Solid-state batteries, an emerging technology revolutionizing the battery industry, are gaining significant market traction. At Energy Taiwan 2024, DIGITIMES Research spoke with Ming Chi University of Technology (MCUT), an academic partner of Formosa Smart Energy, to delve into the challenges in developing all-solid-state batteries and the innovative solutions they are implementing.
Formosa Smart Energy, collaborating with the Battery Research Center of Green Energy at MCUT, is leading Asia's first academic project on all-solid-state battery development. The partnership has invested NT$230 million (approx. US$7.13 million) in a pilot production line using advanced German equipment. Installation is scheduled for completion in the first quarter of 2025, with trial mass production expected by the second quarter of 2027.
The trial mass production aims to produce all-solid-state nickel-cobalt-manganese (NCM) and lithium iron phosphate (LFP) batteries, targeting energy densities of 400 Wh/kg and 300 Wh/kg, respectively.
Solid-state batteries use a solid electrolyte membrane instead of the liquid electrolyte and separator used in conventional lithium batteries, significantly enhancing safety. Traditional batteries risk thermal runaway—a chain reaction causing overheating—due to their flammable liquid electrolyte and separator.
Thermal runaway occurs when conventional lithium-ion batteries overheat due to their flammable liquid electrolyte. In contrast, solid-state batteries use non-flammable solid electrolytes, mitigating these risks and enhancing battery safety.
Solid electrolytes endure higher decomposition temperatures, often exceeding 250°C (482°F) and reaching over 500°C for oxide-based types, effectively preventing battery cell overheating and reducing safety risks.
Most industry-developed solid-state batteries are classified as semi-solid or quasi-solid, containing 10% and 1% liquid electrolyte, respectively, falling short of the fully solid-state battery standard. As liquid electrolyte content rises, battery weight increases. Overcoming interfacial resistance remains the primary challenge to achieving fully solid-state batteries.
A fully solid-state battery comprises a cathode plate, a solid electrolyte membrane, and an anode plate, all made of solid materials, forming a "solid-solid interface" within the cell.
Simply put, combining these three solid materials creates more gaps, limiting lithium-ion pathways. This increased resistance slows lithium-ion transport through the solid electrolyte, unlike in liquid counterparts.
For comparison, lithium-ion movement in a traditional liquid battery is as fast as a runner, while in a solid-state battery, it is akin to a walking pace.
MCUT addresses these challenges by using a composite solid electrolyte, combining inorganic ceramics (oxides) and polymers. The ceramic element promotes lithium-ion conduction, while the polymer fills gaps in the solid interface, boosting lithium-ion transport speed.
This enhancement allows lithium-ion transport speed to resemble a jogging pace, rather than walking.
During a demonstration verifying the fully solid-state battery model, technicians cut the battery in half. The test showed no liquid leakage, and the connected light bulb remained illuminated, confirming the battery's functionality despite the physical cut.
Formosa Smart Energy and MCUT customize battery designs by adding small amounts of liquid electrolyte for specific applications. For example, they incorporate 0.4% liquid electrolyte to meet the high-power discharge needs of drones during takeoff, boosting the battery's discharge capabilities.
The two parties have tackled technical challenges in fully solid-state battery development by using composite solid electrolyte materials to improve lithium-ion transport speed. They also adjust liquid electrolyte usage for various applications, advancing the commercialization prospects of fully solid-state batteries.
