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Binder-free 3D silicon-nickel electrodes for Li-ion batteries show high capacity and cycling stability
13 November 2012
|Cycling characteristics of 700 nm 3D(Si,Ni) at 1C showing a reversible specific capacity of 1,650 mAh/g after 120 cycles of charge/discharge. Credit: ACS, Gowda et al. Click to enlarge.|
Researchers from Rice University and Applied Materials have developed another approach to delivering the theoretically high energy capacity of silicon-based anodes for Li-ion batteries while avoiding the problem of severe capacity fading during cycling associated with the significant volumetric changes resulting from reversible lithium ion insertion.
In a paper published in the ACS journal Nano Letters, they report engineering three-dimensional porous nickel-based current collectors coated conformally with layers of silicon to form high-capacity electrodes. These binder/conductive additive-free silicon electrodes showed excellent electrode adhesion resulting in superior cyclic stability and rate capability. A 700 nm 3D(Si,Ni) material at 1C showing a reversible specific capacity of 1650 mAh/g after 120 cycles of charge/discharge.
The nickel current collector design also allows for an increase in silicon loading per unit area leading to high areal discharge capacities of up to 0.8 mAh/cm2 without significant loss in rate capability.
They attributed the excellent electrode utilization (85%) and improved cyclic stability for the metal/silicon system to reduced internal stresses/fracture upon electrode expansion during cycling and shorter ionic/electronic diffusion pathways that help in improving the rate capability of thicker silicon layers.
Recently the Li ion battery has gained renewed interest as a potential candidate to replace gasoline in vehicular applications...Hence extensive research efforts are underway in search of new battery electrodes to improve the energy density of the Li ion cell.
...there exists a need for the clear understanding and development of stable binder-free Si electrodes that could lead to significant improvements in energy densities and cycling characteristics of silicon based lithium ion batteries. Herein, we demonstrate the ability to fabricate scalable tubular nickel current collectors with variable pore dimension and thickness suitable for thin film battery applications. Conformal amorphous silicon films of different mass loadings have been coated onto the tubular nickel substrates (3D(Si,Ni)) and tested in lithium half cells. The binder free 3D(Si,Ni) electrode has shown improved capacity per unit area and cyclic stability due to the porous structure and excellent electrode adhesion.—Gowda et al.
To fabricate the material, they deposited porous nickel films on stainless steel substrate by co-electrodepositing Cu−Ni film; selectively etched copper from the microstructure of Cu−Ni films; and conformally coated silicon films within the pores of nickel by chemical vapor deposition process. Two types of porous Ni films (types 1 and 2) with different aspect ratios were fabricated by selective etching of the copper from coelectrodeposited Ni−Cu films; they also deposited silicon of different mass loading on the two types of Ni films.
As one example, a 700 nm type 1 3D(Si,Ni) was tested in lithium half cells for its electrochemical performance. They observed first cycle capacity of 0.36 mAh/cm2—about 85% of the theoretical capacity expected for the corresponding Si loading. An irreversible capacity loss of about ∼28% was observed after the first discharge, due to secondary surface reactions, and a capacity loss of only ∼5% was observed between the second and 120th cycle. A stable reversible capacity of ∼0.22 mAh/cm2 was observed for the 700 nm 3D(Si,Ni).
Type 2 3D (Si,Ni) showed a reversible capacity of ∼0.8 mAh/cm2 at a current rate of 0.05 C with 80% of the reversible capacity retained at four times larger current density of 0.2 C.
The electrochemical method based on pore size and film thickness engineering is scalable and has the potential to control the aspect ratio of the pores which could lead to the development of higher capacity Si anode. The binder free approach of developing scalable, stable Si anodes, could have a huge impact in realizing high energy density lithium ion batteries.—Gowda et al.
Sanketh R. Gowda, Victor Pushparaj, Subramanya Herle, G. Girishkumar, Joseph G. Gordon, Hemtej Gullapalli, Xiaobo Zhan, Pulickel M. Ajayan, and Arava Leela Mohana Reddy (2012) Three-Dimensionally Engineered Porous Silicon Electrodes for Li Ion Batteries. Nano Letters doi: 10.1021/nl302114j
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