Transition to zero pollution

By Waseem Marzook, a member of the Transition to Zero Pollution cohort.

Electric vehicles (EVs) are key to achieving a carbon neutral and pollution free society. Transportation makes up a significant proportion of the global carbon footprint; one of the quickest and easiest way to greatly reduce that footprint is through the mass adoption of EVs, replacing all the fossil-fuel-powered vehicles on the road.

The most important component in any EV is the battery pack. Primarily powered by several lithium ion cells, EVs need long driving ranges, fast charging, and long warranties to compete with their fossil-fuel powered counterparts. This requires high capacity battery packs that are efficiently cooled and optimised for weight and cell lifetime.

Batteries age?

Unlike a petrol fuel tank, batteries age over time; the more they are used, and the more time that passes, the more their performance deteriorates. They store less charge, become more inefficient and deliver less peak power. For EVs this means that the maximum range and power are always reducing. Slowing the rate of this ageing, therefore, is a key component in improving EVs.

There are many factors that affect the rate of ageing such as current and the amount of charge in the battery. One of the biggest factors is temperature, extreme temperature both hot and cold have negative effects on battery life.

Keeping them cool

The key problem with fast charging is keeping the battery pack within a safe operating temperature. The battery pack generates a lot of heat while fast charging and this heat needs to be removed efficiently to keep all the cells at a safe and uniform temperature. Battery packs need to be cooled uniformly, as if you have one side of you pack in an optimal range but the other getting very hot, the hot side will age faster than the cold side. This can lead to premature failure of the entire pack.

Cell Cooling Coefficient

The Cell Cooling Coefficient (CCC) is a new universal measurement metric for characterising how efficiently a cell can be cooled. It tells you the temperature difference that will occur in a cell when a specified amount of heat is removed from it. My research involves developing this metric for cylindrical cells. Carefully designed rigs are used to experimentally measure the CCC of cylindrical cells of different sizes and under different cooling schemes, such as cooling the base of the cylinder or the sides. Longer term testing will show which cooling schemes are better at slowing down the ageing rate, coupling this with modelling of the CCC, this work will help identify where the thermal performance of these cells can be improved.

Cell manufacturers can use this metric optimise to their cells and produce the best thermally performing cell. As well as helping pack manufactures to compare a wide range of cells from different manufacturers, they will also be able to pick the best cell based on thermal performance for their cooling system. Ultimately, this will help develop battery packs that can be charged faster and which last longer. This will help mitigate some of the biggest downsides to electric vehicles and increase their desirability over fossil-fuel-powered vehicles, taking us a step closer to achieving a zero-pollution and carbon neutral planet.

Read PhD Insights: Making electric vehicles work for a better future in full

By Albert Fabregas Flavia, a member of the Transition to Zero Pollution cohort.

According to a recent UN report, the world’s population is expected to rise from 7.7 billion to 9.7 billion by 2050 and reach 11 billion by 2100. Such an increase in population will inevitably lead to a proportional increase in the demand for food. Producing enough food to satisfy the needs of this growing population (and doing so sustainably) is, therefore, a pressing global challenge.

Currently, staple food production relies heavily on the use of synthetic nitrogen fertilisers. However, considerable amounts of synthetic nitrogen are lost to the environment in the form of nitrate leaching or as ammonia and nitrous oxide emissions, causing air and water pollution across the globe and contributing to global warming.

Interestingly, a few soil-dwelling bacteria have long been known to be capable of converting the nitrogen in the atmosphere into nitrogen fertiliser. Using these bacteria as bio-fertilisers has therefore been proposed as a way to reduce agriculture’s harmful over dependence on synthetic nitrogen fertilisers. Yet, the process for converting atmospheric nitrogen into fertiliser is highly demanding for the bacteria and is likely to result in a severe “fitness cost” (that is, a negative impact on the bacteria’s ability to grow and replicate and therefore its viability as an eco alternative), preventing the potential use of these bacteria as bio-fertilisers in agriculture.

As part of Imperial’s commitment towards a zero-pollution future, our project we will be taking an innovative approach to tackling the bacterial fitness cost associated with synthesising nitrogen fertiliser from the air. Because, to paraphrase Bob Dylan, we think the answer to the question of how to feed the world sustainably might well be “blowing in the wind”.

Read PhD Insights: Finding new ways to feed the world in full

By Marcus Annegarn, member of the Transition to Zero Pollution cohort of PhD students

The title of my project is ‘Understanding the electronic and physical structure of particulate matter through theory and experiment’, and its aim is to help experimentalists detect and analyse particulate matter in London’s air.

What is particulate matter?

Particulate matter (or PM for short) are microscopic particles that exist in the air that we breathe. They can consist of a wide range of materials and across many shapes and sizes. They are often categorised by their size.

For example, PM10 is used to denote particles which are less than 10 microns in size and PM2.5 denotes particles that are less than 2.5 microns in size.  For reference, a human hair is about 180 microns in width.

So what’s the big deal? Short answer: Your lungs! Exposure to PM has been linked to both minor and severe health risks. This can result in short term affects such as a runny nose, coughing and shortness of breath.  Prolonged exposure has been linked to increased mortality and prevalence of respiratory diseases, particularly amongst at risk groups such as children, the elderly, and those with pre-existing conditions such as asthma.

The smaller particles are believed to be more dangerous as they can penetrate deep into your lungs, even so far as into the membranes where oxygen is passed into your blood. The smaller particles also have a large surface area to volume ratio and more surface area allows for more harmful interactions with your lungs; for example, it is believed that small metallic particles can promote oxidation and thus severe damage to lung tissues.

However, the mechanism by which they affect our lungs is not yet fully understood. Nor which sizes and materials may be the most harmful. It is also hard to identify the exact size and composition of the particles.

Where does PM come from? 

PM can come from a wide range of sources. Outdoor sources include any sort of combustion engine as well as other vehicular sources such as brake pads, car tyres, roads, train tracks etc. Factories, open fires, and power plants can also contribute.

Indoor sources can come from fires, using gas heaters and stoves, cooking oil and even other household appliances such as air-conditioners.

How do we detect them? (Where I fit in)

The techniques often used to detect and analyse PM include X-ray absorption spectroscopy (XAS) and Electron Energy Loss Spectroscopy (EELS).

Both techniques result in a characteristic spectrum that gives information about the energy of the core electrons in the PM. From this information you can deduce which elements are present in the PM and in what configuration (i.e what material). The difficulty is that, to get this information, you need to match the spectra to a pre-existing spectrum of a known material.

My work involves using quantum chemistry software to try and predict spectra from theory so that we can use them to fingerprint and identify experimental spectra.

The hope is that this can lead to better understanding of what is out there and, in the future, which forms of PM are the most dangerous so that we can develop a targeted approach to mitigating the effect of air pollution on human health.

Read PhD Insights: Why Particulate Matter matters in full