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Owing to high specific capacity of ∼250 mA h g, lithium-rich layered oxide cathode materials (LiNi CoMnO) have been considered as one of the most promising candidates for the next-generation cathode materials of lithium ion batteries. However, the commercialization of this kind of cathode materials seriously restricted by voltage decay upon cycling though Li-rich materials with high cobalt content have been widely studied and show good capacity. This research successfully suppresses voltage decay upon cycling while maintaining high specific capacity with low Co/Ni ratio in Li-rich cathode materials. Online continuous flow differential electrochemical mass spectrometry (OEMS) and in situ X-ray diffraction (XRD) techniques have been applied to investigate the structure transformation of Li-rich layered oxide materials during charge-discharge process. The results of OEMS revealed that low Co/Ni ratio lithium-rich layered oxide cathode materials released no lattice oxygen at the first charge process, which will lead to the suppression of the voltage decay upon cycling. The in situ XRD results displayed the structure transition of lithium-rich layered oxide cathode materials during the charge-discharge process. The LiNiMnO cathode material exhibited a high initial medium discharge voltage of 3.710 and a 3.586 V medium discharge voltage with the lower voltage decay of 0.124 V after 100 cycles.

Lithium-ion batteries with both low-temperature (low-T) adaptability and high energy density demand advanced cathodes. However, state-of-the-art high-voltage (high-V) cathodes still suffer insufficient performance at low T, which originates from the poor cathode–electrolyte interface compatibility. Herein, we developed a shallow surface Zr-doped and Li+ conductive Li2Zr­(PO4)2 (LZPO) interspersed massage-ball-like LiCoO2 (LZPO-LCO). The surface-interspersed LZPO can induce an electrolyte superwettability of LZPO-LCO, which helps to form a high-quality cathode–electrolyte interphase with strong stability and low interface resistance. Without changing electrolyte, even at a low T of −25 °C and a high V of 4.6 V, LZPO-LCO shows an ultrahigh capacity of ∼200 mAh g–1 at 0.2C and 137 mAh g–1 at 5C, maintaining 94% capacity after 100 cycles with an average Coulombic efficiency of 99.9%. Besides, the fabricated full cells deliver a high energy density of ∼340 Wh kg–1 and maintain 92% capacity after 200 cycles at −25 °C. This work provides a significant leap forward for high-performance low-T cathodes.

Improving the durability of cathode materials at low temperature is of great importance for the development nowadays of lithium ion batteries, since the practical capacity and cycling stability of the electrode are reduced significantly at low temperature. Herein, by amorphous Zr3(PO4)4 surface engineering, we realize a stable high-voltage LiCoO2 operation (4.6 V) at −25 °C. The highly amorphous surface layer can help to form a high-quality cathode-electrolyte interphase with strong stability and low interface resistance, especially at low temperature. Such a surface-engineered LiCoO2 shows a capacity of 179.2 mAh g–1 at 0.2C and an excellent cyclability with 91% capacity retention after 300 cycles (1C). As a comparison, bare LiCoO2 shows only 161.6 mAh g–1 and 1% capacity retention under the same circumstances. This work confirms that surface regulation and control engineering is an effective route to improve the high-voltage and low-temperature performance of LiCoO2.

Advanced lithium-ion batteries (LIBs) for applications in electric vehicles, energy storage, and high-power devices call for novel designs of the electrochemical materials and the cell architecture. Among the candidates are bipolar LIBs which have an advanced stack configuration, simplify the cell components, and hold the promise to revolute the integrated cell design in the future. [1][2][3] In typical bipolar LIBs, cathode and anode slurries consisting of active materials, conductive carbon, and binders are separately coated on two sides of a current collector so that n (≥2) units of such can be serially connected to assemble a high-voltage cell. The design minimizes the internal resistive loss between neighboring cells in a stack, offers uniform current and field distributions, and allows high-power cell operations. It also minimizes the usage of inactive cell components such as those for housing and connecting, thus increases the gravimetric and volumetric energy density and lowers the cost compared to conventional LIB design. [3] Therefore, bipolar LIBs are more competitive in many applications, e.g., in electric vehicles which require high-voltage battery packs with 300-500 V working voltages. [4,5] As the preferred current collector in bipolar LIBs is aluminum foil (which has a lithiation voltage of ≈0.3 V vs Li/ Li + ), low-redox-voltage anodes such as graphite, carbon-silicon composite, and lithium metal cannot be used, and the conventional choice is lithium titanate Li 4 Ti 5 O 12 with a relatively low capacity (theoretical capacity: 175 mAh g −1 ). [3,5] It is therefore the goal of the present study to develop a cheap high-capacity anode with a suitable redox potential and stable cycling performance for high-energy-density bipolar LIBs. We chose conversion-type iron oxide FeO x because of its non-toxicity, earth abundance, low processing cost, high crystal density (5.24 g cm −3 for Fe 2 O 3 and 5.18 g cm −3 for Fe 3 O 4 , compared to 2.16 g cm −3 for graphite, 2.33 g cm −3 for Si, and 0.534 g cm −3 for Li), proper redox potential (lower cutoff voltage: 0.5 V vs Li/Li + , average delithiation voltage: 1.5 V vs Li/Li + ), and high capacity (the theoretical capacity is 1007 mAh g −1 for Fe 2 O 3 and 926 mAh g −1 for Fe 3 O 4 ). [6][7][8][9] Despite of the high capacity, FeO x like other conversion-type TM oxides, has poor cycling stability High-capacity metal oxides based on non-toxic earth-abundant elements offer unique opportunities as advanced anodes for lithium-ion batteries (LIBs).But they often suffer from large volumetric expansion, particle pulverization, extensive side reactions, and fast degradations during cycling. Here, an easy synthesis method is reported to construct amorphous borate coating network, which stabilizes conversion-type iron oxide anode for the highenergy-density semi-solid-state bipolar LIBs. The nano-borate coated iron oxide anode has high tap density (1.6 g cm −3 ), high capacity (710 mAh g −1 between 0.5 -3.0 V, vs Li/Li + ), good rate performance (200 mAh g −1 at 50 C), and...