Li-ion Diffusion Coefficient Research Articles

Disentangling Cation and Anion Dynamics in Li3PS4 Solid Electrolytes.

A prerequisite for the realization of solid-state batteries is the development of highly conductive solid electrolytes. Li3PS4 is the archetypal member of the highly promising thiophosphate family of Li-ion conductors. Despite a multitude of investigations into this material, the underlying atomic-scale features governing the roles of and the relationships between cation and anion dynamics, in its various temperature-dependent polymorphs, are yet to be fully resolved. On this basis, we provide a comprehensive molecular dynamics study to probe the fundamental mechanisms underpinning fast Li-ion diffusion in this important solid electrolyte material. We first determine the Li-ion diffusion coefficients and corresponding activation energies in the temperature-dependent γ, β, and α polymorphs of Li3PS4 and relate them to the structural and chemical characteristics of each polymorph. The roles that both cation correlation and anion libration play in enhancing the Li-ion dynamics in Li3PS4 are then isolated and revealed. For γ- and β-Li3PS4, our simulations confirm that the interatomic Li-Li interaction is pivotal in determining (and restricting) their Li-ion diffusion. For α-Li3PS4, we quantify the significant role of Li-Li correlation and anion dynamics in dominating Li-ion transport in this polymorph for the first time. The fundamental understanding and analysis presented herein is expected to be highly applicable to other solid electrolytes where the interplay between cation and anion dynamics is crucial to enhancing ion transport.

Using the synergistic effect of co-doping to engineer magnesium and chlorine co-doping to improve the electrochemical performance of Li2FeSiO4/C cathodes

To compensate for the insufficiency of single doping and to exert the synergistic effect between the elements, further improving the electrochemical performance, a series of Mg and Cl co-doped Li2Fe1−xMgxSiO4–2xCl2x/C (x = 0, 0.01, 0.02, 0.03) nanocomposites (LFS, LFS-1, LFS-2, and LFS-3) have been synthesized by solvothermal method. Experimentally, Mg and Cl co-doping in Li2Fe1−xMgxSiO4–2xCl2x/C were confirmed by X-ray diffraction, X-ray photoelectron spectroscopy, high resolution transmission electron microscope, and field-emission gun scanning electron microscopy elemental mapping, while electrochemical cycling performance showed improved performance. According to the results, LFS-2 outperforms other nanocomposites in terms of electrochemical performance, rate capability, and initial discharge capacity, with a capacity of 238.3 mAh·g−1 after 100 cycles of charging and discharging at 0.05 C. This is because it has a stable monoclinic structure free of impurities, a lower charge transfer resistance, and a higher Li-ion diffusion coefficient. Our findings suggest that Mg and Cl co-doping might be a feasible low-cost technique to enhance the electrochemical performance of silicate-based cathode materials, taking into account potential and electronic conductivity advantages.

Appraisal the effective diffusion coefficients of Li-ions by PITT and network thermodynamic methods in thin-layer Fe-sulfidic electrodes of Li-accumulator

In this work, we explored the possibilities of network thermodynamics to determine the most important kinetic parameter of the diffusion process, the diffusion coefficient of lithium ions (DLi) in iron sulfide. Iron sulfides have been electrolytically synthesized in thin aluminum-based layers for implementation in miniature lithium batteries. A comparison is made of the results obtained by the method of network thermodynamics and the method of potentiostatic pulse titration PITT. The theoretical aspects of both methods are presented. The task was reduced to obtaining curves I (current) - time (t), their analysis and calculation of coefficient values (DLi), using the theoretical foundations of diffusion and the methods used. At the early stages of applying the method of network thermodynamics to the study of diffusion in lithium current sources, it was not clear why the method is suitable for determining DLi not in the entire working range of potentials. A wide range of studies using the PITT method helps to answer questions related to the application of the network thermodynamic method. When using both methods, it is important to establish the potential range with diffusion kinetics and to reveal the accompanying electrode processes. Thus, it was found that both methods used are unable to provide reliable results in the FexSy electrode potential range of 2.8–1.8 V, since the diffusion nature of the electrode process is not a priority in this potential range.

