Lower Cycle Life Research Articles

Linker length-dependent lithium storage of pyrene-4,5,9,10-tetraone-based conjugated organic polymer cathodes

Conjugated organic polymers (COPs) have been emerged as a class of cathode materials for lithium-ion batteries (LIBs) because of the rigid structural units and tunable properties. Nonetheless, their applications are still limited due to the poor conductivity and low cycling life. Herein, we design a series of pyrene-4,5,9,10-tetraone-based COPs (P(PTODB)-1, P(PTODB)-2, P(PTODB)-3), containing different number of benzene rings as linking units. Consequently, prolonging the linker lengths could effectively improve structural stability and extend π-conjugation, leading to the enhanced charge-storage capability. When tested as cathode materials for LIBs, the P(PTODB)-2 electrode delivers a better electrochemical performance with high capacity of 203 mA h g-1 after 100 cycles at 0.1 A g-1 (coulombic efficiency almost 100%) and excellent rate performance (150 mA h g-1 at 5 A g-1). In addition, the Li+ storage mechanism was carried out by ex situ Fourier transform infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS) analysis. Eventually, our study brings forward the appropriately extended linker lengths to fabricate COP cathodes with high electrochemical properties.

Novel metal-organic anode material by in-situ chelating Ni2+ with tannic acid on carbon nanotube for high-performance Li storage

Lithium-ion batteries (LIBs) with natural organic anode are attracting intensive interest for application owing to their structural diversity, cost-effectiveness, eco-friendliness, and high specific capacity. However, directly usage of natural organic materials as anode materials usually encounters poor electrochemical properties such as low reversible capacity and short cycling life. Thus, developing high-performance organic electrode materials for LIBs remains a great challenge. Herein, we present a rational design and fabrication of TA-Ni@CNTs by in-situ coating TA-Ni polymers onto the surface of carbon nanotubes (CNTs) as a superior anode material for LIBs. Specifically, the highly conductive CNTs can effectively relieve the aggregation of TA-Ni and improve the electronic conductivity. Meanwhile, the strong chelation among nickel irons and catechol groups enhances the structure stability and inhibits the dissolving property. Consequently, as an anode material for LIBs, the resulting TA-Ni@CNTs achieves a high reversible capacity of 1418.8 mAh·g−1 at 0.1 A·g−1 after 216 cycles and an outstanding cycling stability with 951.1 mAh·g−1 at 0.5 A·g−1 after 323 cycles. The presented design strategy holds great promise for developing more-efficient electrode materials for LIBs.

Optimize Electrolytes and Additives for Lithium-Ion Batteries Using C/SiO2 Synthesized from Rice Husk As an Anode Material

