Building batteries for the Chevrolet Bolt

By Christopher A. Sawyer
The Virtual Driver

(April 22, 2016) There’s a lot of money in the battery business. A lot. And it’s not just in the design and development of new chemistries. Much of the money is tied up in inventory as it takes a minimum of 30 days to go from completed battery cell to one that is capable of being packaged and installed in a car.

The length (and cost) of this conditioning process puts a lot of pressure on automakers and battery suppliers to guarantee a steady volume of product as cash flow pays for product in-process. Which explains the acquiescence of both parties to regulatory policies that increase production of both hybrid and full-electric vehicles. They guarantee there will be demand for the batteries in production and conditioning today, and

LG Chem’s battery plant on Michigan’s west coast (known as LGCMI) delivered its first shipment to GM — batteries for the first generation Volt — in November of 2013. Within seven months it had built and shipped its one millionth cell. Less than 12 months after that, it had changed over to producing cells for the second generation Volt battery.

All this took place in a facility that includes both the main offices and assembly buildings, the latter of which includes one electrode and three
assembly lines. But a quick look around shows that LG Chem has plenty of room for both a Phase 2 and Phase 3 expansion; a combination that would more than triple the output of the facility. Apparently, vehicle electrification has a solid future.

A carbon/lithium-ion slurry is deposited on a foil carrier and sent through an oven where the jumbo roll is reversed and printed on the opposite side. From there it is sent through a press where it is rolled to a pre-determined thickness to increase potential energy density.

GM is LGCMI’s biggest customer, but not its only one. (The others have yet to be announced.) It’s quite a change from 2007 when, according to Bill Wallace, GM’s Director of Global Battery Systems Engineering, “No one in the industry knew if you could create an automotive cell that would last for 6,000 cycle and 10 years.” Yet the anonymous data compiled from the OnStar system in customer Volts has shown:

    No Volt battery has worn out electromechanically.
    The oldest battery is nearly five years old and producing at or above expectations.
    LG Chem’s defect rate is 2 ppm, one-ninth that of Lego.

“A battery is only as good as its weakest cell,” says LGCMI President Nick Kassanos, “and of the nearly 23 million cells produced thus far, fewer than 46 have failed in service. Legos may be precision-molded plastic blocks, but we’re pretty darn proud of our failure rate, though we are working to get it even lower. Zero defects is our goal.”

Part of what makes the plant so successful is that it is a clean room environment. Walk past the reception area, and you are directed toward a sitting area and a row of built-in lockers. There you swap your shoes for a pair of Crocs. You can’t go anywhere within the facility without them. Tour the assembly area, and the fun continues. Hair nets and ridiculously undersized “bunny suits” await, as do large sticky mats at each entrance, and air showers designed to keep the work areas contaminant free.

Mark Song is the manager of the Electrode Department, and as comfortable in a bunny suit as any man can be. He leads you past the slitters and roller to the back of the building where the whole process begins. There, in a large white room stands an enormous stainless steel mixer mounted to a stainless steel floor.

“Everything has to travel four floors to move from raw materials to this mixer,” he says, “which is where a high-speed impeller turns the ingredients into a slurry.”

The paste is almost black, the color of dark chocolate, and coats the copper foil that acts as the substrate for the battery anode. (The cathode side uses aluminum foil.) It is made up of carbon (which, depending upon what it is mixed with, acts as both the conductive material and binder) and lithium ion material that has been granulated, sifted and mixed to a pharmaceutical-level consistency.

A proprietary ceramic-coated film separates cathode from anode in a folded five-layer sandwich that makes up a single battery cell. Once placed in a pouch, filled with electrolyte and sealed, the clock starts on the cell’s life.

“Electrode coating looks a lot like a printing plant,” says Song. “It’s a two-story process that places the slurry on the substrate, sends it though the oven, then coats the bottom of the substrate, repeats the oven step, and then winds the electrodes into jumbo rolls.” Each roll has three wide stripes of cured slurry separated by thick bands of uncoated substrate. Two other bands of clear substrate act as the outside margins. “It’s essential that we control the amount of slurry on the substrate,” says Kassanos, “in order to get the properties we require. And each jumbo roll is sent through a press that controls its thickness.” By pressing each roll to a pre-determined thickness, the energy density and capacity of the material is increased.

