Mapping the trends and prospects of battery cathode materials based on patent landscape

Abstract

Advancing portable electronics and electric vehicles is heavily dependent on the cutting-edge lithium-ion (Li-ion) battery technology, which is closely linked to the properties of cathode materials. Identifying trends and prospects of cathode materials based on patent analysis is considered a kernel to optimize and refine battery related markets. In this paper, a patent analysis is performed on 6 popular cathode materials by comprehensively considering performance comparison, development trend, annual installed capacity, technology life cycle, and distribution among regions and patent assignees. In the technology life cycle, the cathode materials majorly used in electric vehicle have entered maturity stage, while the lithium cobalt oxide (LCO) cathode that is widely used in portable electronics is still in the growth stage. In global patent distributions, China holds more than 50% of total patents. In the top 10 patent assignees of 6 cathode materials, 2 institutes are from China with the rest being Japan (6) and Republic of Korea (2), indicating that the technology of cathode materials in China is relatively scattered while cathode research is highly concentrated in Japan and Republic of Korea. Moreover, the patent distribution has to consider practical issues as well as the impacts of core patents. For example, the high cost discourages the intention of applying international patents. This paper is expected to stimulate battery research, understand technical layout of various countries, and probably forecast innovative technology breakthroughs.

Graphical abstract

Keywords

patent analysis / cathode / batteries / technology life cycle

1 Introduction

Lithium-ion (Li-ion) batteries have been widely used in portable electronics and on-road transportation in response to the attempt of diminishing or curtailing fossil fuel emissions that are partially released by internal engineering conversion vehicles [1–3]. The surging of battery electric vehicles (BEVs) is enabled by ever-advancing battery technologies, which is considered as a game-changing power source to drive further development of BEVs [4–6]. It is estimated that in the entire cost of BEVs, the battery pack accounts for 30%–40%, of which cathode materials occupy 40% [4,7]. The key role and high cost of cathode materials endow them with superior consideration in the design of battery pack and BEVs.

Pushing the cathode materials toward commercialization is a holistic consideration in terms of safety, capacity, potential, stability, and sustainability [8,9]. Whittingham and coworkers developed the first rechargeable Li-ion battery prototype by employing titanium disulfide (TiS₂) cathode and lithium metal anode [10], but the low operation voltage of cathode and intrinsic dendrite growth incurring hazardous safety issue discourage their prospects in wide applications [11]. In 1980, Goodenough pioneeringly reported layer-structure lithium cobalt oxide (LiCoO₂, denoted as LCO) as cathode, laying a solid foundation for high-performing cathode materials due to the superior cyclability and rate capability [12]. The first commercialized Li-ion battery was then realized by Sony Corporation in 1991, and successfully applied in portable electronics in view of lightweight, energy dense [13], non-memory effect compared with lead-acid and nickel-cadmium batteries [14].

Before LCO entered the market, Goodenough group discovered a spinel structure lithium manganese oxide (LiMn₂O₄, denoted as LMO) cathode in 1983, featuring the low cost, high-power density, and long-term cycling stability [15]. However, the structure distortion during operation and poor cycling stability at elevated temperature (> 55 °C) restrain their commercial application [16,17]. In 1997, Goodenough and coworkers proposed a new cathode material based on the olivine structure, with a formulation of LiFePO₄ (denoted as LFP) [18]. The LFP does not enter the market of portable electronics due to inferior energy density. However, these cathode materials are popularized after approximately 10 years in the automotive field attributed to ultra-stable cyclability, superb thermal stability, and abundant materials sustainability [19]. Despite of its mild energy density, LFP cathode is still prevalent and pursued by BEV makers through assembly of module and pack optimization [20].

