Daniel P. Duffy 2017-01-17 17:37:58
There is an old military saying that “Amateurs talk about tactics, professionals talk about logistics.” Nowhere is this more true than in the fuel and energy requirements of a military formation deployed in a combat theater. Battery Basics: How Do They Work? Batteries are devices that can be considered electron “pumps,” in which each cell is a contained package of the working chemical—referred to as an electrolyte—inside the battery. The electrolyte is a solvent containing dissolved chemicals that provide ionic conductivity. In addition to its cell(s), a standard battery has two electrodes, a cathode and an anode. The cathode is its “positive” electrode and usually consists of a graphite or carbon rod located inside the chemical cell. The anode is the “negative” electrode, located on the outside casing surrounding the chemical cells. In simple commercial batteries this casing is typically made of zinc. Anodes and cathodes have to always be made of different metals; one must have a tendency to give up electrons and the other an affinity for receiving electrons. Once an electric circuit is connected to the anode and cathode, an electrochemical reaction takes place in the electrolyte. During this reaction, positively charged ions flow through the electrolyte to the positive cathode, while electrons flow around through the circuit in the opposite direction to the cathode, thus creating electrical current. The electrolyte acts as an insulator preventing the direct flow of electrons from the anode to the cathode, in effect, forcing the electrons through the circuit. This current is referred to as direct current (DC), as opposed to alternating current (AC) created by a generator, since the current only flows in one direction. As the battery generates current over time, the electrolytes are slowly converted into different chemicals and the battery “wears out.” Once depleted, the electrolyte can no longer generate ions for the cathode or electrons for the anode. And since this chemical reaction can only happen once, most commercial batteries cannot be recharged. Disposable batteries of this type include zinc-chloride and alkaline batteries. Battery capabilities are generally defined by their energy density, specific energy, and specific power. Energy density is the amount of energy stored per unit volume (Wh per liter). Specific energy is the amount of energy stored per unit mass (Wh per Kg). In both cases, only the extricable energy is counted. Energy that cannot be generated as electrical discharge would not be considered, and therefore, the energy density and specific energy of a battery may fall over its operational lifetime. Specific power derives from energy density and specific energy, and relates to loading capacity. Also referred to as gravimetric power density, batteries can have small specific power but high specific energy, whereas similar energy storage devices such as super capacitors can have high specific power but low specific energy. Rechargeable batteries are a mature technology that has been on the market for decades. By applying an electrical current, the chemical reactions that generated the initial electrical charge can be reversed and its electrical potential restored. These types of batteries include nickel-cadmium, nickel metal hydrides, and lithium-ion (Li-ion) batteries. So what makes Li-ion batteries superior to their rivals? Advantages of Li-ion Batteries First and foremost, lithium-ion batteries are lightweight—approximately one-third the weight of lead-acid batteries. This reduces the physical load requirements for transporting a battery of the same size. Logistically, this is a great advantage, as load discipline has always been a serious concern for any military force. Despite their low weight, Li-ion batteries can store twice as much energy per unit of volume than nickel-cadmium batteries, making them ideal for small-scale applications in computers, electronics, and cell phones. Li-ion batteries also have an advantage in operational efficiency, being able to achieve 100% efficiency in both discharging and recharging (i.e., using the same number of amp hours of current both into and out of the battery). Depth of discharge for lithium batteries is also greater, achieving 100% versus only 80% for standard lead-acid batteries. The number of charge and discharge cycles is 10 times greater for Li-ion batteries (over 5,000 cycles) compared to lead-acid batteries (only about 500 cycles). Voltage remains constant for Li-ion batteries throughout their discharge, while lead-acid batteries slowly lose voltage over time of discharge. All of the above reduces the overall lifetime costs of Li-ion batteries compared to standard lead-acid batteries even though their upfront costs are greater, making Li-ion batteries far more cost-effective. Currently lead-acid batteries can cost around $300 per kWh while an equivalent Li-ion battery can cost between $2,000 to $5,000. However, these