Sheet-Like Stacking SnS2/rGO Heterostructures as Ultrastable Anodes for Lithium-Ion Batteries

In Situ Encapsulation of SnS2/MoS2 Heterojunctions by Amphiphilic Graphene for High-Energy and Ultrastable Lithium-Ion Anodes

Lithium-ion batteries with transition metal sulfides (TMSs) anodes promise a high capacity, abundant resources, and environmental friendliness, yet they suffer from fast degradation and low Coulombic efficiency. Here, a heterostructured bimetallic TMS anode is fabricated by in situ encapsulating SnS2/MoS2 nanoparticles within an amphiphilic hollow double-graphene sheet (DGS). The hierarchically porous DGS consists of inner hydrophilic graphene and outer hydrophobic graphene, which can accelerate electron/ion migration and strongly hold the integrity of alloy microparticles during expansion and/or shrinkage. Moreover, catalytic Mo converted from lithiated MoS2 can promote the reaction kinetics and suppress heterointerface passivation by forming a building-in-electric field, thereby enhancing the reversible conversion of Sn to SnS2. Consequently, the SnS2/MoS2/DGS anode with high gravimetric and high volumetric capacities achieves 200 cycles with a high initial Coulombic efficiency of >90%, as well as excellent low-temperature performance. When the commercial Li(Ni0.8Co0.1Mn0.1)O2 (NCM811) cathode is paired with the prelithiated SnS2/MoS2/DGS anode, the full cells deliver high gravimetric and volumetric energy densities of 577 Wh kg-1 and 853 Wh L-1, respectively. This work highlights the significance of integrating spatial confinement and atomic heterointerface engineering to solve the shortcomings of conversion-/alloying typed TMS-based anodes to construct outstanding high-energy LIBs.

Robust bond linkage between boron-based coating layer and lithium polyacrylic acid binder enables ultra-stable micro-sized germanium anodes

Micro-sized alloy type germanium (Ge) anodes possess appealing properties for next-generation lithium ions batteries, such as desirable capacity, easy accessibility and greater tapdensity. Nevertheless, volume expansion accompanied by severe pulverization and continuous growth of solid electrolyte interlayer (SEI) still represent fundamental obstacles to their practical applications. Herein, we propose a fresh strategy of constructing robust bond linkage between boron-based coating layer and lithiated polyacrylic acid (PAALi) binder to circumvent the pulverization problems of Ge anodes. Facile pyrolysis of boric acid can introduce an amorphous boron oxide interphase on Ge microparticles (noted as Ge@B2O3). Then in situ crosslinking reaction between B2O3 and PAALi via BOC bond linkage constructs a robust Ge anode (Ge@B-PAALi), which is proved by FTIR and Raman characterizations. Post morphological and compositional investigations reveal the minimized pulverization and a thinner SEI composition. The robust bond linkage strategy endows Ge anode with ultra-stable cycling properties of 1053.8 mAh/g after 500 cycles at 1 A/g vs. 500.7 mAh/g for Ge@PAALi and 372.7 mAh/g for Ge@B2O3, respectively. The proposed bond linkage strategy via artificial coating layer and functional binders unlocks huge potential of alloys and other anodes for next-generation battery applications.

Fast Energy Storage of SnS2 Anode Nanoconfined in Hollow Porous Carbon Nanofibers for Lithium-Ion Batteries

The development of conversion-typed anodes with ultrafast charging and large energy storage is quite challenging due to the sluggish ions/electrons transfer kinetics in bulk materials and fracture of the active materials. Herein, the design of porous carbon nanofibers/SnS2 composite (SnS2 @N-HPCNFs) for high-rate energy storage, where the ultrathin SnS2 nanosheets are nanoconfined in N-doped carbon nanofibers with tunable void spaces, is reported. The highly interconnected carbon nanofibers in three-dimensional (3D) architecture provide a fast electron transfer pathway and alleviate the volume expansion of SnS2 , while their hierarchical porous structure facilitates rapid ion diffusion. Specifically, the anode delivers a remarkable specific capacity of 1935.50 mAh g-1 at 0.1 C and excellent rate capability up to 30 C with a specific capacity of 289.60 mAh g-1 . Meanwhile, at a high rate of 20 C, the electrode displays a high capacity retention of 84% after 3000 cycles and a long cycle life of 10 000 cycles. This work provides a deep insight into the construction of electrodes with high ionic/electronic conductivity for fast-charging energy storage devices.

