What’s Up with Batteries?

A breakthrough in battery technology has made lithium-ion batteries meet the specific energy, power, mass and durability requirements of the Opel Ampera.

Battery testing is progressing as planned with no significant roadblocks in lab or on-road testing.  Active battery testing is conducted by engineers in Mainz-Kastel, Germany.

After extensive testing of different lithium-ion battery solutions, the engineers have a much greater understanding of lithium-ion cells, control hardware and the manufacturability of the battery components needed for the Ampera's battery pack.

Why Lithium-Ion is the Right Battery

While the majority of hybrid-electric vehicles (HEVs) on the road today use nickel metal hydride (NiMH) battery technology, the Opel Ampera will be powered by a 16-kWh lithium-ion battery pack comprised of more than 200 lithium-ion cells.

Lithium-ion batteries provide nearly two to three times the power of a NiMH battery in a much smaller package.

Contrary to popular belief, all lithium-ion chemistries are not alike. In fact, lithium-ion is a family of dozens of chemistries with different capabilities and performance characteristics. The characteristics required for automotive applications differ greatly from consumer electronics, such as laptop computers.

Lithium-ion battery chemistry is the fastest-growing and most promising battery chemistry for several reasons, including:

   • Superior specific energy and power
   • Long life
   • High efficiency
   • Durability
   • Lower initial material cost and fewer replacements
   • High cell voltage means fewer cells are needed to give desired voltage 
     range
   • Higher energy-to-weight ratio, an important consideration in automotive    
     applications since excess mass affects efficiency
   • Configurable into a wide variety of shapes and sizes so as to efficiently fill    
     available space in the devices they power
   • Suffers little or no memory (lazy battery) effect, which can occur when 
     batteries gradually lose their maximum energy capacity if they are 
     repeatedly recharged after being only partially discharged
   • Encounters low loss of charge (also known as self-discharge) when not
     in use 
  
   • Battery technology is much improved over time
   • Nickel metal hydride batteries focus on "power" for hybrids, NOT "energy"  
     for plug-ins and pure battery-electric vehicles
   • Lithium-ion chemistry can provide both power and energy
   • Develop large lithium-ion battery packs.
   • Individual cells that meet our requirements now exist 

The Battery Cell

The battery cell delivers electric current as the result of an electrochemical reaction. Electrical current is carried by lithium ions from the positive electrode (cathode) to the negative electrode (anode) during charging, and from negative to positive during discharging. The ions are small and reside within the crystal structure of the electrode materials.

Different electrode materials have different current-carrying capacities, and this affects the storage capacities of the cells. Each of the Ampera's more than 200 cells is a "building block" within the larger battery module and pack. An individual cell is about the size of a 12.7-centimeter by 17.7-centimeter (5-inch by 7-inch ) photo frame, is less than 1 centimeter (a quarter-inch ) thick and weighs nearly a pound (0.45 kilogram).

Each battery cell contains a carbon anode (the negative electrode), a manganese-based cathode (the positive electrode) and a safety-reinforced separator, which provides the medium for the transfer of electrical charge ions between the anode and the cathode inside the battery cell.

The protective polymer-coated aluminum cover encases the cell, helps prevent gas permeation and improves battery cooling efficiency. Tabs at the top of the cell are used to link the cells within the module

The Battery Module
 
Numerous designs are possible for assembling cells into a battery pack for an electric or hybrid vehicle. A modular design is used in most cases, with a number of cells packaged together into a unit called a “module.” Controls are used to monitor the voltage and current of a cell to determine when to charge or discharge. Multiple modules are combined into a battery pack sized to match the requirements of the vehicle. The same modules could be used in a variety of different battery packs.

The Battery Pack

   • A battery pack is the final assembly used to store and discharge electrical
     energy for a hybrid or electric vehicle. The Voltec propulsion system features
     a 16-kWh lithium-ion battery pack that weighs less than 400 pounds
     (181.4 kilograms) 
   • The Ampera’s battery pack consists of multiple modules, configured in series,
     retained within an enclosure for underbody installation. All together the
     modules contain more than 200 battery cells
   • Components for the control and monitoring of discharge or charge energy
     are also housed within the pack
   • Modules are clamped to a battery tray and joined by flexible interconnects
   • Relays and mechanical assemblies allow for automated or manual control
     of subassembly output voltage
   • Temperature sensors allow for inlet/outlet coolant measurement 
   • Manifolds and coolant lines allow for heat exchange with the cell surfaces
   • Connectors allow for single point entry/exit of high voltage loads
   • Battery cover/enclosure protects and insulates the pack from the ambient
     environment

Design & Integration

   • The battery pack is T-shaped, allowing designers to create unique
      vehicle designs
   • Steel tray, plastic cover
   • The pack is part of the vehicle structure
   • The pack is an underbody-mounted component

Safety

   • The LG Chem cell uses manganese-based cathode chemistry
     with additives to improve battery life under high-temperature conditions
   • Numerous measures have been taken to help prevent safety
     issues - namely short circuiting and overheating - that have occurred
     in lithium-ion batteries used in consumer electronics. LG Chem's exclusive
     Safety Reinforced Separator consists of semi-permeable membranes
     separating the electrodes in the cells, which are mechanically and thermally
     superior to commonly used separators
   • Primary as well as backup battery pack controls regulate voltage, current
     state of charge and temperature
   • Rigorous testing of lithium-ion battery packs in battery labs and on the road
     in early engineering development cars has not revealed any safety or
     performance issues

Durability

   • Automotive batteries operate in a rugged and hostile environment with
     the expectation they will last the life of the vehicle. Opel is currently testing
     battery packs in the lab and engineering development vehicles. This testing
     will help to better understand how these packs will operate in real-world
     driving conditions, including extreme hot and cold climates
   • The Opel Ampera’s battery cell is encased in a polymer-coated aluminum 
     package. This thermally efficient and safe package is designed to be more
     forgiving under harsh conditions and help reduce the cost and complexity
     of the battery cooling system

Looking Ahead

Future generations will produce batteries with:

   • Less cost due to better use of parts commonality (fewer parts)
   • Higher energy density through more efficient use of packaging
   • Better cold-weather performance
   • More efficient insulation/energy conservation
   • Lower mass
   • Increased power performance