Overcoming the Four Killer Problems of Silicon to Create a Better Battery
Part 1 — Defining the Challenge
Rapidly evolving consumer devices and sustainability efforts that are actively working to clean up and benefit our planet — all require better batteries. Historically, advancements in battery performance have come primarily from improvements in the active cathode and anode materials of the battery. While other companies focus on incrementally improving batteries through new chemistries, we’ve completely reimagined the battery architecture — throwing out the more than 100-year-old “jelly roll,” where long strips of anode, separator and cathode are wound together in a jelly roll form, and replaced it with a precise, laser cut design where strips of anodes, separators and cathodes are stacked.
This new architecture allows for more efficient use of the volume of the battery in contrast to the jelly roll, where significant volume is wasted at the corners and in gaps at the center of the battery given the lack of precision in the winding process. Our novel 3D battery architecture improves the packing efficiency of the active material inside the battery, enables exceptional thermal performance and abuse tolerance, as well as accommodates the use of a 100% active silicon anode.
Silicon is a plentiful and sustainable ingredient that can theoretically store more than twice as many lithium ions as a graphite anode, which is used in most conventional Li-ion batteries today. The use of silicon within our battery architecture translates to a higher energy dense battery in an efficient form factor.
However, using 100% active silicon anodes in a conventional battery architecture presents many problems, such as unacceptable battery cycle life, i.e., a low number of times (~100) a battery can be fully charged and discharged during its life. Our advanced 3D cell architecture has solved the four killer problems associated with 100% active silicon anodes.
Uniquely Enabling Silicon Anodes
Looking at a problem from a different perspective often yields new opportunities and solutions that would otherwise not be possible. This is the case with the Enovix 3D cell architecture. Rather than having long, wound electrodes that run parallel to the face of the battery, Enovix cells have many small electrodes that are orthogonal to the largest face of the battery. This seemingly small difference has huge benefits. Specifically, the 3D cell architecture is well-suited to accommodate the use of a silicon anode and therefore capitalize on the higher energy density it provides.
Silicon’s high energy density, however, creates four significant technical problems that must be solved:
- 1. Formation expansion. “Formation” is the term for the first charging of the battery, when lithium moves from the cathode, through the separator, to the anode. When fully charged, a silicon anode can more than double in thickness, resulting in significant swelling that can physically damage the battery, causing failure.
- 2. Formation efficiency. When first charged, a silicon anode can absorb and permanently trap as much as 50%-60% of the original lithium in the battery, reducing the battery’s capacity by 50%-60%.
- 3. Cycle swelling. A silicon anode will swell and shrink when the battery is charged and discharged, respectively, causing damage to both the package and the silicon particles in the anode, which can crack, and further trap lithium on the fresh silicon surfaces exposed by the crack.
- 4. Cycle life. Silicon particles can become electrically disconnected from the electrode when the silicon anode is in its shrunken state and can crack when the silicon anode is swollen, both of which can lower cycle life. In addition, when silicon particles become disconnected from the electrode, they are no longer able to accept lithium and neighboring particles must absorb the excess, causing over charging and further opportunities for physical damage.
Left unaddressed, these four problems have limited the practical application of silicon anodes in conventional lithium-ion battery cells.
In the next blog, we’ll describe how our cell architecture uniquely solves these four technical problems to enable 100% active silicon anodes.