Zero-Strain Insertion Anode Material of Lithium-Ion Batteries.

The insertion type materials are the most important anode materials for lithium-ion batteries, but their insufficient capacity is the bottleneck of practical application. Here, LiAl5 O8 nanowires with high theoretical capacity and Li-ions diffusion coefficient are prepared and studied as an insertion anode material, which exhibits zero-strain properties upon electrochemical cycling. However, the poor electronic conductivity of LiAl5 O8 definitely sacrifices the capacity and limits the rate performance. Therefore, compact LiAl5 O8 and carbon composite are further synthesized, in which nanosized LiAl5 O8 particles are uniformly embedded in an amorphous carbon matrix. It displays a reversible capacity of 490.9 mAh g-1 at 1 A g-1 , and the capacity rises continuously to 996.8 mAh g-1 after 1000 cycles due to the interfacial storage mechanism, that the excess Li+ ions can be accommodated in the grain boundaries and C/LiAl5 O8 interfaces.

Designing the 3D Porous Anode Based on Pore Size Dependent Li Deposition Behavior for Reversible Li Metal-Free Solid-State-Batteries

Li metal-based all-solid-state batteries (ASSBs) can potentially combine the high energy of Li metal anodes and the safety of ASSBs. Among Li metal-based ASSBs, lithium-free or anodeless ASSBs are considered optimal battery configurations because of their higher energy density and economic advantages attributed to the absence of Li metal during the battery assembly process. Despite the extensive interest in Li-free ASSBs, they continue to suffer from low Coulombic efficiency and poor cycle performance. One reason for this inferior performance is the unstable interface between the current collector and solid electrolyte (SE), which can eventually lead to inhomogeneous Li deposition, dendritic Li growth, and internal short circuits. Various approaches including 3D porous anodes have been proposed to control the Li deposition behavior and improve the reversibility of anodeless ASSBs; however, there is no clarity on the mechanism and conditions for determining the Li deposition behavior in this emerging system.In this study, we systematically investigate the Li deposition behavior depending on the pore size of 3D anode and successfully demonstrate the strategy to obtain a highly reversible 3D porous anode for Li-free ASSBs. We found that more Li deposits could be accommodated within the pores of the anode with a smaller pore size using stacked Ni particles as the Li-hosting porous anode; this implies that the Li movement into the anode occurs via diffusional Coble creep. We proposed the modification of the Ni surface with carbon coating and Ag nanoparticle decoration (Ni_C_Ag particles) to further improve the Li storage capacity of the Ni-based 3D anode and, thereby, secure the interfacial contact between the 3D Ni anode and SE. The resulting Ni_C_Ag 3D anode successfully accommodated the entire Li deposit of 2 mAh cm−2 within the porous architecture without the separation of the anode/SE interface. We clarified the improved Li storage capacity of the Ni_C_Ag anode as follows.(1) C and especially Ag electrochemically react with Li ions above 0 V; thus, Li ions can be transported to 3D Ni_C_Ag porous anode before Li deposition at the SE/anode interface at < 0 V. Further, the high Li ion diffusion coefficient of lithiated carbon and Li-Ag alloy can further reduce Li ions within the pores of the 3D anode; therefore, Li deposition can occur within the porous 3D Ni anode.(2) Lithiophilic C and Ag facilitated the movement of Li via diffusional Coble creep. In particular, Ag with solid solubility in Li (Li(Ag)) can significantly enhance Li adatom mobility because of the identical structure of Li(Ag) with pure Li.(3) Li(Ag) is widely known to lower the energy barrier for Li nucleation.With the significantly reduced nucleation overpotential and interfacial resistance, the Ni_C_Ag anode showed high reversibility in Li deposition and stripping. The Ni_C_Ag anode could be cycled for more than 60 and 100 cycles with Li3PS4 and Li6PS5Cl0.5Br0.5 SE in half cells with a capacity limit of 2 mAh cm−2 and a current density of 0.5 mA cm− 2maintaining the CE of 97.9% and 96.9 %, respectively. Further, the synergistic effects of the stable anode/SE interface and reduced nucleation energy barrier enable stable NCM full-cell cycling at a room temperature of 30 °C. The NCM811 cathode/Ni_C_Ag anode full cell in the Li-free configuration showed an initial areal discharge capacity of 2 mAh cm−2, and it operated stably with a CE of 99.47% for 100 cycles. Figure 1

