Abstract
Conductive metal sulfides are promising multi-functional additives for future lithium-sulfur (Li-S) batteries. These can increase the sulfur cathode’s electrical conductivity to improve the battery’s power capability, as well as contribute to the overall cell-discharge capacity. This multi-functional electrode design showed initial promise; however, complicated interactions at the system level are accompanied by some detrimental side effects. The metal sulfide additives with a chemical conversion as the reaction mechanism, e.g., CuS and FeS2, can increase the theoretical capacity of the Li-S system. However, these additives may cause undesired parasitic reactions, such as the dissolution of the additive in the electrolyte. Studying such complex reactions presents a challenge because it requires experimental methods that can track the chemical and structural evolution of the system during an electrochemical process. To address the fundamental mechanisms in these systems, we employed an operando multimodal x-ray characterization approach to study the structural and chemical evolution of the metal sulfide—utilizing powder diffraction and fluorescence imaging to resolve the former and absorption spectroscopy the latter—during lithiation and de-lithiation of a Li-S battery with CuS as the multi-functional cathode additive. The resulting elucidation of the structural and chemical evolution of the system leads to a new description of the reaction mechanism.
Highlights
Architectural designs for innovative functions – such as devices that can provide high energy-density and power simultaneously[17]
Sulfur-CuS hybrid electrodes experienced Cu cation dissolution and deposition on lithium that destroys the anode’s solid-electrolyte interface (SEI) layer, which leads to cell failure in a few cycles
We combine X-ray Powder Diffraction (XPD), X-ray Absorption Spectroscopy (XAS), and X-ray Fluorescence (XRF) microscopy to address the changes in material structure, chemistry, and elemental distribution
Summary
Ke Sun[1], Chonghang Zhao[2], Cheng-Hung Lin[2], Eli Stavitski[3], Garth J. Conductive metal sulfides are promising multi-functional additives for future lithium-sulfur (Li-S) batteries These can increase the sulfur cathode’s electrical conductivity to improve the battery’s power capability, as well as contribute to the overall cell-discharge capacity. By reacting with lithium in the voltage range of 2.6 V-1.0 V vs Li/Li+, they are compatible with the operational voltage of a Li-S battery through either intercalation or conversion mechanisms They have been investigated individually as sulfur electrode additives and showed beneficial effects in capacity retention and high power performance. Sulfur-CuS hybrid electrodes experienced Cu cation dissolution and deposition on lithium that destroys the anode’s solid-electrolyte interface (SEI) layer, which leads to cell failure in a few cycles This observation represents a design challenge in multi-functional electrodes: while introducing new components with desirable properties, parasitic reactions may occur and hinder the original design intentions. We are able to further validate the hypothesis that one of the mobile polysulfide species generated by sulfur-component discharge is responsible for Cu+ dissolution from CuS or Cu2S25, while demonstrating an approach to support future multi-functional electrode developments
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