Why Do Battery Factories Use Grading Systems Before Shipment?

In lithium battery manufacturing, shipment is not the end of the process. For battery factories, and particularly those in the tricky business of providing power battery packs, energy storage systems or solar applications, cell grading prior to shipment is as much of a necessity as it is not an option.
No matter whether the factory builds 18650, 21700, prismatic or pouch cells, grading systems help assure consistency, safety and long term guaranteed performance for downstream customers.
Battery cells are never exactly the same
Even when battery cells are built in exactly the same production line, with the same materials and equipment, small differences will form between them. These differences usually arise in:
Capacity (mAh or Ah)
Internal resistance (IR)
Voltage after formation
Self-discharge rate
If these ungraded cells were shipped directly without a final APC process, the differences may not become immediately apparent, but will quick become apparent once assembled batteries begin to be built with the cells.
This is the first of the reasons battery factories like battery grading and sorting machines prior to shipment.
Grading protects battery pack performance
Battery packs will connect several cells in series or parallel. In a multi-cell structure like that, the weakest cell dictates performance levels for the entire assembly.When cells with different capacities/IR are simply mixed:
Capacity of the pack will decrease
Temperature mismatch (current) will increase
Some cells will be over discharged/overcharged
Cycle life will deteriorate
To resolve this, factories will allow mix of cells with same capacity and IR values, using a battery cell sorting machine, leading to a more reliable battery pack in terms of performance.
Safety is a big one as well.
If a factory fails to properly grade cells, they risk
Overheating in a particular area
Swelling
Thermal runaway
Premature failure of cell or battery pack (high-load applications)
To combat this issue battery grading systems identify cells with unstable voltage or excessive IR then remove them from the batch load.
In an application like EV, home battery storage, solar battery packs, the following step is extremely important.
Grading, means less after-sales trouble
For a battery factory, to ship random ungraded cells results in:
Complaints from customers
Increased return rate
Warranty costs
Objectives is lost
Reputation at stake
With automatic or semi-automatic battery sorting machine, factories have the option to ship cells based on definite parameters as per technical specifications and lesser discussions help achieve long relationship with the end user.
Many serious battery manufacturers actually see grading as an investment and not so much at a cost.
Different application means different grading
Not all buyers request the same cell or battery for their application.
Application of cell mainly deals with:
Power tools – concern mostly discharge current and IR
Energy storage systems – emphasis upon capacity
Solar battery packs require long life and stability
Different EV application grading tolerance mean battery grading systems can enable factories to make the product that suit market niches and realise multiple sales targets from a single production line.
Why factories really want automated grading systems
As battery volume increases, manual testing proved slow and less accurate of late.
Modern battery cell factory in design prefer:
Automatic cell sorting machines for high produce
IR pogo pin testing system
Multi-channel capacity sorting equipment
Conveyor style, automobile type prismatic cell sorting machines
These upgrade the accuracy even of cell testing with excellent recycling rates and cut-out time and of time and lessen number of testers needed.
At a scale of shipment, automation is the way!
Battery grading prior to shipping is not just another tick to put in the box, but literally to tick or not tick off every membrane fitted inside that box.