Synthesis of nitrogen-doped oxygen-deficient TiO2-x/reduced graphene oxide/sulfur microspheres via spray drying process for lithium-sulfur batteries

Active Sulfur-Host Material VS4 with Surface Defect Engineering: Intercalation-Conversion Hybrid Cathode Boosting Electrochemical Performance of Li-S Batteries

Transition-metal sulfides as late-model electrocatalysts usually remain inactive in lithium-sulfur (Li-S) batteries in spite of their advantages to accelerate the rapid conversion of lithium polysulfides (LiPSs). Herein, a series of cobalt-doped vanadium tetrasulfide/reduced graphene oxide (x%Co-VS₄/rGO) composites with an ultrathin layered structure as an active sulfur-host material are prepared by a one-pot hydrothermal method. The well-designed two-dimensional ultrathin 3%Co-VS₄/rGO with heteroatom architecture defects (defect of Co-doping and defect of S-vacancies) can significantly improve the adsorption ability on LiPSs, the electrocatalytic activity in the Li₂S potentiostatic deposition, and the active sulfur reduction/oxidation conversion reactions and greatly boost the electrochemical performances of Li-S batteries. On the one hand, the ultrathin 3%Co-VS₄/rGO possesses good conductivity inheriting from rGO which contributes to the capacity of internal redox reactions on lithiation from VS₄. On the other hand, the hybrid architectures provide strong adsorption and excellent electrocatalytic ability on LiPSs, which benefit from the surface defects caused by heteroatom doping. The S@3%Co-VS₄/rGO cathode displays a high specific capacity of 1332.6 mA h g^-1 at 0.2 C and a low-capacity decay of only 0.05% per cycle over 1000 cycles at 3 C with a primary capacity of 633.1 mA h g^-1. Furthermore, when the sulfur loading (single-side coating) reaches 4.48 mg cm^-2, it still can deliver 756.2 mA h g^-1 after the 100th cycle at 0.2 C with 89.5% capacity retention. In addition, the in situ X-ray diffraction test reveals that the sulfur conversion mechanism is the processes of α-S₈ → Li₂S → β-S₈ (first cycle) and then β-S₈ ↔ Li₂S during the subsequent cycles. The designing strategy with heteroatom doping and self-intercalation capacity adopted in this work would provide novel inspiration for fabricating advanced sulfur-host materials to achieve excellent electrochemical capability in Li-S batteries.

A Comparative Study of Cobalt Chalcogenides as the Electrode Materials on Lithium-Sulfur Battery Performance

Lithium-sulfur batteries, as viable options for energy storage, have gained popularity because of their high energy density. However, the poor conductivity of sulfur and Li₂ S, as well as the shuttling effect of lithium polysulfides, seriously limits their commercialization. Herein, cobalt chalcogenides (Co₃ O₄ , CoS, and Co₃ Se₄ ) supported by reduced graphene oxide are synthesized as the electrode materials, which feature high conductivity, rapid kinetic conversion, and catalytic effect. Based on complementary experimental outputs and advanced computation, it is revealed that the change in anion results in distinctive performance. Among them, the cathode material based on Co₃ Se₄ /reduced graphene oxide is the best. The reasons can be ascribed to the conductive and catalytic improvement. This comparative study provides guidelines in the design of lithium-sulfur batteries via the meticulous regulation of the anions.

Boron nitride nanosheets wrapped by reduced graphene oxide for promoting polysulfides adsorption in lithium-sulfur batteries

The polysulfides shuttling and slow redox kinetics of sulfur-based cathodes have severely hindered the commercialization of lithium-sulfur (Li-S) batteries. Herein, distinctive three-dimensional microspheres composed of boron nitride (BN) nanosheets and reduced graphene oxide (rGO) were applied to act as efficient sulfur cathode hosts for the first time using in a spray-drying process. Using this construction, the robust microsphere structure could shorten ion diffusion pathways and supply sufficient spaces to alleviate the volumetric expansion of sulfur during lithiation. Besides, the synergistic effect between BN and rGO significantly enhanced polysulfides adsorption capability and accelerated their conversion, verified by the density functional theory (DFT) calculations and adsorption experiments. Consequently, the S-BN@rGO cathode could manifest the high initial capacity (1137 mAh g^-1 at 0.2 C) and remarkable cycling/stability performance (572 mAh g^-1 at 1 C after 500 cycles). These results shed light on a design concept of high-performance sulfur cathode host materials.

