Why does the tower base station use a ladder LiFePO4 battery

With energy shortages and environmental pollution issues becoming increasingly prominent, electric vehicles have received widespread attention for their energy saving and environmental protection advantages. When the capacity of the power battery used in electric vehicles falls to the extent that it does not meet the requirements for the range of electric vehicles, it is necessary to decommission the power batteries. As the electric vehicle market becomes more prosperous, the problem of the "outlet" of retired power batteries is becoming increasingly apparent. The capacity of the electric vehicle's power battery has declined to 80%, and it has been retired due to insufficient battery life. However, it can still be used for base station power backup after a step utilization process. The vehicle power battery pack uses the 48V backup power supply for communication as the basic module. The electric vehicle power battery is connected in series and connected through multiple sets of 48V modules to form a vehicle power battery module for powering the car. Can be directly applied in the field of communication.

BASIC CHARACTERISTICS OF LADDER LIFEPO4 BATTERY

  1. Battery capacity rate characteristics

As the discharge current increases, the discharge capacity of the battery will decrease. When the discharge rate is less than 0.33C10, the discharge capacity of the lithium-ion battery is little affected by the discharge rate, and the difference in discharge capacity is not large. The capacity can be released 100%.

  1. Temperature characteristics of battery capacity

When the ambient temperature is above 0 ° C, the battery capacity decays slowly, and when the ambient temperature is below 0 ° C, the battery capacity decays faster, and the internal resistance of the battery increases sharply as the temperature decreases.

  1. Comparison of Ladder LiFePO4 Battery with Traditional Lead Acid
  2. High temperature resistance: The stable operating temperature range of lead-acid battery is 25 ~ 28 ℃. The temperature rise will damage the battery and reduce the battery life.
  3. High energy density: The weight specific energy of LiFePO4 battery products can exceed 130Wh / kg (0.2C, 25 ° C), the volume specific energy is 210Wh / L; the weight specific energy of lead-acid battery products is 32 ~ 37Wh / kg (0.2 C, 25 ℃), volume specific energy is 70Wh / L.
  4. High-current charge and discharge performance: The LiFePO4 battery can be charged and discharged quickly at a large current of 2C, and the starting current can reach more than 5C. Lead-acid batteries do not have this performance now. So the LiFePO4 battery has a short charging time.
  5. Environmental protection: LiFePO4 battery does not contain any heavy metals and rare metals (nickel metal hydride batteries need rare metals) and is non-toxic (SGS certification passed); a large amount of lead exists in lead-acid batteries. Improper will still cause enough pollution to the environment.

The comparison between lead-acid batteries and stepped LiFePO4 batteries is shown in Table 1.

Battery performance index

Lead-Acid

Ladder LiFePO4 battery

Cycle life (times)

200

1200~2000

Mass specific energy (Wh/kg)

30~45

60~110

Volume specific energy (Wh/L)

70

125~250

Mass specific power (W/kg)

200~300

4000

Volume specific power (W/L)

 

10000

Self-discharge rate

High

Low

range of working temperature (℃)

25~28

-20~+55

Operating voltage range (V)

1.75~2.35

2.5~3.65

Nominal cell voltage (V)

2

3.2

Memory effect

Yes

No

 

  1. The use of cascade power lithium batteries has a long service life and a large number of cycles. After cascade use, theoretically, it can still have 6 years of actual life and 400~2,000 actual cycles, which is 3~6 years compared with the traditional lead-acid battery The actual number of cycles of 200 times has been greatly improved.
  2. High temperature resistance, lithium battery meets the use of extreme working conditions below 45 ° C, and the current upper limit of lead-acid batteries commonly used in communication base stations is only 35 ° C.
  3. Good discharge characteristics, high capacity utilization when high current discharge.
  4. High charge-discharge conversion efficiency, the energy conversion efficiency of the cascade battery is 10% -15% higher than that of the lead-acid battery.
  5. Small footprint, light weight, low transportation costs, the weight and volume of the step battery is 1/2 or 2/3 of the lead-acid battery of the same capacity.

