The amount of energy that can be stored by a battery depends on the specific battery technology being used and on the amount of material in the battery. For large-scale battery applications, therefore, such as storage of energy for grid-scale applications, the availability of battery materials is critical. However, other factors are also important, such as processing costs, battery assembly, and the cost of secondary components.
The integration of batteries into the energy supply system on a large scale is ultimately a systems problem that involves processing, structure, properties, and performance of materials with considerations of cost, policy, and environmental impacts. Furthermore, the system is so large that it will take at least a decade or two for a new technology to mature and have a significant impact.
“Grid-scale energy storage is considered to be the holy grail for electricity storage,” said David Bradwell. “Whether it’s supporting conventional resources such as nuclear, solar, or wind, there is a great demand to have storage on the grid in order to balance electricity supply and demand.”
The current electrical grid supplies power in real time in response to demand. When demand increases, output must increase. As demand changes throughout the day, generators ramp up and down to meet that demand. When supply and demand become decoupled, the result can be catastrophic failure, as was the case with the 2003 blackout that affected millions of people in the northeastern United States. When a few generators went down, there was no buffer in the system to account for the sudden decrease in supply.
Energy storage can act as a buffer on the grid. It can smooth out the power from intermittent renewables, such as solar and wind, and it can match the supply from generators on the grid powered by nuclear energy, natural gas, and coal.
Power, Energy, and Material Constraints
There are two important considerations for energy storage: power and energy. Power, Bradwell explained, is a surface area effect. To produce more power from solar cells requires a larger surface area of photovoltaics to capture more light. There are other ways to capture more light without changing surface area, such as with concentrating mirrors or changing the thickness of the semiconductor layers, and those approaches to optimizing the use of a given amount of surface area can have a significant impact on the amount of active material required to produce a given amount of power. New materials, such as cadmium telluride, also play a role in the amount of material required to produce a given amount of power.
Energy is a function of volume. Battery storage capacity is directly related to the amount of active material used. “If you want to store a lot of energy in a battery, you need a lot of active material,” said Bradwell. “There is no way to get around it. There is no opportunity for optimizing the amount of material used with battery storage.”
As a result of this basic limitation, it is important when thinking about battery storage on the scale needed for energy grid applications to consider the various constraints regarding battery materials. A major constraint is the abundance of a given material on Earth, as described in previous talks. For example, iridium might prove to be a great battery material, but its low abundance rules it out as a real candidate for large-scale battery applications. The same holds true for tellurium, for which some phenomenal battery chemistries exist. On the other hand, lithium’s crustal abundance is quite high, as is that of magnesium and antimony, two materials that also hold promise in battery technology.
The scale of production, the reserve base, and the cost also can be limitations. Focusing on three specific
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6 Critical Materials in Large-Scale Battery Applications Power, Energy, and Material Constraints The amount of energy that can be stored by a battery depends on the specific battery technology being used and on There are two important considerations for energy stor- the amount of material in the battery. For large-scale battery age: power and energy. Power, Bradwell explained, is a applications, therefore, such as storage of energy for grid-scale surface area effect. To produce more power from solar cells applications, the availability of battery materials is critical. requires a larger surface area of photovoltaics to capture However, other factors are also important, such as processing more light. There are other ways to capture more light with- costs, battery assembly, and the cost of secondary components. out changing surface area, such as with concentrating mirrors The integration of batteries into the energy supply system or changing the thickness of the