Enhanced Rate Performance Research Articles

Novel Composite Separators Based on Heterometallic Metal‐Organic Frameworks Improve the Performance of Lithium‐Ion Batteries

AbstractThe separator is an essential component of lithium‐ion batteries as it affects ion transport and safety performance. Herein, a novel class of separators fabricated from poly(vinyl alcohol) and heterometallic metal‐organic frameworks, which affords a higher density of open bimetal sites, stronger complexation with anions, more porous structure, and enhanced thermal stability and electrolyte wettability is reported. The adoption of such separators substantially increases lithium‐ion conductivity and lithium‐ion transference number, leading to batteries with prolonged lifespan, improved low‐temperature performance, and enhanced rate performance.

Reduced graphene oxide (rGO) integrated sodium titanate nanocomposite as a high-rate performance anode material for sodium ion batteries

Sodium titanates were found as impressive anode materials for sodium-ion batteries (SIBs) because of its low working potential, high energy density and cost effectiveness. However, the major obstacle is low conductivity, which limits the improvement in electrochemical performances. In this report, based on the high conductivity and large surface area of reduced graphene oxide (rGO), a nanocomposite of sodium titanate integrated with rGO nanosheets (Na2Ti6O13/rGO) was fabricated through a facile solvothermal method and further employed as an anode for SIBs. In order to avoid the sluggish movement of sodium ions, the rGO nanosheets act as electrically conductive paths and facilitate the intercalation/de-intercalation of Na+ ions. In comparison to bare sodium titanate, the Na2Ti6O13/rGO nanocomposite electrode showed the enhanced rate performances, high capacity and an excellent long-range cycling stability, demonstrating the superiority of this unique nanostructure.

Multifunctional fullerene protective layer for dendrite-free Zn metal anode

Although the aqueous zinc batteries are deemed as the most competitive alternatives in the next-generation batteries, there are still annoying issues, including obdurate dendrites formation and side reactions, limiting practical applications. Hence, a uniform artificial C60 layer via an ex-situ approach is successfully assembled to construct robust Zn anode (denoted as Zn@C60). The functional C60 layer allows the formation of the ohmic contact interface between the C60 layer and Zn anode, inducing a low nucleation barrier and restraining 2D diffusion of Zn ions. More importantly, density functional theory calculations and simulation of the electric field contribution demonstrate that the C60 layer can facilitate the deposition of Zn on the Zn(002) plane and homogenize the electric field distribution. Consequently, the Zn@C60 electrode is obtained with a cycling stability over 3800 h at 0.25 mA cm−2 in symmetric cells, excellent coulombic efficiency for 1400 h in half cells, and together with better cycling stability and enhanced rate performance in full cells. Significantly, the C60 layer protection strategy provides a new view for an excellent dendrite-free Zn metal anode.

A Facile Li2TiO3 Surface Modification to Improve the Structure Stability and Electrochemical Performance of Full Concentration Gradient Li‐Rich Oxides

Full concentration gradient lithium‐rich layered oxides are catching lots of interest as the next generation cathode for lithium‐ion batteries due to their high discharge voltage, reduced voltage decay and enhanced rate performance, whereas the high lithium residues on its surface impairs the structure stability and long‐term cycle performance. Herein, a facile multifunctional surface modification method is implemented to eliminate surface lithium residues of full concentration gradient lithium‐rich layered oxides by a wet chemistry reaction with tetrabutyl titanate and the post‐annealing process. It realizes not only a stable Li2TiO3 coating layer with 3D diffusion channels for fast Li+ ions transfer, but also dopes partial Ti4+ ions into the sub‐surface region of full concentration gradient lithium‐rich layered oxides to further strengthen its crystal structure. Consequently, the modified full concentration gradient lithium‐rich layered oxides exhibit improved structure stability, elevated thermal stability with decomposition temperature from 289.57 °C to 321.72 °C, and enhanced cycle performance (205.1 mAh g−1 after 150 cycles) with slowed voltage drop (1.67 mV per cycle). This work proposes a facile and integrated modification method to enhance the comprehensive performance of full concentration gradient lithium‐rich layered oxides, which can facilitate its practical application for developing higher energy density lithium‐ion batteries.

