Battery Material Characterization Advancements Boost Renewable Energy Innovation

Climate change is a top priority on the global agenda and is impacting the way all industries operate and are regulated or governed. The 2016 Paris Agreement set out to limit temperature increases to “1.5 °C above pre-industrial levels”, with an end goal of restricting the increase in the global average temperature to “well below 2 °C above pre-industrial levels”.¹

In response to this, 18 governments around the globe have joined the Net-Zero Government Initiative (NZGI). Countries that commit to the NZGI must pledge to achieve net-zero emissions by 2050, and must also publish a roadmap for achieving this, with set targets based on each country’s individual context.²

In light of these initiatives and targets, the race is on for researchers to develop efficient and scalable renewable energy sources, to reduce the global reliance on fossil fuels. Battery performance is one key area of innovation and improvement, with the global battery market expanding at a rapid pace. Valued at nearly $112 billion in 2021, it is forecast to quadruple to $424 billion by 2030.³

For researchers innovating in the battery space, it is essential that new solutions have improved performance and practical, real-world, large-scale applications. Crucially, an understanding of the best suited materials and configurations is central to unlocking a battery-powered future by delivering powerful battery performance in an environmentally friendly way.

Three research groups across the UK, Spain and China have been using specialist analytical equipment to analyze new ways of developing lithium- and potassium-based batteries to advance the global drive towards renewable energy.

Thin film innovation for lithium-ion batteries

Lithium-ion (Li-ion) batteries set the benchmark for rechargeable battery performance and are used in a variety of applications, from small electronics, such as toys and wireless headphones, to power tools and electric vehicles.⁴ As such, research is ongoing to optimize their use and improve charging and reliability.

To achieve this, researchers are looking closely at different configurations of Li-ion batteries to identify new avenues for their development. Researchers at the University of Cambridge have examined the use of vertically aligned nanocomposite (VAN) thin films for solid-state batteries, as their three-dimensional (3D) architectures could allow for enhancements in battery capacity, current and power density.⁵

The team developed the first reported anode VAN battery system, and they conducted a series of measurements to determine its suitability in real-world uses. One set of measurements was taken by electrical impedance spectroscopy (EIS), which involved using a temperature-controlled probe stage to measure the electrical impedance of the film between 25 and 100 °C, at a rate of 5 °C min^-1. These measurements concluded that the VAN anode exhibited a high Li⁺ ionic conductivity and, when combined with their other results, this determined that VAN films exhibit all the essential properties required for use within solid-state thin film batteries.⁵

Researchers in Spain have also been examining new configurations for thin film Li-ion batteries. Although Li-ion batteries are one of the most commonly used battery types, they have some limitations, including a reduced electrochemical stability window, high toxicity and flammability, and the formation of lithium dendrites which could result in short circuiting and significant limitations to battery life.⁶ To remedy this, the researchers developed and tested a high-voltage, all-solid-state lithium-ion thin film battery – comprising a LiNi_0.5Mn_1.5O₄ cathode, a LiPON solid electrolyte and a lithium metal anode – to determine whether this would mitigate some of these challenges.

To evaluate ionic conductivity of the LiPON electrolyte, an air-tight, temperature-controlled electrical testing stage was used to conduct in-plane ionic conductivity measurements on the LiPON thin films at 150, 200 and 250 °C. The results of this experiment determined that ionic conductivity increased with temperature. These results, combined with other findings, demonstrated commercial viability for a high-voltage, all-solid-state Li-ion thin film battery.⁶

Opportunities for potassium-ion batteries

Potassium-ion batteries (KIBs) are also emerging as a promising option for innovation, with comparable performance to Li-ion batteries. They are generally regarded as a more sustainable and cost-effective alternative to traditional Li-ion batteries. This is because KIBs are free from critical minerals such as nickel, cobalt, copper and lithium, addressing supply chain concerns and reducing the ecological impact of battery production. Instead, they utilize commonly available components, including graphite anodes, separators and electrolyte formulations.

However, KIBs are not without their own limitations – K⁺ ions are large, which impacts their speed, leading to low capacity and fast performance degradation.⁷ Layered transition metal oxides (LTMOs) have shown promise as cathode materials for KIBs, however these come with their own challenges due to time-intensive and complicated synthesis requirements, as well as high energy consumption. To overcome this, researchers in China have developed an ultra-fast synthesis strategy of Mn-based LTMOs directly from metal organic frameworks (MOFs).

Part of the investigation of the phase transition from MOF to LTMO involved variable temperature optical microscopy, to observe the changes as the MOF was subject to different temperatures. The results of this investigation showed that there was a small weight loss of the sample from 700 to 800 °C, which could be attributed to the sublimation of the potassium due to its 759 °C boiling point. It also showed that between 300 and 400 °C, the crystalline morphology of the KM-MOF changed and displayed signs of damage (Figure 1), which is consistent with the results from the thermogravimetric analysis also conducted within the study.

Figure 1. Variable temperature optical microscopy photograph images. Images b–d show the changes to the crystalline morphology of the KM-MOF as the temperature increased in 50 °C intervals from 300 °C to 400 °C. Credit: Li et al., 2022, licensed under CC BY-NC 3.0.

These results contributed towards the conclusion that it is possible to successfully facilitate the fast synthesis of an LTMO cathode from a MOF. This new method saved time and energy in comparison to traditional time-intensive and high-temperature methods, and the cathode itself demonstrated superior performance compared to previously reported LTMO cathodes. This work may contribute to mitigating some of the drawbacks of KIBs, so that they can be more widely used in future.

A battery-powered future?

The advancements being made in battery characterization and analysis will play an important part in achieving the goals of the Paris Agreement, and ongoing research to discover and optimize suitable renewable sources is essential to keep up with global energy demands.

The studies explored above are just a few examples of the work being done in this space, and they demonstrate the importance of materials characterization and configuration in battery innovation, especially as the demand for renewable energy skyrockets. While the race is not over yet, the future looks promising for high-performance batteries, and the work of researchers around the globe to improve their composition and performance is helping to make net-zero goals more achievable.