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Why do tower base stations use Renewable LiFePO4 batteries?

2020-10-13


With the problem of energy shortage and environmental pollution becoming more and more prominent, electric vehicles have attracted wide attention for their advantages of energy saving and environmental protection. Power batteries need to be decommissioned when the power battery capacity used in electric vehicles drops to a level that does not meet the range requirements of electric vehicles. With the increasing prosperity of the electric vehicle market, the "way out" problem of decommissioned power batteries is becoming more and more prominent. The power battery capacity of electric vehicles has been reduced to 80% and has been decommissioned due to insufficient battery life, but it can still be used for power storage at base stations after step-by-step utilization. Vehicle power battery pack to communications with 48V backup power supply as the basic module, electric vehicle power battery through a number of 48V modules in series, the formation of vehicle power battery module for electric vehicle use, after the end of power battery service can be directly used in the field of communications.

The basic characteristics of the Renewable LiFePO4 battery.

1, The multiplied characteristics of battery capacity.

With the increase of discharge current, the discharge capacity of the battery will be reduced, when the discharge ratio is less than 0.33C10, the discharge capacity of the LiFePO4 battery is affected by the discharge multiply rate is very small, the discharge capacity is not very different, it can be basically determined that the battery capacity can be 100% released.

2, The temperature characteristics of the battery capacity.

When the ambient temperature is above 0 , the attenuation speed of the battery capacity is slower, while when the ambient temperature is below 0 , the attenuation speed of the battery capacity is faster, and the internal resistance of the battery increases sharply with the decrease of the temperature.

3,Renewable LiFePO4 battery and lead-acid comparison advantages.

1, High temperature resistance: lead-acid battery stable operating temperature range of 25 to 28 , rising temperature will damage the battery, reduce battery life.

2, High energy density: LiFePO4 battery product weight ratio energy can exceed 130Wh/kg (0.2C, 25 oC), volume ratio energy of 210Wh/L.

3, High current charge and discharge performance: LiFePO4 battery can be high current 2C fast charge discharge, starting current up to 5C or more, lead-acid battery now has no such performance. Therefore, LiFePO4 battery charging time is short.

4, Green environmental protection: LiFePO4 battery does not contain any heavy metals and rare metals (nickel hydride batteries need rare metals), non-toxic.

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

Battery performance index

Lead-Acid

Renewable 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

5, Rung use of power lithium battery life is long, the number of cycles, Renewable utilization can still theoretically remain 6 years of actual life and 400 to 2000 times of actual cycle times, compared with the lead-acid battery 3 to 6 years of service life, 200 times of the actual number of cycles has been greatly improved.

6, High temperature resistance, lithium battery to meet the limit operating conditions below 45 , the current communication base station commonly used lead-acid battery temperature limit is only 35 .

7, Discharge characteristics are good, high capacity utilization rate when high current discharge.

8, Charge and discharge conversion efficiency is high, the energy conversion efficiency of the rung battery is 10% to 15% higher than the lead-acid battery.

9, Small footprint, light weight, low transportation costs, rung battery weight and volume of the same capacity lead-acid battery 1/2 or 2/3.

Technical solutions for the application of LiFePO4 batteries (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, The decommissioned power battery for centralized disassembly, core centralized screening, reassembly into a standard module, is conducive to the centralized screening and maintenance of decommissioned core to ensure quality.

2, On the basis of decommissioned power battery direct transformation, is conducive to the battery set Renewable utilization of simple modularity, capacity advantage, easy production methods, low labor costs, but the land requirements are higher.

3, Step battery process: screening battery core, test voltage, core distribution group, internal cable, BMS, chassis or rack.

The basic structure of the Renewable LiFePO4 battery.

LiFePO4 battery consists of positive and negative plate (positive active substance is LiFePO4, negative active substance is graphite), diaphragm, electrolyte, polar ear and aluminum plastic membrane shell. Positive and negative plate is the area of electrochemical reaction, diaphragm, electrolyte to provide Li transmission channel, through the process of chemical processing after the battery plate surface will form a dense SEI membrane (also known as solid electrolyte interface membrane), the polar ear plays a role in guiding the current. The positive active substance is LiFePO4, which is an olivine structure.

