Battery Enclosure For Lithium-ion Batteries: Safety, Materials, Manufacturing, And Personal Protective Equipment

Battery enclosure in general

Lithium ion batteries are extensively applied in electric vehicles as cover batteries. LIB defines a whole battery chemistries family which contains the lithium element that is light-weighted, which provides a higher density of energy than other batteries with higher capability of storage in the voltage of cells, and also with a higher retaining power of charges, usually five to ten years.  For lower cover protection, electric cover batteries is the most considered battery, and also used in other numerous consumer products such as electric bicycles, equipment maintenance of lawn and tools of power. Typically, the cell voltage of LIB a cover battery is between 3-4 volts. The LIBs are the best energy sources for applications as a result of their high density of energy, reduced rate of self-discharge and unavailability of memory, for instance, reduced in capacity as a result of partial discharge and charge of a battery (1).

Increase in density of energy gives EVs an increase in power and an extended range. In return, these increases have got an impact on the safety of those who work on EV LIBs. An LIB system that is charged in full exists between a numbers of volts in hundreds. Besides the high voltage, measurement has been done on the current of the short circuit and a number of amps in thousands in large developed systems of batteries. Systems that contain these features are hazardous in the working environment and need particular personal protection equipment, procedures of working and particular environments of work. Batteries with reduced voltage are considered not dangerous in many cases (2).

Shock boundaries are the basic requirement regulation in the battery enclosure whose intention is to generate a distance between the electric source and the person who is working on the electric vehicle, regardless of if that worker is doing his or her work on the source or may possibly have a contact with the source. They include limited, restricted and prohibited approach boundaries. Every boundary has got an exclusive purpose that distance differentiates. The distance of the boundary is determined by the type of the power source, either AC or DC, and also the rating of the nominal voltage (3).

To be aware of a supplemental boundary, the arc flash boundary should be used. An arc flash boundary danger is not electric shock exactly but is ongoing plasma generated from the current gas that may be breaking down, in a medium that is nonconductive typically, for instance air. An arc flash takes place when a fault occurs, or during the condition of the short circuit, which goes through the gap of the arc. The initiation of the arc flash can occur as a result of accidental contact, corrosion or deterioration of equipment, tracking over or contamination over surfaces that are insulated, underrated equipment for the current of the short circuit that is available, and several other causes (4).

An event of an arc flash is capable of expelling a huge deadly amount of energy. The arc leads to air ionization, and in return, the temperatures of an arc flash can go up to 35000 Fahrenheit degrees. These temperatures that are on their extreme can lead to fire to clothing and so many burns on the skin of a human being within a very short period of time, usually in fractions of a second, at a great length from an event. Its heat also can lead to ignition of any materials that are combustible in the nearby. Arc flash temperatures have got also the ability of liquefying or vaporizing parts of metal in the vicinity of an occurrence like aluminum or copper conductors or parts of equipment of steel.  This material expands rapidly in volume while it is changing its state to vapor from solid, which results in acoustic energy and pressure that is explosive (5). This wave of pressure is capable of knocking the workers off ladders or off balance and even throwing them against the wall, across the room or on other equipment. The blasting of sound can result to rupturing of eardrums, which can lead to permanent or temporary loss of hearing. The spraying of molten metal can be done all through the vicinity by the blast. Solid metal debris together with other objects which are loose, for instance tools of an electric vehicle can be changed into projectiles that are very deadly due to these explosions. Also, the bright flash which results from the event can lead to permanent or temporary blindness. All of these can lead to the damage of an electric vehicle, possible deaths or even personal injuries (6).

Current materials used in battery enclosure

Personal protective equipment defines items that are worn typically by a worker who may be working on the EV to ensure he or she is protected from recognized risks and hazardous acts. Depending on the task of the job to be carried out, PPE for the industry of electric power generally involves face shields, safety shoes, safety glasses, hard hats, sleeves that are insulated, insulated rubber gloves which have leather protectors, and clothing that is resistant to flames. Extra PPE like respirators, fall protection equipment, cut-resistant gloves or chemical resistant gloves and chaps might be needed, relying on the assessment of the hazard. Electrical PPE is particularly to protect an individual from electrical risks and hazardous activities (7).

Lower cover protection batteries have got various manufacturing techniques for consumer initial electronic batteries and a number of the mature technological works have been taken to the production of the battery of the state-of-the-art. Even though manufacturers of these batteries have got various designs of cells which includes cylindrical, pouch and prismatic, the techniques of manufacturing the cell are very similar. The current state-of-the-art manufacturing technique involves three parts which are preparation of electrode, assembling of cell and battery electrochemistry instigation (8).  