Another breakthrough in cathode materials is the discovery of layer-structured ternary material, with a formulation of Li[Ni_0.8Co_0.15Al_0.05]O₂ (denoted as NCA) and Li[Ni_1−x−yCo_xMn_y]O₂ (0 < x < 1, 0 < y < 1, denoted as NCM) by Matsubara et al. in 1998 [21] and Liu et al. in 1999 [22], respectively. The ternary materials balance the energy density, power density, and low-temperature performance, rendering them as promising candidates for portable electronics and BEVs [23]. Currently, the ternary materials have dominated the BEV market. However, NCM and NCA exhibit inferior thermal runaway temperature compared with LFP competitor, leading to safety concerns when encountering harsh or abuse working conditions [24]. This issue is exacerbated by enhancing nickel content in NCM in order to further enhancing energy density. Elevating nickel content and depressing safety risk have been a hot research trend both in academic and industrial communities [25]. An emerging cathode beyond ternary materials is the lithium-rich manganese-based oxide material (LRMO), which is anticipated to deliver a higher energy density of 30%–50% than NCM cathode, and reduce cathode cost due to the elimination of costly cobalt element [26]. However, anion redox reactions and release of oxygen during battery operation impact cycling ability and incur safety issues, which discourage their pace to move toward practical applications [27–29]. Successful overcoming the drawbacks of LRMO would result in paradigm shift in the battery technology, and would definitely power longer and cheaper BEVs.

Fingerprinting the trends and prospects of battery cathode materials makes the development of promising battery systems possible for BEV market, and offers an opportunity to refine the BEV market that different types of electric vehicles adopt suitable battery chemistries. Patent analysis integrates technical, economic, and legal information into a competitive intelligence source, allowing transforming individual and likely unrelated information into systematic and complete information [30,31]. The World Intellectual Property Organization (WIPO) estimates that the patent information has a possibility of reducing research time by 60% and research cost by 40% [32]. In addition, 90%–95% of research and development results can be documented in patents [32]. Extra benefits of the patent analysis include grasping the trend of industrial development, forecasting the development direction, and providing a guideline to formulate critical strategies [33,34]. Therefore, patent analysis has been extensively applied in various fields to predict the industry dynamics [35–38].

Patent analysis has been conducted on battery and BEV technologies. For the battery technology, patent analysis focuses on components [39–42] (such as cathode, anode, electrolyte and their shapes) and industry-orientated research activities [43,44] to forecast battery trends. The patent analysis on BEV majorly concentrates on battery chain [45,46] and technology roadmap [47] for vehicle development. However, a handful of patent analysis place special attention on different cathode materials in terms of performance comparison, development trend, annual installed capacity (AIC), technology life cycle, and distribution among regions and patent assignees. In depth analysis of the information is anticipated to stimulate battery research, understand technical layout of various countries, and probably forecast innovative technological breakthroughs. Based on these considerations, this paper comprehensively analyzes patent information on 6 popular cathode materials with respect to application field, patent assignees, and technology life cycle, to figure out the regional and global development trend of cathode materials. It needs to mention that patent distribution should also consider practical issues and the impacts of core patents. Currently, nearly 80% cathode materials are produced in China. However, many Chinese companies do not apply international patents due to cost. Therefore, the data analysis based on Derwent database has certain limitations. In addition, the impact of patent is not only related to the number, but also determined by the early original contribution.

2 Methodology

Herein, the Derwent Innovation Index was used as a data source to search the patent information of battery cathode materials. The Derwent Innovation Index combines the Derwent World Patents Index and Derwent Patents Citation Index, covering 110 million patents from nearly 61 patent issuers around the world, as well as creating a patent family for each patent to facilitate retrieval and avoid duplication [48,49]. Moreover, the Derwent Innovation Index has stored the data since 1963 to ensure the integrity and comprehensiveness of the data. The patent search in this paper is up to January 18, 2023, and covers global patent applications for Li-ion battery cathode materials. To ensure the integrity and applicability of patent data for cathode material examination, the meaningful patent data lies before December 31, 2020, as there is an 18-month lag for patent disclosure. Therefore, the patent data after 2020 cannot exactly reflect the patent trends of cathode materials.

Six promising cathode materials were selected for patent analysis. To obtain the quantity of patents for each cathode material, a set of search criteria dependent on cathode keywords and International Patent Classification (IPC) codes was developed. First, the search items in lithium battery fields were constrained 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*))). Then, IPC codes and keywords were applied 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 Y02E-060/10 (energy storage using batteries). The keywords contain materials formulations, structures and chemical names, such as manganese oxid*, LiMn₂O₄, LMO, spinel and mangan* were used for the retrieval of LMO.

