Technical Assessment of Reusing Retired Electric Vehicle Lithium-Ion Batteries in Thailand

Abstract

A rapid growth in electric vehicles has led to a massive number of retired batteries in the transportation sector after 8–10 years of use. However, retired batteries retain over 60% of their original capacity and can be employed in less demanding electric vehicles or stationary energy storage systems. As a result, the management of end-of-life electric vehicles has received increased attention globally over the last decade due to their environmental and economic benefits. This work presents knowledge and technology for retired electric vehicle batteries that are applicable to the Thai context, with a particular focus on a case study of a retired lithium-ion battery from the Nissan X-Trail Hybrid car. The disassembled battery modules are designed for remanufacturing in small electric vehicles and repurposing in energy storage systems. The retired batteries were tested in a laboratory under high C-rate conditions (10C, 20C, and 30C) to examine the limitations of the batteries’ ability to deliver high current to electric vehicles during the driving operation. In addition, the electric motorcycle conversion has also been studied by converting the gasoline engine to an electric battery system. Finally, the prototypes were tested both in the laboratory and in real-world use. The findings of this study will serve as a guideline for the sorting and assessment of retired lithium-ion batteries from electric vehicles, as well as demonstrate the technical feasibility of reusing retired batteries in Thailand.

1. Introduction

Humanity is currently facing global environmental concerns, including environmental problems, the energy crisis, and global warming. The fundamental source of these issues is the ecological imbalance caused by human activity. As a result, many countries are becoming aware of the issues and the need for sustainable development. The advancement of electric vehicles (xEVs) has received significant attention as a major global trend [1,2]. The purpose of employing xEVs instead of internal combustion engine vehicles (ICEVs) has two key aspects: the first is to reduce the use of fossil fuels, which are not renewable sources. Based on current consumption levels, the worldometer predicts that oil and natural gas will run out within 47 and 53 years, respectively [3]. The second is to minimize greenhouse gas emissions and other combustion caused by the use of fossil fuels, which are most likely the main contributors to global warming, climate change, pollution, and health problems. The International Energy Agency’s (IEA) Stated Policies Scenario (STEPS) estimates that by 2030, the entire fleet of xEVs (excluding two- and three-wheelers) will reach 240 million, with total xEV sales exceeding 20 million and 40 million in 2025 and 2030, respectively [4]. Furthermore, xEVs are projected to account for one-quarter of the worldwide road transport fleet by 2040 [5].

Thailand has also taken part in this environmental policy. The Thai government has adopted a strategy to encourage the Thai automotive industry to transition to a new era of electric power, which is one of Thailand’s target S-curve industries. According to data from the Electric Vehicle Association of Thailand (EVAT) [6], the number of newly registered electric vehicles of all sorts (battery electric vehicles (BEV), hybrid electric vehicles (HEV), and plug-in hybrid vehicles (PHEV)) increases every year, with over 300,000 vehicles accumulated. Assuming an 8-year battery life [7,8] and a lithium-ion battery (LiB) energy usage of 50 kWh/vehicle for BEVs and 1 kWh/vehicle for HEVs and PHEVs, the number of retired LiBs might total 1.6 GWh by 2030. Therefore, the government must implement an efficient and comprehensive management strategy for retired electric vehicle batteries after their first-life application, which includes investment policy, the domestic market, infrastructure, and academic research on reuse and recycling technologies.

