A safer electrolyte for lithium-ion batteries, containing the flame retardant trimethyl phosphate, is a non-flammable high-concentration electrolyte that is unlikely to burn or explode even at high temperatures. In addition, the electrolyte can be reliably charged and discharged more than 1,000 times, which is longer than traditional lithium-ion batteries.
When charged, the lithium atoms on the positive electrode lose electrons and oxidize to lithium ions. Lithium ions pass through the electrolyte to the negative electrode, where they enter the battery, gain an electron, and then return to the lithium atom. When discharging, the whole process is reversed. In order to prevent the positive and negative of the battery from directly contacting and short-circuiting, the battery will have a number of fine holes in the diaphragm paper to prevent short-circuit. A good diaphragm paper can also automatically close the hole when the battery temperature is too high, so that lithium ions cannot pass through, which not only wastes martial arts, but also prevents danger.
When the lithium battery is overcharged to a voltage above 4.2V, side use begins to appear. The higher the overcharge voltage, the higher the risk. When it exceeds 4.2V, less than half of the lithium atoms in the cathode material remain, and the battery often bends, thereby permanently reducing the battery's capacity. If the charge continues, since the anode battery is already full of lithium atoms, subsequent lithium metal will accumulate on the surface of the anode material. These lithium atoms form dendrites from the cathode surface to lithium ions. These lithium crystals pass through the diaphragm paper to short-circuit the positive and negative electrodes. Sometimes the battery explodes before the short circuit occurs. This is because during the overcharging process, the electrolyte and other materials crack and produce gas, which causes the battery casing or pressure valve to expand and rupture, causing oxygen to react with lithium atoms, and lithium atoms accumulate on the surface of the negative electrode and explode. Therefore, when charging a lithium-ion battery, the upper voltage limit must be set so as to take into account the battery's life, capacity and safety at the same time. The optimal charging voltage limit is 4.2V. When the lithium core is discharged, there should also be a lower voltage limit. When the core voltage drops below 2.4V, some materials will begin to breakdown. And because the battery will self-discharge, the longer the discharge time, the lower the voltage will be. Therefore, it is best not to stop after discharging 2.4V. Li-li battery only releases about 3% of the battery capacity between 3.0V and 2.4V. Therefore, 3.0V is the ideal discharge cut-off voltage.
In charging and discharging, in addition to voltage limitation, current limitation is also necessary. When the current is too large, lithium ions have no time to enter the battery and concentrate on the surface of the material. When these lithium ions gain electrons, they form lithium atom crystals on the surface of the material, which is as dangerous as overcharging. If the battery case is broken, it will explode.
Therefore, the protection of lithium batteries should include at least three items: the upper limit of charging voltage, the lower limit of discharge voltage and the upper limit of current. Under normal circumstances, in the lithium battery package, in addition to the battery, there will be a protection board. The important point of the protection board is to provide these three types of protection. However, these three types of protective panels are obviously not enough, and lithium battery explosions are still spreading frequently around the world. In order to ensure the safety of the battery system, it is necessary to conduct a more careful analysis of the cause of the battery explosion.