Solvent Induced Activation Reaction of MoS2 Nanosheets within Nitrogen/Sulfur-Codoped Carbon Network Boosting Sodium Ion Storage.

MoS2 , as a classical 2D material, becomes a capable anode candidate for sodium-ion batteries. However, MoS2 presents a disparate electrochemical performance in the ether-based and ester-based electrolyte with unclear mechanism. Herein, tiny MoS2 nanosheets embedded in nitrogen/sulfur-codoped carbon (MoS2 @NSC) networks are designed and fabricated through an uncomplicated solvothermal method. Thanks to the ether-based electrolyte, the MoS2 @NSC shows a unique capacity growth in the original stage of cycling. But in the ester-based electrolyte, MoS2 @NSC shows a usual capacity decay. The increasing capacity puts down to the gradual transformation from MoS2 to MoS3 with the structure reconstruction. Based on the above mechanism, MoS2 @NSC demonstrates an excellent recyclability and the specific capacity keeps around 286 mAh g-1 at 5 A g-1 after 5000 cycles with an ultralow capacity fading rate of only 0.0034% per cycle. In addition, a MoS2 @NSC‖Na3 V2 (PO4 )3 full cell with ether-based electrolyte is assembled and demonstrates a capacity of 71 mAh g-1 , suggesting the potential application of MoS2 @NSC. Here the electrochemical conversion mechanism of MoS2 is revealed in the ether-based electrolyte and significance of the electrolyte design on the promoting Na ion storage behavior is highlighted.

Surface engineering of core-shell MoS2@N-doped carbon spheres as stable and ultra-long lifetime anode for sodium-ion batteries.

MoS2 is regarded as a hopeful anode candidate for sodium-ion batteries (SIBs) due to their various merits such as high specific capacity, abundant raw material reserves and low cost. However, their practical application is impeded by unsatisfied cycling ability due to the intense mechanical stress and unstable solid electrolyte interphase (SEI) during Na+ insertion/extraction process. Herein, spherical MoS2@polydopamine derived highly conductive N-doped carbon (NC) shell composites (MoS2@NC) are designed and synthesized to promote the cycling stability. The internal MoS2 core is optimized and restructured from the original micron-sized block to the ultra-fine nanosheets during initial 100-200 cycles, which not only improves the utilization of electrode materials but also shortens the ion transport distance. The outer flexible NC shell effectively maintains the original spherical structure of the overall electrode material and prevents the occurrence of large-scale agglomeration, which is conducive to form a stable SEI layer. Therefore, the core-shell MoS2@NC electrode presents a remarkable cyclic stability and a capable rate performance. Under a high rate of 20 A g-1, the high capacity of 428 mAh g-1 can be acquired after over ultra-long 10,000 cycles without obvious capacity loss. Moreover, the MoS2@NC‖Na3V2(PO4)3 full-cell assembled by employing commercial Na3V2(PO4)3 cathode can achieve a high capacity retention of 91.4% after 250 cycles at 0.4 A g-1. This work reveals the promising prospect of MoS2-based materials as anode of SIBs, and also has some inspirations on the structural design for conversion-type electrode materials.

Sulfur-Decorated Ti3 C2 TX MXene for High-Performance Sodium/Potassium-Ion Batteries.

As post-lithium ion batteries, both sodium-ion batteries (SIBs) and potassium ion batteries (PIBs) possess great potential for large scale energy storage. However, the application of both SIBs and PIBs are hindered by the lack of suitable electrode materials. Here, we synthesized the sulfur decorated Ti3 C2 Tx (S-T3 C2 Tx ) MXene as electrode material for SIBs and PIBs. Thanks to the sulfur functional group and the formation of Ti-S bond, which facilitates the sodium in-/desertion and strengthens the potassium ion adsorption ability, as well as enhances ion reaction kinetics and improved structure stability, the S-T3 C2 Tx exhibit excellent sodium/potassium storage performance, high reversible capacities of 151 and 101 mAh g-1 at 0.1 mA g-1 were achieved for SIBs and PIBs, respectively. Moreover, the S-T3 C2 Tx exhibits remarkable long-term capacity stability at a high density of 500 mA g-1 , providing an impressive storage of 88 mAh g-1 for SIBs and 41 mAh g-1 for PIBs even after 2000 cycles. This work could give a deep comprehension of the heteroatom modification influence on the MXene-based framework and promote the application of MXene electrodes.

Three-dimensional Ti3C2Tx and MnS composites as anode materials for high performance alkalis (Li, Na, K) ion batteries.

