plating/stripping. [7][8][9][10][11][12][13][14][15] As a result, LMB always suffer from rapid capacity deterioration and high safety risk, especially at high charge/discharge rates and over a wide temperature range (from subzero temperatures to high temperatures). Encouragingly, varied strategies have been devoted to explore the Li-dendrite growth mechanism and Li-metal protection. [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] Wherein, one of the most effective and feasible strategy in protecting Li metal is electrolyte optimization, such as developing ionic liquids, [16] dual-salt electrolytes with additives, [20] gel polymer electrolyte, [18,27,28] concentrated electrolytes, [9,[24][25][26]29,30] etc.Undoubtedly, wide temperature range high-energy LMBs are urgently demanded for special applications, such as carrying out special missions in polar areas, desert areas, snowy mountains region, and outer space. [31] However, the operation of LMBs over a wide temperature range is seldom reported because of the fact that it is a huge challenge to find a compromise between subzero temperature performances and high temperature performances. [31][32][33] At subzero temperatures, due to the significantly reduced Li + conductivity (increased viscosity) of electrolyte and simultaneously increased charge transfer resistances, the severe growth of Li dendrites will become more uncontrolled. [31,34] At high temperatures, the bottlenecks are thermal instability of conventional LiPF 6 salt, severe solid electrolyte interphase (SEI) layer destruction-reformation accompanied by severe gas evolution, and accelerated transition metal dissolution-migration-deposition. [31] Significantly, formulating an electrolyte will play a dominant role in enabling the wide temperature operation of LMBs.Dual-salt electrolyte systems adopting two thermally stable main lithium salts have been proposed to significantly enhance the performances of both LIBs and LMBs. [20,[33][34][35][36][37][38][39][40][41][42] For the wide temperature operation of LIBs, thermally stable lithium borates (such as lithium tetrafluoroborate (LiBF 4 ), lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalate)borate (LiDFOB), etc.) dissolved in low melting point and high boiling point carbonatebased solvents (such as propylene carbonate (PC, T m = −48.8 °C, T b = 242 °C), ethyl methyl carbonate (EMC, T m = −53 °C, T b = 110 °C), etc.), have been investigated. [33][34][35][36][37][38] Recently, we have reviewed the potential application of functional lithium-borate salts in high performance lithium batteries, [43] and have successfully synthesized a bulky anion lithium trifluoro(perfluoro-tert-butyloxyl)borate (Li[(CF 3 ) 3 COBF 3 ], LiTFPFB), which exhibits high Li + conductivity and oxidation stability, as well as noncorrosivity to In this study, self-synthesized lithium trifluoro(perfluoro-tert-butyloxyl) borate (LiTFPFB) is combined with lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) to formulate a novel 1 m dual-salt electrolyte, which contain...
O3-type layered transition metal oxides have shown great promise as high-capacity cathode materials for sodium-ion batteries in large-scale energy storage, due to their low cost and the abundance of sodium resources. However, the limited interlayer spacing and the unstable structure of the O3 phase result in inferior cycling stability and poor rate capability, which could even hinder their practical application process. Hereby, we present that doping with nonelectrochemically active Al in NaAl x (Ni 0.5 Mn 0.5 ) 1−x O 2 (x = 0, 0.02, 0.06, 0.1) can effectively alleviate these issues. Among these materials, materials with x = 0.02 exhibited the best electrochemical behavior with improved capacity and better cycling property than other materials. Specifically, the discharge capacity of a 2 mol % Al-doped material possesses 63.2% capacity retention after 200 cycles at a current density of 240 mA g −1 , which is 21.4% higher than that in NaNi 0.5 Mn 0.5 O 2 . In addition, a 2 mol % Al-doped electrode also shows outstanding rate capability and delivers 90 mAh g −1 at a high rate of 480 mA g −1 , compared to only 67 mAh g −1 for that of the pristine one. X-ray diffraction (XRD), cyclic voltammetry (CV), and galvanostatic intermittent titration technique (GITT) analysis elucidated that the introduced Al dopant can effectively improve the structural stability and promote kinetics of Na + diffusion mobility. Therefore, the strategy of doping inactive aluminum elements for optimizing the electrochemical performance of NaNi 0.5 Mn 0.5 O 2 was verified, which could also open an avenue for the design of other O3-type sodium cathode materials.
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