As people's demand for energy storage continues to grow, higher and higher requirements are being placed on the performance of rechargeable batteries. Nanotechnology can make batteries "lighter" and "faster," but due to the low density of nanomaterials, "smaller" has become a major challenge for researchers in the field of energy storage.
A research team led by Professor Yang Quan Hong of the School of Chemical Engineering at Tianjin University, a recipient of the National Science Fund for Distinguished Young Scholars, proposed the "sulfur template method." Through the design of high volumetric energy density lithium-ion battery anode materials, they ultimately achieved a "tailor-made" process of encapsulating active particles with graphene, making it possible to make lithium-ion batteries "smaller." This achievement was published online in *Nature Communications* (2018.9.402) on January 26.
As the most widely used rechargeable battery, lithium-ion batteries boast high energy density. Non-carbon materials such as tin and silicon hold promise as a next-generation anode material, potentially replacing commercially available graphite and significantly improving the mass energy density (Wh/kg⁻¹) of lithium-ion batteries. However, their substantial volume expansion severely limits their volumetric performance advantages. Carbon cage structures constructed from carbon nanomaterials are considered a crucial solution to the problem of massive volume expansion during lithium intercalation in non-carbon anode materials; however, the construction of carbon buffer networks often introduces excessive pre-existing space, leading to a significant reduction in electrode material density and limiting the volumetric performance of lithium-ion battery anodes. Therefore, the precise customization of carbon cage structures is not only a significant academic challenge but also an essential path to the industrialization of novel high-performance anode materials.
Professor Yang Quan Hong's research team, in collaboration with Tsinghua University, the National Center for Nanoscience and Technology, and the National Institute for Materials Science in Japan, has achieved a breakthrough in the design of high volumetric energy density lithium-ion battery anode materials. Based on graphene interface assembly, they invented a sulfur template technology for precisely customizing dense porous carbon cages. During the construction of a dense graphene network using capillary evaporation technology, they introduced sulfur as a flowable volumetric template, customizing the graphene carbon coating for non-carbon active particles. By modulating the amount of sulfur template used, the three-dimensional graphene carbon cage structure can be precisely controlled, achieving a perfectly sized coating of non-carbon active particles. This effectively buffers the significant volume expansion of non-carbon active particles during lithium intercalation, resulting in excellent volumetric performance as a lithium-ion battery anode.
The sulfur template method cleverly utilizes the fluidity, amorphous nature, and ease of removal of sulfur—like a "Transformer"—within a dense three-dimensional graphene network to achieve tight encapsulation of non-carbon active particles, such as tin dioxide nanoparticles, within a carbon cage structure. Compared to traditional "shape" templates, the biggest advantage of sulfur templates is their ability to function as malleable volumetric templates. This allows the compact graphene cage structure to provide shape-fitting and precisely sized pre-reserved space, ultimately achieving a "tailor-made" solution for active tin dioxide. This carbon-non-carbon composite electrode material, with its suitable pre-reserved space and high density, contributes extremely high volumetric capacity, significantly improving the volumetric energy density of lithium batteries and enabling smaller lithium batteries. This "tailor-made" design concept can be extended to a universal strategy for constructing electrode materials for next-generation high-energy lithium batteries, lithium-sulfur batteries, and lithium-air batteries.
In recent years, Professor Yang Quan Hong's research team has made a series of important advances in the field of dense energy storage, which emphasizes the volumetric performance of devices. They invented a capillary evaporation densification strategy for graphene gels, solving the bottleneck problem of the "cannot have both high density and porosity" of carbon materials, and obtaining high-density porous carbon materials. Pursuing small volume and high capacity of energy storage devices, they proposed design principles for high volumetric energy density energy storage devices from five aspects: strategy, method, materials, electrodes, and devices. Finally, they have realized the construction of high volumetric capacity energy storage materials, electrodes, and devices from supercapacitors, sodium-ion capacitors, lithium-sulfur batteries, lithium-air batteries to lithium batteries, laying the foundation for the practical application of carbon nanomaterials and powerfully promoting the practical application of new electrochemical energy storage devices based on carbon nanomaterials.
