**Author details**

Zhao Qu1,2\*

**5. Discussion and conclusion**

being patented.

patent database.

with relevant IPC codes.

Limitations and drawbacks

144 Scientometrics

highlighted by those articles are explored in depth.

The present findings drawn from the bibliometric and sentence-by-sentence analysis of 48 journal papers indicate that patents, as indicators or references alike, still occupy an irreplaceable position in tracking the rise of emerging technologies. Since 2001, a sequence of structural data extracted from patents, like counts, grants, or classifications, has been employed to assess industry structure and examine the patterns of technological change. Assignees, organizations, and portfolios involved in patents are analyzed to measure the R&D and commercialization aspects of innovation strategies. New technologies' forecasting has been increasingly produced by keywords and patent citations accompanied with the emergence of advanced data search and mining techniques. Details of e-mobility technologies, ranging from batteries to smart grids, are scrutinized as references based on patent documents. Contents are continuously being specified and updated in line with the overall trend in the development of e-mobility, accounting for elements behind pure statistics. Even the patent study on e-mobility has not already accumulated a remarkable number of publications; the potential topics revealed by extended use of recent highly citied papers are researchable, including the analysis of automotive supply industry, technology diffusion, and landscape as well as the evaluation of green innovation system and policies. A specific focus in latter the e-mobility patent study is to expound key technical problems regarding free-piston linear generator. Drivers, the current momentum, and policies are constantly analyzed to answer the question of how EV development is accelerated. However, limitations rooted in patent data concerning patentability, search engine, willingness to publish, and the IPC-based bias with the onesidedness of certain patent-based indicators mentioned as earlier should be noticed in further adoption of patents in e-mobility analysis, especially for improving its efficiency in plotting evolution of technologies and interpreting patents in a specific context. The limitation of such a study is that characteristics of patent study could not be fully identified because they are only identified from publications in an emerging field and the relevant search terms have not been unified in the past research. Nevertheless, it could be a sign of renewal when issues

**Category Limitations of patents or data sources in itself Shortcomings of patent-based indicators or** 




**Table 2.** Recent research limitations stated in conclusive parts of publications (since 2015).

**approaches**

not guaranteed.




numbers within the technologies.

keywords is qualitative judgment.

\*Address all correspondence to: zhaoqu@dzhw.eu

1 Department of Social Sciences, Humboldt University of Berlin, Berlin, Germany

2 German Centre for Higher Education Research and Science Studies (DZHW), Berlin, Germany