The Adoption of Lithiophilic Nano Sn on Cu Current Collector By Electroplating Techniques to Improve the Stability of Lithium Metal Anode

The growing demand for higher energy density batteries is increasing due to needs of electric vehicle (EV) [1]. Until now, it cannot exceed the one-time charging distance of an internal combustion engine vehicle, due to energy limit of batteries. Li metal anode (LMA) is one of the attractive anode candidates because of the lowest electrochemical redox electrode potential (-3.04 V vs. SHE) and the extremely high theoretical gravimetric capacity (3,860 mAh g-1) compared to graphite anode (372 mAh g-1) [2]. However, uneven Li deposition causes dendritic growth leading to low Coulombic efficiency (CE) and safety hazards which is impeding the practical use of LMAs [3]. Recently, to suppress such dendritic growth, various solutions such as introduction of solid-state electrolyte (SSE) [4], artificial solid electrolyte interphase (ASEI) [5], 3D current collector (CC) [6], and lithiophilic materials [7] have been proposed.Among the several approaches, introducing lithiophilic material on a CC is one of the facile and effective strategies to increase the lithiophilicity, and hence to induce the planar growth of Li. Also, assuming that electroplating is largely divided into two steps: nucleation and growth, lithiophilic material can change the intrinsic nucleation behavior by preferentially forming a different phases such as Li alloys [8]. Since the Li nucleation process significantly influences the final growth of Li, different cycling behaviors of LMAs would be expected depending on lithiophilic material [9]. As for the methods to adopt the lithiophilic materials, the electrodeposition is very attractive, since it can easily control the surface morphology, which might affect the Li deposition morphology and the related behavior. In this regard, we chose the tin (Sn) as a lithiophilic material, which can be deposited on Cu CC by electroplating, and moreover have a fast Li ion diffusion coefficient [10].Specifically, in this work, we study the effect of surface morphology of lithiophilic Sn deposited on copper CC by testing Li deposition/stripping behavior for a LMAs. For different morphology, a direct current electrodeposition (DC) and pulsed electrodeposition (PED) were used. Fig.1 is FE-SEM images of Cu@Sn with DC growth and PED growth. Fig.1 (a) shows Sn particles are growing without filling the pores. However, Fig.1 (c) shows Sn particles are growing with filling the pores. At Fig.1 (b) and (d), the morphology difference is conspicuous between DC and PED growth. Fig.1 (b) presents island growth in which nuclei grow on existing nuclei because there is only Ton without relaxation time. While, Fig.1 (d) shows that after rearrangement of deposited atom at Toff, new nucleation sites are created by continuously applying pulses, thereby obtaining the coalescence growth. At Fig.2, Cu@Sn (PED) shows the longer cycle life than bare Cu and Cu@Sn (DC) because Cu@Sn (PED) has an uniformly distributed nano Sn morphology, which provides more sites for Li nucleation to prevent dendritic growth.

Multifunctional surface modification with Co-free spinel structure on Ni-rich cathode material for improved electrochemical performance

