There has been a surge in innovation activity targeting next generation battery technology with the aim of reducing capital costs for battery energy storage systems and improving their performance. With improved performance, it is hoped that they can be used for both short duration (SDES) and long duration (LDES) applications in the future.
We have seen some notable advances in sodium-ion battery technology recently, some of them resulting from work conducted over the past decade by Faradion. With sodium-ion technology offering similar performance to lithium-ion, at a lower cost and often with improved cold performance relative to lithium-ion systems, there is huge potential for this technology and the market for sodium-ion is expected to grow significantly in the future. However, sodium-ion batteries have lower energy densities than their lithium-ion counterparts, and so current research has focused primarily on remedying this weakness. Patent protection has recently been sought by research scientists in China (CN111994890A), the invention is a new sodium vanadium phosphate cathode material and a method for producing it. The material has been shown to enhance the conductivity, capacity, and cycling stability of sodium-ion batteries, which could make them viable for a wider range of static energy storage applications in the future.
Other possible alternatives to Li-ion batteries for energy storage applications include redox-flow batteries and metal-air batteries.
Redox-flow batteries have a long history, with the first patent filing relating to this technology appearing as early as 1880. They were also trialled in electric vehicles as early as the 1970s. Redox-flow batteries operate by storing energy in electrolyte solutions that are pumped through the cell stack to store or release energy. Power is determined by the surface area of the electrodes, and energy by the size of the tanks that store the electrolyte. This, combined with a huge range of available chemistries, provide for a highly flexible technology that can be tailored for the specific application.
Although suffering from low energy and power densities, as a result of the potentially large volumes of electrolyte needed, redox-flow batteries are long lasting, making them well suited to LDES applications.
UK-based Invinity Energy Systems is a leader in this field, with a carbon-based bipolar plate (patent pending as GB2610372A), which is less susceptible to corrosion and mechanical damage. Invinity has installations at the Energy Superhub in Oxford, UK, where it provides battery load shifting, and Chappice Lake, Alberta, where it works with a solar power grid.
Metal-air batteries combine a metal anode with oxygen taken from ambient air as the cathode. Current technology offers the hope of low costs and design simplicity, but energy efficiencies and cell lifetimes remain low. Zinc-air batteries are commonly used in hearing aids, and can provide capacities similar to AA alkaline batteries, although they have a lifetime of only a few weeks. Aluminium-air batteries have been found to offer good energy densities, but until now costs have been prohibitive. Similarly, lithium-air systems are under consideration, but many challenges remain to be overcome, and the integration of lithium brings with it the supply chain concerns of the more developed lithium technologies.
Of most interest in the LDES sector could be iron-air technologies. Iron-air batteries are theoretically inexpensive, relying on iron oxide (rust) as the key component. Iron-air batteries would typically be hybrid fuel cell systems, and show potential, but many operational obstacles remain to be overcome.
Regardless of the electrochemical chemistries employed, it is thought that battery systems alone won’t be able to meet growing energy storage requirements in the future. As well as having complex supply chains and being reliant on rare earth metals in high demand, existing Li-ion batteries primarily provide short-term storage, and even the alternative chemistries which have reached the market are a number of years from being widely available.
To take the example of the UK, the National Energy System Operator (NESO) and National Infrastructure Commission estimate that 25 TWh of LDES twill be needed to support the electricity grid by 2050 – so where is it going to come from?
To complement BESS and to boost LDES capacity, one potential solution is thermal energy storage. Sensible heat storage (SHS) techniques use high heat capacity materials for longer term storage of heat, employing either directly generated heat or electrical energy from other sources converted to heat for storage.
For example, there is interest in ‘molten salts’ for storing heat energy for several weeks or even months. Innovators at the Xi’An Thermal Power Research Institute in China have recently filed an international patent application for a molten salt storage apparatus – WO2023193487A1 – offering extensible thermal energy storage.
Another innovative form of TES utilises bricks of high heat capacity material, which can store excess renewable energy as heat for longer and more cheaply than Li-ion battery based chemical energy storage. Many systems use bricks made from readily available materials, such as graphite, aluminium, clay and iron ore, which are cheaper and easier to source than those required for Li-ion batteries. Recent advances aim to facilitate effective conversion of stored heat energy to usable electrical energy via arrays of thermophotovoltaic cells to convert infrared from TES bricks.
A technology that could complement both TES and BESS systems in the future is superconducting magnetic energy storage (SMES). SMES systems have extremely high energy conversion efficiencies, can deliver bursts of high power quickly, and offer the ability to store energy indefinitely as electric current induced in a superconducting coil. Although SMES systems are primarily used in power quality applications due to the high costs associated with keeping the superconducting coils below their critical temperature, the advent of high temperature superconducting materials is opening up the possibility of larger scale, efficient energy storage.
Converting electrical energy to gravitational potential energy for storage is a well-established principle in the form of pumped hydropower. This same principle is now also being put into practice using weighted electric winch systems housed in vertical shafts (for example former mine shafts). At times of excess supply, electrical energy is used to raise a weight via an electric motor. When the energy is needed in the grid, the weight is lowered, driving a generator. This technology has the advantages of being relatively cheap and very long-term.
Backed by crowdfunding, UK-based Gravitricity has recently secured patent protection in the US for its efficient, gravity-based energy storage system, US11965490B2, which offers a large storage capacity per shaft and enables a continuous flow of power input and output.
As the transition to renewables accelerates globally, demand for clean energy storage is set to grow exponentially. From an IP perspective, patent protection is vital to ensure that the commercial potential of early breakthroughs is fully protected for the future, incentivising the investment necessary to bring the technology to market and help mitigate climate change.
