Battery Materials

Battery Materials Literature Project

by Fiona S. Oberbeck

Chemistry 713 Chemistry of Representative Elements Dr. Hans-Conrad zur Loye

Battery Materials Fiona S. Oberbeck

Table of Contents 1. Introduction

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2. Conventional Batteries

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3. Future Battery Materials

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3.1 Ultra-fast Chargeable Batteries -43.2 Biological Components in Batteries

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3.3 Flexible Batteries

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4. Conclusions

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5. References

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Battery Materials Fiona S. Oberbeck 1)

Introduction: [9,10,11]

Since the dawn of the computer age, everything has to be tiny, fast and portable and the need for more improved battery materials is a big issue for researchers. Making batteries which are light in weight, easy to recharge, and especially non toxic if they ever get damaged is a goal that is not yet manageable, but research has gone a long way in the last two centuries. The first battery-like device was published by L. Galvani in 1791 who did studies with froglegs6 finding that there is a current if the tissue of the animal leg is connected to metal electrodes which was followed by A. Volta’s experiments with electrochemical cells in 1800. Supposing that there are no chemical reactions in a cell and that the cells are inexhaustible, Volta was disproved by M. Faraday in 1834 who showed that the reactions in those cells are not inexhaustible, but that there is an ion flow between the electrodes. In 1836 J.F. Daniell managed to build the first battery with a somewhat reliable current made of a zinc and a copper electrode with the respective sulfate solutions, connected by a salt bridge to provide the ability of ion flow. Because of this assembly’s simplicity it is still used in classrooms to teach students the concept of batteries and the theories behind it. Twenty three years later, in 1859, G. Planté invented the lead-acid battery which is nowadays the oldest known rechargeable cell and the most commonly used battery in cars. Using lead oxide and sulfuric acid,, it is also a quite dangerous element whenit’s casing is compromised. In 1868 G. Lechlanché invented the first single fluid electric generating battery which is still used today in the zinc-carbon dry cell as a small rechargeable device. In the following years the research for new battery materials had its renaissance and is still a very important field since rechargeability, size of voltage output and lifetime are still in development and have not yet been brought to perfection. While the old devices with metal electrodes are still dominating the market, researchers try to find various new ways to approach new concepts for storing energy in ways that sick out compared to the last 150 years.

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Battery Materials Fiona S. Oberbeck

2)Conventional Batteries The most common and best known battery of today is the lead-acid battery invented by Planté. It’s simple setup and its high voltage output makes it an essential device for the auto industry since it can undergo about 500-800 recharges. Damaging on the mantle though can be dangerous for its user since it holds diluted sulfuric acid which can cause serious irritation of the skin and corrode random materials. Also the sulfuric acid can cause an explosion of the battery if the engine gets too hot. Another very common version is the alkaline battery which is commercially available in various sizes and brands. The electrodes are made out of zinc powder as the anode and manganese dioxide as the cathode with potassium hydroxide serving as the electrolyte. With its nominal output of 1.5 V and the ability to achieve higher voltage by adding several cells together, it is mostly used for small electrical devices like digital cameras or portable video game consoles. The alkali batteries are rechargeable, but over the time it is more than likely that the potassium hydroxide will leak out and can cause skin irritation. The rival of the alkali batteries is the zinc-carbon dry cell which is also known as a Leclanché cell. This cell consists of a zinc liner which serves as the anode, a carbon rod in the middle surrounded by manganese (IV) oxide which serves as the cathode, and ammonium chloride as the electrolyte. It is a primary cell, meaning it is not rechargeable and has to be disposed after it is discharged. Equally popular but with a broader range of voltage, the lithium battery reaches from an output of 1.5 V up to 3.7 V. Since there a many different combinations of cathodes and electrolytes, the lithium battery can be used with different cathodes but it always uses lithium as an anode. As well as the cathode/electrolyte range, the toxicity of the components varies from setup to setup. The downside of this cell is not just that it is mostly a primary cell like the zinc-carbon dry cell, but also that it can discharge very rapidly when Page 4

