Executive Summary
- Silicon has emerged as a game-changing anode material for lithium-ion batteries.
- The unique design of Group14’s SCC55® overcomes the typical hurdles of silicon (Si) anodes and enables Si-dominant anode designs with stable cycling.
- Sionic Energy has integrated its breakthrough technology and expertise in electrode, electrolyte, and cell design into its Rapid Integration Silicon Platform™ to produce silicon batteries that maximize the 100% SCC55® performance and delivers energy densities up to 400 Wh/kg with exceptional cycling performance and cell expansion at parity with graphite without any pre-lithiation or external compression.
- Described herein, Sionic Energy has addressed one of the known Si-dominant anode performance issues by integrating its proprietary additives, solvent systems and experience into the electrolyte formulation to achieve exceptional cycling stability under elevated temperatures while preserving overall performance metrics.
- Fueled by the extraordinary elevated-temperature (HT) robustness, Sionic is now validating the HT performance on its 400+ Wh/kg platform, also incorporating 100% SCC55®.
Background
The demand for energy-dense, fast-charging, and low-cost lithium-ion batteries (LIBs) is driving innovation beyond cathode chemistry toward optimization of the anode. To this end, silicon (Si) has emerged as the premier next-generation anode material. Silicon oxides (SiOx) were an early option, but severe volume changes, poor conductivity, low first-cycle coulombic efficiency (FCE), and formation of an unstable solid-electrolyte interphase (SEI) limited their performance. Whereas nanostructured SiOx materials could have higher stability, they remain costly, complex, and only practical when blended with Gr. Pure micron- and nano-silicon have shown promise but have struggled with stability, scalability, and long-term cyclability. Silicon–carbon (Si–C) composites have emerged as the most viable path, using a carbon matrix to protect nano-Si while leaving internal void spaces to accommodate most of the expansion during cycling of the Si.
Group14’s novel, high-performing Si anode material: SCC55®
Group14’s expertise in nano-engineering battery materials has culminated in the commercialization of SCC55®—a scalable, high-performing Si-C composite anode material. This approach utilizes a porous hard-carbon scaffold ideally suited for the encapsulation of amorphous nano-Si. This novel design provides void space within the particles to accommodate expansion. Importantly, it reduces Si exposed to the electrolyte, thereby minimizing side reactions and lithium loss, and maintains the structural integrity of the particle throughout long-term cycling.
Proven at scale, SCC55® enables Si-dominant anodes that deliver high energy density and fast charging at commercial volumes. With SCC55®, the industry now has a practical foundation to meet the next generation of battery performance targets. SCC55® powers high-performance Si batteries for EVs, AI-enabled devices, eVTOLs, and grid storage. Indeed, recently reported data from 20+ customers worldwide shows a significant leap in Si battery cycle life, ranging from 1,500 to over 3,000 charge cycles, achieved over a wide range of battery designs, cathode chemistries, and displacement of graphite (Gr) with SCC55® up to 100% in the anode[1].
Sionic Energy teams with Group14 to raise the bar for Si battery performance
While SCC55® is a critical breakthrough anode material, fully displacing graphite as anode active material requires years of development in electrode formulation, processing, and scaling, as well as electrolyte and holistic cell design optimizations. Equipped with +5 years of Si-anode experience and IP alongside 11+ years of electrolyte IP legacy, Sionic Energy has enabled stable LIBs using 100% SCC55® and maximizing its performance in its Rapid Integration Silicon PlatformTM, at room and elevated temperatures[2].
