**3. Motivation of using RLIB**

Demand for urban vehicles focusing on sustainable transportation has prompted a substantial trend towards automotive electrification such as hybrids and EVs. With more than 70% of EVs likely to be introduced in 2015 with Li-ion based battery chemistry, the recycling of Li-ion has become a crucial topic in the automotive industry. When the battery packs in a lithium-ionpowered vehicle are deemed too worn out for driving, they still have up to 80% of their capacity left. Before they ever arrive in a recycling center, these batteries are used to prop up the grid, especially alongside energy sources that may not be quite as steady, such as wind or solar power

**Figure 5.** About 8 hectares huge space in the second deck of aeration tank in Dihua plant.

**Figure 3.** Reused Lithium-ion battery used in pure electric vehicles (left: LiFePO<sup>4</sup>

**Figure 4.** Flowchart of RLIB.

, right: LiMnNiCoO<sup>2</sup>

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).

**Figure 3.** Reused Lithium-ion battery used in pure electric vehicles (left: LiFePO<sup>4</sup> , right: LiMnNiCoO<sup>2</sup> ).

**Figure 4.** Flowchart of RLIB.

**Figure 2.** Potential renewable energies in Dihua WWTP.

**Figure 1.** Unsteady renewable energies in Dihua WWTP.

166 Energy Systems and Environment

Demand for urban vehicles focusing on sustainable transportation has prompted a substantial trend towards automotive electrification such as hybrids and EVs. With more than 70% of EVs likely to be introduced in 2015 with Li-ion based battery chemistry, the recycling of Li-ion has

**3. Motivation of using RLIB**

**Figure 5.** About 8 hectares huge space in the second deck of aeration tank in Dihua plant.

become a crucial topic in the automotive industry. When the battery packs in a lithium-ionpowered vehicle are deemed too worn out for driving, they still have up to 80% of their capacity left. Before they ever arrive in a recycling center, these batteries are used to prop up the grid, especially alongside energy sources that may not be quite as steady, such as wind or solar power (**Figure 2**). Furthermore, the cost of RLIB is roughly cheaper than 1/3 of a new battery. This merit enhances strong competition compared with other cheap flow batteries or NAS batteries.

**5. Development of EMS**

gaining life cycle.

time of the lower arm of the switch module.

To reduce the peak current in LIB pack, a physical battery is employed in LIB effectively, but range extension is still limited in the case study [33]. The effect of life cycle extension is discussed [34] by the transient supply of physical battery. Given the traditional large DC/DC converter in EMS, a small prototype of DC-DC and simple circuit may be proposed to isolate the battery pack and not harvest energy from random peak power [35, 36]. The scenarios of usage cover the regenerative power supply and charging/discharging between individual and physical batteries. Some studies have focused on the design of levering DC-DC converter [37, 38], but several researchers have introduced a converterless circuit in EVs based on a DC inverter [39, 40]. The literature implies the possibility of EMS with high efficiency and low cost. Specific control strategies including neutral networks are illustrated in [40–42]. Economic analysis shows that the high price of LIB leads to superior benefits in elongating life cycle. Real-time simulators are a powerful platform before on-board tests [42]. In [43], a simple circuit of elongating life cycle life was reported. Without a complex DC-DC converter, only duty control using a suitable physical battery can narrow DoD of LIB and elongate the life cycle of batteries [44–48]. **Figure 6** shows the relationship between DoD and life cycle. None of the lines in **Figure 8** are linear, thereby indicating that DoD plays a major role in

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**Figure 7** shows a simple, converterless parallel circuit. EMS can achieve active control by switching the discharging ratio between LIB and auxiliary physical battery at unit time. The architecture of EMS is shown in **Figure 8**. It is modified from battery management system. EMS is disposed as an interface among RLIB, auxiliary physical battery (ultracapacitor, UC), and systematic grid. The control strategy aims to keep the switch periodically close and open by a predetermined duty cycle, namely, the sharing ratio of RLIB's loading controlled by EMS. In detail, EMS generates a PWM (pulse width modulation) signal to control the on/off

**Figure 6.** Relationship between DoD and charge/discharge cycles (life cycles) modified from [49].

For instance, two packs of RLIBs are shown in **Figure 3**. Both of them are originally applied in pure EVs. After working for several years, they are used as experimental targets before cycling and recuperation by chemical method. In this study, two different types of packs are selected. The flowchart in **Figure 4** shows that suitable cells are activated and selected based on log file and DC internal resistance, and each new module is assembled with EMS. Subsequently, the module is installed in a test bench to update voltage of open circuit (VOC). In addition to establishing water, energy, and reusing nexus in urban areas, the Dihua WWTP is chosen for its large area of 8 hectares. Thus, an extensive enclosed space is available for placing RLIB between the aeration tank and green park in the ground (**Figure 5**).
