| Energy and environmental issues have prompted more active development and utilization of new energy around the world.At the same time,energy storage devices have become a research hotspot in the field of new energy.Due to their high specific energy and other advantages,lithium-ion batteries（LIB）have become one of the mainstream electrochemical energy storage devices.However,the current commercialized LIB based on graphite（G）anodes are increasingly difficult to meet the demand for high-performance（high specific energy,high specific power,long cycle life）energy storage devices in the new energy market.As one of the core components affecting the key performance of LIB,the graphite anode,its poor rate characteristics and cycle stability severely restrict the power performance and cycle life of LIB.Therefore,optimizing the modification of commercial graphite anodes to improve the performance of LIB is particularly important for expanding the large-scale market application of LIB.In this paper,the simple and easy mechanical ball milling method is combined with multi-component carbon nanomaterials to study the composite modification of the graphite anode to improve the rate characteristics and cycle stability of the graphite anode,so as to achieve the synergistic improvement of the power performance and cycle life of LIB.Based on the above research ideas,the main research contents of this paper are as follows:（1）First,commercial graphite materials were modified by a simple mechanical ball milling method to prepare ball milled graphite（BMG）,and the effects of ball milling conditions（time,rotation speed）on the morphology,structure and electrochemical properties of graphite materials were explored.In an inert atmosphere and a rotating speed of 200 rpm,the ball milling time was optimized to 4 h.The prepared BM4h G material had a larger specific surface area and mesoporosity than the benchmark graphite（G）,and showed better rate characteristics(1 C charging capacity and 1 C/0.1C capacity retention rate:270.95 m Ah g-1and 78.41%vs.232.81 m Ah g-1and 64.94%;3 C charging capacity and 3 C/0.1 C capacity retention rate:65.78 m Ah g-1and 19.04%vs.47.01 m Ah g-1and 13.11%)and cycling stability(charge capacity and capacity retention for 100 cycles at 1 C:139.27 m Ah g-1and 50.53%vs.117.46 m Ah g-1and44.89%).Further,under the above optimal ball milling conditions,carbon nanotubes（CNT）were introduced into the graphite material for composite modification,and the proportion of CNT was optimized to explore the morphological characteristics,pore structure and distribution of the composite materials by the introduction of CNT.and the effect of electrochemical performance.Benefiting from the improvement of the internal conductive network structure and pore structure distribution of the composite material by fibrous high-conductivity CNT,and its effective inhibition of the agglomeration of conductive carbon black（Super P）and better connection of active substances,the prepared composites It has an efficient"dot-line-dot"conductive network structure and increased specific surface area and mesoporosity,thereby improving the better rate characteristics of the obtained BM（G+0.2CNT）binary composite material than BM4h G material(1 C charging Capacity and 1 C/0.1 C capacity retention rate:287.86 m Ah g-1and 78.82%;3 C charging capacity and 3 C/0.1 C capacity retention rate:75.68 m Ah g-1and 20.72%)and cycle stability（1 C cycle for 100 times）Charging capacity and capacity retention rate:153.43 m Ah g-1and 66.36%).（2）At the same time,under the above optimal ball milling conditions,graphene（GN）was introduced into the graphite material for composite modification,and the proportion of GN was optimized to explore the effect of the introduction of GN on the morphology,pore structure and distribution of the composite material.,and the effect of electrochemical performance.The introduction of highly conductive graphene,on the one hand,its high specific surface area and high porosity effectively improve the pore structure and distribution of the composite material,and promote the effective infiltration of the composite material by the electrolyte.On the other hand,the graphene two-dimensional sheet structure builds an efficient"point-surface-point"conductive network structure for the composite material,and effectively alleviates the volume effect of the graphite material during cycling,making the as-prepared BM（G The conductivity and structural stability of the+0.0125GN）binary composite can be effectively improved,and it has a higher specific surface area and mesoporosity than the BM（G+0.2CNT）composite,thus showing enhanced rate characteristics(1 C charging Capacity and 1 C/0.1 C capacity retention rate:299.04 m Ah g-1and 81.96%;3 C charging capacity and 3 C/0.1 C capacity retention rate:103.56 m Ah g-1and 28.38%)and cycle stability（1 C cycle for 100 times）Charging capacity and capacity retention rate:167.9 m Ah g-1and 66.57%).（3）On the basis of the above,GN and CNT were added to the graphite at the same time by the best ball milling method,and the preparation of multcomponent nanocarbon/graphite composite material（BM（G+0.0125GN+0.2CNT））was studied.Zero-dimensional granular SP,one-dimensional fibrous CNT and two-dimensional lamellar GN are intertwined with bulk graphite materials to construct a"dot-line-plane"three-dimensional high-efficiency conductive network structure,which can significantly improve the conductivity of the composite material It can also improve the distribution of the internal pore structure of the composite material,and at the same time,it can make the component materials closely cross-linked,improve the electrochemical utilization rate of the active material and the overall structural stability of the composite material,and realize the specific surface area and the medium.Maximize porosity.Thus,the as-prepared BM（G+0.0125GN+0.2CNT）ternary composite exhibits the best rate characteristics and cycling stability among all the materials studied in this paper,the charging capacity at 1 C（and the 1 C/0.1 C capacity retention）rate)up to 321.30 m Ah g-1（86.39%）,a nearly 1.4-fold improvement compared to the benchmark graphite’s232.81 m Ah g-1（64.94%）,charging capacity at 3 C（and 3 C/0.1 C capacity retention）It reaches 118.85 m Ah g-1（31.96%）,which is 2.5 times higher than the benchmark graphite’s 47.01 m Ah g-1（13.11%）.The charge capacity of 190.24 m Ah g-1（capacity retention:76.95%）was still maintained after 100 cycles at 1 C,which was 1.6 times that of the benchmark graphite(117.46 m Ah g-1,44.89%).In conclusion,in this paper,multi-component nano-carbon/graphite composites were prepared by combining the simple and easy mechanical ball milling method with multi-component nano-carbon materials.The introduction of multi-component carbon nanomaterials builds a multi-dimensional three-dimensional conductive network structure for the composite material,improves the distribution of the internal pore structure of the material,and improves the stability of the overall structure,thereby achieving a significant improvement in the rate characteristics and cycle stability of the composite material.The research on the modification of graphite anode provides a feasible process idea and experimental method,and provides a simple and easy way for the preparation of high-power,long-cycle lithium-ion batteries. |
PDF Full Text Request