Safety requirements for the reuse of echelon-use battery



1. What is the echelon use battery


After the electric vehicle power battery is decommissioned, it is reused after processing and reorganization, that is, the power battery is reused. We usually refer to this battery as a echelon use battery.

2. What are the characteristics of echelon use battery

The main characteristics of echelon use battery lie in:

  • Safe and stable, with good performance at high temperatures.
  • Small size and light weight.
  • No memory effect (supports on-demand use, is convenient and is fast)
  • High-efficiency output for fast charging
  • Energy saving, emission reduction, and green environmental protection.
  • High battery life.

3. Echelon use battery usage scenarios

The lifepo4 battery has an optimal operating temperature range, and safety problems are prone to occur beyond the range of use. The upper limit of the battery use temperature is preferably lower than 45 °C, and it is easy to cause thermal runaway safety problems when used at higher temperatures.

Low-temperature charging of the anode is prone to lithium precipitation, to control the charging mode, temperatures below 0 °C should appropriately reduce the charging current or prohibit charging. If you need to work for a long time outside the temperature range, you should use the battery's built-in heating or cooling element or use the constant temperature of the air conditioner to control the batteries at the appropriate temperature.

Batteries that have been stored for more than half a year should be activated by charging and discharging with a small current before normal use. Charging speed is strongly correlated with service life and safety risks, so when conditions permit, choose small magnification charging. Batteries that are fully charged and stored for a long time at high temperatures should be avoided to prevent degradation of battery performance and increased safety risks.

Echelon-use battery usage scenarios


For the echelon use battery used for backup power, it is advisable to consider the appropriate amount of battery charge during long-term power backup, so as to ensure sufficient backup power and achieve a safe state of battery live storage. For echelon use batteries used in energy storage, it is advisable to set an appropriate shallow charge, shallow discharge charge and discharge strategy. Achieve the purpose of extending battery life and reducing safety risks.

4. Requirements for echelon use battery

● Charging and discharging current, voltage, protection function requirements

When the battery is used, the charge and discharge current and voltage should be adjusted appropriately according to the use environment. When the use temperature tends to the batteries use temperature limit, the charge and discharge current and voltage should be appropriately reduced.

● Battery installation and construction requirements

Smaller capacity echelon batteries allow reliable anchor fixation. The heat dissipation capacity, load-bearing capacity, and stability of the box should be considered to prevent safety risks caused by temperature accumulation, battery slipping or accidental movement.

Echelon use batteries with large capacities should be installed in battery cabinets. The battery cabinet should be ventilated and dissipated well. The battery cabinet should be reliable and firm, and it will not deform after long-term use and load-bearing.

● Operational monitoring requirements

When the battery is used, the battery parameter information should be monitored. When the parameters exceed the security risk level, the charging and discharging should be stopped and the alarm should be activated. For large-scale deployment, the battery is used, and the BMS data needs to be verified during operation. Real-time monitoring of key parameters of the batteries, such as total battery voltage, monomer voltage, SOC and other information.

Requirements for echelon-use battery


● Echelon use battery necessity

The lithium battery is 100% capacity when fully charged. When the battery is used for a period of time, its capacity will decay. When the battery capacity decays to 80%, it cannot be used in the car, and the power batteries will be decommissioned. Not all cells in a retired or end-of-life battery pack are in a scrapped state, and it is usually only the cells of individual units that are scrapped due to inconsistencies.

Many batteries in the group are still in a good life cycle and still have high echelon use value. Waste heat can continue to be exerted with a suitable echelon use scheme. After the power battery is retired, some power batteries still have good electrical performance, and their remaining capacity can meet the needs of application scenarios such as energy storage and power backup. Under normal circumstances, the power battery pack is composed of several modules or monomers.

Even if the battery pack cannot continue to be used due to internal damage to individual modules or monomers, other modules and monomers in the battery pack still have a large space for secondary use. In the process of recycling used vehicle power batteries, if the waste power batteries are directly recycled into materials, it will cause a great waste of resources.

Echelon use batteries can maximize the value of the whole life cycle of power batteries, reduce carbon emissions during the life cycle of power batteries, and alleviate the tension in supply demand for upstream raw material manufacturers in subdivided fields. Therefore, starting from the principle of maximizing resource utilization, the echelon use of power batteries is necessary.

5. The main problem of echelon use battery

● Battery life is difficult to measure

The total energy that can be provided during the battery life cycle describes the battery life, but it has different meanings. In power batteries, this capacity means the total mileage of the electric vehicle, but in the energy storage market, it means battery life.

The main problem of echelon-use battery


It can be seen that the biggest difference between energy storage batteries and power batteries is that they require long-term operation. In order to extend battery life, energy storage battery packs are often guaranteed to operate in 20%–90% of the working area. Even so, there is no guarantee that every energy storage battery will meet the design requirements.

● Cost remains a sensitive issue

If you want to use batteries to further reduce the cost of lithium batteries, the actual cost of these projects may be very different from the cost predicted by the economic model. Under the premise of no guarantee of subsidy mechanism, whether the battery cost of echelon use can really be accepted by the energy storage market remains to be verified.

● There are still many technical problems

There have always been several technical bottlenecks in the echelon use battery : The health status of the battery is difficult to evaluate, especially the risk of thermal runaway, which is difficult to prevent and control. Battery capacity consistency is difficult to control, especially with nonlinear capacity attenuation. Battery capacity calibration is inefficient, and rapid capacity detection technology is difficult.

6. Reorganization and echelon utilization scenarios

● Reorganization of retired batteries

When realizing the echelon use, it is reorganized in the form of a cell cell, which can ensure the SOH of each battery and keep the retired batteries with high consistency during the echelon use. However, a single-level reorganization takes a long time, is costly, and it is difficult to ensure the integrity of the disassembly. Considering the cost and benefit, it is reasonable to use the battery hookup. By doing so, battery pack or module can maximize the echelon use battery.

● Echelon use scenarios

The performance of lithium iron phosphate-powered lithium ion batteries is used in backup batteries, grid energy storage and grid frequency regulation. Under analog standby power conditions, the service life can be up to 8 years. Under the conditions of grid energy storage, the cycle life can exceed 5,000 times.

Reorganization and echelon utilization scenarios


Under the condition of frequency regulation of the power grid, the cycle life is about 10,000 times. Some scenarios for the use of batteries in echelons include mobile charging piles, low-speed electric vehicles, AGV power supplies, home energy storage power supplies, uninterruptible power supplies, wind and street lamp energy storage, etc.

And when the cycle life of the echelon use battery is more than 400 times, it begins to make a profit, so the retired lithium iron phosphate battery has a good application prospect.

7. Conclusion

The key technologies of power echelon use battery are introduced, and the methods used in battery testing are summarized. At the same time, it is also noted that the echelon use battery still needs to be strengthened in some aspects. In terms of detection and screening, the detection method is relatively simple, most experiments are only studied for battery cells, and the echelon use of batteries is mainly based on modules.

Therefore, it is necessary to design more effective detection and screening methods according to the characteristics of battery modules on the basis of single cell research technology. Establish a battery life prediction system for echelon use, and intervene in time for problems existing in the echelon use energy storage system.


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