SK On presented its latest findings on solid-state battery research in collaboration with academic partners, highlighting its commitment to advancing next-generation battery solutions. SK On, part of South Korea’s SK Group, said that its research, conducted in collaboration with Dr. Dong-Won Kim’s group at Hanyang University in Seoul, discovered a method to improve the cycle life of sulfide-based all-solid-state lithium metal batteries (ASSLMBs).

The study, published last month in ACS Energy Letters, introduces a method for forming a protective layer on the lithium metal anode surface to enhance battery safety and extend its lifespan. The team also filed patent applications for its key findings both domestically and internationally.

Lithium metal is considered a next-generation anode material due to its high capacity—around 10 times greater than that of graphite—and its low electrochemical potential which enables enhanced energy density and high-performance power. However, lithium metal is also known for challenges such as its high reactivity with air, which lead to the uneven formation of inorganic compounds on its surface. This layer hinders the movement of lithium ions, reducing both charging and discharging efficiency, while promoting dendrite formation which further threatens battery life. Also, all-solid-state batteries using lithium metal anodes have generally demonstrated limited charge-discharge cycles, often around 100.

To address the issue of limited lifespan, the research team removed the resistive surface layer by immersing the lithium metal anode in a specially formulated solution containing nitromethane, dimethoxyethene, and lithium nitrate. This approach resulted in the formation of a protective layer featuring high ionic conductivity, attributed to lithium nitrate, and enhanced mechanical strength due to lithium oxide.

SK On said this method ensured interfacial stability, with experimental results showing that the surface-modified lithium metal anode enabled stable cycling for more than 300 charge-discharge cycles at room temperature, tripling the cycle life compared to conventional lithium metal all-solid-state batteries.

In collaboration with Dr. Jong Hyeok Park of Yonsei University, SK On announced another achievement, uncovering the relationship between battery life and the thermal curing time of gel polymer electrolytes (GPEs). Their study was abolished in the journal Angewandte Chemie in February.

According to the study, longer thermal curing times for the GPEs resulted in better retention of battery performance. The study showed that batteries using electrolytes with 60 minutes of thermal curing showed a 9.1% decrease in discharge capacity, while those with just 20 minutes of thermal curing experienced a 34% decrease.

Choi et al.

It suggests that shorter thermal curing time leads to the easy decomposition of the cathode protective layer, which in turn reduces capacity and ultimately shortens battery lifespan.

Also in the study, the team applied density functional theory (DFT) calculations to identify the cause and mechanism of cathode performance degradation and investigate residual monomer-induced side reactions during the initial charging stage. SK On said the findings from this study is expected to contribute to improving the lifespan of polymer-oxide composite-based batteries.

SK On is developing two types of ASSBs: polymer-oxide composite and sulfide-based, with commercialization targeted for 2028 and 2030, respectively.

• Surface-Modified Lithium Enabling High-Performance All-Solid-State Lithium Metal Batteries; Hui-Tae Sim, Myung-Keun Oh, Hyo-Jin Kim, Ye-Eun Park, Yun-Sun Cho, Jaeyoung Choi, Seong-Jin Park, and Dong-Won Kim; ACS Energy Letters 0, 10 doi: 10.1021/acsenergylett.5c00656

• Residual Monomer-Induced Side Reactions in Gel Polymer Electrolytes: Unveiled High-Ni Cathode Failure in Lithium Batteries; Min Su Choi, Sang Goo Kang, Jaehoon Choi, Jeonghyun Ko, Prof. Jong Hyeok Park; Angew. Chem. Int. Ed. 2025, 64, e202424568. doi: 10.1002/anie.202424568