xEVs are being developed to reduce greenhouse gas emissions and fossil fuel consumption; however, the rapidly increasing number of xEVs worldwide raises concerns about the environmental impact of battery waste and energy consumption during charging. The improper handling of end-of-life batteries may result in environmental problems similar to those previously encountered. After their initial use, retired LiBs can be managed through three basic technologies: disposal, recycling, and reuse [9,10,11,12,13]. The retired LiBs with poor quality have to be adequately landfilled to avoid environmental contamination. If valuable materials can be recovered from the retired LiBs, then recycling is a viable option. However, if the battery retains over 80% of its original capacity and the battery packs/modules meet the electric vehicle requirements, they can be remanufactured for automotive applications. If not, the battery, which has a capacity of 60–80%, can be repurposed in energy storage systems. As a result, the reuse approach is regarded as the most effective method for increasing the value chain of LiB and extending its lifespan [14]. The life cycle assessment was studied to compare the environmental impact of using the repurposed LiBs and the new lead-acid batteries in conventional energy storage systems for communication base stations [15]. It is found that the use of repurposed materials can reduce the environmental impact in all categories except metal depletion. This is due to the high recovery rate of lead components from lead-acid batteries. Currently, the recycling efforts of end-of-life LiBs are insufficient to match the recovery rate of lead-acid batteries. This is the main reason why the study of retired LiBs technology has received more attention in the past decade. In some cases, the use of retired batteries instead of new batteries has no significant environmental benefits but can slow down the growth of waste batteries in the near future. For example, the study of the battery storage system in a six-flat residential building with a total area of 477 m² and an average electricity consumption of approximately 25,000 kWh/year [16]. It is demonstrated that employing five used batteries offers the same energy functionality as using four new batteries, but the two systems provide comparable environmental assessments. However, it is expected that extending battery life to 8–10 years should be enough time to develop recycling technology and facilities. Other factors, such as the combination of renewable energy sources with repurposed LiBs [17,18,19], the study of degradation and end-of-life conditions that affect the battery’s first life [20,21,22], or the fast performance test strategy for retired LiBs [23], have also been theoretically and experimentally studied in order to improve environmental sustainability and economic values. In reality, examples of the second-use application of LiBs include:

• The retired Toyota Camry Hybrid battery packs were used to store energy generated from solar panels to power a cluster of buildings in a remote part of Yellowstone National Park [24];
• The use of second-life Nissan Leaf batteries in factory-automated guided vehicles to deliver parts to workers in a car factory [25];
• The repurposed Nissan Leaf batteries were used to replace lead-acid batteries in the emergency power supply unit at the Atago railroad crossing on the Joban line [26].

This work presents the technical assessment of reusing retired electric vehicle LiBs in appropriate applications in Thailand. The paper is organized as follows: Section 2 covers preliminary screening and electrical test techniques [27,28,29]. This section also includes the battery management system (BMS) used in this work. The prototype battery designs for electric golf carts, electric motorbikes, and energy storage systems, as well as laboratory and real-world testing results, are shown in Section 3. Finally, the conclusion is given in Section 4.

2. Methods

2.1. The Retired Electric Vehicle Battery

The retired LiB used in this work is an HPB04-56A power-type battery dismantled from a Nissan X-Trail Hybrid car. As shown in Figure 1, a battery pack comprises four modules, each containing 14 single cells connected in series. According to the battery cell specifications in

Table 1. Battery specification details for HPB04-56A from a Nissan X-trail hybrid car [30].

Item	Specification
Size (mm)	40$\varnothing$ × 92
Weight (kg)	0.26
Average voltage (V)	3.6
Capacity (Ah)	4.4
Output density (W/kg)	3000
Energy density (Wh/kg)	61

, the energy of a battery module is 222.04 Wh and 888.16 Wh for a single pack. Prior to the evaluation, the retired battery pack was disassembled into individual modules, which were then subjected to three stages of testing as follows:

Step 1: The battery modules undergo a visual inspection to ensure that they are suitable for their secondary usage, which involves a physical examination to detect any signs of cracking, deformation, bulging, liquid leakage, or unclean marks on the modules.

Step 2: The modules undergo safety and health checks through voltage, capacity, and internal resistance testing as part of the performance assessment (Figure 2). Only the battery modules that meet the required criteria are retained for reuse, while those that do not are recycled to retrieve valuable materials.

For the capacity test, a constant current test is conducted on the module using the ITECH IT6000C Series bidirectional DC power supply at a 1C rate with a 2-h rest period or battery temperature at steady state. The charge stage was started with a constant current profile until the voltage reached 4.2 V (as specified in Table 1), and then continued with a constant voltage profile. When the current change is less than C/50 (88 mA), the process will be terminated. In the discharge stage, the voltage and current were recorded every second until the voltage dropped below 2.5 V. The results were used to calculate the capacity of the battery.

The BK Precision Battery Analyzer BA6011 and Battery Impedance Meter BT4560 were used to conduct the internal resistance test. The internal resistance of the battery module is measured using BA6011, while the internal resistance of the cell with a voltage less than 5 V is measured using BT4560.

