Optimization of morphology, structure, and electrochemical properties of ball-milled graphene through modulating the ratio of grinding balls with different sizes

In ball milling, the process parameters are decisive in influencing the quality and performance of the final ball-milled product, and crucial but often neglected is the ratio of the grinding balls in terms of their size. Here, for a given number of large grinding balls, the ratio of large to small ones is set to 1:2, 1:3, 1:4, and 1:5 by altering the number of small ones, and how this affects the morphology, structure, and electrochemical properties of ball-milled graphene nanosheets is investigated. The results show that changing the ball ratio causes distinct changes in the morphology, structure, and properties of the graphene nanosheets. Increasing the number of small (6 mm) grinding balls decreases the nanosheet grain size monotonically; meanwhile, the crystal plane spacing, defect density, and specific surface area increase and then decrease, but the graphitization degree decreases and then increases. Ball-milled samples are then used as anodes for lithium-ion batteries, and both the specific capacity and rate capability exhibit the same trend of increase and then decrease. The ball ratio of 1:3 gives the best electrochemical performance, i.e., a reversible specific capacity of 262.09 mA ⋅ h/g at a current density of 100 mA/g, and even after 2000 cycles at 2000 mA/g, the reversible specific capacity is 87.4% of the optimal value.