https://orcid.org/0000-0002-6120-7510
Abstract
The ceiling of energy density of batteries in materials level motivates the innovation of cell, module and pack that constitute the battery assembly for electric vehicles (EVs). Patent analysis is a powerful means to inform technology life cycle and forecast upcoming innovations. To date, only a handful of research have quantitatively analysed and compared battery assembly in the EV field, resulting in a lack of information to discern the battery layout. Herein, battery patents are categorized into cell, module and pack levels, and are recorded with a function of timeline and technology life cycle to identify their development status. It indicates the maturity stage of the cell level while noting the growth stage of module and pack levels, which probably results from the intensive demand of large-size and high-quality batteries for EVs. Moreover, the global patent distribution reveals that China and Japan possess most patents among cell, module and pack levels, and that patent assignees are scattered in China, whereas concentrated in Japan and Korea. This work is expected to figure out the battery technology trends to construct energy-dense batteries in the EV field, as well as provide instructive information for decision-makers to lay out battery technologies in the future.
1 INTRODUCTION
High-performing lithium-ion (Li-ion) batteries are strongly considered as power sources for electric vehicles (EVs) and hybrid electric vehicles (HEVs), which require rational selection of cell chemistry as well as deliberate design of the module and pack [1–3]. Herein, the term battery assembly refers to cell, module and pack that are sequentially assembled for EV fields. The individual electrochemical cell can be applied in portable electronics such as cellphones, cameras and laptops [4, 5]. Once high power and energy capability are demanded in specific scenes, like solar energy storage panels, automotive starter devices and energy storage devices for small electric vehicles, electrochemical cells shall be connected in parallel, series or both, to form modules by integration of additional cell monitoring and temperature control [6, 7]. The EV fields need substantial increase in cell quantity to provide sufficient power/energy output, and hence modules have to be integrated into the battery pack to achieve multiple purposes in terms of safe, lasting and reliable properties [8, 9]. This cell–module–pack (CMP) pattern is the conventional scheme to enlarge energy storage.
Enhancing the battery integration efficiency from cell to pack is an effective avenue to boost battery energy density in the pack level. The conventional CMP pattern only realizes ~60%, indicating the significant mass and volume portion of auxiliary parts in the entire battery system [2, 10]. Therefore, a body of battery and automobile companies has explored the integration mode to tap the potential of batteries. For example, in 2019, Contemporary Amperex Technology Co., Limited (CATL) proposed the CTP (Cell-to-Pack) mode [11]. This pioneering concept skips the module and directly integrates the pack by the cell, by which the integration efficiency increases up to 70–75%, while the manufacturing cost is significantly reduced [12]. Another successful CTP mode that omits the module is called ‘Blade Battery’, proposed by BYD in March 2020 [13, 14]. This battery pack consists of a unique dimensional cell (L × D × H = 905 × 13.5 × 118 mm) that is inserted into the battery pack like a ‘blade’, which increases the volumetric energy density by 50% and reduces the cost by 30% [11, 15]. Tesla proposed the Cell-to-Chassis (CTC) mode that embeds 4680 cells into the chassis, which have the advantages of reducing battery weight and improving overall battery capacity, leading to an increase of driving range by 14% and reduction of cost by 7% [16, 17]. All these innovations reveal the significance of battery integration in improving spatial usage, reducing costs, enhancing production efficiency and strengthening safety operation. Therefore, the analysis and tracking of technical trends of cell, module and pack not only provide informative indications for innovation of the battery integration mode, but also offer opportunities for manufacturers and governments to lay out well the future landscape of battery technologies.
(a) Schematic illustration of battery assembly from cell to module and pack. (b) The number of patents as a function of timeline for battery assembly.