prices are decreasing and are projected to fall to around $500 per kWh. As with other types of batteries, a Li-ion battery consists of power generating cells composed of a positive electrode, negative electrode, and an electrolyte. The positive electrode is made from lithium-cobalt oxide (LiCoO2) or lithium-iron phosphate (LiFePO4). The negative electrode remains a standard carbon graphite rod. The most commonly used electrolyte material is comprised of lithium salt (LiPF6) in an organic solution. Battery designers can optimize a lithium-ion battery for either maximum operational lifetime, specific power as measured by load current, or specific energy expressed by high capacity. The addition of recharging power causes a chemical reaction that moves lithium ions (lithium atoms that have lost an electron and are now positively charged as a result) through the electrolyte to the negative graphite electrode where they are stored for future use. Using a device powered by a Li-ion battery reverses this process and all of the stored lithium ions move in an opposite direction, causing an electrical current to flow through the battery’s circuit. Whether charging or discharging, electrons flowing in the exterior circuit move in opposite directions to the flow of lithium ions within the battery (electrons never actually flow through the electrolyte inside the battery). Li-ion batteries also come equipped with internal circuits that can temporarily stop charging and discharging operations to prevent overheating and avoid excessive discharging. Types of Li-ion Batteries There is not just one kind of Li-ion battery. The term “Lithium-ion” designates a whole family of chemical batteries, each with differing characteristics and applications. Each type is designated by the kinds of chemical used to make up its anode, cathode, and electrolyte—either by its chemical formula or the abbreviation of its name: • Lithium-Titanate (chemical formula: Li4Ti5O12) is a more radical design that replaces the graphite in the anode with titanite material formed in a spinel structure. Specifically, it utilizes lithium-titanate nano-crystals covering the surface of the anode instead of solid carbon. These nano crystals have incredibly high surface areas for their volume—up to 100 square meters per gram of material. Standard carbon anodes have only 3 square meters per gram. This 33-fold increase in surface area allows for rapid entrance and exit of electrons, and therefore, makes rapid charge and discharge possible (at 10 times its rated capacity). It also has a higher life cycle count and high temperature resistance, combined with low temperature discharge characteristics. Its ability to rapidly recharge allows for convenient opportunity recharging by vehicle (such as buses being able to recharge at passenger pickups). It also has a relatively high energy storage density of 177 Wh per liter. Its main drawback is lower voltage (specific energy). And it tends to have a higher cost than similar batteries. Despite their high cost, with their superior capabilities, lithium-titanate batteries are usually utilized for high-scale applications such as electric vehicle power trains and solar powered lighting systems. • Lithium-Iron Phosphate (chemical formula: LiFePO4) utilizes a cathode made from nano-scale phosphate material. This configuration achieves high efficiency and low internal resistivity. Its primary advantage is its long cycle life and high resistance to heat damage, but is sensitive to the effects of cold temperatures. As a result it can be operated at high charge for prolonged periods without structural stress and strain. However, it has lower voltage and specific energy. This kind of battery is often used as a direct replacement for older lead-acid batteries. • In a Lithium-Cobalt Oxide (chemical formula: LiCoO2), the cathode consists of cobalt oxide (CoO2) with a layered structure. This type of battery has a specific energy (ratio of voltage discharge to battery weight). However, it has a relatively short lifespan (with fewer recharge cycles over its operational lifetime), limited power capacity, and experiences chemical instability at relatively low temperatures. The problem of limited lifespan is being addressed by new designs that incorporate nickel, aluminum, and manganese. A Lithium-Cobalt Oxide battery can only be charged and discharged at its rated milli-amps (anything higher can result in overheating and even physical stress on the battery itself). An internal battery protection circuit will automatically limit the charge and discharge rates to acceptable levels. These types of batteries are used in electronics, computers, and communications. • Lithium Manganese Oxide (chemical formula: LiMn2O4) batteries utilize a three-dimensional spinel structure for its cathode, a design that greatly improves ion flow. This, in turn, results in lower resistance to ion flows, greater current, and higher voltage. This improved flow capacity allows for faster recharge