Integration of Silicon in Lithium-ion batteries by Cidetec
By Ane Muguruza Sánchez and Iratxe de Meatza
CIDETEC is a research and innovation organization founded in 1997. Located in Donostia-San Sebastián, CIDETEC gathers three international technological reference institutes in Energy Storage, Surface Engineering and Nanomedicine. CIDETEC Energy Storage specializes in advanced battery technologies by designing, developing and testing batteries of many different technologies. The institute has the capacity to develop complete products and processes and offers material validation, pilot manufacture, pack engineering and battery testing services.
In ICARUS, CIDETEC leads the activities related to the reuse of graphite and silicon kerf-loss in Lithium-Ion Batteries (LiB). Among other things, CIDETEC performed the evaluation of recycled graphite and Silicon Kerf as active materials in LiB anodes, demonstrated in Li-ion cell anodes the reliability of graphite and Si obtained from recycling from Si kerf and estimated benefits once industrialized.
The Materials for Energy Unit at CIDETEC brings its know-how on Li-ion electrode formulations and coating processing, as well as cell design and testing. Thus, CIDETEC team focuses on electrode formulation and processing optimization to manufacture anode electrodes based on the recovered/recycled graphite and silicon.
Principle of the lithium-ion batteries
The current technology and its limits
Presently, graphite is the most commonly used anode active material in LIBs for electric vehicles (EV), due to its abundance, low-toxicity and relatively high specific capacity (370 mAh/g). However, the requirements of LIBs with high energy density cannot be met with this anode material. The research for an alternative that can ensure the energy density target, safety and availability of resources is key for the progress of the EVs market in which next-generation anodes have already been explored: silicon-based materials, alloy materials etc.
Advantages of using silicon in LiB
Among all potential alternative materials, silicon is one of the most promising anode candidates for LIBs, with a capacity of 4200 mAh/g, about ten times higher than conventional graphite anodes. Its lithiation voltage plateau (∼0.4 V vs. Li/Li) is slightly higher than that of graphite anodes (∼0.05 V vs. Li/Li), reducing unnecessary lithium plating and dendrite formation. It also mitigates the safety concerns and offers a better environmental respect and abundance. Silicon is, therefore, a promising anode material for next-generation EVs or hybrid electric vehicles that need to be powered by LiB with higher gravimetric/volumetric energy density and fewer safety concerns. Unfortunately, the alloying process, in which each silicon atom can host up to four lithium atoms, generates a huge volumetric change. It induces the pulverization of the silicon particles and material cracking, eventually leading to significant capacity fade, severely hindering its commercial application.
Challenges related to using silicon in LiB
The main obstacle in the implementation of silicon anodes is the volume expansion that occurs during the lithiation and delithiation processes. The volume expansion can be as high as 300%, causing cracking and pulverization of the silicon particles, leading to loss of electrical contact and capacity fading. Moreover, the repeated volume change results in an unstable Solid Electrolyte Interphase that protects the anode during the cycling of the cell and which is constantly destroyed and rebuilt, causing electric disconnection and continuous consumption of the electrolyte which lowers the ionic conductivity and increases the resistance of the cell.
ICARUS’s first results
Several silicon materials have been tested as anodes in silicon-graphite blends (mixture of both materials) and silicon composites (silicon embedded in carbon matrix) to increase the capacity of the anode with the silicon and contain the volume change caused by the alloying of the silicon with lithium.
It has been proved that recycled silicon can be used in 10-12wt% in the anode and capacities above 700 mAh/g for the silicon-graphite blend (theoretical 720 mAh/g) and 470 mAh/g for the composites (theoretical 480 mAh/g) with stable cycling have been achieved in coin cell testings.
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| Slurry preparation by mechanical mixing of the materials with the solvent. | Coin cell format electrodes being cut from a calendered electrode strip |
Next steps
After the validation of the silicon containing materials and the upscaling suitability of the anodes, 1 Ah pouch cells will be assembled to demonstrate the suitability of the silicon blend and silicon composite anodes on a larger scale.