Advanced Battery Materials Research at Nazarbayev University: Review

With the rapid development of new and advanced technologies, the request for energy storage device with better electrochemical characteristics is increasing as well. Therefore, the search and development for more novel and efficient energy storage components are imperative. In Kazakhstan there are several groups that were established to conduct research in the field of energy storage devices. One of them is professor Mansurov’s research group with we have a long time fruitful collaboration. Group at Nazarbayev University do research in design and investigation of advanced energy storage materials for high performance energy storage devices, including lithium-ion batteries, sodium-ion batteries, lithium-sulfur batteries, and aqueous rechargeable batteries, employing strategies as nanostructuring, nano/micro combination, hybridization, pore-structure control, configuration design, 3D printing, surface modification, and composition optimization. This manuscript reviews research on advanced battery materials, provided by Nazarbayev University scientists since the last 10 years.

Employing synergetic effect of ZnSe quantum dots and layered Ni(OH)2to boost the performance of lithium-sulfur cathodes

The low sulfur utilization, cycling instability, and sluggish kinetics are the critical obstructions to practical applications of lithium-sulfur batteries (LSBs). Constructing sulfur hosts with high conductivity, suppressed shuttle effect, and rapid kinetics is essential for their practical application in LSBs. Here, we synthetically utilized the merits of ZnSe quantum dots (QDs) and layered Ni(OH)₂to boost the performance of LSBs. A novel core-shell ZnSe-CNTs/S@Ni(OH)₂was constructed using the ZnSe-CNTs network as framework to load sulfur and following with Ni(OH)₂encapsulation. The CNT network decorated with ZnSe QDs not only serves as a conductive framework providing fast electron/ion transfer channels, but also limits polysulfide diffusion physically and chemically. Layered Ni(OH)₂, the wrinkled encapsulation, not only permits fast electron/ion transfer, but also buffers the expansion, confines active materials, and limits the polysulfide dissolution chemically. When used as a cathode, ZnSe-CNTs/S@Ni(OH)₂presents enhanced electrochemistry performance compared with ZnSe-CNTs/S and CNTs/S. The average specific capacity decreases from 1021.9 mAh g^-1at 0.2 C to 665.0 mAh g^-1at 2 C, showing rate capacity much higher than ZnSe-CNTs/S and CNTs/S. After 150 cycles, the capacity at 0.5 C slowly reduces from 926.7 to 789.0 mAh g^-1, showing high retention of 85.1%. Therefore, our investigation provides a new strategy to construct a promising sulfur cathode for LSBs.

Elevated electrochemical performances enabled by a core-shell titanium hydride coated separator in lithium-sulphur batteries

To date, the lithium–sulphur battery is still suffering from fast capacity fade and poor rate performance due to its special electrochemical mechanism. The interlayer or separator with conductive coatings is considered effective in inhibiting the shuttle effect. Here, we proposed a novel metal hydride with high conductivity and preferably chose TiH₂ as the conductive coating because of its low cost, high conductivity, and good stability in air. The TiH₂ powder was prepared by a simple ball-milling method, and the effect of the atmosphere was also investigated. A core–shell heterostructure formed, in which the TiH₂ core acted as an electron transfer pathway, and the titanium oxide nano-shell functioned as the absorber for polysulfides. Thus, with the combination of fast electronic transfer and strong absorption ability, the TiH₂ coated separator could improve the cycling stability, the rate performances, and the self-discharge rate. The TiH₂ separator could increase the capacity of the lower plateau and delay the oversaturation points at high rates, promoting the liquid–solid conversion. It is believed that the promotion resulted from the high conductivity and polysulfide absorption of the TiH₂ separator. Although the preparation process still needs further optimization, the core–shell metal hydride provided a novel strategy for designing the heterostructure, which could provide high conductivity and strong absorption ability toward polysulfides simultaneously.

A TiO_2−x@TiH₂ core–shell microstructure formed spontaneously, in which the TiH₂ core acts as an electron transfer pathway and the shell functioned as the polysulfide absorber.

Enhanced Cycle Stability of Crumpled Graphene-Encapsulated Silicon Anodes via Polydopamine Sealing

Despite silicon being a promising candidate for next-generation lithium-ion battery anodes, self-pulverization and the formation of an unstable solid electrolyte interface, caused by the large volume expansion during lithiation/delithiation, have slowed its commercialization. In this work, we expand on a controllable approach to wrap silicon nanoparticles in a crumpled graphene shell by sealing this shell with a polydopamine-based coating. This provides improved structural stability to buffer the volume change of Si, as demonstrated by a remarkable cycle life, with anodes exhibiting a capacity of 1038 mA h/g after 200 cycles at 1 A/g. The resulting composite displays a high capacity of 1672 mA h/g at 0.1 A/g and can still retain 58% when the current density increases to 4 A/g. A systematic investigation of the impact of spray-drying parameters on the crumpled graphene morphology and its impact on battery performance is also provided.

