Basic Principles and Terminology of Batteries （1）

Basic Principles and Terminology of Batteries

1. What is a battery?

Batteries is a device for energy conversion and storage. It converts Chemical energy or physical energy into electrical energy through reaction. According to the different energy conversion of batteries, they can be divided into chemical batteries and physical batteries.

Chemical battery or chemical power supply is a device that converts Chemical energy into electrical energy. It consists of two kinds of electrochemical active electrodes with different components, which respectively form positive and negative electrodes. A chemical substance that can provide media conduction is used as electrolyte. When connected to an external carrier, it provides electrical energy by converting its internal Chemical energy.

A physical battery is a device that converts physical energy into electrical energy.

2. What are the differences between primary and secondary batteries?

The main difference is the difference in active substances. The active substances in secondary batteries are reversible, while the active substances in primary batteries are not reversible. The self discharge of a primary battery is much smaller than that of a secondary battery, but the internal resistance is much greater than that of a secondary battery, resulting in a lower load capacity. In addition, the mass and volume specific capacity of a primary battery are greater than those of a general rechargeable battery.

3. What is the electrochemical principle of Nickel–metal hydride battery?

Nickel–metal hydride battery uses Ni oxide as positive electrode, hydrogen storage metal as negative electrode, and alkaline solution (mainly KOH) as electrolyte. When charging Nickel–metal hydride battery:

Positive electrode reaction: Ni (OH) 2+OH - → NiOOH+H2O e-
Negative reaction: M+H2O+e - → MH+OH-
When the Nickel–metal hydride battery is discharged:
Positive electrode reaction: NiOOH+H2O+e - → Ni (OH) 2+OH-
Negative reaction: MH+OH - → M+H2O+e-

4. What is the electrochemical principle of lithium-ion batteries?

The main component of the positive electrode of lithium-ion batteries is LiCoO2, and the negative electrode is mainly C. During charging,
Positive electrode reaction: LiCoO2 → Li1-xCoO2+xLi++xe-
Negative reaction: C+xLi++xe - → CLix
Total battery reaction: LiCoO2+C → Li1-xCoO2+CLix
The reverse reaction of the above reaction occurs during discharge.

5.What are the commonly used standards for batteries?

Common battery IEC standard: Nickel–metal hydride battery standard is IEC61951-2:2003; The lithium-ion battery industry generally follows UL or national standards.
Common national standard of battery: the standard of Nickel–metal hydride battery is GB/T15100_ 1994, GB/T18288_ 2000; The standard for lithium batteries is GB/T10077_ 1998, YD/T998_ 1999, GB/T18287_ 2000.
In addition, the commonly used standards for batteries also include the Japanese industrial standard JIS C for batteries.
IEC, the International Electrotechnical Commission, is a worldwide standardization organization composed of national electrotechnical commissions. Its purpose is to promote the standardization of the world's electrotechnical and electronic fields. IEC standards are formulated by the International Electrotechnical Commission.

6. What are the main structural components of Nickel–metal hydride battery?

The main components of Nickel–metal hydride battery are: positive plate (nickel oxide), negative plate (hydrogen storage alloy), electrolyte (mainly KOH), diaphragm paper, sealing ring, positive cap, battery shell, etc.

7. What are the main structural components of lithium-ion batteries?

The main components of the lithium-ion battery are: the upper and lower covers of the battery, the positive plate (the active material is Lithium oxide cobalt oxide), the diaphragm (a special composite film), the negative plate (the active material is carbon), the organic electrolyte, the battery shell (divided into steel shell and aluminum shell), etc.

8. What is battery internal resistance?

It refers to the resistance experienced by the current flowing through the interior of the battery during operation. It consists of two parts: ohmic internal resistance and polarization internal resistance. A large internal resistance of the battery can lead to a decrease in the working voltage of the battery discharge and a shortened discharge time. The size of internal resistance is mainly influenced by factors such as battery material, manufacturing process, and battery structure. It is an important parameter for measuring battery performance. Note: The standard is generally based on the internal resistance in charge state. The internal resistance of the battery needs to be measured using a dedicated internal resistance meter, rather than using a multimeter's ohm range for measurement.

