硅基锂电池负极材料的仿生梯度化设计与制备

The rapid development of emerging industries such as electric vehicles and wearable electronics demands high-performance power supplies, which are commonly performed by the rechargeable Li-ion batteries (LIBs). High-performance LIBs necessitate anode materials with high capacity and long lifespan. Due to its matchless capacity, silicon (Si) was deemed as one of the most promising anode materials for the next-generation LIBs. Unfortunately, such bright prospect of Si is dimmed by its large volume change during the process of lithiation and delithiation, which would lead to the mechanical damage of the anode materials and delamination from the current collector. Although a lot of efforts have been made so far to tackle this problem, the attentions of previous studies were mainly focused on the development of various structured nano Si particles. Inspired by the design strategies learned from the natural biological materials, in this project we plan to study the mechanical behavior of Si-based anode material with graded Si content in the process of lithiation and delithiation. The objective of this project is to mitigate or even remove the concentration of interface stress between the anode material and current collector induced by the large volume change of Si by controlling the gradient of Si content in anode materials. This project is expected to obtain prospective results that would be of great value to the improvement of electrochemical performance of Si-based anode material for LIBs and facilitate the advent of the next-generation high-performance LIBs.

随着新能源汽车、可穿戴电子产品等新兴产业的蓬勃发展，常用碳基锂电池负极材料因比容量较低渐渐不能满足产业的要求。寻求高性能锂电池负极材料势在必行。硅因其出众的比容量被视为最具前景的下一代锂电池负极材料。但硅在充放锂过程中体积变化很大，不仅会导致其自身结构的破坏，而且会引起其与外围结构（如集流体）的脱离，最终导致锂电池电化学性能的急速下降。为了解决这个问题，人们尝试了许多方法，但主要还是集中在硅纳米颗粒的功能结构化方面。受天然生物材料设计理念的启发，本项目将从功能梯度的角度出发，研究梯度硅含量对硅基负极材料在充放锂过程中的力学行为和电化学性能的影响。力求通过调控和优化硅基负极材料中硅含量的空间分布来减小或消除其与集流体之间在充放锂过程中产生的界面应力集中，从而提高锂电池的循环稳定性。本项目的预期成果将促进下一代高性能硅基锂电池的问世，帮助相关新兴产业摆脱能源瓶颈问题的束缚。

硅基负极材料由于其出众的比容量，在新一代高性能锂电池中具有巨大的应用潜力。然而，硅材料在充放锂的过程中，会产生高达300-400%的体积变化，从而造成硅材料自身的碎裂以及与所贴附的集流体之间脱层等一系列的力学问题。本项目针对硅基负极材料层与集流体之间的脱层问题，对硅基负极材料层的结构进行了梯度化的结构优化设计与改进。传统的硅基负极材料层厚度均匀，且内部硅纳米颗粒随机均匀分布。我们分别采用了两种不同的梯度化策略。一种是将硅颗粒浓度沿厚度方向进行梯度化，但负极材料层厚度均匀；另一种是硅颗粒浓度均匀，而负极材料层由中心向外厚度递减。实验测试结果表明，两种梯度化设计都能有效地解决脱层问题，并且提高锂电池的电化学性能，包括循环性能，以及容量和负载等。此外，我们还对两种策略的有效性进行了力学分析，从界面力学的角度阐明了上述梯度化设计有效性的力学机理，即梯度化设计可以有效减小界面因负极材料膨胀所造成的剪应力的应力集中，增加了负极材料层和集流体界面的有效强度，从而提高了负极材料层和集流体之间的导电性以及锂电池的电化学性能。在此基础上， 我们还进一步地从理论上提出了能使界面剪应力完全均匀的最优的梯度厚度设计方案，并进行了实验验证。本项目对涂层和基底系统由于应变错配引起的界面剪应力的均匀化调控提供了理论基础和可行性方案。同时，本项目在不改变材料组份，不增加材料成本的基础上，通过结构优化提高了硅基锂电池的电化学性能。该技术对新型锂电池的设计与优化具有重要的意义和应用价值。