Friday, September 24, 2010

Lithium Battery Manufacturing For Automotive Use and the Associated Manufacturing Facility Requirements

In 2009 the Department of Energy provided over $2 billion in grants and $25 billion in funding for low interest loan guarantees for the proliferation of the manufacture of alternate energy vehicles. The lion’s share of that funding went to automobile manufacturers and suppliers to that industry for the process development and construction of facilities for the manufacture of battery packs for battery operated vehicles. This should not be confused with Hybrid Vehicles, which utilize a combination of battery and internal combustion dry trains. The Nissan “Leaf” and Chevy “Volt,” to name just two, will be 100% battery operated.
Between late 2010 and early 2012 nearly ten different fully battery operated models will hit the market. The battery pack manufacturing infrastructure is the first step. If the market catches on there will be requirements for recharging stations, battery replacement facilities, and waste disposal plants, as for now the government is funding the development with grants that require matching funds from the company. The names of those companies include A123, SAFT America, Johnson Controls, Compact Power, and Enerdel to name just a few.
The processes used for manufacturing Lithium batteries are very similar to those used in the production of Nickel Cadmium cells and Nickel Metal Hydride cells with some key differences associated with the higher reactivity of the chemicals used in the Lithium cells. The anodes and cathodes in Lithium cells are of similar form and are made by similar processes. The active electrode materials are coated on both sides of metallic foils which act as the current collectors conducting the current in and out of the cell. The anode material is a form of Carbon and the cathode is a Lithium metal oxide. Both of these materials are delivered to the factory in the form of black powder and to the untrained eye they are almost indistinguishable from each other. Since contamination between the anode and cathode materials will ruin the battery, great care must be taken to prevent these materials from coming into contact with each other. For this reason the anodes and cathodes are usually processed in different rooms. The metal electrode foils are delivered on large reels, typically about 500 mm wide, with copper for the anode and aluminum for the cathode, and these reels are mounted directly on the coating machines where the foil is unreeled as it is fed into the machine through precision rollers. The first stage is to mix the electrode materials with a conductive binder to form slurry which is spread on the surface of the foil as it passes into the machine. From the coater, the coated foil is fed directly into a long drying oven to bake the electrode material onto the foil. As the coated foil exits the oven it is re-reeled. The coated foils are subsequently fed into slitting machines to cut the foil into narrower strips suitable for different sizes of electrodes. Later they are cut to length. Any burrs on the edges of the foil strips could give rise to internal short circuits in the cells so the slitting machine must be very precisely manufactured and maintained.
The first stage in the assembly process is to build the electrode sub-assembly in which the separator is sandwiched between the anode and the cathode. Two basic electrode structures are used depending on the type of cell casing to be used, a stacked structure for use in prismatic cells and a spiral wound structure for use in cylindrical cells.
  • Prismatic cells are often used for high capacity battery applications to optimize the use of space. These designs use a stacked electrode structure in which the anode and cathode foils are cut into individual electrode plates which are stacked alternately and kept apart by the separator.
  • For cylindrical cells the anode and cathode foils are cut into two long strips which are wound on a cylindrical mandrel, together with the separator which keeps them apart, to form a jelly roll.
The next stage is to connect the electrode structure to the terminals together with any safety devices and to insert this sub-assembly into the can. The can is then sealed in a laser welding or heating process, depending on the case material, leaving an opening for injecting the electrolyte into the can.
The following stage is to fill the cell with the electrolyte and seal it. This must be carried out in a “dry room” since the electrolyte reacts with water. Moisture will cause the electrolyte to decompose with the emission of toxic gases. Lithium Hexafluoride (LiPF6) for instance, one of the most commonly used electrolyte materials, reacts with water forming toxic hydrofluoric acid (HF).
Once the cell assembly is complete the cell must be put through at least one precisely controlled charge/discharge cycle to activate the working materials, transforming them into their useable form. During formation, data on the cell performance such as capacity and impedance, are gathered and recorded for quality analysis and traceability. The spread of the performance measurements also gives an indication of whether the process is under control.
Tight tolerances and strict process controls are essential throughout the manufacturing process. Contamination, physical damage, and burrs on the electrodes are particularly dangerous since they can cause penetration of the separator giving rise to internal short circuits in the cell and there are no protection methods which can prevent or control this. Cleanliness is essential to prevent contamination and cells are normally manufactured in cleanroom conditions with controlled access to the assembly facilities often via air showers. When constructing a Lithium Ion Battery Facility for Fuel Cell or Field Device use, a particular portion of the facility is required to be a dry (see Figure “A” Cell Assembly) and/or clean (see Figure “B” Electrode Coating) room. Additionally several preliminary assembly steps (Case Manufacturing, Sub Assembly, and Welding) possibly will require cleanroom assembly and/or cleaning and packaging due to the need to ensure the substrates do not add or contribute contamination to the process. Most notably the facilities will have the following parameters:
  • Class 10,000 (ISO Class 7) to Class 1,000 (ISO Class 6)
  • 70° F Temperature Parameters
  • 2% to 10% Relative Humidity (As low as -40 degree dewpoint)
Given the above requirements there are several significant technologies, both from an engineering and construction material perspective, developed for pharmaceutical and semiconductor cleanrooms and BSL (Biological Safety Level) facilities that can or should be applied to these facilities.
Desiccant Drying capability will be required to meet the needs of the dry rooms, due to the low level of humidity and dewpoint of the factory air. Low leakage ductwork (both on the supply and return side) commensurate with the requirements of BSL facilities will be required (meeting ASHRAE heavy duty duct parameters); however, it will be a polar opposite application (i.e. BSL facilities are designed to be negative pressure with Lithium Ion facilities being designed to be positive pressure) to help guard against moisture migration. We must be observant that unlike biological organisms, moisture can migrate against pressure. Additionally buffer zones will be required to provide a degree of safety for the facility, to allow for the ability to provide for access without compromising the internal “dry” zone. What we have learned in BSL facilities in terms of pressurization testing and sealing of ducts, dampers, conduits, and doors is directly applicable for dry rooms.
Figure A
Figure B
Hot Buttons, Concepts, and Ideas
  1. Ducting systems must be inspected and maintained on a continual basis. Potentially a buffer zone may be appropriate for interstitial area.
  2. Possibly create a sealed plenum overhead and use return as the “buffer” zone.
  3. People loads are an issue that is significant and the old ASHRAE load assessment is outdated and/or inappropriate. Traditional engineers need an education.
  4. Require air locks and pass thrus for material and personnel entry. NO openings. Vapor equalizes against pressure. Use cleanroom and BSL technology.

