Degradation Of Electrode Materials Research Articles

Conducting nitrogen-incorporated ultrananocrystalline diamond coating for highly structural stable anode materials in lithium ion battery

In lithium ion battery (LIB), the structural changes and degradation of electrode materials during intercalation/deintercalation, leading to reversible capacity loss and short cycle life, have plagued LIB from advancing forward. In order to overcome these hurdles, a novel conducting nitrogen-incorporated ultrananocrystalline diamond (N-UNCD) is proposed to coat on the model electrode material of natural graphite (NG) by microwave plasma-enhanced chemical vapor deposition (MPCVD), demonstrates the superior improvement on electrode stability. The electrochemical results of the N-UNCD coated NG anode reveal excellent cyclability, rate capability and conductivity over a hundred cycles as compared to the pristine NG. Furthermore, the underlying high structural stability of the N-UNCD coating for the anode material and the failure mechanism of the pristine NG anode is fully elucidated by combining diffraction and imaging techniques based on in-situ synchrotron X-ray diffraction and high-resolution transmission electron microscopy (HR-TEM). These results show that the amorphization of NG originates from the accumulation of internal stress by periodic volume changes, which leads to mechanical fading with loss of strength and toughness. However, the N-UNCD film serves as a strong buffer layer to accommodate the volume changes, and also maintains the mechanical integrity of the pristine anode by suppressing from the continuous damage and the thickening of the solid electrolyte interphase during charging/discharging. Optimally, our investigations systematically explain the failure mechanism of the pristine anode and shed light on constructing a high capability and long cycle N-UNCD coated anode for LIBs.

Wearable Textile-Based Co-Zn Alkaline Microbattery with High Energy Density and Excellent Reliability.

Wearable in-plane Zn-based microbatteries are considered as promising micropower sources for wearable electronics due to their high capacity, low cost, high safety, and easy integration. However, their applications are severely impeded by inadequate energy density arising from unsatisfactory capacity of cathode and poor cycling stability caused by degradation of electrode materials and Zn dendrite. Additionally, the short-circuit induced safety issue caused by Zn dendrite is still a roadblock for Zn-based microbatteries. Herein, a textile-based Co-Zn microbattery with ultrahigh energy density and excellent cycling stability is demonstrated. Benefiting from the fast electron transport of three-dimensional (3D) porous Ni-coated textile and synergistic effect from the hierarchical Co(OH)2 @NiCo layered double hydroxide (LDH) core-shell electrode, the fabricated Co-Zn microbattery with high flexibility delivers superior energy/power densities of 0.17 mWh cm-2 /14.4 mW cm-2 , outperforming most reported micro energy storage devices. Besides, the trench-type configuration as well as the 3D porous Zn@carbon clothes can avoid the short-circuit-induced safety issues, resulting in excellent cycling stability (71% after 800 cycles). The unique core-shell structure and novel configuration provide a brand-new design strategy for high-performance wearable in-plane microdevices.

Mechanical degradation of electrode materials within single particle model in Li-ion batteries for electric vehicles

Mechanical degradation of electrode materials, in the form of particle cracking and fragmentation, disintegration, fracturing, and loss in contact between current collectors and the active electrode materials, can affect or deteriorate the performance of Li-ion batteries dramatically and even lead to the battery failure in electric vehicle. This paper firstly built a single particle model (SPM) based upon kinetics of electrochemical reactions. Then the Li-ion concentration, evolution of diffusion induced stresses within the SPM under potentiostatic or galvanostatic operating conditions were analyzed by utilizing a mathematical method. Next, evolution of stresses or strains in the SPM, at the core of relates with mechanical degradation of electrode materials, are elaborated in detail. Finally, surface and morphology of the electrodes dismantled from fresh and degraded cells after galvanostatic charge/discharge cycling have been analyzed to verify the hypothesis aforementioned by observing scanning electron microscopy and analyzing X-ray diffraction.

Analysis of Surface Reaction of LiMnxFe1-XPO4 /Li4Ti5O12 Cell during High Temperature Cycle

