Solid-state batteries (SSBs) represent a significant advancement in battery technology, leveraging solid electrodes and a solid electrolyte instead of the liquid or polymer gel electrolytes found in conventional lithium-ion or lithium-polymer batteries (Janek and Zeier, 2023).
Solid-state batteries are particularly relevant for both freight and passenger vehicles due to their potential to enhance performance and safety (Gao et al. 2018).
According to Karabelli et al. (2021) several types of solid-state batteries that hold promise for future land transportation.
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Source: Karabelli et al. (2021).
The core benefits of solid-state batteries include enhanced safety, higher energy density, longer lifespan, and fast charging capability. Solid-state batteries are inherently safer because solid electrolytes are non-flammable, significantly reducing the risk of thermal runaway and fires, a crucial benefit for automotive applications (Mauger et al. 2019).
Solid-state batteries (SSBs) have several current limitations despite their advantages. Commercial-scale production of SSBs presents significant challenges, such as maintaining material purity and achieving uniformity in solid electrolytes. The manufacturing processes for SSBs are more complex and costly compared to traditional lithium-ion batteries. Ensuring the stability of solid electrolytes and their interfaces with electrodes is crucial for long-term performance and reliability, but this remains a significant hurdle. Many solid electrolytes suffer from chemical degradation and poor contact with electrodes, and some may exhibit poor performance at lower temperatures, impacting the battery's efficiency and lifespan in different climatic conditions. These issues are current topics in the increased scientific literature, as displayed in the following analysis of a scientific literature analysis.
Solid-state batteries: scientific publications
The visualization displays the number of scientific documents related to solid-state batteries published annually from 2004 to 2023. The data shows a steady increase in the number of documents over the years, with a significant surge starting around 2017. Between 2004 and 2016 the number of documents related to solid-state batteries remains relatively low and increases gradually. Within 2017 to 2023 a noticeable spike in the number of publications can be observed, indicating a growing interest and focus in the scientific community on solid-state batteries overcoming the mentioned challenges for commercializing solid state batteries.
The visualization shows the number of scientific publications on solid-state batteries by country. China leads with approximately 850 publications, followed by the United States with around 600, reflecting strong emphasis and investment in this field. Japan has about 300 publications, showcasing its ongoing innovation in battery technology. India and Germany each contribute around 200 publications, indicating substantial research efforts. South Korea, driven by its electronics and automotive industries, has approximately 180 publications. Canada and the United Kingdom each have around 100 publications, while France and Australia have slightly fewer. Overall, the chart highlights the global effort in solid-state battery research, with China and the United States at the forefront.
Solid state batteries: patent data
The patent analysis also reveals an increase in patenting activity in solid state batteries. The number of published patent families has increased from only 290 in 2010 to 2033 in 2023.
On a country level, most of the solid state battery patent families were published from inventors from Japan (more than 7000 patent families between 2000 and 2023). Japan is responsible for almost 40% of all solid state battery patent families published within that time period.
Solid state batteries: patent examples
Patent activities in the field of solid-state batteries have surged in the last decade, reflecting the intense research and development efforts by companies and academic institutions. Leading companies in the automotive and battery industries, such as Toyota, BMW (e.g. Solid Power), and QuantumScape, are at the forefront of patent filings, focusing on various aspects of solid-state technology from material innovations to manufacturing processes. For instance, Toyota plans to showcase its solid-state battery technology in a prototype vehicle by the mid-2020s, emphasizing advancements in range and safety.
Toyota's patent (WO2011142150A1) outlines a solid-state battery technology featuring an ionic conductor with a spinel structure, represented by the formula (AxM1−xyMy′)Al2O4(AxM1−xyMy′)Al2O4, where "A" is a monovalent metal like lithium, "M" is a divalent metal such as magnesium or zinc, and "M'" is aluminum. This conductor is used in various layers of the battery, including the cathode, anode, and solid electrolyte layers, with specific materials like LiMn2O4LiMn2O4 for the cathode and Li4Ti5O12Li4Ti5O12 for the anode. The design aims to improve battery performance and stability by optimizing the conductor's composition and integration.
The use of a spinel structure ionic conductor, specifically tailored with lithium, magnesium, zinc, and aluminum, can enhance the ionic conductivity and stability of the battery. By incorporating these materials into the cathode, anode, and solid electrolyte layers, the design addresses key challenges in solid-state battery development, such as improving energy density, safety, and longevity. If successfully implemented, this could lead to more efficient, durable, and commercially viable solid-state batteries.
QuantumScape's patent US10439251B1 focuses on lithium-stuffed garnet materials suitable for use as electrolytes and catholytes in solid-state battery applications. The core invention involves garnet compositions, including those doped with alumina, which enhance the ionic conductivity and stability of the battery. The patent also describes the creation of lithium-stuffed garnet thin films with fine grains, which are integral for improving battery performance. Additionally, it outlines methods for manufacturing these garnet materials and preparing dense, thin free-standing membranes (less than 50 micrometers) for use in various battery components.
The patent further details innovative sintering techniques, such as field-assisted sintering (FAST), to optimize the fabrication of solid-state energy storage devices and their components. This technology aims to advance solid-state batteries by improving their performance, stability, and manufacturability.
While spinel materials offer high thermal stability, good electrical conductivity, and cost-effectiveness, garnet materials provide high ionic conductivity, chemical stability, and resistance to dendrite formation. These distinct advantages make both types of materials essential for the development of advanced solid-state batteries, each contributing to different aspects of battery performance and safety.
The adoption of solid-state battery technology in land transportation is influenced by evolving regulations and standards aimed at promoting safety, performance, and environmental sustainability. Organizations like the International Electrotechnical Commission (IEC) and the Society of Automotive Engineers (SAE) are working on developing standards specific to solid-state batteries, addressing testing protocols, safety requirements, and performance benchmarks to ensure their reliable integration into commercial and passenger vehicles.