Sodium-Ion Intercalation Mechanism in MXene Nanosheets

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• 作者：Satoshi Kajiyama ; Lucie Szabova ; Keitaro Sodeyama ; Hiroki Iinuma ; Ryohei Morita ; Kazuma Gotoh ; Yoshitaka Tateyama ; Masashi Okubo ; Atsuo Yamada
• 刊名：ACS Nano
• 出版年：2016
• 出版时间：March 22, 2016
• 年：2016
• 卷：10
• 期：3
• 页码：3334-3341
• 全文大小：545K
• ISSN：1936-086X

文摘

MXene, a family of layered compounds consisting of nanosheets, is emerging as an electrode material for various electrochemical energy storage devices including supercapacitors, lithium-ion batteries, and sodium-ion batteries. However, the mechanism of its electrochemical reaction is not yet fully understood. Herein, using solid-state ²³Na magic angle spinning NMR and density functional theory calculation, we reveal that MXene Ti₃C₂T_x in a nonaqueous Na⁺ electrolyte exhibits reversible Na⁺ intercalation/deintercalation into the interlayer space. Detailed analyses demonstrate that Ti₃C₂T_x undergoes expansion of the interlayer distance during the first sodiation, whereby desolvated Na⁺ is intercalated/deintercalated reversibly. The interlayer distance is maintained during the whole sodiation/desodiation process due to the pillaring effect of trapped Na⁺ and the swelling effect of penetrated solvent molecules between the Ti₃C₂T_x sheets. Since Na⁺ intercalation/deintercalation during the electrochemical reaction is not accompanied by any substantial structural change, Ti₃C₂T_x shows good capacity retention over 100 cycles as well as excellent rate capability.