Innovative Battery Materials Could Extend EV Range

Batteries are the heartbeat of sustainable transportation solutions, ultimately powering propulsion systems and defining the vehicle’s range. As electric vehicles (EVs) continue to reshape the automotive landscape, advancements in battery technology are crucial for achieving longer ranges, faster charging times, and improved overall performance.

Recently, researchers have made numerous breakthroughs in battery technology, each with notable implications for the future of EV performance and range.

 

Electric vehicle battery research. Image used courtesy of Adobe Stock

 

Silicon + Gel Polymer Electrolytes in EV Batteries

Silicon (Si) materials offer a promising avenue to boost battery energy density thanks to the material’s impressive theoretical capacity, reaching up to 3579 mAh g−1 for Li₁₅Si₄, along with its low operating voltage, measuring 0.4 V less than Li/Li+. However, a major challenge facing silicon in batteries is the material experiences substantial volumetric expansion during electrochemical cycling, causing structural damage and premature failure. So far, many studies have focused on nanostructuring to prevent particle fracture and enhance Li-ion kinetics. However, practical solutions remain elusive due to complex synthesis and significant side reactions with electrolytes. 

In the quest for a 1,000 km EV battery range, researchers at Pohang University of Science and Technology (POSTECH) have recently attempted to employ micro (10-6 m) silicon particles and gel polymer electrolytes as battery materials. 

 

Electron beam creates covalent bonds, linking the silicon microparticle anode to gel polymer electrolyte. Image courtesy of the authors

 

Using gel polymer electrolytes, the researchers developed an economical and sturdy silicon-based battery system. Unlike conventional liquid electrolytes, gel variants are solid or gel-like, providing enhanced stability with their elastic polymer structure. Employing an electron beam technique, the team formed covalent bonds between micro-silicon particles and gel electrolytes. These bonds successfully alleviate internal stress from volume expansion during battery operation, bolstering structural stability and performance.

Despite employing micro-silicon particles (5 μm), much larger than those in traditional nano (10^-9 m) silicon anodes, the battery maintained stable performance. Moreover, the silicon-gel electrolyte system demonstrated ion conductivity similar to batteries with liquid electrolytes, boasting a roughly 40% increase in energy density.

 

Stanford Doubles EV Range 

Rechargeable lithium-metal batteries show promise in significantly increasing, or possibly doubling, the specific energy of current rechargeable lithium-ion batteries, positioning them as prime candidates for next-generation high-energy battery technology. However, continuous charging and discharging cycles make micron-sized lithium metal fragments isolated and trapped within the solid electrolyte interphase (SEI), diminishing their involvement in electrochemical reactions. 

Stanford University researchers developed a viable technique highlighting capacity recuperation from prior cycles. Specifically, the researchers combatted the rapid capacity decline in lithium-metal batteries by implementing a simple yet cost-effective solution of draining the battery and allowing it to rest. 

 

Resting the battery decreases degradation. Image used courtesy of Stanford University (by Wenbo Zhang)

 

The team discovered that resting the batteries in a discharged state, as opposed to a charged state, improves capacity retention by recovering isolated Li. This contrasts with the capacity degradation observed during charged state aging. The team used a hybrid cycling protocol, operando optical microscopy, and titration gas chromatography to validate inactive capacity recovery. This showed Coulombic efficiency greater than 100% in both Li||Cu half-cells and anode-free cells. Their findings suggest a new pathway for capacity recovery in Li-metal batteries, emphasizing the impact of cycling strategies on performance.

 

A Battery-Driven Future

As EVs become mainstream, advancements in battery technology are pivotal to a more sustainable and environmentally friendly future.