How to solve the safety problem of lithium battery

 

The safety of lithium batteries is a systematic project, which is related to these four key materials - the design of the positive electrode, the negative electrode, the electrolyte and the battery cell, the assembly process, and the battery management system.

After years of analysis and testing of lithium battery safety issues, the SER technical team believes that the safety of lithium batteries can be improved from the following three aspects: First, improve the thermal stability of lithium battery electrode materials and actively improve the safety of lithium batteries themselves performance; the second is to improve the electrolyte of lithium batteries and use safe electrolytes; the third is to optimize the design and management of lithium batteries through external means, such as adding PCM, PTC, etc., to monitor the charging and discharging process of lithium batteries in real time And timely handling of abnormal problems to ensure the safety of lithium battery use.

1. Improve the thermal stability of electrode materials

Generally speaking, the thermal stability of battery materials is the root of the safety of lithium-ion power batteries. Therefore, in order to fundamentally improve the safety of lithium batteries, it is also necessary to start from the thermal stability of the battery material itself.

Studies have shown that under high temperature conditions, the reaction between the cathode material and the electrolyte is one of the main causes of battery safety problems. Therefore, finding cathode materials with better thermal stability is an effective means to improve the safety of LiSOCL2 battery. It is important to find a cathode material with good thermal stability, but it cannot be ignored by modifying the cathode material to improve its thermal stability. Regarding the thermal stability of the negative electrode material, in addition to the thermal stability of the material itself, the thermal stability of the SEI film at the interface between the negative electrode and the electrolyte is more important.

Electrode material modification is an effective measure to improve the thermal stability of LiSOCL2 battery. Modified spinel lithium manganate, lithium nickel manganese cobalt oxygen ternary composite oxide and LiFePO4 batteries are the focus of current research on cathode materials. The commonly used modification methods are mainly surface coating and doping modification. Surface coating can reduce the reaction between the active material and the electrolyte, and at the same time reduce the oxygen released during the overcharge of the positive electrode material, stabilize the phase transition of the matrix material [7], and thus achieve the purpose of improving the thermal stability of lithium batteries. At present, there are many types of coating materials, such as: oxide-coated aluminum oxide (Al2O3), titanium dioxide (TiO2), phosphate (MPO4) coating [M=aluminum (Al), iron (Fe) , cobalt (Co)], aluminum hydroxide [Al(OH)3] coating, carbon coating and organic coating, although it cannot theoretically determine which type of coating material is most suitable for surface modification, but to a certain extent The thermal stability of the cathode material is improved. Cho et al. [8] found that coating LixCoO2 with nano-aluminum phosphate (AlPO4) particles can effectively suppress the exothermic reaction between the cathode material and the electrolyte.

 

2. Use safe lithium battery electrolyte.

The electrolyte plays the role of transporting lithium ions (Li+) between the positive and negative electrodes of the Lipo battery. The electrolyte participates in almost all the reactions that take place inside the battery, including not only the reaction between the electrolyte and the negative electrode material and the positive electrode material, but also the decomposition reaction of the electrolyte itself. It can be seen that the thermal stability of the electrolyte plays a crucial role in the safety of lithium batteries. Therefore, safe electrolyte systems have attracted attention and become a hot spot in the research and development of lithium polymer battery electrolytes.

For the electrolyte, its flammable organic solvent is the main element when the battery is burned. Therefore, it is necessary to develop an electrolyte that prevents combustion and has the function of preventing combustion. Adding additives to the conventional electrolyte is a common solution, generally using Phosphorus or halogen series materials.

3. By adding a protection board, the design and management of lithium batteries are optimized, etc.

The lithium battery protection board is the charge and discharge protection for the series-parallel lithium thionyl chloride battery pack; when fully charged, it can ensure that the voltage difference between the individual cells is less than the set value (generally ±20mV), so that each cell of the battery pack can be realized. The equal charging of the battery effectively improves the charging effect in the series charging mode; at the same time, it detects the overvoltage, undervoltage, overcurrent, short circuit and overtemperature status of each single cell in the battery pack to protect and prolong the battery life; The voltage protection prevents each single cell from being damaged due to over-discharge when it is discharged. In practical applications, PTC often appears as a thermistor, and the lithium battery protection board is through the large resistance value of the device material, so as to become a circuit breaker in disguise, cutting off the current to achieve the function of protection, such an explanation, everyone It is easy to think that PTC is a very important component in the LiFePO4 battery protection board, and the main protection function is also realized through it.