Many clients are confused by the quality standard of lithium-ion battery cells. Some
claimed that they are grade A, grade B. And what is the standard? How the manufactures
define each level? Today, we're going to share with you something about the quality grades.
Grade A: All parameters (voltage, capacity, internal resistance, self-discharge rate,
dimensions, etc.) within the required ranges. Sometimes, there’s different standard
range to sorting Grade A+ and Grade A- battery cells
Grade B: Some parameters are higher or lower than the standard ranges (high
self-discharge rate, low capacity, high internal resistance, appearance default, etc.)
Grade C: Some manufacturers will define the cells that exceed self-discharging rate
as Grade C
Used cells: Tear down from devices
So what causes the battery cells to be sorted to different levels? There're some factors
that affect the performance of final product during the manufacturing process.
1. Raw material preparing
Factor 1 - Raw material
Anode materials and cathode materials are different. The purity of raw materials has great
effect on battery cell’s reliability and performance.
Factor 2 - Mixing
The anode material and cathode material will be mixed separately in tanks. And the
homogeneity of the material mixing also greatly influences the final product.
Factor 3 - Coating/Calendering
After mixing, the material will be coated onto a piece of foil. Anode material pasted onto
an aluminum foil, and cathode materials pasted onto a copper foil. And with the limitation
of coating technology, manufactures cannot distribute the materials evenly.
Factor 4 - Slitting
As the mixed materials are coated onto the foil of a width up to one meter. So precision
cutting has a deep impact to ensure the correct self-discharge of battery cells. After
cutting, both edges of the foil will leave some notches, which have the risk of piercing
the separator between anode and cathode pad. Then resulted in internal
short-circuit and higher self-discharge. This is also a very important reason that
causes battery explosion.
Factor 5 - Winding/Assembling
In this process, it’s not easy to inject exactly the same volume of electrolyte inside the
battery cell. So it’s also a factor that will affect the perseverance of final product.
For all the factors mentioned above, there are no two battery cells being exactly the same
for all the parameters, so manufacturers or clients will define a standard parameter range
of a batch of battery cells. And different batches of product have different standards.
After activating the finished battery cells with formation process. Manufactures
sort the cells within the standard parameters range into grade A battery cell group. And
for the ones that are out of provided range, factories will sort them into unqualified
battery cell groups. Those battery cells cannot meet the standard of car level
homogenizes. However, some clients find it works for single cell or small series/parallel
utilized after resorting. That is grade B/C battery cells. Which is much cheaper than
grade A cells.
Note: Anyway, since the evacuate factors including battery dimensions, weight,
stock time, voltage, capacity, internal resistance, self-discharge rate, etc.,
there’s a risk to use grade B battery cells even after resorting.
We have made a video to explain more details of grade B cells if you’re interested.
And next time we’ll share some tips about how to distinguish Grade A and Grade B cells.