Lithium Batteries,Lithium polymer Batteries,and LISOCL2 batteries manufacture-VAIMA

How to remove passivation of ER batteries

2013-3-18 12:02:31 Category:Professional News


It is the characteristic of the lithium thionyl chloride battery to form passivation on the anode to prevent self-discharge, which makes ER battery having a long storage life. If there is no any passivation formed in the ER batteries, ER batteries will not have low self-discharge rate which is one of the important reasons to select ER batteries.  Customers should understand it thoroughly and make full use of the high performance of ER batteries for their instruments.  This will also help customer’s capability to market its products.

 

1. Voltage of battery

ER Batteries generate power by chemical components. Before use, the open circuit voltage and load voltage have to be checked to detect any problem batteries.

 

1.1 Open circuit voltage

Open circuit voltage of batteries is based on the electric potential difference of anode and cathode material which is a very stable value for ER batteries.   The standard open circuit voltage for ER batteries is 3.65 ~ 3.67V.  There will be some deviations when you measure the OCV by digital meters due todifferent accuracies of digital meters.  Using the same mater, the measured value should be fixed.  So if the OCV of a certain battery is less than the other batteries measured by same meter, the battery is defective one. For example, the open circuit voltages for a batch of batteries are 3.653.66V measured by a certain meter.  However the OCV measured for few cells are 3.64V using the same meter, these cells are not qualified and should not be used.  If they are put in use, these cells will be failed immaturely. So it is necessary to check the batteries after they are manufactured for half month and before put in use. Passivation acts as internal resistance.  Since there is not electrical flow when measuring OCV, passivation does not impact OCV readings.

 

1.2 Load voltage of battery

Since the thickness of the passivation film formed on the anode surface varies during storage, the voltage with load is variable after long storage. Storage condition and storage time have significant impact on passivation forming. It is necessary to check the voltage with load for every single cell. The method is connecting the battery with a prescribed resistor and measuring the voltage across the battery. The voltage reading should rise to a preset value within preset time period usually 10s.  If the battery has been stored for a long time or stored in hot environment, the operating voltage of the battery could not rise to the preset value in time.  This indicates long voltage delay.  The definition of the voltage delay is the time needed for the voltage of the battery rising to the cut-off voltage (minimum voltage for battery to work).  If the voltage delay is longer than it should be, the battery needs activated.  The recommended storage temperature for storing ER batteries is below 30­oC. 

 

2. Battery activation

After storage for a long time in the warehouse, the ER batteries may need activated as described in the above Section.  The way to activate ER batteries is to discharge certain current from the battery for a preset time period.  Since the thickness of passivation film is a function of storage time, the time needed to activate ER batteries depends on the storage time.  The larger discharge current can break the passivation film faster than smaller discharge current.  To reduce activation time, it is recommended to use twice the maximum working current to activate ER batteries.  Table 1 gives the recommended activation time for various storage times.  The recommended time may be increased for higher storage temperature.

Table 1: Activation Current and Time

Battery Type

Current for Activation

Relation between Activating time and Storage Time

Voltage after Activation

Three Months

Storage

Six Months

Storage

Twelve

Months

Storage

Lithium

Thionyl

Chloride

Twice the Maximum Working Current

15s

30s

60s

>3.0V


This activation process should make the battery can be normally used; even the passivation film may not be fully removed.  The remaining passivation film could be removed after the batteries put on use. 

2.1Online battery activation and cut-off voltage sampling

Some applications of ER batteries require very large pulse discharge currents, while the discharge current between the pulses is small (for example less than 100µA).  Since very small discharge current can not fully prevent the formation of passivation, the passivation film could grow between the pulses.  If the time between the pulses is long, the passivation may cause low operating voltage (below cut-off voltage) when large discharge pulses are required.   For this type application, it may require on-line de-passivation to discharge a large current periodically to remove the passivation film.  The size of the discharge current and the length of the discharge needed for the on-line de-passivation depend on how large the pulse discharge current and the time between the discharge pulses.

  

ER batteries have long plateau operating voltage.  For activated spiral wound ER batteries, the operating voltage should be over 3.0V for 90% of their capacity.  For activated bobbin type ER batteries, the operating voltage should be over 3.0V for 85% of their capacity.  If the operating voltage shows accelerated decline, the capacity of the battery is near drained.  When the operating voltage is below cut-off voltage, the battery should be removed.  The operating voltage should be based on the pulse discharge current.  For small discharge current between the pluses, the battery voltage can remain at high value for much longer time.