Wistek's Quality Grading Standards for LiFePO4 Prismatic Cells
Why does Wistek have its own quality grading system?
If there were a universally accepted standard for battery cell quality grading, Wistek would not use quality descriptions that are difficult for customers to understand. Unfortunately, no such universally accepted standard exists in the market.
In this article, we will explain Wistek's definitions of Grade A cells and ESS grade cells, and attempt to answer some customer questions regarding the definitions of different battery cell descriptions currently on the market.
How do we define Grade A cells and ESS grade cells?
See the comparison chart below:
| Feature | Grade A | ESS Grade | Grade B | Grade C |
| Application | High Voltage ESS | Low Voltage ESS | Laboratory demonstrations or teaching | No Recommed to use |
| Discharge Rate | Stable | Slightly unstable | Unpredictable | Unpredictable |
| Cycle Life | Meets the specifications | Meets the specifications | Lower Cycle Life | Unpredictable |
| Internal Resistance | Lowest | Lower | Unpredictable | Unpredictable |
| Condition | Brand New | Brand New | Brand New | Used |
| Original Shipping Test | Availiable | Availiable | No | No |
| QR | Intact | Intact | Mark B or Reprint | Reprint |
| Appreance | Neat and without bulges. | Neat and without bulges. | Slight bulging | bulges |
Market descriptions of battery cell quality:
EV grade cells:
First, we may need to clarify which battery cell models can be used in EV systems? Which battery cell models can be used in energy storage systems?
What are the differences between EV system battery cells and energy storage system battery cells? Can they be used interchangeably?
Energy storage systems: Home energy storage systems, commercial and industrial energy storage systems...
EV systems: New energy vehicles, passenger cars, ships, forklifts...
For more information on this topic, please visit our blog post.
EV Battery Cell and ESS Battery Cell
Simple answers to the above questions:
Question 1, please see the table below
Question 2，EV system battery cells require higher charge and discharge rates, capable of withstanding instantaneous high current output and input. Energy storage system battery cells require a continuous and stable discharge rate. Another key difference is the cycle life. Generally, EV system battery cells have a cycle life of 3500-4000 cycles, while energy storage system battery cells have a cycle life of over 8000 cycles. This data is based on the specifications of EVE LF105, EVE L304, EVE LF280K, and EVE MB31 battery cells.
We need to choose the appropriate battery cell based on the application scenario.
In fact, energy storage system battery cells are best suited for energy storage system applications.
So why do we need to differentiate between battery cells?
Grade A, ESS grade
The differences between the two are:
Analysis from the perspective of the entire batch of goods obtained from EVE:
1. Capacity Difference.ESS grade cells have a tolerance of 10Ah for the entire batch, while Grade A cells have a tolerance of 3-5Ah for the entire batch.
2. Production date. Grade A cells have very close production dates for the entire batch, within 2-3 consecutive days. In contrast, ESS grade cells have more scattered production dates, potentially spanning 3-4 months.
3. Internal Resistance. The internal resistance of Grade A cells, before welding the terminals, is close to the positive and negative tolerance range. For example, if the MB31 cell specification states 0.18±0.05mΩ, the internal resistance will be approximately 0.18-0.20mΩ, while ESS grade cells have an internal resistance of 0.21-0.23mΩ.
Can ESS grade cells be used?
The answer is: Yes, they can be used. Furthermore, they perform well in low-voltage residential energy storage systems.
Theoretically, Grade A cells are mainly used in high-voltage energy storage systems, such as industrial and commercial energy storage systems. Because these systems use a large number of cells, the requirements for individual cells are very high, requiring absolute consistency in voltage, capacity, and internal resistance.
We hope this article provides you with some useful information.
