CryoPhase: Electrical Interfacial Control for Sustained Ionic Transport in Subzero Energy Systems

CryoPhase: Turning freezing from a failure point into a functional system.

In subzero environments, electrochemical systems don’t fail because it’s cold; they fail because ionic pathways collapse.

This project shows that by stabilizing the ice–liquid interface, conductivity can be preserved down to −15°C without bulk heating.

By engineering the phase boundary itself, CryoPhase introduces a new design framework for energy systems in extreme conditions.

In cold environments, failure is rarely gradual—it is sudden. Energy systems that perform reliably at room temperature can lose a significant portion of their functionality below freezing, with lithium-ion batteries losing up to 40–60% of their usable capacity near −20°C. This loss is not driven by material degradation alone, but by the breakdown of ionic transport as freezing disrupts conductive pathways.

Conventional mitigation strategies approach this as a bulk problem. Heating systems and insulation attempt to maintain uniform temperature, but freezing is inherently non-uniform. As ice forms, ions are excluded from the crystal lattice and concentrated at the advancing boundary, forming a dynamic interfacial region. Despite retaining partial conductivity through interconnected brine channels, this region is transient and collapses as freezing progresses, resulting in abrupt system failure.

A more precise approach considers the phase boundary itself. Rather than preventing freezing, controlling the interfacial region offers a pathway to preserve conductivity under subzero conditions. By stabilizing this boundary, ionic transport can be maintained even as surrounding regions solidify.

Several key objectives were defined:

Quantify conductivity loss in untreated systems under controlled subzero conditions

Investigate the evolution of the ice–liquid interface during directional freezing

Evaluate whether electrical input can stabilize interfacial ionic pathways

Assess structural and mechanical stability across repeated freeze–thaw cycles

This approach reframes freezing not as a limitation, but as a controllable system, one that can be engineered to maintain functionality where conventional methods fail.

A controlled experimental system was constructed to isolate and study ionic transport at the ice–liquid boundary under subzero conditions. Background research was conducted using peer-reviewed electrochemistry and cryosphere literature to identify key variables influencing conductivity loss, including temperature gradient, salinity, and phase boundary dynamics.

A saline solution was prepared at defined concentrations (2%, 3.5%, 5% NaCl by mass) to investigate the effect of ionic density, with 3.5% selected as a seawater analogue. Solutions were transferred into a transparent acrylic tank and placed on a laboratory thermoelectric cold plate (−20°C to 90°C range), enabling precise bottom-up freezing through controlled thermal gradients. Foam insulation was applied to all non-observational surfaces to suppress lateral heat loss and ensure directional solidification.

Electrical conditions were introduced using rubber-wrapped graphite electrodes positioned at the interfacial boundary and within the bulk liquid. Trials were conducted at controlled voltages (2 V, 4 V, 6 V; ≤0.2 A) to evaluate the influence of electric field strength on interfacial stability, alongside control trials with no electrical input.

Conductivity was measured using a calibrated conductivity probe (standardized with 12.88 mS/cm KCl solution) positioned directly at the interface. Temperature was monitored continuously using an infrared thermometer, and measurements were recorded at defined intervals from 0°C to −15°C. Resistance was measured using a laboratory multimeter.

Repeated freeze–thaw cycling (n = 30) was performed to assess structural stability, interfacial persistence, and reproducibility of conductivity trends. Data were compared directly between control and electrically stabilized conditions to evaluate the effectiveness of interfacial regulation.

Conductivity Retention

Conductivity measurements, obtained using a calibrated probe positioned directly at the ice–liquid interface during controlled bottom-up freezing, revealed a sharp failure threshold in control systems. Conductivity dropped from ~50 mS/cm at 0°C to near-zero values below −5°C, indicating complete loss of ionic pathways.

Under CryoPhase conditions, where a constant-voltage input was applied across the interfacial region, conductivity decreased gradually, retaining ~25–28 mS/cm at −5°C, ~17–19 mS/cm at −10°C, and remaining measurable near −15°C. Rather than collapsing, the system maintained a continuous conductive network, demonstrating sustained ionic transport under subzero conditions.

Resistance Behaviour

Electrical resistance was monitored concurrently using a laboratory multimeter. Control trials exhibited rapid divergence, exceeding >1300 Ω by −4°C and approaching open-circuit behavior shortly thereafter.