9. What is the nominal voltage?

The nominal voltage of the battery refers to the voltage displayed during normal operation. The nominal voltage of the secondary nickel cadmium Nickel–metal hydride battery is 1.2V; The nominal voltage of the secondary lithium battery is 3.6V.

10. What is open circuit voltage?

Open circuit voltage refers to the potential difference between the positive and negative poles of a battery when there is no current flowing through the circuit in a non working state. Working voltage, also known as terminal voltage, refers to the potential difference between the positive and negative poles of a battery when there is current in the circuit during its working state.

11. What is the capacity of a battery?

The battery capacity can be divided into Nameplate capacity and actual capacity. The Nameplate capacity of the battery refers to the provision or guarantee that the battery should discharge the minimum amount of electricity under certain discharge conditions when designing and manufacturing the battery. The IEC standard stipulates that the Nameplate capacity of the Ni Cd and Nickel–metal hydride battery is the amount of electricity discharged when they are charged at 0.1C for 16 hours and discharged at 0.2C to 1.0V under the environment of 20 ℃ ± 5 ℃, expressed in C5. For lithium-ion batteries, it is required to charge for 3 h under the charging conditions of normal temperature, constant current (1C) - constant voltage (4.2V) control, and then discharge at 0.2C to 2.75V as its Nameplate capacity. The actual capacity of the battery refers to the actual capacity of the battery under certain discharge conditions, which is mainly affected by the discharge rate and temperature (so strictly speaking, the battery capacity should specify the charging and discharging conditions). The units of battery capacity are Ah, mAh (1Ah=1000mAh)

12. What is the residual discharge capacity of a battery?

When the rechargeable battery is discharged with a large current (such as 1C or above), due to the "bottleneck effect" of the internal diffusion rate caused by excessive current, the battery has reached the terminal voltage when the capacity cannot be fully discharged, and can continue to discharge with a small current (such as 0.2C) until 1.0V/piece (nickel cadmium and Nickel–metal hydride battery) and 3.0V/piece (lithium batteries) are called residual capacity.

13. What is a discharge platform?

The discharge platform of nickel hydrogen rechargeable batteries usually refers to the voltage range within which the working voltage of the battery is relatively stable when discharged under a certain discharge system. Its value is related to the discharge current, and the larger the current, the lower its value. The discharge platform of lithium-ion batteries generally stops charging when the voltage is 4.2V and the current is less than 0.01C at a constant voltage, and then leaves it for 10 minutes to discharge to 3.6V at any rate of discharge current. It is an important standard for measuring the quality of batteries.

Battery identification

14. What is the identification method for rechargeable batteries according to IEC regulations?

According to IEC standard, the identification of Nickel–metal hydride battery consists of five parts.
01) Battery type: HF and HR represent Nickel–metal hydride battery
02) Battery size information: including the diameter and height of circular batteries, the height, width, thickness, and numerical values of square batteries separated by slashes, unit: mm
03) Discharge characteristic symbol: L represents an appropriate discharge current rate within 0.5C
M represents an appropriate discharge current rate within 0.5-3.5C
H represents an appropriate discharge current rate within 3.5-7.0C
X indicates that the battery can operate at a high discharge current of 7C-15C
04) High temperature battery symbol: represented by T
05) Battery connection piece representation: CF represents no connection piece, HH represents the connection piece used for battery pull series connection piece, and HB represents the connection piece used for battery strip parallel series connection.
For example, HF18/07/49 represents a square Nickel–metal hydride battery with a width of 18mm, a thickness of 7mm, and a height of 49mm,
KRMT33/62HH represents a Nickel–cadmium battery with a discharge rate between 0.5C-3.5. High temperature series single battery (without connector) has a diameter of 33mm and a height of 62mm.

