Tech Insights

A Better Balance: Water-Based vs. Lithium-Ion Batteries

May 28, 2024 by Jake Hertz

Scientists have developed an aqueous battery that could surpass conventional lithium-ion batteries. 

High energy density is a key requirement for longer battery operating times, such as in electric vehicles. However, safety must also be ensured to prevent potential hazards like overheating, fires, or explosions. Striking the right balance between high energy density and safety features is essential in guaranteeing reliable and secure battery operation.

Chinese scientists claim they have developed an aqueous battery to surpass conventional lithium-ion batteries in energy density and safety. The battery uses an iodine and bromine process to produce energy density and avoid fire risks.

 

Water-based battery.

Water-based battery. Image adapted from Adobe Stock

 

The Energy Density Dilemma

Energy density in batteries refers to the energy stored per battery mass or unit volume. It measures a battery's capacity to hold energy, usually expressed in watt-hours per liter (Wh/L) or watt-hours per kilogram (Wh/kg). Battery energy density is essential because the greater it is, the longer a battery can sustain a charge relative to its size. This makes high-energy-density batteries valuable when space is limited but high-energy output is required, as seen in EVs and other devices.

However, when a battery contains more energy, it has greater potential for release in case of an incident such as thermal runaway or combustion. As a case scenario, liquid electrolytes in lithium-ion batteries are volatile and can cause combustion, posing fire risks. These safety concerns arise because the materials and chemistry enabling high-energy storage are also more reactive. 

 

Video used courtesy of UL Research Institutes

 

Conversely, batteries with lower energy density, such as nickel-metal hydride or lead acid, are typically more stable and less prone to catastrophic failure. However, they are bulkier and heavier, limiting their use in space-constrained applications. 

Balancing these factors involves improving battery management systems, enhancing thermal regulation, and developing new materials offering high energy density and inherent safety. Safety features are available in these batteries to address this, but they limit their compactness and weight. 

 

More Power, Less Risk with Aqueous Batteries

Researchers from the Chinese Academy of Science’s Dalian Institute of Chemical Physics have developed a water-based battery with nearly double the energy density of lithium-ion batteries. Moreover, they claim the battery’s chemistry makes it inherently safer than lithium batteries.

The team’s iodine and bromine-based aqueous battery achieves an impressive energy density of up to 1,200 watt-hours per liter (Wh/L), surpassing the 700 Wh/L of non-aqueous lithium batteries. The team found that combining iodine and bromine allows the battery to deliver the maximum electron transfer. With an iodine electrolyte concentration of 6 M, the battery can transfer over 30 M electrons and store over 840 Ah of energy. Another battery using this liquid and cadmium (Cd/Cd2+) as the anode was found to store over 1,200 Wh of energy. Even when connected to a strong load, the battery maintained 72% efficiency. 

The researchers also highlighted the safety advantages of this aqueous battery over non-aqueous lithium batteries. Generally, aqueous batteries are less risky to hazards than lithium-ion batteries because they use water-based electrolytes, which are less flammable and volatile than the organic electrolytes used in lithium-ion batteries.

 

Powering the Next Generation

Professor Li Xianfeng, one of the study’s authors, noted that the findings could expand the application of aqueous batteries in the power battery field. Currently, the majority of EVs depend on lithium-ion batteries for operation. According to the Department of Energy, a single electric car's lithium-ion battery pack typically contains around 8 kg of lithium. This innovation could impact the industry by offering higher energy density and enhanced safety in a single package.