Many of today’s consumer electronic products include batteries, so buying lithium batteries from China is a common requirement for many importers. But when you’re sourcing battery suppliers, what are the key criteria you’re going to need to research in order to find the right fit? Find out here…
You shouldn’t skimp on battery quality
As I wrote on QualityInspection.org:
Batteries often make up for a relatively high percentage of the overall product cost. The temptation is very strong for the supplier to substitute batteries from the local market (the cost is often 2-4 times lower) and to save a lot of money.
Knowing that they are original batteries made by [a major brand] would ensure a level of safety and performance for your product and is a USP worth mentioning when selling to your customers.
So you should not be looking to select ‘the cheapest’ lower-quality batteries, or will run the risk of turning your product into a safety hazard. We’ve all heard the stories of exploding cell phones and hoverboards that burst into flames… the common denominator between these products is that they were powered by lithium batteries.
Here’s a real photo we took of sub-standard batteries that did actually catch fire during testing…don’t forget that these are high-risk items:
(That’s not to say that cheap batteries guarantee accidents, as this can be a design issue, or caused by users; however, poorer quality generally comes with high performance variation, poor ‘packing’ design, incomplete BMS, and other factors that increase risks).
Criteria to research when buying lithium batteries in China
Regardless of what type of lithium battery you’re sourcing, you need to find one that reaches your quality standard. So, here’s a list of criteria we suggest you find out from potential battery suppliers when you’re buying lithium batteries in China.
(Note: if you don’t purchase a high quantity of batteries, you need to reduce this list accordingly, or you won’t get many responses.)
General Company Information
- Company name
- Founded in?
- Manufacturing capacity (units/year) for cells
- Manufacturing capacity (units/year) for packs
- List main customers
- Key applications the products are usually used in
Cell Manufacturing Process
- Are you producing your own cells or are they produced by another company?
- Who manufactures the active materials?
- Who manufactures the separator?
- Who manufactures the current collectors?
- Is your manufacturing process done under a controlled atmosphere? Provide details.
- During the slurry preparation process, the coating process, and the calendering process, what critical control points do you measure & monitor?
- During the electrolyte filling process, and during the cell winding process, what are the biggest risks and how do you control them?
- Which post-formation tests and ageing tests are performed?
- Manufacturing quality – can you share statistical process control data?
- What is the reject rate? What are your rejection criteria?
Pack Manufacturing Process
- How do you control the quality of welding points?
- How do you select which cells to assemble together in a pack?
- Are there physical protections against shocks?
- Please provide photos of the inside of the pack.
Cell Information
- Please provide the cell reference, its datasheet, and its Material Safety Data Sheet
- Please provide the UN38.3 certification and test report
- Please provide a list of other standards the cell is compliant with
- Please provide a list of tests carried out on the cells so far and associated test reports
- What is the chemistry of your lithium-ion cells?
- Capacity (Ah) – please indicate at which C-rate it is measured
- Energy capacity (Wh) – please indicate at which C-rate it is measured
- Nominal voltage
- Minimum voltage
- Maximum voltage
- Nominal C-rate
- Maximum discharge current
- Maximum charge current
- Maximum impedance (mΩ)
Pack Information
- Please provide the pack reference, its datasheet, and its Material Safety Data Sheet
- Please provide the UN38.3 certification and test report
- Please provide a list of tests carried out on the pack so far and associated test reports
- Capacity (Ah) – please indicate at which C-rate it is measured
- Energy capacity (Wh) – please indicate at which C-rate it is measured
- Nominal voltage
- Minimum voltage
- Maximum voltage
- Maximum discharge current
- Maximum charge current
- Expected lifetime and associated conditions: at which C-rate; which temperature; which end-of-life criteria
- Cells connection arrangement (parallel and series configuration)
Temperature Management
- How is the ventilation of the pack ensured?
- A temperature increase of the pack during discharge, at different C-rates
- A temperature increase of the pack during charge, at different C-rates
- How does the BMS safely protect the pack at high/low temperatures? At which values?
- Is the distribution of temperature inside the pack homogeneous? How is this monitored?
Battery Management System (BMS)
- Who is the BMS designer and manufacturer?
- Can you provide the list of securities implemented in the BMS?
- Could you provide the list of sensors inside the battery pack?
- How does the balancing system work?
- Could you describe the BMS qualification process?
- How is the BMS fixed on the battery pack?
- What is the self-consumption of the BMS?
Protections
- What are the protections at the cell level?
- What are the protections at the pack level?
- Have you carried out abusive tests on cell and pack? If so, can you share the test methodology and the report(s)?
- Maximum temperature after short circuit (UN38.3 test)
(Note: all this information is usually collected in a spreadsheet, for easy comparison.)
We review some of these checkpoints, and others, in our process audits on battery manufacturers. The battery is often one of the most expensive parts on the bill of materials, and managing associated risks is sometimes as important as keeping a close eye on the final assembly!
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