随着全球能源需求的不断增长和环境保护意识的日益增强，开发高效、可持续的能源存储和转换技术成为科研领域的重要课题。锂-二氧化碳（Li-CO₂）电池作为一种新兴的能源存储技术，以其独特的双重优势——既能实现CO₂的转化利用，又能提供高能量密度的能量存储，近年来引起了广泛的关注和研究。然而，Li-CO₂电池在实际应用中仍面临诸多挑战，如动力学迟滞、产物不可逆堆积以及锂负极稳定性差等问题，这些问题严重限制了其商业化进程。本文针对锂-二氧化碳（Li-CO₂）电池存在的反应动力学迟滞、放电产物不可逆堆积等关键科学问题，通过创新性设计高效正极催化材料及优化电解液体系，系统开展了性能提升机制与反应路径调控研究。主要研究成果如下：

(1) 通过热退火处理Ti₃C₂T_x表面官能团以提升Li-CO₂电池性能，旨在探索通过热退火处理对Ti₃C₂T_x MXene材料的表面官能团的影响。通过系统研究不同退火温度（500-800℃）对Ti3C₂Tₓ表面端基的影响规律，发现500℃（TC500）是最佳退火温度，该条件下制备的Ti3C₂Tₓ能够保持MXene的层状结构，同时去除表面不利官能团，避免了因生成TiO₂而导致的结构坍塌及活性位点失活。电化学测试表明，基于TC500的Li-CO₂电池展现出15740.38 mAh g^-1的高比容量（100 mA g^-1）和700小时的长循环稳定性，在500 mA g^-1大电流密度下可稳定循环110次。非原位表征和理论计算进一步揭示了精确热退火策略能减少不可逆反应，促进碳酸锂的分解。该研究为MXene基催化剂在Li-CO₂电池中的应用提供了新的设计思路和理论指导。

(2) 二维V₂CT_x MXene材料V元素具有多价态特性及高氧化活性，但层间堆叠导致的活性位点遮蔽、离子扩散受限及结构坍塌等问题严重制约电化学性能。开发三维多孔VO_x@V₂CT_x/rGO（VVrG）复合气凝胶正极催化剂。通过水热-冷冻干燥协同策略，成功构建VVrG复合气凝胶，V-O-C异质界面诱导的局域电子富集效应，显著加速CO₂转化动力学。XPS与SEM分析证实，VVrG独特的空间限域效应可调控放电产物以花簇状疏松形态生长，避免致密钝化层形成。组装的Li-CO₂电池在200 mA g^-1电流密度下实现1900小时超长循环寿命。本研究为突破二维MXene材料在金属-气体电池中的动力学瓶颈提供了结构-界面协同优化新思路。

(3) 针对其放电过程中碳酸锂Li₂CO₃分解动力学缓慢导致的极化严重和循环寿命短的问题，提出了一种创新的解决方案。通过DFT理论计算预测了在不同电解液中Li-CO₂电池的放电产物，结果显示，双溶剂体系通过形成独特的Li⁺-溶剂配位结构，有效稳定C₂O₄²⁻中间体，配合柔性Ru nanodots@CNTs正极催化剂更容易生成易分解的Li₂C₂O₄放电产物。采用湿化学法制备的Ru nanodots@CNTs催化剂具有优异的结构、组成和电化学性能。实验结果表明，采用LiTFSI/双溶剂电解质的Ru nanodots@CNTs正极表现出高可逆放电容量（18962 mAh g^-1）、高放电平台（2.97 V）和卓越的循环稳定性（1500小时），并有效稳定锂金属负极界面。提高了电池的整体性能。该研究通过"催化剂设计-电解液调控"的协同策略，为高能量密度金属-气体电池的开发提供了新范式。