and higher discharge rates (with currents between 20 to 30 amps). The design also allows for radiation of heat, which improves its resistance to overheating. This improves safety and minimizes the chance of fire. However, like the Lithium-Cobalt Oxide battery, its service lifetime is limited, as is the number of charge and recharge cycles. Even so, its heat limit is relatively high at 176°F. Also, its capacity is only one third of Lithium-Cobalt Oxide batteries. These characteristics allow the Lithium Manganese Oxide battery to be used in heavier power load applications such as major hand tools, power tools, medical instrumentation, and as an actual driving force for hybrid electric vehicles. • Lithium Nickel Manganese Cobalt Oxide (chemical formula: LiNiMnCoO2), also referred to as an NMC battery, uses a cathode made from a combination of nickel, manganese, and cobalt (each typically representing one-third of the total, or a one-to-one-to-one ratio). Its increased capacity and operational flexibility allows an NMC battery to be used as either an energy cell or as a power cell, depending on the designer’s optimization goal. The use of a silicon-based anode will double the power output, but at the cost of lower loading and reduced cycle life. This type of anode can also grow and shrink with each charge and discharge, causing structural stress and strain within the battery. Combining nickel and manganese in the same cathode provides the best of both worlds. The spinel structures formed by manganese reduce internal resistance, but provide low specific energy. Nickel, on the other hand, creates high specific energy but lacks the stability provided by the spinel structure. Both together complement each other and cover each other’s weaker characteristics. In addition to the standard one-to-one-to-one combination of nickel, manganese, and cobalt, newer designs use a five parts nickel, three parts cobalt, and two parts manganese combination (five to three to two), with other combinations in development. NMC batteries represent the next level of power output and are used in heavier applications such as large power tools, electric bikes or scooters, and vehicle power trains. • Lithium Nickel Cobalt Aluminum Oxide (chemical formula: LiNiCoAlO2), also designated as an NCA battery, is similar in operating characteristics to the NMC battery, but is more sensitive to heat (and therefore less safe), and has higher overall costs. Its use is limited to specific applications. Li-ion Batteries: Potential Military Applications A German general of the Second World War once commented “Anyone can command a panzer division, but it takes a genius to supply one.” All of modern warfare requires near genius to provide proper logistics and support. Light-weight but powerful Li-ion batteries make supply easier and simpler to achieve. Reliable, secure electrical power becomes ever more vital for the successful completion of military missions as these missions become more remote, sophisticated, and difficult to supply. The battlefield is the harshest of all environments and military batteries have to be designed to withstand continuous and extreme abuse. This includes the shock generated by explosions, the vibrations of heavy equipment moving at high speed over rough terrain, crushing pressures from impacts, excessive heat, clinging mud, and choking dust. Operational temperatures can range from -60°F to over 140°F. Besides providing engine start up for major weapons systems such as tanks and helicopters as well as field transport from supply tucks to Humvees, batteries are now the power source of choice for advanced battlefield technologies. A short list of these systems includes: sensors, robotics, lighting, guidance, jamming, communications, radar, sonar, electronic countermeasures, drones, and lasers. All of these systems require reliable and heavy power loads from lightweight power sources that are durable and require minimal maintenance in order to properly function. In short, members of the modern military need Li-ion batteries in order to fight. In addition to becoming commonplace in electronics, Li-ion batteries have been adapted to power military vehicles. The standard for Western military vehicles is the NATO 6T standard battery. It is used by 95% of military ground vehicles and weapons platforms. These are used to power up all kinds of military vehicles (Humvees utilize two 6T, while an Abrams tank requires six to 12 depending on its operating conditions). Improvements in the design and operation of these batteries will have a major impact on force readiness. Modern, high-tech armed forces require reliable autonomous power sources for battlefield electronics, propulsion, and control. Military specifications and standards can be exacting. They must be understood completely and clearly defined. With regard to battery power, the military tends to overspecify power requirements to provide an extra (and often vital) margin of performance. The downside of