Abstract
Silicon has been the subject of an extensive research effort aimed at developing new anode materials for lithium ion batteries due to its large specific and volumetric capacity. However, commercial use is limited by a number of degradation problems, many of which are related to the large volume change the material undergoes during cycling in combination with limited lithium-diffusivity. Silicon rich silicon oxides (SiOx), which converts into active silicon and inactive lithium oxide during the initial lithiation, have attracted some attention as a possible solution to these issues. In this work we present an investigation of silicon rich amorphous silicon nitride (a-SiNx) as an alternative convertible anode material. Amorphous SiN0.89 thin films deposited by plasma enhanced chemical vapour deposition show reversible reactions with lithium when cycled between 0.05 and 1.0 V vs. Li+/Li. This material delivers a reversible capacity of approximately 1,200 mAh/g and exhibits excellent cycling stability, with 41 nm a-SiN0.89 thin film electrodes showing negligible capacity degradation over more than 2,400 cycles.
Highlights
In this work we show that a-SiN0.89 thin films exhibit high reversible capacity of approximately 1,200 mAh/g and excellent cycling stability over more than 2,400 cycles
As seen in the high angle annular dark field (STEM-HAADF) image of the film cross section in Fig. 1c, the thickness of this film was measured to be 116 nm, which is within the experimental margin of error
The film quality was confirmed in the scanning transmission electron microscopy (STEM) analysis, which showed a dense film with a uniform thickness over the area which was analysed (~10 μm), despite the relative roughness of the substrate surface
Summary
The purpose of this work has been to investigate the performance of substoichiometric silicon nitride as an alternative in-situ formed alloy anode material for lithium ion batteries. While the exact form of the conversion reaction has not been determined, silicon nitride has been proposed to convert into active silicon and inactive Si3N4 and/or Li3N37,38, or one of several lithium silicon nitride ternary phases during the initial lithiation[36] This solid state conversion is expected to produce finely dispersed domains of the different phase constituents, and combine the high lithium storage capacity of silicon with the lithium ion conductivity and structural support of the other phases[37]. In this work we show that a-SiN0.89 thin films exhibit high reversible capacity of approximately 1,200 mAh/g and excellent cycling stability over more than 2,400 cycles
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