Cu基类液态热电材料铜离子析出机理和服役稳定性研究

Recently, Cu-based Liquid-like thermoelectric (TE) materials have attracted great attentions in TE community because of their inherent abnormal electrical and thermal transport properties, such as the reduced specific heat, extremely low lattice thermal conductivity and its weak-temperature dependence, and ultra-high TE figure of merit. However, the poor stability and reliability of these Cu-based liquid-like materials are the key problems for their long-term service during the real applications. The presence of liquid-like ions inside the crystal structure is the main reason for the poor stability and reliability. Under electric field or the temperature gradient, these liquid-like ions can migrate among different sites with similar energies and even precipitate from the crystal structure forming the pure metal. Therefore, the ion migration and ion precipitation must be restricted or blocked to improve the liquid-like material’s stability and reliability before starting any further study for industrial applications. In this program, we plan to reveal the physical origin of ion migration and precipitation phenomenon via systematically investigating the mobile ion’s behavior in various Cu-based liquid-like materials (e.g. Cu2-mX (X = S, Se, Te), CuAgSe, and Cu5FeS4) under electric field and temperature gradient. The ionic activation energy and ionic self-diffusion coefficient will be calculated and the main factors that affect these parameters will be clarified. Then, we will try to improve the service reliability by optimizing the chemical composition or the microstructure. In addition, we will also systematically characterize the evolution of the liquid-like materials’ chemical composition, crystal structure, microstructure, electrical and thermal properties under electric field and temperature gradient. Based on these characterizations, the critical electric field strength, current density, and temperature gradient corresponding to the ion precipitation will be also illustrated. Finally, some strategies to suppress the ion precipitation will be proposed. This study will open a possibility of reconsidering the application of Cu-based liquid-like materials in thermoelectrics.

具有极低晶格热导率和优良热电性能的Cu基类液态热电材料成为了近年来热电领域的研究热点。然而，Cu基类液态热电材料中的Cu离子在电场或温度梯度下容易析出，影响该类热电材料在实际应用中的服役稳定性。揭示Cu基类液态热电材料中Cu离子的析出过程和机理，提升Cu基类液态热电材料的服役稳定性，已成为热电研究领域高度关注的问题。最新的研究结果表明，化学组成、微观结构等材料自身要素可以影响Cu离子的迁移和析出行为，但是具体机制目前尚不清楚。本项目拟以Cu2X(X=S,Se,Te)、CuAgSe、Cu5FeS4等几种代表性Cu基类液态热电材料为主要研究对象，深刻理解Cu离子迁移和析出行为发生的根本物理和化学机制，探索定量表征不同外部驱动力(电场和温场)作用下材料服役稳定性的手段，建立可以抑制Cu离子析出同时维持优良热电性能的有效方法，最终开发兼具高性能和高服役稳定性的新型Cu基类液态热电材料。

本项目以Cu基类液态热电材料的服役稳定性为主要研究对象，围绕Cu离子迁移和析出现象开展相关研究，取得了系列创新性成果。揭示了Cu基类液态热电材料的离子输运机理，提出利用材料在电场下不发生分解时所能承受的最大外加电压（即临界电压）作为指征因子定量评价材料服役稳定性；自主搭建了可以在电场和温度梯度下测量临界电压的设备，通过监测电场（和/或温差）作用下材料电阻/电压变化，获得了系列Cu基材料的临界电压；提出“阳离子空位+钉扎离子”和“离子阻挡-电子导通”界面两种提高材料稳定性的方法，开发了Cu1.90Fe0.0325S化合物、Cu1.96Se0.8S0.2化合物等兼具高热电性能和高服役稳定性的Cu基类液态热电材料；超越传统热电器件设计方法，提出通过器件结构尺寸和界面的优化与调整同时实现高能量转换效率和服役稳定性的器件设计方法，成功开发出高效（9.1%）高稳定的Cu2Se基新型热电器件；将研究拓展至Zn基和Ag基类液态热电材料，系统表征其中Zn离子和Ag离子的析出行为，揭示了Zn4Sb3、Ag2S、Ag2(S,Te)等材料的稳定性机理。在Adv. Mater.、Adv. Funct. Mater.、Joule等国内外核心期刊上发表受本项目资助的SCI收录的论文10篇，申请专利2项；培养博士生2人，硕士生2人。项目负责人在项目执行期内获得了国家自然科学基金委优秀青年科学基金项目的资助（2021），入选上海市青年科技启明星计划（2019）和上海市青年拔尖人才（2020）。