OVERVIEW OF LITHIUM ION BATTERIES
Meeting the Needs of Portable Electronic Devices:
Lithium Ion Batteries
Panasonic lithium ion batteries, products of Panasonic’s long experience with batteries and leading-edgebattery technology, are excellent sources for high-energy power in a variety of portable devices, such as por-table computers and cellular phones. Light weight and boasting high voltage ratings (3.6 V), these high-energydensity batteries provide a variety of features that will contribute to the weight reduction and downsizing ofportable products.
The lithium ion battery has a three-layer, coiled
The Structure of Lithium Ion Batteries (Cylindrical)
structure within its case. These three layers arecomprised of a positive electrode plate (made withlithium cobalt oxide as its chief active ingredient),
a negative electrode plate (made with a specialty
carbon as its chief active ingredient), and a
The battery is equipped with a variety of measures
to insure safety, along with an anti-explosion valve
that releases gas if the internal pressure exceeds a
specific value, thereby preventing the battery from
Panasonic’s lithium ion batteries (CGR17500,CGR17670HC, CGR17670HG, CGR18650HM,CGR18650HG, CGR18650B, CGP30486,CGP34506, CGP345010 and CGP345010G,CGA533048, CGA633450A and CGA103450,) haveobtained UL1642 approval.
OVERVIEW THE LITHIUM ION BATTERIES - CONTINUED
• Battery Reaction
The lithium ion battery makes use of lithium cobalt oxide (which has superior cycling properties at high volt-ages) as the positive electrode and a highly-crystallized specialty carbon as the negative electrode. It uses anorganic solvent, optimized for the specialty carbon, as the electrolytic fluid.
The chemical reactions for charge and discharge are as shown below:
Battery as a Whole
The principle behind the chemical reaction in the lithium ion battery is one where the lithium in the positiveelectrode lithium cobalt oxide material is ionized during charge, and moves from layer to layer in the negativeelectrode. During discharge, the ions move to the positive electrode and return to the original compound.
Schematic Diagram of the Chemical Reaction of the Lithium Ion Battery
FEATURES OF THE LITHIUM ION BATTERIES
• High Energy Density
Because the lithium ion batteries are high
voltage/light weight batteries, they boast ahigher energy density than rechargeable
nickel cadmium (Ni-Cd) batteries or nickelmetal hydride (Ni-MH) batteries.
• High Voltage
Lithium ion batteries produce 3.6 volts,approximately three times the voltage ofrechargeable Ni-Cd batteries or Ni-MHbatteries. This will make it possible to
• No Memory Effect
Lithium ion batteries have none of the memoryeffects seen in rechargeable Ni-Cd batteries
( “memory effect” refers to the phenomenon
where the apparent discharge capacity of a
battery is reduced when it is repetitively
discharged incompletely and then recharged).
Constant voltage: 4.1 V, with a
133 mA at 20 C
2.5 maximum of 500 mA current for two hours at 20 C
133 mA, completed after two hours,
at 20 C
• Flat Discharge Voltage
The use of the specialty carbon creates an
extremely flat discharge voltage profile, allowing
the production of stable power throughout the
OVERCHARGE/OVERDISCHARGE/OVERCURRENT SAFETY CIRCUITS
• The Functions of the Safety Circuits (Typical Functions)
The voltages listed below are typical values and are not guaranteed. The charge voltage varies according tomodel number.
1. The Overcharge Safety Function
The charge stops when the voltage per cell rises above 4.30 ± 0.05 V.
The charge restarts when the voltage per cell falls below 4.00 ± 0.15 V.
2. The Overdischarge Safety Function
The discharge stops when the voltage per cell falls below 2.3 ± 0.1 V.
The discharge restarts when the voltage per cell rises above 3.0 ± 0.15 V.
3. The Overcurrent Safety Function
The discharge is stopped when the output terminals are shorted.
The discharge restarts when the short is removed.
• Reference Example of the Safety Circuits
• The safety circuits in the diagram above are for overcharging, overdischarging, and overcurrent for a single
cell battery pack. Please contact Panasonic when two or more cells are connected or when actually usingthis or other circuits.
OVERCHARGE/OVERDISCHARGE/OVERCURRENT SAFETY CIRCUITS - CONTINUED
• Battery Pack Block Diagram (Reference Example)
The diagram below shows a diagram of a lithium ion battery pack. The battery pack includes the batteries, thesafety circuits, and thermistors.
1. The Safety Circuits
1.1 The Controller IC
The controller IC measures the voltage for each cell (or for each parallel battery block) and shuts off acontrol switch to either prevent overcharging (if the voltage exceeds the specified voltage range) or toprevent overdischarging (if the voltage falls below the specified voltage range). Moreover, the voltage ofthe control switch is measured on both ends and in order to prevent overcurrent, both control switchesare shut off if the voltage exceeds specifications.
1.2 The Control Switches
The control switches usually comprise FET structures, and they turn off the charge or dischargedepending on the output of the controller IC.
1.3 The Temperature Fuse (Reference Materials)
If the control switches experience abnormal heating, this fuse cuts off the current (non-restoring).
2. The Thermistors
The thermistors are included in order to accurately measure the battery temperature within the lithium ionbattery packs. The battery or charger measures the resistance value of the thermistor between the T-terminal and the negative terminal and during the charging process, controls the charge current along withcontrolling until the charge is terminated.
• The battery pack must be equipped with a noise filter at the voltage detectors in the block diagram above to
insure that outside noise does not cause the battery to malfunction. Please check against the final product.
• Please include a total charge timer and a charge completion timer on the charging circuit in order to provide
HOW TO CHARGE THE BATTERIES
We recommend the following charging process to insure the optimal performance of the lithium ion battery.
Applicable Battery Packs
The discussion below assumes that the battery packs are equipped with internal safety circuits to prevent
overcharging and overdischarging, and assumes that the battery is a single cell battery.
The lithium ion battery can be charged by the constant voltage/constant current charging method found in the
“Notes and Precautions” at the beginning of this document. (See page 2, “Notes and Precautions” )
Functions and Performance Required in the Charger (Recommendations)
(1) Charge Voltage
The voltage between the charging terminals should be no more than 4.20V (Set this at 4.20 V (max) after
taking into account fluctuations in power supply voltages, temperature deviations,etc.).
(2) Charge Current
The reference charge current should be 0.7 ItmA.
(3) Ambient Temperature of the Battery Pack During Charge
(Consult Panasonic if the battery pack is to be used outside of this temperature range).
(4) Low-Voltage Battery Pack Charge
When the voltage per cell is 2.9V or less, charge using a charge current of 0.1 ItmA or less.
(5) Termination of Charging
The system will determine that the battery is full by detecting the charge current.
Stop charging once the current has reached 0.1 ItmA to 0.07 ItmA. Note that there will be some degree of
variation for each individual battery.
(6) Charge Timer
A total charge timer and a charge completion timer should be included.
(7) Countermeasures for Battery Problems
Select an overvoltage guard in the power supply so that there will be no excessive voltage applied to the
battery even if there is a problem with the power supply.
The discussion above assumes a single cell battery. If two or more cells will be used or if there are other
situations, please consult with Panasonic.
Lithium Ion Batteries
FLOWCHART FOR CHARGING THE LITHIUM ION BATTERY PACKS
Lithium Ion Battery Pack Charge Flowchart (Example)
Reference example of charging a single-cell lithium ion battery pack
: Low temperature threshold setting value
tmax : High temperature threshold setting value
Is voltage check 1 (no load) higher than the charge completion voltage?
Lithium Ion Batteries
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