Stung by the fact that electric vehicle (EV) sales leveled off somewhat in 2024 (but are still expected to increase overall), the engineering community has gone on the offensive looking for technical solutions to existing problems. One, particularly evident during winter months, is that the lithium-ion batteries used in most battery electric vehicles suffer reduced charging efficiency, capacity loss and accelerated aging in low temperatures. This has a negative effect on electric vehicle driving range – how far they can travel between charges.
SOURCE: TTI MarketEye
Current electric vehicle batteries are designed for optimum use at around 70° F. The batteries in an EV’s battery cell age four times faster during the charge and discharge cycles at -5° C than a set that is charged and discharged at room temperature. Research by AAA conducted in -6.7° C (20°F) weather found the average EV’s driving range decreases by 41% when the outside temperature dips to 20 degrees and the car’s heating system is on.
Chief reasons include: 1) the movement of lithium ions slows down when it is cold which, in turn, reduces electricity generation; and 2) cabin heating, which in IC vehicles can be drawn from the engine but in EVs requires heaters powered by the battery.
Microwave Energy
EV manufacturers are confronting these technical challenges to ensure that EVs can be a reliable option regardless of weather conditions.
The car’s climate control system can consume a significant amount of electric power and subsequently reduce the driving range (by as much as 40%). Recently, however, University of Birmingham researchers looked into a novel energy storage system to boost EV driving range during hot or cold weather using microwave energy. The method, invented by University of Birmingham (UK) Professor Yongliang Li, couples a chemical heat pump with microwave energy and produces heating or cooling on demand with higher energy density than can come from battery packs.
Called e-Thermal bank, the system is charged by using microwave energy. Microwaving is a fast-heating method, because microwaves penetrate uniformly through materials and so deliver energy evenly into the body of the material.
By replacing conventional HVAC, e-Thermal banks would provide efficient cabin temperature control and a range extension of up to 70% at a lower cost than increasing battery capacity, according to Professor Li, who is Chair in thermal energy engineering at Birmingham’s School of Chemical Engineering.
The e-Thermal bank aims to alleviate thermal management tasks and can potentially extend the driving range by up to 70%.
Pre-Warming the Battery
Some solutions for dealing with frigid temperatures include the use of heat pipes and cooling liquids which have the potential to conserve energy in electric vehicles.
Warming the battery before the car is driven in cold weather reduces energy loss and helps maintain range. Electric vehicles consume a lot of electricity for heating cabin interiors. Gas and diesel vehicles draw heat from their engine, but EV batteries must maintain both cabin heat and power.
On the downside, by adding external insulation and/or heat, you are also adding bulk. Hauling that additional weight itself brings down driving range.
Sinomas, a Meerbusch, Germany-based supplier of customized heating solutions with a factory in China, offers a flexible answer for heating EV batteries. Its heating elements can be tailored to fit between battery cells, wrap around them or adhere to cold plates beneath modules.
Hyundai and others are working on advanced radiant heating panels that similarly could significantly increase the range of electric vehicles in cold climates.
Tesla, for example, has developed an innovative heat pump. A heat pump uses the thermodynamic cycle of a refrigerant gas. Its design enhances efficiency and adaptability, particularly in extreme cold conditions. All new Tesla electric vehicles come with heat pumps as standard, and this can make a big difference when it comes to cold weather efficiency and range.
Hardware is not the only way to combat this issue. Tesla also has developed an improvement to its battery preconditioning via a software update. The Tesla 2024.44.31 update aims to precondition batteries by warming them up, which should help decrease charging times at its popular Supercharging stations during cold winter months.
Valeo’s R-744 smart heat pump dual technology improves energy efficiency for EV batteries, particularly in cold weather. The solution is said to help preserve battery life and can extend an electric vehicle’s range by up to 30% in winter. Valeo’s heat pump design integrates the refrigerant loop and the coolant loop in a single module, reducing the volume of refrigerant and piping.
3D Electrode Structures
Three-dimensional electrode architectures allow for faster charging or discharging rates in lithium-based batteries. The enhanced heat transfer and dissipation of 3D electrodes help prevent cold-induced performance degradation by ensuring uniform temperature distribution and minimizing the risk of freezing.
Conventional Li-ion batteries often use graphite anodes. The standard architecture is made up of sheets of anode, separator and cathode rolled together, which can be an inefficient use of volume. Enovix has devised a 3D cell structure and high-capacity active silicon anode resulting in a battery said to have superior energy density, extended cycle life and rapid charging capabilities.
Silicon anodes can theoretically store more than twice as much lithium as the graphite anode used in most Li-ion batteries today. Enovix stacks its cathodes, anodes and separators side by side, allowing a more efficient use of the battery’s volume, leading to the ability to use a 100% active silicon anode.
Solid-State Batteries
Since solid-state batteries (SSBs) use solids rather than liquids to generate energy, they are more dependable in cold weather. SSBs employ a sulfide-based electrolyte and have demonstrated improved energy, stability and range in cold temperatures. However, SSBs require as much as 30% more lithium than traditional Li-ion batteries. And they’re costly to produce.
Microvast’s SSB utilizes a bipolar stacking architecture that enables internal series connections within a single battery cell. This bipolar design significantly reduces the number of interconnections between cells, modules and packs. That simplifies the overall system architecture and enhances both energy efficiency and operational safety.
Furthermore, Microvast has developed its proprietary all-solid electrolyte separator membrane based on a polyaramid separator, which is non-porous and tailored specifically for solid-state applications. This separator ensures improved ionic conductivity, structural stability and long-term durability, addressing one of the most critical technical challenges in solid-state battery technology.
Volkswagen and Toyota also have developed production-ready solid-state EV batteries while Nissan and Samsung are expected to begin pilot production of SSBs. VW’s technology comes from California-based battery company QuantumScape, which will license its formula to PowerCo, Volkswagen’s internal battery division. This is a semi-solid state cell with no anode that uses lithium metal, a ceramic separator and liquid electrolyte.
Toyota is focused on using a sulfur-based electrolyte in its prototypes as it is said to provide a more efficient power transfer. Toyota is developing the solid-state batteries through Prime Planet Energy & Solutions Inc., a joint venture with Panasonic that started operations in April 2020. The company says it is on track for limited production this year.