Battery Materials Fiona S. Oberbeck

high currents are needed. One of the mostly used lithium cells is the lithiumion battery in which lithium is used as the anode, carbon as the cathode and manganese or cobalt salts as the electrolytes. The lithium ions travel trough the cell and are intercalated in the porous carbon. Unlike most lithium batteries this process is reversible and the cell is therefore rechargeable. It is, like the alkali battery, most commonly used in small electric devices. Since all of the batteries listed above only have a very limited output and lifetime, the need for long lasting, rechargeable, and powerful batteries with outputs that can exceed the conventional devices nowadays the need for new battery materials is given.

3) Future Battery Materials 3.1) Ultra-fast Chargeable Batteries5 A bright vision of the future are plug-in electric cars which do not pollute the atmosphere, have a piped down engine noise and run at least the same mileage per “tank” as conventional cars do. Sadly the reality is far away from this vision. The first models of this kind are without a doubt more silent than regular cars, but their efficiency is by far not comparable with a gasoline powered car. The major problem though seems to be the charging time of the batteries. Discharging times are too short and the time needed to recharge the device is simply too long. In studies done in the past this problem was faced in various ways. Since the lithium battery seems to be the most promising application the studies were focused on the different types of this battery and especially on the procedures on the surfaces of the compounds. A recent project on this research was done at the Massachusetts Institute of Technology using lithium phosphate assemblies. Given that the main problem with lithium devices is the migration through the electrolyte and the composites on the electrodes, the goal is to improve the ion and electron transport along the surface and through the bulk of the structure. One strategy to increase the rate performance was to shorten the path length of the electrons as well as the ions by introducing conducting nano-sized materials. During the studies it was found that the lithium ions only move along the [010] direction into the bulk and therefore attention was brought to increase the diffusion only in this Page 5

Battery Materials Fiona S. Oberbeck

direction since it is most efficient. Because it was found in previous studies that doped lithium phosphates are very stable and efficient conductors, LiFePO4 was used. To achieve the most effective compound, various compositions of the LiFePO4 were synthesized and analyzed. Finally LiFe0.9P0.95O4-δ was used for charge/discharge studies with very promising results (figure 1).

Figure 15: a Discharge rate capability after a slow charge and hold at 4.3 V of different discharge times (nC corresponds to a full discharge in 1/n hours); b Capacity retentions for full 50 full charge-discharge cycles at constant 20C and 60C current rates. The voltage varied between 2.3-4.3 V

The electrodes for the charge/discharge studies are made out of 80 wt% active material, 15 wt% carbon and 5 wt% polyethylenetatrafluoride as binder. In figure 1a, between the longest and the shortest discharging time there are surprisingly small differences in the capacity. For the 2C study the element still discharged to its theoretically estimated capacity of about 166 mA h/g and for the 50C study it only lost about 20% of its theoretical capacity. In figure 1b it is shown that even after 50 full charge/discharge cycles the capacity retention is still given for the 20C rate as well as for the 60C rate which is very important for a reliable device. Further studies were made to retrieve information about electricity delivery at high rates and therefore at very fast discharging times. In figure 2 the discharge capability after three different cycles for a discharge time of 18.3 seconds (197C) as well as Page 6

