So, Next-generation battery! A new mathematical model has brought together the physics and chemistry of highly promising lithium-metal batteries, providing researchers with plausible, fresh solutions to a problem known to cause degradation and failure.
Close cousins of the rechargeable lithium-ion cells widely used in portable electronics and electric cars, lithium-metal batteries hold tremendous promise as next-generation energy storage devices. Compared to lithium-ion devices, lithium-metal batteries hold more energy, charge up faster, and weigh considerably less.
To date, though, the commercial use of rechargeable lithium-metal batteries has been limited. A chief reason is the formation of “dendrites” – thin, metallic, tree-like structures that grow as lithium metal accumulates on electrodes inside the battery. These dendrites degrade battery performance and ultimately lead to failure which, in some instances, can even dangerously ignite fires.
A direction for design
Experimentalists have long strived to understand the factors leading to dendrite formation, but the laboratory work is labor intensive, and results have proven difficult to interpret. Recognizing this challenge, the researchers developed a mathematical representation of the batteries’ internal electric fields and transport of lithium ions through the electrolyte material, alongside other relevant mechanisms.
With the results of the study in hand, experimentalists can focus on physically plausible material and architecture combinations. “We hope that other researchers can use this guide from our study to design devices that have the right properties and reduce the range of trial-and-error, experimental variations they have to do in the lab,” Tchelepi said.
Specifically, the new strategies for electrolyte design called for by the study include pursuing materials that are anisotropic, meaning they exhibit different properties in different directions. A classic example of an anisotropic material is wood, which is stronger in the direction of the grain, visible as lines in the wood, versus against the grain. In the case of anisotropic electrolytes, these materials could finetune the complex interplay between ion transport and interfacial chemistry, thwarting buildup that proceeds dendrite formation. Some liquid crystals and gels display these desired characteristics, the researchers suggest.
Building and testing
The team looks forward to seeing other scientific investigators follow up on the “leads” identified in their study. Those next steps will involve manufacturing real devices that rely on experimental new electrolyte formulations and battery architectures, then testing out which might prove effective, scalable, and economical.
“An enormous amount of research goes into materials design and experimental verification of complex battery systems, and in general, mathematical frameworks like that spearheaded by Weiyu have been largely missing in this effort,” said co-author Tartakovsky, a professor of energy resources engineering at Stanford.
Following through on these latest results, Tartakovsky and colleagues are working on constructing a fully-fledged virtual representation – known as a “digital avatar” – of lithium-metal battery systems, or DABS.
Latest developments in battery technology provide a range of improvements over conventional technologies, such as:
- Improved specific energy and energy density (more energy stored per volume/weight)
- Longer lifetime
- Better safety / less flammable
- Require less time to be fully charged
- Reduced Levelized cost of energy (LCOE)
Before we delve into the current and upcoming battery technologies, let’s first look at the anatomy of batteries. The table below lists the key parts of a battery and its functions:
|Battery components||Typical composition||Function|
|Cathode||Lithium, Nickel, Cobalt, Manganese, Aluminum, Iron, and Phosphate||Contributing Li-ions through the channel of electrolyte and electrons to be stored at the anode side|
|Anode||Graphite, Silicon (Si)||Keeping Li-ions stored when the battery is charged and releasing Li-ions and electrons back to the cathode when discharged|
|Separator||Polyethylene (PE)||Keeping cathode and anode materials separated while allowing Li-ions capable of travel between them|
|Current collector (Cathode)||Aluminum (Al)||Collecting electrons generated from the electrochemical reaction at the cathode side while preventing it from being oxidized by cathode materials|
|Current collector (Anode)||Copper (Cu)||Collecting electrons generated from the reaction at the anode side while preventing it from being oxidized by anode materials|
|Electrolyte||Solvents (EC, DMC, DEC, EMC, PC, etc.); Salts (LiPF6, LiClO4, LiBF4, etc.)||Providing Li-ions with good conductivity while maintaining good thermal stability and a wide operable voltage window|
The future of Li-ion battery technology is based on three specific technological advancements.
Improvements in battery technology can be achieved in a huge range of different ways and focus on several different components to deliver certain performance characteristics of the battery. While there are various paths that battery technology evolution could take, S&P Global has defined three new alternatives to lithium-ion batteries in the table below.
Overview of next-generation battery technologies:
|Current Conventional Li-ion||Next-generation 1 Gr-Si Anode / Hi-Ni Cathode:||Next-generation 2 Solid State Battery (SSB)||Next-generation 3 Lithium Sulphur / Air|
|Most favorable technologies for today’s EV and stationary energy storage applicationsCathode material: NMC 532, NMC 622, NCA, or LFPAnode material: artificial graphite or natural graphiteElectrolyte: carbonate-based liquid organic solvent separator: Polymer thin film current collector: Cu and Al foils||Most likely to be adopted on light vehicle EVs that require longer ranges and fast charging.Cathode material: NMC 811 or NCA 90Anode material: natural/artificial graphite with SiOx or pure SiElectrolyte: carbonate-based liquid organic solvent separator: Polymer thin film current collector: Cu and Al foils||The key technology to eliminate battery fire concerns and deliver moderate performance improvements.Cathode material: NMC 811, NCA 90, LNMO (high-voltage)Anode material: graphite with a large amount of pure Si or Li-metal electrolyte: ceramic, polymer, or sulfur-based solid electrolyte separator: as part of solid-state electrolyte current collector: Cu and Al foils||Revolutionary technologies that diverge from all previous chemistry systems.Cathode material: Li-metal anode material: Sulphur or Oxygen/AirElectrolyte: solid-stage separator: as part of solid-state electrolyte current collector: Porous carbonaceous material, noble metal catalysts, and Cu foil|
98% of next-generation end-market battery demand comes from the automotive and transport sector.