This section presents the information of the document collection examined and goes over different aspects of the documents. Specifically, the number of published documents and the number of citations received are examined, the sources used are explored, and the authors’ affiliations and countries are looked into. Moreover, the documents are further analyzed using keywords to identify the trend topics, the conceptual structure map, the thematic map, and the evolution of the topic.
3.3. Sources
Of the 840 documents examined, the vast majority were published as journal articles (90.0%). To a significantly less extent, documents were published as conference/proceedings paper (7.6%) and review articles (2.1%). Only two documents (0.2%) were published as book chapters. Additionally, “ACS Applied Materials & Interfaces” (h-index: 25 and total citations: 2208), “Journal of Materials Chemistry A” (h-index: 23 and total citations: 1810), “Electrochimica Acta” (h-index: 22 and total citations: 1874), “Journal of Power Sources” (h-index: 21 and total citations: 1406), and “Electrochimica Acta” (h-index: 19 and total citations: 997) emerged as the top-5 sources when considering the h-index and total citations received. The detailed list of the most impactful sources is depicted in
Table 3.
Using Bradford’s law, the sources were further examined. The documents were further analyzed using clustering by coupling. Specifically, documents were set as the analysis unit, references were used as the coupling measurement and citation score was used as the impact measure. Moreover, the clustering algorithm used was Walktrap, the number of units were set to 250, and the min cluster frequency was set to 5 which are the default values suggested by the tool used in this study. Specifically, the sources were grouped into three clusters. Cluster 1 has the most impactful sources, followed by cluster 2 and cluster 3. Based on the outcomes, cluster 1 had 11 (4.4%) sources, cluster 2 had 42 (16.9%) sources, and cluster 3 had 195 (78.6%) sources. Moreover, cluster 1 had a total of 292 (34.8%) published documents, cluster 2 had 274 (32.6%) published documents, and cluster 3 also had 274 (32.6%) published documents.
Table 4 presents the top-10 sources according to Bradford’s law. Out of all sources, “ACS Applied Materials & Interfaces”, “Electrochimica Acta”, “Journal of Materials Chemistry A”, “Chemical Engineering Journal”, and “Journal of Alloys and Compounds” arose as the top-5 most impactful ones following Bradford’s law.
3.5. Countries
The documents of the document collection examined were written by 2183 authors from 32 countries. For each document, the country of the corresponding author was used. In the case that there was no corresponding author indicated in the document, the country of the first author was used. The top-10 countries according to the number of documents published are presented in
Table 5. Based on the results, China (517 documents), the United States (70 documents), Sweden (52 documents), South Korea (37 documents), and Australia (31 documents) emerged as the top-5 countries that have contributed the largest number of relevant to the topic documents. When examining the SCP and MCP, once again, China (SCP = 515), the United States (SCP = 70), Sweden (SCP = 51), South Korea (SCP = 37), and Australia (SCP = 29) were the countries with the highest number of intra-country collaborations. When considering the low levels of inter-country collaborations and taking into account the extremely low rate of international collaborations (1.43%), the drastic need for more international collaboration to materialize to advance this field of study becomes evident. This fact becomes more obvious when examining the country collaboration network (
Figure 6) and collaboration map (
Figure 7) in which the limited number of international collaborations can be seen.
Furthermore,
Table 6 presents the top countries based on the total citations received. According to the findings, China (20,033 citations), the United States (2963 citations), Sweden (1694 citations), Australia (1408 citations), and South Korea (934 citations) were the top-5 countries that have received the most citations. Among the top-10 countries in terms of total citations received presented in
Table 7, Georgia (ACR = 90), Czech Republic (ACR = 88), Singapore (ACR = 74.8), Hong Kong (ACR = 55.6), and Australia (ACR = 45.4) were the countries with the largest number of ACR per document.
The number of total citations received was also examined to identify the most impactful countries in terms of the total number of citations the documents written by authors affiliated with an institute in this specific country received. Particularly, the United States (1752 total citations), Australia (1124 total citations), Israel (705 total citations), and China (572 total citations) were the top-4 countries which received the most citations. The list of the top-10 countries in terms of the total citations received is presented in
Table 6. Additionally, when looking at the average article citations for each country, the documents written by authors in Israel received a significantly higher number of average citations per document (352.5). Documents coming from Australia (62.4) and Denmark (43.2) also showcased a high level of average citations received (ACR) per document.
