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Battery classification

2021-06-30 18:31:04

Primary Batteries

Small secondary batteries: NiCd, NiMH, Li-ion

Lead-acid batteries

Power batteries

Fuel Cell

Solar battery-ground photovoltaic power generation

Other new batteries

Basic knowledge of battery terminology and use

The amount of power a battery can give under certain discharge conditions is called the capacity of the battery and is expressed by the symbol C. The common unit is ampere-hour, referred to as ampere-hour (Ah) or milliampere-hour (mAh).

The capacity of a battery can be divided into theoretical capacity rated capacity actual capacity.

The theoretical capacity is the highest theoretical value obtained by calculating the mass of active material according to Faraday's law. In order to compare different series of batteries, the concept of specific capacity is commonly used, i.e. the theoretical power that can be given by a unit volume or unit mass of battery, in Ah/kg.

The actual capacity is the amount of electricity that the battery can output under certain conditions. It is equal to the product of discharge current and discharges time, the unit is Ah, and its value is less than the theoretical capacity.

Rated capacity is also called guaranteed capacity, which is the minimum capacity that the battery should discharge under certain discharge conditions according to the standards promulgated by the state or relevant departments.

Inner resistance

The resistance to the current passing through the interior of the battery reduces the voltage of the battery, and this resistance is called the internal resistance of the battery.

The internal resistance of a battery is not constant and changes over time during discharge because the composition of the active material, electrolyte concentration, and temperature are constantly changing.

The internal resistance of the battery includes ohmic resistance and polarization resistance, and the polarization resistance includes electrochemical polarization and concentration polarization. The existence of internal resistance makes the end voltage of the battery lower than the battery electric potential and open-circuit voltage when discharging, and higher than the electric potential and open-circuit voltage when charging.

Ohm's resistance obeys Ohm's law: polarization resistance increases with current density, but not linearly, often linearly with the logarithm of current density.

When the positive and negative ends of the battery are connected to the appliance, the output power when driving the appliance to work is the load capacity of the battery.

Lithium battery internal pressure

It refers to the internal air pressure of the battery, which is caused by the gas generated during the charging and discharging process of the sealed battery and is mainly affected by the battery material, manufacturing process, battery structure, and other factors. The cause is mainly due to the accumulation of gas inside the battery caused by the decomposition of water and organic solutions inside the battery.

The multiplier discharge capacity of lithium batteries

C is the first letter of Capacity, which is used to indicate the size value of the current when charging and discharging the battery.

For example: when the rated capacity of rechargeable battery is 1100mAh, it means that the discharge time can last for 1 hour with 1100mAh (1C), such as the discharge time can last for 5 hours with 200mA (0.2C), and the charge can also be calculated according to this comparison.

Lithium battery discharge cut-off voltage

It means that when the battery is discharged, the voltage drops to the lowest working voltage value at which the battery should not be discharged further.

According to different battery types and different discharge conditions, the requirements for the capacity and life of the battery are different, so the specified termination voltage for battery discharge is also different.

Open circuit voltage of lithium battery

When the battery is not discharged, the potential difference between the two poles of the battery is called the open-circuit voltage.

The open-circuit voltage of a battery varies according to the material of the positive and negative electrodes and electrolytes.

Operating voltage of lithium battery

The operating voltage refers to the voltage displayed during the discharge process after the battery is connected to the load, also known as the discharge voltage. The operating voltage at the initial discharge of the battery is called the initial voltage.

After the battery is turned on to the load, the operating voltage of the battery is lower than the open-circuit voltage due to the presence of ohmic resistance and polarization overpotential.

Discharge depth of lithium battery

In the process of battery use, the percentage of the capacity discharged by the battery in its rated capacity is called discharge depth.

There is a deep relationship between the discharge depth and the charging life of the secondary battery. The deeper the discharge depth of the secondary battery, the shorter the charging life. Therefore, the deep discharge should be avoided as far as possible.

