**1.1. Energy supply**

Utilizing an inexpensive, clean and sustainable supply of energy is one of the world's foremost challenges heading into the future. The present energy supply scenario is dominated by fossil fuels, which are both a finite resource and a substantial contributor greenhouse gas emissions. Many renewable sources of energy (e.g., nuclear, solar, wind, etc.) exist for consumer use, although they all have associated pros and cons which means they cannot be used ubiquitously across the planet [1]. As a result, the future supply of energy is not likely to be centralized in a limited number of large power stations, but rather much more distributed as smaller scale renewable energy sources are utilized.

Much has been made in the literature concerning solar energy harvesting, both in terms of photovoltaics and solar thermal. Of all the renewable forms of energy, solar energy has the capacity to completely replace society's dependence on fossil fuels. However, of course, the challenge remains to make this a reality, particularly so with the high cost of photovoltaics [1]. Another perceived problem with the use of photovoltaics, and indeed with many other renewable energy sources, is their intermittency. Whether this be over short time frames, such as with cloud cover, or extended periods of time, such as overnight, steps need to be taken to ensure the consistency of power supply. In other words, some form of energy storage must be present to complement the primary source of energy.

## **1.2. Energy storage**

Energy can be stored in many different ways, some examples of which include [2]:

© 2012 Dose and Donne, licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 Dose and Donne, licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Each of these types of energy storage has its own set of performance characteristics in terms of the energy and power that they can deliver, ultimately meaning that they will be best suited in specific applications. Of course cyclability is also a key performance characteristic.

Monitoring the Effects of Thermal

Treatment on Properties and Performance During Battery Material Synthesis 271

Material properties such as phase purity, crystallinity and particle size (or extent of

Many different synthetic routes have been used to prepare the materials mentioned in the previous section, so much so that to list them here would be excessive (note the recent review in reference [6]). Nevertheless, the more common approaches can be categorized as being based on either (i) thermal methods, (ii) solvothermal methods, (iii) mechanical methods, and (iv) electrochemical methods. It is also reasonably common to find that a combination of these methods has been used to produce the resultant material. As an example, LiFePO4 can be made by first using a solvothermal process to intimately mix the precursors, with the resultant mixture then subjected to a thermal treatment to make the final product [7]. Overall, the majority of the positive electroactive materials listed above

The overall objective of any synthesis method is to obtain the final product in the desired form for immediate use. This is particularly true for thermal synthesis methods where there is a delicate balance between heat treatment temperature and duration so as to produce the desired material. Of course the choice of these thermal parameters is also dependent on the effectiveness of precursor mixing, with various solvothermal methods being used to ensure appropriate mixing on the molecular level. Contrast this with some of the initial solid state mixing methods (grinding) used in some synthetic efforts, and the implications it has on the

Let us begin by assuming that we have sufficient mixing of our precursors, since the focus of the discussion here is on the actual thermal conditions to be used. Under these circumstances if we were to thermally treat this mixture the temperature and duration of heat treatment would determine the phase purity and crystallinity of the resultant material. Of course a higher heat treatment temperature, and a longer heat treatment duration would ensure phase purity, as well as lead to a more crystalline material. The question at this time

Many positive electroactive materials in Li-ion batteries require very small crystallite sizes so as to minimize Li+ ion diffusion paths, which is commonly regarded as a key limiting factor in performance [7]. Therefore, excessive heat treatment temperatures and durations, while they may ensure phase purity, also lead to excessive crystallization, which is detrimental. Additionally from a commercial perspective, excessive material heating leads to a waste of energy, which can be costly. What is required, therefore, is a method for predicting the optimum heat treatment temperature and duration so as to ensure phase

involve a thermal processing step as the last step in their synthesis.

**1.5. Pitfalls of thermal processing methods** 

then becomes: What is the preferred material crystallinity?

thermal conditions necessary [8].

purity and small crystallite size.

agglomeration) all affect performance.

**1.4. Common synthetic routes** 

Chemical energy, stored as a fuel, can deliver very high specific power and energy, with reasonable efficiency, particularly when it is used in an internal combustion engine [3]. However, such a combustion reaction does little to abate the demand for fossil fuels (which are used most commonly in this domain) or the contributions to greenhouse gas emissions.

Chemical energy storage has an added advantage in the sense that it can also be released electrochemically (rather than thermally), through devices such as batteries, supercapacitors and fuel cells [4]. While the specific energy and power performance of these devices is much less than that of the internal combustion engine, their efficiency is much higher, in some instances approaching 100%, meaning that they ultimately utilize any fuel much better.