3.6. Document Analysis
Table 8 presents the most impactful documents based on the global citations they have received. Based on the results, the studies of R. Zhang et al. (2018), Zhu et al. (2013), Fu et al. (2014), W. Zhang et al. (2018), and Zhong et al. (2018) emerged as the top-5 most impactful ones. Taking these outcomes into account, it can be inferred that the focus is on developing high-performance, durable electrochemical anodes by exploring various coatings on carbon fiber that incorporate nanoparticles and lithium. This is because the practical use of non-coated lithium metal anodes has been limited by challenges such as low cycling efficiency, short lifespan, and safety concerns.
To better understand the scope and breadth of the topic and how it has been shaped throughout the years, keywords plus were used to further analyze the documents. Specifically, keywords plus result in more accurate and representative outcomes when compared to author’s keywords (Zhang et al., 2016) and therefore, have been used in the analysis. Among the keywords plus used, “carbon fibers” (n = 560), “anodes” (n = 317), “lithium-ion batteries” (n = 288), “electrodes” (n = 179), and “lithium compounds” (n = 177) emerged as the top-5 most commonly used.
Figure 8 summarizes the top-10 most frequently used keywords plus.
Based on the outcomes, the scientific community has focused on three main areas. Firstly, the most investigated is the development of anodes for lithium-ion batteries, as this area faces high global demand and presents greater challenges compared to cathodes. Anodes are subject to issues such as dendrite formation during charging [
60], significant volume changes of lithium during charge and discharge, leading to crack formation [
61], and potential side reactions with the electrolyte, which generate products that can degrade battery performance and reduce capacity [
62]. Secondly, the development of a new generation of carbon fiber-based cathodes involves activating them with coatings of LiFePO
4, LiCoO
2, or their derivatives. Additionally, recent efforts have focused on developing cobalt-free cathodes due to the high cost and difficulty of extraction. These cobalt-free alternatives offer more sustainable solutions for large-scale production while maintaining comparable performance metrics [
63,
64]. The final area of focus is the development of solid electrolytes, which must simultaneously achieve high ionic conductivity and elevated mechanical properties to guarantee the multifunctionality of the composite. However, it has been demonstrated that these two properties are often in conflict [
18,
65].
The keyword co-occurrence network presented in
Figure 9 revealed three main areas. Specifically, the central and most prominent cluster is focused on ‘carbon fibers’, which is heavily linked to “lithium-ion batteries” and “anodes”. This central cluster indicates a strong relationship between these terms within the research or context provided. Surrounding this main cluster are two other significant areas: one that includes terms like “vanadium”, “flow batteries”, and “energy storage” suggesting a focus on alternative battery technologies and energy storage solutions. Here, vanadium-based energy storage, particularly in vanadium redox flow batteries, has shown promise for large-scale applications due to its high energy capacity and long cycle life. Flow batteries, in general, provide a scalable solution for renewable energy integration, as they allow for independent scaling of power and energy capacities, making them ideal for grid-level storage. The other area includes terms such as “solid electrolytes”, “redox reactions”, and “electrochemical performance”, pointing towards research in advanced battery materials and their performance.
Figure 10 presents the relationships among the top countries, keywords, and sources.
Furthermore,
Figure 11 displays the most popular topics and their progression over the years based on keywords plus. According to the outcomes, the current focus in the development of carbon fiber-based batteries is on creating low-cost batteries utilizing sodium ions, with an optimized structural design. Moreover, we can see the importance of scanning electron microscopy in the development of these devices, as it is a critical machine to master their operation and optimization.
