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<2024> Aqueous Secondary Battery Technology Development Status and Forecast

Amidst the urgent global necessity to move away from fossil fuels, renewable energy sources like solar and wind power are becoming more common. In this environment, where sustainable energy storage technologies are constantly evolving, companies are relentlessly seeking efficient and eco-friendly solutions. Therefore, a promising new solution that has emerged is aqueous batteries.

As of the end of 2023, global renewable energy capacity is predicted to exceed 2,600 GW, accounting for nearly 30% of total global power generation capacity. Battery storage systems such as lithium-ion batteries play a crucial role in mitigating the intermittency of renewable energy sources like solar and wind power. For instance, they store surplus energy during periods of high generation and release it during times of high demand or low generation, ensuring a stable power supply.

Aqueous batteries are expected to solve safety issues of power batteries. Current energy density is relatively low with only at 75Wh/kg, however, in the future, new nanomaterials are planned to be applied to electrodes to increase energy density. It is anticipated that within the next 10 years, they could replace a portion of lithium-ion batteries. However, due to the relatively low energy density, further performance improvements are necessary to meet the demand for high-energy-density batteries in automotive and other fields.

As the importance of the lithium-ion battery supply chain and geopolitical risks increase, the US and EU are actively establishing policies and strategies to reorganize the supply chain. In line with global trends, the Korean government also released a strategic roadmap for secondary batteries in the second half of 2023 and began securing key source technologies such as electrode materials and solid electrolytes to replace existing materials. In particular, they plan to actively support securing ‘next generation’ source technologies such as lithium-air batteries, aqueous zinc batteries, multi-ion batteries, and seawater batteries, which can be ‘game changers.’

Among aqueous ion batteries, there are already commercialized batteries such as Ni-MH, Ni-Fe, Ni-Zn, and Zn-Br, but this report excludes Ni-based batteries and covers aqueous lithium batteries, aqueous zinc batteries, multi-ion batteries, and seawater batteries. We plan to focus on technology for next-generation batteries.

In the case of Ni-MH batteries, bipolar nickel-hydrogen batteries were jointly developed by Toyota Motor Company and Toyota Industries, and are being used as driving batteries for the Toyota “Aqua” released in July 2021. And in 2022, adoption has also been decided for the Lexus brand like “RX” and Toyota “Crown.” Toyota Industries responds to future demand expansion by producing bipolar batteries at its second plant.

A major advance in aqueous ion battery technology can be seen as the application of water-in-salt electrolyte. As the concept of high-concentration electrolytes has been proposed, technology has been developed to significantly increase the electrochemical stability window of aqueous electrolytes, brightening the prospects for the development of high-voltage, high-energy-density aqueous secondary batteries.

For example, in the case of hydrate melt technology developed in 2016, two types of lithium salts are mixed in a certain ratio and liquefied by simply adding a small amount of DI water. The limit is 2V or less and 100Wh/kg of general aqueous solution. However, when hydrate melt was used as the electrolyte, the voltage was 2.4~3.1V, the energy density greatly exceeded 100Wh/kg, and it was found that ultra-fast charge and discharge of less than 6 minutes, equivalent to almost 10C, was possible, and commercially available lithium using organic electrolyte solution was found to be possible. Equivalent to ion batteries was achieved.

Recently, with the introduction of electrolytes using soluble PEG, most lithium cathode materials can be applied, the range of anode choices has expanded to include vanadium-based, sulfide-based, and manganese-based, and the stable potential window has also expanded to 3.2V.

Meanwhile, the market for aqueous ion batteries is expected to grow at a CAGR of 25% from approximately 62.3 million USD in 2018 to 578 million USD in 2028.

In this report, we detailed the current status of technology development that can be applied up to 3V beyond the decomposition voltage of water by applying water in salt electrolyte, as well as the status of aqueous zinc batteries, seawater batteries, and multi-ion batteries, which are in the midst of technology development for commercialization. Projects and programs from each country are introduced, and each country's response status is included.

The strong points of this report are as follows.

① Detailed information on recent technological trends surrounding aqueous secondary batteries

② Detailed technical development and trends of aqueous lithium battery and aqueous zinc battery companies

③ Introduction to the current status of aqueous battery development programs and projects in each country