semiconductor layers, and on a large scale is ultimately a systems problem that involves those approaches to optimizing the use of a given amount processing, structure, properties, and performance of mate- of surface area can have a significant impact on the amount of rials with considerations of cost, policy, and environmental active material required to produce a given amount of power. impacts. Furthermore, the system is so large that it will take New materials, such as cadmium telluride, also play a role in at least a decade or two for a new technology to mature and the amount of material required to produce a given amount have a significant impact. of power. Energy is a function of volume. Battery storage capacity CRITICAL MATERIALS FOR BULK ENERGY STORAGE is directly related to the amount of active material used. “If you want to store a lot of energy in a battery, you need a lot “Grid-scale energy storage is considered to be the holy of active material,” said Bradwell. “There is no way to get grail for electricity storage,” said David Bradwell. “Whether around it. There is no opportunity for optimizing the amount it’s supporting conventional resources such as nuclear, solar, of material used with battery storage.” or wind, there is a great demand to have storage on the grid As a result of this basic limitation, it is important when in order to balance electricity supply and demand.” thinking about battery storage on the scale needed for energy The current electrical grid supplies power in real time in grid applications to consider the various constraints regard- response to demand. When demand increases, output must ing battery materials. A major constraint is the abundance of increase. As demand changes throughout the day, generators a given material on Earth, as described in previous talks. For ramp up and down to meet that demand. When supply and example, iridium might prove to be a great battery material, demand become decoupled, the result can be catastrophic but its low abundance rules it out as a real candidate for large- failure, as was the case with the 2003 blackout that affected scale battery applications. The same holds true for tellurium, millions of people in the northeastern United States. When a for which some phenomenal battery chemistries exist. On few generators went down, there was no buffer in the system the other hand, lithium’s crustal abundance is quite high, as to account for the sudden decrease in supply. is that of magnesium and antimony, two materials that also Energy storage can act as a buffer on the grid. It can hold promise in battery technology. smooth out the power from intermittent renewables, such as The scale of production, the reserve base, and the solar and wind, and it can match the supply from generators cost also can be limitations. Focusing on three specific on the grid powered by nuclear energy, natural gas, and coal. 37
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38 THE ROLE OF THE CHEMICAL SCIENCES IN FINDING ALTERNATIVES TO CRITICAL RESOURCES chemistries—sodium sulfur, lead oxide or lead acid, and are inventing the chemistries and batteries and the experts lithium iron phosphate—Bradwell explained that it is impor- who could ultimately help build and deploy these systems. tant to look not just at raw material costs, but at total battery New approaches to making batteries can use lower-cost costs. The elemental cost of sodium sulfur is tiny, less than processes and assembly methods. In addition, it may be pos- $0.10/kilowatt-hour (kWh), whereas that for lead acid is sible to develop batteries that use lower-purity, and therefore much higher, between $10 and $30/kWh, and lithium iron lower-cost, materials. There may also be ways of improving phosphate costs come in around $1/kWh. Looking at the total lithium extraction processes to enable the use of lower- cost of the battery paints a different picture. Sodium sulfur quality ores or brines. batteries cost $300 to $500/kWh, while a lead acid battery costs between $100 and $300 kWh and a lithium iron phos- Grid-Scale Storage phate battery costs between $300 and $1,000/kWh (Wadia et al., 2011). The Advanced Research Projects Agency-Energy While the conventional metrics for battery storage are goal is $100/kWh (Figure 6-1). energy density and power density, the key metrics for grid- Electrode material costs are not the only driver of bat- based storage are cost, lifespan, and energy efficiency, said tery cost. Processing costs to produce high-purity starting Bradwell. Looking at energy density, lithium and sodium sul- materials, battery assembly, and the expense of secondary fur batteries score well, while pumped hydroelectric power components such as the electrolyte, current collector, cur- compares poorly. However, for grid