LiFePO4 is mixed with conductive agents and binders in a certain proportion, coated on aluminum foil to form a positive pole, negative active substances are usually graphite-like materials, attached to copper foil by adhesive. The positive and negative poles are separated by a polyethylene diaphragm (or polypropylene and polyethylene composite diaphragm) to prevent short circuits in the battery. The diaphragm is a porous film in which Li passes through its pores during charge and discharge, while electron e-cannot pass through. The electrolyte of the battery is an organic solvent of lithium hexafluorophosphate.

Renewable LiFePO4 battery works.

When the battery is charged, Li migrates from the LiFePO4 material to the crystal surface, from the positive plate material, under the effect of electric field force, into the electrolyte, through the diaphragm, and then by electrolyte to the surface of the negative graphite crystal, and then embedded in the negative polar layer graphite material. At the same time, the electron flow through the positive aluminum foil, through the polar ear, battery pole column, load, negative pole column, negative ear flow to the negative pole of the copper foil electrode, and then through the conductive body flow to the graphite negative pole, so that the charge up to balance.

When the battery discharges, Li is de-embedded from a layered graphite crystal, enters the electrolyte, passes through the diaphragm, and then migrates through the electrolyte to the surface of the LiFePO4 crystal, which is then re-embedded in the material of LiFePO4. At the same time, electrons flow through the conductive body to the negative copper foil electrode, through the polar ear, battery negative pole column, load, positive pole column, positive ear flow to the battery positive aluminum foil electrode, and then through the conductive body flow to the LiFePO4 positive pole, so that the charge up to balance.

Management system for Renewable LiFePO4 batteries.

Battery management system is mainly used to manage the battery charging process and discharge process, improve battery life, and provide users with relevant information of the circuit system.

Battery management system, composed of monitoring, protection circuit, electrical, communication interface, thermal management device, is the core component of battery protection and management, not only to ensure the safe and reliable use of batteries, but also to give full play to the performance of the battery and extend the service life, as a backup energy for communication, management system between the switch power supply and battery plays an important role in the bridge. The requirements of the battery management system must meet 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. Battery management system mainly includes data acquisition unit, calculation and control unit, equalization unit, control execution unit and communication unit.

The practical application of LiFePO4 battery pack in the tower base station.

For the characteristics of the lithium battery pack, in the base station DC switch power application settings, only the floating charging voltage and the average charging voltage adjusted to the lithium battery pack required charging voltage can be, (at the same time must be in the communication equipment DC supply voltage range) because the lithium battery pack even if long-term in the charging state, due to its own BMS protection function, battery performance will not change.

For example: a base station backup battery pack, using 48V-300Ah Renewable LiFePO4 battery pack, each set of batteries consists of 16 3.2V/100Ah single battery series, of which 300Ah battery is composed of 3 groups of 100Ah battery pack in tandescing, each battery pack has a BMS control system.

After installing the battery pack to recharge the battery pack, the battery pack was tested and discharged online at 0.33C10.

After testing with a smart battery pack discharger, it is included online in the DC power supply system. At this point, the switching power charging voltage is set to 56.8V and the charging current is limited to 30A per set.

Renewable LiFePO4 battery configuration requirements.

1, Rung battery module in accordance with the standard capacity can be divided into 15, 25, 30, 50, 100, 130, 150, 200Ah and other capacity series. The standard capacity shall be the post-group capacity of the decommissioned lithium battery.

2, Rung battery specification series in accordance with the installation method can be divided into embedded, floor-to-ceiling frame and floor-to-ceiling box three, the capacity of 50Ah and below the rung battery, mainly embedded.

3, Capacity requirements: rung battery in different operating temperature conditions should meet the capacity requirements shown in Table 3:

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

4, Rung battery cell requirements: Renewable battery used by the single core capacity to reach 70% of the initial standard capacity of the cell.

5, Output voltage range: rung battery should use 16 series mode, battery pack rated voltage of 51.2V, operating voltage range of 41.6V to 60.0V.

6, Environmental requirements: rung battery packs should be non-corrosive, explosive and damage to insulation gas and conductive dust environment. Operating temperature range: -5 to 45 . Note: Heating and insulation measures should be taken below -5 . Relative humidity range: ≤95% (45 ±2 ), atmospheric pressure range: 70kPa to 106kPa.

7, Service life: under the ambient temperature of 25 ±2 , the battery pack 80% DOD0.33C3 cycle life should not be less than the number of times listed in Table 4 operating conditions.

The life of the lithium iron± phosphate battery pack should not be less than 6 years under the condition of electricity preparation under the condition that the ambient temperature is 25 and 2 .

The function requirements of the Renewable LiFePO4 battery.

