Battery Chemistries

Li-ion Battery

BOKA Li-ion Rechargeable Battery Data Sheets Tables
1.Li-ion Prismatic Rechargeable Battery Data Sheets Table.
2.Li-ion Cylindrical Battery Data Sheets Table.

Overview
Developing the high-tech is to serve human better. In the last decade, the Lithium ion battery has made great progress, which make it be used widely in society. It is proved that lithium battery not only can provide higher energy density to meet the needs of ever smaller and lighter devices but also is environmentally friendly.
It is called Lithium ion battery because there is no metallic lithium at any charge depth during normal usage. Lithium ion battery uses carbon material for an anode and lithium ion exists in the carbon material. Chemical stability of carbon anode is higher than that of metallic lithium; there fore lithium ion battery is a safe system.
Lithium ion battery has excellent features, such as high energy density, high voltage, good storage and cycle life characteristics. So it is widely used for 3C applications such as Personal Computers, Cellular Phones and also for personal cordless electronic applications i.e. Portable CD Players, PDA etc.

Li-ion Battery Features
A. High Energy Density
The weight of lithium ion battery is approximately one half compared to a nickel-cadmium or nickel-metal hydride battery of similar capacity. Moreover, the volume of the lithium ion battery is 40% to 50% smaller than that of a nickel-cadmium and 20% to 30% smaller than that of a nickel-metal hydride battery.

B. High Voltage
A single lithium ion cell has a voltage of 3.7V (mean value), which is equal to either three nickel-cadmium or nickel-metal hydride cells connected in series.

C. Pollution-free
The lithium ion battery does not contain any polluting substances such as cadmium, lead, mercury, etc.

D. Non-metal Lithium
The lithium ion battery does not employ any lithium metal. It is not governed by aircraft transportation rules relating to carrying lithium batteries in passenger airplanes.
E. Long Cycle Life
Under normal conditions, the lithium ion battery has a life of more than 500 charge/discharge cycles.
F. No Memory Effect
The lithium ion battery is free from the so-called memory effect, a phenomenon seen in nickel-cadmium in which the apparent battery capacity decreases when shallow charge and discharge cycles are repeated.
G. Fast Charge Capacity
The lithium ion battery can be fully charged in 2 to 3 hours, using a constant-current / constant-voltage (CC/CV) type dedicated charger with a rated voltage of 4.2V per cell.

Characteristics of BOKA Li-ion Batteries
1.Electrical characteristics during charge
A.Charge Characteristics
A dedicated CC/CV battery charger is required to charge the lithium ion battery. It controls the charging current until direct voltage reaches 4.2 volts per cell.
The lithium ion battery will be charged over the current range of 0.1 CmA to l.0 CmA. (C is a value that expresses the rated capacity of a battery. Charging and discharging current are generally expressed as a multiple of C.For example, if the rated capacity is 1020 mAh, a current of 0.01 C is equal to 1020 x 0.01=10.2 mA).
As long as constant-voltage charging is applied, the charging current will taper down to zero. The charging current will no longer flow, thus eliminating any overcharging of the battery

 Fig.5 Charge Characteristic

B.Charge Time and Charge Rate
The lithium ion battery will be charged up to approximately 90% of rated capacity at a charging current of 0.5 to 1.0 CmA within 70 to120 minutes.

Fig.6 Charge Time and Charge Rate

C.Charge Temperature Characteristics
The next Fig.7 Shows the charge temperature characteristics from 0 ℃ to 45 ℃ for lithium ion battery.

 Fig.7 Charge Temperature Characteristics

2.Electrical characteristics during discharge
A.Discharge Characteristics
The following Fig.8 Shows the discharge curves of lithium ion batteries discharged continuously at a constant current.
Normally, lithium ion batteries start to discharge at 4.2 V, and terminate at a cut-off voltage of 3.0V/Cell

Fig.8 Discharge Characteristic

B.Discharge Temperature Characteristics
Fig.9 shows the 0.2C discharge temperature curves for Li-ion battery (For example,L-P083448). At the low temperature dischage, the battery voltage drops and the discharge capacity also decreases. However, even at -20 ℃, a discharge capacity of about 90% of that at 20 ℃ is available.