Stable zinc metal anode with an ultrathin carbon coating for zinc-ion batteries

Owing to the good safety, low cost, environmentally friendliness, and relatively high energy density, aqueous zinc-ion batteries (ZIBs) are promising alternatives to lithium-ion batteries. However, the zinc metal anode in aqueous ZIBs is prone to dendrite growth and side reactions. Herein, an ultrathin carbon coating is fabricated on the Zn metal anode to suppress dendrite growth and alleviate side reactions. The symmetrical cell containing the modified Zn electrode shows a long cycling life of 3500 h at 0.5, 1 and 2 mA cm−2 with areal capacities of 0.5, 1 and 2 mAh cm−2, respectively. The cycling life is superior to those of previously reported Zn metal anodes with carbon-based coatings. Meanwhile, the full ZIB using Zn anode with ultrathin carbon coating deliver enhanced rate performance and cycling stability compared to that of using bare Zn anode.

Effect of dual improved electronic and cationic conductivity via W doping on cyclability and rate performance of LiNi0.90Co0.04Mn0.03Al0.03O2 cathode for rechargeable LiBs

Ni-rich layered cathodes are considered to be the most suitable high-capacity electrode material for current needs since their reversible capacity of over 200 mAh·g−1 and high operating voltage. However, the conventional Ni-rich layered cathodes inevitably go through rapid capacity degradation and poor rate performance. Herein, a designed strategy is proposed that W doping can regulate the electronic structure of NCMA(LiNi0.90Co0.04Mn0.03Al0.03O2) materials, presenting upgraded cyclability and enhanced rate performance. In this study, combined with density functional theory (DFT) calculation and conventional electrochemical measurements, revealed that the dual improvements of electronic and cationic conductivity are the possible reasons for the promoted electrochemical behavior. The bandgap of W-doped cathode material is reduced from 1.3857 to 1.2479 eV, which arises from the increased amount of electrons near Fermi energy after W doping. Such enhancement in electronic conductivity subsequently diminishes the polarization of the electrodes, thus the capacity retention of W-doped material after 100 cycles at 0.5C is greatly improved from 32.3 % to 95.0 %. Meanwhile, the strong WO bond intensifies cationic conductivity, facilitating Li+ diffusion. The introduction of W cations expands the thickness of Li slab up to 2.71 Å. Such improvements thereafter lead to a specific capacity of 155 mAh·g−1 at 5C. Compared to the pristine sample, W-NCMA cathode displays high potential for EV application.

Mitigated lattice distortion and oxygen loss of Li-rich layered cathode materials through anion/cation regulation by Ti4+-substitution

Lithium-rich layered cathode material (LLM) can meet the requirement of power lithium-ion energy storage devices due to the great energy density. However, the de/intercalation of Li+ will cause the irreversible loss of lattice oxygen and trigger transition metal (TM) ions migrate to Li+ vacancies, resulting in capacity decay. Here we brought Ti4+ in substitution of TM ions in Li1.2Mn0.54Ni0.13Co0.13O2, which could stabilize structure and expand the layer spacing of LLM. Moreover, optimized Ti-substitution can regulate the anions and cations of LLM, enhance the interaction with lattice oxygen, increase Ni3+ and Co3+, and improve Mn4+ coordination, improving reversibility of oxygen redox activation, maintaining the stable framework and facilitating the Li+ diffusion. Furthermore, we found 5% Ti-substitution sample delivered a high discharge capacity of 244.2 mAh/g at 50 mA/g, an improved cycling stability to 87.3% after 100 cycles and enhanced rate performance. Thereby Ti-substitution gives a new pathway to achieve high reversible cycle retention for LLMs.

