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Characteristic research on lithium iron phosphate
battery of power type
Yen-Ming Tseng1,Hsi-Shan Huang1,Li-Shan Chen2,*,and Jsung-Ta Tsai1
1College of Intelligence Robot, Fuzhou Polytechnic,No.8 Lianrong Road, Fuzhou University Town,
350108, Fuzhou City, Fujian Province, China
2School of Management,Fujian University of Technology,No.3 Xueyuan Road, Fuzhou University
Town, 350108, Fuzhou City, Fujian Province, China
Abstract. In this paper, it is the research topic focus on the electrical
characteristics analysis of lithium phosphate iron (LiFePO4) batteries pack
of power t ype. LiFePO4 battery of power type hasperformance advantages
such as high capacity, lower toxicity and pollution, operation at high
temperature environment and many cycling times in charging and
discharge and so on. The charging and dis charging charact eristics for
LiFePO4 batteries of power type pack have been verified and discussed by
the actual experiment.Base on the 12V10AH LiFePO4 battery was
proceeding on charging and discharging test with over high current value
and which investigatethe parameters such as the internal resistance, the
related charge and discharge characteristics ofLiFePO4 battery pack , the
actual value of internal voltage and internal resistance of the battery pack
and by polynomial mathmatic model to approach the accury of inner
resistance on discharging mode.
1Introduction
The battery is storage and energy conversion components which can be stored in the
original physical energy, chemical energy or other type energy and that can be converted
into electricity and released to attach circuit for application [1, 2]. In accordance with the
energy storage and release methods that can be divided into physical batteries and chemical
batteries. The former are convert from the light, heat and other renewable energy to
electricity and to storage in batteries or release in transmission line to loadings and
consumption the power which the description type are such as solar cell [3], wind power[4],
atomic force batteries and so on. Chemical bat ter ies are chemical substances through the
material of the redo reaction which by the active substances reactive effect convert from
chemical energy to electricity that base on the charging and discharging apply recycle can
divided into primary battery and secondary battery. Primary battery just can only discharge
once and till to not drive the electrical loading so far. At the end of time in discharging
mode that the battery does not chemical substances all played a chemical effect can no
longer be able to provide electricity and it cannot be provided by the external power supply
at after the full discharge make this battery useless. That is because its electrochemical
__________________________________
*Corresponding author: Sun56@ms8.hinet.net
© The Authors, published by EDP Sciences. This is an open access article distributed under the terms of the Creative Commons
Attribution License 4.0 (http://creativecommons.org/licenses/by/4.0/).
MATEC Web of Conferences 185, 00004 (2018) https://doi.org/10.1051/matecconf/201818500004
ICPMMT 2018
reaction is irreversible by the reasons of electrolyte cannot be restored by recharging
step. The secondary battery is chemically converted into electrical energy and can be
recharged into a battery by recharging the battery that effect is re-converted into
chemical energy and it can be reused. The number of times uses will varywith the
material and the application. In general, that exists in the market such as the lead-acid
batteries, nickel-cadmium batteries, nickel-metal hydride batteries and lithium family
batteries [5]. Different chemical type batteries rely on its working voltage, capacitance
and safety of the relationship that made different applications. A lithium battery mainly
refers to lithium-ion batteries. At present in the market can be found for the lithium
cobalt material, lithium manganese material but the both in the use of secur ity on the
doubt there will be cause high temperature resulting in explosion or the decline in
capacity of the problem. T o improve the lithium batteries to lithium phosphate iron
(LiFePO4) batteries [6, 7, 8]for these problems, can eliminate the user's security
concerns. In this paper, the charging and discharging characteristics of power type
LiFePO4 batteries pack will be by the actual experiment to verify and discussion. The
study steps are following :
1) Explore and compare the dynamic characteristics of different secondary batteries
of power type.
2) Discuss and decide the lithium iron phosphate (LiFePO4)battery of po wer type
pack rated to voltage and capacity as the subject of research.
3) Discussion on the parameters and characteristics of power type LiFePO4 pack in
charging mode and discharging mode.
4) To investigate the power type LiFePO4 pack by charging and discharging test
with heavy duty.
