P2-Na_(2/3)Ni_(2/3)Te_(1/3)O_(2)Cathode for Na-ion Batteries with High Voltage and Excellent Stability

Air-stable layered structured cathodes with high voltage and good cycling stability are highly desired for the practical application of Na-ion batteries.Herein,we report a P2-Na_(2/3)Ni_(2/3)Te_(1/3)O_(2) cathode that is stable in ambient air with an average operating voltage of~3.8 V,demonstrating excellent cycling stability with a capacity retention of more than 92.7%after 500 cycles at 20 mA g^(-1) and good rate capability with 91.9%capacity utilization at 500 mA g^(-1) with respect to capacity at 5 mA g^(-1) between 2.0 and 4.0 V.When the upper cutoff voltage is increased to 4.4 V,P2-Na_(2/3)Ni_(2/3)Te_(1/3)O_(2) delivers a reversible capacity of 71.9 mAh g^(-1) and retains 91.8%of the capacity after 100 cycles at 20 mA g^(-1).The charge compensation during charge/discharge is mainly due to the redox couple of Ni^(2+)/Ni^(3+)in the host with a small amount of contribution from oxygen.The stable structure of the material without phase transformation and with small volume change during charge-discharge allows it to give excellent cycle performance especially when the upper cutoff voltage is not higher than 4.2 V.

Towards high-performance lithium metal anodes via the modification of solid electrolyte interphases

Li metal has been regarded as one of the most promising anodes for high-energy-density storage systems due to its high theoretical capacity and lowest electrochemical potential.Unfortunately,an unstable and non-uniform solid electrolyte interphase(SEI)deriving from the spontaneous reaction between Li metal anode and electrolyte causes uneven Li deposition,resulting in the growth of Li dendrites and low Coulombic efficiency,which have greatly hindered the practical application of Li metal batteries.Thus,the construction of a stable SEI is an effective approach to suppress the growth of Li dendrites and enhance the electrochemical performances of Li metal anode.In this review,we firstly introduce the formation process of inferior SEI of Li metal anode and the corresponding challenges caused by the unstable SEI.Next,recent progresses to modify SEI layer through the regulation of electrolyte compositions and exsitu protective coating are summarized.Finally,the remained issues,challenges,and perspectives are also proposed on the basis of current research status and progress.

Stabilizing sodium metal anode through facile construction of organicmetal interface

Implementation of sodium metal anode is highly desired for sodium batteries due to its high theoretical capacity and low redox potential.Unfortunately,formation of unstable solid electrolyte interphase(SEI)and uncontrollable growth of dendrites during charge/discharge cycles greatly hinder the practical application of sodium metal anode.In this study,an organic-metal artificial layer made of PVdF and Bi was constructed to protect Cu current collector via a facile coating method,leading to smooth and dense sodium plating/stripping,which in retern enables stable cycling and high coulombic efficiency(CE).At 1 mA cm^(−2),PB@Cu current collector presents extended lifetime of~2500 h with high sodium utilization of 50%,which is approximately six times higher than Cu current collector.PB@Cu electrode also displays high average CE of 99.92%and 99.95%over 2500 and 1300 cycles at 1 and 2 mA cm^(−2) respectively,which is in sharp contrast to the low and tremendously fluctuant CE gained from bare Cu electrode.Moreover,stable capacity of>90 mAh g^(−1) over 150 cycles is realized for PB@Cu-based full cell assembled with NVP cathode at a low negative-positive capacity ratio of~3.5,which is significantly higher than 37.2 mAh g^(−1) obtained from NVP/Cu at 150th cycle.The superior electrochemical performance of PB@Cu current collector is revealed to originate from the alloyed Na_(3)Bi phase with high sodium conductivity and robust mechanical strength as well as the formation of NaF-rich SEI with fast sodium ion migration,which enable dendrite-free morphology during plating/stripping cycles.

具有增强界面稳定性的阻燃型电解液用于实际锂金属电池

开发匹配高电压正极的锂金属电池是实现高能量存储系统的关键.因此,研发可以同时为锂金属负极和高电压正极产生稳定界面相的先进电解液非常必要.LiNO_(3)作为高效的固体电解质界面相添加剂被广泛应用于醚基电解液中,然而其在碳酸脂类电解液中的低溶解性严重限制了其在高压锂金属电池中的应用.本文利用磷酸三甲酯助溶剂提高LiNO_(3)在碳酸乙基甲酯/氟代碳酸乙烯酯电解液中的溶解度,并赋予电解液阻燃性能.此外,通过添加双草酸硼酸锂(LiBOB)进一步提高正负极的界面稳定性.结果表明,该电解液对锂金属负极和高电压层状氧化物正极均具有较高的兼容性.在2.8–4.3 V电压范围内,Li||LiCoO_(2)和Li||LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2)(NCM811)电池在1.2 mA cm^(-2)电流密度下循环300周后的容量保持率分别为80.2%和84.2%.更令人惊喜的是,负/正极容量比为3.33的Li||NCM811电池在相同的充放电条件下循环150周后的容量保持率仍高达~80%.本论文对富含LiNO_(3)的阻燃型高压电解液的研究将为通过界面相调控研发安全的高比能锂金属电池提供理论指导.

On the added value of multi-scale modeling of concrete

This review of the added value of multi-scale modeling of concrete is based on three representative examples.The first one is concerned with the analysis of experimental data,taken from four high-dynamic tests.The structural nature of the high-dynamic strength increase can be explained by using a multi-scale model.It accounts for the microstructure of the specimens.The second example refers to multi-scale thermoelastic analysis of concrete pavements,subjected to solar heating.A sensitivity analysis with respect to the internal relative humidity(RH)of concrete has underlined the great importance of the RH for an assessment of the risk of microcracking of concrete.The third example deals with multi-scale structural analysis of a real-scale test of a segmental tunnel ring.It has turned out that multi-scale modeling of concrete enables more reliable predictions of crack opening displacements in tunnel segments than macroscopic models taken from codes of practice.Overall,it is concluded that multi-scale models have indeed a significant added value.However,its degree varies with these examples.In any case,it can be assessed by means of a comparison of the results from three sources,namely,multi-scale structural analysis,conventional structural analysis,and experiments.