this overspecifying is that it can make a battery system practically unaffordable. This is especially true for batteries designed for military use original equipment manufacturers (OEMs). These batteries are an adjunct power system that needs to be perfectly compatible with the overall vehicle or system that it is powering. And there is a multitude of military systems that rely on Li-ion batteries for power, from the most sophisticated communications, computers, guidance systems, and sensors, to the most powerful weapons platforms and vehicles. Though other types of batteries remain in use (lead-acid batteries are still very common in military applications), Li-ion batteries have the physical and operational characteristics to make them the preferred choice even for older legacy systems. System designers have come to rely on the light weight, long life, and superior performance of Li-ion batteries when designing new military systems and upgrading old ones. It is the job of the designers to customize a battery power system to its application, while at the same time making it compatible with other uses to simplify overall logistics in regards to equipment and replacement parts (having specific batteries for each type of transport, tank, helicopter, etc. would be a logistical nightmare) and anticipate emerging technologies—an almost impossible and contradictory task. Even the mundane design aspects like battery casing materials, battery size, and configuration are of vital importance. Some plastic casings typically used for battery manufacturing may not be applicable for certain situations. In addition to extreme heat and cold affecting battery performance, they can also impact the structural integrity of the battery casing and repair and replacement operations. For example, the design of a battery installation may make it impossible for a repairman to wear heavy gloves while working in a cold environment. Sand abrasion and dust clogging can also impact battery casings, mountings, and electrode contact points. In addition to allowing for practical maintenance operations, safety is a primary concern. Batteries can overheat. And when they do, they can catch fire with disastrous results for military craft and operating systems. This has been a concern with regard to Li-ion batteries. A heat failure resulting in flame can spread to adjacent battery cells resulting in a thermal cascade failure. To avoid this and other safety concerns, military systems require multiple levels of safety. The first level is electronic protection to guard against overcharging. A thermal fuse would trigger once the battery begins to overheat, cutting off its operation and forcing a cool down. Additional safety features include a built-in, pressure-activated circuit breaker, a safety vent to allow the escape of built up pressure, and circuit breakers that shut down when exposed to extreme temperatures. Since these systems are used by multiple NATO and allied forces, the specifications need to meet the most stringent standards of the user pool. Though protecting the environment is not usually the first thing that comes to mind when specifying a battlefield system, Federal Law (Waste Electrical and Electronic Equipment, WEEE) requires military batteries and electronic equipment to be fully recyclable. And this makes sense in the long run, as the money saved can be used for additional military acquisitions. Since a Li-ion battery can have an operational life of 600 to 1,000 charge cycles, the ability to reuse these batteries instead of throwing them away constitutes a significant budget savings. Major Manufacturers and Suppliers of Li-ion Batteries Saft (Euronext: Saft) is a world leading designer and manufacturer of advanced technology batteries for the industry. The group is a leading manufacturer of nickel batteries and primary lithium batteries for the industrial infrastructure and processes, transportation, civil, and military electronics’ markets. Saft is the world leader in space and defense batteries with its Li-ion technologies, which are also deployed in the energy storage, transportation, and telecommunication network markets. A leading developer in the field of military battery power applications, Saft has developed the Xcelion 6T. Li-ion technology delivers the equivalent power of two lead-acid batteries at a quarter of the weight and half the volume. The battery’s power density and energy efficiency help streamline logistics, as there are fewer items requiring storage, transportation, and distribution. This new battery goes a long way towards solving the problem of supplying power to the multitude of sensors and communication systems installed in today’s military vehicles. Saft’s long life technology ensures that fewer replacement batteries will be needed, further reducing strains on the army’s logistical system. With built-in diagnostics, a vehicle or supply train will need to carry fewer spares. “Our new technology creates tangible cost savings for