Application and safety issues of lithium-ion batteries: Lithium ion batteries are widely used due to their high energy density, high output power, and high average output voltage. However, accidents caused by battery failures occur every year, and few people actively understand safety risks. Therefore, identifying and mitigating the safety hazards of lithium batteries is crucial.
The main content of the article: Firstly, the phenomenon of thermal runaway is analyzed and various monitoring systems are discussed. Then, the application of fiber Bragg grating sensors (FBG) in real-time detection of battery data is emphasized. Finally, methods for reducing safety issues in lithium batteries are summarized, including the use of electrode surface coatings, electrolytes, separators, and suppression of lithium dendrite growth. These contents have reference value for future research on lithium battery safety.
1. Introduction
The application and safety issues of lithium-ion batteries are highlighted: the development of renewable energy is a trend of the times, and batteries are ubiquitous in daily life. Lithium ion batteries are widely used and crucial for the development of new energy fields. However, in recent years, their overheating problem has affected the development of electric vehicles, and battery safety has been of concern.
Research direction and purpose of the article: Scientists use various technologies to improve the safety of lithium-ion batteries. Currently, safety monitoring research on battery thermal runaway prediction and warning methods is a popular direction. The article aims to summarize relevant advanced methods and introduce the latest research progress.
2. Current methods for improving safety factors
Cause of safety accident: When lithium batteries are improperly used (such as overcharging, overheating, impact, short circuit), the temperature rises abnormally, causing internal chemical reactions and producing gas and smoke. The safety valve opens, and the heat further increases the temperature, which may lead to combustion or explosion.
The ways to improve safety: mainly include monitoring and avoiding safety accidents, upgrading battery structures, or replacing problematic components.
Specific methods to improve the safety of lithium-ion batteries
Prevent thermal runaway
Thermal runaway principle: The exothermic reaction of materials inside the battery causes the battery to rapidly heat up and release chemical energy. Multiple factors can cause overheating, such as structural deformation, short circuit, overcharging, component aging, cooling system failure, etc. The high energy density of batteries and the use of flammable electrolytes increase the risk of thermal runaway.
Cooling system: Scientists have developed battery thermal management systems (BTMS), including air cooling and liquid cooling systems, but both have drawbacks. The hybrid cooling system combines the advantages of both and can better regulate and manage battery heat dissipation, and the specific choice should be determined according to the situation.
| Cooling systems | Advantages | Disadvantages |
|
Air cooled BTMS |
Lightweight in structure Low cost in development and maintenance. |
1. Low thermal conductivity and vulnerability to thermal melting. 2. Hard to use in electric vehicles. |
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Liquid cooled BTMS |
High heat capacities and thermal conductivities. |
1. Prone to liquid leakage 2. Difficult to improve the system due to complex structure |
| Hybrid BTMS | Better cooling effectiveness | 1. More components and complexity |
Fiber Bragg Grating Sensor (FBG)
Monitoring principle: Prevent safety hazards by monitoring multiple symptoms of the battery in real-time. Modern methods often indirectly reflect the battery state by monitoring heat flow or detecting electrode cracking, while FBG sensors can directly or indirectly measure the temperature and strain response inside and outside the battery, and study electrolyte degradation through the interaction between light carried by optical fibers and the surrounding chemical environment.
Advantages: FBG sensors have the characteristics of minimally invasive, anti electromagnetic interference, and insulation. They can still accurately provide data under high temperature and high pressure. When the indicators reach the critical value, battery operation can be adjusted or terminated in a timely manner, improving the safety of battery use.
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Temperature Monitoring |
External Temperature Monitoring: FBG sensor is directly attached to the surface of the battery (which can be in the shape of a coin or cylinder) to achieve real-time temperature detection. |
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Internal Temperature Monitoring: is directly implanted into the battery for internal temperature detection. |
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| Strain Monitoring |
External Strain Monitoring: FBG monitors the external strain caused by factors such as temperature changes, mechanical compression, or impacts. |
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Internal Strain Monitoring: FBG monitors the strain inside the battery during use or during charging and discharging. |
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| Simultaneous Monitoring of Temperature and Strain | |
Improve battery separator to stabilize the battery
The role and design challenges of a separator: A separator is a physical barrier in a battery that prevents direct contact between the positive and negative electrodes and accommodates electrolytes to promote ion movement. The design needs to balance mechanical durability and porosity or transport performance, making it a challenge for use in large-scale battery systems.
Improvement method: The current research mainly focuses on improving commercial polyolefin (PP) membranes, such as coating or grafting organic/inorganic compounds, and treating the surface with heat-resistant compounds. Electrospinning technology can also be used to manufacture nanofiber membranes, which can enhance thermal stability. Adding hydrophilic materials can improve performance and inhibit lithium dendrite growth.
