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Glossary

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Amorphous
having an atomic structure that is not periodic.

Ampere-hours (Ah)
measure of cell capacity. Product of current in amperes multiplied by the discharge time.

Anode
an electrode where an oxidation reaction occurs. The negative electrode is the anode on discharge, the positive is on charge.

Battery
one or more cells connected to form one unit and having provisions for external connections.

Battery Pack
The system level form of a battery. Often includes: battery modules, mechanical housing, electronics, and so forth.

Capacity
the rated amount of energy stored in the cell (battery), normally measured in ampere-hours (Ah).

Cathode
an electrode where a reduction reaction occurs. The positive electrode is the cathode on discharge and the negative is the cathode on charge.

Cell
an electrochemical device capable of the interconvertion of electrical and chemical energy. Electrochemical cells include battery cells, fuel cells, and electrolyzer cells.

Cell Voltage
the nominal individual cell voltage.

Charge Depleting
the process in which more energy is removed from a battery than is restored.

Charge Sustaining
the process where the total average energy removed and restored to a battery is zero.

Crystalline
having a repeating atomic structure in all three dimensions.

Cycle Life
the number of times a battery can be charged and discharged. This is dependent upon the conditions such as the state-of-charge limits and the charge and discharge rates. Electric vehicle (EV) applications typically require a cycle life of over 1000 deep cycles. Hybrid electric vehicle (HEV) applications require a cycle life of over 100,000 shallow cycles.

Depth of Discharge (DOD)
the percentage of the battery capacity that is discharged (100%- SOC.)

Disordered
minimizing and lifting of lattice constraints, which provides new degrees of freedom, permitting the placement of elements in multi-dimensional spaces where they interact in ways not previously available. This allows the use of multi-elements and complex materials where positional, translational, and compositional disorder remove restrictions so that new local order environments can be generated controlling the physical, electronic, and chemical properties of the material, thereby permitting the synthesis of new materials with new mechanisms.

Electrochemical Cell
a chemical reactor containing reactive and electrically conductive materials which react in a controlled manner to produce direct current electricity.

Electrode (battery)
component of the battery that stores chemical energy on charge and generates electrical energy on discharge. Contains charge storage materials, nickel hydroxide in the positive electrode and metal hydride in the negative electrode for a nickel-metal hydride battery. Also, contains electronically conducting substrate for electrical path to battery terminals.

Electrolyte
serves as the path for completing the electrical circuit inside of the cell via the transport of ions from one electrode to the other.

Energy Density
the amount of energy stored in a specific volume or weight. Usually, this refers to the volumetric energy density measured in Wh/L. However, this can also refer to the gravimetric energy density, which is the same thing as specific energy in Wh/kg.

EV (Electric Vehicle)
a vehicle propelled exclusively by an electric drive system powered by an electrochemical energy storage device, typically a rechargeable battery.

FCEV (Fuel Cell Electric Vehicle)
an electric vehicle that derives its electricity from a fuel cell.

FCHEV (Fuel Cell Hybrid Electric Vehicle)
a vehicle that is propelled both by a fuel cell and an electrochemical energy storage device coupled to an electric drive.

Float Charge
charging a battery at a fixed or temperature-compensated voltage to maintain state of charge (SOC).

Gravimetric Energy Density
measure of how much energy can be stored in the battery per unit weight (Watt hours per kilogram (Wh/kg)).

HEV (Hybrid Electric Vehicle)
a vehicle that is propelled both by an electrochemical energy storage device coupled to an electric drive and an auxiliary power unit power by a conventional fuel, such as reformulated gasoline, direct injection diesel, compressed natural gas, or hydrogen.

Memory Effect
effects seen by shallow discharges of a battery. Typically a problem with NiCd batteries and not demonstrated in NiMH batteries.

NiMH (Nickel metal hydride) Battery
battery consisting of one or more nickel electrode, which utilizes nickel hydroxide as an active material, and one or more metal hydride electrodes, which utilize metal hydride as an active material. This battery — developed by Energy Conversion Devices, Inc. (ECD Ovonics) over the past 25 years — is a high-energy, high-power battery with excellent life characteristics and excellent environmental attributes. It has a nominal voltage of 1.2.

Nominal Energy
the energy available from a battery usually in Wh, delivered at a standard constant current discharge condition, such as C/3 (current needed to provide complete discharge in 3 hours).

Nominal Voltage (V)
approximate voltage of battery under load or under typical discharge conditions, normally rounded off to an even number. Nickel metal hydride (NiHM) batteries have a nominal voltage of 1.2V/cell.

Ovonic
[after S.R. Ov(shinsky) + (electr)onic] - the term used to describe our proprietary materials, products, and technologies.

Parallel
interconnecting cells or batteries by joining negative terminals together and separately joining positive terminals together. The parallel cells or batteries have the same voltage as the individual units; however, the capacity is the sum of the capacities of the individual units.

Peak Power
the maximum amount of power available for a sustained period of time, typically 10 to 30 seconds under specified conditions of voltage limits. Typically, the USABC has specified that it is the power that can be delivered above 2/3 of the open circuit voltage for the battery.

Peukert Effect
the effect of discharge current on the stored energy available for discharge. In contrast to the undesirably large Peukert effect for lead-acid batteries, Ovonic NiMH batteries have a minimal Peukert effect.

Primary Battery
a non-rechargeable battery that can be discharged only once; single use.

Power Density
the peak power available from a specific volume or weight. Usually, this refers to the volumetric power density measured in W/L.

Power Per Cell
the amount of power that can be drawn from each cell at the end of discharge voltage (watts per cell(W/cell)). This is a function of cell capacity, impedance, and end of discharge voltage.

Regenerative Power ("Regen")
the charge power applied to the battery during the recovery of kinetic energy from electric and hybrid vehicles. Electric propulsion vehicles can generate energy during braking by turning the motor backwards so it operates as a generator.

Secondary Battery
a rechargeable battery, such as the Ovonic NiMH battery.

Self Discharge
the loss of available battery capacity on stand, due to chemical side-reactions at battery electrodes.

Separator
provides physical isolation between the electrodes to prevent shorting and to separate the electrode reactions from one another. It also must be able to pass ions through its structure to allow for current flow.

Series
interconnecting cells or batteries by connecting the positive terminal of one unit to the negative terminal of the next in sequence. The series cells or batteries have the same capacity as the individual units; however, the voltage is the sum of voltages of the individual units.

Specific Energy
the amount of energy capacity divided by the weight or volume of the battery, usually measured in Wh/kg.

Specific Power
the peak power available from a specific weight, usually measured in W/kg.

State of Charge (SOC)
the amount of charge available for discharge from a battery in comparison to the rated capacity, usually given in percent.

USABC
United States Advanced Battery Consortium.

Voltage (V)
fundamental electrical concept, the electrical potential given in volts (V). Electricity will flow through conductors proportionally to the difference in potential.

Volumetric Energy Density
measure of how much energy can be stored in the battery per unit volume (watt hours per liter (Wh/L)).

Watt-hour (Wh)
a measurement of energy that a battery is capable of producing. This measurement is calculated by the product of watts (power) times a time period. Unit of electrical energy typically used to rate batteries.

W/cell
watts per cell.

W/kg
watts per kilogram.

Wh/kg
watt hours per kilogram.

Wh/L
watt hours per liter.

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