The controlled release of active substance from one-dimensional inorganic nanocarrier for the stability enhancement of lithium batteries
Graphical abstract
Introduction
As an essential part of energy storage systems, lithium rechargeable batteries are widely used in our everyday life. There is also an urgent demand for high-energy-density batteries for global needs for the electrification of transport. For example, rechargeable battery packs should achieve densities of approximately 235 Wh kg−1 to accommodate a driving range of 500 km in an electric vehicle (EV) to succeed conventional car with an internal combustion engine. However, the energy density of state-of-the-art automotive lithium-ion battery (LIB) packs shows about 130–140 Wh kg−1 [1]. In this regard, the new energy storage devices with alternative battery chemistry, including lithium metal battery, lithium-sulfur battery, lithium-oxygen battery, and all-solid-state lithium battery, are suggested to surpass the energy density of the conventional lithium rechargeable batteries [2], [3], [4].
However, the new energy storage devices, which use lithium (Li) anode, severely compromise the cycle life in favor of a high energy density due to the instability of battery components. During the charge-discharge process, complications such as dendritic Li growth and various uncontrolled electrochemical reactions at the Li metal surface unavoidably emerge, which may cause low cycling stability and poor safety issue [3], [5]. Since the mid-2010s, several methods have been explored to stabilize the Li anode, including the use of novel liquid electrolyte systems [5], fabricating protective coating [3], the modification of anode morphology [6], the use of the solid electrolytes [4], the use of the 3D framework [7], employing a functional separator [8], and introducing functional additives [9].
Among the approaches, the formation of artificial SEI (Solid electrolyte interphase) via an appropriately selected functional additive provides a straightforward but practically formidable route that decelerates the decomposition of battery components, especially during the early stage of cell operation. Therefore, by establishing the long-term functionality of the additive, the artificial SEI is anticipated to retain its real-time protective properties over the Li surface, thus preserving the battery’s performance levels. However, the viscosity increase and resulting ionic conductivity decrease, and additive integrity maintenance limit the amount of additive in cell assembly [10], [11]. It is anticipated that a prolonged supply of the additive overcoming the initial temporary treatment of additive in a conventional system can enhance the long-term stability of the high-energy-density batteries. Since the higher amount of additives are consumed to establish robust SEI at the first several cycles, and the continuous repairing of SEI follows with the lesser amount of additive, it requires a challenging, sophisticated method.
Recently, an initial approach to combine sustained release system with Li battery system has been proposed [12]. The method utilized the limited solubility of LiNO3 in the carbonate electrolyte, where the passive release takes place when the dissolved LiNO3 is consumed. Although this proved the effectiveness of the continuous supply of LiNO3 additive in improving the battery's performance, the system has drawbacks in the additive selection and active control of amount release that has limitations in providing broader solutions for various additives.
When the human body is treated for a certain period of time through drug administration, multiple-dosage (e.g., three times a day) are generally an integral part of the treatment. It maintains the drug concentration between the minimum toxicity level and the minimum effective concentration [13]. Multiple dosages inevitably cause fluctuations of the active substance concentration in plasma resulting in unwanted side effects or diminishing the intended therapeutic benefit to the patient.
A controlled release system (CRS) is a sophisticated treatment method that can deliver the therapeutic dosage of the drug over an extended period of time, with a single dose (Fig. 1a) [13]. CRS provides a plethora of advantages, including the enhancement of therapeutic performance, easy control of administration period, prevention of side effects, enhanced drug stability efficiency, improved patient compliance (due to fewer administrations), and the reduction of the treatment cost [13], [14]. As such, they have been widely commercialized and systematically used for delivering medical agents, such as vaccines, hormones, and nucleic acids [14], [15]. The realization of a CRS largely depends on the appropriate selection of carriers and active substances [15], [16]. On a related note, the CRS approach of enveloping the active substance in a carrier is achieved either by coating or encapsulation [13].
Inspired by the feature of CRS, the treatment for a certain period of time by multiple dosing, which cannot be possible in a completely assembled device, can be realized in the energy storage devices. By adjusting CRSs to operate in conjunction with energy storage devices, it is projected that a new platform capable of extending the cycle life of next-generation energy systems will be created. It is vital to optimize the selection of the carrier, as well as control release behavior, thus restricting the establishment of CRSs in the advanced battery system.
Herein, the effective combination of a CRS with an energy storage device (Fig. 1b) was achieved and systemically demonstrated. To investigate their synergistic functionality, an encapsulation system with the appropriate specifications was initially designed and fabricated by choosing functional additive as active substance and one-dimensional inorganic nanotube as carrier material. Next, the method for evaluating the accumulative active substance release in the environment of energy storage systems was determined and calibrated by using gas chromatography. LiNi0.6Mn0.2Co0.2O2 (NMC622)/Li cell was chosen as a model energy storage device to evaluate the effect of CRS in the Li rechargeable battery. The electrochemical performance of the battery, along with the robust SEI formation, was studied and elucidated. Furthermore, the potential of the scalability of CRS of this work to various additives was also confirmed using a different type of model additive.
Section snippets
Preparation of polyethyleneimine (PEI) coated halloysite nanotubes (HNTs)
The as-received HNTs (Sigma-Aldrich) were calcinated in a tube furnace at 400 °C at a heating rate of 10 °C min−1 under an argon atmosphere with a constant flow rate of 1 L min−1 to remove the physically combined water and volatile impurities then cooled to room temperature in a desiccator. 1.0 wt% polyethyleneimine (PEI, Mw = 800, Sigma-Aldrich) in methanol solution was prepared to coat the HNT surface (HNT:PEI = 1:0.03, based on wt.%). 1.0 g of HNTs were immersed in 3.0 g of 1.0 wt%
Results and discussion
In this work, we selected vinylene carbonate (VC), an extensively applied additive for Li battery system, as an appropriate active substance to explore the concept of a CRS for energy storage devices. Numerous researchers have confirmed the film-forming properties of VC additive on both anode and cathode [11], [17], [18], [19]. It was reported that an abundant (>5%) amount of VC led to improved cycle performance in Li metal batteries through the continuous VC decomposition at the surface of the
Conclusions
In summary, we successfully developed a novel approach of fusing the controlled release systems typically used in biotechnology applications with energy storage devices, resulting in the enhancement of the stable cycle performance. GC analysis confirmed that the selected active substance and carrier, namely vinylene carbonate and halloysite nanotubes, respectively, successfully demonstrated the expected release behavior. Our CRS significantly improved the performance of NMC622/Li cell, by
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement
This work was supported by the National Research Foundation of Korea (NRF) granted Mid-Career Research Program (No. 2018R1A2B6003422) and Electronics and Telecommunications Research Institute (ETRI) grant funded by the Korea government [21ZB1200, Development of ICT Materials, Components and Equipment Technologies].
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These authors contributed equally to this study.