I. Some important concepts
Lithium iron phosphate battery (LFP) and ternary lithium battery (NCM/NCA) are two mainstream lithium-ion battery technologies. The following are their main differences:
1. Chemical composition and working principle
Ternary lithium battery : Nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) alloy is used as the positive electrode material, and graphite is commonly used as the negative electrode. It stores and releases electrical energy through the migration of lithium ions between the positive and negative electrodes, contains highly active metal elements, and has a higher energy density。
Lithium iron phosphate battery : uses iron phosphate as the positive electrode material and graphite as the negative electrode. Its working principle is similar to that of ternary lithium battery. However, lithium iron phosphate battery has stronger chemical stability and performs steadily during charging and discharging.。
2. Energy density
Ternary lithium battery : The energy density is usually between 150-250Wh/kg, and some high-end models even exceed 300Wh/kg, which is suitable for application scenarios that require high energy output and long battery life.。
Lithium iron phosphate battery : The energy density is relatively low, usually 120-160Wh/kg. Although there have been improvements in recent years, more battery cells are often required in scenarios with high energy storage requirements.。
3. Security
Ternary lithium battery : Because it contains highly active materials such as nickel and cobalt, its chemical reaction is complex and can easily lead to thermal runaway under extreme conditions, which may cause short circuits or even fires.。
Lithium iron phosphate battery : Due to its excellent thermal stability, the probability of thermal runaway is extremely low even under high temperature or overcharge conditions, making it suitable for fields with strict safety requirements.。
4. Cycle life
Ternary lithium battery : cycle life is usually 1000-2000 times。
Lithium iron phosphate battery : can reach 2000-5000 times, which means that lithium iron phosphate battery has obvious advantages in applications with long-term use and low maintenance costs。
5. Cost-effectiveness
Ternary lithium battery : The production cost is relatively high because it contains precious metal materials with large price fluctuations, and the production process is relatively complex。
Lithium iron phosphate battery : lower cost, mainly due to the stable price of raw materials and simplified production process. Although its energy density is lower, from the perspective of economy, lithium iron phosphate battery is undoubtedly more advantageous。
6. Environmental impact
Ternary lithium battery : The impact on the environment cannot be ignored. The mining process of materials such as nickel and cobalt has a great impact on the ecological environment. In particular, the mining of cobalt is often accompanied by human rights issues.。
Lithium iron phosphate battery : relatively environmentally friendly, iron phosphate resources are abundant and the mining process has little impact on the environment, which is in line with the concept of sustainable development。
7. Application Scenarios
Ternary lithium battery : more suitable for electric cars, driverless cars and other applications that require high energy output and long battery life。
Lithium iron phosphate battery : suitable for electric buses, large energy storage systems, home energy storage and other fields that require high safety and long-term use。
project | Lithium Iron Phosphate (LFP) | NCM |
Specific capacity/(Wh*kg) | 160~200 | 200~300 |
Cycle life (times) | >3 000 | 1200~2000 |
High temperature resistance | 600~800℃ | 300℃ |
cost | good | better |
Low temperature -20℃ discharge rate | 60% | 70% |
Spontaneous combustion and explosion | no | yes |
In summary, ternary lithium batteries and lithium iron phosphate batteries each have their own advantages and disadvantages. The choice of which battery to use should be based on the specific application, budget, and the need for safety and service life.。
Energy storage can be divided into mechanical energy storage and chemical energy storage. Mechanical energy storage can be divided into pumped storage, compressed air storage, and flywheel storage; chemical energy storage (what we usually call batteries) can be divided into lead-acid batteries, nickel batteries, lithium batteries, flow batteries, and sodium-sulfur batteries
Lead-acid battery : a battery whose electrodes are mainly made of lead and its oxides, and whose electrolyte is sulfuric acid solution. When the lead-acid battery is discharged, the main component of the positive electrode is lead dioxide, and the main component of the negative electrode is lead; when it is charged, the main components of the positive and negative electrodes are lead sulfate. The advantages of lead-acid batteries are: safe sealing, venting system, simple maintenance, long service life, stable quality, and high reliability; the disadvantages are that the lead pollution is large and the energy density is low (that is, too heavy).