Sionic Energy delivers market-leading energy density and performance in its drop-in “Rapid Integration Silicon Platform™
1. Pushing the energy density in LIBs: challenges and Sionic’s solution.
Maximizing energy density in LIBs requires precise optimization of active materials, electrode structures, and electrolyte chemistry. Industry-standard component designs, such as use of thin current collectors as well as thin but safe ceramic-coated separators, can reduce inactive weight while maintaining cell safety. However, Si-dominant systems face unique challenges: achieving high first-cycle efficiency (> 92%) and cathode utilization (> 95%) is significantly harder than in Gr cells due to Si’s large irreversible capacity loss, unstable SEI, and particle as well as electrode-level swelling. To maximize energy density, high Si utilization must be paired with cathode loadings around 5 mAh/cm². At the same time, anode loadings must remain above 5 mAh/cm² with uniform thickness and consistency in roll-to-roll processing. Low electrolyte volumes are necessary to minimize inactive mass but can make effective electrode wetting and ionic transport more difficult, particularly under high-rate operation. Finally, cell expansion, typically only ~2% for Gr, is a major hurdle in Si-dominant cells where the particle-level volume change during cycling can drive irreversible swelling, mechanical instability, and cycle fade. Sionic’s proprietary anode binder and design architecture build upon Group 14’s SCC55® superior particle design to significantly mitigate particle and electrode swelling without the need for stack compression.
Sionic Energy has developed a comprehensive drop-in platform solution to these barriers through its next-generation Si-rich anode designs, optimized cell architecture, and proprietary electrolyte formulations. With more than 40 granted and pending patents, and foundational IP licensed from the University of Colorado Boulder and Cornell University, Sionic has built a technology platform specifically aimed at stabilizing high-capacity Si-dominant anodes, maximizing performance, while extending cycle and calendar life. Its versatile binder materials and composite anode designs enable high Si loading without the expansion penalties typical of conventional Si-dominant systems. Most critically, Sionic has developed advanced electrolyte chemistries that promote the formation of highly stable SEI layers and simultaneously stabilize high-Ni cathodes, directly addressing the first-cycle efficiency and elevated temperature (HT) performance challenges often encountered in these systems. Sionic’s capabilities are currently exemplified by its 100% Gr-free Si–C composite 20-Ah pouch cells that achieve < 4% cell-level expansion. Sionic has demonstrated a range of design options for customers to choose from, with up to 370 Wh/kg, 1000 Wh/L, and 600-1400 cycles depending on the design. This is complemented by impressive power capabilities— <10 min fast charge and 4C-5C continuous discharge. This combination of mechanical stability, market-leading energy density, and high-rate performance represents a practical path to scaling Si-dominant LIB technology for high-demand applications. After successful third-party validation of the GEN3 20-Ah cell (+620 cycles at 1C/-1C, 4.2 V – 2.2 V Element Materials Technology), Sionic is currently optimizing its GEN4 designs in a pouch format to achieve 400 Wh/kg while maintaining the same 100% drop-in platform technology, as shown in Fig. 1.
Figure 1. Energy density trend in progressive generations of Sionic 20-Ah pouch cells utilizing 100% SCC55® and displaying the extensibility of design & performance on Sionic’s Rapid Integration Silicon Platform
The focus of this paper is to highlight the elevated temperature (HT) performance improvements achieved in Sionic cells by rational electrolyte design. Stable HT performance during fast charge and discharge is critical for LIBs used in electric vehicles, aerospace systems, consumer electronics, and renewable energy storage. In these applications, the battery must deliver high power reliably even in hot environments, avoiding significant performance loss or safety risks.
All batteries, including the current standard Gr-based LIBs, encounter HT performance degradation. These challenges need to be understood and mitigated at the material, process, and design levels. Several factors contribute to HT performance degradation, including the composition of electrode active materials, electrolyte components, and additives. Electrolyte additives can have a significant impact on the stability of the electrolyte-electrode interphases. Beyond materials and chemistry, electrode processing conditions —slurry mixing, electrode coating, and electrode calendaring— can also lead to particle damage and performance degradation in the absence of appropriate care and diligence. Electrolyte additives can mitigate negative effects stemming from any impurities in the anode or in the electrolyte itself.
Improving HT performance therefore requires a multi-pronged approach. Prudent selection of high-performing active materials and careful processing of the electrodes are critical to stable and reliable performance. Sionic has chosen high-quality active materials (e.g., SCC55®), binders, and conductive additives. However, even with the best available active materials, the electrolyte plays a critical role in the stability and performance of the cell, particularly at elevated temperatures. Specially formulated electrolytes are therefore essential for optimal performance as is demonstrated in this paper.