storage, pumped hydro rent lead, housing, and safety features can be important cost dominates (Figure 6-2) because of its low cost to deploy, long factors. High-purity sodium and lithium iron phosphate are lifespan, and its greater than 70 percent efficiency. Bradwell expensive to produce. In contrast, if the cost of lithium were noted that there is a nice relationship between the cost of a to increase by a factor of 10, it would have little effect on the technology and its deployed capacity. At a cost of between price of a lithium battery, said Bradwell. $100 and $200/kWh, adoption takes off. Supply issues can be a concern. The United States has Other promising battery technologies include flow bat- substantial reserves of lithium brines, and China, Canada, teries, magnesium batteries, and zinc manganese oxide Brazil, and Australia have reserves of lithium carbonate. batteries. Lead acid batteries, a technology that has been Bolivia has the largest resources of lithium brines, but their around for a long time, also have the potential to contribute profitability is uncertain. There are strategic concerns about to grid-based storage. lithium supplies, but lithium ranks at the low end of supply Challenges must be solved for all of these new battery risk in terms of minable reserves. chemistries. Dendrite formation, a particular problem with “Cost and natural abundance alone do not appear to be zinc batteries, occurs when metal is deposited on a battery major limitations for lithium,” said Bradwell. “There are electrode, extends across the electrode, and eventually shorts opportunities for better understanding the system and the the battery. Electrode cracking and deterioration is still a processing costs and materials. In the academic world, challenge that arises when material intercalates within the people get very excited about making something that works structure of the electrode. This is a major mechanism for elec- and works well, but for these broad-scale applications, we trode failure in batteries. Nanostructured materials may solve should be thinking about assembly, processing, manufactur- this problem, but these materials are more expensive to use. ability of the system, and scalability.” He added that there is Interfacial film growth caused by the slow reaction with an opportunity for possible collaboration between those who electrolytes is another major challenge. The electrolyte in a FIGURE 6-1 Costs of raw electrode material affect final battery costs. SOURCE: Adapted from Wadia et al. (2011, p. 1596, in Bradwell 2011a).
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39 CRITICAL MATERIALS IN LARGE-SCALE BATTERY APPLICATIONS FIGURE 6-2 Grid-based energy storage technologies have different energy densities and installed capacities. SOURCES: ESA (2010); Bradwell (2011b). lithium battery is actually unstable. It reacts with the elec- aluminum ions to liquid aluminum. This pools underneath trode and forms a layer on the surface of the electrode that the electrolyte and reduces oxygen to carbon dioxide, which grows slowly. The layer is necessary for battery performance, is vented to the atmosphere. Though a simple reaction in but it should be stable. As the layer grows, it increases the theory, it proved to be difficult to carry out in practice. battery’s impedance and lowers performance. Before this process was developed, aluminum was more Flow batteries are an interesting technology in which expensive than gold. energy is stored in an electrolyte that is pumped across a In essence, Bradwell explained, an aluminum smelter is membrane surface. Fuel cells are getting increasing atten- half of a battery that cannot be recharged because it generates tion, but efficiency is the big challenge there. Lithium bat- a gaseous product that cannot be reclaimed. The solution was tery efficiencies reach 90 to 95 percent, while the round-trip to replace this gaseous component with another liquid metal. efficiency on a fuel cell is typically closer to 50 percent. In the liquid metal battery, an electropositive liquid metal is What is encouraging, said Bradwell, is that most of the new separated from an electronegative metal by a liquid electro- approaches that researchers are pursuing use Earth-abundant lyte. The three liquids self-segregate based on contiguous materials such as zinc, magnesium, lithium, manganese, immiscibility between the metal and electrolyte layers. The sodium, and lead. Very few of the new chemistries use battery operates at high temperature, though less than that of resource-constrained materials. an aluminum smelter, and uses low cost materials. The alu- In his work, Bradwell took inspiration from the metals minum industry’s experience suggests that the electrodes will industry’s experience that prices drop as