Graphene Pliable Pockets Remedying Nanocrystalline Metal Anode for All Li-Ion Types Energy Storages Induced By Polymer-Triggered Synthesis Process in an Expeditious, Scalable and Inexpensive Way
Authors: Won Jong Ho , Kang Jeung Ku 
Published: February 2020

Lithium-ion type energy storage is the most popular energy storage method, but now is a time when significant improvement is needed. Major attempts have been made to improve the various components that makeup energy storage devices such as lithium-ion batteries (LIBs) and capacitors (LICs), the most promising of which is the anode part. Nanocrystalline metals are promising building units to realize high-capacity anodes replacing graphite are enabling ever-increasing gravimetric and volumetric energy densities in lithium-ion type energy storage. However, their fading capacities upon both pulverization and electrical disconnection caused by large volume changes during repetitive lithiation/delithiation reactions must be remedied. Another challenge is the lack of a fast and scalable process to fabricate nanocrystalline metals into real electrodes. Herein, we report graphene pliable pockets (GPPs) remedying the limitations of nanocrystalline metals for high-performance LIBs and LICs, and Metal_encapsulated GPPs (M_GPPs) can be fabricated via the ultrafast dynamic polymerization and evaporation of specific polymers on nanocrystalline metals. This process is also shown to enable scalable mass production upon increasing the batch size. The method we use is very different from the traditional way of coating nano metal materials with conventional carbon materials. Although many attempts have been made to coat nanocrystalline metals with carbon materials, such methods are expensive and degrade the performance of the nanocrystalline metals anode than expected. We simply mix the graphene and metal nano particles in solution, then add the polymer and mix them well. At this time, we have learned how to accurately control the molecular weight of the polymer, and the molecular weight controlled polymer plays a crucial role in the formation of M_GPPs. We remove the polymer through a low temperature heat treatment below 400 degrees of Celsius, and then we can get the M_GPPs structure we want. This process is complete within one hour, and there is no change even if the amount you want to obtain is very large. In addition, the yield of M_GPPs is 100% compared to the mixed graphene and metal particles, and the synthesis cost is very low. From our standpoint, this synthesis method has never been attempted and is a very efficient method. We applied the GPP structure to silicon, a most promising but also difficult to handle electrode material. Utilizing Si_GPPs with high tap densities exhibits excellent rate capability and robust cycle life. We discover that the inner graphene pliable layers allow electrical conductance to Si and the outer GPP controls formation of solid-electrolyte interface (SEI) layers, while both of them provide pliable compartments to prevent volume expansion and pulverization of Si nanocrystals during repeated lithiation/delithiation cycles. Full-cell LIBs of the Si_GPP electrodes assembled with representative cathodes of LiCoO2 (LCO), LiMnO2 (LMO), and LiFePO4 (LFP) demonstrate remarkably high gravimetric and volumetric energy densities. Moreover, Si_GPPs can be used as the battery-type electrodes for LICs, such an attempt lead to a result in much faster charging/discharging and strikingly longer life performance while maintaining high energy densities. GPP structures are superior and feasible than other promising anode structures, thereby applicable to industries and attainable shortly. Now, many battery manufacturers now want to make electrodes by mixing graphite with high-performance materials such as silicon particles, which means that materials such as silicon are added to the electrode as a kind of additive. Even though a very small amount of metal particles, such as silicon, are added in the form of additives, surface physical differences between the graphite and metal particles cause them to aggregate together during electrode manufacturing, which negatively affects the electrode and battery life. We believe that our M_GPPs structure can be used as an additive in the current market and we would like to report it.

Figure 1