Silicon-based anodes derived from agricultural waste, particularly rice husks, have recently been focused on replacing conventional graphite due to its abundance, low cost, fast charge ability, and remarkable theoretical capacity (~ 3600 mAh.g-1). SiO2 has several drawbacks, including low electrical conductivity and short cycling life associated with high-volume expansion (~ 300%) during the charge-discharge process. Hence, a hybrid composite C/SiO2 was an ideal solution to overcome these challenges.To strengthen the electrochemical properties of LIBs, the compatibility between electrodes and electrolytes plays a crucial role. Lithium hexafluorophosphate (LiPF6) and Lithium bis(trifluoromethylsulfonyl) imide (LiTFSI) are promising candidates for investigation due to their effectiveness cost. Regarding LiPF6, widely used in LIBs, offers high solubility and stability, while LiTFSI provides enhanced ionic mobility. However, LiTFSI is corrosive to aluminum current collectors, and LiPF6 unexpectedly dissociates to form HF acid and PF5, leading to cycling degradation. To mitigate these issues, additives such as Fluoroethylene-carbonate (FEC) and Vinylene Carbonate (VC) are introduced to enhance battery performance. This study employed FEC and VC, adding in the optimal electrolyte to stabilize the SEI layer, prevent lithium loss during cycling due to the instability of the interfacial layer, as well as to enhance high-rate performance. In detail, FEC could effectively prevent SEI degradation by enhancing the F-based component of this layer, stabilizing the SEI layers, and protecting electrodes. Simultaneously, VC offers a synergistic effect on the interphase modulation by reinforcing the inorganic/organic components. Thus, we investigate various electrolyte systems to evaluate half-cell performance of C/SiO2 synthesized from rice husk as the anode. Then, the optimal-chosen electrolytes were used to assemble full-cell LFP||C/SiO2 and investigated at high-rate performance.According to the experimental sections, there are two main lithium-salts comprised of LiPF6 and LiTFSI, which dissolved in three solvent systems, including EC: DEC (1: 1-v/v); EC: DMC (1:1-v/v), and EC: DMC: DEC (1:1:1 – v/v/v). After optimizing the solvents, the system of EC: DEC (1: 1-v/v) shows the highest performance, which was chosen to investigate the impact of various ratios of FEC and VC additive. The 1M LiPF6 in EC: DEC (1:1-v/v) + 5 wt% FEC has the highest specific capacity compared to the LiPF6 samples, reaching the value of 220.0 mAh.g-1. Meanwhile, the 1M LiTFSI in EC: DEC (1:1-v/v) 2.5 wt% FEC + 2.5 wt% VC is the best electrolyte to offer a stable capacity of 223.4. mAh.g-1 after 50 cycles in comparison to LiTFSI samples. This phenomenon is plausible with the conductivity of 6.16 and 7.45 mS.cm-1, respectively. Furthermore, they undergo remarkable oxidation at 4.05 and 4.23 V at a current density of 0.002 mA, demonstrating they have a good stability potential window. Since there is no significant difference in half-cell performance, they were used to evaluate full-cell properties. According to battery performance, the full-cell LFP||C/SiO2 using LiPF6 + 5 wt% FEC shows that the initial capacity reaches 111.6 mAh.g-1 and is maintained 40% after 50 cycles with a stable CE above 96%. Full cell LiTFSI +2.5 wt% FEC + 2.5 wt% VC shows an initial discharge capacity of 159.9 mAh.g-1. However, this capacity value is significantly reduced to only 28.5 mAh.g-1 after 50 cycles and CE ~ 94%. Regarding rate capability results, full cell 1M LiPF6 in EC: DEC (1:1-v/v) + 5 wt% FEC illustrates better performance in all discharged rates than full cells using LiTFSI salt. Moreover, this full-cell shows a discharge capacity of ~ 50 mAh.g-1 at high-rate performance while full-cell using LiTFSI-based electrolyte displays a negligible capacity value. To explain, the total resistance of 25 Ohm is obtained for full cell LiPF6 + 5 wt%. FEC is three times lower than full-cell 1M LiTFSI + 2.5 wt% FEC + 2.5wt% VC. Furthermore, the HR-TEM ex-situ indicates that the stability of SEI layer formation is consistent in thickness but exhibits uneven distribution when using different electrolytes. Besides, the SEI components analyzed by XPS data indicate the presence of carbonate groups and LixPFyOz-based compounds due to the irreversible reactions on the SEI layer after the initial discharge cycle. This research brings some remarkable information to study the electrolyte compatibility for full-cell performance using C/SiO2 as an anode material. Figure 1

A Volcano Correlation between Catalytic Activity for Sulfur Reduction Reaction and Fe Atom Count in Metal Center.

Sulfur reduction reaction (SRR) facilitates up to 16 electrons, which endows lithium-sulfur (Li-S) batteries with a high energy density that is twice that of typical Li-ion batteries. However, its sluggish reaction kinetics render batteries with only a low capacity and cycling life, thus remaining the main challenge to practical Li-S batteries, which require efficient electrocatalysts of balanced atom utilization and site-specific requirements toward highly efficient SRR, calling for an in-depth understanding of the atomic structural sensitivity for the catalytic active sites. Herein, we manipulated the number of Fe atoms in iron assemblies, ranging from single Fe atom to diatomic and triatomic Fe atom groupings, all embedded within a carbon matrix. This led to the revelation of a "volcano peak" correlation between SRR catalytic activity and the count of Fe atoms at the active sites. Utilizing operando X-ray absorption and X-ray diffraction spectroscopies, we observed that polysulfide adsorption-desorption and electrochemical conversion kinetics varied up and down with the incremental addition of even a single iron atom to the catalyst's metal center. Our results demonstrate that the metal center with exactly two iron atoms represents the optimal configuration, maximizing atom utility and adeptly handling the conversion of varied intermediate sulfur species, rendering the Li-S battery with a high areal capacity of 23.8 mAh cm-2 at a high sulfur loading of 21.8 mg cm-2. Our results illuminate the pivotal balance between atom utilization and site-specific requirements for optimal electrocatalytic performance in SRR and diverse electrocatalytic reactions.