If the terminal voltage of the battery is not exceeded during discharge, the internal pressure of the battery may increase and the reversibility of the positive and negative active substances will be damaged when the battery continues to discharge

Overcharge of lithium battery

When the battery is charging, if it reaches the full state, if it continues to charge, it may lead to the increase of the internal pressure of the battery, the deformation and leakage of the battery, and the performance of the battery will also be significantly reduced and damaged.

Energy density of lithium battery

The average unit volume or mass of a battery that releases electrical energy.

Generally, under the same volume, the energy density of Li-ion battery is 2.5 times that of Ni-Cd battery and 1.8 times that of the Ni MH battery. Therefore, when the battery capacity is equal, the volume and weight of Li ion battery will be smaller and lighter than that of Ni-Cd Ni MH battery.

Self-discharge of lithium battery

No matter whether the battery is in use or not, due to various reasons, it will cause the phenomenon of power loss.

After the battery is fully charged, place it for one month. Then discharge to 3.0V with 1C, the capacity is C2; The initial capacity of the battery is recorded as C0

Industry-standard lithium-ion battery monthly self-discharge rate is less than 12%

The self-discharge of the battery is related to the placement performance of the battery, and its size is related to the internal resistance structure and material performance of the battery

When the Li ion battery is fully charged, the capacity when it is discharged to 3.6V is recorded as C1, and the capacity when it is discharged to 3.0V is recorded as C0. C1 / C0 is called the discharge platform of the battery

Industry-standard 1C discharge platform is more than 70%.

Cycle life of lithium batteries

The battery is fully charged and then fully discharged and cycled until the capacity decays to 75% of the initial capacity, at which time the number of cycles is the cycle life of the battery.

Cycle life is related to battery charging and discharging conditions.

The cycle life of lithium-ion battery can be 300-500 times (industry standard) and up to 800-1000 times under 1c charge/discharge at room temperature.

Memory Effect

The memory effect is for Ni Cd batteries. Because the negative electrode is sintered in the traditional process and the cadmium grains are coarse, if the Ni Cd batteries are recharged before they are fully discharged, the cadmium grains are easy to aggregate into blocks and form a secondary discharge platform when the batteries are discharged. The battery will store this platform and use it as the end point of discharge in the next cycle, although the capacity of the battery itself can make the battery discharge to a lower platform. The battery will only remember this low capacity in the future discharge process. Similarly, in each use, any incomplete discharge will deepen this effect and make the battery capacity lower.

There are two ways to eliminate this effect, one is to use low current deep discharge (such as 0.1C discharge to 0V), the other is to use high current charge and discharge (such as 1c) several times.

Neither Ni MH battery nor Li ion battery has memory effect.

Formation of lithium battery

After the battery is manufactured, the process of activating the internal positive and negative materials, improving the charge discharge performance and self discharge storage of the battery is called the formation. Only after the battery has been converted can the real performance be reflected.

Overcharge protection of lithium battery

Overcharge protection: the principle of overcharge protection IC is: when the external electrical appliances charge the lithium battery, in order to prevent the internal pressure rise caused by the temperature rise, it is necessary to terminate the charging state. At this time, the protection IC needs to detect the battery voltage. When it reaches 4.25v (assuming that the overcharge point of the battery is 4.25v), it starts the overcharge protection, turns the power MOS from on to off, and then stops charging.

Over discharge protection

Over discharge protection: IC principle of over discharge protection: in order to prevent the over discharge of lithium battery, assuming that the lithium battery is connected to the load, when the voltage of lithium battery is lower than its over discharge voltage monitoring point (assumed to be 2.5V), the over discharge protection will be started to make the power MOSFET switch from on to off and cut off the discharge, so as to avoid the over discharge of battery, And keep the battery in the low quiescent current standby mode, the current is only 0.1ua. When the lithium battery is connected to the charger and the voltage of the lithium battery is higher than the over discharge voltage, the over discharge protection function can be removed. In addition, considering the situation of pulse discharge, the over discharge detection circuit has a delay time to avoid errors.

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