In-depth analysis on thermal hazards related research trends about lithium-ion batteries: A bibliometric study

Highlights

• Advanced bibliometric tools are used to access appropriate database for thermal hazards related publication about LIBs.

• Key information about the collected publications is visualized and analyzed.

• Thermal failure propagation in LIB modules/packs is identified as the recently hot topic.

Abstract

Lithium ion batteries (LIBs) play an ever-increasing role in our daily life due to their excellent energy storage performance. However, the thermal hazards of LIBs, occasionally accompanied with fires or explosions, are also severe and worrying issues, which have been concerned by numerous scholars for decades. This paper aims to perform a macroscopic bibliometric reivew on publications related to the thermal hazards of LIBs to date. A total of 826 relevant publications are retrieved from the Web of Science Core Collection database in the period of 1996–2019. A bibliometric study of research on thermal hazards of LIBs is conducted by means of visualization software VOSviewer and CiteSpace. The results are analyzed from the perspectives of the annual publications, countries, institutions, authors, terms, and references. As a result, the analysis presents networks of geographical and institutional cooperation, co-authorship, terms co-occurrence, and co-cited references, as well as corresponding clusters, indicating their contributions to the publications on thermal hazards of LIBs. The results provide a comprehensive overview on the evolution of research hotspots in this domain and can help those researchers who are willing to engage in this research field to quickly understand the research frontier and overall situation.

Introduction

In 2019, the Nobel Prize in Chemistry has been awarded to John B. Goodenough (USA), M. Stanley Whittingham (UK) and Akira Yoshino (Japan) for their original contributions to lithium-ion batteries (LIBs). Since the first LIB cell was commercialized by Sony Corporation in 1991, billions of LIBs have been produced and applied for portable electronics and various other large electric devices due to their high energy density and efficiency, and lack of a memory effect compared with other cell chemistries [1], [2], [3], [4]. Each LIB cell mainly contains four components, i.e. cathode (typically as a lithium metal oxide), anode (most commonly carbon), electrolyte (lithium salt dissolved in an organic solvent mixture), and separator (a thin layer of porous polymer) [5]. The lithium ions move from cathode to anode during charging, and this process is reversed during discharging to drive the electrical devices. Thus, the LIB cell is also termed as “rocking-chair battery” since the lithium ion moves back and forth between anode and cathode during charge-discharge cycles [6]. As a renewable energy storage system, the LIB plays an increasingly important role in modern society, most specifically in the development towards energy sustainability [3]. Based on the technical and economic indicators, lithium ion batteries are the primary choice for renewable energy vehicle and play a key role in assuring national energy safety [7,8]. However, the continuously emerging fire and explosion accidents caused by the LIBs also attract extensive public attentions [9], [10], [11].

In fact, the probability of failure of LIB cells is estimated to be one in 40 million if they are stored and operated within the manufacturer-recommended limitations [1]. At the same time, LIBs have some conspicuous defects such as narrow operational temperature range (20~40 °C) [12] and charge/discharge rates [13,14]. Once subjected to abnormal environments including thermal abuse (overheating and fire exposure), electrical abuse (overcharge / overdischarge and external / internal short circuit), and mechanical abuse (crash, penetration and bend) [1], LIBs are readily to irreversibly fail through a rapid self-heating or even thermal runaway, which in turn leads to fire and explosion, posing treats to surrounding cells or facilities. Specifically, the thermal runaway of LIBs encompasses three self-propagating steps along with the increasing temperature of the LIB: (1) The anodic reactions start at about 80~90 °C, and the decomposition of the solid-electrolyte interphase (SEI) layer intensifies as the temperature rises above 120 °C; (2) After reaching above 140 °C, exothermic reactions at the positive electrode begin; (3) The cathode decomposes and the electrolyte becomes exothermically oxidized at the onset temperature larger than 180 °C, yielding a high temperature rise rate of more than 100 °C per minute [4, 15]. As a result, the LIBs can release a significant amount of energy in the form of heat, simultaneously ejecting a large amount of flammable electrolytes, cathode and anode materials accompanied with jet fires or explosions [16].

In order to achieve high power requirements, multiple LIB cells are combined together to form a module, and multiple modules can be assembled as a battery pack [17]. In such arrays, thermal hazards of an individual battery can be sufficient to trigger the thermal runaway of adjacent cells. The thermal hazards will be exponentially magnified with a domino effect during the failure propagation within the pack [18], [19], [20], [21], [22], [23], which is a highly hazardous phenomenon referred to as cascading failure [24], [25], [26].

Given the severe consequences caused by the LIBs undergoing thermal runaway, considerable research effects have been dedicated to understanding energetics of the thermally-induced failure of LIBs [5]. Accelerating Rate Calorimetry (ARC) [27], [28], [29], [30], Differential Scanning Calorimetry (DSC) [31], C80 calorimetry [32,33], modified bomb calorimetry [16], Copper Slug Battery Calorimetry (CSBC) [24], [25], [26], and cone calorimetry based on oxygen consumption principle [34], [35], [36] are employed to measure the total (inside and outside) energy release. It is indicated that the parameter of the LIB such as states of charge (SOCs), cathode chemistries, and electrolytes significantly affect its ignition time, burning rate, heat generation or fire load [34,[37], [38], [39]]. Meanwhile, the thermal runaway propagation through the whole battery module or pack are also experimentally investigated by many researchers [18], [19], [20], [21], [22], [23], [24], [25], [26]. It is found that the heat release by module or pack is not simply the sum of combustion heat of each single battery, but is exponentially increased with the cell number [40]. However, due to the difficulties and expenditure of conducting full-scale LIB fire tests, investigations of macroscopically thermal failure propagation of bulk packed cells especially large pack conditions are still relatively scarce, and need further examinations.

With the development of LIB, its thermal hazards are continuously concerned, and a large number of articles are published to investigate this issue and put forward possible solutions, forming a huge knowledge network. Although some excellent reviews [[1], [2], [3], [4], 8, 10, 11] on this theme can be found in the literature, there is no macroscopic overview of the existing works to visualize their intellectual structure. Bibliometrics is a mature research method based on the retrieved literature and can be employed to analyze their key information such as source journals, prolific countries, organizations, and etc. in a certain domain [41, 42]. The relevance between documents and the research trends can be revealed by analyzing the connections among titles, abstracts, keywords, and references. It has the potential to provide a systematic, transparent, and reproducible review process, and thus improve the quality of review [43]. At present, the bibliometrics becomes a popular method in identifying and predicting the development tread of science and technology using mathematical, statistical, and other measurement methods [44]. In the field of safety research, it has been used to investigate various research topics, such as the domino effect in the process industry [45], forest fires in tropical rainforests [46], pool fires [47], process safety [48], natural hazards, emergency, and disaster management [49,50]. At the same time, this method has been employed to analyze the energy and fuels research in many countries such as China [48,[51], [52], [53], [54]], Spain [55], Japan, and Korrea [54]. The bibliometric techniques and methods have been comprehensively applied in the analysis of research topics associated with different hazards or energy and fuels, while such studies are still scarce in LIB research.

From the above, due to the importance of research on thermal hazards of LIBs from either a safety or security perspective, this paper attempts to use the bibliometric and visualization methods to systematically examine all the relevant publications included in the Science Citation Index Expanded (SCI-Expanded) database. The objective of this work is therefore to evaluate the research on this topic, seeking to provide a structural overview of available publications and identify the potential or possible research areas in the future.