3rd International Conference on Electrical, Electronics, Engineering Trends, Communication Optimization and Sciences (EEECOS)-2016
Comparative Study of Charging and Discharging Characteristic
of Ni-Mh, Li-ion, and Lead Acid Battery
Prashant Shrivastava1
M. Saad Alam2
Yasser Rafat3
M. Tech Student,
ZHCET, AMU, Aligarh, India
prashant90616@gmail.com
Associate Professor
Electrical Engineering Department,
Faculty of Engineering,
ZHCET, AMU, Aligarh, India
Assistant Professor
Mechanical Engineering Department,
Faculty of Engineering,
ZHCET, AMU, Aligarh, India
Keywords: Battery, Charging, Discharging, Charging
Methods, XEV, Battery Management system (BMS).
Abstract
With the regards to the exponential upsurge in energy demand
and greenhouse gas emissions from the conventional vehicles,
the Indian government has been undertaken numerous steps for
sustainability in the field of transportation such as FAME-India
mission. According to FAME India mission, 0.2 million
electric vehicles would be on the road by 2020. The storage
system has been the major roadblock in the development of
electric vehicle and plug-in electric vehicle. Most of the
technologies associated with storage systems are still under
development. In this research work a simulation model for the
charging and discharging of lithium-ion (Li-ion), Nickel-metal
hydride (NI-Mh) and Lead acid has been developed. For their
charging and discharging hardware demonstration analysis
also carried out. Comparative study of said batteries has also
been performed.
1 Introduction
Electrified Transportation has been the most viable solution to
achieve clean and eco-friendly nature which is crucial to the
sustainable development as well as human health. In
forthcoming days, XEVs i.e. numerous kind of electric and
hybrid electric vehicle will capture the clean and efficient
transportation market.
Each day more and more electric vehicles are being unified into
the utility grid. Their impacts include are fluctuating load on
the grid which leads to the frequency regulation problem,
fluctuation in voltage profile, and load mismatching.
Currently, nickel metal hydride (NI-Mh) and lithium ion (Liion) are two battery technologies being used in XEVs as energy
storage system. While, in most of HEVs NI-Mh batteries, are
being use due to the mature technology. Now-a-days for XEVs
Li-ion battery are gaining more popularity because of higher
specific energy as well as higher energy density. XEVs
batteries are very much different from the batteries which are
being used in consumer electronic devices such as laptops and
calculator and mobile phones etc. XEVs batteries are made up
of high power in few of kW with higher in storage capacity in
the order of 10 kWh under within a limited space and light
weight [1].
Along with the electrical performance such as energy capacity,
fast charging and slow discharging the safety and limited space
and economical as well as financial aspects of the said batteries
are also being considered. Even after a rapid growth in the
technology development the cost of energy storage in XEVs
i.e. batteries is still high. Currently, Li-ion batteries have the
most attractive chemistry, first and foremost due to strict
requirements in power and energy [2].
Numerous combinations of electrochemistry for the
development of Li-ion batteries have been designed
concerning the cost and safety factor, electrical performance
and life cycle. Due to fast development of the technology
related to the battery such as NI-Mh, Lead acid, Li-ion and
others the cost of said batteries has been reduced up to 35%
from the last decade [3-4].
Flooded lead-acid batteries have been known as cheapest in
concern with cost factor. While, Deep-cycle lead type batteries
are most expensive as well as short life cycle than the XEVs
other components, they need to be replaced after three years
[5]. The lead-acid battery is the most developed technology and
is being use in the most of the XEVs. Higher availability rate,
the lower cost makes it more favourable. Sulphur, oxygen, and
hydrogen content generally emitted from the charging and
discharging process of said batteries, which normally are
harmless in nature. Being most developed Lead-acid batteries
which are capable of driving up to 130 km for each charge [6].
After the Lead acid, NI-Mh batteries are also more developed
as compared to other batteries. NI-Mh batteries are being used
in the large numbers of PHEVs such as Toyota. NI-Mh
batteries are less efficient (60–70%) than lead-acid. While, it
has the higher energy density of 30 to 80 Wh/kg. But the Liion battery has higher energy density than NI-Mh batteries.