Bamboo-derived flake-layer hierarchically porous carbon coupling nano-Si@porous carbon for advanced high-performance Li-ion capacitor

Lithium-ion capacitors (LICs) are increasingly being developed for energy storage as a consequence of their high power/energy density and ultra-long cycle lifetime. Herein, flake-layer hierarchically porous carbon (FPC) was obtained from bamboo liquid converted from bamboo powder using flake-layer Mg(OH)2 as template combined with KOH activation. Meanwhile, FPC-Si was obtained via loading nano-Si on the FPC surface through magnesiothermic reduction strategy. FPC has a high-specific surface area (SSA) of 1430.1 m2 g−1 and total pore volume of 2.84 cm3 g−1 with 90 % of mesopores. The high-SSA and mesopore volume contribute to superb capacitance and enhanced rate performance when used as the cathode in LIC. FPC-Si anode presents a rate capability of 720.5 mAh g−1 at 5 A g−1 with good cyclability. Therefore, the assembled LIC composed of FPC-Si anode and FPC cathode presents high energy/power density (179 Wh kg−1, 27.5 kW kg−1) and protracted lifetime of 8000 cycles (82.3 % capacitance retention). The current research indicates that the cathode requires not only high-SSA but also high mesopore volume. The mesopores as ions spreading highways can advance the ions transport and enhance the ions storage, causing high capacity and fine rate performance. The scalable methods offer a novel pathway for synthesizing biochar-based high-performance LICs.

Enhancing cation storage performance of layered double hydroxides by increasing the interlayer distance.

Layered double hydroxides (LDH) can be transformed from alkaline supercapacitor material into metal-cation storage cathode working in neutral electrolytes through electrochemical activation. However, the rate performance for storing large cations is restricted by the small interlayer distance of LDH. Herein, the interlayer distance of NiCo-LDH is expanded by replacing the interlayer nitrate ions with 1,4-benzenedicarboxylic anions (BDC), leading to the enhanced rate performance for storing large cations (Na+, Mg2+, and Zn2+), whereas almost the unchanged one for storing small-radius Li+ ions. The improved rate performance of the BDC-pillared LDH (LDH-BDC) stems from the reduced charge-transfer and Warburg resistances during charge/discharge due to the increased interlayer distance, as revealed by in situ electrochemical impedance spectra. The asymmetric zinc-ion supercapacitor assembled with LDH-BDC and activated carbon presents high energy density and cycling stability. This study demonstrates an effective strategy to improve the large cation storage performance of LDH electrodes by increasing the interlayer distance.

K+-doped P2-Na0.67Fe0.5Mn0.5O2 cathode for highly enhanced rate performance sodium-ion battery

Fe/Mn-based layered oxides are considered as competitive cathode materials for sodium-ion batteries (SIBs) owing to their satisfactory theoretical specific capacity, economy, and environmental friendliness. However, the inferior cycling performance and poor rate capability caused by structural evolution hinder their practical application. Herein, a novel K+-doped P2-Na0.67Fe0.5Mn0.5O2 cathode for SIBs is successfully achieved to address these issues. Due to the doping of 0.05 K+, the cathode displays good cycling stability at 1 C, with a capacity retention of 70% after 100 cycles, while the pristine one only yields 49% capacity retention. Even at a high rate of 3 C, it still maintains 72% capacity retention. The characterizations and calculations demonstrate that interplanar distance is enlarged by introducing large-sized K+ in the edge-sharing Na+ sites. Galvanostatic intermittent titration technique (GITT) results reveal that the Na+ diffusion coefficient is well enhanced by K+ doping. In-situ XRD investigation suggests that the K+ in the Na layer can act as a pillar to stabilize the host layered structure. The theoretical calculation demonstrates that the conductivity and the interaction between transition metal (TM) ions and oxygen of K+-doped samples are well improved, thus suppressing the structural evolution.