关键词: Li-CO₂电池；正极催化剂；MXene材料；碳纳米管；电解液

研究类型: 基础研究

With the increasing global energy demand and growing environmental awareness, the development of efficient and sustainable energy storage and conversion technologies has become a significant focus in the scientific research community. Lithium-carbon dioxide (Li-CO₂) batteries, as an emerging energy storage technology, have garnered widespread attention and research interest due to their unique dual advantages: the ability to convert and utilize CO₂ while providing high energy density storage. However, Li-CO₂ batteries still face numerous challenges in practical applications, such as kinetic hysteresis, irreversible product accumulation, and poor lithium anode stability, which severely hinder their commercialization. This paper addresses key scientific issues in Li-CO₂ batteries, including reaction kinetic hysteresis and irreversible discharge product accumulation, through innovative design of efficient cathode catalytic materials and optimization of the electrolyte system. The research systematically explores performance enhancement mechanisms and reaction pathway regulation. The main research findings are as follows:

(1) This study innovatively developed a precise thermal annealing strategy based on low-oxygen Ti₃C₂ MXene. By systematically investigating the effects of different annealing temperatures (500-800°C) on the surface terminal groups of Ti₃C₂Tₓ, it was found that 500°C (TC500) was the optimal annealing temperature. Under this condition, the prepared Ti₃C₂Tₓ maintained a complete two-dimensional layered structure while effectively removing unfavorable functional groups on the MXene surface, avoiding structural collapse and active site deactivation caused by TiO₂ formation. Electrochemical tests demonstrated that Li-CO₂ batteries based on TC500 exhibited a high specific capacity of 15740.38 mAh g^-1 (at 100 mA g^-1) and long cycle stability of 700 hours, with stable cycling for 110 cycles at a high current density of 500 mA g^-1. Ex situ characterization and theoretical calculations further reveal that a precise thermal annealing strategy can reduce irreversible reactions, promoting the decomposition of lithium carbonate and thereby enhancing the battery's electrochemical performance. This study provides new design insights and theoretical guidance for the application of MXene-based catalysts in Li-CO₂ batteries.

(2) The V element of the two-dimensional V₂CT_x MXene material has polyvalence characteristics and high oxidation activity, but the problems caused by interlayer stacking such as active site masking, limited ion diffusion and structural collapse seriously limit the electrochemical performance. Development of a three-dimensional porous VOx@V₂CT_x/rGO (VVrG) composite aerogel cathode catalyst. The VVrG composite aerogel was successfully constructed by the synergistic strategy of hydrothermal-freeze-drying, and the local electron enrichment effect induced by the V-O-C heterogeneous interface significantly accelerated the CO₂ conversion kinetics. XPS and SEM analysis confirmed that the unique spatial confinement effect of VVrG could regulate the growth of discharge products in a loose flower cluster and avoid the formation of a dense passivation layer. The assembled Li-CO₂ battery achieves an ultra-long cycle life of 1900 hours at a current density of 200 mA g^-1. This study provides a new idea for structure-interface co-optimization to break through the dynamic bottleneck of two-dimensional MXene materials in metal-gas batteries.

(3) This study designed a ruthenium nanodot/dual-solvent electrolyte synergistic catalytic system. DFT theoretical calculations predicted the discharge products of Li-CO₂ batteries in different electrolytes. The results showed that the dual-solvent system, by forming a unique Li⁺-solvent coordination structure, effectively stabilized the C₂O₄²⁻ intermediate. Coupled with the flexible Ru nanodots@CNTs cathode catalyst, it facilitated the formation of thermally unstable Li₂C₂O₄ discharge products. The Ru nanodots@CNTs catalyst, prepared via wet chemistry, exhibited excellent structural, compositional, and electrochemical properties. Experimental results demonstrated that the Ru nanodots@CNTs cathode with LiTFSI/dual-solvent electrolyte displayed high reversible discharge capacity (18962 mAh g-1), high discharge plateau (2.97 V), and outstanding cycle stability (1500 hours), while effectively stabilizing the lithium metal anode interface. This study, through a "catalyst design-electrolyte regulation-interface optimization" multi-level synergistic strategy, provides a new paradigm for the development of high-energy-density metal-gas batteries.

Key words: Li-CO₂ batteries; cathode catalysts; MXene materials; carbon nanotubes; electrolytes 

Thesis: Fundamental Research