Non combustible polymer electrolyte
Traditional electrolyte problems and improvement directions: Traditional electrolytes may experience thermal runaway under extreme conditions, leading to oxidation, electrode material mixing, and even explosion. Improvement requires comprehensive consideration of the physical and chemical properties and stability of electrolytes and electrodes. Solid polymer electrolytes (SPEs) are the future trend, with no leakage, high mechanical strength, and stability, which can reduce the volume change of electrode materials.
| SPEs types | Characteristics |
| Poly ethylene oxide SPEs |
1. Higher conductivity 2. Adjustable size 3. Lower cost 4. Outstanding electrochemical properties |
| Polysiloxane SPEs |
1. Better thermal stability 2. Nonflammability 3. Higher dielectric constants |
Characteristics and flame retardants of SPEs: Different SPEs have different advantages, such as high conductivity and adjustable size of polyethylene oxide SPEs; Polysiloxane SPEs have good thermal stability and are non flammable. Most SPEs require the addition of flame retardants, and inorganic flame retardants are safer and cheaper, which can improve the performance of SPEs and inhibit lithium dendrite growth. However, SPEs research is relatively new and their applications are limited, and commercial electrolytes cannot be replaced.
| Flame Retardant | Properties |
| Halogen Flame Retardant |
1. Ultra-light, Ultra-thin 2. Difficult to ignite 3. Generated free radicals mitigate pyrolysis 4. The product dilutes the concentration of combustible gases and oxygen |
| Organophosphorus Flame Retardants |
1. Better fire safety 2. The cycle stability of batteries was improved 3. The growth of lithium dendrites was inhibited 4. Decomposition products can combine with combustible freeradicals |
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Inorganic Phosphorus-Based Flame Retardants |
1. Low toxicity 2. Low Price 3. Can make the charge on the surface of metal lithium uniform 4. Prevent lithium dendrites. |
| Inorganic Nano-Filler Flame Retardant |
1. Facilitate the movement of lithium ions and enhance ion conductivity. 2. Avoid growth of lithium dendrites 3. Ability to inhibit thermal propagation 4. Improved thermal stability |
Inhibition of lithium dendrite growth
Formation and hazards of lithium dendrites: Lithium dendrites are caused by uneven deposition of lithium ions during the migration of positive and negative electrodes, which can lead to electrode expansion, reduced Coulombic efficiency, decreased battery capacity, and deterioration of safety performance, ultimately resulting in battery failure.
Inhibition method: Inhibit from two directions: electrolyte and lithium metal negative electrode. Adding additives to electrolytes can enhance the functionality of the solid electrolyte interface (SEI) layer, such as lithium polysulfides and lithium nitrate, which can effectively inhibit the formation of lithium dendrites; From the perspective of electrodes, three-dimensional lithium negative electrodes can reduce the volume change of negative electrodes, such as graphene composite electrodes. There are also some new SEI layers that can effectively inhibit lithium dendrite growth.
Surface coating electrode method
The role and application of surface coating: Surface coating is the main technology for protecting cathodes and improving the thermal stability of cathode materials, which can suppress phase transition and enhance material conductivity. The use of surface coating technology in nickel cobalt manganese ternary (NMC) cathode materials can improve microstructure, electrochemical performance, thermal conductivity, ion diffusion coefficient, and thermal stability, reduce internal structural damage, increase cycling stability, and prevent metal ion leaching.
Specific methods and effects: If the "coating+perfusion" synthetic method is used to coat specific materials at room temperature, or the sol gel technology is used to create a uniform coating on the cathode surface at low temperature, the cycle stability can be significantly improved.
| Aspect(s) | Improvement after coating |
| Microscopic morphology and structure |
1. A more compact surface structure in positive electrode and ordered lattice structure 2. An increased stability. |
| Electrochemical performance characterization |
1. Significantly improved cycle stability 2. Material multiplier increased 3. Material resistance reduced 4. Electron transport performance improved |
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Thermal conductivity,ion diffusion coefficient and thermal stability |
1. Heat transfer performance of pure materials improved 2. Battery cooling and thermal safety performance improved 3. lon diffusion performance improved |
3. Summary
Method classification: Methods to improve the safety of lithium-ion batteries can be roughly divided into two categories: one is to monitor battery parameters in real-time as an early warning system to prevent safety accidents, and the other is to improve the internal materials or structure of the battery.
Specific measures and effects
In the first category, battery thermal management systems (BTMS) can prevent thermal runaway, and hybrid BTMS has the best cooling effect, but the structure is complex and the cost is high. Fiber Bragg Grating (FBG) sensors can monitor battery temperature, strain, and pressure in real-time, and can quickly identify overheating or abnormal conditions.
In the second category, researchers have improved the safety of lithium-ion batteries by improving separators, electrolytes, inhibiting lithium dendrite growth, and treating the cathode surface.