In our previous work, a Li reactive-spinel coating using Co and Mn sources is suggested to solve microcracks and residual Li. However, the importance of reducing Co content is increasing due to the cost and environmental issues of Co as well as obstacles caused by patents. In this work, we focus on finding a coating material that can replace Co to overcome the shortcomings of Ni-rich cathode materials. The Ni/Hf coated sample with a multifunctional surface has a higher initial capacity compared to the pristine material. It is attributed to the decrease in residual Li, which hindered Li transportation. The rate capability (3 C/0.2 C) of the Ni/Hf = 2:1 sample is 90.8%. This is due to the unique 3D diffusion channels of the spinel structure. Thus, the Ni/Hf = 2:1 coated sample has a Li-ion diffusion coefficient higher than twice that of the pristine sample. Additionally, the coating layer suppress side reactions and large volume change, with higher reversibility of H2-H3. The charge-transfer resistance of the Ni/Hf = 2:1 coated sample is reduced by 48% compared to that of the pristine sample. Furthermore, it has an enhanced cycle retention of 89.6% after 50 cycles. The uniform Ni/Hf coating on the surface gave stability to the cathode powder, thereby improving performance compared to other coatings and pristine • DFT calculations predicted the components of the Ni/Hf coating layer. • XRD was confirmed that the materials present in the coating layer. • The spinel coating improved the reversibility of the H2-H3 transition. • The spinel and rock-salt coatings suppress side reactions.

Electrochemical redox of Li2S–CaS and –CaX2 (X = Cl, Br, and I) cathode materials for all-solid-state lithium-sulfur batteries

In this study, we have evaluated the cell performances of Li2S–CaS and –CaX2 (X = Cl, Br, and I) cathode materials prepared by high-energy ball milling in all-solid-state lithium-sulfur batteries. The cell using 85Li2S·15CaS (mol%) cathode exhibited the highest capacity of 819 mAh g−1 after 15 cycles among the prepared (100−x)Li2S–xCaS cathodes (x = 0, 5, 10, and 15). The electrochemical tests showed that the electrochemical redox reactions of the Li2S–CaS cathodes involved a large contribution of the degradation products from solid electrolytes. Additionally, the cells using the Li2S-CaX2 (X = Cl, Br, and I) showed a higher utilization than Li2S cathode. Cyclic voltammetry at different scan rates demonstrated that the addition of CaX2 (X = Cl, Br, and I) increased the Li-ion diffusion coefficient of cathode materials, which was the highest value for the 90Li2S·10CaI2 cathode material among the fabricated cathodes. In the electrochemical redox of the 90Li2S·10CaI2 cathode, an additional oxidation reaction appeared at a slightly higher reaction voltage than the oxidation voltage of Li2S. These electrochemical properties allow to excellent capacity, performance stability, and reversibility of the all-solid-state lithium-sulfur batteries using the 90Li2S·10CaI2 cathode material.

Influence of the SEI Formation on the Stability and Lithium Diffusion in Si Electrodes.

Silicon (Si) is an attractive anode material for Li-ion batteries (LIBs) due to its high theoretical specific capacity. However, the solid–electrolyte interphase (SEI) formation, caused by liquid electrolyte decomposition, often befalls Si electrodes. The SEI layer is less Li-ion conductive, which would significantly inhibit Li-ion transport and delay the reaction kinetics. Understanding the interaction between the SEI components and Li-ion diffusion is crucial for further improving the cycling performance of Si. Herein, different liquid electrolytes are applied to investigate the induced SEI components, structures, and their role in Li-ion transport. It is found that Si electrodes exhibit higher discharge capacities in LiClO4-based electrolytes than in LiPF6-based electrolytes. This behavior suggests that a denser and more conductive SEI layer is formed in LiClO4-based electrolytes. In addition, a coating of a Li3PO4 artificial SEI layer on Si suppresses the formation of natural SEI formation, leading to higher capacity retentions. Furthermore, galvanostatic intermittent titration technique (GITT) measurements are applied to calculate Li-ion diffusion coefficients, which are found in the range of 10–23–10–19 m2/s.