Effectively collecting information of battery technologies is the first step to analyse, group, evaluate and forecast battery integration mode. It is estimated that patents contain >90% technical information and that effective use of patents would shorten 60 and 40% of research and development (R&D) time and cost, respectively [18, 19]. Patent analysis has been used to evaluate technology flow and track technological evolution in the energy sector [20]. In the EV field, a patent is majorly applied to analyse trends of prospective EV types and battery technologies [21, 22], such as positive/negative electrode materials and electrolytes [23, 24]. However, there are limited reports to explore the battery assembly of cell, module and pack, as well as to compare them by considering the technology life cycle and distribution among global enterprises based on patent analysis. Saw et al. [25] investigated the integration issues of the EV battery pack from different aspects, namely battery assembly, thermal management, monitoring and control, services and maintenance. Golembiewski et al. [26] analysed the battery value chain of EVs based on patent activities. The battery value chain starts with the extraction and processing of raw materials to synthesize cell components, and then different components are assembled into cells and are further packed into battery packs.
In this contribution, patent analysis is applied to systematically study battery assembly from cell to module and pack, and figure out their technology life cycles aiming at revealing their development status. It is indicated that the cell level has entered the maturity stage, whereas module and pack levels are still in the growth stage. In addition, the patent distribution among global regions reveals that China and Japan possess most patents among cell, module and pack levels, and that patents from Chinese companies are more scattered, whereas patents from Japanese and Korea companies are concentrated. This work is expected to provide instructive reference for decision-makers of companies and government.
2 METHODOLOGY
The data source used in this study is based on the Derwent Innovation Index for the patent search due to the wide coverage of 110 million patents from nearly 61 patent issuers globally, which facilitates retrieval and avoids duplication [27, 28]. The patent search in this work was ended on 2 February 2023 and covers global patents for battery assembly including cell, module and pack. To ensure the integrity and applicability of patent data for subsequent analysis, the meaningful patent data are before 31 December 2020 because there is an 18-month lag period for patent disclosure. Therefore, the patent data after 2020 cannot exactly reflect the patent trends of battery assembly.
The cell, module and pack were selected for patent analysis. To accurately acquire the patent quantity, a set of search criteria are made based on battery keywords and International Patent Classification (IPC) codes. Firstly, we limited the search items in lithium battery fields by setting the search formula of TS = (cathode OR (positive AND (electrode OR active material OR pole material))) AND TS = (lithium OR lithium-ion OR (lithium w5 ion) w5 (cell% OR secondary batter* OR batter* OR accumulator OR rechargeable batter*))). After that, IPC codes and keywords are used to update the search items. The IPC codes include H01M (processes or means, e.g. batteries, for the direct conversion of chemical into electrical energy) and H02J (circuit arrangements or systems for supplying or distributing electric power; systems for storing electric energy). The keywords contain cell, module and pack.
The number of patents as the function of patent assignees for (a) cell, (b) module, (c) pack levels. (d) Timeline of technology life cycle for the battery assembly.
Because the term ‘lithium-ion batteries’ was not recorded until the commercialization of Li-ion batteries by Sony, we combined the formula of TS = (cell% OR secondary batter* OR batter* OR accumulator OR rechargeable batter*), IPC code and keywords to search for patents, and then manually added these patents in corresponding battery levels. We consequently obtained the number of patents for cell (23 178), module (6711) and pack (13 488).
3 RESULTS AND DISCUSSION
Figure 1 schematically presents the battery assembly for EVs. Such conventional CMP pattern results in a low integration efficiency, with 40% reduction of energy density from CTP levels [2]. Therefore, many leading companies around the world have been devoted to innovations of battery integration modes, such as CTP, CTC and cell to body (CTB) [11, 29] to efficiently reduce the auxiliary parts. Patent applications in the cell level can be tracked back to the 1980s [30]. The development of Li-ion batteries can be divided into three stages based on the patent quantity versus year, as shown in Figure 1b. The first stage is basically from 1980 to 1990, during which <10 patents per year appeared, and it is in the emerging stage of technology. The milestone discoveries in this period included the concept of rechargeable batteries (titanium disulfide cathode paired with lithium metal anode) proposed by Whittingham [31], star cathodes of lithium cobalt oxides (LiCoO2) [32] and lithium manganese oxides (LiMn2O4) [33] discovered by Goodenough. These pioneering discoveries laid a critical foundation for future commercialization of Li-ion batteries.