Technical solution for the application of ladder LiFePO4 battery (Table 2)

Technical solutions

specific contents

Supply side

Processing side

Processing cost

Cell-level reorganization plan

Disassembling the cascade battery into the cell level, sorting, reorganizing, and processing into a battery product

Battery companies

Battery companies

High

Module-level reorganization plan

Disassembling cascaded batteries into module levels, sorting, reorganizing, and processing into battery products

Battery and automotive companies

Foundry companies

Medium

PACK application scheme

Measure and divide the entire retired battery pack and apply it to the base station

Automotive companies

Foundry companies

Low

 

  1. Centralized disassembly of retired power batteries, centralized screening of cells, and reassembly into standard modules are conducive to centralized screening and maintenance of retired cells to ensure quality; the source of retired cells is not limited to the guaranteed number of specific electric vehicle projects; The final battery module can be standardized to ensure compatibility.
  2. The direct transformation on the basis of retired power batteries is conducive to the simple modularization of the battery pack's step utilization, which has advantages in capacity, simple and easy production methods, low labor costs, but high land requirements.
  3. Ladder battery process: Screen battery cells, test voltage, battery cell assembly, internal connection lines, BMS, chassis or rack.

BASIC STRUCTURE OF LADDER LIFEPO4 BATTERY

The LiFePO4 battery is composed of a positive electrode plate and a negative electrode plate (the positive electrode active material is LiFePO4 and the negative electrode active material is graphite), a separator, an electrolyte, a tab, and an aluminum plastic film shell. The positive and negative plates are the areas for electrochemical reactions. The separator and electrolyte provide a Li + transmission channel. After the process of chemical conversion and other processes, a dense SEI film (also called a solid electrolyte interface film) will be formed on the surface of the battery plate. To the role of the pilot current. The positive electrode active material is LiFePO4, which has an olivine structure.

LiFePO4 is mixed with a conductive agent and a binder in a certain ratio, and is coated on an aluminum foil to form a positive electrode. The negative electrode active material is usually a graphite material and is attached to a copper foil through a binder. Positive and negative electrodes are separated by a polyethylene separator (or a polypropylene and polyethylene composite separator) to prevent battery short-circuiting. The separator is a thin film with a porous structure. During the charge and discharge process, Li + can pass through its pores, while electrons e- cannot pass through. The electrolyte of the battery is an organic solvent of lithium hexafluorophosphate.

WORKING PRINCIPLE OF LADDER LIFEPO4 BATTERY

When the battery is charged, Li + migrates from the LiFePO4 material to the crystal surface, and is released from the positive plate material. Under the action of the electric field force, it enters the electrolyte, passes through the separator, and then migrates to the surface of the negative graphite crystal through the electrolyte. Then it is embedded in the anode layered graphite material. At the same time, electrons flow through the aluminum foil of the positive electrode, through the tab, battery pole, load, negative pole, and negative electrode to the copper foil electrode of the negative electrode, and then flow to the graphite negative electrode through the conductor to balance the charge.

When the battery is discharged, Li + is de-embedded from the layered graphite crystal, enters the electrolyte, passes through the separator, migrates to the surface of the LiFePO4 crystal through the electrolyte, and then re-embedded in the LiFePO4 material. At the same time, electrons flow through the conductor to the copper foil electrode of the negative electrode, flow through the tab, the battery negative pole, the load, the positive pole, and the positive pole electrode to the aluminum foil electrode of the battery, and then flow through the conductor to the LiFePO4 positive electrode. Equilibrium the charge.

MANAGEMENT SYSTEM OF LADDER LIFEPO4 BATTERY

The battery management system is mainly used to manage the charging and discharging processes of the battery, to improve the battery life, and to provide users with the general information of the circuit system.

The battery management system BMS is composed of monitoring, protection circuits, electrical, communication interfaces, and thermal management devices. It is a core component of battery protection and management. It must not only ensure the safe and reliable use of the battery, but also give full play to the performance and extension of the battery. Service life, as a backup energy source for communication, the management system plays an important bridge role between the switching power supply and the battery. The requirements for the battery management system must conform to the requirements of the communication power supply system, so the safety management mode of the battery management system is very important to the safety of the battery. The battery management system mainly includes a data acquisition unit, a calculation and control unit, an equalization unit, a control execution unit, and a communication unit.

