Blue Current’s Progress with Silicon in the Fully Dry Elastic Composite Chemistry System

Blue Current’s Technical Progress with Silicon in the Fully Dry Elastic Composite Chemistry System

Blue Current has been developing solid state batteries with silicon anodes since 2018.  The company realized early on that silicon provides the best path to achieve high energy density, but that it must be deployed in a fully dry system to achieve long cycle life. In this post, we explore how Blue Current is solving the challenges of high silicon content anodes by using a fully dry and elastic composite battery system.

The challenge of silicon active materials

Silicon can hold ten times more lithium ions than graphite on a per-gram basis, resulting in a specific capacity exceeding 3,500 mAh/g for silicon versus 372 mAh/g for graphite.  Silicon active materials have already been integrated into existing lithium-ion battery manufacturing processes, albeit at very low loadings.  This ability to store lithium so efficiently, combined with it being a drop-in material, has made silicon a highly sought after ingredient for next generation batteries.

The challenge of using silicon active materials is that it undergoes a substantial volume expansion (up to 300%) as it alloys with lithium during charging, and a concomitant volume contraction during discharge. This repeated expansion and contraction can lead to cracking, and pulverization of the silicon particles. The structural integrity of the electrode is compromised due to this volume change.  (Figure 1)

Figure 1. Overview of the Challenges and Representative Strategies Associated with the Si Anode [1] 


The interface between silicon particles and liquid electrolyte is inherently unstable in the potential range of lithium-based batteries.  In this respect, it is no different than currently used graphite particles.  The spontaneous formation of a solid electrolyte interface (SEI) layer during “formation” cycles stabilizes the particle-electrolyte interface and is the underpinning of long cycle-life graphite-based lithium-ion batteries.  However, if a particle expands and contracts by 100-300%, there is no way for the SEI, which is like a shell covering and  egg, to expand and contract synchronously with the particle.

As a result of these issues, state-of-the-art cells have only been able to implement 5-10% silicon content.  Going beyond this silicon content results in a significant loss in battery capacity and cycle lifetime.

A Solid Approach

Since 2018, Blue Current has worked to develop a fully dry silicon elastic composite battery system to maximize silicon content.  Blue Current’s fully dry electrolyte allows silicon to expand and contract but the forces that the solid electrolyte exerts on the silicon particles prevent them from cracking and pulverizing.  In addition, there is strong evidence that the SEI formation in our composite solid electrolytes negligible when compared to liquid electrolytes.  This allows the team to introduce high silicon contents to achieve high energy density – going well beyond the 5-10% silicon content ceiling without compromising cycle life.

Of course, cycling silicon in a fully dry electrolyte still has its challenges, and it’s these challenges that Blue Current has been working since 2018 to resolve.  Silicon particles still expand and contract in a dry environment and contact between the silicon particles and the solid electrolyte must be maintained throughout the expansion/contraction process.

Blue Current’s elastic composite electrolyte approach can solve these challenges.  We have demonstrated that sulfide-based composite electrolytes can be easily integrated into solid-state electrodes, forming a compatible and intimate interface. Utilizing an elastic polymer enhances the mechanical integrity and mitigates silicon pulverization due to volume expansion.  Moreover, the elasticity of this system also allows the team to limit the amount of pressure applied to the cell that’s typically required for fully dry solid state cells.  (Figure 2)


Figure 2: Impact of high Si content on anode thickness 


Through these advancements, Blue Current has been able to achieve superior cycling stability at high silicon contents.  The team has demonstrated battery cycle life of over 1,000 cycles with 80% of initial cell capacity at silicon loadings 10x higher than state-of-the-art lithium-ion cells. In 2023, the team was able to increase anode capacity by 50%, without sacrificing the cell performance at low pressure.

Lower cost silicon active materials

Looking ahead, we are confident that this approach will be the critical enabler for lower cost silicon materials that have traditionally been incompatible with liquid electrolytes.  For example, materials like recycled, raw silicon powders as well as low cost silicon composite materials have already demonstrated high cycle life performance in Blue Current’s fully dry cell.  These materials achieve the benefits of low costs, ambient air stability, and environmentally benign properties compared to sophisticated silicon nanostructures and highly engineered silicon active materials.


Blue Current’s vision is to maximize battery energy density by integrating high silicon content anodes that leverage our fully dry composite electrode design.  With our core technology innovation, we proved the possibility of achieving both good mechanical elasticity and ionic conductivity with our composite solid electrolytes. Through thoughtful designs, fully dry silicon anodes can deliver outstanding energy density and rate capability, facilitating rapid charging and discharging. This is especially crucial in electric vehicles where extended range and fast charging are desired.


1 – Chae, Sujong. et al., “Confronting issues of the practical implementation of Si anode in high-energy lithium-ion batteries.” Joule, 2017; 1(1), 47-60