Sleep function.

The rung battery should have a sleep function, in the transport, storage or offline state, the battery pack BMS should be in a completely disconnected state, when the battery pack from the online state (i.e., the battery pack output positive and negative, communication interface and the outside world connected state) to the offline state (i.e. the battery pack output positive and negative, communication interface and the outside state disconnected state), BMS should have the screening function, according to the power and battery pack conditions automatically into hibernation. When the battery pack is brought online from the offline state (i.e., the positive and negative of the battery pack output, the communication interface is disconnected from the outside world) to the online state (i.e., the positive and negative of the battery pack output, the state of the communication interface connected to the outside world), the BMS shall be able to judge and activate automatically, and adjust the working state according to the power and battery pack conditions.

Electric heating function.

When the rung battery is used for scenes of -5 and below, the DC heating device should be configured (the temperature should be controlled according to the actual situation), and the battery pack should have a special thermal design to ensure that the heating is uniform so that the equipment works properly.

Charging limited flow management function.

The rung battery should have an autonomous limited-flow charging function to ensure that the battery pack can charge properly when the voltage input is in the operating range. The charging limit should be set between 0.1C3(A) and 0.2C3 (A), with a default value of 0.2C3 (A).

The total charge voltage is too high to protect.

Renewable battery should have the function of charging the total voltage too high protection function, when charging to the total voltage alarm point alarm, to the protection point protection, acting on the cut-off, when the total voltage falls to the recovery point to resume charging.

The total discharge voltage is too low to protect.

The rung battery should have a low discharge total voltage protection function. When discharge to the total voltage low warning point should be cut off the discharge circuit and alert, after a period of time the battery pack should enter sleep mode.

The discharge unit voltage is too low to protect.

Renewable battery should have the function of low single battery voltage when discharged, alarm when discharged to single-body voltage warning point, protection at protection point, acting on cutting off, after a period of time the battery should enter sleep mode.

Discharge overflow management.

Renewable batteries should have output overflow protection based on the user's needs, and the circuit should be cut off and alerted during protection.

Battery high temperature protection.

Renewable battery itself should have the battery high temperature protection function, when the battery temperature reaches the alarm point alarm point, to the protection point protection, act on cutting off, the temperature falls back to a certain value after automatic recovery.

Battery low temperature protection.

The rung battery itself should have the low temperature protection function of the battery, alert when the battery temperature reaches the alarm point, protect it when it reaches the protection point, act on the cut-off, and automatically recover when the temperature returns to a certain value.

Battery pack charge status (SOC) calculation.

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

Output short-circuit protection.

In the event of a direct short circuit at the positive and negative ends of the rung battery output, the circuit should be automatically cut off and alerted in an instant, and the BMS and cell should not be damaged (including non-fire, deformation, leakage, smoke, fire or explosion).

Renewable battery monitoring technology requirements.

Remote measurement.

The functions of battery pack/battery voltage, charge state (SOC), battery pack charging/discharge current, cycle times (discharge exceeding 80% of the standard capacity is 1 cycle), ambient temperature/battery pack temperature, battery pack resistance (optional) telemetry monitoring, as well as historical data query, fault log query, etc. can be carried out.

Remote confidence.

The charging/discharge status of the rung battery can be collected, the battery pack overcharge/overflow alarm, the battery pack discharge underpressurization/overflow alarm, the monocharge overpressurization alarm (optional), the single discharge under voltage alarm (optional), the battery pack polarity reverse alarm Remote confidence indicators such as ambient/battery pack/PCBA board high temperature alarm (optional), ambient cryogenic alarm, battery pack capacity too low alarm, battery pack temperature/voltage/current sensor failure alarm, monosome failure alarm (optional), battery pack failure alarm (optional).

The amount of remote control.

Remote control operations such as alarm sound on/off, intelligent intermittent charging, limited-flow charging, charging on/off, discharge start/stop, etc. can be carried out.

Remotely adjusted.

The functional status and parameter setting range of the various detection items of the BMS of the rung battery should include the contents shown in Table 5.

Renewable LiFePO4 battery installation and maintenance requirements.

1, Battery pack surface should be clean, no obvious deformation, no mechanical damage, interface contacts no rust, battery pack surface should have the necessary product identification, and clear identification, battery pack positive, negative extremes and polarity should be clearly marked, wiring mode should be front-line mode, easy to connect, battery pack power interface, communication (or alarm) interface should be clearly identified.