Step 3: The state of health (SOH) of the selected modules is determined by calculating the ratio between the full charge capacity and the initial charge capacity (as indicated by the manufacturer). SOH is a crucial parameter that reflects a battery’s energy and power delivery capabilities and is used to evaluate the suitability of a retired battery module for a second-life application. Generally, the estimated SOH of a battery is defined as the ratio of the present capacity ($C_i$) to the nominal capacity ($C_0$) [31,32]:

$$SOH=\frac{C_i}{C_0}\times 100\%$$

(1)

If SOH > 80% (remanufacturing), batteries will be reconditioned and repacked for reuse in electric vehicles such as electric cars, electric motorcycles, electric bicycles, and electric golf carts;

(2)

If SOH = 60–80% (repurposing), batteries will be repacked for reuse in energy storage systems connected to alternative energy sources (solar, wind) or uninterruptible power supplies (UPS). It should be noted that the batteries used in this project are power-type batteries, suitable for repurposing;

(3)

If SOH < 60% (recycling), batteries will be sent to the recycling stage for the recovery of valuable materials. The two main recycling technologies used for LiBs are pyrometallurgical and hydrometallurgical processes [33]. However, Thailand is not ready in terms of recycling technology and infrastructure. The collection, separation, and sorting of battery wastes are not properly managed, so reuse technology would be the best solution for battery management in Thailand.

2.2. Smart BMS

Designing a battery management system (BMS) to control battery performance is one of the most critical steps for retired battery reuse. In practice, the built-in BMS given by the battery manufacturer can be used in the second-use application if the whole battery packs are repurposed as the energy storage system and the battery voltage is equivalent to the voltage of the inverter. However, in this study, the battery pack was disassembled into four separate modules and used in three different applications. As a result, an appropriate BMS for reuse applications must be designed to replace the built-in BMS (Figure 3). A 48 V-100 A DALY BMS was selected to regulate battery performance, with its functionality controlled through a free application supported by the BMS manufacturer. To connect the new BMS to the battery modules through the voltage acquisition wires, we have to use the connector of the built-in BMS (the green connector in Figure 3) because this connector fits perfectly onto the battery board. Therefore, it is necessary to weld the voltage acquisition wires of the built-in BMS and the new BMS together by using shrink soldering tubes. As demonstrated in Figure 3, the voltage acquisition wires will have a built-in BMS connector (green) on one end and a new BMS connector (white) on the other. Each module has its own BMS, and 14 s BMS wires were used to individually control the voltage of each cell. The standard specification for BMS should include:

• Charging current: 50 A; discharging current: 50–300 A;
• Balance current: 200 mA;
• Voltage accuracy: error within 3 mV.
• Drop wire protection: detect wires that do not weld well, causing the wrong voltage;
• Overcharge/over-discharge protection: can be connected to Bluetooth to set up high-precision detection voltage;
• Short circuit protection: can be connected to Bluetooth to set the short circuit protection value;
• Overcurrent protection: can be connected to Bluetooth to set up the overcurrent protection value (maximum 300 A);
• Temperature control protection: prevent high-temperature danger.
• The user can monitor the battery’s status using the following channels:
• Using a Bluetooth module to access a mobile application;
• Using RS485 or CANBUS to communicate with the inverter;
• Using RS485 or CANBUS to connect computer programs to BMS;
• Connecting to the touch screen;
• Connecting to the Coulomb meter (Figure 4) to display the state of charge.

Figure 3. Built-in BMS produced by the battery manufacturer and shrink soldering tube.

Figure 3. Built-in BMS produced by the battery manufacturer and shrink soldering tube.

Figure 4. Coulomb Meter.

Figure 4. Coulomb Meter.

3. Results and Discussions

After LiBs reach the end of their first life in electric vehicles, they can be reused in less stressful scenarios if they meet the requirements of the secondary application. Therefore, this section is divided into two main parts. The first part presents the performance test results, showing the electrical parameters of the retired battery. The second part provides examples of possible second-life applications in Thailand.

3.1. Performance Test

In this work, forty battery modules were obtained by disassembling ten retired LiB packs. As part of the preliminary test, the voltage of disassembled modules was measured. As shown in Figure 5a, the results indicate that the voltage of each module in the same retired battery pack is approximately the same. After performing the capacity test and resting the battery module for one month, the voltage of the cells was measured once again. One module was chosen randomly from each battery pack, and the voltage of all cells in that module was measured. The box plot in Figure 5b shows that the voltages of cells in the same module are similar, indicating cell voltage balance.