Fig.9 Discharge Temperature Characteristics

3.Cycle Life Characteristics
The charge/discharge cycle characteristics of Li-ion battery (For example,L-P083448) is shown in Fig. 10. When a lithium ion rechargeable battery is charged and discharged cyclically, the discharge capacity of the battery gradually decreases, because of the deterioration of electrode materials, electrolyte, etc. The degree of deterioration depends on ambient temperature during charging and discharging. If a battery is charged at a higher voltage than the allowable maximum voltage, the discharge capacity may decrease excessively or battery safety may be jeopardized. Be sure to maintain the allowable voltage and the temperature ranges for charging and discharging. 

Fig.10 Cycle Characteristics

4.Storage Characteristics
The following Fig.11,Fig.12 show the storage data for Li-ion battery (For example,L-P083448). Recovered capacities (discharge capacities after recharging) vary depending on storage period, ambient temperature, and battery voltage. As battery voltage and ambient temperature are higher, recovery capacities are decreased. Store battery within the ambient temperature range of -20 ℃ to 40 ℃. If battery voltage or temperature is higher, battery performance characteristics may deteriorate faster. If battery are stored for a long time, they may be overdischarged due to self-discharge.

Fig.11 Storage Characteristics

Fig.12 Recovered capacity ratio at 20 ℃ after storage

 

Electrochemical Processes
The BOKA lithium ion battery uses of lithium cobalt Dioxide (which has superior cycling properties at high voltage) as the positive electrode and a highly crystallized carbon as the negative electrode. It uses an organic solvent, optimized for the special carbon, as the electrolytic fluid.
It is made of a substance capable of cyclic transfer of lithium ions between two electrodes. The cell operates on the rocking chair principal that is charging and discharging cause lithium ions to “rock” back and forth between the positive and negative electrodes. This principle of operation is fundamentally different and safer from that of a rechargeable lithium metal battery since neither the anode nor cathode material of the lithium ion battery essentially changes.
Principle of Electrochemistry
The electrochemistry of the BOKA Li-ion battery is generally represented by the following charge and discharge reactions:
1)Charge
When the battery is charged, the lithium ions in the cathode material (lithium compound) migrate via a separator to between the layers of carbon material that form the anode, and a charging current flows.

LiCoO₂+Cn —> Li1-XCoO₂+CnLix

2)Discharge
When the battery is discharged, the lithium ions in the carbon material that form the anode migrate via a separator to the cathode material (lithium compound), and a discharging current flows.

Li1-XCoO₂+CnLix —> LiCoO₂+Cn

3)Schematic diagram of the chemical reaction of the lithium ion battery

Structural Designs
There are four structures of Li-ion battery cylindrical type, aluminum shell prismatic type, aluminum round corner prismatic type, and steel shell prismatic type. The following two figures are schematic drawings of the cylindrical and steel shell prismatic lithium ion batteries.
A. The interior of the Nermst lithium ion battery has a spirally wound construction with a finely porous polyethylene film separator sandwiched in a vortex between sheet-like positive and negative electrodes.

Fig.1 Crlindrical Li-ion battery

B. The positive electrode employs a Li-ion collector made of lithium and cobalt metal Dioxides and a current collector made of aluminum foil. The electrolyte is organic solvent with LiPF₆ in it.

Fig.2 Prismatic Li-ion Battery (Al case)

C. The BOKA lithium ion battery is also equipped with a safety vent, which will release pressure under abusive situations.