Introduction Energy storage has a key role in balancing to the grid and providing emergency back-up. Li-ion batteries containing olivine metal phosphates (LiMPO4, M = Mn, Fe) as cathode and spinel lithium titanate (Li4Ti5O12: LTO) as anode are promising solutions for energy storage[1,2]. Because of LiMPO4 has a rigid poly-anion structure and Li4Ti5O12 has “zero strain” characteristic during charge-discharge cycling, LiMPO4/Li4Ti5O12 cell shows high safety and cyclability over wide temperature region. In particular, Mn-rich olivine cathodes (LiMnxFe1-xPO4: LMFP) have been paid attentions for stationary applications due to their high energy density. Moreover, high energy density and stability in high temperature region enable to exclude cooling systems and downsize cell modules. However, there are a few reports about high temperature performance of LMFP/ LTO cell[1]. This research is aimed to reveal cyclability of LMFP/LTO cell under high temperature condition including surface and impedance analysis and show the potential for stationary power applications. Experimental Laminated LMFP/LTO cells using 1.2M LiPF6 in 1:2 ethylene carbonate (PC) / diethyl carbonate (DEC) electrolyte with 500mAh capacity were used for electrochemical measurements. The charge-discharge tests were carried out between 2.7 and 1.5V with 2C rate at 60°C. XPS analysis was performed to analyze electrode surfaces. Results and discussions Fig. 1 shows discharge curves and cycling performance of LMFP/LTO cell under high temperature condition of 60°C. LMFP/LTO cell showed stable capacity retention over 95.9% after 500 cycles. Considering high capacity retention after 500 cycles, it was suggested that degradation of electrode materials were significantly small. Fig. 2 shows Cole-Cole plots of (a) half-cells and (b) LMFP/LTO cell. Corresponding to half-cells measurement, semicircles in low and high frequency region of LMFP/LTO cell are attributed to charge transfer resistances of LMFP cathode and LTO anode, respectively. Semicircle of low frequency expanded, while that of high frequency was almost same during initial 100 cycles, indicating that LMFP resistance increased while that of LTO anode increased little. Fig. 3 shows surface compositions of LMFP and LTO before cycling and after 100 cycles at 60°C estimated from XPS analysis. As for LMFP cathode, the amount of LiF increased after 100 cycles, meaning LiPF6 decomposition was a main side reaction. In addition, surface coverage on LMFP cathode increased after 100 cycles. It resulted in impedance increase and during initial 100 cycles. As for LTO anode, the amount of LiF did not increase and surface coverage was almost same during initial 100 cycles. In the literature, capacity fade has been reported due to LiF formation during cycling test[1]. LiF is a reaction product of PF5 or HF and active Li of LTO. Thus, LiF formation led to capacity fade of the cell. In this research, capacity fade was suppressed, because Li loss from LTO due to LiF formation has not observed during cycling test. This difference possibly results from the amount of H2O impurity or/and surface reactivity of LTO. In this research, LMFP/LTO cell demonstrated excellent capacity retention and small impedance increase at 60°C. According to XPS analysis, surface coverage increased for LMFP cathode after 100 cycles. Cole-Cole plots showed resistance increase of LMFP cathode only during initial 100 cycles, but impedance increase was negligible above 100 cycles. Based on above results, it is suggested that stable SEI formed after 100 cycles and decomposition of electrolyte on LMFP cathode was suppressed above 100 cycles. As for LTO anode, LiF formation was suppressed and Li loss from LTO anode was not occurred during cycling test unlike previous report[1]. These results indicate that stable SEI formation on LMFP cathode and LTO anode enabled to realize excellent cycling performance of LMFP/LTO cell under high temperature conditions. Cycle life performance after a prolonged cycling tests and detailed analysis will be reported. References V. Borgel et al, J. Electrochem. Soc, 160 (4) A650-A657 (2013) R. Castaing et al, J. Power Sources, 744-752, 267 (2014) Figure 1

Degradation of Electrode Materials in Vanadium Redox Flow Batteries

Recent works in vanadium redox flow batteries (VRFBs) have been successful in improving the energy density by increasing vanadium solubility in the electrolyte1 and achieving high power density through electrode modification, membrane selection, and superior cell design 2,3. These accomplishments lead to significant reduction of the system cost and therefore enhance the economic attractiveness of VRFB technology.To achieve market implementation, the large-scale energy storage system requires a balance between performance, cost, and durability. While power and energy densities have been recently improved, the investigation of component durability, which is equally important, has yet to be reported in significant detail.In this work, we demonstrate an approach to study the electrode degradation in single-cell VRFBs. Ex-situ electrolyte soaking experiments were used to determine conditions under which the electrodes degrade, and the extent of the degradation. Several techniques were adopted to characterize property changes in the degraded materials. Various carbon materials were investigated to determine viable candidates and characteristics required for long-term use in VRFB systems.Additionally, in-situ cycling tests of various carbon materials have been carried out to illustrate the relationship between material degradation and cell performance decay. Declines in performance (Fig. 1) are monitored and correlated to changes in the material properties. Modification of the cycling parameters reveals operating conditions leading to the most severe decay in the carbon material, so that accelerated degradation protocols can be developed for evaluation of additional materials.

Emissions of particles and trace elements from coal gasification

Some of the trace elements in coal are easily emitted with the syngas obtained from coal gasification in the gaseous phase and condensed as fine particles. Such impurities in syngas could result in corrosion and/or degradation of electrode materials in fuel cells if the coal gasification process is applied to Integrated Gasification Fuel Cell (IGFC). Thus, to realize the coal gasification process combined with fuel cells, it is extremely important to control the emission behavior of hazardous trace elements in coal gasification. In this study, particles in the coal gasification gas were sampled and analyzed in detail to determine their particle size distributions and elemental compositions. A drop tube type furnace was utilized for the coal gasification experiment. Pb and Se were evaluated in terms of their distribution behavior to particles. Pb is one of the most typical volatile heavy metals, and Se is known as a corrosive substance for Solid Oxide Fuel Cells (SOFC). Thermal equilibrium calculations were also conducted to derive the chemical forms of Pb and Se during their emissions. As a result, particles entrained in syngas from the coal gasification process were confirmed to have bimodal peaks in their particle size distributions. The peak larger than 7.8μm in the super-micron size range consists of ash with unburnt carbon, while the smaller peak at 0.5μm in the sub-micron range consists of soot with mineral deposits. Se and Pb were found to react together during coal gasification process. In addition, almost all of them were vaporized in the reactor and deposited on soot particles in the sub-micron range during the gas cooling process.