High energy ball milling as a strategy to improve electrochemical performance in sodium titanate anodes

High energy ball milling has emerged as a method for both mechanosynthesis and post processing to control the particle size and crystallinity in Li and Na ion battery materials. Sequentially higher ball milling speeds were applied to commercially available Na2Ti3O7 as a post-processing method, followed by chemical and electrochemical characterisation. At lower milling speeds, the Na2Ti3O7 phase was preserved, but with some degradation of crystallinity and phase. At higher milling speeds, full amorphitisation occurred, followed by recrystallisation into the rarely-observed trigonal Na4Ti5O12 phase. The sequential changes in electrochemical properties of the materials following increasing ball mill speeds are reported, with the partially degraded Na2Ti3O7 showing increases in specific capacity which we attribute to a decrease in crystallite size and associated access to kinetically limited sites. Trigonal Na4Ti5O12 by contrast, is measured to have superior rate capability (40 mA h g−1 at 5C), and high cycle stability, alongside a promising specific capacity of 115 mA h g−1 after 50 cycles. This material is therefore a promising anode candidate for Na-ion batteries.