5) Analyze the charging and discharging curves of LiFePO4 of power type wit h the
polyno mial method.
6) To find the power type LiFePO4 pack the inner resistance in charging and
discharging test with heavy duty to reach the relative errors.
2 Comparison with the LiFePO4 and the other different
secondary battery
Currently on the market mainly using the most extensive secondary battery are lead-
acid batteries pack, and lithium batteries such as lithium-cadmium batteries, nickel-metal
hydride battery, lithiu m cobalt batteryand LiFePO4 battery packs. Lead-acid battery
because of the widely operating temperature, simple structure, technology is mature and
low price characteristics to form the higher usage rate but the lower cycle life and discharge
coefficient (or called Crate), higher internal resistance and high toxicity caused by high
pollut ion shortcomings to make the replace effect by other chemical Battery packs. in this
paper, it is discussed the LiFePO4 battery packs which have the advantages of high
capacitance, low toxicity and no pollution, high temperature environment and good
circulation performance under heavy duty charge and discharge mode, and wide sources of
raw materials.Compared with other lit hium family batteries packs which LiFePO4 battery
packs have high efficiency energy conversion up to 95% and posses the more life cycle up
to 2000 times than the other lithium family batteries packs life cycle about from 400 to 500
times. LiFePO4 battery packs is also very suitable with power supply for electric motors
and for power management such as electricity scooter, pure electricity scooter and hybrid
cars applications and so on, and in the future will become the mainstream of electric
vehicles.
2
MATEC Web of Conferences 185, 00004 (2018) https://doi.org/10.1051/matecconf/201818500004
ICPMMT 2018
reaction is irreversible by the reasons of electrolyte cannot be restored by recharging
step. The secondary battery is chemically converted into electrical energy and can be
recharged into a battery by recharging the battery that effect is re-converted into
chemical energy and it can be reused. The number of times uses will varywith the
material and the application. In general, that exists in the market such as the lead-acid
batteries, nickel-cadmium batteries, nickel-metal hydride batteries and lithium family
batteries [5]. Different chemical type batteries rely on its working voltage, capacitance
and safety of the relationship that made different applications. A lithium battery mainly
refers to lithium-ion batteries. At present in the market can be found for the lithium
cobalt material, lithium manganese material but the both in the use of secur ity on the
doubt there will be cause high temperature resulting in explosion or the decline in
capacity of the problem. T o improve the lithium batteries to lithium phosphate iron
(LiFePO4) batteries [6, 7, 8]for these problems, can eliminate the user's security
concerns. In this paper, the charging and discharging characteristics of power type
LiFePO4 batteries pack will be by the actual experiment to verify and discussion. The
study steps are following :
1) Explore and compare the dynamic characteristics of different secondary batteries
of power type.
2) Discuss and decide the lithium iron phosphate (LiFePO4)battery of po wer type
pack rated to voltage and capacity as the subject of research.
3) Discussion on the parameters and characteristics of power type LiFePO4 pack in
charging mode and discharging mode.
4) To investigate the power type LiFePO4 pack by charging and discharging test
with heavy duty.
5) Analyze the charging and discharging curves of LiFePO4 of power type wit h the
polyno mial method.
6) To find the power type LiFePO4 pack the inner resistance in charging and
discharging test with heavy duty to reach the relative errors.
2 Comparison with the LiFePO4 and the other different
secondary battery
Currently on the market mainly using the most extensive secondary battery are lead-
acid batteries pack, and lithium batteries such as lithium-cadmium batteries, nickel-metal
hydride battery, lithiu m cobalt batteryand LiFePO4 battery packs. Lead-acid battery
because of the widely operating temperature, simple structure, technology is mature and
low price characteristics to form the higher usage rate but the lower cycle life and discharge
coefficient (or called Crate), higher internal resistance and high toxicity caused by high
pollut ion shortcomings to make the replace effect by other chemical Battery packs. in this
paper, it is discussed the LiFePO4 battery packs which have the advantages of high
capacitance, low toxicity and no pollution, high temperature environment and good
circulation performance under heavy duty charge and discharge mode, and wide sources of
raw materials.Compared with other lit hium family batteries packs which LiFePO4 battery
packs have high efficiency energy conversion up to 95% and posses the more life cycle up
to 2000 times than the other lithium family batteries packs life cycle about from 400 to 500
times. LiFePO4 battery packs is also very suitable with power supply for electric motors
and for power management such as electricity scooter, pure electricity scooter and hybrid
cars applications and so on, and in the future will become the mainstream of electric
vehicles.
