A primary lithium battery is a new type of high-energy battery with advantages such as high energy, high voltage, wide operating temperature range, long storage life, etc. However, any battery selected must be suitable for the conditions of the appliance in use. We will explain some technical issues that need to be considered when selecting a primary lithium battery for your reference.
When the battery is open-circuited, its voltage is the open-circuit voltage, which is determined by the electrochemical system itself. In the most commonly used primary lithium batteries, the lithium-manganese dioxide battery is rated at 3.0V, and the lithium-thionyl chloride battery is rated at 3.6V.
Once a primary lithium battery has current output, there is deviation between its voltage and open-circuit voltage, which is called polarization.
Polarization is composed of three parts:
①Ohmic polarization: caused by the internal resistance of the battery, proportional to the working current;
②Activation polarization: determined by the slow electron transfer step in the electrochemical reaction;
③Concentration polarization: determined by the concentration gradient of ions near the electrode;
④Polarization is a positive value of working current. The greater the working current, the more severe the polarization.
Because the primary lithium battery has polarization problems when outputting current, its working voltage is different under different working currents: it decreases with the increase of working current.
For example, in the smart flow meter, the working current is usually low, and the working voltage is relatively high and stable. Once a larger pulse current is required (such as the operation of an electric valve), the current value will increase significantly, which will inevitably cause a significant decrease in the working voltage. This is determined by the nature of the battery. In other words, the working voltage during a large current pulse must be significantly lower than the usual working voltage value, which must be noted by the user.
The capacity of the battery is expressed in ampere-hours (Ah), which is the product of the working current and the working time. The working time is the time when the battery is discharged to the termination voltage. The capacity is determined by the amount of active material in the battery and is proportional to it. That is, the larger the volume of the battery, the more active material and the greater the capacity.
The rated capacity specified by manufacturers usually refers to the time and current product of the battery continuously discharged to the termination voltage under a certain ambient temperature (23°C±3) and the prescribed standard discharge current. A temperature that is too low or a discharge current significantly greater than the standard discharge current can cause the battery's capacity to not be fully released.
In addition, the performance of new batteries and batteries used for a certain period of time is definitely different. As the active material is continuously consumed, the performance of the battery will also decline, so users should leave a certain safety factor when choosing battery capacity.
The standard discharge current refers to the continuous discharge current that can reach the rated capacity of the battery when continuously discharged to the termination voltage (2V) at a certain temperature condition. The specific data is determined by the production plant.
It refers to the maximum continuous working current value that can make the battery discharge 50% of the rated capacity continuously when discharged to 2.0V termination in an environment of 20±3°C.
Maximum pulse working current: under the condition of 23±3°C, when discharging at a specific current and 0.1 second/2 minutes pulse form on a specific base current, the battery voltage value should not be lower than 2.7V.