The cell, module and pack were developed rapidly in the second stage from 1991 to 2006, with an average annual growth rate of 33%. The speedy development originated the stimulation of the first commercial Li-ion secondary batteries that could be repeatedly charged and discharged. After that, these companies established close cooperation with upstream and downstream companies of the industrial chain and achieved high automation. Moreover, the rise of Internet Technology (IT) between 1995 and 2002 prompted the portable electronics that are ubiquitously powered by Li-ion cells [34]. With the saturation of the portable electronics market, there was a slight decline for the single-cell level. The power sources of global new energy vehicles were in the uncertainty stage before 2006. In this stage, many countries put emphasis on developing hydrogen fuel cells as the power source. [35]. Since 2007, with strong government subsidies and support, many countries have established clear road maps for EVs, with a focus on Li-ion batteries. From then on, R&D of Li-ion batteries entered an accelerated stage [36].
The third stage was from 2006 to 2020, during which the patents of cell, module and pack surged profoundly, especially for the cell level. Such high enthusiasm in cell-level research was aided by the smart mobility revolution and energy revolution, which are featured by further exploration of cathode and anode materials for EV markets. The year 2011 is considered to be the first year of an era of EVs, thereby offering an opportunity to strongly demand for high-performance modules and packs and thus resulting in encouraging battery design and related patents in module and pack levels.
Technology life cycle theory is derived from industry life cycle theory and is primarily used to construct technology projections [37]. Herein, the technology life cycle can be reflected by the number of patents per year as the ordinate, with the number of assignees per year as the abscissa. Foster proposed four stages of technology life cycle including the emerging stage, the growth stage, the maturity stage and the saturation stage [38]. Figure 2a–c shows the technology life cycle of cells, modules and packs based on the patent quantity as a function of patent assignees, respectively.
(a) Patent distribution of the battery assembly in different regions. Patent layout of top 10 assignees for (b) cell, (c) module and (d) pack.
The densely distributed patents of cell, module and pack from 1980 to 1990 imply their emerging stage. In this period, Goodenough proposed LiCoO2 in 1980, and the first commercial Li-ion batteries were produced in 1991 [30, 32]. After 1991, the Li-ion batteries characterized by light, high energy density and non-memory effect quickly dominated portable electronics markets [5]. The prevailing cell prototypes, such as cylindrical, prismatic and pouch cells, are proposed and produced to meet various requirements of electric bicycles and medical equipment [39–41]. The demand of high-energy and high-power battery systems provides a chance to develop the module and pack, whereas the patent quantity was still <10 annually before 2010, signifying the emerging stage for module and pack.
Li-ion batteries with higher energy and power densities are steeply increased in accordance to the wide spread of bigger electronics due to the maturity of popular cathode materials, such as LiCoO2, LiMn2O4 and nickel cobalt manganese ternary oxides (NCM). The number of patents and assignees for module and pack has been continuously increasing since 2000, with an annual growth rate of >10%. The collective data inform that the cell level has entered maturity stage, whereas module and pack are in the growth stage. When technology enters the mature stage, the number of companies entering this field is reduced due to market saturation, and only a few companies continue to engage in technology research in this field, leading to a slower growth rate of patent application. Figure 2a shows that the quantities of patents and patent assignees for cell reduced from 2017 to 2018, indicating that the technical development of cell is gradually maturing, and that the companies engaged in research in this field tend to be stable. The module and pack designs have received widespread attention from research institutions and companies. The technology life cycle of cell, module and pack are schematically summarized in Figure 2d.
