Studentprojekt inom strukturkemi

Förslag till masteruppsats 2019/2020

Ångström Advanced Battery Centre

Novel analytical techniques:

Assembling and validating Archimedes’ in situ gas evolution setup for battery pouch cells

The student will begin with developing and assembling an Archimedes’ in situ gas evolution setup. The setup is based on Archimedes’ law, and utilizes a thin film load cell to measure the volume changes (see Aiken et al., Journal of the Electrochemical Society 2014 161: A1548-A1554). The setup will be validated using different gassing electrodes in pouch cell batteries. Optimization of the setup will be carried out to decrease noise as much as possible. Finally, extension of the setup to have multiple cells cycling at the same time will be looked into.


Solid state ceramic electrolytes:

Investigating the Li-LLZO interfacial properties as a function of synthesis method and current density

Garnet oxide solid-state electrolytes are one of the most promising solid-state electrolytes for practical use of the Li-metal anode for safe high energy density lithium-ion batteries. However, garnet oxides such as the Li7La3Zr2O12 (LLZO) suffer from lithium dendrite growth from the Li-metal anode during charging which causes short-circuiting of the battery. In this work, the student will study the effect of the different synthesis methods for LLZO on the critical current density (current density at which short-circuiting occurs) in Li-LLZO cells. The synthesis-structure relationship and associated physicochemical properties can affect the conductivity and grain boundaries of the LLZO powders. The relationships and results observed in this work can be used to better understand the Li-LLZO interface stability. Microscopy (SEM) and electrochemistry (EIS, CD) will be used as principal investigation techniques. Spectroscopy (XPS, Raman and ICP) and diffraction (XRD) will be used to further study the materials.


Binder systems:

Functional Binders for Silicon-based Lithium-ion Battery Anodes

Silicon is an abundant element, cheap and non toxic. Compared to traditionally used graphite, silicon offers higher gravimetric storage capacity (ten-fold) thanks to its ability to form an alloy with lithium. Unfortunately, this electrochemical reaction leads to a drastic volume change generating cracks on the electrode, limiting its mechanical stability and losing contact among the different constituents. The polymer binder, which is usually an inactive component, could be used to solve some of these issues. For example, incorporating functional groups to enhance the adhesion and mechanical properties as well as to facilitate the redox reaction of silicon. Therefore, the aim of this project is to prepare new polymer binders changing the chemical structures to achieve the desired properties. The project will involve the synthesis of polymers with different functional groups. Several techniques will be used to characterise these polymers, such as NMR, FTIR, TGA and DSC. Furthermore, their binding properties and compatibility with silicon will be explored.


Li-metal batteries:

Surface passivation of metallic lithium and its role in advanced Lithium-metal batteries

The need for higher energy densities in Li-ion batteries has spurred reconsideration of Li metal as advanced anode, thanks to its lightness, conductivity, very low redox potential and very high storage capacity, despite its critical drawback of surface instabilities upon cycling. The latter lead to severe disruption of the SEI layer and growth of dendrites, mossy deposits upon repeated charge/discharge, which cause early cell failure and internal short circuits. The goal of this project is to study the stability of passivated Li surfaces in both symmetrical Li/Li cells and full cells with LiFePO4 electrodes and the impact of such passivation on their electrochemical properties and related surface morphology. The project will comprise: 1) Literature study on Li plating/stripping, 2) Surface cleaning/modification of Li surface 3) Electrochemical experiments to study interface stability, 4) Electrolyte modification, 5) Optical and electron analyses of surface morphology, 6) Data analysis and result evaluation.


Lithium-sulfur batteries:

Photoelectron spectroscopy studies of coated and uncoated Li-metal

Li metal is particularly attractive as an anode for Li-ion batteries due to its high capacity. However, the high thickness of electrodes adds ‘dead’ weight while it typically suffers from Li dendrite growth and instability towards the electrolyte. The development of ultrathin (<20 µm) Li metal anodes and protective coatings may help to overcome these challenges. This thesis will investigate surface reactions between Li and various promising novel liquid electrolytes, especially those for Li-S batteries such as LiTFSI in DME/DOL solution with LiNO3 additive. Clean Li metal with/without protective coatings, will be soaked in the electrolyte formulations for fixed durations, and then the interfacial reactions will be studied by characterisation methods such as X-ray photoelectron spectroscopy and scanning electron microscopy. This will be complimented by selected cycling stability experiments and resistance measurements of symmetrical Li cells performed using the intermittent current interruption (ICI) method.


Spectroscopy and modelling of the SEI:

Understanding the electrode/electrolyte interphase on relevant Li-ion battery model systems through SERS and DFT

Despite its maturity, Li-ion battery systems involve very complex charge and mass transport phenomena, in particular near to, or in the interphase formed between the electrode and electrolyte, the so-called Solid Electrolyte Interphase (SEI) layer. To identify and gain a deeper understanding of such phenomena, we will in this project make use of Surface Enhanced Raman Spectroscopy  (SERS) in combination with computational materials modeling using the density functional theory (DFT). While conventional Raman spectroscopy is suitable for studying the near-surface changes occurring in electrode materials, SERS is a powerful tool in order to acquire a better understanding of interfacial phenomena, which could potentially lead to a breakthrough in the field. The idea of the project is to employ SERS in order to study the behavior of relevant Li-ion electrolyte molecules (organic carbonates, lithium salts, and additives) on gold model surfaces, and correlate the experimental results with those of simulations. The aim of this project is thus two-fold: i) develop strategies for efficient identification and classification of various active components in SEI layers, and 2) find routes to stabilize and tailor the composition of the SEI layer for long-term stability and optimal battery performance.


Battery materials recycling:

Recycling of lithium battery materials using a novel and green method

Along with the increase in development and use of lithium-ion batteries for different applications, there exist a serious concern regarding access too raw materials used for lithium-ion batteries. Cobalt (Co) and nickel (Ni) are two elements that are commonly used to prepare cathode materials such as LiCoO2, LiNi0.8Co0.15Al0.05O2 etc. However, these two elements are not abundant in nature and thus regarded as critical elements. One approach to solve this issue is to recycle materials used in lithium-ion batteries. The common methods for recycling have so far been based on pyrometallurgy and hydrometallurgy, but they suffer from complicated process and high cost. A novel and environmentally-friendly method based on using “deep eutectic” solvents has recently develop suggested. This project aims to develop efficient and cost-effective methods to recycle cobalt from lithium-ion batteries using environmentally friendly and green solvents. UV-Vis spectrometry and inductively coupled plasma optical emission spectrometry (ICP- OES) will be to evaluate the efficiency of recycling. The recycled cobalt will be characterized using x-ray diffraction.


Electrochemistry modelling:

Influence of electrochemical parameters and electrode morphology on Li-ion battery behaviour

Modeling and simulations have become necessary tools for accelerated understanding of battery performance. For better modelling the battery electrochemical processes, the utmost step is to have better understanding of electrochemical parameters and effect of electrode morphology on these parameters, which in turn controls the capacity of battery. Time and frequency dependent experiments are the most common techniques to study battery capacity and aging. This project will be focus on the effect of material characteristic parameters (like diff. coeff., rate constant, particle size) and morphology parameters (like porosity, tortuosity) on such time and frequency studies. The purpose of this project will be to identify the domains in time and frequency studies that are sensitive to particular parameters, so that we know which parameter should be controlled to have desired results.


Senast uppdaterad: 2021-03-11