Si-dominant LIBs paired with high-Ni cathodes may face accelerated degradation under demanding conditions at elevated temperatures. There is greater particle and electrode expansion during cycling that can cause the SEI to break down and reform, consuming more electrolyte and lithium. Further, non-reversible electrode expansion during cycling can contribute to loss of electrical contact and impedance increase. On the cathode side, impedance build-up at elevated temperatures due to surface rearrangements and electrolyte oxidation can pose additional challenges. High discharge rates intensify internal heat generation and electrolyte decomposition, potentially leading to gas generation, impedance growth, and capacity decay.
2. Optimizing LIBs for performance at both ambient and elevated temperatures through rational design of electrolyte.
A high-performance Si-C material like Group14’s SCC55® sets the stage for exceptional Si battery performance, but optimization of the electrolyte formulation is needed to truly unlock stability and reliability at elevated temperatures. HT-stable solvents, lithium salts with wide electrochemical windows, and additives that form robust, elastic SEI layers can significantly improve stability at elevated temperatures and during high-rate cycling. Proper formulations could also suppress gas generation, enhance ionic conductivity, and reduce parasitic reactions, directly improving both safety and cycle life. However, these optimizations typically come with trade-offs. Formulations and additives that improve HT performance may increase viscosity or reduce low-temperature conductivity, while some high-stability salts are costly or less commercially available. Additionally, overly passivating SEI layers can slow lithium transport and reduce peak power output. Balancing thermal stability, conductivity, cost, and manufacturability is therefore essential. With careful electrolyte engineering performed at Sionic Energy, Si-dominant LIBs including 100% SCC55® cell designs, can deliver both the high power and temperature resilience required for demanding real-world applications.
3. High energy density requires minimizing electrolyte fill volume: Problematic for fast discharge at elevated temperatures.
In addition to factors discussed in the previous section, minimizing electrolyte volume is critical in achieving high energy density cells (e.g., >350 Wh/kg). In-house modeling predicts a steep linear decline in energy density with increasing electrolyte amount, as depicted in Fig. 2. ELth denotes an experimentally determined threshold electrolyte fill amount below which the cells fail during cycling at high HT. Informed by the cell design and the porosity of the components, our in-house modeling also predicts a lower theoretical limit for the electrolyte mass per unit capacity of the cathode.
Figure 2. Cell-level energy density as a function of electrolyte amount for Sionic Energy GEN3 and GEN4B 20-Ah pouch cell designs.
However, HT cycling performance in multilayer pouch cells, particularly at high discharge rates (1C or higher), is extremely sensitive to the electrolyte fill amount. Li-metal level electrolyte fill amounts (>4 g/Ah) are routinely used in academic studies on Si-containing multi-layer pouch LIBs[3], generally to buffer any loss of salt or solvent. However, practical energy-density considerations push the limit to much lower than < 2.5 g/Ah[4], at or barely above the minimum threshold set by the porosity of the cell.
Conventional formulations (e.g., baseline discussed below) fail at low electrolyte fill amounts. In multiple systems using a high-Ni NMC cathode, our root-cause analyses have delineated a failure mechanism involving generation of gas and impedance growth when cells are cycled at 1C/-1C or higher, potentially caused and exacerbated by de-wetting of the electrode layers due to rapid volume fluctuations during cycling. An example of this is shown in Fig. 3, wherein the cells using the baseline electrolyte formulation fade abruptly at 1C/-1C rate at 45 °C when the electrolyte fill amount is equal to or less than ELth, yet perform well at higher electrolyte fill amounts.
Figure 3. Effect of electrolyte amount on 4-Ah pouch cycling stability at 45 °C and 1C/-1C.
Therefore, the HT performance of electrolyte formulation cannot be comprehensively assessed using small-format single-layer pouch cells that are typically flooded with 3g/Ah or higher amounts of electrolyte. HT formulations need to be tested at practical conditions for high-energy density systems, e.g., 4 to 20-Ah pouch cells equipped with ELth or less g/Ah. The larger footprint of these cells coupled with the large number of factors involved necessitates efficient experimental design, use of modeling and simulations, and an established infrastructure for large-scale testing of high-capacity pouch cells.