Since the term of “lithium-ion batteries” was not established before commercialization of Li-ion batteries by Sony Corporation, the formula of (TS = (cathode OR (positive AND (electrode OR active material OR pole material))) AND TS = (cell% OR secondary batter* OR batter* OR accumulator OR rechargeable batter*)) was used to search for patents of cathode materials, and these patents in corresponding cathode families were added manually. Consequently, the number of patents was obtained for LCO (2907), LMO (4708), LFP (8509), NCM (11795), NCA (6348) and LMRO (531).

The AIC of different cathode materials is collected from Huaan Securities [50] Forward Industry Research Institute [51] and S&P Global Commodity Insights [52].

3 Results and discussion

The battery performances based on different cathodes are comprehensively and quantitively compared in Fig.1(a). NCA, NCM, and emerging LRMO cathode materials outperform the early applied materials (LCO, LMO, and LFP) in terms of energy density [53,54]. Previous studies indicate that the maximum amount of cobalt required for electric vehicles (EV) will exceed the total cobalt reserves by 2030, and that the demand for cobalt will be twice the total reserves by 2050 [55]. Therefore, it is urgent to reduce the content of cobalt to ensure the price stability of ternary materials, which is also the driving force to explore low-cobalt or even free-cobalt cathode materials (LMO, LFP, and LRMO), especially in heavy battery demand fields, like BEV markets [56,57]. Nickel-rich and cobalt-free layered material is one of the current research focuses. When the nickel content exceeds 80%, the layered nickel-rich NCM or NCA materials can provide a reversible capacity of more than 200 mAh/g [55]. The large amount of battery capacity (50–100 kWh) installed on BEV and necessarily long operation distance (> 150000 km) place the safety and cyclability in priority in the selection of cathode materials, which render the NCM, NCA, and LFP standing out in this field [58]. The superiorities in operating temperature and power density for NCA and NCM endow them as the critical option for BEV. For example, Tesla, Inc. adopts thousands of 18650 cells with the NCA cathode to power BEV [4]. Ni-rich layered NCM have garnered significant research attention due to the potential of enhancing energy density and reducing cost. However, severer expansion and shrinkage of layered lattice accelerate the stress generation and accumulation and contribute to microcracks formation. How to mitigate the impact of stress accumulation and prevent electrolyte permeation along microcracks have been considered decisive tasks to prolong the cyclic life of Ni-rich cathode [59].

The LRMO cathode with an exciting energy density is also considered for the next-generation battery system, provided that the working temperature, gas-induced safety and cyclability are well addressed [26,60]. However, it suffers from the vulnerable cathode/electrolyte interface, which presents the huge challenges of surface degradation and gas release, particularly at high state of charge. Thereby understanding interfacial degradation mechanism and proposing effective optimization strategies of LRMO are crucial for the manufacture of commercial batteries with good performance and long life [61]. In low-capacity required fields with tame operation conditions, such as computer, communication, and consumer electronics (also called 3C fields), high-voltage LCO and high-nickel-content NCM still dominate due to the energy dense feature, despite of high cost and inferior safety that impede their application in BEV fields [14,62].

The power density is related to the delivery of energy at a specific current density. Among 6 cathode materials, LFP has a relatively low power density due to the poor electrical conductivity. The commercial LFP with desired power density has to couple carbon coating technology to overcome the sluggish electron transfer. Ternary materials exhibit a satisfying power density in view of layered structure, which facilitate lithium mobility across the layer. The mild power density for LRMO poses another challenge to its commercialization, and LRMO is still in the research and development stage.

In recent years, Li-ion batteries are mainly used in three major fields, consumer electronics, electric vehicles, and energy storage. According to multiple characteristics of different materials such as energy density, power density, and cost, they are applied to diverse scenarios. LCO is costly and energy dense, which is suitable for portable consumer electronics. LCO accounts for 80% of the mobile phone battery market, and 34% of the tablet and laptop market [57]. Although the energy and power densities of LMO are not satisfying, the abundant raw materials, low cost, and good safety allow it to be widely used in the field of electric vehicles, accounting for about 20% in the market of electric bicycle and BEVs [57]. LFP batteries dominate the field of BEVs and energy storage. With the gradual rise of cobalt prices and the occurrence of ternary-layered battery safety issues, LFP batteries have also received widespread attention. The market share of LFP batteries in energy storage was more than 15% in 2022 [63]. NCM and NCA with high energy/power densities are still the mainstream of cathodes in BEVs, consumer electronics and other fields, accounting for more than 60% [64].

