Architecting hierarchical shell porosity of hollow prussian blue‐derived iron oxide for enhanced Li storage
Authors: ZHAO Z. , LIU X. , LUAN C. , LIU X. , WANG D. , QIN T. , SUI L. , ZHANG W. 
Published: October 2019

Delicate architecture of active material enables improving the performacne of lithium ion batteries. Environmental‐friendly Fe2O3 anode has high theoretical specific capacity (1007 mAh g−1) in lithium ion batteries, but suffers from structural collapsing and poor electronic conductivity. Herein, we design an unique hierarchical iron oxide by regulating the initial precursor prussian blue and targeting hollow‐shell structures with full consideration of temperature controls. Among them, Fe2O3 with a sheet‐crossing structure at 650°C, affords obvious advantages of improved electronic conductivity, short ionic diffusion length, prevented particle agglomeration, and buffer volume change. Thus, we achieve a superior discharge specific capacity of 611 mAh g−1 at 500 mA g−1. Regulating hierarchical structure of prussian blue‐assisted oxides enables effectively enchancing Li storge performance.

Lay Description

Nanoparticle self‐assembly, one of bottom‐up methods is often used to prepare hollow hierarchical structures, whereas it suffers from low productivity and insufficient stability. Hence, we designed a unique hierarchical iron oxide by top‐down method with regulating the initial precursor PB and targeting hollow‐shell structures through full consideration of temperature controls.

Delicate architecture of active material enables improving the performacne of lithium ion batteries. Environmental‐friendly Fe2O3 anode has high theoretical specific capacity (1007 mAh g−1) in lithium ion batteries, but suffers from structural collapsing and poor electronic conductivity. Hence, we prepared Prussian Blue (PB) materials with different sizes and calcined them at different temperatures. We found that no matter what the size of PB, the sheet‐crossing morphology appeared at 650°C, and the interlaced morphology was the key to improve the performance of lithium batteries. If the size of PB precursor is too large or too small, it has adverse effects on lithium batteries. Only when the size and calcination temperature of PB precursor reach the optimum state, the best performance can be obtained. The calcination PB‐K‐3 at 650°C has a unique hierarchical structure of sheet‐crossing. An obvious advantages include the prevention of particle agglomeration, short ionic diffusion lengths, and buffering volume changes. As a consequence, 611 mAh g−1 was obtained at the current density of 500 mA g–1.

In addition, we observed the structural changes of electrode plates at different reaction potentials, according to the reaction equation of Fe2O3+xLi++xe→LixFe2O3. With the proceeding charge process, the voltage increases from 0.01 to 3 V, the lithium ions gradually comes out of the iron oxide electrode surface. Whereas the discharging process reverses the aforementioned phenomena. Even if the changing volumes, however, the shape of cubic blocks for the PB‐K‐3 is preserved at different potentials.

Taking these advantages into account, our designed MOFs‐derived struture was an effective way to prepare hollow hierarchical structure with enhanced Li storage performacne. Such work is expected to facilitate the design of new electrode structure of lithium batteries.