Failure Analysis of Batteries
Failure Analysis of Lithium-ion batteries is a systematic investigation of why a battery failed either during normal operation, storage, testing, or under abusive conditions. This process is essential for improving battery design, manufacturing, safety, and reliability, particularly in high-risk industries like EVs, aerospace, medical devices, and consumer electronics.
Most common mode of failures:
| Failure Mode | Description | Potential Consequences |
|---|---|---|
| Internal Short Circuit | Caused by separator failure, lithium dendrites, or debris | Thermal runaway, fire, explosion |
| Overcharging | Charging above the rated voltage | Gas generation, swelling, venting, fire |
| Overdischarging | Discharging below safe voltage (e.g., <2.5V) | Capacity loss, copper dissolution, fire risk |
| Thermal Runaway | Self-heating cycle caused by internal failure or external heat | Fire, explosion |
| Swelling / Gassing | Electrolyte breakdown or overcharging leads to gas formation | Mechanical deformation, leakage |
| Loss of Capacity | Reduction in energy storage over time or cycles | Shortened run time |
| Increased Internal Resistance | Due to SEI layer growth or corrosion | Voltage drop under load, overheating |
| External Short Circuit | Terminal short due to mishandling, tools, or water ingress | Rapid heating, fire, or explosion |
| Electrolyte Leakage | Seal failure or corrosion | Fire risk, chemical hazard |
| Thermal Abuse | Operation/storage outside the safe temperature range | Swelling, venting, or ignition |
| Mechanical Damage | Crushing, puncturing, or impact | Internal short circuits, immediate failure |
Root Causes of Failures
| Category | Examples |
|---|---|
| Design Defects | Inadequate separator thickness, lack of vents, poor BMS design |
| Manufacturing | Contaminants, misaligned electrodes, welding defects |
| Material Issues | Poor electrode materials, unstable electrolytes, defective cells |
| User-Induced | Use of wrong charger, over-discharge, exposure to extreme temperatures |
| Environmental | Moisture ingress, vibration, mechanical shock |
| Aging & Cycling | SEI growth, lithium plating, capacity fade |
A typical failure analysis could include the following:
- Cell history analysis
- Visual inspection includes swelling, electrolyte leak, rusting / discoloration, mechanical deformation, burn mark or smoke residue
- Non-destructive testing includes:
- X-ray / CT scan – to detect internal short, misalignment, gas pocket
- Thermal imaging – identifies hot spots or self-heating
- Electrochemical impedance spectroscopy (EIS) – internal degradation
- Open circuit voltage (OCV) – indicaes state of charge and internal state
- Electrical testing:
- Capacity test
- Resistance check
- Self-discharge rate
- Voltage recovery behavior
- Destructive analysis:
- 3-Electode test – identifies capacities of individual electrodes, electrode imbalance
- Cell disassembly
- Separator inspection: melting, shrinking, internal short
- Anode/Cathode analysis: Lithium plating, degradation, particle detachment
- Electrolyte analysis: contamination, decomposition, gas generation
- Surface characterization: SEM/EDS for morphology and elemental analysis, XPS- surface chemistry, XRD – structural changes in electrode materials
Picture 1: Cell disassembly
Picture 2: CT scan
Belmont Scientific’s experience:
Our experts have conducted root cause failure analyses of cells and battery packs used in laptops, power tools, HEV cells, cell phones, and other consumer electronics. This work was done on several battery chemistries (Li-ion, Li-polymer, Lead acid, Nickel metal hydride, and Alkaline) and designs (cylindrical, prismatic, pouch, and coin cells). During the late 1990’s and early 2000’s, our experts worked with major laptop and Li-ion cell manufacturers to find the root cause of these failures. Various issues were found such as improper winding of the jelly roll, uneven coatings, unbalanced effective electrode mass, and foreign contaminant particles. This study found that two of the major causes of cell failure were the presence of contaminants and spot welding of the current collector.