Moisture barriers in slabs are of particular concern. Not only will barriers be required to reduce moisture transfer from ground water, but additional precautions must be taken commensurate with technologies utilized for sub-water table foundation work even in areas where the facility does not come in contact with the water table. Low moisture foundation pours will be a standard and hydrostatic resistant slab treatments, as well as moisture barrier built up (aggregate) epoxies, will be required to eliminate moisture migration through the floor. This technology is a direct transfer from Pharmaceutical applications but will have the additional requirement to dissipate static (due to the dry conditions), withstand stains from chemicals utilized, and the ability to be cleaned without utilizing water. Ergonomics of personnel working on these surfaces should also be incorporated into the correct product selections.
Hot Buttons, Concepts, and Ideas
  1. Vapor Barrier when pouring the slab. Tapped seams, topped with sand prior to rebar and concrete, so barrier is not punctured during installation or concrete pour. Inspected during installation and certified to be sealed.
  2. “High Early” concrete mix to minimize moisture content in the slab.
  3. Enclose the box that the facility will be constructed within and use desiccant driers during construction. Create a build clean/dry protocol to ensure the minimization of latent moisture as well as particulate.
  4. Use a slab treatment to seal against moisture penetration through the slab (Koester manufactures a particularly good product).
  5. Use epoxy slab coating to ensure slab is not compromised.

