离子嵌入型电极材料记忆效应的研究

Owing to increasing fossil-fuel consumption and environmental pollution, saving energy and reducing emission are very significant to realize the sustainable development of present society, which accelerates the evolution of traditional motor vehicles to modern electric vehicles. The bottleneck of electric vehicles’ technology is to develop rechargeable batteries with large capacities and high powers, of which a most promising candidate is lithium-ion battery (LIB). Although the memory effect of LIB is much less than that of nickel-cadmium (Ni-Cd) and nickel-metal-hydride (Ni-MH) batteries, it indeed affects the estimation of the state of charge and the electrochemical kinetics during operation. In this project, we will study the memory effect of ion-insertion electrode materials, especially for LiFePO4 and Al-doped Li4Ti5O12. First, study the electrochemical phase transition and improve the many-particle model of memory effect, so that to describe the time-dependent memory effect in the presence of two-phase-coexisted particles; Second, change the electrochemical kinetics with cutoff voltages and analyze the unsymmetrical evolution of material states, in order to reveal the physical mechanism of memory effect; Third, control element doping and particle size to regulate the memory effect of two-phase materials. Thereby, this fundamental research in the memory effect of ion-insertion electrode materials will give some theoretical and practical supports to promote electrode materials, battery systems and electric vehicles.

面对能源和环境的压力，节能减排成为当今社会可持续发展的重要任务，这推动了传统汽车电气化技术变革。电动汽车技术的瓶颈是大容量、大功率的动力二次电池，其中锂离子电池最受关注。虽然锂离子电池的记忆效应远小于镍镉和镍氢电池的，但依然会对容量检测和输出功率等造成影响。本项目将研究离子嵌入型电极材料的记忆效应，尤其是两相材料LiFePO4和铝掺杂的Li4Ti5O12的记忆效应。通过对电极材料电化学相变的研究，改进记忆效应的多颗粒相变模型，描述记忆效应随两相共存颗粒变化的动态结果；利用截止电压来改变两相材料的动力学性能，研究材料状态的非对称变化，从而揭示记忆效应的物理机制；控制元素掺杂和颗粒尺寸来调控记忆效应，揭示相应的调控规律和机制。总之，本项目将通过对离子嵌入型电极材料记忆效应的基础研究，指导电极材料和电池系统的改进，促进电动汽车的发展。

对于锂离子电池，在几种商用的两相材料中都发现了记忆效应，即在充放电平台上的电压突起和台阶。我们通过自制的喷雾干燥设备合成了LiFePO4，其记忆效应显著取决于相变后的弛豫时间。到目前为止，尚未报道粒径对记忆效应的影响。我们研究了不同粒径的橄榄石LiFePO4的记忆效应，发现LiFePO4的记忆效应取决于粒径。值得注意的是，我们首次发现纳米LiFePO4的相变先于充电和放电过程，而微米LiFePO4的则同时或滞后发生。.铝掺杂可以导致Li4Ti5O12表现出显著的记忆效应，然而其背后的机理仍不清楚，除了基于电化学动力学的解释。我们深入研究了铝掺杂的Li4Ti5O12的记忆效应，并指出铝掺杂Li4Ti5O12的记忆效应源于尖晶石结构中8a和16c位之间的铝离子可逆迁移。在铝掺杂Li4Ti5O12复合材料中，我们还发现记忆效应和电化学振荡可以同时发生于充电过程，并且可以通过调节记忆效应来控制电化学振荡。.在锂离子电池中，微电极在基础研究和应用技术中都起着非常重要的作用。我们通过喷雾干燥法制备了具有丝状同轴结构的LiFePO4微电极，并且所制备的LiFePO4微电极具有高的比容量和良好的循环稳定性。我们还通过喷雾干燥法制备了无粘结剂的LiFePO4/C薄膜电极，所制得的电极显示出优异的循环稳定性，即使经过2000次循环也能很好地工作。近年来，原位表征技术取得了重大进展，尤其是在电化学领域。我们设计了两种基于纽扣电池的原位XRD和拉曼纽扣电池，它们具有许多令人赞叹的优点，例如成本低，循环寿命长，易于携带等。利用原位XRD和拉曼纽扣电池测量Li4Ti5O12和LiFePO4可以获得很好的结果。这些技术对于锂离子电池记忆效应的研究非常关键。