lithium-ion.According to Wei's study, we created three patterns for transition metal alignment for LiNi0. 33Co0. 33Mn0. 33O2(NCM333). Then, MD simulations were performed for the three types of NCM333. The Lithium-ion transport properties are considered in different Lithium-ion content rate (100%, 88%, 77%, 66%, 55%, 44%, 33%, and 22%) which represent different state of charge (SOC). The occupied positions of Lithium-ion in the initial NCM structure were randomly constructed for different percentages of Lithium-ion content. According to Zhu's research, we used the Morse potential energy in the LAMMPS as the basis and added the corresponding Coulomb force and long-range repulsive interaction force. In the end, the potential model based on Morse-type interaction, Coulomb interaction and a long-range repulsive interaction were used. The size of the simulation box was 34.74 Å×29.72 Å×28.54 Å. The total number of atoms was 3456. The temperature of the system during the MD simulation was set at 300 K, the timestep was set at 1.0 fs, and the sampling interval for trajectories was 500 steps. To relax the system, a 0.5 ns NPT process was first applied. After 10 ns of NVT process was performed, the size of the simulation box at the final equilibrated state was compared with that of 100% Lithium-ion content. The results showed that the simulation box volume variation was less than 2% in all calculated Lithium-ion content. Radial distribution function (RDF) analysis was also performed using the same conditions, and the results were consistent with Lee's study. These two analyses confirmed the integrity of the structural NCM in the simulation.The mean-squared displacement (MSD) analysis was performed on the NCM333 material throughout the trajectories in the 10 ns NVT process. From the MSD data, all three patterns of NCM333 have very minimal Lithium-ion mean square displacement at 100% Lithium-ion content, and the values of Lithium-ion mean square displacement for each pattern were very close to each other, which was not only consistent with the structural properties of NCM333, but also with the Lee's study. In the simulation of Pattern 1 with different Lithium-ion contents, it can be seen that there was a more significant migration of lithium ions compared to 100% Lithium-ion content, which was also reflected in the mean square displacement data. The mean square displacement data at 88% Lithium-ion content was significantly smaller than those at 55% Lithium-ion content, but all rang of the mean square displacement data were much larger than those at 100% Lithium-ion content. Because at 100% Lithium-ion content, there was no vacancy around the Lithium-ion, so only vibrations occured. When the Lithium-ion content is less than 100%, vacancies appear, so the Lithium-ion occur in vibration and diffusion.The Lithium-ion diffusion coefficient was obtained by linear fitting the MSD data in the region of 2.5ns-5ns. The figure shows the Lithium-ion diffusion coefficients (DLi) of the NCM333 material for different Lithium-ion contents. As shown in the figure, the experimental value is 3.3x10-11cm2/s and the theoretical value of the Wei's study is 5x10-9cm2/s when the Lithium-ion content of NCM333 was 33%. Also the calculated value was approximately one hundredth times larger than the experimental, consistent with the Wei's study. The diffusion coefficient maximum peak exists around 50% Lithium-ion content, which was inconsistent with our prediction. Our predictions suggest that as the Lithium-ion content decreases, more vacancies will occur and therefore the DLi should increase. Further refinement and improvements will be considered to confirm these phenomena. Figure 1

KOH selective etching synthesis and electrochemical performance of nano porous Li2FeSiO4/C composite

Nano porous Li2FeSiO4/C composite (LFS-10S) was prepared by KOH selective etching Li2FeSiO4-(SiO2)0.1/C composites. This method allows directly pore-creating on Li2FeSiO4 crystal. Common porous Li2FeSiO4/C (LFS) were also prepared as a control. LFS-10S and LFS were characterized by XRD, SEM, TEM and nitrogen adsorption/desorption test. XRD analysis shows that the LFS-10S material was composed of crystalline particles with a monoclinic crystal system in the P21 space group. SEM and TEM tests indicate that the particle size of LFS-10S is 20 ∼ 30 nm. The nitrogen adsorption/desorption test shows that the specific surface area of LFS-10S is 123.23 m2/g, larger than that of LFS (71.56 m2/g). These features make LFS-10S exhibit better electrochemical performance over LFS. The specific discharge capacity of LFS-10S at 0.1 C is as high as 235.2 mA h g−1, higher than that of LFS (158.4 mA h g−1). Moreover, the rate performance, cycling performance and lithium ion diffusion coefficient of LFS-10S are all better than those of LFS.

