Well‐defined, monolithic TiO₂ nanotube thin films have been used as model anode electrodes to study Na‐ion storage in anatase TiO₂. It is shown that anatase TiO₂ nanotubes with wall thicknesses up to 50 nm can be transformed into amorphous sodium titanate (e. g. Na_0.2TiO₂) nanotubes via an electrochemical activation process at about 0.2 V vs. Na⁺/Na. Due to the Na⁺ insertion and extraction reactions at about 0.55 and 0.75 V vs. Na⁺/Na, respectively, the activated TiO₂ nanotubes exhibit reversible capacities of 170 mAh g⁻¹. For the first time, it is shown that the nanotube length and wall thickness play critical roles in determining the electrochemical performances of this type of electrodes in Na‐ion cells. An excellent rate performance, yielding capacities of about 33 mAh g⁻¹ at 20 C and 161 mAh g⁻¹ at C/5 rates, as well as a capacity retention of more than 97 % after more than 350 cycles, could be achieved with nanotubes with a wall thickness of up to 20 nm. The cycling rate for the nanotubes with a tube length of 4.5 μm should, however, be limited to 1 C to guarantee a cycle life of about 200 cycles.

中文翻译：

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钠离子电池整体式锐钛矿型TiO2纳米管阳极的尺寸依赖性电化学性能

定义明确的整体式TiO ₂纳米管薄膜已用作模型阳极电极，以研究Na-离子在锐钛矿型TiO _2中的存储。已经表明，壁厚最高达50nm的锐钛矿型TiO ₂纳米管可以通过在约0.2V vs.Na ⁺ / Na下的电化学活化过程转化为非晶态钛酸钠（例如Na _0.2 TiO ₂）纳米管。由于分别在约0.55和0.75 V（相对于Na ⁺ / Na）的Na ⁺插入和萃取反应，活化的TiO ₂纳米管显示出170 mAh g ^-1的可逆容量。。首次表明，碳纳米管的长度和壁厚在决定此类离子在Na离子电池中的电化学性能方面起着至关重要的作用。优异的倍率性能，20 C时的约33 mAh g ^-1的容量和C / 5速率下的161 mAh g ^-1的容量以及超过350次循环后的容量保持率可达到97％以上。壁厚不超过20 nm的纳米管。但是，应将管长为4.5μm的纳米管的循环速率限制为1 C，以确保约200个循环的循环寿命。