Fig.3 Construction safety vent for Cylindrical Battery

Charge Methods of BOKA Li-ion Batteries
In order to ensure the optimal Li-ion battery performance and safety function, the following charging method is recommended.
1.Applicable battery packs
The battery pack must have a built-in protection module to protect the Li-ion batteries against a possible overcharge or over-discharge. The description given below is for a battery pack composed of a single cell for reference.
2.Charging method
Generally, higher constant current value for constant current region is thought to enable shorten total charging time. But total charging to full-charged state cannot be shortened to the degree as it is expected in fact .At the same time, lower current value is advantageous to cycle characteristics.However.as battery also has temperature depending ability for charging, charging time will become longer, if charged at low temperature.
Next the Fig.13 shows general charging flow that we advise for Lithium-ion battery.
At first, battery temperature is monitored with a thermostat inside battery pack, and when it is in the range for charging, voltage of battery pack is checked. If battery voltage is less than 3V,it should be preliminary charged at approximately 0.1C. If voltage becomes more than 3V,then proceed to charge it at 0.5-1C.when current attenuates to 0.01-0.05C or less .the charging should be terminated.
3.Functions and performance required for Li-ion battery charger
A.Charging voltage(charging voltage between the terminals): 4.200±0.049V
In principle, it is desirable to charge the Li-ion batteries at 4.20V. The tolerance specified above is provided for variations in equipment, design and fabrication.
B.lnitial charging current
Standard charging current: 0.5CmA
Maximum charging current: 1.5CmA
C.Charging temperature
The temperature of the Li-ion batteries will rise by approximately 5 ℃ while the batteries are being charged at stronger current. After switching to the constant -voltage charge mode, the cell temperature will gradually decrease.
D.Low-Voltage Battery Pack Charge
When the voltage per cell is 3.0V or less, charge using a charge current of 0.1 CmA or less.
E.Completion charging
Whether or not the Li-ion battery is fully charged should be determined by detecting the charging current. A detected current of 0.1 CmA indicates that the battery is charged to 93% or 94% of its capacity.
F.Protection features
a) If the charging voltage exceeds 4.2V,the charging should be completed.
b) If the battery voltage remains at less than 3.0V for a specified duration of time in the trickle-charging mode during battery check, the battery should be deemed abnormal and charging should be avoided.
c) The Li-ion battery has characteristics that allow for trickle charging within the temperature range from 0 ℃ to 45 ℃. however, it is recommendable to provide the timer for the safety purposes.
G.Countermeasure for abnormalities in power supply unit
To prevent an over-voltage to the battery in the event of a malfunction in the power supply unit, select the unit equipped with over-voltage protection.

Electrical & Mechanical Test Methods
1.Electrical Safety Tests

Items	Condition	Test Method	Specification	Result
Short Circuit at 25 ℃	Fully charged	Connecting the positive and negative terminals of the battery with copper wire having a maximum resistance load of 0.1 ohm.	No explosion or no fire; and the temperature of the battery shall not exceed 150 ℃	Pass
Short Circuit at 60 ℃	Fully charged	Tests are to be conducted at room temperature and at 58 to 62 ℃	No explosion or no fire; and the temperature of the battery shall not exceed 150 ℃	Pass
Abnormal Charging	Fully discharged	Cell is initially charged at 3C rate by connecting to a 12V DC-power supply for 48 hours.	No explosion or no fire; and the temperature of the battery shall not exceed 150 ℃	Pass
Over-charging	Fully discharged	The battery is charged at 1CmA to 250% of its rated capacity.	No explosion, no fire, no leakage, or no venting	Pass

2.Mechanical Safety Tests

Items	Condition	Test Method	Specification	Result
Vibration	Fully charged	Cell is under vibrations of amplitude 0.8 mm, frequency between 10 and 55 Hz., swept at 1Hz./min. for 90min orthogonally in XYZ directions.	No explosion, no fire, no leakage, or no venting	Pass
Shock	Fully charged	Cell is accelerated during the initial 3 msec. with the minimum average acceleration of 75 G, and the peak acceleration between 125 G and 175 G, in XYZ directions.	No explosion, no fire, no leakage, or no venting	Pass
Crush test	Fully charged	Cell is placed between two parallel flat steel plates and the electrodes are parallel to the plates, a force of 13 kN is applied	No explosion or no fire	Pass
Impact test	Fully charged	A round rod of 15.8 mm diameter is placed near the center of the cell, parallel to the electrodes and perpendicular to the upper terminal of the cell, and a 9.1 kg weight is dropped from a height of 61 cm to the rod.	No explosion or no fire	Pass
Drop test	Fully charged	Battery is dropped in a free-fall manner for ten times from a height of 1.9m onto a concrete floor, with arbitrary orientation.	No rupture or ignition	Pass

