[Bojo, Battery] The Barrier Blocking Lithium Metal Anodes... What Exactly Is 'Dendrite'?

Battery Performance and Lifespan Decrease Due to Separator Damage
Formed on Anode Surface During Charging/Discharging
Key Technology Suppresses Damage by Treating Lithium Metal Surface

Editor's Note'Bojo, Battery' is a series that takes a closer look at the battery industry, which has emerged as the center of next-generation advanced industries. It examines the agile movements, strategies, and conflicts among governments and companies worldwide vying to dominate the battery manufacturing ecosystem. We will also cover the technological competition to create safer and longer-lasting batteries. We aim to serve as an 'assistant' to help readers and investors better understand the battery industry. We will share battery stories that are easy to approach.

Battery anode materials are limited compared to cathode materials, and so far, the only commercialized materials are graphite and silicon. Therefore, lithium metal anode materials are regarded as the 'final boss' of anode materials following graphite and silicon.

Batteries using lithium metal as the anode are lighter and more compact than those using graphite. They also excel in energy density because graphite stores lithium between its molecular layers, whereas lithium metal can store more lithium.

However, to commercialize lithium metal batteries, a technical challenge must be overcome: preventing the formation of 'dendrites.' Dendrites are tree-branch-shaped crystals that form as lithium accumulates on the anode surface, which degrade battery performance and safety. Researchers and companies studying lithium metal batteries are fiercely competing to solve this issue.

Why do dendrites form? To understand the cause, one must first understand the properties of lithium. Lithium is a highly reactive material that easily reacts with other substances. The chronic explosion risk of lithium-ion batteries arises from lithium's high reactivity and flammability.

In lithium-ion batteries, lithium moves between the cathode and anode through a liquid electrolyte, and due to its high reactivity, it immediately reacts upon contact with the electrolyte. As a result of this reaction, a lithium layer forms on the lithium metal surface, called the 'SEI (Solid Electrolyte Interphase).' This SEI layer thickens as the battery is used.

The problem is that the SEI layer does not form smoothly. SEI is an uneven layer composed of various components appearing in a mosaic pattern on the surface. Because of this, lithium moves unevenly?reaching some areas quickly and others slowly.

The SEI layer thickens in areas where lithium moves quickly, creating a vicious cycle where thicker layers accumulate material faster. When a critical point is reached, dendrites form on top of this layer.

As dendrite crystals grow, they damage the separator, reducing battery performance. Rapid volume changes during charge and discharge create 'dead lithium' that is electrically disconnected from the anode, shortening battery life. Conversely, sudden current surges can cause fires.

Ultimately, solving the uneven SEI layer is key to using lithium metal batteries. Currently, research focuses on creating artificial SEI layers on lithium metal surfaces. Normally, SEI forms unevenly upon contact with the electrolyte, but by pre-forming a uniform layer before electrolyte contact, uneven formation can be prevented.

A representative example is the dendrite suppression method introduced by smart optical solutions company iL Science. This technology coats the copper current collector surface, which contacts lithium metal, with lithium transition metal oxides to suppress dendrite formation or reduce the frequency of uneven formation.

Battery company LG Energy Solution's approach is somewhat different. In December last year, LG Energy Solution and a joint research team from KAIST developed the world's first technology applying a borate-pyran-based liquid electrolyte to lithium metal batteries. This electrolyte reconstructs the SEI into a dense structure to maintain charge-discharge efficiency and blocks reactions between the electrolyte and lithium metal.

In addition, last January, LG Energy Solution invested in the U.S. next-generation battery venture company Sion Power and began technical collaboration to develop next-generation lithium metal batteries. Sion Power holds over 470 international patents, including patents related to lithium metal battery anode protective layers.