| Lithium-ion batteries(LIBs)have become the focus of many modern electronic devices due to their advantages of light weight,high energy density,high voltage,and long service life.However,the theoretical specific capacity of graphite anode,which is closely related to the performance of LIBs,cannot meet the current demand for large-capacity batteries,and there are some defects such as difficult preparation and non-renewable.Biomass carbon attracts increasing attention in the field of LIBs anode due to its abundant yield,renewable and unique morphology.In recent years,self-standing electrodes have attracted widespread attention,because they do not require additional binder,conductive and other additives,which can greatly improve the overall energy density and performance of the electrode.At the same time,they can also be applied to the current wearable flexible devices.In order to further improve the LIBs performance of the self-standing carbon anode,it is necessary to compound it with highly capacity active materials.Therefore,this paper developed CoO/carbon fiber anode using corn straw as a material carbon source.Further,Reduced graphene oxide(RGO)/Si NPs/copper mesh self-standing electrodes were fabricated by a simple spray method.The structure-activity relationship of the anode and the mechanism of LIBs performance enhancement were emphatically studied as follows:(1)In this work,we proposed a facile method to prepare the CoO/carbon fiber(CoO/CF)hybrid electrode by employing the corn straw as the procurer and its LIBs characteristics were studied.The results show that CoO nanosheets perpendicularly grow on the CF,which is beneficial to promote the diffusion rate of Li+.Meanwhile,the CF can also alleviate the structural strain caused by CoO during the charge/discharge process.Further,the electrochemical measurement discloses the presence of Co2+/Co0 redox couple.LIBs performance test results show that the CoO/CF composite anode has a highly reversible specific capacity of 847 mAh·g-1 after 100 cycles at current density of 0.1 A·g-1.At the same time,CoO/CF composite anode has a well rate performance,and it still has a reversible specific capacity of 182.5 mAh·g-1 under the high current density of 2 A·g-1.In the whole charge/discharge process,diffusion control is dominant,indicating that Li+storage is mainly a diffusion-controlled Faraday redox reaction.And in the subsequent cycle process,the charge transfer resistance of the battery is significantly reduced,and the capacity is slightly increased,indicating that the Co metal produced in the cycle process can effectively improve the conductivity of the entire electrode,speed up the electron transmission,so as to improve the cycle performance.(2)In this work,we developed a self-standing hybrid anode that composed of the tandem structured reduced graphene oxide(RGO)/Si nanoparticles(NPs)/copper mesh(RGO/Si/Cu)by a facile spray method for lithium-ion batteries(LIBs).It delivers a high capacity of 1070.2 mAh·g-1 at 1 A·g-1 after 400 cycles.Even at 2 A·g-1,the specific capacity still reaches to 1005.1 mAh·g-1.The electrochemical measurement features that the charge transfer resistance of RGO/Si/Cu is only 65Ω,which is far less than that of RGO/Si(990 Ω),indicating that the copper substrate can effectively improve electron transport.In addition,the Li+ diffusion coefficient of RGO/Si/Cu is 10-8～10-12 cm2·s-1,which is higher than that of the conventional RGO/Si electrode(10-9～10-13 cm2·s-1).Meanwhile,the storage of Li+ in RGO/Si/Cu is mainly controlled by diffusion process.Most importantly,the volume expansion of RGO/Si/Cu is as low as～27%,indicating that RGO can significantly inhibit the large volume expansion effect of Si NPs.Moreover,the stress-strain simulation results show that the average stress of the electrode is 6-7 GPa at the expansion rate of 27%,which is far less than the tensile strength(180 GPa)of graphene,further demonstrating the cyclic stability of the electrode. |
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