The rapid development of lithium ion batteries (LIBs) as core components of new energy vehicles has been driven by their compact size and high energy density. However, increasing energy density also amplifies safety risks, particularly thermal runaway—a catastrophic failure mode characterized by uncontrolled temperature rise, gas emission, and potential fire or explosion. This article synthesizes patent data, technical literature, and industry trends to analyze global innovations in thermal runaway monitoring, warning, and protection for lithium ion batteries.
1. Mechanisms of Thermal Runaway in Lithium Ion Batteries
Thermal runaway in LIBs is a chain reaction triggered by internal and external factors. Key stages include:
- SEI Layer Decomposition: At temperatures exceeding 80°C, the solid electrolyte interphase (SEI) layer on the anode decomposes, exposing lithium metal to electrolyte reactions.
- Separator Meltdown: At ~190°C, the separator disintegrates, causing internal short circuits.
- Exothermic Reactions: Cathode decomposition and electrolyte oxidation release heat and gases (e.g., CO₂, H₂, CH₄), accelerating temperature rise.
Factors influencing thermal runaway include:
- Internal: Manufacturing defects, dendrite growth, aging.
- External: Overcharging, mechanical damage, high ambient temperatures.
Material systems also dictate failure modes:
- NMC (Nickel Manganese Cobalt): Prone to violent combustion.
- LFP (Lithium Iron Phosphate): Generates smoke without open flames.
2. Macro Patent Analysis
Using a specialized automotive patent database, 40,315 thermal runaway-related patents were analyzed (as of December 31, 2023).
2.1 Patent Application Trends
Global and Chinese patent filings are summarized below:
| Year | Global Patents | China Patents | China’s Share |
|---|---|---|---|
| 2010 | 320 | 85 | 26.6% |
| 2015 | 1,502 | 812 | 54.1% |
| 2020 | 4,873 | 3,128 | 64.2% |
| 2023 | 5,210 | 4,486 | 86.1% |
Key Observations:
- China’s dominance surged post-2015, driven by EV market growth and safety incidents.
- Global filings grew steadily, with a CAGR of 18.3% (2010–2023).
2.2 Geographic Distribution
Top countries in patent filings:
| Rank | Country | Patents | Share (%) |
|---|---|---|---|
| 1 | China | 21,136 | 52.4 |
| 2 | South Korea | 5,895 | 14.6 |
| 3 | USA | 5,043 | 12.5 |
| 4 | Japan | 2,599 | 6.4 |
China’s leadership reflects its dual role as the largest EV market and battery producer.
2.3 Key Patent Applicants
Top 10 global applicants account for 2.5% of total filings, indicating a fragmented innovation landscape:
| Rank | Applicant | Patents | Category |
|---|---|---|---|
| 1 | LG Chem | 1,208 | Battery Supplier |
| 2 | CATL (Ningde) | 987 | Battery Supplier |
| 3 | Samsung SDI | 845 | Battery Supplier |
| 4 | Korea Institute of Technology | 732 | Research Institution |
| 5 | FAW Group | 698 | OEM |
Chinese entities dominate domestic filings, while Korean firms lead globally.
3. Key Technologies in Thermal Runaway Mitigation
3.1 Thermal Runaway Warning Systems
3.1.1 Feature Parameter Monitoring
Critical parameters for early detection include:
- Battery State: Voltage (VV), current (II), temperature (TT), state of charge (SOCSOC).
- Gas Emissions: Concentrations of CO₂, H₂, and volatile organic compounds.
Material-specific monitoring strategies:
- NMC LIBs: Voltage drop (ΔVΔV) and localized TT spikes are primary indicators.
- LFP LIBs: Smoke density and pressure changes (ΔPΔP) are more reliable.
Example Patents:
- CN112880082A: Monitors voltage, temperature, and swelling force (FswellFswell).
- US202117349289: Uses pressure sensors in modules to predict thermal runaway.
3.1.2 Warning Models and Algorithms
Machine learning (ML) enhances prediction accuracy by analyzing multi-parameter datasets. Common approaches include:
- Local Outlier Factor (LOF):LOFk(p)=∑o∈Nk(p)lrdk(o)lrdk(p)⋅∣Nk(p)∣LOFk(p)=lrdk(p)⋅∣Nk(p)∣∑o∈Nk(p)lrdk(o)where lrdklrdk is the local reachability density.
- Random Forest-SVM Hybrid:
- Feature importance extracted via random forest.
- SVM classifies risk levels:
Example: CN117454259A combines these models for staged risk assessment.
3.2 Thermal Runaway Protection Strategies
3.2.1 Cell-Level Protection
Design innovations vary by cell format:
| Cell Type | Protection Mechanism | Example Patent |
|---|---|---|
| Prismatic | Pressure relief vents, fuse structures | CN108428820A (CATL) |
| Cylindrical | Dual-pressure vents | CN117028628A (Sunwoda) |
| Pouch | Integrated fire retardant | CN110073517A (LG Chem) |
3.2.2 System-Level Protection
- Battery Management System (BMS) Wake-up:
Patents like CN111907329A (Dongfeng) activate BMS during thermal events. - Fire Suppression:
Liquid nitrogen (CN114976310A) and flame-retardant immersion (CN220420688U) mitigate propagation.
4. Future Outlook
China will remain the epicenter of lithium ion battery innovation, with patent filings focused on:
- AI-Driven Predictive Models: Enhancing ML algorithms for real-time risk assessment.
- Material Advancements: Developing non-flammable electrolytes and robust separators.
- Standardization: Addressing fragmented patent landscapes through global safety protocols.
The integration of multi-parameter monitoring and intelligent protection systems will define the next generation of lithium ion battery safety.