3.1.1. Capacity Test

The battery modules were tested for 60 s under a high C-rate discharge profile (10C, 20C, and 30C) to examine their ability to deliver energy in high-current situations, which are the dynamic conditions of EVs (golf carts and motorbikes) during the diving operation. As the nominal capacity is 4.4 Ah, we determine the current discharge of −50 A, −100 A, and −150 A, corresponding to the C-rate of 10C, 20C, and 30C, respectively. The results show that the module with 100% SOC (Figure 6a) can provide energy at 10C and 20C while maintaining the voltage above the cut-off level of 35 V. However, if the initial SOC is less than 100% SOC, as shown in Figure 6b for 63% SOC, the module would be unable to produce energy for the entire 60 s period of 20C discharging because the voltage would reach the cut-off voltage. For discharge rates over 30C (Figure 7), a discharged current of 150 A with a time period of 100 s causes a rapid voltage decrease from 58 V to 35 V.

3.1.2. Internal Resistance Test

The internal resistance of the battery was measured at two levels: the module level using the BK Precision Battery Analyzer BA6011 and the cell level using the Battery Impedance Meter BT4560. The cell’s internal resistance is found to be roughly 1.4993 Ω. One module is composed of 14 cells connected in series, with a resistance of 1.4993 × 14 = 20.9902 mΩ. This calculated module resistance is consistent with the measurement obtained from the BA6011 test.

3.2. Second Life Application

As mentioned earlier, the secondary usage of retired LiBs can be categorized into two categories based on the battery’s state of health (SOH): (1) electric vehicles and (2) energy storage systems. A prototype product was developed using ten battery packs (40 modules) donated by the Department of Primary Industries and Mines (DPIM). Following the capacity test, the module with the lowest performance is chosen and sent to the recycling process, while the remaining 39 modules are employed for second-life applications. The specifics are as follows:

3.2.1. Remanufacturing

Electric golf cart: the 6-seater A4 + 2 electric golf cart (Figure 8), initially powered by six 8V-150Ah batteries connected in series, was replaced with eight retired battery modules connected in parallel, resulting in an energy capacity of 1.76 kWh. The number of retired battery modules used was determined by the size of the golf cart’s battery compartment, which needed sufficient space between each module to disperse heat. This is because higher temperatures can reduce battery performance and lifespan. The output power of batteries also varies with temperature [30]. As a result, this 6-seater A4 + 2 electric golf cart has eight battery modules (Figure 8, right).

The eight retired battery modules have a capacity of 35.2 Ah and an operating voltage ranging from 42 to 58.8 V. If the voltage falls below 42 V, the drive circuit will be disabled, and the golf cart will not be able to operate. In addition, the onboard charger was upgraded to a maximum current of 30 A, increasing the total energy capacity to 1.76 kWh. An alternative way to charge an electric golf cart is wireless technology, which is a trend in the future [34]. The battery can be charged in approximately 1 h and 10 min, and the golf cart can run for around 11 km (on regular roads) with a maximum current of 150 A. The details are presented in

Table 2. Performance test of electric golf cart.

Quantity	Test #1	Test #2	Test #3
Initial Capacity (Ah)	35.0	34.0	35.0
Final Capacity (Ah)	4.4	5.6	4.1
Initial Voltage (V)	58.0	56.5	58.0
Final Voltage (V)	43.5	41.8	43.1
Distance (km)	11.68	10.85	12.38
Time (min)	67.40	58.65	49.90
Average Velocity (km/h)	10.4	11.1	14.9
Maximum Velocity (km/h)	25.3	25.2	25.2

.

Electric motorcycles: an electric motorcycle was fitted with two retired battery modules with an energy capacity of 0.44 kWh. This can be accomplished in two ways: A swapping E-bike is one that replaces the original battery in an electric motorbike with a retired battery, while a conversion E-bike is one that converts a gasoline engine to an electric battery. In the case of the conversion E-bike, the motor and gasoline tank must be replaced with the motor control and batteries illustrated in Figure 9. The retired batteries obtained from DPIM have a voltage of 48 V and an energy capacity of 0.22 kWh, which is the most important characteristic to consider in design. Batteries can be connected in series, parallel, or combined to alter the voltage and energy capacity. For instance, two modules can be connected in series to raise the operational voltage of electric motorcycles from 48 V to 96 V.