They are also characterized by the absence of memory effects
and low self-discharge rate. [7]
Traditionally the Li-ion batteries are being manufactured by
using cobalt oxide cathode system and graphite as an anode.
Having energy density 200 Wh/kg and 80 to 90 % charging as
well as discharging efficiency. The new developed Li-ion
battery technology having the capability to drive 320 to 480
km in a single charge [8].
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3rd International Conference on Electrical, Electronics, Engineering Trends, Communication Optimization and Sciences (EEECOS)-2016
The cost of Li-ion batteries is a function of its size, battery
capacity, and materials. About 75% of total cost comes from
material requirement. While manufacturing cost is only 5%
and another miscellaneous cost is approx. 20% [9].
The relationship between the state of charge (SOC) and open
circuit voltage (OVC) is non-linear in nature. As in the cell, the
concentration of polarization and discharge current increases
the voltage drop increases due to the internal resistance of the
battery, due to increases in the voltage drop the discharge
capacity of the battery decreases and the discharge rate
increase. [10].
The lithium ion diffusion rate depends on upon the temperature
and the temperature rise increases discharge capacity. [11]
Temperature is one of the most factors behind the degradation
of battery life and operation performance, and existing Battery
Management System (BMS) have thus employed simple
thermal management policies so as to prevent battery cells
from very high and low temperatures which will likely cause
their explosion and malfunction, respectively. If we use a more
accurate and adaptive abstraction model instead of the
fundamental model of the current version, the performance
would be enhanced [12].
In the large size of battery packed the cells are very close to
higher energy density, in this case, in order to monitor the
battery system the number of thermostats also increases.
Online applicable temperature prediction model for xEV
battery pack while minimizing the number of sensors and
keeping the monitoring capability [13]. Based on the particular
condition, different approaches should be applied in order to
improve the performance of BMSs in future xEVs.
Figure 1: Voltage and Current waveform of constant voltage
charging
Figure 2: Voltage and Current waveform of constant current
charging
2.3 Constant Voltage-Constant Current Charging
In constant voltage - constant current charging methods as
discussed in, both voltage across and current the battery
terminals is kept constant, throughout charging process. Proper
charging time mainly depends on discharge rate of a battery
[14].
2.4 Two Step Constant Voltage Charging
2 Charging Methods
In this section various kind of charging method has been
investigated such as constant voltage charging, constant
current charging, Constant Voltage-Constant Current
Charging, Two Step Constant Voltage Charging, Trickle
Charging, Float Charging and Multi-step Constant Current
Charging.
In two-step constant voltage charging, as presented in [14],
two-step constant voltage charging method uses two paths for
charging the battery. The method consists of two charging
voltage levels. Firstly the battery is charged at a high voltage
level. When the battery voltage reaches a specific/desired
potential level, charging voltage is reduced to a lower level and
is then charged for a longer time.
2.5 Trickle Charging
2.1 Constant Voltage Charging
In constant voltage charging method, the voltage across battery
terminals are kept constant throughout charging process as
shown in figure 1 [14]. Initially, in this process, current flows
towards battery from power source/charging source is
relatively higher than flow in the latter hours. This is mainly
due to charge accumulation in battery and reduction in the
potential difference between voltage levels of battery and
charging source.
2.2 Constant Current Charging
In the constant current charging method as shown in figure 2,
current to charge the battery kept constant. If the charging
current is too high, the stress on the electrode increases.
In trickle charging method, the small current is constantly
supplied to a battery with a small duty cycle [14]. This type of
charging is required for those batteries that are used for backup
when the normal power supply gets cut. The small current is
just used to compensate the self-discharge that occurs in
batteries.
2.6 Float Charging
In float charging, batteries are connected in parallel with load
and power supply [14].The power supply provides the load
with required voltage and current ratings and at the same time,
some of the voltages and currents are consumed by the
batteries. Just as the main power supply gets interrupted, the
batteries supply power to the load.
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3rd International Conference on Electrical, Electronics, Engineering Trends, Communication Optimization and Sciences (EEECOS)-2016
2.7 Multi-step Constant Current Charging
Multi-step Constant Current charging as shown in figure 3
provides a higher charging current until a certain voltage is
reached and reduce the current level step by step during the
later charging period. These hybrid or multi-steps charging
techniques are useful for fixing the problem suffered in
constant voltage or constant current charging method [14].
