MIT’s new concept packs more power in a battery, making it more durable. These new systems could allow a smartphone to last for 3 days without needing to be recharged. (Image Credit: MIT News)
Engineers at MIT have developed a new battery electrode that could lead to more durable batteries that pack a large amount of power per pound. The research is based on MIT’s long-sought goal of utilizing pure-lithium metal as the anode, one of the two electrodes used in batteries. MIT’s electrode design comes from the lab of Ju Li and is part of a concept for developing all-solid-state batteries. The team published their findings in the journal Nature on February 3, 2020.
The design eliminates the liquid or polymer gel that’s used as the electrolyte material between both electrodes in the battery. An electrolyte allows lithium ions to move back and forth while a battery is in its charging and discharging cycles. Researchers say that an all-solid battery would be safer than liquid electrolytes that exhibit high volatility and have been known to cause explosions in lithium batteries.
One of the biggest issues for solid-state batteries is that when they’re charged up, atoms accumulate within the lithium metal, which causes it to expand. Whenever the battery is discharging, the lithium metal shrinks again. These frequent changes make it difficult for solids to maintain constant contact and are likely to cause the solid electrolyte to breakdown or detach.
Another problem is that none of the suggested solid electrolytes are chemically stable when they’re in contact with the lithium metal, which causes it to eventually degrade. To overcome these challenges, researchers worked on developing solid electrolyte material that is completely stable against lithium metal, which is difficult. Li and his team implemented an unusual design that uses an additional two groups of solids, “mixed ionic-electronic conductors” (MIEC) and “electron and Li-ion insulators” (ELI), which are chemically stable when they come in contact with the lithium metal.
The researchers built a 3D nanoarchitecture in the shape of a honeycomb-like array of hexagonal MIEC tubes. Part of the nanoarchitecture is infused with the solid-lithium metal to form an electrode of the battery, but with more space in each tube. When the lithium expands as the battery is charging, it flows into the vacant space in the tubes’ interior, moving like a liquid, while maintaining its solid crystalline structure. This flow, trapped inside the honeycomb structure, eases the pressure from the expansion caused by charging without altering the electrode’s outer dimensions or the existing boundary between the electrolyte and electrode. The ELI serves as an important mechanical binder between the solid electrolyte layer and the MIEC walls.
Since the honeycomb-like walls are made of chemically stable MIEC, the lithium doesn’t lose electrical contact with the material. As a result, the solid battery remains mechanically and chemically stable as its being used. The team successfully experimented on the concept by running a test device through 100 cycles of charging and discharging without causing the solids to breakdown.
This new system could create safe anodes that only weigh a quarter as much as traditional counterparts in lithium-ion batteries for the same proportion of storage capacity. Coupled with new concepts for a lightweight version of the other electrode, the system could result in weight reductions in lithium-ion batteries. This could allow devices, such as smartphones, to be charged once every 3 days without making the device heavier.
The team has developed small-scale devices in the lab, but they expect it to be scaled up very soon. The materials needed for this device are less costly than nickel or cobalt being used in other systems. As a result, these cathodes could cost as little as a fifth as much as traditional versions.
Have a story tip? Message me at: cabe(at)element14(dot)com