Nickel battery : Nickel-metal hydride battery is a good performance battery. The positive active material of nickel-metal hydride battery is Ni(OH)2 (called NiO electrode), the negative active material is metal hydride, also called hydrogen storage alloy (the electrode is called hydrogen storage electrode), and the electrolyte is 6mol/L potassium hydroxide solution. The advantages of nickel battery are: high energy density, fast charge and discharge speed, light weight, long life, no environmental pollution; the disadvantages are slight memory effect, more management problems, and easy formation of monomer battery separator melting.
Lithium battery : Lithium-ion battery is a type of battery that uses lithium metal or lithium alloy as the negative electrode material and uses non-aqueous electrolyte solution. Due to the very active chemical properties of lithium metal, the processing, storage and use of lithium metal have very high environmental requirements. With the development of science and technology, lithium-ion batteries have now become mainstream.
Its important advantages include: long service life, high storage energy density, light weight and strong adaptability; its disadvantages are poor safety, easy explosion, high cost and limited use conditions.
Liquid flow battery : Liquid flow energy storage battery is a type of device suitable for fixed large-scale energy storage (electricity storage). Compared with the currently commonly used lead-acid batteries, nickel-cadmium batteries and other secondary batteries, it has the advantages of independent design of power and energy storage capacity (energy storage medium is stored outside the battery), high efficiency, long life, deep discharge, and environmental friendliness. It is one of the preferred technologies for large-scale energy storage technology. The advantages of liquid flow batteries are: flexible layout, long cycle life, fast response, and no harmful emission; the disadvantage is that the energy density varies greatly.
Sodium-sulfur battery : Sodium-sulfur battery is a secondary battery with metallic sodium as the negative electrode, sulfur as the positive electrode, and a ceramic tube as the electrolyte membrane. Under a certain working temperature, sodium ions pass through the electrolyte membrane and undergo a reversible reaction with sulfur, resulting in the release and storage of energy. Advantages and disadvantages of sodium-ion batteries : specific energy up to 760Wh/kg, no self-discharge, discharge efficiency of almost 100%, and life span of 10 to 15 years; the disadvantage is that the high temperature of 350ºC melts sulfur and sodium.
Ternary lithium-ion battery : Ternary polymer lithium-ion battery refers to a lithium-ion battery that uses nickel cobalt manganese oxide (Li(NiCoMn)O2) as the positive electrode material. The ternary composite positive electrode material is made of nickel salt, cobalt salt and manganese salt. The ratio of nickel, cobalt and manganese can be adjusted according to actual needs. The battery with ternary material as the positive electrode is safer than cobalt oxide lithium-ion battery, but the voltage is too low. When used in mobile phones (the cut-off voltage of mobile phones is generally around 3.0V), there will be a clear feeling of insufficient capacity. The advantages of ternary lithium-ion batteries are: good cycle performance; the disadvantage is that their use is limited
Lithium iron phosphate : Lithium iron phosphate battery refers to a lithium-ion battery that uses lithium iron phosphate as the positive electrode material. The positive electrode materials of lithium-ion batteries are mainly lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, ternary materials, lithium iron phosphate, etc. Among them, lithium cobalt oxide is the positive electrode material used by most lithium-ion batteries. The advantages of lithium iron phosphate are: improved safety performance, improved life, good high temperature performance, large capacity, no memory effect, light weight, and environmental protection; the disadvantages are that it will cause micro short circuits, low energy density, high manufacturing costs, poor product consistency, and intellectual property issues.
The above content is the common classification of energy storage batteries. Of course, there are some other related knowledge about energy storage batteries, such as how to classify batteries and why energy storage batteries should be classified. Let’s take a brief look at it below.