Enhanced lithium storage in pomegranate-like carbon via dual confinement of lithiophilic seeds and Li deposition

The uncontrollable dendrite growth and infinite volume expansion of Li during cycling lead to low Coulombic efficiency (CE) and short cycling life, severely impeding the commercial progress of lithium metal batteries (LMBs). In this work, nitrogen-doped carbon nanospheres (CSs) with ultrafine lithiophilic ZnO nanoparticles encapsulated by interconnected pomegranate-like carbon sheets (denoted as ZnO@NPCS) have been designed and constructed to serve as novel lithium hosts. The ultrafine ZnO nanoparticles uniformly distributed in the CSs can significantly reduce the Li nucleation barrier, while the well-designed pomegranate-like carbon sheets within the CSs can provide continuous and fast electron/ion transport channels, accelerating the Li+ transfer kinetics. Moreover, the internal interconnected carbon networks can confine the lithiophilic nanoparticles, preventing them from detaching or aggregating during cycling, and meanwhile offer individual voids to accommodate deposited Li. Thus, both lithiophilic seeds and deposited Li can be well confined in the pomegranate-like structure. Such a dual-confinement effect enables the ZnO@NPCS electrode to exhibit ultralong cycling life for more than 1000 cycles with ultrahigh CE (>99.5 %) without Li dendrites growth, which is further validated by in-situ transmission electron microscopy and phase-field simulations. Therefore, this dual-confinement strategy provides an inspiring insight to design superior Li hosts for developing superior LMBs and can be extended to other battery systems.

Low-Potential Iodide Oxidation Enables Dual-Atom CoFe─N─C Catalysts for Ultra-Stable and High-Energy-Efficiency Zn-Air Batteries.

The low energy efficiency and limited cycling life of rechargeable Zn-air batteries (ZABs) arising from the sluggish oxygen reduction/evolution reactions (ORR/OERs) severely hinder their commercial deployment. Herein, a zeolitic imidazolate framework (ZIF)-derived strategy associated with subsequent thermal fixing treatment is proposed to fabricate dual-atom CoFe─N─C nanorods (Co1 Fe1 ─N─C NRs) containing atomically dispersed bimetallic Co/Fe sites, which can promote the energy efficiency and cyclability of ZABs simultaneously by introducing the low-potential oxidation redox reactions. Compared to the mono-metallic nanorods, Co1 Fe1 ─N─C NRs exhibit remarkable ORR performance including a positive half-wave potential of 0.933V versus reversible hydrogen electrode (RHE) in alkaline electrolyte. Surprisingly, after introducing the potassium iodide (KI) additive, the oxidation overpotential of Co1 Fe1 ─N─C NRs to reach 10mAcm-2 can be significantly reduced by 395mV compared to the conventional destructive OER. Theoretical calculations show that the markedly decreased overpotential of iodide oxidation can be ascribed to the synergistic effects of neighboring Co─Fe diatomic sites as the unique adsorption sites. Overall, aqueous ZABs assembled with Co1 Fe1 ─N─C NRs and KI as the air-cathode catalyst and electrolyte additive, respectively, can deliver a low charging voltage of 1.76V and ultralong cycling stability of over 230h with a high energy efficiency of ≈68%.

Compatibility of low thermal conductivity and high infrared emissivity of plasma-sprayed Sm2Hf2O7 and Pr2Hf2O7 coatings

In order to develop thermal-protection coatings, rare earth hafnates Sm2Hf2O7 (SHO) and Pr2Hf2O7 (PHO) coatings with pyrochlore structure were prepared on different substrates by atmospheric plasma spraying (APS). The infrared radiation, flame-ablation resistance, and thermal cycle performance were investigated in relationship with their morphologies, phase stabilities, thermophysical and mechanical properties. The results showed that both SHO and PHO coatings had compatible thermal-protection performance with lower thermal conductivity (0.711 and 0.779 W·m−1·K−1 at 1000 °C) and higher infrared emissivity (0.814 and 0.894 at 1000 °C) in the 3–5 μm band. Moreover, the supersonic flame ablation resistance of PHO coatings at high temperatures was greater than that of SHO coatings. Both SHO and PHO coatings have long thermal cycling life at low and medium temperatures and short thermal cycling life at high temperatures. The failure mechanisms of both type coatings were mainly associated with thermal expansion mismatch stress and fatigue stress generated during multiple thermal cycling.

