Lithium-ion batteries (LIBs) are clean energy sources used in electronic devices. Compared with other batteries, LIBs have various advantages of high specific energy, high energy density, long endurance, low self-discharge, and long shelf life. However, in a high-temperature environment, LIBs may produce thermal runaway.
Study: Hierarchically Structured Metal Carbides as Conductive Fillers in Thermo‐Responsive Polymer Nanocomposites for Battery Safety. Image Credit: Veleri/Shutterstock.com
Although incorporating thermo-responsive polymer switching materials (TRPS) into LIBs could prevent thermal runaway, the existing preparation methods for TRPS restrict their practical applications. An article published in the journal Nano Energy discussed developing a versatile strategy to prepare various metal carbides for their integration into TRPS to restrain the thermal runaway when used in batteries.
The prepared metal carbides had a hierarchical structure with a surface protrusion; this was critical for rapid thermal response and high conductivity. The studies on phase and morphology evolutions illustrated that the reduction rate and reducing agent were crucial in endowing a specific morphology to the metal carbide.
The separated reduction-carbonization process and uniform carbon coating layer benefited in maintaining the initial architecture of final metal carbides. TRPS embedded with as-prepared spherical-spiky metal carbides exhibited a five-order improvement in conductivity and demonstrated protection against thermal abuse to ensure battery safety.
Metal Carbide in LIBs
LIBs are extensively applied in electronic devices and serve as a clean energy source. The persistent contribution by researchers over the past three decades has improved the energy density of LIBs from 60 to 300-Watt hour per kilogram along with their availability at a cheaper price and low charging rate.
Nevertheless, the battery safety of LIBs is still a major concern due to the combustion and explosion of LIBs, which are easily triggered by mechanical (deformation), electrical (overcharge), and thermal abuses (overheating). These extreme situations may lead to thermal runaway.
The strategies explored to address the issue of thermal runaway in LIBs to date can be divided into three categories: at the systematic level using external battery management systems, at the structural level using well-separated cell-matrix or solid metallic frameworks, and at the material level using thermally stable electrodes, flame-resistant electrolytes, and thermal shutdown separators.
TRPS is composed of a thermo-responsive polymer matrix embedded with conductive fillers. These conducive fillers form a conducive network within the polymer matrix and ensure electron transfer across the TRPS films at room temperature. When integrated into LIBs, the TRPS can protect the battery from the detrimental consequences of thermal abuse preventing thermal runaway and ensuring battery safety.
Transition metal carbides have special metallic structures in which carbon atoms are distributed in the interstitial voids of a densely packed host lattice. These metal carbides exhibit high electronic conductivity, mechanical stability, and good corrosion resistance. The combination of such exceptional properties has led to numerous technical applications and theoretical investigations, with most efforts focusing on the catalytic activity of metal carbides. Due to their high electronic conductivity, metal carbides are often used as anode materials in LIBs.
Metal Carbides as Conductive Fillers
Metal carbides like tungsten carbide (WC) are used as conductive filler materials attributing to the good electrical and thermal properties of the base polymer matrix. The spiky structured nickel-based fillers were reported to increase the number of contact sites in the composites and improve the polymer network’s conductivity, triggering the quantum tunneling effect.
The susceptibility of nickel to oxidation and degradation under extreme conditions calls for a protective coating layer, increasing the overall production cost. Thus, the performance of TRPS can be improved by the integration of metal carbides with controlled morphologies which are commercially unavailable.
In the present work, a universal strategy was adopted to synthesize various metal carbides with controlled morphologies. The separated reduction-carbonization process and uniform carbon coating layer from the hydrothermal process helped maintain the initial architecture of final carbides.
Consequently, the formation of spiky WC (s-WC), sphere WC (p-WC), and hollow-sphere molybdenum carbide (Mo2C) confirmed the versatility of this strategy. Utilizing the prepared metal carbides as conductive fillers in TRPS increased the electrical conductivity by five-fold compared to commercially available WC, and ensured secure, quick, and reversible shutdown with battery safety.
Furthermore, the TRPS material’s thermal protection was verified in different cathode chemistries by constructing 70WC-TRPS-integrated fuel cells and was analyzed for their switching response to abuse scenarios. The results confirmed the potential of TRPS materials in increasing battery safety.
Overall, metal carbides with desired morphologies were prepared via a two-step conversion method. The results of phase and morphology evolution studies revealed that regulation of reduction temperature and using hydrogen as a reducing agent were critical to maintaining the morphology of metal carbides. The current strategy of controlling the morphology of metal carbides provides insights into other fields, like catalyst design.
Spherical-spiky WC was synthesized to improve the electrical conductivity of TRPS by five-folds, demonstrating that WC-embedded TRPS can achieve high conductivity and protect LIBs against thermal abuse, assuring battery safety.
Li, M. et al. (2022) Hierarchically Structured Metal Carbides as Conductive Fillers in Thermo‐Responsive Polymer Nanocomposites for Battery Safety. Nano Energy. https://www.sciencedirect.com/science/article/pii/S2211285522008047