2, Rung lithium battery pack 19-inch standard mechanical electrical unit container housing, mounting frame or box should be metal material, and structurally easy to handle.

3, the installation of rung battery in order to facilitate testing and post-maintenance, the LiFePO4 battery panel needs to be outward-facing, the Renewable battery is reliably fixed to the battery rack or integrated cabinet.

4, Rung battery cloth Renewable battery cable, the battery cable is connected to the power cabinet insurance copper row terminal or battery management empty open, do a good job of cable label identification.

5, put the battery monitoring line, the lithium iron battery pack connected to the FSU-RS485 communication terminal.

6, LiFePO4 battery rung battery access system, all kinds of cable connection is completed, with a million meter on the battery's output voltage, testing will detect the data to do a good job of recording, adjust the switch power output voltage to the current voltage value of the Renewable battery.

7, Adjust the switch power parameters, all kinds of cable connection is completed, with a million meter to detect the output voltage of the battery, the detection of the data to do a good job of recording.

8,Renewable LiFePO4 battery operating environment requirements: according to the environmental requirements of the battery, room temperature should not exceed 55 , to avoid direct sunlight on the battery, windows should be shaded, to ensure that the battery pack between the reserved sufficient maintenance space.

9,Renewable LiFePO4 battery use precautions through the dynamic ring centralized monitoring system and BMS real-time monitoring of the total voltage of the battery pack, current, unit voltage SOC, SOH, temperature monitoring. At the same time, through the battery monitoring device to understand the battery charge and discharge curve and performance, regular measurement, found that the fault timely treatment.

10,Renewable LiFePO4 battery often check the items: should often check the Renewable LiFePO4 battery module pole wire (bar) is loose, whether there is damage, deformation or corrosion and other phenomena. BMS data cable contact, and the battery pack output insurance temperature check and signal insurance alarm test. According to the technical parameters and field environmental conditions provided by the manufacturer, through the BMS system to check whether the total battery pack voltage and unit voltage meet the requirements, to detect the battery pack intermittent charging current is within the required range. Check that the switching power supply, the charging voltage of the battery pack, and the limit values are set correctly. Detect whether the battery pack's low-voltage alarm, high-voltage alarm, high-temperature alarm, etc. are set correctly.

The technical and economic demonstration of the LiFePO4 battery pack of the Renewable.

At present, compared with the application of lead-acid batteries, electric vehicle decommissioned batteries have high energy density, high power density, (small size, light weight), good temperature characteristics, long cycle life, low self-discharge rate, these excellent characteristics make it more suitable for the tower base station backup power supply, the current step battery, its cycle life of more than 800 times, strong manufacturers, its battery cycle life is longer. The cycle life of decommissioned batteries will generally be better than 1000 times, and the quality is expected to reach 2000 times.

At present, according to the current market situation, the cycle life is low (as long as more than 400 times can be achieved at present) batteries for one, two, three, four types of municipal electrical conditions and high temperature conditions, high cycle life batteries for new energy (more than 800 times) and peak filling (more than 1200 times) conditions.

Decommissioned batteries are remanded and applied to the battery pack of base station backup power supply, and their cost composition includes the remanding process of core procurement, transportation, testing, screening, recombination, etc. According to the indicators of the 13th Five-Year Plan, it is expected that the number of decommissioned batteries will increase significantly in the future, and the recovery and re-manufacturing system will have a scale effect, and the cost is expected to be further reduced.

In the treatment of end-of-life power batteries, because the base station is mainly used in commercial vehicles decommissioned LiFePO4 batteries, the main material value is not high, so the scrap LiFePO4 battery residual value is very low. But there are already some end-of-life battery treatment manufacturers to start this business, and is expected to recycle end-of-life batteries for free.

In short, Renewable battery applications should follow the principles of small modules, low voltage, high redundancy, small current, non-mobile use, so communication base stations are more suitable for Renewable battery applications than other scenarios. Compared with lead-acid batteries, Renewable batteries have certain advantages in cycle life, energy density and high temperature performance, and the performance indicators are better than lead-acid batteries. Renewable battery in technology to fully meet the current network of various operating conditions to prepare electricity needs, different cycle life Renewable battery is suitable for different applications, the economy also has certain advantages. Renewable battery application is a major innovation in the development of national strategic emerging industries, such as energy conservation and environmental protection, new energy, and so on, which is of great practical significance for promoting the development of low-carbon economy, green economy and circular economy.


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