Abstract
We show full Li/S cells with the use of balanced and high capacity electrodes to address high power electro-mobile applications. The anode is made of an assembly comprising of silicon nanowires as active material densely and conformally grown on a 3D carbon mesh as a light-weight current collector, offering extremely high areal capacity for reversible Li storage of up to 9 mAh/cm2. The dense growth is guaranteed by a versatile Au precursor developed for homogenous Au layer deposition on 3D substrates. In contrast to metallic Li, the presented system exhibits superior characteristics as an anode in Li/S batteries such as safe operation, long cycle life and easy handling. These anodes are combined with high area density S/C composite cathodes into a Li/S full-cell with an ether- and lithium triflate-based electrolyte for high ionic conductivity. The result is a highly cyclable full-cell with an areal capacity of 2.3 mAh/cm2, a cyclability surpassing 450 cycles and capacity retention of 80% after 150 cycles (capacity loss <0.4% per cycle). A detailed physical and electrochemical investigation of the SiNW Li/S full-cell including in-operando synchrotron X-ray diffraction measurements reveals that the lower degradation is due to a lower self-reduction of polysulfides after continuous charging/discharging.
Highlights
Lithium-sulfur batteries are pointed out as one of the most promising systems for advanced application in automotive or stationary electrical energy storage
We present a balanced Li/S battery with high capacity and long cycling stability using a prelithiated Si nanowires (SiNWs)/C composite as anode material (6.0 mAh/cm2) and a S/C composite for the positive electrode (2.4 mAh/cm2) to overcome the battery failure due to typical Li dendrite formation resulting from state-of-the-art metallic Li foils
The third part covers the integration of SiNW/C anodes in high capacity balanced Li/S full-cells by means of in-operando synchrotron X-Ray diffraction (SXRD) measurements and detailed electrochemical characterization
Summary
For practical applications of Li/S cells, an areal capacity of 6.0 mAh/cm[2] is required to reach energy densities of commercial lithium-ion batteries[25] This outstanding high value is reproducibly exceeded by the SiNW composite anodes presented in this work. The reflection intensities of Li2S and β-sulfur remain almost unchanged in each cycle which points to low self-discharge and low sulfur consumption on the Si negative electrode surface This finding may be attributed to the lower reactivity of Si and its SEI compared to Li metal as shown for Si nanoparticles by Jaumann et al.[4]. The integration of SiNWs on carbon meshes is a promising approach for achieving high capacity batteries in conjunction with sulfur cathodes to avoid dendrite formation and gain improved cycling stability
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