Search

Abstract The low ion transport is a major obstacle for low‐temperature (LT) sodium‐ion batteries (SIBs). Herein, a core‐shell structure of bismuth (Bi) nanospheres coated with carbon (Bi@C) is constructed by utilizing a novel Bi‐based complex (1,4,5,8‐naphthalenetetracarboxylic dianhydride as the ligand) as the precursor, which provides an effective template to fabricate Bi‐based anodes. At −40°C, the Bi@C anode achieves a high capacity, which is equivalent to 96% of that at 25°C, benefitting from the core‐shell nanostructured engineering and Na+‐ether‐solvent cointercalation process. The special Na+‐diglyme cointercalation behavior may effectively reduce the activation energy and accelerate the Na+ diffusion kinetics, enabling the excellent low‐temperature performance of the Bi@C electrode. As expected, the fabricated Na3V2(PO4)3//Bi@C full‐cell delivers impressive rechargeability in the ether‐based electrolyte at −40°C. Density functional theory calculations and electrochemical tests also reveal the fast reaction kinetic mechanism at LT, thanks to a much lower diffusion energy barrier (167 meV) and a lower reaction activation energy (32.2 kJ mol−1) of Bi@C anode in comparison with that of bulk Bi. This work provides a rational design of Bi‐based electrodes for rechargeable SIBs under extreme conditions.

The severe “shuttle effect” of dissolved polysulfide intermediates and the poor electronic conductivity of sulfur cathodes cause capacity decay of lithium–sulfur batteries and impede their commercialization. Herein, we synthesized a series of well-designed yolk-shelled Fe3O4@carbon (YS-Fe3O4@C) nanocavities with different proportions of Fe3O4 as efficient sulfur hosts to stabilize polysulfide intermediates. The yolk-shelled nanocavity architectures were prepared through a facile method, which could effectively confine the active materials and achieve high conductivity. The polysulfide intermediate shuttle was successfully suppressed by a physiochemical synergism effect combining the retention of carbon shells and the adsorption of Fe3O4 nanoparticle cores. The highly conductive carbon shell provides efficient pathways for fast electron transportation. Meanwhile, the visible evolution of active materials and a reversible electrochemical reaction are revealed by in situ X-ray diffraction. With the balanced merits of enhanced electrical conductivity of carbon shell and optimal adsorption of Fe3O4 cores, the S/YS-27Fe3O4@C cathode (Fe3O4 accounts for 27 wt% in YS-Fe3O4@C) had the best electrochemical performance, exhibiting a high reversible specific capacity of 731.9 mAh g−1 and long cycle performance at 1 C (capacity fading rate of 0.03% over 200 cycles).

TiNb2O7 (TNO) compound has been pursued tremendously due to its high theoretical capacity, high potential, and excellent cycle stability. Unfortunately, an intrinsic low electronic and ionic conductivity feature has restricted its broad applications in electrochemical energy storage fields. Two-dimensional (2D) nanostructures can effectively shorten Li-ion transport path and enhance charge transfer. Here, hierarchical structure TNO was constructed by using ethanol and acetic acid as particularly important organic chemicals of basic raw materials via a simple solvothermal reaction. Ethanol was found to play a critical role in the formation of 2D sheet structure. Meantime, reduced graphene oxide nanosheets can effectively improve electronic conductivity. As-obtained TiNb2O7 were wrapped further by graphene oxide nanosheets through a flocculation process. Their unique structure is beneficial to the final electrochemical performance. This study not only provides a general approach for the design of novel 2D nanomaterials wrapped by graphene because of the advantage of esterification reaction and flocculation reaction, but also improves the electronic and ionic conductivity simultaneously.

The cycling performance of the LiNi0.5Mn1.5O4/graphite cells cycled to 4.8 V versus Li/Li+ at room temperature has been investigated. The control electrolyte is 1.0 M LiPF6 ethylene carbonate (EC)/ethylmethyl carbonate (EMC)/fluoroethylene carbonate (FEC) (10/70/20, v/v) with 2 wt% lithium bis(oxalate)borate (LiBOB). Biphenyl (BP) (0.5 wt% and 1 wt%) is employed as the in situ electrochemical coating additive for LiNi0.5Mn1.5O4 cathode. The results indicate the potential window of electrolyte without BP is up to 5.5 V versus Li/Li+ on Pt electrode, but still decomposed seriously on both cathode and anode surfaces during prolonged cycles. The improved cycling performance with added 0.5 wt% BP in the control electrolyte can be attributed to the in situ electrochemical coating film on LiNi0.5Mn1.5O4 surface derived from BP electro-polymerization, which decreases the Mn dissolution and the lattice changes of LiNi0.5Mn1.5O4 cathode, and further inhibits Mn deposition and additional SEI formation on graphite surface. However, the thicker and compact BP electro-polymerization film using 1BP electrolyte on the cathode surface might inhibit the lithium intercalation/deintercalation and increase the polarization, then accelerates the capacity fading. [ABSTRACT FROM AUTHOR]

The cycling performance of the LiNi0.5Mn1.5O4/graphite cells cycled to 4.8 V versus Li/Li(+) at room temperature has been investigated. The control electrolyte is 1.0 M LiPF6 ethylene carbonate (EC)/ethylmethyl carbonate (EMC)/fluoroethylene carbonate (FEC) (10/70/20, v/v) with 2 wt% lithium bis(oxalate)borate (LiBOB). Biphenyl (BP) (0.5 wt% and 1 wt%) is employed as the in situ electrochemical coating additive for LiNi0.5Mn1.5O4 cathode. The results indicate the potential window of electrolyte without BP is up to 5.5 V versus Li/Li(+) on Pt electrode, but still decomposed seriously on both cathode and anode surfaces during prolonged cycles. The improved cycling performance with added 0.5 wt% BP in the control electrolyte can be attributed to the in situ electrochemical coating film on LiNi0.5Mn1.5O4 surface derived from BP electro-polymerization, which decreases the Mn dissolution and the lattice changes of LiNi0.5Mn1.5O4 cathode, and further inhibits Mn deposition and additional SEI formation on graphite surface. However, the thicker and compact BP electro-polymerization film using 1BP electrolyte on the cathode surface might inhibit the lithium intercalation/deintercalation and increase the polarization, then accelerates the capacity fading.