In contrast, CryoPhase conditions produced a predictable increase in resistance, remaining within ~400–420 Ω at −10°C and finite near −15°C. This indicates preserved electrical continuity, rather than abrupt pathway disruption.

Interfacial Mechanism

Directional freezing, enforced through a thermoelectric cold plate and lateral insulation, consistently produced a distinct ice–liquid boundary. Visual calibration and image-based estimation showed gradual thinning of this interface from ~3.2 mm at 0°C to ~2.3 mm near −10°C, without collapse.

Conductivity measurements aligned spatially with this region, supporting the presence of a percolating brine network that remained connected under electrical stabilization.

Mechanical Stability

Repeated freeze–thaw cycling (n = 30) was used to evaluate structural response. Control systems exhibited brittle fracture and discontinuities due to volumetric expansion during freezing.

CryoPhase conditions showed no observable cracking. The interfacial region acted as a compliant layer, redistributing stress and maintaining structural integrity across repeated cycling.

Operational Regime

System performance was evaluated across varying electrical inputs and salinity levels. Trials conducted at 2 V and 4 V, and 2%, 3.5%, and 5% NaCl, revealed that 4 V and ~3.5% NaCl provided the most stable conductivity retention.

Lower voltages reduced interfacial stability, while higher concentrations limited ion mobility at lower temperatures, indicating a balance between ionic availability and transport efficiency.

Key Outcome

Rather than delaying failure, CryoPhase fundamentally altered how conductivity is lost. The system transitioned from abrupt collapse (control) to controlled degradation (CryoPhase), maintaining functional ionic transport down to approximately −15°C.

Implications

These results indicate that subzero system failure is governed by interfacial connectivity rather than temperature alone. Stabilizing this boundary enables sustained functionality without reliance on bulk heating, with direct relevance to energy systems operating in cold environments.

Electrochemical systems are typically treated as bulk systems, where maintaining temperature is assumed to be the primary requirement for functionality. However, the results demonstrate that failure in subzero conditions is not governed by temperature alone, but by the loss of ionic connectivity at the phase boundary.

Across all trials, control systems exhibited a distinct failure threshold, with conductivity collapsing below −5°C. In contrast, CryoPhase conditions eliminated this threshold, maintaining a continuous conductive pathway down to approximately −15°C. This shift from abrupt failure to controlled degradation indicates that ionic transport can persist when the interfacial region is stabilized.

These findings suggest that the ice–liquid boundary is not merely a transient feature of freezing, but a functional region that can be engineered. The persistence of conductivity, alongside the absence of structural failure across repeated freeze–thaw cycles, supports the presence of a stable, percolating network capable of sustaining both electrical and mechanical continuity. The key insight is that system performance in extreme cold is governed by interfacial behavior rather than bulk conditions. By targeting this boundary directly, it becomes possible to preserve functionality without relying on energy-intensive heating methods.

This has implications for energy storage, transportation, and infrastructure in cold environments, where maintaining reliability is critical. More broadly, these results introduce a new framework for designing electrochemical systems that operate under extreme conditions by controlling, rather than avoiding, phase transitions.

Future work will focus on translating CryoPhase into practical electrochemical systems. This includes integration into simplified battery architectures to evaluate interfacial control under realistic operating conditions, as well as extending testing to lower temperatures to define stability limits. Additional work will investigate alternative electrolytes and electrode materials to improve efficiency and reduce energy input. Higher-resolution imaging techniques could also be used to directly visualize interfacial dynamics. Ultimately, scaling the system and testing under real-world conditions will be essential to assess performance in applications such as electric vehicles and cold-region infrastructure.

This project was shaped by the support and perspectives of several individuals who helped refine both its direction and impact.

We would like to thank Guus Luupens for sharing insights into the realities of energy reliability in extreme cold environments, which helped ground this work in real-world challenges. We are also grateful to Amanda Ackroyd and Daniel Choi for their guidance on electrochemical systems and interfacial behaviour, which strengthened the scientific foundation of this project.

We would like to acknowledge David R. Moore for offering perspective on infrastructure and accessibility in remote communities, reinforcing the broader significance of maintaining system functionality in harsh conditions.

Finally, we are deeply thankful to our parents and teachers for their constant support, encouragement, and patience throughout the many iterations, setbacks, and long hours that went into developing this project.

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