How many categories for electric vehicle batteries?

Electric vehicle batteries have two categories: batteries and fuel cells. The battery is suitable for pure electric vehicles, including lead-acid batteries, nickel-hydrogen batteries, sodium-sulfur batteries, secondary lithium-ion batteries, and air batteries.

Fuel cells are dedicated to fuel cell electric vehicles, including alkaline fuel cells (AFC), phosphoric acid fuel cells (PAFC), molten carbonate fuel cells (MCFC), solid oxide fuel cells (SOFC), proton exchange membrane fuel cells ( PEMFC), direct methanol fuel cell (DMFC).

There are slight differences depending on the type of electric vehicle. In a pure electric vehicle equipped only with a battery, the battery functions as the sole source of power for the vehicle drive system. In a hybrid vehicle equipped with a conventional engine (or fuel cell) and a battery, the battery can play the role of the main power source of the vehicle drive system, and can act as an auxiliary power source. It can see that at low speed and start-up, the battery plays the role of the main power source of the vehicle drive system; when it is fully loaded, it acts as the auxiliary power source; it acts to store energy during normal driving or deceleration and braking. Character.

The fuel anodizes the fuel cell and the oxidant reduced at the cathode. If gaseous fuel (hydrogen) continuously supplied to anode (ie, anode of the external circuit, also referred to as the fuel electrode). In addition, oxygen (or air) continuously supplied to the cathode (ie, the anode of the external circuit, also referred to as the air electrode), it is possible to continuously react an electrochemical reaction on the electrode and generate an electric current. This shows that fuel cells and conventional electricity

Unlike a pool, its fuel and oxidant are not stored in the battery, but in a storage tank external to the battery. When it works (outputs current and does work), it is necessary to continuously input fuel and oxidant into the battery while discharging the reaction product. Therefore, from a working mode, it is similar to a conventional gasoline or diesel generator. Since the fuel cell continuously fed with fuel and oxidant into the battery during operation, the fuel and oxidant used in the fuel cell are both fluid (gas or liquid). The most commonly used fuels are pure hydrogen, various hydrogen-rich gases (such as reformed gas) and certain liquids (such as aqueous methanol). The commonly used oxidants are pure oxygen, clean air and other gases (such as peroxidation). An aqueous solution of hydrogen and nitric acid, etc.).

The role of the fuel cell anode is to provide a common interface for the fuel and electrolyte, and to catalyze the oxidation of the fuel, while transferring the electrons generated in the reaction to the external circuit or to the current collector and then to the external circuit. The role of the cathode (oxygen electrode) is to provide a common interface between oxygen and the electrolyte, catalyzing the reduction of oxygen, and transporting electrons from the external circuit to the reaction site of the oxygen electrode. Since most of the reactions occurring on the electrodes are multiphase interfacial reactions, in order to increase the reaction rate, the electrodes are generally made of a porous material and coated with an electro catalyst.

The role of the electrolyte is to transport the ions generated by the fuel electrode and the oxygen electrode in the electrode reaction, and to prevent the electrodes from being straight.

Transfer the electrons.

The role of the membrane is to conduct ions, prevent electrons from passing directly between the electrodes, and separate the oxidant from the reducing agent. Therefore diaphragm

It must be resistant to electrolyte corrosion and insulation and has good wettability.

Battery

An electric vehicle battery pack is composed of a plurality of batteries stacked in series. A typical battery pack has about 96 batteries. For a Li-Ion battery that charged to 4.2V, such a battery pack can produce a total voltage of more than 400V. Although the automotive power system treats the battery pack as a single high-voltage battery, charging and discharging the entire battery pack each time, the battery control system must consider each battery condition independently. If one of the battery packs has a slightly lower capacity than the other batteries, the state of charge will gradually deviate from the other batteries after multiple charge/discharge cycles. If the state of charge of this battery not periodically balanced with other cells, it will eventually enter a deep discharge state, causing damage and eventually forming a battery pack failure. To prevent this from happening, the voltage of each battery must monitored to determine the state of charge. In addition, there must be a device to allow the batteries to individually charge or discharge to balance the state of charge of these batteries.

An important consideration in battery pack monitoring systems is the communication interface. For communication within the PC board, common options include the Serial Peripheral Interface (SPI) bus and the I2C bus, each with low communication overhead for low-interference environments. Another option is the Controller Area Network (CAN) bus, which is widely used in automotive applications. The CAN bus is very good, with error detection and fault tolerance characteristics, but it has a large communication overhead and high material cost. Although the connection from the battery system to the car's main CAN bus is worthwhile, it is advantageous to use SPI or I2C communication within the battery pack.

There are many varieties of chemical batteries with different performances. Commonly used indicators to characterize its performance are electrical properties, mechanical properties, storage properties, etc., sometimes including performance and economic costs. We mainly introduce its electrical properties and storage performance. Electrical properties include: electromotive force, rated voltage, open circuit voltage, operating voltage, termination voltage, charging voltage, internal resistance, capacity, specific energy and specific power, storage performance and self-discharge, and life. Storage performance depends mainly on the self-discharge size of the battery.

Electromotive force

The electromotive force of a battery, also known as the battery standard voltage or the theoretical voltage, is the potential difference between the positive and negative poles when the battery is disconnected.

Rated voltage

Rated voltage (or nominal voltage) is the recognized standard voltage for the operation of the battery of the electrochemical system.

Open circuit voltage

The open circuit voltage of the battery is the battery voltage without load. The open circuit voltage is not equal to the electromotive force of the battery. It must pointed out that the electromotive force of the battery calculated from the thermodynamic function, and the open circuit voltage of the battery is actually measured.

Operating Voltage

Refers to the actual discharge voltage of a battery under a load, usually refers to a voltage range.

(5) Termination voltage

Refers to the voltage at the end of discharge, depending on the load and usage requirements.

Charging voltage

Refers to the voltage at which the external circuit DC voltage charges the battery. The general charging voltage is greater than the open circuit voltage of the battery, usually within a certain range.

Internal resistance

The internal resistance of the battery includes the resistance of the positive and negative plates, the resistance of the electrolyte, the resistance of the separator, and the resistance of the connector.

Positive and negative resistance

At present, the positive and negative plates of lead-acid batteries commonly used are paste-type, consisting of lead-bismuth alloy or lead-calcium alloy grids and active materials. Therefore, the plate resistance is also composed of the grid resistance and the active material resistance. The grid is in the inner layer of the active material, and does not undergo chemical changes during charge and discharge, so its resistance is the inherent resistance of the grid. The electrical resistance of the active material varies with the state of charge and discharge of the battery.

When the battery is discharged, the active material of the plate is converted to lead sulfate (PbSO4), and the larger the lead sulfate content, the greater the resistance. When the battery charged, lead sulfate reduced to lead (Pb), and the smaller the lead sulfate content, the smaller the resistance.

Electrolyte resistance

Electrical resistance varies depending on its concentration. Once a certain concentration select a specified concentration range, electrolyte resistance will vary with degree of charge and discharge. When battery charged, concentration of electrolyte increases while the active material of electrode plate reduced, and electrical resistance thereof decreases. When battery discharged, concentration of electrolyte decreases while active material of the electrode plate sulfated, and resistance thereof increases.

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