production increases have a 5- to 10-year lifespan before they need refurbishing. and that prices drop more when materials are processed as The first generation battery he and his collaborators built liquids. “Both iron and aluminum are produced as liquid used liquid magnesium and antimony as the two electrodes. metals [that are] handled and processed in a continuous At low current densities, this battery was 74 percent efficient, manner, which also keeps the costs low,” said Bradwell. “In with a coulombic efficiency—a measure of self-discharge— particular, the aluminum smelter was the inspiration for the of 99.7 percent per cycle. The voltage of this initial battery liquid metal battery project.” was low, only 0.5 V compared to 3.5 V for a lithium-ion An aluminum smelter is a huge electrolysis machine that battery. Fundamental research and chemical development works as follows: aluminum oxide is poured into a layer efforts have raised the output to 0.9 V, which is still low but of molten cryolite, which at 960°C is so corrosive that it sufficiently high to continue work on this system, and cou- dissolves aluminum oxide and dissociates it into aluminum lombic efficiency has increased to greater than 99.9 percent. ions and oxygen ions. A 700-milliampere/cm2, 4-volt (V) Projected costs for such a battery would be less than $100/ current is passed from cathode to anode, which oxidizes kWh. Bradwell acknowledged that a significant amount of
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40 THE ROLE OF THE CHEMICAL SCIENCES IN FINDING ALTERNATIVES TO CRITICAL RESOURCES work needs to be done on failure mechanisms, chemistry optimization, scale-up, and systems engineering. Semiconductor Recycling During the course of developing the liquid metal battery, Bradwell and his collaborators came up with a new method for recycling or reprocessing intermetallic compounds such as tellurium. While running electrochemical experiments on molten zinc chloride, the researchers noted that, under an applied potential, zinc would start depositing on one of the electrodes, with the corresponding release of chlorine gas. This is standard electrochemistry and not a surprise, but when they added zinc telluride to the system, experimental data showed that tellurium was dissolving as an anion, a totally unexpected finding because metals usually dissolve as cations. This finding prompted Bradwell and his colleagues to develop a system for producing zinc and tellurium from zinc telluride, which while interesting is not relevant to anything FIGURE 6-3 Factors in energy technology engineering can be practical because zinc telluride is not widely used. Cadmium envisioned as occupying the corners of a polyhedron. telluride is, however, so the researchers created a method for SOURCE: Whitacre (2011). taking cadmium telluride manufacturing scrap and convert- ing it into high-purity cadmium and tellurium. This is not a technology relevant to batteries, he said in closing, but it could play a role in addressing concerns about tellurium The second assumption is that a systems-level perspec- supplies. tive is the only one that matters for energy technologies. “The economy and policy makers only care about the macro implications of energy technologies,” said Whitacre. “At the ALTERNATIVE MATERIALS FOR ENERGY SYSTEMS end of the day, they have to decide what to fund and what to Energy policy, said Jay Whitacre, can be represented as a give emphasis to if they are making policies that will affect polyhedron that connects characteristics subject to research the implementation of some technologies over others.” As a and development such as structure, processing, properties, result, black-boxing is critical—think of a technology in terms and performance with considerations of cost, policy, and of a box that either produces electrons or stores and releases environmental impact (Figure 6-3). If the field does not them. Then, determine how that box will fit in the existing address issues of cost, policy, and environmental impact as system, how it will function in the system’s environment, how part of its research on characteristics, the impacts of new it can improve the system in which the box sits, and how the energy technologies will be small. box affects the cost, performance, and lifetime of the system. When considering whether a new technology has market Whitacre added that the movement of materials through potential, Whitacre makes two assumptions specific to the supply chain and value chain also should be examined materials-intensive energy technologies. The first assump- this way—an analysis should determine what materials move tion is that cost is everything. To have an impact, projects into the box and what materials move out of the box. It is nec- must be huge, particularly