Battery Power - Fall 2016 - 5

Feature Lithium-Ion Batteries The advantages of lithium-ion batteries are, among others: * High density storage that possess a smaller footprint allowing manufacturers more design freedom and/or longer range capabilities for vehicles without increasing the size and weight of their vehicles. * The flexibility to not have to be fully discharged before recharging, without losing capacity. This 'memoryless' nature of lithium-ion batteries makes it more suitable for use in hybrid vehicles that requires constant charges and discharges of its batteries in stop and go traffic. * A low self-discharge property allowing vehicles to be parked for longer periods of time without losing its stored electrical energy. Who wants to return to a dead car battery after a long vacation? The challenges of lithium-ion batteries are: * The energy capacity of a lithium-ion battery slowly diminishes over time, even when they are not in use. It is also generally known that existing lithium-ion batteries based on intercalation chemistry will lose approximately 20 percent of their storage capacity after 1,000 charge-discharge cycles. Therefore, lithium-ion batteries installed in electric vehicles at this point of time may have to be replaced every four to six years, resulting in cost to the consumer. * High costs are also yet another challenge for manufacturers. Currently, the cost of storing electrical energy using lithium-ion batteries is above $500/kWh. According to an article in February 2016 issue of Renewable World magazine, recent data suggests that this cost is expected to decrease by 50 percent+ to $230/kWh in the next five to seven years. Unfortunately, even then, electric vehicles will gain a competitive edge in relation to conventional vehicles only when the cost reaches at or below $100/kWh. * A substantial portion of the cost of manufacturing a lithium-ion battery is in the manufacturing of its cathode. Currently, cathodes and anodes are formed onto metal substrate by spraying electrode material in a slurry form, which requires continued mixing for even distribution. To achieve the desired cathode thickness, materials are sprayed and then dried to a specific temperature and viscosity before heavy calendaring. Furthermore, to avoid cracking, a winding of the electrode sheet has to occur before the cathode is completely dry. Therefore, one effective way to reduce the cost of lithium-ion battery is to reduce the cost of cathode materials and manufacturing. terminals); pouch (soft, flat body, such as those used in cell phones); and prismatic (semi-hard plastic case with large threaded terminals, for vehicle traction packs). Typical manufacturing process for laptops and electric vehicle batteries entail mixing materials to form cathodes and anodes (into a slurry form); coating of the electrode material on the collector foil; drying followed by calendaring (pressed to evenly distribute the coating material); and cutting electrode sheets into final assembly to be fitted into cylindrical casing and hermetically sealed. Manufacturing process for cylindrical cells requires the electrolytes be formed from pastes of active material powders, binders, solvents and additives to be fed to coating machines and spread on current collector foils, such as aluminum for the cathode side and copper for the anode side. Next, there is a subsequent calendaring for homogeneous thickness and particle size, followed by slitting to the correct width. These components are then stacked to separator-anode-separator-cathode stacks, followed by winding to cylindrical cells, insertion in cylindrical cases, and welding of a conducting tab. These cells are then filled with electrolytes. The electrolyte has to wet the separator, soak in, then wet the electrodes. The wetting and soaking process is the slowest step and therefore is the determining factor in the speed of the line. All other needed insulators, seals and safety devices are then attached and connected before the cells are charged and tested for the first time. It is quite common for cells to be vented during the first charge. First charging cycles follow sophisticated protocols to enhance the performance, cycling behavior, and service life of the cells, as they have a direct impact on long-term efficiency. Recently, efforts have been made in combined and hybrid processing, such as direct deposition of separators onto electrodes and rapid heat treatments. Unfortunately, the use of slurry to manufacture cathodes has many disadvantages. One, there is no solubility, as a slurry is just another name for a suspension. There is also no guarantee of material homogeneity with slurries. When the solvent is removed from the slurry, the resulting film is very rough and instead of coalescing, analogous pieces stick together like 'Rice Crispy Treats.' This issue is How Today's Lithium-Ion Batteries are Made In general, the negative electrode of a conventional lithium-ion cell is made from carbon. The positive electrode is a metal oxide, and the electrolyte is a lithium salt in an organic solvent. Cells of lithium ion batteries can generally be classified into four groups according to its shapes: small cylindrical (solid body without terminals, such as for laptop batteries); large cylindrical (solid body with large threaded www.BatteryPowerOnline.com Fall 2016 * Battery Power 5 http://www.BatteryPowerOnline.com

Table of Contents for the Digital Edition of Battery Power - Fall 2016

Improving Lithium-Ion Battery for Future Energy Storage Needs
Protecting Lithium Batteries and Battery Packs from Runaway Thermal Events
Sorting Busbar Choices for Electric Vehicle Power Distribution
2016 Battery Power Resource Guide
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Battery Power - Fall 2016 - Improving Lithium-Ion Battery for Future Energy Storage Needs
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Battery Power - Fall 2016 - Protecting Lithium Batteries and Battery Packs from Runaway Thermal Events
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Battery Power - Fall 2016 - Sorting Busbar Choices for Electric Vehicle Power Distribution
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