Patent distribution across the world is a critical signal to evaluate the superiorities of regional technology and market development status. Figure 3a shows the top five regions that hold global patents in cell, module and pack, with the sequence of China, Japan, the USA, Korea and the European Union (EU). Specifically, China and Japan account for dominant quantity over other regions. Such patent distribution is probably attributed to the wide spread of EVs and related production chains [42]. Before 2000, Japan and the USA dominated the Li-ion batteries due to prosperous markets in electronics, which fostered a number of big companies such as Sony, Asahi Chemical and General Motors. Japan has conducted early and rapid research in the field of Li-ion batteries, but was gradually surpassed by China lately at least in part ascribed to the rapid growth of the EV market in China. Compared with other regions, although EU countries lag behind in the field of Li-ion batteries, they hold plentiful patents in the battery assembly for EVs. As a giant in the automotive industry, the first patent applied for by Bosch from Germany for cell and module was as early as 2006, and the battery pack was dated back to 2005. Therefore, EU countries attach great importance to cooperation with global new-energy companies in battery R&D, such as Bosch and Japan’s Gsyuasa battery company, which have reached a partnership to focus on the manufacturing of efficient and lightweight Li-ion batteries.
Figure 3b–d displays the global top 10 assignees that hold battery patents in cell, module and pack. Overall, LG Chem is the leader in R&D on batteries from cell to module and pack. The superiority of LG Chem in this field can be attributed to the early investment in Li-ion batteries in consumer electronics since 1995 and quickly entering this market through high-quality battery products [43]. Lately, LG Chem switched its research trend to EV batteries and became the battery supplier for Tesla, General Motors and Ford Motor [44, 45]. Samsung is another large battery company in Korea besides LG Chem. Although there are only two companies from Korea to enter the top 10 assignees, they have a total global share of 66.9, 76.3 and 80.9% for cell, module and pack, respectively, indicating that Korean companies have the leading R&D for battery assembly.
Aside from Korean companies, Japanese companies also account for a significant portion of battery assembly, such as Toyota, Hitachi, Panasonic, Nissan, Sanyo, Sony, Daikin and Toshiba. Among them, Toyota and Hitachi are representative companies, and they both enter into the top 10 assignees in the design of battery assembly. The patents from Japan are also concentrated in these leading companies. On the contrary, China ranks first in the total number of patents for battery assembly. However, only two companies (CATL and Guoxuan High Tech) and just one company (CATL) are listed in the top 10 assignees in the battery module and pack, respectively. There are no companies from China to enter the top 10 battery assignees in the cell level. This patent distribution shows that R&D of battery assembly is rather scattered in China. The broad adoption of EVs endows Chinese companies with high enthusiasm in the design of module and pack, as manifested by the proposed conception of CTP and CTB [11, 29].
As one of the earliest countries to develop Li-ion battery technology, the USA has original patents of Li-ion batteries for cell and module. The core patent (WO9740541-A1), applied for by the Goodenough team in 1997, has been cited 436 times, becoming the highest cited patent worldwide. However, in the following decade after the commercialization of Li-ion batteries, the USA focused on hydrogen fuel cells and does not sufficiently support R&D for EVs [46]. In addition, the hollowing out of the US manufacturing industry and the increasing cost of global production have collectively made it difficult to extend the application of Li-ion batteries [47]. In the battery pack level, US companies collaborate with companies of other countries, leading to a relative decline in R&D activities and reduced patent quantity [48].
4 CONCLUSIONS
EVs have entered in the era of Li-ion batteries, and the battery integration mode has played a critical role in determining driving range and safety of EVs. Further increase of battery energy density principally relies on innovations of cell, module and packs. This work analyses the patent trends by recording patent quantity with a function of timeline and technology life cycle. The cell has fallen into the maturity stage, whereas module and pack are in the growth stage, indicating the strong demand of large-size and high-quality batteries for EVs. The patent distribution of battery constitutions reveals that China and Japan possess large quantities of patents among all cell, module and pack levels. However, the patents from Chinese companies are more scattered, evidenced by only two companies entering in the top 10 assignees, whereas patents held in companies from Japan and Korea are concentrated. This work is expected to provide instructive information for decision-makers to lay out battery technologies and to forecast technology trends for the design of energy-dense batteries.
Acknowledgements
This work was supported by the Shaanxi Provincial Philosophy and Social Science Research Project (2023QN0169) and National and Regional Research projects of Ministry of Education (2021-G37). We also appreciate data collection and insightful discussions from Ms. Xin-Yu Mu.
Data Availability
The data that support the findings of this study are available from the corresponding author upon reasonable request.