Cell Type
Ni-Mh
Lead acid
Li-ion
Gravimetric
Density(Wh/kg)
Volumetric
Density(Wh/L)
Self-discharge
@20 ͦ C
(%/month)
Internal
resistance
(mΩ/V)
Cycle Life(80%
discharge)
Self-discharge
@Room
Temperature
(%/month)
60-120
30-50
90-250
180
100
210
20-30
3-20
5-10
33-50
Less than
8.3
6.6-42
300-500
200-300
500-2000
Up to 20%
Up to 5%
Full
discharge
every 90
days when
full use
Thermally
Stable,
Fuse
protection
Moderate
3-6
Months
(toping
charging)
Less than 5%
(Protection
circuit
consumes
3%/month)
Maintenance
Free
Maintenance
Requirement
Figure 3: Voltage and Current waveform of multi-step constant
current charging method
There are another two types of charging methods: pulse
charging and reflex charging as shown in figures 4 and 5.
Safety
Requirement
Cost
Thermally
stable
Protection
circuit
mandatory
Low
High
Table 1: Comparison of Ni-Mh, Lead Acid and Li-ion battery
4 Simulation and Experimental Result
Figure 4: Pulse Charging
Figure 5: Reflex Charging
3 Comparison of Battery Characteristics
The electrical characteristics of a battery define how it will
perform in the circuit and the physical properties have a huge
impact on the overall size and weight of the product that it will
power. The key properties and specifications for Lead-acid, NiMH, and Li-Ion have been presented in Table I for easy
comparison.
To study the charging and discharging characteristics of energy
storage system in XEVs, NI-Mh, Li-ion, and Lead Acid battery
are investigated. Simulation has been carried out using
Matlab/Simulink tool and simulation results of charging and
discharging characteristic of said batteries are shown in figure
6 to 11. The hardware required for performing the experiment
has been tabulated in Table II. The experimental setup is shown
in figure 12. The experiment was performed in the NonConventional lab of Electrical Department-Aligarh Muslim
University. Copious methods of charging has been discussed
in section II. In the performed study, constant voltage method
was chosen to charge the batteries. The charging and
discharging characteristic of said batteries are shown in figure
13 to 17, in order to achieve the discharge characteristic a
resistive load of 5.3 ohms was used. From the figure of 6 to 11,
it is observed that SOC increases during charging and
decreases during discharging. For the same load resistance of
5.3 ohms, the rate of discharge is different for said batteries.
From figure 14, 16 and 18 it can observed that the initial
discharge rate of NI-Mh battery is much higher than Lead Acid
and Li-ion battery. After some discharge time, the discharging
rate of Lead Acid battery becomes higher than NI-Mh and Liion battery. This happens due to different internal resistance
profiles of said batteries during discharging of the said
batteries. From the figure 13, 15, and 17 it can be observed
that the charging rate of Lead Acid battery is slower as
compare to NI-Mh and Li-ion battery. It is also observed that
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3rd International Conference on Electrical, Electronics, Engineering Trends, Communication Optimization and Sciences (EEECOS)-2016
the charging rate of Li-ion battery is higher than the NI-Mh and
Lead Acid battery.
Time (Seconds)
Time (Seconds)
Figure 6: 12V and 6.4Ah NI-Mh Battery Discharging
Characteristics for RL=5.138Ω
Figure 8: 12V, 7.2 Ah Lead Acid Battery Constant voltage
Charging Characteristics at 14.5V
Time (Seconds)
Time (Seconds)
Figure 7: 12V, 6.4Ah NI-Mh Battery Constant voltage
charging Characteristics at 14.5V
Figure 9. 12V, 7.2 Ah Lead Acid Battery Discharging
Characteristics for RL=5.138Ω
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3rd International Conference on Electrical, Electronics, Engineering Trends, Communication Optimization and Sciences (EEECOS)-2016
During the charging of batteries, the battery SOC changes with
the time. As shown in figure 7, the 12V and 6.4Ah NI-Mh
battery SOC change from 20% to 90% in 2000 seconds during
constant voltage charging. As shown in figure 8, the 12V, 7.2
Ah Lead Acid Battery SOC change from 20% to 100% in 2000
seconds during constant voltage charging. As shown in figure
10, the 14.8V, 8.0Ah Li-ion Battery SOC change from 20% to
100% in 3500 seconds during constant voltage charging. In all
the cases, the initial charging current is high but as the battery
SOC reaches to its final value i.e. 100%, the charging current
decreases exponentially and finally reaches to minimum value.
