锂电池凭借其高比能量、长循环寿命和环境友好等众多优势，在大规模储能、电动汽车及便携式电子设备等领域具有广阔的应用前景。然而，目前商业化锂电池多采用易燃的有机液态电解质，诸多因素可能引发电池起火，严重威胁到使用者的生命和财产安全。全固态锂电池采用不可燃的固态电解质取代有机电解液和隔膜，从根本上杜绝了电池的热失控风险，在高安全性的同时还有望具有更高的能量密度和更宽的工作温度范围。但是，全固态锂电池中负极界面的枝晶生长和界面副反应成为限制其性能的关键。为深入了解枝晶生长及界面反应机理，本文利用多尺度表征手段系统观测了-20 ℃~90 ℃范围内固态电解质中锂沉积的原始形貌，研究了不同温度下锂金属-硫化物界面的阻抗演化、反应产物及反应层纳米结构。进一步地，运用分子动力学模拟和第一性原理计算，阐明了温度对锂成核及生长过程的影响机理，及界面不稳定性的根源。在此基础上，进一步提出了非对称温度调控策略，通过在锂沉积的最佳温度进行充电，锂负极的循环寿命和容量保持率得到同步提升。将锂负极与其他金属复合形成合金负极，是抑制枝晶生长和界面反应的有效策略。以锂铟合金为代表，研究者普遍认为，锂铟负极与硫化物电解质的界面是十分稳定的。然而，与常规认知相悖，本研究首次发现，使用锂铟负极的全固态锂电池在高负载、大电流循环过程中存在锂铟枝晶的生长现象。进一步，本研究在时、空两个尺度上对锂铟枝晶的生长形貌进行了表征，并阐明了锂铟枝晶的生长机理，研究发现大电流、高负载和界面反应是引起枝晶生长的主要原因，这一发现为合金负极的开发和应用提供了重要指导。为抑制锂/锂铟枝晶生长和界面反应，提高电池能量密度，本文进一步开发了一种厚度仅为65 μm的改性硫化物固态电解质薄膜。通过对硫化物电解质和聚合物分别进行改性，该薄膜兼具高离子电导率和高电化学稳定性。电化学测试结果显示，该薄膜可在60 ℃下以1 C的倍率稳定循环1000圈以上，库伦效率高达99.99%。与传统固态锂电池相比，电池的能量密度和功率密度提升1个量级。
Due to the high energy, long cycling life and environmental friendliness, lithium batteries have broad application prospects in large-scale energy storage, electric vehicles, and portable electronic devices. However, the commercial lithium ion batteries use flammable organic liquid electrolytes, and many factors may cause the batteries to catch fire, seriously threatening the lives and property safety of users. All-solid-state lithium batteries (ASSLBs) replace organic electrolytes and diaphragms by non-flammable solid-state electrolyte, which fundamentally eliminates the risk of thermal runaway of batteries. In addition to the high safety, ASSLBs are expected to have higher energy density and wider operating temperature range. However, the problems of dendrite growth and interfacial side reactions at the anode interface become the bottleneck that seriously limit the development of ASSLBs.To understand the underlying mechanism of dendrite growth and interface reactions, we systematically observe the original morphology of Li deposition in sulfide electrolyte (SE) in the range of -20 ℃~90 ℃, and study the impedance evolution, products and nanostructures of the interphase layer at different temperatures by using multi-scale characterization methods. Furthermore, molecular dynamics simulations and first-principles calculations are used to elucidate the temperature effect on lithium nucleation and growth processes, as well as the source of interface instability. On this basis, an asymmetric temperature control strategy is further proposed. By charging at the optimal temperature of Li deposition, the cycling life and capacity retention of Li metal anode are simultaneously improved.Combining lithium metal with other metal to form alloy anode is an effective strategy to suppress dendrite growth and interfacial reactions. Represented by lithium-indium (Li-In) alloy, researchers generally believe that the interface between Li-In anode and SE is quite stable. However, contrary to the conventional cognition, this study firstly discover the growth of Li-In dendrites in ASSLBs during cycled at high-load and high-current. Based on this, the morphologies of Li-In dendrites are systematically chacracterizied in both time and space scale, and the growth mechanism of Li-In dendrites are further clarified by cryogenic transmission electron microscopy, electron energy loss spectroscopy and Ab Initio Molecular Dynamic simulations. The work find that high current, high load and the inerfacial reaction between SE and Li-In anode are important factors for the growth of Li-In dendrite, which provides important guidance for the development and application of alloy anodes.To suppress Li/Li-In dendrites and interfacial reactions of Li-SE interface, a modified sulfide electrolyte film with ~65 μm thickness is further developed. Through the separate modification on SE and polymer, the prepared electrolyte film both has high ionic conductivity and high electrochemical stability. The electrochemical measurements show that the full cell with electrolyte film can be stably cycled for more than 1000 cycles at 1 C rate at 60 ℃ with high Coulombic efficiency of 99.99%. Compared with the traditional solid-state lithium batteries, the specific energy and specific power of the battery are both increased by an order of magnitude.