Improving High-Nickel Cathode Active Material Performance in Lithium-Ion Batteries with Functionalized Binder Chemistry

As the lithium-ion battery (LIB) market expands, driven mostly by the mass adoption of electric vehicles, LIB development is continually being pushed in the direction of higher energy density and lower cost. Both of these trends are leading to widespread development of LIB formulations using high-nickel cathode active materials, such as NMC811. In these materials, the high nickel content increases the amount of electrochemically accessible lithium in the cathode, increasing the cell energy density, while decreasing the amount of cobalt used, which decreases the cost of the cathode material. However, these materials also have drawbacks. First, NMC811 suffers from lower cycle life than higher-Co NMC materials such as NMC111 or NMC622. Second, NMC811 has poorer safety characteristics than lower energy density materials. Finally, NMC811 cathodes are known to experience gassing issues during cycling, which creates challenges in commercialization, especially for pouch cell battery designs.Many approaches have been explored in the industry to address these shortcomings, including active material modification, electrolyte design, etc. In this presentation, binder functionalization will be presented as an alternative pathway to improve high-Ni cathode performance. LIB cathode binder is commonly high molecular weight PVDF, which provides good mechanical properties at low weight fractions as well as high electrochemical stability, but it is predominantly inert. Here, approaches of introducing novel binders tailored for high-Ni cathode systems will be discussed. Effectiveness of modifications, specifically their impact on LIB cycle life and safety, will be discussed.

Porous interface for fast charging silicon anode

AbstractFor next‐generation powering batteries, silicon with high energy density is considered the most promising anode material. However, the low rate performance and limited cycling life of silicon anode confines its commercial application. Porous interface constructed on the silicon‐based anode could provide relatively short electrolyte pathways, high transport rate of both lithium ions and electrons, and more stabilized surfaces, which are considered as one of the effective ways to maintain both high energy density and fast charging ability. Here, with a focus on porous interface construction and highlighting the advantages of surface coating, we aim to point out how porous interface affect the fast charging ability for silicon anode.

Metal-organomecapto complex-derived mesoporous Co1-xS/N,S-codoped carbon composite for superior lithium ion storage

Cobalt sulfide-based electrode materials were believed to have bright future in lithium-ion batteries (LIBs) application for their high theoretical capacity and excellent electrochemical stability. However, their relatively low electronic conductivity and the large volume variation during lithiation/delithiation processes usually result in low rate capability and short cycling life. Herein, a novel mesoporous Co1-xS/N,S-codoped carbon (Co1-xS/N,S–C) composite was prepared by direct pyrolysis of a cobalt-2-mercaptobenzothiazole (CoMBT) complex. High-content (91.14 ​wt%) and ultrafine (∼10 ​nm) Co1-xS nanocrystals were in-situ generated and composited with high conductive N,S-codoped carbon. The Co1-xS/N,S–C demonstrates superior Li+-ion storage performance, delivering high discharge capacities of 1207 ​mAh g−1 at 200 ​mA ​g−1 after 50 cycles and 425 ​mAh g−1 at 5 ​A ​g−1 after 1000 cycles.

Toward High‐Performance Dihydrophenazine‐Based Conjugated Microporous Polymer Cathodes for Dual‐Ion Batteries through Donor–Acceptor Structural Design

AbstractRecent studies have demonstrated that dihydrophenazine (Pz) with high redox‐reversibility and high theoretical capacity is an attractive building block to construct p‐type polymer cathodes for dual‐ion batteries. However, most reported Pz‐based polymer cathodes to date still suffer from low redox activity, slow kinetics, and short cycling life. Herein, a donor–acceptor (D–A) Pz‐based conjugated microporous polymer (TzPz) cathode is constructed by integrating the electron‐donating Pz unit and the electron‐withdrawing 2,4,6‐triphenyl‐1,3,5‐triazine (Tz) unit into a polymer chain. The D–A type structure enhances the polymer conjugation degree and decreases the band gap of TzPz, facilitating electron transportation along the polymer skeletons. Therefore the TzPz cathode for dual‐ion battery shows a high reversible capacity of 192 mAh g−1 at 0.2 A g−1 with excellent rate performance (108 mAh g−1 at 30 A g−1), which is much higher than that of its counterpart polymer BzPz produced from 1,3,5‐triphenylbenzene (Bz) and Pz (148 and 44 mAh g−1 at 0.2 and 10 A g−1, respectively). More importantly, the TzPz cathode also shows a long and stable cyclability of more than 10 000 cycles. These results demonstrate that the D–A structural design is an efficient strategy for developing high‐performance polymer cathodes for dual‐ion batteries.