Incorporation ZnS quantum dots into carbon nanotubes for high-performance lithium-sulfur batteries

Constructing sulfur hosts with high electronic conductivity, large void space, strong chemisorption, and rapid redox kinetics is critically important for their practical applications in lithium-sulfur batteries (LSBs). Herein, by coupling ZnS quantum dots (QDs) with carbon nanotubes (CNTs), one multifunctional sulfur host CNT/ZnS-QDs is designed via a facile one-step hydrothermal method. SEM and TEM analyses reveal that small ZnS-QDs (<5 nm) are uniformly anchored on the CNT surface as well as encapsulated into CNT channels. This special architecture ensures sulfur direct contacting with highly conductive CNTs; meanwhile, the catalytic effect of anchored ZnS-QDs improves the chemisorption and confinement to polysulfides. Benefiting from these merits, when used as sulfur hosts, this special architecture manifests a high specific capacity, superior rate capability, and long-term cycling stability. The ZnS-QDs dependent electrochemical performance is also evaluated by adjusting the mass ratio of ZnS-QDs, and the host of CNT/ZnS-QDs 27% owns the optimal cell performance. The specific capacity decreases from 1051 mAh g^-1 at 0.2 C to 544 mAh g^-1 at 2.0 C, showing rate capability much higher than CNT/S and other CNT/ZnS-QDs/S samples. After 150 cycles, the cyclic capacity at 0.5 C exhibits a slow reduction from 1051 mAh g^-1 to 771 mAh g^-1, showing a high retention of 73.4% with a coulombic efficiency of over 99%. The electrochemical impedance spectroscopy analyses demonstrate that this special architecture juggles high conductivity and excellent confinement of polysulfides, which can significantly suppress the notorious shuttle effect and accelerate the redox kinetics. The strategy in this study provides a feasible approach to design efficient sulfur hosts for realizing practically usable LSBs.

A novel sulfur@void@hydrogel yolk-shell particle with a high sulfur content for volume-accommodable and polysulfide-adsorptive lithium-sulfur battery cathodes

High-energy-density secondary batteries are required for many applications such as electric vehicles. Lithium-sulfur (Li-S) batteries are receiving broad attention because of their high theoretical energy density. However, the large volume change of sulfur during cycling, poor conductivity, and the shuttle effect of sulfides severely restrict the Li-storage performance of Li-S batteries. Herein, we present a novel core-shell nanocomposite consisting of a sulfur core and a hydrogel polypyrrole (PPy) shell, enabling an ultra-high sulfur content of about 98.4% within the composite, which greatly exceeds many other conventional composites obtained by coating sulfur onto some hosts. In addition, the void inside the core-shell structure effectively accommodates the volume change; the conductive PPy shell improves the conductivity of the composite; and PPy is able to adsorb polysulfides, suppressing the shuttle effect. After cycling for 200 cycles, the prepared S@void@PPy composite retains a stable capacity of 650 mAh g^-1, which is higher than the bare sulfur particles. The composite also exhibits a fast Li ion diffusion coefficient. Furthermore, the density functional theory calculations show the PPy shell is able to adsorb polysulfides efficiently, with a large adsorption energy and charge density transfer.

Three-dimensional Co9S8 nanotube network/sulfur composite cathode with enhanced lithium-sulfur battery performance

The poor conductivity of sulfur and the 'shuttle effect' of polysulfide intermediates have hindered the development of next generation lithium-sulfur (Li-S) batteries with high energy and low consumption. Herein, novel Co₉S₈-S composite nanotubes are developed to efficiently alleviate the above-mentioned problems. Experiments and theoretical calculations show that Co₉S₈ has strong adsorption on soluble polysulfides. This not only restrains polysulfides diffusion and ensures their utilization, but also enhances the intimate contact between the active materials and the conductive substrates to promote the kinetics of conversion reactions. The three-dimensional (3D) conductive network with a high surface area formed by interlinking Co₉S₈ nanotubes further improves the electronic conductivity of the composite cathode. As a result, the Co₉S₈-S cathode shows a high capacity of 1153 mAh g^-1. After 500 cycles, a high capacity of 462 mAh g^-1 (2 C) is demonstrated with a negligible capacity decay of ~0.04% per cycle.