Screening and activating small-molecule Se in microporous S-decorated/N-doped carbon spheres for an enhanced rate performance

Breaking the Sen into short chains and accelerating the phase transformation kinetics are of fundamental importance in achieving high-performance Se cathodes. However, challenges remain in the unraveled function of the microporosity and strategy to increase the affinity of the host material towards active Sen species. Herein, S-decorated N-doped carbon spheres with a range of micropores are prepared to regulate different sized short-chain Sen. Combined with the density functional theory (DFT) simulation on the geometry of Sen (2 ≤ n ≤ 8) small molecules, different micropores of the host in screening Sen (2 ≤ n ≤ 8) with higher activity, accelerated kinetics and optimized performance are elaborated. The sulfur molecules decoration provides abundant polar sites to enhance the chemisorption of both Sen and Li2Se and thus boosting the redox kinetics and Sen utilization rate of the Li-Se battery. The obtained S@NPC/Se-7 cathode displays an extraordinary rate capability (430.4 mAh g−1 at 5 C) and maintains an ultrastable cycling property (at 1 C over 500 cycles).

Realizing Holistic Charging–Discharging for Dendrite-Free Lithium Metal Anodes via Constructing Three-Dimensional Li+ Conductive Networks

Lithium (Li) metal is a promising candidate for next-generation anode materials with high energy densities. However, Li dissolution/deposition processes are limited at the upper surface in contact with the electrolyte, which brings a locally high current density and then results in dendritic Li growth. This restraint of the local surface reaction during cycling has not been solved by commonly used modification strategies. In this study, a three-dimensional (3D) Li+ conductive skeleton is activated from atomic layer deposition (ALD) coating Li3PO4 (LPO) on the surface of the Ni foam (LPNF). Then, the skeleton is efficiently constructed in the Li metal anode by the lower-temperature Li infusion. Ionic conductor LPO layers and electronic conductor Ni fibers supply charge transport channels between the electrolyte and the internal Li. The mixed conductive network realizes holistic charge transfer, which is proved by in situ scanning electron microscopy experiments. In virtue of dispersive dissolution/deposition and optimized electrochemical kinetics brought by a Li+ conductive network, the composited Li electrode presents an excellent symmetric battery cycling stability (over 1200 h) and enhanced rate performances (stable cycling even at 10.0 mA cm-2). When matching with a LiCoO2 (LCO) cathode, LCO||Li@LPNF full batteries exhibit a capacity retention of 80.8% over 250 cycles. During cycling, there was no evidence of dendrite growth and the remaining Li in the composited anode showed a smooth, compact, and well-combined condition with LPNF. Through constructing a 3D Li+ conductive network, the composited Li metal anode breaks through the limit of the local surface reaction; this work proposes a novel insight of realizing holistic charging/discharging for the dendrite-free Li metal anode.

Nb2C MXenes with surface chalcogenation and halogenation as high capacity electrode materials for lithium-ion batteries

MXenes show extremely competitive potential applications in electrode materials for lithium-ion batteries (LIBs) due to their excellent specific surface area, high electrical conductivity, and compositional tunability. However, limited interlayer spacing and undesired surface functional group on MXene surface impede the Li-ions accessibility and mobility. Herein, the structural, electronic, mechanical and electrochemical properties of the representative Nb2C MXene with surface chalcogenation and halogenation resulting in the formation of Nb2CT2 ([Formula: see text], S, Se, Cl and Br) materials as anodes for LIBs were investigated using first-principles calculations based on density functional theory. The results reveal that Nb2CT2 can exhibit metallic conductivity with improved mechanical strength, which renders the enhanced rate performance and endures the repeated lattice expansion and contraction during charge/discharge process, respectively. In particular, Nb2CS2 and Nb2CCl2 render the enhanced Li-ion storage and mobility with a theoretical Li storage capacity of 613.76 mA[Formula: see text]h/g and 597.79 mA[Formula: see text]h/g and diffusion energy barrier of 0.275 eV and 0.294 eV, respectively. Moreover, chalcogenation and halogenation yield the expanded interlayer spacing, which improve the Li-ions accessibility in Nb2CT2. The results demonstrate that sulfurized and chlorinated Nb2C MXenes are the promising anode materials with high capacity, low diffusion barrier and lower open circuit voltage for next-generation LIBs.