The completed jumbo rolls are sequestered in a holding area ­— anodes on one set of racks, cathodes on another — before making their way to the slitting room. Here the rolls are cut along the exposed substrate into three smaller rolls called pancakes. From there they are sent out for notching.

Approximately 30 days after assembly, the cells are ready for shipment. LG Chem’s defect rate is currently less than 2 ppm on 23 million cells produced

This is Aaron Svacha’s bailiwick. He has been at LGCMI from the beginning, and wastes no time telling you that the plant is running 24 hours a day over three shifts. “The notching is done by machine to a tolerance of one one-thousandth of a millimeter, and overseen by a machine vision system that monitors part dimensions continuously,” he says.

Almost faster than you can say the words, a punch and die slices away the unneeded portion of the uncoated electrode, and the offal is sucked out and sent to a collection bin for recycling. Also sent for recycling is the relative humidity. The area is like Chile’s Atacama Desert as it has a relative humidity of just one percent. This prevents the pancakes from absorbing humidity (“It’s kryptonite to an electrode,” says Kassanos.) after they are run through the heated vacuum dryer.

Lamination sees the anodes and cathodes laminated into a bi-cell where a proprietary ceramic-coated base film acts as a safety separator between the electrodes. This five-layer sandwich places an anode on the top and bottom with an electrode in the middle, and the bi-cells are folded to create a single cell with 20 anodes and 19 cathodes welded together. A machine-formed pouch sealed on three of its four sides houses each cell, and this is placed in a wetting chamber.

Here vacuum draws the electrolyte through the cell, and though the fourth edge is sealed, a large flap is formed to allow the gasses created in the formation process to rise into. “The clock starts at sealing for the cells,” says Formation Manager Steve Zachar, “and normal aging of a fully wet cell takes anywhere from 24 – 72 hours, depending on the cell.” The initial charge takes from two to six days in the charge box, and high-temperature aging (24 hours at 60˚C) not only speeds the process but weeds out underperforming cells.

The entire formation process is computer controlled and automated, with 100% inspection. Once the high-temp aging is complete, the cells are degassed and resealed in a vacuum chamber, then aged for a further 14 days while they await shipping. Each cells’ voltage, weight, dimensions and performance are checked at seven and 14 days, and performance is monitored up to the time it is shipped. “This is an inventory heavy business like wine making,” says Kassanos, “where your product — your money — spends at least 30 days being assembled and processed before it can be used.”

Sidebar: After the Bolt

In addition to the Volt, LGCMI’s cells will be used in the diminutive Chevy Bolt crossover. There they will be assembled into a battery pack that extends across much of the underside of the floorpan. According to GM’s chief of Global Product Development, Mark Reuss, “The joint work we did [with LG] on the Volt led directly to development of the Bolt, and has gotten us down the [battery] cost curve faster.”

LG will supply the Bolt’s battery cells and pack, high-power distribution module and battery heater. It also will supply the GM-designed electric drive motor, power inverter module, on board charger, accessory power module, power line communication module, electric HVAC compressor, instrument cluster and infotainment system. “Working with LG in the past opened up opportunities for LG, and GM, through the Bolt program and future products,” says Pam Fletcher, Engineering Director, Electric Vehicles. Especially, as Fletcher points out, the technology is changing so quickly, “You don’t want to get tied into a technology, especially in the early days when the volumes are uneven and prices are changing.”

The early days for the Bolt program took place in the fourth quarter of 2012. Given its forward-looking technology, it’s no surprise that the first concept was a wild, futuristic small car. In fact, it proved to be too futuristic. This resulted in the second concept, a bland, timid design that owed much to the then-current GM small car fleet. It also failed in customer clinics. That led to the Bolt concept rolled out at the 2015 auto show in Detroit. Like Goldilocks’ porridge, it was just right. It also benefited from a rethink of the entire EV program that moved from one vehicle built on a modified production small car platform, to a family of vehicles built on a VW MQB-like modular structure that used some componentry from GM’s production small cars to keep costs in check.

Confident that they have the driving range where customers want it (at least 200 miles on a full charge in everyday use), GM can concentrate on expanding the EV market with additions to the line. Under consideration are vehicles like a small two-seat sports coupe and convertible, an affordable sport sedan, an urban monobox and city car, and more. All would be built on the Bolt platform, altering the wheelbase, width, height and overhangs to suit the vehicle.

As with the production Bolt, GMDAT in South Korea will act as the homeroom for these vehicles, which could start hitting the road as early as 2018.

The Virtual Driver