given that the goal is to alter the essary, he said, to determine how this material flow affects way that the world consumes or distributes power and energy. the manufacturing cycle and disposal cycle. The conclusion This is a tremendous materials challenge, and not just with from this assumption is that trade issues are crucial and the cost of the materials. Other costs include the capital to should inform even fundamental research on technologies. manufacture these new technologies, the cost of production It is important, too, to keep a 10- to 20-year timeframe in throughput, operational expenditures, transportation costs, mind because that is how long it will take a technology being and the expense of integrating new supply. Developers of developed today to make a significant impact on the system. these technologies also need to make a profit and return on their investments, which adds to a technology’s costs. “We’re Lithium-Ion Batteries not just doing this as a philanthropic exercise,” said Whitacre. “You can’t change the world with technology unless those There is plenty of lithium in the world. According to technologies are profit-bearing.” the U.S. Geological Survey, there are some 32.5 million
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41 CRITICAL MATERIALS IN LARGE-SCALE BATTERY APPLICATIONS metric tons of lithium reserves worldwide, enough to make tion, research and development, and parts each accounted for 32.5 billion vehicles equipped with today’s lithium-ion bat- a larger percentage of the cost of the battery. teries. Today, developed reserves are dominated by Chile The most expensive part of a lithium-ion battery is actu- and China, and the market is currently flooded with supply. ally the electrolyte. Manufacturing costs associated with the Battery-quality lithium carbonate costs less than $5/kg, and organic solvent electrolyte are high, and its ionic conduc- the other materials in a lithium-ion battery—cobalt oxide, tivity is relatively low compared to aqueous electrolytes. manganese oxide, copper, and aluminum, among others—are Lower ionic conductivity means that the electrodes must be also relatively inexpensive and plentiful. thinner, which in turn boosts the costs of the ancillary mate- What is expensive is the system that all of these materials rials needed to support thin electrodes. A quick sensitivity fit into to make a battery (Figure 6-4). The system includes study shows that batteries become cheaper as electrodes get current collectors, separators, and the electrodes them- thicker, but this demands a higher-conductivity electrolyte selves, which are active materials and quite thin at less than and clever electrode structural engineering. In addition, the 100 microns per anode or cathode for high-powered devices. rate capability goes down. In addition, ancillary support such thin electrodes, and in The bottom line is that adoption of lithium-ion battery fact the thinner the electrode, the more ancillary material is technology is not constrained by materials. Rather it is con- needed to support it. strained by the way the materials function and the complexity There are trade-offs involving costs. Power costs more of the device itself. per unit of active material, but power is also worth more in many applications. More complex batteries may perform Bulk Stationary Storage better and command a better price, but more complexity can create yield problems if cell-to-cell consistency is critical The development of bulk stationary storage devices is for performance. critical to the next-generation grid and large-scale use of An examination of the bill of materials for a generic plug- renewable energy sources. A handful of companies are mak- in hybrid vehicle lithium-ion battery reveals that, of the $300 ing progress not through the use of innovative chemistry but to $400/kWh cost of this battery, all of the materials cost through clever engineering and by filling specific niches about $100/kWh. Even if the lithium cathode cost went to $0, where higher prices are justified. A technology developed the next-generation automobile lithium-ion battery would still by Xtreme, for example, is being installed on Maui, which cost over $400/kWh. An assessment by the Boston Consulting has a major problem with frequency regulation because of Group (BCG, 2010) came to a similar conclusion, finding that all the wind power being generated there. Power developer materials represent about 12 percent of the cost of a lithium- AES Corporation is installing A123 Systems’s batteries at ion battery supplied to an automobile manufacturer. Deprecia- what Whitacre called extreme pain points—places where FIGURE 6-4 A lithiumlithium-ion cell has multiple components. SOURCE: HowStuffWorks, circa 2006, Bryan Christie Design.
