Researchers at the Paul Scherrer Institute (PSI) have made a major advance toward the practical use of lithium-metal all-solid-state batteries—the next generation of energy storage that offers higher energy density, improved safety, and faster charging compared with conventional lithium-ion batteries.
All-solid-state batteries are widely seen as a promising technology for electric vehicles, portable electronics, and stationary energy storage, largely because they eliminate flammable liquid electrolytes and are therefore inherently safer than conventional lithium-ion batteries.
Key Challenges Blocking Commercialization
Despite this potential, two major challenges still hinder their commercialization. First, the formation of lithium dendrites at the anode remains a serious issue. These microscopic, needle-shaped metal structures can pierce the solid electrolyte that transports lithium ions between the electrodes, grow toward the cathode, and eventually trigger internal short circuits. Second, electrochemical instability at the interface between the lithium-metal anode and the solid electrolyte can degrade long-term performance and reliability.
To address both challenges, a team led by Mario El Kazzi, head of the Battery Materials and Diagnostics group at the Paul Scherrer Institute (PSI), developed a novel manufacturing approach. “We combined two strategies that simultaneously densify the electrolyte and stabilize the interface with lithium,” El Kazzi explains. The team’s findings have been published in the journal Advanced Science.
The challenge Of Achieving Adequate Densification
At the heart of the PSI study is the argyrodite-type compound Li₆PS₅Cl (LPSCl), a sulfide-based solid electrolyte composed of lithium, phosphorus, and sulfur. This material features high lithium-ion conductivity, allowing fast ion movement within the battery—an essential requirement for high performance and rapid charging. As a result, researchers consider argyrodite electrolytes strong candidates for solid-state battery applications. However, achieving sufficient densification—necessary to eliminate voids that lithium dendrites could infiltrate—has so far limited their practical use.
To densify solid electrolytes, research teams have typically followed one of two strategies: applying extremely high pressure at room temperature or using methods that combine pressure with temperatures above 400 °C. In the latter, known as conventional sintering, heat and pressure cause the particles to bond together into a more compact structure.
Both approaches, however, come with significant drawbacks. Compression at room temperature often produces a porous microstructure and promotes excessive grain growth, while processing at very high temperatures risks degrading the solid electrolyte itself. As a result, PSI researchers were compelled to develop an alternative strategy to achieve a mechanically robust electrolyte and a stable electrode–electrolyte interface.
The Heat-Based Solution
To create a uniform argyrodite electrolyte, El Kazzi and his team did use heat, but in a much more controlled way. Rather than following traditional sintering, they applied a gentler method, compressing the material under moderate pressure and a relatively low temperature of around 80 °C.
This mild sintering approach was highly effective. The combination of moderate heat and pressure allowed the particles to settle into an optimal arrangement without compromising the chemical stability of the material.
Within the mineral, particles formed strong connections, porous regions became denser, and small cavities closed up. The outcome is a compact, dense microstructure that resists penetration by lithium dendrites, while remaining ideally suited for fast lithium-ion transport.
However, gentle sintering by itself was not sufficient. To guarantee stable performance even at high current densities—such as during fast charging and discharging—the all-solid-state cell needed an additional modification. For this, a lithium fluoride (LiF) coating just 65 nanometers thick was uniformly deposited onto the lithium surface under vacuum, forming an ultra-thin passivation layer at the interface between the anode and the solid electrolyte.
This intermediate layer serves two key purposes: it prevents the solid electrolyte from undergoing electrochemical decomposition when in contact with lithium, thereby reducing the formation of inactive “dead” lithium, and it provides a physical barrier that blocks lithium dendrites from penetrating the solid electrolyte.
Optimal Performance After 1,500 Cycles
In laboratory tests using button cells, the battery showed exceptional performance even under demanding conditions.
“Its cycle stability at high voltage was impressive,” says doctoral candidate Jinsong Zhang, the study’s lead author. After 1,500 charge-discharge cycles, the cell still maintained around 75% of its initial capacity, meaning that three-quarters of the lithium ions continued to move effectively between the cathode and anode.
“An outstanding achievement. These results rank among the best reported so far.” Zhang believes this indicates a strong potential for all-solid-state batteries to soon outperform conventional lithium-ion batteries with liquid electrolytes in both energy density and longevity.
In this way, El Kazzi and his team have, for the first time, shown that combining mild sintering of the solid electrolyte with an ultra-thin passivation layer on the lithium anode effectively prevents both dendrite formation and interfacial instability—two of the most persistent obstacles in all-solid-state batteries.
This combined strategy represents a significant step forward in all-solid-state battery research, not least because it also brings environmental and economic benefits. The low-temperature process reduces energy consumption and associated costs. “Our method provides a practical pathway for the industrial production of argyrodite-based all-solid-state batteries,” says El Kazzi. “With a few more refinements, we could be ready to scale up.”
Read the original article on: Tech Xplore
Read more: A New Robot Powered by Solar Energy Serves as an Actual Butler