the military,” says Annie Sennet, executive vice president of Saft’s Space & Defense division. “Saft batteries provide the reliability necessary for crucial missions and enhance capabilities of military vehicles, including supporting extended silent watch operations . . . This reduction in replacement batteries translates to over $200 million in cost savings for a fleet of 20,000 vehicles over a 20-year life. This is the kind of technology that contributes to the innovation found at Special Operations Forces Industry Conference, and we are looking forward to showing defense leaders how it can transform the way they power their vehicles.” G.S. Battery USA, Inc., an American subsidiary of the GS Yuasa Corp. of Japan (GYLP), is a manufacturer of Li-ion batteries, lead-acid batteries, and motorcycle batteries. They are an industry leader in battery power applications for motorcycle and standby storage batteries, power sports, telecommunications, UPS, emergency lighting, and commercial-scale renewable energy. The solar array installation on the roof of their headquarters in Roswell, GA, is the first commercial solar array with storage in the state of Georgia. Installed in 2010, this system utilizes 37 kWh of roof-mounted solar panels. The energy generated by the solar panels is stored in a 3,000-amp battery array. GYLP partners with customers to match the right LIM cell to their requirements by means of system modeling. This capability can simulate battery performance, including expected useful life, based on anticipated system duty cycle. System modeling is critical in selecting the right cell or battery for optimal system performance. Their LIM cells and batteries have found applications in hybrid gantry cranes, light rail trains, electric and hybrid electric vehicles, hybrid electric railway cars, load leveling applications, and EV-PV charging systems. Their battery technology can also be used for military and civilian applications such as unmanned vehicles like robots and drones, tracking systems, and shipboard power, as well as large energy storage systems for renewable power stations. Altairnano is a leading manufacturer of Li-ion batteries and a provider of engineering design and power technology research services. Designed for power-dependent applications, Altairnano’s family of advanced Li-ion energy storage systems and batteries meets the demands in energy generation, utilization, and policy. In doing so, the company’s goal is to achieve sustainable and economically sensible power and energy management practices. As part of this effort, in 2005, Altairnano became the first company to replace traditional graphite materials used in conventional lithium-ion batteries with a proprietary, nanostructured lithium-titanate. Their research revealed that nanostructured lithium-titanate, when used to replace graphite in conventional lithium-ion batteries, results in extremely fast charge and discharge rates, higher round-trip efficiencies, long cycle life, improved safety, and the ability to operate under diverse environmental and extreme temperature conditions. Greater thermal stability, resulting from the removal of highly reactive graphite from the battery and its replacement with nanostructured lithium-titanate materials, improved battery safety. This causes all significant chemical interactions to take place in the electrolyte. Longer life means that the battery can be recharged 1,000 times before losing its usefulness. Laboratory tests have shown that the battery can receive over 16,000 charge and discharge cycles at rates up to 40 times greater than common batteries and still retain up to 80% of initial charge capacity. Additional cell measurements performed with high-powered cell designs indicate specific power as high as 4000 W/kg and power density over 7,500 W/liter. Johnson Controls Power Solutions is the world’s largest manufacturer of automotive batteries, supplying approximately 146 million every year to automakers and aftermarket retailers. The company’s full range of lead-acid and lithium-ion battery technology powers nearly every type of vehicle including traditional, start-stop, micro-hybrid, hybrid, and electric. Johnson Controls’ recycling system has helped make automotive batteries the most recycled consumer product in the world. Globally, 15,000 employees develop, manufacture, distribute, and recycle batteries at more than 50 locations. Recently the company announced that it is investing $780 million and is expanding its global production of absorbent glass mat batteries, an improved lead-acid battery optimized for vehicles with stop-start systems. The company believes that 50% of vehicles built in North America will have stop-start systems, up from 10% now. They expect 80% of vehicles built in Europe will have it, up from 60% now. And more than half of China’s new vehicles will have it. DE Daniel P. Duffy, P.E., writes on topics of energy and the environment.
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