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42 THE ROLE OF THE CHEMICAL SCIENCES IN FINDING ALTERNATIVES TO CRITICAL RESOURCES transmission problems are severe enough to justify the high Whitacre and his colleagues are developing an aqueous cost of these systems. lithium-ion system based on intercalation technologies Pumped hydro, a well-established technology, is not uni- (Manjunatha et al., 2011; Shivashankaraiah et al., 2011). versally cheap, Whitacre noted. It requires a vertical gradient The electrolyte is typically a neutral pH salt—either lithium and plenty of cheap water, and it is not very energy dense. nitrate or lithium sulfate—in water. Devices built so far The real competitors for bulk storage are small natural gas have energy densities in the range of 55 kWh/kg, but most turbines used for peak-hour demands and renewable level- are stable for only hundreds of cycles and their voltage is at ing. They cost about $750/kW installed, and they can run for the low end. between 1 and 6 hours at times of peak demand. One device that has displayed stability over thousands Whitacre said he has been told by a major utility provider of cycles uses a high-surface-area activated carbon anode that at $1/W and a greater than 10-year lifetime, utilities and an intercalating and de-intercalating lithium manganese will buy all the storage a company can produce. That means oxide cathode (Wang and Xia, 2006). Whitacre explained the cost of production must actually be less than that if the that he took notice of this system when asked if sodium could storage device manufacturer hopes to turn a profit. “That is replace lithium, since sodium is a much cheaper material. a hefty goal and not an easy one,” he said, “and if you can There had been some research on aqueous sodium batteries, do this, you will change the world.” but the results were not promising (Sauvage et al., 2007; Using a simplified economic analysis, Whitacre derived a Zhuo et al., 2006). maximum cost of $5/kg, or under $50 watt-hours (Wh)/kg, Whitacre, however, found that sodium manganate with for the entire cost of an economically feasible bulk storage an orthorhombic structure had very interesting cathode device. This calculation took into account the number of properties. This material, Na0.44MnO2, can be made in a cycles required of a relevant device, the amount of kilowatt- variety of ways from baking soda and manganese dioxide, hours delivered per cycle, the cost of goods sold, the cost of both of which are very inexpensive. The simplest way to materials, and the cost of assembling those materials into a make it is to mix the two starting materials and heat them device that would be sold in the market. The calculation also in a furnace, though they can also be made by sol-gel and assumed that any device would have to cost approximately hydrothermal processes. The material has a needle-like mor- $100/kWh delivered over the device’s lifetime. phology, is very anisotropic, and can have nanodimensional These results, while based on an admittedly simplified cross sections. With care, solid-state synthesis can produce analysis, suggest that there is a steep hill for any technol- high-purity material, contaminated with a small amount of ogy to climb. Lithium-ion batteries, for example, cost in the manganese trioxide, that displays suitable properties for a multiple hundreds of dollars of watt-hours per kilogram, cathode material. and their total cost of goods is much higher, in the multiple For an anode, activated carbon is the material of choice, hundreds of dollars per kilowatt-hour. but activated carbon is actually a very expensive material, Moving to higher-energy-density materials could be a and the cost proposition for using it in a bulk storage device solution, but these are typically not as stable. “This is not is impossible. To solve that problem, Whitacre has been a law,” said Whitacre, “and I’m hoping somebody finds using molasses as a source of carbon via pyrolysis and then things that have 1,000 watt-hours per kilogram and can last activating it using potassium hydroxide, another relatively 10,000 cycles. But in general the more energy you get out inexpensive material. Using a process that preheats the of a battery material per cycle, the more transition it has to material and then completes the pyrolysis at 800°C in the go through in each one of those cycles, and the less stable it presence of potassium hydroxide, Whitacre and collaborators generate a material with a surface area of nearly 3,000 m2/g. will be over thousands of those cycles.” Another solution would be to find a battery system that Electrically, this material has properties that “put it above the has a low energy density but extremely low cost, less than laugh test.” He said that if he can make this material for $3 $5/kg. If this device could cycle rapidly or be more efficient to $4/kg, it would be a viable candidate. and have a very long lifetime, it could prove economically When an anode made from this material is combined feasible. with a sodium manganate cathode and aqueous sodium sul- Whitacre is working on an aqueous electrolyte battery that fate as the electrolyte, the resulting cell was stable to 1.8 V might fit the latter scenario of low cost, low energy densities, and could be cycled between 0.4 and 1.8 V for thousands and long lifetime. Aqueous electrolyte batteries are based of cycles with negligible loss of capacity and 100 percent on an old technology. Aqueous electrolytes have an order- coulombic efficiency. The one area in which this cell fell of-magnitude-higher conductivity than organic electrolytes short was in energy density, which was on the order of 15 so they can be used with thick electrodes that can be much to 20 Wh/kg versus the 30 to 40 Wh/kg that would make a cheaper to manufacture and assemble into a final device. battery made of these materials cost competitive. However, Lead acid, nickel metal hydride, and alkaline systems switching to a cubic spinel manganese dioxide cathode pro- are all examples of batteries that use an aqueous electrolyte. duced a cell that had an energy density of around 30 Wh/kg