Sionic’s solution:
Using advanced Design of Experiments (DOE) approaches, including Taguchi methodology, Sionic Energy has investigated a matrix of electrolyte formulations around its proprietary additives to identify parameter spaces that enable robust HT performance at low electrolyte amounts, while preserving other critical metrics. The electrolyte development program used structured DOE to explore formulations for high-performance in LIB pouch cells (4-Ah to 20-Ah). The goal was to achieve a balance between cycling stability at elevated temperatures and rate capability at room temperature, while maintaining electrolyte levels suitable for high energy density.
The principal Taguchi DOE[5] incorporated seven most critical design factors spanning Sionic’s proprietary anode and cathode additives, secondary and tertiary salt systems, linear and fluorinated carbonate optimization, and ester content. Each factor was studied at three to five levels, informed by Sionic’s in-house expertise in HT electrolyte systems and several prior screening studies. Whereas a traditional full factorial study would have required >4000 runs given the large parameter space, an orthogonal array design enabled optimization using only eighteen candidate formulations varying in solvent composition, salt type, and Sionic additive selection, with some additional blends included to address specific performance needs. Formulations were used in 4-Ah pouch cells and evaluated for key metrics such as formation behavior, rate performance, transport properties, and long-term cycling stability under both standard and elevated temperature conditions. Upon identifying the optimized parameter space, confirmation trials were conducted using the champion designs in 4-, 10-, and 20-Ah pouch cells.
Importantly, Taguchi methodology enabled optimization of design factors with respect to noise factors. The electrolyte amount was programmed into the noise factor to identify electrolyte design factors that are most robust to the variations in electrolyte volume per active materials. The above-described program culminated in the identification of an array of electrolyte formulations that delivered exceptional cycling stability at elevated temperatures when used at ELth, while maintaining rate capability and room-temperature cycling performance. One selected example is discussed below.
1C/1C Cycling stability at 45 °C: Sionic HT electrolyte is very stable cycling at 45 °C at high charge/discharge rate of 1C/-1C, as shown in Fig. 4. Unlike the baseline electrolytes, the Sionic HT formulation demonstrated very stable cycling in 4-Ah pouch cells.
Figure 4. HT cycling performance through rational electrolyte design (4-Ah pouch cells).
Critically, the cycling profile (45 °C, 1C/1C) remains robust in cells with even lower electrolyte amounts and larger form factors. Fig. 5 highlights the cycling performance of a 10-Ah pouch cell equipped with the theoretically determined minimum electrolyte amount (EL < ELth). Whereas the cell reaches the end of life (to 80% capacity retention) after ~830 cycles at 25 °C, the cell operating at 45 °C lasts ~580 cycles, equivalent to 70% of its life at 25 °C.
Figure 5. HT cycling performance through rational electrolyte design (10-Ah pouch cells)
Storage testing at 45 °C and 60 °C: The stability of Sionic HT formulation is attributed to both chemical and electrochemical stability at elevated temperatures. To highlight the chemical stability of Sionic HT electrolytes in the context of high-Ni NMC cathodes and SCC55®, storage tests were conducted at 45 °C on fully charged cells at 4.2V. Fig. 6 shows the 45 °C storage performance metrics of Sionic HT electrolyte vs. the baseline electrolyte. Gassing, growth of impedance, and both reversible and irreversible capacity losses are all largely suppressed by rational design of the electrolyte.
Figure 6. Comparative storage performance at 45 °C in 4-Ah pouch cells: (a) % capacity retention, (b) % thickness increase, (c) % capacity recovery, and (d) % ACIR increase.
Similar advantages to the baseline electrolyte were observed in storage testing of Sionic HT electrolyte during similar storage testing at 60 °C. As shown in Fig. 7, cells with the baseline electrolyte exhibited rapid degradation, with pronounced capacity loss, low recovery, and a steep rise in ACIR, all of which indicate severe electrolyte decomposition and unstable electrode interfaces. In contrast, cells equipped with the Sionic HT electrolyte demonstrated far greater stability, maintaining higher capacity retention and recovery, and much smaller ACIR growth over the same period. These results confirm that the Sionic HT electrolyte effectively suppresses parasitic reactions, gas generation, and interfacial breakdown at elevated temperatures, delivering a durable and chemically robust platform for silicon–carbon anode systems under harsh thermal conditions.
