Electrochemical behavior and cyclic fading mechanism of LiNi_(0.5) Mn_(0.5) O_2 electrode in LiNO_3 electrolyte

Electrochemical behavior of layered LiNi0.5Mn0.5O2 in LiNO3 aqueous solution and its cyclic fading mechanism in electrolytes with different pH values were investigated. CV results show that LiNi0.5Mn0.5O2 has good electrochemical reversible behaviors in 5 mol/L LiNO3 solution. Meanwhile, the electrode in 5 mol/L LiNO3 with pH value of 12 demonstrates the best electrochemical stability. Based on the electrochemical impedance spectroscopy （EIS）, X-ray diffraction （XRD） and scanning electron microscopy （SEM） results, it is proposed that suppressed charge-transfer resistance is the major reason, which is probably ascribed to the more stable electrode surface and less structure change.

Revisiting the capacity-fading mechanism of P2-type sodium layered oxide cathode materials during high-voltage cycling

P2-type sodium layered oxide cathode (Na_(2/3)Ni_(1/3)Mn_(2/3)O_(2)P2-NNMO) has attracted great attention as a promising cathode material for sodium ion batteries because of its high specific capacity. However, this material suffers from a rapid capacity fade during high-voltage cycling. Several mechanisms have been proposed to explain the capacity fade, including intragranular fracture caused by the P2-O2 phase transion, surface structural change, and irreversible lattice oxygen release. Here we systematically investigated the morphological, structural, and chemical changes of P2-NNMO during high-voltage cycling using a variety of characterization techniques. It was found that the lattice distortion and crystal-plane buckling induced by the P2-O2 phase transition slowed down the Na-ion transport in the bulk and hindered the extraction of the Na ions. The sluggish kinetics was the main reason in reducing the accessible capacity while other interfacial degradation mechanisms played minor roles. Our results not only enabled a more complete understanding of the capacity-fading mechanism of P2-NNMO but also revealed the underlying correlations between lattice doping and the moderately improved cycle performance.

Electrochemical properties of SnO_2 nanorods as anode materials in lithium-ion battery

Well-dispersed SnO2 nanorods with diameter of 4-15 nm and length of 100-200 nm are synthesised through a hydrothermal route and their potential as anode materials in lithium-ion batteries is investigated. The observed initial discharge capacity is as high as 1778 mA.h/g, much higher than the theoretical value of the bulk SnO2 （1494 mA.h/g）. During the following 15 cycles, the reversible capacity decreases from 929 to 576 mA-h/g with a fading rate of 3.5% per cycle. The fading mechanism is discussed. Serious capacity fading can be avoided by reducing the cycling voltages from 0.05-3.0 to 0.4-1.2 V. At the end, SnO2 nanorods with much smaller size are synthesized and their performance as anode materials is studied. The size effect on the electrochemical properties is briefly discussed.

Real-time in situ TEM studying the fading mechanism of tin dioxide nanowire electrodes in lithium ion batteries

Fading mechanism of tin dioxide （SnO2） electrodes in lithium ion batteries has attracted much attentions, which is of great importance for the battery applications. In this paper, electrochemical lithiation-delithiation cycles of individual SnO2 nanowires were conducted in situ in a high-resolution transmission electron microscopy （TEM）. Major changes in volume with expan- sions of 170%~300% on SnO2 nanowire electrodes were observed during the first lithiation process in electrochemical cycling, including conversion reaction of SnO2 precursor to Li20 matrix and active lithium host Sn, and alloying of Sn with Li to form brittle Li-Sn alloy. SnO2 nanowire electrodes were inclined to suffer from thermal runaway condition in the first two cycles. During cycling, morphology and composition evolution of SnO2 nanowire electrodes were recorded. Cyclic lithiation and del- ithiation of the electrode demonstrated the phase transition between Lii3Sn5 and Sn. Metallic Sn clusters were formed and their sizes enlarged with increasing cycle times. Detrimental aggregation of Sn clusters caused pulverization in SnO2 nanowire elec- trodes, which broke the conduction and transport path for electrons and lithium ions. The real-time in situ TEM revealed fading mechanism provides important guidelines for the viable design of the SnO2 nanowire electrodes in lithium ion batteries.

Room-temperature metal-sulfur batteries:What can we learn from lithium-sulfur?

Rechargeable metal-sulfur batteries with the use of low-cost sulfur cathodes and varying choice of metal anodes(Li,Na,K,Ca,Mg,and Al)represent diverse energy storage solutions to satisfy different application requirements.In comparison to the highly-regarded lithium-sulfur batteries,the use of nonlithium-metal anodes in metal-sulfur batteries offers multiple advantages in terms of abundance,cost,and volumetric energy density.Although with the same sulfur cathode,metal-sulfur batteries show considerably differences in the electrochemical reaction pathway and capacity fading mechanism.Herein,we provide an overview of correlations and differences in metal-sulfur batteries,highlighting the knowledge and experience that can be transplanted from lithium-sulfur to other metal-sulfur batteries.We first discuss the historical development and the electrochemical reaction mechanism of various metal-sulfur batteries.This is then followed by an analysis of key challenges of metal-sulfur batteries including polysulfide shutting,cathode passivation,and anode stability.Finally,a short perspective is presented about the possible future development of metal-sulfur batteries.