Peking University, Apr. 29, 2016: Recently, Professor Hou Yanglong’s Lab from College of Engineering has made an important progress in the research of advanced materials for energy application.

The results titled “Rational Design of Si/SiO2@Hierarchical Porous Carbon Spheres as Efficient Polysulfide Reservoirs for High-Performance Li–S Battery” have been published in the journal Advanced Materials.         

Another paper titled “3D Vertically Aligned and Interconnected Porous Carbon Nanosheets as Sulfur Immobilizers for High Performance Lithium-Sulfur Batteries” has been published in the journal Advanced Energy Materials.           

Owing to the increasing demands of energy storage in portable electronics, vehicle electrification and grid-scale stationary storage, advanced batteries with high energy density have recently attracted intensive interests.

Among the existing myriad of energy storage technologies, lithium–sulfur batteries (LSBs) show the appealing potential for the ubiquitous growth of next-generation electrical energy storage application, owing to their unparalleled theoretical energy density of 2600 Wh kg−1 that is over five times larger than that of conventional lithium-ion batteries. It is one of the most promising electrochemical energy storage technologies due to its high theoretical capacity of 1672 mAh g−1, reduced cost, and environmental benignancy.

Despite the significant advances of LSBs, its large-scale implementation is plagued by multitude issues: particularly, the intrinsic insulating nature of the sulfur (10-30 S cm-1), mechanical degradation of the cathode due to large volume changes of sulfur up to 80% during cycling, and loss of active material (producing polysulfide shuttle effect). The underlying primary hurdle behind the poor performance of LSBs is the dissolution of polysulfide intermediate species, initiating in the process of battery discharging.

To tackle the aforementioned problems associated with LSBs, exciting progress has been made, however it is still a great challenge to solve the hurdles associated with LSBs and enhance its electrochemical performance.

To address these problems, the Hou group designed a unique structure, namely, silicon/silica (Si/SiO2) cross-link with hierarchical porous carbon spheres (Si/SiO2/C), and used it as a new and efficient sulfur host to prepare Si/SiO2@C-S hybrid spheres to solve the hurdle of the polysulfide dissolution. They employ the concept of both physical and chemical adsorptions of polysulfides via the carbon and Si/SiO2 of developed hybrid spheres, respectively. Different from the traditional porous carbon structures, the developed hybrid spheres afford the intriguing structural advantages. As a result of their multiple advantages, the developed Si/SiO2@C-S hybrid spheres show high cycling stability and maintain high reversible capacity of 614 mAh g−1 at the high current density of 2C over 500 cycles (with ultraslow capacity decay of 0.063% per cycle).

To date, 3D porous carbon nanostructures (3D-PCNs) are attractive candidates for rechargeable batteries because they can integrate multiple advantages of unique collective effects and great potential electrochemical applications. The group proposed a simple carbonization method to make novel 3D highly micro-mesoporous, vertically aligned and interconnected carbon nanosheets (3D-VCNs) for solving the hurdles associated with LSBs to bring high performance at low cost.

The present 3D nanostructures with very high surface area of 1750 m2g-1 are highly particular for enhancing the performance of LSBs in the terms of capacity, rate ability, and cycling stability. The developed porous structure is beneficial in facilitating the easy access of electrolyte through the structure of 3D-VCNs infiltered with sulfur (3D-S-VCNs) during the cycling process.

As a consequence, the unique 3D-S-VCNs show high initial discharge capacity of 1240 mAh g−1 at the current density of 167 mA g−1 with excellent Coulombic efficiency of ≈100% and presents a long stability up to 300 cycles with high reversible specific capacity of 844 mAh g-1 and capacity retention of ≈80.3% (a capacity decay of only 0.082% per cycle) at the current density of 837 mA g-1. Furthermore, the electrode bears the excellent rate capability and maintains a high reversible capacity of 738 mAh g-1 at the high current density of 3340 mA g-1.

 

(a) Hierarchical porous Si/SiO2@C-S Hybrid Spheres (b) Three dimensional vertical aligned porous carbon nanosheets (3D-VCNs) as an efficient sulfur host for high performance lithium sulfur battery.

The Project was mainly completed by PhD student, Sarish Rehman. Its co-operators included: Professor. Guo Shaojun from College of Engineering at Peking University.

The research was supported by the NSFC-RGC Joint Research Scheme (51361165201), Beijing Project of Science and Technology (Z141100003814012), NSFC (51125001 and 51172005), Doctoral Program of the Ministry of Education of China (20120001110078), the Interdisciplinary Project of Beijing New Star Plan of Science and Technology, start-up funding from Peking University, Young Thousand Talented Program, Opening Funds of National Laboratory of Molecular Science and Key Laboratory of Functional Inorganic Material Chemistry (Heilongjiang University), Ministry of Education of China.

Edited by: Zhang Jiang
Source: College of Engineering