高稳定性锰基混合磷酸盐正极材料的构筑及其储钠行为研究

Mn-based mixed phosphate has an opened 3D framework structure，low-cost and environmental-friendliness, and exhibits the obvious advantages as high rate cathode material of sodium-ion batteries. However, the unstable potential platform, low reversible specific capacity and poor cycling stability of this material have been caused by the easily distorted structure during charging and discharging and low conductivity, and these have been the bottleneck issues of research and development. Aiming at the structure distortion caused by trivalent manganese ion Jahn-Teller effect of this material in this project, the large-size and light metal-ions have been selected for doping and controlling the structure of manganese-base mixed phosphate, and reducing the lattice change caused by the trivalent manganese ions for inhibition of multiphase transformation during charging and discharging. On the basis of the constructed large-size and highly stable frame structure, the stability of potential platform and highly specific capacity have been achieved. Through the In-situ characterization technique and theoretical calculation of crystal structure, the changes of metal bond-spacing and corresponding binding energy before and after doping have been studied, the regularity on the effect of stable frame-structure has been clarified, and the sodium storage mechanism of highly stable manganese-based mixed phosphate has been revealed. By compositing with porous carbon fiber cloth with high conductivity, the flexible self-supporting manganese-based mixed phosphate/porous carbon fiber composite electrode has been prepared for avoiding the binder and its high potential decomposition, and improving the conductivity of the prepared material. This research will provide the theoretical foundation and technical support for the development of high-performance sodium-storage electrodes and devices.

锰基混合磷酸盐具有开放式三维框架结构且成本低、环境友好，作为高倍率钠离子电池用正极材料优势明显。但其充放电过程中结构易被扰动及电导率低，导致电位平台不稳定、可逆比容量低及循环稳定性差是该类材料研发的瓶颈问题。本项目针对该类材料由于三价锰离子Jahn-Teller效应引起的晶格形变，拟选用大尺寸轻金属离子对锰基混合磷酸盐体相掺杂调控，获得大尺寸高稳定框架结构，缓解三价锰离子引起的结构扰动，达到抑制充放电过程中材料多相转变，实现材料电位平台稳定和比容量提高；通过原位表征技术和晶体结构理论计算，研究掺杂前后金属键间距及相应结合能的变化，阐明稳定框架结构的基本规律，揭示掺杂高稳定锰基混合磷酸盐的储钠机制；通过与高导电性多孔碳纤维布复合，制备柔性自支撑锰基混合磷酸盐/多孔碳纤维复合电极，达到避免粘结剂存在及其高电位分解缺陷，改善制备材料电导率。研究将为构筑高性能储钠电极及器件提供理论依据和技术支持。

钠离子电池由于低成本和有效能量密度，成为理想储能器件之一。而研究低成本、大容量和高稳定性的正极材料是获得高性能钠电池的关键。锰基储钠正极材料具有资源丰富、成本低廉和环境友好等优势，然而Mn3+Jahn-Teller效应和大尺寸Na+脱/嵌易引起材料晶格形变，从而造成电极扩散动力学迟缓和低寿命。本项目以框架型锰基混合磷酸盐和层状锰氧化物材料为基础，主要围绕构筑高稳定锰基电极材料开展研究工作，并探究了构筑其它稳定电极材料新策略。具体开展以下几方面工作：1.采用轻金属离子取代策略，构筑高稳定框架结构NaMn2.7Mg0.3(PO4)2P2O7@C复合储钠正极材料。该电极呈现了高工作电势（3.8 V）、大比容量（119 mAh g-1）、高倍率性能和循环稳定性（1000圈，64%容量保持率）。通过XRD精修和理论计算，确定了Mg取代最优占位，Mg-O间耦合作用和Mg/Mn间相互作用加固了材料框架晶体结构，有效缓解了Jahn-Teller效应影响和提高电导率。2.采用电化学活化法，构筑了高稳定包覆型NaMn3(PO4)2P2O7@Mn3O4复合正极材料。该材料具有NaMn3(PO4)2P2O7颗粒表面附着Mn3O4纳米片的分级结构形貌，且存在Mn2+和Mn3+可变价离子。该电极展现了大比电容、超长循环寿命（20000圈, 90%容量保持率）和用作双极性电容器潜力。3.采用超晶格结构设计策略，构筑了高稳定阵列有序结构NaMn0.6Al0.4O2材料。层板超晶格结构的构筑，抑制了Mn元素的脱落，为Na+嵌/脱提供了更宽且更稳定通道，有利于Na+稳定快速传输，从而呈现优异的储钠性能。该策略被推广制备蜂窝有序型Na3Ni2RuO2储钠正极材料，呈现了超长工作电位平台和优异循环性能。4.采用表面偏析技术，制备了缺陷型氧化物包覆结构的NaMn0.6Al0.4O2@AlOx复合材料。该工作的设计在降低制备和原料成本基础上，减弱了层状锰基氧化物材料对潮湿环境敏和电解液的敏感，为构筑宽温度范围储钠电极材料提供了新策略。5.探究了高稳定结构Nb2O5、KNb3O8和硅氧烯等电极材料的制备方法，为构筑其它高稳定电极材料提供新思路。相关研究结果已被发表在Adv. Mater.、Angew. Chem.、ACS Nano、Small等国际知名期刊(7篇)，申请发明专利2项，培养硕士和博士研究生多名。