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The high-temperature failure mechanism of K-based additives in a Mg(NH2)2–2LiH system was clarified for the first time.

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Using KH as an additive to Mg(NH2)2/LiH drastically improves hydrogen desorption, which begins at ca. 80 °C (see graph). Circa 5 wt % of hydrogen can be reversibly desorbed and absorbed at about 107 °C. The presence of potassium in the reacting system weakens the amide NH and imide LiN bonds, leading to enhanced reaction kinetics.

High operating temperature and slow kinetics retard the practical applications of the Li-Mg-N-H system for hydrogen storage. To alleviate these problems, a first attempt was carried out by synthesizing Li(2)MgN(2)H(2) through sintering a mixture of Mg(NH(2))(2)-2LiNH(2) and investigating its size-dependent hydrogen storage performance. A dramatically enhanced kinetics for hydrogen absorption/desorption was achieved with a reduction in the particle size. For the dehydrogenation reaction, a three-dimensional diffusion-controlled kinetic mechanism was identified for the first time by analyzing isothermal hydrogen desorption curves with a linear plot method. The experimental improvement and mechanistic understanding on the dehydrogenation kinetics of the Li-Mg-N-H system shed light on how to further decrease the operating temperature and enhance the hydrogen absorption/desorption rate of the amide/hydride combined materials.

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energy density of commercialized LIBs still cannot meet the requirements for practical applications. Success in these fields will mostly depend on further studying and developing new electrode materials with higher energy density.Li-and Mn-rich layered oxide (LMRO) has been considered as a promising cathode material for the next-generation LIBs due to its high energy density more than 1000 W h kg −1 . [3][4][5][6][7] However, this material also suffers from several fatal drawbacks, such as severe capacity and voltage fading during cycling, [8][9][10] poor rate performance, [5,11,12] large initial irreversible capacity. [13,14] Among these problems, the capacity and voltage fading are the key scientific issues needing to be solved first. It is generally accepted that the structure instability of the LMRO cathode material is one of the intrinsic reasons of its fast capacity and voltage fading. [15][16][17] The phase transformation from layered to spinel structure gives rise to the crystal instability when the LMRO cathode is charged to 4.8 V. [18][19][20][21] The gradual growth of spinel phase during cycling brings about the appearance of a 3.0 V plateau resulting in the voltage fading and then consequently leading to the capacity fading. [22] On the other hand, the capacity fading is also caused by the dissolution of metal elements into the electrolyte. [23,24] Zheng et al. [8] believe that the loss of MnO and NiO results in the capacity loss of the Li[Li 0.2 Ni 0.2 Mn 0.6 ]O 2 electrode because of the formation of spinel phase and subsequent fragmentation and deactivation of transition metal ions. Moreover, the dissolution of metal elements is also due to the corrosion of hydroflouric acid (HF) coming from the reaction of the residual moisture with LiPF 6 . [25] Presently, several strategies have been proposed to suppress the capacity and voltage fading of LMRO cathode material. Surface coating with inert phases is one of the effective ways, such as MnO x , [26,27] Al 2 O 3 , [28,29] MoO 3 , [13] TiO 2 , [30] ZrO 2 , [31] AlPO 4 , [32,33] AlF 3, [34,35] to stabilize the structure of the LMRO cathode materials. Choi et al. [36] reported that the 0.3Li 2 MnO 3 -0.7LiMn 0.60 Ni 0.25 Co 0.15 O 2 cathode material coated by Al 2 O 3 improved not only its discharge capacity but also its cycling stability compared with the prinstine. Guo et al. [37] discovered that the Li 1.2 Ni 0.16 Co 0.068 Mn 0.56 O 2 coated by 3 wt% MnO 2 delivered the capacity retention of 93% after 50 cycles. Chen et al. [38] demonstrated that CePO 4 layer coating onto Poor cycling stability is one of the key scientific issues needing to be solved for Li-and Mn-rich layered oxide cathode. In this paper, sodium carboxymethyl cellulose (CMC) is first used as a novel binder in Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O 2 cathode to enhance its cycling stability. Electrochemical performance is conducted by galvanostatic charge and discharge. Structure and morphology are characterized by X-ray diffraction, scanning electronic microscopy, high-resolution transmiss...

The superior catalytic effects derived from a 2D Ti3C2 (MXene), synthesized by the exfoliation of Ti3AlC2 powders, towards the hydrogen storage reaction of MgH2 were demonstrated. The 5 wt% Ti3C2-containing MgH2 releases 6.2 wt% H2 within 1 min at 300 °C and absorbs 6.1 wt% H2 within 30 s at 150 °C, exhibiting excellent dehydrogenation/hydrogenation kinetics.