Redox (reduction-oxidation) chemical reactions take place in electrochemical cells; they include the transfer of electrons. Each cell stores and transforms chemical energy into electrical energy. They consist of an anode, which is negatively charged, a cathode, which is positively charged, a separator between the two, and an electrolyte solution, which permits ion migration. A battery can be made up of one or more electrochemical cells.
The electrolyte of a lithium ion battery is made up of a lithium salt (Li+) in an organic solvent. The anode in a lithium ion battery is typically a carbon based compound, and the cathode is a metal oxide. Li ions move in opposite directions during charging and discharging in the process shown below:
Where M is the metal in the oxide (e.g. Co, Ni, Fe, W, etc.).
Secondary batteries are rechargeable batteries with a longer life cycle and improved mobility, such as the lithium ion battery. This makes it possible to employ these batteries in devices like phones, computers, power tools, electric bikes, and electric vehicles. On the other hand, there are also non-rechargeable primary batteries, such as the standard alkaline AA and AAA batteries often found in shops, which are commonly used in devices like TV remote controls and alarm clocks. Although primary batteries are sometimes thought of as more convenient, they end up costing more over the course of a lengthy period of time because they are considered disposable after usage.
When designing a battery-powered device, thermal management (TM) is a crucial component that must be optimised since, in the worst scenarios, it can result in catastrophic failures that result in explosions or fires. Safety is the first consideration when considering the deployment of the battery. The phenomenon of thermal runaway, which occurs when an exothermic chemical reaction takes place inside the electrochemical cell and results in elevated pressure and temperature that the cell cannot adequately dissipate, increases the risk of fires and a significant risk associated with batteries. The temperature of a lithium ion cell is determined by the balance between heat created and its capacity to disperse; it’s thought that thermal runaway can occur spontaneously above 80 °C (Wang et al., 2012). In addition to compromising safety, insufficient thermal management can result in a battery that is less effective, has a shorter lifespan, less capacity for repeated charging cycles, and is less efficient overall.
Due to their lack of memory effect, high energy density, and low self-discharge levels, lithium batteries are an effective source of energy; nontheless, extensive testing of each component is necessary to guarantee that the battery maintains its efficiency. Thermal conductivity is a significant parameter tested on all materials utilised in the construction of battery cells, including the casing, thermal interface materials, electrolytes, and cooling materials. This data can be evaluated to ascertain the suitability of the material.
Thermal conductivity is an integral characteristic required from the material, not only helping to accurately determine the thermal characteristics of a material and the charging-discharging process, it can also help with the design of the battery thermal management system (Wei et al., 2020). Analysing the temperature distribution inside the cell using both isotropic and anisotropic thermal conductivities can result in advancements in the efficiency and design of the cooling system.
A platform that can capture data for all circumstances, including elevated temperatures or pressures, as well as all materials, including powders, pastes, thin films, liquids. and solids, is necessary for the optimisation of thermal management systems. The Trident platform from C-Therm is a modular system consisting of multiple sensors for various uses that can measure the thermal conductivity and diffusivity of samples, facilitating a deeper comprehension of a material and assisting in the design optimisation of the thermal management system.
For more information about the C-Therm Trident platform with battery applications, visit the C-Therm website, or watch their most recent webinar about preventing thermal runaway in lithium ion batteries.
For any enquiries or contract testing using the C-Therm Trident, contact us.