3.Environmental Safety Tests

Items	Condition	Test Method	Specification	Result
Heating Test	Fully charged	The temperature of the oven is to be raised at a rate of 3 to 7 ℃/min. to a temperature of 148 to 152 ℃ and remain for 10 minutes at this temperature.	No explosion or no fire	Pass
Temperature Cycling	Fully charged	(1)Raise the temperature from 25 to 70 ℃ within 30 min, and then maintain the temperature for 4 hrs. (2)Reduce the temperature from 70 to 25 ℃ within 30 min, and then maintain the temperature for 2 hrs. (3)Reduce the temperature from 25 to -40 ℃ within 30 min, and then maintain the temperature for 4 hrs. (4)Raise the temperature from -40 to 25 ℃ within 30 min, and then maintain the temperature for 2 hrs. (5)Repeat the sequence for further 9 cycles.(6)After 10 cycles, store the cell for 7 days prior to examination.	No explosion no fire no leakage, or no venting	Pass
Altitude Simulation	Fully charged	Cell is left for 6 hours in an environment with an atmospheric pressure of 11.6 kPa.	No explosion, fire, leakage, or venting.	Pass
High Humidity Storage Performance	Fresh cell	After full charge, store at 60 ℃ and 90%RH for 30 days.	No gassing and no leakage	Pass
High Temperature Storage Performance	Fresh cell	(1)After full charge, store at 85 ℃ for 48 hours. (2)After full charge, store at 90 ℃ for 4 hours.	No gassing and no leakage	Swelling less than 2%

The Functions of the Safety Circuits (Typical Functions)
The voltages listed below are typical values and are not guaranteed. The charge voltage varies according to model number.
1.The Overcharge Safety Function 
   The charge stops when the voltage per cell rises above 4.35 V.
   The charge restarts when the voltage per cell falls below 3.85 V.
2. The Overdischarge Safety Function
   The discharge stops when the voltage per cell falls below 2.4V.
   The discharge restarts when the voltage per cell rises above 3.15 V.
3. The Overcurrent Safety Function
   The discharge is stopped when the output terminals are shorted.
   The discharge restarts when the short is removed.
4.Reference Example of the Safety Circuits
5.The safety circuits in the diagram above are for overcharging, overdischarging, and overcurrent for a single cell battery pack. Please contact BOKA when two or more cells are connected or when actually using this or other circuits.

Battery Pack Block Diagram (Reference Example)
The diagram below shows a diagram of a lithium ion battery pack. The battery pack includes the batteries, the safety circuits, and thermistors.
1.The Safety Circuits
1) The Controller IC
The controller IC measures the voltage for each cell (or for each parallel battery block) and shuts off a control switch to either prevent overcharging (if the voltage exceeds the specified voltage range) or to prevent overdischarging (if the voltage falls below the specified voltage range). Moreover, the voltage of the control switch is measured on both ends and in order to prevent overcurrent, both control switches are shut off if the voltage exceeds specifications.
2) The Control Switches
The control switches usually comprise FET structures, and they turn off the charge or discharge depending on the output of the controller IC.
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 ion battery packs. The battery or charger measures the resistance value of the thermistor between the Tterminal and the negative terminal and during the charging process, controls the charge current along with controlling until the charge is terminated.

1) 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.
2) Please include a total charge timer and a charge completion timer on the charging circuit in order to provide redundant safety control.

Battery Pack Configurations Designation System

1.Designation System For Battery Packs
The designation of a battery pack is composed of 7 sections each of them are used to identify different information:

XX-X-ABCDEFG HIJK M N PQ

XX——————Shenzhen DGT Technology Development Co.,Ltd.
X——————–Chemical System. H–Nickel/Metal Hydride Battery.D–Nickel/Cadmium Battery.L–Li-ion Battery.LP–Li-ion PolymerBattery.
ABCDEFG——–Size of Cell
HIJK—————-Capacity
M——————-Number of Cells in a Pack
N——————-Configuration Code
PQ——————Tag or Connector Type Code

2.Standard Configurations For Battery Packs
The following are the standard pack configurations for Ni-Cd batteries. Refer to these configurations when designing the battery pack.
A Type
The repuired number of single cells are stacked in a vertcial column and connected by nickel plates, and covered with an external heat-shrink PVC tube.
B Type
The repuired number of single cells are arranged in a row and connected by nickel plates, and covered with an external heat-shrink PVC tube.
G Type
The repuired number of single cells are stacked in two vertical columns of inequality numbers cells and connected by nickel plates, and covered with an external heat-shrink PVC tube.
S Type
The repuired number of single cells are stacked in multiple columns ared layers and connected by nickel plates, and covered with an external heat-shrink PVC tube.
T Type
The repuired number of single cells are arranged in a horizontal triangle and connected by nickel plates, and covered with an external heat-shrink PVC tube.
W Type
The repuired number of single cells are arranged in horizontal triangle rows in one or more layers and connected by nickel plates, and covered with an external heat-shrink PVC tube.
Y Type
The repuired number of single cells are arranged in more horizontal rows and connected by nickel plates, and covered with an external heat-shrink PVC tube.