1.What is a battery?
Batteries are devices that convert and store energy. They convert chemical energy or physical energy into electrical energy through reactions. Batteries can be divided into chemical batteries and physical batteries according to the different energy conversion methods.
A chemical battery or chemical power source is a device that converts chemical energy into electrical energy. It consists of two electrochemically active electrodes of different compositions, one positive and one negative, and a chemical substance that can provide medium conduction as an 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 batteries and secondary batteries?
The main difference is the active material. The active material of secondary batteries is reversible, while the active material of primary batteries is not. The self-discharge of primary batteries is much smaller than that of secondary batteries, but the internal resistance is much larger than that of secondary batteries, so the load capacity is lower. In addition, the mass capacity and volume capacity of primary batteries are greater than those of general rechargeable batteries.
3.What is the electrochemical principle of nickel-hydrogen batteries?
NiMH batteries use Ni oxide as the positive electrode, hydrogen storage metal as the negative electrode, and alkaline solution (mainly KOH) as the electrolyte. When charging NiMH batteries:
Positive electrode reaction: Ni(OH)2 + OH- → NiOOH + H2O–e-
Negative electrode reaction: M+H2O +e-→ MH+ OH-
When NiMH battery is discharged:
Positive electrode reaction: NiOOH + H2O+e- → Ni(OH)2 + OH-
Negative electrode 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. When charging,
Positive electrode reaction: LiCoO2 → Li1-xCoO2 + xLi+ + xe-
Negative electrode reaction: C + xLi+ + xe- → CLix
Overall 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?
Commonly used IEC standards for batteries: The standard for nickel-metal hydride batteries is IEC61951-2:2003; the lithium-ion battery industry generally follows UL or national standards.
Common national standards for batteries: The standards for nickel-hydrogen batteries are GB/T15100_1994, GB/T18288_2000; the standards for lithium batteries are GB/T10077_1998, YD/T998_1999, GB/T18287_2000.
In addition, the commonly used battery standards also include the Japanese Industrial Standard JIS C standards for batteries.
IEC is the International Electrotechnical Commission (IEC), a global standardization organization composed of electrotechnical committees from various countries. Its purpose is to promote standardization in the world's electrical and electronic fields. IEC standards are standards developed by the International Electrotechnical Commission.
6.What are the main structural components of nickel-metal hydride batteries?
The main components of nickel-hydrogen batteries are: positive electrode (nickel oxide), negative electrode (hydrogen storage alloy), electrolyte (mainly KOH), diaphragm paper, sealing ring, positive electrode cap, battery shell, etc.
7.What are the main structural components of lithium-ion batteries?
The main components of lithium-ion batteries are: upper and lower battery covers, positive electrode (active material is lithium cobalt oxide), diaphragm (a special composite membrane), negative electrode (active material is carbon), organic electrolyte, battery shell (divided into steel shell and aluminum shell), etc.
8.What is the internal resistance of a battery?
It refers to the resistance encountered by the current flowing through the battery when the battery is working. It consists of two parts: ohmic internal resistance and polarization internal resistance. A large internal resistance of the battery will lead to a lower discharge voltage and a shorter discharge time. The size of the internal resistance is mainly affected by factors such as the battery material, manufacturing process, and battery structure. It is an important parameter for measuring battery performance. Note: Generally, the internal resistance in the charged state is used as the standard. The internal resistance of the battery needs to be measured with a special internal resistance meter, and cannot be measured with the ohm range of a multimeter.
9.What is the nominal voltage?
The nominal voltage of a battery refers to the voltage displayed during normal operation. The nominal voltage of a secondary nickel-cadmium or nickel-metal hydride battery is 1.2V; the nominal voltage of a secondary lithium battery is 3.6V.
10.What is open circuit voltage?
