Lithium-based cells are widely used, but problematic. The most obvious alternative is solid-state cells, but much development is still needed. Our battery technology expert Martin Neilson explores the state of play in the battery industry and highlights the value of patents in the race to create a commercially viable lithium alternative.
The trouble with lithium
From disposable batteries to giant storage hubs connected to the power grid, to advanced electric vehicles (EVs) like the Tesla Model S, lithium-based cells are everywhere. While their design enables us to extract as much as possible in terms of performance, our addiction to such ‘wet’ batteries comes with some major drawbacks, including:
Global demand for lithium continues to rise, with supply set to almost triple by 2025 to more than 1.5 million metric tons. This level of activity has environmental consequences — in recent years, we’ve seen a number of water pollution disasters, impacting marine life and fresh water supplies. At the other end of the spectrum, the ultimate disposal or recycling of lithium cells still poses a significant challenge.
Concerns around the safety of lithium cell technology is well documented. Fire and explosive risks arise due to microscopic metal particles converging at one or more specific regions within a cell. These provide a major current surge between electrodes to electrically short the cell/battery. People have been injured and flights grounded due to the flammable characteristics of lithium fuel cells when operating under certain conditions.
Lithium v solid-state
In a conventional ‘wet’ lithium battery, the organic solvent-based liquid electrolyte provides a medium for the transport of lithium ions and salts (e.g. LiPF6) between the electrodes. In a solid-state cell, both the electrodes and electrolytes are solids.
These cells can be made thinner, more flexible and to provide higher energy density. The non-liquid electrolyte is safer, more resistant to temperature change, physical damage and leaking. Solid-state batteries may also provide longer running times and total battery lifetime due to improved energy density and charge-discharge cycles.
Combined, such innovations have given rise to a large body of patents, as competitors scramble to protect their R&D efforts to secure their market position and avoid gifting developments away.
A solid challenge to commercialisation
While solid-state cells are superior on paper, their development has been hampered by challenges. It has been difficult to innovate towards a commercially viable solid-state battery, but a couple of recent patents could be game changing.
One major problem is the accumulation of metal deposits at the anode in the form of branch-like dendrites. Once the dendrites grow the full length between the electrodes, the cell will short. A new potassium-based cell by Rensselaer (patent WO 2019/191530) is designed to operate at relatively high charge, discharge rate and temperature, such that the anode is described as ‘self-healing’. As temperature increases, potassium ions are displaced from the anode. This is beneficial for many applications, as the battery cells can be pushed to higher operating temperatures to ‘purge’ the anode of deposited metal and maintain cell operation.
The patent is for ‘a method of prolonging service-life of an energy storage device’ and its technology may help to extend the range of possible applications beyond conventional ‘wet’ fuel cells — as well as ease the challenges of sourcing lithium and the operating temperature limitations of lithium cells.
Another key development is described in WO 2019/191054. The inventors at the University of Texas describe an electrochemical cell including a solid glass electrolyte, a specific cathode and anode, as well as an insulator relay layer that separates the electrolyte and the electrodes.
The solid glass electrolyte is doped with combinations of constituents including Li, Na, K, Mg or Al. The patent is part of an agreement between the University of Texas and Hydro-Québec, which aims to integrate these new cells into batteries for use in a wide range of electronic products and (hopefully) EVs.
As you will know, the potential for solid-state batteries is massive. Without an organic liquid inside, there is no fire risk. They’re also very light, so their range of uses is virtually never-ending. We could truly be on the cusp of big things and thousands of new patent applications are filed each year in the race to tick all the performance, safety and environmental boxes.
Electrolyte innovations represent the majority of these, with patents focused to new polymers, inorganic materials, inorganic-polymer materials, sulphide glass-ceramics, oxide glass-ceramics, perovskites, LISICONs, garnets, hydrides and more.
Managing and optimising the interface between the solid electrolytes and electrodes is another major area of activity. The patenting of insulating/conducting films at this electrolyte/electrode junction appears to be the focus of a huge volume of R&D efforts. Patents are also being filed for the plating and stripping of metal at the anode/electrolyte interface and the general overall integration of solid-state electrolytes into the cell architecture, with a view to creating an efficient, reliable and high-performance battery system.
Ultimately, there are many possibilities when it comes to patenting battery technologies.