The patent application of the 6 cathode materials selected started from 1981 [12,65], and evolved into three characteristic stages in the last approximately 40 years (Fig.1(b)). The time period from 1981 to 1991 represents the first stage, which is featured by appearance of LCO and LMO patent applications. Despite limited patents issued in the embryonic stage, most of them are groundbreaking discoveries. For example, Goodenough’s group, for the first time, reported the reversibility of lithium insertion and de-insertion for LCO in 1980 [12], and evaluated LMO as a potential cathode material in 1983 [15]. The second stage (from 1991 to 2006) witnesses a rapid growth of patent applications compared with the first stage, but the total patent quantity is still in the mild level. This stage is characterized by the development of new materials and the improvement of energy density.

In this stage, LCO and LMO cathode materials are well developed, and Sony Corporation in February 1991 announced the first commercial Li-ion batteries with LCO as a cathode and hard carbon as an anode [66,67], which boosted 3C electronic products. After introducing LFP in 1997 [18], this cathode material experienced pronounced increase, and the patent quantity surpassed LCO and LMO in 2002, becoming the largest number of patent applications. In addition, the lately popular ternary cathodes (NCM and NCA) applied in BEVs have also attracted significant attentions in this stage, and their patent quantities are comparable with LMO.

The cathode materials of LCO, LMO, LFP, NCA, and NCM in the third stage (2007–2020) exhibit an exceptional growth thanks to the booming of portable electronics and BEV developments, manifesting a surging in the total number of patent applications for LCO (2163), LMO (3845), LFP (6893), NCM (9819), and NCA (5332). The patent quantity of NCM, NCA, and LFP that are prevalent in BEV market accounts for more than 78% of the total patents. The cathode materials of LRMO with greater capacity also display a promising growth in patent application, indicating an urging demand for high energy density battery system. Except novel materials, the patents in this stage mainly focus on innovations of the overall system, such as thermal management systems, module and pack design, as well as battery sensor and diagnosis, which are cooperatively endowed battery safer and more durable [68]. A representative battery design is the direct integration of cell into pack without module [20].

The technological maturity and applicability are evidenced by AIC, as shown in Fig.1(c). The LRMO cathode is not counted because it is not yet commercialized. AIC in 2016 was 121.7 GWh, of which LCO accounted for the largest proportion (43.1%), followed by LFP (28.4%), NCM (18.9%), NCA (6.4%), and LMO (3.2%). The commercialization of cathode materials with a high energy density and a low cost lead to the fact that NCM occupies 64% of AIC (424 GWh), while previously dominant LCO only accounts for 7%, followed by LMO (< 1%) and LFP (14%) in 2022. According to the forecast based on the current trend, the low energy density LFP and LMO appears to decrease continuously and high-energy density NCM and NCA will grow rapidly with the aid of technological breakthroughs. It is expected that NCM will account for more than 80% of AIC by 2025 [52]. Such changes are ascribed to the diverse functionality and property of cathode materials and different demands of application scenarios [69–71]. First, the enormous growth of the BEV market significantly dwarfs AIC for 3C product. It is estimated that the BEV and 3C markets account for approximately 96% and approximately 0.5% during 2016–2050, respectively [57]. Therefore, the dominant LCO cathode in 3C market would ultimately have a small portion in the entire battery market. Next, the costly LCO in the 3C market may be replaced by the NCM cathode with a high nickel content, as this cathode has an appealing energy density and a competitive cost, which also takes responsibility for the intrinsic option of the BEV market. Finally, the low-cost and low-energy-density LMO is still suitable for some consumer electronics and two-wheeled electric vehicles that do not weight the energy density in superiority but concerns the cost and safety in the expected operation life span [57]. It is of note that the market share of the LFP cathode strongly depends on the innovations of battery module and pack in the future. For example, the battery integration based on a novel cell to pack (CTP) pattern has promoted the battery integration efficiency to 75%, driving the pack level energy density of LFP battery system even greater than that of NCM [1,20].