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43 CRITICAL MATERIALS IN LARGE-SCALE BATTERY APPLICATIONS using very thick electrodes that are extremely stable and easy the benefits. The battery in a Chevy Volt, for example, costs to manufacture. Moreover, cells made from this material can about $16,000, and load leveling would generate about cycle far more than lead acid batteries. $1/day in revenue. Aquion, the company Whitacre founded, is now manufac- In response to a question about what fundamental research turing batteries using this technology. The cells are encased needs to be done in the battery field, Bradwell responded in industry-proven polypropylene casings using industry- that he would like to see modeling work done on the proven sealing technologies. The batteries have a modular thermodynamics of liquid alloys. He noted that quantum- product form factor that allows them to be strung together mechanical analyses have been applied successfully to into eight-battery, 15-V modules that can then be stacked crystalline systems, and he would like to see similar work and connected in series or parallel as needed. Hundred-volt done for liquid alloys. strings are now in use and 1000-V strings are being tested. In response to a question about whether this battery is The batteries have performed well when tested under condi- actually a capacitor, Whitacre said that it is officially known tions that simulate wind power generation over a period of as an asymmetric energy storage device or a “capattery” days. since it behaves as a hybrid of a battery and a capacitor. Responding to a comment about how storage devices would be incorporated into the grid, Whitacre noted that DISCUSSION a New York utility company recently put out a call for In response to a question about the power versus energy proposals for a peaking gas turbine to supply 1,600 GWh of demands on a battery intended for use on the grid, Bradwell power, and one of the responses was not for a power plant said that the real issue is the ratio of rated power to rated but for batteries that would be housed in several warehouses energy. Batteries for frequency regulation need to discharge distributed across Long Island. The proposal has received for 15 to 45 minutes. A battery can have high power but not high marks despite being slightly more expensive because much energy and discharge repeatedly throughout the day. To residents in the Hamptons liked the idea of a warehouse- support wind and solar, however, a battery needs to be able to based solution with no emissions compared to a large gas discharge over a much longer period of time. Such batteries turbine. The project is moving forward. would need large energy storage capacity but, at lower power Whitacre was critical, in responding to a question about output, would create relatively low-stress demands on a intellectual property protection, of the U.S. Patent Office. battery. “You still need big batteries, but in terms of how He said that patents covering new chemistries are worth very fast you get the energy in and out of the system, it’s not as little. What are valuable are patents that control specific ways restrictive,” said Bradwell. of using batteries and control algorithms for specific chemis- Responding to a question about the energy needed to tries. Aquion’s patents actually cover the high-voltage strings heat a liquid metal battery, Bradwell noted that, once these that the company can make from its batteries. He explained batteries reach a certain size, they maintain temperature as that it is impossible to make such high-voltage strings with- a result of the heat generated as the battery cycles. He also out using batteries with the performance characteristics of noted that these batteries can be cycled at 90 percent effi- the company’s batteries. ciency, though at lower current densities. When asked about other promising technologies, Whitacre When asked about the potential for metal-air batteries, said that there is some very interesting work being done with Bradwell explained that the main problems with those bat- lithium sulfur chemistry, which uses simple and inexpensive teries have to do with the kinetic difficulties in oxidizing materials. oxygen, resulting in inefficient batteries. Metal-air batteries In response to a question about what fundamental research also have limited life cycles based on the experience with needs to be done in the battery field, Whitacre said that he zinc-air batteries. would like to know more about the fundamental nature of Bradwell was asked about the potential for lithium bat- pseudocapacitance in different types of electrolytes. He also teries in cars to serve as load leveling devices for the grid. cited the areas of dendrite formation and dendrite blocking He replied that in his opinion the negative impact that this as needing good fundamental research. would have on the lifetime of the battery would far outweigh
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