Management of mobile device lithium-ion batteries

Lithium-ion battery:

Discharge voltage: minimum 2.7V/cellfor lithium cobaltate, 2.5Vfor lithium iron phosphate, 1.5V for lithium titanate;

Charge voltage: typical 4.2V for lithium cobaltate (4.35Vfor electrolyte modified), 3.6V for lithium iron phosphate, 2.7V for lithium titanate.

Battery structure: There are three structures, a cylindrical structure, a prismatic structure, and a laminated structure. The characteristics are as follows:

A, since the lithium carbon chimera is very active, only organic electrolyte can be used;

B, it must be waterproof and airtight;

C, the use of microporous insulation material to prevent lithium dendrite growth, and turn off charging when overheating;

D, the electrode uses a metal foil, the anode is a copper foil, and the cathode is an aluminum foil;

E, the active material is suspended on the electrode and has a thickness of 50 to 100 um.

Charging mode: constant current / constant voltage method; charging voltage (taking into account voltage fluctuations and temperature fluctuations) must not exceed 4.2Vfor lithium cobalt oxide, overvoltage will cause the battery to accelerate degradation, and even cause an explosion;

Multi-cell series battery: Each cell can't exceed the maximum voltage, so the status of each cell should be monitored independently. There should be multiple sets of independent overvoltage, over temperature and over current protection circuits. For multi-cell series batteries, the cell balancing algorithm is required; the charging current should be controlled at 1C, and when charging is completed, the temperature should not exceed 50 °C.

Charging temperature: The ambient temperature should be between 0 and 45 degrees Celsius. The low temperature will cause the precipitation of lithium, which will cause the battery to degrade. The high temperature will accelerate the reaction of the lithium electrolyte and accelerate the degradation.

Low-voltage charging: When the cell voltage is lower than 2.9V, a trickle charge of 0.1C should be used. If 0.1C is charged for 30 minutes, the cell voltage has not reached 3.0V, indicating that the cell has an internal short circuit, and the charging chip should alarm.

Cutoff state: When the charging current is less than 0.05C.

Discharge power: the thinner the active material on the electrode, the higher the power, but the smaller the capacity; the lithium iron phosphate and lithium titanate have higher discharge power; when the temperature is lower than 0 °C, the conductivity of the organic electrolyte decreases, the battery The discharge power will be severely degraded.

Battery health: 50% power is most stable; high voltage will accelerate corrosion and electrolyte degradation; must not exceed the full charge voltage of the battery; short-time over-discharge will not damage the battery, but long-term low-power storage will affect the battery's discharge capacity To avoid high temperature heat sources, low temperature storage can prolong life; to avoid unnecessary charge and discharge, do not need to be full like nickel cadmium, nickel metal hydride batteries.

Battery degradation mechanism:

A, the reaction of the lithium carbon mixture with the electrolyte: when the temperature is high, the reaction is intensified; the reaction makes lithium into an insoluble mixture, which blocks the pores of the separator and reduces the conductivity of the surface of the active material, thereby Lead to increased internal resistance of the battery;

B, electrode corrosion: aluminum foil and copper foil electrodes are prone to corrosion at high pressure, so the battery is generally stored at 50% capacity. When the battery discharge voltage is lower than 2V, the copper foil is dissolved.

Application scenario: High-capacity, long-time use, such as digital products.

Trend: Since the introduction of lithium-ion batteries in 1990, the capacity has increased at a rate of 7% per year; the initial lithium cobaltate, to the addition of nickel-manganese (low cost), to lithium iron phosphate (high power, but only energy density is half of lithium cobalt oxide). lithium titanate has better power and cycle life, but energy density is also insufficient. The recently developed silicon negative battery can increase the energy density by 30%, but the cycle life is poor; the longer-term development is lithium sulfide battery and air lithium battery. The lithium sulfide battery has high energy density, but the cycle life is poor, the air lithium theoretical energy density of the battery is the highest, but it is still difficult to implement temporarily.

The page contains the contents of the machine translation.