Some important concepts of power batteries

2019-03-29 09:49:28 0

Friends who are engaged in the new energy automobile industry believe that everyone will have a certain understanding of their core power battery, but when they really discuss related issues, they feel that they have a little understanding. Xiao Bian will interpret the related concepts, structure and working principle of the power battery in the most easy-to-understand way, so that everyone can have a deeper understanding of the power battery.

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1, several important concepts

(1), voltage (V)

[1] Open circuit voltage: refers to the voltage of the battery when no external circuit or external load is connected. The open circuit voltage has a certain relationship with the remaining energy of the battery, and the power display uses this principle.

[2] working voltage: refers to the potential difference between the positive and negative terminals of the battery when the battery is in working state, that is, the current flowing in the circuit, also known as the load voltage. When the battery is discharged, when the current flows through the inside of the battery, the resistance of the internal resistance must be overcome, so the operating voltage is always lower than the open circuit voltage.

[3] Discharge cut-off voltage: refers to the voltage that is discharged after the battery is fully charged, and is discharged when the battery is discharged (if it continues to discharge, it is over-discharged, which may damage the battery life and performance).

[4] Charging limit voltage: The voltage from constant current to constant voltage charging during charging.

2, battery capacity (Ah)

[1] Definition: Battery capacity refers to the amount of electricity that a battery can store. Capacity is an important indicator of the electrical performance of a battery. It is determined by the active material of the electrode.

[2] units: The capacity is expressed by C, and the unit is expressed by Ah (Ah) or mAh (mAh).

[3] Formula: C=It, ie battery capacity (Ah) = current (A) x discharge time (h).

[4]Example: A battery with a capacity of 10 amps can be discharged for 2 hours with 5 amps and 1 hour with 10 amps.

[5] Influencing factors: The actual capacity of the battery depends mainly on the following factors: the quantity and quality of the active substance, and the utilization rate of the active substance.

[6] Rated capacity: The battery capacity given by the manufacturer, measured under specified conditions.

[7] Usable capacity: The amount of electricity released from a fully charged battery under specified conditions.

[8] Theoretical capacity: Assuming that the active substance is fully utilized, the capacity that the battery can release.

3, battery energy (Wh)

[1] Definition: refers to the amount of energy stored in the battery, expressed by Wh

[2] Formula: Energy (Wh) = rated voltage (V) × operating current (A) × working time (h).

[3] Example: The energy of the 3.2V15Ah single cell is 48Wh, and the energy of the 3.2V100Ah battery pack is 320Wh.

Battery energy is an important indicator to measure the work done by the battery, and the capacity cannot determine how much work is done.

4. Energy density (Wh/Kg)

[1] Definition: refers to the energy released per unit volume or unit mass, usually expressed by volume energy density (Wh / L) or mass energy density (Wh / kg).

[2] Example: If a lithium battery weighs 325g, the rated voltage is 3.7V, and the capacity is 10Ah, the energy density is 113Wh/kg. The following table is the theoretical value. In practical applications, the housing in the battery structure needs to be considered. Various factors such as parts.

At present, the energy density of lithium batteries is 3 and 1.5 times that of nickel-cadmium and nickel-hydrogen batteries. The energy density is determined by the material density and structure.

5, power and power density

[1] Power refers to the energy output by the battery per unit time under a certain discharge system, and the unit is W or kW.

[2] Power density, also known as specific power, is the power output per unit mass or unit volume, in W/kg or W/L. Specific power is an important indicator to evaluate whether the battery and battery pack meet the acceleration and climbing ability of electric vehicles. More professional interpretation and latest information on the new energy vehicle industry, can focus on the electric Zhixin WeChat public number.

6, discharge rate (A)

[1] Definition: The discharge rate is the current value required to discharge its rated capacity (C) within a specified time, which is numerically equal to a multiple of the rated capacity of the battery.

[2] Example: Taking a 10Ah battery as an example, when discharging at 2A, the discharge rate is 0.2C, and when it is discharged at 20A, the discharge rate is 2C.

7, charging method

[1] CC/CV: CC is constant current, charging the battery with a fixed current; CV is constant voltage, charging the battery with a fixed voltage, and the charging current will gradually decrease with the battery full.

