What is an integrated protection circuit for lithium-ion batteries? In today's highly advanced technological world, all sorts of high-tech solutions have appeared in our lives, bringing us convenience. But did you know that these high-tech solutions might contain integrated protection circuits for lithium-ion batteries?
Overcharging, over-discharging, and overcurrent are significant factors affecting the lifespan and performance of lithium-ion batteries during use. Integrated protection circuits for lithium-ion batteries effectively monitor and prevent damage through various protection units. A typical lithium-ion battery charge/discharge protection circuit consists of two field-effect transistors, a control integrated circuit, and several resistors and capacitors.
Because of the high energy density of lithium-ion batteries, it is difficult to ensure their safety. In an overcharged state, the battery temperature rises and excess energy is generated, causing the electrolyte to decompose and produce gas. This can lead to spontaneous combustion or rupture due to increased internal pressure. Conversely, in an over-discharged state, the electrolyte decomposes, causing the battery's characteristics and durability to deteriorate, thereby reducing the number of rechargeable cycles.
The maximum charging termination voltage for a single lithium battery is 4.2V. Overcharging is not allowed, otherwise the battery will be ruined due to excessive loss of lithium ions at the positive electrode. When charging lithium batteries, a dedicated constant current and constant voltage charger should be used. First, charge at a constant current until the voltage across the lithium battery reaches 4.2V, then switch to constant voltage charging mode. When the constant voltage charging current drops to 100mA, charging should be stopped.
Lithium-ion batteries require constant current and constant voltage charging. Initially, charging is done at a constant current. As charging progresses, the voltage gradually increases to 4.2V (depending on the cathode material, some batteries require a constant voltage up to 4.1V). If the charger circuit malfunctions during charging and the voltage exceeds 4.2V, the lithium-ion battery will continue charging at a constant current, causing the voltage to rise further. When the lithium-ion battery voltage exceeds 4.3V, the chemical byproducts of the lithium-ion battery will intensify, potentially leading to battery damage or safety issues.
The protection circuit of a lithium-ion battery is designed to ensure safety during overcharging and discharging, and to prevent performance degradation. The protection circuit consists of a protection IC and two power MOSFETs. The protection IC monitors the battery voltage and switches to the external power MOSFETs to protect the battery when overcharging or discharging occurs. The protection IC provides overcharge protection, over-discharge protection, and overcurrent/short-circuit protection.
Due to the internal structure of lithium batteries, not all lithium ions can move to the positive electrode during discharge; a portion must remain at the negative electrode to ensure they can readily intercalate during the next charge. Otherwise, battery life will be shortened. To ensure that some lithium ions remain in the graphite layer after discharge, the minimum discharge termination voltage must be strictly limited; in other words, lithium batteries cannot be over-discharged.
Of course, the goal of making functional components single-chip is unchanging. For example, mobile phone manufacturers are currently moving towards chipsets that combine peripheral circuits such as protection ICs, charging circuits, and power management ICs with logic ICs to form dual-chip chipsets. However, it is currently difficult to reduce the open-circuit impedance of power MOSFETs and integrate them with other ICs. Even if they are made into single chips using special technologies, the cost would probably be too high. Therefore, the single-chip solution for protection ICs will take some time to resolve.
