lithium ion electric car battery.

A new water-based battery design is safer and more energy-efficient than traditional lithium-ion batteries, Chinese researchers claim.

The water-battery has a lifetime of over 1,000 charge-discharge cycles, the team reported April 23 in the journal Nature Energy.

One of the most important properties of any battery is the energy density — how much energy the battery contains relative to its size or weight. Lithium-ion batteries have a particularly high energy density and are widely used in electric cars and portable devices. However, the liquid component, known as the electrolyte, typically contains organic chemicals which can catch fire or explode if the system overheats.

In contrast, water-based batteries are much safer but generally have a lower energy density thanks to the narrow voltage window in which they operate. However, by hacking the chemistry taking place inside the water electrolyte, Li’s team have dramatically boosted both the energy density and the overall performance of aqueous batteries.

Electrolyte solutions are actually a mixture of many different chemicals, each controlling a different aspect of the battery's performance. Additives called mediators help move electrons across the solution by undergoing a series of supporting oxidation and reduction (redox) reactions.

For aqueous batteries, the most common mediator is iodine: through a sequence of individual redox reactions, this halogen element can transfer up to six electrons per cycle, converting iodide (I–) to iodate (IO3–). However, slow reaction rates and unwanted byproducts mean that this additive usually results in a low-energy-density battery.

To improve the efficiency of this mediating redox sequence (and therefore the overall energy density), Xianfeng Li from the Chinese Academy of Sciences, and colleagues developed a mixed halogen electrolyte, containing both I– and bromide (Br–) ions in an acidic solution. Introducing bromine, another halogen element capable of transferring electrons, provided a stepping stone for this difficult chemistry, increasing the reaction rate and suppressing the formation of nuisance byproducts.

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Through detailed electrochemical and spectroscopic analyses, the team demonstrated that the bromide ions participated in the redox reactions alongside the iodide, forming a vital intermediate and boosting the speed and efficiency of the electron transfer sequence.

The researchers then began a series of experiments to evaluate the impact of this “hetero-halogen” electrolyte on the overall performance of several common battery types using different materials as the negative terminals (anodes).

The new electrolyte nearly doubled the energy density compared with standard lithium-ion batteries when used with cadmium anodes, which are typically found in high-energy portable devices such as power tools. . Meanwhile, vanadium systems, which are often attached to power plants and renewable energy generators for grid energy storage, demonstrated particularly long lifetimes, maintaining peak performance over more than 1,000 charge-discharge cycles.

In both cases, the team reported improved energy efficiencies and calculated that the aqueous hetero-halogen system would be cost-competitive compared with current lithium-ion technologies.

The team hopes that this substantial performance enhancement will lead to wider use of water-based batteries as a safer, high-energy-density alternative to existing systems.

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China’s lead on EV battery innovation has not slipped an inch

The world is lagging behind China on EV battery innovation to the extent that global manufacturers are barely able to compete.

Japanese auto giant Nissan, for instance, last month announced a “breakthrough” in the development of solid-state batteries — light alternatives with longer range compared to traditional lithium-ion EV batteries.

But China beat them to the punch. In April, EV maker Nio became the first manufacturer to commercially roll out solid-state batteries in their cars, complete with the promise that they are fully replaceable. Meanwhile, China also opened its first large-scale sodium-ion battery energy storage station, which could pave the way for next-gen EV batteries that do not rely on scarce, pricey lithium.

The race underscores the concern in Europe and the US that China faces little real competition when it comes to EVs.

Japan needs solid-state batteries to make its EV sector run

Japan’s need for lots of solid-state EV batteries, fast, is “particularly urgent,” Nikkei Asia wrote, as the country — a large auto exporter — struggles to emerge as a key player in the EV market. Multiple Japanese companies are pumping millions of dollars (some of it from the government) into research and development to accelerate their production — but it might not be enough. One Japanese engineer said there is “no chance” solid-state batteries will replace more than 10% of lithium-ion batteries by 2030.

Sodium-ion batteries could replace lead-acid for gas-powered cars

While sodium-ion batteries hold the potential to significantly reduce the price of EVs, some battery makers see a more immediate use for their technology under the hood of traditional gas-powered vehicles, according to TechCrunch. US companies like Bedrock Materials see the value in a “disrupt from the bottom” approach: Sodium-ion batteries aren’t quite good enough to replace lithium in EVs, but they can replace the lead-acid in typical cars’ batteries. The strategy enables the company to improve the tech and make money while doing it. But again, Chinese battery manufacturers are already years-ahead in the development process.

Solid-state batteries offer more efficiency for EVs, but they aren’t the only way

Solid-state batteries are “not the only way automakers could achieve lighter, cheaper and faster charging electric vehicles,” CNN automarket journalist Peter Valdes-Dapena reported. The current designs for solid-state EV batteries tend to conduct electricity slowly, meaning they take longer to charge and don’t allow for fast vehicle acceleration (although Harvard University researchers said they are on the cusp of a new design framework that charges in minutes). Solid-state appeals because they can be made with fewer rare earth minerals, including lithium, but right now, they tend to use more lithium than other EV batteries, according to Valdes-Dapena. In turn, some automakers like GM see more promise in making lithium-ion batteries more efficient instead, he wrote.

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