Exploring capable and universal electrode materials could promote the development of alkalis (Li, Na, K) ion batteries. 2D MXene material is an ideal host for the alkalis (Li, Na, K) ion storage, but its electrochemical performance is limited by serious re-stacking and aggregation problems. Herein, we cleverly combined electrostatic self-assembly with gas-phase vulcanization method to successfully combine Ti3C2Tx-MXene with ultra-long recyclability and high conductivity with MnS, which presents high specific capacity but poor conductivity. The as-prepared 3D hierarchical Ti3C2Tx/MnS composites have an unique sandwich-like constituent units. The tiny MnS nanoparticles are restricted between the Ti3C2Tx layers and play a key role in expanding the Ti3C2Tx interlayer spacing. As a result, the 3D Ti3C2Tx/MnS composites as the anode of LIBs exhibits a superior capacities of 826 and 634 mAh/g after 1000 and 3000 cycles at 0.5 and 1.0 A/g, respectively. More importantly, we reveal the reaction mechanism that the specific capacity first increases and then gradually stabilizes with the increase of charge and discharge cycle times when the as-prepared 3D Ti3C2Tx/MnS was used as the anode of LIBs. In addition, we have also used this material in SIBs and PIBs and achieved remarkable electrochemical capability, with a specific capacity of 107 mAh/g after 2500 cycles at 0.5 A/g or 127 mAh/g after the 2000th cycle at 0.2 A/g, respectively.

A Novel Graphene Based Bi-Function Humidity Tolerant Binder for Lithium-Ion Battery.

Binders play a critical role in rechargeable lithium-ion batteries (LIBs) by holding granular electrode materials, conductive carbons, and current collectors firmly together to form and maintain a continuous electron conduction phase with sufficient mechanical strength. In the commercial LIBs, the dominant binder is polyvinylidene fluoride for the cathode (LiCoO2 , LiFePO4 , LiNix Coty Mnz O2 , etc.) and carboxyl methylcellulose/styrene-butadiene rubber for the anode (graphite and Li4 Ti5 O12 ). However, these polymer binders have several drawbacks, particularly, a lack of electronic and lithium-ion conductivities. Here, a novel organic/inorganic hybrid conductive binder (LAP-rGO) for both the anode and cathode of LIBs is reported. The binder consists of 2D reduced graphene oxide sheets with anchored long alkane chains. Electrodes prepared using this binder exhibit sufficient high bond strength, fast electrolyte diffusion, high rate charge/discharge performance, and excellent cycling stability. Around 130 mAh g-1 capacity enhancement at 5C is demonstrated for LiFePO4 and Li4 Ti5 O12 electrodes owing to the combined improvement in electron and lithium ion transportation. LAP-rGO bond graphite anode shows specific capacity beyond its theoretical value. Electrode slurries prepared using this new binder have superior processing and coating properties that can be prepared under a high humidity and dried using less energy.

3D tremella-like nitrogen-doped carbon encapsulated few-layer MoS2 for lithium-ion batteries.

MoS2 is regarded as an attractive anode material for lithium-ion batteries due to its layered structure and high theoretical specific capacity. Its unsatisfied conductivity and the considerable volume change during the charge and discharge process, however, limits its rate performance and cycling stability. Herein, 3D tremella-like nitrogen-doped carbon encapsulated few-layer MoS2 (MoS2@NC) hybrid is obtained via a unique strategy with simultaneously poly-dopamine carbonization, and molybdenum oxide specifies sulfurization. The three-dimensional porous nitrogen-doped carbon served both as a mechanical supporting structure for stabilization of few-layers MoS2 and a good electron conductor. The MoS2@NC exhibits enhanced high rate performance with a specific capacity of 208.7 mAh g-1 at a current density of 10 A g-1 and stable cycling performance with a capacity retention rate of 85.7% after 1000 cycles at 2 A g-1.

Coral-like CoMoO4 hierarchical structure uniformly encapsulated by graphene-like N-doped carbon network as an anode for high-performance lithium-ion batteries.

Encapsulation of metal oxide anode material with hierarchical structure in graphene-like high conductivity carbon network is conducive to improving the lithium storage performance of the anode material. However, it is very challenging to rational synthesizing anode materials with such structure. Herein, a mesoporous spiny coral-like CoMoO4 (SCL-CMO) self-assembled from the mesoporous nanorods made of nanoparticles is prepared by a simple one-step solvothermal method. The layered coral-like CoMoO4@N-doped Carbon (LCL-CMO@NC) composite is synthesized by polymerization of DA on the surface of SCL-CMO at room temperature and the subsequent sintering treatment. This LCL-CMO@NC composite perfectly combines the comprehensive advantages of the spiny coral-like hierarchical architecture and the N-doped graphene-like carbon coating, which not only effectively improve the electron and Li+ ion transport dynamics and accommodate the large volume changes, but also prevent hierarchical structure aggregation and pulverization during cycle process. Therefore, LCL-CMO@NC composite exhibits superior electrochemical kinetics and stability. The reversible specific capacity remained 1321.6 and 132 mA h g-1 after 900 and 10,000 cycles at 0.4 and 5 A g-1, respectively.