The technology life cycle theory is derived from the industry life cycle theory and is primarily used to construct technology projections [72]. Herein, the technology life cycle can be reflected by the number of patent applications per year as the ordinate and the number of patent assignees per year as the abscissa (Fig.2(a)–Fig.2(f)). Based on Haupt theory [73], the technology life cycle of six cathode materials can be generally divided into four stages, the emerging stage, the growth stage, the maturity stage, and the saturation stage. The emerging stage defines a relatively both limited number of patent applications and number of patent assignees, while the growth stage shows a rapid increase in patent applications and assignees. The mature stage indicates a relatively stable quantity of patent applications and assignees. The technology life cycle is ended by the saturation stage that represents a both obvious decrease of the quantity of patent applications and assignees. Fig.2(g) summarizes the technology life cycle of individual cathode materials according to dynamic patterns of patent applications and assignees. Although LCO is first discovered, the emerging stage is extended to 2012, lagging behind LMO (2008), LFP (2005), NCM (2007), and NCA (2009). This is probably due to the lately developed materials with unique properties to fulfill specific applications, and thus scattering the interests of LCO. The high-energy LRMO is still in the emerging stage. In the growth stage, the quantities of patent and assignee grow equally fast. The rise of BEV and 3C markets stimulates the extensive exploration of different cathode materials from various aspects, enabling their continuous growths in the market segments, which are the root causes for these cathodes (except LRMO) that are still in the growth stage before 2019. Quantitative inspection of patents and assignees reveals a slight decrease in LMO, LFP, NCM, and NCA, indicating that these materials enter into maturity stage.

Analyzing the technology life cycle of 6 cathode materials has four implications. First, the early matured LCO is still in the growth stage and rapidly increase in patent applications principally due to the development of high-voltage LCO that is expected to output a higher energy density [62]. Second, the reduction of patent applications for LMO in 2013 and LFP in 2012–2014 linked to the research interests in high energy density cathode materials such as NCM and NCA. Third, the steady growth of cheap and safe LMO and LFP is the result of material optimizations and battery pack innovations. For example, LMO is usually mixed with NCM in the BEV field to reduce the battery cost while tamely affect battery energy density [56]. The CTP pattern for LFP significantly enhances the pack-level energy density and revives the interests of LFP. Lastly, the pursuit of a greater energy density in materials chemistry places a special attention on LRMO, and entering the growth stage of the technology life cycle for LRMO is likely necessary to realize the practical usage.

Derwent Class Codes (DCCs) provide the category of inventions or technology functions of the invention [74,75]. Therefore, this paper selects the top 5 DCCs for six cathode materials and identifies their technology functions. Tab.1 shows that all these cathode materials have undergone extensive research in the fields of electrochemical energy storage and electrical applications. Similarly, electric vehicles are also a key area for battery applications. Considering the high cost and poor cycle life of LCO, as well as unmatured LRMO, these two materials are not applicable in electric vehicles.

Collecting the most active assignees in the selected cathode materials, and categorizing these patents with respect to research institutions and enterprises are expected to precisely forecast the trend and rationally evaluate cathode advantages from the holistic perspective. Except for LRMO, the remaining five cathode materials exhibit the fact that patents from enterprises far exceed those from research institutions, of which the enterprises and research institutions account for about 73% and 23%, respectively (Fig.3). The commercialized LMO and LCO had patents of 2573 and 4217 by the end of 2020, respectively, and the top five patent assignees for these two materials were mainly Republic of Korean and Japanese enterprises, such as LG, Samsung, and Toyota. The popular cathode materials of LFP, NCA, and NCM in BEV fields are more scattered, coming from China (CATL and CAS), Republic of Korea (LG and Samsung), and Japan (Sumitomo, Toyota and Panasonic). The patents of emerging LRMO are dominated by Chinese enterprises and research institutions. In particular, the top five patent assignees for LRMO are all from China.

Based on above analysis, two aspects need to be considered. First, when it comes to the development of emerging materials, it is generally assumed that research institutions devote more efforts to research and development than enterprises. However, in the battery fields, enterprises make great efforts in developing new technologies and materials. For example, enterprises dominate the top five patent assignees for commercialized cathode materials (LMO, LFP, LCO, NCM and NCA). Second, commercialized cathodes are still the focus of enterprises and research institutions, which heavily invest in structure, performance, and device optimization in an attempt to push the performance of these cathode materials to the limit.

