Ordered Vacancies as Sodium Ion Micropumps in Cu-Deficient Copper Indium Diselenide to Enhance Sodium Storage.

Unordered vacancies engineered in host anode materials cannot well maintain the uniform Na+ adsorbed and possibly render the local structural stress intense, resulting in electrode peeling and battery failure. Here, the indium is first introduced into Cu2Se to achieve the formation of CuInSe2. Next, an ion extraction strategy is employed to fabricate Cu0.54In1.15Se2 enriched with ordered vacancies by spontaneous formation of defect pairs. Such ordered defects, compared with unordered ones, can serve as myriad sodium ion micropumps evenly distributing in crystalline host to homogenize the adsorbed Na+ and the generated volumetric stress during the electrochemistry. Furthermore, Cu0.54In1.15Se2 is indeed proved by the calculations to exhibit smaller volumetric variation than the counterpart with unordered vacancies. Thanks to the distinct ordered vacancy structure, the material exhibits a highly reversible capacity of 428 mAh g-1 at 1 C and a high-rate stability of 311.7 mAh g-1 at 10 C after 5000 cycles when employed as an anode material for Sodium-ion batteries (SIBs). This work presents the promotive effect of ordered vacancies on the electrochemistry of SIBs and demonstrates the superiority to unordered vacancies, which is expected to extend it to other metal-ion batteries, not limited to SIBs to achieve high capacity and cycling stability.

Three-dimensional nanocomposites with Co3O4 nanosheets parallelly embedded in carbon network walls for enhanced lithium-ion storage.

Three-dimensional Co3O4/C nanocomposites are synthesized via a hydrogel assisted synthesis route. The carbon has a three-dimensional interconnected network structure, and ultrathin Co3O4 nanosheets (≈5.0 nm) are parallelly and uniformly embedded in the two-dimensional carbon network walls. This unique structure restricts the aggregation and pulverization of active materials, and ensures the continuity and efficiency of electron and ion transmission during the lithiation/delithiation process. As a result, the Co3O4/C nanocomposites exhibit excellent cycling performance at different current densities. The discharge capacities remain at 905 mA h g-1 after 190 cycles at the current density of 100 mA g-1 and 561 mA h g-1 after 500 cycles at the current density of 2000 mA g-1. Since this approach is facile and large-scale, it is a rational way to engineer high capacity anodes to achieve improved electrochemical performances.