According to the IEC61960 standard, the identification of secondary lithium batteries is as follows:
01) Battery identification composition: 3 letters followed by 5 numbers (cylindrical) or 6 numbers (square).
02) First letter: Indicates the negative electrode material of the battery. I - represents lithium ion with built-in battery; L - represents a lithium metal electrode or lithium alloy electrode.
03) Second letter: Indicates the positive electrode material of the battery. C - Cobalt based electrode; N - Nickel based electrode; M - manganese based electrode; V - Vanadium based electrode.
04) The third letter: represents the shape of the battery. R - represents cylindrical battery; L - represents a square battery.
05) Number: Cylindrical battery: 5 numbers represent the diameter and height of the battery, respectively. The unit of diameter is millimeters, and the unit of height is one tenth of a millimeter. When the diameter or height of any dimension is greater than or equal to 100mm, a diagonal line should be added between the two dimensions.
Square battery: 6 numbers represent the thickness, width, and height of the battery, in millimeters. When any of the three dimensions is greater than or equal to 100mm, a diagonal line should be added between the dimensions; If any of the three dimensions is less than 1mm, add the letter "t" before this dimension, which is measured in tenths of a millimeter.
For example, 

ICR18650 represents a cylindrical secondary lithium-ion battery, with a positive electrode material of cobalt, a diameter of approximately 18mm, and a height of approximately 65mm.
ICR20/1050.
ICP083448 represents a square secondary lithium-ion battery, with a positive electrode material of cobalt, a thickness of approximately 8mm, a width of approximately 34mm, and a height of approximately 48mm.
ICP08/34/150 represents a square secondary lithium-ion battery, with a positive electrode material of cobalt, a thickness of approximately 8mm, a width of approximately 34mm, and a height of approximately 150mm

15. What are the packaging materials for batteries?

01) Non drying meson (paper) such as fiber paper and Double-sided tape
02) PVC film and trademark tube
03) Connecting piece: stainless steel sheet, pure nickel sheet, nickel plated steel sheet
04) Lead out piece: stainless steel piece (easy to solder)   Pure nickel sheet (spot welded firmly)
05) Plug type
06) Protection components such as temperature control switches, overcurrent protectors, and current limiting resistors
07) Cartons, Cartons
08) Plastic shells

16. What is the purpose of battery packaging, combination, and design?

01) Aesthetics and brand
02) Limitation of battery voltage: To obtain a higher voltage, multiple batteries need to be connected in series
03) Protect the battery to prevent short circuits and extend its service life
04) Dimensional limitations
05) Easy to transport
06) Design for special functions, such as waterproofing, special exterior design, etc.

Battery performance and testing

17. What are the main aspects of the performance of secondary batteries commonly referred to?

Mainly including voltage, internal resistance, capacity, energy density, internal pressure, self discharge rate, cycle life, sealing performance, safety performance, storage performance, appearance, etc. Other factors include overcharging, overdischarge, corrosion resistance, etc.

18. What are the reliability testing items for batteries?

01) Cycle life
02) Discharge characteristics at different rates
03) Discharge characteristics at different temperatures
04) Charging characteristics
05) Self discharge characteristics
06) Storage characteristics
07) Over discharge characteristics
08) Internal resistance characteristics at different temperatures
09) Temperature cycling test
10) Drop test
11) Vibration testing
12) Capacity testing
13) Internal resistance test
14) GMS testing
15) High and low temperature impact test
16) Mechanical impact testing
17) High temperature and humidity testing

19. What are the safety testing items for batteries?

01) Short-circuit test
02) Overcharge and discharge tests
03) Voltage withstand test
04) Impact test
05) Vibration test
06) Heating test
07) Fire test
09) Temperature cycling test
10) Trickle charging test
11) Free fall test
12) Low-pressure area test
13) Forced discharge test
15) Electric heating plate test
17) Thermal shock test
19) Acupuncture test
20) Squeeze test
21) Heavy object impact test

