high energy density and low self-discharge rate, lithium-ion batteries (LIBs) have been widely applied to millions of portable electronic devices and electric vehicles since 1991. [1,2] Nevertheless, driven by the rising cost of LIBs, the limited content (0.0065%) and uneven distribution of lithium resource on the earth, [3,4] post-lithium ion battery technologies have worldwidely dragged researchers' attentions. Sodium is naturally abundant and has chemical properties similar to lithium, while do not form alloys with aluminum collectors. [5][6][7] Thus, sodium-ion batteries (SIBs) have been considered as an ideal candidate for cost-effective energy storage. However, the cycling stability, rate capability, and capacity of SIBs still need to be enhanced for practical systems and further development. There still remains a challenge that high-performance and low-cost electrode materials, especially the suitable anode materials, are urgent to develop.Compared with the poor structure stability of sodium alloy, [8,9] low reversible capacity of titanium-based oxide, [10,11] and complicated strategies of composites, [12][13][14] carbon materials are regarded as the most promising anode materials of SIBs for practical applications. Various carbon materials, including graphite, [15,16] expanded graphite, [17] amorphous carbon, [18][19][20] and graphene, [21][22][23] have been investigated, which indicates favorable sodium ions de/insertion reactions in host structure due to the lattice defect and larger interlayer space. Among all the carbon anode candidates, amorphous carbon, such as hard carbon and soft carbon, has attracted much attention due to high electrochemical activity and relatively low cost. Hard carbon contains plenty of disordered structures with defects and voids, which contribute to high reversible capacities yet large initial irreversible capacity loss. [24][25][26][27] Moreover, the disordered structures in hard carbon cause low electronic conductivity and the resulting poor rate performance. [28] On the contrary, soft carbon has abundant graphitic regions yet relatively few defects, which results in high electronic conductivity and low initial Coulombic efficiency. Mesophase carbon microbead (MCMB), one of the typical soft carbon materials, has been widely used as a high-rate anode material with a reversible capacity of ≈330 mA h g −1 for LIBs. [29] However, soft carbon usually delivers a low reversible capacity Sodium-ion batteries (SIBs) have a promising application prospect for energy storage systems due to the abundant resource. Amorphous carbon with high electronic conductivity and high surface area is likely to be the most promising anode material for SIBs. However, the rate capability of amorphous carbon in SIBs is still a big challenge because of the sluggish kinetics of Na + ions. Herein, a three-dimensional amorphous carbon (3DAC) with controlled porous and disordered structures is synthesized via a facile NaCl template-assisted method. Combination of open porous structures of 3DAC, the increase...
We prepare a totally nonflammable phosphate-based electrolyte composed of 5 mol L-1 (M) Li bis(fluorosulfonyl) imide (LiFSI) in a trimethyl phosphate (TMP) solvent. The concentrated 5 M LiFSI/TMP electrolyte shows good compatibility with graphite and no Al corrosion. More attractively, such a concentrated electrolyte can effectively suppress the growth of Li dendrites in Li metal batteries because of a stable LiF-rich SEI layer. Therefore, this highly concentrated electrolyte is promising for safe Li batteries.
We present a general strategy to synthesize uniform MnCo2O4 submicrospheres with various hollow structures. By using MnCo-glycolate submicrospheres as the precursor with proper manipulation of ramping rates during the heating process, we have fabricated hollow MnCo2O4 submicrospheres with multilevel interiors, including mesoporous spheres, hollow spheres, yolk-shell spheres, shell-in-shell spheres, and yolk-indouble-shell spheres. Interestingly, when tested as anode materials in lithium ion batteries, the MnCo2O4 submicrospheres with a yolk-shell structure showed the best performance among these multilevel interior structures because these structures can not only supply a high contact area but also maintain a stable structure.
The safety hazards and low Coulombic efficiency originating from the growth of lithium dendrites and decomposition of the electrolyte restrict the practical application of Li metal batteries (LMBs). Inspired by the low cost of low concentration electrolytes (LCEs) in industrial applications, dual‐salt LCEs employing 0.1 m Li difluorophosphate (LiDFP) and 0.4 m LiBOB/LiFSI/LiTFSI are proposed to construct a robust and conductive interphase on a Li metal anode. Compared with the conventional electrolyte using 1 m LiPF6, the ionic conductivity of LCEs is reduced but the conductivity decrement of the separator immersed in LCEs is moderate, especially for the LiDFP–LiFSI and LiDFP–LiTFSI electrolytes. The accurate Coulombic efficiency (CE) of the Li||Cu cells increases from 83.3% (electrolyte using 1 m LiPF6) to 97.6%, 94.5%, and 93.6% for LiDFP–LiBOB, LiDFP–LiFSI, and LiDFP–LiTFSI electrolytes, respectively. The capacity retention of Li||LiFePO4 cells using the LiDFP–LiBOB electrolyte reaches 95.4% along with a CE over 99.8% after 300 cycles at a current density of 2.0 mA cm−2 and the capacity reaches 103.7 mAh g−1 at a current density of up to 16.0 mA cm−2. This work provides a dual‐salt LCE for practical LMBs and presents a new perspective for the design of electrolytes for LMBs.
The notorious lithium (Li) dendrites and the low Coulombic efficiency (CE) of Li anode are two major obstacles to the practical utilization of Li metal batteries (LMBs). Introducing a dendrite-suppressing additive into nonaqueous electrolytes is one of the facile and effective solutions to promote the commercialization of LMBs. Herein, Li difluorophosphate (LiPOF LiDFP) is used as an electrolyte additive to inhibit Li dendrite growth by forming a vigorous and stable solid electrolyte interphase film on metallic Li anode. Moreover, the Li CE can be largely improved from 84.6% of the conventional LiPF-based electrolyte to 95.2% by the addition of an optimal concentration of LiDFP at 0.15 M. The optimal LiDFP-containing electrolyte can allow the Li||Li symmetric cells to cycle stably for more than 500 and 200 h at 0.5 and 1.0 mA cm, respectively, much longer than the control electrolyte without LiDFP additive. Meanwhile, this LiDFP-containing electrolyte also plays an important role in enhancing the cycling stability of the Li||LiNiCoMnO cells with a moderately high mass loading of 9.7 mg cm. These results demonstrate that LiDFP has extensive application prospects as a dendrite-suppressing additive in advanced LMBs.
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