Comprehensive Overview of Lithium-Ion Battery Enclosures in Electric Vehicles

Comprehensive Overview of Lithium-Ion Battery Enclosures in Electric Vehicles

General overview of battery enclosures

Lithium-ion batteries are widely used in electric cars as auxiliary batteries. Lithium-ion batteries (LIB) encompass a comprehensive family of battery chemistries that incorporate the lightweight lithium element, offering superior energy density compared to other batteries. They possess enhanced storage capacity at the cell voltage level and exhibit a prolonged charge retention capability, typically lasting five to ten years.  For minimal cover protection, electric cover batteries are the most often used batteries, also employed in various consumer items such as electric bicycles and maintenance equipment for lawn and power tools. The cell voltage of a lithium-ion battery often ranges from 3 to 4 volts. Lithium-ion batteries (LIBs) are optimal energy sources due to their high energy density, minimal self-discharge rate, and absence of memory effect, which prevents capacity reduction during partial discharge and charge cycles (1).

An increase in energy density enhances the power and extends the range of electric vehicles (EVs). Consequently, these increases have affected the safety of those employed in EV LIBs. A fully charged LIB system operates within a range of hundreds of volts. In addition to the high voltage, measurements have been conducted on the short circuit current, with amperage reaching thousands in extensive developed battery systems. Systems exhibiting these characteristics pose risks in the workplace and need specific personal protective equipment, operational procedures, and designated work settings. Batteries with diminished voltage are often deemed non-hazardous in several instances (2).

Shock boundaries are essential regulatory measures in battery enclosures designed to establish a safe distance between the electrical source and individuals working on electric vehicles, irrespective of whether the worker is directly engaging with the source or may potentially come into contact with it. They include limited, restricted, and forbidden approach borders. Each border serves a distinct role that is defined by distance. The border distance is dictated by the kind of power supply, whether AC or DC, as well as the nominal voltage rating (3).

To recognize a supplementary border, one should use the arc flash boundary. An arc flash boundary hazard is not an electric shock per se, but rather a continuous plasma produced by the current gas that may be undergoing breakdown in a generally nonconductive medium, such as air. An arc flash happens when a fault arises or during a short circuit situation that traverses the gap of the arc. The onset of an arc flash may happen from inadvertent contact, equipment corrosion or degradation, tracking or contamination of insulated surfaces, inadequately rated equipment for available short circuit currents, among other factors (4).

An arc flash event may release a substantial and lethal quantity of energy. The arc results in air ionization, and hence, the temperatures of an arc flash may reach up to 35,000 degrees Fahrenheit. Extreme temperatures may ignite garments and cause severe burns to human flesh within a matter of seconds, even at a considerable distance from the source of the heat. The heat may potentially ignite any adjacent flammable items. Arc flash temperatures may liquefy or vaporize nearby metal components, such as aluminum, copper conductors, or steel equipment parts.  This material undergoes fast volumetric expansion during its phase transition from solid to vapor, generating explosive acoustic energy and pressure (5). This surge of pressure may dislodge people off ladders, destabilize their equilibrium, and propel them into walls, across the room, or onto other equipment. The exposure to loud sounds may cause eardrum rupture, perhaps resulting in permanent or temporary hearing loss. The explosion may disseminate molten metal across the area. Solid metal debris, along with other loose things such as electric vehicle tools, may be transformed into lethal missiles as a result of these explosions. The intense flash produced by the incident may cause either permanent or temporary blindness. All of these factors may result in damage to an electric vehicle, potential fatalities, or personal injury (6).

Materials now used in battery enclosures

Personal protection equipment refers to things worn by workers engaged in electric vehicle tasks to safeguard against identified dangers and hazardous activities. PPE for the electric power business often includes face shields, safety shoes, safety glasses, hard helmets, insulated sleeves, insulated rubber gloves with leather protectors, and flame-resistant apparel, contingent upon the specific work requirements. Additional personal protective equipment such as respirators, fall protection gear, cut-resistant gloves, or chemical-resistant gloves and chaps may be required, depending on the danger assessment. Electrical PPE is specifically designed to safeguard individuals from electrical hazards and dangers associated with hazardous tasks.

Lower cover protection batteries use diverse manufacturing procedures for consumer-grade electronic batteries, using many advanced technical processes in their creation. Despite the many shapes of cells produced by manufacturers, including cylindrical, pouch, and prismatic forms, the production procedures for these cells are mostly similar. The contemporary state-of-the-art manufacturing process has three components: electrode preparation, cell assembly, and the initiation of battery electrochemistry (8).  