Next, the distribution of patent assignees discussed in terms of countries, enterprises and research institutions to illustrate patent roadmap. In the global distributions, the number of patents for the six cathode materials can be ranked in the sequence of China, Japan, Republic of Korea, America, and Europe (Fig.4(a)). In general, LFP and NCM as the promising cathode materials for power batteries are the focus of research in all countries and regions. Especially, the number of NCM patents in the total number of six material patents in various countries and regions account for more than 30%. China has the leading patent applications in all selected cathode materials, accounting for more than 50% in the global patents. Especially, the emerging LRMO occupies almost 97%. Except China, Japan shows great advantages in LMO. The number of LMO patents accounts for 20% of the total number of six materials from Japan. Nichia, BASF-Toda, and Tosoh are important material manufacturers for the LMO material. The number of NCA patent is over 24% of the total number of applications for six materials from Republic of Korea. LG Chemical and Samsung SDI rank in the top two in patent quantity in the field of NCA.

Citation analysis is a valuable method for investigating mutual citation patterns and technological origins of different patents. Citation analysis is divided into backward citation and forward citation. Backward citation refers to prior documents cited by this patent, while forward citation is later patents that cite this patent of interest. If a patent has higher forward citation counts, it means that later patent documents cite this patent many times. It further indicates that this patent contains significant innovative technology and might enjoy a larger technological impact than others [74,76]. Therefore, forward citation is used in this paper to explore the core patents with high forward citation counts for six cathode materials. The patent citation data was obtained from Derwent Innovation System, which are listed in Tab.2. Among six cathode materials, the core patents with high forward citation counts for LCO, LMO, LFP, and LRMO are all applied from Europe and America patent assignees. These results indicate that the overall number of patents in Europe and America is relatively small compared to Asia countries while the significance of these patents has been identified (Fig.4(a)).

Fig.4(b) shows the top 10 patent assignees of six cathode materials in their patent layouts in China, Japan, Republic of Korea, America, and Europe. Although China holds the largest number of patent applications for cathode materials, only one company and one research institute enter the top 10 patent assignees, with the rest being Japan (6) and Republic of Korean (2). This indicates that the technology of cathode materials in China is relatively scattered, but that of Japan and Republic of Korea are highly concentrated. From the patent layout perspective globally, patent assignees apply the largest patents from their home countries. Enterprises from Japan and Republic of Korea have more international battery patent layouts, while China pays more attention to domestic patent applications. For example, Toyota and Panasonic hold a certain number of patents in China, Republic of Korea, America, and other countries.

Fig.4(b) also indicates that enterprises have special patent layout overseas. Enterprises from Republic of Korea and Japan place the America in the priority followed by China in their patent layout. For example, approximately 20% of the patents from LG and approximately 30% patents from Samsung are applied in America. Toyota has 25% of patents in America for LMO and NCA cathode materials. Panasonic hold an even larger proportion of LCO patents than domestic patents. Moreover, China is still in the initial stage in patent layout overseas, and these limited patents are mainly applied in Europe and America.

4 Conclusions

Cathode materials are critical components for Li-ion batteries and majorly determine specific applications in different battery related markets. This paper maps the trends and prospects of cathode materials based on patent analysis, and identifies their technology life cycle and distribution among regions and research institutions. The cathode materials widely used in electric vehicles are currently in the maturity stage, while the LCO cathode prevalently used in portable electronics is still in the growth stage. Collecting patents and assignees globally implies that China accounts for more than 50% of the total patents. However, only 2 institutes from China enter the top 10 patent assignees. Japan and Republic of Korea, having 6 and 2 institutes, respectively, are in top 10 patent assignees. Such patents and assignees distribution across the world suggest that there is relatively scattered research in China but comparatively concentrated research in Japan and Republic of Korea in the field of cathode materials. This paper, extending the battery technology into patent analysis in consideration of technology life cycle and patent layout globally, aims at forecasting cathode materials in the future battery technology and refine different battery technologies in specific markets.

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