When examining the conceptual structure map of the topic, four main dimensions arose as it can be seen in
Figure 12. According to the results, the dimensions were related to: (i) carbon fibers, anodes, and lithium, (ii) carbon fibers, anodes, and metal ions, (iii) carbon fibers, lithium-ion batteries, and anodes, and (iv) carbon fibers, lithium-ion batteries, and electrodes. Based on the dimensions that emerged, it can be inferred that carbon fibers play a central role in the development of advanced battery technologies. The repeated association of carbon fibers with anodes, lithium, and lithium-ion batteries highlights their importance in enhancing the performance and efficiency of these components. Additionally, the inclusion of metal ions and electrodes in the dimensions suggests a focus on optimizing the materials and structures used in batteries to improve their overall functionality and longevity.
The thematic map of the topic which is displayed in
Figure 13 presents the six themes that emerged. The themes are separated into basic themes, emerging or declining themes, niche themes, and motor themes. Two basic themes arose that were related to: (i) lithium compounds, electrodes, and lithium and (ii) electrochemical electrodes, redox reactions, and cyclic voltammetry. One emerging or declining theme arose which was associated with (i) energy efficiency, flow batteries, and vanadium. Two niche themes were identified that were related to (i) structural batteries, multifunctional composites, and polyelectrolytes and (ii) zinc, oxygen, and electrolytic reduction. The motor theme that arose was associated with (i) carbon fibers, anodes, and lithium-ion batteries. Based on these outcomes, it can be noted that the development of carbon fiber-based batteries is a central focus, particularly in enhancing the performance and efficiency of lithium-ion batteries. The emphasis on electrochemical electrodes and redox reactions highlights the importance of understanding and optimizing the fundamental processes within these batteries. Additionally, the exploration of structural batteries and multifunctional composites indicates a trend toward integrating multiple functionalities into battery materials –structural and energy storage functions especially–leading to more versatile and efficient energy storage solutions.
The thematic evolution of the topic is presented in
Figure 14 in five time periods. The first time period (2013–2015) reveals that the focus was primarily on “anode”, “carbon fibres”, “energy storage”, and “mechanical properties”. These themes indicate an early emphasis on understanding and improving the fundamental components and properties of energy storage systems. As we move to the second time period (2016–2017), the themes evolve to include “cathodes”, “carbon fibres” and “energy efficiency”, reflecting a shift towards optimizing both the anode and cathode materials and improving the overall efficiency of energy storage devices. In the third time period (2018–2019), the focus expands to “carbon fibres”, “anodes”, and “composite materials” suggesting advancements in integrating carbon fibres into composite materials to enhance the performance and durability of batteries. The fourth time period (2020–2021) shows a continued emphasis on “carbon fibres”, “anodes”, and “energy storage” indicating ongoing research into improving these critical components. Additionally, “structural batteries” and “carbon nanofibers” emerge as significant themes, highlighting innovations in battery design and materials. Finally, in the fifth time period (2022–2023), the themes include “carbon fibres,” “anodes”, and “lithium-ion batteries,” demonstrating a mature focus on integrating carbon fibres into lithium-ion batteries to enhance their performance. The emergence of “energy efficiency” and “structural batteries” as consistent themes throughout the periods underscores the importance of these areas in the ongoing development of advanced energy storage solutions.
Considering the bibliometric analyses of the paper,
Figure 15 presents key trends and future perspectives in energy storage technologies based on carbon fiber-based batteries. The bibliometric analysis highlights three primary areas: the development of carbon fiber-based anodes for lithium-ion batteries, advancements in next-generation carbon fiber-based cathodes, and progress in solid electrolytes. Each domain faces significant challenges, such as dendrite formation and volume expansion in anodes, as well as the urgent need for cobalt-free alternatives in cathodes due to the high costs and extraction difficulties associated with cobalt. Efforts in solid electrolytes focus on balancing high ionic conductivity with strong mechanical properties to ensure the multifunctionality of these composite materials. Moreover, gel-based electrolytes, due to their semi-solid nature, help to reduce electrode polarization and maintain stable performance under high charge/discharge rates, making them highly suitable for demanding energy storage applications. Additionally, the geographical distribution of research contributions, with leading countries showing high citation impacts, although international collaboration remains limited. This suggests that while some nations dominate high-impact research, global collaboration needs to be strengthened to accelerate progress in this field.