Figure 7. Storage performance at 60 °C in 4-Ah pouch cells: Comparative (a) capacity retention, (b) capacity recovery, and (c) ACIR increase.
Storage testing at 60 °C is a critical benchmark because it simulates years of battery aging in just weeks, exposing weaknesses in stability, safety, and cycle life. At this elevated temperature, cells are pushed to their limits. Electrolytes break down faster, gas generation and swelling accelerate, and interfaces like the SEI are stressed. Demonstrating robust performance under these conditions demonstrates that Sionic’s HT electrolyte and Si-C anode designs can maintain durability even in demanding real-world environments such as hot climates or automotive applications.
Conclusion
Sionic Energy and Group14 Technologies have jointly demonstrated the viability of graphite-free anode designs that deliver exceptional energy density, cycling stability, and HT performance. By integrating Group14’s superior SCC55® Si–C anode material with Sionic’s Rapid Integration Silicon Platform™ and HT electrolyte design, the companies have addressed long-standing barriers in Si-based LIBs, including first-cycle efficiency, excessive electrode expansion, and HT performance degradation. Through rational electrolyte design and advanced DOE methodologies, Sionic has shown that high-energy-density pouch cells can achieve robust performance even at reduced electrolyte volumes and elevated temperatures. These advancements position Sionic’s platform as a scalable, drop-in solution for next-generation LIBs, enabling practical pathways for consumer electronics, electric vehicles, aerospace, and other demanding applications.
About Sionic Energy
Originally established in 2011, with the technology and team of Cornell University scientists, Sionic Energy has been a leading provider of advanced technologies and electrolytes for next-generation Li-ion batteries, partnering with leading automotive, mobile device, battery, and chemical manufacturing companies. Incorporating these technologies into its Rapid Integration Silicon Platform™, Sionic is now accelerating the industry’s pivot from Gr to Si. Built on standard Li-ion manufacturing lines—and verified by independent labs and global automotive companies—this drop-in technology delivers 370 Wh/kg, <10-minute charge capability, and over 1,000 cycles with operating temperatures from -30 °C to 45 °C.
About Group14 Technologies
Group14 Technologies is a global leader in advanced silicon battery materials, transforming the future of rechargeable energy storage. Group14’s material, SCC55®, delivers unparalleled performance to any battery and any application – powering millions of devices from EVs to AI-enabled technologies. With commercial-scale factories in the U.S. and Asia, and customers representing 95% of global lithium-ion battery production, Group14 is accelerating the global transition to electrification and ushering in the silicon battery era.
[1] https://www.prnewswire.com/news-releases/group14s-SCC55-resets-benchmark-for-silicon-battery-performance-1-500-cycles-with-faster-charging-and-higher-energy-density-302490273.html
[2] https://www.prnewswire.com/news-releases/sionic-energy-uses-group14s-SCC55-advanced-material-to-fully-displace-graphite-for-100-silicon-battery-designed-to-achieve-a-42-energy-density-increase-302326865.html
[3] (a) Weiling, Matthias, et al. “Mechanistic Understanding of Additive Reductive Degradation and SEI Formation in High‐Voltage NMC811|| SiOx‐Containing Cells via Operando ATR‐FTIR Spectroscopy.” Advanced Energy Materials 14.5 (2024) (b) Schmiegel, Jan-Patrick, et al. “Case study of N-carboxyanhydrides in silicon-based lithium-ion cells as a guideline for systematic electrolyte additive research.” Cell Reports Physical Science 2.2 (2021).
[4] Kim, Jung-Hui, et al. “Upscaling high-areal-capacity battery electrodes.” Nature Energy (2025): 1-13.
[5] Tsui, Kwok-Leung. “An overview of Taguchi method and newly developed statistical methods for robust design.” IIE Transactions 24.5 (1992): 44-57.