LFP, NMC, solid state, silicon, the list of battery chemistries goes on and on! With such a variety of chemistries available on the market, understanding their advantages and drawbacks for the EV industry is crucial when deciding which one to opt for. For any manufacturer including automotive Original Equipment Manufacturers (OEMs), deciding on which battery technology to go for is a huge strategic decision.
Currently, LFP and NMC are existing battery technologies that are the most widely used in the EV space. While LFP is known for its safety, long lifespan and being cost effective, NMC is known for its higher capacity. Future technologies that are considered next-gen and will take more time before reaching commercial adoption include solid state, known for its faster charging and longer range, and silicon, whose reputation precedes it for having higher energy density. Indeed, over the last few years, silicon has started to go commercial however, it suffers from safety issues and a short lifecycle, which many companies are focusing on improving. With these limitations surrounding its physical expansion, how and can it be the next best battery chemistry?
The Ins and Outs of Silicon
Batteries are generally a combination of a lithium metal cathode and an anode, a separator that allows the lithium ions to move between the two electrodes using the liquid electrolyte, and a fluid that enables the movement of the ions. After a number of overheating and explosion incidents were reported, most lithium-ion batteries are now made with graphite anodes and layers of carbon sheets. The space between these layers houses lithium atoms coming in and out of the anode as the battery charges and discharges. Silicon anode batteries function as an extension of lithium ion batteries. Indeed, they use silicon anodes that utilize silicon nanotubes, or a comparable coating process. This results in significantly higher energy storage and a longer battery life.
Going Further with Silicon
With up to ten times the capacity of current graphite anodes, meaning a higher energy density per volume, silicon is a very sought-after anode material. Indeed, silicon-based batteries have a high tolerance to electrode volume changes during charging and discharging cycles, they can reduce damage to the electrode structure, and shorten charging times all while increasing the battery capacity.
However, when a silicon battery charges and discharges, the lithium ions go back and forth between the anode and the cathode via a liquid electrolyte. As the ions enter a silicon anode, they push the silicon atoms aside, causing the anode to swell up to four times its original size. Once the lithium ions leave again, an empty space is created, causing the battery to fail. This cycle happens every time the battery is charging and discharging, causing a strain on the battery, which leads to degradation.
Silicon Limitations
On the other hand, silicon batteries are held back in two main ways: how they expand and contract while the battery charges and how they degrade with the liquid electrolytes. Similarly to a balloon filling up with air, silicon's volume increases when it stores lithium. This swelling causes stress on the anode structure, making the battery less stable and eventually leads to degradation, device breakdown, and an overall shorter life. This is one of the main reasons why silicon has been kept out of commercial batteries.
Safety is one of the most important parameters, especially when it comes to consumer-facing products and EVs, and automakers will not take the risk with or allow hazardous battery technologies to be implemented in their fleets. However, they understand the potential performance and commercialization reach that silicon can have. Consequently, carmakers are heavily investing in silicon battery technologies and startups, in addition to other technologies that can improve silicon safety and help the commercialization of this battery chemistry.
Jumping on the Trend
With such great potential, leading car makers including Tesla, GM, Porsche and BMW are all stepping up their silicon battery development.
Tesla
The American EV-maker has been working on its own solution that could be up to 10 times cheaper than current and previous methods used. To achieve this, Tesla is using an elastic binder and electrode design, and an elastic, ion-conducting, polymer coating, that is designed to work with the expansion rather than trying to prevent it.
General Motors
In August 2022, GM opened the Wallace Battery Cell Innovation Center, its new facility where it will continue to work on battery cell technology operations, and accelerate the development and commercialization of longer range, more affordable EV batteries. The battery engineering team based at the new center will experiment with many types of battery chemistries including pure silicon.
Porsche
The luxury German automaker is researching high-performance batteries that use silicon rather than graphite anodes. With the aim of achieving an even higher energy density and better fast-charging capabilities, it will start using this technology in limited-production, high-performance vehicles and in customer motorsport. Additionally, with its first EV outselling its classic 911 sports car, Porsche injected $100 million into Group14 Technologies, a lithium-silicon battery developer.
BMW
The carmaker is partnering with Sila Nano who’s main products are silicon-based anode materials that replace conventional graphite electrodes. To accelerate development, the German carmaker has been working with Sila Nano to develop Sila Nano's silicon anode material for the automotive market.
Reducing the Cons of Silicon with 3D Design
A simulation of silicon swelling captured by Addionics’ 3D structure
While silicon is a very energetic material, for it to be used in practical lithium batteries, various issues must be addressed. This includes the volumetric change these batteries experience, simplified manufacturing and a lower cost of production. Indeed, during charging and discharging cycles, battery electrodes expand and contract, limiting battery life and performance. Furthermore, silicon is also less mechanically less stable, which leads to accelerated degradation.
3D current collectors structural design provides silicon batteries with a higher mechanical stability, adhesion and handles battery swelling better by minimizing cracking and delamination. Indeed, the metal structure acts as a skeleton that holds the silicon when it swells and shrinks. This minimizes the negative effects including degradation, that leads to a shorter lifetime, and safety issues. On the performance side, it allows a significantly higher loading of the active material, enabling a much higher energy density. As such, 3D current collectors might be the way for silicon to be fully adopted by the industry. Explore Addionics’ technology or get in touch for collaboration opportunities.