Rational Engineering of p-n Heterogeneous ZnS/SnO2 Quantum Dots with Fast Ion Kinetics for Superior Li/Na-Ion Battery

Constructing heterogeneous nanostructures is an efficient strategy to improve the electrical and ionic conductivity of metal chalcogenide-based anodes. Herein, ZnS/SnO2 quantum dots (QDs) as p-n heterojunctions that are uniformly anchored to reduced graphene oxides (ZnS-SnO2 @rGO) are designed and engineered. Combining the merits of fast electron transport via the internal electric field and a greatly shortened Li/Na ion diffusion pathway in the ZnS/SnO2 QDs (3-5 nm), along with the excellent electrical conductivity and good structural stability provided by the rGO matrix, the ZnS-SnO2 @rGO anode exhibits enhanced electronic and ionic conductivity, which can be proved by both experiments and theoretical calculations. Consequently, the ZnS-SnO2 @rGO anode shows a significantly improved rate performance that simple counterpart composite anodes cannot achieve. Specifically, high reversible specific capacities are achieved for both lithium-ion battery (551 mA h g-1 at 5.0 A g-1 , 670 mA h g-1 at 3.0 A g-1 after 1400 cycles) and sodium-ion battery (334 mA h g-1 at 5.0 A g-1 , 313 mA h g-1 at 1.0 A g-1 after 400 cycles). Thus, this strategy to build semiconductor metal sulfides/metal oxide heterostructures at the atomic scale may inspire the rational design of metal compounds for high-performance battery applications.

A facile precursor route towards the synthesis of Fe1-xS@NC-rGO composite anode materials for high-performance lithium-ion batteries

Iron-based sulfides are considered promising anode materials for lithium-ion batteries (LIBs) due to their low cost and high theoretical specific capacities. However, low conductivity and dissolution of lithium polysulfides during the reaction hamper their practical applications. Herein, we firstly synthesized N-doped carbon-coated Fe_1-xS (Fe_1-xS@NC) sheets through vacuum pyrolysis of the precursor Fe_1-xS(en)_0.5 (en = ethylenediamine). Then Fe_1-xS@NC-rGO composites (rGO = reduced graphene oxide) were prepared in which the Fe_1-xS@NC sheets were anchored on the rGO. The performance of the composites as an anode material for LIBs has been investigated. It is found that coating N-doped C on Fe_1-xS surfaces can improve the surface conductivity and electrochemical kinetics of Fe_1-xS, which is beneficial for the conversion between lithium polysulfides and Fe_1-xS. In addition, the coated N-doped C on the Fe_1-xS sheets can serve as a barrier to direct contact between the electrolyte and the material, reducing the dissolution of polysulfides and preventing the loss of active ingredients. More importantly, the double protection of the N-doped C layer and the flexible rGO substrate minimizes the structural damage caused by the cyclic expansion of Fe_1-xS@NC-rGO. As expected, Fe_1-xS@NC-rGO exhibits good rate performance with a reversible capacity of 939.5 mA h g^-1 after 1690 cycles at a current density of 1.0 A g^-1, along with outstanding charge and discharge performance and excellent long-term cycling stability. This work shows that the introduction of NC coating and the rGO matrix into Fe_1-xS would synergistically enhance the performance of Fe_1-xS for LIBs and highlights the effectiveness of the synthetic strategy for double carbon-based materials-protected sulfides in developing superior LIB electrodes.