ZnS-SnS@NC Heterostructure as Robust Lithiophilicity and Sulfiphilicity Mediator toward High-Rate and Long-Life Lithium-Sulfur Batteries.

Lithium-sulfur (Li-S) batteries are severely hindered by the low sulfur utilization and short cycling life, especially at high rates. One of the effective solutions to address these problems is to improve the sulfiphilicity of lithium polysulfides (LiPSs) and the lithiophilicity of the lithium anode. However, it is a great challenge to simultaneously optimize both aspects. Herein, by incorporating the merits of strong absorbability and high conductivity of SnS with good catalytic capability of ZnS, a ZnS-SnS heterojunction coated with a polydopamine-derived N-doped carbon shell (denoted as ZnS-SnS@NC) with uniform cubic morphology was obtained and compared with the ZnS-SnS2@NC heterostructure and its single-component counterparts (SnS@NC and SnS2@NC). Theoretical calculations, ex situ XANES, and in situ Raman spectrum were utilized to elucidate rapid anchoring-diffusion-transformation of LiPSs, inhibition of the shuttling effect, and improvement of the sulfur electrochemistry of bimetal ZnS-SnS heterostructure at the molecular level. When applied as a modification layer coated on the separator, the ZnS-SnS@NC-based cell with optimized lithiophilicity and sulfiphilicity enables desirable sulfur electrochemistry, including high reversibility of 1149 mAh g-1 for 300 cycles at 0.2 C, high rate performance of 661 mAh g-1 at 10 C, and long cycle life with a low fading rate of 0.0126% each cycle after 2000 cycles at 4 C. Furthermore, a favorable areal capacity of 8.27 mAh cm-2 is maintained under high sulfur mass loading of 10.3 mg cm-2. This work furnishes a feasible scheme to the rational design of bimetal sulfides heterostructures and boosts the development of other electrochemical applications.

Surface Modification of Sputtered Carbon Supercapacitor Electrode by Hydrogen Annealing

In the applications of renewable energy; use of energy in the electric vehicles and many other electronic devices such as mobile devices and computers; electrical energy storage is essential. Batteries are used to store electrical energy but have low power density and lower cycle life. Using extremely porous electrode materials for supercapacitors, based on quick ion transport, are specialized to provide high power density, long stability and effective energy storage. Using graphene-based electrode is the best way to boost the energy density of supercapacitor. Graphene synthesized by chemical exfoliation, ultrasonic exfoliation and solution based chemical reduction suffers agglomerations that tends to restack the graphene sheets. In the present work, we studied the option of hydrogen gas annealing to obtain graphene from amorphous carbon film, coated on Cu substrate using sputtering. For electrochemical assessment, in situ developed film was compared with graphene applied from other methods of graphene synthesis. Atomic force microscopy (AFM) results revealed that annealed carbon sputtered electrode has high route mean square (RMS) roughness i.e 181.5 nm, most probably because of graphene formation. Cyclic voltammogram (CV) results show less area curve for annealed electrode which depicts high active area for charge storage and enhanced conductivity due to deposited graphene layer.

Comparison of the impact of fast charging on the cycle life of three lithium-ion cells under several parameters of charge protocol and temperatures

Fast charging of lithium-ion batteries is crucial for electric vehicles. As the charge current is a known degradation factor, assessing the impact of fast charging on battery ageing under several operating conditions is necessary to derive usage strategies for system integrators. To bridge existing knowledge gaps, this article reports on a comparative experimental ageing study in fast charging conditions. Three cells, differing in their materials and energy densities, were investigated. The impacts of the following three parameters are compared on these cells: charge current, end-of-charge voltage, and ambient temperature. The results reveal that the impact of fast charging on cycle life strongly depends on battery materials and internal design. The degradation of two of the cells significantly increased when the charge current and voltage increased, whereas that of the third cell was nearly independent of these parameters. While considering thermal conditions, the ageing of each cell was minimised at a different temperature, either cold, moderate, or warm. An analysis of degradation root causes indicates that distinct dominant degradation mechanisms occurred depending on the cell materials. The cells with higher energy density had a lower cycle life (between 100 and 900 cycles) than the most high-power cell (more than 1700 cycles). Experimental results allow the identification of three strategies for reducing charging time while minimising battery degradation. These strategies present several contributions to the design of energy storage systems for electric vehicles, including the choice of a cell, design of thermal management systems, and design of optimised fast charging protocols.