An Insoluble Amino-Functionalized Hexaazatriphenylene as Stable Organic Cathode in Lithium-Ion Batteries

Organic electrode materials have received increasing attention in rechargeable batteries due to their earth abundance and variable structures. However, the practical application of most organic electrode materials is limited by the high solubility in the electrolyte. Herein, an insoluble amino-functionalized hexaazatriphenylene (defined as HATN-[NH2]3) in the electrolyte is developed as stable organic cathode material for lithium-ion batteries (LIBs). The resultant HATN-[NH2]3 electrode achieves a high reversible capacity of 192.5 mAh g−1 at a current density of 0.05 A g−1. Remarkably, the electrode exhibits almost no capacity fade after 500 cycles at 0.5 A g−1. The high stability can be ascribed to insoluble property caused by hydrogen bonds between HATN-[NH2]3 molecules. Moreover, density functional theory calculations suggest that amino functionalization can reduce the band gap of HATN, in favor of improved conductivity and thus enhanced rate performance. This work offers a simple but efficient strategy to develop stable organic electrode materials in LIBs and beyond.

Enhanced rate performance and mitigated capacity decay of single-crystal LiNi0.8Co0.1Mn0.1O2 by the synergism of Mg doping and V2O5 coating

High nickel cathode material is considered as the most promising material in power battery. However, the material has serious structural instability and poor cycling performance. In this paper, Mg doped and V2O5 coated single crystal LiNi0.8Co0.1Mn0.1O2 (NCM811) material (labeled as NCMMg0.02@V2O5) has been successfully synthesized. Electrochemical tests show that its first discharge specific capacity reaches 177.3 mAh/g at 1 C (1 C = 200 mA g−1) within 2.8–4.3 V, the capacity retention remains 89.1 % after 100 cycles, and the discharge specific capacity achieves 125.6 mAh/g at 10 C, indicating excellent electrochemical performances. Obviously, the synergism of single crystal structure, Mg doping and V2O5 coating can effectively improve structural stability and Li+ diffusion coefficient, prevent surface/interface side reactions, and thus achieve the ideal cycle and rate performance.

3D Artificial Array Interface Engineering Enabling Dendrite-Free Stable Zn Metal Anode

HighlightsThe design concept of 3D artificial array interface engineering was proposed to achieve eliminated volume stress, preferred orientation growth and dendrite-free Zn metal anode.The mechanism of MXene array interface on modulating the growth kinetics and deposition behavior of Zn atoms were firstly uncovered at a multiscale level.The engineered electrode exhibits comprehensive enhancements in the resistance of corrosion and hydrogen evolution reaction, as well as the rate capability and cyclic stability.3D MXene array@Zn/VO2 batteries with enhanced rate performance (214.1 mAh g−1 at 10 A g−1) and cycle lifespan can be demonstrated.

Suppressing zinc dendrite growth in aqueous battery via Zn–Al alloying with spatially confined zinc reservoirs

Rechargeable aqueous zinc-ion batteries are attractive candidates as energy storage technology, but the uncontrollable Zn dendrite formation and low stripping/plating coulombic efficiency when using bare Zn metal foil as anode have severely limit the battery reliability and energy density. Thus, to develop a more robust ZIB anode with lower extent of dendrite growth, Zn–Al alloy is proposed in this work. The passivating Al2O3 shell formed on the Al phase can provide two key functions; (1) selective electrochemical stripping of Zn due to electrochemically inert Al2O3, and (2) guiding the electrodeposition of Zn on the available Zn sites. The as-prepared Zn–Al alloy anode is able to outperform the bare Zn anode as bare Zn anode shows signs of short circuit after cycling. When paired with V6O13 cathode, the Zn–Al//V6O13 cell delivers enhanced rate performance and a nearly 95% capacity retention after 1000 cycles at 3 A g−1, with a specific capacity of 280 mA h g−1. The strategy demonstrated that Zn–Al alloy is suitable for aqueous zinc-ion batteries due to its low corrosion rate, low dendrite formation, low corrosion current, and high capacity retention.

