With the increasing adoption of electric vehicles, the use of power batteries has become more widespread. However, a major challenge faced by lithium-ion batteries is the significant reduction in driving range during cold winter months. This issue is closely related to the inherent characteristics of lithium-ion batteries, which exhibit poor kinetic performance at low temperatures. As a result, their capacity, rate capability, and especially charging performance are severely compromised. This problem is particularly pronounced in northern regions with harsh winters, where battery heating systems are commonly used to maintain performance. Unfortunately, traditional heating methods are inefficient, often taking tens of minutes to warm up the battery, which significantly hinders the convenience of electric vehicle usage. Therefore, effective thermal management for lithium-ion batteries at low temperatures remains a critical challenge in battery design.
Recently, Guangsheng Zhang from the University of Pennsylvania proposed an innovative thermal management strategy that utilizes internal heating within lithium-ion batteries. This method allows the battery to quickly return to normal operating temperature, restoring its performance in just 112 seconds at -40°C. The technology also significantly improves the vehicle's driving range—by as much as 49% at such extreme temperatures.
The core of this technology is a self-heating battery design. As shown in the diagram, two nickel sheets are placed inside the battery at 1/4 and 3/4 of its thickness. Each sheet has an impedance of 78mΩ and is connected in parallel to the battery’s positive and negative terminals through a switch. This switch controls whether the battery is heated. Zhang developed a control scheme that adjusts the switch based on the vehicle’s load conditions.
In electric vehicles, energy recovery occurs during braking. Normally, this recovered energy is stored directly when the battery is at an acceptable temperature. However, at low temperatures, the battery cannot be charged safely, so the energy is often wasted. Zhang’s system uses the rapid self-heating capability of the self-heating battery to first heat the battery before storing the recovered energy. This ensures that no energy is lost during cold weather.
The figures illustrate the current and power changes under simulated driving conditions. When the external discharge current is applied, the battery current remains the same, but during charging or rest, the internal current is used for heating. The power curve reflects similar behavior, indicating that the strategy does not interfere with normal vehicle operation. Moreover, it maximizes the utilization of braking energy by using it first for heating and then for charging.
Another figure shows the battery temperature and internal resistance over time. At -40°C, the battery temperature rises to 10°C in just 112 seconds, while the internal resistance drops rapidly from 125mΩ to 10mΩ. This rapid temperature rise leads to a quick recovery of battery performance. At various low temperatures (-40°C, -30°C, -20°C, -10°C), the battery recovers to 10°C in 13s, 33s, 46s, and 56s respectively, making it highly beneficial for winter use.
The next set of data compares the experimental group (with self-heating battery) and the control group (without). The self-heating battery warms up much faster, reaching 20°C in 112 seconds, allowing full recovery of braking energy. In contrast, the control battery only reaches 0°C after 3000 seconds and fails to recover any braking energy.
A further graph highlights the proportion of usable energy for driving. The experimental group shows a significant increase in usable driving energy compared to the control group, due to better energy recovery and battery warming.
At different temperatures, the battery can provide 78%, 80%, 85%, and 90% of the driving energy compared to room temperature. Even with higher energy density batteries (e.g., 300Wh/kg), the energy required for heating decreases, and the usable driving energy increases significantly.
Overall, Zhang’s strategy effectively leverages the self-heating capabilities of the battery, ensuring efficient and safe operation in cold environments. This innovation not only enhances the convenience of electric vehicles but also greatly improves their driving range in low-temperature conditions.
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