Figure 25: Discharge capability at very high rates

Battery Materials Fiona S. Oberbeck

9 seconds (397C) are shown. Since the electrodes need to be able to keep up with the high electron and ion migration, the composition of the electrodes has been changed for the high rate studies into 30 wt% active material, 65 wt% carbon and 5 wt% binder. The capacity was lowered enormously but still 100mA h/g for the 197C rate and 60mA h/g for the 397C rate were achieved. Considering that there is only the [010] travel direction makes the lithium ions traveling with a speed of less than 1 ms per 50 nm, which is the approximated particle size in the element. Since the limiting factor for successful batteries is the delivery of the lithium ions and the electrons to the surface and not just through the bulk, an amorphous layer with high lithium ion mobility was added to take away the anisotropy of the surface properties and therefore increase the ion delivery in the aspect of the [010] traveling direction of the LiFePO4. As a real application this battery might first be used in small devices like MP3 players or cell phones where the charging time could be reduced to 10 s by using a 360 W source and a 360C rate for a 1 W h device. Taken to a further level these results might allow electric cars holding a 15 kW h battery to be charged within 5 minutes using a 180 kW source. It is shown that the described batteries are able to deliver two orders of a magnitude more energy than a conventional lithium-ion battery and the charging time is only limited by the surface adsorption and surface transfer, which makes it able to compete with supercapacitors. 3.2) Biological Components in Batteries2 A new and widespread method that can be found in nearly all fields of research is the work with bacteriophages and viruses as templates for nanostructures. Since tiny electric devices are more common than ever the idea was near to use the well available natural templates also in the battery research as a biological toolkit. Special bacteriophages are easy to modify genetically by changing the sequence of the bases in the RNA or take out or add whole sequence chains. Also the surface of the bacteriophages can be easily modified by using the functional groups sticking out on the surface since the structure of the common species is well known. Because the biological templates have different structures on both endings the bacteriophages can be assembled to long nanowires or in highly organized structures. A.M. Belcher et al. at the Massachusetts Institute of Technology Page 7

Battery Materials Fiona S. Oberbeck

focused on using the M13 bacteria phage, which is 900 nm long and 6 nm in diameter. In figure 3 a schematic image of the M13 bacteriophage and its use in a high power device is shown. For better usage the major capsid gene VIII protein was modified to make it usable as an a-FePO4 template and the gene III protein was engineered to have high binding affinities for singlewalled carbon nanotubes (SCNs). Also a schematic diagram for the fabrication of genetically engineered M13 is shown and its application in a high-power lithium-ion battery cathode by powering a green light-emitting diode.

Figure 32: a schematic image of a genetically engineered M13 bacteria phage; b schematic diagram of building a high-power lithium-ion battery using the genetically engineered M13 bacteria phage as cathode with a photograph of the device used to power a green LED

The modified M13 bacteriophage has tetraglutamate (EEEE) added to the N terminus of each pVIII major coat protein subunit and is therefore called E4. Since the presence of carboxylic acid groups is majorly increased, the E4 can be used as a template for material growth hence the interaction with cations is also increased. To increase the attachment to the SCNs the already modified bacteriophage E4 had to undergo a second modification which does not interfere with the original one. For this case the minor coat protein gene III, which is located on the end of the bacteriophage, was chosen since the insertion of a foreign DNA can be controlled independently from the pVIII gene and the foreign DNA can encode the displayed peptides of the pIII gene. In order to find the ideal DNA with a very high affinity to the SCNs a variety of sequences were tried. The sequences N’-HGHPYQHLLRVL-C’, Page 8

Battery Materials Fiona S. Oberbeck

named MC#1, and N’-DMPRTTMSPPPR-C’, named MC#2, were chosen for further experiments. It turned out that even that the histidine found in the beginning of the sequence of MC#1, was observed often in bindings with carbon nanotubes, the MC#2 clone had a binding affinity that was about four times as high as the one from the MC#1 clone which again was about 2.5 times as high as the one found for the wild-type M13 bacteriophage. Even with the SCN it was not possible to align the genetically engineered bacteriophage, only the SCNs showed a highly organized structure (see figure 4).

