Volt and Its Battery Pack Converging on Product and Process Validation in February 2010; Fine-Tuning in Preparation for Start of Regular Production in Nov 2010
Both the Chevy Volt extended range electric vehicle and its battery pack are converging on the beginning of the product and process validation (PPV) stage of GM’s development and manufacturing process, scheduled to start in February 2010, according to an online status update given by Andrew Farrah, Volt Vehicle Chief Engineer and Bill Wallace, Engineering Group Manager, Voltec Battery Systems.
Both the vehicle and the pack have undergone some expected tweaking on the run-up to PPV based on the testing to date. On the vehicle side, these have included adjustments to address NVH (noise, vibration and harshness) issues when running in electric mode. On the pack and cell side, GM has made minor adjustments in the chemistry (LG Chem’s Li-ion manganese spinel) in collaboration with LG Chem for improved life. The current cell chemistry for the Volt, now in its fourth generation, is the one that will head into production.
Relative to tweaking [the cell], these are very small adjustments. Remember, this application is not a cell phone, we use this [cell] in a significantly different way. The adjustments are primarily for life. That is one of our largest challenges, but also one of the biggest assets for our battery. We think we’ve done some good things...this will be out production chemistry.—Bill Wallace
GM’s fleet of 80 pre-production Volts has logged more than 250,000 miles of testing so far, and has undergone hot weather testing in Death Valley, as well as mountain testing at Pike’s Peak and Baker’s Grade. During a briefing on the OnEVLAB in October (earlier post), Tony Posawatz, GM’s Vehicle Line Director for the Volt, noted that some Volts are also heading out overseas for testing under other harsh conditions.
|GM Battery Technology Evaluation|
|In a briefing on Li-ion battery chemistries provided in October, Andrew Leutheuser, GM Lead Battery Systems Engineer said that GM uses a four-phase evaluation process that resulted in the selection of the LG Chem cells for the Volt:
Volt battery development. The cells and packs have hit a number of testing milestones of their own, at the cell, module and pack levels.
More than 50,000 cells have been on test, all without failure, and GM has built more than 300 prototype battery packs. There have been more than 300,000 miles of customer use lab testing to date. Twenty of the 60 Battery Systems Lab pack channels are fully dedicated to Voltec.
The Volt team has access to another 20 channels on a shared basis, and the remaining 20 are for other GM technology programs, Wallace said.
(In a tour of the Battery Lab in October, about 10 the Volt T-packs were visible, showing four different configurations of interfaces and connectors. Asked about the differences, Andrew Leutheuser, Lead Battery Systems Engineer, explained that they reflected generational learnings to optimize pack function over the course of the pre-production process.)
|Battery module impact test. Source: GM.|
GM’s new Brownstown Battery Assembly Plant, where the production Voltec packs will be made, is installing its production equipment and is currently in process tests developed in the Battery Systems Lab prior to plant launch.
GM has conducted more than 150 tests (abusive and in-use) on the prismatic battery cells themselves, including cell penetration; crush; life cycling; thermal stress; overcharge;and performance characterization.
The battery modules have gone through high dynamic impact testing; static crush; sustained pressure; short circuit; thermal stress; and seal integrity tests.
|Result of a 30° forward impact at 65 km/h (40 mph). The orange T is the battery pack (the vehicle is tipped up to expose the bottom), and appears protected from the impact by the vehicle structure. Source: GM. Click to enlarge.|
The packs have undergone more than 20 tests, including crash; mechanical vibration (a shaker table); corrosion; thermal cycling and shock; and customer use lifecycle. Vehicle crash testing has shown that the pack is well protected by the vehicle structure.
One learning from the process to date is that the pack internal environment conditions are somewhat different than initially expected. The in-use evaluations, however, have shown that the cells are performing as expected.