3Internal resistance varying characteristics in charging and
discharging mode of LiFePO4 battery pack
In Figure 1 which Vbis inside voltage of battery pack and Rin is inner resistance of
battery pack. Generally, battery equivalent circuit will not show Rcov and C. The resistance
Rcov and capacitor C in parallel configuration and in series with the former circuit that
simulation the in over-voltage states will produce the pheno menon. So that made the
analogy charging process of this battery equivalent circuit diagram is more realistic and
therefore improves the shortcomings of the linear model and is therefore more accurate than
the linear model. And Req is the equivalent battery resistance seen by side of the voltage
source, since the capacitance Cis the open state so that equivalent over-voltage will
produce the phenomenon, and the general battery equivalent resistance Req is equal as
equation (1).
Req=Rin+Rcov (1)
Fig. 1. Battery pack equivalent circuit diagram.
Form view of the battery pack capacity in fixed that the capacit y is full or not with its
battery pack inner resistance is closely related in charging mode or proceeding. In general,
each battery pack capacity of the full percentage greater relative inner resistance will be
made greater. In contrast, the smaller the degree of filling of each battery packs company
with the smaller its internal resistance. The relationship between the external voltage and
the magnitude of the battery pack resistance is b y the actual circuit to test and explain.
3.1 The relationship between with the charging voltages and currents
Basedon the specification of A123 26650 LiFePO4 battery cell as shown in the Table 1.
Table 1. LiFePO4 battery cell specification [9, 10].
Type A123
Rate voltage 3.3V
Rate capacity 2300mAh
Weight 73g
Charging time
Conventional charging about 1C-2C or 3-4A and fast charging
about 5C or 10A.
3
MATEC Web of Conferences 185, 00004 (2018) https://doi.org/10.1051/matecconf/201818500004
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A constant voltage charging circuit is designed for a 12V 10Ah LiFePO4 battery pack
to keep the charging voltage constant and allow the charging current to be less than 3C
which let charging current between in conventional charging and fast charging areas. The
charging data is shown in Table 2. When the time is 0 for start, the initial value of the
voltage is 11.48V and charging current is 30A. When the time passes 5 seconds, the
voltage rose to 11.66V and then the charging current dropped to 25A. When the time after
50 seconds which the inside battery pack voltage rose to 12.22V and then the charging
current is14A. According to the design of charging voltage for the battery pack, when the
battery pack inside voltage reach the charging voltage will let the charging current become
about 0A, that is called full charging. When the time passes 100 seconds, the voltage rose
to 12.61V and then the charging current is 11.7A.When the time passes 230 seconds, the
voltage rose to 13.00V and then the charging current dropped to 8.5A. And the time after
240 seconds, voltage rose to 13.00 V and then the charging current dropped to 3.2A we can
see that when the battery slowly filling the voltage will stabilize, the current will slowly
decline. Base on the data we can drown the charging curve shown in Figure 2.
Fig. 2. LiFePO4 battery pack charging.
Table 2. LiFePO4 battery pack charging trace constant with voltage method.