Figure 42: TEM images of multifunctional M13 bacteria phages. A EC#2 covered with a-FePO4 without SCNs; B SCN only without any interaction with the EC#2 a-FePO4; C-E SCN attached to EC#2 a- FePO4 on different magnifications

In order to show the electrochemical properties the E4 a-FePO4 bacteriophage was tested without the SCNs first (see figure 5). The measurements were done at different discharge rates hence the rates were kept low. The rate performance in figure 5D shows the Ragone plot representing the specific power versus the specific energy. It was found that all of the E4 aFePO4 nanowires hold anhydrous Figure 5 : Characterization of the E4 a-FEPO4 nanowire system; A TEM image of E4 a-FePO ; B TGA curve of E4 asilver attached to functional FEPO4 nanowires; C and D electrochemical performance of E4 groups on the bacteriophage. a-FEPO4 nanowires tested between 2.0 and 4.3 V 2

4

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Battery Materials Fiona S. Oberbeck

In further studies the SCN attached bacteriophages, holding 5 wt% of singlewalled carbon nanotubes, were tested for their electrochemical properties. To see the actual difference cause by the special designed genetically engineered bacteriophage various different clones were tested in figure 6A. Furthermore a Ragone plot was used to show the improvement in the highpower performance. Compared to figure 5D the improvement is clearly visible for the SCN attached nanowire systems. In figure 6C the capacity retention is shown which was taken for 50 cycles at a 1C rate.

Figure 62: Electrochemical properties of the a-FePO4 covered E4 clones of the M13 bacteria phage attached to SCNs; A discharge curve at different rates for three different clones of the bacteria phage; B Ragone plot for different modifications; C capacity retention for 50 cycles at a 1C rate

Overall it was found by comparing the two electrochemical studies that the EC#2 modification with the SCN attachment is by far the better battery material. The energy density of the EC#s clone was found to be three times as big as the one for E4 for a specific power of 4 kW/kg at a rate of 10C. The EC#2 clone showed a capacity of 134 mA h/g which shows the well improved high-power performance. At a very low discharge rate of C/10 (10 hours) the E4 clone showed a capacity of 143 mA h/g whereas the EC#2 clone outplayed it by 27 mA h/g by showing a capacity of 170 mA h/g, which is an incredible improvement.

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Battery Materials Fiona S. Oberbeck

3.3) Flexible Batteries8 After tiny MP3 players flooded the market, the next possible new device might be a music player embedded in cloth or in back packs. The major problem is that all the batteries are stiff and cannot be bent at all. Flexible devices would open this possibility for the market, but what does it take to get a flexible battery? Currently there are some studies about building batteries which are made out of mostly plastic and avoid toxic and ignitable substances like acids or heavy metals. Since those materials are primary elements, and therefore not rechargeable, and have to be discarded after usage they are not very efficient yet. To solve this problem miniature lithium-ion batteries have been made with nanoparticles, like cobalt oxide covered virus templates as the cathode and lithium foil as the anode. Because of the incredibly small diameter of the metal oxide covering, the inorganic structure is very flexible. It also has a very high rate of counter-ion and electron transport throughput. Since inorganic structures sometimes can make it difficult for ions to move because they bend them in intercalations and migrations there are still some problems that are not completely solved yet. As mentioned above, plastic elements were taken in consideration as well. Because many problems can be controlled by changing different components of the polymer, they have a big advantage over lithium-ion devices. Primarily doped poly-acetylene compounds were used since their electric conductivity is known since the 1970s. This research did not succeed though since the poly-acetylene compounds have very low stability. As other polymers were considered, polyaniline and polypyrrole were obvious choices since they have reversible electrochemical doping behaviors. Unfortunately the doping levels of these compounds were too low and also not very chemically stable, which lead to self-discharge and therefore those materials were not efficient enough for everyday use. Other attempts were made to build a “sandwich” battery out of organic materials (see figure 7) in which the R groups in the electrodes had different redox potentials. The various R groups were attached to each other by polymer chains which gave the device its flexibility and also made an Page 11

Battery Materials Fiona S. Oberbeck

electron hopping between neighboring R groups possible. During the charging process the charge was stored by oxidation or respectively reduction on the different R groups. The difference of the redox potentials was the decisive factor for the voltage output.

Figure 78: Example of a flexible battery using an electrolyte captured between layers of polymers.