PRACTICAL APPLICATION OF LIFEPO4 BATTERY PACKS IN TOWER BASE STATIONS

According to the characteristics of the lithium battery pack, when the base station DC switching power supply application is set, it is only necessary to adjust the floating charging voltage and the average charging voltage to the charging voltage required by the lithium battery pack. (At the same time, it must be within the DC power supply voltage range of the communication equipment. ) Because the lithium battery pack is in a long-term charging state, the battery performance will not change due to its own BMS protection function.

For example, a base station backup battery pack uses a 48V 300Ah LiFePO4 battery pack. Each battery pack consists of 16 pieces 3.2V 100Ah single cells connected in series, of which 300Ah batteries are composed of 3 pieces 100Ah battery packs in parallel. Yes, each battery pack has a BMS control system.

After testing with a smart battery pack discharge meter, it is incorporated into the DC power supply system online. At this time, the charging voltage of the switching power supply is set to 56.8V, and the charging current is limited to 30A per piece.

LADDER LIFEPO4 BATTERY CONFIGURATION REQUIREMENTS

  1. Cascade battery modules can be divided into 15, 25, 30, 50, 100, 130, 150, 200Ah and other capacity series according to their nominal capacity. The nominal capacity should be the capacity of the decommissioned lithium battery after grouping;
  2. The cascade battery specifications series can be divided into three types according to the installation method: embedded, floor-standing and box-type.
  3. Capacity requirements: The cascade battery should meet the capacity requirements shown in Table 3 under different operating temperature conditions:

Ambient temperature

Discharge current

Battery capacity requirements

-10℃

1.0I3

The measured capacity should not be less than 70% of the nominal capacity

0℃

1.0I3

The measured capacity should not be less than 80% of the nominal capacity

25℃

1.0I3

The measured capacity should be between 100% -110% of the nominal capacity

40℃

1.0I3

The measured capacity should not be less than 98% of the nominal capacity

55℃

1.0I3

The measured capacity should not be less than 97% of the nominal capacity

 

  1. Requirements for cascade battery cells: The capacity of the single cell used by the cascade battery must reach 70% of the initial nominal capacity of the battery cell.
  2. Output voltage range: The cascade battery should use 16 series, the rated voltage of the battery pack is 51.2V, and the working voltage range is 41.6V ~ 60.0V.
  3. Environmental requirements: The cascade battery pack should work normally in a non-corrosive, explosive, and insulating gas and conductive dust environment. Operating temperature range: -5 to 45 ° C; Note: Heating and insulation measures should be taken below -5 ° C. Relative humidity range: ≤95% (45 ℃ ± 2 ℃), atmospheric pressure range: 70kPa ~ 106kPa;
  4. Service life: At an ambient temperature of 25 ° C ± 2 ° C, the cycle life of the battery pack 80% DOD0.33C3 should be not less than 2000times.

At an ambient temperature of 25 ° C ± 2 ° C, the life of the LiFePO4 battery pack under electrical conditions should not be less than 6 years.

FUNCTIONAL REQUIREMENTS OF STEPPED LIFEPO4 BATTERIES

Sleep function

The cascade battery should have the hibernation function, and the battery pack BMS should be completely disconnected in the state of transportation, storage or offline; when the battery pack is switched from the online state (that is, the state of the battery pack output terminal and negative pole, and the communication interface is connected to the outside world) When it is offline (that is, the state where the positive and negative terminals of the battery pack output terminal and the communication interface are disconnected from the outside world), the BMS should have a discrimination function and automatically go to sleep according to the power and battery pack conditions. When the battery pack is switched from offline state (i.e., the state of the battery pack output terminal, the communication interface is disconnected from the outside world) to online state (i.e., the state of the battery pack output terminal, the communication interface is connected to the outside world), the BMS should be able to identify and Automatic activation, and adjust the working status according to power and battery pack conditions.

Electric heating function

When the cascade battery is used in the scene of -5 ℃ or below, a DC electric heating device should be configured (the temperature should be controlled and adjusted according to the actual situation), and the battery pack should have a special heat dissipation design to ensure uniform heating and normal operation of the equipment.

