Investigation of energy density limitation for lithium sulfur batteries

锂离子电池的能量密度有限，需要一种替代电池化学方法来继续改变当前的能源格局。可充电锂硫（Li-S）电池是未来储能应用中最有前途的高能量密度电化学设备之一。然而，锂硫电池的内在限制可能会降低其可实现的能量密度。迄今为止，这种类型的电池的性能一直受到容量损失和退化的限制，这是由于电极上活性物质（硫）的永久损失以及电极与电解质的反应造成的。到目前为止，开发人员已经使用多余的电解质来稀释导致性能降低的副反应。该项目将采用实验和理论相结合的方法来研究高负载高能锂电池的关键问题。将建立专门设计的阴极结构和电解质配置来分析锂多硫化物（Li polysulfide species, LiPS）溶解度对电池容量和电池比能的影响。该项目将提供有关导致产能损失和退化的操作条件的知识。该项目还将把研究成果整合到公开可用的电化学系统模拟器（ESS）中。基础研究项目将侧重于采用实验和理论相结合的方法研究高负载和高能锂电池的两个关键问题。第一个主题包括研究多硫化锂（LiPS）溶解度对电池容量的影响。实验将解决具有不同和明确的初始放电状态的LiPS饱和条件的创建，然后表征Li-S电池在这些LiPS饱和条件下的性能。实验还将研究lip还原的潜在反应途径的速率依赖性。第二个主题是关于固体产品在阴极上沉积的实验验证和理论建模。本主题的重点是利用电化学测量结合材料表征方法，包括透射电子显微镜（TEM）和x射线光电子能谱（XPS），研究Li2S/Li2S2的沉积过程。Li-S电池的可行性建模将包括实验验证的固体产品沉积过程，以及在所建模型中分析LiPS的溶解度效应。该项目的基础知识和成果也将纳入电化学系统模拟器（ESS），这是一个电化学系统的仿真包，将理论模型纳入用户友好的电池和电路模拟器。ESS将是一个统一的框架，用户可以在其中定义自己的电化学设备，将其离散在有限元网格上，并进行一维（1D），二维（2D）和三维（3D）模拟，以研究传输并预测电池的充放电曲线和电化学阻抗谱。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Lithium ion batteries have limited energy density, and an alternative battery chemistry is needed to continue to transform the current energy landscape. Rechargeable lithium-sulfur (Li-S) batteries are among the most promising high-energy-density electrochemical devices for future energy storage applications. However, there are intrinsic limitations that potentially lower the achievable energy density of Li-S batteries. To date, performance of this battery type has been limited by capacity loss and degradation due to permanent loss of active material (sulfur) from the electrode and from reactions of the electrode with the electrolyte. To date, developers have used excess electrolyte to dilute the side reactions that occur that result in lowered performance. This project will use combined experimental and theoretical approaches to study critical issues for high-loading and high-energy Li-S batteries. Specially designed cathode structures and electrolyte configurations will be built to analyze the effects of Li polysulfide species (LiPS) solubility on cell capacity and battery specific energy. The project will yield knowledge on the operating conditions that lead to capacity loss and degradation. The project will also integrate the research outcomes into publicly available electrochemical system simulator (ESS). The fundamental research project will focus on using combined experimental and theoretical approaches to study two critical issues for high loading and high energy Li-S batteries. The first theme includes studies of the effect of lithium polysulfide (LiPS) solubility on cell capacity. Experiments will address the creation of LiPS saturated conditions with different and well-defined initial states-of-discharge and then the characterization of Li-S cell performance under these LiPS saturated conditions. The experiments will also investigate the rate dependence of the potential reaction pathways for LiPS reduction. The second theme addresses experimental verification and theoretical modeling of solid product deposition on the cathode. Focus of this theme is on the study of the Li2S/Li2S2 deposition process using electrochemical measurement combined with material characterization methods, including transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The accompanying feasibility modeling of a Li-S battery will incorporate the experimental verified solid product deposition process, as well as the analysis of the LiPS solubility effect in the built model. The fundamental knowledge and outcomes of this project will also be incorporated into an Electrochemical Systems Simulator (ESS) which is a simulation package for electrochemical systems that incorporates the theoretical models into a user-friendly battery and circuit simulator. The ESS will be a unified framework, in which users can define their own electrochemical devices, discretize them on finite element grids, and perform one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) simulations to study the transport and predict charge and discharge curves and the electrochemical impedance spectra of the cells.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.