# A Review on the Thermal Hazards of the Lithium-Ion Battery and the Corresponding Countermeasures
## 4 Thermal Hazards of Lithium-Ion Battery
### Thermal Hazards of Typical Battery Components
#### 4.1.2 Thermal Hazards of the Electrodes  
Nowadays, lithium nickel manganese cobalt oxide (NMC) ternary positive electrode material is one of the most widely used cathode materials, with high capacity, low cost and relatively good safety, which has been vigorously promoted in the current power battery industry [85]. The researchers found that with the higher content of Ni element, the cost would be significantly reduced, and the specific capacity would be higher [86]. However, the battery cycle life and the stability of electrode and electrolyte would be lower. Therefore, it is important to study the effect of element content in the NMC ternary material. [PERSON] et al. compared the thermal runaway behavior of various NMC cathode materials with electrolytes at high temperature by accelerating calorimeter (ARC), while the results showed that under different cut-off voltages, using a traditional carbonate solution as the electrolyte, with the increase of Ni content, the initial temperature corresponding to the reactions between electrode and electrolyte was reduced, i.e., the fire risk of the LIB increased [16]. The material used in previous research was a common NMC cathode, made from a hydroxide precursor system, with a powder particle size of about 10 \(\upmu\)m. The surface was not coated or modified to improve the performance. On the basis of traditional polycrystalline NMC materials, new single-crystal NMC materials have been developed, which are expected to improve battery stability at elevated temperatures [87].  
For positive electrode materials, the amount of lithium embedded will directly affect the amount of heat produced. The more lithium that is embedded, the less heat the whole LIB system will generate. If there is only the electrode material without electrolyte, almost no heat will be released [88] and the reactivity between positive materials and different electrolytes will also be different. [PERSON] et al. analyzed the heat production from the reaction between cobalt acid lithium batteries and differentelectrolytes using a C80 micro-calorimeter, and the results showed that when compared with chain solvent, the annular solvent was more stable. Among the various chain carbonate solutions, DMC showed the highest reactivity, while diethyl carbonate (DEC) presented the lowest [89]. According to the above research, the heat production mechanism of positive electrode with electrolyte can be summarized as follows: The stability of electrode material will decrease and the temperature will increase, resulting in the decomposition of the positive electrode material and oxygen release during the charging process. The oxygen will react with the electrolyte and negative electrode leading to substantial heat release and gas generation, thus greatly increasing the risk of thermal failure.  
For negative electrode materials, most of the commercial anode material is carbon such as graphite. On the anode surface, a layer of SEI would be formed during the first charge and discharge cycle. The SEI layer will not affect the lithium ion transport and can also prevent direct contact occurring between the anode and the electrolyte, which reduces the cycle performance. While the existence of the SEI will to some extent influence the capacity of LIBs, and its thermal stability under high temperature is poor. [PERSON] et al. investigated the graphite anode with organic electrolyte containing LiPF\({}_{6}\) using ARC and differential scanning calorimetry (DSC), and the results indicated that the initial exothermal temperature of the system was about 80 \({}^{\circ}\)C, while the starting temperature of rapid heat production was about 150 \({}^{\circ}\)C, which was regarded as the thermal runaway temperature of the LIB. At the same time, other scholars have studied the pyrolysis of the SEI. With the increase of temperature, the initial structure of the SEI would be destroyed, thus losing its protective function, leading to the reaction between electrode and electrolyte and the release of heat [90; 91; 92].