Highly N-doped and flexible carbon nanofiber membrane as cathode host for Li-Se batteries

Se as an active material attracts tremendous attention because of its high volumetric capacity and better conductivity than S for rechargeable batteries. Herein, a carbon nanofiber membrane (PM-CNF) is designed and prepared as free-standing Se host by electrospinning the solution of polyacrylonitrile (PAN) and poly(styrenesulfonic acid)-melamine salt, followed by carbonization and activation process. PM-CNF shows super flexibility and high N-doping level of 8.92 % (pyrrolic-N: 2.15 % and pyridinic-N: 3.07 %), which is beneficial for ions diffusion and electrons transformation. The free-standing PM-CNF/Se cathode delivers a high reversible capacity of 570 mAh g−1 at 0.5 C, superior rate capacity of 375 mAh g−1 at 8 C, and stabile cycling over 1800 cycles. The excellent electrochemical performance can be ascribed to high Li-ion diffusion coefficient (2.99 × 10−9 cm2 s−1) and capacitance-contributed ratio (77.1 % at 0.1 mV s−1). The analysis of the charge/discharge process reveals that no polyselenide intermediates are observed during the first cycling process and thus the inhibited shuttle effect of polyselenides over cycling, which primarily contributes to the long cycling stability.

Operando monitoring of single-particle kinetic state-of-charge heterogeneities and cracking in high-rate Li-ion anodes

To rationalize and improve the performance of newly developed high-rate battery electrode materials, it is crucial to understand the ion intercalation and degradation mechanisms occurring during realistic battery operation. Here we apply a laboratory-based operando optical scattering microscopy method to study micrometre-sized rod-like particles of the anode material Nb14W3O44 during high-rate cycling. We directly visualize elongation of the particles, which, by comparison with ensemble X-ray diffraction, allows us to determine changes in the state of charge of individual particles. A continuous change in scattering intensity with state of charge enables the observation of non-equilibrium kinetic phase separations within individual particles. Phase field modelling (informed by pulsed-field-gradient nuclear magnetic resonance and electrochemical experiments) supports the kinetic origin of this separation, which arises from the state-of-charge dependence of the Li-ion diffusion coefficient. The non-equilibrium phase separations lead to particle cracking at high rates of delithiation, particularly in longer particles, with some of the resulting fragments becoming electrically disconnected on subsequent cycling. These results demonstrate the power of optical scattering microscopy to track rapid non-equilibrium processes that would be inaccessible with established characterization techniques.

Solvent-free dry cyclized polyacrylonitrile-coated LiNi0.87Co0.13O2 cathode for improving the electrochemical performance of Li-ion batteries

A Ni-rich LiNi0.87Co0.13O2 cathode was modified through dry surface-coating with cyclized-polyacrylonitrile (c-PAN). The c-PAN coating was obtained by heat treatment of polyacrylonitrile (PAN), used as a coating material for improving the electrochemical performance of the cathode. The cyclized PAN structure was confirmed by Raman spectroscopy, with the appearance of two carbon sp2 peaks in the range of 1200–1800 cm−1. Electrochemical tests showed that over 80% of the first discharge capacity was retained for the 2 wt% c-PAN coated electrode, whereas the capacity retention of the uncoated electrode was only about 77% after 100 cycles at a rate of 0.5C. At a high rate of 5C, the coated sample delivered a discharge capacity of 180.7 mAh g−1 in the 5th cycle and retained a discharge capacity of 212.6 mAh g−1 at 0.1C in the rate performance test, which is higher than the values of 165.2 and 198.6 mAh g−1 for the uncoated sample at 5C and 0.1C, respectively. These improvements could be attributed to the c-PAN coating layer, which limited the side reaction between the electrode and electrolyte, resulting in a higher Li-ion diffusion coefficient and a slower increase in the charge transfer resistance.

(Digital Presentation) Parameterization of a Commercial 18650 High-Power Lithium-Ion Cell for a Physico-Chemical Model

