A long-lasting lithium battery!

A long-lasting lithium battery to compensate the limitations of lithium metal batteries.

Sradha Subash A

Xin Li, Associate Professor of Materials Science at the Harvard John A. Paulson School of Engineering and Applied Science (SEAS) | credits: Harvard John A. Paulson School of Engineering and Applied Science

Researchers have developed a solution to a forty year problem. For decades they have been trying to make use of the energy of solid-state, lithium-metal batteries, which can hold substantially more energy in the same volume and can be charged in a short time as compared to traditional lithium-ion batteries.

Xin Li, Associate Professor of Materials Science at the Harvard John A. Paulson School of Engineering and Applied Science (SEAS), said that, even though the lithium-metal batteries are considered as a 'holy grail' for battery chemistry due to its high capacity and energy density but still the stability of these batteries has always been poor. Long-lasting, quick-charging batteries are needed for the growth of the electric vehicle market, but today's lithium-ion batteries are too heavy, expensive and slow to be used in this industry and also demand more time to get charged.
 
Now, Li and his team have developed a stable lithium-metal solid state battery that can be charged and discharged at a high current density for at least 10,000 cycles, far more cycles than previously demonstrated. The new design is paired with a commercially high energy density cathode material.
 
The lifetime of electric vehicles could be increased from 10 to 15 years to that of the gasoline cars by using this battery technology. Also, there is no need to replace the battery. Due to its high current density, the electric vehicles could get fully charged within 10 to 20 minutes. The research is published as a journal in 'Nature' magazine. Li said that as per their research, the solid-state battery could be fundamentally different from the commercial liquid electrolyte lithium-ion battery, also he added that by studying the fundamental thermodynamics of these batteries, the superior performance and abundant opportunities can be unlocked.

$ads={1}

The big challenge with lithium-metal batteries is their chemistry. During charging, lithium batteries move lithium ions from cathode to anode. A needle-like structures known as dendrites form on its surface, when the anode is made with lithium metal. These root-like structures grow into the electrolyte and pierce the barrier separating anode and cathode. This causes the battery to get short or even catch fire. Li and his team devised a multilayer battery that sandwiches various layers of materials with differing stabilities between the anode and cathode to solve this issue. This multilayer battery made up of multi-material, prevents the penetration of lithium dendrites by controlling and containing them other than stopping them altogether.
 
Imagine the battery as a BLT sandwich. First comes the lithium metal anode (bread), followed by a coating of graphite (lettuce). Next comes the first electrolyte(a layer of tomatoes) and the second electrolyte (a layer of bacon) and then finishes it off with another layer of tomatoes and the last piece of bread which is the cathode.
The first electrolyte (chemical name Li5.5PS4.5Cl1.5 or LPSCI) is more stable with lithium but it is exposed to dendrite penetration. The second electrolyte (Li10Ge1P2S12 or LGPS) is less stable with lithium but it helps to resist dendrites. This design allows dendrites to grow through graphite and the first electrolyte but the growth of dendrites gets controlled when it reaches the second. In simpler terms, the dendrites grow through the lettuce and tomato but they stop at the bacon. The bacon barrier stops the dendrites from piercing through and thereby shorting the battery. 
 
Luhan Ye, co-author of the research paper and graduate student at SEAS said that their strategy of incorporating instability in order to stabilize the battery might seem illogical but just like how an anchor guides and controls a screw going deep into a wall, the multilayer design too guides and controls the growth of dendrites. The only difference is that the anchor quickly becomes too tight for the dendrite to pierce through, therefore, the growth of the dendrite is stopped. Also, the battery is self-healing because its chemistry allows it to backfill the holes created by dendrites.
 
Li said that the feasibility study of design proves that lithium-metal solid-state batteries could be competitive with commercial lithium-ion batteries. This multilayer design's stability and durability make it theoretically competitive with mass manufacturing procedures in the battery industry. Scaling its size up to the commercial battery may not be easy and there are still some practical challenges to overcome.
 
The Harvard Data Science Initiative Competitive Research Fund and the Dean's Competitive Fund for Promising Scholarship funded the research. Harvard’s Office of Technology Development has protected a portfolio of intellectual property concerned with this project, which is being advanced toward commercial applications with support from Harvard’s Physical Sciences and Engineering Accelerator and the Harvard Climate Change Solutions Fund.