The open circuit voltage refers to the potential difference between the positive and negative electrodes of the battery when the battery is not in operation, that is, when there is no current flowing through the circuit. The operating voltage, also known as the terminal voltage, refers to the potential difference between the positive and negative electrodes of the battery when the battery is in operation, that is, when there is current flowing through the circuit.
11.What is the capacity of a battery?
The capacity of a battery can be divided into rated capacity and actual capacity. The rated capacity of a battery refers to the minimum amount of electricity that should be discharged under certain discharge conditions, which is stipulated or guaranteed when the battery is designed and manufactured. The IEC standard stipulates that the amount of electricity discharged by nickel-cadmium and nickel-metal hydride batteries under 20℃±5℃ environment when they are charged at 0.1C for 16 hours and then discharged at 0.2C to 1.0V is the rated capacity of the battery, expressed as C5. For lithium-ion batteries, it is stipulated that the amount of electricity discharged when charged for 3 hours under normal temperature, constant current (1C)-constant voltage (4.2V) controlled charging conditions and then discharged at 0.2C to 2.75V is the rated capacity, while the actual capacity of a battery refers to the actual amount of electricity discharged by the battery under certain discharge conditions, which is mainly affected by the discharge rate and temperature (so strictly speaking, the battery capacity should indicate 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 a rechargeable battery is discharged with a large current (such as 1C or above), the battery reaches the terminal voltage before its capacity is fully discharged due to the "bottleneck effect" of the internal diffusion rate caused by the excessive current. It can continue to discharge with a small current such as 0.2C until it reaches 1.0V/cell (nickel-cadmium and nickel-metal hydride batteries) and 3.0V/cell (lithium battery). The capacity released is called the residual capacity.
13.What is a discharge platform?
The discharge platform of NiMH rechargeable battery usually refers to the voltage range in which the working voltage of the battery is relatively stable when the battery is discharged under a certain discharge system. Its value is related to the discharge current. The larger the current, the lower its value. The discharge platform of lithium-ion battery is generally the discharge time when the constant voltage is charged to 4.2V and the current is less than 0.01C, then the charging is stopped, and then it is left for 10 minutes, and discharged to 3.6V at any discharge current rate. It is an important criterion for measuring the quality of batteries.
Battery identification
14.What is the IEC standard for labeling rechargeable batteries?
According to IEC standards, the label of NiMH batteries consists of 5 parts.
01) Battery type: HF, HR stands for nickel-metal hydride battery
02) Battery size information: including the diameter and height of round batteries, the height, width and thickness of square batteries, the values are separated by slashes, unit: mm
03) Discharge characteristic symbol: L indicates that the appropriate discharge current rate is within 0.5C
M indicates that the suitable discharge current rate is within 0.5-3.5C
H means the suitable discharge current rate is within 3.5-7.0C
X means the battery can operate at a high rate discharge current of 7C-15C
04) High temperature battery symbol: represented by T
05) Battery connecting piece indication: CF represents no connecting piece, HH represents the connecting piece for battery pull-type series connection, and HB represents the connecting piece for battery strip parallel series connection.
For example: HF18/07/49 means a square nickel-metal hydride battery with a width of 18mm, a thickness of 7mm, and a height of 49mm.
KRMT33/62HH indicates nickel-cadmium battery, discharge rate between 0.5C-3.5, high temperature series single cell (without connector), diameter 33mm, height 62mm.
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According to the IEC61960 standard, the identification of secondary lithium batteries is as follows:
·
01) Battery identification consists of 3 letters followed by 5 numbers (cylindrical) or 6 numbers (square).
02) The first letter: indicates the negative electrode material of the battery. I—indicates lithium ions with built-in batteries; L—indicates lithium metal electrodes or lithium alloy electrodes.
03) The 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: Indicates the shape of the battery. R—indicates a cylindrical battery; L—indicates a square battery.
05) Numbers: Cylindrical batteries: The five numbers represent the diameter and height of the battery. The unit of diameter is millimeter, and the unit of height is one tenth of a millimeter. When either the diameter or height is greater than or equal to 100mm, a slash should be added between the two dimensions.