Li-ion battery is an integral part for the electric or hybrid electric vehicles, as they provide high energy density and power density with extended cycle-life compared to their closest rivals, Ni-MH batteries [1]. Electric vehicles (EVs) require an advanced real-time based battery management system (BMS) that ensure a safe and efficient energy utilization, estimate state-of-charge (SOC) and state-of-health (SOH), and cell balancing [1]. A high performing BMS needs an accurate cell model that can precisely capture the cell dynamics in EVs. Due to the inherent complexity of the physics-based model, BMS are often based on equivalent circuit models [2-4] that are relatively easy to implement but lack the important underlying physico-chemical processes. In order to predicts an accurate cell response, a physico-chemical model based on fundamental governing equations of migration and diffusion processes as well as the kinetics of intercalation require precisely evaluated model parameters for the material under consideration [5].In this work, a commercial 18650 cell is analyzed in order to parameterize a physico-chemical model. The parameters are estimated by the results of experiments performed on the cell material under investigation. For this, the fully discharged cell was opened in a glove box under inert environment with both moisture and oxygen level below 0.5 ppm. The material samples were collected in an air tight desiccator and analyzed using different methodology.The results obtained based on the proposed methodology are presented as: electrodes, electrolyte, and separator composition; kinetic, transport, and thermodynamics parameters; electrodes and separator physical properties, e.g., porosity, microstructure, particle size distribution etc.; cell internal configuration, e.g., jelly roll dimension, electrode tab location and their dimension etc.; and full-cell electrode balancing determination. A range of electrochemical techniques were used to determine the kinetic and thermodynamic properties of the electrode materials, e.g., galvanostatic intermittent titration technique (GITT) was used to estimate the diffusion coefficient of Li-ion in anode and cathode at different state of charge (SOC) also, to ascertain the open circuit voltage (OCV) of the respective electrodes. In order to estimate the exchange current density, electrochemical impedance spectroscopy (EIS) was employed. The SEM images to illustrate the microstructures of cathode, anode and separator and the particle size distribution of cathode and anode are shown in Figure.

The Influence and Degradation Mechanism of the Depth of Discharge on the Performance of NMC-Based Cathodes for Li-Ion Batteries

Many factors affect the degradation behavior of lithium-ion (Li-ion) batteries and one of these is the depth of discharge (DOD). As Li-ion batteries are used, a reasonable DOD can not only extend their service life (by reducing the degradation rate) but can also reduce the frequency of the re-charging. Therefore, to investigate and clarify the effect of the DOD on cathode performance, we performed cycle aging tests on coin cells considering three DODs. Furthermore, we proposed a degradation mechanism, to account for the influence of the DOD on the cathode performance, through ex-situ post-mortem analysis.The investigated positive electrode was from a commercial cathode NMC 532, assembled with a lithium metal anode in a 2016 type coin cell. The initial discharge capacity was about 163 mAh g–1 at a 1 C rate (1C taken as 160 mAh g–1). After every certain number of cycles, the 100% DOD (2.75 – 4.3 V) capacity was measured and recorded for all DOD ranges.Our cycle aging test experiment results (in the below Figure) show that the capacity fades faster in the higher DOD range (i.e., 3.65 – 4.3 V); the capacity of coin cells showed an initial increase due to the initial activation and a rapid decline thereafter. In contrast, the battery capacity faded slower in the two lower DOD ranges (i.e., 2.75 – 4.3 V and 3.55 – 4.3 V). The results also show that the higher DOD makes the battery more active during the initial cycles, as shown in the Figure.We refined and analyzed the XRD results of different states of the charged cathode to calculate the change in unit cell volume in initial different DOD cycles. By calculating the Li-ion diffusion coefficient through the EIS measurements, it was found that it is larger in the higher state of charge (SOC) state, which explains the higher activity of the cathode in a higher DOD range. Furthermore, we disassembled and analyzed the coin cells, after the same numbers of equivalent full cycles. Surface microcracks of the cathode were observed by SEM, and the cathode-electrolyte interphase (CEI) film was analyzed and quantified by XPS technology.Based on these results, we concluded that higher DODs enable the material to maintain a faster Li-ion diffusion rate and are always in a highly activated state. At the same time, it leads to a faster cathode decay. The post-mortem analysis showed the detailed mechanism of degradation. Looking at the results of this study, frequent charging, making the battery operation at a higher voltage, aggravates deterioration of the cathode.AcknowledgmentsThis project has received funding from the China Scholarship Council (no. 202006370035; no. 202006220024). Furthermore, the authors would like to thank Haidi company for providing the cathode material. Figure 1