In spite of all those well elaborated features, the device still failed as well since the redox reaction of the core-shell turned out to be electrochemically irreversible and therefore it does not fulfill the requirements for a forward looking battery. Finally a successful application was found using organic polymers with radicals like nitroxides. These devices have a completely reversible redox reaction with fast electrode kinetics. Functioning as both electrodes (cathode as well as anode), the radical polymers have a big advantage since they can be easily tuned by changing the organic substituents in the two layers. These radical polymer batteries are very flexible, semitransparent and can be charged in less than 30 seconds. These new plastic batteries are compared to the conventional lithium-ion batteries non toxic, safer, since they do not hold an fluid electrolyte, and very easy to dispose. Also they are not limited by natural resources since their main elements are carbon and hydrogen. Page 12

Battery Materials Fiona S. Oberbeck

4)Conclusions Battery materials dominated a big research area over the last two decades and yet it seems to the eye of a layman like there were no innovating improvements. By taking a closer look, the research is rapidly progressing and new ideas are realized every day. However the methods are not yet improved enough to start large-scale productions. In 3.1 it was shown that ultra fast chargeable and dischargeable batteries are impending and that they are able to compete with the filling time of a gas tank and might even be faster depending on the size of the electrochemical element. Even though other metal compounds show equal properties, lithium provides the biggest storage of energy with less weight which could be important for the efficiency of an electric car. More optimized electrode structures might push this device even further in its active energy storing by improving the conductivity for high outputs over a very short timeframe. A research field that sounds at least as promising as the ultra fast charging of lithium-ion batteries is the usage of biological components in energy storage devices. The combination of the genetically engineered M13 bacteriophage together with the single-walled carbon nanotubes is not just fast in charging and discharging but can also build miniature batteries which are still surprisingly efficient with the good retention of the capacity for various clones. By using different viruses or bacteriophages with equal abilities for genetic modifications but smaller in size, the batteries might even become more efficient since the area between the two electrodes might be used even more efficiently. For further studies, it is necessary to test shorter discharge time rates to get more information about useful Page 13

Battery Materials Fiona S. Oberbeck

changes on the electrodes or electrolytes of the battery. The simplicity, affordability, and availability of the particles make this field very promising for the future. The flexible devices described in 3.3 also give a broad outlook for the future since they open a whole field for energy storing with the organic radical polymers. Given a broader variety of R groups, the devices might be able to become even more efficient. Because there are no metals used they are more environmentally friendly in case of damage on the electrochemical element. Because of the wide variety of battery materials, only three different fields were mentioned in this paper. Yet there is still a large number of other promising fields like completely biological devices or an inexhaustible number of solid state elements which were not discussed. Overall the research on new battery materials is not yet exhausted but gives hope of a soon coming innovation on the large-scale market.

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References: 1) M. Armand, J.-M. Tarascon; Building better batteries; Nature, 451

(2008), 652-657 2) Y. J. Lee, H. Yi, W.-J. Kim, K. Kang, D. S. Yun, M. S. Strano, G. Ceder, A.

M. Belcher; Fabricating Genetically Engineered High-Power Lithium-Ion Batteries Using Multiple Virus Genes; Science, 324 (2009), 1051-1055 3) J. Alper; The Battery: Not Yet a Terminal Case; Science, 296 (2002),

1224-1226 4) B.C. Sales; Smaller Is Cooler; Science, 295 (2002), 1248-1249 5) B. Kang, G. Ceder; Battery materials for ultrafast charging and

discharging; Nature, 458 (2009), 190-193 6) N. Kipnis, Luigi Galvani and the Debate on Animal Electricity, 1791-

1800; Annals of Science, 44 (1987); 107-142 7) http://www.nature.com/news/2008/080818/full/news.2008.1047.html Page 14

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8) H. Nishide, K. Oyaizu; Toward Flexible Batteries; Science, 319 (2008),

737-738 9) E. Riedel, “Anorganische Chemie” 6th Edition, Walter de Gruyter, Berlin

2004 10)http://acswebcontent.acs.org/landmarks/drycell/history.html

11)http://www.ideafinder.com/history/inventions/battery.htm

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