Charging current limit management function

The cascade battery should have an autonomous current-limiting charging function to ensure that the battery pack can be charged normally when the voltage is input within the working range. The charging current limit value should be set between 0.1C3 (A) to 0.2C3 (A). The default value is 0.2C3 (A).

Overcharge protection

The cascade battery should have the function of protecting the total charging voltage from being too high. It will alarm when charging reaches the total voltage warning point, and protect when reaching the protection point.

Low total discharge voltage protection

The cascade battery should have the protection function of low total discharge voltage. When the discharge reaches the low alarm point of the total voltage, the discharge circuit should be cut off and alarmed, and the battery pack should enter the sleep mode after a period of time.

Low discharge cell voltage protection

The cascade battery should have the protection function of the low voltage of the single cell when discharged. It will alarm when the single cell voltage is discharged to the point of protection, and it will protect when it reaches the protection point.

Discharge overcurrent management

The cascade battery should have an output overcurrent protection function set according to the needs of the user. The circuit should be cut off and an alarm should be provided during the protection.

Battery high temperature protection

The cascade battery itself should have a high-temperature battery protection function. When the battery temperature reaches the alarm point, it will warn; when it reaches the protection point, it will protect and act on the cutoff; the temperature will automatically recover when the temperature drops to a certain value.

Battery low temperature protection function

The cascade battery itself should have a low-temperature battery protection function. When the battery temperature reaches the alarm point, it will warn; when it reaches the protection point, it will protect and act on the cutoff; the temperature will automatically recover after the temperature rises to a certain value.

Battery pack state of charge (SOC) calculation

The cascade battery should have a dynamic charge capacity calculation function, and the error between the calculated value and the actual battery capacity should not be greater than 5%.

Output short circuit protection

When there is a direct short circuit between the positive and negative terminals of the output of the cascade battery, the circuit should be automatically cut off and alarmed immediately. The BMS and battery should not be damaged (including no fire, deformation, leakage, smoke, fire or explosion); Can resume work manually or automatically.

Technical requirements for cascade battery monitoring

Telemetry

Can perform battery pack / battery voltage, state of charge (SOC), battery pack charge / discharge current, number of cycles (discharge once 80% of the nominal capacity is a cycle), ambient temperature / battery pack temperature, battery pack internal resistance (Optional) Telemetry monitoring and historical data query, fault log query and other functions.

Telemetry

Can collect the charging / discharging status of the cascade battery, battery pack overcharge / overcurrent alarm, battery pack undervoltage / overcurrent alarm, single charge overvoltage alarm (optional), single discharge undervoltage alarm (optional) , Battery pack polarity reverse alarm, environment / battery pack / PCBA board high temperature alert (optional), low ambient temperature alert, low battery pack alert, battery pack temperature / voltage / current sensor failure alert, cell failure alert ( (Optional), remote signal indicator such as battery pack failure alarm (optional).

Remote control

Remote operation such as alarm sound on / off, intelligent intermittent charging, current limiting charging, charging on / off, discharge start / stop, etc.

Remote adjustment

The functional status and parameter setting range of various BMS test items for cascade batteries.