20. What are the common charging methods?

Charging mode of Nickel–metal hydride battery:
01) Constant current charging: The charging current during the entire charging process is a certain value, which is the most common method;
02) Constant voltage charging: During the charging process, both ends of the charging power supply maintain a constant value, and the current in the circuit gradually decreases as the battery voltage increases;
03) Constant current and constant voltage charging: The battery is first charged with constant current (CC). When the battery voltage rises to a certain value, the voltage remains unchanged (CV), and the current in the circuit decreases to a very small value, eventually tending to zero.
Charging method for lithium batteries:
Constant current and constant voltage charging: The battery is first charged with constant current (CC). When the battery voltage rises to a certain value, the voltage remains unchanged (CV), and the current in the circuit decreases to a very small value, eventually tending to zero.

21. What is the standard charge and discharge of Nickel–metal hydride battery?

IEC international standards stipulate that the standard charge and discharge of Nickel–metal hydride battery is: first discharge the battery at 0.2C to 1.0V/piece, then charge it at 0.1C for 16 hours, after being put aside for 1 hour, discharge it at 0.2C to 1.0V/piece, which is the standard charge and discharge of the battery.

22. What is pulse charging? What is the impact on battery performance?

Pulse charging generally adopts the method of charging and discharging, that is, charging for 5 seconds, then discharging for 1 second. This way, most of the oxygen generated during the charging process is reduced to electrolyte under the discharge pulse. Not only does it limit the gasification amount of the internal electrolyte, but for old batteries that have already been heavily polarized, after using this charging method for 5-10 times of charging and discharging, they will gradually recover or approach their original capacity.

23. What is Trickle charging?

Trickle charging is used to compensate for the capacity loss caused by the self discharge of the battery after it is fully charged. Pulse current charging is generally used to achieve the above objectives.

24. What is charging efficiency?

Charging efficiency refers to the measurement of the degree to which the electric energy consumed by the battery in the charging process is converted into the Chemical energy stored by the battery. It is mainly affected by the battery process and the working environment temperature of the battery. Generally, the higher the ambient temperature, the lower the charging efficiency.

25. What is discharge efficiency?

Discharge efficiency refers to the ratio of the actual electricity discharged to the terminal voltage under certain discharge conditions to the Nameplate capacity, which is mainly affected by the discharge rate, ambient temperature, internal resistance and other factors. Generally, the higher the discharge rate, the lower the discharge efficiency. The lower the temperature, the lower the discharge efficiency.

26. What is the output power of a battery?

The output power of a battery refers to the ability to output energy per unit time. It is calculated based on the discharge current I and discharge voltage, P=U * I, in watts.

The smaller the internal resistance of the battery, the higher the output power. The internal resistance of the battery should be less than the internal resistance of the electrical appliance, otherwise the power consumed by the battery itself will also be greater than the power consumed by the electrical appliance. This is uneconomical and may damage the battery.

27. What is self discharge of secondary batteries? What is the self discharge rate of different types of batteries?

Self discharge, also known as charge retention capacity, refers to the ability of a battery to maintain its stored energy under certain environmental conditions in an open circuit state. Generally speaking, self-discharge is mainly affected by manufacturing process, materials and storage conditions. Self discharge is one of the main parameters for measuring battery performance. Generally speaking, the lower the storage temperature of a battery, the lower its self-discharge rate. However, it should also be noted that low or high temperatures may cause damage to the battery and render it unusable.

After the battery is fully charged and left open for a period of time, a certain degree of self discharge is a normal phenomenon. IEC standard stipulates that after fully charged, the Nickel–metal hydride battery shall be kept open for 28 days at a temperature of 20 ℃± 5 ℃ and a humidity of (65 ± 20)%, and the 0.2C discharge capacity shall reach 60% of the initial capacity.

