Scientists from Nanjing University have developed an energy-efficient electrochemical unit that makes it possible to extract lithium directly from seawater. The system produces hydrogen and accumulates some of the expended energy at the same time, which makes it more efficient. This technology opens up the possibility of using the ocean as a virtually inexhaustible source of lithium, a key raw material for electric vehicle batteries and energy storage systems.
Although the world’s oceans contain some 230 billion tons of lithium, its water concentration is extremely low at about 0.17 mg per liter. Furthermore, it is dissolved alongside many other ions – sodium, potassium, magnesium and calcium – which makes it very difficult to extract. It is especially hard to separate lithium from magnesium, which is thousands of times more abundant in water and has properties very similar to lithium.
The existing lithium extraction methods require significant amounts of energy to transport ions through special membranes. A major portion of the energy is spent on secondary processes, primarily water electrolysis releasing oxygen and chlorine, which are of little value. The Chinese researchers have proposed a different approach: accumulating energy in the system instead of wasting it. To achieve this, they used a special electrode that can accumulate energy in chemical form. As a result, lithium extraction is combined with energy storage.
The new unit consists of two chambers filled with seawater, separated by a ceramic membrane based on lithium-aluminum-germanium-phosphate (LAGP), which primarily allows lithium ions to pass through. One of the chambers uses a nickel hydroxide electrode, while the other uses a catalyst based on nickel-molybdenum compounds. When voltage is applied, lithium ions pass through the membrane into the receiving solution, with hydrogen released at the cathode. The catalyst reduces energy losses in the process. At the same time, energy is accumulated at the other electrode.
After the cycle is completed, this energy can be recovered: the system works like a small battery using zinc and nickel. This way, only about a third of the energy goes directly to lithium extraction, with the rest stored as hydrogen in the electrode. For every gram of lithium, about 807 ml of hydrogen is produced, with a net energy consumption of some 6.40 Wh per gram.
Experiments show that this approach is highly efficient. In 48 hours, lithium concentration in the solution rose from 0.183 mg/L to 306.2 mg/L, while the magnesium-to-lithium ratio fell from 6615 to 4.9×10⁻⁴, a reduction by 13–14 million times. This was caused partly by the increased alkalinity of the medium: magnesium and calcium converted into insoluble compounds and precipitated without the addition of reagents. This made it possible to obtain lithium carbonate with a purity of 99.6% from the resulting solution, which meets the battery industry requirements.
The high efficiency is due to a combination of factors. The membrane allows lithium to pass through, the catalyst reduces the amounts of energy needed for hydrogen release, and the process itself becomes more efficient: alkalinity increases, interfering ions are removed more quickly, and the solution gets purified.
Technological flexibility is a significant advantage as well. The system consists of individual blocks that can be combined to increase productivity. Plus, the expensive LAGP membrane can be replaced with a cheaper alternative: lithium-aluminum-titanium-silicon-phosphate (LATSP). Experiments with this membrane showed comparable results: lithium concentrations reached 301.8 mg/L with a similar reduction in magnesium content.
However, the technology is still in the laboratory stage. The unit’s productivity remains relatively low, about 0.97 grams of lithium per square meter of membrane per hour, which is why it has yet to be scaled up for industrial use. Nevertheless, the paper’s key point is that lithium can be extracted from seawater with moderate amounts of energy expended, simultaneously producing hydrogen and other useful products. Since lithium demand might grow by 8–10 times by 2050, this could be a promising direction for the energy sector in the future.