Initially, the active material, designated as AM, together with the binder and conductive additive, is combined to create a homogeneous slurry with the solvent. In the cathode situation, N-methyl pyrrolidone is typically used to dissolve polyvinylidene, the binder, whereas in the anode example, the styrene-butadiene rubber binder is solubilized in water using carboxymethyl cellulose (9).  Subsequently, the slurry is pumped into a slot die, which is covered on both sides of the current collector, and then directed to drying equipment to facilitate solvent evaporation.  The organic solvent typically used in the cathode slurry is hazardous and subject to stringent emission regulations. Consequently, the solvent recovery process is crucial for cathode production during drying, with the recovered NMP being reapplied in battery manufacture, resulting in a loss of 20 to 30 percent. The vapor from the water-based anode slurry, which is innocuous, may be immediately released into the surrounding environment. The calendaring procedure may aid in modifying the physical characteristics of the electrodes, including porosity, density, conductivity, and bonding. Upon completion of all procedures, the completed electrodes are stamped and slitted to the dimensions necessary for the cell's design. Subsequently, the electrodes are placed in the oven's vacuum to eliminate excess moisture. The moisture content on the electrodes will be assessed post-drying to ensure the minimization of corrosion and side reactions (10).

After the electrodes have been adequately prepared, they are sent to the dry room for cell manufacture with the dried separators. The separator and electrodes are arranged in layers to constitute the internal structure of the cell. The copper and aluminum tabs are welded to the anode and cathode current collectors, respectively.  The predominant welding technology used is ultrasonic welding, however some manufacturers may choose resistance welding in their cell design. The cell stack is thereafter sent to the designated enclosure, which now lacks a common standard. Each manufacturer has certain preferences based on the intended use of the cells. The electrolyte is used to fill the enclosure prior to its final sealing and the conclusion of cell production (11).

Shock bounds

From 2011 until 2019, the hybrid Chevrolet Volt, spanning two generations, was manufactured as one of the lower cover protectors for electric automobiles. The Chevrolet Bolt has replaced the Volt and is a fully electric car anticipated to be produced over the next decades. Since 2010, around 150,000 volts have allegedly been sold in the United States. Consequently, an average of 43,200,000 LIB cells has been produced to satisfy the need, given that each cell comprises 288 individual cells.   Moreover, each electric vehicle (EV) during its lifespan may use a minimum of one battery, indicating that the quantity of produced batteries might be at least thrice (12).

The examination and disassembly of the Generation One (Gen-1) Chevrolet Volt lasted 18 minutes and 15 seconds. A Midtronics EL-50332 battery discharging system was used to gather information, including the charge state, VIN number, health status, and its capability to execute section, pack, and module discharges, as well as section balancing and de-powering of both pack and section. The gen-1 battery pack has three sections, containing nine modules: five in section one and two in both sections two and three. Each module has many cell numbers that determine the energy capacity and voltage rate. The EL-50332 is a valuable instrument for servicing a battery outside of the vehicle, enabling the battery interface cable to be directly connected to the module, pack, and section. The identification of the pack is the primary component of the ORNL disassembly procedure. ID can ascertain the disassembly procedure, which varies for each type or brand of battery. Power and communication lines were connected to the battery interface in a matter of seconds. Upon powering the EL-50332, one may operate on the park or its three components, either inside or outside the vehicle, and may choose to discharge, charge, or balance. The Chevrolet received was at 30% state of charge for disassembly and was in excellent shape. The high-voltage and communication wires are unplugged, allowing for the system to be powered off. It can now be concluded that the battery pack may be securely dismantled (13).

Two qualified electrical personnel from ORNL, equipped with appropriate personal protective equipment, may physically unhook or remove the plug. The fasteners of the outer cover are then detached using insulated tools, allowing for the removal of the protective plastic cover. A further examination may be conducted after the cover is removed to assess any damage inside the package that may not be visible while the cover is in place. The DC voltage may be verified to confirm the accuracy of the midtronics service data. The battery pack should be examined for any indications of scratches, dents, discolouration, and swelling. In the event of significant mechanical damage, work is halted immediately (14).

Companies anticipate the use of substantial battery enclosures, fabricated from thermoplastics, in electric vehicle production as early as 2024, due to continuous developments in the field. A plug-in hybrid electric car type is now used in China, using the Sabic PP compound instead of aluminum for its battery pack cover, which provides warpage control, extensive design flexibility, weight reduction, and further benefits. Current global manufacture of other electric vehicles use various materials for components such as battery enclosures, battery modules, cell housings, and carriers.  Furthermore, the newly created materials that meet electric vehicle criteria are being used by several industries to enhance technologies for large-scale production, crashworthiness, assembly and joining, battery heat management, performance testing, electrical characteristics, and retardancy.

References

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