Modular systems used for Pharmaceutical and BSL facilities lend themselves particularly to application in this marketplace (with particular modifications to address static dissipation), due to their precise manufacturing parameters and durability. We are not concerned with the ability to hold up to harsh cleaners but we are concerned with the ability to withstand caustic chemicals used in the cells and to provide for static dissipation due to extremely dry conditions, while being required to create a strong vapor barrier. Manufacturers with both experience in wafer fab facility wall systems (for the chemical resistance of the surface coating and static dissipative capabilities) and Pharmaceutical/BSL applications (for the pressure maintenance and door seals) are the only firms that can provide a system delivered to meet the unique combination of this application, not to mention that a good portion of the facility will also be a cleanroom in nature. Particular concerns relate to panel to panel seal, flexible yet moisture barrier caulking, internal penetration seals, and interface with the floor installation. Applying pharmaceutical door openers with interlocks, and entrance control prevalent in Pharma facilities, may be an important application to control facility access.
The ceiling is of considerable concern and a panelized Pharma type modular ceiling has particular attraction for several reasons. A standard 2' x 4' T-Bar type ceiling is not practically viable in this type of environment due to the required vapor barrier and inability of a T-Bar ceiling to create and maintain that barrier over time. A gel type ceiling, used for cleanroom wafer fabs, is appropriate, and will maintain the vapor barrier, but is not cost effective. A standard drywall lid as is used for rated corridors (1 hr. and 2 hr. construction) can be constructed to meet the vapor transmission requirements but that would require an elaborate catwalk system to maintain and inspect the ducting system overhead, and over time the maintenance required to the envelope would be costly. A modular panelized ceiling that is also walk-able for maintenance and service would achieve the desired barrier and provide for all ceiling maintenance to be done from above (as is the goal in Pharma facilities for different objectives) without requiring catwalks for maintenance.
Hot Buttons, Concepts, and Ideas
  1. Need cam locked panels for seal to ensure zero vapor transmission.
  2. Require air locks and pass thrus for material and personnel entry. No openings, vapor equalizes against pressure. Use cleanroom and BSL technology. Must create vapor barrier and maintain seal. Can’t move with building movement, independent support from floor. Not issue if floor above is fan deck and not single story.
  3. Must use materials that do not hold moisture (drywall or fiberboard ceiling tiles are an issue) or dry and crack.
  4. Maintenance must be achieved without penetrating without compromising the envelope seal.
  5. Light fixtures must be maintained from above so no penetration of the ceiling is required. Ideally they should be vapor sealed to sealing (Wet area application and/or explosion proof housings) to achieve the desired control.

Applying what we have learned in the Pharma, BSL, and Semiconductor Industries, and incorporating Dry Room design experience from industry, provides us a strong base of knowledge to deliver a cost effective facility for Lithium Ion Battery manufacturing that can meet the manufacturing and environmental control parameters for the clean/dry rooms desired to meet the constraints. Modular components will provide long term performance with minimal maintenance as has been the conclusion in the Pharma Industry. Additionally utilizing modular components will provide the clients an additional advantage allowing for accelerated depreciation, sales tax exemptions for material purchases (as has been the precedence for the Semiconductor and Pharma Industries) in line with capital equipment purchases, and potentially allow for facility leasing and/or off the balance sheet transactions which will be of desire for startup firms that want to minimize capital outlays and/or wish to accelerate the write off for tax purposes, or to transfer costs to operational expenses vs. capital expenditure.
Tim Loughran is the principal of Cleanroom Construction Associates. Tim has over 25 years designing and constructing cleanrooms for the Microelectronics, Semiconductor, Biopharma, and Nanotechnology industries. Formerly a Founder and Managing Partner of AdvanceTEC, LLC, Manager of Design/Build Services for Performance Contracting, Inc., and Division Manager for the Cleanroom Engineering Division of Cleanroom Products. He has published papers on numerous subjects including Clean Packaging Technology, Fan Filter Evaluation, Air Shower Performance, Retrofitting Cleanrooms, Tool Matrix Development, and Design/Build Cleanroom Specification and Proposal Evaluation. He is a frequent contributor to Controlled Environments Magazine and former president of his local chapter of the IEST. Most notably Tim was on the faculty of The National Institute of Standard and Technology’s (N.I.S.T.) Building for Advanced Technology Workshop in 2003.

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