Valence‐Tuned Lithium Titanate Nanopowder for High‐Rate Electrochemical Energy Storage

Abstract

In recent years, numerous studies have explored ways to overcome the low intrinsic electrical conductivity of lithium titanate (Li 4 Ti 5 O 12 , LTO) for energy storage with lithium-ion batteries. These approaches almost exclusively considered element doping and elaborate LTO-carbon nanocomposites, whereas simple adjustment of the defect concentration remains largely unexplored. In our study, we tune the Ti 3 + /Ti 4 + concentration of a commercial LTO nanopowder through oxygen vacancy formation during thermal annealing in hydrogen atmosphere. We investigate the impact of the treatment on material properties like energy band structure, electrical conductivity, crystallinity, phase distribution, surface chemistry, and particle morphology, and correlate these parameters to the electrochemical performance. At optimum treatment conditions, the intrinsic electrical conductivity can be greatly improved, while circumventing LTO phase transformations or amorphization. This enables the reduction of the carbon concentration to 5 mass%, while yielding a high electrode capacity of about 70 mAh/g (82 mAh/g based on active mass) at ultrahigh C-rates of 100C. When combined with an activated carbon/lithium manganese oxide composite cathode, an excellent energy and power performance of 70 Wh/kg and 47 kW/ kg were obtained (82 Wh/kg and 55 kW/kg based on active mass), while maintaining 83 % of its energy ratings after 5000 cycles at 10C (78 % after 15000 cycles at 100C).often neglected when calculating the capacity (i. e., capacity is only normalized to the LTO mass of the electrode). Yet, such a normalization is questionable as the electrode may contain up to 20-50 mass% carbon and only the performance of the entire electrode is of importance for an actual device (not how well a small quantity of LTO performs in a massive matrix of electrochemically inactive carbon).The electrical conductivity of carbon and its distribution can also severely influence the electrochemical stability of a composite electrode as we have demonstrated recently. [14] LTO doping (e. g., with Cu 2 + , [41] Mg 2 + , [42] Zn 2 + , [43] Fe 3 + , [44] Cr 3 + , [45] Al 3 + , [46] Sn 4 + , [47] Zr 4 + , [48] Ta 5 + , [49] V 5 + , [50] Nb 5 + , [51] W 6 + [52] ) is another effective way to improve the intrinsic electronic conductivity of LTO. Such doping elements have been reported to reduce a fraction of Ti 4 + into Ti 3 + and hence increase the overall electron concentration. [53] Nevertheless, element doping might entail additional problems related to the toxicity of certain doping elements and possible detrimental side reactions. [54] In 2006, Wolfenstine et al. [55] discovered that Ti 3 + valence states may form during prolonged annealing (36 h) of LTO at 800 8C in hydrogen containing atmosphere, although the root cause of this effect remained unknown. This simple strategy is free of waste products and does not require the addition of any other additional chemicals or catalysts, [56] but has only attracted little attention in literature so far (especially i...

Can Metallic Sodium Electrodes Affect the Electrochemistry of Sodium‐Ion Batteries? Reactivity Issues and Perspectives

“…The electrochemical properties of LTOh aveb een well investigated for Li-ion insertion/extraction [8,24,30] as well as for Na-ion intercalation/deintercalation. [8,9,19,25,31] In the case of Na ions, Sun et al [19] predicted at hree-phase storagem echanism, 2Li 4 Ti 5 O 12 + 6Na + + 6e À ÐLi 7 Ti 5 O 12 + Na 6 LiTi 5 O 12 ,a nd provedi t by in situ X-ray diffraction measurements.…”

Sodium‐Ion Hybrid Battery Combining an Anion‐Intercalation Cathode with an Adsorption‐Type Anode for Enhanced Rate and Cycling Performance

“…Exploiting rechargeable battery technologies with enhanced performance as well as low cost and environmental friendliness has become a global and urgent demand since the explosive growth of portable electronic devices, electric vehicles as well as large‐scale energy storage . Meanwhile, the limited and uneven distribution of lithium resource has stimulated extensive investigations of energy storage devices based on other abundant metal ions, such as Na + , K + , Al 3+ ,, etc.…”

“…Consequently, attributed from the hybrid battery design, this SHB exhibits excellent rate capability and cycling performance with a reversible capacity of 80 mAh g À1 at 2 C over a voltage window of 0-3.8 V and capacity retention of 87 % after 1000 cycles at 10 C.Exploiting rechargeable battery technologies with enhanced performance as well as low cost and environmental friendliness has become a global and urgent demand since the explosive growth of portable electronic devices, electric vehicles as well as large-scale energy storage. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] Meanwhile, the limited and uneven distribution of lithium resource has stimulated extensive investigations of energy storage devices based on other abundant metal ions, such as Na + , [12][13][14][15][16][17][18][19][20][21][22][23][24][25] K + , [26][27][28][29][30] Al 3 + , [31,32] etc. Among them, sodium-ion batteries (SIBs) have attracted increased attention owing to the merits of low potential (À2.71 V vs. standard hydrogen electrode (SHE)), high natural abundance, low cost, and similar electrochemical properties to lithium.…”

Metal Oxides with Distinctive Valence States in an Electron‐Rich Matrix Enable Stable High‐Capacity Anodes for Li Ion Batteries

“…However, highvalence transition metal-oxide anodes own the intrinsic limits of sluggish ion diffusion kinetics and poor electronic conductivity, which restrains their practical applications. [30,31] Herein, we report a MoO x /N-doped carbon nanotubes (NCNTs) nanocomposite synthesized with a novel pyrolysis method. [32] A MoO 2 /MoO 3 double-oxide anode with an adjustable valence state of Mo is produced by controlling the amount of reductive carbon in the synthesizing process.…”