A Coral-Like FeP@NC Anode with Increasing Cycle Capacity for Sodium-Ion and Lithium-Ion Batteries Induced by Particle Refinement.

We present a coral-like FeP composite with FeP nanoparticles anchored and dispersed on a nitrogen-doped 3D carbon framework (FeP@NC). Due to the highly continuous N-doped carbon framework and a spring-buffering graphitized carbon layer around the FeP nanoparticle, a sodium-ion battery with the FeP@NC composite exhibits an ultra-stable cycling performance at 10 A g-1 with a capacity retention of 82.0 % in 10 000 cycles. Also, particle refinement leads to a capacity increase during cycling. The FeP nanoparticles go through a refining-recombination process during the first cycle and present a global refining trend after dozens of cycles, which results in a gradually increase in graphitization degree and interface magnetization, and further provides more active sites for Na+ storage and contributes to a rising capacity with cycling. The capacity ascending phenomenon can also extend to lithium-ion batteries.

Understanding the High-Performance Anode Material of CoC2 O4 ⋠2 H2 O Microrods Wrapped by Reduced Graphene Oxide for Lithium-Ion and Sodium-Ion Batteries.

Metal oxalate has become a most promising candidate as an anode material for lithium-ion and sodium-ion batteries. However, capacity decrease owing to the volume expansion of the active material during cycling is a problem. Herein, a rod-like CoC2 O4 ⋅2 H2 O/rGO hybrid is fabricated through a novel multistep solvo/hydrothermal strategy. The structural characteristics of the CoC2 O4 ⋅2 H2 O microrod wrapped using rGO sheets not only inhibit the volume variation of the hybrid electrode during cycling, but also accelerate the transfer of electrons and ions in the 3 D graphene network, thereby improving the electrochemical properties of CoC2 O4 ⋅2 H2 O. The CoC2 O4 ⋅2 H2 O/rGO electrode delivers a specific capacity of 1011.5 mA h g-1 at 0.2 A g-1 after 200 cycles for lithium storage, and a high capacity of 221.1 mA h g-1 at 0.2 A g-1 after 100 cycles for sodium storage. Moreover, the full cell CoC2 O4 ⋅2 H2 O/rGO//LiCoO2 consisting of the CoC2 O4 ⋅2 H2 O/rGO anode and LiCoO2 cathode maintains 138.1 mA h g-1 after 200 cycles at 0.2 A g-1 and has superior long-cycle stability. In addition, in situ Raman spectroscopy and in situ and ex situ X-ray diffraction techniques provide a unique opportunity to understand fully the reaction mechanism of CoC2 O4 ⋅2 H2 O/rGO. This work also gives a new perspective and solid research basis for the application of metal oxalate materials in high-performance lithium-ion and sodium-ion batteries.

Heterostructured SnS/TiO2@C hollow nanospheres for superior lithium and sodium storage.

Tin(ii) sulfide (SnS) is considered to be one of the most promising anode materials for lithium/sodium ion batteries (LIBs/SIBs) due to its high theoretical capacity and low-cost. However, its practical applications are severely impeded by its low electrical conductivity and large volume change upon cycling. Herein, we demonstrate a high-performance SnS/TiO2 encapsulated by a carbon shell (SnS/TiO2@C) synthesized by facile coprecipitation and annealing treatment. The exterior carbon coating can not only improve the conductivity, but also effectively relieve volume variation to maintain the structural integrity during cycling. Significantly, the internal SnS/TiO2 heterostructure formed a built-in electric field to provide favorable driving force for ion transfer. Consequently, the synthesized SnS/TiO2@C delivered a reversible capacity of 672.4 mA h g-1 at 0.5 A g-1 after 100 cycles for lithium storage and 331.2 mA h g-1 at 0.2 A g-1 after 200 cycles for sodium storage. Meanwhile, ultra-long lifespans of 3000 cycles at 5.0 A g-1 with a capacity of 394.5 mA h g-1 for LIBs and 750 cycles at 5.0 A g-1 with a capacity of 295 mA h g-1 for SIBs were achieved. The electrochemical reaction mechanisms of the SnS/TiO2@C electrode have been investigated by in situ XRD, ex situ XRD, and ex situ HRTEM. Our work may offer further understanding of the hierarchical structure to boost the electrochemical properties of the electrode materials.

Coordination Polymers-Derived Three-Dimensional Hierarchical CoFe2O4 Hollow Spheres as High-Performance Lithium Ion Storage.

Hierarchical CoFe2O4 (CFO) hollow spheres were successfully synthesized via solvothermal method and calcination treatment. The obtained CFO completely inherited the hollow structure and spherical morphology of its precursor of cobalt-based ferrocenyl coordination polymers (Co-Fc-CPs). The three-dimensional (3D) porous hierarchical hollow structure can not only promote the permeation of electrolyte and shorten the lithium-ion transfer distance but also provide a cushion for the volume change during insertion/extraction of lithium ions. To improve the electrochemical properties, the CFO was combined with two forms of carbonaceous materials to controllably obtain 3D CoFe2O4@C (CFO@C) and CoFe2O4@reduced graphene oxide (CFO@rGO) composites. Compared with bare CFO and CFO@C, CFO@rGO exhibited a superior electrochemical performance, achieving a high specific capacity of 933.1 mA h g-1 at a current density of 100 mA g-1 after 100 cycles and showing an outstanding cycling life with a capacity of 615.6 mA h g-1 at 1000 mA g-1 after 600 cycles. In situ X-ray diffraction technique was applied to investigate the lithium storage mechanism during discharge/charge processes. This work provides a new approach to prepare hierarchical hollow bimetallic oxides composites for lithium-ion anode materials.