In the quest for safer, more sustainable energy storage solutions, sodium-ion batteries (SIBs) have emerged as a promising alternative to their lithium-ion counterparts. Unlike lithium, which is scarce and geopolitically sensitive, sodium is abundant and inexpensive, making SIBs ideal for large-scale applications like grid storage and electric vehicles. However, safety has long been a hurdle, with thermal runaway—a chain reaction of heat, gas, and potential fire or explosion—posing risks even in SIBs. A groundbreaking advancement from China's Institute of Physics at the Chinese Academy of Sciences (CAS) changes that equation entirely.
Led by Professor Yong-Sheng Hu, the team has developed a polymerizable non-flammable electrolyte (PNE) that achieves complete blockage of thermal runaway in ampere-hour-level SIBs. Published in Nature Energy on April 6, 2026, this innovation demonstrates batteries stable up to 300°C, passing rigorous nail penetration and hot-box tests without smoke, fire, or explosion. This marks the world's first verified "zero thermal runaway" in practical-scale SIBs, positioning China at the forefront of next-generation battery technology.
The Challenge of Thermal Runaway in Rechargeable Batteries
Thermal runaway occurs when internal short circuits, overcharging, or external abuse generate heat faster than it dissipates, triggering electrolyte decomposition, oxygen release from cathodes, and anode reactions that escalate into catastrophe. In lithium-ion batteries (LIBs), this has led to high-profile incidents in EVs, consumer devices, and storage systems worldwide. SIBs offer inherent advantages—higher thermal stability thresholds around 220-260°C versus 170-220°C for LIBs, lower heat release, and reduced toxic gases—but propagation risks persist without advanced electrolytes.
Traditional non-flammable electrolytes suppress flames but fail to halt propagation in large cells due to electrode crosstalk, side reactions, and gas buildup. Hu's team addressed this with a multifaceted approach, proving that true safety demands more than flame retardancy: it requires physical isolation, interface stability, and self-healing mechanisms.
Innovating with Polymerizable Non-Flammable Electrolyte (PNE)
The PNE is a dual-salt system of sodium tetrafluoroborate (NaBF₄) and sodium hexafluorophosphate (NaPF₆) dissolved in triethyl phosphate (TEP). This formulation leverages a synergistic anion-cation solvation effect for optimal ionic conductivity while remaining non-flammable.
- Room-temperature operation: Liquid state ensures high sodium-ion transport, enabling energy densities of 211 Wh/kg—competitive with commercial LIBs.
- Thermal trigger: Above 150°C, TEP undergoes endothermic decomposition, releasing radicals that initiate polymerization of vinyl groups in the salts.
- Solid barrier formation: Cross-linked polymer network rapidly solidifies the electrolyte, physically separating anode and cathode to block ion/electron pathways and gas diffusion.
- Interface protection: Forms boron-rich cathode electrolyte interphase (CEI) and phosphate-rich solid electrolyte interphase (SEI) on hard carbon anodes, suppressing decomposition and dendrite growth.
This "three-in-one" system—thermal stability, chemical passivation, and mechanical isolation—transforms passive safety into active defense. Molecular dynamics simulations confirmed the solvation structure's role in polymerization kinetics.
Rigorous Safety Validation in Real-World Scales
The team tested 3.5 Ah pouch cells at 100% state of charge under extreme abuse:
| Test | Conditions | Result |
|---|---|---|
| Nail Penetration | 5 mm steel nail at 20 m/s | No smoke, fire, or explosion; voltage drop contained |
| Accelerating Rate Calorimetry (ARC) | Heated to 300°C | No self-heating or propagation; max temp stable |
| Hot Box | 300°C oven | Intact structure, no venting failure |
Cryo-TEM and XPS analyses revealed uniform, stable interfaces post-abuse, with minimal gas evolution compared to conventional electrolytes. Cells operated reliably from -40°C to 60°C and voltages over 4.3 V, showcasing versatility for diverse climates and applications. The full study details these experiments.
Professor Yong-Sheng Hu and the CAS Legacy in Sodium-Ion Research
Professor Hu Yong-Sheng, director of CAS IOP's Key Laboratory for Renewable Energy, has pioneered SIBs since 2011. With a PhD from CAS IOP (2004), postdocs at Max Planck and UC Santa Barbara, and over 180 publications (H-index 62), Hu chairs HiNa Battery Technology—the world's first SIB firm, launching 100 kWh grid projects in 2019. Previous breakthroughs include high-voltage cathodes and alloy anodes, earning awards like China's National Science Fund for Distinguished Young Scholars (2017) and ISE Tajima Prize (2015). His HiNa spin-off drives commercialization, with cells nearing LIB cost parity by 2027.
The CAS IOP team, including Jiao Zhang and Lin Zhou, builds on China's SIB ecosystem, supported by national strategies for energy independence. CAS highlights this as a global first.
Performance Metrics: Balancing Safety and Power
Beyond safety, PNE cells deliver:
- Energy density: 211 Wh/kg (pouch), scalable to cylindrical formats.
- Cycle life: Excellent retention after 500+ cycles at high rates.
- Rate capability: Supports fast charging without degradation.
- Cost: Leverages cheap Na, hard carbon; projected $70/kWh vs. LIB $100+/kWh.
These specs rival LFP LIBs while surpassing safety, ideal for China's grid demands.
China's Sodium-Ion Momentum: From Lab to Grid Dominance
China leads SIB commercialization, with 9 GWh shipped in 2025 (150% YoY growth). CATL's Naxtra line, HiNa's truck batteries (20% range boost), and BYD pilots target EVs and storage. Key projects include Datang's 100 MWh Hubei station (2024) and utilities mandating SIBs 2025-2027. Market forecasts: China SIB to $9.25B by 2033, global 292 GWh by 2034. Lower costs (Na $0.05/kg vs. Li $10+/kg) and supply chain maturity accelerate adoption amid Li price volatility.
SIBs suit stationary storage (lower density tolerance) and low-end EVs, complementing LIBs. Industry analysts see this safety leap as pivotal.
SIBs vs. LIBs: A Safety and Sustainability Comparison
| Parameter | SIBs (PNE) | LIBs (NMC/LFP) |
|---|---|---|
| TR Onset Temp | >300°C (zero TR) | 170-260°C |
| Max Temp | Stable | 500-750°C |
| Gas Toxicity | Low H2, no HF | High HF (LFP), HCN |
| Cost/kWh (2026) | $70 | $80-120 |
| Raw Materials | Abundant Na | Scarce Li, Co |
SIBs excel in safety margins, with PNE eliminating propagation risks LIBs still face despite mitigations like BMS.
Challenges Ahead and Path Forward
While transformative, SIBs lag LIBs in density (160-220 Wh/kg vs. 250+), needing anode/cathode advances. Scalability, recycling, and standardization remain priorities. China's policy support—subsidies, mandates—will drive pilots to GW-scale by 2030.
Stakeholders praise the work: experts note it "redefines SIB viability for high-stakes deployments." Future outlooks include hybrid packs and global exports, bolstering China's energy security.
Broader Impacts on China's Clean Energy Strategy
This aligns with China's dual-carbon goals, enabling terawatt-hour storage for renewables. Reduced fire risks lower insurance/ops costs, accelerating urban/grid rollout. Academic-industry synergy, via HiNa, exemplifies tech transfer.
As SIBs mature, expect cost convergence by 2027, reshaping global supply chains. Researchers worldwide eye PNE adaptations for other chemistries.
Photo by Jorick Jing on Unsplash