Fast capacity estimation for lithium-ion battery based on online identification of low-frequency electrochemical impedance spectroscopy and Gaussian process regression

Accurate capacity estimation is critical to improving the safety and reliability of lithium-ion (Li-ion) battery systems. Traditional capacity estimation mainly extracts capacity-related features by passively collecting the battery voltage, current, and temperature signals, which requires high integrity and regularity of charging curves. In this paper, six health indicators (HIs) are extracted through the online identification of Low-frequency electrochemical impedance spectroscopy (LEIS) by step wave, combined with Gaussian process regression (GPR) to achieve a fast capacity estimation for Li-ion batteries. The step wave is injected into the battery system during the charging process through BMS and bi-directional converter cooperation. Compared with square and multi-sine waves, the stress and response of each frequency step wave are equivalent to that of the sine wave. Moreover, HIs are resolved from the actual Warburg impedance angle instead of the empirical angle π/4. Three novel HIs related to the Li-ion diffusion coefficient are proposed: Warburg factor Wd, pseudo-Li-ion diffusion state PLDS and residual signal of empirical mode decomposition PLDSr. The volume of GPR training data is only 34% of the whole frequency band EIS data. The results show that the identified LEIS achieves 0.96 goodness-of-fit (R2) at the minimum sampling frequency of 50 Hz, and the novel HIs significantly improve the state of health (SOH) estimation accuracy with R2 above 0.95, root mean squared error below 1%, and mean absolute percentage error of about 0.9%. This method is an effective way to the active SOH detection for Li-ion battery, which is vital for the online SOH evaluation and early safety warning.

Enhancing lithium storage performance of Na2Li2Ti6O14 by biomass carbon coating for Li-ion batteries

In order to enhance the electrochemical performance of Na2Li2Ti6O14 anode material, biomass carbon was induced for promoting poor electrical conductivity and Li + diffusion coefficient of Na2Li2Ti6O14. Na2Li2Ti6O14@C composites were synthesized by a solvothermal method, which showed a spherical morphology composed of nanoparticles with a particle size of 2–5 μm. The result of electrochemical tests show that biomass carbon decorated Na2Li2Ti6O14 anode material can improve electrochemical performance of pristine Na2Li2Ti6O14 material. Meanwhile, the Na2Li2Ti6O14@C (5 wt%) exhibits the highest specific capacity of 195 mAh g−1 at 500 mA g−1 among all samples. Na2Li2Ti6O14@C (5 wt%) exhibits an excellent rate performance with specific capacities of 283.3, 244.7, 226.6, 212.3 and 193.4 mAh g−1 at the current density 50, 100, 200, 300 and 500 mA g−1, respectively. The porous spherical structure combined with high conductive biomass carbon shell shows an enhanced electron conductivity, reduced charge transfer resistance and increased Li-ion diffusion coefficient. Hence, the enhanced electrochemical performance of Na2Li2Ti6O14@C can be attributed to the constructed elaborate architecture and component.

Hollow Hemispherical Lithium Iron Silicate Synthesized by an Ascorbic Acid-Assisted Hydrothermal Method as a Cathode Material for Li Ion Batteries.

High-capacity and high-voltage cathode materials are required to meet the increasing demand for energy density in Li ion batteries. Lithium iron silicate (Li2FeSiO4) is a cathode material with a high theoretical capacity of 331 mAh·g−1. However, its poor conductivity and low Li ion diffusion coefficient result in poor capability, hindering practical applications. Morphology has an important influence on the properties of materials, and nanomaterials with hollow structures are widely used in electrochemical devices. Herein, we report a novel hollow hemispherical Li2FeSiO4 synthesized by a template-free hydrothermal method with the addition of ascorbic acid. The hollow hemispherical Li2FeSiO4 consisted of finer particles with a shell thickness of about 80 nm. After carbon coating, the composite was applied as the cathode in Li ion batteries. As a result, the hollow hemispherical Li2FeSiO4/C exhibited a discharge capacity as high as 192 mAh·g−1 at 0.2 C, and the average capacities were 134.5, 115.5 and 93.4 mAh·g−1 at 0.5, 1 and 2 C, respectively. In addition, the capacity increased in the first few cycles and then decayed with further cycling, showing a warm-up like behavior, and after 160 cycles the capacities maintained 114.2, 101.6 and 79.3 mAh·g−1 at 0.5, 1 and 2 C, respectively. Such a method of adding ascorbic acid in the hydrothermal reaction can effectively synthesize hollow hemispherical Li2FeSiO4 with the enhanced electrochemical performance.