3.Tag Type Specifications

4.Tag Direction Codes

5.Connector Type Specifications

Precautions  for Using BOKA Li-ion Batteries
In order to take full advantage of Li-ion batteries characteristics in use and in the design of battery-operated products, and also to prevent problems due to improper use, please pay proper attention to the following points.
1.Charging
1) Charge voltage
Do not exceed the specified charging voltage (4.2Vx number of cells connected in series).
While taking into account the environmental temperature in the charging process, fluctuations of the power supply voltage fed to the lithium ion battery, and its voltage control accuracy, the charging voltage should be limited to 4.2V x number of cells connected in series as the maximum. Moreover,select a battery charger that will supply the proper or lower charging voltage even if the external supply power should exceed the specified voltage or the failure of the battery charger or other cause.
2) Charge current
Charge the lithium ion battery at the specified charging current (1.0CmA) or less. If the battery voltage has been reduced 3.0V x number of cells connected in series, charge the battery at small trickle current of 0.1 CmA or less.

3) Charge temperature
Charge battery within a temperature range of 0 ℃ to 45 ℃. Do not charge the battery at a higher temperature, which cause the battery pace to over-charged. Consideration should be given to the arrangement of the battery pack, So that it is in that temperature range even though it is affected by heat generated from the battery charger. At a temperature of 0 ℃ or less, the battery may not only fail to be charged sufficiently, but its performance might also deteriorate in various ways.
4) Reverse charge
The battery must be protected from reverse charge.
2. Discharging
1) Discharge current
Discharge the lithium ion battery at the specified discharge current (1.0CmA) or less. In the case of pulse discharge, set the mean current to 1.0CmA or less. A peak current of higher than 2A depending on the pulse interval, may reduce the battery capacity due to the characteristics of the PTC.
2) Discharge temperature
Discharge the lithium ion battery within a temperature range of -20 ℃ to 60 ℃, at a temperature of -20 ℃ or less, the battery will show a signification decrease in discharge capacity.
3) Over-discharge
Avoid discharging at voltages less than 3.0V per cell. Over-discharge will damage the performance of the battery, usually caused by self-discharge and consumption current of protection. Efforts should therefore be made to minimize leak current of the battery charger etc.
3. Storage/Inventory
1) Storage environment
Store the lithium ion battery in an environment with low humidity (65±20%)free from corrosive gas.
Store less than 1 month: -20 ℃ –  +60 ℃
Store less than 3 months: -20℃ – +45 ℃
Store less than 1 year: -20 ℃ – +25 ℃
A temperature of 60 ℃ or higher and/or extremely high humidity will accelerate the deterioration of battery performance. Keep the battery away from fire.
2) Inventory control
It is recommended to strictly observe the first-in first-put (FIFO) principle through manufacturing and distribution of the product.
3) Long-term storage
A higher battery voltage during storage will accelerate the deterioration of capacity. When storing the lithium ion batteries for an extended period, it is recommended to keep them at a lower voltage (about 3.8V/cell) throughout the period of storage.
When storaging the battery for a period longer than one year, charge it at least once a year (to about 3.8V/cell) so as to prevent the battery from being over-discharged.
Storage for a very long period may result in over-discharge, due to self-discharge of the battery.
4. Comments related to equipment design
1) Reverse polarity prevention
The dedicated battery charger or the equipment powered by the lithium ion battery should be designed and should have terminals so shaped as to prevent the lithium ion batteries from being in sorted in a reverse manner when connected to equipment.
In addition, the1 construction and terminal shape should be so designed as to protect the battery against possible short-circuit due to a mental necklace or chain. Clip, or similar objects.
2) Battery location
The lithium ion battery should be mounted in such away that locations subjected to heating in the equipment are avoided. Furthermore, the equipment should be designed around the lithium ion battery with consideration of any abnormal safety conditions including liquid leakage.
Additionally, if the equipment emits electromagnetic waves, the battery should be located so that the protection module may not be readily affected.
3) Countermeasures against dropping
The equipment containing the lithium ion battery should be so constructed as to sufficiently absorb an impact from mechanical shock, the equipment, even if given a hard impact by dropping, should not have misplace wiring, should not displace cells causing shorting nor should it cause cells to leak. The design should also be carried out with due consideration given to abnormal safety conditions (including liquid leakage).