In recent years, the market demand for lithium-ion batteries has been increasing daily, and higher requirements have been placed on their energy density and safety. However, safety incidents caused by lithium-ion battery combustion and explosion have been frequent in recent years, such as the Samsung Galaxy Note7 battery explosion and fire, the Tesla electric vehicle spontaneous combustion incident, and the Boeing 737 passenger plane lithium battery smoke incident. These incidents have severely damaged consumer confidence and caused panic and safety concerns throughout the lithium battery industry.
lithium battery development trend
01 Development Trends of Lithium Batteries
As lithium batteries are used more and more widely in electronic devices and other products, and even in satellites and special applications, people's understanding of lithium batteries is becoming more and more profound. At the same time, higher requirements are being placed on the safety of lithium batteries.
02 Problems Facing the Development of Lithium Batteries in my country
Many crucial raw materials for lithium-ion battery development in my country still rely on imports, and the raw material supply chain for anode materials is not yet fully developed. Therefore, there is still a long way to go to perfect my country's lithium-ion battery production supply chain.
(Future development trends in lithium battery technology)
Analysis of the causes of lithium-ion battery safety issues
From an external perspective, overcharging, over-discharging, battery short circuits, thermal shock, and puncture can all lead to safety issues with lithium-ion batteries.
From an internal perspective, the main causes of lithium-ion battery safety issues are as follows:
01 Lithium plating at the negative electrode
Due to the slow internal kinetics of the embedded negative electrode material, under conditions of low-temperature overcharging or high-current charging, metallic lithium can directly precipitate on the negative electrode surface, potentially leading to lithium dendrites, causing micro-short circuits. The highly active metallic lithium directly reacts with the liquid electrolyte, resulting in the loss of active lithium, increased internal resistance, and impaired battery performance. As cycling continues, lithium dendrites further increase, eventually piercing the separator, leading to battery short circuits, leakage, or even explosions.
02 Oxygen release and structural damage of cathode materials
When the positive electrode is charged to a high voltage, it is in a high oxidation state. Oxygen in the crystal lattice easily loses electrons and is released as free oxygen. Free oxygen will react with the electrolyte to produce an oxidation reaction, releasing a large amount of heat. Moreover, organic electrolytes with low ignition points are extremely unsafe in the presence of oxygen and when the temperature rises, so the battery is very prone to combustion and explosion.
03 Electrolyte decomposition and reaction
The electrolyte in liquid lithium-ion batteries is a mixture of lithium salt and organic solvent. Commercially available lithium salt is lithium hexafluorophosphate (LiPF6), which is prone to thermal decomposition at high temperatures and undergoes thermochemical reactions with trace amounts of water and organic solvents. The organic solvent in the electrolyte is a carbonate, which has low boiling and flash points and readily reacts with the PF5 released from the lithium salt at high temperatures, making it easily oxidized. In the presence of lithium and oxygen, a series of exothermic side reactions occur, directly affecting battery performance and even leading to battery fires and explosions.
04. Poor diaphragm uniformity and shrinkage rupture
When lithium dendrites pierce the separator or the separator shrinks and ruptures due to high temperature, a short circuit will occur between the positive and negative electrodes of the battery, which can cause a safety accident in severe cases.
05 High-temperature failure
High temperatures can originate from external causes or internal factors such as short circuits, electrochemical and exothermic chemical reactions, and Joule heating from high currents. High temperatures can lead to a series of adverse reactions within the battery, including SEI film decomposition, reactions between highly active positive and negative electrode materials and the electrolyte, lithium salt self-decomposition, oxygen release from the positive electrode, and electrolyte reactions. These reactions can potentially cause thermal runaway.
Both industry and academia have implemented various improvement measures to address the safety issues of lithium-ion battery technology, covering aspects such as materials, electrodes, cells, modules, power management, thermal management, and system design. While some progress has been made, the ideal results have not yet been achieved, and safety issues remain prominent. Therefore, it is both necessary and urgent to overcome this technological bottleneck, meet the needs of high-safety battery technology, and develop lithium-ion batteries that are non-flammable and non-explosive.