Large-scale carambola-like V2O5 nanoflowers arrays on microporous reed carbon as improved electrochemical performances lithium-ion batteries cathode

Abstract To search for new cathode materials with high energy density of Lithium-ion batteries (LIBs) is one of the most challenging issues. Vanadium pentoxide (V2O5) with high theoretical specific capacity is believed to be a promising candidate for the next generation cathode materials, yet still suffers from low lithium ion diffusion coefficient and poor electronic conductivity resulting in low cycling life and poor rate performances. Here, we report new large-scale carambola-like V2O5 nanoflowers arrays anchored on microporous reed carbon as high performances LIBs cathode. Each individual pore space of the microporous reed carbon is like a hexagonal cylinder, and the area of each carbon wall is more than 103 um2, which is favorable for the growth of V2O5 nanostructure arrays. After hydrothermal, the large-scale carambola-like V2O5 nanoflowers arrays can directly grow on the surface of microporous carbon. Due to the novel composite structures, the V2O5 nanoflowers arrays@microporous carbon stabilizes at 273 mA h g−1 after 100 cycles at 0.2 C. When cycling at 1.0 C over 500 cycles, the capacity still maintains at 180 mAh g−1. The demonstrated approach in this work paves the way for the development of high rate capability and excellent cycling stability V2O5-based cathode materials.

A Facile Preparation of λ-MnO2 as Cathode Material for High-Performance Zinc-Manganese Redox Flow Battery

Aqueous-based rechargeable zinc-manganese redox flow batteries have displayed a great advantage in the field of large-scale energy storage due to low cost of zinc and manganese resources and environmentally-safe. Various types of MnO2, including α and δ have been proposed as cathode material, but low capacity and cycling life limited their large scale application. Herein, we report highly crystalline, spinel-type λ-MnO2 as cathode for zinc-manganese (Zn/λ-MnO2) redox flow battery system which derived from LiMn2O4 via mild acid treatment. This system exhibits diffusion controlled insertion mechanism of Li+ in λ-MnO2 spinel structure with little contribution of surface controlled process in 1 M Li2SO4 + 1 M ZnSO4 electrolyte. The obtained λ-MnO2 cathode delivers two high discharge voltage platforms of 1.97 and 1.81 V with specific capacity of 128 mAh g−1 at a current rate of 2 C under the operating potential window of 1.5–2.1 V. The assembled battery system exhibits excellent rate performance and cyclic stability with high capacity retention of 83% after 1,000 continuous cycles at a high current density of 10 C. This mechanism enables an outstanding energy efficiency of 98% and provides key insights for the development of high-performance, low-cost and reversible zinc-manganese redox flow batteries.

(Invited) Process Development and Quality Control for Manufacturing of Lithium-Ion-Batteries

The development of efficient and sustainable low cost manufacturing techniques for the next generation lithium-ion cells with improved energy density is a key technology for industrial success. There is a strong need for further development of energy-efficient, resource and time saving electrode and cell manufacturing processes, which includes the identification of bottleneck factors along the whole production chain and the replacement of environmentally harmful intermediate steps (e.g. replacement of NMP for the cathode processing). One promising approach to increase both energy density of the cell and process efficiency is the reduction of passive materials in the cell by increasing the mass loading of active material on the electrodes. These thicker electrodes, however, suffer from some drawbacks like lower rate capability, lower mechanical flexibility and reduced adhesion to the current collector. In addition, the mixing and coating process parameters have to be adapted to avoid inhomogeneous binder distribution and mechanical disintegration of particles. The electrochemical and mechanical properties of the electrodes are strongly dependent on the 3D microstructure of the electrode (distribution of carbon black, porosity, distribution of the binder network). Both the mixing strategy during slurry preparation as well as the drying conditions during coating have a strong influence on the mechanical and electrochemical properties of the electrodes, which will be discussed in detail in the presentation. Another approach to optimize electrodes with high areal capacity is the preparation of 3D structured electrodes (e.g. gradient electrodes). We studied the addition of various pore forming additives and the preparation of multilayer electrodes via coating with a dual slot die system. On the anode side silicon based materials are quite attractive due to high specific capacity and energy. However, practical use of silicon is still limited to low amounts of silicon < 5wt% in commercial cells. Anodes with higher silicon content suffer from low cycling life due to high volume change and electrode swelling. A promising approach to improve the cycling life of silicon based electrodes is the use of alternative 3D structured current collectors in combination with adapted binder systems. In general, the cell manufacturing of Li-ion batteries requires precision and accuracy and includes a complex process chain with numerous process parameters. Optimized parameters for critical manufacturing steps during cell assembly as drying, slitting, electrolyte filling and formation will be presented and discussed in more detail.

