How Lithium-Metal Doubles the Energy Density of Rechargeable Batteries

A new generation of rechargeable lithium-metal batteries have double the energy capacity of lithium-ion batteries.

SolidEnergy Systems, a company founded by Qichao Hu in 2012, has announced a new rechargeable lithium-metal battery which offers two times the energy capacity of a conventional lithium-ion battery for a given battery size and weight.

The new battery is as safe and long-lasting as a lithium-ion battery. Considering the widespread use of lithium-ion batteries in smartphones, electric cars, drones, and more, the invention is a big stride. The battery can make these devices work twice as long or make their miniature version feasible.

The Holy Grail of Battery Industry

Researchers have known the advantages of lithium-metal batteries (i.e., a higher energy density and a smaller size) for decades. However, these batteries have been so far non-rechargeable and have been known to burst into flame. These two characteristics stem from the reaction which takes place between the lithium metal and the battery’s electrolyte.

This reaction not only produces compounds which increase the resistance in the battery and reduce the cycle life, but also forms mossy lithium-metal bumps on the anode which leads to short circuits. A short circuit generates high heat and ignites the flammable electrolyte.
Generally, the measures taken to make these batteries safer degrade its energy performance.
This new generation of lithium-metal batteries combats this issue by altering the materials inside the battery in order to change the chemistry, itself.

Lithium-Metal Foil Anodes

To increase the energy capacity, SolidEnergy utilizes a very thin high-energy lithium-metal foil instead of the conventional anode material, graphite. This doubles the energy density due to the increased number of ions held by the lithium metal.
In addition, using the ultrathin lithium-metal foil—which is five times thinner than the traditional lithium-metal anode and several times thinner than traditional graphite, carbon, or silicon anodes—researchers have reduced the battery size by a factor of two.

The first working prototype of the new battery, presented in October 2015, was half the size of a lithium-ion battery for an iPhone 6. It provided 2.0 amp hours, whereas the lithium-ion battery provides 1.8 amp hours. This successful debut earned $12 million of investment for the company.

The lithium-metal battery compared to a lithium-ion battery seated in an iPhone. Image courtesy of Business Wire.

A Rechargeable and Safe Lithium-Metal Battery

Hu employed an ultrathin lithium-metal foil as the anode to significantly reduce the battery size. However, the achieved battery worked only at 80 degrees Celsius or higher and could not be used in many commercial applications.
Lithium-metal batteries are often more volatile and short-lived than the lithium-ion ones. In order to arrive at a rechargeable and safe solution, the company had to make chemical modifications to the electrolyte. Their solution was to develop a solid and liquid hybrid electrolyte.
Hu utilized a solid electrolyte as a coating for the lithium-metal foil to bring the operating temperature of the battery down. Moreover, he introduced a novel quasi-ionic liquid electrolyte which is inflammable and does not adversely react with the lithium metal.
The outcome was a battery which offered the energy capacity of lithium-ion batteries at room temperature and had the safety and longevity of lithium-ion batteries.

Manufacturing Scalability

Another impressive feature is that the manufacturing equipment required to create these batteries is the same as that of lithium-ion batteries. This means that they could be commercially available relatively quickly.
Achieving this manufacturing capability is actually a story of circumstance influencing design.
When Hu was establishing SolidEnergy in 2012, the well-known MIT battery startup A123, which had been developing lithium-ion batteries, was filing for bankruptcy. At first, this was intimidating for SolidEnergy. However, Hu ended up using A123’s then-idle manufacturing line to build the first generation of lithium-metal batteries.

The development of the lithium-metal battery. Image courtesy of the MIT Technology Review.

Since SolidEnergy had no facilities, no funding, and no labs to build batteries, the company was forced to adapt its prototyping with the existing lithium-ion manufacturing equipment. The final result was a new technology manufactured with commercially available tools.
According to Hu, many battery companies do the opposite by mainly concentrating on the materials and building their own labs based on the materials they are going to work with. Since they do prototype using completely new manufacturing processes, their battery cannot be easily adapted to the commercial manufacturing line.

Target Markets: Starting with Drones

SolidEnergy has an incredibly aggressive timetable to sell batteries for smartphones and wearables in early 2017 and for the electric cars in 2018. The company's first target, though, is the drone market which they aim to cover this November.

Considering the increasing interest of some companies to provide internet access to rural areas using drones and balloons, SolidEnergy plans to offer its first series of batteries for drone applications. Selling batteries for drone applications could be a good strategy for introducing the new battery to the market.

Note that there are battery companies which have failed because of the established battery providers such as Panasonic which, as an example, has a multi-billion-dollar contract with electric car manufacturer Tesla. However, the recently growing specialized drone market could give SolidEnergy the chance to attract the attention of other customers and bring the technology to market.

Unfortunately, the company has not released many details such as a cost per kWh figure for the battery. However, if the technology hits the market, it will have a huge societal impact.
As an example, an electric car, which now goes 200 miles on a single charge, will be able to either go 400 miles per charge or reduce its battery size and weight by a factor of two. A development of that import could finally help consumers overcome the largely overblown fear of "range anxiety" when it comes to electric cars.


In short, these batteries could change the way the world views energy. And with the manufacturing and investment behind lithium-metal batteries, it might not be long until we find out.