Battery Technical Info

5 Technical Points of Prismatic Lithium Iron Phosphate Energy Storage Battery Pack

Prismatic Cells for solar battery

Nowadays, deep cycle LiFePO4 batteries are very popular on the global energy storage market for Wind/Solar off grid or on grid system, home battery backup, telecommunication base,UPS station, etc.
This paper mainly introduces 5 technical points of Solar lithium battery factory pack process for prismatic lithium iron phosphate energy storage battery for indoor & outdoor use. Scope of application:

12V100AH Lithium Battery12.8V100AHLead acid replacement
12V200AH Lithium Battery12.8V200AHLead acid replacement
24V100AH Lithium Battery25.6V100AHLead acid replacement
24V200AH Lithium Battery25.5V200AHLead acid replacement
48V100AH Lithium Battery48V100AH 
48V200AH Lithium Battery48V200AH 
51.2V100AH Lithium Battery 51.2V100AH 
51.2V200AH Lithium Battery51.2V200AH
SmartPropel replace lead acid battery pack

Pack process of lithium iron phosphate battery is relatively simple, mainly as follows:

1.Customer demand  

We support solar energy storage batteries customize, Customer demand is mainly voltage/capacity/charge/discharge current/life/installation mode.  

ESS battery
SmartPropel battery energy storage system

2. Design

Engineers design/select materials according to customer requirements.  

3.The production

The factory processed and produced according to engineering drawings, strictly operation based on the technical guide, aged and packed for shipment.  

4.Technical highlights

1.Expansion Force

During design, engineers should consider the expansion of the cell, expansion will affect the life of the battery cycle and safety.There are many ways to test the expansion force of the battery cells. At present, the most common method is to use a clamp with a sensor to clamp the cells according to a certain torque value, and then to test the electric cells by charging and discharging cycle according to a certain working condition, sensor data, such as Agilent Technologies’s, read in the background and converted into pressure values.

The prismatic cells expansion force of a lithium iron battery, such as BYD/CATL/Guoxuan Battery, generally conforms to the rule that there are three peaks when charging, and the expansion force will always decrease when discharging. According to this law, the BMS can be written logic to control the rate of charge and discharge, thereby reducing the expansion force of the cell and improving the cycle life of the battery.

In addition to control charge and discharge to reduce the expansion, can also design structure, that is, set steel strip on the battery pack module, so that small modules get a long-term pressure. This pressure value will not damage the cell, but can improve the cell cycle life.

Battery expansion is usually written in the battery specifications, for example, BYD A level battery cell, the standard expansion is 5,000 cycles, less than 6,000N.

2.Fixed mode of battery module

Put Iron or aluminum gaskets on both sides of the module, with a 400N Press machine to add pressure to the module, and then slip into the steel, forming a stable small module. Put the small module into the case, will both sides of the gasket and the case with screws locked, then slip into the plastic bracket, with screws locked, the next step and then laser welding.

3.Laser welding

3.1. Weld area

——The welding area can be calculated according to the polished end surface of the welding, in order to calculate the flow.

——Current = welding area * conductivity

3.2 Depth of fusion

——The welding depth is usually 1 ~ 2mm, which can be obtained by dissecting the end surface of the electric-cored welding and observing it with a high-precision scanner.

3.3 The bus bar fits into the gap between the Poles

——Gap requirement no more than 0.1 mm.

3.4 Solder joint height

——Height requirement less than 1 mm.

3.5 Pull-out force of bus bar

——Required drawing force greater than * * * N.

——Test method: The cell is clamped in the tiger mouth under the pulling machine, the bus bar is clamped at 90 ° angle with the top pulling rod, the rod is drawn at the speed of 5mm/min, and the fracture data is read in the background. Note that the fracture value is read here, not the maximum tensile value; usually the fracture value is less than the maximum tensile value.

4.Insulation withstand voltage test

Voltage * KV

——Chassis to ground, leakage current < * * * mA;

——Positive to ground, leakage current < * * * mA;

——Negative to ground, leakage current < * * * mA.

5.Electrical performance test

The electrical performance test is mainly to check the battery performance and eliminate the bad ones. The main points are as follows.

5.1. Voltage

The voltage is mainly the whole battery voltage/cell pack voltage/cell voltage.

——The whole battery voltage is the voltage of the entire battery with BMS.

——The cell pack voltage is only the cells, does not contain BMS, the general requirement is the voltage difference l (Cell pack voltage-the whole battery pack voltage) l< 300 mV;

——The cell voltage difference is generally required to be less than 20 mv.

5.2. Capacity

Capacity > 95% * quota capacity

5.3 Temperature warming up

At 25 °C, 0.2 C discharge to the cut-off voltage, temperature less than 40 °C is considered normal.

5.4 DCIR

DC internal resistance calculation method: 25 ° C, 50% SOC, 0.2 C discharge 30S, 1c Discharge 5s, using voltage difference and current difference to calculate DCIR.

5.5 CAN/RS485 Communication

Can support multi units Series and parallels. Detect whether system can meet the use requirements.

The introduction of solar battery pack pack process in this paper has a good guide to the purchaser who need to purchase batteries, some of the technical parameters of the paper, because of SmartPropel technical confidentiality requirements, it is not convenient to write directly. If in doubt, contact the author directly.
No reprint without permission.

Author: SmartPropel Andy Luo
Email: [email protected]