Four main choices of terminal processing for prismatic LFP cells 2022-04-18

LFP (LiFePO4 or lithium iron phosphate) battery cells are durable, reliable, safe and powerful. With their advantages gradually recognized and adopted by renewable energy storage systems and LFP battery packs become more and more popular in recent years, many customers start to buy cells to build their own. Prismatic cells have gained popularity due to their large capacity and rectangular shape that brings the product designer more choice, and makes it easy to connect 4 cells together and create a 12V battery pack. They are quite ideal for those applications which requires a high output capacity and limited space such as RV, boat, golf cart, etc. It’s also an excellent choice to improve consistency, as well as optimize battery efficiency with less cells.

To increase energy density, now many lithium battery manufacturers have changed the shell of prismatic lithium ion batteries from plastic shells to aluminum shells. The positive and negative tabs are also made of aluminum and usually with internal M4/M5/M6 screw holes (mostly M6) or flat. For those cells with internal threaded holes, it' s very easy to assemble them together with busbars and screws, they are just like LEGO.

And for other cells with flat terminals, laser welding is the best choice. But a laser welding machine is very expensive, most customers don' t have one. OSN POWER can provide extra service with drilling holes or welding studs etc. on tabs of positive and negative for customer' s easier assembly.

At present, there are mainly four types of terminal processing for prismatic LFP cells: drilling holes, welding screw holes, welding studs and welding aluminum blocks, in which drilling holes and welding studs on the positive and negative terminals of those prismatic LFP cells is the most common ways.

1. Drilling holes

Drilling holes, the processing is the same as the one with internal screw hole, just we can decide the hole spec (M4/M5/M6) and the depth that can be punched according to customer' s requirements and the cell actual situation. Not all battery cells can be punched. For some cells, the terminals are too thin to punch. If drilling hole on the original tab, it will be likely to penetrate the positive and negative battery poles and cause leakage. So always be careful with the depth of the hole when punching, never drill too deep. The hole depth is usually within 5mm. In this way, the torque is small, and screws come off easily, so the shock resistance is also weak.

2.Welding screw holes

Welding screw holes, it' s kind of extension of drilling holes. Instead of drilling hole directly on the original terminals of the cell, it is welded with M6/M5 screw holes. The depth of the screw hole can be deeper. This is a good choice for those who want holes but don' t want to take the risk of breaking cells. Same with drilling hole, the contact area is also small so can' t pass large current. It' s suitable for the applications which don' t require large current, such as small low speed vehicles.

3.Welding studs

Welding studs is a more common way for prismatic cells with round terminals. Laser welding screw bolts for LiFePO4 battery enables easy connection and DIY, helps save your time. It is generally M6*12mm or 15mm and can customize as per customer' s request (12mm is the height of the studs, we suggest no less than 10mm in consideration of assembly with busbars and screws). The base of this connector is made of aluminium and studs is stainless steel. It mainly conducts electricity through the base when connecting with busbars, so the contact area is also small and the conductivity is not so good, which is more suitable for small current projects as well.

4. Welding aluminum blocks

Welding aluminum blocks, there are various forms available, which can be customized according to the shapes of the cell terminals and customer requirements.

The hole of the aluminum block can be M6 or M8 as per customers request. The depth of the screw holes is deeper than the others, can be at least 9mm. Its overall material is aluminum alloy, which is harder than pure aluminum. And for aluminum blocks with suspended threaded holes, the torque can withstand up to 10 Nm. So it has better shock resistance. Besides, It has a much larger contact area with good conductivity and therefore is able to deliver higher current. It is the optimal choice for those relatively large electric vehicles and large energy storage projects. The only disadvantage is that the cost of this terminal is rather high, and the welding is more troublesome and labor-intensive.

In addition to the above terminal processing methods, there is an older welding method: nickel welding (pre-weld the nickel plate to the tab). It is rarely used now and often used on some NCM cells in the condition of limited size and relatively thin terminals that are not allowed for drilling.

In conclusion, you can choose the one that suits you best according to your needs, depending on your application, working current required, and size limitation etc. Generally, drilling holes and welding studs are the most common and relatively cost-effective.  Unless there is special requirements, we recommend that customers purchase studs terminal LiFePO4 batteries instead of drilling holes. If cost is not a problem, for large projects we would highly encourage customers to try the latest double M6 screw holes for LFP prismatic batteries cause it makes screws more tightened and allows better contact surface to deliver higher current, and has the strongest shock resistance.

Leave a message

Leave a message

    Click Here to Get Solution and Quotation.