[2] Trickle charging: refers to charging the battery with a current less than 0.1C. Generally, when the battery is nearly full, it is used when charging. If the battery does not have strict charging time, it is recommended to use trickle charging.

[3] float charging: Charge the battery with constant voltage at any time to maintain a certain state of charge.

8. Charge and discharge depth (SOCDOD): A method for expressing the value of the battery retention capacity.

[1] state of charge state-of-ge (SOC): the percentage of the remaining capacity of the battery after discharge and the total charge capacity.

[2] Depth of depth depth ofdisge (DOD): A parameter indicating the state of discharge of the battery, equal to the percentage of the actual discharge capacity and the rated capacity.

[3] Deep discharge deepdisge: Indicates the extent to which the capacity of 50% or more of electricity is released.

[4] Example: The filling and discharging depth is expressed by percentage rate. For example, the capacity of the battery with a capacity of 10 Ah is 2Ah after discharge, which can be called 80% DOD; the capacity is 10Ah, and the capacity after charging is 8Ah, 80% SOC. Described as full, usually called 100% DOD.

9, internal resistance

[1] Definition: The internal resistance of the battery refers to the resistance that the current flows through the inside of the battery when the battery is working. The internal resistance is mainly affected by factors such as the material of the battery, the manufacturing process, and the structure of the battery.

[2] classification: battery internal resistance includes ohmic internal resistance and polarization internal resistance. The ohmic internal resistance is composed of electrode material, electrolyte, diaphragm resistance and contact resistance of various parts. Polarized internal resistance includes electrochemical polarization and concentration. Resistance caused by polarization.

[3] Influencing factors: The internal resistance of the battery is a very complicated and very important characteristic. The factors affecting the internal resistance are materials and structures.

[4] results: due to the existence of internal resistance, when the battery is discharged, the current through the internal resistance to generate heat, consume energy, the greater the current, the more energy, so the smaller the internal resistance, the better the performance of the battery, not only the battery The actual working voltage is high, and the energy consumed on the internal resistance is also small.

10, self-discharge rate (% / month)

[1] Definition: During the storage process, the capacity will gradually decrease, and the ratio of the reduced capacity to the battery capacity is called the self-discharge rate.

[2] Reason: Due to the instability of the electrode in the electrolyte, the two electrodes of the battery reacted chemically, the active material was consumed, the chemical energy converted to electrical energy was reduced, and the battery capacity was decreased.

[3] Influencing factors: Ambient temperature has a greater impact on it, too high temperature will accelerate the self-discharge of the battery

[4] indicates: the expression method and unit of battery capacity attenuation (self-discharge rate) are: %/month.

[5] Result: The self-discharge of the battery will directly reduce the capacity of the battery. The self-discharge rate directly affects the storage performance of the battery. The lower the self-discharge rate, the better the storage performance.

11, cycle life (times)

[1] Definition: A secondary battery undergoes a charge and discharge. It is called a cycle or a cycle. After repeated charge and discharge, the capacity of the battery will gradually decrease. Under certain discharge conditions, when the battery capacity drops to 80%, the battery is subjected to a cycle. The number of times is the cycle life.

[2] Influencing factors: incorrect use of batteries, battery materials, electrolyte composition and concentration, charge and discharge rate, depth of discharge (DOD%), temperature, manufacturing process, etc. have an impact on the cycle life of the battery.

12, memory effect

[1] Definition: The memory effect of a battery is the percentage of a battery that is not fully discharged and can be charged at the next charge.

[2] Reason: The material in the battery is crystallized. For example, in the nickel-cadmium battery, Cd continuously aggregates to form a large piece of metal cadmium, which reduces the activity of the negative electrode.

[3] Avoid: In order to eliminate the memory effect of the battery, it must be completely discharged before charging, and then recharged.

Lithium-ion batteries have no memory effect.

13, the discharge platform

Refers to the portion of the discharge curve where the voltage is substantially maintained. The higher, longer and smoother the discharge platform, the better the discharge performance of the battery.

14, battery consistency

The battery pack is composed of a plurality of unit cells connected in series and connected in parallel. The overall performance and longevity of the battery pack depends on one of the cells with poor performance, which requires high consistency in performance of each cell in the battery pack. In addition to the performance error of the individual cells and the quality of the raw materials, the most important reason is the manufacturing process, and the improvement of the process is very important to improve the quality of the battery.