Square battery: The six numbers represent the thickness, width and height of the battery, in millimeters. If any of the three dimensions is greater than or equal to 100 mm, a slash should be added between the dimensions; if any of the three dimensions is less than 1 mm, add the letter "t" before the dimension, and the dimension unit is one tenth of a millimeter.
For example: ICR18650 represents a cylindrical secondary lithium-ion battery with a positive electrode material of cobalt, a diameter of about 18 mm and a height of about 65 mm.
ICR20/1050。
ICP083448 represents a square secondary lithium-ion battery whose positive electrode material is cobalt, with a thickness of about 8 mm, a width of about 34 mm, and a height of about 48 mm.
ICP08/34/150 represents a square secondary lithium-ion battery with cobalt as the positive electrode material, a thickness of about 8 mm, a width of about 34 mm, and a height of about 150 mm.
ICPt73448 represents a square secondary lithium-ion battery with cobalt as the positive electrode material. Its thickness is about 0.7mm, width is about 34mm, and height is about 48mm.
15.What are the packaging materials for batteries?
02) PVC film, trademark tube
03) Connecting piece: stainless steel sheet, pure nickel sheet, nickel-plated steel sheet
04) Lead-out sheet: Stainless steel sheet (easy to solder)
Pure nickel sheet (spot welded)
05) Plugs
06) Protection components such as temperature control switches, overcurrent protectors, and current limiting resistors
07) Cartons and boxes
08) Plastic shells
16.What is the purpose of battery packaging, assembly and design?
01) Beauty and brand
02) Battery voltage limitation. To obtain a higher voltage, multiple batteries need to be connected in series.
03) Protect the battery, prevent short circuit and extend the battery life
04) Size restrictions
05) Easy to transport
06) Design of special functions, such as waterproof, special appearance design, etc.
Battery performance and testing.
17.What are the main aspects of the performance of secondary batteries?
It mainly includes voltage, internal resistance, capacity, energy density, internal pressure, self-discharge rate, cycle life, sealing performance, safety performance, storage performance, appearance, etc. Others include overcharge, over-discharge, corrosion resistance, etc.
18.What are the reliability test 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 cycle test
10) Drop test
11) Vibration test
12) Capacity test
13) Internal resistance test
14) GMS test
15) High and low temperature impact test
16) Mechanical shock test
17) High temperature and high humidity test
19.What are the battery safety test items?
01) Short circuit test
02) Overcharge and over discharge test
03) Withstand voltage test
04) Impact test
05) Vibration test
06) Heating test
07) Fire test
09) Temperature cycling test
10) Trickle charge test
11) Free drop test
12) Low pressure test
13) Forced discharge test
15) Hot plate test
17) Thermal shock test
19) Acupuncture test
20) Extrusion test
21) Heavy object impact test
20.What are the common charging methods?
Charging method of NiMH battery:
01) Constant current charging: The charging current is a constant value during the entire charging process. This method is the most common;
02) Constant voltage charging: During the charging process, the two 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 at a constant current (CC). When the battery voltage rises to a certain value, the voltage remains unchanged (CV), and the current in the circuit drops to a very small value and eventually approaches 0.
How to charge lithium battery:
Constant current and constant voltage charging: The battery is first charged at a constant current (CC). When the battery voltage rises to a certain value, the voltage remains unchanged (CV), and the current in the circuit drops to a very small value and eventually tends to 0.
21.What is the standard charge and discharge of NiMH batteries?
The IEC international standard stipulates that the standard charge and discharge of nickel-metal hydride batteries is: first discharge the battery at 0.2C to 1.0V/piece, then charge it at 0.1C for 16 hours, leave it for 1 hour, and then 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 its effect on battery performance?