Sulfur-doped carbonized bacterial cellulose as a flexible binder-free 3D anode for improved sodium ion storage.

Carbon-based materials have received wide attention as electrodes for energy storage and conversion owing to their rapid mass transfer processes, outstanding electronic conductivities, and high stabilities. Here, sulfur-doped carbonized bacterial cellulose (S-CBC) was prepared as a high-performance anode for sodium-ion batteries (SIBs) by simultaneous carbonization and sulfidation using the bacterial cellulose membrane produced by microbial fermentation as the precursor. Doping sublimed sulfur powder into CBC results in a greater degree of disorder and defects, buffering the volume expansion during the cycle. Significantly, the three-dimensional (3D) network structure of bacterial cellulose endows S-CBC with flexible self-support. As an anode for sodium ion batteries, S-CBC exhibits a high specific capacity of 302.9 mA h g-1 at 100 mA g-1 after 50 cycles and 177.6 mA h g-1 at 2 A g-1 after 1000 cycles. Compared with the CBC electrode, the S-CBC electrode also exhibits enhanced rate performance in sodium storage. Moreover, theoretical simulations reveal that Na+ has good adsorption stability and a faster diffusion rate in S-CBC. The doping of the S element introduces defects that enlarge the interlayer distance, and the synergies of adsorption and bonding are the main reasons for its high performance. These results indicate the potential application prospects of S-CBC as a flexible binder-free electrode for high-performance SIBs.

One-dimensional H2V3O8 nanorods and two-dimensional lamellar MXene composites as efficient cathode materials for aqueous rechargeable zinc ion batteries.

The energy crisis is a the worldwide problem which needs humans to solve immediately. To solve this problem, it is necessary to develop energy storage batteries. It is worth mentioning the aqueous rechargeable zinc ion batteries (ARZBs) which have some advantages, such as low cost, good safety and no need for an organic electrolyte as in the traditional lithium-ion batteries. However, it is still a challenge to find suitable and reliable electrode materials. In this work, as-prepared H2V3O8 nanorods and MXene composites are used as cathode materials in ARZBs which were designed well using a hydrothermal method after optimizing the reaction time. The results showed that H2V3O8/MXene ARZBs could provide a good transport path for zinc ions, which were based on special 1D H2V3O8 nanorods and 2D multi-layered MXene materials, which exhibited an outstanding initial specific discharge capacity of 373 mA h g-1 at 200 mA g-1, good rate capability and a long lifecycle with only 15.8% capacity decay at 500 mA g-1 after 5000 cycles. The H2V3O8/MXene composites with a good electrochemical performance bring insight into their promising applications for energy storage batteries. They provided enhanced rate performance and excellent cycling stability, which was ascribed to the multi-step and multi-mode zinc ion insertion/extraction process. This was confirmed by the use of the 1D/2D integrated structure of the H2V3O8/MXene composites, which was conductive to zinc ion diffusion.

Amorphous TiO<sub>2</sub> ultrathin nanosheet for stable high-rate lithium storage

The use of intercalation-type metal oxides as anode materials in rechargeable lithium-ion batteries is appealing due to their reduced risk of Li plating at low voltages. However, their implementation for fast-charging applications is limited by their lower energy and power density, as well as cycling instability. Herein, we present an amorphous TiO<sub>2</sub> nanosheet that exhibits exceptional cycling stability with a high capacity of 231 mA <b>·</b> h <b>·</b> g<sup>−1</sup> after 200 cycles at 500 mA <b>·</b> g<sup>−1</sup> and 156.7 mA <b>·</b> h <b>·</b> g<sup>−1</sup> after 1000 cycles at a high current density of 6 A <b>·</b> g<sup>−1</sup>. We attribute the enhanced rate performance to the amorphous nature with high isotropy, which facilitates low energy migration paths and ion availability and can accommodate large changes in volume. This work suggests that amorphization represents a promising strategy for developing unconventional metal oxide electrode materials with high-rate performance.