Firstly, the active material referred to as the AM, binder and conductive additive are mixed, forming a slurry that is uniform with the solvent. For the case of the cathode, N-methyl pyrrolidone is usually applied in dissolving the polyvinylidene, the binder, and in the case of the anode, the styrene-butadiene rubber binder is liquidized in water using carboxymethyl cellulose (9).  After that, the pumping of the slurry is done into a slot die, which is coated on the current collector’s two surfaces, and delivered to equipment that is used for drying so as the solvent is evaporated.  For the slurry of the cathode, the usual organic solvent is toxic and also has got strict rules of emissions. Therefore, a process of recovering the solvent is important for producing the cathode when drying and he NMP recovered is reapplied in manufacturing of battery with 20 to 30 percent loss. In the case of the slurry of the anode that is water based, the vapor that is harmless can be exhausted directly to the ambient environment. The following process of calendaring can assist in adjusting the physical properties which include porosity, density, conductivity, bonding, etc. of the electrodes. Once all these processes are done, the electrodes finished are stamped and slitted to the dimension required in fitting the design of the cell. After that, the electrodes are sent to the oven’s vacuum so that extra water is removed. The level of moisture on the electrodes will be looked on after drying to make sure the corrosion and the side reaction are minimized (10).

Once proper preparation of electrodes has been done, the electrodes are transferred to the dry room for the production of the cell with separators that have been dried. The separator and the electrodes are stacked or winded in layers to form the cell’s internal structure. The tabs of copper and aluminum are welded on the anode and the cathode current collector, in that order.  The most technique of welding commonly used is ultrasonic welding, and other manufacturers may opt to use resistance welding while designing their cell. The stack of the cell is then sent to the designed enclosure, which currently does not contain a standard that is consistent. Every manufacturer has got what they prefer depending on the cells purpose. The electrolyte is used in filling the enclosure before it is finally sealed and its completion in producing the cell (11).

Shock boundaries

From the year 2011 to 2019, the hybrid Chevrolet volt of two generations which is one of the lower cover protections for electric vehicles was produced. The bolt of Chevrolet has taken over the volt and is a full electric vehicle which is predictable to be generated over the next decades. More than 150,000 volts have been reportedly sold since the year 2010 in the United States. Thus, averagely, 43,200,000 cells of LIB have been generated so that to meet the demand since every cell has got 288 cells.   Besides, every EV over its lifetime might use at least one battery, which suggests that there can be at least 3 times the number of the manufactured batteries (12).

The inspection of the Generation-one (Gen-1) Chevrolet Volt and its disassemblement was done for 18 minutes and 15 seconds. A  Midtronics EL-50332 discharging battery system was applied in collecting the information, like the charge state, the vin number, the health state and also if it can perform section, pack and module discharge, balancing of the section and also de-powering of pack and section. There are three parts in the gen-1 battery pack, which consists of nine modules, five of them in part one and two each in part two and three. Every module has got various cell numbers that builds the capacity of energy and also the rate of voltage. The EL-50332 is a beneficial tool in giving a service to a battery that is not within the car, which allows the battery interface cable to be directly been placed on the module, pack and section. Identification of the pack is the main element of the process of disassembling the ORNL. ID is able to determine the routine of disassembling, which is different for every model or make of a battery. Power and communication cables were put into the interface of the battery in very few seconds. After the EL-50332 is powered, one is able to work on the park or its three parts out or in of the car and can choose to discharge, charge or balance. The received Chevrolet was at 30 SOC percent for disassembly in good condition. High cables of voltage and communication are disconnected and the powering off of the system can be done. At this time, it can be determined that the pack of the battery could be safely be disassembled (13).

Two ORNL skilled electrical workers with proper PPE can manually disconnect or remove the plug by hand. Fasteners of the exterior cover are then disconnected through the application of insulated tools, so as the protective plastic cover is removed. A second inspection can be carried out once the cover has been removed to check cases of damage within the pack that may be observed while the cover is on. The voltage of the DC can be checked to ensure that the midtronics service measurements are validated to be correct. The battery pack also can be looked on for any signs of scratches, dents, discoloration and swelling. In case of any mechanical damage that are serious, work is stopped immediately (14).

Through the current ongoing work in the sector, companies are expecting a number of large battery enclosures, cast with its thermoplastics, to be applied in producing EVs as soon as early 2024. Already, one plug-in hybrid electric vehicle model is being used in China with the application of the Sabic PP compound in place of aluminum for its battery pack cover, offering warpage control, wide design freedom, weight savings and other advantages. Other EVs production around the world today is applying a number of these materials for components like battery enclosures, battery modules, cell housings and carriers, etc.  Additionally, the new materials developed in meting EV specifications, many companies are working to ensure enabled technologies fo huge section manufacturing, crashworthiness, assembly and joining, battery thermal management, performance testing, electrical properties and retardancy (15)

References

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