S. No
1
2
3
4
5
7
Equipment
NI-Mh battery
Li-ion Battery
Lead
Acid
Battery
Multimeter
Clamp meter
Battery Charger
8
Rheostat
Range/Specification
12V,6.4Ah
14.8V,8Ah
12V,7.2Ah
0-100V
0-10 A
230V AC input,6V-12V24V-48V DC output
0-10 ohm, 10 A
Table 2: Hardware required to perform the experiment
Time (Seconds)
Figure 10: 14.8V, 8.0Ah Li-ion Battery Constant voltage
charging Characteristics at 17V
Figure 12: Experimental Setup
15
00:00:00
00:15:00
00:27:00
00:39:00
00:54:00
01:19:00
01:46:00
02:01:00
02:53:00
04:24:00
06:40:00
12:11:00
Charging 10
voltage
(V) and 5
current
0
(A)
Charging time(min)
battery charging current
battery voltage
Time (Seconds)
Figure 11: 14.8V, 8.0Ah Li-ion battery discharging
characteristics for RL=5.138Ω
Figure 13: 12V, 6.4Ah NI-Mh battery Constant Voltage 14.5V
charging Characteristics
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3rd International Conference on Electrical, Electronics, Engineering Trends, Communication Optimization and Sciences (EEECOS)-2016
Discharging time(min)
battery charging current
battery voltage
Discharging voltage(V)
and current(A)
8
10
Dischargin 8
g voltage 6
4
(V) and
current (A) 2
0
6
4
2
0
Discharging Time (min)
Discharging Voltage
Charging voltage(V)
and current(A)
Figure 14: 12V, 6.4Ah Ni-Mh
characteristics with RL=5.3 ohm
battery
Figure 18. Lead Acid battery discharging characteristics 7.6V,
4.5Ah with RL=5.3 ohm
15
4 Conclusion
10
5
0
Charging Time (min)
Charging Voltage
Charging Current
Figure 15: 14.8V, 8Ah Li-ion battery Constant Voltage 16V
charging characteristics
Discharging voltage(V)
and current(A)
Discharging Current
discharging
20
15
Electric vehicle (EV) is a very promising technology for
reducing the environmental impacts road transportation sector.
Energy storage system is a pivotal component of PEVs.
Comparative study of NI-Mh, Li-ion, and Lead Acid battery
has been a part of the presented study. To charge the said
batteries constant voltage method is chosen. Li-ion and NI-Mh
are charged by C/5 rating while the Lead acid battery is
charged by C/10 rating. It is observed that Lead acid is sluggish
and cannot be charged as quickly as other battery systems and
also Lead acid battery have better self-discharge characteristic
than NI-Mh. The terminal voltage of Li-ion and NI-Mh found
more stable than the Lead acid battery. From table- I, it is
concluded that Li-ion has most favourable performance.
Acknowledgements
10
5
0
Discharging time(min)
Discharging Voltage
Discharging Current
Charging voltage(V) and
current(A)
Figure 16: Li-ion battery discharging characteristics 14.8V,
8Ah with RL=5.3
8
6
4
2
0
Charging Time (min)
Charging Volatge
The authors are gratefully acknowledges the NonConventional Energy (NCE) laboratory and Research
laboratory of Department of Electrical Engineering, Zakir
Hussain College of Engineering & Technology, Aligarh
Muslim University, Aligarh, India for providing hardware
experimental facilities.
Charging Current
Figure 17: Lead Acid battery Constant Voltage 7.6V charging
characteristics 6V, 4.5Ah
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3rd International Conference on Electrical, Electronics, Engineering Trends, Communication Optimization and Sciences (EEECOS)-2016
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