Rational Design of Lithium/Sodium Ion Battery Anode for High Performance Energy Storage
The rapid increasing consumption of fossil fuels since the industrial revolution has brought about environmental and ecological contamination and its depletion, thus, humankind must stop to utilize more clean and renewable energy such as solar, hydraulic power, wind power as alternative. In this case, an effective and efficient medium is a must since those sorts of renewable energy are difficult to be stored and utilized in a standard way. As the invention and improvement of battery, electrical power come up to be the chosen solution. Therefore, electrical vehicles are already commercialized for a long time and growing up rapidly, grabbing the market share from traditional Inner Combustion Engine vehicles. Among the various battery chemistries, Lithium-ion Batteries (LIBs) have acquire most of attention from both academia and industry. With a similar mechanism, Sodium-ion Batteries (SIBs) are acting as an alternative for LIBs for their low cost.
However, the current battery performance cannot satisfy the market of electrical vehicle and consumer electronics, thus, energy density and power density as two of the crucial factors for battery performance must be enhanced. To address these issues, the anode of LIBs and SIBs need to be improved. In this dissertation, novel ideas for anode materials design were given, towards not only the current anode modification, but next generation anode production as well.
With a high theoretical capacity of 2595 mAh g-1 from alloy reaction, phosphorus is one of the most promising candidates as next generation anode material for lithium/sodium ion battery. Nonetheless, it is suffering volume expansion (300% for LIBs and 500% for SIBs) and low conductivity during cycling, leading to sacrificed robustness of the electrode. Herein, we developed an efficient and effective high energy ball milling route to crystalline phosphorus within carbon matrix as anode material for LIB and SIB. The special structure offers many advantages: enhanced the conductivity; shortened distance for Li+ or Na+ diffusion; buffered volumetric expansion and more stable structure. Benefitting from the merits, the composite delivers a capacity over 1000 mAh g-1 for about 300 cycles at a specific current of 1 A g-1. Both half-cell and full cell cycling test show an 80% retention around 300th cycle. More essentially, crystalline phosphorus can be still found after many cycles. As-prepared material also delivered a high sodium capacity over 700 mAh g-1 over 300 cycles.
For increasing utilization in electrical vehicles, the limitation of power density has become a severe issue for LIBs. Therefore, LIBs with advanced high rate performance is highly desirable. A major issue for developing high rate battery is the performance of anode as their sluggish intercalation kinetics. Herein, we provide a new strategy for advanced performance LIB anode design and its demonstration. To fabricate anode with both high energy and power density, two different materials with each character respectively were mixed to achieve the goal, meanwhile, they need to have different charge and discharge plateaus. As the redox plateaus of these materials are different, the electrochemical interaction will occur when they are being charged or discharged as composite, thus enhance the performance as anode for LIBs. Phosphorus-carbon composite and commercialized LTO were utilized to demonstrate this strategy.
The current anode system in commercialized LIBs are difficult to be substituted in the near future because of their low charging potential which leads to a high energy density for full cell. In this case, the development of LIBs in EV are highly depends on modification of the current system in recent years. Therefore, we developed a new route for graphite anode improvement with the additive of Metal-organic Framework (MOF). With its special structure, open metal sites (OMS), MOF can immobilize the anion of electrolyte by forming coordination bond, thereby prevents the electrolyte from decomposition, so as to eliminate the byproduct and heat release. With these advantages from MOF additive, the graphite anode performance was improved a great deal especially fast discharging (full cell). And post-cycle characterization explores that MOF keeps higher crystallinity of graphite and lower down the decomposition of the electrolyte LiPF6.