Enhancement of performance and kinetics of layered Li2MnO3 by Fe doping

Layered Li2MnO3 exhibits great potential as a high-capacity cathode used in lithium-ion batteries, but materials synthesized by traditional solid-phase methods exhibit poor activity and poor cycling stability. In this work, Li2MnO3 nanoparticles were synthesized by solid state method combined with high-energy ball milling, in which Fe was doped at transition metal sites to obtain a Li-rich cathode material (Li1.32Fe0.034Mn0.64O2). We systematically studied the effects of Fe doping and calcination temperature on the crystal structure and electrochemical properties and conducted kinetic studies using the galvanostatic intermittent titration technique (GITT), electrical impedance spectroscopy (EIS) and density functional theory (DFT) calculations. Our results demonstrate that the performance was significantly improved, its discharge capacity is about 235 mAh g−1 after 10 cycles compared 138 mAh g−1 of the pristine sample. The GITT and EIS results show that the Fe-doped sample had smaller charge transfer impedance, larger lithium-ion diffusion coefficient and lower internal polarization than the pristine. The activation energy results show the Fe-doped sample has larger activation energy at the late discharging period due to the anion redox reaction activation, indicting its O activation is more active than Li2MnO3. Moreover, the DOS results showed that the Fe-doped sample had a narrow band-gap, indicating good electrical conductivity. The CI-NEB results showed that the Fe-doped sample had a high transition metal ion migration energy barrier, indicating that its structure was stable. In conclusion, Fe doping is helpful to active the anion redox reaction in Li2MnO3 and improve its electrochemical performance as a low cost and high-capacity cathode materials.

A doping strategy for improving high rates performance of LiNi0.90Co0.05Mn0.05O2 cathode

The Li1-x(Ni0.9Co0.05Mn0.05)MgxO2 (MNCM) cathode materials are prepared by ball milling-drying spray method. XRD and XPS proved that Mg2+ occupied the Li layer, reduced Li/Ni mixture and inhibited phase transition, which stabilized the structure of Li(Ni0.9Co0.05Mn0.05)O2 (NCM). Mg doping can improve capacity and cycling stability by reducing voltage attention at high rate. The Li0.99(Ni0.9Co0.05Mn0.05)Mg0.01O2 (MNCM1) cathode shows an excellent capacity of 164 mAh/g, and the corresponding cycle retention is 89 % at 5C (1C = 200 mAh/g) after 150 cycles, much higher than NCM (144.5 mAh/g and 50.1 %). The results of EIS show that Mg doping can effectively improve the lithium ion diffusion coefficient and reduce the impedance generated during the cycles. In addition, the cycle performance of NCM/graphite full battery is also significantly improved with the help of Mg doping. After cycling, SEM of electrode materials shows that MNCM1 retained more secondary spherical particles, which proved that Mg doping can improve the structural stability of materials during cycles.

Analysis of lithium diffusion and overpotential in lithium nickle cobalt aluminum oxide based lithium ion cells

Cathode degradation during the charge and discharge process is inevitable due to phase transformations during the de-/lithiation process. Various factors such as temperature, cut-off voltage, and current rates tend to cause irreversibility in the phase transformations during cycling, resulting in the quick aging of lithium-ion batteries for electric vehicle applications. This study aims to evaluate the trends of the lithium-ion diffusion coefficient as a function of the lithium-ion concentration and potential in the lithium nickel cobalt aluminum oxide (NCA) cathode of the VTC5 lithium-ion cell through measurements by the galvanostatic intermittent titration technique (GITT). The lithium-ion cell has shown the lowest diffusion coefficient value of 1.08E−17 m2 s−1 at 0.2C rate at 25 °C temperature and the highest diffusion coefficient of 7.2829E−16 m2 s−1 at the lowest current rate of 0.05C rate and 45 °C temperature during discharging. The trend of diffusion coefficient values for lithium de-/intercalation with changing temperature and current rates is investigated and correlated with the phase transformations in the structure of the cathode and is indicative of a mixed-phase reaction mechanism. The electrochemical impedance spectroscopy data reinforces the dependence on lithium-ion diffusion on temperature, and voltage values and is supported by comparative analysis.

Construction of flower-like Ni-Cu@C/HC nanoparticles capable of inhibiting polysulfide shuttling for high-performance lithium-sulfur batteries

High-performance lithium-sulfur (Li-S) batteries show high energy density while the commercialization process has been hampered by the shuttle effect. Herein, separators with flower-like nickel-copper alloy (Ni-Cu) nanoparticles loaded on hard carbon (HC) were designed to alleviate the polysulfide shuttle. The lithium-ion (Li+) diffusion coefficients and Tafel slopes of the three separators were calculated, demonstrating that Ni-Cu@C/HC can significantly accelerate polysulfides conversion. The separation modification layer’s influence on the discharge curve was first explored using COMSOL software under linear dimensions. The lithium polysulfides (LiPSs) reaction behavior and Li+ diffusion behavior were simulated, and the voltage change mechanism of the discharge curve was elucidated. The effect of Ni-Cu@C on Li2S conversion was investigated using Galvanostatic Intermittent Titration Technique and Li2S deposition experiments. The Ni-Cu@C/HC separator constructed in this work has multiple catalytic sites and catalytic core for LiPSs, which can significantly boost the polysulfides conversion and provide a good Li+ diffusion environment, contributing to the production of high-performance Li-S batteries.