P‐Doped SiOx/Si/SiOx Sandwich Anode for Li‐Ion Batteries to Achieve High Initial Coulombic Efficiency and Low Capacity Decay (Small Methods 3/2022)

Inside Front Cover In article number 2101052, Kim, Yoon, Cho, and co-workers provided new sandwich-structured trilayer Si thin-film anodes demonstrating enhanced electrical conductivity and Li-ion diffusion coefficient from the synergy between structural properties and P-doping. Consequently, a Si anode with the highest initial Coulombic efficiency of 90.4% is achieved, thereby exhibiting superior electrochemical properties as anode material for advanced Li-ion batteries.

Introduced oxygen vacancies in cadmium ferrite anode materials via Zn2+ incorporation for high performance lithium-ion batteries

Cationic substitution strategy was recognized as an effective approach to create a defective structure and increase the oxygen vacancies in the crystal structure for improving the electrochemical performance of Li-ion batteries components. In this study, ZnxCd1-xFe2O4 nanoparticles were synthesized via a facile inexpensive process at low temperature. The collected XRD data confirmed the formation of cubic structure with Fd3m space group. HR-TEM investigations showed the size enlargement of spherical-like crystals with increasing the concentration of doping Zn2+ ion. FESEM and BET measurements indicated the conversion of micropores in pure CdFe2O4 into mesopores and macropores in Zn-doped CdFe2O4 samples. XPS results of O1s spectra elucidated that Zn-doped CdFe2O4 samples have higher conductivity due to the created lattice defects and oxygen species. Zn-doped CdFe2O4 anodes exhibit great improvement in their initial discharge capacities ∼1618 and 1880 mAhg−1 upon substitution of Cd with 5% and 10% Zn, respectively. Furthermore, 10% Zn-doped CdFe2O4 anode displayed the highest Li-ions diffusion coefficient and exchange current density due to the enhanced Li+ ions mobility. The increase in zinc content (0.0–0.1) led to a decrease in the DC activation energy from 0.11 to 0.09 eV.

Ultrastable Interfacial Contacts Enabling Unimpeded Charge Transfer and Ion Diffusion in Flexible Lithium-Ion Batteries.

Deteriorating interfacial contact under mechanical deformation induces large cracks and high charge transfer resistance, resulting in a severe capacity fading of flexible lithium‐ion batteries (LIBs). Herein, an oxygen plasma treatment on a polymer separator combined with high‐speed centrifugal spraying to construct ultrastable interfacial contacts is reported. With the treatment, abundant hydrophilic oxygen‐containing functional groups are produced and ensure strong chemical adhesion between the separator and the active materials. With single walled carbon nanotubes (SWCNTs) sprayed onto the active materials, a dense thin film is formed as the current collector. Meanwhile, the centrifugal force caused by high‐speed rotation together with van der Waals forces under fast evaporation produces a much closer interface between the current collector and the active materials. As a result of this ultrastable interfacial interaction, the integrated electrode shows no structural failure after 5000 bending cycles with the charge‐transfer resistance as low as 35.8% and a Li‐ion diffusion coefficient nearly 19 times of the untreated electrode. Flexible LIBs assembled with these integrated electrodes show excellent structural and electrochemical stability, and can work steadily under various deformed states and repeated bending. This work provides a new technique toward rational design of electrode configuration for flexible LIBs.