Strategies for Building Robust Traffic Networks in Advanced Energy Storage Devices: A Focus on Composite Electrodes

Abstract

portable electronics, cell phones, electrical vehicles (EVs), aerospace, etc. For advanced batteries, higher and higher energy density and/or power density, long cycling stability, good device safety, and low-cost are the primary goals. Since the energy density is mainly dependent on the specific capacity and loading level of active materials (AMs), AMs usually dominate the volume and weight inside the batteries. Because of this, tremendous efforts have been focused on high-performance AMs. However, the electrochemical performance of energy storage devices (ESDs) is fundamentally determined by a collective contribution or teamwork of all the components: AMs, electrolyte, separator, conductive agent, binders, etc. More importantly, with the increasing interests on high-capacity AMs (e.g., silicon, sulfur, Li-rich cathode, etc.), it becomes very clear that the "traffic system" (i.e., the charge transport system) plays very critical roles in the performance of the high-capacity AMs. Take silicon anode for example, a durable and flexible conductive network inside the electrode composite has been vital for addressing the big volume change issue. In this case, high-performance binders and conductive agent that can generate advanced conductive network are the keys. [2] In addition, with the increasing interests on EVs and flexible electronics, building a powerful and robust charge transport system inside ESDs is an urgent and critical task to support fast charging/ discharging capability and even flexibility of ESDs. In short, with the fast development of energy storage technologies, EVs, cell phones, etc., there is a critical, urgent, and challenging task on building powerful and durable charge transport system in next-generation advanced ESDs. Charge Transport Inside ESDsThe thriving of big cities highly relies on a powerful traffic system that transports the people, foods, products, etc. Similar to this picture, ESDs are powered by the transportation of charges, including both ions and electrons. As illustrated in Figure 1a, one can analogize the charge transport system and AMs in the electrodes of ESDs to the traffic system and buildings (i.e., host system of people), respectively. This analogy example not only help to explain the relationship between The charge transport system in an energy storage device (ESD) fundamentally controls the electrochemical performance and device safety. As the skeleton of the charge transport system, the "traffic" networks connecting the active materials are primary structural factors controlling the transport of ions/electrons. However, with the development of ESDs, it becomes very critical but challenging to build traffic networks with rational structures and mechanical robustness, which can support high energy density, fast charging and discharging capability, cycle stability, safety, and even device flexibility. This is especially true for ESDs with high-capacity active materials (e.g., sulfur and silicon), which show notable volume change during cycling. Therefore, there is an ur...

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