The most prominent and widely discussed case of a supplier failing battery safety tests is Samsung SDI (Samsung Display Innovation), specifically regarding the batteries they supplied for Samsung's Galaxy Note 7 smartphones in 2016. This incident became a landmark case study in battery safety failures.

1. The Product: Samsung Galaxy Note 7 smartphones.
2. The Supplier: Samsung SDI, a subsidiary of Samsung Group and a major manufacturer of lithium-ion batteries.
3. The Failure Mode: Thermal Runaway - Batteries overheated, caught fire, or exploded during use or charging. This was caused by design flaws introduced during manufacturing:
   • Anode Tab Welding Issue: The negative electrode (anode) tab was incorrectly bent and welded too close to the corner of the battery cell. This created sharp points that could pierce the separator (the thin film preventing anode/cathode contact), leading to internal short circuits.
   • Separator Design Flaw: The separator itself was too thin in certain areas, reducing its ability to prevent shorts under pressure or deformation.
4. The Tests Failed: Internal Samsung safety tests after the initial launch revealed these critical flaws. Subsequent independent investigations confirmed the design/manufacturing defects were the root cause.
5. Consequences:
   • Massive Global Recall: Samsung initiated the largest and most expensive product recall in consumer electronics history at the time. An initial recall (replacing phones with batteries from a different supplier) failed to stop incidents, leading to a second recall and ultimately the permanent discontinuation of the entire Note 7 line.
   • Financial Loss: Estimated costs exceeded $17 billion for recalls, lost sales, compensation, and damage control.
   • Reputational Damage: Severe damage to both Samsung Electronics (brand trust) and Samsung SDI (reliability as a supplier).
   • Safety Concerns: Raised global awareness about the dangers of lithium-ion battery failures and the importance of rigorous testing.

Why it's a Critical Case Study:

• Scale & Impact: Affected millions of devices globally, causing property damage and injuries.
• Root Cause: Failure wasn't just one bad batch; it was a fundamental flaw in the design and manufacturing process approved by the supplier.
• Supplier vs. Manufacturer: Highlighted the complex relationship where a component supplier (SDI) can cripple a finished product manufacturer (Samsung Electronics) through failure.
• Industry Lesson: Forced the entire electronics industry to significantly enhance battery safety testing protocols, design standards, and supplier oversight. It underscored the critical need for:
  • More rigorous internal and third-party safety testing (including abuse tests like nail penetration, crush, overcharge, high temp).
  • Better understanding of failure modes and root cause analysis ("5 Whys").
  • Enhanced quality control during manufacturing.
  • Transparency and swift action upon safety concerns.

Other Notable Suppliers Failing Battery Safety Tests:

While Samsung SDI/Note 7 is the most famous, other instances include:

• Hoverboard Suppliers (Mid-2010s): Numerous low-cost suppliers failed safety tests, leading to fires caused by poor quality cells, inadequate chargers, and lack of basic protection circuits. Resulted in widespread bans and recalls.
• E-Cig/Vape Battery Suppliers: Some suppliers of batteries for vaping devices have failed safety tests, leading to explosions and fires due to counterfeit cells, improper charging circuits, or physical damage risks.
• Automotive Battery Suppliers: While less publicized than Note 7, suppliers to automakers have occasionally failed internal validation tests, leading to delays or rejection of battery packs before they enter vehicles. For example, LG Chem faced scrutiny over fires in some of its battery packs used in GM vehicles (though complex root causes were involved).

In summary: Samsung SDI is the prime example of a major battery supplier whose products failed critical safety tests, leading to a catastrophic product failure, massive recalls, and lasting industry changes. The case serves as a powerful reminder of the paramount importance of battery safety throughout the entire supply chain.