Time(second) Inner voltage of battery pack (V) Charging current(A)
011.48 30
511.66 25
10 11.75 23
20 11.27 19
30
12.02
16
40 12.17 15.7
50 12.22 14
60 12.42 13.5
70 12.45 13.3
4
MATEC Web of Conferences 185, 00004 (2018) https://doi.org/10.1051/matecconf/201818500004
ICPMMT 2018
A constant voltage charging circuit is designed for a 12V 10Ah LiFePO4 battery pack
to keep the charging voltage constant and allow the charging current to be less than 3C
which let charging current between in conventional charging and fast charging areas. The
charging data is shown in Table 2. When the time is 0 for start, the initial value of the
voltage is 11.48V and charging current is 30A. When the time passes 5 seconds, the
voltage rose to 11.66V and then the charging current dropped to 25A. When the time after
50 seconds which the inside battery pack voltage rose to 12.22V and then the charging
current is14A. According to the design of charging voltage for the battery pack, when the
battery pack inside voltage reach the charging voltage will let the charging current become
about 0A, that is called full charging. When the time passes 100 seconds, the voltage rose
to 12.61V and then the charging current is 11.7A.When the time passes 230 seconds, the
voltage rose to 13.00V and then the charging current dropped to 8.5A. And the time after
240 seconds, voltage rose to 13.00 V and then the charging current dropped to 3.2A we can
see that when the battery slowly filling the voltage will stabilize, the current will slowly
decline. Base on the data we can drown the charging curve shown in Figure 2.
Fig. 2. LiFePO4 battery pack charging.
Table 2. LiFePO4 battery pack charging trace constant with voltage method.
Time(second) Inner voltage of battery pack (V) Charging current(A)
011.48 30
511.66 25
10 11.75 23
20 11.27 19
30
12.02
16
40 12.17 15.7
50 12.22 14
60 12.42 13.5
70 12.45 13.3
80 12.54 12.8
90 12.58 12.1
100 12.61 11.7
120 12.67 11.2
190 12.8 8.9
220 12.9 5.4
230 13 3.6
240 13 3.2
3.2 Calculation the dynamic internal voltage and equivalent inner resistance
of the battery pack
Figure 3 is a 12V10AHLiFePO4 battery pack for the power source supply and by series
with a DC motor which internal resistance RMis 0.07 ohm to form a closed loop for
measure the battery pack dynamic inner resistance in discharge mode under different
voltage equalization. The equivalent resistance Req seen from the power supply side is
shown in equation (2) and the dynamic internal resistance Rin of the battery pack is shown
in equation (3). According to the discharge battery pack voltage level is divided into 13
measurements points sown in t able 3. At first time the battery pack side voltage 13.2V,
current is 2.8A, supply side equivalent resistance Req is 4.71 ohm and the battery pack
internal resistance Rin is 4.64 ohm. At sixth time the battery pack side voltage 12.8V,
current is 3.3A, supply side equivalent resistance Req is 3.88 ohm and the battery pack
internal resistance Rin is 3.81 ohm. And at the last time the battery pack side voltage 10.7V,
current is 3.3A, supply side equivalent resistance Req is 3.24 ohm and the battery pack
internal resistance Rin is 3.17 ohm. From the table 3, it is made a result which is the higher
the supply voltage with the smaller the discharging current will reach the resistance larger
by loading with unchangedor fixed resistance.
Fig. 3. LiFePO4 battery pack charging.
Req=V/I=Rin+RM(2)
Rin = Req - RM(3)
Wit h the relationship between the battery internal resistance Rin and the voltage Vin
Table 3 that by using the third-order polynomial mathemat ical mo del o f vo lt age Vis used
to approach the internal dynamic intermal resistance Rin and predictive internal resistance
M
-
+
I
V
Rin
DC Motor
RM=0.07 ohm
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MATEC Web of Conferences 185, 00004 (2018) https://doi.org/10.1051/matecconf/201818500004
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value o f the battery, as shown in equation (4). Using the relative error REv% as sho wn in
equation (5) to confirm the accuracy of the mathematical model and the Table 4 is shown in
the table for each voltage class approaching the battery block internal resistance and
relative error.
Rin=a0+a1
×
V+a2
×
V2+ a3
×
V3(4)
where
Rin: internal resistance of battery pack
V: discharging voltage
%100
,
|,,|
%×
−
=
actualRin
fitRinactualRin
RE
V
(5)
where
Rin, actual: internal resistance of battery pack which equal to Rin
Rin, fit: internal resistance approach by polynomial mathematic model.
Table 3. LiFePO4 battery pack charging trace constant voltage method.
