Although the pressure for the decommissioning and recycling of electric
vehicle power batteries cannot be said to be imminent, there is no doubt that we
should take precautions now and make early preparations for this approaching
problem. The age of oil is coming to an end and the age of electric cars is
coming. According to calculations and predictions, my country will have GWh of
power batteries retired in 2017, and will usher in a scale of 10GWh in 2020. In
addition to dismantling and recycling raw materials that are determined to be
scrapped, it is more environmentally friendly and efficient to reuse the
remaining batteries that can be reused in other scenarios to maximize the
residual value of power batteries and achieve a circular economy. However, in
order to realize the echelon utilization of power batteries, in addition to the
difficulties and deficiencies in commercial operations and policies and
regulations, the purely technical level will first face great obstacles. If the
basic technical implementation problems cannot be solved, the wonderful ideas
that follow will inevitably Through the mirror, we will repeat the mistake of
wasting lead-acid battery resources and polluting the environment.
Ladder utilization, to put it bluntly, is the reuse of second-hand goods,
such as second-hand cars, second-hand furniture, and second-hand equipment. What
needs to be determined most is the residual value of the second-hand goods.
Generally speaking, the residual value of second-hand goods is usually judged
based on its production date or service life, that is, time. However, power
batteries are special. It is impossible to judge the remaining value only from a
single data of time, such as the date of manufacture and cumulative usage time,
because the remaining value of the battery has a non-linear relationship with
time and is not a single function of time. SOH and other key factors are also
required. Data, which are generated by BMS (battery management system)
measurement and calculation during use. The technical difficulties lie in this.
The first is the accuracy of the data, the second is the integrity of the data,
the third is the availability of the data, and the fourth is the security of the
data. These issues are inseparable from BMS. Therefore, BMS is the key to the
step-by-step use of power batteries.
The first thing to determine is which configuration of power battery to
reuse. Single cell, single string (multiple cells connected in parallel), module
(multiple single strings connected in series and parallel), or power battery
PACK (multiple modules connected in series). The single battery cell and battery
PACK is obviously unrealistic: the number of single battery cells is huge, and
the BMS does not have data records for the single battery cells. Reorganization
requires repeated matching work, which is not cost-effective; each single string
battery in the entire PACK The performance may vary greatly, and it is not
appropriate to reuse it in PACK units. For the same reason, it is not
appropriate to use modules as a unit. The most suitable unit is a single string
of batteries.
The accuracy of data mainly targets SOC and SOH. There is currently no
authoritative standard for these data models. Although the battery model itself
can be said to be standard, in dynamic applications, the algorithms for
important data such as SOH are different for each company. Some are conventional
algorithms, and some claim to be unique. Which algorithm can be called a
recognized standard. Of course, there may be manufacturers whose algorithms are
quite accurate, but due to corporate competition, it is impossible to release
them publicly. This can only rely on the market and time to test them to become
the actual standard. Or a professional organization can develop an accurate
algorithm, integrate it into a dedicated IC, and use it in the form of standard
hardware for BMS manufacturers. In short, from the current point of view,
solving the problem of data accuracy can only rely on the evolution of time.
Either the number of BMS manufacturers has dropped sharply through competition,
and only a few have relatively monopolized the entire market, or it has been
used by many BMS manufacturers in the form of standard hardware. , the current
situation of individual calculations and no standards cannot meet the
comprehensive echelon utilization of power batteries.
Data integrity. The data is divided into two parts according to time. The
first is the original factory data, which mainly includes nominal voltage,
capacity, and cycle life; the second is important data during use, mainly the
cumulative discharge amount, number of deep discharges, SOC, SOH, and static
terminal. Voltage and SOC corresponding curve, etc. Data such as cumulative
discharge capacity, number of deep discharges, and the corresponding curve
between static terminal voltage and SOC are currently not recorded in most BMS
products. These data are indispensable in the calculation of the residual value
of the battery pack, and the corresponding curve between static terminal voltage
and SOC is indispensable. Battery regrouping is of great significance. It can
further reduce the inconsistency of single strings in the battery pack based on
SOH data matching, reduce the cost of classifying retired batteries into groups,
and improve the life of new battery packs. If power batteries want to be
utilized step by step, data recording standards must be developed for BMS.
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