Constructing hierarchical cobalt doped SnO2/carbon cluster as high reversible and high capacity anodes for sodium storage

Problems of low initial Coulombic efficiency and low cycling life are main limitation factors for SnO2-based materials in sodium storage application. Herein, a cobalt-doped SnO2/carbon cluster is prepared via a simple and fast microwave assisted hydrothermal method. It reveals an iconic hierarchical structure including SnO2 nanoparticles and whiskers, to be demonstrated with excellent electrochemical performance in sodium storage application. In details, a high specific capacity of 576 mAh g−1 can be obtained at a current density of 50 mA g−1 after 250 cycles; an impressive rate capacity of 242 mAh g−1 can be obtained even at a high current density of 1600 mA g−1. It is found that the cobalt dopant can inhibit the SnO2 coarsening, increase the overall conductivity and improve the reversibility of conversion reactions of Sn to SnO2. As a result the as-prepared cobalt-doped SnO2/carbon cluster presents a high initial Coulombic efficiency and an enhanced Na+ diffusion rate, corresponding to high specific capacity and excellent rate performance in sodium storage application. This work demonstrated a promising technique to prepared cobalt-doped nanostructured SnO2/carbon nanocomposites with excellent electrochemical performance as anode for sodium storage application.

A facile and large-scale synthesis of NiCo-LDHs@rGO composite for high performance asymmetric supercapacitors

Nickel cobalt hydroxides have been regarded as a potential candidate for energy storage devices owing to the attractive high theoretical capacitance. However, practical application of NiCo hydroxides is hindered by their poor chemical stability which leads to low cycling life. To overcome the obstacles, a facile, large-scale and low cost method for fabricating NiCo layered double hydroxides (NiCo-LDHs) with reduced graphene oxide (rGO) or polypyrrole (PPy) is developed. The synthesized composite with significantly enhanced electrochemical performances displays a uniform and loose nanostruture owing to the property of PPy or rGO which reduces the aggregation of NiCo hydroxides. Particularly, the as-prepared NiCo-LDHs@rGO composite exhibits a high specific capacitance of 1703 F g−1 at 0.5 A g−1 and an extraordinary rate capability with 76.3% capacitance retention after 100-fold increase in current density. Furthermore, an asymmetric supercapacitor (ASC) composed of NiCo-LDHs@rGO (positive electrode) and activated carbon (negative electrode) was fabricated. The ASC reveals an excellent energy density (47.1 Wh kg−1 at 399.9 W kg−1) and shows great long-term cycling stability (73.3% capacity retention after 10000 cycles), and so it holds great promise for future practical application.

Recent development of Supercapacitor Electrode Based on Carbon Materials

AbstractSupercapacitor has gained significant attention due to its fast charging/discharging speed, high power density and long-term cycling stability in contrast to traditional batteries. In this review, state-of-the-art achievements on supercapacitor electrode based on carbon materials is summarized. In all-carbon composite materials part, various carbon materials including graphene, carbon nanotube, carbon foam and carbon cloth are composited to fabricate larger specific surface area and higher electrical conductivity electrodes. However, obstacles of low power density as well as low cycling life still remain to be addressed. In metal-oxide composites part, carbon nanotube, graphene, carbon fiber fabric and hollow carbon nanofibers combine with MnO2respectively, which significantly address drawbacks of all-carbon material electrodes. Additionally, TiO2is incorporated into graphene electrode to overcome the low mechanical flexibility of graphene. In organic active compounds part, conducting polymers are employed to combinate with carbon materials to fabricate high specific capacitance, long-term thermal stability and outstanding electroconductivity flexible textile supercapacitors. In each part, innovation, fabrication process and performance of the resulting composites are demonstrated. Finally, future directions that could enhance the performance of supercapacitors are discussed.