By virtue of high theoretical capacity and appropriate lithiation potential, phosphorus is considered as a prospective nextgeneration anode material for lithium-ion batteries. However, there are some problems hampering its practical application, such as low ionic conductivity and serious volume expansion. Herein, we demonstrated an in situ preoxidation strategy to build a oxidation function layer at phosphorus particle. The oxide layer not only acted as a protective layer to prolong the storage time of phosphorus anode in air but also carbonized N-methyl pyrrolidone and poly (vinylidene fluoride), strengthening the interfacial interaction between phosphorus particles and binder. The oxide layer further induced the formation of a stable solid electrolyte interface with high lithium-ion conductivity. The oxidized P-CNT maintained high specific capacity of 1306 mAh g −1 and 89% capacity after 100 cycles, much higher than that of pristine P-CNT (17.1%). The strategy of in situ oxidation is facile and conducive to the practical application of phosphorus-based anodes.
Cobalt‐free LiNixMn1−xO2 (NM, x ≥ 0.5) layered oxides are considered to be promising cathode materials for next‐generation lithium‐ion batteries because of exceptionally high capacity and low cost, yet the fundamental role of manganese ions in the NM layered structure and rate performance has not been fully addressed to date. Herein, a series of Ni‐fixed LiNi0.6Co0.4−xMnxO2 (x = 0, 0.1, 0.2, 0.3, and 0.4) systems are employed as cathode materials to investigate the functionality of Mn ions on their structures and electrochemical properties. It is found that contrary to prior reports, the change in the c‐axis lattice parameter is not in close connection with the rate performance of NM cathodes. In particular, superconducting quantum interference device (SQUID) measurements are performed to verify the fact that Mn3+ and Mn4+ ions with high spin states cause severe magnetic frustration in the structures of cathode materials, which profoundly aggravates the Li/Ni ionic disorder and blocks Li+ migration, contributing to inferior rate performance. In addition, Li+ migration hindered by Li/Ni disorder, is theoretically demonstrated by ab initio calculation. This work not only provides fresh insight into the role of Mn in NM layered oxide cathodes but also proposes an effective strategy to resolve their inferior rate performance.
Lithium cobalt oxides (LiCoO 2 ) possess a high theoretical specific capacity of 274 mAhg −1 . However, when LiCoO 2 is charged at the voltage higher than 4.2 V, there exist significant structure transition and capacity fade. In this study, we used HRTEM to observe the phase evolution of LiCoO 2 cathode material after 100 cycles, and found that LiCoO 2 phase would degrade to Co 3 O 4 phase. The phase transition of Co 3 O 4 from LiCoO 2 gave rise to lattice expansion, by which the anisotropic strain was proposed by first-principles calculation to inhibit LiCoO 2 degradation. Results show that the anisotropic strain via the extension of lattice parameter c and the compression of a enables to simultaneously impede lattice oxygen loss and structure transition of LiCoO 2 during delithiation at high voltage. In this case, the elongation of interplanar spacing also increases the diffusivity of Li ions in LiCoO 2 , contributing to rate performance.
Sodium‐ion batteries (SIBs) are expected to replace partial reliance on lithium‐ion batteries (LIBs) in the field of large‐scale energy storage as well as low‐speed electric vehicles due to the abundance, wide distribution, and easy availability of sodium metal. Unfortunately, a certain amount of sodium ions are irreversibly trapped in the solid electrolyte interface (SEI) layer during the initial charging process, causing the initial capacity loss (ICL) of the SIBs. A separator capacity‐compensation strategy is proposed, where the capacity compensator on the separator oxidizes below the high cut‐off voltage of the cathode to provide additional sodium ions. This strategy shows attractive advantages, including adaptability to current production processes, no impairment of cell long‐cycle life, controlled pre‐sodiation degree, and strategy universality. The separator capacity‐compensation strategy is applied in the NaNi1/3Fe1/3Mn1/3O2 (NMFO)||HC full cell and achieve a compensated capacity ratio of 18.2%. In the Na3V2(PO4)3 (NVP)||HC full cell, the initial reversible specific capacity is increased from 61.0 mAh g−1 to 83.1 mAh g−1. The separator capacity‐compensation strategy is proven to be universal and provides a new perspective to enhance the energy density of SIBs.
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