28. What is a 24-hour self discharge test?

The self discharge test of lithium batteries is generally conducted by using 24-hour self discharge to quickly test their charge retention ability. The battery is discharged at 0.2C to 3.0V, charged at constant current and constant voltage 1C to 4.2V, with a cut-off current of 10mA. After 15 minutes of storage, the discharge capacity C1 is measured at 1C to 3.0V, and then the battery is charged at constant current and constant voltage 1C to 4.2V, with a cut-off current of 10mA. After 24 hours of storage, the 1C capacity C2 is measured, and C2/C1 * 100% should be greater than 99%.

29. What is the difference between charging state internal resistance and discharging state internal resistance?

Charging state internal resistance refers to the internal resistance of a battery when fully charged; Discharge state internal resistance refers to the internal resistance of a battery after full discharge.

Generally speaking, the internal resistance in the discharge state is unstable and relatively large, while the internal resistance in the charging state is small and the resistance value is relatively stable. During the use of batteries, only the charge state internal resistance has practical significance. In the later stages of battery use, due to the depletion of electrolyte and the decrease in internal chemical activity, the internal resistance of the battery will increase to varying degrees.

30. What is a static resistor? What is dynamic resistance?

Static internal resistance refers to the internal resistance of the battery during discharge, and dynamic internal resistance refers to the internal resistance of the battery during charging.

31. Is it a standard overcharging test?

IEC stipulates that the standard overcharge resistance test of Nickel–metal hydride battery is: discharge the battery at 0.2C to 1.0V/piece, and charge it continuously at 0.1C for 48 hours. The battery shall be free of deformation and leakage, and the time of discharging from 0.2C to 1.0V after overcharging shall be more than 5 hours.

32. What is the IEC standard cycle life test?

IEC stipulates that the standard cycle life test of Nickel–metal hydride battery is:
After discharging the battery at 0.2C to 1.0V/cell
01) Charge at 0.1C for 16 hours, then discharge at 0.2C for 2 hours and 30 minutes (one cycle)
02) Charge at 0.25C for 3 hours and 10 minutes, discharge at 0.25C for 2 hours and 20 minutes (2-48 cycles)
03) Charge at 0.25C for 3 hours and 10 minutes, and discharge at 0.25C to 1.0V (cycle 49)
04) Charge at 0.1C for 16 hours, let it stand for 1 hour, discharge at 0.2C to 1.0V (50th cycle). For Nickel–metal hydride battery, after repeating 1-4 for 400 cycles, its 0.2C discharge time should be more than 3 hours; Repeat 1-4 for a total of 500 cycles for the Nickel–cadmium battery, and the 0.2C discharge time should be more than 3 hours.

33. What is the internal pressure of a battery?

The internal pressure of a battery refers to the gas generated during the charging and discharging process of the sealed battery, which is mainly affected by factors such as battery material, manufacturing process, and battery structure. The main reason for its occurrence is due to the accumulation of water and gas generated by the decomposition of organic solutions inside the battery. Generally, the internal pressure of the battery is maintained at a normal level. In the case of overcharging or discharging, the internal pressure of the battery may increase:

For example, overcharging, positive electrode: 4OH -4e → 2H2O+O2 ↑; ①
The generated oxygen reacts with the hydrogen gas precipitated on the negative electrode to generate water 2H2+O2 → 2H2O ②
If the speed of reaction ② is lower than that of reaction ①, the generated oxygen will not be consumed in time, which will cause an increase in the internal pressure of the battery.

34. What is the standard charge retention test?

IEC stipulates that the standard charge retention test of Nickel–metal hydride battery is:
The battery is discharged at 0.2C to 1.0V, charged at 0.1C for 16 hours, stored at 20 ℃± 5 ℃ and 65% ± 20% humidity for 28 days, and then discharged at 0.2C to 1.0V, while the Nickel–metal hydride battery should be more than 3 hours.
According to national standards, the standard charge retention test for lithium batteries is as follows: (IEC has no relevant standards) The battery is discharged at 0.2C to 3.0/cell, then charged at 1C constant current and voltage to 4.2V, with a cut-off current of 10mA. After 28 days of storage at a temperature of 20 ℃± 5 ℃, it is discharged at 0.2C to 2.75V, and the discharge capacity is calculated. Compared with the nominal capacity of the battery, it should not be less than 85% of the initial capacity.