The main components of an electric motorcycle are:

(1)

Motor: The power rating is a crucial factor to be considered. Commercial motors are available in three sizes: 1 kW, 3 kW, and 5 kW, with varying voltage levels. In this project, a motor with a power rating of 3 kW and a voltage of 96 V was chosen.

(2)

Motor control equipment: also known as the control box, must have the same power rating and voltage as the motor.

(3)

Battery: The 3 kW motor was chosen in this work, which has an operating voltage ranging from 72 V to 96 V. To achieve a voltage of 96 V, two retired battery modules connected in series, each with a voltage of 48 V, were used. If more energy is required, two series-connected battery modules can be added in parallel to the original set. The distance or duration of use will be determined by the amount of energy stored in the battery.

Converting a gasoline-powered motorcycle into an electric motorcycle:

In this project, the Honda Scoopy I motorcycle (Figure 10, top left) was chosen for modification because its structure allows for battery installation (Figure 10, bottom left). The modification procedure is divided into two stages. The first is a structural change, which is the installation of the swing arm. Considering that the original wheel was attached to the engine, which was the main portion of the motorbike, when the engine and original wheel were removed, a swing arm was required to retain the motor wheel (Figure 10, right). The electrical alteration is the second. The electrical circuit was connected to the battery and motor via the control box.

To evaluate the battery performance of a swapping e-bike, the two modules were fully charged (100% SOC), and a cut-off SOC of 30% was set. The average fully charged time was around 30 min. On a single full charge, the e-bike could travel a distance of around 6 km at an average speed range of 20–24 km/h. The working status of each module, including voltage, current, and temperature, could be monitored in real-time via a smartphone application (Figure 11). For a conversion E-bike, the dyno test was performed to measure the engine’s torque and rotational speed. The engine speed was accelerated to 100 km/h, with a maximum power of 16.4 HP at 35 km/h and a maximum torque of 260 Nm at 75 km/h. The maximum current consumption of 120 A was observed (Figure 12).

3.2.2. Repurposing: Energy Storage System

This study employed 29 retired battery modules for the uninterruptible power supply (UPS) system, as shown in Figure 13 Each module consists of 14 battery cells with a voltage of 48 V, a capacity of 61.6 Ah, and a maximum current output of 150 A. However, in practical applications, a maximum current of 50 A is required. In addition, there must be features on the BMS to protect the battery, such as:

• Standard charge control circuit;
• The board should be waterproof and capable of charging and discharging over the same line;
• The board should support the voltage and current that can be delivered based on the battery’s properties;
• Over-charge protection function;
• Over-discharge protection function.

A system diagram is presented in Figure 13, where a bidirectional inverter with a 48 VDC–220 VAC configuration was connected to the battery and the power grid. The bidirectional inverter enables direct current (DC) to flow back and forth to the battery, allowing surplus electricity from the power grid to be fed to the battery for charging. During a power outage, the electricity stored in the battery is delivered to the load. The UPS was tested by connecting a 1–4 kW load and measuring the voltage and current in each case. Figure 14 depicts the voltage and current of the electrical grid and load. It is observed that the battery can provide electricity to the load instantly, in less than 20 ms after the power grid is turned off, as shown by the reduction of load voltage and current at 150 ms.

Figure 13. Battery prototype for use in uninterruptible power supplies (UPS).

Figure 13. Battery prototype for use in uninterruptible power supplies (UPS).

Figure 14. Voltage and current of 4-kW load connected to a UPS.

Figure 14. Voltage and current of 4-kW load connected to a UPS.

4. Conclusions

Three primary ways to manage retired batteries, including remanufacturing, repurposing, and recycling, were analyzed based on the remaining capacity or battery health. This study focuses on exploring the reuse of retired electric vehicle LiBs in Thailand, with a particular emphasis on remanufacturing and repurposing techniques. The retired LiBs from Nissan X-Trail Hybrid cars were implemented to construct the prototype batteries for small electric vehicles (remanufacturing) and energy storage systems (repurposing). Through the performance test, the battery pack was disassembled into module and cell levels, and all disassembled modules were electrically tested under standard conditions to evaluate the SOH of the battery modules. The ten best battery modules (high SOH) were remanufactured in the electric golf cart (eight modules) and motorcycle (two modules), while the rest were repurposed in the uninterruptible power supply (UPS) system. The prototype batteries were successfully tested at laboratory scale and in practical use, demonstrating the technical feasibility of technologies for reusing retired LiBs in Thailand.