Paramet ers
order Voltage(V) Current(A) Req(ohm) Rin(Ohm)
113.2 2.8 4.71 4.54
213.0 2.7 4.81 4.74
313.0 2.9 4.48 4.41
412.9 3.1 4.16 4.09
512.9 3.3 3.91 3.84
612.8 3.3 3.88 3.81
712.8 3.5 3.66 3.59
812.8 3.6 3.56 3.49
912.4 3.5 3.54 3.47
10 11.7 3.4 3.44 3.37
11 11.5 3.4 3.38 3.31
12 11.1 3.3 3.36 3.29
13 10.7 3.3 3.24 3.17
It can be seen from Table 4 that the results of the polynomial calculated by the relative error
formula (5) and the measured internal resistance of the battery are within 2.21% which the
maximum difference value is 0.07ohm and REV%is 2.21%, and the minimum difference
value is only 0.01ohm and REV%is 0.26% and the total average REV%is 1.41% , so it can
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MATEC Web of Conferences 185, 00004 (2018) https://doi.org/10.1051/matecconf/201818500004
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value o f the battery, as shown in equation (4). Using the relative error REv% as sho wn in
equation (5) to confirm the accuracy of the mathematical model and the Table 4 is shown in
the table for each voltage class approaching the battery block internal resistance and
relative error.
Rin=a0+a1
×
V+a2
×
V2+ a3
×
V3(4)
where
Rin: internal resistance of battery pack
V: discharging voltage
%100
,
|,,|
%×
−
=
actualRin
fitRinactualRin
RE
V
(5)
where
Rin, actual: internal resistance of battery pack which equal to Rin
Rin, fit: internal resistance approach by polynomial mathematic model.
Table 3. LiFePO4 battery pack charging trace constant voltage method.
Paramet ers
order Voltage(V) Current(A) Req(ohm) Rin(Ohm)
113.2 2.8 4.71 4.54
213.0 2.7 4.81 4.74
313.0 2.9 4.48 4.41
412.9 3.1 4.16 4.09
512.9 3.3 3.91 3.84
612.8 3.3 3.88 3.81
712.8 3.5 3.66 3.59
812.8 3.6 3.56 3.49
912.4 3.5 3.54 3.47
10 11.7 3.4 3.44 3.37
11 11.5 3.4 3.38 3.31
12 11.1 3.3 3.36 3.29
13 10.7 3.3 3.24 3.17
It can be seen from Table 4 that the results of the polynomial calculated by the relative error
formula (5) and the measured internal resistance of the battery are within 2.21% which the
maximum difference value is 0.07ohm and REV%is 2.21%, and the minimum difference
value is only 0.01ohm and REV%is 0.26% and the total average REV%is 1.41% , so it can
be resulted, the calculation result of formula (3) is very close to the actual value of internal
resistance of battery pack. Figure 4 is relative error chart by polynomial mathematic model.
Table 4. The relative error by polynomial mathematic mode l.
Paramaters
order Voltage(V) Rin,actual
(ohm)
Rin,fit
(ohm) Rev%
113.2 4.64 4.59 1.08%
213.0 4.26 4.31 1.17%
312.9 4.09 4.02 1.71%
412.8 3.81 3.80 0.26%
512.4 3.47 3.44 0.86%
611.7 3.37 3.32 1.48%
711.5 3.31 3.24 2.11%
811.1 3.29 3.23 1.82%
910.7 3.17 3.10 2.21%
average 1.41%
Fig. 4. The relative error chart by polynomial mathemat ic mode l.
4Conclusions
For the actual circuit design to do charge and discharge test obtained the battery pack
voltage, resistance and other parameters and to determine which each other dependency.
And deduce the battery internal dynamic resistance and in order to other applications before
the lead operations. In t he charging mode, when the charging voltage is fixed that result of
the battery voltage, current and internal resistance are closely related to each other.
V
%
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MATEC Web of Conferences 185, 00004 (2018) https://doi.org/10.1051/matecconf/201818500004
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Similarly, in the discharge mode is also the same. In the discharge mode, the battery
internal resistance and the battery potential can be approximated by the mathematical
model o f t he third-order polynomial to the internal resistance of the battery pack and obtain
its value. Through the every voltage level to statistics the total relative error is 1.41%. In
this article, through the relevant simple circuit can be accurate and quickly know the
dynamic resistance of the battery pack and the relevant internal resistance and electricity
residue of battery pack.
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