Design of Nickel-rich Layered Oxides Using <i>d</i> Electronic Donor for Redox Reactions

Through first-principles calculations and experimental observations, we first present the correlation between the Ni and Mn ratio and the redox behaviors of the layered NCM cathodes. The equilibrium potentials based on redox reactions of Ni²⁺/Ni³⁺ are highly dependent on the Mn ratio (NCM523 and NCM721: ∼3.7 and 3.5 V) because of a donor electron, in the e_g band, transferred from Mn to Ni owing to their crystal field splitting (CFS) with different electronegativities, leading to oxidation states of Ni²⁺-like and Mn⁴⁺. Considering the electronic donor (Mn) based on CFS with electronegativity of transition metals (TMs), we finally expect V as a promising doping source to provide donor electrons for Ni redox reactions in Ni-rich layered oxides, leading to be higher delithiation potentials (NCV523: 3.8 V). From our theoretical calculations in the NCV oxide, the oxidation states of Ni and V are stable Ni²⁺-like and V⁵⁺, respectively, and the fractional d-band fillings of Ni are the highest value as compared with NCM523 and LiNiO₂ because of two donor electrons in the t_2g band. Based on the underlying understanding on the CFS with electronegativity of TMs, it would be possible to design new Ni-rich layered cathodes with higher energy for use in Li-ion batteries

High-Performance Si/SiO_<i>x</i> Nanosphere Anode Material by Multipurpose Interfacial Engineering with Black TiO_2–<i>x</i>

Silicon oxides (SiO_<i>x</i>) have attracted recent attention for their great potential as promising anode materials for lithium ion batteries as a result of their high energy density and excellent cycle performance. Despite these advantages, the commercial use of these materials is still impeded by low initial Coulombic efficiency and high production cost associated with a complicated synthesis process. Here, we demonstrate that Si/SiO_<i>x</i> nanosphere anode materials show much improved performance enabled by electroconductive black TiO_2–<i>x</i> coating in terms of reversible capacity, Coulombic efficiency, and thermal reliability. The resulting anode material exhibits a high reversible capacity of 1200 mAh g^–1 with an excellent cycle performance of up to 100 cycles. The introduction of a TiO_2–<i>x</i> layer induces further reduction of the Si species in the SiO_<i>x</i> matrix phase, thereby increasing the reversible capacity and initial Coulombic efficiency. Besides the improved electrochemical performance, the TiO_2–<i>x</i> coating layer plays a key role in improving the thermal reliability of the Si/SiO_<i>x</i> nanosphere anode material at the same time. We believe that this multipurpose interfacial engineering approach provides another route toward high-performance Si-based anode materials on a commercial scale

Li₂RuO₃ as an Additive for High-Energy Lithium-Ion Capacitors

A high-energy lithium ion capacitor that has Li₂MoO₃ as an alternative lithium source instead of metallic lithium has been proposed. For further improvement, we suggest Li₂RuO₃ as a new additive to improve the energy density in the positive electrode. The choice of Li₂RuO₃ is made based on its highly reversible characteristics for Li⁺ insertion and extraction and its structural stability in the operating voltage window of advanced lithium ion capacitors. The electrochemical and structural properties of Li₂RuO₃ have been thoroughly investigated to demonstrate its potential use in lithium ion capacitors. The high reversibility of Li₂RuO₃ and the metallic feature of Li_2–<i>x</i>RuO₃ may be responsible for improvements in the volumetric energy density and safety. This versatile approach may yield higher energy density without significant power loss in lithium ion capacitors