35. What is a short circuit experiment?

Connect a fully charged battery in an explosion-proof box with an internal resistance ≤ 100m Ω wire to short-circuit the positive and negative poles, and the battery should not explode or catch fire.

36. What is a high temperature and humidity test?

The high temperature and high humidity test of Nickel–metal hydride battery is:
After the battery is fully charged, store it under constant temperature and humidity conditions for several days, and observe whether there is any leakage during the storage process.
The high temperature and humidity test for lithium batteries is: (National Standard)
Charge the battery 1C at a constant current and voltage of 4.2V, with a cut-off current of 10mA, and then place it in a constant temperature and humidity box at (40 ± 2) ℃ with a relative humidity of 90% -95% for 48 hours. Remove the battery and let it stand for 2 hours at (20 ± 5) ℃. Observe the appearance of the battery and there should be no abnormalities. Then discharge the battery at a constant current of 1C to 2.75V. Then, perform 1C charging and 1C discharging cycles at (20 ± 5) ℃ until the discharge capacity is not less than 85% of the initial capacity, But the number of cycles should not exceed 3 times.

37. What is a temperature rise experiment?

After fully charging the battery, place it in an oven and heat it up from room temperature at a rate of 5 ℃/min. When the oven temperature reaches 130 ℃, maintain it for 30 minutes. The battery should not explode or catch fire.

38. What is a Temperature cycling experiment?

The Temperature cycling experiment consists of 27 cycles, and each cycle consists of the following steps:
01) Change the battery from room temperature to 1 hour at 66 ± 3 ℃ and 15 ± 5%,
02) Change to 1 hour of storage at a temperature of 33 ± 3 ℃ and a humidity of 90 ± 5 ℃,
03) Change the condition to -40 ± 3 ℃ and let it stand for 1 hour
04) Leave the battery at 25 ℃ for 0.5 hour
This 4 step process completes a cycle. After 27 cycles of experiments, the battery should have no leakage, alkali crawling, rust, or other abnormal conditions.

39. What is a drop test?

After fully charging the battery or battery pack, it is dropped three times from a height of 1m onto concrete (or cement) ground to obtain a random direction impact.

40. What is vibration experiment?

The vibration test method of Nickel–metal hydride battery is:
After discharging the battery at 0.2C to 1.0V, charge it at 0.1C for 16 hours, and let it stand for 24 hours before vibrating according to the following conditions:
Amplitude: 0.8mm
Shake the battery between 10HZ-55HZ, increasing or decreasing at a vibration rate of 1HZ per minute.
The voltage change of the battery should be within ± 0.02V, and the internal resistance change should be within ± 5m Ω. (Vibration time is within 90 minutes)
The vibration experimental method for lithium batteries is:
After discharging the battery at 0.2C to 3.0V, charge it at 1C constant current and voltage to 4.2V, with a cut-off current of 10mA. After 24 hours of storage, vibrate according to the following conditions:
Conduct vibration experiments with a vibration frequency ranging from 10 Hz to 60 Hz and then to 10 Hz within 5 minutes, with an amplitude of 0.06 inches. The battery vibrates in the three axis direction, with each axis vibrating for half an hour.
The voltage change of the battery should be within ± 0.02V, and the internal resistance change should be within ± 5m Ω.

41. What is an impact experiment?

After the battery is fully charged, place a hard rod horizontally on the battery and use a 20 pound weight to fall from a certain height to hit the hard rod. The battery should not explode or catch fire.

42. What is a penetration experiment?

After the battery is fully charged, use a nail with a certain diameter to pass through the center of the battery and leave the nail inside the battery. The battery should not explode or catch fire.

43. What is a fire experiment?

Place the fully charged battery on a heating device with a special protective cover for burning, without any debris penetrating the protective cover.