Pulse charging generally adopts the method of charge and discharge, that is, charge for 5 seconds and discharge for 1 second. In this way, most of the oxygen generated during the charging process will be reduced to electrolyte under the discharge pulse. Not only does it limit the gasification amount of the internal electrolyte, but also for those old batteries that have been severely polarized, after charging and discharging 5-10 times using this charging method, they will gradually recover or approach the original capacity.
23.What is trickle charging?
Trickle charging is used to compensate for the capacity loss caused by self-discharge of the battery after it is fully charged. Pulse current charging is generally used to achieve the above purpose.
24.What is charging efficiency?
Charging efficiency refers to the degree to which the electrical energy consumed by the battery during the charging process is converted into the chemical energy that the battery can store. 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 amount of electricity discharged to the terminal voltage under certain discharge conditions to the rated capacity. It is mainly affected by factors such as discharge rate, ambient temperature, and internal resistance. Generally speaking, 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 the battery?
The output power of a battery refers to its ability to output energy per unit time. It is calculated based on the discharge current I and discharge voltage, P=U*I, and the unit is watt.
The smaller the internal resistance of the battery, the higher the output power. The internal resistance of the battery should be smaller than the internal resistance of the electrical appliance, otherwise the power consumed by the battery itself will be greater than the power consumed by the electrical appliance, which is not economical and may damage the battery.
27.What is the self-discharge of secondary batteries? What are the self-discharge rates of different types of batteries?
Self-discharge is also known as charge retention capacity, which refers to the ability of a battery to retain the amount of electricity stored in it under certain environmental conditions when it is in an open circuit state. Generally speaking, self-discharge is mainly affected by manufacturing processes, materials, and storage conditions. Self-discharge is one of the main parameters for measuring battery performance. Generally speaking, the lower the battery storage temperature, the lower the self-discharge rate. However, it should also be noted that too low or too high a temperature may damage the battery and make it unusable.
After the battery is fully charged and left open for a period of time, a certain degree of self-discharge is normal. IEC standards stipulate that after a NiMH battery is fully charged and left open for 28 days at a temperature of 20°C ± 5°C and a humidity of (65 ± 20)%, the 0.2C discharge capacity reaches 60% of the initial capacity.
28.What is the 24-hour self-discharge test?
The self-discharge test of lithium battery is as follows: generally 24 hours of self-discharge is used to quickly test its charge retention ability. The battery is discharged to 3.0V at 0.2C, and charged to 4.2V at 1C with constant current and constant voltage, with a cut-off current of 10mA. After leaving it for 15 minutes, it is discharged to 3.0V at 1C to measure its discharge capacity C1. Then the battery is charged to 4.2V at 1C with constant current and constant voltage, with a cut-off current of 10mA. After leaving it for 24 hours, the 1C capacity C2 is measured. C2/C1*100% should be greater than 99%.
29.What is the internal resistance in charging state and what is the difference between the internal resistance in discharging state?
The internal resistance in the charged state refers to the internal resistance of the battery when it is 100% fully charged; the internal resistance in the discharged state refers to the internal resistance of the battery after it is fully discharged.
Generally speaking, the internal resistance in the discharge state is not very stable and is relatively large, while the internal resistance in the charge state is small and the resistance value is relatively stable. During the use of the battery, only the internal resistance in the charge state has practical significance. In the later stage of battery use, due to the depletion of the electrolyte and the decrease in the activity of the internal chemical substances, the internal resistance of the battery will increase to varying degrees.
30.What is static resistance? What is dynamic resistance?
The static internal resistance is the internal resistance of the battery during discharge, and the dynamic internal resistance is the internal resistance of the battery during charging.
31.Is it a standard overcharge resistance test?
The IEC standard overcharge test for NiMH batteries is as follows: discharge the battery at 0.2C to 1.0V/piece, and charge it continuously at 0.1C for 48 hours. The battery should not be deformed or leaking, and the time it takes to discharge from 0.2C to 1.0V after overcharging should be greater than 5 hours.
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