LADDER LIFEPO4 BATTERY INSTALLATION AND MAINTENANCE REQUIREMENTS

  1. The surface of the battery pack should be clean, without obvious deformation, no mechanical damage, and no rust on the interface contacts; the surface of the battery pack should have the necessary product identification, and the identification should be clear; the positive and negative terminals and polarity of the battery pack should be clearly marked The wiring method should be the front outlet method for easy connection; the power interface and communication (or alarm) interface of the battery pack should be clearly marked;
  2. The 19-inch standard mechanical and electrical unit of the stepped lithium battery pack should be made of metal, and the structure should be easy to handle;
  3. Installation of step batteries in order to facilitate commissioning and subsequent maintenance, the lithium-ion battery panel should be facing outwards, and the step batteries should be reliably fixed to the battery rack or integrated cabinet;
  4. Lay the battery in the cascade. Connect the battery cable to the upper terminal of the safety copper bar in the power cabinet or the battery management circuit breaker, and label the cables.
  5. Lay the battery monitoring cable and connect the LiFePO4 battery pack to the FSU-RS485 communication terminal;
  6. LiFePO4 battery cascade battery access system. After the connection of various cables is completed, use a multimeter to test the output voltage of the battery, record the detected data, and adjust the output voltage of the switching power supply to the current voltage value of the step battery.
  7. Adjust the parameters of the switching power supply. After the various types of cables are connected, use a multimeter to test the output voltage of the battery and record the detected data;
  8. Requirements for operating environment of Ladder LiFePO4 battery: According to the environmental requirements of the battery, the room temperature should not exceed 55 ° C, avoid direct sunlight to the battery, and the sun-shading windows should be shaded to ensure that sufficient maintenance space is reserved between the battery packs;
  9. Precautions for using LiFePO4 battery in a step-by-step manner Monitor the total voltage, current, cell voltage SOC, SOH, and temperature of the battery pack in real time through the moving ring centralized monitoring system and BMS. At the same time, understand the battery charge and discharge curve and performance through the battery monitoring device, and perform regular measurements to find faults and deal with them in time;
  10. Items that are frequently checked for ladder-type LiFePO4 batteries: You should always check whether the pole connecting wires (bars) of the ladder-type LiFePO4 battery module are loose, and whether they are damaged, deformed, or corroded. Check whether there is any damage, leakage and deformation of the battery, whether the temperature rise of the battery and the connection is abnormal; the contact condition of the BMS data line; and conduct warning experiments on the output fuse temperature check and signal fuse of the battery pack. According to the technical parameters and on-site environmental conditions provided by the manufacturer, check whether the total voltage of the battery pack and the cell voltage meet the requirements through the BMS system, and check whether the charging current during the intermittent charging of the battery pack is within the required range. Check whether the charging voltage and current limit of the switching power supply, battery pack are set correctly. Check whether the low voltage alarm, high voltage alarm, and high temperature alarm of the battery pack are set correctly.

TECHNICAL AND ECONOMIC JUSTIFICATION FOR LADDER LIFEPO4 BATTERY PACKS

Compared with lead-acid batteries currently used, electric vehicle retired batteries have high energy density, high power density, (small size, light weight), good temperature characteristics, long cycle life, and low self-discharge rate. These excellent characteristics make them more suitable As a backup power source for tower base stations, the current ladder battery has a cycle life of more than 800 times. Strong manufacturers have longer battery cycle life; with the development of electric vehicles, by the end of the 13th Five-Year Plan and 2020 In the future, the cycle life of retired batteries will generally be better than 1,000 times, and good quality is expected to reach 2,000 times.

At present, according to the current market conditions, batteries with a low cycle life (as long as more than 400 times can be achieved at present) are used in the first, second, third, and fourth categories of municipal electrical conditions and high-temperature conditions. The battery is used in new energy (more than 800 times) and peak cutting and valley filling (more than 1200 times).

The remanufactured battery is used in the battery pack of base station backup power after remanufacturing. Its cost structure includes the remanufacturing process of cell purchase, transportation, testing, screening, and reorganization. According to the indicators of the 13th Five-Year Plan, it is expected that the number of retired batteries will increase significantly in the future, and the recycling and remanufacturing system will form a scale effect, and the cost is expected to further reduce.

In terms of disposal of scrapped power batteries, since the base station mainly uses LiFePO4 batteries decommissioned for commercial vehicles, its main material value is not high, so the residual value of scrapped LiFePO4 batteries is very low. However, there are already some manufacturers of waste battery treatment starting this business, and it is expected to recycle the waste batteries free of charge.

In short, the application of ladder batteries should follow the principles of small modules, low voltage, high redundancy, small current, and non-mobile, so communication base stations are more suitable for ladder battery applications than other scenarios. Ladder batteries have certain advantages over lead-acid batteries in terms of cycle life, energy density, and high-temperature performance, and various performance indicators are superior to lead-acid batteries. Ladder batteries technically fully meet the backup power requirements of various operating conditions on the existing network. Different cycle life ladder batteries are suitable for different application scenarios and also have certain economic advantages. Ladder battery application is a major innovation in the development of national emerging industries such as energy conservation, environmental protection, and new energy. It has very important practical significance for promoting the development of a low-carbon economy, a green economy, and a circular economy, which benefits both the country and the people.

If you want to know more information, you can click this link.

https://www.ctechibattery.com

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