Na 0.72 [L i0.24 Mn 0.76 ]O 2 , with reversible anionic redox reaction (ARR) and Mn 3+ / Mn 4+ redox, delivers the highest energy density (700 Wh/kg, 270 mAh/g, 1.5-4.5 V) among all Na cathode materials reported to date, surprisingly showing suppressed phase transition and low-strain characteristics. Our findings break the traditional cognition that ARR could only help increase the capacity. It is demonstrated in this work that ARR also plays a key role in stabilizing the structure to induce an even higher capacity with low strain.

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Successfully commercialized poly(ethylene oxide) (PEO)based solid polymer batteries (SPBs) are expected to continuously play a key role in the next generation of high-energy density lithium-ion battery technologies. However, the introduction of high-voltage cathodes, accompanied by safety concerns such as PEO decomposition and the associated gas release, is worthy of more attention. This study employs in situ DEMS to study the gassing behavior of LiCoO 2 |PEO-LiTFSI|Li SPBs. The experiments, together with theory calculations, reveal that a surface catalytic effect of LiCoO 2 is the root cause of the unexpected H 2 gas release of PEO-based SPBs at 4.2 V. The surface coating of LiCoO 2 with a stable solid electrolyte Li 1.4 Al 0.4 Ti 1.6 (PO 4 ) 3 (LATP) can mitigate such a surface catalytic effect and therefore extend the stable working voltage to >4.5 V. The crossover effect of HTFSI, which is generated at the cathode side due to oxidation/dehydration of PEO and reacts with lithium at the anode side, is proposed to explain the H 2 generation behavior.

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Nanosized SnSb alloy exhibits much higher reversible capacity as an anode active material for Li-ion batteries. However, rather large capacity loss at the first charge and discharge cycle as well as capacity fading during cycling for pure nanosized alloy has been observed. These phenomena originate from the following factors: the decomposition reaction of surface oxide and the formation of solid electrolyte interphase on the surface of alloy, the irreversible trapping of Li ions by host atoms, serious aggregation of alloy particles during electrochemical cycling, and the existence of an impure phase. Several strategies have been proposed to overcome these drawbacks, including surface modification, addition of dispersant, and coating on stable frame cores, such as mesophase carbon microbeads, to form composite materials.Recently, much attention has been given to the exploration of novel electrode materials in order to enhance the energy density of Li-ion batteries. Compared with carbonaceous materials, tin-based composite oxides ͑TCO͒ and alloys show higher specific capacity as anode active materials. 1-10 However, for oxide anode materials, a large irreversible capacity loss was observed at the first charge and discharge cycle due to a reduction/replacement reaction. 2 As a result, the cathode has to provide an extra Li source to compensate for the lost capacity, leading to a decrease of the energy density of the battery. On the other hand, alloy particles with larger size always pulverize rapidly during discharge and charge cycles, due to drastic volume variation. Consequently, their reversible capacities faded significantly with cycling. 7,11,12 In order to overcome this problem, superfine intermetallic compounds and active/inactive composite alloy materials have been studied recently, such as Sn/SnSb x , Sn/SnAg x , and SnFe/SnFeC. [7][8][9][10] Although direct structural evidence has not been presented yet, two conclusions can be accepted. First, a nanosized metal or alloy electrode can keep a rather stable microstructure during cycling because it has high endurance to volume variation due to their superplasticity and high ductility. 7,9,13 Second, for intermetallic compounds and active/inactive composite materials, the active component is produced in situ and dispersed into the matrix of inactive component uniformly at an atomic or nanometer scale, as with the situation in oxide anodes. 10 As a result, the volume variation of the active element could be alleviated effectively. In addition, inactive elements with higher conductivity can also provide a better conductive environment. Owning to these beneficial factors, the cyclic performance of alloy anode materials with superfine particles has been improved impressively. Based on this idea, nano-Si/carbon black composite materials have been studied by us, and better cyclic performance and a reversible capacity of 1700 mAh/g have been achieved. 12 However, it has been noticed recently that the Coulombic efficiency of superfine alloys was not as high as that of ...

Stable lattice oxygen redox (l-OR) is the key enabler for achieving attainable high energy density in Li-rich layered oxide cathode materials for Li-ion batteries. However, the unique local structure response to oxygen redox in these materials, resulting in energy inefficiency and hysteresis, still remains elusive, preventing their potential applications. By combining the state-of-the-art neutron pair distribution function with crystal orbital overlap analysis, we directly observe the distinct local structure adaption originated from the potential O-O chemical bonds. The structure adaptability is optimized based on the nature of multi transition metals in our model compound Li 1.2 Ni 0.13 Mn 0.54 Co 0.13 O 2 , which accommodates the oxygen redox and at the same time preserves the global layered structure. These findings not only advance the understanding of l-OR, but also provide new perspectives in the rational design of high-energy-density cathode materials with reversible and stable l-OR.

Commercial cathode material LiCoO 2 was modified by coating its surface with a thin layer of amorphous magnesium oxide ͑MgO͒. The surface morphology, crystalline structure, and electrochemical performance of the modified cathode material were characterized and compared with that of pristine LiCoO 2 . It is found that surface modification can improve the structural stability of LiCoO 2 without decreasing its available specific capacity. Specific capacities of 145, 175, and 210 mAh/g were obtained in test cells composed of MgO-coated LiCoO 2 cathode material when charged to 4.3, 4.5, and 4.7 V (Li ϩ /Li), respectively. This improvement is attributed to the pillaring effect of the Mg 2ϩ ions in the interslab space of the lattice and the protective effect of the MgO film against the escape of Co 4ϩ ions from the bulk of LiCoO 2 particles.

LiNi 1/3 Co 1/3 Mn 1/3 O 2 has been prepared by solid-state reaction as a novel positive electrode material for lithium-ion batteries. The structural evolution of the material with charge potential is studied using X-ray diffraction. The electrochemical performance of this material is investigated using cyclic voltammetry and galvanostatic cycling. The formation and composition of the solid electrolyte interphase layer on the material are studied by Fourier transform infrared spectroscopy at various potentials and compared with those formed under other conditions. These studies lead to questions of compatibility between the electrode and the electrolyte components and the necessity of surface modification to the electrode material.